Vacuum Evaporation of a Liquid Digestate from Anaerobic Digestion: A Techno-economic Assessment

Abstract

The current boom of biogas plants (BGP) in Europe is associated with major digestate production. Digestate contains large amounts of nutrients but in low concentrations compared to artificial fertilizers. Storage and transportation of the digestate represents significant financial burden for BGP owners, especially in areas with intensive agricultural production. Vacuum evaporation (VE) is a technology which allows to efficiently reduce volume of the digestate. Benefits of VE include a simple design, operational reliability, and ability to utilize available waste heat. Integration of evaporation technology in BGP must respect concrete operating conditions and should be properly justified in terms of technical and economic aspects. This paper discusses central part of a mathematical model which may be used for technical-economic assessment of VE. Typical BGP is used in a case study to show how the integration of VE is facilitated with the increase in transportation distances and a decrease of electricity feed-in tariffs. It is shown that integration of VE is not necessarily beneficial for every BGP.