Boiler Water Feed Tank
What is the purpose of a boiler water feed tank?
It is a vessel where cold fresh water meets hot condensate return water therefore heating up the cold water which performs several key functions:
- Forces oxygen out of the fresh cold water therefore greatly reducing the danger of corrosion to inside boiler including boiler tubes and the entire heating system. Oxygen is highly corrosive when present in hot water. Even small concentrations can cause serious problems: iron oxide generated by the corrosion can produce iron deposits in the boiler. Without proper mechanical and chemical deaeration, oxygen in the feed water can enter the boiler. Much is flashed off with the steam; the remainder can attack boiler metal. Oxygen in the water attacks the boiler’s metal producing pitting that is very severe because of its localized nature. Water containing ammonia, particularly in the presence of oxygen, readily attacks copper and copper bearing alloys. The resulting corrosion leads to deposits on boiler heat transfer surfaces and reduces efficiency and reliability. This is a form of mechanical deaeration.
- Being the hot condensate helps to increase the temperature of the feed water this greatly reduces the possibility of thermal shocking. Thermal shock occurs when cold water enters a hot boiler. When a boiler is running at or near full power, it is full of boiling water, so the sudden introduction of cold water will cause a serious reaction with the hot water currently in the boiler. The stark difference in water temperature causes the rapid expansion and contraction of equipment inside the boiler, including its tubes, tube sheets, valves, fittings, and piping. This rapid expansion and contraction in the boiler can cause cracks in the steel resulting in water leaking from the tubes and seams.
- Increases boiler efficiency by tempering the boiler feed water. The lower the boiler feedwater temperature, the more heat is required in the boiler to produce steam. It is important to maintain the feed tank temperature as high as possible, to maintain the required boiler output.
Problems that can occur with the boiler water feed tank isn’t maintained:
- A clogged strainer or impeller which will prevent condensate from returning to the feed tank. Too much sediment in the water feed tank can cause your strainer to clog. Which can decrease the temperature of the water in the feed tank being the hot condensate is being blocked and can increase the chance of thermal shocking happening to your boiler.
- A boiler water feed tank system is comprised of various valves and steam traps. Without proper maintenance the seals on the valves may loosen or erode (due to acidic condensate) and steam traps can fail. If one or more of these valves or traps become faulty it can cause thousands of dollars of damage to your boiler and increased energy cost from the lack of efficiency.