Chemical Engineering January 2017 - 56

Environmental Manager
Eye on Flare Systems
Proper gas sampling is essential to meet operating and regulatory objectives
Michael Bequette
SOR Controls Group, Inc.
F
lares are used extensively in
chemical process industries
(CPI) facilities and petroleum
refineries, to combust flammable
hazardous gases. When designed
and operated properly, they
provide a proven mechanism to
handle upset conditions in a safe
manner. For instance, flares are typically
used to handle the unwanted
gas streams produced during upset
conditions and to reduce overpressure
conditions (for instance, when
a pressure-relief valve or rupture disk
is used to help reduce natural gas
pressure in a line). Similarly, during
oil-and-gas production, when natural
gas is extracted with the petroleum,
flaring the gas stream may be
the only alternative if the infrastructure
to pipe the gas to another location
is not in place.
When flares are used to combust
a waste stream from a process, the
Equipment
Pumps are used to move fluids from one point
to another. Two types of pumps extensively used
in petroleum refineries and checmical plants are
centrifugal pumps and positive displacement, or
reciprocating pumps
Valves are used to either restrict or allow the movement
of fluids. Valves come in numerous varieties
and with the exception of connectors, are the most
common piece of process equipment in the CPI
Connectors are components such as flanges and
fittings used to join piping and process equipment
together. Gaskets and blinds are usually installed
between flanges
Sampling connections are utilized to obtain samples
from within a process
Compressors are designed to increase the pressure
of a fluid and provide motive force. They can have
rotary or reciprocating designs
Pressure-relief devices are safety devices designed
to protect equipment from exceeding the
maximum allowable working pressure. Pressurerelief
valves and rupture disks are examples of
pressure-relief devices.
Open-ended lines are pipes or hoses open to the
atmosphere or surrounding environment
composition of the postcombustion
exhaust
gases will depend on
the composition of the
inlet gas received by the
flare. To protect workers,
neighboring communities
and wildlife
around
the plant, and to reduce
long-term impacts on the
environment, a variety
of state and federal requirements
are in place
to regulate the emissions
stream. Such regulations
seek to control the type
and amount of specific
air pollutants that are
discharged from flares, and they
typically require operating facilities
to quantify the amount of pollutants
in the exhaust stream that is
ultimately discharged.
Hazardous air pollutants (HAPs;
TABLE 1. COMMON SOURCES OF LEAKAGE AND FUGITIVE EMISSIONS [3]
Source of leaks
Leaks typically occur at the seal
FIGURE 1. Flares are wisely used to destroy unwanted pollutants,
but proper sampling is required to ensure that their own emissions
meet regulatory limits
referred to as toxic air pollutants),
create significant environmental
Leaks usually occur at the stem or gland area of the
valve body and are commonly caused by a failure of
the valve packing or O-ring
Leaks commonly result from gasket failure and
improperly torqued bolts on flanges
Leaks usually occur at the outlet of the sampling
valve when the sampling line is purged to obtain the
sample
Leaks most often occur from the seals
Leaks can occur if the valve is not seated properly,
operating too close to the set point or if the seal is
worn or damaged. Leaks from rupture discs can
occur around the disk gasket if not properly installed
Leaks occur at the point of the line that is open to
the atmosphere; they are usually controlled by using
caps, plugs and flanges. Leaks can also be caused
by the incorrect implementation of the block-andbleed
procedure
56
concerns and potential health risks.
HAPs have been associated with
cancer and neurological, respiratory,
and reproductive problems. In addition
to health concerns, such emissions
contribute to acid rain, smog,
water supply pollution and climate
change. The U.S. Environmental Protection
Agency (EPA) currently lists
187 compounds as HAPs, many of
which are commonly generated during
CPI process operations [1].
Most HAPs are defined by the
mode of production; for instance
mobile sources (exhaust gases from
vehicles), stationary sources (HAPS
produced by petroleum refineries,
power plants and other CPI facilities),
and indoor sources (this includes
HAPS produced by activities
such as cleaning).
Regulatory framework
In 1990, the U.S. Clean Air Act (CAA)
was amended to drive compliance
by establishing actionable dates to
achieve the reduction in the amount
of HAPs released. As a result of the
1990 CAA Amendments, a new requirement
of technology-based standards
emerged for so-called major
sources and certain area sources.
Major sources are stationary sources
that produce (or have the potential
to produce) 10 ton/yr or more of any
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