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 method and 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.
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0. 34. A system for chilling inlet air to a gas turbine plant, comprising:
a. a gas turbine that includes a gas turbine air inlet;
b. an air cooler disposed adjacent the gas turbine air inlet, the air cooler having an air inlet, an air outlet, a liquid water inlet and a liquid water outlet; and
c. a chilled water circulation system comprising a first duplex chiller and a second duplex chiller, each of the duplex chillers having an inlet and outlet, wherein the outlet of the first duplex chiller is in fluid communication with the water inlet of the second duplex chiller, the outlet of the second duplex chiller is in fluid communication with the air cooler, and the inlet of the first duplex chiller is in fluid communication with the water outlet of the air cooler.
0. 71. A system for chilling inlet air to a gas turbine plant, comprising
a. a gas turbine that includes a gas turbine air inlet;
b. an air cooler disposed adjacent the gas turbine air inlet, the air cooler having an air inlet, an air outlet, a liquid water inlet and a liquid water outlet;
c. a thermal energy storage tank having a warm water port and a cool water port, and
d. a first water circulation system comprising a duplex chiller with a duplex chiller outlet in fluid communication with the cool water port of the thermal energy storage tank, and a duplex chiller inlet in fluid communication with the warm water port of the thermal energy storage tank;
e. wherein the liquid water inlet of the air cooler is in fluid communication with the cool water port of the thermal energy storage tank and the liquid water outlet of the air cooler is in fluid communication with the warm water port of the thermal energy storage tank.
0. 50. A system for chilling inlet air to a gas turbine plant, comprising:
a. a gas turbine that includes a gas turbine air inlet;
b. an air cooler disposed adjacent the gas turbine air inlet, the air cooler having an air inlet, an air outlet, a liquid water inlet and a liquid water outlet; and
c. a water circulation system having water disposed therein, the water circulation system comprising a first chiller having a first chiller inlet and outlet, a second chiller having a second chiller inlet and outlet, a third chiller having a third chiller inlet and outlet, wherein the outlet of the first chiller is in fluid communication the inlet of the second chiller and the outlet of the second chiller is in fluid communication with the inlet of the third chiller such that the first, second and third chillers are arranged in series, the outlet of the third chiller is in fluid communication with the water inlet of the air cooler, and the inlet of the first chiller is in fluid communication with the water outlet of the air cooler.
0. 57. A system for chilling inlet air to a gas turbine plant, comprising:
a. a gas turbine that includes a gas turbine air inlet;
b. an air cooler disposed adjacent the gas turbine air inlet, the air cooler having an air inlet, an air outlet, a liquid water inlet and a liquid water outlet;
d. a water circulation system comprising water disposed therein, a first chiller having a first chiller inlet and outlet and a second chiller having a second chiller inlet and outlet, wherein the outlet of the first chiller is in fluid communication with the inlet of the second chiller such that the first and second chillers are arranged in series, the outlet of the second chiller is in fluid communication with the air cooler, wherein the water has a first temperature at the inlet of the first chiller and a second temperature, cooler than the first temperature, at the inlet to the second chiller and the water has a third temperature at the second chiller outlet that is cooler than the second temperature; and
e. an additive disposed in the water within the water circulation system, wherein the additive is capable of reducing the freezing point of water.
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.
1. A method of chilling inlet air to a combined cycle gas turbine plant, comprising:
a. a gas turbine that includes a gas turbine inlet and a steam turbine;
b. providing a system of circulating liquid chilling water including a chilling system that includes a first chiller;
c. 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;
d. 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. chilling the inlet air by 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. 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 plant.
0. 58. A system for chilling inlet air to a gas turbine plant, comprising:
a. a gas turbine that includes a gas turbine air inlet;
b. an air cooler disposed adjacent the gas turbine air inlet, the air cooler having an air inlet, an air outlet, a liquid water inlet and a liquid water outlet;
c. a chilled water circulation system comprising a first water chiller and a second water chiller, each of the chillers having an evaporator with an inlet and outlet, wherein the outlet of the first water chiller evaporator is in fluid communication with the water inlet of the second water chiller evaporator, the outlet of the second water chiller evaporator is in fluid communication with the liquid water inlet of the air cooler, and the inlet of the first water chiller evaporator is in fluid communication with the water outlet of the air cooler; and
d. a condenser water circuit, wherein each of the first and second water chillers has a condenser water inlet and outlet, wherein the condenser water inlet of the first water chiller is in fluid communication with the condenser water outlet of the second water chiller, whereby water flow through the condenser water circuit is in a direction opposite of chilled water flow through the chilled water circulation system.
