Coal Combustion Hazards Carriage And Storage

DBTG

John Lowenhaupt | October 4, 2018

COAL FORMATION

Dead Trees and Plants + Time + Pressure + Heat = Coal

§  360 - 300 million year ago - Paleozoic Era (aka Carboniferous Period) :

•  Wooden trees with bark emerged during this time.

•  Microorganisms and Mushroom did not yet evolve to decompose the wood fully, and sedimentation slowed decomposition further by blocking air (oxygen). The presence or absence of Oxygen plays a crucial role later in the talk… FORESHADOWING…

•  Low sea levels created swampy environments – which is the perfect

place to form peat – decomposing plant matter. •  Sedimentation turns cellulose to peat. Peat to lignite; with more time,

heat, and pressure - Bituminous and Anthracite coals are formed.

Coal Formation

COAL RANK

Different Types of Coal are ranked according to their carbon and volataile matter composition. §  Anthracite – Highest Rank. Highest Carbon content, least risk for carriage. §  Bituminous – used in metallurgy to make coke. Typically does not self heat*,

but does emits methane. Main carriage risk is methane liberation in enclosed vessel holds.

§  Sub-bituminous – used in industrial boilers and for power generation.

Carriage risk is methane and self-heating risk. §  Lignite – Lowest Rank, can be used in industrial boilers/power generation.

HIGH self heating risk, LOW risk of methane emission. §  Peat – not technically coal, but still used for heating purposes in some parts

of the world.

Asteriks

•  ALL COALS HAVE THE POTENTIAL TO EMIT METHANE AND SELF HEAT. All coals should be treated as though they WILL emit Methane and Self-Heat. It’s just good practice.

•  HOWEVER, there is a correlation between rank, methane emission, and self heating.

•  The higher the rank, there is a higher risk of methane liberation (except Anthracite) but the self-heating risk lessens.

•  The lower the rank, there is a lower the risk of methane emission, but a higher risk of self-heating.

•  WHY? OXIDATION. The higher the rank, the less likely it will oxidize because there is more fixed carbon. Oxidation creates… HEAT.

HOW TO MITIGATE COMBUSTION RISKS

Though coal has the inherent properties that pose combustion risks, proper management of the cargo in stockpiles and vessel holds can reduce, even eliminate, the risks – most, if not all, accidents onboard ships occur due to human mistake.

SPONTANEOUS COMBUSTION

Spontaneous combustion occurs by self-heating (increase in temperature due to exothermic internal reactions, usually OXIDATION), followed by thermal runaway (self heating which rapidly accelerates to high temperatures) and finally, autoignition. Spontaneous implies SUDDEN. Coal does not instantaneously burst into fire. Self-heating, the precursor to spontaneous combustion, occurs when the heat from oxidation cannot escape faster than it is generated.

ON VESSELS – Control Methods

Self heating: If no methane emission detected, DO NOT VENT. Coal in a hold can range from 25 deg C to 40 deg C. If no other oxygen is introduced during transit, the oxidation, and thusly self heating risk, lessen. 50 deg C to 55 deg C – red flag, but nothing happening yet. Past 65 deg C, there is a problem. Although coal has a high ingnition temp, smaller particles will burn first at a lower temperature and the increase the rate of self heating to the spontaneous combustion threshold. So, if no significant amount of methane is detected, depriving the cargo of oxygen should keep it from self heating.

ON VESSELS – Control Methods

Methane: vent the holds. KEEP ALL LIGHTS, OPEN FLAME, AND ELECTRICAL CURRENTS AWAY FROM THE HOLDS. Methane auto-ignites at 580 degrees Celsius. That’s 1076 degrees Fahrenheit. Methane ignition onboard vessels is typically the result of open flame near the hold(s), or failure to ‘lock-out lights’ properly – shut off electrical current in or around the hold. Can self heating coal ignite a methane explosion? At 580 degrees Celsius, yes. What if coal is emitting methane AND self heating? Good question…

ON VESSELS – Control Methods

To Vent, or not to Vent… Venting releases the Methane, but introduces… OXYGEN. Oxygen leads to oxidation, which in turn can fuel self heating. Monitor both temperature and methane levels. Obviously. If temps are below 40 degrees C(104F), vent away. If temps are above 40, vent but double the frequency of temperature readings. If there is a rapid rise from 40 to 50 degrees C, close the vents. Remove Oxygen from entering the holds. Coal at 50 degrees C is not an issue, YET. It is a red flag.

