Exergetic efficiency and options for improving sewage sludge gasification in supercritical water

Abstract

SUMMARYThe present article deals with an exergy analysis of a process under development for the gasification of biomass in supercritical water (supercritical water gasification, SCWG). This process is aimed at generating hydrogen out of the biogenic feedstock sewage sludge. The principle of the process is based on making use of the modifications of specific physical and chemical properties of water above the critical point (T ¼ 3748C, p ¼ 221 bar). These properties allow for a nearly complete conversion of the organic substance contained in the feed material into energy-rich fuel gases, containing hydrogen, carbon dioxide and methane. Based on a steady-state model of the process, exergy flow rates are calculated for all components and a detailed exergy analysis is performed. From the exergetic variables, options to improve the individual plant components as well as the overall plant are derived. The components with the highest proportion of exergy destruction in the complete process are identified and possibilities of improving them and the complete system in order to increase the overall efficiency are demonstrated. The combustion chamber necessary for heat supply is found to be the component with the highest proportion of exergy destruction of the complete plant. Moreover, the components of air preheater, reactor contribute significantly to the exergy destruction of the complete system.

Partial oxidation of municipal sludge with activited carbon catalyst in supercritical water

“…Nevertheless, the hydrocarbon in sludge, if utilized wisely, would be a renewable source of energy to produce hydrogen. The topic of municipal sludge reforming for hydrogen production has received some attention [1,2].…”

Life Cycle Assessment in Chemical and Micro Reaction Engineering

“…Compared to the case studies from Jödicke, Khan, and Dufour, which utilized experimental or literature data for the LCI of the foreground processes, the following two case studies applied the process simulation software Aspen Plus [38] and the thermodynamic calculation software THESIS [39].…”

Supercritical Water Gasification of Municipal Sludge: A Novel Approach to Waste Treatment and Energy Recovery

“…Supercritical water gasification productcomposition studies using actual sludge are limited and expected supercritical product yields are variable (Afif et al, 2011;Cao et al, 2011). The assumed, basic expected, reaction kinetics (using glucose as a model compound) are represented by the formulas (1-2) listed below (Gasafi et al, 2007;Schmieder et al, 2000):…”

“…Plus, hydrolysis and hydropyrolysis reactions in SCW quickly dissolve sludge educts before they can dehydrate, thus suppressing polymerization of cleavage products and tar formation (Gasafi et al, 2007). Although small quantities of an oxidant can produce partial oxidation, catalysts appear to be the key for reliably achieving both char and tar avoidance and selectivity for efficient H2 production (Balat et al, 2009;Calzavara et al, 2005;Ding et al, 1996).…”