Real Time Power attended the 4th Annual Gas Power Conference in June. We showcased our new display of our AirSonic ™ and AirSonic ™ Flex which enables users to get a better idea of how the hardware would be installed in a gas turbine inlet duct. It also provides a great side by side comparison to show the difference between the AirSonic ™ and AirSonic ™ Flex in regards to installation and functionality.
Our next conference will be in San Antonio at the Combined Cycle Users Group Annual Conference on August 22 through 25th. We are looking forward to playing Top Golf with everyone and connecting with Users to discuss our AirSonic™ and how measuring the real time air mass flow rate can help your power plant run to more efficiently and enhance existing diagnostics and forecasting capability.
We will have our top engineers available to discuss the importance of measuring air mass flow rate as well as a very hot topic right now with Turbine Inlet Cooling and Thermal Energy Storage and how the Real Time Power TES Adviser can help optimize your profits while simplifying day-ahead and real time operation schedules.
For more information, please contact Gina Calanni at 281 971 9756
Our very own Ray Boucher presented a paper about our Real Time Power’s accurate ultrasonic Air Mass Flow Measurement system for gas turbines along with the challenged and new develops planned. The conference was held in London November 3-5, 2015.
EVI-GTI Gas Turbine Conference brings together the global gas turbine engine test instrumentation and development community in 2015 to showcase their latest research and results to an international community of like-minded specialists.
The air mass flow rate into the compressor of a gas turbine is a key parameter for determining and predicting the performance of combined cycle gas turbine (CCGT) power generation units. An accurate measurement of air flow rate can be used to improve the prediction of the gas turbine generator power output at the point when the exhaust gas temperature constraint is reached, and the subsequent calculation of thermal energy flow rate into the heat recovery steam generator (HRSG) improves the prediction of the steam turbine generator power output.
The direct measurement of air mass flow rate is difficult because of the complex geometry of the air intake duct, and also because of the high levels of noise, vibration and air turbulence that are present. The paper presented the experiences gained from deploying a direct ultrasonic measurement of air speed in the intake duct, which is used in combination with static pressure measurements and the results of computational fluid dynamics (CFD) simulations to produce a real-time measurement of air mass flow rate. The challenges, accuracy and benefits of ultrasonic air mass flow rate measurement was discussed using experiences gained over the last six years from 28+ field installations covering five different types of large (> 150 MW) industrial gas turbines.
For more information see our Air Mass Flow Rate Measurement for Gas Turbines.
The main factors we at Real Time Power have observed which affect industrial gas turbine air mass flow rate are:
- Shaft rotational speed
- Inlet guide vane (IGV) angle
- Air density at the compressor inlet
- Compressor extraction flow rates
The compressor is well approximated as a constant volumetric flow rate machine when at synchronous speed with fixed IGV angle. The volumetric flow rate is then most influenced by the IGV angle, and the relationship between IGV angle and volumetric flow rate is nonlinear, because the effect of the IGV opening involves either a cosine or sine function, depending on how the angle is defined. This document will use the convention of IGVs fully open as 0° and fully closed would be -90°. In this case, a cosine curve would be a good fit to the volumetric flow rate response, since cos(-90°) = 0 and cos(0°) = 1. It is often the case that some additional flow rate can be generated by going beyond 0° opening, up to 5-6° is typical. This extra flow is created due to aerodynamic interactions between the IGVs and the first stage of rotating compressor blades, and is not predicted from simple “area of opening” calculations.
With constant volumetric flow rate, mass flow rate will then vary as a function of compressor inlet air density. The main factor which affects air density is the temperature of the air, and this is why evaporative coolers, chillers and foggers are deployed in order to lower the ambient temperature and therefore increase the air density and the air mass flow rate, and ultimately the power output of the gas turbine (which is directly proportional to air mass flow rate). Air pressure and relative humidity also affect air density, and the disadvantage of evaporative coolers and foggers over closed cycle chillers is that the lower density water vapor introduced into the air flow reduces some of the gains of the cooling. The air pressure at the compressor inlet is affected by the ambient air pressure and also by pressure drops across air filters and air conditioning equipment. Fouling of air filters and evaporative cooler media can lead to increased pressure drops and lower gas turbine power output.
The fourth factor listed is compressor extraction flow rates, which typically vary based upon ambient conditions, as well as the condition of the gas turbine. Extracting more flow from the compressor stages will in general increase the mass flow rate into the compressor inlet. When compressor extraction flows are scheduled roughly in proportion to IGV opening, then normalized compressor ratio (compressor discharge pressure / compressor inlet pressure) x (ISO air density / air density) correlates extremely well with the volumetric flow rate measured by Real Time Power’s AirSonic system.
One thing not on the list of major influencers is compressor efficiency (or cleanliness). Only in extreme cases of fouling does the volumetric flow rate decrease. In most normal situations, the effect of compressor fouling is to increase compressor discharge temperature, which will in turn increase turbine exhaust gas temperature and limit the maximum power output of the engine. So the main effect of compressor fouling is on maximum achievable MW output from the gas turbine.