Abstract:
Embodiments of the present invention relate to an electrostatic collection device and method for extracting impurities from gas. The collection devices includes at least one electrical field for charging particles, where the particles are in a gas, and at least one collection surface for collecting charged particles. The device further includes at least one heating element for heating the at least one collection surface to vaporize the collected particles.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND 
       [0003]    In many instances, it is necessary to determine impurities in a gas, such as air. For instance, collection and testing of a gas sample may be done to determine if any biological and chemical warfare agents are present in the sample. For instance, government facilities, mail rooms, high-profile events, transportation and urban areas may monitor the air for biological and chemical warfare agents. 
         [0004]    Collection and testing of air may also be done to determine whether any environmental toxins are present in the air. For example, indoor and outdoor environments may be sampled to determine environmental impurities present in the air. Impurities may include, micro and submicron bioaerosols, target airborne pathogens, including viruses and bacteria, as well as some explosive vapors and certain chemicals. 
         [0005]    Many current detection techniques require impurities in a gas, such as air, to be concentrated before analysis. Previous methods of concentrating impurities in air have employed filtering technology and collection of impurities in a liquid medium. These prior methods present serious disadvantages of both lowered extraction efficiency and are limited as to the type of particles that may be collected. 
       SUMMARY 
       [0006]    In one embodiment, a collection device for collecting particles from a gas is provided. The device comprises at least one electrical field for charging particles, where the particles are in a gas and at least one collection surface for collecting charged particles. The device further comprises at least one heating element for heating the at least one collection surface to vaporize the collected particles. In one embodiment, the collected particles are biological organisms that pyrolize when the collection surface is heated. 
         [0007]    In another embodiment, a collection device for collecting particles from a gas is provided. The collection device comprises at least one passage defined by a wall and at least one electrical field in the at least one passage for charging particles, where the particles are in a gas. The device further comprises at least one collection post for collecting charged particles, where the at least one collection post is located within the at least one passage and at least one heating element for heating the at least one collection post to vaporize the collected particles. 
         [0008]    In yet another embodiment, a method of extracting impurities from a gas is provided. At least one air passage defined by a wall and at least one electrical field within the at least one air passage are provided. Gas having particles through the at least one electrical field to charge the particles in the gas and at least some of the charged particles are collected onto a collection surface. The collection surface is heated to vaporize at least some of the collected particles. 
         [0009]    In still another embodiment, a method for visual examination of impurities from a gas is provided. At least one air passage defined by a wall and at least one electrical field within the at least one air passage are provided. Gas having particles is passed through the at least one electrical field to charge the particles in the gas and at least some of the charged particles are collected onto a collection surface. A visual inspection of the collection surface is performed to view at least some charged particles collected on the collection surface. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    The present invention is described in detail below with reference to the attached drawing figures, wherein: 
           [0011]      FIG. 1  is a perspective view of a collection device constructed in accordance with an embodiment of the invention; 
           [0012]      FIG. 2  is a side plan view of a collection device constructed in accordance with an embodiment of the invention with a portion of the body device removed in accordance with an embodiment of the present invention; 
           [0013]      FIG. 3  is an exploded view of a corona charging zone in accordance with an embodiment of the present invention; 
           [0014]      FIG. 4  is a side plan view of a non-perforated collection post in accordance with an embodiment of the invention; 
           [0015]      FIG. 5  is a side plan view of a perforated collection post in accordance with an embodiment of the present invention; 
           [0016]      FIG. 6  is a graphical representation of collection efficiency of a collection device in accordance with an embodiment of the present invention; 
           [0017]      FIG. 7  is a graphical representation of a sample collection cycle in accordance with an embodiment of the present invention; 
           [0018]      FIG. 8  is a perspective view of a collection device constructed in accordance with an embodiment of the invention; 
           [0019]      FIG. 9  is a perspective view of a collection device and corona charging zone constructed in accordance with an embodiment of the present invention; and 
           [0020]      FIG. 10  is a perspective view of a collection device in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Embodiments of the present invention relate to an electrostatic device that utilizes electrostatics to collect particles from gas, such as air. The particles are collected onto a collection surface such as walls or a collection post to concentrate the particles. The particles collected may be analyzed by visual inspection of the collection surface and/or heating the collection surface to vaporize the particles for subsequent detection by a downstream collector. Target particles collected may include, but are not limited to, biologicals, such micron and submicron bioaerosols, molds, pollen, fungi, bacteria, viruses and bacteriophages, chemicals such as low vapor pressure chemicals (LVPCs), explosives, toxins and other particles. 
