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ScienceDirectEnergy Procedia 00 (2017) 000–000

www.elsevier.com/locate/procedia

IV International Seminar on ORC Power Systems, ORC201713-15 September 2017, Milano, Italy

Low temperature heat recovery in engine coolant for stationary and road transport applications

Pierre Leduca*, Pascal Smaguea, Arthur Lerouxb, Gabriel Henryb

aIFP Energies nouvelles, 1 et 4 avenue de Bois-Préau, 92852 Rueil-Malmaison, France ; Institut Carnot IFPEN Transports EnergiebENOGIA, 19 avenue Paul Héroult, 13015 Marseille, France

Abstract

Small scale, low-temperature ORC (heat source at around 358 K – 85°C) is a specialty of ENOGIA which has sold to date more than 40 stationary ORC systems, with electrical power outputs ranging from 5 to 40 kW. These ORC cover a large variety of applications: agricultural biogas combined heat and power engines, landfill biogas plants, biomass boilers, concentrated solar thermal systems and small geothermal plants. With IFPEN, new developments have been made to deliver a 100 kW stationary ORC model.Regarding the transport industry, most of projects related to ORC systems propose performance optimized solutions with heat recovery in engine exhaust gas, where the exergy content of the heat loss is high. However recovery potential is important, real life is much more difficult, with severe thermal constraints on the system and complicated control strategy in transient behavior. This generates important development and manufacturing costs and risks in terms of system durability.IFPEN and ENOGIA have joined forces to investigate another way for heat recovery for transportation means, aiming at reducing the cost of the system and facilitating its integration on-board a truck or a passenger car. The development is focused on the design of ORC turbine-based components. As heat source, engine coolant is selected for its low and stable temperature conditions. At the end, ORC operating pressure and temperature are low, allowing a lightweight, compact and low-cost solution.

© 2017 The Authors. Published by Elsevier Ltd.Peer-review under responsibility of the scientific committee of the IV International Seminar on ORC Power Systems.

Keywords: ORC, heat recovery, low temperature, truck, vehicle

* * Corresponding author. Tel.: +33 147526479E-mail address: [email protected]

1876-6102 © 2017 The Authors. Published by Elsevier Ltd.Peer-review under responsibility of the scientific committee of the IV International Seminar on ORC Power Systems.

http://www.sciencedirect.com/science/journal/22126716

2 P. Leduc, P. Smague, A. Leroux and G. Henry / Energy Procedia 00 (2017) 000–000

Nomenclature

AcronymsHT High temperatureLT Low temperatureORC Organic Rankine Cycle

Symbolsh specific enthalpy (J/kg)m mass flow (kg/s)P power (W) efficiency

Subscriptscond condensercw cold waterelec electricalevap evaporatorgrid feed in to the gridhw hot waterin at inletis isentropicout at outletshaft on turbine shaftturb turbinewf working fluid

1. Introduction

Since 2009, ENOGIA has developed a range of Organic Rankine Cycle (ORC) products for heat recovery on waste heat, especially for stationary engines. To date, more than 40 ORCs from ENOGIA have been sold in more than ten countries around the world. The specialty of ENOGIA is to make the most of "low temperature" heat source, at temperature around 360 K (87°C / 188°F). This allows to recover waste heat in the coolant of combustion engines.

At low temperature, the challenge is to maintain a reasonable thermal efficiency of the ORC system, while the theoretical Carnot efficiency is drastically reduced. To tackle the challenge, ENOGIA has developed dedicated ORC turbogenerators. Today low temperature ("LT") ORC family from ENOGIA is composed by ENO10-LT, ENO20-LT and ENO40-LT products, with electrical outputs power ranging from 10 to 40 kW (see Fig. 1). It makes possible to recover heat in the coolant of engines from about 100 kW to 1500 kW of mechanical power. Heat recovery in exhaust gas is also possible, thanks to an intermediate water loop.

It appeared rapidly that the availability of a more powerful version would be of interest. Then, ENOGIA and IFPEN decided to join forces to develop ENO100-LT, in the framework of a partnership. ENOGIA would be in charge of developing the whole system and especially the turbine, whereas IFPEN would conduct the development of a dedicated electric generator of 100 kW and associated power electronics. The latter has been done with the help of MAVEL, its industrial partner in electrical parts development.

Finally, the main objective of the alliance of IFPEN and ENOGIA is to transfer this low-temperature ORC turbine technology to the transportation industries. The two partners have recently launched the design of ORC turbines for trucks and passenger cars. Both developments – for stationary engines and for road engines – are presented here.

