Sources of Biogas

Renewable Energy Sources | Biogas | Sources of biogas

Biogas can be obtained from disparate starting materials with slight differences in the preparation and production. The basic prerequisites to any waste material could be used economically as a raw material for the production of biogas are:

  • to be available in sufficient quantities throughout the year
  • in composition to the efficient and economical production of biogas
  • if it did not have toxic substances.


We distinguish several types of biogas from raw materials for its production: landfill biogas biogas from agriculture production, biogas from wood waste and biogas waste water from industry and cities.


         Landfill gas

In industrialized countries it is produced 300-400 kg of waste per person per year. This garbage is collected and disposed of in safe sanitary landfills, which include the protection of ground water and air protection from dirty and dangerous landfill gas, by putting the cover over the storage of waste. The aforementioned landfill gas is generated by decomposition of organic matter under the influence of micro-organisms under anaerobic conditions. At the heart of waste generated overpressure, and landfill gas passes into the environment. The average composition of landfill gas is 35-60% methane, 37-50% carbon dioxide and small amounts are found carbon monoxide, nitrogen, hydrogen sulfide, fluoride, chlorine, aromatic hydrocarbons, and other trace gases.

Based on this composition of landfill gas, it can be seen that it is very dangerous for the environment, for the health of living organisms, and the infrastructure facilities in the vicinity of landfills, because the methane in certain conditions is very explosive. Methane is over 20 times more harmful to the climate and the ozone layer than carbon dioxide, which means that 1 tonne of methane ozone depleting refrigerants (greenhouse effect) as 21 tons of carbon dioxide. The average time of reaction for methane with ozone is on the order of 25 years and the carbon dioxide reaches the order of 80 years, which also greatly affects the methane is approximately 21 times more harmful to the ozone layer than CO2, and primarily the reason, you need 3 ozone molecule O3 to turn methane into carbon dioxide CO2.

In order to remove the negative effects of uncontrolled proliferation of landfill gas, collection is carried out planned and forcibly directing gas to the place of burning. This process favors the rapid stabilization of the fresh parts of the landfill, reducing the pollution of wastewater. Landfill gas can use energy in processes of heating, hot water, or electricity production.

The legal obligation of collecting and burning landfill gas arises as countries makes pollution effect measurements done by CH4. Usage of biogas can be: burning gas for energy purposes while creating economic benefits. This concept involves placing vertical perforated pipes in the landfill body (wells, pins, probes) and their horizontal connection. Over a compressor plant, landfill gas is sucked out, compressed, dried and directed to the gas engine – CHP engine. For security reasons it is advisable to install a high-temperature flares, which takes excess product gas.

Image displays system for collecting landfill gas, 1 landfill cover 2 vertical perforated tubes for collection of biogas, 3 drainage of excess liquid and biogas, 4 biogas extraction system, 5 biogas filtration, 6 burn excess biogas, 7 CHP - cogeneration biogas 8.transformator, 9 heating system

As a starting value for the calculation of the energy balance is used to figure per ton of municipal waste generated in the period of 20 years, the average 200Nm3 (at p = 1.013 105 Pa and at t = 0°C) of landfill gas. For an annual output of 50,000 tons of municipal solid waste (a city of 150,000 inhabitants), and charging time of 20 landfills, the landfill would be created by 200 million cubic meters of landfill gas. If the gas collection system and control of the quality of available gas engines power output about 50% of entire landfill gas mix is CH4 that can be energy usable. It would mean that for the calculation of the energy balance it is generated about 100 million Nm3 of landfill gas, or approximately 5 million Nm3 per year or 625 Nm3/h. This amount of gas with has power output of Hu = 5kWh/Nm3 through CHP - cogeneration module provides an annual production of 9 million kWh of electricity and 12 million kWh of heat. This is the amount of electricity that covers the needs of 2500 family homes. With the production of electricity, saves in a lignite-fired power plant about 18,000 tons of lignite per year. In this way, about of 300Nm3/h, or about 215 kg/h of methane contained in landfill gas is not released in the atmosphere, which is a very important aspect of the application of gas engine in the preservation of the ozone layer.


               Biogas - synthetic gas from wood biomass

Gasification of waste wood can solve a significant environmental problem of contamination of the soil, waterways and air, which usually appear on the landfill of waste from sawmills, wood processing industry, paper industry, forest – forest cutting residues and agricultural solid waste.

