US2457594A

US2457594A - Turbine compressor plant

Info

Publication number: US2457594A
Application number: US443000A
Authority: US
Inventors: Nettel Frederick; Kreitner Johann
Original assignee: Individual
Current assignee: Individual
Priority date: 1942-05-14
Filing date: 1942-05-14
Publication date: 1948-12-28
Anticipated expiration: 1965-12-28

Description

Dec. 28, 1948. F. NETTEL EI'AL 2,457,594

I TURBINE COMPRESSOR PLANT Filed May 14, 1942 3 Sheets-Sheet 1 Fig.5 u

IN V EN TORS BY M 7mm.

1948- F. NETTEL ETAL TURBINE COMPRESSOR PLANT 3 Sheets-Sheet 2 Filed May 14, 1942 HOTWIND 136 TORS . HOTWIND INV quantity and/or pressure.

Patented Dec. 28, 1948 OFFICE TURBINE COMPRESSOR PLANT Frederick Nettel, Manhasset, and Johann Kreitner, New York, N. Y.

Application May 14, 1942, Serial No. 443,000

9 Claims. 1

This invention relates to a novel method of producing compressed gas, preferably air, particularly for consumer systems of widely fluctuating flow resistance, causing large fluctuations of requirements in gas quantity and/or pressure.

Known plants for gas compression provide power producing means in driving relation to air compressing means, and conduit means connecting the outlet of said air compressing means to the consumer system. Any change in said consumer system thus necessarily reacts directly on the compressing means, so that the entire performance of these plants depends on the performance characteristics of said compressing means.

Certain types of compressors and blowers permit only comparatively small decreases in gas quantity at their outlet, while any substantial reduction causes a dangerous unstable condition generally known as surging. This phenomenon has so far excluded the otherwise very efflcient multistage axial flow compressor from many uses, and even radial type compressors often require inconvenient and complicated regulating systems to operate blow-off valves discharging certain quantities of gas when the quantity consumed falls under a certain minimum, which varies with the resistance offered by the consumer system.

It is the basic object of this invention to provide a. gas compressing system wherein the compressor means remain practically unaffected by any changes occurring in the consumer system, so that the highly efllcient multistage axial flow compressors with their known very narrow surging limits may be used to supply consumer systems of the most difficult requirements as regards This invention permits to use such normally extremely surge-sensitive" compressors even where at certain times the required gas quantity drops to zero, which is equivalent to operation of a plant as known in the art against closed pressure valve, without any danger of surging and without the use of any blow-ofi valve. Thus new wide fields of application are made accessible to the axial flow compressor of superior efliciency, from which it has been barred so far.

This object is achieved basically by compressing the gas to a pressure substantially higher than that of the consumer system, and by expanding it in turbine means interposed in the gas stream between the compressor means and the consumer system, so that no direct conduit connection exists between the compressor means and the point in the gas streams where variations in presexpansion stages.

2 sure and quantity may occur. The turbine means by their inherent characteristic of periormance, act as a very effective buffer, shielding the compressor means from the effects of variations in the consumer system.

Where the turbine means are located close tow the compressor means, they may preferably be arranged in driving relation with the latter. Where hot compressed gas may be supplied, the gas stream may preferably be energized by heating it in front of the turbine means.

The blower system as described may be in driving relation with additional power supply means, or may be self-sufllcientin power. For the latter purpose it is preferable to compress more gas than is required in the consumer system to a pressure substantially higher than required, energize it by heating, expand it in multistage turbine means, and branch oil the quantity required for the consumer system at a suitable intermediate stage of the turbine means, while the remainder is expanded to the starting pressure. Such an arrangement offers a still more effective shielding of the compressor means from changes in operating conditions, due to the high pressure stages of the turbine means interposed as buffer between compressor and consumer system. The reason for this shielding effect is found in the well-known performance characteristic of extraction-backpressure steam turbines, and consequently of any elastic fluid turbine, in which changes in the extraction quantity and/or pressure are compensated inside such turbines without tangible reaction on the supply source of the working fluid, which in the case of steam turbines is the steam boiler, and in case of gas turbines, the compressors. The conditions are similar to those in extraction steam turbines working under constant admission pressure, which are known to consume a practically constant quantity regardless of variations that may occur in the lower Thus also in the system according to this invention, the working conditions of the compressor supplying a gas turbine remain almost unchanged, even if the supply pipe to the consumer system, i. e. the extraction pipe, is completely closed. The gas which cannot flow to the consumer, due either to smaller demand, or with the supply pipe closed altogether, will simply flow through the low pressure stages of the gas turbine which acts, so to speak, as an automatic useful blow-off.

