A Smoke Tube Boiler is a conventional multi-pass smoke-tube steam boiler with an internal furnace (where combustion of fuel takes place). This type of boiler is fully wet-back,and most suitable for a manual firing. These boilers work on either Solid Fuel (like Coal, Wood, Briquette or Agro-waste), or Gas (like LPG, CNG, Diesel, or Oil etc.)
Smoke tube means that the flue gases or smoke,generated from the fuel, travels inside the tubes at high velocities, thereby transferring convective heat to the water. Generally, tube passes are made in a boiler in order to achieve high heat transfer rates. On the basis of heat transfer rates, the heating area is designed to achieve desired boiler capacity.
The furnace of the boiler is completely submerged in the water, this helps in capturing the maximum heat from the furnace, all around its periphery and the grate bars are placed in the furnace to ensure desired grate area for Fuel Firing. The fuel of the boiler is fired on the grate and the flue gases travel from the furnace to the final pass of smoke tubes, reversing from smoke boxes on their way out. An Induced Draft Fan is provided in the Boiler assembly, for proper combustion and Forced Draft in the furnace. This conventional design also ensures effective distribution of thermal and mechanical stresses in the heating equipment.
Due to its Internal Furnace & Smoke Tube Design, most of the combustion heat is transferred to the surrounding water and only small amount of heat is lost to the environment which can also be taken care of, using various techniques.