US3165302A - Apparatus for heating blast furnace feed gas - Google Patents

Description

Jan. 12, 1965 LE ROY M. KRousE APPARATUS FOR HEATING BLAST FURNACE FEED GAS 3 Sheets-Sheet l Filed March 2l, 1960 mmwzuozoo INVENTORZ Le ROY M. KROUSE B2i/@W AGENT Jan. 12, 1965 LE ROY M. KRousE APPARATUS FOR HEATING BLAST F'URNACE FEED GAS INVENTOR LeROY M. KROUSE BY g AGENT Jan.' 12, 1965 Filed March 2l, v1960 LE ROY Mu KROUSE APPARATUS FOR HEATING BLAST FURNACE FEED GAS Le ROY M. KROUSE United States Patent 3.165,3@2 APPARAEUS EUR HEATRNG BLAST FURNASE FEED GAS Le Roy l Mouse, lullaio, NSY., assigner' to .ley Manufactoring Company, Pittsburgh, ha., a corporation of Pennsylvania Filed Mar. 2l, wel?, Ser. No. 16,5527 4 (Claims. (Ci. Zeil-d) This invention relates to a method and a particular association of apparatus for a fluid heating cycle. More specifically this invention relates to the heating of blast feed gas for a blast furnace by an association of apparatus which eliminates the conventional blast air feed gas preheating stoves.

As is presently known it is essential in the eilicient operation of a blast furnace that the air for combustion, which is supplied to the combustion zone of a typical blast furnace, to reduce iron ore to essentially pure iron be preheated. Heretofore, it has been the universal practice to use one or more preheating stoves, generally known as Cowper stoves, for preheating such air. rThese stoves are usually. tubular bodies, the interior of which is par- .tially lined in a particular manner with a ceramic material, commonly referred to as checkerwork. By burning the blast furnace eillux gas with air in the stoves a resultant gas temperature of about 2500 is achieved. The resulting products of combustion heat the stoves thus constituting the stove heating cycle. The process continues until the checkerwork arrives to a maximum steady state temperature. To heat the large volume of airabout 3.5 tons of air per ton of iron-the stoves must contain a large heat transfer area which, therefore, requires the stoves to be very large. It is not uncommon to find a single stove to be 25 feet in diameter and 125 feet in height. To achieve continuous blast furnace operation several stoves are required per blast furnace. A customary installation has three stoves to a furnace; one stove for on blast at a time when the other two stoves are on gas with the result that each stove is on gas twice as long as it is on blast. Intermittent heating and cooling of the ceramic heat transfer surfaces causes deterioration thereof and consequently replacement of the heat transfer surfaces is necessary. The thermal cycle causes spalling, deforming and clogging of the checkerwork.

it is readily apparent therefore that the existing methods of heating blast furnace feed gas require very expensive equipment which is subject to cyclic failure. Conventional equipment is very large and difficult to maintain and requires many complex controls to regulate the heating and cooling cycle. The large size of a stove requires a greater amount of plant space and large and expensive service equipment.

This invention is directed to the elimination of preheatiug stoves and as a consequence elimination of the problems connected therewith.

Accordingly one object of this invention, broadly speaking, is to provide a new and improved method and apparatus of heating fluid for supporting combustion in a blast furnace.

A further object of this invention is to provide a new and improved method of utilizing blast furnace efflux gas for heating combustion supporting fluid in a blast furnace.

A specific object of this invention is to provide a new and improved method and -apparatus of heating blast furnace blast feed gas by combusting blast furnace elllux gas in a combustor to form products of combustion and discharging the products of combustion in a continuous stream to a heat transfer device which transfers heat from the products of combustion to a stream of blast furnace blast feed gas prior to introduction thereof into the blast furnace.

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Another object of this invention is to provide a new and improved steady ow process of heating blast feed gas for a blast furnace.

Another object of this invention is to provide a new and improved steady flow process of heating blast feed gas for a blast furnace including means for controlling the temperature of the medium for heating the blast feed gas.