If the turbine means interposed between compressor and consumer system are, .for example, of an expansion ratio of two or more, a ten per cent 3 change of pressure in the consumer system causes less than two per cent change of pressure at the compressor outlet. This shielding eifect increases rapidly with increasing expansion ratio of the interposed turbine means; with an expansion ratio of about four it amounts to a practically complete isolation of the compressor means fro watever occurs in the consumer system.

Where the compressor need only be protected against moderate variations of pressure or resistance in the consumer system, a device of utmost simplicity may be provided by interposing only one or two stages of turbine means without heating of the gas in front of them. In such cases the turbine blading is simply added to the compressor blading as an additional stage or stages within the same casing and on the same rotor, thus forming an integral compressor of improved surging characteristics; The power requirements of such compressor, as compared with one of straight compression to the consumer pressure, i. e. without turbine stages, is of course increased due to the internal losses caused by the additional compression and re-expansion, but these losses are very small in case of only one or two interposed turbine stages.

The great advantages of inserting turbine means between compressor means and consumer system become particularly apparent if means are provided for keeping the rotative speed of the compressor means and interposed turbine means constant, such as speed governors influencing the heating of'the compressed gas, or complementary coupling to an A. 0. motor or generator connected to an electric power system of substantially constant frequency. The practically constant pressure at the compressor outlet, achieved by the interposing of turbine means, together with a constant speed imposed by the abovementioned design measures, results in a constant delivery characteristic of the system. In other words, the compressor can be designed to operate always near its best efliciency point, which is advantageous both for economy and convenience of operation. Besides, the new system makes the highly efhcient axial flow compressor with its very steep speed-quantity characteristic available for satisfying constant-quantity requirements involving large pressure variations, while running at constant speed driven for example electrically.

Certain embodiments of this invention are well suited for the simultaneous production of power, other than that required for driving the compressors, still others offer additional advantages in efliciency and/or performance by reheating the whole or part of the gas or air during expansion. Examples of such embodiments will be described as this specification proceeds.

The invention will be now described more specifically in its, preferred application to the production of wind for metallurgical furnaces and similar consumers. 1

It is known to produce wind by means of combustion turbine-driven compressors. The known arrangements compress air to the pressure required in the furnace, and lead one portion ofthe air to the furnace as wind, while the rest is generally compressed further and passed through the cycle of the combustion turbine driving the compressor.

' Such known arrangements are not widely used because they offer little advantage over other known drives. In addition some of them pollute 31c wind by the products of internal combusefficient manner. It is a specific object to economically produce -wind of low moisture content, and unpolluted by It is also known in the art of air drying, to cool the air either before or after compression. Cooling after compression is more effective because the partial pressure of the water vapor at a, certain temperature represents a smaller fraction of the total pressure of the compressed air, so that the water weight represents a smaller fraction of the air weight.

.Modern blast furnace operation requires a sharp drying of the wind to three grains water per 0. ft. at atmospheric pressure, or less. The required dryness was often unobtainable by cooling with naturally available cooling media under the required wind pressure, which in most cases is too low for this purpose. For example, 30 to 35 lbs. per sq. in. absolute are necessary in blast furnaces. Cooling is further limited by the temperature of the available cooling medium, mostly water of60 to deg. F. Thus it became neces sary to intensify drying by using chilled water or even brine, produced in rather complicated and expensive refrigeration apparatus.

It is another object of this invention to improve the thermal emciency of wind production in industrial furnaces and in particular in blast furnaces, and of the blast furnace plant as a whole.

It is still another object to combine production of compressed air with power production in an products of combustion.

It is finally an additional object of this invention to reduce the size and weight of the necessary apparatus for the production of a given quantity of compressed air.

The economy of wind drying is achieved by cooling the wind at apressu're higher than the 'furnace pressure, which is made possible by the process described above. A modification provides for cooling between stages of compression, and/or after compression; it is only essential for this invention that the last cooling is carried out at a pressure substantially higher than the required wind pressure.

This invention thus makes double use for the intercoolers provided, namely for intercooling of the working fluid in a combustion turbine cycle and for drying the furnace air to a p t mined degree, 1

A further improvement of the method described above is obtained by using the excess air expanded to near-atmospheric pressure as combustion air for heating the whole of the compressed air before it enters said first power producing expans'lon means, an d/or for wind heating.

