Edinburgh Instruments Ltd

Methane and Carbon Dioxide Sensing for Biogas Applications - Energy - Bioenergy

Application: Anaerobic Digestion plants produce various gas components from a source material (or feedstock) that can be composed either solely or as a mixture of slurries, purpose-grown crops, food and organic waste material. The composition of the gas produced varies depending upon the feedstock and the Anaerobic digestion process itself. As a consequence, it is normal to measure various components of the resultant gas produced to evaluate the efficiency of the Anaerobic Digestion process. Furthermore, due to the flammable nature of Methane, and the risk of asphyxiation, most plants feature ambient air monitoring to protect personnel from any unplanned accumulation of leaked gas.

Methane (CH4) is the gas component fuel, which is the intended end product of the anaerobic digestion process. In biogas plants, the concentration of Methane in a working plant varies between 50%-75%, which is well above the Upper Explosive Limit (UEL). However, at start-up lower concentrations can occur which need to be carefully monitored. Methane is normally measured both in the process gas stream and, in addition, in the ambient area.

Carbon Dioxide is a by-product which occurs in concentration levels between 19% and 50%, and is often also measured in the gas stream.

In 1956, the founder of Edinburgh Instruments published a paper on the design and fabrication of infrared band pass filters, which are a key component of modern IR bench sensors. Edinburgh Sensors has actively commercialised this technology over the last 40 years, resulting in a reputation for reliable, accurate, long term stability and low maintenance gas-sensing products, which are used extensively worldwide in a range of safety and process critical applications. The reputation of these sensors has resulted in their widespread adoption as the sensor of choice on instrumentation on many biogas plants shipped worldwide over the last 7 years.

Gascard NG is an ideal OEM sensing solution, for measuring either Methane (CH4) or Carbon Dioxide (CO2) having been designed for ease of integration.

Available with a 0-100% range for both CO2 and CH4 the sensor features on board Barometric Pressure Correction, and extensive Temperature compensation.

The Gascard NG has a range of different interface options, including analogue 4-20mA/0-20mA/0-5v, true RS232 communication, optional on board LAN support, and a serial interface for interfacing relay alarms. The on-board firmware supports either a traditional 4 segment LCD or a modern graphical display.

For OEM development, Edinburgh Sensors, can provide an evaluation kit consisting of a Gascard NG sensor, an advanced graphical display interface, and relay board allowing easy evaluation of the Gascard NG functions.

Technical support is available from our Engineers who are available to provide one-to-one customer service and technical support throughout the evaluation and system integration process.

In addition to OEM Gas sensors, Edinburgh Sensors have been providing Gas Monitors based upon our proprietary infrared sensor technology for many years, with tens of thousands of our monitors in operation worldwide. It is hardly surprising, therefore, that these monitors have been put to widespread use in the Anaerobic digestion Biogas market.

As part of the ISO9001 Quality accreditation, Edinburgh Sensors undertakes extensive calibration and burn in of IR sensors during production. The final stage of the production process for all Gascard NG and Guardian NG products includes a factory calibration and, when requested by the customer, this calibration can be undertaken using a biogas background gas mixture.