GB1582828A - Apparatus for the controlled removal and cleaning of settled oversize material from an operating fluid - Google Patents

Description

(54) APPARATUS FOR THE CONTROLLED REMOVAL AND CLEANING OF SETTLED OVERSIZE MATERIAL FROM AN OPERA rnG FLUID BED (71) We, WEST'S ( US:ALASIA) LIMI- TED, a company incorporated under the laws of the United Kingdom, of 1 Chandos Street, St. Leonards, New South Wales 2065, Australia, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an apparatus for the controlled removal and cleaning of settled oversize particulate material from an operating fluid bed.

In a typical alumina feed material sample, 90% of the sample would be of a size less than 150 microns with the remainder of the material being up to 10 to 15 mm. Preferably the desired final feed material would contain particles less than 300 microns.

Screening at particle sizes of less than 1 or 2 mm requires large screen areas where the large particle size component is only a small part of the total feed. Thus screening efficiency is low and additionally considerable blinding may occur.

Where the feed material has come from a kiln the temperature may be in excess of 1000 C which is too hot for screen-type units which develop structural problems at such high temperatures.

In the fluidization of solid particles with a gas it is well known that for any given gas velocity the particle size range of the solid must be kept within certain limits. Particles which are too fine are carried out of the bed in the gas stream and any oversize particles tend to settle out in a layer at the bottom of the bed. The fine particles present little problem as they can be collected in a cyclone but the oversize, if allowed to accumulate, will eventually cause the bed to de-fluidize.

To avoid interference with fluidization when dealing with materials containing oversize particles, it is necessary to discharge the settled particles at the rate at which they are being deposited and if this can be done in a controlled manner it provides a convenient means of separating coarse and fine particles, the coarse being discharged from the bottom and theThi-e--overllowing from the top of the fluidized bed.

Various schemes have been put forward ifl the prior art for discharging oversize particles from a fluidized bed. All the schemes so far proposed suffer from one or more of the following disadvantages a) There is no easy means of discharging the coarse material without interrupting the fluidization process.

b) There is no system of determining when the correct quantity of material is being discharged.

c) A certain amount of fine material is liable to be discharged with the coarse.

The object of the present invention is to provide a system which overcomes all these disadvantages, firstly by encouraging the oversize particles to settle out in the region of the exit port, secondly by passing the oversize from the exit port into a narrow vertical zone where the depth of accumulated material can be monitored by measuring the pressure drop, and thirdly where a rising flow of gas can be introduced to return any fine material to the fluidized bed above. The oversize can then be discharged from the bottom of the vertical zone either continuously or intermittently by means of a rotary or other form of air-lock valve.

In one broad form the invention provides an apparatus for the controlled removal and cleaning of settled oversize material from an operating fluid bed, comprising a fluid disi tributor plate disposed across the chamber of a fluidized bed apparatus to divide the cham- ber into an upper and a lower portion; a feed entry port at one end of said upper portion; a fluid entry port into said lower portion, a fluid exit port from said upper portion; an overflow material exit port between the distributor and the top of the upper portion; at least one underflow material exit port from the upper portion leading to a substantially vertical underflow discharge zone and a further fluid inlet into the vertical zone to direct a fluid countercurrently to the underflow.

Material having a mixed particle size range is introduced into the unit on a continuous or intermittent basis. It enters a chamber (preferably rectangular) which may be part of, or all of, the fluidised zone. In this zone, the material is fluidised by air or other gas and the settlement of the oversize material encouraged.

The design of the gas distributor is such that the larger particles are concentrated towards an underflow offtake. This offtake is also fluidised to give continued cleaning of the larger particles. A typical unit would incorporate a collection zone of about one metre square but -a widely varying size range is envisaged to suit particular applications.

The process is aimed at achieving continuous or intermittent removal of the collected coarse fraction from the offtake either by automatic or manual means, as required.

Sensing equipment may be added to the system to establish the accumulation of the coarse fraction and to initiate a display or alarm when the accumulation reaches certain predetermined proportions. Alternatively, such sensing equipment could initiate other ancillary equipment to permit discharge or removal of the oversize material until the accumulated proportion is reduced to an acceptable predetermined level. Such ancillary equipment could be a rotary or double dump type valve with the sensing system involving the monitoring of the pressure differences within the fluidised bed or the offtake.

