Microgasification cookstoves and pellet fuels from waste biomass: A cost and performance comparison with charcoal and natural gas in Tanzania

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Cooking with wood and wood charcoal is done by over 90% of Africa's population; it has two major challenges: deforestation and indoor air pollution from cooking smoke, the latter being the top risk factor for disease in Tanzania. Microgasification stoves (top lit up draft [TLUD]) that burn pellets produced from agricultural waste have potential to address both of these issues. We examined the relative efficiency and cost of the major urban cooking fuels - charcoal and liquefied natural gas (LNG) – and compared them to cooking with waste biomass-based pellet fuels; we also compared the performance of three models of natural draft (ND) TLUD stove (Troika, Jiko Bomba, St. John's) and one forced air (fan) stove (Philips). The Philips and averaged ND stoves used 83 and 133% more pellets by weight respectively to cook beans than charcoal, costing 47 and 93% more at 2013 charcoal and pellet prices. Cooking with LNG costs 387 to 647% more than cooking with charcoal, depending on gas flow rate. The high cost of LNG and LNG stoves will be barriers to the great majority of Tanzanians to move to this improved cookstove technologies (ICTs). Biochar production averaged 59 and 29% of total fuel in the ND and Philips, respectively. Interviews of 30 ND TLUD stove users showed that 60% abandoned use within one month, 80% stating that they produce too much smoke and 40% stating that controlling the air vent is too much trouble. Seventy five percent said that the TLUD cooks significantly faster than charcoal. Due to the continued 33-99% annual increase in charcoal prices in Tanzania, work on introducing TLUD stoves is justified. Key words: Microgasification stoves, TLUD, improved cooking technologies, deforestation, pellet fuels.

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Vol. 9(6), pp. 573-583, June 2015
DOI: 10.5897/AJEST2015.1901
Article Number: F5D72F753831
ISSN 1996-0786
Copyright © 2015
Author(s) retain the copyright of this article
http://www.academicjournals.org/AJEST

### _Full Length Research Paper_

## African Journal of Environmental Science and Technology

# Microgasification cookstoves and pellet fuels from waste biomass: A cost and performance comparison with charcoal and natural gas in Tanzania

Don Lotter 1 *, Nathan Hunter 2 , Mary Straub 3 and David Msola 1

1Institute of Development Studies, St. John‟s University of Tanzania, Dodoma, Tanzania.
2Groundwork Hudson Valley, Yonkers, New York, USA.
3School of Veterinary Medicine, University of California Davis, Davis, California, USA.

Received 27 February, 2015; Accepted 8 May, 2015

Cooking with wood and wood charcoal is done by over 90% of Africa’s population; it has two major
challenges: deforestation and indoor air pollution from cooking smoke, the latter being the top risk
factor for disease in Tanzania. Microgasification stoves (top lit up draft [TLUD]) that burn pellets
produced from agricultural waste have potential to address both of these issues. We examined the
relative efficiency and cost of the major urban cooking fuels - charcoal and liquefied natural gas (LNG)

– and compared them to cooking with waste biomass-based pellet fuels; we also compared the
performance of three models of natural draft (ND) TLUD stove (Troika, Jiko Bomba, St. John’s) and one
forced air (fan) stove (Philips). The Philips and averaged ND stoves used 83 and 133% more pellets by
weight respectively to cook beans than charcoal, costing 47 and 93% more at 2013 charcoal and pellet
prices. Cooking with LNG costs 387 to 647% more than cooking with charcoal, depending on gas flow
rate. The high cost of LNG and LNG stoves will be barriers to the great majority of Tanzanians to move
to this improved cookstove technologies (ICTs). Biochar production averaged 59 and 29% of total fuel
in the ND and Philips, respectively. Interviews of 30 ND TLUD stove users showed that 60% abandoned
use within one month, 80% stating that they produce too much smoke and 40% stating that controlling
the air vent is too much trouble. Seventy five percent said that the TLUD cooks significantly faster than
charcoal. Due to the continued 33-99% annual increase in charcoal prices in Tanzania, work on
introducing TLUD stoves is justified.

Key words: Microgasification stoves, TLUD, improved cooking technologies, deforestation, pellet fuels.

INTRODUCTION

Cooking with wood and wood charcoal, done by 90% drastically unsustainable 2 million metric tons, consuming
Tanzanians (Peter and Sander 2009) and 70% of Africa‟s the equivalent of 327,190 ha of forest/woodland per year
population (Taylor and Nakai, 2012), presents two major (Kaale, 2014). Continued rapid population growth challenges that require action: deforestation, and indoor Tanzania‟s population will double from its 2010 level by
air pollution from cooking smoke. Annual consumption of the year 2050 to 90 million (Rweyemamu, 2013),
charcoal in Tanzania, nearly all for cooking, averages a intensifies this issue. Indoor air pollution from cooking

*Corresponding author. E-mail: don@donlotter.net.

[Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0](http://creativecommons.org/licenses/by/4.0/deed.en_US)
[International License](http://creativecommons.org/licenses/by/4.0/deed.en_US)

smoke has been found to substantially increase rates of
acute respiratory infections, chronic obstructive pulmonary
disease, lung cancer, tuberculosis, and asthma (Smith,
2000). Indoor air pollution from cooking smoke is the top
risk factor for disease in Tanzania and is the third highest
cause of premature death after HIV/AIDS and malaria
(Horton, 2012). Programs are needed in the transition of
households to improve cookstove technologies (ICTs)
and in transition to more sustainable sources of cooking
fuel such as waste biomass. A widespread grassroots
transition to these alternatives will depend heavily on the
cost of the ICT. Our research at St. John‟s University in
Central Tanzania addresses both of these problems,
fuels and stoves. In this paper, we examined the relative
efficiency and cost of the major cooking fuels compared
to waste biomass-based pellet fuels, as well as the
performance of three models of biomass gasification
cookstove, a class of stove with potential to replace
unsustainable and unhealthy traditional cooking
techniques.

