Combustion Melting Characterisation of Solid Fuel Obtained from Sewage Sludge

Dongju Kim,Yong-Taek Lim,Soo-Nam Park,Kyunghyun Kim,Yeong-Su Park,Dong-Kyoo Park

doi:10.3390/en14040805

Abstract

Solid fuelization technology can increase the heating value of sewage sludge such that it can be utilised as a fossil fuel substitutes. Reducing landfilling of bottom and fly ash resulting from heavy metals contained in sewage sludge is challenging. Hence, combustion melting technology (CMT), which can discharge bottom ash in the form of slag, has been proposed herein as an alternative to the conventional incineration technology. However, further research is required to improve the flowability of slag. Applicability of CMT for the stable treatment of heavy metals in the ash generated during the energisation of sewage sludge solid fuel has been reviewed. The change in the degree of fluidity was identified via a laboratory-scale fluidity measurement experiment following changes in melting temperature, mixing ratio of sewage sludge and sawdust, and basicity. The pouring index (PI) of sewage sludge solid fuel (pellet) was maintained at a level of about 60% at a basicity index of 0.8. Based on the results, the slagging rates and volume reduction rates, exhaust gas analysis, and heavy metal elution characteristics under oxygen enrichment were derived from a 2 ton/day combustion melting pilot plant experiment; thereafter, the feasibility of combustion melting of sewage sludge solid fuel was determined.

Highlights

The sewage sludge showed the highest pouring index (PI) throughout its melting temperature range, and the PIs of all three samples demonstrated a tendency to increase with an increase in the reaction temperature
Based on the results of the measurement of the PI, solid fuel of the sewage sludge with a sawdust ratio of 32% was used for the pilot plant operation, at a reaction temperature of 1300 ◦ C where the pouring index was above 60%
This study reviewed the applicability of combustion melting technology (CMT) in the energisation of sewage sludge solid fuel

Summary

Introduction

In South Korea, 11,219 tons of sewage sludge are produced daily, and this amount has rising since 2009, owing to an increase in population [1]. Sewage sludge incurs high treatment costs due to high moisture contents (73~84%) as well as the heavy metals contained in ash [2,3,4]. Sewage sludge has an 80% moisture content before drying. The high heating value (HHV, dry basis) of sewage sludge solid fuel is approximately 85% (14.7 MJ/kg), while that of wood pellets is slightly higher (16.7 MJ/kg) [2]. The sewage sludge generated in South Korea, as of 2018, amounts to 11,219 ton/day, from which the solid fuel produced is estimated to be

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