When separating solids from a liquid, flocculation is used to maximize the rate and degree of separation. In the paper industry, flocculation is used to maximize production throughput and product quality. Regardless of the process, these goals need to be met by using the least amount of chemicals possible as well as meeting quality assurance requirements. By maximizing throughput, the scale of equipment needed can be reduced, which is especially important with gravity thickeners when conducting flocculation for mining or wastewater. One of the main challenges with flocculation is that it can be very difficult to actually track the flocs as they exist in process. One problem with characterizing flocs is that they tend to settle or float, therefore, achieving a representative sample can be challenging as the sampling location will have a direct effect on the results.
Another problem is that the flocs themselves tend to be very fragile, requiring great care and significant amounts of time for sample preparation. This preparation can include changing the temperature or diluting the flocs in some kind of solvent. Dilution may cause further flocculation or aggregation of the sample, requiring sonication to bring the flocs to their original dimension. If so much sample manipulation is required, it becomes questionable how representative offline measurements of the process can be. This is the critical issue that most people trying to characterize flocs run into when using an offline method. Also, because so much time is needed for each offline measurement, there might be an insufficient number of samples taken from the process to capture process dynamics.
The solution to these challenges is to use FBRM® and PVM® as in situ monitoring technologies in order to characterize and understand flocculation.
FBRM® (Focused Beam Reflectance Measurement) provides a precise and sensitive measurement of the rate and degree of change to the size and number of particles and particle structures as they naturally exist in the process. FBRM® instantly detects and quantifies changes in the size and population of flocs and unflocculated material. PVM® (Particle Vision Microscopy) provides images of the flocs as they exist in process, allowing the observation of all particles which, in turn, offers understand as to what is happening. Both of these technologies are probe-based, allowing the probe to be inserted directly into the process and observe flocculation in real time. There is no need to pull a sample or manipulate it in order to obtain a measurement.
Important parameters, such as floc strength or fines capture can now be quickly and easily determined with confidence. This enables users to understand how the flocs are affected by process parameters, such as shear, flocculent type including any effects from e.g., temperature and conductivity. In addition, users can directly observe how the flocs relate to downstream product and performance parameters.
FBRM® and PVM® can ensure that the rate and degree of separation is optimal in solids and liquids separation. In paper manufacturing, FBRM® and PVM® can be used to maintain production throughput while ensuring product uniformity. These tools can be used to instantly detect process upsets, minimize chemical flocculant use and quickly develop new processes.