Practical experiences in additive screening using a torque-based flocculation analyzer.

Application: This study describes a method to measure the impact of typical papermaking additives on the degree of flocculation and the resulting floc's resistance to shear.

Laboratory evaluation of a retention/drainage aid program should be the first step before any process change and a regular part of technical service programs. This saves time and money.

This paper describes results from in-mill polymer screening experiments using a novel flocculation analysis technique. The method is useful for measuring the impact of typical papermaking additives on the degree of flocculation and the resulting floc's resistance to shear. As a sample is stirred at a constant speed, a retention aid is added and flocs begin to form. These flocs increase the load on the impeller motor. Therefore, the degree of flocculation, which is proportional to the increase in load, can be measured in real time. As the flocs break up, the load decreases, correlating to the floc's strength or resistance to shear. This information can be used to screen polymeric treatments of paper mill furnishes and also to optimize chemical programs.

The device's applicability is based on the wide range of samples it can analyze and its sensitivity to small changes in polymer chemistry and dosage. The data generated by the analyzer are dependent on the type of chemical applied, its dosage, and the sample being studied. This seven mill study included samples from sludge press influent at 6% solids to primary cleaner accepts as lean as 0.4% solids. The paper includes results for various furnishes and retention aid chemistries.

This device provides an objective, numeric value for the degree of flocculation and deflocculation. This technique can also measure the state of flocculation continuously and allows the user to record the signal as a function of time. Data are available for the user immediately. A limitation is that this technique measures torque or viscosity eta sample and not retention or drainage.

The work reported here was collected on-site at mill locations, showing that this device is rugged enough for in-mill chemical screening and optimization use. The data are repeatable and correlate well with traditional lab techniques such as free drainage and Britt jar tests.

Anker is a project manager in the Technology group at Ashland Specialty Chemical Company, One Drew Plaza, Boonton, New Jersey, USA, 07005; his email is [e-mail].