Research On Optimization Design Of Light Hydrocarbon Recovery Process In Shandong LNG Receiving Station

With the increasing consumption of natural gas in China,liquefied natural gas(LNG)has become a supplementary way for domestic natural gas.However,the gaseous source LNG for domestic LNG receiving station has high heavier hydrocarbon content,resulting in the calorific value of gasified LNG is higher than that of the natural gas in downstream pipeline,and bringing about a series of safety and environmental problems.The light hydrocarbon recovery device in LNG receiving station can not only avoid the issue of interchangeability with downstream,but also obtain additional economic benefits.Therefore,it is of great significance to study the LNG light hydrocarbon recovery process in LNG receiving station to ensure the safe operation of natural gas pipeline and improve the economic efficiency of the receiving terminal.Based on the main feed conditions of Shandong LNG receiving station and the requirement of natural gas pipeline network,the light hydrocarbon recovery process in the LNG receiving station has been designed and optimized in this paper.The main content of this paper is as follows:(1)Based on the condition of source components of Shandong LNG receiving station,the interchangeability of LNG products in receiving station and natural gas in natural gas downstream pipeline network has been studied,and the fluctuation range of the Wobbe index for LNG products after light hydrocarbon recovery has been identified as 49.29?52.33 MJ/m3.(2)A superstructure light hydrocarbon recovery process model and a mixed integer linear programming model based on optimization method are proposed.The annual net profit is defined as objective function,and a light hydrocarbon recovery process for Shandong LNG receiving station is designed.The results show that:for the feed components of' Shandong LNG receiving station,the net income for light hydrocarbon recovery process reached the highest when methane and ethane tower operating pressure were 2.9 MPa and 0.9 MPa.(3)Based on pinch point design method,heat integration of heat exchanger network for light hydrocarbon recovery process is made,and its heat exchanger network is also designed and optimized.Heat exchanger network of light hydrocarbon recovery process after optimization only requires 4 heat exchangers and 2 reboiler,and total energy consumption of its system reduce to 5.805 MW.Economic comparison between the proposed process and the original light hydrocarbon recovery process in receiving station was made,and the results show that the proposed process was 8.59%higher than that of the original process on total energy consumption and 11.7%higher than that of the original process on net income.Therefore,the proposed light hydrocarbon recovery process has a certain economic value.(4)Based on basic characteristic number relation of heat transfer and flow,the structure optimization method of plate fin heat exchanger was studied on the basis of fmincon function.The total annual cost and volume of heat exchanger are defined as objective function,and the structure of fin of demethanizer flash condenser and demethanizer overhead condenser are optimized.The optimization results show that the heat exchanger has optimal economic performance when the fin type of demethanizer flash condenser and demethanizer overhead condenser both use the domestic 7 fin and the condensing channel sets 14 layers and 11 layers respectively.Under this situation,the total annual cost of heat exchanger reaches 18898.06yuan and 37830.77 yuan respectively,and their volume is 0.768 m3 and 0.772 m3 respectively.