Collaborative Optimization Of Process Units And Steam Power System In Thermal Power Plant

The production system of large petrochemical enterprises is more complex,and there are many process units,both oil refining units and chemical units.The steam and power required for the production process in the petrochemical industry are usually provided by the steam power system of the thermal power plant,there is a dense energy connection between the petrochemical industry and the thermal power plant,but most researchers optimize them as separate parts,which cannot guarantee the global optimality of the optimal configuration scheme.In this paper,the thermal power plant and process units are studied as a whole,and the system engineering methodology is used for collaborative optimization.The research contents of this article is as follows:(1)The superstructure of the steam power system proposed by Bruno is classified and simplified by thermodynamic analysis,and the configuration of the steam condenser and the electric heater is removed.If ratio of power to steam for system is high,the structure containing gas turbine,waste heat boiler,high pressure boiler,feed water heater,back pressure and condensing turbine is selected for optimization.If ratio of power to steam for system is low,the structure containing medium pressure boiler and back pressure turbine is selected for optimization.On this basis,taking the minimum annual cost as the objective function,a mixed integer nonlinear programming(MINLP)model is established,and a customized solution strategy is proposed.By linearization of the nonlinear equation,the solution efficiency is greatly improved and the global optimality of the solution is guaranteed.In order to explore the configuration law of steam power system in thermal power plants under different ratios of power to steam,three cases were optimized and analyzed.(2)Based on the connection relationship between the thermal power plant and the units,a synchronous optimization method for the steam power system of the thermal power plant and the units is proposed.This method divides the units into three types: the first type of units can not adjust the steam and power demand;the second type of units can adjust the steam demand by reducing temperature and pressure;The third type of units can adjust the steam demand by reducing temperature and pressure,and can also adjust the steam and power demand by driving selection.Firstly,the data of steam and power demand of various units are collected,and then the constraint of steam power system is established.Finally,the coupling model is established by connecting with the steam power system of the thermal power plant.The coupling model takes the minimum annual cost as the objective function,and this paper takes the synchronous optimization of thermal power plant and alkane dehydrogenation unit as an example to demonstrate the superiority of the synchronous optimization method.(3)The problem of collaborative optimization between the operation of the thermal power plant and the process flow of the units is explored,and the steps of energy saving optimization and separation sequence selection under the global system are introduced.For energy saving optimization,firstly,the process flow is simulated,and the effective energy of the process flow is analyzed by using the simulation data.Then,the improvement measures are put forward for the position where the effective energy loss is large.Finally,the improvement measures are evaluated by the thermal power plant operation model.For the selection of separation sequence,multiple candidate separation sequences are determined by heuristic and evolutionary strategy,and then the process flow is simulated.According to the principle of energy consistency,the composite curve of the process is made,and the thermal integration measures are obtained by analysis.Finally,the operation cost of the separation sequence is evaluated by the operation model of the thermal power plant,and the separation sequence with lower operation cost is selected.The effectiveness of global optimization method is illustrated by examples of energy saving optimization of ethylene plant and separation sequence selection of reforming plant.