A Review of Knowledge, Practices and Technologies Christian Riu Lohri, Dan Sweeney, Hassan Mtoro Rajabu
This report reviews existing knowledge on char-making to help stakeholders understand under which circumstances carbonization of municipal biowaste may be feasible. The report starts with a general overview of common municipal solid waste management challenges in low-and middle-income countries. It then summarizes the current situation regarding conventional charcoal production and consumption as cooking fuel, reviewing some of the trends and theories behind the concept of ‘household fuel switching’. It also describes biomass carbonization in details, i.e., input requirements, chemical conversion processes and output properties, and reviews information on existing biomass-to-char technologies: e.g., process and reactor types, capacity, construction materials, conversion efficiency, energy source, residence time, emissions, fixed carbon yield, auxiliary requirements, working life and capital cost. This part of the report draws heavily from literature on wood pyrolysis because there is limited information on slow pyrolysis of biowaste. The last chapter draws an analysis of the feasibility of biowaste carbonization in cities of developing countries and highlights challenges, opportunities and areas for further research. This review concludes that the high demand for carbonized fuel in cities of low-and middle-income countries has created the market for waste-derived char briquettes. Yet, a major challenge to their production is having continuous access to dry, unmixed, homogeneous, uncontaminated substrates, which are available at no or low costs. In other words, a good supply of source-separated wastes that can be obtained near the point of their production is needed. Furthermore, most existing carbonization systems are either inefficient and polluting or relatively expensive. For a sustainable and financially viable waste-to-char business an appropriate, locally manufactured and operated, cost-effective system is required, which is non-polluting and energy-efficient with controlled use of all combustible by-products and waste heat.
Keywords Carbonization, char briquettes, charcoal, cooking fuel, organic solid waste, slow pyrolysis, decentralized recycling, waste-to-energy, low- and middle-income countries Bibliographic reference Lohri, C.R., Sweeney, D., Rajabu, H.M. (2015): Carbonizing Urban Biowaste for Low-Cost Char Production in Developing Countries - A Review of Knowledge, Practices and Technologies. Joint Report by Eawag, MIT D-Lab and UDSM.