EP0275798A1 - Multifuel heat generator with an integrated circulating fluidized bed for in-situ combustion gas desulfurization - Google Patents

Abstract

The present invention relates to a thermal generator comprising a combustion chamber, a circulating bed and a recovery boiler. According to the present invention, the circulating bed (16) and said combustion chamber (1) have a common wall (17). The present invention can be used for the combustion of fuel with a high sulfur content.

Description

The subject of the invention is a thermal generator capable of burning fuels with a high sulfur content and which, in the form of a compact assembly, makes it possible to decouple the production of useful heat and the desulfurization of the combustion gases.

Strict regulations limiting the emission of sulfur oxides from gaseous effluents from heat generators in protected areas prohibit the use of fuels with a high sulfur content, which, moreover, can have certain economic advantages: This is the case with certain coals similar to lignites, and petroleum residues from refining processes.

Apart from the downstream smoke treatment processes which are generally intended for very high power installations, some thermal units supplied with fossil fuels carry out desulfurization during combustion, by injecting directly into the hearth an absorbent based on calcium (limestone, lime, dolomite ...).

This in-situ desulphurization process is mainly envisaged for solid fuels, and its efficiency (between 30 and 60%) is largely dependent on the temperature distribution in the combustion chamber, while requiring significant consumption of limestone

A different way consists in using fluidized bed boilers called "dry ash", which operate at around 800-900 ° C and in which combustibles and absorbent are intimately brought into contact.

In particular, within a "fast" or "circulating" fluidized bed, comprising a systematic recirculation of solid particles, very high desulfurization rates (85-90%) can be obtained with relatively modest Ca / s ratios. (1.5 to 2 moles / mole).

However, the self-desulfurizing circulating bed heat generator poses a certain number of technological problems.

In particular, its reliability is closely linked to the resistance of the heat exchange bundles, to abrasion and corrosion phenomena.

The essential advantage of the proposed device is that it is weak since it can be implemented using proven techniques. In addition, the generator according to the present invention is compact and compact.

The guiding idea is based on the combination of three main elements arranged in such a way that the exchange surfaces are removed from the rapid flow of solid particles which are often responsible for rapid degradation of these surfaces.

Thus, the proposed generator essentially comprises a combustion chamber or combustion chamber preferably with cold walls, a recovery boiler capturing the sensible heat of the combustion gases and an intermediate circulating bed with no significant internal exchange surface, and whose function is to desulfurize the gases passing between the upstream hearth and the downstream exchanger.

By "cold wall" here is meant that the wall includes means for extract heat.

In general, the present invention relates to a thermal generator comprising a combustion chamber, a circulating bed and a recovery boiler. According to the present invention, the circulating bed and the combustion chamber have a common wall.

This common wall may include at least one orifice for feeding the bed circulating in primary fluid flow and / or at least one orifice for feeding the bed circulating in secondary fluid flow.

This common wall may be a cold wall. Similarly, the other walls of the combustion chamber could be cold walls.

The various cold walls may include a circulation of a fluid.

According to the present invention, the circulating bed and the recovery boiler may have a common wall.

Similarly, the combustion chamber and the recovery boiler may have a common wall.

The walls of the circulating bed may have a coating of thermal insulating material.

The desulphurizing circulating bed, the entrained solid material of which consists essentially of the absorbent, has as its working fluid the hot gases coming from the hearth.

Since the temperature of the gases may vary with the generator load, maintaining the bed at the optimum desulfurization temperature (800-900 ° C) can be obtained by injecting an additional fuel into the reactor, the combustion taking place with excess oxygen from the upstream hearth, and possibly with a supply of fresh oxidant.

The compactness of the generator according to the invention is obtained by an original spatial distribution of the three main elements arranged vertically. This compactness facilitates pre-production.

• - la figure 1 illustre un schéma général du générateur thermique selon l'invention,
• - la figure 2 une vue simplifiée en perspective d'un tel générateur thermique, et
• - les figures 3 et 4 montrent deux variantes particulières de disposition de différents éléments du génétateur thermique.

The present invention will be better understood and its advantages will appear more clearly on description which follows of particular examples, in no way limiting, illustrated by the appended figures among which:

• FIG. 1 illustrates a general diagram of the thermal generator according to the invention,
• FIG. 2 a simplified perspective view of such a heat generator, and
• - Figures 3 and 4 show two particular variants of arrangement of different elements of the thermal generator.

