US2394253A

US2394253A - Air expansion power system

Info

Publication number: US2394253A
Application number: US401703A
Authority: US
Inventors: Nettel Frederick; Kreitner Johann
Original assignee: Individual
Current assignee: Individual
Priority date: 1941-07-10
Filing date: 1941-07-10
Publication date: 1946-02-05
Anticipated expiration: 1963-02-05

Description

Feb 5, 1946- F. NETTEL Erm.

AIR EXPANSION POWER SYSTEM Filed. July 10, .941 3 Sheets-Sheet 1 INVENFORS Peb 5, 1945- F. NETTELl-:rAL 2,394,253

AIR EXPANSION POWER SYSTEM Filed July 10, 1941/' 3 Sheets-Sheet 2 Feb. 5, 194s. F, NETTL mL 2,394,253

vAIR ExANsIo-N POWER SYSTEM Filed July 10, 194i '-3 sheets-sheet 3f Patented Feb. 5, 1946 AIR MANSION lfwER SYSTEM Frederick Nettel, Manhasset, and Johann Breitner, New York, N. Y.

Application July 10, 1941, Serial N0. 401,703

,9Claims.

The present art of expansion power systems uses open cycles with heating of the working medium by internal combustion of fuel in it, or closed cycles with heating through heating surfaces.

Closed cycles can utilize any type of fuel, but they are suering from many defects which impeded their practical use.

The broad object of this invention is to avoid these defects, simplify the arrangement and to improve the emciency.

It is a further specific object of this invention to provide a power system for double fuel operation.

The broad object is achieved by burning the fuel in a portion oi' the expanded air branched oil? after passing through part or the whole of the heat exchanger and by leading the gases and the exhaust air in separate streams through said heat exchanger and thence to the atmosphere.

Pure air only is working in the expansion machine. The temperature limit for the heated air is mostly dictated by the blading material of the turbine, and the surface heaters are designed for said limiting temperature. There are, however, other cases, where the metallurgical properties of the tube material of said heaters restrict the air temperature at the heater outlet to lower values than the turbine blading can stand. Since the overall thermal emciency of'air expansion power plants rises sharply with increasing turbine inlet temperature, this invention includes a combination of indirect heating as described hereinbefore, with additional direct heating by internal combustion. According to this invention, the bulk of the heat input is supplied by burning cheap fuel, for example coal, in air discharged from the turbine, and the combustion heat transferred through heating surfaces to the compressed air, which is thus heated 11p to the metallurgical limit for the heater tubes. Thereafter a comparatively small quantity of fuel suitable for internal combustion, namely one whichburns practically free from ash, residue or other deleterious concomitants, is injected into the hot compressed air and burned therein, whereby the air is heated further, up to the temperature permissible for the turbine blading. Such double fuel ,operation may be continuous or only temporary, such as for instance in power plants where base load is' produced by burning cheap fuel, and peak `load by additional internal combustion of gaseous or liquid fuel in an internal combustion chamber disposed in iront of the turbine inlet.

In the drawings amxed to this specication and forming part thereof, several embodiments oi this Fig. 3 represents an alternative embodiment of the regenerative heat exchanger.-

Fig. i shows a modification of Fig. 2 with subdivided combustion chamber served by two travelling gratos and an induceddraft fan for the eases discharged from the heat exchanger.

Fig. 5 represents a modication of Fig. 1 with the furnace air branched ofi behind the regenerative heat exchanger and fed back into the air pipe from the turbine before said heat exchanger, and an additional internal 'combustion chamber ior burning liquid fuel during double fuel operation. i

