GB2108399A - Dispensing particulate abrasive material into a gas stream - Google Patents

Abstract

Particulate abrasive material is supplied from a container 7 to a stream of gas in a line 1 via dispensing means including a conveyor belt 9 and a duct 6. A pressure equalizing conduit 13 extends between the interior of the container 7 and said gas supply line 1 and has its lower end facing upstream in the line 1 so that owing to the ram effect of the gas, which is throttled by a valve 3 and an orifice plate 4, the pressure in the container 7 is kept higher than that at the outlet of the duct 6. The higher pressure is also maintained around the conveyor belt 9 and at the upstream end of the duct 6 by a gas-tight housing 12. The arrangement enables small quantities of abrasive material to be metered accurately into the gas stream. <IMAGE>

Description

SPECIFICATION Apparatus and method for dispensing particulate abrasive material into a gas stream This invention relates to apparatus and methods for dispensing particulate abrasive material into a gas stream. The apparatus comprises a supply line for the gas having means for controlling the extent of the stream of gas through the supply line, a supply container for the abrasive material, the container being connected through dispensing means to the gas supply line, and a discharge line for the discharge of the gas stream laden with the abrasive material.

Such apparatus is disclosed in Dutch Patent Application 7708990, and is intended for cleaning and/or decoking the interior of pipelines. For this purpose the stream of gas laden with abrasive material is introduced into the pipeline to be cleaned via a suitable injection head. The abrasive material impinges on the pipeline wall, which is to be cleaned, at a high radial velocity owing to turbulent and vortex movements in the stream of gas.

For the cleaning of the pipelines, use can be made of abrasive material having sharp edges, such as sand or steel grit, but also abrasive material in the form of steel balls, so-called steel shot, and other materials may be used.

It has been found that the decoking and cleaning of pipelines having a relatively large diameter, such as are found in hydrocarbon furnaces in refineries, can be carried out by the use of such apparatus in a particularly effective way, it being possible for the pipelines to be stripped of every kind of material deposit.

It has also been found, however, that the cleaning of pipelines having a small diameter, i.e. diameters in the order of only a single or a few centimetres, is impossible by means of the existing apparatus. This is because the small amount of abrasive material that must be supplied to the stream of gas for the cleaning of these small pipelines cannot be properly metered using the existing apparatus. In fact, in the existing apparatus the abrasive material is metered by means of a plate provided with a suitable aperture. The apertures in the plate would have to be so small for the quantity of abrasive material required for cleaning pipelines of small diameters that the aperture would immediately become clogged with abrasive material.

Small-diameter pipelines, however, are very widely used, for example, in heat exchangers in refineries. In these heat exchanger pipes, a carbonaceous layer is desposited in the course of time, and this layer adversely affects heat transfer and accordingly must be removed. Pipe banks in heat exchangers have hitherto been cleaned, for example, by means of water under high pressure. One disadvantage of this is that cleaning with water leaves residues of the hard carbon layer and an oxide layer in the tubes, and a second disadvantage is that the water, which is highly contaminated, issuing with great force from the end of the pipe bank causes a major water burden.

It is accordingly an object of the present invention to provide an apparatus for dispensing particulate abrasive material into a stream of gas, with which it is possible to meter accurately any quantity of abrasive material into the gas stream.

To this end, according to this invention, apparatus as initially described is characterised by a pressure equalizing conduit connecting the interior of the container to the gas supply line, the pressure equalizing conduit communicating with the gas supply line at a point intermediate the control means and a duct through which the dispensing means supplies the abrasive material to the gas stream.

Because, when cleaning piping in a heat exchanger for example, the stream of gas is subject to a varying counter-pressure in the discharge line of the apparatus owing to variations in the resistance to flow through the heat exchanger piping dependent on the degree of fouling thereof, the provision of the equalizing conduit ensures that nevertheless the correct quantity of abrasive is supplied to the gas stream with every possible counter-pressure.

A portion of the gas from the gas stream in the supply line flows into the equalizing conduit and is thus supplied to the container. As the pressure at the point where the equalizing conduit is connected to the gas supply line is a little higher than the pressure at the point of communication of the abrasive supply duct with the supply line, a minor gas flow is generated from the container to the supply duct.

This minor gas flow ensures that, irrespective of the counter-pressure which occurs, abrasive material can be supplied to the stream of gas.

