WO2016067049A1 - Methods and apparatus relating to particulate monitors - Google Patents

Methods and apparatus relating to particulate monitors Download PDF

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Publication number
WO2016067049A1
WO2016067049A1 PCT/GB2015/053282 GB2015053282W WO2016067049A1 WO 2016067049 A1 WO2016067049 A1 WO 2016067049A1 GB 2015053282 W GB2015053282 W GB 2015053282W WO 2016067049 A1 WO2016067049 A1 WO 2016067049A1
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WO
WIPO (PCT)
Prior art keywords
gas
sample
sample flow
walls
curtain
Prior art date
Application number
PCT/GB2015/053282
Other languages
French (fr)
Inventor
Roger Bradley Millington
Ed MCCALL
Peter Barton
Original Assignee
Pcme Limited
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Publication date
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Publication of WO2016067049A1 publication Critical patent/WO2016067049A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G01N21/53—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke
    • G01N21/532—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke with measurement of scattering and transmission
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2202—Devices for withdrawing samples in the gaseous state involving separation of sample components during sampling
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2247—Sampling from a flowing stream of gas
    • G01N1/2258—Sampling from a flowing stream of gas in a stack or chimney
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0205—Investigating particle size or size distribution by optical means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/2247—Sampling from a flowing stream of gas
    • G01N1/2258—Sampling from a flowing stream of gas in a stack or chimney
    • G01N2001/2261—Sampling from a flowing stream of gas in a stack or chimney preventing condensation (heating lines)
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path
    • G01N2021/151—Gas blown
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path
    • G01N2021/158—Eliminating condensation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G01N21/53—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke
    • G01N21/534—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke by measuring transmission alone, i.e. determining opacity
    • G01N2021/536—Measurement device mounted at stack
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G01N21/53—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke

