Patent GB-921615-A (GB)
Title: Apparatus for determining the purity of gases
Inventor: DIJKEMA LEENDERT FREDERIK WILL
IPC: G01N7/04
Filed: 1960-04-13
Abstract: In estimating the (insoluble) gaseous impurity in a (soluble) main gas by dissolving the main gas in an absorbent liquid and measuring the volume of impurity, a sample is passed into an absorption vessel (5) completely filled with absorbent and having a narrow riser tube (6) into which insoluble gas rises and the resistance of a pair of electrical elements (9I, 9II) one at least of which extends over the length of the riser tube is measured.  The numerals <PICT:0921615/III/1> <PICT:0921615/III/2> <PICT:0921615/III/3> relate to Fig. 1 which illustrates a preferred apparatus including a mercury seal 4 at the entry of the gas into the vessel, a regulating device 11 for the gas in main conduit 1 controlled by the measuring device 10, and a storage vessel 13 or manometric riser tube by means of which the vessel 5 may be filled with absorbent.  A cock 7 for release of unabsorbed gas may be coupled with a sampling device 2 and if desired a driving unit provided to enable repetitive samples to be estimated automatically.  Where it is desired to alter the course of the gas stream flowing through the main conduit (e.g. to a vent line or to a storage or other line) when a threshold value of impurity is present, a contact may be provided in tube 6 connected to a relay connected to a further contact permanently immersed in the liquid or to one of the elements 9I, 9II; the relay rather than the measuring device 10 may operate control device 11 and the measuring device may be employed to operate a recording device. Fig. 5 shows an alternative construction of the riser tube in which the lower part of said tube is of greater bore than the upper part so that a greater volume of impure gas can be accommodated, and also the method of supporting the electrical elements 9I, 9II in the tube.  The tube is also graduated to read the volume of gas directly.  The electrical elements are of high resistance and the resistance of the liquid is neglegibly small; a salt or other electrolyte may be added if necessary to make the liquid conducting: if the resistance of the liquid varies during the measurements, a compensating pair of resistance elements may be placed in the absorbent and incorporated with the first pair in a Wheatstone bridge circuit. The elements may be of spiral or other form.  Alternating current is preferably used to avoid electrolysis.  The cock may be in the form of a face valve in two parts 7I, 7II, as shown in Fig. 3 in relation to another embodiment.  The sampling device comprises two displacers 2I and 2II having float valves 25I, 25II which are operated by means of further passages in the face valve (Figs. 4a and 4b, not shown) making the following sequence of events possible: (1) gas from the main conduit is passed through line 21 to the valve and thence vented to atmosphere whilst the previous sample in tube 6 is vented to the top of the storage vessel through line 18I, or to the atmosphere through another hole in the fixed part 7I; (2) line 21 is placed in communication through the valve with line 22I thereby filling displacer 2I with a sample and displacing a liquid which originally filled said displacer into displacer 2II; this in turn displaces the immediately preceding sample from displacer 2II through line 22II which is in communication through the valve with line 23II; through line 23II the sample flows into a helical coil 26 in storage vessel 13 and thence through absorption vessel 28, unabsorbed gas rising into tube 6 for measurement; (3) the valve is returned to the original position and the gas to be tested and the tested sample are vented; and (4) the valve is turned to place line 21 in communication with line 22II to effect a second sample taking &c with the displacers functioning in a reciprocal manner to that described in (2) above.  The helical coil 26 is provided with apertures 29 to assist circulation of absorbent through the coil and back into the storage vessel.  The displacers 2I, 2II may be replaced by a single displacer operating in a similar way in conjunction with a reservoir. A suitable liquid is glycerin or a mineral oil, e.g. paraffin oil. Gases which may be tested, and corresponding aqueous absorbing agents are: acid gases, e.g. CO2(KOH), O2 (alkaline Na2S2O4), CO (alkaline CuCl o alkaline PdCl2-in which case CO2, which dissolves in the alkali, is formed) and basic gases, e.g. NH3 (H2SO4, H3PO4).  The impurity may be air or other gases and it may be desirable initially to remove one component or to use several apparatus in parallel with different absorbing agents.  Where the absorbent is a solution of an absorbing agent or where an electrolyte is used it is desirable that the concentration should be high to minimise absorption of impurities.  Fresh absorption liquid may be supplied and spent absorption liquid removed continuously if desired.  The apparatus is said to be capable of measuring 0,005% of impurity.