Fundamentals of biogas technologies. Encyclopedia of radio electronics and electrical engineering

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What is a biogas plant?

A biogas plant, as a rule, is a hermetically sealed container in which, at a certain temperature, the organic mass of waste, wastewater, etc. is fermented. with the production of biogas.

The principle of operation of all biogas plants is the same: after collecting and preparing raw materials, which consists in bringing it to the desired moisture content in a special container, it is fed into the reactor, where conditions are created to optimize the processing of raw materials.

The process of obtaining biogas and biofertilizer from raw materials is called fermentation or fermentation. Fermentation of raw materials is carried out due to the vital activity of special bacteria. During fermentation, a crust appears on the surface of the raw material, which must be destroyed by mixing the raw material. Mixing is carried out manually or with the help of special devices inside the reactor and promotes the release of the resulting biogas from the feedstock.

The resulting biogas, after cleaning, is collected and stored until the time of use in the gas tank. From the gas tank to the place of use in household or other appliances, biogas is carried out through gas pipes. The raw materials processed in the reactor of the biogas plant, turned into biofertilizers, are unloaded through the unloading opening and applied to the soil or used as a feed additive for animals.

Fig.1. Scheme for the processing of organic waste at biogas plants

Optimization of the processing of raw materials

The conditions necessary for the processing of organic waste inside the reactor of a biogas plant, in addition to observing an oxygen-free regime, include:

• Compliance with the temperature regime;
• Availability of nutrients for bacteria;
• Choosing the right fermentation time and timely loading and unloading of raw materials;
• Compliance with acid-base balance;
• Compliance with the ratio of carbon and nitrogen;
• The correct proportion of solids in the raw material and mixing;
• No process inhibitors.

Types of biogas plants

There are many different designs of biogas plants. They are distinguished by the method of loading raw materials, by their appearance and by the components of the structure and the materials from which they are constructed.

According to the method of loading raw materials, installations of batch and continuous loading are distinguished, which differ in the time of fermentation and the regularity of loading raw materials. The most efficient in terms of biogas production and biofertilizer production are continuous loading plants.

In terms of appearance, the installations differ depending on the method of accumulation and storage of biogas. The gas can be collected in the upper solid part of the reactor, under a flexible dome, or in a special gas holder, floating or standing separately from the reactor.

Benefits of using biogas technologies

A well-functioning biogas plant brings a number of benefits to its owner, society and the environment in general:

Saving money:

• Save money previously spent on fuel and electricity.
• Money spent on the purchase of fertilizers and herbicides is saved.

Possibility of getting extra money:

• You can sell biogas and biofertilizers.
• You get extra money when you increase the yield of your crops through the use of biofertilizers.
• You get extra money when raising animals and poultry through feed additives made from recycled raw materials.

Fast payback of installations:

• A biogas plant with raw material heating of any capacity pays off in about a year of operation.
• The risk of respiratory and eye diseases is reduced by cleaning the air as a result of reducing the amount of organic waste in places where they are stored.
• The epidemiological situation is improving as a result of the death of some of the microorganisms contained in the waste in the bioreactor.
• Health is improved by obtaining environmentally friendly agricultural products using environmentally friendly fertilizers.

Saving time, space and women's labor:

• Saves time spent on oven maintenance compared to ovens using coal, wood, etc.
• The time spent earlier on collecting, transporting, drying fuel and the space occupied by fuel - dung, coal, firewood, etc. is saved.
• When using biofertilizers, time is saved when weeding weeds introduced with ordinary manure, as their seeds die during the fermentation process in the reactor of a biogas plant.

Environmental benefits:

• Reduced emissions of methane (greenhouse gas) from outdoor storage of manure.
• Reducing carbon dioxide emissions and products of combustion of coal, firewood and other fuels.
• Reducing air pollution by nitrogenous compounds that have an unpleasant odor.
• Reducing pollution of water resources by manure.
• Preservation of forests from deforestation.
• Reducing the use of chemical fertilizers.

