ABSTRACT

Inadequate boiler system corrosion protection results in failures and increased operational costs. Traditionally, operators of steam generating systems have utilized neutralizing and filming aminesto reduce corrosion in their steam condensate systems. Over the past several years, the environmental, health and safety concerns raised by use of these compounds has encouraged the search for alternative treatments. A novel green (nontoxic) condensate corrosion inhibitor is introduced. Field and lab data demonstrating performance is presented.

INTRODUCTION

Feed water quality is key to proper boiler system corrosion protection. The better the feed water, the less likely water-related problems will occur. There are many sources of feed water, and returned condensate is usually the best overall economic choice. The quantity and quality of steam condensate returned to the feed water system impacts final feed water quality. Generally, it contains fewer impurities than make-up water and has a high heat content. It is essentially free. The higher the amount of condensate returned to the boiler, the lower the amount of make-up water needed to run the boiler. This increases efficiency and lowers operation costs. Often~ higher boiler cycles of concentration are made possible through increased condensate return, reducing boiler operating costs further.

As a result, it is necessary to be aware of problems incurred in the condensate system. Corrosion in the condensate system imparts impurities to the condensate which ultimately become part of the feed water. Returned condensate may contain iron~ copper, and their oxides which can be formed by metal dissolution from a corrosive environment or separation of accumulated oxide layers from the metal surface during system startup or shutdown.

Most condensate corrosion problems find their root causes into corrosive gases: carbon dioxide and oxygen. Oxygen attack is characterized by pitting type corrosion. Carbon dioxide, liberated from the boiler through the thermal decomposition of boiler alkalinity, dissolves in the condensate, forming carbonic acid. The carbonic acid depresses the condensate pm increasing its corrosivity. Carbonic acid attack is characterized by a smooth thinning of metal. Both types of corrosion damage plant process equipment and reduce the quality of the returned condensate due to corrosion products. This directly impacts plant profitability and reliability. One way to deal with these two corrosive species is to prevent their entry into the boiler system.

Deaeration removes dissolved, corrosive gases mechanically. Dealkalyzers remove alkalinity, the source of the carbon dioxide in the steam from which carbonic acid is formed. Often filters and ion exchange are used to polish condensate, removing soluble ions and particulate. Since all problems cannot be solved mechanically, chemical treatment programs are necessary to optimize boiler operations.

Neutralizing and filming tines have been in common use as condensate system corrosion inhibitors since the late 1940s. Neutralizing amines reduce corrosion by neutralizing carbonic acid and raising the condensate pH. Common amines used for neutralization include cyclohexylamine, morphine, diethylaminoethanol (DEAE), methoxypropylamine (MOPA), and monoethanolamine (MEA). These amines are not effective against oxygen corrosion. Filming arnineslike octadecylamine and other long chain amine surfactants protect condensate systems horn both oxygen and carbonic acid attack by forming a very thin protective film on the condensate pipe which acts as a barrier to aggressive species.

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