GB2282980A

GB2282980A - High temperature gas filter

Info

Publication number: GB2282980A
Application number: GB9418706A
Authority: GB
Inventors: Urquijo Ignacio Abellanal; Barreras Vicente Peral; Calvo Ignacio Martin; Aburto Ignacio Bilbao
Original assignee: Babcock and Wilcox Espanola SA
Current assignee: Babcock and Wilcox Espanola SA
Priority date: 1993-10-22
Filing date: 1994-09-16
Publication date: 1995-04-26
Anticipated expiration: 2014-09-16
Also published as: SE515542C2; SE9403371D0; ES2077508B1; GB2282980B; SE9403371L; DE4431816A1; GB9418706D0; ES2077508A1

Description

1 HIGH TEMPERATURE HIGH PRESSURE GAS FILTER USING CERAMIC CANDLES 2282980

This invention relates to a high temperature high pressure gas filter using ceramic candles, which are filter elements comprising hollow porous cylinders which are sealed at one end and open at the other. made of ceramic material. Filtration takes place when the dust-laden gases pass through the unit from the outside, where the dust particles carried by the gas are deposited, to the inside, where the clean gases are collected. As the gases are filtered. the layer of dust on the outside of the elements grows, and so also does the resistance to the passage of the said gases. In order to regenerate the elements it is necessary to apply an internal excess pressure pulse within the elements which instantaneously reverses the direction of flow of the gases and detaches the layer of dust adhering to the elements.

The expansion coefficient of ceramics is of the order of three or f our times less than that of steel, which gives rise to connection problems. On the other hand the behaviour of the ceramic elements under tension is very much poorer than it is under compression, and this is another factor which has to be borne in mind when securing the elements.

In industrial applications the number of filter elements becomes large, and therefore the arrangement of these elements must permit an optimum relationship between filter volume and filtering surface area.

In the simplest filter known so far, the candle elements are supported on a tube plate from which the elements are suspended downwards.

2 The upper end of a candle is in the shape of a ball, which provides a good seat on the joint located between the element and the tube plate. The element is secured to the plate by means of a weight placed on the candle.

The tube plate divides the vessel into two parts, a clean upper part and a soiled lower part.

When it is desired to increase the number of filter elements, the diameter of the tube plate must be increased, and thus the thickness of the plate must also be increased, reaching limits for this dimension. The seal provided by the means of counterweights may fail under some circumstances, when the loss of head in the filter exceeds particular values, due to lifting of the candles.

If the candles are secured in a more rigid fashion than that provided by the counterweights, the candles may be damaged due to the appearance of bending moments at the time of attachment.

European patent 0 328 862 discloses a filter in which the candles are supported vertically on horizontal collectors in such a way that the candles are sealed by their own weight and with the help of the differential pressure which is produced during filtration. In addition to this a weight is placed on the candles.

Different levels of collectors and candles can be located within the filter, optimising the space.

When cleaning is in progress, depending on the thickness of the layer of dust and the permeability of the said dust, when an internal pressure builds up in the filter element the sealing force may again be lost due to lifting of the candles. In addition to this the dust which f alls is deposited very close to the place where the seal is made, and if there is a 1 3 leak through the connection a large quantity of dust may be drawn through.

1 The applicant has developed a filter whose essential feature lies in the f act that the sealing f orce f or the candles always subjects them to compression. This force is greater than that which can be achieved by means of counterweights, and is also a f orce which can easily be controlled by controlling the pressure within the expansion joints.

According to the invention there is provided a f ilter f or high temperature high pressure gas using ceramic candles, characterised in that the candles are arranged to open into the lower part of primary collectors, with expansion elements being allocated at a lower support for the candles.

It is also characterised in that the expansion elements are expansion joints whose internal pressure can be adjusted.

It is also characterised in that the expansion elements are sof t.

It is also characterised in that the candles are placed in line with respect to each primary collector, in that each set of primary collectors opens into a secondary collector which in turn opens into the main clean gas outlet collector.

