US3869350A - Process for a thermal pretreatment of coking bituminous coal - Google Patents

Abstract

The present process prepares coking bituminous coal for the subsequent briquetting operation by subjecting the coal, which has a swelling index smaller than five, in granular form with a grain size of up to 14,000 Mu to a heating treatment in a hot gas stream. The temperature is regulated in such a manner that an average heat-up speed of about 1,000* C per second is assured, whereby the final temperature is about 400* C. The present process is performed in an elongated tubular member. The granular coal and a hot gas stream are supplied to one end of the tubular member and a particle gas separator at the other end of the tubular member separates the pretreated product from the exhaust gas. For the control of the temperature intermediate inlet means, one or several, are arranged between the ends of the tubular member for supplying additional granular material into the tubular member.

Description

ite States Patent 11 1 11] 3,869,350 Goossens et al. [45] Ma 4, 1975 PROCESS FOR A THERMAL 3,175,888 3/1965 Krejci 423/450 x PRETREATMENT O O I lcohinson 423/449 O S BITUMINOUS COAL 3,736,233 5/1973 Sass a a]. 48/210 [75] Inventors: Walter Goossens; Wolfgang Hermann, both of Bardenberg, Primary E.\'aminrWilbur L. Bascomb, Jr. r any Assistant Examiner-David Edwards [73] Assignee: Eschweiler Bergwerks-Verein Agent 0r1Flrm W' Passe Aktiengesellschaft, Kohlscheid, Germany [57] ABSTRACT [22] Filed: June 5, 1972 The present process prepares: coking bituminous coal for the subsequent briquetting operation by sub- PP 2593957 jecting the coal, which has a swelling index smaller than five, in granular form with a grain size of up to [30] Foreign Application Priority Data 14,000fl. to a heating treatment in a hot gas stream. June H 1971 Germany 4 i I n 7128949 The temperature 18 regulated 1n such a manner that an average heat-up speed of about l,000 C per second 1s assured, whereby the final temperature is about 400" 201/32 8 23; C. The present process is performed in an elongated [58} Fie'ld "56 36 38 tubular member. The granular coal and a hot gas 201/5 6 5 stream are supplied to one end of the tubular member 134 135 5 456' 23/271 and a particle gas separator at the other end of the tubular member separates the pretreated product from [56] References Cited the exhaust gas. For the control of the temperature in' termediate inlet means, one or several, are arranged UNITED STATES PATENTS between the ends of the tubular member for supplying 1,781,614 11/1930 Trent 201/31 additional granular material into the tubular member. 2,658,862 ll/1953 Homer 201/31 2,998,354 8/1961 Brown a a]. 201/17 6 Claims, 1 Drawmg Figure COOLIN 6 WATER SPRAV NOZZLES 5 GOAL INLET CONDUIT EXHAUST GAS COOLING WATER SPRAY NOZZLES so1 1nseAs [Eb SEPARATOR v 1 o souus OU'II'LET 11 counurr INTERMEDIATE STORAGE am BACKGROUND OF THE INVENTION The present invention relates to a process and apparatus for a thermal pretreatment of coking or baking bituminous coal having a swelling index smaller than five. The treatment is accomplished in a hot gas stream or current-and the treatment prepares the bituminous coal for the subsequent hot briquetting.

In order to make briquettes from coking bituminous coal having a swelling index smaller than five, in a hot briquetting step, it is necessary to subject the bituminous coal to a thermal pretreatment which assures that a certain consistency and type of the granular spectrum of the inert bituminous coal components is maintained intact during the main thermal treatment. Such inert components are the components which will not soften.

The prior art has developed a number of processes for thermally treating fuels or combustible materials in dust or granular form in order to degas these materials. These prior art processes are too involved and too expensive for the pretreatment intended by the invention because due to the type of transport of the materials to be treated, as well as due to the manner of supplying heat to the materials to be treated, it is necessary to assure that the material to be treated has a grain size which falls into a very narrow range. Meeting this grain size requirement is necessary in the prior art in order to avoid that the coking or baking of the bituminous coal which occurs during its heating, does not continuously clog the equipment used. Heretofore, it was the general understanding that a starting material meeting a narrow grain size range is a good condition for the quality of the final product. Therefore, the involved and expensive pretreatment steps prior to the actual thermal treatment of the coal; namely, the drying, the milling, and the careful sifting have been accepted as unavoidable necessities in prior art degassing.

