AU7192300A

AU7192300A - Method and apparatus for on line analysis

Info

Publication number: AU7192300A
Application number: AU71923/00A
Authority: AU
Inventors: Michael Francis Edwards; Walter James Howarth; Kenneth Graham Smith
Original assignee: SCANTECH Ltd
Current assignee: SCANTECH Ltd
Priority date: 1999-11-30
Filing date: 2000-11-30
Publication date: 2001-05-31
Anticipated expiration: 2020-11-30
Also published as: AU772405B2

Description

Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Name of Applicant(s): Scantech Limited, A.C.N.087 557 426, of 40 Maple Avenue, Forestville, South Australia 5035, Australia o Actual Inventor(s): Walter James Howarth Kenneth Graham Smith Michael Francis Edwards Address for Service: DAVIES COLLISON CAVE, Patent Attorneys, of 1 Little Collins Street, Melbourne, Victoria 3000, Australia Invention Title: "Method and Apparatus for On Line Analysis" Details of Associated Provisional Application No: PQ4353/99 The following statement is a full description of this invention, including the best method of performing it known to us.

*oeo Q:\OPER\LKA\2364909 cap.doc 30/11/00 P:\OPER\LKA\SCANTECH.CAP.DOC- 30/I 1/00 -2- Method and Apparatus for On Line Analysis This invention relates to the direct on line measurement of composition of bulk material of variable hydrogen content transported via conveyor belt. The invention has particular application to the measurement of coal composition. Although the invention is described with particular reference to the determination of the composition of coal it will be understood that it is equally applicable for use with other bulk materials of variable hydrogen content.

One of the most convenient and efficient ways to move coal is by conveyor belt.

Conveyor transportation of coal is used at a variety of stages during the initial production, transportation, and the ultimate use of the coal in some form of combustion process. An analysis of the composition of the coal is required for a number of purposes at various times in the production and use of coal. It has long been recognized that direct on line measurement of coal composition as the coal is transported by a conveyor belt would be particularly effective and provide considerably improved efficiencies in the production and use of coal.

A class of analytical techniques are available for elemental analysis of coal which are based on the interaction of neutrons with the atomic species to generate characteristic gamma rays that are detected and analysed to provide information about the composition of the coal. These techniques include Prompt Gamma Neutron oleo Activation (PGNA), Neutron Inelastic Scattering (NIS) as well as some techniques based on neutron capture and delayed gamma ray emissions. In these techniques neutrons are supplied from an either isotopic source, such as Californium 252, or Americium/Beryllium, or from a neutron generator. The characteristic gamma rays are usually detected by a scintillation detector or similar device. The analysis of the gamma rays typically involves recording and interpreting the energy distribution spectrum of the gamma rays.

The current application of these techniques to the determination of coal composition on a conveyor belt rely on continual sampling of the coal from the moving P:\OPER\LKA\SCANTECH.CAP.DOC 30/11/00 -3conveyor. The coal is passed through a chute or a similar device where the geometry of the analysis zone can be controlled. This class of devices are generally termed "byline" analysers, and several instruments are commercially available. Instruments are also commercially available for the direct on line elemental analysis of materials such as limestone moving on a conveyor. One example of this is the product known as "Geoscan" sold by the present applicant. Techniques which are suitable for materials like limestone are not generally applicable to coal because of the high and variable level of hydrogen content in the coal combined with the difficulty of maintaining a constant bed depth on the conveyor for analysis in the high throughput operations characteristic of the coal industry. The variable hydrogen content of coal arises from variation in the hydrogen content of the coal matter itself and in variation in the amount of moisture present. Analysis techniques based on interaction of neutrons and detection of gamma ray emissions suffer from the problem that it is not possible to compensate for simultaneous variation in bed depth and hydrogen content. Attempts at using these techniques for the measurement of coal have required strict control of the coal bed depth and independent measurement of the coal moisture content.

The present invention provides a technique for the on line analysis of bulk material of variable hydrogen content on a conveyor belt to provide a measure of the hydrogen content as a proportion of the mass of the material. This technique can then be used in combination with techniques based on the interaction of neutrons to generate characteristic gamma rays to compensate for the variable hydrogen content.

In one aspect this invention provides a method for the on line analysis of bulk material of variable hydrogen content travelling on a conveyor belt including the steps of directing high energy neutrons through a volume of the material, directing gamma ooo* rays through substantially the same volume of the material, obtaining a measure of the go*go absorption of the high energy neutrons by the material, obtaining a measure of the absorption of the gamma rays by the material, and producing from the two measures of absorption a measure of the hydrogen content of the material as a proportion of the mass of the material.

P:\OPER\LKA\SCANTECH.CAP.DOC 30/11/00 -4- In another aspect this invention provides an apparatus for the on line analysis of bulk material of variable hydrogen content travelling on a conveyor belt including means to direct high energy neutrons through a volume of the material, means to direct gamma rays through substantially the same volume of the material, means to produce a measure of the absorption of the high energy neutrons by the material, means to produce a measure of the absorption of the gamma rays by the material and processor means to produce a measure of the hydrogen content of the material as a proportion of the mass of the material from the two measures of absorption.