Definitions

  • the present invention concerns a particulate monitor and method of monitoring particulates, for example dust, using scattering of light. More particularly, but not exclusively, this invention concerns the measurement of particulate matter in a sample of gas extracted from a stack or flue which contains condensable matter.
  • Emissions from stacks and other flues are monitored for environmental and other reasons. Typical measurements include measurement of the quantity of particulate matter. Particulate matter is potentially polluting and many countries have strict controls over the levels of
  • One approach to the detection and measurement of particulates in a flue is to extract continuously a sample of the gas flowing in the flue and then pass the sample into a measurement instrument, usually outside the flue.
  • One approach to measurement of particulate levels in the sample gas in the instrument is to shine laser or other high- intensity light into the sample, so that the light is scattered from the particulates, and measure a variation of the intensity of the scattered light.
  • an example prior-art extractive sampling system sucks a gas stream sample out of a stack and directs it through a remotely situated laser beam where any solid particulate or liquid drops will scatter light.
  • the region of the laser beam where scattering occurs is called the measurement region because the intensity of scattered light is interpreted as a measurement of particulate matter.
  • Measuring instruments based on the detection of scattered light can be used to detect solid particulates, but they are sensitive to other materials that scatter.
  • such measuring instruments are highly sensitive to the presence of liquid droplets in the sample volume.
  • Such droplets may result from condensation of a vapour - such as, for example, water or sulphuric acid - and give a false measurement of particle density.
  • the distribution of scattered light can be affected by modified or additional particles or droplets, or changes in particle or droplet size.
  • a false measurement can result from condensation or precipitation of other material into crystal or amorphous solid particles.
  • Such materials or others like them are present in a variety of industrial stacks, with the composition of the gas mixture depending on the purpose of the plant feeding into the stack, the process and any chemical additives used in the process; for example, ammonium compounds will be present from mitigation processes such as SCR (selective catalytic reduction) involving injection of ammonia upstream of the extraction point.
  • SCR selective catalytic reduction
  • Two different monitoring scenarios can be identified.
  • One is monitoring of the particulates inside the flue; the other is monitoring of the particulates as they are emitted from the flue.
  • the aim is for the measured sample to be identical in its make-up to the gases in the relevant monitoring region.
  • the gases being sampled will include condensation and precipitation and so create, in th
  • the present invention provides a method of monitoring particulates flowing in a stack or flue, the method
  • an apparatus for monitoring particulates flowing in a stack or flue comprising:
  • sample chamber for receiving a sample flow from the gas flowing in the flue or stack, the sample chamber being at least partly defined by walls;
  • a source of gas arranged to form a curtain of gas between the sample flow and the walls of the sample chamber to thermally isolate the sample flow from the walls .
  • Figure 1 is cross-sectional view of a sample chamber, according to an example embodiment of the invention, showing elements of the sample chamber;
  • Fig. 2 is the view of Fig. 1, showing gas flows in the sample chamber.
  • Example embodiments of the invention aim to mimic, as closely as possible, at the measurement region where light scatter occurs, the relative concentrations of particulate species present inside the stack at the sampling nozzle or the relative concentrations of particulate species emitted into the atmosphere from the top of the stack.
  • Extractive sampling can introduce errors in the measurement if particle size is changed or new condensable particulate are created in the measurement region. Such errors have been found to be caused by phenomena such as temperature, mixing with an air purge protecting the optics of the apparatus, or physical initiation of condensation in and around the measurement region. Control of those phenomena does two things: it minimises their effect and it minimises the variation in their effect.
  • the first aspect of the invention provides a method of monitoring particulates flowing in a stack or flue, the method comprising:
  • the gas curtain is a purge that acts as a thermal barrier between the sample flow and the walls.
