WO2001077647A1

WO2001077647A1 - A method and optical analyser for measuring the content of ashes

Info

Publication number: WO2001077647A1
Application number: PCT/PL2001/000001
Authority: WO
Inventors: Bogdan Niewczas; Janusz Piecha; Tomasz Piwowarczyk
Original assignee: Zaklad Aparatury Pomiarowej Kw; Bogdan Niewczas; Janusz Piecha; Tomasz Piwowarczyk
Priority date: 2000-04-11
Filing date: 2001-01-05
Publication date: 2001-10-18
Also published as: PL339635A1; PL192035B1; AU2001225603A1

Abstract

The method under this invention consists in measuring of light reflected from a sample adhering to the transparent window and determining the dust component content by comparing the result of this measurement with a standard established from chemical analysis of the sample. The result for given sample is the mean value from at least two measurements. Each measurement is made after fluidisation mixing of the sample. The optical analyser comprises: a sampling unit (A) with a deposit chamber (8) covered with the window (17) of the measuring unit (B). In the lowest zone of the deposit chamber (8) there is an ejection nozzle which is connected with the conduit supplied with compressed air by two branches, each of them is equipped with shut-off solenoid valve (11, 13) and compressed air pressure regulator (12, 14). The analyser is equipped with the control sample unit (D) comprising a control cyclone (22) with tangential inlet channel (22) connected with the slanting channel (21) made as a branch of the discharge unit (7) directed upwards inside the body (9) of the sampling unit (A). The central outlet channel (24) is connected with the source of underpressure (27). There is a lateral nozzle (28) installed in the wall of the slanting channel (20).

Description

A METHOD AND OPTICAL ANALYSER FOR MEASURING THE CONTENT OF ASHES

The subject of this invention is a method for optical measuring of the content of dust component distinguishable by its colour and an optical analyser of the content of dust component in gas stream. Both methods are used for technological measuring of the amount of light-absorbing dust component, for example, carbon residues in flue fly ash from a coal dust -fired boiler.

There are known optical dust analysers in which the result of measurement is derived from the intensity of light directly reflected from the surface of a sample adhering at one side to the transparent window. The reflectometric measurement of a sample is made in one cross-section adjacent to the transparent window of the measuring head. It is impossible to reach high accuracy with reflectometric measurements made in one cross-section only, as a dust sample is highly inhomogeneous, both in grain size distribution and chemical composition .

There is an analyser described in the Polish patent application no P- 319853 comprising: a sampling unit, a measuring unit and a control unit. The sampling unit is a cyclone, which is parallelly connected with the gas emission duct through a tangential inlet channel and a central outlet channel. The outlet channel is connected with a source of suction (subatmospheric pressure), especially in a form of an injection reduction pipe fastened onto the end of the outlet channel which is inserted in the emission duct.

The cyclone bottom channel is connected with a discharge channel inserted into a deposit chamber. The lower end of the discharge channel is covered with a flat window of the measuring unit. The window is inclined, in relation to the horizon at an angle of inclination larger than the dust discharge angle. An ejection nozzle is installed at the lowest point of the deposit chamber. The nozzle is connected with a compressed air conditioning unit (drying and preheating) through a cut-off solenoid valve. The window is inclined in relation to the horizon at an angle larger than the dust discharge angle, thus causing the dust from previously blown out sample remaining in the cyclone slides down into the corner, outside the measuring zone, thus not affecting measurements of next sample. The measuring unit of optical reflectometer design is equipped with the measuring head containing two laser diodes, as a source of light, and photoelectric cells receiving the reflected light The latter are connected to measuring electronic block The measuring unit is mounted on the body with a quick-release joint

The accuracy of analyser measurements requires the measuring unit setting to be checked and adjusted, if necessary, every 48 hours on the average and at each change of raw material For example, a change of coal brand burnt in boilers results in changes of fly ash colour, thus the background for measuring the unburnt carbon content of fly ash For the analyser described in P-319853 it is necessary to unfasten the body with the discharge channel and the deposit chamber with the measuring unit attached A dust sample taken from the deposit chamber is than subjected to chemical analysis that provides correction for settings of the measuring unit Such time-consuming procedure affect also the technical condition of optoelectronic elements inside the measuring unit