ON VESSELS – Control Methods

So if coal does self heat and combust… the whole product in the hold will not catch at once. It will be progressive. There will be ‘hot spots.’ It’ll be a smolder, from 150 deg C to 250 deg C for some time. In other words, not hot enough to ignite a methane explosion immediately. AND, since coals that emit methane have a lower risk of self heating, the risk of both occurring is minimal.

ON VESSELS

So now we have coal on fire in a ship’s hold – what do we do? DO NOT. REPEAT, DO NOT USE WATER TO FIGHT A COAL FIRE IN ENCLOSED SPACE. The atmosphere and heat in a hold, or other contained area, could cause a rapid separation of the Hydrogen and Oxygen Atoms. AKA:

ON VESSELS

If at sea: close the hold vents. Hopefully, the fire will smother itself as the oxygen depletes itself. Proceed to the nearest port. DO NOT OPEN THE HOLD and add more oxygen. Be sure to call for HELP so a shore team is ready on arrival to assist. Introduce CO2, N2, or another inert gas. The fire will smother itself with no oxygen to burn.

TERMINALS

Covered storage? Follow same venting procedures for vessels and monitor pile temperatures. Open Storage? Methane emission? Who cares? Not a risk… Any enclosed space, however, could have methane and coal dust that pose an ignition risk. Always employ safe practices. So if an enclosed conveyor belt, feeder, sampler, or storage silo exists on the terminal property, be sure to monitor gas levels and mitigate coal dust as much as possible.

TERMINALS

The best way for shippers and terminals to help vessels safely carry coal is to ensure that “hot” coal is not loaded onboard in the first place. How do we do this? Proper stockpile management: -- Consistent Temperature Monitoring -- Ensure piles are angled and compacted properly -- ‘turn’ product promptly – excessive time in stockpile can lead to self heating. -- all of this is to: PREVENT OXIDATION

TERMINALS

Recommendations for handling of sub-bituminous coals, i.e., coals with the greatest risk of self heating: 1. It is recommended that "in-place" densities approach 1120kg/m^3 if at all possible. This is best accomplished through the use of a large wheel dozer such as a CAT 834 or 988. This equipment yields the best point loading for the greatest compaction. As mentioned below, stockpile shaping and maintenance is critical. Any washouts or gullies must be repaired promptly. Care must be taken to avoid high density/low density interfaces that will promote airflow through the pile at interface regions.

TERMINALS

Recommendations for handling of sub-bituminous coals, i.e., coals with the greatest risk of self heating: 2. Any amount of compaction will leave loose material at the surface. This uncompacted thin surface coal will quickly dry out surface moisture and expose the interstices micro structure which will deplete inherent moisture and allow oxygen to enter. This can quickly lead to autogenous heating and a potential fire. It is recommended that a surface pile treatment be used for storage exceeding one month. A semi-hardening latex chemical tarp applied with a hydro seeder will give excellent results if maintained with routine applications every 6 months.

TERMINALS

Recommendations for handling of sub-bituminous coals, i.e., coals with the greatest risk of self heating: 3. With regards to stockpile configurations, recommend side and rear slopes of 20 to 25 degrees and a front slope of approx 15 degrees. Such configurations will take a larger area for equivalent tonnages but result in very manageable and safe coal piles. All material stocked and reclaimed should be layered on or shaved from the front slope. This will maintain a good compaction and configuration integrity. When stocking out coal, layers of 12 to 24cm will yield the best compaction. NEVER dig into the side of a coal pile except for the repair of washed out areas.

TERMINALS

These general principals should be used for all coal types regardless of rank. The lowest rank coals (peat and lignite) require the most care when building a coal pile. Anthracite requires the least care. Remember that any coal can self-heat under favorable conditions. FIN Thank you.