WO2011120602A1

WO2011120602A1 - Method and device for drying coal

Info

Publication number: WO2011120602A1
Application number: PCT/EP2010/068737
Authority: WO
Inventors: Stefan Lechner; Hans-Joachim Krautz
Original assignee: Brandenburgische Technische Universität Cottbus
Priority date: 2010-04-01
Filing date: 2010-12-02
Publication date: 2011-10-06
Also published as: DE102010003612A1

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 dried coal is removed from the fluidised bed drier (1), vapours are removed from the fluidised bed drier (1), said vapours containing coal dust, the coal dust is separated from the vapours, and the coal dust separated from the vapours is mixed (5) with the coal to be dried before said coal to be dried is supplied to the fluidised bed drier (1), and/or the dried coal removed from the fluidised bed drier (1) is mixed with the coal to be dried before said coal to be dried is supplied to 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 known to dry and grind the raw coal, which processes can also be carried out simultaneously in a grinding drying. However, the required drying energy is high. Another known approach is to dry the raw coal before it is used in a power plant boiler in a steam fluidized bed dryer. A corresponding method and a corresponding steam fluidized-bed dryer are described, for example, in DE 196 20 047 C2. It is envisaged that a subset of the steam exiting the dryer cleaned, thereby deposited with the steam discharged coal dust and then the separated coal dust in the lower part of the fluidized bed dryer this is returned again. The mixture of steam and coal dust removed from the fluidized-bed dryer is also referred to as vapor. When entering raw coal in a fluidized bed dryer, the problem arises that by additional humidification of the coal, which is caused for example by leakage steam before the dryer and / or heating by condensation of coal in the dryer, depending on the starting water content more or less severe danger the formation of irreversible agglomerations of the raw coal, that consists of growing coal lumps. However, such agglomerations are disadvantageous and to be avoided, for example, because they are energetically disadvantageous and can clog the heat exchanger of the fluidized bed dryer.

To avoid the formation of agglomerations, it is known to heat all carbon-contacted parts in the entry area in such a way that their temperature is above the saturated steam temperature. It is also known, in order to avoid agglomeration in the case of coal in the fluidized bed dryer in this complex distribution facilities such as rotary chutes, pendulum chutes and drop body to use. The known means for avoiding agglomeration are structurally and energetically complex and yet can not reliably avoid lump formation.

The present invention has for its object to provide a method and apparatus for drying coal, which allow a satisfactory drying of raw coal without the formation of irreversible agglomerations at the entrance of a fluidized bed dryer.

This object is achieved by a method having the features of claim 1 and an apparatus having the features of claim 9. Embodiments of the invention are specified in the subclaims.

Thereafter, the invention provides to compensate for additional humidification and the resulting risk of agglomeration by the addition of already dried coal to the raw coal. For this purpose, the coal to be dried coal dust is added, which was separated from the vapor of the fluidized bed dryer. Additionally or alternatively, the coal to be dried is added to the fluidized bed dryer, removed dried coal. The admixing takes place before the coal to be dried is fed to the fluidized bed dryer.

It is therefore anyway accumulating, separated from the vapor purification dust and / or a partial flow of the regular Drockneraustrags the coal to be dried admixed. There is thus a partial coal recirculation. When using coal dust from the vapor purification in the admixture results as an additional benefit advantageous recycling of the finest proportions of the fluidized bed dryer, which were taken with the vapors from this, in the fluidized bed dryer. This advantageously increases the heat transfer and avoids segregation in the fluidized-bed dryer.

The invention is preferably used for drying lignite, which is fed after drying a power plant boiler of a lignite power plant. In principle, however, the invention is also suitable for drying hard coal and other water-containing bulk materials. Raw coal has a comparatively low water content of about 10%. The water content of hard coal but relatively easy to z. B. reducible up to 4%. A lower drying potential is thus partially compensated by a higher efficiency. Drying hard coal according to the invention is particularly useful in the production of coke.

