Steamline Treatment (Amines)
It is commonly accepted throughout the water treatment industry that neutralizing amines for boiler water treatment should be chosen based upon their distribution, but is this justified?
Rightfully so, volatile amines have become a key component in effective boiler water treatment programs. Without proper amine treatment in boilers, steam condensate can become acidic and may lead to severe corrosion damage to the condensate pipe system. Bicarbonate present in boilers will produce carbon dioxide, which passes completely into the steam and dissolves in the condensate to form carbonic acid.
The objective when introducing amines is to neutralize any carbon dioxide that may be present in steam and condensate systems. The intent is to raise condensate pH to a specific range and is typically injected into the feedwater tank, although large industrial facilities may introduce amines prior to the boiler plant. There are many amine-based products on the market and the ultimate choice of products to be used in specific applications is based upon factors such as cost, fluid velocity, pressure, oxygen concentration, length of stream distribution lines and safety.
Figure 1: Chemical Structures of Amines Commonly used in Boiler Water Treatment
The most commonly prescribed amines outside of ammonia are morpholine, cyclohexylamine, DEAE, and AMP. Referring back to organic chemistry amines can be derived when one of more hydrogen atoms of ammonia is replaced with an alkyl group. Amine compounds are quite sophisticated and are chosen primarily upon their characteristics in the water treatment industry.
Figure 2: Properties of Amines from 0 – 300 ºC (Cobble and Turner, EPRI NP-4209)
The graphs above illustrate the pH of solutions containing the same concentrations of each amine commonly utilized in boiler water treatment programs. As all of them, except morpholine, achieve similar pH for the same concentration, there is no reasonable way to select one over the other on the basis of pH specification by itself. It is more important to look at the balance between the base strength and most appropriate partitioning of the amine between the liquid and steam phases at the system temperature (distribution). The amine choice becomes important in applications with long distribution lines where conditions change passing down the steamline. As illustrated in the middle graph, morpholine may offer better protection at the start of a line but may require DEAE or cyclohexylamine to provide the required protection as the system cools toward the far end of the condensate return network.
Outside of distribution, both morpholine and DEAE have been shown to be effective oxygen scavengers when introduced to the feedwater. The use of amines for chemical deaeration has become popular due to the safety concerns of other chemicals. For health-related reasons, there are a select few amines allowed in the food/dairy industry. Where steam is used for humidification purposes, OSHA has set permissible exposure limits (PEL) which need to be taken into consideration.
There are many parameters that need to be taken into consideration when choosing amines for boiler water treatment. I would agree that amine distribution would be the first characteristic to consider, but giving no attention to safety, oxygen removal, and PEL could provide devastating results. As always, consult a professional water treater when deciding which amine/amine combination is most suitable for each boiler application.