Gas Detection 61
prevent permanent damage to expensive equipment and the overall plant safety due to gas leaks and the possibility of explosion.
The more efficient the upgrade process, the better efficiency of the generator and the more electrical units are generated from the same volume of gas. This reflects in higher revenues from the electricity fed into the national grid. This in turn will create a faster return on the large initial capital investment in the biogas plant.
What sensor technology could be used to monitor the biogas upgrade?
A method of ensuring the efficiency of the above process can involve the measurement of the gas concentration before and after the upgrade process. Methane and carbon dioxide volume gas measurement is generally carried out by gas monitoring systems, which utilise either thermal conductivity or infrared gas sensor technology.
Thermal conductivity sensors are low cost and easy to use but are only recommended to be used to monitor methane or carbon dioxide separately due to the sensors cross sensitive to both gases. Thermal conductivity sensors consist of two fine wire platinum coils, so the fragility of
application, can be combined with the IR-EK2 development kit so that any instrument manufacturers can be competently taking infrared gas measurements on their own PC within minutes.
Monitoring the hydrogen sulphide level in raw biogas requires the use of a different technology sensor as the gas concentration levels are much lower, parts per million (ppm). In this case electrochemical cells are normally used. For oxygen measurement there are two main types of electro chemical oxygen sensor technology available today.
The older sensor design is based on lead acid battery technology, whereas the newer sensor design is based on a lead-free oxygen pump technology. The older lead based sensors have a fixed life time set by the sensor internal volume, the sensor output current and how much lead wire (gog) can be crammed inside the sensor, the maximum life time is approximately 3 years in the current sensor types. The new oxygen pump technology sensor has some major advantages over the older lead based sensor, such as there is no consumption of any materials within the sensor, the sensor life expectancy is > 5 years and being RoHS compliant it is ready for the future.
There is however a requirement for a constant low voltage bias to be
the thermal conductivity sensor will need to be a consideration on the sensor suitability, low cost is not always the best solution.
Infrared sensors are now miniature in size and are very effective in the measurement of percent volume methane and carbon dioxide without any of the cross sensitivity issues which are apparent in thermal conductivity sensors. Infrared sensors are slightly more expensive and require more thought in the electronics design to use, but they do offer the ability to measure both methane and carbon dioxide at the same time and now with the availability of “plug and play” electronic development kits. Infrared sensors also offer a more precise long term solution. This is certainly the case with new infrared sensors being developed specifically for biogas applications such as the new dual gas infrared sensor option from manufacturers such as e2v technologies. The IR15TT-R dual infrared gas sensor allows the user to monitor methane and carbon dioxide at the same time, utilising two independent channels fitted into a 4 series 20mm diameter package resulting in a much lower cost than two individual sensors.
The IR15TT-R sensor, which is specifically designed for the biogas
connected to the sensor just like other biased toxic electrochemical cells. Currently the new pump technology type of oxygen sensor is only available from one sensor manufacturer e2v technologies.
The environment within the bio-digester can be harsh and all of the sensors used will need to be designed to meet that challenge, robust sensors in stainless steel housings and inert gold optic construction are recommended.
All gas sensors used within this environment are classed as electrical components and they will need to be tested and approved as an electrical component fit for use in hazardous area locations.
The sensors can be Ex or Intrinsically safe for use and they will carry certification marking of the approval usually UL, ATEX, CSA, or a national standard of the country where the plant is fitted. Biogas can be explosive if mixed with air or oxygen in the correct concentration and is considered a hazardous environment where an explosion could occur.
For further information on sensors that are applicable to biogas applications or industrial and air quality applications please visit
www.e2v.com/gassensors and download the e2v air application.
AUTHOR DETAILS
Terry Brown Head of
Instrumentation Gas Sensors ISIS Division
Tel: +44(0)1245453675 Fax: +44(0)1245453604 Mob: +44(0)7801723903 Web:
www.e2v.com/gassensors
For immediate information on products featured in this issue please email us today!
info@iet-pub.com
SENSOR+TEST 2010 – The Measurement Fair Increase in Visitor Interest and Sense of Anticipation
The upturn of the economic situation in sensor, measuring, and testing technology as well as the economic strength and spirit of innovation in this industry were im pressive ly reflected by the lively course of this year’s SENSOR+TEST exhibition. A total of 509 exhibitors showed their novelties and interesting applications on 16,000m². With about 7,400 visitors, the figures of the previous year were significantly exceeded and almost reached numbers of 2008.
The exhibitors at the SENSOR+TEST were generally satisfied
with the fair. Alexander Koprian of Endress+Hauser GmbH + Co. KG, for instance, stated that “The SENSOR+TEST is one of the few trade fairs where we see our OEM customers for our sensor technology. We’re satisfied with the fair and definitely had an increase compared with 2009.”
Justin Drake of International Environmental Technology at the busy Sensor exhibition
Next year the SENSOR+TEST will be held from the 7th to the 9th of June, 2011, at the Nürnberg Exhibition Centre. On the programme parallel to the trade fair will again be the SENSOR+TEST conferences of the AMA Association – the SENSOR, OPTO, and IRS2. The focal topic of next year’s fair
will be “Ease to Use”, which concentrates on usability and user friendliness of sensors and measuring systems. Reader Reply Card no 192 Reader Reply Card no 193
Annual Buyers Guide 2010
IET
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