CA2303742A1

CA2303742A1 - Centrifugal separator

Info

Publication number: CA2303742A1
Application number: CA 2303742
Authority: CA
Inventors: Klaus Dieter Tigges; Werner Bischoff
Original assignee: BBP Energy GmbH
Current assignee: BBP Energy GmbH
Priority date: 1999-05-19
Filing date: 2000-04-04
Publication date: 2000-11-19
Also published as: DE19923109A1; EP1053797A3; JP2000343040A; EP1053797A2

Abstract

A centrifugal separator for separating a mixture of matter to be separated and a carrier gas has an entry portion, an exit portion having a plurality of removal conduits coupled thereto, and a ring of guide elements. The mixture flows through the guide elements in a substantially radial manner from the outside to the inside. The guide elements surround an internally located, axial exit cross-section. The exit cross-section is divided into a plurality of segments and each segment is coupled to a removal conduit.

Description

CENTRIFUGAL SEPARATOR
This invention relates to a centrifugal separator and in particular to a separator for separating a mixture of matter to be separated and a carrier gas.
Centrifugal separators are employed in technical and engineering processes producing a mixture of dust and a carrier gas. Further, they are employed in grinding and drying processes of moist raw materials. The separators are used for adjusting a predetermined particle fineness of the mixture of matter to be separated and the carrier gas.
Prior art static centrifugal separators are known which are flap separators having stationary tangential flaps. The tangential flaps are fixed or moveable by hand or a motor as described in Jahrbuch der Dampferzeugungstechnik, 5. Ausg., 1985/86, pp. 182-192.
Once the flap separators can no longer fulfill the requirements for dust fineness, a dynamic centrifugal separator is chosen as described in Jahrbuch der Dampferzeugungstechnik, 5. Ausg., 1985/86, pp. 182-192.
Such a dynamic centrifugal separator consists of a separator rotor with vanes and a rotation frequency controller.
Furthermore, slat separators are known, such as disclosed in EP-PS 496 142, consisting of a rotating cage having tilted or vertically arranged slats. A stationary guide apparatus is arranged in front of the slat separator in the flow direction of the mixture of carrier gas and matter to be ground. Combined static-dynamic centrifugal separators are also known. In all centrifugal separators, the matter to be separated flows from the outside to the inside. Hence, the matter to be separated has a substantially radial entry path into and a substantially axial exit path from the separator.
The separation between coarse matter and fine matter is an equilibrium separation between gravitational forces and flow forces depending upon a construction of the separator with different contributions from upward flows, redirected flows, centrifugal force fields, and vortex valleys.

