GRC Transactions, Vol. 36, 2012

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KeywordsORC, Organic Rankine Cycle, low temperature geothermal, turbo expander, variable inlet guide vanes, working fluid, air cooled condenser, annual cumulative power, turbo expander, expander generator, radial inflow turbine

ABSTRACT

This white paper describes the preliminary configuration and technical characteristics of what will be the largest geothermal power plan in Turkey, with a nominal capacity of 50MW. In addition to resource data, the document outlines the plant configu-ration, ORC optimization and the design of critical components of the power plant.

The Pamukuren Geothermal Organic Rankine Cycle Power Plant (ORC) will be located in the Aydin Province of Turkey.

Background

Pamukuren City (Figure 1) is located in an area known for its abundant geothermal resources. As a result, the number of geothermal projects in Turkey has accelerated dramatically over the past several years. An ORC plant has been selected for this project based on the medium temperature resources required.

The first ORC plant was installed in the Aydin Province in the early 1990s and there are currently several geothermal flash and ORC power plants in operation.

The Consortium of Project Contributors

Çelikler Jeotermal is a geothermal power company of Ce-likler Holding that owns the geothermal concession in Pamukuren.

Atlas Copco Gas and Process was awarded a turnkey order to design, procure and construct a nominal 50 MW geothermal Organic Rankine Cycle (ORC) plant, in June 2011. Atlas Copco has the lead role in a consortium with process-design experts Exergy, and SPIG (an air-cooled condenser specialist).

Technical InformationCelikler Jeotermal Co has chosen inflow radial turbine tech-

nology for their Pamukuren concession. The first phase consists of two trains Organic Rankine Cycles with nominal capacity of 25 MW each.

Pamukuren Geothermal Organic Rankine Cycle Power Plant in Turkey

Reza Agahi

Atlas Copco Gas and Process

Figure 1. Pamukuren City and Pamukuren Concession, Aydin Province, Turkey.

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Geothermal Resource DataThe following lists brine conditions interpolated from an early

exploratory test well and a production well:

Brine flow 1,400 t/hSteam flow 55.0 t/hNon Condensable Gas (NCG) flow 22.0 t/hNCG assumed as 100% CO2

Reference brine inlet temperature 161.0 °CReference steam + NCG inlet temperature 161.0 °CReference specific heat calculated as pure waterReference brine inlet pressure 15 bar aReference steam + NCG inlet pressure 7.5 bar aMinimum brine reinjection temperature 80 °C

Inflow Radial Turbine With Variable Inlet Guide Vanes

The use of a variable geometry turbine alleviates the need for an evaluation of plant performance if the brine data differs from the geothermal resources (by plus or minus 5%) listed in the table below (see Figures 3 and 4).

The inflow radial turbine with variable inlet guide vanes accommodates off-design conditions and operates with high ef-ficiency (see Figures 3 and 4).

Organic Rankine Cycle Design

Configuration of the proposed plant was planned based on existing knowledge and experience of ORC and turbo expanders with variable inlet guide vanes.

Decision Parameters The choice of working fluid is fundamental for the design of

an ORC system and each component must be optimized to suit the conditions. The teams considered the following primary selection criteria for the working fluid:

• Ability to remain thermally stable in the working tempera-ture range of operation

• Market availability in the event of leakage (standstill avoidance)

• Non-toxic• Excellent cycle performance• Low/no environmental impact• Reasonable product price

The team ultimately selected commercial grade normal butane for the ORC working fluid. Consistent with the objectives, com-mercial grade normal butane is stable in the entire possible range of operating temperatures and it is widely available in large and small quantities.

The T-Q diagram of normal butane (Figure 5) enables the most efficient use of heat available from the geothermal brine and hence delivers an optimal cycle efficiency.

Figure 2. Pamukuren Site, Drill Rig and Resource Testing.

Figure 3. Turbo Expander with variable Inlet Guide vanes.

Figure 4. Typical Performance Curve for Turbo Expander with Variable Inlet Guide Vanes.

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Optimized Volumetric Flow

The critical temperature of normal butane results in an opti-mized volumetric flow for turbo expander design. In all ambient conditions the condensing pressure is higher than atmospheric pressure avoiding any risk of air leaking into the condenser. The fluid is inexpensive, generic and available in all markets.

Turbo Expander

The variable geometry turbine is the key feature of the plant. The turbo expander (radial inflow expander) is equipped with variable inlet guide vanes.

The main parameters of geothermal brine are flow and tem-perature. Heat source flow and temperature frequently differ in operation as compared to the initial projections and test results. They typically change over the life of a power plant.

To maintain an optimal efficiency for a power plant the in-stalled turbine geometry should be capable of adapting to changing brine conditions. The ability to adapt based on brine conditions is only possible with the turbo expander and variable inlet guide vane technology.

Ambient Temperature Conditions for Plant Design

The meteorological data for the Aydin Province reveals the following average ambient air temperatures:

Average ambient temperature °C 18.0Maximum ambient temperature °C 27.0Minimum ambient temperature °C 7.0

ConfigurationProper configuration of the ORC system requires consideration

of the average and extreme temperatures of the region to ensure

that all equipment and components are sized and optimized appro-priately. The project specification requires an air cooled condenser for the power plant. The historical ambient temperature in Izmir area is shown in Figure 6.

Results: Geothermal ORC Plant Performance per Train (optimized)

Average Winter ConditionsGross Power at Generator Output Terminal kWe 24,300

Reference Average ConditionsGross Power at Generator Output Terminal kWe 22,510Internal Auxiliaries Consumption kWe 3,350Binary Cycle Net Power kWe 19,108

Average Summer ConditionsGross Power at Generator Output Terminal kWe 18,800

Figure 5. QT Diagram for Normal Butane.

Figures 6. IWEC Dry Bulb Temperature and Duration for Izmir, Turkey.

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Conclusions

The Pamukuren geothermal concession in Ayden Province will utilize an ORC plant with turbo expander and variable inlet guide vanes as the turbine technology. The variable turbine technol-ogy adapts to inherent uncertainties associated with geothermal resource and the project requirement for an air cooled condenser. The choice of normal butane as the working fluid for the ORC considering the resource data, turbo expander requirements and extreme ambient conditions is appropriate and meets or exceeds the selection criteria.

References

1. Agahi R., Allen, M., Geothermal Energy Recovery Using Turbo Expand-ers, Geothermal Power in Asia 97, 24-28 February 1997, Bali, Indonesia.

2. Agahi R., Spadacini, C. Comparison between Variable and Fixed Geom-etry in Geothermal Power Plants, Proceeding World Geothermal Congress 2010, 25-29 April 2010 Bali, Indonesia.

3. Agahi, R. Frassinnetti, M.,Spadacini, C., Xodo, L., Optimum Air Cooled Condenser Sizing for an Organic Rankine Cycle Geothermal Power Plant, UCTEA, Chamber of Mechanical Engineers, University of Izmir, April 13, 2011, Izmir, Turkey.