An experimental study of ash behaviour and the potential fate of ZnO/Zn in the Co-combustion of pulverised South African coal and waste tyre rubber

Abstract

A Novel combustion application utilising waste tyre rubber (WTR) as a secondary fuel in pulverised coal power plants is presented. Co-combustion of a South African coal (SAf) with WTR at the fuel fractions (FF) 4.1%, 14.1% and 19.7% along with the pure firing of WTR was conducted in an 80 kWth combustion test facility (CTF). This study assessed the potential slagging and fouling behaviour of the resultant ashes produced from co-firing SAf/WTR and pure fired WTR. XRF and ICP/OES analysis of the co-fired SAf/WTR and pure fired WTR ashes revealed a high composition of acidic oxides. Based on the fusibility indices (B/A, RS, SR, F and Fu) it was determined that co-fired SAf/WTR and pure fired WTR ashes carry a low risk of slagging and fouling. ZnO is incorporated in the manufacturing of tyres as a compounding additive. ZnO is present within raw WTR, posing the question as to its fate during combustion. In this study ash collected and analysed from the pure fired WTR and co-fired SAf/WTR exhibited lower levels of Zn than anticipated. It is suggested that ZnO remains in the vapour phase within the CTF at temperatures >1200 o C. Experimental analysis found Zn enrichment at lower temperatures was not significant within the fly ash collected by the cyclone trap or ash deposits collected from the water cooled sections of the CTF. This suggests that Zn could be forming a submicron aerosol. It is further noted that ZnO/Zn is not likely to contribute significantly in the slagging/fouling mechanisms, due to its volatile nature. However this present study highlights the need for further experimental assessment of co-firing SAf/WTR required prior to any industrial application.

Review on the Current Status of the Co-combustion Technology of Organic Solid Waste (OSW) and Coal in China

“…In addition to the cofiring of coal and sludge, few researchers explored the slagging/fouling behavior during the co-combustion of coal and other OSWs. For example, Singh et al peerformed the co-combustion experiments of a South African coal with waste tire rubber in an 80 kWth combustion test facility. The results indicated that the co-combustion ashes had a low risk of slagging/fouling and ZnO would not contribute to in-furnace slagging, showing the potential use of waste tire rubber as a secondary fuel within coal-fired boilers.…”

2014 Atomic Spectrometry Update – a review of advances in X-ray fluorescence spectrometry

“…A reduction of ash loops reduced the amount of potassium transferred from the combustion reactor to the gasication reactor. Singh et al 175 assessed the potential slagging and fouling behaviour of the ash produced from cocombustion of a South African coal with waste tyre rubber (WTR) along with pure red WTR. Zinc oxide is incorporated during the manufacture of tyres as a compounding additive and was also present within raw WTR.…”

Combustion Characteristics and Slagging during Co-Combustion of Rice Husk and Sewage Sludge Blends

“…This liquid phase, slag-melt, might cause serious ash deposition problems. Meanwhile, alkali earth and alkali metals (K, Mg, Ca and Na) are likely to condense on the cooler zones of the boiler [30]. The total content of SiO 2 and Al 2 O 3 decreased with an increase in sewage sludge content, indicating that the ash generated from co-combustion would weaken hydration activity when used in the preparation of cementious materials.…”