Any amount of air in a coal stock pile is an ingredeint for a coal fire.

A dense compacted coal pile will still allow air to enter it unless its under water.

The question begs me to ask are you referring to bituminous coal in a horizontal stock pile bunker or an overhead fuel bunker in a steam station feeding a boiler using pulverised coal?

A lot of it depends on the broken coal size, coal dust density in the broken coal, coal type and its moisture content hence added weight.

You will have to opportunity for spontaneos combustion in either case as the soft coal is more affected by normal atmosperic pressure and friction from being conveyed or being drawn down by the feeder at the bottom of the overhead bunker which feeds the pulveriser which drops the ground coal to the blower which blows it into the boiler to be burned. say that five times really fast :^)

Atmosperic air at one atmospere of pressure(14.28 PSI) is lazy just like water or electricity where it finds the path of least resistance.

to be more definitive you would have to take a cubic foot of soft or hard coal and put it in a vacuum chamber to actually see the amout of air is actually in that cubic foot of broken coal-displacing a cubic foot of coal in given amount of water-let say a two cubic foot cylinder would do the same thing -the conversion is a bit messier especially when cleaning it up :^).

If you had a tube filled with soft coal and stuck a fan on one end you will still get air through it to some extent but it will be resisitant to the pressure due to the coal filling up the area in the tube-plus if it combusts you will have a big flame thrower:^).

If you are thinking along the lines of an "auger fed stoker retort" that takes a huge amount of blower driven air at one atmospere for both soft and hard coal.

My two cents from the soon to be frozen "Eastern

wilderness"@1140 feet above mean sea level.

lzaharis ■

I dont think you will find much of anything other than weight of soft coals in relation to areas in question. no matter what you are looking at: 1 atmospere of air pressure in any situation so what ever air is in the coal pile is the result of 1 atmospere of pressure in relation to the coal in the bunker/feeder throat and the only sure way is to do a volumetric measure with H2O as there are a lot of nooks and crannies just like "Thomas english muffins".

another good example is the use of stoker stoves and boilers-

the recommended size of soft or hard coal for burning is rice coal as it allows for an easier burn due to its small surface area and is easily ignited with a start up heat source and air pressure/oxygen source from a blower at the end of an auger-not quite the flame thrower-because of the physical break from the auger to the burning coal.

If you do build the flame thrower let me know how well it works:^) ■

I too don't know the answer but I think I know who does and I invite them to offer their input.

Years ago I was involved in the design and supply of five sandwich belt high-angle conveyors to the Sasol (coal gasification) projects in South Africa. The coal was carefully sized for a desired air flow permeability then raised by the high angle conveyors into respective bunkers. It was very important that the coal not be further degraded as any fines production in transit would reduce the permeability and this would be detrimental to the gasification process.

So, there are people at Sasol that know the answer to your question. I invite them to provide this forum with their input.

Joe Dos Santos ■