WO2012062964A1 - Apparatus and method for monitoring particles - Google Patents

Apparatus and method for monitoring particles Download PDF

Info

Publication number
WO2012062964A1
WO2012062964A1 PCT/FI2011/050987 FI2011050987W WO2012062964A1 WO 2012062964 A1 WO2012062964 A1 WO 2012062964A1 FI 2011050987 W FI2011050987 W FI 2011050987W WO 2012062964 A1 WO2012062964 A1 WO 2012062964A1
Authority
WO
WIPO (PCT)
Prior art keywords
particles
sample
flow
aerosol flow
diameter larger
Prior art date
Application number
PCT/FI2011/050987
Other languages
French (fr)
Inventor
Kauko Janka
Original Assignee
Pegasor Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Pegasor Oy filed Critical Pegasor Oy
Publication of WO2012062964A1 publication Critical patent/WO2012062964A1/en

Links

Classifications

    • 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
    • G01N15/0255—Investigating particle size or size distribution with mechanical, e.g. inertial, classification, and investigation of sorted collections
    • 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
    • G01N1/2252—Sampling from a flowing stream of gas in a vehicle exhaust
    • 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
    • G01N15/0255—Investigating particle size or size distribution with mechanical, e.g. inertial, classification, and investigation of sorted collections
    • G01N2015/0261—Investigating particle size or size distribution with mechanical, e.g. inertial, classification, and investigation of sorted collections using impactors

