The levels of CO2 and H2S in the exhaust gas from low-temperature methanol washing are severely excessive. Help.

You can make samples separately to see what the problem is

Comparing with previous analyses, let’s see if there are any changes in other indicators besides an increase in the H2S level; for example, have there been any changes in the hydrogen and carbon monoxide concentrations? Has there been a significant decrease in carbon dioxide purity? Also, check whether there are any leaks in the heat exchangers of the carbon dioxide gas pipeline. Furthermore, it is possible to check whether there is any change in the pressure of the flash tower

Check the gas composition in the desulfurization and decarbonization sections of the absorption tower to determine whether desulfurization in the desulfurization section is effective enough, whether the carbon dioxide product tower is capable of retaining liquids, and whether the flow distribution in the hydrogen separation tank is reasonable.

There are only a few reasons for the excessive levels of CO2 and H2S in exhaust gases. 1. The flow rate of the wash liquid at the top of the CO2 separation tower and the stripping tower is insufficient ； 2. The cleaning solution itself contains hydrogen sulfide. That is to check those two parts. Increase the flow rate of the washing liquid, or increase the flow rate of the washing liquid in the desulfurization section of the washing tower, to ensure that the liquid flowing out of the decarboxylation section contains no sulfur and no hydrogen sulfide; alternatively, increase the flow rate of the washing liquid at the top of the CO2 recovery tower and the stripping tower. Additionally, the first and most important step is to analyze whether the hydrogen sulfide level in the methanol wash inlet shift gas has increased. It seems that the increase leads to hydrogen sulfide being present in your methanol without sulfur. Adjust and see.

Forgot to mention that it could also be caused by leakage of the gas flowing through the heat exchanger tubes of the system into the exhaust gases and CO2 gas.

I’m not familiar with your process flow. In the past, we encountered situations where the feed gas created a short circuit at the differential pressure transmitter, resulting in high H2S levels; in such cases, it was necessary to adjust the nitrogen supply and tower pressure. If methanol is used for tower washing, attention should be paid to the hydrogen sulfide content in that methanol.

1. Check whether the H2S content in the lean methanol is excessively high. 2. If the H2S level in the CO2 product is too high, it may be due to insufficient amounts of methanol being used in the lower section of the absorption tower, which results in the rich methanol coming out of the upper section of the absorption tower containing H2S (which should not be present under normal conditions). If semi-poor methanol is used, attention should be paid to the H2S content in it (which is normally absent). 3. The high level of H2S in the exhaust gas may be related to the large amount of nitrogen used for stripping; it is also connected to point 2, as the feed at the very top of the hydrogen sulfide concentration tower contains H2S. 4. A high level of H2S in the exhaust gas may also be caused by a mismatch between the upstream and downstream flow rates in the absorption tower, resulting in as little hydrogen sulfide as possible at the very top of the concentration tower (which is equivalent to a low return flow rate). But based on what you’ve described, with excessive H2S in the CO2 product, the second possibility is more likely

Check whether the sulfur content in the feed gas is increasing, whether methanol is contaminating the decarburization section, and whether the flow rates in the rectifier and concentrator towers are sufficient