  • the gas curtain does not mix with the sample flow until the gas curtain and sample flow have passed a measurement region.
  • gas curtain is annular. It may be that the gas curtain is concentric with the sample flow in the sample chamber.
  • the gas forming the gas curtain is air.
  • the temperature or flow rate of the gas curtain is adjusted to prevent condensation of material in the sample flow.
  • the gas curtain is heated.
  • the heated air curtain may be at the same temperature as, or a higher temperature than, the sample flow. Heating the curtain helps to prevent local cooling adjacent to the sample flow, for example by preventing radiation loss and consequential cooling of the sample flow.
  • the gas curtain has a speed that is the same as the speed of the sample flow. Matching the speed of the gas curtain to the speed of the sample flow can help prevent shear-induced turbulence. It may be that the speed of the gas curtain is
  • the method includes the step of selecting the size and shape of the sample chamber to control the speed of the gas curtain.
  • the temperature or flow rate of the gas curtain is adjusted to deliberately condense material known to be present in condensed form in the flow in the stack or flue. It may be that the deliberately condensed material is material which would condense at the outlet of the stack or flue to the atmosphere.
  • Turbulence can cause condensation and particle growth.
  • the sample chamber has no corners that cause vortices in the sample flow. Vortices are a potential source of condensation.
  • the light is from a laser.
  • the light is directed through the sample flow in a direction orthogonal to the direction of the sample flow.
  • An air purge may be provided to protect the optical components of the system.
  • the air purge may be directed, for example by the shape of optical apertures, so that it does not mix with the sample flow within the measurement region.
  • the optical apertures and/or the air curtain guides may be shaped to ensure that the air purge is swept away from the measurement region.
  • the flow rates of the gas curtain and the air purge may be chosen to ensure that the air purge is swept away from the measurement region.
  • Flow guides in and around the measurement region may be shaped to minimise or at least reduce turbulence or vortices (which may cause condensation or particle growth by local cooling) .
  • Sample flow channels may be of a finish which minimises or at least reduces surface vortices, which may cause condensation or particle growth by local cooling.
  • a second stream of gas (that is, additional to the gas curtain, the first stream of gas) is provided along the direction of the light. It may be that the second stream of gas is around and co-axial with the light. It may be that the second stream of gas flows transversely relative to the curtain of gas between the sample flow and the walls of the sample chamber. It may be that the second stream of gas is entrained by the curtain of gas flowing between the sample flow and the walls of the sample chamber. By entraining it in the curtain of gas between the sample flow and the walls of the sample chamber, the second stream of gas may be prevented from reaching a sample region within the sample chamber, the sample region being where light scattering occurs. It may be that the second stream of gas is at a different, for example cooler, temperature than the curtain of gas between the sample flow and the walls of the sample chamber. It may be that the temperature of the second stream of gas need not be
  • the conical conduit may have an axis that is for example on or parallel to the axis of the light.
  • the conical conduit may have a wide end that is further from the sample flow and a narrow end that is closer to the sample flow.
  • the conical conduit may be a cone, or a part of a cone, having an apex angle small enough to prevent unwanted scatter of stray light.
  • the conical conduit may be a cone, or a part of a cone (e.g.
  • a frustocone having an apex angle large enough to accelerate the second curtain of gas so as to keep walls of the conduit free or substantially free from condensate or other particulate accumulation.
  • the gas flowing in the flue or stack includes water or acid.
  • the second aspect of the invention provides apparatus for monitoring particulates flowing in a stack or flue, comprising :
  • sample chamber for receiving a sample flow from the gas flowing in the flue or stack, the sample chamber being at least partly defined by walls;
  • An example sample chamber 10 (Fig. 1) includes a tube 20 through which flows a sample gas 30 extracted from the flow to be measured.
  • the chamber 10 includes an inlet 40 and an outlet 50, which open into opposite sides of the tube 20, respectively.
