Thermal effects of pretreatment of dark fermentation feedstocks in a vortex layer apparatus

Abstract

Anaerobic digestion is an efficient way to process organic waste to produce biogas. At the same time, one of the stages of anaerobic digestion so called dark fermentation (DF), which makes it possible to obtain biohydrogen. To increase the bioavailability and efficiency of mass transfer between feedstock particles and hydrolytics and, as a result, increase the DF efficiency, it is advisable to pretreat organic waste by various methods. One of the most promising and energy efficient methods of preparing the feedstock for anaerobic fermentation, including DF, is its processing in the vortex layer apparatus (VLA). However, not all aspects of VLA application in anaerobic digestion feedstock pretreatment systems have been fully considered: in order to introduce the VLA into the organic waste DF system, it is necessary to determine, among other things, the energy characteristics of VLA under various modes of its operation, and the data obtained must be used in the development of the energy balance of the anaerobic processing system. Thus, the purpose of this work is to experimentally determine the thermal effects of pretreatment of DF feedstocks in VLA under various modes of its operation using the response surface methodology. To achieve this goal, an experimental setup was developed and created, which made it possible to conduct an experiment based on the central composite design (CCD) using Design-Expert software. The resulting models and their response surfaces have a determination coefficient of more than 0.99, which indicates their adequacy. The coefficient of conversion of electricity into heat on the VLA coil is on mean at the level of 0.54 ± 0.11, and the coefficient of useful use of heat VLA for heating the feedstock is 0.42 ± 0.06, which indicates a high potential for using waste heat. Thus, the obtained models of thermal effects of pretreatment of DF feedstocks in the VLA can be used to determine both the heat directly introduced into the feedstock during pretreatment and the heat removed by the heat exchanger to maintain the VLA operating mode. In this case, the heat removed by the heat exchanger can be used as a source of low-grade heat.