EP0045890A1 - Fluidized-bed combustion apparatus - Google Patents

Abstract

1. Fluidized bed combustion apparatus, in which, in a container (14) with an inflow floor (10) above an air chamber (1) divided into a plurality of segments, a fluidized bed (2) comprising of an inert material is provided above the inflow floor (10), and the fuel can be supplied to the fluidized bed (2) by way of a plurality of delivery points (9) after heating the fluidized bed (2) by means of a heating burner (8) disposed above a single air chamber segment to the ignition temperature of the fuel, and heat exchanger tubes (7) are disposed in only part of the area of the fluidized bed (2), excluding the area of the fluidized bed (2) with the heating burner (8), characterized in that a) the starting area (2b) of the fluidized bed is directly bounded on three sides by additional available fluidized bed areas (2a, 2c, 2e) ; b) the fluidized bed itself is kept free of partitions ; c) a part of the activatable areas (2a, 2c, 2d, 2f) are only approximately half as large as the starting area (2b) and a further activatable area (2e) ; d) approximately half the fluidized bed area (2d, 2e, 2f) is provided with submerged heat exchanger tubes ; e) the inflow floor (10) slopes towards the ash outlet ; f) at least the walls (3, 4, 11, 11a) of the container (14) are cooled.

Description

The invention relates to a fluidized bed combustion according to the preamble of claim 1.

In particular, fluidized bed furnaces are used for the combustion of lumpy, dusty or muddy fuels for steam or hot water production. The combustion air supplied via nozzles in the inflow floor ensures that the air is evenly distributed on the one hand, and on the other hand this air causes a constant swirling of the fluid.

It is known that the thermal performance of a fluidized bed furnace when the minimum possible fluidized air velocity is set - that is in the partial load range - is limited by the ratio of the volume of the fluidized bed to the heat-dissipating surface. This lower thermal output limit is higher for cooled furnace walls than for non-cooled ones; therefore with small fluidized bed furnaces with the Most commonly used fin tube walls do not manage the amount of heat supplied by coal combustion in order to keep the fluidized bed at operating temperature in this situation. Because of the good heat transfer from the fluidized bed to the fin tube walls, there is always too much heat extraction (Chem. Ing. Techn. 46 (1974), page 180, and process engineering 13 (1979), page 886).

It is also known that fluidized bed furnaces for partial load control are divided into segments on the air box side and this subdivision is continued on the fluidized bed side by built-in walls or fin tube walls, a pressure tube (jet feed tube) being fed through each segment of the inflow floor to supply the fuel. However, it is important to ensure that no partial bed cools down too much at partial load and that the ignition temperature falls below when restarting; Therefore, partial beds that are in operation are switched off and shutdowns are put into operation with a constant partial load (DE-OS 28 14 239).

In order to be able to give preference to the combustion of coal in a fluidized bed furnace over gas or oil furnaces, the unfavorable part-load behavior known especially in the case of small fluidized bed furnaces must be solved. This has not yet been satisfactorily resolved with the fluidized bed combustion plants which have become known to date (VGB-Kraftwerkstechnik 56, (1976), page 509, Energie 31 (1979), page 236).

In addition, the burnout of the coal in the fluidized bed and the heating of the fluidized beds require improvement (VDI report No. 322 (1978), page 37).

The object of the invention is to provide a fluidized bed combustion with simple means, in which a greater burnout and a longer dwell time of the coal in the fluidized bed is achieved, in which the heating is simplified despite the reduction in the number of heating burners and which covers the entire load range in smaller stages .

This object is achieved in a fluidized bed firing of the type mentioned at the outset in relation to a device according to the invention by the characterizing features of claim 1 and in relation to a method by the characterizing features of claim 7. Further developments of the invention are listed in the subclaims.

In the solution according to claim 1, it is therefore possible to approach a small area of the entire fluidized bed by 'whirling up the inert material and bringing it to ignition temperature by means of the heating burner; after the coal has been fed in and ignited, the operating temperature is to be maintained solely by the combustion process of the coal. This is surprisingly possible by keeping the area of the fluidized bed in question free from heat exchange tubes immersed in it. The heat dissipation from the aforementioned

Fluidized bed area can be further reduced in that this area adjoins at least two sides of further fluidized bed areas; here it comes into play that the boundary layer in the swirling and the non-swirling material has a surprisingly high thermal insulation effect - accordingly, in order to achieve the least possible heat dissipation, an area of the fluidized bed that is as central as possible is chosen for the start-up.

