What are the key operating points for low-temperature methanol washing?

Key operating points: 1. The lower the temperature of the circulating methanol, the greater its solubility; therefore, a lower temperature for the methanol-poor stream is the goal for operation (the temperature for the methanol-poor stream is -50°C). The system is equipped with an acrylic refrigeration system to provide additional cooling, with the cooling capacity generated by the flashing (stripping) of exhaust gases being used to achieve the required operating temperature. The main factors affecting the temperature of circulating methanol are: a. Cooling capacity supplementation from the propylene refrigeration system ； b. Nitrogen stripping flow rate ； c. Ratio of the flow rate of circulating methanol to the flow rate of shift gas. 2. The methanol circulation rate is used to control the gas composition parameters at the output section (ΣS≤0.1ppm), and it represents the primary means of adjustment. The system is equipped with a proportional control system that ensures the circulation volume is proportional to the gas volume, thereby producing high-quality purified gas. 3. Pressure (the operating pressure of the main washing tower): According to Henry’s law, the higher the pressure, the better the absorption effect. The pressure in the purification main wash tower depends on the pressure of the syngas generated by gasification. The system uses Texaco gasifiers for gas production, and the pressure of the syngas entering the system is 5.4 MPa; due to this high pressure, the absorption efficiency is significantly improved. 4. Concentration (water content, regeneration degree of methanol): The water content in lean methanol is an important control parameter in normal production; the system is designed to keep this water content at ≤1%. A higher water content not only affects the efficiency of methanol absorption but also increases corrosion of the equipment. To achieve the recycling of methanol and obtain good absorption results, it is essential to effectively regenerate methanol. The methods used in the system for methanol regeneration include flash evaporation, stripping, and thermal regeneration. A methanol-water separation tower is used to control the water balance in the solution system. 5. Parameters of the converted gas (temperature and gas composition): The parameters of the converted gas directly affect the operation of the purification cycle. The system controls the composition of the converted gas through the gas treatment section, and adjusts the HPC ratio by controlling the temperature of the carbon scrubbing tower. The composition of the reformate gas entering the system stage is 44% H2, 19% CO, 34% CO2, and 1.3% H2S.

The cooling capacity for low-temperature methanol washing can also come from liquid ammonia, which is used to cool methanol to -39°C. Reexpansion yields methanol at below -60°C.