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AS ADVERTISERS vie to promote this or that fuel inthe media, the attributes
of one unassuming formof energy read like a copywriter’s dream. This fuel
doesn’t add to the greenhouse gases in the atmosphere, and could actually
help to halt global warming. It creates little or no pollution, but could
solve pollution problems around the world. It provides the US with as much
energy as does nuclear power, but without the hazards. It is also potentially
infinitely renewable. The fuel is called biomass.

We have burnt biomass for the past 150 000 years, and even today, more
people rely on it for their domestic needs than on any other fuel. Furthermore,
the energy stored by plants each year is equivalent to 10 times the world’s
consumption of primary fuels. And yet biomass is almost absent from world
energy records.

Biomass is the stuff that plants are made of. The term biomass energy,
or bioenergy, embraces all fuels that are derived from plants, notably wood
and residues from the agricultural and forestry industries, and dung. Green
plants and some algae use the Sun’s energy to create simple sugars from
carbon dioxide and water. Plants store the energy in molecules of glucose,
starch, oils or lignocelluloses. When biomass fuels are burnt, this energy
is liberated, and the carbon dioxide is released back into the atmosphere.
As biomass is composed of carbohydrate polymers consistingof mainly carbon,
hydrogen, oxygen and nitrogen, there isvery little pollution if all the
fuel is completely burned. Furthermore, if the biomass harvested for energy
is replanted,there is no net increase in atmospheric carbon dioxide: thecarbon
dioxide released on burning the fuel is taken up bythe growing plant.

Around 2.5 billion people, about half the world’s population, rely on
biomass for virtually all their cooking, heating and lighting. Most of these
people live in the rural areas of developing countries. According to David
Hall, professor of biology at King’s College in London, biomass accounted
for 14 per cent of the world’s energy consumption in 1987, the equivalent
of 1257 million tonnes of oil (Mtoe). He calculated that, as a group, developing
countries derive 35 per cent of their energy from biomass, or 1088 Mtoe;
in industrialised countries, biomass accounts for only 3 per cent of energy
budgets, but this still amounts to about 169 Mtoe every year.

Biofuels are varied and versatile. They come as solids,gases and liquids
that can match and replace any fossil fuel. Biomass can be burnt in its
crude, raw state, or converted tomore convenient forms . Sources for bioenergyrange
from biomass that is freely available at the side of theroad to biofuels
that are cultivated in state-of-the-scienceenergy plantations.

The great advantage of crude biomass, such as wood, cereal straws, rice
husks, coconut shells, coffee-bean husks and animal dung, is that it can
be scavenged. The main disadvantage is its bulk, which makes it cumbersome
to store and expensive to transport. Fresh biomass often also contains a
high percentage of moisture, which reduces its heat value. Transforming
the raw biomass to more convenient solids, liquids or gases can overcome
these difficulties.

The combustion of crude biomass is by far the most common way of using
the fuel. The way the biomass burns depends on its chemical and physical
make-up. Chemistry determines both the heat content of the biomass, and
the readiness with which the various components burn. Physical properties
include the density, moisture content, shape and size of the pieces of fuel.
Small, dry particles tend to burn quickly and produce a hotter flame than
larger, moist lumps. In practice, this means that the skilled operator of
an open fire controls the heat by burning a particular size and species
of wood, and maybe altering the size of the fire to the dimensions of the
pot. At the other end of the technological scale, a furnace is designed
for a particular biomass fuel. To achieve the most effective combustion,
the biomass is made as uniform as possible: wood is dried and chipped, and
residues are compressed into briquettes. Initially, combustion involves
heating the fuel to drive off water vapour. As the temperature rises, the
celluloses and lignin begin to decompose into a complex of gases, tars and
solid charcoal, which then oxidise to give, ultimately, carbon dioxide and
water.

In the US, more wood is used as fuel than to produce lumber, pulp or
paper. Figures from the United Nations show that the US is the fifth largest
producer of wood fuel, after India, Brazil, China and Indonesia. Electricity
companies are installing wood-burning generators in several states; California
already has more than 500 megawatts on line. By the end of the century,
biomass could meet 10 per cent of the US’s energy demand. The European Community
consumes about 5.5 Mtoe of fuelwood per year: more than 7 million tonnes
of wood, about 2.5 Mtoe, are burnt in French hearths alone.

