It is a commonly known fact that every place in the world experiences different kinds of weather conditions. That said, some countries tend to lean more towards a particular kind of climate. For example, countries in the north are more prone to cold weather while the countries in the tropical zone are more familiar with the heat. Whatever’s the case, weather conditions play a big role in people’s daily lives — if it gets too hot or too cold, it’s easy to feel uncomfortable. For that reason, the industry of heating, ventilation, air conditioning, and refrigeration (HVACR) is steadily growing nowadays due to the rise in demand for HVAC systems. And one of the most popular HVAC systems out there is the boiler.

What Is A Boiler?


        Generally speaking, a boiler is a closed vessel in which fluid (usually water) is heated. The fluid does not necessarily boil; rather, the heated or vaporized fluid exits the boiler for use in various processes or heating applications. Some of these applications include water heating, central heating, boiler-based power generation, cooking, and sanitation. 

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Heat Sources

         Boilers can generally run on a number of fuels, depending on the application they are used for. For example, in a fossil fuel power plant that uses a steam cycle for power generation, the primary heat source for boilers will be combustion of coal, oil, or natural gas. In some cases, byproduct fuels like the carbon monoxide rich off gases of a coke battery can be burned to heat a boiler. Additionally, biofuels like bagasse can also be used. 

         Meanwhile, in a nuclear power plant, boilers — which are called steam generators in this scenario — are heated by the heat produced by nuclear fission. Where a large volume of hot gas is available from some process, a heat recovery steam generator or recovery boiler can use the heat to produce steam — with little or no extra fuel consumed. This configuration is relatively common in a combined cycle power plant where a gas turbine and a steam boiler are used. 


         The pressure vessel of a boiler is more often than not made of steel — or alloy steel — or wrought iron. Stainless steel, especially of the austenitic types, is not used in wetted parts of boilers due to corrosion and stress corrosion cracking. However, that said, ferritic stainless steel is often used in superheater sections that will not be exposed to boiling water. 

         Meanwhile, in live steam models, copper or brass is often used because it is more easily fabricated in smaller size boilers. Historically speaking, copper was sometimes used for fireboxes (particularly for steam locomotives) because of its better formability and higher thermal conductivity. But in more recent times, the high price of copper often makes this an uneconomic choice, and cheaper substitutes, such as steel, are used instead. 

         Moreover, cast iron may also be used for the heating vessel of domestic water heaters. Although such heaters are usually termed “boilers” in some countries, their purpose is usually to produce hot water, not steam, and so they run at low pressure and try to avoid boiling. However, even though cast iron can be used for water heaters, it is not ideal for them to be used in high-pressure steam boilers because of its brittleness. 

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What Are the Basic Components of a Boiler?

         More often than not, designs vary from one boiler to another, and so some boilers may have components that other boilers don’t have. However, even though that is the case, all boilers have three main parts. And these are the burner, the combustion chamber, and the heat exchanger. 


         A boiler burner is the functional component of boilers that provides heat input by combustion of a heat source. In other words, it is the one that initiates the combustion reaction within the boiler. 

The way this particular component operates is that thermostats will send messages to the burner electronically when the system needs to produce heat. And then, after that, fuel will be pumped by a filter mechanism to the boiler from an outside source — usually an adjacent fuel tank. A nozzle on the burner will then turn this fuel into a fine spray and ignites it, thus creating the reaction in the combustion chamber. 

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Combustion Chamber

         As the name suggests, a combustion chamber is the part of a boiler in which the fuel/air mix is burned. For that reason, the combustion chamber is usually made of cast iron, and the temperatures inside can rise to several hundred degrees, usually in a very short amount of time. After the combustion, the heat generated in this chamber is going to be transferred to the boiler’s heat exchanger.  

         Additionally, the combustion chamber is also used to refer to an additional space between the firebox and boiler in a steam locomotive. Just like the other kinds of combustion chambers, this one is also used to allow further combustion of the fuel, thus providing greater heat to the boiler. 

