Coal hold cleaning: removing coal dust, stains and residue for the next cargo

What makes coal residue awkward

Coal isn't as stubborn as green petcoke, but it has its own habits:

• Fine dust gets everywhere. It films every surface and settles on every ledge. Sweep a hold after coal and you can watch the dust come back down on the tank top over the next hour.
• It stains. Coal fines work into the surface of the coating, especially where the paint is old or rough. The black marks that survive a wash are usually staining, not loose dust.
• Some coals are oily or sticky. Depending on the grade, some leave a film that behaves more like petcoke than dust.
• It's a gas and heat risk. Coal can release methane and can self-heat, producing carbon monoxide. Holds that carried coal need proper atmosphere testing before entry. More on that in the safety section below.

How to remove coal dust from cargo holds

The basic method is sweep, wash, then decide whether you need chemicals.

1. Sweep down during discharge. Ask the stevedores to clear hopper tops and ledges while their equipment is still in the hold.
2. Clean hatch covers and coamings first. Coal dust on the cover tops will fall straight into your clean hold.
3. Dry sweep the hold, top to bottom. Don't try to sweep between grabs. The dust just resettles. Sweep once the discharge is complete.
4. Clear the bilge wells of solids.
5. Seawater wash, top down, with a combi-gun or HP washer. This removes most of the loose dust.
6. Inspect for stains and film. If you're going to another coal, iron ore or similar cargo, you may be done after a rinse and dry. If you're going to grain, you almost certainly need chemical treatment.

How do you remove coal stains from tank tops and frames?

Stains are coal particles bonded into or onto the coating. To shift them, use an alkaline cleaner formulated for coal residue, applied as the manufacturer directs, left to dwell, then washed off with high pressure. Many suppliers sell one product labelled for both coal and petcoke.

On tank tops, where the coating takes a beating from grabs and bulldozers, stains can sit in scratches and pitting. A second chemical pass on those areas, worked with a stiff brush or a high-pressure lance at close range, usually does it. If a mark won't move after two passes and doesn't come off on a white cloth, it may be discolouration of the paint itself rather than transferable residue. Some surveyors accept that and some don't, so ask the charterer what their load-port surveyor's usual line is.

Coal to grain hold cleaning procedure

Coal to grain is the classic upgrade. The sequence:

1. Maximise removal during discharge.
2. Clean hatch covers, coamings and drain channels.
3. Dry sweep thoroughly and remove sweepings.
4. Clear bilge wells.
5. Seawater wash, top down.
6. Allow surfaces to drain as the chemical requires.
7. Apply coal-cleaning chemical to all surfaces, including the upper frames, brackets and the underside of the hatch covers.
8. Respect the dwell time; don't let it dry on.
9. High-pressure wash, top down.
10. White-cloth test at several heights. Treat again where needed.
11. Fresh water rinse.
12. Clean, test and cover the bilge wells.
13. Dry and ventilate thoroughly, then pre-inspect to grain standard.

The full grain checklist is in our guide on how to prepare cargo holds for grain.

Coal to fertiliser

Fertilisers are usually loaded to grain clean standard, and some receivers are fussy about black contamination in a white or light-coloured product. Follow the coal-to-grain procedure. Pay extra attention to the fresh water rinse and drying, because many fertilisers are hygroscopic: they draw in moisture, cake and become corrosive if the hold is damp.

Coal to cement

Cement is also normally loaded to grain clean standard, and it's sensitive to moisture for obvious reasons. Clean as for grain, and make sure the hold is genuinely dry, including the bilge wells and the underside of the hatch covers. A cement cargo that meets a damp patch will set in place, and then you have a much bigger cleaning job on the way out.

Coal to iron ore: does the hold need washing?

Often not. Coal to iron ore is usually a normal clean or even shovel/sweep clean change, depending on the charterparty. Sweeping out and removing residue may be all that's asked for. But check the voyage instructions. Some charterers or receivers still want a wash, and if the ship is going to need a higher standard on the voyage after, washing now while the residue is fresh is cheaper than doing it later through a layer of ore.

Safety after coal cargoes

Before anyone enters a hold that carried coal, test the atmosphere for oxygen, flammable gas (methane) and carbon monoxide, and follow the ship's enclosed space entry procedure. The IMSBC Code entry for coal sets out its hazards, and the shipper's declaration should tell you whether the particular coal is prone to self-heating or methane emission. Ventilate before entry and keep monitoring while people are inside. Coal dust is also an explosion hazard in high concentrations, so avoid creating dense dust clouds near ignition sources.

How long does it take?

Coal to coal: a sweep and maybe a wash, often done within the port stay. Coal to grain: several days of work for a five-hold ship, most of it in the chemical stage and on the upper structure. If the ballast leg is short, start the chemical work as soon as the first hold is empty, or bring in a riding crew to finish on passage.