Chemical Engineering January 2017 - 57

single chemical or 25 ton/yr or more
of HAPs; area sources are stationary
sources that do not follow the definition
of a major source.
For these major sources of HAPs,
EPA has established metrics for
emissions that will determine the effectiveness
of the control technology
- commonly referred to as Maximum
Achievable Control Technology
or MACT standards [2]. Meeting the
MACT standards doesn't necessarily
require the addition of costly
emissions-control systems, such as
scrubbers and thermal oxidizers;
rather, in some cases, the MACT
standards can be met through modifications
to processes and methods
that can both determine and limit the
quantity of HAPs being produced.
These MACT standards constrain
to
users
specific
objective emissions
parameters. MACT standards
are set by EPA (for each source category)
based on the emissions performance
that has been achieved
by the best-performing processes in
that category. This level is then set
as the baseline throughout the industry.
The MACT standards establish
the so-called National Emission
Standards for Hazardous Air Pollutants
(NESHAPs), which specifically
exist to safeguard against emissions
of HAPs from major sources.
Leakage from valves, flanges,
connectors and pumps are some of
the leading sources for the release
of HAPs and other volatile organic
compounds (VOCs). According to
EPA's Leak Detection and Repair
(LDAR) Best Practices Guide [3]:
" A typical refinery or chemical plant
can emit 600-700 ton/yr of VOCs
from leaking equipment, such as
valves, connectors, pumps, sampling
connections,
compressors,
pressure-relief devices and openended
lines. " Two methods are typically
used to reduce emissions from
leaking equipment: the use of " leakless
components, " and implementation
of LDAR techniques. LDAR refers
to a methodology that reduces
emissions from leaks by identifying
the leak as it occurs and repairing it
within regulated time frames. Table 1
shows common sources of leaks.
Sampling systems for flares
To comply with LDAR, CPI operators
must quantify the amount of
pollutants being released. In order
to properly and safely measure pollutants
from flares, a sample of flare
emissions must be taken. Automatic
sampling systems provide a safe
and environmentally friendly way to
extract needed samples. However,
if not properly installed and maintained,
sampling systems themselves
can be a source of leaks and
they too must comply with LDAR.
Sampling systems come in many
different styles and configurations,
and no two sampling systems are
exactly alike. For example, some
sampling systems can take a process
sample with operator interaction,
while others can automatically
collect samples without any operator
interaction. Each approach has
its pros and cons.
Manual sampling. Manual operation
allows for surveillance of the
process at random (unscheduled)
times. In some instances, due to
variability in the operating conditions
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Chemical Engineering January 2017

Table of Contents for the Digital Edition of Chemical Engineering January 2017