The method for optical measuring of the content of dust component distinguished by its colour according to this invention characterises in that the result for a sample is defined as a mean value from at least two measurements of the intensity of light that is reflected from the surface of dust sample and each next measurement is conducted after fluidisation mixing of a sample Thus, each sample is measured several times The dust distribution in the window varies with each fluidisation mixing The mean result of measurements is very close to the real value obtained by chemical analysis The analyser under this invention, like the apparatus described above, comprises a sampling unit which includes a cyclone, a body, a deposit chamber covered with an inclined window, an ejection nozzle, a measuring unit which a head and a measuring electronic block, and processor control unit The invention characterises in that the duct connected with the ejection nozzle is fed by two branches and each of them is controlled with cut-off solenoid valve and compressed air pressure regulator Such solution allows the ejection nozzle to be supplied with compressed air from two regulators One of them is set at pressure value used for fluidisation mixing of dust sample in the deposit chamber, while the second one is set at required pressure value to reject a dust sample into the emission duct The control unit program initiates a few measurements for each sample The fluidised mixing of a sample separates each of these measurements

The further improvement of analyse under this invention consists in providing it with a unit for control sample taking This unit comprises a control cyclone connected to the slanting channel through the tangential inlet channel

The slanting channel is an upward branch of the discharge channel The central outlet channel is connected with a source of undeφressure, especially in the form of injection reduction pipe which is supplied with compressed air by a cutoff solenoid valve There is a fitting and a control sample replaceable vessel under the control cyclone outlet Such solution enables the same sample to be sucked through the slanted channel into the control sample vessel, after examination by the measuring unit The process of control sample suction is effectively supported by ejection nozzle working at pressure used for sample mixing The control sample vessel is replaced and installed without interrupting operation of the analyser

Another improvement in this invention characterises in that there is a lateral nozzle installed in the slanting channel, adjacent to the discharge channel The nozzle is connected with the compressed air conditioning unit through a cut-off solenoid valve When a dust sample is discharged pneumatically from the deposit chamber through the sampling unit cyclone, a signal from the control unit at the same time opens the cut-off valve of the lateral nozzle Air flowing through the lateral nozzle serves as an air curtain that prevents dust of test sample from penetrating into the slanting channel and mixing with a test sample in the vessel under the control cyclone

It is advantageous to install a filter between the central outlet channel of the cyclone and the source of suction to eliminate dust from the analyser housing when taking a control sample Thus there are no necessity to divert air flowing from the injection reduction pipe into an additional channel leading to the emission duct

The next improvement in this invention consists in installing an automatic check valve between the filter and the source of suction The valve allows flow toward the source of suction and isolates the control sample unit from the outside, thus eliminating flow disturbances inside the analyser and protecting

100 the inner walls against moistening

The said solution allows for high accuracy of measurements and much more easier operation No mobile mechanical parts in dusty environment decides on high reliability of the unit

The analyser described above is shown in drawing The method for

105 measuring of dust component content is explained along with operation of the

The analyser comprises four main assemblies sampling unit A, measuring unit B, control unit C and control sample unit D The sampling unit A is equipped with a cyclone 1 connected in parallel through no the tangential inlet channel 3 and the upper outlet channel 4 with emission duct

2 of dust loaded gas The gas flow through the cyclone 1 is initiated by underpressure existing in the emission duct 2 which is supported by the source of underpressure 5 being an injection reduction pipe fastened onto the outlet channel 4 and inserted into the emission duct 2 The cyclone 1 is fastened with

115 a quick-release flanged joint 16 onto the body 9 The lower channel 6 of the cyclone 1 is connected with the discharge channel 7 in the body 9 The channel ends inside the deposit chamber 8 The lower surface of the body 9 adjacent to the measuring unit B is cut at angle of 45° C The bottom of the deposit chamber 8 is closed with the window 17 of the measuring unit B The ejection

120 nozzle 10 is installed in the lowest zone of the deposit chamber 8 The ejection nozzle 10 is supplied with compressed air from two branches of compressed air conditioning unit 15 On each of these branches a check valve 11 , pressure regulator 12 and compressed air regulator 14 are installed Air is thoroughly cleaned and heated up to temperature of 85°C at the compressed air 25 conditioning plant 15 The measuring unit B is an optical reflectometer, which measures the dust component content through the transparent window 17 The measuring head 18 with the laser diodes and the measuring electronic block 19 is installed centrally under the window 17 The slanting channel 20 in the body 9 is an upwardly directed branch of discharge channel 7 The slanting channel 20 30 is connected with the inlet channel 21 tangentially inserted into the control cyclone 22 which is the main element of the control sample unit D The control sample vessel 23 is fitted under the control cyclone outlet 22 The central -> discharge channel 24 of the control cyclone 22 is connected through a filter 25 and automatic check valve 26 with the source of underpressure 27 in the form

135 of injection reduction pipe The nozzle supplied with compressed air by an shut- off solenoid valve 28 is directed centrally towards the reduction pipe There is a nozzle 29 connected with the compressed air conditioning unit 15 through a shut-off solenoid valve 30 The nozzle is installed inside the body 9 in the slanting channel wall 20

