Acoustic pyrometer

• US 6,726,358 B2
• Filed: 12/14/2001
• Issued: 04/27/2004
• Est. Priority Date: 07/05/1997
• Status: Expired due to Term

• Current Assignee: Valmet Automation Oy (Valmet Oyj)
• Original Assignee: Combustion Specialists Incorporated
• Inventors: Kychakoff, George, Hogle, Richard E., Draxton, Dean E., Droppo, James G. III
• Primary Examiner(s): Gutierrez, Diego
• Assistant Examiner(s): Guadalupe, Yaritza
• Application Number:
  US10/020,106
• Publication Number:
  US 20020131472A1
• Time in Patent Office: 865 Days
• Field of Search: 374/115, 374/117, 374/118, 374/119, 702/130, 736/62, 736/71
• US Class Current: 374/115
• CPC Class Codes: G01K 11/24 of the velocity of propagation of sound

Abstract

An acoustic pyrometer measures the average gas temperature across a wide space of known distance, especially turbulent, high temperature gas loaded with caustic particulates. It includes an acoustic signal generator that generates a high amplitude acoustic signal with a short rise time and a detector positioned adjacent the signal generator that detects the onset of the acoustic signal in the signal generator and generates a first electrical signal corresponding in time to the onset of the acoustic signal in the signal generator. A receiver, positioned across the space from the signal generator, receives acoustic signals from the space and generates electrical signals corresponding to amplitude and frequency of the acoustic signals received in the receiver. A signal processor processes the electrical signals from the receiver to distinguish the onset of the acoustic signal from background noise in the space as detected in the receiver, and processes the electrical signals from the receiver to produce a distinct differentiation between background noise and the onset of the acoustic signal in the receiver. The signal processor then compares the time of the onset of the acoustic signal in the receiver with the onset of the acoustic signal in the signal generator to determine the transit time of the acoustic signal to traverse the space, and also calculates the temperature of the gas in the space based on the transit time.

Claims

1. A method of measuring the average gas temperature along a line through an open space, comprising:

generating an acoustic signal with a high amplitude sudden onset;

detecting said onset of said acoustic signal and generating a first electrical signal corresponding in time to said onset of said acoustic signal;

propagating said acoustic signal across a space of known distance to a receiver;

generating electrical signals in said receiver corresponding to amplitude and frequency of said acoustic signals received in said receiver;

processing said electrical signals from said receiver to produce a distinct differentiation between background noise and said acoustic signal in said receiver;

comparing the time of onset of said acoustic signal in said receiver with said onset of said acoustic signal in said signal generator to determine the transit time for said acoustic signal to traverse said space; and

calculating said temperature of said gas in said space based on said transit time;

wherein said acoustic signal generating step includes;

closing an exit throat in an enclosed space with a slidable plug slidably sealed in said throat;

charging said enclosed space with pressurized gas to create a pressurized gas volume;

accelerating said plug in said throat and then withdrawing said plug at high speed from said throat to effect complete opening of said throat in a short time to release said pressurized gas volume through said throat in a burst to produce said acoustic signal with a fast rise time from zero amplitude to an amplitude greater than 170 db in a less than 5 ms.

2. A method of measuring the average gas temperature along a line through an open space, comprising:

generating an acoustic signal with a high amplitude sudden onset;

detecting said onset of said acoustic signal and generating a first electrical signal corresponding in time to said onset of said acoustic signal;

propagating said acoustic signal across a space of known distance to a receiver;

generating electrical signals in said receiver corresponding to amplitude and frequency of said acoustic signals received in said receiver;

processing said electrical signals from said receiver to produce a distinct differentiation between background noise and said acoustic signal in said receiver, including digitally pre-filtering said acoustic signals received in said receiver to facilitate differentiation between background noise in said open space and said acoustic signal so as to locate the beginning of said acoustic signal in said background noise;

