binary power plants in new zealandgeothermal.jogmec.go.jp/report/file/session_160602_10.pdf ·...
TRANSCRIPT
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GNS Science
Binary Power Plants in New Zealand
Greg Bignall & John Burnell
JOGMEC-GNS Workshop, Tokyo
2 June 2016
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GNS Science
Outline
• Situation in NZ
• Ngatamariki
• Ngawha
• Discussion
Slide 2
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GNS Science
Situation in NZ
Slide 3
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GNS Science
Binary Power Turbines in New Zealand
• Fields operating with only binary plants
– Mokai, Ngatamariki, Ngawha, Tauhara
• Binary plants alongside steam turbines
– Rotokawa, Wairakei, Kawerau
Slide 4
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GNS ScienceSlide 5
Mokai
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GNS Science
Mokai
• Staged development by Maori Land Trust
• Combined Cycle technology
– Back pressure steam turbine and binary plant
• Initial 60 MWe development
• Currently 110 MWe
• Best option for the reservoir may have been a
steam turbine
• Choice has added complexity to managing the
reservoir
• Modular design has benefits
Slide 6
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GNS Science
Tauhara
• 25 MWe development originally planned for specific use
• Binary plant was the best option for this stage
• Reservoir would support steam turbine
– 250 MWe development has been planned
– Currently stalled due to low electricity demand in NZ
Slide 7
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GNS Science
Steam Turbines Alongside Binary Plants
• Wairakei
– 14 MWe binary plant added to utilise energy from separated brine
• Kawerau
– 3 small scale units used by local operators
– 14 MWe in total
• Rotokawa
– Staged development was planned
– A small scale initial stage development
– 35 MWe binary plant was most suitable
Slide 8
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GNS Science
Ngatamariki
Slide 9
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GNS Science
Ngatamariki Resource
• Recent development
• Exploration of the reservoir occurred in 2004-9
• High temperature resource > 285 C
• Liquid dominated
• Extensive cap
• Localised connection to surface
Slide 10
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GNS Science
Location
Slide 11
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GNS Science
Resource Boundary
Slide 12
Boseley et al, 2010
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GNS Science
Reservoir Temperatures
Slide 13
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GNS Science
Conceptual Model
Slide 14
Burnell, 2010
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GNS Science
Reservoir Modelling
Slide 15
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GNS Science
Match to Measured Temperatures
Slide 16
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GNS Science
Match to Discharge Test
Slide 17
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GNS Science
Development Scenarios
• Model was used to assess different development options
• For steam turbine (75% injection) downflowsinto the reservoir were predicted
Slide 18
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GNS Science
Project History
• Based on modelling predictions a decision was made to design for 100% reinjection
• Resulted in minimising the impact on the environment
• From this decision, the only viable technology
was a binary plant
• Impacted project economics
– More competition around steam turbines
• Viable economics over the lifespan of project
Slide 19
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GNS Science
Project Design
• 100 MWe power station
• Largest all binary single-site plant
• Four 25 MWe Ormat Energy Converters
• 3 deep producing wells
• 100% cooled geothermal fluid is reinjected
• 4 reinjection wells around periphery of field
– Deep wells – 3000m
– Located to reduce cooling of production wells
• Injection wells thermally stimulated
• Operating since 2013 with > 96% availability
Slide 20
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GNS Science
Ngawha
Slide 21
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GNS Science
Development History
• Developed by a community owned trust
• Developed in stages
– 10 MWe
– 15 MWe
– Proposed 50 MWe expansion
• Lower enthalpy resource
• Staged approach to assess potential of reservoir
• Size of the stages meant binary plant was
preferred option
• 100% injection was used
Slide 22
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GNS Science
Development History II
• For the second stage – 15 MWe – there were community concerns about impact on the springs
• Reservoir modelling showed that the spring
flows were sensitive to reservoir pressure
• Even though 100% injection was being injected there were:
– losses due to gas loss and spillage
– pressure drop due to density effect of cold injection
Slide 23
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GNS Science
Development History III
• This resulted in a plan to add supplemental injection
• Historical declines had been small
– About 0.1 Mpa
• Needed to avoid future decreases in pressure
• A trial was conducted which demonstrated that pressures could be changed through
supplemental injection
• Permission was granted to proceed with second
stage
Slide 24
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GNS Science
Development History IV
• Second stage commenced in 2008
• No clear impact on surface features
– Some changes observed, but significant natural
variation
• A further expansion has been planned
– To a total of 75 MWe
• Conditions imposed on the development
– Must maintain reservoir pressure to within 0.1 MPa
of 2008 levels
– No effect on the characteristics of springs
Slide 25
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GNS Science
Discussion
Slide 26
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GNS Science
Use of Binary Plants in New Zealand
• Major use is for small-scale or staged developments
– Project economics are important
– Adds flexibility due to modularity
• Can also be driven by need to minimise the impact on the reservoir or the surface features
– 100% reinjection
• Projects have all been successful and resulted
in expansions from initial stages
• Ngatamariki, Ngawha, Mokai, Tauhara, Rotokawa, Kawerau
Slide 27
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GNS Science
Use of Binary Plants II
• Staged developments:
– Initial stage with a small-medium binary plant
– Assess reservoir performance
– Add expansion
– Reduced risk
• Can also complement a steam turbine
– Utilise heat in separated geothermal brine
– Will result in cooler reinjection fluid
– Depends on reinjection strategy
Slide 28