The principle of the compact self-desulfurizing unit according to the invention is illustrated by FIG. 1, which deals with a particular example adapted to the combustion of a solid or liquid fuel, injected in sprayed form into the upstream hearth or combustion chamber .

The combustion chamber 1 is preferably with cold walls, the exchange surfaces 2 being for example of the "membrane wall" type, that is to say that means for circulating a fluid are associated and / or integrated into the walls of the combustion chamber. These cold walls are dimensioned so that the temperature of the combustion gases at the end of the furnace can be in the range 600-850 ° C for all operating stages.

The burner 3 can advantageously be a burner with "low NO _x emission" to limit the emissions of nitrogen oxides, and thus contribute to making the generator completely anti-pollutant.

Under these conditions, the excess air or oxidant can be adjusted so that the quantity of residual oxygen is at least equal to that necessary to carry out the second combustion in the circulating bed 16, which comprises a reactor 6 and a separator 10 which may be of the cyclone type.

The reactor 6 of the circulating bed 16 is attached to the hearth 1 by means of a common wall 17, the communication between these two elements taking place directly by one or more passages arranged in this wall. The flow 41 of primary gas supplying the circulating bed coming from the combustion chamber 1 takes place through the lower passage 4, while the secondary gas flow takes place through the upper passage 5.

The internal walls consist of a layer of insulating refractory material which can be thin 7 resistant to abrasion, and the heat losses are, for the most part, recovered by the heat transfer fluid irrigating the envelope of the hearth 1.

In the example of FIG. 1, the auxiliary fuel and / or the material absorbing sulfur oxides are injected through at least one orifice 9 in the lower part of the reactor 6, which constitutes the dense phase of the circulating bed. However, it will not depart from the scope of the invention if these products are injected at another location in the circulation loop of the circulating bed, in particular by injecting one or both products at the level of the return leg 20.

The oxidizing gases or fumes 41 and 51 coming from the lower 4 and upper 5 passages defined above and serving as the driving fluid and oxidizer in the circulating bed are injected on either side of the dense phase 18 of this bed.

The gases or fumes from the primary flow 41 enter the dense phase 18 via a perforated grid 8, or any other device capable of ensuring good distribution of the gases in the mass of fluidized solids.

The gases or fumes from the secondary flow 51 are injected into the transition zone or diluted zone of the reactor 19 also called the release zone. They can also be distributed by several orifices along the same straight section or staged sections relative to the axis of circulation in the reactor 6. It is the same for the introduction of the primary flow.

The distribution controlled by appropriate means such as flaps of fumes between primary flow 41 and secondary flow 51 makes it possible to control the course of combustion in the reactor 6 and to act on the flow rate of the solids entrained outside the dense zone 18 to be recycled. .

This recycling takes place via the separator 10 which can conveniently be a cyclone as has already been said previously. The recirculation flow is adjusted by a valve 12 which can be of mechanical or hydraulic design, for example a fluidized siphon or an "L-valve".

The reactor 6, cyclone 10 and connecting leg 20 assembly, which constitutes the desulfurizing circulating bed 16, is thermally protected by insulating refractory coatings 7 and 11.

The desulphurized gases 21 leave the upper part of the separator 10 to supply the recovery boiler 13 and transfer heat energy to the exchange surfaces 14 which may consist of tubular bundles.

The fumes are finally discharged through line 15 and directed to the filtration system not shown in the diagram, which can be of a type known to those skilled in the art.

The withdrawal of solid waste not recycled or having escaped from the separator 10 of the circulating bed 16 can be carried out at the base of the combustion chamber, through the orifice 22 which can be closed by a valve 23, at the base of the dense phase 18 of the bed circulating at the level of the grid 8, through the orifice 24 which may include a valve 25 and / or the base of the recovery boiler, through the orifice 26 which can be closed by the valve 27.

In the embodiment illustrated in FIG. 1 which relates to the production of non-superheated steam, the heat transfer fluid 28 such as a water vapor emulsion coming from the combustion chamber is directed to a pressurized tank or tank 29 by a pipe 30. This tank located in the upper part of the generator in the example of Figure 1 also receives in this example the steam water emulsion 28a from the recovery boiler 13, via the pipe 30a. The fluid stored in the capacity 29 is transferred in the form of vapor via a pipe 31 to a member of use such as a turbine 32, a heating network, etc. The heat transfer fluid, after having transferred part of its energy and after condensation in a condenser, not shown, is distributed by a valve means 33 between the supply of heat transfer fluid to the tubular bundles 14 of the recovery boiler 13 and the supply of heat transfer fluid of the irrigation circuit of the combustion chamber 1, this circuit possibly comprising conduits forming an integral part of the walls of this combustion chamber or being able to be formed by a sheet of water.

