All operational questions and answers on water-coal slurry gasification – does anyone have them?

There are ones from Texaco as well as from SHELL; take a look for yourself – they’re also on our forum. 100 Questions and Answers on Coal Gasification 1) The issue of Shell carbon monoxide levels as a function of the oxygen-to-coal ratio. An increase in the oxygen-to-coal ratio results in more coal undergoing combustion, leading to an increased heat release. This raises the temperature of the gasifier, providing more heat for the endothermic gasification reaction, which is beneficial for such reactions. Therefore, the carbon conversion rate, cold gas efficiency, and gas production increase, while CO2 and specific oxygen consumption as well as specific coal consumption decrease. As the oxygen-to-coal ratio increases further, the carbon conversion rate increases only slightly. Meanwhile, the excess oxygen entering the gasifier leads to an increase in CO2, which results in a decrease in the efficiency of cold gas production and in the gas yield, as well as an increase in specific oxygen consumption and specific coal consumption. Therefore, there should be an optimal value for the oxygen-to-coal ratio; it is generally considered that an atomic ratio of oxygen to carbon around 1.0 is appropriate. The C element needs to be balanced; ignoring the factor of carbon conversion rate, the trend of CO concentration should be opposite to that of CO2. If the C conversion rate is taken into account, the situation is slightly different, but the overall trend remains the same. Overall, the trend in the amount of CO generated as the oxygen-coal ratio changes is to increase first, then decrease, with a maximum value occurring in between. The gasification reaction of water-coal slurry is slightly different, as the shift reaction also has a significant impact on the gas composition; an increase in oxygen content leads to an increased proportion of carbon oxidation to CO2. However, an increase in temperature reduces the occurrence of the shift reaction. A detailed analysis is needed for the specific circumstances, but it seems that the overall trend remains the same. 2) What interlocks should be installed for the shutdown of the Texaco gasifier due to low liquid level? Should a low-flow trip interlock be installed for the quench water? Should a low-liquid-level trip interlock be installed in the water washing tower? Set a interlock at 15% liquid level in the quench chamber (this value was determined through discussions between the design institute and GE Company; the size of the gasifier is 3200mm*3800mm). It is very necessary to set up a interlock for the quench water. As for the liquid level interlock for the carbon scrubber, it’s not very useful and can be completely omitted. The low-low liquid level interlock for the gasifier has a three-to-two selection; this interlock should be activated during operation! For safety! There is no need to set up a low-flow trip interlock for the quench water; since the vaporizer system already has a low quench water interlock, when the quench water level is low, the emergency quench water supply valve will open fully! There is even no need to install an emergency shutdown interlock for the water washing tower, as there is enough time to deal with it! The gasifier level must be monitored during normal operation. Indeed, these two valves close automatically when the liquid level is low, but this level is only slightly above the shutdown threshold. As for the low liquid level in the gasifier causing these two valves to close in sequence, this is mainly to prevent gas leakage due to low liquid levels, and it is not intended to protect the liquid level in the gasifier. If there is a problem with the cooling water pump, the backup pump will start automatically. Supplying water to the gasification furnace directly via the deaeration water pump by manual means is a last-resort option and is not used under normal circumstances. Furthermore, during operation, unless there is an operational error or a problem with the lock-hopper control system, it is impossible for the liquid level in the gasifier to reach the shutdown value instantly. If the low liquid level in the gasifier is caused by water contamination, I support lifting the interlock associated with the coolant chamber’s liquid level as a way to assist in addressing this issue. 3) What are the common problems that occur in the quench ring of Texaco gasifiers during operation, and how should they be repaired and maintained? Clogging of the quench ring is a relatively common issue, manifested mainly by a decrease in the flow rate of the quench water and an increase in the pressure difference between the quench water and the vaporization furnace. When the flow rate of the quench water drops to a certain level, the plant must be shut down to clean the quench ring. Process-related measures: a) Strengthen the control of graywater quality, and strive to discharge water and replenish fresh water in accordance with the design requirements. b) Test and select appropriate ash water dispersion stabilizers under high temperature and pressure to effectively prevent scaling and corrosion in the quenching rings and their water inlet pipes; this prevents a reduction in the amount of water used for quenching due to scale buildup, as well as wear on the inner walls of the quenching ring tubes caused by an excess of ash. c) Control the number of consecutive submissions; try to avoid submitting in sequence, and the operation cycle should not be too long. d) Optimize operations to prevent process gas from containing ash and water, thereby avoiding deterioration of the water quality in the wash tower. 4) Reasons for the high temperature of the Texaco gasifier support plate. An uneven distribution of the quench water film can cause slag formation in the downcomer, leading to blockages; slag formation at the slag outlet also results in gas buildup inside the gasifier. This can easily lead to high temperatures on the support plates, as well as an increase in the overall temperature of the gasifier. Therefore, it is important to maintain a stable temperature in the gasifier that is suitable for the ash melting point of this type of coal. When the temperature of the support plate in the gasification furnace rises, reduce the load while maintaining system stability. Also, pay attention to the furnace’s temperature and avoid keeping it under pressure for too long, as this can easily cause the gasification furnace to bulge, thereby having a significant impact on its future operation. The reasons for the high temperature of the support plate are: a) The refractory bricks at the bottom of the gasification furnace cone thin out, reducing thermal resistance and allowing heat to be transferred in large amounts to the support plate, thus raising its temperature. b. Cracks appear on the support plate, allowing gas from the gasification furnace to leak through these cracks. c. The thermocouple is covered with a large amount of dust, preventing heat from being carried away by the rising air currents. d. An increase or fluctuation in pressure inside the gasifier causes air leakage through the cone-bottom bricks. The main reasons for the high temperature of the Texaco gasifier support plates are: a) downward movement of the fire zone ； b. The gaps between the cone bricks are large; either the bricks have reached the end of their useful life or severe ablation has occurred due to quality issues ； c. Misalignment of the burner leads to localized damage of the cone bricks, resulting in high temperatures ； d. Uneven water distribution in the quench ring, or local dry areas ； e. Changes in coal quality, untimely reactions on the part of operators, and improper operation. 5) What issues should be taken into consideration when using German-style old third-generation burners? How long has anyone managed to use them for? The burners at Lunan Fertilizer Plant were operated for up to 151 days, and there was constant concern during that time! The service life of the burners and refractory bricks in Lunan is relatively long, and there are many reasons for this; of course, it is closely related to the operational skills of the workers in Lunan as well as the technical management capabilities of the supervisors. It is worth mentioning, however, that the operating pressure of the gasification furnaces in Lunan is only 2.7 MPa, and the blending of different coal types for use in these furnaces is done quite well; the operation cycle also depends to a large extent on the type of coal used. The operation of the burner at Luhua for 151 days was entirely within the planned timeframe. Before it was shut down for maintenance, all parameters of the gasifier were normal, the atomization effect of the burner was satisfactory, and no significant abnormalities were observed in the combustible substances in the slag. Burners with a longer operating time are currently under investigation. When the gasification furnace is in operation, the following should be noted: a. It is strictly prohibited to cut off the cooling water. b. Minimize the number of start-up and shutdown cycles. c. Try to use coal with a high grindability index. d. The temperature of the gasification furnace should not be too high. The Texaco burner is the core equipment in the Texaco gasification process; generally, at the beginning of operation, it provides good atomization effects, stable gas composition, and stable system performance ； As operation progresses, the nozzle tip deforms, resulting in poor atomization. At this point, the composition of the gas changes significantly, and the concentration of the effective gas components decreases. Especially when misfiring occurs, it leads to excessively high local temperatures that can damage the thermocouples; in severe cases, gas leakage can cause the furnace walls to overheat. To maximize the operating cycle of the burner, the following points should be taken into consideration: a) The quality of the coal and the coal slurry are the main factors affecting the burner’s lifespan; the ash melting point of the coal should preferably not exceed 1300°C, and a coal slurry concentration of 55-56% is appropriate. b. The gasification temperature should be kept as low as possible, as this can effectively extend its operational cycle; it generally should be maintained below 1350°C. c. In cases of significant changes in the coal feeding rate of the system, it is necessary to adjust the coal/oxygen ratio in advance to an appropriate range to firmly prevent excessive temperature rise. 6) Causes of burnout in the Texaco gasification downcomer and troubleshooting? The quenching ring was clogged, and the water distribution in the downcomer was uneven; as a result, no water film of sufficient thickness could be formed on the inner side of the downcomer to protect it, leading to its damage. It is mainly because the furnace temperature is extremely high, causing blockage of the quenching ring. The high furnace temperature is mainly due to the following reasons: a. An increase in the oxygen-coal ratio, which in turn leads to an increase in the oxygen content. b. Unstable coal quality leads to a decrease in the ash melting point ； Either the amount of flux added is insufficient or too low, resulting in a lower ash melting point. c. Problems with the various quench water supply channels have resulted in an insufficient amount of quench water. The reasons for the burnout of the downcomer include: a) the flow rate of the quench water being below the specified values, or an uneven distribution of the quench water across the quenching ring, resulting in partial loss of water supply to the downcomer; b) quality issues with certain welding points; c) inappropriate selection of material for the downcomer; d) instability during production, with too low a liquid level control in the vaporizer, leading to instability in the downcomer. Through observation and analysis inside the furnace, as well as comprehensive comparison with parameters during operation, it is believed that the root cause lies in the formation of a dry zone: firstly, the low water volume in the quenching ring is the main factor ； Secondly, the excessive heat load of the gasifier destroys the water film in the downcomer, resulting in slag deposition ； Thirdly, the burner sprays unevenly and the flame zone moves downward significantly, directly tearing apart the water film in the downcomer and resulting in slag accumulation ； Fourth, the properties of the ash are unstable. 7) Blockage at the slag outlet of the German-style ancient gasifier. If the slag outlet gets blocked, you first need to find out why it’s blocked. Generally, it rarely gets blocked during operation, unless the temperature is very low and the load is increased slowly, which can lead to unstable coal slurry flow. Under normal conditions, the slag outlet gets blocked due to large fluctuations in temperature or because the CH4 level is controlled too high; it should not exceed 5000 PPM, with a maximum of around 3000 PPM. However, this level shouldn’t be maintained for too long, as that increases the risk of blockage. If it does get blocked, you can increase the temperature, but not too quickly – about 10 degrees per half hour. The oxygen level at the center also needs to be controlled, around 20 percent. It’s important to monitor the PDI1214 value, which represents the pressure difference. But sometimes this value shouldn’t be relied on entirely; it’s better to check the furnace pressure and the pressure at the syngas outlet and calculate the pressure difference yourself, as this gives more accurate results. In most cases, if the blockage isn’t severe, it’s possible to unblock the slag outlet. The most important things are to avoid large temperature fluctuations and to consider the ash melting point. The proportion of limestone used also needs to be adjusted properly to ensure an appropriate ash melting point. On one hand, this issue can be caused by improper operating temperatures in the gasification furnace. The principle for controlling the temperature of the gasification furnace is to maintain a low temperature as much as possible while ensuring liquid slag discharge. However, if the temperature is controlled too low, the fluidity of the slag decreases, and more slag accumulates at the conical slag outlet, resulting in a reduction in the size of this outlet. This increases the residence time of the gas in the combustion chamber, thereby altering the composition of the gas. On the other hand, it is caused by an increased opening angle of the Texaco burner. The opening angle of the Texaco burner has strict design specifications; after operating for an extended period, the burner wears out, causing the opening angle to increase. This leads to poor combustion, and more ash and slag are carried toward the furnace wall under high pressure. When enough slag accumulates, under the combined effect of gravity and gas pressure, it flows along the furnace wall toward the slag outlet. The slag accumulates at this outlet, causing it to shrink over time. When there is poor slag discharge, the oxygen-coal ratio should be adjusted promptly to raise the furnace temperature and facilitate the melting of the slag. This process should not be rushed, and oxygen addition must strictly follow the principle of adding small amounts multiple times to prevent the slag outlet from narrowing again, as the amount of slag increases at that time. At the same time, pay attention to the trend of furnace temperature changes. If this is detected in a timely manner, increasing the oxygen-coal ratio can usually restore normal conditions within 8 hours. Once the slag outlet returns to normal and the gas composition stabilizes, the oxygen-coal ratio can be reduced slightly, and after observing for a few more hours to ensure there are no signs of recurrence, operations can be resumed at normal temperatures. Methods for determining if the slag outlet is blocked: 1. Check the pressure difference – calculate the pressure in the gasification furnace and the outlet pressure of the scrubber tower; a large pressure difference indicates some blockage. 