Biogas production takes place in special, corrosion-resistant cylindrical sealed tanks, also called fermenters. In such containers, the fermentation process takes place. But before getting into the fermenter, the raw material is loaded into the receiver tank. Here it is mixed with water until homogeneous, using a special pump. Further, the already prepared raw material is introduced into the fermenters from the receiver tank. It should be noted that the mixing process does not stop and continues until nothing remains in the receiver tank. When empty, the pump stops automatically. After the start of the fermentation process, biogas begins to be released, which enters the gas tank located nearby through special pipes.
Figure 5. Generalized diagram of a biogas plant
Figure 6 shows a diagram of a biogas plant. Organic effluents, usually liquid manure, enter the receiver-heat exchanger 1, where they are heated by heated sludge supplied through the heat exchanger pipe by a pump 9 from the digester 3, and diluted with hot water.
Figure 6. Diagram of a biogas plant
Additional dilution of wastewater with hot water and heating to the desired temperature is carried out in apparatus 2. Field crop waste is also fed here to create the desired C / N ratio. The biogas formed in the digester 3 is partially burned in the water heater 4, and the combustion products are discharged through the pipe 5. The rest of the biogas passes through the purification device 6, is compressed by the compressor 7 and enters the gas tank 8. The sludge from the apparatus 1 enters the heat exchanger 10, where additional cooling heats up cold water. The sludge is a disinfected highly effective natural fertilizer that can replace 3-4 tons of mineral fertilizer such as nitrophoska.
Usually, biogas leaves the reactors unevenly and with low pressure (no more than 5 kPa). This pressure, taking into account the hydraulic losses of the gas transmission network, is not enough for the normal operation of gas-using equipment. In addition, biogas production and consumption peaks do not coincide in time. The simplest solution to eliminate excess biogas is to burn it in a flare plant, however, energy is irretrievably lost. A more expensive, but ultimately economically justified way to equalize the uneven production and consumption of gas is the use of various types of gas tanks. Conventionally, all gas tanks can be divided into "direct" and "indirect". In "direct" gas tanks there is always a certain amount of gas pumped in during periods of decline in consumption and taken off at peak load. "Indirect" gas holders provide for the accumulation of not the gas itself, but the energy of an intermediate coolant (water or air) heated by the combustion products of the combusted gas, i.e. there is an accumulation of thermal energy in the form of a heated coolant.
Biogas, depending on its quantity and direction of subsequent use, can be stored under different pressures, respectively, and gas storages are called gas holders of low (not higher than 5 kPa), medium (from 5 kPa to 0.3 MPa) and high (from 0.3 to 1. 8 MPa) pressure. Low pressure gas holders are designed to store gas at a low fluctuating gas pressure and a significantly changing volume, therefore they are sometimes called gas storage facilities of constant pressure and variable volume (provided by the mobility of the structures). Gas holders of medium and high pressure, on the contrary, are arranged according to the principle of constant volume, but changing pressure. In the practice of using biogas plants, low-pressure gas holders are most often used.
The capacity of high-pressure gas tanks can be different - from a few liters (cylinders) to tens of thousands of cubic meters (stationary gas storages). Storage of biogas in cylinders is used, as a rule, in the case of using gas as a fuel for vehicles. The main advantages of high and medium pressure gas holders are small dimensions with significant volumes of stored gas and the absence of moving parts, and the disadvantage is the need for additional equipment: a compressor unit for creating medium or high pressure and a pressure regulator for reducing gas pressure in front of the burners of gas-using units.
Farms annually face the problem of manure disposal. Considerable funds are wasted, which are required for organizing its removal and burial. But there is a way that allows you not only to save your money, but also to make this natural product serve you for the benefit.
Prudent owners have long been using eco-technology in practice, which makes it possible to obtain biogas from manure and use the result as fuel.
Therefore, in our material we will talk about the technology for producing biogas, we will also talk about how to build a bioenergy plant.
The volume of the reactor is determined based on the daily amount of manure produced on the farm. It is also necessary to take into account the type of raw materials, temperature and fermentation time. In order for the installation to work fully, the container is filled to 85-90% of the volume, at least 10% must remain free for gas to escape.
