US2993686A - Manufacture of briquettes - Google Patents

Description

July 25, 1961 o, sc 2,993,686

MANUFACTURE OF BRIQUETTES Filed Nov. 18, 1958 4 Sheets-Sheet 1 T DECEASED. 8y BERT/L OLAUS SCHLYTtR, INVENTOR.

HA RA 1. 0 FRED/9M A004 F 55/? m0; 0, ADMIN/S m4 rm ATTORNEY.

July 25, 1961 B. o. SCHLYTER 1 2,993,686

MANUFACTURE OF BRIQUETTES Filed Nov. 18, 1958 4 Sheets-Sheet 2 CHL YTER DCEA8ED. 8y BER T/L 04 A06 INVENTOR- HARALD FREDR/K ADOLF BERN/0L0, ADMINISTRATOR.

A T TOR/V5 Y.

July 25, 1961 B. o. SCHLYTER 2,993,686

MANUFACTURE OF BRIQUETTES Filed Nov. 18, 1958 4 Sheets-Sheet 3 ,T ULAUS SCHLYTER DECEASED. er BE? lL INVENTOR.

HA R A L 0 FRED/PIA A 00L F BERTHOL 0, ADMIN/S r/m ToR.

BY W262i ATTORNEY.

July 25, 1961 B. o. SCHLYTER MANUFACTURE OF BRIQUETTES 4 Sheets-Sheet 4 Filed Nov. 18, 1958 R m 0mm 5 N T E M E D DA, w mo TH 5 5 C F L S m A A m R L WM R F B p L m v: M

ATTORNIE).

Unite rates Patent 2,993,686 MANUFACTURE OF BRIQUE'ITES Berti! Olaus Schlyter, deceased, late of Stockholm, Swe- It is previously known to briquette certain powdered fuels by mixing with tar, pitch and similar binding agents and subsequent heating of the mixture thus obtained until degasifying and coking of the binding agent begins. The binding together of the individual particles of the pulverulent material in larger solid pieces depends on the fact (1) that the binding agent, which may have been converted into liquid or melted state by the action of the heat, flows out as a continuous liquid phase, which in itself contains a large number of the individual particles of the pulverulent material, and 2) that on coking this liquid will form a compact skeleton which holds the individual particles of the powder together.

The present invention, which relates to a further development of this known method, aims at rendering possible the manufacture of strong briquettes of combustible material-such as are intended solely for producing heat while burning, as well as such as are intended for certain metallurgical processes. The method comprises the steps of admixing binding agents of cokeable material such as pitch, resin, bitumen, tar and/or concentrated sulphite lye in finely powdered fuel and heating the mixture, possibly while introducing steam, .to about 95100" C., and subsequently forming the mixture into briquettes, which are heated by direct contact with burnt or .burning gases originating from coking or pyrolysis of the same kind of briquettes as have just been subjected to the abovementioned treatment. Previously it has not been possible to manufacture such briquettes strong enough for practical use without giving off dust. This applies primarily to coke, coal or anthracite dust, or wood waste, such as sawdust, and peat. Thanks to the present invention it is now possible to utilize these .fuels to a much larger extent than earlier.

The invention relates to a continuous process for producing hard briquettes of combustible material by rnixing finely divided combustible material with a binding agent and forming the resulting mixture into briquettes of desired shape, drying and coking said briquettes by supplying them into a tunnel-shaped elongated furnace provided with conveying means for the briquettes continuously conveying the briquettes in said tunnel in succession through a low temperature drying zone in the vicinity of the charging end of the tunnel and subsequently through a high temperature coking zone closer to the discharge end thereof for coking said briquettes while introducing into said tunnel hot burnt or burning gases through at least one .gas inlet substantially in the middle section of the tunnel, causing the hot gases to flow in the travelling direction of the briquettes in said high temperature zone of the tunnel and substantially in counter-current to the briquettes in the drying zone by sucking of gases through at least one outlet and recirculating the latter gases to the tunnel after heating them in a combustion chamber, discharging the briquettes from the tunnel and cooling them. The gases together with gases released from the briquette material are removed from the furnace, and are introduced into an external combustion chamber in which they are mixed with air and, if necessary, with additional fuel and subsequently burnt and reintroduced into the furnace, the major portion of the reintroduced gases being caused to 110w towards the discharge place of the briquettes that' 2,993,686 Patented July 25, 1961 there will arise a circulation of burning or burnt gases whereby the briquettes will be coked. In this way there will be obtained briquettes of a uniform and regular shape and of such a thermal and mechanical strength that they can be used in furnace processes in which they are exposed to pressure from material in high layers.

