Method of chilling inlet air for gas turbines

Abstract

A method for cooling inlet air to a gas turbine is provided. For example, a method is described including passing inlet air through a cooling coil that includes an opening for receiving the inlet air and that is operably connected to a gas turbine power plant. The gas turbine power plant may include at least one gas turbine, and at least one gas turbine inlet which receives the inlet air. The method may further include passing circulating water through a water chiller at a first flow rate to reduce the temperature of the circulating water, the water chiller including a conduit through which the circulating water is capable of passing and passing the circulating water having the first flow rate through the cooling coil in an amount sufficient to lower the temperature of the inlet air. Additionally, the method may include reducing the flow rate of the circulating water passing through the water chiller, passing the circulating water through a water chiller at a second flow rate to reduce the temperature of the circulating water, the second flow rate being lower than the first flow rate, and passing the circulating water having the second flow rate through the cooling coil in an amount sufficient to lower the temperature of the inlet air. A system for cooling inlet air to a gas turbine is provided. In order to maintain a desired level of efficiency for a gas turbine plant, water is passed through a chiller to lower the water temperature. The cooled water is then circulated through coils disposed in the inlet air of the gas turbine, thereby cooling the inlet air to the gas turbine. The system may include a thermal energy storage tank for storing chilled water prior to circulation through the coils. The system may also utilize an air temperature set point selected to achieve a desired output or to meet load requirement for the gas turbine plant. The temperature or flow rate of the cooled water may be adjusted to achieve the selected air temperature set point.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 10/206,856, filed Jul. 26, 2002, now U.S. Pat. No.
Q=mCpΔT=mΔh
Q_coil=UA(LMTD);
As shown above, when the Δh of the air is reduced, the ΔT of the water is also reduced when the mass flowrate (m), the temperature of the air leaving the cooling coil (T_oa), and the heat transfer coefficient (C_p) remain nearly constant. The air leaving the cooling coil is typically saturated, i.e., the air has about a 100 percent relative humidity, therefore the wet bulb temperature and dry bulb temperatures of the leaving air are substantially the same.

In a preferred embodiment of the invention, a high system efficiency is achieved by maintaining a high water ΔT, rather than a high circulating water flowrate. Preferably, achieving a high system efficiency at a low circulating water flowrate (e.g., about 1 gpm/ton) depends, in part, on reducing the temperature of the circulating water at least two times before it chills the inlet air, i.e., sequential chilling. A preferred embodiment of the method includes using at least two water chillers to sequentially chill the circulating water.

As shown above, the traditional chilled water designs which utilize a high flowrate, e.g., from about 2 gpm/Ton to about 1.5 gpm/Ton circulating water flowrate at full load results in a lower circulating water ΔT (from 12° F. ΔT to 16° F. ΔT respectively) resulting in colder water (e.g., from about 52° F. to about 56° F. respectively) water returning to the upstream chiller. For example, the GE LM6000 is provided with a cooling coil that has been optimized for inlet cooling of their turbine. This coil is designed for a maximum design ambient case of 2200 tons of cooling using 3300 gpm of circulating chilled water flow. This equates to 1.5 gpm/ton or a 16° F. ΔT. This chilled water ΔT will get proportionately smaller as the ambient temperature drops below design because the flow rate (gpm) remains constant in conventional designs while the load (tons) is fluctuating with the ambient temperature. A preferred embodiment of the present invention includes reducing the circulating water flowrate to provide or maintain a higher water ΔT. It has been discovered that in the specific context described herein, reducing the circulating water flowrate reduces the amount of heat transfer through the cooling coil, i.e., heat transferring from the inlet air to the circulating water passing through the cooling coil. As shown in the above equations, a lower circulating water flowrate results in higher water ΔT when the inlet air flowrate and air Δh remain constant. As a result, the temperature of the circulating water leaving the cooling coil is higher at a lower flowrate than at a higher flowrate, thereby resulting in a high water ΔT. The use of sequential cooling via series chillers and/or multiple compressors allows high upstream compressor efficiency as a result of relatively warmer refrigerant temperatures. The warmer refrigerant temperatures are possible because the circulating water returning from the cooling coil is warmer. In addition, the power required to drive the circulating water pump will be lower since the power consumption required is proportional to the circulating water flowrate cubed.

In certain embodiments of the invention, the circulating water flowrate is reduced to maintain the chilled water ΔT within a specific design range. This ΔT should be maintained within a range of about 40° F. to 16° F. to maintain maximum efficiency with a sequential chilling system with the higher end of this range being better for thermal storage applications & high ambient climates. The lower end of this range is better for on-line applications with moderate ambient climates. In another specific embodiment, the leaving chilled water temperature setpoint and the circulating water flowrate setpoint may be changed to maintain the leaving air temperature and the chilled water ΔT within the design parameters. As used herein, the term “setpoint” refers to any predetermined point or event that results in the flowrate through the chillers and the coil being changed, or a change in the temperature of the water leaving the chiller. The setpoint may be or include a predetermined air Δh, or change in wet bulb temperature across the coil or the setpoint may be a predetermined ambient temperature or change in temperature or the setpoint may be a change in chilled water temperature. In addition, the setpoint may be derived from input parameters such as the chilled H₂O flowrate and chilled H₂O Δh. The setpoint may be changed depending on the time of the day or depending on system needs or the ambient temperature. As used in preferred embodiments herein, the “setpoint” is based upon maintaining a chilled water ΔT of at least 16° F. It is believed that the characteristics of a particular system are primarily determined by the wet bulb temperature of the ambient air and the leaving air temperature since this determines the load on the coil and also determines the temperature of the cooling tower water going to the chiller. As used herein, the term “wet bulb temperature” refers to the temperature measured by a thermometer with its bulb wrapped in wet muslin, although the wet bulb temperature may also be measured by any means known to those skilled in the art but most commonly is calculated electronically by simultaneously measuring dry bulb temperature and relative humidity. Preferably, the wet bulb temperature is electronically calculated by simultaneously measuring the dry bulb temperature and the relative humidity of the air. The wet bulb temperature is typically lower than the dry bulb temperature because the water on the bulb evaporates, resulting in cooling. Therefore, the difference between wet bulb temperature and dry bulb temperature depends on the humidity in the air. In carrying out certain specific embodiments of the method, the wet bulb temperature of the inlet air leaving the cooling coil is equal to its dry bulb temperature, in which case the air is considered to be “saturated” or 100% R.H.

