Study On The Control Strategy Of Marine Central Cooling System

The research content of this work is marine central cooling systemequipped on57,000-ton bulk carrier. The design and control strategysimulation of energy saving marine central cooling system were carried out.The purpose is to reduce emission and improve IMO’s Energy EfficiencyDesign Index (EEDI). The significance of this work is to enhance ship’s fuelconsumption efficiency and adapt newly built ship to the energy efficiencystandards proposed by the International Maritime Organization.At first, three tasks of system design are carried out. Firstly, in orderto remedy the problem of high operation cost of traditional marine centralcooling system, a design proposal of seawater pumps with frequencyconversion technology is presented according to the similarity principle ofthe pump and heat transfer theory. By applying square law reduction torquefrequency inverter, the control unit can realize real time control according tothe flow of cooling water required under any working condition. Researchresults show that the application of variable frequency technology on marinecentral cooling system can effectively improve the energy efficiency of theship. The additional investment can be recovered in six months by savingfuel oil consumption. Market prospects of the energy saving system arequite positive. Secondly, design principles and process of plate cooler areestablished so as to rationalize the procurement cost. Thirdly, in order tomimimize the initial investment and operation cost of marine central coolingsystem, this work applies non-linear programming method to build theoptimum flow rate calculation model. The objective function is to minimizetotal investment and operating costs of the pipeline network. The optimalvariable is pipe diameter. Constraint conditions are water supply of cooling system and pump head.Then, a cascade control strategy is proposed in order to improve thecontrol performance of central cooling system and reduce the dynamicdeviation of the outlet temperature of fresh cooling water caused by inertiaof cooling water system using traditional PID control model. The hydraulicmodel, steady heat transfer model and thermodynamic model of the centralcooling system are presented in this paper based on working principleanalysis of pipe system and heat exchanger by applying fluid mechanics andheat transfer theory. Then dynamic simulation model is established by usingSIMULINK simulation tool of MATLAB software and applying modularmodeling method. After validating consistence between dynamic responseof the system and given data, a cascade control scheme is established byusing classical control theory. The control performance of the PID controlscheme and cascade control scheme is compared by using MATLAB. Thesimulation results show that the cascade control scheme improves stabilityof the system and possesses better control performance. It has a goodapplication prospect in the control design of central cooling system.Finally, marine central cooling system design and simulation softwarewith a friendly human-machine interface is developed based on the pipelineflow rate optimization model, plate cooler design process and centralcooling system simulation model. The purpose of the software is to assit thedesign of marine central cooling system. Development platform of thesoftware is Windows XP. Development environment is VisualStudio.NET2010. Development tool is VB.NET. Three main functions of the softwareare Pipeline Economic Calculation, Plate Cooler Design and CentralCooling System Simulation.