The invention also relates to a furnace plant for performing the process now described and according to the invention this plant comprises a tunnel furnace with conveying means therein for conveying the briquettes through the tunnel furnace, and at least one external combustion chamber communicating with the interior of said furnace through gas passages, one gas passage including a fan for passing the gases from the place of the tunnel at which the briquettes are discharged, to the combustion chamber provided with means for 'the supply of air and, if necessary, other fuel than said gases, said combustion chamber also through gas passages being in communication with the tunnel furnace, the arrangement being such that the major portion of "the gases thus reintroduced into the tunnel furnace being caused to flow towards the discharge place of the briquettes by means of said fan.

The accompanying drawings illustrate diagrammatically some embodiments of an arrangement or .plant with the aid of which the process according to theinvention can be carried out.

FIG. '1 shows .a side view of the plant, partly in vertical section;

FIG. 2 is a horizontal section thereof;

FIG. 3 shows in a similar manner a side view of another embodiment, partly in vertical section;

FIG. 4 is a horizontal .section thereof; and

FIG. 5 is a side view, partly in vertical section, of a further embodiment.

In FIGS. 1 and 2, 1 indicates a kiln or oven having 'a gas or oil burner 8, normally in operation when starting the process only. This oven communicates through passages 13, 1.4 with a combustion and distributing chamber divided into two compartments 2 and 3, being in open communication with each other as well as with a tunnel furnace 6, 7, in which the briquettes are dried in the first section 6 and coked in the second section '7 while being conveyed through the tunnel. The briquettes are supplied and removed, stacked in layers 3M0 cm. deep for instance, through narrow apertures in the end walls 9a and 95, respectively of the furnace, either on an endless, perforated conveyor belt or in perforated baskets on a conveyor 6a or placed in carriages, said baskets permitting free contact between the .gases in the tunnel and the individual briquettes. Such a basketv 6b is shown to the right in FIG. 1. A temperature of ZOO-400 C., which is gradually increased towards the central section in the longitudinal direction of the tunnel, is maintained in the drying section 6. In the degassing or coking section 7 the temperature is kept considerably higher than in the drying section 6, for example at 600-650", though always at a considerably lower temperature than that .prevailing in the conventional retorts of gas works. Infiammable gases generated in the coking section 7 are entirely or partially burnt in the process and their combustion heat is utilized for carrying out the process. The gases from the coking section 7 are evacuated by a fan 10 driven by a motor 10a and then forced into the combustion chamber 3 where they are mixed with a very small quantity of air, and burnt entirely or partially. Burning and/or burnt gases pass from the combustion chamber 3 back into the tunnel.

Part of the gases are pass-ed through a ductltle to a fan 10b driven by a motor 10c and this fan passes the gases to 'a chimney 16 through a duct 10d. If desired another .sawdust as well as peat.

part of these gases can be passed to the burner 8. A fan g driven by motor 10) supplies air to the burner 8 through a passage 10h.

As shown in FIG. 2 the gases in the drying section 6 and the coking section 7 are not separated from each other. A portion of the burning or burnt gases from the combustion chamber 2, 3 pass, into the drying section 6 by means of fans 11 and 12. From the drying section 6 gases are evacuated by fan 11 (driven by a motor 11a) and forced into the combustion chamber 2 through a duct 11b. Scarcely any appreciable combustion takes place here except on starting the process, when burning gases and air from the oil burner 8 and combustion chamber 1 force their way into the chamber 2 through aperture 13. From the last-mentioned chamber 2 the gases flow into the end of the drying section 6 adjacent to the coking section 7 and from there they return in a direction opposite to that of the briquettes. A portion of these gases is seized by the suction from the fan 11 and circulates anew through the chamber 2 into the drying section 6 of the tunnel furnace. Fan 12 driven by a motor 12a circulates the gas in the front part of the drying section 6 and also drives out part of the damp gases through a chimney 17.

