GB2223574A - Radiometric analysis - Google Patents
Radiometric analysis Download PDFInfo
- Publication number
- GB2223574A GB2223574A GB8919125A GB8919125A GB2223574A GB 2223574 A GB2223574 A GB 2223574A GB 8919125 A GB8919125 A GB 8919125A GB 8919125 A GB8919125 A GB 8919125A GB 2223574 A GB2223574 A GB 2223574A
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- United Kingdom
- Prior art keywords
- sample
- rays
- intensity
- measurement cell
- measuring
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/20—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by using diffraction of the radiation by the materials, e.g. for investigating crystal structure; by using scattering of the radiation by the materials, e.g. for investigating non-crystalline materials; by using reflection of the radiation by the materials
- G01N23/20083—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by using diffraction of the radiation by the materials, e.g. for investigating crystal structure; by using scattering of the radiation by the materials, e.g. for investigating non-crystalline materials; by using reflection of the radiation by the materials by using a combination of at least two measurements at least one being a transmission measurement and one a scatter measurement
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- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Analysing Materials By The Use Of Radiation (AREA)
Abstract
A method of measuring the ash content of a sample of coal slurry comprises the steps of: a) passing the sample through a first measurement cell (12) and irradiating the sample with gamma-rays; b) measuring the intensity of gamma-rays transmitted through the sample; c) passing the sample through a second measurement cell (13) where the sample is irradiated with X-rays; d) measuring the intensity of backscattered X-rays; e) measuring the intensity of the iron K alpha X-ray photopeak of emitted X-rays; and, f) using the measurements of transmitted gamma-ray intensity, backscattered X-ray intensity and the intensity of the iron K alpha photopeak to compute a value for the ash content of the sample which includes a correction for the effect of iron minerals in the sample.
Description
RADIOMETRIC ANALYSIS
The invention relates to improvements in a method of measuring the comoosition of coal slurries by radiometric analysis, in particular to a method of measuring the ash content of a sample of coal slurry and to an apoaratus for carrying out the method.
In froth flotation cells at coal washery plants it is necessary, in order to ascertain the efficiency of the cleaning process, to monitor the composition of the coal slurry tailings output from the flotation cells. Coal slurries comprise essentially a combustible carbonaceous fraction, referred to as the "combustibles", an incombustible mineral fraction referred to as the "ash", and water.
In particular, it is desirable to monitor the ash content of the coal slurry.
It is known in the art to determine the relative proportions of ash and combustibles of the solids present in such slurries by making measurements of the intensity of backscattered X-rays of apDropriate energy, toqether with measurements of the transmitted intensity of high energy gamma-rays. Such a method is described in the publication "A Technique for Measuring the Ash Content of Coal in a Tailinqs Stream" I.S. Boyce. Int. J. Appl. Radiot. Isot. Vol. 34 No. 1 pp 45-54 1983.
In essence, the intensity of X-rays of selected energy backscattered from the sample is used as an index of the mass absorption co-efficient, and hence the composition of the sample. The gamma-ray transmission measurements are used to determine the density of the sample and by inference, the solids content of the slurry.
Since the mass absorption co-efficient of water may be taken as a known constant, and the overal mass absorption co-efficient of the sample is an additive function of the mass absorption co-efficients of the aqueous and solid phases, the effective mass absorption co-efficient of the solid phase can be calculated, given a knowledge of the solids content.
By making certain assumptions as regards the values of the mass absorption co-efficients of the coal fraction and the ash fraction, a fiqure for the ash content of the solids can be computed.
In practice two major difficulties arise with the above method which adversely effect the accuracy obtainable. Firstly, the sensitivity of the backscatter- measurement is greatly influenced by the solids content of the sample, so that errors become unacceptably high at the low solids levels often found (commonly less than 4) in the slurries. By way of example, the following typical figures (computed for coals having an ash fraction of constant average composition for different solids contents), illustrate the relation between solid content and measurement sensitivity.
tO Solids in Sample Y Chanqe in Count Rate
Correspondinq to 1 change in
Ash Ash Content of Drv Solids
10.0 0.333
6.0 0.275
4.0 0.154
2.0 0.097
Thus, a small error in the computation of the solids content of the sample at low solids content will effectively result in a significant error in the computed ash content.
Secondly, the backscatter measurements are greatly influenced bv the chemical composition of the ash fraction. This arises because of the different values for the mass absorption co-efficient for the various elements present in the ash. Computation of mass absorption co-efficients for typical mineral compositions reveal that it is the iron content in particular which exerts a major influence on the overall value of the total mass absorption co-efficient for the ash fraction. An indication of the magnitude of the effect is provided by the fact that, in a typical system, a change of 1% in the Fe203 content of the ash will give rise to a shift of some 2.7 in the computed ash content of the solids phase.
