Organic Rankin Cycle

ORC flow chart01There are a few companies that sell ORC  turbines and complete systems for use with the ORC cycle, some of these companies sell complete systems at a very high price. we at Cebu Solar are developing a system that will be cost effective for the consumer for a more attractive ROI based on cost per watt invested and maximum out-put per square foot of space used. below is a summary of just one ORC project

Technological and Economical Survey of Organic Rankine Cycle
Sylvain Quoilin and Vincent Lemort

Thermodynamics Laboratory

University of Liège

Campus du Sart Tilman B49

B-4000 Liège, BELGIUM

[email protected]


This paper presents an overview of current R&D in the field of small and middle scale Organic Rankine
Cycles (ORC’s). Major ORC’s applications are described and their technical and economical maturity is
analyzed. The paper also emphasizes the selection criteria for the expander and for the working fluid.

Keywords: Organic Rankine cycles, heat recovery, biomass, combined heat power, Solar ORC, fluid
selection, ORC expanders

The interest for low grade heat recovery has been growing for the last ten years, due to the increasing
concern over energy shortage and global warming.

An important number of new solutions have been proposed to generate electricity from low temperature
heat sources. Among the proposed solutions, the Organic Rankine Cycle (ORC) system is the most widely
used. This system involves the same components as in a conventional steam power plant (a boiler, a
work-producing expansion device, a condenser and a pump). However, for such a system, the working
fluid is an organic component characterized by a lower ebullition temperature than water and allowing
reduced evaporating temperatures.

The success of the ORC technology can be partly explained by its modular feature: a similar ORC system
can be used, with little modifications, in conjunction with various heat sources. This success was
reinforced by the high technological maturity of most of its components, due to their extensive use in
refrigeration applications. Moreover, unlike with conventional power cycles, local and small scale power
generation is made possible by this technology.

Today, Organic Rankine Cycles are commercially available in the MW power range. However very few
solutions are actually suitable for the kW scale. This paper presents an overview of current R&D in the
field of small-scale ORC’s. Major small-scale ORC’s applications are analyzed and their technical and
economical maturity is discussed.

2.1. Biomass combined heat and power
Biomass is widely available in a number of agricultural of industrial processes such as agricultural waste
or wood industry. It is best used locally for two main reasons : the energy density of biomass is low, which
increases transportation costs; and heat and electricity demand are usually available on-site, which makes
a biomass plant particularly suitable in the case of off-grid or unreliable grid connection. Local generation
leads to smaller scale power plants (<1 MWe) which excludes traditional steam cycles that are not cost-
effective in this power range.

The ORC presents several advantages over the traditional steam cycle:

-The boiler operates at a lower temperature and at a lower pressure since it only heats up thermal
oil at a temperature of about 300°C and at low pressure. Steam boilers on the contrary need to
superheat the steam up to a temperature higher than 450°C in order to avoid droplets formation
during the expansion. The pressure of about 60 to 70 bars and the thermal stresses increase
dramatically the complexity and the cost of the steam boiler in comparison with a thermal oil boiler.
-The ORC has a lower operating pressure than the steam cycle. This decreases the installation
cost and the management of the installation with respect to security standards.

The efficiency of power generation with ORC’s is lower than that of traditional steam cycles, and generally
decreases with the plant size. Heat demand is therefore a prerequisite to increase the overall plant energy
conversion efficiency. This heat demand can be fulfilled by industrial processes (such as wood drying) or
space heating. Plant load can be controlled either by the on-site heat demand, or by maximizing power
generation. The second solution involves wasting the additional heat but has the advantage of increasing
the annual full load operating hours.

