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A tentative suggestion; Source: http://bbs.hcbbs.com/thread-428065-1-1.html. Question: Adjustment of the feed position in the stabilizer. It is necessary to maintain stable pressure at the top of the stabilizer; if there is an increase in the amount of liquid hydrocarbon components in the deethanized gasoline, the feed position of the stabilizer can be adjusted downward accordingly. Can this sentence be understood as follows: If there are many liquefied gas components in the deethanized gasoline, then the pressure at the top of the stabilizer rises, and the feed position of the stabilizer should be adjusted downward to reduce this pressure? 　　What is the correct understanding? Analysis: The adjustment of the feed position in the stabilizer is primarily carried out based on the product quality of the stabilized gasoline. In quality control, vapor pressure is generally considered as a process parameter for both summer and winter conditions, and adjusting the feed position is done to meet these requirements. Raising the feed position of the stabilizer tower and increasing the number of plates in the stripping section helps to control the vapor pressure of gasoline, but it is not favorable for controlling the C5 content in the liquid hydrocarbons. Below the feed level of the stabilizer column, the increase in the number of plates in the distillation section helps to control the C5 content in the liquid hydrocarbons, but it is not conducive to controlling the vapor pressure of gasoline. Therefore, assuming that the degasified gasoline contains a high amount of liquefied gas components, this will increase the pressure at the top of the stabilizer; the feed point to the stabilizer can be adjusted downward to reduce this pressure. The stabilizer column is a standard separation column. The middle part of it serves as the feed zone; the upper part of this zone is the distillation section, while the lower part is the stripping section. When the components in the feed are light, the vapor load increases, which corresponds to an increased load on the distillation section. Therefore, increasing the number of trays in the distillation section, or moving the feed inlet downward, can reduce the load at the top of the stabilizer column, thereby lowering the pressure at its top. As the feed composition becomes heavier, it indicates an increase in the load at the bottom of the tower; therefore, the number of trays in the stripping section must be increased, and the feed inlet moves upward. The meaning of the sentence above is that the liquefied gas content in denatured gasoline increases, meaning the gas-phase load rises; therefore, the number of trays in the distillation section should be increased and the feed inlet should be moved downward. Lowering the feed inlet allows the light components in the feed to be pushed downward, thereby reducing the load on the top of the tower. However, it is important to ensure that the C4 components in the stable gasoline meet the required standards. The most direct and effective way to adjust the pressure at the top of the stabilizer is to adjust the three-valve assembly there; such adjustment has a lesser impact on the stable operation of the entire stabilizer compared to adjusting the feed position. Since the feed contains a large amount of gaseous components, lowering the position of the feed inlet appropriately aims to increase the contact time between the gas phase and the liquid phase inside the tower (the reflux in the tower), thereby facilitating better mass exchange. Reducing the heavy components in liquid hydrocarbons also lowers the pressure at the top of the stabilizer. If the feed rate remains constant: as the feed moves downward, the pressure at the top of the tower decreases. However, in order to ensure that the gasoline at the bottom of the tower meets the required standards, it is necessary to increase the reboiling amount at the bottom of the tower. As a result of this increased reboiling, the pressure at the top of the tower rises, thus creating a vicious cycle. Obviously, the operation is unfavorable. Unless the feed load is reduced. The feed has become lighter; the normal procedure is to raise the feed inlet, and control the pressure at the top of the tower by adjusting the three-valve assembly there. This also helps to reduce the load on the lower part of the tower and improve the quality of the product at the bottom of the tower.