2. Check the PDI1214 value, though this isn’t very accurate. 3. Observe the liquid level in the gasification furnace; if there is a blockage, the liquid level will fluctuate greatly. 4. Analyze the syngas composition – there will be less CO and more CO2, with significant fluctuations in CH4 levels. 5. Examine the slag sample by looking at it at the bottom of the lockhopper. 8) What are the causes, consequences, and solutions for water contamination in the process gas at the outlet of the Texaco gasification scrubber tower? There are generally two reasons for water accumulation in the wash tower: one is an excessive increase in load, which leads to a sudden rise in gas flow velocity, leaving no time for water and gas to separate; the other is an excessive amount of fine ash in the gas, which makes separation difficult. The presence of water directly results in liquid water being carried in the gas entering the shift converter, which saturates the shift catalyst and leads to increased conversion resistance and catalyst deactivation; in the most severe cases, this can prevent production from continuing. Generally, when engineering companies carry out design work, a moisture separator is required to separate water before the transformation; in addition to considering water carried in the stream, condensate water also needs to be taken into account. To avoid water ingress, first ensure that the coal quality remains as stable as possible, and second, avoid significant increases in load. (1) Under high load in the gasification furnace, the liquid level cannot be increased and does not reach the designed normal level, which directly affects the water bath effect for syngas; the first washing stage for the syngas is inadequate, and some ash is carried into the washing tower. (2) The gasification furnace may experience water contamination; since the quench chamber is in direct contact with slag and fly ash coming from the combustion chamber of the gasification furnace, the water quality within the system is poor. A large amount of ash will be carried into the scrubber along with the water present in the syngas, which affects the water quality in the scrubber and as well as the cleanliness of the syngas at the outlet. (3) The deterioration of water quality in the scrubber affects the quality of the quench water drawn from it; prolonged operation will exacerbate scaling in the quenching ring of the gasifier, ultimately leading to the shutdown of the gasifier. (4) The spray water at the syngas outlet of the gasifier comes from the condensate pump; due to an outlet pressure of 4.8 MPa, the pressure difference with the gasifier outlet is low. The small orifice used for spraying water has been blocked by the ash present in the syngas, and without the washing effect of this spray water, the fly ash in the syngas is not wetted. (5) Venturi scrubbers are prone to scaling, which affects the efficiency of spray washing. (6) There may be issues with the design of the internal components of the scrubber, resulting in poor scrubbing efficiency; as a consequence, a large amount of water vapor and ash is carried in the syngas, which increases the resistance in the shift system. 9) Regarding the pressure difference between Texaco gasification oxygen and the gasifier. The operating pressure of the device varies, and thus the required pressure difference also changes; it is related to the size of the nozzle. What you are referring to is probably the Lunan plant, where the operating pressure is 2.8–3.0 Mpa. The pressure difference between oxygen and the medium under normal operation should be around 1.0 Mpa, while the pressure difference between oxygen and the coal slurry is about 0.5 Mpa, in order to ensure proper atomization. If the operating pressure is 6.5 Mpa, the oxygen pressure entering the furnace should be between 8.0 and 8.2 Mpa, while the pressure of the coal slurry entering the furnace should be between 7.5 and 7.8 Mpa. If the operating pressure is 4.0 Mpa, the pressure difference between oxygen and the gasifier is around 1.2 Mpa, and that for the coal slurry is around 0.5 Mpa. 10) How to adjust the load in a multi-nozzle gasification unit? The oxygen flow rate is adjusted using control valves, while the coal slurry flow rate is adjusted by the coal slurry pump. A slurry pump is divided into two counter-acting burners, and the regulation of the slurry flow rate is currently carried out entirely through frequency conversion, so there is no need to worry ； As for the oxygen flow rate, relatively precise control valves are generally used for adjustment, so the error is not significant. Even if it is larger, after being ejected through the burner inside the furnace and then colliding, it will not directly erode the furnace bricks. Even with oxygen flow fluctuations of 5% and slurry fluctuations of 12%, there was no misfiring in the gasifier; this is true especially for equipment of good quality. 11) Are black water and gray water the same concept? What is the conceptual relationship between black water treatment and flash evaporation? Black water: superficially, it refers to water that is black in color; in reality, it is water containing a large amount of carbon residues from vaporization, which is discharged directly from the bottoms of the vaporization furnace and the scrubber tower ； Gray water – literally, water that is gray in color. In reality, it is water containing a large amount of carbon residues from the gasification process, which is discharged directly from the bottoms of the gasification furnace and the scrubber tower. This water undergoes flash evaporation, followed by sedimentation and clarification to remove the impurities ； In other words, with flash evaporation as the boundary, the water before the line is black water, and the water behind the line is gray water. In the Texaco process, the black water is discharged from the gasifier into the flash system, and then it enters the sedimentation tank. After preliminary separation, part of the slurry is sent to the filter press, while the remaining grayish water goes into the gray water tank – this is what is known as gray water. This gray water is mixed with the condensate from the conversion unit, then sent to the deaerator; after that, it is combined with water from the flash tank and fed into the scrubber tower. In the TAXECO gasification process, the water that has undergone flashing and sedimentation for ash removal can be referred to as gray water. 12) What are the reasons for water presence in the gasifier during Texaco water-coal slurry pressurized gasification? What measures should be taken to address these issues caused by various reasons? 1. The system’s load is too high; the amount of syngas produced is excessive. The only solution is to reduce the load.
2. The pressure in the downstream system suddenly dropped; I’m not sure what to do, haha.
3. The liquid level in the quench chamber is high, and the temperature there is also high. More black water should be added, along with more quenching water.
4. The downcomer in the quench chamber is damaged; it needs to be stopped for repair.
5. It’s possible that there’s some blockage in the syngas pipeline, which causes a buildup of pressure. I’m not sure how to deal with this, haha.
6. The operating temperature is too high. The temperature needs to be reduced, as does the ash melting point. The temperature of the process gas at the outlet of the carbon washing tower is too high; adding too much condensate from the trays can also introduce water into the system.
1: When pressure or load increases, the heat flow intensity rises, which can lead to film boiling. This results in a significant decrease in the conversion efficiency, and water can end up in the gases inside the furnace.
2: A higher load means a higher gas flow rate, which also leads to the introduction of water ； 3: The upper and lower circulation pipes are matched to the original production load; increasing production will also cause supersaturated steam and water to be carried away ； 4: When the distribution plate is separated, the water entrained with it cannot be effectively separated, and this also causes the water to be carried away with the airflow. 13) Reasons for the high temperature at the base of the cone in the gasifier during normal operation: The excessive temperature at the cone area cannot be attributed solely to the flame moving downward, as the temperature inside the furnace is above 1300 degrees; therefore, even if the flame moves upward, the temperature at the cone area will not drop. Therefore, I believe the reasons for the high temperature in the cone are as follows: 1) There are issues with the cone structure or the quality of furnace construction, which leads to air leakage; high-temperature slag enters the gaps between the cone bricks, causing the temperature there to rise ； 2) Slag accumulation at the slag outlet causes deformation of the outlet, while the deviation of the process gas affects its cooling in the downcomer, resulting in an increase in the temperature of the cone in areas where the flow velocity is higher ； 3) Slag accumulation in the cone: When the furnace conditions are abnormal, the slag forms into needle-like shapes; these slag particles rise with the process gas and accumulate in the cone, resulting in a reduced heat exchange efficiency in that area and an increase in the temperature of the cone. The first one is the most common cause; adjusting the central oxygen level at this time also leads to changes in the cone temperature. There are also special situations, such as a large pressure difference at the slag outlet combined with damaged gaskets, which can cause hot gases to leak out; another issue is when the downcomer is burned through, which can also lead to an increase in the temperature of the cone bottom. These are all serious problems. In fact, the reason why patent holders installed temperature measurement points was, first, to prevent gas leakage through the cone bottom bricks, and second, to avoid the burning through of the downcomer – both of which are serious accidents. Therefore, an increase in the temperature of the cone bottom is an issue that should be taken seriously. An excessive temperature in the cone area, or high temperatures in the bricks forming the cone, can be attributed to the following factors: 1) High ash content in the coal and high load levels, resulting in severe erosion of the cone by the slag; 2) Problems with the structure of the cone or the quality of its construction, leading to gas leakage, with high-temperature gases or slag entering the gaps between the cone bricks and causing a rise in temperature ； 3) Excessive oxygen flow at the center causes the high-temperature zone to shift downward, or an excessive load leads to erosion of the cone, resulting in an increase in temperature; 4) Slag accumulation at the slag outlet causes deformation of that outlet, and the deviation of the process gas affects its cooling within the downcomer, leading to an increase in the temperature of the cone in areas where the flow velocity is high ； 5) Slag accumulation in the cone: When the furnace conditions are abnormal, the slag takes on a thread-like shape and rises with the process gas, accumulating in the cone. This reduces the heat exchange efficiency of the cone, leading to an increase in its temperature. 6) Fluctuations in the flow rate of the cooling water in the quenching ring. Among them, reasons related to items 3 and 6 are the most common; in such cases, adjusting the oxygen level in the reactor or stabilizing the flow rate of the quench water will lead to an improvement. 14) How to deal with backflow during the heating up of a gasification furnace? The main reason for backflow during the heating process is that the pressure inside the furnace is higher than that outside, causing gases to flow in the direction of lower pressure. Therefore, it is necessary to maintain a negative pressure inside the furnace, which is achieved by increasing the suction force. At the same time, it is important to exhaust gases promptly so that they do not accumulate inside the furnace; otherwise, it will be difficult to create a negative pressure. As mentioned earlier, the liquid level in the gasification furnace should not be too high, otherwise it will be hard to expel the gases. 1. Immediately turn off the fuel for the oven. 2. Replace the combustible gas in the gasification furnace. 3. Identify the reasons for backfire in the gasification furnace (high liquid level in the gasification furnace, low suction air volume, blocked suction air path, excessive fuel, incomplete sealing of the gasification furnace, and failure to remove the condensate from the suction air separation tank in a timely manner) and eliminate them. 4. Re-heat the furnace according to the furnace heating curve. 15) Regarding the ignition method of gasifiers, igniting a water-coal slurry gasifier is not as complicated as igniting a Shell gasifier. In a Shell gasifier, the IB (ignition burner) is used first to start the combustion, followed by the SUB (operational burner), and finally the CB (coal burner). Generally, the IB burner functions very well; the main problems arise with the SUB burner. Several factories in China have experienced damage to their SUB burners, with the damage usually occurring at the burner tip. Replacing the burner tip allows the burner to be used again. In Shell’s original design, the SUB burner tip is a replaceable component, and there are strict requirements regarding its usage duration – it seems that the tip needs to be replaced after a certain number of hours of continuous use or after a certain number of times it has been used; I can’t remember the exact figures. Hehe! The amount of coal that can be fed into a Shell gasifier per batch is several times higher than that in a water-coal slurry gasifier. If only one ignition burner is used to ignite the CB burner, the requirements for that ignition burner become too high.

