Historically, positive displacement machines and turbomachines, such as blowers and compressors, have been used to generate compressed or pressurized gas. Turbomachines are high technology machines that typically involve high engineering, production and assembly costs in order to achieve and maintain desired levels of performance and efficiency with reduced repair and safety concerns. Such high costs are typically due to complex design issues, lengthy assembly procedures, and detailed maintenance requirements, all greatly influenced by the operational requirements for the machinery. For example, fuel cell systems used in diverse stationary, mobile, military and commercial applications use blowers and compressors to pressurize high-temperature process gas. However, such systems typically require the machinery to fit into a tight footprint so as to not take up too much space, without compromising operation and efficiency of the overall system. Additionally, suitable blowers and compressors have long been desired to achieve high reliability and maintain high efficiency at high operating temperatures. Because of the high temperatures exerted on and by any systems using such machines, adequate insulation, cooling, design and safety precautions are required. Additionally, it is desirable to minimize waste, and thus, efforts have been made to minimize and eliminate leakage of process gas from the system, and more preferably, reuse the process gas for operation and cooling of the turbomachine. However, these concerns must be addressed without affecting the desired operation of the blowers and compressors used in such turbomachinery.
Hermetically-sealed high-temperature turbomachines are needed for several applications, such as fuel cell systems, nuclear plants, chemical processing plants, waste heat recovery systems, and the like. Adequate turbomachines are presently not available for handling handle high-temperature process gases without significant drawbacks. For example, for applications such as waste heat recovery systems, the process cycle fluid needs to be recirculated through the internal system components at high temperatures without effecting operation of the system, damaging system components, or leaking any processing fluid. Accordingly, high-temperature (e.g., ≥850° C.) operation of turbomachines must be reliable. Turbomachinery that is hermetically sealed so that the high-temperature process gas is adequately contained is also a prime concern.
Existing state-of-the-art technologies are not completely gas-tight or leak proof. Undesired leakage of process gas both within and from the turbomachine can effect operation of the system. In high-temperature operations, leakage of process gas can also be unsafe. Such state-of-the-art technologies are also often limited in temperature capability due to bearing and electric component failure. Major causes of failure are poor suppression of heat transfer from hot process gas to the turbomachine components, deficient cooling schemes, and, again, undesirable leakage within and from the machine housing.
FIG. 1 illustrates a conventional turbomachine configuration 10, such as for a blower or a compressor, designed to handle high-temperature process gas. The conventional turbomachine design for such operations generally comprises a rotor device 12 for handling the hot process gas disposed within a “hot end” machine housing, illustrated as reference numeral 14 in FIG. 1. A motor 16 and roller bearings 18 are commonly placed outside the “hot end” of the machine 10. A mechanical seal 20 is installed near the “hot end” housing 14 to hermetically seal the machine housing 14 and thus reduce leakage therefrom.
A representative prior art hermetically-sealed small blower concept is described in more detail in U.S. Pat. No. 6,830,842 B2, where hydrogen gas is fed at a higher pressure from an aft end of the blower to cool the motor and bearings therein. The described concept in this patent is insufficient for applications where a cooler purge gas that is also compatible with the process gas is not readily available. Also, in this representative design concept, the blower fore end processing the hot process gas is directly connected to the motor end by a common rotating shaft, which exposes the blower to high heat flux via the common rotating shaft. The high heat flux generated by the common rotating shaft compromises the temperature capability of the blower. The described concept is therefore feasible only for small-sized blowers and cannot easily be scaled up for larger sized turbomachines of about a few hundred kilowatts, where the amount of heat flux conducted through the common rotating shaft could cause failure of the internal electric components and bearings.
Another hermetically-sealed small blower concept that is representative of the prior art is described in copending U.S. Application Publication No. 2009/0087299 A1, assigned to the owner of the present invention and incorporated herein by reference, where a self-sustaining cooling process is achieved by recirculation of entrapped process gas in the motor housing of the blower. Such a self-sustaining cooling process relies on natural convection of fins formed on the blower housing for sufficient cooling of relevant machine components. The described concept is feasible for small-sized blowers only, as it relies on natural convection. Natural convection is a poor mode for heat removal, especially for larger-sized blowers. Also, in such a design, the rotating shaft extends from the “hot end” of the machine to the motor side as a single, integral component, which conducts high heat flux in the blower. Accordingly, the applicability of the blower concept is again limited to only small-sized blowers—e.g., less than 1 kilowatt—because of the high heat flux generated by the common rotating shaft.
The conventional turbomachine configuration illustrated in FIG. 1 has numerous disadvantages. For example, such conventional turbomachine configurations are often not truly hermetically-sealed and, as a result, the leakage rate of hot process gas from the “hot end” of the machine housing greatly depends on the type of mechanical seal used. Mechanical-type seals, as are commonly used in conventional configurations such as illustrated in FIG. 1, leak process gas continuously. Wear of such seals due to rotation of a common rotating shaft will eventually increase the leakage rate and expedite failure of the seal. In alternate configurations of conventional turbomachines of the type illustrated in FIG. 1, a purge gas, such as nitrogen or air, may be used to keep the mechanical seals from leaking the hot process gas. In such designs, however, the purge gas is usually undesirable as it may contaminate the process gas. Purge gases also require an extraneous feed system to continuously provide purging for the system. Purge gas sealing may still leak hot process gas depending on the process gas pressure and the capability of the extraneous purge feed system to respond to system pressures.
Additionally, roller element bearings lubricated by oil or grease, as are commonly used in conventional configurations, such as illustrated in FIG. 1, contaminate the process gas and cannot withstand high operational temperatures, as the lubrication will coke and cause failure of the bearings. As a result, conventional turbomachine configurations often need mechanical seals to place the bearings far enough from the hot gas rotor to reduce and preferably avoid coking of the lubricant. Often, the threat of coking and the likely resultant bearing failure also limit the operational temperature capability of the machine.
Still additionally, commercial electric motors, generators and alternators used in conventional turbomachine configurations of the type illustrated in FIG. 1 are usually rated at maximum ambient temperature of about 180° C. Operation of the turbomachine above this temperature will cause insulation break down and failure of the machine.
Attempts are constantly being made to achieve complete hermeticity and reliable operation for turbomachine configurations at high temperatures (e.g., ≥850° C.). To this end, there is a need for a turbomachine configuration, adaptable to both motor-driven blower and compressor designs, and turbine-driven generator and alternator designs, whereby the machine housing is hermetically sealed, the internal components are adaptable to operating at extremely high temperatures without affected operation and premature failure, and whereby the machine includes a self-contained cooling process utilizing the process gas already in the machine.
In view of the foregoing, there is a need for a turbomachine design that can operate efficiently at high temperatures with a hermetically sealed housing design, without suffering from the drawbacks common to prior art blower, compressor, generator, and alternator designs that tend to affect performance, operation and efficiency, require frequent repair, and moreover, tend to compromise product safety. Accordingly, it is a general object of the present invention to provide a high-temperature turbomachine, be it a motor-driven blower or compressor, or a turbine-driven generator or alternator, that overcomes the problems and drawbacks associated with the use of such machines at high temperatures on the order of 850° C. or greater.