In a preferred embodiment of the invention, it is provided that the admixture of the coal dust separated off from the vapor and / or the admixture of the coal which is regularly taken from the eddy current dryer takes place within the scope of a forced mixing. Such forced mixing is provided, for example, by a mill which grinds together the coal to be dried and the recycled coal. This forced mixing in the mill provides a homogeneous product with reduced water content. The admixture of the separated from the vapor coal dust and / or the fluidized bed dryer regularly removed, dried coal is accordingly at least before the last grinding stage before the fluidized bed dryer.

Forced mixing allows the provision of a substantially homogeneous coal product, although dry coal and raw coal are basically difficult to mix. The addition of recycled dry coal (from the vapor purification and / or from the regular dryer discharge) takes place continuously and metered to the raw coal stream.

The removal of coal dust from the vapor takes place for example by means of a cyclone, an electrostatic precipitator or a fabric filter, wherein a plurality of such separators can be arranged one behind the other in order to improve the quality of the deposition process. The vapors purified by coal dust can be used in known per se used both for fluidization in the fluidized bed dryer and this recycled to the fluidized bed dryer in the circulation, as well as discharged and used in other ways. In one embodiment, the invention provides a control such that the recirculated portion of the coal dust separated from the vapor and / or the carbon discharged from the fluidized bed dryer is adjusted such that the coal to be fed to the dryer or discharged from the fluidized bed dryer, dried coal has a certain desired water content. For this purpose, for example, the water content of the fluidized bed dryer removed coal is measured and the proportion of recirculated and mixed with the raw coal coal adjusted so until a desired water content of the supplied or dried coal is present. Since the water content of the raw coal can vary, this control is preferably continuous.

The invention also relates to a device for drying coal, which has the following:

a fluidized-bed dryer for drying coal to be dried,

a feed device via which the coal to be dried is fed to the fluidized-bed dryer,

at least one discharge of the fluidized-bed dryer, via which vapors formed in the fluidized bed dryer are removed from the fluidized-bed dryer, the vapor containing pulverized coal,

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

- First transport, return the separated in the separator coal dust to a point in front of the feeder, wherein the separated from the vapor coal dust of the coal to be dried is added before it is fed to the fluidized bed dryer, and / or

- Second transport, the discharged from the fluidized bed dryer, dried coal back to a point in front of the feeder, wherein the dried coal is added to the coal to be dried before it is fed to the fluidized bed dryer. The transport means transport the coal dust separated in the separator and / or the coal discharged from the fluidized-bed dryer to a mixing device in which a forced mixing of the coal takes place. As explained, such forced mixing takes place in particular by a mill, wherein the continuously recycled coal and the coal to be dried undergo compulsory mixing in the mill. The invention will be explained in more detail with reference to the single figure of the drawing with reference to an embodiment.

FIG. 1 shows an apparatus for drying coal, in particular lignite. The device is for example part of a coal power plant, the coal is fed after drying a power plant boiler.

The apparatus comprises a steam fluidized-bed dryer 1 (hereinafter also referred to as fluidized-bed dryer), a separator 2, a mill 3, a feed device 9, via which coal to be dried is fed to the fluidized-bed dryer 1, and a device 7 for discharging and conveying dried coal out of the Fluidized bed dryer 1.

The fluidized-bed dryer 1 is a fluidized-bed dryer designed in a manner known per se, as described, for example, in DE 196 20 047 C2. In particular, the fluidized-bed dryer 1 has a gassing bottom in the lower region of the dryer, which comprises a plurality of tubes from which a fluidizing medium emerges. Above the gassing floor heat exchangers are arranged, which consist for example of stacked horizontal tubes or vertical plates. Within the fluidized-bed dryer 1, a fluidized bed is formed in the normal operation of the apparatus, in which the reduced carbon fed to the fluidized-bed dryer 1 is dried. The fluidized bed ends just above the heat exchanger. Above the fluidized bed is a mixture of water vapor and coal dust, which is referred to as vapors. A discharge line 10 is provided in the upper region of the fluidized-bed dryer 1, via which vapor emerging in the eddy-current dryer 1 is discharged 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 10 for the discharge 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. The coal to be dried is fed as raw coal along the arrow A first a mill 3, which crushes the raw coal. The particle size of the comminuted coal is, for example, an average of less than 2 mm, that is, a fine grain size is provided. The ground coal is then supplied to the feed device 9, which is, for example, an entry lock, from which the coal is fed via a feed 13 to the upper region of the fluidized bed dryer 1. After drying the coal in the fluidized bed dryer 1, the dried coal is removed via a discharge 1 1, for example in the form of a discharge funnel the fluidized bed dryer 1 and the means 7 supplied to the dried coal, also referred to as dry coal, transported in the direction of arrow B, for example to a power plant boiler.

