GB2324379A

GB2324379A - Measurement of parameters of flowable material

Info

Publication number: GB2324379A
Application number: GB9808065A
Authority: GB
Inventors: Michael Stanley Arthur Bradley; Alexander Naylor
Original assignee: Birtley Engineering Ltd; University of Greenwich
Current assignee: Birtley Engineering Ltd; University of Greenwich
Priority date: 1997-04-17
Filing date: 1998-04-16
Publication date: 1998-10-21
Anticipated expiration: 2018-04-16
Also published as: GB9707777D0; GB2324379B; GB9808065D0

Abstract

The present invention provides a method and apparatus for measuring a selected parameter, preferably the rate of flow of material in the stream. The method comprises arranging in the flow stream at least one barrier that occupies only part of the cross-section of the flow stream and measuring the force exerted on the barrier by the flowing material. Preferably, the barrier is made up of a series of parallel bars (14), the leading face (20) of which is slanted at 45‹ to the direction of flow (A); the impact of the material on the leading face (20) provides a force Y that is proportional to the rate of flow of the bulk material. By measuring the force Y, the rate of flow can be calculated. The slow stream may comprise a fluid or a flowable particulate material. In addition the "noise" from the measurement of force can be used to discern other properties of the slow, such as homogeneity or particle size.

Description

MEASUREMENT OF PARAMETERS OF FLOWABLE MATERIALS Field of Invention The present invention relates to an apparatus and method for measuring the rate of flow and other parameters of flowable materials and in particular of bulk solids in particulate form, for example crushed or ground minerals, powders or cereal grains. However, the present invention also extends to the measurement of such parameters of liquids.

Background Art It is known to measure the rate of flow of a stream of a bulk solid by placing a plate in the flow path that diverts the stream; the force exerted by the action of diverting the flow is a measure of the flow rate. An instrument based on this principle has been manufactured the well-known German firm, Endress & Hauser.

The diversion of the bulk stream, however, is disadvantageous in that often the flow of material is required to be in a straight line and therefore the flow has to be redirected along its original path.

It is also known to detect the presence of material on a conveyor belt by placing a bar above the belt; the bar is struck by material on the belt, thereby indicating that there is material on the belt but such an arrangement does not indicate the amount of material being conveyed, merely whether or not material is present on the conveyor.

Disclosure of the Invention The present invention provides a much simpler arrangement than the prior art for measuring the flow rate of a material in a stream that avoids the need to divert the direction of the bulk flow.

According to the present invention, there is provided a method of measuring a selected parameter of a flow stream of a material (which parameter may include but is not limited to the bulk flow rate, the velocity and the density of the stream), which method comprises arranging in the flow stream one or more barriers that together occupy only part of the cross-section of the flow stream and measuring the force exerted on the barriers by the flowing material; such a force will give a measure of the rate of flow of the material (or other parameter) in the flow stream.

Although the invention will primarily be used for measuring the rate of flow of a flowable material in a flow stream (measured in units of mass of material flowing per unit time in the flow stream), it can also be used in certain circumstances for measuring parameters related to the flow rate, for example, the velocity or density of the stream of the flowing material.

According to a second aspect of the present invention, there is provided an apparatus for measuring a selected parameter of a flow stream of a material (which parameter may include but is not limited to the bulk flow rate, the velocity and the density of the stream), which apparatus comprises at least one barrier that can be placed in the flow stream while allowing the material to flow on either side past it, means for measuring the force exerted by the flowing material on the said barrier and means for calculating from the said force the said selected parameter (e.g. the rate of flow of the material in the stream).

The or each barrier may include a surface that is slanted obliquely to the direction of flow of material in the flow stream, so that the impact of the flowing material on the said surface causes a force on the barrier at an angle to the direction of flow of the flow material in the flow stream, in which case the force-measuring means can measure the force exerted at an angle to the direction of flow of the flowable material in the flow stream. Preferably, the said surface is placed at an angle of approximately 450 to the direction of the flow stream, in which case the force may be measured at an angle of 90" to the direction of flow of the flow stream. Preferably, such a surface is provided as the end face of each barrier.

Most preferably, the or each barrier is a bar, preferably made of metal or some other material that will resist the abrasion of the flowable material. If more than one barrier is placed in the flow stream, such barriers should be spaced apart to allow the flowable material to flow between the barriers.

The barriers preferably occupy less than 40% of the cross-sectional area of the flow stream, more preferably less than 25 %, e.g. 10 to 20%.

The barriers are preferably connected together, e.g. into a grating, in which case, the force exerted on the connected barriers as a whole can be measured rather than the force on each individual barrier.

Detailed Description of the Drawings Figure 1 is a schematic side view of an example of an apparatus of the present invention; and Figure 2 is a plan view of the apparatus of Figure 1.

Detailed Description of the Invention Referring to Figures 1 and 2, there is shown a flow stream 10, which may be constricted within a duct or it may free-flowing, i.e. unconstrictedby any side walls. A grid 12 made up of bars 14 is placed in a flow stream. The bars are joined together by cross pieces 16 and end pieces 18.

