Process flow of coal to methanol?

Method for producing methanol from coal

gasify

A) preparation of coal slurry

Raw coal dry basis (

In order to reduce the viscosity of coal slurry and make coal slurry have good fluidity, additives need to be added, and lignin sulfonic acid additives are selected initially.

For coal slurry gasification, it is necessary to adjust the PH value of slurry to 6 ~ 8. Dilute ammonia or lye can be used. Dilute ammonia water volatilizes ammonia, which is harmful to human body and pollutes the air. Therefore, this project plans to use lye to adjust the PH value of coal slurry, and the concentration of lye is initially set at 42%.

In order to save water, purified wastewater and methanol rectification wastewater containing a small amount of methanol can be used as pulping water.

B) gasification

In this part, the coal slurry reacts with oxygen to generate crude synthesis gas.

After being pressurized by the coal slurry tank and the coal slurry booster pump, the coal slurry enters the gasifier through the burner together with the hyperbaric oxygen sent by the air separation, and the coal slurry reacts with oxygen as follows:

cmh nsr+m/2o 2——→mCO+(n/2-r)H2+rH2S

Carbon monoxide+H2O-→ H2+carbon dioxide

The reaction was carried out at 6.5MPa(G),1350 ~1400℃.

The gasification reaction is completed instantly in the reaction section of the gasifier, producing carbon monoxide, H2, CO2, H2O and a small amount of methane, H2S and other gases.

The hot gas and slag leaving the reaction section of the gasifier enter the quenching chamber for water bath, and after water quenching, the temperature is reduced and saturated with water vapor, and then they leave the gasifier; After being washed, dusted and cooled by Venturi scrubber and carbon scrubber, the gas is sent to the shift section.

The slag generated by the gasification furnace reaction enters the quench chamber for water bath, then is separated, discharged into the lock hopper, regularly discharged into the slag pool, fished out by the slag scraper, and loaded and transported abroad.

The washing water (called black water) discharged from gasifier and carbon washing tower is sent to grey water treatment.

C) grey water treatment

In this part, the gasified black water is separated from slag and water, and the treated water is recycled.

The high-temperature black water discharged from the gasifier and the carbon scrubber respectively enters their respective high-pressure flashers, and the black water concentrated by high-pressure flash evaporation is mixed, and then enters the clarifier after low-pressure and two-stage vacuum flash evaporation concentration, and flocculants are added into the water to accelerate precipitation. The fine slag slurry at the bottom of the clarifier is pumped out and sent to the feed tank of the filter. Pressurized by the feed pump of the filter, it is sent to the vacuum filter for dehydration, and the slag cake is pulled out of the factory by car.

After the high-pressure gas flashed is recovered by the grey water heater, the condensate is separated by the gas-liquid separator and enters the stripping tower of the shift section.

The flashed low-pressure gas is directly sent to the feed tank of the washing tower, and the clear water in the upper part of the clarification tank overflows to the ash tank, which is sent to the feed tank of the washing tower, gasification lock hopper and coal grinding tank respectively by the ash pump, and a small amount of ash water is treated as wastewater.

The water in the feed tank of the washing tower is pressurized by the feed pump, and then exchanges heat with the high-temperature gas discharged from the high-pressure flash evaporator, and then is sent to the carbon washing tower for recycling.

2) Transformation

In this part, the carbon monoxide in the gas is partially converted into H2.

The chemical reaction in this part is a transfer reaction, which is expressed by the following formula:

Carbon monoxide+H2O-→ H2+carbon dioxide

After being separated by the gas-liquid separator, the crude water gas from the gasified carbon scrubber enters the gas filter to remove impurities, and then it is divided into two streams. One stream (about 54%) enters the feed gas preheater to exchange heat with shift gas to about 305℃, and then enters the shift furnace, where it undergoes shift reaction with the carried water vapor under the action of sulfur-tolerant shift catalyst. The high-temperature gas leaving the shift furnace exchanges heat with the medium-pressure steam produced by methanol synthesis shift through the steam superheater. The medium-pressure steam is overheated, and after its temperature is lowered, it exchanges heat with the crude water gas entering the shift furnace in the feed gas preheater. The temperature is about 335℃, and it enters the medium pressure steam generator to generate 4.0MPa steam. After the temperature is reduced to 270℃, it enters the low-pressure steam generator, and the temperature is reduced to 180℃, then enters the desalted water heater and water cooler, and finally cools to 40℃.

