Patent Description:
<CIT> discloses an absorption heat pump comprising an evaporator and an absorber that are connected with one another by means of a conduit for providing water vapor from the evaporator to the absorber. The absorber is in addition in flow connection with a regenerator device. The evaporator is fluidically connected to an indoor cooling unit. Make-up water may be supplied by a separate water supply passage into the evaporator.

<CIT> discloses a gas turbine intake air cooling apparatus comprising an air cooler and an absorber that are in communication with one another. For evaporation water films are created flowing down into heat transfer tubes, thereby cooling combustion air of a gas turbine. The water vapor is absorbed by the absorber and subsequently condensed by means of a condenser.

Other cooling systems are, for example, known from <CIT> or <CIT>. In these systems a condenser is provided as part of the cooling system. Such systems are complex.

A large number of industries require cooled air that is also dry. Examples include beverage manufacturers such as breweries; as well as food packaging and storage facilities. Moreover, homes, apartment buildings, municipal buildings, and countless office buildings and indoor-recreational facilities throughout the world require air-conditioning systems that can provide a highly controlled environment, in terms of air temperature and humidity.

Yet another important use for cooled air can be found in the case of "air-breathing" engines, such as gas turbines. Gas turbine engines are used in many applications, including aircraft, power generation, and marine systems. (The desired engine operating characteristics vary, of course, from application to application). When these types of engines operate in an environment in which the ambient temperature is reduced in comparison to other environments, the engines are usually capable of operating with a higher shaft horse power (SHP) and an increased output, without increasing the core engine temperature to unacceptably high levels. Conversely, when the ambient temperature (air inlet temperature) is increased, the efficiency of the engine can decrease dramatically. For example, for certain types of gas turbine engines, a <NUM>°F (<NUM>) increase in ambient temperature can cause more than a <NUM>% loss of power. Moreover, the temperature increase can lead to increased fuel consumption, as well as higher levels of NOx emissions.

To address the need for cool, dry air for all of these purposes, a large number of systems and techniques have been developed. Many of these techniques rely on vapor compression systems that take advantage of the expansion and compression of a refrigerant to provide cooling for ambient spaces. Another type of system uses a hydroscopic material, such as a desiccant, to remove water from an airstream, cooling the ambient environment. Various combinations of these systems have also been developed. Evaporative cooling techniques are especially attractive in some circumstances, in that they don't rely on energy-intensive, mechanical compression.

However, challenges remain in the design of systems based on evaporative cooling techniques - even the more advanced systems that have been developed recently. The systems are often complex, relying on a closed-loop design that often requires a condenser as part of a refrigeration unit within the system. The evaporator design can also involve some complexities, requiring at least one built-in cooling system within the unit. Furthermore, in the case of larger power generation systems now being developed, cooling systems with an even greater capacity for delivering cooled air to an engine compressor will be necessary in the future. Thus, improved systems and processes would be welcome in the art.

One embodiment of the invention is directed to a cooling system for providing chilled air according to claim <NUM>.

Another embodiment of the invention is directed to a gas turbine engine comprising the inventive cooling system.

Still another embodiment of the invention is directed to a method for providing chilled air to a gas turbine engine according to claim <NUM>.

In regard to this disclosure, any ranges disclosed herein are inclusive and combinable (e.g., compositional ranges of "up to about <NUM> wt%", or more specifically, "about <NUM> wt% to about <NUM> wt%", are inclusive of the endpoints and all intermediate values of the ranges). Moreover, the terms "first," "second," and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Moreover, approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about," is not limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value.

<FIG> is a schematic, cross-sectional view of a cooling system <NUM> according to one embodiment of the present invention. The system includes a cooling coil <NUM> that is configured to accept air at a higher temperature and then emit air at a lower temperature. The lower-temperature air can be used for a variety of purposes, as illustrated previously. Non-limiting examples include air-conditioning systems used in a wide variety of stationary locations; vehicles; machines; and other devices. In many instances, the cooling system can lower the temperature of air by about <NUM> to <NUM>, depending, of course, on the end use application.

