Power plants – Combustion products used as motive fluid – Combined with regulation of power output feature
Reexamination Certificate
2000-12-28
2003-10-21
Koczo, Michael (Department: 3746)
Power plants
Combustion products used as motive fluid
Combined with regulation of power output feature
C060S039530
Reexamination Certificate
active
06634165
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of gas turbine control systems and, in particular, to water-injection systems that saturate and/or supersaturate with water the air stream entering the gas turbine.
BACKGROUND OF THE INVENTION
The saturation and supersaturation of air with water at the inlet of a gas turbine generally increases turbine power output. The injection of water into the inlet air is often done when operating gas turbines in conditions of high ambient-air dry-bulb temperature. Water will generally evaporate as it is injected into the compressor inlet air and before the air/water mixture enters the compressor inlet, provided that the mixture is no more than saturated with water as it enters the compressor.
Existing water-injection systems saturate or supersaturate the compressor inlet air to augment the gas turbine power output. Mechanical water-injection systems are available that cool the inlet air supplied to a gas turbine compressor by injecting water through an array of manifolds and atomizing nozzles. Water evaporation desirably cools the air entering the inlet guide vanes (IGVs) of the compressor. Generally, the lowest working fluid inlet temperature is achieved by saturating the inlet air with water. Thus, power output can be increased in a gas turbine with a water-injection system.
Supersaturation of the air/water mixture at the compressor inlet provides water in the inlet air that is not evaporated as it enters the compressor. Supersaturation performs at least two beneficial functions useful for increasing gas turbine power output including:
1. Injected water (which is not evaporated as it enters the compressor) does eventually evaporate as the working fluid (air/water mixture) flows through the compressor. Inter-compressor evaporation cools the working fluid passing through the compressor. Cooling of the working fluid within the compressor (intercooling) reduces the power required for its compression. The net gas turbine power output is the total turbine power output minus the compressor power input requirement. Any reduction in the power required by the compressor results in a net increase in gas turbine power output. This net power output gain is substantially equal to the reduction in compression power input.
2. The mass flow of the working fluid is increased by supersaturation. The compressor provides a constant volume of working fluid to the combustor of the gas turbine. The mass of the working fluid can be increased by supersaturating the air/water mixture entering the compressor. The specific volume of the liquid water mist is approximately {fraction (1/800)}
th
of the specific volume of the air. Inversely, the mass flow of a supersaturated water mist is greater than that of a saturated air/water working fluid mixture. Turbine power output is directly proportional to the mass flow of working fluid. Due to its high mass, the added water in a supersaturated working fluid increases gas turbine power output. Accordingly, supersaturating the working fluid with water increases the mass flow of that fluid and the power output of the turbine.
The power output of a gas turbine can be increased when operating at high ambient-air dry-bulb temperature by injecting finely atomized water into the air flowing into the intake duct of the compressor, so that the compressor inlet air is supersaturated when entering the compressor. Conventional supersaturation water-injection systems might consist of a single set of manifolds and nozzles in the duct, or might be divided into two injection sections of manifolds and nozzles. Gas turbine power augmentation can be maximized by dividing the injection system into two sections, the upstream section which saturates the air with water and a second downstream section located at or near the compressor inlet that supersaturates the air.
An atomized water spray-type saturation system (fogger) with controls is described in U.S. Pat. No. 5,463,873. Prior systems for supersaturating the air supplied to a compressor inlet of a gas turbine have generally consisted of a single grid of atomized spray nozzles located in the air intake duct. Systems typical of these are described in U.S. Pat. Nos. 5,867,977 and 5,930,990. European Patent No. EP 0 781 903 A2, entitled “Gas Turbine with Water Injection” describes systems for supersaturating air supplied to the compressor inlet of a gas turbine, including a divided saturation and supersaturation system. A divided water-injection/cooling system divides the water-injection system into two sets of manifolds and nozzles. A first injection system of manifolds and nozzles provides sufficient atomized water to “saturate” the inlet air, and sufficient residence time of the water in the air to enable complete evaporation of the water in the air before it enters the IGVs of the compressor. The water-saturated air from the first injection system enters a second injection system with its own set of manifolds and nozzles to inject additional water in order to supersaturate the air.
A potential danger of supersaturating the air/water mixture entering the compressor is that water droplets can damage the compressor. Droplets can agglomerate from the fine water mist in the fluid or from excess water mist that is injected into a supersaturated air/water mixture. Large water droplets in the mist can impact and corrode compressor blades and stators. Blade erosion can occur due to large water droplets in the working fluid of a compressor. A control system is needed to operate water-injection systems for gas turbines. The control system is needed to maximize power augmentation due to water injection, and to avoid the compressor blade erosion and other harmful effects of excessive water injection.
BRIEF SUMMARY OF THE INVENTION
Applicants have invented novel control systems for saturation and saturation/supersaturation water-injection systems for gas turbines. The control systems regulate the quantity of water injected into the inlet air supplied to the compressor by the saturation and/or supersaturation sections of a water-injection system. The control systems optimize power augmentation and limit water injection to comply with certain gas turbine limitations. These control systems also regulate the injection of water to maximize the power increase and minimize the potential for compressor-blade erosion.
Specifically, the control systems start, stop and modulate/regulate the quantity of water injected into the compressor air. These systems maximize power output of the gas turbine, minimize erosion of the compressor blades, and limit operation of the power-augmentation system to suitable and advantageous conditions. When the water-injection grids (e.g., manifolds and atomizing nozzles) are divided, water injection to each grid is controlled so that the air is at or near saturation when discharging from the saturating grid, and then modulates the water flow to the supersaturating section, within limits as indicated by air flow and other gas turbine parameters.
Individually controlling the water injected by each section of a divided injection system provides several advantages including:
(i) Ensuring that the injected air fully saturates the air/water mixture at the compressor inlet. Saturating the air using a first injection grid enables the temperature of the air/water mixture to be reduced to near or at the wet-bulb temperature for the air/water mixture by the first grid. The temperature is reduced due to evaporation of the water added by the first system.
(ii) Increasing the power output of the gas turbines by reducing as the temperature of the working fluid (air/water mixture) entering and passing through the compressor. The power output increases because of: (1) an increase in cycle mass flow of the working fluid through the gas turbine caused by an increase in the density of that fluid, and (2) an increase in the cycle temperature ratio (ratio of firing temperature to compressor inlet temperature) due to a decrease in compressor inlet temperature.
Separating the water mist inje
Tomlinson Leroy Omar
Trewin Richard Robert
General Electric Company
Koczo Michael
Nixon & Vanderhye P.C.
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