Another part of unconverted raw water gas enters a low-pressure steam generator to be cooled to 180℃, and the by-product is low-pressure steam of 0.7MPa, then enters a desalted water heater to recover heat, and finally is cooled to 40℃ with water in a water cooler, and then is sent to a low-temperature methanol washing 2# absorption system.

The high-temperature process condensate separated from the gas-liquid separator is sent to the carbon scrubber in the gasification section.

The low-temperature condensate separated from the gas-liquid separator passes through the stripper, and CO2, H2S and NH3 dissolved in water are extracted by high-pressure flash steam and medium-pressure steam, and then sent to the feed tank of the scrubber for recycling; The acid gas produced by stripping is sent to the torch.

3) low-temperature methanol washing

In this section, low-temperature methanol washing process is adopted to remove CO2, all sulfides, other impurities and H2O from shift gas.

A) absorption system

This device plans to adopt two sets of absorption systems to treat shift gas and non-vented air respectively, and the shift gas and non-vented air are mixed after being absorbed and purified by methanol to be used as fresh gas for methanol synthesis.

The shift gas from shift enters the feed gas primary cooler, ammonia cooler and separator. After the shift gas from the separator is mixed with circulating high-pressure flash steam, a small amount of methanol is injected to prevent the water vapor in the shift gas from freezing after cooling, then it enters the secondary cooler of feed gas to cool to -20℃, enters the methanol absorption tower of shift gas to remove H2S+COS and CO2 in turn, then leaves the absorption tower at -49℃, and passes through the secondary cooler of feed gas to mix with the primary feed gas. The CO2 content in the purified gas is about 3.4%, and H2S+COS.

The cooled methanol from the methanol regeneration tower enters from the top of the methanol absorption tower at -49℃, and the upper part of the absorption tower is the CO2 absorption section. The methanol liquid is in countercurrent contact with the gas from top to bottom, and the CO2 removal index in the gas is controlled by the methanol cycle. The secondary methanol solution in the middle is cooled by ammonia cooler to reduce the temperature rise caused by solution heat. In the lower section of the absorption tower, most of the extracted methanol liquid enters the high-pressure flash evaporator; The other part of the solution is cooled by the ammonia cooler and then refluxed to the H2S absorption section to absorb H2S and COS in the shift gas, and the sulfur-containing rich liquid at the bottom of the tower enters the H2S concentration tower. In order to reduce the loss of H2 and carbon monoxide, the gas flashed from the high-pressure flash tank is pressurized and sent to the shift gas secondary cooler, where it is mixed with shift gas to recover H2 and carbon monoxide. ..

The absorption process of constant ventilation is the same as that of variable gas.

B) solution regeneration system

A set of devices is used for the regeneration system of constant ventilation and variable gas solution.

Sulfur-free methanol rich liquid and sulfur-containing methanol rich liquid respectively generated at the upper part and the bottom of the high-pressure flash evaporator enter the H2S concentration tower for flash stripping. Stripping the methanol-rich solution with low-pressure nitrogen. The sulfur-free methanol rich liquid in the upper part of the high-pressure flash evaporator enters from the top of the tower without H2S, and expands at the top of the tower under reduced pressure. The rich liquid of sulfur-containing methanol in the lower part of the high-pressure flasher enters from the middle of the tower, and the nitrogen added at the bottom of the tower lifts CO2 vapor from the top of the tower, which is recovered by the stripping nitrogen cooler and discharged as a tail gas high point.

