GB2155161A

GB2155161A - Furnace equipment for processing a mixture of substances

Info

Publication number: GB2155161A
Application number: GB08504613A
Authority: GB
Inventors: De Voorde Leopold Carlos Van; Julien Jean Leopold Gijbels
Original assignee: Centre dEtude de lEnergie Nucleaire CEN
Current assignee: Centre dEtude de lEnergie Nucleaire CEN
Priority date: 1984-02-24
Filing date: 1985-02-22
Publication date: 1985-09-18
Also published as: IT8547720A0; BE901774A; JPS60178209A; GB2155161B; FR2560425B1; GB8504613D0; FR2560425A1; DE3506352A1

Abstract

Equipment for processing a mixture of combustible and incombustible substances, e.g. radio-active wastes, includes a furnace (2) comprising an outer shell (14); a bottom (15) with a discharge opening (5); an inner body (16) which defines with the shell (14) an annular space (42) and is spaced from the bottom (15) to define a combustion chamber (43); a burner (3) inside the top of a bell (29) of the inner body; a device (1,4) for feeding the charge into the space (42); means (30,31,37 and 25,36) for feeding combustion air; and, within the space (42), a rotary charge distributing device (17) and a rotary charge feeding device (19). The feeding device (19) lies between the inner body (16) and the distributing device (17) below which it projects, and is provided with members (20) to press down the charge and members (21) to advance the charge into chamber (43). A cover (26) closes completely the space (42) so that all discharge is via the opening (5), beyond which are after burning chambers and a slag granulator. <IMAGE>

Description

SPECIFICATION Equipment for processing a substance mixture, and method to be worked with such an equipment The invention relates to an equipment for processing a substance mixture, with an incineration furnace which is comprised of - an outer wall which comprises - an outer shell and - a bottom with a discharge opening, - an inner body which reaches down to a distance from the bottom, bounds together with the outer shell a ring-like space, and forms inwardly a bell, whereby the space between the lower edge of the bell and the bottom forms a combustion chamber, - a cover which closes the ring-like space at the top, - a burner which is arranged inside the top of the inner body bell, - a device for feeding the substances or mate- rials to be processed, which opens at the top into the ring-like space, means for feeding combustion air to the furnace, - a distributing jacket which lies inside the ring- like space level with that location where the feeding device opens and thereunder, and means to rotate said distributing jacket.

Equipment of this kind is particularly used for processing a mixture of combustible and incombustible waste materials, notably radio-active waste products. The mixture falls in the shape of a natural-slope cone on the furnace bottom. Said natural-slope cone forms the bottom of the actual combustion chamber and protects the furnace bottom. On the surface of said natural-slope cone, the uncombustible materials melt to leave the furnace in molten form through the opening in the bottom.

Equipment of this kind is known from British patent no. 1 420 782.

In said known equipment, the cover which closes at the top the ring-like space is provided with a discharge opening through which part of the combustion gases escapes at the top from the ring-like space. Moisture is thereby removed from the waste products before same fall on the furnace bottom. The post-treatment of the combustion gases is thereby made more difficult.

The invention has among its object to obviate this drawback and to provide an equipment of the above-defined kind the incineration furnace of which has a good efficiency without having to discharge part of the combustion gases through the ring-like space.

In the above-mentioned known equipment, the distribution of the substances to be processed inside the ring-like space is performed by the rotating distributing jacket, but the downwards movement of the fed substances is caused substantially exclusively by gravity. The substances to be processed may thereby be distributed irregularly over the bottom, which may influence disadvantageously the working of the equipment.

A second object of the invention is to provide an equipment of the above-defined kind wherein the substances to be processed are fed more regularly to the bottom of the incineration furnace.

To seek to realise these objects, it is provided - the incineration furnace is further provided with -a feeding jacket, which lies inside the ringlike space between the inner body and the distributing jacket, reaches down to below the distributing jacket, and is provided adjacent the lower edge of the inner body, with feeding scoops, and means for rotating said feeding jacket, and - the cover closes completely the ring-like space at the top.

