In the last weeks, we described the importance of water recovery and the investments that help to improve the recovery of valuable minerals. This week, we will focus on the efficient use of flocculants.
Flocculants are chemicals by which fine particles are caused to clump together into a floc. These flocs of particles weight more than one fine particle itself, therefore the effect of gravitational forces is increased, and so is the sedimentation rate.
Inefficient use of flocculants leads to extra reagent costs and a less effective operation. Therefore, the operator sets a target density in the feed of the thickener. Process operators want to target the highest solids percentage by weight of the feed slurry at which free settling of particles can occur in the thickener.
Measuring the density of feed slurry in the thickener is important for process control, to improve flocculant use and efficient control of the mixing process. The feed slurry is monitored in real-time by an in-line density meter to “see” if the density value complies with the target density.
Example of different measurement points at a thickener tank
Insufficient process control may lead to poor settling conditions in the tank, reduced underflow density and increased overflow solids. Poor settling could indicate flocculation problems, air (foam) in the tank or a high percentage of solids in the feed. Beyond measuring in-line, instrumentation can also be used for measurements in tanks.
For example, bed level measurement is crucial for immediate detection of rising solids. Different layers (from clarified water to mud and heavy mud) can be detected by submerged ultrasonic probes. The so-called ‘diver’ probes are constantly moving upwards and downwards in the tank to measure mud levels, settling zones and overflow clarity. Bed level can be important for some control strategies, because it can be used in a control loop for flocculation.
Operators ideally want to create steady operating conditions in the thickener, with a clarified overflow containing minimal solids and a dense underflow with minimal liquid. However, process conditions are subject to changes over time. When changes occur, instrumentation and automation can help operators to keep control of the process by real-time detection of events.
Please contact Rhosonics if you want to learn more about the importance of density measurement in the thickening process. Also, you can click here to read the first blog about water recovery in the thickening process. You can click here to read the second blog about investments that help to improve the recovery of valuable minerals.