WO1998002729A1

WO1998002729A1 - Method and apparatus for measuring reflections from unburned carbon

Info

Publication number: WO1998002729A1
Application number: PCT/DK1997/000300
Authority: WO
Inventors: Anders Sten Wedell; Matthias Nissen Pedersen; Soeren Kragh Nielsen
Original assignee: Anders Sten Wedell; Matthias Nissen Pedersen; Soeren Kragh Nielsen
Priority date: 1996-07-05
Filing date: 1997-07-07
Publication date: 1998-01-22
Also published as: DK173406B1; CN1225170A; EP1009997A1; RU2180744C2; DK74796A; CN1093937C; AU3255597A

Abstract

In a method and an apparatus for reflection measurement of the content of unburned carbon in fly ash from a heating plant, whereby is used a residue coal or carbon meter with a transparent measuring tube, preferably of glass, wherein an ash sample taken from the flue duct of the heating plant can be passed through one end of the measuring tube, and be deposited inside the measuring tube and after completion of the reflection measurement can be blown out of the measuring tube or back to the flue duct. The reflection measurement is made by directing wave trains of infrared light emitted from sources towards each of at least two different areas on the surface of the ash sample located in the tube and at a certain distance from the sources, that the part of the wave train, which thereby is reflected, is returned to respective infrared detecting receivers, and that the proportion between the energy of mutually dependent wave trains respectively emitted towards the ash sample surface and reflected therefrom is measured, so that at least one reflection measurement is made on at least two different areas abutting the inner side of the measuring tube on the outer surface of the ash sample, and that the results of the reflection measurements are compared in the form of reflection coefficients. Thereby is achieved a very fast, sturdy, simple and easy operable method and apparatus without using hazardous microwaves.

Description

Method and Apparatus for Measuring Reflections from

Unburned Carbon.

The invention relates to a method and an apparatus for reflection measurement of unburned carbon in fly ash from a heating plant, whereby is used a residue coal or carbon meter with a transparent measuring tube, preferably made of glass, wherein an ash sample taken from the fly ash in the flue duct of the heating plant can be passed through one end of the measuring tube and deposited inside the measuring tube and after completion of the reflection measurement can be blown out of the measuring tube or back to the flue duct.

By a reflection measurement is obtained a reflecting coefficient providing a relative expression for the content of unburned carbon in the fly ash. By a filled measuring tube a reflection measurement on a surface area of the ash sample, said area abutting the inner surface of the measuring tube, can be made e.g. by means of electromagnetic waves which e.g. may provide a colour measuring. The result of a reflection measurement can be shown by an apparatus with digital reading or analog output of residue carbon as percentage.

By a measuring tube filled with ash the following irregularities can be watched.

The ash might have stratified so as to provide "black carbon stripes" or carbonless "white ash stripes". If measuring takes place in one of said "stripes", the measuring will erroneously show an excessively high or excessively low residual carbon content, respectively, in the ash.

An air pocket may occur in the ash, which air poc- ket cannot reflect an electromagnetic wave train, e.g. from infrared light. Thus, a reflection measurement on the air pocket will also erroneously show an excessively high residual carbon content.

Large black particles may be present in the ash. A reflection measurement on such particle will therefore also erroneously show an excessively high residual carbon content.

Normally, the ash is relatively homogeneous but might from time to time be very inhomogeneous. In the latter case a reflection measurement will show a different residual carbon content depending on the position of the area on the ash surface where the masure ent is made. By known methods whereby solely one reflection measurement is made, the waves may have hit one of the ment.-oned "stripes", a black particle or an air pocket in an otherwise white ash surface and may thus have provided an erroneous picture of the content of carbon in the ash and thus of the operational status of the heating plant.

By said known methods it is therefore necessary to make a reflection measurement on at least two ash samples taken after each other, the measuring results of which must be compared. Only if two such measurings were practically iden- tical, there was a fair possibility that the measurings were correct. If the measurings differed essentially from each other, then one or possibly more further ash samples had to be measured.

By a method and an apparatus, known from US-PS 5,173,662 for determination of carbon contents in fly ashes is used wave trains of microwaves with a frequence of preferably about 2450 MHz corresponding to a wave length of about 122 mm. Here the following content of wave energy is measured, namely the content emitted towards a fly ash sa p- le, and then the content passing through the fly ash sample and the content being reflected from the fly ash sample. Based on said measurements the content of energy being absorbed by the fly ash can be calculated. The energy content coefficient thus calculated will draw a picture of the relative amount of carbon in the fly ash sample.

