CN1625648A - Equipment and method for cooling combustion turbine inlet air using liquid hydrocarbon fuel - Google Patents

Abstract

Liquid fuel for a power plant is vaporized against a heat-exchange fluid, cooling the fluid. A re-circulation circuit enables cooled fluid to be re-directed back for further cooling, when desired. The cooled fluid is used to cool the inlet air for a combustion turbine. Some of the cooled fluid is periodically directing to the bottom of a stratified tank, from which it can be drawn during times when the need for or value of cooling the inlet air is higher. The fluid is warmed as its cools the inlet air, and may be returned for use in vaporizing additional fuel, or returned to the top of the stratified tank.

Description

Apparatus and method for cooling gas turbine inlet air using liquid hydrocarbon fuel

Background of the invention

This invention relates generally to power plants, and more particularly to power plants using gas turbines powered by hydrocarbon gases, such as natural gas or propane, to generate electricity.

The hydrocarbon gases used to power the above equipment are often provided in liquefied form and need to be vaporized before use. Vaporization is traditionally achieved by burning some fuel or heating the liquid by other heat sources.

The performance of a gas turbine is affected by many factors. One of the factors is ambient air pressure. Air pressure is in turn affected by altitude, weather-induced changes in air pressure, and associated pressure losses from air flow through inlet ducts, filters, etc.

Gas turbine performance is also affected by inlet air temperature. Gas turbines typically exhibit a loss of output power if the ambient air temperature increases. The performance rating of a gas turbine is defined as 100% when operating at ISO conditions of 15°C (59°F) and sea level. Although the actual relationship between temperature and performance varies, power output typically drops to 80 or 85% of its ISO rated output if the inlet air temperature rises to around 35°C (95°F). On the other hand, if the inlet air temperature is only 7°C (45°F), the power output can be increased to 105% of its ISO rated output value, a 30% improvement over its high temperature performance.

The electrical power (and current value) demand is often greatest when the air conditioning load is at its maximum and the ambient air temperature is high. Co-pending application 09/591 250 (filed 09.06.2000) describes how to use heat exchange fluid stored in stratified tanks to cool the inlet air of such equipment.

Summary of the invention

The invention effectively captures the "cooling capacity" of the refrigerated liquid hydrocarbon fuel and uses it to cool the inlet air entering the gas turbine. The invention enables power plant equipment to operate more efficiently and at a lower cost by reducing the need to burn part of the fuel for vaporization or wasting "cold" relative to other heat sources, while also reducing the need for separate cooling sources .

Refrigerated liquid hydrocarbons that fuel power generating equipment are vaporized in a vaporization chamber against a heat exchange fluid. The heat exchange fluid can be any liquid of various types, including water or methanol/water solution. During vaporization, the heat exchange fluid is cooled. A recirculation loop connecting the upstream and downstream sides of the vaporization chamber may be provided for selectively recirculating the cooled heat exchange fluid back into the vaporization chamber for further cooling.

Periodically some cooled heat exchange fluid is introduced to the storage device. The heat exchange fluid is preferably stored under stratified conditions, such that the cooled heat exchange fluid is directed to the bottom of the storage device. When fluid is needed to vaporize liquid hydrocarbon fuel, it is directed from the top of the storage facility.

The cooled heat exchange fluid is sent to the inlet air cooler connected to the gas turbine. The cooled heat exchange fluid can come directly from the vaporization chamber or storage device or a combination of both. The heat exchange fluid used to cool the intake air may periodically draw cooled heat exchange fluid from storage. Regardless, the inlet air cooler cools the gas turbine inlet air, improving gas turbine efficiency.

The heat exchange fluid warms as it cools the intake air. The warmed heat exchange fluid can be returned to the vaporization chamber for vaporization of other liquefied fuel. The warmed heat exchange fluid is periodically recycled to the storage vessel. When the heat exchange fluid is stored under stratified conditions, the warmed heat exchange fluid is recycled to the upper level of the storage device, from where it is drawn to the vaporization chamber for use as needed.

Brief description of the drawings

The invention can be more clearly understood with reference to the accompanying drawings.

Figure 1 is a schematic diagram of a power plant incorporating an embodiment of the present invention.

Detailed description of the drawings

The power plant shown in Figure 1 comprises a set of vaporization chambers 10, storage means 12 in the form of stratified tanks, and a pair of inlet air coolers 14 for a pair of gas turbines 16. Gas turbines run on hydrocarbon fuels, such as natural gas or propane. Fuels are provided in refrigerated liquid form, such as liquefied natural gas (LNG) or liquefied petroleum gas (LPG).

