Apparatus for detection of phosphorus or sulfur containing vapors or aerosols
United States Patent 1 1 Haas [ Apr. 15, 1975 APPARATUS FOR DETECTION OF PHOSPHORUS 0R SULFUR CONTAINING VAPORS OR AEROSOLS [75] Inventor: Edward C. Haas, Rapid City, S.  
 Dak.  
 [73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.  
 [22] Filed: Feb. 21, 1968 [21] Appl. No.: 707,926  
 [58] Field of Search 23/254, 255, 232, 230 PC, 23/253 PC; 250/71; 88/14 SE; 356/87, 187;  
 3,807,863 4/1974 Raillere et al. 431/126 X Primary Examiner-Benjamin R. Padgett Assistant ExaminerE. A. Miller Attorney, Agent, or Firm-Richard S. Sciascia; Arthur A. McGill; Prithvi C. Lall [57] ABSTRACT A hydrogen burner capable of detecting phosphorous and sulfur-bearing vapors and aerosols. The burner is a block of aluminum with borings within forming burning chambers and a flame channel. The air sample and hydrogen gas are drawn through at a high velocity which requires burning in a first chamber to eliminate the excess oxygen and then a second burning near a narrow flame channel, the flame being drawn into the flame channel and the reducing portion thereof being observable through a viewing port. The  
 431/4, 126 burner is cooled by a water-circulating system.  
  The air contaminant is detected by utilizing the [56] References C&#39;ted chemiluminescence phenomenon. The light emitted UNITED STATES PATENTS by the reducing portion of the flame is passed through 2,203,036 6/1950 Van Briessen et al 88/14 a two-color (blue and g rotatory. color filter 3,174,393 3/1965 Dewey et al. 88/14 which allows pulses of different intensity to strike a 3,213,747 10/1965 Van Der Smissen 23/232 phototube. The difference in intensity is amplified and 3,239,311 Luehrmann 8t 31. 23/254 used to activate some type of indicator or alarm 3,428,401 2/1969 Buzza 356/187 3,489,498 1/1970 Brody et a1. 356/187 7 Claims, 7 Drawing Figures F.%7PAE//p P40707085 65 l l o 60 keMoTe flMFA $76K [Na/6&#39;97? i Pan/5 SUPPLY :3&#34;  
 [Now/170R APPARATUS FOR DETECTION OF PHOSPI-IORLS OR SULFUR CONTAINING VAPORS OR I AEROSOLS The invention described herein may be manufactured and used by or for the Government ofthe United States of America for governmental purposes without the payment of any royalties thereon or therefor.  
  This invention relates to means for detecting airborne contaminant elements which emit characteristic colors while burning chemiluminescently and especially to such means which utilizes a novel reducing burner.  
  Military and naval activities have an interest in the detection of poisonous gases. especially the vapors or aerosols of phosphorusor sulfur-containing compounds. Various methods of detection are possible but do not meet the stringent requirements for high stability. reliability and resistance to extreme environmental conditions such as shock. vibration. and atmospheric conditions which may occur in the naval service. for example.  
  One method of detecting the presence of a chemical element such as phosphorus or sulfur is by means of the color spectrum it emits when it is burned. Phosphorus and sulfur (in addition to some other elements) exhibit the phenomenon of chemiluminescence when exposed to free radicals in a hydrogen-rich flame. The emission spectrum for hydrogen shows approximately equal emission in blue and green light; that for phosphorus is higher in green than in blue; and that for sulfur is higher in blue than in green.  
  Problems which must be solved in the ordinary burner when it is employed under harsh naval conditions include reduction of background light which interferes with the detection of low concentrations of phosphorus and sulfur. reduction of flame flicker which sets the detection sensitivity at a level not lower than the highest background level and stabilization of the flame against sudden pressure changes such as those caused by shell blasts.  
  An object of this invention is to provide a burner capable of being used to detect airborne contaminant elements such as phosphorus and sulfur. said burner being reliable. insensitive to sudden pressure changes and rapid and sensitive in its detection of the contaminant elements.  
  The objects and advantages of this invention are accomplished by a detection system which utilizes a hydrogen burner in which the velocity of the gases. the flame temperature and the level of background light are carefully controlled to provide the desired results. A viewing port. placed at the proper point in the flame channel. permits the flame to be viewed. The light emitted by the flame is choppedby a rotating optical filter of two different colors and the difference in intensity of the filtered colors is utilized to provide an indication of the presence of the sought-for contaminant in the air sample.  
