401072 A Case Study on the Application of Aspen HYSYS to Optimise the Performance of an Existing Gas Sweetening Process Plant

Tuesday, April 28, 2015: 2:30 PM
13B (Austin Convention Center)
Nasir Al Lagtah, Chemical Engineering and Advanced Materials, Newcastle University, Singapore, Singapore

Gas sweetening process using Methyldiethanol (MDEA) amine is widely used to remove the acid gases, hydrogen sulphide (H2S) and carbon dioxide (CO2) from natural gas produced in oil or gas wells. The process is energy intensive due to the large heating and cooling requirements. The reduction of the energy consumption by optimising the operating parameters like amine circulation rate, temperature, or pressure is limited. Modifications in the process can make a considerable reduction in the plant operating costs.

This research reviews the current operation of the case plant (Lekhwair plant, Oman) considering the main operating parameters (lean solvent circulation flow rate, lean amine temperature and MDEA concentration) that can be changed by the plant operator. The simulation and sensitivity analysis were carried out using the new package of DBR amine provided by Aspen HYSYS.

The first part of the review of the current process was operational approach (not designing), where common operational problems like foaming were discussed. It was found that the simulation outcomes were almost matching with the plant data. To save some operating costs by taking an advantage of the 5 ppm H2S concentration allowance in the sweet gas, two modifications (side draw and modified split loop) were proposed, simulated and discussed. An optimization procedure was followed to achieve maximum savings and still avoid process limitations. It was found that the side draw modification can save 50% of the current operating expenses with only around £175,000 increase in the capital investment and an increase of 1.0 ppm in H2S concentration in the sweet gas which is still well below the pipeline gas specification. To make the plant more sustainable and environmentally friendly, a sulphur recovery unit was proposed. Two modifications to the conventional process were discussed to make the furnace flame temperature stable. The best process was selected based on the least total annualized costs and the highest sulphur production. It was found that a sulphur recovery unit with 35% bypassed gas stream over the furnace and 100% O2 enrichment in the air stream can reduce the gas emissions and produce valuable sulphur.

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