Professor Páll Valdimarsson, Atlas Copco Geothermal Competence Center and Reykjavik University Iceland Geothermal Conference 2013 March 5-8, 2013, Harpa, Reykjavík

1. Producing Tomorrow’s Energy
Hellisheidi Power Plant - is there an optimal design?
Professor Páll Valdimarsson, Atlas Copco Geothermal Competence Center
and Reykjavik University

2. Hellisheidi Power Plant
- is there an optimal design?
 The question of an optimal design in the sense of power production is
discussed
 The use of temperature versus heat duty and Carnot efficiency versus heat
duty diagrams for the analysis is presented
 The problem of defining design conditions for the plant is discussed
 The present well production is discussed from that point of view
 An attempt is made define an "optimal" plant for the present well
production, and the power production is estimated for a few configurations.

3. Real life power plant design
 The process has to be designed before any real production experience is
available from the wells
 The only available data is from exploratory wells and geophysical models
 The good earth scientist makes a safe and conservative estimate of the
expected well enthalpy
 The good and experience engineer makes a safe and conservative design
based on these estimates
 There is no other way to do the design!!!
 If everybody is roughly right, then the plant will be conservative, and could
produce more power if the design was aggressive.

4. Optimal design for power
 The power output is the score function
 The thermodynamic process parameters are optimized
 Investment cost is not minimized here
– but a “state of the art” technical level is assumed
 The well enthalpy is assumed constant
 The well flow is dependent on the wellhead pressure
– but within boundaries given by operational experience.

5. Simplified steam system
 The well production is determined by the wellhead pressure
 The collection system unifies flow from different wells and conveys it to the separator
 The separator pressure is a main design parameter for a steam plant
 The turbine design is based on the separator pressure
 Off-design separator pressure will influence turbine efficiency
 Pressure reduction will cause increased steam fraction and exergy losses.
P
P
Wellhead pressure
Collection system
Separator pressure
Steam for turbine
Mineralized brine
Well
Wellhead valve
Orifice or valve
Separator
cPbPam wellwellwell  2


8. 1 km
Ring Road #1
Power Station
Wellpad
Wellpad
Wellpad
Wellpad
Ring Road #1
Wellpad

9. Main Power Station
Wellpad
Wellpad
Wellpad
Collector line 8
Collector line 26
Power Station for Units V and VI
Separator station 1
Separator station 2
Separator station 3
Supply line
Supply line

10. HE-05 HE-29 HE-43
HE-06 HE-11 HE-17
HE-31 HE-44 HE-48
HE-24 HE-27 HE-38
HE-03 HE-32 HE-51
HE-09 HE-14 HE-18 HE-50 HE-56
HE-15 HE-30
HE-47
Supply line 7
Supply line 6
Supply line 5
Supply line 1
HE-07 HE-12 HE-16
HE-41 HE-42
Supply line 4
HE-19HE-45
Supply line 2
Supply line 3
V
VI
I
II
III
IV
XI
Main Power Station
Power Station for Units V and VI
Separator station 1
Separator station 2
Separator station 3

11. Scenario from 2012 12 07
 Total flow from wells 1080 kg/s
 Average enthalpy 1737 kJ/kg
 HP gross power 268,5 MW
 LP gross power 23 MW
 Plant net power 276 MW
 This corresponds to 19,5 bar
gage unified wellhead
pressure
Well
Maximum
wellhead
pressure
Minimum
wellhead
pressure
Operating
wellhead
pressure
[bar g] [bar g] [bar g] a b c
HE-3 22 14 14 -0,1787 3,2647 15,27
HE-5 22 14 14 -0,3479 5,3899 50,35
HE-6 30 14 17 -0,0187 0,5304 25,77
HE-7 30 20 22 -0,0249 0,251 80,23
HE-9 30 14 22 -0,0033 0,0322 10,03
HE-11 30 16 16 -0,0042 -1,0015 67,39
HE-12 30 18 21 -0,0363 0,6606 66,87
HE-14 30 14 12 -0,0103 -0,138 34,81
HE-15 30 14 25 -0,0221 0,3316 38,81
HE-16 30 14 57 -0,009 0 29,2
HE-17 30 22 17 -0,029 0,7146 61,22
HE-18 27 14 13 -0,1453 2,8174 30,11
HE-19 30 22 22 -0,0458 0,6245 104,09
HE-24 30 14 17 -0,029 0,7146 61,22
HE-27 30 14 24 -0,0472 1,1312 19,35
HE-29 30 14 16 -0,0041 -0,0948 20,37
HE-30 30 18 16 -0,016 0,2279 42,47
HE-31 18 14 16 -0,1652 4,3899 56,42
HE-32 30 14 15 -0,0308 0,3701 49,38
HE-38 18 14 36 -0,0376 0,5779 22,78
HE-41 30 14 27 -0,0052 0,0507 25,69
HE-42 30 14 26 -0,0052 0,05 21,96
HE-43 30 14 15 -0,0148 0,5125 7,7
HE-44 30 14 18 -0,0472 1,0853 63,66
HE-45 30 20 25 -0,0085 0,2332 35,91
HE-46 18 14 30 -0,1183 2,9048 19,3
HE-47 30 22 18 -0,0073 -0,0686 58,38
HE-48 18 14 16 -0,0378 0,7752 55,78
HE-50 30 14 16 -0,0063 0,1487 16,14
HE-51 32 14 20 -0,0145 0,2191 7,793
HE-56 30 14 16 -0,0086 -1,5603 82,95
Production curve parameters

