Patent Application
20130129488
The present invention relates generally to the conception, design and manufacture of turbomachinery, such as blowers. More particularly, the present invention relates to a blower designed for movement of gas, especially dry gas, that has high efficiency, high reliability, and a small size and weight. The present invention also relates to a fuel cell system incorporating a motor-driven blower designed to move and circulate dry gas.
All fuel cells require air or gas to be supplied to the cathode side of the fuel cell for proper operation. Movement of air or gas to the cathode side of a fuel cell is typically accomplished using a blower. However, in fuel cells, the largest parasitic load in the system is the air blower. Thus any improvement in blower efficiency will have a dramatic effect on the overall efficiency of any fuel cell system.
To achieve high efficiency and reliability in turbomachinery to be used to move dry process gas for a fuel cell system, the turbomachine must be able to run at high rotational speeds without risk of failure. As rotational speed increases, the overall machine size can be made smaller and lighter without compromising a blower's output power. Heretofore, known problems with blowers generally arose due to the excessive size, weight, and complexity of such devices. Requirements for running at high speeds include properly designed rotating and non-rotating assemblies, and bearings to support a high-speed rotating shaft. Proper attention to such requirements, along with an appreciation of proper cooling methods to accommodate high-speed operation, permit smaller devices to be used without affecting operative efficiency and power.
However, many prior art turbomachines designed to operate at high speeds have not adequately cooled the internal components of the machine, especially the bearings. For example, the rotating parts of a blower often require lubrication and coolant for efficient operation. As a result, turbomachines operating at high speeds, without proper cooling methods, often experience low efficiency, low reliability, and a high risk of damage and over-heating.
Existing blower technologies, such as the ventilator described in U.S. Pat. No. 1,739,082, commonly use conventional bearings (e.g., ball bearings and sleeve bearings) to support the rotating assembly of the blower. Blowers using such conventional bearings typically run at low speeds and, as a result, occupy a large space and operate at low efficiency levels. Conventional bearings have not been able to withstand high rotational speeds without increasing the complexity of the blower design. Additionally, conventional bearings often require oil lubrication that can contaminate the blower and the fuel cell and result in damage, reduced efficiency and reduced reliability.
High-speed rotating machines supported on foil gas bearings have made significant progress during the last 35 years. Reliability of many high-speed rotating machines with foil bearings has shown a tenfold increase compared to those with rolling element bearings. Many high-speed rotating machines are Air Cycle Machines (ACM) used in Environmental Control Systems (ECS) of aircraft that manage cooling, heating and pressurization of the aircraft. Today, ACM for almost every new ECS system on military and civilian aircraft and on many ground vehicles use foil air bearings. Old ECS systems with rolling element bearings are being converted to foil air bearings. The F-16 aircraft ACM used rolling element bearings from 1974 to 1982, but all such aircraft built since 1982 use foil air bearings. The 747 aircraft ACM used rolling element bearings from 1970 to 1989. All such aircraft built since 1989 have foil air bearings. ECS on the older model 737 aircraft have rolling element bearings, whereas ECS on the new 737 aircraft use foil air bearings. An overview of foil air bearing technology is provided in an ASME paper (97-GT-347) by Gin L. Agrawal. However, even use of foil bearings in blowers have not automatically translated into higher efficiency and reliability of the machines. Fully addressing the high temperatures associated with high speed operation has still proven difficult for prior art blower designs.
Movement and circulation of a process gas, such as dry gas in a fuel cell system, are typically accomplished using a blower in which the motor and bearings for the blower are isolated from the process gas flow through the blower using various seal arrangements within the blower housing. Isolating the internal components of the blower from the process gas prevents corrosion and contamination of the components. However, as the internal components can generate high temperatures during operation, especially at high operating rotational speeds, isolating the internal components of the blowers often requires a separate lubrication and cooling system to be incorporated into the blower design to prevent damage and failure of the blower. Accordingly, sealing the rotating parts from the process gas while permitting a separate coolant flow through the blower housing requires a more complex design than for typical blowers. Moreover, leakage from the lubricant or coolant for the blower's rotating parts may cause contamination of the process gas, and vice versa.