  • a laser source 60 directs a laser beam 70 through the inlet 40, into the tube 20, through the sample flow 30, where it is scattered to form scattered light 80, which passes out of the outlet 50 to the detector 90.
  • the passage of the laser beam 70 through the flow of sample gas 30 defines a sample measurement region 100.
  • the sample chamber also includes an annular cavity 110 that surrounds the tube 20 above the inlet 40 and the outlet 50.
  • the annular cavity 110 is in fluid (Fig. 2)
  • a temperature-controlled air curtain 120 passes through the annular cavity 110 into the tube 20 via the annular aperture 170.
  • the air curtain 120 acts as a thermal barrier to prevent unwanted condensation in the incoming flow of sample gas 30.
  • the geometry of the annular aperture 170 and the shape of its annular edge are chosen to minimise the formation of vortices in the flow.
  • the resultant annular air curtain 120 does not mix in the sample measurement region with the sample gas 30 in the tube 20.
  • a second stream of gas in the form of a transverse gas purge 130a passes into the inlet 40, and there is a
  • the inlet 40 has a cylindrical portion 42 closer to the interior of the tube 20 and a frustoconical portion 47 further from the interior of the tube 20.
  • the truncated cone of the frustoconical portion 47 has its base further from the interior tube 20, i.e. the internal diameter of the frustoconical portion 47 decreases towards the cylindrical portion 42. That decrease in diameter speeds up the transverse gas purge 130a towards the annular edge of the frustoconical portion 47, which helps to prevent ingress of flowing material onto optical components and to keep the edge of the aperture of the frustocone clean.
  • the cylindrical portion 42 has a diameter larger than that of the frustoconical portion 47.
  • the transverse gas purge 130a is slowed down by that increase in diameter, and entrained in the air curtain 120.
  • the outlet 50 has a cylindrical portion 52 closer to the interior of the tube 20 and a frustoconical portion 57 further from the interior of the tube 20.
  • the truncated cone of the frustoconical portion 57 has its base further from the interior tube 20, i.e. the internal diameter of the frustoconical portion 57 decreases towards the cylindrical portion 52. That decrease in diameter speeds up the transverse gas purge 130b towards the annular edge of the frustoconical portion 57, which helps to prevent ingress of flowing material onto optical components and to keep the edge of the aperture of the frustocone clean.
  • the frustoconical portion 57 of the outlet 50 is wider (larger diameters) than the frustoconical portion 47 of the inlet 40, because the outlet 50 has to be large enough to accommodate the optical path of the scattered light 80.
  • the transverse gas purges 130a, 130b are entrained by the annular gas curtain away from the sample measurement region 100, at 140a, b (downstream from the sample
  • the sample flow 30, the air curtain 120 and the transverse purge flows 130a, 130b combine in a downstream region 150.
  • the temperature and flow rate of the air curtain 120 is adjusted to prevent condensation of material in the sample flow 20.
  • the constituents of the sample measurement region 100 are controlled by deliberately producing conditions that have the same effects as emission conditions.
  • temperature and flow rate of the air curtain 120 is adjusted to deliberately condense material which would condense at the outlet of the stack or flue to the atmosphere.
  • Provision of an air curtain 120 which does not mix with the sample gas flow 30 until it has passed the measurement region and which is elevated in temperature from ambient prevents the temperature of the sample flow 30 dropping below the dew point for any condensable material present in it.
  • the air curtain 120 acts to thermally insulate the measurement region 100 from the internal walls of the instrument.
  • the temperature and flow rate of the air curtain 30 can be adjusted to deliberately and selectively condense material entering the measurement region 100.
  • the second air purge 200 is provided to protect the optical components of the system and is directed by shaped optical apertures to avoid mixing within the sample
  • both the optical apertures and the air curtain guides are selected so that the second air purge 200 is swept away from the measurement region 100 and no condensation or particle growth occurs in the measurement region 100.
  • the shapes of the edges of all flow guides in and around the measurement region 100 are selected to minimise turbulence or vortices which may cause condensation or particle growth by local cooling.
  • the surfaces of the flow channels are of a finish which minimises surface vortices which may cause condensation or particle growth by local cooling .