Typically, in a working installation, the equivalent Fe203 content of the ash is likely to vary by at least +3 from the mean on a week to week basis. If pyritic minerals are intermittently present, this estimate can be greatly exceeded. A change of 3 in the equivalent Fe203 content of the ash fraction would correspond to an error of about 8% in computed ash content. This factor can be seen, therefore, to be a major cause of error in existing systems.
The present invention seeks to provide a method which overcomes the problems associated with the effect of iron minerals by including in the method a direct determination of the iron content of the sample by means of an X-ray fluoresence measurement, this measurement being used to provide an appropriate correction in the determination of the ash content. The X-ray fluoresence measurement involves a measurement of the 6.4 keV iron Kd( X-ray characteristic photopeak.
This latter measurement is achieved by using an X-ray detector which is capable of resolving the low energy characteristic iron K X-rays from the higher-energy backscattered radiation. In this manner, not only is the apparatus simplified (and rendered less costly); but also, the precise identity of the sample material involved in both the X-ray measurements is assured.
It is a further aim of the invention to reduce the difficulties associated with making measurements on slurries of very low solids content by increasing the solids concentration in a pre-measurement concentration process.
The increase of solids content is achieved by means of a hydrocyclone assembly. By appropriate choice of the hydrocyclone characteristics, a coal slurry of 5 solids content such as is typically found, may be increased to 10 - 20t0 solids content, while the loss of solids particles can be effectively restricted to the less than 10 micron fraction, with less than 10% of the total solids by weight being lost from the system.
It should be noted that analysis suggests that the distribution of ash between the different size fractions does not exhibit any significant bias at the lower end of the particle size spectrum, so that measurements made on the de-watered solids should be fully representative of the whole sample.
According to the present invention there is provided a method of measuring the ash content of a sample of coal slurry comprising the steps of: a) passing the sample through a first measurement cell and
irradiating the sample with gamma-rays; b) measuring the intensity of gamma-rays transmitted through the
sample; c) passing the sample through a second measurement cell and
irradiating the sample with X-rays1 d) measuring the intensity of backscattered X-rays; e) measuring the intensity of the iron K X-ray photopeak of emitted X-ray; and, f) using the measurements of transmitted gamma-ray intensity,
back scattered X-ray intensity and the intensity of the iron Ko( photopeak to compute a value for the ash content of the sample
which includes a correction for the effect of iron minerals in
the sample.
According to a further aspect of the invention there is provided an apparatus for measuring the ash content of a sample of coal slurry comprising:
a first measurement cell through which the sample is passed;
a first radioisotope source of gamma-rays situated adjacent the
first measurement cell;
a detector giving an output signal related to the intensity of
the gamma-rays transmitted through the sample;
a second measurement cell through which the sample is passed
subsequent to its passage through the first measurement cell;
a second radioisotope source of X-rays situated adjacent the
second measurement cell; and.
a detector giving an output signal related to the intensity of
the X-rays backscattered from the sample, and the intensity of
the iron Kcç X-rays emitted from the sample.
An embodiment of invention will be described, by way of example only, with reference to the following drawing in which:
Fig. 1 is a schematic diagram showinq the essential elements of an apparatus according to the present invention.
A primary samPle of coal slurry is continuously cut from the tailings process stream and is admitted to the measuring system via a trash screen 1 and an input receiver 2. Trash screen 1 serves to prevent unwanted debris from entering the system. A typical flow-rate of sample taken from the process stream is of the order or 20 to 25 gallons per minute. Removal ofthe sample from the process stream is simply achieved using a standard "Y" - branch pipe sampler.
A by-pass launder 4 and overflow launder 5 are arranged adjacent to the input receiver 2. The former allows the sample to return to the process stream without passing through the measuring system, while the latter collects excess primary sample together with sample which has passed through the measuring system, and returns the combined streams to the process stream. An automatically controlled sample selector 6 permits switching of the primary flow between the by-pass and measurements modes. Automatic rubber-lined pinch valves 7 and 8 are provided to admit wash water and to allow draining of the system when required.
Sample flows from the input receiver 2 via a pump 3 and a control valve 10 arranged on conduit 21 to a hydrocyclone assembly 9 comprising one or more high efficiency hydrocyclones.
The hydrocyclone assembly effects dewatering of the sample, the dewatered sample passing via the spigots of each hydrocyclone into the under-flow receiver 11, and then by gravity through the gamma-ray measurement cell 12 and X-ray measurement cell 13 and then back. to the process stream via the overflow launder 5. The water fraction passes from the overflow of each hydrocyclone, by gravity, directly to the overflow launder 5 and is then returned to the process stream.
