| With the improvement of people’s awareness of environmental protection,with the increasing pollution caused by fuel exhaust,the control standards for ship exhaust emissions are becoming stricter and stricter.In order to reduce emissions from the source,natural gas has become an international trend as a source of power for ships.Dual fuel engines are currently widely accepted because both fuel and natural gas can be burned to generate power.Natural gas is stored in liquid form.Before combustion,a gas supply system is required to heat it to the engine’s allowable temperature and pressure.During the low-temperature storage of liquefied natural gas(LNG),it is likely to absorb heat from the environment to generate boil-off gas(BOG).The accumulation of BOG in storage equipment is detrimental to the security of the system.Based on this,the gas low-pressure gas supply system for the 9L34 DF marine dual-fuel engine is studied.First of all,the main functions and modules of the LNG gas supply system are analyzed and Aspen HYSYS software is selected to simulate the gas supply system and complete the thermodynamic calculation.Next,the steady-state simulation of the heat exchange module is discussed on the basis of that of the whole system.Using matlab calculation software,we discuss the LNG gasification scheme with spiral-wounded heat exchangers.The heat exchange module is the core part of the system when the gas supply system is working.It is considered that the scheme of heating LNG with water glycol through two continuous heat exchangers is better.LNG is not consumed for a period of time when the system stops running.The BOG generated in the storage tank will increase the pressure inside the tank,which is not conducive to the safe storage of LNG.In order to deal with excess BOG,a BOG recovery system is designed.BOG is absorbed by LNG which is sub-cooled in this system.Compared with the traditional BOG re-liquefaction mode,the system consumes 110.8 k W,which is 26.4% lower than that of re-liquefaction.Then,the dynamic performance of the gas supply system is studied.A dynamic model of the system is established and the dynamic simulation of it by means of PID module in HYSYS is completed.The change of the engine’s working conditions during gas supply is simulated.Regulates the flow rate of the heat source and the intermediate heating medium respectively to maintain a stable gas temperature.Comparing the benefits and drawbacks of the two ways of regulating,it is recommended to combine them in actual use.Finally,this paper proposes an experimental scheme for the LNG gas supply system.The purpose is to test the performance of it and investigate the system’s adaptability to change conditions and LNG components.Besides,how well the heat exchangers work under stable and changing conditions is studied. |