There are three main groups of cooking fuels in
Tanzania and much of Africa: 1) firewood, 2) charcoal,
and 3) fossil natural gas and kerosene. Livestock
manure, biogas, and biomass waste account for insignificant proportions in Tanzania (National Bureau of
Statistics, Tanzania, 2013) 1 . Gas cooking is limited to the
upper 0.5% of society (National Bureau of Statistics
2013) and is nearly all by liquefied natural gas (LNG) via
portable gas tank. With 90% of rural households cooking
with firewood, wood will for the foreseeable future be the
primary fuel in rural areas, nearly all by 3-stone fire. ICTs
that are specifically designed for firewood such as the
Rocket Stove (Raman, 2013), which has a mouth on the
side for progressively pushing in long pieces of wood and
a combustion chamber that uses secondary air to
efficiently burn emitted gases, can increase firewood
efficiency and reduce smoke by 50% or more (MacCarty,
2010).
Charcoal is the primary fuel in urban and peri-urban
Tanzania, used by 70% of households, and this sector is
the focus of this paper. Charcoal cooking, done in simple
perforated clay bowls, does not emit nearly the amount of
smoke as 3-stone firewood cooking, generating less than
10% of the smoke (PM2.5) as an equivalent 3-stone fire
(Taylor and Nakai, 2012). Thus, our efforts to replace
charcoal cooking with ICTs are driven primarily by the
need to reduce deforestation.

A number of ICT introduction projects have been
implemented in Tanzania, although there is no comprehensive recording or listing of ICT (or other types of)
projects. Such projects can be locally active but unknown
outside of the locale. It appears that most ICT
introduction efforts address more efficient firewood
cooking, such as the Maasai Stoves program
(bioenergylists.org 2014) or the Tanzania Stoves Project

1 Statistics in the next two paragraphs are based on (National Bureau
of Statistics, Tanzania, 2013) unless otherwise cited.

of the Anglican Church (Emmanuel International UK
2014). Others have introduced more efficient charcoal
stoves such as the EnviroFit stove, sold countrywide and
tested in this research. At least two projects have
introduced pellet-burning microgasification stoves along
with pellet production – stove engineer Bjarne Laustsen‟s
project introducing the Jiko Bomba stove (Roth, 2014),
tested here; and a project based in Arusha run by TREE
Ltd. (Treetanz, 2014). Other East African projects
introducing microgasification stoves are: Inyenyeri Inc. in
Rwanda, a ground-breaking social enterprise that makes
available fan-driven stoves to its customers (Inyenyeri,
2014). In Zambia, the Swedish company Vagga till Vagga
(Vaggatillvagga 2014) produces pellets from the massive
amounts of sawdust generated from lumber production
from tree plantations and offers microgasification pellet
stoves to its customers. Awamu Biomass Energy in
Kampala Uganda (Awamu Biomass Energy, 2014)
makes available the Troika stove tested in this research.

The objective of this research was to evaluate the cost
of cooking using various commonly used and potentially
useful fuels in urban and peri-urban environments. These
fuels consist: traditional (charcoal), fossil (LPG), and
sustainable (pelletized waste biomass). Additionally we
evaluated microgasification stoves designed for burning
biomass pellet fuels, as well as an improved charcoal
stove. If ICTs such as pellet systems are to be counted
on to reduce demand for charcoal it is imperative that the
cost and performance of each cooking technology be
assessed. In this research we begin this process with a
limited assessment of each of the major cooking
technologies used in urban and peri-urban areas. ICTs
for rural areas were not assessed, as these areas are not
the major sink for charcoal, using mostly firewood.

Biomass densification for cooking fuels

Waste biomass, particularly from agriculture, holds
significant potential to replace unsustainably produced
tree-based charcoal. The current practice in most of
Tanzania for waste and crop residue that cannot be used
for livestock is to burn it in the field or at the processing
site (that is, rice hulls). Most waste biomass is of
insufficient density to be transported and used as cooking
fuel in typical households and needs to be either a)
shredded and densified into discrete pieces of minimum 1
cm 3 that allow pore space and air flow, or b) used in
stoves designed for low-density biomass such as
sawdust, wood shavings, rice hulls, maize cobs, livestock
manure and tree litter. Some programs suggest that rural
households should use dry livestock manure as fuel, as is
common in India. A systems analysis is needed on this,
as the nitrogen, phosphorus, and microbes in manure,
which are lost and become pollutants in combustion, are
valuable soil amendments in the perpetually nutrient
deficient African soils (AGRA 2013). Biogas systems
harvest both the energy and the nutrients from manure;

the carbon (methane) is utilized for cooking and the
nutrients and microbes retained in ejected slurry that can
be used as fertilizer.

Despite the cost of machine densification of waste
biomass in terms of energy and capital investment
compared to raw and hand processed fuels, this
technology will likely play an important role in making
profitable the transport and sale to urban areas of fuels
made from waste biomass. Additionally, densification
operations allow for the blending of sub-optimal with
super-optimal biomass creating a relatively uniform fuel
and achieving the optimal mix of components such as
lignin and oil. Machine densification of shredded biomass
is being done by two main technologies in Tanzania –
pelletization and briquetting. We found that densification
via hand-powered lever press (Hands on Engineering
2014) of a slurry of shredded biomass and paper
produced a briquette of insufficient density for use in
microgasification stoves, but which would be useful in
Rocket stove types. Machine densification creates
pressure and heat to melt lignin which acts as glue and
gives a pellet or briquette that is approximately twice the
density of hardwood (Roth 2014). Not all biomass
contains sufficient lignin; therefore some feedstocks need
a binder such as molasses to be added.

Pelleting technology uses a roller to press shredded
biomass through a die plate with 100+ holes, creating the
required pressure. Friction and steam from the moisture
content of the feedstock creates the heat and pressure.
Two problems with pelleting machines have been
encountered in Tanzanian projects:

1) machines that were originally designed for pelleting
feed grains were purchased for pelletizing woody and
cellulosic biomass and failed to create sufficient pressure
to make a dense pellet, and
2) the biomass mix becomes stuck in the die holes and
each of the hundred or so holes periodically needs to
drilled out by hand.

