GB2136325A

GB2136325A - Improvements In or Relating To Cyclone Separators

Info

Publication number: GB2136325A
Application number: GB08306735A
Authority: GB
Inventors: Peter William Sage; Alan Ellis; Alan Frank Hitchman
Original assignee: Bigwood Joshua & Son Ltd; Coal Industry Patents Ltd
Current assignee: Bigwood Joshua & Son Ltd; Coal Industry Patents Ltd
Priority date: 1983-03-11
Filing date: 1983-03-11
Publication date: 1984-09-19
Also published as: GB8306735D0; GB2136325B

Abstract

In a cyclone separator (1) having an expansion chamber (14) at the base thereof, a suction member (22) extends into the chamber (14) and terminates therein on or near the axis thereof at the equilibrium point of the vortex generated. A proportion of the gas flow is drawn off from the equilibrium point and is passed to a filter for removal of particulates. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Cyclone Separators This invention concerns improvements in or relating to cyclone separators.

In particular, the present invention has reference to such separators for use in the cleaning of particle laden gases, for example those issuing from a solid fuel combustion system. Conventional cyclone separators have shown themselves to be inadequate for the purpose of separating substantially all the particles entrained in the gaseous combustion products from some combustion systems. A reason for this is that the vortical flow generated within the cyclone proceeds bidirectionally: initially the vortex passes downwardly until it reaches an equilibrium point and then reverses back upon itself travelling upwardly through the centre of the cyclone to exhaust at the top of the cyclone.During the passage of the vortex through the cyclone, particles are centrifuged to the side and move down the cyclone wall to the base, other relatively larger particles precipitating out at an earlier stage than the relatively fine particles. It has been observed that some of the relatively fine particles tend to become re-entrained at the equilibrium point and are thus transported out of the cyclone with the discharging gas which thereby remains more heavily contaminated with particulates.

In view of the environmental regulations now in being, at least in the United Kingdom, it has become necessary to investigate ways of improving gas cleaning efficiency. It has been found that one alternative to cyclone separation is the bag filter. However, in order to achieve the requisite degree of efficiency, large units would be necessary and the cost would be correspondingly high. Attention has, therefore, been focussed upon the cyclone to improve performance by reducing particulate emissions.

An object of the present invention is, therefore, to provide an improved cyclone separator.

A further object of the invention is to provide a method of operating the improved cyclone separator.

According to a first aspect of the invention then is provided a cyclone separator including a body having an upper cylindrical section and a relatively lower hollow frusto-conical section integral therewith, the upper section having a tangential inlet and an axial outlet, the lower section having an axial discharge port leading to an expansion chamber, and a suction member extending into the expansion chamber beneath the port.

The suction member may conveniently be an open-ended pipe terminating on or near the axis of the expansion chamber. The open end of the pipe may be orientated radially or may be directed downwardly within the chamber. The pipe itself may be angularly or radially directed in relation to the axis of the chamber.

The suction member is preferably connected to a filter externally of the chamber, the filter being of either the metallic or the non-metallic type. An example of a non-metallic filter suitable for use in the invention is a bag filter constructed of a suitable flexible filter fabric. Alternatively the filter may be a cyclonic type high efficiency filter.

A suction fan is connectible to the downstream side of the filter to induce gas flow therethrough.

An induced draught fan is connectible to the axial outlet of the upper section of the cyclone separator body.

The axial outlet may be formed of a vortex finder tube extending part way into the upper section of the body.

In an alternative embodiment the axial outlet may comprise two concentric tubes, the relatively inner tube opening to exhaust and the relatively outer tube being provided with a further suction member communicating with the annular space between the two tubes.

The further suction member is preferably connected to a further filter being of either the metallic or non-metallic type. A suction fan is connectible to the downstream side of the filter.

According to a second aspect of the invention a method of operating the cyclone separator of the first aspect, the method including the steps of inducing flow of a particle laden gas through the tangential inlet of the upper section of the body to generate vortical flow which passes downwardly into the lower section, particles being centrifuged to the wall of the body, the vortical flow passing down through the port into the expansion chamber wherein it reverses at an equilibrium point, and drawing off through the suction member a proportion of the flow at or near the equilibrium point.

The proportion of the flow drawn off through the suction member preferably lies in the range of 5 to 25% represented as a percentage of the flow through the tangential inlet to the cyclone separator.