With the features of claim 3, the part-load behavior is improved, since the load levels can thus be selected in relatively small steps, especially in the lower part-load range, without a division into a particularly large number of individually operable fluidized bed regions being necessary for this.

Due to the features of claim 4, a circulation of the inert vortex material and the coal is achieved, which has a positive effect both on the improvement of the burnout and on the ash separation, which is particularly important with regard to the partial load mode of operation.

The at least partially cooled walls of the container in which the fluidized bed is operated (claim 5) have the effect that the individual fluidized bed areas in the region of the side walls, the end walls and the inflow floor can be set up specifically for the delivery of a predetermined thermal output.

The outlet ends of the jet feed tubes, which are guided parallel to the inflow floor, extend the dwell time of the carbon particles near the ground and support their circulation in the fluidized bed, which results in an improvement in the burnout.

Individual or group-wise loading of air box segments with vortex air (claim 7) makes it possible to set specific partial load values, it not being necessary to operate the individual segments with fluctuating amounts of vortex air, rather they can be operated under optimal vortex conditions and fine gradations in the partial load can be achieved as a result that different fluidized bed areas with different predetermined power outputs are combined with each other. Approaching a newly to be switched on air box segment and corresponding to a further fluidized bed area can be clocked according to claim 8, i.e. that the segment to be switched on is started up first and when the resulting mixing temperature in the fluidized bed drops below a predetermined value, the newly connected air box segment is first again off u _m. then being hit again; this process can also be repeated several times - this prevents, among other things, that the amounts of vortex air in the individual air box segments have to be variable in order to make it easier to connect a new segment.

Further goals, features, advantages and possible applications The present invention is derived from the following description of an exemplary embodiment with reference to the accompanying drawing. All of the described and / or illustrated features, alone or in any meaningful combination, form the subject matter of the present invention, regardless of their summary in the claims or their relationship.

• Fig. 1: Einen Längsschnitt durch die Wirbelfeuerung im Leerzustand.
• Fig. 2: Den Luftkasten des Anströmbodens in Aufsicht mit Segmenteinteilung.
• Fig. 3: Einen Längsschnitt durch die Wirbelbettfeuerung (_Strömungsverlauf)bei Betrieb) entsprechen Fig. 1.
• Fig. 4: Einen Querschnitt durch das Wirbelbett der Feuerung.
• Fig. 5: Die Leistungsanteile der Luftkastensegmente 1a - 1f.

Show it:

• Fig. 1: A longitudinal section through the vortex firing in the empty state.
• Fig. 2: The air box of the inflow floor in supervision with segmentation.
• 3: A longitudinal section through the fluidized bed firing ( _S flow profile during operation) corresponds to FIG. 1.
• Fig. 4: A cross section through the fluidized bed of the furnace.
• Fig. 5: The power shares of the air box segments 1a - 1f.

In Fig. 1, 1 denotes the air box of the fluidized bed combustion in a container 14, which is divided, for example, by partition walls 12 into air box segments 1a to 1f and thus also the inflow floor 10 into inflow floor segments 10a to 10f. The corresponding ones are located above these segments of the inflow floor 10 Sections 2a to 2f of the fluidized bed (not shown in Fig. 1). 7 with a heat exchanger tube is designated, which is arranged in the water-cooled end wall 11a. In the possibly also water-cooled other end wall 11, a heating burner 8 is mounted opposite the heat exchanger tube 7. The water-cooled tubes of the inflow floor 10, which are equipped with air nozzles (not shown here), through which the so-called jet feed tube ⁹ for the coal extend, which are angled at their outlet end 9a parallel to the inflow floor 10, are designated by 13.

2 shows the division of the air box into the air box segments 1a to 1f, the segments 1a and 1c and 1d and 1f each being approximately half the size of the segments 1b and 1e. The heat exchanger tubes are located above the segments 1d to 1f on the side remote from the heating burner 8. The four beam feed tubes 9_ are located in the segments 1b and 1e. The side walls of the container 14 are designated 3 and 4, respectively.

The movement of the particles in the fluidized bed is also indicated in FIG. 3.

In Fig. 4, the side air box segments 1a and 1c and the middle air box segment 1b are separated from each other by the partitions 12a and 12b. 2b denotes the fluidized bed in motion above the air box segment 1b loaded with combustion air and 2a or 2c denotes the two fluidized bed layers at rest above the air box segments 1a and 1c not loaded with air. 5 and 6 the separating surfaces between the dormant layers and the moving layer.

