Problems with coal for water-coal slurry gasifiers!

What I saw on other websites was likely written by experts from Nanhua; I hope it can be helpful to you. A brief discussion on the key points for the stable operation of Texaco gasifiers. Abstract: Based on the actual operating conditions of the Texaco gasification unit at Weihe, this article discusses the key aspects for ensuring the stable operation of Texaco gasifiers, focusing on three areas: improving the quality control of raw coal, selecting appropriate operating temperatures, and proper preparation of the gasifier. Keywords: Texaco, gasifier, stable operation, key points. The Texaco water-coal slurry gasification unit in our plant is currently the one with the highest pressure level in operation in China. Its long-term stable operation not only enables our group company to raise its production standards to a new level but also provides valuable insights for the development of coal chemical industry in our country. Based on the actual operating conditions of our company and my many years of operational experience, I would like to share my views on the key points for the stable operation of Texaco gasifiers. 1. Strengthen the quality management of raw coal and increase the slurry concentration. This is done in order to further enhance the production capacity of the gasifier, ensure its long-term, safe, and stable operation, and achieve high yields, high quality, and low consumption. Firstly, it is necessary to strengthen the quality control of coal; parameters such as fixed carbon, chemical activity, mechanical strength, thermal stability, and ash fusion point must be strictly checked before the coal enters the plant, with efforts to improve these qualities ； Try to minimize the content of impurities such as sulfur and ash. The ash content should be given priority attention, as it needs to be as low as possible. At the same time, ensure proper preparation of the coal slurry, stabilize its concentration, and increase it as much as possible. 1.1 Strengthening coal quality management: Ash content is given priority for the following reasons: Firstly, ash directly affects the effective components in coal, which in turn influences the efficiency of coal gasification. Practice has shown that for every 1% increase in ash content, the production capacity decreases by about 1.8% under the same condition of coal slurry fed into the furnace; this will severely restrict the high-load operation of our facility. Secondly, SiO2 is the main component in the ash. Based on years of analysis of the raw coal used in our plant, a higher ash content indicates an increased amount of coal gangue in the coal, which in turn leads to a higher SiO2 level. This results in a decrease in the ratio of CaO+Fe2O3+MgO to SiO2+Al2O3 in the coal ash. This acid-base ratio is directly related to the viscosity and melting point of the ash. Whenever the ash content increases, we are forced to raise the furnace temperature in order to ensure that the slag can be discharged properly. This inevitably increases oxygen consumption, reduces the service life of the refractory bricks, and negatively affects the company’s economic performance. Furthermore, the ash content is high, with a high level of SiO2 in it; the fine ash contains numerous sand-like particles that are hard and prone to settling. This can cause wear and even leakage in pipes, or it can lead to blockages in those pipes due to sedimentation. In the past, when Huangling coal was used, its high ash content caused severe pipeline erosion, sometimes requiring shutdowns for repairs, which directly affected the normal operation of the gasifier. Finally, when the ash content is high, transportation costs increase. For example, when purchasing coal with a carbon content of 80%, 10% less waste is generated compared to coal with a carbon content of 70%, and thus the transportation cost is reduced by 10% as well. At the same time, the transportation costs for slag disposal and the costs associated with storing the slag increase, which is detrimental to reducing production costs. Coal management should be aimed at serving production, with strict control over the quality of coal entering the plant, in order to minimize the ash content in the coal. After switching to Huating coal, the ash fusion point of our company has decreased significantly compared to before; it now generally remains at 1250°C. With the addition of solvents, this value drops to between 1150°C and 1180°C. Based on operational performance, oxygen consumption has decreased, and the service life of the furnace bricks has increased markedly, reaching 19,000 hours – they can still operate for another 2,000 hours or more. Maintenance costs have decreased, and production costs have also dropped significantly. Therefore, for our company, ash content should be given priority attention, and its changes should be monitored to provide guidance for the operation of the gasification furnace. 1.2. Preparation of coal slurry During the preparation of coal slurry, it is necessary to stabilize the operation of the coal grinder and increase the concentration of the coal slurry as much as possible. 1.2.1 Optimize the ratio. The ratio of large to small rods in the coal grinder is determined based on the particle size distribution and grindability index of the coal, in order to achieve an optimal particle size distribution of the coal slurry and thus ensure a high concentration of the slurry. Selecting appropriate process conditions (the ratio of coal to water) and achieving the optimal particle size and particle size distribution are key to preparing high-concentration water-coal slurry with good fluidity and stability. After operating for a certain period of time, a comparative analysis is conducted on the wear condition of the coarse and fine rods in the coal grinder as well as the particle size distribution of the coal slurry, to determine whether it is necessary to replenish the number of rods in the coal grinder. 