Fresh thinking on renewable energy
Gasification is a process that converts organic or fossil fuel-based carbonaceous materials into carbon monoxide and hydrogen. It is achieved by bringing the materials to a high temperature (>700 °C), with a controlled amount of oxygen and/or steam. The resulting gas mixture, called syngas (synthesis gas) or producer gas, is itself a fuel.
If the gasified compounds' materials are obtained from biomass – wood waste, plant material, sewage, etc. – the power derived from gasification and combustion of the resultant gas is a source of renewable energy, with a potential net zero increase in greenhouse gas emissions.
Theoretically at least, gasification can help eliminate otherwise useless or even polluting biodegradable waste using a relatively clean and environmentally benign process. In the gasification process, corrosive elements such as chlorine, sulfur and nitrogen can be effectively removed, allowing clean gas production from otherwise problematic fuels. Gasification creates a syngas that may be burned directly in gas engines, used to produce other fuels including methanol and hydrogen, or converted via the Fischer-Tropsch process into liquid fuel. The syngas is potentially more efficient than direct combustion of the original waste material because it can be combusted in well controlled conditions or converted to hydrogen and used in fuel cells.
In actual practice, however – in terms of efficiency, cleanliness and quality of fuel produced – and from their crude beginnings nearly 200 years ago – conventional gasification processes have delivered less that spectacular results.
From the moment they teamed up in 2009 to reinvent the process, Highbury founding scientists Dr. Paul Watkinson and Dr. Yonghua Li knew in their hearts that significantly higher energy outputs and lower emission levels could be achieved.
Years of testing and research would entail building a single-stage steam gasifier that provided data on synthesis gas composition and yields from various types of biomass: sawdust wastes from sawmills, tree bark and used railway ties – showing how the H2/CO ratio in their gases could be manipulated by the process conditions in the gasifier, and demonstrating the use of semi-catalysts in the gasification step.
A multi-purpose dual-bed gasifier constructed in the UBC Pulp & Paper Centre under the joint leadership of senior engineer Dr. Yonghua Li's and UBC's Gasification Group was used in a study by Dow Chemical, one of its capital cost contributors. Preliminary hot tests with biomass injection were followed by a series of full biomass trials beginning in late autumn 2014 that handled approximately 10 times the amount of biomass than was processed through the small single-scale unit. Major objectives were met: learning how to establish the desired hydrodynamic multi-phase flow condition and control the circulation of solids between the gasifier and the combustor, and showing that the gasifier could be run solely with heat provided from the hot solids recirculated from the combustor stage.
From the long hours of trial emerged a catalytic tar-removal process (patent application approved) to lower tar content by as much as 95%. Their work also showed that steam gasification can produce an excellent syngas – one with more than double the heat content of the usual air-blown process, and which can become a superb fuel gas for power and heat production as well as downstream conversion to valuable liquid fuels and chemicals.