In one or more specific embodiments of the invention, the circulating water is passed through at least one pump to vary the flowrate of the circulating water before it is subjected to sequential chilling, e.g., using two in-series chillers as shown in FIGS. 1 and 4. Alternatively or additionally, the circulating water may be passed through any number of pumps. Preferably the pumps are generally mounted in parallel to allow the flow to be changed by sequencing a combination of pumps on and off. Preferably, at least a portion of the circulating water is passed through one centrifugal pump, e.g., a horizontal split case pump, and a different portion of circulating water is diverted and passed through at least one additional pump the output streams of the two or more pumps then being combined. More preferably, the circulating water is split, then passed through two or more centrifigal pumps in parallel, then combined. Optionally, one or more of the pump motors may be wired to a Variable Frequency Drive for greater flexibility in flow control and greater partial load efficiency. The circulating water may be passed through a pump anywhere in the system. Preferably, however, as shown in FIG. 4, the circulating water is passed through at least one pump 60, referred to as a primary pump, located in the piping that circulates the chilled water through the chillers. Although the circulating water flowrate is preferably varied only at the primary pump, the circulating water may additionally or alternatively be passed through other pumps at any location in the system. When circulating water is passed through those other pumps, those pumps are typically not used to reduce the circulating water flowrate through the water chillers, but rather are used for another purpose, such as to pass water from a bank of chillers to the cooling coils.

In a preferred embodiment, the circulating water passes through at least one pump at full flow when the ambient wet bulb temperature is at a maximum (e.g., from about 72° F. to about 87° F.), typically at some point in time between noon and 3:00 pm during the summer season. As used herein, the term “full flow” refers to the maximum circulating water flowrate of the system. In this particular embodiment, when the ambient temperature drops (e.g., to a lower wet bulb period such as during the morning or afternoon) the water ΔT also drops. When the chilled water ΔT reaches a first setpoint (e.g., from about 75% to about 50% of design ΔT), one of the centrifugal pumps is preferably turned off. Shutting off one of the two operating centrifugal pumps should accordingly reduce the circulating water flow rate from about 100 percent flow to about 70 percent flow, thereby increasing the water ΔT, e.g., by about 43 percent. Then, when the circulating water reaches a second setpoint(e.g., from about 75% to about 50% of design ΔT), the VFD on the first VFD pump is reduced, further reducing the circulating water flowrate enough to maintain the chilled water ΔT to at least about 16° F.

Water Chilling. Another important aspect of one or more specific embodiments of the invention includes reducing the temperature of the circulating water from an initial temperature, e.g., a first temperature, to an intermediate temperature, e.g., a second temperature, that is lower than the initial temperature, e.g., first temperature, and then further reducing the circulating water from the intermediate, e.g., second, temperature, to a final temperature, e.g., a third temperature, that is lower than the intermediate temperature, e.g., second temperature. In the aforementioned method, the circulating water temperature may thus be reduced in stages by passing circulating water sequentially through two or more water chillers. An example is shown in FIG. 4, which shows circulating water passing from a cooling coil 54 to a first water chiller 62, then to a second water chiller 64, then through an optional third chiller 66 and fourth chiller 68, and then back to the cooling coil 54. As used herein, the term “water chiller” refers to an apparatus for lowering the circulating water temperature that includes at least a single compressor. Preferably the water chiller includes at least one opening for receiving the circulating water, at least one outlet for dispensing the circulating water. A conduit through which the circulating water is capable of passing should operably connect the one opening for receiving circulating water with the one outlet for dispensing circulating water. Preferably, the circulating water is passed through at least two water chillers, which can form part of a single “duplex chiller,” although it could alternatively consist of two simplex chillers with the evaporators piped in series. Preferably, at least a portion of the circulating water is passed from and through the first water chiller to and through the second water chiller. More preferably, all, or substantially all, of the circulating water is passed from and through the first water chiller to the second water chiller.

Passing the circulating water through a water chiller, e.g., a conventional mechanical or absorption chiller, reduces the circulating water temperature. When the circulating water is sequentially passed through two water chillers whose evaporators are piped in series (or through a single duplex chiller), the circulating water temperature is reduced twice. Preferably, in carrying out certain methods of the invention, the sequential circulating water temperature reductions are accomplished by passing the circulating water through a duplex chiller such as the Trane duplex centrifugal CDHF water chiller. As shown in FIG. 4, staged or step-wise circulating water temperature reductions can be accomplished by passing circulating water 58 through an evaporator 62a within the duplex chiller CH2. The evaporator chills the circulating water by receiving a refrigerant such as ammonia, R-22, R-134a, or R-123 available from Dupont. Preferably, R-123 or a similar refrigerant is passed from a condenser 62b to the evaporator 62a to chill the incoming circulating water. The refrigerant is then passed from the evaporator 62a back through a compressor 62c to the condenser 62b for condensing the vaporized refrigerant back to a liquid. The refrigerant is cooled and condensed by condenser water 72a passed from a cooling tower 70 to the condenser 62b (typical of one chiller).

