Experimental testing of a small-scale supercritical ORC at - - PowerPoint PPT Presentation

▶
experimental testing of a small scale supercritical orc
SMART_READER_LITE
LIVE PREVIEW

Experimental testing of a small-scale supercritical ORC at - - PowerPoint PPT Presentation

Aug 28, 2022 47 likes •252 views

Experimental testing of a small-scale supercritical ORC at low-temperature and variable conditions George Kosmadakis, Dimitris Manolakos, and George Papadakis Department of Natural Resources and Agricultural Engineering, Agricultural University

slide-1
SLIDE 1

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

Experimental testing of a small-scale supercritical ORC at low-temperature and variable conditions

George Kosmadakis, Dimitris Manolakos, and George Papadakis Department of Natural Resources and Agricultural Engineering, Agricultural University of Athens (AUA), Greece

slide-2
SLIDE 2

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

Presentation Outline  Concept and objectives  Description of the installed ORC engine  Test results at subcritical operation  Test results at supercritical operation  Conclusions

2

slide-3
SLIDE 3

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

 Concept and objectives  Description of the installed ORC engine  Test results at subcritical operation  Test results at supercritical operation  Conclusions

3

slide-4
SLIDE 4

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

Research project FP7-SME: CPV/Rankine (duration: 2013-2014), www.cpvrankine.aua.gr

CPV/T field (100 m2, 10 kWp, 41 kWth) Supercritical ORC engine (~3 kW) Supercritical heat exchanger (41 kWth)

4

Concept and objectives

slide-5
SLIDE 5

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

 Concept and objectives  Description of the installed ORC engine  Test results at subcritical operation  Test results at supercritical operation  Conclusions

5

slide-6
SLIDE 6

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

ORC engine – design (single-stage)

  • Selection of appropriate organic fluid: R-404a.
  • Heat input: 41 kWth with max. pressure almost 40 bar

(~1.04 P/Pcr).

  • Thermal efficiency at design conditions: 6.8% with net

power production 2.9 kW.

  • Condensation temperature ~30 oC and pressure ~15

bar, depending on the condenser operation.

  • The pump and expander are equipped with frequency

inverters for controlling their rotational speeds.

  • Maximum temperature ~85 oC with a 10 K pinch-point

temperature difference (at the outlet side).

  • Further details about the HEX are provided by UGent.

Expander Condenser ORC pump Supercritical heat exchanger

G

Generator

M

Motor Heat rejection (kWth)

50 100 150 200 250 300 350 102 103 104 104

h [kJ/kg] P [kPa]

100°C 80°C 60°C 40°C 20°C 0°C 0.2 0.4 0.6 0.8 . 8 . 9 1 1.1 1.2 kJ/kg-K

4 3 2 1

6

Description of the installed ORC engine

slide-7
SLIDE 7

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

  • The scroll expander is a hermetic scroll compressor in

reverse operation, manufactured by Copeland (ZP series: ZP137KCE-TFD with swept volume 127.15 cm3/rev), suitable for high-pressure A/C applications (usually with R-410a).

  • Max. isentropic efficiency at compressor mode is 75.2%

at pressure ratio ~2.8.

  • A new casing was installed and some internal parts

have been re-designed for higher performance (e.g. the inlet volume before the fluid enters the steady scroll). Hermetic scroll compressor (Copeland: ZP137- KCE-TFD)

7

Description of the installed ORC engine

slide-8
SLIDE 8

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

Top: Hermetic scroll expander and side view of ORC Right: ORC engine

8

Description of the installed ORC engine

slide-9
SLIDE 9

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

  • ORC engine installed in the laboratory.
  • Heat input from a controllable electric heater (10-

48 kWth).

  • HTF temperature adjusted to the desired set

point (65-100 oC).

  • HTF pump at constant speed (2900 rpm - 50 Hz).

ORC pump and expander speed can be controlled (10-50 Hz).

  • Pump:

diaphragm pump (20 l/min) by Wanner/Hydra Cell (G-10), with an inlet pressure limit of 17 bar.

  • Condenser: shell and tube HEX using cold water

(~15 oC) from a 320 m3 reservoir.

9

Description of the installed ORC engine

slide-10
SLIDE 10

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

 Introduction  Description of the installed ORC engine  Test results at subcritical operation  Test results at supercritical operation  Conclusions

10

slide-11
SLIDE 11

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

All test results presented concern a HTF temperature of 95 oC. Main parameters varied during operation:

  • Pump speed (-> heat input)
  • Expander speed (-> max. pressure and pressure ratio)

10 15 20 25 30 35 40

Pump frequency (Hz)

20 25 30 35 40 45 50

Heat input (kWth)

THTF=95 oC

10 15 20 25 30 35 40 45 50

Expander frequency (Hz)

40 42 44 46 48 50

Heat input (kWth)

THTF=95 oC Pump frequency=35 Hz

Effect of pump and expander speeds on heat input

11

Test results at subcritical operation

slide-12
SLIDE 12

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

Scroll expander operation and performance

  • Max. expander power: 3 kW for moderate speeds (pump: 35 Hz, expander: 30 Hz)
  • Max. power production is observed for pressure ratio of 2 with max. pressure ~24 bar

(almost constant condenser pressure of 12 bar) Effect of expander speed on power, pressure and pressure ratio

10 20 30 40 50

Expander frequency (Hz)

1 2 3 4

Expander power production (kW)

Pump freq.