According to another known process, expanding coal prepared to have a fine grain size may be degassed and converted into fine coke or breeze in a so called whirlpool or whirling bed by means of a hot gas stream. In this process a portion of the produced breeze is supplied in batches to the whirling bed or chamber as an additional heat carrier. The supply of these additional batches is accomplished in such a manner that upon the addition of fine grained coal which has not yet been thermically treated the temperature of the mixture is abruptly reduced to about 420C. Thereafter, the temperature of the mixture comprising breeze and finely grained expanding coal is uniformly raised again to a degassing temperature of about 550 C, whereby the heat-up speed is about 5 to C per minute. This heat-up process of the coking coal is required to be uniform and slow in order to transform the coking coal into a breeze having a solid structure. I The disadvantages of the just described method are seen in that a turnover of large quantities of breeze is required, that due to the use of granular coke or breeze the equipment following the actual coking step is subjected to a quick wear and tear, that the briquetting rollers are also subject to a large wear and tear due to the brittleness of the material and in that the breeze must necessarily be supplied in hot quantities because it is used as a heat carrier.

Another prior art method for transforming coking bituminous coal into cinder dust or breeze employs several Whirlpools or whirling beds arranged in series in order to form a reactor. The heat quantity necessary for the degassification is supplied through hot combustion gases as well as by a partial combustion of the breeze being produced and by the combustion of the pyrolitic products resulting from the practice of this process. This prior art method, contrary to the above described method, provides the possibility of continuously feeding the raw materials into the reactor and continuously withdrawing the breeze.

A disadvantage of the just described process is seen in the consistency or structure of the resulting product which has consistently a foamlike, spongy structure due to the fact that the treatment temperature is not easily regulated or controlled. Such a structure inherently involves the difficulties encountered during the briquetting; namely, that the briquettes cannot be sufficiently densified.

Another prior art process for producing cinder dust or breeze employs a vertically arranged system of tubes for the reactor. The finely granulated, swelling or expanding coal is transported through the reactor by means of a gas stream which simultaneously preoxidizes and degasses the coal. The carrier gas stream used in this prior art process is an oxygen enriched air stream. This system comprises two stages. The first stage serves for the above mentioned preoxidation of the coal, whereas the following second stage serves for the degassing of the coal dust of produce the breeze. The raw material is maintained in suspension in the first stage where it is heated in about 0.5 seconds to 430 C, and maintained at that temperature level for about 1 to 3 seconds. Thereafter, the raw material is heated in the second stage for about 1 second to 530 to 560 C. As a result of the preoxidation process, the finely granulated swelling coal is provided with a clearly brownish outer oxidation layer due to the increased oxygen content and the respective residence time. This oxidation layer has a penetration depth of about 1p The oxidation layer is supposed to prevent during the subsequent degassing of the preoxidized coal into breeze that the coal itself will still be caking whereby the equipment would be clogged.

The just described prior art process has, just as has been described with reference to the process employing the whirlpool beds or chambers, the disadvantage that the starting material is limited to granular coal of rather predetermined size to make the treatment possible at all. Accordingly, it is necessary to employ costly milling and sifting stages in order to assure that the grain size of a maximum of about 200p. is not exceeded. Another disadvantage is seen in that the throughput capacity of these treatment types is rather limited because the load which may be supported by the gas stream is only a few kilograms per n.cubic meter. Another disadvantage resides in the fine granular and uniform structure of the pretreated product which is used as the main component in the subsequent briquetting. Such fine and uniform structure causes difficulties in the briquetting because its high brittleness results in rather high wear and tear. Besides, the component of fine granules can be enveloped only to an insufficient degree by the baking component added prior to the actual briquetting.

In view of the above, it is the aim of the invention to achieve the following objects singly or in combination:

to avoid the drawbacks of the prior art, whereby an efficient pretreatment in a relatively inexpensive and simple equipment may be accomplished;

to provide a pretreatment process for swelling bituminous coal which does not require any premanipulation of the coal in milling and sifting equipment so that the latter may be avoided and whereby coal within a wide range of granular sizes may be pretreated;

to provide an intermediate product which in the subsequent main thermal treatment will require merely a partial further degassing and which will be thermally comminuted while simultaneously retaining a consistence advantageous to the subsequent briquetting;

to provide an intermediate product for the subsequent hot briquetting which will be easily enveloped by the binder components so that the finished briquettes will have a relatively smooth surface;

to provide a pretreatment for coking coal where the raw material may have any grain size up to about l4,000p.;

to provide means for efficiently controlling the pretreatment temperature;

to increase the carrying efficiency of the supporting hot gas stream; and

to provide a pretreatment process for bituminous coal having a swelling index smaller than five.

SUMMARY OF THE INVENTION According to the invention there is provided a pretreatment process for bituminous baking or coking coal having a swelling index smaller than five to make such coal ready for the subsequent hot briquetting whereby the pretreatment employs a hot gas stream for heating the raw material having a substantially unsifted grain size of up to about 14,000u, to an end temperature of about 400 C with a mean heating-up speed of about l,000 C per second whereby the pretreated material comprises proportions of semi-coke, proportions of expanded perforated grains, and proportions of well preserved granules having degassing pores. Preferably, the raw material will be transported through the pretreatment operation in a substantially horizontal path.

