Comparison And Optimization Design Of Hydrogen Production Process Based On Exergic And Tech-economic Analysis

With the increasing problems of global warming and environmental pollution,actions to combat climate change and the constraints on resources and environment are being strengthened,and the development of clean and renewable energy sources is imperative.Hydrogen energy is considered to be the ultimate energy source for human beings because of its high energy density,storability,renewable,zero emission and zero pollution.There are various sources of hydrogen energy,and different methods of hydrogen production have different energy consumption,economy and environmental impact.Addressing the key issue of which hydrogen production method is the most suitable for obtaining hydrogen source on a large scale and at low cost at this stage,this paper firstly selects three mainstream hydrogen production processes with competitive advantages,based on the research and analysis of each hydrogen production method.Then,exergy analysis model and technoeconomic analysis model are established,and this paper analyzes and compares the unit energy consumption,the exergy efficiency of the system and equipment,unit hydrogen cost,economic benefit and carbon dioxide emission of the selected three hydrogen production processes,and comprehensively evaluates the most suitable hydrogen production method for the large-scale commercial development of hydrogen energy industry at this stage and further optimizes its design.The results show that in terms of comprehensive energy consumption,the hydrogen production process by water electrolysis is the highest,followed by the hydrogen production process by coal gasification,and the hydrogen production process by natural gas steam reforming is the lowest,with unit energy consumption of 55.10 k W/kg H₂,16.26 k W/kg H₂,and 15.78 k W/kg H₂,respectively.As for exergic efficiency,the hydrogen production process by natural gas steam reforming was the highest,followed by the hydrogen production process by water electrolysis,and the hydrogen production process by coal gasification is the lowest,which are 77.03%,62.51%,49.46%,respectively.In terms of unit hydrogen cost,hydrogen production process by coal gasification is the lowest,followed by hydrogen production process by natural gas steam reforming,and hydrogen production process by water electrolysis is the highest,which are 7.70 CNY/kg H₂,11.75 CNY/kg H₂,43.21 CNY/kg H₂,respectively.In terms of carbon dioxide emission,hydrogen production process by coal gasification is the highest,followed by hydrogen production process by natural gas steam reforming,and hydrogen production process by water electrolysis is the lowest,which are 13.42 CO₂/kg H₂,5.74 CO₂/kg H₂,0.42～3.11 CO₂/kg H₂,respectively.Compared with hydrogen production process by coal gasification,hydrogen production process by natural gas steam reforming is less economical,but it has more advantages in energy consumption,exergic efficiency and carbon dioxide emission.Although the carbon dioxide emission of hydrogen production process by water electrolysis is lower,its energy consumption and hydrogen production cost are much higher than that of coal gasification and natural gas steam reforming.Therefore,in order to realize the development of large-scale hydrogen energy industry to achieve China’s two targets of reducing carbon emissions at the present stage,the most suitable source of hydrogen energy is the hydrogen production process by steam reforming of natural gas.Hydrogen production by water electrolysis will be the ultimate hydrogen production method in the future with the continuous progress of electrolysis technology and the mature development of renewable energy power in the future.Finally,this paper addresses the problem of high CO₂ emissions in the hydrogen production process by natural gas steam reforming and optimizes the design of this process.The new process utilizes the high quality cold energy released from the raw LNG during gasification to capture and recover the CO₂ generated during the process.The CO₂ recovery rate of the hydrogen production unit and the overall process reaches 69.72%and 99.5%,which realizes the capture and storage of CO₂ and the effective utilization of LNG cold energy,and the economic efficiency increases by 145500 CNY/h.