140 After collecting a dust sample of required volume inside the deposit chamber 8, a signal from the control unit C initiates the work of the measuring unit (B) which performs the measurement of light reflected from the dust surface Then the control unit sends a signal for opening the shut-off valve 1 , thus starting compressed air flow at pressure of 2,2 bar through the conduit that supplies the

145 ejection nozzle 10 The value of the pressure is adjusted on the pressure reducer 12 The fluidisation mixing of dust sample for around 5 seconds changes the particle arrangement on the window 17 Than the next measurement of reflected light is made The algorithm of control program repeats the mixing and measuring operations three times and than calculates

150 the mean value which is a result for examined sample The sample is then rejected into the emission duct 2 through the inlet 3 and outlet 4 channels To do it compressed air is fed to the ejection nozzle 10 through opened shut-off valve 13 installed on a branch with pressure reducer 14 set at 8 bar The shut- off valves 13 and 30 are opened at the same time, thus air flowing from the

155 nozzle 29 prevents dust from penetrating into the slanted channel 20

In established periods, for example every 48 hours and whenever the process conditions are changed, i e fly ash flowing through the emission duct 2 is changed, the sample is not rejected from the deposit chamber 8 into the emission duct 2 after the measuring cycle is completed but is diverted into the

160 control sample unit D through the slanting channel 20 To do it the shut-off valves 28 and 11 are opened Underpressure generated by compressed air flow through the injection reduction pipe 27 results in opening the check valve 26 and sucking dust fluidised inside the deposit chamber 8 into the control cyclone 22 through the slanting channel 20 When dust is separated the shut-off valves

165 28 and 11 are closed and the control sample vessel 23 is replaced with an empty one Dust from the vessel is then subjected to chemical analysis at a laboratory to determine the dust component content is measured. The differences between the results obtained from chemical analysis and those of the analyser works are used as a base for adjusting the measuring electronic block 19.

Claims

The method for optical measurement of the content of dust component distinguished by its colour, in particular carbon residues in flue fly ash emitted from the coal dust fired boilers, that consists in measuring light reflected from a dust sample adhering from the other side to the transparent window and determining the dust component content by comparison with the results obtained by chemical analysis for control sample The said method characterises in that the result for given sample is defined as the mean value calculated form at least two measurements, and each next measurement is made after fluidisation mixing of the sample

Optical analyser of dust component distinguishable by its colour, especially carbon residues in flue fly ash emitted from the coal dust fired boilers, comprising - a sampling unit equipped with a cyclone inserted in parallel into the gas emission duct through a tangential inlet channel and a central outlet channel with built-in source of underpressure, especially in the form of injection reduction pipe mounted onto the end of outlet channel inserted into the emission duct, in addition, the lower channel of the cyclone is connected with the discharge channel inserted into the deposit chamber of the body The bottom of the chamber is a flat window inclined in relation to the horizon at an angle larger than the dust discharge angle In the lowest zone of the deposit chamber there is a ejection nozzle which is connected by the conduit with the compressed air conditioning unit through a shut-off solenoid valve

- The measuring unit of optical reflectometer design, comprising a window, a measuring head installed perpendicularly under the window, a measuring electronic block, and - Processor control unit characterised in that the conduit connected with the ejection nozzle (10) is supplied by two branches, each of them is WO 01/77647 _Q PCT/PLOl/00001

equipped with shut-off solenoid valve (1 1 , 13), pressure regulator (12, 14) and the compressed air regulator.

205 3. The analyser as claimed in claim 2, characterised in that it is equipped with the control sample unit (d) comprising: a control cyclone (22) with tangential inlet duct (21 ) connected with the slanting channel (20) made as a directed upwards branch of the discharge channel (7) in the body (9) of the sampling unit (A), central outlet channel (24) of the control cyclone (22) is connected

2io with a source of underpressure (27), usually in the form of an injection reduction pipe supplied with compressed air through the shut-off solenoid valve (28), whereas a replaceable vessel for control sample is attached under the control cyclone outlet.

215 4. The analyser as claimed in claim 3 is characterised in that there is a lateral nozzle (9) installed in the wall of the slanting channel (20), near to the discharge channel (7) and this nozzle is connected with the compressed air conditioning unit (15) through a shut-off solenoid valve (30).

220 ^"5. The analyser as claimed in claim 3 is characterised in that there is a filter

(25) installed between the central outlet channel (24) of the control cyclone (22) and the source of underpressure (27).

6. The analyser as claimed in claim 5 is characterised in that between the filter 225 (25) and the source of underpressure (27) there is an automatic check valve

(26) installed which flow is directed towards the source of underpressure (27).