Still higher efllciency is realized by a process comprising cooled compression of more air than n is required in the furnace, heating it after compresslon in a surface type heater, expanding it in power producing expansion means to'the required furnace pressure, leading the excess air at furnace pressure to said surface type heater,

burning fuel in it to heat the high pressure air sideration of the ensuing description of the em-,

bodiments of'apparatus for carrying the invention into effect which are illustrated in the accom-- panying drawings by way of non-limiting exam Z ples in which:

Fig. 1 shows a plant for gas compression in which the compressor is coupled to a synchronous motor, and the turbine to a synchronous generator.

Fig. 2 represents an embodiment with both compressor and turbine coupled to a synchronous motor.

Fig. 3 shows another embodiment of arrangement as per Fig. 2 with compressor and turbine arranged in a common casing.

Fig. 4 is a combination of'arrangement as p r Fig. 2 with heating of the compressed gas before partial re-expansion. A synchronous machine is coupled to compressor and turbine.

Fig. 5 is a combination of arrangement as per Fig. 4 in which the turbine is of the extractionbaclrpressure type.

Fig. 6 represents a plant with an intercooler for wind drying, surface heater, and an air turbine from which the wind is discharged from an intermediate stage to the furnace.

Fig. 7 shows an embodiment with two inter- 4 coolers and one wind heater towhich the combustion air is supplied from the turbine exhaust.

Fig. .8 is another combination with a reheater for the excess air, and use of the turbine exhaust first for wind heating and thereafter for heatin the air at top pressure.

Fig. 9 is still another combination with tw coolersfor wind drying, a surface air heater for top pressure, an air turbine for expansion of the wind to furnace pressure, a wind heater, a reheater and a second turbine for the excess air. The turbine exhaust is used in heaters.

Fig. 10 shows another alternative arrangement with an air turbine for expanding to furnace pressure, an internal combustion-turbine for expanding the excess air to atmosphere, wlth'separate combustion chamber for the latter; wind heater and surface air heater are supercharged on the gas side at furnace pressure.

Fig. 11 shows a simple arrangement without excess air, with one dryer-intercooler,'s'urface air heater and drive by a synchronous A. C. motor designed to run as asynchronous motor during starting.

Fig. 12 represents a high-efllciency' plant for production of hot wind with dryer-intercooler-of the water contact (spray) type, reheating at a pressure higher than the furnace pressure, and additional combustion chamber for reheater.

The arrangement as per Fig. l, which represents the simplest embodiment of the new method of gas compression, operates as follows: Gas taken in at i is compressed in multistage axial fiow compressor 2, in driving relation with an electric motor 3, to a pressure higher than required in the consumer system. The latter is represented by pipe 8 with several branch pipes .8. The thus compressed gas flows through pipe I4 to gas turbine 5 arranged in driving relation with an electric generator 6. In turbine 5 the'Sasexpands to the pressure required in said consumer system, into which it is discharged through pipe I. The power developed by said expansion is utilized in the electric generator 6 which may be connected to the same electric supply as motor 3 or to another electric, system. The speedsat which compressor and .turbine operate may be the same or different.

As explained before this arrangement is able to supply gas against a greatly varying pressure or resistance in the consumer system without requiring variation of the rotative speed of the compressor and without danger of surging.

are coupled mechanically with motor 6 supplying the required power. If this set is running at constant speed. driven for example by a synchronous motor, the plant will supply a substantially constant gas quantity into system 8, irrespective of pressure variations in pipe 1 within wide pressure ranges.

Where these pressure variations are moderate, an arrangement of extreme simplicity can be provided, such as shown in Fig. 3 where the compressor stages c and turbine stages t are arranged on a common rotor r driven by power supply means (motor) :2. Thus the gas taken in at i is compressed and re-expanded in the same stator housing s equipped with turbine guide vanes ii, in addition to compressor guide vanes 01. The gas is discharged at d at a pressure which may vary much more than would be permissible for an ordinary axial flow compressor.

