File #2 7437 .002/DHE
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`PATENT APPLICATION
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`SYSTEM FOR CHILLING INLET AIR FOR GAS TURBINES
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`by
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`TOM L. PIERSON
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`CERTIFICATE OF MAILING
`37 C.F.R. 1.10
`I hereby oertify that this correspondence is being deposited with the
`U. S. Postal Service as Express Mail Post Ofiioe to Addressee
`Service, as Express Mail No. ELl57447310US, prior to the last
`scheduled pickup,
`in an envelope addressed to: Assistant
`Commissioner for Patents, Washington, D.C. 20231, on the date
`indicated below.
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`’Date
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`?- :2; ~ W:
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`GZJKDKV!3112
`EXHIBIT 2001
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`BACKGROUND OF THE INVENTION
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`1.
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`Field Of The Invention
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`This invention relates broadly to cooling inlet air to a gas turbine. In a specific embodiment,
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`the invention relates to an apparatus and method for storing water in a thermal storage tank, and
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`using the stored water to cool the inlet air to a gas turbine.
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`2.
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`Description Of The Related Art
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`A conventional gas turbine system includes: an air compressor for compressing the turbine
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`inlet air; a combustion chamber for mixing the compressed air with fuel and combusting the mixture,
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`thereby producing a combustion gas; and a power turbine that is driven by the combustion gas,
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`thereby producing an exhaust gas and useful power.
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`Over the ‘years, various technologies have been employed to increase the amount of useful
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`power that the power turbine is able to produce. One way of increasing the power output of a gas
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`turbine is to cool the turbine inlet air prior to compressing it in the compressor. Cooling causes the
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`air to have a higher density, thereby creating a higher mass flow rate through the turbine. The higher
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`the mass flow rate through the turbine, the more power the turbine produces. Cooling the turbine
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`inlet air temperature also increases the turbine’s efficiency.
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`Various systems have been devised for chilling the inlet air to the compressor. One such ,
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`system uses evaporative cooling, wherein ambient temperature water is run over plates or over a
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`cellular media inside of a chamber, thereby creating thin films of water on each plate, or on the
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`media. The turbine inlet air is then drawn through the chamber, and through evaporative cooling,
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`the air is cooled to near the wet bulb temperature. This system is limited to cooling the air to the wet
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`bulb temperature, which is dependent upon the atmospheric conditions at any given time. Another
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`system uses a chiller to chill water that is then run through a coil. The inlet air is then drawn through
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`the coil to cool the air. This system requires parasitic power or steam to drive the chilling system
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`which has the further drawback that when inlet air cooling is needed the most, i.e. during the day
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`when the temperature is the highest, is also the time when power demand from the turbine is the
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`highest, i.e. during the day when power users are in operation. In order to run the chiller, power from
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`the turbine is required, but this power is needed by the users of the turbines power. On the other
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`hand, when cooling is needed the least, i.e. at night when the temperatures are the lowest, surplus
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`power from the turbine is available because the consumers of the turbine’s power are largely not in
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`operation.
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`Accordingly, a continuing need exists for a turbine inlet air coolingsystem which:
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`would efficiently cool turbine inlet air; would take advantage of surplus power available during times
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`of low consumer power demand; and would not drain the system of power during times of high
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`consumer power demand.
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`SUMMARY OF THE INVENTION
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`The claimed invention may be directed to a method for chilling inlet air to a gas turbine
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`power plant, which may include: providing a system of circulating chilling water including a chilling
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`system; providing an inlet air chiller for lowering the temperature of the inlet air being fed to a gas ‘
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`turbine compressor through heat transfer between the circulating chilling water and the inlet air,
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`providing a thermal water storage tank which is operably connected to the system of circulating
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`chilling water, the thermal water storage tank containing chilling water having a bottom;.during a
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`charge cycle, removing a first portion of chilling water from the thermal water storage tank, passing
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`the removed first portion of water through the chilling system to lower the temperature of the
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`removed first portion of water and to provide a chilled removed first portion of water, and then
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`introducing the chilled removed first portion of water into the thermal water storage tank at a point
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`proximate the bottom of the tank, wherein the chilled removed first portion of water is introduced
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`to the tank in an amount sufficient to lower the average temperature of the chilling water in the
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`thermal water storage tank; and during a discharge cycle, chilling the inlet air by removing a second
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`portion of chilling water from the thermal water storage tank, from a point proximate the bottom of
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`the tank and then passing the second portion of chilling water to the inlet air chiller to make heat
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`transfer contact between the second portion of chilling water and the inlet air, such that the
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`temperature of the inlet air is lowered.
