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Not all coal is the same

I’d never really thought about it, but it turns out that not all coal is the same. This is particularly important for steam locomotives, because different coals may burn differently inside the engine. This has been hinted at at various issues of The Cornishman that I’ve read; this note is a place to gather the snippets I’ve seen. I’m sure I saw something in a previous issue about buying coal from Polish mines, but I’ve lost the quote.

Pete Mason in “35006”, winter 2023:

The last Welsh open cast mine has closed, the planning permission for operating the mine having run out quite some time ago.

All heritage railways have the same problem and the GWSR have been sourcing coal from wherever they can get a supply. The coal currently being used shatters when heated and drops through the grate unburnt. In the ashpan the coal ignites, causing a number of problems.

We have installed mesh screens over the damper openings to prevent hot ash and ignited coal escaping onto the track bed and perhaps causing a line side fire. If there is an ashpan fire, these screens quickly burn away. The other main problem is that a fire in the ashpan causes the sides of the ashpan to overheat and distort; a problem made worse when the dampers are left slightly open. The resulting blast of air over a small area acts locally like a blacksmiths [sic] forge and very high temperatures can result.

He goes on to discuss some of the problems caused by the high temperatures. The damper and hopper doors no longer open, so the locomotive had to be withdrawn from service until they could be repaired. The overheating also distorted some of the spray pipes which are used as part of the “ashpan sprinkler system”, which sprays water into the ashpan to reduce the risk of fires.

The way this is phrased, I assume the coal in use previously wouldn’t shatter and overheat this way?

Maurice Wilsdon in “Narrow Gauge News”, spring 2024:

In November we took advantage of the opportunity to buy some of the last Welsh coal before the closure of the Ffos y Fan opencast mine. A lorry arrived carrying 80 25kg sacks which we transferred on to a agon on the rans-shipment siding. Before we could unlaod them, we had to tidy up our coal store which meant moving the current stock of about 40 plastic sacks to make room for the new supply so that we now have the old at the front which we will use before the new which is at the back.

I’m guessing Ffos y Fan is the mine mentioned by Pete Mason.

I wonder if there’s any chemical justification for operating the coal store as a FIFO queue, or whether this is just convention. Can coal “go off”?