Without doing the sums for nowt I think your belt is a bit big for the duty. So an increased troughing angle is not going to improve the loss of surcharge is it? Speed is slow enough for low disturbance. Your mixture just won't climb the slope, whatever it is. Drop back to 200tph & try that. After all; you're not getting the added 20 tph at all either way now are you? ■

Dear Rajeev,

10 degrees is approx the natural slope angle of fluidized cement.

By mixing the flyash you might have decreased that natural angle of repose, reaching the limit of stable belt conveying.

It seems, that you have triggered a fluidization problem.

Increasing the belt speed will increase the problem of fluidized cement rolling back, because of increased vibrations and a higher differential speed of the upper air and the cement bed in the trough.

Changing the trough angle will not change the fluidization and thereby not change the problem.

Maybe the cement temperature, heating up the trapped (fluidizing) air is of influence on the fluidizing behavior, explaining the occasional occirence.

Completely covering the belt, with an additionally upward airflow in the flow direction inside, could help.

(under pressure to prevent dust and not garanteed)

Pneumatic conveying could solve the problem, but might to be too expensive (and destroy the investment in the belt)

success

teus ■

We need to know a bit more about your system to provide useful comment. Is it blended product or mixed on the belt? There is a world of difference between the handling properties of hot cement and cold cement so temperature change could be part of the problem. This also applies to fly ash which will compound the problem.

How you feed the fly ash may also prove to be a source of your problems. If air slides are used upstream of the conveyor or blending occurs just before the feed point excessive airation can be a cause.

If mixing is carried out on the belt (which I suspect is the case)then the proportion of mix can cause the runback. The condition you describe would suggest that you have a temerature variation and are feeding one product on top of the other.

In their hot and airated state both products behave as a fluid.

Fitting skirts will aggravate the problem since they hold the material back. rather cure the problem by addressing the above or removing the agitation caused by idler indentations and belt deformities. ■

You are adding just 10% of fly ash today. This percentage may increase tomorrow. You are grinding product to more fineness when adding fly-ash. That increases fluidity and tendency of roll-back. So you need a more permanent solution.

One solution can be lowering slope of conveyor and adding a short vertical screw conveyor or elevator either at feed end or adjoining silo. In the absence of layout, I can not comment (which is a better solution).

Vinayak Sathe Tel: +91 832 2538294 ■

Then it sound like you increased the airflow to your air slides when you increased the tonnage or may even have added an aeration type transfer box. Either way you need to de-aerate the product to get out of your problems.

CEMA quotes a maximum angle of 6 deg for areated cement so at 10 deg you can expect problems. Screws also do not like aerated cement. Tackelling the problem at source is much cheaper than spending a fortune to overcome it. ■