How to Consider Lifetime Costs for Powder And Bulk Conveying

Related Vendors

Italvacuum, Srl

TRM Filter d.o.o.

Donadon SDD Srl

Volkmann GmbH

Advantages of Ejectors for Vacuum Conveyors

The vacuum pump which provides the driving force for powder transfer can be driven by either electricity or compressed air. The latter is not generally a cheap source of energy, but Volkmann’s Multijector multi-stage venturi pump is five times more efficient than conventional single-stage ejectors. In addition, ejectors can operate cyclically to match demand, whereas electric pumps must run continuously. As a result, the energy costs of the Multijector are often comparable with those of electric pumps.

Other advantages of the Multijector include maintenance-free operation, small size, light weight, easy control, low noise, no need for lubrication, and no heat generation. The performance curve of the Multijector is more like that of an electric positive displacement pump than a conventional single-stage ejector. As a result, the Multijector can provide both high flowrates (e.g. for dilute-phase conveying) and vacuum right down to 90 mbar a (e.g. for dense-phase and plug flow conveying), allowing it to handle a wide range of bulk materials.

The ability of Multijectors to build up and break the vacuum rapidly is well adapted to intermittent conveying, in which the bulk material hopper is filled and discharged in cycles. During discharge the ejector can be turned off and so uses no energy.

Pneumatic Conveying

Pneumatic Conveying at 1.5 Bar Maximal Pressure to a Height of 65 m

Being able to operate a conveying systems entirely on compressed air simplifies application in hazardous atmospheres. In fact, these vacuum conveying systems are the only ones to be fully Atex certificated for all relevant dust and gas Ex zones. There is even an inerting system available.

Designing to Match the Application

Most vacuum conveying applications are for capacities in the range 10–6,000 kg/h, or up to 16 t/h in extraordinary circumstances. Distances vary from just a few meters up to 100 m horizontally and 40 m vertically.

A wide range of ejector sizes, plus the ability to fine-tune performance by adjusting the air pressure, allows the characteristics of the conveyor to be matched to the application. For example, the small VS200 system is able to convey 540 kg/h of sugar into a mixer at a height of 4 m. The complete conveyor is only 450 mm high and 210 mm in diameter, and weighs just 9 kg.

The operating characteristics of a vacuum conveyor depend on the total distance, height and number of bends, the design of the pick-up point, the volume of the separation container, and the choice of vacuum pump or ejector. A vacuum of 90 mbar a can lift a closed water column through approximately 9 m, but with bulk solids the height range can be much greater because the material always contains some air. A vertical distance of more than 40 m may be possible, depending on the material.

Throughput also depends very much on the properties of the material. Bulk density, adherent or bridging characteristics, particle size, surface shape, humidity and fat content are crucial variables. It is common for the same conveyor to show differences in throughput of up to 1,000 kg/h with different products.

Modular construction makes the design of complex systems straightforward. For example, multiple destinations can be served by a single control system and a central vacuum pump. All types of sources, including big bags, sacks, and silos, can be connected to many different destinations — mixers, reactors, sieves — by rigid pipes, flexible hoses and diverter valves.

(ID:35343230)