US 3544089 A
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United States Patent Inventor Pierre Ledent Parc de Sainval, Tilfl, Belgium Appl. No. 741,743 Filed July 1,1968 Patented Dec. 1, 1970 Priority July 12, 1967 Belgium No. 701,295
PNEUMATIC ELEVATORS FOR LIFIING GRANULAR SOLIDS 5 Claims, 2 Drawing Figs.
US. Cl 263/21, 34/57 int. Cl. F27b 15/00 Field of Search 263/ 19(B), 21(A); 34/57(A), 57(T) FUN  References Cited UNITED STATES PATENTS 3,030,089 4/ 1962 Johnson, Jr 263/21A 3,373,504 3/1968 Mclntire et al. 34/5 7A Primary Examiner-John J. Camby Attorney-Jacob L. Kollin ABSTRACT: Apparatus for the pneumatic elevation of granular solid products utilising a compressed carrier gas, comprising a closed receptacle the bottom of which is constituted by a porous surface, through which a gas may be blown at such a speed as to fluidize a bed of granular solids situated in said receptacle when the apparatus is in use, and a vertical elevator tube passing through the top wall of said receptacle and extending inside it, wherein means are provided for introducing a flow of high-temperature gas into said receptacle outside the elevator tube.
Paiited Dec. 1, 1970 3,544,089
I fag. 2
INVENTOR 519915 1605A? ATTORNEY PNEUMATIC ELEVATORS FOR LIFTING GRANULAR SOLIDS various devices for the transport and pneumatic elevation of solid granular substances are known. In installations of this type, the rate of flow is generally high, above 20 to 25 meters per second, and the ratio between the feeds by weight of solid end carrier gas is generally low, more often of the order of 2 and more rarely from 8 to 10.
Such installations may function below atmospheric pressure but in that case the solid gas ratio is very low and the installation must comprise large fans and vast filtering devices for refining the carrier gas. One way also have recourse to a compressed carrier gas but there is then the problem of introducing the solid into the said carrier gas; this problem is solved by relatively complicated mechanical devices, such as sieves, screws or honeycombed sluices.
An apparatus for the pneumatic elevation of granular solid products, utilizing a compressed carrier gas and previously imagined by the applicant, comprises two receptacles communicating with one another at their lower part, the bottom of the said two receptacles being constituted by a porous surface, through which a gas may be blown at such a speed as to fluidize two intercommunicating beds of granular solids situated in the two receptacles when the apparatus is in u'se, in which the first receptacle acting as a feeding device is open at its upper part so that it may contain fluidized bed, the surface of which is at atmospheric pressure, and the second receptacle is a closed receptacle through the roof of which pass one or more vertical tubes capable of acting as a pneumatic elevator.
This apparatus can be employed simultaneously as a pneumatic elevator and as a heat exchanger in which heatexchange takes place between the carrier gas and the granular solids. However, since the gas is introduced through the porous surface acting as the base of the fluidized bed, the temperature at which the gas can be introduced is limited to the temperature which can be tolerated by the material of which said porous surface is composed.
The apparatus of the present invention enables this dra back to be overcome and is characterized by the fact that the quantity of gas introduced through the porous surface acting as the base of the fluidized bed is limited to the absolute minimum which is necessary to ensure fluidization of the granular solids, and that another flow of gas at a higher temperature is introduced above the level of the fluidized bed.
The total gas flow rises up through the vertical elevator tube or stack, which acts as a heat exchange by creating direct contact between the hot gases and the granular solids.
The effective cross section of the vertical elevator tube is generally so selected that the speed of circulation of the rising gases does not exceed a level of between 10 and 15 meters per second. this limitation on the speed of circulation increases the time during which the solids and the gases are in contact and this, of course, promotes heat transfer. Moreover, it also reduces the power consumption of and the rate of wear in the installation.
ln high-capacity installations, operating at elevated temperatures, it may be necessary or desirable to employ an elevator tube of very large diameter which will result in a reduction in the amount of heat transfer between the gas flowing up the tube and the granular solids, the latter preferably following a boundary layer close to the tube wall. In such cases as this, to overcome this disadvantage, it is generally advantageous to employ an elevator stack comprising two or more concentric tubes, the central tube being sealed at .at least the lower end thereof and the annular space or spaces between the said tubes being the only space utilized for the circulation of the gases and solids.
