Boilers are closed vessels in which water or some other fluid is heated. In the United States, when the purpose of the boiler is not to boil water, it is more commonly called a furnace or, domestically, a water heater. These utilities are used in industrial, commercial, and domestic settings to offer heated air and hot water, as well as steam in steam-operated machinery.
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The purpose of a boiler is to provide hot water or to generate steam. While it can boil fluid, it does not have to. The hot water or steam produced by a boiler can be used for many different applications in many different industries. For example, hot water boilers provide hot water for heating systems, which are used for providing optimum room temperature, as protection against freezing, for dishwashing at large scales, car washing, and many other applications. Whereas, industrial boilers, which generate steam, are used for power generation, cement and brick production, as well as soil steaming in agriculture.
Boilers are most commonly used in these industries:
- Food Processing
- In the food processing industry, all food items need to be heated to inhibit microbial growth. Steam is used for cooking, sterilization of vessels, pasteurization, sanitization of packaging material, and general cleaning.
- Wineries and breweries use large boilers to heat raw materials for several hours. This starts the fermentation process, which breaks the material down into alcohol. Steam is used for cleaning barrels and other equipment to eliminate cross-contamination.
- Heated water is vital in the laundry industry, as it cleans dirty clothes and removes tough stains. The steam produced by boilers is also used for ironing.
- In the building industry, boilers are used to manufacture bricks. Steam hardens the brick in a special chamber under high pressure.
- Sewer Cleaning
- In the sewer cleaning industry, steam is used to clean jammed piping systems by exposing the pipes to high-pressure steam, which cleans the blockades.
History of Boilers
The earliest boilers were invented in the 1700s. They were kettle-esque and used on a small scale. The first industrial boilers, though, weren’t invented until 1867, patented by George Babcock and Steven Wilcox. In those early days, the steam boiler powered steam locomotives and engines. Its uses were industrial and often dangerous, as early operators did not fully understand the relationship between temperature and pressure. Because steam boiler applications were so dangerous, concerned citizens and workers contemplated getting rid of steam boilers altogether, or at least until engineers made advances in their safety.
Today, boilers operate in many settings such as schools and office buildings. Boiler material, design, and construction have all improved to the point that fear is no longer a factor. Accidents do still occur but with less frequency and fewer injuries or fatalities. Boilers are now a vital part of everyday life and can be found in almost any environment.
Once quite large, boilers are becoming smaller and smaller in order to fit into tight spaces. Some boiler designs, like those used industrially, must continue to be of a larger size in order to produce the necessary amounts of steam and water. Mobile boilers are now available and can be used in military, emergency, or temporary situations to provide steam for heat or power. Even as technology continues to make significant advances, boilers will remain a critical part of life for years to come.
How Boilers Work
Depending on a boiler’s heating source and whether it produces heated water or steam, an individual boiler will vary in its working process.
In general, though, they have a cylinder-shaped heating chamber and a burner that generates heat. The heat moves through a heat exchanger to the water, and then the heat warms the water.
When the boiler’s main purpose is to produce steam, the steam moves under its own pressure and is transported to the desired areas through a cache of tubes. For efficiency and to save water, condensed steam will return to the furnace to be heated again. The furnace itself is furnished with water continuously to compensate for lost water.
Boiler Design and Customization
Boiler manufacturers tend to rely on fire-tube or water-tube designs as their baseline design. There are many different types of boilers, including custom boilers. To make configuration decisions, manufacturers consider factors like system load type, ideal application fuel source, the size of the operation, application standard requirements and restrictions, the temperatures that need to be reached, and the nature of the fluid being heated.
Manufacturers typically construct boilers from stainless steel, aluminum, or cast iron. The pressure vessel itself is usually made of steel or alloy steel. This part of the boiler is not made from stainless steel because it’s susceptible to corrosion and stress corrosion cracking. Heating areas that will not be exposed to boiling water are made from ferritic stainless steel. Electrically heated shell boilers can be made from stainless steel in the European Union, under the European "Pressure Equipment Directive," for sterilizer and disinfector steam production.
An industrial boiler consists of a heating chamber, also known as a vessel or a furnace (typically in the shape of a cylinder), a burner, and a heat exchanger, which is made up of pipes and tubes. The other parts include a chimney to emit combustion gases, a pump or a fan, and a pressure safety mechanism.