Gasification of waste wood can solve large environmental problems and has important economic feature, as it enables the utilization of the energy potential contained in the waste wood for combined heat and power. In this way, the energy potential of the old and waste wood can be used to make combustible gas to consumers. Customers separate wood biomass from other forms of waste, and produced gas is transported to consumers of energy or electricity is then sold to electric distribution network, and then to consumers (industry, residential areas, tourist resorts)

For each kilogram of dry wood matter or pulp, can produce about 2Nm3 of synthetic gas with energy value of 1.6 to 2.4kWh/Nm3. Prepared wood pulp is fed into the reactor, where the process of drying, thermal decomposition, reduction, oxidation and gasification is undergoing. The result is a degradation of long organic molecules such as, CHmOn and create molecules C, CO, CO2, H2 and CH4. Gas phase leaving the reactor, a solid (slag, ash, coal), depending on the composition, is used as a raw material in agriculture as a part of fertilizer in mixure of compost.

The produced synthetic gas is prepared (cooling, condensation and soot removal, filtering), stored or direct implemented to the cogeneration plant – CHP module or turbine system, producing electricity and heat energy. The energy produced is used for internal purposes or sold to the electric power grid, or heating system. The proposed process of working with wood biomass gasification in the system is a complex process and more expensive compared to thermogeneration process of raw wood biomass in cogeneration, especially if the technology allows combustion in raw form or up to 60% of moisture, compared with the production of methane from agricultural waste is also expensive and not well researched. The leader in development of this technology, is the Institute of Agricultural Sciences in Munich.

Image - principle of production technology of synthetic gas from biomass, which is one of the products that can burn, methane


                 Biogas from waste water

At the water treatment plant from the anaerobic sludge stabilization, this separated sludge can produce biogas, which is a very interesting source of energy. It is considered to be very effective to build additional biogas plant for sludge, since harmfull waste is used to generate heat and electric power and lower the levels of pollutans. The efficiency of biogas production is ensured by maintaining temperature (about 35°C), pH, stirring and removing oxygen and toxic substances. In anaerobic reactors - biogas digesters occurs as a mixture of combustible and non-combustible gases with average composition of: 55-75% methane, carbon dioxide, 25-45%, and other gases, such as hydrogen, oxygen, carbon monoxide, nitrogen, hydrogen sulfide ammonia and water vapor.


        Agricultural biogas

Agricultural biogas is produced from waste - the leftovers in agricultural production. The raw material used is liquid manure from livestock production, plant residues from agriculture and any type of biomass, which is connected with carbon materials, and that also have increased the percentage of humidity. It is possible to grow energy plantations for biomass to be used as silage for biogas systems, if some part of growing plant can be used for other purposes. Otherwise, it is considered more appropriate to use biomass above of 25% moisture content in the production of biogas. In livestock raising substantial amounts of liquid manure is used for biogas production, and the amount of biogas produced depends on the concentration of dry matter, total organic matter and the presence of nutrients needed for the growth of microorganisms in manure, and plant construction is being carried out in an anaerobic fermentation. According to estimates, the world each year receives about 5 billion tons of biomass waste can be used as raw materials. According to expert analysis of the potential of biomass in the Republic of Serbia, of every year is 12.5 million tonnes of biomass, and in Autonomous Province of Vojvodina about 9 million tons of biomass, where 25% of the biomass is cinsidareble to be suitable for use for the production of biogas or about 2:25 million tons of biomass, which is enough to run the biogas production capacity of 300MW. According to the classification of biomass that could be used for biogas production, and that in agriculture we can make the following division:

  • biomass obtained from silage, or surpluses in agricultural production,
  • biomass is obtained from secondary agricultural production - Food Industryliquid manure from livestock manure and faeces of animals
    • remnants of the meat industry - biodegradable confiscates blood, flesh, skin
    • some remains from the secondary fine meat industry meat products
    • industry pasta
    • juice production - rotten fruit juice that is long, the excess carbohydrates in juice production - unrefined fructose
    • production of alcoholic beverages - nearly all remains in production, especially suitable manufacturing processes for the production of beer
  • rendering houses confiscate (deat animals, meat, animal waste) - waste that may be even biohazard, because the process of anaerobic digestion and eliminate pathogens.

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