GB1569721A

GB1569721A - Cooling of solids

Info

Publication number: GB1569721A
Application number: GB53103/77A
Authority: GB
Original assignee: Saint Gobain Industries SA; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Industries SA; Compagnie de Saint Gobain SA
Priority date: 1976-12-23
Filing date: 1977-12-20
Publication date: 1980-06-18
Also published as: CA1079079A; FR2374950B1; AU508637B2; SE7714518L; AU3178177A; IT1088656B; OA05835A; DE2757131A1; FR2374950A1; ES465401A1; BE862204A; ZA777530B

Description

(54) COOLING OF SOLIDS (71) We, SAINT-GOBAIN INDUSTRIES, a Body Corporate organised under the laws of the French Republic, of 62 Boulevard Victor Hugo, 92209 Neuilly Sur Seine, France, 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: The present invention relates to cooling of particulate solids. It finds applications in treatment of minerals and in particular in the treatment of uranium minerals.

Consequently, in the description which follows the invention will be described as applied to uranium minerals, but it is understood that it may be put to use with any other particulate solid. When processed uranium minerals are generally ground, then calcined to be freed from organic matter and water. At the end of these operations the mineral is generally at about 550"C. and the final stage, that is treatment with acid, requires a temperature of about 110 C.

Cooling is often carried out by making a fluidised bed of finely divided solid, said fluidised bed is cooled and the cooled product is removed and the fluidised bed is recharged with hot solid. To cool the fluidised bed it is known to immerse in it a serpentine in which gaseous or liquid cooling fluid circulates. It has also been suggested to inject into the middle of the fluidised bed, at the foot of a discharge duct descending in said fluidised bed directly in contact with the solid, a cold gas under pressure, most frequently air. The gas assures cooling and causes a supplementary expansion at the foot of the duct which causes evacuation of the product in said duct. Rather than inject a cold gas it has been suggested to inject a gas charged with a pulverised liquid, particularly water, to ensure cooling of the fluidised bed. The water is vaporised in its injection duct as the latter penetrates into the fluidised bed and causes expansion, there is assured a certain pressure of gas injected to avoid back flow of the solid into said injection duct and further to deliver a certain rate of feed of gas below the discharge duct in order to carry out discharge in the duct.

To avoid back flow of the solid in the injection duct and on the other hand to allow discharge through the discharge duct, the proportion of water is limited which causes a reduced cooling.

The present invention is intended to make this cooling more efficient in order to allow obtaining on large quantities of solid product with a large drop in temperature.

According to one aspect of the invention there is provided a method of cooling solid particulate material in which the material is fluidised in a fluidised bed and discharged upwardly from the bed through a discharge duct extending into the bed, and a cooling fluid in the liquid state is injected into the bed at a point adjacent the lower end of the discharge duct.

According to another aspect there is provided apparatus for cooling solid particulate material, comprising a fluidisation reactor to form a fluidised bed of the material, at least one tube forming a discharge duct extending upwardly and having a lower end in the fluidised bed, and means to feed a cooling fluid in the liquid state to the bed at a point therein adjacent said lower end.

The liquid preferably should be a liquid of which the temperature of evaporation is less than the desired temperature of the powder solid contained in the fluidised bed.

Advantageously when the desired temperature of the solid is greater than 100"C., the liquid is water.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings which show: Figure 1, a diagram of cooling apparatus according to one embodiment of the invention, Figure 2, a diagram of part of apparatus according to another embodiment.

The cooling device for powder solid shown in Figure 1 of the drawings comprises: - an assembly A for fluidisation and removal of the powder solid means B for recovering the cooled powder solid; - a circuit C for cooling liquid.