Here are some considerations for boiler customization:
- System Load
- A system load is measured at a specific temperature and pressure in terms of Btus or pounds of steam. There are three types of loads: heating load, process load, and combination load. System load helps to select the size of a boiler that will serve the requirement.
- Combustion Efficiency
- This is the percentage of potential energy that is converted when the chemical potential energy of a fuel is changed to produce thermal energy.
- Thermal Efficiency
- This is the percentage of potential fuel energy converted to thermal energy for producing steam or heated water.
- Fuel Type
- You can choose from a number of fuel sources, such as propane, natural gas, and light oil. For most applications, we recommend natural gas, as it leaves little residue and requires less time spent on maintenance. Sources like heavy oil and solid fuel are currently being phased out under new guidelines.
Boiler Safety and Standards
With the advent of stricter environmental regulations, it is important that you consider the rules and codes implemented regarding boilers. The rules that you must research include the American Society of Mechanical Engineers rules, insurance guidelines, and state rules.
When using an industrial boiler, it is recommended to review the literature given in the American Society of Mechanical Engineers (ASME), which explores the various factors affecting these boilers in more specific detail.
Points to Consider When Selecting a Boiler
- How many boilers do you need? Additional boilers offer the advantage of backup. Some systems, though, do realistically require a backup. Figure this out by assessing the risk level of system breakdown, weighing future maintenance costs against the upfront costs of a larger operation, and whether or not you are planning to expand your application in the future.
- What space do you have for boiler installation?
- Talk over your fuel options with your supplier. In a standard operation, almost 10 percent of an operating budget goes to fuel. Thus, you must estimate boiler-fuel consumption rate, annual fuel use, annual fuel cost, and potential annual fuel savings.
After considering all of these factors, you will need to determine potential incremental efficiency, as well as what the payback period against the investment will be.
Choosing the Right Boiler Manufacturer
With the number of options available on the market, choosing an industrial boiler can be a daunting task. To help guide you, you need a boiler supplier on whom you can rely. The right manufacturer for you must not only be competent, but also intuitive, experienced, and able to deliver on all of your specifications, including those related to turnaround times and budget. Find a great manufacturer like this by perusing the websites of the high-quality companies we listed near the top of this page.
Notable Types of Boilers
Boilers categorized by their fuel source:
- Gas Boiler
- Fueled by natural gas and use a natural gas flame to heat water to a specified temperature or its boiling point, thereby producing steam. They are the most common type of boiler used for heating applications in the United States.
- Oil Boiler
- Use oil either as fuel for the furnace or to replace the water generally found in boilers. They produce hot gases that travel through the piping system.
- Electric Boiler
- Offer efficient, clean, and safe water heating. Unlike appliances that provide heating through the process of combustion, electric boilers eliminate problems with carbon monoxide, backdrafting, pilot lights, gas piping, and venting.
- Biomass Boiler
- A less common boiler heat source is biomass, such as wood logs, wood chips, or wood pellets.
Boilers categorized by their heat exchanger arrangement:
- Water Tube Boiler
- In the water tube boiler design, water tubes are installed in the boiler drum. When the water-filled tubes are exposed to heated flue gas, the water boils and evaporates to make steam. This design is preferred when demand for steam is high and when high pressure is required, therefore, they are also called high pressure boilers.
- This type of boiler is more thermally efficient and saves a significant amount of energy, but the design has downfalls, too. First, their construction is complex. Second, the water fed into the system needs to be treated, since water with contaminants can clog tubes; all solids in the water are required to be filtered out before water enters the boiler.
- Firetube Boiler
- Generate steam using tubes that carry hot gases from the furnace, which then pass through a water-filled drum. This design is a common construction found in the boiler industry. It is used when low-pressure steam is required (as such, they are also known as low-pressure boilers).
- The fire boiler is easy to operate in comparison with the water boiler. Unlike the water tube design, fire tube boilers are not complex, which makes them less expensive than the alternative. However, they are bulky because of their chunky outer shell.
- This design has evolved and three variations are available on the market. The first is the horizontal return tubular boiler, which has horizontal tubes and a separated furnace. The second design is known as the scotch marine or shell boiler, in which both the firetubes and combustion chamber are designed in a single shell. The last variation is known as a firebox boiler, which has a specialized water-jacketed firebox.
- Sectional Boiler
- Have the most basic design, in which different sections are cast and bolted together. The combustion chamber surrounds the water chamber and heat is exchanged directly. These boilers are used for hot water needs, as they are made from cast iron.
