Abstract
In this work, a new process for the recovery of ethane liquid from Wafa exported gas was developed with the aim to use ethane as a feed stock for petrochemical industries at Mellitah complex. All technologies available for ethane recovery were reviewed. The turbo expander was chosen, because of its ability to recover more ethane and heavier components with less energy required than traditional liquid recovery processes. The process design was optimized using HYSYS process simulation software with Bing Robinson equation of state. The proposed flow diagram process consists of four major sections: Pretreatment section, liquefaction, cryogenic separation of methane and ethane, and recompression of the residual Wafa gas. The simulation results showed that the ethane recovery plant was able to produce over 12000 bbl/day of liquid ethane with the purity of 97 % and 3500 bbl/day of LNG mostly methane with the purity of 99.97%. The recovery of ethane using a turbo expander was 79.166%. The results showed that only 32MMSCFD of Wafa gas (from 275MMSCFD of Wafa gas) was converted to liquids with high content of ethane. The residual sale gas specifications satisfied the standard specification of the exported sale gas from Mellitah. The work also includes the design of some of the process equipment. These were: dehydration column, distillation column, separator, heat exchanger, compressor, and pump. Economic evaluation was also made based on the developed process. Total capital and operating costs were estimated. The results were found to be with DCFROR 9.14 % and a payback period of 12 years. Sensitivity analysis was also made to check the effect of the product prices and the capital costs. The results are even higher (DCFROR = 12.016%, and payback period = 9 years). The ethane recovery was tested economically as a feed stock for a petrochemical plant producing ethylene. This was the aim for the ethane recovered. The results are even better when it is used in the petrochemical industries. The DCFROR was 31.23 % and the payback period was 4 years. It is recommended that ethane should be recovered and used with the available LPG (propane and butane) at crackers in a petrochemical plant for the production of ethylene, propylene, and butadiene. This opportunity will start a development of petrochemical industries in Mellitah west of Libya