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Measuring wet H2S in a scrubber or duct application

Odour control in wastewater treatment plants, sewage collection systems and industrial applications often requires the use of biological and chemical scrubber systems. Many of these scrubbers employ a wet process, using hypochlorite solution to remove H2S from air streams prior to discharge.

As a specialist manufacturer of both analytical gas and water sensors, ATi recognise that trying to measure gas in a wet air stream is problematic as the membrane on the electro-chemical sensor is probably going to be wet. There will also be a level of contaminant coming through the system, especially on the inlet where the gas stream is raw and dirty. In any normal instance, this type of ‘blinding’ would see the levels seen by the sensor drop to zero, with maintenance being required immediately. The ATi ‘wet stack sensor’ can work in both wet and dry applications. This design allows the sensor to be used in either application which is advantageous because the chemistry with these scrubbers can change from design to actual start up. The gas sensor is protected by a pre-filter membrane, which allows for simple maintenance when required. The added protection isolates the sensor from the sample and can be replaced easily on a quarterly basis when required. The Q45S can be verified and then calibrated, if necessary, by using a bottle of H2S gas, a calibration adaptor and half a litre a minute regulator. This can be completed at the same interval as the pre filter membrane replacement.

Reliable and effective air blast for maximum sensor efficacy

Because Q45S systems are often monitoring gas streams with condensing levels of water vapour, provision has been made for eliminating water droplets from the sensor that could present a barrier to the diffusion of H2S into the sensor. An optional air-purge system controlled by the transmitter will periodically deliver a blast of air across the critical sensor surfaces to remove water droplets. This system ensures a clear gas diffusion path to the sensor and reliable measurements on a continuous basis.

The Q45S is used by many UK water companies on waste-water sites. The system has proven successful as a continuous ‘break through monitor’. There are over one hundred installations in the Middle East on their scrubbers as H2S can be a particular problem in hot countries. With little maintenance and simple verification/calibration, it is the monitor of choice as a cost-effective option when compared to more complicated systems on the market.


• Specialist H2S sensors for wet and dry applications

• Ranges for both inlet and outlet protection using the same sensor

• Unique ‘integrated’ air purge system for reduced maintenance

• Simple calibration checks

• Alarm relays and analogue outputs for connection to existing site systems

• Cost-effective solution for odour management

This entry was posted in ATi UK, Gas Monitoring, Hydrogen Sulphide, Monitoring, Water Treatment. Bookmark the permalink.

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