Thermodynamic Analysis And Optimization Of Minitype Marine Steam Power System

Marine steam power plant is one of the main power plants of marine in China. Domesticshipping industry has developed rapidly in recent years, and it has an increasing requirementfor the economy and environmental protection of the steam power systems. Now the energyanalysis methods used in china analyse economy of system from the view of quantity merely,it is unable to reveal the weak link of energy utilization. Thus it is critical to explore the fullpotential of making use of energy and improve the economy with advanced thermodynamicanalysis methods. Analysis and optimization on a minitype marine steam power system arecarried on in this paper with thermodynamic theories and computer simulation technique anda set of visual software for thermal system analysis is developed on basis of the results.Based on the first law of thermodynamics, that the steam production can meet thedemand of the devices in different operating conditions with the theory of heat and mass isverified, and the design calculation for device is carried on, at last the final configuration ofthe system is deterrmined in this paper. On this basis, the boiler thermal calculation is carriedon; the design is proved to be reasonable. At the same time, performance calculations on thesteam turbine, condenser and steam storage cylinder are carried on，and it laid the foundationfor the exergy analysis.Simulation models are builded with MATLAB/SIMULINK and thesystem performance of steam supply in different operating conditions is conducted. Theresults show that: boiler efficiency increases with the system load reducing when supplysteam to turbine separately; the quality and time of filling steam reduce and flash evaporationratio increases with the reduction of pressure drop on the condition of maintaining constantinitial pressure when supply steam to steam storage cylinder separately and thus the steamstorage cylinder is a saving energy device, which can be served to produce and store muchenergy; the releasing and filling time of steam storage cylinder will increase if the output ofsteam remain constant when supply steam to both of them. At last the results verify thecalculation accuracy through comparing the experimental data with theory calculation data. Itcan provide theory support and guidance for actual running.To learn the energy using situation of the system, and to analyze the weak link of energyutilization, the exergy analysis to each device of the system are carried on with the exergyanalysis method based on the second law of thermodynamics. The results show that, in thecondition of the turbine running separately, the boiler average losses coefficient is69.4%, the condenser is11%, and the turbine is6.8%, so the boiler is the weakest link;the detailedcalculation for the boiler is conducted and the conclusion shows that the exergy loss of heattransfer process, combustion process and discharge smoke process account the mainproportion, thus improving combustion and reducing heat transfer temperature differenceshould be considered to reduce the exergy loss; exergy loss of filling and discharging steamprocess on different conditions are carried on in this paper, and the result is obtained that theexergy loss of filling steam process is more than the discharging steam process.Based on the principles of minimum entropy production, an endoreversible Carnot cyclemodel is established with the method of finite time thermodynamics.The best temperaturedifference equations are also established with average temperature method and optimizationanalysis are carried on combining with actual parameters. It shows that the best endothermictemperature difference and exothermic temperature difference are183.4℃and25℃respectively, as well as the too high average exothermic temperature is major cause of theinefficiency of the overall cycle.A set of visual analysis software of thermal system is realized through combining GUIwith SIMULINK models.It can provide some guidance and suggestions to other thermal system through the aboveefforts and results analysis.