EnginePage 6 of 7
Burning sludge on passage: incinerator hours
Why it matters Sludge must be burned or landed, with every step in the Oil Record Book; a plan that does not add up shows at the next inspection.
Words on this page
- Sludge
- the oily waste left over when the fuel and oil are cleaned on board.
- Sludge tank
- the tank where that waste is collected.
- Incinerator
- a small furnace on board that burns oily waste.
- Throughput
- how much the incinerator can burn in one hour.
- Waste oil
- used oil with little water in it; it burns faster than a wet sludge.
- Suction
- the pipe opening that draws liquid out; it cannot reach the very bottom.
- Surveyor's sample
- a small amount kept back so that an inspector can test it.
- Oil Record Book
- the official log where every handling of oil and oily waste is written down.
- Reception facility
- a place in port that takes the ship's waste ashore.
An everyday picture
Picture a big water bottle on an office dispenser. The tap cannot draw the last bit at the bottom.
You also keep one glass aside, in case someone wants to test the water.
To know how long the bottle lasts, take those two off first. Then divide what is left by how much is drunk each hour.
In the ship, the bottle is the sludge tank. The hourly amount is the incinerator's throughput for this kind of waste.
The rule
- Not all of it can be burned. The tank bottom the suction cannot reach, and the surveyor's sample, stay in the tank. Take them off first.
- Hours = quantity to burn ÷ throughput. Use the throughput for THIS feed (waste oil), not the lower figure for a wetter sludge.
- One machine runs at one feed rate at a time. Never add the two throughputs together.
- Burn only where shipboard incineration is allowed, not in port. Write the tank quantities before and after in the Oil Record Book. Or land it to a reception facility.
Formula
- Hours = (residue in the tank − quantity retained) ÷ throughput for this feed
Worked example
| Residue in the sludge tank | 26 m³ |
| Quantity to be retained for the surveyor’s sample and the tank bottom | 6 m³ |
| Incinerator throughput on waste oil | 0.09 m³/h |
| Incinerator throughput on sludge of higher water content | 0.055 m³/h |
- To burn = 26.0 − 6.0 = 20.0 m³We take off what has to stay in the tank.
- Hours = 20.0 ÷ 0.090 = 222.2 h (about 9.3 days of running)We divide what is left by the amount burned each hour.
Answer222.2 h
Common mistake
Burning the whole 26.0 m³, the retained 6.0 m³ included.
What stays is the tank bottom out of the suction's reach and the surveyor's sample. Planning 288.9 h means planning to run the machine dry. The Oil Record Book will not add up either.
Note for mariners Check local rules too; some ports and coastal states ban incineration in their own waters.