The present invention generally relates to apparatus and methods for operation of an air recharge system. More specifically, the present invention relates to apparatus and methods relating to desorbing water from a desiccant dryer and to filling an air storage tank of an air recharge system.
In various aircraft, a stored energy system may include a combustor to combust jet fuel using compressed air, as an energy source to drive a turbine that may be used to start an auxiliary power unit (APU), or to generate electrical and hydraulic power during in-flight emergencies. In addition, the APU may be used to start a main engine of the aircraft, and thus may be used on every flight, and in maintenance actions that require power.
Examples of systems used to start an APU include U.S. Patent Application Publication No. US2003/0140635 A1 to Benham, Jr. et al., (Benham) directed to a jet fuel and air system for starting an APU, which includes a source of pressurized air from at least one storage vessel joined with a fuel source to a turbine power module through a combustor. In Benham, the APU is started by energizing control valves within the system to allow the flow of the compressed air and the fuel into the combustor, wherein the mixture is ignited and the gas generated therefrom is used to turn the turbine of the turbine power module.
Another example of a system for starting an APU is shown in U.S. Pat. No. 5,097,659 to Lempe et al., (Lempe) which is directed to a system similar to that disclosed by Benham. Lempe also discloses the use of pressurized air from a storage vessel in operation of the system disclosed therein.
Accordingly, energy may be stored in such systems in the form of compressed air located in an air storage tank or tanks (e.g., one or more air cylinders or bottles). Depletion of the stored air, in whole or in part, thus may require the air storage tank to be recharged. In order to minimize ground support equipment and to limit the size of the air storage tank(s), an on-board air recharge system may be added to the aircraft to refill/replace the compressed air in the air storage tank as it is utilized for various functions.
In general, an air recharge system (ARS) designed for use in aircraft applications may be used in flight or on the ground to recharge an air storage tank of a stored energy system. The ARS may include a compressor which delivers compressed air from a conditioned air source for storage in an air storage tank. However, ambient air may contain a humidity level of up to about 160 grains of water per pound, and the conditioned air used in one particular application contains about 26 grains of water per pound of air (gr-H2O/lb-air), to about 38 gr-H2O/lb-air. As ambient air may be compressed, the partial pressure of water in the compressed air, and therefore the saturation temperature of the compressed air, may be greatly increased. This may cause water to condense as the pressure of the compressed air is increased. This condensed water may thus be present within the air storage tank. Water contained within an air storage tank may then be allowed to flow into various aircraft systems, wherein water may cause excessive wear and corrosion of the various parts of the aircraft. Water vapor in the compressed air may also lead to ice forming within various aircraft systems, which may result in a system malfunction. Accordingly, it may be necessary to remove moisture from the compressed air of a stored energy system prior to the compressed air being stored in an air storage tank, to prevent a possible system failure, which may result in a loss of the emergency power function or APU starting capability.
As shown in FIG. 1, an ARS according to the prior art, referred to as a prior art air recharge system 10, may include an air compressor 12 that may be used to compress or pressurize ambient air 16. The compressed air 40 may then be directed into a desiccant dryer 50 wherein moisture may be removed from compressed air 40 to produce discharge air 56 having a pressure higher than ambient, and also having a lower water content than ambient air 16. Discharge air 56 may then flow through a desiccant outlet check valve 58 to ultimately be retained within an air storage tank 14. Discharge air 56 retained within air storage tank 14 may then be released for use through tank valve 94 to the various aircraft systems, represented generally as 96.
However, once desiccant 25 within desiccant dryer 50 becomes “wet” (e.g., desiccant 25 has absorbed an amount of water limiting the ability of desiccant 25 to absorb a sufficient amount of water from compressed air 40 to produce discharge air 56) desiccant 25 may need to be regenerated, wherein water retained by desiccant 25 (i.e., water adsorbed and/or absorbed by desiccant 25) may be removed from air recharge system 10. Methods of regenerating desiccant 25 may include heating of desiccant 25, and/or passing a dry gas (i.e., a gas having a moisture content at or below the partial pressure of water vapor above desiccant 25) over desiccant 25, to remove water adsorbed by desiccant 25. Desiccant regeneration accomplished by heating of desiccant 25 may require direct thermal contact between desiccant 25 and a heat source (not shown). Such an approach may add complexity, cost, and weight to an aircraft system, and thus may not be desired. Regeneration of desiccant 25 by flowing a dry gas there over may also be employed by utilizing a dry gas from an independent source (not shown). A separate dry air source (not shown) may also add complexity, cost, and weight to the aircraft, and thus, may not be a desired approach.