         [0022]    With reference to  FIGS. 1 and 2 , one embodiment the present invention relates to an electrostatic device  10  for the collection and concentration of particles. The device  10  comprises an air passage  16 , at least one corona charging zone  18 , a collection post  22 , an air mover  14  and housing  12 . The device  10  brings gas, such as air, into the primary air passage  16  utilizing the air mover  14 , passing the air through primary air passage  16  and at least one charging zone  18  and forcing airborne particles onto collection post  22 . The electrostatic device  10  concentrates particles in the air to a concentrically located post  22  to obtain particle concentration. 
         [0023]    With reference to  FIG. 3 , a corona charging zone  18  is created by a plurality of electrodes  24 . A series of electrodes  24  are spaced substantially equal angular distances on or within a duct  17  forming the primary air passage  16 . Each series of electrodes  24  forms a row  19  of electrodes. The electrodes  24  are used to create multiple ion streams  26  forming a corona charging zone  18  within the primary air passage  16  surrounding collection post  22 . The amperage for each electrode may be about 0.5 to 5 Microamps with a nominal of 1 microamp being preferred. The corona charging zone  18  may be a substantially uniform electrical field. In the present embodiment, the corona charging zone  18  is shown as being round, however, it may be a variety of shapes, including polygonal, square, rectangular and oval. It will be appreciated that charging zone may be created in a variety of ways. An exemplary charging zone  18  is described in described in U.S. Patent Application Publication No. 2004/0179322, the entirety of which is hereby incorporated by reference. 
         [0024]    Multiple rows  19  of electrodes  24  may be used to help improve collection efficiency. Each additional row of electrodes  19  improves collection efficiency by increasing the plasma area of the corona charging zone  18 . There are three rows  19  of electrodes  24  shown in  FIGS. 1 and 2 . It will be appreciated that device  10  may have any number of electrodes  24  and rows  19  of electrodes  24 . 
         [0025]    Exemplary collection post  22  is shown in  FIG. 4 . The exemplary collection post  22  in  FIG. 4  is a non-perforated post that has a domed or curved hemispherical top. Collection post  22  may be of any diameter depending of the flow rate of the air through the air passage  16  and the voltage used to control the device  10 . For instance, the post  22  may be about 0.125 to about 0.75 inches in diameter. In the electrostatic device  10 , the majority of the charged particles are collected on the tip of the collection post  22 . However, one of skill in the art will appreciate that the particles may be collected on any part of the collection post  22 . 
         [0026]    More than one post  22  may be located in the electrostatic device  10 . The collection post  22 , while shown as being round, may be polygonal, rectangular, square or any variety of other shapes. Round is preferred, however, to minimize the occurrence of reverse corona generation which can affect collection efficiency. The one or more collection posts  22  may be removable. It will be appreciated that the post  22  may be non-perforated or perforated. 
         [0027]    To improve the particle collection, or enable the ability to collect vapors, on the surface of the collection post  22 , a chemical adsorbent may be used to coat the surface of the collection post  22 . Exemplary chemical adsorbents may include polymers such as polyether ether ketone and polytetrafluoroethylene. 
         [0028]    Referring again to  FIGS. 1 and 2 , the air passage  16  may be formed by enclosure such as walls or a duct  17 . While the air passage  16  of  FIGS. 1 and 2  is formed by a round duct, the primary air passage may be any variety of shapes including polygonal, square, rectangular and oval. The primary air passage  16  surrounding the collection post  22  may any size necessary for collection. In one embodiment, the air passage  16  is about 1-2 inches in diameter and the collection post is about 0.125 to 0.75 inches in diameter. 