A second drawback of the ORC over the steam cycle is the higher flue gases temperature at the exhaust
of the boiler: the thermal oil supply temperature is indeed about 300°C, while the temperature of the feed
water of a steam cycle is about 100°C. With flue gases leaving at a higher temperature, the boiler
efficiency is decreased. This can be addressed by adding additional heat exchangers to preheat the ORC
working fluid and the combustion air, as shown in Figure 1.
Figure 1: Schematic representation of an ORC CHP system

Concurrent technologies for electricity generation from solid biofuels also include gasification: biomass is
transformed into a synthetic gas composed mainly of H2, CO, CO2, CH4. This synthetic gas also contains
solid particles and needs to be treated and filtered before being burned in an internal combustion engine
or in a gas turbine.
Rentizelas et Al (2008) compared the technology and the costs of Biomass CHP using an ORC or using
gasification. They showed that gasification yields higher investment costs (about 75%) and higher
operation and maintenance costs (about 200%). On the other hand, gasification shows a higher power-tothermal
ratio, which makes its exploitation more profitable. It should also be noted that ORC is a well-
proven technology, while gasification plants actually in operation are mostly prototypes of for
demonstration purpose.
2.2. Solar power plant
Concentrating solar power is a well-proven technology: the sun is tracked and reflected on a linear or on a
punctual collector, transferring heat to a fluid at high temperature. The heat is then transferred to a power
cycle generating electricity. The three main concentrating technologies are the parabolic dish, the solar
tower, and the parabolic though. Parabolic dishes and solar towers are punctual concentration
technologies, leading to a higher concentration factor and to higher temperature. The best suited power
cycles for these technologies are the Stirling engine (small-scale plants), the steam cycle, or even the
combined cycle, for solar towers.

Parabolic troughs work at a lower temperature (300°C to 400°C). Up to now, they were mainly coupled to
the traditional steam Rankine cycle for power generation (see for example Steinhagen, 2004). The same
limitation as in geothermal or biomass power plants remains: steam cycles need high temperature, high
pressures, and therefore high installed power in order to be profitable.

Organic Rankine cycles seem to be a promising technology in a view to decrease plant size and
investment costs. They can work at lower temperatures, and the total installed power can be reduced
down to the kW scale. Technologies such as Fresnel linear concentrators (Ford, 2008) are particularly
suitable for solar ORC’s since they require lower investment cost, but work at a lower temperature.

Up to now, very few CSP plants using ORC are available on the market:

-A 1MWe CSP plant working with ORC was completed in 2006 in Arizona. The ORC module was
provided by ORMAT, uses n-pentane as the working fluid and shows an efficiency of 20 %. The
global solar to electricity efficiency is 12.1% on the design point (Canada, 2004).
-A 250 KWe prototype plant was built in Germany in 2005 by GMK. It should be noted that,
although this plant aims at simulating a solar system, the heat source was provided by a natural
gas boiler. The electrical efficiency of the system was about 15%.
-Some very small-scale systems are actually studied for remote off-grid applications. Figure 2
shows a 1 KWe system installed in Lesotho by the “Solar Turbine Group” for rural electrification.
The goal of this project is to develop and implement a small scale solar thermal technology
utilizing medium temperature collectors and an ORC to achieve economics analogous to large-
scale solar thermal installations. This configuration aims at replacing or supplementing Diesel
generators in off-grid areas of developing countries, by generating clean power at a lower
levelized cost (~$0.12/kWh compared to ~$0.30/kWh for Diesel) (Quoilin et Al., 2008).
Figure 2 Solar ORC in field trials in Lesotho, southern

Figure 3 Tradeoff between collector and ORC efficiency

Africa 2007 (Solar Turbine Group)

It is worthwhile to note that the choice of the temperature in the collector results of a tradeoff between
collector efficiency and ORC efficiency (Figure 3): Increasing the temperature will lead to higher collector
ambient heat losses, but also to a higher conversion efficiency.
2.3. Heat recovery on mechanical equipments and industry processes
Many applications in industry reject heat at relatively low temperature. This heat can be converted into
heat sources for other on-site applications, or used for space heating (e.g. district heating). For instance,
Engin et al. (2004) demonstrated through a case study that 40% of the heat used in cement industry was
lost in flue gases, whose temperature varies between 215 and 315 °C. For economical reasons (Hung,
2001), traditional steam cycles wouldn’t allow recovering heat in this range of temperatures. A huge
potential market is therefore available for the ORC technology in this application field.

