How does a marine incinerator work and what can it burn?

The shipboard incinerator exists because a ship generates waste streams that cannot simply be pumped over the side or landed everywhere it goes, and burning them down to a small volume of ash is often the only practical option between ports, provided it is done within MARPOL's rules.

On the liquid side, the incinerator burns waste lubricating and fuel oil, and sludge, the oily residue collected from the fuel oil purifiers, the lube oil purifiers, and bilge separation, which is usually held in a sludge tank and pumped to the incinerator's waste oil burner, where it is atomised and ignited in the combustion chamber alongside or after a warm-up on the pilot diesel burner, since sludge alone often will not sustain stable combustion from a cold start. On the solid side, galley waste, packaging, oily rags and other combustible garbage are loaded into the solid waste chamber and burned in batches, with the combustion chamber designed to reach and hold a high enough temperature, generally in the range of 850 to 1200 degrees Celsius depending on the unit and what is being burned, so the waste is destroyed thoroughly rather than just charred, leaving a manageable quantity of ash to be collected, cooled and stored for landing ashore.

MARPOL Annex VI sets out what a shipboard incinerator may and may not burn: cargo residues from certain MARPOL Annex I, II or III substances, with specific restrictions, polychlorinated biphenyls, garbage containing more than trace heavy metals, and refined petroleum products containing halogen compounds are all prohibited, and plastics of any kind are banned from shipboard incineration entirely because burning them produces dioxins and other toxic emissions. Annex VI also restricts incinerator use within port limits and inside designated special areas, and every incineration event, what was burned, when, and the position of the ship, is logged in the garbage record book and machinery space records, which Port State Control inspectors routinely check.

Engineers operating the incinerator watch combustion temperature, exhaust smoke, and the state of the burner nozzles and refractory lining, since poor atomisation or a fouled nozzle produces incomplete combustion, excess smoke, and can trip temperature alarms or damage the refractory. The incinerator sits alongside the oily water separator and the shore reception facility arrangements as one leg of the ship's overall waste management plan, and a chief engineer who runs it casually, burning what is convenient rather than what is permitted, is taking on a compliance risk that shows up immediately during an Annex VI inspection.