US3512723A

US3512723A - Installation for simultaneously drying pulverising and grading granular materials

Info

Publication number: US3512723A
Application number: US740381A
Authority: US
Inventors: Jacques A Geoffroy
Original assignee: Charbonnages de France CDF
Current assignee: Charbonnages de France CDF
Priority date: 1967-06-30
Filing date: 1968-06-26
Publication date: 1970-05-19
Anticipated expiration: 1987-05-19
Also published as: LU56378A1; BE717404A; AT281717B; FR1555546A; JPS5432976B1; DE1767913A1; GB1193761A; NL6809141A

Description

3,512,723 SING May 19, 1970 J. A. GEOFFROY INSTALLATION FOR SIMULTANEOUSLY DRYING PULVERI AND GRADING GRANULAR MATERIALS 5 Sheets-Sheet 1 Filed June 26, 1968 kin. tJ racts May 19, 1970 J. A. sEoFFhoY 3 512,723

9 INSTALLATION FOR SIMULTANEOUSLY DRYING PULVERISING AND GRADING GRANULAR MATERIALS Filed June 26, 1968 3, Sheets-Sheet 2 M y-19, 1910 J A. GEQFFROY 3,512,723

INSTALLATION FOR SIMULTANEOUSLY DRYING PULVERISING AND GRADING GRANULAR MATERIALS Filed June 26, 1968 3 Sheets-Sheet 5 United States Patent 4 int. c1. B02: 13/134, 13/288, 21/00 U.S. Cl. 241-34 8 Claims ABSTRACT OF THE DISCLOSURE Improved installation for simultaneously pulverizing in a fluidized bed, grading and drying or preheating nonagglutinant granular materials at the temperature of the drying or preheating treatment, wherein the chamber connected to a lower combustion chamber and to an upper dust removing cyclones comprises in an upward direction:

A zone for homogenising the flow of hot gases issuing from the combustion chamber,

A drying zone wherein the product to be treated is introduced,

A pulverising zone wherein the product formed a fluidized layer and is subjected to the impact of a pulverisor, and

A gravity grading zone.

The present invention relates to an improved apparatus for simultaneously pulverising, grading and drying or preheating non-agglutinant granular materials at the drying or preheating temperature.

It is known that simultaneous pulverising, grading and drying or preheating operations on non-agglutinant materials can easily be carried out in a fluidisation reactor having an impact pulverisor, for example a cage type pulverisor, partially or totally immersed in a fluidised layer of the material to be treated.

In a known apparatus, the fluid layer is fed with material to be treated by pneumatic transport of the material by means of hot gases arriving in the fluidised layer beneath the moving portion of the cage type pulverisor. Such a device is described in the French Pat. No. 1,357,803.

An advantage of this device is that gases at temperatures higher than those occurring in a conventional drying or preheating in a fluidised bed can be used and this enables the contact time of the very fine products with the gases which propel them to be reduced.

In order to encourage the introduction of the materials to be pulverised into the interior of the movable portion of the pulverisor, it has been proposed to divide this portion into several cages placed side by side on a single shaft and separated by a clear space, a deflector assembly if necessary directing the products to be pulverised towards the interiors of cages adjacent to the deflector assembly. Such a device is described in French IPat. No. 1,444,902 corresponding to US. Pat. No. 3,381,901.

The present invention concerns an improved installation for simultaneously pulverising in a fluidised bed, grading and drying or reheating non-agglutinant granular materials at the temperature of the drying or preheating treatment, essentially characterised in that it comprises in combination:

Means to produce a constant flow of hot gases;

A fluidisation chamber of rectangular section having a pyramidal base which is upwardly diverging and of section such that the materials to 'be pulverised form a fluidised suspension therein;

ice

A vertical hot gas inlet conduit connected to the base of the fluidisation chamber, the section of the conduit being smaller than that of the fluidisation chamber and composed of two portions connected by a convergent-divergent portion;

Means for feeding the material to be pulverised leading into the vertical hot gas inlet conduit between the convergent-divergent portion and the base of the vertical fluidisation chamber;

A horizontally disposed pulzerisor having hammers and being located within the zone of the vertical fluidisation chamber where the products form a fluidised suspension;

An evacuation conduit connected to the upper part of the vertical fluidisation chamber and leading into a pneumatic transport duct;

A dust removing installation having suction cyclones, cognected to the outlet of the pneumatic transport duct; an

means for maintaining the temperature of the fluidised layer at a constant value.

