| Light hydrocarbons are more valuable as the chemical feedstock,e.g.,cracking for ethylene and propylene,which can reduce the production cost of olefins.Consequently,the recovery of light hydrocarbons has been gathering more and more significance.Oilfield associated gas is the main source of light hydrocarbons.Shallow condensation is widespread in oilfields for light hydrocarbon recovery from associated gases.Nevertheless,the classical condensation system with external refrigeration is inadequate for the scattered associated gases,due to the intensive capital investment and labor cost.Therefore,there is a need for a cost effective,simpler configuration,more efficient method for recovering light hydrocarbons in oilfield associated gas.In this work,a compact retrofitted system was designed without external refrigeration,which was replaced by the internal refrigeration cycle based on liquefied light hydrocarbons.In this custom design,associated gas and refrigerant were pressurized simultaneously in the same compressor.In comparison with the classical condensation system,this retrofitted one can remarkably reduce investment and labor cost for scattered associated gases,although its power consumption is increasing.First of all,the classical shallow condensation was simulated,providing the data foundation for subsequent analysis and comparison.Aspen HYSYS has designed a new integration of compression/ refrigeration system process(Case 1)and optimized the important parameters based on the unit energy consumption.The influence of temperature,pressure and composition changes on the performance of the system has been analyzed.The analysis of the new process shows that the process have the advantage of operational flexibility and strong adaptability.The exergy analysis of main components of the system shows that there is still room for improvement in the thermodynamic efficiency of the new process.It is necessary to further improve the thermodynamic efficiency of the process by adjusting the process structure and optimizing the operating conditions.Second,from the adjustment of the process structure of the system to further improve the thermodynamic efficiency of the system,the modified integration of compression/ refrigeration system is proposed(Case2).The comparative analysis of the cold box composite curves,the exergy losses of main equipment,power consumption,and economic performance was conducted.The comparative analysis revealed that the energy consumption of the Case 2 was smaller than that of the Case 1,and the cold box composite curves matching well with the cold one,resulting in relatively low exergy loss Through the comparative analysis of economics,it is known that the major difference is that the cost of heat exchangers between Case 1 and Case 2.Compared with the traditional process,the investment and the labor cost were saved by 64 % and 40 % respectively.The sensitivity of three case processes to the processing scale of the system is reviewed,the superior status is available for gas sources with flow rate less than 1200 Nm3/h and 2100 Nm3/h respectively.Finally,in order to further recover the light hydrocarbons in non-condensable gases,a membrane-compression/ refrigeration integrated system coupling process was designed.The influence of various parameters in the coupling system on the system performance was studied,It is resulted that the optimum membrane area is about 20 m2 and the membrane permeate pressure is about 300 k Pa.The light hydrocarbon recovery rate increased from 76.7% to 97.1%.Through economic analysis,the equipment and operation cost of the coupling process were calculated.The final annual economic benefit was 5.5×106 CNY,and the recovery period was 7 months. |
PDF Full Text Request