US2126724A - Furnace and the operation thereof - Google Patents

Description

2 Sheets-Sheet 1 Aug. 16, 1938. A. J. BOYNTON FURNACE AND THE OPERATION THEREOF Filed Aug. 1. 1936 IIIIIIIIIII 4 IIIIIIIIIIIIII F 5 l 4 9 5 r 5 5 I 5 I 4 v Jrf/wr J50 1, A. J. BOYNTON 2,126,124

FURNACE AND THE OPERATION THEREOF Filed -Aug;. 1, 1936 v 2Sheets-Shgt 2 VIII/1111 Patented Aug 16 1 8 I I FURNACE AND THE OPERATION manor- Arthur J. Boynton, Chicago, Ill., assignor to H. A.

Brassert & Company, Chicago, Ill.,. a corporatlon of Illinois '7 Application August 1,

13 Claims.

The present invention relates to improvements in furnaces and the operation thereof.

More particularly the present invention relates to industrial furnaces operating on gaseous fuels containing hydrocarbons. Among such fuels may be mentioned coke oven gas, natural gas, and mixtures of either of these gases with blast furnace gas. The invention is equally applicable to gurnaces using othergases containing hydrocarons.

It has long beenrecognized that heat transfer from the products of combustion in a furnace or the likeis greatly promoted by luminosity of the flame. Luminoslty'results in absorption of heat as a result of radiation. In the absence of luminosity, heat is transferred by conduction, and to accomplish a predetermined result a temperature is required within the furnace much higher than where luminosity exists. The result of lack of luminosity is decreased efliciencyin furnace operation.

Luminosity of aflame is understood to result from the presence within the fuel stream of minute particles of solid carbon. These particles become heated to incandescence and give to the flame its luminous appearance, at the same time radiating heat.

Fuel containing hydrocarbons may be made to burn with a luminous flame by the decomposition of some or all of the contained hydrocarbons prior to combustion. Such decomposition, often called cracking, results in the formation within the gas of solid carbon particles-capable of radiation and of producing a luminous flame. The present invention relates to novel means for producing cracking in the operation of an industrial furnace and the luminosity attendant thereto.

' The present invention will be described in connection with furnaces such as are employed in the manufacture of steel. Such furnaces employ various gases, among which may be gas resulting from liquid fuels such as tar and oil for the creation of the necessary heating and melting eifect. It is common practice to preheat such gases. in

.regenerators. Another example of the type of gas which is usedis a mixture of coke oven gas and blast furnace gas. Such gases are commonly available at steel works and are frequently wasted except in connection with the manufacture of steel. The purpose of regeneration of the fuel gas is, in part, to recover the heat from the outgoing waste gases'by raising the temperature of the ingoing fuel. A second and very important object is, however, to crack the hydrocarbons, chiefly methane, in the gaseous .mixture, and

1936, Serial-No. 93,804

thereby impartluminosity to the flame. According to prior constructions and prior methods, regeneration under these conditions involves certain expensive, and undesirable constructional features and imposes limitations on the opera-f tion. For example", the port through which gas passes to an industrial furnace is ordinarily small in cross sectional area in comparison with the air port. At the outgoing end of the furnace, therefore, the exit gases tend. to pass throughv the air port .to the air regenerator and to heat up this regenerator to a higher temperature than furnace with removable gas ports to permit the necessary increased flow of outgoing gases into the gas regenerator. In addition to the inconvenience and expense of a removable port and the necessity of-maintaining a minimum tem-. perature in the gas regenerator, there are incidental disadvantages connected with the practice of heating a mixture of coke oven gas and blast furnace gas in a regenerator. Among these disadvantages is the loss of gas by reversal, since a regenerator flow of gas goes to the chimney at each reversal. The loss just mentioned may be partly overcome by shutting off the more valuable coke oven gas before reversal, but this necessity is an undesirable feature.

Among objectionable characteristic of this practice is a certain danger of explosion during reversal whichv attends the use of a gas mixture of high calorific power. Furthermore, it is necessary to maintain a velocity above a certain minimum within the gas regenerator, if cracking is taking place therein, in order that the particles of solid carbon may be swept along with the gas stream and not deposited in the checkerwork of the regenerator. According to the prior suggestions referred to, the regenerator must be designed for the double purpose of heating and of carrying over into the furnace all of the solid particles of carbon. In short, the objection to the prior suggestions in connection with the cracking of the gas by regeneration are of such consequence that they have resulted in the abandonment of gas regeneration in certain localities,

the operators preferring to use cold gas, for the reason that the added simplicity, together with the reduction of cost of repairs and reduction of the loss of gas, more than offsets the nominal 3 thermal benefit of regeneration.

