Browsing by Author "Rajabu, Hassan"

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    Carbonizing urban biowaste for low-cost char production in developing countries - A review of knowledge, practices and technologies
    (2015-01) Lohri, Christian R.; Sweeney, Daniel; Rajabu, Hassan
    Solid waste in the cities of low- and middle-income countries is characterized by a high organic fraction and management of this municipal solid waste is known for low collection and recycling rates, and inadequate disposal methods. Most of these countries also face the major challenge of supplying an affordable, reliable and sustainable cooking fuel to urban households. The majority of city residents use wood-based charcoal and the number of charcoal users is expected to rise over the years with increasing urbanization. Wood-based charcoal has several advantages compared to other cooking fuels, including continuous availability in local markets (even in small quantities), ease of storage, higher heating value, lightweight, cleaner burning compared to wood, cheap stoves, and in many countries it is sold at lower price compared to liquefied petroleum gas (LPG) and electricity. However, wood-based charcoal is derived from a predominately informally organized supply chain, which is linked to unsustainable forest logging, low efficiency production methods and long transportation routes, which are all factors that contribute to environmental degradation. Since improving the sustainability of charcoal production is considered the most effective and realistic measure to enhance the sustainability of household cooking, several developing countries have started to initiate biomass energy strategies, which include efforts to promote access to appropriate, alternative sources of bioenergy. The current state of the environment in cities of developing countries and their increasing charcoal demand raise the question if organic solid waste could be a suitable feedstock for low-cost char production. The char generated through slow pyrolysis of organic solid waste could be further processed into charcoal briquettes, a product of economic value with stable market demand and advantageous distribution properties. Use of municipal biowaste could stimulate their collection and, thereby, diminish the amount destined for disposal at dump sites. This approach could lead to reduced emissions linked to the uncontrolled decomposition of inappropriately disposed waste and reduced waste transportation, as well as the partial substitution of an unsustainably produced cooking fuel (wood-derived charcoal) without causing significant changes in traditional cooking appliances and behaviour. 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. On the policy level, there is a need to address the broader regulatory and tax framework in the charcoal sector. The current cost of charcoal in most developing countries does not reflect its true value because of lack of clear policies and enforcements, hence efforts to promote sustainably produced alternative cooking fuels will always be undercut by illegal charcoal, which is unregulated, bypasses many costs and reaches consumers at lower price at the expense of diminishing forests, adverse consequences on the environment and lost gov
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    Char fuel production in developing countries – A review of urban biowaste carbonization
    (2016-05) Lohri, Christian R.; Rajabu, Hassan; Sweeney, Daniel; Zurbrügg, Christian
    Urban households in low- and middle-income countries (LAMICs) face the challenge of finding affordable, reliable and sustainable cooking fuel supplies. Most city residents use wood-based charcoal derived from mostly informal supply chains, which are linked to unsustainable forest logging, low efficiency production methods and long transportation routes, all factors that contribute to environmental degradation. At the same time, the provision of adequate and equitable solid waste management (SWM) services remains a major urban challenge, with municipal solid waste mainly consisting of organics. Sales of briquettes made from carbonized biowaste can potentially foster waste collection and enhance cost-recovery of SWM systems, while contributing to a sustainable energy supply.
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    Energy efficiency in current tobacco-curing practice in Tanzania and its consequences
    (Elsevier, 1996-02) Siddiqui, K.M.; Rajabu, Hassan
    The energy efficiency of tobacco-curing practice in Tanzania is investigated. A one-quarter size laboratory model of a traditional, fuelwood-fired, rural barn is used. The energy consumed in the tobacco-curing process is monitored together with emissions of CO and CO2. An average of 14 kg of fuelwood is consumed to obtain 1 kg of cured tobacco. The emission of CO is 0.6% of total volume. It is estimated that 0.6 hectare of woodland have to be cleared to cure 1 hectare of tobacco, leading to a deforestation rate of 13,000 hectares per annum. Alternative sources of energy to fuelwood should be developed.
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    High Free Fatty Acid (FFA) Feedstock Pre-Treatment Method for Biodiesel Production
    (Trans Tech Publications, Switzerland, 2011) Kombe, Godlisten G.; Temu, Abraham K.; Rajabu, Hassan; Mrema, Godwill D.
