Substantiation of constructive and technological parameters of strainers methanetic of biogas installation

Abstract

One of the necessary conditions for the continuous process of methanogeneration and the increase in its intensity in biogas plants is mixing by means of special mixers.

The purpose of the studies is to substantiate the design and technological parameters of the agitators of the biogas plant's methane tank for possible replacement in the event of failure.

The substrate in the methane tanks is mixed several times a day, as a result of which: mixing of the fresh substrate with the seed portion for the purpose of migration and multiplication in the new material of active bacteria, the distribution of heat in order to retain, as far as possible, a uniform temperature distribution in the fermentor; destruction of the formed crust; improving the metabolism of bacteria due to the withdrawal of biogas vials and the supply of new nutrients.

The necessary mixing intervals are determined for each biogas plant individually by an experimental method. After starting the biogas plant, the substrate is mixed more often than in the normal regime, and decreases after the formation of a floating crust can already be distinguished. Bacteria grow in colonies. Rapid stirring breaks them and prevents bacteria from developing, so the optimal is slow mixing.

To mix the substrate in the methane tank, stirring devices (agitators) are used, which can be mechanical, hydraulic and pneumatic. To reduce the formation of sediment and prevent the occurrence of a floating crust, it is necessary to provide turbulence in all areas of the reactor. Therefore, such agitators can be effectively used only in small reactors. However, when it comes to substrates of low viscosity, containing few substances prone to precipitation or the formation of a floating crust, mechanical mixing devices are also effective for large reactors. For simple small installations with low biogas yield, mechanical agitators are an acceptable solution. Recently, deep mechanical agitators are often used to mix the substrate in methane tanks. The agitator from the point of view of the processability of the mixing process is a specific equipment, since its placement in different containers helps to maintain hydrodynamic flows of different orientations. Unlike surface-type mixing devices, whose flows are directed from the surface of the liquid to the bottom of the tank, submersible mixers are able to realize hydrodynamic fluid flows of various types.

Electro-mechanical stirrers are usually installed to mix the substrate in a methane tank in a suspended state.

Two hydrodynamic mixing principles can be realized in methane tanks, let's call them conditionally "zone" and "carrousel". With the band principle, one mixer is assumed, but it has limitations on the maximum possible length of the mixing zone. The inability to maintain long structures is caused by the geometry of the cross section of the methane tank. The carousel principle assumes a powerful intercorridor recirculation of the substrate by means of a stirrer, which ensures the maintenance of adjacent volumes.

Submersible mixers in classical terms are divided into: high-speed gearless, low-speed gearboxes with large-diameter blades and medium-speed ones. Mixers with recirculating axial pumps are also used to provide interband recirculation. When placing submersible mixers in tanks, it is necessary to observe the basic dimensions of the depth of the stirrer installation and its positioning relative to the walls of the tank.

The main parameter for selecting a stirrer is the power input for mixing the required volume of the substrate. Based on the application of the proposed method, the design and technological parameters of the agitators of the biogas plant methane are valid for possible replacement in case of failure. In the future, the obtained research results can be effectively used in the design of promising biogas plants.