12. Flow from individual wells
10 14 18 22 26 30
0
20
40
60
80
100
Pwell
mdot;well
High pressure wells
A single well accounts for 10% of the plant flow!
Medium pressure wells
Low pressure wells

13. Flow from all wells, common wellhead pressure
10 14 18 22 26 30
700
800
900
1000
1100
1200
Pwell
m

14. Average enthalpy, common wellhead pressure
10 14 18 22 26 30
1675
1710
1745
1780
1815
1850
Pwell
haverage

15. Temperature as a function of removed heat
 The ideal case is if we could utilize the full flow without any boiling
 Pressure loss in the formation and in the transport up the well will cause
boiling and exergy loss
 Four curves are presented:
 Temperature assuming that the wellhead pressure is so high that no boiling
occurs, with the same flow and enthalpy as in the real operating scenario
 Temperature if the wellhead pressure is 10 bar g for all wells
 Temperature if the wellhead pressure is 19,5 bar g for all wells
 Temperature if the wellhead pressure is 30 bar g for all wells.

16. Temperature – heat duty diagram
-1400 -1200 -1000 -800 -600 -400 -200 0
100
150
200
250
300
350
400
Q [MW]
Temperature[°C]

17. Carnot efficiency as a function of removed heat
 The unit of area is MW of exergy (power producing potential)
 The ideal case is if we could utilize the full flow without any boiling
 Pressure loss in the formation and in the transport up the well will cause
boiling and exergy loss
 Four curves are presented:
 Carnot efficiency assuming that the wellhead pressure is so high that no
boiling occurs, with the same flow and enthalpy as in the real operating
scenario
 Carnot efficiency if the wellhead pressure is 10 bar g for all wells
 Carnot efficiency if the wellhead pressure is 19,5 bar g for all wells
 Carnot efficiency if the wellhead pressure is 30 bar g for all wells.

18. -1400 -1200 -1000 -800 -600 -400 -200 0
0,25
0,3
0,35
0,4
0,45
0,5
0,55
0,6
Q [MW]
hc
-1400 -1200 -1000 -800 -600 -400 -200 0
0,25
0,3
0,35
0,4
0,45
0,5
0,55
0,6
Q [MW]
hc
-1400 -1200 -1000 -800 -600 -400 -200 0
0,25
0,3
0,35
0,4
0,45
0,5
0,55
0,6
Q [MW]
hc
-1400 -1200 -1000 -800 -600 -400 -200 0
0,25
0,3
0,35
0,4
0,45
0,5
0,55
0,6
Q [MW]
hc
Carnot efficiency – Heat duty diagram
Wellhead pressure 19,5 bar g
No pressure loss and same flow
and enthalpy as if wellhead
pressure was19,5 bar g
Lost power potential because
of well pressure loss
Wellhead pressure 30 bar g
Wellhead pressure 10 bar g

19. Optimization
 Three alternatives:
 Modification of HP separator pressure, double flash plant
 Individual HP wellhead turbines and common MP plant
 HP steam turbines and ORC bottoming plant.

