The issue of desulfurization in natural gas purification
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There is currently a natural gas purification plant that uses an amine-based purification process; there is a significant discrepancy between the designed parameters and the actual operating parameters. I would be extremely grateful if Lord Haichuan could help analyze the reasons for this. Below is a comparison of the design parameters and the actual operating parameters: Design parameters for the absorption tower: Operating pressure: 4 MPa; Operating temperature: 40°C; Designed processing capacity: 23,000 Nm3/h; Amine solution flow rate: 50 m3/h, with a concentration of 43%; Type of packing: BX500 structured packing; Packing height: 12 m (2 sections); Diameter of the absorption tower: 1.3 m. Design specifications for the purified gas: CO2 content not exceeding 3%, H2S content not exceeding 4 ppm. Components of the feed gas: Component | Molecular content Methane 0.8528 Ethane 0.0003 Propane 0.0001 n-Butane 0.0001 i-Butane 0.0001 n-Pentane 0.0001 i-Pentane 0.0001 n-Hexane 0.0000 n-Heptane 0.0000 n-Octane 0.0000 n-Nonane 0.0000 n-Decane 0.0000 H2O 0.0000 H2S 0.0108 CO2 0.0800 Nitrogen 0.0554 MDEAmine 0.0000 Oxygen 0.0001 Actual operating parameters: Operating pressure: 3 MPa Operating temperature: 30°C Processing capacity: 12,500 Nm3/h Amine solution circulation volume: 43 m3/h, with a concentration of 43% Outlet specifications for the purified gas: CO2 content of 0.5%, H2S content of 50 PPM Actual components of the feed gas: Component | Molecular fraction % Component | Molecular fraction % Hydrogen (H2) 0.0437 Methyl ethyl sulfide (CH3SC2H5) 2.74×10-6 Helium (He) 0.0345 Methyl mercaptan (CH3SH) 2.22×10-5 Nitrogen (N2) 1.09 Ethyl mercaptan (C2H5SH) 5.04×10-3 Carbon dioxide (CO2) 5.34 Dimethyl sulfide (CH3SCH3) 8.08×10-7 Methane (CH4) 93.08 Ethyl sulfide (C2H5SC2H5) Not detected Ethane (C2H6) 0.0328 Carbon disulfide (CS2) 1.61×10-5 Propane (C3H8)
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Personal opinion: 1. The processing capacity is low and the load on the absorption tower is low; in such cases, the circulation rate of the amine solution should be increased to achieve saturation inside the tower. 2. The higher the pressure, the better the absorption effect; effective measures should be taken to gradually increase the pressure to the design value. 3. Are there any means to raise the absorption temperature? If so, appropriately increase the absorption temperature.
Check whether the operation of the amine solvent regeneration tower and the H2S content in the regenerated lean solution are normal. If they are normal, it’s possible that there is an issue with the analytical data regarding the H2S content in the purified natural gas; in other words, certain organic sulfurs that weren’t removed might have been mistakenly identified as H2S.
1. How long has the equipment been in operation, and was the absorption rate low from the beginning? 2. Is the purification of the amine solution relatively complete? 3. Does particulate matter or other impurities clog the packing after the amine solution has been in use for a period of time? 4. Does the amine solution foam?
The actual operating volume is almost half of the designed volume; it is estimated that this exceeds the operational flexibility range. If the quality specifications for hydrogen sulfide are not met, adjusting the porosity rate might be a solution.