US3150865A

US3150865A - Fluid heating process and apparatus

Info

Publication number: US3150865A
Application number: US233553A
Authority: US
Inventors: Goeke Eberhard
Original assignee: Heinrich Koppers GmbH
Current assignee: Heinrich Koppers GmbH
Priority date: 1961-10-28
Filing date: 1962-10-29
Publication date: 1964-09-29
Anticipated expiration: 1981-09-29
Also published as: NL284129A

Description

P 9, 1964 GOEKE 3,150,865

FLUID HEATING PROCESS AND APPARATUS Filed Oct. 29, 1962 2 Sheets-Sheet 1 4 FIG 7 INVENTOR fiemiard 6b Sept. 29, 1964 E. GOEKE FLUID HEATING PROCESS AND APPARATUS 2 Sheets-Sheet 2 Filed Odt. 29, 1962 TNVENTOR. 5 61PM $0 4 United States Patent 3,150,865 lFlLUlllD HEATHNG PRUCESS AND AIPARATUS Eberhard Goehe, Essen, Germany, assignor to Heinrich Koppcrs G.m.b.H., Essen, Germany Filed Oct. 29, 1962, Ser. No. 233,553 Qlaims priority, application Germany, Oct. 28, 1961,

K 45,668; Jan. 5, 1962, K 45,585 6 Claims. (Cl. 263-49) The present invention relates to the heating of fluids and in particular to the heating of air which is blown into a blast furnace to form the blast therein.

In the heating of air or other fluids when used for a blast furnace, for example, it is conventional to recover some or" the heat from the gas issuing from the blast furnace and to use this heat for raising the temperature of the blast air which is blown into the furnace, and for this purpose various arrangements of regenerators and recuperators are Well known in the art.

Modern operation of blast furnaces require that the blast which is blown into the furnace have higher temperatures than were heretofore customary. For example, until recent times it was conventional to blow into the blast furnace air having a temperature of 800 1000 C., but modern practice requires that the temperature of the blast extend up to l300 (3., so as to save coke and improve the performance of the blast furnace.

Of course, assumim that the interior of the regenerator is provided with a sufilciently heat-resistant material, it is possible to direct through the regenerator a hot fluid which will provide in the regenerator the temperature necessary to heat the air which subsequently passes there through to the desired temperature. In using such installations with blast furnaces, it is of course very desirable to be able to use the blast furnace gas which issues from the blast furnace for the purpose of heating the regenerator, because of the relatively low cost of the blast furnace gas, but such gas is of relatively small heating capability and burns at a relatively low temperature. If,

for example, it is desired to provide blast air at a fem perature of 1360 (3., then during heating of the regenerator, before the blast air passes therethrough to be heated therein, it is necessary to provide in a combustion chamber from which the hot fluid for heating the regenerator is derived a temperature of approximately 1609 C., and such temperatures can be obtained from blast furnace gas only when the blast furnace gas together with the combustion air which is added thereto is preheated, before being burned in the combustion chamber, up to a temperature of approximately 490 C.

Of course, it is possible to simply heat the regenerator with the products of combustion derived from a suitable gas of high caloric content which will burn at an extremely high temperature, and it is also possible to avoid any preheating of the combustible fluid and to mix the blast furnace gas with an additional gas which burns at high temperature so as to obtain the desired but fluid for heating the regenerator in this way, but in both of these cases the cost of the operations is undesirably high.

Therefore, in order to obtain the desired high temperature of the regenerator required by modern practice, it is necessary with conventional apparatus and processes to use with the blast furnace gas an additional gas which will burn at a relatively high temperature or to preheat the blast furnace gas and air, with the use of an additional source of heat for the preheating purposes.

It is a primary object of the present invention to provide a process and apparatus of the type referred to above which is capable of producing the desired relatively high temperature in the regenerator without requiring the use of expensive additional combustible fluid which will burn at a relatively high temperature either for the purpose of directly providing heat without preheating of the blast furnace gas or to be used in the preheating of the blast furnace gas.

it is also an object of the present invention to provide a process and apparatus which will produce the desired high temperature in the regenerator while at the same time maintaining the loss of gas substantially lower than has heretofore been possible.

It is also an object of the present invention to provide a process and apparatus which will operate with an efliciency greater than has heretofore been attainable.