0. 76. A system for chilling inlet air to a gas turbine plant, comprising:
a. a gas turbine that includes a gas turbine air inlet;
b. an air cooler disposed adjacent the gas turbine air inlet, the air cooler having an air inlet, an air outlet, a liquid water inlet and a liquid water outlet;
c. a thermal energy storage tank having a warm water port and a cool water port and a water reservoir defined within the tank, the reservoir having an upper first portion and a lower second portion, wherein the warm water port is in fluid communication with the first portion of the reservoir and the cool water port is in fluid communication with the second portion of reservoir; and
d. a first water circulation system comprising a first chiller having a first chiller inlet and outlet and a second chiller having a second chiller inlet and outlet, wherein the outlet of the first chiller is in fluid communication the inlet of the second chiller such that the first and second chillers are arranged in series, the outlet of the second chiller is in fluid communication with the cool water port, and the inlet of the first chiller is in fluid communication with the warm water port of the thermal energy storage tank,
e. wherein the liquid water inlet of the air cooler is in fluid communication with the cool water port and the liquid water outlet of the air cooler is in fluid communication with the warm water port.
0. 65. A method for chilling inlet air to a gas turbine, comprising:
providing a chilled water circuit having a first water chiller and a second water chiller, the first and second water 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 water chiller and then through the first water 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 water chiller, wherein the chilled water passing through the first water 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 water chiller through the second water 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; and
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.
0. 21. A system for chilling inlet air to a gas turbine plant, comprising:
a. a gas turbine that includes a gas turbine air inlet;
b. an air cooler disposed adjacent the gas turbine air inlet, the air cooler having an air inlet, an air outlet, a liquid water inlet and a liquid water outlet;
c. a thermal energy storage tank having a warm water port and a cool water port and a water reservoir defined within the tank, the reservoir having an upper first portion and a lower second portion, wherein the warm water port is in fluid communication with the first portion of the reservoir and the cool water port is in fluid communication with the second portion of reservoir; and
d. a first water circulation system comprising a first chiller having a first chiller inlet and outlet and a second chiller having a second chiller inlet and outlet, wherein the outlet of the first chiller is in fluid communication the inlet of the second chiller such that the first and second chillers are arranged in series, the outlet of the second chiller is in fluid communication with the cool water port, and the inlet of the first chiller is in fluid communication with the warm water port of the thermal energy storage tank,
e. wherein the liquid water inlet of the air cooler is in fluid communication with the second portion of the reservoir and the liquid water outlet of the air cooler is in fluid communication with the first portion of the reservoir.
0. 53. A system for chilling inlet air to a gas turbine plant, comprising:
a. a gas turbine that includes a gas turbine air inlet;
b. an air cooler disposed adjacent the gas turbine air inlet, the air cooler having an air inlet, an air outlet, a liquid water inlet and a liquid water outlet;
c. a thermal energy storage tank having a warm water port and a cool water port and a water reservoir defined within the tank, the reservoir having an upper first portion and a lower second portion, wherein the warm water port is in fluid communication with the first portion of the reservoir and the cool water port is in fluid communication with the second portion of reservoir;
d. a water circulation system, the water circulation system comprising a first chiller, the first chiller having a first chiller inlet and outlet, wherein the outlet of the first chiller is in fluid communication with the cool water port, and the inlet of the first chiller is in fluid communication with the warm water port of the thermal energy storage tank;
e. a sensor system having at least one sensor adjacent the air outlet of the air cooler; and
f. a control system disposed to alter a characteristic of the water in the water circulation system based on the sensor system and a first predetermined set point,
g. a pump system having a pump inlet, wherein the pump inlet is in fluid communication with the second portion of the reservoir and the liquid water outlet of the air cooler is in fluid communication with the first portion of the reservoir.