Preferably, the equalizing conduit terminates with an opening facing upstream in the gas supply line so that the ram effect of the gas flowing through the supply line causes the pressure in the conduit and hence in the container to be greater than the pressure in the supply line at the duct.

Preferably also, the dispensing means comprises conveyor means to which the abrasive material is supplied from the container, the conveyor means in operation, transporting the abrasive material to the duct which terminates in an orifice in the gas supply line.

The conveyor means preferably comprises a channel shaped conveyor belt.

It has been found that by controlling the rate of circulation of the conveyor belt it is possible to supply even the smallest possible desired quantity of abrasive to the gas stream.

The invention also consists, according to another of its aspects, in a method of dispensing particulate abrasive material into a stream of gas, in which the abrasive is contained in a container, and gas is supplied via a gas supply line, characterized in that the gas pressure in the container is maintained, through an equalizing conduit, higher than the gas pressure at a point where the abrasive material enters the stream of gas.

It is noted that although the cleaning of pipelines having a relatively small diameter is emphasized, the apparatus and method according to the invention can be employed with the same effect for cleaning large diameter pipes. The greater amount of abra sive required therefor, in apparatus comprising conveyor means, can be obtained by increasing the speed of 3h3 conveyor means.

An example of apparatus and of a method in accordance with the invention will now be described ':ith reference to the accompanying draviings, in which Figure 1 is a diagrammatic sectional view of the apparatus; Figure 2 is a cross-sectional view to a larger scale of a detail of the apparatus; and Figure 3 is a view taken on the line Ill-Ill of Figure 2.

As shown in Figure 1, a gas supply line 1 is connected to a source of gas (not shown) for supplying a suitable propellant gas for particulate abrasive material. The gas is for example nitrogen or air. Provided in the gas supply line 1 are, successively, a shut-off valve 2, a control valve 3, and an apertured plate 4. Furthermore a pressure gauge 5 is coupled to the line intermediate the control valve 3 and the apertured plate 4. The aperture in the plate 4 is dimensioned so that a critical pressure is generated, so that the velocity of the gas is proportional to the opening of the control valve 3. Connected to the line 1 at some distance downstream from the apertured plate 4 is a supply inlet duct 6 for the supply of particulate abrasive material. The supply inlet duct preferably tapers towards the line 1.

A container 7 for the abrasive material is closed at the top with a cover in a gas-tight manner. The container 7 has a funnel-shaped bottom to optimize flow of the abrasive material from it. Connected to the bottom of the container is a supply conduit 8, which terminates a short distance above a, preferably channel-shaped, conveyor belt 9. The shape of the conveyor belt 9 and the shape of the mouth of the supply conduit are best shown in Figures 2 and 3, which illustrate details of the area where the supply conduit terminates at the conveyor belt.

The conveyor belt 9 is connected in the usual way to a prime mover, such as a motor, and is guided overtwo pulleys 10 and 11. In operation, the belt 9 circulates in a clockwise direction, as viewed in Figure 1. The right-hand pulley 11 is so positioned that the point where the abrasive material lying on the belt leaves the belt under the influence of gravity is located over the centre of the supply duct 6 leading to the gas line 1. The supply conduit 8, conveyor belt9 and pulleys 10 and 11 are all housed in a gas-tight housing which is connected at its top with the container 7 and at its bottom terminates in the supply duct 6.

In order to ensure that, at any counter-pressure encountered at the effluent end of the line 1, the desired quantity of abrasive material is metered into the gas stream, an equalizing conduit 13 is provided.

The conduit 13 is connected at one end with the interior of the container 7, preferably at the top thereof, and at the other end with the gas supply line 1, at a location intermediate an outlet orifice of the supply duct 6 and the apertured plate 4. The equalizing conduit 13 preferably terminates in the gas line 1 in such a way that the velocity of the gas in the line 1 raises the pressure of the gas in the conduit. As a result, a pressure can be generated within the container 7 through the conduit 13, which is a little higher than the pressure in the line 1 adjacent to the outlet orifice of the duct 6.The result is a positive pressure dil lerentia! for the introduction of the abrasive material into the stream of gas in the line 1 independent of the counter pressure experienced by the gas, the counter pressure being daterniinad by the diameter and the degree of fouling of a pipe which is being cleaned and into which the line I discharges.

The duct 6 preferably also enters the supply line 1 at an angle, whereby the abrasive material is essentially supplied with a component in the direction of flow of the gas. By virtue of this, vortices adjacent the orifice of the duct 6 are substantially prevented.