         [0029]    Housing  12  encases the air passage  16 , corona charging zone  18 , collection post  22  and air mover  14 . It will be appreciated that housing  12  may be any type including modular housing. Air mover  14  may be any variety of air movers, including fans. Exemplary air movers include commercial, of the shelf fan, such as small muffin fans like those generally used to aid in the cooling of computer processors. 
         [0030]    Utilizing a muffin fan, the sampling flow rate for the collection device  10  can be varied from about 20 to 100 L/min with a collection efficiency about &gt;90% for 1 μm particles at a flow rate of about 20 L/min.  FIG. 6  shows efficiency vs. flow rate for about 2.3 μm particle diameter for one embodiment. As can be seen from  FIG. 6 , exemplary collection efficiency is near linear with flow rate. Collection efficiencies range from about 60% to 80% for particle diameters between about 0.5 μm and 2 μm, respectively. The target particulate size is in the range of about 0.5 to 10 μm in diameter. It will be appreciated that the flow rate, collection efficiency and target particle size collected by device  10  may vary dependent on device configuration. 
         [0031]    A variety of power supplies may be utilized to power collection device  10 . The power supplies include internal and external power supplies. The power supply may power the air mover  14 , electrodes  24 , heating of the collection post  22  and removal of the vaporized particles. 
         [0032]    After collection is completed, particles collected on the collection post  22  may be analyzed by 1) visual inspection of the collection post  22  and/or 2) heating the collection post  22  to vaporize the collected particles for subsequent detection by a downstream collector. 
         [0033]    For visual inspection, the particles are concentrated onto small collection surface, such as collection post  22 , for visual inspection. The decreased size of the collection surface allows more collected particles to be viewed by visual inspection. Visual inspection may be aided by the use of microscopes, raman laser interrogation, UV spectroscopic techniques and the like. 
         [0034]    The heating of the collection post  22  after collection converts collected particles into a vapor form usable by detectors, such as chemical detectors, mass spectrometry (such as a MEMS mass spectrometer), and ion mobility spectrometry. The detectors may be part of the collection device  10  or may be located separate from the collection device  10 . 
         [0035]    The heating method used to heat the collection post  22  may vary depending on the target particle(s) to be vaporized for collection. Different particles will vaporize at different temperatures and vapor pressure. For instance, the collection post  22  may be continuously heated to just below the vaporization temperature of the target material during and/or after collection. This is done to avoid concentration of “interferent” particles while still allowing the concentration of the target particles. Alternatively, the collection post  22  may be heated slowly after collection. For quick vaporization of collected particles, the collection post  22  may be rapidly heated after collection. The collection post  22  may be heated in stages at different temperatures to obtain the vapor from selected particles at varying time periods or to find out more information about the collected particles. The vaporization temperature of the particles depends on its chemical makeup, for instance readily available pesticides may vaporize between 160 and 250° C., while biological organisms may pyrolize at or above 400° C. 
         [0036]    Heating of collection post  22  may be done in a variety of ways including, but not limited to, an internal cartridge heater, coil heating, contact heating, and laser ablation of particles on collection surface. 
         [0037]    By way of example, and not by limitation, a COTS heating element is utilized to heat the collection post after the collection process is complete. Because of the small size and low mass of the collection post  22  as well as heating unit, the ramp rate is targeted to be 15° C,/second enabling the post to change from about 0° C. to 200° C. in less than 15 seconds. After the collection post  22  has met the targeted maximum temperature it dwells for a brief pre-determined period of time to ensure that all material has been vaporized. 
         [0038]    Vaporization of particles can occur in fixed air volume contained or moved through the air passage  16 . The concentration of vapor from the particles will depend on the airflow rate. 
         [0039]    Once the particles have been vaporized, the resulting vapor is drawn through either an external port in the device  10  or through the existing outlet by the air mover  14 , or through perforations in the collection post for subsequent detection. The transport of the vapor will be controlled either through a secondary port on the side of the device  10 , or by the primary exit by re-activating the air mover  14 . 
