The boiler blowdown procedure is the purposeful discharge of water from the boiler. This practice works to avoid the build-up of concentrated impurities inside of the system. These byproducts and impurities are the result of the continual evaporation of steam.
While most people think boiler water is pure, it's actually chemically treated in a manner similar to tap water. If you were to take a pot, fill it with water, and boil it, you may find a black or brown residue at the bottom. These are impurities that couldn't be boiled away with the water.
Since steam boilers produce steam from water, they require the regular replenishment of feed water. As a result, you can expect the accumulation of impurities of waste by products. The boiler blowdown procedure is an effective way of removing those impurities to ensure your long life and efficiency of your boiler. Continue reading to learn more about the boiler blowdown procedure.
Is the Boiler Blowdown Procedure Necessary?
When steam is produced, only pure water leaves your boiler. As a result, any of the impurities that were in the water are left behind. While the condensate is fed back into the boiler, some of it is lost and has to be replenished with make-up water.
Over periods of time, the dissolved solid concentration levels in the makeup water spikes as the pure water is removed as steam. The relationship between the dissolved solids in the feed water and dissolved solids in your boiler are termed in concentration cycles.
The boiler blowdown procedure is conducted periodically to ensure there are a consistent number of concentration cycles. This practice is vital in preventing corrosion and scale in your boiler as well as bolstering efficiency.
The Effects of Polluted Boilers
Water has the ability to capture miniscule, tiny pieces of solids that may be present in boilers. Components, such as valves and piping, are never sealed or manufactured completely perfect. As a result, there will always be a certain amount of impurities or particulate floating around in your boiler.
Over time, the repeated production of steam causes these impurities to become concentrated. They can show up in a variety of forms, such as a soft sludge to a calcium like scale that accumulates in the bottom of the boiler. This is known as mud drum.
These impurities diminish your boiler's ability to transfer heat, which reduces the overall efficiency of your equipment. Without the boiler blowdown procedure, impurities would achieve saturation levels and start to precipitate within the boiler.
Skimmer Blowdown Procedure vs Bottom Blowdown Procedure
There are two main points where water can be removed from the boiler: the skimmer drain valve and the bottom drain valve. The skimmer valve enters the boiler just below the surface of the water.
Sludge concentration is typically the highest in bottom of the boiler, which is why the bottom blowdown is performed to get rid of sludge that precipitates during boiling. On the other hand, dissolved solid concentration is the highest at six to eight inches below the surface of the water.
Skimmer blowdowns are designed to get rid of the most solids in a minimal amount of boiler water, but bottom boiler blowdown is still necessary to prevent sludge buildup.
The frequency of boiler blowdowns and volume will be based on the condensate amount returned to your boiler as well as the quality of your makeup water. It's best to develop a routine to make sure your boiler gets the right blowdown amount at regularly scheduled intervals.
Most boilers have a bottom drain line with two different valves: a knife valve and a gate valve. The optimum way to blowdown a boiler is to begin with the valves fully closed. Start by opening the knife valve, then open and close the gate valve.
This should be done to both back and front valves if the boiler comes equipped. Repeat this process approximately three times, which will rock the boiler water and maneuver any sludge toward the drain line.
It's important to conduct a skimmer blowdown on a regular schedule. Make sure to use a conductivity meter calibrated to determine how much skimmer blowdown you need. Always maintain the conductivity of your boiler water in the range prescribed by your Applied Technologies of New York technician. Finally, make sure to blowdown the level switch, safety valves, and sight glass around once a week to ensure they will work when you need them.
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