FIG. 5 shows the individual power fractions of the segments 1a to 1f, each of which corresponds to an area fraction of 25% or 12.5% on the inflow floor 10. By selectively connecting individual segments, all partial load cases with power levels from 10 to 100% can be set.

Embodiment

The fluidized bed consists of inert material, for example sand, ash or limestone. When the furnace starts up, the air box segment 1b is always put into operation. Since the other air box segments are not acted upon by combustion air, forms on this Schichtgut a slope such as _e (Fig. 4 _{(5), (6))} can be seen. The fluidized bed in region 2b of the fluidized bed is then heated using the heating burner (8). The absence of heat exchanger tubes (7) in this area shortens the heating time of the fluidized material, since no additional heat is extracted from the fluidized bed.

After the ignition temperature of the fuel has been reached, coal with a conveying fluid is introduced into the fluidized bed through the jet feed pipes (FIG. 2 (9)) in FIG. 2 (9) and the fluidized material is heated further until an operating temperature of about 850 C is reached. In this operating state, only heat is extracted through the water-cooled inflow floor (FIG. 3 (10)) and the water-cooled end wall (FIG. 3 (11)). The thermal insulation compared to the resting good Material in the other fluidized bed areas is so large that there are no significant heat losses. In this operating state, only 10% of the nominal load (Fig. 5 (1b)) is achieved.

In order to increase the output, the area 1a can now be fluidized, for example, which results in a mixing temperature. If the temperature drops below a predetermined minimum value, the fluidization in area 1a is temporarily set and area 1b is further heated by charging coal. This process is repeated until both areas have the desired operating temperature. Then the fluidized bed combustion has reached 20% (FIG. 5) output. By switching on the area 1c in the same way, a further increase in performance to 30% (FIG. 5) can be achieved. In this operating state, in which the areas 1d to 1f are not fluidized, the slope runs across the center of the fluidized bed.

The heat exchanger tubes installed in the areas 1d to 1f (Fig. 3 (7)) allow further increases in performance of respectively 20 and 30% to be achieved (Fig. 5). The connection of these areas happens in the manner described. With a desired output of 80%, e.g. B. only areas 1b, 1d to 1f in operation. In this case, coal is also fed into the fluidized bed through the steel feed pipes (FIG. 2 (9)) located in area 1e.

Thus, by switching individual sections on and off, any desired output of the fluidized bed furnace can be operated between 10 and 100% in load levels of 10%.

Claims (8)

1. fluidized bed combustion, in which in a container (14) with an Antsrömboden (10) over a z. B. divided into segments 1a to 1f air box (T) is provided from a comparatively inert material continuous fluidized bed (2) above the inflow floor (10) and fuel after heating the fluidized bed by means of a heating burner (8) to the ignition temperature of the fuel can be applied in the fluidized bed, characterized in that a) only one area (2b) of the fluidized bed (2) is provided with the heating burner (8) over a single air box segment (1b), b) at least the fluidized bed region (2b) has one or more feed points for the fuel supply (jet holder pipes (9)) and c) Heat exchanger tubes (7) are only arranged in the areas (2a and 2c to 2f) excluding the area (2b) of the fluidized bed (2) with the heating burner (8) above the air box segments (1a and 1c to 1f) there. 2. Fluidized bed firing according to claim 1, characterized in that the area (2b) of the fluidized bed is adjacent to at least two sides of further fluidized bed areas. 3. Fluidized bed combustion according to claim 1 or 2, characterized in that the fluidized bed areas (2a, 2c, 2e) adjoining the area (2b) of the fluidized bed are at least partially free of immersed heat exchanger tubes (7). 4. fluidized bed combustion according to one or more of claims 1 to 3, characterized in that the inflow floor (10) is inclined. 5. fluidized bed combustion according to one or more of claims 1 to 4, characterized in that the walls of the container (14) are at least cooled. 6. Fluidized bed combustion according to one or more of claims 1 to 5, characterized in that the outlet ends (9a) of the jet feed tubes (9) are guided parallel to the inflow floor (10). 7. A method for operating a fluidized bed combustion according to claim 1, characterized in that the air box segments are acted upon individually or in groups with fluidized air. 8. The method according to claim 7, characterized by clocked application of a swirling air box segment to be switched on.

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