AP246A

AP246A - Installation for the treatment of a pulverulent raw material such as calcium sulphate, for preparation of a hydraulic binder.

Info

Publication number: AP246A
Application number: APAP/P/1991/000292A
Authority: AP
Inventors: Christian Dussel
Original assignee: Christian Dussel
Priority date: 1990-06-21
Filing date: 1991-06-21
Publication date: 1993-03-04
Also published as: OA09371A; PL293742A1; BG96103A; HU9200951D0; IL98567A0; CA2064775A1; MA22187A1; FI920686A0; BR9105795A; PT98033A; AU8074391A; FR2663626A1; JPH05502657A; IE912127A1; TNSN91053A1; YU148391A; CN1058764A; WO1991019685A1; EP0462678A1; ZA914746B

Abstract

The invention relates to an

Description

INSTALLATION FOR THE TREATMENT OF A PULVERULENT '

RAW MATERIAL SUCH AS CALCIUM SULFATE,

FOR PREPARATION OF A HYDRAULIC BINDER

This invention relates to an installation for the treatment of a material in a pulverulent form, such as natural calcium sulfate (gypsum) or synthetic calcium sulfate (sulfogypsum, phosphogypsum, ana other related products of the same type), in order to transform the material into a hydraulic hinder of a desired type (in particular high strength anhydrite plasters).

Calcium sulfate is a material which, by appropriate thermal treatments, permits preparing plasters of several varieties, in particular certain plasters of high strength (particularly semi-hydrates or anhydrites, of the or other variety) which, upon hardening, have mechanical characteristics much greater than those of other varieties ( /3 plaster).

However, treatment processes for this type of material, for obtaining the desired variety, are very delicate to carry out because the treatment must be precisely homogeneous and controlled, under the penalty of obtaining materials having characteristics very different from those desired ; in particular, each granule of the raw material must be subjected to precisely the same conditions of temperature

Several processes have been conceived for operate such treatments : French patents 2,445,940 ; U.S. patents 5,145,980 and

Ml and humidity.

attempting to 2,572,721 and

2,269,530. In these processes, the raw material is arranged in more or less thick layers and falls from one plate to another for being subjected to the thermal treatment in a controlled atmosphere. However, calcium sulfate is a poor thermal conductor and has a great tendency to adhere to itself or agglomerate in such a manner that a uniform treatment is very difficult to obtain by carrying out these known processes, and one encounters great difficulties in preparing the desired type of product in a strictly reproductible manner.

For attempting to resolve these difficulties,

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AP Ο Ο Ο 2 4 6 it has been proposed to carry out the treatment in a fluidized bed, the bed of fluidized pulverulent material being obtained by subjecting the material to a flow of gas through a distributor arranged at the base of the bed (French patent 2,389,855)· However, this type of material produces very quickly a clogging of the distributors in such a manner that it becomes very difficult to fluidize by these known processes ; moreover, these processes can only be carried out very expensively, because of the gas flows needed, especially when the material must be treated in several superimposed fluidized beds, as in the case in the aforeaentioned French patent.

The present invention proposes to resolve the difficulties above mentioned and to provide an installation for the treatment of pulverulent material which permits a uniform and controlled treatment of the raw material, without risk of clogging or agglomeration of the granules together, and at a moderate cost, much lower than that of processes working in conventional fluidized bed.

To this end, the installation provided by the invention comprises an enclosure in the form of a hood closed on its sides and on the upper portion, a plurality of superimposed trays extending into said enclosure, each being essentially horizontal, means for the distribution of the raw material arranged in the upper portion of the enclosure for delivering the material to the upper tray, and means for evacuating the treated material arranged in the lower portion of the enclosure for receiving said treated material from the lover tray (by the expression essentially horizontal tray” is meanc a tray having an inclination with respect to the horizontal less than 15*) ; the installation according to the present invention is characterized essentially in that :

-each tray comprises a plurality of transverse rotors, each extending across the width of the tray and arranged one adjacent another, in such a manner as to cover the entire length of the tray,

