A simalar problem is currently being worked on here, ours is a hazemag impactor used as a tertiary waste recovery crusher. we want to increase our fines, does anyone have any tips regarding: blow bar rotation (will be done in august), apron gaps, rpms? sorry to post a question in a question but this situation is somewhat simalar ■

The choice of an impact crusher to crush coal is a fundemental mistake!

Impact crushers are indescriminate and can knock the heck out of lumps coming in direct contact with the impact bars while other lumps can migrate through without any major reduction.

Coal is too friable to be subject to the attrition created be the impact bars.

Impact crushers create too many fines and a high percentage of oversize that may have to be recycled to achieve the correct product size.

They were the norm up to the end of the 70's but we have progressed along way in crushing technology since then

Take my advice (based on over 43 years of coal handling experience), install a roll crusher to provide a sized cubical product with minmal fines and oversize.

Roll crushers will descriminate, if its oversize it will crush it and undersize will flow through between the rolls will minimal additional reduction.

Generally you can work on a 4 to 1 reduction with a single stage (two roll crusher) and double that with a dual stage four roll crusher.

My experience is that "Gundlach type" roll crushers are the industry standard for coal crushing.

Regards,

Chris Atkin. ■

Dear Sir,

Could you please tell us what is the rpm you are running the crusher. Normally impact crushers produce more than 25% below -1mm and you have to run the crusher at a slow speed to reduce the fines percentage. Is the crusher is a non reversible or reversible impactor. ■

Sankarji,

To answer your questions, the proposed roll crusher is neither a non-reversible or reversible impactor.

The roll crusher has two or four rolls with teeth sized to generate the required product size. The coal passes between the rolls and the teeth on the rolls crush the coal to size.

My experience with the installation of this type of unit has been generally in association with coal fired power plants requiring a product size to the power plant storage bunkers in the range of 20 to 30 mm x 0. At this product size a single stage (two roll) crusher could accept a feed size of around 100 to 150 mm x 0.

However roll crushers can accept a much larger feed size and with a two stage (four roll) crusher can reduce the feed size from say 300 mm x 0 to 75 mm x 0 on the first set of rolls and then be further reduced to 20 mm x 0 on the second set of rolls.

Generally the roll speed is around 300 RPM, but it will be dependent on tonnage through-put.

Should you require a smaller product size, say minus 10 mm, Gundlach would probably recommend a cage packtor.

However, I am not a representative of Gundlach, I am an independant consultant, and suggest that you contact them directly. You can email Jim Korte @ jkorte@gundlach.us

Hope that this helps. ■

Is it possible to crush the coal from 300 to 25 mm in single stage. If possible suggest crusher type. Please give suggestions. ■

Hi Karthik,

Yes, it is possible to crush coal from 300 to 25 mm. The normally used crushers will be either reversible or non-reversible slow speed fixed blade impactors. Reversible impactors operates on high speed and generates -6mm more and non-reversible impactors can be operated at a slow speed which can reduce the -6 mm fines. It also depends on your requirement of -25 mm split. How much you can accept the fines.

Regards

H. Sankaranarayanan

Vice-president operations

Taurian Engineering Pvt Ltd

Mobile: 9819715435

Web: www.taurianengg.com

E-mail h.sankar@taurianengg.com ■

Run your crusher info thru AGGFLOW software and it will tell exactly how many TPH you should get on that impactor and how to optimize the reduction of fines being produced.

Generally: You are probably trying to handle too much in one stage of CRUSHING....happens all time.....to save cost of buying bigger crushers, more crushers to do the proper job. ■

This is a really tall order for the forums. You will have to buy one. ■

Hi Surri,

I'd have a look at your recycling of feed. The more you recycle the more fines you generate - it's like autogenous milling.

If you can increase the raw feed you should be able to stop the re-milling of the product ■

First things first:

(1) what amount of screening and primary crushing are you doing if any?

(A) what brand of primary screen?

(B) what brand of secondary screen?

(c) are you wet screening or dry screening?

(d) what brand and model of primary crusher are you using?

(e) what band of secondary crusher are you using?

(f) what are its crushed material size settings?

(2) what type of coal are you crushing?

(3) what is the physical condititon of the coal in questipon?

Is it wet or dry?

(4) what is the feed rate per hour to primary crushing and

screening?

If your coal is of poor quality perhaps you should think about a compactor? ■

The problem,,, is impact crushers do not have a positive setting like most other crushers. they generally produce more fines also. the gradation is very wide generally and secondary crushing and screening are usually required. ■

I/we still do not know if he has a centrifugal crusher or a hammermill. he could be using a shorthead cone crusher for all we know. ■

Dear sir,

The crushing efficiency of impact crushers get reduced if amount of fines in the feed material is more.

Do you have screen at the receiving end of crusher. If not try to have it. That may solve the problem to a large extent. ■

This is typical of impact crushers, if you get 100% to pass the 6mm you will have a very large increase in the minus 1mm also.

compression crushing creates less fines by far than impacting. ■