Dear Dr. Ergun,

Sometimes, lignite is also mentioned as coal by some people. The characteristics of lignite and black bituminous coal are quite different and the design of the coal handling plant for these materials is also remarkably different. For example, lignite can be quite sticky and can become somewhat muddy in a wet condition but black coal will not become so sticky etc. Although black coal is comparatively hard but the abrasive index of lignite is often more, due to inbuilt sand content. So, it is advisable to be specific whether the coal handling plant referred here is lignite handling plant or black bituminous coal handling plant.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Coal is coal & lignite is lignite. Where's the issue? Where does technology, as we understand it, come into coal handling? ■

Coal Handling? try us with our bulk conveying and handling machinery! ■

There are many coal storage installations that experience flow problems, particularly when handling fine coal that is moist. Retrofits usually have to accomodate a variety of constraints, but measurement of the flow related values and exploitation of established design methods and techniques to improve flow channels can usually bring about a radical improvement. Recent modifications to a 4,000 tonne hopper system, with wall not considered strong enough for mass flow, converted an operation plagued by flow stoppages and ratholes to a reliable discharge by transforming the flow channel in the outlet region and then expanding the path to be greater than the critical rathole diameter.

Apart from historical installations, it is remarkable that some large hoppers are still constructed without being based upon quantified flow values of the the material to be stored or employ a single form of geometry and wall inclination for the whole hopper section. Structural strength is always taken into account, but refinement for optimum flow seems to receive far less consideration. ■

In theory it should be possible to design a handling system according to the coal to be handled. i.e. the coal from a particular seam or a specified grading from outside sources. Unfortunately operating conditions can vary wildly which are usually the cause of problems on a otherwise well designed plant.

The rush of water during the start up of an underground operation after maintenance day is one example. This puts paid to the best designed bunker etc. Likewise when the slurry reaches the surface, the effects on sample plants bins, transfers and stockpiles creates additional headaches. De-watering facilities usually underestimate the instantaneous quantity of water on the belts in these conditions and fail in their task to efficiently dewater. Generous de-watering systems designed for peak water flow (without coal) should therefore be installed.

Stockyard belts are generally open topped for both stacking and reclaim. The cost of covers suitable for catering for the stackers and reclaimers is generally prohibitive. This raises the question of what to do in a thunderstorm. The options here are run the belts empty and stop them followed by dewatering of the belts (not to good for production) or run the belts at maximum capacity. The quantity of water discharged at the head of a long open conveyor can be horrific during a thunderstorm. Calculate the catchment area of the belt, the belt speed and the litres/second at the discharge. If the belt is running empty the water is a problem and will spill on any incline. Coal sent before the water has cleared the system will fluidise on an incline causing spillage (and collapse of the gantries if allowed to spill often enough). If the belt is lightly loaded, the coal will fluidise on the incline inclines causing spillage. If the belt is fully loaded the ratio of coal and water can be maintained within acceptable limits. i.e. no spillage or runback. ■

All aspects of the coal dust industry which is really what you refer to are found on www.cypherltd.com under Dust Stop. Good luck and please be assured that the product is exceptional and is used by the worlds largest coal company and the largest construction site on earth.

Norm Burns ■

For discharging stubborn ratholing and bridging coal from bunkers:

http://www.navco.us/files/1000.010%2...or%20Power.pdf

For unclogging coal chutes and pipes:

http://www.navco.us/pipe.html

For unloading rapid discharge coal railc ars completely:

http://www.navco.us/hopper-car-unloa...s%20video.html

YouTube Videos of Railcar Unloading difficult coal:

http://www.youtube.com/watch?v=Kl1YjkXmOqk

Did you know Pneumatic Industrial Vibrators are safer than Air Cannons and Blasters for discharging coal for several reasons? This article explains why:

http://www.navco.us/pneumaticvscannon.html

There are two basic types of vibration that can be applied to storage vessels such as bins, hoppers and railcars as flow aids. In this article the differences and advantages or disadvantages of each are described:

http://www.navco.us/vibrationcomparison.html ■

Not everyone has the luxury of water. You may not have a water source or may need permits to pump water from source and handle the excess water into the water table or near by rivers, etc... We handle coal all year round. It's not very fun in the winter. Cap your coal for dust control with water daily (if available) or coat with liquid calcium or waste oils if prohibited. Calcium is expensive so you will have to manage piles closely to ensure piles are opened up and reclaimed right. No unnecessary traffic on piles once capped. In the winter we screen the coal to get rid of frozen lumps and keep material (fluffed up). Lots of heat around hoppers in winter. Like one of the prior posts, keep the product going, hoppers and belts full at all times. Scrapers! Scrapers! Scrapers! Oh yeah, a few well placed vibrators won't hurt. ■

Dr.Ergun,

Concerning with your abrasion problem in conveying coal, how about trying use super abasion beltings, for example, DIN W (abrasion 90 mm3 ), AS-1332-A (abrasion: 70 mm3),or using chevron belt,such as Chevron Height = 5mm, multi-V pattern, this pattern is very popular in our European clients and it did a good job in conveying coal, concrete and iron powder.

Hope that this can give you some valuable references.

Regards,

Molly

Qingdao Huaxia Rubber Industrial Co., Ltd.

E-mail: export@huaxiarubber.com

MSN: lemon316@hotmail.com ■

I recall a recent statement on the forum that water will run up a slope in the teens of degrees. I haven't looked up the exact figure because I still find it hard to believe. Ponding, particularly with coal, is disatrous to a conveying system, precious little is done about it and the topic is conveniently ignored in the available literature. ■

Dear louispanjang

Both statements are true.

Water will run up a steep slope, and will cause problems on a shallow slope. The problem in both cases is the length of time it takes for the water to clear. The water travels very slowly up a steep slope e.g.14deg but will eventually clear. Even on a relatively shallow slope (± 6º) the water may only travel at +-25% of belt speed, but this depends upon additional factors such as water volume and purity, initial dryness of the belt and of course belt speed. A simple way to test the water /belt speed ratio is to measure the time it takes the tail of the water stream to clear a section of the conveyor.

When no other information is available, I find the 25% rule reasonable to initially estimate the water volumes that will spill from the belt due to ponding and the time an empty belt should run before material can be added. No doubt others will have different methods of determining the true figures but as long as you consider the consequences of the water and cater accordingly you will remove or reduce an operational nightmare before it becomes a reality. ■

Do you mean to handle coal without creating nuisance?

Coal can be transported in slurry form ( coal water mixture ). I used to work with this project before (pilot project) where you can mitigate the probelm of dust, upgrading the quality of coal (removal of high percentage of sulfur content and moisture content).

But to implement this method to the industry, the cost wise is become an issue (whether this method is feasible or not).

Rgds,

Leo ■