Marginal land fertile for biofuel

Harvesting in neglected woodland could boost the use of fuelwood still
further. France and Italy have 5 million hectares of unmaintained coppice
that they are gradually restoring. If the European Community revises the
Common Agriculture Policy and reduces the subsidies that encourage farmers
to cultivate land that is not very fertile, some experts estimate that this
would release 10 million hectares of ‘marginal’ farmland. Farmers could
turn this surplus agricultural land into energy plantations where they could
cultivate fast-growing, high-yielding coppice species, mostly willow, poplar,
aspen and alder. France has around 400 hectares of experimental plots across
the country where it is investigating these ‘short-rotation forestry’ techniques.
In Northern Ireland, which has the largest area of marginal agricultural
land in Britain, the Horticultural Centre at Loughgall is investigating
short-rotation coppice on poor soils. Biomass in the form of chipped willow
wood costs less than one-third of the oil it replaces for heating greenhouse
crops of early tomatoes. In Sweden, the government aims to plant a minimum
of 10 000 hectares of ‘energy forests’ every year for the next decade.

As supplies of fuelwood disappear in many areas of the developing world,
the poor respond, as did their counterparts in England and the US at the
beginning of the Industrial Revolution, by falling back on agricultural
residues and animal dung. The World Bank estimates that at least 800 million
people are now wholly dependent on residues and dung for their domestic
energy. On the lowland plains of India, China and Bangladesh, dung and residues
account for 90 per cent or more of domestic fuel. The average heat value
of air-dried agricultural residues and dung is 13 gigajoules per tonne,
which is only about 15 per cent less than that of wood. For cooking on open
fires, people prefer to use the slower-burning woody residues such as corn
cobs, coconut shells, jute sticks and the stems from the pigeon pea plant.
These give better control over the heat and are easy to collect. Straws
and husks from rice and other grains are not ideal as they burn too quickly,
and are difficult to collect and store.

Another option is the bacterial digestion of vegetable and animal waste
in biogas digesters to produce both fuel and fertiliser. People often prefer
the compost to the original dung because the digestion process kills pathogens
and the seeds of weeds; it also has a sweet odour. Unlike dung, the compost
does not deteriorate during storage. Dung is the main waste fed to a biogas
plant, and the two countries with the most experience of biogas also have
large numbers of stabled animals; China with pigs, and India with cattle.

The first biogas digesters in China in the 1960s were unreliable. Since
1980 the government has laid down strict standards for their design and
construction, which has improved the performance of the plants considerably.
Today there are around 4.5 million small domestic digesters operating in
the country. India is keen to expand its network of 25 large digesters,
which are serving communities nationwide. At the Indian Institute of Science
at Bangalore, a team of scientists, led by Amulya Reddy, director of the
Centre for the Application of Science and Technology to Rural Areas, has
helped to build a community plant in the nearby village of Pura. The villagers
have two biogas digesters, which supply compost to farmers and biogas to
power an electricity generator. The electricity is used to pump water to
a reservoir, which serves eight public taps. Excess electricity powers domestic
lights.

Pura is now thinking of building a wood gasifier to provide ‘producer
gas’ to supplement its supply of biogas. This would mean growing trees to
feed the unit. Worldwide, tree planting schemes have generally been a dismal
failure. Fuelwood is regarded as a byproduct, so trees are rarely planted
specifically for fuel. By providing Pura with clean water and lighting,
however, biogas has raised the villagers’ standard of living. Reddy is confident
that villagers will grow trees to power the gasifier to maintain their new
lifestyle.

While biomass gases are an excellent source of energy, liquid energy
is more convenient to use, store and distribute. As a result, several developed
countries have programmes for making bioethanol from sugars and starches.
The US fermented3 billion litres of fuel ethanolin 1987, mostly from surplus
maize. About 30 per cent of the country’s petrol has some alcohol mixed
with it, usually in a 9-per-cent blend. The European Community is also looking
to bioethanol as a means of reducing food surpluses, while the International
Energy Agency says that ethanol made from surplus sugar alone would satisfy
2 per cent of the petrol market.

Zimbabwe has pioneered the fermentation of fuel alcohol in Africa. The
distillery at Triangle in southeast Zimbabwe has been operating for nine
years. The only problem is the weather. Drought has curtailed the growth
of sugar cane this year, limiting the quantity of alcohol that Triangle
can produce. The alcohol is mixed in a 12- to 15-per-cent blend with petrol,
a ratio that could double when more alcohol becomes available.

The success of the alcohol scheme in Zimbabwe has eased the way for
other liquid biofuel programmes in Africa. Malawi has built a plant at Dwanga
that regularly produces about 9 million litres a year. Petrol is blended
with 15 per cent ethanol, but there are also plans to run cars on pure alcohol.

