US3140985A

US3140985A - Method of oxidation hardening of briquettes

Info

Publication number: US3140985A
Application number: US58120A
Authority: US
Inventors: Schmalfeld Paul
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1959-09-26
Filing date: 1960-09-23
Publication date: 1964-07-14
Anticipated expiration: 1981-07-14

Description

July 14, 1964 P. SCHMALFELD 3, ,98

METHOD OF OXIDATION HARDENING OF BRIQUETTES Filed Sept. 23, 1960 2 Sheets-Sheet 1 Ally;

y 14, 1 P. SCHMALFELD 3,

METHOD OF OXIDATION HARDENING OF BRIQUETTES Filed Sept. 23, 1960 2 Sheets-Sheet 2 United States Patent 3,140,985 METHOD OF OXIDATION HARDENING 0F BRIQUETTES Paul Schmalfeld, Bad Hamburg, Germany, assiguor to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany Filed Sept. 23, 1960, Ser. No. 58,120 Claims priority, application Germany Sept. 26, 1959 10 Claims. (Cl. 202-15) This invention relates to the hardening of briquettes composed of solid fuels and/or metal ores and a binder.

It is known that fine-grained fuels and/ or ores having a particle size less than 3 mm. can be mixed with lowtemperature carbonisation tar fractions having a boiling point above 250 C. and made into briquettes. Alternatively, tar pitches from low temperature carbonisation tars can be used as a binder and the soft and green briquettes then hardened by means of oxygen-containing gases having a temperature of from about 150 to 300 C. The hardening occurs by reason of the polymerization of the low-temperature tar into a resin in the presence of oxygen, with the result that the grain structure of the briquettes becomes extraordinarily hard. It is also known that briquettes so hardened can be converted into coke in the presence of even higher temperatures as from 500 to 700 C. whereupon the briquette is made even more solid and the volatile component of the briquettes is lowered to the value desired for metallurgical coke.

As these green briquettes are very soft immediately after being initially formed, the oxidizing hardening is ordinarily done by placing the briquettes in a shallow bed on a conveyer belt or a sinter band or in small cars which are placed through a tunnel furnace. The oxidizing gases are drawn through the bed of briquettes on the conveyer belt or small cars, each of which has a bottom pervious to gas. This hardening with oxygen takes at least three hours. Following this are the final coking and cooling steps so that the entire process takes at least five hours. The conveyor belts, sinter bands, or tunnel furnaces are considerably expensive. In addition, such mechanically complicated installations require a rather large maintenance expense.

For the purely heat hardening of briquettes, the combination of a conveyor with a shaft furnace has been used. In such, the green briquettes are embedded with hot fine coke on the conveyor belt and are thereby transferred to the shaft furnace. Hot inert gases flow upwardly in the furnace countercurrent to the downwardly moving briquettes. These gases carry the fine coke upwardly so that the coke can be recovered in a dust separator and recycled to the conveyor belt.

The object of this invention is to improve upon the method and apparatus for hardening briquettes While using the combination of a conveyor belt and a shaft furnace.

It has been found by this invention that the method and apparatus can be substantially simplified by taking advantage of a characteristic occuring during the course of hardening the green briquettes with oxygen. It has been discovered that briquettes formed with a binder of low-temperature tar products when heated with oxygencontaining gases attain within a period of thirty to sixty minutes a crushing and abrasive strength such that the briquettes will not disintegrate when stacked to 2 meters or more and that the briquettes can even be moved slowly downwardly when in a compact stack and can be even moved over baffles to change their flow direction. According to this invention, only the first stage of oxygen hardening is performed on a conveyor belt or in a tunnel furnace with the green briquettes arranged in a bed from 0.3 to 0.6 meter thick and with a processing time of from about thirty to sixty minutes. Then further hardening, coking, and cooling steps take place in a shaft furnace coupled to the conveyor belt and in which furnace a compact stack of briquettes passes from the top to the bottom of the furnace. With this arrangement, the conveyor belt only needs to be about one-fourth of the length of the belt heretofore required.

