GB2248441A - Device and method for material discharge - Google Patents

Abstract

A device 1 for discharging particulate material, for example fines from a gasifier operating at an elevated pressure and temperature, includes a housing 2 defining a chamber 12 which contains a packed bed 14 of e.g. glass or metal beads resting on a mesh 16. The housing 2 has an inlet 4 connected to a feed tube 6 for retaining a leg of material to provide a seal against the high pressure. A means 22 for vibrating the bed is provided, and in use, upon vibration, fines material bridging and blinding the bed is dislodged and discharges through the outlet 18. <IMAGE>

Description

DEVICE AND METHOD FOR MATERIAL DISCHARGE This invention relates to a device and a method for material discharge for use in particular, but not exclusively, in association with high pressure process environments.

One process environment to which the present invention has reference is that of a pressurised gasifier in which solid fuel, eg coal, is gasified advantageously employing a fluidised bed to provide a gas at high pressure and a char for combustion in a fluidised bed combustor which may be of conventional type or of circulating bed type. During the gasification process, fine material is elutriated from the fluidised bed and has to be separated from the high pressure gas prior to the latter's usage, for example in gas turbine operation. The fines so separated are then fed to the combustor which is may be operated at atmospheric pressure.

Accordingly, the fines have to be removed from the high pressure gas stream with a minimum loss of gas.

Conventionally, lock hoppers have been employed for their capability to isolate high pressure from low pressure environments whilst allowing flow across the boundary between the two. Generally, the use of equipment of this type has proved satisfactory, however their efficacy is dependent upon the characteristics of the material to be handled. In this connection, the fines elutriated from a gasification bed tend to be abrasive and thus the lock hopper valves are subject to considerable erosion, and corrosion by the associated product gas.

An object of the present invention is to provide a material discharge device which is operational in harsh environments with an improved performance compared with existing equipment without the use of valves.

Accordingly there is provided as a first aspect of the present invention a material discharge device including a housing having an inlet for connection to a high pressure environment, a feed tube connected to the inlet, the inlet communicating with a chamber defined within the housing for containing a packed bed of discrete particles, an outlet from the chamber for connection to a relatively lower pressure environment, and means for imparting vibration to the chamber.

The packed bed of discrete particles may completely or partially fill the chamber within the housing and the particles may advantageously be in the form of beads, which may be ceramic, metal or another suitable medium.

The means for imparting vibration to the chamber may be mechanical or in the alternative may be electromagnetic or ultrasonic or may employ audio frequency.

A second aspect of the present invention provides a method of discharging material including the steps of passing a stream of particulate material borne in a high pressure gas in flow communication with a housing having a feed tube leading to an inlet thereof, depositing material on a packed bed of discrete particles contained within a chamber of the housing, maintaining a leg of the particulate material within the feed tube, and imparting vibration to the packed bed of discrete particles to effect discharge of the deposited particulate material through an outlet from the housing to a relatively lower pressure environment.

The deposition on the discrete particles, which may be in the form of beads, is such as to blind the bed by the bridging mechanism thereby preventing any material flow therethrough, the leg of particulate material restricting leakage of the high pressure gas through the outlet.

Upon vibration of the packed bed, the bridging by the deposited material and the bed is no longer blinded, the deposited particulate material being discharged through the outlet from the housing. The leg of material within the feed tube maintains a seal between the packed bed and the high pressure environment to restrict egress of the high pressure gas. When discharge is complete, the vibration is interrupted and the packed bed of discrete particles again becomes blinded with bridged particulate material freshly deposited thereon.

The particulate material may be fines borne by high pressure product gas from a fluidised bed coal gasifier, the fines being subsequently burnt in a fluidised combustion bed.

By way of example only, two experimental embodiments of a device for and a method of discharging material are described below with reference to the accompanying drawings in which figure 1 is a schematic representation of a first embodiment and Figure 2 is a schematic representation of a second embodiment of the device.

Referring to Figure 1, there is shown generally at 1 a device for the discharge of material, the device 1 comprising a housing 2 having an inlet 4 provided with a vertical feed tube 6 in which a control valve 8 is located. A reservoir 10 for particulate material is provided upstream of the valve 8.

