Some information on low-temperature methanol washing

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Please forgive us, as many details of the metadata are confidential and cannot be shared with everyone! 1 Cooling of the feed gas: The feed gas is sent from the CO conversion unit to the low-temperature methanol washing unit, where it is cooled through a series of heat exchangers. In the feed gas/syngas heat exchanger E-40001 and the feed gas quencher E-40002, the temperature of the incoming gas is reduced to about 10°C. In E-40001, this is achieved by heat exchange with syngas, whereas in E-40002 it is accomplished by evaporating the 4°C refrigerant. Then the raw gas passes through the ammonia scrubber T-40001. Here, the raw gas is washed with boiler feed water (BFW) (which comes from the boundary zone and is cooled to the required temperature via BFW cooler E-40016) in order to reduce the levels of NH3 and HCN. This wash water is discharged into the boundary zone. Finally, the raw material gas stream is divided into two series, each of which includes the raw material gas final cooler E-40003, the absorption tower T-40002, the CO2 methanol intermediate cooler E-40004, and the H2S-absorption tower feed cooler E-40005. In each series, a small amount of methanol is injected into the feed gas to prevent freezing of water at low temperatures. Thereafter, the feed gas is first cooled in the feed gas final cooler E-40003 by cold syngas, cold CO2 product, and cold recycle gas. 2 H2S/CO2 absorption: This gas passes through the absorption tower T-40002 in the pre-washing section, where trace amounts of NH3 and HCN are absorbed using a small stream of cold, rich methanol liquid originating from the H2S absorption tower feed cooler E-40005. The pre-washed methanol exits from the bottom under level control, and then, together with the streams from the two series, it is supplied to the thermal regeneration tower T-40005 via the pre-washed methanol final heater E-40017. Then the gas passes through the main H2S washing section led to T-40002 by the chimney tray, where H2S and COS are removed using CO2-saturated methanol from the CO2 absorption tower T-40002. The methanol solvent is supplied to the top of the T-40002 H2S-absorption tower at a flow rate controlled according to a flow ratio relative to the feed gas flow rate of each series. This H2S-enriched methanol liquid exits the main underground tank T-40002 under level control, and then the normal materials from the two streams are sent to the MP-vaporization tower T-40003 for vaporization and regeneration. The desulfurized gas then passes through another chimney tray into the low-washing section of the CO2 absorption tower T-40002. In the T-40002 CO2 absorption tower, cold, flash-regenerated methanol is used as the main washing methanol, while cold and hot regenerated methanol are used as the polishing methanol to wash this gas. Thereafter, through flow ratio control, the gas is supplied to the feed gas stream. Since CO2 absorbs heat, this methanol is significantly heated. Therefore, this methanol is cooled on its way back to the container. In this way, at the lower part of the tower, the gas is washed with CO2-enriched methanol liquid, while the rest is cooled by a refrigerant in the CO2-methanol intercooler E-40004. After exchanging heat with the incoming feed gas in the final feed gas cooler E-40003, the materials from the two streams converge in this cooler and are then cooled in the feed gas/syngas heat exchanger E-40001. Then, this syngas is led to the boundary zone (B.L). 3 Flash regeneration and H2S concentration: Some of the methanol from the underground tank of the CO2 absorption tower T-40002 is sent to the CO2 absorption tower T-40002 via the H2S absorption tower feed cooler E-40005. After the streams from these two sources are combined and balanced, they flow to the upper part of the MP flash tower T-40003. There, flash evaporation takes place under medium-pressure (MP) conditions to remove part of the CO2 as well as the dissolved H2 and CO. This gas is sent to the lower part of T-40003 to reduce the CO2 content. The normal stream of methanol-rich liquid from the T-40002 H2S-absorption tower also flows to the lower part of T-40003, where a considerable amount of H2, CO, and CO2 are flashed off together. To depressurize the recompressed gas, a very small stream of cold methanol from the thermal regeneration feed pump P-40003AB/C is used to reabsorb the flashed CO2. After being divided into two streams and heated in the feed gas final reactor