It is also characterised in that each set of primary collectors with their secondary collector f orm a rhombusshaped unit.

It is also characterised in that the rhombus-shaped unit has sliding supports on one of its sides.

It is also characterised in that each expansion joint is supported on a support.

4 It is also characterised in that the support is fixed to the collectors.

It is also characterised in that each candle is joined to a primary collector by means of a supporting cap within which is housed a sealing joint of ceramic material on which the mouth of the candle is supported.

It is also characterised in that the expansion joint is precompressed from the outset and its interior is pressurised when the temperature increases.

It is also characterised in that the expansion joint has a unidirectional guide with a stop.

It is also characterised in that the supports for each unit are joined together.

For a better understanding of the subject matter of this invention, a preferred embodiment to which additional changes may be made without detracting from its fundamental features is shown in the drawings.

Figure 1 is a diagrammatical view in elevation of the filter according to the invention.

Figure 2 is a diagrammatical view in plan of Figure 1.

Figure 3 is a view in elevation of the arrangement of candles (8) in Figures 1 and 2.

Figure 4 is a view in half -cros s- section of another embodiment of the lower support for the candle.

Figure 5 is a view in cross-section of another embodiment of the upper joint between a candle and collector.

A non-restrictive practical embodiment of this invention is described below. Other embodiments introducing additional changes which do not detract from its fundamental characteristics are not ruled out: on the contrary,, this invention includes all variants thereof.

A body (9) has an inlet (11) for dirty gases which have to be filtered and an outlet (12) for unfiltered solid residues such as e.g. ash.

The dirty gases are filtered by candles (8) of ceramic material which open. for the transport of clean filtered gas, into primary collectors (1) which in turn open into corresponding secondary collectors (2) which open into a main collector (13) for discharge of the clean gases.

Given that the operating temperatures reach some 800C, with the result that expansion is great, and in order to achieve good economy in the utilisation of space, and given that the operating pressures may reach some 16 atmospheres or more, which makes cylindrical vessels (9) compulsory, it is provided that the primary collectors (1) form rhombusshaped units (r) with their corresponding secondary collectors (2).

In this embodiment (Figure 2) the primary collectors (1) are joined at one end by welding (20) to the secondary collector and have at their other end a common connector unit (21) which is supported with the ability to slip e.g. on two trays (22) which may both be fixed to the vessel (9) or, as in Figure 2, one may be attached to the secondary collectors (2) and the other to the vessel (9).

The arrangement of the candles (8) with their seals can be seen in Figure 3.

At the top is located a cap (5), which in this case is of metal and is welded to the primary collectors (1), which acts 6 as a support for candles (8), on the inside of which there is a joint/seat (6) of ceramic material, e.g. ceramic fibre, which ensures a perfect connection and technical operation, e.g. from the point of view of thermal expansion, sealing, alignment of forces, etc.

As the connection (5), (6) between candles (8) and primary collectors (1) is in the lower part thereof, the accumulation of dust therein is prevented, and possible minor leaks through the said connection yield a negligible dust content.

Each candle (8) is provided with a support (4) which in this embodiment is attached to the primary collectors (1) and secondary collectors (2).

This support (4) may be joined to its adjacent members in each rhombusshaped unit (r) by means of corresponding separator members and form frames as in Figure 1.

Each candle (8) is supported on each support (4) by an expansion joint (3) which on some occasions may be replaced by a compression spring.

Expansion joint (3) in this embodiment comprises: a first blank flange (23) which directly supports candle (8).

a second blank flange (24) supporting support (4). a bellows (25) of coarse ceramic fibre.

a unidirectional guide (26) with a stop. a gasket (28) of woven ceramic fibre between flanges (23) and (24).

The interior (27) of expansion joint (3) is in communication with an external source of pressure by means of a connection (7).