2.4. Geothermal energy
The range of temperatures of geothermal heat sources is large. Lowest possible temperature for ORC
heat recovery is about 100 °C, while other ORC geothermal plants work at a temperature higher than

Higher temperature (>150°C) geothermal heat sources enable combined heat and power generation: the
condensing temperature is set to a higher temperature (e.g. 60°C), allowing the cooling water to be used
for space heating. The global energy recovery efficiency is therefore increased, at the expense of the
electrical efficiency.

2.5. Heat recovery on internal combustion engines
An Internal Combustion Engine only converts roughly one third of the fuel energy into mechanical power.
For instance, for a typical 1.4 liter Spark Ignition ICE, with a thermal efficiency ranging from 15 to 32%, 1.7
to 45 kW are released through the radiator (at a temperature close to 80 -100°C) and 4.6 to 120 kW
through the exhaust gas (400 -900°C) (El Chammas and Clodic, 2005).

The heat recovery Rankine cycle system is an efficient means for recovering heat (in comparison with
other technologies such as thermo-electricity and absorption cycle air-conditioning). The idea of
associating a Rankine cycle to an ICE is not new and the first technical developments followed the 70’s
energy crisis. For instance, Mack Trucks (Doyle and Patel, 1976) designed and built a prototype of such a
system operating on the exhaust gas of a 288 HP truck engine. A 450 km on-road test demonstrated the
technical feasibility of the system and its economical interest: an improvement of 12.5% of the fuel
consumption was achieved. Systems developed today differ from those of the 70’s because of the
advances in the development of expansion devices and the broader choice of working fluids. The literature
survey indicated that, at the present time, Rankine cycle systems are under development, but no
commercial solution seems to be available yet.

Most of the systems recover heat from the exhaust gas (Endo et al., 2007; Nelson 2008) and, in addition
from the cooling circuit (Freymann et al., 2008). By contrast, the system developed by Oomori and Ogino
(1993) only recovers heat from the cooling circuit.

The control of the system is particularly complex due to the (often) transient regime of the heat source.
However, optimizing the control is crucial to improve the performance of the system. For instance, Honda
(Endo et al., 2007) proposed to control the temperature by varying the water flow rate through the
evaporator (by varying the pump speed) and to control the expander supply pressure by varying its
rotational speed

Performance of the recently developed prototypes of Rankine cycles is promising. For instance, the
system designed by Honda (Endo et al., 2007) showed a maximum cycle thermal efficiency of 13%. At
100 km/h, this yields a cycle output of 2.5 kW (for an engine output of 19.2 kW). This represents an
increase of the thermal efficiency of the engine from 28.9% to 32.7%.
ORC manufacturers have been present on the market since the beginning of the 80’s. They provide ORC
solutions in a broad range of power and temperature levels, as shown in Table 1.

Table 1 Non-exhaustive list of the main ORC manufacturers

Manufacturer Applications Power range Heat source Technology
ORMAT, US Geothermal, 200 KWe – 72 150°-300°C Fluid : n-pentane
WHR, solar MWe
Turboden, Italy CHP, 200 KWe – 2 MWe 100 -300°C Fluids : OMTS,
geothermal Solkatherm
Axial turbines
Adoratec, CHP 315 – 1600 KWe 300°C Fluid: OMTS
GMK, Germany WHR, 50 KWe – 2 MWe 120°-350°C 3000 rpm Multi-stage
Geothermal, axial turbines (KKK)
CHP Fluid: GL160 (GMK
Koehler-Ziegler, CHP 70 – 200 KWe 150 – 270°C Fluid: Hydrocarbons
Germany Screw expander
UTC, US WHR, 280 KWe >93°C
Cryostar WHR, n/a 100 – 400 °C Radial inflow turbine
Geothermal Fluids: R245fa, R134a
Freepower, UK WHR 6 KWe -120 KW 180 -225 °C
Tri-o-gen, WHR 160 kWe >350°C Turbo-expander
Electratherm, US WHR 50 KWe >93°C Twin screw expander
Infinity Turbine WHR 250 KWe >80°C Fluid: R134a
Radial Turboexpander

Sources: Manufacturers websites; Citrin, 2005; Gaia, 2006; Lorenz, 2006; Holdmann, 2007; Schuster,

The market for ORC’s is growing at a rapid pace. Since the first installed commercial ORC plants in the
80’s, an exponential growth has been stated. Figure 4 shows for instance the evolution of the installed
power and of the number of plants in operation, based on a compilation of manufacturer data over the
Figure 4 ORC market evolution (data source : Enertime, 2009)
Figure 5 Share of each application in the ORC market

Figure 5 also shows that the ORC is a mature technology for waste heat recovery, biomass CHP and
geothermy but is still very uncommon for solar applications. Moreover, as stated in Table 1, those
technologies are mainly developed in the MW power range and very few ORC plants are available in the
KW power range.