Before the liquefied hydrocarbon fuel can be fed to the gas turbine 16, it must be vaporized from a liquid state to a gaseous state. The illustrated vaporization chamber 10 can be used to vaporize refrigerated fuel. Vaporization is achieved by contacting the liquid fuel with a warmer heat exchange fluid without freezing the heat exchange fluid. In some applications, the vaporization chamber as shown may be a vertical shell and tube heat exchanger designed to handle a flow rate of 1200 ^m3 /hr of heat exchange fluid. Other types and sizes of heat exchangers can also be used, and the number of heat exchangers used can vary.

Various liquids can be used as heat exchange fluids. Under certain conditions, water may be used. Sometimes, the heat exchange fluid may be a solution comprising methanol and water, such as a solution comprising 30% by weight methanol and 70% by weight water. Other possibilities include solutions containing one or more of sodium chloride, calcium chloride, potassium acetate, potassium formate, potassium nitrate, sodium nitrate, potassium nitrite, ethylene glycol, propylene glycol, ammonia or anhydrous ammonia. While there are times when it is preferable to use a single heat exchange fluid throughout the system, there are other conditions where it is preferable to use different heat exchange fluids in different parts of the system.

In the illustrated embodiment of the invention, refrigerated liquid fuel enters vaporization chamber 10 through supply line 20 at about -160°C (-260°F). In the vaporization chamber, refrigerated liquid fuel is placed in thermal contact with a relatively warm heat exchange fluid that is sent to the vaporization chamber through warm liquid supply line 22 . In this case, the temperature of the heat exchange fluid in the warm fluid supply line is about 20°C (70°F), and the heat exchange of the warm heat exchange fluid with the liquid fuel vaporizes the frozen liquid fuel into a gaseous fuel while allowing Heat exchange fluid cooling. The gaseous fuel exits the vaporization chamber through a gas line 24 and enters the gas turbine 16 . Cooled heat exchange fluid exits the vaporization chamber through lower stage supply conduit 26 . Here, the temperature of the gaseous fuel is about 10°C (50°F), and the temperature of the cooled heat exchange fluid is about 0°C (30°F).

Intermediate fluid line 28 can be used to direct cooled heat exchange fluid to stratified tank 12 or inlet air cooler 14 . In some cases, the cooled heat exchange fluid temperature may be higher than required. Thus, it is necessary to provide a secondary cooler for cooling the heat exchange fluid to a temperature lower than that provided by the single pass through the vaporization chamber 10 . A useful way to further cool the heat exchange fluid is to use a recirculation loop as shown.

The recirculation loop as shown includes a vaporization chamber pump 30 and recirculation conduit 32 which can be used to selectively recirculate cooled heat exchange fluid back to the upstream side of the vaporization chamber 10 for further cooling.

In the illustrated embodiment of the invention, recirculation line 32 includes a separate conduit for each vaporization chamber 10 . Each conduit has a recirculation valve 44 for controlling the flow of heat exchange fluid to its respective vaporization chamber. Recirculating some of the cooled heat exchange fluid through the vaporization chamber a second time causes the temperature of the cooled heat exchange fluid in the lower stage supply line 26 to decrease.

The inlet air cooler 14 is adapted to cool the inlet air of the gas turbine 16 with a cooled heat exchange fluid. For example the air cooler may be a finned tube heat exchanger. Cooled heat exchange fluid may be provided from intermediate line 28 . Additional air coolers can be used to supplementally cool the gas turbine inlet air.

In the illustrated embodiment of the invention, ambient air enters the inlet air cooler 16 via conduit 46 . In some cases, the temperature of the ambient air may be 35°C (95°F) or higher. In the air cooler, ambient air is in thermal contact with relatively cooler heat exchange fluid from intermediate fluid supply line 28 . An air cooler valve 50 on the intermediate supply line 28 controls the flow rate of the heat exchange fluid. The type and location of the air cooler valves can vary.

In inlet air cooler 14, warm ambient air from conduit 46 is in thermal contact with cooler heat exchange fluid from intermediate stage line 28, cooling the inlet air while heating the heat exchange fluid. Cooled inlet air, preferably at a temperature of 5°C (45°F) or less, is provided to the gas turbine 16 through the turbine inlet 52 . Using inlet air at around 5°C (45°F) instead of 35°C (95°F) can increase gas turbine power output by 30% or more.

Warm heat exchange fluid exits the inlet air cooler 14 through return line 54 . In the illustrated embodiment of the invention, the temperature of the warm heat exchange fluid in the return line is around 20°C (70°F). A branch of the return line returns to the warm fluid supply line 22 . Another branch of the return line leads to the top of stratified tank 12 . Tank valve 56 on the branch of the return line controls how much warm heat exchange fluid is introduced into the stratified tank. The type and location of tank valves can vary.