A specific embodiment of the invention includes passing circulating water through a duplex chiller to reduce its temperature from a first temperature to a second temperature lower than the first, then to a third temperature lower than the second (FIG. 4). The circulating water can then be passed through another duplex chiller to further reduce the water temperature twice. Any number of water chillers may be included to reduce the temperature of circulating water for large tonnage applications on large gas turbines (above 60 MW) in a greater number of sequential steps although two duplex chillers in series (4 stages of cooling) is considered the optimum. For larger gas turbine installations that would require more capacity than can be accomplished with 2 duplex chillers, additional pairs of duplex chillers can be provided that divide the total flow of water into the parallel trains of chillers (similar to the 2 parallel trains shown in FIG. 4).

The discussion of the embodiments has focused primarily on the sequential chilling of the chilled water by using progressively colder evaporator refrigerant temperatures. However, there is also increased efficiency available by utilizing sequential heat rejection from the refrigerant to the condenser water through two or more condensers in series. It is preferred that the condenser water be piped in a counterflow arrangement to that of the chilled water, i.e., the coldest condenser water is adjacent to the coldest circulating water.

Sequential chilling of the circulating water in the evaporator, which results in sequential vaporization of the refrigerant, can be combined with sequential heating of the cooling tower water, which results in sequential condensing of the refrigerant, thereby equalizing the head on each compressor, e.g., by passing all, substantially all, or at least a portion, of circulating water from a first water chiller to a second water. Equalizing the head on each compressor can increase the compressor efficiency, shown in greater detail below. As used herein, the term “head” refers to the compressor pressure ratio, which is the pressure of the condenser divided by the pressure of the corresponding evaporator. For example, referring to FIG. 4, the upstream compressor 62c head is equal to the pressure of the upstream condenser 62b divided by the pressure of the corresponding Evaporator 62a.

In a preferred embodiment of the invention, the circulating water is passed from a cooling coil through two duplex chillers (CH 2 & CH 4), sequentially. The circulating water passing through the duplex chillers is reduced from a high temperature resulting from a high water ΔT through the cooling coil (from about 55° F. to about 70° F.) to a final temperature of from about 34° F. to about 44° F., that is the coldest in the system. Example data in such a system is shown in Tables 1 and 2 and FIG. 7.

TABLE 2
		Circulating Water
	Circulating Water Inlet	Outlet Temperature
	Temperature (° F.) 58b	(° F.) 58a
Temperature Profile through Water Chillers at 6600 gpm (full flow) &
Full Load (75 F. Ambient Wet Bulb Temp) chilled to 50 F. T2 Air Temp
First Water Chiller 62	61.5	F.	55.6	F.
Second Water Chiller 64	55.6	F.	50.5	F.
Third Water Chiller 66	50.5	F.	45.6
Fourth Water Chiller 68	45.6		41.4
Temperature Profile through Water Chillers at 4620 gpm
(70% of full flow) & Part Load (70 F. Ambient Wet Bulb Temp) &
50 F. T2 Temp
First Water Chiller 62	62	F.	55.5	F.
Second Water Chiller 64	55.5	F.	50.0	F.
Third Water Chiller 66	50.0	F.	44.6	F.
Fourth Water Chiller 68	44.6	F.	40	F.

One benefit of sequentially chilling the circulating water is that only the downstream compressor 68c needs to compress the refrigerant to a low enough pressure to chill the circulating water to the lower leaving chilled water temperature which is required with a lower circulating water flowrate (FIG. 4).

When the circulating water flowrate is reduced, the power consumption of the downstream compressor may increase. The compressor power consumption increases as a result of chilling the refrigerant to a lower temperature due to the lower leaving water temperature than that required at a high circulating water flowrate. The circulating water entering the downstream evaporator is at a higher temperature than when circulating water is at full flow because the coil will heat up the circulating water more at lower flow. Therefore, at a reduced flowrate, the downstream refrigerant must be at a lower temperature to maintain the required LMTD and heat transfer required at the cooling coil.

An alternative, when water is unavailable for use in a water-cooled condenser, an air-cooled condenser may be used to reject the heat from the refrigerant to the ambient air An air-cooled condenser typically cannot be used to sequentially reject heat to the ambient like that of series piped water-cooled condensers, but it will still provide an increase in the upstream compressor efficiency as a result of sequentially chilling the circulating water using staged evaporators to allow sequentially lower refrigerant temperatures with the different compressors. A preferred embodiment of this invention is to combine sequential chilling of the circulating water with a chilled water thermal storage tank as discussed earlier. This is especially beneficial when no water is available due to the great variability in the dry bulb temperature between daytime and nighttime. The lower nighttime dry-bulb temperature will significantly increase the capacity and the efficiency of the chillers to generate chilled water off-peak and minimize the daytime on-peak parasitic power required.

Air Chilling. Another important aspect of the invention includes reducing the temperature of the inlet air, which may include passing circulating water through a cooling coil in an amount sufficient to reduce the temperature of the inlet air. The reduction in inlet air temperature increases the density of the air, allowing a higher mass flow rate through the compressor of the gas turbine power plant. Therefore, a higher mass flowrate allows the gas turbine power plant to produce more electricity.

