450390006C
Chapter 10
HOODS, DUCTWORK, and STACKS
William M. Vatavuk
Standards Development Branch, OAQPS
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
March 1994
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Contents
10.1 Introduction 10-3
10.2 Equipment Description 10-4
10.2.1 Hoods 10-4
10.2.1.1 Types of Hoods 10-4
10.2.2 Ductwork 10-8
10.2.2.1 Ductwork Components 10-10
10.2.3 Stacks 10-13
10.3 Design Procedures 10-14
10.3.1 Design Fundamentals 10-15
10.3.1.1 The Bernoulli Equation 10-15
10.3.1.2 Pressure: Static, Velocity, and Total 10-18
10.3.1.3 Temperature and Pressure Adjustments . 10-21
10.3.2 Hood Design Procedure 10-22
10.3.2.1 Hood Design Factors 10-22
10.3.2.2 Hood Sizing Procedure 10-26
10.3.3 Ductwork Design Procedure 10-29
10.3.3.1 Two Ductwork Design Approaches . . . . 10-29
10.3.3.2 Ductwork Design Parameters 10-29
10.3.3.3 Ductwork Pressure Drop 10-32
10.3.4 Stack Design Procedures 10-37
10.3.4.1 Calculating Stack Diameter 10-38
10.3.4.2 Calculating Stack Height 10-38
10.3.4.3 Calculating Stack Draft 10-40
10.4 Estimating Total Capital Investment 10-41
10.4.1 Equipment Costs 10-41
10.4.1.1 Hood Costs 10-42
10.4.1.2 Ductwork Costs 10-44
10.4.1.3 Stack Costs 10-50
10.4.2 Taxes, Freight, and Instrumentation Costs . . 10-53
10.4.3 Purchased Equipment Cost 10-53
10.4.4 Installation Costs 10-54
10.5 Estimating Total Annual Cost 10-55
10.5.1 Direct Annual Costs 10-55
10.5.2 Indirect Annual Costs 10-56
10.5.3 Total Annual Cost 10-56
10.6 Acknowledgements 10-57
References 10-58
10-2
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10.1 Introduction
Most control devices are located some distance from the
emission sources they control. This separation may be needed for
several reasons. For one thing, there may not be enough room to
install the control device close to the source. Or, the device
may collect emissions from several sources located throughout the
facility and, hence, must be sited at some convenient,
equidistant location. Or, it may be that required utility
connections for the control device are only available at some
remote site. Regardless of the reason, the waste gas stream must
be conveyed from the source to the control device and from there
to a stack before it can be released to the atmosphere.
The kinds of equipment needed to convey the waste gas are
the same for most kinds of control devices. These are: (1)
hoods, (2) ductwork, (3) stacks, and (4) fans. Together, these
items comprise a ventilation system. A hood is used to capture
the emissions at the source; ductwork, to convey them to the
control device; a stack, to disperse them after they leave the
device; and a fan, to provide the energy for moving them through
the control system. This chapter covers the first three kinds of
equipment. However, because they constitute such a broad and
complex subject, fans will be dealt with in a future Manual
chapter. Also, the kinds of stacks covered are short stacks
(100-120 feet high or less). Typically, these are included with
packaged control systems or added to them. So-called "tall
stacks" ("chimneys"), used at power plants or other sources where
the exhaust gases must be dispersed over great distances, will
not be discussed in this chapter.
This chapter presents all the information one would need to
develop study (± 30%-accurate) cost estimates for hoods,
ductwork, and stacks. Accordingly, the following sections
include: (1) descriptions of the types of equipment used in air
pollution control ventilation systems, (2) procedures for sizing
(designing) this equipment, and (3) methodologies and data for
estimating their capital and annual costs. Also, sprinkled
throughout the chapter are several illustrations (example
problems) that show the reader how to apply the various sizing
and costing methodologies.
10-3
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10.2 Equipment Description
In this section, the kinds of hoods, ductwork, and stacks
used in air pollution control systems are described, each in a
separate subsection. These descriptions have been based on
information obtained from standard ventilation and air pollution
control references, journal articles, and equipment vendors.
