Gaussian modelling of the dispersion of hydrogen sulphide from Hellisheidi power plant, Iceland

Abstract

Hydrogen sulphide is a colourless, toxic gas naturally present in geothermal fields. When released to the atmosphere it can be a nuisance at low concentrations, but toxic at higher concentrations when it becomes non-detectable by humans. The exploitation of natural geothermal fields for energy production, such as Hellisheidi in Iceland, increases hydrogen sulphide emissions to the atmosphere and can reduce the air quality of surrounding areas. Since Hellisheidi power plant opened in October 2006, hydrogen sulphide emissions have doubled in the area from 0.007 ppm to 0.014 ppm; this increase is thought to have affected air-quality in Reykjavík. Monitoring of hydrogen sulphide levels in Reykjavík showed episodes of increased concentrations before the opening of the power plant, and later registered up to 0.09 ppm on September 4, 2006, and up to 0.11 ppm on February 7, 2007. These increases coincided with the bleeding and testing of wells, low air temperatures, high wind-speed and a southeasterly wind direction in February. The Gaussian models of the plume of dispersion revealed that the concentrations emitted by the power plant in three different periods (October 2006, November 2006 and February 2007) were reduced to 1 ppm when dispersed, and only in special weather conditions or in connection with anomalies at the power plant, was the air quality in Reykjavík affected. Given plans to intensify power production at Hellisheidi, it is recommended that hydrogen sulphide levels are monitored closely in the region, as expansion of the plant could lead to emissions that might affect air-quality in Reykjavík and the surrounding regions.