In addition to the disadvantages presented by the issues of leakage and contamination within a blower, the isolation of the motor and other internal blower parts from the process gas makes it difficult to adequately contain the heat that is generated by these parts during operation of the blower. The heat is lost to the environment, which affects the efficiency of the system. To contain the heat using prior art blower designs, an additional system is needed to collect and manage the heat, which adds to the complexity, size, weight and cost of the system.
Accordingly, an important aspect for improving efficiency and reliability of a turbomachine, especially one operating at high speeds, is cooling the internal components of the machine. Axial fans are often used for cooling applications, particularly where the required pressure rise for a turbomachine is very low (few H2O pressure rise). Indeed, axial fans are often used for cooling computers and electronic enclosures. However, some designs that use axial fans or rotating impellers, such as U.S. Pat. Nos. 7,855,882 and 8,016,574 do not adequately cool the bearings and other internal components, and as noted above, such systems are not acceptable for blowers operating at high speeds.
Applicants' co-pending U.S. Application Publication No. 2012/0082575, which is incorporated herein by reference, discloses a mechanical vapor recompression system and cycle incorporating a motor-driven blower designed to move and circulate water vapor. That invention provides an internal cooling flow through an internal passage to cool the internal operating components and bearings of the machine to allow heat generated by the blower to pass into the water vapor that the blower circulates. An additional coolant may also be provided for additional cooling of the machine and its internal components.
In view of the foregoing, there is a need for a blower designed to move dry gas that can operate efficiently and reliably at high speeds without suffering from the drawbacks common to prior art blower designs that tend to affect performance, operation, lifespan and efficiency. Accordingly, it is a general object of the present invention to provide a blower for moving dry gas that removes the problems of leakage and heat loss. Gas foil bearings used in the present invention are lubricated by the process gas itself, as opposed to a separate lubricant, so there is no possibility of the above-mentioned contamination typically associated with prior art blowers and the drawbacks associated therewith. Further, heat generated by the blower is transferred to the process gas, and the heat can then be recovered as desired. Additionally, there is a need for a blower that can occupy a small space and have a light weight without compromising operational efficiency and reliability.
The present invention is generally directed to a motor-driven blower especially adapted for moving and circulating dry air or gas. The blower is particularly designed for highly reliable and efficient movement, circulation and compression of dry process gas in a fuel cell air management (both stationary and mobile systems).
In a first aspect of the present invention, a blower for moving dry process gas comprises an outer blower housing having an inlet and an outlet, a flow compressor or fan mounted within the outer blower housing at the inlet end thereof for rotation about an axis, and an inner blower housing mounted within the outer blower housing adjacent to the flow compressor. The inner blower housing defines an internal passage therethrough between an inlet and an outlet of the inner blower housing which houses a motor, a rotating assembly operatively associated with the motor and mounted within the inner blower housing for rotation about the axis, at least two journal bearing assemblies and at least one thrust bearing assembly. Rotation of the rotating assembly effects rotation of the flow compressor or fan, which generates a flow of dry process gas through the outer blowing housing between the inlet and outlet thereof.
An annular cavity is defined between the outer blower housing and the inner blower housing. A plurality of three-dimensional diffuser vanes and a plurality of flow-straightening vanes are mounted to the outer surface of the inner blower housing and project into the annular cavity for redirecting and guiding the dry process gas flow passing through the annular cavity. The diffuser vanes and the flow-straightening vanes assist in heat transfer from the inner blower housing to the annular cavity during operation of the blower.
The present invention provides movement and circulation of gas through the blower and ductwork operatively connected thereto without contamination and without heat loss from the blower to the environment. In accordance with an aspect of the present invention, a cooling scheme is provided to allow heat generated by the blower to pass into the process gas that the blower is moving. For example, during operation of the blower, a portion of the dry process gas flow generated in the outer blower housing flows into the inlet of the inner blower housing, through the internal passage defined therein, and out of the outlet of the inner blower housing, where such portion of dry process gas flow mixes with the dry process gas flow generated by the compressor.