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`In one specific embodiment of the claimed method, the average temperature of the chilling
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`water in the tank may be lowered to about 33 °F to about 40 °F during the charge cycle and may be
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`raised to about 60 °F to about 70 °F duringthe discharge cycle. In another specific embodiment,
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`the times of the charge and discharge cycles may be such that, before the temperature of the chilling
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`water proximate the bottom of the tank reaches about 36 °F during the discharge cycle, the charge
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`cycle is initiated.
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`In another specific embodiment of the method for chilling inlet air, the first
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`portion of chilling water removed from the thermal water storage tank during the charge cycle may
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`be removed through a top outlet. In yet another specific embodiment, the second portion of chilling
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`water removed from the thermal water storage tank during the charge cycle may be removed through
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`a bottom inlet. In yet another specific embodiment, the chilling water in the tank may have an
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`average temperature that can be lowered during the charge cycle and raised during the discharge
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`cycle. In a further specific embodiment of the claimed method, the discharge cycle may be carried
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`out during the night~tirne and the charge cycle may be carried out during the day—time. In still
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`another specific embodiment, the water level in the tank may remain substantially constant during
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`the charge and discharge cycles. In still a further specific embodiment, the one or more chillers may
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`be deactivated during the discharge cycle. In another specific embodiment, the discharge cycle may
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`occur during peak power usage of the gas turbine power plant. In another specific embodiment, the
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`discharge cycle may be performed after the removing of at least a portion of the volume of chilling
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`water from the thermal water storage tank during the charge cycle, such that the chilled removed
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`water that is introduced into the thermal water storage tank at a point proximate the bottom of the
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`tank may remain substantially at the point proximate the bottom of the tank. In another specific
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`embodiment, the first portion of chilling water removed during the charge cycle may be sufficient
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`to chill substantially all of the water in the thermal water storage tank to a temperature below the
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`temperature ofmaximum water density. In yet another specific embodiment ofthe claimed method,
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`the second portion of chilling water removed during the discharge cycle may be substantially all of
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`the chilling water in the tank. In a ‘further specific embodiment of the method of the present
`invention, the thermal water storage tank contains a volume of chilling water that is sufficient to
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`lower the temperature of the inlet air to a range of from about 45 °F to about 55 °F for a period of
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`between about 4 hours to about 12 hours.
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`The present invention is also directed to a method of chilling water delivered to the air chiller I
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`in a gas turbine power plant system having at least one air chiller for lowering the temperature of
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`inlet air, at least one air compressor for compressing the inlet air, at least one combustor for burning
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`the compressed air and providing combustion gas, and at least one power turbine driven by the‘
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`combustion gas for producing useful power, a method of chilling water delivered to the air chiller,
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`the method including the steps of: providing the at least one air chiller with an air chiller inlet that
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`may receive water, and an air chiller outlet that may expel water; providing a thermal water storage
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`tank, having a bottom portion, a top portion, at least one bottom opening proximate the bottom
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`portion and at least one top opening proximate the topeportion, and containing a volume of stored
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`water having an average temperature, and temperature of maximum water density; performing a
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`charge cycle, by introducing through the at least one bottom opening a first quantity of chilled water
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`which has a chilled water temperature that is below the temperature of maximum water density,
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`thereby lowering the average temperature of the volume of stored water, wherein the first quantity
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`of chilled water being introduced through the bottom opening is sufficient to lower the average
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`temperature of the volume of stored water to a temperature that is below the temperature of
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`maximum water density; and performing a discharge cycleby removing a second quantity of chilled
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`water from the tank through the at least one bottom opening and passing the second quantity of
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`chilled water to the air chiller inlet, to lower the temperature of the inlet air, thereby raising the
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`temperature of the second quantity of chilled water and providing high temperature water, then
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`introducing the high temperature water to the at least one top opening in the tank.