For this reason, at least one biomass densification project
has transitioned to briquetting technology to produce
stove fuels (Laustsen, 2014). All of the pelleting and
briquetting machines are currently imported to East
Africa. Hammer mills for shredding biomass are made in
East Africa, and hand-driven shredder machine designs
are available for local manufacture (Armstrong, 2007).
The energy density of biomass pellets has been shown to
be approximately: 27% of petroleum oil, 35% of mineral
coal, 38% of ethanol, 146% of hardwood, 213% of
softwood, 270% of wood chips, and 375% of sawdust (at
moisture content of 4.5%, 10%, 15% for petroleum,
pellets, and other biomass respectively) (Roth, 2014).

Obtaining cheap or free biomass for pellet production is
important for keeping fuel costs low. The availability of
waste biomass varies by region, and pellet production is
best done in areas where agricultural and forestry
productivity is high due to optimal rainfall. Best is  to

locate production near to where large amounts of preshredded waste biomass, such as sawdust, are
generated. The Vagga till Vagga project does this in the
copper region of Zambia. In Rwanda an innovative
biomass sourcing model that has been developed by
Inyenyeri Inc. is to incentivize rural households to deliver
biomass to company hubs, where they receive credit for
buying pellets and stoves. Our project in central
Tanzania, a semi-arid, low-productivity region, is
assessing the cost of using local biomass waste for pellet
fuel vs. purchasing pellets from areas up to 500 km away
where waste biomass is more readily available and
pellets are inexpensive.

Microgasification stoves

Biomass gasification is a process of separating the heatgenerated gases from the solid biomass for the purpose
of controlling the burning of the gases (a fire wood is the
burning of unseparated gases given off by the heated
wood). Portable metal biomass microgasification stoves
have been developed for the purpose of cooking in
developing countries (Figures 2, 3, 4, 5) as well as for
recreational use (Roth, 2014).

There are four stages in the microgasification stove
combustion process after initial lighting of the biomass
with a small amount of starter fuel such as kerosene:

1) biomass drying, in which water vapour is given off;
2) pyrolysis, in which temperatures over 300°C and
limited oxygen from the primary air flow (Figure 1)
generate energy-rich gases, leaving solid black carbon
(char, also known as biochar);
3) Migration of the gases (also known as wood gases)
upward to the second combustion zone which when
mixed with oxygen (secondary air flow), combusts; and
4) char combustion and conversion to ash. This last
stage can be interrupted and the char conserved as
biochar for its soil amendment value.

Many biomass stove programs do not attempt to have
their users stop char combustion for saving biochar due
to the extra work and attention it takes. Biochar in the last
ten years has emerged as a valuable soil amendment
that enhances fertility and plant health (Reddy et al.
2013), particularly in tropical soils. Currently (2014) in
Tanzania char of particle size below about 5 mm
diameter, such as collects around charcoal sale sites,
has no market value due to lack of awareness of its
agricultural value.

Microgasification stoves control the flow of primary air
to the solid fuel combustion area (Figure 1) such that
pyrolysis and off-gassing occurs at an optimal rate; and
then further control the secondary air input into the gas
combustion zone such that all of the gases are burned
and the cooking flame is clean as described in Roth

Figure 1. Elements of a TLUD (top lit up draft)
microgasification stove. The pyrolysis front is shown
here nearly midway through its migration downward
through unburned fuel (From Roth 2014).

Figure 2. Troika (left) and Jiko Bomba TLUD stoves.
Primary air vent can be seen at bottom of both.

Figure 3. St. John‟s (SJUT)
stove.

Figure 4. Philips fan stove as advertised in Rwanda by Inyenyeri
Inc.
Credit: Inyenyeri: A Rwandan Social Benefit Company

Figure 5. Charcoal stoves. Improved stove, left (Ecofit), traditional
stove, right. Ecofit diameter is 31 cm.

(2014). As the combustion of pellets progresses, the
pyrolytic zone migrates downward until all of the fuel has
been converted to char. At this stage, the flame
disappears and glowing char is seen and can be either
emptied or extinguished in order to preserve the char as
biochar, or it can be allowed to continue burning and
producing heat for cooking.

The most common type of microgasification stove
being developed worldwide and targeted for use in
developing countries is the top-lit-up-draft (TLUD) stove,
in which the top surface of the biomass fuel is lit and
gases move upward from the pyrolytic zone. Dozens of
models of TLUD stove exist. Some are simply designs for
householders to build a stove from local materials such
as discarded metal containers (also called tincanium
stoves), others are designed for mass manufacture by
local metal crafters, while others are sold as
prefabricated assembly kits or are fully assembled and
ready to use.

Fan-drivenforcedair(FA) versusnaturaldraft(ND) appears

to be the most important categorical divider of
microgasification stoves. The fan and its power source
drive up the cost of stoves and make these more
challenging to introduce to low-income communities.
However, the improved performance of well-designed fan
stoves has been reason for at least one large scale
biomass fuel enterprise in Africa to feature them as their
primary cookstove (Inyenyeri, 2014). Thermo-electric
generators built into stoves for charging the fan battery
using the stove heat are increasingly common and
overcome the problem of lack of electricity. However,
households that lack electricity are less likely to be able
to bear the increased cost of these technology-laden
stoves.

International Organization for Standardization (ISO)
standards are being developed for ICTs that will influence
stove development and dissemination (Global Alliance for
Clean Cookstoves, 2013). A tier system from 0 (3-stone
fire) to 4 (satisfies strict health and environmental criteria)
is currently being put in place (Partnership for Clean
Outdoor Air 2012).

Socio-economics of cooking

Challenges, limited success, and outright failure have
beset the hundreds of projects worldwide that have
attempted to introduce improved cookstove technologies
to the nearly half of the world‟s population who cook with
solid fuels such as firewood and charcoal (Lewis and
Pattanayak, 2012; Urmee and Gyamfi, 2014). Successful
adoption of ICTs has been positively correlated with
income, education, and urban location, a limited
demographic worldwide. However, the development of
“game-changing” conditions such as the rapidly
increasing cost of traditional unsustainable fuels, the
implementation of micro-credit programs, and a new
generation of ICTs (such as TLUD technology) make for
more optimism in the arena of implementing ICTs in the
developing world (Lewis and Pattanyak, 2012). All three
of these game-changing conditions currently exist or are
developing in Dodoma and much of Tanzania.

