Energy Production Requires Energy Input to Digesters - A Review of Digester Mixing and Development of Improved Digester Mixing Design Methodologies

摘要

It is widely recognized that good mixing is important to successful operation and performance of anaerobic digestion. However, the wastewater industry has lacked a holistic approach to design and operations that account not only the for the need to have good blending, but also recognize the role of mixing in preventing grit deposition, and more recently the role of mixing in prevention of frequent rapid volume expansion and maintaining active volume by reducing gas holdup. Designers have relied on rules of thumb and past experience rather than any developed science around good design practices. In the last couple of decades, tracer studies and more recently, computational fluid dynamic (CFD) modeling have been used as design or analytical tools, however, these have focused strictly on blending and predicting active volume. There has been little effort focused on the other important aspects of digester mixing, including a rational analysis of how mixing configuration plays into each of these important aspects. The goal of this paper is to synthesize the theory, data, and observations generated to date with respect to these important mixing design questions and propose design calculation methodologies to help optimize mixing design and thereby assure optimum digester performance. These proposed design methodologies are intended to help design engineers and operators better understand the mechanisms at play and which can be controlled in designing and operating digesters.