Biogas- Natural Energy

Biogas is formed when microorganisms, primarily bacteria, break down organic matter in the absence of the oxygen of the air. This biological transformation of plant and animal residues occurs naturally in many ecosystems where the oxygen supply is limited, for example in wetlands, sea sediments, rice cultivations and in the stomach of ruminants. In today's society, large amounts of organic waste are produced that need to be treated in one way or another before being returned to the natural cycle. Organic waste can, for example, be sludge from sewage treatment plants, food waste from households, catering kitchens, shops and restaurants, process water from the food industry and more. In a biogas process, the natural ability of microorganisms to break down such material into a nutritious end product which can be used as a fertilizer is utilized. At the same time, biogas is formed, whose main constituent of methane is very energy-rich. Man has for a long time been able to utilize the energy in this gas for various purposes. One common area of application is heat and electricity production. The biogas can also be purified to vehicle fuel and then constitutes a very environmentally friendly alternative to diesel and gasoline. This writing is mainly about how biogas can be produced and used under controlled conditions. At the same time, it should be remembered that the formation of biogas in the natural systems is considerably greater than that which we humans intentionally achieve.

Man has utilized the ability of bacteria
to convert organic material into biogas
ever since the second half of the 19th century.
The pioneers include China
and India, where biogas is formed from manure and
leftovers have long been used for cooking and lighting.
In Sweden, biogas has been produced in the country
sewage treatment plant since the 1960s. From
The beginning was primarily to reduce the sludge volumes. The two oil crises of the 1970s came
however, to act as an alarm clock and
stimulated both research and development
as direct extensions of biogas processes. The purpose was now to reduce oil dependency
and environmental problems.
First in this development was the industry,
where sugar consumption and pulp mills began
use the biogas process to purify
process water in the 1970s and 1980s.
During the same period, a number were also built
small farms on agriculture for
digestion of manure.
In the 1980s, many places began
in the country extract biogas from landfills,
a business that greatly increased in scope during the 1990s. Then the middle of
The 1990s have many new biogas plants
which deals with various organic materials
built. In these, waste is digested for example
food industries and slaughterhouses and food waste from households, catering and restaurants.

Depending on the production conditions biogas consists of 45-85% methane (CH4 ) and 15-45% carbon dioxide (CO2 ). In addition, hydrogen sulphide (H2 S) ammonia (NH3 ) and nitrogen (N2 ) in small amounts. The biogas is usually saturated with steam. Methane made from artificial road, for example from wood fuel through such called thermal gasification, is sometimes called incorrectly for biogas. This is also renewable methane, but not treated in this publication. The amount or volume of biogas is usually indicated in the unit normal cubic meters (Nm3 ). By this is meant the volume of gas at 0 ° C and atmospheric pressure. The energy value of the gas is usually expressed in the joule unit (J) or watt hour (Wh). Pure methane has an energy value of 9.81 kWh / Nm3  (9810 Wh / Nm3 ). Depending on the distribution between methane, carbon dioxide and other gases vary widely the biogas energy value between 4.5 and 8.5 kWh / Nm3 . Both methane and carbon dioxide are odorless gases. If raw biogas smells it is usually due of its contents of various sulfur compounds. Biogas can ignite at concentrations of about 5-20% in air, depending on the current methane concentration. Methane is easier than that air while carbon dioxide is heavier. This is beneficial from a safety point of view, because methane easily rises up and quickly dilutes out into the air.

Substrates used in biogas processes can have very different properties, to examples of water content. municipal and industrial wastewater have the character of liquids with dry matter content, that is say an "anhydrous" portion, below 5%, while sludge material such as sewage sludge, fl fertilizer and effluent waste mixtures have dry matter contents between 5 and 15%. Household waste and plant material are included solids with dry matter contents above 20-25%. The composition of the biogas varies considerably depending on which material digested, but the choice of process technology, temperature, mode of operation, gas collection system also plays more. CO-DIGESTION GIVE MORE METAN The biogas extracted from wastewater, agricultural crops, manure and more are called sometimes for raw gas, while the gas being formed in landfill sites is usually called landfill gas. The methane content is generally higher in raw gas, which is partly because it is formed during more controlled forms in a digester, partly that the landfill gas is supplied with some air when it is sucked out of the landfill using fans. For raw gas, gas is also distinguished from gas from co-digesting substrate and gas from digestion only sewage sludge. Coincidence means that Many substrates are digested together in a process, eg household waste sorted by source or slaughterhouse waste together with manure or sewage sludge. This usually results in higher content of methane and hydrogen sulphide than when digging solely from sludge from a sewage treatment plant.

