Coal Processing

“Coal is a combustible, sedimentary, organic rock, which is composed mainly of carbon, hydrogen and oxygen. It is formed from vegetation, which has been consolidated between other rock strata and altered by the combined effects of pressure and heat over millions of years to form coal seams. Coal is a fossil fuel and is far more plentiful than oil or gas, with around 112 years of coal remaining worldwide.”

Derrick Stack Sizers


Derrick Stack Sizers in Coal Preparation

Derrick Corporation have been successfully installing Stack Sizers into coal preparation plants since 2004. Numerous coal screening tests have been performed since 2000 on the Stack Sizer. This vibrating screening machine is capable of efficient, high capacity sizing from 3.2mm to 75 microns. The key parameter for use of the Stack Sizer vibrating screening machine is the feed density. For efficient fine sizing, the feed density should be approximately 20% solids by-volume (for coal with a dry solids specific gravity of approximately 1.65 – feed density is approximately 28% solids by-weight). Capacity is a complex function of feed density, % oversize, % near size, slurry linear velocity, particle shape, screen panel opening, screen panel tension, and presence of chemicals in the slurry.

Derrick Corporation now has over 40 5-Deck units operating at various coal processing locations in Pennsylvania, West Virginia, Illinois, and Indiana.  There are two major fine sizing applications in coal for the Stack Sizer vibrating screening machine which are outlined as follows:

1. Screening clean coal spiral discharge at 150 or 100 microns to remove clay and other inert particles to reduce ash content.


Clean Coal Spiral Flow Diagram

Prior to the Stack Sizer installations, sieve bends were used in an attempt to remove the high ash fraction from the clean coal produced by the spirals. The sieve bends normally produced a clean coal product that was approximately 15 to 17 percent ash. This ash content exceeded the desired ash content of 10 percent or less.

Months of continuous production have confirmed that the Stack Sizer, fitted with Derrick 100 micron urethane screen panels, consistently produces a clean coal fraction that ranges from 8 to 10 percent ash. Currently, each five-deck Stack Sizer operating is producing approximately 33 short tons per hour of clean coal containing about 9 percent ash. This represents a clean coal yield of about 75 percent and an ash reduction of about 11 percent from the feed slurry.

2. Screening 6″ hydrocyclone underflow at 75 microns to recover 100 by 200 mesh coal prior to froth flotation or prior to clarifiers.


6″ Hydrocyclone Underflow Flow Diagram

With the success of the Stack Sizer reducing ash in clean coal spiral circuits, Derrick Corporation began evaluation of other applications for the coal industry. Full-scale tests with the Stack Sizer have proven the machine’s capability for ash reduction from 6-inch hydrocyclone underflow.

A Stack Sizer fitted with Derrick 75 micron urethane screen panels can effectively reduce the ash content from 6-inch hydrocyclone underflow by over 40%. One five-deck Stack Sizer is capable of processing about 20 short tons per hour of feed slurry, having 15 percent solids by weight. The Stack Sizer reduced the ash content of the cyclone underflow from 37 percent in the feed to 8 percent in the oversize fraction.

Since January 2009, eight five-deck Stack Sizers have begun processing clean coal hydrocyclone underflow at several coal preparation plants in Illinois and Kentucky.


Case Study

Screening tests of representative slurry is the only accurate way to predict the machine’s screening capacity and screening efficiency. Derrick offers to perform screening tests at no charge to the customer; however, the customer is responsible for all costs associated with sample collection, packaging, and shipping to Derrick’s facility in Buffalo, New York, USA and with returning the sample material to its place of origin if the material cannot be disposed locally at the conclusion of the test program.

Follow this link for more information on Derrick Stack Sizers.

Eriez Wet Drum Magnetic Separators

Wet drums in heavy media applications provide continuous recovery of magnetite or ferrosilicon. Eriez has set the industry standards in the heavy media industry developing both the design criteria of the magnetic circuit and the benchmark of operation.

The counter–rotation wet drum tank style is preferred for heavy media applications. The drum rotates against the slurry flow in the counter–rotation tank style. The slurry enters the feedbox and flows directly into the magnetic field generated by the drum. The magnetite is attracted by the magnetic field, collected on the drum surface, and rotated out of the slurry flow. Any magnetite that is not immediately collected will pass through to a magnetic scavenging zone. The short path that the magnetic material must be conveyed between the feed entry point and the magnetics discharge lip, combined with the magnetic scavenging zone, results in high magnetite recoveries.

Follow this link for more information on Wet Drum Magnetic Separators.

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