Engine exhaust gas contains particulates which consist of partially burnt fuel and/or lubricating oil and ash. These particulates can form deposits on boiler Tubes. Especially during prolonged low load operation, which reduces exhaust gas velocity, it may lead to higher soot deposition. It may be due to
burning poor quality fuel,
poor combustion due to defective injection equipment, or
inefficient fuel treatment.
These deposits on the tubes may get heated and rise above self ignition temperature. Soot deposits may be ignited by glowing carbon particulates in the exhaust gases. The ignition temperature of the soot is usually less than 400 C, however if the deposits stick, it could fall below 200 C.
Soot fires can occur after the engine has shut down, therefore it is important to maintain water circulation after shut down.
The fire will be indicated by
dark smoke coming out of funnel
large rise in exhaust gas temperature after the boiler.
If fire does occur the engine should be stopped immediately and the turbocharger air intake covered to starve the fire of air.
Ensure full water circulation is maintained.
A small fire may burn itself out as the heat will be conducted away by the circulating water.
If water washing system is fitted, it can be used to extinguish the fire.
Soot Blowers : Soot blowing should be carried out on regular basis to ensure soot and ash deposits do not build up on tubes. It should be carried out more frequently when the engine is operating at low loads or when fuel has high ash content. It should be carried out after water washing of main engine turbocharger (water side).
Water Washing of Exhaust gas Boiler : The combustion of residual fuel results in formation of slag. These slag gradually build up on the boiler tubes. Soot blowing keeps these deposits at low levels, however it does not reach all areas of boiler. These slag are soluble in water and can be removed by hot water washing.