Energy Contrastive Study Of Solar-Driven Biomass Different Gasification For Hydrogen Production

Due to problems such as energy shortage and climate deterioration caused by the use of fossil energy,increasing the use of renewable energy has become a strategic choice to solve energy problems.Hydrogen energy is a sustainable energy carrier due to the use of pollution-free.As the only renewable carbon source,biomass energy uses it to produce hydrogen in line with the needs of China’s development of a low-carbon economy.Among them,biomass gasification to hydrogen production is the most promising industry.Biomass absorbs heat during gasification,and requires external energy to trigger the reaction.Using solar energy as the heat source for the endothermic reaction can make the syngas without combustion by-products,and at the same time convert the solar energy into chemical energy in the syngas.The solar energy is stored to make up for its instability and dispersion.Therefore,from the perspective of the sustainability of energy utilization,it is of great significance to study solar energy-driven biomass gasification for hydrogen production.The research on solar-driven biomass gasification mainly focuses on steam gasification technology and supercritical water gasification technology,but the research on influencing factors focuses on single-factor research,no interaction and combination optimization are analyzed,and there is no comparative study of the two gasification technologies from the energy point of view.In addition,the results of different biomass raw material selection are also different.Therefore,based on the thermodynamic method,three biomasses of apple tree chips,cotton straw and rice straw are selected from the three energy angles of exergy of raw materials,each component of syngas and loss to evaluate the effects of hydrogen production in two different gasification agents.The study concluded:(1)Based on the stoichiometry model in the thermodynamic equilibrium model,the different gasification processes of three biomasses are analyzed by one factor,and when the steam is gasified,the hydrogen exergy efficiency increases with the increase of temperature,and when a certain temperature is reached,it is basically stable;with the increase of the water vapor ratio and the moisture content of the biomass,it increases first and then decreases.The influence of temperature,water vapor ratio and biomass moisture content on gasification is obvious,so the combination of three influencing factors is optimized.In the supercritical water gasification,hydrogen exergy efficiency with temperature,concentration increase first increases and then become smaller,with the increase of pressure has been decreasing,but the reduction of the amplitude is only within5%,the impact is minimal,so in the optimization,the temperature and concentration of the two factors are combined optimization.(2)Based on the results of one-factor analysis,the factors with obvious influence are optimized by the response surface method with hydrogen exergy efficiency as the target.During steam gasification,the largest hydrogen exergy efficiency of apple tree chips is obtained at a temperature of 1333 K,the water vapor ratio of 1.33 and the biomass moisture content of 17%,which is 45.6%;the largest hydrogen exergy efficiency of rice straw is obtained of 45.7% at a temperature of 1332 K,the water vapor ratio of 1.96 and the biomass moisture content of 21%.When the temperature of cotton straw is 1342 K,the water vapor ratio is 1.65,and the moisture content of biomass is 18%,the hydrogen exergy efficiency is the largest,which is 47.7%.The maximum hydrogen exergy efficiency obtained by the three biomass under its optimized conditions is comparable,the reaction temperature gap is small,and the reaction temperature is related to the matching degree of solar energy,and the lower the temperature,the easier it is to match with solar energy,so the degree of matching between the three biomass and solar energy is also comparable.However,based on the optimization conditions,the energy analysis of the three biomass species showed that the solar thermal exergy required for apple tree chips,rice straw and cotton straw are 8.7 MJ/kg,13.2 MJ/kg,13.1 MJ/kg,respectively.The exergy losses are 6.1 MJ/kg,6.8 MJ/kg,6.8 MJ/kg,respectively.The smaller the solar thermal exergy and the exergy loss,the better the effects,so the three types of biomass in the steam gasification,apple tree chip is the best.(3)When optimizing the supercritical water gasification of the three biomass species,it is obtained that the apple tree chips have the highest hydrogen exergy efficiency of 41.1%at a temperature of 1675 K and a concentration of 55%,rice straw have the highest hydrogen exergy efficiency of 42.2% at a temperature of 1675 K and a concentration of56%,and cotton straw have the greatest hydrogen exergy efficiency of 43.8% at a temperature of 1675 K and a concentration of 54%.Through energy comparison,it is found that from the perspective of exergy of absorbing solar energy,each component of syngas and loss,supercritical water gasification technology is not as good as steam gasification technology,but from the perspective of solar matching,when supercritical water is gasified,the lower the concentration,the smaller the reaction temperature to achieve the maximum hydrogen production,the easier it is to match with solar energy.But the cost is the need for more exergy of raw materials,so when it is easy to match with solar energy,the hydrogen exergy efficiency of supercritical water gasification technology will be much smaller than that of steam gasification technology.