Boilers are a critical component in keeping the industrial plants running effectively with production. However, they aren’t exclusively used in chemical plants. They are manufactured in a variety of types to handle the specific job they need to do as well as the geographical region they are to be used in. From fire tube to water tube and steam versus hot water…there is a lot to be learned about boilers.
Major Categories Of Boilers
Fire Tube – Fire tube boilers feature have tubes containing hot gases from a “fire” or heat source which pass through a sealed tank of water. As a result, the water is heated by the tubes through the process of thermal conduction. The heated water ultimately converts into steam which can be used for heat or energy.
Fire tube boilers represent an earlier form of boiler technology as compared to water tube boilers. They played a large role in the Industrial Revolution and most early steam power, especially locomotives featured a fire tube boiler. However, fire tube boilers generally require more maintenance and typically have lower pressure restrictions than water tube boilers.
Though fire tube boilers are still manufactured and in use today, they have largely been supplanted by water tube boilers in most industrial settings. Fire tube boilers remain more prevalent in the railway locomotive sector. They may have vertical or horizontal tanks, though horizontal tanks are more common, especially in locomotive applications. Modern fire tube boilers may also feature modified designs to make them more efficient or compact, such as Reverse Flame boilers in which the combustion gases double back on themselves.
Water Tube – Water tube boilers consist of water-filled tubes which are surrounded by a heat source. The heated water will then rise into a steam drum where it may then be used for power or heat. However, some configurations have the steam returning to the furnace so that it can be superheated. Superheated steam is important for use in energy generation because superheated steam is dry and water droplets could damage the blades of a turbine.
In contrast to boilers that produce a superheated dry steam are those that produce saturated steam. At a given pressure, saturated steam is in equilibrium with heated water, which means that saturated steam has not been heated past the boiling point for that pressure. Thus if saturated steam is reduced in temperature water droplets will reform, which may or may not be suitable and useful for a given application.
Water tube boilers are the most widely-used type of boiler in contemporary times. Water tube boilers come in a wide range of different types and sizes which are specialized for various purposes. Water tube boilers are popular because they are able to handle much higher pressure than fire tube boilers.
Water tube boilers are used for power generation, heating, and many industrial processes. Additionally water tube boilers are by far the preferred type of boiler for marine settings.
Steam Boilers Vs. Hot Water Boilers
Boilers can be classified as either hot water boilers or steam boilers. Steam boilers are the most commonly used in industrial settings, while hot water boilers are common in residential or commercial settings to provide heat or hot water.
- Hot Water Boilers – Hot water boilers are also known as hydronic boilers. This type of boiler utilizes hot water rather than steam for its purposes. Once the water reaches boiling point it is circulated through pipes or into a radiator to provide heating. Additionally sometimes it is the hot water itself that is desired for personal or commercial use, in which case the boiler is generally known as a hot water heater. These types of boilers may also feature reserve tanks so that the hot water is always ready on demand.
- Steam Boilers – A steam boiler is the more commonly referred to type of boiler in industrial settings and is generally the one we have been referring to throughout this article. This type of boiler utilizes the steam rather than the water for its purposes. Steam boilers can be further classified based on how the steam circulates throughout the system.
- Natural Circulation – As the name implies, natural circulation steam boilers allow the steam to circulate naturally. Through the process of convection heated water molecules become less dense and naturally rise to the surface while cooler water molecules sink to the bottom. For this reason with natural circulation boilers the tubes are setup at an incline to facilitate the pressured steam rising and circulating through the pipes. This type of steam boiler is commonly used on navy vessels.
- Forced Circulation – In contrast to natural circulation, forced concentration use a pump to force the steam through the pipes. This allows for much greater pressure and may be necessary in some industrial applications.
- Zero Circulation – Zero circulation steam boilers are also often called supercritical pressure steam boilers. These boilers operate at extremely high pressures, often over 3,200psi. Because the pressure is so high no actual boiling can occur. Instead the pressure is above the critical pressure at which steam bubbles can form. Thus calling these systems “boilers” is actually somewhat of a misnomer. This type of boiler is most commonly used for electricity generation and it releases very few greenhouse gases.
Types And Uses Of Boilers By Fuel Source
Another major way to classify boilers is by the type of fuel source that they use. This is also an important contributing factor in determining which type of boiler will be used by a particular industry or in a particular geographic area because of course the most economic and widely-available fuel source will be preferred.
- Coal Boilers – Coal fired boilers use coal as their fuel source. Coal is a popular choice because it is typically a relatively inexpensive fuel source. Coal has a reputation of being a “dirty” fuel source, but when handled and combusted correctly it can actually be a relatively clean, low-polluting option. Coal fired boilers are popular in the energy generation industry and are also frequently chosen for areas which have an abundant nearby coal supply.
- Gas Boilers – Gas fired boilers are an extremely popular option for industrial, residential, and commercial use. Gas boilers can be skid mounted for improved mobility and integration at worksites and they can also be designed in a modular, turnkey fashion to increase production speed and overall efficiency. Thanks to the natural gas boom, the costs associated with this fuel source are decreasing and the fuel source is widely available.
- Oil Burners – Oil fired boilers are also a popular option for industrial, residential, and commercial use. Like gas fired boilers, oil fired boilers are also commonly manufactured in a modular, turnkey fashion and skid mounted for maximum cost efficiency, quality, speed of production, and overall convenience. Once again, due to our nation’s oil boom boilers (which utilize oil as their fuel source) these are becoming more cost effective.
- Electric Boilers – Electric fired boilers can be designed for either high or low pressure steam production. These boilers may be found in a wide range of settings such as factories, hospitals, laboratories, and more. This type of boiler can also be designed to operate on different volts.
- Wood Boilers – Wood fired boilers are also gaining traction because wood is a renewable energy source. This type of fuel source is popular in areas that routinely harvest timber. However, wood boilers can be modified to burn many different wood byproducts.
- Bark Boilers – A subset of wood burning boilers are bark burning boilers which use bark as their fuel source. Bark burning boilers are extremely popular and useful in pulp and paper mills because bark is a natural waste byproduct in the production of pulp and paper.
- Alternative Fuel Boilers – Alternative fuel boilers are designed to use non-traditional fuel sources. These types of boilers are gaining popularity as a more “green” option to standard boilers and may be in use at environmentally focused facilities. The exact type of fuel may vary from type to type.
Boilers are the workhorses at just about every industrial plant or refinery. They provide the energy source, heating and cooling for personal comfort, and the heat or steam needed for many industrial processes. Boilers have come a very long way since they helped launch the Industrial Revolution and they can now be customized to just about any pressure requirement with ever greater efficiency and reliability. The fact that boilers can also be designed to utilize a wide range of different fuel sources further adds to their efficacy and allows the type of boiler to be selected in part based on the most economic and convenient fuel source for a given industry or geographic area.