Also, the objects of the present invention include the provision of a process and apparatus which will use only air and relatively inexpensive gas of low heating capability, such as blast furnace gas, which will burn at a relatively low temperature, so that the cost of the operation can be maintained relatively low.

It is also an object of the present invention to provide a process and apparatus which are capable of maintaining constant the temperature of the preheated combustible fluid which is burned for heating the regenerator, irrespective of the temperature of the fluid which is received in a recuperator for the purpose of preheating the combustible fluid which is burned after passing through the recuperator in order to heat the regenerator.

With these objects in view the invention includes, in a process for heating a fluid, the steps of applying to a regenertaor, in order to heat the same, the products of combustion derived from the burning of a combustible fluid, and in accordance with the present invention this combustible fluid, before it is burned, is preheated not only with gases discharging from the regenerator but also with an additional heat which together with the heat derived from the gases from the regenerator will maintain the temperature of the preheated gas, just before it is burned, substantially constant, and of course at a value which will provide upon burning of this combustible fluid the desired relatively high temperature, as referred to above.

The apparatus of the invention includes a regenerator and a combustion means communicating therewith for directing combustion products thereto. A recuperator means is provided, and a first conduit means provides communication between the regenerator and the recuperator means for directing to the recuperator means the gasses which discharge from the regenerator. Second conduit means passes through the recuperator means to the combustion means, and directs a combustible fluid to the latter, so that this combustible fluid will of course be preheated by the gas which discharges from the regenerator and passes through the first conduit means into the recuperator means. In accordance with the present invention there is located in the first conduit means an adjustable burner means which will add to the gas which flows from the regenerator to the recuperator means an amount of heat which will maintain the temperature of the preheated combustible fluid substantially constant as ,ing of the combustion means 4.

it flows from the recuperator means to the combustion means. Thus, a thermostat means in the second conduit means at the part thereof located betweenthe recuperator means and the combustion means senses the tempertaure of the combustion fluid and is connected with the adjustable burner means to regulate the latter to automatically add to the fluid which flows into the recuperator means the amount of heat required to maintain the preheated combustible fluid at a constant temperature just before it is burned. The adjustable burner means burns some of the combustible fluid from the secnd conduit means before this portion of the combustible fluid reaches the recuperator means.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a schematic side elevation of structure which illustrate the principle of the invention;

FIG. 2 is a top plan view diagrammatically illustrating the invention; and

FIG. 3 is a flow diagram illustrating one possible operation with the process and apparatus of the invention.

Referring to FIG. 1, there is shown therein a regenerator 3 which can have the construction of a conventional checkerbrick interchanger well known in the art. A combustion means 4 communicates with the dome at the upper part of the regenerator 3. As is well known in the art, after the regenerator 3 has been heated sufiiciently, air which is to be heated passes therethrcugh, and for this purpose the air will enter the regenerator through the conduit 7 shown at the lower left of FIG. 1, and after passing upwardly through the regenerator 3 the air will move into the combustion chamber of the combustion means t, and will discharge from the latter out through the discharge conduit 23, from which the heated air will flow to the blast furnace, for example.

In order to heat the regenerator 3, the products of combustion provided in the interior of the combustion means 4 are directed into the regenerator 3 to flow downwardly therealong, and these products of combustion discharge from the interior of the regenerator through the conduit 6 shown at the lower right portion of the regenerator 3 in FIG. 1. The conduit '7 carries a suitable valve, as indicated at the lower left portion of FIG. 1, and in the same way the conduit 6 carries a suitable valve iii for closing and opening the conduit 6, depending upon whether the regenerator is being heated or whether it is giving up heat to air passing upwardly therethrough. In other words during heating of the regenerator the conduit 7 will be closed and the discharge conduit 6 will be open, while when the regenerator is giving up heat the conduit '7 is open and the conduit 6 is closed.

A combustible iluid is directed by a suitable conduit means to the combustion chamber 4-, so as to be burned therein, and for this purpose a burner of conventional construction is located at the lower portion of the hous- Of course, when a combustible fluid is burned in the combustion means 4 the discharge conduit 8 is also closed. The conduit means for directing the combustible fluid to the burner 5 includes the pair of conduits 3.3 and 14 shown at the right portion of FIG. 1, the conduit 13 receiving blast furnace gas from the blast furnace while the conduit 14 receives combustion air which is combined with the blast furnace gas at the burner 5' so as to provide in the combustion means 4 products of combustion of the required high temperature which is on the order of l6b0 CI, for modern blast furnace practice, as pointed out above.