  Other objects and advantages will appear from the following description of an example of the invention. and the novel features will be particularly pointed out in the appended claims.  
 In the accompanying drawings:  
 FIG. I is an isometric illustration of the reducing burner;  
  FIG. 2 is a schematic showing of a cross-sectional side view of the burner of FIG. I taken vertically through the viewing port.  
  FIG. 3A is a mechanical drawing showing the construction of the lower two sections of the burner:  
  FIG. 3B is a mechanical drawing showing a top view of FIG. 3A:  
  FIG. 4 is a bottom view of the rectangular section which fits over the viewing port of the burner:  
  FIG. 5 is a schematic showing the detection system components: and  
  FIG. 6 is an isometric illustration of a burner which can be used to simultaneously detect both phosphorusand sulfur-bearing air contaminants.  
  The phenomenon of chemiluminescence. which is the emission of light when certain chemical elements burn in a hydrogen-rich flame. can be used to detect the presence of these elements-by utilizing the colors of the emitted light. Both phosphorus and sulfur chemiluminescence. Carbon and hydrogen give emission spectrograms comparable to sulfur in dispersion but far lower in intensity. About 1000 times as much carbon is required to equal the emission given by phosphorus and the maximum amount of hydrogen which will burn in air produces a flame luminance merely equal to the signal produced by phosphorus at a concentration of 0.01 micrograms per liter of air burned.  
  There is a difference in intensity of emission of blue and green light by phosphorus. the intensity of the green light being greater than that of the blue (for sulfur. the reverse is true). This difference in intensity permits detection of the presence of vaporous or aerosolic phosphorus or phosphorus-bearing compounds in the air. as will be explained hereinafter in connection with FIG. 5. I  
  The reducing burner I0 which is used is shown in FIG. I. It consists of a substantially rectangular. rigid block which may be made of aluminum. for example. The block is sectioned for ease of assembly and disassembly and for ease of boring. There is in the top section an air inlet (sample-in) port 12., a hydrogen inlet (hydrogen-in) port 14 and a water outlet (water-out) port 16. The middle section contains an ignitorelectrode port 18. The bottom section contains a water inlet (water-in) port 20 and a gas exhaust port 22. It also contains a viewing port 24 formed by undercutting the front of the rectangular block down to the flame channel connecting the hydrogen-in port 14 with the exhaust port 22.  
  The burner comprises a first-stage burner and a second-stage burner. The first stage burner can be considered to include a wide first-burner inlet channel 32 through which hydrogen is drawn from the left (see FIG. 2) and air from the right. the burner chamber 34 and a narrow first-burner exhaust channel 36. Arrows show the direction of gas flow in these channels.  
  The second-stage burner can be considered to include the second-burner chamber 38 the bottom of which includes a boring in which the ignitor electrode 18 is located. the narrow flame channel 26 and the exhaust chamber 40.  
  A water channel 42 connects the water-in port 20 to the water-out port 16.  
  FIGS. 3A and 3B are mechanical drawings showing the bottom two sections of the reducing burner in front and top view. respectively. The view shown in FIG. 3A is a 90 clockwise rotation of the view shown in FIG. 2.  
  The rectangular viewing-port cover 44 for the undercut portion of the reducing burner is shown in bottom view (i.e.. the side shown is that which fits into the undercut) in FIG. 4. A rubber gasket 46 encloses the cir cumference of an oval-shaped pane .of glass or window 48 and these are glued or otherwise fastened to the cover 44. The gasket 46 fits into the oval undercut 30 so that the viewing port 24 is covered by the glass window 48.  
  The problems encountered in designing this burner to obtain the required characteristics are solved by rapid mechanical mixing of gas and air. proper cooling and high flame velocity. To obtain the necessary chemiluminescence reaction. burning must take place in the reducing zone ofthe flame. In the normal flame. the sample. which enters with an excess of oxygen. is converted to an oxide and swept out of the flame in the oxidizing sheath. Three methods of rapid mechanical mixing of air and hydrogen are used. The principal method is by turbulent flow along a surface and this is augmented by some cross-jet action between the hydrogen gas coming down thru chamber 38 and the partially burned sample coming t-hru channel 36 and by premixing of the hydrogen-and-air sample delivered by the first-stage burner. The air sample enters with such velocity that excess oxygen is present. The first-stage burner uses up some of this excess oxygen and the rest of the sample is burned in the reducing flame of the second-stage burner.  