- driving means associated with the rotors for rotationally driving them in such a manner that the rotors of one tray turn in the same direction and that the rotors of

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the two adjacent trays turn in the opposite direction,

- each rotor is provided with peripheral paddles passing during the rotation in proximity to the bottom of the tray and in proximity to the paddles of the two adjacent rotors in such a manner as to assure placing the material in suspension and advancing it along the tray in a direction corresponding to the direction of displacement of the paddles at the low point of their rotation,

- each tray comprises at one end, means for passage by gravity of the material toward the lower adjacent tray, and at the other end, a receiving zone for the material coming from the passage means of the next above tray, this receiving zone being situated between two rotors in such a manner as to assure the suspension of the material at its inlet in the tray and its transport toward the other end of the tray,

- at least in the upper stages, heating means is arranged in sheets between the trays, each sheet extending between two trays, below the bottom of the tray above and directly above the tray below in such a manner as to heat the material contained in the tray above by conduction and that contained in tne tray below by radiation.

Thus, in the installation of the invention, the raw material is placed in suspension in each tray and the bed of material presents substantially the properties of a fluidized bed, and in particular those of assuring excellent heat exchange with each granule of material, assuring excellent transfer of material (water vapor), and enabling a uniformity of treatment conditions at the center of the bed and avoiding agglomerations of granules together. The bed of material obtained in the invention may be described as a pseudo-fluidized bed”. It must be stressed that this bed which travels along the trays is obtained mechanically in the absence cf a fluid and distributors, such that the installation of the invention is free from the deficiencies of known installations working in a fluidized bed.

According to a preferred embodiment, the bottom of each tray is provided, between each pair of adjacent rotors, with an inter-rotor piece occupying the accumulation

AP000246 zone not swept by the paddles : each inter-rotor piece is arranged such that the paddles of the two rotors concerned pass in proximity to said piece during rotation. The quality of the pseudo-fluidized bed is thus improved while suppressing the zones of accumulation and the heterogeneities of treatment which they may cause.

Preferably, driving means for the rotors is adapted to permit driving them at a.speed comprised between 60 and 150 rotations per minute, and the rotors and their paddles, are arranged to assure a linear advancing speed of the material between 1 and 2 meters per minute. Experiments have shown that such arrangements permit obtaining in practice a pseudo-fluidized bed which is very homogeneous, and a treatment which is easy to check, while using moderate mechanical power, compatible with a satisfactory cost of the installation and a reduced energy consumption (considerably lower than that required by known fluidized beds).

The number of trays equipping the installation may vary according to the application. For application to the treatment of calcium sulfate, this number of trays will advantageously be between 8 and 15, these trays being in metal for transmitting by conduction the heat furnished from the heating sheets. These sheets are arranged between the trays situated in the upper part of the enclosure in such a manner that a proportion from 60 % to 80 % of the trays are heated. In this application, the heating means is advantageously adapted to permit assuring in the midst of the material contained in the upper trays a temperature comprised between 500 ’C and 500 *C. In this upper part of the enclosure, the granules of the pseudo-fluidized bed are thus subjected to an heat supply (identical for each granule) coming from the conduction by the trays (heating, by conduction, from the base of the pseudo-fluidized layer) and from radiation by the sheets (heating by radiation from above the layer). This heat supply produces a transformation of the granules and a release of water vapor (interposition water, and water of crystallization of the raw material) : the treatment is thus carried out in a dry vapor atmosphere, under remarkable conditions of uniformity.

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By adjusting the flow of material, the distribution of the heat supply and the temperatures all along the treatment, the installation according to the invention permits, starting with raw materials of varying origins, obtaining a well defined product, or, from a same raw material, adjusting to the needs, the characteristics of the final product obtained.