Desiccant 25 may also be recharged by flowing a portion of the air previously dried by desiccant 25 there over, (i.e., a portion of the air which previously had water removed by desiccant 25). In this approach, discharge air 56 may be allowed to flow back over (i.e., back flush) desiccant 25 at a pressure and at a flow rate which may be less than the pressure and the flow rate at which discharge air 56 was produced. To accomplish a back flush of desiccant 25, a portion of discharge air 56 may be retained in a purge reservoir 60 prior to discharge air 56 entering storage tank 14. Accordingly, purge reservoir 60 may be located downstream of desiccant dryer 50, but upstream of air storage tank 14, such that a storage tank check valve 66 disposed in fluid communication between purge reservoir 60 and air storage tank 14 allows discharge air 56 to flow from purge reservoir 60 into air storage tank 14, but not the reverse.
During back flush of desiccant 25, discharge air 56 may be supplied to desiccant 25 from purge reservoir 60 through a purge orifice 62. After discharge air 56 comes in contact with desiccant 25, the flow of air may include moisture removed from desiccant 25, and may be directed through a purge vent valve 64 to an external environment 114. In this approach, purge orifice 62 may allow dry discharge air 56 to flow back over desiccant 25 at a pressure and at a flow rate which may be less than the pressure and flow rate at which compressed air 40 was previously dried to produce the quantity of discharge air 56 contained within purge reservoir 60.
The method of utilizing this approach practiced in the prior art, referred to herein as a prior art filling method, is generally represented in FIG. 2 as 300. Prior art filling method 300 may include a producing discharge air step 302, wherein actuation of the method resultant from an input, e.g., a storage tank pressure sensor input 92 from a storage tank pressure sensor 90, may actuate air compressor 12 such that compressed air 40 may be produced from ambient air 16 utilizing air compressor 12. Compressed air 40 may then be placed in contact with desiccant 25 to produce discharge air 56. This step may then be followed by a filling air storage tank step 304, wherein discharge air 56 may be directed through desiccant outlet check valve 58 into purge reservoir 60, through storage tank check valve 66, and into air storage tank 14 for a first prior art period of time, wherein such time period may be limited by the ability of desiccant 25 to remove water vapor from compressed air 40 to produce discharge air 56.
After the first prior art period of time at which desiccant 25 may be unable to effectively remove water vapor from compressed air 40 to produce discharge air 56, a partial fill back flush step 306 may be performed, wherein prior to air storage tank 14 being filled with discharge air 56 to a “full” level, as determined by the particular requirements of the system (e.g., a pressure in air storage tank 14), air compressor 12 may cease operation, purge vent valve 64 may be opened such that desiccant 25 may be in fluid communication with external environment 114 through purge vent valve 64. Discharge air 56 may then be allowed to flow through purge orifice 62 and in contact with desiccant 25, wherein at least a portion of moisture adsorbed or absorbed by desiccant 25 may be removed from desiccant 25 into discharge air 56. This moisture laden air (not shown) may then be removed from prior art air recharge system 10 to external environment 114 though purge vent valve 64.
In the art, producing discharge air step 302 may be in operation to produce discharge air 56 for the first prior art period of time during which both purge reservoir 60 and air storage tank 14 are filled. Partial fill back flush step 306 may then be performed for a second prior art period of time, which may be greater than a third prior art period of time which may be required to fill purge reservoir 60. Once partial fill back flush step 306 has concluded (i.e., the second prior art period of time has expired such that purge reservoir has a pressure about equal to ambient pressure), producing discharge air step 302 may then be repeated, as may partial fill back flush step 306, a plurality of times until air storage tank 14 has been fully recharged or filled.
Prior art filling method 300 may further include a stopping step 308, wherein at any point in the method where air storage tank 14 may be determined to be at a full level, operation of air compressor 12 may be stopped, purge vent valve 64 may be opened, and any discharge air 56 contained within purge reservoir 60 may be allowed to back flush desiccant 25.
However, actuation of prior art filling method 300 may only take place when air storage tank 14 requires filling, thus, utilization of prior art filling method 300 may be time consuming in that desiccant 25 may remain at near saturation levels, requiring one or more partial fill back flush step(s) 306 during each cycle of filling method 300. For example, the first prior art period of time may proceed for about 10 minutes, while the second prior art period of time may require 8 minutes (i.e., producing discharge air step 302 and filling air storage tank step 304 for 10 minutes, followed by partial fill back flush step 306 for 8 minutes). This process may need to be repeated 10 or more times to produce enough discharge air 56 to fill air storage tank 14. The time delay caused by partial fill back flush step 306 may thus become undesirable when an operation, such as a maintenance operation, requires a complete discharge, and refill of air storage tank 14. In such a situation, external equipment may need to be procured which may be capable of producing an amount of discharge air 56 sufficient to fill air storage tank 14.
As can be seen, there is a need for improved apparatus and methods of operation of an air recharge system to minimize recharge time of an air storage tank of an emergency power system.