Where the expansion ratio of the interposed turbine is considerable, heating of the gas in front of said turbine is preferable for eflicient power production from said re-expansion. Fig. 4 shows such an arrangement. Itoperates as follows:

Air taken in at I is compressed in compressor 2 to a pressure higher than that required in consumer system 8, thereafter lead via pipe 4 into a heater coil 4', in which the gas is heated by flame 4". The thus heated gas continues to the gas turbine 15 wherein it expands to the pressure required in the consumer system 8 and is discharged into the latter through pipe I. Depending on the pressure in system 8 and on the intensity of heating in coil 4', turbine 5 may develop less power than is consumed by compressor 2. To cover the power deficit, an electric motor 6, preferably of the synchronous type, is mechanically coupled to compressor and turbine, maintaining the speed of the whole set constant. Under other working conditions turbine 5 may just cover the requirements of compressor 2. In this case motor 6 will run at no-load and may be omitted altogether. Under again other conditions turbine 5 may produce more power than required by compressor 2, causing the motor 6 to operate as generator supplying power into the electric system to which it is connected.

If machine 6 is of the synchronous type, for example, it will under all working conditions maintain the speed of the set constant, resulting in a substantially constant delivery characteristic, as explained for Fig. 2. Taking into consideration the peculiar performance characteristic of the axial flow compressor, preferably employed in the examples described, there are practical limits to the pressure rise in pipe I, but by proper selection of the expansion ratio for turbine 5 the permissible range of pressures in the consumer system can be made wide enough to permit successful use of the axial flow compressor; furthermore very diflicult supply problem can by this invention be solved by compressor means of constant rotative speed; thus the simple and cheap condition would require a blow-off valve in the I arrangements as per Figs. 1-4. The arrangement shown in Fig. 5 is capable o supplying any gas quantity down to zero without blow-off. Its operation is basically the same as for Fig. 4, except that more gas, preferably air,

than required in the consumer system is taken in, compressed and heated. Turbine 5' is, more over, in this example an extraction-back pressure turbine with the gas entering through pipe 4. The gas expands to the pressure prevailing in the consumer system 8, into which the required quantity is branched off from'an extraction point be: tween stages of said turbine through pipe 1, while the excess gas quantity I expands in the lower stages of turbine 5' to the starting pressure, be-

ing discharged through pipe 1'. With. motor 6 driving the set at constant speed, basically the same performance characteristic results as for Fig. 4. If, however, the requirements of the consumer system 8 drop very much, or if the pipe 1 is closed altogether by valve 8', part or all the gas not flowing to the consumer system continues to expand in the lower pressure turbine stages,

as already mentioned. With the turbine 5' properly designed, the compressor 2 will be little affected by anything that happens in pipe 1, and surging will not occur even with valve 8 closed tight.

The example as per Fig. 6 for production of warm furnace wind operates as follows: Air ent-ers the first stage compressor H at H, flows through the surface intercooler l2, with cooliiiag; Through cooling under pressure part of the mois-. ture contained in the air condenses out and is; discharged at l4. Dried air continues through. conduit I5 into the second stage compressor i6, being discharged at top pressure through pipe l1, to flow-into surface type air heater l8, through. it, as indicated by-dotted line, then through pipe water inlet and outlet indicated under H into a second surface heater l9, through the latter as also indicated by dotted line, and through pipe to the air turbine2 The action of the surface heaters will be described later. At the outlet of stage compressor H the air pressure is high enough to dry it by cooling it with water Y of natural temperature for the requirements of i In turbine 2| the heated air is expanded to furnace pressure'and the quantity required by the furnace discharged from an appropriate stage through pipe 22 to the furnace. The

the furnace.

remainder of the air is further expanded in the lower stages of said air turbine to near-atmospheric pressure, leaving through pipe 23 into chamber 24, disposed between the surface heaters i8 and |9, thence through the tubes of heater f8, and to the atmosphere at 25. The heat for the plant is produced by combustion of fuel, preferably blast furnace gas, in combustion chamher 26, the fuel entering-through pipe 21, and

air from the atmosphere at 28. The hot combustion gases fiowv from chamber 26 upwards through the tubes of surface heaters I3 and i8 and also to the atmosphere at 25, heating through heat transfer the compressed air of said heaters on its way to turbine 2|. In order to keep the speed of the set practically constant, the fuel valve 29 is influenced by speed governor 30 as shown in the drawing. Starting oi the set is effected by electric motor 30' in the usual way.