In specific embodiments of the invention, the circulating water makes more than one pass through the cooling coil. Most preferably, the circulating water makes four or more passes through the cooling coil. In a specific embodiment shown in FIG. 5, the circulating water is passed through the cooling coil 54 six times which is the preferred method if a thermal storage tank in used with a high ambient climate. As used herein, the term “pass through the cooling coil” refers to each time that the circulating water changes directions inside the cooling coil. Passing circulating water through the cooling coil four to six times achieves a very high water ΔT (from about 20° F. to about 40° F.). In addition, four or six passes achieves good heat transfer at low water flow rates between the circulating water and the inlet air due to the turbulence of the water in the tubes. On each pass, the temperature of the circulating water is increased. For example, on the first pass 82a, the circulating water temperature may increase from about 39° F. to about 44° F. The circulating water temperature may increase from about 65° F. to about 74° F. on the final pass, 82f. Example data in such a system is shown in Table 3.

TABLE 3
Temperature Profile through cooling coil at 0.69 gpm/Ton
		Circulating Water	Circulating Water
		Temperature entering	Temperature leaving
		pass (° F.)	pass (° F.)
	First Pass 82a	39.00	44.04
	Second Pass 82b	44.04	48.94
	Third Pass 82c	48.94	53.53
	Fourth Pass 82d	53.53	58.72
	Fifth Pass 82e	58.72	65.40
	Sixth Pass 82f	65.40	74.00

Passing inlet air through a cooling coil including multiple circulating water passes provides a significant reduction in the inlet air temperature (from about 80 to 125° F. to about 43 to 60° F.). The inlet air may be passed through any number of cooling coils as required to provide enough face area to keep the air velocity through the coil at between 400 to 650 ft/min. Preferably, the inlet air is passed through a single coil in the direction of airflow to the gas turbine power plant but it may also flow through a second coil if required to get the high delta T desired. More preferably, the circulating water is passed through only one cooling coil in the direction of airflow with multiple coils placed above or on the side as needed to provide sufficient face area.

Water Addition. In another embodiment of the invention, water may be added to the inlet air after it has been chilled at least to some extent. Preferably, water is added to the compressor feed air, which is the inlet air after it passes through and exits the cooling coil, i.e., no longer contacts the coil, and before the inlet air enters, i.e., first contacts, the turbine power plant compressor. Such compressor feed air is typically the coldest inlet air in the system. Preferably, the water is added in the form of finely atomized water droplets or mist. Adding water to the compressor feed air provides (supplies) entrained water to the inlet air. As used herein, the term “entrained water” refers to water trapped within the air that does not evaporate. The water in the inlet air does not evaporate when the cooled inlet air, e.g., the condenser feed air, is already fully saturated, i.e., at “saturation,” as a result of being chilled by passing through the cooling coil. Entraining water in the compressor feed air provides cooling in the interstages of the compressor within the gas turbine power plant. The compressor intercooling occurs as the inlet air passes through the compressor. As the inlet air passes through the compressor and is compressed, the inlet air is heated, thereby vaporizing the entrained water. The heat absorbed by the vaporization of the liquid mist into water vapor cools the air in the compressor. Intercooling of the compressor can increase the compressor efficiency and may improve the power output by approx 140 KW per gallon of water added per minute. Thus, any of the methods described herein for cooling inlet air may advantageously further include the addition of water as described above.

Although the water may be added to the chilled inlet air from any source, e.g., from a vessel such as the storage tank, water is preferably added from the cooling coil condensate 70, as shown in FIG. 4. As used herein, the term “cooling coil condensate” refers to water condensed out of the inlet air, e.g., the air stream passing through the cooling coil. Adding cooling coil condensate, rather than water from another source, utilizes water that is already available. The water may be added to the inlet air at any location. Preferably, the water is added before the inlet air enters the gas turbine power plant 76 but after it leaves the cooling coil 54. Alternatively, this water may be stored and used when the chilling system is off but the gas turbine is still operating by providing an evaporative cooling effect.

Heating. In another embodiment of the invention, the circulating water is passed from the cooling coil 54 to the heater 84 and back to the cooling coil, as shown in FIG. 4. For example, the circulating water can be passed to the heater on cold days (e.g., when the ambient temperature is below about 10° F.). The circulating water is heated from about 10° F. to about 20° F. to prevent icing of the turbine within the gas turbine power plant. This may be particularly useful on certain aeroderivative gas turbines such as the LM6000. Any heater may be included, e.g., gas fired or electric water heater of steam or hot water exchanger. Passing the circulating water through a heater may increase the efficiency of some gas turbines during very cold periods (when ambient temperature is below about 30° F.). For example, some turbines have a limit on the amount of mass flow they can accept due to their compressor design such as some of the Westinghouse 501F models. During very cold ambients these turbines must use Inlet Guide Vane control or other means to limit the mass flow of air into the compressor. Since this tends to be a less efficient operating point, it would be advantageous to warm the air to reduce the density of the air and thus keep the engine within a desirable mass flow range.