comparing the time of onset of said acoustic signal in said receiver with said onset of said acoustic signal in said signal generator to determine the transit time for said acoustic signal to traverse said space; and

calculating said temperature of said gas in said space based on said transit time;

wherein said prefiltering includes;

a) measuring N consecutive samples of said signal received in said receiver;

b) predicting what an N+1^th signal will be from the previous N samples;

c) measuring said N+1^th sample to obtain an actual measured value of said N+1^th sample;

d) subtracting said predicted N+1^th signal from said actual measured N+1^th signal value; and

e) repeating steps a)-d) with each new sample taken to produce a small amplitude modified signal having more characteristics of said acoustic signal from said signal generator.

3. A method of measuring the average gas temperature along a tine through an open space, comprising:

generating an acoustic signal with a high amplitude sudden onset;

detecting said onset of said acoustic signal and generating a first electrical signal corresponding in time to said onset of said acoustic signal;

propagating said acoustic signal across a space of known distance to a receiver;

generating electrical signals in said receiver corresponding to amplitude and frequency of said acoustic signals received in said receiver;

processing said electrical signals from said receiver to produce a distinct differentiation between background noise and said acoustic signal in said receiver

comparing the time of onset of said acoustic signal in said receiver with said onset of said acoustic signal in said signal generator to determine the transit time for said acoustic signal to traverse said space;

calculating said temperature of said gas in said space based on said transit time;

wherein, said electrical signal processing includes;

a. forming a stochastic model having two or more states, each state behaving like a stationary random variable that produces uncorrelated white Gaussian noise, said model able to move from state to state as time progresses

b. said model having a first state representing said background noise of said filtered signal without said acoustic signal imposed, and a second state acting like said acoustic signal;

c. normalizing said filtered signal to zero-mean as part of said pre-filtering process,

d. estimating the statistical variance of the samples from said first state using signal samples known to contain only background noise with said acoustic signal absent, using samples that occur before generation of said acoustic signal by said acoustic signal generator;

e. estimating the statistical variance of samples from said second state from samples located directly around said sample with maximum amplitude in the filtered signal;

f. determining the mast probable time for the shift from said first state to said second state, and the most probable time for the arrival of said acoustic signal, by labeling each time index with a stale using said filtered signal from said receiver and said stochastic.

4. A method of measuring the average gas temperature along a line through an open space in a boiler, said boiler having a boiler nose with an interior wall defining an interior boundary of a hot interior chamber within said boiler nose, and said boiler having a “

penthouse”

space above a top tube wall of said boiler and below a top wall of said boiler, said method comprising;

generating an acoustic signal with a high amplitude sudden onset;

detecting said onset of said acoustic signal and generating a first electrical signal corresponding in time to said onset of said acoustic signal;

propagating said acoustic signal across a space of known distance to a receiver;

generating electrical signals in said receiver corresponding to amplitude and frequency of said acoustic signals received in said receiver;

processing said electrical signals from said receiver to produce a distinct differentiation between background noise and said acoustic signal in said receiver, said electrical signals processing including modifying said electrical signal in a digital prefilter to a modified signal having an increased ratio of amplitudes of said acoustic signal to said noise;

comparing the time of onset of said acoustic signal in said receiver with said onset of said acoustic signal in said signal generator to determine the transit time for said acoustic signal to traverse said space;

calculating said temperature of said gas in said space based on said transit time;

said acoustic signal is produced in a signal generator placed beyond said interior wall, outside said interior chamber in said boiler nose in said boiler and transmitted through a long output barrel extending through said interior chamber and through a tube wall of said boiler nose and opening into the interior of said boiler through said boiler nose tube wall;

said receiver is placed in the top end of a cable drop tube extending through said top tube wall, through said “

penthouse”

space and out through said top wall of said boiler;

whereby said signal generator is isolated from said hot interior chamber behind said boiler nose and said receiver is protected from excessive temperatures inside said “

penthouse”

while producing valuable temperature data about an entrance plane into pendant tube banks inside said boiler.