Feasibility study for a 300kW pilot scale hydrogen production process from wood biomass : The case of Sandviksverket, Växjö

Abstract: Historically, fossil fuel sources (coal, oil and natural gas) have played significant role in meet global energy demand. As global population continue to rise, more and more energy resources are needed and there is a continuous depletion of these energy resources. The prices of these fuels have often fluctuated over the years and this has greatly affected the economy of several nations. The use of these fossil-based fuels has had enormous impact on the environment. This is as a result carbon dioxide and other greenhouse gases emissions. Many nations are continuously showing great interest and efforts to work together to address some of these issues, for example, the global response to combat climate change (Paris Agreement), which has been ratified by over 188 states. There is a growing interest in the technological development of renewable sources like biomass, in the production of heat, electricity and synthetic fuels. The renewable energy consumption target by the European union, stands at 32%, with a minimum of 14% in the road and transport sector. Sweden as a member state, has made tremendous progress in reducing its dependence on fossil fuels and increase its use of renewables (particularly biomass) over the years. Sweden has a target to reduce its CO2 emission in the transport sector by 79% and an independence of fossil fuels in its vehicle fleets by 2030. The thermochemical conversion of biomass to hydrogen, to power hydrogen fuel cell vehicles, has been suggested as one route to achieve this target. Biomass has high volatile content and the kinetics and stoichiometry of thermochemical conversion is very complex. This study evaluates the feasibility of a 300 kW hydrogen pilot scale production unit from biomass (wood pellet) in Växjö. Mass and energy balance calculations were performed, mainly in the first two reactors, in the envisage design and the lower heating value of the product gas was determined. Data that were used for this study was gotten from the plant in Växjö, literature survey of related systems and tools that were used to facilitate the calculations include Microsoft Excel and HSC chemistry for equilibrium calculations. The result of mass and energy balance analysis on the 1MW fuel feeding system, showed that, the flow rate of sand required for the pyrolysis process (700°) is 2610 kg/h, and the energy of pyrolysis equals 217 MJ/h. Partial burning of the pyrolysis gas in the secondary reactor produces product gas consisting of mainly CO, CO2 H2 and H2O with volume percent equal 47.08%, 6.94%, 30.29% and 15.69% respectively. The calculated lower heating value of this gas is 9.04 MJ/Nm3 when pure oxygen was used in partial burning of pyrolysis gas and approximately 6.0 MJ/Nm3 when air was used for burning. The 1MW fuel (wood pellet) feeding via thermochemical conversion has a production potential of 229 kW of hydrogen gas. Based on the parameters considered in this thermochemical process, the calculated Cold Gas Efficiency equal 59.7% and a Carbon Conversion Efficiency equal to 70.3%.