Circulating Water Additives. Any of the methods described herein may include adding one or more additives to the circulating water to either protect the circulating water from freezing or to allow colder circulating water supply temperatures (from about 28° F. to about 35° F.). Any additive may be added, including glycol. Preferably, an organic or inorganic salt is added. More preferably, sodium nitrate is added to prevent the detrimental effects of glycol on the heat transfer properties and viscosity of water, which tend to increase the power requirements for pumping and for the chiller compressor. In addition, sodium nitrate is not corrosive like other salts. Sodium nitrate would be the most preferable additive if a chilled water thermal storage tank were used due to its low cost. However for on-line systems where no thermal storage tank is used, the most preferable additive is potassium formate. The ability of potassium formate to protect the coil and piping from freezing during winter ambients, combined with its excellent heat transfer properties and low viscosity at low temperatures makes this an ideal additive for closed loop chilled water systems in Turbine Inlet Cooling applications.

Packaging. The chilling system may be installed by any method, but preferably, the system is mounted on a prepackaged factory built skid. The entire skid is enclosed, climate controlled and equipped with an overhead monorail crane to facilitate maintenance.

In addition, the skid package would optionally include all of the motor starters for the chillers and pumps. An optional heat rejection system may also be provided which would include one or more cooling water pumps to circulate water from a cooling tower through the condenser tubes of the chiller and then carry the heated water back to the cooling tower, if water is available. A packaged cooling tower may optionally be provided as part of the system and would preferably be mounted above the skid to minimize footprint and provide sufficient net positive suction head to the circulating water pumps mounted on the skid to prevent any cavitation with the pumps. Alternatively, for sites with water restrictions, an optional air-cooled condenser may be provided and would preferably be mounted above or along side the skid. Additionally an optional variable frequency drive may be mounted on the skid to modulate the flow of water through the evaporator of the chillers, which would result in lower energy consumption during reduced ambient periods. This optional VFD may also be applied to the cooling tower fans and the cooling water pumps. The skid may include one or more water chillers, one or more chilled water pumps capable of varying the flow of circulating water through the evaporator tubes of the chillers, and a controls system to optimize and control the proper amount of chilled water flow and temperature to minimize the total amount of electricity required to power the inlet chilling system. The skid may incorporate a microprocessor or PLC based controls system responding to temperature sensors and flow measurement. This system may communicate with the power plant's control system. The skid control's system could enable the turbine operator to monitor remote sites from a single location via modem or internet communication.

Optimized Efficiency Control vs Optimized Capacity Control. Normally the controls of the Turbine Inlet Cooling system will be designed to provide a constant inlet air temperature to the compressor of the gas turbine to maintain its capacity during high ambient periods. This compressor inlet air temperature (normally called “T2”) is typically maintained at a setpoint of approximately 45° F. or 50° F. to maintain the gas turbine manufacturers minimum temperature to prevent icing in the bellmouth of the turbine. For simple cycle gas turbines (i.e, no steam turbine) this lower T2 air temperature also results in greater gas turbine efficiency (defined at BTU/KWH) as well as increased capacity (defined as KW or MW). However, for combined cycle plants, it has been found through modeling the plant operations with computer simulation software, that the overall heat rate (efficiency) of the plant goes down slightly when reducing T2 utilizing Turbine Inlet Cooling even though the capacity output is significantly increased. This is because the colder inlet air to the gas turbine increases the mass flow and results in lower temperature exhaust and thus lower steam pressure at the Heat Recovery Steam Generator (HRSG). This results in a lower percentage increase of steam turbine output vs the gas turbine output when compared to the same plant at higher entering air temperature. This fact combined with the parasitic power required to drive the mechanical chilling system will usually result in a slight decrease in overall combined cycle efficiency. This efficiency degradation can be mitigated through the use of a special control algorithm whereby the inlet air dry bulb temperature and relative humidity are precisely measured and the dew point calculated. By controlling the leaving air temperature off the cooling coil to maintain a temperature slightly above the dew point temperature, the coil can be prevented from producing condensate which will greatly reduce the parasitic power associated with the mechanical inlet chilling system. An alternative method that accomplishes the same thing would employ an accurate relative humidity sensor downstream of the coil and limit the leaving air temperature to where the RH is maintained at about 95-99% and not allowed to become fully saturated whereby moisture would be condensed on the coil (see FIG. 6 Psychrometric Chart). This reduced parasitic power will allow the overall combined cycle plant to maintain its original high net efficiency and still get much of the capacity improvement associated with inlet cooling. This method of control will normally only be employed when the economics of operating the power plant favor maximum efficiency over maximum capacity.

Claims

1. A method of chilling inlet air to a combined cycle gas turbine plant, comprising:

a. a gas turbine plant that includes a gas turbine and a gas turbine air inlet and a steam turbine;

b. providing a system of circulating liquid chilling water including a chilling system that includes a first chiller;

c. providing a storage tank which is operably connected to the chilling system, the storage tank containing a column of water characterized by a top and a bottom;

c. d. removing water from the storage tank, passing at least a portion of the liquid chilling water through the first chiller, the liquid chilling water passing through the first chiller being lowered to a first temperature and then introducing at least a portion of the removed water into the water column, wherein the average temperature of the water in the storage tank is lowered;

d. e. providing an inlet air chiller, comprising a cooling coil through which liquid chilling water passes, for lowering the temperature of inlet air being fed to the gas turbine compressor through heat transfer between the liquid chilling water passing through the cooling coil and the inlet air, wherein the inlet air chiller provides a liquid chilling water temperature rise;

e. f. chilling the inlet air by removing water from the water column and then directing the liquid chilling water through the cooling coil of the inlet air chiller to make heat transfer contact between the liquid chilling water and the inlet air; and

f. g. controlling the leaving air temperature off the cooling coil to maintain a leaving air temperature slightly above the dew point temperature of the ambient air to maintain high efficiency on the power gas turbine plant.