In accordance with another aspect of the present invention, the diffuser vanes provided on the outer surface of the inner blower housing assist in transferring heat from the inner blower housing to the outer blower housing. More preferably, three-dimensional diffuser vanes are used to help convert kinetic energy of the process gas to pressure within the annular cavity between the inner and outer blower housings.
In accordance with still another aspect of the present invention, the flow-straightening vanes provided on the outer surface of the inner blower housing enhance the heat transfer from the inner blower housing. The flow-straightening vanes also assist in flow improvement of the process gas through the blower.
In accordance with embodiments of the present invention, the movement of the process gas is caused by a single-stage compressor or fan mounted for rotation about an axis on a rotating assembly. The compressor can be an axial fan or a mixed-flow impeller. The compressor or fan is driven by a motor operatively connected to the rotating assembly and housed within the inner housing of the blower.
In accordance with embodiments of the present invention, the motor preferably comprises a brushless permanent magnet synchronous motor, mounted for rotation within the inner blower housing. The motor is preferably powered by a variable frequency drive. Cooling of the motor is provided by process gas flowing over the inner blower housing. The diffuser vanes and the flow-straightening vanes provide on the outer surface of the inner blower housing provide enhanced heat transfer.
The blower includes a rotating assembly operatively connected to the motor that is supported by at least two gas foil journal bearings (radial load) and a set of gas foil thrust bearings (axial load) mounted within the inner housing of the blower. The rotating assembly comprises a rotating shaft and the compressor, which may be formed with or fitted onto the shaft on one end thereof. The bearings are lubricated with a small amount of process gas that passes through the inner passages of the inner blower housing. This internal flow of the process gas is driven by a small pressure difference between the inlet and outlet of the internal passage. The pressure difference occurs from the diffusion of the main flow from one end of the inner blower housing to the other and is influenced by the affect on the dry process gas flow by the diffuser vanes and the flow-straightening vanes projecting into the annular cavity around the inner blower housing.
During operation of the blower in accordance with the present invention, the flow of gas passes through an annular cavity formed between the inner blower housing and the outer blower housing. The blower is mounted in-line with inlet and outlet ducting through flanges at either end. The inner and outer blower housings may be attached together by points of contact on the flow-straightening vanes to simplify construction.
An advantage of the present invention is that there is no possibility of oil or lubricant contamination in the water vapor flow since the blower is oil-free.
Another advantage of the present invention is that heat generated by the blower is moved into the process gas flow, which is useful for energy savings.
Another advantage of the present invention is that the blower of the present invention is readily adaptable to various application and systems where gas and air, and in particular, dry process gas, must be moved and circulated.
Another advantage of the present invention is that the blower of the present invention can be mounted in a vertical or horizontal direction without affecting operation or efficiency.
Another advantage of the present invention is that the bearings can run cooler, which, in turn, allows the blower to run faster (i.e., at higher speeds).
Another advantage of the present invention is that the cooling scheme for the blower of the present invention reduces the number of parts in the blower, resulting in lower manufacturing costs, and permitting the blower to have a small size and comparatively light weight.
Another advantage of the present invention is that design features used to improve heat transfer and cooling of the blower, such as the diffuser vanes and flow-straightening vanes, also improve the aerodynamic flow and fluid dynamics of the process gas flowing through the blower, for example by helping convert kinetic energy in the process gas to pressure.
There are many applications for the blower of the present invention where the desired result is movement and circulation of dry process gas. For example, the present invention generally relates to fuel cell air management (both stationary and mobile systems). Other fields of application for the present invention can be utilized, including, for example, aeration units, printing systems, and air knifes.
These and other features of the present invention are described with reference to the drawings of preferred embodiments of a gas foil bearing-supported, high-speed oil-free blower for moving and circulating dry process gas. The illustrated embodiments of the blower in accordance with the present invention are intended to illustrate, but not limit, the invention.
