Predicting calculating scaling tendency in membrane plants

Predicting scale formation in desalination plants is a matter of a number of calculations. The accuracy of these calculations is dependent on accurate data, and representative operating conditions. These calculations are normally carried out by using software, supplied either by the membrane manufacturers or by antiscalants manufacturers. Often the user will accept the results without question, and without fully understanding their meaning or the methods and assumptions used to generate the results. The paper outlines the steps that the software undertakes to reach its results. It will also show the sensitivity of the results to the accuracy of the initial data, and the value of having a complete water analysis. The paper will also outline some of the common errors made when using scale prediction software. It will also introduce the use of calcium carbonate precipitation potential (CCPP) as a method of predicting scale, and linking this with the dose rate of antiscalant.

5. Common errors Although the software can carry out a few basic checks, such as ensuring the water analysis balances, it is not capable of checking if the user has not made an input error. The more common mistakes that are made are; 1. Errors in the units for the water analysis. The most common is to confuse values for hardness measured as calcium carbonate with values measured as the actual ion. This is The software produced by antiscalant manufacturers is a reliable method for providing the user with the required dose rates for antiscalants. Although the formulae used by the different manufacturers for their products differ, the general approach is similar. The calculations can only ever be as accurate as the information used, and therefore it can be beneficial to seek advice from the manufacturers representatives to ensure the projection is accurate.