Abstract
Although the makeup water of a low-pressure boiler is usually pre-softened, the boiler is still exposed to the risk of hardness leakage (Ca, Mg, etc.) from the feedwater. In the case of returning the drain of the condensate system into the boiler, Fe, Zn ions and sometimes hardness generated or contaminated in this process will also enter the boiler. These hardness ions, Fe and Zn, lead to scale formation in the boiler. It will cause the energy efficiency to deteriorate and result in tube failures in the worst case. Polymer-based technologies have been introduced and developed for a long time to deal with this problem. However, when the hardness leakage surpasses the capability of the polymer-based dispersant, scale formation will occur. Acid or chelating agents are widely adopted, but the generated waste has to be treated separately, and the inner surface of the boiler may suffer from corrosion. The newly developed polymers described in this paper work like other traditional polymer-based dispersants with a unique feature: they can remove scale even in the case of temporary excessive hardness leakage. As a result, they combine the function of the prevention and removal of scale at the same time. The heating surface remains clean throughout the entire operation period. In addition, it proves to be highly effective in the case of serious silica contamination (~1000 mg/L), reducing the cost by allowing the system to work non-stop with minimal blowdown in a highly concentrated state. Furthermore, by applying it to systems in which the drain is disposed of due to serious hardness or Fe contamination, the drain can be rerouted into the boiler so that the operation cost can be reduced. The effectiveness of these polymers has also been confirmed in over one thousand systems operating in Japan, Southeast Asian countries and European countries.