7 The said joint (3) is fitted precompressed so that under cold conditions it acts as a spring with its own actual compression force, acting against the lower part of ceramic element (8) and keeping it pressed against primary collector (1).

As the filter comes up to temperature, expansion joint (3) is pressurised through connection (7) applying a controllable force on filter element (8) merely by control of the pressure within joint (3). This force is independent of any losses of head or weight in the system and remains constant throughout all the period when the f ilter is in operation, but these conditions can be changed by the user, as he has control over the pressure which is transmitted through connection (7).

In Figure 4, in another embodiment, it will be seen that the supporting beam (4) for the expansion elements which support candles (8) is secured by welding to the outer sleeve (C.) and bottom plate (tf) of an expansion compensator (3,.) which is sealed at the top by the upper plate (t,) which incorporates an orifice (0,J through which slides spacer cap (C,). Internally there is a bellows (f) joined at the top to the upper plate (t, ) and at the bottom to the head (cc) of spacer cap (Cd), which has a diameter (dl) which is less than the internal diameter (d2) of outer sleeve (CJ,, creating a leaktight chamber (ct) between the moving and fixed parts of the expansion compensator (3j.

It is arranged that at the top the head (cc) of cap (Cd) 'S subjected to environmental pressure (P.J, as this cap has a longitudinal perforation (02) while from below it is subjected to a pressure (P2) controlled by the user and normally greater than the (pressurised) environmental pressure P2 > P,, thus controlling the height of head (cc) and as a consequence the height of spacer cap (Cd)- Controlled pressure (P2) is passed e.g. through a gauged orifice (03) in the bottom plate (tf) or laterally.

8 The gauge of orif ice (03) may be large to avoid excessive f low loss if a candle (8) should fracture in the expansion compensator (3,), af f ecting the stability of the other candles (8).

Many of the members included in these f ilter installations such as collector (1) and supporting beam (4) are steelwork permitting larger manufacturing and assembly tolerances than those which can be accepted for the joints between the expansion compensators (3,) and candles (8), and it has therefore been shown that the misadjustments must be levelled out. In order to achieve this it is provided that spacer cap (cd), which is threaded at the top, has a levelling support (s) which is threaded into it at the base and supports candle (8) above.

A female sleeve (c.) of the outer sleeve (c.) is also fixed to spacer cap (C,,).

Over the course of time the (porous) ceramic walls of candles (8) become clogged, with the result that countercurrent (CJ cleaning is necessary (Figure 5).

There is a long way between the source of pressure creating the countercurrent to the last candle which receives this pressure,, so that the f irst upstream candles are cleaned rapidly, while the last downstream candles are still beginning to be cleaned.

Under these circumstances the countercurrent air tends to escape, as it does not encounter any resistance due to the candles already cleaned, which makes cleaning of the last candles difficult.

In order to avoid this problem a constriction in the flow of f luid is provided at the junction between collector (1) and candle (8) in such a way that the loss of head (AH) to which 9 it is subjected increases as the pressure difference between the pressure inside (PJ and the pressure (P2) outside the candle decreases, i.e. as the candle becomes clean, and offers less resistance to the passage of air through its walls.

In this specific case which is shown in Figures 1 and 2, a cap (5) with a perforation (0,) which is subjected to a constriction (e) such that as the air velocity increases the laminar f low regime is disturbed and turbulence increases, increasing the loss of head.

Cap (5) incorporates an upper bevel (50) for welding to collector (1), a recess (51) in its lower base for housing candle (8) and a peripheral projection (52) which acts as a stop for a safety cap (53) which slides externally over cap (5) so that when in the raised position (dashed line) candle (8) is released for repositioning/fitting and in its lower position (continuous line) clasps the upper part of candle (8) preventing it from becoming loose.

The materials, dimensions, proportions and, in general, those other accessory or secondary details which do not alter, change or modify the essential nature of what has been proposed may vary.