As was also pointed out above, in order to obtain such a high temperature from the combustion of a fluid made up of blast furnace gas and air, it is necessary to preheat the combustion fluid, and for this purpose a recuperator 12 is provided. The

conduits

13 and 14 communicate respectively with the pair of coils which pass along the interior of the recuperator 12, and these coils respectively communicate with the conduits l7 and 18 which in turn respectively communicate with the conduits 15' and 16 which lead to the burner 5, and thus the conduit structure 1348 forms a conduit means for directing a combustible fluid through the recuperator 12 and to the combustion means 4 to be burned therein so as to provide hot combustion products which will fiow from the combustion means 4 through the regenerator 3 to heat the latter.

In many known arrangements of the type shown in FIG. 1 and described above, the products of combustion which flow downwardly through the. regenerator 3 are simply discharged to a chimney or the like, so that no further heat is obtained therefrom, and of course in order to make the most economical use of the heat in such products of combustion the lower end of the regenerator 3 is maintained at relatively low temperature and of course the regenerator 3 must be made of relatively large size in order to contain in its interior a sufficient amount of checkerbrick to store economically the heat from the products of combustion to be subsequently given up to the air which enters through the conduit 7. With the structure of the invention, however, instead of connecting the discharge conduit 6 to a chimney, this conduit 6 communicates with a conduit 9 which in turn communicates with the recuperator 12, and it is the dis charge conduit 11 of the recuperator 12 Which is connected with a chimney, for example, so that the products of combustion issuing from the combustion chamber 4, after they have passed downwardly through the regenerator 3, will pass through the recuperator 12 to give up part of the heat in these products of combustion to the combustible fluid flowing in the coils which extend along the interior of the recuperator 12, so that in this way at least partial preheating of the combustible fluid, before it reaches the burner 5, is obtained.

In accordance with the resent invention there is ar ranged in the conduit 9 an adjustable burner 23 which willed-d heat to the products of combustion which pass through the conduit 9 into the recuperator 12, and also in accordance with the present invention the adjustable burner 23 is regulated automatically in such a way that the amount of heat which it adds to the products of combustion entering the recuperator 12 through the conduit 9 will be suflicient to maintain the preheated cornbustible fluid leaving the recuperator 12 and flowing to the burner 5 at a constant temperature, so that in this way the combustion means 4 will provide during its entire operation a substantially constant relatively high temperature in the combustible fluid which flows therefrom to the regenerator 3. Bearing in mind that during the continued heating of the regenerator 3 the products of combustion which discharge through the conduit 6 will necessarily have initially a relatively low temperature and will gradually increase in temperature to a relatively high temperature at the end of the heating of the regenerator 3, it is clear that the burner 23 will be regulated so. as to add to the products of combustion a diminishing amount of heat which will, when added to the heat in the products of combustion, preheat the combustible fluid flowing to the burner 5 in such a way as to maintain the temperature thereof constant.

Although in practice there will be several regenerators which are heated and have heat removed therefrom in a given sequence, as is well known in the art, FIG. 2 illustrates an arrangement where they are only two regenerators 1 and 2., for the sake of clearly illustrating the invention. The regenerators 1 and 2 have a construction identical with regenerator '3 of FIG. 1, and it will be seen that each regenerator 1 and 2 communicates with a conduit '7 through which air to be heated is delivered into the interior of the regenerator, and the upper, dome-shaped end of each regenerator communicates with a combustion means 4 from which the heated air issues through the conduit 8, as described above, this heating of the air taking place when the combustion chamber 4 is not operating since it derives its heat from the previously heated regenerator.

FIG. 2 also illustrates the pair of discharge conduits 6 and their valves 10, as well as the conduit 9 which communicates with both of the discharge conduits 6 and which leads through a branch 21 into the recuperator 12 from which the products of combustion discharge to a suitable chimney or the like through the conduit 11. It is in the branch 21 or" the conduit 9 that the adjustable burner 23 is located. During operation of an assembly of the type shown in FIG. 2, one of the combustion chambers 4 will be operated to heat the regenerator with which it communicates, While the other previously heated regenerator will give up its heat to air which is being fed to the blast furnace. For example, the left valve of FIG. 2 may be opened and the left combustion means 4 will be operated to heat the regenerator 3t, while the right valve 10 of FIG. 2 is closed and the right combustion means 4 is not operated during flow through the conduit 7 shown at the right of FIG. 2 of air into the regenerator 2 to be heated therein and then pass out through the conduit 8 to the blast furnace, and after the regenerator i has been heated for a given period of time the right valve 10 will be opened and the left valve 10 will be closed, and then the air will be heated through the left regenerator of FIG. 2, while the right combustion means 4 of FIG. 2 will be set into operation so as as to heat the regenerator 2 at this time, and in this way the regenerator assemblies are alternately heated and give up their heat, as is well known.

