pH and ORP sensors as used for process control in bleaching operations at pulp mills - Case Study
- Specially Engineering Dissolved Chlorine Gas Resistant Solid State Reference
- Flat, yet rugged break resistant glass minimize cleaning requirements
- Application specific engineered thermoplastics and conductive polymer materials of construction lead to optimized sensor lifetime and accuracy
A pulp and paper producer wanted to improve their control and reduce their maintenance time and costs for their ClO2 bleaching process lines. They wanted to better control the brightness of the resultant pulp and reduce down time due to pH and ORP sensor failure and cleaning requirements. This meant that they were replacing their sensor every 1-2 months and cleaning and calibrating biweekly.
Conventional pH/ORP sensors experienced fast intrusion into the reference element due to the high temperature (from 100 to 150 ºC, 212 to 302 ºF) and pressure (50 to 100 psi) in the presence of high concentrations of chlorine dioxide gas. Previously used pH and ORP sensors required frequent calibrations due the drift of the reference element. The strong bleaching agent attacked both the sensor’s internal “O”-rings and other external “O”-rings that sealed it to the titanium sheath. Failure of these “O”-rings permitted the dangerous process gas to intermittently escape intermittently during removal and insertion of the multi-component valve retractable sensor assembly. The sealing agent for the junction and pH components were dissolved and eroded, allowing the gas to intrude all the way through the reference element and to the back of the sensor.