Biogas Plant
Biogas Plant – Profitable Organic Waste Treatment
Biogas plant generates income by producing renewable energy and fertilizers from organic waste and by-products.
The produced biogas can be:
- utilized for electricity and heat production (read more about CHP »)
- refined to be used as transport fuel (see Gas Upgrading unit »)
- injected into the natural gas grid network as a substitute for fossil gas.
Biogas plants are scalable almost limitlessly. Among the biogas producers are:
- Food industry companies
- Agriculture sector
- Sewage treatment plants
- Waste management companies
What is Biogas?
Biogas is generated when organic waste decomposes in oxygen-free environment. Depending on the feedstock, biogas contains about 50-70% methane with excellent fuel properties. The rest of the gas mixture is mainly carbon dioxide. To produce one cubic meter of methane, about 7 kg of biowaste is needed, and the energy content is equivalent to one liter of diesel fuel.
Almost all organic materials are suitable for biogas production, e.g.:
- Agricultural manure and energy crops
- Food industry side streams
- Slaughterhouse waste
- Fish processing waste
- Municipal separately collected bio-waste, or organic fractions of MSW
- Wastewater treatment plant sewages
- Pulp and paper industry side streams
In order to ensure optimal and functional biogas production, the biogas project requires feedstock pre-treatment and feeding equipment for processing and transferring it to the biogas reactor.
Biogas project profitability
The payback period for a biogas project can be just a few years. The profitability assessment of a project takes into account, among other things:
- Feedstock properties, methane yield
- Gate fees or savings in handling charges
- Gas utilization method and revenue flows
- Income flows and/or savings related to the fertilizer
- Technology used and energy efficiency of the plant
Biogas Technology Choice and Feedstocks
Dry Fermentation vs. Traditional Wet Process
Biogas has traditionally been produced in cylindrical so-called wet fermentation reactors (CSTR, continuous stirred-tank reactor). It is often an optimal biogas production process for wet feedstock materials such as liquid manure and sewage sludge. From the point of view of the operation of the reactor, the content of the wet fermentation biogas reactor must be very uniform. Also more than 90% of it must be water in order for the plant to operate properly.
Due to the smaller required reactor volume and higher load capacity, liquid manure is nowadays often dried prior to the biogas process. Thereby the feedstock material is more advantageous for transporting and can be handled with the so-called plug flow (PFR, plug flow reactor) technology. Dry fermentation process allows handling even challenging feedstocks in the biogas process. Dry fermentation is less susceptible to floating and sedimentation challenges than the wet process. In the dry fermentation process feedstocks with total solids up to 35%, such as dry hay and a wide range of biowaste streams, can be handled without adding external water.
Dry and Wet Digestion Advantages in a Combi-Plant
The combi-plant consists of both dry and wet fermentation technology plants combining the key benefits of both technologies. High loading rate of the dry fermentation ensures high usability and gas production per reactor cubic meter. Long retention time of the wet fermentation process, in turn, allows a larger portion of the organic feedstock material to degrade.
The combi-plant has the following advantages:
- Plug flow reactor as the first step to handle difficult feedstocks
- Post-digester reactor to ensure optimal decomposition of the organic material and the best biogas yield
- Modular reactor structure; treatment capacity can be easily increased by installing parallel reactors
- Very low total energy consumption
- Ability to recycle liquid digestate within the process, reducing the need to add external water and often even removing it completely.