Monitoring & metering G

overnments from around the world have implemented environmental regulations to reduce the emissions of volatile

organic compounds (VOCs) from industrial processes. For example, according to the European Solvents Industry Group, total VOC emissions in the EU have been reduced by more than 60 per cent since 1990.

BaCkGrOund VOCs are released from industrial activities that utilise organic chemicals such as solvents, as well as from engines and incinerators that burn organic materials and fuels. Both types of application require similar monitoring equipment, but this article will focus on those applications that involve solvents. Solvents are used widely in the chemical

industry as well as for cleaning and degreasing products and machinery, or dissolving, thinning and dispersing coatings, adhesives, paints and inks. Solvents evaporate readily at room temperature and represent a significant safety hazard in the workplace, so they are generally vented away from workers and the emissions from such vents frequently require abatement prior to release. Solvent emissions have to be minimised

because of their environmental effects, which include the formation of ozone, a constituent of photochemical smog. At ground level, ozone is generated when VOCs react with nitrogen oxides (NOx) in the presence of sunlight. Ozone can have both acute and chronic effects on humans; affecting the respiratory, cardiovascular and central nervous system, as well as reproductive health. Ground level ozone can also have harmful effects on vegetation and sensitive ecosystems. In most countries, the emissions of regulated

processes with the potential to release VOCs are issued with permits that include an emission limit for total organic carbon (TOC). The Standard Reference Method for the measurement of TOC is with a Flame Ionisation Detector (FID). In some cases, it may be necessary for the monitoring activity to speciate toxic VOCs or to distinguish between methane and non-methane VOCs.

EurOpEan VOC SOlVEnt EmISSIOnS dIrECtIVE (SEd) The main objective of the SED is to reduce the emissions of VOCs, and operators have two main compliance options. They may demonstrate compliance with a VOC emission limit value and fugitive emission limits by submitting monitoring data. This data will either include annual or continuous monitoring results depending on the size of process’s VOC emissions. Alternatively, processes may use a solvent reduction approach to achieve the results that would be obtained from meeting a mass emission limit. The reduction scheme enables the operator to attain emission reductions, equivalent to those that would have been achieved if the emission limit values were to be applied. This could be by substituting products with a high solvent content for low solvent or solvent free products and/or changing to solvent free production processes.


Monitoring solvent eMissions

to ensure coMpliance With over 40 years of experience in designing VOC analysers, Signal Group has specialised in developing instruments that enable process operators to demonstrate compliance. In the following article Signal’s Stephane Canadas will explain the vital role of monitoring. Under the SED, regulators require continuous

monitoring where the average emission, following abatement, is more than 10 kg/h of total organic carbon. Continuous monitoring is also required where the regulator considers it necessary to demonstrate compliance with VOC emission limits. If continuous monitoring is not necessary, the regulator will require periodic measurements. For periodic measurements of VOC at least three readings must be obtained during each measurement exercise. Where there is consistent compliance with emission limits, regulators may consider reducing the monitoring

frequency requirement. However, the monitoring frequency should be increased, for example, as part of the commissioning of new or substantially changed activities, or where emission levels are close to the emission concentration limits. Clearly, VOC monitoring, both continuous and

periodic, have a key role to play in demonstrating compliance. However, Signal’s customers also use FIDs to measure the effects of mitigation measures; to check the performance of abatement equipment; for process control, and to investigate diffuse emissions.

April 2021 Instrumentation Monthly

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