Is it essential to add inhibitor with sulfuric acid for descaling ?

Hi Friends,

We all are well aware that scaling of equipment and pipelines is one of the critical issues in Alumina refineries. The scales deposited in white area of Alumina refinery are generally soft but the scales of red area of the plant are hard in nature. 

Different chemical cleaning methodologies have been developed and practiced by different Alumina refineries. In most of the Alumina refineries, the scales developed on the inner surface of heat exchangers of digestion circuit is cleaned by circulating dilute sulfuric acid for certain hours in almost Alumina refineries of the World. 

Since the dilute sulfuric acid is corrosive in nature, hence it may eat away the metals causing leakages in the tubes of heat exchangers. In order to protect the heater tubes during descaling,  addition of suitable inhibitor to sulfuric acid is a must.

There are variety of sulfuric acid inhibitors available in the market. The dosing rate of inhibitor varies from 0.10% to 0.50% of  concentrated sulfuric acid by mass. The inhibitor acts as protective buffer between the metal and dilute sulfuric acid.

The addition of inhibitor not only protects the equipment from corrosion rather it also reduces the consumption of sulfuric acid for descaling purpose as well.

Therefore, we can conclude that addition of inhibitor to dilute sulfuric acid used for descaling of equipment is essential.

Hope, I have covered the inhibitor issue to the extent possible.Please process your suggestions / remarks / views / comments, if any.

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Thanks and regards.

Kunwar Rajendra