The present invention is directed to a motor-driven blower for movement, circulation and compression of gas and air, preferably a dry process gas. More preferably, the present invention is directed to a high-speed, single-stage, motor-driven blower. A perspective view and a cross-sectional view of an exemplary blower in accordance with the present invention, generally designated by reference numeral 10, are illustrated in
The blower 10 of the present invention is preferably a small, high-efficiency, oil-free device that can be used in various applications, such as for fuel cell air management (both in stationary and mobile designs), and for aeration units, printing systems and air knifes.
Referring to
The inner blower housing 14 houses a motor 22, a rotating assembly 24 operatively associated with the motor 22 for rotation about an axis A, front and rear journal bearing assemblies 26, and a thrust bearing assembly 28. The rotating assembly 24 generally includes a rotating shaft 30 that is radially supported within the inner blower housing 14 by the pair of journal bearing assemblies 26, and axially supported by the thrust bearing assembly 28.
A flow compressor or fan 32 is disposed within the outer blower housing 12 for drawing process gas, preferably a dry process gas, through the blower 10 between the inlet 18 and the outlet 20 of the outer blower housing 12 so as to generate a process gas flow through the annular cavity 16 within the blower 10. In a first embodiment of the present invention, the flow compressor is an axial-flow fan 32, as illustrated in
Though generally shown and described herein as an axial-flow compressor or fan 32, the blower 10 in accordance with the present invention may utilize a mixed-flow compressor or impeller for moving process gas through the blower 10 without affecting the efficiency and reliability benefits of the present invention. Preferably, whether an axial fan or a mixed-flow impeller, the flow compressor 32 is a single-stage compressor.
In accordance with preferred embodiments of the present invention, the blower 10 is preferably a high-speed, single-stage, motor-driven blower designed to move and circulate dry process gas in numerous applications. The motor 22 used in the blower 10 is preferably a brushless permanent magnet synchronous motor powered by a remotely located variable frequency drive (not shown). As shown in
As noted above, the rotating assembly 24 is also operatively connected to the flow compressor 32, typically via the rotating shaft 30. Accordingly, in the design shown in
The motor components and bearing assemblies are protected against contamination by encapsulating them within the inner blower housing 14, which protects them from direct exposure to the main process gas flow. However, because the operational components of the blower 10—i.e., the motor 22, the rotating assembly 24 and the bearings 26 and 28—typically generate heat during operation, it is desirable to cool these components to avoid damage and premature failure of the blower 10 and to maintain efficient operation and production. Therefore, in accordance with preferred embodiments of the present invention, a small, controlled portion of the process gas flow moving through the blower 10 between the inlet 18 and the outlet 20 is leaked into and redirected back through the inner blower housing 14 for cooling internal components of the blower 10, such as the motor 22, the rotating assembly 24, and the bearings 26 and 28. The portion of the dry process gas flow passing through the internal passage of the inner blower housing 14 is driven by a pressure difference between the ends of the inner blower housing 14.
Referring to
Still referring to
During operation of the blower 10, the rotor blades of the axial fan 32 compress the process gas and distribute the process gas over and around the inner housing 14, through the diffuser vanes 38 and the flow-straightening vanes 40. The main flow of the process gas is then forced out of the blower 10 through the outlet 20. As noted above, a small portion of this flow travels back through the rear end of the inner housing 14, through internal operative components housed in the inner blower housing 14 for cooling purposes.
Cooling of the blower 10, and more particularly the internal operating components, is provided by the main process gas flow over the inner blower housing 14 and through the annular cavity 16. The flow of the process gas through the blower 10 is illustrated in
When the process gas flows through the diffuser vanes 38 and the flow-straightening vanes 40, heat generated within the inner blower housing 14 is also absorbed into the main process gas flow. Thus, the diffuser vanes 38 and the flow-straightening vanes 40 help cool the internal components of the blower 10 by enhancing the heat transfer from the inner blower housing 14. More particularly, the vanes 38 and 40 work with the conduction of the inner blower housing 14 to the outer blower housing 12, natural convection from the inner blower housing 14, and forced convection from the main process gas flow.
