What makes coal burn

Combustion appears to be-a very simple operation, but we do not know a chemical phenomenon more difficult of a clear explanation. It consists of decomposition and recomposition.

This gas can only be formed of carbon and oxygen, by the chemical action which we eall combustion, as exhibited in a fire we do not speak of fermentationslow combustion. The question may well be asked, what is the cause of combustion ' It is an important one, and like a great many others, it is easier asked than answered. We only know that when II certain amounirloof heat is generated in fuel, by the particles of it changing their condition and arrangement, the oxygen of the atmosphere separates from the nitrogen with which it is chemically united, and combines with these carbon particles forming carbonic acid gas.

This action is called combustionfire great heat is developed, the coal is said to be decomposed by it, and the union of the carbon 'particles with the oxygena new composition forming a gM, which, strange to tell, extinguishes flame and fire, although it is itself the direct product of fire. The heat generated by combustion imparts a like action to water, through bars of brass and plates of iron, and changes its condition from water to steam, which occupies 1, times the space of water. It is this expansive forcethe' combination of water and heat, which i.

There is just lis much philosophy to be learned in investigating the causes of making a tea kettle boil, ail thoBe of volcanic eruption, and the ' infoima- tion to be derived is'more practical and useful. As carbonic acid gas is formed of CO' it requires two pounds of oxygen to saturate every pound of coal to form this gas. If, when burning coal, it is not completely saturated with oxygen, a gas called carbonic oxide CO is formed With one pound of oxygen to one of carbon, which is not so ejpansive, consequently a great loss of heat is experienced.

We1 then see the necessity of supplying fuel in a state of combustion, especially when' fresh coal is put on the fire with a plentiful supply of oxygen. As the atmosphere is composed of 21 volumes of oxygen to 79 of nitrogen, it follows that a great quantity of air must pass through a fire to suppl y a few pounds of coal with sufficient oxygen to form perfect combustion. For every two pounds of oxygen extracted from the atmosphere, exactly 7 pounds of nitrogen must also pass through a fire nitrogen is the heaviest gas, consequently nine pounds of air must pass through a fire for the perfect combustion of every pound of pure carbon coal.

Now, as cubic inches of the sir weigh 31' grains, and as 5, - grains is one pound, and 1, cubic. In furnaces, it is calculated that nearly, cubic feet of air pass through the fuel for the combustion of one pound of coal. We see by this what an amount of air is necessary to be admitted into rooms during the winter season for the complete combustion of the fuel in stoves and grates. This must be supplied through crannies, cracks, or open seams, for it is chemically impossible that the fire will burn unless supplied with its due proportion of oxygen.

This is the reason why, in a close w m rom, it we lay our hand upon any seam near a window, we feel a rapi! These mining operations remove the soil and rock above coal deposits, or seams.

The largest surface mines in the United States are in Wyoming's Powder River Basin, where coal deposits are close to the surface and are up to 70 feet thick.

Mountaintop removal and valley fill mining has affected large areas of the Appalachian Mountains in West Virginia and Kentucky. In this form of coal extraction, the tops of mountains are removed using explosives. This technique changes the landscape, and streams are sometimes covered with rock and dirt.

The water draining from these filled valleys may contain pollutants that can harm aquatic wildlife downstream. Although mountaintop mining has existed since the s, its use became more widespread and controversial beginning in the s. Some electric power plants use scrubbers flue gas desulfurization equipment to reduce the amount of sulfur exiting their smokestacks.

The power plants use electrostatic precipitators or baghouses to remove particulates and heavy metals from the smoke. Underground mines generally affect the landscape less than surface mines. However, the ground above mine tunnels can collapse, and acidic water can drain from abandoned underground mines. Methane gas that occurs in coal deposits can explode if it concentrates in underground mines.

This coalbed methane must be vented out of mines to make mines safer places to work. Some mines capture and use or sell the coalbed methane extracted from mines. In the past, fly ash was released into the air through the smokestack, but laws now require that most emissions of fly ash be captured by pollution control devices. In the United States, fly ash and bottom ash are generally stored near power plants or placed in landfills.

Pollution leaching from coal ash storage and landfills into groundwater and several large impoundments of coal ash that ruptured are environmental concerns. The coal industry has found several ways to reduce sulfur and other impurities from coal. The industry has also found more effective ways of cleaning coal after it is mined, and some coal consumers use low sulfur coal. Power plants use flue gas desulfurization equipment, also known as scrubbers , to clean sulfur from the smoke before it leaves their smokestacks.

In addition, the coal industry and the U. Equipment intended mainly to reduce SO2, NOx, and particulate matter can also be used to reduce mercury emissions from some types of coal. Scientists are also working on new ways to reduce mercury emissions from coal-burning power plants. What are the impacts?

The bushfires burning across Australia during this long hot summer pose a particular risk to areas where coal is being mined. In Morwell in Victoria, bushfires have ignited the coal seam face in an open cut mine which supplies a nearby electricity plant. Such coal fires, says University of Queensland mining safety expert Professor David Cliff, are much harder to put out than burning bushland.

This Victorian brown coal is a low rank coal, geologically young, and very prone to being ignited. This is a thick-seam coal mine, 30 metres thick and very close to the surface so anything that intrudes into the mine will set fire to the seam," says Cliff.

Coal is made up of carbon between 60 and 90 per cent — higher grades contain more carbon than lower grades , hydrogen 6 - 7 per cent , oxygen as well as very small amounts of nitrogen and sulphur. Coal fires are created by the interaction of carbon, oxygen and heat, which in turn produces carbon monoxide, carbon dioxide, and more heat to fuel the reaction. Meanwhile, hydrogen in the coal is converted to water vapour, nitrogen to nitrogen dioxide and sulphur to sulphur dioxide.

While coal fires can be triggered by external sources of heat such as bushfires and lightning strikes, they can also start spontaneously as the coal oxidises, says Cliff. Coal, and particularly brown coal, is very reactive to oxygen, and will generate CO2 and that creates heat.

Coal miners work to minimise interaction between air and coal to try to remove as much heat as possible and reduce the fire risk. If coal is stockpiled they will often place a coating over the top to keep the air out, and design stockpiles so that wind doesn't blow too much air into them and cause the coal to oxidise.

In Victoria, says Cliff, coal is historically not stockpiled but mined by massive machines and sent straight to the power stations to burn.