Fuel Production From Gasified Biomass-A Feasibility Study

To produce fuel from gasified biomass is a way to manufacture carbon dioxide neutral fuels for transport purposes. The biomass is gasified by heat in a gasification unit, with or without nitrogen, and the resulting mixture consist of hydrogen, carbon dioxide, carbon monoxide, methane, steam, higher hydrocarbons in low concentration and tars. The gas will also contain nitrogen, argon, ammonia, hydrogen sulphide and carbonyl sulphide. This gas mixture can be treated and upgraded in various ways depending on what fuel is the desired product.
To increase the hydrogen content a reforming reactor can be added. This reactor will enhance the reaction between methane and higher hydrocarbons with steam or oxygen producing additional carbon monoxide, carbon dioxide and hydrogen. Two ways to do this is by using catalytic conversion or by thermal reforming. In the first case a catalyst is used and the yield is higher but there are problems associated with catalyst deactivation by sulphur, alkaline metals, heavy metals etc. In the thermal reforming the temperature is raised by adding oxygen to the gas and at the elevated temperature the equilibrium concentration of methane is low. This approach is less sensitive to poisoning but has a lower overall yield.
The reformed gas or the gas leaving the gasifier is fed to a water-gas-shift reactor which adjusts the ratio between carbon monoxide and hydrogen. This ratio is decided depending on the desired fuel, 2 for DME, MeOH and Fischer Tropsch.
This paper investigates various approaches to producing fuels from biomass through gasification, investigating such things as chemically bound energy and co-production of fuels. The various methods will be looked into and advantages and disadvantages will be compared. There will be no attempt to suggest any optimal method for fuel production from biomass through gasification since every case is unique regarding available biomass and desired fuels. Various ways to produce different fuels and the efficiency to chemically bound energy will be reported as will the effects of co-production of fuels. The results show that a catalytic reforming outperforms a thermal reforming and that co-production of fuels is beneficial.