The elements of the device described so far are standard and well known to those skilled in the art, so that will be omitted from a further explanation.

As already explained, 10 vapors containing coal dust from the fluidized bed dryer 1 is derived via the discharge. 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. The purified vapor is discharged via a line 12. It can be provided that the purified vapor is recirculated to the fluidized bed dryer 1 and serves there, for example, as a fluidizing medium of the gassing 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 recycled via transport 5 according to the arrow C to a point 4 in front of the mill 3 and there mixed the raw coal to be dried. The transport 5 can be formed in any way. They include, for example, conveyor belts and / or transport tubes, which return the separated coal dust.

It can further be provided that at a point 8 behind the device 7 a partial flow of the regular Drockneraustrages branched off and also returned according to the arrow D by means of transport 6 to the point 4 in front of the mill 3 and there is also added to the raw coal to be dried. It should be noted that a return of both separated coal dust by means of transport 5 as well as regular discharge of the dryer by means of the transport means 6 can be done, but not necessarily. It is also within the scope of the invention that only one of these sources of dried coal is used and thus either recycled only separated from the separator 2 coal dust and admixed to be dried raw coal or recycled a partial flow of the regular Drockneraustrags and the raw coal to be dried is added. The recirculation and admixture of coal dust, which was separated by the separator 2, has the particular advantage that finest fractions of the coal are recycled and then added back to the fluidized bed dryer 1 after admixing. The overall reduced average particle size leads to a better heat transfer in the dryer 1.

In both cases, d. H. Both in the return from the separator 2 separated coal dust and in the return of regular dryer discharge is reduced by the admixing of the dried coal, the relative water content of the dryer 1 fed coal. As a result, unwanted agglomerations are avoided at the dryer inlet and additionally achieved heating of the dryer 1 fed coal.

The recirculated to the point 4 coal is fed together with the raw coal of the mill 3, in which the raw coal and the recycled coal undergo compulsory mixing. This is advantageous because dry coal and raw coal are difficult to mix. The forced mixing in the mill 3 produces a substantially homogeneous product with a reduced water content, which is then fed to the feed device 9 and further to the fluidized-bed dryer 1. It should be noted that several mills 3 may be provided. The return of coal by means of the transport 5, 6 need not be done before the last stage mill, but can also be done before previous mill stages or before the first stage mill. It can also be provided that the recirculated coal is divided into different partial flows, which are supplied to different mill stages. It can also be provided that the extracted by means of the transport 6 coal Dryer discharged coal is added to the raw coal elsewhere than the separated from the separator 2 coal dust. The latter is fed, for example, to the last mill stage, while the former is fed to an earlier mill stage.

The return of coal by means of the transport 5, 6 takes place continuously. The metering is preferably carried out by means of a regulation, within which the water content of the raw coal to be supplied to the dryer or the dried coal discharged from the fluidized bed dryer 1 is determined regularly and the reflux of coal is regulated by the transport means 5 and / or 6 depending on this, so that the dried or dried coal has a certain, desired water content.

