Last spring, Wilson Goddard, a California-based engineer with more than two decades of experience in the field of geothermal energy development, prepared answers to several frequently asked questions about geothermal energy in general and Puna Geothermal Venture’s operations in particular. Here is an abridged version of some of those questions and answers.
For the record, Goddard strongly favors geothermal energy, which he says can be an important element in the development of a reliable, environmentally sound energy strategy. However, his criticisms of the manner in which geothermal energy has been regulated and developed in Hawai`i causes him to be regarded by many of its proponents as a less than staunch ally.
Explain in simple terms how geothermal development produces electricity.
In geothermal development, a well is drilled deep into the Earth and hot water and other fluids come up to the surface under pressure, bringing the Earth’s heat with them. When the pressure is reduced in special equipment, some of the fluids ‘flash’ into steam, which is passed through the blades of electrical turbines, causing the blades to turn. This produces electricity. (In some resources, the fluids are already in the form of steam.) The heat-spent fluids and steam are then cooled, producing condensate. The excess condensate along with the heat-spent brine is injected back into the Earth.
What kind of system does PGV propose to use?
PGV has proposed a well field consisting of six to eight production wells and injection wells for returning the heat-spent brine and non-condensible gases back into the producing geothermal resource. The geothermal fluids would be transported through insulated pipelines to separation vessels. There, steam and other gaseous constituents would be separated from the fluid. The resulting brine would then be injected back down into the geothermal resource.
Insulated pipelines would then transport the steam and non-condensible gases to the steam turbines, which are like fans. The turbines would be turned by the flowing, expanding steam and would drive generators, producing the electricity.
Further heat would be extracted from the steam and non-condensable gases using binary units. These use a chemical called isopentane as a working fluid, circulating in a closed loop. The isopentane, heated by the fluid, would drive turbines that in turn would drive the electrical generators.
After that, the steam would be condensed by air-cooling fans. The non-condensible gases — containing more than 50 percent hydrogen sulfide and such other toxics as radon 222, mercury vapor and arsenic — would be compressed, mixed with the brine and injected back into the Earth.
Transmission lines would feed power produced by PGV would be fed into the Big Island electrical grid.
Is it dangerous to have geothermal plants in residential areas?
Any complex technical development has associated risks. Geothermal development involves the potential for release of small amounts of toxic materials to the air and water. One of the ways to reduce the adverse impacts of these releases is to undertake development in areas where the population is low and, therefore, the risk of exposure to humans is lessened. Geothermal development in residential areas increases the risk of exposure to humans.
If the decision is made to proceed with development in populated areas, extra effort must be made to make the development fail-safe and to abate fully all toxic releases. This has not been the case at PGV or the prior geothermal producing plant in the Puna area, HGP-A. It is all the more important to make this extra effort during the exploratory well-drilling stage of geothermal development, when there is still incomplete information about the geochemical toxics and the engineering characteristics of the new resource.
Analysis of the hazards associated with PGV operations has been hampered by the lack of geochemical data on the toxics contained in PGV wells, despite the fact that Condition 20 of the Health Department’s permit has required these data for years. For the same reason, it has been impossible to assess the full toxicity and the health impacts of air toxics released during venting, testing, and upset conditions at the PGV plant.
In what way does the Puna geothermal resource differ from geothermal fields elsewhere?
The PGV well field and power plant are located on a 1955 lava flow. This is a good indication that the area is subject to rapid and significant volcanic activity. The USGS topographic maps of the area indicate many fumaroles and cracks. This suggests the existence of vertical anomalies, which increases the complexity of well drilling and the likelihood of well blow-outs.
The KS-8 well blew out underground from June 15, 1991 until October 1991 before being brought under full control. Were such a blow-out to reach the surface, it is likely to result in a venting of geothermal fluids. Such an upset could force the evacuation of the public from all areas within seven miles of the blow-out site. The blow-out could last for extended periods — from weeks to years. This has in fact happened. A blow-out in the Geysers area of California that began in 1957 has not yet been brought under control.
The Puna geothermal resource is typified by an unusually high percentage of hydrogen sulfide in the non-condensible gases, but a relatively low percentage of non-condensible gas in total, high concentrations of radon 222, and high concentrations of heavy metals.
Temperatures and pressures much higher than typical were encountered in well KS-8. The concentrations of the non-condensible gases hydrogen sulfide and carbon dioxide were unusually high, which may cause extreme corrosion and well-casing embrittlement. This may lead to increased failures of well casing, pipeline, and power plant equipment.
Have Hawai`i’s geothermal developers (Ormat and True/Mid-Pacific) been allowed to proceed without thorough environmental, safety and health assessments?
Based on procedures used in other geothermal developments, adequate environmental review has not been conducted and the Best Available Control Technologies (BACT) have not been utilized. Two elements of the review of the June 1991 blow-out (Elements I and III) support this conclusion. These reviews and subsequent hazards analysis have been continually hampered by the lack of geochemical data on the contained toxics of the PGV wells, even though the data have been required for years in Condition 20 of the Health Department’s Authority to Construct.
Volume 3, Number 6 December 1992