WO2011120603A1

WO2011120603A1 - Method and device for drying coal

Info

Publication number: WO2011120603A1
Application number: PCT/EP2010/068739
Authority: WO
Inventors: Stefan Lechner; Hans-Joachim Krautz; Jörg WASKE; Siegfried Zwiebler
Original assignee: Brandenburgische Technische Universität Cottbus
Priority date: 2010-04-01
Filing date: 2010-12-02
Publication date: 2011-10-06
Also published as: DE102010003613A1

Abstract

The invention relates to a method and a device for drying coal, especially brown coal. Said method comprises the following steps: coal to be dried is provided, the coal to be dried is introduced into a fluidised bed drier (1) and dried therein, the fluidised bed drier (1) comprising a gassing bottom (11) and a heat exchanger (12) arranged above the gassing bottom and comprising heating surfaces, vapours are removed from the fluidised bed drier (1), said vapours containing coal dust, the coal dust is separated from the vapours, and the separated coal dust is fed back into the fluidised bed drier (1), the coal dust being supplied to the fluidised bed drier (1) at at least one point located inside or above the heating surfaces of the fluidised bed drier (1).

Description

Method and apparatus for drying coal

description

The invention relates to a method and an apparatus for drying coal, in particular for drying lignite.

Mine moisture Lignite, also known as raw coal, is largely saturated with water and has a water content of usually between 50 and 60%. For their use in a lignite power plant, it is necessary to dry the raw coal.

To this end, a known approach to dry the raw coal prior to their use in a power plant boiler in a steam fluidized bed dryer. The intensity of the heat transfer in the fluidized beds of a fluidized-bed dryer depends inter alia on the particle size of the fluidized material. Milled lignite is highly polydisperse, ie it has a broad particle size distribution, with a focus on the finer fractions. For this reason - depending on the desired state of fluidization - a more or less strong discharge of coal dust from the fluidized bed occurs. This coal dust is discharged from a vapor outlet of the fluidized bed dryer and separated as part of a vapor purification. In particular, at higher fluidization speeds it comes in this way to an undesirably high dust discharge. A high dust discharge is associated with several disadvantages: apart from the drying of the dust in the fluidized bed dryer, which may not have been completed by the short residence time of the dust, a reduction in the average heat transfer coefficient and segregation of the fluidized bed are undesirable consequences of such dust discharge.

From the document DE 196 20 047 C2, a method and an apparatus for drying brown coal using a steam fluidized bed dryer are known. It is envisaged that a subset of the steam exiting the dryer cleaned, thereby deposited with the steam discharged coal dust and then the deposited coal dust is re-entered into the fluidized bed dryer. For this purpose, a line is provided which returns the coal dust in the lower region of the fluidized bed dryer, namely between the lower edge of the formed in the fluidized bed dryer heat exchanger and the gassing bottom of the fluidized bed dryer.

It is an object of the present invention to provide a method and apparatus for drying coal using a fluidized bed dryer which provides good heat transfer in all layers of the fluidized bed dryer and is accordingly characterized by high drying efficiency. This object is achieved by a method having the features of claim 1 and a device having the features of claim 8. Embodiments of the invention are specified in the subclaims.

Thereafter, the invention provides to register the separated from the vapor purification coal dust back into the fluidized bed dryer, wherein the recycling takes place at a point of the fluidized bed dryer, which is located within or above the heating surfaces of the fluidized bed dryer.

Unlike the document DE 196 20 047 C2, the dust return is thus not in the area between the nozzle bottom and heat exchanger, but in the area or even above the heating surfaces of the heat exchanger. The invention is based on the surprising finding that the undesirable effects of a Dust from the fluidized bed dryer can be reduced to the behavior of the fluidized bed and the dryer performance or even largely eliminated when a return of the deposited coal dust takes place at a suitable point of the fluidized bed dryer.

The proposed in DE 196 20 047 C2 feedback in the area between the nozzle plate and the heating surfaces causes the desired in the fluidized bed dust is discharged too quickly. In contrast, the solution according to the invention is based on the knowledge that the return should take place in the region of the heating surfaces of the dryer, since the edge flow of a fluidized bed is typically directed downwards. The return is therefore according to the invention above the nozzle bottom. In this case, even a return to the dryer is also possible above the heating surfaces and even above the fluidized bed. The teaching of the invention not only allows complete drying of the dust. Also, a reduction of the average heat transfer coefficient and a segregation of the fluidized bed due to excessive dust discharge are avoided, so that a satisfactory dryer performance can be provided even at high fluidization rates.

