POWER December 2016 - 36

TOP PLANTS
POWER POINTS
Winning Attributes
First binary geothermal plant to
employ a two-pressure cycle
using a single turbine
Greater efficiency allows
exploitation of low-temperature
geothermal resources that would
be uneconomic with conventional
geothermal technology
of megawatts, and rely on high-temperature
resources. To further build out the nation's
capacity, exploitation of lower-temperature
resources will be necessary. Because of this,
newer binary plants are beginning to see development,
and one of the newest, Tosunlar
1 in the Denizli-Tosunlar geothermal field,
employs a new technology that promises to
make low-temperature binary geothermal
generation significantly more efficient.
Dual Innovation
What sets the Tosunlar plant apart is that
it uses a two-pressure ORC system with
only one single-disk turbine. Typical binary
systems use one turbine per pressure level,
with the working fluid entering the highpressure
side after leaving the evaporator,
before passing through the recuperator and
the low-pressure evaporator (which draws
heat from geothermal fluid after it leaves the
high-pressure evaporator).
Italian firm Exergy has developed a different
approach that it calls the radial outflow
turbine. In this approach, the turbine
uses a single disk with multiple stages (Figure
1). The high-pressure fluid enters at the
center of the disk while the low-pressure
fluid enters further out, toward the edge
(Figure 2).
The single-disk configuration means substantially
fewer components for the turbine
system. This lowers overall costs and reduces
operational and maintenance demands
because of the reduced amount of rotating
equipment and associated auxiliaries. In addition,
because the radial outflow turbine is
much smaller than a conventional two-stage
turbine, the plant footprint is smaller, meaning
reduced construction costs.
Compared to a single-pressure turbine of the
same size, Exergy says the radial outflow turbine
can achieve up to 22% higher efficiencies.
This makes it ideal for sites where temperatures
are lower and geothermal flows are limited and
conventional designs would be uneconomic.
Turkish firm Akca Enerji is a subsidiary
36
1. One disk, two stages. Exergy's radial outflow turbine, designed for binary Organic
Rankine Cycle systems, is driven by both high- and low-pressure vapor across a single disk.
The company says this approach is both more efficient and less expensive than conventional
designs. Courtesy: Exergy
2. Dual-drive. Shown here installed on the Akca Tosunlar plant, the radial outflow turbine
takes the working fluid through the center of the disk. The vaporized fluid flows outward and
exits out the sides. Using only a single turbine disk means fewer rotating components and a
smaller footprint for the plant as a whole. Courtesy: Exergy
of Akca Holding that specializes in renewable
energy. In 2013, it contracted with
Exergy to build a small geothermal plant
in the Denizli region of southwest Turkey.
Geothermal temperatures at the site were
low, at 105C, and the flow was fairly small,
at 12 tons/hour of steam/brine mixture. The
plant draws cooling water from a nearby
river.
The 3.8-MW facility entered operation in
June 2015 and has so far exceeded expectations,
performing more than 10% above contracted
results. The plant was awarded the
European Geothermal Innovation Award by
www.powermag.com
the European Geothermal Energy Council as
the best innovation in the geothermal sector
in 2016. A video of the project can be viewed
at https://youtu.be/RAT6LK3aLNM.
Exergy has since supplied several other
larger geothermal plants in Turkey using the
radial outflow turbine design. The 12-MW
Denizli Umurlu I plant entered operations in
November 2015; a second unit on the same
site came online this fall, along with six others
the company has supplied for Turkey so
far. ■
-Thomas W. Overton, JD is a POWER
associate editor.
POWER | December 2016

https://www.youtu.be/RAT6LK3aLNM http://www.powermag.com

POWER December 2016

Table of Contents for the Digital Edition of POWER December 2016