0. 8. A system for chilling inlet air to a gas turbine plant, comprising:
a. a gas turbine that includes a gas turbine air inlet;
b. an air cooler disposed adjacent the gas turbine air inlet, the air cooler having an air inlet, an air outlet, a liquid water inlet and a liquid water outlet;
c. a thermal energy storage tank having a warm water port and a cool water port and a water reservoir defined within the tank, the reservoir having an upper first portion and a lower second portion, wherein the warm water port is in fluid communication with the first portion of the reservoir and the cool water port is in fluid communication with the second portion of reservoir;
d. a first water circulation system comprising a first chiller and a first pump system, the first chiller having a first chiller inlet and outlet, wherein the outlet of the first chiller is in fluid communication with the cool water port, and the inlet of the first chiller is in fluid communication with the warm water port of the thermal energy storage tank, the first pump system having a first pump inlet and first pump outlet, wherein the first pump system is in fluid communication with the first chiller,
e. wherein the first pump inlet is in fluid communication with the second portion of the reservoir and the liquid water outlet of the air cooler is in fluid communication with the first portion of the reservoir, and
f. a second water circulation system comprising a variable speed pump system having a variable speed pump, wherein variable speed pump system is in fluid communication with the second portion of the reservoir and the liquid water inlet of the air cooler.
2. The method of
3. The method of
4. The method of
6. The method of
7. The method of
0. 9. The system of claim 8, wherein the first and second water circulation systems comprise water disposed therein, wherein the water in the first water circulation system has a first temperature at the inlet of the first chiller and a second temperature, cooler than the first temperature, at the outlet to the first chiller.
0. 10. The system of claim 9, further comprising an additive disposed in the water within the first and second water circulation systems, wherein the additive is capable of reducing the freezing point of water.
0. 11. The system of claim 8, wherein the first water circulation system further comprises a second chiller arranged in parallel with the first chiller.
0. 12. The system of claim 8, wherein the first water circulation system further comprises a second chiller arranged in series with the first chiller.
0. 13. The system of claim 8, wherein the first chiller is a duplex chiller.
0. 14. The system of claim 8, wherein the variable speed pump system comprises at least two variable speed pumps in parallel.
0. 15. The system of claim 8, further comprising a sensor system having at least one sensor adjacent the air outlet of the air cooler and a control system disposed to alter a characteristic of the second water circulation system based on the sensor system.
0. 16. The system of claim 15, wherein the sensor comprises a temperature sensor.
0. 17. The system of claim 15, wherein the sensor comprises a relative humidity sensor.
0. 18. The system of claim 15, wherein the sensor system comprises a relative humidity sensor and a temperature sensor.
0. 19. The system of claim 15, wherein the control system is disposed to alter the temperature of water in the second water circulation system based on the sensor system.
0. 20. The system of claim 15, wherein the control system is disposed to alter the flow rate of water within the second water circulation system based on the sensor system.
0. 22. The system of claim 21, wherein the first water circulation system comprises water disposed therein, wherein the water has a first temperature at the inlet of the first chiller and a second temperature, cooler than the first temperature, at the inlet to the second chiller and the water has a third temperature at the second chiller outlet that is cooler than the second temperature.
0. 23. The system of claim 22, further comprising an additive disposed in the water within the first water circulation system, wherein the additive is capable of reducing the freezing point of water.
0. 24. The system of claim 21, further comprising a second water circulation system, the second water circulation system comprising a variable flow pump system, the variable flow pump system having a pump inlet and pump outlet, wherein the pump outlet is in fluid communication with the liquid water inlet of the air cooler.
0. 25. The system of claim 24, wherein the variable flow pump system comprises a variable speed pump.
0. 26. The system of claim 24, wherein the variable flow pump system comprises at least two variable speed pumps in parallel.
0. 27. The system of claim 21, wherein the first and second chillers together comprise a single duplex chiller.