Advancing the mixture of coal and gas through a horizontal pretreatment path as taught by the invention has the advantage that a predrying step as well as a milling step and also a sifting step have been obviated. Using a wide range of granular sizes up to 14,000 1. provides the additional advantage that the pretreated material is transformed so that it comprises three distinctly different components which are essential for the subsequent main thermal "treatment. Another advantage of the invention has been shown in tests according to which the horizontal guiding of the hot gas stream makes it possible to load the gas stream with to 14 kgs. of material per standard cubic meter of gas, whereby the throughput capacity has been substantially increased for the same gas volume as compared to the known methods.

The desirable three distinct components of the goods after pretreatment may be achievedin an especially advantageous manner according to the invention by feeding the material to be treated into thehorizontal path at several positions located at spaced intervals downstream of a main feed-in position. In this manner it is possible to control and vary the residence time of the various material batches in the gas stream. In this connection it has been found that the temperature drop in the gas stream at the additional feed-in positions does 7 not impair in any manner the intended quality of the material which is treated for a maximum residence time of about 0.3 seconds.

According to a further teaching of the invention, it is possible to control the temperature very effectively by means of varying the dosage of the additional material which is fed in at spaced points along the flow direction. In this manner it is especially possible to exactly I regulate or control the end temperature in accordance with the respective type of coal employed by controlling the quantities of materials supplied to the different positions per unit of time.

In order to avoid the burning of the material which subsequent to the thermal pretreatment has a relatively high temperature, it is suggested according to the invention to cool the material before and/or immediately after the discharge of the material from the gas stream. Such a sudden cooling of the material causes a breakup of the granulation of the material which facilitates the subsequent thermal treatment in the following main treatment process. This break-up of the granulation is accomplished without changing the consistency of the granules.

The apparatus according to the invention comprises a preferably horizontally arranged tubular member to which are supplied in a coaxial direction the heating gases which act as heat-up means as well as a carrier medium for the raw coal.

Preferably, the tubular member is provided with a plurality of infeed means spaced from each other along the tubular member downstream of the infeed end of the tubular member. A solidsgas separator is connected to the outlet end of the tubular member.

In order to assure an efficient cooling of the thermally pretreated materials, an intermediate piece is provided according to the invention between the tubular member and the solids-gas separator. The intermediate member is cooled by water jets spraying in a direction extending substantially perpendicularly to the flow direction of the material through the tubular member and through the intermediate piece.

BRIEF FIGURE DESCRIPTION In order that the invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawing, wherein the single FIGURE illustrates in a somewhat schematic manner an apparatus which is used in performing the present pretreatment process.

DESCRIPTION OF A PREFERRED EXAMPLE EMBODIMENT Bituminous coking coal is stored in the supply bin 1. The coal has merely been washed without the need for any drying. Further, the coal does not need to meet any specific grain size range except that the grans should be anywhere within the range of up to l4,000p.. A portion of the coal is supplied through the conduit 2 into a combustion chamber 3 which is also supplied with hot heating gases as well as with air. The combustion chamber 3 is connected to the inlet end of a tubular member 4 which is preferably arranged in a substantially horibular member 4 is arranged along its length down- I stream of the combustion chamber 3. The further inlet 6 is connected to the supply bin 1 by means of a conduit 5. A portion of the coal is supplied through this conduit 5 to the inlet 6. By properly dosing the quantity of coal supplied to the inlet 6 relative to the quantity supplied through the conduit 2, it is possible to exactly regulate the end temperature to the desired value since the quantity of the coal which has already been heated up is mixed with the quantity supplied at the inlet 6.

The gas stream is controlled to provide a maximum residence time of about 0.3 seconds where after the stream comprising a mixture of coal and gas leaves the tubular member 4 and enters through an intermediate pipe 7 into a solid-gas separator 8. Laterally adjacent to the pipe 7 there are arranged cooling water jets 9 which direct cooling water substantially perpendicularly relative to the flow direction of the coal gas mixture.

In the solids-gas separator 8 the granular material is separated from the gas stream. The gas stream is exhausted through an exhaust gas conduit and the particles are conveyed through a conduit 11 into a storage bin 12. The outlet conduit ll is also cooled by means of cooling waterjets arranged to spray the water jets substantially perpendicularly relative to the longitudinal extension of the outlet conduit 11. The material treated in the just described apparatus has within its structure material which is similar to coke as well as expanded and perforated grains or granules. Further, the material treated according to the invention comprises well preserved granules having degassing pores. The material will be taken in appropriate quantities or dosages from the storage bin 12 for the main thermal treatment.

The intermediate three phase product according 'to the invention has the advantage that it requires only a partial additional degassing in the following thermal main treatment whereby it is further thermally comminuted. However, such comminution, contrary to prior art methods, does not result in a material having a homogeneous phase.