According to a first embodiment, the heating means, which assures the heat supply, comprises a heating apparatus for a heat transfer fluid, sheets of tubes fixed by metal cross-pieces below the bottoms of tray, an inlet collector connected to the heating apparatus and to the lower sheet for feeding the heat transfer fluid in parallel to the tubes of the lower sheet, means for distributing the heat transfer fluid from one sheet to the sheet above, an outlet collector connected to the tubes of the upper sheet, and, in the upper part, a recovery apparatus for the heat transfer fluid.

In this type of arrangement, the generators may in particular be burners, situated at the foot of the enclosure and the heat energy necessary for the treatment of the material is conducted by hot gases or hot fumes coming from these burners, the recovery apparatus in the upper portion being constituted by a chimney traversing the upper wall of the hood. The chimney may be provided with an exchanger permitting recovery, before release to the atmosphere, of a portion of the heat contained in the fumes for preheating the air which may either be fed to the burners as fuel, or injected into the lowest collector. In a variation, the fumes themselves may be recovered and reinjected into the collectors at one or several levels judiciously selected. It is also possible to direct a portion of these fumes toward storage silos or to raw material feed conveyors for producing a preheating of this raw material, and reducing its humidity if it is excessive. These embodiments improve the thermal efficiency of the installation.

According to another embodiment, the heating means comprises sheets of electrical resistances fixed below the bottoms of tray, along with means for supplying electric bad ORIGINAL

AP 0 ο η 2 ί r current to the sheets of resistances.

During the course of its treatment, the raw material releases water vapor, as indicated above, as veil as various other gases depending on its origin. These products accumulate in the enclosure where they are extracted by an exhaust conduit extending through the top of the enclosure and having a damper for controlling the pressure herein. The vapor and the gaseous extracts may he directed toward a water tank to which are eventually added reactants for purifying the same and cooling it hy bubbling, which permits assuring a production of hot water, and the concentration of the noxious products before sending them to specialized treatments units.

It should be noted that the installation of this invention may, if desired, be arranged on a towed vehicle or may be provided with a series of axles permitting its easy and rapid displacement either for use of dispersed primary material sources, or the production of the treated product directly at the places of use.

Other characteristics, objects and advantages of the invention will become apparent from the description which follows, with reference to the accompanying drawings which show, by way of example, one embodiment of the invention ; in these drawings, which form an integral part of the present description :

- figure 1 is a longitudinal cross-section of the installation through a vertical axial plane ;

- figure 2 is a transverse cross-section along plane A-A (for the purpose of simplifying the description, ail of the rotors are not shown in figures 1 and 2) ;

- figure 5 is a detailed longitudinal crosssectional view partially showing two superimposed trays and their rotors ;

- figure 4 is a schematic view in perspective, showing the arrangement of the trays, the rotors, and the heating means ;

- figure 5 is a perspective schematic view of one rotor, and figure 6 is a cross-section along plane 3-B ;

- figure 7 is a schematic view in perspective

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showing the driving of the rotors of one tray ; and

- figure 8 is a schematic view showing the operation of the installation and the placing in suspension of the pulverulent raw material for establishing a pseudofluidized bed L.

The installation shown by way of example in the drawings, may in particular be applied for transforming into a hydraulic binder, natural or synthetic gypsum being prior to treatment in a pulverulent form (up to 5/10 mm), with its natural moisture content and at ambient temperature. It comprises a parallelepipedic hood 1 (enclosure) constituted of metal walls provided internally with insulating refractory elements 2, and supported by a framework of members 3- This enclosure contains a series of superimposed horizontal trays such as 4, in the shape of a U with a flat bottom, of refractory sheet steel, on the interior of which rotate the rotors 5 controlled from the outside of the enclosure by a system of drive chains 23 and pinions 24 shown by way of example in figure 7.

The installation comprises means for the distribution of the raw material constituted by a feed hopper 6 situated on the top of the enclosure, forming two lock chambers 7a, 7b between three rotary distributors 8a, 8b,

8c, the length of the distributors increasing and their diameter decreasing from top to bottom, in such a manner as to distribute the feed over the width of the transporters, while assuring a constant flow through their homokineticism ; a distribution conduit 9 at the base of the lower distributor 3c opens, through the enclosure, onto an extremity of the upper tray. After its travel from top to bottom in the successive trays, the material is discharged into a receiving hopper 10, which feeds an evacuation apparatus toward storage silos (not snown,

In the example, the installation comprises eleven superimposed trays, the eight upper trays being provided with heating means.