The assembly A for fluidisation and removal of the powder solid is formed essentially of a fluidisation reactor 1 with a fluidisation grill 2 at its base, a duct 3 for input of fluidisation gas, generally air, through the grill 2 and a discharge duct 4 for removing the powder solid arranged approximately along the vertical axis of the reactor 1, descending inside the reactor to the proximity of the grill 2 and extending above the reactor at its other end. The reactor 1 receives in its upper part a duct 5 for input of solid to be cooled; the reactor is advantageously pierced at its upper part with an orifice 6 to allow passage of air, possibly provided with a filter and means for recovering dust. The fluidisation grill, in the embodiment described, is a plate of perforated steel, sold under the trade mark PORAL. The duct 4 has at its lower end 7 a widening in the form of a trunk of a cone to favour reception of the powder solid, its upper end being provided with a lateral bend 8 or a "Chinese hat", to cause ejection of the cooled powder solid from the duct and prevent it falling back towards the reactor. A pipe 9 for feed of cooling fluid, in this case water, passes through the removal duct 4 and descends inside to the widened end of the trunk of the cone. This pipe 9 opens into the base of the trunk of the cone 7 of the duct 4 by one or more nozzles 10, fixed or rotatable, or by a portion provided with holes. Heat insulation 11 surrounds the part of the pipe 9 inside the duct 4. This heat insulation may be obtained by surrounding the pipe 9 with an insulating material or covering said pipe 9 with a jacket 11 in which there circulates a fluid, suitably air. Advantageously this pipe 11 also opens in the middle of the fluidised bed in the same region as the pipe 9 for feeding water and may use the same nozzles 10.

The body of the fluidisation reactor 1 is equipped with controls for the level of the product which it contains. These controls 12 are at least three in number and situated at different heights, a control 12a in a low position just above the level of widening out of the lower end of the duct 4 and two controls 12b and 12c at a small distance one from the other in the upper part of the body of the reactor 1. The input duct 5 for the solid product is equipped with a system 13 for stepwise adjustment of the feed functioning under the control of three leveldetecting devices 12a, 12b and 12c, the device 12a controlling admission of the product and the device 12c interrupting feed, the device 12b regulating the feed to an average value. The input for water 9 is provided with two valves for adjustment, a valve 14 altering the feed of water under the action of a thermo-metric probe 15 measuring the temperature of the cooled solid at the upper end of the duct 4 and an "all or nothing" valve 16 controlled by the device 12a interrupting the feed of water when the level of the solid powder product to be cooled descends below the level of device 12a and re-establishing the feed when the same level is reached.

The inputs for water, air and the product will also be equipped with manual valves.

The means B for recovering the cooled powder solid are essentially formed by: an expansion chamber 17 into which opens the duct 4, intended to recover the cooled product; a multi-cyclone dust extractor 18 in communication with the expansion chamber 17 and following it and a belt conveyor 19 situated below the expansion chamber and the dust extractor intended to transport the product towards a subsequent treatment station.

The expansion chamber 17 has an~empty- ing orifice situated in the lowest part, said orifice being provided with a rotating fluid lock or a siphon 20 to avoid any discharge of vapour of cooling fluid.

The use of the dust extractor 18 following the expansion chamber 17 avoids any loss of product and any pollution: the dust extractor is further equipped with a ventilator 21. The dust extractor feeds the fines which it receives onto the conveyor 19 by orifice situated in the lower part, said orifice itself being provided with a siphon or a rotating fluid lock 22.

Following the ventilator 21 which is associated with the dust extractor 18, there is installed the circuit C for recovery of the cooling liquid. It comprises a battery of condensors 23, a holding tank 24 provided with a pipe 25 for feed of fresh liquid and a pump 26 for reinjecting the liquid in the injection pipe 9.

The apparatus described above functions in the manner which will now be described.

Air for fluidisation is sent through the grill 2 by the duct 3. The manual valve for admission of powder solid to be cooled is opened. The solid progressively fills the reactor. The feed of fluidisation air is adjusted such that there is fluidisation and the fluidised bed is dense (about 100% expansion). The levels of the products are equalised in the duct 4 and in the reactor vessel.

When the fluidised bed reaches the level of device 12a, there is produced discharge (that is to say the ascent of the product in the duct 4 and subsequent removal). When there exists a heat insulating duct 11 feeding into the middle of the fluidised bed at the foot of the duct 4, one starts by beginning the discharge by feeding compressed air in said duct 11. If, further, the duct 11 extends to the injection nozzles 10 for water, the sweeping by the air favours unblocking of the nozzles which could become blocked by the powder solid. On feed of this compressed air is present the expansion increases in duct 4 causing rising of the level of solid in duct 4. Solid then flows by the bend 8 into the expansion vessel.

Up to this stage the cooling obtained is small, only produced by contact of the solid with colder air. A manual valve for admission of water is then opened in the pipe 9. Water passes through the pipe 9, heat insulated by the duct 11 containing the circulating air and arrives in the liquid state at the bottom of the duct. It is then injected by the nozzles 10.

