orc and kalina analysis and experience -...

1

ORC and KalinaAnalysis and experience

Páll Valdimarssonprofessor of mechanical

engineering

Sabbatical December 2003Lecture III

2

Energy and energy use

• Energy is utilized in two forms, as heat and as work

• Work moves, but heat changes temperature (moves the molecules faster)

• These are two totally different products for a power station

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3

Convertability

• Work can always be changed into heat (by friction since ste stone age)

• Conversion of heat into work is difficult and is limited by the laws of thermodynamics. A part of the heat used has always to be rejected to the surroundings

4

Heat and work again

• Work is the high quality, high priced product

• Heat is second class quality, a low priced byproduct



3

5

A power plant

Source

Heat

Fuel

Rejected heatLosses

Electricity

Sellable heat

Power plant

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Single flash - condensing

Production well Injection well

Separator

TurbineCooling tower

Pump

Condenser

Pump



4

7

T-s diagram

8

ORC with regenerator

Production well

Injection well

Turbine

Condenser

Pump

Regenerator

Boiler



5

9

T-s diagram

-2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0-50

0

50

100

150

200

250

s [kJ/kg-K]

T [°

C]

2300 kPa

1000 kPa

350 kPa

90 kPa 0,2 0,4 0,6 0,8

0,00

45

0,02

6 0

,063

0

,15

0,37

0,

89 m

3/kg

Isopentane

10

ORC with paralell single flash


Separator

Turbine Cooling tower

Condenser

Pump

Condenser

Cooling towerTurbine

Boiler



6

11

ORC with serial single flash


Separator Turbine

Condenser

Cooling towerTurbine

Boiler

Throttling valve



7



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15

Rogner, Bad Blumau

• The 250 kW air-cooled geothermal CHP plant generates electrical power as well as district heating using a low temperature geothermal resource.

• One standard containerized ORMAT CHP module, generating 250 kW electricity and 2,500 kW heat.

• The power plant is in commercial operation since July 2001.

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Mokai, New Zealand

• The 60 MW Geothermal Power Plant is comprised of:» one 50 MW module operating on geothermal

steam» two 5 MW units operating on geothermal brine

• The power plant uses air-cooled condensers and achieves 100% geothermal fluid reinjection to produce electrical power with virtually no environmental impact.



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18

Kalina

Production well

Injection well

Separator

Turbine

Condenser

Boiler

Throttling valve

Cooling tower

Regenerator

Pump

Brine hx



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19

Geothermal experience

• Rough surroundings• Aggressive chemistry• Simple and reliable solutions• Geothermal energy - a mayor economic

factor

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21

Conversion of heat to electricity

• The Carnot efficiency applies for infinite heat sources

• The maximum efficiency is lower than the Carnot efficiency for a source stream with finite heat capacity

• Kalina reduces entropy generation in the heat exchange process

22

Carnot efficiency

Hot reservoir

Cold reservoir

Work output

Heat in

Heat out

1

01TT

Carnot −=η



12

23

Maximum efficiency for a liquid source

−−=

21

2

1

0)(

ln1*

TTTT

THE hx

1T

2T

0T 0T

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What is a Kalina process?

• A modified Rankine cycle, or rather:• a reversed absorption cycle• Ammonia - water working fluid• Patented by Exergy Inc and A. Kalina



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25

The characteristics

• Heat is added in a combined boiling and separation process» at a variable temperature

• Heat is rejected in a combined condensation and absorption process» as well at a variable temperature

260 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

60

80

100

120

140

160

180

200

220

240

Tem

pera

ture

[°C

]

Ammonia mass fraction [-]

Mixture boiling at 30 bar



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27

Heat addition - boiler

Source

Kalina

ORC

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The working fluid

• Ammonia has a molar mass of 17, so steam turbines can be used

• The mixture properties are more complex, usually three independent properties are needed for the calculation of the fourth

• Therefore the cycle is more flexible, and can be closely optimized to the source



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29

The benefit

• The working fluid is almost at the temperature of the source fluid when leaving the boiler

• The variable heat rejection temperature makes regeneration possible

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Kalina vs. ORC

• Kalina is better when the heat source stream has a finite heat capacity

• ORC and Kalina are similar when the source is condensing steam



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31

Boiling curves for Húsavík

0 200 400 600 800 1000 120020

30

40

50

60

70

80

90

100

110

120

Tem

pera

ture

[°C

]

Enthalpy [kJ/kg]

Water KalinaORC

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17

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34

Kalina again

Production well

Injection well

Separator

Turbine

Condenser

Boiler

Throttling valve

Cooling tower

Regenerator

Pump

Brine hx



18

35

36



19

37

38

0 200 400 600 800 1000 1200 1400 1600

0

50

100

150

200

Enthalpy [kJ/kg]

Tem

pera

ture

[°C

]

T - h diagram

6.5

6.56.5

6.5

31

3131

31

6.5

6.5

6.5

6.5

31

31

31

31

6.5

6.5

6.5

6.5

31

31

31

31



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39

Comparison

Power[kW]

1. law 2. law Maxliquideff.