An economic biofuel substitute is available for diesel, which powers
a large part of the world’s agricultural vehicles, road freight trucks,
rail locomotives and electricity generators. Vegetable oils extracted from
the seeds of annual plants such as sunflower, rape, hemp and soya, or from
perennials such as coconut and oil palm, are the most promising alternatives
for diesel. With the same energy value as diesel, they are richer in energy
than other liquid biofuels. Oil-bearing seeds from annuals are easy to harvest,
transport and store. The oil is easily extracted, and the residue, or oilcake,
is often valuable as a protein-rich feed for animals.

Although diesel engines run well on vegetable oils for a short while,
the neat oils are more viscous than diesel and leave the engines clogged
with carbon residues, or ‘coked up’, after a few hours’ running. One promising
line of research to overcome this difficulty involves heating the oils with
alcohols in the presence of a catalyst. This converts the triglycerides,
which make up vegetable oils, into less viscous methyl or ethyl esters.
Diesel engines have run on methyl esters without problems for well over
a thousand hours.

Some plants produce hydrocarbons that are suitable for making liquid
fuels. An oil-like latex from Euphorbia lathyris, a shrub that grows in
semi-arid lands, can be converted to afuel similar to petrol. For the moment,
‘euphorbia oil’ is uneconomic to produce, but there are around 2000 speciesof
the plant and work continues in several countries to findhigher yielding
varieties. Asclepias speciosa, the milkweed that grows in the US, also produces
latex. Pittosporum resiniferum, a tree that grows in the Philippines, bears
fuit that people burn for fuel.

Alternatively, after hydrogenation, the oil from the fruit produces
a fuel similar to petrol. Other trees, such as those of the Copaifera and
Croton genera that grow in tropical climates, produce oils similar to diesel.
Some researchers have discovered that they can put the sap from Copaifera
multijuga straight into the tank of a diesel vehicle. At the other end of
the plant kingdom, Botryococcus braunii, the freshwater algae, consists
of up to 85 per cent oil; it is the oil that appears to keep the algae buoyant.
Processing this oil gives mostly petrol, some aviation fuel and diesel,
and a small amount of heavy oil.

Even with our limited knowledge of how useful plants can be as a source
of fuel, it is clear that biomass is as diverse and as versatile as fossil
fuels. But the cultivation of energy crops instead of food harvests has
prompted serious criticism of biomass. With many millions of people dying
of starvation every year, how can it be right not to grow food on precious
farmland? Biomass protagonists argue that globally we regularly harvest
more than enough food to feed the world. Hunger today is essentially a problem
of poverty. We need both food and energy, but our neglect of biomass could
make the provision of energy even more of a problem than feeding the world.
After all, a cold cooking pot is useless.

Ironically, concern over the global environment could provide the impetus
for determined research and development of biomass. We could halt global
warming resulting from carbon dioxide by planting trees over an area the
size of India. This may sound fantastic, but it is about the area we need
to plant anyway to ensure fuelwood for a growing population into the next
century, and to stop soil erosion and to restore watersheds ruined by our
relentless destruction of vegetation. Ultimately, we all depend on plants.

* * *

How to turn raw biomass into something special

THERE are four ways to convert raw biomass into a more convenient fuel:
pyrolysis, gasification, anaerobic digestion and fermentation.

Pyrolysis involves the thermal decomposition of raw biomass in the absence
of oxygen. The pyrolysis of wood, for example, produces solid charcoal,
liquids that include methanol and tars, and gases.

The proportion of gases, liquids and solids depends on the temperature,
the rate of heating and the length of time the biomass undergoes pyrolysis.
Heating quickly to high temperatures produces more gases, whereas slow,
steady heating over longer periods gives a high proportion of solid charcoal,
which has about twice the energy value of wood of the same weight and burns
more uniformly.

Gasification involves the complete thermal decomposition of the biomass
in the presence of regulated quantities of air or oxygen. Air gasification
of wood gives ‘producer gas’, a mixture of 50 per cent or more of nitrogen,
20 to 25 per cent carbon monoxide, and smaller amounts of hydrogen, carbon
dioxide and methane.

Producer gas can be burnt to produce heat or to power modified petrol
and diesel engines. Gasification with oxygen gives ‘synthesis gas’, a mixture
of mainly carbon monoxide and hydrogen. Synthesis gas is used in the chemicals
industry to make ammonia, methanol and synthetic petrol.

Anaerobic digestion uses a cocktail of symbiotic bacteria to break down
organic matter in stages to produce mainly carbon dioxide and methane. The
bacteria involved are commonly found in the guts of ruminants, so the addition
of cow dung to the digester is sufficient to start the reaction.