1.2.2 Select high-quality additives. Additives have a dispersing effect in water, and can reduce the hydrophilicity and charge density on the surface of coal particles. Appropriate additives can reduce the hydration film on the surface of coal particles as well as the forces between them, thereby altering the fluidity of the coal slurry; the finer the particle size of the coal slurry, the more pronounced this effect is. Select appropriate additives and their dosage based on the properties of the coal. If the addition amount is too small, the viscosity of the coal slurry increases, which is unfavorable for pumping ； If the amount added is too large, the cost of the additive will be high; the optimal amount to add should be determined through experiments. 1.2.3 Reduce the frequency of coal mill shutdowns and ensure stable operation. During the operation of the coal grinder, try to minimize the number of times it stops, as this can lead to a decrease in the concentration of the coal slurry due to water being used to flush the pipelines. During the operation of the coal grinder, pay close attention to changes in the grinder’s power and the current of the agitator in the outlet tank. When skilled in operation, one can use this to determine changes in the slurry concentration, thereby making timely adjustments to maintain a high slurry concentration. During on-site mill maintenance, minimize the number of times the mill drum screen is flushed in order to reduce the amount of water that enters the coal slurry tank directly, which helps maintain a high concentration of the coal slurry. After switching the coal used for gasification in our company to Huating coal, through the joint efforts of everyone, it is entirely possible to keep the concentration of the coal slurry above 61%. In the event of ink leakage, the cause should be identified first, rather than simply dealing with it by reducing coal usage or adding water. Without stopping the coal slurry flow, increase its concentration as much as possible to provide high-quality coal slurry for gasification. 2 Selecting an appropriate operating temperature is essential for stable and efficient operation. The principle for choosing the vaporization temperature is to select the lowest possible temperature while ensuring the liquid slag can be discharged. The specific method to determine this is to set the viscosity of the liquid slag slightly below 250 CP, which represents the optimal operating temperature. During the operation of the gasifier, the control of operating temperature is particularly important, as it directly affects whether the gasifier can operate stably over a long period of time. By resolving the temperature issue in the gasifier, the main problems associated with Texaco gasification are solved. In practical operations, differences in individual capabilities and varying levels of expertise lead to significant variations in the control of temperature. Therefore, the fluctuation in furnace temperature significantly affects the stable operation of the gasification furnace. The control of furnace temperature is mainly achieved by adjusting the oxygen-coal ratio. During operation, an excessively high oxygen-to-coal ratio increases the system’s thermal load, reduces the composition of the useful gases, and raises the CO2 level. Additionally, if the gasification temperature is too high, it accelerates the corrosion of refractory materials, affecting or shortening their service life, and may even cause the refractory lining to be damaged. Practice has shown that when the operating temperature of the gasifier is increased by 50°C for 3 to 5 days, the lifespan of the furnace bricks is significantly reduced; in severe cases, problems such as brick detachment and cracks occur. This can lead to overheating of the furnace walls, resulting in shutdown. If the oxygen-to-coal ratio is too low, the furnace temperature drops, the slag outlet narrows, the pressure difference in the gasification furnace increases, resulting in unstable operation and greater difficulties in handling the process. At the same time, the amount of fine ash increases, putting more strain on the ash treatment system, which in turn leads to a deterioration in the overall performance of the gasification water system and hinders the long-term stable operation of the gasification furnace. In actual operation, the furnace temperature is determined mainly from the following aspects. 2.1 Temperature: When the thermometer in the vaporization furnace indicates accurately, we compare the displayed temperature with the FT temperature, striving to keep the operating temperature as close as possible to the FT temperature. Run it for 24 hours to check if everything is working properly, and then decide whether to make any adjustments. 2.2 Observe the trend in the composition of the process gas. Among the four online analysis tables for H2, CH4, CO, and CO2, the composition of H2 remains relatively stable; if its concentration changes significantly, it indicates that the furnace temperature has changed greatly, and adjustments must be made promptly. The variation in H2’s concentration should not exceed 1%. It is also feasible to regulate the furnace temperature using the relationship between CO and CO2; in operation, CO2 should be used as the main control parameter. This parameter is related to the type of coal and the slurry concentration; we generally keep it between 18% and 21%. To observe the trend in furnace temperature by tracking changes in CH4 levels, based on my many years of experience, maintaining CH4 levels at 400–800 ppm for Huating coal ensures stable operation and optimal results. 