The H2S-rich methanol solution comes out from the bottom of the H2S concentration tower, which is pressurized by the feed pump of the thermal regeneration tower, and the methanol lean liquid cooler heats up to the top of the methanol regeneration tower by heat exchange. The residual CO2 and dissolved H2S in methanol are thermally regenerated by the heat provided by reboiler, and the mixed gas is separated from the top of the tower through multistage cooling, and the primary condensate of methanol flows back, and the secondary condensate enters the bottom of H2S concentration tower through heat exchange. Desulfurization and recovery device for separate acid gas.

The methanol aqueous solution from the feed gas separator and the bottom of the methanol regeneration tower is pressurized by a pump and then separated into methanol and water by distillation. The methanol-water separator is provided by the reboiler. The overhead gas is sent to the middle of methanol regeneration tower. The wastewater with methanol content less than 100PPm discharged from the bottom of the tower is sent to the coal slurry preparation process or the sewage treatment system of the whole plant.

C) ammonia compression refrigeration

The ammonia at -33℃ evaporated from the purification refrigeration point enters the ammonia-liquid separator to separate the liquid particles in the gas, then enters the primary inlet of the centrifugal refrigeration compressor, is compressed to the condensation pressure corresponding to the condensation temperature, and then enters the ammonia condenser. Gaseous ammonia is condensed into liquid by exothermic cooling water and then discharged into liquid ammonia storage tank by gravity. Liquid ammonia is delivered to refrigeration equipment through distributor.

4) methanol synthesis and rectification

A) methanol synthesis

After methanol washing, desulfurization and decarbonization, the pressure of the generated synthesis gas is about 5.6MPa, which is mixed with the methanol synthesis recycle gas, boosted to 6.5MPa by the methanol synthesis recycle gas compressor, preheated to 235℃ in the cold tube reactor (air cooling reactor), and then enters the shell-and-tube reactor (water cooling reactor) for methanol synthesis. Under the action of Cu-Zn catalyst, crude methanol is synthesized from CO, CO2 and H2. The temperature of the reaction gas leaving the shell-and-tube reactor is about 240℃, and then it enters the shell side of the air-cooled reactor to continue the methanol synthesis reaction, while preheating the process gas in the cold tube. The gas outlet temperature of shell side of gas-cooled reactor is 250℃, and then it is cooled to 40℃ by low-pressure steam generator, boiler feed water heater, air cooler and water cooler, and enters methanol separator. Unreacted gas from the upper part of the separator enters the circulating gas compressor for compression and returns to the methanol synthesis loop.

Part of the circulating gas is discharged from the system as purge gas to adjust the content of inert gas in the synthesis circulation loop, and the synthesis purge gas is sent to the membrane recovery device to recover hydrogen, and the generated hydrogen-rich gas is compressed by the compressor and used as methanol synthesis feed gas; The tail gas recovered by the membrane is sent to the methanol steam heating furnace to overheat the medium-pressure saturated steam (2.5MPa) produced by the methanol synthesis reactor, and the medium-pressure steam is superheated to 400℃.

The crude methanol is discharged from the bottom of the methanol separator, released by the methanol expansion tank under reduced pressure, and sent to the methanol rectification section.

The purge gas of the system is mixed with the expansion gas generated by the methanol expansion tank and sent to the fuel system of the factory boiler.

Medium-pressure steam, a by-product of water-cooled reactor for methanol synthesis, is heated and sent to the medium-pressure steam pipe network of the factory.

B) methanol rectification

Crude methanol from methanol synthesis expansion tank enters the rectification system. The rectification system consists of pre-rectification tower, pressure tower and atmospheric tower. The methanol-rich liquid from the bottom of the pre-rectifying tower is pressurized to 0.8MPa at 80℃ and enters the lower part of the pressurizing tower. After the gas at the top of the pressurized tower is condensed, part of it is sent to the storage system as reflux and the other part as product methanol. The methanol solution at the bottom of the pressurized tower flows into the lower tower of the atmospheric tower for further distillation, and part of the reflux liquid at the top of the atmospheric tower is refluxed, and the other part is pumped into the storage system as refined methanol. The wastewater containing methanol at the bottom of atmospheric tower is sent to the coal grinding section as coal grinding water. The lower part of the atmospheric tower is provided with a side line for extraction. After the mixture of methanol, ethanol and water is extracted, it is pumped to the stripper by the stripper feed. The liquid product at the top of the stripper partially refluxes, and the rest is sent to the refined methanol intermediate tank or the crude methanol storage tank as products. A side line is pumped out from the lower part of the stripper, and some of the extracted isobutyl oil is mixed with a small amount of ethanol to enter the isobutyl oil storage tank. The wastewater containing a small amount of methanol discharged from the bottom of the stripper enters the sedimentation tank to separate fusel alcohol and water, and the wastewater is sent to the wastewater treatment device by the wastewater pump.

