I. Gaseous and Aerosol Contaminants Drawn In by Gas-Phase Backflow

Volatile organic waste gases from the workshop

Aerosols of alcohols, organic acids, electroplating complexing agents, and pickling agents evaporating around equipment are drawn directly into the tanks due to negative pressure created by falling liquid levels. This causes an increase in COD and acidity in the condensate, and when the water is reused in the evaporator, it exacerbates foaming.

Drifting salt-containing mist

Fine salt crystal mist escaping in small amounts from the evaporator’s demister screen and aerosols from concentrated mother liquor float in the workshop air; negative pressure airflow continuously draws them into the storage tanks, causing a rapid increase in electrical conductivity.

II. Solid Particulate Impurities

Metal Rust Dust

Rust powder generated by corrosion of unit supports, piping, tanks, and steel structures is drawn in, introducing iron ions into the water; when reused, this accelerates pitting corrosion in plate heat exchangers.

Insulation and Coating Debris

Fragments of rock wool insulation, flaking paint, floor silt, and dust accumulated on fans enter the system, causing the condensate to become turbid and clogging spray lines and sensors.

Fine Activated Carbon Powder

Carbon powder drifting from the exhaust gas adsorption tank is sucked back into the tank, turning the water black and forming composite sticky scale.

III. Microorganisms and Flocculent Contaminants

Mold spores, insect carcasses, fiber flocs, and dust clumps from the workshop’s hot and humid environment are drawn in by negative pressure. Long-term storage in the tank fosters the growth of mucus-producing bacteria, which significantly increase foaming intensity upon reuse and adhere to the heat exchange plates.

IV. Risk of Backflow from Liquid Waste on the Floor

Gaps in tank flanges, access hatches, and drain ports allow negative pressure to draw in standing water from low-lying areas—including equipment rinse wastewater, spilled acid-cleaning waste liquid, and rainwater mixed with salt-laden wastewater. Once drawn in, these substances instantly and significantly increase the salt content and organic matter levels.

V. Compounded Contamination from Vacuum System Backflow

If the vacuum piping carries even a small amount of material, salt-containing organic mist droplets will disperse into the space above the tank; without a breather valve to balance the pressure, the negative pressure draws these contaminants back into the system, causing continuous accumulation of contamination in the condensate.

Derived Process Hazards

When contaminated condensate is reused for preheating the feedstock or as system makeup water:

It introduces silicon, heavy metals, and salts, shortening the acid washing cycle of the evaporator;

Organic matter promotes the formation of stable foam, exacerbating foam entrainment and material loss;

Acidic impurities accelerate the emulsification of vacuum pump oil and corrode the pump housing.