Frequently Asked Questions


Frequently Asked Questions

1. Introduction

This document outlines the common questions customer have regarding the OptiFlash technology. If you have any further questions regarding this technology and its suitability for your power plant, please contact for a prompt response.

2. Common Questions and Answers

2.1. What is OptiFlash?

OptiFlash is hot water Wet Compression technology which has been developed to address the problem of compressor blade erosion which occurs with traditional wet compression technologies.
OptiFlash delivers the following capabilities to a gas turbine power plant:

  • Increase power output of up to 14%
  • Reduction of NOx emissions by 40%
  • Heat rate improvement of up to 3%
  • Reduction of Compressor Discharge Temperatures by 50°C extending hot component life
  • Additional power available within 60 seconds
2.2. How does OptiFlash work?

OptiFlash uses hot boiler feed water through specially designed nozzles to create droplets which are 5µm or smaller. Droplets of this size behave like an aerosol which due to their low mass follow the air stream around compressor blades rather than impacting the blades. The small size of the droplets effectively eliminated compressor erosion entirely.

The droplets rapidly evaporated to saturate the air stream, and remaining droplets enter the compressor and progressively evaporate as the temperature and pressure rises through each compressor stage. The evaporating water within the compressor absorbs heat, reducing the temperature of the compressed air (otherwise known as the intercooling effect).

The intercooling effect within the compressor causes the compressor to operate at a higher pressure ratio, with more mass flow and a lower compressor discharge temperature (CDT). These conditions cause a turbine control system to increase fuel flow to maintain the appropriate Turbine Inlet Temperature (TIT) and as a result produce more power.

2.3. How does OptiFlash reduce emissions?

NOx is produced through the reaction of Nitrogen and Oxygen at high temperatures (typically above 1,600°C). The levels of NOx produced by a gas turbine increases as temperature and/or exposure time increases.

As OptiFlash reduces CDT by up to 50°C, the mixing air entering combustion chambers is cooler, this reduces the temperatures of NOx producing hot spots, and reduces exposure time of the gas in these regions. The relationship between firing temperature and exposure time on NOx formation is illustrated below.

2.4. What are the operating conditions of OptiFlash?

OptiFlash operates on boiler feed water with the following conditions:

  • Water Temperature 170 to 210 °C
  • Water Pressure 80 to 130 Bar
2.5. If our boiler does not have sufficient pressure, can OptiFlash still be installed?

Yes, OptiFlash can still be installed, the only modification is the addition of a pressure boosting pump to achieve the required operating pressure.

2.6. How is OptiFlash different to Fogging?

Fogging systems typically spray demineralised water behind the fine air filters in the filter house. The amount of water sprayed is continuously controlled so that the air will be humidified to approximately 85% to 90% relative humidity to ensure droplet evaporation.

The key principle of a fogging system is that all the droplets evaporate before reaching the gas turbine compressor, so that the compressor always operates on humid air only (no droplets present).

While fogging systems are effective in hot & dry climates, when ambient humidity rises above 70%, gains become limited because of the small amount of water that can be added to the air to absorb heat.

OptiFlash injects very fine water droplets under 10 µm in size in front of the compressor, which instantly evaporate to saturate the air and cooling it. The remaining aerosol droplets travel into the compressor and evaporate internally as the temperature rises through each successive compressor stage. This intercooling effect is the primary effect in boosting power output. Even in conditions where ambient humidity rises above 70% OptiFlash delivers power gains because all of the injected water is evaporated within the compressor.

2.7. How is OptiFlash different to Wet Compression?

OptiFlash is a variation of Wet Compression. Both systems inject water into the compressor to create an intercooling effect, however the key difference is the droplet sizes. Wet compression systems use cold water under extremely high pressure to produce small droplets. While these systems produce 90% of their droplets below 20µm (which are safe for compressors), the remaining 10% of the droplets can be as large as 40µm which are very erosive due to their mass:

Because of the presence of these large droplets, Wet Compression systems will require compressors to be coated, or be limited for short periods of use only to manage the amount of erosion created.

OptiFlash operating on hot water through specially designed nozzles combines the benefits of nozzle design and a flash boiling effect to produce water droplets which are no larger than 10µm in size. Droplets of this size do not cause erosion to compressor blades because their mass is so low that they behave like an aerosol.

2.8. Why is hot water used in OptiFlash systems?

OptiFlash requires hot pressurised water to create a strong Flash Boiling effect after the water leaves the nozzle and experiences as sudden drop in pressure. This Flash Boiling breaks up the relatively large droplets leaving the nozzle into a fine aerosol under 10 µm. The flashing is common phenomena which can be found in many vapor compression refrigeration cycles.

2.9. How does hot water cool air?

In summary, the energy required to change the phase of water from liquid to vapor is much higher than the energy which liquid water carries at 180◦C.

As the water evaporates due Flash Boiling and evaporation in the compressor, the latent heat is absorbed from the surrounding air causing it to cool. The energy absorbed by latent heat is significantly higher than the sensible heat carried by the liquid water.

An approximated example demonstrating the effect is provided below where 1L of water at 20°C and 180°C is added to an air stream at approximately 30°C.

As can be seen in the numbers above, the heat to evaporate 1 litre of water is the same regardless of whether it is hot or cold (2,256kJ). The amount of energy for evaporation is significantly higher than what is introduce by 1L of water at 180°C. As a result, the air is cooled, even with water at 180°C.

