Method and measuring apparatus for determining physical properties of gas

Abstract

A method to determine a physical property or a quantity of gas related to combustion including: flowing a gas from a reservoir through a critical nozzle and past a microthermal sensor wherein the mass flow of the gas through the critical nozzle is the same as the mass flow through the microthermal sensor; measuring the pressure drop in the reservoir as a function of time; deriving a first gas property factor based on a time constant of the pressure drop; determining a second gas property factor which depends from a flow signal generated by the microthermal sensor; determining a thermal conductivity of the gas; and determining the physical property or quantity based on a correlation between the physical property or quantity, and the first and / or second gas property factors and the thermal conductivity.

Description

RELATED APPLICATIONS[0001]This application is a continuation of U.S. patent application Ser. No. 14 / 282,562 filed May 20, 2014, and claims priority to European Patent Application No. 13002708.9 filed May 24, 2013, the entirety of both applications are incorporated by reference.BACKGROUND OF INVENTION[0002]The invention relates to a method and a measuring apparatus for determining physical properties and quantities relevant to combustion of gas and gas mixtures. Physical gas properties mean in particular the density, thermal conductivity, heat capacity and viscosity as well as correlatable quantities relevant to combustion, such as the energy content, calorific value, Wobbe index, methane number and / or air requirement of the gas or gas mixture.[0003]In gas-fuel firing control systems it is important to keep the load in the burner constant even at changing fuel gas qualities. The Wobbe index, formed from the calorific value and the root of the density ratio between air and this gas, i...

AI Technical Summary

Benefits of technology

This approach provides a high degree of accuracy in determining combustion-related properties using three independent measured variables, making it more cost-effective than existing commercial devices and enabling validation and adjustment of measurements.

Problems solved by technology

An identical Wobbe index will then result in a constant thermal load in the burner.

Soot (flue gas) usually forms if there is too little air, and this may damage fuel cells in particular.

Too much air during combustion results in reduced performance.

However, due to the high acquisition costs, none of these devices is suitable for mass distribution.

However, the information on the correlation of quantities relevant to combustion is limited to two more or less independent measured variables and thus does not permit validation of the measured data.

Since the described sensor is not a microthermal sensor, it is not possible to draw conclusions regarding thermal conductivity; this means that the determination of the heat capacity and the quantities relevant to combustion derived therefrom is only possible up to one proportionality factor.

Furthermore, the accuracy of this method is limited by the occurring variations of the inaccessible thermal conductivity λ.

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