10.2.1 Hoods
Of the several components of an air pollution control
system, the capture device is the most important. This should be
self-evident, for if emissions are not efficiently captured at
the source they cannot be conveyed to and removed by a control
device. There are two general categories of capture devices: (1)
direct exhaust connections (DEC) and (2) hoods. As the name
implies, a DEC is a section of duct (typically an elbow) into
which the emissions directly flow. These connections often are
used when the emission source is itself a duct or vent, such as a
process vent in a chemical manufacturing plant or petroleum
refinery. (See discussion below on "Ductwork".)
Hoods comprise a much broader category than DECs. They are
used to capture particulates, gases, and/or mists emitted from a
variety of sources, such as basic oxygen steelmaking furnaces,
welding operations, and electroplating tanks. The hooded
processes are generally categorized as either "hot" or "cold", a
delineation that, in turn, influences hood selection, placement,
and design.
The source conditions also influence the materials from
which a hood is fabricated. Mild (carbon) steel is the material
of choice for those applications where the emission stream is
noncorrosive and of moderate temperature. However, where
corrosive substances (e.g., acid gases) are present in high
enough concentrations, stainless steels or plastics (e.g.,
fiberglass-reinforced plastic, or FRP) are needed. As most hoods
are custom-designed and built, the vendor involved would
determine which material would be optimal for a given
application.
10.2.1.1 Types of Hoods
Although the names of certain hoods vary, depending on which
ventilation source one consults, there is general agreement as to
how they are classified. There are four types of hoods: (1)
enclosures, (2) booths, (3) captor (capture,) hoods, and (4)
receptor (receiving) hoods.li2
10-4
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Enclosures are of two types: (1) those that are completely
closed to the outside environment and (2) those that have
openings for material input/output. The first type is only used
when handling radioactive materials, which must be handled by
remote manipulators. They are also dust- and gas-tight. These
kinds of enclosures are rarely used in air pollution control.
Total enclosures, the second type, have applications in
several areas, such as the control of emissions from electric arc
furnaces and from screening and bin filling operations. They are
equipped with small wall openings (natural draft
openings—"NDO's") that allow for material to be moved in or out
and for ventilation. However, the area of these openings must be
small compared with the total area of the enclosure walls
(typically, 5% or less).
Another application of total enclosures is in the
measurement of the capture efficiency of VOC (volatile organic
compound) control devices. Capture efficiency is that fraction
of all VOC's generated at, and released by, an affected facility
that is directed to the control device. In this application, a
total enclosure is a temporary structure that completely
surrounds an emitting process so that all VOC emissions are
captured for discharge through ducts or stacks. The air flow
through the total enclosure must be high enough to keep the
concentration of the VOC mixture inside the enclosure within both
the Occupational Safety and Health Administration (OSHA) health
requirement limits and the vapor explosive limits. (The latter
are typically set at 25% of the lower explosive limit (LEL) for
the VOC mixture in question.) In addition, the overall face
velocity of air flowing through the enclosure must be at least -
200 ft/min.3
The surfaces of temporary total enclosures are usually
constructed either of plastic film or of such rigid materials as
insulation panels or plywood. Plastic film offers the advantages
of being lightweight, transparent, inexpensive, and easy to work
with. However, it is flimsy, flammable, and has a relatively low
melting point. In addition, the plastic must be hung on a
framework of wood, plastic piping, or scaffolding.
Although rigid materials are more expensive and less
workable than plastic, they are more durable and can withstand
larger pressure differentials between the enclosure interior and
exterior. Total enclosure design specifications (which have been
incorporated into several EPA emission standards) are contained
in the EPA report, The Measurement Solution: Using a. Temporary
Total Enclosure for Capture Testing.*
Booths are like enclosures, in that they surround the
emission source, except for a wall (or portion thereof) that is
omitted to allow access by operators and equipment. Like
10-5
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enclosures, booths must be large enough to prevent particulates
from impinging on the inner walls. They are used with such
operations (and emission sources) as spray painting and portable
grinding, polishing, and buffing operations.
Captor Hoods: Unlike enclosures and booths, captor hoods
(also termed active or external hoods) do not enclose the source
at all. Consisting of one to three sides, they are located at a
distance from the source and draw the emissions into them via
fans. Captor hoods are further classified as side-draft/back-
draft, slot, downdraft, and high-velocity, low-volume (HVLV)
hoods. A side-draft/back-draft hood is typically located to the
side/behind of an emission source, but as close to it as
possible, as air velocities decrease inversely (and sharply) with
distance. Examples of these include snorkel-type welding hoods
and side shake-out hoods.
