Abstract
Gasification of organic matter under the conditions of supercritical water (T > 374 °C, p > 221 bar) is an allothermal, continuous flow process suitable to convert materials with high moisture content (<20 wt.% dry matter) into a combustible gas. The gasification of organic matter with water as a solvent offers several benefits, particularly the omission of an energy-intensive drying process. The reactions are fast, and mean residence times inside the reactor are consequently low (less than 5 min). However, there are still various challenges to be met. The combination of high temperature and pressure and the low concentration of organic matter require a robust process design. Additionally, the low value of the feed and the product predestinate the process for decentralized applications, which is a challenge for the economics of an application. The present contribution summarizes the experience gained during more than 10 years of operation of the first dedicated pilot plant for supercritical water gasification of biomass. The emphasis lies on highlighting the challenges in process design. In addition to some fundamental results gained from comparable laboratory plants, selected experimental results of the pilot plant “VERENA” (acronym for the German expression “experimental facility for the energetic exploitation of agricultural matter”) are presented.
Highlights
Throughout the past two decades, various feed materials have been tested in the VERENA pilot plant
To model compounds such as methanol or glycerol, different biomass and waste materials have been converted to a combustible product gas
Gasification under the conditions of supercritical water is a promising process for the conversion of wet waste biomass and wastes
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. There are several motivating forces for the treatment of wet waste biomass. Most important is the need to treat a waste stream that, if not treated, would pollute the environment. Harmful bacteria, dangerous proteins (prions), harmful DNA, residual pharmaceuticals, and last, but not least, uncontrolled emission of methane should be prevented. Other aims are the need to recover phosphorous as a nutrient [1,2,3] and the need to recover or save energy and reduce CO2 emissions by converting biomass to a combustible gas and substitute fossil fuels [4,5]
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