I have been involved in tender parameters for coal clearance equipment and conveyors and have been associated with numerous coal types that have been mined by long wall methods. Depending on the coal type and hardness, the tendering documentation varies from about 15% in hard coals to 80% in friable coal deposits for <50mm particules. The conveyors I have been involved in show huge variations of product grading, even from one end of the long wall shear to the opposite end, in some mines. Some mines have a fairly homogenized admixture of product. It is dependent on type of coal.

Hope this helps.

Mech Doctor ■

Originally Posted by blakeyg

Longwall % fines for Coal

Hey all,

Does anyone have any idea an approximate % fines coming from an underground coal mine. The underground uses longwall mining method.

I am guess it will be 30%-40%.

Fines I am calling <50mm

1.It All depends on how fast the shearer head is running across

the face.

a. How much coal they leave in the roof or floor if any.

b. How level the seam is.

c. what the tonnage per hour of the shearer is.

2. whether the type of bit used either conical or flat.

3. How friable the bituminous coal is.

4. Who the customer is.

5. Do they burn coal in stoker or use pulverised coal boilers with or with out fluidized bed combustion?

6. Anything below thirty mesh is the rule for most fines; anything below thrty is gold as it will burn quick and anything above it will require grinding or a hammer mill.

leon ■

In the old NCB days most of the machine-got coal was quoted as being -3 which I thought was hard to justify until I saw the r-o-m in coming up the drift belt at Selby. There weren't many lumps of coal +50 and the largest items on the belt were new shovels, boots & oil drums.

In short I'd say 80% was about right. In those days the old timers scorned the technique of throwing horsepower at the coal face to get a disproportionate increase in output. Much of the extra power went into the generation of dust & that brought the silicosis element into prominence; which in turn upped the water spraying; which in turn gave us wetter coal at the pit brow. Just go nuclear!

PS. What has killed more people, mining accidents or nuclear accidents? ■

There are primarily two aspects which drive the % of fines;

1. The Hardgrove index of the coal - Which is the hardness, or perhaps better discribed as how brittle the coal is. The higher the index number the more fines are generated. Soft coals might have an index # as low as 40, many AUstralian coking coals are around 70, while most Canadian coking coals are in the 90s.

2. The second factor is the pull out nature of the longwall cutting head. Some cutting heads do a nice job at leaveraging the coal off the face, while others almost grind the face off. Many operate somewhere in between. Getting the right cutting edge for your seam is critical. Very seam specific.

Hope this helps.

www.dbaglobal.net ■