Abstract:
A regenerative heat exchanger for transferring heat from the exhaust gas to the intake working fluid of a prime mover and from the pressurized working fluid to the exhaust vapor of a heat pump. Application is especially useful in a system in which liquid air or nitrogen made by a heat pump provides compression cooling for a gas turbine prime mover. The heat exchanger employs circulating element heat transfer surface such as wire belts or ceramic balls, which circulate in turn through working fluid exhaust and intake channels while absorbing and rejecting heat between the two channels. Effectiveness exceeding 98% increases thermal efficiency of small low-pressure ratio gas turbines.

Description:
REFERENCES 
       [0000]    
       
         1.) Kaufman, Jay S., U.S. Pat. No. 7,398,841 B2, Jul. 15, 2008 
         2.) Kaufman, Jay S., U.S. patent application Ser. No. 12/315,002, Nov. 26, 2008 
       
     
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to regenerative heat exchangers for heat recovery in prime movers, heat pumps and other mechanical equipment for vehicle and stationary use and pertains particularly to an improved regenerator for gas turbine engines and gas liquefiers. References 1 and 2 describe a gas turbine with refrigerated compression by a liquefied or solidifed gas for increasing thermal efficiency of the engine. The regenerator of the present invention is designed to minimize the refrigerant requirement by decreasing regenerator terminal temperature difference relative to turbine expansion temperature drop, thereby increasing the ratio of compressed air to refrigerant. Similarly, reduction of terminal temperature difference of a heat pump regenerator increases specific yield of the heat pump supplying refrigerant to the gas turbine. In addition, high effectiveness of the regenerator of the present invention acts to increase thermal efficiency of conventional gas turbines with ambient air compression. 
         [0004]    The regenerator of the present invention employs circulating elements, such as a continuous belt or non-connected ceramic balls, which circulate in the upstream direction to absorb heat from the lower pressure exhaust side and reject heat to the pressurized side of the regenerator. The material of the circulating elements has high thermal storage capacity and conductivity. Heat duty of the regenerator is matched to the heat transfer rate from the low to high pressure side by adjusting speed of the circulating elements, providing effectiveness of up to 98% with minimal differential temperature between the working fluid and circulating elements. The belt type element is supported on pulleys at each end of the regenerator and passes through seals having minimal leakage area between the working fluid and surrounding atmosphere. Ball type elements are similarly sealed, and are guided while immersed in the working fluid in the exhaust flow channel of the regenerator. The ball type configuration is adaptable to very high temperature applications using ceramic components. 
         [0005]    Current practice for most gas turbines utilizing heat recovery to increase thermal efficiency is to employ recuperators with fixed surface area. Because of surface area constraints, especially in motor vehicle application, terminal temperature difference of counter-flow recuperators is excessive and the resulting low effectiveness reduces gas turbine efficiency. The majority of these recuperators are constructed of numerous tubes, brazed or welded in complex header arrangements. More advanced state-of-the-art stationary recuperators rely upon laminar flow of the working fluid in a plate type matrix with numerous parallel flow passages to realize acceptable effectiveness. Both types of recuperators are expensive, especially with high temperature alloys, because of the large number of closely spaced joints. Another kind of heat exchanger in use is the rotary regenerator which attains higher effectiveness than recuperators by providing passage of the low and high pressure flow streams over the same heat transfer surface. Parallel passage seals are required to minimize leakage from the high to low pressure side and application is limited to moderately pressurized systems. Rotary regenerators also require numerous parallel flow passages with closely spaced brazing or welding. In addition, metal recuperators and rotary regenerators are limited to inlet gas temperature of about 1000 K (1800 R). 
         [0006]    Another application of heat exchangers with fixed surface area is for cooling compressed working fluid prior to two-phase expansion in heat pumps. There is also a need to improve effectiveness and simplify construction of these heat exchangers for liquefiers and solidifiers. 
         [0007]    The regenerator of the present invention provides variable heat transfer surface area dependent on speed of the circulating belt or other circulating elements to increase effectiveness. Another feature of the regenerator of the present invention is replacement of the multiple parallel heat transfer circuits by an upstream and a downstream channel connected in series to a prime mover or heat pump. As a result it is only necessary to seal the relatively small cross sectional area of the heat transfer elements against the pressure differential between working fluid and atmosphere. Fabrication is simplified by elimination of brazed and welded tube and plate construction, which also reduces working fluid pressure loss. Energy input required to drive the heat transfer elements is negligible. Circulation speed of belts or balls is determined by their configuration including material, quantity and surface area in addition to working fluid flow parameters. Effective heat transfer area of the circulating belt is less than 10% as compared to a fixed area heat exchanger of the same heat duty. In addition, high effectiveness improves the potential for low temperature heat addition from recovered heat in sub-ambient prime mover application. Available heat sources include overcast solar, building exhaust and vehicle drive train energy loss. 