Cooled heat exchange fluid that is not immediately used to cool the inlet air can be sent to stratified tank 12 via cold supply line 60 . The cold supply line communicates with the bottom of the stratified tank where the heat exchange fluid is stored under stratified conditions. In some cases, as indicated, tanks need to have a capacity of about 50,000 to 100,000 m ³ . In this case, the tank should be externally insulated and should include top and bottom distribution systems specially designed to enhance thermal stratification of the stored heat exchange fluid.

The cold high density fluid is stored at the bottom of the tank 12 and the warm low density fluid is stored at the top of the tank, thereby achieving stratified storage. When temperatures need to be below about 4°C (39°F), the use of fluids other than fresh water is required because the temperature/density relationship of fresh water makes it difficult to maintain stratified conditions below these temperatures.

Storage valve 62 on cold supply line 60 can be used to control when and how much cooled heat exchange fluid is introduced to stratified tank 12 . Typically, the cooled heat exchange fluid is sent to storage during the evening hours when the value or amount of air required to cool the gas turbine 16 inlet air is low. The cooled heat exchange fluid sent to the stratified tank forms a reserve of cooled heat exchange fluid that can be drawn for use when the vaporization of the refrigerated liquid fuel does not provide sufficient cooling to cool the inlet gas to the desired level.

Warm heat exchange fluid can be drawn from the top of stratified tank 12 through return line 54 if desired. Pumps can be provided if required. Warm heat exchange fluid can be introduced into the vaporization chamber 10 to be cooled, and then returned to the bottom of the stratified tank after cooling.

Reserve cooled heat exchange fluid can be withdrawn from the bottom of stratified tank 12 and directed to inlet air cooler 14 through makeup supply line 64 leading from the bottom of the tank to intermediate line 28 . A secondary valve 66 on the make-up supply line controls when and how much cooled heat exchange fluid is drained from the stratified tank. A secondary pump 68 is preferably provided on the supplemental supply line to provide the required pressure for the cooled heat exchange fluid withdrawn from storage. The type and location of secondary valves and secondary pumps can vary.

This detailed description is for the purpose of illustration, not limiting the scope of the invention. The full scope of the invention is set forth in the following claims.

Claims (19)

1. A method comprising the steps of: Cooling the heat exchange fluid by vaporizing the frozen liquid hydrocarbon fuel with the liquid heat exchange fluid; Periodically direct some of the cooled heat exchange fluid to storage; and The gas turbine inlet air is cooled using the cooled heat exchange fluid. 2. The method of claim 1, wherein the refrigerated liquid hydrocarbon fuel is liquefied natural gas. 3. The method of claim 1, wherein the refrigerated liquid hydrocarbon fuel is liquefied petroleum gas. 4. The method of claim 1, wherein the liquid heat exchange fluid is water. 5. The method of claim 1, wherein the liquid heat exchange fluid is methanol/water solution. 6. The method of claim 1, wherein the liquid heat exchange fluid comprises sodium chloride, calcium chloride, potassium acetate, potassium formate, potassium nitrate, sodium nitrate, sodium nitrite, ethylene glycol, propylene glycol, ammonia and anhydrous ammonia A solution of at least one of them. 7. The method of claim 1, wherein the heat exchange fluid is stored under stratified conditions. 8. The method of claim 1, wherein a secondary cooler is provided to supplementally cool the heat exchange fluid. 9. The method of claim 1, wherein the cooled heat exchange fluid is periodically recirculated against the liquid hydrocarbon fuel. 10. The method of claim 1, wherein the heat exchange fluid used to cool the inlet air is periodically withdrawn from the stored cooled heat exchange fluid. 11. The method of claim 1, wherein some of the heat exchange fluid used to cool the inlet air is periodically returned to storage. 12. An apparatus comprising: a vaporization chamber for vaporizing the liquid hydrocarbon fuel against the liquid heat exchange fluid to cool the heat exchange fluid; a storage facility that receives at least some of the cooled heat exchange fluid; and A gas turbine having an inlet air cooler that utilizes cooled heat exchange fluid to cool gas turbine inlet air. 13. The apparatus of claim 12, wherein the liquid hydrocarbon fuel is liquefied natural gas. 14. The apparatus of claim 12, wherein the liquid hydrocarbon fuel is liquefied petroleum gas. 15. The apparatus of claim 12, wherein the storage device is a layered tank. 16. The apparatus of claim 12, further comprising a secondary cooler for supplemental cooling of the liquid heat exchange fluid. 17. The apparatus of claim 12, further comprising a recirculation circuit comprising a pump and a conduit for selectively recirculating the cooled heat exchange fluid back to the vaporization chamber. 18. The apparatus of claim 12, further comprising a conduit for selectively withdrawing and delivering cooled heat exchange fluid from the storage device to the inlet air cooler. 19. The apparatus of claim 12, further comprising a conduit for selectively directing heat exchange fluid from the inlet air cooler to the storage device.