  Flame variability normally changes the intensity of the flame background light by a factor of two. with a 5 second or greater time constant. when using burners having a flame channel diameter of A inch or greater. This effectively sets the detection sensitivity at a level not lower than this background unless some form of compensation is employed. which is not easily accomplished with a random variable such as flame flicker. Accordingly. action is taken in the present burner to reduce the background level of light to the lowest possible intensity and to minimize the effect of flame fluctuations.  
  The background light cannot be reduced below the level set by chemiluminescence of hydrogen. However. increase of the background by thermal excitation and emission of other substances in the hotter. oxidizing portion of the flame where fuel-air mixing begins can be avoided by excluding this zone from view of the phototube. Increased light due to incandescence of heated surfaces may be prevented by adequate cooling of the burner. Cooling is accomplished by thermal conduction through the aluminum body of the burner to a heat sink and is supplemented by circulating water thru the body. Excessive cooling is avoided to prevent the condensation of water vapor formed by the hydrogenoxygen combustion. Cooling is also required to keep the interior surfaces which are exposed to the flame below 350 C. to avoid decomposition of the hydride of phosphorus which produces the characteristic green emmission.  
  It is very difficult to prevent flame flicker but. by increasing flame velocity. flicker frequency can be increased. With greater than l00 feet per second flow of gas in the flame channel. the flicker-effect time constant is reduced below 0.1 second. At a light-chopping frequency of 5 cycles per second, dwell time per filter segment is 0.1 second (this is with a circular filter having two semicircular segments). This is greater than the average light variation cycle so that these variations are cancelled to a large extent. Starting with a gas pump of a fixed pumping rate. the rate of flow of the gas in the flame channel can be varied by varying the diameter of i the gas channel. With the particular pump used. it was found that a flame channel of approximately /4 inch diameter would provide the desired gas velocity.  
 In addition to reducing the effect of flame. flicker. the  
 high velocity flame has other advantages. Of first im-. portance is the fact that interference from sulfur. is:  
 along the flame channel below the first viewing port and to utilize the proper viewing filter and associated equipment as will be explained below:  
 Additionally. the blowtorch-like flame confined in a channel burns in any direction. which makes it insensitive to the inclination of the burner. By directing the flame downward as in the present invention. condcn-l sates and aerosols are eliminated more quickly with less effect on flame stability.  
 Further, the high velocity of the flame makes it much more stable when subjected to blasts or other sudden pressure changes.  
  The special-purpose use for which this burner is intended requires a response within five seconds when the phosphorus concentration of the sampled air is one microgram per liter or greater. Sincethe phosphorus reacts almost instantaneously in the flame. any delay in. response is caused primarily by holdup through sorption of the contaminant on the exposed surfaces of the sample intake. In general. this delay becomes excessive when an air pump is placed in the intake line to forcefeed the burner because of the great increase in surface area resulting from the location of the pump at this point. As a consequence.the pump is placed in the exhaust line of the burner (see the system schematic. FIG. 5). This requires that the burner be inclosed. Enclosure of the burner requires that internal cavities be minimized to avoid excessive buildup of pressure which would rupture the viewing window or snuff the flame on initial ignition. Although no firm upper limit may be specified. it has been found desirable to restrict the I cavities to no more than V2 inch diameter by /2 to 1 inches in length. The dimensions chosen for the particular embodiment being described have been governed more by the need to compromise between a high surface-to-volume ratio (to promote best mixing of fuel and air) and the bore diameter below which the flame will become, unstable at the flow rates of hydrogen 1.5  
 liters per minute) and air (2.5 liters per minute) which are used. Best results were obtained with the burner chamber between 3/16 and A inch inside diameter. En-  
 closure of the burner requires. in addition. a burner lighting device such as a sparkplug or electrically heated wire. of which the former is the more reliable choice.  
  It should be noted that. to improve speed of response. an. air pump was chosen which has an air-flow capacity much in excess (5 times) the burner requirements; the excess air is burned in the first-stage burner. This brings the air to the second-stage burner more quickly than would otherwise have been the case. not only because of faster air flow but also because the exposed surfaces of the intake lines are more rapidly saturated with the contaminant.  