As also explained above, one important use for the cooling system is a power generation device that requires an inflow of air, such as a gas turbine engine <NUM>, shown in <FIG>. A decrease in the temperature of the inlet air directed into compressor <NUM> can provide much greater power and efficiency for the engine. As one example for an industrial gas turbine, a cooling system like that described herein can lower the temperature of ambient air (e.g., air as hot as about <NUM>) to a temperature in the range of about <NUM>-<NUM>. For many applications, this would be referred to as "chilled" air.

Coolant coil <NUM> usually includes one or more tubes or conduits through which cold water flows, interacting with the relatively warm air, and providing the cooling effect that results in the chilled air. Cooling coils of this type are known in the art, and can often be thought of as "air-to-water heat exchangers". The transfer of heat from the air to the water results in a content of relatively warm water, as compared to the initially-cold water.

The relatively warm water from the cooling coil (along with make-up water, as described below) is directed through an evaporator <NUM>. The evaporator is usually contained within a conventional type of vacuum chamber <NUM>. (Any suitable conduit/pipe <NUM> can be used to channel the water to the evaporator). Various types of evaporators can be used for the present invention; and all perform the general function of converting at least a portion of a liquid medium into its gaseous form, i.e., by absorbing heat from the warm water. Non-limiting examples of suitable evaporator-types include falling film evaporators (e.g., falling film plate evaporators) and multiple-effect evaporators. In some preferred embodiments, the evaporator is configured to absorb enough heat from the warm water to lower the temperature of the water by at least about <NUM>. Moreover, preferred embodiments call for the evaporator itself to be configured to function in the absence of a cooling coil. Additional information regarding preferred evaporator systems is provided below. The cooled water can then be pumped back (e.g., using pump <NUM>) to the cooling coil <NUM>, for re-use, via conduit <NUM>, for example.

According to the invention, cooling system <NUM> includes an external source of make-up water <NUM>. The make-up water replenishes water lost during any cycle in operation of the system, e.g., during operation of the evaporation or absorption cycles; along with water which will be lost during passage of water or vapor through any conduits in the system. It is usually introduced from any suitable supply at ambient temperature. According to the invention, the make-up water combines with warm water exiting the cooling coil via conduit <NUM>, and the combined flow enters evaporator <NUM>. The system with an external source of make-up water can be thought of as an "open-loop system", which has advantages over a closed-loop system. For example, the open loop system is simpler in design than closed systems that may require a greater number of vacuum compartments. The open-loop design system also allows for easier integration with other components in the entire cooling system, and can be operated less expensively in some situations. The open-loop design can also exhibit a faster response to changes in various environmental conditions and material characteristics, such as water temperature; air temperature; and water vapor content.

As noted above, passage of the warm water through the evaporator results in the formation of a content of water vapor. According to the invention, the water vapor is directed to an absorber <NUM>. The absorber is contained within the same vacuum chamber <NUM> as the evaporator. Not in accordance with the invention, conduits may be used to direct the water vapor to the absorber. However, a small pressure difference between the two units (i.e., higher pressure in the evaporator, lower pressure in the absorber) is usually sufficient to direct all of the water vapor to absorber <NUM>.

In addition to accepting the water vapor, the absorber <NUM> also accommodates a flow of a concentrated desiccant <NUM>. As described below, the desiccant is carried through, directly or indirectly, from a regenerator. The desiccant comprises a material that is capable of absorbing the water vapor. Absorption of the water vapor results in an increase in the temperature of the desiccant, while also diluting the desiccant. A number of desiccants may be employed. Non-limiting examples include lithium chloride (LiCl), lithium bromide (LiBr), calcium chloride (CaCl<NUM>), zinc bromide; various alkali nitrates and ionic liquids; as well as activated carbon, zeolites, and silica gel. According to the invention, liquid desiccants, or those that can be prepared as liquids, e.g., aqueous solutions are employed. Specific examples include LiBr and LiCl. However, not in accordance with the invention, solid desiccants can be used in some instances, with steps being taken to ensure that the solid material be arranged for maximum contact with the water vapor.

