Design And Analysis Of Utility System Of Chemical Plants

Chemical industry is a large energy consumer.It is very important to increase the energy efficiency of the chemical industry to reduce energy consumption in China.Utility system(this article mainly considers steam systems)provides power,electricity and heat for the process in chemical industry.The optimal design and retrofit of utility system can play important role in energy savings.In addition,there is often a large amount of waste heat in the chemical industry.The energy efficiency can be increased through waste heat utilization,thereby resulting in primary energy savings.This dissertation studies the design,optimization of steam system and waste heat recovery of the heat pump.The main contents are as follows:(1)A step-by-step method and a one-step method are proposed for calculating the cogeneration potential of utility system.In the new methods,Aspen Plus software is used to calculate the temperature and flow rate of steam generated by the boiler and steam mains,and the shaft power generated in the steam turbines.The step-by-step method is divided into three steps: First,temperatures of steam mains are calculated,then flow rates of steam mains are calculated.Finally,shaft powers of steam turbines are calculated based on temperatures and flow rates obtained above.The one-step method only needs to build a simulation flowsheet in the software.Then “Design Spec”,“Calculator” and “Transfer” in the software are used to calculate the temperatures,flow rates of the steam mains and shaft powers of steam turbines.Compared with the literature methods,the new methods do not require the development of mathematical model,and do not require tedious iterative calculations.It is only necessary to establish a suitable flowsheet in Aspen Plus software and perform the necessary settings.The calculation process of the new method is relatively simple and the results obtained are accurate.(2)Aspen Plus software is used to simulate utility system.A heuristic rule is proposed for the optimization procedure.The goal is to minimize the operating cost of the steam system.Aspen Plus software is used optimize steam flow of boiler,exhaust steam of steam turbines,steam flow through valves and steam amounts in different turbines.The heuristic rule presented in this paper needs not to establish the mathematical model in the process.The results obtained by this paper are comparable to those obtained by the mathematical methods in the literature.(3)The effect of some parameter changes on the operation of the water-lithium bromide absorption heat pump is analyzed.Aspen Plus software is used to simulate the process of recycling the waste heat of circulating water in the thermal power plant with absorption heat pump.The operating feature of the absorption heat pump unit is analyzed by changing conditions of evaporator pressure,generator pressure and driving steam flow in the heat pump system respectively.The obtained results can provide useful references for the operation and optimization of the system.