8. 9. 12. 13. 16. 15. 11. 20. 21. 6. 14. 22. 5. O2. N2. 10. 18. 17. 19. To data acquisition system. To gas analyzers. Li
Biomass Energy Systems and Resources in Tropical Tanzania
Lugano Wilson
Licentiate Thesis in Furnace Technology Stockholm, Sweden 2010 19
17 6
13
12
11
F
4
2
To data acquisition system
F F
O2
10
8
3
20 To gas analyzers
9
N2 7
5
21
1 15
14
18
16
22
Biomass Energy Systems and Resources in Tropical Tanzania
Lugano Wilson
Licentiate Thesis
Stockholm 2010 Royal Institute of Technology School of Industrial Engineering and Management Department of Material Science and Engineering Division of Energy and Furnace Technology SE-100 44 Stockholm Sweden
Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan I Stockholm framlägges för offentlig granskning för avläggande av teknologie licentiatexamen fredagen den 17 September 2010, kl. 10 i sal B1, Brinellvägen 23, Kungliga Tekniska Högskolan, Stockholm.
ISRN KTH/MSE--10/44--SE+ENERGY/AVH
ISBN 978-91-7415-732-1
ii
Lugano Wilson.
Biomass Energy Systems and Resources in Tropical Tanzania
Royal Institute of Technology School of Industrial Engineering and Management Department of Material Science and Engineering Division of Energy and Furnace Technology SE-100 44 Stockholm Sweden
ISRN KTH/MSE--10/44--SE+ENERGY/AVH
ISBN 978-91-7415-732-1 © The author
iii
ABSTRACT
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 iv
process designers and researchers. Furthermore, since the properties are originspecific, 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.
v
ACKNOWLEDGEMENT
The Swedish International Development Cooperation Agency (SIDA) through the Department for Research Cooperation (SAREC) is acknowledged for the financial support through the Capacity Building Project at the College of Engineering and Technology (CoET) of the Universality of Dar es Salaam, Tanzania. Additional financial support came from the Swedish Research Council (Vetenskapsrådet), which is highly acknowledged.
My Supervisors at KTH, Prof. Weihong Yang and Wlodzimierz Blasiak, including those at the University of Dar es Salaam, Prof. Geoffrey R. John and Cuthbert F. Mhilu are acknowledged for their academic support throughout the study period. Life at KTH and Stockholm in general was interesting through the social interaction and academic challenges from my colleagues at the Division of Energy and Furnace Technology: Aliaksandr Alevanau, Amit Kumar Biswas, Xiaolei Zhang, Owden Robert Mwaikondela, Pawel Donaj, Lan Zhang, Efthymios Kantarelis, and Qingli Zhang.
The continued moral support from my family and family members is highly appreciated as it was the main foundation leading to this output. Unfortunately, it is not possible to mention all those who contributed to this work, in one form or another, I am taking this opportunity to thank all of you. May the blessing of our Almighty God be extended to you, THANK YOU!
vi
To my Wife Grace (Mandiga) and our beloved children: Priscilla (Lahabu), Maureen, and Joylyn
vii
Papers Included in the Thesis Supplement 1: Lugano Wilson, Geoffrey R. John, Cuthbert F. Mhilu, Weihong Yang, and Wlodzimierz Blasiak, (2010) “Coffee Husks Gasification Using High Temperature Air/Steam Agent”, Fuel Processing Technology, Volume 91, Issue 10, pp. 1330 – 1337 Supplement 2: Lugano Wilson, Weihong Yang, Wlodzimierz Blasiak, Geoffrey R. John, Cuthbert F. Mhilu, (2010), “Thermal Characterization of Tropical Biomass Feedstocks”, Energy Conversion and Management, doi:10.1016/ j.enconman.2010.06.058
Papers not Included in the Thesis 1.
L. Wilson, G. R. John, C. F. Mhilu, W. Yang, and W. Blasiak; (2009), “Combustion Characteristics of Cashew Nut Shells and Coffee Husks by Thermogravimetry and Calorimetry”, 17th European Biomass Conference & Exhibition, 29th June – 3rd July, CCH - Congress Center Hamburg, Germany
2.
L. Wilson, G. R. John and C. F. Mhilu; (2008), “Thermal Characteristics of Sugar Cane Bagasse with Storage”, The 9th Asia-Pacific International Symposium on Combustion and Energy Utilization, 2nd – 6th November, Beijing, China
3.
L. Wilson, W. Yang, W. Blasiak, G. R. John and C. F. Mhilu; (2007), “Opportunities and Challenges of Biomass Energy for Heat and Power Production in Tanzania”. 3 rd International Green Energy Conference, 18th – 20th June, Västerås, Sweden
The author is the main contributor to the supplemented papers whereas coauthors provided the necessary support in literature, experimental design, and interpretation.
viii
TABLE OF CONTENTS ABSTRACT .........................................................................................................IV ACKNOWLEDGEMENT ......................................................................................VI LIST OF TABLES ................................................................................................XI LIST OF FIGURES ..............................................................................................XI ABBREVIATIONS ..............................................................................................XII SYMBOLS .........................................................................................................XIII 1
INTRODUCTION ............................................................................................ 1 1.1
ENERGY BALANCE ......................................................................... 1
1.2
POTENTIAL ENERGY RESOURCES .................................................... 3
1.2.1
Hydropower ................................................................................. 3
1.2.2
Natural Gas ................................................................................. 5
1.2.3
Biomass ....................................................................................... 5
1.2.4
Coal ............................................................................................. 9
1.2.5
Solar ............................................................................................ 9
1.2.6
Wind .......................................................................................... 10
1.2.7
Geothermal ................................................................................ 11
1.2.8
Tidal and Wave.......................................................................... 12
1.2.9
Petroleum Oil and Uranium Exploration .................................... 13
1.3
ELECTRICITY GENERATION MIX ..................................................... 15
1.4
BIOMASS COGENERATION............................................................. 18
1.4.1
Kilombero Sugar Company........................................................ 18
1.4.2
Mtibwa Sugar Estate Limited ..................................................... 18
1.4.3
Tanganyika Planting Company Limited (TPC) ........................... 19
1.4.4
Kagera Sugar Limited (KASC) ................................................... 19
1.4.5
Saohill Sawmill .......................................................................... 19
1.4.6
Tanganyika Wattle Company (TANWAT) .................................. 20
1.5
ELECTRICITY DEMAND .................................................................. 21
1.6
ELECTRICITY DISTRIBUTION AND DISTRIBUTION NETWORK .............. 22
2. LITERATURE REVIEW ................................................................................ 23
ix
2.1
BIOMASS GASIFICATION ................................................................23
2.2
HIGH TEMPERATURE AIR/STEAM GASIFICATION (HTAG) .................24
2.3
EFFECTS OF HEATING RATE AND TEMPERATURE ............................25
3. OBJECTIVES ...............................................................................................26 4. METHODOLOGY .........................................................................................27 4.1