At least one of Lewis and Pattanayak‟s (2012) criteria
for successful ICT adoption, urban location, has
significant potential in Tanzania, as nearly one third of the
population of Tanzania is urban, with that proportion
growing at 5% per year (National Bureau of Statistics,
Tanzania, 2013). However, working against potential ICT
adoption success is that the level of income and
education of the vast majority of this population is low.
The skyrocketing cost of charcoal along with foreseeable
government enforcement of existing laws against tree
cutting may drive change.

Charcoal is produced in rural areas from trees. The
felled trees are cut into pieces, placed into a pit, ignited,
and buried. Just enough air enters the pit to maintain
combustion. This hypoxic combustion causes pyrolysis

and off-gassing of non-carbon constituents such as
water, nitrogen etc., leaving pure carbon (charcoal). The
charcoal is put into 40-50 kg nylon/plastic bags and
brought into cities and towns by truck and bicycle in an
informal and often illegal system of trade. Cooking is
generally done on a simple perforated clay bowl-shaped
stove (Figure 5) that costs under US$5.

Tanzania has some of the world‟s largest reserves of
natural gas, expected to reach over 5 trillion cubic
meters, and investments in LNG development are
substantial and growing (Daly, 2014). Whether this will
translate to large-scale subsidised programs to transition
Tanzanians to LNG-based cooking is unknown, since the
LNG development is for export. It is our view that the gap
between a future of widespread grassroots LNG-based
cooking and the current solid fuel-based cooking is likely
to persist for at least another decade, and that the
introduction of sustainable biomass-based ICT is
necessary to fill this gap.

_Research location_

Dodoma urban district is situated in the central (Dodoma)
region of Tanzania and is the country capital. The region
is semi-arid, with an annual rainfall averaging 570 mm.
The biome was originally Miombo woodland savannah,
characterized by _Acacia_, _Brachystegia_, and baobab
trees. Most of the former two genera have been cut for
firewood and charcoal, while the latter tree survives due
mostly to its low wood value, difficulty to cut, and famine
food value.

The regional population of nearly a half million is
predominantly of the Gogo tribe, with a large minority of
people from the many other tribal groups from all over
Tanzania. The Gogo people have traditionally practiced a
mix of pastoralism (cattle, goats, sheep) and crop
production (maize and the indigenous millets and
sorghum).

Cooking is done by the women of the extended family,
in rural areas on a 3-stone fire in a cooking room/kitchen
that is part of a long U-shaped mud-clay house that
surrounds a courtyard. Ventilation is generally via a
doorway. The nearly constant wind in this highland region
(1,120 m elevation) generally necessitates cooking
indoors. The urban district of Dodoma is made up of a
higher proportion of non-Gogo people, and houses are
generally of a design inherited from colonial times –
rectangular and made of clay-cement brick. The cooking
area is at the back of the house where the portable stove
can be situated either indoors or out, depending on
weather conditions. Charcoal is the predominant fuel and
can be cooked with more readily outdoors in windy
conditions than can the 3-stone fire or TLUD stove.

In order to gain a picture of the potential for the
implementation of ICT and renewable biomass cooking in
the Dodoma urban and peri-urban area we designed a

basic set of stove and fuel test criteria that were
consistent with our research resources and capabilities.
We developed a cooking test that simulates typical
household cooking conditions and compares the common
fuels, charcoal and LNG, with biomass pellets; and
compares the performance of three TLUD stoves with
each other and with charcoal and gas stoves. The
objectives were to 1) compare the cost of cooking with
different fuels, and 2) compare the performance of a
selection of ICTs, traditional charcoal stoves, and an LNG
stove. We also carried out interviews of TLUD stove
users to find out their views of the new technology.

MATERIALS AND METHODS

Cooking test

The cooking test was done using a common food, dry beans
_(Phaseolus vulgaris)_ . Beans were selected as a cooking test over
standard water boiling tests, as we desired to test the cooking
performance of stoves, not only the time to boil. Sustained boiling
can occur at a low boil or at a vigorous boil, giving different times to
cook a food like beans. The very limited laboratory resources at our
disposal simply did not allow the precise measurement of such
things as combustion efficiency and particulate emissions.
In a covered aluminum pot, 5 L water of temperature 22°C was
brought to a boil and 250 ml dry red beans was added. The same
type of beans was used for each test. Beans were considered
cooked when they were easily mashed with a fork. Time to boil and
time to cook was recorded. This was done 5-6 times for each stove.
Following cooking the amount of soot on the bottom of the pot was
recorded on a scale of 1-10; with 1 clean and 10 completely soot
covered that included tar. All stoves were managed as the average
African household would manage them, therefore performance
results may differ substantially from results from stove developers
and laboratories.

Fuel

Biomass for pellet fuel consisted of fallen leaves and stems of
Eucalyptus tree species, rice hulls from the local rice mill, prunings
from the many shrubs and trees on the university campus, waste
from the harvest and threshing of sunflower, and maize cobs. The
latter two are seasonal, from May to August. Biomass was first
pulverized a hammer mill (Yulong SG40 hammer mill, Yulong
Machine Co, Zhangqiu,China) with 3mm diameter sieve holes,
resulting in shredded biomass of 1-3 mm diameter particles.
Shredded biomass was blended to approximately one third each of
Eucalyptus, rice hulls, and post-harvest sunflower field waste
(stalks, inflorescences, leaves) and fed into the pellet mill (Yulong
SJK-200 flat die, 6mm die diameter) along with approximately 250
ml water per 20L bucket of biomass. We found it best to add water
simultaneously with the biomass. Extruded pellets were sun dried
and stored in bags. Occasional plugging of the die holes, especially
with new die plates, was a problem. These had to be individually
drilled out. Higher oil content of the biomass stock helps to lubricate
but also can result in a more smoky fuel. The same batch of pellets
was used for each test.

