Patent GB-670880-A (GB)
Title: Improvements in measuring instruments for steam generators
IPC: F22D11/00
Filed: 1949-03-22
Abstract: 670,880. Electric analogue calculating systems. BAILEY METERS & CONTROLS, Ltd. March 22, 1949 [March 23, 1948], No. 7748/49. Class 37. [Also in Group XXXVIII] In measuring apparatus for a steam generator, temperature and flow meters in the feedwater inflow adjusts the parameters of a computing network in accordance with the magnitudes of the measured quantities to produce a signal representing the total rate of heat inflow with the feedwater, and a steam flow meter measuring the rate of heat outflow in the steam adjusts a parameter of a further computing circuit, in combination with the heat inflow signal, to produce a signal representing the difference between heat inflow and outflow, i.e. the rate of heat absorption by the working fluid. The parameters of further computing circuits are varied in accordance with the rate of air flow to the furnace and its air temperature, or the rate of fuel delivery and its calorific value, to produce a signal representing the rate of heat liberation by the fuel, and a proportion of this signal is derived from a motor-driven potentiometer and balanced against the rate of heat absorption signal so that the unbalance operates the motor to restore balance and position a recording pointer to indicate the ratio of heat absorption to heat liberation, i.e. the generator efficiency. A steam generator 1 (Fig. 1) heated by a furnace supplied with fuel by an automatic stoker 5 has a separation drum 2 receiving feedwater from a conduit 3 and discharging steam through a main 4. A steam flow meter 7 of the manometric float type responsive to the pressure difference across an orifice in the conduit 4, which may be of the kind described in U.S.A. Specification 1,064,748, operates a pointer 9 over a scale 10 reading in lb. per hour (SF) and positions the core 22 of a variable transformer (Fig. 2) having an A.C. fed primary 23 and a pair of bucking secondary windings 24, 25, so that a signal representing the rate of heat outflow is developed across a variable calibration resistance 32 (X). A thermometric device in the feedwater conduit moves a pointer 16 over a scale 21 reading feedwater temperature T1, and operates a cam device 35 to position the core 17 of a variable transformer having bucking secondary winding 19, 20 connected to a load resistance 28, which is variable in accordance with the feedwater flow FW by a flow meter 61 in the conduit 3 to develop a signal representing the rate of heat flow into the boiler with the feedwater, the cam 35 introducing a correction # for density variation with temperature. The signals across resistances 32, 28 are subtracted, so that the combined signal across potentiometer 34 then represents the rate of heat output of the boiler. An airflow meter 11 measures the rate of passage of air (TA) through the furnace, and positions a core 38 in a variable transformer having bucking secondary windings 40, 41 which develop a corresponding signal across the potentiometer 45, whose slider 44 feeds a potentiometer 46 whose slider is adjustable by a motor M, which also drives a recording indicator for the thermal efficiency. The slider 37 of the potentiometer 34 is adjusted in accordance with the indications by a continuous gas analyser 14 of the ratio of total air flow to the theoretical combustion requirement of the fuel (R) and slider 44 is adjustable in accordance with the heat developed per pound of air when the combustion is theoretical (which is found to be 1333 B.T.U./lb. air). The voltage on slider 37 is balanced against that on slider 47, and the resultant unbalance voltage is applied to an amplifier control circuit 52 (which may be of the kind described in Specification 660,105) driving the motor M to restore balance and operate the thermal efficiency indicator. At balance A mathematical analysis is given. The variable signal representing the heat liberated may be produced by positioning core 38 in response to a continuous weighing-machine operated by a solid fuel conveyer, or by a tachometer measuring the stoker speed, and adjusting slider 37 for calibration and slider 44 in accordance with the fuel calorific value, Figs. 3, 4, 7, 8 (not shown). Alternatively where two fluid fuels are used, flow meters operate variable transformer cores to develop signals representing the heat liberated by each fuel, which are added and balanced as described against the combined heat output signal, Figs. 8, 9 (not shown).