In a particular embodiment of the invention, the feeding jacket may be provided underneath the distributing jacket but above the feeding scoops, with press-down scoops on the outer surface thereof.

In an advantageous embodiment of the invention, the means for rotating the distributing jacket may rotate said jacket with a speed in the range from zero to fifty revolutions per hour.

In a particularly useful embodiment of the invention, the means for rotating the feeding jacket may rotate same with a speed in the range from a quarter to nine revolutions per hour.

In a particularly useful embodiment of the invention, the incineration furnace may comprise means for cooling the bottom.

Said means may be formed by a wind box secured against the lower side of the bottom and/or by cooling ducts for a cooling liquid, which may also be secured against the lower side of the bottom.

The invention also relates to a method which may be worked by means of the above-described equipment.

The invention thus pertains to a method for the processing of a mixture of combustible and incombustible substances, which comprises feeding said mixture at the top into a space closed at the top which is comprised of a mainly vertical ring-like top part and a mainly horizontal lower part connecting thereto, whereby said mixture fills said horizontal part at least up to the level of the vertical part and forms, inside said horizontal part, a natural-slope cone which opens at the bottom on an opening cut out in the horizontal part, whereby a combustion occurs inside the horizontal part and the complete discharge occurs through the opening.

An object of the invention is to provide a new process of this kind with a better distribution of the substances to be processed.

For this purpose a first series rotating means distribute the mixture at the top inside the vertical part over the whole circumference and other rotat ing means press down the mixture at a lower level inside said vertical part and lead the mixture to the horizontal part.

Other features and advantages of the invention will stand out from the following description of an equipment for processing a substance mixture, and of a method to be worked with such an equipment according to the invention; this description is only given by way of example and does not limit the invention; the reference numerals pertain to the accompanying drawings.

Figure 1 is a diagrammatic lengthwise section through equipment for the processing of a substance mixture according to the invention; and Figure 2 is a diagrammatic lengthwise section through the incineration furnace of the equipment as shown in Figure 1, but drawn on a larger scale and with somewhat more details.

In both Figures, the same reference numerals pertain to the same elements.

The equipment as shown in Figure 1 comprises a supply tube 1 which opens into the uppermost end of an incineration furnace 2 which is fitted at the top with a main burner 3. Said main burner 3 may feed pressurized fuel and air to the incineration furnace 2, in such a way that said furnace may operate under pressure, for example in the range of 2 kPa. The incineration furnace 2 may however also operate under a slight underpressure, for example in the range of -2 kPa. By means of a screw conveyor 4, the substances to be processed, particularly radio-active, contaminated waste, are fed to the incineration furnace 2 through the supply tube 1. The substances to be processed will generally be comprised of a mixture of combustible and incombustible materials.Although the substances to be processed may essentially be comprised for 100 % of incombustible material, the equipment will usually be used for a mixture of 10 to 90 % by weight, preferably 80 to 90 % by weight, combustible substances, and thus of 90 to 10 % by weight, preferably 20 to 10 % by weight, incombustible substances.

Melting agents may be added to the substances to be processed.

The incineration furnace 2 has in the bottom thereof, an opening 5 for substances which are released or formed during the heating or the combustion. Consequentiy the melt of incombustible substances, the combustion gases and combustion residues of combustible substances and the volatile substances released by heating are discharged through said opening.

The incineration furnace 2 opens with opening 5 on an auxiliary combustion chamber 6. Said chamber is made in refractory metal and coated on the inside with refractory material. The liquid combustion residues are separated from the gaseous residues inside the auxiliary combustion chamber 6.

Said auxiliary combustion chamber 6 opens at the bottom into the air-tight sealed water bed of a granulator 8, by means of a water-cooled twinwalled connecting pipe 7. The water bed has a temperature in the range of 80"C. The liquid combustion residues coagulate in the water bed and form pellets which are periodically removed from the water bed by means of a chain conveying device not shown in Figure 1 for clearness'sake, through air-tight sealable openings.