The provision of separate measurement cells 12 and 13 for the gamma-ray measurements and for the X-rays measurements allows each measurement to the made under its specific optimum conditions.
The ganra-ray transmission measurement cell 12 comprises a "Z" tube through which sample is passed in a fully turbulent manner, thus keeping the solids in homogenous suspension. A source of qamma-rays 22, for example, a 137 ceasium radioisotope source giving gamma-rays predominently of 661 keV is situated adjacent the Z tube in order to direct gamma-rays in a direction parallel to the length of the Z tube. The depth of sample parallel to the incident beam must be known and maintained precisely constant. A convenient sized Z tube typically has a depth of 15cm with a cross-sectional area of about lcm square. Preferably the Z tube is moulded in a wear resistant plastics composition, for example polyurethane.
The gamma-ray detector 14 is positioned on the opposite side of the Z tube 12 from a gamma-ray source 22. The detector comprises a
NaI/Tl Crystal and photo multiplier assembly of known form.
The X-ray measurement cell 13 is arranged so as to maintain the solids of the sample in continuous homogenous suspension. In addition, the cell must be of sufficient depth so that the depth of sample therein is such that the X-ray back scattered intensity measured is the true saturation backscattered intensity. Typically the depth of sample must be of the order or 35 to 40cm. The X-ray cell 13 includes a window of material which is substantially transparent to low energy iron Ko( (6.4 keV) X-rays. A suitable window is made of a high strength plastics film of low thickness, for example 50 microns thickness.
The X-ray source 23 is a 109 cadmium radioisotope source giving
X-rays predominantly of 22 and 25 keV. The source is shielded so as to prevent direct emission into the detector.
X-ray detector 15 comprises a high resolution NaI/Tl crystal and photomultiplier assembly appropriate for the measurement of X-rays having energies substantially in the range 5-25 keV and capable of resolving the iron K, photopeak at 6.4 keV from the higher energy back scattered radiation. The detector 15 is housed in a protected metal sheath fitted with a thin polycarbonate radiation window.
The gamma-ray detector 14, and X-ray detector 15 are linked via local nucleonics modules 16 and 17 to a central nucleonics module and micro-computer sub-system 18. The signals from the detectors 14 and 15 are processed in the central nucleonics module to yield count rates precisely proportional to the three radiation intensities of interest, ie. the transmitted gamma-ray intensity, the backscattered X-ray intensity, and the intensity of the iron K, X-ray radiation.
These radiation intensity values are transmitted to the micro-computer and are used in the computation of the solids content and ash-in-solid content of the sample. These computations employ a working equation based on a mathematical model of the measurement physics, aided by calibration data acquired with samples of determined composition.
In a typical application, the working model can be expressed in the terms of three equations, the constants and coefficients for these being determined by regression analysis using measurement data obtained with samples of known composition.
W = kl + k2Ib - k3IX (1)
Fe = k4 + ksIFe/W + k6/W (2)
A = k7 + k8Iy - kgIb - klO IyIb - kllFe (3)
Where: 16 = standardised gamma count rate.
Ib = standardised Cd-109 backscatter count rate
IFe = standardised Fe k xpeak count rate
W = % solids in slurry (w/w)
Fe = % iron in solids (w/w)
A = to ash in solids (w/w)
and K1 to K11 are constants
If the composition range for a given sample stream is unusually large, it may be necessary to expand the above equation by the provision of second order terms for the primary variables e.g. terms in I / and I2.
The central nucleonics unit performs the additional function of maintaininq the precision of the radiation measurements by the known method of spectrum stabilisation in cooperation with the local nucleonics modules. Measurements made with clean water flowing through the apparatus may be used to provide standard readings for comparative purposes under the control of the micro-computer.
Additional standardising measurements may also be made with a test piece replacing the analysis cells in the case of either or both of the detectors involved, said test pieces being introduced either manually or automatically under control of the micro-computer.
The micro-computer may be programmed so as to carry out a predetermined sequence of standardising and sample measurements as desired. Provision can also be made to admit two or more samples into the apparatus in sequence under control of the micro-computer, which will also undertake the appropriate computations on each sample and furnish an output as a hard copy or in other suitable form indicating the sample origin and its composition in terms of solids content and ash content. Alternatively, a sequencing device may be provided to control the mechanical functions of the apparatus and to initiate the measurements through a micro-computer associated with the central nucleonics.
Local 19 and remote 20 input and output modules of optional design are connected to the micro-computer sub-system to provide facilities for setting up programming and manual control of the system as required.