Another object of this invention is to provide Ya new and improved method of heating blast feed gas for a blast furnace including means for supplying a controlled amount of additional fuel energy to raise the temperature of a medium for heating the blast feed gas.

A more specific object of this invention is to provide a new and improved method and apparatus of heating blast furnace blast feed gas which includes means, responsive to the temperature of the medium for heating the blast feed gas, for controlling the amount of additional energy supplied to the medium for heating the blast feed gas.

Another object of this invention is to provide a new and improved method and apparatus of a steady flow fluid heating system wherein the power required to cause ilow of the heating fluid is substantially equal to the power required to cause flow of the heated fluid.

A further object of this invention is to provide a new and improved method of immediately and continuously transferring heat from the heating iiuid to the blast furnace blast feed gas. y

These and other objects of this invention will become more apparent upon consideration of the following detailed description and a preferred embodiment when taken in conjunction with the following drawings in which:

FIG. l is a schematic representation of a system constructed for heating blast furnace blast feed gas in accordance with the principles of this invention.

FIG. 2 is a modification of the representation shown in FIG. l with the blast feed gas compressor prime mover and the gas compressor prirne mover in other operative positions.

FlG. 3 shows means for introducing supplemental fuel to the combustor as shown in FlG. l.

As will become apparent from the description herein this invention relates to both a new and improved method for heating a gas and in addition to various arrangements of apparatus to accomplish such heating of a gas. Although particular apparatus is employed in this invention the construction of such apparatus is well known in the art and does not constitute a part of this invention. Accordingly the various apparatus employed are schematically illustrated. rfhus, in FlG. l a blast furnace 4 of conventional design is shown having conventional gas take-up conduits 6, suitably connected to a conduit 8 which directs the efflux gas from the blast furnace to` a conventional gas cleaner ld. For the purposes of this invention the gas cleaner l@ is employed to remove particles such as ily ash, from the blast furnace efflux gas, however, in other environments or in instances where the impurities in the blast furance effi-ux gas do not interfere with the operation of apparatus subsequently employed to treat the efflux gas the use of the gas cleaner lil is optional as the apparatus, hereinafter described, will operate under normal operating conditions efficiently without the gas cleaner lu. Such blast furnace efux gas is cornmonly identified as bosh gas and after treatment in the gas cleaner l@ the efflux gas is directed by conduit means l2 to a suitable compressor f4 which pressurizes the cleansed efflux gas to provide a sulcient pressure head to cause flow of the cleansed efflux gas through the subsequent portion of the system described herein. For the purposes of this invention the compressor le is preferably of a radial or axial flow type.

in order to utilize the thermal energy of the efflux gas for heating blast -feed gas the pressurized efflux gas is mixed with atmospheric air in combustible ratios and thereafter the mixture is combusted. To obtain tl e precombustion air a compressor 2@ such as a radial or axial type compressor, Vcompresses cleaned atmospheric air induced'through a conduit 13 to cause flow of said atmospheric air through hereinafter described apparatus. The compressed atmospheric air is discharged from the compressor to a suitable combustor 26 through a conduit 22 suitably connected therebetween. Upon reception by the combustor 26'of compressed efflux gas by means of conduit 16, and compressed atmospheric air by means of conduit 22, intimate mixing results by means Well known in the combustor design art. Complete cornbustion of the mixed compressed air and efflux gas requires, principally, a combustion supporting ratio and a relatvely homogeneous mixture.

