Title of Invention

"PROCESS OF REMOVING GRANULAR SOLIDS FROM A STATIONARY FLUIDIZED BED"

Abstract

A process of removing granular solids from a stationary fluidized bed which fluidizing gas is introduced into the fluidized bed from the bottom, distributed through a jet bank, where a conveying tube is disposed in the fluidized bed above the jet bank, In which conveying tube a gas Jet directed Into the conveying tube pneumatically carries solids upwards through the conveying tube and out of the fluidized bed wherein the Inlet opening (11,11a, 11b) of the conveying tube (10,10a,10b) is disposed 10 to 500 mm above the jet bank (2), that a vertical gas line (13) is disposed at a distance below the inlet opening the upper end of said gas line being disposed approximately at the level of the jet bank that by a gas jet from the gas fine (13) into the Inlet opening of the conveying tube coarse-grained solids are preferably pneumatically discharged from the fluidized bed through the conveying tube, the gas velocity in the conveying tube being at least twice as high as that of the fluidizing gas in the fluidized bed, and that the solids are supplied upwards to a bend (15) of the conveying tube and then downwards to an outlet (12).

Full Text

-1A- DESCRIPTlON: This invention relates to a process of removing relatively coarse-grained solids from a stationary fluidized bed, which contains solids of different grain sizes, wherein fluidlzfng gas Is Introduced Into ih* fluidized bed from the bottom, distributed through a jet bank. Stationary fluidized beds of this kind are generally known. They are characterized by a more or less precisely defined bed surface, which moves for Instance like a boiling flquld. During an extended operation of the fluidized bed solids of a relatively large grain size accumulate in the lower portion of the bed above the jet bank, as they are not or hardly fluidized. This accumulation of coarse grain can be disturbing in many cases, as it can for instance lead to different dwell times of the solids in the fluidized bed and also to an overheating and sintering in the vicinity of the jet bank. The withdrawal of this coarse grain under the influence of gravity downward through the jet bank or laterally through the container wall requires a considerable effort in terms of equipment and control technology. FR patent 2,159,182 to Sames discloses a process for removing granular solids from a Fluidized bed in which air, distributed by a jet bank, is introduced into the fluidized bed from the bottom. Additionally, sir is introduced into the fluidized bed >na gas tines whose inlet openings are disposed-at a significant distance from the jet bank-within the fiuidized bed blowing part of the solids into several conveying tubes. There is no disclosure of arranging the upper end of the gas line approximately at the level of the jet bank (feature d) nor of arranging the inlet openings of the conveying tubes 10 to 500 mm above the jet bank (feature e). Further Sames does not contain any reference to the influence of the distance between the upper end of the gas line on the one hand and that of the inlet openings of the conveying tubes on the other hand each wfth regard to the jet bank, Also If the powder was of different grain siz^s, the arrangement provided by Sames does not allow to remove the coarser (thus heavier) particles because these would accumulate on the jet bank without being subjected to the gas stream out of the air tubes. Accordingly, the process requires powder of uniform size in order to function property/ - 2 - It is the object underlying the invention to be able to at least partly and easily remove the relatively coarse-grained solids accumulating in the lower portion of a stationary flu-idized bed. In accordance with the invention this is achieved in the above-mentioned process in that by means of at least one upwardly directed gas jet supplied separate from the flu-idizing gas part of the solids disposed above the jet bank are blown into a conveying tube, and these solids are pneumatically removed from the fluidized bed through the conveying tube. Since the relatively coarse-grained solids accumulate directly above the jet bank, the same are, as far as they are disposed in direct vicinity of the inlet opening of the conveying tube, blown out of the fluidized bed through the conveying tube together wxth the fine grain solids present near the inlet opening. The solids discharged in this way can be separated into a coarse grain fraction and a fine grain fraction by screening them outside the fluidized bed, where for instance the fine grain fraction is directly recirculated to the fluidized bed and the coarse grain fraction is first of all comminuted or subjected to a special treatment in a second container. The solids in the fluidized bed may have any temperature, the spectrum of grain sizes may include grain sizes in the range from 0.1 to 10 mm, but there are no absolute size limits for this method. The gas velocities of the fluidizing gas usually lie in the range from 0.1 to 1 m/sec, where these figures are measured as empty-tube velocities, here and later on. One or several gas jets are upwardly directed from the bottom against the inlet opening of the conveying tube, they entrain the solids and guide them through the conveying tube, through which they leave the fluidized bed. The gas velocities in the conveying - 3 - tube usually are at least twice as high as the velocity of the fluidizing gas in the fluidized bed. Usually, the gas velocities in the conveying tube are twice to five times as high as in the fluidized bed. It may be sufficient to install in the fluidized bed a single conveying tube with at least one associated gas jet coming from the bottom, but there may very well also be provided a plurality of conveying tubes at different points in the fluidized bed, to each of which at least one gas jet is associated. Embodiments of the method will be explained with reference to the drawing, wherein: Fig. 1 shows a vertical section along line II-II of Fig. 2 through a fluidized-bed reactor in a schematic representation, Fig. 2 shows a horizontal section along line I-I through the reactor illustrated in Fig. 1, and Fig. 3 shows a vertical section