Bioenergy installations. Biomass as a constantly renewable source of fuel. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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Biomass is a term that includes all organic substances of plant and animal origin. Biomass is divided into primary (plants, animals, microorganisms, etc.) and secondary - waste during the processing of primary biomass and waste products of humans and animals. In turn, waste is also divided into primary - waste during the processing of primary biomass (straw, haulm, sawdust, wood chips, alcohol stillage, etc.) and secondary - products of the physiological metabolism of animals and humans.

The annual amount of organic waste in various sectors of the national economy of Russia is more than 390 million tons. Agricultural production produces 250 million tons, of which 150 million tons come from animal husbandry and poultry farming, 100 million tons from crop production. Timber and wood processing produce 700 million tons, municipal solid waste - 60 million tons, municipal wastewater - 10 million tons (all given values ​​are given for absolutely dry matter).

The energy stored in primary and secondary biomass can be converted into technically usable fuels or energy in several ways.

1. Obtaining vegetable hydrocarbons (vegetable oils, high molecular weight fatty acids and their esters, saturated and unsaturated hydrocarbons, etc.). For example, for the southern regions of Russia, this may be rapeseed oil added to diesel fuel.
2. Thermochemical conversion of biomass (solid, up to 60%) into fuel: direct combustion, pyrolysis, gasification, liquefaction, festpyrolysis.
3. Biotechnological conversion of biomass (at a moisture content of 75% or more) into fuel: low-alcohols, fatty acids, biogas.

At the present stage of Russia's economic development, in accordance with the State Scientific and Technical Program "Environmentally Clean Energy", renewable energy is developing in the last two directions.

Thermochemical conversion of biomass

The most active development and creation of equipment for the gasification of solid biomass is being carried out in order to create autonomous heat and power plants operating on generator gas.

On the basis of such gas generators, autonomous installations or stations that do not depend on centralized power supply can be created for heat and power supply to consumers in any regions of the country that have raw materials and are deprived of energy supply. These regions primarily include the regions of Siberia, the Far North, as well as most rural areas that have forestry waste (sawdust, bark, wood chips, tree stumps) and crop production (any straw, sunflower stalks, corn, etc.).

Biotechnological conversion of biomass

In biotechnological conversion, as a rule, biomass is used and, first of all, various organic wastes with a moisture content of at least 75%.

The biological conversion of biomass into fuel and energy is developing in two main directions:

1. fermentation to produce ethanol, lower fatty acids, hydrocarbons, lipids - this direction has long been successfully used in practice;
2. obtaining biogas.

At present, the production of biogas is primarily associated with the processing and disposal of waste from animal husbandry, poultry farming, crop production, the food industry, the alcohol industry, municipal wastewater and precipitation.

According to the developed technology, the main stages of which have been tested under production conditions, liquid manure is pre-treated with coagulants-flocculators to flocculate the bulk of organic substances. The latter are removed by separator centrifuges with a capacity of 25 and 50 m3/h. The resulting paste with a moisture content of 70% is subjected to thermal composting to obtain organic fertilizers (33-35 tons/day). The liquid fraction with a moisture content of 99% is fermented in digesters of the "second generation" with a fixed microflora with a retention time of 5 days. Estimated yield of biogas is 2500 m23/day with a calorific value of 25-3 ​​thousand kJ/m360 (under normal conditions). The fermented mass (370-3 m20) is further cleaned in a system of ponds with a surface area of ​​5 ha. With this technology, the volume of capital investments will decrease by 6-6 times. The surface area of ​​ponds and the withdrawal of land for them will be reduced by XNUMX times. Serious study will be required when creating a "second generation" digester and selecting substrate carriers for fixing the microflora.

The creation of a diversified agricultural production in Russia and the emergence of new owners in the person of farmers and independent peasants required the development, creation and mastering of the production of biogas systems of small capacity and easy to operate.

Under natural conditions, the destruction of any type of biomass, including animal manure, occurs in soil humus by decomposition into elemental compounds under the action of decomposing organisms, fungi, and bacteria. Dampness, heat, and the absence of light are preferred for this process. At the final stage of the process, complete decomposition occurs under the action of a variety of bacteria classified as either aerobic or anaerobic. Aerobic bacteria develop mainly in the presence of oxygen; with their participation, biomass carbon is oxidized to CO₂. Anaerobic bacteria develop in closed volumes with insufficient oxygen supply from the external environment, which also exist due to the decomposition of carbohydrates.

Ultimately, due to their activity, carbon is divided between fully oxidized CO₂ and fully restored CH₄. Nutrients such as soluble nitrogen compounds are retained as soil humus fertilizers. Biomass decomposition reactions performed by microorganisms also refer to fermentation processes, however, for processes taking place under anaerobic conditions, the term "fermentation" ("fermentation") is more often preferred.

Biogas - mixture CH₄ and CO₂, formed in special devices - biogas generators (Fig. 5.1), designed and controlled in such a way as to ensure maximum methane release (in the literature for these devices you can still find the name "methane tank"). The energy obtained by burning biogas can reach from 60 to 90% of the original, which has a dry source material. However, the gas is obtained from a liquid mass containing 95% water, so that in practice the yield is rather difficult to determine. Another and, apparently, a very important advantage of the process is that its waste contains significantly fewer pathogens than the original material. True, we note that not all parasites and pathogenic microorganisms die in the process of anaerobic digestion.

The production of biogas becomes economically justified and preferable when the corresponding biogas generator works on the processing of the existing waste stream. Examples of such streams are wastewater from sewerage systems, pig farms, slaughterhouses, etc. The economy in this case is due to the fact that there is no need for pre-collection of waste, organization and management of the process of their supply. It is known how much and when the waste will arrive, and it remains only to process it into biogas and fertilizers.

Fig.5.1. Varieties of biogas generators (click to enlarge): 1 - material input; 2 - gas pipeline; 3 - removable cover; 4 - output of processed material; 5 - dividing wall; 6 - fermenter; 7 - gas; 8 - receiver; 9 - valve; 10 - mixer; 11 - glass; 12 - container for processed products; 13 - gas generator; 14 - gas supply; 15 - burner; 16 - heat exchanger; 17 - water gas holder

Biogas production is possible in installations of various sizes. It is especially effective in agro-industrial complexes, where it is advisable to achieve the implementation of a complete ecological cycle. In such complexes, manure is subjected to anaerobic digestion followed by aerobic treatment in open pools. Biogas is used for lighting, driving mechanisms, transport, power generators, and for heating. Algae can be grown in pools to feed livestock. After aerobic fermentation, the fully processed waste can be fed to fish tanks and waterfowl ponds before being used as fertilizer.

The success of the implementation of such schemes directly depends on the quality of the system study of the entire project, the degree of standardization of structures, and the regularity of maintenance.

Author: Magomedov A.M.

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