CHEMICAL COMPOSITION ..............................................................27
4.2
THERMAL DEGRADATION CHARACTERISTICS ..................................27
4.3
LABORATORY EXPERIMENTATION ..................................................28
5. RESULTS AND DISCUSSION .....................................................................30 5.1
CHEMICAL COMPOSITION OF TROPICAL BIOMASSES........................30
5.2
THERMAL DEGRADATION OF TROPICAL BIOMASSES ........................34
5.2.1
Mass Loss Characteristics .........................................................34
5.2.2
Rate of Mass Loss Characteristics.............................................35
5.2.3
Burnout Temperature .................................................................37
5.3
LABORATORY GASIFICATION OF COFFEE HUSKS ............................38
5.3.1
Effects of Gasification Agent on Heating Rate ...........................38
5.3.2
Gasification Rate........................................................................39
5.3.3
Syngas Evolution .......................................................................43
5.3.4
Syngas Heating Value ...............................................................49
5.3.5
Estimation of Coffee Husks Kinetic Parameters.........................51
6. CONCLUSION ..............................................................................................53 7
FUTURE WORK ...........................................................................................54
REFERENCES ....................................................................................................55
x
LIST OF TABLES Table 1: Petroleum fuels importation detail .......................................................... 2 Table 2: Planned Macro hydropower plants ........................................................ 4 Table 3: Existing small-scale hydropower schemes ............................................ 4 Table 4: Waste generated (Tones) in Tanzania Cities ......................................... 8 Table 5: Wind stations with annual mean wind speeds ≥ 4.5 m/s ..................... 10 Table 6: Oil and gas exploration companies ..................................................... 14 Table 7: Installed generation capacity and source ............................................. 17 Table 8: Potential additional cogeneration capacity ........................................... 21 Table 9: Tropical biomasses chemical composition ............................................ 31 Table 10: Mass loss summary ............................................................................ 35 Table 11: Material’s characteristic properties summary ...................................... 36 Table 12: Residue mass summary for steam injected experiments .................... 41 Table 13: CO evolution characteristics summary ................................................ 48 Table 14: Syngas composition summary ............................................................ 51
LIST OF FIGURES Figure 1: Geothermal potential sites in Tanzania ............................................... 12 Figure 2: Installed generation capacity and share (%) by source ....................... 16 Figure 3: Electricity generation and consumption, million kWh ......................... 22 Figure 4: Existing and proposed grid and isolated transmission system ........... 23 Figure 5: The high temperature gasification test rig ............................................ 29 Figure 6: Coalification diagram for the tropical biomasses.................................. 33 Figure 7: TG thermogram characteristics based on the coffee husks sample .... 34 Figure 8: Material‟s characteristic properties based on palm stem degradation . 37 Figure 9: Sample temperature profiles ................................................................ 40 Figure 10: Gasification rate under different experimental conditions .................. 42 Figure 11: Syngas (CO/CO2) evolution profiles................................................... 47 Figure 12: Syngas evolution profiles ................................................................... 50 Figure 13: ln[g(α)/T2] versus 1/T for 900°C N2 condition experiment .................. 53
xi
ABBREVIATIONS AVGAS CNG CNS DSC DTG GC GDP GEF HHV HiTAC HTAG IEA IGCC IPTL KASC LHV LPG m.a.s.l MEM MRP NGOs OECD OTEC PSMP PV SIDA TANESCO TANWAT TCH TG TOE TPC TPDC UNDP
Aviation Gasoline Compressed Natural Gas Cashew Nut Shells Differential Scanning Calorimetry Derivative TG Gas Chromatograph Gross Domestic Product Global Environmental Fund Higher Heating Value (Gross Calorific Value) High Temperature Combustion High Temperature Air/Steam Gasification International Energy Agency Integrated Gasification Combined Cycle Independent Power Tanzania Limited Kagera Sugar Limited Lower Heating Value (Net Calorific Value) Liquid Petroleum Gas Meters Above Sea Level Ministry of Energy and Minerals Mkuju River Project Non-Government Organizations Organization for Economic Co-operation and Development Ocean Thermal Energy Conversion Power System Master Plan Photovoltaic Swedish International Development Authority Electric Supply Company Limited Tanganyika Wattle Company Tones of Cane Per Hour Thermogravimetry Tons of Oil Equivalent Tanganyika Planting Company Tanzania Petroleum Development Corporation United Nations Development Program
xii
SYMBOLS
Mass loss fraction
A
Apparent frequency factor (Avogadro's constant) [/min]
Heating rate [K/min]
E
Apparent activation energy [kJ/mole]
k
Arrhenius constant
n
Reaction order
R
Universal gas constant [kJ/kmole K]
2
R
T
Coefficient of Determination Absolute temperature [K]
xiii
1
INTRODUCTION
Tanzania has a characteristic developing economy of the world. The economy is dependent on agricultural productivity. Information available from the National Bureau of Statistics [1] shows that the agricultural sector contributes more than 44.70% of the total gross domestic product (GDP). It accounts for almost 56 percent of total merchandise exports and employs nearly 80% of the population. Major agricultural exports are coffee, cotton, tea, tobacco, cashew nuts, and sisal. The developing economy is reflected in inadequate infrastructure like roads and electricity. On the other hand, the agricultural sector (in terms of agricultural waste and dedicated energy crops), provides a potential energy source when harnessed sustainably. This requires putting in place sustainable and innovative biomass energy technologies that will contribute to the economic development.
1.1
ENERGY BALANCE
The Tanzania energy policy document [2] shows that over 90% of Tanzania‟s primary energy consumption is accounted by biomass whereas petroleum and electricity accounts for 8% and 1.2%, respectively.
Other energy sources
including coal, solar, biogas and wind account for less than 1% of the total primary energy consumption. The distribution of the primary energy consumption by sector is such that households consume 89.8%, agriculture 3.6%, transport 3.1%, industry 1.9%, commerce 0.2% and other sectors 1.4%. The total final energy consumption amounts to over 22 million tons of oil equivalent (TOE) or 0.7 TOE per capita. The Commercial energy consumption pattern shows that the contribution by individual end users is: transport sector 40.5%, industry 24.6%, household 18.6%, agriculture 8.2%, commerce 2.6% and others 5.5%. Imported petroleum, whose importation per annum averages 850,000 metric tones, supplies over 90% of the commercial energy needs. Its importation per annum consumes more than 30% of the foreign exchange earned by the country. petroleum fuels importation.
