MISSION™ OS BOILER SD9210#01.

MISSION™ OS boiler

1 Description
The MISSION™ OS boiler is a vertical oil-fired auxiliary marine boiler, insulated
and assembled as a unit with the boiler mountings mounted on the boiler body.
The boiler mountings are mainly mounted on top of the boiler body in order to allow
a simple connection to the piping systems on board the ship.
The burner is ready for mounting in the furnace and connection of pre-marked
electric wiring.
The control system supplied with the MISSION™ OS boiler unit provides fully
automatic operation of the boiler and burner.

1.1 Boiler pressure part

The pressure part of the MISSION™ OS boiler is shown in Figure 1. Basically, the
boiler is designed as a vertical cylindrical boiler with a shell surrounding a
cylindrical furnace, and a convective section consisting of pin tube elements.

Principle drawing of the MISSION™ OS boiler

S te am
s pa c e
NW

P in -tu b e

O u ter tu b e

F lu e g a s F u rn a c e

F ire h o le

Figure 1 os_001a.cdr

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The pin tube elements consist of an outer tube enclosing the pin tube. The pin tube is
a plain seamless steel tube provided with an inlet pipe at the bottom and an outlet
pipe at the top. A large number of pins are welded around the outside of the tube
creating an extended heating surface. This extended heating surface transfers heat
from the flue gas to the steam/water mixture 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.
As shown in Figure 1, the boiler mountings such as safety valves, steam outlet valve
and water level electrode are mainly mounted on top of the boiler body in order to
allow a simple connection to the piping system on board the ship.

1.2 Heat transfer and water circulation

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 element occurs because the density of water is
higher than the density of steam. The density of the water outside the pin-tube
element is higher than the 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 boiler is designed so that approximately half of the steam is generated in the
pin-tube elements and the rest by radiation in the furnace.

1.3 Steam space

The steam space in the oil fired boiler is designed to absorb the shrink and swell
volumes. However, it is advisable to avoid sudden and large load variations as this
might create instability in the steam system, and cause level alarms.
It is very important to note that a boiler plant consisting of one or more exhaust gas
boiler(s) using the steam space in the MISSION OS boiler is not designed for
simultaneous operation in its basic design. In some cases the volume of the steam
space should be enlarged.

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