AU721894B2

AU721894B2 - Process for comminuting and drying brown coal

Info

Publication number: AU721894B2
Application number: AU25059/97A
Authority: AU
Inventors: Malte Knizia; Stefan Laux
Original assignee: L&C Steinmueller GmbH
Current assignee: Hitachi Power Europe GmbH
Priority date: 1996-03-27
Filing date: 1997-03-26
Publication date: 2000-07-13
Anticipated expiration: 2017-03-26
Also published as: DE59705088D1; DE19612187C2; ES2166534T3; EP0891404B1; PL329156A1; WO1997035944A1; EP0891404A1; TR199801936T2; DE19612187A1; AU2505997A

Description

2 PROCESS FOR COMMINUTING AND DRYING BROWN COAL The invention concerns a process for comminuting and drying brown coal, wherein the brown coal is subjected to at least two stages of comminution and is dried in an indirectly heated fluidised bed drier and wherein at least one first comminution stage takes place before the fluidised bed drying and vapours are drawn off from the fluidised bed drier through a dust separator.

In the case of the so called WTA drying process the deducted vapours are compressed and are used for the indirect heating of the fluidised bed drier.

In the case of the so called DWT drying process the fluidised bed drier is heated with steam and the o: 15 vapours are condensed and the heat obtained in this process is used for other purposes.

99* 9 S.In neither process does a separation take place after the first stage of comminution, so that the entire :ground material, i.e. including the fines material, is *999 20 subjected to a second comminution stage, so that the comminuting equipment connected downstream has to be unnecessarily large S: The object of the invention is to specify a process of the generic type for comminuting and drying brown coal, whereby the cost of the comminution is reduced.

This objective is achieved in that the vapours of the fluidised bed drier are used as separating vapour for separating the comminuted brown coal. The fine material resulting from this separation is not subjected to further comminution.

Since the fluidised bed drier operates in an environment of slightly overheated steam, the vapours can be used without any problem of safety for the separation 32593.1 .DOC -3 of the ground material. The fine material resulting the separation, can be returned to the fluidised bed drier or to the dust separator, in fact by using the vapours.

Four methods of conducting the process according to the invention are described by way of example with reference to the accompanying drawings. In the drawings: Fig.l shows an embodiment in which the comminution is carried out in two baffle splitters connected in a cascading manner with an interposed vapour separation before the fluidised bed drier, S: Fig.2 shows an embodiment of the process in which 15 the comminution is carried out in a comminuting equipment with a return of separated coarse material before the fluidised bed drier, Fig.3 shows an embodiment of the process in which a first comminuting equipment is connected upstream from the fluidised bed drier and a second comminuting equipment with a downstream connected vapour separator is connected downstream from the fluidised bed drier, and Fig.4 shows an embodiment of the process, comparable with the embodiment of the process according to Fig.3, wherein a separator is omitted and the fluidised bed drying equipment itself is used as a separator.

When the process is conducted according to Fig.l, the raw brown coal RK is conveyed to a comminuting equipment 2. The comminuted coal 3 is introduced by means Sof a feeder into a separator 5 by means of a vapour flow B 32593.1.DOC 4 introduced through a pipeline 4. The coarse material of the separator 5 is introduced into a second comminuting equipment 7 by means of a feeder 6.

The comminuted material is conveyed via a pipeline 8' from the comminuting equipment 7 to a fluidised bed drier 9 with the aid of a vapour flow introduced via the pipeline 8. The fluidised bed drier 9 is indirectly heated by at least one heating area 10, which, for example in the WTA process, can be charged with compressed vapour. The fluidised bed drier 9 is charged with a fluidising agent through the schematically illustrated nozzles 11. The dried brown coal GK is removed from the fluidised bed drier, as illustrated schematically by the discharge "equipment 12. The vapours drawn off via the pipeline 13 15 from the fluidised bed drier 9 are dedusted in an •to, electrostatic-vapour filter 14. The coal dust SK is removed via a discharge equipment 15. The pipeline 4 and the branch line 8 are connected to the outlet of the o :electrostatic-vapour filter, and a vapour pump 16 is cote 20 provided in the line. Furthermore, a vapour discharge o: pipeline 17 is connected to the outlet of the electrostatic filter 14. As in the case of the WTA process, this can be conveyed to a vapour compressor (not i illustrated) or, as in the case of the DWT process, to a vapour condenser (not illustrated) or released into the atmosphere.

Any known form of comminuting equipment that is suitable for comminuting wet coal may be employed in the above described process. Such equipment includes hammer mills, in which comminution is carried out by impacting on baffle edges. Crusher-wheel mills and baffle splitters, for example, are also suitable.

1. DOC As far as possible, in Fig.2 the same reference numerals are used as in Fig.l.

The raw brown coal RK is conveyed to a comminuting equipment 19 via a feeder 18. The design of the comminuting equipment is such that it can aspirate nondedusted vapours via a pipeline 20, which is directly connected to the fluidised bed drier 9.

The coal comminuted in the comminuting equipment 19 is conveyed to a separator 21 via a pipeline 21'. The coarse material of the separating separator 21 is returned to the comminuting equipment 19 via the pipeline 22, whereas the fine material is conveyed to the fluidised bed drier 9 via a pipeline 23.

In this case as comminuting equipment a naturally aspirated crusher-wheel mill can be used, in which case S: the comminution and conveying of the transporting gas are carried out in one step. If necessary, it is possible to superheat additionally the vapours aspirated via the S: pipeline 20 with steam conveyed from a turbine (not 20 illustrated), and this is illustrated schematically by numeral 24. The operation of this arrangement is similar to that of a crusher-wheel mill in a raw brown coal furnace.