As a further preference, the proportion lies in the range of 10 to 16%.

The method of the invention also includes the step of drawing off a proportion of the flow of gas exhausting through the axial outlet. This proportion is drawn off from the annular space formed between the concentric tubes of the axial outlet and through the further suction member.

The proportion of flow drawn off at the equilibrium point and, when appropriate, that drawn off at the axial outlet are passed through the filter to clean the gas. For convenience, when part of this flow is drawn off at both locations, a single suction fan and single filter may be employed.

By way of example only, two embodiments of a cyclone separator according to the present invention and a method of operating the same are described below with reference to the accompanying drawings: Figure 1 is a cut-away perspective and diagrammatic view of a first embodiment; and Figure 2 is a cut-away perspective and diagrammatic view of a second embodiment.

With reference to Figure 1, a cyclone separator is shown generally at 1 and comprises a body 2 having an upper cylindrical section 4 provided with a tangential inlet 6 and an axial outlet 8 in the form of a vortex finder tube 1 0. A relatively lower hollow frusto-conical section 1 1 is formed integrally with section 4 and has an axial discharge port 12 which communicates with an expansion chamber 14. The chamber 14 also has a cylindrical upper section 1 6 and an integral, lower hollow frusto-conical section 18 provided with a discharge outlet 20.

A suction member 22 in the form of a pipe 24 protrudes through the wall of section 1 6 into the chamber 14 and has its free open end curved downwardly as shown at 26. The end 26 is located on or near to the axis of the chamber 14 and substantially at the equilibrium point of the vortex which is generated in use within the separator.

In operation, the inlet 6 is connected to a supply of particle-laden gas which may, for example, be provided by the exhaust from a solid fuel combustor. An induced draught fan 30 is coupled to the axial outlet 8. A suction fan 32 is coupled to the suction member 22 through a filter 34 which may be a bag filter.

The draught induced by fan 30 causes the particle-laden gas to enter through inlet 6 thereby to create a vortex within the body 2 of the separator 1, as indicated by the arrows. Particles entrained in the gas are centrifuged to the wall of the body 2 and slide down through sections 4 and 11 and through the axial discharge port 12, into the expansion chamber 14.

Just beneath the port 12 within chamber the vortex reaches equilibrium at which point it reverses upon itself and travels upwardly through the body 2 of the separator 1, the gas exhausting through the axial outlet 8. It is believed that in convential cyclone separators fine particles precipitated above the region of the equilibrium point tend to become re-entrained as they approach port 1 2, thus recontaminating the gas. In the present invention, a proportion of the gas flow, represented as a percentage of the total gas inlet flow, is withdrawn at or near the equilibrium point through the suction member 22; the gas together with any entrained particulates is induced by the fan 32 through the filter 34 which captures such particulates. The gas spiralling upwardly from the equilibrium point is then cleaner than would otherwise be the case in the absence of such withdrawal.

Tests have indicated that a marked reduction in emission of particulates from a cyclone separator can be achieved by employing the present invention. The proportion of gas withdrawn at the equilibrium point may be within the range 5 to 25% of the inlet gas flow. Table 1 below gives performance characteristics using the present invention and a datum constituted by the performance of a cyclone separator lacking the facility for withdrawing a proportion of the gas flow at the equilibrium point, and known to be free of air leaks into the expansion chamber from the surrounding atmosphere.

TABLE 1

Gas Withdrawal Overall Rate at Equilibrium Cyclone Reduction Point (% of Separator in Cyclone Separator Collection Emission Emission Inlet Flow Efficiency (%) (%) Conventional Cyclone Separator 0 99.23 0.77 0 Cyclone Separator according 5 99.39 0.61 21 to the present situation 10 99.51 0.49 36 15 99.59 0.41 47 20 99.63 0.37 52 25 99.67 0.33 57 Referring now to Figure 2, similar parts have been assigned the same reference numerals as those in Figure 1. The cyclone separator 1 of the second embodiment is substantially the same as the first embodiment except that the axial outlet 8 in the upper cylindrical section 4 is of different form. In the second embodiment, the axial outlet 8 is formed of two concentric tubes, a vortex finder tube 50 having an open end 51 extending into section 4 and terminating in a closed end 52 outside this section. An inner tube 54 of shorter length than tube 50 is disposed concentrically therewithin and extends out through the end 52 of tube 50 to form an exhaust pipe 56. An annular space 58 is defined between the tubes 50, 54 and at the top of the tube 50, outside section 4, a further suction member 60 penetrates the tube 50 to communicate with the space 58.The suction member 60 is coupled via a filter 62 to a suction fan 64.

