Research On Energy Saving Of Ship Pneumatic System Based On Independent Air Intake And Exhaust Control

Pneumatic transmission system is an important power system for ship navigation.It is widely used because of its simple composition,convenient operation,easy maintenance,pollution-free,and suitable for long-distance transportation and centralized air supply.At present,the power consumption of compressed air production accounts for about 10% of the total power generation in China and about 6% of the total power rate of marine generators.However,the efficiency of ship pneumatic system is less than 20%,which has great energy saving potential.This thesis combines the key technologies of system modeling,nonlinear dynamic optimization and multi-way digital valve design to realize the high efficiency and energy saving of the bridge-type pneumatic circuit whose air inlet and exhaust are controlled independently.The research finally provides a new solution for the energy saving of the ship pneumatic system.The main research contents are as follows:(1)Based on the ideal air state equation and system dynamics theory,the mathematical model of bridge-type pneumatic circuit with cylinder as actuator has been constructed.The accuracy of the mathematical model has been verified by comparing the model-based simulation results and experimental results,which can objectively express the changes of various state variables in the actual system.(2)Based on the theory of energy conservation and enthalpy change of compressed air,this thesis analyzes the energy conversion and external work process of pneumatic system with independent air intake and exhaust control.This thesis also studies the energy-saving method of using expansion energy of compressed air to do work in piston’s working stroke,especially in horizontal point-to-point situation,and finally forms the results of reducing air consumption through timing air intake and exhaust method and quantitative air intake method.Through theoretical analysis and experimental verification,the two methods can save air consumption by 58% and 77% respectively.(3)In order to solve the problem of the lack of constraints on the system dynamics variables in timing air intake and exhaust method and quantitative air intake method,an energy-saving method of independent air intake and exhaust control,based on nonlinear dynamic optimization theory,has been studied.In this method,the air consumption of the system is taken as the optimization objective,and the dynamic parameters of the pneumatic system are taken as the constraints.By combining the idea of constraint relaxation,4-stage Lobatto orthogonal collocation method and improved interior point method,the independent air intake and exhaust control strategy,which can meet the optimal conditions and make the compressed energy be used efficiently has been obtained.Compared with the traditional pneumatic system,77% air consumption could be reduced.(4)In order to improve the response speed and accuracy of the independent air intake and exhaust control and also simplify the system structure,a multi-position and multi-way directional control valve with rotating spool has been developed.The multi-position and multi-way directional control valve integrates nonlinear dynamic optimization algorithm,which has the advantages of fast response speed and flow rate proportional control.According to the optimization results,it can realize the energy-saving control requirements of the bridge-type pneumatic circuit independently.Compared with the circuit composed of four on-off valves,the action frequency could be increased from the original 20 Hz to 600 Hz,and compared with the traditional pneumatic system,the air consumption of the system could be reduced 80%.(5)According to the demand of multiloop direction control in ship compressed air system,this thesis introduces the application of multi-position and multi-way direction control valve for compressed air distribution of ship engine starting system,and in loop control of adsorption compressed air dryer.The multi-position and multi-way directional control valve has the advantages of simple structure,multiple loop control and flexible control.It will play a greater role in the future automation and intelligent development of ship and marine engineering.