Source: http://bbs.hcbbs.com/thread-473338-1-2.html Title: Issue of reduced density in catalytic slurry Analysis: I. There are three options for what to do with the slurry at the bottom of the distillation tower: 1. Send it back to the riser for reprocessing, 2. Return it to the distillation tower after heat removal, or 3. Discharge it as residue from the plant. II. The most direct measure: The reduced density of the oil slurry discharged by the device indicates an increase in the light components within it; distilling out these components is the most direct approach. Specific approach: In terms of operation, first reduce the heat absorbed by the slurry (such as the heat absorbed by the steam generator) to raise its temperature, and then increase the slurry circulation rate to allow the light components in the slurry to evaporate. Once the requirements are met, reduce the oil slurry circulation rate. If the temperature drops, on one hand heat extraction is reduced, and on the other hand the amount of reprocessed oil returned to the tower is decreased; with less oil returning to the tower, external heat extraction also decreases naturally. Once the requirements are met, increase the oil slurry circulation rate. Note: Prevent coking in the catalytic fractionator! The fractions of diesel and similar substances should become heavier, while remaining within the specified quality range. Secondly: other methods to increase the bottom temperature of the distillation column. III. More in-depth approaches: 1. From the perspective of the entire system, the fact that the slurry has become lighter indicates that the degree of reaction has decreased; in other words, as mentioned on floor 7, it is necessary to increase the degree of reaction. This is closely related to the product distribution; it is important to note an increase in the olefin content in gasoline, a decrease in the cetane number of diesel, an increase in the amount of dry gas, and so on. 2. Increase the amount of oil reused in the reprocessing process; as mentioned on floor 8, this will raise the yield of light oil, but it will also increase the amount of coke produced, resulting in a decrease in the plant’s processing capacity. 3. Improve the quality of the catalyst, or add additives; the effect of adding additives is quite significant.

Source: http://bbs.hcbbs.com/viewthread.php?tid=365271&extra=page%3D1%26amp%3Bfilter%3Dtype%26amp%3Btypeid%3D7 Title: Pressure Fluctuations in the Catalytic Settler – Preliminary Analysis: The pressure in the settler of catalytic cracking units often rises suddenly and without any warning, by 10–20 kPa, before dropping back to normal levels shortly thereafter. Before the sudden increase in precipitator pressure, all other parameters remained unchanged, and the speed of the air compressor, etc., also stayed the same. It was found that the pressure at the partition top preceded the fluctuations in the pressure at the settler top by about 5 seconds. The pressure at the compressor inlet lags behind the peak pressure fluctuations by about 10 seconds and shows an upward trend. The pressure drop in the settler centrifuge decreases, basically in sync with the separation peak. The riser pressure drop decreases, lagging behind the split top by about 3 seconds. The steps are as follows: the pressure at the dividing top rises, while simultaneously (or slightly later than the dividing top) the pressure drop in the separator of the settler decreases. After 3 seconds, the pressure drop in the lift pipe decreases; after 5 seconds (based on the time of fluctuation in the pressure at the dividing top, the same applies hereafter), the pressure in the settler rises. After 10 seconds, the pressure at the inlet of the air compressor increases. (The time data may have slight discrepancies, but the order of events should be correct.) During fluctuations, there is no significant change in the level of the oil-gas separator. The control valve for the pressure pump’s oil supply line remains in automatic mode, with no significant change in its position. It generally occurs every 6–8 hours. The steam used in my setup has a pressure of 1.0 MPa and a temperature of over 260°C; it contains no water. The temperature in the raw material buffer tank is around 250°C. If the raw material contains water, the pressure in the settler should fluctuate continuously, the reaction temperature will vary, and the levels in various vessels will be unstable. Our anti-backflow valve is kept fully closed at all times, as the air compressor operates at near full load. The settler pressure and the top partition pressure fluctuate synchronously. Furthermore, as the pressure in the settler increased, the reaction temperature dropped sharply; therefore, the possibility of instrument malfunction can be ruled out. The facility is located in the Central Plains region. Pressure fluctuations have nothing to do with temperature; they occur sometimes during the day and sometimes at night. Generally, a fluctuation occurs every 6 to 8 hours. There are two sources of feedstock: one is the hot feedstocks such as reduced-pressure distillate oil and reduced-pressure residue from the distillation unit, and the other is the so-called cold feed – deasphalted oil coming from the tank farm, at around 90°C. The mixing