0. 28. The system of claim 21, further comprising a sensor system having at least one sensor adjacent the air outlet of the air cooler and a control system disposed to alter a characteristic of the water in the water circulation system based on the sensor system.
0. 29. The system of claim 28, wherein the sensor comprises a temperature sensor.
0. 30. The system of claim 28, wherein the sensor comprises a relative humidity sensor.
0. 31. The system of claim 28, wherein the sensor system comprises a relative humidity sensor and a temperature sensor.
0. 32. The system of claim 28, wherein the control system is disposed to alter the temperature of water in the water circulation system based on the sensor system.
0. 33. The system of claim 28, wherein the control system is disposed to alter the flow rate of water within the water circulation system based on the sensor system.
0. 35. The system of claim 34, the chilled water circulation system further comprising water disposed therein, wherein the water in the chilled water circulation system has a first temperature at the inlet of the first duplex chiller and a second temperature cooler than the first temperature at the first duplex chiller outlet.
0. 36. The system of claim 35, further comprising an additive disposed in the water within the water circulation system, wherein the additive is capable of reducing the freezing point of water.
0. 37. The system of claim 34, wherein at least one of the duplex chillers comprises a first chiller and a second chiller.
0. 38. The system of claim 34, further comprising a condenser water circuit, wherein each of the first and second duplex chillers has a condenser water inlet and outlet, wherein the condenser water inlet of the first duplex chiller is in fluid communication with the condenser water outlet of the second duplex chiller, whereby water flow through the condenser water circuit is in a direction opposite of chilled water flow through the first chiller inlet and outlet.
0. 39. The system of claim 34, further comprising a variable flow pump system, the variable flow pump system having a pump inlet and pump outlet, wherein the pump outlet is in fluid communication with the liquid water inlet of the air cooler.
0. 40. The system of claim 39, wherein the variable flow pump system comprises a variable speed pump.
0. 41. The system of claim 39, wherein the variable flow pump system comprises at least two variable speed pumps in parallel.
0. 42. The system of claim 34, further comprising a sensor system having at least one sensor adjacent the air outlet of the air cooler and a control system disposed to alter a characteristic of the water in the water circulation system based on the sensor system.
0. 43. The system of claim 42, wherein the sensor comprises a temperature sensor.
0. 44. The system of claim 42, wherein the sensor comprises a relative humidity sensor.
0. 45. The system of claim 42, wherein the sensor system comprises a relative humidity sensor and a temperature sensor.
0. 46. The system of claim 42, wherein the control system is disposed to alter the temperature of water in the water circulation system based on the sensor system.
0. 47. The system of claim 42, wherein the control system is disposed to alter the flow rate of water within the water circulation system based on the sensor system.
0. 48. The system of claim 47, further comprising a variable speed pump.
0. 49. The system of claim 47, further comprising at least two variable speed pumps in parallel.
0. 51. The system of claim 50, the water circulation system further comprising water disposed therein, wherein the water has a first temperature at the inlet of the first chiller and a second temperature, cooler than the first temperature, at the inlet to the second chiller and the water has a third temperature at the second chiller outlet that is cooler than the second temperature and the water has a fourth temperature at the third chiller outlet that is cooler than the third temperature.
0. 52. The system of claim 50, further comprising a thermal energy storage tank having a warm water port and a cool water port and a water reservoir defined within the tank, the reservoir having an upper first portion and a lower second portion, wherein the warm water port is in fluid communication with the first portion of the reservoir, the cool water port is in fluid communication with the second portion of reservoir, the warm water port is in fluid communication with the third chiller inlet and the cool water port is in fluid communication with the third chiler outlet.
0. 54. The system of claim 53, wherein the sensor comprises a temperature sensor.
0. 55. The system of claim 53, wherein the sensor comprises a relative humidity sensor.
0. 56. The system of claim 53, wherein the sensor system comprises a relative humidity sensor and a temperature sensor.
0. 59. The system of claim 58, wherein the condenser water inlet and outlet of the first water chiller are comprised of a first condenser and the condenser water inlet and outlet of the second water chiller are comprised of a second condenser.
0. 60. The system of claim 58, wherein the first and second water chillers comprise a duplex chiller.