The function of the digester is to provide an environment similar to
that found in the stomach of a cow: warm, dark and oxygen-free. The final
composition of the biogasis between 50 and 80 per cent methane, between
15 and 45 per cent carbon dioxide and around 5 per cent water.

Fermentation of sugars to produce ethanol involves, unlike digestion,
just one specifically cultured yeast or bacterium and three types of raw
material. The first type contains carbohydrates in the form of simple sugars
with 6 or 12 carbon atoms, such as glucose, fructose and maltose. The fermenting
microorganisms act directly on these simple sugars to produce ethylalcohol.
Simple sugars are found in feedstocks such as sugar cane and sugar beet,molasses
and fruit.

The second type of feedstock contains more complex, starchy carbohydrates.
They include cereals, such as wheat and maize, and tubers such as potatoes,
Jerusalem artichokes and cassava. Before fermentation can occur, enzymes
or acids must break down these starchy carbohydrates to simpler sugars.

The third source of feedstock contains cellulose, such as wood, straw,
various crop stalks and waste paper. Again, enzymes or acids must first
break down the celluloseto simple sugars before fermentation.

Lignocellulose is cheap and widely available. If we could break it down
economically, biomass could replace all the oil we use to produce energy
and chemicals. One promising line of research involves the fungus Phanerochaete
chrysoporium, which naturally breaks down dead wood on the forest floor.
At present, however, the cultivation of edible mushrooms on wood and straw
residues is the only commercially successful use of raw lignocelluloses.

* * *

An organisation with ambitions to make the most of biomass

BIOMASS is the single, vital element that links hunger, poverty, fuel
shortages, mounting debt and environmental destruction in the developing
world, and nothing short of a new resolve to promote its cultivation and
use can now help poorer countries. This is the view of the Biomass Users
Network (BUN), an organisation of developing countries that believes its
ideas are at last receiving serious attention, three years after the body
was created.

Members of BUN are sure that they can tackle the complex problems of
development where so many others have failed. In a world teeming with development
gurus, what makes BUN so confident? The network is convinced that the quality
of life remains low in most of the developing world largely because those
countries have failed to take advantage of their greatest asset: the wealth
available from plants.

BUN focuses its work in four key areas. First, the protection or restoration
of degraded land through revegetation, and the development of land that
is difficult to farm to produce food, fuel, animal feed or natural chemicals.

Secondly, BUN is continuing the campaign it has run since its inception
to encourage the sugar industry to switch its emphasis from sugar production
alone to the development of products that can be sold for more money. The
idea is to do for sugar cane what the industrialised countries successfully
achieved for soya beans, peanuts and corn. Although farmers began to grow
those crops for profit only within the past 50 to 100 years (more recently
than sugar cane), industries now make 10 or 15 readily marketed products
from each.

BUN’s third aim is to produce biofuels in programmes tailored to the
environment, and national and local needs. The energy needs of the poor,
usually fuelwood, will not disappear. Biomass, however, also offers an opportunity
for the local production of high-quality, gaseous and liquid fuels.

Finally, BUN is seeking non-polluting uses for agricultural and forestry
residues, which are often regarded as wastes.

Better use of sugar cane is a primary target. About 150 years ago, sugar
was such a lucrative commodity that it earned itself the title ‘King Sugar’.
Sugar remains the largest industry in the tropics, with a highly developed
infrastructure. It provides a livelihood for 50 million skilled workers.

Al Binger, BUN’s Jamaican-born president, argues that by concentrating
only on making sugar, much of the potential of sugar cane is wasted. The
fibrous residue of sugar cane, bagasse, is mostly treated as waste even
though it has approximately the same energy value as wood. One estimate
suggests that, worldwide, the sugar industry could burn bagasse to produce
around 50 000 megawatts of electricity.

BUN is currently involved in a Jamaican scheme in which four sugar mills
will produce a total of 70 megawatts of electricity from bagasse for the
national grid. The first plant should start to generate electricity early
in 1992. BUN is also involved in similar schemes in Costa Rica, and a study
undertaken by BUN says that electricity generated from bagasse could also
play a part in helping to diversify the sugarindustry in the Philippines.

In Zimbabwe, BUN is helping the sugar industry to produce fertiliser
by usingenzymes to break down boiler ash andother factory wastes. It has
also broughtto Zambia a technology for making paperfrom bagasse that was
originally developed in Cuba and India. Ethanol fermented from sugar can
also be convertedto ethylene, a feedstock for the chemicalsindustry. As
far as BUN is concerned,King Sugar may be dead, but citizen caneis alive
and raring to go.

Peter de Groot is a freelance writer and researcher based in London.