It should also be pointed out that the coal dust separated off from the separator 2 does not necessarily have to be completely recirculated and mixed with the coal to be dried. For example, in the context of the regulation, only a partial stream of the coal dust separated off from the separator 2 can be returned, while another partial stream is stored in a coal bunker or supplied to another use. It can also be provided that a partial flow is fed directly to the fluidized bed dryer 1 again. 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 separator may be different than illustrated and the transport means may be designed differently than described. 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),

Discharging dried coal from the fluidized bed dryer (1),

- removing vapors from the fluidized bed dryer (1), wherein the vapor

Contains coal dust,

- separating coal dust from the vapor, and

Admixing (5) the coal dust separated from the vapor to the coal to be dried before it is fed to the fluidized-bed dryer (1), and / or

- mixing (6) of the fluidized bed dryer (1) removed, dried coal to the coal to be dried before it is fed to the fluidized bed dryer (1).

2. The method according to claim 1, characterized in that the admixture of the separated from the vapor coal dust and / or from the fluidized bed dryer (1) discharged, dried coal to the coal to be dried is carried out as part of a compulsory mixture, which is substantially homogeneous Carbon product with reduced water content leads.

3. The method according to claim 1 or 2, characterized in that the coal to be dried before introducing into the fluidized bed dryer (1) passes through one or more grinding stages (3) and the admixture of the separated from the vapor coal dust and / or from the fluidized bed dryer (1) discharged, dried coal to the coal to be dried at the latest before the last grinding stage (3).

4. The method according to any one of the preceding claims, characterized in that the admixture of the separated from the vapor coal dust and / or from the fluidized bed dryer (1) discharged, dried coal to the coal to be dried is carried out continuously.

5. 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).

6. The method according to any one of the preceding claims, characterized in that only a part of the separated from the vapor coal dust is added to the coal to be dried.

7. The method according to any one of the preceding claims, characterized in that the recycled portion of the separated from the vapor coal dust and / or from the fluidized bed dryer (1) discharged, dried coal is set in the context of a scheme such that the mixed and / or dried coal has a certain desired water content.

8. The method according to any one of the preceding claims, characterized in that the admixture in particular fine fractions of the separated coal dust to the coal to be dried leads to an improvement of the heat transfer in the fluidized bed dryer (1).

9. Apparatus for drying coal, in particular lignite, comprising:

a fluidized-bed dryer (1) for drying coal to be dried,

a feed device (9) via which the coal to be dried is fed to the fluidized-bed dryer (1),

- At least one derivative (10) of the fluidized bed dryer (1), via which in the fluidized bed dryer (1) resulting vapor from the fluidized bed dryer (1) is derived, 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) is connected to the discharge line (10),

- First transport (5), in the separator (2) separated coal dust to a point (4) in front of the feed device (9), wherein the separated from the vapors coal dust of the coal to be dried is added before this the fluidized bed dryer (1) is supplied, and / or

second transport means (6) returning dried coal discharged from the fluidized-bed dryer (1) to a location (4) in front of the feed device (9), the dried coal being admixed with the coal to be dried before it reaches the fluidized-bed dryer (1) is supplied.

10. The device according to claim 9, characterized in that the first and / or second transport means (5, 6) in the separator (2, 21, 22, 23) separated coal dust and / or discharged from the fluidized bed dryer (1) coal to a mixing device (3) forcibly mixing the recycled coal with the coal to be dried, wherein a substantially homogeneous

Coal product with reduced water content is formed.

1 1. Apparatus according to claim 9 or 10, characterized in that the device at least one of the feed device (9) upstream mill (3) for crushing the coal prior to its supply to the fluidized bed dryer (1) and the transport means (5, 6) are formed in that the recycled coal is mixed with the coal to be dried at the latest before the last mill (3) in front of the feed device (9).

12. Device according to one of claims 9 to 1 1, characterized in that the separator (2) as a cyclone (21), as an electrostatic filter (22) and / or as a fabric filter (23) is formed.

13. Device according to one of claims 9 to 12, characterized by a control which causes the recycled portion of the separated from the vapor coal dust and / or from the fluidized bed dryer (1) discharged, dried coal is adjusted such that the mixed and / or dried coal has a certain, desired water content.

14. Device according to one of claims 9 to 13, characterized in that in the fluidized bed dryer (1) there is an overpressure.

15. coal power plant with a device for drying coal according to claim 9.