E-40003, the combined flash vapor is recompressed in two stages by the recompressor C-40001, via the recompressor K.O. vessel D-40001. After compression, it is cooled in the intercooler E 40006 of the recompressor, which is located between the two stages and the recompressor after-cooler E-40007. The CO2-laden methanol from the upper MP-vaporization section of T-40003 is cooled at low temperature in the methanol flash quencher E-40008. Then, part of the methanol is sent to the middle part at the top of the reabsorption tower T-40004, where it flashes and releases sulfur-free CO2. This CO2 product is reheated in the Claus gas/CO2 product heat exchanger E-40020 and the thermal flash quencher E-40015, and then sent to the boundary zone (B.L). The flashed methanol is then led to the upper part at the bottom of the reabsorption tower T-40004. Furthermore, some of the methanol is used in T-40002 of the two series via the main washing pump P-40001A/B as the main methanol for absorbing CO2. The additional methanol from the flash methanol quencher is cooled in the methanol recooling coil and then sent to the top of the reabsorption tower T-40004, where it is used as a medium for absorbing sulfur compounds, thereby purifying the CO2 product gas and removing the sulfur contained in the methanol. The sulfur contained in methanol is sent from the lower section of T-40003 via flashing to the top of the reabsorption tower T-40004. There, sulfur absorbed a large amount of the remaining CO2 load, forming H2S and COS. These components are then reabsorbed using the methanol free of sulfur mentioned above. The CO2 product gas exits the tower, while the mixed stream from the two series is separated and, after being cooled in the feed gas cooler E-40003, is sent to the boundary zone (B.L.). At the very bottom of T-40004, a large amount of CO2 is released as a result of nitrogen stripping; this nitrogen has already been pre-cooled in nitrogen cooler E-40010 together with part of the exhaust gas. The CO2 released from methanol needs to be heated intermittently. This methanol is drawn from the chimney tray, pumped by the reabsorption circuit pump P-40002A/B through the methanol/lean methanol heat exchanger E-40012 in the reabsorption tower, where it is heated by hot regenerated methanol, and then returned to the stripping section at the lower end of T-40004. The N2/CO2 mixture from the stripping section is mixed with the hot flash vapor, and the acidic gases are returned. Methanol from the top tray at the bottom of T-40004 is used to backwash sulfur-containing compounds. The exhaust gas leaving the bottom top is partially heated in the nitrogen cooler E-40010 and the refrigerant cooler E-40011. The sulfides in the exhaust gases are washed with water in the exhaust gas scrubber T-40007 to reduce the methanol content, and are then released into the atmosphere through a chimney of sufficient height. The H2S-rich methanol liquid from the bottom of the reabsorption tower T-40004 is pumped by the hot regeneration tower feed pump P-40003AB/C, passes through the pre-washing methanol cooler E-40009, and then, after being separated into two streams, goes through the H2S-absorption tower feed cooler E-40005. The combined H2S-enriched methanol is first sent to the rich/lean methanol heat exchanger E-40013, where it is heated using hot regenerated methanol, and then sent to the thermal flash section of the thermal regeneration tower T-40005. Some of the methanol from P-4003AB/C is also used in the lower section of the MP-vaporization tower T-40003 as a methanol for re-washing the recycled CO2 gas. 4. Thermal regeneration: The sulfur-rich methanol is first sent to the thermal flash section located at the top of the thermal regeneration tower T-40005. The gas released from the thermal flash section is cooled by cooling water in the thermal flash condenser E-40014, and it is also cooled together with the CO2 product in the thermal flash quencher E-40015. Then, this hot vapor and condensate are sent to the reabsorption tower T-40004 to increase the sulfur content in methanol. The methanol that enters the thermal regeneration section of the thermal regeneration tower T-40005 is completely regenerated by methanol vapor stripping; this methanol vapor comes in part from the water concentration section located below the regeneration section, and is in equilibrium with the overhead distillate from the methanol-water tower T-40006. Then, the methanol vapor/gas coming from the top of the thermal regeneration section is condensed through a series of heat