The semi-coke, that is, the material having characteristics similar to that of coke constitutes in the following hot briquetting process the frame for the briquettes whereas the perforated grains will be melted by the rather viscous bituminous mass of the softening bituminous coal which is later added. lnspite of this melting,

the perforated grain retains the advantage which in a thermotechnical sense could be referred to as breezing whereas the material component which has coke similar characteristics remains in a thermotechnical sense in an inert state.

Further, the well preserved grains or granules constitute an additional required supporting element for the briquette. Such supporting element enters into an intimate bond with the binder components during the actual pressing step due to its remaining shrinking capability.

The present invention has shown, contrary to the conventional assumption that a starting material of a uniform structural composition and having a normal grain size distribution is advantageous for the hot briquetting, that it is possible to produce a briquette having a suitable appearance and mechanical strength from a baking component and the three phases of a material pretreated according to the method of the invention. This is a surprising advantage of the invention be. cause the coal slack or dross produced according to prior art methods is not capable of entering into a sufficient bond with the binder components clue to its thermotechnical characteristics or behavior and due to its homogeneous structure, whereby a rough briquette surface is produced which results on the one hand in the undesirable high wear and tear for the equipment employed and on the other hand in the relatively low mechanical strength of the briquettes.

Although the invention has been described with reference to specific example embodiments, it is to be understood, that it is intended to cover all modifications and equivalents within the scope of the appended claims.

We claim:

1. In a process for thermally preparing, in a heating gas stream, coking bituminous coal having a swelling index smaller than five, for the subsequent hot briquetting, the improvement comprising providing a horizontally flowing heating gas stream, supplying the bituminous coal as raw material having a substantially unsifted grain size of up to 14,000u into said heating gas stream, assuring an average heat-up speed of about l,0O0 C per second to bring the material to an average end temperature of about 400 C at the most by exposing different portions of the raw material to the heating gas stream for different lengths of time by supplying the different material portions to the heating gas stream at different locations downstream of a first feed in location, and upon reaching said end temperature, suddenly cooling the material by means of cooling water, whereby predrying and milling of the raw material have been obviated.

2. The process according to claim 1, further comprising regulating the pretreatment temperature by varying the quantities of said different portions of the raw material supplied to said different locations.

3. The process according to claim 1, wherein said sudden cooling of the heat treated material takes place immediately before its removal from the heating gas stream.

4. The process according to claim 1, wherein said sudden cooling of the heat treated material takes place immediately after its removal from the heating gas stream.

5. The process according to claim 1, wherein the maximum residence time of the material in the heating gas stream is about 0.3 seconds.

6. The process according to claim ll, wherein air is added to said heating gas stream as a carrier vehicle.

Claims (6)

1. IN A PROCESS FOR THERMALLY PREPARING, IN A HEATING GAS STREAM, COKING BITUMINOUS COAL HAVING A SWELLING INDEX SMALLER THAN FIVE, FOR THE SUBSEQUENT HOT BRIQUETTING, THE IMPROVEMENT COMPRISING PROVIDING A HORIZONTALLY FLOWING HEATING GAS STREAM, SUPPLYING THE BITUMINOUS COAL AS RAW MATERIAL HAVING A SUBSTANTIALLY UNSIFTED GRAIN SIZE OF UP TO 14,000U INTO SAID HEATING GAS STREAM, ASSURING AN AVERAGE HEAT-UP SPEED OF ABOUT 1,000*C PER SECOND TO BRING THE MATERIAL TO AN AVERAGE END TEMPERATURE OF ABOUT 400*C AT THE MOST BY EXPOSING DIFFERENT PORTIONS OF THE RAW MATERIAL TO THE HEATING GAS STREAM FOR DIFFERENT LENGHTS OF TIME BY SUPPLYING THE DIFFFERENT MATERIAL PORTIONS TO THE HEATING GAS STREAM AT DIFFERENT LOCATION DOWNSTREAM OF A FIRST FEED IN LOCATION, AND UPON REACHING SAID END TEMPERATURE, SUDDENLY COOLING THE MATERIAL BY MEANS OF COOLING WATER, WHEREBY PREDRYING AND MILLING OF THE RAW MATERIAL HAVE BEEN OBVIATED.

2. The process according to claim 1, further comprising regulating the pretreatment temperature by varying the quantities of said different portions of the raw material supplied to said different locations.

3. The process according to claim 1, wherein said sudden cooling of the heat treated material takes place immediately before its removal from the heating gas stream.

4. The process according to claim 1, wherein said sudden cooling of the heat treated material takes place immediately after its removal from the heating gas stream.

5. The process according to claim 1, wherein the maximum residence time of the material in the heating gas stream is about 0.3 seconds.

6. The process according to claim 1, wherein air is added to said heating gas stream as a carrier vehicle.

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