It used to be So Simple! CES
Back in the day testing for dust within a duct was not so much a simple task, but a task that had few of the regimented requirements of current times. There was basic equipment, few Standards, no accreditation and lots of dust and grit. The most common Standards were BS 3405 (Method for measurement of particulate emission including grit and dust (simplifi ed method)) and ISO 9096 (Stationary source emissions — Manual determination of mass concentration of particulate matter). The equipment required to test to these methods was basic, consisting in the main of a large nozzle, probe, glass fi bre wool fi lter assembly, dropout bucket and a large vacuum pump. Preliminary velocity and temperature measurements were taken using a pitot and temperature indicators. Calibration of the equipment was either optional or non-existent.
Where Plant had Emission Limits for dust, they were often set in hundreds of mg/m³.
With the large extracted volumes and the collected dust and grit in grams, it was easy to establish concentrations at a set particle size by the use of a sieve.
Abatement was often optional and the most common type available was the unmaintained cyclone or electrostatic precipitator (ESP) which at the larger combustion plants would later be backed with sulphur trioxide (SO3
) injection.
As emitted dust concentrations became unpopular and air quality became under scrutiny by environmental groups, established dust monitor manufacturers started to produce
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equipment that could successfully track the trend of the emitted dust from many processes. However, it was quickly realised that this trend was meaningless if it was not related to manual isokinetic extractive tests. It became apparent that with certain types of combustion processes the instrument response varied quite considerably depending on how the plant was being operated. This was particularly evident on coal fi red plant where an expected dust concentration displayed on an analyser, could be many times greater when the gas stream contained unburnt fuel in the form of carbon.
Emission Limits on large combustion plant eventually started to be reduced. This gave rise to improvements in the extractive measuring Standards and advancement in the dust monitor measuring techniques. In the year 2000 the Environment Agency introduced the Environment Agency’s Monitoring Certifi cation Scheme (MCERTS) and companies and personnel needed to be accredited to the MCERTS scheme and additionally to the International Standard ISO 17025 (General requirements for the competence of testing and calibration laboratories). The introduction of BS EN 13284 (Stationary source emissions – Determination of low range mass concentration of dust) was a big step towards improved and consistent extractive dust measurements throughout industry. For all the improvements made to the companies and personnel undertaking the extractive tests, very little improvement has been made to the actual sampling equipment used by test houses. Whilst there are one or two automated computer driven low dust extractive systems, the majority of test houses are still using the original type of manual sample trains designed many years ago.
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