          Large steam locomotives typically have a combustion chamber in the boiler to allow the use of shorter fire tubes. This is primarily because long fire tubes have a theoretical advantage in providing a big heating surface, but, beyond a certain length, this is subject to diminishing returns. Additionally, very long fire tubes are prone to sagging in the middle, thus making them less ideal for large steam locomotives. 

Heat Exchanger

         As the name suggests, a heat exchanger is a component of a boiler that allows heat to be exchanged between two fluids or substances, usually water and gas, without letting the substances mix together. 

         When a boiler system is turned on, water circulates around the radiators but will only be able to heat the space if it’s hot. This is where the heat exchanger comes in. Gas boilers burn gas, which then heats up and rises towards the heat exchanger that cold water passes through. As the water circulates, the heat is then transferred from the gas to the water, which then heats up to effectively warm the radiators or provide hot water for a tank. Long story short, the process begins with hot gas and cold water, but because of the heat exchanger, the process ends with cooler gas and hotter water. All this transformation happens without the two substances even having to meet. 

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Other Components in a Boiler System

         Now that we’re aware of the three main components of a boiler, it’s time to know the other components that make up this particular HVAC system. The following are the other components of a boiler system that are just as important as the above-mentioned ones. 

  • Supply Lines. Hydronic heating systems use piping to deliver the heated water or steam to the distribution points, and the supply lines are the pipes that achieve this task. 
  • Return Lines. When the water cools or the steam cools and changes states back into water, the return lines bring this water back to the boiler for reheating. 
  • Firebox. The firebox is where the fuel or system meets the air, thus creating a flame. 
  • Refractory. Refractory actually refers to refractory materials that are used for filling any gaps and/or openings that may be around the firebox. Because of this, refractory is needed to ensure that the fire stays in the firebox. 
  • Circulator Pumps. Circulator pumps are the ones that push the hot water or steam from the system and into the heat distributors of a place. 
  • Deaerators/Condensers. A deaerator is a device that removes oxygen and other dissolved gases from liquids. Meanwhile, a condenser is a heat exchanger that removes the latent heat from the exhaust so that it condenses and can be pumped back into the boiler. 

           Deaerator and condenser tanks are only used in steam boiler systems and not in hot water and hot oil boilers because, in these tanks, the fluid is always in on the liquid form. The construction of these two types of tanks is almost identical, but actually, these tanks are used for different purposes. There are two primary principles that are used with this form of tank design: thermal and vacuum. 

    • Thermal Principle. A tank using the thermal principle is connected to the atmosphere. This design is normally used in smaller plants. Here, the steam is used to maintain the tank water temperature at around 105°C, which removes air from the water.
    • Vacuum Principle. In this principle, an ejector pump is used to create a vacuum in the tank. This causes the tank water to start boiling because of the low temperature, which in turn removes air from the water. This principle is normally used for steam turbine applications. 
  • Economizer. An economizer is a heat exchanger that is placed in the exhaust from a boiler or in the exhaust funnel of the main engine of a ship. Pump requirements differ greatly, depending on where the economizer is installed.
  • Superheater. A superheater is an integral part of a boiler and is placed in the path of hot flue gases from the furnace. The heat recovered from the flue gases is used in the steam before entering into the turbine. The primary purpose of the superheater is to increase the temperature of saturated steam without raising its pressure. 

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           Boilers are incredibly important for a lot of people. This is because there are some places in the world that gets unbearably cold during certain times of the day or seasons of the year, and boilers — a vessel that is commonly used in heating systems — offer a solution to combat this problem. And that is one of your primary jobs as an HVAC professional: to provide boiler systems and other related services to your customers. 

           However, before you could serve your customers, you must first have to know all about the necessary components of a boiler system. This is the information that you have found in this post. By knowing about the important components of a boiler system, you will understand better how the system actually works. And that, in turn, will help you be able to provide the best products and services to your customers. 



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