2. The method of claim 1, wherein an amount of circulating chilled water flow rate is varied to the cooling coil to maintain a leaving air temperature slightly above the dew point temperature of the ambient air.

3. The method of claim 1, wherein the temperature of the circulating chilled water is varied to the cooling coil to maintain a leaving air temperature slightly above the dew point temperature of the ambient air.

4. The method of claim 1, wherein a circulating chilled water flow rate or the circulating chilled water temperature is varied to the cooling coil to maintain a relative humidity off the coil to below about 95% to about 99% RH.

5. A method of chilling inlet air to a gas turbine, comprising:

a. a gas turbine that includes a gas turbine inlet;

b. providing a system of circulating liquid chilling water solution wherein the water solution contains water plus an additive which is capable of reducing the freezing point of water;

c. passing at least a portion of the liquid chilling water solution through a first chiller and then a second chiller, the liquid chilling water solution passing through the first chiller being lowered to a first temperature; and the liquid chilling water solution passing through the second chiller being lowered to a second temperature which is lower than the first;

d. providing an inlet air chiller, comprising a cooling coil through which the liquid chilling water solution passes, for lowering the temperature of inlet air being fed to the gas turbine compressor through heat transfer between the liquid chilling water solution passing through the cooling coil and the inlet air, and

e. chilling the inlet air by directing the liquid chilling water solution through the cooling coil of the inlet air chiller to make heat transfer contact between the liquid chilling water and the inlet air.

6. The method of claim 5, wherein the chilling water solution comprises an additive of sodium nitrate in an amount sufficient to decrease the freezing temperature of the chilling water solution.

7. The method of claim 5, wherein the chilling water solution comprises an additive of potassium formate in an amount sufficient to decrease the freezing temperature of the chilling water solution.

8. The method of claim 1, wherein the controlling the leaving air temperature off the cooling coil is accomplished by maintaining a leaving air temperature slightly above the dew point temperature of the ambient air.

9. The method of claim 1, wherein the controlling the leaving air temperature off the cooling coil is based on an identified operating parameter associated with the gas turbine plant.

10. The method of claim 9, wherein the operating parameter is the dew point temperature of the ambient air.

11. The method of claim 10, wherein the leaving air temperature is maintained slightly above the operating parameter.

12. The method of claim 9, wherein the operating parameter is the humidity of the ambient air.

13. The method of claim 9, wherein the operating parameter is the capacity requirement for the gas turbine plant.

14. The method of claim 1, wherein the inlet air temperature is adjusted by changing the flow rate of the liquid chilling water passing through the cooling coil.

15. The method of claim 14, wherein the inlet air temperature is adjusted when the temperature difference between the liquid chilling water entering the cooling coil and the liquid chilling water leaving the cooling coil reaches a desired level.

16. The method of claim 14, further comprising:

providing a pump for circulating the liquid chilling water,

wherein the flow rate of the liquid chilling water is reduced by lowering the speed (RPM) of the pump via a variable frequency drive on the pump.

17. The method of claim 1, wherein the inlet air temperature is adjusted by lowering the temperature of the liquid chilling water when the inlet air temperature increases above a setpoint.

18. The method of claim 1, wherein the inlet air temperature is adjusted by providing a wet bulb temperature sensor to monitor the ambient air wet bulb temperature entering the cooling coil and lowering the temperature of the liquid chilling water when the ambient air wet bulb temperature increases.

19. A method for chilling inlet air to a gas turbine, comprising:

providing a system of circulating water including a chilling system having a first chiller, wherein water can pass through the first chiller, the water passing through the first chiller being lowered to a first temperature;

providing an inlet air chiller for lowering the temperature of air being fed to a gas turbine compressor through heat transfer between the circulating water and the air;

providing a storage tank which is operably connected to the system of circulating water, the storage tank containing a column of water characterized by a top and a bottom;

during a charge cycle, removing water from the storage tank, passing at least a portion of the removed water through the chilling system to lower the temperature of water passing through the chilling system and then introducing at least a portion of the removed water into the storage tank at a point proximate the bottom of the water column, wherein the average temperature of the water in the storage tank is lowered;

during a discharge cycle, chilling the air by removing water from the storage tank from a point proximate the bottom of the water column and then passing at least a portion of the removed water through the inlet air chiller to make heat transfer contact between that portion of the removed water and the air, such that the temperature of the air is lowered; and

adjusting the temperature of the air based on an air temperature setpoint that is varied by a control setpoint signal from a controls system which adjusts the air temperature setpoint to maintain the desired gas turbine output.

20. A method for chilling inlet air to a gas turbine, comprising:

providing a system of circulating water including a chilling system having a first chiller, wherein water can pass through the first chiller, the water passing through the first chiller being lowered to a first temperature;

providing an inlet air chiller for lowering the temperature of air being fed to a gas turbine compressor through heat transfer between the circulating water and the air;

providing a storage tank which is operably connected to the system of circulating water, the storage tank containing a column of water characterized by a top and a bottom;

during a charge cycle, removing water from the storage tank, passing at least a portion of the removed water through the chilling system to lower the temperature of water passing through the chilling system and then introducing at least a portion of the removed water into the storage tank at a point proximate the bottom of the water column, wherein the average temperature of the water in the storage tank is lowered;

during a discharge cycle, chilling the air by removing water from the storage tank from a point proximate the bottom of the water column and then passing at least a portion of the removed water through the inlet air chiller to make heat transfer contact between that portion of the removed water and the air, such that the temperature of the air is lowered;

selecting a desired air temperature setpoint based on load requirements of the gas turbine; and

adjusting the temperature of the air to the desired air temperature setpoint.