As alluded to above, when the concentrated desiccant <NUM> flows through the absorber <NUM>, the desiccant absorbs the water vapor from the evaporator, and becomes diluted. In some embodiments, vapor transfer to the desiccant is enhanced by lowering the temperature of the desiccant, using an optional heat exchanger mechanism <NUM>, here incorporated into the absorber itself. Various types of heat exchangers may be used, and many comprise a series of heat exchange pipes, as depicted in <FIG>. The presence of the heat exchanger may remove enough heat so that the temperature-rise in the desiccant is not as great as in the absence of an integrated heat exchanger, as mentioned below.

The diluted desiccant, having absorbed most or all of the water from the water vapor, is then routed to a regenerator <NUM>, via any suitable conduit <NUM>. As alluded to previously, the desiccant gives off moisture in the regenerator, so that the desiccant can be used again in the absorber. Many different types of regenerators can be used. In some embodiments, they are filled or partially filled with various types of packing media <NUM> (<FIG>), through which the diluted desiccant travels in a path through the regenerator.

As a non-limiting illustration, a suitable nozzle (not shown) can be situated at or near the top end <NUM> of the regenerator, through which the desiccant can flow. The nozzle can spray droplets of the desiccant into the regenerator chamber, so that it travels in a downward path through the packing media, exiting at or near regenerator bottom <NUM>. Movement of the desiccant is enhanced by exposure to a source of external air <NUM>, which can be blown by a fan <NUM>, for example, into the regenerator. The extended residence time of the desiccant through the packing ensures maximum, desired removal of water from the desiccant. In this manner, the desiccant is re-concentrated to a desired concentration value.

In some embodiments, the heated, diluted desiccant being transported from absorber <NUM> is contacted with at least one external heat source. This will increase the temperature of the desiccant, decreasing the amount of energy needed to remove water during passage through the regenerator. In some especially preferred embodiments, the external heat source is exhaust gas that exits gas turbine engine <NUM>. As those skilled in the art understand, industrial gas turbines with a typical output rating of about <NUM> MW can emit/discharge large amounts of exhaust gas from one or more suitable thermal outlets, at temperatures in the range of about <NUM>-<NUM>. Any portion of the high-temperature exhaust gas (waste heat) can be directed along pathway <NUM> to a suitable heat exchanger <NUM> or other type of recuperator device, thereby providing further heat to the desiccant. (The remainder <NUM> of exhaust from the power generation device is usually released to the atmosphere). Any excess moisture <NUM> exiting heat exchanger <NUM> can also be released to the atmosphere. Use of the exhaust gas provides an efficient means of lowering the amount of energy needed in the regeneration stage, to recycle the desiccant. In some embodiments, a direct conduit can extend from the external heat source to the desiccant, i.e., in the absence of heat exchanger <NUM>.

The re-concentrated desiccant can then be directed back to the absorber, along pathway/conduit <NUM>, with at least one pump <NUM> often being used to move the desiccant along the pathway. However, in many embodiments, pump <NUM> may not be necessary. This is due to the fact that the regenerator unit is maintained at atmospheric pressure, while the absorber is maintained under vacuum. The pressure difference is often sufficient, on its own, to move the desiccant solution from the regenerator to the absorber. The desiccant at this stage (being returned to the absorber) is at a temperature low enough to permit it to absorb additional water vapor within the absorber, thereby completing the cycle within the cooling system.

Additional features may also be present in the cooling system of <FIG>. In some embodiments, a pump or compressor <NUM> may be used to pump out gasses that might interfere with operations going on within vacuum chamber <NUM>. For example, the pump may be used to continuously remove non-dissolvable gasses (i.e., gasses other than water vapor), such as nitrogen, oxygen, and hydrogen.

In other embodiments, a cooling tower <NUM> can be incorporated into the absorber section of the cooling system. The cooling tower can be supplied from a feed water source <NUM>, and can be connected to the absorber through entry line <NUM> and exit line <NUM>. In this manner, the cooling tower circuit functions to remove additional heat resulting from the absorption of water vapor in the absorber. (Feed water source <NUM> can also be supplied from make-up water source <NUM>, through appropriate conduits that are not illustrated).

In some embodiments, particular types of evaporators and absorbers are preferred for the cooling system <NUM>. <FIG> depicts a combined evaporator-absorber unit contained within a suitable vacuum chamber <NUM>. The absorber <NUM> includes a set of heat transfer tubes <NUM>, usually concentric, and surrounding evaporator <NUM>, which includes a central region <NUM>. The tubes within the absorber accelerate the absorption of water vapor from the evaporator.