Definitions

  • the present invention relates to an apparatus for monitoring particles and especially to an apparatus as defined in the preamble of independent claim 1 .
  • the present invention further relates to a method for monitoring particles and more particularly to a method as defined in the preamble of independent claim 14.
  • the present invention further to a use according to claim 26.
  • Fine particles having diameter are formed in many industrial processes and combustion processes. For various reasons these fine particles are measured.
  • the fine particle measurements may be conducted because of their potential health effects and also for monitoring operation of industrial processes and combustion processes, such as operation of combustion engines, especially diesel engines.
  • Another reason for monitoring fine particles is the increasing use and production of nanosized particles in industrial processes. The above reasons there is need for reliable fine particle measurement equipments and methods.
  • the clean gas flow and the ejector together cause suction to the sample inlet such that a sample aerosol flow is formed from the duct or the space to the inlet chamber.
  • the sample aerosol flow is thus provided as a side flow to the ejector.
  • the ionized clean gas charges the particles.
  • the charged particles may be further conducted back to the duct or space containing the aerosol.
  • the fine particles of the aerosol sample are thus monitored by monitoring the electrical charge carried by the electrically charged particles. Free ions may removed further be removed using an ion trap.
  • the stabilization of the flow rate is based on balancing the pressures between the ejector throat pressure gain and the pressure drops caused by orifices in the flow path.
  • the inlet orifice is designed to be the main pressure-drop generator.
  • the size distribution of the diesel engine exhaust particles generally shows three different modes: the nuclei mode consists of particles having a diameter of less than approximately 50 nm, the accumulation mode consists of particles having diameters between 50 nm and 1 ⁇ and in the coarse mode the particle diameter is greater than 1 ⁇ . A majority of the diesel engine exhaust particles is born after the exhaust gases escape from the exhaust pipe and these particles typically belong to the accumulation and nuclei mode.
  • the fine particle monitoring apparatuses may be operated long time periods without need for maintenance. In many applications, such as monitoring fine particles of combustion engines, it is further preferable that the monitoring apparatus may be operated continuously fro conducting fine particle measurements in real-time.
  • the prior art fine particle measurement method in which the sample aerosol is sucked from a duct or space containing aerosol by using ionized gas flow and an ejector, is that the throat of the ejector and the ion trap area will easily be contaminated as particles of the sample aerosol are adhered to the wall of the throat of the ejector and ion trap area.
  • This problem is mainly caused by the coarser particles having particle diameter greater than 1 ⁇ .
  • the coarser particles become adhered to the walls of the throat of the ejector and ion trap area as they impact on the walls due to the swirling flow. Although the number of these coarse particles may be negligible to affect the sensor reading, their mass or volume may still be dominant. For this reason the coarse particles typically dominates the deposits on sensor surfaces. Contamination of the throat of the ejector and the walls of the ion trap area makes the flow paths more narrow deteriorating the operation of the fine particle monitoring apparatus and further leading to unreliable measurement of the fine particles and need for frequent maintenance work.
  • US patent application 2006/0284077 describes an aerosol particle sampling device.
  • the device is configured to facilitate adjustments to simulate particle deposition in the lung or elsewhere in the respiratory system.
  • An aerosol is received at an inlet conduit and directed through a large-particle separator such as a cyclone.
  • the publication does not teach the use of the particle separator for flow stabilization, which is a problem in the ejector-based devices as described above.
  • the particle separator is an extra part of the apparatus, which makes the construction of the device more complex. It also creates extra pressure drop in the sample flow which requires a more efficient air feeding device.
  • UK patent application 2 346 700 describes a particle measurement apparatus where orthogonal arrangement of tubes 1 and 2 form a virtual impactor which ensures that all particles larger than a certain maximum size (much larger than 1 ⁇ ) are removed from the sample entering the precipitator/charger/detector. In this way such large particles are excluded from the sample analysis system; this is an advantage primarily in terms of keeping the instrument clean. Also this publication fails to teach the use of particle separator for flow stabilization in ejector-based devices. The particle separator is an additional part of the system, and the described inertial separator requires extra sample-air-feeding power. Brief description of the invention
  • the object of the present invention is to provide an apparatus and method so as to overcome the prior art disadvantages.
  • the objects of the present invention are achieved with an apparatus according to the characterizing portion of claim 1 , which apparatus comprises a particle separation arrangement which is arranged to the sample-inlet arrangement or in the inlet chamber in direct fluid communication with the sample-inlet arrangement.
  • the objects of the present invention are further achieved with a method according to the characterizing portion of claim 12, which method comprises generating, with the aim of the particle separation means, a pressure drop which stabilizes the sample aerosol flow (A).
  • the present invention is based on the idea of providing an apparatus for monitoring particles in a channel or a space comprising aerosol with a particle separation arrangement arranged to separate from the sample aerosol flow particles having mean diameter larger than D-i .
  • the particle separation arrangement is arranged to separate the particles having mean diameter larger than D by means of inertia separation. This means that the inertia or linear momentum of the particles of the sample aerosol flow is used for separating the particles having mean diameter larger than D-i .
  • the inertia separation of the particles having diameter greater than D1 may be carried out by cyclonic separation, in which the sample aerosol is guided to a rotating or spiral flow.
  • the coarser particles in the rotating flow have too much inertia to follow with the flow and thus the coarser particles become drifted on outer part of the rotating flow and further they may impact on the collection surface surrounding the flow.
  • the sample inlet is arranged to supply the sample aerosol flow substantially tangentially or asymmetrically into the inlet chamber such that the particles having mean diameter larger than D are separated walls of the inlet chamber.
  • the particle separation arrangement is arranged to separate the particles having mean diameter larger than D-i by impaction separation.
  • the particle separation arrangement is provided with one or more impaction surface towards which the sample aerosol flow is directed.
  • the apparatus may comprise one or more impaction surfaces and at least one of the impaction surfaces is arranged to the sample inlet or to the inlet chamber down stream of the sample inlet in direct fluid communication with the sample aerosol flow.
  • the direction of the sample aerosol flow will change.
  • the gas phase and the finer particles of the sample aerosol will continue to flow past the impaction surface, but the coarser particles having diameter greater than D will collide or impact on the impaction surface due to their greater amount of inertia and linear momentum as they cannot flow the rest of the sample aerosol flow.
  • the particle separation arrangement is arranged to separate the particles having mean diameter larger than Di by a virtual impactor.
  • the apparatus and method of the present invention may be arranged to separate from the sample aerosol flow particles having diameter D larger than 5 ⁇ , preferably larger than 3 ⁇ and more preferably larger than 1 ⁇ .
  • a typical problem using inertial particle separation in conventional prior art fine particle monitoring apparatuses is due to the fact that the sample gas containing particles to be separated need to be accelerated to high velocity.
  • the velocities needed are especially high, if small (i.e. diameter down to 1 ⁇ ) particles should be separated.
  • the acceleration of a sample flow to high velocities causes high pressure drop across the accelerating nozzle.
  • the additional pressure drop generated by the inertia based particle separation causes typically problems for the sample air feeding system. Therefore inertia based particle separation is not usually suitable for such particle monitoring apparatuses which require low power for sample-air feeding.
  • the sample flow feeding is based on ejector-pump principle (i.e.
  • the stabilization of the flow rate is based on balancing the pressures between the ejector throat pressure gain and the pressure drops caused by orifices in the flow path.
  • the inlet orifice is designed to be the main pressure-drop generator.
  • the pressure drop caused by the inertia-based particle separation arrangement can be utilized as the balancing pressure drop. For this reason the disadvantage (additional pressure drop) of inertial separation system can be eliminated.
  • the present invention has the advantage that separating coarser particles from the sample aerosol flow will reduce contamination of the apparatus, and especially the throat of the ejector and the ion trap area. Reduced contamination will extend the operating time without need for maintenance work. Furthermore, separating the coarser particles will provide more reliable and accurate measurement results of fine particles. It has also been surprisingly realized that the pressure drop caused by the inertia based separation of the coarser particles will be utilized as balancing pressure drop for the flow system. For this reason the separator causes no extra harmful pressure dissipation. In addition, the resulting combined sensor-separator structure is simplified.
  • Figure 1 is a schematic view of one embodiment of an apparatus for monitoring fine particles
  • Figure 2 is a schematic view of one embodiment of a particle separation arrangement according to the present invention based on cyclonic separation
