BY: Marion Carrier; JF Gorgens and Hansi Knoetze
The uncertainty of long-term fossil resources, electricity and fuel prices and increasing carbon dioxide emissions have generated much interest in renewable-energy projects. Among the renewables technologies available, the conversion of biomass through thermo- chemical processes is investigated worldwide and also in South Africa. Raw biomass feedstocks (agricultural and forest residues) can be converted into bioenergies such as heat, electricity, second-generation biofuels and value-added products like chemicals, soil amendments and activated carbon.
Thermochemical conversion of plant biomass makes use of a chemical reactions induced by elevated temperatures and pressures to change the molecular struc- ture of the feedstock. Thermochemical conversion processes are primarily combustion, pyrolysis, gasification and direct liquefaction.
Over the last ten years, the Department of Process Engineering at Stellenbosch University has been developing the research area of thermochemical conversion of plant biomass in close collaboration with South African industry partners – including Sasol, the Paper Manufacturers Association of South Africa and the sugar industries – and academic institutions (the North-West University and the Sugar Milling Research Institute). International collaborations with institutions such as the Karlsruhe Institute of Technology, of Germany, and Cranfield University, in the UK, have also supported development of this research area.
Recently, the department organised a workshop entitled ‘From biomass to Bioenergies via thermochemical processes’ in association with the UK’s Aston and Cranfield universities. The aim of the workshop was to gather perspectives on the future of thermochemical technologies for biomass conversion in South Africa. Professor Tony Bridgwater, of Aston University, who plays a key role in several major European-funded projects on bio- energy, biofuels and biorefineries, and Professor Sai Gu, of Cranfield University, promoted the organisation of this work- shop by sponsoring it through the Engi- neering and Physical Sciences Research Council. The workshop attracted 65 delegates from various countries and fields, includ- ing academics and representatives of municipalities and industries.
The overall objective of the workshop was to promote the thermochemical pro- cessing technologies related to the con- version of plant biomass resources into bioenergy and value-added products such as chemicals and biochar. Nineteen oral presentations were delivered and these mentioned the progress made on pyroly- sis and gasification development, the application of pyrolytic and gasifica- tion products and technicoeconomic assessment in South Africa.
One of the major issues relating to the use of biomass as a source of energy is the assessment of existing and available bio- mass. The Council for Scientific and Industrial Research has developed an analytical framework and decision-support tools to assist in assessing, managing and monitoring the sustainability of bio- energy. This work mapped the woody biomass distribution in South Africa. The outcome of the work was a national resource map for the woody biomass, projecting the growth and estimates of potential quantities. Resources such as invasive alien plants and bush encroachment, presenting the highest potential, are only available for a defined period, estimated to be 20 years. Agricultural and forest residues could be considered as well.
The type of conversion technologies has also to be considered. During this workshop, the focus was on thermochemi- cal technologies, which are, primarily, combustion, pyrolysis, gasification and direct liquefaction.
Research on pyrolysis and gasification of plant biomass has moved forward in South Africa. These technologies can contribute to the production of heat, electricity, transport fuels and bioproducts like biochar, activated carbon and chemicals, besides others. However, data on the overall energy balance for these processes and feed- stock preparation are lacking. A proposal was made to academia to come up with a matrix of technologies. The matrix should consider feedstock, energy balance (taking into account transport, pretreatment, conversion, post-treatment) and efficiency (reactor type) among its criteria.
The discussion concluded that the conversion of biomass into energy and value-added products is a viable opportunity in South Africa. Markets should be made aware of the alternative energy products derived from biomass, which could encourage the use of renewable products and stimulate further investment and competitiveness in the industry. A joint lobby from industry and aca- demia should be established to promote the audit and approval of technologies and assist investors in obtaining finance.
Recognised for its valuable educational outputs, the workshop has been accredited with two points for continuing professional development by the Engineering Council of South Africa.
Dr Carrier is a postdoctoral researcher in the Department of Process engineering at Stellenbosch University, while Gorgens is a professor in the same department and Knoetze is dean of the university's engineering faculty - he spent 30 years as an academic in the Department of Process Engineering.