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`In one specific embodiment of the method of chilling water, the temperature of maximum
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`water density may be from about 20°F to about 39.2°F.
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`In another specific embodiment,
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`the
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`temperature of maximum water density may be about 39.2°F. In another specific embodiment, the
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`temperature of the stored water may have a temperature of from about 34 °F to about 40 ‘’F. In yet
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`another specific embodiment of the claimed method the temperature of the stored water may have
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`a temperature corresponding to the maximum water density of about 39.2 °F. In another specific
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`embodiment sodium nitrate may be added to depress the freezing temperature of the water thereby
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`allowing stored water to be in the range of about 25°F to about 34°F.
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`In another specific
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`embodiment ofthe method ofthe present invention, the useful power produced by the power turbine
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`may be consumed at a variable rate, and the charge cycle may be performed when the rate is at a
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`minimum. In a further specific embodiment, the useful power produced by the power turbine may
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`be consumed at a variable rate, and the discharge cycle may be performed when the rate is at a
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`maximum. In yet another specific embodiment of the method ofthe present invention, the quantity
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`of water expelled during the discharge cycle may be less than the volume of stored water.
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`In a
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`further specific embodiment, the quantity of chilled water may be chilled by passing water through
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`at least one chiller. In still another specific embodiment of the claimed method, the temperature of
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`inletair may be lowered from a high temperature of from about 85 °F to about 95 “F to a low
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`temperature of from about 45 °F to about 55 °F.
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`In still a further specific embodiment, the high
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`temperature may be about 90 °F and the low temperature may be about 50 °F. In yet another specific
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`embodiment, the output ofthe gas turbine power plant system may be from about 50 megawatts to
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`about 250 megawatts.
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`The present invention is also directed to a gas turbine power plant system, wherein the
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`system includes: one or more air chillers for lowering the temperature of inlet air; one or more air
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`compressors for compressing the inlet air; one or more combustors for burning the compressed air
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`and providing combustion gas; and one or more power turbines driven by the combustion gas for
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`producing useful power, and an improvement that may include: a thermal water storage tank for
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`[containing chilled water, wherein the thermal water storage tank has a bottom portion with a bottom
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`outlet and a top portion, and the tank is operably connected to the air chiller such that the chilled
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`water passes from the bottom outlet to the air chiller to lower the temperature of the inlet air and is
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`returned to the thermal water storage tank; and a Water chilling system for chilling the water in the
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`thermal water storage tank, wherein the water chilling system is configured to receive high
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`temperature water from the top portion ofthe tank, and wherein the system is configured to introduce
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`low temperature water to the bottom portion of the tank, such that the average temperature of the
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`water in the tank is lowered; and wherein the water chilling system includes one or more chillers for
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`lowering the temperature of the high temperature water from the top portion of the tank to provide
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`low temperature water.
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`In one specific embodiment ofthe claimed gas turbine power plant system, the thermal water
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`storage tank may have a bottom, and the bottom outlet may be positioned at a height that is less than
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`about 10 feet from the bottom of the tank. In another specific embodiment of the gas turbine power
`plant system, the thermal water storage tank may have a bottom, and the bottom outlet may be
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`positioned at a height that is less than about 5 feet from the bottom of the tank. In another specific
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`embodiment,
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`the thermal water storage tank may have a bottom, and the bottom outlet may be
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`positioned at a height that is less than about 18 inches from the bottom of the tank.
