EP0080399A1 - Boiler using solid fuels - Google Patents

Abstract

Sulfur is readily and efficiently removed from solid fuel in a boiler installation which comprises a hearth for burning and thereby gasifying the solid fuel, the hearth including a grid supporting a fluidized bed of the solid fuel spread thereover, and a tubular boiler body superimposed on, and integral with, the hearth, the boiler body including a lower portion receiving the gasified fuel from the hearth, an upper portion, a common transverse wall dividing the tubular boiler body into the lower and upper portions, and a burner extending into the upper boiler body portion near the dividing transverse wall and receiving a supply of secondary combustion air. A conduit connects the lower boiler body portion to the burner for feeding the gasified fuel therefrom to the burner, and dust removing and desulfurization cyclones in the conduit remove dust and sulfur from the gasified fuel.

Description

The present invention relates to a solid fuel boiler, and more particularly a coal boiler or any other solid fuel, shale for example, having a significantly high sulfur content.

There is already known a solid fuel boiler, in particular a coal boiler, comprising a fluidized bed hearth constituted by a fluidization support above which the fuel is poured, primary combustion air being blown through said support, and a boiler body with tubular walls over said hearth, a secondary air inlet being provided in said boiler body.

The removal of sulfur poses a delicate problem. This elimination cannot be carried out near the hearth because of the high temperature which is of the order of 1200 ° C. It is then necessary to carry out the desulfurization of the cold flue gases at the outlet of the boiler. This results in a number of drawbacks. On the one hand, the gas volume to be treated is considerable, on the other hand the temperature conditions at this location are no longer favorable to suitable desulfurization, hence the need to reheat the fumes.

The main object of the invention is to avoid the above-mentioned drawbacks.

It essentially consists in applying the technique of fluidized beds to the gasification of fuel. To this end, it plans to combine a gasifier with a conventional boiler, inside a same heating body with two-stage tubular walls, the gases produced by the gasifier being, after desulfurization, burned in the upper stage. forming combustion chamber. The invention is specifically applied to a solid fuel boiler installation comprising a fluidized bed hearth constituted by a fluidization support above which the fuel is poured, primary air being blown through said support, and a body boiler with tubular walls surmounting said hearth of which it is integral, characterized in that the fluidized bed hearth constitutes a gasifier, in that the boiler body is divided into two superimposed parts, respectively lower and upper, by a common transverse wall , and in that a circuit is provided for supplying at least one burner arranged at the base of the upper part, with gas leaving the lower part, said burner being simultaneously supplied with secondary combustion air, and said circuit comprising dust removal and desulfurization means.

The fluidization support is constituted by a mobile mechanical grid ensuring the distribution of the fluidization air and the evacuation of bottom ash.

The transverse wall is a tubular wall formed by folds of the vertical tubes of the boiler body.

The dedusting means advantageously consists of a cyclone capable of separating the flue gases from the hearth from the gas, said takeoffs being recycled into said hearth.

The desulphurization means advantageously include a station for injecting a desulphurizing agent into the circuit, downstream of the dedusting cyclone, a circuit section of a length sufficient to allow the gas desulphurization reaction to be ensured, and a cyclone capable of separating the residues from the desulfurization reaction from the gas.

The section of the circuit corresponding to the gas desulfurization reaction has the shape of an inverted U.

A fan is provided to supply air, on the one hand the fluidized bed hearth, on the other hand the burner.

An air heater is also provided at the outlet of the fan, said air heater being traversed by the fumes discharged by the boiler.

There is also provision, downstream of the air heater, bypass piping allowing direct injection of part of the air supplied by the fan into the lower part of the boiler body.

According to a characteristic of the invention, the cyclones for dedusting and separating the desulfurization residues, integral with the supply columns of the boiler, form therewith an assembly suspended from the frame of the installation, at the same level as the boiler body also suspended from said frame.

In the case where the lower part of the boiler body has four gas outlets, the eight cyclones are arranged around said body and mounted on a support in the form of a frame surrounding said body and fixed to the supply columns of the boiler with which it forms an assembly suspended under the same conditions as above.

• La figure 1 représente schématiquement, en coupe-élévation l'installation de la chaudière ;
• La figure 2 représente, de façon également schématique, une vue de l'ensemble suspendu ;
• La figure 3 est une coupe suivant la ligne A-A de la figure 2 ;
• La figure 4 représente, dans le cas particulier d'une installation comportant quatre sorties de gaz, une coupe du corps de chaudière effectuée au niveau des dites sorties, et une vue de dessus des circuits extérieurs au corps de chaudière.
• La figure 5 représente, vu en plan, le support des cyclones drune telle installation.

