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US 5,635,626 AGranted
Measurement of a gas characteristic
AssigneeBritish Gas Corporation
InventorsPaul S. Hammond, Robert R. Thurston
Life of this patent
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AssigneeBritish Gas Corporation
InventorsPaul S. Hammond, Robert R. Thurston
Estimating the term…
Apparatus to measure the calorific value and/or the Wobbe index of fuel gas supplied along a pipe. A control can operate two outlet valves and cause an inlet valve to be locked in a closed position or be unlocked to stay in a normally open state until the gas pressure in a chamber of predetermined volume reaches a preset pressure difference above the pressure in the pipe. Under direction of the control, a pump moves fuel gas from the pipe into the chamber whilst the outlet valves are closed. Once the pressure in the chamber attains the preset difference, the inlet valve closes automatically to be held locked closed by the control. Certain properties of the gas in the chamber, such as thermal conductivity, specific heat capacity and speed of sound, are measured and corrected to STP conditions. The pump moves two samples of gas into the chamber at two sequential times, each time until the gas pressure therein attains the preset value and the inlet valve again closes automatically in a locked position. Then 1 of 2 outlet valves is opened to allow gas from the chamber to discharge to the pipe through either an orifice place or a capillary passage. This discharge allows the control to measure the gas density or viscosity at STP, from which the calorific value and/or the Wobbe index of the gas is/are determined.
A combustionless method of measuring the calorific value and/or the Wobbe index of a fuel gas comprises taking a fuel gas sample from a supply of said fuel gas and raising a predetermined volume of said sample gas to a predetermined pressure, returning said sample to the supply, making measurement of at least one of a value of the property of density or of the property of viscosity of said gas forming the sample using data obtained during the course of said return and deriving the calorific value and/or the Wobbe index by using said measured value of the density and/or of the viscosity, and wherein a said measured value of at least one of said properties is compared with a plurality of prederived values of the property each correlated to a particular respective calorific value and/or to a particular respective Wobbe index, whereby from said comparison substantially the calorific value and/or Wobbe index of the fuel gas can be inferred.
A test apparatus for measuring the calorific value and or the Wobbe index of a fuel gas without loss or consumption of a fuel gas sample under test comprising an enclosure having a predetermined volume therewithin, pump means for delivering a sample of said fuel gas from a supply into said enclosure, delivery stopping means for stopping delivery of said gas into the enclosure when the gas therein of said predetermined volume reaches substantially a predetermined pressure, return conduit means for returning the sample gas from said enclosure to said supply, measuring means for measuring at least one of a value of the property of density or the property of viscosity of the gas as it flows along said conduit means, said measuring means comprising at least a part thereof disposed in said conduit means for use in the measuring of at least one of the value of said property of density or of said property of viscosity, another part of said measuring means comprising control means, said enclosure being provided with gas pressure sensing means and temperature sensing means, and the gas pressure sensing means and the temperature sensing means being connected to said control means arranged for calculating a value of the property of density of the gas corrected to standard temperature and pressure and/or for calculating a value of the property of viscosity of the gas corrected to standard temperature and pressure, said control means comprising means for comparing the measured value of at least one of said properties with a plurality of prederived values of the property stored in said control means, each of said prederived values of the property being correlated to a particular Wobbe index, and for inferring from said comparison substantially the calorific value and/or Wobbe index of the fuel gas.
Dependencies are inferred from the claim text.