The water participates by contact in the cooling of the solid and further it vaporises thus increasing considerably the cooling and further increasing the degree of expansion of the fluidised bed which has the effect of increasing the rate of ascent of the product in the duct 4. The cooled product leaves by the bend 8 of the duct and falls into the expansion vessel 17. The fines are caught by the dust extractor 18, the expansion vessel 17 and the dust extractor 18 then delivering cooled solid onto the conveyor 19.

The water vapour is directed through the ventilator 21 towards a battery of condensors 23, the condensor liquid is returned to the bottom of recuperator 24 and recycled with new water by reinjection pump 26. The evacuation of the product through the duct having been started, the feed of air in the duct 11 may be discontinued.

The expansion of the bed above the expansion necessary for fluidisation is then ensured by the water vapour which forms at the base of the duct.

If the heat insulation of the pipe 9 is only ensured by surrounding it with insulating material or by a double wall forming a jacket which does not open into the bottom of the duct starting is carried out with water at a feed rate which is initially small then progressively increased when the temperature of the bed is small compared with the temperature of vaporisation of the water, but starting may be carried out directly with a large feed when this temperature difference is large.

The water injected absorbs the calories of the solid by contact initially and then by vaporising. When the level in the reactor reaches the device 12b the feed of product is reduced, then automatic adjustment of the level of the product is carried out by the devices 12a, 12b and 12c coupled with the valves for regulating the feed. The feed of water is also automatically adjusted by the valve 14 so that the tempera- ture of the cooled solid can remain constant at temperature sensed by the probe 15.

If the level of a powder product in the reactor vessel 1 descends, because of stoppage of the installations upstream of the apparatus to a level lower than that of the device 12a, the feed of water is stopped by the action of the valve 16 coupled with said device 12a and this prevents the formation of mud in the bottom of the reactor.

The means B and C are heat insulated to ovoid the formation of mud in the expansion vessel and in the dust extractor by premature condensation.

In another embodiment, shown in Figure 2, the water is no longer sent by a pipe 9 inside the duct 4 but by a pipe 27 passing horizontally to the base of the reactor and opening level with the bottom of the widened end 7 of duct 4. In this embodiment the heat insulation of the pipe 27 is effected by the duct 3 for fluidisation air outside the reactor 1 and inside the reactor, the length of the pipe 27 through the hot solid being quite small, the water does not risk being vaporised before being injected into the fluidised bed by nozzle 10.

It is possible with advantage to add to the pipe 27 for feeding water a duct for feeding air opening to the same nozzle 10.

In the case of large units for cooling the duct 4 will not be single but formed of a series of independent ducts all extending into the middle of the same fluidised bed and leading into one or more expansion vessels. Each duct may have its own input of water 9 and possibly its own input of air, or on the other hand it is possible to use a common source for water and pos-sibly for air introduced at the bottom of the reactor and having injection orifices arranged at the base of each duct. The injection of air at the same time as the water at the base of the duct, even though not strictly necessary, has the advantages that it facilitates starting by unblocking the nozzles which otherwise might be obstructed by the powder product and creating starting of discharge, and on the other hand it allows control of the humidity to avoid, in the expansion vessel and dust extractor, condensations which would form muds with the powder product.

Trials with cooling installations of different sizes have been carried out, the powder solid to be cooled being a sand of fine grain size such as the whole product has a grain size less than 300 b and 506my a grain size less than 60 ,a.

Thus for large apparatus having a reactor of diameter from 800 to 1000 cm, a discharge duct of 350 cm diameter, feeding fluidisation air at 100 m3/hr and inject ing 3.75 tonnes of water per hour, there were cooled 20 tonnes of sand per hour from 550 to 110 C.

Trials for determining optimum conditions on a reduced scale gave comparable results, thus with a reactor of 50 cm height, 20 cm diameter, a discharge duct 4 cm in diameter and 250 cm high there was cooled 2 kg of sand from 530 to 200"C. per minute injecting per minute half a litre of water at the base of the duct at 5 cm above the fluidisation grill.

Further, with 350 cm of height of duct, there was cooled per minute 4 kg of sand from 510 to 1600C. injecting d of a litre of water.

The apparatus can be operated without the devices 12b and 12c, the level of the product being a function of the feed of water, said feed being itself determined by the temperature of the product leaving.

