Flow Problem With Excess Fines
The flow characteristics will worsen with extra amp fines, so the question is how the flow channel can be improved. Quite often rotating plows do not undercut the back wall, to leave a narrow band of residue that can provide support for the contents and resist wall slip; this is, presuming that the wall are steep and smooth enough for slip to take place. A drawing giving the cross sectional geometry and material of construction of the bunker is ssential to advise on possible modifications. Add details here or send to lyn@ajax.co.uk. Liners may be an option, depending on a detailed assessment and comparison of wall friction values.
Assuming then that reliable flow can be achieved, any shortfall in the extraction capacity is down to the plow speed of rotation and traverse. ■
Re: Extraction Of Fine Coal From Bunker
Originally Posted by Lyn Bates
Assuming then that reliable flow can be achieved, any shortfall in the extraction capacity is down to the plow speed of rotation and traverse.
Dear Lyn
Thank you for your prompt reply , I am arranging to send the drawing soon at yn@ajax.co.uk
*********************
Please note: The email address is lyn@ajax.co.uk
Reinhard Wohlbier
Admistrator ■
Pasty Business
From your previous thread.....
"Every little breeze....
...seems to whisper Louise.
These machines are the finest in the business.
You face intolerable downtime if you replace the plough with something different, inferior and, as yet, unknown. Further, your storage will decrease if you modify the bunker without disturbing the foundations. You should have a standby Louise anyway. If you haven't got one, and if you really need one, buy now while stocks last.
Mark Dekker, son of Louise (named after his mother), manufactures a N American version somewhere in N Carolina. Great guy, straight & honest, very busy in the extraction of FGD gypsum. In respect for Mark you can be excused for the wrong spelling of plough.
All the above is written assuming that you have already failed with some modifications to the plough blades.
What does your O&M documentation suggest?"
Additionally:
Consider your lining options. Plastic liners will swell and deform under moist coal and a detached metal liner might severely disagree with the plough blades. Ensure that your lining anchors do not interfere with the rebars lurking 50mm beneath. Is the rebar shown on the as built drawing?
Please explain how the extraction rate is restored? If the problem is so serious then your bin would fill with fines product inside a day and a bit due to the 200tph building up. So you pull back the jigs. Then you get on spec (How come the fines were not recognised during the FEED?) coal and feed it on top of the fine product. Is there any mixing?: because it suggested that mass flow is not a feature of the bin. Bridgeing seems unlikey given the radii of the plough blades so the reduction might be due to fines just flowing over the moving blades. Can the behaviour of the blades and fine product be seen? Has it been seen?
Looking forward to the next installment..... ■
Extraction Of Fine Coals From Stockpile
Originally Posted by louispanjang"Every little breeze....
...seems to whisper Louise.
These machines are the finest in the business.
You face intolerable downtime if you replace the plough with something different, inferior and, as yet, unknown. Further, your storage will decrease if you modify the bunker without disturbing the foundations. You should have a standby Louise anyway. If you haven't got one, and if you really need one, buy now while stocks last.
Mark Dekker, son of Louise (named after his mother), manufactures a N American version somewhere in N Carolina. Great guy, straight & honest, very busy in the extraction of FGD gypsum. In respect for Mark you can be excused for the wrong spelling of plough.
All the above is written assuming that you have already failed with some modifications to the plough blades.
What does your O&M documentation suggest?"
Additionally:
Consider your lining options. Plastic liners will swell and deform under moist coal and a detached metal liner might severely disagree with the plough blades. Ensure that your lining anchors do not interfere with the rebars lurking 50mm beneath. Is the rebar shown on the as built drawing?
Please explain how the extraction rate is restored? If the problem is so serious then your bin would fill with fines product inside a day and a bit due to the 200tph building up. So you pull back the jigs. Then you get on spec (How come the fines were not recognised during the FEED?) coal and feed it on top of the fine product. Is there any mixing?: because it suggested that mass flow is not a feature of the bin. Bridgeing seems unlikey given the radii of the plough blades so the reduction might be due to fines just flowing over the moving blades. Can the behaviour of the blades and fine product be seen? Has it been seen?
Looking forward to the next installment.....
Hello
Thanks for your reply
Theory explained by Mr LYN Bates that “ Quite often rotating plows do not undercut the back wall, to leave a narrow band of residue that can provide support for the contents and resist wall slip; this is, presuming that the wall are steep and smooth enough for slip to take place. “
is quite feasible and perhaps that is what is happening in this case.
-At the time of designing this above ground stockpile (about 20 years) back the feed coals from the mines had different HGI than what is being received now. Now the proportion of fines (-0.5mm) some times are in excess of 25 % where as at the time of design the fines proportion considered were 17-18%.
-Yes , any modification carried out inside the stockpile would reduce the capacity ( not desirable) simultaneously the execution of the work would be very difficult in a RCC bunker without taking long plant shut down.
-Obviously whenever the fines percentage increases the stockpiles get filled up and some down of the plant time occurs.
-Can any one suggest an effective design of the plough feeder blades so hat in the worst cases also the same can scoops the fines so that no band of residual fines can accumulate ?
-In the bottom most portions we have liners of steel material but those are not effective to restrict the fines build up. If Polymer or similar liners provided –will that eliminate the problem?
-How effective is air canons in such cases? ■
Coal Hopper
Liners are not effective if slip does not take place so the wall friction and surface cohesion values should be obtained and compared with the hopper geometry. Sight of the drawings will allow a better understanding. Storage capcity is actually the amount that can be extracted, not necessarily the volume of the hopper. ■
Bang Away.
If steel liners wooden work, detached or not, it is very possible that polymer liners steel won't work. Then you have wasted cash and left a set of liners lying about the plant or scrapyard. Steel liners directly upstream of plough blades....your plant has had 20 years of good fortune. Or has it?
Since the steel liners don't work why not take then out and while the bunker walls are exposed you can take time to fit air cannons. Mind the sparks when cutting the rebar.
Air cannons will not prevent the plough from missing the corners though. Until you know what the actual restricting mechanism is, you risk its persistence.
You might also have the option of approaching the manufacturer, or the documentation, regarding blade modification etc. ■
Extraction of Fine Coal from Bunker
Problem of extraction of fine coal from the bunker
We have coal washeries. After processing of raw coal clean coal produced are stored in a concrete overhead bunker of nearly 6000 tonnes capacity. Below the bunker a moving plow feeder is there which moves over rails with the help of electrical drive simultaneously scoops the coal from the slot area of the bunker with the help of circulatory rotating plows. In this way the clean coal from the bunker are extracted and fed to the belt conveyor placed below the plow feeder. Generally this clean coals are having surface moisture of 11-12%. The clean coals are on an average 75% coarse ( 13mm x 0.5mm) & the balance are fines (-0.5mm)
Problem: Normally there is no issue in the operation till the composition of clean coals are around 80:20 or so. In case of some raw coal seams the fines quantity increases which results into very high fines quantities in clean coal. At these circumstances the fines increases beyond 35% and goes up to 50%. . During such instances the extraction from the bunker by plow feeder becomes too difficult and this directly impacts on the productivity of the plant. Normally the plow feeder extracts at the rate of 450-500 tph but whenever the fines quantities increases the feed rate comes down to 300-350 tph.
We are looking for solutions which may be achieved within a shorter period ( short range) without going for longer shutdowns or injecting major investments.
If no workable short range solutions are not found the long range solutions may be advised keeping in mind that such massive concrete bunkers can not be replaced or modified very easily. However option of replacing the extracting device may be thought of if the same are already proven equioment. ■