The end face 20 of each bars is cut at an angle of 45" to the flow of material in the flow path (shown by arrow A in Figure 1). As the flowable material hits the end faces 20 of the bars, it exerts a force X on the grid as a whole that can be resolved into horizontal and vertical components Y and Z. This force X (or its components) is measured by a load cell (not shown) and gives a direct measure of the rate of flow of material in the flow stream.

The signal from the load cell can be calibrated to give a direct read-out of the flow rate.

Such load cells are extremely well known and are readily available commercially and accordingly further description of them will not be given. The particular nature of the load cell does not form part of the present invention.

The advantage of setting the end faces 20 of the bars at an angle to the direction of flow in the flow stream is that the measure of the force component Y perpendicular to the direction of flow is less susceptible to errors caused by different particle sizes than a direct measurement of force X or vertical component Z.

The number of bars provided in the grid will obviously depend on a number of factors, including the homogeneity of the flow stream, the cross section of the flow stream and the sensitivity of the load cell(s). The bars should not, however, obstruct substantially the flow of material. Thus, sufficient gaps must be left between the bars to allow the free flow of the material through the grid.

Although the bars are shown in Figures 1 and 2 as being parallel, alternatives are possible, e.g. a lattice arrangement of bars.

The angle of the faces 20 can be greater or less than 45" to the direction of flow A.

Additional information concerning the flowable material and the flow stream can be gleaned by measuring the "noise" in the signal from the load cells and in particular it is possible to discern the homogeneity of the stream and whether it is composed of small or large particles.

Claims

1. A method of measuring a selected parameter of a flow stream of a material (which parameter may include but is not limited to the bulk flow rate, the velocity and the density of the stream), which method comprises arranging in the flow stream at least one barrier that occupies only part of the cross-section of the flow stream and measuring the force exerted on the barrier by the flowing material to give a measure of the said selected parameter.

2. The method as claimed in claim 1, wherein the or each barrier includes a surface that is slanted obliquely to the direction of flow of material in the flow stream, whereby the impact of the flowing material on the said surface causes a force on the barrier at an angle to the direction of flow of the flow material in the flow stream and the method includes measuring the force exerted at an angle to the direction of flow of the flowable material in the flow stream.

3. The method as claimed in claim 2, wherein the or each surface is placed at an angle of approximately 45" to the direction of the flow stream.

4. The method as claimed in claim 2 or claim 3, wherein the or each surface is provided as the end face of the or each barrier.

5. The method as claimed in any one of claims 2 to 4, wherein the force exerted on the at least one barrier is measured substantially perpendicular to the direction of flow of the flow stream.

6. The method as claimed in any one of claims 1 to 5, wherein the or each barrier is a bar.

7. The method as claimed in any one of claims 1 to 6, wherein at least two barriers are provided and the barriers are connected together and wherein the force exerted on the connected barriers as a whole is measured.

8. The method as claimed in any one of claims 1 to 7, wherein the at least one barrier occupies 10 to 40 % of the cross-sectional area of the flow stream.

9. The method as claimed in any one of claims 1 to 8, wherein the said selected parameter is the rate of flow of the material in the stream.

10. An apparatus for measuring a selected parameter of a flow stream of a material (which parameter may include but is not limited to the bulk flow rate, the velocity and the density of the stream), which apparatus comprises at least one barrier that can be placed in the flow stream while allowing the material to flow on either side past it, means for measuring the force exerted by the flowing material on the said barrier and means for calculating from the said force the said selected parameter.

11. The apparatus as claimed in claim 10, wherein the or each barrier includes a obliquely slanted surface and the said force measuring means is arranged to measure the force exerted on the barrier at an angle to the obliquely slanted surface.

12. The apparatus as claimed in claim 11, wherein the or each surface is placed at an angle of approximately 450 to the direction of the flow stream.

13. The apparatus as claimed in claim 11 or claim 12, wherein such an obliquely slanted surface is provided as the end face of the or each barrier.

14. The method as claimed in any one of claims 10 to 13, wherein the force measuring means measures the force exerted on the at least one barrier substantially perpendicular to the direction of the flow stream.

15. The apparatus as claimed in any one of claims 10 to 14, wherein the or each barrier is a bar.

16. The apparatus as claimed in any one of claims 10 to 15, wherein at least two barriers are provided, each adjacent pair of barriers being spaced apart by a gap and wherein the barriers together have a cross-sectional area that is 10 to 40% of the combined cross-sectional area of the barriers and the said gaps.

17. The apparatus as claimed in any one of claims 10 to 16, wherein at least two barriers are provided and the barriers are connected together and wherein the force measuring means measures the force exerted on the connected barriers as a whole.

18. The apparatus as claimed in any one of claims 10 to 17, wherein the said selected parameter is the rate of flow of the material in the stream.

19. A method of measuring a selected parameter of a flow stream of a material, substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

20. An apparatus for measuring a selected parameter of a flow stream of a material substantially as hereinbefore described in connection with, and as shown in, Figures 1 and 2 of the accompanying drawings.