The price for pellets was set by assessing the cost of production
and sourcing of biomass. Our price of $0.21 kg -1 is also a
convenient 350 TZ shillings (TZs) per kg or 3 kg for TZs 1,000
($0.63). We found that this price was independently very close to
other pellet projects in Tanzania and close to that of Inyenyeri in
Rwanda.

Charcoal was locally sourced from charcoal vendors and was

made from common tree species from Miombo woodland such as
_Brachystegia_ and _Acacia_, as well as numerous shrub species. LNG
was obtained in portable tanks from Mihan Gas Inc., Dar es
Salaam.

Stoves

Jiko Bomba Stove (Figure 2) (Bjarne Laustsen, Karatu, Tanzania,
www.kiwlau.com, $15). According to Roth (2014) The Jiko Bomba
is “double-walled, locally produced TLUD-ND [natural draft] made of
mild steel, optimised for pellets composed of mixtures of agricultural
residues as a fuel. Diameter is 23 cm, height 37 cm. The stove is
composed of two vertically stacked assemblies: the bottom part is
the stove unit comprising a fuel reactor and a primary air regulator.
The top part comprises a mixing chamber, an internal chimney
space and pot-rests. Its perforated bottom plate enhances premixing of wood-gas and oxygen before ignition in order to achieve
clean combustion. Both assemblies have handles and pot-rests.”
Metal thickness is approximately 20 gauge (0.9 mm).

Troika Stove (Figure 2) (Awamu Biomass Energy Ltd., Kampala,
Uganda. Designed by Dr. Paul Anderson, www.drtlud.com, $16).
From Roth (2014): “The Troika model is the 2013 addition to the
„Champion Family‟ of TLUD cooking stoves that include Champion
(2009), Mwoto (2010), and Quad (2012). All four stoves have the
same basic dimensions and performance, but with distinct
constructions. The Troika can be either ND (Natural Draft) or FA
(Forced Air). The portable Awamu Troika TLUD is based on pre-cut
parts with tabs and slots for easy local assembly without rivets and
cheaper shipping as flat pack pieces. It has a metallic body with
four wooden handles that allow for safe handling and also serve as
legs to provide stability. Flatpacked parts weigh 4 kg; dimensions of
assembled stove: 30 x 30 x 50 cm. The Troika can be made as a
TChar variation to continue cooking with char.” Metal thickness: 24
gauge (0.6 mm).

St. John‟s Stove (SJUT) (Figure 3). The St. John‟s Stove was
constructed by our project and consists of two concentric cylinders
with perforations in the bottom plate for primary air as well as
perforations at the lower end of the inner wall. The SJUT stove has
no primary air vent. The SJUT2 has additional air vents at the top of
the outer cylinder. The pot stand is inserted on top when initial
lighting is complete and channels secondary air to the gases rising
from the pellets.

Philips Fan Stove HD4012 (Figure 4) (African Clean Energy,
Maseru, Lesotho. www.africancleanenergy.com, $72. From The
description in Roth (2014): The Philips stove is: “a high efficiency
TLUD gasifier stove with forced air, stainless-steel construction; the
inner combustion chamber is ceramic. The stove is virtually
smokeless due to a good air-gas mixture for complete combustion
that is created by the fan at the bottom of the combustion chamber.
The battery can be charged either from the grid, if available, or
using a solar charger.” A knob allows the fan to be adjusted from 4
to 12 V. The fan provides both primary and secondary air flow to
the fuel. The Philips stove is designed primarily for the use of
pellets but can also burn found fuels and small pieces of wood. The
battery is said to drive the fan for 40-60 h, or 2-3 h per day for three
weeks.

Traditional charcoal stove (Figure 5). This is generally an open
bowl design of approximately 30 cm diameter with metal casing and
1-2 cm clay liner; the bottom is perforated with 1 cm holes. A
closable air vent allows a small measure of turn-down. Improved
charcoal stove (Figure 5) Envirofit CH2300 (www. arti-africa.org,
$33): Is an insulated open bowl (15x31x23 cm HxWxD) charcoal
stove with adjustable air inlet.

Gas stove with a LNG/LPG gas burner (Hangzhou Tianlong Steel
Cylinder Co., Zhejiang China) was used. The steel/chromium frame
fastens directly to LNG tank.

Table 1. Summary of factors in choice of cooking system in Dodoma Tanzania 2013-14. Cost of cooking was done using consolidated data from Tables 2 and 3.

1 2 3 4 5 6 7 8 9

US$/kg

Cooking
system (stove)

Soot on pot Smoke

Time to
boil 5 L

Estimated cost

to cook beans

Fuel type

Weight of fuel
to cook beans

Fuel cost

Time from lighting

to begin cooking

(US$)

(kg) (US$) cost (min) water

Natural Draft (ND) Pellet 1 1.4 $0.21 $0.29 $20 High High 3 33
Forced Air (FA) Pellet 2 1.1 $0.21 $0.22 $75 Very low Low 1 18
Charcoal 3 0.6 $0.26 $0.15 $4 Med Med 30 55
Liquefied natural gas (LNG) 0.28 – 0.47 $2.06 $0.64-$1.01 $70 5 None None 0 19-51 6

(kg)

cost

(min)

1Average of Troika, Jiko Bomba, SJUT2. Does not include SJUT1 due to performance problems of that stove, 2Philips stove, 3Average of traditional and improved charcoal stoves
4Average of six tests at two different flow rates as described in Materials and Methods, 5Cost includes 15 kg capacity gas tank (US$40) and basic 2-burner counter-top stove (US$30.