21. The method of claim 20, wherein the temperature of the air is adjusted by changing the flow rate of the circulating water passing through the first chiller.

22. The method of claim 20, wherein the temperature of the air is adjusted in response to predetermined changes in ambient air wet bulb temperature.

23. The method of claim 20, wherein the temperature of the air is adjusted in response to predetermined changes in ambient air enthalpy.

24. The method of claim 20, wherein the temperature of the air is adjusted by varying the circulating water flow rate.

25. The method of claim 20, wherein the temperature of the air is adjusted by varying the circulating water temperature.

26. The method of claim 20, wherein the temperature of the air is adjusted by heating the circulating water.

27. The method of claim 26, wherein the circulating water is passed from the inlet air chiller to a heater and back to the inlet air chiller to increase the temperature of the air.

28. The method of claim 26, wherein the circulating water is heated to keep the mass flow of the air within a desirable mass flow range.

29. The method of claim 20, wherein the air temperature setpoint is a function of both ambient wet bulb temperature of the air and the temperature difference between the circulating water entering the inlet air chiller and the circulating water leaving the inlet air chiller.

30. The method of claim 20, further comprising:

providing chilling system controls and turbine controls,

wherein the chilling system controls communicate with the turbine controls to control setpoints to optimize gas turbine output.

31. The method of claim 20 wherein the first chiller is turned off during peak periods to minimize the total amount of electricity required to power the chilling system.

32. The method of claim 20, wherein the air temperature is adjusted by changing the flow rate of the circulating water passing through the inlet air chiller.

33. The method of claim 20, wherein the air temperature is adjusted when the temperature difference between the circulating water entering the inlet air chiller and the circulating water leaving the inlet air chiller reaches a desired level.

34. A method for chilling inlet air to a gas turbine, comprising:

providing a system of circulating water including a chilling system having a first chiller, wherein water can pass through the first chiller, the water passing through the first chiller being lowered to a first temperature;

providing an inlet air chiller for lowering the temperature of air being fed to a gas turbine compressor through heat transfer between the circulating water and the air;

providing a storage tank which is operably connected to the system of circulating water, the storage tank containing a column of water characterized by a top and a bottom;

during a charge cycle, removing water from the storage tank, passing at least a portion of the removed water through the chilling system to lower the temperature of water passing through the chilling system and then introducing at least a portion of the removed water into the storage tank at a point proximate the bottom of the water column, wherein the average temperature of the water in the storage tank is lowered;

during a discharge cycle, chilling the air by removing water from the storage tank from a point proximate the bottom of the water column and then passing at least a portion of the removed water through the inlet air chiller to make heat transfer contact between that portion of the removed water and the air, such that the temperature of the air is lowered; and

maintaining the temperature of the air at a desired air temperature setpoint based on load requirements of the gas turbine.

35. The method of claim 34, wherein the air temperature is maintained by reducing the flow rate of the circulating water passing through the inlet air chiller.

36. The method of claim 34, wherein the air temperature is maintained by reducing the flow rate of the circulating water passing through the first chiller.

37. The method of claim 34, wherein the air temperature is maintained by adjusting the temperature of the circulating water entering the inlet air chiller.

38. The method of claim 34, wherein the air temperature is maintained by heating the circulating water.

39. The method of claim 34, wherein the air temperature setpoint is a function of both ambient wet bulb temperature of the air and the temperature difference between the circulating water entering the inlet air chiller and the circulating water leaving the inlet air chiller.

40. The method of claim 34, wherein the air temperature is maintained by utilizing a temperature sensor contacting the air to monitor the temperature of the air.

41. The method of claim 34, wherein the air temperature is maintained by providing a wet bulb temperature sensor to monitor the ambient air wet bulb temperature entering the inlet air chiller.

42. A method for chilling inlet air to a gas turbine, comprising:

providing a system of circulating water including a chilling system having a first chiller, wherein water can pass through the first chiller, the water passing through the first chiller being lowered to a first temperature;

providing an inlet air chiller for lowering the temperature of air being fed to a gas turbine compressor through heat transfer between the circulating water and the air;

providing a storage tank which is operably connected to the system of circulating water, the storage tank containing a column of water characterized by a top and a bottom;

during a charge cycle, removing water from the storage tank, passing at least a portion of the removed water through the chilling system to lower the temperature of water passing through the chilling system and then introducing at least a portion of the removed water into the storage tank at a point proximate the bottom of the water column, wherein the average temperature of the water in the storage tank is lowered;

during a discharge cycle, chilling the air by removing water from the storage tank from a point proximate the bottom of the water column and then passing at least a portion of the removed water through the inlet air chiller to make heat transfer contact between that portion of the removed water and the air, such that the temperature of the air is lowered;

selecting a desired air temperature setpoint for the air; and

altering the air temperature setpoint of the gas turbine.

43. The method of claim 42, wherein the air temperature setpoint is altered based on changes in the load requirements of the gas turbine.

44. The method of claim 42, wherein the air temperature setpoint is altered based on the time of day.

45. The method of claim 42, wherein the air temperature setpoint is altered based on the ambient temperature.

46. The method of claim 42, wherein the air temperature setpoint is altered at off-design ambient temperatures.

47. The method of claim 46, wherein the air temperature setpoint is increased at reduced off-design ambient temperatures.

