An industrial Boiler is a closed pressure vessel that produces high or low-pressure steam or hot water for industrial use. Generally, there are two types of boilers used in industrial applications—Fire-tube and Water-tube boilers.
The use of a fire-tube or water-tube industrial boiler depends on the industrial process for which they are going to generate steam or hot water.
Fire-tube Industrial Boiler
Fire-tube boilers are a cylindrical vessel in which the flames in a furnace produce hot gases that pass through tubes surrounded by water. Consequently, the heat contained in the tubes transfers to the water, heating it, and producing steam.
A fired-tube industrial boiler is employed in processes that require low pressures, up to 250 PSIG. Furthermore, due to their size limitations, up to 50,000,000 BTU/hr, do not produce large amounts of steam.
The fire-tube boiler holds a firebox where flames produce hot combustion gases. A cooling jacket that contains water surrounds the firebox and connects to the long cylindrical boiler shell. The water surrounds a series of fire-tubes or flues that heat the water, generating saturated (wet) steam. That steam rises to the boiler’s highest point, called steam dome, where it accumulates.
A regulator located in the steam dome controls the exit of the steam. A series of larger flues (tubes) situated at the top of the boiler, conduct the saturated (wet) steam back, turning it into dry or superheated steam. The boiler produces superheated steam and exhaust gases, feeding a steam engine’s cylinders. Those machines turn the energy of the steam into mechanical work. The exhaust gases are recycled to preheat the water that enters the boiler, thus increasing its efficiency.
- The maintenance and cleaning operations of a fire-tube steam boiler relatively simple. They have easy access to its firesides, allowing the change of the fire tubes without further repair of the boiler.
- The control systems are less complicated than the ones on water tube boilers.
- The accessories required by a fire-tube boiler are available at economical prices, due to the relatively low pressures that they have to stand.
- They are not only easy to operate, but they are also fuel-efficient.
Water-tube Industrial Boiler
A water-tube industrial boiler has a larger size than a fire-tube. It feeds large amounts of steam (several million pounds-per-hour), at very high pressures up to 5,000 PSIG, to industrial processes.
Water-tube boilers are highly efficient machines that, by their design, produce superheated dry steam at very high pressures. They are the kind of boilers capable of feeding the processes of heavy industry and utility companies.
In general, the water tube boiler design includes several drums. Specifically, the lower water drum and the upper steam drum. They are connected by tubes that form the furnace and convection section. The tubes that make up the furnace walls receive the heat and transfer it to the water contained in them, producing steam. Afterward, the hot water rises and enters the upper steam drum. There, the saturated (wet) steam exits off the top of the drum to feed processes or to produce superheated steam.
- The larger the amount of steam and pressure produced, the larger the size of the boiler. As a result, they have to be assembled and installed on the site of their operation.
- The preassembled “packaged” boilers, up to 1,500 PSIG, are easier to maintain than the larger ones.
- The assembly and installation process of the boilers at the site where they are going to work can be comparatively difficult and time-consuming.
- The difficulty of the cleaning process makes the maintenance process a complicated task that requires highly skilled personnel.
- It is not possible to replace the tubes, because there is not a common standard of fabrication.
Fire-tube boilers are widely available in packaged form, allowing smooth relocation and installation. They are also easy to operate, control, and maintain. Nevertheless, due to their design, they are limited in their capacity to produce both–Large amounts of steam and very high pressures.
Water-tube boilers are highly efficient, produce large amounts of steam at very high pressures. The packaged type boilers are easier to maintain than the larger ones. Most water-tube boilers with a pressure capacity beyond 1,500 PSIG have to be custom assembled and installed in their working location. Due to their design and large sizes, they are challenging to maintain.
For information about the operation and maintenance of industrial boilers, contact our steam team here.
Sources: Superior Boilers