EP0489226A1 - Process and installation for the improvement of the bed mass combustion during the fluidized bed firing - Google Patents

Abstract

In a process and installation for the improvement of the bed mass combustion in furnaces with a circulating fluidised bed, at least a part of the fly dust arising in the filter (6) is fed to a slag-tap fired furnace and finally burnt therein at such a high temperature that the ash melts and can be taken off as molten slag. The flue gases from the slag-tap chamber (12) are fed to the fluidised-bed furnace in an oxygen-deficient zone, so that the pollutants present in the flue gas are removed in the fluidised-bed furnace. <IMAGE>

Description

The invention relates to a method and a device for improving the bed mass burnout in furnaces with a circulating fluidized bed.

Steam generator systems with a separation of solids in a bed ash fume cupboard, a cyclone ash fume cupboard and a filter, storage of the bed ash and the fly ash in intermediate bunkers and recirculation of the ashes are known. Ash recycling or landfilling is problematic because the low fluidized bed temperatures - the most favorable temperatures for a low NO _x content of the flue gases and good SO₂ incorporation through limestone or dolomite are between 800 and 950 ^o C - no melting of the ash takes place and the grain shape is preserved. Since the bed mass also contains residual coke and calcium sulfate from the desulfurization, ashes from fluidized-bed furnaces differ from those of classic coal dust furnaces. For this reason, such ashes can often not be reused and then have to be disposed of, which is undesirable not only because of the costs but also because of the associated environmental pollution.

In the case of steam generators with a circulating fluidized bed, a burnout of up to 99% can theoretically be achieved. At Low ash contents in the fuel nevertheless result in high proportions of unburned material in the dust, which require a very high return ratio of the mass flow of the dust to the mass flow of the coal. In addition, in many cases the dust can not be used in the cement industry, for example, and must be landfilled or used as backfill mortar in mines.

The invention has for its object to provide a method and an apparatus for improving the burnout of the bed mass, which work properly without excessive increase in the recycle ratio, result in solids that can be used in industry or landfill and avoid an increase in the pollutant content of the flue gases.

The solution to this problem is that in the method mentioned at the beginning, at least part of the flying dust is drawn off according to the invention and fed to at least one furnace furnace.

The combustible solids of the extracted dust are practically completely burned in the melting chamber firing at high temperature, while the solid (ash) can be drawn off as molten slag and granulated in a wet deslagger.

In order to achieve the required combustion temperature in the melting chamber, the extracted dust can be burned in the melting chamber with the addition of air, preferably preheated air and / or an additional fuel. In this way, the temperature of the melting chamber furnace can be adjusted by regulating the air and / or the amount of additional fuel. The additional fuel can consist of coal dust, fuel gas or heating oil.

The flue gases from the melting chamber firing can be fed to the fluidized bed firing in a zone with a lack of oxygen. The NO _X arising in the melting chamber due to the high temperature is then largely reduced to nitrogen and oxygen or CO₂ in this zone. Furthermore, the SO₂ formed during combustion in the melting chamber from the fuel sulfur and the gypsum disintegration and the SO₂ from the fuel sulfur of the fluidized bed furnace are bound to the lime or dolomite added to the fluidized bed. This means that there are no other emission products than normal low-temperature combustion in a circulating fluidized bed; Heavy metals contained in the flying dust are incorporated into the liquid slag in the melting chambers.

Since the combustion in the melting chamber takes place at high temperatures, other solids to be disposed of which are unsuitable for low-temperature combustion in the fluidized bed furnace can be added to the filter dust removed. These solids do not need to come from fluidized bed furnaces or other furnaces.

The device according to the invention is designed in such a way that at least part of the flying dust is fed to at least one burner in at least one melting chamber, which is preferably a ceiling burner.

In order to supply the flue gases from the melting chamber to the fluidized bed furnace, the melting chamber can be connected to a vortex combustion chamber via nozzles or to the wind box under the nozzle floor of the vortex combustion chamber and preferably open into a zone with a lack of oxygen. Such a zone with a lack of oxygen can be located in the lower part of the vortex combustion chamber, so that it is ultimately Excess oxygen required for the burnout only results in the area of the supply of secondary air in the upper area of the swirl combustion chamber.

In order to achieve a sufficiently high ignition temperature for the combustible constituents of the airborne dust when the melting chamber firing is started up, a start-up burner can be arranged in the melting chamber, which can be operated with coal dust, fuel gas or heating oil.

The fluidized bed reactor for the fluidized bed combustion can have a rectangular cross section in the usual way, the lower region of which is tapered. At least one immersion pot, at least one fluid bed cooler for bed mass returned via at least one cyclone separator and at least one melting chamber can then be arranged laterally next to this lower part.

Fig. 1

eine schematische, schnittbildliche Seitenansicht eines Teils eines Großdampferzeugers mit Wirbelschichtfeuerung;

Fig. 2

einen Schnitt entlang der Linie II-II in Fig. 1; und

Fig. 3

eine vergrößerte Darstellung der Schmelzkammerfeuerung.

The invention is explained below with reference to an embodiment shown in the drawing. The drawing shows:

Fig. 1

is a schematic, sectional side view of part of a large steam generator with fluidized bed combustion;

Fig. 2

a section along the line II-II in Fig. 1; and

Fig. 3

an enlarged view of the melting chamber firing.