through a fluidized-bed reactor with two conveying tubes. The reactor 1 illustrated in Figs. 1 and 2 has a stationary fluidized bed 3 above a jet bank 2. Solids of different grain sizes are charged into the reactor through line 4, and fluidizing gas is supplied through line 5. The fluidizing gas first of all enters a distribution chamber 6, before it flows through the jet bank 2 into the fluidized bed 3. The fluidized bed has a solid surface 8, through which the gas escapes in upward direction, where a certain amount of the fine-grained solids is entrained. The gas leaves the reactor through the outlet 9, and is supplied for instance to a de-dusting not represented here. - 4 - At the wall of the reactor 1, see Figs. 1 and 2, a conveying tube 10 is provided, which has an inlet opening 11 and an outlet 12. The inlet opening 11 lies above the jet bank 2 by the vertical distance (a), where (a) usually is 10 to 500 nun. Below the conveying tube 10 and also directly below the jet bank 2 a vertical gas line 13 is provided, through which in a manner not represented here a gas jet is blown from the bottom upwards through the inlet opening 11 into the conveying tube 10. The upper end of the line 13 is disposed approximately at the level of the jet bank 2, so that solids from the fluidized bed 3 constantly flow into the range of influence of the gas jet, which carries the same into the conveying tube 10 and to the outlet 12. It may be expedient to supply the solids coming through the outlet 12, which are relatively coarse-grained, to a comminution or to a not represented second fluidized bed. The fine grain contained in the solids may first be screened out. The number of the conveying tubes installed in the fluidized bed of a reactor may be chosen as desired. In Fig. 3, two conveying tubes 10a and 10b are represented, to which gas lines 13a and 13b, respectively, are associated. The conveying tube 10a is slightly inclined towards the top, and it protrudes beyond the surface 8 of the fluidized bed. On the other hand, the upper bend 15 of the conveying tube 10b lies in the fluidized bed 3 slightly below its surface 8. The inlet openings lla and lib of the two conveying tubes shown in Fig. 3 are slightly flared towards the bottom, but this is not absolutely necessary. The remaining reference numerals of Fig. 3 have the meaning explained already in conjunction with Figs. 1 and 2. Example: Into a continuously operated fluidized bed reactor, which is designed in accordance with Figs. 1 and 2, 1125 kg/h quartz - 5 - sand are charged. 90 wt-% of the sand have a grain size of 0.1 to 0.4 nun, 10 wt-% of the sand have a grain size of 0.5 to 2-2 mm. The jet bank 2 has a surface area of 4.2 m2, the height of the bed is 0.6 m. For fluidizing purposes air is used, whose empty-tube velocity in the vicinity of the bed is 0.2 m/s. In the vicinity of the orifice 11, the air supplied to the conveying tube 10 through line 13 has an empty-tube velocity of 0.6 m/s. The conveying tube has a cross-sectional area of 166 cm , its distance (a) from the jet bank is 100 mm. During an operation of 4 hours, the sand blown out through the conveying tube is collected in a container- The total amount of this sand is 270 kg, of which 180 kg (~ 66.7 wt-%) have a grain size of 0.5 - 2.2 mm, so that preferably coarse grain solids have been descharged. -6-WE CLAIM: 1. A process of removing granular solids from a stationary fluidized bed which fluidizlng gas Is Introduced Into the fluidized bed from the bottom, distributed through a jet bank, where a conveying tube is disposed in the fluidized bed above the jet bank, in which conveying tube a gas jet directed Into the conveying tube pneumatically carries solids upwards through the conveying tube and out of the fluidized bed wherein the inlet opening (11,11a, 11b) of the conveying tube (10,10a,10b) is disposed 10 to 500 mm above the Jet bank (2), that a vertical gas line (13) Is disposed at a distance below (he Inlet opening (he upper end of said gas fine being disposed approximately at the level of the jet bank that by a gas jet from the gas line (13) into the inlet opening of the conveying tube coarse grained solids are preferably pneumatically discharged from the fluidized bed through the conveying tube, the gas velocity in the conveying tube being at feast twice as high as that of the fluidizing gas in the fluidized bed, and that the solids are supplied upwards to a bend (15) of the conveying tube and then downwards to an outlet (12). 2. The process as claimed in claim 1, wherein teet the solids discharged from the fluidized bed through the conveying tube are Introduced into a second fluidized bed. A process of removing granular solids from a stationary fluidized bed which fluidizing gas is introduced into the fluidized bed from the bottom, distributed through a jet bank, where a conveying tube is disposed in the fluidized bed above the jet bank, In which conveying tube a gas Jet directed Into the conveying tube pneumatically carries solids upwards through the conveying tube and out of the fluidized bed wherein the Inlet opening (11,11a, 11b) of the conveying tube (10,10a,10b) is disposed 10 to 500 mm above the jet bank (2), that a vertical gas line (13) is disposed at a distance below the inlet opening the upper end of said gas line being disposed approximately at the level of the jet bank that by a gas jet from the gas fine (13) into the Inlet opening of the conveying tube coarse-grained solids are preferably pneumatically discharged from the fluidized bed through the conveying tube, the gas velocity in the conveying tube being at least twice as high as that of the fluidizing gas in the fluidized bed, and that the solids are supplied upwards to a bend (15) of the conveying tube and then downwards to an outlet (12).

Documents:

00600-cal-1999 abstract.pdf

00600-cal-1999 claims.pdf

00600-cal-1999 correspondence.pdf

00600-cal-1999 description (complete).pdf

00600-cal-1999 drawings.pdf

00600-cal-1999 form-1.pdf

00600-cal-1999 form-18.pdf

00600-cal-1999 form-2.pdf

00600-cal-1999 form-3.pdf

00600-cal-1999 g.p.a.pdf

00600-cal-1999 letters patent.pdf

00600-cal-1999 priority document others.pdf

00600-cal-1999 priority document.pdf

600-CAL-1999-FORM 15.pdf