To eliminate the risk of explosions and fire in the plant to a very high gas velocity should be selected, for example between 5 and m./sec. in the tunnel proper.

'If the tunnel has a cross-sectional area of about 1 m? the fan 10, which sucks the gases from the end-portion of. the coking section 7, should have a capacity of about 7 m. /sec. The fans 11 and 12 for sucking and circulating the gases in the drying section 6 should have capacities of about 5 or 6 m. /sec. The rapid circulation of gas has, as a matter of fact, the effect of speedy expulsion of gases and volatile matter from the briquette substance so that the individual particles of the latter are baked into clinkers by the simultaneous coking of the binding agent as well as of the raw material. The rapid gas circulation also prevents explosive gas mixtures from being accumulated in any part of the furnace as the gases almost immediately on their generation are conveyed to the combustion chamber 3, where they are burnt calmly and effectively.

In manufacturing briquettes of sawdust, bark and/or peat or other fuels which develop gases when heated, the fuel-gas mixture obtained from the gases removed from .the end portion of the coking section 7 can, after com- V bustion, be passed to the intake 9a for the briquettes in the drying section 6. It has been found that the entire process is hastened up, and also results in better coke briquettes if the briquettes are rapidly exposed to a high temperature while still being moist and raw. It should be observed, however, that the raw briquettes, especially when treated in this manner, should hold a certain moisture content which has been carefully determined by preliminary tests and should lie between 40 and 45% for It is important to use cheap binding agent when cheap raw material is used, for example peat or sawdusst having a moistness of 65 to 68%. Tar and resin can be used to advantage as binding agent in this case, especially if mixed with substances which react with certain substances of the tar and resin, such as carbolie acid or other phenols, for example formaldehyde or formaldehyde preparations and/or derivatives, so that plastics or plastic-like, pasting and hardening substances are formed when the tar becomes coked.

When utilizing the last-mentioned gas-generating raw material large quantities of tar are of course formed to eg n With but th y a e largely or mostly burnt within the furnace and form the coke which bakes the individual particles of the briquette material into clinkers. Certain quantities of tar can, however, be extracted in the said processes. A certain amount of tar thus collects on the bottom of the coking section 7 of the tunnel furnace; it can be drained off continuously through a slightly heated U-shaped drain-pipe fitted with a liquid-trap. Tar can however, also be extracted from the flue gases from the chimneys 16 and 17. This can be done by cooling the gases, for example by spraying them with water.

The arrangement for carrying out the processes need not, of course, be designed as shown in FIGS. 1 and 2. It may be to advantage to arrange the bottom of the tunnel furnace some metres above the ground and to arrange all gas outlets as well as intakes at the bottom of the tunnel. This makes the gas circulation more symmetrical and results in a more uniform product, as in the device shown in the drawing the briquettes lying on the side of the conveyor belt nearest the combustion chambers may become more coked than those which lie on the other side.

The furnace can also be arranged vertically. Such an arrangement may in principle be designed in the same way as that shown in the drawings. The conveying arrangement for the briquettes must, however, in this case be made in the form of a bucket chain, or as a continuously or intermittently running lift with the aid of which a row of buckets or baskets with perforated bottoms and sides are either raised or lowered through the tunnel. In the first-mentioned design the drying section must naturally be located in the lower part of the tunnel and the coking section in the upper part, while the drying section must of course be placed in the upper part of the tunnel and the coking section in its lower part if the conveying baskets are to be lowered through the oven shaft.

Dampers can be fitted in the ducts of the furnace to control the circulation of gas in the tunnel, thus enabling the furnace to be operated in the most suitable manner and without varying or regulating the speed of the fans, that is to say so that the briquettes are neither broken up by steam and gases generated from them or become ignited while being degassed and coked.