In order that abrasive material may be supplied from the container to the conveyor belt without any problems even at low velocities of the conveyor belt, it has been found to be beneficial to bevel the end of the supply conduit 8 at an acute angle relative to the bottom surface of the conveyor belt, as clearly shown in Figures 2 and 3.

It has been found that by means of the dispensing apparatus in accordance with the invention, even small quantities of abrasive material can be supplied to a stream of gas in a highly accurate manner. The quantity of abrasive required depends on the gas throughput in the line 1 and can be controlled by controlling the velocity of the conveyor belt. The gas laden with abrasive material is supplied via a discharge conduit, not shown, to a suitable injection nozzle.

It has also been found that, by means of the apparatus in accordance with the invention, pipes having a diameter in the range of from 0.5 to 7.5 cm can be cleaned in an extremely effective manner without there being any residual carbonaceous and/or oxide layer in the pipes.

Although the invention has been described in the foregoing with reference to an exemplary embodiment, it is noted that the invention is not so limited.

A large number of modifications can be made. Thus various means, well known to those skilled in the art, for the control of the gas stream in the gas line 1 can be provided. When a conveyor belt is provided as the dispensing means, this belt may be flat instead of being channel-shaped, and there are also various obvious possibilities for the shape of the container, the supply conduit 8, and the supply duct 6. A further possibility is to use, instead of the conveyor belt 9, a transporting wheel, mounted for rotation under the supply conduit 8, and provided around its circumference with recesses for receiving abrasive material and transporting it through the supply duct 6. For this purpose the transporting wheel must be capable of rotating in the same plane as, e.g. the pulley 10.

Finally also other conveying means such as, for example, a screw feed device can be used.

Claims (11)

1. Apparatus for dispensing particulate abrasive material into a stream of gas, the apparatus compris ing a supply line for the gas having means for controlling the size of the gas stream through the supply line, a supply container for abrasive material, the cont3iner being connected through dispensing means to the gas supply line, and a discharge line for the discharge of the gas stream laden with the abrasive material, characterized by a pressure equalizing conduit connecting the interior of the container to the gas supply line, the pressure equalizing conduit communicating with the gas supply line at a point intermediate the control means and a duct through which the dispensing means supplies the abrasive material to the gas stream.

2. Apparatus according to Claim 1, in which the equalizing conduit terminates with an opening facing upstream in the gas supply line so that the ram effect of the gas flowing through the supply line causes the pressure in the conduit and hence in the container to be greater than the pressure in the supply line at the duct.

3. Apparatus according to Claim 1 or Claim 2, in which the dispensing means comprises conveyor means to which the abrasive material is supplied from the container, the conveyor means, in operation transporting the abrasive material to the duct which terminates in an orifice in the gas supply line.

4. Apparatus according to Claim 3, in which the conveyor means is a channel-shaped conveyor belt and the container supplies the abrasive material to the conveyor belt via a supply conduit, which terminates a small distance above the bottom of the channel-shaped conveyor belt

5. Apparatus according to Claim 4, in which the supply conduit terminates in an opening which lies in a plane at an acute angle relative to the bottom of the channel-shaped conveyor belt.

6. Apparatus according to any one of the preceding Claims, in which the duct through which the abrasive material is supplied into the stream of gas is tubular and tapers towards the supply line.

7. Apparatus according to Claim 6, in which the orifice at the end of the duct is arranged in the gas supply line in such a manner that the abrasive material flows from it with a component in the direction of flow of the gas.

8. A method of dispensing particulate abrasive material into a stream of gas, in which the abrasive is contained in a container, and gas is supplied via a gas supply line, characterized in that the gas pressure in the container is maintained, through an equalising conduit, higher than the gas pressure at a point where the abrasive material enters the stream of gas.

9. A method according to Claim 8, in which the abrasive material is supplied from the container to a conveying means, which transports the abrasive material to a supply aperture, through which the abrasive material is introduced into the stream of gas.

10. A method of cleaning a pipeline, which comprises supplying a stream of gas laden with particulate abrasive material to the interior of the pipeline via an injection nozzle, characterized in that the diameter of the pipeline being cleaned is in the range of from 0.5 to 7.5 cm.

11. Apparatus according to Claim 1, substantially as described with reference to the accompanying drawings.