FIG. 2 illustrates the conduits l5 and 16 which receive the combustible fluid after it has been preheated in the recuperator 12, and these conduits and 16 carry suitable thermostats 2 2 which sense the temperature of the combustible fluid in the conduits l5 and 16. These thermostats 22 are connected with (the burner 23 in a known way so as to regulate the burner 23 to provide more heat when the temperature or" the combustible fluid in the conduits l5 and is: is relatively low and less heat when the temperature of the combustible fluid in the conduits 15 and 16 is relatively high, the controls being arranged in such a way as to maintain the temperature of the combustible fluid flowing through the conduits 1543 to the burners or" the combustion means 4 substantially constant. Thus, FIG. 2 shows diagrammatically connections 22a and 22b between the thermostats 22 and valves 23%: and 23b which are respectively located in conducts 23a and 231) which feed combustible fluid to the burner 23, so that through these connections in a manner Well known in the art the valves 23'a and 231) will be automatically regulated to control the amount of combustible material reaching the burner 23. As may be seen from FIG. 2, the conduits l7 and 18 carry valves 19 and 20, respectively, and of course when the right combustion means 4 of FIG. 2 is operating the right valves 1? and 20 of FIG. 2 will be opened, while the left valves 19 and 26 will be closed, at this time the air being introduced through the conduit 7 into the regenerator 1 to be heated therein, and when the changeover is made the right valves id and 20 will be closed while the left valves 19 and 20 will be opened so that the left regenerator of FIG. 2 will be heated while air is delivered to the regenerator 2 of FEG. 2 to receive heat therefrom. The fluid which is burned in the adjustable burner means 23 is derived from the conduits 13 and M by suitable additional conduits which communicate with the burner 23 as well as with the

conduits

13 and 14 upstream of the recuperator 12, so that the additional heat provided by the burner 23 is obtained also from the blast furnace gas as well as the additional combustion air which flows in the conduit 14.

The invention also can be practiced with arrangements where the combustion means 4 is arranged within the regenerator 1 or 2.

As was pointed out above, the temperature of the products of combustion issuing through the conduit 6 into the conduit 9 during the heating of a regenerator will gradually increase during the heating period. For example, at the beginning of the heating of a regenerator the temperature of the products of combustion reaching the conduit 9 may be on the order of 300 C., while at the end of the heating period the temperature may be 450 C. It may be desired, for example, to preheat the combustible fluid reaching the combustion means 4 to a temperature of 350 C. Thus, under these conditions the thermostats 22 will be adjusted so that the burner 23 will heat the products of combustion flowing through the conduit 9 into the recuperator 12 to such an extent that an average temperature of 500 C. is maintained in the products of combustion entering the recuperator 12, these products of combustion issuing through the conduit 11 at a temperature of 180 C., and of course giving up to the combustible fluid a heat suflicient to maintain a constant temperature of 350 C. in the preheated combustible fluid which reaches the burner 5.

The process and apparatus of the invention can also be used with arrangements where the gas discharging from the heated recuperator is at a lower temperature, except that in this case more heat must be added to the products of combustion in order to provide the desired temperature in the preheated combustible fluid which reaches the burner 5. For example, if at the beginning of the heating of the regenerator the temperature of the products of combustion issuing through the conduit 6 are on the order of C. and at the end of the heating of the regenerator this temperature has increased to 250 C., while the average temperature of the gas issuing from the conduit ill is 180 C., then the thermostats are adjusted so as to provide through the burner 23 an average temperature of 500 C. in the gases which enter into the recuperator 12 so as to heat the combustible fluid flowing through the recuperator, and in this case the combustible fluid may be heated to a temperature of 400 C., for example. Of course, instead of heating the gas and air in the same recuperator, it is possible to provide separate recuperators for the blast furnace gas and for the combustion air, respectively. Moreover, it is possible to provide a separate recuperator for each regenerator.