In accordance with other characteristics of the invention, combinations of which can be used:

The hammers of the pulverisor are constituted by bars of constant thickness;

The feed means for the material to be pulverised are constituted by a band screw in which the width of the band increases in the direction of movement of the materials;

The evacuation conduit is provided at its base with a connecting element, the section of which converges in an upward vertical direction;

The height of the base of the connecting element of the evacuation conduit with respect to the fluidised bed is adjustable;

The means for producing a constant flow of hot gases are constituted in known manner by a combustion cham her in which a fuel is burned under neutral combustion;

The means for maintaining the temperature of the fluidised layer at a constant value are constituted by a variable speed motor driving the feed screw for the material to be pulverised, a temperature sensing device immersed in the fluidised layer and a device known per se for causing the rotational speed of the motor driving the feed screw to be varied according to the temperature variation in the fluidised layer.

In an alternative embodiment, the means for maintaining the fluidised layer at a constant temperature are constituted by a temperature sensing device immersed in the fluidised layer and a device known per se to cause the flow of fuel to vary inversely as the temperature of the fluidised layer.

Other characteristics and advantages of the present invention will appear from the following description with reference to the accompanying drawings, in which:

FIG. 1 is a general view of the installation of the invention;

FIG. 2 is a sectional view to a larger scale of the zone in which pulverisation, drying and grading proper of the materials to be treated are carried out;

FIGS. 3 and 4 are two detail views showing the movable portion of the hammer pulverisor in vertical and horizontal section respectively; and

FIG. 5 is a view in partial section of the stufling box installed at each end of the shaft driving said movable portion.

The installation of the present invention shown by way of example in the drawings comprises a vertical chamber of rectangular transverse section designated by the general reference 1, which chamber is connected at its lower portion to a combustion chamber 2 and, at its upper portion, to a dust removing installation having cyclones 3 and 4.

Considering the vertical chamber 1 in an upward direction, four zones can be distinguished:

(a) A zone 5 for homogenising the flow of hot gases issuing from the combustion chamber 2 having the shape, at its upper portion, of a converging-diverging neck 6 whose outlet section is smaller than the inlet section so as to increase the speed at which the hot fumes rise.

(b) A drying zone 7 through which the products to be pulverised, stored in the hopper 8 and introduced at the bottom of the drying zone by means of a conveyor screw 9, are transported pneumatically.

(c) A pulverising zone 10 whose transverse section is greater than the transverse section of the drying zone 7 such that, as the speed of the gases decreases therein, the mass of products to be pulverised propelled by the gases assumes the form of a fluidised layer 11. The movable portion 12 of an impact pulverisor, described hereinafter, is installed in the fluidised layer 11.

((1) Finally, a gravity grading zone 13 having a section equal to that of the pulverising zone 10.

The operation of the installation will be better understood by referring more particularly to FIG. 2 and to the following description of the path followed by the products to be pulverised. The products stored in the hopper 8 are introduced at the base of the drying zone 7 by means of the conveyor screw 9. Since the products to be pulverised are damp and thus clinging together, the conveyor screw is preferably a band screw, the width of the band increasing in the direction of flow of the products. This type of conveyor screw is described in French Pat. No. 1,483,954 corresponding to US. application Ser. No. 641,900 filed May 29, 1967, and now abandoned. It enables the products to be pulverised to be continuously extracted over the whole length of the base of the hopper 8, whilst at the same time avoiding the formation of curved cavities within the hopper and preventing the products from sticking to the walls.

The products to be pulverised are propelled and predried by the rising current of hot gases.

The speed of the gases decreases in the pulverising zone 10 because of the widening of the conduit, and the mass of products to be pulverised forms a fluidised layer 11 if the ratio of the flow of gases to the section of the conduit in the pulverising zone is calculated as a function of the granulometry of the products to be pulverised.

The movable part of a hammer pulverisor 12, rotatably driven by means of a motor 14 and driving chain 15, is completely immersed in the fluidised layer. In this layer the drying of the products to be pulverised is completed and the products are pulverised by the hammers 16 between which they penetrate.

