Schematic of a biogas plant
Biogas plant - is a complex of buildings and technological equipment integrated into a single automated system of the controlled methane fermentation.
Biogas production technology and construction of biogas plant is different depending on the raw material and the specifics of the project. There are two-stage and one-stage biogas complexes. One-stage technology is used for most of the substrates and this technology may be considered as a base. Two-stage technology is used for substrates that are rapidly decomposed, and so have a tendency to oxidize. Two-stage technology differs from one stage by presence of the additional hydrolysis reactor. The base biogas plant scheme consists of the following components and structures:
1. Receiving tank
2. Heating system
3. Mechanical agitators
4. Biomass supply system
6. Gas storage tank
7. The dome of rubberized PVC for protection of the gas storage tank
8. Gas offtake system and gas supply system with the condensate drainage system and sulphur recovery system
10. Lagoon or storage tank for liquid fertilizer
11.The automation system, the system of the process display and control
12. Heat supply station
The principle of biogas production retuires maximum automation and minimum human labor. Wastes enter the receiving tank (1).There they are preliminary accumulated, heated(2) and thoroughly mixed (3). Raw material supply in the fermenter (5) takes place 4-6 times a day by using a special pump for liquid and viscous substrates. Fermenter (5) is gas-tight, sealed tank. To maintain a stable temperature, the fermenter inside is equipped with a heating system of a bottom and the walls (2). In the conditions of cold climates, to avoid heat loss, the fermenter is heat-insulated from outside. The substrate is continuously stirred by using the low speed mechanical agitators(3), which ensures a complete and careful mixing. Depending on the physical and mechanical properties of the substrate, different types of agitator systems are used: mechanical, hydraulic or pneumatic systems.
The process of the fermented substrate discharge is automatic with the same frequency as the loading. The whole biogas plant control is performed on signals from the automation system (11). Biogas is collected in a gas-storage tank (6). The gas-storage tank (6) is used as a gas-tight cover of the fermenter and fulfils a function of gas accumulation. Outer dome (7) has a high ultraviolet resistance, resistant to arson and is highly extensible. High elasticity allows the secure fixing of the construction.
Biogas is discharged by using pipeline (8) which is equipped with automatic condensate drain and safety devices that protect the gas-storage tank (6) from the excess pressure. The continuous supply of biogas forwards from the gas-storage tank (6) to the cogeneration plant or a biogas purification system. Refined substrate after the installation proceeds to the separator (9. Mechanical separation system works about 4-6 times a day and parts fermented remains from the fermenter on solid and liquid biofertilizers. All equipment is controlled by the automation system (11). Technology of production of biogas has two modes of system management and control on the areas of biogas plant are used:
• Program timing control of the technological stages is performed at time intervals and synchronized between the systems.
• According to the values of the control instruments. Automatic control systems of critical or alarm values of the production operations are organized according to this principle.
For synchronous operation of the entire system, the signals come to a central program-logic controller. The controller investigates the entire manufacturing chain of the complex and displays information on the screen. The screen indicates all the buildings and units, equipped with actuating devices and data sensors. All operating parameters of the biogas plant are displayed on the monitor of the central control room. Control room is equipped with a central control panel, which allows to change the work of all sections of the biogas plant from manual mode to automatic and vice versa, for local or remote control.