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Bulk Powder Handling - Kaolin & Calcined Kaolin

Kaolin (China Clay) and Calcined Kaolin in powder form are produced using a heated pulverisation process that results in a light fluffy product. This material is usually classified as "sluggish " and does not flow freely. It does however respond to aeration and direct contact vibration.


Bulk Density

This will vary from product to product.



Tipping tankers having top pressurisation and an aerated outlet are recommended. Transporting clays in such tankers does not unduly compact the material. Tanker discharge usually takes between 1 and 1.5 hours depending on payload and blower capacity.

The filling pipe to the silo should be 100mm diameter and enter the silo tangentially to assist disentrainment of solids from the air stream.

The conveying line should be as short as possible and ideally rise vertically from the fill point, at the base of the silo, to the inlet point. If this is not possible the line should be as short as possible with the minimum number of bends.Vertical conveying should be done in one rise, ideally before any horizontal section. On no account should any section of the conveying line be installed at an angle other than vertical or horizontal.

Both dense phase (pulse jet) and dilute phase pneumatic systems can be used. Where dilute phase systems are used, the rotary valve should be the blow through type.


Silo Capacity

125 cubic metres would be suitable for approx 46 tonnes (two loads) of most powder grades. A larger silo may be more suitable depending on usage rate.


Silo Design

The silo and support structure should be designed in accordance with the latest British Standards and the relevant Codes of Practice. The silo should not be less than 2.5 m diameter and if possible should be greater than 3 m. This will prevent bridging in the parallel section of the silo.


The cone angle should ideally be 70 degs and suitable for easy discharge of the product. It should be equipped with a bin activator and slide valve to isolate product from the discharge equipment beneath the silo.


The cone could be fitted with air slides, for intermittent use, should the contents bridge. The roof should have a suitable camber to shed rainwater.


Silo Fittings

The shell should be supplied complete with:-

A combined pressure/relief valve.

A 1.5" BSP Socket for a high level probe (e.g.Vega,Type Vegavib vibrating probe with minimum length of 235 mm).

A suitable manhole/inspection hatch to be located within the roof complete with personnel grid.

A 150 N.B. flanged connection with NB80 downpipe to ground level terminating in a unicone and valve suitable for blowing product to silo from road tanker.

The silo should be fitted with a suitable bag filter (e.g. DCE type bag filters with combined fan having a minimum area of 15m2. This gives air to cloth ratio of 0.93 since a tanker will normally discharge at 14m3/min).

The air to cloth ratio should not exceed 1 metre per minute for our products.

The unit should be suitably shrouded against the weather.

The installation should include load cells as complete silo weighing has been found to be the most accurate way of measuring the contents.


Silo Surface Finish

All structural steelwork should be galvanised to BS729 Shell external surfaces should be specified by the supplier Internal finish should be shot blast to Swedish standard 2.5 and coated with an epoxy paint finish.


Silo Access

The silo should be equipped with suitable access ladders not exceeding 6m in any one lift and equipped with protective hoops.


The top of the silo should have suitable handrails and kicking boards.

Both handrails, ladders and toeboards should be galvanised for protection.



There is no explosive hazard when handling and storing powdered kaolins. The pipework and silo should however be earthed to prevent static build up.


For product specific information please contact us.


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