Moisture problems in bulk silos and how to handle them

Bulk silos

Storing dry bulk materials in silos is a challenge because the “empty” space right above the stored product in the silo – known as the ullage space – often suffers from condensation issues. This condensation may be caused by

• Transport air that blows the product from the lorry into the silo. Transport air is often warm and has a high moisture content. When it cools, condensation will inevitably form.
• Fluctuating outdoor temperatures and humidity levels
• Reverse jet cleaning of dust plants on top of silos

Products inside silos can often be hygroscopic. Condensation cause the product to

• Bridge across the silo
• Adhere to the sides of the silo
• Block the silo
• Spoil the product
• Affect aeration of the product at the bottom of the silo preventing the product leaving the silo.
• Storage silos require stable humidity to prevent condensation and to improve product flow and reduce the spoiling of products.

Why is that a problem?

Many of the substances that are stored in bulk silos are hygroscopic which means they are prone to absorb moisture. Examples of hygroscopic materials include, ammonium sulfate, baking powder, calcium phosphate, caustic soda, cocoa, coffee concrete, corn sugar, dextrose, salt, flour, gelatin, gypsum, lime, plastic pellet resin, potassium chloride, starch and urea to name a few.

This then becomes a problem because excessive moisture from the air inside the silo spurs bacterial growth, potentially spoiling the stored product. In addition, absorbing moisture can cause hygroscopic products to bridge across the silo, adhere to the sides of the silo, block the silo, spoil the product, affect aeration of the product at the bottom of the silo preventing the product leaving the silo. To minimise the effects of product build-up, mechanical devices like hammers and vibration pads will often be fitted to bulk handling equipment before delivery. However, this approach does not solve the core problem – moisture – and, as a result, the powders still lump together.

Therefore, storage silos require stable humidity to prevent condensation and to improve product flow and reduce the spoiling of products.

Dehumidification is your friend

Silos serve the purpose of providing bulk storage for various industries such as storing powdery materials and grain in the foodstuff and agricultural sectors. However, these are susceptible to spoilage due to condensation, mould growth and more. This can be avoided by applying dehumidifiers in connection with the silos.

Dehumidifiers can help regulate the moisture content of the stored commodity to levels that prevent condensation and mould growth.

If condensation issues are not taken seriously, it may result in loss of product quality, hampered production, blocked pipes, increased maintenance requirements that ultimately lead to lower productivity and higher production costs.

Conventionally, aeration is commonly used to cool the stored products in a silo to reduce moisture migration and condensation potential near the top of the stored products. But this type of aeration process is highly dependent on prevailing exterior climatic conditions. Thus, aeration during rainy seasons and in humid tropical areas is very difficult.

By using a desiccant dehumidifier that incorporates cooling coils, you will be able to control the relative humidity within the silo as well as the product moisture content and temperature.

This ensures that the quality of your product can be maintained for longer storage periods irrespective of the prevailing weather conditions.

How it works

The solution is to simply condition the space above the product – the ullage space – with dry air. Keeping the air in the ullage space at a lower dew point than the coldest surface will eliminate condensation.

This is done with a desiccant dehumidifier. It can be installed in a small enclosure next to the lorry loading pipe and then connected via a coupling that can easily be disconnected when loading into the silo.

Once installed, the principle is to deliver dry air using the silo lorry loading pipe or a dedicated dry air pipe. This pipe runs up the outside of a silo. A lorry will connect to the pipe to discharge product into the silo. When not in use for loading, this pipe can be utilised to deliver dry air into the silo. If permanently connected a diverting valve or shut off valve will be needed to isolate the dehumidifier when lorry loading is taking place.

During operation, dry air is delivered into the silo on a total loss basis. The air is discharged from the silo either from the silo vent or via the dust plant.

Any questions in relation to the control of condensation using desiccant dehumidifiers in bulk silos then please contact our team.