Patent GB-1012268-A (GB)
Title: Apparatus for detecting the presence of oil in a gas flow
Inventor: CHURCHILL JOHN GODWYN
IPC: G01N21/53
Filed: 1961-10-24
Abstract: 1,012,268. Photo-electric detection of oil in a gas flow. GRAVINER MANUFACTURING CO. Ltd. Aug. 20, 1962 [Aug. 22,1961(2); Oct. 24,1961; June 8, 1962], Nos. 30172/61, 30173/61, 37983/61, and 22194/62. Heading G1A. In a photo-electric arrangement for determining the concentration of oil suspended in a gas flow the oil is converted into an oil mist the density of which determines the amount of light which impinges on a photo-electric detector. Figure 1, shows the schematic arrangement in which the gas, which may e.g. be derived from the down stream side of a blower in the carbon-dioxide circulating system of an atomic power station, is fed via a pipe 12 (preferably heated to prevent deposition of the oil), terminating in an atomizing nozzle 25, into a tube 11 through which light from a source 15 is directed via a mirror 17 on to a photo-electric cell 16 the light being also directed via a mirror 18 through a reference tube 27 to a second photoelectric cell 29. The diminution of the light received by cell 16 due to the absorption or scattering effect of the oil mist is then a measure of the amount of the latter present. The gas is removed via outlets 21, 22 (a suction pump being provided if necessary to cause a sufficient pressure drop across nozzle 25 to produce the required mist) and to prevent contamination of the end windows 13,14 (which are readily removable to allow cleaning) by oil, cuffs 23 surrounding each window and forming annular passages with the inner bore of the tube adjacent the outlets 21, 22 are employed. Additionally, to prevent reduction in the apparent oil mist content of the gas due to the gas, which is directed radially across the tube, impinging on the wall of the tube an expansion chamber 26 is provided. For balancing the response of the two photo-electric cells the tube 11 is connected to an oil free nitrogen or carbon dioxide supply and the mirror 18 or the detecting, measuring or warning devices operated by the response of the cells suitably adjusted. A practical realization of the scheme of Fig. 1, is illustrated by Figs. 2 and 3 (not shown). Figure 4 shows a practical arrangement of a second embodiment in which the tube 11 and its end windows are formed as a single unit which may be readily removed from the assembly for cleaning or replacement by a new unit by means of releasable screw couplings 42. In this embodiment the reference tube is not employed the optical path thus comprising mirrors 32.... 35 and tube 11 between the light source 31 and the photo-electric cell 36 and to allow adjustment of the apparatus the cell 36 is made rotatable or is provided with an adjustable screen to vary the amount of light which it receives. The casing 30 may contain the circuitry associated with the measuring or warning device and may additionally contain a motor driving a suction pump for withdrawing gas samples from the tube. Additionally a rotary valve driven by the motor may be provided for selecting gas samples from different sources. Where, as in an atomic power station, the apparatus must be located at a considerable distance from the point in the gas duct where the oil contaminates the gas, the delay between the evolution of the oil droplets and their detection which a long sampling pipe 12 would introduce is avoided by providing a by-pass duct connected to the mirror gas-duct and passing adjacent to the detecting device to which it is connected by a sampling pipe 12 of minimum length.