Cooking procedures the total weight of fuel used calculated by subtracting the a subsidized trial price to the local community, as

unburned fuel from the total loaded. The char was weighed this stove was the only one available in sufficient

_Solid fuels_ and quantified as a percent of total fuel used. With the

quantity. Careful instructions on using the stove,

charcoal the coals were extinguished with sand and

Pellets were placed in the fuel chamber and ignited with weighed to assess total fuel used. particularly the air vent, were given. The first 30
approximately 30 ml of kerosene. The initial amount of purchasers of the Jiko Bomba
pellets was 1 kg except the Philips, whose capacity was interviewed for their experience with the stoves.
600 g. The primary air vent in the Jiko Bomba and Troika _Gas_

Interviews were conducted in Swahili language,

stoves was open fully, and when the flame was strong the
top part of the stoves was put in place and the primary air Weighing the amount of gas to cook each pot of beans was the language of the respondents, by a Tanzanian
vent closed in increments. The St. John‟s stove lacks a not possible; therefore we did the following in order to post-Master‟s degree worker with experience in
primary air vent. The stove top serves to channel account for the fact that most people cook beans initially at conducting interviews. The same questionnaire
secondary air to the upward-moving gases in the ND high gas flame, then turn it down to different simmering was used for all of the respondents.
stoves, as well serving to support the pot. When the flame rates:
gave the appearance of burning mostly gas cleanly (gas A full tank of LNG was lit, set to medium-high flame, and
plus secondary air), the primary air in the Jiko Bomba and the time recording started. Three lots of beans were
Troika was adjusted to approximately ¼ open and the pot cooked at medium-high flame and the time for each was RESULTS AND DISCUSSION
with water was then placed on the stove. For the Philips, recorded. The time to totally deplete the tank of gas, the
stove ignition was without fan for the first 30 s followed by entire time at the same medium-high flame, was recorded Evidence for the continued preference for
medium fan power to get the flame going, and finally high and the weight of gas used per minute calculated. The charcoal-based cooking in Tanzania can be seen
power for the remainder of the cooking. The charcoal weight of gas per lot of beans was calculated as weight of

in Table 1. With charcoal, both cooking cost and

stoves had an initial ignition period of about 30 min before gas used per minute times the time to cook the beans (gm
pot placement; this is one of the main disadvantages of gas min -1 x min). stove cost are substantially lower than natural
charcoal. A second full tank was lit, set to low flame, time draft and forced air pellet systems and LNG, while

a subsidized trial price to the local community, as
this stove was the only one available in sufficient
quantity. Careful instructions on using the stove,
particularly the air vent, were given. The first 30
purchasers of the Jiko Bomba stove were
interviewed for their experience with the stoves.
Interviews were conducted in Swahili language,
the language of the respondents, by a Tanzanian
post-Master‟s degree worker with experience in
conducting interviews. The same questionnaire
was used for all of the respondents.

RESULTS AND DISCUSSION

Evidence for the continued preference for
charcoal-based cooking in Tanzania can be seen
in Table 1. With charcoal, both cooking cost and
stove cost are substantially lower than natural
draft and forced air pellet systems and LNG, while
pot soot (a proxy for smoke) is moderate. For the
Philips fan stove and natural draft stoves
respectively 83 and 133% more pellets by weight
(column 2) were needed to cook beans than
charcoal, costing 47 and 93% more than charcoal
at 2013 charcoal prices. This cost difference will
make it difficult to introduce pellet stoves. For

All of the solid fuel stoves needed to be refilled when the
fuel was depleted and reignited to finish bean cooking
beans. When pellets were burned down to char (no flame,
only glowing coals) the char was emptied and extinguished
with sand and the fuel chamber refilled and reignited and
time recording resumed. When the beans were fully
cooked, this second batch of partially burned fuel was
emptied, the char separated from unburned pellets, and

the total weight of fuel used calculated by subtracting the
unburned fuel from the total loaded. The char was weighed
and quantified as a percent of total fuel used. With the
charcoal the coals were extinguished with sand and
weighed to assess total fuel used.

_Gas_

Weighing the amount of gas to cook each pot of beans was
not possible; therefore we did the following in order to
account for the fact that most people cook beans initially at
high gas flame, then turn it down to different simmering
rates:

A full tank of LNG was lit, set to medium-high flame, and
the time recording started. Three lots of beans were
cooked at medium-high flame and the time for each was
recorded. The time to totally deplete the tank of gas, the
entire time at the same medium-high flame, was recorded
and the weight of gas used per minute calculated. The
weight of gas per lot of beans was calculated as weight of
gas used per minute times the time to cook the beans (gm
gas min -1 x min).

A second full tank was lit, set to low flame, time
recording started, and three batches of beans cooked at
constant low (simmer) flame. The same method was used
to calculate the time to cook the beans at low flame.

Stove introduction and interviews

The Jiko Bomba stove was promoted and sold at

successful adoption of such new technologies, the cost
advantage must be substantial.

While this cost advantage for charcoal has devastating
effects on the environment due to the continued
drastically unsustainable cutting of trees, householders
are likely to continue to ignore new types of ICT until the
fuel cost is substantially lower than charcoal and the
stove cost is not too high. However, given the steady
price increase of charcoal, the transition to a situation in
which cooking with charcoal costs substantially more
than with pellets is inevitable. In Dodoma, charcoal prices
are more than doubled from 2011 to 2014. According to
the World Bank (Peter and Sander 2009), the price in Dar
es Salaam for a 40-50 kg bag of charcoal rose from
$3.50 to $13.30 between 2003 and 2007. Currently (end
of 2014) that price is around $40. Another report (Energy
and Environment Partnership 2013) shows charcoal
prices increasing from US$0.09 to US$0.82 per kg from
2003-2012, an average annual increase of 99%. These
figures indicate a 33%-90% annual increase in price, with
the higher end being in the main city, Dar es Salaam. For
this reason we continue to work on pellet-fueled systems
despite current low rates of sustained adoption.

Smoke and soot from the natural draft stoves were a
problem (Table 1). A thick layer of shiny tar-laden soot
often coated the bottom of the pot after cooking. In
laboratories and workshops microgasification stove
developers are able to operate many of these stoves (i.e.
Troika, Quad) with minimal smoke and soot, commonly
attaining ISO Tier 3 (very little smoke) in the PM 2.5
(smoke) emission category and even attaining the much
sought after and difficult to attain completely clean Tier 4
(Anderson, 2014). However, transferring the ability to
attain even Tier 3 performance to African householders is
going to be a challenge. Householders use different types
of fuels and pellets made from different biomass stocks
whose components frequently fall outside the parameter
range that the stove is tuned for. Stove owners often
hand off the stove to a maid with minimal instructions and
walk away. The stove program workers who carried out
the tests on the TLUD stoves for this research tended to
have more knowledge than the average householder
about using the stoves properly, that is, the primary air
vent; but they were unable to use the natural draft stoves
on biomass pellets without creating excessive smoke.

