Some calcium carbonate scaling indexes are shown to be ineffective and inaccurate in concentrated cooling tower water at pH levels above 7.5. In addition, there is a misunderstanding by many water treatment vendors on the use of the indexes. This has resulted in confusion by both end-users and vendors. More importantly, these indexes are shown to be inaccurate and ineffective for calcium carbonate scale prediction. This paper will review many of the available indexes, the basis for their calculations, how they compare, and which are effective in cooling water systems.
The development of a new index was started over 10 years ago and has been verified in operating systems. Since most cooling water treatment programs now operate at a pH level above 7.5 and as high as 9+, the index provides a more accurate and practical estimation of calcium carbonate scaling tendencies. Case histories are provided to show a comparison with other indexes, such as the Ryznar and Langelier indexes.