16) How to reduce the amount of residual carbon in the ash: It is necessary to analyze the reasons for high residual carbon levels in the slag: 1) The particle size of the raw materials is uneven, with large differences between particle sizes, or the gangue contains a high proportion of fine particles, which prevents the furnace temperature from rising and results in incomplete reaction of the raw materials. 2. The upward blowing time is long and the steam consumption is high, causing the gasification layer to rise and the furnace temperature to drop, resulting in incomplete reaction of the raw materials. 3. There are scars and lumps inside the furnace, or the airflow distribution and gasification layer are poor; as a result, the raw material stays in the gasification layer for a short time and does not react completely. 4. Defects in the equipment: uneven grating ventilation and poor slag breaking capacity. The furnace rod machine pulls too fast, leaving the raw material no time to react. The retaining plates on both sides of the producer furnace are malfunctioning, causing coal to spill out. 5. The raw coal has poor activity. Solutions: 1. Strengthen raw material processing to ensure that the coal used as feedstock into the furnace has a uniform particle size, and remove all gangue. 2. Adjust the percentage of upper and lower blowing, or the steam used for upper and lower blowing, to keep the gasification layer at the appropriate position, with the right thickness and temperature. 3. Treat the slag blocks in the furnace wind tunnel to optimize furnace operation. 4. Inspect and repair or replace the furnace grates, adjust the appropriate speed of the grate drive mechanism, and inspect and repair the stop plates. 5. Replace coal types with poor activity. 17) Why don’t water-cooled wall systems be used in coal-water slurry gasifiers, and why are refractory bricks used instead? There is no patent issue with water-cooled wall structures; this is a common practice in the boiler industry, and boiler manufacturers with sufficient capabilities should be able to design and manufacture such systems. In fact, the reason for not adopting a water wall structure, I believe, can be analyzed from the principle of water-coal slurry gasification. The excessive moisture introduced into the system through coal water slurry gasification forces part of the carbon in the coal to be oxidized into carbon dioxide in order to generate sufficient heat for the gasification system; this is why the carbon dioxide content in the crude syngas produced by coal water slurry gasification is much higher than that in syngas produced by pulverized coal gasification. If water-cooled walls are used, the gasification system loses an additional amount of heat to these walls, which leads to a further increase in carbon dioxide levels and a further decrease in the ratio of useful gases, thereby affecting the efficiency of gasification. This is very different from pulverized coal gasification. 18) How should slag blockage be handled when detected in the lock hopper? I. Reasons for slag blockage: Slag blockage in the lock hopper generally occurs in two situations: 1. Blockage caused by slag lumps. This is generally caused by the high ash melting point of the coal burned in the gasifier, sludging due to temperature fluctuations in the gasifier, or rapid cooling-induced sludging in parts of the gasifier such as its water-cooled walls, burner flame shields, and thermal skirts, as well as the detachment of suspended slag accumulated at the slag discharge outlet. In the Texaco-type gasifiers, \"brick slag\" can also form as a result of the peeling off of refractory bricks due to temperature fluctuations. If such slag accumulation is larger than the channels in the slag discharge hopper or causes bridging, it will impede the smooth discharge of slag; in severe cases, slag cannot be discharged at all. 2. Sludge blockage. (Coal with a low ash fusion point) burns incompletely at too low temperatures in the gasification furnace; it begins to form ash particles before rapid cooling occurs. The high ash content results in fewer particles, while excessive moisture leads to a mud-like consistency with high viscosity. This substance can accumulate at the bottom of the hopper, and once it settles and compacts, it can form bridges that block the discharge process. II. Treatment methods 1. Preventive measures: Analyze the ash fusion point of coal in a timely manner, add an appropriate amount of flux, maintain stability in the material composition and an optimal oxygen-to-coal ratio, keep the temperature in the gasification furnace stable, and ensure good fluidity of the slag. In case of slag blockage, the operating conditions should be adjusted gradually and promptly ； 2. Maintain the appropriate water level in the lock chamber and ensure proper water flow to prevent slag from settling and forming bridges ； 3. Slag blockage treatment: The most effective method is to install a pressurized water flushing pipeline at the bottom of the lock hopper. When slag blockage occurs, manual \"bridge removal\" is carried out by switching from programmed control to manual intervention; intermittent backwashing with high-pressure water is used to loosen the blockage, followed by slag removal. Repeating this process several times will yield results. The pressure of the flushing water should be higher than the pressure inside the lock hopper, but not too high; too low a pressure will not achieve the desired loosening effect, while too high a pressure can cause a sudden increase in the water content inside the gasifier, or even the entry of liquid water, leading to equipment safety hazards. The theoretical data for differential pressure control needs to be calculated based on the specific furnace; personal experience shows that a control range of 1.0–1.5 MPa yields good results. Generally, this method is more effective for the second reason than for the first. The first method is slightly more difficult to handle. Of course, if the check valve cannot be opened or if large pieces of slag fail to loosen and fall out, they will not be removed, and ultimately the operation has to be stopped for handling. 19) Dry coal powder gasification technologies such as shell and GSP require nitrogen for material transportation; are there any special requirements regarding the quality specifications of this nitrogen? Can a conventional air separation unit meet its requirements? For the power nitrogen used in the raw material conveying section, as long as its oxygen content is below 5% – that is, it is dirty nitrogen – a concentration of 50% at the lower limit is sufficient to ensure safety during coal powder preparation or conveying. The nitrogen used for tasks such as purging and back-purging after the reaction section will enter the crude syngas, and this could have an impact on downstream chemical plants; therefore its purity is important, generally requiring levels in the PPm range, although this requirement can be relaxed in the case of IGCC. Generally, large-scale air separation units can easily meet this requirement, unless there are design or modification errors that result in the ASU functioning as a nitrogen-producing unit. 20) GSP coal powder gasification pressure: 1. The statement that \"the operation pressure of the gasifier in GSP gasification technology can be selected between 2.5–8.0 MPa\" is a theoretical concept; in practice, the maximum operating pressure is currently only 4.0 MPa, and this is determined by the coal powder transportation system. If the operating pressure is increased further, on the one hand there may be issues with the production of ultra-high-pressure nitrogen, and on the other hand, rising operating pressures will also lead to a significant increase in equipment costs. 2. The largest GSP unit currently in operation worldwide is the 130 MW gasification plant built in 1984 at Blackwater Pump in Germany (with a lignite feed rate of 720–750 t/d, a gas production rate of 50,000 Mm3/h; the inner diameter of the gasification furnace is 1.9 m, and the inner diameter of the pressure vessel shell is 2.4 m). Its design pressure is only 3.0 MPa, while its operating pressure is 2.5 MPa. 8.0 MPa powder gasification is merely a concept. Whether it is GSP, SHELL, or two-stage furnace gasification pressures, the current limit is only 4 MPa. No matter how high the pressure, there is not only a lack of design experience, but also no need for it at the moment. Just take a look at how Shell drives – he performs better when the pressure is low. Therefore, there is no need to increase the pressure in powder coal gasification at present; the top priority is to address the issue of stable operation and reduce the number of shutdowns. Do not impose a burden on this process. 21) Why does TEXACO’s raw gas have to be mixed with process condensate before entering the venturi for washing, after coming out of the gasifier? Can I go to the venturi right after coming out? When designing its units, Texaco did indeed add some condensate at the outlet of the gasification furnace, with the main purpose being to prevent blockages at that outlet. However, as China has become more proficient in using Texaco’s technology, operational skills have improved, and many plants no longer use this method; consequently, condensate is no longer included in the design of new plants. Some condensate was supposed to be added at the outlet of the gasifier; it was part of the original design, but it is not included in modern designs. Moreover, it is not used for cooling the quench water under normal conditions. Based on long-term experience, this water also does not serve an optimal purpose in slag removal, which is why it is not included in current designs. The actual cooling, dust removal, and saturation of the process gas take place in the quench chamber of the gasifier. 22) Are there any requirements for the temperature of the syngas exiting the quench chamber? Some literature states it to be around 220°C, while the process package data from Huainan is 227°C. The temperature in the quench chamber is generally kept around 220 degrees, but it can vary depending on the production conditions. For a given furnace and type of coal, variations in temperature usually reflect changes in the water level in the quench chamber; there is no upper limit for the temperature, but there is a lower limit for the water level. Within this temperature range, no damage will occur to the downcomer. The temperature of the syngas as it exits the quench chamber is typically the saturation temperature at that pressure. Since the syngas contains water, it is saturated with water, so the temperature is usually a bit lower. The pressure of the Huainan gasifier is 4 MPa, with a corresponding saturation temperature of 250.3°C; therefore, 227°C is reasonable for the process package. 23) Are the water inlet flow rate to the trays of the carbon scrubber tower and the make-up water flow rate at the tower bottom fixed? Are they related to the liquid level control of the scrubber tower? Once production becomes stable, these two values should remain relatively constant; they are related to the liquid level in the scrubber tower, while the amount of water on the tray is primarily determined by the ash content in the gas exiting the tower. Water supply to the trays of the carbon scrubber is extremely important in actual operation; the amount of water supplied has a significant impact on the amount of ash present in the syngas. In simple terms, it is used for washing the syngas. If the amount of water supplied is low, the syngas exiting the carbon cleaning tower will contain more ash. If this situation persists over time, it will lead to a decrease in the conversion efficiency of the reforming unit due to the excessive amount of ash present. The amount of water supplied to each tray varies; it must be determined based on the degree of ash in the syngas. Additionally, more water needs to be added when the load is high. As for water replenishment in the tower bottom. The water replenishment amount also needs to be adjusted based on the liquid level of the carbon scrubber tower. 24) Water cut-off after shutdown of the gasifier under various conditions 1. Shutdown during operation: If the gasifier is shut down while it is in operation, water cut-off is ordered after the burner valves are closed on-site. Since pressure retention in the gasifier is only possible under ideal conditions, no gasifier can maintain pressure perfectly; to prevent high liquid levels in the gasifier due to insufficient pressure that would hinder water drainage, water must be cut off and directed to the startup pipeline as soon as possible. 2 Planned shutdown: Reduce the load of the furnace under planned shutdown to half load, then divert water to the startup pipeline and proceed with shutdown. Also to prevent water from not being able to drain. 