| Title | THE USE OF VENTURI DURING BINARY PLANT PENTANE EVACUATION |
|---|---|
| Authors | F. Hanik |
| Year | 2021 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Venting, Binary plants, Eductors, Evacuation, Ngawha, Vacuum pump, Nitrogen, Purge |
| Abstract | The use of a binary cycle to extract energy from geothermal fluid for power generation is a well-established method. The main Achilles heel with these systems is the common use of a hydrocarbon based motive fluid in the process and the accompanying risks which are present when managing a flammable substance. One such instance of exposed risk occurs during maintenance work when breaking into the closed system. It has now become common in NZ to demand a full pentane evacuation and inert gas purge, utilising a vacuum pump and nitrogen gas generation plant, before a permit is issued to the work party; In doing so, striving for a full elimination mindset of workplace risk reduction. An additional method has been developed by Ngawha Generation Limited which can be used in conjunction and complements existing practices to reach desired Lower Explosive Limits. The utilisation of an air driven Venturi known as an Air Horn or Eductor has been trialed. These are commonly used in meeting confined space ventilation requirements for underground storage tanks in the industrial and wastewater sectors. In the application it was used at Ngawha, the eductor was placed on the shell side of the recuperator vessel just downstream of the turbine outlet spool. During the works involving the removal and re-installation of the spool piece the eductor drew in air at the work front and expelled it to a safe location using ducting. The air carried away any pentane vapor that was still being liberated. The large volume of air displacement compared to that of pentane vapor resulted in a vented mixture which did not reach lower explosive limits at the discharge point. No hydrocarbons were detected at the work front, which is something current methods often fail to achieve. |