Different locations or zones are possible in which a return of the separated coal dust can take place. In a first embodiment, the coal dust is fed to the fluidized bed dryer at a location which lies in the lower half of the heating surfaces of the fluidized bed dryer. In a second embodiment, the return takes place in the upper half of the heating surfaces of the fluidized bed dryer. In a third embodiment, it is provided that the coal dust above the heating surfaces, but still takes place within the fluidized bed formed in the fluidized bed dryer. In a fourth embodiment, the coal dust is supplied at a location which is still above the fluidized bed formed in the fluidized bed dryer and thereby above the level of the fluidized bed dryer.

The dried coal dust can thus be reintroduced into the fluidized bed dryer within different vertical return zones. In one embodiment of the invention, it is provided that only a portion of the separated from the vapor coal dust is returned to the fluidized bed dryer. Another part can be used in other ways. The invention further relates to a device for drying coal, which comprises:

a fluidized-bed dryer for drying coal to be dried, wherein the fluidized-bed dryer comprises a gassing floor and a heat exchanger arranged above the gassing floor, comprising heating surfaces, at least one discharge of the fluidized-bed dryer, via which vapors formed in the fluidized-bed dryer are discharged from the fluidized-bed dryer, wherein the vapor Contains coal dust,

- At least one separator for separating coal dust from the vapor, wherein the separator is connected to the discharge, and

- Return means for returning separated coal dust in the fluidized bed dryer, wherein by means of the return means of the coal dust is fed to the fluidized bed dryer at least one location which is within or above the heating surfaces of the fluidized bed dryer. The invention will be explained in more detail with reference to the figures of the drawing with reference to an embodiment.

1 shows schematically a device for drying coal with a

Fluidized bed dryer, and

Fig. 2 shows the device of Figure 1 under more detailed representation of individual vertical

Return zones of the fluidized bed dryer.

Figures 1 and 2 show an apparatus for drying coal, especially lignite. The device is for example part of a coal power plant, the coal is fed after drying a power plant boiler. The device comprises a steam fluidized-bed dryer 1 (also referred to below as a fluidized-bed dryer) and a separator 2. The fluidized-bed dryer 1 has in its lower region a gassing bottom 1 1, which comprises a plurality of tubes and gassing nozzles 110, from which a fluidizing medium emerges in a manner known per se. Above the gassing floor 1 1 and at a defined distance from this, a heat exchanger 12 is provided, which has a vertical area F heating surfaces (which are also referred to as Tauchheizflächen because they are immersed in the fluidized bed). The heating surfaces are formed for example by stacked horizontal tubes or tube bundles or by vertical plates. Such heat exchangers are known per se. Within the fluidized-bed dryer 1, a fluidized bed is formed during normal operation of the apparatus, in which comminuted coal supplied to the fluidized-bed dryer 1 is dried. The fluidized bed ends slightly above the heat exchanger 2. The upper limit 13 of the fluidized bed is shown in FIG. Above the fluidized bed upper limit 13 is a mixture of water vapor and coal dust, which is referred to as vapors.

Raw coal to be dried in the fluidized bed dryer 1 is first comminuted in a mill (not shown). The particle size of the comminuted coal is, for example, an average of less than 2 mm, d. h., a fine grain is provided. The ground coal is fed to a feed device (not shown), from which the coal is fed via a feed 5 to the upper region of the fluidized-bed dryer 1.

The heating surfaces located in the dryer 1 or the heat exchanger tubes forming these are flowed through in the interior of heating steam. They transfer the heat energy necessary for drying to the material to be dried in the fluidized bed. After drying the coal in the fluidized bed dryer 1, the dried coal is removed via a drain 6, for example in the form of a discharge funnel the fluidized bed dryer 1 and further transported, for example to a power plant boiler.

