Kizildere II: Geothermal energy in Turkey

November 20th, 2014, Published in Articles: Energize

 

Zorlu Energy, a large Turkish contractor, is an innovative and forward-thinking firm which is a part of the Zorlu Group of companies, a huge Turkey conglomerate. Zorlu Energy entered in the geothermal arena after they purchased the 15 MW Kizildere I Geothermal Power Plant in 2008.

The Kizildere site is located in the Menderes Graben area of Anatolia with geological features known for relatively accessible hydrothermal resources with geothermal potential. Zorlu Energy decided to develop the resource and expand by developing a new, 60 MW (gross) power plant. They hired Power Engineers in 2009 to prepare a feasibility study for the new plant. Power, in turn, hired a resource specialty firm, Geologica, and a gathering and injection system specialty firm, Veizades and Associates, to assist with their areas of expertise.

Fig. 1: Indicative schematic.

Fig. 1: Indicative schematic.

Although the Kizildere resource has a high enthalpy, it also presents a considerable challenge with respect to very high concentrations of NCG, chiefly carbon dioxide, in the reservoir. To evaluate an appropriate way of extracting the energy from the resource and converting it to electricity, various power cycles were evaluated. The evaluation considered power output, capital, operating and maintenance costs over the projected thirty year design life. The costs included those from the wells, field facilities and the plant. It was concluded in the initial study that a triple flash plant would provide the best return on investment.

Geologica, after analysing the data and preparing a resource model, also concluded that the resource was adequate for the new 60 MW as well as the existing 15 MW plant over the 30 year life. An additional feasibility study was conducted to ascertain whether additional power generation via the addition of a bottoming cycle to the high pressure steam turbine exhaust would be beneficial. The study indicated that this option would also provide favorable economics, so Zorlu made the decision to include a bottoming cycle.

Power Engineers, again supported by Geologica and Veizades and Associates, was hired to perform engineering, design, procurement, commissioning and startup services for the plant. Zorlu acted as their own general manager and hired local subcontractors to construct the facility.

Study

The company was first engaged in 2009 by Zorlu to perform and deliver a feasibility study exploring costs and technology options for developing a large new plant at the Kizildere resource, adjacent to the existing Kizildere I single-flash plant. The study reviewed options for geothermal power generation cycle technology and recommended an advanced (patented by Power) triple-flash cycle as the optimal method to using the Kizildere resource for power generation. This unique approach was required due to the high NCG content of the geothermal fluid.

08_ST_Power-Engineers_Fig.02

Evidence strongly indicated that the Kizildere geothermal field is able to support an additional 60 MW (gross) generating plant for at least 30 years as well as the existing 15 MW plant for a further 30 years. The quality of the resource supports a flash plant which has a higher efficiency and lower specific capital cost (in terms of
$/kW installed) than an alternative binary cycle plant.

The nature of the resource, particularly its enthalpy and gas content, suggests that a power plant using a triple pressure steam flash design would be most appropriate. The company recommended a triple-flash plant to take full advantage of the resource quality and to efficiently deal with the non-condensable gases. The geothermal resource can be reliably produced using conventional technology. The intermediate reservoir produces NCG, mainly CO2, of 1,5% (wt) and fluids at approximately 190 to 200°C. The deep resource appears to produce about 3% (wt) of NCG and fluids at approximately 235 to 240°C. This must be accounted for in the design of the facilities, but it can be handled using conventional methods with well-understood costs.

The Kizildere geothermal resource model includes two developed reservoirs at different depths, enthalpies and chemistry that are most likely inter-connected and are overlain by a shallow reservoir, which is not currently producing. While the reservoir has been explored by drilling of over
20 wells, production from the intermediate depth reservoir has been maintained for over 25 years from approximately seven of those wells. The deeper, hotter reservoir has been produced from a single well for almost ten years.

The resource gathering system uses a mix of centralised and satellite separation. The resource gathering system for the existing plant was recommended to be revised and integrated with the gathering system for the new plant.

The feasibility study considered standard flash plant designs to handle the high NCGs as well as novel approaches tailored to this specific type of resource. In addition to the novel NCG system approach, it was recognised that the addition of a bottoming cycle would allow beneficial use of the low pressure steam/NCG stream that would otherwise be wasted. This steam/NCG stream is also capable of supplying energy to the local district heating system and a local greenhouse.

Design

In 2011, Zorlu decided to develop the new plant as recommended and engaged Power Engineers and its team to continue with detailed design and equipment specification for the new well field and power plant. As recommended in the feasibility study, the new plant consisted of a 60 MW triple-flash plant employing two turbines – a high-pressure turbine and a separate condensing IP/LP turbine – with the condensing turbine served by a wet cooling tower.

This plant configuration was chosen to match the equipment and parasitic load requirements to the distinctive characteristics of the Kizildere hydrothermal resource, and to allow the plant system to cost-effectively respond to anticipated changes in resource characteristics over the project’s life cycle, as resource gas content and enthalpy change over time.

Fig. 3: View looking south, binary units in foreground, powerhouse and separation station in background.

Fig. 3: View looking south, binary units in foreground, powerhouse and separation station in background.

The Kizildere plant is considered a hybrid or combined cycle geothermal plant. In additional to its principal flash stages, it provides for a 20 MW bottoming cycle to recover additional energy from the flash plant’s HP turbine exhaust. This HP heat recovery also incorporates the ability to generate hot water to several nearby greenhouses as well district heating to a neighboring community.
This combined cycle relies on a bottoming IP/LP flash plant instead of a bottoming brine binary plant. Since the binary unit is driven by condensed steam, this relatively clean water is available for makeup water use, allowing wet cooling to be used also for the binary units; this may not have been possible with a brine bottoming binary cycle. The HP and LP turbines may be housed in separate casings driving a single generator – or may be two separate turbo generator units. Fig. 1 shows the indicative cycle schematic.

Conclusion

On October 31, 2013, the 80 MW KizildereII Geothermal Power Plant was accepted by the Turkish Energy Ministry (after passing all performance tests).The plant, now
80 MW with the addition of the 20 MW binary cycle, is the largest geothermal power plant in Turkey. Since commissioning, the plant has had an availability over 99,75% in 2014 to date. As Zorlu’s flagship plant, Kizildere II is a prominent landmark in the rapidly developing Turkish geothermal plant fleet. It is also an example of how a combined cycle configuration is able to overcome some of the limitations that accompany a typical flash or binary cycle. With a resource high in enthalpy and NCG content, the Kizildere II plant sets a new standard for innovative and ambitious heat recovery from a renewable energy resource.

Contact Wynand Venter, Power Engineers, Tel 012 665-2023, wynand.venter@powereng.com

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