  • Figure 3 is a schematic view of another embodiment of a particle separation arrangement according to the present invention based on cyclonic separation
  • Figure 4 is a schematic view of one embodiment of a particle separation arrangement according to the present invention based on impaction separation
  • Figure 5 is a schematic view of another embodiment of a particle separation arrangement according to the present invention based on impaction separation
  • Figure 6 is a schematic view of one embodiment of a particle separation arrangement according to the present invention comprising a virtual impactor. Detailed description of the invention
  • the figure 1 shows one embodiment of an apparatus 1 for monitoring fine particles, especially particles having diameter less than 1 ⁇ .
  • the apparatus comprises a body 1 7 inside which the sample aerosol flow is guided for monitoring or measuring the fine particles.
  • the apparatus 1 is connected to an aerosol duct 1 1 in side which is an aerosol flow F.
  • the aerosol duct may be exhaust duct of a combustion engine or the like.
  • aerosol duct may be any space comprising aerosol or any duct or channel having an aerosol flow F.
  • the apparatus 1 comprises a sample inlet 2 for guiding a sample aerosol flow A into the apparatus 1 .
  • the sample inlet 2 is in fluid communication with the aerosol duct 1 1 and inside of the apparatus 1 .
  • the apparatus 1 preferably also comprises a sample outlet 1 0 through which the analyzed sample aerosol flow B exhausted from the apparatus 1 .
  • the analyzed sample aerosol B is returned to the aerosol duct 1 1 .
  • the sample outlet 1 0 may also be arranged to conduct the analyzed sample aerosol B directly to the ambient atmosphere or some other location. Accordingly the apparatus 1 does not collect or store the sample aerosol A.
  • the apparatus may also comprise a sample- inlet arrangement 2 comprising one or more sample inlets.
  • the apparatus may also comprise a sample outlet arrangement 10 comprising one or more sample outlets.
  • the apparatus 1 comprises an inlet chamber 4 and the sample inlet 2 is arranged to provide a fluid communication between the aerosol duct 1 1 and the inlet chamber 4.
  • the apparatus further comprises a gas supply for supplying clean particle free gas C into the inlet chamber 4.
  • the gas supply comprises gas supply connection 18 via which the clean gas may be brought from a gas source.
  • the gas may be cleaned in a filter or the like for essentially removing particles from the gas.
  • the clean gas may be air or some other suitable gas.
  • the clean gas may be fed from the gas source to a temperature regulator, which can either heat or cool the air.
  • a magnetic valve may be switched to feed the gas to a flow controller, so that the clean gas flow C may be set to a desired value.
  • the flow controller can be e.g.
  • the flow controller may be connected to a filter, which essentially removes particles from the pressurized gas, so that the particle concentration in the pressurized gas is remarkably lower than the particle concentration in the sample aerosol flow A.
  • the clean gas is then fed to the measurement apparatus 1 through the gas supply connection 18.
  • the apparatus 1 further comprises a clean gas supply channel 16 through which the clean gas is fed to inlet chamber 4 of the apparatus 1 .
  • the clean gas supply channel comprises a nozzle head 6 opening into the inlet chamber 4.
  • the clean gas supply is also provided with an ionization device 14 for ionizing at least a portion of the clean gas before or during feeding the clean gas from the nozzle head 6 into the inlet chamber 4.
  • the ionization device is a corona needle 14 extending in the clean gas supply channel 16.
  • the nozzle head 6 and the corona needle 14 are advantageously arranged such that corona needle 14 extends essentially to the vicinity of the nozzle head 6. This helps the corona needle 14 to stay clean and improves the ion production.
  • the corona needle 14 is isolated from the clean gas flow channel and the body 17 of the apparatus 1 by one or more electrical insulators 20.
  • the gas supply channel 16 is arranged to provide an essentially particle free ionized gas flow C to the inlet chamber 4.
  • the apparatus is further provided with an ejector 24.
  • the ejector 24 comprises a converging-diverging nozzle 24 forming thus a converging-diverging flow channel, the throat 8 of the ejector 24.
  • the ejector 24 is a pump-like device utilizing Venturi effect of a converging-diverging nozzle to convert the pressure energy of a main fluid flow to kinetic energy which creates a low pressure zone that draws in and entrains suction for a side fluid flow.
  • the main fluid flow and the side fluid flow are at least partly mixed in the ejector 24.
  • the apparatus may also comprise one or more clean gas supply channels 16, corona needles 14 and ejectors 24.
  • the essentially particle free ionized gas flow C is fed to the throat 8 of the ejector as a main flow. Therefore the clean gas supply channel 16 and the nozzle head 6 are arranged to feed the essentially particle free gas flow C at a high velocity into the throat 8.
  • the velocity of the essentially particle free gas flow C is preferably sonic or close to sonic.
  • the essentially particle free gas flow C forms a suction to the sample inlet 2 such that the sample aerosol flow A may be sucked into the inlet chamber 4.
  • the sample aerosol flow A forms a side flow of the ejector 24.
  • the flow rate of the sample aerosol flow A is depended essentially only on the geometry of ejector 24 and the flow rate of the essentially particle free ionized gas flow C.
  • the ratio of the main flow C to the side flow A is small, preferably less than 1 :1 and more preferably less than 1 :3. According to the above mentioned there is no need for actively feed the sample aerosol flow A into the apparatus 1 , but it may be sucked by the by means of the clean gas supply and the ejector 24.
  • the apparatus 1 further comprises ion trapping chamber 22.
  • the ion trapping chamber 22 comprises an ion trap 12 for removing ions that are not attached to the particles of the sample aerosol flow A.
  • the ion tarp 12 is provided with a collection voltage for removing the mentioned free ions. The voltage used for trapping free ions depends on design parameters of the apparatus 1 , but typically the ion trap 12 voltage is 10v - 30kV.
  • the ion trap 12 voltage may also be adjusted to removed nuclei mode particles or even the smallest particles in the accumulation mode.
  • the sample aerosol and the essentially clean gas mixed together are discharged from the apparatus 1 through the outlet 10 together with the ionized particles of the sample aerosol.
  • the outlet 10 is provided in fluid communication with the ion trapping chamber 22 for exhausting the discharge flow B out of the apparatus 1 .
  • the outlet 10 may be arranged to supply the discharge flow B back to the aerosol duct 1 1 or to ambient atmosphere or some other location.
  • Particles of the aerosol F in the aerosol duct 1 1 are monitored by measuring the electrical charge carried by the electrically charged particles of the sample aerosol flow A.
  • particles of the aerosol F are monitored by measuring the electrical charge escaping with the electrically charged particles from the apparatus 1 .
  • the measurement of the charge carried by the electrically charged particles may be measured by many alternative ways.
  • the charge carried by the electrically charged particles is measured by measuring the net current escaping from the sample outlet 10
  • the whole apparatus 1 is isolated from the surrounding systems..
  • An electrometer may be assembled between the isolated apparatus (i.e. a pint in the wall of body 17) and a ground point of the surrounding systems. With this kind of setup, the electrometer may measure the charge escaping from the isolated apparatus 1 together with the ionized particles. In other words this kind of setup measures the escaping current.
  • the apparatus 1 for monitoring particles in a channel or a space further comprises a particle separation arrangement arranged to separate from the sample aerosol flow A particles having mean diameter larger than D-i.
  • the particle separation arrangement may be arranged to separate from the sample aerosol flow A particles having diameter Di larger than 5 ⁇ , preferably larger than 3 ⁇ and more preferably larger than 1 ⁇ .
  • the particle separation arrangement may be further arranged to separate the particles having mean diameter larger than D by means of inertia separation. In other words the inertia or linear momentum of the particles in the sample aerosol flow is used for separating the particles having diameter larger than D-i.
  • the separation of the particles having diameter larger than D are preferably separated before they enter the inlet chamber 4 of the apparatus 1 , or when they enter the inlet chamber 4, immediately after they have entered the inlet chamber 4 or in the inlet chamber 4.
  • Figure 2 shown one embodiment of the present invention in which the particle separation arrangement is arranged to separate particles 50 having mean diameter larger than Di by cyclonic separation.
  • the inlet chamber 4 is at least partly cylindrical or conical.
  • the particle separation arrangement is provided such that it utilizes the at least partly cylindrical or conical wall 5 of the inlet chamber 4 for separating particles 50 from the sample aerosol flow A.
  • the sample aerosol flow A is guided to an rotational flow path 26 in the inlet chamber 4 such that the particles 50 having diameter larger than D collide on the at least partly cylindrical or conical wall 5 of the inlet chamber 4 due to the inertial or linear momentum of the particles 50.
  • the particle separation arrangement comprises the sample inlet 2 arranged to supply the sample aerosol flow A substantially tangentially or asymmetrically into the inlet chamber 4 such that the particles 50 having diameter larger than D are separated on the cylindrical or conical wall 5 of the inlet chamber 4 as the flow path 26 of the sample aerosol flow becomes rotational.
  • the sample inlet 2 may be arranged tangentially to the inlet chamber 4 or alternatively the sample inlet 2 may be provided with a flow guide (not shown) to feed the sample aerosol flow A substantially tangentially into the inlet chamber 4.
  • the rotational flow 26 of the sample aerosol flow A in the inlet chamber also enhances the mixing the sample aerosol flow A, and the essentially particle free ionized gas flow C, thus enhancing the ionization of the particles of the sample aerosol flow A.