Conventional blast furnace operation produces an eiiux .gas having a heating value which varies to such an extent that combustion thereof ina definite ratio with combustion air causes a raisingV or loweringV of the combustion temperature as the heating value increases or decreases, respectively. Therefore, in order to provide etiicient operation and insure the systems reliability, means are provided to continuously control the etiiux gas-combustion air ratio so that a relatively constant combustion temperature is maintained. v ln order 4to maintain a constant combustion temperature combustion air is bypassed by a conduit 24 connected to cause flow of the compressed atmospheric air about the combustor 25 by being connected to the discharge conduit 22 of compressor 2t? and the discharge conduit dit of combustor 26. Means is provided for continuously controlling the amount of air bypassed by conduit 24 which includes a suitable valve 23 connected to conduit 2.4. Valve 23 is a conventional motor opera-ted servo-valve having a passageway whose opening can be varied. The extent to which the passageway is opened is a function of the value of the voltage impressed on the motor. Therefore a variation in the voltage causes a corresponding change in the'valve opening. Valve 28 is electrically connected to a control device 31) through conductors 3d and 38.' As is well known, changes in temperature canl be detected by` a thermocouple which reacts to changes in temperature by generating a corresponding change in voltage. A voltage is applied to Ithe control 3G through a thermocouple 32 positioned within combustor 2d so that thermocouple 32 senses the temperature of the products of combustion derived from the combustion of blast furnace elux gas, and the atmospheric air which, as described, are delivered to combustor 26 by conduits 16 and 22 respectively. VThe electrical conductor 33 connects the voltage from the valve 23 tothe control 3Q which'rnatches the output voltage to the voltage impressed on the control 3@ by the thermocouple 32. When such `voltages are equal inmagnitude the valve Z8 is moved to the proper opening to bypass the correct amount of air about combustorV 2e to maintain a predetermined temperature for the products of combustion. ri`he conduit 24 is also connected to the conduit 4t? so that the compressed air in the conduit 24 which has bypassed the combustor 26 is entrained and flows with the products of combustion from the combustor 26 to a heat exchanger 44 connected to the other end of the conduit 40.

For the purposes of this invention the heat exchanger 44 is of any suitable commercial design available which transfers heat immediately and continuously between fluids of different temperature as distinguished from the conventional stoves, previously described, which go through an intermittent cycle of heating and cooling. Several types of such heat exchangers are available that function properly for this inven-tion'and it is contemplated that any of such continuous type heat exchanger, such as shell and tube; rotary regenerator; or a ceramic pebble bed will be employed. As hereinafter described heat is transferred to the compressed blast feed gas by the high temperature combusted air gas mixture which temperature and thermal energy is accordingly reduced upon passage through the heat exchanger.- After such transfer of heat from the products of combustion to the blast feed gas in the heat exchanger 44,.the remaining available energy of the products Vof combustion are further-utilized I by being discharged to a's'uitable expansion engine 48 by Y blast feed gas.

a conduit d6 which is connected to the gas discharge side of heat exchanger 44 and the inlet conduit 46 of the expansion engine 43,. The expansion engine 48 is of any suitable type such as an axial or radial flow turbine. After utilization of the energy of the products of combustion the products of com-bustion are rejected -to the atmosphere in a manner suitable to the installation and herein shown,

,by way of example, through stack 52.

Energy in the form of mechanical work, derived from the expansion engine 4d, is utilized to drive a suitable compressor 56 by means of a rotatable shaft 54 connected therebetween. Cleaned atmospheric air, or any other combination of blast feed gas, such as an-oxygen enriched atmosphere is induced, by way of intake conduit 5S, into compressor 5d. The compressed blast feed gas is discharged in a continuous stream by compressor 56 to the cold side of heat exchanger 44 by a conduit 6d, where heat which is given up by the stream of the products of combustion is immediately and continuously transferred to the stream of pressurized blast feed gas. The heated blast feed gas is then directed into the blast furnace 4 through conventional tuyere 66 which are connected to communicate with bustle pipe 64 which in turn receives the blast feed gas discharged by heat exchangers 44 by means of a conduit 62. Y

It has been vfound that the horsepower required to drive the etiiux gas compressor 14 and the combustion air compressor Ztl is substantially the same asV the horse power required to drive the blast feed gas compressor S6. rTherefore the modification of FIG. 2 shows the arrangement whereby the steam turbine 17, or other suitable prime mover means, is connected to drive the blast air compressor by means of a rotatable shaft 54. The products of combustion discharged from heat exchanger 4d into conduit 46 are directed, as in .the preferred ernbodiment, to an expansion engine 48. However, instead of driving the blast feed gas compressor Se with expansion engine 4S, the efflux gas compressor 14- and the combustion air compressor 2t) are driven in `tandem by expansion engine 48. It is obvious from the embodiment shown, in FIG. l that the efflux gas compressor. 14 and the atmospheric air compressor Ztl can be driven by individual suitable prime movers as distinguished from the tandem drive illustrated.

