Patent GB-929885-A (GB)
Title: Systems of gas analysis
IPC: G01N33/00
Filed: 1960-03-07
Abstract: Gases are analysed by placing a flowing or static body of said gases in commjnication with a flowing or static body of a diluent gas through one or more bleed channels not greater than 0,01 sq. mm. in cross section and not greater than 5 mm. long and bringing the diluent gas containing the gas to be analysed into contact with an analyser, there being maintained across said channel or channels either no pressure difference or a small pressure difference such that passage of a gas through said channel can take place by diffusion with or against the flow of gases.  The method enables trace analysers to be used to estimate high proportions of a constituent in the original gas.  In the illustrated embodiments: (1) up to 100% oxygen in gases, e.g. the atmosphere of mines, manholes, oxygen tents, incubators, respiratory masks and aircraft, may be analysed with an analyser linearly responsive only up to 0,001%: in Fig. 2, the stationary or flowing gas 1 to be tested diffuses through bleed channel 2 and is brought into contact via a static diluent gas with the analyser 3; a tube 4 opening into the gas to be analysed via an absorber 6 for the constituent to be estimated (or in Fig. 1, not shown, a tube containing an oil drop) keeps the pressures equal on both sides of the bleed channel: (2) Fig. 4, shows a system in which the diluent gas is circulated by a pump 7 (e.g. a turbine operated from outside by inductance), through an absorber 6 and thence to a reagent 9 after collecting diffused sample gas from 2 and before analysis; this is adapted for the indirect estimation of carbon monoxide in producer gas by release of iodine from iodine pentoxide reagent and using an amperometric or galvanic iodine analyser.  By omitting reagent 9 the system may be used for direct analyses using, e.g. a coulometric cell, reducing chlorine to chloride or a calorimetric detector consuming a combustible gas: (3) in Fig. 5, a flowing stream of diluent gas is employed with a throttle 4 creating a pressure differential across the bleed channel 2: (4) Figs. 6 and 7 illustrate alternative methods of adjusting the relative proportions of hydrogen and oxygen in the gas passing to the analyser 3 when estimating hydrogen in air.  In Fig. 6, hydrogen and oxygen diffuse through first bleed channel 2a into nitrogen diluent and absorber 6 removes the oxygen: a smaller bleed <PICT:0929885/III/1> <PICT:0929885/III/2> <PICT:0929885/III/3> <PICT:0929885/III/4> <PICT:0929885/III/5> channel 2b introduces a suitable amount of oxygen for combustion of the hydrogen present plus a further small amount of hydrogen, combustion takes place over a catalyst at 9 and residual oxygen is measured at 3.  In Fig. 7, the diluent stream carrying diffused oxygen and hydrogen is divided at 11, the major portion passed through absorber 6 for oxygen the resultant mixture burnt at 9 and the residual oxygen measured at 3.  These systems may also be used to determine methane in air, organic vapours in air or alcohol in breath.  Suitable bleed channels may be made by high voltage sparking through a glass wall, by fusing a thin wire, e.g. of platinium, in a wall of smaller coefficient of expansion, e.g. a borosilicate glass wall, so that on cooling an annular crevice is obtained.  If desired numerous channels may be employed by using a small window of a thin porous material.  A bleed channel may allow 0,1 cu. m.m./min. of gas to pass.  A trace oxygen analyser is mentioned which comprises a porous sheet of polymer soaked with caustic soda and lined on one side with a noble metal and on the other with a base metal.  This may be confined within a glass envelope having a bleed channel therein.