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`In another
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`specific embodiment, the tank may have a top outlet and a bottom inlet such that, in a charge cycle
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`the high temperature water may be removed through the top outlet and may be fed to the one or more
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`chillers, and the low temperature water may be introduced to the tank through the bottom inlet; In
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`a further specific embodiment of the gas turbine power plant system, the tank may have a bottom
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`outlet such that, in a discharge cycle, chilling water maybe removed from the tank through the
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`bottom outlet. In still a further specific embodiment of the gas turbine power plant system, the tank
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`may have a bottom outlet such that, in a discharge cycle, chilling water may be removed from the
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`tank through the bottom outlet, fed to the air chiller and is returned to the tank, bypassing the one
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`or more chillers ofthe water chilling system. In still a further specific embodiment ofthe gas turbine
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`power plant system, the top portion may be separated from the bottom portion by a thermocline.
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`In yet another specific embodiment, during the charge cycle, the bottom inlet may receive a quantity
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`of chilled water that is sufficient to supply the air chiller with water having a temperature below the
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`temperature of maximum water density for four or more hours. In another specific embodiment,
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`during the charge cycle, the bottom inlet may receive a quantity of chilled water that is sufficient to
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`supply the air chiller with water having a temperature below the temperature of maximum water
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`density for eight or more hours. In still another embodiment, during the charge cycle, the bottom
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`inlet may receive a quantity of chilled water that is sufficient to supply the air chiller with water
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`having a temperature below the temperature of maximum water density for twelve or more hours.
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`In still another specific embodiment, the thermal water tank may have a height of from about 25 feet
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`to about 70 feet. In ‘yet another specific embodiment, the thermal water tank may have a diameter
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`of from about 50 feet to about 250 feet. In another specific embodiment, the thermal water tank may
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`have a diameter, and a height, and the diameter may be greater than the height.
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`In yet another
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`specific embodiment ofthe claimed invention, the volume of stored water may be greater than about
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`eight hundred thousand gallons. In still a further specific embodiment, the temperature of the water
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`in the top portion may be about 15 °F to about 35 "F greater than the temperature of the water in the
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`bottom portion. In another specific embodiment, the thermal water storage system may include a
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`plurality of thermal water storage tanks, each of the plurality of tanks may have a bottom inlet and
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`a bottom outlet, and each of the plurality of tanks may have a top inlet and a top outlet. In another
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`specific embodiment, the bottom inlet may have a bottom diffuser, and the top inlet may have a top
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`diffuser, whereby the water entering the bottom inlet is diffused, and the water entering the top inlet
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`may be diffused. In yet another specific embodiment, the temperature of the water in the top portion
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`of the tank may have a temperature ranging from about 60 °F to about 70 °F.
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`In still a further
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`specific embodiment, the temperature of the water in the bottom portion of the tank may have a
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`temperature that is above the freezing temperature.
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`In -another specific embodiment, the water
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`chilling system may include at least one mechanical chiller. In still another specific embodiment
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`of the present invention, the water chilling system may include at least one absorption chiller. In still
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`a further specific embodiment, the water chilling system may include at least one mechanicalchiller
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`and at least one absorption chiller. In yet another specific embodiment, the mechanical chiller may
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`receive chilled water from the absorption chiller, and the mechanical chiller may further chills the
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`chilled water. In another specific embodiment, the gas turbine power plant system may additionally
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`, including a heat recovery steam generator and a steam turbine, wherein the absorption chiller may
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`be driven by steam from the heat recovery steam generator. Another specific embodiment of the gas
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`turbine power plant system may additionally include a heat recovery steam generator and a steam
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`turbine, wherein the absorption chiller is driven by back pressure from the steam turbine exhaust.
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`In another specific embodiment, the inlet air may be lowered from a first temperature of about from
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`85 °F to about 95 °F to a second temperature of from about 45 °F to about 55 °F in the inlet air
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`chiller.
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`In yet another embodiment, the first temperature may be about 90 “F and the second
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`temperature may be about 50 °F.
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`In another specific embodiment of the gas turbine power plant
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`system, the chilling water being fed to the inlet air chiller may have a temperature of from about 34
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`°F to about 40 "F.
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`In another specific embodiment, the gas turbine power plant system may
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`additionally include a steam turbine and a heat recovery steam generator, and the heat recovery
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`steam generator may receive exhaust gas from the power turbine and may provide high pressure
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`steam to the steam turbine, and the steam turbine may provide low pressure steam.
