Mitigation of unconfined releases of hazardous gases via liquid spraying Page: 3 of 5
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HGSPRAY5 is a two-dimensional spray model that
describes absorption of gases by water sprays, air
entrainment and heat transfer. It is a complete model
of mass, momentum, and heat transfer between air/HF
and drops injected by water sprays or monitors. It has
been verified in the Hawk field tests performed at the
DOE Nevada Test Site (as part of the ICHMAP) that
the HFSPRAY model predictions are within 6 percent
of the experimental results obtained in the Hawk field
tests.56 In addition, the model replicated the
dispersion patterns observed from boundary layer wind
tunnel modeling of water spray mitigation systems
from actual industrial installations.4
HGSPRAY can be linked with the HGSYSTEM
models,' which describe the physical transformations
and the dispersion of a jet or plume upstream and
downstream of the water-spraying region. The
HGSYSTEM models describe all the phases of an
accidental gaseous release, including depressurization,
phase-change, and atmospheric dispersion of buoyant
or denser-than-air gases. The HGSPRAY5 model has
been independently verified with experimental data
involving releases of HF. The HGSYSTEM models
have also been independently verified by comparisons
with a wide range of experimental databases.
It is emphasized that the assessment of the
performance of a mitigation system requires modeling
of the strongly-coupled mass transfer and momentum
effects; calculations based only on mass transfer may
result in erroneous results.
Sprs
Fm
FLUID
MODELING
HFPLUME IGSPIRAY HEGADASDISPERSION OF
RELEASE FR7iOM
PRESSURED
VESSELOUANMY LATER
SPRAY EFCT7VENESS1NTE.3MEDIATE
E FA$W-H D
ATMOSPHRC
DISPERSIONFigure 1. Mitigation Modeling Regimes
IV. CASE STUDIES
Two cases are considered, one involving sprays in a
"curtain" setting and the other involving water
monitors.
A. Case A -Water Curtain
This case involves modeling of an actual HF
mitigation system based on sprays encircling an
alkylation unit.4 In the following we highlight
elements of this study which illustrate the link between
fluid and mathematical modeling.
1. Eight scenarios of release were identified after
reviewing system, site and meteorological
characteristics.
2. Fluid modeling experiments were conducted to
generate concentration, velocity and turbulence data.
3. The air entrainment relationships of HGSPRAY
were compared with the data obtained from the fluid
modeling tests.
4. Simulations using HGSPRAY, produced estimates
of the mitigation effectiveness of the system.
The spray configurations considered are: a) two
headers at about 30 ft off the ground, one equipped
with spray nozzles pointing upwards and the other
with the same nozzles pointing downwards, and b) two
headers at different elevations (e.g., 30 ft and 60 ft)
with nozzles pointing horizontally toward the release.
Two different types of spray nozzles producing drops
of different size were tested. HF releases at two
elevations and flow rates were considered to bracket
the range of potential releases. At grade (i.e., 1 m
above the ground) the release rate was 43 kg/s and at a
15-m elevation the release flow rate was 37 kg/s. The
water flow rate in the entire water curtain system was
33,000 gpm. The lateral spread and the concentration
of the plume as it intersects the spray were determined
from fluid modeling tests. According to the
HGSPRAY simulations, the two-tier horizontal
configuration removed HF somewhat more effectively
than the up-and-down configuration for the specific
release heights. Effectiveness of HF removal ranged
from 70 percent for high wind speeds (e.g., 17 m/s) to
96 percent for light wind speeds (e.g., 5 m/s). The
corresponding effectiveness of the up-and-down system
ranged from 53. percent to 97 percent. The main reason
for the advantage of the horizontal sprays, is that these
sprays reached higher and covered elevated releases,
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Fthenakis, V. M. Mitigation of unconfined releases of hazardous gases via liquid spraying, article, February 1, 1997; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc675310/m1/3/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.