Method and apparatus for detecting particles in a gas flow

• US 20030089159A1
• Filed: 10/11/2002
• Published: 05/15/2003
• Est. Priority Date: 04/12/2000
• Status: Active Grant

• Current Assignee: Goyen Controls Company Pty Limited (Pentair Plc (Ireland))
• Original Assignee: Goyen Controls Company Pty Limited (Pentair Plc (Ireland))
• Inventors: Roe, Morris Anthony
• Granted Patent: US 7,063,731 B2
• Time in Patent Office: Days
• US Class Current: 73/28.04
• CPC Class Codes: G01N 15/0656 using electric, e.g. electrostatic methods or magnetic methods by investigating individual particles G01N15/1031, G01N15/12
• CPC Class Codes: G01N 27/60 by investigating electrostatic variables , e.g. electrographic flaw testing G01N27/007 takes precedence

Abstract

The application discloses several methods of detecting particles moving in a gas flow, a detection means (70), a method of improving the linearity of the signal produced by a triboelectric particle detector, a method to test a signal path of an emission monitor, an emission monitor for detecting particles, and a method of detecting faults in a triboelectric probe of system for detecting particles entrained in a gas flow. The particle detection means (70) includes a gas flow deflection means (40) having an upstream face (43) and a downstream face (45) and a detector (42, 44) associated exclusively with the downstream face (45). Deflecting the gas flow creates vortices that have little effect on the large particles, but cause the small particles to move close to the detectors on the downstream face. Therefore the downstream detectors (42, 44) are particularly sensitive to light particles. The method improves of small particles and provides accurate particle counts.

Claims

1. A detection means for detecting particles entrained in a gas stream, said detection means comprising:

a body adapted to be located in said gas stream and having an upstream face and a downstream face;

a detector associated with said downstream detection face adapted to detect particles impinging on or passing over said downstream face; and

said body being shaped and configured to deflect said gas stream around said body in a manner to cause generally turbulent gas flow of said gas stream adjacent said downstream face;

said detector being adapted to generate a detection signal as a consequence of particles entrained in said turbulent gas flow impinging on or passing over said downstream face.

2. A detection means as claimed in claim 1, wherein said detection signal is used to calculate a detection value that is representative of said particles entrained in said turbulent gas flow.

3. A detection means as claimed in claim 1, wherein said detector is adapted to detect particles impinging on or passing over said upstream face of said body.

4. A detection means as claimed in claim 1, comprising a further detector adapted to detect particles impinging on or passing over said upstream face of said body.

5. A detection means as claimed in claim 1, wherein said at least one detection value includes any one or more of the following detection values for said particles:

mass concentration;

mass flow rate;

numerical concentration;

volume concentration;

class concentration;

or particle size.

6. A detection means as claimed in claim 1, wherein said detector is a triboelectric detector or an optical dynamic opacity detector.

7. A detection means as claimed in claim 1, wherein said body is substantially symmetrical about a plane which lies parallel to the direction of flow of said gas stream.

8. An emissions monitoring system for detecting particles entrained in a gas stream comprising:

a detector adapted to be placed within said gas stream and to generate a detection signal as said particles entrained in said gas stream impinge on or pass over said detector;

a measuring means;

a signal processing means adapted to be coupled to said measuring means and to said detector to form a signal path between said detector and said signal processing means;

validation signal generating means capable of producing a validation signal to be transmitted to said signal processing means;

wherein said signal processing means combines said detection signal generated by said detection means with said validation signal produced by said validation signal generating means to produce a combined signal;

wherein said signal processing means filters said combined signal to produce a processed detector signal and a processed validation signal;

wherein said measuring means uses said processed detector signal to detect particles entrained in said gas stream; and

wherein said measuring means compares said processed validation signal with a predetermined control signal to detect faults in said signal path.

9. A detection means as claimed in claim 8, wherein said signal processing means passes detection signals within a predefined frequency pass band to said measuring means.

