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Biogas plants, or energy from nature
The world needs an energy transition and the ever-increasing demand for electricity is forcing diversification of electricity sources. Without changing the energy production model, humanity will not cope with the problem of climate change, which is mainly caused by the emission of harmful substances into the environment, including primarily carbon dioxide. Renewable energy sources are expected to play a key role in this process. One of them is biogas. What is it and how can it help in the fight for a better future?
Biogas: definition
What is biogas? Biogas is a fuel that is produced from biomass. This organic material comes from, for example, agricultural waste such as straw, beet and potato leaves, corn silage or livestock manure and other organic waste, which undergoes methane fermentation without oxygen. This is how biogas is produced. It is a combustible gas. Biogas production takes place in biogas plants. In the case of agricultural biogas plants, the completion of the biogas production process involves obtaining the so-called digestate.
What does biogas production involve?
The planned obtaining of biogas is carried out in professional biogas plants. The process itself begins with the delivery of the aforementioned substrate – e.g. agricultural waste which is crushed in a special tank. Next, the waste goes to the heart of the biogas plant, which is the digester. In the digester, anaerobic fermentation takes place, which consists of four phases: hydrolysis, acidogenesis, acetanogenesis and methanogenesis. A very important stage in the entire process of obtaining biogas is the removal of excess hydrogen sulphide. This is a necessary process if we want to use biogas as a fuel to power, for example, gas engines.
In addition to biogas production, the digester yields fermentation residue, which goes into special storage tanks and is then used as fertilizer.
Types of biogas
What can biogas be made from? As already mentioned, the deliberate formation of biogas is a process carried out in special biogas plants. In addition to agricultural facilities, which often use plant waste or animal excrement in their operations, biogas can also be produced in biogas plants operating at wastewater treatment plants. Biogas from wastewater treatment plants is produced through sewage sludge fermentation. It is also worth noting that landfills can spontaneously produce such a substance, which is referred to as landfill biogas. To sum up, the creation of biogas and the matter that is used in this process determines the distribution of this biofuel. It is the substrates for biogas production that influence what type of biogas will ultimately be produced.
Properties of biogas worth knowing
The composition of biogas is largely methane and carbon dioxide. Based on information on how much methane percentage is in the biogas, its calorific value can be determined. In this case, the relationship is simple – as the methane content of biogas increases, so does its calorific or energy yield. The calorific value of biogas is influenced by what substrates were used in its production process. Moreover, it is worth noting that biogas has no odour or colour.
Use of biogas in practice – cogeneration (CHP)
Biogas is a renewable energy source, and it is produced using relatively inexpensive substrates. Accordingly, the biogas can be used at various levels. What is biogas used for? First of all, it can be used to power CHP units. In the process of biogas combustion, as a result of supplying the engine with the chemical energy contained in the fuel, we get electricity and heat. Such power generators are especially suitable for farms that have seamless access to the substrates required for biogas production. The process of cogeneration using biogas fuel is shown in the diagram below:
Example of biogas cogeneration (Eneria)
GAĆ Waste Management Facility.
Location: Oława
Two CAT CG132-12 containerised CHP units fuelled by landfill biogas were installed along with a biogas preparation plant
The installation produces: electricity 2 x 600 kWe
What is the efficiency of biogas production?
The efficiency of biogas production is crucial to the overall process. The basic requirement is to carry out the process skilfully and to guarantee a suitable environment for the fermentation process. The type of substances used is also important for the efficiency of this process. When planning to use biogas as a renewable energy source, it is worth checking the correlation between the type of substrates used and the production efficiency.
The fermentation process can be adversely affected by, among other things, various technical problems and malfunctions or mishandling of substrates. Also important is the adequate amount of substrate for a particular digester, as well as the use of the necessary types of microorganisms and their correct ratio.
Biogas in Poland
The biogas as a renewable fuel can be used in many areas. The biogas market in Poland is still in the development stage and has promising prospects, especially for agricultural biogas plants.
So far, however, Poland is using only a fraction of its biogas potential. On Vistula River, there are just over 100 agricultural biogas plants and twice as many units producing environmental biogas and biogas from wastewater treatment plants. The installed capacity of biogas is about 350 MW. Meanwhile, according to experts, Polish capacity is enough to build several thousand biogas plants and produce about 8 billion cubic meters of biomethane per year. By comparison, domestic gas demand for the year is currently 18 billion cubic meters.
The president of the Polish Oil and Gas Company Jerzy Kwieciński has spoken many times about the opportunities facing the sector. The potential for biogas produced in agricultural biogas plants is closely related to the share of agricultural land in Poland. In practice, agricultural biogas plants are based on the use of suitable residues left over from agricultural activities.
The benefits of biogas have long been recognised by other European Union countries. There are more than 10,000 biogas plants in Germany today. Biomass accounts for almost 10% of the energy mix there. In France, meanwhile, there are more than 600 such units and 1,300 in Italy. Most EU countries with adequately developed biogas markets are intensively developing the biomethane segment.
Poland is trying to make up for these shortcomings. According to information from the Ministry of Development, about 200 biogas plants are to be built on the Vistula in the next two years, with dozens of projects already in the pipeline. Much in this regard depends on support systems. The recently announced reference prices for RES auctions, however, offer great opportunities for agricultural biogas producers. They can count on the highest price for each 1 MW of biogas produced, reaching as much as PLN 760.
What is worth remembering? Biogas is a gas produced using biomass. The composition of biogas includes methane and carbon dioxide. In the case of agricultural biogas plants, biogas production often uses agricultural waste or livestock manure.
Written by: Michał Soja
Sales Expert in CHP Department
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