FIG. 3 shows in a flow diagram the actual operation of a specific installation according to the present invention.

As may be seen from FIG. 3, the blast furnace gas and combustion air flow along the conduits l3 and 1'4 shown at the lower part of FIG. 3 to the recuperator 12. Upstream of the recuperator 12 part of the combustible fluid is directed through suitable conduits from the conduits l3 and 14 to the burner 23. As may be seen from PEG. 3, at the beginning of the heating of the regenerator 5200 cubic meters of blast furnace gas per hour are delivered to the burner 23 while 4100 cubic meters of combustion air are delivered to the burner 23, and as the heating of the regenerator 3 continues these amounts gradually diminish so that at the middle part of the heating of the regenerator 3 there will be 3930 cubic meters per hour of blast furnace gas and 3100 cubic meters per hour of combustion air delivered to the burner 23, and at the end of the operation there will be 2640 cubic meters per hour of blast furnace gas and 2100 cubic meters per hour of air delivered to the burner 23. All of the values for flow of gas in cubic meters per hour are at standard temperature and pressure (S.T.P.).

As may also be seen from FlG. 3, the products of combustion issuing from the regenerator 31 during the heating thereof flow out of the latter at the rate of 72,600 cubic meters per hour, and at the beginning of the heating of the regenerator'the temperature of the products of combustion will be 372 C., while at the middle of the heating of the regenerator the temperature of the products of combustion is 442 C., and at the end of the heating of the regenerator the temperature of the products of combustion is 572 C. Thus, it is to the products of combustion at these temperatures that heat is added by the burner 23, and the regulation of the burner 23 is such that downstream of the burner 23 the products of combustion entering the recuperator 12 will have at the beginning of the operation a temperature of 536 C., at the middle of the operation a temperature of 542 C., and at the end of the operation a temperature of 548 C., so that the temperature is maintained substantially constant for the products of combustion entering into the recuperator 12. It will also be noted that because different amounts of combustible fluid are directed toward the burner 23' difierent amounts are of course added to the products of combustion to be received in the recuperator 12. Thus, the amount of combustible fluid constantly diminishes during the progress or" the operation, and at the beginning of the operation the total amount of fluid flowing through the recuperator is 81,440 cubic meters per hour, while at the middle of the operation the fluid 'fiowing through the recuperator is in an amount of 79,850 cubic meters per hour, while at the end of the operation there is only 77,142 cubic meters per hour of combustible fluid flowing through the recuperator and beyond the latter to the chimney. Thus, it is clear that with the arrangement of the invention because the amount of combustible fluid delivered to the products of combustion constantly diminishes the amount of gas which fiows through the recuperator is maintained relatively small and gas losses are diminished very greatly in this way with the process and apparatus of the invention. In contrast, if the gases issuing from the recuperator 3 were led directly to a. chimney and only gas from the conduits i3 and 14 upstream of the recuperator were used at the burner 23 to provide the heat necessary for preheating the combustible fluid reaching the burner, then 7 a far greater amount of gas would be required, which is to say the total of the 72,600 cubic meters per hour of the products of combustion would have added to it a far greater amount of gas from the conduits l3 and 14, so that the products of combustion together with this latter amount of gas, representing the total gas, would be much greater and of course the gas losses would be correspondingly much greater.

As may be seen from FIG. 3, with this arrangement the blast furnace gas and combustion air which enter the recuperator at 20 Cleave the latter at 440 C. for the combustion air and 320 C. for the blast furnace gas, and when preheated to this temperature, these gases when burned in the combustion means 4 will provide a temperature of 1600 C. enabling the blast air which is blown into the furnace to be heated to a temperature of 1300 C. As may be seen from FIG. 3 the combustion air flows through the burner at the rate of 33,000 cubic meters per hour, while the blast furnace gas flows through the burner at the rate of 42,300 cubic meters per hour.

After the heating operation has been completed, all ofthese operations are terminated and then the relatively cool air is delivered to the bottom of the regenerator 3 at a temperature or" 70 C., for example, and at a rate of 80,000cubic meters per hour, and this air will issue at a temperature of 1300 C., as indicated in FIG. 3, bearing in mind that this heating of the air takes place of course when all of the above operations are completed and the regenerator has been heated so as to be'in a condition for giving up its heat to the air. As is apparent from the headingof FIG. 3, the particular operations illustrated therein took place with an installation where there were three regenerators and combustion means associated therewith, respectively, each regenerator being heated for a period of one hour and giving up its heat for a period of one half hour, so that with this assembly the starting of the heating or the three regenerators takes place at intervals of one half hour while at the end of every half hour the regenerator which has been heated for one hour has the air delivered thereto to be heated therein and after one half hour has been cooled sufiiciently to terminate the heating of the air and to start again the v heating up of the regenerator.