The choice of the working fluid for a given application is a key-issue and has been treated in numerous
studies. Some general relevant characteristics can be extracted from those studies:

Thermodynamic performance: the efficiency and/or output power should be as high as possible for the
given heat source and heat sink temperatures. This generally involves low pump consumption and
high critical point.
Positive or isentropic saturation vapor curve. A negative saturation vapor curve (“Wet” fluid) leads to
droplets at the end of the expansion (Quoilin, 2007). The vapor must therefore be superheated at the
turbine inlet in order to avoid turbine damages, which decreases cycle performance (Yamamoto et al.,
2001). In the case of positive saturation vapor curve (“Dry” fluid), a recuperator can be used in order to
increase cycle efficiency.
High vapor density: this parameter is of key importance, especially for fluids showing a very low
condensing pressure (e.g. silicon oils). A low density leads to very large equipments at the expander
and condenser level.
Acceptable pressures: as already stated with water, high pressures usually lead to higher investment
costs and increasing complexity.
High stability temperature: unlike with water, organic fluids usually suffer from chemical deteriorations
and decomposition at high temperatures. The maximum heat source temperature is therefore limited
by the chemical stability of the working fluid.
Low environmental impact and high safety level: the main parameters to take into account are the
Ozone Depleting Potential (ODP), the Greenhouse Warming Potential (GWP), the toxicity and the
Good availability and low cost
Some of the main representative papers dealing with the selection of the working fluid for ORC
applications are given in Table 2. Fluids are typically compared by fixing the evaporating and condensing
temperatures (with respects to the nature of the heat source and sink).
Table 2 Summary of different comparisons of working fluids

Author(s) Application Cond.
Considered fluids Recommended
fluids (in terms of
efficiency and/or
Saleh et al. Geothermal 30°C 100°C alkanes, fluorinated
alkanes, ethers and
fluorinated ethers
RE134, RE245,
R600, R245fa,
R245ca, R601
Maizza and Maizza
n/a 35 –
80-110 Unconventional
working fluids
R123, R124
Liu et al. (2004) Waste heat
30°C 150 –
R123, iso-pentane,
HFE7100, Benzene
Toluene, p-xylene
Benzene, Toluene,

El Chammas and ICE 55°C 60 -150°C Water, R123, Water, R245-ca and
Clodic (2005) (100°C (150 – isopentane, isopentane
for water) 260°C for R245ca, R245fa,
water) butane, isobutene
and R-152a

Drescher and Biomass CHP 90°C *


Toluene, OMTS
Hettiarachchia et Geothermal 30°C* 70 – 90°C Ammonia, n-Ammonia
al. (2007) Pentane, R123,


Lemort et al. Waste heat 35°C 60 – 100°C R245fa, R123, R123, n-pentane
(2007) recovery R134a, n-pentane
Hettiarachchia et Geothermal 30°C* 70 – 90°C Ammonia, n-Ammonia
al. (2007) Pentane, R123,
Lemort et al. Waste heat 35°C 60 – 100°C R245fa, R123, R123, n-pentane
(2007) recovery R134a, n-pentane

Borsukiewicz-Geothermal 25°C 80 – 115°C propylene, R227ea, Propylene, R227ea,
Gozdur and Nowak RC318, R236fa, R245fa
(2007) ibutane, R245fa

