I use this method, and can have the boiler up & stable from dead cold in 2 - 3 hrs. I know there's many other methods used to light this type of boiler, some maybe quicker, but I like to make sure the entire firepot is burning, and to bring the temperatures up slowly to avoid expansion stresses in the steel and welds.
Materials: old ashes, lump charcoal, charcoal lighter fluid (or kerosene, or diesel), non-flamable cover to block the bottom of the coal hopper (I use a 1 gal paint lid), dry coal.
I believe this design boiler needs proper combustion air management to properly start a coal fire, meaning the combustion blower MUST draw exclusively from the bottom of the firepot, and not from other sources such as the bottom opening of the coal hopper.
First: pour in enough ashes to fill the firepot about 1/3 from the bottom. If you don't have any ashes, I suppose you could use fresh coal, and mix in some dry sand to simulate ash density.
Second: soak the lump charcoal in your prefered starter fluid. I use diesel fuel. You need enough soaked charcoal to fill anouther 2" in the firepot. The add more dry charcoal on top for another 1".
Third: block the bottom of the coal hopper (w/paint lid) to prevent air from being drawn when the blower starts. I put a rock on top to hold in place. Now light a piece of paper, and throw into the firepot through the combustion air port, with the flapper help open. When the charcoal begins to light, let it go for a minute, then turn on the boiler & combustion fan, LEAVE THE GRATE TURNED OFF. Keep the air flapper open for the next 3 - 4 minutes to allow the charcoal to get going, thus the fan is only drawing off smoke from the top. After the charcoal is burning well, let the air flapper close off the port, and the charcoal to burn by itself for another 10 - 15 minutes, checking to get all of the charcoal glowing red.
Finally: Turn up room thermostat(s) all the way, to make sure there's enough demand on the boiler to make the combustion blower stay on during the next process, and not be turned off by the aquastat. Add some coal to fire by pouring through the hopper, just enough to put about 1" over the charcoal, and replace the paint lid to block the air. Let this coal get going, and burning red, then add another 1" of fresh coal. I find about 10 minutes between additions. Continue this pricess until the entire firepot is full of burning coal. Then and ONLY then add coal to fill the hopper to your normal level.
Finishing up: Set your room thermostat(s) to nomal, let the boiler shut down against the aquastat setting, and then turn on the grate. As I said, there's lots of other ways to start up this boiler, but this method brings it up (rather) slowly, and has never resulted in gas explosions (bumps). And it ensures that the entire firepot is burning fully, not just a small area in the center.