Energy Technologies: How They Work and Their Induced Seismicity Potential - Induced Seismicity Potential in Energy Technologies - page 41

Steam Flow
Metering

Net Plant Output Metering

Main Steam Line

13.8 KV 230 KV

Auxiliary
Steam
Line

Transformer

Generator

Gas
Ejector

Turbine

From
Steam
Wells

Cooling
Tower

Secondary H 2 S
Abatement System

Stretford
System

Condenser

Hot Well

Condensate Pump

Reinjection System

Circulating Water Pumps

FIGURE 3.3 Elements of the power plant cycle for vapor-dominated geothermal resources. The steam is
directed by the main steam line into a turbine that spins the connected generator unit, typically generating
electricity at 13.8 kilovolts (kV), which a transformer increases to 230 kV for distribution by a transmis-
sion line. The steam leaving the turbine enters the condenser that contains a network of tubing through
which cool water is circulated, facilitating the condensation process. The condensate is then pumped to the
cooling tower where it is cooled by evaporation, with the cooled water being in part recirculated by the
circulating water pumps back to and through the condenser. Because some noncondensable gases usually
occur naturally in the steam, those gases are removed from the condenser by the gas ejector system that
creates a partial vacuum by the flow of a small amount of steam delivered by the auxiliary steam line.
Those gases, in particular H 2 S, are chemically processed commonly by a Stretford System before delivery to
the cooling tower where they are vented. SOURCE: Adapted from the Northern California Power Agency.

the geothermal development operations were taking place. As the area of steam field devel-
opment expanded, the areal distribution of seismic events similarly expanded, and the
number of the events progressively increased (Figure 3.4).
With the addition of more seismometers of increased sensitivity distributed throughout
the expanded development area, a clear association became evident between these induced
events and the active injection wells and volume of water being injected. Figure 3.5 shows
where injection took place in the southeastern part of The Geysers in 1998, the year follow-
ing the startup of the first wastewater pipeline that more than doubled the injection vol-
ume. During 1997-1998, 1,599 events of M ≥ 0.6 were recorded, an increase of just over
50 percent compared to the prior 12 months.
The history of steam production, water injection, and seismic history at The Geysers
since 1965 is shown in Box 3.1. Steam production and therefore electricity generation
reached a maximum in 1987, followed by a fairly rapid decline until the wastewater pipelines