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Biomass and Biofuels explained PDF Print E-mail
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Biomass is the total dry organic matter or stored energy content of living or recently living organisms. Biomass can be used for fuel directly by burning it, indirectly by fermentation to an alcohol, or extraction of combustible oils. Biomass also includes biodegradable wastes that can be burnt as fuel.

Bio fuel is a fuel that is derived from biomass. It is a renewable energy source; the CO2 released when it is burnt was absorbed from the atmosphere during plant growth.

Bio fuels include:- Bio ethanol, Bio butanol, Bio diesel, Biogas Bio ethanol Bio ethanol is increasingly used as an oxygen additive in petrol. Inclusion levels can be increased to 10%, but beyond that level specially designed engines, are required. 

Ethanol can be produced from Maize and sugar beet. Production from wheat will dominate domestic production. Three tonnes of wheat are required to produce one tonne of ethanol. If this is all produced domestically from wheat a new market for 2.8M toneswill exist.

There are currently plans for the construction of nine plants in the UK to produce 1.175M tonnes. Only two are under construction. US production of ethanol topped 20B litres in 2006, with Brazil producing 16.5B litres.Europe produced 3.4B litres, the UK none. 

Biobutanol 

Similar to ethanol in characteristics and the biofuel produced from sugarbeet by British Sugar at Wissington plant under construction. Butanol has advantages in that it is less evaporative than ethanol and petrol and is more resistant to absorption of water, enabling it to be transferred in existing pipelines. 

Biodiesel 

A substitute fuel for compression-ignition (diesel) internal combustion engines, produced by the transesterification of waste or vegetable oils and animal oils or fats to form methyl esters, rape methyl ester (RME)

Soyamethyl ester (SME).At 100% inclusion 5-6% more fuel is required to maintain the same level of power and performance in an engine as fossil fuel.

EN14214 is the European standard for bio diesel. The standard limits the percentage of soya oil used to 20%. Fuel additives are necessary to prevent the waxing of bio diesel in lower temperatures. Biogas Biogas can be cleaned to remove hydrogen sulphide and compressed and used as a vehicle fuel as Compressed Natural Gas, CNG.

This carries a duty concession in the UK of 40 ppl, but unlike Sweden where it is used as a fuel, particularly in captive vehicle fleets, its use as a vehicle fuel is limited. 

Second generation biofuels 

Bio ethanol produced from cellulose, hemicellulose and lignocellulose, (straw, wood, biomass crops, paper, grass etc) by enzyme breakdown, acid hydrolysis or thermophilic conversion of the cellulose after the lignin has been separated into sugars that are fermented to ethanol. 

Synthetic biodiesel produced by gasification of cellulose,hemicellulose and ligno cellulose, (straw, wood, biomass crops) and conversion of the “syn gas” into biodiesel through the Fischer Tropsch

Second generation technology is in its infancy so production costs are high.Future biofuel production will move towards second generation as too much land would be necessary to satisfy higher levels of biofuel substitution for fossil fuels relative to food production.  

Biofuels for electricity 

Biomass for the energy market can be broken down as follow:

Dedicated energy crops 

Miscanthus and short rotation coppice 

Maize, grass, whole crop wheat grown and ensiled for energy

Agricultural crops residues

Forestry residues

Wood waste

Animal wastes and slurries

The organic fraction of municipal waste 

Biomass has a major advantage over wind and photovoltaic in that energycan be produced on demand.

There are three routes for biomass to be converted into electricity 

Burning to produce heat and power through heating water toproduce steam and drive a steam turbine.

Co firing with coal Gasification

Biomass is heated not burned at very high temperatures,producing hydrogen, methane and carbon monoxide.The gases produced can be converted into synthetic bio fuels, or used to fuel a gas engine to generate electricity. 

Anaerobic digestion - Biogas Biomass (usually animal slurries, food/vegetable waste organicwaste) is digested anaerobically by bacteria to produce methane which is used to fuel a gas engine to generate electricity and heat. 

Straight vegetable oil and bio diesel can be used as a replacement for fossil fuel diesel in a generator set.With the generation of electricity the following levels of efficiency apply:-

Generation of electricity only – 20-30% efficient

Biomass for heating – 85-95% efficient

Generation of electricity and heat together - 75-90% efficient

(Combined heat and power) In the UK we waste more heat energy from central generation of electricity than would be needed to satisfy the heat requirements of the country.Combined heat and power offers an efficient use for biomass, particularly if a “year round” use of heat can be found.

Medium scale CHP technology is more efficient than small scale CHP, so successful projects must be linked to significant heat usage such as a district heating network. 

Heat from biomass 

Heat only systems on a medium scale offer the most efficient and cost effective use of biomass.

Fuels for biomass heating systems include:-

Wood chipsWood pellets (for confined areas - pellets can be blown into a gravity feed hopper)

Miscanthus

Cereal grains (wheat, oats)Rape (by product after oil extraction) 

Biobutanol An alcohol made from sugar or starch crops, which can be used as a petrol substitute.Has a lower vapour pressure, a more similar energy value to petrol, can be blended athigher levels without engine modifications than bio ethanol.

Biodiesel A methyl ester diesel substitute made from vegetable oil, recycled cooking oil or tallow.

Bioethanol An alcohol made from sugar and starch crops, which can be used as a petrol substitute.

Biogas

Combustable hydrocarbon gases, mainly methane, carbon dioxide and hydrogensuphide produced by the anaerobic digestion of any organic material; animal slurries,food waste, vegetable, green waste, crops and sewage.

 
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