Depending'on the ymaximum steady state temperature at which the combustor 26 and the hereinabove described heat exchanger 44 canbperate, meansmay be provided for increasing the temperature of the products of combustion by introducing an independent source of suitable fuel, such as oil, to the combustion zone of combustor 25. In this manner, 'if desired, the temperature of the products of combustion can'be raised to 40G0 F. It will be recognizedbyrthose skilled in the art that a higher product of combustion temperature will result in a higher rate of energy transfer by the heat exchanger 44 to the l It will also be recognized by those skilled in the Vart that the maximum temperature to` which the products Yof combustion can be Vraised is mainly limited by the metallurgical limit of the combustor 26 and the heat exchanger 44.

A scheme for introducing additional fuel to combustor 26 for increasing the temperature of theprodlcts of combustion is shown in'FIG'. 3.l A tank luis adapted to contain the additional fuel which is delivered to the combustor 26. A pump 72 of appropriate capacity and characteristics has its inlet portion in communication with the fuel tank 7tl'through conduit 74 and the'pump discharge is connected to aservo valve 7S by conduit 76. Conduit 82 receives thev fuelA metered byV valve v78, and

aisance discharges the fuel to combustor 26 through conduit 82. The servo valve 78 adjusts the amount of fuel oil delivered Ato the combustor 2o by being electrically connected to a thermocouple 92 which is contained in the combustion zone of combustor 26, and through a control device 8S which amplilies a signal from therrnocouple 92. Servo valve '78 also has an electrical feedback conductor 34 which transmits a voltage proportional to the opening of valve 7S which voltage is matched to the voltage impressed on valve 78 through conductor 86. When the voltages through conductors 84 and 86 are measured to be equal by control 88 then valve 78 allows a rate of fuel flow proportional to the temperature sensed by thermocouple 92.

It is readily recognized by those skilled in the art that the tank 70, pump 72, servo valve '78, control 88 and thermocouple 92 are readily available commercial items, and, per se, they do not form any part of this invention.

In describing the operation of this invention a specilic set of conditions will be assumed. It is to be understood that the chosen values are subject to change due to different types of equipment which may be used and due to changes of conditions. The following example also assumes the existence of an ideal fluid and discounts the pressure drops through the conduits which would be encountered in an actual installation. To burn one pound of CO, 2.46 lbs. of air is required, assuming an air to etilux gas ratio-of .68 to be substantially correct. However, in actual practice it is assumed that the above ratio will increase by supplying 20% excess air. The inlet conditions of efllux gas compressor 14 and combustion air compressor 2h are assumed to be the same. The inlet pressure for each compressor is assumed to be 14.7 p.s.i.a. and the inlet temperature to be 66 F. It is also assumed that the efllux gas Will have the same compressing characteristics as air. The heat of compression will raise the exit temperature in conduits 16 and 22 to 315 F. and the pressure to 49.7 p.s.i.a. Efflux gas compressor 1.4 Will compress 86.3 lbs. eilux gas per second and combustion air compressor 2h will cornpress 61.7 lbs. of air per second. Depending upon the heating value of the elliux gas the amount of combustion air shunted by combustor 26 will vary. However, for purposes of this example it will be assumed that no combustion air is bypassed about combustor 26. The temperature of the products of combustion in conduit 42 will be approximately 2600" F. and the corresponding pressure will be 48.3 p.s.i.a. In the event a regenerator type heat exchanger is incorporated care must be taken that the pressure on the gas side of the heat exchanger 44- is substantially the same as the pressure on the blast feed gas side or air side. This type of heat exchanger is very susceptible to losses due to a pressure difference which causes circulation of duid Within the heat exchanger. rlhe products of combustion are then conveyed to neat exchanger 44 by conduit ft2 Where heat is transferred to blast feed gas which is at a lower temperature. The temperature of the products of combustion after passage through heat exchanger 44 is reduced to 830, at substantially the same pressure. The residual avail-able energy of the products of combustion is further diminished by being exhausted to expansion engine d3 by Way of conduit 46 and after passage thereof through the expansion engine the products of combustion are rejected to the atmosphere. Turning again to the blast feed gas compressor 56 the temperature and pressure of the blast feed gas is 60 F. and 14.7 p.s.i.a. The mass flow rate through compressor 56 is calculated to be 159 lbs. per second. Upon compression the blast feed gas temperature, due to the Work of compression has its exit temperature raised to 315 and its vpressure 49.7 p.s.i.a. The blast feed gas is then discharged to the air side of heat exchanger ed by Way of conduit 69 Where heat is continuously and immediately transferred thereto from the products of combustion. At the air side exit of heat exchanger 44 the blast feed gas has had its temperature raised to 1900" F. and its pressure is 48.3 p.s.i.a. which, it will be noted, is the same as the pressure designated for the products of combustion. The blast feed gas is then discharged to the combustion zone of the blast furnace by conduit 62, bustle pipe 64 and tuyere 66.

