US2657034A

US2657034A - Oxygen lancing of furnace flues and checkers

Info

Publication number: US2657034A
Application number: US174259A
Authority: US
Inventors: Thomas A Thompson
Original assignee: National Steel Corp
Current assignee: National Steel Corp
Priority date: 1950-07-17
Filing date: 1950-07-17
Publication date: 1953-10-27
Anticipated expiration: 1970-10-27

Description

T. A. THOMPSON Filed July 17, 1950 l l l l f l f l l f OXYGEN LANCING OF' FURNACE FLUES AND CHECKERS lil] Oct. 27, 1953 mvsNrOR. THOMAS A. THOMPSON lATTORNEY Patented Oct. 27, 1953v OXYGEN LANCIN G OF FURNACE FLUES AND CHECKERS Thomas A. Thompson,

to National Steel Co of Delaware Toronto, Ohio, a'ssignor rp'oration, a corporation Application July 17, 1950, serial No. 174,259

8 Claims.

This invention relates to the removal of dust from passages, the dust having previously been deposited in the passages from gaseous products of combustion owing therethrough, and more particularly relates to the removal of such dust while at an elevated temperature through the use of oxygen or oxygen rich gas.

In the present type of `open hearth furnace, for example, there is a smelting or hearth chamber in which the metal is melted and refined. The furnace installation includes at least one regenerator for each end of the furnace. In some furhaces oil is used for fuel. Usually an oil burner i's provided at each end of the furnace. In operation, air is blown through a hot regenerator and the preheated air then passes into one end of the furnace to provide the oxygen to support combustion in the furnace. The incoming air is preheated to an elevated temperature to reduce the quantity of heat which must be supplied by the fuel. The hot gaseous products of combustion produced in the hearth chamber pass out the opposite end of the chamber and then through a second, previously cooled regenerator to heat this Y second regenerator-` The gases from the second regenerator pass through ues to a stack and to the atmosphere. Periodically the direction of gas flow is reversed so that each regenerator alterately is heated by the hot gaseous products of combustion and is then cooled by the countercurrently flowing air. Each regenerator is made up of refractory hrickwork arranged so that there is' a large number of relatively small passages through the brickwork. This brickwork is commonly referred to as checkerwork- The gas'- eous products of combustion are laden with dust. This dust is deposited in the passages leading to, through and from thecheckerwork. These deposits of dust build up, and the removal of this dust, particularly from the flue passages, is quite difficult. It is lnecessary periodically to shut down the furnace and have a crew of workmen clean the dust out of these flues and the checkerwork.

Itis an object of the present invention to effect the removal of dust from passages quickly and with a minimum of effort.

Another object of the present invention is to provide an improved method of and apparatus for removing dust that previously has been `deposited in a passage from gaseous products of combustion,

Another object of the present invention is to effect the removal of dust deposits from a passa-se without the necessity of shutting down the ape paratus associated with the passage or interrupting the flow of gas through the passage.

Another object of the present invention i's to provide an improved method of and apparatus for removing dust from passages leading to, through or from regenerators of refractory brick- Work.

I have discovered that dust deposited from gaseous products of combustion can be readily and thoroughly removed from a passage, for example, an open hearth ue, by impinging a stream of oxygen or oxygen rich gas against the dust deposit while the dust is at an elevated temperature. I have found that when a stream of oxygen or oxygen rich gas impinges on the hot dust in an open hearth flue, dust glows and apparently deteriorates into a residue of fine particles and gases, which the draft through the flue will carry out of the iiue and up the stack. The oxygen converts the relatively heavy dust, which the draft normally will not move, into a residue which the draft will carry out of the flue.

The necessary purity of the oxygen that is used for removing the dust is a function of the temperature of the dust. When the dust is at a temperature of at least 1000D F. or higher, the dust removing gas should contain at least by volume of free oxygen. When the dust is at a higher temperature of at least 1400 F. or higher, a gas that is predominately oxygen may be used. Normally the oxygen rich gas will be composed of oxygen and nitrogen. Any gas may be used which contains the requisite amount of free gaseous oxygen. The portion of the gas which is not oxygen should be an inert gas that will not combine with the oxygen.

These and other objects of the present invention will become more readily apparent from the following description, taken with the accompanying drawings, in which:

Figure 1 is a side View, on open hearth furnace;

Figure 2 is a horizontal sectional view of the furnace of Figure 1 and illustrating one embodiment of the present invention; and

Figure 3 is a fragmentary sectional view of a partially in section, of

portion of the apparatus shown in Figure 2,

illustrating a different embodiment of the present invention.