EXPOSURE OF DEPONIGAS In the extraction of landfill gas, vertical perforated gas pipes are usually used, so-called gas wells that are drilled or depressed landfill. Horizontal pipe systems also occur. The gas yield can increase through that leachate from the waste storage is returned to the landfill, so that the organic substance in the leachate can be converted into gas. Traditional landfill gas extraction is a slow process which from mixed waste can last for 50 years or more. In a well-functioning biocell, it wants to say where the material is posted on such way that the anaerobic digestion can optimized for temperature, moisture content etc., the treatment can be completed within a five-year period. The most common use of landfill gas is for heating of nearby buildings. If the gas does not If any use is made, it will still be collected and flared away. This is done partly because of it of methane's strong effect as greenhouse gas, partly due to the methane being accumulated the waste warehouse can pose a risk of explosion. The combustion also means a smell reduction. RED OFF AGRICULTURE CROPS There is a great deal of interest in these areas to develop biogas technology so that it gets increased importance for the energy supply. Examples include factors such as the environment and security of supply in this context. The substrate that has a dominant role when talking about the society's biogas potential are cultivated crops of various kinds. In areas that have long been dominated by cereal cultivation without elements of grazing animals and hay crops can have a lower organic content materials give a deteriorated soil structure with reduced crop yield as a result. To Let some of the cultivated crop go into one biogas process and from there get a digestive residue which turns into mold and nutrients in its own The field can be a way to replace it the livestock manure would otherwise contribute. The biogas process turns into a "mechanical cow" which also produces energy-rich gas as can be used on the farm. If additionally nitrogen-producing crops, such as for example cloverfish or pea plants, included in the crop rotation, this contributes to significant quantities nitrogen can be bound from the air. When these crops are digested, nitrogen remains in the digestate, which can then be used to nitrogen fertilize the soil with relatively good precision.

substrate compilation

Organic material consists mainly of fat, protein and carbohydrate. Anaerobic degradation of pure fat gives greater amount of biogas even when digesting protein or carbohydrate. Purely protein and fat theoretically provide both biogas with about 70% methane and 30% carbon dioxide, while biogas from pure carbohydrate contains about 50% methane and 50% carbon dioxide. If both of these factors are combined - biomass amount and composition - can be obtained complete decomposition of 1 kg fat can give about 0.85 Nm 3  methane, while the equivalent amount of 1 kg protein and carbohydrate is 0.5 and 0.4 Nm 3, respectively  methane. Meat or fiber waste containing relatively much fat and protein, thus giving in theory greater methane amount per kg organic substance than, for example, manure and sewage sludge. However, high protein content causes a significant formation of hydrogen sulphide which is one disadvantage because it is corrosive and toxic. Although fat in theory gives a high methane exchange, it is in practice not appropriate to have too much admixture of high-fat substrates in a biogas process because the microorganisms may have a hard time dealing with this. It is important to add "just right" much substrate of consistent quality because the sensitive cooperation between the micro-organisms can otherwise easily be disturbed and cause technical problems.

The potential for biogas in Sweden is estimated to be up to 17 TWh (17x) 1012 Wh) per year, of which approximately 80% is found in agricultural residues. This should be compared with Sweden's total energy use which is about 400 TWh per year. If the entire estimated potential for biogas is utilized, this corresponds to this is a large part of the total diesel use in Sweden or about 20% of the fuel requirement of the country's passenger cars. However, it is a bit left before we reach this level. The total production of biogas in Sweden today (2003) corresponds to about 1.5 TWh per year. Production is conducted at approximately 140 sewage treatment plants, 60 landfills and, at another ten biogas plants, spread across the country, small-scale facilities not included. Increased expansion of biogas technology is well in line with this the environmental quality goals adopted by the Riksdag and, among other things, limited climate impact, fresh air, just natural acidification and a good built environment is included. The Riksdag has also decided that at least 35% of the food waste from households, catering, restaurants and stores should be recycled by biological treatment by the year 2010. The biogas process can be important in fulfilling EU fuel directive, which aims to equal 2% of sold petrol and diesel be biofuels in 2005. The target for 2010 is 5.75%. The expertise that is now being built up The natural gas and biogas area is also very valuable in the development of technology and infrastructures for the future introduction of hydrogen as an energy carrier.

INTERNATIONAL OUTLOOK

The biogas process is well established in many countries of the world. Above all, it is at the sewage treatment plants which this technology is utilized. Environmental degradation and climate change have led to globalization measures are now being taken to reduce the use of fossil fuels. Security of supply in the energy field for individual countries is not least important in this context. Increased utilization of biogas as fuel can become part of a development that leads away from today's oil dependency while reducing the greenhouse effect. In Europe, an increased interest is felt small-scale biogas production, primarily for digestion of manure at farm level. Germany has invested Big of this, but also in Austria, Denmark and the UK an increased expansion is noticed. In addition to heat production, the production of electricity is an important provision for the formed biogas, and many European countries, like Sweden, have introduced government grants for the sale of "green electricity". Sweden is among the leading countries when it comes to biogas technology and many Swedish companies have delivered complete plants for digestion, upgrading and distribution of biogas. Sweden has also come along with Switzerland the furthest when it comes to utilizing biogas for vehicle operation. This opens for an export of knowledge and technology in the field.