  • An additional benefit of the swirling flow is that it stabilities the mixed flow. This relaxes the tolerance demands of the nozzle feeding the ionized air.
  • the inlet chamber 4 does not have an at least partly cylindrical or conical wall 5, but the inlet chamber 4 may be formed as rectangular or polygonal and the sample aerosol flow A is supplied to the inlet chamber 4 asymmetrically, towards wall 5 or substantially parallel to at least a portion of the wall 5 for providing the rotation flow path 26.
  • the apparatus comprises a flow guide (not shown) provided to the sample inlet 2 such that the sample aerosol flow A is guided to a rotational flow path inside the sample inlet 2.
  • the rotational flow path of the sample aerosol flow A in the sample inlet 2 causes the coarser particles 50 having diameter larger than D-i to collide on the walls of the sample inlet 2 due to the inertia and linear momentum.
  • the particles 50 having diameter larger than Di are separated in the sample inlet 2 by cyclonic separation.
  • Figure 3 shows an alternative embodiment of the present invention.
  • Figure 3 shows a cyclone 80 having an at least partly cylindrical and/or conical separation chamber 28.
  • the separation chamber 28 is provided with an inlet 2 through which the sample aerosol flow A is supplied to the separation chamber 28.
  • the separation chamber 28 further comprises an cyclone outlet 30 through which particle separated sample aerosol flow A' is discharged from the separation chamber 28.
  • the sample inlet 2 is provided to feed the sample aerosol flow A substantially tangentially or asymmetrically into the separation chamber 28 such that the sample aerosol flow A flows along a rotational flow path 26 inside the separation chamber 28.
  • the particles 50 having diameter larger than D will collide to the walls 7 of the separation chamber 28 as they are not able to follow the rotational flow path 26 due to their inertia and linear momentum.
  • the particles 50 having diameter larger than Di will thus impact on the wall 7 to be separated from the sample aerosol flow A by means of known cyclonic separation.
  • the separated sample aerosol flow A', having particles with diameter larger than D removed, may be further supplied to the inlet chamber 4 of the apparatus 1 .
  • the above described separate cyclone separator 80 for separating from the sample aerosol flow A particles 50 having mean diameter larger than D may be arranged to the sample inlet 2 or in the inlet chamber 4.
  • the cyclone separator 80 is arranged to the inlet chamber 4 it is preferably provided in fluid communication with the sample inlet 2.
  • the separate cyclone separator 80 may be arranged in front of the sample inlet 2 such that the sample aerosol flow A enters directly the cyclone separator 80 when supplied into the inlet chamber 4.
  • Figure 4 shows another embodiment of the present invention in which the particle separation arrangement is arranged to separate the particles 50 having mean diameter larger than D by impaction separation.
  • the particle separation arrangement comprises an impact surface 32 provided in the inlet chamber 4.
  • the impact surface 32 is arranged in fluid communication with the sample inlet 2 such that the sample aerosol flow A supplied to the inlet chamber 4 is directed towards the impaction surface 32.
  • the impaction surface 32 is arranged in from of the sample inlet 2, as shown in figure 4. When directed towards the impaction surface 32 the sample aerosol flow A will change the direction of the flow such that it will flow past the impaction surface, as shown by the flow path 34 in figure 4.
  • the impaction surface 32 forces the sample aerosol flow A to turn.
  • the particles 50 having diameter larger than Di have too much inertia and linear momentum such that they are not able to follow the flow path 34 and they will collide on the impaction surface 32. Therefore the impaction surface 32 removes particles 50 having diameter larger than Di from the sample aerosol flow A by impaction separation.
  • the impaction surface may be an impaction plate or the like and the may also be two or more impaction surfaces arranged in succession the flow direction of the sample aerosol flow A.
  • Figure 5 shows an alternative embodiment of impaction separation.
  • Figure 5 shows a separate impactor 82 having an sample inlet 2 through which the sample aerosol flow A is supplied to the impactor 82, and an impactor outlet 40 through which separated sample aerosol flow A' is discharged from the impactor 82.
  • the separated sample aerosol flow A' does not contain particles having diameter greater than D-i .
  • the impactor 82 is shown as a cascade impactor having two impaction stages. It should however be noted that the impactor 82 may also comprise one or more than two impaction stages.
  • Impactor 82 comprises a first impaction chamber 42 having a first impaction surface 32 and second impaction chamber 44 having a second impaction surface 36.
  • the sample aerosol flow A flows through the impactor 82 along the first flow path 34 flowing pass the impaction surfaces 32, 36.
  • the largest particles 50 of the sample aerosol flow A will follow the second flow path 51 and collide to the first impaction surface 32 due to their inertia and linear momentum.
  • the sample aerosol flow A is conducted through the aerosol nozzle 38 in which the velocity of the sample aerosol flow A is increased towards the second impaction surface 34.
  • the sample aerosol flow A will again turn and flow pass the second impaction surface 36 along the first flow path 34.
  • the particles 52 of the sample aerosol flow A will follow the third flow path 53 and collide to the second impaction surface 36 due to their inertia and linear momentum.
  • the particles 52 separated by the second impaction surface 36 are usually smaller than particles 50.
  • the separation of the particles 50, 52 may be adjusted by adjusting the velocity of the sample aerosol flow A, impactor-nozzle dimensions and the location of the impaction surfaces 32, 36.
  • the above described separate impactor 82 for separating from the sample aerosol flow A particles 50, 52 having diameter larger than D may be arranged to the sample inlet 2 or in the inlet chamber 4.
  • the impactor 82 is arranged to the inlet chamber 4 it is preferably provided in fluid communication with the sample inlet 2.
  • the separate impactor 82 may be arranged in front of the sample inlet 2 such that the sample aerosol flow A enters directly the impactor 82 when supplied into the inlet chamber 4.
  • Figure 6 shows still another embodiment of the present invention in which the particle separation arrangement is provided with a virtual impactor 84 for separating from the sample aerosol flow A particles 50 having mean diameter larger than D-i .
  • Figure 6 shows schematically a single-stage virtual impactor 84 having a sample inlet 2 through which the sample aerosol flow A is supplied to the virtual impactor 84.
  • the virtual impactor 84 comprises an aerosol chamber 60 for receiving the sample aerosol flow A comprising particles 54 having diameter smaller than Di and particles 54 having diameter greater than D-i.
  • the virtual impactor 84 further comprises an impaction nozzle 62 for feeding the sample aerosol flow A to the virtual impactor nozzle 56 through virtual impaction chamber 64.
  • the virtual impaction nozzle 56 is arranged to separate particles 54 having diameter smaller than Di from particles 50 having diameter larger than Di by letting the particles 50 having diameter greater than Di to pass the virtual impactor nozzle 56.
  • the virtual impaction chamber 64 comprises a first outlet 66 for supplying the separated sample aerosol flow A' to the inlet chamber 4 of the apparatus 1 .
  • the particles 50 having diameter greater than Di are removed from the separated aerosol flow A'.
  • Particles 50 having diameter greater than D go through the virtual impactor nozzle 56 into the collection chamber 68, from which they may be discharged as discharge flow D through discharge outlet 70.
  • the particles 50 having diameter greater than D1 may also alternatively be stored to the collection chamber 68.
  • the separate virtual impactor 84 may be arranged in the sample inlet 2 or in the inlet chamber 4 in direct fluid communication with the sample aerosol flow A.
  • the separate particle separators described above may be provided to the sample inlet 2, substantially to the inlet opening of the inlet 2, inside the inlet chamber 4 just in front of the inlet 2 or inside the inlet chamber 4 in fluid communication with the sample aerosol flow A. Also in a preferred embodiment the particle separation arrangement is provided to separate from the sample aerosol flow particles 50, 52 having diameter D1 greater than 1 ⁇ .
  • the present invention further relates to a method for monitoring particles 54 in a channel 1 1 or a space comprising aerosol.
  • the method comprises feeding essentially particle free ionized gas flow C to an ejector 24, sucking a sample aerosol flow A from the channel 1 1 or the space by means of the essentially particle free ionized gas flow C and the ejector 24, and mixing at least a fraction of the sample aerosol flow A with the essentially particle free ionized gas flow C for charging at least a fractions of the particles 54 of the aerosol.
  • particles 50, 52 having diameter larger than D are separated from the sample aerosol flow A.
  • the separation of the particles 50, 52 having diameter larger than Di may be carried out by means of inertia separation.
  • the inertia separation may be conducted by cyclonic separation or by impaction separation.
  • Cyclonic separation may be carried out by a separate cyclone or by feeding the sample aerosol flow A tangentially or asymmetrically into the inlet chamber for separating the particles 50, 52 having mean diameter larger than D-i on the walls 5 of the inlet chamber 4.
  • the impaction separation may be carried out by using one or more impaction surface 32, 36 for separating the particles 50, 52 having mean diameter larger than D-i.
  • the impaction separation is carried out by using one or more virtual impactors.
  • separating from the sample aerosol flow A particles 50, 52 having mean diameter larger than Di is carried out substantially before mixing the sample aerosol flow A with the essentially particle free ionized gas flow C.
  • the present invention further relates to use of inertia of particles 50, 52, 54 in a sample aerosol flow A for separating from the sample aerosol flow A particles 50, 52 having diameter larger than D-i.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Molecular Biology (AREA)
  • Biomedical Technology (AREA)
  • Engineering & Computer Science (AREA)
  • Dispersion Chemistry (AREA)
  • Sampling And Sample Adjustment (AREA)

