Sensor Technology 17


analysis of the potentially odorous compounds present. Odour threshold limits were established using the dilution method outlined in ASTM E679. This enabled ELLONA to create a quantitative fi ngerprint for the site’s odours and to thereby install monitors that are capable of detecting the specifi c odorous compounds that exist at the site. Using the same training, a quantitative fi ngerprint allows the identifi cation of the nature of the odours as well as their sources.


At Green Star, the incinerator is burning domestic waste, from which odour production varies according to the weather (temperature), which is why continuous monitoring is so important.


Each of the ELLONA monitors (WT1) at Green Star features a comprehensive array of sensors measuring temperature, humidity, pressure, hydrogen sulphide, ammonia and VOCs. Other important variables are wind speed and direction, which have obvious effects on odours. Wind is therefore monitored at the site continuously; not just to be able to model the movement of odour plumes but also to be able to differentiate any odours that arrive from an external source. ELLONA therefore worked in partnership with the high-performance computing and modelling company NUMTECH to model the complex air fl ows that take place in the plant and in the surrounding urban environment. Meteorological conditions determine whether the site’s emissions are dispersed in the local streets. The combination of numerical simulations (forward and backward) and the network measurements make it possible to identify the contribution of the site and the potential sources.


the method is appropriate. However, the major disadvantage, apart from the time delay and the cost, is that the gas sample represents one moment in time, so it cannot be truly representative. This is because odour levels may have been much higher or lower before or after the sample was taken, but there would be no data to show this. Continuous monitoring is therefore preferable, but only if the data are representative of the local odours.


A further complication with odour is that it is rarely the result of one individual chemical. Frequently, odours are caused by a mixture of chemicals, and there may be synergistic effects between different odorous compounds. For this reason, the standard method (grab samples) is based on human perception. In order to be able to monitor odour continuously, it is necessary to utilise an ‘electronic nose’ or IOMS (Instrumental Odour Monitoring System), with the capability to measure all of the most common odorous compounds. For this reason, the ELLONA monitors employ a suite of monovariant and multivariant sensors that are capable of measuring volatile organic compounds (VOCs), sulphurous compounds such as hydrogen sulphide, mercaptans and other odorous compounds such as amines or aldehydes. The detection of specifi c gases, however, is not suffi cient on its own, to effectively monitor odour; it is also necessary to be able to identify site-specifi c odours and to conduct multidimensional mapping so that sources can be identifi ed.


Prior to the confi guration of Green Star monitors, ELLONA collected representative Tedlar bag samples from the site, and conducted comprehensive laboratory and dynamic olfactometry


The WT1 units store measurements internally, but the data are also transferred to the Cloud every 10 seconds for processing. Data from the physical sensors and from the virtual sensors (created from the physical sensors’ data and mathematical models) provide information on air quality, odour identity, intensity and duration. The measurements and the derived odour information are provided in real-time to Syctom via a dedicated website, which also provides the facility to view historical data.


The advantages of network monitoring


It would have been possible to install a single ELLONA monitor at the Green Star site, and to model odour around that point, but by installing a network of 19 WT1 monitors Syctom derives a number of important advantages. For example, networks of IoT monitors improve the capability to track the speed and direction of odour as it moves across the network, which in turn helps to identify odour sources. Similarly, if all of the monitors report an unrecognised odour moving across the network, it is likely that


it is derived from a diffuse external source or a distant point source. However, if one monitor in the network reports an odour incident; it is more likely to be derived from a point source within the network.


Odour levels at any point are generally comprised of odours from different sources, so the ability of the ELLONA system to identify sources means that it is able to measure the relative contribution of the different individual sources to each odour incident.


Most of the WT1 monitors are located within the local neighbourhood. This enables the evaluation of the amplitude of odour change in comparison with the reference situation. Alarm thresholds have been set for the physical and the virtual sensors, and an alert is issued each time a threshold is exceeded. Consequently, Syctom is able to respond quickly to any odorous incident.


Summary


Continuous, smart odour monitoring has been shown to offer major advantages over spot sampling. However, the unique features of the ELLONA solution are that the monitoring network is developed to match the specifi c odours that exist at the Syctom site, and ELLONA’s mathematical models enable the continuous delivery of source identifi cation with both qualitative and quantitative data.


