Non-mechanical, high-energy, non-damaging polymer activation and blending systems from dynaBlend.
What is Polymer?
A polymer is composed of many monomer units joined together via a chemical reaction called polymerization. The degree of polymerization is the number of monomer units in the chain. The chain can be very long - this tremendous length gives polymers some of their unique properties.
The molecular weight of a polymer is the degree of polymerization multiplied by the molecular weight of the monomer unit. Acrylmide monomer has a molecular weight of 71. A polymer molecule with a degree of polymerization of 100,000 is made up of 100,000 acrylmide monomer units and will have a molecular weight of 7.1 million (100,000 x 71).
Organic polymers (or polyelectrolytes) are essentially water soluble linear polymers with molecular weights as low as a few hundred thousand and as high as ten million or greater. These products are characterized by the existence of ionized (electrically charged) site groups on the polymer molecule. The electrical charge on the polymer molecule can be negative (anionic), positive (cationic) or no charge (nonionic).
LIQUID EMULSION POLYMER
LIQUID DISPERSION POLYMER
Maximizing liquid polymer activation requires that high, non-damaging mixing energy be applied to the neat, concentrated polymer.
Emulsion-based polymers will gel if insufficient mixing energy is applied. High mixing energy is required to optimize emulsion polymer performance. However, exposing emulsion polymer to this high mixing energy after the polymer is activated will damage the polymer.
Mannich polymer chains are extended (activated) in their as-supplied form, which accounts for their high viscosity. These polymers are immediately susceptible to damaging mixing energy.
The dynaBLEND® has no mixing impellers to damage the polymer molecular structure. Its ultra-high, non-damaging mixing energy is produced through its multiple-stage process.
To optimize a dry polymer's performance is effectively wetting each individual particle of polymer. To accomplish this task requires that the polymer be dispersed prior to being introduced into water. Systems which merely meter polymer into a bowl of water fail to meet this first criteria, and polymer gelling occurs and additional extended mixing and aging is generally required. Reaching optimum polymer performance is difficult, if not impossible, after polymer gelling occurs.
Simply preparing the proper solution concentration. Industry standard is between a 0.25% to 0.5% solution concentration. Preparing a solution concentration in excess of this will result in increased viscosities. As viscosity increases, so does the aging time required to reach optimum polymer performance. Note that initial make-down solution concentration often is different than final feed concentration. Final feed concentration can be as low as 0.1%. To achieve final solution concentration a post dilution system is provided after the solution metering pump.
Providing adequate aging time. Recommended minimum aging is 30 minutes for simple-to-hydrate polymers. As a general rule, though, and for design purposes, a minimum of 45 to 60 minutes is recommended when preparing solution concentration of up to 0.5%. Anionic polymers (negatively charged) can be more difficult to hydrate than cationic polymers (positively charged). The general rule of thumb for Anionic polymers is to double the aging time.
Don't over-mix. The amount of mixing time highly depends on the polymer being used. Simple-to-hydrate polymers should be mixed only long enough to prevent the polymer particles from settling out. These particles will not settle out after they have hydrated to the point where they cannot be seen. For more difficult polymers, longer mixing may be required. Over-mixing will damage the polymer and reduce the polymer's effectiveness.
Polymer performance can be severely limited when polymer is overexposed to impellers that induce damaging mixing energy or other cause of excessive shear. Optimum polymer performance is unattainable when polymer is exposed to insufficient mixing energy. The result is only partial activation and the formation of "fish-eyes," a term used to describe agglomerations of unblended polymer that is ultimately wasted.
"It is generally recognized that the velocity gradient or G-value concept is a gross, simplistic and totally inadequate parameter for design of rapid mixers". (A. Amirtharajah, Design of Rapid Mix Units, Water Treatment Plant Design for the Practicing Engineer, Edited by R.L. Sanks, Ann Arbor Science, Ann Arbor, MI, 1978)
Camp's "G" value is not intended for design or comparison of different impeller types, and has not been shown to accurately correlate mixing effectiveness for different mixing processes.
The criteria set forth for Camp's "G" value may be useful for determining average mixing intensity per unit volume for a particular mixing process. It cannot be used to compare the dynaBLEND's "HydroShear" mixing process to any impeller-type mixer.
Camp's "G" is an expression for the average power applied per unit volume, and does not account for the much higher energy density, and therefore shear stress, near the impeller. Thus, it does not account for the damage of the polymer's molecular structure caused by impeller-type polymer mixers.
The dynaBLEND's patented "HydroDynamic" mixing process circumvents this problem. Its track record of proven performance and reliability substantiates the fact that Gt values can not be used for comparison purposes or as a means for inferring a polymer blending system's performance capabilities.
Emulsion & Dispersion Polymers:
The decision to provide aging largely hinges on the size of the application. It is more difficult to justify the investment of the tank, solution metering pump and controls required for aging in a small versus large application. There is also a benefit to the simplicity of a simple in-line polymer activation and feed system. The vast majority of dynaBLEND installations do not include aging.
Polymer aging may make sense in larger applications such as applications where multiple dewatering devices are used or in very large filtering or clarifying applications. Even when a small percentage of polymer savings is achieved in these large polymer volume applications, a substantial dollar savings may be realized.
Mannich polymers are already activated in their as-supplied form, therefore aging of Mannich polymers is typically not required.
A common misperception is that having an aging tank eliminates the need for a high performing polymer make-down system. This couldn't be further from the truth. Optimum polymer performance with or without aging still hinges on how effectively the polymer activation/blending system does its job.
FAQs About Polymer Systems
If aging is used, how much aging time do you need?
This depends on the performance of the activation/blending system. The minimum recommended is 20 minutes, and is based on the dynaBLEND's performance. However, low-energy inducing polymer systems may need 1 to 2 hours to fully benefit from the aging process.
What concentration should the system blend?
Liquids 0.5% to 1% is typical, on the solution metering pump skid to prepare a final feed concentration from 0.1% to 0.25%.
What is the maximum time the polymer can be aged?
Polymer in solution should not be stored for more than 24 hours.
Will the polymer solution stratify?
It is very uncommon for polymer solution to stratify, particularly if properly prepared. However, dilution water quality can impact the effectiveness of the activated polymer solution. Using poor quality dilution water can cause the polymer to begin reacting with contaminents in the dilution water before the solution reaches the point of application.