Fankam et al. Solar 35°C 60 – 100°C Refrigerants R152a, R600, R290

* Max/min temperature of the heat source/sink instead of evaporating or condensing temperature
For the particular case of ICE heat recovery applications, the selection of the working fluid is strongly
correlated to the choice of the heat source(s). Honda (Endo et al., 2007) selected water as the working
fluid of their prototype of Rankine cycle system. The prototype developed by BMW (Freymann et al., 2008)
is based on two cycles: the first recovers heat from the exhaust gas and uses water and the second is
associated to the cooling circuit and uses ethanol. The system proposed by Cummins (Nelson, 2008)
recovers heat from both the exhaust gas and the Exhaust Gas Recirculation (EGR) and used R245fa.
4.1. Temperature profile
The temperature profiles of the heat source and of the heat sink are an essential parameter to take into
account when optimizing the performance of an ORC. This is illustrated hereunder on the basis of a
simplified simulation model of an ORC, built on the following assumptions:

-Turbine efficiency s ,exp
( h su ,exp
h su ,exp ex ,exp

)h ex ,exp,s

is set to 0.75
-Pump efficiency s ,pp
( Pv ex ,pp
) ( hP ex ,pp su ,pp

)h su ,pp

is set to 0.80
-Recuperator effectiveness is set to 0.8
-Temperature pinch points are set to 10 K at both the condenser and the evaporator.
-The heat source and heat sink temperature profiles are evaluated by the temperature differences
between supply and exhaust ( ev T.
hf ,su ,ev T=
hf ,ex ,ev T-
and cd T.
cf ,ex ,cd T=
cf ,su ,cd T-

For the purpose of the modeling, a heat source consisting of hot air at a temperature of 130°C and
characterized by a flow rate of 15 kg/s is defined. The heat sink is also assumed to be air, whose supply
temperature is 10°C, and flow rate is adapted to maintain the imposed temperature pinch point. The
considered working fluid is R245fa. The superheating at the evaporator exhaust is set to 10K, and the
subcooling at the condenser exhaust is set to 5K.

Figure 6 shows the T-s diagram of the cycle in three different cases: Case A corresponds to a small
temperature glide in the evaporator, with a recuperator in the cycle, which is typical of a CHP, or solar
plant. Case B corresponds to a high temperature glide in the evaporator, without recuperator, which is
typical of waster heat recovery application. Case C corresponds to a high temperature glide, but using a

In case A, the heat capacity flow rate in the heat exchangers is high. This allows high and low evaporating
and condensing pressures respectively. Increasing the pressure ratio leads to a higher efficiency. Case B
is typical of a waste heat recovery ORC: the temperature glide of the heat source is very important, since
the goal is to recover as much heat as possible from the heat stream. The pinch point limitation leads to a
lower evaporating pressure and thus to a lower cycle efficiency (7.8% instead of 12.5%), but the amount of
heat recovered is higher and the output power is increased (71 KW instead of 28 KW).

This limitation highlights the necessity of a pinch point analysis for a given application. In general, in heat
recovery applications, the objective will be to maximize the output power rather than the efficiency. In
contrary, in solar or biomass applications, the heat source can be almost constant and maximizing the
output power is therefore similar to maximizing the efficiency,


Figure 6 T-s diagram of the cycle with superposition of the secondary fluids temperature profiles

For the same reason, the benefits of a recuperator in the cycle will depend on the considered application.
Comparison of cases B and C indicates that the recuperator increases the cycle efficiency (from 7.8% to
8.9%) but decreases the output power (from 71 KW down to 68 KW). This is explained by a higher heat
source temperature at the exhaust of the evaporator, which reduces the amount of heat recovered, and
the output power.

In summary, in heat recovery applications, the output power, and not the efficiency should be maximized,
and a recuperator will generally decrease the performance.

4.2. Comparison between working fluids
This section aims at comparing the most commonly used working fluids for three typical applications:

-The first application corresponds to an evaporating temperature of 85°C and to a condensing
temperature of 20°C. These temperature levels are typical of a geothermal application.
-The second application corresponds to an evaporating temperature of 150°C and to a condensing
temperature of 30°C, which could correspond to a low-temperature solar collector.
-The third application corresponds to an evaporating temperature of 280°C and to a condensing
temperature of 100°C, which is typical of biomass CHP plant.

Four different fluids are considered because they seem to be the most common in ORC applications (see
tables 1 and 2): R134a, R245fa, n-pentane, and silicon oil. The selected silicon oil is
octamethylcyclotetrasiloxane (‘D4’) and its thermodynamic properties are calculated according to
Colonna’s Multiparameter Equation of State (Colonna, 2004).