P. Leduc, P. Smague, A. Leroux and G. Henry / Energy Procedia 00 (2017) 000–000 3

Fig. 1. ENOGIA's 40 kW electrical output ORC skid in a landfill near Paris (France).

2. Development of a 100 kW output ORC for stationary engines

2.1. Objective

The target of the development is to design, built and test a complete ORC system capable of exploiting low-temperature (350 - 370 K ; 77 - 97°C) heat flux representing from about 1 to 2 MW of thermal power. The ORC must be able to produce from 50 to 100 kW of electrical power to be re-injected into the grid. This prototype is called ORC100 and prefigures the future product. Based on the former experience of ENOGIA with smaller ORCs, the new project requires the development of a dedicated turbine and electric generator and their integration into a complete system, buying all other components, as for example adapted heat exchangers (evaporator and condenser) and a main pump for circulating the working fluid.

2.2. Turbine development and working fluid

A turbine stage has been calculated using ANSYS-CFX software (see Fig. 2), taking into account the thermodynamic properties of the ORC working fluid chosen for the demonstration: the usual hydrofluorocarbon HFC R245fa (C3H3F5). For the computation, fluid's equation of state has been fitted using RefProp database [1]. This fluid is retained due to its wide use in the industry and its moderate cost. Although this fluid is not toxic, not flammable and not ozone depleting, it presents a high global warming potential (GWP). For the long term, it should be replaced by the hydrochlorofluoroolefin HCFO R1233zd (C3H2F5Cl) that offers a much lower GWP [2,3].

Combining the low temperature heat source to R245fa working fluid produces a moderate pressure ratio at turbine stage, corresponding to values from 2.0 to 3.0. Predicted performance of the turbine stage reaches isentropic efficiencies of about 0.80 on a large running map, isentropic efficiency being defined by :

ηis ,turb=hturb,∈¿−hturb ,out

hturb ,∈¿−his , turb , out¿¿ (1)


Fig. 2. Velocity map at turbine blades

2.3. Electrical parts

A dedicated high-speed permanent-magnet electric machine has been designed and tested (Fig. 3a), with the help of an industrial partner of IFPEN, MAVEL Powertrain, specialist of high speed electric machines. An associated power electronics gathering an active front end – for the piloting of the electric machine at high speed – and a grid inverter – for the adaptation of the produced electricity to the features required by the grid – was also realised and validated. The efficiency (see equation 2) of the system has been evaluated at the test cell. It reaches a high 0.90-0.91 value on a large running map at high speed, covering a 30 to 100 kW area (Fig. 4).

ηelec=Pelec , gridPturb ,shaft

(2)

where Pelec,grid represents the electric power fed in to the grid and P turb,shaft is the mechanical power available on the turbine shaft.

Finally, the electric generator and the turbine stage are integrated together by ENOGIA (Fig. 3b), realising an ORC turbogenerator that, associated with the back-to-back inverter, is capable of feeding in to the grid a power of close to 100 kW.

a b Fig. 3. (a) electric generator during testing at IFPEN premises ; (b) complete turbogenerator.


Fig. 4. Efficiency map of the electrical system (generator + back-to-back inverter) measured at test cell.

2.4. ORC demonstrator

The complete ORC100 demonstrator has been assembled by ENOGIA. In order to facilitate its integration into a testing site, the ORC skid has been implemented into a maritime container fitted onto a trailer. A dry-cooler has also been installed beside, to make the demonstrator self-sufficient (see Fig. 5). Finally, ORC100 has taken place in a landfill in the south of Paris area. Its connecting to the customer's facility has been made very easily:

hot water connection thanks to 2 flexible hoses – one inlet and one outlet (see Fig. 5). This represents the hot source for the ORC. In our case, the hot water is coming from a heating network fed by the cooling circuits of several Combined Heat and Power (CHP) engines running with the landfill biogas;

one electrical connection to the electric cabinet of the CHP facility (to be seen in the foreground of Fig. 5)

Measurements made in the landfill confirm that every major component of the ORC system presents a high efficiency. For example, at mid-load (ORC production of around 50 kW), the estimated efficiencies are as follows:

Evaporator thermal efficiency: 0.90 Turbine stage efficiency: 0.75 (see eq. 1) Generator and inverter global efficiency: 0.91 (see eq. 2) Condenser thermal efficiency: 0.90

where the evaporator and the condenser thermal efficiencies are respectively defined by:

ηevap=mwf ¿¿ (3)ηcond=mcw ¿¿ (4)

In the end, the global ORC system thermal efficiency is around 5% (ratio between the electric power fed in to the grid to the amount of heat taken from the heating network at evaporator). In comparison, the theoretical Carnot efficiency at this temperature is around 15% (Fig. 6).