0. 61. The system of claim 59, wherein the first and second water chillers comprise a duplex chiller.
0. 62. The system of claim 59, further comprising a cooling tower having a water inlet and water outlet, wherein the water inlet of the cooling tower is in fluid communication with a water outlet of the condenser of the first chiller and the water outlet of the cooling tower is in fluid communication with a water inlet of the condenser of the second chiller.
0. 63. The system of claim 58, further comprising a thermal energy storage tank having a warm water port and a cool water port and a water reservoir defined within the tank, the reservoir having an upper first portion and a lower second portion, wherein the warm water port is in fluid communication with the first portion of the reservoir and the cool water port is in fluid communication with the second portion of reservoir, wherein the outlet of the second chiller is in fluid communication with the cool water port, and the inlet of the first chiller is in fluid communication with the warm water port of the thermal energy storage tank.
0. 64. The system of claim 63, wherein the cool water port is disposed between the outlet of the evaporator of the second chiller and the liquid water inlet of the air cooler and the warm water port is disposed between the inlet of the first chiller evaporator and the water outlet of the air cooler.
0. 66. The system of claim 24, wherein the variable flow pump system comprises a flow control valve.
0. 67. The system of claim 39, wherein the variable flow pump system comprises a flow control valve.
0. 68. The system of claim 59, wherein the first and second water chillers comprise a duplex chiller, whereby the first condenser is joined directly to the second condenser such that both the first and second condensers share the same condenser tubes.
0. 69. The system of claim 58, wherein the first and second water chillers comprise a duplex chiller whereby the first evaporator is joined directly to the second evaporator such that both the first and second evaporators share the same evaporator tubes.
0. 70. The method of claim 65 wherein the wherein the first and second chillers together comprise a single duplex chiller.
0. 72. The system of claim 71 wherein the duplex chiller comprises a centrifugal water chiller.
0. 73. The system of claim 72 wherein the centrifugal water chiller is a Trane duplex centrifugal CDHF water chiller.
0. 74. The system of claim 71, wherein the duplex chiller has a first condenser that is joined directly to a second condenser such that both the first and second condensers share the same condenser tubes.
0. 75. The system of claim 71, wherein the duplex chiller has a first evaporator that is joined directly to a second evaporator such that both the first and second evaporators share the same evaporator tubes.
0. 77. The system of claim 76 whereby the first and second chillers are comprised of a single duplex chiller having two compressors and two refrigerant circuits.
0. 78. The system of claim 77 whereby the duplex chiller comprises two evaporators arranged in series with circulating evaporator water at a first stage having a first temperature, circulating evaporator water at a second stage having a second temperature lower than the circulating evaporator water first temperature and circulating evaporator water at a third stage having a third temperature lower than the circulating evaporator water second temperature.
0. 79. The system of claim 77 whereby the duplex chiller comprises two condensers arranged in series with circulating condenser water having a first temperature at a first stage, circulating condenser water at a second stage having a second temperature higher than the circulating condenser water first temperature and circulating condenser water at a third stage having a third temperature higher than the circulating condenser water second temperature.
0. 80. The system of claim 77 whereby the duplex chiller comprises a counterflow, wherein evaporator water flow is in a direction opposite to condenser water flow.
0. 81. The system of claim 77 wherein the duplex chiller comprises a centrifugal water chiller.
0. 82. The system of claim 81 wherein the centrifugal water chiller is a Trane duplex centrifugal CDHF water chiller.
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This application
Q=mCpΔT=mΔh
Qcoil=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 (Toa), and the heat transfer coefficient (Cp) 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
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
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
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 (
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
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
TABLE 2
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
Circulating Water
Circulating Water Inlet
Outlet Temperature
Temperature (° F.) 58b
(° F.) 58a
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
TABLE 2
Temperature Profile through Water Chillers at 4620 gpm
(70% of fall flow) & Part Load (70 F. Ambient Wet Bulb Temp) &
50 F. T2 Temp
Circulating Water
Circulating Water Inlet
Outlet Temperature
Temperature (° F.) 58b
(° F.) 58a
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 (
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
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
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
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
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