A vortex combustion chamber 1 can be operated from a large steam generator with fluidized bed combustion, not shown in detail have cooled walls and / or cooling internals. At the top of the fluidized bed combustion chamber 1 there is at least one return cyclone 2, which is used to separate most of the solids or bed mass discharged from the fluidized bed furnace. The separated bed mass passes through a chute 3 into at least one immersion pot or siphon 8. The flue gases and entrained flue dust pass from the return cyclone 2 via a train 4 to secondary heating surfaces 5 and are fed from there via a filter or deduster 6 to a chimney (not shown).

A bed ash extractor 7 is located on the tapered lower part 11 of the vortex combustion chamber 1. The primary air for the vortex combustion chamber 1 is distributed in a wind box 22, which is preferably cooled by tube walls.

Part of the bed mass fed to the immersion pot 8 is fed to a fluidized bed cooler 9 by means of a control valve 10. The bed mass of the immersion pot 8 and the fluidized bed cooler 9 is partly returned to the lower part 11 of the vortex combustion chamber 1 and partly withdrawn.

A melting chamber 12 is arranged in the area of the lower part 11, the immersion pot 8 and the fluidized bed cooler 9. In the upper area of the melting chamber 12 there is a ceiling burner 13 with an air supply 14 and a flight dust supply 15. A start-up burner 21 is arranged in the center of the main burner and serves to set an ignition temperature which is so high that the combustible solid components are in a stable flame 16 burn. The flight dust supply 15 is connected to the deduster 6. The flight dust supply 15 can also be supplied with other solids, for example from the bed ash extractor 7, the immersion pots 8 and the fluid bed cooler 9. Likewise, if the capacity of the melting chamber 12 is sufficient, use further solids, for example ashes from other coal dust furnaces.

The ceiling burner 13 is set, if necessary by supplying additional fuel in the form of coal dust, heating oil or fuel gas in conjunction with preheated air, so that a flame 16 is formed, the combustion temperature of which is so high that the solids melt and melt as liquid slag into a liquid slag extractor 18 reach. There they are granulated in a wet deslagger 19 and taken to downstream settling and transport devices, not shown.

The melting chamber 12 consists of radiation chambers 17 and the flue gases are guided through these radiation chambers 17 to nozzles 20 which open into the lower part 11 of the vortex combustion chamber 1. This lower part 11 forms a zone with a lack of oxygen or reducing conditions, so that the NO _x formed at the high combustion temperatures of the melting chamber 12 is largely reduced. If the combustible constituents of the solids introduced via the dust supply 15 and / or the additional fuel contain sulfur or sulfur compounds, the SO 2 formed during the combustion passes with the flue gases from the melting chamber 12 via the nozzles 20 into the lower part 11 of the vortex combustion chamber 1 it with the lime or dolomite usually supplied to the vortex combustion chamber 1 and is set in this way. Depending on the degree of primary incorporation of the gypsum that is removed from the swirl combustion chamber during desulphurization, there is a different need for lime.

Thus, despite the very high combustion temperatures of the melting chamber 12 as a result of the reductions in the fluidized bed 1, there are no other emission products than in the conventional combustion with a circulating fluidized bed.

In the center of the ceiling burner 13 there is a start-up burner 21 which can be operated with lignite dust, heating oil or fuel gas.

The granulated slag from the melting chamber 12 is practically free of unburned and elutable constituents and can be treated or reused in the same way as the slag of a large steam generator with conventional smelting chamber firing, but without the pollutants which are inevitably formed in a conventional smelting furnace being emitted with the flue gas and by downstream desulphurization and denitrification plants must be disposed of.

Claims (12)

Process for improving the bed mass burn-out in furnaces with a circulating fluidized bed, characterized in that at least part of the fly dust is fed to a melting chamber furnace. A method according to claim 1, characterized in that the flying dust is burned in the melting chamber with the addition of air. Method according to claim 1 or 2, characterized in that the flying dust is burned in the melting chamber with the addition of an additional fuel. Method according to one or more of claims 1 to 3, characterized in that the flue gases from the melting chamber of the fluidized bed furnace are supplied in a zone with a lack of oxygen. Method according to one or more of claims 1 to 4, characterized in that other solids are added to the flying dust. Device for carrying out the method according to claims 1 to 5, characterized in that the circulation system (1, 2, 3, 7, 8) is connected to a melting chamber (12). Apparatus according to claim 6, characterized in that the melting chamber (12) is provided with at least one ceiling burner (13). Apparatus according to claim 6 or 7, characterized in that the melting chamber (12) is connected to a swirl combustion chamber (1) via nozzles (20). Device according to claim 8, characterized in that the nozzles (20) open into a zone (11) of the vortex combustion chamber (1) with a lack of oxygen. Device according to one of claims 6 to 9, characterized in that the melting chamber (12) is connected to the wind box (22) of the vortex combustion chamber (1). Device according to one or more of claims 6 to 10, characterized in that a starting burner (21) is arranged in the melting chamber (12). Device according to one or more of claims 6 to 11, characterized in that at least one immersion pot (8) and at least one fluid bed cooler (9) are arranged under at least one cyclone separator (2) for circulating bed mass, to the side of the swirl combustion chamber (1).

Images