Preferably, the analysis also includes directing thermalised neutrons into the bulk material and detecting the emitted gamma rays to obtain information about the elemental composition and using the measure of hydrogen content to correct the elemental analysis information. The technique involving detection of characteristic gamma ray emissions can be any one of the known techniques including PGNA, NIS, neutron capture techniques and delayed gamma emission techniques.

In one preferred form of the invention a suitable source and moderator geometry can be used to simultaneously provide fast neutron emissions, gamma ray emissions and thermalised neutron emissions. In other forms of the invention ***separate sources of neutrons and gamma rays can be used. The source of neutrons can be any suitable isotopic source or a neutron generator.

.O

o* Preferably the high energy neutrons are directed from one side of the bulk material on the conveyor belt to a detector on a remote side of the conveyor belt. In most applications one or other of the detector or source will be respectively above and below the belt although other configurations are possible. The detector is typically a scintillation type detector. In one form of the invention gamma rays produced by source of neutrons can also be detected by the same scintillation detector but can be distinguished from the neutrons by the use of known pulse shape discrimination techniques. In most applications, separate detectors are used to detect characteristic gamma rays resulting from the interaction of neutrons with the atomic species in the bulk material. In the case for example of PGNA techniques the gamma ray detectors P:\OPER\LKA\SCANTECH.CAP.DOC 30/11/00 are substantially opposite the source of thermalised neutrons used to generate the characteristic gamma ray spectrum. In the case of delayed gamma ray emission techniques the gamma ray detector is spaced apart in the direction of travel of the conveyor. In some applications two sets of detectors respectively detecting prompt gamma ray emissions and delayed gamma ray emissions can be used.

Preferably, the present invention provides for the measurement of the mass per unit area of the total material and of hydrogen content in a moving bed of bulk material on a conveyor belt while simultaneously recording the gamma ray spectrum resulting from thermal neutron capture. These three measurements in combination allow a more precise measurement of the elemental content of the bulk material than previously known techniques.

The bulk material is preferably coal. The measure of mass per unit area of total material and hydrogen content is achieved by measuring the transmission of fast neutrons and gamma rays through the moving bed of coal on the conveyor. By .o :comparing the transmission in the absence of a bed of coal the degree of absorption .i o of both neutrons and gamma rays can be determined. The degree of absorption of fast neutrons gives a direct measure of the hydrogen content of the coal through which the neutron beam passes. The degree of absorption of gamma rays provides a measure of the total mass per unit area of the coal through which the gamma ray and beam passes. This can be used to provide a measure of the percentage by weight of o.

hydrogen in the coal.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: o Figure 1 shows the typical configuration of a PGNA based analyser for coal on a conveyor belt; Figure 2 is a schematic cross section showing the configuration of an on line analyser for coal travelling on a conveyor belt according to this invention.

P:\OPER\LKA\SCANTECH.CAP.DOC 30/11/00 -6- As shown in Figure 1 of the typical PGNA based system involves having a neutron source 10 such as Californium 252 positioned below a conveyor belt 11 carrying a bed of coal 12. A gamma ray detector 13 such as a scintillation detector is positioned above the coal 12. The source 10 is surrounded by a gamma ray shield 14 which prevents gamma rays from source 10 passing through the coal to the detector 13. A moderator and reflector arrangement 15 also surrounds the source to thermalise the neutrons and appropriately direct them toward the coal bed 12.

Figure 2 shows an arrangement according to the present invention. The same reference numerals have been used to identify corresponding features to those described in relation to Figure 1. In this arrangement a neutron and gamma ray collimator 16 is used to direct a relatively narrow beam of high energy neutrons from the source 10 toward the coal bed 12. Gamma rays produced by the source are also directed in a relatively narrow beam by collimator 16 into the coal bed 12. The high energy neutrons that are not scattered by the hydrogen in the coal bed 12 pass through to a liquid scintillation type detector 17 positioned above the coal bed 12 and :directly opposite the neutron source 10. The detector 17 also detects the gamma rays from the source that pass through the coal bed 12. The neutrons and the gamma rays can be distinguished using known pulse shape discrimination techniques. The 0detector 17 can thus provide a measure of the transmission of fast neutrons and gamma rays through the same volume of the moving bed. By obtaining a calibration o :measurement corresponding to the amount of transmission in the absence of a coal bed the degree of absorption of both neutrons and gamma rays can be determined.

0: A processor 18 receives the output from detector 17. The degree of absorption of fast

S

neutrons gives a direct measure of the hydrogen content of the coal through which the beam is passed. The degree of absorption of gamma rays provides a measure of the total mass per unit area in the gamma ray beam. These two measures can be combined by the processor to determine the percentage by weight of hydrogen in the coal.

Gamma ray detectors 13 are positioned adjacent the detector 13 to record the gamma ray spectrum from the coal produced by thermal neutron interactions. It will P:\OPER\LKA\SCANTECH.CAP.DOC 30/11/00 -7be apparent that the geometry of the three detectors must be arranged so as to efficiently and representatively record this gamma ray spectrum from the coal bed.

