EP2352960B1 - Method and apparatus for generating process steam through combustion of lignite - Google Patents

Description

The invention relates to a process for producing process steam by burning dried lignite in a steam generator, comprising drying moist brown coal in a fluidized bed dryer with heat exchanger components through which a heating medium, at least some of the water being expelled from the lignite and as vapors from the dryer is led out, the vapors are dedusted in a dedusting and the dried lignite is cooled in at least one of the fluidized bed dryer downstream cooler.

Such a method according to the preamble of claim 1 is for example from the DE 195 18 644 A1 known.

The DE 195 37 050 A1 discloses an apparatus for cooling lignite according to the preamble of claim 5.

According to DE195 18 644 is for the drying of the pit-wet lignite prior to firing in a steam generator, a fluidized bed dryer or fluidized bed dryer provided within which the lignite is heated by means of a tube bundle heat exchanger whose outer walls are in contact with the brown coal for a heat exchanger. At least one partial flow of the vapors discharged from the fluidized bed is compressed and fed to the heat exchanger as a heating medium, the vapors at least partially condense. The vapor withdrawn from the dryer is dedusted in an electrostatic precipitator. The dried lignite is fed from the dryer to a cooler, which is exposed directly to cooling air. The cooled lignite is then ground and burned in the form of lignite dust within the steam generator.

The dry coal discharged from the dryer can have an average particle size of about 0.4 to 2 mm. This can be dried in a cascade cooler, as it is for example in the DE 195 37 050 A1 is described. Alternatively, the brown coal withdrawn from the dryer may be cooled in a fluidized bed cooler in which the cooling is cooled by direct contact with a cold gas, for example with air.

The filter dust discharged from the vapor by means of a solids separator, for example by means of an electrostatic precipitator, has an average particle size of less than 100 .mu.m, so that it would be discharged as far as possible in a cascade cooler or fixed-bed cooler owing to the very low particle sinking rate and the required high quantities of cooling gas. Therefore, for example, in the DE 195 37 050 A1 described cooler not suitable to cool filter dusts.

For the cooling of filter dust therefore indirectly working cooler are more suitable. However, the use of such coolers is less suitable in the context of steam-drying processes, since the transition from the steam atmosphere to the air atmosphere results in the evaporation and condensation of water due to the lower partial pressure of steam prevailing in the air atmosphere. In particular, the condensation of steam leaks from the dryer discharge causes contamination of the cooling surfaces of such an indirectly operating dryer, so that the cooler would lose effectiveness relatively quickly.

The invention is therefore based on the object to improve the procedure according to the invention with regard to the cooling of brown coal fine dust.

The object is first achieved by a method for generating process steam by burning dried brown coal in a steam generator, comprising the drying of moist brown coal in a fluidized bed dryer with heat exchangers flowed through by a heat exchanger installations, wherein at least a portion of the water expelled from the lignite and Vapors are led out of the dryer, the vapors are dedusted in a dedusting and the dried lignite is cooled in at least one of the fluidized bed dryer downstream cooler, the process is characterized in that the obtained in the dedusting brown coal dust in direct contact with the dried and cooled Lignite is layered or mixed, the cooled lignite is used as a cooling medium in a cooler for lignite dust application.

The invention can be summarized in that in an advantageous manner, the already dried and cooled brown coal with a grain diameter of 0 to 2 mm is used as a cooling medium for cooling the filter dust.

It is particularly advantageous if the stratification takes place during the transport of the cooled lignite.

The mixing can also take place during the transport of the layered material streams. With such an approach cooling with air as a result of post-evaporation can be provided at the same time.

It is particularly advantageous if at least three layers of cooled lignite and lignite dust are stratified, with cooled lignite and lignite dust being poured alternately on one another. Subsequent intimate mixing of the layers ensures good heat transfer.

Conveniently, the cooled lignite and lignite dust are consecutively an endless conveyor, preferably in the form of a trough chain conveyor, abandoned.

For example, the material layers of lignite dust and cooled brown coal can be mixed together by means of stationary mixing devices during transport.

The object underlying the invention is further achieved by a device for cooling lignite dust according to the method described above, comprising an encapsulated conveyor with at least two in the conveying direction at a distance successively arranged inlet devices and at least one material discharge, wherein the inlet devices are arranged so that the conveyor material flows different temperatures are available in layers. As a conveyor disposed in a housing endless conveyor is provided, and at least one with respect to the conveyor stationarily arranged mixing device.

As a mixing device stationary mixing internals can be arranged in the housing.

As conveyor a trough chain conveyor is expediently provided, which rotates in an encapsulated housing.

As mixing internals flow obstacles can be provided, which are arranged so that they dive into the conveyed material and cause a mixing of the material. These internals may be formed, for example, in the manner of plowshares, which protrude into the loading cross section of the conveyor.

