Regenerator Strongback Design

Abstract

A heat exchanger adapted to preheat the inlet air of a gas turbine by transmitting heat from its exhaust gases and including heat exchange core sections formed of a plurality of spaced parallel plates between which the air and gas flows. The plates are held adjacent to one another against forces produced by compressed air within the core by a number of separate bands which extend around the core in planes substantially normal to the flow of hot gases passing through the core. The separate bands around the core permit it to expand without being greatly restrained by a less expansive or cooler single member around the core.

Description

This invention relates to heat exchangers of the plate-fin type and specifically to a particular support structure around a plate-fin heater core to reduce thermal stresses.

In large stationary gas turbine installations, it is common to utilize a heat exchanger or regenerator for warming air prior to entering the turbine by using exhaust heat. Regenerators as used in this application refer to heat transfer devices in which two fluids are separated by stationary walls and the heat passes between the fluids through the walls.

The subject regenerator is a plate-fin type with fluid passages formed between spaced adjacent plates. A prior regenerator of which the present regenerator is an improvement over is disclosed in the U. S. Pat. No. 2,526,135 to Holmes et al. This patent discloses a heat exchanger also of the plate-fin type. When the turbine is first started, the exhaust gases quickly reach high temperatures. Thus, in a brief period, one end of the regenerator is subjected to these high temperature gases. The plate-fin core structure of the regenerator which is in good heat transfer relation to these hot exhaust gases quickly begins to expand. However, the support structure which encircles the core will not expand as rapidly due to a poorer heat transfer relation between it and the exhaust gases. When a rigid, one piece support structure surrounds the core, thermal stresses may be developed in the core due to the less rigid expansion of the outer structure. This might lead to leakage which reduces the regenerator's efficiency.

The present regenerator has a support structure comprising individual bands which encircle the core in planes substantially normal to the direction of exhaust gas flow. When the turbine is started and the core begins to rapidly expand, the separate bands move with the core without restricting movement of the core. The present regenerator with separated bands around the core also permit rapid contraction of the core which may occur when the turbine is shut down.

Therefore, an object of the invention is to provide a heat exchanger of the plate-fin type which is relatively free to expand and contract upon being subjected to temperature increases and decreases without producing excessive stresses on the core.

A further object of the invention is to provide a regenerator for gas turbines having a heater core of spaced plates which are held together by separate and unconnected band members which move relative to one another upon expansion and contraction of the core.

A still further object of the invention is to provide a regenerator for gas turbine applications having spaced plates with fluid passages formed between adjacent plates for air and gas flow which are held together by separate support members and which move relative to one another in the direction of the flow of hot gas to prevent subjecting the plates to thermal stresses.

Still further objects and advantages of the invention will be apparent from the following detailed description, reference being had to the drawings in which:

FIG. 1 is a perspective view of the plate-fin regenerator;

FIG. 2 is an enlarged view of the regenerator taken along section line 2--2 in FIG. 1;

FIG. 3 is an enlarged partially sectioned view of the regenerator taken along section line 3--3 in FIG. 2;

FIG. 4 is an enlarged section view of the regenerator taken along section line 4--4 in FIG. 2; and

FIG. 5 is an enlarged view of the heat exchange core.

In FIG. 1, a vertical flow type regenerator 10 is illustrated. Horizontal and angled flow types are also possible. In the present application, the regenerator is used to preheat the air passing from a gas turbine compressor to the turbine's combustion chamber. Hot exhaust gas from the turbine is used to preheat the air. The regenerator 10 has two elongated core sections 12 and 14 through which the hot exhaust gases and the compressed air are passed. The cores 12 and 14 are composed of substantially parallel plates 16 as shown in FIG. 5. The plates 16 are spaced one from another by bars 18 and 20 extending along plate edges and brazed or welded thereto. The bars 18 and 20 extend between the plates along a pair of opposing edges 19 of the core. The space between adjacent plates forms alternating gas channels 22 and air channels 24. Corrugated fins 26 are within the hot gas channels 22 and are copper-brazed to the adjacent plates 16 to increase the transfer of heat from the hot gases. Other type welding methods may also be used. As shown in FIG. 5, the bars 18 also enclose the air channels 24 along the top 21 and bottom 23 surfaces of the cores 12 and 14.

Duct means (not shown) transmit the hot exhaust gases from an associated gas turbine to the bottom surface 23 of cores 12 and 14. Likewise, duct means (not shown) which extend from the top surface 21 carry off the cooled exhaust gases of cores 12 and 14 after the hot gases pass through the regenerator.