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Abstract

In a method of monitoring particulates flowing in a stack or flue, a sample flow (110) from the gas flowing in the stack or flue is provided in a sample chamber (10), the sample chamber (10) being at least partly defined by walls (30, 40, 50, 60). Light (130) is directed through the sample flow (110) in a direction at a non-zero angle to the direction of the sample flow (110). Scattering of the light (130) from particles in the sample flow (110) is detected. A curtain of gas (160) is provided between the sample flow (110) and the walls (30, 40, 50, 60) of the sample chamber (10). The curtain of gas (160) thermally isolates the sample flow (110) from the walls (30, 40, 50, 60), thereby controlling condensation of material in the sample flow (110).

Description

Methods and apparatus relating to particulate monitors
Field of the Invention
The present invention concerns a particulate monitor and method of monitoring particulates, for example dust, using scattering of light. More particularly, but not exclusively, this invention concerns the measurement of particulate matter in a sample of gas extracted from a stack or flue which contains condensable matter.
Background of the Invention
Emissions from stacks and other flues are monitored for environmental and other reasons. Typical measurements include measurement of the quantity of particulate matter. Particulate matter is potentially polluting and many countries have strict controls over the levels of
particulate emission that are permitted.
One approach to the detection and measurement of particulates in a flue is to extract continuously a sample of the gas flowing in the flue and then pass the sample into a measurement instrument, usually outside the flue. One approach to measurement of particulate levels in the sample gas in the instrument is to shine laser or other high- intensity light into the sample, so that the light is scattered from the particulates, and measure a variation of the intensity of the scattered light. Thus, an example prior-art extractive sampling system sucks a gas stream sample out of a stack and directs it through a remotely situated laser beam where any solid particulate or liquid drops will scatter light. The region of the laser beam where scattering occurs is called the measurement region because the intensity of scattered light is interpreted as a measurement of particulate matter.
Measuring instruments based on the detection of scattered light can be used to detect solid particulates, but they are sensitive to other materials that scatter. For example, such measuring instruments are highly sensitive to the presence of liquid droplets in the sample volume. Such droplets may result from condensation of a vapour - such as, for example, water or sulphuric acid - and give a false measurement of particle density. The distribution of scattered light can be affected by modified or additional particles or droplets, or changes in particle or droplet size. Similarly, a false measurement can result from condensation or precipitation of other material into crystal or amorphous solid particles. Such materials or others like them are present in a variety of industrial stacks, with the composition of the gas mixture depending on the purpose of the plant feeding into the stack, the process and any chemical additives used in the process; for example, ammonium compounds will be present from mitigation processes such as SCR (selective catalytic reduction) involving injection of ammonia upstream of the extraction point.
Processes in which the gases are saturated or near-saturates are the most vulnerable to condensation and precipitation.
Two different monitoring scenarios can be identified. One is monitoring of the particulates inside the flue; the other is monitoring of the particulates as they are emitted from the flue. In each case, the aim is for the measured sample to be identical in its make-up to the gases in the relevant monitoring region. In the case of monitoring particles as they are emitted from the flue, the gases being sampled will include condensation and precipitation and so create, in th
tal condition
o cause those
the sample r
that scatter
tion seeks to
ternatively o
s to provide
method relating to measurement of particulates in a gas sample so as to provide a result as close as possible to the particulate composition of the stack gas itself.
Summary of the Invention
The present invention provides a method of monitoring particulates flowing in a stack or flue, the method
comprising :
(a) providing in a sample chamber a sample flow from the gas flowing in the flue or stack, the sample chamber being at least partly defined by walls;
(b) directing light through the sample flow in a
direction at a non-zero angle to the direction of the sample flow and detecting scattering of the light from particles in the sample flow; and (c) providing a curtain of gas between the sample flow and the walls of the sample chamber to thermally isolate the sample flow from the walls.
According to a second aspect of the invention there is also provided an apparatus for monitoring particulates flowing in a stack or flue, comprising:
(a) a sample chamber for receiving a sample flow from the gas flowing in the flue or stack, the sample chamber being at least partly defined by walls;
(b) a light source arranged to direct light through the sample flow in a direction at a non-zero angle to the direction of the sample flow;
(c) a detector arranged to detect scattering of the
light from particles in the sample flow; and
(d) a source of gas arranged to form a curtain of gas between the sample flow and the walls of the sample chamber to thermally isolate the sample flow from the walls .
It will of course be appreciated that features
described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the apparatus of the invention may incorporate any of the features described with reference to the method of the invention and vice versa.
Description of the Drawings
Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 is cross-sectional view of a sample chamber, according to an example embodiment of the invention, showing elements of the sample chamber;
Fig. 2 is the view of Fig. 1, showing gas flows in the sample chamber.
Detailed Description