Abstract

The present invention relates to an apparatus and method for monitoring particles (54) in a channel (11) or a space comprising aerosol. The apparatus comprises- an inlet chamber (4), an ejector (24), gas supply (6, 16, 18) arranged to feed essentially particle free gas flow (C) to ejector (24) via the inlet chamber (4), a sample-inlet arrangement (2) arranged to provide a sample aerosol flow (A) from the channel (11) or the space into the inlet chamber (4) by means of suction provided by the gas supply (6, 16, 18) and the ejector (24) and a particle separation arrangement (80, 82, 84) arranged to separate from the sample aerosol flow (A) particles (50, 52) having mean diameter larger than D1 by means of inertia separation. The particle separation arrangement (80, 82, 84) is arranged to the sample-inlet arrangement (2) or in the inlet chamber (4) in direct fluid communication with the sample-inlet arrangement (2).

Description

Apparatus and method for monitoring particles
The present invention relates to an apparatus for monitoring particles and especially to an apparatus as defined in the preamble of independent claim 1 . The present invention further relates to a method for monitoring particles and more particularly to a method as defined in the preamble of independent claim 14. The present invention further to a use according to claim 26.
Background of the invention
Fine particles having diameter are formed in many industrial processes and combustion processes. For various reasons these fine particles are measured. The fine particle measurements may be conducted because of their potential health effects and also for monitoring operation of industrial processes and combustion processes, such as operation of combustion engines, especially diesel engines. Another reason for monitoring fine particles is the increasing use and production of nanosized particles in industrial processes. The above reasons there is need for reliable fine particle measurement equipments and methods.
One prior art method and apparatus for measuring fine particles is described in document WO2009109688 A1 . In this prior art method clean, essentially particle free, gas is supplied into the apparatus and directed as a main flow via an inlet chamber to an ejector provided inside the apparatus. The clean gas is further ionized before and during supplying it into the inlet chamber. The ionized clean gas may be preferably fed to the ejector at a sonic or close to sonic speed. The ionizing of the clean gas may be carried out for example using a corona charger. The inlet chamber is further provided with a sample inlet arranged in fluid communication with a channel or a space comprising aerosol having fine particles. The clean gas flow and the ejector together cause suction to the sample inlet such that a sample aerosol flow is formed from the duct or the space to the inlet chamber. The sample aerosol flow is thus provided as a side flow to the ejector. The ionized clean gas charges the particles. The charged particles may be further conducted back to the duct or space containing the aerosol. The fine particles of the aerosol sample are thus monitored by monitoring the electrical charge carried by the electrically charged particles. Free ions may removed further be removed using an ion trap.
When the sample flow feeding is based on ejector-pump principle, the stabilization of the flow rate is based on balancing the pressures between the ejector throat pressure gain and the pressure drops caused by orifices in the flow path. Practically the inlet orifice is designed to be the main pressure-drop generator.
In addition to the above mentioned fine particles industrial processes and combustion processes form usually also particles having particle diameter greater than 1 μιη, or greater than 2 μιη, 3 μιτι, 5 μιτι or even greater. These coarse particles having particle diameter greater than 1 μιη may be formed in small amounts in normal operation conditions, but especially in special operation conditions such as during start ups, shutdowns, malfunction conditions. The size distribution of the diesel engine exhaust particles generally shows three different modes: the nuclei mode consists of particles having a diameter of less than approximately 50 nm, the accumulation mode consists of particles having diameters between 50 nm and 1 μιτι and in the coarse mode the particle diameter is greater than 1 μιη. A majority of the diesel engine exhaust particles is born after the exhaust gases escape from the exhaust pipe and these particles typically belong to the accumulation and nuclei mode.
One important demand for the fine particle monitoring apparatuses is reliable operation. Furthermore, it is also preferable that these fine particle monitoring apparatuses may be operated long time periods without need for maintenance. In many applications, such as monitoring fine particles of combustion engines, it is further preferable that the monitoring apparatus may be operated continuously fro conducting fine particle measurements in real-time. it has been surprisingly discovered that one problem of the prior art fine particle measurement method in which the sample aerosol is sucked from a duct or space containing aerosol by using ionized gas flow and an ejector, is that the throat of the ejector and the ion trap area will easily be contaminated as particles of the sample aerosol are adhered to the wall of the throat of the ejector and ion trap area. This problem is mainly caused by the coarser particles having particle diameter greater than 1 μιη. The coarser particles become adhered to the walls of the throat of the ejector and ion trap area as they impact on the walls due to the swirling flow. Although the number of these coarse particles may be negligible to affect the sensor reading, their mass or volume may still be dominant. For this reason the coarse particles typically dominates the deposits on sensor surfaces. Contamination of the throat of the ejector and the walls of the ion trap area makes the flow paths more narrow deteriorating the operation of the fine particle monitoring apparatus and further leading to unreliable measurement of the fine particles and need for frequent maintenance work.
US patent application 2006/0284077 describes an aerosol particle sampling device. The device is configured to facilitate adjustments to simulate particle deposition in the lung or elsewhere in the respiratory system. An aerosol is received at an inlet conduit and directed through a large-particle separator such as a cyclone. The publication does not teach the use of the particle separator for flow stabilization, which is a problem in the ejector-based devices as described above. In US 2006/0284077 the particle separator is an extra part of the apparatus, which makes the construction of the device more complex. It also creates extra pressure drop in the sample flow which requires a more efficient air feeding device.
UK patent application 2 346 700 describes a particle measurement apparatus where orthogonal arrangement of tubes 1 and 2 form a virtual impactor which ensures that all particles larger than a certain maximum size (much larger than 1 μιτι) are removed from the sample entering the precipitator/charger/detector. In this way such large particles are excluded from the sample analysis system; this is an advantage primarily in terms of keeping the instrument clean. Also this publication fails to teach the use of particle separator for flow stabilization in ejector-based devices. The particle separator is an additional part of the system, and the described inertial separator requires extra sample-air-feeding power. Brief description of the invention
The object of the present invention is to provide an apparatus and method so as to overcome the prior art disadvantages. The objects of the present invention are achieved with an apparatus according to the characterizing portion of claim 1 , which apparatus comprises a particle separation arrangement which is arranged to the sample-inlet arrangement or in the inlet chamber in direct fluid communication with the sample-inlet arrangement. The objects of the present invention are further achieved with a method according to the characterizing portion of claim 12, which method comprises generating, with the aim of the particle separation means, a pressure drop which stabilizes the sample aerosol flow (A).
The preferred embodiments of the invention are disclosed in the dependent claims.
The present invention is based on the idea of providing an apparatus for monitoring particles in a channel or a space comprising aerosol with a particle separation arrangement arranged to separate from the sample aerosol flow particles having mean diameter larger than D-i . In a preferable embodiment the particle separation arrangement is arranged to separate the particles having mean diameter larger than D by means of inertia separation. This means that the inertia or linear momentum of the particles of the sample aerosol flow is used for separating the particles having mean diameter larger than D-i .
The inertia separation of the particles having diameter greater than D1 may be carried out by cyclonic separation, in which the sample aerosol is guided to a rotating or spiral flow. The coarser particles in the rotating flow have too much inertia to follow with the flow and thus the coarser particles become drifted on outer part of the rotating flow and further they may impact on the collection surface surrounding the flow. In a preferable embodiment of the present invention the sample inlet is arranged to supply the sample aerosol flow substantially tangentially or asymmetrically into the inlet chamber such that the particles having mean diameter larger than D are separated walls of the inlet chamber. In another embodiment of the present invention the particle separation arrangement is arranged to separate the particles having mean diameter larger than D-i by impaction separation. In this embodiment the particle separation arrangement is provided with one or more impaction surface towards which the sample aerosol flow is directed. The apparatus may comprise one or more impaction surfaces and at least one of the impaction surfaces is arranged to the sample inlet or to the inlet chamber down stream of the sample inlet in direct fluid communication with the sample aerosol flow. When the sample aerosol flow is directed towards the impaction surface the direction of the sample aerosol flow will change. The gas phase and the finer particles of the sample aerosol will continue to flow past the impaction surface, but the coarser particles having diameter greater than D will collide or impact on the impaction surface due to their greater amount of inertia and linear momentum as they cannot flow the rest of the sample aerosol flow. In yet another embodiment of the present invention the particle separation arrangement is arranged to separate the particles having mean diameter larger than Di by a virtual impactor.
The apparatus and method of the present invention may be arranged to separate from the sample aerosol flow particles having diameter D larger than 5 μιτι, preferably larger than 3 μιτι and more preferably larger than 1 μιη.
A typical problem using inertial particle separation in conventional prior art fine particle monitoring apparatuses is due to the fact that the sample gas containing particles to be separated need to be accelerated to high velocity. The velocities needed are especially high, if small (i.e. diameter down to 1 μιτι) particles should be separated. The acceleration of a sample flow to high velocities causes high pressure drop across the accelerating nozzle. The additional pressure drop generated by the inertia based particle separation causes typically problems for the sample air feeding system. Therefore inertia based particle separation is not usually suitable for such particle monitoring apparatuses which require low power for sample-air feeding. When the sample flow feeding is based on ejector-pump principle (i.e. an apparatus described in document WO2009109688 A1 ), the stabilization of the flow rate is based on balancing the pressures between the ejector throat pressure gain and the pressure drops caused by orifices in the flow path. Practically the inlet orifice is designed to be the main pressure-drop generator. In the present invention the pressure drop caused by the inertia-based particle separation arrangement can be utilized as the balancing pressure drop. For this reason the disadvantage (additional pressure drop) of inertial separation system can be eliminated.