The trough chain conveyor according to the invention may for example be additionally flowed through with cold or preheated air, whereby a further cooling of the funded material flow, essentially by evaporation, is effected in an advantageous manner and condensate formation is prevented. The invention will be explained below with reference to an embodiment shown in the drawings.

• Figur 1 ein Fließbild eines Teils eines Dampferzeugungsprozesses umfassend die Trocknung von Braunkohle,
• Figur 2 eine schematische Ansicht eines Kühlers gemäß der Erfindung,
• Figur 3 eine Draufsicht auf den Kühler gemäß der Erfindung und
• Figur 4 einen Schnitt durch den Kühler entlang der Linien IV-IV in Figur 2.

Show it:

• FIG. 1 a flow diagram of a part of a steam generation process comprising the drying of lignite,
• FIG. 2 a schematic view of a cooler according to the invention,
• FIG. 3 a plan view of the cooler according to the invention and
• FIG. 4 a section through the radiator along the lines IV-IV in FIG. 2 ,

It is first referred to FIG. 1 FIG. 1 represents a part of a steam generation process. Crude lignite extracted from an open pit is first crushed and fed to a multistage fine grain treatment. The brown coal from the Feinkomaufbereitung with a mean grain diameter of 0 to 2 mm and a water content of about 55 to 65% is then fed to a fluidized bed dryer 1. In the fluidized bed dryer 1, the coal is dried outside the combustion process to a residual moisture content of about 12%, optionally ground again and fired in a boiler, not shown, for the purpose of generating steam. The steam is expanded in a known manner in steam turbines for the purpose of generating electricity. As already mentioned above, the fluidized-bed dryer 1 (also referred to in the literature as a fluidized-bed dryer) serves to dry the lignite-wet lignite which comes into direct contact with the heat exchanger 2 arranged inside the fluid-bed dryer 1. As a heat exchanger can be provided, for example, a tube bundle heat exchanger whose outer wall comes into contact with the brown coal for heat exchange. The heat exchanger 2 or another heat exchanger can be flowed through, for example, with compressed vapors, as for example in the DE 195 18 644 A1 is described.

The withdrawn from the fluidized bed dryer 1 vapors are dedusted in an electrostatic precipitator 3. For example, at least a portion of the vapors can be recompressed and used to heat the fluidized bed dryer 1.

The dry lignite accumulating in the fluid bed dryer 1 is fed via two screw conveyors (4) and downstream Zellenraddosiereinrichtungen (5) two parallel operated fluidized bed coolers (6). The lignite coal discharged from the fluid bed coolers (6) is in each case subjected to subsequent grinding in a downstream dry lignite coal mill (7) and fed to the cooler (8) according to the invention via a further cell wheel metering device (5).

As can be seen from the flow chart, the already dried, cooled and post-milled brown coal is deposited at two spaced locations of the cooler (8) as a cooling medium. The cooler (8) is designed as an air-flow, encapsulated Trough chain conveyor. The housing (9) of the cooler (8) is provided in total with three in the conveying direction at a distance successively arranged inlet devices 10a, b and c, with 10a a first upstream inlet device, with 10b a second downstream behind arranged inlet device and 10c downstream the second inlet device 10 b arranged third inlet device is called.

The material flows are introduced in layers into the cooler (8) via the inlet devices 10a, 10b and 10c connected in series, lignite dried and cooled via the first inlet device 10a, lignite dust not cooled via the second inlet device 10b and cooled brown coal dried via the third inlet device 10c is supplied.

About a discharge conveyor (11) lignite dust from the electrostatic precipitator (3) is withdrawn and fed via a Zellenraddosiereinrichtung (5) and the second feed device (10b) to the radiator (8).

The conveying direction prevailing in the upper run (12) of the trough chain conveyor designed as a cooler (8) is in FIG ) from left to right, also in FIG. 2 where the conveying direction or the direction of rotation is shown by arrows.

In the following reference is made to the FIGS. 2 to 4 from which the construction of the radiator (8) can be seen in detail.

The cooler (8) comprises a substantially closed housing (9) with a peripheral conveyor chain (13). Within the housing (9) a trough-shaped upper run (12) and a trough-shaped lower run (14) is provided.

Furthermore, an air inlet (15) and an air outlet (16) are provided on the housing (9). In the conveying direction of the conveyor chain (13) in Untertrumm (in FIG. 2 from left to right), an air inlet (15) for cooling air is initially provided. Downstream of the air inlet (15), the first, second and third inlet devices (10a, 10b and 10c) are each provided in the form of an inlet chute in succession. The air outlet (16) in the form of a fume hood is arranged downstream of the third inlet device. This is followed by an optionally provided fourth inlet device 10d downstream.

