Separation of Unburned Carbon from Coal Conversion Ash: Development and Assessment of a Dry Method

Authors

Charlotte J. Badenhorst, CIMERA Department of Geology, University of Johannesburg, PO Box 524, Auckland Park, Johannesburg, 2006, South Africa
Nicola J. Wagner, CIMERA Department of Geology, University of Johannesburg, PO Box 524, Auckland Park, Johannesburg, 2006, South Africa
Bruno R.V. Valentim, Instituto de Ciências da Terra (ICT), Pólo da Faculdade de Ciências da Universidade do Porto, e Departamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, S/N, 4169-007 Porto, Portugal
Karel S. Viljoen, Instituto de Ciências da Terra (ICT), Pólo da Faculdade de Ciências da Universidade do Porto, e Departamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, S/N, 4169-007 Porto, Portugal
Ana C. Santos, Instituto de Ciências da Terra (ICT), Pólo da Faculdade de Ciências da Universidade do Porto, e Departamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, S/N, 4169-007 Porto, Portugal
Alexandra Guedes, Instituto de Ciências da Terra (ICT), Pólo da Faculdade de Ciências da Universidade do Porto, e Departamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, S/N, 4169-007 Porto, Portugal

Document Type

Article

Abstract

Unburned carbon found in coal conversion ash has the potential to be used in a variety of value-added applications. However, it is first necessary to separate the unburned carbon from the rest of the ash phases. This poses challenges due to the relatively low starting carbon-in-ash values (0.4 to 7.8 wt% reported for South African sources), and the high carbon grades (ideally ∼90 wt% carbon) and recoveries that need to be achieved. In this study a dry method for the separation of unburned carbon from coal ash was developed and assessed using fly, bottom, and gasification ash samples obtained from various South African coal conversion utilities. The idea is to subsequently use the unburned carbon product as a precursor for synthetic graphite manufacturing. The separation consisted of a combination of size, electrostatic (CoronaStat), and magnetic separation steps, and the carbon grades (as loss on ignition [LOI]) and recoveries were assessed for each step. Precharacterization included X-ray diffraction, LOI, and petrography (carbon-mineral associations) analyses. The carbon grades increased from 4.01 and 7.04 wt% to 56.55 and 65.74 wt%, respectively, for two fly ash samples. The process was less efficient for the bottom and gasification ash samples, where final carbon grades of 53.21 and 45.10 wt% were achieved from a starting base of 5.47 and 6.90 wt%, respectively. The carbon recoveries for all samples were low (<35%), possibly due to the mineral inclusions that form part of the carbon matrix. The suggested separation method is promising but still requires further modification.

First Page

89

Last Page

96

DOI

10.4177/CCGP-D-19-00002.1

Publication Date

1-1-2019

Recommended Citation

Badenhorst, Charlotte J., Nicola J. Wagner, Bruno R.V. Valentim, Karel S. Viljoen, Ana C. Santos, and Alexandra Guedes. 2019. “Separation of Unburned Carbon from Coal Conversion Ash: Development and Assessment of a Dry Method.” Coal Combustion and Gasification Products 11 (2): 89–96. https://doi.org/10.4177/CCGP-D-19-00002.1.