| Using clean energy is one of the requirements of sustainable development in our country.As a high quality energy,natural gas is one of the main energy used in the world,which is of high calorific value and low pollution.For ease of storage and transportation of large amounts,natural gas is usually first treated with pretreated process such as acid gas removal and dehydration,and then is liquefied and turned into liquefied natural gas(LNG).The world’s LNG production application is at an average annual growth of 20%,and the LNG annual output reached 240 billion m3 in 2010,which provided a good foundation for the LNG cold energy recycling and utilization.In the next 10 years,China’s demand for imports of liquefied natural gas(LNG)will reach 20 million tons per year.The number of LNG liquefaction plants which have been built or are under construction has reached 23 in our country,and not only a lot of energy are imported by the way of importing LNG,but also large amounts of valuable cold energy are imported at the same time,which is mainly because when LNG reach the receiving station,they need heating and regasification for the convenience of the natural gas users’ use.One certain enterprise plans to construct a large LNG project adjacent to a large refinery,which can provide cold source for the refinery,and at the same time take liquid nitrogen produced by the refining project as the source of nitrogen for LNG project.Combination of LNG receiving station and refining project so as to realize intensive operation and facilities sharing can reduce construction investment and achieve better economic benefit.In this paper,based on the status quo that the air separation,light hydrocarbon separation,continuous reforming and circulating water unit in the refinery have a high demand on the cold energy,combining with the fact that the LNG cold energy utilization rate and utilization efficiency is still low at present,study on the LNG cold energy’s comprehensive cascade utilization in the refinery plant.Main contents include the effective,comprehensive and quantitative calculation for the cold energy and exergy of LNG,and also contain analysis of influencing factors on these two important parameters.The process models were established based on the HYSYS process simulation software,and simulation analysis which mainly include thorough analysis and quantitative calculation of the heat transfer process of existing devices was carried out,so as to grasp all the devices’ demand on cold energy both in quality and quantity.The existing air separation unit in the refinery was modified,and a comprehensive,quantitative calculation and analysis on the process of LNG cold energy used in air separation plant was conducted and the LNG consumption and LNG export temperature was calculated,which was ready for providing LNG cold source of high temperature suited for some other cold energy demanding devices.Then the LNG remaining cold energy was used for light hydrocarbon separation,continuous reforming and circulating water system,LNG flow rate was assigned and the outlet temperature of LNG was calculated.The still remaining cold energy was used for other circulating water systems,and eventually formed a comprehensive cascade utilization overall plan.Finally based on the cold energy analysis,exergy balance analysis and energy level analysis of LNG cold energy utilization process,a LNG cascade utilization process thermodynamic auxiliary software was developed.Through the input and output of the software,not only users can intuitively analyze and judge the process of LNG cold energy utilization and export thermodynamics index such as cold energy utilization rate and exergy efficiency directly,but also in macroscopic LNG flow distribution,temperature distribution and other cold process data are available,which can provide some guide on the operation of specific cold project for engineering and technical personnels. |
PDF Full Text Request