Only one energy content coefficient for each ash sample is obtained. More energy content coefficients are obtained by measuring by means of one and same apparatus on subsequent ash samples or by simultaneous measurings by moans of several apparatuses each measuring its respective ash sample.

This known method thus demands an extensive number of measurings on different ash samples and subsequent extensive calculations in order to obtain a useful measuring result.

Consequently, is the object of the present inven- tion for reflection measurement to provide a method and an apparatus being less time consuming, and whereby the mentioned disadvantages have been eliminated, and whereby a high probability of a correct measuring result can be obtained quickly. According to the invention this is achieved by a method of the kind mentioned above, which is characterized in that the reflection measurement is made by directing wave trains of infrared light emitted from sources towards each of at least two different areas on the surface of the ash sample located in the tube and at a certain distance from the sources, that the part of the wave train which thereby is reflected, is returned to respective infrared detecting receivers, and that the proportion between the energy of mutually dependent wave trains respectively emitted towards the ash sample surface and reflected therefrom is measured, so that at least one reflection measurement is made on at least two different areas abutting the inner side of the measuring tube on the outer surface of the ash sample, and that the results of the reflection measurements are compared in the form of reflec- tion coefficients.

Thereby is achieved that at least two reflection coefficients is obtained which can be immediately compared and on the basis hereof be accepted or rejected, by means of only one measuring operation comprising all measurings of the strength of several emitted and reflected wave trains of infrared light having a wave length from about 7600 A and up to about 1 mm, and which are emitted towards and reflected from only one ash sample. The method according to the invention is therefore more simple with respect to measurings, as well as time saving compared to the known methods. If the reflection coefficients measured are practically identical, the measuring operation is accepted. If one or more of the coeffici- ents differs more than a predetermined value from the average of the coefficients, such coefficients are extracted, and a new average based on the remaining coefficients is then the result of the measuring operation. In case one of the remai- ning coefficients is zero, the measurement is extracted and a measuring operation on a new ash sample should be made.

Furthermore, the method in an embodiment of the invention be characterized in that measurements are made in ash sample surface areas located at different planes perpen- dicularly to the axis of the measuring tube.

In another embodiment of the invention the me-thod may be characterized in that measurements are made in ash sample surface areas being mutually angularly displaced around the axis of the measuring tube. In a further embodiment of the invention the method may be characterized in that measurements are made in six ash sample surface areas located in two radial planes with three ash sample surface areas in each plane.

By said embodiments of the method according tc the invention it is achieved that measurements can be made on several areas on the surface of the ash sample, not only in one plane, but also in ash sample surface areas located on vertical lines, inclined lines or on curved lines. Thereupon an average coefficient is calculated based on the reflection co- efficients measured. The reflection coefficients differing essentially from said average coefficient will be extracted. Thereupon a new average coefficient is calculated, which can be considered as the valid reflection coefficient, the result of the measuring operation. The method according to the invention may also be characterized in that transmission measurements are made regularly through the measuring tube when it has been emptied for ash, for achieving a transmission coefficient for the set point correction or for calibration purposes. Thus, it can be ascertained to which extent the tube is worn and/or to which extent the soot which might be left on the inner surface of the empty measuring tube arfter the ash sample having been blown out, influences the measurements when the measuring tube is full of ash. The transmission coefficient measured by an empty measuring tube can be used as calibration value by subsequently measured reflec- tion coefficients when the measuring tube is filed. If the measuring tube transmits too little light, the measuring tube should be cleaned with respect to adhering soot or should be changed due to wear and tear.

The method can be carried out by means of an appa- ratus of the kind mentioned in the introductory clause, which method according to the invention is characterized in that the apparatus has radiation sources for emitting wave trains of infrared light towards each of at least two different areas on the surface of the ash sample, the surface of which abutting the inner surface or side of the measuring tube, receivers for reception of the reflected wave trains from the respective areas, means for measuring the proportion (reflection coefficient) between the energy of interconntected wave trains respectively emitted towards the ash sample surface area and reflected therefrom, means for comparing the reflection coefficients, means for calculation and showing their average value after the most differing reflection coeffici- ent/s has/have been extracted. Thereby the advantages mentioned in connection with the method are obtained, and thus without the disadvantages connected to the prior apparatuses.

