Investigation of sewage sludge gasification with use of flue gas as a gasifying agent

Izabella Maj,Edyta Kudlek,Piotr Ostrowski,Marek Pronobis

doi:10.1051/e3sconf/20171402001

Izabella Maj, Edyta Kudlek + Show 2 more

Open Access

https://doi.org/10.1051/e3sconf/20171402001

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Abstract

The paper presents results of investigation of low-temperature sewage sludge gasification with use of flue gas as a gasifying agent. Tests were conducted in a laboratory stand, equipped with a gasification reactor designed and constructed specifically for this purpose. During presented tests, gas mixture with a composition of typical flue gases was used as a gasifying agent. The measuring system ensures online measurements of syngas composition: CO, CO2 , H2 , CH4 . As a result of gasification process a syngas with combustible components has been obtained. The aim of the research was to determine the usability of sewage sludge for indirect cofiring in power boilers with the use of flue gas from the boiler as a gasifying agent and recirculating the syngas to the boiler’s combustion chamber. Results of presented investigation will be used as a knowledge base for industrial-scale sewage sludge gasification process. Furthermore, toxicity of solid products of the process has been determined by the use of Microtox bioassay. Before tests, solid post-gasification residues have been ground to two particle size fractions and extracted into Milli-Q water. The response of test organisms (bioluminescent Aliivibrio fischeri bacteria) in reference to a control sample (bacteria exposed to 2% NaCl solution) was measured after 5 and 15 minutes of exposure. The obtained toxicity results proved that thermal treatment of sewage sludge by their gasification reduces their toxicity relative to water organisms.

Highlights

Gasification is a process of thermochemical conversion of a carbon-based feedstock into a combustible product gas with the use of a gasifying agent, such as steam, air or gas mixtures
The gasification temperature is defined above 700-950 ° C, with a combustible gas as a main product of the process, what differs gasification from pyrolysis
The technology discussed in this paper is defined as a low-temperature gasification, due a temperature range lower than in typical gasification process and a combustible gas as a main product

Summary

Introduction

Gasification is a process of thermochemical conversion of a carbon-based feedstock into a combustible product gas with the use of a gasifying agent, such as steam, air or gas mixtures. In recent decades ono- and co-combustion of sewage sludge are probably the most developed thermal utilization methods, technologies of gasification and pyrolysis are developing constantly [3, 4]. Results of presented investigation will be used as a knowledge base for industrial-scale sewage sludge gasification process. In field of sewage sludge gasification and pyrolysis some studies of rotary kiln and fixed bed reactors are known [5, 6] but mainly in a laboratory scale. No studies were found in the literature about the gasification of sewage sludge with use of flue gases as gasifying agent. The main aim of presented laboratory study is to investigate an usability of sewage sludge to gasification process in an industrial-size rotary reactor prior to cofiring the process’ product (syngas) in power boilers

Laboratory research

Parameter Lower heating value Ash Moisture

Sewage sludge

Findings

Conclusions and further operation