Thermoeconomic Analysis And Optimization For Marine Diesel Engine Waste Heat Recovery System

With an increasing price of international crude oil,proportion of fuel cost in the ship operating cost has been growth sharply,and improvement of energy efficiency for marine main engine has get more attention by the whole shipbuilding industry.Recently,Energy Efficiency Design Index?EEDI?of ship has been revised by International Maritime Organization?IMO?to alleviate the greenhouse effect and reduce CO₂ emission discharged from ship.According to the rules,owners of ships which cannot meet the standard of energy consumption would be punished for the environmental pollution.In the marine diesel,energy in the exhaust flow and cooling water can be further utilized by waste heat recovery system,and whole ship's energy efficiency can also be improved to save energy and reduce emissions from marine diesel.Waste heat recovery system for marine diesel of 6S50ME-C8.2 is taken as research objective,and Exergetic analysis models for the major components are proposed in the thesis.By the model,analysis of energy and exergy balances was carried out,and the parameters including exergy destruction,exergy efficiency,exergy destruction rate and exergy destruction ratios were achieved.Owing to finding weak links of waste heat recovery system,the thermal performances were valuated clearly in the thesis.Moreover,effects of the main engine load variation on the exhaust exergy destruction,cooling exergy destruction and exergy efficiency were studied,and generating capacities of steam Rankine Cycle,Organic Rankine Cycle and power turbine with different engine load were also get with the proposed model.According to basic theory of matrix model thermoeconomics,fuel and product of each subsystem were analyzed,event matrix and supplementary equations were established in the thesis.And exergetic cost and unit exergetic cost of each stream and subsystem in the waste heat recovery system were calculated with the equations.According to investment cost equations of the major components,thermoeconomic cost and unit thermoeconomic cost of each stream and subsystem in the waste heat recovery system were predicted to evaluate the system's thermoeconomic performances.And then the thermoeconomic performances under different main engine loads were also analyzed.It is found that,with the increasing of main engine load,unit exergetic cost and unit thermoeconomic cost of each stream and subsystem are decreased firstly and then increased.And the smaller unit exergetic cost and unit thermoeconomic cost of the system is found with 75%of full load.On the basis of Genetic Algorithm?GA?,sum of cost rates of all fuel consumption,capital investment and exergy destruction was treated as objective function,22 parameters related to the design and operation of heat recovery steam generator?HRSG?,steam turbine,organic working fluid evaporator,organic working fluid turbine and other components were taken as the decision variables,and thermoeconomic optimum of waste heat recovery system in the marine diesel engine under 75%load were carried out in the thesis.After optimization of GA,the value of objective function is decreased by 2.50%,the total exergy destruction is decreased by 2.59%,the overall exergy efficiency is increased by 22.21%,the weighted cost of power generation is decreased by 13.89%,and the total investment cost is increased by5.31%.Consequently,thermoeconomic performances of the waste heat recovery system were optimized in the thesis.With the conclusions,a comprehensive thermoeconomic assessment and optimization method for waste heat recovery system in the marine diesel can be provided,which have a certain guiding significance for energy saving and optimization of ship energy system.