Where coke oven gas unmixed with blast furnace gas is used in furnaces of the type being discussed, regeneration of the gas is usually not practiced, but liquid fuel such as oil or tar is employed as a second fuel, the reason for the use of this liquid fuel being, in considerable measure, to furnish luminosity to the flame.

The advisability of gas regeneration varies with the gas, and, inversely, with the volume of air necessary to burn a unit volume of gas. Natural gas requires somewhat more than ten times its own volume of air for complete combustion; coke oven gas requires about flve volumes; producer gas or blast furnace gas requires a much smaller ratio of air to gas, the requirement of blast furnace gas being somewhat less than the volume of the gas itself. It is well understood, therefore, that the relative advantage of regeneration of gas for the sake of increased temperature is a minimum with natural gas and a maximum with blast furnace gas.

An object of the present invention is to provide an improved construction for industrial furnaces or the like whereby the cracking of hydrocarbon gases for use in such furnaces may be accomplished eillciently.

A further object is to provide apparatus of the kind just referred. to having means for cracking hydrocarbon gas by preliminary combustion of a portion of the gas to raise the temperature of the entire mass of fuel gas and products of combustion to a cracking temperature.

A further object is to provide improved apparatus of the kind referred to in which hydrocarbon gas may be used in mixture with blast furnace gas and in which the blast furnace gas may be regenerated, to the end that it will be introduced hot into the gas port of the furnace.

A further object is to provide a construction of the kind immediately above referred to in which gas ports of ordinary construction may be empl ye A further object is to provide an improved method of operating an industrial furnace whereby the desired luminosity of flame may be accomplished emciently and'at relatively low cost.

A further object is to provide a furnace construction and an improved method of furnace operation well adapted to meet the needs of commercial service.

Further objects will appear as.the description proceeds.

Referring to the drawings- Figure 1.is a top plan view, more or less diagrammatic in its nature, illustratinga portion of an industrial furnace embodgng the principles of the present invention; I g

Figure 2 is a sectional view takemalong the plane indicated by the arrows 2-'2 of Figure 1;

Figure 3 is an end view taken in the direction of the arrow I of Figure 1;

Figure 4 is a view similar in many respects to Figure 2 but omitting the gas regenerator of Figure 2;

Figure 5 is a sectional view on an enlarged scale illustrating a gas port which may be used in the practice of the present invention;

Figure 6 is a view taken along the plane indicated by the arrows 6-6 of Figure 5; and

through heat.

Figure 7 is a view similar to Figures 2 and 4 but showing another modification.

Referring first to Figures 1, 2 and 3, the numeral H indicates as a whole an open hearth furnace, this furnace having been chosen for purtive reversible furnace. The numeral I2 indicates a gas regenerator and the numeral l3 indicates an air regenerator cooperatively associated with the furnace II in the manner well understood by 7 those skilled in the art. The numeral i4 indicates an uptake from the gas regenerator I2 communicating through the port IS with the hearth of the furnace. The numeral it indicates a pair of uptakes from the air regenerator l3 leading to the air port i1, through which communication is had to the hearth of the furnace. A pipe i8 leads from the top of the air regenerator iii to the cracking chamber ita, preferably located on the outside of the furnace. Said'cracking chamber i8a is located between the elbow is communicating with the pipe [8 and the elbow 20 communicating with the gas port l5. Also communicating with the elbow i9 is the pipe 2| for conducting fuel gas, such as coke oven gas or other hydrocarbon gas, to the cracking chamber l8a. As so connected, said pipe 2| will increase the flow of air from the air regenerator I: by aspiration.

The pipe I! communicating from the air regenwhich is adapted to shut ofi completely composes of illustration as being typical of a regeneraerator I3 is provided with the regulating valve'22,

munication between the cracking chamber Ilia and the air regenerator [3. For the control of said valve 22, a thermocouple is provided, indicated by the numeral 23, which thermocouple communicates with the interior of the elbow 20. Said thermocouple 23 is connected to the controller 24, which in turn is connected to the operating cylinder 25 for operating said valve 22. In operation, the thermostat 23 will control temperatures at the'entrance of the cracking chamber Ila at the minimum at which satisfactory cracking takes place, and the gases entering the port I! by way of said cracking chamber I8a will becracked by partial combustion in said cracking chamber to a sufficient extent to provide a luminous flame. At the same time, excessive combustion of the gas delivered through the pipe 2| is avoided. Though a thermostatic control for the valve 22 has been shown, it will be understood that any other control means may be used if preferred.

