Advanced water treatment chemicals and industrial solutions
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Advanced water treatment chemicals and industrial solutions Attention! The contents of this site cannot be printed. Please visit our download section for a hard copy. |
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CONDENSATE RETURN SYSTEMS When steam has performed its work in manufacturing processes, turbines, building heat, etc. it transfers heat and reverts back to a liquid phase called steam condensate. However, not all the energy used in producing steam is lost when condensate is formed. As most condensate return is still relatively hot (130OF to 225OF) , it is very valuable as a source of feedwater. There is a significant fuel savings related to the heat required to raise the temperature of makeup water at (50OF to 60OF) to equal that of the return condensate, not to mention the additional cost in pretreating (softening) the makeup, as well as basic water cost itself. When pure water H2O is used to produce steam, then its condensate is also pure H2O however, as we have learned the water we use to produce steam is not pure containing many dissolved minerals and gases. The heat and pressure of the boiler break down the alkalinity in the boiler water to form carbon dioxide gas CO2. Leaving the boiler with the steam it travels throughout the plant supply system. When the steam condenses, the carbon dioxide dissolves in it to form carbonic acid. This reaction is chemically expressed as:
H2O + CO2 = H2CO3
This acid depresses the condensates pH and causes corrosion to take place. This corrosion appears as grooving or gouging in the bottom of steam headers or condensate return lines. Most often it weakens pipe walls at threaded joints and the resultant metal loss can lead to large amounts of copper and/or iron being returned to the boiler to cause troublesome deposits. Oxygen, as in the boiler system, can cause localized attack in the form of pitting when present in the condensate system. This type of corrosion can generally cause equipment to fail more quickly than the generalized corrosion caused by carbonic acid attack due to it concentrating in a small area. Oxygen can infiltrate the system from open condensate receivers, poor deaeration or leaky siphons. There are three main chemical programs to control corrosion in the condensate system, being NEUTRALIZING AMINES are high pH materials which neutralize the carbonic acid formed in condensate systems. By raising and controlling pH level in condensate from 7.5 to 9.0, neutralizing amines retard acid attack and greatly reduce the amount of corrosion products entering the boiler. The three primary neutralizing amines in use today are:
The distribution ratio is used to predict the amine concentration in the steam and condensate phases and impacts significantly regarding proper amine selection. Distribution Ratio = Amine in Steam Phase / Amine in Condensate Phase Neutralizing amines have low flashpoints and therefore can be fed directly to the feedwater or boiler water, or they can be fed directly into the steam header. The feed rate is based on the amount of alkalinity present in the feedwater. Neutralizing amines offer excellent protection against carbonic acid attack, but little protection against oxygen attack. FILMING AMINES are various chemicals that lay down a vary thin protective barrier on the condensate piping protecting it against both oxygen and carbonic acid attack. The protective film barrier is not unlike the protection afforded an automobile by an application of car wax. The protective film barrier is continuously being removed (a little at a time), requiring continuous feeding of the filming amine based on steam flow rather than feedwater alkalinity. Care must be taken to start this program slowly with an initial feedrate of one fifth that of the final feedrate to prevent the removal of old corrosion products from the system and their subsequent return to the boiler. Additionally, the filming amine should be fed using an injection quill to the steam header to insure proper vaporization and distribution throughout the steam system. The formation of gunk balls (Gunking) can occur due to overfeed, contaminants in the condensate or wide pH swings causing deposits to form in low flow areas like steam traps. COMBINATION NEUTRALIZING AND FILMING AMINES As its name implies, are the combination of neutralizing and filming amines and are a successful alternative to protect against both carbonic acid attack and oxygen attack. It combines the elevated pH approach to neutralize carbonic acid in conjunction with the protective barrier film approach. The neutralizing amines, although they will elevate pH, main purpose is to provide better distribution of the filming amine throughout the condensate system which in turn helps to prevent gunking. As with filming amines it is better to be fed directly to the steam header utilizing an injection quill. SUMMARY. Clearly each program or approach has certain features and benefits as well as limitations. Each different set of operating conditions will tend to dictate the appropriate treatment that is required. The expected steam pressure, temperature, system metallurgy and the plants systems pH level all play an important role in determining the most effective treatment program. Clearly each program or approach has certain features and benefits as well as limitations. Each different set of operating conditions will tend to dictate the appropriate treatment that is required. The expected steam pressure, temperature, system metallurgy and the plant systems pH level all play an important role in determining the most effective treatment program. Offers a full range of neutralizing amines, filming amines and mixtures, as cover any system needs. Please contact us for more details.
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