3 Planned furnace switching: After the furnace scheduled for shutdown is reduced to half load, the furnace scheduled for operation is fed with material, and after that, water is sent through the startup pipeline. When the pressure in the feed furnace rises to that of the operating furnace, the water is diverted to the flash system. It is planned to shut down the furnace by cutting off the water supply and connecting it to the startup pipeline. Some people may be concerned about the pressure levels in the start-up pipelines. In fact, the pressure design for these pipelines is based on the pressure generated when a single furnace is operating at full capacity. If there are problems with the flash vaporization system, it is still necessary to divert water to the start-up pipelines for isolation; of course, this should not take too long. 25) How is the central oxygen level adjusted in multi-nozzle systems during startup/shutdown and when adjusting the production load? What is the purpose of the adjustment? The single-nozzle gasifier for water-coal slurry uses a premixed burner, which requires a longer flame, with the oxygen concentration at the center being controlled at around 15% of the total oxygen amount ； The four nozzles are pre-film type burners; the flames, emerging in opposite directions, form a plum blossom shape. A shorter flame is required, and the oxygen content at the center plays a significant role in determining the length of the flame, with the control range being 8% to 12% of the total oxygen amount. If the control ratio is too high, it can easily cause overheating of the gasifier dome and damage to the refractory bricks. 26) In a multi-nozzle system, what should be done if one pair of burners fails while the other pair continues to operate for a short period? This type of gasification furnace is equipped with two slurry pumps, each supplying one pair of burners; if one pair fails, the other pair can still keep operating, but it is necessary to reduce the load and pressure, resolve the fault as quickly as possible, and then bring the failed burner back into use. After a pair of burners fail to operate, in order to prevent damage to the non-functional burners due to dry burning, a large amount of nitrogen is supplied to the failed burners for protection. If the materials can be fed in as soon as possible, and since it is an ammonia synthesis plant, short-term protection has little impact on the system ； If methanol is to be synthesized, there are many complications. If the feed cannot be added as soon as possible, a large amount of nitrogen will enter the syngas, worsening its composition and having a significant impact on subsequent processes in the plant. Therefore, theoretically, there is no major issue with this setup. However, in actual industrial production, it is generally not necessary to shut down the plant when a pair of burners is out of service for a short period of time; if the downtime is longer, the plant should be shut down. After one pair of burners is taken out of service, it is necessary to reduce the load. As for starting the burners again while the system is still under pressure, since the system pressure drops naturally after the load is reduced, it is sufficient to directly introduce slurry and oxygen to gradually restore normal operation. 27) What are the reasons for abnormal pressure fluctuations in the gasification furnace? 1. Fluctuations in the pressure of the downstream system cause fluctuations in the pressure inside the gasification furnace. 2. Fluctuations in oxygen flow rate, pressure, and purity (this possibility is low) lead to changes in the reactions taking place inside the gasification furnace. 3. Fluctuations in the concentration and flow rate of the coal slurry (such as problems with the high-pressure coal slurry pump or the presence of large particles in the slurry) result in changes in the gasification reactions. 4. It’s possible that surging occurs in the self-regulating valve downstream of the syngas, affecting the system pressure (especially when this valve is a disc-type self-regulating valve). Due to abnormal fluctuations in the pressure inside the furnace, and without any adjustment to the oxygen valve, the oxygen flow rate decreases as the furnace pressure rises and increases as the pressure drops. Such fluctuations in oxygen flow rate inevitably lead to fluctuations in the temperature inside the furnace; therefore, it is necessary to adjust the oxygen flow rate promptly when there are abnormal pressure fluctuations, in order to prevent excessive temperature variations inside the furnace. 28) In Texaco’s water-coal slurry pressurized gasification, how can one determine whether there is water in the gasifier and the carbon scrubber? Water in the gasifier: The water inflow to the gasifier remains unchanged, while the water outflow decreases, resulting in a high liquid level. This may also be caused by too rapid addition of water, or an excessively high oxygen-to-coal ratio. Water in the scrubber: The temperature of the process gas at the top of the scrubber drops, and the liquid level rises; there is too much water on the tray. 29) What is a reasonable pressure difference for the burner? A high burner pressure difference is beneficial for atomization, but it also increases the wear on the burner, affecting its service life. Texaco specifies a burner pressure difference of 1.2 to 2.4; I think it is more appropriate to keep it around 0.5 Mpa. In our plant, the burner pressure difference at full load in the gasification furnace is around 0.6 Mpa. A too low pressure difference in the burner is certainly not good, as it can cause problems with the dome bricks; on the other hand, if the pressure difference is too high, it exacerbates the erosion of the cone-bottom bricks. Therefore, after years of experience, it has been determined that a value of 0.6 Mpa is appropriate. This requires adjusting the burner gap properly when designing the burner! 30) For a four-nozzle gasification furnace, how is operation adjusted when the flow rates of the two opposing nozzles are not equal? If the flow difference between the two nozzles exceeds a certain range, is there any interlock for control? The flow rate of the slurry pump depends only on the pump’s speed; however, it is not possible to ensure that the resistances in the two pipelines are identical. In design, the resistances in these two pipelines are assumed to be the same, but in practice this is not always the case. The flow rate produced by our slurry pumps is not exactly consistent. It is the issue of flow rate difference that the original poster is concerned about; technically, a certain degree of flow rate difference is acceptable. As mentioned below, when the flow rate difference reaches a set value, it will cause a cascade shutdown, but the flow rates in the two pipes connected to the same pump cannot be adjusted. There is also a flow interlock between the two pairs of burners; that is, a large flow difference between the two pairs of burners is not allowed, as this can also lead to shutdown. 31) Water-coal slurry with good slurry-forming properties has a certain range for its particle size distribution. A higher proportion of coal powder with a coarser particle size results in an increased concentration and better fluidity of the water-coal slurry ； A higher proportion of finely ground coal results in a slurry with better stability. So, please discuss based on your own practical production experience: what impact does the particle size distribution of water-coal slurry (or the ratio of coarse to fine particles in the water-coal slurry) have on Texaco gasification? Either too high or too low a particle size of the coal slurry is detrimental to production. When the proportion of larger particles is high, the gasification efficiency decreases, but the concentration of the coal slurry increases; accordingly, the amount of moisture entering the furnace decreases, resulting in lower energy consumption. A higher proportion of fine particles leads to an improved gasification efficiency. Although the slurry remains stable, its concentration is affected, resulting in increased moisture content carried into the furnace and higher energy consumption. Therefore, a uniform particle size distribution of the coal slurry helps to improve gasification efficiency and reduce energy consumption. 32) What are the reasons for the high temperature of the gasifier support brick (support plate)? How to handle it? There are probably several possibilities: 1. Excessive ash accumulation at the upper part of the quench chamber; 2. Air leakage in some areas; 3. The burners are not properly adjusted; 4. The load is too high; 5. There is a problem with the spray water (in the case of new-type quench chambers). In such cases, the conical bricks may fall off severely, resulting in high temperatures; this requires shutdown for maintenance and replacement of the bricks. Alternatively, a decrease in the flow rate of the cleaning water can lead to high temperatures, so the flow rate needs to be increased. Another possibility is that the operating temperature of the gasifier is too high, in which case the operating temperature should be reduced. It’s also possible that the thermocouples are giving incorrect readings. 33) What is the difference between Texaco’s coal-water slurry gasification technology, which uses premixed nozzles, and the multi-nozzle opposed-type coal-water slurry gasification technology that employs film-forming nozzles? What are the structural differences between these nozzles? Similar to Texaco’s coal-water slurry gasification burners, the film-forming burners used in the four-nozzle opposed-type coal-water slurry gasifiers also have a three-channel structure: the oxygen stream entering the burner is divided into two channels, with the central oxygen flowing through the interior of the small nozzle, while the external oxygen flows through the annular space formed between the exterior of the large nozzle and the outer surface of the middle nozzle ； The water-coal slurry flows through the annular gap formed between the inner cavity of the middle nozzle and the outer surface of the internal small nozzle. The pre-coated burner head is also equipped with a water jacket and cooling coils to protect it from the high temperatures inside the furnace that could otherwise damage the external nozzles. Unlike the Texaco water-coal slurry gasification burner, the end faces of the small and medium nozzles in the pre-film type burner are each recessed by only 1 mm relative to the end face of the external large nozzle; oxygen and water-coal slurry exit the burner simultaneously, and there is no premixing chamber for oxygen and water-coal slurry at the burner head, making it an externally mixed type burner ； In the Texaco water-coal slurry gasification burner, the intermediate nozzle is recessed axially several millimeters inward compared to the outer nozzle, while the inner smaller nozzle is recessed axially dozens of millimeters inward relative to the outer nozzle. This arrangement creates a premixing chamber for oxygen and water-coal slurry at the burner head, resulting in a burner of the internal-external mixing type. The end structure of the pre-film burner enables the three streams of material to be ejected in a coaxially intersecting pattern. Since the water-coal slurry is in the form of an annular film before being ejected from the burner, it is called a pre-film burner. 34) When the slag outlet becomes blocked during Texaco gasification, the slag sample contains glass fibers. Why is this? The fibrous structure is likely due to the low viscosity of the slag. The blockage of the slag outlet indicates that, prior to this, the slag had accumulated in the furnace due to its high viscosity and poor fluidity; when the furnace temperature rose rapidly, the flow rate increased beyond the capacity of the slag outlet. Of course, the above applies to the current coal quality; even with the same oxygen-to-coal ratio or gasification temperature, such a situation can arise due to the sharp changes in the viscosity-temperature characteristics of the coal ash. According to infrared spectroscopy analysis, at around 1300 degrees, the main components of coal ash in the slag are Al2O3, SiO2, CaO, etc., while the primary constituents are silicate substances such as mullite, periclase, cyanite, and amorphous glass. When the temperature of the gasification furnace is high, the molten glassy substance in the liquid slag, which is primarily composed of SiO2, is blown into filaments by the high-speed airflow; after being cooled by rapid water cooling, it takes on a shiny appearance (sometimes yellowish, sometimes white) in the form of needles and filaments. In actual production, the presence of needle-like or filamentous structures in the slag is often used as one of the indicators to indicate that the temperature in the gasification furnace is too high. 35) What are the reasons for the damage to the Shell burner flame arrestor and the startup burner? Are there conditions that could lead to the formation of iron carbide near the CB Muffle, and could this pose a threat to it? If the formation of iron carbonyl is possible, how can it be suppressed? 