Energy Model for an Industrial Plant Using Geothermal Steam in New Zealand

Abstract

Fletcher Challenge Paper Australasia Ltd operates a kraft pulp and newsprint paper mill at Kawerau, New Zealand. The energy requirements for the millís operation are large, complex and varied. The process itself produces energy sources (ìfuelsî) in the form of wood waste and spent cooking liquors where both are burnt in power boilers (for wood waste) and chemical recovery boilers (liquors) to produce 400 oC steam at 45 barg. This amounts to 75% of the process steam requirement. Geothermal steam provides the remainder. Electrical energy is produced from this steam amounting to 15-20% of the millís needs of 180 MW. Steam Plant operators are required to manage the process of supplying the pulp and paper mills with steam and generating power internally. They have a number of options for doing this and substantial savings are available if the lowest cost options can be determined at any time, and then followed. A model of the millís energy system has been developed utilising mixed integer linear programming techniques and real time data from the millís information system to provide operations staff the lowest cost option in meeting the millís energy requirements from the available ìfuelsî.