Air is introduced into the regenerator 10 through an inlet 32 which extends between the cores 12 and 14. The air channels 24 are fluidly communicated with an elongated chamber 34 of inlet 32 which extends between the two cores 12 and 14 near the top surface 21. Likewise, an outlet 36 receives heated compressed air from an outlet chamber 38 which extends between the cores 12 and 14 near the bottom surface 23. The outlet chamber 38 is fluidly communicated with the air channels 24. Thus, air enters at the top of the cores 12 and 14 and flows downward through both cores to the outlet 38. Flanges 40 on the ends of the inlet 32 and outlet 36 are adapted for connection to pipes or conduits (not shown). The chambers 34 and 38 are formed by elongated tubular members having circular portions 42. The circular shape of the portions 42 provides maximum strength for containing the pressurized air in the chamber 38. This is important because the compressed air reaches a pressure of up to 90 psi in a typical gas turbine application. The circular cross section 42 of the chambers 34 and 38 are best able to withstand this pressure. They are stronger than less curved or flat members of the same thickness. Because of the greater temperature at the gas inlet end, it is especially advantageous that the plenum chamber 38 be curved. By using thicker material, plenum chamber 34 may satisfactorily be made flat.

As previously stated, cores 12 and 14 comprise spaced plates which are stacked in sandwich fashion to form gas and air channels therebetween. The cores are strengthened against pressure force caused by compressed air between the plates by a support structure encircling the cores 12 and 14. The support structure illustrated in FIG. 1 and adjacent the top of the cores 12 and 14 near the gas outlet end 21 is of conventional design. It includes end plates 44 and side plates 48 to reinforce the core sections 12, 14 at the upper end (cooler end).

The lower portions of cores 12 and 14 are encircled by individual band members 50 which extend around each of the cores 12 and 14. Each band member 50 includes two end members 52 and two side straps 54. The end members 52 and side straps 54 are welded together around the core members 12 and 14 to form a plurality of separate band members 50 which are vertically spaced from one another. The end members 52 have a T-shaped cross section shown in FIG. 3 which includes two strips 56 and 58 which are welded in a T-configuration. The T-shaped configuration is better able to withstand the pressure forces exerted by the compressed air within the core against the ends of the regenerator in a direction generally normal to the plane of the plates 16.

The subject regenerator is particularly suitable for large stationary gas turbine applications or for use in marine engineering. Typically, the regenerator as shown in FIG. 1 will have an approximate dimension of 8 feet high by 6 feet wide by 12 feet long. A typical regenerator as illustrated may weigh 53 tons. The temperature of the two fluids entering the regenerator are as follows. The air enters inlet 32 at approximately 500.degree.F. at 90 psi and leaves outlet 36 at about 900.degree.F. The hot exhaust gas from the turbine enters the bottom 23 of the regenerator at over 1,000.degree.F. and leaves the top surface 21 of the regenerator at about 600.degree.F. This represents an air temperature rise of about 400.degree.F. Fuel is burned with the hot air in the turbine combustion chamber to produce gases at about 1,600.degree.F. which is another 700.degree.F. increase in temperature. Thus, of a total air temperature rise of 1,100.degree.F. from the compressor to the combustion chamber, the regenerator has contributed about 36 percent of the total heat. In other words, the regenerator theoretically saves about 36 percent of the fuel a simple cycle turbine (without a regenerator) would use. Because the effectiveness of the regenerator is approximately 80 percent of the theoretical value, the actual net fuel saving is usually about 31 percent.

Experience with regenerators which have a rigid outer support structure around the heat exchange cores shows that it is desirable to provide a less restrictive structure to permit relatively free thermal expansion of the core plates in the direction of the flow of exhaust gases. This minimizes the production of stresses in the cores because of a differential in thermal expansions between the core plates and the support structure.

The cores 12 and 14 of the subject regenerator are subjected to hot exhaust gas at about 1,000.degree.F. very quickly after the startup of the turbine. The gas enters at the bottom of the cores 12 and 14 shown in FIG. 1. The support structure consisting of the band members 50 around the cores is subjected to the heat of the hot gas exhaust indirectly through conduction. Thus, the support structure increases in temperature more slowly than the cores 12 and 14 upon startup. Consequently, the plates 16 expand more than the surrounding support structure expands. The support structure around the lower portions of the cores 12 and 14 are formed of individual and separated band members which extend around each core in a plane substantially perpendicular to the direction of the flow of hot gases. Thus, when the core sections 12 and 14 expand in the direction of the hot gas flow, the band members move with the core plates and from each other. This minimizes stresses from being produced in the core structure.

The actual movement of the core plates in the hot gas flow direction upon subjection to 1,000.degree.F. may be quite large.

In a regenerator of the type illustrated in FIG. 1, having a height of approximately 8 feet, the core plates may expand a total of 0.6 inches. If this expansion is restrained, welded bonds between the plates and spacers and/or the plates and spacers themselves may fail. This produces air and gas leakage which decreases regenerator and turbine or cycle efficiency.

