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Biomass Energy Systems and Resources in Tropical Tanzania
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Tanzania has a characteristic developing economy, which is dependent on agricultural productivity.  About 90% of the total primary energy consumption of the country is from biomass.  Since the biomass is mostly consumed at the household level in form of wood fuel, it is marginally contributing to the commercial energy supply.  However, the country has abundant energy resources from hydro, biomass, natural gas, coal, uranium, solar, wind and geothermal.  Due to reasons that include the limited technological capacity, most of these resources have not received satisfactory harnessing.  For instance: out of the estimated 4.7GW macro hydro potential only 561MW have been developed; and none of the 650MW geothermal potential is being harnessed.  Furthermore, besides the huge potential of biomass (12 million tons of oil equivalent), natural gas (45 million cubic metres), coal (1,200 million tones), high solar insolation (4.5 – 6.5 kWh/m2), 1,424km of coastal strip, and availability of good wind regime (> 4 m/s wind speed), they are marginally contributing to the production of commercial energy.  Ongoing exploration work also reveals that the country has an active system of petroleum and uranium.  On the other hand, after commissioning the 229km natural gas pipeline from SongoSongo Island to Dar es Salaam, there are efforts to ensure a wider application in electricity generation, households, automotive and industry.

 

Due to existing environmental concerns, biomass resource is an attractive future energy for the world, Tanzania inclusive.  This calls for putting in place sustainable energy technologies, like gasification, for their harnessing.  The high temperature gasification (HTAG) of biomass is a candidate technology since it has shown to produce improved syngas quality in terms of gas heating value that has less tar.

 

This work was therefore initiated in order to contribute to efforts on realizing a commercial application of biomass in Tanzania.  Particularly, the work aimed at establishing characteristic properties of selected biomass feedstock from Tanzania.  The characteristic properties are necessary input to thermochemical process designers and researchers.  Furthermore, since the properties are origin-specific, this will provide baseline data for technology transfer from north to south.  The characteristic properties that were established were chemical composition, and thermal degradation behaviour.  Furthermore, laboratory scale high temperature gasification of the biomasses was undertaken.

 

Chemical composition characteristics was established to palm waste, coffee husks, cashew nut shells (CNS), rice husks and bran, bagasse, sisal waste, jatropha seeds, and mango stem.  Results showed that the oxygen content ranged from 27.40 to 42.70% where as that of carbon and hydrogen ranged from 35.60 to 56.90% and 4.50 to 7.50% respectively.  On the other hand, the elemental composition of nitrogen, sulphur and chlorine was marginal.  These properties are comparable to findings from other researchers.  Based on the results of thermal degradation characteristics, it was evident that the cashew nut shells (CNS) was the most reactive amongst the analyzed materials since during the devolatilization stage the first derivative TG (DTG) peak due to hemicellulose degradation reached (-5.52%/minute) compared palm stem whose first peak was -4.81%/minute.  DTG first peak for the remaining materials was indistinct.

 

Results from the laboratory gasification experiments that were done to the coffee husks showed that gasification at higher temperature (900°C) had an overall higher gasification rate.  For instance, during the inert nitrogen condition, 7% of coffee husk remained for the case of 900°C whereas the residue mass for the gasification at 800 and 700°C was 10 and 17% respectively.  Steam injection to the biomass under high temperature gasification evolved the highest volumetric concentration of carbon monoxide.  The CO peak evolution at 900°C steam only was 23.47 vol. % CO whereas that at 700°C was 21.25 vol. % CO.  Comparatively, the CO peaks for cases without steam at 900°C and 2, 3, and 4% oxygen concentrations were 4.59, 5.93, and 5.63% respectively.  The reaction mechanism of coffee husks gasification was highly correlated to zero reaction order exhibiting apparent activation energy and the frequency factor 161 kJ/mol and 3.89x104/minute respectively.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , xiii, 61 p.
Keyword [en]
Tanzania; Tropical Biomass Energy; High Temperature Gasification (HTAG)
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-24705ISBN: 978-91-7415-732-1 (print)OAI: oai:DiVA.org:kth-24705DiVA: diva2:352935
Presentation
2010-09-17, entrepl (B1), Brinellvägen 23, KTH Stockholm, 12:04 (English)
Opponent
Supervisors
Note
QC 20100923Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2010-09-23Bibliographically approved
List of papers
1. Coffee husks gasification using high temperature air/steam agent
Open this publication in new window or tab >>Coffee husks gasification using high temperature air/steam agent
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2010 (English)In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 91, no 10, 1330-1337 p.Article in journal (Refereed) Published
Abstract [en]