1
Table 1 details the
Table 1: Petroleum fuels importation detail [Tanzania Petroleum Development Corporation (TPDC) internal reports] FUEL DESCRIPTION
CONSUMPTION PER YEAR, „000 TONS 1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
LPG (45% Household)
3.15
4.02
1.26
1.57
1.67
1.47
1.64
2.21
1.08
0.99
0.90
LPG (55% Industrial)
3.85
4.92
1.54
1.92
2.05
1.80
2.00
2.70
1.32
1.21
1.10
AVGAS (Civil Aviation)
4.19
3.94
1.58
4.76
4.82
1.46
2.7
2.5
2.2
2
1.8
103.61
107.05
108.56
106.74
83.72
120.80
142.98
163.89
150
156
165
6.49
7.40
7.31
6.72
6.01
7.96
8.34
10.52
9.40
9.80
10.20
18.70
21.00
17.55
19.28
20.09
20.51
21.53
21.49
24.43
23.57
21.33
0.69
0.80
0.76
0.79
0.83
0.71
0.81
0.93
0.85
0.87
1.18
298.40
340.94
340.01
309.29
273.40
368.74
386.30
493.18
435.32
455.77
477.29
38.63
33.25
23.89
18.56
37.65
20.99
25.73
14.82
16.5
14
12
116.97
114.12
105.67
114.38
109.57
114.28
99.97
100.77
100
97
96
36.34
36.34
38.13
40.00
39.19
40.08
40.09
40.19
41.5
42.1
42.7
PETROL (100% Road Transport) DIESEL (2% Off road) DIESEL (Rail Transport) DIESEL (Waterborne Navigation) DIESEL ( Balance -> Road Transport) INDUSTRIAL DIESELa (Industrial) FUEL OIL (Industrial) JETFUEL – Civil Aviation JETFUEL – International Bunkers (Aviation) PARAFFIN (100% Domestic)
19.81
18.72
17.39
10.95
15.01
15.07
23.01
27.10
22
23
24
154.38
202.80
177.62
122.63
76.07
87.21
115.60
122.97
80
70
58
TOTAL
805.21
895.30
841.26
757.59
670.06
801.09
870.69
1,003.27
884.60
896.30
911.50
AVERAGE:
2
848.81
The high dependence on biomass is contributed by the fact that majority of Tanzanians (75% of the population) live in rural areas that are far from modern energy service infrastructure. As a result, the biomass energy is consumed at the household level with a marginal contribution from commercial energy.
A
sustainable harnessing of available potential energy resources is therefore necessary to realize the commercial energy to the economy.
1.2
POTENTIAL ENERGY RESOURCES
Tanzania has abundant natural resources that can be harnessed into commercial energy.
These natural resources include hydro, biomass, natural gas, coal,
uranium, solar, wind and geothermal. 1.2.1 Hydropower Tanzania‟s hydropower resource comprise of macro (large scale) and micro (small scale) systems. The macro hydro potential is about 4.7GW out of which only 561MW have been developed [3].
The micro hydropower potential is
estimated at more than 314MW out of which 1.5% has been developed [4].
The 561MW developed macro hydro-electricity power system comprises six TANESCO owned and operated hydropower plants at Mtera (80MW), Kidatu (204MW), Hale (21MW), Pangani Falls (68MW), Nyumba ya Mungu (8MW) and Kihansi (180MW). As detailed in Table 2, other hydropower sites identified and studied for further development include Rumakali (222MW), Ruhudji (358MW), Mandera (21MW), Stigler‟s Gorge (1,200 to 1,400MW), Mpanga (200MW), Masigira (250), and Upper Kihansi (120MW).
Tanzania has an estimated mini hydro potential of about 315MW, out of which only 4.74MW is developed.
A sustainable harnessing of this resource could
contribute significantly to the overall country‟s energy production and the overall electrification. Details available in Table 3 show that religious missions have installed most of the existing small-scale hydropower schemes the majority of which are located in the southern highlands regions of Tanzania. 3
Table 2: Planned Macro hydropower plants [5, 6] SITE Rumakali Ruhudji Mandera Stigler‟s Gorge – Phase I and II Mpanga Masigira Upper Kihansi TOTAL
CAPACITY (MW) 222 358 20 1,200 145 80 120 2,145
RIVER Rumakali Ruhudji Pangani Rufiji Mpanga Ruhuhu Kihansi
LEVEL OF STUDY Feasibility Feasibility Feasibility Prefeasibility Prefeasibility Prefeasibility Prefeasibility
Table 3: Existing small-scale hydropower schemes (TANESCO records) LOCATION TANESCO Owned Tosamaganga (Iringa) Kikuletwa (Moshi) Mbalizi (Mbeya) Missions Owned Kitai (Songea) Nyagao (Lindi) Isoko (Tukuyu) Uwemba (Njombe) Bulongwa (Njombe) Kaengesa (Sumbawanga) Rungwe (Tukuyu) Nyangao (Lindi) Peramiho (Songea) Isoko (Tukuyu) Ndanda (Lindi) Ngaresero (Arusha) Sakare (Soni) Mbarari (Mbeya) Ndolage (Bukoba) Ikonda (Njombe) Tosamaganga (Iringa)
TURBINE TYPE/MANUFACTURER
INSTALLED CAPACITY (kW)
Gilkes & Gordon/Francis Boving & Voith Reaction Gilkes & Gordon/Francis
1220 1160 340
Cross Flow/Ossberger Cross Flow/Ossberger Cross Flow/Ossberger Cross Flow/Ossberger Cross Flow/Ossberger
45 15.8 15.5 800 180.0
Cross Flow/Ossberger
44.0
Cross Flow/Ossberger Cross Flow/Ossberger Cross Flow/Ossberger Cross Flow/Ossberger Gilbsk Geiselbrecht Chinese B. Maler CMTIP Information not available Information not available TOTAL:
4
21.2 38.8 34.6 7.3 14.4 15.0 6.3 700.0 55.0 40.0 Information not available 4,737.9
1.2.2 Natural Gas
Ongoing petroleum exploration in Tanzania through the Tanzania Petroleum Development Corporation has discovered natural gas along SongoSongo Island and Mnazi Bay both of which are located in southeastern Tanzania.
The
SongoSongo natural gas reserve is estimated at 30 million cubic metres whereas the Mnazi Bay reserve is estimated to contain 15 million cubic metres. Exploitation of the SongoSongo gas started in July 2004 after completion of the 229km gas pipeline from SongoSongo Island to Dar es Salaam. Todate, the natural gas is utilized to generate 331MW of electricity through thermal power plants located in Dar es Salaam City. Other uses of the gas include thermal applications in factories, households, and automotive based within the City. Natural gas application in automotive commenced following the commissioning of the natural gas filling station project. The project has been implemented by the Government of the United Republic of Tanzania in collaboration with the TPDC. It has a capacity to benefit over 8,000 cars and some 30,000 households. Motor vehicles conversion to run on compressed natural gas (CNG) from this project commenced in mid 2009. Starting with the city of Dar es Salaam, two initial CNG stations are designated at Ubungo and Mikocheni areas. 1.2.3 Biomass Tanzania has about 33.5 million hectares of forest and woodlands, which is about 38% of total land area [7]. Out of this total area, almost two thirds are woodlands on public lands that are under enormous pressure from human activities also being an energy source.