Since the elevator stack operates as a concurrent heat exchanger, the temperature of the gas leaving the tube is always slightly higher than the temperature of the solids. In order, therefore, to improve the thermal efficiency of the system, it is generally advantageous to include a waste-heat recovery system which can be used for air heating purposes and possibly to heat the gas which is used for the heating function and for the fluidization.
The invention is further illustrated with reference to the accompanying drawings, in which:
FIG. 1 is a diagrammatic sectional view of one embodiment of the apparatus of the present invention, and
H6. 2 is a section along line ll-ll of H6. 1.
The apparatus illustrated comprises an assembly of two associated receptacles l and 2 communicating with one another at their lower parts through an opening 3. I
The bases of these receptacles are in each case constituted by a porous surface 4 which may be a porous slab or any other appropriate kind of diffuser arrangement such as a perforated plate or grid of refractory steel. 7
The receptacle 2, all the internal walls of which are lined with a refractory material, communicates with a burner 5 which produces high-temperature gases; these gases are in troduced into the receptacle 2 above the surface of the fluidized bed and are evacuated through the elevator tube 6 which also acts as a heat exchanger between the gases and the granular product. The elevator device comprises two concentric tubes of which the central one 7, sealed at its bottom end, the annular space between the two tubes being the sole space employed for the circulation of the gases and the solid materi-' als.
At the top end of the elevator device, the gases and the solids are separated in chamber 8. The granular solid material is evacuated across a screen and the gases are discharged through a flue after having passed through a heat exchanger 9 which preheats the air, compressed by the fan 10, used to produce the hot gases and to fluidize the bed of solid granular material contained in the receptacles l and 2.
An installation of this kind enables a granular solid to be heated to temperatures in the order of 800 C. with an overall thermal efficiency of as much as 80 percent. The power consumed in lifting the granulated solids is very low as a result of the fact that the air compression takes place at ambient temperature but the air used for the lifting is at high temperature. By way of example, in an installation designed to lift fine sand through a height of 8 meters, reaching a final temperature of 800 C., the power taken by the fan increases by only I kw. for an increase in sand throughput from 20 to 40 metric tons per hour.
In certain industrial applications, it may be desirable to employ for the heating function residual gases (stack gases, exhaust gases etc. the pressure of which is insufficient to permit operation of the installation in the manner described. In cases of this kind, the device is supplemented by the fan 11 located beyond the exchanger 9, in order to produce a forced draught in the system.
1. an apparatus for the pneumatic elevation of granular solid products utilizing a compressed carrier gas, comprising' a closed receptacle the bottom of which is constituted by a porous surface, through which a gas may be blown at such a speed as to fluidize a bed of granular solids situated in said receptacle when the apparatus is in use, and a vertical elevator tube passing through the top wall of said receptacle and ex-;
tending inside it, wherein means are provided for introducing t a flow of high-temperature gas into said receptacle outside the elevator tube above the fluidized bed.
2. an apparatus according to claim 1, wherein said means for introducing the flow of high-temperature gas comprise one or more gas burners or oil burners located in a vertical wall of said receptacle.
3. an apparatus according to claim 1, wherein said elevator tube comprises at least two concentric tubes, the centre one of said tubes being sealed at at least its lower end.
4. an apparatus according to claim 3, in which said elevator tube comprises two concentric tubes only.
5. an apparatus according to claim 1, wherein the air and possiblyalso the gas, used to supply the burner or burners and to produce fluidization in the vessel, is/are preheated in a heat exchanger by recovery of the heat still contained by the gases which have been used to raise the solid product. I