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6.3 Energy Conversion System: Geothermal Power Plants: Principles, Applications, Case Studies and Environmental Impact

This document discusses geothermal power plants that use a double-flash system for energy conversion. In a double-flash plant, high temperature geothermal fluid first flashes into steam in a separator. The remaining hot liquid then flashes again into additional steam in a second flasher. Both the high and low pressure steams are then used to drive a turbine that generates electricity. The turbine can be a dual-admission, single-flow machine that merges the steam flows, or it can use two separate turbines with a common or separate condensers. Larger plants over 55 MW often use double-flow turbines to minimize the height of the last turbine blades.

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Juan Ponce Manríquez
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19 views1 page

6.3 Energy Conversion System: Geothermal Power Plants: Principles, Applications, Case Studies and Environmental Impact

This document discusses geothermal power plants that use a double-flash system for energy conversion. In a double-flash plant, high temperature geothermal fluid first flashes into steam in a separator. The remaining hot liquid then flashes again into additional steam in a second flasher. Both the high and low pressure steams are then used to drive a turbine that generates electricity. The turbine can be a dual-admission, single-flow machine that merges the steam flows, or it can use two separate turbines with a common or separate condensers. Larger plants over 55 MW often use double-flow turbines to minimize the height of the last turbine blades.

Uploaded by

Juan Ponce Manríquez
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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114 Geothermal Power Plants: Principles, Applications, Case Studies and Environmental Impact

economic analysis, taking into account site-specific conditions including the tempera-
ture, pressure, and chemical nature of the geofluid, the location of production and
injection wells relative to the powerhouse, topography of the site, and method of fluid
disposal, including any required scale-control techniques. The latter are now routinely
used at many plants and involve both down-well treatment to prevent calcite scaling
in the production wells, and/or post-plant treatment to prevent silica deposition in the
injection piping and wells. These potential problems are common to both single- and
double-flash plants and will be discussed in Sect. 6.6.
The formulations presented in Sect. 5.2.2 for pressure drops need not be repeated
since they apply equally well for pipelines at double-flash plants.

6.3 Energy conversion system


The schematic diagram for a double-flash plant is shown in Fig. 6.6 [1]. The design differs
from the single-flash plant in Fig. 5.6 in that a flasher F has been added and there is a low-
pressure steam line from it to the turbine in addition to the high-pressure one from the sepa-
rator. The cooling tower that provides the cooling water CW is not shown in Fig. 6.6.
The turbine shown is a dual-admission, single-flow machine where the low-pressure
steam is admitted to the steam path at an appropriate stage so as to merge smoothly with
the partially expanded high-pressure steam. Other designs are possible; for example, two sep-
arate turbines could be used, one for the high-pressure steam and one for the low-pressure
steam. In this case, the turbines could exhaust to a common condenser (see Fig. 6.7(A))
or to two separate condensers operating at different levels of vacuum (see Fig. 6.7(B)). For
larger power ratings, say, 55 MW or higher, double-flow turbines would be a good choice in
order to minimize the height of the last-stage blades. Usually, the last-stage blades in geo-
thermal turbines are at most 2527 in (635686 mm) long, but at least one plant, the
Darajat Unit 2 in Indonesia, uses 30 in (762 mm) long blades [2].

Fig. 6.6 Simplified double-flash power plant schematic [1].

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