Fig. 5. ORC100 demonstrator in a landfill near Paris: hot water and electrical connections.

Fig. 6. ORC measured efficiency and comparison to Carnot theoretical efficiency (The 2 green dots correspond to measurements realised on ORCs from ENOGIA: on the left : ORC100 demonstrator; on the right : ORC prototype recovering heat in the exhaust gas of a diesel engine).

3. Development of ORC turbines for low temperature heat recovery in cars and trucks

3.1. Interest of the approach

In cars and heavy duty trucks cruising on expressway, about 60% of fuel's energy is wasted as thermal loss. Recovering part of it to improve engine efficiency would allow a further reduction in fuel consumption. As Waste Heat Recovery (WHR) system, ORC shows promising potential and is largely investigated by Original Equipment Manufacturers and vehicle manufacturers [4,5]. But complexity and cost of this solution remain major limitations for its commercial deployment. Today most of the work done when developing WHR systems for trucks or cars is devoted to the high temperature loss, in the engine exhaust gas or in the EGR loop (Exhaust Gas Recirculation). Whereas it is clear that exhaust WHR will produce higher power than in-the-coolant recovery [6,7,8], it represents a more difficult challenge. Severe thermal constraints on the system and difficult control strategy in transient behavior generate important development and manufacturing costs.

To date ENOGIA has sold more than 40 ORC units around the world, a number of them being small units producing between 5 and 10 kW output power, using, once again, low temperature heat source. This correspond to the power range that is encountered when speaking of heat recovery onboard a long haul truck. The waste heat


recovery in the coolant would offer interesting features for an in-vehicle-embedded technology. Especially due to the low temperature heat source (coolant at about 360 K / 87°C / 188°F):

no part of the ORC loop is at temperature higher than 360 K. There is no need to use costly, high-temperature material, for example for the evaporator. Regarding the latter, there is no risk for hot spot occurrence that could damage the working fluid. This is still true in the case of a malfunctioning of the main ORC pump;

there is no contact of the ORC system with the exhaust gas. Then, there is no need to use material compatible with exhaust corrosive mater;

in combination with a well-chosen working fluid, ORC running pressure may remain at a low level, leading to a lightweight sizing of the parts (heat exchangers, piping);

the hot source is dense, in liquid form, leading to a compact evaporator; the hot source presents a stationary temperature making easier the control of the ORC system, despite

the transient behavior of the engine. Especially, the superheating temperature control is more safely ensured;

in combination with a non-flammable working fluid, the low-temperature, low-pressure working fluid makes the ORC system safer. This is especially true in case of vehicle crash.

Despite a lower output power production, an ORC device harvesting heat from the engine coolant will be cheaper, more compact, safer and probably more reliable than an exhaust gas ORC. For the end-user, the payback time should be significantly quicker than for a high-temperature ORC.

Moreover, the acceptance of a low temperature ORC system onboard a vehicle should be better, perhaps allowing a quicker market introduction. On the basis of this analysis, IFPEN and ENOGIA decided to launch the development of small low-temperature ORC turbines for trucks and passenger cars.

In the long term, one could also imagine to increase the heat content in the engine coolant using heat-to-heat technologies (for example EHRS-type heat exchangers – Exhaust Heat Recovery System [9] – to transfer some additional heat from the exhaust gas to the coolant) to improve low temperature ORC output power ; or even to combine onboard a truck two ORCs, one for in-the-coolant low-temperature WHR and the second for heat recovery in the exhaust gas, making a kind of "ultimate WHR". This would of course drastically increase the cooling requirements in front of the truck...

3.2. Working fluid selection and first results

The low-temperature ORC should advantageously be combined with a low running pressure ORC cycle. System simulation (0D) have been realised in order to identify a suitable working fluid. As input parameters, it was considered a heat recovery on engine coolant at 368 K (95°C), combined with a cold temperature source at 308 K (35°C). Considering realistic pinch in both ORC heat exchangers, the thermodynamic cycle was designed between 363 K and 313 K (90°C / 40°C), allowing some superheating and subcooling at evaporator and condenser outlets. Computation shows that a working fluid like the fluoroketone NOVEC 649 (C6F12O), for example, appears as well-adapted (Table 1). Calculation of turbine power has been made assuming a constant turbine isentropic efficiency. For a given level of heat content in the coolant, turbine power is less with NOVEC 649 than with R245fa, but the required working fluid mass flow is higher in case of the use of NOVEC 649. This facilitates the design of a higher efficiency turbine wheel.

