Research On Combination Optimization Of Variable Frequency Sea Water Pump Of Cooling Water System On M.V "YU PENG"

Fossil energy is the non-renewable energy.The consumption of fossil energy in ship transportation is quite huge.The technology of variable frequency water pump has the positive effects on the energy saving and emission reduction of ships.So in this paper,M.V."YU PENG" as the target ship,the operation characteristics,energy efficiency and combination optimization scheme of variable frequency sea water system were studied.Firstly,the relevant data at home and abroad was consulted and mathematical models of the cooling water system were established.The thermodynamic model of the main heat exchanger,the hydraulic model of the pipeline and the speed calculation model of the variable frequency sea water pump were included.On the basis of research on frequency conversion technology,speed control model of sea water pump based on direct torque control was established.The whole model reflected the relationship between the heat load of the main engine or the inlet temperature of the sea water and the speed of the main sea water pump.Then,simulation modules of the central cooling water system and sea water pump motor were established by Simulink software,and the simulation of key parameters under constant frequency and variable frequency mode was analyzed with variation of the load of the main engine and the inlet temperature of the sea water.According to the simulation results,the conclusions were drawn.When the drop of the load of main engine or the temperature of sea water are very large,the sea water flow in variable frequency mode is greatly reduced to the minimum flow rate of the pump corresponding to the minimum speed ratio.When the load of main engine or temperature of sea water changes,the opening of low temperature three-way valve changes to maintain the temperature of low temperature fresh water under the constant frequency mode.The minimum flow rate of the pump is 200m3/h.When the sea water flow is above 200m3/h,the temperature of fresh water is maintained by changing the sea water flow under the variable frequency mode,the opening of low temperature three-way valve is 1.Finally,through theoretical calculation and genetic algorithm,taking the minimum shaft power of the sea water pump group as the optimization criterion,the operation schemes of double variable frequency and single variable sea water pump group under different sea water flow demand were analyzed.Voyage information of M.V."YU PENG" from August 2017 to December 2017 as reference,the energy saving and economic benefits of different schemes were analyzed.When the load is 50%MCR-75%MCR,the sea water temperature is 24?-30?,the energy saving benefits of double variable frequency and single variable frequency are the same,especially when the load is 50%,energy-saving rate is 68.13%.Based on double frequency and single frequency of the investment,combined with cost saving of two schemes,the investment payback period is that double variable frequency scheme is about 4.79 years,single variable frequency scheme is about 3.35 years,so for the transformation of old ships,the scheme of single variable frequency sea water pump group can be adopted.For new shipbuilding,the scheme of double or single variable frequency sea water pump group can be both adopted.