The present invention has the advantage that separating coarser particles from the sample aerosol flow will reduce contamination of the apparatus, and especially the throat of the ejector and the ion trap area. Reduced contamination will extend the operating time without need for maintenance work. Furthermore, separating the coarser particles will provide more reliable and accurate measurement results of fine particles. It has also been surprisingly realized that the pressure drop caused by the inertia based separation of the coarser particles will be utilized as balancing pressure drop for the flow system. For this reason the separator causes no extra harmful pressure dissipation. In addition, the resulting combined sensor-separator structure is simplified.
Brief description of the figures
In the following the invention will be described in greater detail, in connection with preferred embodiments, with reference to the attached drawings, in which
Figure 1 is a schematic view of one embodiment of an apparatus for monitoring fine particles;
Figure 2 is a schematic view of one embodiment of a particle separation arrangement according to the present invention based on cyclonic separation;
Figure 3 is a schematic view of another embodiment of a particle separation arrangement according to the present invention based on cyclonic separation;
Figure 4 is a schematic view of one embodiment of a particle separation arrangement according to the present invention based on impaction separation; Figure 5 is a schematic view of another embodiment of a particle separation arrangement according to the present invention based on impaction separation; and
Figure 6 is a schematic view of one embodiment of a particle separation arrangement according to the present invention comprising a virtual impactor. Detailed description of the invention
The figure 1 shows one embodiment of an apparatus 1 for monitoring fine particles, especially particles having diameter less than 1 μιη. The apparatus comprises a body 1 7 inside which the sample aerosol flow is guided for monitoring or measuring the fine particles. The apparatus 1 is connected to an aerosol duct 1 1 in side which is an aerosol flow F. Thus the apparatus 1 is arranged to monitor fine particles in the aerosol flow F. The aerosol duct may be exhaust duct of a combustion engine or the like. Alternatively aerosol duct may be any space comprising aerosol or any duct or channel having an aerosol flow F. The apparatus 1 comprises a sample inlet 2 for guiding a sample aerosol flow A into the apparatus 1 . The sample inlet 2 is in fluid communication with the aerosol duct 1 1 and inside of the apparatus 1 . The apparatus 1 preferably also comprises a sample outlet 1 0 through which the analyzed sample aerosol flow B exhausted from the apparatus 1 . In the embodiment of figure 1 the analyzed sample aerosol B is returned to the aerosol duct 1 1 . The sample outlet 1 0 may also be arranged to conduct the analyzed sample aerosol B directly to the ambient atmosphere or some other location. Accordingly the apparatus 1 does not collect or store the sample aerosol A. In an alternative embodiment the apparatus may also comprise a sample- inlet arrangement 2 comprising one or more sample inlets. Furthermore the apparatus may also comprise a sample outlet arrangement 10 comprising one or more sample outlets.
The apparatus 1 comprises an inlet chamber 4 and the sample inlet 2 is arranged to provide a fluid communication between the aerosol duct 1 1 and the inlet chamber 4. The apparatus further comprises a gas supply for supplying clean particle free gas C into the inlet chamber 4. The gas supply comprises gas supply connection 18 via which the clean gas may be brought from a gas source. The gas may be cleaned in a filter or the like for essentially removing particles from the gas. The clean gas may be air or some other suitable gas. The clean gas may be fed from the gas source to a temperature regulator, which can either heat or cool the air. A magnetic valve may be switched to feed the gas to a flow controller, so that the clean gas flow C may be set to a desired value. The flow controller can be e.g. adjustable valve, critical aperture, flow meter, mass flow controller or the like. The flow controller may be connected to a filter, which essentially removes particles from the pressurized gas, so that the particle concentration in the pressurized gas is remarkably lower than the particle concentration in the sample aerosol flow A. The clean gas is then fed to the measurement apparatus 1 through the gas supply connection 18. The apparatus 1 further comprises a clean gas supply channel 16 through which the clean gas is fed to inlet chamber 4 of the apparatus 1 . The clean gas supply channel comprises a nozzle head 6 opening into the inlet chamber 4. The clean gas supply is also provided with an ionization device 14 for ionizing at least a portion of the clean gas before or during feeding the clean gas from the nozzle head 6 into the inlet chamber 4. In the embodiment of figure 1 the ionization device is a corona needle 14 extending in the clean gas supply channel 16. The nozzle head 6 and the corona needle 14 are advantageously arranged such that corona needle 14 extends essentially to the vicinity of the nozzle head 6. This helps the corona needle 14 to stay clean and improves the ion production. The corona needle 14 is isolated from the clean gas flow channel and the body 17 of the apparatus 1 by one or more electrical insulators 20. According to the above mentioned the gas supply channel 16 is arranged to provide an essentially particle free ionized gas flow C to the inlet chamber 4.
The apparatus is further provided with an ejector 24. The ejector 24 comprises a converging-diverging nozzle 24 forming thus a converging-diverging flow channel, the throat 8 of the ejector 24. The ejector 24 is a pump-like device utilizing Venturi effect of a converging-diverging nozzle to convert the pressure energy of a main fluid flow to kinetic energy which creates a low pressure zone that draws in and entrains suction for a side fluid flow. The main fluid flow and the side fluid flow are at least partly mixed in the ejector 24. After passing through the throat 8 of the ejector 24, the mixed fluid expands and the velocity is reduced which results in recompressing the mixed fluids by converting velocity energy back into pressure energy. In an alternative embodiment the apparatus may also comprise one or more clean gas supply channels 16, corona needles 14 and ejectors 24.
In the embodiment of figure 1 the essentially particle free ionized gas flow C is fed to the throat 8 of the ejector as a main flow. Therefore the clean gas supply channel 16 and the nozzle head 6 are arranged to feed the essentially particle free gas flow C at a high velocity into the throat 8. The velocity of the essentially particle free gas flow C is preferably sonic or close to sonic. In the ejector 24 the essentially particle free gas flow C forms a suction to the sample inlet 2 such that the sample aerosol flow A may be sucked into the inlet chamber 4. The sample aerosol flow A forms a side flow of the ejector 24. The flow rate of the sample aerosol flow A is depended essentially only on the geometry of ejector 24 and the flow rate of the essentially particle free ionized gas flow C. In a preferred embodiment the ratio of the main flow C to the side flow A is small, preferably less than 1 :1 and more preferably less than 1 :3. According to the above mentioned there is no need for actively feed the sample aerosol flow A into the apparatus 1 , but it may be sucked by the by means of the clean gas supply and the ejector 24.
The essentially particle free ionized gas flow C and the sample aerosol flow are mixed in the inlet chamber 4 and in the ejector 24 such that the particles of the sample aerosol flow A are electrically charged during the mixing by the ionized clean gas flow C. The apparatus 1 further comprises ion trapping chamber 22. The ion trapping chamber 22 comprises an ion trap 12 for removing ions that are not attached to the particles of the sample aerosol flow A. The ion tarp 12 is provided with a collection voltage for removing the mentioned free ions. The voltage used for trapping free ions depends on design parameters of the apparatus 1 , but typically the ion trap 12 voltage is 10v - 30kV. The ion trap 12 voltage may also be adjusted to removed nuclei mode particles or even the smallest particles in the accumulation mode. The sample aerosol and the essentially clean gas mixed together are discharged from the apparatus 1 through the outlet 10 together with the ionized particles of the sample aerosol. The outlet 10 is provided in fluid communication with the ion trapping chamber 22 for exhausting the discharge flow B out of the apparatus 1 . The outlet 10 may be arranged to supply the discharge flow B back to the aerosol duct 1 1 or to ambient atmosphere or some other location.
Particles of the aerosol F in the aerosol duct 1 1 are monitored by measuring the electrical charge carried by the electrically charged particles of the sample aerosol flow A. In a preferred embodiment particles of the aerosol F are monitored by measuring the electrical charge escaping with the electrically charged particles from the apparatus 1 . The measurement of the charge carried by the electrically charged particles may be measured by many alternative ways. In one embodiment the charge carried by the electrically charged particles is measured by measuring the net current escaping from the sample outlet 10 To be able to measure the small currents, typically at pA level, the whole apparatus 1 is isolated from the surrounding systems.. An electrometer may be assembled between the isolated apparatus (i.e. a pint in the wall of body 17) and a ground point of the surrounding systems. With this kind of setup, the electrometer may measure the charge escaping from the isolated apparatus 1 together with the ionized particles. In other words this kind of setup measures the escaping current.
According to the present invention the apparatus 1 for monitoring particles in a channel or a space further comprises a particle separation arrangement arranged to separate from the sample aerosol flow A particles having mean diameter larger than D-i. The particle separation arrangement may be arranged to separate from the sample aerosol flow A particles having diameter Di larger than 5 μιτι, preferably larger than 3 μιτι and more preferably larger than 1 μιη. The particle separation arrangement may be further arranged to separate the particles having mean diameter larger than D by means of inertia separation. In other words the inertia or linear momentum of the particles in the sample aerosol flow is used for separating the particles having diameter larger than D-i. The separation of the particles having diameter larger than D are preferably separated before they enter the inlet chamber 4 of the apparatus 1 , or when they enter the inlet chamber 4, immediately after they have entered the inlet chamber 4 or in the inlet chamber 4.
