Miscellaneous Organic Chemical Manufacturing
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Emission Sources
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 The
majority of emissions that occur from batch chemical manufacturing
operations are from volatile organic solvents that evaporate during
manufacturing. Particulate matter emissions may also occur from the
handling of solid powders that are used in manufacturing. Several
air emission sources have been identified for chemical manufacturing
operations; they are as follows:
- Process operations
- Process vents
- Storage tanks
 Equipment
leaks/ process line transport
- Wastewater collection and treatment
- Solvent recovery
- Cleaning
- Spills
- Transfer/loading operations
Process Operations
Material charging emissions
Volatile Organic Compounds (VOC) emissions may occur during material
loading of equipment due to the displacement of organic vapors.
Particulate matter (PM) and PM equal to or less than 10 micrometers
in diameter (PM10) emissions may also occur during the material
loading process from handling of solids in powder form. VOC and
PM emissions during material loading operations may occur as
point source or fugitive, depending on whether a PM emissions
collection system is in place.
 Emissions
from process heating
Many processes involve batch heating in conjunction with a reaction
or in preparing for distillation. Vapors from vessel headspace
are emitted through the process vent until the final temperature
is reached.
Emissions from process depressurization
Reducing the system pressure is one way that solvents can be recovered
from the batch at a lower temperature than would normally be
possible. In some cases it is desired to replace the primary
process solvent with a different one at reduced temperature.
In other cases it may be desired to concentrate the batch through
solvent stripping at reduced temperature to avoid thermal decomposition
of compounds in the batch. When the pressure of the batch is
reduced then solvent vapors are drawn from the vessel (and connected
equipment) by the vacuum system.
Emissions from gas evolution processes
Some reactions produce off gases such as hydrogen chloride, sulfur
dioxide, and others that evolve from the batch and exit the process
through the vessel vent. These off gases will also carry solvent
vapors from the batch with them.
 Emissions
from gas sweep and purge operations
Nitrogen is frequently applied to the process vessel as a means
of establishing inert conditions for safety purposes or to prevent
moisture from entering the system and avoiding undesirable chemical
reactions to take place. As nitrogen enters the vessel it must
exit the vessel through the process vent along with solvent vapors
from the vessel.
Surface Evaporation
Surface evaporation may occur during mixing and blending operations
if the vessel contents are exposed to the atmosphere.
Process Vents
  A
chemical manufacturing process consists of reactors, recovery
units, or a combination of the two. The design of a process will
vary at each facility depending on the product, the type of process,
and the design capacity. Therefore, each process will have a
different number, type, and configuration of process vents. Reactor
and air oxidation processes are conversion processes involving
chemical reactions that alter the molecular structure of chemical
compounds and form one or more new compounds. Reactors may have
an atmospheric vent, may vent to one or more recovery devices,
or both. Also, any vent from a reactor or recovery device may
vent to a combustion device.
 
Storage Tanks
 Various
types and sizes of storage tanks are used to store solvents and
resins used in the chemical manufacturing process. Most of these
tanks have a fixed-roof design. The two significant types of
emissions from fixed-roof tanks are breathing and working losses.
Breathing loss is the expulsion of vapor from a tank through
vapor expansion and contraction that result from changes in ambient
temperature and barometric pressure. This loss occurs without
any liquid level change in the tank. The combined loss from filling
and emptying tanks is called working loss. Evaporation during
filling operations results from an increase in the liquid level
in the tank. As the liquid level increases, the pressure inside
the tank exceeds the relief pressure and vapors are expelled
from the tank. Evaporative emissions during emptying occur when
air drawn into the tank during liquid removal becomes saturated
with organic vapor and expands, expelling vapor through the vapor
relief valve. Emissions from tanks are characterized as a point
source because VOCs are released through a vent.
Equipment Leaks
 In
order to transport stored materials (e.g., organic solvents and
resins) from storage tanks to the chemical manufacturing operation,
a network of pipes, pumps, valves, and flanges is employed. As
liquid material is pumped from the storage tanks to the particular
process area, the pipes and supporting hardware (process line
components) may develop leaks over time. When leaks occur, volatile
components in the transported material are released to the atmosphere.
This generally occurs from the following process line components:
- Pump seals
- Valves
- Compressor seals
- Safety relief valves
- Flanges
- Open-ended lines
- Sampling connections.
Emissions from equipment leaks can be characterized as fugitive.
Wastewater Treatment
 A
chemical manufacturing facility may use a wastewater treatment
system to treat contaminated water generated during the chemical
manufacturing process (e.g., water that has been used to clean
equipment, extractions, crystallizations, and other operations).
Wastewater treatment systems generally consist of a series of surface
impoundments that are used for equalization, neutralization, aeration,
and clarification of the waste stream. Fugitive VOC emissions may
occur from each type of basin.
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