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`DRIEF DESCRIPTION OF THE DRAWINGS
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`In the drawing:
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`FIG. 1 is a schematic diagram ofthe turbine inlet air cooling system of the present invention;
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`FIG. 2 is a schematic diagram of an alternative embodiment of the turbine inlet air cooling
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`system of the present invention; and
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`FIG. 3 is a side View of a storage tank used in a specific embodiment ofthe present invention.
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`DETAILED DESCRIPTION OF THE INVENTION
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`Specific embodiments of the invention will now be described including a preferred system
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`(apparatus and method), referring to attached FIG. 1, All references to the “invention” below are
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`intended to be directed to the specific embodiments and not necessarily, in limiting fashion, to the
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`broad invention in the claims.
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`Generally, referring to FIG. 1, the overall apparatus 10 includes a conventional gas turbine
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`system 12 having an air chiller 14, e.g., a conventional cooling coil, for lowering the temperature
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`of inlet air, shown schematically by arrow 15a, from ambient temperature (Tl, e.g., about 90 °F
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`(about 32” °c), or in the range of from about 70 “F (about 21 °c') to about 85 "F (about 29°C) to a
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`range of from about 100 °F (about 38 °C) to about 115 °F (about 47 °C)) to provide compressor feed
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`air, shown schematically by arrow 15b, having some lower temperature (T2, e.g., about 50 °F (about
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`10 °C), or in the range of about 45 °F (about 7 °C) to about 55 °F (about 13 °C)). The air chiller 14
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`can be a conventional cooling coil that provides for heat transfer contact, e.g., across a set of coils
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`within the air chiller 14, between the circulating chilling water 160 (preferably at a T3 of about 34
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`°F ( or about 1 °C to about 2 °C) to about 40 °F (or about 4 °C to about 5 °C)) and the inlet air 15a,
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`forming chilled compressor feed air 15b, and resulting in a higher temperature circulating water 16d
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`(T4, e.g., about 54 °F(about 12 °C) to about 60 °F (about 16 °C)). A preferred cooling coil may be
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`specially circuited so as to achieve relatively high changes in the temperature of the water flowing
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`through the tubes in the cooling coil. This rise in temperature is preferably in a range of about 20
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`°F (about 11 °C) to about 35 “F (about 19 °C) on a hot design day. As used herein a “design day” is
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`the maximum temperature that the ambient air is expected to reach - the temperature upon which the
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`system design is based. The chilled compressor teed air 15b may then be introduced to a
`conventional gas turbine (GT) compressor 32, where it is compressed, combined with fuel and
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`burned in a conventional combustor 34 to produce a combustion gas that can be used for driving the
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`power turbine 36, resulting in “exhaust gas.”i FIG. 1 shows the overall system as including only one
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`gas turbine system 12, one air chiller 14, one water chilling system 13, and one tank 18. However,
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`depending upon system requirements as well as geographical, geological, and other constraints, it
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`may be desirable to have more than one gas turbine system 12, more than one air chiller 14, more
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`than one water chilling system 13, or more than one tank 18.
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`Another specific embodiment ofthe invention is directed to a combined cycle system. There,
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`the exhaust gas from the power turbine 36 can be passed through a heat recovery steam generator
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`(HRSG) 38 to produce steam, shown schematically by arrow 44, and “stack gas,” shown
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`schematically by arrow 45. Further, in another embodiment of a combined cycle system, a heat
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`recovery coil 42 may receive the exhaust gas 45 from the power turbine 36 and produce hot water
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`or steam, shown schematically by arrow 48. The hot water or steam 48 produced either by the
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`HRSG 38 or the heat recovery coil 42 may advantageously be used to supply power to an absorption
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`chiller 26, the importance of which will be discussed below.
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`As mentioned, it is advantageous to lower the temperature of the inlet air 15a to a
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`temperature T2 that is as low as possible. The change in air temperature from T1, before entering
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`the air chiller 14, to T2, after exiting the air chiller 14, is referred to herein as AT. Even small
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`increases in AT, i.e., lowering T2 can effect significant increases in the capacity of the gas turbine
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`system. For example, in a particular gas turbine, an increase in AT of about 2.6 °F (about 1 °C to
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`-about 2 °C) may increase the turbine output byoabout one percent.
