MISCONCEPTIONS ABOUT THE BIOGAS PLANT
Anaerobic fermentation technologies are of genuine interest to a wide range of individuals. Still – you can get almost gratuitous energy and heat the house, fuel the car, fertilize the garden. High energy prices stimulate people’s desire for an alternative source. Is it possible to do this in every household? Let’s figure it out.
Biogas from waste
To obtain biogas, several components are required:
- organic waste;
- biogas complex (designed strictly for a specific type of waste, taking into account humidity, degree of grinding, temperature, mixing mode and the necessary cleaning technology);
- consumption device (cogenerator, boiler, etc.).
The problem of waste management is facing many enterprises and households. However, for the normal operation of the installation, a number of conditions must be observed:
- waste should be received regularly and in sufficient quantity;
- the composition of the waste must be stable (moreover, it is necessary to exclude the ingress of substances that inhibit the process of methanogenesis into the substrate, namely antibiotics, heavy metals, etc.);
- it is necessary to withstand the fermentation technology (temperature, stable mixing, to prevent the formation of excessive sediment or the formation of crusts on the surface).
To start a biogas station, an inoculum (fresh manure or substrate from a working biogas plant) will be required. Biogas processing is a complex technological process and access to performance also has a number of technological difficulties and requires appropriate training and knowledge.
Of course, you can build a tank with a heating system, mixing and manually loading / unloading the substrate, connect some primitive gas holder bag, but in this case there will be no talk of a stable process for obtaining biogas. For example, a temperature change of 1 degree Celsius in a reactor can completely stop production. And the equipment of all the necessary systems to support the process (pumps, mixers, compressors, level sensors, volume sensors, and especially gas analyzers) entails a large capital investment. The cost of capital costs per 1 kW of electricity generated by a biogas plant for low power facilities is very high. In most cases, it is not economically viable. From the experience of Ecodevelop specialists, only complexes with an electric capacity of 1-1.5 MW have an acceptable payback period of 4-5 years (depending on the technology and raw materials adopted).
Generation of electricity from waste
Suppose you built a small structure for anaerobic digestion in a private plot, loaded it, withstood the set time and got, say, up to 50 cubic meters per day. Next, you want to receive electricity from this raw material for your farm. You will need a cogenerator – gas piston or gas turbine. They are produced, but, unfortunately, only of great productivity, designed to work on an industrial scale.
Industrial cogenerators are designed to produce from 50 kW of electricity. For example, when using high-energy raw materials such as corn silage, you will need at least 3 tons / day to produce this capacity. You do not have enough power of your mini-installation to start and maintain the operation of such a cogenerator, not to mention its price (and it starts from 500 USD per 1 kW).
There is low-power equipment, the so-called backup power generators, consuming small amounts of fuel. Their minus is that (as the name implies) they are able to work 3-5 hours as a backup power source, after which a stop is required. But it is impossible to temporarily stop the release of the biogas mixture! If you do not feed the bacteria, they fall into suspended animation and to exit this condition, it will take a lot of effort.
Processing biogas into thermal energy
Can biogas be used instead of expensive natural gas in heating equipment?
Yes, you can, but first consider how much you need to heat your home?
This is easy to do, focusing on the indicators of natural gas consumption (if you have a meter, of course). Multiply your number by a factor of 1.5, and you will get the required amount.
Where did the coefficient come from? From a simple count. The composition of natural gas contains at least 90% of methane – this is the substance that gives all the thermal energy. Biogas obtained by the artisanal method contains methane not more than 60%, therefore, its heat transfer is one and a half times lower. Whether the game is worth the candle – consider for yourself. Moreover, without purification, biogas contains one or another percentage of hydrogen sulfide (can reach 1000 ppm), while even designed burners are designed for a maximum of 200 ppm. The high hydrogen sulfide content in biogas will lead to the failure of such a burner much faster than their service life.
Is it really to use biogas in cars?
A car equipped with a gas installation is no longer a curiosity. Instead of a gas tank, a gas cylinder is installed in it with natural gas compressed under a pressure of 200 atm.
Biogas from a home mini-plant contains a large amount of impurities, mainly carbon dioxide, a by-product of fermentation. Carbon dioxide cannot be compressed so much, it will become solid. If you refill the cylinders under less pressure, the fuel supply will be too small, you will not go far on it.
There is one more problem. Impurities of “home” biogas during combustion form insoluble and non-volatile compounds that settle in the engine and lead to its breakdown.
Processing biogas in order to clean sulfur, carbon dioxide, water, etc. from compounds is possible only on special equipment using certain reagents. Such industrial units are too large and expensive to use in domestic conditions.
Getting biogas from waste in Ukraine is easy. Is it so?
It is believed that building a sealed container with your own hands and getting cheap fuel is very simple. I dug a hole, erected walls, brought out a pipe for the exit of finished products, filled up raw materials, sealed them, and it was done. Get biogas and heat the house – cheap and cheerful. But only in theory.
In practice, for the formation of at least any acceptable quality of gas, it is necessary to understand how much and what kind of raw material we load in a fermentation tank. The fact is that oxygen-free fermentation occurs subject to a certain temperature and acidity of the medium. If the acidity of the substrate is increased – the bacteria will die or will not work quite productively. Can you determine the acidity of the initial composition by eye? But to ensure the consistency of the substrate in quality?
The second parameter is temperature. For fermentation, it must be at least 20 ºС. In a vault buried in the ground without heating in Ukraine, the temperature regime will reach that level unless in a very sultry summer, and then only in the afternoon. The rest of the time, the soil will work as a cooler, so you will need to arrange additional heating. So, instead of heating the house, you need to warm the installation itself. Isn’t it easier to get by with firewood or pellets?
The biogas plant is explosive. Truth or myth?
Any technological production has this or that degree of danger. For example, a leak may occur and gas will enter the air. The risk of poisoning is minimal if it did not occur indoors. But exactly the same risk from an ordinary gas stove.
Can a fermentation tank explode? No, it can’t, inside it the pressure is much lower than atmospheric.
Can a drive (gas holder) explode? No, it cannot, because a mixture of methane with air is needed for ignition, but there is no air in the gas tank. After all, fermentation takes place in anoxic conditions, and biogas directly from the digester goes to the storage tank or for purification.
Along the way, we note that waste from the substrate after fermentation is an environmentally friendly and safe product that does not even contain plant seeds.
It is possible to produce biogas from waste in a single household. In the climate of Ukraine, it will be necessary to arrange additional heating of the installation.
For use in automobiles, biogas must be processed into biomethane, i.e. additional serious cleaning of impurities, which is not feasible at home.
Processing biogas into electricity at the household level is difficult, as the equipment is either too expensive or inefficient.
It is best to use gas in heating boilers. It is beneficial to produce it if you have a problem with waste disposal, i.e. we are talking about several tens of tons. If you just have accumulated plant waste in the garden or garden, better arrange a compost pit.