The shaft furnace of this invention is subdivided into three zones which are separated from each other by means of inclined bafiles for the purpose of introducing and removing the processing gases. The briquettes are rehardened in the uppermost furnace zone by oxygencontaining gases having a temperature of from 200 to 300 C. This step lasts from one to three hours depending upon the kind of fuel and/0r ore and bonding agent used in making the briquettes. It is autothermic or slightly exothermic. The exhaust gases from this step are so hot that they are used to supply a part of the heat for the preheating and hardening of the green briquettes on the conveyor belt. This uppermost furnace zone can be further sub-divided into two or three sections separated by baflles wherein different temperatures or gases of different oxygen content can be used in each subsection.

This coking of the briquettes takes place in the middle zone of the furnace in which the briquettes are heated with gases ranging from 500 to 700 C. so that the binder is converted into coke and the thus formed tarfree briquettes are very solid and the briquettes are thereupon degassed. It is noted that when coke briquettes are formed from coke and binder it is not advisable to degas the briquettes by heating to temperatures which are higher than those used for the production of the coke. Experience has shown that when such higher temperatures are used the coke particles decrease in size, whereby the solidity of the briquettes is reduced.

The gases used for the degasifying of the briquettes are recycled and the excess of gas which occurs contains traces of tar and is for preheating the gases required for the conveyor belt or for producing waste heat steam or the like.

The lowermost zone of the shaft furnace forms the cooling zone into which inert gases or gases low in oxygen content are introduced. These cooling gases reach a temperature of 300 to 400 C. when in contact with the coke and are recycled through a waste heat boiler so that their temperature drops to to 200 C., and then the gases are cycled back into the lowermost cooling zone of the furnace by means of a blower. The cooled briquettes are continuously removed from the bottom of the furnace by a rotary gate valve and, if necessary, are further cooled with water to the ambient temperature. This further cooling can also be effected in the bottom of the furnace with gases which are cooled in a watersprayed cooler and then recycled through the furnace.

The conveyor belt or tunnel furnace coupled to the shaft furnace is sub-divided into several sections within which oxygen-containing gases of different temperatures or oxygen content are, respectively, recycled through each individual section.

The shaft furnace has a height of from 10 to 15 meters. The conveyor belt is positioned at the level of the top of the furnace in order that the initially hardened briquettes have only a slight drop, if any, into the furnace from the belt. In a modified form of the invention, the difference in height from the top of the furnace to the conveyor belt is bridged by a bucket conveyor. Such a bucket conveyor can replace the conveyor belt. The buckets have bottoms permeable to the passage of gas. A hood sub-divided into sections encloses the conveyor belt or the bucket conveyor and gases of different temperatures or oxygen content are passed through each section.

The means by which the objects of the invention are obtained are disclosed more fully with reference to the accompanying diagrammatic drawing of the apparatus of this invention.

FIGURE 1 is a diagram of a plant for carrying out the method according to the invention, and

FIGURE 2 is a modification of this plant.

In the two figures like parts are designated by like references.

The apparatus is composed of the briquette press 1 from which the briquettes drop onto an endless feed conveyor 2 and are transferred to the initial hardening conveyor belt 3 and from there into the shaft furnace 4. Belt 3 is enclosed by a housing 5 which is continued into the cover 6 for the top of the shaft furnace. Wind boxes 7 are mounted beneath belt 3 and through which gases of different temperatures or of different oxygen content can be directed to flow through the bed of briquettes on belt 3. Furnace 4 is subdivided by

inclined baflies

10, 10a and 10b and 11, 11a and 11b into three zones 12, 13 and 14 through which separate streams of gases can be directed. A discharge rotary gate valve 15 is positioned in the bottom of the furnace 4 for the removal of the treated briquettes. The green briquettes coming from press 1 are transferred through a gas-sealed entrance 16 onto an inclined sliding plate 17 and thus onto belt 3 where they form a uniform layer or bed having a thickness of from 30 to 60 cm. In each section 9, 9a and 9b, respectively, the briquettes are treated with gases of progressively higher temperature and/or of different oxygen content. These gases are recycled in each section. In section 9, the gas is recycled by means of a blower 18. Likewise

blowers

19 and 20, respectively, are used to recycle the gases in sections 9a and 9b. The number of separate sections can be made as needed. For making up the oxygen consumed during the hardening of the briquettes on belt 3, fresh air is furnished by blower 21 through pipe 22 and

pipes

23, 24 and 25, respectively. The volume of make-up air added to the gas being recycled through

blowers

18, 19 and is regulated by means of valves 26. Excess gas from the briquette bed is exhausted through chimney 27 containing a throttle valve 28 for regulating the pressure within housing 5.

