Selecting a stirrer and optimizing the process of mixing the substrate in the fermenter of biogas unit

The relevance of the work is related to the problem of soil degradation as a result of pollution by livestock waste and the need for timely disposal of waste into effective organic fertilizer and biogas. Increasing the share of the use of organic fertilizers makes it possible to develop organic farming technologies, and accordingly leads to the production of healthy crop products. The work investigated the process of substrate mixing in the fermenters of an operating pilot biogas plant. The technological line is designed for processing liquid organic waste, mainly manure or litter, by anaerobic digestion to produce innovative environmentally friendly organic fertilizers on an industrial scale. The purpose of the study was to select a stirrer and optimize the conditions for mixing the substrate in the fermenters of a biogas plant. The physicochemical properties of the substrate were studied by laboratory methods. The mathematical model of the mixing process is based on a semi-empirical description of the hydrodynamics of flows in the reactor, modernized taking into account the current state of the issue under the conditions of a fermenter with specific geometric characteristics. As a result of the work carried out, the optimal options for the geometric dimensions of the stirrers were determined (three variants for three-blade stirrers intermittent with a blade angle of 30°, differing in the size of the impeller and rotation speed) and the parameters of the mixing process were calculated. Based on a laboratory experiment and the results of calculating the sedimentation rate, the frequency of turning on the stirrer (once a day) and the time of its continuous operation to homogenize the suspension were determined. The results of the work can be used in the design of mixing devices and substrate mixing modes in bioreactors.