Example embodiments of the invention aim to mimic, as closely as possible, at the measurement region where light scatter occurs, the relative concentrations of particulate species present inside the stack at the sampling nozzle or the relative concentrations of particulate species emitted into the atmosphere from the top of the stack. Extractive sampling can introduce errors in the measurement if particle size is changed or new condensable particulate are created in the measurement region. Such errors have been found to be caused by phenomena such as temperature, mixing with an air purge protecting the optics of the apparatus, or physical initiation of condensation in and around the measurement region. Control of those phenomena does two things: it minimises their effect and it minimises the variation in their effect.
The first aspect of the invention provides a method of monitoring particulates flowing in a stack or flue, the method comprising:
(d) providing in a sample chamber a sample flow from the gas flowing in the flue or stack, the sample chamber being at least partly defined by walls; (e) directing light through the sample flow in a
direction at a non-zero angle to the direction of the sample flow and detecting scattering of the light from particles in the sample flow; and
(f) providing a curtain of gas between the sample flow and the walls of the sample chamber to thermally isolate the sample flow from the walls.
Thus, the gas curtain is a purge that acts as a thermal barrier between the sample flow and the walls.
It may be that the gas curtain does not mix with the sample flow until the gas curtain and sample flow have passed a measurement region.
It may be that the gas curtain is annular. It may be that the gas curtain is concentric with the sample flow in the sample chamber.
It may be that the gas forming the gas curtain is air.
It may be that the temperature or flow rate of the gas curtain is adjusted to prevent condensation of material in the sample flow.
It may be that the gas curtain is heated. The heated air curtain may be at the same temperature as, or a higher temperature than, the sample flow. Heating the curtain helps to prevent local cooling adjacent to the sample flow, for example by preventing radiation loss and consequential cooling of the sample flow.
It may be that the gas curtain has a speed that is the same as the speed of the sample flow. Matching the speed of the gas curtain to the speed of the sample flow can help prevent shear-induced turbulence. It may be that the speed of the gas curtain is
controlled by an external flow control valve. Alternatively, it may be that the method includes the step of selecting the size and shape of the sample chamber to control the speed of the gas curtain.
It may be that the temperature or flow rate of the gas curtain is adjusted to deliberately condense material known to be present in condensed form in the flow in the stack or flue. It may be that the deliberately condensed material is material which would condense at the outlet of the stack or flue to the atmosphere.
It may be that there is substantially no turbulence inside the sample chamber. Turbulence can cause condensation and particle growth. For example, it may be that the sample chamber has no corners that cause vortices in the sample flow. Vortices are a potential source of condensation.
It may be that the light is from a laser.
It may be that the light is directed through the sample flow in a direction orthogonal to the direction of the sample flow.
An air purge may be provided to protect the optical components of the system. The air purge may be directed, for example by the shape of optical apertures, so that it does not mix with the sample flow within the measurement region. The optical apertures and/or the air curtain guides may be shaped to ensure that the air purge is swept away from the measurement region. The flow rates of the gas curtain and the air purge may be chosen to ensure that the air purge is swept away from the measurement region. Flow guides in and around the measurement region may be shaped to minimise or at least reduce turbulence or vortices (which may cause condensation or particle growth by local cooling) . Sample flow channels may be of a finish which minimises or at least reduces surface vortices, which may cause condensation or particle growth by local cooling.
Thus, it may be that a second stream of gas (that is, additional to the gas curtain, the first stream of gas) is provided along the direction of the light. It may be that the second stream of gas is around and co-axial with the light. It may be that the second stream of gas flows transversely relative to the curtain of gas between the sample flow and the walls of the sample chamber. It may be that the second stream of gas is entrained by the curtain of gas flowing between the sample flow and the walls of the sample chamber. By entraining it in the curtain of gas between the sample flow and the walls of the sample chamber, the second stream of gas may be prevented from reaching a sample region within the sample chamber, the sample region being where light scattering occurs. It may be that the second stream of gas is at a different, for example cooler, temperature than the curtain of gas between the sample flow and the walls of the sample chamber. It may be that the temperature of the second stream of gas need not be
controlled, because any condensation forming in or ad acent to it is not in the sample region where light scatter occurs .
It may be that the second stream of gas is guided through the curtain of gas between the sample flow and the walls of the sample chamber by a conical conduit. The conical conduit may have an axis that is for example on or parallel to the axis of the light. The conical conduit may have a wide end that is further from the sample flow and a narrow end that is closer to the sample flow. The conical conduit may be a cone, or a part of a cone, having an apex angle small enough to prevent unwanted scatter of stray light. The conical conduit may be a cone, or a part of a cone (e.g. a frustocone) , having an apex angle large enough to accelerate the second curtain of gas so as to keep walls of the conduit free or substantially free from condensate or other particulate accumulation. There may be at least two such conical conduits, forming at least one inlet and at least one outlet for the light.
It may be that the gas flowing in the flue or stack includes water or acid.
The second aspect of the invention provides apparatus for monitoring particulates flowing in a stack or flue, comprising :
(a) a sample chamber for receiving a sample flow from the gas flowing in the flue or stack, the sample chamber being at least partly defined by walls;
(b) a light source arranged to direct light through the sample flow in a direction at a non-zero angle to the direction of the sample flow;
