(1) shift gasification section

The desulfurized methane gas returns to the convection section to be mixed with the steam from the waste heat boiler, heated to 500-5 10℃, and then enters the primary reformer (referred to as the primary reformer for short), and the water-carbon ratio is controlled at 3.5-4.0. The feed gas is converted into hydrogen, carbon monoxide and carbon dioxide under the catalysis of Liu. The reaction temperature should be controlled at 760-780℃, and the residual methane content in the outlet gas should be less than 10%. The first-stage outlet gas is mixed with the air sent by the air compressor and enters the second-stage reforming furnace (hereinafter referred to as the second-stage reforming furnace) for combustion. When the temperature reaches 900-950℃, methane is converted into carbon monoxide and carbon dioxide under the action of catalyst. The residual methane in the outlet gas of the secondary furnace should be less than 0.3%. At the same time, the nitrogen required for synthesis gas is obtained, and the hydrogen-nitrogen ratio is controlled between 2.8-3. 1. In the whole conversion process, the total carbon analysis of feed gas and the analysis of residual methane in the outlet gas of primary and secondary furnaces should be carried out. The gas from the secondary furnace enters the waste heat digestion boiler. Steam is obtained by using heat energy, and the gas temperature is reduced to 350-380℃, and then it enters the medium temperature shift furnace (hereinafter referred to as the medium temperature shift furnace). Under the action of shift catalyst, carbon monoxide reacts with water vapor to generate hydrogen and carbon dioxide. The carbon monoxide content should be reduced to about 3.5% 0, and the gas temperature at the outlet of the intermediate shift furnace should reach about 400℃. Heat is recovered through the intermediate shift furnace to generate steam, and at the same time, the gas temperature is reduced to 180-200℃, and then enters the low-temperature shift furnace (hereinafter referred to as the low-temperature shift furnace). Under the action of low temperature shift catalyst, carbon monoxide further undergoes shift reaction, so that carbon monoxide is reduced to below 0.3% and the outlet gas temperature reaches 200-220℃. At this time, the gas still contains a lot of sensible heat and latent heat. Part of the heat is exchanged between boiler feed water heater and refrigeration reboiler, so that the temperature is reduced to 40℃, and the remaining oil is sent to decarbonization system. In the process of conversion, the content of carbon monoxide is mainly controlled and the conversion efficiency is evaluated.

(2) decarbonization section

The shift gas is pressurized to 65438±0.8 Mpa in three stages, and the temperature is less than 40℃. It is introduced by the inlet valve and separated by the shift gas separator and then enters the lower part of the absorption tower. Contact with semi-lean liquid and lean liquid in counter-current in the tower, absorb CO2 and then draw it out from the top of the tower. The gas leaving the tower top is cooled by the purifier cooler, and then the water is separated by the purifier separator. When the temperature is less than 40℃ and the CO2 in the gas is less than or equal to 0.2%, it enters the methanation process through the outlet valve of the purifier.

The MDEA solution that absorbs CO2 in the absorption tower is called rich solution, the temperature is about 80℃, 65438±0.8 Mpa, and the pressure is reduced to 0.4 Mpa by the pressure reducing valve. After being preheated by the rich liquid preheater, it enters the top of the atmospheric desorption tower, and after CO2 desorption, it comes out from the bottom of the tower, which is called semi-lean liquid. About two-thirds of the semi-lean liquid is cooled by the semi-lean liquid cooler, pumped to 2.2 Mpa and enters the middle of the absorption tower to absorb CO2. After being filtered by mechanical impurities, about 65,438+flows into the tube of the solution heat exchanger, and the solution outlet heat exchanger (94℃) enters the upper part of the stripper. After partial CO2 decomposition, the solution comes out from the middle and flows into the solution reboiler. Under the action of steam, the gas-liquid mixture heated from the reboiler to 1 13℃ enters the lower part of the stripper again, and CO2 in the solution is almost completely dissolved. The solution coming out from the bottom of the stripper is called lean solution. At the temperature of 1 13℃, it enters the tube of solution heat exchanger to exchange heat with semi-lean liquid. After cooling to 93℃, it enters the tube of lean liquid cooler, and the lean liquid cooled with water is controlled at 60℃. Pressurized to 2.4 Mpa by lean liquid pump, and sent to the top of absorption tower through regulating valve to absorb CO2.

The fresh gas with the temperature of 102℃ and the pressure of 0.05Mpa coming out from the top of the stripper is called stripping gas, which enters the top of the atmospheric desorption tower and comes out from the top of the tower together with the gas desorbed from the rich liquid in the atmospheric desorption tower, which is called regeneration gas. After the regeneration gas enters the regeneration gas cooling tower for cooling, it enters the regeneration gas separator to separate water. The separated regeneration gas CO2 is more than or equal to 98%, the temperature is less than or equal to 40℃, and the pressure is 5-65438 00 kPa, and it is sent to the urea production workshop as the raw material of urea.

(3) Carbonization section

The low-temperature gas with the pressure of 0.85 Mpa sent from the conversion post in the gas-making workshop enters the main carbonization tower from the bottom, and bubbles in countercurrent with the auxiliary tower liquid added at the top to absorb most CO2. The tail gas containing 25.0%-10% co is led out from the top, enters the tower from the bottom of the auxiliary carbonization tower, and is further absorbed in countercurrent with the concentrated ammonia water added at the top, so that the CO2 content is reduced to ≤ 1.6%. It enters the tower from the bottom of the fixed sub-tower, and is further absorbed in countercurrent with the concentrated ammonia water or dilute ammonia water added at the top of the tower, so that CO2 is further reduced to ≤0.4%; the gas is led out from the tail gas pipe, enters the recovery cleaning tower from the bottom of the recovery section, and the soft water added from the purification tower and the top of the recovery tower is absorbed in countercurrent again, so that the CO2 content is reduced to ≤0.2%; the gas is led out from the tail gas pipe of the purification tower, and enters the compressor for three-stage compression after water separation.

Concentrated ammonia (1.0- 1.2Mpa) enters from the auxiliary tower and reacts with CO2 in the outlet gas of the main carbonization tower to generate ammonium bicarbonate solution, which is pumped out from the bottom of the tower. Pressurize to 1.4- 1.6 Mpa, add the main carbonization tower from the top, further absorb CO2 in the shift gas, generate ammonium bicarbonate suspension, take it out from the bottom of the tower, send it to a thickener, and separate it with a centrifuge. 0.7- 1.2 Mpa soft water sent by the soft water post enters the recovery tower from the top of the tower to the overflow pipe of the cleaning tower. Ammonia and carbon dioxide in the outlet gas of the fixed auxiliary tower are purified and recovered, and part of the generated dilute ammonia water is extracted from the recovery tower and pressurized to 0.8-65438±0.2 MPa. After absorbing carbon dioxide and ammonia are added from the top of the fixed auxiliary tower, the dilute ammonia water is pressurized to the absorption recovery purification tower. The other part of dilute ammonia water is pressurized to 0.8-0.9Mpa, and then sent to the ammonia washing tower to absorb ammonia in the gas discharged from the synthesis tank, and then pressurized to the dilute ammonia water storage tank through the automatic pneumatic diaphragm valve.