Referring to the drawings and more particularly to Figures 1 and 2, the open hearth furnace I0 contains a hearth Of smeltg Cl'ianl Il which the netal 1S heated and iend while Supported On the hearth bottom l2. At opposite ends of the furnace there are slag pockets l and 14, each of which is in communication with or opens into a respective end of the chamber. Il.

`the relatively cool air, the Vso that dampers and 35 are open and dampers .29 and 35 are closed. With this arrangement the gas, respectively.

The slag pocket I3 is in communication with the checker or regenerator chamber I4 containing refractory checker brick l5. A passage Iii connects slag pocket i3 and the checker work I5. At the opposite end of the furnace the slag pocket Id opens through a passage I'I into checker chamber I containing refractory checker brick IS. The slag pockets It and I. and the regenerators or checker work I5 and it are similar. As shown more clearly in Figure l, at the bottom of the checker work IQ there are four flues 2l which are separated by the spaced apart walls 22 extending between the bottom of the checker work I9 and the base of chamber It. At the bottom of the checker work I5 there Vare walls 23 similar to walls 22 which define fluesridentical with flues 2l. The fiues of checker chamber I4 open into flueV 25 which is, in turn, in communication with stack 25. The flues 2l, which are beneath checker work I9, open into flue 2l, which inY turn opens to the stack 2S. The flues 25 and 2'! contain dampers 29 and Sil. These dampers are shown in the closed position but either damper may be moved to the open position. A motor driven air blower 3l is connected through conduit 32 to flue 25 and is also connected through conduit 33 to flue 2l. A damper 35 is provided in flue 32 and a similar damper 35 is provided in fluels. be used without the blower to draw the gases through the apparatus.

Oil burners 37 are provided at each end of the furnace. These burnersl are of customary construction and are designed to inject an atomized stream of oil into the chamber il where the oil burns to heat the chamber and the metal therein. In operation and assuming that dampers 3B and3r5 are closed, and the dampers 2S and 3B are open, then air is blown by the blower 3| into flue 2l and through the checker work I9 where the air is heated. The heated air flows through the passage Il, slag pocket I4 and into the furnace to supply the oxygen for effecting combus- Alternatively, the draft of the stack may Y tion of the fuel oil. The hot gaseous products of combustion flow from the chamber I I through slag pocket I3, passage I@ and then down through regenerator I5. The hot gases heat the regenerator I5 and then flow through iiue 25 to thestack 255.Y 'When the regeneratorlfa becomes sufficiently heated and the regenerator I9 becomes cooled by dampers are reversed air is blown into flue 25 andthroughthe `re- Agenerator l5 where the air is heatedand then The hot gaseous products I4, regenerator IS, flues Thus, each reinto the chainberl I. flow 'through slag pocket 2! and then flue 2l to stack 25.

generator is' alternately heatedand cooled bythe countercurrently flowing hot gaseous products of combustion and relatively cool air. Y Y

. As described Yso far in detail, the open hearth furnace is of customary construction and may be of any type customarily used in the steel industry. Where gas is used as the fuel, then two regenerators may be installed at each end of the furnace so that one of each pair of regenerators can be used for heating the air and the fuel The open hearth furnace a described so far in detail, constitutes no part of the present invention, and the present invention is not limited to the exactdetails of open hearth structure n shown in the drawing. It is to be noted that the walls ofthe passages arerlined With refractory Ypocket and one of the regenerators and then through the flues to the stack is ladened with or contains suspended dust particles. These dust particles collect in the passages, particularly Vin the passages of the checker work and on the bottoms of the fiues. These dust deposits restrict the size of the passages and it is necessary at intervals to clean the checker work and the fiues to remove the dust. Attempts have been made to use air or steam to blow the dust out of the passages Without success. This dust has a high specific gravity and while the dust can be cleaned off of the checker brick by means of a high velocity air or steam jet, the dust merely falls down to the bottom of the flues so that the dust in the checker. work is shifted tothe flues. The dust has been found to collect in the nues to a depth of, for example, 20 inches. Attempts to clean the flue passages with air or steam have not been satisfactory. Accordingly it is necessary to periodically shut down the furnace and allow the furnace to cool down sufficiently to enable a crew of workmen to manually scrape the dust out of the flue passages. This is a time consuming operation and is relatively costly.

