To obtain optimum control of many chemical processes, it is essential to monitor the level of undissolved solids in bulk fluids. It is also essential this be done in real time, thus, on-line or at-line. Currently, there are many commercial optical devices on the market which can determine particulate concentration in fluids. Measuring instruments used on-line generally use light scattering methods. This technique is very limited as the undissolved solids must be very reflective and of uniform size and shape. It also has a very limited range, usually under 0.1% total undissolved solids.
Ultra sound has also been applied for the measurement of undissolved solids in bulk aqueous solutions, such as water treatment and municipal waste treatment facilities. Limitations of this technique include: 1) the particles must be of uniform size and shape; 2) a maximum temperature of 50 C. for the process solution as temperatures above that change the physical parameters of the focusing lenses and 3) organic solvents can swell or dissolve the polymer focusing lenses required for these systems.
The most commonly applied methods employ off-line gravimetric techniques. A given volume of sample is filtered to remove the liquid. The residue is then weighed. The weight of the residue versus the bulk sample determines the undissolved solids concentration. This technique is time consuming, not usually within the real time of the process and requires expensive manual labor.