The process of decomposition of organic matter in a mesophilic plant at an average temperature of 35 degrees lasts from 12 days, after which the fermented residues are removed and the reactor is filled with a new portion of the substrate. Since the waste is diluted with water up to 90% before being sent to the reactor, the amount of liquid must also be taken into account when determining the daily load.
Based on the given indicators, the volume of the reactor will be equal to the daily amount of the prepared substrate (manure with water) multiplied by 12 (time required for biomass decomposition) and increased by 10% (free volume of the container).
Now let's talk about the simplest installation, which allows you to get at the lowest cost. Consider building an underground system. To make it, you need to dig a hole, its base and walls are poured with reinforced expanded clay concrete.
From opposite sides of the chamber, inlet and outlet openings are displayed, where inclined pipes are mounted for supplying the substrate and pumping out the waste mass.
The outlet pipe with a diameter of about 7 cm should be located almost at the very bottom of the bunker, its other end is mounted in a rectangular compensating container into which waste will be pumped out. The pipeline for supplying the substrate is located approximately 50 cm from the bottom and has a diameter of 25-35 cm. The upper part of the pipe enters the raw material receiving compartment.
The reactor must be completely sealed. To exclude the possibility of air ingress, the container must be covered with a layer of bituminous waterproofing.
The upper part of the bunker is a gas holder having a dome or cone shape. It is made of metal sheets or roofing iron. It is also possible to complete the structure with brickwork, which is then upholstered with steel mesh and plastered. On top of the gas tank, you need to make a sealed hatch, remove the gas pipe passing through the water seal and install a valve to relieve gas pressure.
To mix the substrate, the unit can be equipped with a drainage system operating on the bubbling principle. To do this, vertically fasten plastic pipes inside the structure so that their upper edge is above the substrate layer. Poke a lot of holes in them. Gas under pressure will go down, and rising up, the gas bubbles will mix the biomass in the tank.
If you do not want to build a concrete bunker, you can buy a ready-made PVC container. To preserve heat, it must be overlaid around with a layer of thermal insulation - polystyrene foam. The bottom of the pit is filled with reinforced concrete with a layer of 10 cm. Polyvinyl chloride tanks can be used if the volume of the reactor does not exceed 3 m3.
How to make the simplest installation from an ordinary barrel, you will learn if you watch the video:
The simplest reactor can be made in a few days with your own hands, using available tools. If the farm is large, then it is best to buy a ready-made installation or contact specialists.
Owners of private houses located in regions with limited access to traditional fuels should definitely pay attention to modern biogas plants. Such units make it possible to obtain biogas from a variety of organic waste and use it for personal needs, including heating residential premises.
Gas can be obtained from almost any biomass - waste from the livestock industry, food production, agriculture, foliage, etc. At the same time, you can build such an installation yourself.
Both homogeneous raw materials and mixtures of different biomass are suitable for biogas production. A biogas plant is a volumetric hermetic structure equipped with devices for supplying raw materials, heating biomass, mixing components, diverting the resulting biogas into a gas collector and, of course, protecting the structure.
In the reactor, under the influence of anaerobic bacteria, the biomass is rapidly decomposed. During the fermentation of organic raw materials, biogas is released. Approximately 70% of the composition of such a gas is methane, the rest is carbon dioxide.
Biogas is characterized by excellent calorific value, it has no pronounced odor and color. In terms of its properties, biogas is practically in no way inferior to the more traditional natural gas.
In developed countries, additional installations are used to clean biogas from carbon dioxide. If you wish, you can buy the same installation and get pure biomethane.
Biogas plants on a silo. 1 Silos. 2 Biomass loading system. 3 Reactor. 4 Fermentation reactor. 5 Substrater. 6 Heating system. 7 Power plant. 8 Automation and control system. 9 Gas pipeline system
On average, one cow or other animal weighing half a ton is capable of producing enough manure per day to produce about 1.5 m3 of biogas. The daily manure of one average pig can be processed into 0.2 m3 of biogas, and a rabbit or chicken - into 0.01-0.02 m3 of fuel.