Analyses made on the world's biomass energy potential show that biomass energy is the most abundant sustainable renewable energy. The available technical biomass energy potential surpasses the total world's consumption levels of petroleum oils, coal and natural gas. In order to achieve a sustainable harnessing of the biomass energy potential and to increase its contribution to the world's primary energy consumption, there is therefore a need to develop and sustain contemporary technologies that increase the biomass-to-energy conversion. One such technology is the high temperature air/steam gasification (HTAG) of biomass. In this paper we present findings of gasification experimental studies that were conducted using coffee husks under high temperature conditions. The experiments were performed using a batch facility, which was maintained at three different gasification temperatures of 900 °C, 800 °C, and 700 °C. The study findings exhibited the positive influence of high temperature on increasing the gasification process. Chars left while gasifying at 800 °C and 700 °C were respectively 1.5 and 2.4 times that for the case of 900 °C. Furthermore, increased gasification temperature led to a linear increment of CO concentration in the syngas for all gasification conditions. The effect was more pronounced for the generally poorly performing gasification conditions of N2 and 2% oxygen concentration. When gasification temperature was increased from 700 °C to 900 °C the CO yield for the 2% O2 concentration increased by 6 times and that of N2 condition by 2.5 times. The respective increment for the 3% and 4% O2 conditions were only twofold. This study estimated the kinetic parameters for the coffee husks thermal degradation that exhibited a reaction mechanism of zero order with apparent activation energy of 161 kJ/mol and frequency factor of 3.89 × 104/min.

Keyword
Agricultural waste, CO/CO2 index, Coffee husks, High temperature gasification (HTAG), Kinetics
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-24710 (URN)10.1016/j.fuproc.2010.05.003 (DOI)000280916300020 ()2-s2.0-77954845622 (Scopus ID)
Note
QC 20100923Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2017-12-12Bibliographically approved
2. Thermal characterization of tropical biomass feedstocks
Open this publication in new window or tab >>Thermal characterization of tropical biomass feedstocks
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2011 (English)In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 52, no 1, 191-198 p.Article in journal (Refereed) Published
Abstract [en]

The processing of agricultural crops results in waste, which is a potential energy resource for alleviating commercial energy supply problems to agricultural-led economies like Tanzania. The energy content of the individual agricultural waste is largely dependent on its chemical composition (C, H and O) and it is negatively affected by the inclusion of inorganic elements and moisture. In this work, fifteen tropical agricultural wastes emanating from export crops for Tanzania were analyzed. The methods used to analyze involved performing proximate and ultimate analysis for determining the biomass composition. Thermal degradation characteristic was established to five selected wastes (coffee husks, sisal bole, cashew nut shells, palm stem, and bagasse) using a thermogravimetric analyzer type NETZSCH STA 409 PC Luxx at a heating rate of 10 K/min. On the basis of elemental composition, the palm fibre and cashew nut shells exhibited high energy content due to their higher H:C ratio with relatively low O:C ratio. Results of the thermal degradation characteristic study showed that the cashew nut shells were the most reactive feedstocks due to their highest overall mass loss and lowest burnout temperatures of 364 °C. Further, kinetic studies done to the five tropical biomass feedstocks under the pseudo single-component overall model established the activation energy for the bagasse, palm stem, and cashew nut shells to be 460 kJ/mole, 542 kJ/mole, and 293 kJ/mole, respectively. The respective activation energies for coffee husks and sisal bole were 370 kJ/mole and 239 kJ/mole. With the exception of the sisal bole, which exhibited zero order reaction mechanism, the remaining materials´ reaction mechanism was of first order. These experimental findings form a basis for ranking these materials for energy generation and provide necessary input to equipment and process designers.

Keyword
Thermogravimetry, Kinetics, Tropical biomass composition, Agricultural waste, Bioenergy, Tanzania
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-24713 (URN)10.1016/j.enconman.2010.06.058 (DOI)000284746800022 ()2-s2.0-78049526069 (Scopus ID)
Note
QC 20100923Available from: 2010-09-23 Created: 2010-09-23 Last updated: 2017-12-12Bibliographically approved

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