As a result of this invention certain advantages are obtained in the attainment of the designated objects. The vast area required by conventional preheating equipment, as hereinbefore described, is materially reduced. The heat available to the blast feed gas is more efficiently utilized and steady oW operation ofthe blast feed gas heating apparatus resul-ts in a continuous cycle of blast feed gas heat as opposed to the heating and cooling cycles of combustion stoves. The amount and nature of equipment required to insure continuous operation is reduced. This invention also reduces the frequency of major repair which the prior art combustion equipment requires. Control apparatus for maintaining the proper functional relationship between the various elements, which manipulate the heating and heated fluid, is reduced in quantity.

Having described preferred embodiments of this invention in accordance with the patent statutes, it is to be realized that further modifications thereof may be made without departing from the broad spirit and scope of this invention. Accordingly it is respectfully requested that this invention be interpreted as broadly as possible and be limited only by the prior art.

What is claimed is:

1. An apparatus for heating blast furnace blast feed gas by combusting blast furnace efflux gas, a compressor for pressurizing blast furnace elilux gas to cause flow thereof ina continuous stream, a second compressor having its inlet portion in communication with the atmosphere for pressurizing atmospheric air to cause ow thereof in a continuous stream, a combustor in communication With the above mentioned pressurized continuous streams for mixing and combusting such streams, a heat exchanger communicating with a discharge conduit of said com buster for transferring heat from the stream of the products of combustion formed in said combustor by the combustion of said elux gas and atmospheric air, an expansion engine having an inlet portion communicating with the products of combustion discharged from said heat exchanger, a third compressor driven by said expansion engine for pressurizing blast feed gas for delivery thereof in a continuous stream to such blast furnace through said heat exchanger where the heat of the products of combustion is transferred thereto continuously and immediately.

2. An 'apparatus for heating blast furnace blast feed gas by combusting blast furnace elux gas, a compressor for pressurizing blast furnace efliux gas to cause ow thereof in a continuous stream, a second compressor for pressurizing atmospheric air to cause flow thereof in a continuous stream, la combustor in communication with the above mentioned pressurized continuous streams for mixing and combusting such stream, a heat exchanger communicating with a discharge conduit of said combustor for transferring heat from the stream of the products of combustion formed in said combustor by combusting said mixture of elllux gas and atmospheric air, an expansion engine driven by said stream of said products of combustion, a third compressor driven by said eX- pansion engine for pressurizing blast feed gas for delivery thereof in a continuous stream to such blast furnace through said heat exchanger where heat is transferred continuously and immediately thereto by said products of combustion.