It should be noted that the gas leaves the recuperator 12 at the beginning of the operation at a temperature of 185 C., at the middle of the operation at a temperature of 180 C., and at the end of the operation at a temperature of C., so'that the gas discharging from the recuperator 12 to the chimney has a substantially constant temperature of C.

It should be noted that because the products of combustion issue from the regenerator 3 at a relatively high temperature, this regenerator 3 can be made of relatively small size since it is unnecessary for the checkerbricktherein to store as much heat 'as would be required if the temperature of the products of combustion were leaving the regenerator at a lower temperature. For example, it is of course possible, as when discharging the products of combustion directly from the regenerator to a chimney, to have these products of combustion issue from the regenerator at a temperature of approximately 130 C., but in this case the regenerator itself would have to have a far greater construction. In fact, the regenerator shown in FIG. 3 requires only 60% of the checkerbrick required for a regenerator where the products of combustion issue therefrom at a temperature of approximately 180 C. Moreoventhe gas losses are maintained lower than has hitherto been possible, as was pointed out above, so that the efi'iciency of the operation is increased substantially.

It has been found that thethermal efiiciency' of the entire system may be increased as much as 8%' with the process and apparatus of the invention, particularly as a result of thelowering or" the gas loss. For example, in conventional arrangements where there is an outside source of energy for preheating the combustible gas, the gas loss is on the order of 30%, whereas with the process and apparatus of the invention the gas loss is only on the order of 10%.

It should be noted that if the products of combustion from the regenerator were delivered to the recuperator while adding thereto a constant amount of heat, then because of the increasing temperature of the products of combustion during the heating of the regenerator there would be at the end of the heatingoperation an undesirably high temperature atthe dome of the recuperator, and this undesirable result is avoided with the process and apparatus'of the invention. Thus, by reducing gradually the amount of heat added by the burner 23 as the temperature of the products of combustion increase, the temperature in the combustion chamber of combustion means 4 is maintained substantially at 1600 C. at all times, and an undesired increase in the temperature at the upper part of the recuperator at the end of the heating thereof is reliably avoided. Of course, more'than one burner 23 may be located in the conduit leading from the regenerator to the'recuperator, and also other types of heating structures may be used.

The conduitswhich respectively lead from the

conduits

13 and 14 to the burner 23 carry adjustable valves which are controlled from the thermostats in a manner known in the art so that these valves will be automatically adjusted to provide regulated amounts of combustible fluid for theburner 23 in the manner described above.

It will be understood that each offthe elements described above, or two'or more together, may also find a useful application in other types of heating process and apparatus differing from the types described above.

While the invention has been illustrated and described as embodied in process and apparatus for heating air for blast furnaces, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A fluid-heating process comprising the steps of burning a combustible fluid; directing the products of combustion from the burning of said combustible fluid through a regenerator in which fluid will subsequently be heated; preheating combustible fluid prior to said burning thereof with the products of combustion which discharge from the regenerator as well as by additional heat added to the products of combustion; and adjusting the amount of additional added heat so that the resulting preheating will maintain the temperature of the preheated combustible fluid substantially constant throughout the entire heating of the regenerator.

2. A regenerator-heating process comprising the steps of directing a combustible fluid through a recuperator; burning the combustible fluid after it leaves the recuperator; directing the products of combustion from the burning of the combustible fluid to a regenerator; directing the gases which discharge from the regenerator through the recuperator to heat combustible fluid before it is burned; adding to the recuperator an amount of heat in addition to that derived from the products of combustion which discharge from the regenerator; and adjusting said amount of heat and the heat derived from said regenerator to an amount which will maintain the temperature of the combustible fluid leaving the recuperator to be burned substantially constant.

