Dear Tamer, Citric acid can ...

Dear Tamer,

Citric acid can be used for cleaning the scaling after its formation. Other acids canbe used for cleaning (sulphamic, formic, hydrochloric) and the choice is based on the material of the tubes. All these cleaners are effective for carbonates and magnesium hydroxide with negigible efficiency for calcium sulphate.

The prevention of the scaling by carbonates can be carried out in two alternative ways:

a)  by venting all CO2 out before heating. According to the carbon curves, the carbon Equilibrium is 100% to free CO2 for acid pH (below about 5,8). Acidification is typically achieved by injecting Sulphuric acid (rather inexpensive)

b) by dosing antiscalant (typically a few ppm of polyphosphates or other brands such as Nalco 72990 or Belgard V)

Scaling by Sulphates is much more critical and the best prevention is to keep the temperature and Ca++ concentration below the precipitation curves (curves available). Some efficiency is ensured by special antiscalant brands (like Genesys) which are effective anyhow only at low working temperature (let's say below 60°C). After the formation, the only effective cleaning technique is the mechanical brushing.

In some cases, Ca++ was reduced by a pre-treatment of Nano-Filtration, thus preventing the formation of both sulphates and carbonates.

Mg(OH)2 scales only for very high temperature or very high alkalinity (curves available) but may scale along with carbonates and form a composite incrustation