Co-firing wood fuel with coal
With some designs of coal fuelled heat plant it is possible to co-fire wood fuel with the coal. This can be an economic opportunity where wood fuel is available at a cheaper price than coal, or it can be done to get the air emissions below limits set by the plant’s resource consent conditions. Care needs to be taken in doing that as the equipment will not have been designed for wood fuel and wood fuel has very different combustion characteristics than coal. The most significant difference can be in the reduction in heat output from the heat plant.
Conversion of an existing coal fuelled boiler to using wood fuel should be undertaken by advisers who are conversant with doing this and can show that they have been successful on other sites. This is a situation where reference checking is important.
If a new site is looking to co-fire wood fuel and coal then a good option is to have one boiler on coal and another on wood fuel so that the wood fuel plant performance can be optimised.
The Dunedin Hospital coal boilers are often run on wood fuel and a report on their performance is available here.
Fonterra have announced (watch Youtube video), that they will run wood and coal as the fuel for their expansion at Studholme.
Silverfern Farms are using wood pellets in their coal boiler in Dargaville and that has now got the air emissions compliant with their resource consent conditions.
A guide to co-firing wood with coal is available here.