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How Coal Burns

Chunk-of-anthracite-coal-on-fire-smallSteady burning Anthracite home heating coal

When you look at a piece of coal it certainly looks like a rock and feels like a rock. So how can it burn? Well like anything else you need oxygen and heat and an ignition source then fuel to continue burning.

Specifically we are talking about Anthracite coal and how it burns. The reason for this is that is the type of coal we sell and is the type of coal that is best for home heating. The prinicples are the same but the specifics regarding composition mentioned below are focused on Anthracite coal.

Grades of Anthracite Coal

There are three grades of anthracite coal and this dictates how it is used. Typically the standard grade is used for home heating. Some of the reason we show this is to be able to see that all coal is not a like and quality of the product counts. So some times when you see prices below a reasonable market price including trucking to New England there are either variations in actual quantity supplied or grade of the coal.

Physical Properties of Coal does Vary
 Standard grade anthracite  HG anthracite  UHG anthracite  Coke Coa l
Moisture (maximum)15%15%13%5%
Ash (maximum)20%15%12%14%
Volatiles (maximum)10%10%5%2%
Fixed carbon (minimum)73%80%85%84%
Sulphur (maximum)1%1%0.6%0.8%
Phosphorus0.02%0.002%0.002%0.04%

Coal Physical Properties 250
With this chart you can see that the moisture and sulphur content goes down. The Carbon content goes up. Carbon is the fuel for the fire so the higher grades of coal have more carbon thus more available BTU’s per ton.

When something burns and gives of a gas the presence of the gas is what creates a flame. The flame is an indication of heat forcing gas from a burning substance. The combinations of what substances are forced out of what is burning gives the flame it’s color. The coal flames come from the combination of these gases coming out of the coal being mixed with oxygen in the air. When a coal fire shows flames, you see it because gas is being released from the coal, and the carbon and hydrogen in the gas combine with oxygen to “Burn”.

So being a hard rock like material with the combustible material tightly locked inside both high steady amounts of heat need to be added to release the gases and an ample supply of air needs to circulate. Once the fire is started and up to temperature the stove or furnace will only need periodic shaking to keep airflow up and around the coal pieces. This hot flame combined with lack of impurities is why creosote does not formed in a chimney like you find with burning wood. The moisture in the wood and sap gives off a lot that does not full burn. These gases create the nice romantic dancing flames but they also leave behind deposits on the chimney that coal avoids.

Benefits of Bruning Coalcoal stove

The benefits to burning Anthracite coal is it will burn longer and hotter than the other types of coal, and a lot better than wood or pellet fuels. So you have to handle less total material to heat the same amount of house and with less expense per heat unit given off.

Coal Burns Consistently

Knowing that coal is a different material to burn you need to adjust how you do it. Burning wood or pellets in a stove the air flow can be dampened way back to create a smoldering fire. With coal this can be done but not the fire is still hotter since it burns hotter. Being a very hard material it takes more heat to release the carbon and gases to burn so the range it functions in is just relatively higher. If you cut back the air too much the fire will just go out. Once you get used to that adjustment it is no problem other than early or late in the heating season. When the stove is set up to burn efficiently almost all of the coal with burn down to a fine ash with very little to dispose of which is another proof of its efficiency compared to fuels.

Other types of coal

So you can see the quality of the coal counts and the use of Anthracite coal is because it burns the cleanest and hotter. For comparison sake here are some of the details on other coal types. The softer bituminous coal typically contain about 70% carbon, the balance of its composition is higher sulfur content and moisture so it not burn as hot. The next lower grade of coal being common brown lignite coal has a carbon content of only about 30%. These types of coal have not been compressed as long and have other contaminates in them that turn to gas and are burned. So when these types of coal are burned for heating, they produce more smoke and give off a strong odors that high in sulfur and not pleasant. These coals would be what are referred to as dirty coal and the kind of coal that was burned in the old days in Europe that is talked about in history books creating smog and unpleasant breathing.

Power Plant Coal Burning

In power plants large volumes of Bituminous and subbituminous coal is burned to create heat to turn turbine to generate electricity. These large volumes of coal are crushed and ground down to very small particle size so the coal can be blown into the furnace in an air stream. This finely pulverized coal is blown into the furnace where it burns as it is kept airborne. So it is sort of like fuel injection in a car. They work very hard and get a lot of air exposed to a high amount of coal surface area so it will burn fast and hot. This is different from how a stove works since there are large pieces and the voids between the pieces are what let the air circulate around the coal providing oxygen for it to burn.

For a quote on coal delivery please call us at 1-718-254-2773 or go to our coal quote form and we will get back to you