10. A method of detecting particles entrained in a gas stream using a detector means, a signal processing means and a measuring means said method being substantially independent of the velocity of said particles and including the steps of:

(a) placing said detector means in said gas stream such that particles in said gas stream cause said detector means to produce a detection signal;

(b) coupling said detector means to said signal processor means, said signal processor means adapted transmit signals within a predefined frequency pass band to reach said measuring means, said signal processing means adapted to generate a frequency response for signals within said predefined frequency pass band, whereby the gain of said signal processing means is inversely proportional to said frequency; and

(c) coupling said signal processing means to said measuring means to allow measurement of a processed detector signal.

11. A method of detecting particles entrained in a gas stream using a detection means, signal processing means and measuring means, said method being substantially independent of the velocity of said particles and including the steps of:

(a) placing said detector means in said gas stream such that particles entrained in said gas stream cause said detector means to produce a detector signal, said detector signal having a low frequency band centred around a predetermined first frequency and a high frequency band centred around a predetermined second frequency;

(c) coupling said detector means to said signal processing means;

(d) coupling said signal processing means to a measuring means, wherein said measuring means compares the signal in the high frequency band to the signal in the low frequency band to determine an estimated velocity of said particles based on a predetermined relationship;

12. A method as claimed in claim 11, further including the step of

(e) using said estimated velocity to remove the velocity dependence of the detection of particles entrained in said gas stream.

13. A method of detecting faults in a probe used in a system for detecting particles entrained in a gas stream, said system including a signal processing means and measuring means, said probe including at least one electrode adapted to produce a current when said particles entrained in said gas stream impinge on or pass over said electrode, said method including the steps of:

(a) measuring the admittance of the probe;

(b) using either the real or imaginary part, or real and imaginary parts, of the admittance of said probe to detect a fault in the probe.

14. A method as claimed in claim 13, wherein the step of measuring the admittance of the probe further includes the steps of:

(c) applying an admittance measuring signal of a predetermined frequency to said probe through a high impedance circuit;

(d) measuring the vectorial signal at the probe as a result of the application of the admittance measuring signal;

(e) calculating the admittance of the probe based on said vectorial signal.

15. A method as claimed in claim 13 wherein said real component of said admittance is used to detect a change in conductance of an insulator supporting said probe.

16. A method as claimed in claim 13 wherein said imaginary component of said admittance is used to detect a change in the capacitance or susceptance of said probe.

17. A method as claimed in claims 13 wherein said admittance measurement is performed either alternately with particle detection or simultaneously with particle detection.

18. A method as claimed in claims 13 wherein said signal processing means includes a means for providing a high input admittance for signals within a measurement signal pass band and a low input admittance for signals at the frequency of the admittance measuring signal.

19. A method as claimed in claim 18 wherein the means for providing a high input admittance for signals within a measurement signal pass band and a low input admittance for signals at the frequency of the admittance measuring signal includes an inverting integrator within a frequency independent shunt feedback loop.

20. A method of detecting particles moving in a gas stream, said method comprising the steps of:

(a) introducing a detector means into said gas stream, said detector means including a body having an upstream face and a downstream face, said detector further including a detector associated with said downstream face;

(b) deflecting said gas stream moving around said body by said body being shaped and configured to thereby cause generally turbulent gas flow of said gas stream adjacent said downstream detection face;

(c) generating a detection signal using said detector as said particles entrained in said turbulent gas flow impinge on or pass over said downstream face.

21. A method as claimed in claim 20, wherein said method further includes the step of:

(d) calculating at least one detection value of said particles in said gas stream from said detection signal generated in step (c).

22. A method of detecting particles moving in a gas flow including the steps of

a) locating a particle detection means in said gas flow to measure particles in a portion of said gas flow to be sampled;

b) separating out of said portion of said gas flow to be sampled, via a separation means, a substantial number of particles whose presence is not to be detected while causing same to remain in said gas flow;

c) causing said portion of said gas flow to be sampled to cooperate with said particle detection means to enable particles, which remain in said portion of said gas flow to be sampled, to be detected by said particle detection means.