Volumeto

turbine[m3/s]

Kalina 2000 0,13 0,45 0,56 0,57ORC 1589 0,10 0,36 0,45 2,06Flash cycle 1589 0,10 0,36 0,45 22,4Themoelectricity 720 0,05 0,16 0,20 0

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Comparison of Kalina and ORC

• Heat (10MW) is available down to 80°C• Cooling water (120kg/s) is available at

20°C• Heat exchangers have a pinch of 3°C• Condensers have a pinch of 10°C



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90 95 100 105 110 115 120 125 130 135 1400

0.05

0.1

0.15

0.2

0.25

Temperature [C]

Effi

cien

cy [-

]CarnotLiquidKalinaORC

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Húsavík geothermal power plant



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General design parameters

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Summary

• Commissioned in the summer 2000• Running at ~1500 kW net 2000 - 2001• Running at ~1700 kW net since

November 2001• Final acceptance certificate issued• Total investment cost 3,7 MEUR



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Processdiagram

G121 °C

80 °C

90 kg/s1950 kW

5 °C

24 °C

118 °C31 bara

5,5 bara

12 °C

67 °C

16,3 kg/s

173 kg/s

0,81 NH3

130 kW

11,2 kg/s

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The power plant



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Design

• Standard industrial components• Turbine-generator from KKK, Germany• Electrical components CE marked• Heat exchangers from USA• Most of the tanks made in Iceland• Installed by a local contractor

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Equipment

• Evaporator, shell and tube, 1600 m2

• Separator• Turbine• Recuperators• Condenser, plate, 2 x 750 m2

• Hotwell• Circulation pump



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Auxillary equipment

• Ammonia storage tank• Demineralized water tank• Blow down tank

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Thermal equilibrium

Power output

Power input

14.000 kWCooling water

1.700 kWElectricity, net

15.700 kWBrine



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Start-up problems

• Separator• Evaporator• Axial sealing of the turbine, ammonia leakage• Condensers• Miscellaneous

» Main pump» Safety valves» Magnetite

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Separator

• Difficult to measure the performance of the separator

• Mist eliminator module wrongly installed• New separator installed November 2001



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Evaporator

• Ammonia leaking into the hot water• All tubes rolled again in November

2001, no leakages since

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Axial sealing

• One axial sealing on the low pressure side

• N2 used in the sealing• The sealing has been replaced once• Leakage caused by carry-over from

separator



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Condensers

• Plate heat exchangers• Important to mix liquid and vapor• Spraying nozzles modified• Increase power output by improving

performance of the condensers

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Miscellaneous

• Safety valves, leakage• Circulation pump, seals and

guides/bushings for shaft• Improvment of spraying system in

recuperator 2• Magnetite (Fe3O4)



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Turbine corrosion

• Ferritic material in the turbine corrodes• Austenitec material is unharmed• Corrosion is from the turbine control

valve until abt 1 metre after the turbine• Influence of rotor magnetic field?

» Elimination of ferritic material in the steam side of the turbine

58

Operating experience

• Maximizing the output by optimizing the strength of the NH3 – H2O solution

• Prevent air entering the system• Improvement of flushing and filters• The system is stable in operation



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59

Lessons learned

• The technology is proven• Standard equipment has been adjusted• The plant is running according to specs• Individual equipment still may be

improved to increase output• Engineering details will improve future

plants

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What do we have?

• New thermodynamic cycle with better efficiency in particular when the heat source cooled down while heat is extracted

• Theoretical and technical descriptions of the processes involved.

• Mathematical models that have been tested up against Husavik Plant

• Known media and known machinery



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The knowledge

• Real experience and know how from the Husavik plant

• Mathematical models and ,,steam tables”, worked out in cooperation with University of Iceland.

• Over 30 years of experience in electrical generation from low and mid heat sources (Geothermal)

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Kalina references

• Canoga Park, USA, demonstration plant 3 – 6 MW, 1991-1997

• Fukuoka, Japan, incineration plant, 4,5 MW, 1999

• Sumitomo, Japan, waste heat recovery from a steel plant, 3,1 MW

• Husavik, Iceland, geothermal plant, 2,0 MW, 2000



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Krafla 1970, 60 MWel

Svartsengi 1980, 37 MWel, 60 MWdh

Nesjavellir 1990, 90 MWel, 250 MWdh

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Were does it fit?