More about biogas

Biogas is formed by bacteria during the decomposition of organic material under anaerobic (without air access) conditions and is a mixture of methane and other gases in the following proportions:

Table 1. Composition of biogas

The calorific value of one cubic meter of biogas, depending on the methane content, is 20-2S MJ/m3, which is equivalent to burning 0,6 - 0,8 liters of gasoline; 1,3 - 1,7 kg of firewood or use 5 - 7 kW of electricity'3.

Biological fermentation process

During the fermentation of raw materials in biogas plants, methane-producing bacteria decompose organic matter and return the decomposition products in the form of biogas and other components to the environment. Knowledge of the digestion process is essential for the design, construction and operation of biogas plants.

Composition of feedstock and biogas production

In principle, all organic substances are subject to fermentation and decomposition processes. However, in simple biogas plants, it is preferable to process only homogeneous and liquid organic waste: excrement and urine of livestock, pigs and birds, human feces.

In more complex biogas plants, it is possible to process other types of organic waste - plant residues and solid waste. The amount of biogas produced depends on the type of feedstock used and the temperature of the digestion process.

Use of biogas

Fig.2. The effect of the use of biofertilizers on the growth of wheat Photo: Vedenev A.G., OF "Fluid"

Biogas can be used in any gas appliances, just like natural gas is used. The most efficient use of biogas is for cooking, space heating, power generation and vehicle fueling.

About biofertilizers

In Kyrgyzstan, as in many other developing countries, there is a direct link between the problem of fertilizers and land degradation, as well as the problem of deforestation due to the high demand for firewood. In rural areas, dried manure (dung) and organic waste are often burned for cooking and heating of dwellings.

This use of organic waste causes a significant loss of plant nutrients, which agriculture needs so much to maintain soil fertility. The use of biogas technologies will ensure the maximum use of the resources available to the rural population: the biosludge remaining after the production of biogas is an effective fertilizer that improves the overall quality of the land and increases productivity.

Features of biofertilizers

The bio-fertilizer contains a number of organic substances that contribute to increasing the permeability and hygroscopicity of the soil, while at the same time preventing erosion and improving general soil conditions. Organic matter is also the basis for the development of microorganisms that convert nutrients into a form that can be easily absorbed by plants. Practice shows that the yield of plants with the use of biofertilizers is significantly increased.

History of the development of biogas technologies

Individual cases of using primitive biogas technologies have been recorded in China, India, Assyria and Persia, starting from the 3,5th century BC. However, systematic scientific research on biogas began only in the XNUMXth century AD, after almost XNUMX thousand years.

Fig.3. The simplest Chinese installation. Source: Y. Kalmykova, A. German, V. Zhirkov "Project Biogas", Karaganda Ecological Museum, 2005

In 1764, Benjamin Franklin, in his letter to Joseph Priestley, described an experiment in which he was able to set fire to the surface of a shallow swampy lake in New Jersey, USA.

The first scientific justification for the formation of flammable gases in swamps and lake sediments was given by Alexander Volta in 1776, establishing the presence of methane in swamp gas. After the discovery of the chemical formula of methane by Dalton in 1804, European scientists took the first steps in research into the practical application of biogas.

Russian scientists also made their contribution to the study of biogas formation. The effect of temperature on the amount of gas released was studied by Popov in 1875. He found that river sediments begin to release biogas at temperatures around 6°C. With an increase in temperature to 50°C, the amount of gas released increased significantly, without changing in composition - 65% methane, 30% carbon dioxide, 1% hydrogen sulfide and a small amount of nitrogen, oxygen, hydrogen and carbon monoxide. V.L. Omelyansky studied in detail the nature of anaerobic fermentation and the bacteria involved in it.

Shortly thereafter, in 1881, European scientists began experimenting with the use of biogas for space heating and street lighting. Beginning in 1895, street lamps in one of the districts of Exeter were supplied with gas, which was obtained as a result of the fermentation of sewage and collected in closed containers. Two years later, there was a report of biogas production in Bombay, where the gas was collected in a collector and used as motor fuel in various engines.

At the beginning of the 1914th century, research was continued in the field of increasing the amount of biogas by increasing the fermentation temperature. German scientists Imhoff and Blank in 1921-XNUMX. patented a number of innovations, which consisted in the introduction of constant heating of containers. During the First World War, the spread of biogas plants in Europe began, associated with a shortage of fuel. Farms with such installations were in more favorable conditions, although the installations were still imperfect and they used far from optimal modes.

