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Waste minimization: Pollution control at source

By : New Cloth Market
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By: Atul Kumar & Y. K. Saxena


Waste is a common problem throughout the companies comprising the chemical process industries as well as textile industry also. It is especially a concern to these who manage solid waste, wastewater systems, and hazardous waste or air pollution control devices - typically systems for handling 'end-of-the-pipe' wastes.

Regardless of its type, waste is almost always composed of purchased raw materials that did not become part of a final product. For example, some chemical manufacturers, such as liquid latex producers, have found that their wastewater stream is a dilute form of their primary product. Much of this waste is the result of process inefficiencies that cause entrapment and loss of raw materials. These are conventionally disposed through equipment cleaning. However rethinking and improving process design, piping and vessel design and material-handling techniques can improve process efficiency. The result is reduced waste generation, reduced operating costs, cleaner equipment and increased profits.

A Closer Look at Cleaning

In process industry, equipment is cleaned to remove residues that have a negative effect on the final product or cause production problem. For instance, batch mixing consumer product, such as a water-soluble liquid laundry detergent. may leave a viscous residue that is incompatible with the next product due to colour, content, pH or other properties. Process equipment is washed to remove residues to the point that the amount left in the system will have a negligible effect on the next product.

Flushing the equipment once with water may remove 90% of the residue; and flushing again may remove 90% of the remaining residue, leaving only 1 % of the original contaminant.

Additional washing removes more residues, but at some point the equipment is clean enough to produce the next batch. Additional washing, at this point, only increases downtime, labour costs, water use and wastewater-treatment costs. The goal of cleaning is not to leave the equipment perfectly clean (which is impossible to achieve, in any case), but to remove only as much contaminant as is necessary to cause the process or product to function as required. Some manufacturers have found that eliminating cleaning steps cause no product or process problems.

Doing the Math

The residue left inside a vessel may me insignificant. But this material, plus the amount of cleaning done to remove it, is far from negligible, once costs are calculated over the Iong run.

Residual costs

These residues may seem to minimally impact the bottom line, but their effect on revenues is actually high.

Besides the revenue lost through wasted product, costs are incurred through cleaning. Removing the residue by cleaning is one method to reduce the residue volume, but this does not reduce cost.

Improved Equipment Design

Equipment can be designed to reduce the volume of a chemical that adheres to an interior surface or becomes trapped in the system. Process equipment includes not only large mixing vessels but also piping. mixers, pumps, baffles, filters, strainers, valves, reactor, and any other components that come in contact with the product.


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