Patent GB-1118645-A (GB)
Title: Method and device for determining calorific quantities
IPC: G01K17/12
Filed: 1966-03-14
Abstract: 1,118,645. Measuring electrically. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. March 14, 1966 [March 15, 1965], No. 11065/66. Heading G1N. The rate of flow of potential heat, #, or the amount of potential heat W which flows during a given time interval, is determined by measuring the rate of flow Q of a fuel, its density or specific gravity γ T , and its temperature T and calculating the quantity Q.f (γ T , #T), or its integral with respect to time, #T being the difference between T and a reference temperature. The term f(γ T , #T) represents the combustion heat of the fuel and may include additional variables such as the sulphur content and ratio of carbon to hydrogen in the fuel. The term f(γ T , #T) may be represented by any one of a number of different equations depending upon the type of flowmeter used and the accuracy required. Using a mass flowmeter, f(γ T , #T) may be represented by k 1  + k 2  γ Tr , or by k 14  + k 15  γ T <SP>2</SP> r , where γ Tr  = γ T (1 + ##T), and # is the cubic coefficient of expansion of the fuel, while for a volumetric flowmeter it may be represented by k 3  + k 4  γ Tr  + k 5  γ T <SP>2</SP> r . The measurement is made more accurate by including an additional term proportional to the sulphur content. Still greater accuracy is obtained by means of the relationship where C s  is the sulphur content. The carbon to hydrogen ratio may be taken into account by adding terms of the form k 18  C c /C H  + k 19  γ Tr  C c /C H  to the terms quoted for use with the mass flow meter. If the density, or specific gravity, is measured by a method using radio-activity, it is stated that the measured value depends upon the hydrogen atom concentration and that the relationship may be used. When a volumetric flowmeter is used the measured value Q  T  is corrected for temperature in accordance with the relationship Q Tr  = Q T /1+##T. Figure 3 shows a circuit for calculating W, in which a signal indicative of the density or specific gravity γ T  of the fuel is supplied to terminals 10. Resistors R T1 , R T2  are temperature sensitive, with a temperature coefficient α, and R 0  are fixed resistors equal to <SP>α-#</SP> # .R Tr , where R Tr  is the resistance of R T1  and R T2  at the reference temperature. As a result voltages E1 and -E1 are set up which are proportional to y Tr . Resistance R 2  is adjusted manually or automatically in accordance with the sulphur content of the fuel so that I 2  is equivalent to (k 11  + k 13  Cs) Y Tr , resistance R 1  and voltage V 2  are selected so that I 1  is equivalent to k 10 , and resistance R 3  and voltage V 3  are selected so that Is is equivalent to <SP>k12</SP> γTr . The input E2 to circuit is therefore proportional to f(γ T  #T). A switch 26 is controlled at a frequency f 1  proportional to the flowrate Q of the fuel, and a switch 27 is controlled at a frequency f 2  originating from a comparator 29 which emits a pulse when its input exceeds a certain value. Capacitor C1 is thus charged by voltage E2 at frequency f 1  and capacitor C 3  is charged by voltage E3 at frequency f 2 . E3 is derived from temperature sensitive resistor R T3 , resistor R 0  and constant current source 31. It is shown that the frequency f 2  is then proportional to the potential heat flow-rate #. The heat flow W is determined by counter 32. If a temperature compensated flowmeter and specific gravity gauge are used resistors R  T1 , R  T2 , R  T3  may be replaced by constant resistors. In a system in which three furnaces are supplied from a common fuel line Fig. 4 (not shown) the temperature and specific gravity of the fuel in the common line are measured and supplied to a calculating unit (47), corresponding to 18 in Fig. 3, the output of which is fed to four separate units 49, 64, 65, and 66, each corresponding to unit 19 in Fig. 3, and supplied with temperature and flow-rate signals corresponding to the common line and each of the individual lines to the three furnaces.