“Weekly Topic”: Low-temperature methanol washing and NHD desulfurization

1. In terms of increasing the size of the unit: Low-temperature methanol washing is significantly superior to NHD systems in this regard, as it has a high absorption capacity, which results in a lower circulation volume. For example, in a 200,000-ton coal-to-methanol plant operating at a pressure of 3.3 MPa, low-temperature methanol washing requires a circulation rate of 200 M3/h, while NHD requires 900 M3/h (referring to carbon removal). Therefore, in terms of scale-up, the low-temperature methanol washing process has advantages over NHD units. 2. Regarding material selection: On the contrary, the low-temperature methanol washing process requires much higher-quality materials than NHD units; for units with the same production capacity, the investment cost for low-temperature methanol washing is approximately twice that of NHD units. 3. In terms of operation: Operating the low-temperature methanol washing process is more difficult than operating NHD units (especially during startup and shutdown, as sudden changes in temperature have a significant impact on the lifespan of the materials). But once driving is normal, the difference in difficulty of operation isn’t very large. 4. In terms of hazards: It is clear that low-temperature methanol washing poses a greater risk than NHD, as methanol is harmful to the human body whereas polyethylene glycol dimethyl ether is harmless. 5. In terms of energy consumption: Since the circulation volume in the low-temperature methanol washing process is smaller than that in the NHD unit, its energy consumption is much lower than that of the NHD unit. Low-temperature methanol washing purification can completely and effectively remove various harmful components within the same unit, such as CO2, H2S, COS, C4H10S, HCN, NH3, H2O, hydrocarbons with more than 2 carbon atoms (including light oils, aromatics, naphtha, olefins, and gums), as well as other compounds

1. Absorption capacity and solvent circulation volume: When absorbing an equal amount of acidic gases, a smaller volume of methanol solvent is required. Methanol’s ability to absorb CO2 is more than 4 times that of NHD solution, and the heat consumption required for regenerating the NHD process is also much higher than that in the low-temperature methanol washing process. 2. Comparison of effective gas loss and purity: The H2 loss in the NHD process is greater than that in the low-temperature methanol washing process ； Its purity is also lower than that of methanol washing, so a precision desulfurization unit must be added after NHD. 3. Comparison of regeneration temperatures: The amount of steam required for regeneration in the NHD process is **higher** than that in the low-temperature methanol washing process; however, the higher operating and regeneration temperatures result in reduced electricity consumption for the chillers. 4. Comparison of solvothermal stability and chemical stability: The solvothermal stability and chemical stability of the NHD solvent are both inferior to those of the low-temperature methanol washing process. 5. Comparison of solvent foaming: The NHD solvent tends to foam during production, and antifoaming agents generally need to be added; methanol does not have this problem. 6. Comparison of volume price and sources: The price of NHD solvents is much higher than that of methanol, and its sources are highly limited. 7. Comparison of solvent heat and mass transfer properties: The methanol washing process exhibits better heat and mass transfer performance. 8. Maturity and reliability of process technology: At present, the largest facility using NHD is one with an annual production capacity of 180,000 tons of synthetic ammonia, while there are no restrictions for methanol washing. 9. In terms of technical royalties and total investment, investing in NHD is lower than that of low-temperature methanol washing. 10. Comparison of operating costs: Taking various factors into account, for medium-sized ammonia or methanol production plants, the operating costs of the two are similar.