Figure 2 shown one embodiment of the present invention in which the particle separation arrangement is arranged to separate particles 50 having mean diameter larger than Di by cyclonic separation. In this embodiment the inlet chamber 4 is at least partly cylindrical or conical. The particle separation arrangement is provided such that it utilizes the at least partly cylindrical or conical wall 5 of the inlet chamber 4 for separating particles 50 from the sample aerosol flow A. As shown in figure 2, the sample aerosol flow A is guided to an rotational flow path 26 in the inlet chamber 4 such that the particles 50 having diameter larger than D collide on the at least partly cylindrical or conical wall 5 of the inlet chamber 4 due to the inertial or linear momentum of the particles 50. To achieve this, the particle separation arrangement comprises the sample inlet 2 arranged to supply the sample aerosol flow A substantially tangentially or asymmetrically into the inlet chamber 4 such that the particles 50 having diameter larger than D are separated on the cylindrical or conical wall 5 of the inlet chamber 4 as the flow path 26 of the sample aerosol flow becomes rotational. The sample inlet 2 may be arranged tangentially to the inlet chamber 4 or alternatively the sample inlet 2 may be provided with a flow guide (not shown) to feed the sample aerosol flow A substantially tangentially into the inlet chamber 4. The rotational flow 26 of the sample aerosol flow A in the inlet chamber also enhances the mixing the sample aerosol flow A, and the essentially particle free ionized gas flow C, thus enhancing the ionization of the particles of the sample aerosol flow A. An additional benefit of the swirling flow is that it stabilities the mixed flow. This relaxes the tolerance demands of the nozzle feeding the ionized air.
In an alternative embodiment of figure 2 the inlet chamber 4 does not have an at least partly cylindrical or conical wall 5, but the inlet chamber 4 may be formed as rectangular or polygonal and the sample aerosol flow A is supplied to the inlet chamber 4 asymmetrically, towards wall 5 or substantially parallel to at least a portion of the wall 5 for providing the rotation flow path 26. In yet another embodiment the apparatus comprises a flow guide (not shown) provided to the sample inlet 2 such that the sample aerosol flow A is guided to a rotational flow path inside the sample inlet 2. The rotational flow path of the sample aerosol flow A in the sample inlet 2 causes the coarser particles 50 having diameter larger than D-i to collide on the walls of the sample inlet 2 due to the inertia and linear momentum. Thus the particles 50 having diameter larger than Di are separated in the sample inlet 2 by cyclonic separation.
Figure 3 shows an alternative embodiment of the present invention. Figure 3 shows a cyclone 80 having an at least partly cylindrical and/or conical separation chamber 28. The separation chamber 28 is provided with an inlet 2 through which the sample aerosol flow A is supplied to the separation chamber 28. The separation chamber 28 further comprises an cyclone outlet 30 through which particle separated sample aerosol flow A' is discharged from the separation chamber 28. The sample inlet 2 is provided to feed the sample aerosol flow A substantially tangentially or asymmetrically into the separation chamber 28 such that the sample aerosol flow A flows along a rotational flow path 26 inside the separation chamber 28. The particles 50 having diameter larger than D will collide to the walls 7 of the separation chamber 28 as they are not able to follow the rotational flow path 26 due to their inertia and linear momentum. The particles 50 having diameter larger than Di will thus impact on the wall 7 to be separated from the sample aerosol flow A by means of known cyclonic separation. The separated sample aerosol flow A', having particles with diameter larger than D removed, may be further supplied to the inlet chamber 4 of the apparatus 1 .
The above described separate cyclone separator 80 for separating from the sample aerosol flow A particles 50 having mean diameter larger than D may be arranged to the sample inlet 2 or in the inlet chamber 4. When the cyclone separator 80 is arranged to the inlet chamber 4 it is preferably provided in fluid communication with the sample inlet 2. Thus the separate cyclone separator 80 may be arranged in front of the sample inlet 2 such that the sample aerosol flow A enters directly the cyclone separator 80 when supplied into the inlet chamber 4.
Figure 4 shows another embodiment of the present invention in which the particle separation arrangement is arranged to separate the particles 50 having mean diameter larger than D by impaction separation. In the embodiment of figure 4 the particle separation arrangement comprises an impact surface 32 provided in the inlet chamber 4. The impact surface 32 is arranged in fluid communication with the sample inlet 2 such that the sample aerosol flow A supplied to the inlet chamber 4 is directed towards the impaction surface 32. In a preferred embodiment the impaction surface 32 is arranged in from of the sample inlet 2, as shown in figure 4. When directed towards the impaction surface 32 the sample aerosol flow A will change the direction of the flow such that it will flow past the impaction surface, as shown by the flow path 34 in figure 4. The impaction surface 32 forces the sample aerosol flow A to turn. The particles 50 having diameter larger than Di have too much inertia and linear momentum such that they are not able to follow the flow path 34 and they will collide on the impaction surface 32. Therefore the impaction surface 32 removes particles 50 having diameter larger than Di from the sample aerosol flow A by impaction separation. The impaction surface may be an impaction plate or the like and the may also be two or more impaction surfaces arranged in succession the flow direction of the sample aerosol flow A.
Figure 5 shows an alternative embodiment of impaction separation. Figure 5 shows a separate impactor 82 having an sample inlet 2 through which the sample aerosol flow A is supplied to the impactor 82, and an impactor outlet 40 through which separated sample aerosol flow A' is discharged from the impactor 82. The separated sample aerosol flow A' does not contain particles having diameter greater than D-i . In figure 2 the impactor 82 is shown as a cascade impactor having two impaction stages. It should however be noted that the impactor 82 may also comprise one or more than two impaction stages. Impactor 82 comprises a first impaction chamber 42 having a first impaction surface 32 and second impaction chamber 44 having a second impaction surface 36. Between the first and second impaction chamber 42, 44, there is an impaction nozzle 38 for supplying the sample aerosol flow A at a desired velocity the second impaction chamber 44. The sample aerosol flow A flows through the impactor 82 along the first flow path 34 flowing pass the impaction surfaces 32, 36. The largest particles 50 of the sample aerosol flow A will follow the second flow path 51 and collide to the first impaction surface 32 due to their inertia and linear momentum. After the first impaction surface 32 the sample aerosol flow A is conducted through the aerosol nozzle 38 in which the velocity of the sample aerosol flow A is increased towards the second impaction surface 34. The sample aerosol flow A will again turn and flow pass the second impaction surface 36 along the first flow path 34. The particles 52 of the sample aerosol flow A will follow the third flow path 53 and collide to the second impaction surface 36 due to their inertia and linear momentum. The particles 52 separated by the second impaction surface 36 are usually smaller than particles 50 The separation of the particles 50, 52 may be adjusted by adjusting the velocity of the sample aerosol flow A, impactor-nozzle dimensions and the location of the impaction surfaces 32, 36.
The above described separate impactor 82 for separating from the sample aerosol flow A particles 50, 52 having diameter larger than D may be arranged to the sample inlet 2 or in the inlet chamber 4. When the impactor 82 is arranged to the inlet chamber 4 it is preferably provided in fluid communication with the sample inlet 2. Thus the separate impactor 82 may be arranged in front of the sample inlet 2 such that the sample aerosol flow A enters directly the impactor 82 when supplied into the inlet chamber 4.
Figure 6 shows still another embodiment of the present invention in which the particle separation arrangement is provided with a virtual impactor 84 for separating from the sample aerosol flow A particles 50 having mean diameter larger than D-i . Figure 6 shows schematically a single-stage virtual impactor 84 having a sample inlet 2 through which the sample aerosol flow A is supplied to the virtual impactor 84. The virtual impactor 84 comprises an aerosol chamber 60 for receiving the sample aerosol flow A comprising particles 54 having diameter smaller than Di and particles 54 having diameter greater than D-i. The virtual impactor 84 further comprises an impaction nozzle 62 for feeding the sample aerosol flow A to the virtual impactor nozzle 56 through virtual impaction chamber 64. The virtual impaction nozzle 56 is arranged to separate particles 54 having diameter smaller than Di from particles 50 having diameter larger than Di by letting the particles 50 having diameter greater than Di to pass the virtual impactor nozzle 56. The virtual impaction chamber 64 comprises a first outlet 66 for supplying the separated sample aerosol flow A' to the inlet chamber 4 of the apparatus 1 . The particles 50 having diameter greater than Di are removed from the separated aerosol flow A'. Particles 50 having diameter greater than D go through the virtual impactor nozzle 56 into the collection chamber 68, from which they may be discharged as discharge flow D through discharge outlet 70. The particles 50 having diameter greater than D1 may also alternatively be stored to the collection chamber 68. The separate virtual impactor 84 may be arranged in the sample inlet 2 or in the inlet chamber 4 in direct fluid communication with the sample aerosol flow A.
The operating principles of cyclone, impactor and virtual impactor are generally know and thus they are not explained in detail, the separate particle separators described above may be provided to the sample inlet 2, substantially to the inlet opening of the inlet 2, inside the inlet chamber 4 just in front of the inlet 2 or inside the inlet chamber 4 in fluid communication with the sample aerosol flow A. Also in a preferred embodiment the particle separation arrangement is provided to separate from the sample aerosol flow particles 50, 52 having diameter D1 greater than 1 μιη.
The present invention further relates to a method for monitoring particles 54 in a channel 1 1 or a space comprising aerosol. The method comprises feeding essentially particle free ionized gas flow C to an ejector 24, sucking a sample aerosol flow A from the channel 1 1 or the space by means of the essentially particle free ionized gas flow C and the ejector 24, and mixing at least a fraction of the sample aerosol flow A with the essentially particle free ionized gas flow C for charging at least a fractions of the particles 54 of the aerosol. According to the present invention particles 50, 52 having diameter larger than D are separated from the sample aerosol flow A. The separation of the particles 50, 52 having diameter larger than Di may be carried out by means of inertia separation. The inertia separation on the other hand may be conducted by cyclonic separation or by impaction separation. Cyclonic separation may be carried out by a separate cyclone or by feeding the sample aerosol flow A tangentially or asymmetrically into the inlet chamber for separating the particles 50, 52 having mean diameter larger than D-i on the walls 5 of the inlet chamber 4. The impaction separation may be carried out by using one or more impaction surface 32, 36 for separating the particles 50, 52 having mean diameter larger than D-i. In an alternative embodiment the impaction separation is carried out by using one or more virtual impactors. In a preferable embodiment separating from the sample aerosol flow A particles 50, 52 having mean diameter larger than Di is carried out substantially before mixing the sample aerosol flow A with the essentially particle free ionized gas flow C.
The present invention further relates to use of inertia of particles 50, 52, 54 in a sample aerosol flow A for separating from the sample aerosol flow A particles 50, 52 having diameter larger than D-i. It is apparent to a person skilled in the art that as technology advanced, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.