For comparison: 1 m3 of biogas from manure gives about the same amount of thermal energy as 3.5 kg of firewood, 1-2 kg of coal, 9-10 kWh of electricity.
The simplest biogas mixture recipe includes the following components:
This amount of biomass will be enough to produce biogas for half a year of operation with moderate consumption. On average, biogas begins to be released within 1.5-2 weeks after loading the mixture into the plant.
Gas can be used to heat the house and a variety of household and household buildings.
The main components of a complete biogas system are:
A domestic installation will have a somewhat simplified design, however, for completeness of perception, you are invited to read the description of all the listed elements.
This part of the installation is usually assembled from stainless steel or concrete. Externally, the reactor looks like a large hermetic container, on top of which a dome is installed, usually having a spherical shape.
Currently, the most popular are the collapsible design reactors made using innovative technologies. Such a reactor can be easily assembled with your own hands with minimal time. If necessary, it is just as easy to disassemble and transport to another place.
Steel is convenient in that you can easily create holes in it for connecting other elements of the system. Concrete is superior to steel in terms of strength and durability.
This part of the installation includes a waste receiving bin, a water inlet pipe and a screw pump designed to send the humus to the reactor.
A front loader is used to load the dry component into the bunker. At home, this task can be done without a loader, using various improvised means, for example, shovels.
In the bunker, the mixture is moistened to a semi-liquid state. After reaching the desired level of moisture, the screw transfers the semi-liquid mass to the lower compartment of the reactor.
Fermentation of humus in the reactor should occur evenly. This is one of the most important conditions for ensuring intensive release of biogas from the mixture. It is in order to achieve the most uniform fermentation process of the mixture that the design of a typical biogas plant includes agitators with electric drives.
There are submersible and inclined type mixers. Submersible mechanisms can be lowered into the biomass to the required depth to ensure intensive and uniform mixing of the substrate. Usually such mixers are placed on a mast.
Inclined mixers are mounted on the side surfaces of the reactor. An electric motor is responsible for the rotation of the screw in the fermenter.
For successful production of biogas, the temperature inside the system must be maintained at +35-+40 degrees. To do this, automated heating systems are included in the design.
The source of heat in this case is a hot water boiler, in some situations electric heating units are used.
Biogas is collected in this structural element. Most often, the gas holder is placed on the roof of the reactor.
The production of modern gas tanks is usually carried out using polyvinyl chloride - a material that is resistant to sunlight and a variety of adverse natural phenomena.
In some situations, instead of a conventional gas tank, special bags are used. Also, these devices allow you to temporarily increase the amount of biogas produced.
For the manufacture of a gas tank bag, a special polyvinyl chloride with elastic properties is used, which can inflate as the volume of biogas increases.
This part of the system is responsible for drying the spent humus and, if necessary, obtaining high-quality fertilizers.
The simplest separator consists of a screw and a separator chamber. The chamber is made in the form of a sieve. This allows the biomass to be separated into a solid component and a liquid part.
The drained humus is sent to the shipping compartment. The system sends the liquid part back to the receiving chamber. Here, the liquid is applied to moisten the new feedstock.
A domestic biogas plant will have a somewhat simplified design, but its manufacture should be approached with the utmost responsibility.
First step. Dig a hole. At its core, a biogas plant is a large pit with a special finish. The most important and at the same time the most difficult part of the manufacture of the system under consideration is the correct preparation of the walls of the bioreactor and its base.
The pit must be sealed. Strengthen the base and walls with plastic or concrete. Instead, you can purchase ready-made solid-bottomed polymer rings. Such devices provide the necessary tightness of the system. The material will retain its original characteristics for many years, and if necessary, you can easily replace the old ring with a new one.
Second step. Equip a gas drainage system. This saves you the hassle of purchasing and installing agitators, which reduces the amount of time and money required to assemble the plant.
The simplest version of the gas drainage system is vertically fixed PVC sewer pipes with many holes in the body.