The evaporator <NUM> includes at least one platform or layer of a porous material, such as paper, plastic, cellulose. In this illustrative embodiment (<FIG>), three porous platforms are depicted as an illustration: upper platform <NUM>, middle platform <NUM>, and lower platform (e.g., at the base) <NUM>. The platforms are positioned to accommodate the passage of water droplets formed from the warm water flowing from the cooling coil. The shape, thickness, and location of each platform will be determined by various factors. They include: the amount of warm water entering the evaporator; the shape and opening size of the supply nozzle (mentioned below); and the degree of mixing that is required to enhance water evaporation and temperature reduction in the water.

As shown in <FIG>, the warm water from a cooling coil (not shown) is directed into the evaporator/absorber via conduit <NUM>, in the manner described previously. A supply of make-up water <NUM> is also directed to the evaporator/absorber, by way of the same conduit as the warm water, or, not in accordance with the invention, by way of a separate conduit. The water is preferably introduced through nozzle <NUM>.

As the water leaves the nozzle, it usually becomes super-heated, due to the sudden drop in pressure. The super-heated water breaks up into droplets <NUM>, and some portion of the water is converted into vapor, due to vigorous boiling. As alluded to above for the illustrated embodiment, the water droplets first contact upper platform <NUM>, and this initial impact can enhance evaporation, e.g., by reducing a temperature difference that may exist between the central "core" of each water droplet, and its outer surface.

In the illustrated embodiment of <FIG>, the water droplets pass through a succession of porous platforms <NUM>, <NUM>, and <NUM>. In this manner, a substantial amount of heat is released from the warm water, and the temperature of the water becomes cool enough for recirculation back to the cooling coil, via conduit <NUM>. The platforms also advantageously minimize the amount of water that might otherwise splash into absorber <NUM>. In this embodiment, the concentrated desiccant solution from the regenerator (not shown) is directed to the absorber <NUM>, usually through conduit <NUM>. Within vacuum chamber <NUM>, the desiccant comes into contact with the water vapor from evaporator <NUM>. In the manner described above, the desiccant absorbs the water vapor and becomes diluted, and can then be directed back to the regenerator through conduit/pathway <NUM>, depicted in simple form. The heat from the absorption can be released to the cooling water from the cooling tower (not shown in this figure), as described previously. Pathway arrows <NUM> and <NUM> provide a simplistic depiction of a water pathway into and out of the absorber/evaporator system, respectively.

One key advantage for the evaporator depicted in <FIG> is that the central region <NUM> of evaporator <NUM> is free of heat exchange tubes, and is instead based on a stream of water droplets moving through a pattern of porous structures. In contrast, conventional evaporator systems require heat exchange tubes in the central area of the evaporator. The "tubeless" evaporator exhibits less thermal resistance than a conventional evaporator, since bundles of tubes can be the source of considerable thermal resistance. Elimination of the tubes can also reduce the cost of the evaporator.

Another advantage residing in the overall cooler system design of the present invention is the absence of a condenser for condensing water that is directed through the evaporator, as described previously. In this regard, the cooling system is simplified as compared to some of the prior art systems, which always require the use of a condenser device. The elimination of this type of condenser device can also decrease the overall cost of the system and process.

Yet anther advantage of this cooling system design lies in the fact that the thermal resistance between the processed air and the refrigerant (water) is smaller than that present for a conventional absorption chiller. This is due in part to the fact that the refrigerant directly contacts the coolant, without any intervening metallic walls. This low-resistance design is especially useful when air entering a power generation device has to be at a very low temperature.

<FIG> is a schematic of an overall cooling system according to another embodiment of the invention. In this embodiment, multiple heat exchangers are employed along various pathways in the system. (In the figure, features and units that are similar to those of <FIG> may not be labelled). The cooling system <NUM> includes cooling coil <NUM>, serving the function described previously, e.g., supplying cold air to gas turbine engine <NUM>, or another type of engine or device requiring such air. The warm air and make-up water is directed through evaporator <NUM>, contained within a vacuum chamber along with absorber <NUM>. The absorber also accommodates the flow of desiccant <NUM>, capable of absorbing water moisture. As noted previously, the desiccant becomes diluted, and often rises in temperature.