A removal conduit is arranged on the separator casing on top of the separator. In case multiple consumers have to be serviced, the flow from the removal conduit is adjusted in a so-called dust distributor such that it is distributed between the required number of consumers. There are also separators equipped with several removal conduits going directly to the consumers. In a prior art vane separator, such as disclosed in DE-PS 31 21 937, a collection area is disposed in the separator casing on top of the separator rotor from which one or more removal conduits extend. All these technical solutions have in common that the distribution of the dust to the individual consumer is not even. Often, there are large differences between the mass flows to the consumers.
It is an object of the invention to design the exit of the centrifugal separator such that there is an even dust distribution in the removal conduits.
This object is accomplished in accordance with the present invention in the generic centrifugal separator by the characterizing features disclosed in claim 1. The dependent claims contain further advantageous embodiments of the present invention.
The present invention is based on the recognition that prior art centrifugal separators have an uneven dust distribution in the area above the separator whereas the dust is evenly distributed in the mixture of the matter to be separated and the carrier gas is evenly distributed at an exit cross-section of the separator. Thus, in accordance with an embodiment of the present invention the mixture of the matter to be separated and the carrier gas is withdrawn directly from the exit cross-section of the separator and provided to the removal conduits. Each removal conduit then withdraws from the mixture of the matter to be separated and the carrier gas an equal amount of matter to be separated.
This is advantageous if each removal conduit is assigned to one consumption area. In a preferred embodiment of the invention the separator is connected to a coal mill and each removal conduit is connected to a burner such that the coal is evenly combusted in a combustion area equipped with such burners.
Several exemplary embodiments of the invention are further described by way of the following drawings in which:
Figs. 1 to 4 show longitudinal sections of various separators; and Fig. 5 shows a top view of the separator presented in Fig. 1.
The depicted separators are centrifugal separators of static, dynamic, or static-dynamic construction. They are employed in technical process installations in order to adjust a desired dust fineness in a mixture of a carrier gas and matter to be separated. The centrifugal separator is also employed in a mill for the dry grinding of moist raw material, e.g. coal, by use of a hot carrier gas. Mills used in accordance with the invention are roller mills, ball mills, beater mills, or tube mills, for example.
The centrifugal separator is composed of a separator casing 1 that can be placed on the casing of a mill (not shown). In this case, the interior of the separator casing 1 is connected at the entry side with the grinding chamber of the mill. At the exit side, the separator casing 1 is closed by a lid 2. A supply conduit 3 is disposed along the vertical longitudinal axis of the separator casing 1 to supply raw coal to the mill. The supply conduit 3 extends into the grinding_chamber of the mill. The upper end of the supply conduit 3 extends through the lid 2 of the separator casing 1 to the outside and is connected to a coal supply.
A funnel 4 that widens towards the top and is open at the bottom is spaced from the wall of the separator casing 1 and the supply conduit 3. The funnel 4 is supported on the wall of the separator casing 1.
A stationary ring of guide elements is arranged between the upper edge of the funnel 4 and the lid 2 of the separator casing 1. The static centrifugal separator depicted in Fig. 1 is a flap separator in which the guide elements are formed by flaps 5 which are arranged in a stationary manner or are radially or tangentially adjustable by means of an adjusting mechanism 6. A dipping tube 7 is concentrically arranged inside the ring and spaced apart from the supply conduit 3. The dipping tube 7 is sealingly connected with the lid 2.
The mixture of ground matter and carrier gas/drying gas generated in the mill, or any other mixture of carrier gas and matter to be separated, flows upwards through the spacing between the funnel 4 and the wall of the separator casing 1 and enters the ring in a radial manner from outside through flaps 5. When passing through flaps 5 the flow of the mixture encounters a redirection and occasionally shear.
This causes the coarse grains of the matter to be separated to sink to the bottom and pass through funnel 4 such that it is guided back to the mill against the flow of the mixture of matter to be separated and carrier gas. The fine grains of the matter to be separated together with the carrier gas exit the separator in an axial manner through the ring area between dipping tube 7 and supply conduit 3 and is supplied to the consumer through several removal conduits 8. In the present invention, the consumer is a coal dust combuster having several burners. In this case, each burner is connected to one of the removal conduits 8.
The separator depicted in Figs. 2 and 3 is of the same principle construction as the separator depicted in Fig. l, but is constructed as a dynamic centrifugal separator that has a separator rotor with a rotating ring of vertically aligned and tilted slats 9 in place of the stationary ring of flaps 5. This ring is mounted on a driven hollow shaft 10, which surrounds the supply conduit at a small distance. The separator rotor is surrounded by a ring of stationary blinds 11 that serve as a guide apparatus to radially supply the flow of the mixture to the separator rotor. The operation of the separator rotor is substantially the same as that of the flap separator shown in Fig. 1. However, the separator rotor yields a larger degree of dust fineness as opposed to the flap separator.
Furthermore, it is possible to adjust the number of revolutions with the separator rotor and thus it is possible to further affect the dust fineness.
Turning to Fig. 3, the blinds 11 of the separator depicted in Fig. 2 are replaced with a flap separator 12 as shown and discussed in Fig. 1. Thus, the separator depicted in Fig. 3 is a centrifugal separator of static-dynamic construction.
In accordance with another embodiment of the invention, the central supply conduit 3 of the separators shown in Figs. 1 to 3 is replaced with a coal supply conduit leading directly into the grinding chamber of the mill. The separator is then constructed as shown in Fig. 4, for example. The ring of slats 9 of the separator rotor is mounted to a solid shaft 13. The solid shaft 13 is adjoined to a driving motor 14. The solid shaft 13 is surrounded by a protective casing 15. The protective casing 15 and the shaft 13 extend through the lid 2 into the separator casing 1.
Furthermore, the separator according to Fig. 4 is constructed such that it is connected to a beater mill or a tube mill, if desired. The funnel 4 below the separator rotor turns into a return conduit 16 that extends through the separator casing 1 into the coal supply of the beater mill or into the return conduit of the tube mill.
All of the discussed centrifugal separators have in common that their axial exit cross-section 17 is formed by the annular area between the dipping tube 7 and the supply conduit 3, as shown in Fig. 1, or the hollow shaft 10, as shown in Figs. 2 and 3, or the protective casing 15, as shown in Fig. 4. The dust distribution within the exit cross-section 17 is even as a result of the flow conditions in the centrifugal separators. The exit cross-section 17, as shown in Fig. 5 for a static centrifugal separator for example, is divided into segments 18 in order to remove the mixture flow of the mixture with an even dust distribution and, for example, to supply it to a coal dust combuster.
The segments 18 are preferably of the same size. Each of the segments 18 is connected with one of the removal conduits 8 via a transitional part 19 starting from the exit cross-section 17. According to Figs. 1 and 5, there are four removal conduits 8 connected to the centrifugal separator. Thus the exit cross-section 17 is divided into four segments 18.
According to Fig. 5, the removal conduits 8 are spatially located at the extension of the centre line of the segments 18. The transitional parts 19 are then radially outwardly bent. If desired, the exit cross-section 17 is divided into segments such that the removal conduits 8 are spatially shifted from the centre line of the segments 18.
In this case, the connecting transitional parts 19 are radially and tangentially bent towards the outside.

Claims

1. A centrifugal separator for separating a mixture of carrier gas and matter to be separated, comprising:
(a) an entry portion;
(b) an exit portion having a plurality of removal conduits coupled thereto, said exit portion being in communication with said entry portion; and (c) a plurality of guide elements coupled to said exit portion, said plurality of guide elements forming a ring surrounding an axial exit cross-section of said exit portion, said axial exit cross-section being divided into a plurality of segments, wherein each of the plurality of segments is coupled to a removal conduit of the plurality of removal conduits.

2. A centrifugal separator as defined in claim 1, wherein said centrifugal separator is disposed at an end of a mill for cutting and dry grinding of a raw material

3. A centrifugal separator as defined in claim 1 or 2, wherein said centrifugal separator is a static centrifugal separator having a stationary ring of adjustable flaps.

4. A centrifugal separator as defined in claim 1 or 2, wherein said centrifugal separator is a dynamic centrifugal separator having a rotating ring of one of stationary and adjustable slats, said slats are vertical or inclined.

5. A centrifugal separator as defined in claim 1 or 2, wherein said centrifugal separator is a static-dynamic centrifugal separator having a stationary ring of adjustable flaps followed by a rotating ring of one of stationary and adjustable slats.

6. A centrifugal separator as defined in any of claims 1 to 5, further comprising a supply conduit for supplying a raw material, said supply conduit extending through the ring of the plurality of guide elements into a grinding chamber of the mill, and wherein said exit cross-section is circular.