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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Biogas from landfills. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Alternative energy sources Over the past decades, the amount of municipal solid waste (MSW) has increased significantly. Approximately 400 million tons of MSW enter the biosphere every year, and this amount increases by 3-6% annually, which exceeds the rate of increase in the world's population. A significant amount of MSW is food waste, paper, cardboard, wood. Part of the organic fractions of MSW ranges from 56% in developed countries to 62% in developing countries. In world practice, there are three main ways to dispose of solid waste:
In some developed countries, especially those with a high population density (Switzerland, Japan, etc.), MSW and even sewage sludge are predominantly burned. MSW incineration requires the use of complex and expensive technologies for cleaning combustion products from heavy metals and harmful gases. The problem of cleaning flue gases from dioxins has not yet been solved in any country. Most likely, composting will not be used for a long time, since the problem of cleaning compost from salts of heavy metals, the migration of which into fertile soil is unacceptable, has not been solved. Currently, in many countries of the world, MSW disposal at special landfills is considered the most economical way to dispose of them. The amount of solid waste that is taken to landfills or landfills is 45-55% in the Netherlands, 62-85% in the USA, 93-96% in Canada, and 97% in Russia. Extraction and utilization of biogas from solid waste landfills in different countries Biogas is formed in MSW without access to oxygen. Under the action of bacteria, part of organic matter decomposes with the formation of methane (50-70%) and carbon dioxide (30-50%), a mixture of which forms biogas, in addition, it contains small amounts of nitrogen, oxygen and hydrogen. Biogas is combustible and has a high calorific value of more than 18 MJ/m3. The most economically justified is the collection and utilization of biogas at large landfills and landfills, where more than 1 million tons of waste is located, the layer of which exceeds 10 m. It is desirable that most of the waste has an “age” of no more than 10 years. The territory of the landfill must be reclaimed: covered with a layer of soil of at least 30-40 cm. The average yield of biogas from such a landfill will be at least 5 m3 per 1 ton of MSW over 20 years. Of great importance is the proportion of organic matter (construction waste does not generate biogas). The total potential of biogas in the EU reaches 9 billion m3/year, in the USA - up to 13 billion m3/year. With the utilization of methane from all MSW landfills in the United States, its amount will be 5% of the total natural gas consumption in the country. In 1992, 481 biogas collection systems were in operation worldwide (175 in the EU countries, 264 in America, 4 each in Asia and Australia, and 2 in Africa). But it should be noted that about 25-50% of biogas was used for commercial purposes, the rest burned in flares. Biogas is one of the main greenhouse gases According to the degree of harm to the environment, methane is considered the second harmful gas after carbon dioxide. The concentration of methane in the atmosphere is growing at about 0,6% annually and has doubled over the past two centuries (the concentration of carbon dioxide is growing annually by 0,4%). Methane has a shorter "life" in the atmosphere (11 years), while carbon dioxide has 120 years. Therefore, stabilization or reduction of methane emissions into the atmosphere will lead to rapid positive climate change. The global release of methane into the atmosphere is an important factor in climate change. In the United States, a law has been enacted that obliges all solid waste landfills, without exception, to be equipped with systems for the extraction and utilization of biogas. Back in 1987, it was determined that the total methane emission from the Earth's landfills is 30-70 million tons per year, or 6-18% of its total emission into the atmosphere. The expert group of the Intergovernmental Commission on Climate Change has included landfill methane in the list of the world's main greenhouse gases. The spread of biogas in the environment causes a chain of negative phenomena. Its accumulation can create explosive and fire hazardous conditions in houses and structures that are located near solid waste dumps. The accumulation of biogas in a closed space is also dangerous from the toxicological point of view. Many cases of poisoning have been registered during the maintenance of deep engineering communications. Biogas also has a detrimental effect on the plant layer ("suffocating" the root system). All this indicates the need to combat its emissions into the atmosphere. The main method by which this can be done is the collection and utilization of biogas. Technologies for the collection / production of biogas at landfills The most common biogas collection system consists of a network of vertical