       SUMMARY AND OBJECTS OF THE INVENTION 
       [0008]    It is the primary object of the present invention to provide an improved regenerator for increasing thermal efficiency of prime movers and other mechanical equipment. In accordance with a primary aspect of the present invention, a linear regenerator for recovering heat in prime movers and other mechanical equipment comprises a two-channel assembly and a circulating element assembly. The two-channel assembly directs the flow of working fluid in a pressurized channel from an air pressurizer such as a compressor or fan to a working fluid heater such as a combustor or solar absorber and in an exhaust channel from a discharge port of a prime mover to atmosphere. The circulating element assembly transfers heat from the exhaust channel wherein heat is absorbed by the elements to the pressurized channel wherein heat is rejected from the elements. The two-channel assembly comprises a support structure for holding the channels in spaced relation while maintaining position of working fluid connections between the regenerator and the pressurizer, air heater and prime mover. In addition the two-channel assembly comprises insulation for minimizing heat loss from the channels to atmosphere, and seals for minimizing working fluid loss between the element to channel interface and atmosphere. The circulating element assembly with belt type elements comprises hot and cold end pulleys with bearings for guiding the heat transfer belt and an electric motor for driving the belt at a selected speed. Similarly, a circulating ball type assembly comprises one or more open conduits for guiding the heat transfer balls and a controllable feed mechanism with an electric motor for circulating the balls at a selected speed. 
         [0009]    It is another object of the present invention to provide a regenerator constructed with ceramic components for use with prime movers and other mechanical equipment having very high working fluid gas temperatures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The above and other objects and advantages of the present invention will become apparent from the following description when read in conjunction with the accompanying drawings wherein: 
           [0011]      FIG. 1  is a front elevation section view illustrating a preferred embodiment of the circulating belt regenerator of the present invention for below ambient heat transfer as part of a gas turbine with refrigerant cooled compression. 
           [0012]      FIG. 1A  is a side elevation view of the regenerator of  FIG. 1 . 
           [0013]      FIG. 2  is a front elevation section view illustrating a preferred embodiment of the circulating belt regenerator of the present invention for below ambient heat transfer as part of a heat pump. 
           [0014]      FIG. 3  is a front elevation section view illustrating a preferred embodiment of the circulating belt regenerator of the present invention for below and above ambient heat transfer as part of a gas turbine with refrigerant cooled compression. 
           [0015]      FIG. 4  is a front elevation section view illustrating a preferred embodiment of the circulating ball regenerator of the present invention for heat transfer above the upper temperature limit of a connected heat exchanger. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]      FIG. 1  is a front elevation section view illustrating a circulating belt regenerator  10  of the present invention with exemplary embodiments of a circulating wire belt assembly  12  and a two-channel assembly  14  for connection to gas turbine of a motor vehicle. An air intake channel  16  directs air working fluid  18  from atmosphere via an air intake nozzle  20  and a compressor intake nozzle  22  to a compressor  24  with cooling by liquid nitrogen  26 . Simultaneously, a pressurized channel  28  directs working fluid from the compressor via a compressor discharge nozzle  30  and a heater nozzle  32  to a heater  34 , connected in turn to a turbine  36  of the gas turbine. Heat addition to the heater is by re-circulated drive train transmission fluid  38 . A hot box  40  and a cold box  42  close the ends of each channel, providing retention of belt seals  44 ,  46 ,  48  and  50 . The seals minimize leakage of working fluid between a circulating wire belt  52  and the closed ends of each channel. The wire belt and seals are part of circulating belt assembly  12  which also includes a hot pulley, bearing and shaft assembly  54  supported by the hot box and a cold pulley, bearing and shaft assembly  56  supported by the cold box. 
         [0017]      FIG. 1A  is a side elevation view from  FIG. 1  rotated ninety degrees to illustrate attachment of a belt drive motor  58  which drives the wire belt via the cold pulley, bearing and shaft assembly. 
         [0018]    Performance of the regenerator is estimated for installation in a sub-compact vehicle. The gas turbine develops 6.7 kW (9 HP) at a cruising speed of 80 km/hr (50 mph) with a pressure ratio of 3 and turbine inlet gas temperature of 370 K (670 R). Heat addition is by recovery of motor vehicle drive train heat using re-circulated transmission fluid at 390 K (700 R). At these conditions regenerator inlet gas temperature from the turbine is 294 K (530 R), effectiveness is 98%, and belt speed is 8.7 m/min (29 ft/min), corresponding to 11 rpm for a channel length of 0.3 m (1 ft), during 1 hour of operation. 
