Utilisation of Geothermal Energy - Renewable Energy: Technology, Economics and Environment - page 486

source for an ORC process. Another possibility is that the drained liquid from the
first separation step is not reduced a second time within a second flash vessel, but
heats the evaporator of an ORC plant (Fig. 10.21). Combined systems offer com-
paratively high efficiencies (Fig. 10.15).

Cooling
tower

O C u b e/Ge e a o

Cooling
tower

Kühlturm

Turbine Kühlturm

Flash-Behälter

Turbine

Flash
vessel

Generator

G

G

Gene-
rator

Condenser Kondensator

Verdampf er

Evaporator

Sepa-
ration
of gases

Gasab-
scheidung

Condenser

Kondensator

Vor-
wärmer

Econo-
miser

Feinfilter

Filter

Production well Injection well

Fig. 10.21 Simplified schematic diagram of a combined facility of single flash process and
ORC

10.3.2 Economic and environmental analysis

The following sections contain an analysis of economic and environmental as-
pects of geothermal power generation and combined heat and power generation.

Economic analysis. For the following considerations geothermal resources with a
reservoir temperature of 150 °C and a production rate of 100 m 3 /h are assumed.
The geothermal reservoir is tapped by means of a two-well system consisting of a
vertical and a diverted well. The exploited reservoir is located in areas of a normal
geothermal gradient at about 4,600 m depth (average geological conditions) or in
areas with much more favourable geothermal gradients at about 2,700 m depth
(promising geological conditions). Successful stimulation ensures production rates
of 100 m 3 /h. Based on this concept, two plant configurations are examined.
− Plant A. The assumed exclusively geothermal power generation is provided by
means of an ORC plant of an electrical efficiency of 11 % and an electrical ca-
pacity of 1,000 kW. Additionally, four further power plant cycles will be exam-
ined (i.e. Kalina, single flash, double flash and a combined single flash and
ORC). The power generation plant is operated providing base load with
7,500 h/a. It covers its own electricity demand.
− Plant B. For Plant B combined heat and power (CHP) generation exclusively
based on an ORC is assumed. As for Plant A the technical maximum electrical