Boilers and thermal liquid heaters generate heat for use in other operations. They differ in the fluid medium used to transfer this heat.
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 returns to the boiler to start the cycle again.
There are three main types of steam boilers: Fire tube, water tube, and cast iron.
In fire tube boilers, the combustion gases travel within the tubes to heat the surrounding water.
Fire Tube Boiler
Water Tube Boiler
In water tube boilers, on the other hand, the water travels inside the tubes and the heat on the outside, as shown above.
Cast iron boilers are similar to water tube boilers, but the water is contained in cast iron sections instead of in tubes.
The diagram below shows the components of a fire tube boiler.
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 air flow for fuel combustion, and the steam system collects and controls the produced steam.
The most commonly used fuels are coal, natural gas, and oil.
Most fire tube boilers are portable and are used in oil fields, saw mills, 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.
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.
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.
Aalborg Keystone, Inc., Erie, PA
Alstom Power Inc., Energy Recovery, Wexford, PA
Babcock & Wilcox Volund, Denmark
Cici Boiler Rooms, Inc., Evansville, IN
Heatec Industries, Inc., Chattanooga, TN
SICESGROUP, Varese, Italy
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