AU645517B2

AU645517B2 - Method and device for adjusting the level of the bed in a fluidized bed kiln

Info

Publication number: AU645517B2
Application number: AU61844/90A
Authority: AU
Inventors: Rene Biche
Original assignee: Fina Research SA
Current assignee: TotalEnergies Onetech Belgium SA
Priority date: 1989-09-01
Filing date: 1990-08-31
Publication date: 1994-01-20
Anticipated expiration: 2010-08-31
Also published as: DK0489766T3; DE69018267D1; BE1002715A3; EP0489766A1; DE69018267T2; WO1991003316A1; PL164343B1; ATE120381T1; PL286705A1; ES2070333T3; EP0489766B1; AU6184490A

Abstract

The excess material is extracted from the fluidized bed by a conduit suitable for the outflow of this excess. The extraction point in the fluidized bed is at the desired height for the bed, and extraction is controlled by a pneumatic seal. The excess material can be retrieved, cooled and possibly recycled in whole or in part after being crushed and sifted.

Description

Translation of replacement sheets filed in respect of PCT/BE90/00048 PROCESS OF TREATMENT OF COALS IN A FLUIDIZED BED KILN The invention relates to a method of treating coals by surface extraction for fluidized bed kilns. The invention relates more particularly to a method enabling coals to be treated in a fluidized bed kiln by the adjustment of the level of the fluidized bed. The invention also relates to a device for the treatment of coals in a fluidized bed kiln by the adjustment of the level of the fluidized bed.

In a fluidized bed kiln the velocity of the gas, which ensures fluidization (in general, air or a mixture of air and recycling gas), is generally adequate to enable the ash to fly away, since it is sufficiently fine. More particularly, if coals are used whose combustion produces less than approximately ash, the sand particles of the bed are able to abrade the ash, enabling it to be eliminated from the bed.

However, at present it must be possible to use coals with higher ash contents which produce more ash, since considerable reserves of such coals exist. Considerable reserves also exist of coals with a high sulphur content; to be able to burn the latter, while respecting the progressively stricter standards concerning atmospheric pollution by sulphur oxides, it is important to trap the latter with lime (whether added or present in the coal), which forms calcium sulphate in a quantity which is larger in proportion as the coal has a high sulphur 2 content. However, when it is produced in a considerable quantity in the fluidized bed, the calcium sulphate tends to form into excessively large masses, which can no longer be abraded or fly away from the bed.

The consequence of the accumulation of ash and/or calcium sulphate in the bed or on its surface, in the case of the largest masses, is that the level of the bed rises, so that constant fluidization and combustion cannot be maintained.

A need therefore exists for a method of treatment in a fluidized bed kiln of coals having a high ash content and/or a high sulphur content. More particularly, a need exists for a method of treatment in a fluidized bed kiln of coals having a high ash content and/or a high sulphur content by the extraction of the excess fraction of material present in the bed.

US Patent 4,167,819 discloses a method of adjusting the pressure of a fluidized bed. The pressure is adjusted by controlling the height of the bed. European Patent 0162599 discloses a principle of coating particles in a fluidized bed at elevated temperature. It proposes a system for retrieving the coated particles as soon as they have reached an adequate size.

It has already been suggested that the excess material should be extracted from the bed from below, but apart from the danger of performing extraction in a zone supporting the fluidization pressure, fluidization losses, extraction vents and overheating 3 of the tubes at the extraction level are observed, and even the local vitrification of the sand.

The process according to the invention for the treatment in a fluidized bed kiln of coals having a high ash content and/or a high sulphur content is characterized in that the excess material present in the bed is extracted via a conduit adapted to the flow of sai.d excess material, the extraction point in the fluidized lbed being at the desired height for the bed, and extraction being controlled by a pneumatic seal adapted to close the said conduit.

In one embodiment of the invention the method also comprises the retrieval and cooling of the excess material.

In another embodiment of the invention, the process also comprises the retrieval of the excess material, (ii) the cooling of said excess material, (iii) the crushing of the coarsest particles, and (iv) the recycling in the fluidized bed of all or part of the crushed particle.

In a third embodiment of the invention, crushing can be replaced by the sifting prior to recycling of some or all of the finest particles.

The device according to the invention for the treatment in a kiln with a fluidized bed of coals having a high ash content and/or a high sulphur content by the extraction of the excess material present in the bed, comprises an inclined conduit whose El4pper end is welded to the inside wall of the kiln at the 4 required height for the bed, and a means for intermittently creating pneumatic seal in the conduit.

