There are issues with the decarburization system of the synthesis unit; experts, please analyze the causes
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Background: Our plant is an ammonia synthesis plant using natural gas as feedstock; the decarbonization unit employs BASF’s MDEA technology, and the unit has been in operation for six years. Question: At the time of commissioning, the decarburization unit was able to meet the design requirements, with the residual carbon dioxide level at the outlet of the absorption tower being below 0.05%. The hydrogen content in the recycled carbon dioxide product is about 0.3%. As the unit operates, the level of carbon dioxide at the outlet of the absorption tower increases gradually, posing a serious constraint on production. More importantly, the hydrogen content in the regenerated carbon dioxide is continuously increasing, rising from 0.3% at the time of operation to around 1% at present. Reason analysis: (1) Equipment aspect – After shutting down the plant and inspecting each column in the decarburization system, the packing and trays were found to be in good condition. There is slight scaling on the surface of the filler (in industrial production, scaling is inevitable – it’s my personal opinion; everyone can discuss whether scaling has a significant impact on absorption!) ) (II) Regarding the solution – there are no significant changes in the solution analysis data or at the time of production start (in our production process, new solution is added regularly based on consumption and losses). Only the formic acid content in the solution was above the limit (formic acid is a by-product obtained from the oxidation in the previous system conversion stage). (III) Operation aspect — The various operational parameters show no significant difference from those during commissioning, and remain basically in line with the design values. The regeneration degree of the solution meets the design requirements, and its foaming behavior is within the normal range. *************************************************************************** Please, experts from all walks of life, analyze and determine what the problem is. I will share everything I know without reservation. Prized discussion! Process and Material Diagram.jpg (50 KB) Downloads: 0 1 second ago
It should be a problem with absorption. Recommendation: 1 Check the installation of the liquid distributor and gas distributor to prevent uneven distribution of material, which could lead to flow deviation ； 2 Check the outlet pressure of the pump inside the tower, or check whether the pump’s delivery pipeline has an increased resistance due to scaling (an increase in resistance reduces the pump’s outlet pressure, leading to uneven liquid distribution and thus gas deviation) ； 3 Check whether the packing is crushed, which could increase local pressure losses in the packing layer and lead to deflection of the gas and liquid flow.
2# tofomy, congratulate yourself – you’ve upgraded to fourth grade in elementary school!
Please analyze it from three aspects: absorption, regeneration, and amine solution. 1. If the absorption tower is inspected carefully and it is confirmed that everything is normal, I think it can be ruled out that there is a problem with the absorption process ； 2. Regarding regeneration, you mentioned earlier that the carbon dioxide content in the lean solution was high, but then said it was normal – this is a bit contradictory. If it is elevated, there is a problem with regeneration; if it is normal, then regeneration is fine. 3. If there are no problems with the first two items, then the issue must lie with the amine solution. Some subtle differences in its composition may not be detectable, so it is possible to replace the amine solution.