Patent FR-2827961-A1 (FR)
Title: Determining at least one energy property of gaseous mixture comprises measuring its physical properties
Inventor: RAHMOUNI CAMAL
IPC: G01N33/22
Filed: 2001-07-30
Abstract: The process involves (1) measuring n physical properties phi i of the gas at a temperature T and/or one physical property phi i at n different temperatures; (2) determining from these physical properties the composition of a gas with n+1 components equivalent to the mixture, and (3) deriving from the composition of the equivalent gas the energy properties of the gaseous mixture  The physical properties are chosen from: the speed of sound; thermal conductivity; dynamic viscosity; density; refractive index; dielectric constant and infrared absorption. The gaseous mixture is a natural gas, biogas or gasification gas. The components of the equivalent gas are chosen from methane, 2-5C alcanes, nitrogen, inert gases, hydrogen and carbon monoxide. In particular, the gaseous mixture is a natural gas or biogas and the equivalent gas is a ternary gas made of methane and two 2-5C alcanes or methane, one 2-5C alcane and nitrogen or inert gas. Alternatively, the equivalent gas is a quaternary gas made of methane, two 2-5C alcanes and nitrogen or inert gas. The physical properties phi 1 and phi 2 are chosen from dynamic viscosity and thermal conductivity; thermal conductivity at temperatures T1 and T2; refractive index and thermal conductivity, and the speed of sound and refractive index. Before stage 1 a calibration is done either by producing a series of measurements of physical properties of an equivalent gas with n+1 components with a known composition, or by using a numerical method to determine the relationships between the physical properties and the concentration in each component of the equivalent gas. The composition of a ternary equivalent gas is determined by the equations: X1=X10 + (1-(a1 phi 1)/(3)<0.5>((b1 phi 1-b2 phi 2)/(a2 phi 2-a1 phi 1)) - (b1 phi 1)/(3)<0.5>) X2=X20 + ((2a1 phi 1)/(3)<0.5>)((b1 phi 1-b2 phi 2)/(a2 phi 2-a1 phi 1)) + (2b1 phi 1)/(3)<0.5> X3=1-X1-X2 Where phi 1 and phi 2 are the two physical properties, X1, X2 and X3 are the concentrations of the three components of the gas, X10 is the lower limit of the X1 axis, X20 is the lower limit of the X2 axis and a1, b1, a2 and b2 are coefficients which depend on the physical properties. phi 1, phi 2 = phi 1(T), phi 2(T) for two different properties or phi 1, phi 2 = phi 1(T1), phi 1(T2) for two temperatures. The composition of a quaternary equivalent gas is determined by the equations: X1=X10 + (1-(a1 phi 1X4)/(3)<0.5>)((b1 phi 1X4-b2 phi 2X4)/(a2 phi 2X4-a1 phi 1X4)) - (b1 phi 1X4)/(3)<0.5> X2=X20 + ((2a1 phi 1X4)/(3)<0.5>)((b1 phi 1X4-b2 phi 2X4)/(a2 phi 2X4-a1 phi 1X4)) + (2b1 phi 1X4)/(3)<0.5> X4=f( phi 3); X3=1-X1-X2-X4, where phi 1, phi 2 and phi 3 are the three physical properties, X1, X2, X3 and X4 are the concentrations of the four components of the gas, X10 is the lower limit of the X1 axis, X20 is the lower limit of the X2 axis and a1, b1, a2 and b2 are coefficients which depend on the physical properties. phi 1, phi 2 = phi 1(T), phi 2(T) for two different properties or phi 1, phi 2 = phi 1(T1), phi 1(T2) for two temperatures. The index of methane, the Wobbe index, the lower calorific power or the fuel index are calculated. An Independent claim is also included for a device for carrying out the above process, with at least n detectors for measuring the physical properties and an electronic module for determining the composition of the equivalent gas and the researched energy properties.