| Hydrogen is one of the most promising renewable energy,and biomass gasification is an efficient,energy saving and environmental friendly technology for hydrogen production.There are obstacles to the industrial application of gasification,such as poor product quality,low calorific value and scaling of downstream processing equipments caused by the generation of CO2 and tar.The addition of CaO in biomass steam gasification process is a very effective method to improve the product quality,which is called adsorption enhanced gasification.CaO plays important roles in adsorbing carbon dioxide and catalyzing tar cracking.China has a wide range of industrial solid wastes,applying calcium-based wastes as the source of CaO to biomass gasification can realize efficient resource utilization.Clarifying the mechanism of CaO obtained from calcium-based wastes in biomass gasification process and optimizing its physical and chemical properties to improve the adsorption,catalytic effect and stability are the key to expand the application prospect of biomass gasification for hydrogen production.Based on this,the influence mechanism of calcium-based wastes on adsorption enhanced biomass gasificationw was deeply studied,and the preparation conditions and modification methods of adsorbents which can realize efficient conversion of biomass were also investigated.The process flow of adsorption enhanced biomass gasification was simulated and optimized by ASPEN PLUS.The main conclusions are as follows:Firstly,bamboo and carbide slag were selected as biomass sample and adsorbent respectively to study the variation of gasification products under different operating conditions and recycling in a two-stage fixed-bed reactor.It was found that the addition of carbide slag and steam,the increase of reforming temperature could promote the generation of H2.The suitable conditions are CaO/C molar ratio of 1,temperature of 650-700℃,S/B mass ratio of 1-1.5.After 5 times of recycling,the adsorption capacity of the adsorbent decreased due to sintering and agglomeration.The pore structure strength of adsorbents increased after doping fly ash and high alumina cement,and it was not easy to collapse and coking.The Ni/#1/F adsorbent has the best modification effect,witch the yield of H2 is increased by 30.06%compared with that of unmodified carbide slag.Then,the cyclic calcination/carbonation adsorption experiments of different calcium carbide slags were carried out by thermogravimetric analyzer.The carbonation process and the long cycle process were simulated.It was found that the carbonation conversion of carbide slag increased with the increase of temperature and CO2 concentration.The highest conversion rate of carbide slag#2 was 69.93%due to its higher specific surface area,pore volume and more alkaline sites.The cycling stability of calcium carbide slag was greatly improved after modification,and the order from high to low is:Ni/#1/F>#1/C>#1/F>Ni/#1/C>carbide slag 2#>carbide slag 1#.The Logistic equation can well fit the change curve of the rapid reaction stage,and the variation characteristics of CO2 adsorption under long cycle can be predicted by the formula.Finally,a calcium-based adsorption enhanced biomass gasification model was established using Aspen Plus software.The influence of different conditions on hydrogen production was studied,and the optimal scheme of different factors on a key index was determined by orthogonal simulation.It was found that the maximum hydrogen concentration was 63.36%when S/B mass ratio is 1.2,CaO/C molar ratio is 0.5,and the gasification temperature is 670℃.The highest hydrogen yield was 1.62 m3/Kg biomass when S/B mass ratio is 1.2,CaO/C molar ratio is 0.25,and the gasification temperature is 700℃.The possibility of biomass autothermal gasification using CO2 as agent was confirmed by energy consumption analysis of two gasification models.This study not only enhances the quality of products obtained from biomass gasification,but also realizes the utilization of industrial solid waste and emission reduction of carbon dioxide.It provides a new approach to optimize and improve the utilization of biomass gasification process. |
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