  The presence of a phosphorus-bearing contaminant in the air sample is indicated in the following manner. A light chopper. consisting of a light filter 50 and a motor 56 for rotating the filter 50. is provided. The filter 50 consists of two semicircular sections. one being a green filter 52 and the other a blue filter 54. The light filter 50 is placed between the viewing port 24 of the burner (see FIG. 5) and a phototube 58. Thus. alternate flashes or pulses of green and blue light are received by the phototube 58 and are passed through capacitive coupling through an amplifier 60 to some sort of indicator62 which may comprise a visual or audible indicator. The speed at which the color filter is rotated gives the pulses a frequency of about 5 cps. A remote indicator 64 may also be provided.  
  The remainder of the system consists of the support system for the burner 10. It includes an exhaust pump 66. a hydrogen supply system 68. and a water cooling system with a pump 70 and reservoir 72.  
  Although the low background and high velocity of the flame minimizes variations due to flicker. it does not prevent zero drift due to changes in flame size which are caused by changes in either the quantity of air or hydrogen supplied to the burner 10. To correct for this drift. advantage is taken of the fact that hydrogen emits light of approximately equal intensity in both the green and blue portions of the spectrum. By suitable adjustment of the color of the blue and green sections of the light filter 50. the phototube 58 can be made to respond equally to either color of the hydrogen emission and will therefore result in a steady d.c. signal from the phototube. The capacitive coupling of the amplifier 60 will not pass this do signal so that the hydrogen light will give no indication whatever.  
  However. since the green light from any phosphorus emission is greater than the blue light. the alternate pulses will differ in amplitude and a difference signal will be passed through the capacitive coupling. amplified and sent to the indicator 62 which will show the presence of the contaminant.  
  With a second viewing port located in the proper place for a sulfur-bearing contaminant and a second color filter and phototube connected to the amplifier or to another amplifier and indicator. as desired. the system can be used for detecting phosphorus and sulfur contaminants simultaneously. FIG. 6 is a rough sketch showing the relative location of the viewing port 74 for the sulfur emission.  
  The electronic circuits for the detection system are conventional and within the capabilities of any skilled worker in the electronic art and therefore will not be described herein.  
  The dimensions for a typical embodiment of the invention are roughly the following:  
 block: 5 A high X 1% wide X 1 inch deep first-burner inlet channel: A diam. X 1 /11 inches long first-burner chamber: A diam. X 2% inches long first-burner exhaust channel: 1/16 diam. X 5/16 inch long second-burner chamber: A diam. X 2% inches long flame channel: 1/16 diamv X 2 /8 inches long water channel: 3/16 diam. X 5 inches long.  
  It will be understood that various changes in the details materials. and arrangements of parts (and steps). which have been herein described and illustrated in order to explain the nature of the invention. may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.  
 1 claim:  
  1. A hydrogen burner for producing a color spectrum from the chemiluminescent burning of contaminantbearing vapors and aerosols comprising. in combination:  
 a substantially rectangular block of metal having borings therethrough forming a first burner. a second burner. a flame channel. an ignition chamber. at least one viewing port and a water channel.  
 said first burner comprising a transverse channel near the upper end of said block having a hydrogen inlet port at one end thereof and an air inlet port at the other end. a longitudinal burning chamber connecting with said inlet channel and extending downward therefrom. and a transverse exhaust channel which extends orthogonally from said burning chamber and is narrow in diameter relative to the diameters of said inlet channel and said burning chamber.  
 said second burner comprising a longitudinal burning chamber and a transverse ignition chamber. said burning chamber connecting at one end with said hydrogen inlet port and one end of said first-burner inlet channel and connecting near its other end with said first-burner exhaust channel. said ignition chamber connecting with said second-burner chamber at the level of said first-burner exhaust channel and forming a virtual extension thereof to an outer surface of said block.  
 said flame channel connecting with the other end of said second-burner chamber and extending downward therefrom. the diameter of said flame channel being narrow relative to that of said second-burner chamber but increasing in diameter at its other end to form an exhaust port connecting with an outer surface of said block. the diameter of the flame channel being designed to provide a high-velocity flow of gas therethrough.  
 said viewing port comprising an undercut portion extending from a surface of said block to said flame channel in a location which permits the chemiluminescent color spectrum of the burning contaminant to be viewed but is sufficiently far from the oxidizing portion of the flame in said second burner to exclude the light from the oxidizing portion from view.  
 said water channel extending longitudinally through said block and having an inlet and an outlet port:  
 a cover for said viewing port comprising a transparent pane and holding means therefor. said holding means being shaped to fit into said viewing port and to be held therein so that said flame channel can be viewed through said pane; and  
 an ignition device seated in said ignition chamber for igniting the gases in said first and second burners.  