(c) a detector arranged to detect scattering of the
light from particles in the sample flow; and
(d) a source of gas arranged to form a curtain of gas between the sample flow and the walls of the sample chamber to thermally isolate the sample flow from the walls . If an extracted gas stream is guided by a conduit with cold walls, there is likely to be nucleation of condensed material. Where the walls are also rough, nucleation is exacerbated, stimulating particle growth. Local condensation will also occur within vortices, due to the effects of temperature reduction dominating the effects of vapour pressure reduction, under adiabatic conditions. The effect is similar to that seen in vortices from the trailing edge of an aircraft wing, where moisture condenses in the vortex, more so when the air is more humid. Celani et al, Europhys . Lett., 70 (6), pp. 775-781 (2005) describe how turbulent flow enhances droplet growth in saturated gases.
An example sample chamber 10 (Fig. 1) includes a tube 20 through which flows a sample gas 30 extracted from the flow to be measured. The chamber 10 includes an inlet 40 and an outlet 50, which open into opposite sides of the tube 20, respectively. A laser source 60 directs a laser beam 70 through the inlet 40, into the tube 20, through the sample flow 30, where it is scattered to form scattered light 80, which passes out of the outlet 50 to the detector 90. The passage of the laser beam 70 through the flow of sample gas 30 defines a sample measurement region 100.
The sample chamber also includes an annular cavity 110 that surrounds the tube 20 above the inlet 40 and the outlet 50. The annular cavity 110 is in fluid (Fig. 2)
communication with the tube 20 via an annular aperture 170. In use, a temperature-controlled air curtain 120 passes through the annular cavity 110 into the tube 20 via the annular aperture 170. The air curtain 120 acts as a thermal barrier to prevent unwanted condensation in the incoming flow of sample gas 30.
The geometry of the annular aperture 170 and the shape of its annular edge are chosen to minimise the formation of vortices in the flow.
The resultant annular air curtain 120 does not mix in the sample measurement region with the sample gas 30 in the tube 20.
A second stream of gas in the form of a transverse gas purge 130a passes into the inlet 40, and there is a
corresponding transverse gas purge 130b which passes into the outlet 50.
The inlet 40 has a cylindrical portion 42 closer to the interior of the tube 20 and a frustoconical portion 47 further from the interior of the tube 20. The truncated cone of the frustoconical portion 47 has its base further from the interior tube 20, i.e. the internal diameter of the frustoconical portion 47 decreases towards the cylindrical portion 42. That decrease in diameter speeds up the transverse gas purge 130a towards the annular edge of the frustoconical portion 47, which helps to prevent ingress of flowing material onto optical components and to keep the edge of the aperture of the frustocone clean.
The cylindrical portion 42 has a diameter larger than that of the frustoconical portion 47. The transverse gas purge 130a is slowed down by that increase in diameter, and entrained in the air curtain 120.
The outlet 50 has a cylindrical portion 52 closer to the interior of the tube 20 and a frustoconical portion 57 further from the interior of the tube 20. The truncated cone of the frustoconical portion 57 has its base further from the interior tube 20, i.e. the internal diameter of the frustoconical portion 57 decreases towards the cylindrical portion 52. That decrease in diameter speeds up the transverse gas purge 130b towards the annular edge of the frustoconical portion 57, which helps to prevent ingress of flowing material onto optical components and to keep the edge of the aperture of the frustocone clean.
The frustoconical portion 57 of the outlet 50 is wider (larger diameters) than the frustoconical portion 47 of the inlet 40, because the outlet 50 has to be large enough to accommodate the optical path of the scattered light 80.
The transverse gas purges 130a, 130b are entrained by the annular gas curtain away from the sample measurement region 100, at 140a, b (downstream from the sample
measurement region 100, in terms of the direction of the sample flow 30) .
The sample flow 30, the air curtain 120 and the transverse purge flows 130a, 130b combine in a downstream region 150.
The temperature and flow rate of the air curtain 120 is adjusted to prevent condensation of material in the sample flow 20.
In the case where stack-emission conditions, as distinct from in-stack conditions, are to be simulated, the constituents of the sample measurement region 100 are controlled by deliberately producing conditions that have the same effects as emission conditions. Thus, the
temperature and flow rate of the air curtain 120 is adjusted to deliberately condense material which would condense at the outlet of the stack or flue to the atmosphere.
Provision of an air curtain 120 which does not mix with the sample gas flow 30 until it has passed the measurement region and which is elevated in temperature from ambient prevents the temperature of the sample flow 30 dropping below the dew point for any condensable material present in it. The air curtain 120 acts to thermally insulate the measurement region 100 from the internal walls of the instrument.
Alternatively, the temperature and flow rate of the air curtain 30 can be adjusted to deliberately and selectively condense material entering the measurement region 100.
The second air purge 200 is provided to protect the optical components of the system and is directed by shaped optical apertures to avoid mixing within the sample
measurement region 100. The shape of both the optical apertures and the air curtain guides, along with both respective purge rates, are selected so that the second air purge 200 is swept away from the measurement region 100 and no condensation or particle growth occurs in the measurement region 100.
The shapes of the edges of all flow guides in and around the measurement region 100 are selected to minimise turbulence or vortices which may cause condensation or particle growth by local cooling. The surfaces of the flow channels are of a finish which minimises surface vortices which may cause condensation or particle growth by local cooling . Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.
Where in the foregoing description, integers or elements are mentioned which have known, obvious or
foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other
embodiments.

