Mill dust removal entails some extraction technology that I prefer to leave to the more scientific among us.

Truck dust containment ought to be a pretty straightforward issue, but it isn't. For all the tonnage handled at cement works, & the like, the market demand for good bulk transport loading & unloading equipment pales into insignificance compared with the retail distribution business demand for modular loading bays. Apart from some good tanker loading spouts there is nothing in our maketplace to compare with the ranks of sealed docking bays at any modern wharehouse or distribution centre. Because of the dirty conditions in bulk solids handling such loading operations are carried out as quickly as possible, promoting a vicious circle. Why so?

In Retail Distribution

Security: product values differ. Twenty three tonnes of food is worth considerably more than 23 tones of gravel. So personnel access is controlled.

Energy: Frozen foods can be cooled to -27C. Energy bills are a large chunk of food retail pricing. So there is effective sealing.

Integrity: Thawed frozen foods have no retail value & also incur a disposal cost. So there is even more effective sealing.

Throughput: It takes between 10 & 180 minutes to load a semitrailer on a bay. So several bays are required.

Health & Safety: personnel activity is closely monitored. Large workforce.

In Solid Bulk Transport

Security: almost no requirement except weighing for invoice preparation.

Energy: height of lift governs.

Integrity: tipper loads are required to be covered in some countries which does protect the product from rain. Some tipper bodies are heated to sustain product integrity.

Throughput: gravity loading & discharge is very fast. Minimal equipment can handle many consignments.

Health & Safety: personnel often work in isolation. Small workforce.

There are no technical obstacles to complete dust containment during truck loading & unloading. Most obstacles are pecuniary; supported by inadequate legislation. The other spin-off obstacle is market intent. It is difficult to expect a manufacturer of inflatable loading bay seals to develop equipment to latch onto a tipper body or the underside of a bottom dump powder tanker. The market is small & the client might back out at the last minute depending on the contractual possibilities. Even if a plant engineer has the demand, the supply is hard to convince.

On a practical note: if you provide rear wheel guidance the reversing vehicle can be located within a lateral tolerance of 50mm with comparative ease (I can). With adequate wheel stops you can locate the tailgate completely. Vehicles are built to the limit of the Construction & Use Regulations. If properly designed they should all be the same limiting size. FACT. Having now trapped the beast it should be quite easy to arrange flexible curtains around the discharge orifices of any type of vehicle. It is no hard matter to minimise the volume where dust can exist.

Low volumes of dust confinment require less air evacuation. Dust takes advantage of the available space.

Loading is not so easy, except where tank loading spouts are concerned. Whereas the cover sheet can stay on during emptying it must be removed during loading a simple tipper body. So the empty box will allow dust generation & the rising material level

will displace the dust cloud against any overhead canopy. Tippers are normally fitted with a remotely controlled top sheeting device which covers the load by sideways extension of a tarpaulin. If you retract the canopy sideways ahead of the advancing tarpaulin the dust cloud can be contained.

It simply simply depends on how much money you have & are you really prepared to spend it: if there are no laws to force you. ■