3. An apparatus for heating blast furnace blast feed gas by combusting blast furnace efflux gas, `a compressor in communication with the blast furnace efllux gas discharge for pressurizing eiux gas to cause flow thereof in a continuous stream, a second compressor for pressurizing atmospheric air to cause flow thereof in a continuous mentioned pressurized continuous streams for mixing and combusting such stream, a heat exchanger communicating with a discharge conduit of said combustor for transferring heat from the stream of the products of cornbustion formed in said combustor by combusting said mixture of elux gas and atmospheric air, an expansion engine driven by said streamV of said products of cornbustion, and means for controlling the temperature of said products of combustion by adjustment of the pressurized elux gas and atmospheric air ratio, a third cornpressor driven by said expansion engine for pressurizing blast feed gas for delivery thereof in a continuous stream to such blast furnace through said heat exchanger where heat is transferred thereto continuously and immediately by said products of combustion.

4. An apparatus for heating blast furnace blast feed gas by combusting blast furnace efflux gas, a compressor in communication with the blast furnace elux gas discharge for pressurizing efflux gas to cause flow thereof in a continuous stream, a second compressor for pressurizing atmospheric air -to cause flow thereof in a continuous stream, a combustor in communication with the above mentioned pressurized continuous streams for mixing and combusting such stream, a heat exchanger communicating with a discharge conduit of said combustor for transferring heat from the stream of the/,products of cornbustionrformed in saidy combustor by combusting said mixture of efflux gas and latmospheric air, an expansion engine driven by said stream of saidproducts of combustion, means for controlling the temperature of said products of combustion by adjustment of the pressurized efflux gas and atmospheric air ratio, means for supplying additional fuel from independent source to said combustor for elevating the temperature of said products of combustionand means responsive to the temperature of said products of combustion for controlling the supply of fuel from said independent source, a third compressor driven by said expansion engine for pressurizing blast feed gas for delivery thereof in a continuous stream to such blast furnace through said heat exchanger where heat is transferred thereto continuously and immediately by said products of combustion. Y

References Cited -in the le of this patent UNITED STATES PATENTS 2,544,697 Lewis Mar. 13, 1951 2,778,018 Strassburger Ian. 15, 1957 2,822,257 Hanna et al. Feb. 4, 1958 2,859,954 Grey Nov. 11, 1958 2,970,901 Rice Feb. '7, 1961

Claims (1)

1. AN APPARATUS FOR HEATING BLAST FURNACE BLAST FEED GAS BY COMBUSTING BLAST FURNACE EFFLUX GAS, A COMPRESSOR FOR PRESSURIZING BLAST FURNACE EFFLUX GAS TO CAUSE FLOW THEREOF IN A CONTINUOUS STREAM, A SECOND COMPRESSOR HAVING ITS INLET PORTION IN COMMUNICATION WITH THE ATMOSPHERE FOR PRESSURIZING ATMOSPHERIC AIR TO CAUSE FLOW THEREOF IN A CONTINUOUS STREAM, A COMBUSTOR IN COMMUNICATION WITH THE ABOVE MENTIONED PRESSURIZED CONTINUOUS STREAMS FOR MIXING AND COMBUSTING SUCH STREAMS, A HEAT EXCHANGER COMMUNICATING WITH A DISCHARGE CONDUIT OF SAID COMBUSTOR FOR TRANSFERRING HEAT FROM THE STREAM OF THE PRODUCTS OF COMBUSTION FORMED IN SAID COMBUSTOR BY THE COMBUSTION OF SAID EFFLUX GAS AND ATMOSPHERIC AIR, AN EXPANSION ENGINE HAVING AN INLET PORTION COMMUNICATING WITH THE PRODUCTS OF COMBUSTION DISCHARGED FROM SAID HEAT EXCHANGER, A THIRD COMPRESSOR DRIVEN BY SAID EXPANSION ENGINE FOR PRESSURIZING BLAST FEED GAS FOR DELIVERY THEREOF IN A CONTINUOUS STREAM TO SUCH BLAST FURNACE

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