In order to encourage penetration of the products to be pulverised between the hammers 16 and thus avoid seizing of the installation by accumulation of products under the movable part of the pulverisor, the hammers 16 are preferably constituted by simple bars of uniform rectangular transverse section as shown in FIGS. 3 and 4.

The driving shaft 17 of the movable part of the pulverisor is mounted by means of a known system of bearings and air swept stufiing boxes (FIG. 5) in order to protect the seals 18 from contact with atmospheric dust and to prevent rapid wear of the seals and of the shaft 17 in the vicinity of the bearings.

The zone of the vertical chamber 1 located above the fluidised bed is connected to the transport duct 19, leading to the dust removing installation, by means of a conduit 20 having at its lower portion a connecting element 21 which converges in the upward vertical direction. The grading zone 13 is defined by the upper level of the fluidised layer 11 and the base of the connecting element 21.

In this zone, the non-pulverised or insufiiciently pulverised particles in the fluidised layer 11 and propelled by the gases leaving the fluidised layer separate out and fall back into the fluidised layer 11 where they are subjected to additional pulverisation, while the dried and pulverised particles which have attained the desired fineness are propelled pneumatically through the transport duct 19.

In order to produce eflicient grading, taking into account the spec dof the gases, it is necessary for the rising gases to travel, above the fluidised layer, through a height, known as the return height, which is sufficiently great for a regular rate to encourage grading.

Expressed differently, the return height, i.e. the vertical distance H separating the upper level of the fluidised layer from the base of the connecting element 21, must be large enough to allow the large particles, ejected from the bed and whose speed of fall in the rising gases is greater than the speed of rise of the gases, to fall back.

Since the return height H to be provided is principally in proportion to the granulometry to be achieved, the optimum height of the grading zone 13 is adjusted experimentally by altering the height of the lower end of the connecting element 21 with respect to the upper level of the fluidised layer, for example by altering the length of the conduit 20.

The pneumatic transport duct 19 takes the mixture of the gases and the dried and sufliciently pulverised products to the dust removing installation which has a first cyclone 3 and second cyclone 4. The particles trapped by the two cyclones are led to their place of use by any known means which are not shown.

Since the gas producing power of the fuel burning under neutral combustion is almost equal to its combustive power, the quantity of hot combustion gases leaving the combustion chamber 2 may be regarded as constant, whatever may be the amount of fuel used.

There are two possible methods of regulating the temperature of the fluidised bed:

1) The temperature of the combustion gases leaving the combustion chamber is maintained at a constant value by adjusting once and for all the amount of fuel as a function of the quantity of gases to be produced and thus of the quantity of combustive air, and the rate of introduction of the products to be pulverised is adjusted as a direct function of the temperature of the fluidised layer.

The apparatus in this case comprises a temperature sensing device 22 immersed in the fluidised layer 11, and a regulating device 23, known per se, causing the speed of rotation of the motor 24 driving the screw 9 to be varied in the same sense as the observed temperature variation.

(2) The rate of introduction of the products to be pulverised is maintained at a constant value and the temperature of the gases is adjusted as an inverse function of the temperature of the fluidised layer.

In this case, the apparatus comprises a temperature sensing device 22 immersed in the fluidised layer, and a regulating device 25, of any known type, acting on a valve 26 in such a manner that the amount of fuel flowing increases when the temperature of the fluidised layer 11 fal s and vice-versa.

The fact that a hammer pulverisor is used'lessens the risk of the products to be pulverised accumulating beneath the movable portion of the pulverisor, such accumulation occurring in a Carr pulverisor due to the difliculty experienced by the products to be pulverised in penetrating within the case thereof through the bars.

Moreover, the replacement of worn elements on the movable part of the pulverisor (notably the hammers) is an easyoperation not requiring prolonged halting of the installation.

The apparatus of the invention was used to pulverise coal granules having the characteristics shown in the first line of the following table.

W J Granulometry Humidity mm. 3.15 mm. 2mm. 1mm. 0.5 mm. 0.2 mm. 0.1 mm.

Before ulverisation perce t 4. 4 100 93. 1 78 57. 1 35 20. 1 7. 6 After ulverisation perc nt 1.1 100 98. 2 91. 7 78. 2 62 45. 7 25. 6

The installation operated for three hours with a flow (g) an evacuation conduit having a section smaller of coal of9t./h. 10 than that of the vertical fluidisation chamber and The temperature of the gases was 360 C. and the temperature of the fluidised layer was maintained at The pulverising and grading zone had the following dimensions: 0.49 m. X 1 m. and the movable part of the pulverisor had a diameter of 0.90 m. The speed under no load of the fumes in the pulverising zone was 3.6 m./s.