Boilers categorized by the level of pressure they maintain:
- High Pressure Boiler
- Another way to increase efficiency is by using a high-pressure boiler, which maintains an operating pressure greater than 15 psi. Some models achieve pressures as high as 1,000 psi.
- Low Pressure Boiler
- Have pressure less than 15 psi and are used mostly in smaller buildings for heating a space.
Other types of boilers:
- Industrial Boiler
- Used either as part of a heating system or to individually generate hot water or steam for various industrial and manufacturing processes. They are much larger and built from heavy-duty materials to ensure safety, durability, and performance.
- The working principle of an industrial boiler is the same as the pressure cooker in your kitchen. The difference is in the scale and ability to withstand high pressure. Industrial boilers are specially designed to manage pressure as high as 30 bars and are thus made from chunky steel plates that are welded together. However, just like pressure cookers, they are enclosed vessels made to withstand high pressures and heat water by a fuel source. Steam generated by boilers is used for humidification and industrial heating.
- Combi Boiler
- Different from conventional hot water boiler models because they do not store hot water but rather heat it rapidly on demand. They have a second heating element to speed the heating process and maintain a steady supply for as long as the boiler runs.
- Condense Boiler
- Can recover energy that would normally be expelled through the flue by condensing the escaping water vapor back into liquid water. Because the boiler uses latent heat to boost its efficiency to above 90%, it is considered a high efficiency boiler.
- Industrial Steam Boiler
- Steam boilers produce steam for heating large buildings such as factories and warehouses. They can also be used to create steam for power. Hot water boilers such as the steam boiler are an important part of hydronics because they heat the water that circulates through pipes and into radiators, baseboards, and other heat exchangers.
- Thermic Fluid Heater
- This type of industrial heating equipment is only used to heat water. It does not create steam. As its name suggests, it uses thermic fluid.
- Hybrid Boiler
- The last option that you can come across is the hybrid design, which uses a different arrangement of heat exchangers and combustion chamber to achieve high efficiency. One example is the electric steam boiler.
- Accumulation Test
- A test that measures the relieving capacity of boiler safety relief valves.
- Ambient Air
- The air that surrounds the equipment.
- Aspirating Burner
- A burner in which fuel is drawn through one or more openings by lower static pressure created through the velocity of the fuel stream. In either a gaseous or finely divided form, it then comes into contact with combustion air and is burned in suspension in a combustion chamber.
- Boiler Accessories
- Includes accessories such as a safety valve to release pressure, a water level indicator, a low-water cutoff switch, a top feed for water injection, and a chemical injection line.
- Boiler Lay-Up
- The removal of a boiler from service for a length of time. A boiler may be laid-up dry or wet.
- Boiler Parts
- Boilers use a variety of different large and small parts, including valves, level indicators, switches, piping, heating components, and pressure vessels. To keep a boiler running efficiently, it is important to maintain or replace these components as they begin to function less effectively or stop working altogether.
- Boiler Pressure
- The pressure of the steam in a boiler, generally expressed in pounds per square inch (psi) and the corresponding temperature.
- Boiler Vent
- A valved port used to vent air from a full boiler and to prevent a vacuum from forming when the boiler is drained. Boiler vent openings are located on the highest part of the waterside of the boiler.
- Bottom Blowdown
- The draining of a portion of the water in the boiler to remove the heavy sludge that tends to settle at the bottom. This process is done periodically.
- Btu (British Thermal Unit)
- The amount of heat needed to raise or lower the temperature of one pound of water by one degree Fahrenheit under standard pressure.
- By-Pass Line
- A pipeline that passes around a control to allow the boiler to be operated manually without having to use the control.
- Continuous Blowdown
- A small, continuously draining stream of water that controls the quantities of impurities in a boiler.
- Cut-In Pressure
- A pressure control setting at which the boiler automatically turns on.
- The connections between parts of a boiler to equalize pressures.
- Explosion Door
- A door in a furnace or boiler setting designed to be opened by a predetermined gas pressure.
- Flash Point
- The lowest temperature at which, under specified conditions, fuel oil gives off enough vapor to flash into a momentary flame when ignited.
- The enclosed space of a boiler in which fuel undergoes combustion.
- The flame utilized to ignite the fuel at the main burner or burners.
- A vertical conduit that, due to the difference in density between internal and external gases, creates a draft at its base.
- The vapor phase of water, unmixed with other gases.
- The change from a liquid or solid phase to a vapor phase.