The heat supply is, in the example shown, provided by the circulation of hot fumes circulating in the dO sheets of tubes 11 arranged between two adjacent trays. In the bad original

APnnnjAR example, these tubes have rectangular cross-sections and are fixed to cross-pieces 33 soldered on the bottom of the trays. The fumes may be replaced by any appropriate heat transfer fluid, and the tubes may be replaced by electrical resistances. The tubes of one sheet are feed in parallel by a collector 12 which receives the fumes leaving the sheet situated below, for distribution toward the sheet above. The inlet collector 13 and the outlet collector 14 are only connected to one sheet of tubes. The lower trays (in the example, three in number) are not equipped with heater sheet in order to permit the material to be stabilized without heat supply, then to be cooled to temperatures which can be on the

2C order of 120 to 150 *C.

The tubes are fed with hot gas by one or several hot fumes generators (in the example, two burners :

15a, 15b) arranged on a chassis at the lower part of the hood. These generators are branched to one or several collectors according the needs of the material to be treated and the desired distribution of temperatures.

The number of sheets of tubes 11, the number of trays not provided with heating tubes, the number of hot fumes generators, the number and position of the hot gases supply branch conduits on the collectors may vary according to the needs (the configuration of figure 1 being given solely by way of non-limiting example).

In the upper portion, the fumes collected in the collector 14 are evacuated by a chimney 22 provided with a damper 16 permitting manual or automatic adjustment cf the pressure and the speed of circulation of the hot gases in the tubes. This chimney may be provided with a branch conduit 17 permitting recovery cf a portion of the hot gases leaving, in order tc be re-injected upstream cf the heating apparatus for improving the efficiency. To this reinjection of hot fumes is added a heat exchanger 27 which serves, by cooling the fumes, to generate hot air useable for feeding to the generator as combustion air or for direct feed from the heating circuit between the generators and the sheets of tubes. Further, one part of the fumes may be sent into the silos containing the raw material and onto the conveyor assuring its transport

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toward the installation to assure its preheating.

The hood is equipped on its top with an exhaust conduit 18 passing through the metal wall and its insulating filling 2 for evacuating the atmosphere of dry water vapor and the various gases released from the material and accumulating in the upper portion of the hood. This conduit is equipped with a control damper 19 which is controlled manually or automatically, and permits the control of the pressure in the top of the hood. The extracted gases are directed toward a receptacle (tank) 20 containing water and reactants, where by bubbling, they are purified and cooled. By concentration, the process thus proceeds for the purification of the gases of noxious products and ultimately the evacuation thereof to specialized treatment units. Further, an associated water circuit 21 permits the production of hot water.

As is shown in figures 5 and 4, the rotors 5 extend all cross the width of each tray 4 and are arranged one next to another, in such a manner as to cover the length of the tray. Between each pair of rotors is fixed, on the bottom of the tray, an inter-rotor piece 25 which rests in the accumulation zone not swept by the rotors.

Each rotor is constituted by a hollow rotating shaft 5a, along which, are distributed several supports 5b, shown in the example to be of triangular shape. These supports carry paddles 5c, shown to be three in number, spaced apart by 120*.

As shown in figuri constituted by a substantially plana:

each paddle blade, inclined with he radial direction at an angle -i- between 20* in the example shown). Each rotor is caused to respec' and 40‘ to ‘ ( 50 * ;ate in the same direction R as the direction of inclination

Further, as shown in figure 5, each interrotor piece 25 has the shape of an inverted V of which the two inclined sides form, with the bottom cf the tray, an angle -jcomprised between 50* and 50* (about 40’ in the example shown). The height of the inter-rotor piece above the bottom is between O.55H and 0.5H, where K is the distance separating

V

AP 0 0 0 2 4 6 ,0 the axis of the rotor and the bottom.