Preferably, the furnace is constructed in the form of a straight elongated tunnel having an essentially circular section of sheet-iron, of 6 mm. thickness for example, which is shaped as a cylinder and Welded at the joints. The discharge end 9b of the furnace may be connected to a cooling channel 15 in which the wholly or partially coked briquettes are sprinkled with water from a sprinkler 15a to prevent their catching fire when leaving the oven. This cooling channel 15 is made of flat sheet iron and preferably has a square shape, which will make it cheaper to construct than the oven proper.

Another embodiment of the invention is shown in FIGS. 3 and 4. The tunnel furnace 21 is equipped with a charging funnel 22 for the briquettes, which first are dried and then partially degassed and carbonized inside the tunnel with the aid of hot burning or burnt gases. These gases derive largely from gases generated from the briquettes which are being dry-distilled in the tunnel and in a shaft furnace 25 connected to this tunnel. The briquettes drop from the charging funnel 22 on to an endless belt 24a, running around pulleys 24 at the ends and having a pitch angle of 1015 for example. On this belt the briquettes are conveyed through the tunnel 21 continuously for a period of 30-60 minutes, after which they leave the conveyor belt and drop down into the shaft furnace 25. The temperature at the discharge point for the briquettes from the furnace 21 to shaft furnace 25 may be 500-600 C. During its passage through the tunnel the layer of briquettes piled on the conveyor belt can be percol-ated by gases flowing from above and below and entering the tunnel from the gas duct 26 through a series of short connecting tubes 27. The briquettes entering the shaft furnace 25 descend therethrough (in about 30-60 minutes) and are then passed through the gate feeder 28 out of the oven. From the gate feeder, which must not admit any air, the briquettes fall down into water in a tank 28a to be cooled therein so that they do not self-ignite when they are afterwards being continuously conveyed by a belt 29 into storage. In the shaft furnace 25 the layer of briquettes is percolated by an essentially horizontal urrent of burning or burnt gases with a temperature of between 700 and 1200 C., appro-. priately between 900 and 1200 C. These gases are generated on starting the furnace with burning oil, which is burnt in a combustion chamber 30 communicating through passages 30a, 30b with two distributing chambers 31 and 32, respectively. From distribution chamber 31 the burning or burnt gas flows through a gas duct 33 to one side of the shaft furnace 25 and escapes through a passage 34 from the opposite side, now mixed with the dry-distillation gases generated from the briquettes in the shaft 25. Preferably the passage 34 is air-cooled and insulated and leads to the gas duct 26 from which it flows through the distribution pipes 27 into the tunnel furnace at its top. When the gases have passed through the layer of briquettes on the conveyor belt 24 and have been mixed with dry-distillation gases generated from these briquettes they are sucked out by means of a fan 35a through a pipe 35 from the parts of the tunnel at the bottom and close to the shaft 25 and are fed by this fan through a passage 35b into the combustionchamber 30. Having actually entered the combustion chamber 30 the gases are consumed and possibly mixed with the burning oil gas from a burner (not shown) in chamber 30. Part of the gas mixture which thus formed is then passed in circulation to the shaft furnace 25 through conduit 33 while another portion is passed into the gas duct 26 from chamber 32 through a passage 32a. In the process in tunnel 21 large quantities of gas are of course generated and these are forced successively, possibly after having passed once or several times through the circuit mentioned above, down towards the lowest parts of the tunnel. From the central part of the tunnel gases are sucked off through the pipe 36 and then forced by fan 38 either into the combustion chamber 30 through a pipe 37 or into the distribution chamber 32 through a pipe 37a, and from there returned in circulation to the tunnel through the duct 26.

The surplus of burnt gases are successively forced farther and farther down into the tunnel 21 and pass out through a chimney 21a which communicates with the interior of the tunnel approximately where the briquettes are fed on to the conveyor belt 24. Of course a drying only but no dry distillation or degassing takes place in the vicinity of the intake for the briquettes.

