| The central cooling water system of the ship is generally combined with a fixed speed motor and a centrifugal pump.When the sea water temperature is lowered or the thermal load of the main and auxiliary equipment is reduced,in order to keep the constant temperature of the low temperature fresh water outlet only by the three-way valve to control.Therefore,the amount of seawater required by the theory is much less than the actual amount of seawater,but the fixed speed motor has been running,which causes waste of energy.In this paper,by simulating the central cooling water system of the actual ship,according to the distribution of heat load,the temperature and flow rate of the seawater,the characteristic curve of the pump are compared and analyzed.When the seawater temperature is lowered or the load of the main and auxiliary machines is reduced,the motor speed is reduced by the frequency conversion technology to match the characteristic curve of the pump,and the motor speed is reduced to reduce the energy consumption,thereby saving energy consumption.This paper introduces the principle,structure and related equipment of the ship’s central cooling water system,and analyzes the basic principle of the centrifugal pump,the flow characteristics of the centrifugal pump series and parallel output,the pump similarity law,and the structural schematic diagram of the three-phase motor and the frequency converter.According to the typical design of the central cooling system of the ship,the method of energy saving is obtained by the method of heat balance calculation and constant temperature control.According to the actual situation,the energy saving performance of the central cooling system of the ship is studied by the constant temperature control method.The Matlab/Simulink program was used to simulate the ship’s central cooling system,and the plate heat exchanger,temperature-controlled three-way valve and heat load system were modeled separately and combined on this basis.Modeling and simulation according to the heat balance distribution diagram of a container ship.When the heat load of MCR is 100%,90%and 25%and the seawater temperature is 32℃ and 25℃,the constant pump and the variable pump are separately modeled and analyzed,and the output of the low temperature fresh water temperature and the opening degree of the three-way valve are simulated,on the basis of the seawater pump variable flow and constant flow energy assessment,from the simulation results of seawater variable flow,it is concluded that the frequency of the seawater pump is changed by using the frequency converter,and the energy consumption of the seawater pump is estimated according to the pump similarity law under the premise of ensuring that the seawater quantity meets the cooling requirements of the cooler.Considering that the temperature of the ship’s engine room is relatively high,the frequency of the inverter output should ensure that the cooling seawater pump motor will not be damaged due to overheating during operation.This article uses 34Hz as the minimum setting frequency.When the seawater temperature is 32℃,the thermal load of the main and auxiliary machinery changes.At the time,the simulation output can save energy by about 80%.Considering the actual general mechanical efficiency of the pump is about 0.8,it is concluded that the energy saving rate by frequency conversion control is about 60%.From this simulation result,the central cooling water based on frequency conversion control is evaluated.The system control method is practical and feasible in ship energy saving and consumption reduction,and can well realize energy saving and emission reduction. |