• Temperature above 150°C and good size stands on its own.

• Cogeneration of electricity and water for district heating.

• Good cold end helps• Environmental issues and subsidizing

changes these values



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Budgetary unit price

• Budgetary price for 500 kW unit 720.000 USD

• Equals 1440 USD/kW• Turbine/generator most costly unit (30-

35%)• Presuming cooling water available

66

Opportunities

Where there may be hot water or other fluid/gas available at temperatures between 120 and 300°C

• Geothermal• Waste heat

» Industrial processes» Gas and diesel engine exhaust



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Kalina plant benefits

• Energy cost efficient• Environmental issues• Green energy• Reduced emissions• Standard off the shelf equipment

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General marketconditions

• General market price 4 eurocents/kWh• General pay-back time 4 years required• General investment 1000 USD/kW

• So how can 1440 USD/kW be competitive?



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German law

“Green” electrical power generation bonus

• 2002-2004 1,74 eurocents/kWh• 2005-2006 1,69 eurocents/kWh• 2007-2008 1,64 eurocents/kWh• 2009-2010 1,59 eurocents/kWhProvided plant in operation before end of 2005

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Competitive investment ?

• Given 1,65 eurocents/kWh bonus• 4 year pay-back period• Additional investment acceptable for

“green” energy USD 528.000/MW• Total acceptable investment cost thus

USD 1.528.000/MW or 764.000 USD for our 500 kW unit.



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“Green” energy?

• Is waste heat recovery=green energy?• Waste heat recovery reduces emissions• CO2 quotas pricing as high as 20-25

USD/tonCO2

• Average emission 800 gCO2/kWh in fossil fuel plants

• Equals values of 1,8-2,2 eurocents/kWh

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Summary

• Given green energy bonuses or CO2 evaluation the investment in a Kalina waste heat recovery electrical generating plant is feasible

• The investment is competitive to other investments for industrial improvements

• Pay-back time of 4 years in a green energy technology is short



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Introduction

• Finite source heat capacity lowers this upper bound due to the reduction of the source temperature as heat is removed from the source

• This results in high cost for such low temperature power plants, as they have to handle large heat flows

• The Kalina cycle is a novel approach to increase this efficiency

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The Models

• It is assumed that a fluid is available at temperatures ranging from 100 to 150°C

• A heat customer is assumed for the primary outlet water at the temperature of 80°C

• Primary flow of 50 kg/s is assumed• Cooling water source is assumed at 15°C,

and cooling water outlet is fixed at 30°C• It is assumed that a cooling water pump has

to overcome a pressure loss of 1 bar on the cooling water side in the condenser



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Solution

• The software Engineering Equation Solver (EES) is used to run the models

• The cost model keeps the logarithmic mean temperature difference for each heat exchanger at the same value as found in the cycle data for the tenders for the Husavik power plant

• Estimated cost figures for individual components were then added together in order to obtain the final cost value

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Process assumptions

• The OCR model is based on a system without regeneration

• Isopenthane is assumed as a working fluid

• A Kalina cycle for generation of saturated vapour for the turbine is used



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ORC flow sheet

Production well

Injection well

Turbine

Condenser

Pump

Boiler

78

Kalina flow sheet

Production well

Injection well

Separator

Turbine

Condenser

Boiler

Throttling valve

Cooling tower

Regenerator

Pump

Brine hx



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Kalina assumptions

• This cycle will be limited by the dew point of the mixture, that is when the boiling of the mixture is complete, and no liquid remains at the boiler outlet

• The bubble temperature of the mixture has to be lower or equal to the primary fluid outlet temperature to ensure safe operation

• The feasible region will be in the area between the 70 and 80°C bubble contours

• The feasible area regarding the dew temperature is limited to a value some 2-4°C lower than the maximum temperature of the primary fluid

Bubble temperature

1020

3040

0.6

0.8

120

40

60

80

100

Pressure [bar]

Bubble temperature

Ammonia ratio [-]

Bub

ble

tem

pera

ture

[°C

]



41

Dew temperature

1020

3040

0.6

0.8

150

100

150

200

Pressure [bar]

Dew temperature

Ammonia ratio [-]

Dew

tem

pera

ture

[°C

]

Bubble contours

10 15 20 25 30 35 400.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Pressure [bar]

Amm

onia

ratio

[-]

Bubble temperature contours

3040

4050

5060

6070

70

70

80

80

80

90



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Dew contours

10 15 20 25 30 35 400.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Pressure [bar]

Am

mon

ia ra

tio [-

]

Dew temperature contours

80 90

100100

110

110110

120

120120 120

130

130

130130

140

140

14014

0

150

150

150

160

160

160

170

170 180

190

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More Kalina

• Both high pressure level and ammonia content are design variables in the Kalina cycle