It is provided in the upper region of the fluidized bed dryer 1, a discharge line 7, is derived via the vapors produced in the eddy current dryer 1 from the fluidized bed dryer 1. The vapor contains coal dust. The particle size of the coal dust is relatively small and is on average less than 1 mm. The discharge line 7 for the removal of vapors from the fluidized bed dryer 1 is formed in the upper region of the fluidized bed dryer 1, specifically above the fluidized bed formed in the fluidized bed dryer 1. About the derivative 7 coal dust containing vapor is derived from the fluidized bed dryer 1. This coal dust is deposited in the separator 2. For this purpose, a cyclone 21 and / or an electrostatic filter 22 and / or a fabric filter 23, which are each shown schematically, are used as separators 2. The purified vapor is discharged via a line 4. It can be provided that the purified vapor is recirculated to the fluidized bed dryer 1 and there for example serves as a fluidizing medium of the gassing 1 1 and / or a fluidization medium is added. Likewise, it can be provided that the purified vapor is partially or completely derived in another way and fed to a use.

The separated in the separator 2 coal dust is reintroduced into the fluidized bed dryer 1 via a line 3. For this purpose, at least one line 8 is provided, which opens at a certain point of the fluidized bed dryer 1 in this. This is shown in more detail in FIG.

As can be seen from FIG. 2, the fluidized-bed dryer 1 forms a plurality of vertically superimposed zones. A lowermost zone A is located below the gassing floor 1 1 or is formed between it and the lower end of the housing of the fluidized-bed dryer. An overlying zone B is located between the nozzle bottom 1 1 and the lower edge of the heating surfaces of the heat exchanger 12. Within the heating surfaces, which occupy the vertical region F, two sub-areas C1, C2 are defined, namely the lower half C1 of the heating surfaces and the upper half C2 of the heating surfaces. Vertically above a zone D, which is formed between the upper edge of the heating surfaces and the upper limit 13 of the formed in the fluidized bed dryer 1 fluidized bed. Finally, located above the fluidized bed, a vertical zone E. From the separator 2 separated coal dust is as described via the line 3 the fluidized bed dryer 1 returned. In principle, the recycling can take place in each of the mentioned vertical return zones A, B, C1, C2, D, E. A return in the vertical zones A, B according to the invention, however, is not provided, since the recirculated dust in these zones is partially or completely discharged with the coal leaving the dryer. Rather, there is a return of the separated coal dust in the return zones C1, C2, D and / or E, where a maximum interference in the fluidized bed is ensured. For this purpose, return lines 81, 82, 83 and 84 are provided in the corresponding areas, which are connected to the line 3 or represent mouths of the line 3. It can be provided that only one of the return lines 81, 82, 83, 84 is present. The entry of coal dust into the fluidized-bed dryer 1 always takes place in this case at a certain point in one of the vertical return zones C1, C2, D or E. In alternative embodiments, however, several or all of the return lines 81, 82, 83 shown in FIG , 84 provided. In this case, it may additionally be provided that the lines 81, 82, 83, 84 are provided with controllable valves or the like, so that an entry of coal dust into the fluidized bed dryer 1 via one or more of the return lines 81, 82, 83, 84 respectively can be adjusted. Depending on, for example, the dryer performance to be achieved and the humidity of the raw coal to be dried, the return lines 81, 82, 83, 84 can be switched differently.

It should be noted that it can be provided that the return lines 81, 82, 83, 84, which are only shown schematically in the figures, are made e.g. extend circular or semicircular around the also formed circular fluidized bed dryer 1 and optionally form a plurality of inlets into the fluidized bed dryer 1 in a plane considered. By an entry of the separated coal dust in the fluidized bed dryer 1 in one or more of the vertical return zones C1, C2, D or E, an optimized heat transfer in the fluidized bed dryer 1 is possible. By returning the coal dust well above the nozzle plate 1 1 an undesirably high dust discharge from the fluidized bed is avoided and thereby reliably prevents a reduction of the mean heat transfer coefficient in the fluidized bed. At the same time it is achieved that the recycled coal is optionally completely dried.

Due to the forced recycling of coal dust separated from the vapor, the particle size distribution effectively present in the dryer can be set even finer by dust accumulation than on average of the dry product, so that the heat transfer in the dryer is increased by this effect. It should be noted that in a preferred embodiment, the fluidized bed dryer 1 is under pressure. As a result, a higher average heat transfer coefficient can be realized. The overpressure is for example between 4 and 6 bar. In principle, however, the invention relates to all system pressures, whether ambient, negative or positive pressure.

The invention is not limited in its embodiment to the embodiment shown above, which is to be understood only as an example. For example, the vapor purification can be done other than described. Also, the fluidized bed dryer may include, for example, other elements that are not described or illustrated. The device according to the invention can be used wherever coal has to be dried. The use in a coal-fired power plant represents only one embodiment.