On the one side, an auxiliary burner 9 with its own combustion chamber 10, is connected to the auxiliary combustion chamber 6. Said auxiliary burner 9 retains the temperature inside the auxiliary combustion chamber 6 in the range from 13000 to 1600 C.

On the opposite side, a postcombustion chamber 11 in refractory metal connects to the auxiliary combustion chamber 6. The inner side of chamber 11 is coated with refractory material. The postcombustion chamber 11 opens into outlet 12. Through said outlet the combustion gases escape from the equipment, whereafter they are cooled, possibly washed, and filtered.

The walls of the auxiliary combustion chamber 6 and of the afterburning chamber 11 are of twin design and cooling air passes therethrough.

Secondary air is fed through lines 13 between the auxiliary combustion chamber 6 and the postcombustion chamber 11.

As it appears mostly from Figure 2, the incineration furnace 2 comprises an outer wall comprised of a cylinder-shaped outer shell 14 and a funnelshaped bottom 15, an inner cylinder-shaped wall 16 co-axially fixedly mounted therein which is part of an inner body, a distributing jacket 17 which is rotatably mounted between the outer shell 14 and the inner wall 16 and bears a plurality of outwardly-directed distributing scoops 18, and a feeding jacket 19 which is rotatably mounted between the distributing jacket 17 and the inner wall 16 and bears a plurality of helix-shaped press-down scoops 20 and a plurality of feeding scoops 21.

The outer shell 14 is made of metal. The bottom 15 is made of refractory metal. The opening 5 lies in the centre of said bottom 15 and is surrounded by a cooling duct 22 through which flows cooling water. Said cooling duct 22 is surrounded by a ring 23.

Against the lower side of bottom 15 are formed cooling ducts 24 through which cooling liquid is pumped, and wind boxes 25 through which air is blown.

The innermost parts of the incineration furnace 2, namely the inner wall 16, the distributing jacket 17 and the feeding jacket 19 hang from a removable cover 26 which bears on the outer shell 14.

The inner wall 16 is fast to the cover 26 and thus fixed relative to the outer shell 14.

Between the uppermost edge of the rotatable feeding jacket 19 and the fixed inner wall 16 lies a water seal 27. A water seal 27 is also present between the uppermost edge of the rotatable distributing jacket 17 and the feeding jacket 19 and outer shell 14, respectively.

The inner body comprises besides the inner wall 16, a cone-shaped bell mounted therein, which is comprised of a refractory coating 29. On the smallest uppermost (as viewed) end thereof, the bell 29 bears a wind box 30 which is fed with combustion air through the pipe 31. On the wider lowermost end of the bell 29 is mounted a cooling duct 32 through which cooling liquid is pumped.

The main burner 3 mounted in the centre of the uppermost closed end of bell 29 is fed with liquid fuel through the line 33. The air for the burner 3 is fed through the line 34. Through lines 35 flows cooling liquid for cooling burner 3.

Air for the combustion is fed with an overpressure of 0.2 to 5 kPa relative to the pressure inside the furnace, to the pipe 31 which feeds through wind box 30, pipes 37 which open into bell 29. Air for the combustion is fed also with an overpressure between 0.2 to 5 kPa relative to the pressure inside the furnace, to wind boxes 25 which open through openings 36 inside the furnace.

The combustion air is used simultaneously for cooling the furnace, particularly bottom 15, and it is pre-heated before reaching the inner side of the furnace.

Inspection tubes 38 and 39 pass through the walls of bell 29.

The substances to be processed are fed by the screw 4 driven by a motor not shown, at the top into the ring-like space 41 between the outer shell 14 and the distributing jacket 17. The distributing scoops 18 which are secured to the lowermost end of distributing jacket 17, lie level with the opening of supply tube 1 and distribute the substances to be processed uniformly over the circumference of said ring-like space 41. The distributing jacket 17 is rotated with a speed of twenty revolutions/hour by a motor (not shown in Figure 2).

Said motor drives a transmission mechanism, corresponding to the below-defined transmission mechanism 45 for driving feeding jacket 19. A crown gear 46 is thus set into motion; said crown gear 46 is fixed relative to distributing jacket 17.