Claims

Claims
1. A method of monitoring particulates flowing in a stack or flue, the method comprising:
(a) providing in a sample chamber a sample flow from the gas flowing in the flue or stack, the sample chamber being at least partly defined by walls;
(b) directing light through the sample flow in a
direction at a non-zero angle to the direction of the sample flow and detecting scattering of the light from particles in the sample flow; and
(c) providing a curtain of gas between the sample flow and the walls of the sample chamber to thermally isolate the sample flow from the walls.
2. A method as claimed in claim 1, in which the gas curtain is annular and concentric with the sample flow in the sample chamber.
3. A method as claimed in claim 1 or claim 2, in which the gas forming the gas curtain is air.
4. A method as claimed in any preceding claim, in which the temperature or flow rate of the gas curtain is adjusted to prevent condensation of material in the sample flow.
5. A method as claimed in any preceding claim, in which the temperature or flow rate of the gas curtain is adjusted to deliberately condense material known to be present in condensed form in the flow in the stack or flue.
6. A method as claimed in claim 5, in which the
deliberately condensed material is material which would condense at the outlet of the stack or flue to the
atmosphere .
7. A method as claimed m any preceding claim, m which the light is directed through the sample flow in a direction orthogonal to the direction of the sample flow.
8. A method as claimed in any preceding claim, in which a second stream of gas is provided along the direction of the light.
9. A method as claimed in claim 8, in which the second stream of gas flows transversely relative to the curtain of gas between the sample flow and the walls of the sample chamber .
10. A method as claimed in claim 9, in which the second stream of gas is entrained by the curtain of gas flowing between the sample flow and the walls of the sample chamber.
11. A method as claimed in any of claims 8 to 10, in which the second stream of gas is at a different temperature than the curtain of gas between the sample flow and the walls of the sample chamber.
12. A method as claimed in any of claims 8 to 11, in which the second stream of gas is guided through the curtain of gas between the sample flow and the walls of the sample chamber by a conical conduit.
13. A method as claimed in claim 12, in which the conical conduit is a cone, or a part of a cone, having an apex angle small enough to prevent unwanted scatter of stray light.
14. A method as claimed in claim 12 or claim 13, in which the conical conduit is a cone, or a part of a cone, having an apex angle large enough to accelerate the second stream of gas so as to keep walls of the conduit free or
substantially free from condensate or other particulate accumulation .
15. Apparatus for monitoring particulates flowing in a stack or flue, comprising:
(a) a sample chamber for receiving a sample flow from the gas flowing in the flue or stack, the sample chamber being at least partly defined by walls;
(b) a light source arranged to direct light through the sample flow in a direction at a non-zero angle to the direction of the sample flow;
(c) a detector arranged to detect scattering of the light from particles in the sample flow; and
(d) a source of gas arranged to form a curtain of gas between the sample flow and the walls of the sample chamber to thermally isolate the sample flow from the walls .
PCT/GB2015/053282 2014-10-31 2015-10-30 Methods and apparatus relating to particulate monitors WO2016067049A1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107677574A (en) * 2017-11-03 2018-02-09 济南微纳颗粒仪器股份有限公司 A kind of laser particle analyzer sample window
CN109187887A (en) * 2018-10-17 2019-01-11 信丰县包钢新利稀土有限责任公司 A kind of rare earth extraction polluted gas discharge detection device

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4746215A (en) * 1986-04-24 1988-05-24 Pacific Scientific Company Particle counter air inlet assembly
US4839529A (en) * 1986-08-19 1989-06-13 Impulsphysik Gmbh Arrangement for in situ determination of quantity of turbid matter aerosol and/or dust in fluid which flows through a space
US7173257B1 (en) * 2005-02-18 2007-02-06 Hach Ultra Analytics, Inc. Integrated assembly for delivery of air stream for optical analysis

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1316752A (en) * 1970-02-12 1973-05-16 Atomic Energy Authority Uk Apparatus for analysing suspended particles
JP2696561B2 (en) * 1989-06-01 1998-01-14 日立電子エンジニアリング株式会社 Elimination method of fluctuation noise of laser in particle detector
USH1027H (en) * 1991-06-25 1992-03-03 The United States Of America As Represented By The Secretary Of The Army Aerosol modulating nozzle
US20070097366A1 (en) * 2005-10-31 2007-05-03 General Electric Company Optical system and method for detecting particles
AT11938U3 (en) * 2011-03-15 2012-01-15 Avl List Gmbh LENS METER
GB2510854B (en) * 2013-02-15 2015-08-05 Univ Hertfordshire Higher Education Corp Improved apparatus and method for detection of asbestos fibres

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4746215A (en) * 1986-04-24 1988-05-24 Pacific Scientific Company Particle counter air inlet assembly
US4839529A (en) * 1986-08-19 1989-06-13 Impulsphysik Gmbh Arrangement for in situ determination of quantity of turbid matter aerosol and/or dust in fluid which flows through a space
US7173257B1 (en) * 2005-02-18 2007-02-06 Hach Ultra Analytics, Inc. Integrated assembly for delivery of air stream for optical analysis

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CLIVE KERR ET AL: "An overview of the measurement errors associated with gas turbine aeroengine pyrometer systems; Measurement errors in optical pyrometry", MEASUREMENT SCIENCE AND TECHNOLOGY, IOP, BRISTOL, GB, vol. 13, no. 6, 1 June 2002 (2002-06-01), pages 873 - 881, XP020063527, ISSN: 0957-0233, DOI: 10.1088/0957-0233/13/6/307 *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107677574A (en) * 2017-11-03 2018-02-09 济南微纳颗粒仪器股份有限公司 A kind of laser particle analyzer sample window
CN109187887A (en) * 2018-10-17 2019-01-11 信丰县包钢新利稀土有限责任公司 A kind of rare earth extraction polluted gas discharge detection device
CN109187887B (en) * 2018-10-17 2019-08-02 信丰县包钢新利稀土有限责任公司 A kind of rare earth extraction polluted gas discharge detection device

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