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Dangerous and toxic powders

Supplier: Kockums Bulk Systems
11 November, 2013

'Containment' is the keyword in handling dangerous and toxic powders and IBC offers a path which is ideally suited to ensure safety in handling these products.

Over the last few years Control Automation has designed, manufactured and completed the installation of projects involving the handling of dangerous powders in FIBC's, drums, sacks and IBC's for materials such as sodium cyanide, sodium dithionite, sodium silicofluoride and glycophosphate. These materials include those that are poisonous, carcinogenic, tonic and explosive. In most case operators have to be body suited to handle.

Control Automation was perceived as having, equipment, design, engineering, and manufacturing capability to handle these projects. In bring these projects to life involved working closely with designated consultants, material supplier and the end user.

There were two projects, which involved the handling of sodium dithionite, which exemplify the problems that needed to be solved and the approach that had to be taken to handle dangerous powders. Sodium Dithionite (sodium hydrosulphite) is a strong bleaching and reducing which is used for bleaching in the paper industry and for reducing in the mineral processing industry. It can be spontaneously combustible, harmful if swallowed and liberates a toxic gas with acids. In handling this powder, it must be fully contained. The material is hydroscopic and the mix with air causes it to lose activity requiring the mix with air has to be kept to a minimum. Thus any form of pneumatic transportation was not considered.

The material supplier in both cases was Orica Chemicals, who can supply the material in 200 litre steel drums or one tonne bulk bags. In the case of bulk bags these are contained in a steel casing for transport.

Drum handling system

Due to the process demand it was not practical to empty the drums straight to process as the client wanted to hold the material in a buffer hopper from which he could meet his shift requirement without the need to continuously change drums. An approach using Control Automation Autobin IBC's System was selected as it offered total dust containment in filling the IBC's and discharge to process.

In order to achieve dust containment during filling of 2000 litre stainless steel IBC's from the drums, a special cone that could be band clamped to the drum after the drum lid was removed, was developed. The cone outlet was fitted with pneumatically operate butter fly valve fitted with a quick coupling pneumatic connection. A filling station was designed to provide dust free transfer of the product, so that an IBC could be located under a pneumatically operated fill head which provided a dust free seal when filling an IBC. A twin tube fill head was incorporated which allow the product flow through the inner tube and displaced airflow out through the outer tube when filling.

The fill frame was fitted with guides so that the drum could be lifted and inverting by mobile drum lifter that could place the drum on the fill station. There was a soft glove type dust seal in place between the drum outlet and fill inlet. The butterfly now could be opened allowing dust free transfer of the product to the IBC.

The IBC fill head and drum tip hopper was connected to a common dust collector so that no dust is released to atmosphere during the tipping and filling process.

The product now could be stored in these Autobin IBC's and moved to process by forklift when required.

Metering system

The metering process was achieved through placing the Autobin on the IBC Discharge station under which was fitted a buffer hopper over flexible wall feeder. The discharge valve on demand fills the feeder buffer hopper from which the sodium dithionite is metered volumetric feeder to the process mixing tanks. The Autobin IBC discharge hopper when gloved to the IBC cone creates an internal variable flow valve, which vibrates to promote smooth, complete and consistent mass flow discharge. The Autobin Intermediate Bulk Container guarantees total product containment during transportation, discharge and after discharge. With the Discharge Station, controlled discharge is guaranteed for all stored flowable solid materials without bridging, ratholing, flushing or segregation

FIBC/IBC handling system

Based on the successful operation of the above system, when another Orica had another client wishing to use the product in their process, a visit to the view the installation was arranged. Their client was happy with the general operation of the system and Control Automation was commissioned to work with their consultant to design manufacture supply and commission a similar system. However their usage was up to 8 ton/day and the delivery in drums was considered unsatisfactory, but they were able to obtain the material in bulk bags. This involved a change to decanting bulk bags into an IBC, which were specially designed stainless steel bins holding 3.5 ton of material. Two discharge stations were required on ensure continuity of flow to the plant, which runs 24 hours a day, so that one runs online and the other on standby.

A problem arising from this it is difficult to empty a bulk bag dust free, Control Automation addressed this with their BulkaFil Super Hygiene Bulk Bag Station. This required the bulk bag to be of special type in that the outlet spout had to be at least 800mmm long that can be clamped to a spigot. The client was able to negotiate with his supplier to have the bags delivered with these spouts.

The FIBC Super Hygiene Discharge station was designed for Multi-trip FIBC specified with tubular liner 1210 mm dia, un-shaped. These bags extrude below the outlet by up to 1700mm when it is emptied and a pneumatic liner tensioner was fitted to whined the bag as it empties onto spool. The bag is lowered by the overhead crane on to rigging support arms to ensure tension is properly applied to the bag and liner. The bulk bags fill the IBC by a gravity based system, with the bags being loaded onto the bulk bag discharge frame by overhead crane, into 3600 litre IBC's in a secure area. The FIBC Discharger System hopper was specially designed to promote flow, fitted with dust containment enclosure for untying and removing the bag. It is a sealed system that contains any dust produced while handling and discharging product from the bag. The bag is supported by a hopper fitted with a vibrator to assist flow.

The bag liner outlet spout the bag is fed through an open jaw (Flo-stop) and around a clamp flange. The liner spout is clamped between to flanges to secure the spout, after which it can be untied. As the bag empties a pneumatic tensioner draws the bag slack so the liner is drawn into a tube when finally empty, ensuring all material is fully discharged.

The Flostop then is only used to close and to clamp the bag before releasing the tie or tie off a partially emptied bag. When the bag is discharged, the bag is retied, the clamp released and the bag may be withdrawn by the crane. The IBC fill head is connected to a dust collector so that no dust is released to atmosphere during discharge and filling process. On reverse pulse the dust is returned to fill head buffer hopper.

The IBC is placed on a weigh platform fitted with forklift guides and under the fill head. The lid in the IBC which is hinged and when opened swing away in the horizontal plain, operator with the bin place stops while climbing the platform to open the bin and when the bin is full close the lid. Once the bin is open he operates a push button, which pneumatically lowers the fill head sealing the IBC inlet. The operator climbs to a higher platform to connect the air hose for the liner tensioner, open the door on the containment enclosure connect the bag spout to a spigot and clamp. After closing the door, a push button to operates the fill head isolating valve allowing the IBC to fill. The sealing lid incorporate paddle type level probe as safety device as a back up to the weigh system to prevent an overfill situation. This will be interlock through the bin full circuit to ensure the fill head isolating valve is closed.

The weigh controller controls the bin fill, so that it is filled desired to capacity. This controller will control the isolating valve located at the interface with buffer hopper spigot and fill head, closing when the bin has reached capacity. This valve also isolates the bag discharge system allowing the operator to change bins with a partially emptied bag and in association with the dust collector on the fill head, ensures no powder is spilt when the bin is removed.

When the bag is empty the air supply to the tensioner is turned off so relaxing the tension on the liner. The spout of the liner is then released by opening the clamping mechanism. The spout of the liner is folded back and tied off. The frame with bag is lifted after disconnecting the air line and replaced with a new bag. As with the drum system the filled IBC are stored, lifted to process when required and placed on the discharge station where the material is metered to process mixing tank.

In working with supplier, consultant and end user these projects were brought to a successful conclusion.