Coal Crushing

For enlarging burning surface. Why don;t you ask why firewood should be sawn up?

Fuel when introduced into a furnace burns from it's outer surface, the larger the surface, the longer it burns, a boiler is not only pressure but also temperature, so the longer the fuel burns from its surface, the further it is carried up into the boiler, and that means higher temperatures. So it is a question of pressure and temperature, this in turn is also governed by the air flow, which in turn is governed by the combustibles in the back end of the boiler. So it boils down to the time it takes for the coal to burn to produce pressure with out excessive temperature, while getting complete combustion of the fuel.

Regards JD

I'd go on to say that its also to do with the "stoichiometric ratio" which is the ratio between the oxidiser (Air/Oxygen) and the fuel (coal)

There is a point where you balance the amount of air being blown in and the amount of fuel that is carried with it to generate the maximum amount of heat, crushing the coal into finer granuals allows better control of this ratio.

Leaving the coal in the chunk or briquet's will give a certain amount of heat over a extended period of time, but its vastly inefficient.

Yes the air/fuel ratio is important, hence the reason I mentioned the O2 meter readings taken at the back end of the boiler and hopefully no unburnt fuel or combustibles. There are two methods of feeding coal, not including shovelling. (1) on to a grate where the thickness of the layer of coal is varied, (2) by crushing the coal into a fine powder, normally referred to as PF (pulverized fuel), and blown into the furnace with a regulated air flow. Hope this adds to the discussion.

Regards JD.

In a very simplified way, think of kerosene being burned two ways:

You can take a cup of kerosene and light it and it burns only at the surface and usually requires something like a wick to sustain the flame.

Now, inject the same kerosene in a fine mist mixed with air and it is very easy to ignite and gives a 3 dimension burning.

That's similar to the comparison between a bed of solid coal and an injection of pulverized coal.

Also the coal needs cleaned for some applications, large pieces can hold large inclusions of impurities and rock.

Brad.

Adding to all replies of Respected members, There is moisture which largely present in Lump of coal, in crushing and pulverising this moisture get reduced by heat, thus increasing efficiency.

Please clear if any discrepancy's

coal must be crushed down to burn it easily, generate a big mount of energy in small time.

To increase the area of surface per unit of volume. Large lumps burn slowly. Fine dust is explosively quick.

I do not wish to appear to be melodramatic, or thought to be a tree hugger............ perish the thought...........BUT................isn't it about time we got rid of these inefficient, polluting dinosaurs.

That depends. We have something like a 300-year supply of coal. It would reduce or eliminate our dependence on Islamo-Fascists for energy. There is clean coal technology by use in a slurry or as a bio-diesel (I'll steal their term) or even coke gas. Selective Catalytic Conversion on stacks is very clean and is getting better every year. It also provides useable by-products. The Germans made diesel from coal at least as far back as WWII and we have come a long way since then. If they ever get rid of the Nuclear stigma, we could reduce oil and gas, but it will be many years of building plants to do so. Solar and Wind both have their problems of which footprint and consistency are two of of the biggest problems. If they would let us drill for oil and gas on our own shores, unlike the Chinese who are drilling off of our shores near Cuba, would also allow us to burn more cleanly and reduce our foreign dependence. Finally, I don't think that you can use the word inefficient with today's plants, especially if they would let us build new ones (thanks to all of those tree-huggers).

I agree with you 100%.

Regards JD.

Outside of everything said, the main reason for pulverising the coal (remember it cost allot of money and energy to do this) is so you can better control the oxygen to fuel ratio. Remember one to many "O"s in CO2.

Crushing coal increases the surface area of the coal allowing it to burn more rapidly. It also allows air to circulate between the particles more effectively. Both fuel (and exposed surface) as well as the amount of air (O2) available to that surface impact the ability of the fuel to combust.

Harmonic frequency can fracture coal into talcum powder, with extremely high efficiency, at reasonably low cost; versus crushing.

Coal when burned conventionally contains sulphur percentages depending on its quality, the poorer the maximum content. Coal burning releases sulphur into the air.

Conventional coal burning reaches high temperature above 3000F and nitrogen is released. Both sulphur and nitrogen when comes in contact with oxygen becomes Sox & NOx and harmful for environment therefore stringent environment laws prevents you from burning coal as fuel in conventional boilers.

Recently(year 2000) modern coal-fired in operation known as "Fludized-bed or Bubbling Fludized-bed" Coal fired Boilers.

The Coal is crushed and pulverized in fine powder form and blown into the furnace area, ignited and the flame floats & bubbles in form of a fluid bed hence, the name " bubbling/ fludized-bed".

When coal is floating as a powder, the limestone & sulphur too is floating. Limestone is like a sponge to sulphur and it absorbs it tumbling down the furnace as calcium sulphate and removed as raw materials for dry walls. Hence, NO/LESS Sox into the environment.

The boiler burns clean fuel because it operates at 1400F whereas conventional boilers operate at 3000F. NOx forms when the fuel burns hot enough to be release or break off nitrogen molecules in the air and cause the nitrogen atoms to mix with oxygen atoms.

At 1400F it is not hot enough for nitrogen to break off therefore, NO/LESS NOx into the environment.

Results – burns all and even very very bad quality coal since 90% sulphur is taken care initially by mr.limestone and mr.1400F does not open gate for nitrogen to leave.

The Boiler passes all environment laws and coal-burning is not a threat to global warming *.

Trust this explains why coal need to be crushed.

*

(All the bombings to test all new bombs in Afghanistan & Iraq and the past Kuwait Oil well fires due to bombings and the 2 Atom Bombs at Japan plus all the bombings of both WWI & WWII actually did nothing to the global warming.

It's the cars that we drive and the fuel we burn , the actual cause of global warming).