3. In a process for heating air which is to be used as the blast when blown into a blast furnace, the steps of directing blast furnace gas and air through a recuperator; burning the blast furnace gas and air after they pass through the recuperator; directing the products of combustion resulting from the burning of the blast furnace gas and air through a regenerator in which the air which is to be blasted into the blast furnace is subsequently heated; discharging the products of combustion from the regenerator through the recuperator to preheat blast furnace gas and air before they are burned; adding to the recuperator an amount of heat; and adjusting said amount of heat together with the heat derived from the regenerator to a total amount which will maintain the preheated blast furnace gas and air at a substantially constant temperature just prior to the burning thereof.

4. In a process for heating air to be used as a blast when blown into a blast furnace, the steps of directing blast furnace gas and air to a combustion chamber where they are burned; directing the products of combustion from the combustion chamber through a regenerator in which air to be blown into the blast furnace is subsequently heated; heating a recuperator by directing the gases which discharge from the regenerator through said recuperator While simultaneously passing blast furnace gas and air through the recuperator before they are burned so that the blast furnace gas and air will be heated by the heat in the gases discharging from the regenerator and passing through the recuperator; additionally heating the recuperator by burning some of the blast furnace gas and air before they reach the recuperator; and adjusting said additional heating to an amount which when added to the heat of the gas discharging from the regenerator will maintain the temperature of the blast furnace gas and air reaching the combustion chamber substantially constant.

5. In an apparatus for heating a fluid, in combination, regenerator means; recuperator means; first conduit means communicating with said regenerator means and said recuperator means for directing fluid which discharges from said regenerator means into said recuperator means; second conduit means extending through said recuperator means for directing a combustible fluid through said recuperator means to be heated therein by the fluid which reaches said recuperator means from said first conduit means; combustion means communicating with said sec ond conduit means and with said regenerator means for burning the combustible fluid after it has been heated in said recuperator means and for directing the products of combustion of said combustible fluid through said regenerator means, said products of combustion then forming the fluid which passes through said first conduit means from said regenerator means to said recuperator means; adjustable burner means carried by said first conduit means for additionally heating the fluid which passes through said first conduit means from said regenerator means to said recuperator means, said adjustable burner means being adapted to add to the fluid passing through said first conduit means an amount of heat which will maintain the temperature of the combustible fluid leaving said recuperator means and flowing to said combustion means substantially constant; thermostat means carried by said second conduit means at a portion thereof located between said recuperator means and said combustion means for sensing the temperature of the combustible fluid in said second conduit means; and means operatively connecting said thermostat means to said adjustable burner means for automatically regulating the latter to add to the fluid passing through said first conduit means said amount of heat which will maintain constant the temperature of the combustible fluid flowing from said recuperator means to said combustion means through said second conduit means.

6. In an apparatus for heating a fluid, in combination, regenerator means; recuperator means; first conduit means communicating with said regenerator means and said recuperator means for directing fluid which discharges from said regenerator means into said recuperator means; second conduit means extending through said recuperator means for directing a combustible fluid through said recuperator means to be heated therein by the fluid which reaches said recuperator means from said first conduit means; combustion means communicating with said second conduit means and with said regenerator means for burning the combustible fluid after it has been heated in said recuperator means and for directing the products of combustion of said combustible fluid through said regenerator means, said products of combustion then forming the fluid which passes through said first conduit means from said regenerator means to said recuperator means; adjustable burner means carried by said first conduit means for additionally heating the fluid which passes through said first conduit means from said regenerator means to said recuperator means, said adjustable burner means being adapted to add to the fluid passing through said first conduit means an amount of heat which will maintain the temperature of the combustible fluid leaving said recuperator means and flowing to said combustion means substantially constant; thermostat means carried by said second conduit means at a portion thereof located between said recuperator means and said combustion means for sensing the temperature of the combustible fluid in said'second conduit means; and means operatively connecting said thermostat means to said adjustable burner means for automatically regulating the latter to add to the fluid passing through said first conduit means said amount of heat which will maintain constant the temperature of the combustible fluid flowing from said recuperator means to said combustion means through said second conduit means; and third conduit means communicating with said second conduit means upstream of said recuperator means and also communicating with said burner means for directing to the latter part of the combustible fluid in said second conduit means before the combustible fluid reaches said recuperator means, so that the combustible fluid which is burned in said combustion means also is burned at said adjustable burner means to provide said additional heat.

References Cited in the file of this patent UNITED STATES PATENTS 1,376,479 Stoughton May 3, 1921 1,689,042 McGee Oct. 23, 1928 3,061,292 Kinney Oct. 30, 1962