Simulation and Optimization of Refrigeration Based Natural Gas Liquid Recovery Process: Exergy and Economic Analysis

Abstract

The raw natural gas from the well head contains methane, gaseous hydrocarbon, water, and condensate. Most natural gas (NG) processing plants separate the dry gas and liquid condensate without extracting the high-priced natural gas liquids. And thus, natural gas liquids (NGL) are sold along with the cheaper dry gas and liquid condensate. The NGLs are separated from the NG to control the dew point and also yield a source of revenue. Due to the storage of condensate at atmospheric pressure, the lighter components like propane and butane are escaped from the breathing valve and harm the environment. A comprehensive literature review has been presented on the NGL recovery process with a focus on process description, energy requirements, NGL production, operating cost, and propane recovery. The conventional industrial single-stage process was considered as a base case for simulation and modeling on Aspen Hysys and compared with the optimized process in terms of exergy and economic analysis. In the optimized process, two modifications are proposed, recycling of gas condensate for more butane and propane absorption and the use of mixed refrigerant for the refrigeration loop. The results show that reabsorption of NGLs due to condensate recycling improves the overall recovery of propane and butane and also better the quality of sales gas. The mixed refrigerant reduces the exergy destruction and capital cost of the refrigeration loop. Optimized flow sheet shows better economic results compared to a conventional process.