1. Iron is a transition element, and its atoms have electron shells that are not fully filled. When it reacts with carbon monoxide to form Fe(CO)5, the iron atom obtains the missing electrons from 5 CO molecules. 2. Production conditions: Fe(CO)5 (pentacarbonyl iron) is synthesized from CO and elemental iron under high pressure. The production process uses relatively coarse sponge iron powder as raw material; after granulation, it is annealed and activated in hydrogen at 350 degrees. It is then placed in a reactor where the iron particles are exposed to circulating CO at a gas pressure of 6 OPMa and a temperature of 160 degrees, resulting in a reaction between iron and CO to produce the gaseous compound Fe(CO)5. The material of the CB muffler in shell gasification is 15CrMoG; the coal powder ejected from the burner burns to form upward-swirling gases. There are no areas with high CO concentrations in the radial plane of the burner, and the temperature inside the gasifier is around 1600 degrees. The outer surface of the flame shield is also around 460 degrees, which do not meet the conditions necessary for the formation of iron carbide. The CB muffs that were damaged during operation were found, through phase analysis, to have suffered from high-temperature ablation leakage; local pitting and corrosion spots were present on their surfaces, but no widespread surface corrosion was observed. Currently, the three Sinopec companies have successfully resolved this issue without changing the material. Among them, Anqing did not suffer any damage during the shutdown period from March to October, and Zhijiang in Hubei also saw no damage after May; recent inspections during the shutdown period revealed no issues. Therefore, under the operating conditions of the shell gasifier, the current material of the CB Muffle makes it unlikely for iron carbide to form. 36) SHELL coal burners: Why are coal burners prone to damage? What methods can be used to avoid this, or what measures can be taken to reduce the likelihood of damage to coal burners? Since the three Sinopec plants began operation at the end of 2006, none of them has experienced any damage to their coal burners; only the flame shields of the burners and the burners used during startup have been damaged. However, among the 5 manufacturers that have already started production, one of them did damage one coal burner; a domestic research institute was hired to develop and produce a replacement burner, but I can’t go into too many details regarding this. But what I want to say is that the prototype burners have not been put into use yet, mainly due to concerns; currently, the imported spare burners are still being used to replace those that were damaged. There isn’t much discussion about the cause of the damage; my personal analysis points mainly to *oxygen ablation. Peroxides mainly appear during driving or when there are fluctuations in the coal line. Another situation that requires attention is when there is a change in the type of coal, and adjustments are not made in a timely manner; this leads to changes in the fluidity of the slag. The slag then covers some of the oxygen/coal channels in the burner, forcing a change in the direction of the flow. As a result, oxygen and coal cannot mix properly, and oxygen may even flow back through gaps. This can lead to an oxygen-rich condition in certain areas or on the sides of the burner head, and it is possible that localized high-temperature oxidation and overheating erosion may occur in those areas. For a coal burner that has already been manufactured, the cross-sectional area of its cooling water channels and its heat exchange capacity are already determined; the maximum water flow capacity cannot be changed. Therefore, I believe there are two points that need to be taken into account. First is ensuring water quality; if scaling or blockages occur within the water channels, the water flow rate and heat exchange capacity will decline significantly, which will severely affect the service life of the burner. Secondly, it is necessary to ensure that the heat load does not exceed the limit of the heat exchange capacity, which means strict control over the oxygen-to-coal ratio is required. Changes in the oxygen-to-coal ratio lead to variations in combustion; the reasons for this include issues related to gas delivery, as fluctuations in the delivery of coal during transportation (gas delivery) can easily result in an imbalance between coal and oxygen. This is also a defect inherent in SHELL’s system. 37) Reasons for the continuous increase in the exit temperature of the SHELL gasification syngas cooler: 1. A decrease in the flow rate of the quenching gas; it is necessary to conduct an immediate inspection to resolve the issue and restore normal flow rates. 2. If the O/C ratio increases, it should be adjusted to an appropriate level immediately. 3. If the circulating water flow rate is low, it should be increased immediately. 4. Accumulation of dust inside the gasifier and cooler reduces heat exchange efficiency; the shaking device should be activated immediately to remove the dust. Additional disposal methods: 1. Where possible, reduce the pressure drop in the subsequent systems; operating the gasification furnace at the lowest possible pressure helps with dust removal. 2. When the load is low, ash cleaning can be carried out alternately using coal with high ash content or high iron content. 3. Improve the control level of the gasifier temperature. 38) Key points for operating a fixed-bed gasifier with low-quality coal: Due to the current shortage of coal resources, the lump coal used in fixed-bed gasifiers is subject to price constraints, and lower-quality coal may also be mixed in; therefore, stable operation is of utmost importance. It can be approached from the following aspects: 1. Strictly control the bed resistance. That is, to maintain a certain thickness of the fire layer ； 2. Ensuring a certain ash layer is the basis for fixed-bed gasification. When the gray layer is damaged, talking about anything else is pure nonsense ； 3. When the quality of coal deteriorates or changes, different handling methods should be adopted based on the coal quality analysis results, rather than sticking to the same approach at all times. a. If the ash content in coal is high, it is possible to increase the speed of the furnace rod machine appropriately; at the same time, the duration of top-blowing or the amount of steam used for top-blowing should be increased. It is essential to avoid letting the furnace temperature drop ； b. There is a large amount of crushed coal and coal powder; in this case, the resistance of the bed layer increases. It is necessary to focus first on reducing this resistance, but care must be taken to prevent excessive oxygen from being blown in. It is possible to reduce the bed height and the thickness of the combustion layer; at the same time, the speed of the grate mechanism can be slowed down to prevent damage to the ash layer, which could lead to a drop in furnace temperature and subsequent carbon collapse. Once the resistance becomes similar to that under normal conditions, the speed can be increased again ； Furthermore, at this time one must not increase the resistance merely for the sake of the fire layer ； Adjust the ratio of upper and lower blowing as well as the blowing intensity appropriately, and use a gentle breeze for a longer period to maintain the furnace temperature ； c. When the ash melting point changes, leading to phenomena such as caking, wind tunnel formation, overturning, abnormal furnace temperature, and discoloration to red, the blowing intensity must be reduced first; however, the furnace temperature must not be lowered! Methods such as assisting with manual block removal, suppressing ash, or reducing the load. In short, maintaining uniform resistance in the ash layer, fire layer, and bed layer is key. (1) Selection of air pressure and volume: The key to burning low-quality coal lies in the selection of air pressure and volume, with a high volume and low pressure being the preferred approach. If the air volume is too low, it takes longer to raise the temperature, which makes it more likely to cause uneven airflow, localized overheating and scorching, as well as the formation of carbon deposits. If the wind pressure is not chosen appropriately, being too high (above 26 kPa) makes it difficult to control the temperature of the upper part of the furnace, and it can easily cause the contents to be blown off the walls. (2) Selection of cycle time percentage: The cycle time percentage should be determined based on the actual conditions of each factory. Due to the low heat storage capacity of the bed with low-quality coal, the gasification layer should not be too thick; therefore, a long cycle should be used primarily. (3) Selection of steam consumption for top and bottom injection: It is essential to maintain stable steam pressure entering the furnace. In our company, the steam pressure for burning lump coal is controlled at 0.06±0.05 MPa. Given the characteristics of lower-quality coal, the steam pressure can be increased by 0.005 MPa; simultaneously, the handwheel of the top-injection steam valve should be turned 1–2 turns further, so that the amount of steam used for top injection is slightly greater than that for bottom injection. This results in better aeration within the gasification layer and longer contact time between the various substances involved, thereby increasing the rate of steam decomposition and reducing heat loss. It also helps to loosen the lumps formed, leading to the creation of a stable ash layer. When the coal quality and furnace conditions are stable, the CO2 levels in the upper and lower streams are analyzed in order to adjust the steam output (the CO2 level in the upper stream should be maintained between 7.0% and 8.0%, while that in the lower stream should be kept between 4.0% and 5.5%). (4) Control of carbon layer height and furnace temperature: Effective control of the carbon layer height is key to stabilizing furnace operation. A relatively stable carbon layer height ensures a stable gasification zone. Large fluctuations in the carbon layer height can severely disrupt the gasification conditions, ultimately leading to reduced gas production and increased consumption. Operating with a high carbon layer is not advisable. In our daily operations, we have observed that once the carbon layer reaches 2.2 meters or more, the higher the layer, the slower its rate of decline (which means gasification becomes poor). This leads to an increasing thickness of the carbon layer, and the puller used to adjust it has to work harder, creating a vicious cycle. When the temperature in the ash bin and at the bottom of the furnace rises, causing the ash to ignite, the puller cannot increase its pulling force any further; as a result, the carbon layer rises even faster, the gasification process becomes chaotic, and ultimately the temperature in the upper part of the furnace rises sharply, leading to the furnace overheating and collapsing. Therefore, the control of the carbon layer thickness must be strict. Regarding furnace temperature control, we choose an upper temperature below 260 ℃, with 220–240 ℃ being the optimal range ； The downstream temperature is controlled at 250±30°C. It is advisable for the downstream temperature to be 20℃ higher than the upstream temperature. It should be specifically noted that the upper limit of the furnace temperature must be strictly controlled; an increase in this temperature is a precursor to deterioration in furnace conditions, and it is necessary to monitor and control it rigorously. 39) Where does the quench water enter the gasifier? Generally, there is a connection point below the syngas outlet of the gasifier; on the drawings, this is indicated as pipe port N5. This is the entrance for the quench water to enter the gasifier. At the production site, there should also be a quench water distribution ring on the platform above this entrance. The incoming quench water first flows into this distribution ring and then enters the four N5 pipe ports. Basically, the quench water is pumped by a quench water pump, filtered through filtration facilities, and then divided into four streams that enter the gasifier. Inside the gasifier, it flows through four connectors (of varying lengths) connected to the quench water pipes via flanges, into the annular flow channels of the quench ring which is welded to the top of the downcomer. From there, it flows downward along the outer wall of the downcomer in a nearly circular pattern, eventually reaching the water area at the bottom of the quench chamber. 