Claims (10)
1. A method measuring the ash content of a sample of coal slurry comprising the steps of: a) passing the sample through a first measurement cell and
irradiating the sample with gamma-rays; b) measuring the intensity of gamma-rays transmitted through the
sample; c) passing the sample through a second measurement cell where the
sample is irradiated with X-rays; d) measuring the intensity of backscattered X-rays; e) measuring the intensity of the iron X-ray photopeak of emitted
X-rays; and, f) using the measurements of transmitted gamma-ray intensity,
backscattered X-ray intensity and the intensity of the iron Kcç photopeak to compute a value for the ash content of the sample
which includes a correction for the effect of iron minerals in
the sample.
2. A method according to claim 1, characterised in that the sample is passed through a dewaterinq means to increase the solids content of the sample prior to passing through the first measurement cell.
3. A method according to claim 2, characterised in that the dewatering means comprises at least one hydrocyclone.
4. An apparatus for measuring the ash content of a sample of coal slurry comprising:
a first measurement cell through which the sample is passed;
a first radioisotope source of gamma-rays situated adjacent the
first measurement cell;
a detector giving an output signal related to the intensity of
the gamma-rays transmitted through the sample;
a second measurement cell through which the sample is passed
subsequent to its passage through the first measurement cell;
a second radioisotope source of X-rays situated adjacent to the
second measurment cell; and,
a detector giving an output signal related to the intensity of
the X-rays backscattered from the sample, and iron KCX X-rays
emitted from the sample.
5. An apparatus according to claim 4, characterised in that the apparatus further comprises a dewatering means to increase the solid content of the coal slurry sample prior to its introduction into the first measurement cell.
6. An apparatus according to claim 5, characterised in that the dewatering means comprises at least one hydrocyclone.
7. An apDaratus according to any one of claims 4 to 6, characterised in that the second measurement cell is provided with a window of plastics material which is substantially transparent to iron Kcy X-rays.
8. An apparatus according to any one of claims 4 to 7, characterised in that the first gamma-ray measurement cell comprises a "Z" tube.
9. A method of measuring theash content of a sample of coal slurry substantially as hereinbefore described with reference to the accompanying drawing.
10. An apparatus for measuring the ash content of a sample of coal slurry substantially as hereinbefore described with reference to the accompanying drawing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB888820074A GB8820074D0 (en) | 1988-08-24 | 1988-08-24 | Improvements in radiometric analysis |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8919125D0 GB8919125D0 (en) | 1989-10-04 |
| GB2223574A true GB2223574A (en) | 1990-04-11 |
Family
ID=10642618
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB888820074A Pending GB8820074D0 (en) | 1988-08-24 | 1988-08-24 | Improvements in radiometric analysis |
| GB8919125A Withdrawn GB2223574A (en) | 1988-08-24 | 1989-08-23 | Radiometric analysis |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB888820074A Pending GB8820074D0 (en) | 1988-08-24 | 1988-08-24 | Improvements in radiometric analysis |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8820074D0 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006117106A1 (en) * | 2005-04-30 | 2006-11-09 | Elisabeth Katz | Method and device for the online determination of the ash content of a substance conveyed on a conveying means, and device for carrying out such an online determination |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB893961A (en) * | 1957-07-29 | 1962-04-18 | Bergwerksverband Gmbh | A method for the sorting of coal in accordance with its ash or water content |
| GB2059581A (en) * | 1979-09-27 | 1981-04-23 | Atomic Energy Of Australia | Analysis of coal slurries |
| GB2065876A (en) * | 1979-12-20 | 1981-07-01 | Atomic Energy Of Australia | Annihilation radiation analysis |
| GB2116698A (en) * | 1982-02-26 | 1983-09-28 | Coal Ind | Coal analysis using x-rays |
-
1988
- 1988-08-24 GB GB888820074A patent/GB8820074D0/en active Pending
-
1989
- 1989-08-23 GB GB8919125A patent/GB2223574A/en not_active Withdrawn
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB893961A (en) * | 1957-07-29 | 1962-04-18 | Bergwerksverband Gmbh | A method for the sorting of coal in accordance with its ash or water content |
| GB2059581A (en) * | 1979-09-27 | 1981-04-23 | Atomic Energy Of Australia | Analysis of coal slurries |
| GB2065876A (en) * | 1979-12-20 | 1981-07-01 | Atomic Energy Of Australia | Annihilation radiation analysis |
| GB2116698A (en) * | 1982-02-26 | 1983-09-28 | Coal Ind | Coal analysis using x-rays |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006117106A1 (en) * | 2005-04-30 | 2006-11-09 | Elisabeth Katz | Method and device for the online determination of the ash content of a substance conveyed on a conveying means, and device for carrying out such an online determination |
| US8306188B2 (en) | 2005-04-30 | 2012-11-06 | Elisabeth Katz | Method and device for the online determination of the ash content of a substance conveyed on a conveyor, and device for carrying out such an online determination |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8820074D0 (en) | 1988-09-28 |
| GB8919125D0 (en) | 1989-10-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |