Pin Down the Sedimentation Process

KROHNE (Germany) introduces the OPTISYS SLM 2100 optical measuring system for sedimentation profile measurement and continuous tracking of sludge blanket. It allows for reliable tracking of sedimentation layers in industrial and municipal applications, e.g. in sedimentation bassins of power plants, waterworks etc., as well as sludge blanket measurement in clarifiers and sludge thickeners in sewage treatment plants.

OPTISYS SLM 2100 is the successor of the OPTISENS OAM 2080 sludge blanket measuring system, but has been completely re-engineered to extend its area of application to sedimentation processes. It uses a optical suspended solids sensor, which is submerged into the basin. Unlike ultrasonic-based sludge level meters, the optical measuring principle is not subject to echo returns from walls or separating zones as well as signal damping by fluff or floating sludge.

OPTISYS SLM 2100 is the first sedimentation measuring system to offer three measuring modes: measurement of sedimentation profile, two-zone monitoring and zone-tracking. For sedimentation profile measurement, the system directly measures the suspended solids concentration at all heights as the sensor travels through all layers of the medium. The two-zone monitoring feature enables to monitor the heights of two predefined concentrations, e.g. fluff and sludge. It can be used to prevent sludge washout into the next stage.

For continuous level measurement of a predefined concentration, also known as zone-tracking, the optical sensor moves within the medium until it detects the concentration and follows or tracks this zone continuously. This can be used e.g. to monitor the change of the sludge blanket level when de-pumping the sludge. Here, OPTISYS SLM 2100 can replace two measurements commonly used in this application: with an ultrasonic level meter, disturbances of sludge blanket can lead to false measurements or even loss of signal for the ultrasonic device. To compensate for this, an additional turbidity measurement is installed in the depumping line. Both can be replaced by the new OPTISYS SLM 2100.

The integrated signal converter of the OPTISYS SLM 2100 is the well-known MAC 100 multiparameter converter for analytical measuring devices. It shares the same operating concept as KROHNE flow and level signal converters and thus supports quick familiarisation. KROHNE is the only measuring instruments manufacturer to offer a common operating concept for both physical and analytical parameters.

OPTISYS SLM 2100 has two 4…20mA outputs that communicate height and concentration according to the selected measuring mode. Inputs include a rake guard switch that protects the sensor from being catched by the rake. Also maintenance mode and interim measurements can be started remotely via digital inputs.

Both sensor and housing are made of stainless steel. The protection rating IP54 housing has a build-in fan to cool down electronics in hot environments. It also houses a heater for cold conditions to prevent the cable and mechanics from freezing. As option, an integrated spray cleaning system cleans both the sensor and the transport cable following each measuring cycle, keeping maintenance costs to a minimum. While this was standard with the previous system, it became an option as in many applications the clear zone is sufficient to clean the sensor, and thus the base price of the system is lower.