Optimizing Dust Control: Adding Chemicals To Dust Suppression

Enhancing Dust Suppression: The Role of Surfactants in Water Treatment

Adding Chemicals to Water

It is common practice to enhance the dust-suppression performance of water by adding surfactants—surface-acting agents. These chemicals improve the wetting characteristics of water, reducing overall water usage and minimizing the drawbacks associated with excessive moisture addition.

When dust from coal, petroleum coke, or similar materials, falls onto a puddle of water, the dust particles can remain on the surface for hours if undisturbed. This occurs because these materials are hydrophobic and do not mix well with water. Since it is impractical to alter the nature of the dust particles to increase their affinity for water, chemicals are added to modify the water particles so they attract or at least join with the dust particles more readily.

By adding surfactants, the surface tension of water is reduced, allowing dust particles to become wet. Surfactants are substances that, when added to water, improve its ability to wet surfaces and form fine droplets. Surfactants lower water’s surface tension, overcoming the internal attraction between water molecules and ultimately resulting in improved droplet formation.

In the proportioning system, water and surfactant are mixed, and the resulting solution and compressed air are sent independently to foam canisters.

To understand surface tension, imagine a drop of water lying on a smooth, flat surface. It usually forms a liquid bubble with well-defined sides. The surface tension of the water prevents the droplet walls from collapsing. However, a drop of water mixed with a surfactant, such as dishwashing soap, will not form a liquid bubble because its surface tension has been drastically reduced. The “walls” of the droplet cannot support its weight, as the forces holding the walls together have been altered. This is why surfactant technology is applied to dust control. If the water droplets no longer have a surface that is a barrier to contact with the dust fines, then random collisions between droplets of water and dust will result in the wetting and enlargement of the fines to the point where they drop out of suspension in the air.

Choosing a Surfactant

The number of surfactants and surfactant blends currently in use is extensive. Several specialty chemical companies have products formulated to address specific dust-control needs. Choosing the correct product and addition rate for a given application requires material testing as well as an understanding of the process and the method of application.

Objections to chemical-additive-enhanced water suppression systems include the ongoing costs of purchasing the chemical additive. Costs can be higher, particularly when considering the amortization and depreciation of the equipment. Additionally, these systems require regular maintenance, adding labor expense to the continuing operating costs.

As contamination of materials or the process can be a concern in some industries, the additive chemical must be reviewed in this light. It is important that chemical additives are compatible with the process, bulk materials, and system equipment, including conveyor belting. Although the use of a surfactant reduces the amount of water added to the dusting material, water/surfactant sprays may still add more water than is acceptable. It is common practice for a chemical supplier to provide samples to the customer for testing the effects on the end product.

Application by Spray or Foam

Once an efficient wetting agent has been selected, the decision must be made whether to apply the material as a wet spray or as foam. Both systems offer advantages. Generally speaking, the moisture-addition rate of a wet-spray system is higher than that of a foam-generating system. Although the dilution rate is lower for the foam suppression system, the expansion of the foam allows it to provide effective suppression with less moisture added to the materials. Recent developments have improved surfactant technology to the point that some mixtures can be applied as a spray at the lower moisture levels of a foam system while providing good dust suppression. This offers the benefit of limited moisture addition with minimal chemical cost due to the higher dilution rates with spray-applied surfactants.