2.3 Inspecting the slag: The slag is a product of the gasification furnace, and it provides an immediate indication of the temperature within the furnace. The normal size of coarse slag is between 5 and 8 mm; it is normal for this type of slag to account for 7% to 8% of the total slag volume, which indicates that the furnace temperature is at the appropriate level, and this condition should be maintained. If the particle size decreases and the number of large particles reduces, it indicates that the furnace temperature is too high; the oxygen-to-coal ratio should be reduced ； If the particle size increases, meaning there are more large particles, it indicates that the furnace temperature is too low; in such cases, the oxygen-to-coal ratio should be increased to adjust the furnace temperature. If there is needle-shaped slag, it indicates that the slag outlet has narrowed, due to an excessive flow rate of the slag. In such cases, the furnace temperature can be increased slightly to slow down the melting of the slag and restore the size of the slag outlet. This process should not be carried out too quickly; moreover, oxygen should be added in small amounts multiple times to prevent the slag outlet from narrowing again, as this would result in an increased amount of slag being discharged. 2.4 Vaporizer pressure difference: As long as the vaporizer operates smoothly and the temperature is within the appropriate range, the pressure difference remains balanced. If the furnace temperature is low, the slag outlet becomes smaller, the pressure difference increases, and the composition of the gases also changes significantly. During operation, after reducing the oxygen-coal ratio, the pressure difference remained almost unchanged in the short term; however, after 6 hours, it began to increase gradually, posing a risk for future operations. During the operation of the gasifier, it is necessary to consider four aspects together to determine whether the oxygen-coal ratio is appropriate and whether the furnace temperature is reasonable; conclusions regarding the level of the oxygen-coal ratio should not be drawn in a superficial manner. The author believes that once we know the composition of the coal slurry and the ash fusion point of the coal, we should have a definite operating temperature. At the very least, there should be a definite and relatively narrow temperature range for a certain period of time. In other words, there is a fixed oxygen-coal ratio over a certain period of time. Considering the actual conditions of our plant and the available coal types, it is appropriate to maintain an oxygen-to-coal ratio of 490–495 Nm3/m3. 3. Doing a good job in furnace preparation is key to stable and efficient operation. Under the current production conditions, the gasification process is becoming increasingly stable, and the situation is very favorable. However, we must not be careless. In previous production, problems such as pipe leaks, poor slag discharge, and water in the gasification furnace occurred frequently; these have decreased significantly now, but new issues may still arise. On the premise of maintaining stable production, think about what might happen, and how we should handle it and what actions we need to take. Think more, observe more, maintain stable production, and optimize operations. During the preparation of the gasification furnace, tasks such as pipeline flushing, removal of slag accumulated inside the furnace, maintenance of pumps and machinery, inspection of furnace bricks, and regular inspection and cleaning of the trays in the carbon scrubbing tower must be carried out with utmost care. This ensures stable operation of the gasification process over extended periods, and it can also serve as a reference for technical upgrades. As time goes by, the wear and tear on the equipment increases steadily; therefore, in our operations, we need to consider more factors and think ahead on a longer term basis. The operation of the standby furnace in a two-in-use-one-backup system is particularly important; the workshop strictly controls the time spent preparing the furnace, ensuring that all tasks are completed in the shortest possible time. Table 1: Preparation time for the gasification furnace and work schedule. Work item: Preparation time – The time required to complete post-shutdown processing of the gasification furnace and to cool it down. Inspect the blind end at the bottom of the carbon scrubber tower, inspect the filter and connect hoses, flush the quench water pipeline, and reset the filter. Venturis for water pipelines in the gasifier ash system – inspection and repair, pipeline cleaning. Remove the manhole after 48 hours, inspect and clean the distributor blind ends. Disassembly and inspection of the inlet and outlet valves of pump P1301. 4h: Remove the thread plug and short tube, then clear and clean it. Removal of slag accumulation in the furnace. Reset plug, short tube. Disassembly, inspection, and calibration of control valves. At 14 hours, a water distribution test was conducted in the vaporization furnace; after no leaks were detected, the scaffolding was removed and the manhole was restored to its original position. Heating burner. Heat with LPG for 6 hours; after reaching 600°C, switch to diesel, start H1301, and maintain a constant temperature at 850°C. Regular inspection and cleaning of the 24h carbon scrubber trays, as well as other routine inspection tasks. All work related to preparing the furnace was completed within 96 hours. I believe that focusing on these tasks will undoubtedly be highly beneficial for the long-term stable operation of our plant’s gasification furnace. As long as we persevere and continue to carry out these tasks consistently, the Texaco gasification unit will not only be able to operate stably over extended periods but also save oxygen and reduce coal consumption, thereby making further contributions to increasing the company’s production and efficiency. Only by carrying out these tasks to ensure the high-quality and efficient operation of the equipment can the advancement, reliability, and cost-effectiveness of the Texaco gasification technology be fully demonstrated, thereby laying a foundation for the widespread adoption of this gasification technology. This post was last edited by kaike8899 on 2009-3-13 22:18.]

It’s very beneficial to read it carefully! Thanks for the info from the 2nd floor! Saved! ! !