The invention will also be described with reference to FIGURES 1 and 2, which illustrate two embodiments of the invention.

FIGURE 1 shows a portion of a kiln (11) with a fluidized bed An inclined conduit (13) is attached by its upper end (14) to the inside wall (15) of the kiln (11) at the required height (16) for the bed When the level of the fluidized bed (12) rises in the kiln (11) above the required level the excess material flows by gravity into the conduit When the flow is to be stopped, a means (not shown) enables a pneumatic seal to be created in the conduit as soon as said joint is removed, the flow of the excess material can resume.

FIGURE 2 shows another embodiment of the invention wherein the device illustrated in FIGURE 1 is completed by a receptacle (18) to which the lower end (17) of the conduit (13) is connected. The receptacle retrieves the excess material flowing from the bed (12) into the conduit To cool said material quickly enough, the receptacle (18) must generally have a cooling device In its lower portion the receptacle (18) has a valve When the receptacle (18) has been substantially filled, a pneumatic seal is created in the conduit (13) to temporarily stop the flow of the excess material from the bed As soon as the material has cooled adequately in the ,,,receptacle the valve (20) is opened and said material is 5 recovered. After the closure of the valve the pneumatic seal in the conduit (13) is eliminated, thus enabling the flow of the excess material to resume.

In all the embodiments the pneumatic seal can be created in general by means of any gaseous fluid; however, most frequently use is made of recycling gas, air or a mixture of the two.

It is not necessary to retrieve the excess material. In one embodiment the coarsest particles are crushed, taking care not to crush the sand, and the mixture is partially or wholly recycled in the kiln. In another embodiment the coarsest particles are removed by sifting, and some or all of the finest particles are recycled. Most frequently, for reasons of facility the recycled particles are reintroduced into the kiln with the fuel and by the same methods. The recycled ash is either fine enough to fly away or is re-extracted subsequently.

The method and device according to the invention are more particularly suitable for adjusting the level of the bed in fluidized bed kilns using coal-with a high sulphur content, such as Gardanne coal, which contains in the order of 4 to 5% sulphur.

Gardanne coal, considerable reserves of which exist in the form of thick and flat veins, contains approximately 20% mainly calcareous ash; during combustion the limestone is converted into lime, which reacts with the sulphur oxides to finally give calcium sulphate or gypsum in pieces of a size which may reach mm. With such a coal the atmospheric pollution standards can be observed as regards sulphur oxides, with the disadvantage that 6 it would be impossible without the method and device according to the invention to use a fluidized bed kiln, since the level of the fluidized bed rises as a result of the content and nature of the ash. In the case of other coals having a high sulphur content which do not contain enough limestone for the sulphur oxides formed to be adequately trapped by a -jaction with the lime produced, it is generally necessary to add limestone or lime to observe the atmospheric pollution standards concerning sulphur oxides; it would therefore appear to be impossible to use such coals in a fluidized bed kiln without the method and device according to the invention.

Claims

2. A process according to claim i, characterized in that it also comprises the retrieval and cooling of the excess material.
3. A process according to claim 1, characterized in that it also comprises the retrieval of the excess material, (ii) the cooling of said excess material, (iii) the crushing of the coarsest particles, and (iv) the recycling in the fluidized bed of all or part of the crushed particle.
4. A process according to claim i, characterized in that 20 it also comprises the retrieval of the excess material; (ii) the cooling of said excess, (iii) the 0• removal of the coarsest particles by sifting, and (iv) the S. recycling in the fluidized bed of all or part of the finest particles. 25 5. An extraction device for treating coals having a high ash content and/or a high sulphur content in a kiln with a fluidized bed, said apparatus comprising an inclined conduit whose upper end is welded to the inside wall of the kiln at the required height for the bed, said conduit being adapted to allow flow of excess material therethrough, and a means for intermittently creating a pneumatic seal in the conduit. pneumatic seal in the conduit. 8
6. A device according to claim 5, wherein a lower end of the conduit is connected to a receptacle for the retrieval of the excess material, said receptacle comprising a means for cooling the excess material and (ii) a valve.
7. A method of treatment in a fluidized bed of coals substantially as hereinbefore described with reference to the accompanying drawings.
8. An extraction device for treating coals having a high ash content and/or a high sulphur content in a kiln with a fluidized bed substantially as hereinbefore described with reference to the accompanying drawings. DATED this 23 day of September 1993 FINA RESEARCH SA Patent Attorneys for the Applicant: F.B. RICE CO. 0