Package type boilers is an internal furnace Boiler, this is the conventional multi-pass smoke-tube design steam boiler having the internal furnace (where combustion of fuel takes place). This packaged Type Boiler comes in dry back, semi-wet back, and fully wet-back options and is most suitable for a manual firing of Solid Fuel likes coal, wood or briquettes.
Smoke tube means that the flue gases or smoke travel inside the tubes at high velocities thereby transferring convective heat to 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 heat transfer 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 packaged type Boiler is fired on the grate and the flue gases travel from the furnace till the flue gas outlet through the second and third pass smoke tubes, reversing from smoke boxes on their way out. An induced draft fan is provided in the Boiler assembly, for proper combustion and balanced 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 using various techniques.