A motor (also not shown in Figure 2) drives the transmission mechanism 45 which drives in turn crown gear 47. Said crown gear 47 is fixed relative to feeding jacket 19.

The rotation speed of feeding jacket 19 is three revolutions/hour. In contradistinction to distributing jacket 17, feeding jacket 19 reaches down to the lower edge of inner wall 16. The feeding jacket 19 lies moreover right next to said inner wall 16.

Distributing scoops 20 are distributed spiral-like over that portion lying below distributing jacket 17, of the outer side of feeding jacket 19. Said scoops have such a shape as to exert during the revolution of feeding jacket 19, a downwards pressure on the substances which lie in the space 42 between said portion of feeding jacket 19 and the outer shell 14. Said press-down scoops 20 thus press the waste materials uniformly downwards.

Feeding scoops 21 are secured to the lowermost end of feeding jacket 19 and press the substances to be burned out of space 42, into the combustion space 43 proper, between bottom 15 and bell 29.

Said substances form on said bottom 15, a natural-slope cone or funnel the opening of which connects to opening 5.

The main burner 3 starts the combustion of the waste materials inside combustion space 43 and maintains as far as necessary such combustion.

The refractory walls of bell 29 reflect during the combustion, the heat radiation towards the naturalslope cone formed by the materials on bottom 15.

Consequently there is reached inside the combustion space, a temperature which is dependent on the flow rate of the fuel which is burned by burner 3 and on the flow rate and the composition of the waste materials which are fed by screw 4. Said temperature lies in the range from 1300 to 1600or.

In any case said temperature has to lie above the melting point of the incombustible waste materials, in such a way that the uppermost layer of the natural-slope cone reaches said melting point. On the upper surface of the natural-slope cone are formed liquid droplets which flow through opening 5 downwards and as already described hereinabove, are converted inside granulator 8, into solid pellets.

The waste materials proper and the liquid upper layer thereof inside combustion space 43 insulate bottom 15 from the heat, so that the temperature of said bottom, together through the fact that said bottom is cooled on the underside thereof, seldom rises above 70or.

The combustion air which is fed through the openings 36 in bottom 15, to space 43, passes through the burning materials. There are thus formed inside the natural-slope cone on bottom 15, four zones merging into one another, which are respectively comprised of a lowermost layer where the substances are dried by the combustion air, a pyrolysis or pre-combustion layer where heat-unstable waste materials are broken up by the heat from the above-lying layers and from which those gases which are formed therein are carried along with the combustion air, a combustion layer where the combustible components and the gases generated by pyrolysis react with the air oxygen, and a molten layer where the incombustible waste materials and ashes melt into a basic slag.

The combustion gases may only leave the furnace through opening 5, that is thus through the liquid layer on the surface of the natural-slope cone, which layer acts as filter and retains a substantial amount of substance. Due to such flow of the combustion gases, the waste materials burn with a turbulent flame.

The separating of the liquid and gaseous combustion residues occurs, as already described, inside the auxiliary combustion chamber 6.

After the combustion gases have been separated from the liquid combustion residues, burning of the gases is completed inside the postcombustion chamber 11.

During the furnace operation, slightly-pressurized nitrogen is fed through supply tube 1 to the combustion furnace. It is thereby avoided that combustible or explosive gases should rise inside spaces 42 or 41.

The invention is in no way limited to the abovedescribed embodiment and within the scope of the patent application, many changes might be brought to the described embodiment, notably as regards the shape, the composition, the arrangement and the number of the components which are used to embody the invention.

The distributing jacket and the feeding jacket do not necessarily have to have the above-mentioned speeds. Said jackets do not either have necessarily to rotate in the same direction. Wide advantageous speed ranges are given above.