Besides wood fuel, the country has considerable
biomass resources in form of agricultural and forest residues and animal wastes which, in combination with the woodlands, meet the majority of household energy requirement. Biomass potential can therefore be estimated from existing plantation forests and agricultural waste. Currently, there are about 80,000 hectares of state owned plantation forests that were mostly linked to state owned wood based panel industry (veneer and plywood, hardboards, and chipboards) and the pulp and
5
paper industry. It is also estimated that there are 20,000 – 25,000 hectares of private owned plantations, and in addition, there are up to 80,000 hectares of plantations
belonging
to
villagers,
local
Governments,
non-Government
organizations (NGOs), civil societies, and religious organizations [8]. At 20% residue factor from the harvested wood, it is estimated that the total biomass potential from plantation forests residue is over 205,400 m 3 [8, 9]. About 75% of this potential is within the Saohill plantation forests followed by Buhindi plantation that shares 4.67% of total potential. On the other hand, evaluation of agricultural production data available from the National Bureau of Statistics [1] shows that the total amount of waste that originates from agricultural activities is over 12 million tones. With a share of 61.15% to total waste potential, corn stalks and cobs have the highest potential of agricultural waste.
Rice straw and husks follow in their contribution to the
potential stock, sharing 32.69% of total waste. Waste from sugarcane processing (bagasse) is already being used for cogeneration in all four Tanzania‟s sugar plants. The available bagasse shares 3.55% of total agro waste potential. It can therefore be implied that agricultural wastes from corn, rice, and sugarcane have the overall importance since they contribute 97.39% of the existing agricultural waste potential. From the available biomass resources in terms of 12 million tones of agricultural waste; 205,400 tones of forestry waste; including planting the available 19 million hectares with biomass forests, Wilson et al. [10] estimated that the total biomass energy potential amounts to 12 million TOE. Currently, Tanzania imports a total of 850,000 tones of petroleum oils per annum, the estimated biomass surpasses the demand and, it suggests that Tanzania may become a net exporter of this renewable energy. A study by Kaseva and Mbuligwe [11] established that per capita waste generation in the city of Dar es Salaam is 0.40kg/person/day. This shows that a considerable solid waste is being generated in urban areas, and hence, the potential energy and materials recovery. Shown in Table 4 is the municipal solid waste data for 21 municipalities and major cities in Tanzania. Major Cities like Dar es Salaam, Mwanza, Shinyanga, Kagera, Mbeya and Kigoma have relatively 6
higher potential energy from the waste. However, all over Tanzania urban waste collection is marginal, at 32 percent of the total generated amount. Therefore for this waste to be applied in energy generation there is a need to put in place organized waste collection and management procedures and infrastructure.
7
Table 4: Waste generated (Tones) in Tanzania Cities [12]
NO. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
CITY/TOWN Dar es Salaam Mwanza Shinyanga Kagera Mbeya Kigoma Tabora Morogoro Dodoma Tanga Iringa Mara Kilimanjaro Arusha Rukwa Lindi Ruvuma Mtwara Singida Manyara Pwani TOTAL
AMOUNT GENERATED (TONES/DAY)
AMOUNT AMOUNT AMOUNT AMOUNT DUMPED/ OPEN GENERATED GENERATED GENERATED GENERATED DUMPED IN 2000 IN 2003 IN 2005 RATIO (TONES/DAY) (TONES/DAY) (TONES/DAY) (TONES/DAY)
2,200 210 100 24 145 60 120 260 156 400 36 30 92 200 45
80 25 8 66 15 12 54 42 190 11 7 45 125 16
38 25 31 46 25 10 21 27 48 31 23 49 63 36
56 50 65
21 15 17
38 30 26
4,249
749
33
8
2,000 751 564 64 442 274 405 391 395 519 382 303 354 413 240 206 249 222 253 193 203 8,823
2,848 977 898 242 662 537 550 563 544 657 479 438 442 414 390 253 358 361 349 332 284 12,577
3,100 1,036 991 714 712 620 612 608 585 554 500 472 464 440 407 385 385 380 374 373 305 14,017
1.2.4 Coal
Coal reserves in Tanzania are estimated at about 1,200 million tones of which 304 million tones are proven. Coal sites include Kiwira, northwest of Lake Nyasa and Mchuchuma/Katewaka on the southeast of the Lake.
Generally, the
available coal is bituminous, with an average ash content of about 25% and calorific value of between 22 and 28 MJ/kg. Some coal from Kiwira is generating electricity (6 MW) and is also used for other thermal requirements in industries like cement and textiles most of which are located in the neighbouring regions of Mbeya, Iringa and Morogoro.
The coal has been analyzed to contain high content of sulphur (up to 9.2 wt.%), which calls for the application of cleaner technologies [13, 14]. As indicated in the National Power System Master Plan (PSMP) it is planned to utilize coal from Mchuchuma and Kiwira to generate, respectively, 600 and 400MW of electricity. While increasing the electrification level, such developments will also improve the existing generation mix by relieving its strong bias to the hydropower.
1.2.5 Solar Tanzania lies between 10 and 110 South of the Equator, with long sunshine hours.
The average daily insolation is about 4.5 – 6.5 kWh/m2 [15].
This
insolation provides an opportunity for installing solar photovoltaic (PV) and solar thermal energy systems. However, todate there is a limited harnessing of the solar resource as only about 1.2MWp of PV are installed countrywide as solar home
systems.
The
main
PV
applications
in
Tanzania
include
telecommunications, lighting, vaccine refrigeration, water pumping, cathodic protection of Tanzania Zambia oil pipeline and providing power backup systems. Furthermore, solar thermal applications in Tanzania include solar water heaters/pasteurizers, crop driers and solar cookers.
Some of the bottlenecks to the wider application of solar PV systems include: high initial cost, limited market infrastructure, and lack of local technical capacity. In its effort to bridge this, The Ministry of Energy and Minerals (MEM) initiated two 9
programs, respectively, supported by UNDP/GEF (2004 – 2009) and Sida (2005 – 2010). Besides putting in place PV systems demonstration facilities, the main project output were: training to local technicians, development of PV standards, and increased PV market infrastructure.
1.2.6 Wind
Preliminary wind pattern mapping for majority Tanzania regions show adequate annual average wind speed for various applications (Table 5). Annual average speeds suitable for stand alone and grid connected electricity generation purposes (> 4 m/s) are strongly available along the Indian cost strip mainly Tanga, Dar es Salaam, Zanzibar, and Mtwara regions. Other mainland regions such as Mbeya, Iringa, Tabora, Mwanza and Dodoma have adequate wind speeds. Table 5: Wind stations with annual mean wind speeds ≥ 4.5 m/s [16] NO
STATION
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Amani – Tanga Dar es Salaam Dodoma Iringa Lindi Mbeya Mombo – Tanga Mtwara Mwanza Saohill – Iringa Songea Tabora Tanga Zanzibar Karatu Mkumbara Litembe
ANNUAL MEAN WIND SPEED (m/s) 4.97 5.31 4.76 4.51 4.59 5.36 5.10 4.68 4.85 5.11 4.68 5.36 6.29 4.76 5.5 4.9 4.5
RECORDING REFERENCE TIME AT GMT 1200 1200 0600 1200 1200 1200 1200 0600 1200 0600 1200 0600 1200 1200 1500 1500 1500
A study by Nzali and Mushi [17] on the state of wind energy technologies in Tanzania reported that there are no commercial electricity generation windmills. Instead, there are over 106 windmills providing mechanical power for water
10
pumping in 11 regions of Tanzania.