As noted above, a small portion of the process gas flow is redirected back through the inner blower housing 14. As shown in
The internal flow of the process gas through the inner blower housing 14 is driven by a small pressure difference between the inlet 42 and outlet 44 of the internal passage within the inner blower housing 14. The pressure difference is created, in general, by the diffusion of the main flow of the process gas around the inner blower housing 14 from one end thereof to the other. The pressure difference between the inlet 42 and the outlet 44 of the inner blower housing 14 is influenced by the affect on the dry process gas flow by the diffuser vanes 38 and the flow-straightening vanes 40 projecting into the annular cavity 16 around the inner blower housing 14. The process gas exits the outlet of the inner blower housing 14 through a gap 46 between the axial fan 32 and the inner blower housing 14 and other openings 48 in the inner blower housing 14, as shown in
The heat that is generated by the motor 22 and rotating assembly 24 is therefore moved into the main process gas flow, which is useful for energy savings and efficient operation of the blower 10. Thus, improved flow circulation formed through the inner blower housing 14 between the inlet 42 and the outlet 44 increase heat transfer from the operating components of the blower 10 to the main process gas flow.
The bearing assemblies 26 and 28 used in the present invention are preferably gas foil bearings that are lubricated and cooled by the process gas itself, thereby eliminating the need to use oil or lubricant, and as a result eliminating the contamination common with prior art blower designs and avoiding the drawbacks associated with such contamination. Thus, in accordance with the present invention, all bearings in the blower are preferably oil-free to maximize performance and life of the blower. For example, in the journal bearing assemblies 26, foil gas journal bearings sit inside journal bearing sleeves that are attached to the inner blower housing 14, as illustrated in
In preferred embodiments of the present invention, pairs of foil-type hydrodynamic gas journal and thrust bearings support the rotating shaft 30. Alternatively, the present invention can be used for blowers supported on oil-free, ceramic-type ball bearings or pressurized hydrostatic bearings without compromising design or operation of the blower. As noted, a potion of the dry process gas flow generated in the outer blower housing 12 is leaked into the internal passage of the inner blower housing 14 via the inlet 42 thereof, with said leaked portion of the dry process gas flow passing through the internal passage to lubricate the bearings 26 and 28. After lubricating the bearings 26 and 28, the portion of the dry process gas flow in the inner blower housing 14 exist the outlet 44 of the inner blower housing 14 and mixes with the main dry process gas flow generated by the flow compressor 32.
Referring to
As illustrated, the fuel cell system 100 includes a Fuel Processor 110 that provides a hydrogen rich gas to a Fuel Cell 120, which generates a power supply. More particularly, the Fuel Cell 120 produces DC power that is converter to AC power by a Power Inverter 130 (commonly, an AC inverter). The Fuel Cell 120 also interacts with a Heat and Power Recovery System 140 that generates heat exhaust that can be used to pressurize the natural gas and process gas fed to the Fuel Processor 110.
Within the Fuel Processor 110, a low-pressure natural gas is pressurized by a fuel compressor 112 and pretreated by additional fuel processing equipment 114 (e.g., preheater, desulfurizer, steam ejector, reforming reactor, etc.) common to fuel cell systems. Of great import to the present invention, the Fuel Processor 110 also includes an air blower, such as the blower 10 in accordance with the present invention, for pressurizing a process gas that is delivered to the fuel cell stack module of the Fuel Cell 120 for reacting the natural gas within the Fuel Cell 120. Efficient operation of the air blower 10 is essential to an efficient fuel cell system.
The foregoing description of the embodiments of the invention has been presented for the purpose of illustration and description; it is not intended to be exhaustive or to limit the invention to the form disclosed. Obvious modifications and variations are possible in light of the above disclosure. The embodiments described were chosen to best illustrate the principles of the invention and the practical applications thereof to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated.
This application claims the benefit of U.S. Provisional Application No. 61/561,443, filed Nov. 18, 2011, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61561443 | Nov 2011 | US |