         [0040]    By way of example, an not by limitation, in order to meet a target time of about two minutes for start to alarm for detection—the collection, concentration, and thermal desorption of target particles is less than about 1 minute and 30 seconds. To achieve this target, the projected maximum cycle time for each phase of the collection device is about 45 seconds for collection/concentration, about 30 seconds for thermal desorption, (heating of collection post  22 ) about 15 seconds for vapor transfer and about 30 seconds for the collection post  22  to cool-down. This exemplary cycle is shown in  FIG. 7 . In some instances, to reduce the time to the next detection cycle, collection may resume during the cool-down portion. This overlap can reduce the perceived collection cycle and ensure that a two minute time limit is met consistently. It will be appreciated, however, that the time for collection/concentration, heating of collection post  22 , vapor transfer and cool-down may vary according to need and may be any amount of time. As such, heating and collection may occur continuously and concurrently which would allow continuous collection and conversion of collected material, albeit at the expense of concentration performance. 
         [0041]    The exemplary collection post  23  in  FIG. 5  is a perforated collection post  23 . The perforated collection post  23  may allow for a more concentrated sample to be collected. It will be appreciated that device  10 , when used with a perforated or nonperforated post may be any size. For instance, the device  10  utilized with a perforated post may be less than about twenty cubic inches. With the perforated collection post  23 , the primary airflow is approximately 50 L/per minute and flows past the perforated collection post  23  located centrally in the flow path. A small portion of the air flows through the perforated collection post  23 . The particles suspended in the air become charged as they near the corona charging zone  18  formed by the electrodes  24 . 
         [0042]    The charged particles are attracted by electrostatic forces and are collected on the perforated collection post  23  in the center of the device  10 . The particles are collected on the perforated post  23  until the desorption cycle is initiated. After the post  23  is heated, vapors are drawn through the perforated post  23  and directly into a transfer tube connected at the base of the post and in communication with the inside of the post (not shown), rather than being allowed to fill the primary air passage  16  and device  10  volume before being drawn off. This allows for increased concentration of particles in the desorption vapor. The vapor may then be transferred to a vapor based detection system, or collected in standard available chemical sampling sorbent tubes for storage, transport, or later analysis. 
         [0043]    The perforated post may be heated in a variety of ways including a coiled heater that allows the perforated collection post  23  to be heated quickly to convert the captured particles into vapor rapidly. The perforated collection post  23  may be heated after collection, continuously or in steps. Any number of rows of electrodes may be utilized, preferably, with a perforated post  23  two rows of electrodes are utilized to reduce costs and power consumption. 
         [0044]    It will be appreciated that the electrostatic device  10  described typically uses lower power than other electrostatic applications, primarily due to a current control feedback method which maintains proper power to the array. Furthermore, the radial collector geometry of the electrostatic device  10  shown in  FIGS. 1 and 2 , allows for small collection area improving concentration of the collected particles. 
         [0045]    With reference to  FIGS. 8 ,  9  and  10 , in alternative embodiment the present invention, an electrostatic device  30  for the collection and concentration of particles is shown. The electrostatic device  30  utilizes a long rectangular system geometry and a linear electrode array  37 . 
         [0046]    The device  30  comprises an air passage  52 , at least one corona charging zone  54 , a collection surface  38 , an air mover  50 , shutters  34  and  36  and housing  56 . The device  30  brings a gas, such as air, into primary air passage  52  utilizing air mover  50 . Air mover  50  draws gas, such as air, through the air passing  52  with the shutters  34  and  36  open. The electrodes  48  create at least one corona  54  as shown in  FIG. 9 . For example, at least one corona charging zone  54  emanates from each electrode  48  and terminates at collection surface  38 . As air is flowed  44  through air passage  52 , particles in the air are charged by the at least one corona charging zone  54  and are attracted to the collection surface  38  adjacent and opposite to corona electrodes  48 . 
         [0047]    With reference to  FIG. 9 , each corona charging zone  54  is created by at least one electrode  48 . A substantially uniform corona charging zone  54  is created between each electrode  48  and the opposite collection surface  38 . In this embodiment, electrodes  48  are positioned linearly  37  substantially equidistance from each other along a wall  58 . Wall  58  creates the primary air passage  52 . The corona charging zone  54  may be a substantially uniform electrical field. In the present embodiment, the corona charging zone  54  is shown as being the same shape as the wall  58  creating air passage  52 . The corona charging zone  54  may be a variety of shapes, including polygonal, square, rectangular and oval. A three dimensional effect of the corona charging zone  54  may be created near wall  58  adjacent to the electrodes  48  and cause corona charging zone  54  to warp towards wall  58  adjacent to electrodes  48 . An exemplary charging zone  58  is described in U.S. Patent Application Publication No. 2004/0179322. 
