Filtration in the chemical industry: particles, corrosion and gas treatment

The process and emission sources

A chemical plant may emit dry solids, mists, condensable vapors and gases that will not be retained by the same mechanism. The assessment must identify the phase of the contaminants at the temperature at which each stage operates. Cooling a stream may change this distribution and create liquids or solids that did not exist upstream.

Composition must be assessed during normal production as well as product changeovers, cleaning and startups. Streams that can be treated individually may become incompatible when combined, due to reactions between substances, deposit formation or difficulties in residue disposal.

Characteristics that guide engineering

Construction materials and filter media must be compatible with temperature, concentration and moisture. Where gaseous contaminants are present, neutralization or adsorption stages may be required, followed by collection of the resulting solids.

Solution configuration and sizing

For dry particles, filtration can be combined with local capture and separation of coarser fractions. Where acidic gases or adsorbable compounds are present, the design may incorporate neutralization or adsorption using specific reagents. The reaction tower must provide contact conditions, temperature and distribution consistent with the treatment, and the downstream filter collects the solids produced or added.

Activated carbon does not universally neutralize every gas, just as lime does not replace every adsorbent. Selection and dosage depend on the contaminant and process. Casings, ducts, fibers and seals must be assessed for the combination of composition, concentration and moisture, including at cold spots.

Design parameters

• Characterize contaminants and their phases.
• Assess corrosion and condensation.
• Define the destination of collected material.
• Integrate reagents, dosing and monitoring where chemical treatment is used.

Performance, diagnostics and maintenance

Outlet concentrations must be checked for the pollutants of interest; particle measurement must not be substituted for gas analysis. Where reagents are used, monitoring must also relate consumption, contact conditions and residue generation. Increasing dosage does not guarantee a proportional improvement if distribution is inadequate.

Under-deposit corrosion, caking and leaks can reduce availability even when a spot emissions measurement is satisfactory. The solution must be assessed as a contaminant treatment and handling system, with defined operating and maintenance criteria, rather than solely by the nominal efficiency of a filter element.

Integration with environmental control

The combination of technologies must be defined by the pollutants present and the facility's criteria. Where reagents are dosed, consumption, contact with the stream and solids removal must be assessed together to interpret emission results.