Bioenergy is renewable
energy made available from materials
derived from biological sources. Biomass is any organic material which has
stored sunlight in the form of chemical energy. As a fuel it may include wood, wood waste, straw, manure, sugarcane, and many other byproducts from a variety of agricultural
processes. By 2010, there was 35 GW (47,000,000 hp) of globally
installed bioenergy capacity for electricity generation, of which 7 GW
(9,400,000 hp) was in the United
States.
In its most narrow sense it is a
synonym to biofuel, which is fuel derived from biological sources. In its
broader sense it includes biomass, the biological material used as a
biofuel, as well as the social, economic, scientific and technical fields
associated with using biological sources for energy. This is a common
misconception, as bioenergy is the energy extracted from the biomass, as the
biomass is the fuel and the bioenergy is the energy contained in the fuel.
There is a slight tendency for the
word bioenergy to be favoured in Europe compared with biofuel in
North America.[
Solid biomass
One of the advantages of biomass
fuel is that it is often a by-product, residue or waste-product of other
processes, such as farming, animal husbandry and forestry.
In theory this means there is no competition between fuel and food production,
although this is not always the case.
Biomass is the material derived from
recently living organisms, which includes plants, animals and their byproducts.
Manure, garden waste and crop residues are all sources of biomass. It is a
renewable energy source based on the carbon cycle,
unlike other natural resources such as petroleum,
coal,
and nuclear fuels. Another source includes Animal waste,
which is a persistent and unavoidable pollutant
produced primarily by the animals housed in industrial-sized farms.
There are also agricultural products
specifically being grown for biofuel
production. These include corn, and soybeans and to some extent willow and switchgrass
on a pre-commercial research level, primarily in the United States; rapeseed,
wheat,
sugar beet,
and willow (15,000 ha or 37,000 acres in Sweden) primarily in Europe;
sugarcane in Brazil; palm oil and miscanthus in Southeast Asia; sorghum
and cassava
in China; and jatropha in India. Hemp has also been proven to work as a biofuel. Biodegradable
outputs from industry, agriculture, forestry and households can be used for
biofuel production, using e.g. anaerobic digestion to produce biogas, gasification
to produce syngas
or by direct combustion. Examples of biodegradable wastes include straw, timber, manure, rice husks, sewage, and food
waste. The use of biomass fuels can therefore contribute to waste management as
well as fuel security and help to prevent or slow down climate change,
although alone they are not a comprehensive solution to these problems.
Biomass can be converted to other
usable forms of energy like methane gas or transportation fuels like ethanol
and biodiesel. Rotting garbage, and agricultural and human waste, all release
methane gas—also called "landfill gas" or "biogas." Crops,
such as corn and sugar cane, can be fermented to produce the transportation
fuel, ethanol. Biodiesel, another transportation fuel, can be produced from
left-over food products like vegetable oils and animal fats.Also, Biomass to
liquids (BTLs) and cellulosic ethanol are still under research.
Electricity generation from biomass
The biomass used for electricity
production ranges by region.
Forest by products, such as wood residues, are popular in the United States.
Agricultural waste is common in Mauritius
(sugar cane residue) and Southeast Asia
(rice husks).
Animal husbandry residues, such as poultry litter, is popular in the UK.
Electricity
from sugarcane bagasse in Brazil
Sucrose accounts for little more
than 30% of the chemical energy stored in the mature plant; 35% is in the
leaves and stem tips, which are left in the fields during harvest, and 35% are
in the fibrous material (bagasse) left over from pressing.
The production process of sugar and
ethanol in Brazil takes full advantage of the energy stored in sugarcane.
Part of the bagasse is currently burned at the mill to provide heat for
distillation and electricity to run the machinery. This allows ethanol plants
to be energetically self-sufficient and even sell surplus electricity to
utilities; current production is 600 MW (800,000 hp) for self-use and
100 MW (130,000 hp) for sale. This secondary activity is expected to
boom now that utilities have been induced to pay "fair price "(about
US$10/GJ or US$0.036/kWh) for 10 year contracts. This is approximately half of
what the World Bank considers the reference price for investing in similar
projects (see below). The energy is especially valuable to utilities because it
is produced mainly in the dry season when hydroelectric dams are running low.
Estimates of potential power generation from bagasse range from 1,000 to
9,000 MW (1,300,000 to 12,100,000 hp), depending on technology.
Higher estimates assume gasification of biomass, replacement of current
low-pressure steam boilers and turbines by high-pressure ones, and use of
harvest trash currently left behind in the fields. For comparison, Brazil's Angra
I nuclear plant generates 657 MW
(881,000 hp).
Presently, it is economically viable
to extract about 288 MJ of electricity from the residues of one tonne of
sugarcane, of which about 180 MJ are used in the plant itself. Thus a
medium-size distillery processing 1,000,000 tonnes (980,000 long tons;
1,100,000 short tons) of sugarcane per year could sell about 5 MW
(6,700 hp) of surplus electricity. At current prices, it would earn US$ 18
million from sugar and ethanol sales, and about US$ 1 million from surplus
electricity sales. With advanced boiler and turbine technology, the electricity
yield could be increased to 648 MJ per tonne of sugarcane, but current
electricity prices do not justify the necessary investment. (According to one
report, the World Bank would only finance investments in bagasse power
generation if the price were at least US$19/GJ or US$0.068/kWh.)
Bagasse burning is environmentally
friendly compared to other fuels like oil
and coal. Its ash content is only 2.5% (against 30–50% of coal), and it
contains very little sulfur. Since it burns at relatively low temperatures, it
produces little nitrous oxides. Moreover, bagasse is being sold for use as a
fuel (replacing heavy fuel oil) in various industries, including citrus juice
concentrate, vegetable oil, ceramics, and tyre recycling. The state of São Paulo alone used 2,000,000 tonnes (1,970,000 long tons; 2,200,000
short tons), saving about US$ 35 million in fuel oil imports.
Researchers working with cellulosic ethanol are trying to make the extraction of ethanol from sugarcane
bagasse and other plants viable on an industrial scale.
Environmental impact
Some forms of forest bioenergy have
recently come under fire from a number of environmental organizations,
including Greenpeace and the Natural Resources Defense Council,
for the harmful impacts they can have on forests and the climate. Greenpeace
recently released a report entitled Fuelling a BioMess which outlines their concerns around forest bioenergy.
Because any part of the tree can be burned, the harvesting of trees for energy
production encourages Whole-Tree Harvesting, which removes more nutrients and soil cover than regular
harvesting, and can be harmful to the long-term health of the forest. In some
jurisdictions, forest biomass is increasingly consisting of elements essential
to functioning forest ecosystems, including standing trees, naturally disturbed
forests and remains of traditional logging operations that were previously left
in the forest. Environmental groups also cite recent scientific research which
has found that it can take many decades for the carbon released by burning
biomass to be recaptured by regrowing trees, and even longer in low
productivity areas; furthermore, logging operations may disturb forest soils
and cause them to release stored carbon. In light of the pressing need to
reduce greenhouse gas emissions in the short term in order to mitigate the
effects of climate change, a number of environmental groups are opposing the
large-scale use of forest biomass in energy production.
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