What is the function of semi-poor methanol in low-temperature methanol washing?

Semi-poor methanol is a semi-poor liquid that comes out of the CO2 cooling section; it is methanol enriched with CO2, and after undergoing medium-pressure flashing and treatment in the CO2 product tower, most of the CO2 is removed, leaving behind a liquid that still contains a small amount of CO2. This methanol serves as the feed for the CO2 main washing section. Meanwhile, the methanol in the upper CO2 fine fraction still comes from the lean methanol in the thermal regeneration tower. This design is quite common in Lurgi, but practically absent in Linde; recently, Dalian University of Technology seems to have adopted this low-methanol feed as well. In my opinion, the purpose of this setup is to reduce the operating load on the thermal regeneration tower, while still ensuring that the CO2 levels in the syngas meet the required standards. However, this feed is not a lean liquid after all, and in a sense it may increase the number of theoretical plates in the CO2 absorption section (on the premise that the components and specifications of the syngas remain unchanged).

The process is improved mainly for energy-saving reasons

There are some similarities to the processes used for large-scale propylene carbonate and MDEA, especially regarding the high-concentration raw acid gas

We use the 9-tower process from Dalian University of Technology; the semi-poor liquid is divided into two streams, one of which is sent to the middle section of the carbon dioxide absorption tower to absorb a portion of the carbon dioxide. Another stream absorbs carbon dioxide, hydrogen sulfide from the medium-pressure flash section, as well as the liquid from the reabsorption stage of the exhaust gas from the low-pressure section of the hydrogen sulfide concentration tower. Control the total sulfur in the vent gas.