A sample of flue dust collected from the flues of an open hearth furnace was found to have the following analysis: Y

Per cent The composition of the dust will vary depending'on the fuel usedr and the metal in the hearth,

particularly the composition and type of scrap Y metal used. The high zinc content of this dust Vresulted from Zinc volatilized in the hearth.

Inraccordance with the present invention, this flue dust is quickly removed when the' dust'and flue walls are at an elevated temperature and it is not necessary to shut vdown the furnace to remove the dust. Open hearth'flues and passages are provided with suitable openingsV to permit access to the interior. These openings normally are closed by doors or covers. As shownmore clearly in Figure 2, the side wallofV flue 2,1 is p rovided with an opening 40 normally closed by aY door or cover 4I. A similar Yopening 42 is provided ina wall of flue 25. The opening 42 is normally` closed with a cover like cover`4l, but is shownl as havingV been removed. The

openings

40 and 42 are opposite the respective regenerators I9 and I5. As Yshowna long pipe 44 `may be inserted through opening 42 so as to directa stream of gas into the flues beneath thechecker work'IS. The pipe also may rect gas down toward the bottom of flue 25. VThe pipe or lance 44 is connected through ahose 46 be` positioned to di- Y lance 44 is inse1jtedfand the gas is turned on by opening valve4w5 so thatna stream of oxygen rich gas isdi-rected i-nto the flue and' against the dust deposit thereon. With the dust at an elevated temperature, the stream of gas causes the dust to glow and as a result ofl oxidation of part of the dust constituents,` the dust deteriorates into aj residue of line particles and gases. The draft through the ue carries the residue out the stack and the deposits inrthese ilues are relatively quickly and thoroughly removed in this manner'. Preferably, the draft is left on while the dust is beingrem'oved so that gas is flowing froni the hearththrough the ues and to the stack. This gas will carry out the residue to the stack.V After the dust has been removed the lance 44 is removed and opening 42 `is closed'. Ilfhe pipe' 44 can be inserted through opening 40 to remove the dust from the ilues at the oppositeend of the furnace. l

In order for the dust to be at least partially oxidized by means of a stream of oxygen or oxygen rich gas, the dust mustl be at an elevated temperature. The reaction temperature of the dust depends upon the degree of oxygen purity of the gas and the degree of oxygen purity of th gas in turn' depends iiiA part on the temperature of the dust.- Wl'iifiA the dust is at a temperature of 'l000 F. the gas directed against the dust deposit must contain at least 90% by volume of gaseous oxygen. When the dust is at a higher temperature of at least 714100" F.-, the gas may be one that is predominately free oxygen gas,- thatv is, the gas must contain at least by volume of iree oxygen. Normally the gas other than oxygen present in the stream impinging against the dust will be nitrogen. Other relatively inert gases which do not burn or combine with the oxygen under the conditions existing may be present. Where impure oxygen is used, the impure oxygen may be obtained, for example, by mixing air and relatively pure oxygen.

Referring more particularly to Figure 3, the means for cleaning the ues may be permanently mounted in the furnace ilue. A distributor pipe 41 is mounted on and extends through the wall of flue 21 and has connected thereto tubes or nozzles 48 arranged to direct streams of gas into iiues 2 l. The distributor pipe 41 contains a valve 49 and is connected to a source of oxygen or oxygen rich gas through pipe 50. Tubes 5| extend from pipe 4l into ue 21 for directing gas against the dust on the bottom of flue `27. In operation, the valve 49 is open and. oxygen or oxygen rich gas is directed from nozzles 48 and 5I against the dust in fiues 2| and 21 to remove the dust as previously described.

As pointed out previously, preferably gas is iiowed through the fiues to the stack 28 to carry out the residue resulting from the at least partial oxidation of the dust. When fuel is being burned in chamber Il While the dust is being removed, then the gas owing through the flue is gaseous products of combustion. If no fuel is being burned then the gas may be air that is blown through chamber Il, then through the regenerator and through the ues being cleaned to the stack.

The present invention has been described in detail in connection with an open hearth furnace but is not limited to such a furnace. Its principles may be utilized for removing dust which is at least partially oxidizable, and which has dropped out of other combustion gases. Dust 6 may be removed, as described; from passages leading to, through or from other regenerators or checkerwork, for example, the nues" of coke plants.

