What is the coal like at Ngapara?
The lignite coal at the Ngapara site is characterised by high moisture, ash and sulphur contents, but is quite suitable for use in cement production, as was demonstrated by trial burns carried out at the Burnside cement plant during the 1970s. During the clinkering process, all of the ash and virtually all of the sulphur in the coal is bound into the clinker, rather than emitted. The sulphur from the Ngapara coal would actually be a bonus in the cement-making process. Sulphur is added as gypsum (CaSO3) during the clinker-to-cement grinding process to control the setting behaviour of the cement. Gypsum would be imported as it is not found in New Zealand. The higher levels of sulphur in the clinker as a result of using Ngapara coal would in effect reduce the amount of gypsum required.