In the course of the inventors experiments to make briquettes of different kinds, such as fuel briquettes and such as are suitable for melting of metals, for example in a cupola furnace, and for other metallurgical purposes, it has been found that one of the best materials for the manufacture of strong briquettes which do not give off dust is so-called petroleum coke, of which there are many grades on the market. Particularly favourable results have been obtained with so-called uncalcined petroleum coke. Certain grades of this contain, however, large quantities of sulphur so that it has been found necessary to adopt dry-distillation of the briquettes to remove or reduce the sulphur content. For this purpose the furnace now described can be used. If the sulphur content of the briquettes is very high it may be to advantage to build in a perforated cistern in the middle section of the tunnel furnace, and to charge it with lime or some other substance which will have a binding effect on the sulphur dioxide formed in the process, or to use a so-called absorber by which the attack of sulphur compounds on the apparatus, especially in the drying section will be considerably reduced.

It has been found that these briquettes containing petroleum cokes are particularly suitable for a number of metallurgical processes, especially such as those in which metals for casting purposes are melted, but also for processes in which metals are reduced from ores. The briquettes acquire great mechanical strength with no dust. In addition they become compact and heavy so that they do not burn too rapidly, in a cupola furnace for example, thus rendering the furnace easier to operate and increasing its capacity considerably. The petroleum coke has been found to be particularly suitable for the manufacture of such briquettes as contain alloying elements which are to be fused into the melting metal, such as iron, chrome, manganese, nickel, tungsten, vanadium, silicon and similar metals or elements. Dust of coke, coal or anthracite can therefore, apart from coking binding agents, also be mixed with finely powdered metals or metal alloys, such as silicon iron in forming the desired briquettes.

A somewhat modified form of the invention is shown in FIG. 5. The tunnel furnace 1 1 is here arranged in an inclined position and associated with four separate circulation systems, which operate independently of each other and consist of tubes 41, 42, 43 and 44 communi-' eating with the interior of the furnace 11, and fans 41a, 42a, 43a, 44a placed outside the tunnel so as to suck gases from the bottom parts of the tunnel, that is to say the parts situated below conveyor belt 24, and then return them through conduits 41b, 42b, 43b, 44b to the top of the tunnel, that is to say the parts lying above the conveyor belt 24. The gases thus are caused to flow through the layer of briquettes on the conveyor belt 24 in a downward direction. While the briquettes are being conveyed on the belt 24 from the charging funnel 22 they are exposed to an increasing temperature. The gases passing through the briquette layer at the charging end and subsequently escaping through the chimney 45 arranged at this end have a temperature which slightly exceeds C. Hence, in this part of the tunnel the only essential thing that occurs is an evaporation of water from the briquette. The temperature is maintained by rather hot gases forcing their way successively down from the neighbouring section of the tunnel into which hot gases of a temperature of about 600 C. from the gas duct 26 can be introduced through the distribution tubes 27 and in which the circulation system 44, 44a, 44b gives a necessary draught through the briquette layer. Still higher up and nearer the central section of the tunnel the gas circulation is maintained by the circulation system 43, 43a, 43b. Here also hot gases of about 600 C. can be supplied from the gas drum 26. A dry distillation sets in here, but the amount of combustible gases is probably too low here also for any combustion to be likely to occur, this also being partly due to the fact that the'air surplus is far too small and the moisture content of the gas too high. The temperature in this zone should not exceed 300 C. In the section of the tunnel where the circulation system 42, 42a, 42b operates the temperature has risen to 400 C. and more. The dry distillation is in full operation for most of the briquette materials and part of the gases generated are sucked from here through a piping 47 to a powerful fan 47a which forces them into the combustion chamber 30 shown diagrammatically. This fan is stronger than the fans 41a44a. Air is forced into the combustion chamber 30, which is under superatmospheric pressure, so that complete combustion of the dry distillation gases from the briquettes takes place. If the briquette material, in addition to binding agent, such as pitch, bitumen or tar, consists chiefly of coke dust, only relatively small quantities of dry distillation gases are of course generated, and in this case fuel, such as fuel oil, must-be supplied into the combustion chamber throughout the entire process in order to obtain the required temperature. From the combustion chamber 30 burning or consumed gases, appropriately with a small air surplus, pass through a conduit 48 to the shaft 25, into which the briquettes fall through passage 53 when they have reached the discharge end of the conveyor belt 24, and in which the final car-bonization of the briquette material takes place and clinkers are fused. Conduit 48 has appropriately two branch- pipes 49 and 50, each of which preferably discharging into the lower of one of two distribution chambers 51 and 52, which are located on either side of the parallelepipedic furnace shaft 25. From the distribution chambers 51 and 52 the gases appropriately flow into the briquette layer in shaft 25, appropriately in an oblique upward direction. The shaft should be made wide so that in horizontal projection it has the form of a rectangle along the long sides of which the distribution chambers 51 and 52 extend. The burning or burnt gases entering the furnace shaft 25 should have a temperature between 1000 and 1700 C. Accordingly, at this tem perature the final conversion of the briquette material into clinker takes place and at the same time possible impurities such as sulphur are distilled off and possibly consumed. The gases rise upwards through the briquette layer and pass from the shaft 25 to the gas duct 26 located above the tunnel furnace, and from there they flow to the tunnel furnace 21. Through the distribution pipes 27, which are equipped with adjustable dampers, the hot gases flowing forward approximately at 550 to 650 C. through the gas duct 26 are divided up into sectional currents which flow into different zones of the tunnel furnace and in these zones give the desired temperature in every zone. The first of these branch lines 27 enters the tunnel 1 to 2 metres from the upper end of the conveyor belt 24 so that the current of hot gas from the gas duct 26 shall not be brought into direct contact with the mechanical devices installed here. The intake end of the circulation pipeline 41 should also be placed immediately beneath the inlet of the first distribution pipe 27 from the gas duct 26. The fan 41a effects strong suction through the briquette layer located in this zone of the tunnel furnace. In the last-mentioned zone the briquette material is degassed to such an extent and fused into clinkers that the briquettes will stand falling from the upper end of the conveyor belt 24 down on to the top layer of briquettes in shaft 25 Without being broken or deformed. As previously mentioned the fusion of clinkers and the degassing is completed in shaft 25, and the finished briquettes fall successively through this shaft down to the gate discharger, which is of a design such that no air from it can enter the shaft 25. The gate discharger delivers the finished briquettes successively into a bath 28a of cold water in which they are cooled off so that they cannot be self-ignited when stored.

