Frozen Coal Piles – Myth, or Real Problem?

By ACCCE

A few people have mentioned “frozen coal piles” when they talk about the reliability and resilience of the electric grid during extremely cold weather.[i]   The implication seems to be that frozen coal piles are a big problem.  Naturally, we wanted to see if that’s true, so we looked for data, read reports, talked to consultants, questioned grid operators, and contacted utilities.  We couldn’t find a real problem, especially one that could potentially affect grid reliability and resilience.

How is coal handled at power plants?
Coal arrives at power plants on railcars (the most common method), barges, trucks, or conveyor belts (mine mouth plants).  The coal is unloaded from railcars by either tipping the cars over (rotary dumping) or by opening doors on the bottom of the cars as they pass over a trestle (bottom dumping).  Barges are unloaded by clamshell cranes that scoop the coal out; trucks dump loads of coal.

Once coal arrives at the plant site, it is either sent directly to the plant via conveyor belt or stored in piles.  A typical coal-fired power plant has 70-80 days of coal supply stockpiled onsite.[ii]  Bulldozers constantly manage the pile, keeping its height and size at proper levels and breaking up frozen areas.  Bulldozers push the coal to underground entry points for conveyor belts that carry the coal to the top of the power plant, where it is stored in bunkers until it is fed into the boiler.

How do power plants deal with coal supplies in cold weather? 
We spoke to executives and managers responsible for coal-fired power plant operations at several utility companies in the northern part of the country.  All reported that cold weather can affect normal coal transportation or unloading.  For example, rivers can freeze and ice-breakers must be brought in to break up the ice.  During cold weather, barges or railcars sometimes arrive at power plants with coal that has frozen due to cold temperatures or due to rain and snow falling on the coal and freezing.  It can be challenging to unload coal that has frozen.  However, all the power plant executives we spoke to reported that deicing agents can be applied to the frozen coal, and some plants have “car shakers” to help remove frozen coal from railcars.  But even if the delivery or unloading process is interrupted or slowed, the 70-80 day supply of coal in the stockpile is ready to be fed into the power plant’s boilers.

Do coal piles really freeze and cause problems?
The power company experts we talked to said that all layers of a coal pile would not freeze.  While the outer layers of a coal pile can freeze in very cold weather, coal piles are being constantly worked by bulldozers to break up the frozen layers, and deicing agents can be applied to prevent freezing.  One utility told us the frozen outer layer of the coal pile can act as a shield, allowing the bulldozers to extract unfrozen coal from underneath.  In addition, the feeding point for the conveyors to the plant is typically underground which helps protect coal as it is transported to the plant.  Also, some plants have coal crushers specifically designed to crush frozen coal before it gets to the conveyor system.  And even if frozen coal gets onto the conveyor belts and slides down, coal hoppers in the plant have as many as 12 hours of unfrozen coal waiting to be fed to the boilers.  All in all, these executives reported they did not know of instances where frozen coal piles or even frozen coal had caused outages or de-rates at their power plants.

What’s our point? 
We could not uncover any real problems with “frozen coal piles.”    However, we’re willing to keep an open mind to information that might prove otherwise.  Until then, let’s try to rely on facts, not exaggeration.

[i] For example, FERC Chairman McIntyre testified at a Senate Energy and Natural Resources Committee hearing on January 23 that “[coal] wasn’t exempt from operational problems [during the Bomb Cyclone] … there were some issues as I understand it with frozen coal piles at certain sites.”

[ii] EIA, Electricity Monthly Update, “Electric Power Sector Coal Stocks: November 2017,” January 24, 2018.

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