Thermoeconomic analysis of geothermal power cycles for IDDP-1 chloride mitigation

Alberto Mereto, María S. Guðjónsdóttir, Vijay Chauhan, Guðrún SævarsdóttirReykjavik University

Georg Geothermal WorkshopNovember 24th-25th 2016

#GGW2016

Superheated steam h: 3150 kJ/kg

Potential power output: 30-40 MWe

Source: IDDP

IDDP-1

Objectives - What is the problem?

• Geothermal fluid contains many minerals and non-condensable gases

• Corrosion is a major issue for the components of the plant: increase O&M, decrease useful life

• Mitigation techniques exist, but they have:– different techniques– different efficiencies– different costs

Chloride-induced corrosion

• HCl becomes highly corrosive as it dissolves in water droplets• Reaction of HCl with magnetite film on the steel surface breaking the film:

• Two techniques of corrosion mitigation studied:– Chloride neutralization (wet scrubbing):

– Corrosion mitigation with binary cycle (corrosion is shifted)

Single flash with wet scrubbing

Proposed power cyclesSingle flash with wet scrubbing and heat recovery

Single flash with wet scrubbing and and additional turbine

Binary cycle

Thermoeconomics - Exergy• Important to develop thermal systems able to effectively use energy resources• Exergy represents the maximum theoretical useful work obtainable as two

systems interact to equilibrium. Specific exergy:

[kJ/kg] [kJ/kg] [K] [kJ/kgK]

• Exergy rate:

[kJ/s] [kg/s] [kJ/kg]

• Exergy can be destroyed and/or lost

Thermoeconomics - Economics

• Every stream has a unit cost

[$/s] [$/kJ] [kJ/s]

• Every component has a product, a fuel and a capital cost

• Costs of loss and destruction attributed to product

Cycle analysis

•

5•

𝑐6=𝑐5𝑐22=0

𝑐24=0

𝑐23=0

�̇�21=�̇�20+ �̇�𝐶𝑜𝑜𝑙𝑖𝑛𝑔𝑃𝑢𝑚𝑝 Total plant:

•

Results – Heat recovery cycle

10 20 30 40 50 60 70 80 90 100 110 120 130 1400.0E+00

2.0E-05

4.0E-05

6.0E-05

8.0E-05

1.0E-04

1.2E-04

1.4E-04

1.6E-04

0E+00

2E-06

4E-06

ZHX SF: c3 HR: c5

Wellhead pressure (bar)

Cost

rate

($/s

)

Unit

cost

of e

xerg

y ($

/kJ)

Exergy rates in the heat recovery cycleHeat exchanger cost rate and comparison of unit cost of exergy entering the turbine between SF and HR

Results – Cycles comparison

Net work output and unit cost of exergy of all the cycles

Scenarios’ results - Heat recovery cycle

• Base case:– Well cost: 20 MUSD– O&M: 5%– Life time of plant: 25yrs– Interest rate: 4%

• Total cost of power output of base case at wellhead pressure 40bar: 0.01250 $/kWh

Conclusions

• All the cycles aim at chloride mitigation in IDDP-1

• Best cycle to use for this purpose is the single flash with heat recovery

• HR produces the greatest amount of power among all cycles

• Wellhead pressure at which HR produces highest power output is also

the condition at which the power output has the lowest unit cost

• IDDP-1 was exceptionally expensive, but has exceptional potential

Thank you for your attention!