One of the most important scientific steps in the history of the development of biogas technologies is Buswell's successful experiments on combining various types of organic waste with manure as a raw material in the 30s of the XX century.

The first large-scale biogas plant was built in 1911 in the English city of Birmingham and was used to disinfect the city's sewage sludge. The biogas produced was used to generate electricity. Thus, British scientists are pioneers in the practical application of the new technology. Already by 1920 they had developed several types of sewage treatment plants. The first 10 m3 solid waste biogas plant was designed by Isman and Ducelier and built in Algiers in 1938.

During the Second World War, when energy resources were sorely lacking, in Germany and France, emphasis was placed on obtaining biogas from agricultural waste, mainly animal manure. In France, by the mid-40s, about 2 biogas plants for manure processing were in operation. Quite naturally, this experience spread to neighboring countries. In Hungary there were factories for the production of biogas. This is noted by soldiers of the Soviet Army, mostly from rural areas of the USSR, who liberated Hungary from German troops and were surprised that in peasant farms, cattle manure did not lie in heaps, but was loaded into closed containers, from where combustible gas was obtained.

European installations of the pre-war period could not withstand the competition in the post-war period from cheap energy sources (liquid fuel, natural gas, electricity) and were dismantled. A new impetus for their development on a new basis was the energy crisis of the 70s, when the spontaneous introduction of biogas plants began in the countries of Southeast Asia. High population density and intensive use of all areas of land suitable for cultivation of crops, as well as a sufficiently warm climate necessary for the use of biogas plants in the simplest version without artificial heating of raw materials formed the basis of various national and international programs for the introduction of biogas technologies.

Today, biogas technologies have become the standard for wastewater treatment and processing of agricultural and solid waste and are used in most countries of the world.

The developed countries

In most developed countries, the processing of organic waste in biogas plants is more often used for the production of heat and electricity. The energy produced in this way is about 3-4% of all energy consumed in European countries. In Finland, Sweden and Austria, which encourage the use of biomass energy at the state level, the share of biomass energy reaches 15-20% of all energy consumed.

The use of electricity and heat produced by anaerobic processing of biomass in Europe is concentrated mainly in Austria, Finland, Germany, Denmark and the UK. There are currently around 2000 large anaerobic digestion plants in Germany. The number of biogas plants with reactor volumes over 2000 m3 each in Austria is currently over 120, with about 25 plants under planning and construction.

Figure 4 shows an industrial plant in the town of Ribe, which annually processes 164 thousand tons of biomass and produces 5.5 million m3 of biogas, which is sold to the neighboring town's CHP plant for heating and electricity generation. Manure is supplied daily by farmers who act on the basis of a contract and are interested in receiving already processed manure in the form of biofertilizers.

A high degree of market development for biogas technologies can be found in the areas of municipal wastewater disposal, industrial wastewater treatment and agricultural waste disposal. In Sweden, biomass energy provides 50% of the required thermal energy. In England, in the homeland of the first industrial biogas reactor, with the help of biogas as early as 1990, it was possible to cover all energy costs in agriculture. London has one of the largest domestic wastewater treatment plants in the world.

Fig.4. Industrial biogas plant in Denmark. Photo: A. Sharsheeva, 2010

In the 30s, the experience of Europe was transferred to the USA. The biogas plant for the processing of livestock waste was built in 1939 and has been operating successfully for more than 30 years. In 1954, the first plant for the processing of municipal waste with biogas production was built in Fort Dodge, Iowa, USA. Biogas was fed to an internal combustion engine to generate electricity at a power generator of 175 kW. There are now several hundred large biogas plants in the United States processing animal waste and thousands of plants utilizing municipal wastewater. Biogas is mainly used to generate electricity, house heating and greenhouses.

Rising greenhouse gas emissions, increased water use and pollution, declining land fertility, inefficient waste management and growing deforestation problems are all part of an unsustainable system of natural resource use around the world. Biogas technologies are one of the important components in the chain of measures to combat the above problems. The growth forecast for the contribution of biomass as a source of renewable energy in the world assumes reaching 23,8% of total energy consumption by 2040, and by 2010 the EU countries plan to increase this contribution to 12%.