The alternative as per Fig. 7 for production of hot wind for a metallurgical furnace operates as follows: Air is taken in at 3| through stage compressor 3|, intercooler 32 with cooling water conections 33, pipe 35, second stage compressor 36 in the same way as in Fig. 6. Drain of moisture through pipe 34. From compressor 36 the air flows at top pressure into after-cooler 31 with cooling water connections 38, out through pipe 40, provided with another moisture drain pipe 39, to enter surface heater 4|, passing through it as. indicated bydotted line, thereafter through pipe 42 to the air turbine 43. In the latter the hot air expands to furnace pressure, the quantity required in said furnace being discharged at a suitable stage from said turbine through pipe 44, passing thereafter through surface heater 45 as indicated by dotted line, and leaving through pipe 46 as hot wind for the furnace. The' excess quantity of air expands further in turbine 43 to near-atmospheric pressure, beingled thereafter through pipe 41 to combustion chamber 48 for the heaters 4| and 45. In chamber 48, fuel entering through pipe 4.) is burned in the air coming from turbine 43 and the 'gases from this combustion flow upwards in succession through the tubes of

heaters

45 and 4|, and to the atmosphere at 50. Thus the combustion heat is used to heat' first the wind in heater 45, thereafter the whole air at top pressure in heater 4|. The after-cooler 31 is provided for such plants where the available cooling water is sometimes rather warm (summer-time), so that the cooling after the first stage compressor would not dry the air to the desired degree. By cooling at still higher pressure the desired drying effect may be achieved even with verywarm cooling water.

. In order to control the temperature in the combustion chamber 48, secondary air may be blown in through a pipe 5| by means of a forced draft fan 52. Starting of the plant is effected by starting motor 53.

Another alternative arrangement as per Fig. 8 for hot wind production operates as follows: The flow of the air, in at 6|, through stage compressor 6|, intercooler 62 with cooling connections 63, pipe 65, second stage compressor 56, is basically the same as in Fig. 6. Drain of moisture through pipe 64. From 66 the air continues through pipe 61 into surface heater 68, as indicated by the dotted line, then through pipe 69 to air turbine 10, expanding therein to the furnace pressure, and leaving through pipe 1|. From that pipe the required wind quantity is branched off through pipe 1|, to flow through gases from pipe 18 which still contain sufficient free oxygen. The thus reheatedgases'flow upwards through the tubes of heater 12 and thereafter -of heater 68, to be finally discharged to the atmosphere at 8|. Thus the heat of said second combustion is used to heat first the wind, and thereafter the whole air from the second stage compressor, before said air enters the air turbine 10. Also in this case additional air may be blown intocombustion chamber 19 byfan 82, to control the temperature in chamber 19.

The different combination of a plant for wind production as per drawing Fig. 9 operates as follows: The now of the air in at 9|, through stage compressor 9|, intercooler 92 with cooling water connections 93, drain 94, pipe 95, second stage compresor 96, after-cooler 91 with cooling water connections 98, drain pipe 99 and pipe I is substantially thesame' as shown in Fig. 7. From pipe I00 the compressed air passes through surface heater IOI, flowing as indicated by the dotted line, out through pipe I02 and after brancing off a part of the air through pipe I03, the purpose of which will become clear later, the wind quantity is expanded in air turbine I04 to furnace pressure. Thereafter the wind flows through pipe I05, then through surface type wind heater I08 via pipe I01 to the furnace. The excess air, over what is required in the furnace, is branched off through said pipe I03 into an internal combustion chamber I04 in which fuel, entering through pipe I05 under pressure, is burned, The products from this combustion flow through pipe I06 to gas turbine I01, expanding therein to near-atmospheric pressure,

and via pipe I08 into combustion chamber I09,

disposed below the surface heaters I06 and IN. These two heaters are connected on the gas side through intermediate chamber IIO. In chamber I09 additional fuel is burned, entering through pipe III, in the gases from turbine I01 which still contain free oxygen; The products from this combustion flow upwards through the tubes of said surface heaters, first through wind heater I06, then through air heater fill and out to the atmosphere at II2. Excess power over what may be required for wind production may be utilized for example in electric generator II3 coupled with the turbines. Since it is known in the art to arrange turbines and compressors in a system on separate shafts, it is an obvious further alternative to arrange for example turbine I01 driving generator II3 on a separate shaft. Generator II3 may be so designedas to be used as motor for starting of the plant.

