GB1360140A - Methods of and means for determining the calorific value of combustible gases - Google Patents

Abstract

1360140 Automatic control of temperature PRECISION MACHINE PRODUCTS Inc 25 April 1972 19236/72 Heading G3R [Also in Division G1] To determine the calorific value of a combustible gas, the gas is mixed with a combustionsupporting gas and the resulting mixture is burnt, the temperature of the burned gases being monitored, and the volume ratio of the gases is adjusted until the maximum flame temperature is attained, the ratio corresponding to the maximum flame temperature being proportional to the calorific value of the combustible gas for a given test apparatus. In Fig.1, air and combustible gas supplies are controlled by respective valves 9, 10 and measured by respective flow meters 11, 12 before being mixed in a duct 8 leading to a Meker burner 2. A thermocouple 15 in the burner flame is connected to a controller 16 which actuates one of the valves 9, 10 to automatically achieve and maintain maximum flame temperature. As shown in Figs.1 and 5, the valve 9 is actuated by a reversible D.C. motor 60 energized via single pole double throw relay switches 67, 68 in the controller 16. The switches 67, 68 form parts of alarm switching units 65, 66 respectively. The threshold value of unit 65 is slightly higher than that of unit 66. The units 65, 66 are connected in series with a constant current source 79 giving a current between the threshold values of the units, and a double pole double throw relay switch 77. Oscillators 85, 86 supply positive and negative pulse trains respectively, one or other pulse train being superimposed on the constant current according to the setting of the switch 77. When the E.M.F. of the thermocouple 15 is increasing, the output of a differentiating circuit 81 is such that the switch 77 remains in its existing position so that a train of positive or negative pulses acts on the units 65, 66 to effect intermittent opening or closing movements of the valve 9, to continue the rise in flame temperature. After the flame temperature has passed its maximum, the output signal of the circuit 81 reverses the switch 77 to connect the other oscillator to the control current to reverse the movement of the valve 9 so that the flame temperature re-approaches its maximum. A further reversal occurs each time the maximum is passed. In a modification Fig. 2 (not shown), a small pulsed air-flow is added to the mixed gases supplied to the burner, causing small perturbations in the flame temperature except when the maximum flame temperature exists. The controller 16' Fig. 6 in this system includes a pulse amplitude measuring circuit 122 which actuates a double pole double throw relay switch 115 controlling the motor 110 to approach the zero perturbation condition, and hence the maximum flame temperature. In a further modification Fig. 3 (not shown), two burners are used, the gas supply to one being slightly restricted. At the critical combustion ratio (the gas volume ratio for maximum flame temperature) there is a characteristic temperature difference between the thermocouples 25, 25' Fig.7 in the two flames, a controller 26 acting to achieve and maintain this value. A voltage to current converter 109 with a linear characteristic receives the E.M.F. difference between the thermocouples and controls alarm switching units 95, 96.