Claims

Claims
1 . An apparatus (1 ) for monitoring particles (54) in a channel (1 1 ) or a space comprising aerosol, the apparatus (1 ) comprising:
- an inlet chamber (4);
- an ejector (24);
- gas supply (6, 16, 18) arranged to feed essentially particle free gas flow (C) to ejector (24) via the inlet chamber (4);
- a sample-inlet arrangement (2) arranged to provide a sample aerosol flow (A) from the channel (1 1 ) or the space into the inlet chamber (4) by means of suction provided by the gas supply (6, 16, 18) and the ejector (24); and
- a particle separation arrangement (80, 82, 84) arranged to separate from the sample aerosol flow (A) particles (50, 52) having mean diameter larger than D by means of inertia separation,
characterized in that the particle separation arrangement (80, 82, 84) is arranged to the sample-inlet arrangement (2) or in the inlet chamber (4) in direct fluid communication with the sample-inlet arrangement (2).
2. The apparatus according to claim 1 , characterized in that the particle separation arrangement (80) is arranged to separate the particles (50, 52) having mean diameter larger than D by cyclonic separation (80).
3. The apparatus according to claim 2, characterized in that the inlet chamber (4) comprises a substantially cylindrical or conical wall (5), and that the sample-inlet arrangement (2) is arranged to supply the sample aerosol flow (A) substantially tangentially or asymmetrically into the inlet chamber (4) such that the particles (50, 52) having mean diameter larger than D are separated on the cylindrical or conical wall (5) of the inlet chamber (4).
4. The apparatus according to claim 2, characterized in that the particle separation arrangement comprises cyclone separator (80) for separating from the sample aerosol flow (A) particles (50, 52) having mean diameter larger than D-,.
5. The apparatus according to claim 1 , characterized in that the particle separation arrangement (82, 84) is arranged to separate the particles (50, 52) having mean diameter larger than D by impaction separation (82, 84).
6. The apparatus according to claim 5, characterized in that the particle separation arrangement (82, 84) is provided with one or more impaction surface (32, 36) towards which the sample aerosol flow (A) is directed.
7. The apparatus according to claim 6, characterized in that the at least one of the impaction surfaces (32, 36) is arranged to the sample-inlet arrangement (2), or that at least one of the impaction surfaces (32, 36) is arranged to the inlet chamber (4) down stream of the sample-inlet arrangement (2) in direct fluid communication with the sample aerosol flow (A).
8. The apparatus according to claim 5, characterized in that the particle separation arrangement (82, 84) comprises an impactor or a cascade impactor (82) arranged in the sample-inlet arrangement (2) or in the inlet chamber (4) in direct fluid communication with the sample aerosol flow (A).
9. The apparatus according to claim 5, characterized in that the particle separation arrangement (82, 84) is provided with a virtual impactor (84) for separating from the sample aerosol flow (A) particles (50, 52) having mean diameter larger than D ; and that the virtual impactor (84) is in the sample-inlet arrangement (2) or in the inlet chamber (4) in direct fluid communication with the sample aerosol flow (A).
10. The apparatus according to any one of claims 1 to 9, characterized in that particle separation arrangement (80, 82, 84) arranged to separate from the sample aerosol flow (A) particles (50, 52) having mean diameter larger than D ; wherein D is 1 μιτι.
1 1 . The apparatus according to any one of claims 1 to 10, characterized in that the gas supply (6, 16, 18) arranged to feed essentially particle free ionized gas flow (C) to ejector (24) via the inlet chamber (4).
12. A method for monitoring particles (54) in a channel (1 1 ) or a space comprising aerosol, the method comprising:
- feeding essentially particle free ionized gas flow (C) to an ejector (24); - sucking a sample aerosol flow (A) from the channel (1 1 ) or the space by means of the essentially particle free ionized gas flow (C) and the ejector (24); and - mixing at least a fraction of the sample aerosol flow (A) with the essentially particle free ionized gas flow (C) for charging at least a fractions of the particles (54) of the aerosol; and
- separating (80, 82, 84) from the sample aerosol flow (A) particles (50, 52) having mean diameter larger than D by means of inertia separation,
characterized in that the separating means (80, 82, 84) generates a pressure drop which stabilizes the sample aerosol flow (A).
13. The method according to claim 12, characterized by separating the particles (50, 52) having mean diameter larger than D by cyclonic separation (80).
14. The method according to claim 13, characterized by directing the sample aerosol flow (A) tangentially or asymmetrically into the inlet chamber for separating the particles (50, 52) having mean diameter larger than D on the walls (5) of the inlet chamber (4).
15. The method according to claim 12, characterized by separating the particles (50, 52) having mean diameter larger than D by impaction separation (82, 84).
16. The method according to claim 15, characterized by directing the sample aerosol flow (A) towards one or more impaction surface (32, 36) for separating the particles (50, 52) having mean diameter larger than D-,.
17. The method according to claim 15, characterized by separating the particles (50, 52) having mean diameter larger than D in a virtual impactor.
18. The method according to any one of claims 12 to 17, characterized by separating (80, 82, 84) from the sample aerosol flow (A) particles (50, 52) having mean diameter larger than D ; wherein D1 is 1 μιτι.
19. The method according to any one of claims 12 to 18, characterized by separating from the sample aerosol flow (A) particles (50, 52) having mean diameter larger than D substantially before mixing the sample aerosol flow (A) with the essentially particle free ionized gas flow (C).
20. The method according to any one of claims 12 to 19, characterized by removing ions not attached to the particles (54).
21 . The method according to any one of claims 12 to 20, characterized by monitoring the particles (50) by measuring electrical current carried by the charged particles (54).
PCT/FI2011/050987 2010-11-12 2011-11-08 Apparatus and method for monitoring particles WO2012062964A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI20106194A FI20106194A0 (en) 2010-11-12 2010-11-12 Particle control device and method
FI20106194 2010-11-12

Publications (1)

Publication Number Publication Date
WO2012062964A1 true WO2012062964A1 (en) 2012-05-18

Family

ID=43268974

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FI2011/050987 WO2012062964A1 (en) 2010-11-12 2011-11-08 Apparatus and method for monitoring particles

Country Status (2)

Country Link
FI (1) FI20106194A0 (en)
WO (1) WO2012062964A1 (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014503077A (en) * 2011-01-18 2014-02-06 ペガソー オーワイ Particle monitoring apparatus and method
JP2017020802A (en) * 2015-07-07 2017-01-26 日本特殊陶業株式会社 Fine particle sensor
JP2017020803A (en) * 2015-07-07 2017-01-26 日本特殊陶業株式会社 Fine particle sensor
JP2017512305A (en) * 2014-02-14 2017-05-18 パーキンエルマー・ヘルス・サイエンシーズ・インコーポレイテッドＰｅｒｋｉｎｅｌｍｅｒ Ｈｅａｌｔｈ Ｓｃｉｅｎｃｅｓ， Ｉｎｃ． System and method for automated operation of a multimode inductively coupled plasma mass spectrometer
CN108717010A (en) * 2018-07-12 2018-10-30 清华大学深圳研究生院 A kind of device for generating and screening condensation aerosol
US10424469B2 (en) 2015-11-02 2019-09-24 Pegasor Oy Apparatus and method for particle measurement

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5431714A (en) * 1993-02-25 1995-07-11 Abb Research Ltd. Process for investigating particles situated in a gas
WO1998032001A1 (en) * 1997-01-22 1998-07-23 President And Fellows Of Harvard College Methods and apparatus for continuous ambient particulate mass monitoring
GB2346700A (en) * 1999-01-12 2000-08-16 Cambustion Ltd Particulate size detector
US6688187B1 (en) * 2002-09-10 2004-02-10 The Regents Of The University Of California Aerosol sampling system
US20060284077A1 (en) * 2005-05-23 2006-12-21 Tsi Incorporated Instruments for measuring nanoparticle exposure
WO2009109688A1 (en) * 2008-03-04 2009-09-11 Pegasor Oy Particle measurement process and apparatus

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5431714A (en) * 1993-02-25 1995-07-11 Abb Research Ltd. Process for investigating particles situated in a gas
WO1998032001A1 (en) * 1997-01-22 1998-07-23 President And Fellows Of Harvard College Methods and apparatus for continuous ambient particulate mass monitoring
GB2346700A (en) * 1999-01-12 2000-08-16 Cambustion Ltd Particulate size detector
US6688187B1 (en) * 2002-09-10 2004-02-10 The Regents Of The University Of California Aerosol sampling system
US20060284077A1 (en) * 2005-05-23 2006-12-21 Tsi Incorporated Instruments for measuring nanoparticle exposure
WO2009109688A1 (en) * 2008-03-04 2009-09-11 Pegasor Oy Particle measurement process and apparatus

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014503077A (en) * 2011-01-18 2014-02-06 ペガソー オーワイ Particle monitoring apparatus and method
JP2017512305A (en) * 2014-02-14 2017-05-18 パーキンエルマー・ヘルス・サイエンシーズ・インコーポレイテッドＰｅｒｋｉｎｅｌｍｅｒ Ｈｅａｌｔｈ Ｓｃｉｅｎｃｅｓ， Ｉｎｃ． System and method for automated operation of a multimode inductively coupled plasma mass spectrometer
US10181394B2 (en) 2014-02-14 2019-01-15 Perkinelmer Health Sciences, Inc. Systems and methods for automated optimization of a multi-mode inductively coupled plasma mass spectrometer
JP2017020802A (en) * 2015-07-07 2017-01-26 日本特殊陶業株式会社 Fine particle sensor
JP2017020803A (en) * 2015-07-07 2017-01-26 日本特殊陶業株式会社 Fine particle sensor
US10424469B2 (en) 2015-11-02 2019-09-24 Pegasor Oy Apparatus and method for particle measurement
EP3371570A4 (en) * 2015-11-02 2019-10-09 Pegasor Oy Apparatus and method for particle measurement
CN108717010A (en) * 2018-07-12 2018-10-30 清华大学深圳研究生院 A kind of device for generating and screening condensation aerosol
CN108717010B (en) * 2018-07-12 2020-09-22 清华大学深圳研究生院 Device for generating and screening atomized aerosol

Also Published As

Publication number Publication date
FI20106194A0 (en) 2010-11-12

Similar Documents

Publication Publication Date Title
WO2012062964A1 (en) Apparatus and method for monitoring particles
EP2659257B1 (en) Apparatus for monitoring particles in an aerosol
KR101556252B1 (en) Particle measurement process and apparatus
US9140653B2 (en) Spark emission particle detector
KR200478194Y1 (en) Apparatus for monitoring fine particle concentration
US9574986B2 (en) Apparatus and process for producing acknowledged air flow and the use of such apparatus in measuring particle concentration in acknowledged air flow
US20150102822A1 (en) Particle count measurement device
CA2317830C (en) Particle concentrator
US20030052281A1 (en) Apparatus to collect, classify, concentrate, and characterize gas-borne particles
JP3189910U (en) Particle monitoring device
JP2008542721A (en) Nanoparticle contact measuring device
EP2666007B1 (en) Apparatus and method for monitoring particles
FI126815B (en) PARTICLE MONITORING DEVICE
JP2006349414A (en) Device and method for measuring charged amount distribution

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 11840533

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 11840533

Country of ref document: EP

Kind code of ref document: A1