Claims

claims

1 . Process for drying coal, in particular lignite, comprising the steps of:

- providing coal to be dried,

- Introducing the coal to be dried in a fluidized bed dryer (1) and drying the coal in the fluidized bed dryer (1), wherein the fluidized bed dryer (1) has a Begasungsboden (1 1) and arranged above the Begasungsbodens heat exchanger (12) comprising heating surfaces .

- removing vapors from the fluidized-bed dryer (1), the vapor containing coal dust,

- separating coal dust from the vapor, and

- Returning separated coal dust in the fluidized bed dryer (1), wherein the coal dust is fed to the fluidized bed dryer (1) at at least one point which lies within or above the heating surfaces of the fluidized bed dryer (1).

2. The method according to claim 1, characterized in that coal dust is fed to the fluidized-bed dryer (1) at a location in the lower half (C1) of the heating surfaces of the fluidized bed dryer (1).

3. The method according to claim 1 or 2, characterized in that coal dust is fed to the fluidized bed dryer (1) at a location in the upper half (C2) of the heating surfaces of the fluidized bed dryer (1).

4. The method according to any one of the preceding claims, characterized in that coal dust is fed to the fluidized bed dryer (1) at a location which is above the heating surfaces of the fluidized bed dryer (1) and still within the fluidized bed dryer formed in the fluidized bed (1).

5. The method according to any one of the preceding claims, characterized in that coal dust is fed to the fluidized bed dryer (1) at a location above the heating surfaces of the fluidized bed dryer (1) and thereby above the im

Fluidized bed dryer (1) formed fluidized bed.

6. The method according to any one of the preceding claims, characterized in that the deposition of coal dust from the vapor by means of a cyclone (21), an electrostatic precipitator (22) and / or a fabric filter (23).

7. The method according to any one of the preceding claims, characterized in that only a part of the separated from the vapor coal dust to the fluidized bed dryer (1) is returned. 8. Apparatus for drying coal, in particular lignite, comprising:

a fluidized-bed dryer (1) for drying coal to be dried, wherein the fluidized-bed dryer (1) has a gassing floor (11) and a heat exchanger (12) arranged above the gassing floor (11) and comprising heating surfaces,

- At least one derivative (7) of the fluidized bed dryer (1), on the

Fluidized bed dryer (1) resulting vapor is derived from the fluidized bed dryer (1), wherein the vapor contains coal dust,

- At least one separator (2, 21, 22, 23) for separating coal dust from the vapor, wherein the separator (2, 21, 22, 23) with the discharge line (7) is connected, and

Return means (3, 8, 81-84) for returning separated coal dust to the fluidized-bed dryer (1), wherein by means of the return means (3, 8, 8)

8, 81-84), the coal dust is fed to the fluidized-bed dryer (1) at at least one point which lies within or above the heating surfaces of the fluidized-bed dryer (1).

9. The device according to claim 8, characterized in that the return means (3, 81) are formed such that coal dust is fed to the fluidized bed dryer (1) at a location in the lower half (C1) of the heating surfaces of the fluidized bed dryer (1). lies.

10. The device according to claim 8 or 9, characterized in that the return means (3, 82) are formed such that coal dust is fed to the fluidized bed dryer (1) at a location in the upper half (C2) of the heating surfaces of the fluidized bed dryer ( 1) is located.

1 1. Device according to one of claims 8 to 10, characterized in that the return means (3, 83) are designed such that coal dust the Fluidized bed dryer (1) is supplied at a location which is above the heating surfaces of the fluidized bed dryer (1) and still within the fluidized bed in the fluidized bed dryer (1) formed.

12. Device according to one of claims 8 to 1 1, characterized in that the return means (3, 84) are formed such that coal dust is fed to the fluidized bed dryer (1) at a location above the heating surfaces of the fluidized bed dryer (1) and it is above the fluidized bed formed in the fluidized bed dryer (1).

13. Device according to one of claims 8 to 12, characterized in that the discharge line (7) for discharging vapors from the fluidized bed dryer (1) in the upper region of the fluidized bed dryer (1), specifically formed above the fluidized bed.

14. Device according to one of claims 8 to 13, characterized in that in the fluidized bed dryer (1) during the drying of coal there is an overpressure.

15. coal power plant with a device for drying coal according to claim 8.