40) Is water carryover severe in Texaco water-coal slurry gasification to shift water-gas? Is it necessary to install a separator at the start of the transformation section? How should the amount of water to be separated by the separator be considered (regarding the selection of the level control valve)? Where is this water generally directed to be discharged, and where is the air returned to be vaporized? Generally, a Texaco system with a single nozzle has a low water carryover amount, and a separator may not be necessary (depending on the operator’s skill level). In contrast, furnaces with four nozzles have a higher water carryover amount, so it is advisable to install a separator; the water separated can be reused in the gasification process (this water is quite clean and can be used for gas washing). Similar to systems with a single nozzle, in these systems as well the gas and liquid come into direct contact within the scrubber tower, and the output is saturated gas. When the pressure remains constant, the temperature stays roughly the same, with a vapor-to-gas ratio of between 1.3 and 1.4. The main reason for water carryover is related to the control of the liquid level in the scrubber tower; to prevent liquid water from reaching the conversion catalyst and affecting its performance, it is necessary to install a gas-water separator before the conversion process. Of course, it’s also possible that the distance is too great, resulting in some condensation water (in very small amounts; since the latent heat of vapor is high, condensation is difficult). Therefore, if there are no major issues with the scrubber tower, the focus should be on proper operational control to prevent the presence of water. A separator must be installed: 1. Water can easily be carried in during the initial stages of operation or when the gasification process is unstable! 2. Condensation as gas is transferred into the conversion pipeline is inevitable, with greater amounts of condensation occurring at greater distances ； 3. As a buffer, adjust the water vapor ratio ； 4. Wash and separate the fine coal ash that has been gasified! It is essential to install a separator, as its function is to protect the catalyst in the converter; after all, who can guarantee that the carbon scrubber will not contain any water? ； The severity of water carryover in carbon scrubber towers is primarily related to design parameters, the structure of the tower, and the design of the trays. Of course, operating conditions also play an important role. However, at present, the level of water carryover in carbon scrubber towers manufactured by domestic companies is generally under control; there are only a few cases where water carryover is severe. No further listing. The separator level can be monitored using either a double-flange level gauge or a float level gauge ； Due to the higher temperature and lower volume of water, the water is removed in the deoxygenation tank after pressure reduction. 41) The part of the multi-nozzle vaporization furnace that wears out most easily is the dome, which is also why the top of the dome overheats. Could increasing the height of the vault solve this problem? There is no way to modify a gasifier that has already been built, as the difficulty and cost involved are too high. The only part that can be altered are the refractory bricks; therefore, when constructing the furnace, care should be taken in arranging these bricks. It is best to design the refractory bricks on the furnace roof in such a way that they include channels for guiding the flow of air in a particular direction, thereby promoting convection. This helps to reduce the force of erosion, and thus lessens the impact on the furnace roof. Increasing the space above the burner can prevent wear on the refractory bricks in the dome ； The multi-nozzle technology differs from that used in the Texaco flow field; it operates in a counterflow pattern. Theoretically, this approach is more advanced than the Texaco flow field. In the case of the Guotai gasifier, overheating occurred due to insufficient space in the dome area, which led to accelerated wear of the refractory bricks in that area – overheating was thus inevitable. The operation of the third gasifier also shows that increasing the size of the dome area is indeed the right approach! 42) For the quench water filter, generally one spare unit is used. Is this necessary? If so, should the inlet valve or the outlet valve be opened? It is indeed necessary to have one quench water filter in use and another as a spare! ! If the filter becomes clogged and reduces the flow rate of the quench water, switching to or activating a backup filter can restore stable production. The inlet and outlet valves of the standby quench water filter must both be *closed before it is put into use. No matter which valve you open, it will create a dead zone inside the backup filter, which gets clogged as sediment accumulates, rendering it completely ineffective as a backup. During the operation of the gasifier, it is absolutely forbidden to stop the quench water; even a brief interruption in its supply can lead to serious consequences such as damage to the quenching ring. Therefore, backup equipment must be installed for safety reasons. 43) During the commissioning phase of the system, interlock testing of the instruments is required; what tests should be carried out on the lock hoppers at this time? 1. Lockfight program operation and debugging ； 2. Interlocked testing of the lockhopper slag inlet valve and lockhopper slag outlet valve ； 3. Low liquid level in the vaporizer – test of the lockhopper safety valve interlock \"off\" function ； 4. Low level of lock-tank liquid – test the interlock that causes the slag discharge valve to close ； 5. Hopper operation, hopper holding, manual/automatic mode testing of the hopper ； 6. Testing of valve operation caused by high and low pressure differences between the lock hopper and the gasifier. 44) What are the technical requirements for coal quality in coal-to-gas production? Different gasification technologies have varying requirements regarding coal quality. The general overview is roughly as follows: 1. The ash fusion point of fixed-bed gasification technology must be above a certain temperature, as *-state slag discharge ； High ash content doesn’t matter. 2. In dry powder gasification technology, the ash fusion point must not exceed a certain temperature; the coal ash melts during the gasification process and is then discharged in a highly solid state after being cooled ； A higher ash content isn’t a problem (at least in theory). 3. The ash fusion point requirement for water-coal slurry gasification technology is between the above two (? ? ） ； It seems that high ash content is not acceptable. 45) General information indicates that the optimal temperature for the gasification reaction of water-coal slurry should be 50°C higher than the ash fusion point (T4); this is a theoretical value. In actual production, there must be a specific reaction temperature. During the commissioning process, what testing methods should be used to determine this reaction temperature? Manufacturers that currently use GE Texaco gasifiers typically determine the oxygen-to-coal ratio and operating temperature based on experience. The common approach is as follows: 1. At the beginning of operation, while the thermocouples can accurately indicate the temperature inside the gasifier, a curve showing the relationship between the CH4 content in the syngas and the temperature is created, to serve as one of the guidelines for subsequent operations. 2. After the thermocouple fails, several parameters can be used to determine the oxygen-to-coal ratio and thereby adjust the operating temperature: (1) the contents of CH4 and CO2 in the syngas ； (2) Pressure difference at the gasifier slag outlet ； (3) Slag discharge status (seems to be used very little). However, a rather interesting phenomenon has been observed recently: normally, liquid slag discharge furnaces are required to operate at temperatures 50–100 degrees above the ash melting point. Yet in many actual water-coal slurry gasification furnaces, the operating temperature is below the ash melting point, and no slag clogging issues occur during operation; nevertheless, the service life of the refractory bricks can be **extended**. This issue is worth studying. The main properties of coal cinder that need to be considered include the ash fusion temperature, ash composition, and ash morphology. For coal types with excessively high ash fusion temperatures, fluxes must be added to lower the ash fusion temperature of the coal slurry. This is necessary both for the efficient removal of slag in a molten state and to enable operation at lower furnace temperatures, thereby extending the service life of the refractory bricks. The Texaco gasification process requires that the operating temperature of the gasifier be 50 ℃ to 100 ℃ above the ash fusion temperature, in order to ensure smooth slag discharge from the gasifier. Practice has shown that the principle used to control the operating temperature of the gasifier is not scientific, as some coal types have low ash fusion temperatures and high viscosity. Even at temperatures above its ash fusion temperature of 100 °C, slag discharge is not possible smoothly due to the high viscosity of the ash; therefore, operating temperatures selected based on traditional foreign experience did not yield satisfactory results. Later, a principle was established that takes the viscosity of the liquid slag as the control target for regulating the temperature of the gasification furnace; in other words, the optimal operating temperature for the gasification furnace should be such that the viscosity μ of the resulting ash sludge falls within the range of 25 Pa·s to 40 Pa·s. To reflect the melting fluidity of ash at different temperatures, it is necessary to analyze the viscosity-temperature characteristics of the coal ash used, and to determine the optimal operating temperature for the gasification furnace by taking into account the allowable range of ash viscosity. Adding an appropriate amount of flux, limestone, to the coal slurry can lower the ash fusion temperature; it also changes the acid-base ratio in the ash and alters the morphology of the slag. The addition of an appropriate amount of flux reduces the operating temperature of the gasification furnace, but the degree of flexibility in this operating temperature needs to be determined through specific analysis. Where conditions permit, an analysis of the specific morphology and physicochemical structure of the slag should also be conducted to understand its melting and polymerization properties as well as its physical abrasion resistance, thereby providing a solid theoretical basis for the stable operation of the slag system. 46) How should the slag water from the gasification furnace be treated? Besides three-stage and four-stage flashing, what other methods are there, and which one is relatively more effective? In Texaco’s coal water slurry gasification process, the ash treatment system typically employs a combination of high-pressure flashing and vacuum flashing. Due to differences in the gasification pressure levels and the uses of the flashed vapor, the flashing pressures and process configurations vary; the existing processes mainly include two-stage flashing, three-stage flashing with stripping, and four-stage flashing. The purpose of high-pressure flashing is waste heat recovery; the heat from the flashed vapor is generally used for the deoxygenation and heating of recycled graywater. In comparison, the temperature of the graywater after four-stage flashing or stripping processes is lower, which facilitates its clarification; therefore, four-stage flashing is a better choice for graywater treatment. In this approach, high-pressure flashing is used to separate the blackwater from the vaporization furnace from that from the carbon scrubber, followed by sedimentation in a clarification tank and separation of fine residues using a vacuum filter. 47) Regarding the oxygen flow rate control in the four-nozzle gasification furnace, is it better to use a cascade control system or a self-regulating system? The control of both oxygen flow rate and water-coal slurry flow rate constitutes a dual-cross regulation system, with the oxygen-to-coal ratio set as a fixed value. Theoretically, this control system can meet the process requirements while ensuring that the gasification furnace does not experience an excess of oxygen; that is, when the load increases, the water-coal slurry flow rate increases first, followed by the oxygen flow rate ； When the load is reduced, the oxygen flow rate decreases first, followed by the coal water slurry flow rate ； Ensure that the water-coal slurry is increased first and decreased later to prevent excess oxygen in the gasifier. Based on general industrial experience, the load of the gasifier does not change frequently; therefore, single-loop control is also used for oxygen regulation and water-coal slurry regulation respectively, in which case the oxygen-to-coal ratio needs to be determined manually. If the water-coal slurry flow rate is set, the oxygen flow rate value is calculated based on the oxygen-to-coal ratio, and then the oxygen flow rate is adjusted. 