48. A method for chilling inlet air to a gas turbine, comprising:

providing a system of circulating water including a chilling system having a first chiller and a second chiller, the first and second chillers being arranged in series, wherein water can pass through the first and second chillers, the water passing through the first chiller being lowered to a first temperature, the water passing through the second chiller being lowered to a second temperature that is lower than the first temperature, thus providing a staged temperature drop;

providing an inlet air chiller for lowering the temperature of the air being fed to a gas turbine compressor through heat transfer between the circulating water and the air;

providing a storage tank which is operably connected to the system of circulating water, the storage tank containing water and having a bottom;

during a charge cycle, removing water from the storage tank, passing at least a portion of the removed water through the chilling system to lower the temperature of water passing through the chilling system and then introducing at least a portion of the removed water into the storage tank at a point proximate the bottom of the tank, wherein the average temperature of the water in the storage tank is lowered; and

during a discharge cycle, chilling the air by removing water from the storage tank from a point proximate the bottom of the tank and then passing at least a portion of the removed water to the inlet air chiller to make heat transfer contact between that portion of the removed water and the air, such that the temperature of the air is lowered.

49. The method of claim 48, further comprising adjusting the air temperature by changing the flow rate of the circulating water passing through the inlet air chiller.

50. The method of claim 48, further comprising controlling leaving air temperature from the inlet air chiller based on an identified operating parameter associated with the gas turbine.

51. The method of claim 50, wherein the operating parameter is the capacity requirement for the gas turbine.

52. A method for chilling inlet air to a gas turbine, comprising:

providing a system of circulating water including a chilling system having a first duplex chiller and a second duplex chiller, the first and second duplex chillers being arranged in series;

providing an inlet air chiller for lowering the temperature of air being fed to a gas turbine compressor through heat transfer between the circulating water and the air;

passing water through the first and second duplex chillers, wherein the water passing through the first duplex chiller is lowered to a first temperature and then a second temperature that is lower than the first temperature,

passing water through the second duplex chiller, wherein the water temperature passing through the second duplex chiller is lowered to a third temperature that is lower than the second temperature and then a fourth temperature that is lower than the third temperature, thus providing a four stage temperature drop of the water; and

passing at least a portion of the chilled water through the inlet air chiller resulting in heat transfer between the chilled water and the air, such that the temperature of the air is lowered.

53. The method of claim 52, further comprising storing a portion of the chilled water from one of the chillers in a storage tank which is operably connected to the inlet air chiller.

54. The method of claim 52 wherein at least some of the circulating chilling water is circulated through a thermal water storage tank during a charging cycle.

55. A method for chilling inlet air to a gas turbine, comprising:

providing a system of circulating water including a chilling system having a first chiller and a second chiller and a third chiller, the first and second and third chillers being arranged in series;

providing an inlet air chiller for lowering the temperature of air being fed to a gas turbine compressor through heat transfer between the circulating water and the air;

passing water through the first, second and third chillers, wherein water passing through the first chiller is lowered to a first temperature, water passing through the second chiller is lowered to a second temperature that is lower than the first temperature, and water passing through the third chiller is lowered to a third temperature that is lower than the second temperature, thus providing a staged temperature drop of the water; and

passing at least a portion of the chilled water through the inlet air chiller resulting in heat transfer between the chilled water and the air, such that the temperature of the air is lowered.

56. A method for chilling inlet air to a gas turbine, comprising:

providing a system of circulating water including a chilled water circuit having a first duplex chiller and a second duplex chiller, the first and second duplex chillers being arranged in series for circulating chilled water in a first flow direction through the chilled water circuit;

providing a circulating condenser water circuit that circulates cooling water through the second duplex chiller and then through the first duplex chiller such that the condenser water circuit is counterflow to the chilled water circuit;

providing an inlet air chiller for lowering the temperature of air being fed to a gas turbine compressor through heat transfer between the circulating water and the air;

passing chilled water through the first duplex chiller, wherein the chilled water passing through the first duplex chiller is lowered from a first temperature to a second temperature that is lower than the first temperature;

passing the chilled water from the first duplex chiller through the second duplex chiller, wherein the chilled water temperature is lowered to a third temperature that is lower than the second temperature, thus providing a staged temperature drop of the chilled water;

passing at least a portion of the chilled water from the chilled water circuit through the inlet air chiller resulting in heat transfer between the chilled water and the air, such that the temperature of the air is lowered.

57. A method for chilling inlet air to a gas turbine, comprising:

providing a system of circulating water including a chilling system having a first chiller and a second chiller, the first and second chillers being arranged in series;

passing water through the first chiller to lower the water temperature to a first temperature;

thereafter, passing the water through the second chiller to lower the water temperature to a second temperature that is lower than the first temperature, thus providing a staged temperature drop;

providing an inlet air chiller for lowering the temperature of the air being fed to a gas turbine compressor through heat transfer between the circulating water and the inlet air;

providing a thermal water storage tank which is operably connected to the system of circulating water, the thermal water storage tank containing chilling water;

during a charge cycle, removing water from the storage tank, passing at least a portion of the removed water through the chilling system to lower the temperature of water passing through the chilling system and then introducing at least a portion of the removed water into the storage tank; and

during a discharge cycle, chilling the air by removing chilling water from the thermal water storage tank and then passing at least a portion of the removed water to the inlet air chiller resulting in heat transfer between the chilled water and the air, such that the temperature of the air is lowered; and

varying the flow of chilling water through the inlet air chiller.

58. The method of claim 57, wherein the staged temperature drop is maintained at least 20° F. or above.

59. The method of claim 57, wherein the inlet air chiller is a specially circuited cooling coil designed to provide a staged temperature rise of at least 20° F. or above.