         [0048]    Air passage  52  is formed by an enclosure such as walls  58  or a duct. Air passage  52  may be any shape including, round, polygonal, square, rectangular and oval. The air passage  52  may be any size necessary for collection. 
         [0049]    The walls  58  or the primary air passage  52  may also serve as a collection surface  38  as shown in  FIGS. 8-10 . It will be appreciated that collection surface  38  may be formed by a single wall or duct or may be formed by multiple walls or pieces. This collection surface may also be perforated, if desired. To improve the particle collection on the collection surface  38 , an adsorbent may used to coat the collection surface  38 . The adsorbent may enable the collection of gas and vapors on collection surface  38 . Exemplary adsorbents may include polymers such as polyether ether ketone and polytetrafluoroethylene. 
         [0050]    Housing  56  encases the primary air passage  52 , one or more corona charging zones  48 , collection surface  38  and air mover  50 . It will be appreciated that housing  56  may be any type including modular housing. Air mover  50  may any variety of air movers, including fans. Exemplary air movers include a COTS fan. 
         [0051]    Utilizing an air mover, the sampling flow rate for the collection device  30  can be varied depending on the efficiency needed. It will be appreciated that the flow rate, collection efficiency and target particle size may vary. 
         [0052]    A variety of power supplies may be utilized to power the collection device  30 . The power supplies include internal and external power supplies. Exemplary power supplies may power one or more of the air mover, electrodes, heating of the collection surface and removal of vaporized particles. 
         [0053]    After collection is completed, particles collected on the collection surface  38  may be analyzed by 1) visual inspection of the collection surface and 2) heating the collection surface to vaporize the collected particles for subsequent detection by a collector. 
         [0054]    For visual inspection, the particles are concentrated on the collection surface  38  for visual inspection. Visual inspection may be aided by the use of microscopes and the like. 
         [0055]    The heating of the collection surface  38  after collection converts collected particles into a vapor form usable by detectors, such as chemical detectors, mass spectrometry, ion mobility spectrometry, and differential mobility spectrometry. The detectors may be part of the collection device or may be located separately from the collection device  30 . 
         [0056]    The heating method used to heat the collection surface  38  may vary depending on the target particle(s) to be vaporized for collection. Different particles will vaporize at different temperatures and vapor pressure. For instance, the collection surface  38  may be continuously heated during and/or after collection, just below the vaporization temp of the target material to avoid concentration of “interferent” particles while still allowing the concentration of target particles. The collection surface  38  may be heated slowly after collection. For quick vaporization of the collected particles, the collection surface  38  may be rapidly heated after collection. The collection surface  38  may also be heated in stages and at different temperatures to obtain the vapor from selected particles at varying time periods or to find out more information about the collected particles. 
         [0057]    It will be appreciated that conversion of collected particles on collection surface  38  may occur continuously or after air mover  50  has stopped. When conversion of captured particles on collection surface  38  is desired after air mover  50  is stopped, collection surface  38  is heated to drive off the collected particles as a vapor with the shutters  34  and  36  closed to minimize escape of the desorbed vapor. 
         [0058]    The heating of collection surface  38  may be done in a variety of ways, including, but not limited to, utilizing an internal cartridge heater and/or a coil heater, contact heating, laser ablation of particles on the collection surface. 
         [0059]    Once the particles are driven off as vapor, the vapor  46  may be transferred via transfer port  40 . The vapor  46  may be transferred to a variety of detectors or may be collected as a sample. Although transfer port  40  is shown as being centrally located in the collection device  30 , it will be appreciated that the transfer port  40  may be located anywhere within the device  30 , upstream of air mover  50 . Device  30  allows for a high collection area and high capture and conversion efficiency. 
         [0060]    From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent in the structure. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.