C) intermediate tank farm

When the methanol rectification process is temporarily stopped, the crude methanol produced in the methanol synthesis process enters the crude methanol storage tank for storage. When the methanol rectification process resumes production, the crude methanol is pressurized by the crude methanol pump and transported to the methanol rectification process.

The refined methanol produced in the process of methanol rectification enters the methanol metering tank. Qualified refined methanol is boosted by refined methanol pump and sent to the methanol storage tank in the finished product tank farm for storage and sales.

5) Air separation device

The process flow of the device is molecular sieve air purification, air pressurization, oxygen-nitrogen internal compression, medium-pressure air pressurization turboexpander, structured packing fractionator, and argon production by full distillation.

Raw air is sucked in from the suction port, and dust and other mechanical impurities are removed by the self-cleaning air filter. The filtered air enters a centrifugal air compressor, is compressed to about 0.57MPa(A) by the compressor, and then enters an air cooling tower for cooling. Cooling water is water cooled by a water cooling tower. The air passes through the air cooling tower from bottom to top, and is purified while cooling.

The air cooled by the air cooling tower enters the molecular sieve purifier for switching use, and carbon dioxide, hydrocarbons and moisture in the air are adsorbed. The molecular sieve purifier is used by two switches, one working and the other regenerating. The switching cycle of the purifier is about 4 hours, and it is automatically switched at regular intervals.

A small part of purified air is extracted as instrument air and factory air.

The rest air is divided into two streams, one of which directly enters the low-pressure plate heat exchanger, and then enters the lower tower after being pumped out from the bottom of the heat exchanger. And the other enters the air booster.

The medium-pressure air passing through the air supercharger is divided into two parts, one part enters the high-pressure plate heat exchanger, cooled and then enters the low-temperature expander, and the expanded air enters the lower tower for rectification. Another part of the medium-pressure air is compressed into high-pressure air by the second-stage air booster, enters the high-pressure plate heat exchanger, is cooled and throttled by the throttle valve, and enters the lower tower.

After the air is preliminarily rectified in the lower tower, oxygen-enriched liquid air, low-purity liquid nitrogen and low-pressure nitrogen are obtained, wherein the oxygen-enriched liquid air and low-purity liquid nitrogen are subcooled by a cooler and throttled into the upper tower. After further rectification in the upper tower, liquid oxygen is obtained at the bottom of the upper tower, compressed by the liquid oxygen pump, then enters the high-pressure plate heat exchanger, reheated, and then comes out of the cold box and enters the oxygen pipe network.

The low-pressure nitrogen pumped from the lower tower top enters the high-pressure plate heat exchanger, and then is heated and sent to the low-pressure nitrogen pipe network of the whole plant.

The dirty nitrogen from that upper part of the upper tow passes through a cool, a low-pressure plate heat exchanger and a high-pressure plate heat exchanger, and is reheated in a cold box and then divide into two parts: one part enters the steam heater of the molecular sieve system as regeneration gas, and the other part goes to the water cooling tower.

A certain amount of argon fraction is extracted from the middle of the upper tower and sent to the crude argon tower, which is structurally divided into two sections. The reflux liquid at the bottom of the second argon column is sent to the top of the first section as reflux liquid by the liquid pump, with a temperature of 99.6? The crude argon of Ar, 2ppmO2 is sent to the middle of the refined argon tower, and after rectification by the refined argon tower, argon with the purity of 99.999%Ar is obtained at the bottom of the refined argon tower, and then it is pumped out as a product and sent to the storage tank.