The continuous odour monitoring system has improved Syctom’s understanding of the processes that affect odour, including specifi c events and the volume of waste being handled for example. In addition, the availability of trustworthy transparent data has provided reassurance to local residents.


Explaining the value of the insights that the ELLONA solution delivers, Claire Bara says: “The monitoring system has confi rmed the main odour sources that we have on-site; in particular, it has demonstrated that odours arising from waste truck movements are more important than we initially expected. To-date, the measurement network has helped us to identify and implement the most effective mitigation measures. That work is currently ongoing, but we expect the system to show us that these measures have enabled odour improvement, for the benefi t of our staff and local residents.”


Looking forward, now that the concept has been proven, the plan at the Green Star site is to further lower odour nuisance by implementing odour mitigation measures and identifying those which are the most successful. As time passes, the constituents of household waste are likely to change, but with the monitoring system in place, Syctom will be able to respond accordingly to any changes in odour generation.


Author Contact Details Graham Meller • Email: gmeller@buttonwoodmarketing.com Miguel Escribano • Ellona • Address: 3 avenue Didier Daurat, 31400 Toulouse, France • Tel: +34 605 977 027 • Email: miguel.escribano@ellona.io • Web: www.ellona.io


Graham Meller Miguel Escribano


New, sub-miniature, low-cost, high sensitivity and fast-response detector with built- in preamplifi er provides the ideal choice for industrial gas analysis applications


Hamamatsu has developed a new InAsSb photovoltaic detector (P16702-011MN) with built-in preamplifi er offering high sensitivity to mid-infrared light, up to 11 micrometers (μm) in wavelength. Hamamatsu achieved this by combining the latest InAsSb (indium arsenide antimonide) mid-infrared detector with their unique circuit design technology. Compared to Hamamatsu’s previous detector modules with same level of sensitivity, the P16702-011MN size and cost is drastically reduced, and it exhibits fast response time. This makes it an ideal choice for portable gas analysers able to immediately analyse exhaust gas components at measurement sites around factories.


The P16702-011MN is a compound semiconductor photodetector with built-in preamplifi er for electrical signal amplifi cation.


Each molecule has its own vibration and absorbs infrared light at a specifi c wavelength determined by its energy. This property can be used to analyse and identify the type and quantity of chemical components contained in a sample. Therefore, mid-infrared light is widely utilised in the analysis of nitrogen oxides and sulphur oxides contained in exhaust gases from factories, etc.


To meet needs in applications such as gas analysis and monitoring of processing laser equipment, Hamamatsu develop and sell InAsSb mid-infrared detectors and detector module products with enhanced sensitivity, by integrating these with electronic circuits and components including preamplifi ers. To keep up with the growing market demand of further downsizing equipment, Hamamatsu have been working on a sub-miniature, low-cost mid-infrared detector device that also offers high-speed response.


In designing this new device, Hamamatsu adopted the latest back-illuminated type InAsSb mid-infrared detector with a sensitivity 1.5 times higher than the regular type. Hamamatsu encapsulated it into a small cylindrical package with a diameter of approximately 9 mm. The device was drastically downsized to about 1/200th the volume of Hamamatsu’s module products, yet it still offers the same level of sensitivity capable of detecting mid-infrared light at wavelengths up to 11 μm. What’s more, the wiring in the package is optimised to increase the response speed up to 100 megahertz, which is twice as high as Hamamatsu’s module products, thus improving measurement accuracy. It also has a lower manufacturing cost since the number of required components was reduced.


The P16702-011MN will speed up the replacement of mercury-cadmium-telluride (MCT) infrared detectors which is currently the mainstream in high-precision mid-infrared spectroscopy but contains toxic substances restricted by the RoHS Directive (*1). Hamamatsu Photonics is one of the few companies in the world that manufacture both photodetectors and light sources. Using the P16702- 011MN in conjunction with a quantum cascade laser or QCL (*2), which they also manufacture, allows making measurements at even higher speeds, resolution, and sensitivity.


For More Info, email: email:


For More Info, email: 59648pr@reply-direct.com WWW.ENVIROTECH-ONLINE.COM


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