Table 1. Working fluid selection for a 363 / 313 K ORC cycle.

Working fluid ORC high pressure level (Mpa)

ORC low pressure level (Mpa)

Relative working fluid mass flow (-)

Relative turbine power (-)

R245fa 0.90 0.32 1.00 1.00

HFE 7000 0.45 0.15 1.25 0.93

NOVEC 649 0.30 0.10 1.67 0.83


Two prototype turbines have been designed: one for truck and one for passenger car applications. System sizing is clearly targeting to realise an efficient heat recovery most of the time when the vehicle is in use. Then the turbine has been optimized for a car running at 70 km/h and for a truck cruising on a highway, on a flat road. At higher engine power, the ORC system efficiency is reduced. The ORC turbine for cars is expected to produce about 400 W of power for a car running at 70 km/h (Fig. 7), whereas the one for trucks should produce about 5 kW for a long haul truck cruising on highway. Those prototypes are currently being manufactured and should be tested during the next months.

Fig. 7. Low-temperature ORC turbogenerator for passenger car application.

4. Conclusion

ENOGIA is commercializing a range of ORC systems, producing from 5 to 40 kW of electrical power, harvesting low-temperature stationary heat sources. With IFPEN, a more powerful version has been developed. It reaches up to 100 kW, taking benefit from sources with a heat content from 1 to 2 MW.

On the basis of the accumulated experience about low-temperature ORC turbines, IFPEN and ENOGIA have launched the development of dedicated components for trucks and cars. To the difference of most of the Waste Heat Recovery research and development currently under progress in the transport industry around the world, another way for WHR is being explored. It aims at reducing the cost of the system for the end user and facilitating its integration for the vehicle manufacturer. As heat source, engine coolant is selected for its ability to offer low-temperature, cheaper, more compact, safer and more reliable ORC solutions. Obviously recovered power through this source is lower than for exhaust gas or EGR heat recovery, but IFPEN and ENOGIA target to propose a low-cost middle-performance ORC solution, enabling a fuel economy improvement of about 2 to 3% with a targeted return on investment for the end-user within 2 years.

Acknowledgements

The authors would like to thank warmly their colleagues for their help in these developments: N. Holaind, J. Drouineau and N. Goubet from ENOGIA; J.P. Dumas, C. Dufresnes, P. Pagnier, B. Talvard, C. Lechard, S. Venturi and C. Gros from IFPEN.

References

[1] Lemmon E, Huber M, McLinden M. Reference fluid thermodynamic and transport properties REFPROP. National Institute of Standard and Technology; 2007.

[2] Ryan J. Hulse, Rajat S. Basu, Rajiv R. Singh, Raymond H. P. Thomas. Physical Properties of HCFO-1233zd(E). 18th Symposium on Thermophysical Properties; 2012. Journal of chemical and engineering data, pubs.acs.org/jced.

[3] Guillaume L, Legros A, Desideri A, Lemort V. Performance of a radial-inflow turbine integrated in an ORC system and designed for a WHR on truck application: An experimental comparison between R245fa and R1233zd. Appl Energy; 2016. http://dx.doi.org/10.1016/j.apenergy.2016.03.012.


[4] Bettoja F, Perosino A, Lemort V, Guillaume L, Reiche T, Wagner T. NoWaste: waste heat re-use for greener truck. 6th Transport Research Arena; Transportation Research Procedia 14 (2016) 2734 – 2; 2016.

[5] Espinosa N, Tilman L, Lemort V, Quoilin S, Lombard B. 2010. Rankine cycle for waste heat recovery on commercial trucks: approach, constraints and modeling. Proceedings of the Diesel International Conference and Exhibition, SIA; 2010.

[6] Bourhis G et al. Energy and Exergy Balances for Modern Diesel and Gasoline Engines. Les rencontres scientifiques de l'IFP – Advances in Hybrid Powertrains; 2008.

[7] El Habchi A et al. Potential of waste heat recovery for automotive engines using detailed simulation. ASME Conference on Thermal and Environmental Issues in Energy Systems; 2010.

[8] Serrano D. et al. Improving train energy efficiency by Organic Rankine Cycle for recovering waste heat from exhaust gas. 3rd International Seminar on ORC Power Systems, Brussels; 2015.

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