48) For a four-burner gasification furnace, if two burners fail, is it necessary to use nitrogen for purging in order to enable simultaneous operation? If so, how should the purging be carried out? A multi-nozzle gasification furnace has four pairs of burners, with each pair having its own interlock system; these two interlock systems do not interfere with each other! One pair of burners tripped; only that pair did, with moderate-pressure nitrogen being used for slight protection ； The other pair of burners is working properly; the gasification furnace only operates at reduced capacity. If the problem isn’t related to the burners, the burner that stopped functioning can be put back into use immediately, and this is the biggest advantage! 49) Use of coal water slurry additives. The rheology of coal water slurry is an important property that affects its atomization and combustion characteristics. High-quality coal water slurry not only has a high concentration but also exhibits good shear-thinning behavior, ensuring that the slurry has excellent pumping and atomization properties. This helps to reduce the energy consumption required for transporting the coal water slurry and improves its combustion efficiency. Since coal is hydrophobic, the main function of the additive is to improve the hydrophilicity of the coal surface, reduce the surface tension between coal and water, thereby enabling the coal particles to be fully wetted and evenly dispersed in a small amount of water. This improves the flow properties of the water-coal slurry and reduces its viscosity, while also ensuring that the coal particles remain evenly dispersed in water over time. In water-coal slurry, different types of coal require different additives, and the amounts and methods of addition also vary. Additives usually include dispersants, stabilizers, and other auxiliary chemicals. Dispersants and stabilizers are essential in the preparation of water-coal slurry. Dispersants can promote the uniform dispersion of the dispersed phase in the dispersion medium by reducing viscosity. The mechanism of action of dispersants can be considered from three aspects: wetting and dispersion, electrostatic repulsion for dispersion, and steric hindrance and entropy-driven repulsion for dispersion. Most dispersants are surfactants, consisting of a hydrophobic group and a hydrophilic group. When dissolved in water, the hydrophilic group is attracted to water molecules, while the hydrophobic group is repelled by them; as a result, the hydrophobic groups arrange themselves at the water surface, with their hydrophobic ends facing the gas phase and their hydrophilic ends submerged in water. When water contains hydrophobic substances such as coal dust, it will also arrange itself in an orderly manner on the surface of the coal dust, thereby effectively dispersing the coal dust particles. Dispersants can significantly reduce the surface tension of water and improve the wettability of the coal particle surface. The role of stabilizers is to ensure the stability of the water-coal slurry, that is, to maintain its uniform properties during storage and transportation. Water-coal slurry is a coarsely dispersed system composed of solid and liquid phases; the forces of molecular Brownian motion, the van der Waals forces between particles, and the electrostatic attraction between particles are all insufficient to prevent the particles from settling. Stabilizers, on the other hand, enable the particles already dispersed in the water-coal slurry to bond with other surrounding particles and water to form a three-dimensional structure that is weak but still possesses a certain degree of strength. This structural framework exerts mechanical resistance to the settlement of the particles, thereby ensuring the stability of the water-coal slurry. Typically, inorganic salts, polymeric organic compounds, and the like are used as stabilizers. At present, China has successfully developed three types of chemical agents that can alter the surface properties of coal and facilitate better adsorption of additive molecules on the coal powder surface, for use as stabilizers in the preparation of water-coal slurry. 50) What is the main purpose of high-pressure nitrogen in slurry coal gasification? Is it used for protecting the thermocouples in the gasifier? 1. It is used for purging the coal slurry and oxygen pipelines. 2. It serves as sealing nitrogen. 3. It is used as soot-blowing gas for the pressure guiding pipelines in the gasifier. High-pressure nitrogen refers to nitrogen with a pressure of 12 MPa. During normal operation, in the first furnace, the pressure-taking tube is used for nitrogen to blow away the ash and slag carried out by the gasification furnace; it also serves to reduce the temperature ； II. Used to protect the thermocouple at the temperature measurement point ； III. It is used to purge the oxygen and coal slurry pipelines during startup and shutdown, to remove gas from the furnace, and to partially replace the gas in the gasification furnace ； IV. When the gasification furnace is shut down, some of it is used to isolate oxygen and prevent hazards caused by leaks. Also, before introducing oxygen, nitrogen that has been partially depressurized (to 6.5 MPa) is used to dilute the oxygen; however, this is not high-pressure nitrogen. Furthermore, high-pressure nitrogen is not used for replacement after the system is shut down; at this time, the pressure of nitrogen is approximately 5.9 MPa. 51) What is the designed outlet temperature of the carbon scrubber in a Texaco water-coal slurry gasifier with a height of 2.8 meters, operating at a pressure of 6.5 MPa? What is the outlet temperature of the carbon scrubber during actual operation? What factors related to the gasifier’s operation affect the outlet temperature? The temperature of the syngas coming from the gasification unit of a 6.5MPa gasifier is generally around 240 degrees, with a water vapor ratio of about 1.4. After being washed and dust-removed in a venturi scrubber and a scrubbing tower, the crude gas from this gasifier has a temperature of approximately 241.9°C, a pressure of 6.28 MPa(G), and a water vapor/dry gas ratio of around 1.5; it is then sent to the shift reaction process. At 6.5 MPa, the process gas undergoes thorough wet heat exchange; the temperature of the gas exiting the carbon scrubber is approximately 243°C, which corresponds to the saturation vapor pressure of water. At this point, the water vapor ratio should be around 1.4. If the amount of quench water is insufficient, the temperature of the process gas leaving the vaporization furnace will be high, which may result in more water being carried along. The theoretical water vapor ratio is 1.4, but in practice it can reach at most 1.2. The main reason for this is that most manufacturers set the amount of water used for quenching to a much higher level than the designed value; in order to prevent damage to the quenching system, most of the heat from the syngas is transferred to the black water system, which results in a large amount of steam being produced in the deoxygenation tank and sedimentation tank, preventing the sludge from settling. 52) What is the function of the balance hole in the downcomer of the gasifier? Is there any difference? The balance hole can create vortices that help to wash away the slag accumulated on the defoaming strips. The original design concept was likely to eliminate the slag breaker and rely on this swirl effect to reduce the formation of large amounts of slag. But personally, I think that under the conditions of the quench chamber, there won’t be a large pressure difference between the inside and outside of the downcomer, so it’s likely difficult to create high-speed swirls; in my opinion, these four holes are useless. 53) Can the burner valve of the oxygen tube be removed? Mainly for safety reasons, some manufacturers still use manual valves for the oxygen feed section valves, which have to be opened manually on-site; I consider this to be very dangerous. The oxygen tube burner valve can be considered for removal for the following reasons: 1. The nitrogen filling valve opens after shutdown ； 2. Formation of a nitrogen plug between the two oxygen cut-off valves ； 3. After cutting the oxygen tube, a small flow of nitrogen is used for blowing. The system pressure has been reduced to atmospheric pressure; after nitrogen purging, the burner tip has been removed, so whether there is a burner valve or not makes little difference. 54) What role do the pins on the inner wall of the gasifier play in slag hanging? The size, arrangement, and angle of the pins have an impact on the degree of slag retention; can improvements in the pin arrangement lead to better slag retention results? The reason why there are many pins on the outer wall of the water wall tubes is twofold: 1. To secure the refractory lining. 2. Remove the water-cooled wall tubes that conduct heat from the surface of the refractory lining in a timely manner, so as to maintain a constant temperature in the refractory lining (the thermal conductivity of refractory linings is generally only 1/5 that of metal pins). The technological feature of shell is to use slag to resist slag. Slag pins are generally over 10 centimeters long and are used to hang slag. During operation, it is necessary to control the fluidity of the slag; if the temperature is too high, increased slag fluidity will reduce the thickness of the slag layer (and an excess of limestone will increase the viscosity of the slag), causing the slag pins to become exposed and get damaged. At too low a temperature, the conversion rate of carbon in the vaporization reaction decreases. 55) Shell feeds coal when the pressure in the gasifier reaches 1 MPa; feed is added after a certain pressure is established. Is the furnace pressure stable? Why was 1MPa chosen as this value? It is still closely related to the compressor. 1. This is mainly to ensure an adequate amount of quenching air when coal is fed in, in order to cool the molten fly ash generated as a result. 2. The quench compressor of the shell type is of single-stage cantilever design; it experiences a large axial thrust when starting at low pressures, and therefore should generally be started under pressure. It is understandable that domestically produced imitation machines of this kind have to be started under low pressure or at normal pressure due to the fact that such problems have not been properly resolved. 3. According to the performance curve of the quenching compressor, a pressure of over 0.6 Mpa is required; generally, a pressure in the range of 0.8–1.2 Mpa ensures that the amount of cooling air needed for coal feeding is met. 4. If SUB can withstand 2.0 Mpa or higher, it is then possible to feed coal as well; at this point, the transportation of pulverized coal becomes more stable, and the furnace pressure remains more consistent, which also places higher demands on SUB. 5. If coal is to be fed at a lower pressure such as 0.8 Mpa, the coal powder transportation system will still meet the requirements in this case. In order to feed coal at low pressure, it is usually because the SUB has not been properly tuned – there is a lack of confidence – so efforts are made to start feeding coal quickly in order to prevent a failure of the SUB. However, this increases the intensity of operations; many checks and preparatory actions need to be carried out in a very short period of time. 6. For the above reasons, it is appropriate to feed coal at a pressure of 0.8–1.2 Mpa; generally, 1.0 Mpa is used for coal feeding. 56) According to their operation manuals and control instructions, Shell’s gasification interlocks 12US-0105 and 12U5-0106 are designed for overpressure protection. It is not clear which equipment they are meant to protect, nor under what conditions this protection comes into effect (i.e., whether it operates during processes such as discharge or pressurization, or regardless of such processes) This is an isolation interlock on the coal supply line, intended to ensure that the high-voltage and low-voltage systems do not connect. Safety interlocks are designed to prevent valves that should not be opened from opening accidentally. Although the sequence control system has been designed in accordance with the principle of high-voltage and low-voltage isolation, the function of this safety interlock is to ensure that the required conditions are met before the valve is opened, under any circumstances or conditions (manual operation, other interlocks); otherwise, the valve is closed to achieve high-voltage and low-voltage isolation. 