,By reason of the construction referred to, a saving in original and maintenance costs is provided, together with good thermal performance due to regeneration of the blast furnace gas in the regenerator l2. It will be understood that wherever in this specification or in the claims the term "coke oven gas is used, it will apply with equal correctness to natural gas or any gas containing hydrocarbons capable of being cracked The term hydrocarbon gas is intended to be generic to the gases referred to in this paragraph.

Figure 4 illustrates a construction in which the gas regenerator is omitted, a single fuel gas being employed, which gas contains hydrocarbons. Where such a fuel as natural gas or coke oven gas is to' be used, it is'not necessary or desirable to regenerate the gas, since regeneration of the air will pre-heat a very large proportion of the mixture of air and gas which unite in the furnace.

As indicatedabove, however, it is extremely de'-" sirable to obtain luminosity in the flame. It is a it 2,120,724.

indicates a pair of air uptakes leading to the air port i1. Said air port i'i servesto conduct the products of combustion from the furnace to the regenerator l3 when the furnace is reversed. Gas

containing hydrocarbons is conducted to the cracking chamber 26a through the pipe 2|. If preferred, the gas containing hydrocarbons may be introduced through the pipe 2ia into the pipe 26, whereby to produce aspiration of'air by the gas issuing from the pipe 2la. The thermocouple 23 is connected in the pipe 21. Said thermocouple controls the regulator 24, which in turn controls the operating cylinder 25. Said operating cylinder 25 controls the position of the valve 28 located in the pipe 26 leading to the cracking chamber 26a. Said valve 28 is adapted to close completely communication between the cracking chamber 26 and the air regenerator l3. It will be understood, of course, that any other control means for the valve 28 may be utilized if preferred, instead of the thermostatic control illustrated. J

The mode of operation of the structure shown in Figure 4 is to permit a regulated amount of air to rise in the cracking chamber 26a. and to unite with the gas from the pipe 2| or the pipe 2 I a,- the combustion within said cracking chamber raising the temperature of the gas to the cracking point. On reversal of the furnace, the valve 28 may be either open or closed, since there is but a single regenerator at each end of thefurnace and the use of the pipe 26 and the cracking chamber 26a as a downtake is optional. However, impor tant results are accomplished by closing the valve 28 when products of combustion are going into the regenerator 2. The volume of the fuel gas entering the furnace is small and the area of the port i5 may be very small and still afford sufficient area for passage of gas into the furnace. The volume of air in relation to that of gas is so large that there is an advantage in bringing the gas into closercommunication with the air than is possible in a single port. If the valve 28 be held closed during reversal, there will be no passage of gases, solid matter, or slag vapors into the port i5; This fact permits a port construction in which multiple exits for the gas passing to the furnace are possible. Such'a construction is illustrated in Figures 5 arid 6, in which the gas port I! has disposed therein the multitubular insert 29,

by means of which it is possible to influence both speed of entry of gas into'the furnace and the conformation of the surface along which mixture of air and gas takes place for combustion purposes. v

Referring now to Figure 7, the air regenerator i2 has two uptakes I6 leading to the air port I'lsimilar to the construction shown in Figures 1 and 2, and has a central uptake 30 leading to the gas port I 5. Gas containing hydrocarbons is introduced through the pipe 3i into the gas port l5.

In the construction illustrated in Figure '7, the

air which has passed up through the central uptake 30 flows through the port i5 in a stream parallel to and surrounding the gas delivered by the pipe 3i. By this means cracking will occur as a result of combustion of the outer layer of the gas body. The port 36 is provided with the valve 32, which may be controlled by a cylinder 25 responsive to conditions at any preferred point, as for example in the port i5.

Though a preferred embodiment of the present invention has been described in detail, many modifications will occur tothose skilled in the art. It is intended to cover all such modifications that fall within the scope of the appended claims.

What is claimed is- 1. The method of operating a reversing 'regencarbons which consists in admitting a regulated quantity of regenerated air into contact with said fuel prior to its introduction to the furnace, raising the temperature of the resulting mixture by erative furnace fired with a fuel containing hydropartial combustion to crack part of the hydrocarbons contained in said fuel and thereafter introducing the resulting mixture to the furnace, admitting regenerated air to said furnace in contact with said gaseous'mixture, and, when the furwhich does not contain hydrocarbons, and burning saidtwo fuels in said furnace.

3. The method of operating a reversing regenerative furnace using a gaseous fuel which contains hydrocarbons and a gaseousfuel which does not contain hydrocarbons which consists in regenerating the fuel which does not contain hydrocarbons and admitting it to the furnace, admit ting 'a regulated quantity of regenerated air to the gaseous fuel which contains hydrocarbons, bringing said last mentioned fuel to a cracking temperature and admitting it to contact with said gaseous fuel which does not contain hydrocarbons, burning said two fuels in said furnace,

and,'when said furnace is reversed, stopping the flow of products of combustion along the path of i said regenerated air.