  2. A hydrogen burner as in claim 1. including a second viewing port and associated cover. said second viewing port being located farther down along said flame channel at a location at which the chemiluminescent color spectrum of a slower-reacting contaminant than the first is visible.  
  3. A system for detecting the presence of contaminant-bearing aerosols and vapors by means of the color spectrum emitted from the chemiluminescent burning thereof comprising. in combination:  
 a high-velocity-flame hydrogen burner comprising a substantially rectangular block of metal having borings therethrough forming a first burner. a second burner. a flame channel. an ignition chamber. at least one viewing port and a water channel. said first burner comprising a transverse channel near the upper end of said block having a hydrogen inlet port at one end thereof and an air inlet port at the other end. a longitudinal burning chamber connecting with said inlet channel and extending down-ward therefrom. and a transverse exhaust channel which extends orthogonally from said burning chamber and is narrow in diameter relative to the diameters of said inlet channel and said burning chamber. said second burner comprising a longitudinal burning chamber and a transverse ignition chamber. said bunting chamber connecting at one end with said hydrogen inlet port and one end of said first-burner exhaust channel. said ignition chamber connecting with said secondburner chamber at the level of said first-burner exhaust channel and forming a virtual extension thereof to an outer surface of said block. said flame channel connecting with the other end of said second-burner chamber and extending downward therefrom, the diameter of said flame being narrow relative to that of said second-burner but increasing in diameter at its other end to form an exhaust port connecting with an outer surface of said block. the diameter of the flame channel being designed to provide a high-velocity flow of gas therethrough. said viewing port comprising an undercut portion extending from a surface of said block to said flame channel in a location which permits the chemiluminescent color spectrum of the burning contaminant to be viewed but is sufficiently far from the oxidizing portion of the flame in said second burner to exclude the light from the oxidizing portion from view. said water channel extending longitudinally through said block and having an inlet and an outlet port. a cover for said viewing port comprising a transparent pane and holding means therefor. said holding means being shaped to fit into said viewing port and to be held therein so that said flame channel can be viewed through saidpane. and. an ignition device seated in said ignition chamber for igniting the gases in said first and second,  
 burners:  
 means connected to said hydrogen inlet port for supplying hydrogen gas thereto;  
 means connected to said &#39;ater inlet and outlet ports for circulating water through said water channel;  
 exhaust means connected to said exhaust port. for pulling air and hydrogen gas through said first and second burners and said flame channel: and  
 color detection means arranged to view the light emitted from said viewing port. said detection means being adapted to provide a signal output proportional to the difference in intensity of two colors. I 4. A system as in claim 3, wherein said color detection means comprises:  
  color filter means including a filter consisting of two semi-circles of translucent material. each being of a different color for passing one component of the chemiluminescent color spectrum of said contaminant element. and means for rotating said filter at a predetermined speed whereby the dwell time per filter segment is greater than the average light variation cycle resulting from flame flicker; phototube means arranged to view light passed by said filter and provide an electrical output proportional to the intensity thereof; amplifying means for receiving the output of said phototube means for amplifying the differences in its output caused by differences in intensity of the two colors transmitted by said filter; and means connected to receive the output of said amplifying means for indicating the existence of a difference signal 5. A system as in claim 3, wherein said exhaust means includes pump means having the capacity to provide a high-velocity flow of the incoming gases.  
 6. A system as in claim 4. wherein said two segments 1 of said filter are blue and green. respectively. and are color balanced to provide equal outputs from the color spectrum of a hydrogen flame. and said viewing port is.  
 means associated therewith. said second viewing port being located farther down along said flame channel at a point atwhich the chemiluminescent spectrum of a sulfur contaminant is visible.  
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