I would recommend you talk to a reliable Baghouse Vendor or Dust Consultant.

If you are pulling 1400 m3/h though an 8 inch duct the transport velocity is well below settling velocity (that's only 12.4 m/s. Most industrial dust systems are designed on 18 - 20 m/s). Potentially this could cause settlement of dust in the duct, and over time, block the duct. We experience this quite regularly in ducting running at such low velocity (We have installed compressed air purge nozzles to break the blockages at critical points. When required the Operators open the air lines and blow out the blockage out).

As long as the dust point is enclosed it is possible to control the dust with reasonable sized ducts. But with an open area the suction loses power to control the air flow at more than one or at most two duct diameters from the suction inlet.

Our hopper is only 3800 x 2500 mm fed by a front end loader. We are building a shed, or enclosure over the top of the hopper. This will be fitted with a extraction hood in the roof and draw off 8,000 m3/h through a 14 inch duct. We have another hopper with a 12 inch duct, but that cannot stop plumes of dust billowing out during loading. Our Operators have learned to be very carefull in the way they discharge product into the hopper. The existing Baghouse helps, but cannot provide a complete solution. ■

John has the right approach. Enclose the hopper, back, roof and sides, and reduce the dust generated by careful use of the loader.

If the hopper is exposed to wind, you may need more than 8,000 cu.m/h.

Michael Reid. ■

You are about to leave the realm of Engineering Science and enter the world of black magic.

We do have a facility at the wharf - a drive-over hopper for bottom dump trucks. It has a roof and cladding each side of the roadway. And we have side suction dust extraction grilles which seem to work adequately. We dump 750 tph of product into the hopper.

Because I don't have good control of the air flow, my approach is to study the dust cloud. What does it do, where does it naturally want to go? When you dump product into the hopper you displace air. It can go sideways, or it can go up, or both. Then I design the hoods to try and capture this dust cloud as much as practical.

At the wharf it took several years of experiment, and much money, to come up with a final happy solution. The body of the truck forces the dust to flow around it - towards the dust extraction grilles.

With front end loaders the product falls into the hopper and forces air upwards - that's why we are using a ceiling mounted hood. ■

Depending on the lump size of your product, Burnley baffles can work in your favour, for both truck dumping and front loader. Exhaust from below the baffles at the rate of 25 cfm per sq.ft.

Burnley baffles are brilliant in containing dust from granular products (grain, fertilizer). Google will bring up plenty of references.

Michael Reid. ■

I agree with Michael on the Burnley baffles

I did a truck dump hopper some years ago...about 3 x 4m. I had 25m3/sec of dust extraction from the sides - that is a lot and the baghouse/fan etc are quite large as a result as well as the ducts.

It worked well as the dust cloud could not quick break away from the hopper during dumping - tip truck.

If U can minimise the fall distance...U will minimise the dust cloud generation and speed.

Cheers

James ■

TG,

Some critical numbers are not given such as the product size distribution, mass transfer rate and physical properties. In addition, the configurations of the chamber, size you wish to control to and dump method used are needed to render a solution.

I see the large velocities mentioned and wonder:

At terminal velocity, a 1 micron diameter of coal, falling one meter in still air, takes about 19700 seconds to settle, 10 micron about 200 seconds and 100 microns about 2 seconds.

Is the particle range to control visible dust, explosive conditions, or respiratory hazards?

A computational fluid dynamics (CFD) model and particle air current model can give you great insight on how to control fugitive dust. Maybe you do not need a baghouse. In addition to the above notes of this post and others, it depends on bulk discharge dynamics, hopper configuration, frequency at discharge and control of discharge.

Some USA coal truck dump stations are designed with special stilling chambers that do not require powered dust collection.

CDI designs special stilling chambers for controlling dust in belt conveyor transfers and have the CFD capabilities. ■

Mall,

If you use Burnley baffles, the lack of a roof is not a problem. More of an issue is the range of lump sizes. I would think that +50 mm would be a problem. For clinker, the baffles would have to be built especially rugged. You might need a grizzly over the top.

Michael Reid. ■

Mall,

Go to www.mcgillairclean.com to see the details.

Michael Reid. ■

Mall,

Go to www.mideco.com.au to see an amimation.

Michael Reid. ■