Choose pipes of such length that their upper edges rise slightly above the upper level of the loaded humus.
Third step. Cover the outer layer of the substrate with foil insulation. Thanks to the film, conditions will be created for the accumulation of biogas under the dome under conditions of slight overpressure.
Fourth step. Mount the dome and mount the exhaust pipe at its highest point.
Gas consumption should be regular. Otherwise, the dome over the biomass tank may simply explode. In summer, gas is formed more intensively than in winter. To solve the last problem, buy and install suitable heaters.
Thus, it is not difficult to assemble a simple biogas plant on your own. However, for its successful operation, you must remember and follow a few simple rules.
One of the most important requirements is that the loaded organic mass should not contain any substances that can have a negative impact on the vital activity of anaerobic microorganisms. Prohibited inclusions include various kinds of solvents, antibacterial preparations and other similar substances.
A number of inorganic substances can also lead to deterioration of vitality and bacteria. In view of this, it is forbidden, for example, to dilute humus with water left after washing clothes or washing a car.
Remember: a biogas plant is a potentially explosive unit, so follow all safety regulations relevant to the operation of any gas equipment.
Thus, even manure and, in principle, almost everything that you previously tried to get rid of with all your might can be useful on the farm. You just need to properly build a home biogas plant, and very soon your house will be warm. Follow the recommendations received, and you will no longer have to spend huge amounts on heating.
Successful work!
For owners of large farms, there is an acute issue in the form of manure, bird droppings, and animal remains. To solve the problem, you can use special installations designed to produce biogas. They are easy to make at home and operate over a long period with a high yield of ready-to-use product.
Biogas is a substance obtained from natural raw materials in the form of biomass (manure, bird droppings) due to its fermentation. Various bacteria are involved in this process, each of which feeds on the waste products of the previous ones. There are such microorganisms that take an active part in the process of biogas production:
The technology for obtaining biogas from ready-made biomass is to stimulate natural processes. Bacteria in manure should be provided with optimal conditions for rapid reproduction and efficient processing of substances. To do this, biological raw materials are placed in a tank closed from oxygen.
After that, a group of anaerobic microbes enters the work. They allow you to convert phosphorus-, potassium- and nitrogen-containing compounds into pure forms. As a result of processing, not only biogas is formed, but also quality approvals. They are ideal for agricultural use and are more efficient than traditional manure.
Thanks to the efficient processing of biological waste, valuable fuel is obtained. Establishing this process helps prevent methane emissions into the atmosphere, which have a negative impact on the environment. This compound stimulates the greenhouse effect 21 times more than carbon dioxide. Methane can persist in the atmosphere for 12 years.
To prevent global warming, which is a global problem, it is necessary to limit the entry and spread of this substance into the environment. The waste obtained during the recycling process is a high-quality approval. Its use allows to reduce the amount of chemical compounds used. Synthetically manufactured fertilizers pollute groundwater and adversely affect the environment.
With the correct organization of the production process for the production of biogas, from 1 cu. m of organic raw materials receive about 2-3 cubic meters. m of pure product. Many factors influence its effectiveness:
Getting biogas is possible not only from manure or bird droppings. Other raw materials can be used to produce environmentally friendly fuel:
The composition of biogas after passing all the following:
After purification of the product from impurities, biomethane is obtained. It is an analogue, but has a different nature of origin. To improve the quality of fuel, the content of methane in its composition, which is the main source of energy, is normalized.
When calculating the volumes of gases produced, the ambient temperature is taken into account. With its increase, the yield of the product increases and its caloric content decreases. The characteristics of biogas are negatively affected by an increase in air humidity.
Biogas production plays a significant role not only in preserving the environment, but also provides the national economy with fuel. It has a wide range of applications:
For the production of biogas, actions should be taken that will accelerate the process of natural breakdown of organic matter. Before being placed in a sealed container with a limited supply of oxygen, natural raw materials are carefully crushed and mixed with a certain amount of water.
The result is the original substrate. The presence of water in its composition is necessary to prevent the negative impact on bacteria that can occur when substances from the environment enter. Without a liquid component, the fermentation process slows down significantly and reduces the efficiency of the entire biological installation.
