Determining the quality of natural gas and biomethane : Development of a correlative method and instrument prototype for measuring gas quality

Abstract: The composition of natural gas highly depends on its origin: natural gas from various deposits, substitute natural gas that can be produced from fossil fuels or renewable sources. The intermixing of gases from various supply sources during pipeline transportation also leads to more complicated and unpredictable gas composition variations at the consumption site. Gas composition determines its qualitative properties, such as calorific value and Wobbe Index. These properties should be known or measured for efficient consumption and accurate fiscal metering. The industry-standard method, gas chromatography is too costly for widespread applications at end-user sites. Thus, there is a strong interest and need for alternative methods and instruments that would allow more cost-effective measurement of gas quality.The major aim of the research work presented in this thesis is to investigate the possibility of utilizing the measurable physical and specifically ultrasonic properties of a gas mixture for determining the gas quality of hydrocarbon fuel gases such as natural gas and biomethane. It was identified that the measurement of ultrasound attenuation effects in gases is a promising way of obtaining additional information on the gas sample and increasing the performance of gas quality determination in combination with other measurable properties: the velocity of sound, thermal conductivity, and carbon dioxide content by infrared absorption. As the main outcome of the thesis, the correlative method and the prototype of a cost-efficient instrument gas quality determination were proposed, developed, and experimentally tested.