The MISSIONTM OS boiler is a vertical oil-fired auxiliary boiler with a capacity range up to 6t/h. It is insulated and assembled as a unit with boiler mountings mounted on the boiler body. Basically, the boiler is designed as a vertical boiler with a shell surrounding a cylindrical furnace, and a convective section consisting of pin tube elements.
The pin tube elements consist of an outer tube enclosing the pin tube. A large number of pins are welded around the outside of the pin tube creating an extended heating surface. This surface transfers heat from flue gas to the steam/water mixtube in the pin tube.
The furnace floor consists of a steel plate protected from radiation of heat by refractory. The furnace bottom is provided with a socket for drain of washing water.
Oil ignition and combustion take place in the furnace. The produced heat is transferred mainly by radiation from the flame to the furnace shell. Leaving the furnace, the flue gases flow through the vertical uptakes where heat is transferred to the pin-tube elements mainly by convection.
On the water side, the heat is transferred by evaporation of the saturated water adjacent to the furnace shell or tube wall where steam bubbles are formed. As the steam bubbles have a much lower specific density than the water, they will rise rapidly to the steam space where water and steam are separated.
The natural circulation in the pin-tube elements occurs because the density of water is higher than density of steam. The density of the water outside the pin-tube element is higher than steam/water mixture inside the pin-tube element. The difference in the static pressure at the lower connection to the pin-tube creates the driving force for the circulation. The steam/water mixture is discharged into the steam space where the heavier water particles separate from the steam and flow back into the water.
The steam space is designed to absorb the shrink and swell volumes. It is very important to note that a boiler plant consisting of one or more exhaust gas boilers using the steam space in the MISSIONTM OS boiler is not designed for simultaneous operation.
For further information visit www.alfalaval.com