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`An important aspect of the apparatus of this invention is a chilling water system or loop,
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`which includes circulating chilling water 16 that circulates through the specially circuited, high AT
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`air chiller l4 and back through chillers piped in series to a thermal water storage tank 18 for storing
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`the chilling water l6. The term “loop” preferably refers to conventional pipage, e. g. pvc or steel
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`pipes having valves (not shown) where appropriate. The features of this chilling water loop will now
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`be described with reference to FIG. 1, where, for ease of comprehension, the water within the loop
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`is referred to generally with numeral 16, and the various streams of water within the loop are referred
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`to with the numeral 16 followed by an alphabetic character to distinguish between various streams
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`of water where necessary.
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`The chilling water loop includes a water chilling system 13. The water chilling system 13
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`may include any number of conventional water chillers installed either in parallel or in series but
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`preferably with at least two chillers piped in series so as to stage the temperature drop of the water
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`into an intermediate and a lower temperature chiller. This saves power on the upstream chiller and
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`makes the system more efficient.
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`If the power plant is a combined cycle plant and if there is
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`sufficient exhaust energy available fiom either the steam turbine exhaust (stream 46) or heat recovery
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`coil (stream 48), then it is preferableias shown in FIG. 1 for the water chilling system 13 include an
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`absorption chiller 26 which may derive its power from the HRSG 38, or the heat recovery coil 42,
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`or both, and a mechanical chiller 24. The absorption chiller 26 and the mechanical chiller 24 are
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`shown in series, as that is the preferred arrangement with the absorption chiller placed upstream of
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`the mechanical chiller, however they may be placed in parallel depending upon system needs. An
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`object ofthe water chillers is to chill the chilling water 16 to a sufficiently low temperature so that
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`the chilling water 16 can then be used to chill -the inlet air 15a in the air chiller 14 with a minimum
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`water flow rate and maximum Water AT. Preferably, the temperature of the chilling water 16c is
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`about 34 °F (about 1 “C toiabout 2 °C) to about 40 °F (about 4 “C to about 5 °C) prior to entering the
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`air chiller 14. A number of conventional devices can be used to chill the water going to the water
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`storage tank 18. For example, the chilling water can be chilled before it is ever introduced to the
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`tank, by passing the chilling water 16d from the air chiller either through a mechanical chiller 24 or
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`an absorption chiller 26 (driven by hot water or steam 44, 48 from the HRSG or ‘LP steam 46 coming
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`out of the steam turbine 40) to provide chilling water 16a that is/then introduced to the tank 18. A‘
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`hybrid chilling arrangement can also be used whereby both mechanical 24 and absorption 26 chillers
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`are used in combination. The preferred arrangement is to circulate the warm water l6e from the tank
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`18 or the heated water 16d from the air chiller 14 to the upstream absorption (or mechanical) chiller
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`26 first where the water 16d will be chilled from range of about 54 °F (about 12 °C) to about 65 °F
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`(about 19 °C) to a range of about 40 ‘’F (or about 4 °C to about 5 °C) to about 48 °F (or about 8 °C
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`to about 9 °C). The water 16d then circulates through the downstream mechanical chiller 24 where
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`it may be chilled further to about 34 °F (or about 1 “C to about 2 °C) to about 40 °F (or about 4 °C
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`to about 5 °C).
