Low-temperature methanol washing daily question: When regenerating the methanol-rich stream, is it necessary to keep the water content below 0.1%?

A low water content results in better absorption efficiency, but it also increases energy consumption; the requirements for tower equipment are higher, and the operating conditions become more stringent

1. The effects of a high water content on the capacity to absorb methanol are as follows: In actual production, when the water content in methanol exceeds 1%, the efficiency of methanol absorption declines significantly, which affects the system load by about 5%. To achieve the designed load, it is necessary to increase the amount of methanol used and lower the temperature at which methanol is absorbed; this in turn increases the load on the pumps and leads to higher power consumption； At the same time, due to the increased demand for cooling capacity, more liquid ammonia or propylene evaporates, increasing the load on the refrigeration unit. 2. Impact of high water content on equipment corrosion: Excess water content in methanol exacerbates the corrosion of equipment and pipelines caused by carbon dioxide, hydrogen sulfide, and carbonyl sulfide. It also leads to the formation of solid impurities such as carbonyl iron and carbonyl nickel, which reduces the efficiency of coil-type heat exchangers and worsens the absorption process. Therefore, for the procurement of methanol, a water content of less than 0.1% is required to be considered acceptable.

Generally, below 0.5% is sufficient; it shouldn’t be too low either, as a too-low level leads to high energy consumption and is not economical

For normal water, less than 1% is sufficient; however, it depends on what you plan to do after the regeneration process – if storage is intended over a long period, even lower levels of water are required