The terms in which this description are drawn up are a true and accurate reflection of the object described, and are to be understood in their widest sense and not in any restrictive way.

Claims

1. A high temperature high pressure gas filter using ceramic candles, characterised in that the candles are arranged to open into the lower part of primary collectors, with expansion elements being located as a lower support for the candles.

2. A filter for high temperature high pressure gases using ceramic candles according to the foregoing claim, characterised in that the expansion elements are expansion joints whose internal pressure can be adjusted.

3. A filter for high temperature high pressure gases using ceramic candles according to claim 1, characterised in that the expansion elements are springs.

4. A filter for high temperature high pressure gases using ceramic candles according to the forgoing claims, characterised in that the candles are arranged in line with respect to each primary collector, each set of primary collectors opening into a secondary collector which in turn opens into the main collector for discharge of the clean gases.

5. A filter for high temperature high pressure gases using ceramic candles according to claim 4, characterised in that each set of primary collectors forms a rhombus-shaped unit with its secondary collector.

6. A filter for high temperature high pressure gases using ceramic candles according to claims 4 and 5, characterised in that the rhombus- shaped unit has sliding supports on one of its sides.

7. A filter for high temperature high pressure gases using ceramic candles according to claim 2, characterised in that each expansion joint is supported on a support.

4 1.

11 8. A filter for high temperature high pressure gases using ceramic candles according to claim 7, characterised in that the support is secured to the collectors.

9. A filter for high temperature high pressure gases using ceramic candles according to the foregoing claims, characterised in that each candle is joined to the primary collector by means of a supporting cap within which is housed a joint/seal of ceramic material on which the mouth of the candle is supported.

10. A filter for high temperature high pressure gases using ceramic candles according to claim 2, characterised in that the expansion joint is precompressed from the outset and its interior is pressurised when the temperature increases.

A filter for high temperature high pressure gases using ceramic candles according to claim 2, characterised in that the expansion joint has a unidirectional guide with a stop.

12. A filter for high temperature high pressure gases using ceramic candles according to claim 8, characterised in that the supports for each unit are joined together.

13. A filter for high temperature high pressure gases using ceramic candles according to claim 1, characterised in that the expansion members comprise an expansion compensator whose piston comprises a spacer cap into the head of which is threaded a levelling support which receives the base of the candle on its upper end.

14. A filter for high temperature high pressure gases using ceramic candles according to claim 13, characterised in that the opening of the candle into the collector consists of a cap fixed to the collector upon which slides with a stop a safety cap which encloses the candle at the lower base of the cap and which clasps the safety cap in the upper region of the candle.

12 15. A filter for high temperature high pressure gases using ceramic candles according to claim 13, characterised in that the spacer cap comprises:

a) an external sleeve and an end plate fixed to a supporting beam, a top plate a central orifice f ixed to the external sleeve, in which slides b) the spacer cap whose head slides within the outer sleeve c) a bellows attached to the upper plate and the head of the spacer cap.

16. A filter for high temperature high pressure gases using ceramic candles according to claim 15, characterised in that the spacer cap has a blind longitudinal orifice within which atmospheric pressure is set up and has a source of supply pressurising the chamber located between the head of the spacer cap and the bottom plate.

17. A filter for high temperature high pressure gases using ceramic candles according to claim 1, characterised in that the candles are arranged so as to open into the lower part of the primary collectors, wherein provision is made for a constriction of the fluid flow at the collector/candle junction where the loss of head increases as the pressure difference between the inside and outside of the candle decreases.

18. A filter for high temperature high pressure gases substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 3 of the accompanying drawings.

19. A filter for high temperature high pressure gases substantially as hereinbefore described with reference to and as illustrated in Figures 1, 2 and 4 of the accompanying drawings.

20. A filter for high temperature high pressure gases substantially as hereinbefore described with reference to 1 13 Figures 1 to 3. or Figures 1, 2 and 4 of the accompanying drawings as modified by Figure 5.