Fig.5. Balloon plant in Côte d'Ivoire. Source: AT Information: Biogas, GTZ (ISAT), Eshborn, Deutschland, 1996

Developing countries

The share of energy derived from biomass in developing countries is about 30-40% of all energy consumed, and in some countries (mainly in Africa) reaches 90%24.

Among developing countries, it is common to produce energy and heat through the processing of waste in small biogas plants. About 16 million households around the world use energy for lighting, heating and cooking produced in biogas plants. This includes 12 million farms in China, 3,7 million farms in India and 140 farms in Nepal.

In rural China, more than 50 million people currently use biogas as fuel. A typical biogas plant has a reactor volume of about 6-8 m3, produces 300 m3 of biogas per year, runs for 3 to 8 months annually, and costs about $200-250, depending on the province. Most of the plants are very simple and after some training the farmers build and operate the plants themselves. Since 2002, the Chinese government has provided about $200 million annually to support the construction of biogas plants. The subsidy for each installation is approximately 50% of the average cost. Thus, the government has achieved an annual increase in the number of biogas plants to 1 million per year. Several thousand medium and large installations are operating on an industrial basis in China, and it is planned to increase their number.

In India, the development of simple biogas plants for rural homesteads began in the 50s. To date, there are about 3,7 million biogas plants operating in India. The Ministry of Unconventional Energy Sources of India has been implementing biogas plants since the 1980s and has provided subsidies and funding for the construction and operation of biogas plants, farmer training, and the opening and operation of service centers.

Gasification and thermal energy production from biogas plants is a growing industry in many developing countries. In the Philippines, biogas plants have been producing gas to power motors that grind rice and run irrigation since the 1980s. The use of biogas by small commercial companies in India, Indonesia, Sri Lanka (for example, in the textile industry or for drying spices, bricks, rubber) paid off in less than a season.

USSR, CIS and Kyrgyzstan

In the USSR, the scientific foundations of methane fermentation have been studied since the 40s. Throughout the existence of the USSR, institutes of the system of the Academy of Sciences participated in theoretical research, and applied research was carried out at the Academy of Public Utilities. Panfilov and agricultural research and design institutes, such as: the All-Union Institute of Electrification of Agriculture (VIESH), the Ukrainian Research and Design Institute of the Agro-Industrial Complex (UkrNIIgiproselkhoz) and others.

The main center for the development of designs for domestic biogas plants (as well as other machines for processing agricultural waste) was the Zaporozhye Design and Technological Institute of Agricultural Engineering (KTISM). The data collected by scientists formed the basis for the creation of several laboratory and pilot installations, however, only one design, KOBOS-1, was allowed to the state acceptance tests.

The KOBOS-1 unit was successfully tested on the basis of an experimental dairy farm-laboratory and approved for serial production at a plant in the city of Shumikha, Kurgan Region (Northern Urals). It was built according to the program for mastering the technology of anaerobic waste processing as a variant of serial installations for medium-sized livestock farms - dairy farms for 400 dairy cows or medium-sized pig farms for 4000 pigs.

The plant produced 10 sets of equipment, but after the collapse of the USSR, funding ceased. Of the 10 units produced, three were distributed in Ukraine and Belarus, five were sent to Central Asia (two of which were sent to Kyrgyzstan), and two were sent to Russia. But only 1 of them was introduced - on a cattle farm in the Kamenetsky district of the Brest region of Belarus. The plant processes 50 m3. manure and produces 400...500 m3 of biogas per day.

Rice. 6. Installation in LLC BEKPR. Photo: Vedenev A.G. OF "Fluid"

One of the installations that came to Kyrgyzstan was re-equipped by the Fluid PF of the Farmer Association and installed on the basis of the BEKPR OsOO pig farm for 4000 heads, in the village of Lebedinovka, Chui region in 2003, the other is used as a water collector in the private sector of the Osh region.

Authors: Vedenev A.G., Vedeneva T.A.

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