With (17) the outlet chute of the radiator (8) is designated.

The cooler (8) is alternately layered cooled, dried and granular lignite, then brown coal dust and then downstream again cooled, dried, granular lignite abandoned. The dried, cooled brown coal leaves the fluid bed cooler (6) at a temperature of about 30-50 ° C. The lignite dust leaves the electrostatic precipitator (3) at a temperature of about 105-120 ° C.

Due to the layer-by-layer filling of the material streams with different temperatures, a heat exchange takes place, which ultimately causes a cooling of the filter dust to a temperature of less than 80 ° C. These Temperature is considered critical with regard to the auto-ignition tendency of lignite dust.

About the air outlet (16) and the air inlet (15) air at a temperature of about 20 - 40 ° C in the under slightly negative pressure (about 1 - 20 mbar) standing housing (9) retracted. As a result, possibly releasing moisture can be absorbed by evaporation of the carbon water in order to avoid condensation on the inside of the housing (9).

In addition, to avoid condensation, it may be provided to insulate the housing (9).

With 18 inside the housing (9) fixedly installed mixing devices are called, which dive into the delivery cross section of the upper run (12) and cause a mixing of the material flows.

In the drawing, the mixing internals (18) in front of and behind the second inlet device 10b in the upper run (12) of the radiator (8) are arranged. However, such mixing internals (18) may also be provided at any other point downstream. The mixing internals (18) may be formed, for example, as tines, which have the geometry of plowshares.

The solution according to the invention has the technical advantage that the cooling of the warm brown coal fine dust takes place in a conveyor system which is generally required anyway for reasons of plant technology.

The cooling is particularly intense, as the warm dust is embedded and mixed between two cold layers of cooled lignite. The rapid cooling and the intensive mixing is supported by the fixed or static mixing internals (18). The mixing of the warm dust with the cooled lignite also has the advantage that a dust discharge is reliably prevented.

LIST OF REFERENCE NUMBERS

1

Fluidized bed dryer

2

heat exchangers

3

electrostatic precipitator

4

screw conveyor

5

Zellenraddosiereinrichtung

6

Fluidized bed cooler

7

Dry lignite mills

8th

cooler

9

casing

10a, 10b, 10c, 10d

first, second, third and fourth feed device

11

discharge conveyor

12

obertrum

13

conveyor chain

14

strand

15

air inlet

16

air outlet

17

discharge chute

18

mixing internals

Claims (8)

1. Method for generating process steam by burning dried lignite in a steam generator, comprising the drying of moist lignite in a fluidized bed dryer (1) with internal heat exchanger units through which a heating medium flows, wherein at least some of the water is driven out of the lignite and removed from the dryer as vapours, dust is removed from the vapours in a dedusting device (3) and the dried lignite is cooled in at least one cooler (6) arranged downstream of the fluidized bed dryer (1), and wherein the lignite dust accumulating in the dedusting device (3) is brought into direct contact with the dried and cooled lignite,
   characterized in that
   the lignite dust is layered with the dried and cooled lignite, wherein the cooled lignite is employed as cooling medium in a cooler (8) for the lignite dust, the layering is carried out during transport of the cooled lignite and a mixing operation is carried out during transport of the layered material streams.
2. Method according to Claim 1, characterized in that at least a total of three layers of cooled lignite and lignite dust are layered, wherein cooled lignite and lignite dust are alternately poured one on top of another.
3. Method according to either of Claims 1 and 2, characterized in that cooled lignite and lignite dust are charged one after another to an endless conveying means, preferably in the form of a trough chain conveyor.
4. Method according to Claim 3, characterized in that the material layers of cooled lignite and lignite dust are mixed with one another during transport by means of stationary mixing devices.
5. Apparatus for cooling lignite by the method according to any of Claims 1 to 4, comprising as cooler (8) an encapsulated conveying device having at least two feed devices (10a, b, c, d) arranged spaced apart one after another in the conveying direction and at least one material discharge, wherein the feed devices (10a, b, c, d) are arranged in such a way that streams of material at different temperatures can be charged layer by layer to the conveying device, characterized in that an endless conveying means arranged in a housing (9) is provided as the conveying device and that at least one mixing device arranged in a stationary manner with respect to the conveying device is provided.
6. Apparatus according to Claim 5, characterized in that stationary internal mixing elements (18) are provided in the housing (9) as the mixing device.
7. Apparatus according to either of Claims 5 and 6, characterized in that a trough chain conveyor is provided as the conveying device.
8. Apparatus according to either of Claims 6 and 7, characterized in that flow obstacles which are arranged in such a way that they become immersed in the conveyed material and bring about thorough mixing of the material are provided as the internal mixing elements (18).

Images