Advantageously, the orifice 6 releasing air from the fluidisation reactor will also be connected to a dust extractor to avoid any loss of product and any pollution.

WHAT WE CLAIM IS: - 1. A method of cooling solid particulate material in which the material is fluidised in a fluidised bed and discharged upwardly from the bed through a discharge duct extending into the bed, and a cooling fluid in the liquid state is injected into the bed at a point adjacent the lower end of the discharge duct.

2. A method according to Claim 1, in which the solid is cooled to a temperature not less than 100"C. and the cooling fluid is water.

3. A method of cooling solid particulate material, substantially as hereinbefore described with reference to the accompanying drawings.

4. Apparatus for cooling solid particulate material, comprising a fluidisation reactor to form a fluidised bed of the material, at least one tube forming a discharge duct extending upwardly and having a lower end in the fluidised bed, and means to feed a cooling fluid in the liquid state to the bed at a point therein adjacent said lower end.

5. Apparatus according to Claim 4, in which the means for feeding liquid fluid comprises a nozzle situated at the end of a heat insulated pipe.

6. Apparatus according to Claim 5, in which the heat insulated pipe passes downwardly inside said discharge duct.

7. Apparatus according to Claim 5 or 6, in which the pipe is surrounded by heatinsulating material.

8. Apparatus according to Claim 5 or 6, in which the pipe is surrounded by a jacket in which a gas can circulate.

9. Apparatus according to Claim 8, in which the jacket is provided with an opening adjacent said nozzle.

10. Apparatus according to Claim 4 or 5, in which the means to feed the cooling fluid comprises a pipe for feeding said fluid, entering the base of the fluidisation reactor and having a nozzle opening below the end of the discharge duct in the proximity of the base of the reactor.

11. Apparatus according to Claim 10, provided with a pipe for feeding gas to the same location as the cooling liquid.

12. Apparatus according to any one of Claims 4 to 11, provided with a thermometric probe at the output of the discharge duct arranged to control a valve regulating the rate of feed of liquid.

13. Apparatus according to any one of Claims 4 to 12, in which the reactor has detectors sensitive to the upper level of the fluidised bed at three points of different height, the detectors being coupled to valves arranged to control the rate of feed of solid to the fluidised bed.

14. Apparatus according to any one of Claims 4 to 13, in which the upper part of the discharge duct opens into an expansion vessel to recover the cooled product.

15. Apparatus according to Claim 14, in which the expansion vessel is provided with a dust extractor.

16. Apparatus according to Claim 15, in which the expansion vessel and dust extractor, are equipped with siphons or rotating fluid locks.

17. Apparatus according to any one of Claims 4 to 16, comprising a condensor, a decantation tank and a compressor for recycling said fluid.

18. Apparatus for cooling solid particulate material, substantially as hereinbefore described with reference to Figure 1 or 2 of the accompanying drawings.

19. Particulate solids, when cooled by a method according to one of Claims 1 to 3 or by apparatus according to one of Claims 4 to 18.

20. Minerals containing uranium, when cooled by a method according to one of Claims 1 to 3 or by apparatus according to one of Claims 4 to 18.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. discharge duct of 350 cm diameter, feeding fluidisation air at 100 m3/hr and inject ing 3.75 tonnes of water per hour, there were cooled 20 tonnes of sand per hour from 550 to 110 C. Trials for determining optimum conditions on a reduced scale gave comparable results, thus with a reactor of 50 cm height, 20 cm diameter, a discharge duct 4 cm in diameter and 250 cm high there was cooled 2 kg of sand from 530 to 200"C. per minute injecting per minute half a litre of water at the base of the duct at 5 cm above the fluidisation grill. Further, with 350 cm of height of duct, there was cooled per minute 4 kg of sand from 510 to 1600C. injecting d of a litre of water. The apparatus can be operated without the devices 12b and 12c, the level of the product being a function of the feed of water, said feed being itself determined by the temperature of the product leaving. Advantageously, the orifice 6 releasing air from the fluidisation reactor will also be connected to a dust extractor to avoid any loss of product and any pollution. WHAT WE CLAIM IS: -

1. A method of cooling solid particulate material in which the material is fluidised in a fluidised bed and discharged upwardly from the bed through a discharge duct extending into the bed, and a cooling fluid in the liquid state is injected into the bed at a point adjacent the lower end of the discharge duct.