Pentane Evacuation for Binary Plants

Abstract

Mercury owns and operates several Ormat binary plants located in the North Island of New Zealand. For each site n-Pentane is the motive fluid and its flammable nature presents challenges with respect to maintenance activities on pentane plants. Until recently Mercury has relied on specialized contractors or flooding vessels with water to enable hot work such as welding to take place on pentane equipment. With large binary units this approach is not always practical and for the past two years Mercury have undertaken significant research and planning to enable the safe evacuation of pentane plant.
A key focus for the project has been to assess and reduce risks associated with the evacuation procedure. With guidance from Ormat and collaboration with other New Zealand pentane site operators Mercury have established a guideline for evacuation of pentane plants. The approach taken uses a combination of nitrogen purging and evacuation techniques to remove pentane from a unit. A key piece of equipment designed and fabricated by Mercury is a portable pentane evacuation skid for use at any of their pentane sites. This paper discusses the effectiveness of the pentane evacuation, lessons learned along with Mercury’s plans to improve pentane safety in their plants.