Waterberg coal characteristics and SO2 minimum emissions standards in South African power plants

Abstract

Key characteristics of coal samples from the supply stock to the newly commissioned South African National Power Utility's (Eskom's) Medupi Power Station - which receives its supply coal from the Waterberg coalfield in Lephalale (Limpopo Province, South Africa) - were evaluated. Conventional coal characterisation such as proximate and ultimate analysis as well as determination of sulphur forms in coal samples were carried out following the ASTM and ISO standards. Coal was classified as medium sulphur coal when the sulphur content was detected in the range 1.15-1.49 wt.% with pyritic sulphur (≥0.51 wt.%) and organic sulphur (≥0.49 wt.%) accounted for the bulk of the total sulphur in coal. Maceral analyses of coal showed that vitrinite was the dominant maceral (up to 51.8 vol.%), whereas inertinite, liptinite, reactive semifusinite and visible minerals occurred in proportions of 22.6 vol.%, 2.9 vol.%, 5.3 vol.% and 17.5 vol.%, respectively. Theoretical calculations were developed and used to predict the resultant SO₂ emissions from the combustion of the Waterberg coal in a typical power plant. The sulphur content requirements to comply with the minimum emissions standards of 3500 mg/Nm³ and 500 mg/Nm³ were found to be ≤1.37 wt.% and ≤0.20 wt.%, respectively.

Keywords: Flue gas desulphurisation; Macerals; Petrographic properties; Pyritic sulphur; Sulphur emission.