Optimization Of Economic And Environmental Impact For Steam Power Plant Based On NSGA-?

Steam power systems?SPS?,providing such utilities as heat,electricity,mechanical work etc.for industrial process,plays an essential role in the modern industry.Meanwhile,it consumes lots of fossil fuels and impacts environment seriously.With the increasingly serious energy and environmental problems,it is vital to optimize the structure and parameters of steam power system so as to reduce the system cost and the emission of pollutants simultaneously.Using mathematical programming method to optimize the economic and environmental effects of steam power system has attracted extensive attention and research by scholars because it can accurately describe the structure and parameters of steam power plant.Although some progress has been made in decades,many aspects can still be considered to further improve the efficiency of SPS.For example,a)without considering the interaction between steam power system and other systems,the optimal solution cannot be obtained;b)the optimization model is complex,and the traditional algorithm is difficult to solve.Therefore,aiming at these problems,the following research is carried out in this thesisSome constraints of equipment performance are introduced to the superstructure model of steam power plant proposed by Bruno et al.The superstructure model of steam power system which is consistent with the actual operating conditions was established.The models of desulfurization and denitrification are added into the model of steam power plant to solve the problem of SO₂ and NO_X discharge.Considering the complexity of desulfurization and denitrification process,detailed superstructure networks of desulphurization based on limestone wet process?L-FGD-S?and denitrification based on selective catalytic reduction?SCR-FGD-N?were established and embedded in the steam power plant model.Based on this combined superstructure model,Selecting the total annual cost and the environmental impact of the system as the target,mathematical formulation of multiple objective mixed integer nonlinear programming?MOMINLP?describing the steam power plant coupled with desulfurization network and denitrification network was established.In the steam system,the steam flow rate,outlet enthalpy,the consumption of the turbine power of the direct drive equipment and the electricity generated by the turbine are chosen as the optimization variables.In the desulfurization and denitrification networks,the flow rate,desulphurization and denitrification rate are taken as optimization variables.The operating conditions and equipment parameter of the global system are optimized.A program for solving the MO-MINLP using NSGA-II algorithm is developed.The process of complex search solution set is regarded as the process of finding feasible individual,and the generation strategy of initial feasible solution,the treatment strategy of constraint condition and the repair strategy of infeasible solution are put forward.The evolution operators?fast non-dominated sorting,elitist,crowding distance?are modified to fit better for the established multi-objective model.The evolution individuals with lower total annual cost under specific system environmental impact are conserved during solution procedure.Using the multi-objective optimization strategy proposed in this thesis,two cases of different scales are solved,and the relationship between environmental impact and economy of two cases is analyzed.The optimal solutions which meet the pollutant emission standards are selected to compare with the literature,results as follows:the small-scale case 1 optimized both objectives by total annual cost increased by 10.9%and system environmental impact dramatically decreased by 69.2%.It is shown that the proposed optimization strategy can reduce the environmental impact and meet the emission standards by a small margin at the expense of economy.The validity of the model is verified.For the big-scale case 2,the results of optimization mostly dominate the value of literature.Two optimal solutions?A and B?which meet emission standards are selected to compare with the value of literature.The value of environmental impact on chosen optimal solution A decreased environmental impact by5.1%with total annual cost reduced by 1.4%.It shows that the optimization strategy proposed in this thesis can realize the optimization of economy and environment simultaneously.For the chosen optimal B,system environmental impact under the pollutant emission standards is increased by 4.5%with a dramatically decreased in total annual cost?5.1%?.The results show that the strategy of optimization and programming solving proposed in this thesis can solve the scheme with the lowest total annual cost of the whole system under the environmental emission standards.Thus,both the effectiveness and superiority of the multi-objective mixed integer nonlinear programming coupled with the steam power system and desulphurization network and denitrification network proposed in this thesis are verified.