An embodiment of the apparatus is advantageous by the residue carbon meter comprising an element consisting of a section of a hollow cylinder being placed relatively to the measuring tube in such position that the inner wall of the cylinder is located at a distace from and parallel to the outer wall of the measuring tube, and where at least two pairs of channels are provided between the outer wall and the inner wall of the cylinder, said channels being arranged in pairs and so with respect to each other that a wave train of infra- red light can be emitted from an infrared radiation source, such as an infrared diode, through the one channel of a pair and towards an area of the surface of the ash sample, and so that a part of the wave train emitted is reflected from the ash sample surface area and will be returned through the other channel of the pair of channels to a receiver of the infrared light radiation. Thus, it is achieved that measurements can be made simultaneously on more areas of the surface of the ash sample. Hereafter an average coefficient of the measured reflection coefficients is calculated. The reflection coefficients differing considerably from said average coefficient are ex- tracted. Hereafter a new average coefficient is calculated, which can be considered as the valid reflection coefficient.

An embodiment of the apparatus is advantageous thereby that the cylinder contains channel pairs being so arranged that measurements may be made in ash sample surface areas located at different planes perpendicularly to the axis of the measuring tube.

Another embodiment of the apparatus is advantaςreous thereby that the cylinder contains channel pairs being so arranged that measurements can be made in ash sample surface areas located mutually angularly displaced around the ax:-s of the measuring tube.

A further embodiment of the apparatus is advantageous thereby that the cylinder contains six channel pairs; being so arranged that measurements are made in six ash sample surface areas located on two radial planes with three areas in each plane.

Thus it is obtained that six reflection coefficients can be measured simultaneously, whereupon an average coefficient of the measured reflection coefficients after a correction based on a calibration value measured on an empty measuring tube can be calculated. The reflection coefficients differing considerably from said average coefficient can be extracted. Thereupon a new average coefficient is calculated, which can be considered as the valid reflection coefficiE-nt . Thus a reliable reflection coefficient is achieved, which is a picture of the content in the ash of unburned carbon after one measuring cyclus . The invention will now be described in more detail with reference to the drawing which shows a section of 180° of an element in a residual carbon meter, said element consisting of a hollow cylinder 13, which partly may surround the transparent measuring tube in the residue carbon meter. The inner wall 14 of the cylinder 13 is adapted for being located at a certain distance from and parallel to the outer wall of the transparent measuring tube of the residue carbon meter. The wall of the cylinder 13 has at least two channels or pairs of channels 1 and 2, 3 and 4 extending between the inner wall 13 and the outer wall 15 of the cylinder, and the shown embodiment implies six pairs of channels 1 and 2, 3 and 4 etc.

In one of the channel pairs the axis of a first channel 1 is directed radially against an area on the inner side of the measuring tube. The axis of another channel 2 is arranged at the same axial plane as the first channel 1 , below said channel 1 and at an angle of e.g. 25° with respect thereto and directed against the same area on or a small distance behind the inner side of the measuring tube.

At another axial plane, which is angularly displaced 25° about the axis 16 of the cylinder 13 is arranged a subsequent channel pair 3, 4 consisting of a channel 3 arranged at a plane below the first channel 1. The axis of said channel 3 is directed radially against another area on or a small distance behind the inner side of the measuring tube. The other channel 4 in this pair of channels is arranged at the same axial plane as the channel 3 belonging to the pair, above said channel and at an angle relatively thereto and di- rected against the other area on or a small distance behind the inner side of the measuring tube.

In the same way four further channel pairs have been arranged in the cylinder wall, angularly displaced 25° around the axis 16 of the cylinder 13 with respect to each other and so that measurements in total are made on three ash sample surface areas at one radial plane and on three areas at another radial plane being arranged at a distance 6 from the first radial plane.

By reflection measurement on ash in the measuring tube a wave train of infrared light from e.g. an infrared diode is emitted through e.g. the channels 1, 3, ... arranged radially in the channel pairs towards the surface of the ash for illuminating of areas on the ash surface. From each of these areas is returned a part of the infrared light reflected from the areas through the other channels 2, 4, .. etc of the pairs to infrared receivers or vice versa. Thus, a reflection coefficient can be measured from each of six measuring areas on the ash sample, and an average coefficient of said reflection coefficients can be calculated after a correction based on at least one calibration value which as mentioned can be measured on an empty measuring tu- be. For more accurate reflection measurements two calibration values are used, one for dark tube (zero point location) and one for the measuring tube filled with barium sulphate ( full scale). One, two or more of said reflection coefficients which might differ considerably from said average coeffici- ent, may be extracted, seeing that the reflection coeffi- cient/s in question is/are beyond a predetermined limit value. Thereupon a new average coefficient is calculated based on the remaining reflection coefficients, which coefficient can be considered as valid average coefficient. In stead of each channel pair can be used a single channel for emission and reflection of wave trains, e.g. through two of the fiber- optical light guides or bunches thereof arranged in the channel. In case of fiber-optical light guide bunches, a central fiber-optical light guide bunch may advantageously be arrang- ed in each channel, said bunch being totally or partly surrounded by a fiber-optical light guide bunch arranged around the central bunch. The electromagnetic wave train is the emitted through one and reflected through the other fiber- optical light guide bunch. The value calculated as valid reflection coefficient is an intermediate result used for calculation of the weight percentage of unburned carbon in the fly ash, which is the result to be presented.