50 Hz 45 Hz 35 Hz 25 Hz 15 Hz

THTF=95 oC

10 20 30 40 50

Expander frequency (Hz)

16 20 24 28 32

Pressure (bar)

Pressure Pressure ratio

1.2 1.6 2 2.4 2.8 3.2

Pressure ratio (-)

THTF=95 oC Pump frequency=35 Hz

12

Test results at subcritical operation

slide-13
SLIDE 13

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

ORC engine performance

  • Max. expansion efficiency: 85% for moderate speeds (pump: 35 Hz, expander: 35 Hz)
  • Max. thermal efficiency: 5.5%, observed for the conditions with max. expansion

efficiency Effect of expander speed on efficiency of expander and thermal efficiency

10 20 30 40 50

Expander frequency (Hz)

1 2 3 4 5 6

Thermal efficiency (%)

Pump freq.

50 Hz 45 Hz 35 Hz 25 Hz 15 Hz

THTF=95 oC

10 20 30 40 50

Expander frequency (Hz)

30 40 50 60 70 80 90 100

Expansion efficiency (%)

Pump frequency=35 Hz Pump frequency=25 Hz Pump frequency=15 Hz

THTF=95 oC

( )

( )

is ,

  • ut

in e exp

h h m kW production y Electricit n − = 

( ) ( )

th e th

kW input Heat kW production y Electricit n =

13

Test results at subcritical operation

slide-14
SLIDE 14

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

 Introduction  Description of the installed ORC engine  Test results at subcritical operation  Test results at supercritical operation  Conclusions

14

slide-15
SLIDE 15

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

For reaching supercritical operation, the flow rate of the cooling water was decreased, increasing the low pressure to around 16-17 bar.

  • Pressure ratio: around 2.3 at such conditions
  • Expansion efficiency at supercritical conditions: 45% (for expander frequency of 16 Hz),

resulting to low thermal efficiency (4.4%)

  • For higher expander speeds, the expansion efficiency increases up to ~80% (subcritical
  • peration), as well as the thermal efficiency

Effect of expander speed on expansion efficiency and thermal efficiency (choked cooling water)

10 15 20 25 30 35 40

Expander frequency (Hz)

40 50 60 70 80

Expansion efficiency (%)

THTF=95 oC Pump frequency=45 Hz Choked cooling water Supercritical condition

10 15 20 25 30 35 40

Expander frequency (Hz)

4.0 4.4 4.8 5.2 5.6 6.0

Thermal efficiency (%)

THTF=95 oC Pump frequency=45 Hz Choked cooling water Supercritical condition

15

Test results at supercritical operation

slide-16
SLIDE 16

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

 Introduction  Description of the installed ORC engine  Test results at subcritical operation  Test results at supercritical operation  Conclusions

16

slide-17
SLIDE 17

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

Main conclusions from the laboratory tests

  • The small-scale ORC engine operates without any problem and produces power with good

performance at subcritical conditions (max. thermal efficiency almost 6%).

  • The modified scroll expander shows high performance and much higher than any other

expander tests of the AUA research group. Max. expansion efficiency: 85% for a single

  • perating condition, while values around 70% were common for a large range of operation.
  • Stable supercritical operation could be reached for choked cooling water only (increase of

condenser pressure/temperature).

  • At such conditions, operation at low expander speed resulted to high pressure with

expansion efficiency ~45% and thermal efficiency of 4.4% (lower than subcritical operation).

  • For continuous operation at supercritical conditions, the size of the expander (its swept

volume) should be reduced, increasing its speed as well closer to 50 Hz, leading to higher pressure operation at high expansion speeds with increased electric efficiency of the generator.

17

slide-18
SLIDE 18

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

  • By extrapolating the results so far and using a smaller expander, the expansion efficiency

could reach values around 70% at supercritical operation, ending up to a thermal efficiency around 7% (higher than subcritical operation).

  • Such value is higher than any value recorded at subcritical operation during the tests, which

is just an indication that supercritical operation can have a good potential at such low- temperature applications, even at small-scale.

18

Main conclusions from the laboratory tests

slide-19
SLIDE 19

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

  • The ORC engine has been installed at the field and connected with the CPV/T collectors.
  • First test results have been achieved, showing that such concept is feasible and leads to a

total higher production.

  • More tests are planned in the future.

Next steps

19

slide-20
SLIDE 20

Agricultural University of Athens Renewable Energy Systems Group (www.renewables.aua.gr)

Thank you for your attention

Acknowledgements:

  • The research leading to these results has received funding from the European Union's

Seventh Framework Programme managed by REA-Research Executive Agency, http://ec.europa.eu/research/rea ([FP7/2007-2013] [FP7/2007-2011]) under Grant Agreement n° 315049 [CPV/RANKINE], FP7-SME-2012.

  • The AUA research team would also like to thank its project partners for their research work

conducted within the CPV/Rankine project.

This presentation reflects the views only of the authors and the Commission cannot be held responsible for any use which may be made of the information contained therein. 20