Boilers and thermal liquid heaters generate heat for use in other operations. These two types of equipment differ in the fluid medium used to transfer this heat. The table of contents below link to different types of boilers. Each type of equipment usually has sections on general information, information about equipment design, usage examples, and advantages/disadvantages.
Steam boilers heat water to produce steam, which is then used to generate energy or heat for other processes.
Boilers are used to generate steam that then provides heat or power. Water is converted to steam in the boiler. This steam travels through the heating apparatus which can be any piece of equipment that requires steam for operation. The cooled steam is then condensed into water and returned to the boiler to start the cycle again.
All steam boilers have four independent systems. The feed water system supplies water to the boiler, the fuel system transports the fuel, the draft system controls airflow for fuel combustion, and the steam system collects and controls the produced steam. The most commonly used fuels are coal, natural gas, and oil.
There are three main types of steam boilers: Fire tube, water tube, and cast iron.
The diagram below shows the components of a fire tube boiler. In fire tube boilers, the combustion gases travel within the tubes to heat the surrounding water.
In water tube boilers the water travels inside the tubes and the heat on the outside, as shown in the video above. Cast iron boilers are similar to water tube boilers, but the water is contained in cast iron sections instead of in tubes.
Most fire tube boilers are portable and are used in oil fields, sawmills, and at construction sites to generate heat or power. Water tube and cast-iron boilers may be solid fuel fired, or they may operate on standard liquid and gas fuels. The water tube boiler below operates on gas fuel and is part of a cogeneration plant where heat from the fuel is simultaneously converted into electrical and thermal energy.
- Water and fuel, the only two feeds for this type of boiler, are abundant and inexpensive.
- Able to handle large capacities and high pressure.
- Can corrode during shutdown periods.
- Water must be treated to prevent build-up.
- There is always some heat loss.
Waste Heat Boilers
The picture below shows the immense size of some industrial waste heat boilers.
Environmental and economic concerns promoted the development of a boiler that reuses by-products. Waste heat boilers recycle the heat, steam, or combustible by-products of other processes to provide energy.
Because of their unconventional fuel source, waste heat boilers have a unique design. Waste heat boilers generally have larger intake capacities than other types of boilers because the entering fuel is not very efficient.
The waste steam or other fuels enter through the inlet duct and travel to the reheater, where any combustible material is burned. The resulting gases travel through a series of high- and low-pressure tubes to heat the water held in the reservoirs. The resulting steam exits through the outlet stack.
Waste heat boilers are used in many industries. In steel mills, two furnaces supply heat to one boiler. Energy sources are recovered from diesel engine exhaust, ore refineries, and cement kilns. These boilers are also common in the paper and wood industries. The boiler shown below is a tail gas-fired waste heat boiler. Tail gas containing CO is burned in the combustor, along with fuel from the refinery to produce steam.
Waste heat boilers process the waste fuel from joining processes. The picture below shows an example of a waste heat boiler that can be used for waste-fired power plants as well as gas turbines.
- Recycle waste.
- Good for the environment and business.
- Depends on other processes for fuel and heat.
- By-products of other processes are not the most efficient, combustible fuel sources; therefore, waste heat boilers are less efficient than other types of boilers.
Thermal Liquid Heaters
General Information/Equipment Design
Thermal liquid heaters are similar to other boilers in that heat is generated for use in a remote application. In thermal liquid heaters, however, fluids other than water transfer the generated heat.
Thermal liquid heaters are usually liquid tube boilers, comparable to water tube steam boilers. The most common heat sources are gas and oil fuels, and electricity. The thermal fluid heater shown below is used at an asphalt terminal. The oil or gas-fired heater uses thermal fluids to pump generated heat to storage tanks, heat exchangers, or steam generators.
- Better than steam boilers if the process operates near or below the freezing point of water or above 700°F.
- Thermal fluids typically do not transfer heat as well as water.
- Serious containment problems with thermal fluids at high temperatures include corrosion, erosion, and freezing. Other problems come up with toxicity, explosiveness, and odor.
- Thermal liquids and equipment are expensive.
- Aalborg Keystone, Inc., Erie, PA now part of Alfa Laval
- Alstom Power Inc., Energy Recovery, Wexford, PA now part of Schmidtsche Schack
- Babcock & Wilcox Volund, Denmark
- Cici Boiler Rooms, Inc., Evansville, IN
- Heatec Industries, Inc., Chattanooga, TN now part of Astec Industries
- SICESGROUP, Varese, Italy
- Elonka, Stephen M., and Anthony L. Kohan. Standard Heating and Power Boiler Plant Questions & Answers New York: McGraw-Hill, 1984. Print.
- Ganapathy, V. Waste Heat Boiler Deskbook. Englewood Cliffs: Prentice-Hall, Inc., 1991. Print.
- Jackson, James J. Steam Boiler Operation, 2nd ed. Englewood Cliffs: Prentice-Hall, Inc., 1987. Print.
- Kohan, Anthony L. Boiler Operator’s Guide, 4th ed. New York: McGraw-Hill, Inc., 1998. Print.
- Payne, F. William, and Richard E. Thompson. Efficient Boiler Operations Sourcebook, 4th ed. Upper Saddle River: Prentice-Hall, Inc., 1996. Print.
- Perry, Robert H., and Don W. Green. Perry’s Chemical Engineers’ Handbook. 7th ed. New York: McGraw-Hill, 1997: 27-40 – 27-51. Print.
- Shields, Carl D. Boilers . New York: F. W. Dodge Corp., 1961. Print.
- Steingress, Frederick M. Low Pressure Boilers. Chicago, IL: American Technical Society, 1970. Print.
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- Alex Wozniak
- Matthew Robertson
- Joseph Palazzolo
- Keith Minbiole
- Austin Potter