Maintaining a minimum concentration of an effective dispersant polymer is crucial in an alkaline cooling water treatment program. The problem is knowing exactly how much polymer is available in the cooling water to combat fouling and corrosion of heat transfer equipment. Many years of research and effort have gone into the development of a method for tracing the concentration of polymers.
Rohm and Haas has made a tremendous advance in the ability to understand and control a cooling water system by creating two new traceable polymers, Optidose™ 2000 copolymer and Optidose™ 3100 terpolymer. The Optidose polymers are tagged so that a simple and inexpensive field test may be used to determine the amount of free polymer in the cooling water. Use of the Optidose system (polymer and test kits) gives the end user a greater understanding of the cooling water chemistry and the ability to control the level of free polymer. Potentially disastrous fouling situations may be averted before they occur to maintain heat transfer at maximum levels.
Predict And Avoid Fouling Situations
The traceable polymer system will predict and guard against potential fouling and corrosion situations in alkaline cooling water. This has been proven by an extensive battery of tests that also serve to assure users that Optidose polymers will perform at peak levels.
Optidose polymers were evaluated and compared to their untagged equivalents in two independent cooling tower pilot systems which simulate both large and small cooling towers. The polymers were evaluated in both stabilized phosphate and allorganic treatment systems. The tests were conducted over seven- to ten-day periods, and conditions were varied to mimic actual operating situations, including underfeeding to deliberately cause fouling conditions. The resulting data show clearly that monitoring the free polymer level in the system provides valuable information which will allow an operator to maintain control, minimize fouling situations, and maximize heat transfer capability in heat exchangers and other equipment.
The pilot plant tests demonstrate what happens when a cooling system gets out of control. The testing began with a controlled addition of polymer to the system to reach steady state, and then the polymer additive was suddenly stopped (simulating a change in makeup water, the addition of particulate load to the system, failure of a feed pump, etc.) to upset the stability of the system.
The first test simulated use of a stabilized phosphate system containing Optidose polymer (8 ppm feed rate) without tracing. Levels of free polymer were monitored for information only. As the test progressed and stability was lost, there was no observed change in the system until scaling started and the heat transfer (% Uc) began to decrease. At that point, the polymer feed was restarted with a large slug dose, and another slug was added the next day, but it was too late to undo the fouling which had occurred. Heat transfer remained significantly below 100%.
The second pilot run utilized Optidose traceable polymer (8 ppm feed rate) with periodic testing and laboratory analysis of free polymer levels. Because the system was being tested every day, the decrease in free polymer was immediately detected after system stability was interrupted. The free polymer level dropped from about 8 ppm to 2 ppm. Restarting the polymer feed along with a single slug dose of 8 ppm brought the free polymer back to desired levels without adversely impacting heat transfer. In the exact same way, use of the traceable polymer can give an operator the detailed information necessary to avoid fouling situations and keep the cooling system operating at peak efficiency.
The pilot tests proved that if free polymer in the system drops below 2 ppm, fouling occurs within one to two days, probably due to formation of particles that accelerate the removal of remaining free polymer. Therefore consistent use of the Optidose system (polymers and test kit) will enable operators to identify potential fouling situations and increase polymer dosage to avoid problems. Results of pilot tests using the stabilized phosphate system are shown in Figures 1a and 1b for Optidose 2000 and Figures 2a and 2b for Optidose 3100. Figures 3a and 3b and Figure 4a and 4b show similar plots for the all-organic program, run with a polymer feed rate of 5 ppm. No slug feeds were necessary in the all-organic tests because of the short system half-life.