The return height H was 2 m.

The average characteristics of the 27 t. of pulverised and dried coal are shown in the second line of the above table.

The treatment required an average hourly consumption of electrical energy of 17 kwh., or l7/9=1.9 kwh. per ton of pulverised and dried coal.

summarising, the main advantages of the insta lation of the present invention are:

Great regularity of operation,

Easily realisable automation,

Ease of service and maintenance,

And above all, low electrical energy consumption compared with known devices to achieve comparable granulometries.

It is clear that modifications of detail can be made to the installation of the invention without departing from the scope of the invention.

What is claimed is:

1. An improved installation for simultaneously pulverising in a fluidised bed, grading and drying or preheating nonagglutinant granular materials at the temperature of the drying or preheating treatment, comprising from bottom to top:

(a) means for producing a substantially constant flow of hot gaseous fluid;

(b) a vertical conduit for ensuring the circulation of said hot gaseous fluid, composed of two parts corinected together by a convergent-divergent portion;

(c) means for feeding the material to be pulverised leading into said vertical hot gaseous fluid circulation conduit above said convergent-divergent portion;

(d) a vertical fluidisation chamber of substantially uniform rectangular section having a base in the form of a pyramid diverging in an upward direction and connected at its lower part to the top of said vertical hot gaseous fluid circulation conduit;

(e) the outlet section of said pyramidal base is greater than the section of said vertical hot gaseous fluid circulation conduit and causes the materials to be pulverised to form a fluidised suspension in said vertical fluidisation chamber;

(f) a horizontally disposed pulverisor having hammers and being located in the lower part of the vertical fluidisation chamber;

connected to the upper part of said chamber;

(h) and means for maintaining the temperature of the fluidised layer substantially constant.

2. An installation according to claim 1 wherein the pulverising hammers are constituted by bars of unif rm thickness.

3. An installation according to claim 1 wherein the means for feeding the material to be pulverised is constituted by a band screw, the Width of the band of which increases in the direction of movement of the material.

4. An installation according to claim 1 wherein the evacuation conduit is provided at its base with a connecting element whose section converges in an upward vertical direction and which connects the evacuation conduit to the vertical fluidisation chamber.

5. An installation according to claim 4 in which the height of the base of the evacuation conduit connecting element with respect to the fluidised bed is adjustable.

6. An installation according to claim 1 in which the means for producing a substantially constant flow of hot gaseous fluid is constituted by a combustion chamber in which a fuel is burned by neutral combustion.

7. An installation according to claim .1 wherein the means for maintaining the temperature of the fluidised layer at a substantially constant value is constituted by a variable speed motor driving the means for feeding the material to be pulverised, by a temperature sensing device immersed in the fluidised layer and by a device for causing the speed of rotation of said motor to vary as a direct function of temperature variations in the fluidised layer.

8. An installation according to claim 1 wherein the means for maintaining the temperature of the fluidised layer at a substantially constant value is constituted by a temperature sensing device immersed in the fluidised layer and by a device for causing the fuel flow to vary inversely as temperature variations in the fluidised layer.

References Cited UNITED STATES PATENTS 1,814,560 7/1931 Kreisinger 241-59 X 1,875,817 9/1932 London 241-58 2,075,506 3/1937 Crites 24l--188 X 3,050,018 8/1962 Pearson.

FOREIGN PATENTS 1,357,803 3/1964 France.

1,483,954 3/1967 France.

ROBERT C. RIORDON, Primary Examiner D. G. KELLY, Assistant Examiner US. Cl. X.R. 241-62 Dedication 3,512,723.Jaciues A. Geoffrey, Forbach, France. INSTALLATION FOR SIMU TANEOUSLY DRYING PULVERISING AND GRAD- ING GRANULAR MATERIALS. Patent dated May 19, 1970. Dedication filed Dec. 20, 1979, by the assignee, Oharbomwges De France.

Hereby dedicates to the Public the remaining term of said patent.

[Ofi'icial Gazette, M arch 4, 1980.]