The Cascaded Utilization Of Energy In The Natural Gas Chemical Integrated System

The Natural Gas Chemical integrated project is kown for its large scale, long products line and complex process. With the potential of energy saving, the heat exchanger network synthesis and optimization as well as the cascaded utilization of energy in this project will increace the energy utilization rate and set a model in chemical industry.In this article, aiming to achive the cascaded utilization of energy in this project, following contents are included.①Analyze the utilization of energy of the process in 11 plants of the project with the model of black-box. The result indicates that 5 of the 11 plants are energy supported ,including the methanol plant, formaldehyde plant,synthetic ammonia plant, nitric acid plant and acetylene plant.Meanwhile 6 of them are energy needed.they are PVC plant,acetic acid plant, chlor-alkali plant,chloroprene rubber plant, HYCO plant and air separation plant.②Based on the process rsreams data and literature information,the whole process of 6 plants,including methanol plant, formaldehyde plant and acetylene plant are simulated with aspen plus.In this way the heat duty of main heat transfer units and the data of streams in and out the energy equipments are obtained.then these units are transferd into corresponding hot streams and cold streams.Take methanol plant for example,use pinch technology and aspen energy analyzer to match hot streams with cold streams ,thus obtaining a heat network with the lowest energy consumption.After that, analyze the energy grade of heat supported or needed in heat transfer units in methanol plant, formaldehyde plant, synthetic ammonia plant and acetylene plant. Empirical method and heat exchanger network synthesis help us gain a satisfying heat exchanger plan.③Analyze the energy grade and quantities of steams needed and generated in each plant.the result shows that 8 plants get the potential of energy saving ,including methanol plant, formaldehyde plant and acetylene plant.use the method of traditional throttle decompression and ejector type decompression will obtain the total amout of exergy loss of 4.42×10~4MJ/h and 3.90×10~4MJ/h separately.Howener, decreasing the pressure by cogeneration with back pressure steam turbine will lose exergy of 1.14×10~4MJ/h ,which is 25.9% of the throttle decompression process and 29.3% of the ejector type decompression process.It increases the energy efficiency dramatically,as the energy generated reachs 9.95×10~7 kW·h per year,while annual profit reaches 48.01 million yuan when the whole investment is 47.7 million yuan, the period for recovery of investment is only 1.12 years in this case.Therefore,the cogeneration scheme is able to decline the energy loss in decompression effectively ,thus achieving the goal of cascaded utilization of energy in steam system.