The plant according to Fig. 1 operates as follows: Airis taken in at i into the first stage compressor 2, cooled in the interccoler 3, compressed further in the second stage compressor t, from which it Hows into the tube system of the regenerative heat exchanger 5, in which it is preheated as will be explained hereafter. From E it ilows through pipe t and through the heating coil l, which latteris arranged within the combustion chamber t, and through pipe ii to the air turbine it, where it expands to a pressure near the atmospheric pressure while developing mechanical power to drive the compressors 2 and t and the electric generator il, which latter supplies useful power. The expanded, but still very hot air leaves turbine lil at i2 vand flows partly through the heat exchanger 5 where it is used to preheat the compressed air before being discharged to the atmosphere at i3. `another part of the hot air discharged from the turbine flows via a regulating ilap it and duct le to the combustion chamber t where it is used in the burner it, supplied with pulverized coal from source il, to heat the compressed air owing through the heating coil i disposed within said combustion chamber. The combustion gases formed in chamber ii leave the latter at I8 to flow through the regenerative heat exchanger 5, where they also heat the compressed air within the tube system before being expelled to the atmosphere at it. Cooling water for'the intercooler enters at it and is discharged at 2i. From air duct i5 a branch duct 22 leads directly into d with flap valve it arranged at the branching point. Fuel valve 2t, which opens when turned anti-clockwise, is coupled by linkage as shown to thermostat 25 with elastic bellows 26 and to yball governor 21. The latter is driven from turbine shaft.

Load and temperature regulation is effected as I follows: With increasing load the governor sleeve 29 moves downwards while point 30, which is connected to the thermostat bellows, remains stationary during the first moments. Thus point 28 also moves downwards with the result that fuel valve 24 opens and flap 23 admits more air to the burner. The increased heating causes the temperature at 25 to rise and the bellows to.

-time acts as safety device against excess speed and excess air temperature in coil 1.

While for pulverized coal ring highly preheated combustion air is very advantageous, the temperature of such air for grates is limited by design reasons to about 200 deg. C. For such plants the method of air supply is modified as will be shown in Fig. 2.

The power plant as per Figure 2 operates as follows: Air is taken in from the atmosphere at 3 I, compressed' in first stage compressor 32, intercooled in cooler 33, which` is shown in the example as of the water spray type in which cold water is sprayed in counterilow to the compressed air as indicated in Fig. 1 in more detail. The air is further compressed in second stage compressor 34, flowing hereafter through the tube system of the regenerative heat exchanger 35, thence through pipe 36 into the heating coil 31, arranged within the combustion chamber 38, and through pipe 39 into the first stage air turbine 40 which drives the electric generator 4|. From turbine 40 the air ows in a partly expanded condition through a second heating coil 31', also disposed within said combustion chamber 38, in which the air, is reheated, flowing hereafter through the second stage turbine 4U' in which it expands to a pressure near the atmospheric pressure while delivering mechanical power to drive'part compressors 32 and k34, and is finally expelled in part at 43 into the ambient atmosphere. The remainder of-that air is, however. branched oil behind the heat exchanger via nap valve 44 into duct 45, which leads it under the travelling grate 46 disposed in combustion chamber 38, thus supplying warm air for the combustion of the coal which' is fed to said travelling grate from coal chute 41. The combustion gases formed in 38 leave it at 48 to ow also through the regenerative heat exchanger 35, in which they also preheat the compressed air coming from compressor 34, to be hereafter expelled to the atmosphere at 49. For load regulation it may be desirable to regulate the heating of the air in coils 31 and` 31 independently. In such cases it is advantageous to provide separate grate, stokers or for pulverized coal firing separate burners, for each of the heating coils.

The principal difference between the arrangements shown in Fig. 1 and Fig. 2, as regards. the surface heaters, consists in the combustion air being branched off before the regenerative heat exchanger in Fig. 1 and after the heat exchanger 35 in Fig. 2.

In some cases it is desired to supply the air for the combustion chamber at a temperature below that at which it is discharged from the turbine but higher than that at which it leaves the heat exchanger. For this purpose the regenerative heat exchanger is modified as shown in Fig.l 3. 'I'he air discharged from the air turbine enters at 60, ows as indicated by dotted line up to the outlet branch 6i provided with a ap valve 62. At this point part of the air is branched oi to the combustion chamber (not shown) while the remaining portion ows on through the whole length of the heat exchanger, leaving it at 63. The combustion gases from the combustion chamber enter at 64 and ow as also indicated by dotted line, through the whole length of the heat exchanger, leaving it at 65.

