¦TECHNOLOGY
CRITICAL MEASUREMENT TECHNOLOGIES FOR LIVE BIOGAS MONITORING BY NARGE SPARAGES
B
iogas has been produced, cleaned up and used for several decades. Also for several decades, millions of tons of biogas has been lost
every year. However, the focus on optimizing and recovering all the renewable gases produced from biomass, livestock and other waste production has significantly increased over the past few years, driven by climate change and the road to net zero. Still, the growth potential for biogas use is significant. Today, there are critical measurement solutions that support biogas collection and use, regardless of its source. For example, Panametrics deploys process analyzers to monitor the oxygen content in the anaerobic digester and the carbon dioxide content in the biogas separation process, as well as measure the moisture content of biomethane prior to transportation and end use. Ultrasonic flow meters monitor the natural gas flow rate and determine its methane content to provide a good indication of the gas mixture calorific value.
This article will explain how these technologies work, where they are employed and how they enable producers to optimize operations by accurately measuring biogas and biomethane quality and flow, primarily focusing on the upgrading of the biogas to biomethane.
Separating Carbon Dioxide from Methane
The most useful part of the biogas is the biomethane. Most commonly, membrane filters separate the carbon dioxide and methane. Operators will want to know the ratio of the carbon dioxide and methane going into the separation process, and then the amount of methane on either side of the separation process, as an indicator of the efficiency. Given that carbon dioxide and methane are the two predominant components, this can be treated as a binary gas mixture, and a thermal conductivity analyzer like the Panametrics XMTC is used at all three points to measure percent levels of carbon dioxide in methane.
Carbon dioxide and methane have different thermal conductivities. A thermal conductivity analyzer will have one sensor exposed to air and the other exposed to the sample gas. The transmitter is calibrated with a zero and span that represents pure carbon dioxide or methane, as the zero and the span will be a mixture of the two. The transmitter measures the loss of heat from the sensor exposed to the sample gas compared to the loss of heat to air, and can then easily calculate the concentration of methane in carbon dioxide or vice versa. With no moving parts, this methodology requires little maintenance and is easy to implement.
Water Vapor Doesn’t Burn
Compression of the biogas will drop out the bulk of the water vapor that comes off the biogas collection process. The resultant gas is saturated with water vapor at that pressure. After separating the methane from the carbon dioxide, the biomethane will either be used as a fuel locally or sold into the natural gas grid for pipeline transportation
CONTRIBUTION: The claims and statements made in this article belong exclusively to the author(s) and do not necessarily reflect the views of Biomass Magazine or its advertisers. All questions pertaining to this article should be directed to the author(s).
36 BIOMASS MAGAZINE | ISSUE 2, 2022
