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Biomass

Principle & How it works

Biomass, also known as biofuels or bioenergy, is obtained from organic matter, either directly from plants or indirectly from industrial, commercial, domestic or agricultural products. The use of biomass is generally classed as a ‘carbon-neutral’ process because the carbon dioxide released during the generation of energy is balanced by that absorbed by plants during their growth.

Biomass falls into the following groups, dependent resources, dedicated energy crops and multi-functional crops. Dependent resources are the co-products and waste generated from agricultural, industrial and commercial processes. This includes forest products, waste wood, straw, slurry, animal litter and industrial and municipal wastes (such as food processing wastes). Dedicated energy crops are short-rotation crops, such as coppice, miscanthus, willow and poplar, which are grown specifically to generate biomass fuel. Multi-functional crops are crops that can be used to create different types of energy. For example, wheat can be used to create fuel (including bioethanol and biodiesel), while straw can be used to generate electricity.

Biomass can be converted into heat and electricity in a number of ways. Depending on its source, these processes include burning, pyrolysis (the decomposition or transformation of a compound caused by heat), gasification (the conversion of solid biomass into a gaseous fuel), anaerobic digestion (the decomposition of an organic biodegradable material by bacterial action in the absence of air, and in warm, moist conditions) or fermentation.

Biogas is generated from concentrations of sewage or manure. These are usually in the form of slurry comprising mostly water (almost 95 per cent). The slurry is fed into a digester, either continuously or in batches. Digestion takes from about 10 days up to several weeks, at a temperature of 35°C.

Landfill gas arises from waste deposited underground in landfill sites. Biodegradable organic waste decomposes anaerobically to produce a gas that is roughly an even mixture of carbon dioxide and methane. The methane content gives it the potential as a fuel, which can then be used to generate electricity or to provide process heat.

Fermentation occurs when anaerobic digestion converts sugars into ethanol with the use of micro-organisms, usually yeast. Bioethanol can be used as a transport fuel by mixing it with petrol or using it directly in a modified combustion engine. Sugar cane or beet is the most efficient source but potatoes, corn, wheat and barley can also be used.

Advantages

•  Biomass, considered renewable, works with a range of technologies.
• Biomass as a fuel source can be stored, transported and used where and when needed.
•  Alcohols and other biofuels are efficient, viable, and relatively clean-burning as the emissions associated with oil and coal are not present.
•  Growing biomass crops can lead to carbon dioxide absorption in the atmosphere and oxygen production.
•  Biomass offers opportunities to re-use waste such as crop residues and sewage.
  

Disadvantages

• Unfortunately, there has been some evidence that growing corps for energy leads to rising prices for food.
• Increased use of wood for energy generation leads to rising prices for woods and wood products. This adversely affects the poorer segments of societies.
•  The process also requires large areas of land which leads to decreasing supply of land for competing food crops.
•  If biomass is directly burned, this could contribute a great deal to global warming.
•  It is still an expensive source, both in terms of producing the biomass and converting it to alcohols.
•  The environmental impacts include deforestation if trees are uncontrollably felled which leads to soil erosion. In extreme cases, natural disasters become more frequent.
•  The process consumes a great deal of energy because energy must be put in to grow the plant mass and into collecting, drying and transporting the residues to power plants. Therefore, on a small scale there is most likely a net loss of energy.

Where it's working (Syria, Abroad)

A large proportion of Syrian populations live in rural areas and a considerable number of these people continue to use biomass in the form of animal and agricultural wastes for their energy needs such as lighting, heating, hot water production and cooking. The quantity of biomass used in the domestic sector has decreased over the last twenty years with the spread of oil and gas stoves and electrification. Other combustion of biomass for energy includes heat generated from burning olive leaves which is used for heating greenhouses and poultry farms, or drying tobacco.

The Damascus city wastewater is collected in a water treatment plant linked to a 2 MW generation plant.

In addition to direct combustion of biomass there is the following use of biomass in Syria: Two biogas plants (20m3 and 100 m3) owned by the Ministry of Agriculture for cow waste at Gouta, near Damascus; Two biogas plants (12 m3 and 35 m3) in Ezraa village, Daraa. The daily output of the larger unit is 8 m3; Two biogas plants of 12 m3 in Der Alfradese, Hama.

Future Development & integration

In industrialised countries, the main biomass processes utilized in the future are expected to be the direct combustion of residues and wastes for electricity generation, bio-ethanol and biodiesel as liquid fuels, and combined heat and power production from energy crops. In the short to medium term, biomass waste and residues are expected to dominate biomass supply, to be substituted by energy crops in the longer term. The future of biomass electricity generation lies in biomass integrated gasification/gas turbine technology, which offers high energy conversion efficiencies and will be further developed to run on biomass produced fuels.

Local Factors & Conditions

Agriculture in Syria is the primary sector having the one of the highest percentage of contribution to GDP. The popular crops raised include wheat and barley, cotton, olives, sugar beet, tobacco and fruits. All these crops can be used as multi-functional crops for bionergy.

Syria’s wastewater treatment plants and landfills are potential resources for biogas and landfill gas. Wastewater from the main cities equals 1,154,000 m3 per day with 85 % of the contribution from five cities, Damascus, Aleppo, Homs, Hama and Lattakia. On a national scale, waste amounts to between 3.6 and 4.1 million tonnes/year. The proportion of organic waste which decomposes to methane in landfills is about 60 %. Landfills currently passively vent the methane gas into the atmosphere. There are projects in progress to collect and flare this gas so that the harmful emissions are reduced from methane to carbon dioxide. But an even better option is to generate electricity from methane. Homs is the only city which collects the gas but it still does not generate electricity from it. The cities of Aleppo, Damascus, Homs and Hama present good prospects for waste-to-energy plants in Syria.

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