Why Anthracite and Bituminous Coals Should not be Mixed in a Firebox

Updated: 8/9/2023

This is my recollection of an experience which I believe serves as empirical evidence for why anthracite coal should not be mixed with less pure coal.


At the moment this is only a single anecdotal experience that is being used to back up a plausible claim. If I find that my judgment is corroborated by other experienced individuals, I will remove the disclaimer.

SVLS Fall Meet 2018 Saturday October 19th 2018:

I asked Ben Shell at the Sacramento Valley Live Steamers if I could have permission to drive his crab locomotive and he said “yes”. An excerpt about the original crab locomotive can be found here. The crab is a simple diminutive vertical boiler 0-4-0 design with a geared down transmission, jackshaft, and coupling rods. The already simplified design was further simplified when building Ben’s miniature. It has slip eccentrics, a store bought valve for the throttle, only a select few control valves, a hand driven emergency water pump, and a crude hand pulled brake block. The firebox door opening is tiny and the shovel provided just barely fits through it, making it hard if not impossible to control the shape of the fire bed.

At about 5:00 PM, right before dinner we walked to the steaming bay at which his crab was parked. While we were waiting for the crab to get up to steam George Potter was moving Pacific Coast No. 6 to his siding in the steaming bays very close by. I struck up my first conversation with him and found that we got along very well. 4 years later I would form a friendship with him and he became an invaluable mentor to me.

Before firing up Ben Shell asked Chris Donhost if he could use his anthracite. Chris gladly granted the request. Ben shoveled anthracite into the firebox, but when he attempted to light the fire found that he was unable to do so. He gave up on trying to light the anthracite already in the firebox and lit the bituminous coal he had supplied in the tender without removing the anthracite. This time the fire was lit successfuly and we got up to steam quickly.

A different member also named Chris came up to us as we were pulling out of the steaming bays into the yard, and asked if he could have permission to drive the crab as well. Chris was a rather eccentric steam enthusiast. He wore a felt top hat covered with souvenir badges and a feather. He said he needed to leave for a moment and would be back to ride on the crab. Because Chris did this I borrowed and attached another riding car, for a total of two, so he could ride with us. Accompanying me was Ben and his son. Ben told me attaching the extra riding car wasn't a good idea but I didn't listen. Chris didn’t return in a timely manner so we left without him. I didn’t detach the extra pointless riding car. This was a mistake as a loco as small as this crab simply did not have enough tractive effort to comfortably pull two riding cars and three passengers, increasing the difficulty of firing for me who had no experience coal firing.

When we got up to steam and started on the main line steaming was poor. I drove the crab too fast with a heavy load. As a result, it rapidly ran out of steam. I had to stop at the Oasis siding because the boiler pressure had lowered to about 80 psi. We waited about 5 minutes before departing. On the second leg of the journey the steaming rate didn’t improve and I was running out of water. The lack of pressure and water got so severe that I had to stop in the middle of the main line to regain both. I stalled traffic for a couple of minutes before finally regaining just enough pressure and water to make it back to the yard where we started from. At this point the water was low and the pressure was extremely low. Ben inspected the firebox and found one large chunk of clinker. Ben explained to me what clinker was as this was the first time I had heard of it. I was so embarrassed by my performance that I declined to drive it anymore that day. I initially assumed that the poor performance of the loco was entirely due to my inexperience coal firing and driving such a locomotive. To be fair that was a major contributing factor. However later during the running session I asked Ben if the performance had improved. He said that it was performing so poorly while I was driving it due to an unusually large amount of clinker forming. After removing the clinker and the overload of the second riding car, the loco performed as well as it normally did without running out of steam or water.

Reason why excessive clinker formed:

Before reading The Red Devil I did not know the root cause of clinker. All I knew was that use of impure coal correlates with it’s formation. However after reading the sections of The Red Devil covering how clinker forms and the purpose of clinker control steam in the Gas Producer Combustion System, I realized what happened. Clinker is generated when the temperature of the impurities forming ash exceed the ash fusion temperature. The temperature at which anthracite burns is higher than the temperature at which bituminous coal is burned. When burning bituminous coal and anthracite together, the average temperature of the fire grate is higher than when burning bituminous coal alone. When only burning anthracite, the higher temperature poses no risk of clinker because the impurities that generate ash are not present in any of the coal. However, a higher average temperature does pose a problem when burning both together because the impurities in the bituminous coal will melt into clinker more readily at the higher temperature. The lesson to take away from this experience is don’t mix anthracite with less pure coal, unless you want an extra difficult operating challenge.