Table 331 Engineering Designbased Pollution Prevention Strategies

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Storage and Handling Systems

Install geodesic domes for external floating-roof tanks. Store VOCs in floating-roof tanks instead of fixed-roof tanks. Store VOCs in low-pressure vessels instead of atmospheric storage tanks. Use onsite boilers instead of wet scrubbers for air pollution control. Select vessels with smooth internals for batch tanks requiring frequent cleaning. Install curbs around tank truck unloading racks and other equipment located outdoors. Load VOC-containing vessels via dip pipes instead of splash loading. Install closed-loop vapor recycling systems for loading and unloading operations. Process Equipment

Use rotary-vane vacuum pumps instead of steam ejectors.

Use explosion-proof pumps for transferring VOCs instead of nitrogen or air pressure transfer. Install canned or magnetic-drive sealless pumps.

Install hard-faced double or tandem mechanical seals or flexible face seals.

Use shell-and-tube heat exchangers instead of barometric condensers.

Install welded piping instead of flanges and screwed connections.

Install lining in pipes or use different materials of construction.

Install removable or reusable insulation instead of fixed insulation.

Select new design valves that minimize fugitive emissions.

Use reboilers instead of live steam for providing heat in distillation columns.

Cool VOC-containing vessels via external jackets instead of direct-contact liquid nitrogen.

Install high-pressure rotary nozzles inside tanks that require frequent washing.

Process Controls and Instrumentation

Install variable-speed electric motors for agitators and pumps. Install automatic high-level shutoffs on storage and process tanks. Install advanced process control schemes for key process parameters. Install programmable logic controllers to automate batch processes. Install instrumentation for inline sampling and analysis.

Install alarms and other instrumentation to help avoid runaway reactions, trips, and shutdowns. Install timers to automatically shut off nitrogen used for blowing VOC-containing lines.

Recycle and Recovery Equipment

Install inplant distillation stills for recycling and reusing solvent.

Install thin-film evaporators to recover additional product from distillation bottoms and residues.

Recover volatile organics in steam strippers upstream of wastewater treatment lagoons. Selectively recover by-products from waste using solvent extraction, membrane separation, or other operations.

Install equipment and piping to reuse noncontact cooling water.

Install new oil-water separation equipment with improved designs.

Install static mixers upstream of reactor vessels to improve mixing characteristics.

Use a high-pressure filter press or sludge dryer for reducing the volume of hazardous sludge.

Use reusable bag filters instead of cartridge filters for liquid streams.

Source: N. Chadha, 1994, Develop multimedia pollution prevention strategies, Chem. Eng. Progress (November).

Some plants can monitor and reduce nitrogen consumption by installing flow rotameters in the nitrogen supply lines to each building. Within each building, simple engineering changes such as installing rotameters, programmable timers, and automatic shutoff valves can minimize solvent emissions.

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