exchangers. First, before being sent to the thermal regeneration tower T-40005, the overhead distillate from this tower is sent to the pre-washing methanol final heater E-40017 to heat the cold pre-washing methanol. Then, before entering the reflux vessel D-40002, the portion containing methanol is condensed in the thermal regeneration condenser E-40018. Finally, this Claus gas is further heated in the Claus gas reheater E-40019 and the Claus gas/CO2 product heat exchanger E-40020. In the Klaus gas separator D-40003, the remaining condensate is collected and returned to the reflux vessel D-40002. Then the Claus gas is reheated in the Claus gas reheater E-40019, and subsequently discharged to the boundary zone (B.L). A portion of the Claus gas from the Claus gas separator D-40003 is returned as recycle gas to the reabsorption tower T-40004 for sulfur concentration. This Claus gas cycle passes through a small reabsorption tower that is directly connected to the separator vessel. Here, a small stream of cold, rich methanol from the reabsorption loop pump P-40002A/B is used for re-washing to prevent trace components in the Claus gas from forming aggregates in the main circulating methanol. The condensate from each Claus gas condensation stage is collected in the reflux vessel D-40002 and then returned to the hot regeneration tower T-40005 via the hot regeneration reflux pumps P-40006A/B. Then, the fully regenerated methanol collected from the main underground tank of the hot regeneration tower is sent to the top of the absorption tower T-40002 after cracking, using the fine washing booster pumps P-40004A/B and the fine washing HP pumps P-40014A/B. The hot regenerated methanol between the two pumps is cooled by flash-regenerated methanol in the rich/lean methanol heat exchanger E-40013 and the methanol/lean methanol heat exchanger of the reabsorption tower E-40012. 5. Methanol-water distillation: A small amount of hot regenerated methanol is sent to the water concentration section at the lowest part of T 40005. The underground tank of this small distillation section is reboiled by the heat regeneration tower reboiler E-40021. On the one hand, at the bottom of this section the product reaches a concentrated aqueous state; on the other hand, the methanol vapor required for stripping is regenerated. The water-rich methanol drawn from the bottom of the concentration section of T-40005 is sent to the methanol-water tower C-40006 using the methanol-water feed pump P-40005A/B. Here, distillate water and methanol are treated to keep the water content in the main methanol circuit at a low level. The underground tank of this tower is reboiled via the methanol water tower reboiler E-40022. The overhead distillate of T-40006 is methanol vapor, which is mainly sent to the hot regeneration tower T-40005 to serve as a stripping agent. The bottom product of T-40006 is impurity water, which is cooled in the impurity water cooler E-40023 before being sent to the exhaust gas scrubber T-40007. 6. Waste gas treatment system: Due to minor continuous losses of methanol from the low-temperature methanol washing unit, it is necessary to use a make-up pump P-40008 to transfer a small amount of methanol from the fresh methanol tank D-40004 to the top of the regeneration section of the hot regeneration tower T-40005. Additionally, a separate container, the underground drain D-40005, discharges residual methanol from several low points in the low-temperature methanol washing unit. The container is equipped with a submersible pump, the underground sewage pump P-40007, which returns methanol to the process. 7. The bottom product of the methanol-water column C-40006 in the exhaust gas scrubber is water; after being cooled in the impurity water cooler E-40023, it is sent to the exhaust gas scrubber T-40007. Before reaching the top of the tower, a small amount of impure water is discharged to the boundary zone (B.L.), where the desalinated water from the boundary zone (B.L.) is mixed with the wash water used as make-up water. In the exhaust gas scrubber T-40007, the exhaust gas from the reabsorption tower T-40004 is washed with this water through heat exchangers E-40010 and E-40011 to reduce the methanol content. Then the exhaust gas that emerges at the top is released into the atmosphere through a sufficiently tall chimney. The methanol/water leaving the tower at the bottom is pumped by the washing water pumps P-40009A/B to the impurity water cooler E-40023, where it is heated, and then returned to the methanol water tower T-40006 for separation.