For thermal conversion reactors such as gasifiers and pyrolysis retorts, necessary operational parameters such as thermodynamics, reaction kinetics, engine/reactor integration, gas, liquid and solid product management, etc, are outside the scope of a general renewables consultant.

When considering any system, know that all biomass gasifiers produce tar, and be extra cautious when considering systems that claim to accept mixed wastes. Also look at the fuel tolerance values and types of post-processing equipment necessary for any proposed system. If a wet scrubbing method is chosen, remember that this is just transferring the tarry waste to a polluted water waste and that you may have very high disposal costs to pay throughout the lifetime of the system.

Gasification can potentially convert anything containing carbon (waste, plastics, clothing) into a gas which can then be used to generate electrical energy with potential for combined heat and power. Woody biomass such as prunings, and chippings are the proven feedstocks. The process is not a new one, and is based on the ancient principles in charcoal production, where wood is ignited and then starved of oxygen so that there is no flame, but the wood remains hot. In  the second world war, wood gas powered cars were common in northern Europe.

Gasifiers have great potential for small-scale, off grid, sustainable electricity supply. In contrast to wind and solar electricity, they provide energy on demand. Woodchips fill what is essentially the fuel tank, being used as an when electricity demand occurs. They are usually robust systems, built to last rather than break after a few years, and use locally sourced wood scraps, thus making them more environmentally friendly than large-scale biomass use which involves pre-treatment and global transportation.

Dr Andrew Rollinson is a UK trained thermal decomposition energy engineer, with a legal background and engineering experience at Universities in the UK, Qatar, and Australia, plus experience of gasification and pyrolysis systems from Europe, India (Ankur), and USA (GEK All Power Labs systems).