The housing 2 defines a chamber 12 for the containment of a packed bed 14 of discrete particles which in this example are glass beads. The size of the glass beads and their depth within the chamber 12 are selected to provide the requisite performance as hereinafter explained. The packed bed 14 is supported within the chamber 12 on a perforate sheet, for example a mesh 16, which extends across an outlet 18 of the housing 2.

The housing 2 has a lateral extension 20 which intersects the the chamber 12 and accommodates a rod 22 which protrudes beyond the extension 20 to the outside of the housing 2 and is connected to a mechanical vibration means (not shown). A flexible gland 24, for example of rubber, is provided at the outer end of the extension 20 through which the rod 22 passes. The internal end 26 of the rod 22 is bent downwardly and is fully immersed within the packed bed 14.

In operation, the device 1 is associated with a high pressure flow of a gas, in this example a product gas from a fluidised bed gasification process carrying fines material elutriated from the bed. The pressure of the gas may be of the order of 15 bar.

In this experimental embodiment, fines material is held in the reservoir 10 and is pressurised by the gas. A leg of fines is created in the feed tube 6, the fines passing through the valve 8. The fines also are deposited on the glass beads of the bed 14 and bridge thereon; the size and depth of the glass beads are selected to ensure that the fines bridge the beads and thus blind the bed 14, thereby preventing the discharge of the fines material through the outlet 18. The leg of fines within the feed tube 6 ensures that a seal is created to reduce loss of gas.

When it is desired to effect discharge of the bridged fines on the glass beads of the bed 14, the rod 22 is vibrated. The vibration is imparted to the bed particularly by the end 26 of the rod causing movement of the beads such as to dislodge the fines and break the bridges, thereby to allow the fines material to discharge through the outlet 18 past the mesh 16. Once sufficient fines have been discharged, vibration of the rod 22 is discontinued thus bringing the bed to rest and allowing the fines within the chamber 12 to deposit on the glass beads and to bridge, thereby preventing any further discharge.

When it is desired again to discharge material from the housing 2, the above procedure is repeated. The discharge flow rate of material from the housing may be regulated by varying the vibration.

Referring now to Figure 2, a second embodiment of the device is shown and includes substantially all the features of the device of Figure 1 and accordingly like numerals of reference have been employed to denote like parts.

In this embodiment the means for imparting vibration to the housing 2 is located externally thereof as shown at 30 without the need for the lateral extension of Figure 1 and its associated rod 22. Advantageously, the vibration means are ultrasonic.

The present invention thus provides a relatively simple device for and method of discharging material from a high pressure environment to a lower pressure environment. The device is of simple construction and will conveneniently be made of a material capable of operating at high temperatures, for example of the order of 5000C and above. The material of construction may be metal or ceramics or other suitable material.

Claims (8)

1. A material discharge device including a housing having an inlet for connection to a high pressure environment, a feed tube connected to the inlet, the inlet communicating with a chamber defined within the housing for containing a packed bed of discrete particles, an outlet from the chamber for connection to a relatively lower pressure environment, and means for imparting vibration to the chamber and/or its contents.

2. A material discharge device according to claim 1 in which the packed bed of discrete material in practice partially or completely fills the chamber of the housing.

3. A material discharge device according to claim 1 or 2 preceding claims in which the means for imparting vibration to the chamber is mechanical, electromagnetic, ultrasonic, or audio frequency.

4. A material discharge device substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

5. A method of discharging material including the steps of passing a stream of particulate material borne in a high pressure gas in flow communication with a housing having a feed tube leading to an inlet thereof, depositing material on a packed bed of discrete particles contained within a chamber of the housing, maintaining a leg of the particulate material within the feed tube, and imparting vibration to the packed bed of discrete particles to effect discharge of the deposited particulate material through an outlet from the housing to a relatively lower pressure environment.

6. A method according to claim 5 in which the deposition of the material upon the discrete particles is such as to blind the packed bed temporarily until vibration is imparted to the bed.

7. A method according to claim 5 or 6 in which the particulate material is gasifier fines borne by product gas at an elevated temperature.

8. A method substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.