TORREFACTION FOR ENTRAINED-FLOW GASIFICATION OF BIOMASS

Abstract

Biomass, in particular wood, has historically been an important energy source for fires, ovens and stoves.In the industrialization period of the late 19 th century, coal displaced biomass because of its high energy density (28 vs. 18 MJ/kg) and because it is available in large quantities at low cost.At the beginning of the 20 th century, oil (which was discovered in the U.S. in 1859) covered only 4% of the world's energy demand.Decades later it became the most important energy source.Currently, oil covers about 40% of the world's energy demand and 96% of the transportation fuels are produced from oil.With the world energy demand projected to rise by about 40% from now to 2020, it is possible that oil production will not increase accordingly.Natural gas, which covers almost 25% of the world's energy demand today, may overtake oil as the most important energy source by 2025.This trend is also supported by environmental concerns such as global warming which have resulted in calls for increased use of natural gas.Natural gas gives off only one half as much carbon dioxide (CO 2 ) per unit of energy produced as does coal, and 25% less than oil.Worldwide supplies of natural gas are reasonably widespread and should last for 60 years at current rates of production.Eventually, fossil fuel reserves will dwindle.Looking beyond the era of natural gas, coal may become increasingly used, but this requires CO 2 sequestration.Preferably, the world should move towards more sustainable energy sources such as wind energy, solar energy and energy from biomass.Annually, photosynthesis stores 5-8 times more energy in biomass than man currently consumes from all sources.Biomass, currently the fourth largest energy source in the world, could therefore in principle become the main energy source.However, many challenges remain to be solved before biomass can be used on a much larger scale as a sustainable energy source.Some of these challenges are related to biomass production, e.g.land management, competition with food production, etc., but challenges also exist in the handling of biomass as a fuel.The relatively low energy density of biomass, in combination with its high moisture content, makes transport of biomass from production sites to power stations or future bio-refineries costly.Biomass is very fibrous and tough.The production of very small biomass fuel particles is therefore a rather difficult and energy consuming task, which complicates a number of applications in gasification and combustion.The research on torrefaction carried out in collaboration between the Technical University of Eindhoven (TU/e) and the Energy research Centre of the Netherlands (ECN), which is presented in this report, presents solutions to some of these challenges.Such a contribution may extend the lifetime of our fossil fuels resources and alleviate global warming problems.Although the research was focussed on the application of torrefaction for entrained-flow gasification, the project team recognises that the outcomes can also be valuable for other applications, e.g., as a pre-treatment technology in the co-firing of biomass in power stations, the production of densified biomass fuels (e.g.pellets), and generally biomass fuel production chains.