The extraction or discharge of the smaller size fraction of the material would be achieved at a point removed from the underflow offtake and would incorporate a weir or' valve control The initial concept is to remove unrequired material from the feed, e.g. tramp, but this need not necessarily be a discarded fraction.

This invention has the advantage that 1) The material separation can be carried out at an elevated temperature. Processes with a temperature above 1000"C are envisaged. These high temperature processes would be completely out of the range of screen type units.

2) Material heating or cooling can be achieved while the separation is proceeding, the temperature of the fluidising gas being either above or below that of the process material as required.

3) The equipment involves a minimum of moving parts and hence leads to reducing operating and maintenance costs.

4) It is possible to concurrently remove fine or dust particles from the treated materials, this fraction being conveyed from the apparatus in the exhaust gas stream.

5) The unit when appropriately sized may be also used as a conveyor whilst concurrently carrying out the separation duty.

Normally, the fluidising and upper zone velocities would be maintained at levels as to reduce entrainment of fines in the fluidising gas exit stream. The degree of entrainment would depend upon the grading of the material being treated and the wider this grading, the more likely it is that entrainmeiit would occur. If necessary, the offgas would be run through a collector to recover the entrained solids.

An inverted weir may be disposed adjacent the feed entry port to prevent short circuiting.

A rectangular shape discourages such short circuiting (i.e. the material progress through the unit is linear), whereas a circular or square shape encourages back mixing and -short circuiting is more likely to occur.

The separa,tor, can, be incorporated within the cooler of a calcination plant and hence can be added to an existing system quite easily with no additional fluidising gas requirement- dr re-arrangement of equipment.

The apparatus of this invention cleans the underflow by use of gas injection within the underflow pipe.

The flow of material from this pipe is controlled as required and can be automatically triggered by monitoring the pressure drop within the material above the outlet. This pressure drop is a function of the depth of the collected material.

The' discharge is controlled by valves that are external to the unit and hence are easily maintained and not subjected to excessive tempe,ratures.

The collected material that is retained with the whopper shaped bottom of the unit acts as an efficient distributor of the fluidising gases.

The design can ensure that this be retained for long periods thus permitting an extremely high removal of fines. Tests have indicated efficiencies approaching 99 % with a basic -100 micron feed and a cut at 1200 microns.

The presence of this collected material and its operation as a distributor also means that the gas distribution system incorporated within the unit can be very simple and does not need to be of sophisticated materials of construction as the stagnant layer protects it from over-temperature conditions.

The invention will now be described by way of example only, with reference to the accompanying drawings, wherein Fig. 1 is a side elevational section through the apparatus; and Fig. 2 is an end elevation of the apparatus of Fig. 1.

As can be seen from the sectionalised views in Figs. 1 and 2, the feed material comprising unseparated particulate matter is introduced into the apparatus 4 through entry port 5.

The apparatus 4 is preferably of rectangular cross-section to provide a linear flow path from material inlet port 5 to the remote discharge outlets 6 and 7.

An inverted weir 8 disposed across the path from inlet 5 to outlets 6 and 7 prevents short circuiting and/or back-eddies of the feed material.

Fluidising gas is introduced through port 15 into a lower chamber 9 and passes through a series of orifices in a gas distributor 10 to fluidize the particulate matter in the apparatus 4.

The fluidising gas is maintained at an adequate flow to expand the bed but not too excessive as to "blow" the particulate matter out of the apparatus 4 with the used gas through port 11.

The distributor incorporates a sloped portion 10a which channels larger particles towards an additional outlet duct 12. As the larger particles move down the outlet 12 they are further "cleaned" or separated from fines by further fluidising gases which are fed into the outlet duct 12 through jets 12a and travel up the duct 12 against the downwards path of the underflow material.

The fines which comprise the bulk of the particulate matter are discharged from the apparatus 4, after fully traversing the unit, through discharge outlet 6.

The discharge outlet 7 can be used to discharge material that passed through the unit without being collected in the underflow outlet 12.

The outlets 12 and 7 incorporate valves 13 and 14 which allow for continual or intermittent discharge depending upon the requirements of loading in the outlet ducts 12 and 7, or ensuring large retention times for high removal of fines.

Pressure differential sensing means 16 can be utilised to activate automatic discharge valve 13 or increase or decrease air flow through jets 12a or port 15.

