IS IT POSSIBLE TO PRODUCE BIOGAS FROM LEAVES
Biogas is a renewable energy that is produced from raw materials available in the area. Any organic residues are used, from food waste to sewage sludge. In rural areas, plant residues are disposed of – straw, silage, bagasse, husk, as well as livestock excrement. In cities, the raw material base is landfills, food industry enterprises, household waste.
Producing biogas can improve the environmental situation, get rid of the problem of storage, disposal and disposal of waste, reduce greenhouse gas emissions, as well as get a constant flow of renewable energy raw materials for thermal power plants, transport and electric power.
Of all types of renewable transport fuels, biomethane has the least greenhouse gas effect and the best production efficiency, given the entire production chain. In the process of biogas production, not only carbon, but also nutrients are recycled when the final product is used as fertilizer. This means that as a result of economic activity, less artificial fertilizers fall into groundwater. Biogas is needed to transition to an economy independent of fossil fuels.
How is leaf recycling
In every city in autumn, we observe the same picture: dozens of communal workers rake the fallen leaves, then load it onto cars and take it away in an unknown direction. What happens next with the collected leaves? Nothing, they are taken to a landfill and left to rot there. Burning leaves from trees is prohibited by the Law of Ukraine, for this an administrative penalty is imposed in the form of a fine.
During the growth process, leaves accumulate a large number of toxic substances that enter the air with exhaust gases. When foliage is burned, carbon monoxide and carbon dioxide, benzapyrene with carcinogenic properties, and dioxins are released. From one ton of burnt leaves, up to 30 kg of toxic compounds enter the air.
To imagine the scale of the issue, we give the data of the Kyiv city administration. Annually, in autumn, 120 thousand tons of fallen leaves are collected and taken out in Kyiv. This figure made the city authorities think, and in June 2019, plans were announced for the construction of a biogas complex. Such an installation will solve several issues at once:
- dispose of leaves;
- free up space at the landfill, which previously occupied the collected leaves;
- get biogas from waste and use it for the needs of the city;
- avoid release of harmful substances into the atmosphere.
Obtaining biogas from municipal waste is, of course, an excellent idea that deserves all approval. Consider how this process may look like in reality.
How to produce biogas from leaves
Processing of leaves, like any other organic raw material, occurs by anaerobic digestion in special sealed containers – digesters. In order for the leaves to become a full-fledged substrate, they need to be cleaned of impurities (debris, plastic, stone, large branches), then chopped, added water and loaded into a fermentation unit. In order for the process to proceed more actively, the substrate must have certain compositional parameters. To optimize it, other components are added to the mixture. They can be food waste, other plant debris.
The substrate is slightly heated and maintained for a predetermined time. During the fermentation process, a biogas mixture containing from 50% to 70% methane is released. It enters the storage tanks – gas tanks, from where it is then fed either to the boiler or for further cleaning. After enrichment, gas can be used in cogeneration plants, supplied to a common gas transmission network, sold at gas stations for automobiles.
Digestat remains in the fermentation hopper, which can be used as fertilizer. It has no harmful impurities and is quite concentrated. The process of obtaining biogas is described in detail in our article.
How to use biogas produced from leaves?
The biogas mixture that enters the drives contains a valuable energy component – methane. Without additional purification, such gas can be used in heating boilers of a thermal power plant, and thus reduce the consumption of natural gas.
Enrichment of biogas to a level close to natural gives much wider possibilities for its use. For this, the methane content in biogas should be at least 95-97%. There are technologies that can achieve this result. First of all, the gas is purified from water, hydrogen sulfide and carbon dioxide.
Purified gas (commonly called biomethane) can be refueled with vehicles equipped with gas equipment. Biomethane can be used in gas generating plants and thus produce electricity from leaves.
As you can see, fallen leaves can bring considerable benefits and save money on gasoline, natural gas and other energy resources. But most importantly, leaf recycling using anaerobic fermentation technology can improve the ecological situation in the city.
What difficulties can be in producing biogas from leaves?
The organization of any enterprise involves a risk assessment. In our case there are several such moments, we will talk about them below.
- Falling leaves from trees are only in autumn, this is not enough for year-round operation of a biogas plant. To obtain biogas throughout the year, it is necessary to provide for the possibility of working on another substrate.
- Leaves as raw materials need additional cleaning from garbage. When collecting leaves, small stones, sand, branches, plastic, paper, etc. fall into the mass of leaves. These objects can cause crushing of the crushing equipment, as well as reduce the quality of the substrate. Therefore, they must be deleted.
- As an independent raw material, leaves are ineffective; they have a low level of processing by bacteria. It is necessary to use a co-substrate to improve the properties of the initial mixture.
These issues are not only technical, but also economic in nature. The use of additional equipment, delivery of co-substrate and reconfiguration of the station to work with other raw materials lead to an increase in the cost of the project. Therefore, you need to carefully calculate all the data before the start of construction.
How much biogas can be produced from the leaves?
This question is rather complicated, since the biogas yield depends on many parameters. These include:
- composition of the substrate;
- type of technology and equipment used;
- compliance with technological conditions (heating, etc.).
Each of the factors plays a significant role. For a preliminary assessment, you can use approximate calculations.
According to reports, the biogas yield from 1 ton of leaves is 2.85 – 3 cubic meters. Consequently, from 120 thousand tons (we take the data for Kiev), you can get 342 thousand cubic meters of gas. It is a gas mixture with a methane content of up to 60%. In terms of natural gas, this is about 210 thousand m³.
Is it a lot or a little?
The rate of consumption of natural gas for heating is 1 sq.m. area in residential buildings is 11m³. So, with the obtained biomethane, you can heat about 20 thousand square meters. meters of housing. If you consider that other ingredients will be added to the substrate, the amount can significantly increase.
Biogas from waste is a necessary, useful and promising technology. Fallen leaves can also be raw materials for such production along with organic household and industrial waste.
The construction of a recycling complex will require accurate preliminary calculations and additional research to assess the cost of the project.
The main task of any biogas plant is the recycling and development of a renewable energy source – biomethane.