The study reported that 75.47% of the
installed windmills are owned by the local communities whereas church organization owns 9.43% and 8.49% is owned by the Government.
The
remaining 6.6% of the installations are owned by other organizations. With the exception of two installations that used three-bladed horizontal axis and vertical axis savonious rotor, respectively, the remaining installations utilized multi-bladed horizontal axis technology, which is a proven technology for water pumping purposes.
1.2.7 Geothermal
Preliminary
reconnaissance
commenced in late 1970s.
activities
on
Tanzania
geothermal
potential
Between 1976-79 Messrs SWECO, a Swedish
consulting group, in collaboration with Virkir-Orkint, with the financial support of the then Swedish International Development Authority (SIDA) conducted reconnaissance survey of geothermal. The survey and surface exploration were carried out in the north (near Arusha, Lake Natron, Lake Manyara and Maji Moto) and in the south (Mbeya region). About 50 hot springs that are associated with block faulting and recent volcanicity were mapped [18]. Information from the MEM shows that existing geothermal potential is 650MW.
However, these
geothermal resources are yet to be harnessed for energy generation due to the lack of feasibility data. Figure 1 shows the geothermal energy potential sites in Tanzania.
11
Figure 1: Geothermal potential sites in Tanzania (Documents available with the MEM)
1.2.8 Tidal and Wave
Eastern Tanzania is a 1,424km coastal strip along the Indian Ocean. This strip including those along the Zanzibar and Mafia Islands constitute a potential energy source for tidal, wave, and ocean thermal energy conversion (OTEC) technologies. However, the lack of full feasibility assessments and technological capacity has led to the limited deployment.
12
1.2.9 Petroleum Oil and Uranium Exploration
Information available from the Tanzania Petroleum Development Corporation shows that exploration activities over the past 50 years have led to natural gas discovery at SongoSongo and Mnazi Bay. In this period a total of 35 exploration and development wells have been drilled.
Todate no oil has been produced
though available data and geological information reveal the existence of an active petroleum system particularly in deep sea and along Lake Tanganyika. Table 6 details the existing oil and gas exploration companies that are operating in Tanzania.
Ongoing uranium exploration activities in Tanzania are being undertaken by an Australian company, Mantra Resources Limited. The company owns the Mkuju River Project (MRP), which is located in southern Tanzania, some 470km southwest of Dar es Salaam City. The project at the MRP is aimed at advancing the exploration and appraisal of the widespread „Karoo‟ sandstone-hosted uranium mineral, which is identified within the Project area.
Exploration and
drilling undertaken by the company todate has confirmed the presence of widespread surface uranium mineralization and multiple stacked mineralized horizons at shallow depths.
Results of the pre-feasibility study that was
completed in March 2010 confirmed the technical and economic viability of the project. The results show an average annual production of 3.7 million pounds of uranium grade U3O8 at a minimum initial mine lifetime of twelve years [19]. Prior to commencement of the mining operation, the company is in a process of engaging a definitive feasibility study.
13
Table 6: Oil and gas exploration companies [20] COMPANY NAME
COUNTRY OF
EXPLORATION AREA
ORIGIN
Antrim Resources
Canada
Zanzibar/Pemba
Artumas Group
Canada
Mnazi Bay
Dominion Oil & Gas
United Kingdom
Dodsal Resources
United Arab Emirates
Ruvu block
Key Petroleum
Australia
West SongoSongo
Mauriel ET Prom
France
Bigwa and Mafia
Australia
Nyuni, Ruvuma
Ophir Energy
United Kingdom
Deep sea block no 1, 3 and 4
Pan African Energy
United Kingdom
SongoSongo
Petrobras
Brazil
Deep sea block no 5, 6 & 8
United Kingdom
Tanga, Kimbiji and Latham
RAK-Gas company
United Arab Emirates
East Pande
SHELL International
Holland
Statoilhydro ASA
Norway
Deep sea block no 2
Hydrotanz
United Kingdom
North Mnazi Bay
Tullow Oil
United Kingdom
North Lake Tanganyika
Beach Petroleum
Australia
South Lake Tanganyika
Ndovu Resources/ Tullow Oil
Petrodel Resources/ Heritage
Mandawa, Kisarawe, Selous & deep sea block no 7
Deep sea block no 9, 10, 11 & 12
14
1.3
ELECTRICITY GENERATION MIX
As detailed in Table 7 and shown in Figure 2, about 51.43% of the electricity is generated from renewable sources comprising of 47.20% hydro and 4.23% from biomass.
The total country‟s installed electricity generation capacity is
1,190.37MW. Due to the availability of indigenous natural gas, it has acquired the second in importance as 331MW is now being generated from the natural gas. Electricity generated from natural gas will continue to increase so as to diversify power generated and alleviate the current bias to hydro sources, which are prone to climate change particularly the extended drought.
Drought
experience was gained in year 2004 – 2007 when its effect led to extended power shading countrywide.
On 3rd December 2006 water level recorded at
Mtera reservoir was 686.92 meters above sea level (m.a.s.l), which is about 3.08 meters below the dead storage level of 690.0 m.a.s.l [21]. generation
need
also
increase
the
share
of
coal
from
Future power Kiwira
and
Liganga/Mchuchuma from the current 0.50% as supplied by Kiwira only. Currently, isolated and grid connected thermal power plants (from petroleum oils) shares 20.26% of the installed generation capacity. With the exception of the Independent Power Tanzania Limited (IPTL) plant, all petroleum-based power plants are owned by the national utility company (TANESCO). Their operation is intermittent as they are backup sources when the generation from hydro falls below the demand.
The general generation mode has been to run the
hydropower system at near full generating capacity during rainy season and to reduce hydropower generation during dry season.
During the dry season,
thermal generation is increased while suppressing part of the load demand to ensure sufficient water is available to supply the power system throughout the year.
The closure of petroleum-based power plants will be mandatory when
future demand is met by natural gas, coal, and other potential resources.
Tanzania electricity grid is also fed by imported electricity from neighbouring Zambia and Uganda. The importation, respectively, is currently at 5 and 8MW. This trend is expected to reverse after a full capacity harnessing the indigenous energy resources particularly natural gas, coal and uranium.
15
Coal 0.50%
Biomass 4.23%
Petroleum oils 20.26% Hydro 47.20%
Natural gas 27.81%
Figure 2: Installed generation capacity and share (%) by source
16
Table 7: Installed generation capacity and source (TANESCO records, 2010) SNO.