wells connected by horizontal pipes. In the middle of a vertical well with a diameter of 0,6-1,2 m, a plastic pipe with a diameter of 12-25 cm is installed, perforated with holes with a diameter of 3-6 mm. The depth of the well is at least 7 m and corresponds to 50-90% of the thickness of the MSW layer. The well volume around the perforated plastic pipe is filled with gravel or pebbles. The upper part of the well (approximately 0,5 m from the top edge) is compacted with concrete or clay in order to eliminate the release of biogas into the atmosphere. The range of a well is 30-35 m on average. The average number of wells is 2,5 per 1 hectare of the landfill. The construction of a gas drainage system can be carried out both throughout the landfill after the end of its operation, and in separate areas as it is filled. The figure shows a schematic diagram of the production, collection and utilization of biogas. Technologies of utilization/use of biogas There are two main ways to use biogas: using it to generate heat at the production site, and generating electricity and selling it to the grid. The direct use of biogas within a radius of 3 km from the landfill is usually the most cost-effective way to use it. The gas can be used as fuel for boilers in the district heating network, various industrial consumers (cement production, glass production, brick drying). If consumers are further than 3 km, then profitability drops. Feasibility study and prospects for the development of technologies for the production and use of biogas in Ukraine The cities of Ukraine alone generate about 40 million m3/year of MSW. More than 90% of this amount is collected and removed to 655 landfills located 10-20 km from cities. More than 500 landfills in Ukraine do not have basic means of protection against groundwater and air pollution. About 140 landfills are MSW landfills that can be considered suitable for the extraction and use of biogas. Of the 140 landfills, 90 are very large, they contain 30% of all solid waste in Ukraine. It is these landfills that are the most profitable for gas production. The introduction of a biogas collection and utilization system at these 90 landfills will lead to a reduction in carbon dioxide emissions by 3,26 million tons per year. With rather low tariffs for electricity in the domestic market of Ukraine, it is most cost-effective to use biogas for the needs of industrial enterprises located near landfills. If this is not possible, then it is rational to generate electricity in the network. In this case, power plants based on Ukrainian-made internal combustion engines with a capacity of 1 and 1,6 MW (GP Plant named after Malyshev, Kharkov) or 0,40,8 MW (Pervomaiskdizelmash, Pervomaisk) can be used. The table shows a feasibility study for the project for the extraction and use of biogas for electricity generation at the Lugansk landfill, where 1,6 million tons of solid waste is located. Two variants of equipment for a 2 MW biogas mini-power plant with engines manufactured by Pervomaiskdieselmash and American-made Caterpillar engines are considered. The calculations used such parameters as the annual biogas yield of 5 m3/t of waste and the life of the plant - 20 years.
The cost of electricity in both cases is lower than the wholesale cost of electricity in Ukraine ($0,021 per 1 kWh). The above economic calculations do not take into account the potential for "selling" the carbon emissions reduced by this project. The amount of reduced greenhouse gas emissions will be "purchased" at a price of 4,5 to 9 EUR per 1 ton. Due to this, the economic performance of bioenergy projects can significantly improve. The first step for the dissemination of technologies for the production and use of biogas in Ukraine is the implementation of at least one demonstration project, the purpose of which is to show the technical capabilities, economic and technological feasibility of using such technologies. Conclusions: 1. Currently, the disposal of solid waste in landfills and landfills remains the main method of their neutralization in most countries of the world. 2. Emission of methane in landfills is estimated at 6-18% of its total emissions into the atmosphere. The most effective way to reduce methane emissions is to capture and use it. 3. The energy potential of biogas in most countries is about 1% of energy consumption. 4. In most countries, the production and use of biogas is increasing. 5. Projects for the extraction and use of biogas are quite cost-effective, especially if there is an industrial gas consumer nearby. 6. The introduction of technologies for the extraction and use of biogas is very promising in Ukraine, both from an environmental and economic point of view. 7. It makes sense to finance at least one demonstration project for the production and use of biogas in Ukraine from the state budget or the budget of the Ministry of Ecology. Authors: G. Geletukha, K. Kopeikin, Institute of Technical Thermal Physics of the National Academy of Sciences of Ukraine, Scientific and Technical Center "Biomass"
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