temperature inside the raw material buffer tank is approximately 250°C. We also suspect that air leakage occurs when the condensate oil enters the split-top gas-oil separator, but no evidence has been found to date. The workshop carefully examined the historical curves and found no associated abnormal operations. So we’re asking everyone to share their ideas to help identify the cause. In-depth analysis: 1. Has there been any change in the reaction feed temperature, and is the raw material containing water? ； Is the steam used in the settler contaminated with water or subject to pressure fluctuations? The fact that the speed of the compressor does not change does not mean that the inlet pressure remains unchanged; adjust the operating curve to see if there is any change in the flow rate due to backflow. 2. If none of the parameters change, there is a high likelihood that the measuring device is problematic ； If the measuring instrument is fine, there must be corresponding changes in the other parameters. One can check the collecting duct pressure, the preheating temperature of the feedstock, the outlet temperature of the heat exchanger used for distilling the feedstock, the regeneration temperature, the amount of feedstock, the pressure drop in the distillation column, and so on; it might be due to water content in the feedstock or some fixed operating procedures in the tank area. Our installation experienced fluctuations every two hours, caused by the tank area. 3. If the measuring instrument is fine, I think it’s likely that condensation water has formed in that steam line and, to some extent, has entered somewhere in the reaction-distillation system. The most suspicious thing is accident steam. We experienced this before in the coking unit; it lasted for half a year, with regular pressure fluctuations for which no cause could be found. People said it was haunted. It was later found that a steam check valve on the furnace was not sealing properly; there was a long section without insulation, and the design had issues as well, which led to water accumulation. Turn off the steam and everything will be fine. Does the 4.3.5MPA steam also fluctuate simultaneously? Based on the observations, it seems likely that there is water present; it’s not the raw material that contains water, so the anti-coking steam at the top of the settler should be checked. 5. Check the trends to see which pressure – that of the distillation tower or that of the settler – changes first. If the pressure in the distillation tower changes first, then there is no need to check the reactor and the settler; instead, verify whether there are any issues with the instruments related to the second stage of the compressor, and determine when the compressor’s condensate is produced. 6. If the pressure in the settler changes before that in the fractionation tower, check the reaction side. If the temperature and pressure in the riser change before those in the settler, or if changes in the amount of material in the settler occur after the pressure changes, analyze whether there is water in the feed material and whether the pre-riser steam contains water. The focus should be on determining whether water is present, and also check the conditions of the regeneration inclined tubes. If changes in the amount of material in the settler and the density in the stripping section occur before changes in the settler’s pressure, then investigate the issues related to the settler and the stripping section; check whether the stripping steam contains water, whether there is any coking, and whether the conditions of the raw material inclined tubes are normal. If there are circulation inclined tubes, also check whether their conditions are normal. In short, it is necessary to determine whether there is coking or large bubbles forming in the stripping section. 7. Observationally, irregular amounts of condensed steam are entering the reaction pressure system. In our unit, periodic fluctuations in regenerator pressure occurred. After thorough investigation, it was found that the issue was caused by a faulty self-protection valve for accident steam; condensed water was intermittently entering the main air stream and thus the regenerator. Thereafter, we installed a steam trap in front of the vent valve of the main steam accident self-protecting valve, and this phenomenon was eliminated. Final result: The cause of the pressure fluctuations in the settler has been preliminarily identified: Our facility is equipped with a heavy diesel extraction port and a heavy diesel stripping tower; since there is no market for heavy diesel, no production takes place, and thus the extraction port remains blocked. However, there was internal leakage in the stripping steam valve for heavy diesel; steam entered the heavy diesel stripping tower and condensed into water. This water eventually flowed into the fractionation tower via the steam return line at the top of the stripping tower, causing fluctuations in the pressure at the top of the fractionation tower, which in turn affected the pressure at the top of the settler and the inlet pressure of the compressor. It has been nearly 48 hours since we vented the water from that stripping tower, and there have been no more fluctuations in the pressure of the settler.