DESCRIPTION
INSTALLED CAPACITY (MW)
EFFECTIVE (MW)
% SHARE
Hydro Mtera Kidatu Hale 1 Pangani Falls Nyumba ya Mungu Lower Kihansi Uwemba Total hydro
80.00
66.00
204.00
180.00
21.00
5.00
68.00
20.00
8.00
3.50
180.00 0.843
75.00 0.71
561.84
350.21
182.00
180.50
104.00
102.50
45.00
45.00
331.00
328.00
85.70
35.30
55.50
35.3
100.00
100.00
241.20
170.60
6.00
2.00
47.20
Natural gas Songas 2
TANESCO Ubungo
27.81
TANESCO Tegeta Total natural gas
3
Petroleum oils TANESCO grid diesel plants TANESCO isolated diesel plants IPTL plant Total petroleum oils
4
Coal
20.26
0.50
Biomass 5
Bagasse cogeneration
46.80
Wood biomass cogeneration
3.53
Total biomass
3.53
4.23
50.33
Total generation
1,190.37
17
100.00
1.4
BIOMASS COGENERATION
Biomass cogeneration shares a marginal (3.03%) contribution to installed electricity generation capacity of the country. There are three privately owned biomass cogeneration facilities in Tanzania. They are being owned by sugarprocessing factories, a wattle processing plant, and by a forestry plant. Tanganyika Wattle Company (TANWAT) operates a cogeneration plant which is fueled by wood logs and spent wattle barks. On the other hand, Kilombero Sugar Company located in Morogoro region, Mtibwa Sugar Estate Limited also located in Morogoro region, Kagera Sugar Limited from Kagera region and Tanganyika Planting Company (TPC) of Kilimanjaro are utilizing bagasse in their cogeneration plants. Saw mill waste is the fuel for cogeneration plant owned by Sao Hill Saw Mill located in Iringa region.
1.4.1 Kilombero Sugar Company
Sugar processing is through two processing plants known as Msolwa (Kilombero K1) and Ruembe (Kilombero K2).
The Msolwa plant has a cane crushing
capacity of 80 tones of cane per hour (TCH) with total sugarcane plantation amounting to 2,960 hectares and average yield of 70 tones per hectare. Ruembe plant has a cane crushing capacity of 100 TCH. About 3,400 hectares of sugarcane are harvested annually.
Msolwa plant has two steam turbines rated 3MW where as Ruembe has one steam turbine with a rating of 1.2MW and two other steam turbines rated 800kW each.
The installed generation capacity at Kilombero Sugar Company is
insufficient to export the power to the national grid.
1.4.2 Mtibwa Sugar Estate Limited
Mtibwa Sugar Estate Limited has a total sugarcane plantation of 4,200 hectares with an average yield of 80 tones per hectare. The company has three steam boilers that produce steam for running two sets of back-pressure turbo-
18
alternators of 2.5MW and 1.5MW respectively.
In addition, there is a turbo
generator rated 9MW. Up to a total of 10GWh of electricity is generated during production season.
Since the locally produced power is insufficient, about
4.0GWh are imported annually from TANESCO. Imported power is mainly used for irrigation and for domestic uses.
1.4.3 Tanganyika Planting Company Limited (TPC)
The TPC has a total of 16,000 ha of land out of which about 6,100 ha is under cane cultivation. TPC has just commissioned a boiler to produce 90t/hr steam at 45 bar and 450C. The steam will be fed to a generator for producing 17.5MW of electricity. At this capacity the plant will be able to sustain its power requirements to factory, residential areas, irrigation, and export excess power to TANESCO.
1.4.4 Kagera Sugar Limited (KASC)
Kagera Sugar Limited owns 860 hectares of sugarcane plantation with plant cane crushing capacity of 60 TCH.
Cane yield is 70 tones per hectare.
The
cogeneration at KSC is through two steam turbines rated 2.5MW. There is a potential for the extra power to be used for electrifying nearby villages as the national electricity grid is yet to be in Kagera region. 1.4.5 Saohill Sawmill
Saohill sawmill is an integrated wood establishment that operates sawmill, impregnated treated wood poles, planer mill and joinery factory. The company has leased plantation coverage of 35,000 hectares of both hard and soft wood species. Saohill sawmill has installed 4 diesel generators each rated 250kW, which is capable of meeting the installed load capacity of about 850kW. Further to the diesel generators, there is a 1MW electrical generator being coupled to a steam engine. Steam is generated through a water tube boiler, which is fueled by wood chips, sawdust and wood shavings.
19
1.4.6 Tanganyika Wattle Company (TANWAT)
TANWAT is located at Njombe district in the southern highlands of Tanzania, Iringa region. The company owns a 15,000 hectares site out of which 8,000 hectares are wattle plantations, 4,000 hectares pines and 1,000 hectares of eucalyptus. Main activities being the production of tannin extract from the bark of wattle trees. About 3,000 tones of timber are also produced per annum from the pine trees.
Wattle barks are stripped in the fields and transported to the factory for processing and manufacture of the tannin extract. The wood is a waste of the process and resulting in excess of 60,000 tones of wood logs per annum. Once the bark is extracted of the tannin, it is also a waste accumulating to over 10,000 tones of spent barks per annum. Further to these, at a 40% recovery rate there is an added 4,500 tones of pines waste per annum in terms of off cuts and sawdust. Additional volume of wood is available from the eucalyptus plantation.
TANWAT company information shows that its cogeneration plant has an installed capacity of 2,500kW. There are 2 boilers rated 15 tones per hour of superheated steam for generating electricity through a single stage condensing steam turbine. TANWAT does not import power from TANESCO. Instead TANESCO shares 35% of total power generated at TANWAT.
A study by Mwihava and Wilson [22] showed that the immediate potential expansion in cogeneration in these plants amounts to over 120MW (Table 8). Increment of the cane crushing capacity and systems improvement is necessary for realizing the potential.
20
Table 8: Potential additional cogeneration capacity [22] EXISTING S/N
NAME OF COMPANY
COGENERATON CAPACITY (MW)
1 2 3
Mtibwa Sugar Estates
CAPACITY (MW)
5
15
20
14 to 30
8.8
30
0
15
2.5
15
Sao Hill Saw Mill
1.025
3 to 4
Total
35.825
107 to 124
Kagera Sugar Limited Tanganyika Planting Company (TPC)
5
Pangani Sugar Limited
1.5
COGENERATION
15
Kilombero Sugar Company
7
ADDITIONAL
13
Limited
4
6
POTENTIAL
Tanganyika Wattle Company
ELECTRICITY DEMAND
Figure 3 shows the trend of energy generation and consumption in Tanzania. The current total annual electricity generation and consumption, respectively, is 4,800 and 3,600 million kWh.
The difference between generation and
consumption is accounted by system loss, which averages 26%.
Over the
analyzed period covering years 1999 to 2009 the consumption trend is growing at 7.49% per annum.
The growth in power demand is attributed to population
growth and increasing economic activities. The peak demand is suppressed in order to save the national grid from a total collapse, as the existing generation and distribution capacity is far less than sufficient to meet peak demand.
21
VALUE, Mill. kWh
6,000 5,000 Total (Generated + Imported) 4,000
Consumption (Sold)
3,000 2,000 1,000 -
98 19
00 20
02 20
04 20
06 20
08 20
10 20
YEAR Figure 3: Electricity generation and consumption, million kWh (TANESCO records on generation, importation, and sales data, 2010)
1.6
ELECTRICITY DISTRIBUTION AND DISTRIBUTION NETWORK
Shown in Figure 4 is the electricity distribution network, which is solely (98%) owned by the national utility (TANESCO).
