GB826049A - Improvements in or relating to combustion control - Google Patents

Abstract

826,049. Automatic control systems for furnaces. GRUBB PARSONS & CO. Ltd., Sir H. Nov. 27, 1957 [Jan. 2, 1957; March 25, 1957], Nos. 190/57 and 9711/57. Class 38 (4). In a combustion control system for a furnace, signals indicative of the concentrations of CO and CO 2 in the exhaust gases are added in certain proportions such that their sum increases as the air/fuel ratio decreases, this ratio being varied automatically in dependence on said sum. In Fig. 2, infra-red heaters A periodically irradiate chambers E, E, containing a mixture of CO 2 and CO, through a rotating shutter S. In the absence of gas in chambers B, C, or D the gases in chambers E, E expand and contract equally under the influence of the intermittent radiation so that diaphragm F, forming a capacitor with perforated diaphragm G, does not vibrate. If a sample of the exhaust gases is passed into tube D, any CO 2 or CO present will absorb radiation and diminish that incident upon the corresponding chamber E, causing a change in capacity by the diaphragm movement. Furthermore to reduce the sensitivity to the CO 2 in the exhaust gases, i.e. to introduce a constant of proportionality, some CO 2 is sealed in tube C so that the subsequent absorption by the CO 2 of the test sample is reduced. A similar quantity of CO 2 is placed in tube B to compensate for the effect of that in tube C on the gas in chambers E. The variation of capacitor F, G is changed to an A.C. voltage variation, is rectified and applied to meter M, the pointer of which moves between upper and lower limit contacts P and Q. These are in circuit with solenoid-operated valves V 1 and V 2 which reduce or increase the air supply as appropriate. Instead of an analyser responsive to both CO 2 and CO two separate analysers may be used and their outputs electrically combined. Alternatively the analyser may be of the type to respond to radiation from the flame of the combustion process, the radiation being passed through selective filters and detected by a thermocouple, bolometer, semiconductive cell, photo-electric cell or magneto-photo-electric cell. In a further CO 2 analyser (Fig. 3, not shown) sample gas is divided into two paths in a desired ratio and in the path corresponding to the desired proportion of CO, first the CO 2 is absorbed and then the remaining CO is converted to CO 2 . When the paths combine in a CO 2 analyser the total CO 2 corresponds to the desired proportionate sum of CO and CO 2 .