Comprehensive Study Of Low-grade Utility In Petroleum Industry

The petrochemical industry produces a large number of low temperature waste heat. The temperature of the exhaust heat is low,and they are usually been regarded as wasting heat and thrown away, but the temperature of these heat is higher than the temperature of the environment..If we can design the corresponding device and reclaim this part of heat, the economic benefit is very considerable. The use of low-temperature heat in the petrochemical industry has two ways, that is at the same level of utilization and upgrade to use. The same level of utilization is as directly heated by the heat source. But it will cause a large number of available low-temperature heat source waste when there is a shortage in the number of heat sink. This time we must consider the upgrade use, such as heat pumps, low temperature Rankine cycle for power generation, refrigeration, Low temperature desalination and other upgrades technology, of which technology make low-temperature thermal be available power, cold energy or a bit higher temperature heat for the process. There are a lot of way for using of cryogenic heat, but recently it have not been a comprehensive program.So it is in urgent need to propose strategies of petrochemical industry low temperature heat comprehensive utilization.The paper has summarized several ways of taking advantage of low-temperature heat.And the Aspen Plus process simulation software is selected to simulate the processes,including mechanical compression heat pump, The first category and the second category absorption heat pump and electricity generated by the low-temperature heat. Based on the precise simulation,the actual application of various utilization was explored. The temperature rise, superheating and supercooling degree, selection of working medium and the application of multistage pump were studied. The research results show that, the maximum temperature of single stage compression heat pump is45℃. The optimal degree of superheat is5℃. the optimum working fluid is R152a when the condensing temperature arranges from60to80℃, while the comprehensive properties of R143or R123is the best when the temperature range is from80to110or110to160, respectively. The comprehensive performance of cascade heat pump is better than other forms of multistage heat pump. The maximum temperature rise of Multistage pump is limited by working fluids. Currently, the maximum temperature rise is up to115℃. By simulating the factors that making the temperature of the absorption heat pump rise,we have draw some conclusions.It is helpful to improve the temperature by increasing the evaporation pressure and the concentration of the absorbent.Th.e performance of H2O-LiBr absorption heat pump is superior to the NH3-H2O absorption heat pump.The first category absorption heat pump can recycle heat source temperature from30℃to60℃.It can provide the heating temperature from50℃to80℃, and the system heating coefficient is from1.4to1.8.The second category absorption heat pump can recycle heat source temperature from60℃to100℃.It can provide the heating temperature from100℃to150℃, and the system heating coefficient is from0.4to0.6.Based on the simulation of simple low-temperature heat generation processe,we can draw the conclusions that low-temperature thermal power generation is a good means of make full use of low-temperature heat when the low-temperature heat supply the heat elatively stable.The article finally proposes a comprehensive utilization strategy about petrochemical enterprises of low temperature heat, putting forward a project about utilization of low temperature thermal energy which is from MTBE cracking making isobutylene unit,that is,the project means to use the secondary cascade heat pump. Economic evaluation concluds that equipment payback period is1.97years and it can be used as the actual implementation of the program. The comprehensive utilization strategy of low temperature heat proposed by this article can provide petrochemical enterprises a reference about selection and design of low temperature thermal energy utilization projects.