## 2 Materials and Methods  
At the Institute of Technology and Life Sciences (National Research Institute, Poznan Branch), an installation system with a power of (3-40) kW was developed. This is a pilot installation (Figure 2) with an active fermenter capacity of 15 m\({}^{3}\)[28] located on a farm [29] with 1100 fattened pigs kept in a slatted system [30]. The raw biogas production node (Figure 3) is a system for transporting biogas produced in the fermentation tank together with the equipment, enabling the fermentation process to be carried out, controlled and regulated. The fermentation tank is the main and key element of the installation to achieve max. efficiency of fermentation technology. The fermenter, the cylindrical part of which is located vertically, contains a filling in the form of vertical pipes with a rough surface made of plastic, constituting an adhesive bed. In the  
Figure 2: Pilot installation with examples of the location of a mobile agricultural biogas plant (photo by [PERSON]). From the left: livestock building, manhole to the well, the so-called “pre-tank for pig slurry”, digester, container with the installation, tank for the so-called “digestate lagoon”. upper part of the fermenter, there is a common connector through which fresh substrate in the form of slurry and fermenting mass are supplied. Next to it, there is a biogas outlet connector, which is connected to a pipe via a blower, a biogas drainage valve and a biogas inlet connector with a bubbler. The barbotka is located horizontally near the bottom of the fermenter. Vertical pipes, which increase the active surface for the fermentation bacteria flora, are located inside the heating spiral. The heating spiral is connected to a water pump and a heat exchanger, creating a closed water circuit periodically supplied from the outside. In the lower part of the fermenter, there is an outlet port for the fermenting mass, which is connected via the fermenting mass pump to a common port supplying fresh substrate in the form of slurry and fermenting mass to the fermenter. The outer walls of the fermenter are covered with a layer of thermal insulation. The digester has a safety valve, a main digestate outlet connector connected to the digestate pump and a biogas outlet connector through which biogas is discharged for further use. The fermenter is filled with slurry through a connector, preferably in an automatic cycle, ensuring vertical movement of the bio-ferment fraction through the entire tank. The digestate mixed with slurry also flows periodically through this connector. Part of the biogas contained in the gas space of the fermenter is moved to the bubbler and then travels upwards in the form of bubbles, mixing the suspension. The fermenter operates at a temperature of (35-40) \({}^{\circ}\)C. The heating medium is warm water flowing through the heating coil. The digestate is drained (2-3) times a day through the main digestate outlet port. When emptying, the fermenter is not filled. Then, the digester is filled with slurry in the same volume as the digestate was removed. The filling level of the fermenter is controlled in an automatic cycle. During filling, the pressure equalizes after the biogas spontaneously flows through the outlet port to the next part of the installation. Cogeneration node: Technically, this node is a set of a cogenerator, heat exchanger and heat transport system to the operating conditions of the installation. The cogeneration system consists of the following node elements:  
- Cogenerator;  
- Elements for installing a cogeneration unit in a biogas plant (installation elements):  
Figure 3: Biogas production prototype installation (system of technological nodes); block diagram of the test stand (source: [PERSON]). * Circulation pump for central heating,
* Electrically operated valves,
* Exhaust gas cooler adapted to a cogeneration engine,
* Automatically controlled throttle,
* Coolant buffer tank.