Wood gasification in Northern Ontario Canada: Difference between revisions

Introduction

Biomass gasification is the most efficient method to convert organic material into heat. Additionally, this gas may be used to fuel both internal and external combustion engines therebye creating the potential to do work, whether that is generation of electricity or to provide transportation. Gasification of biomass is a process whereby heat is applied to the fuel in an oxygen deprived atmosphere giving incomplete combustion. The gaseous products are tars, carbon monoxide, hydrogen, methane and carbon dioxide. All but the last are capable of supporting further combustion which usually occures in a seperate location or chamber. The gases may be transported over distance similarly to natural gas. Note that tars would need to be scrubbed from the mix if the gas is to be used in an internal combustion engine otherwise the engine will seize. The following will be the record of the design and build of a homebuilt wood gasification unit to provide heat in Northern Ontario Canada. You may need to adapt the design based on resources available in your area.

The gasification process comprises several separate thermal processes conducted in a controlled manner. These processes are drying, pyrolysis, reduction and oxidation. Drying is where free moisture and cell-bound water are removed from the biomass by evaporation. These processes should ideally take place at a temperature of up to about 160ºC using waste heat from the conversion process. In pyrolysis volatile gases are released from the dry biomass at temperatures ranging up to about 700ºC. These gases are non-condensable vapours (e.g. methane, carbon-monoxide) and condensable vapours (various tar compounds. The residuum from this process will be mainly activated carbon. Reduction is where the activated carbon reacts with water vapour and carbon dioxide to form combustible gases such as hydrogen and carbon-monoxide. The reduction (or gasification) process is carried out in temperatures ranging up to about 1100ºC. Finally is the process of oxidation where part of the carbon is burned to provide heat for the previously described processes.

The 1st stage of the project is gathering information on past designs. Three basic designs were apparent from review of literature and the internet; updraft,downdraft and fluidized bed. The last is an industrial process requiring material and energy not readily available to all communities so will not be investigated in the context of a personal energy supply. Othe designs do exist but will not be investigated here. Downdraft technology, see Figure 1 (to be created), has both the fuel added and gas withdrawn from the top of the gasification chamber while air is supplied from the bottom. As a result the pyrolysis of the fuel also occures in the upper portion of the fuel charge and moves downward consuming the fuel. The design is simple and robust but has 1 major drawback for a homebuilt unit, when the lid is opened to add more fuel the operator is exposed to the gases, of which a significant portion is Carbon Monoxide (CO), a deadly poison. As the gases are drawn up the tars are not cracked

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