Claims

C l a i m s :

1. Method by a reflection measurement of unburned carbon in fly ash from a heating plant, whereby is used a residue coal or carbon meter with a transparent measuring tube, preferably of glass, wherein an ash sample taken from the flue duct of the heating plant can be passed through one end of the measuring tube and be deposited inside the measuring tube and after completion of the reflection measurement can be blown out of the measuring tube or back to the duct, c h a r a c - t e r i z e d in that the reflection measurement is made by directing wave trains of infrared light emitted from sources towards each of at least two different areas on the surface of the ash sample located in the tube and at a certain distance from the sources, that the part of the wave train which thereby is reflected, is returned to respective infrared detecting receivers, and that the proportion between the energy of mutually dependent wave trains respectively emitted towards the ash sample surface and reflected therefrom is measured, so that at least one reflection measurement is made on at least two different areas abutting the inner side of the measuring tube on the outer surface of the ash sample, and that the results of the reflection measurements are compared in the form of reflection coefficients.

2. Method according to claim 1, c h a r a c t e r i z e d in that the measurements are made in ash sample surface areas located at different planes perpendicularly to the axis (16) of the measuring tube.

3. Method according to claim 1 or 2, c h a r a c t e r i ze d in that the measurements are made in ash sample surface areas being mutually angularly displaced around the axis (16) of the measuring tube.

4. Method according to any of the preceding claims, c h a r a c t e r i z e d in that measurements are made in six ash sample surface areas located at two radial planes with three ash sample surface areas at each plane.

5. Method according to each of the preceding claims, c a r a c t e r i z e d in that transmission measurement:; are made regularly through the measuring tube when it has been emptied for ash, for achieving transmission coefficients which may form a calibration value for subsequent reflection measurements where a measuring tube is full of ash.

6. Apparatus for reflection measurement of unburned carbon in fly ash from a heating plant, the apparatus having a residue coal or carbon meter with a transparent measuring tube, preferably of glass, wherein an ash sample taken from the flue duct of the heating plant can be passed through the one^* end of the measuring tube and be deposited inside the measuring tube and after completion of the reflection measurement: can be blown out of the measuring tube or back to the flue duct, c h a r a c t e r i z e d in that the apparatus has radiεction sources for emitting wave trains of infrared light towards each of at least two different areas on the surface of the ash sample, the surface of which abutting the inner surface or side of the measuring tube, receivers for reception of the reflected wave trains from the respective areas, means for measuring the proportion (reflection coefficient) between the energy of interconntected wave trains respectively emitted towards the ash sample surface area and reflected therefrom, means for comparing the reflection coefficients, means for calculation and showing their average value after the most differing reflection coefficient/s has/have been extracted.

7. Apparatus according to claim 6, c h a r a c t e r i z - e d in that the residue carbon meter comprises an element consisting of a section of a hollow cylinder (13) being placed relatively to the measuring tube in such a position that the inner wall (14) of the cylinder is located at a distance from and parallel to the outer wall of the measuring tube. that at least two pairs of channels (1 and 2, 3 and 4) are provided between the outer wall (15) and inner wall (14) of the cylinder, that the channels are arranged in pairs and in such mutual relationship that a wave train of infrared light can be emitted from an infrared diode through the one channel ( 2 and 4 ) of a pair and towards an area of the surface of the ash sample and so that a part of the wave train emitted is reflected from the area and will be returned through the other channel (1 and 3) of the pair of channels to an infrared receiver.

8. Apparatus according to claim 7, c h a r a c t e r i z e d in that the cylinder (13) contains channel pairs so arranged that measurements are made in ash sample surface areas located at different planes perpendicularly to the axis if the measuring tube.

9. Apparatus according to claim 7 or 8, c h a r a c t e r i z e d in that the cylinder (13) contains channel pairs so arranged that measurements can be made in ash sample surface areas located mutually angularly displaced around the axis of the measuring tube.

10. Apparatus according to claims 7, 8 or 9, c h a r a c t e r i z e d in that the cylinder ( 13 ) contains six channel pairs arranged so that measurements can be made in six ash sample surface areas located at two radial planes with three areas at each plane.