The rotors of each tray are driven so as to rotate in the same direction R, while the rotors of the adjacent trays turn in the opposite direction R'. During this rotation, the paddles of each rotor pass near the bottom of the tray and in proximity to the inclined sides of the adjacent inter-rotor pieces, as shown in figure 8. The drive members are adapted to enable a rotation speed between 60 and 150 rotations per minute (in particular on the order of 120 rpm). During this rotation, the pulverulent material -which is contained in each tray is placed into suspension for forming a bed equivalent to a fluidized bed, herein called a pseudofluidized bed L. This bed is displaced in its entirety in the direction S (figure 8), because of the rotation of the rotors, at a linear transport speed between 1 and 2 m/minute (particularly on the order of 1.5 m/minute).

Each tray comprises at its downstream end (with respect to the direction of displacement S) an opening 26 for passage by gravity of the material to the tray below (figure 3)· The latter comprises a zone ZR for receipt of the material, this zone is provided with two rotors in such a manner that said material falls between these rotors and is immediately placed in suspension and driven in the opposite direction S’ (since the rotors of this tray turn in the opposite direction). The material thus travels in the pseudofluidized bed toward the other end of the tray, where it falls on the tray below, and then on the lowest tray in the installation. This then permits establishing superimposed layers in suspension, equivalent to fluidized beds.

These layers are heated, for the eight upper trays, on the one hand, by radiation Y from the sheets of tubes 11 placed above the layer, and, on the other hand, by conduction C, through the bottom of the tray which receives the heat of the sheet below (figure 8). A homogeneous thermal treatment is thus achieved, remarkably effective for the pseudo-fluidized layer, without risk of clogging or agglomeration of the granules.

The drive means for the rotors is of a known type. Shown by way of example in figure 7 is one embodiment of

BAD ORIGINAL £ this drive means. The rotor shafts are carried by rolling journal bearings 32 at right angles with the lateral sides of the tray. They are connected outside of the enclosure to a shaft portion 28 by an isolating universal joint 30. This shaft portion 28 supported by two journal bearings 29, is driven by chain and pinion (23, 24), as already mentioned. All these pinions corresponding to the rotors of the same tray are connected by chains assuring their homokineticiam and their rotation in the same direction. Gearing means between one tray and the two adjacent trays permits obtaining equal speeds of rotation and opposite directions of rotation of the rotors of these two adjacent trays with respect to the tray considered.

Claims

1 / - An installation for or a raw material in a pulverulent form such as natural or synthetic calcium sulfate for preparing a hydraulic hinder, comprising an enclosure (1) in the shape of a hood, closed on its sides and in its top portion, a plurality of superimposed trays (4) extending in said enclosure, each being substantially horizontal, means (6) for distribution of the raw material provided in the upper portion of the enclosure for delivering the material to the upper tray, means (10) for removing the treated material provided in the bottom portion of the enclosure for receiving said treated material coming from the lower tray, said installation being characterized in that :

- each tray (4) comprises a plurality of transverse rotors (5) each extending across the width of the tray, and arranged one adjacent the next in such a manner as to cover the entire length of the tray,

- drive means (23, 24) associated with said rotors for rotatably driving the rotors in such a manner that the rotors of a given tray all turn in the same direction and the rotors of two adjacent trays turn in the opposite direction,

- each rotor (5) is provided with peripheral paddles (5c) passing during rotation in proximity to the bottom of the tray and in proximity to the paddles of two adjacent rotors in such a manner as to assure the placing in suspension of the material and transport of the material along the tray in a direction corresponding to the direction of displacement of the paddles at the low point of rotation,

- each tray (4) comprises, in one hand, at one end, means (26) allowing the gravity transport of the material toward the adjacent tray below, and, in the other hand, at the other end, a zone (ZR) for receipt of the material coming from the transport allowing means of the adjacent tray above, this zone of receipt being situated between two rotors in such a manner as to assure the placing in suspension of the material upon its arrival in the tray and

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Z its transport toward the other end of the tray, at least in the upper stages, heating means (11) are arranged in sheets between the trays, each sheet extending between two trays below the bottom of the tray above and directly above the tray below in such a manner as to heat the material contained in the tray above by conduction and that contained in the tray below by radiation.