The distribution network is
concentrated in cities and urban areas leaving most of the rural areas uncovered. As a result only 2% of rural population has access to electricity whereas the portion of urban population with access to electricity is 37% [23, 24]. Electrification is one of key catalysts of development, and consequently, low electrification levels have negative consequences leading to low economic activities, poor access to clean water, low literacy levels, and inferior health services. Increasing the electrification levels has the potential to contribute in accelerating development of the country.
22
Figure 4: Existing and proposed grid and isolated transmission system [25]
2.
LITERATURE REVIEW
2.1
BIOMASS GASIFICATION
In terms of energy supply and environmental conservation, biomass energy is the most important renewable energy. Studies establishing the technical biomass energy potential of biomass show that the annually available biomass is over seven times the current consumption of petroleum oil, coal and natural gas [26, 27]. In year 2000 biomass energy supplied 7% of total renewable energy in the OECD countries being second to hydro, which supplied 87% of total renewables [28]. However, the importance of biomass energy in environmental conservation is from the tendency to recycle the greenhouse gas carbon dioxide in the growing feedstock [29, 30].
23
Biomass gasification is an efficient biomass-to-energy conversion technology. Through integrated gasification combined cycles (IGCC), it is possible to increase the conventional Rankine cycle power generation‟s efficiency from 30% to 50% [31]. Besides the syngas energy from biomass gasification, various other energy streams can be generated. These energy steams are conventionally used for electricity generation and for thermal applications. However, it is foreseeable that the transport sector is the most important end use sector due to its poor environmental performance [32-34].
In this respect renewable hydrogen and
second generation bio-automotive fuels are expected to decarbonize the transport sector. The renewable hydrogen can be produced by upgrading the producer gas from biomass gasification [35, 36], whereas the two main biomass syngas components, H2 and CO, are widely recognized as an important platform in the production of second generation bio-automotive fuels like methanol, ethanol, dimethyl-ether (DME), Fischer-Tropsch (FT)-diesel, synthetic natural gas (SNG), and hydrogen [37].
2.2
HIGH TEMPERATURE AIR/STEAM GASIFICATION (HTAG)
The high temperature air/steam gasification (HTAG) of biomass technology stems from an advanced combustion technology, the high temperature combustion (HiTAC). Tshuji et al. [38] have shown that the key sustainability criterion of the HiTAC technology is from its energy savings, which is a key feature of sustainable energy technologies. Further studies by Rafidi & Blasiak [39] and Tiwari et al. [40] revealed the low NOx emission characteristic of the HiTAC technology. From Le Chatelier's Principle, the high operating temperature of the HTAG process favours achieving a dynamic equilibrium of the endothermic primary water gas reaction (Eq. 1), which becomes significant from 1000C. Studies by Lucas [41] reported that the formation of H2 increased by about 14% with an increase of HTAG feed gas temperature from 350C to 830C. C + H2O CO + H2
(1)
24
2.3
EFFECTS OF HEATING RATE AND TEMPERATURE
Pyrolysis is an important initial stage during thermal degradation of biomass the control of which determines the final product and product distribution [42, 43]. Yield of the main syngas components of CO, H2, CH4, and CO2 is enhanced by increasing temperature and heating rate with longer residence time [44, 45]. However, the tendency of the CO2 and CH4 yield is to increase with temperature to an asymptotic value. The high temperature, high heating rate and longer residence time is sufficient to allow for secondary thermocracking reactions that lead to more syngas yield [46].
2.3
CO/CO2 Ratio of Product Gas
Different fire indices have been traditionally used in characterization of the extent and progression of fires. Such indices as the C/H ratio, CO/O 2 deficiency % and the CO/CO2% are commonly used [47]. During gasification, high concentration of CO will be produced in the oxygen deficient atmosphere and at a proper temperature. CO is produced mainly from devolatilization stages and through the partial oxidation (Eq. 2), Boudouard (Eq. 3) and primary water gas reaction (Eq. 1). Various studies have shown that higher CO/CO2 ratios are favoured by higher gasification temperatures [48, 49]. C + ½ O2 CO
(2)
C + CO2 2CO
(3)
25
3.
OBJECTIVES
Studies that established the potential renewable energy from biomass show the existence of enormous potential. However, biomass is a complex material having varied characteristic properties that poses challenges while harnessing the energy potential. Variations in the characteristics and volume of the biomass components and differences in cellular structure make woods heavy or light, stiff or flexible, and hard or soft. This also implies to the differences in moisture content, volatile matter, heating value, elemental composition, and the inclusion of inorganic materials.
Further, the differences in the growing location and
condition will influence the biomass properties.
While the characteristic properties of biomass feedstock in the developed world are well-studied, those in the developing counterpart are partially studied. It is therefore the objective of this work to establish the characteristic properties of selected biomass feedstock from Tanzania. The characteristic properties to be established will provide the necessary input to thermochemical process designers and researchers.
Furthermore, since the properties are origin-specific, they
provide baseline data for technology transfer from north to south.
26
4.
METHODOLOGY
4.1
CHEMICAL COMPOSITION
In order to correlate the chemical composition to the respective thermal behaviour of the biomass materials under characterization, standard test methods namely proximate and ultimate analysis were done.
The proximate
analysis (ASTM D3172-5) reports volatile matter and ash content, fixed carbon, and higher heating value. On the other hand, the elemental composition of the biomass is determined by the ultimate analysis (ASTM D3176).
4.2
THERMAL DEGRADATION CHARACTERISTICS
A thermal gravimetric analyzer type NETZSCH STA 409 PC Luxx was utilized to establish the thermal degradation characteristics of the biomasses under the study. The STA 409 PC Luxx is a dynamic thermal analyzer that combines both the heat flux Differential Scanning Calorimetry (DSC) and Thermogravimetry (TG). The experiments were carried out under controlled inert nitrogen condition with nitrogen flow rate kept at 60 ml/min while heating the sample at 10 K/min. The TG data acquisition, storage and analysis were done using the “Proteus” software. Prior to testing, the biomasses were dried in oven overnight. This was necessary for removing the naturally absorbed moisture.
27
4.3
LABORATORY EXPERIMENTATION
Besides establishing the chemical composition and thermal degradation characteristic of the biomasses under study, a laboratory scale high temperature gasification of biomass was undertaken. The gasification experiments were done for the purpose of investigating the influence of steam and oxygen oxidizers while varying temperature in three different ranges of 900, 800, and 700°C. During the laboratory gasification experiments, the oxygen level was maintained at three concentrations of 2, 3, and 4%. Coffee husk, which is a tropical agricultural waste, was the material utilized for the laboratory investigation. Fifteen grams of the coffee husk sample was taken for each gasification experimental run. Steam flow to the gasification was set at 0.469 kg/min.
The schematic diagram of the high temperature gasification rig is shown in Figure 5. The rig is batch type, which is preheated to predetermined temperature using a methane burner (7).
