Sampling for DOAS cross-duct CEM systems
Enviro Technology reports that Opsis engineers have developed a solution to the problem sometimes encountered when it is difficult to locate cross-duct DOAS analysers close to the stack due to restricted access and the necessary limit of a maximum 10 metre length of fibre optic cable/
"Fastloop" is a way of diverting exhaust air into a loop arrangement in whereby a conventional Opsis transmitter and receiver is able to measure the gases with the associated analysers positioned close by on 1-2 metres of fibre optic cable. By this means, the monitoring system may be located at ground level in the most convenient position the site sill allow.
By introducing a junction from the exhaust gas route after the exhaust fan, some of the pressurised gas air is forced into the loop and through the open path monitoring system. This air is then fed back into the exhaust system before the fan. Enviro Technology says there is no detrimental effect on the accuracy of the readings taken and, in effect, Fastloop fools the analysers into assuming the measurements taken are from within the stack itself.
The Fastloop solution therefore provides the benefits of DOAS cross-duct systems without the limiting factor of fibre optic cabling.