Briefly describe the low-pressure methanol synthesis process. . . .

The last edit to this post was made by wamj6566 on 2015-10-27 at 11:38. The total sulfur content in the gas coming from the low-temperature methanol washing unit is less than 0.1 ppm; it is a qualified fresh gas with a ratio of (H2-CO2)/(CO+CO2) ranging from 2.05 to 2.15. This gas mixes with the recycled gas coming from the methanol recycle gas compressor in a buffer tank. The gas resulting from this mixing is then divided into two streams and sent to the shell side of the inlet gas preheater, where it is heated to around 225°C by the hot gas exiting the synthesis tower, before entering the top of the synthesis tower. When the syngas enters the catalyst bed, at 5.30 MPa and 220–260°C, CO, CO2, and H2 react to produce methanol and water, with trace amounts of other organic impurities also being formed. Both of the main reactions for methanol synthesis are highly exothermic, and most of the heat released by these reactions is carried away by the boiling water in the shell side of the synthesis tower. The catalyst bed temperature and the outlet temperature of the synthesis tower are controlled by regulating the drum pressure. The hot reaction gas exiting the synthesis tower enters the tube side of the gas inlet preheater, where it exchanges heat in counterflow with the synthesis gas entering the tower; as a result, its temperature is reduced to around 90°C, at which point some of the methanol condenses into a liquid. This gas-liquid mixture is further condensed in a water cooler; after being cooled to ≤40°C, it is combined and then fed into a methanol separator to separate crude methanol. The gas from which crude methanol has been separated has a pressure of approximately 4.8 MPa to 5.0 MPa and a temperature of around 40°C; it is sent back to the methanol recycle gas compressor, where it is pressurized before being fed to an oil separator for the separation of oil and water. The recycle gas after oil and water separation is then sent to a buffer tank to be mixed with fresh gas for reuse. To prevent the accumulation of inert gases in the synthesis system, a small amount of circulating gas is continuously removed from the system; this gas is washed with methanol in a water wash tower before being sent to the hydrogen recovery system for hydrogen extraction. The crude methanol separated by the methanol separator is depressurized to 0.4 MPa and then fed into a methanol expansion tank to remove most of the gases dissolved in it, after which it is sent to the methanol distillation unit or the crude methanol storage tank. The pressure in the methanol expansion tank is controlled at 0.4 MPa, and the expanded gas is sent to the fuel gas network. The crude methanol liquid discharged from the bottom of the wash tower is also sent to the methanol expansion tank ； The drum and the shell side of the synthesis tower are connected by downcomers and vapor-liquid lift pipes to form a natural circulation boiler, which generates 2.5 MPa medium-pressure steam that is sent to the steam distribution network. The boiler water used for the drum comes from the boiler feed main pipe, with a temperature of 160°C and a pressure of 5.2 MPa. To ensure the quality of the boiler water, continuous and intermittent blowdown valves are installed at the bottom of the drum. Continuous wastewater can be discharged into the wastewater expansion tank, while intermittent wastewater can be discharged directly into the sewer system.