In the embodiment of <FIG>, the relatively warm, diluted desiccant is divided into two streams, <NUM> and <NUM> (shown in truncated form at two locations of the figure, for the sake of simplicity). First stream <NUM> (the "A" stream) enters a first heat exchanger <NUM>, where the desiccant absorbs additional heat from another desiccant stream <NUM>, described below, which is a portion of the return-stream from the regenerator. (The content and amount of flow through the various streams in the cooling system are controlled in a manner which substantially balances water flow and desiccant flow into and out of the absorber and evaporator units).

The desiccant stream, now residing at a higher temperature after exiting heat exchanger <NUM>, is directed along pathway <NUM>, to a second heat exchanger <NUM>. The second heat exchanger also receives heat from an external source <NUM>, e.g., gas turbine exhaust, as in <FIG>, thereby "boosting" the temperature of the desiccant, which can be advantageous. In some embodiments, as shown in <FIG>, heat exchanger <NUM> and external heat source <NUM> can constitute an intermediate cooling loop <NUM>, with the aid of pump <NUM>.

After leaving heat exchanger <NUM>, the diluted desiccant is then routed to regenerator <NUM>. As described above for other embodiments, the desiccant comes into contact with external air in the regenerator, and gives off moisture, so that it can be re-used in its primary function. After leaving regenerator <NUM>, the concentrated desiccant is divided into two streams, <NUM> and <NUM>.

First return stream <NUM> is directed to pathway <NUM>, to be mixed with the diluted regenerator material, prior to its entry into heat exchanger <NUM>. Second return stream <NUM> is directed back to heat exchanger <NUM>, to reject at least a portion of its heat content. The resulting stream from heat exchanger <NUM> is then combined with incoming, second stream <NUM> (the "B" stream noted above), and directed to third heat exchanger <NUM>. As the desiccant is passed through this heat exchanger, it rejects additional heat to the fluid on the opposite side (the "cold side") of the heat exchanger. The relatively cold desiccant is then directed through pathway <NUM> to the absorber, to renew its function of absorbing water moisture. Heat released from heat exchanger <NUM> can be directed to cooling tower <NUM>, which can also form a cooling loop <NUM> with this heat exchanger.

Claim 1:
A cooling system (<NUM>) for providing chilled air, comprising
(a) a cooling coil (<NUM>) configured to accept air at a higher temperature and emit air at a lower temperature by passage through a flow of coolant water in the cooling coil (<NUM>), resulting in a content of relatively warm water;
(b) an evaporator (<NUM>) contained within a vacuum chamber (<NUM>), and a conduit (<NUM>) configured to channel the relatively warm water from the cooling coil (<NUM>) to the evaporator (<NUM>); said evaporator (<NUM>) configured to allow the passage of the relatively warm water therethrough, and to absorb heat from the warm water, thereby reducing the temperature of the water, while also forming a content of water vapor;
(c) an absorber (<NUM>) contained in the vacuum chamber (<NUM>), and configured to accept the water vapor formed in the evaporator (<NUM>); while also configured to accommodate a flow of a concentrated desiccant (<NUM>) that is capable of absorbing the water vapor and thereby becoming diluted and heated;
(d) a regenerator (<NUM>) that is capable of receiving at least a portion of the diluted and heated desiccant (<NUM>) , said regenerator (<NUM>) configured to accept and direct external air (<NUM>) to the desiccant (<NUM>) , thereby causing a release of at least some of the water content in the desiccant, to the atmosphere, so as to re-concentrate the desiccant to a selected concentration value;
wherein it further comprises an external source of make-up water (<NUM>) in communication with the cooling coil (<NUM>), configured to replenish water lost during operation of the cooling system (<NUM>), wherein the make-up water combines with the relatively warm water exiting the cooling coil (<NUM>) via the conduit (<NUM>) and the combined flow enters the evaporator (<NUM>),
and that the system (<NUM>) lacks of a condenser for condensing water that is directed through the evaporator (<NUM>).