The length and speed of belt 3 is such that the briquettes remain on the bed from about thirty to sixty minutes. These prehardened briquettes then slide without appreciably dropping into the uppermost zone 12 of furnace 4 where they lie on top of the compact fill within the furnace. A circulation of hot oxygen-containing gases is maintained in this zone. Blower 30 forces hot gas through pipe 31 to the opening beneath baffle 11 with the gas then passing through the hot briquettes to beneath bafiie 10 from which space the gas is withdrawn through pipe 32 for recirculation through blower 30. The excess of gas occuring in this zone rises to reach the discharge end of belt 3 and from there flows through housing 5 to be finally exhausted through chimney 27. Make-up air is supplied to blower 30 from blower 21 through pipe 33 and valve 33a. As shown in FIGURE 2 zone 12 can be further sub-divided by the use of

additional bafiles

110, 111, 210, 211 so that the briquettes can be treated with several independent and recycled flows of gases. These gas cycles are maintained by

blowers

30, 130, 230, are sucked out of the layers of briquettes in the

zones

12, 112, 212 below the

baffies

10, 110, 210 through pipes 32, 132, 232 and returned by

pipes

31, 131, 231 and bafiles 11, 111, 211 into the

zones

12, 112, 212. The individual cycles can be mixed with air supplied through the pipe 33 in quantities regulatable by valves 33a, 133a, 233a.

The middle zone 13 of furnace 4 is used for further hardening and degasifying the briquettes moving downwardly from zone 12. Blower 35 circulates a hot inert purging gas through pipe 36 to beneath baffle 11a with the gas then passing through the briquettes and being collected and withdrawn from the space beneath baffles 10a through pipe 37. A portion of the withdrawn "gas containing volatile combustible products from the degasification is led off through pipe 40 into combustion chamber 41. The hot gases therein produced are fed into a waste heat boiler 42 for the production of steam. A combustion chamber 43 is used for the preheating of the gases used for the bed of briquettes on belt 3. These gases are led to

blowers

18, 19 and 20 through pipe 43a. In degasification zone 13, the briquettes are hardened at temperatures ranging from 500 to 700 C. For coal briquettes, this treatment is important for the liberation of the tar as well as for the degasification of the coal.

The lowermost zone 14 serves for the cooling of the briquettes and from which the cooled briquettes pass over baffles 110 into discharge hopper 44. Blower 45 forces inert gas through pipe 46 into hopper 44 from which the cooling gases flow through the briquettes and are withdrawn from the space beneath bafiles 10b and through pipe 47 into waste heat boiler 48. This cooling zone can be further sub-divided into two cooling zones having separate cooling gas cycles in which case the lowermost subzone is cooled with gas flowing through the briquettes and recycled through a cooling chamber sprinkled with cold water. For this purpose another circulating blower 51 is provided, which forces the inert gas through the pipe 52 into the hopper 44 and thence through the discharging device 11c into the layer of briquettes. Here the inert gas flows upwards to the baffles under which it is sucked off by the blower 51 through the pipe 49 and through the spraying cooler and recycled into the coke layer. Finally, the hardened and cooled briquettes are removed through hopper 44 through gate valve 15.

The invention is hereinafter described in greater detail with the aid of one form of construction:

Fine coke, having a particle size of 0 to 3 mm. and a water-content of 8%, is pressed at a temperature of 50 C. into egg-shaped briquettes with 10% oxidative binder such as pitch of low-temperature carbonization tar from pit coal or lignite. As these briquettes are not very solid, they are carefully fed onto the conveyor belt 3. There they are first dried and preheated to 100 C. by means of hot, oxygen-containing gasses at 180 C. and circulated by the blower 18. The heat necessary for drying the briquettes is supplied by the gases which rise from the uppermost zone of the following shaft furnace 4 and flow through the housing of the prehardening belt in counterdirection to the briquettes and are sucked by means of the circulating

blowers

18, 19 and 20. Excess gas and vapors from the drying process leave the plant through the chimney 27 at a temperature of C.

The dried and preheated briquettes are then treated in the middle portion of the prehardening belt with gases delivered by the blower and having a temperature of 200 C. and an oxygen content of 6%. Hereby the briquettes are heated to 180 C. Very little heat is required for this operation because the commencing exothermal hardening process supplies as much heat as is necessary for heating the briquettes.