20. Double flash simplified
HP turbines
Wells
LP turbine
HP separator
LP separator

21. Double flash and wellhead pressure
 The reference scenario has 11,5 bar difference between the common
wellhead pressure and the HP separator pressure
 There is considerable gain in reducing this pressure difference
 The calculation assumes unchanged LP system

22. Double flash gross power
0 5 10 15 20 25 30
240000
260000
280000
300000
320000
340000
PHP;separator [bar absolute]
Wgross[kW]
Pressure difference 11,5 bar
Pressure difference 5 bar
Pressure difference 3 bar
Pressure difference 1 bar

23. Individual HP letdown turbines for HP wells
 The wells with high flow and pressure are connected to HP backpressure
units
 The HP backpressure is higher than the main plant HP separator pressure,
so the exhaust stem is inlet steam for the main plant
 The main plant is can then be designed for moderate separator pressure
 The concept is flexible and allows more wells to operate at individual
optimum wellhead pressure
 Previous studies indicate that gross power increase in the region of
10 – 15% can be obtained
 Same studies indicate that the economy of such modification is marginal.

24. Individual HP letdown turbines for HP wells
HP letdown separator
HP letdown turbine
Main plant HP separator
Main plant LP separator
Main plant HP turbine
Main plant LP turbine

25. Hybrid power plant
 The hybrid plant consists of HP steam back pressure turbines and a bottoming
ORC cycle with separate vaporizers for steam and brine
 The condensate from the steam heated vaporizer is mixed with the brine before
the ORC preheater to reduce risk of scaling
 The produced power is similar as the best performance of a dual flash plant
 Gas removal is easy from a knockout pot after the steam heated vaporizer at
the same pressure as the turbine backpressure
 The ORC radial turbines employed are with very high efficiency (85-87%) and
have a flat efficiency curve due to variable geometry nozzle guide vanes
 An air cooled cooling tower can be used, avoiding visual effects of steam
plume as well as avoiding need for makeup water
 The ORC plant is a scaled up copy of the Atlas Copco delivered ORC plant in
Pamukören, Turkey.

26. Gas removal knockout pot
Hybrid plant PFD
Steam backpressure turbine
Steam heated vaporizer
ORC turbine
Preheater
Brine heated vaporizer
Recuperator
Air cooled condenser
ORC circulation pump
Steam separator
1
3 2
4
5
6
e2
e1
7
e4
s1
s2
s3
s4
s5 s6
a1
a2
mwf = 3137 [kg/s]
To,1 = 25 [°C]
To,4 = 124,6 [°C]
Ts,1 = 191,6 [°C]
Po,1 = 2,437 [bar abs]
To,3 = 38,79 [°C]
Wpump,wf = 15753 [kW]
Wfan = 10380 [kW]
To,6 = 31,53 [°C]
me,1 = 1193 [kg/s]
xe,2 = 0,4475
Te,4 = 191,6 [°C]
he,1 = 1697 [kJ/kg]
Ts,3 = 127,6 [°C]
mwf,brine,vaporizer = 465,7 [kg/s]
mwf,steam,vaporizer = 2672 [kg/s]
To,7 = 57,11 [°C]
Ts,4 = 100 [°C]
Wpump,condensate = 796,4 [kW]
me,4 = 533,9 [kg/s]
Wsteam = 124999 [kW]
Wbinary = 257280 [kW]
Pe,4 = 13 [bar abs]
Po,4 = 24 [bar abs]
To,5 = 47,84 [°C]
Ts,5 = 127,6 [°C]
Ta1 = 5 [°C]
Ta2 = 20 [°C]
Wbinary,net = 218283 [kW]
Wnet = 336236 [kW]
Fluid$ = n-butane
Psteam,in = 13 [bar abs]
Psteam,out = 2,518 [bar abs]

27. 0 50000 100000 150000 200000 250000 300000 350000
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
Q[i]
etaCarnot;c[i],etaCarnot;h[i]
Condenser Recuperator Preheater Brine vaporizer Steam vaporizer Superheater
Carnot efficiency diagram for the Pamukören plant

28. Conclusion
 The field in Hellisheiði has proven to be better than the original estimate
 The presented analysis is based on a single snapshot of the wells (from 2012
12 07), and well are likely to decline with time, moving the field closer to the
original estimate
 A double flash design optimized for the snapshot production seems to produce
close to 15% more power
 At least the same increase should be possible with individual HP letdown
turbines
 Similar power increase seems to be possible with the more expensive ORC
cycle
– offering easier gas removal
– does not have cooling tower steam plum
– does not need condensate for makeup
– but is more expensive for each kW produced.

29. Committed to
sustainable productivity.