• This gives flexibility in the design of the cycle, and requires as well a certain design strategy

• The plant can be designed for maximum power• or with strong demands on the investment cost• The cost is 100 for the lowest cost, and the power

100 for the highest power• An x denotes an infeasible solution, the cycle will not

be able to run at these ammonia content – pressure combinations



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Cost contours

15 20 25 30 35 400.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Pressure [bar]

Am

mon

ia ra

tio [-

]

Cost contours, 100°C source

101

101

101

102102

102

102103

103

103

103103

104104

104

104

105

105

105

105

106

106

106

106

107

107

107

107

107

108

108

108

108

109

109

109

109

110

110

110

110

110

Power contours

20 25 30 35 400.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Pressure [bar]

Am

mon

ia ra

tio [-

]

Power contours, 100°C source

9090

90 9090

90

90 9090

90

90

909090

9191

91

9191

91 91

91 9191

91

9191

92

92

9292 92

929292

92

9292

92

93

93

9393

9393

9393

9393

93

9494

94

9494

9494

94

9494 94

9595

95

9595

95 9595

9595

96

96

96

9696

96

9696

9797

97

9797

97

9797

9898

98

9898

99

9999



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Cost surface

1020

3040

0.6

0.8

10

200

400

600

Pressure [bar]

Cost function

Ammonia ratio [-]

Cos

t

Power surface

1020

3040

0.6

0.8

10

50

100

Pressure [bar]

Power function

Ammonia ratio [-]

Pow

er



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89

Discussion

• The best power and best cost points are different

• The lowest cost is at 32 bar, 92% ammonia, but highest power is at 34 bar and 88% ammonia

• This leads to the definition of two different Kalinacycles, the best power and the best cost cycles, with different pressure and ammonia content

15 20 25 30 35 400.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Pressure [bar]

Am

mon

ia ra

tio [-

]


101

101

101

102

102

102

102 102102

103

103

103 103 103

104104

104

104104

105

105

105

105105

106

106106

106

107

1071 0 7

107

108

108108

108

108 109

109

109109

110

110

110



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22 24 26 28 30 32 34 36 38 400.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Pressure [bar]

Am

mon

ia ra

tio [-

]


7070

72

72

74

74

76

76

7678

78

78

8080

80

82

82

82

84

84

8484

86

8686

88

8888

90

9090

91

9191

92

9292

93

9393

9494

95

95

96

9697 98

99

18 20 22 24 26 28 30 32 34 360.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Pressure [bar]

Am

mon

ia ra

tio [-

]


101

101101

102

102

102

103103

103 103

104

104

104 104

105

105

105

106

106

106

107

107

107

108

108

108

108

109

109

109

110

110



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22 24 26 28 30 32 34 36 38 400.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Pressure [bar]

Am

mon

ia ra

tio [-

]


70

70

72

7274

74

7 676

7878

8080

82

82

84

84

86 8890

9192

9394

9596

97

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Comparison

• Two ORC companies made a tender in the Husavik bid

• Manufacturer A offered a high power, high cost power plant, where manufacturer B took a more conservative approach

• Following is a comparison with both the low cost and high power Kalina power plants



48

Cost comparison

100 110 120 130 140 1501000

1200

1400

1600

1800

2000

2200

2400

Source inlet temperature [°C]

Net

cos

t [$/

kW]

Kalina vs ORC cost comparison

ORC BORC A

Kalina HP

Kalina LC

Power comparison

100 110 120 130 140 1500

500

1000

1500

2000

Source inlet temperature [°C]

Net

pow

er [k

W]

Kalina vs ORC power comparison

Kalina HP

Kalina LC

ORC A

ORC B



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97

Results

• The maximum power generated for a given source is greater for the Kalinacycle

• Kalina cycle is well positioned against an ORC cycle for applications with high utilization time, a base load application

98

Results II

• A heat consumer is beneficial for the ORC cycle as it results in less temperature change of the primary fluid during the boiling process

• The Kalina cycle has the boiling or vaporization of the fluid happening over a temperature range up to 100°C, which is beneficial when the primary fluid return temperature has to be minimized



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The debate

• The theoretical efficiency and cost/production ratio are better for Kalina as shown above

• Other arguments like difficulties with machinery and lesser operational security or uptime are only temporary discussion items, as always for a new technology

• These arguments were exactly the same between conventional flash cycle and ORC when the latter popped up 30 years ago with better efficiency but little track record

100

Conclusion

• The Kalina cycle is thermodynamically superior or equal to the ORC cycle

• There is no black magic behind the Kalina cycle

• The startup problems that have either been solved, or are solvable



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