Table of Contents
Drying: Regulatory Requirements
The Clean Air Act regulates the emission of
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.
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
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
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