The path of the heat transfer fluid between the outlet of the turbine 32 and the winnowing 33, the supply of the tubular bundles 14 and the conduits 34, is done by the conduits 35, 36 and 37 shown at least partially in phantom. Of course, these conduits can be thermally insulated.

FIG. 2 gives an example of a practical embodiment of a unit for which the optimum compactness has been obtained by grouping edge by edge the hearth 1, the reactor 6 of the circulating bed 16 and the recovery boiler 13.

The cross sections of these various constituent elements are rectangular (see FIG. 3), which makes it possible to establish close thermal contacts between them, and to minimize the fatal losses of the walls towards the environment.

In FIG. 2, the wall 17 is interrupted before reaching the lower part 38 of the hearth 1 and of the circulating bed reactor 6, thus allowing the simple passage of the lower passage 4 to be produced.

In this figure, the cyclone, the pipes for circulation of the heat-transfer fluid and the burner have not been shown.

The reference 39 designates the orifice allowing the installation of the burner 3 (fig. 1).

The orifice 40 designates the outlet orifice of the reactor 6 of the circulating flow 42 in the direction of the separator 10.

The reference 43 designates the gas inlet orifice 21 coming from the separator 10 and directed towards the recovery boiler 13 (fig. 1).

In the embodiment shown in Figure 2, the circulating bed 6 does not extend in height in the same way as the hearth 1, but is interrupted before by the wall 44. The latter is surmounted by a rectangular formwork 45 in direct communication with the recovery boiler 13 which also has a parallelepiped shape.

The orifice 46 corresponds to the connection of the leg 20 (fig. 1) connecting the separator 10 (fig. 1) to the reactor of the circulating bed 6 (fig. 1).

FIG. 3 represents a section at the level of the reactor of the circulating bed of the generator represented in FIG. 2.

In this FIG. 3, it can be seen that the reactor 6 of the circulating bed 16 is thermally insulated on its four faces by the material designated by the reference 47. The combustion chamber has a plane wall 48 common both to the reactor 6 of the bed circulating in 49 and to the recovery boiler in 50.

The recovery boiler 13 and the reactor 6 of the circulating bed have a common wall 52 which is substantially perpendicular to the planar wall 48.

FIG. 4 represents an alternative embodiment of the device according to the invention for which it is the recovery boiler 13 which has a flat wall 53 common both to the hearth 1 and to the reactor 6 of the circulating bed.

The reference 54 designates the wall common to the hearth 1 and to the reactor 6, this wall possibly being substantially perpendicular to the planar wall 53 of the boiler.

In Figure 1 the valve 33 can be controlled taking into account the call for power due to the turbine 32, the amount of fuel consumed by the burner 3 and / or the temperature of the reactor 6 of the circulating bed.

The introduction of an auxiliary fuel into the circulating bed for example at 9, although not imperative, allows more flexible control of the temperature of the circulating bed.

Claims (9)

1. - Thermal generator comprising a combustion chamber, a circulating bed and a recovery boiler, characterized in that said circulating bed and said combustion chamber have a common wall. 2. - A thermal generator according to claim 1, characterized in that said common wall comprises at least one supply orifice for the bed circulating in primary flow. 3. - A thermal generator according to one of claims 1 or 2, characterized in that said common wall comprises at least one orifice for feeding the bed circulating in secondary flow. 4. - A thermal generator according to one of claims 1 to 3, characterized in that said common wall is a cold wall. 5. - A thermal generator according to one of claims 1 to 4, characterized in that said combustion chamber is with cold walls. 6. - Generator according to one of claims 4 or 5, characterized in that said cold walls include a circulation of a fluid. 7. - Generator according to one of claims 1 to 5, characterized in that said circulating bed and said recovery boiler have a common wall. 8. - Generator according to one of claims 1 to 7, characterized in that said combustion chamber and said recovery boiler have a common wall. 9. - Generator according to one of claims 1 to 8, characterized in that the walls of the circulating bed comprise a coating of thermal insulating material.

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