United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-86/016 June 1986
&EPA Project Summary
Technical Manual:
Hood System Capture of Process
Fugitive Paniculate Emissions
E. R. Kashdan, D. W. Coy, J. J. Spivey, T. Cesta, and H. D. Goodfellow
Regulatory officials charged with the
responsibility of reviewing hood sys-
tems for capture of process fugitive
emissions face a difficult task. This
manual provides these officials with a
reference guide on the design and
evaluation of hood systems. Engineer-
ing analyses of the most important hood
types are presented. In particular, con-
sideration is given to design methods
for local capture of buoyant sources,
remote capture of buoyant sources, and
enclosures for buoyant and inertial
sources. A unique collection of case
studies of actual or representative hood
systems has been included to provide
insight into the evaluation of existing
systems or design of a planned system.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory. Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Process fugitive particulate emissions
have been defined as "particulate matter
which escapes from a defined process
flow stream due to leakage, materials
charging/handling, inadequate opera-
tional control, lack of reasonably available
control technology, transfer, or storage."
Secondary hood systems consisting of
enclosures, local hooding, or remote
hooding are the practical means of cap-
turing process fugitive particulate emis-
sions from many sources. Once captured,
the gas stream containing the particulate
matter can be ducted to high-efficiency
air pollution control devices. Frequently,
the capture efficiency of the hood is far
less than the removal efficiency of the
control device. Emissions missed by the
hood usually escape to the atmosphere.
Considering the diversity of sources
classed as process fugitives, it is not
surprising that the design of secondary
hood systems varies greatly; a large range
isfound in size, exhaust rate, and arrange-
ment. Regulatory officials charged with
the responsibility of reviewing hood sys-
tems for either existing or planned sites
face a difficult task. The behavior of
process fugitive particulate plumes is
complex; as a result, the interaction of the
hood and plume is not always predictable.
Moreover, most of the traditional indus-
trial ventilation texts do not specifically
consider process fugitive sources. The
emphasis of these texts has been pri-
marily to provide designers with general
design rules rather than with a thorough
understanding of hood design or the
limitations of design methods. This man-
ual emphasizes the design and evaluation
of actual hood systems used to control
various fugitive particulate emission
sources. Engineering analyses of the
most important hood types are presented
which provide a conceptual understand-
ing of the design process: they identify
source parameters, calculation proce-
dures, and techniques for evaluating hood
performance. Some of the design tech-
niques, introduced in technical papers by
Hatch Associates, have been formalized
in this manual. Case studies of actual
hood systems not only illustrate the
application of these design methods but
also identify their limitations. Several of
-------
the case studies, from the files of Hatch
Associates, provide unique insight into
the diagnosis of an existing system.
Purpose of the Manual
This technical manual provides regu-
latory officials with a reference guide on
the design and evaluation of hood sys-
tems to capture process fugitive panic-
ulate emissions. Much of the hood design
information is of necessity analytical,
based on a mathematical or engineering
approach. However, every effort has been
made to explain the physical processes in
qualitative terms and to separate the
formal equations.
Scope of the Manual
Although many names are used to type
hood systems, hoods are most conven-
iently classified in relation to the emission
source that is controlled. There are three
basic hood types: enclosures, exterior
hoods, and receiving hoods. Exhausted
enclosures (a subcategory of enclosures)
completely surround the source of emis-
sions. Obviously, from the standpoint of
capture efficfency, enclosures are the
preferred method of control because
escape of emissions is limited to leaks
through openings. However, enclosures
are not always suitable, especially when
ready access to the process source is
required. Exterior hoods (commonly re-
ferred to as perimeter and captor hoods)
are so called because they are exterior to
the source. Exterior hoods function by
inducing air flow toward the suction
opening. Because the "reach" of such
hoods is limited, exterior hoods are
always local (i.e., close to the source).
Receiving hoods act as receptors to panic-
ulate plumes that, by virtue of the process
source, possess significant motion. Re-
ceiving hoods may be local to or remote
from the source. An important special
case is a hood system that uses air jets to
assist in the capture of paniculate emis-
sions. This design in this manual is
termed an "assisted exterior hood" be-
cause the hood system (not the process)
directs the motion of the particulate
plume.
Sources of particulate emissions may
be classified as processes giving rise to
buoyant plumes, nonbuoyant plumes, and
plumes having a significant particle in-
ertia (a special case of nonbuoyant
plumes). Sources giving rise to buoyant
plumes are hot (many are 1000°C or
hotter), and the initial plume rise may
reach a velocity of 3 m/s. Nonbuoyant
sources are cold processes, or at least not
very hot; for the nonbuoyant source, the
plume will not exhibit strong plume rise,
and it is therefore likely to be deflected
easily by cross-drafts, even close to the
source. Plumes with significant particle
intertia are generally nonbuoyant, but in
addition, the motion of the coarse partic-
ulate matter entrains additional air.