As shown in the dawings the longitudinal and depth dimensions of the bed can be varied and would depend upon the design parameters dictated by the feed material.

WHAT WE CLAIM IS 1. An apparatus for the controlled removal and cleaning of settled oversize material from an operating fluid bed, comprising a fluid distributor plate disposed across the chamber of a fluidized bed apparatus to divide the chamber into an upper and a lower portion; a feed entry port at one end of said upper portion; a fluid entry port into said lower portion, a fluid exit port from said upper portion; an overflow material exit port between the distributor and the top of the upper portion; at least one underflow material exit port from the upper portion leading to a substantially vertical underflow discharge zone and a further fluid inlet into the vertical zone to direct a fluid countercurrently to the underflow.

2. The apparatus of claim 1 wherein the chamber has a rectangular cross section in the horizontal plane.

3. The apparatus of claim 1 or 2 wherein the underflow material exit port is located at a position closer to the feed entry port than the overflow material exit port and wherein a sloped portion is provided in said distributor said sloped portion 'being sloped at an angle to the horizontal to direct the larger particles towards the underflow exit port.

4. The apparatus of anyone of claims 1 to 3 wherein there is provided an inverted weir extending across said upper chamber between the feed entry port and the material exit ports and having a gap between its lower edge and said distributor.

5. The apparatus of any one of the preceding claims wherein there is provided a further underflow discharge port at the end of the upper portion adjacent said overflow exit port and located at the level of said distributor.

6. An apparatus for the controlled removal and cleaning of settled oversize material from an operating fluid bed substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. circuiting and/or back-eddies of the feed material. Fluidising gas is introduced through port 15 into a lower chamber 9 and passes through a series of orifices in a gas distributor 10 to fluidize the particulate matter in the apparatus 4. The fluidising gas is maintained at an adequate flow to expand the bed but not too excessive as to "blow" the particulate matter out of the apparatus 4 with the used gas through port 11. The distributor incorporates a sloped portion 10a which channels larger particles towards an additional outlet duct 12. As the larger particles move down the outlet 12 they are further "cleaned" or separated from fines by further fluidising gases which are fed into the outlet duct 12 through jets 12a and travel up the duct 12 against the downwards path of the underflow material. The fines which comprise the bulk of the particulate matter are discharged from the apparatus 4, after fully traversing the unit, through discharge outlet 6. The discharge outlet 7 can be used to discharge material that passed through the unit without being collected in the underflow outlet 12. The outlets 12 and 7 incorporate valves 13 and 14 which allow for continual or intermittent discharge depending upon the requirements of loading in the outlet ducts 12 and 7, or ensuring large retention times for high removal of fines. Pressure differential sensing means 16 can be utilised to activate automatic discharge valve 13 or increase or decrease air flow through jets 12a or port 15. As shown in the dawings the longitudinal and depth dimensions of the bed can be varied and would depend upon the design parameters dictated by the feed material. WHAT WE CLAIM IS

1. An apparatus for the controlled removal and cleaning of settled oversize material from an operating fluid bed, comprising a fluid distributor plate disposed across the chamber of a fluidized bed apparatus to divide the chamber into an upper and a lower portion; a feed entry port at one end of said upper portion; a fluid entry port into said lower portion, a fluid exit port from said upper portion; an overflow material exit port between the distributor and the top of the upper portion; at least one underflow material exit port from the upper portion leading to a substantially vertical underflow discharge zone and a further fluid inlet into the vertical zone to direct a fluid countercurrently to the underflow.

2. The apparatus of claim 1 wherein the chamber has a rectangular cross section in the horizontal plane.

3. The apparatus of claim 1 or 2 wherein the underflow material exit port is located at a position closer to the feed entry port than the overflow material exit port and wherein a sloped portion is provided in said distributor said sloped portion 'being sloped at an angle to the horizontal to direct the larger particles towards the underflow exit port.

4. The apparatus of anyone of claims 1 to 3 wherein there is provided an inverted weir extending across said upper chamber between the feed entry port and the material exit ports and having a gap between its lower edge and said distributor.

5. The apparatus of any one of the preceding claims wherein there is provided a further underflow discharge port at the end of the upper portion adjacent said overflow exit port and located at the level of said distributor.

6. An apparatus for the controlled removal and cleaning of settled oversize material from an operating fluid bed substantially as hereinbefore described with reference to the accompanying drawings.