    Biodiesel is an alternative fuel for engine and other appliances that is obtained by transesterifying vegetable oils or other materials largely comprised of triacylglycerols with monohydric alcohols to give the corresponding mono-alkyl esters. The quality of feedstocks for the biodiesel production dictates the method of its production and quality. Based on the initial amount of minor components in feedstocks, a process comparison of acid pre-treatment and caustic pretreatment of feedstock for alkali transesterification was done. Acid pre-treatment was carried out with 0.60 w/w methanol-to-oil ratios in the presence of 2% w/w H 2 SO 4 as an acid catalyst in 2 h reaction at 60 °C. In caustic pretreatment process, the same amount of oil was neutralized with the required amount of sodium hydroxide based on the initial amount of free fatty acid and gums in the oil. The acid pretreatment process gives a 4% loss in feedstock compared to 20% from the neutralization process. The yields 96% and 94% of biodiesel from acid pretreated and caustic pretreatment feedstock were obtained respectively. The oxidation stabilities of biodiesel from acid pretreatment and neutralized feedstock were 1.12h and 3h respectively. The biodiesel from acid pretreatment oil could not pass the ASTM standard.
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    Multiple biomass fuels and improved cook stoves from Tanzania assessed with the Water Boiling Test
    (Elsevier, 2016-04) Grimsby, Lars K.; Rajabu, Hassan; Treiber, Michael U.
    Improved cook stoves can reduce fuel consumption and indoor air pollution, but are not always used as expected. A household survey in rural Tanzania showed that cooking fuels such as firewood and charcoal were supplemented with agricultural residues, and households combined improved and traditional stoves. The WBT was used to assess 7 biomass fuels in 6 stoves. Maize stalks and cobs, and stalks from sunflower showed similar burning parameters to firewood, cow dung significantly different. Ash made agricultural residues unsuitable in improved firewood stoves. The three stone fire was versatile, an advantage where fuels are limited. Okoa-II with firewood was significantly more efficient than the three stone fire, whereas Okoa-I showed no improvement. Improved charcoal stove Jiko Bora was not significantly better than its traditional counterpart. PM across fuels corresponded with «the energy ladder»; CO to lesser degree. A local sawdust stove was functional and is increasingly common in Tanzania. Where access to energy is limited by poverty and multiple fuels are utilised, dissemination of a range of stoves optimised for specific fuels or conversely a cook stove as versatile as the open fireplace, may improve cooking conditions.
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    Urban biowaste for solid fuel production: Waste suitability assessment and experimental carbonization in Dar es Salaam, Tanzania
    (2015-02) Lohri, Christian R.; Faraji, Adam; Ephata, Elia; Rajabu, Hassan; Zurbrügg, Christian
    The poor state of solid waste management in Dar es Salaam (DSM), Tanzania, the large fraction of organic waste generated and a high charcoal consumption by city residents has triggered this research on carbonization of municipal biowaste. Char produced by the thermochemical conversion method of slow pyrolysis can be briquetted and used as cooking fuel alternative to wood-based charcoal. To explore the potential of biowaste carbonization in DSM, the most suitable organic wastes were selected and pyrolyzed in a simple, externally heated carbonization system developed as part of this study. A Multi-Criteria Analysis framework allowed to assess prevailing biowaste types regarding availability and accessibility, and respective suitability in terms of physical–chemical properties. The assessment, using data from a survey and lab analysis, revealed the following biowaste types with highest overall potential for char production in DSM: packaging grass/leaves (PG) used for transportation of fruit and vegetables to the markets, wood waste (WW) from wood workshops, and cardboard (CB) waste. Best practice carbonization of these biowastes in the pyrolyzer showed satisfactory char yields (PG: 38.7%; WW: 36.2%; CB: 35.7% on dry basis). Proximate composition (including volatile, fixed carbon and ash content) and heating value (PG: 20.1 MJ kg-1; WW: 29.4 MJ kg-1; CB: 26.7 MJ kg-1) of the produced char also compare well with literature data. The energy and emission-related aspects of the system still require further research and optimizations to allow financially viable and safe operatio