. The alternative embodiment of the invention as per Fig. 10 operates as follows: Air is taken in at I2I', compressed in stage compressor I2I', passed through intercooler I22 with cooling water connections I23, pipe I25, through second stage compressor I26 and is at top pressure in pipe I21. Drain of moisture from intercooler takes place through pipe I24. From pipe I21 the air continues through the tubes of regenerative heat exchanger I28, leaving it through pipe I29, to enter thereafter surface type heater I30, flowing through it as indicated by the dotted line, and on through pipe I'3I into the air turbine I32. In the latter the air expands to furnace pressure, being discharged through pipe I33. From this the required wind quantity is branched off through pipe I34 into the wind heater I35, through which it flows as indicated by dotted line and finally discharged as hot wind to the furnace through pipe I36. The excess air is led through pipe I31 to combustion chamber I38 disposed below the surface heaters I35 and I30. Blast furnace gas is compressed in gas compressor I38 to substantially furnace. pressure and fed through pipe I40 also to combustion chamber I38, wherein it is burned in the air entering through pipe I31 under furnace pressure. The products from this combustion flow upwards through the tubes of surface heaters I35, then I'30, leaving via pipe I to enter gas turbine I42, where they expand to nearatmospheric pressure, passing thereafter via pipe I43 into regenerative heat exchanger I23. Through the latter they flow as indicated by the dotted line, to be finally rejected to the atmosphere at I44. For metallurgical reasons it is necessary to limit the temperature in combustion chamber I38. This is done by leading into that combustion chamber through pipe I45 with valve I45, a regulatable quantity of compressed air tapped from stage compressor I2I at a point where the pressure is substantially the same as prevails in chamber I38, namely the furnace pressure.

Since the same pressure exists in the wind heater I31 inside and outside the heater tubes, these are relieved completely of any stress from pressure, which is particularly desirable due to the very high temperatures prevailing in said heater.

Fig. 11 represents a particularly simple alternative arrangement which may be adopted where the air pressure required by the consuming device is comparatively low, or when it may be feasible in the future to allow higher air temperatures at the turbine inlet. The plant operates as follows: Air is taken in at I'5I', compressed in stage compressor I5I, flowing thereafter through intercooler I52 with cooling water connections I53. Moisture is drained through pipe I54. The air continues through pipe I55 to second stage compressor I56 and thence at top pressure via pipe I51 to the surface heater I58, through which it flows as indicated by the dotted line. From heater I58 it is led via pipe I59 into air turbine I60, in which it expands to the pressure required in the consuming device, being discharged to the latter through pipe I6I as warm wind. It is evident that by energizing the compressed air through heating, the energy produced in the air turbine can be made to cover the compression work. Heating of the compressed air takes place ina furnace chamber I'62 disposed below heater I58. Air for combustion is taken from the ambient atmosphere through valved pipe I63, fuel through valved pipe I54.

.If the resistance in pipe I6I increases, the pressure in that pipe will rise. The air turbine I60 will under this condition develop less power due to increasing back pressure and the power deficit must be made up by intensifying the combustion in chamber I62, so as to raise the air temperature at the inlet to the air turbine I68. The set may also be coupled with a synchronous motor for supplying power, I65,-which may be used also'for starting of the plant.

Certain kinds of furnaces, for example such serving blast furnaces or Bessemer converters, require wind of varying pressure with the wind quantity constant or varying. If, for example, the same wind quantity is required at fifty per cent higher gauge pressure, it is obvious that more power has to be furnished into the blower drive. Fig. 12 shows a blast furnace blower plant also suited to fulfill these peculiar requirements,

ll combined with wind drying and a wind recuperator replacing the conventional stoves (Cowpers) The plant operates as follows: Air is taken in at IBI'to the stage compressor IBI, leaves it at say 3.5 at absolute through pipe I82, to enter water spray-type intercooler I83, where .it iscooled by water supplied from pump I84 via pipe I84, inlet. valve I85 and outlet valve I85. In such cooler the moisture of the air condenses into the cooling water.- air of 3.6 at absolute is cooled by water of deg. C. to +25 deg. C. the air leaving the intercooler through pipe I82 will have a water contentofabout 0.0056 weight units per weight unit of air (about 3 grains per cbft.) only, which 15 is very desirable for blast furnace operation. The air is then further compressed to say 10 at absolute in stage compressor I86, flows through pipe I81 into-the first surface air heater I88,

through the latter as indicated by the dotted line, leaving 'it via pipe I89 to enter the second surface air heater I90, through the latter as as indicated by the dotted line, and thereafter through pipe I9I to air turbine I92 wherein it expands to, for example, 5 at absolute. The'air or partly in parallel on the same shaft or on continues via pipe I93 to surface type reheater I94, through which it flows as indicated by the dotted line, then through pipe I95 into a second air turbine I95. While expanding in that air turbine, the wind quantity is branched on at the proper pressure, say 2.38 at absolute, while the remainder of the air expands in the lower stages of turbine I96 to near-atmospheric pressure, leaving through pipe I98. The wind is ledinto wind heater I99, through which it flows as indicated by the dotted line, leavinghot through pipe 200 to the furnace. The said remainder of the air from pipe I99 is led into combustion chamber 20I, disposed below the wind heater I99. Fuel, for example blast furnace gas, from pipe 202 is led via regulating valve 202' into chamber 20I' and burned in air from pipe I99.