The plant as per Fig. 4 operates generally in the samermanner as that of Fig. 2. -The combustion chamber, however, is sub-divided by a wall 38' into two part-chambers in communicating connection at the top. Each part-chamber is served by its own travelling grate, 46' and 46" to which air is fed through pipes 45' and 45" respectively. The two grates permit to control vthe heating in the

coils

31 and 31 indithe heat exchanger 35, an induced draft fan 49' is disposed in the outlet pipe 49 from said heat exchanger.

The plant as per Fig. 5 operates in principle in the same manner as that shown in Fig. l. However, the air for the combustion chamber 8 is branched oil' behind the heat exchanger 5E, through pipe l5', fan I5", pipes 22 and the coal burner I6 into the combustion chamber 8. The gases leave lthis chamber by pipe I8' and are led into the pipe coming from the air turbine I0, where they mix with the air discharged from said turbine. 'I'he branched-olf air is not quite pure, containing a very small quantity of combustion products, which, however, have no effects on the combustion in chamber 8. Another special feature of this example of the invention consists in the provision of the internal combustion chamber 52, disposed' in pipe 9, in which additional liquid fuel is burned to heat the Working air to a higher temperature than is done in heater coil 1. This liquid fuel is fed to chamber 52 from fuel tank 56 via fuel pump 55, pipe 54 with regulating valve 53. Thus part of the heat required in the system is produced by pulverized coal in an external furnace, and another part by liquid fuel in an internal combustion chamber.

It is immaterialto this invention what types of turbines, expansion engines, compressors, coolers, regenerative heat exchangers and combustion devices are used and what kind of fuel is burned in the latter. y

Manifestly, variations may be resorted to, equivalents of parts introduced, and parts may be used without others within the broad scope of the invention and its features.

Having now described our invention, we claim:

1. In the method of producing power by successively compressing, heating and expanding a gaseous working uid, the combination of com- A pressing an air stream, preheating it by surface heat transfer from said same stream after its expansion, heating it further by surface heat transfer from the gaseous products of an external fuel combustion eiected at substantially atmospheric pressure, heating it still further by internal combustion of fuel in said compressed air, expanding the resulting compressed and heated air-gas mixture to substantially atmospheric pressure, thereby developing power, cooling said air-gas mixture by said surface heat transgases by said surface heat transfer to said com pressed air, and ejecting said cooled combustion gases to the atmosphere.

2. In a powersystem including means to take in a continuous stream of air from the ambient atmosphere, means to compress it, regenerative heatI exchange means to preheat it after compression, surface type fuel burning means to heat it further, an expansion machine disposed to develop power by expansion of said compressed and heated air, conduit means connecting in succession, the outlet of said compressing means to the inlet of the heated side of said heat exchange means, the outlet of the latter to the inlet of said fuel burning heating means, the outlet of the latter to the inlet of said expansion machine, the outlet of the latter to the inlet of the heating side of said heat exchange means, the outlet of the latter to the atmosphere, conduit means for branching off a portion of th expanded air after it has passed through said regenerative heat exchange means, and for leading it to said fuel burning heating means so as to use said branched oi air as combustion air, said heating means being designed for air inlet temperatures under 200 deg. C.

3. In a power system including means to take in a continuous stream of air from the ambient atmosphere, means to compress it in stage compressors with interposed cooling means, regenerative heat exchange means to preheat said air after compression, surface type fuel burning means to heat it further, an expansion machine disposed to develop useful power by partial expansion of said compressed and heated air, second surface type fuel burning means to reheat the air issuing from said expansion machine, a second expansion machine disposed to develop power for driving said compressors by expansion of the partially expanded reheated air to nearatmospheric pressure, conduit means for connecting in succession, the outlet of the highest pressure stage compressor to the inlet of the heated side of said heat exchange means, the outlet of the latter to the inlet of said first surface type fuel burning heating means, the outlet of the latter to the inlet of said rst expansion machine, the outlet of the latter to the inlet of Iii) said second surface typefuel burning reheating being designed for air inlet temperatures under' 290 deg. C.

e. In a power system according to claim 3, hrst and second surface type fuel burning heating and reheating means for the air being independent of each other as regards adjustment of iiuel feed.