Industrial-type equipment for the processing of organic raw materials is additionally equipped with:
These devices significantly increase the efficiency of bioreactors. Agitation removes the hard crust from the surface of the biomass, which increases the amount of gas released. The duration of processing of organic mass is about 15 days. During this time, it decomposes only by 25%. The maximum amount of natural gas is released when the degree of splitting of the substrate reaches 33%.
Biogas production technology implies daily renewal of the substrate. To do this, 5% of the mass is removed from the bioreactor, and a new portion of the raw material is placed in its place. The waste product is used as an endorsement.
Biogas production at home occurs according to the following scheme:
To determine the required volume of the reactor for processing biomass, it is necessary to calculate the amount of manure produced during the day. It is mandatory to take into account the type of raw materials used, the temperature regime that will be maintained in the installation. The tank used should be filled to 85-90% of its volume. The remaining 10% is necessary for the accumulation of the obtained biological gas.
The duration of the processing cycle is necessarily taken into account. When maintaining the temperature at +35°C, it is 12 days. We must not forget that the raw materials used are diluted with water before being sent to the reactor. Therefore, its quantity is taken into account before calculating the volume of the tank.
For the production of biogas at home, it is necessary to create optimal conditions for microorganisms that will break down the biological mass. First of all, it is desirable to organize the heating of the generator, which will entail additional costs.
For the production of biogas, you can install the simplest installation, deepening it into the ground. The manufacturing technology of such a tank is as follows:
The yield of biological gas depends on the content of dry matter in the raw material and its type:
To determine the efficiency of production, laboratory tests of the raw materials used are carried out. Its composition is calculated, which affects the quality characteristics of biogas.
Rising energy prices make us think about the possibility of self-sufficiency. One option is a biogas plant. With its help, biogas is obtained from manure, litter and plant residues, which, after cleaning, can be used for gas appliances (stove, boiler), pumped into cylinders and used as fuel for cars or electric generators. In general, the processing of manure into biogas can provide all the energy needs of a home or farm.
Building a biogas plant is a way to provide energy resources independently
Biogas is a product that is obtained from the decomposition of organic matter. In the process of decay / fermentation, gases are released, by collecting which you can meet the needs of your own household. The equipment in which this process takes place is called a “biogas plant”.
The process of biogas formation occurs due to the vital activity of various kinds of bacteria that are contained in the waste itself. But in order for them to actively “work”, they need to create certain conditions: humidity and temperature. To create them, a biogas plant is being built. This is a complex of devices, the basis of which is a bioreactor, in which the decomposition of waste occurs, which is accompanied by gas formation.
There are three modes of processing manure into biogas:
The most difficult thing in biogas plants is the thermophilic regime. This requires high-quality thermal insulation of a biogas plant, heating and a temperature control system. But at the output we get the maximum amount of biogas. Another feature of thermophilic processing is the impossibility of reloading. The remaining two modes - psychophilic and mesophilic - allow you to add a fresh portion of prepared raw materials daily. But, in the thermophilic mode, a short processing time makes it possible to divide the bioreactor into zones in which its share of raw materials with different loading times will be processed.
The basis of a biogas plant is a bioreactor or bunker. The fermentation process takes place in it, and the resulting gas accumulates in it. There is also a loading and unloading bunker, the generated gas is discharged through a pipe inserted into the upper part. Next comes the gas refinement system - its cleaning and increasing the pressure in the gas pipeline to the working one.
For mesophilic and thermophilic regimes, a bioreactor heating system is also required to reach the required regimes. For this, gas-fired boilers are usually used. From it, the pipeline system goes to the bioreactor. Usually these are polymer pipes, as they best tolerate being in an aggressive environment.
Another biogas plant needs a system for mixing the substance. During fermentation, a hard crust forms at the top, heavy particles settle down. All this together worsens the process of gas formation. To maintain a homogeneous state of the processed mass, agitators are necessary. They can be mechanical or even manual. Can be started by timer or manually. It all depends on how the biogas plant is made. An automated system is more expensive to install, but requires a minimum of attention during operation.