As can be seen from the drawing, surface heaters I99, I90, I94 and I88 are connected through

intermediate chambers

203, 204 and 205, so that the combustion gases from chamber 20I flow through said surface heaters in the sequence stated and are rejected finally to atmosphere at 206,

with burner and fuel feed pipe 201 with regulating valve 201'. Provision is further made for supplying additional air to combustion chambers,

when wind of normal pressure, say 2.38 at absolute, is delivered with little or no combustion in chamber 204. If the required pressure rises,'due; to some irregularity in the furnace or for some other reason, and the wind quantity is not per-. mitted to drop appreciably, the combustion in chamber 204 is intensified by admitting more fuel and air to it through valves 201' and 209, with'the result that the air at entrance to-turbine I 96 is reheated to a higher temperature. This reheating increases the power produced in turbine I96, thus allowing to cover the increase in compression work caused by the higher pressure. Starting of the plant is effected by a starting motor of any kind as known in the art. (Not shown.)

If for example compressed l0 Intermediate chamber 200 is also equipped 50 Compared with known plants of gas turbine driven compressors, the plantsaccording-to this invention also furnish a much greater portion of the air taken in by the compressor as useful air, which results for a given useful air quantity (wind quantity) in much smaller and cheaper turbines and compressors. The higher top pressure of the compressed air also improves the heat transfer conditions in the heaters with a consequent reduction in size also of these. Finally it deserves mention that the outputof the plants according to this invention is less affected by seasonal changes in intake air temperatures than is the case in known plants.

separate shafts and what number of intercoolers or reheaters are employed.

It is understood, however, that the turbine means interposed between compressor means and consumer system are preferably of the full admission axial flow type.

It is also immaterial what kind of fuel is burned in the surfaceand internal combustion type heaters, or whether different fuels are used in difierent heaters of the same system. See our co-pending application Ser. No. 401,703 filed July 10, 1941, now Patent No. 2,394,253.

For the production of wind for blast furnaces it is, however, understood that blast furnace gas is the preferred fuel for at least part of the heat produced in the system according to this invention.

We claim:

1. In the method of producing wind for metallurgical furnaces or similar consumers in air turbine driven blowers, the steps of compressing more air than required for the furnace to a pressure substantially higher than the required wind pressure, drying it by cooling it at said higher pressure, compressing it thereafter to a still higher pressure, energizing it by heating it at said highest pressure, expanding it in powerproducing expansion means to the required wind pressure, branching off the required wind quantity into wind heating means, and expanding the remainder in power producing expansion means to atmospheric pressure.

2. In apparatus for producing wind for metallurgicai furnaces or similar consumers, the com bination of multistage air compressor means of the axial flow type, air cooling means interposed between stages of said compressor means where the pressure is substantially higher than the re-. quired wind pressure, surface type air heating means, full admission axial fiow multistage air turbine means for expanding the compressed 3. In the method of producing wind for metallurgical furnaces and similar consumers in air turbine driven blowers, the steps of compressing more air than required for the furnace to a pressure substantially higher than the required wind pressure, energizing it by heating it at said higher pressure, expanding it in power producing expansion means to substantially the required wind pressure, branching ofi the required quantity of wind to the furnace, expanding the remainder in power producing expansion means-to near-atmospheric pressure, burning fuel in said expanded air, transferring heat of said combustion through heating surfaces to said compressed air for energizing it at highest pressure, thereafter rejecting the resulting gases to the atmosphere, and using the power produced in said expansion means for supplying the power for compressing said air.

4. In the method of producing wind according to claim 3, the steps of compressing air with intermediate cooling between stages of compression, reheating between said first and second expansion means, both intercooling and reheating taking place at pressures not lower than the required wind pressure.

5. In the method of producing wind for metallurgical furnaces and similar consumers in air turbine driven blowers, the steps of compressing more air than required for the furnace to a pressure substantially higher than the required wind pressure, energizing it by heating 'it through heating surfaces, expanding it in power producing expansion means to substantially the required wind pressure, branching off the required quantity of wind, thereafter discharging itto the furnace, reheating the remainder of the compressed air by internal combustion of fuel in said air, expanding it in power producing expansion means to near-atmospheric pressure, burning additional fuel in said expanded air-gas mixture, transferring heat of said last combustion through said heating surfaces to said air at its highest pressure, thereafter rejecting the resulting gases to the atmosphere, and using the power produced in said expansion means for compressing said air.

