METHOD FOR DETERMINING THE PARAMETERS OF THE HYDROMECHANICAL MIXER OF A BIOGAS PLANT

Abstract

Creation of reliable and relatively cheap mass mixing systems is an important project among the complex of current engineering tasks in the development of small-sized biogas plants, available for implementation at farms and small agricultural enterprises as the efficiency of the whole plant depends to a large extent on this operation. Therefore, the purpose of this study is to substantiate the schematic diagram of a combined-action hydromechanical mixer, to formulate theoretical provisions and a method for calculating of its main parameters, and to determine further stages of developing a mixing system. When designing a substrate mixing system, the key stages are as follows: determining the type of mixer taking into account the viscosity, density of the fractional composition of the substrate; calculating the dimensions of the elements, the required rotation speed, drive power taking into account the geometry of the methane tank; selecting materials, standard parts and serial products that correspond to the chemical properties of the substrate and operating conditions (for example, corrosion resistance). At the same time, at all stages, the requirements for ensuring proper mixing quality, reliability and accessibility of maintenance, compliance with ergonomic, environmental and safety conditions should be taken into account. For mixing the substrate, mechanical mixers of various types are mainly used, each of which works quite effectively in certain ranges of substrate viscosity, but their common feature is that they create local zones of excessive mixing speed. Because of this, a common drawback of mechanical mixers is insufficient quality of mixing of the mass throughout the reactor volume, as well as the problematic nature of a reliable and safe drive. Podillia State University has developed a scheme for a multi-section biogas plant, where one fecal pump that also serves to drive the hydro jet mixer is used to pump the mass between sections. It has been established that to ensure proper quality of operation of the mixer it is necessary to supplement it with vertical mixing elements (shields), and the calculation should be carried out based on the technologically permissible mixing speed. For this purpose, a method has been developed for sequential calculation of the required circular speed of the blade (depending on the size of its operation and the viscosity of the substrate), the frequency of rotation of the mixer, the force and torque for its drive. Based on these data, hydraulic calculations of the substrate supply system are then carried out: the required flow rate through the nozzles, the substrate consumption, the diameters of the channels, the total flow, the pressure and the power of the fecal pump drive. Thus, the peculiarity of this method is that it combines mechanical and hydraulic calculations and can serve as the basis for developing an algorithm for automated design of biogas plants.