Biogas plant by type of location can be:
More expensive to install buried - a large amount of land work is required. But when operating in our conditions, they are better - it is easier to organize insulation, less heating costs.
A biogas plant is essentially omnivorous - any organic matter can be processed. Any manure and urine, plant residues are suitable. Detergents, antibiotics, chemicals negatively affect the process. It is desirable to minimize their intake, as they kill the flora that is involved in processing.
Cattle manure is considered ideal, as it contains microorganisms in large quantities. If there are no cows in the farm, when loading the bioreactor, it is desirable to add some of the litter to populate the substrate with the required microflora. Plant residues are pre-crushed, diluted with water. In the bioreactor, vegetable raw materials and excrement are mixed. Such a “refueling” takes longer to process, but at the exit, with the right mode, we have the highest product yield.
To minimize the costs of organizing the process, it makes sense to locate a biogas plant near the source of waste - near buildings where birds or animals are kept. It is desirable to develop a design so that loading occurs by gravity. From a cowshed or pigsty, a pipeline can be laid under a slope, through which manure will flow by gravity into the bunker. This greatly simplifies the task of maintaining the reactor, and cleaning up manure too.
It is most advisable to locate the biogas plant so that the waste from the farm can flow by gravity
Usually buildings with animals are located at some distance from a residential building. Therefore, the generated gas will need to be transferred to consumers. But stretching one gas pipe is cheaper and easier than organizing a line for transporting and loading manure.
Quite stringent requirements are imposed on the manure processing tank:
All these requirements for the construction of a biogas plant must be met, as they ensure safety and create normal conditions for the processing of manure into biogas.
Resistance to aggressive environments is the main requirement for materials from which containers can be made. The substrate in the bioreactor may be acidic or alkaline. Accordingly, the material from which the container is made must be well tolerated by various media.
Not many materials answer these requests. The first thing that comes to mind is metal. It is durable, it can be used to make a container of any shape. What's good is that you can use a ready-made container - some kind of old tank. In this case, the construction of a biogas plant will take very little time. The lack of metal is that it reacts with chemically active substances and begins to break down. To neutralize this minus, the metal is covered with a protective coating.
An excellent option is the capacity of a polymer bioreactor. Plastic is chemically neutral, does not rot, does not rust. Only it is necessary to choose from such materials that endure freezing and heating to sufficiently high temperatures. The walls of the reactor should be thick, preferably reinforced with fiberglass. Such containers are not cheap, but they last a long time.
A cheaper option is a biogas plant with a tank made of bricks, concrete blocks, stone. In order for the masonry to withstand high loads, it is necessary to reinforce the masonry (in each 3-5 row, depending on the wall thickness and material). After completion of the wall erection process, to ensure water and gas tightness, subsequent multi-layer treatment of the walls, both inside and out, is necessary. The walls are plastered with a cement-sand composition with additives (additives) that provide the required properties.
The volume of the reactor depends on the selected temperature for processing manure into biogas. Most often, mesophilic is chosen - it is easier to maintain and it implies the possibility of daily additional loading of the reactor. Biogas production after reaching the normal mode (about 2 days) is stable, without bursts and dips (when normal conditions are created). In this case, it makes sense to calculate the volume of the biogas plant depending on the amount of manure generated on the farm per day. Everything is easily calculated based on the average data.
Decomposition of manure at mesophilic temperatures takes from 10 to 20 days. Accordingly, the volume is calculated by multiplying by 10 or 20. When calculating, it is necessary to take into account the amount of water that is necessary to bring the substrate to an ideal state - its humidity should be 85-90%. The found volume is increased by 50%, since the maximum load should not exceed 2/3 of the volume of the tank - gas should accumulate under the ceiling.