The invention will be better understood by referring to the description which follows, given with reference to the appended drawings, concerning a particular embodiment given by way of nonlimiting example.

• Figure 1 shows schematically, in sectional elevation the installation of the boiler;
• Figure 2 shows, also schematically, a view of the suspended assembly;
• Figure 3 is a section along the line AA in Figure 2;
• FIG. 4 represents, in the particular case of an installation comprising four gas outlets, a section of the boiler body made at the level of said outlets, and a top view of the circuits external to the boiler body.
• FIG. 5 represents, seen in plan, the support of cyclones of such an installation.

In Figure 1, we see a fluidized bed hearth surmounted by a boiler body 1 with tubular walls. The body 1 has two superimposed parts, respectively lower 1 a and upper 1 b. These two parts are separated by a common transverse wall 2. Said wall is advantageously constituted by folds of the vertical tubes of the boiler cDrps 1.

The fluidized bed hearth essentially comprised a fluidization support 3 integral with the boiler body 1 above which the fuel, coal for example, is poured out, through a chute 4, and under which the primary fluidization air supplied by a fan 5 then heated by a heater 6.

In a particularly advantageous manner, the fluidization support 3 is constituted by a movable mechanical grid, substantially inclined, capable of ensuring the distribution of air and the evacuation of bottom ash through outlet 7.

The gas produced leaves the fluidized bed hearth at a temperature of the order of 1200 °. It passes through part 1a of the boiler body in order to be evacuated therefrom by the piping 8, substantially below the wall 2, at a temperature of approximately 900 ° which is particularly farrable at its desulfurization. Part 1a plays, in this respect, the role of a cooling chamber. The piping 8 brings the gas to a dedusting cyclone 9 capable of separating from the gas the flights from the fluidized bed essentially constituted by unburnt materials and ashes, the latter being normally evacuated with clinkers. These flights collect at the bottom of the cyclone 9 from where they are recycled into the fluidized bed by the pipe 10. The dedusted gas is then desulfurized. For this purpose, there is provided, above the cyclone 9, an injection station 11 for a desulfurizing agent preferably based on C0 ³ Ca in the form of dolomite, limestone or chalk for example. The desulfurization reaction takes place along the piping 12 of the gas circuit. This piping must have a sufficient length to ensure as complete desulphurization as possible. It advantageously has the form of an inverted U, the descending branch of which brings the gas to the inlet of cyclone 13 which ensures the separation of the residues from the desulfurization reaction: CaS, CaO and CO ³ Ca in excess for example. The clean and desulphurized gas leaves the cyclone 13 via the pipe 14 which brings it to a burner 15 arranged at the base of the upper part 1b of the boiler body. The burner 15 is simultaneously supplied with secondary combustion air by the pipe 16 which is connected at 17 to the pipe 18 for supplying primary fluidization air. The upper part 1b constitutes a conventional boiler combustion chamber. The fumes leaving this chamber heat superheater bundles 19 and economizers 20 and the air passing through the heater 6.

A pipe 21 connected to the pipe 18 for example upstream of the point 17 makes it possible, if necessary, to directly bring a certain amount of air into the lower part 1a. This makes it possible to modify the quantity of secondary air admitted to the burner 15. This possibility is particularly advantageous when the installation is operating at reduced speed, to achieve partial secondary scusting in part 1 b of the boiler body, having the effect of limiting the drop in temperature of the gas leaving by 1 a and not going too far from the favorable temperature range gas desulphurization.

Figures 2 and 3 illustrate the installation of the installation. For reasons of clarity, the outline of the boiler 1 has simply been traced and the various elements of the air circuit have been removed.

The frame of the installation includes four posts such as 22 at the top of which are mounted horizontal beams, such as 23, supporting spacers 24 which are suspended all the elements of the boiler (hallon, collectors, walls) as well as the support 25 of cyclones 9 and 13, via supply columns, such as 27, of the boiler which are at least two in number.

