Design And Research Of Pressure Energy Recovery Device For Hydrogen Supply System Of Fuel Cell Power Ship

Before the hydrogen fuel cell system is used,the compressor needs to consume a lot of energy to compress the hydrogen to a very high pressure(35MPa,even 70MPa)and store it in the cylinder.During the operation of the system,the pressure regulating valve usually decompresses the hydrogen to the 0.2 MPa needed by the stack,and the energy stored in the high-pressure hydrogen during the decompression process is wasted but not effectively utilized.In response to this problem,the energy-saving technology of the development of hydrogen supply system has become critical,especially for marine fuel cell system.It has a natural advantage.Because the marine fuel cell system has the characteristics of large power demand,stable operating conditions,and a large number of loading cylinders,which make the recycling of decompression energy relatively simple than land use.With the increasingly applied hydrogen energy system in the ship field,it also brings opportunities for high-pressure hydrogen pressure recycling.Under this background,taking the hydrogen supply system of a hydrogen fuel cell ship as the research object,according to its full-speed operating conditions,an impact hydrogen expander composed of nozzles and impellers is proposed and designed in this thesis.In this regard,the main research contents of this thesis are as follows:First of all,the concept of available energy is introduced in the article to derive the availability model of high-pressure real gases.On this basis,the hydrogen pressure energy recovery potential of a hydrogen fuel cell ship hydrogen storage tank under different pressure zones is evaluated.Secondly,by comparing the advantages,disadvantages and applicability of different structural forms of energy recovery devices,and combined with the working requirements of small flow rate and high-pressure difference in this scene,the structure of the recovery device is determined to be Pelton impact expander.Then,based on the design experience of this type of expander,the key geometric parameters of its key components,nozzle and impeller,are designed and modeled.And then,the flow field characteristics of supersonic nozzles are simulated by Fluent software from the aspects of turbulence model selection,performance analysis of different throat shapes of nozzles,real gas effect of hydrogen high pressure and influence of inlet pressure and temperature on nozzle performance.Finally,the 6DOF model is used as the rotor model to simulate the internal flow characteristics and quantitative output characteristics of the impeller.According to the different outlet flow parameters of the hydrogen nozzle at different inlet temperatures(that is,the impeller inlet gas parameters are different)and the impeller outlet back pressure,its influence on the impeller performance is analyzed.After the above content research,the following conclusions are drawn: First of all,the evaluation of hydrogen pressure energy recovery potential shows that a considerable amount of pressure energy is stored in high pressure hydrogen,so it is necessary to recycle it.Secondly,according to the simulation of the inviscid model of the flow field in the nozzle,the accuracy of the geometric design is verified by comparison;compared with the results of different turbulence models,it is found that the SST k-ω model is well applicable to the simulation of hydrogen supersonic nozzles;The wave structure of the flow field in the nozzles with different throat shapes is different,and the performance of the arc transition nozzle is considered to be the best in comprehensive consideration;The effect of the inlet pressure on the performance of the nozzle shows that with the increase of the pressure,the mass flow rate of hydrogen and the outlet pressure are proportional to the inlet pressure,and the nozzle outlet is in a state of underexpansion;When the pressure is above 20 MPa,the hydrogen deviates from the ideal gas by more than 10%,and the effect of the real gas effect must be taken into account;The effect of inlet temperature on the performance of the nozzle shows that the mass flow rate is inversely proportional to the inlet temperature,and the outlet temperature and velocity are directly proportional to the inlet temperature;Finally,the impeller simulation shows that the oblique shock wave will be produced when the airflow enters the impeller chamber,which will lead to energy loss;In the process of airflow injection,the difference of the velocity field will be caused by the difference of the pressure field between the upper and lower parts of the airflow,and the airflow will deviate from the centerline and rise after ejection;The effects of hydrogen inlet temperature and impeller outlet back pressure on impeller performance are mainly reflected in the injection velocity,and then change the upward trend of gas;The changes of inlet air temperature and back pressure have little influence on torque and great influence on rotational speed.Through the simulation of hydrogen in the nozzle and impeller,this thesis makes a preliminary exploration for the design of the pressure energy recovery device of the marine fuel cell hydrogen supply system,and provides some technical reference for the follow-up structure optimization of the hydrogen expander.