The Philips fan stove was clearly superior to the natural
draft stoves in the smoke and soot category, as well as in
time to boil, over 50% faster than the natural draft stoves
(Table 1). While only one was available to use, the
Philips stove having not been introduced to Tanzania,
users who tried it were unanimous that it is superior. The
375% higher price for the Philips stove (Table 1) is a
barrier however, as well as the requirement to charge the
fan battery, needed for every two to three weeks of
normal cooking. Sincemany Tanzanianswho lack electricity
in their homes are accustomed to charging devices like
cell phones in neighbouring small shops, households that

desire to incorporate the Philips stove into their cooking
can use this method. A detachable battery would be
useful in this case. The Philips stove ability to turn-down
to a satisfactorily low simmer was a minor problem.
According to the manufacturer this problem has been
corrected with a new rheostat mechanism. Additionally,
the stove producer, African Clean Energy, sells a solar
panel charger for $17 (5W PET frameless panel with
regulated 7V output to charge the 6V battery).

The 325 to 570% higher cost of cooking with LNG
(depending on gas flow rate) (Table 1) compared to
charcoal plus the high cost of gas stoves will be barriers
to the great majority of Tanzanians to move to this ICT.
Use of LNG for cooking will likely remain in the upper
echelons of society until gas prices decrease and/or
programs to subsidize equipment purchase are implemented. Targeting these LNG-cooking price barriers and
the implementation of clean cooking should be a
government priority given the astronomical costs to
Tanzanian society of respiratory-related ill-health due to
indoor air pollution from cooking smoke as well as
deforestation for charcoal production.

The potential for reducing the cost of solid fuel cooking
via subsidies from carbon credits (Global Alliance for
Clean Cookstoves, undated) may make TLUD stoves and
agricultural waste based fuels more competitive with
other systems, particularly in combination with price
increases of charcoal. Biochar produced by TLUD stove
users and used as soil amendment may in the future be
an additional source of carbon credit funds via carbon
sequestration in soil (Figure 6) (Whitman et al., 2010;
Interreg IVB project Biochar, 2013).

Biochar production of just under 60% of total fuel
weight for the natural draft stoves (Table 2) is
comparable to the percentage in at least one other study
using microgasification stoves in East Africa (Whitman et
al., 2011). The Philips forced air stove production of one
third (29.8%) of that of the natural draft stoves reflects the
more efficient use of fan-driven primary air reducing
pyrolysis. This stove was not developed to produce
biochar.

Of the 30 people interviewed who bought the Jiko
Bomba TLUD stove, 18 (60%) were not using the stove
after one month, stating that they were dissatisfied with
the stove performance and had returned to using
charcoal. Another three had stopped because pellets
were difficult to obtain, only being available at the SJUT
Stove Project site, which for some is a distance. Over
80% (25 of 30 respondents), said that the stoves produce
too much smoke and blacken pots. However, 75% said
that the pellet stoves heat better and cook faster than
their charcoal stoves, as is evident in Table 2 cook times.
Forty percent of users mentioned that controlling the air
vent, which is the most important factor for controlling
smoke, is too much trouble, and that with charcoal they
can put the pot on and leave it for an hour. It was clear
from the interviews that most of the stove users

Table 2. Performance comparison of two types of charcoal stove with two types of waste biomass pellet fuelled microgasification stove, forced air (FA) and natural draft (ND). Means and
95% confidence intervals are provided.

1 2 3 4 5 6 7 8
Stove Fuel type Stove type N Biochar Percent Weight fuel used (g) Time to boil (min) Time to cook beans 2 (min)
Phillips Pellet FA 6 29.8a (18.9-40.7) 1088bd (918-1258) 18.5a (15.9-21.0) 105a (87-123)
Troika Pellet ND 6 50.8ab (37.8-63.9) 1494c (1294-1694) 26.3b (19.3-33.3) 102.5ab (89-115)
JikoBomba Pellet ND 6 56.8b (49.4-64.2) 1653c (1363-1943) 42.5c (34.0-51.0) 134ab (121-148)
SJUT1 1 Pellet ND 6 61.5ab (48.9-74.0) 728ab (453-1002) 64.2c (37.4-90.9) 165ab (135-195)
SJUT2 Pellet ND 6 51.8ab (37.1-66.6) 1302cd (1079-1525) 63.8c (51.5-76.2) 180b (156-205)
CharTrad Charcoal Trad. 5 - 621a (503-739) 54.2c (30.2-78.2) 150ab (138 -163)
CharImpr Charcoal Improved 4 - 514a (320-514) 55.0c (29.8-80.2) 155ab (112-197)

1The SJUT1 stoves were experimental and the SJUT1 stove gave problems staying lit. We have decided to include it in the data. 2Includes time to boil.

as the 3-phase electric motor. These problems
increased the cost of production beyond the price
to compete with charcoal in 2014. We chose to
test these lower-end technologies because these
are what local entrepreneurs generally buy. To be
economically viable, biomass-based pellet production will likely need to be developed on a larger
scale with higher quality machinery that is more
resistant to wear and tear and that has a
production volume high enough to support a
maintenance and parts replacement program.
Therefore the concept of local pellet-making using
locally sourced biomass may not be viable based
on our experience. Likely to be more viable will be
large-scale plants that can supply the urban
population of an entire region, located near
production and processing operations that generate
large amounts of waste biomass such as lumber
mills and rice mills. The need to engineer a blend
of different biomass stocks that meets the needs
of pellet-making, such as blending eucalyptus
prunings with rice hulls or sawdust, can be fulfilled
by transporting the needed biomass. Hammer
mills for reducing the volume of the transported
biomass can be located at the local level since
hammer mills generally give far fewer problems

Figure 6. Typical soot with tar on pot bottom after
cooking on natural draft TLUD stove with pellets.

had not learned the importance of adjusting the air
vent, despite careful instructions at initial
disbursement and a follow-up visit. This appears
to be a major reason for the excessive smoke
problem. The oil content of the pellets may play a
role in smoke production; however, when the
same pellets that produced smoke in the ND
stoves were used in the Philips fan stove, smoke
was not a problem. The 30 min ignition time for
charcoal reduces its advantages, along with the

longer cooking times.