What is claimed is:

1. A furnace plant for continuous production of hard briquettm by coking briquettes made of a mixture of combustible material and a binding agent, comprising a furnace in the form of an elongated tunnel having a charging end for introducing briquettes into said tunnel, and a discharging end for withdrawing the briquettes from said tunnel, means for charging said briquettes into said charging end, conveying means for continuously feeding the briquettes through said tunnel from said charging end to said discharging end, said tunnel including a low temperature drying zone at said charging end thereof and a high temperature coking zone toward said discharge end, means for circulating hot gases already burnt or burning through said tunnel comprising an external combustion chamber for burning the combustible contents of the gases resulting from the coking, at least one gas inlet formed into said tunnel and arranged substantially in the middle section of said tunnel, means to suck oif gas at said discharge end of said tunnel, and means for withdrawing a minor quantity of gas at the charging end to cause the gases to flow mainly towards said discharge end and in the same direction as the travelling briquettes in said coking zone and in counter-current to the briquettes toward said charging end drying zone of said tunnel, said means for sucking olf the gases from said tunnel comprising a fan and a closed duct system connecting said fan with said external combustion chamber for circulating the gases in opposite directions through said tunnel and back to said combustion chamber.

2. A planttas claimed in claim 1, said discharge end of said tunnel being provided with auxiliary means for further heating said briquettes and means for cooling the briquettes discharged from said tunnel. I

3. A plant as claimed in claim 2 wherein said auxiliary means for further heating the briquettes at said discharge end of the tunnel comprises a vertical shaft provided with a gas inlet, said inlet being connected with said combustion chamber and a fan, and a gas outlet provided in said vertical shaft opposite said gas inlet, said gas outlet communicating with the interior of said tunnel by means of a duct.

References Cited in the file of this patent UNITED STATES PATENTS Dohmen May 20, 1958

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