12US-0105 and 12US-0106 are two logic programs that interact in opposite ways: if the signals indicating that the discharge valve of V1201 and the pressure relief valve of V1204 are closed do not appear, then the connection valve between V1205 and V1204 as well as V1204’s discharge valve will close ； 12US-0106 is the opposite of 12US-0105; its main purpose is to prevent the pressure in V1205 from dropping, that is, to maintain the pressure in the coal pipeline and avoid a shutdown of the system. 57) In the Texaco gasification process, some heat exchangers used for treating ash water, such as wash water coolers and ash water heaters, are mostly floating-head heat exchangers. This is done to facilitate the removal of scale formed by the process fluid. However, this design has disadvantages such as complex structure, high metal consumption and resulting costs, as well as large floor space. Could U-tube heat exchangers be used instead? Is the scaling in the graywater tanks and after the deaerator that severe? Removing the graywater heat exchanger would result in significant heat loss; the sensible heat of the flash vapor could then not be utilized. To bring the temperature of the deaerator to around 108 degrees, a large amount of steam would have to be consumed. The use of a floating-head heat exchanger increases the shell side for heat exchange, enabling more thorough heat transfer and thus maximizing heat recovery. I don’t think the scaling in the deaerator and the graywater tank is that serious; a rinse during maintenance will be sufficient. Actually, it makes sense to use a graywater heater: 1. Scaling in the system is inevitable; don’t expect dispersants to solve all problems. 2. It helps ensure the system operates stably over a long period of time and reduces downtime. 3. A graywater heater costs only a few hundred thousand dollars, while if the system has to be shut down for descaling, it will take at least 3 months, and the scaling may not even be completely removed – the advantages are clear. In the early stages of the project, the factory investigated the operation of various pressurized gasification units in China. It was found at that time that the problem of ash and water accumulation in the quench chamber was a common issue, and this condition was one of the main factors affecting the long-term safe operation of the gasification furnace. In response to this situation, it was suggested that one of the causes of this phenomenon was an excessive heat load inside the quench chamber; therefore, the idea of reducing the temperature of the ash water entering the furnace was put forward, and it was ultimately decided to eliminate the ash water heater. As for the issue of increased steam consumption in the deaerator resulting from the removal of that heater, it was believed at the time that the steam discharged from the high-pressure flasher was relatively dirty and had no suitable use; therefore, using it for deaeration was an acceptable option. After implementing the above modifications, the gasifier operates quite stably, with phenomena of carrying ash and water occurring very rarely. 58) Can semi-coke be used as a raw material for Texaco gas generation? What are the advantages and disadvantages? Advantages: High fixed carbon content; if the ash melting point is low, it can be used to produce a carbon-rich water-based slurry for gas production, thereby improving efficiency and reducing oxygen and coal consumption. Disadvantage: Due to the light components, that is, the loss of volatile substances, it is difficult to ignite during feeding, which can lead to feeding failures. Strictly speaking, it is difficult to use semi-coke as a raw material. There are probably the following reasons: 1. Low volatility – since semi-coke has already removed the volatile components, this leads to reduced reaction activity and a lower carbon conversion rate ； 2. It is relatively difficult to turn semi-coke into a slurry; it is hard to crush, and it places high demands on the grinding mills. 3. Semi-coke absorbs water easily, has a high internal moisture content, and thus the pulp concentration cannot be increased. 4. The petroleum coke and semi-coke mentioned above are entirely different concepts; petroleum coke has much better reactivity than semi-coke. 59) Phenomena, causes, and treatment methods of water in the Texaco gasifier – Large fluctuations in the gasifier liquid level ； The venturi pressure difference fluctuates greatly, with the pressure difference increasing ； The liquid level in the scrubber tower rises; even after the amount of water entering the tower is significantly reduced, it is still not possible to control this rising liquid level ； Temperature of the support plate drops ； The amount of black water exiting the gasification furnace decreases, resulting in a reduced effectiveness of gas washing. Analysis of the reasons for water carryover: 1. As pressure and load increase, the heat flux inside the quenching chamber rises; once it reaches a critical value, the heat transfer mode shifts to inefficient film boiling. As the heat transfer efficiency declines, the gases inside the furnace carry away a large amount of water. 2. Under high-load operating conditions, the gas velocity in the gasifier increases, thereby enhancing its capacity to carry water. 3. Since the dimensions between the downcomer and the upcomer in the gasification furnace were designed to correspond to the original production capacity, when the production capacity increased, these dimensions were not adjusted accordingly; as a result, water clusters can easily form under conditions of water vapor supersaturation and be carried away by the high-speed airflow. 4. When the high-temperature syngas is instantly cooled in the quench chamber through the downcomer, both the temperature of the gas and that of the slag drop rapidly. The slag continues to sink, while the gas, carrying a small amount of water, rises along the annular space between the downcomer and the upcomer and is discharged from the syngas outlet. As the load increases, a large volume of gas impacts the bell shape structure at the lower part of the upcomer; as a result, the gas continues to rise through the liquid seal, inevitably carrying away a large amount of water with it. 5. Excessively high operating pressure and temperature, as well as a lack of experience among operators and unstable operation, are also causes of water carryover. Prevention and treatment methods for water presence: 1. When the liquid level in the vaporizer drops and cannot be controlled effectively, the most effective approach is to reduce the production load accordingly, thereby decreasing the amount of gas generated and lowering the gas flow velocity between the rise tubes. 2. Under high load conditions, it is difficult to keep the liquid level in the gasifier too high. 3. When water is present in the vaporization furnace, the water supply rate to the venturi should be reduced accordingly, in order to lower the excessive pressure difference across the venturi and to facilitate control of the liquid level in the scrubber tower. 4. When water appears in the gasification furnace, the opening of the furnace’s drainage control valve should be increased to disrupt the conditions that lead to the presence of water in it. However, the drainage volume should not be too large, in order to prevent the furnace’s liquid level from dropping too low and causing it to shut down. 5. During operation, stability should be prioritized to prevent the reckless increase of production load. When increasing the production load, it should be done gradually; rapid or excessive increases are strictly prohibited. The operating temperature should be determined based on the ash fusion point of the coal, and it must not be too high. 60) What effects will occur if the operating temperature of the Luzzi furnace reaches the ash fusion point? Will the Luzzi grate slag discharge system be affected? Will it cause the device to stop? What happens if the operating temperature is too low? Logically, the ash fusion point of coal cannot be completely uniform, as it is influenced by various factors such as the type and quantity of impurities in the coal, as well as the inherent composition of the coal. It is entirely possible for the temperature in certain areas of the combustion zone to exceed the ash fusion point; however, as long as the vaporizing agent flows smoothly and evenly at an adequate velocity, the molten ash will cool and form slag without sticking together, resulting in fine granules of slag that can still be discharged smoothly. The presence of small agglomerates in the slag discharged during the actual operation of the Luzzi furnace indirectly supports this conclusion. When the temperature reaches the ash fusion point, coal tends to form slag easily; especially coal with high cohesion can readily cause bridging inside the furnace, material accumulation, and difficulties in ash discharge. Failure to remove ash in a timely manner can cause the ash layer on the furnace body to rise, leading to high outlet temperatures; in severe cases, this can result in oxygen breakthrough, and improper handling can easily lead to the shutdown of the equipment! At too low operating temperatures, coal cannot burn completely; instead, the level of CO2 produced increases, as there isn’t enough thermal energy to facilitate the gasification reaction C + CO2 = 2CO. This results in a decrease in the amounts of the useful components CO and H2, leading to a waste of resources. Additionally, too low a temperature can also cause O2 breakthrough. 61. What are the symptoms, causes, and solutions for leakage in the coal slurry pipeline of the burner? Answer: Phenomenon: (1) The operating temperature of the vaporization furnace increases ； (2) System pressure drops ； (3) Decreased gas production. Reason: There is coal slurry leakage from the drain line of the burner coal slurry pipeline. Handling method: (1) If the process parameters mentioned in 4.5.1 change rapidly, stop the machine immediately ； (2) If the process parameters referred to in 4.5.1 experience only minor changes or changes at a slow pace: ① Discontinue ratio control, and refer to the temperature at the outlet of the gasifier to appropriately reduce the oxygen flow rate ； ②Inform the personnel on site to go to frame 703 and slowly close the drain valve of the furnace coal slurry pipeline ； ③When dealing with coal slurry leaks, if the amount of leakage is very small, it is essential to gradually reduce the leak rate to prevent excess oxygen in the gasifier. If the leakage amount is not extremely small, shut down the system for handling ； (3) Closely monitor the changes in CH4, CO2, CO+H2, and the pressure difference at the slag outlet; take shutdown action if any abnormalities are detected. 62. What are the symptoms, causes, and solutions for sticking or severe wear of valves LV1303A1 and LV1303A3? Answer: Phenomenon: The liquid level in the quench chamber of the vaporization furnace is difficult to control and shows a downward trend. Reason: Worn valve core or stuck scale deposits. Treatment method: (1) Increase the amount of quenching water ； (2) Appropriately close the manual ball valve in front of valves LV1303A1/LV1303A3 ； (3) In severe cases, the production load can be appropriately reduced ； (4) LV1303A1/LV1303A3 for maintenance during shutdown. 63. What are the symptoms, causes, and solutions for clogging at the slag outlet of a gasification furnace? Answer: Phenomenon: (1) Increased pressure difference in PDI203 ； (2) Reduced slag discharge volume from the slag skimmer ； (3) Abnormal temperature TI212 of the support plate. Reason: (1) The combustion chamber temperature is lower than the ash fusion point T3 of the coal slurry ； (2) PDI203 gives inaccurate readings ； (3) The type of coal used for pulp production has changed; coal with a high ash melting point has been mixed in, resulting in sludge with high viscosity and poor fluidity ； (4) Misalignment of the nozzle causes uneven spraying or poor atomization. Treatment method: (1) Slightly increase the furnace temperature and keep it at a normal level, around 50°C above the T3 temperature ； (2) Check and confirm that PDI203 is free of faults ； (3) Conduct timely analysis when changing coal types; the use of coal types with high ash fusion points is strictly prohibited ； (4) If the burner has been in operation for too long, it can be shut down to replace it with a new burner ； (5) Closely monitor the temperature of the gasifier wall; emergency measures must be taken if overheating is detected. 64. What are the phenomena, causes, and treatment methods for the entrainment of large amounts of carbon black in the slag from a gasification furnace? Answer: Phenomenon: (1) High content of combustibles in the slag ； (2) The coal slurry flow rate does not match the oxygen flow rate; the oxygen flow rate is lower than normal ； (3) Low gas production. Reason: (1) In the burner

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