         [0019]      FIG. 2  is a front elevation section view illustrating a circulating belt regenerator  100  of the present invention with exemplary embodiments of a circulating wire belt assembly  112  and a two-channel assembly  114  for connection to a gas turbine. The configuration of regenerator  100  is similar to regenerator  10  of  FIG. 1  with the addition of an over-ambient exhaust channel  117  and a longer pressurized channel  128 . An air intake channel  116  directs air working fluid  118  from atmosphere via an air intake nozzle  120  and a compressor intake nozzle  122  to a compressor  124  with cooling by liquid nitrogen  126 . Simultaneously, a pressurized channel  126  directs working fluid from the compressor via a compressor discharge nozzle  128  and a combustor nozzle  132  to a combustor  134 , connected in turn to a turbine  136  of the gas turbine. Exhaust channel  117  directs exhaust working fluid from the turbine to atmosphere via a turbine nozzle  137  and an exhaust nozzle  139 . 
         [0020]    Performance of the regenerator is estimated for installation in a compact vehicle. The gas turbine develops 14 kW (19 HP) at a cruising speed of 105 km/hr (65 mph) with a pressure ratio of 3 and turbine inlet gas temperature of 1170 K (2100 R). Heat addition is by combustion of fuel. At these conditions regenerator inlet gas temperature is 944 K (1700 R), effectiveness is 98%, and belt speed is 7.6 m/min (25 ft/min) corresponding to 5 rpm for a channel length of 0.6 m (2 ft), during 1 hour of operation. 
         [0021]      FIG. 3  is a front elevation section view illustrating a circulating ball regenerator  200  of the present invention with exemplary embodiments of a circulating ball assembly  212  and a two-channel assembly  214  for connection to an intermediate heat exchanger operating at a lower temperature. A pressurized working fluid channel  228  directs working fluid  218  from a pressurized outlet nozzle  219  of the intermediate heat exchanger via an intake nozzle  226  and a combustor nozzle  230  to the working fluid inlet of a gas turbine  236 . Simultaneously, a low pressure channel  217  directs the working fluid from the turbine via a turbine nozzle  237  and an outlet nozzle  239  back to a low pressure inlet nozzle  221  of the intermediate heat exchanger. Ball seals  244  and  246  minimize leakage of working fluid between falling ceramic balls  252  and the closed ends of channel  228 . The ceramic balls are part of the circulating ball assembly which includes a perforated ball guide  248  attached between a high temperature box  236  and an intermediate temperature box  242 , a ball advance worm  256 , and a worm gear drive motor  258 . High temperature components are of ceramic materials, as required. 
         [0022]    Performance of the ball regenerator is estimated for installation in an electric generating station. The gas turbine develops 300 kW (400 HP) continuously with a pressure ratio of 3 and turbine inlet gas temperature of 1670 K (3000 R). Heat addition is by combustion of fuel. At these conditions regenerator inlet gas temperature is K 1360 K (2440 R), effectiveness is 98%, and ball speed is 124 m/min (400 ft/min), corresponding to 160 rpm for a channel length of 0.3 m (1 ft), during 1 hour of operation. 
         [0023]      FIG. 4  is a front elevation section view illustrating a circulating belt regenerator  300  of the present invention with exemplary embodiments of a circulating wire belt assembly  312  and a two-channel assembly  314  for connection to a gas liquefier. A pressurized channel  328  directs liquefier air working fluid  318  from atmosphere via a liquefier compressor  324 , a compressor discharge nozzle  328  and an expander intake nozzle  330  of the liquefier to the intake of a turbo-expander  336 . Simultaneously, an exhaust channel  317  directs the vapor portion of liquefier working fluid from a liquid-vapor separator  338  via a separator nozzle  337  and an exhaust nozzle  339  to atmosphere while the liquid portion  340  is drawn off to a Dewar  342 . 
         [0024]    Performance is estimated for a circulating belt regenerator of an air liquefier capable of supplying liquid air for compression cooling of the 300 kW (400 HP) gas turbine of  FIG. 3 . Wind energy drives the liquefier compressor. During air liquefaction, regenerator inlet gas temperature is 294 K (530 R), effectiveness is 97%, and belt speed is 6 m/min (20 ft/min), corresponding to 7.5 rpm for a channel length of 0.3 m (1 ft), during 1 hour of operation. 
         [0025]    While I have illustrated and described my invention by means of specific embodiments, it is to be understood that numerous changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. For example, working fluid leakage may be stopped by injection of a purge flow downstream of the seals, the rate of heat transfer between working fluid and heat transfer elements may be enhanced by injection of a non-luminous gas into the channels, and prime mover heat input may include solar.