The St. John‟s stoves (SJUT 1 and 2), while
being the least expensive to produce due to their
lack of a vent door, extinguished regularly after
about 30 min, probably due to lack of a primary air
intake vent. Fuel efficiency is high in the SJUT1
stove (Table 2, column 6) due to a different air
configuration, but this does not overcome the
problem of lack of sustained combustion. There
might be potential for this stove to be used for
short cooking times such as making tea and
cooking corn meal ( _ugali_ ) the most commonly
cooked foods in Tanzania, which takes about 25
min.

The cost of biomass densification into pellets
will need to decrease substantially relative to
charcoal to become competitive. The small-scale
imported machinery that we used gave problems
with the die holes plugging up with the frictionheated biomass mix, slowing production and
increasing its cost, as each of the approximately
100 die holes need to be drilled out. This has
been a problem with other pellet-making groups in
Tanzania. Wear and tear on the machinery
necessitated the expensive replacement of
imported parts such as the die and rollers, as well

Table 3. Cost of cooking with gas at low and high gas flow rates.

Flow

rate
g/min

(min)

Total gas to
cook beans

Cost US$ /

hour

Gas flow
rate

Total
weight gas
in tank (kg)

Total gas

cost 1

Gas cost

Total time to
use all gas in

Time to boil 5 L

Average bean

cook time 2

Aveerage

cost to

(kg) 3

US$/kg

rate cost 1 US$/kg (min) hour cook

in tank (kg) tank g/min (min) (kg) 3

beans
Med-high
6.0 $12.94 $2.16 1231 4.87 19 96.5 0.47 $0.63 $1.01
flame

Low flame 3.0 $6.76 $2.25 1479 2.03 51 140 0.283 $0.27 $0.64

tank

(min)

1Doesn't include tank. 2Includes time to boil. Three tests done for each flow rate. 3Flow rate (g/min) times cook time (min).

than pelletizing machinery. An additional consi- twice the weight of pellets compared to charcoal
deration is the cost of the microgasification stove. (83% and 133% more by natural draft and forced
It appears that forced-air (FA) stoves will be the air stoves, respectively). Therefore, until the price
most viable option in the future; however these of pellets reaches somewhat less than half the
will likely be 5-10 times more expensive than cost of charcoal, there will be resistance to the
natural draft (ND) stoves. While ND stoves are adoption of the new stoves. However, relentless
able to test nearly particulate free in laboratories, tree-based charcoal price increases will inevitably
as discussed above, the everyday reality of drive change, particularly as ICTs improve. The
keeping a ND stove tuned and vented properly optimum configuration of ICT systems for Africa is
may make the ND stoves non-viable for African still in need of shaking out and will likely involve
households. FA stoves are more robust, the numerous trials and failures.
forced air causing consistently complete combustion Although most of the stove testers said that the
of particulates with the simple turning of a pellet stoves cooked food faster than using
rheostat. Such issues as damp pellets during the charcoal, over half ended up abandoning the use
wet season are simply overridden by the of the microgasification stoves because they
combustion-facilitating power of forced air. emitted too much smoke or were too much trouble
Programs that subsidize or provide credit for the to adjust for low smoke. When biochar is evenpurchase of FA stoves would likely facilitate the tually given cash value by the agriculture market,
transition to these ICTs once pellet fuels become microgasification stoves will be a significant
available (Table 3). source of this important soil fertility enhancer, as

over half of the weight of burned pellets was
turned into biochar. This may be significant in

Conclusion

driving adoption of the new stoves.

Widespread adoption of solid fuel ICTs by the Unless large-scale subsidization programs are
lower income 70% of urban and peri-urban African developed for transitioning to gas cooking, the
society will continue to be in a challenge if several-fold (387 - 570%) higher cost of cooking
available ICTs do not substantially cut the cost of with gas will lock most of Tanzania‟s population
cooking while maintaining or improving customary into cooking with biomass for some years to
cooking characteristics. Our results showed that come, despite the exploitation of massive natural
the microgasification stoves used on the average gas reserves in the country. African governments

would do well to assess the needs of the many
entrepreneurial efforts to introduce ICTs and to
help pave the way for them. Education campaigns,
tax breaks, tariff reductions for ICT technologies
as well as strict enforcement of existing treecutting and charcoal selling laws can all facilitate
the transition to ICTs. Justification of lax enforcement of such laws stems from the desperation of
rural populations whose crops frequently fail due
to drought, and must fall back on charcoal
production. The paradox is that deforestation is
associated with a worsening of drought conditions.
Additionally, promotional and education campaigns
to reduce household smoke pollution via better
ventilation should assist with this.

It will be interesting to see how the cooking
milieu and introduction of ICTs shakes out in the
next 5 -10 years. Under trial in Eastern Africa are
large-scale entrepreneurial pellet fuel production
systems such as Inyenyeri in Rwanda, as well as
smaller scale pellet and briquette making efforts.
The production of “green charcoal” (Global
Alliance for Clean Cookstoves, 2014) is being
initiated in East Africa. Additionally, one must not
underestimate the Chinese, who have developed
clean biomass-based solid fuel cooking systems,
particularly advanced pellet stoves, over the past
25 years and have the capacity to come into
Africa on a large scale with low-cost and well
developed solid fuel production and cooking

systems.

Conflict of interest

The authors declared that there was no conflict of
interest.

ACKNOWLEDGEMENTS

We wish to thank Dr. Val Clarke and the Amani
Foundation for their generous financial support and
diligent work for the St. John‟s University Stove Program.
This research was developed, written, and the decision to
submit to this journal was done independently of the
above funding sources.

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