For example, the farm has 5 cows, 10 pigs and 40 chickens. As a matter of fact, 5 * 55 kg + 10 * 4.5 kg + 40 * 0.17 kg = 275 kg + 45 kg + 6.8 kg = 326.8 kg are formed. To bring chicken manure to a moisture content of 85%, you need to add a little more than 5 liters of water (that's another 5 kg). The total mass is 331.8 kg. For processing in 20 days it is necessary: 331.8 kg * 20 \u003d 6636 kg - about 7 cubes only for the substrate. We multiply the found figure by 1.5 (increase by 50%), we get 10.5 cubic meters. This will be the calculated value of the volume of the biogas plant reactor.
Loading and unloading hatches lead directly to the bioreactor tank. In order for the substrate to be evenly distributed over the entire area, they are made at opposite ends of the container.
With the buried installation method of the biogas plant, the loading and unloading pipes approach the body at an acute angle. Moreover, the lower end of the pipe should be below the liquid level in the reactor. This prevents air from entering the container. Also, rotary or shut-off valves are installed on the pipes, which are closed in the normal position. They are only open for loading or unloading.
Since the manure may contain large fragments (bedding elements, grass stalks, etc.), small diameter pipes will often become clogged. Therefore, for loading and unloading, they must be 20-30 cm in diameter. They must be installed before the start of work on the insulation of the biogas plant, but after the container is installed in place.
The most convenient mode of operation of a biogas plant is with regular loading and unloading of the substrate. This operation can be performed once a day or once every two days. Manure and other components are pre-collected in a storage tank, where they are brought to the required state - they are crushed, if necessary, moistened and mixed. For convenience, this container may have a mechanical stirrer. The prepared substrate is poured into the receiving hatch. If you place the receiving container in the sun, the substrate will be preheated, which will reduce the cost of maintaining the required temperature.
It is desirable to calculate the installation depth of the receiving hopper so that the waste flows into it by gravity. The same applies to unloading into the bioreactor. The best case is if the prepared substrate moves by gravity. And a damper will block it off during the preparation.
To ensure the tightness of the biogas plant, hatches on the receiving hopper and in the unloading area must have a sealing rubber seal. The less air there is in the tank, the cleaner the gas will be at the outlet.
The removal of biogas from the reactor occurs through a pipe, one end of which is under the roof, the other is usually lowered into a water seal. This is a container with water into which the resulting biogas is discharged. There is a second pipe in the water seal - it is located above the liquid level. More pure biogas comes out into it. A shut-off gas valve is installed at the outlet of their bioreactor. The best option is ball.
What materials can be used for the gas transmission system? Galvanized metal pipes and gas pipes made of HDPE or PPR. They must ensure tightness, seams and joints are checked with soap suds. The entire pipeline is assembled from pipes and fittings of the same diameter. No contractions or expansions.
The approximate composition of the resulting biogas is as follows:
In order for biogas to have no smell and burn well, it is necessary to remove carbon dioxide, hydrogen sulfide, and water vapor from it. Carbon dioxide is removed in a water seal if slaked lime is added to the bottom of the installation. Such a bookmark will have to be changed periodically (as the gas starts to burn worse, it's time to change it).
Gas dehydration can be done in two ways - by making hydraulic seals in the gas pipeline - by inserting curved sections under the hydraulic seals into the pipe, in which condensate will accumulate. The disadvantage of this method is the need for regular emptying of the water seal - with a large amount of collected water, it can block the passage of gas.
The second way is to put a filter with silica gel. The principle is the same as in the water seal - the gas is fed into the silica gel, dried out from under the cover. With this method of drying biogas, silica gel has to be dried periodically. To do this, it needs to be warmed up for some time in the microwave. It heats up, the moisture evaporates. You can fall asleep and use again.
To remove hydrogen sulfide, a filter loaded with metal shavings is used. You can load old metal washcloths into the container. Purification occurs in exactly the same way: gas is supplied to the lower part of the container filled with metal. Passing, it is cleaned of hydrogen sulfide, collects in the upper free part of the filter, from where it is discharged through another pipe / hose.
The purified biogas enters the storage tank - gas tank. It can be a sealed plastic bag, a plastic container. The main condition is gas tightness, the shape and material do not matter. Biogas is stored in the gas tank. From it, with the help of a compressor, gas under a certain pressure (set by the compressor) is already supplied to the consumer - to a gas stove or boiler. This gas can also be used to generate electricity using a generator.