In operation of the second embodiment, the withdrawal of proportions of gas flow occurs both at the equilibrium point and from the axial outlet 8, suction being applied to the fans 32 and 64. The object of providing a second withdrawal facility at the outlet point is to extract any fine particulates which may still be entrained in the exhausting gas. In practice, the total proportion of gas withdrawn is divided as between the outlet and the equilibrium point. Thus, for example, if the total proportion of gas to be withdrawn were to be of the order of 20% of the inlet gas flow to the separator, 10% may be withdrawn at each location. It is to be understood, however, that the split as between the top and bottom of the separator may be other than equal.

It will be appreciated that particles deposited in the expansion chamber 14 are removed through the outlet 20.

It has been found that by employing this method of withdrawing a proportion of the total gas inlet flow at both points in the cyclone separator, a reduction in emission levels over those obtained using a conventional cyclone can be achieved.

The present invention therefore, represents a novel and inventive departure from current cyclone design and operation whereby particulate emission can be significantly reduced, thus serving to improve environmental standards.

Claims

1. A cyclone separator including a body having an upper cylindrical section and a relatively lower hollow frusto-conical section integral therewith, the upper section having a tangential inlet and an axial outlet, the lower section having an axial discharge port leading to an expansion chamber, and a suction member extending into the expansion chamber beneath the port.

2. A cyclone separator according to claim 1 in which the suction member is an open-ended pipe terminating on or near the axis of the expansion chamber.

3. A cyclone separator according to claim 2 in which the open end of the pipe is orientated radially.

4. A cyclone separator according to claim 2 in which the open end of the pipe is directed downwardly within the chamber.

5. A cyclone separator according to claim 2 in which the pipe is angularly or radially directed in relation to the axis of the chamber.

6. A cyclone separator according to any one of the preceding claims in which the suction member is connectible to a filter externally of the expansion chamber.

7. A cyclone separator according to claim 6 in which a suction fan is connectible to the downstream side of the filter.

8. A cyclone separator according to claim 6 or 7 in which the filter is of the metallic type.

9. A cyclone separator according to claim 6 or 7 in which the filter is of the non-metallic type.

10. A cyclone separator according to claim 9 in which the filter is a fabric filter.

11. A cyclone separator according to any one of the preceding claims in which the axial outlet is formed of a vortex finder tube extending part way into the upper section of the body.

12. A cyclone separator according to any one of claims 1 to 10 in which the axial outlet comprises two concentric tubes, the relatively inner tube opening to exhaust and the relatively outer tube being provided with a further suction member communicating with the annular space between the two tubes.

13. A cyclone separator according to claim 12 as dependent upon claims to 10 in which the further suction member is connectible to the filter or to a further filter.

14. A cyclone separator according to claim 1 3 in which the downstream side of the filter or the further filter is connectible to the suction fan or a further suction fan.

15. A cyclone separator according to any one of the previous claims in which an induced draught fan is connectible to the axial outlet of the upper section of the cyclone separator body.

1 6. A cyclone separator substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

17. A method of operating the cyclone separator as claimed in claim 1, comprising the steps of inducing flow of a particle-laden gas through the tangential inlet of the upper section of the body to generate vortical flow which passes downwardly into the lower section particles being centrifuged to the wall of the body, the vortical flow passing down through the port into the expansion chamber wherein it reverses at an equilibrium point, and drawing off through the suction member a proportion of the flow at or near the equilibrium point.

1 8. A method according to claim 1 7 in which the proportion of the flow drawn off through the suction member lies in the range 5% to 25% of the gas flow through the tangential inlet to the cyclone separator.

1 9. A method according to claim 1 8 in which the proportion of the flow drawn off through the suction member lies in the range 10% to 16% of the gas flow through the tangential inlet to the cyclone separator.

20. A method according to claim 17 and including the step of drawing off a proportion of the flow of gas exhausting through the axial outlet.

21. A method according to claim 1 7 or 20 in which the proportion or proportions of gas flow drawn off are passed through a filter to clean the gas.

22. A method of operating a cyclone separator substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.