This paper proposes and examines an alternative thermo-chemical process for biomethane production from lignocellulosic biomass, termed self-gasification. Self-gasification of biomass is envisaged to utilize a high-pressure steam gasifier (30−80 bar) at temperatures of 600−900 °C and to use the alkali metals in biomass as gasification and methanation catalysts. The concept was studied by performing preliminary process simulations and by several screening experiments with wood. The simulations gave insight into the effect of gasifier operating conditions on methane yield. After screening tests of different alkali metals, KOH was chosen as a model compound for biomass-derived ash for further experimentation. It improves char reactivity by more than an order of magnitude, and thermogravimetric data interpreted by a first-order reaction model showed that it accelerates the pyrolysis reaction reducing the activation energy from E a = 143 kJ/mol to E a = 65 kJ/mol. Methane amounts higher than dictated by equilibrium are produced with and without impregnated KOH.

Biomass torrefaction was tested on pilot scale (50 kg h À1 throughput) for 3 types of wood: spruce, ash and willow at torrefaction temperatures of 250 Ce265 C. Quantitative analysis of process streams was accomplished by utilising on-and off-line analytical methods. The data obtained from the pilot tests could be very well translated into large-scale operations. A theoretical overall thermal efficiency of 88e89% was calculated for a large-scale heat-integrated torrefaction process that uses wet woody feedstock containing a mass fraction of 45% moisture. These results show that a pilot plant is most suitable not only for exploration of (new) feedstocks but also for generating experimental data that provide valuable information for the design of full-scale plants. The detailed mapping of the mass and energy balances presented in this work can be used further as input for process optimisation, evaluation of commercial viability and techno-economic analyses which can further help in up-scaling and commercialisation of the torrefaction technology.

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