2.10. How much water does OptiFlash consume?

Depending on the Gas Turbine and site conditions, OptiFlash systems are configured to deliver water between 1.5% to 2.0% the air mass flow rate of the turbine. For example, GT GE 6561B with air mass flow rate of 134 kg/s requires hot water to be injected at the rate of 2.68 kg/s.

2.11. Does OptiFlash cause any damage to the gas turbine compressor?

No, droplets formed by OptiFlash are all under 10µm in diameter and more than 60 times lighter than droplets formed in wet compression systems. The mass of a droplet 10µm and smaller is so low that the behaves like an aerosol following the flow streams around blades and stators, rather than impacting on these components and causing erosion.

2.12. Is there a risk of Foreign Object Damage (FOD) to the compressor?

No, the OptiFlash lances are constructed from Schedule 120 stainless steel pipe where nozzles are then individually screwed into the lance and seal welded to hold in place making the lance a single piece assembly. The lance design was verified through CFD modelling to ensure flow induced vibration will not cause a failure of the lance.

2.13. What modifications are done to install an OptiFlash system?

The modifications done to a plant to install an OptiFlash system are minor and consist of the following major activities:

  • Installation of spray lances into the gas turbine intake plenum (Turbine Offline)
  • Installation of a viewing window and light onto the intake plenum for inspection purposes (Turbine Offline)
  • Installation of a valve & control skid onto concrete foundations (Turbine Online)
  • Installation of power and control cables (Turbine Online)
  • Routing of insulated pipework from the boiler tie-in point, through the valve skid to the spray lances (Turbine Online except for boiler tie-in)
2.14. Are any modifications required to the gas turbine control system?

No, the turbine control system is not modified as part of an OptiFlash installation. The OptiFlash system can be controlled from the distributed control system (DCS) or by using a PLC. In the case of PLC, several signals from the DCS are used such as gas turbine base load, ambient temperature and amongst other things. However, it is not required to alter the gas turbine controls in either case.

2.15. How long is an outage to install OptiFlash?

OptiFlash is typically installed within any scheduled gas turbine outage which lasts 7 to 10 days. To achieve this, all the basic components are pre-fabricated and the majority of installation is conducted with the gas turbine online.

2.16. Will the generator require any modifications?

OptiFlash will allow a gas turbine to produce more power, which results in the generator producing more electricity and heat. If the generator system is close to the limits of its capacity curve prior to the installation of an OptiFlash system, the generator will require modification in any of the following ways:

  • Uprated insulation
  • Uprated bus bar capacity
  • Upgrading the air or water-cooling system
2.17. How much more power can I get from the Gas Turbine?

The power gains delivered by OptiFlash vary depending on the ambient air conditions and the gas turbine. However, typically power gains range from 9% to 14%. A typical performance graph of an OptiFlash system is shown below.

2.18. Will OptiFlash improve the heat rate of the plant?

The impact of the heat rate of the whole combined cycle plant can only be determined after a detailed heat & mass balance simulation. Typically, OptiFlash systems either preserve the existing heat rate of the plant or achieve a small improvement of heat rate.

2.19. Can OptiFlash be installed on a plant that doesn’t have a boiler?

Yes, an OptiFlash system can be installed on a simple cycle gas turbine. Installation will require the following additional components:

  • Demin water plant
  • Heat exchanger in exhaust system
2.20. Can OptiFlash be installed if the plant already has a Chilling system or Fogging system?

Yes, OptiFlash can be installed downstream of a Chilling or Fogging system. In both cases, the plant will achieve an increase in power output as a result of the intercooling effect in the compressor.

2.21. What is required for the maintenance of an OptiFlash system?

For systems without pressure boosting pumps, the OptiFlash system consists of only valves and instruments which require annual inspection and calibration only. For systems with a pressure boosting pump, the pump will have additional maintenance requirements which will be applicable to the style of pump installed.

In both cases, nozzles on an OptiFlash system require replacement after 8,000 hours of use.

2.22. What are the typical water requirements for an OptiFlash system?

OptiFlash requires boiler quality water typically complying to the following requirements:

2.23. Can OptiFlash be used on a gas turbine which operates at part load?

Yes, however operation of OptiFlash at part load will reduce the benefits which can be achieved by the technology.

2.24. How long does it take for the system to start?

An OptiFlash system can start within 60 seconds making it suitable for reserve power applications.

2.25. Will water droplets be present in any of the compressor take off points?

No, the droplets produced by OptiFlash evaporate within the first 3stages of the compressor. This ensures that all air take off points do not have any water droplets present.

2.26. How does OptiFlash extend the lifetime of hot components?

The life of expensive hot section components is limited due to the extreme operating conditions which they are exposed to. The ability for components to survive these extreme conditions is due to the use of compressed air which extracted from the compressor. This air serves two purposes:

  • To create a protective air film on the outside of the components
  • To actively cool the components through forced convection

Despite the sophisticated cooling technology used in gas turbine hot section components, the life of the components is limited, with replacement defined by the number of operating hours or according to findings during inspections.

Because OptiFlash reduces Compressor Discharge Temperatures by up to 50°C, it causes the temperature of cooling air used for cooling hot section components to reduce accordingly. Also, because OptiFlash cools using evaporating water, the air within the compressor contains more water vapour which improves heat transfer properties of the air – further increasing the cooling effect.

Modelling of the Frame 6 first row turbine blades using the REMLIF program to undertake a life assessment of the blades indicates:

  • Average material temperature reduction of 7°C
  • Component life extension from 32,000 hours to 44,000 hours
2.27. What is the expected lifetime for the nozzles?

Under typical conditions, nozzles last 8000 hours of operation before requiring replacement.