A slot hood operates in a manner similar to a side-
draft/back-draft. However, the inlet opening (face) is much
smaller, being long and narrow. Moreover, a slot hood is
situated at the periphery of an emission source, such as a
narrow, open tank. This type of hood is also employed with bench
welding operations.
While slot and side-draft/back-draft hoods are located
beside/behind a source, a downdraft hood is situated immediately
beneath it. It draws pollutant-laden air down through the source
and, thence, to a control device. Applications of down-draft
hoods include foundry shake-out and bench soldering and torch
cutting operations.
HVLV hoods are characterized by the use of extremely high
velocities (capture velocities) to collect contaminants at the
source, and by the optimal distribution of those velocities
across the hood face. To maintain a low volumetric flow rate,
these hoods are located as close to the source as possible, so as
to minimize air entrainment.
Receptor hoods: The last category is receptor hoods (a.k.a.
passive or canopy hoods). A receptor hood typically is located
above or beside a source, to collect the emissions, which are
given momentum by the source. For example, a canopy hood might
be situated directly above an open tank containing a hot liquid
(a buoyant source) . With entrained air, vapors emitted from the
liquid would rise into the hood. Here, the canopy hood would
function as a passive collector, as the rising gases would be
drawn into the hood via natural draft. (See Figure 10.1.)
Receptor hoods are-also used with nonbuoyant sources,
sources from which emissions do not rise. However, the emissions
can be "thrown off" from a process, such as a swing grinder. The
initial velocity of the emissions typically is high enough to
10-6
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Figure 10.1 Typical Canopy Hood Installation
Source: tank or process
10-7
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convey them into a receiving hood.5
10.2.2 Ductwork
Once the emission stream is captured by either a hood or a
direct exhaust connection, it is conveyed to the control device
via ductwork. The term "ductwork" denotes all of the equipment
between the capture device and the control device. This
includes: (1) straight duct; (2) fittings, such as elbows and
tees; (3) flow control devices (e.g., dampers); and (4) duct
supports. These components are described in Section 10.2.2.1.)
In air pollution control systems, the fan is usually located
immediately before or after the control device. Consequently,
most of the ductwork typically is under a negative static
pressure, varying from a few inches to approximately 20 inches of
water column. These pressure conditions dictate the type of duct
used, as well as such design parameters as the wall thickness
(gauge). For instance, welded duct is preferable to spiral-wound
duct in vacuum applications.6
Ductwork is fabricated from either metal or plastic, the
choice of material being dictated by the characteristics of the
waste gas stream, structural considerations, purchase and
installation costs, aesthetics, and other factors. Metals used
include carbon steel (bare or galvanized), stainless steel, and
aluminum. The most commonly used plastics are PVC (polyvinyl
chloride) and FRP (fiberglass-reinforced plastic), although
polypropylene (PP) and linear polyethylene (LPE) also have been
applied. However, one serious drawback to PP and LPE is that
both are combustible.1
PVC and other plastic ductwork are resistant to a variety of
corrosive substances, from aqua regia to 95% sulfuric acid. But
plastic ductwork cannot tolerate environmental temperatures above
150°F.8 Metal ductwork can handle temperatures up to
approximately 1000°F, but only certain alloys can tolerate
corrosive streams.
In terms of construction, ductwork can be either rigid or
flexible. As the name implies, rigid ductwork, whether metal or
plastic, has a fixed shape. Conversely, flexible ductwork can be
bent to accomodate situations where space is limited or where the
layout is so convoluted that rigid fittings cannot meet
construction requirements. Usually circular in cross-sectional
shape, flexible duct can be fabricated from metals or plastic and
can be either insulated or uninsulated.
Rigid ductwork is fabricated into circular, flat oval, or
square/rectangular cross-sectional shapes. Of these, circular
duct is most commonly used in air pollution control systems.
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Although square/rectangular duct is advantageous to use when
space is limited, round duct offers several advantages. It
resists collapsing, provides better transport conditions, and
uses less metal than square/rectangular or flat oval shapes of
equivalent cross-sectional area.9 Unless otherwise noted, the
following discussion will pertain to rigid, circular duct, as
this is the type most commonly used in air pollution control.