2/ - An installation as in claim 1, characterized in that the bottom of each tray is equipped, between each pair of adjacent rotors, with an inter-rotor piece (25) occupying the zone of accumulation not swept by the paddles, each inter-rotor piece being arranged such that the paddles of two rotors concerned pass in proximity to said piece during rotation.

3/ - An installation as in claims 1 or 2, characterized in that the drive means for the rotors is adapted to permit the driving at a speed comprised between 60 and 1 50 rpm and in that the rotors and their paddles are adapted to assure a linear speed of transport of the material comprised between 1 and 2 m/minute.

4/ - An installation as in one of claims 1, 2 or 3, characterized in that each rotor comprises a rotary shaft (5a), a plurality of supports (5b) of paddles distributed along this shaft, and paddles (5c) extending parallel to the shaft and fastened around the supports in such a manner as to be evenly spaced along the shaft.

5/ - An installation as in claims 2 and 4 taken together, characterized in that :

- each paddle (5c) is constituted by a substantially planar blade inclined with respect to the radial direction at ar. angle -i- comprised between 20’ and dO*, the rotor being driven in the direction of inclination of said paddles, and

- each inter-rotor piece (25) is in the shape of an i.nversed V of which the two inclined sides form, with the bottom of the tray, an angle -j- comprised between 30’ and 50’, and which eight above the bottom is comprised between O.35H and 0.5H, where H is the distance separating the rotor axis and the bottom.

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6/ - An installation as in one of claims 4 or 5, characterized in that each rotor (5) comprises three paddles spaced at 120*.

5

7/ - An installation as in one of claims 1 to 6, characterized in that it comprises between 8 and 15 sheet metal trays, the heating sheets (11) being arranged between the trays situated in the upper portion of the enclosure in such a manner that a proportion of 60 to 80 % of

10 the trays are heated.

8/ - An installation as in one of claims 1 to 7, characterized in that the heating means comprises a heating apparatus (15a, 15b) for a heat transfer fluid, sheets of tubes (11) secured by cross-members (33) below the bottoms

15 of trays, an inlet collector (13) connected to the heating device and to the lower sheets for feeding in parallel with heat transfer fluid, the tubes of said lower sheet, means (12) for distributing the heat transfer fluid from one sheet to the sheet below, an outlet collector (14) connected to the tubes

20 of the upper sheet, and in the top portion, an apparatus (22) for recovering the heat transfer fluid.

9/ - An installation as in one of claims 1 to 7, characterized in that the heating means comprises sheets of electrical resistances secured below the tray bottoms and

25 means for supplying electricity to said sheet of resistances.

10/ - An installation as in one of claims 8 or 9, characterized in that the heating means is adapted to permit assuring in the midst of the material contained in the upper trays a temperature between 300 *C and 500 *C.

30

1 1 / - An installation as in one cf claims 1 to 10, characterized in that the means for distribution of the raw material comprises a feed hopper (6) with two lock chambers (7a, 7'o) between three rotary distributors (8a, 8b, 8c) dimensionned to supply the upper tray over its entire

35 length.

12/ - An installation as in one of claims 1 to 11 , characterized in that it comprises, in the top portion, an exhaust conduit (18) passing through the enclosure and an adjustable damper (19) arranged on this conduit, for recovery

40 of the gases from the enclosure, with control of the pressure

ORIGINAL in the upper portion of said enclosure.

13/ - An installation as in one of claims 1 to 12, in which the enclosure (1) has the shape of a 5 parallelepipedic hood constituted of metal walls, provided internally with insulating refractory elements (2) and supported by a framework (3).