EPA Self-Audit and Inspection Guide
Organic Finishing of Metals

Table of Contents

Drying: Regulatory Requirements

Air
The Clean Air Act regulates the emission of volatile organic compounds (VOCs) (40 CFR Part 60) and hazardous air pollutants (HAPs) (40 CFR Part 61 and 40 CFR Part 63), and provides specific standards of performance to control emissions from various types of coating operations (40 CFR Part 60). Depending on the amount of solvent material remaining on the part after cleaning, sufficient VOC and HAP emissions may develop in the drying oven to subject an operator to major source requirements and Title V permitting requirements. The Act also regulates the formation of nitrogen oxides (NOx) from combustion sources; however, emissions of NOx are often well below compliance levels for small operations.

Controlling VOC emissions can be accomplished in two ways. Lower solvent cleaning systems, such as aqueous cleaning solutions, can be used to prepare parts for organic finishing. Otherwise, air pollution control equipment is required on drying oven exhaust systems to recover or incinerate the VOCs and HAPs before they are released from the facility. Controlling NOx emissions can be achieved by increasing the level of fresh air used for combustion or by adding oxidation systems, scrubbers or absorbers to the exhaust system if necessary.

Self-Audit/Inspection

• Do exhaust air streams have air pollution control equipment attached? Is that air pollution control equipment working properly? Does the final exhaust air have concentrations of pollutants below required levels?

Drying: Common Causes of Violations

• Emission of volatile organic compounds or hazardous air pollutants from drying oven structures may occur and exceed limits allowed by Title V permits. The quantity of VOCs or HAPs released depends on the amount of organic solvent in the cleaning solution formulation. The harmful emissions in the exhaust air stream can be captured and treated to prevent their release to the atmosphere. Common air pollution control tactics include solvent recovery, solvent incineration, and solvent concentration.
 Emission of NOx from drying oven combustion chambers may occur and exceed limits allowed by Clean Air Act Title V permits. The quantity of NOx formed depends on the amount of combustion products and evaporated diluent that combine and come in contact with a direct flame.

Drying: Sources of Pollution Nitrogen oxides (NOx) form when solvent cleaning solution products of combustion contact a direct flame (dependent on the cleaning solution formulation) Heat loss through oven doors, heated work pieces, poorly insulated walls, and improperly sealed panels Volatile organic compounds and hazardous air pollutants (dependent on the cleaning solution formulation)  Parts that have been improperly dried (insufficient removal of solutions or preheated too much) resulting in the need to repeat prior surface preparation steps.

Drying: Pollution Prevention Alternatives Nitrogen oxide (NOx) emissions can be reduced by introducing fresh air into the combustion chamber. Fresh air will lower the flame temperature and prevent NOx formation. Heat loss can be reduced by improving insulation of the structure and sealing panel joints. Proper drying can be achieved consistently by monitoring air flow circulation systems for accurate operation. Volatile organic compound and hazardous air pollutant emissions can be reduced by using aqueous cleaning solutions, rather than solvent cleaning solutions; or by rinsing work pieces in plain water after using solvent cleaning solutions.