Effective condensate protection

Protecting steam and condensate systems from materials corrosion can be problematic in some cases. The causes of condensate corrosiveness may be dissolved oxygen on the one hand, or over-acidity due to dissolved carbon dioxide

on the other.

One of the main causes of oxygen corrosion in condensate systems is incomplete oxygen scavenging in boiler water. For this reason, reliable measurement and monitoring of excess oxygen scavenging agents in boiler water is in the interests of corrosion protection for the condensate system.

Fig. 1:
corrosion problems
If water containing carbonates is used as feed water, stress on the condensate from carbon dioxide is unavoidable due to what is known as sodium carbonate decomposition. Possible protection method for pipes and coolers made of steel are available using a dose of ammonia, neutralising volatile amines or filming amines.

Whether dosages are permitted depends on where steam is used: it is true that the US Food and Drug Administration (FDA) allows a number of neutralising and film forming amines to be used with steam treatment, even if they come into contact with dairy-free food, but it is advisable in general to dispense with this dosage in such cases. In Germany the use of any neutralising or film forming amines in food processing is prohibited. Only ammonia may be used to neutralise condensate, but under no circumstances if the condensate system contains
non-ferrous metals.

Fig. 2:
steam - boiler
If the system itself is likely to be affected by corrosive condensate and a dose of volatile inhibitors cannot be given, the condensate system should be of a corrosion resistant design from the start if possible.

It is generally impossible to dispense with condensate feedback to the feed water tank for financial reasons. For this purpose the condensate has to be sufficiently uncontaminated. Extensive contamination by corrosion products or oil is unacceptable; the condensate should be cleaned to remove them. This may include filtration, adsorption and ion exchange processes. The procedure chosen depends on the type and extent of the contamination.

In complex and involved steam and condensate systems with different pressure stages and condensation zones choosing the right formulation for various neutralising amines may be of crucial importance. In condensate systems of this kind condensation occurs at various points. At the point where condensation of CO2 turns to corrosive carbon dioxide, a neutralising amine has to condense, in order to ensure the material is protected. It may not be possible to achieve precisely the same condensation points of CO2 and the available amines. However, if enough is known about the system and its inner workings, it is usually possible to achieve a very good amine formulation and thus the desired corrosion protection. KURITA offers customers a wide range of products for the avoidance of corrosion problems of this kind. With comprehensive boiler water and steam treatments as well as advice on system-specific problems and solutions plus years of extensive experience, KURITA is a strong, reliable partner in the water treatment business.

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