The output from detectors 13 is also received by a processor 18 and can be analysed in the known manner to produce an apparent hydrogen content of the coal.

This direct measurement however will vary with the bed depth of the coal on the conveyor. If the apparent hydrogen content determined by the PGNA technique is designated H(PGNA) and the percentage by weight of hydrogen in the coal is determined the fast neutron/gamma ray transmission (FNGT) is designated H(FNGT) then a normalisation factor N can be defined as a ratio of the two hydrogen measurements as follows:

N=H(FNGT)/H(PGNA).

This normalisation factor can be used to correct all the other measurements arising from the PGNA measurement. For example the true sulfur content S(true) can be calculated from the apparent sulfur measured by PGNA from the relation S(true) S(PGNA)xN.

The foregoing describes only one embodiment of the invention and modifications can be made without departing the scope of the invention. In particular it will be apparent that various configurations can be used to implement the method and/or apparatus of the invention. For example separate sources of gamma rays and neutrons can be used as well as alternative and separate detection techniques for both fast neutrons and gamma rays.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims

1. A method for the on line analysis of bulk material of variable hydrogen content travelling on a conveyor belt including the steps of: directing high energy neutrons through a volume of the material; directing gamma rays through substantially the same volume of the material; obtaining a measure of the absorption of the high energy neutrons by the material; obtaining a measure of the absorption of the gamma rays by the material, and producing from the two measures of absorption a measure of the hydrogen content of the material as a proportion of the mass of the material.

2. A method according to claim 1, further including the step of directing high energy neutrons from one side of the material on the conveyor belt to a detector on a remote side of the conveyor belt.

3. A method according to claims 1 or 2, further including the steps of directing e othermalised neutrons into the bulk material and detecting the gamma ray spectrum resulting from absorption of thermalised neutrons to obtain a measure indicative of the elemental composition of the material.

4. A method according to claim 3, further including including the step of producing e*l• from the information about the elemental composition and the measure of the hydrogen content to correct the elemental analysis information of the material.

A method according to any one of the preceding claims, further including the step of obtaining the measure of absorption of gamma rays by any one of Prompt e* Gamma Neutron Activation, Neutron Inelastic Scattering, neutron capture or S•delayed gamma emission techniques.

6. A method according to any one of the preceding claims, wherein the method includes the step of simultaneously measuring the mass per unit area of the material, the hydrogen content of the material and the gamma ray spectrum P:\OPER\LKA\SCANTECH.CAP.DOC 30/11/00 -9- resulting from absorption of the thermalised neutrons.

7. An apparatus for the on line analysis of bulk material of variable hydrogen content travelling on a conveyor belt including: means to direct high energy neutrons through a volume of the material; means to direct gamma rays through substantially the same volume of the material; means to produce a measure of the absorption of the high energy neutrons by the material; means to produce a measure of the absorption of the gamma rays by the material, and processor means to produce a measure of the hydrogen content of the material as a proportion of the mass of the material from the two measures of absorption.

8. An apparatus according to claim 7, further including means to direct thermalised o' oo neutrons into the material.

9. An apparatus according to claim 7 or 8, further including means for detecting the gamma ray spectrum resulting from directing the thermalised neutrons to obtain information about the elemental composition of the material.

An apparatus according to claim 9, wherein the processor means uses the information about the elemental composition and the hydrogen content to correct the elemental analysis information of the material.

11. An apparatus according to any one of claims 7 to 10, wherein the means to direct of high energy neutrons is also the means to direct gamma rays.

12. An apparatus according to any one of claims 7 to 10, wherein the means to direct of high energy neutrons is also the means to direct thermalised neutrons. P:\OPERLKA\SCANTECH.CAPDOC 30/11/00

13. An apparatus according to any one of claims 7 to 12, wherein the means to direct high energy neutrons is an isotopic source or a neutron generator.

14. An apparatus according to any one of claims 7 to 10, wherein the means to produce a measure of the absorption of high energy neutrons is also the means to produce a measure of the absorption of gamma rays.

An apparatus according to any one of claims 7 to 10, wherein the means to produce a measure of the absorption of high energy neutrons is also the means to detect the gamma ray spectrum resulting from directing thermalised neutrons.

16. An apparatus according to any one of claims 7 to 15, wherein the means to produce a measure of high energy neutrons is a scintillation type detector.

17. A method according to any one of the preceding claims wherein the bulk material is coal.

An apparatus according to any one of the preceding claims wherein the bulk material is coal.

19. A method for the on line analysis of bulk material of variable hydrogen content travelling on a conveyor belt, substantially as described with reference to the examples and/or drawings.

20. An apparatus for the on line analysis of bulk material of variable hydrogen content travelling on a conveyor belt, substantially as described with reference to the ol examples and/or drawings. a DATED this 30 th day of November 2000 Scantech Limited DAVIES COLLISON CAVE Patent Attorneys for the Applicant