Honeycomb (9) stores heat energy from primary
combustion chamber (8). The heat stored in the honeycomb is then released to heat the secondary combustion chamber (10) to a constant desired experimental temperature. A thermocouple (15) records the secondary chamber temperature, when it reaches the desired level the burner is switched off.
Oxygen
concentration (%) is achieved by setting oxygen and nitrogen flow through respective inlets (3) and (4) that are controlled by Bronkhorst EL-Flow mass flow meters and controllers (6). Steam is injected through inlet pipe (1) whereas inlet pipes (2) and (5) are available for more oxidants. The sample (18) is inserted into the furnace through inlet flange (13) where it is also cooled through the chamber (11). Nitrogen (12) is used to purge air infiltrated while inserting the sample and it is also used to cool down the sample before exiting the furnace. Sample temperature is monitored at the cooling chamber and during the experiments through thermocouples (17) and (16) respectively. The behaviour of the sample during the experiment can be observed through glass window (14). The syngas exits through pipe (20) where the sampling probe (21) collects gas for analysis. Prior to composition analysis, the sampled syngas is cleaned by passing through sampling train (22). The syngas enters the first flat bottomed
28
flask which is in ice bath that allows the collection of syngas condensates that includes water vapour. Further condensation is enhanced by a condenser. On exiting the condenser the syngas enters a series of three bottles that are contained in a second ice bath. Further syngas condensates and particulates are collected in the first bottle that contains water. The second bottle and third bottle contains iso-butanol (Isobutyl alcohol), which allows absorption of all tars remaining in the syngas after exiting the first bottle. A clean syngas exits the third bottle and enters the fourth dry bottle that contains a dry cotton wool. The cotton wool allows further cleaning of the gas and traps all the escaping particulates.
Online carbon monoxide and carbon dioxide analyzer type Maihak Multor 610 was utilized to monitor flue gas composition whereas mass loss data was measured by a digital online balance (19) type Radwag model WPX 1500. Furthermore, a micro GC monitored the syngas composition with respect to CO, CO2, CH4, C2H4, C2H6, and C2H2 species.
All data generated by the
thermocouples, gas analyzer, micro GC, and digital balance were collected in a laptop computer via TCP/IP multiplexer type Keithley 2710.
19
17 6
13
12
11
F
4
2
To data acquisition system
F F
O2
10
8
3
20 To gas analyzers
9
N2 7
5
21
1 15
14
18
16
Figure 5: The high temperature gasification test rig
29
22
5.
RESULTS AND DISCUSSION
5.1
CHEMICAL COMPOSITION OF TROPICAL BIOMASSES
A total of 15 tropical biomasses were analyzed for their chemical composition. The analyzed materials were palm waste, coffee husks, cashew nut shells (CNS), rice husks and bran, bagasse, sisal waste, jatropha seeds, and mango stem. Results of their chemical properties as established by undertaking proximate and ultimate analysis are detailed in Table 9.
With respect to biomass materials
analysis done by Jenkins et al. [50], the analyzed tropical biomasses have comparable heating value and contents of volatiles, carbon, hydrogen and oxygen. Furthermore, the relative content of nitrogen, sulphur, and chlorine is marginal.
The relatively higher presence of chlorine (Cl) and sulphur (S) in biomass as exhibited in the palm branch and jatropha seeds are not desirable combustion properties. Chlorine and sulphur are the major contributing factor to ash formation as they facilitate the mobility of inorganic compounds from the fuel to surfaces where they form the corrosive compounds [51, 52].
30
Table 9: Tropical biomasses chemical composition MATERIAL AND PROPERTY
PALM
PALM
PALM
PALM
COFFEE
MASASI
OLAM
RICE
STEM
BRANCH
FIBRE
SHELLS
HUSKS
CNS
CNS
HUSKS
Proximate analysis (%), dry basis Moisture
9.10
8.10
4.98
8.40
10.10
6.70
6.10
8.80
Volatile matter
81.20
79.60
79.00
75.40
83.20
84.10
84.80
59.20
Fixed carbon
15.30
12.60
9.30
20.00
14.30
14.00
13.10
14.60
3.50
7.80
11.80
4.60
2.50
1.90
2.00
26.20
C
47.50
45.60
52.20
51.50
49.40
56.00
56.90
35.60
H
5.90
5.60
7.10
5.70
6.10
6.90
7.00
4.50
N
0.28
0.19
0.70
0.36
0.81
0.44
0.45
0.19
42.50
39.30
28.00
37.70
41.20
34.70
33.60
33.40
Cl
0.18
1.33
0.06
0.05
0.03
0.03
0.03
0.08
S
0.13
0.16
0.07
0.03
0.07
0.05
0.04
0.02
17.38
16.24
21.98
19.29
18.34
22.38
22.83
13.24
"H:C" Ratio
0.12
0.12
0.14
0.11
0.12
0.12
0.12
0.13
"O:C" Ratio
0.89
0.86
0.54
0.73
0.83
0.62
0.59
0.94
Ash Ultimate analysis (%), dry basis
O (by difference)
Higher heating value (MJ/kg)
31
MATERIAL AND PROPERTY
RICE
TPC MILL
SISAL
SISAL
SISAL
JATROPHA
MANGO
BRAN
BAGASSE
BOLES
POLE
LEAF
SEEDS
STEM
Proximate analysis (%), dry basis Moisture
7.80
9.00
7.50
10.10
8.50
6.60
7.50
Volatile matter
64.60
80.50
84.10
79.30
80.20
80.30
83.50
Fixed carbon
14.20
16.20
12.80
14.60
12.60
14.70
12.00
Ash
21.10
3.30
3.10
6.10
7.20
5.00
4.50
C
37.80
48.10
48.00
47.00
47.00
56.60
48.00
H
5.00
5.90
6.00
6.00
5.70
7.50
5.80
N
0.55
0.15
0.10
1.66
0.14
3.16
0.13
35.40
42.40
42.70
39.10
39.90
27.40
41.50
Cl
0.09
0.07
0.06
0.05
0.04
0.12
0.03
S
0.05
0.02
0.03
0.13
0.03
0.17
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61
Furnace and
Supplement I
Supplement I
Coffee Husks Gasification Using High Temperature Air/Steam Agent
Lugano Wilson, Geoffrey R. John, Cuthbert F. Mhilu, Weihong Yang, and Wlodzimierz Blasiak
Published in the Fuel Processing Technology Journal, Volume 91, Issue 10, (2010), pp. 1330 – 1337
Royal Institute of Technology School of Industrial Engineering and Management Department of Material Science and Engineering Division of Energy and Furnace Technology SE-100 44 Stockholm Sweden
Supplement II
Supplement II
Thermal Characterization of Tropical Biomass Feedstocks,
Lugano Wilson, Weihong Yang, Wlodzimierz Blasiak, Geoffrey R. John, Cuthbert F. Mhilu,
Article in press with the Energy Conversion and Management Journal, (2010), doi:10.1016/j.enconman.2010.06.058
Royal Institute of Technology School of Industrial Engineering and Management Department of Material Science and Engineering Division of Energy and Furnace Technology SE-100 44 Stockholm Sweden