6. In apparatus for producing wind for metallurgical furnaces and similar consumers, the combination of multistage air compressor means of the axial flow type, designed to furnish air of a pressure substantially higher than that required in the metallurgical furnace, air intercooling means interposed between stages of said compressor means, surface type air heater means, multistage air turbine means, a fuel burning furnace, first conduit means for taking air from the ambient atmosphere into" the first stage of said compressor means, second conduit means for connecting the outlet of said stage compressor to said intercooling means and thence to the second stage compressor means, third conduit means for connecting the outlet of said latter compressor means to said surface type air .heater means and thence to the inlet of said air turbine means, fourth conduit means for branching off the required wind quantity from such intermediate stage of said air turbine means where the pressure is substantially equal to the pressure required in the metallurgical furnace and thence to said furnace, fifth conduit means for the remainder of the air after its expansion in said turbine means to near-atmospheric pressure for leading it into said fuel burning furnace to serve therein as combustion air, sixth conduit means for passing the combustion gases from said latter furnace, after heat transfer to the compressed air in said air heater means, to the atmosphere, and coupling means between said air compressor means and said air turbine means.

7. In apparatus for producing hot wind for metallurgical furnaces and similar consumers,

the combination of multistage air compressor means of the axial flow type designed to furnish air of a pressure substantially higher than that required in the metallurgical furnace, air intercooling means interposed between stages of said compressor means, surface type air heater means, multistage high pressure and low pressure air turbine means, fuel burning internal combustion air heater means, a fuel burning furnace, surface type wind heater means, first conduit means for taking air from the ambient atmosphere into the first stage of said compressor means, second conduit means for connecting the outlet of said stage compressor to said intercooling means and thence to the second stage compressor means, third conduit means connecting the outlet of said latter compressor means to said surface type air heater means and thence to the inlet of said high pressure air turbine means, fourth conduit means for branching off the required wind quantity from the last stage of said high pressure air turbine means where the pressure is substantially equal to the pressure required in the metallurgical furnace, for leading it into said surface type wind heater means and thence to the metallurgical furnace, fifth conduit means for the remainder of the air for connecting the outlet of said high pressure turbine means with the inlet of the said fuel burning internal combustion-chamber and thence to the inlet of said low pressure turbine means, sixth conduit means for said remainder of the air, after it has'expanded in said low pressure turbine means to near-atmospheric pressure, for leading it into said fuel burning furnace to serve therein as combustion air, seventh conduit means for passing the combustion gases from said latter furnace, after heat transfer to the wind in said surface type wind heater means and to the compressed air at top pressure in said surface type air heater means, to the atmosphere, and coupling means between said air compressor means and said air turbine means.

8. The method of preventing surging in flowtype compressors producing compressed gas for use in consumer systems which are operationally independent of the producer system and have widely fluctuating flow resistance comprising the steps of compressing more gas than required in said consumer systems to a pressure substantially greater than the pressure required, heating said compressed gas, expanding it in power producing multi-stage gas expansion means, interposing a part of said expansion means in the gas fiow between said compressor and consumer system by branching off the consumer gas at a point between stages of said expansion means where the partly expanded gas has reached the required pressure, expanding the remaining gas further, and, using the power produced in said expansion means for driving said compressor means.

9. In the method according to claim 8, the step of compressing the gas to an absolute pressure more than double the absolute pressure required in the consumer system.

FREDERICK NE'I'IEL. JOHANN KREITNER.

(References on following page) REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Ludewig Feb, 11, 1908 Michell Mar, 3, 1914 Mfiller Sept. 12,1916 Lysholm May 22, 1934 Noack Apr. 9, 1935 Lysholm Oct. 19, 1937 Harris Nov. 9, 1937 Graemiger May 23, 1939 Noack June 27, 1939 Number 2,186,877 2,223,572 2,242,767

16 Name Date Noack "Jan. 9, 1940 Noack Dec. 3, 1940 Traupel May 20, 1941 Meyer July 1, 1941 Noack May 12, 1942 Jendrassik Dec. 22, 1942 DeBolt June 8, 1943 1 Jendrassik July 25, 1944 FOREIGN PATENTS Country Date France Mar. 10, 1926 Great Britain Mar. 4, 1932 'Italy Oct. 20, 1939