Source: http://bbs.hcbbs.com/viewthread.php?tid=260755&extra=&highlight=&page=1 Question: Selection and maintenance of inlet and outlet valves for slurry pumps. Slurry pumps are key equipment in catalytic units; problems with the inlet and outlet valves of these pumps can affect their availability for use or maintenance, posing risks to the long-term safe operation of the unit. Due to the high temperature of the medium, its high viscosity, and the presence of catalyst particles, it is necessary to select appropriate valves and follow proper operating procedures in order to ensure their proper functioning. Discussion results: 1. Strengthen stable operation, strictly control the solid content of the slurry, and reduce wear on valves ； 2. For the inlet and outlet valves of the slurry pump, cemented carbide gate valves are recommended; butterfly valves are prone to internal leakage and have high operating resistance ； 3. If conditions permit, dual valves can be added to increase the safety factor; the valves are used only in the fully open or fully closed position ； 4. Regularly switch the slurry pump, and minimize the dead zone in the outlet pipe of the standby pump to prevent the catalyst-containing slurry from depositing and solidifying ； 5. Regularly monitor the slurry pipelines and valves, and replace the inlet and outlet valves on a regular basis. Areas for investigation: 1. Use of gate valves with high-temperature resistant and wear-resistant linings; 2. Selection of appropriate drive mechanisms for gate valves to reduce the workload on operators

Post source: http://bbs.hcbbs.com/viewthread.php?tid=193043&highlight= Question: How can excess gas be prevented from being sent to the flare when the catalytic unit is started up? (For reference only; no detailed verification has been done.) Preliminary analysis: When starting up a catalytic unit, it is often necessary to light the flare first; the large amount of excess gas generated during reaction and fuel injection is burned by the flare, and the flare can only be turned off once the system is operating stably. The losses are huge. Approach: Stabilize the system stamping process by integrating the air press earlier. Operation method: 1.1 Introduce gas from the pipeline network, carry out absorption and stabilization processes, and once the feed is ready, start the air compressor at the appropriate time. 1.2 During startup, the air compressor should be started in advance; after removing air from the distillation system using steam, gas is introduced into the system to increase pressure, with the gas being reused as the compression medium for the air compressor. The warming-up rate of the turbine before fuel injection should be appropriate, with the temperature rise controlled at no more than 50°C/h. 1.3 The time to start the air compressor in advance for warm-up (at low speed) is set at the moment when catalyst loading in the regenerator is completed and the catalyst begins to be transferred to the reaction settler, approximately 1.5 hours before fuel injection starts in the reaction. A 1.5-hour low-speed warm-up of the compressor meets the requirement that the unit’s temperature rise should not be too rapid, while also preventing the unit from operating at low speeds for too long (as this prevents the bearings from forming a stable oil film and results in poor lubrication). After the reaction injection, the unit can quickly reach normal operating speed. 1.4 To start the air compressor in advance, it is essential to utilize various methods such as gas makeup flow control, anti-surge control, air compressor outlet pressure control, and speed control, in order to maintain stable pressure in the reaction system during the fuel injection process and to prevent the unit from experiencing surge phenomena. 2.1 The distillation unit establishes a full-column circulation; the feed oil at the bottom of the tower is reheated by the slurry steam generator at the bottom of the tower, thereby driving this full-column circulation, particularly the primary circulation, to provide heat for the stabilizer. 2.2 Temperature rise circulation in the stabilizer. 2.3 Temperature rise circulation in the stripping tower. 2.4 Establish the conditions for introducing enriched gas by analyzing the temperature rise in the tower and stabilizer; introduce gas into the inlet of the enriched gas compressor and fully open the anti-backflow valve to enable low-speed operation of the compressor. 2.5 Gradually increase the compressor speed based on the amount of reactants fed in, in order to feed material into the absorption system. At the same time, increase the circulation volume in Stage 1 to ensure a stable heat source for the stabilizer, preventing large amounts of liquefied gas from entering the stabilized light oil.