In travelling along the end portion of the prehardening belt, the briquettes are flushed with gases from a blower 20 at a temperature of 250 C. and thereby heated to 200 C. The oxygen content of these gases also amounts to 6% and is regulated by feeding fresh air by the blower 21. At the end of the belt the prehardening process has progressed so far that the briquettes are already capable of withstanding a certain amount of mechanical stressing and can now be further treated in the shaft furnace extending from the belt. The duration of the prehardening process is primarily dependent upon the piece weight of the briquettes and the kind of binder used, and amounts to about 50 minutes in the case of egg-shaped briquettes weighing about 50 gm. apiece.

The briquettes pass through the shaft in a continuous heap and are thereby flushed with gases. In the uppermost zone of the shaft furnace they are finally hardened. They enter this zone at a temperature of 200 C. and leave it at 280 C. The gas for elfecting the hardening is circulated by a blower 30 and mixed with so much fresh air from the blower 21 that, on entering the heaped briquettes, it contains 7 to 8% oxygen. At the end of the hardening zone the greater part of the gas is drawn off from under the roof-shaped baflles 10 fitted in the furnace and recycled. The remainder of the gas flows through the dome of the furnace into the housing of the prehardening belt. The time during which the briquettes remain in the hardening zone of the shaft furnace varies between 1 /2 and 2 /2 hours in the case of briquettes of the weight indicated above.

In the next lower recoking zone 13, the hardened briquettes are heated to 700 C. within an hour. During this process the gas escaping during the final degasification and small quantities of tar products pass off and the structure of the briquettes is strengthened. For the recoking process purging gas free from oxygen is employed which is circulated by the blower 35 and brought to a temperature of 700 C. by mixing with burned gas from the combustion chamber 38. The purging gas is drawn 01f at the upper end of the recoking zone at 300 C. by the roof-shaped baffies 10a fitted in the furnace and, in as far as it is not recycled, is led off behind the blower 35 and fed into the combustion chamber 41. The resultant flue gas is used for producing waste, heat steam and also for other purposes.

In the lowermost zone of the shaft, the briquettes are cooled by an inert gas current. They enter the cooling zone at 700 C. and leave it after about an hour at a temperature of 170 C. Their heat is given up to the inert gas which is forced into the discharge hopper 44 under the discharging device by means of the blower 45 and enters the cooling zone at about 150 C. At the upper end of the cooling zone it is drawn off over the baffies 10b. Here its temperature is 380 C. It then flows through the waste heat boiler and is again exhausted at 150 C. by the blower 45. The quantity of waste-heat steam produced amounts to about 230 kg. per ton of hardened briquettes.

The cooled briquettes are withdrawn from the hopper 44 through a gate valve and can be used immediately in hot state, for example in a smelting process. They can, however, also be cooled to ambient temperature as described in connection with FIGURE 2.

Having now described the means by which the objects of the invention are obtained, I claim:

1. In the method of oxygen hardening and degasifying briquettes with hot gases, said briquettes comprising cornpactions of a binder and a substance selected from the class consisting of solid fuels, ores and mixtures thereof, the improvement comprising forming a bed of the green briquettes resting on a moving conveyor belt, drawing hot oxygen-containing gas at a temperature of from 150 to 300 C. through said bed to partially harden said green briquettes to the crushing strength needed for forming a layer in the upper zone of a shaft furnace, gently passing the partially hardened briquettes from said belt into the upper zone of a shaft furnace, passing oxygen-containing gas at a temperature from 150 to 300 C. through the upper zone to finally harden the briquettes, lowering said hardened briquettes into a middle zone, passing inert degasifying gas at a temperature of from 500 to 700 C. through said middle zone to degasify said briquettes, lowering the degasified briquettes into a lowermost zone, passing inert cooling gas at a temperature of from to 200 C. to cool the briquettes, and then removing the cooled briquettes from the bottom of the shaft furnace.

2. In the method of claim 1, further comprising moving said bed of briquettes on said conveyor belt through a plurality of partially hardening zones, and recycling 2. gas of predetermined temperature and oxygen content through each partially hardening zone, respectively.

3. In the method of claim 1, further comprising a dividing said upper zone in said shaft furnace into a plurality of sub-zones, and recycling a gas of predetermined temperature and oxygen content through each sub-zone, respectively.