With the foregoing classification of
hoods and processes, the scope of the
technical manual is summarized in Table
1. As shown in Table 1, the design of local
hoods (exterior and receiving) for buoyant
sources is discussed in Section 4, design
of remote hoods (receiving) for buoyant
sources in Section 5, and design of
enclosures for buoyant and inertia!
sources in Section 6. Reference to the
applicable case study is also given in
Table 1. Two situations not included in
the technical manual are exterior hoods
for nonbuoyant sources and receiving
hoods for inertial sources. Both these
situations (the former typified by an open
surface tank, the latter by a grinding
wheel) may be handled by industrial
ventilation guideline texts. In any case,
neither is generally considered a process
fugitive source; therefore, they are beyond
the scope of this report.
Organization of the Manual
This manual is divided into eight sec-
tions. In Section 1, the objectives of this
technical manual are discussed and the
scope of the manual is outlined. In Section
2, pertinent industrial ventilation liter-
ature is summarized, and a bibliography
is supplied. The bibliography is divided
into topical areas including: general in-
dustrial ventilation, hood capture and
plume theory, natural ventilation, local
ventilation, and enclosures for materials
handling operations. In Section 3, general
design methods are reviewed, and hood-
ing practices for many process fugitive
sources in various industries are tabu-
lated. Design data for selected ventilation
systems in the iron and steel, nonferrous
metals, and mineral processing industries
are also presented in Section 3.
Sections 4, 5, and 6 present design
methodology for the various combinations
of hoods and sources. Section 4 covers
local capture of buoyant plumes; Section
5, remote capture of buoyant plumes; and
Section 6, enclosures for buoyant and
inertial sources. The five design methods
discussed in the manual are design by
precedent, design by rule-of-thumb, de-
sign by analytical methods, design by
diagnosis of an existing site, and design
by physical scale model.
In design by analytical methods, con-
servation of mass, momentum, and en-
ergy equations are applied to the source
of emissions to estimate the plume flow
rate arriving at the hood face, and there-
fore the required exhaust rate. The values
of the source parameters used in the
resulting design equations may be calcu-
lated or obtained direclty as part of a field
measurement program on an existing
site. In design by diagnosis of an existing
site, measurements of source parameters
are obtained. Direct measurements of the
plume flow rate, and therefore the re-
quired hood exhaust rate, also may be
obtained. In such a case, it is wise to
check the measured plume flow rate
against that predicted by analytical tech-
niques. For a planned site, field measure-
ments cannot be carried out, but fluid
modeling techniques instead of, or in
addition to, analytical techniques may be
used. If a facility similar to the planned
facility exists, field meaurements could
be made in the existing facility. In design
by fluid modeling, a scale replica of the
proposed hood is placed in a suitable fluid
environment (e.g., water tank), and the
required hood exhaust rate is estimated
by scaling up from the performance of the
model. For design of planned complex
hoods, fluid modeling is recommended.
Moreover, fluid modeling may be used in
conjunction with a field measurement
program to diagnose causes of poor hood
performance or to test modifications to an
existing hood system.
Section 7 presents analyses of six hood
systems for capture of process fugitive
particulate emissions. Each design is
treated as a case study. The studies
represent a varied range of industries,
hood types, and design methods. The
intent of this section is to provide insights
into the design and/or analysis of either
actual installations or representative ex-
amples.
Case studies I and II illustrate analytical
techniques. Case studies III and IV illus-
trate design by precedent; i.e., using a
working system as a model for the case at
hand. Case V illustrates the use of
physical scale modeling in the design of
an enclosure. Case VI illustrates the use
of design by rule-of-thumb, although the
rule has been tested and modified by the
designers. The intent is that the reader
gain an appreciation of the difficulties in
designing hood systems that no simple,
textbook-type problems can provide.
Case I is a canopy hood installation on
an electric arc furnace meltshop. The
shop operates an 18-ft (5.5-m) diameter.
-------
Table 1. Scope of the Technical Manual
Hood Type
Exterior
Assisted
Unassisted
Assisted, unassisted
Receiving
Remote
Local
Local
Enclosures
Process Fugitive Source
Buoyant
Buoyant
Nonbuoyant
Buoyant
Buoyant
Nonbuoyant (inertia!)