The simplified model introduced in section 4.1 with its parameters is used (still assuming 80%
effectiveness for the recuperator). A new performance indicator, the back work ratio (BWR) is defined as
the ratio between the works consumed by the pump and produced by the expander. The density at the
exhaust of the expander is also considered in order to evaluate the required size of the equipment.

Table 3 gives the cycle performance as a function of the fluid and of the considered application. For high
temperatures, the only computed fluid is D4, the other ones being in supercritical state.

Table 3 Cycle performance for 3 different applications

Fluid Pev Pcd cycle BWR ex,exp
[bar] [bar] [kg/m³]
R134a 29.28 5.73969 10.6% 10.8% 26.2
Tcd = 20°C R245fa 8.92 1.28839 11.7% 2.9% 6.775
Tev = 85°C n-pentane 4.16 0.62557 11.5% 1.6% 1.803
D4 0.04541 0.0009533 10.3% 0.0% 0.007966
Tcd = 30°C R245fa 33.79 1.80767 16.4% 8.0% 8.598
Tev = 150°C n-pentane 15.91 0.84297 18.1% 3.9% 2.055
D4 0.50238 0.001985 15.6% 0.1% 0.01437
Tcd = 100°C
Tev = 280 °C
D4 8.04243 0.08718 18.6% 2.2% 0.483

Table 3 indicates that R134a and R245fa have a good comparative performance at low temperature
levels. They also show the highest back work ratio. N-pentane shows good performance for the second
case but with a lower vapor density than R134a and R245fa. The low density becomes prejudicial for the
Silicon Oil at low temperature: it is for example 61 times lower than the density of R245fa at a condensing
temperature of 30°C, which would lead to oversized expander and condenser.

Performance of the ORC system strongly correlates with those of the expander. The choice of the
machine strongly depends on the operating conditions and on the size of the system. Two main types of
machines can be distinguished: the turbo and positive displacement types. Similarly to refrigeration
applications (Figure 7), displacement type machines are more appropriate to the small-scale ORC units,
because they are characterized by lower flow rates, higher pressure ratios and much lower rotational
speeds than turbo-machines (Persson, 1990).
Figure 7: Approximate range of chiller cooling capacity range by compressor type (ASHRAE, 2008)

While technically mature turbomachines are available on the market for large ORC units, it seems that
almost all positive displacement expanders that have been used up to now are prototypes, often derived
from existing compressors (Zanelli and Favrat, 1994; Yanagisawa et al., 2001; Aoun and Clodic, 2008;
Lemort et al., 2008).

Most of the Rankine cycle systems used in automotive applications employ positive displacement
machines. One exception is the Rankine cycle system proposed by Cummins (Nelson, 2008), which is
associated to a truck engine and uses a turbo machine. Toyota (Oomori and Ogino, 1993) used a scroll
expander. BMW (Freymann et al., 2008) initially used 2 vane expanders (one for both cycle) but decided
to replace them by axial piston machines showing efficiencies of 55% (which could probably be improved,
given that the prototype is non-optimized). Honda (Endo et al., 2007) designed a compact swash plate
axial piston type expander, comprising an oil gear pump and a generator motor mounted coaxially with the
expander. Steam Rankine cycle recovering heat from high temperature gas, should operate at high
evaporating pressure to improve the cycle performance. Most of the existing expander technologies can
withstand pressures up to 35 bar (El Chammas and Clodic, 2005). One exception is the swash-plate
piston expander developed by Endo et al. (2007) that operates with pressures up to 100 bars.

Another difficulty associated with the use of a positive displacement machine is its lubrication. An oil
separator could be installed at the expander exhaust. Unlike with compressors, an oil pump is necessary
to drive the separated oil back to the expander suction. Kane (2002) proposed to let the oil traveling with
the refrigerant through the system and to install an oil separator at the evaporator exhaust. Separated oil
is injected into the scroll expander bearings, while the lubrication of the two spirals relies on the slight
inefficiency of the separator. Alternatively, oil-free machines could be used, but generally show lower
volumetric performance due to larger tolerances between moving parts (Yanagisawa et al., 2001; Peterson
et al., 2008).