4. The method of operating a reversingregenerative furnace which consists in admitting inde* pendently regulated quantities of air in two paths,

' admitting hydrocarbon gas into contact with the air in one of said pathsand cracking a portion of said gas by partial combustion thereof, allowing said paths to meet for combustion in the furnace, and on reversal of the furnace delivering products of combustion for regenerating purposes through only that path .to which gas had riot been admitted.

5. In combination, a reversing regenerative furnace having an air port and a gas'port, an air regenerator connected to-said air port for receiving products of combustion from said furnace when said furnace is reversed, a cracking chamber having an outlet for delivering gas to said gas port, means for delivering hydrocarbon gas to said cracking chamber, means connecting the outlet end of said air regenerator with said combustion in said cracking chamber, and means responsive to temperature conditions at said cracking chamber for automatically regulating the ainount of regenerated air delivered from the outlet end of said air regenerator with said cracking chamber whereby regenerative air may be mixed with said hydrocarbon gas in said cracking chamber to partially crack said gas by combustion in said cracking chamber, and means responsive to conditions at said cracking chamber for automatically regulating the amount of regenerated air delivered from said air regenerator to said cracking chamber.

7. In combination, a reversing regenerative furnace having an air port and a gas port, an air regenerator connected with said air port and a gas regenerator connected with said gas port, a cracking chamber, means for delivering hydrocarbon gas; to said cracking chamber, means connecting said air regenerator with said cracking chamber whereby a supply of regenerated air may be mixed with hydrocarbon gas in said cracking chamber to crack a portion of the hydrocarbons in said gas, means for delivering the gas from said cracking chamber to said gas port,

' and means responsive to conditions in said cracka cracking chamber, means for delivering hydrocarbon gas to said cracking chamber, means connecting said air regenerator with said cracking chamber whereby a supply of regenerated air may be mixed with hydrocarbon gas in said cracking chamber to crack a portion of the hydrocarbons in said gas, means for delivering the gas from said cracking chamber to said gas port,'a'nd means responsive to conditions in said cracking chamber for regulating the amount of air delivered from said air regenerator to said cracking chamber, said last mentioned means being adapted to shut 06 communication from said furnace through said cracking chamber to said air regenerator when said furnace is reversed.

9. In combination, a reversing regenerative furnace having an air port and a gas port, an air regenerator connected to said air port; a

cracking chamber, means for admitting hydrocarbon gas to said cracking chamber, means for admitting air from the outlet end of said air regenerator to said cracking chamber whereby a portion of the hydrocarbons in said gas may be cracked, means for delivering gas from said cracking chamber to said gas port, and a valve adapted to shut off communication between said cracking chamber and said air regenerator, said gas port including a multiple-aperture means for causing the flow of gas through said gas port in a plurality of streams.

10. In combination, a reversing regenerative furnace adapted to burn hydrocarbon gas and a gas which does not contain hydrocarbons, said furnace having a. gas port, an air port, an air regenerator connectedwith said air port and a gas regenerator connected with said gas port, means for delivering hydrocarbon gas, a crack ing chamber for receiving said hydrocarbon gas, and means connecting said cracking chamber with said gas port, means connecting said air regenerator with said cracking chamber whereby regenerated air may be mixed with said hydrocarbon gas in said cracking chamber to crack a portion of the hydrocarbons in said cracking chamber by partial combustion, and a shut-off valve in said connecting means between said air regenerator and said cracking chamber.

11. In combination, a reversing regenerative furnace having an air port and a gas port, an air regenerator connected to said air port, said air regenerator also having a connection with said gas port, means for delivering hydrocarbon gas to said gas port,-and a shut-off valve for closing communication between said gas port and said air regenerator upon reversal of said furnace.

12. In combination, a reversing regenerative furnace having an air port and a gas port, an

air regenerator connected to said air port, said air regenerator also having a connection with said gas port, means for delivering hydrocarbon gas to said gas port, and a shut-off valve for closing communication between said gas port and said air regenerator 'upon reversal of said furnace, said gas port having a multiple-aperture nozzle for causing gas to flow into said furnace in a plurality of streams.

13. In combination, a reversing regenerative furnace having an air port and a gas port, an air regenerator connected to said air port, said air regenerator also having a connection with said gas port, said gas port including a passageway located within said furnace and adapted to function as a cracking chamber, conduit means for delivering hydrocarbon gas to said gas port, and a shut oil valve for closing communication between said gas port and said air regenerator upon reversal of said furnace.

ARTHUR J. BOYNTON.

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