1'.. The method of removing dust from a passage comprising flowing gaseous products of combustion through andl then out' of a passage in. one direction, the gaseous products of' combustion carrying dust particles that coliect in the passage, impinging a stream of gas containing at least by volume of free gaseous oxygen against the collected dust in the passage while the dust is at a temperature of" at least 1000 F. and. thereby eiecting oxidation of at least part oi' the dust, and iiowing the dust residue out of the passage in the same direction as the gaseous products of combustion.

2. The method of removing dust from a passagecomprising dowing gaseous products of= combustion through and out of a passage in one direction, the gaseous products of combustion carrying dust particles that collect in the passage, impinging a stream o1' gas containing at least 50% by volume of free gaseous oxygen against the collected dust in the passage while the dust is at a temperature of at least 1400 F. andl thereby effecting oxidation of at least a portion of the dust, and flowing the dust residue out of the passage in the same direction as the gaseous products of combustion.

3.` In the method of cleaning a passage to remove a dust deposited in the passage from dust ladened gaseous products of combustion flowing through the passage, the steps comprising impinging a stream of gas containing at least 90% by volume of free gaseous oxygen against the dust deposit While the dust is at a temperature of at least 1000 F., and thereby effecting oxidation of at least a portion of the dust, and simultaneously owing other gas through the passage to carry the dust residue out of the passage.

4. In the method of cleaning a passage to remove a dust deposited in the passage from dust ladened gaseous products of combustion nowing through the passage, the steps comprising impinging a stream of gas containing at least 50% by volume of free gaseous oxygen against the dust deposit while the dust is at a temperature of at least 1400 F., and thereby eiecting oxidation of at least a portion of the dust, and simultaneously flowing other gas through the passage to carry the dust residue out of the passage.

5. In the method of removing dust from a passage communicating with a regenerator, the steps comprising alternately, countercurrently passing relatively hot gaseous products of combustion and relatively cool gas through such a passage and regenerator so that the regenerator is alternately heated by the hot gaseous products of combustion and cooled by the cool gas, the hot gaseous products carrying dust particles that collect in the passage, and directing a stream of gas containing at least 90% by volume of oxygen against the collected dust in the passage while the dust is at a temperature of at least 1000o F. and thereby effecting oxidation of at least part of the dust, and simultaneously passing gas through the passage in the same direction as the hot gaseous products of combustion to carry the dust residue out of the passage.

6. In the method of removing dust from a passage communicating with a regenerator, the steps comprising alternately, countercurrently passing relatively hot gaseous products of com bustion and relatively cool gas through such a passage and regenerator so that the regenerator is alternately heated by the hot gaseous products of combustion and cooled by the cool gas, the hot gaseous products carrying the dust particles that collect in the passage, and directing a stream of gas containing at least 50% by volume of oxygen against the collected dust in the passage While the dust is at a temperature of at least 1400 F. and thereby effecting oxidation of at least part of the dust, and simultaneously passing Agas through the passage in the same direction as the hot gaseous products of combustion'to carry the dust residue out of the passage.

'7. The method of operating an open hearth furnace comprising passing hot gaseous products of combustion from the hearth of an open hearth furnace through a regenerator of refractory brickwork and then through a flue passage and to a stack and alternately countercurrently passing cool air through the iiue passage and. then through the regenerator to the furnace stream of gas containing at least 90% by volume of gaseous oxygen against the dust While at a temperature of atleast 1000 F. and thereby effecting oxidation of at least part of the dust,

hearth, the hot gaseous products of combustion Y -8 and simultaneously passing gas through the regenerator and then through the flue passage to the stack to carry out the residue.

8. The method of operating an open hearth furnace comprising passing hot gaseous products of combustion from the hearth of an open hearth Yfurnace through a regenerator of refractory brickwork and then through a flue passage and to a stack and alternately countercurrently passing cool air through the flue passage and -then through the regenerator to the furnace hearth, the hot gaseous products of combustion carrying dust from the open hearth furnace and at least part of the dust being deposited in the regenerator and flue passage, periodically removing the dust deposited in the flue passage by applying a stream of gas containing at least 50% by volume of gaseous oxygen against the Ydust While at a temperature of at least 1400 F.

and thereby eiecting oxidation of at least part of the dust, and simultaneously passingV gas through the regenerator and then through the flue passage to the stack to carry out the residue.

THOMAS A. THOMPSON.

References Cited n the file 0f this patent UNITED STATES PA'I'ENTS