These columns 27 are supplied with water at their upper part by pipes such as 28 coming from the balloon 30 of the boiler. They in turn supply the base of the boiler via the pipes 29. The advantage of this support method comes from the fact that, on the one hand, the supply columns 27, traversed by the water from the boiler , are practically at the same temperature as the tubes which constitute the walls of the body 1 of the boiler, and that on the other hand, these columns, suspended from the same support (spacers 24) as the boiler, expand downwards from the same way as this one, the origins of the dilations being practically located in the same horizontal plane.

As a result, the cyclones in all circumstances retain their relative position with respect to the boiler body 1, that is to say respectively opposite the orifice outlet of part 1a of the body and opposite the burner 15.

Figures 4 and 5 relate to a particular embodiment according to which the lower part 1a of the boiler body has four gas outlets. Each gas outlet is then associated with a complete circuit going from said outlet to the corresponding burner. The components of each circuit include a pipe such as 8, a dedusting cyclone such as 9, a desulfurization pipe such as 12, a cyclone for separating desulfurization residues such as 13, a pipe such as 14 and a burner such that 15. These different elements are represented in FIGS. 4 and 5, assigned the indices a, b, c, and d. It can be seen that each outlet pipe 8 c for example is connected to an associated burner 15 c which is arranged on the adjacent face of the tubular wall of the boiler and not on the same face. FIG. 5 illustrates the supports of the eight cyclones mounted on a frame 26 surrounding the boiler body and suspended like the latter, from all of the supports 24 via the supply columns 27 on which it is hung.

Although the invention has been described with reference to a particular embodiment, it goes without saying that it is in no way limited to it and that modifications may be made to it without departing from its field. We can in particular replace any of the means described by a technically equivalent means. The invention therefore covers, in addition to the example described, its various alternative embodiments.

Claims (11)

1. Installation of a solid fuel boiler comprising a fluidized bed hearth constituted by a fluidization support (3) above which the fuel is discharged, primary air being blown through said support, and a boiler body ( 1) with tubular walls surmounting said hearth of which it is integral, characterized in that the fluidized bed hearth constitutes a gasifier, in that the boiler body (1) is divided into two superimposed parts, respectively lower (1 a) and upper (1 b), by a common transverse wall (2), and in that a circuit is provided for supplying at least one burner (15) arranged at the base of the upper part (1 b), with outgoing gas of the lower part (1a), said burner being simultaneously supplied with secondary combustion air, and said circuit comprising means for dedusting and desulfurization. 2. Installation according to claim 1, characterized in that the fluidization support (3) is constituted by a movable mechanical grid ensuring the distribution of the fluidization air and the evacuation of bottom ash. 3. Installation according to claim 1, characterized in that the transverse wall (2) is a tubular wall formed by folds of the vertical tubes of the boiler body (1). 4. Installation according to one of claims 1 to 3, characterized in that the dust removal means is constituted by a cyclone (9) capable of separating the flames from the hearth from the gas, the so-called flaps being recycled into said hearth. 5. Installation according to claim 4, characterized in that the desulphurization means comprise a station (11) for injecting a desulphurizing agent into the circuit, downstream of the dedusting cyclone (9), a circuit section (12 ) of sufficient length to allow ensuring the desulfurization reaction of the gas, and a syclone (13) capable of separating from the gas the residues of the desulfurization reaction. 6. Installation according to claim 5, characterized in that the section (12) of the circuit corresponding to the desulfurization reaction has the shape of an inverted U. 7. Installation according to claim 1, characterized in that there is provided a fan (5) for supplying air, on the one hand the fluidized bed hearth, on the other hand the burner (15). 8. Installation according to claim 7, characterized in that there is provided an air heater (6) at the outlet of the fan (5), said air heater being traversed by the fumes discharged by the boiler. 9. Installation according to claims 7 and 8, characterized in that there is provided, downstream of the air heater (6), a bypass piping (21) allowing direct injection of part of the air supplied by the fan (5) in the lower part (1 a) of the boiler body (1). 10. Installation according to one of claims 1 to 9, according to which the boiler body (1) is suspended from the frame of said installation, characterized in that the dedusting cyclones (9) and of separation of the desulfurization residues ( 13), integral with the supply columns (27) of the boiler, form therewith an assembly suspended from the frame, at the same level as the boiler body (1). 11. Installation according to claim 10, characterized in that four gas outlets are provided from the lower part (1a) of the boiler body (1), and in that the eight cyclones are arranged around the said body and mounted on a frame (26) surrounding the said body, and fixed to the supply columns (27) of the boiler, with which it forms an assembly suspended from the frame, at the same level as the boiler body (1).

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