To create a stable pressure in the system after the compressor, it is desirable to install a receiver - a small device for leveling pressure surges.
In order for the biogas plant to operate normally, it is necessary to regularly mix the liquid in the bioreactor. This simple process solves many problems:
Typically, a small homemade biogas plant has mechanical agitators that are driven by muscle power. In systems with a large volume, the agitators can be driven by motors that are switched on by a timer.
The second way is to mix the liquid by passing through it part of the generated gas. To do this, after leaving the metatank, a tee is placed and part of the gas is poured into the lower part of the reactor, where it exits through a tube with holes. This part of the gas cannot be considered a consumption, since it still enters the system again and, as a result, ends up in the gas tank.
The third mixing method is to pump the substrate from the lower part with the help of fecal pumps, pour it out at the top. The disadvantage of this method is the dependence on the availability of electricity.
Without heating the processed slurry, psychophilic bacteria will multiply. The processing process in this case will take from 30 days, and the gas yield will be small. In summer, in the presence of thermal insulation and preheating of the load, it is possible to reach temperatures up to 40 degrees, when the development of mesophilic bacteria begins, but in winter such an installation is practically inoperable - the processes are very sluggish. At temperatures below +5°C, they practically freeze.
Heat is used for best results. The most rational is water heating from the boiler. The boiler can operate on electricity, solid or liquid fuel, it can also be run on the generated biogas. The maximum temperature to which water must be heated is +60°C. Hotter pipes can cause particles to adhere to the surface, resulting in reduced heating efficiency.
You can also use direct heating - insert heating elements, but firstly, it is difficult to organize mixing, and secondly, the substrate will stick to the surface, reducing heat transfer, heating elements will quickly burn out
A biogas plant can be heated using standard heating radiators, simply pipes twisted into a coil, welded registers. It is better to use polymer pipes - metal-plastic or polypropylene. Corrugated stainless steel pipes are also suitable, they are easier to lay, especially in cylindrical vertical bioreactors, but the corrugated surface provokes sediment build-up, which is not very good for heat transfer.
To reduce the possibility of deposition of particles on the heating elements, they are placed in the stirrer zone. Only in this case it is necessary to design everything so that the mixer cannot touch the pipes. It often seems that it is better to place the heaters from below, but practice has shown that due to sediment at the bottom, such heating is inefficient. So it is more rational to place the heaters on the walls of the metatank of the biogas plant.
According to the way the pipes are located, heating can be external or internal. When located indoors, heating is efficient, but repair and maintenance of heaters is impossible without shutting down and pumping out the system. Therefore, special attention is paid to the selection of materials and the quality of the connections.
Heating increases the productivity of the biogas plant and reduces the processing time of raw materials
When the heaters are located outdoors, more heat is required (the cost of heating the contents of a biogas plant is much higher), since a lot of heat is spent on heating the walls. But the system is always available for repair, and the heating is more uniform, since the medium is heated from the walls. Another plus of this solution is that agitators cannot damage the heating system.
At the bottom of the pit, first, a leveling layer of sand is poured, then a heat-insulating layer. It can be clay mixed with straw and expanded clay, slag. All these components can be mixed, can be poured in separate layers. They are leveled into the horizon, the capacity of the biogas plant is installed.
The sides of the bioreactor can be insulated with modern materials or classic old-fashioned methods. Of the old-fashioned methods - coating with clay and straw. It is applied in several layers.
Of modern materials, you can use high-density extruded polystyrene foam, low-density aerated concrete blocks,. The most technologically advanced in this case is polyurethane foam (PPU), but the services for its application are not cheap. But it turns out seamless thermal insulation, which minimizes heating costs. There is another heat-insulating material - foamed glass. In plates, it is very expensive, but its battle or crumb costs quite a bit, and in terms of characteristics it is almost perfect: it does not absorb moisture, is not afraid of freezing, tolerates static loads well, and has low thermal conductivity.