As far as possible, in Fig.3 once again the same reference numerals are used as in Fig.l. When conducting the process according to Fig.3, the brown coal RK comminuted in the first comminuting equipment 2 is introduced directly to the fluidised bed drier 9 via the feeder equipment 3.

The dried brown coal GK removed by means of the discharge equipment 12 is supplied to a comminuting equipment 25. A separator 25' is connected downstream of Z'iSI7 he comminuting equipment 25 by way of a pipeline 25', the 13.1. DOC -6separator being comparable in its operation with the separator 25' shown in Fig.2. The comminuting equipment is illustrated in Fig.3 as a non-naturally aspirated comminuting equipment, so that dedusted vapours are introduced to it via a pipeline 26 and a blower 27.

The brown coal that is adequately comminuted in the comminuting equipment 25 is removed from the mill via the discharge equipment 28.

The fine material of the separating separator 251 is conveyed via a pipeline 29, not to the fluidised bed drier 9 but to the electrostatic-vapour filter 14, which will consequently dedust not only the vapours exiting from the fluidised bed drier but, also, the separating vapours.

As a non-naturally aspirating comminuting equipment 25, a bowl mill crusher or tube mill a bruising mill) as normally used for the grinding of black coal, can be used. On the other hand it is quite feasible in this case to use a hammer mill. As is shown in dotted outline in Fig.3, it is feasible to include in the pipeline 29 a 20 centrifugal separator 30 with a discharge element 31. This *o facilitates a lower demand from the electrostatic-vapour filter.

ooe• The process according to Fig.4 differs from the S-process according to Fig.3 basically in that no separator is connected downstream from the comminuting equipment In contrast, the ground material discharged from the comminuting equipment 25 is injected by means of the vapour flow B introduced via the pipeline 26 directly into the fluidised bed drier via a pipeline 32. The pipeline 32 enters the fluidised bed drier above the top surface O of the fluidised bed. In this case separation of the fine material is achieved, which is introduced to the A electrostatic-vapour filter 14 via the pipeline 13. The -7 coarse material sinks into the fluidised bed and is conveyed again to the discharge equipment 12. 2 this case it may be useful to provide a baffle plate 33 in the free space above the fluidised bed, onto which the flow of the gas/solids mixture exiting from the pipeline 32 impacts.

However, it would be also conceivable to provide a rotary plate here. These steps, however, become necessary only when the required separation effect cannot be achieved by introducing the returned flow of gas/solids mixture into the main vapour flow HB formed in the drier and directed towards the discharge of the electrostatic-vapour filter.

Finally, it should be pointed out that to each outlet ee: of the fluidised bed drier 9 and of the electrostaticvapour filter 14 a discharge equipment is connected.

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Claims

1. A process for comminuting and drying brown coal wherein the brown coal is subjected to at least two stages of comminution and is dried in an indirectly heated fluidised bed drier, and wherein at least one first comminution stage takes place before the fluidised bed drier and vapours are drawn off from the fluidised bed drier through a dust separator, characterised in that the vapours from the fluidised bed drier are used as separating vapour for separation of the comminuted brown coal, and in that fine material resulting from the separation is not subjected to further comminution. 15

2. The process according to claim i, further characterised in that the brown coal is comminuted in a first comminuting stage and, thereafter, is subjected to separation using vapours from the fluidised bed drier, in that coarse material resulting from the separation is 20 introduced to a second comminuting equipment, and in that ae". "the fine material resulting from the separation and S: preferably the material comminuted in the second comminuting stage is also conveyed to the fluidised bed S• drier by use of the vapours.

3. The process according to claim i, further characterised in that the brown coal is comminuted in a comminuting equipment and, thereafter, is subjected to separation using vapours from the fluidised bed drier, and in that coarse material resulting from the separation is returned to the comminuting equipment and the fine material use is returned to the fluidised bed drier by use of the vapours.

32593.1.DOC -9

4. The process according to claim 3, further characterised in that the separation is carried out using vapours that are naturally aspirated from the fluidised bed drier via the comminuting equipment. The process according to claim 1, further characterised in that the brown coal is comminuted in a first comminuting equipment and is subjected, thereafter, to fluidised bed drying, in that the brown coal is comminuted in a second comminuting equipment and, thereafter, is subjected to separation using vapours from the fluidised bed drier, and in that coarse material resulting from the separation is returned to a second comminuting equipment and the fine material is removed by use of the vapours. 6. The process according to claim 5, further characterised in that the fine material is conveyed through a second separator. 7. The process according to claim 5 or claim 6, further characterised in that the fine material is returned to a dust separator connected downstream from the fluidised bed drier. 8. The process according to any one of the claims 1 to 7, further characterised in that the separation is effected by a centrifugal force separator. 9. The process according to claim 1, further characterised in that the brown coal is comminuted in a first comminuting equipment and conveyed thereafter to the Sfluidised bed drier, in that the dried coal is comminuted 32593.1.DOC 10 in a second comminuting equipment, and in that the comminuted material from the second comminuting equipment is returned to the fluidised bed drier using vapours, in such a manner that separation is carried out by means of the vapours discharged from the fluidised bed drier. The process according to claim 9, further characterised in that the comminuted material of the vapours from the second comminuting equipment are returned to the fluidisation bed drier above the level of the fluidised bed. -11. A process for comminuting and drying brown coal 0" :substantially as hereinbefore described with reference to o 15 any one of Figures 1 to 4 of the accompanying drawings. .i Dated this 8th day of May, 2000 L C STEINMULLER GMBH 20 By their Patent Attorneys GRIFFITH HACK 9*o o* 32593.1.DOC