If you are running a steam boiler system in your facility, you should be treating your system’s condensate to ensure system longevity and peak efficiency. Operating with no condensate treatment could mean big problems in the future.
What is Condensate?
Before we talk about why it is so important to treat your boiler system’s condensate, we should probably first discuss what condensate is and why it is important. (If you already know, please skip to the next section.) If you have a steam boiler, your boiler system produces steam. Steam leaves the boiler through piping to transfer heat to something; usually a heat exchanger or steam jacket. When the steam condenses in the pipe it is called condensate. This condensate water has very little impurities in it. In fact, condensate is practically 100% pure, clean water… and it’s very hot, which makes it the perfect fit for boiler feed water. That’s why one of the best things that you can do at your facility is capture and return as much hot condensate water back to the boiler as possible. Returning the condensate back to the boiler saves water, but more importantly, it saves fuel. If condensate is not returned to the boiler, then the boiler needs to have fresh water introduced, which needs to be pre-heated, which burns fuel. The bottom line is, if you can return most of your condensate and keep it hot, you can save tons of money in energy.
There is, however, a dark side to this seemingly wonderful condensate. As mentioned earlier, condensate is almost 100% pure water, and pure water is one of the most corrosive elements on the planet; especially when it comes in contact with steel and starts to cool.
The problem is CO2. When water cools, carbon dioxide (CO2) easily dissolves in it. At the right pH, it starts to form carbonic acid and carbonic acid eats through steel.
Keeping the pH in the pipes within acceptable ranges is extremely important to boiler operation; just as important as using at deakalizer to remove alkalinity from boiler makeup water or using a water softener to remove hardness from incoming water.
So what needs to be done?
It’s really a compound answer, but here are the basic steps that must be taken:
- The system needs to be checked for leaks and failed steam traps.
- The pipes and condensate receivers need to be properly insulated.
- The steam needs to be treated chemically with a condensate treatment.
There are many types of condensate treatments, but the most common are amines. Amines fall into two major categories: filming and volatile. The volatile amines are completely soluble and therefore, can technically be fed in the boiler. They are considered volatile because they flash off and are carried with the steam into the rest of the system. These types of volatile amines are often referred to as short range, medium range and long range neutralizing amines, because of the distance they are able to travel “down pipe.” Neutralizing amines are alkaline and, therefore, neutralize the acids that can form in the condensate by raising the pH. Neutralizing amines control corrosion in condensate applications by diminishing the effects of carbon dioxide and other acid forming compounds.
Neutralizing amines are used in boiler water treatment to control condensate return line corrosion. The amines do not have any adverse effects on copper or copper alloys under normal treatment conditions where pH is maintained between 7.5 to 9.0 and where only a few ppm of amine are continuously added to the boiler water. This has been confirmed by the long history of amine treatment in thousands of boiler water systems. However, at elevated concentrations, these neutralizing amines may be corrosive to copper and its alloys. To avoid this situation, amines should always be fed continuously in proportion to the feedwater by means of a chemical metering pump.
By contrast, filming amines are not completely soluble, and therefore, cannot be fed directly into a boiler. In fact, feeding this type of amine into a boiler could cause even worse problems than not treating the condensate at all. In order for a filming amine to work properly, it must be direct injected into the steam header. There are specially designed injection quills and pumps that are used to do this so that the filming amine is properly dispersed throughout the steam. When the steam condenses, this type of amine does not dissolve. Instead it coats the inside surfaces of the pipe with a microscopic layer of chemical that is almost oily in nature. When this material deposits on the inside of the pipe, liquid cannot penetrate it, preventing the condensate from coming in contact with the metal. The filming barrier protects the pipe from acid and oxygen pitting.
Amine feed should be examined and evaluated in any system such that:
- The chemical feed pump should be activated only when the feedwater pump is running. At no time should chemical treatment be allowed into an idle feedwater line or boiler.
- Treatment chemicals should be added over a 24-hour period of time. Slug-feed or shortening of daily feed duration may cause temporary high amine concentrations which may attack copper.
- Treatment chemicals should be injected directly into the boiler if a separate chemical feed line is available. Chemical treatment can also be added to the feed water tank or storage tank of the deaerator. The large volume of water in the boiler or feedwater tank allows further mixing and dilution.
- Amines should not be fed before a deaerator since passage through the deaerator will cause some loss of the amine.
- In extremely long steam/condensate piping systems consideration should be given to supplemental amine feed directly to the steam lines in such quantities as are necessary to produce the desired condensate pH.
- Amines should not be fed to boilers in which nitrite is used as a treatment compound since this combination may form nitrosamines which are known carcinogens.
- There may be strict rules regarding the use of an amine product at your facility, especially if the steam generated comes in contact with a product being manufactured. i.e., food processing. (It is extremely important to know what you are allowed to use or not use.)
Most amines are designed to work synergistically with oxygen scavenging, dispersion and other boiler treatment compounds, but the right mix of these chemistries and their proper administration should always be handled by an experienced water treatment expert.
Check with your water treatment provider to make sure that their line of condensate treatment chemicals available will fit your needs, especially if you have specialty applications including comfort heating of extremely large facilities or food processing.