5. In a power system including means to take in a continuous stream of air from the ambient atmosphere, means to compress it, regenerative heat exchange means to preheat it aftercompression, surface type fuel burning heating means to heat it further, an expansion machine disposed to develop powerv by expansion of said compressed and heated air, conduit means for connecting in succession, the outlet of said compressing means to the inlet to the heated side of said heat exchange means, the outlet of the latter to the inlet of said fuel burning heating means, the outlet of the latter to theinlet of said expansion machine, the outlet of the latter to the inlet of the heating side of said heat exchange means, the outlet of the latter to the atmosphere, conduit means -for branching/off a portion of the expanded air Aafter it has passed through said regenerative heat exchange means, and for leading it to said fuel burning means so as to use said branched oif air as combustion air, conduitv means for leading the products of combustion from said fuel burning heater to the heating side of said regenerative heat exchange means, and flow dividing means in said regenerative heat exchange means to allow the air issuing from said expansion machine and the products of combustion from the fuel burning heater to ilow in separate substantially parallel streams through the heating side of said regenerative heat exchange means.

6. In a power system including means to take in a continuousstream of air from the ambient atmosphere, means comprising stage compressors y to near-atmospheric pressure, conduit means for z connecting in succession, the outlet of the highest pressure stage compressor to the inlet of the heated side of said heatexchange means, `they outlet of the latter-to the inlet of said rst fuel burning heating means, the outlet of the latter to the inlet of said rst expansion machine, the outlet of the latter to the inlet of said second fuel burning reheating means, the autistof the latter to the inlet of said se i wpai/:reilen machine, the outlet of the latter to the inlet of the heating side of said heat exchange means, the outlet of the latter to the atzc'icsphere, conduit means for branching o@ a portion of the expanded air after it `has passed through said regenerative heat exchange means, and for leading it .v to both said fuel burning heating and reheating means so as to use said branched on@ air as combustion air, conduit means for leading the products of combustion in said fuel burning heaters to the heating side of' said regenerative heat exchange means, and flow dividing 'means in said regenerative heat exchange means te allow the air issuing from said second expansion machine and the products of combustion from the fuel burning heaters to flow in' separate substantially parallel streams through the heating side of said regenerative heat exchange means.

7. In a power system according tc claim 6, rst and second surface type fuel b heatv it further, an expansion machine disposed to develop power by expansion of said compressed and heated air, conduit means for connecting in succession, the outlet of said compressing means to the heated side of said heat exchange means,

' the outlet of the latter to the inlet of said fuel burning heating means, the outlet of the latter to the inlet of said expansion machine, the outlet of the latter to the inlet of the heating side of said heat exchange means, the outlet of the latter to the atmosphere, conduitr means for branching oil' portion of the expanded air after it has passed through said regenerative heat exchange means, and for leading it to said fuel burning heating means so as to use said branched oir air as combustion air, and conduit means for leading the products of combustion from said fuel burning heater into the heating side of said regenerative heat exchange means, so as to admix them to the air issuing from said expansion machine.

` 9. In the method of producing power by successively compressing, heating and expanding a gaseous working fluid, the combination of compressing an air stream, preheating it by surface heat transfer from said same stream after its expansion, heating it further by surface heat transfer from the gaseous products of an external fuel combustion effected at substantially atmospheric pressure, expanding the compressed and heated air to substantially atmospheric pressure thereby developing power, cooling said expanded air by said surface heat transfer to saidl compressed air stream, ejecting a portion of said expanded and cooled air to the atmosphere, utilizing the remaining portion of said expanded and cooled air as combustion air for said external combustion, cooling the resultant combustion` gases by said surface heat transfer to said compressed air stream, and ejecting said cooled combustion gases to the atmosphere.

FREDERICK NE'I'IEL. JOHANN KREITNER.