Chemical Engineering November 2016 - 58

Engineering Practice
Considering Fugitive Emissions During
the Conceptual Design Stage
The ability to reduce fugitive emissions through the use of strategic design
modifications not only protects workers and the environment, but reduces losses of
valuable process materials
Yieng Shing Seah and
Dominic C. Y. Foo
University of Nottingham (Malaysia
Campus)
Mimi H. Hassim
Universiti Tecknologi Malaysia
T
he industrialized nations of
the world have all placed
increased emphasis on the
control of industrial emissions,
to protect the atmosphere.
Many types of emissions result from
process streams, and as such, can
be controlled by operators with the
right engineering interventions. However,
a considerable proportion of
emissions are unanticipated fugitive
emissions [1]. Fugitive emissions are
defined as a chemical, or a mixture
of chemicals, in any physical form,
released as a result of an unanticipated
or spurious leak in an industrial
site [2,3,4]. Such leaks occur
because of discontinuities
in
the
solid barrier that is intended to maintain
containment.
Worldwide, fugitive emissions
from industrial applications
amount to more than a million
metric tons per year (m.t./yr),
and fugitive emissions in the U.S.
are estimated to be in excess of
300,000 m.t./yr, accounting for
about one third of the total organic
emissions from chemical plants [5].
This situation is mirrored in Europe,
and is likely worse in other parts of
the world, where emission standards
and policing levels may be lower.
Fugitive emissions create not only
environmental and health issues,
but they have economic impacts, as
well. Fugitive emissions represent a
loss of potentially valuable materials
and reduce overall plant efficiency
[6]. In many cases, the true eco58
Stream
Phase
T,
°C
P, bar
EG
Water
IPA
TABLE 1. STREAM CONDITION FOR IPA-WATER SEPARATION EXAMPLE
S
F
Liquid
75
2
100.00
0.00
0.00
Liquid
75
2
0.00
13.90
86.10
D1
Liquid
82
1.01
B1
Liquid
169.4
1.95
Mass composition, wt.%
0.00
0.16
99.84
nomic impacts are not recognized,
because many of the costs associated
with fugitive emissions are not
readily apparent. Since October
2007, all existing processing plants
and power stations within the European
Union (E.U.) have had to comply
with the IPPC directive 96/61/
EU, which aims to improve the management
of industrial processes and
ensure a higher level of protection
for the environment. The challenging
environmental, health and economic
demands that are driving the need to
reduce leaks and fugitive emissions
[7] are more urgent than ever. The
implementation of legislation in the
U.S. governing emissions of volatile
organic compounds, together
with E.U. directives, has provided a
stimulus for work aimed at reducing
fugitive emissions.
Conceptual design and FEED
This article focuses on how fugitive
emissions should be considered
during the conceptual design and
front-end engineering design (FEED)
stages. As shown in the example in
this article, an emission factor is applied
to estimate the amount of potential
fugitive emissions that could
be expected, as well as the potential
atmospheric concentration
92.82
7.18
0.00
D2
Liquid
100.1
1.01
1.61
98.39
0.00
B2
Liquid
209.1
1.43
100.00
0.00
0.00
and associated health risks. The
health risk is then calculated using
the established Health Quotient
(HQ) Index, a dimensionless value
that indicates a relative health risk
between two or more processes
or scenarios based on the amount
of fugitive emissions generated by
both (HQ is typically expressed as a
ratio of emission concentration and
exposure limit).
The example discussed in
this
article demonstrates the estimation
of potential fugitive emissions from
an extractive distillation system that
consists of two distillation units. The
process involves the extraction of
isopropanol (IPA) from water using
ethylene glycol as the entrainer (the
entrainer is the solvent used in an
extractive distillation system). Since
actual plant monitoring data were
not available, an estimation method
was used, based on the Average
Emission Factor approach discussed
in Ref. 8.
The fugitive emissions rate obtained
using that methodoogy was
then used as the input data to determine
the resulting chemical concentration
(based on the volumetric
flowrate of air) within the process
area. In this estimation exercise, the
volumetric flowrate is estimated,
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