Your Complete Guide To How Boilers Work

In this article we will break down the basics of how boilers work into easy to understand bits.

How Boilers Work 101How Boilers Works

In its most basic form, a boiler is designed to take water and produce steam or hot water.  This steam, or hot water, is then used in a number of different applications. This includes heating buildings in the winter and providing heat for industrial applications.

For example, a steam boiler installed at an industrial facility may be used to provide steam to cook raw meat before packaging. A boiler in a school however may be used to provide heat to classrooms during the winter. A hospital on the other hand may use steam to sterilize their surgical equipment. Regardless of the application, the boiler is the vessel used to produce the steam.  

Industrial BurnerThe burner, on the other hand, is appended to the front end of the boiler. It provides the heat necessary for converting water in the boiler into steam. Think of the burner as an industrial flame thrower that is pushing heat into the boiler.  It increases or decreases the heat injected based on steam demand. It also has some pretty high-tech controls (small computers that control the burner) which allows this to be done effectively. Burners work by mixing together air and fuel to create an efficient flame inside of the boiler. This flame heats up the water in the boiler to the point of turning it into steam. Burner fuel varies, but some common fuels are natural gas, propane and #2 fuel oil.

From City Water To Steam

The most common type of boiler we work on in the Midwest is what is known as a “Firetube Boiler”. For this example, we will be describing the components of this style of boiler and some of its common auxiliary equipment.

A boiler by itself isn’t very useful. It requires a number of other pieces of equipment to make it work properly.  Let’s talk through the journey city water takes and the different pieces of equipment it may go through on its way to becoming steam.

  1. Filtration System – We want the water to be as clean as possible before it goes into the boiler. This means we recommend the water be filtered by an RO System (Reverse Osmosis) or some other type of filter system. This removes solids like calcium and magnesium from the water.
  2. Deaerator (DA) – This piece of equipment is designed to remove oxygen and CO2 from the water.  This is important because these gasses can deteriorate metal overtime inside a boiler. 
  3. Chemical Treatment – To further remove any remaining dissolved solids or dissolved gasses, the water is chemically treated.  The chemicals used and amounts needed are managed by a water treatment company.
  4. Feed Pump – This takes the purified and treated water, and forcefully pumps it into the boiler. This is necessary because the boiler system is under pressure.  The pump is able to overcome that pressure to ensure the boiler has sufficient water inside.  
  5. Burner – This is the mechanism providing heat to the boiler.  It does this by shooting flames down the center of the boiler.  
  6. Burner Controls – Nowadays these are generally digital controls. They help to ensure the correct amount of fuel is being injected. They also ensure the correct amount of air is flowing in for proper combustion (which is also known as the Air-To-Fuel ratio).
  7. Inside the Firetube Boiler
    1. Boiler Open with Tubes ExposedMorrison Tube – This is a large cylindrical tube (the largest of all the tubes in the boiler) where the burner is attached.  This provides a large space for the burner to fire. It directs heat to the back of the boiler where the heat goes down a number of smaller boiler tubes.
    2. Boiler Tubes – A series of hollow cylinders inside the boiler that are surrounded by water on the outside. They allow the hot gas to pass through them on the inside.  This is where the heat transfer occurs.
    3. Refractory – Boiler refractory is heat-resistant materials that is used to line the boiler to help it retain heat.  This prevents thermal loss during boiler operation.  It also helps the boiler retain heat even when it is not firing.
  8. Steam Outlet -This is located on the top of a firetube boiler. It is where the steam goes after it is created in the boiler.  Pipes are attached to this section of the boiler and carry the steam to the desired location.
  9. Boiler Stack – This is the exhaust from the burner located at the top of the boiler. It generally terminates out the top of the building.
  10. Condensate Returns – Steam travels through the piping to its destination and releases its energy.  As this energy is released, the steam turns back into water.  This water (condensate) is valuable!  It has already been run through a filter, has been chemically treated and is hot. Returning this condensate back to the boiler means less chemicals need to be added. It also means less heat is needed to get the water back up to temperature.

Understanding Boiler Efficiency

One of the easiest ways for a facility to lower operating costs is to increase boiler efficiency. The goal is to create conditions that generate the smallest possible amount of flue gas at the lowest possible temperature.

Let’s unpack this. The boiler draws in cool air, heats it up using the burner, and sends it through the boiler. Any heat that is not transferred into the water goes out the stack. A high stack gas temperature is bad because it means more energy is leaving with the flue gas out the stack. Another place boilers lose efficiency is anytime steam or hot water is wasted. This is because the boiler has expended energy converting cold water into steam or hot water. This is also why not dumping condensate returns down the drain and using blowdown separators to recapture valuable BTU’s is so important.

Our friends at Muria explain boiler efficiency well; “The two industry standards for measuring efficiency are fuel-to-steam efficiency and in-service efficiency. Fuel-to-steam efficiency, also known as Annual Fuel Utilization Efficiency (AFUE), measures combustion efficiency. That is, what percentage of energy is converted to steam. A limitation of fuel-to-steam efficiency is that it only gives you a measurement of efficiency when the boiler runs at full capacity. Practically speaking, most boilers do not constantly run at full capacity. That’s why it’s important to consider in-service efficiency, which refers to the boiler’s total efficiency in its everyday function.”

Understanding How Boilers Work Conclusion

Understanding how boilers work is important for anyone who works in the boiler room. Now that you understand the basics, you can dive deeper into the intricacies of boiler maintenance. By taking the time to read this article we hope you now understand the basics on how boilers work.

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