4. In the method of claim 1, further comprising conducting excess hot oxygen containing gas from said upper zone to said bed on said belt for partially hardening said briquettes.

5. In the method of claim 1, further comprising recycling said inert degasifying gas through said middle zone in said shaft furnace, removing and burning excess inert gas from said middle zone, and passing the burned gases through a heat exchanger.

6. A method as in claim 1, further comprising recycling said inert cooling gas in said lowermost zone of said shaft furnace through said lowermost zone and a waste heat boiler.

7. A method as in claim 6, further comprising passing a second inert cooling gas through said lowermost zone, and recycling said second inert cooling gas through a direct water cooler.

8. In the method of hardening and degasifying briquettes composed of compactions of a binder and a substance selected from the class consisting of solid fuels, ores and mixtures thereof, and in which green briquettes are treated in a plurality of zones with hot oxygen containing gases on a moving conveyor belt, the treated briquettes then degasified, cooled and removed from the bottom of a shaft furnace, the improvement comprising:

only partially hardening said green briquettes on said conveyor belt to a crushing strength sufiicient for forming a layer in the upper zone of said furnace, gently transferring the partially hardened briquettes into the upper zone of the furnace, and then drawing hot oxygen containing gas through the layer of briquettes in said upper zone to finally harden said briquettes.

9. In the method of claim 8, the improvement further comprising:

recycling gas of predetermined temperature and oxygen content through each of the plurality of zones on said moving conveyor belt.

10. In the method of claim 8, the improvement further comprising:

recycling gas of predetermined temperature and oxygen content through at least one portion of the upper zone in said furnace.

References Cited in the file of this patent UNITED STATES PATENTS 1,496,053 Illingsworth June 3, 1924 1,828,586 Archbald Oct. 20, 1931 1,865,336 Reber June 28, 1932 1,909,421 Parr et a1 May 16, 1933 2,131,702 Berry Sept. 27, 1938 2,380,930 Andersen et al. Aug. 7, 1945 2,448,223 Lantz Aug. 31, 1948 2,536,365 Handwerk et al Jan. 2, 1951 2,560,767 Huif July 17, 1951 2,709,153 Rummel May 24, 1955 2,922,752 Reintjes Jan. 26, 1960 2,955,991 Tufty Oct. 11, 1960 2,997,426 Mansfield Aug. 22, 1961 3,010,882 Barclay et a1 Nov. 28, 1961 FOREIGN PATENTS 753,084 Great Britain July 18, 1956

Claims

1. IN THE METHOD OF OXYGEN HARDENING AND DEGASIFYING BRIQUETTES WITH HOT GASES, SAID BRIQUETTES COMPRISING COMPACTIONS OF A BINDER AND A SUBSTANCE SELECTED FROM THE CLASS CONSISTING OF SOLID FUELS, ORES AND MIXTURES THEREOF, THE IMPROVEMENT COMPRISING FORMING A BED OF THE GREEN BRIQUETTES RESTING ON A MOVING CONVEYOR BELT DRAWING HOT OXYGEN-CONTAINING GAS AT A TEMPERATURE OF FROM 150 TO 300*C. THROUGH SAID BED TO PARTIALLY HARDEN SAID GREEN BRIQUETTES TO THE CRUSHING STRENGTH NEEDED FOR FORMING A LAYER IN THE UPPER ZONE OF A SHAFT FURNACE GENTLY PASSING THE PARTIALLY HARDENED BRIQUETTES FROM SAID BELT INTO THE UPPER ZONE OF A SHAFT FURNACE, PASSING OXYGEN-CONTAINING GAS AT A TEMPERATURE FROM 150 TO 300*C. THROUGH THE UPPER ZONE TO FINALLY HARDEN THE BRIQUETTES, LOWERING SAID HARDENED BRIQUETTES INTO A MIDDLE ZONE, PASSING INERT DEGASIFYING GAS AT A TEMPERATURE OF FROM 500 TO 700*C. THROUGH SAID MIDDLE ZONE TO DEGASIFY SAID BRIQUETTES, LOWERING THE DEGASIFIED BRIQUETTES INTO A LOWERMOST ZONE PASSING INERT COOLING GAS AT A TEMPERTURE OF FROM 20 TO 200*C. TO COOL THE BRIQUETTES AND THEN REMOVING THE COOLED BRIQUETTES FROM THE BOTTOM OF THE SHAFT FURNACE.