Bioreactor. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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A bioreactor is the basis of any biogas plant, and rather stringent requirements are imposed on its design. Thus, the body of the bioreactor must be strong enough with absolute tightness of its walls. Good thermal insulation of the walls and their ability to reliably resist corrosion are required. In this case, it is necessary to provide for the possibility of loading and emptying the reactor, as well as access to its internal space for maintenance.

The forms of reactors are very diverse. So, from the point of view of creating the most favorable conditions for mixing the liquid substrate, accumulating gas, removing sediments and destroying the resulting crust, it is advisable to use a tank shaped like an egg. Large reactors of this shape are usually constructed from concrete, so they are characterized by a high manufacturing cost, which significantly limits their use. On the other hand, auxiliary reactors of smaller volumes are quite easy to make from fiberglass, that is, from polyester resin reinforced with fiberglass, and they are not so expensive.

A cylindrical tank with a conical top and bottom, like an egg-shaped one, is characterized by a small space for gas accumulation, a limited amount of floating crust, and good sludge removal. However, in such reactors, less favorable conditions are created for the movement of the liquid substrate. Large-volume tanks of this shape, used in municipal wastewater treatment and decomposition plants, like egg-shaped reactors, are made of concrete. However, "cylindrical" reactors are somewhat cheaper. In individual farms, reactors of the above form, but, naturally, of a smaller capacity, are made of steel or fiberglass. By the way, in fiberglass reactors it is easier to achieve better conditions for moving the substrate.

Fig.2. The most common types of bioreactor tanks: a - in the form of an egg, b - cylindrical with conical upper and lower parts, c - cylindrical, d - cylindrical with a partition, e - in the form of a parallelepipid (with a partition), f - cylindrical (obliquely located), g - trench in the ground (with a cover).

Cylindrical tanks are relatively easy to manufacture, which is explained by extensive experience in the construction of tanks for agricultural purposes (steel, concrete, fiberglass tanks-bunkers for silage and other feed). However, in comparison with tanks of previous forms, it is impossible to organize sufficiently good conditions for moving the substrate in a cylindrical tank, while one has to reckon with higher costs for removing sediment and destroying the floating crust, which is associated with an increase in energy consumption for mixing the mass.

Fig.3. Two-chamber biogas plant of flow type: 1 - pump; 2 - receiving chamber; 3 - fermentation chamber; 4 - mixing device; 5 - heater; 6 - after-fermentation chamber; 7 - collection of fermented mass; 8 - auger.

If a cylindrical tank is divided into two chambers by a transverse vertical partition, then it is possible to organize a biogas production system with alternate use of the tank chambers. Moreover, the construction of a tank with a baffle will cost less than the construction of two separate tanks. We also note that with such an arrangement, the value of thermal insulation of the outer walls of the tank decreases, and it is not very difficult to integrate any heating device into a partition made of a sufficiently heat-conducting material, which gives the installation additional structural benefits.

Fig.4. Trench biogas plant: 1 - room for animals; 2 - bioreactor; 3 - mixer; 4 - grab; 5 - storage for fermented manure; 6 - gas tank.

In simple, mostly small, self-constructed biogas plants, the fermentation chamber usually has the shape of a parallelepiped (pool or pit with a lid). To improve efficiency, such a reactor is partitioned off with a vertical wall, creating a main fermentation chamber and a chamber for final fermentation and sedimentation of the sludge. True, installations of this type do not make it possible to achieve a high degree of decomposition of the substrate, since it is practically impossible to ensure either uniform mixing of the mass, or control of the loading of the working volume of the chamber, or observance of the residence time of the mass in the reactor, which is necessary to obtain the maximum amount of gas. Yes, and the destruction of the floating crust and sediment is associated here with high costs.

In a horizontal tank, the substrate is mixed in the longitudinal direction. Here, cylindrical reactors made of steel or fiberglass are suitable for small installations. Horizontal tanks of considerable capacity have the shape of a parallelepiped and are made of concrete.

The inclined arrangement of such tanks facilitates the flow of sludge to the discharge opening. This design is convenient for placing the simplest mixing mechanism.

The reservoir in the form of a trench dug in the ground allows the processing of large quantities of substrate. As a building material for the walls of the reactor, as a rule, concrete is used.

Now let's take a closer look at the design of some types of biogas plants that are already used in practice. Now, on the basis of a tank in the form of a parallelepiped with a partition, a two-chamber biogas plant of a flow type has been developed and operates reliably, where the substrate is first directed to one part of the tank (fermentation chamber), and then flows by gravity into another part (after-fermentation chamber). To increase the efficiency of this installation, it is equipped with a stirrer in the fermentation chamber, a heater, and an auger for removing large inclusions in the sludge.

Fig.5. Trench biogas plant: 1 - elastic collector; 2 - foam boards; 3 - fermentation chamber; 4 - heater (boiler).

Fig.6. Elastic bioreactor

Trench biogas plants are becoming more and more common. Take, for example, a trench installation from Germany. Here, directly from the premises where animals are kept, manure, diluted with water, goes to the bioreactor, where it is fermented. The plant is equipped with mechanical mixing of the substrate and a grapple for loading fermented manure.

In another trenching plant (USA), fresh liquid manure enters the fermentation chamber from above, and heated water from below. The gas collector of the installation is elastic, and foam plates are located on the surface of the fermented substrate for thermal insulation.

Let us also draw the reader's attention to flexible reactors commonly used in the countries of Southeast Asia. Such reactors (capacities) are made of dense rubberized fabric or synthetic film. To organize the work of such bioreactors, they must either be buried in the ground, or placed inside a sufficiently strong "circular" fence.

Author: Shomin A.A.

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