In some operating conditions (wet fluids with limited superheat at the expander supply), liquid may appear
at the end of the expansion. This could be a threat of damage for piston (reciprocating) expanders but not
for scroll and screw expanders, since the latter do not use valves (the timing of suction and discharge is
determined by the machine geometry).

Some types of expanders (scroll, screw, vanes) are characterized by a fixed built-in volume ratio. To
optimize the performance of the expander, this built-in volume ratio should match the operating conditions
(in order to limit under-expansion and over-expansion losses). Volume expansion ratios achieved in
Rankine cycle systems are typically larger than those achieved in vapor compression refrigeration
systems, which justifies developing adapted design of such expanders rather than retrofitting existing
compressors. Generally speaking, piston expanders are more appropriate for the applications with large
expansion volume ratio.

Finally, previous studies carried out by the authors also indicated that the tightness of the machine (in
case of open-drive expanders) is an important issue (Quoilin, 2007).
A review of ORC applications has been carried out, with a special focus on the temperature levels and on
the specificities of each application. The main manufacturers are listed, describing their activity field, the
main technological characteristics of their ORC solutions, and their power range. Concurrent technologies
of the ORC include gasification and the water steam power cycle. Advantages and drawbacks of each
technology were described.

The ORC market is growing exponentially since the beginning of the 80’s, mainly in the fields of biomass
CHP, geothermal energy and waste heat recovery. The compilation of the available market data shows
that actual plants size is mainly limited to the MW scale.

The review of the working fluids pointed out the most widely used working fluids, i.e. R134a, R245fa, npentane
and silicon oils. The thermodynamic study showed that each fluid is characterized by an optimal
temperature range in terms of cycle efficiency and density. In general, the higher the critical point, the
higher the optimal temperature range.

Expanders are a key issue in ORC’s. Positive displacement machines are preferably used for small-scale
applications. At the present time, most of the employed positive displacement expanders are obtained by
modifying existing compressors. Turbomachines are mainly designed for larger-scale applications and
show a higher degree of technical maturity.

Aoun, B., and D. Clodic. 2008. Theoretical and experimental study of an oil-free scroll type vapor
expander, Proceedings of the International Compressor Engineering Conference at Purdue: paper

ASHRAE. 2008. ASHRAE Handbook – HVAC Systems and Equipment, Chapter 42.
Borsukiewicz-Gozdur, A., W. Nowak. 2007. Comparative analysis of natural and synthetic refrigerants in
application to low temperature Clausius-Rankine cycle. Energy (32): 344-352.
Canada, S., G. Cohen, R. Cable, D. Brosseau, H. Price. 2004. Parabolic trough organic rankine cycle
solar power plant, NREL/CP-550-37077, In: The 2004 DOE Solar Energy Technologies, Denver, USA.
David Citrin, Power Generation from Cement plant waste heat (Powerpoint presentation), ORMAT
International Inc, CII – Green Cementech 2005
Colonna, P. N.R. Nannan, A. Guardone and E.W. Lemmon, Multiparameter equations of state for selected
siloxanes. 2006. Fluid Phase Equilib. (244).
Doyle, E.F., and P.S. Patel. 1976. Compounding the truck diesel engine with an organic rankine cycle
system. Society of Automotive Engineers (SAE), 760343.
Drescher, U., and D. Bruggemann. 2007. Fluid selection for the Organic Rankine Cycle (ORC) in biomass
power and heat plants. Applied Thermal Engineering (27): 223-228.
El Chammas, R. and D. Clodic. 2005. Combined Cycle for Hybrid Vehicles. Society of Automotive

Engineers (SAE), 2005-01-1171.
Enertime SAS, ORC: Etude du marché, Confidential report, Paris, March 2009
Endo, T., S. Kawajiri, Y. Kojima, K. Takahashi, T. Baba, S. Ibaraki, T. Takahashi and M. Shinohara. 2007.

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Tahsin Engin & Vedat Ari, Energy auditing and recovery for dry type cement rotary kiln systems––A case
study, Energy Conversion and Management 46 (2005) 551–562
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