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`The thermal water storage tank 18 is preferably a thermally insulated vessel, having an upper
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`opening or connection or top inlet/outlet 20. In other specific embodiments, e.g., where an open tank
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`is used, the top “opening” or top inlet can be the open top ofthe tank, so that water can be piped into
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`the tank through the top. The tank 18 may be made from any material having the strength and
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`insulation qualities necessary for a thermal water storage tank, however, preferably, the tank 18 is
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`constructed of steel or concrete. The top inlet/outlet 20 (also referred to herein as an “opening”) both
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`receives heatedwater 16d from the air chiller 14 during a discharge cycle, and expels heated water
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`l6e during a charge cycle. (The charge and discharge cycles will be explained in further detail
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`below) The thermal water storage tank 18 preferably also has a lower connection or bottom
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`inlet/outlet 22 (or “opening”). The bottom inlet/outlet 22 both receives chilled water 16a from water
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`chilling system 13 during the charge cycle, and discharges chilled water 16b to the air chiller 14
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`20
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`during the discharge cycle. Furthermore, the system shown in FIG. 1 also allows a “partial storage”
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`strategy whereby the chilled water in the tank can be used to supplement the water produced by the
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`15
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`GZJKDKV!3112
`EXHIBIT 2001
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`chillers such that both can be provided to the air chiller 14 to allow longer periods of on-peak chilled
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`air going to the gas turbine.
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`In accordance with the invention, the water 16 in the tank 18 is “Stratified” according to
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`temperature. That is, the lower temperature water (about 33 °F (about 0 °C to about 1 °C) to about
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`40 °F (about 4 °C to about 5 °C)) resides at the bottom ofthe tank. Broadly, the temperature at the
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`bottom of the tank may be in the range of from about 33 °F (about 0 °C to about 1 °C) to about 40
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`°F (about 4 °C to about 5 "C). Preferably, the temperature of the water in the bottom of the tank is
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`in the range of from about 33 °F (about 0 °C to about 1 °C) to about 36 °F (about 2 °C to about 3 °C).
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`Most preferably the temperature of the water in the bottom ofthe tank is in the range of from about
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`33 °F (about 0 °C to about 1 °C) to about 34 “F (about 1 “C to about 2 °C). The higher temperature
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`water (typically about 60 °F (about 16 °C) to about 70 °F (about 21 °C), typically having a lower
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`density, remains at the upper portions of the tank.) Preferably, the entire tank 18 will be occupied
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`by lower temperature water (about 33 °F (about 0 °C to about 1 °C) to about 34 °F (about 1 °C to
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`about 2 °C)) after a charge cycle (discussed below) is completed. The tank should be capable of
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`storing sufficient chilled water 16 to provide air cooling during an entire discharge cycle (discussed
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`below). Further, the tank 18 should have a sufficient height so that adequate temperature gradients
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`can be maintained. Preferably, the diameter of the tank 18 is greater than the height. An advantage
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`of using the charge/discharge cycles, and other features of the present invention is realized with
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`respect to the natural tendency of water to “stratify” according to temperature. Generally, in the
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`ill
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`20
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`temperature range of about 39.2 °F (about 4.0 °C) to about 212 °F (100 °C), water decreases in
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`density as temperature increases. As a result, the colder water sinks to the bottom and the warmer
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`16
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`GZJKDKV!3112
`EXHIBIT 2001
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`water rises to the top, thereby forming uniform temperature strata or layers. Further, in the
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`temperature range of about 32 °F (about 0 °C) to about 39.2 “F (4.0 °C), water tends to increase in
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`density according to temperature. As a result, in this temperature range, the warmer water tends to
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`sink to the bottom and -the colder water rises to the top. Generally, pure water reaches its maximum
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`density at about 39.2 °F (about 4.0 °C). However, depending upon atmospheric conditions, or if
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`various chemicals are added to the water, the temperature ofmaximum water density may change.
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`Therefore, if the charge/discharge cycles of the claimed invention are not performed, the coldest
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`water does notsink to the bottom, but instead, water with a temperature of about 39.2 °F (about 4.0
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`°C) naturally tends to settle toward the bottom of the tank. The tank 18 of the claimed invention
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`
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`discharges warm water l6e fiom the top portion 18a of the tank 18, and receives chilled water 16a
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`from the water chilling system 13, which is below the temperature of maximum water density,
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`during the charge cycle into the bottom portion 18b through bottom inlet/outlet 22. In this manner,
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`the coldest but not necessarily the heaviest water is forced into the bottom. Further, as mentioned,
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`the charge cycle preferably is long enough and the charge flow rate is great enough to fill the entire
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`tank 18 with the design cold water temperature by the end of the charge c