Nonbuoyant (inertia/)
Buoyant
Nonbuoyant
Design Section
4
4
Not discussed
5
4
Not discussed
6
6
6
Applicable Case Study
Case II (Copper converter)
None
None
Cases 1 & IV (Electric arc furnaces)
Case III (Basic oxygen furnace)
Case V (Lime unloader)
None
Case VI (Aluminum rolling mill)
80-ton (75 metric ton) furnace powered
by a 35 MW electrical supply. Since
startup in 1975, the feed to the furnace
has been 100 percent scrap charge. The
fugitive particulate emission source is
furnace tapping and charging. These
buoyant emissions are captured by a
canopy hood. The canopy hood and
furnace direct evacuation share a com-
mon fume collection system.
Case II is an air curtain system installed
on a primary copper converter for capture
of low level fugitive emissions. The
installation is at ASARCO's Tacoma
Smelter and is the first domestic full-
scale prototype air curtain hood for this
application. The air curtain capture effi-
ciency was evaluated during extensive
tests. The results of the tests have been
used to describe the hood performance.
The original air curtain design calculation
was not available for assessment. A
design approach is presented for an air
curtain based on application of an analyt-
ical technique to the existing site.
Case III is secondary fume control
system on two 250-ton (230 metric ton)
basic oxygen furnaces (BOF). BOF sec-
ondary emissions are generated during
transfer of blast furnace molten iron
between vessels (reladling), charging of
molten iron and scrap into the refining
vessel, and slagging and tapping of steel.
These emissions are captured by local
hooding with the secondary ventilation
system (SVS).
Of particular interest in this example is
the design approach used in sizing the
capture system. With an appreciation of
how key design parameters affected the
system size, a survey of existing installa-
tions and capture technology was used as
the basic design tool.
Case IV examines another canopy hood
system for capture of charging and tap-
ping fumes from an electric arc furnace.
The original design basis is provided, and
the included results of recent perform-
ance tests suggest excellent capture
efficiency.
The meltshop under consideration con-
tains two ultra-high-power electric arc
furnaces with capacities of 115 and 150
tons (105 and 135 metric tons). The 150-
ton furnace was added to the existing
115-ton furnace to increase shop capac-
ity. It was commissioned in December
1981.
Direct evacuation is used to control
emissions from the furnaces during melt-
ing and refining. The canopy hood system
is used to capture process fugitive emis-
sions during charging and tapping of the
150-ton furnace. The canopy hood system
geometry was based on the designer's
observations of a working system.
Case V involves dust control on lime
transfer by a 15-ton (13.5 metric ton)
capacity clamshell into an enclosed hop-
per. This case is an example of fugitive
particulate control on a nonbuoyant
source. The source is typical for bulk
materials handling at receiving terminals
throughout industry. Large amounts of
loose material is handled in the open,
thus making control of dust generation
and dispersion a constant challenge.
A modeling technique was used to
improve capture of lime dust from the
clamshell unloading operation. To design
an accurate physical model, it was nec-
essary to identify important variables that
were affecting the fugitive emission
problem.
Case VI examines the use of a hood
assisted by an air curtain to control
emissions from an aluminum rolling mill.
Although the example does not represent
an actual installation, dimensions and
conditions are typical of a single-stand
cold rolling mill.
Aluminum rolling mills are used to
reduce the thickness of aluminum sheet.
Both hot and cold rolling mills require that
a fluid be applied to the strip to serve as
both a lubricant and a coolant. In both
mills, the rotary movement of the rolls
and linear movement of the strip generate
fine liquid particles (mechanical atomiza-
tion). Also, rolling the metal generates
sufficient heat by friction to vaporize a
fraction of the coolant. Coolant particles
are objectionable because of worker
exposure to hydrocarbons, reduced in-
plant visibility, and potential fire hazards.
The hood design in Case VI is used for
both hot and cold rolling mills. This hood
design is difficult to clasify within the
scheme used in this manual but is
probably best defined as a partial en-
closure. The manufacturer refers to it as a
slotted-perimeter hood assisted by an air
curtain. This design evolved from modi-
fications to simpler exterior hoods, which
often were not very effective.
-------
E. Kashdan, D. Coy. andJ. Spiveyare with Research Triangle Institute, Research
Triangle Park, NC 27709; and T. Cesta and H. Goodfellow are with Hatch
Associates, Ltd., Toronto, M4TIL9, Ontario, Canada.
Dale L. Harmon is the EPA Project Officer (see below).
The complete report, entitled "Technical Manual: Hood System Capture of
Process Fugitive Paniculate Emissions," (Order No. PB 86-190 444/AS; Cost:
$16.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-86/016
0000329 PS
PROTECTION AGENCY
CHICAGO
------- |