GB1008941A - Flame monitor - Google Patents

Abstract

1,008,941. Flame monitoring devices. BAILEY METER CO. Oct.18, 1961 [May 16, 1961], No. 37425/61. Heading G1A. To monitor the combustion flame in a furnace it is proposed to make use of ultra-violet radiation emanating from the base of the flame. Radiation within the band 2000-2800 angstroms is only produced by a limited part of the flame close to its base and is not present (as are longer wave radiations) in the radiation from the outer parts of the flame or the incandescent refractory walls of a furnace. The detector used is a gas-filled ionization chamber having a pair of similar parallel electrodes. The detector is not self-quenching and to avoid the need for an external quenching circuit it is energized with alternating current. Fig. 2 shows the detector 40 energized from secondary winding 34 of transformer 30 through current limiting resistor 38. If energy within its wavelength sensitivity range is received by the detector when the instantaneous potential is above that necessary to initiate a discharge it will conduct for the remaining part of the half cycle and the resulting signal will be rectified by full-wave bridge rectifier 46 and applied to integrating time delay circuit 59, 78. The potential across this circuit, when it reaches a certain value causes a circuit for relay 60 to be completed through switching transistor 62. Thus if radiation is continuously received by the detector the relay is energized to give a flame present indication by illumination of lamp 94. Failure of the flame, or mal-functioning of the detector arrangement, results in release of the relay and operation of a warning light 96 and audible alarm. Terminals 98 and 100 provide for the transmission of the potential across circuit 59, 78 to a remote meter or recorder and remote flame or no-flame information can be derived from terminals 102, 104. The integrating circuit 59, 78 presents flame flicker from affecting the indication and introduces slight delays both when the burner first ignites and when the flame goes out. It also serves to prevent a false flame-present indication being given by the detector in response to longer wave radiations to which the chamber is relatively insensitive. Fig. 3 shows a number of detectors 10 each monitoring a like number of burners 16 in a multiple burner furnace. Fuel, for example natural gas, is fed to the burners through pipes 22 and duct 18 supplies air. The detectors are mounted in sighting tubes 24 and view with a suitable acceptance angle the base-portions a of the burner flames. Each detector unit may be constructed as indicated in Fig. 5 and comprise a container 110, and cover 132, supported by a flanged collar 112 having key-hole slots for quick-release engagement with bolts 116 threaded into mounting 122 attached to the furnace wall. Detector 40 is mounted inside the container and in line with quartz window 144 and the axis of sighting tube 128. The detector circuit elements may be mounted on panels 140, 142 in the container. The concentration of the source of ultra-violet radiation about the burner is a function of the hydrogen-carbon ratio of the fuel so whilst for a gas flame a narrow solid angle of view directed close to the burner provides sufficient detector output in the case of burners for oil or pulverized solid fuel it is necessary for the detector to view a greater solid angle. This necessitates positioning the detector inside the end of a probe extending the necessary distance into the sighting tube. Fig. 7 shows detector 40 protected by windows 144 at the end of a probe tube 150 projecting from flange 114. Spaced from and concentric with tube 150 is a further tube 156. An air stream flowing between the tubes is used to keep window 144 clean. A mounting providing for adjustment of the positioning of the detector arrangement of Fig. 7 is described with reference to Fig. 8 (not shown). Where a pilot burner is placed to one side of, but close to, a main burner two detector arrangements may be used, one viewing the pilot burner and base of the main flame adjacent the pilot burner and the other viewing the base of the main flame away from the pilot burner so that one indicates the presence of either or both flames and the other responds to the presence of the main burner flame only.