Discussion on several issues regarding low-temperature methanol washing
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1. Under conditions where the volume of the shift gas, the flow rate of the methanol used for washing, and the temperature remain constant, the CO2 content at the outlet fluctuates. What are the reasons for this instability? 2. Control of the total sulfur content in exhaust gases: The Lurgi process specifications require that COS + H2S be ≤ 30 mg/L (which is approximately 20 ppm if it’s all H2S). However, in actual exhaust gases, the COS content is around 100–250 ppm, while the H2S content is around –50 ppm, which far exceeds the specified limits. When the plant operates at varying load levels, the COS content can exceed 100 ppm, resulting in an unpleasant odor in the surrounding area. According to a company outside, their requirements for exhaust gases are more stringent, with H2S limits set at 5 ppm; yet in reality, the total sulfur content in the exhaust gases reaches several hundred ppm. Dear experts, please share information on your process packages, the requirements for actual control parameters, and the actual levels achieved.
I wonder if the patent holder has a solution to this problem. With the environmental situation being so severe these days, it’s necessary to find a solution! In our discussions with some patent holders, they also said that it’s difficult to reach 5 ppm; it seems that we are still a long way away from the goal.
Is the pressure in the flash tower fluctuating?
What process package do you have? What scale should the design be?
Our requirement is that the total sulfur content be 1 ppm; therefore, an additional exhaust gas desulfurization device is needed
The last edit to this post was made by Handan Xuebu on 2015-7-4 at 14:50. Regarding the first issue, it’s possible that the PID parameters of the liquid level control valves at the outlets of the methanol P1 pump, P2 pump, or P3 pump are not set properly, which leads to fluctuations in the local amount of cold energy. The methanol with higher concentration, as a result of these fluctuations, exchanges heat with the methanol of lower concentration; hence, the temperature of the methanol with lower concentration fluctuates, which in turn causes fluctuations in the amount of carbon dioxide； So it is possible to determine which fluctuation is responsible and then adjust the parameters accordingly ； By ruling out this cause and operating these valves manually individually, a judgment can be made! Hope this helps!
1. The methanol circulation rate is controlled properly. 2. The cooling capacity of the system is regulated to ensure an adequate level of cooling. 3. Ensure proper pressure control during flashing
What is it before entering the exhaust gas desulfurization unit?
Is there stripping? Are the control amounts appropriate?
1. Under conditions where the volume of the shift gas, the flow rate of the methanol used for washing, and the temperature remain constant, the CO2 content at the outlet fluctuates. What are the reasons for this instability? There are many reasons, such as: poor regeneration of lean methanol, with CO2 present in the lean methanol ； The composition of the transformed gas has changed ； Temperature of the transformed gas entering the absorption tower ； 2. The cooling situation of the circulating methanol in the middle of the tower, etc. 2. In normal operation, the hydrogen sulfide level in the exhaust gas from our facility is kept below 30 ppm, which is quite stable ； Process package similar to Linde’s ； Pay attention to controlling the temperature and the amount of methanol used for washing