Claims

1. Equipment for processing a substance mixture, with an incineration furnace which comprises: - an outer wall which is formed by - an outer shell and - a bottom with a discharge opening, - an inner body which reaches down to a distance from the bottom, bounds together with the outer shell a ring-like space, and forms inwardly a bell, whereby the space between the lower edge of the bell and the bottom forms a combustion chamber, - a cover which closes at the top the ring-like space, - a burner which is arranged inside the top of the bell of the inner body, - a device for feeding the substances to be processed, which opens at the top into the ring-like space, means for feeding combustion air to the furnace, - a distributing jacket which lies inside the ring- like space level with that location where the feeding device opens and thereunder, and means for rotating said distributing jacket, in which - the incineration furnace is further provided with: - a feeding jacket, which lies inside the ring-like space between the inner body and the distributing jacket, reaches down to below the distributing jacket, and is provided adjacent the lower edge of the inner body, with feeding scoops and means for rotating said feeding jacket, and - the cover closes completely the ring-like space at the top.

2. Equipment according to claim 1, in which the feeding jacket is provided underneath the distributing jacket but above the feeding scoops, with press-down scoops on the outer side thereof.

3. Equipment according to either one of claims 1 and 2, in which the distributing jacket and the feeding jacket rotatably hang from the cover, a first water seal is arranged between the upper edge of the distributing jacket and on the one hand the outer shell, and on the other hand the feeding jacket, and a second water seal is arranged between the upper edge of the feeding jacket and the inner body.

4. Equipment according to any one of claims 1-3, in which the means for rotating the distributing jacket, rotate same with a speed in the range from zero to fifty revolutions per hour.

5. Equipment according to any one of claims 1-4, in which the means for rotating the feeding jacket, rotate same with a speed in the range from a quarter to nine revolutions per hour.

6. Equipment according to any one of claims 1-5, in which the inner body comprises a cylindershaped inner wall and a cone-like refractory coating mounted therein.

7. Equipment according to claim 6, in which the means for feeding combustion air to the furnace, comprise a wind box which is mounted on the uppermost end of the bell of the inner body, an airsupply line which opens on said wind box, and at least one pipe which connects the wind box to the inner side of the bell and runs through the refractory coating.

8. Equipment according to any one of claims 1-7, in which the means for feeding combustion air to the furnace comprise at least one feed which opens on the bottom.

9. Equipment according to any one of claims 1-8, in which the incineration furnace comprises means for cooling the bottom.

10. Equipment according to claim 9, in which the means for cooling the bottom of the outer wall comprise cooling ducts for cooling liquid, which are secured against the lower side of the bottom.

11. Equipment according to either one of claims 9 and 10, in which the means for cooling the bottom of the outer wall comprise a wind box, which is secured against the lower side of the bottom.

12. Equipment according to claims 8 and 11, in which the wind box is part of the means for feeding combustion air to the furnace and communicates through openings with the inner side of the furnace.

13. Method for processing a mixture of combustible and incombustible substances, according to which said mixture is fed at the top to a topclosed space comprised of a mainly-vertical ringlike top part and a mainly-horizontal lower part connected thereto, whereby said mixture fiils the horizontal part at least to the level of the vertical part and forms inside said horizontal part, a natural-slope cone which opens at the bottom on an opening in the horizontal part, whereby combustion occurs inside the horizontal part and the complete discharge occurs through the opening, in which a first series rotating means distribute the mixture at the top inside the vertical part over the whole circumference and other rotating means press down the mixture at a lower level inside said vertical part and lead the mixture to the horizontal part.

14. Method according to claim 13, in which the combustion gases which leave the horizontal part through the opening, are filtered.

15. Method according to. either one of claims 13 and 14, in which a mixture of 10 to 90 weight % combustible substances and 90 to 10 weight % uncombustible substances is processed.

16. Method according to claim 15, in which a mixture of 80 to 90 weight % combustible substances and 20 to 10 weight % uncombustible sub stances is processed.

17. Method according to any one of claims 13- 16, in which the combustion inside the horizontal part occurs at a temperature in the range from 1300 to 16000C.

18. Equipment for processing a substance mixture substantially as hereinbefore described with reference to the accompanying drawings.

19. A method of processing a mixture of combustible and incombustible substances, substan tiaily as hereinbefore described with reference to the accompanying drawings.