Another problem solved by the present regenerator is unequal expansion and contraction of the plates 16 from one end of the cores to the other end. This may be caused by non-uniform flow of the fluids through the channels 22 and 24. The band members 50 also permit one end of the core to expand more rapidly than another without producing great stresses which can rupture welds and/or plates and spacers in the core and produce leakage.

While the illustrated embodiment is a preferred embodiment of the invention, other embodiments might be adapted.

Claims

What is claimed is as follows:

1. A regenerator for the direct transfer of heat from engine exhaust gases to air entering the engine's combustion chamber comprising: a plate-fin type heat exchange core having generally rectangular plates extending parallel to one another with fluid passages formed therebetween; means spacing said plates including bar members extending along the edges of said plates for forming alternating air and gas passages between adjacent plates; said gas passages formed between pairs of adjacent plates and having bars extending along opposite side edges of said plates, the spaces along opposite end edges of said plates being left open for introducing gas to one end of the heater core and discharging the gas from the other end of the heater core; said air passages formed between pairs of adjacent plates alternately with said gas passages and having bars which extend along both side and end edges of said plates; air inlet means adjacent one end of said heater core being fluidly connected to said air passages for introducing air to said heater core; air outlet means adjacent the other end of said heater core being fluidly connected to said air passages for discharging air from said heater core; support means around said heat exchanger core for holding said plates together against the force of compressed air in said air passages which tends to separate the plates from one another; said support means including individual band members extending around said core which are separated from one another to permit relative movement therebetween whereby upon subjection of the core to high temperature gases, the plates may expand in a direction normal to the plane of the band members causing said members to move with respect to one another without exerting a restraining force on said core plates thus minimizing the formation of stresses which might be caused by a less rapidly expanding one piece support structure.

2. A regenerator for the direct transfer of heat from engine exhaust gases to air entering the engine's combustion chamber comprising: a plate-fin type heat exchange core having generally rectangular plates extending parallel to one another with fluid passages formed therebetween; means spacing said plates including bar members extending along the side edges of said plates for forming alternating air and gas passages between adjacent plates; said gas passages formed between pairs of adjacent plates and having bars extending along opposite side edges of said plates, the space along opposite end edges of said plates being left open for introducing gas to one end of the heater core and for discharging the gas from the other end of the heater core; said air passages formed between pairs of adjacent plates alternately with said gas passages and having bars which extend along both side and end edges of said plates; air inlet means adjacent one end of said heater core being fluidly connected to said air passages for introducing air to said heater core; air outlet means adjacent another end of said heater core being fluidly connected to said air passages for discharging air from said heater core; support means around said heat exchange core for holding said plates together against the force of compressed air in said air passages which tends to separate the plates from each other; said support means including individual band members extending around said core in planes normal to the flow of fluid in said passages and which are separated from one another to permit relative movement between said individual band members without exerting a restraining force upon said core plates whereby upon subjection of the core to high temperature gases, the plates expand in a direction normal to the plane of the band members which causes said band members to move with respect to one another thus minimizing the formation of stresses which would be caused by a less rapidly expanding one piece support structure.

3. A regenerator for the direct transfer of heat from engine exhaust gases to air entering the engine's combustion chamber comprising: two rectangular heat exchange cores extending along side one another with their adjacent side walls spaced from one another; each heat exchange core having generally rectangular plates which extend parallel to one another with fluid passages formed therebetween; means spacing said plates from each other including bar members extending along the side edges of said plates for forming alternating air and gas passages between adjacent plates; said gas passages formed between adjacent plates and having bars extending along opposite side edges of said plates; the spaces along the opposite end edges of said plates being left open to define a gas inlet in one end of the heater core and an outlet in the other end of the heater core; said air passages formed between adjacent plates alternately with said gas passages and having bars which extend along both side and end edges of said plates; air inlet means extending between said side-by-side cores near one end of said heater core and being fluidly connected to said air passages for introducing air to said heater cores; air outlet means extending between said cores near the other end of said heater cores and being fluidly connected to said air passages for receiving air from said cores; said inlet and outlet means including elongated members between said cores having spherically shaped portions which enclose the space between said cores for passing the relatively high pressure air therein; support means around said heat exchange cores for holding said plates together against the force of pressurized air in said air passages which tends to separate the plate from each other; said support means including individual band members extending around said core in planes normal to the flow of hot gases in said gas passages and which are separated from one another to permit band members to move with respect to each other in a direction parallel to the flow of hot gas through the cores whereby upon subjection of the cores to high temperature gases, the plate expands in a direction generally parallel to the flow of hot gases through the cores which causes said band members to move with respect to one another for minimizing the formation of stresses which would be caused by a less rapidly expanding one piece support member.