Rigid metal circular duct is further classified according to
method of fabrication. Longitudinal seam duct is made by bending
sheet metal into a circular shape over a mandrel, and butt-
welding the two ends together. Spiral seam duct is constructed
from a long strip of sheet metal, the edges of which are joined
by an interlocking helical seam that runs the length of the duct.
This seam is either raised or flush to the duct wall surface.
Fabrication method and cross-sectional shape are not the
only considerations in designing ductwork, however. One must
also specify the diameter; wall thickness; type, number, and
location of fittings, controllers, and supports; and other
parameters. Consequently, most ductwork components are custom-
designed and fabricated, so as to optimally serve the control
device. Some vendors offer prefabricated components, but these
are usually common fittings (e.g., 90° elbows) that are available
only in standard sizes (e.g., 3- to 12-inch diameter)10'11.
If either the gas stream temperature or moisture content is
excessive, the ductwork may need to be insulated. Insulation
inhibits heat loss/gain, saving energy (and money), on the one
hand, and prevents condensation, on the other. Insulation also .
protects personnel who might touch the ductwork from sustaining
burns. There are two ways co insulate ductwork. The first is to
install insulation on the outer surface of the ductwork and cover
it with a vapor barrier of plastic or metal foil. The type and
thickness of insulation used will depend on several heat
transfer-related parameters. For instance, one vendor states
that 4 inches of mineral wool insulation is adequate for
maintaining a surface ("skin") temperature of 140°F (the OSHA
workplace limit) or lower, provided that the exhaust gas
temperature does not exceed 600°F.12
The second way to insulate ductwork is by using double-wall,
insulated duct and fittings. Double-wall ductwork serves to
reduce both heat loss and noise. One vendor constructs it from a
solid sheet metal outer pressure shell and a sheet metal inner
liner with a layer of fiberglass insulation sandwiched between.
The insulation layer is typically 1-inch, although 2- and 3 - inch
thicknesses are available for more extreme applications. The
thermal conductivities of these thicknesses are 0.27, 0.13, and
0.09 Btu/hr-ft2-°F, respectively.13
10-9
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10.2.2.1 Ductwork Components
As discussed above, a ductwork system consists of straight
duct, fittings, flow control devices, and supports. Straight
duct is self-explanatory and easy to visualize. The "fittings"
category, however, encompasses a range of components that perform
one or more of the following functions: change the direction of
the ducted gas stream, modify the stream velocity, tie it to
another duct(s), facilitate the connection of two or more
components, or provide for expansion/contraction when thermal
stresses arise.
The most commonly used fittings are elbows ("ells"). These
serve to change the gas stream direction, typically by 30°, 45°,
60°, or 90°, though they may be designed for other angles as
well. The elbow centerline radius determines the rate at which
this directional change occurs. (See Figure 10.2.) The standard
centerline radius (Rcl) is 1.5 x the elbow cross -sectional
diameter (De) . However, in "long-radius" elbows, in which the
directional change is more gradual than in standard elbows, Rcl =
> 2D.14
°
Tees are used when two or more gas streams must be
connected. In straight tees, the streams converge at a 90
angle, while in angle tees ("laterals", "wyes") the connection is
made at 30° , 45° , 60°, or some other angle. (See Figure 10.2.)
Tees may have one "tap" (connection) or two, and may have either
a straight or a "conical" cross -sect ion at either or both ends.
Crosses are also used to connect duct branches. Here, the two
branches intersect each other at a right angle.
Reducers (commonly called "expansions" or "contractions")
are required whenever ducts of different diameter must be joined.
Reducers are either concentric or eccentric in design. In
concentric reducers, the diameter tapers gradually from the
larger to smaller cross section. However, in eccentric reducers,
the diameter decreases wholly on one side of the fitting.
To control the volumetric flowrate through ventilation
systems, dampers are used. Dampers are usually delineated
according to the flow control mechanism (single blade or
multiblade) , pressure rating (low/light or high/heavy) , and means
of control (manual or automatic) . In single blade dampers, a
circular plate is fastened to a rod, one end of which protrudes
outside the duct. In the most commonly used type of single blade
damper (butterfly type) , this rod is used to control the gas flow
by rotating the plate in the damper. Fully closed, the damper
face sits perpendicular to the gas flow direction; fully open,
the face- is parallel to the gas flow lines. Several single blade
"control" dampers are depicted in Figure 10.2.
10-10
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Figure 10.2 Selected Circular Ductwork Componentst
LONGITUDINAL
SEAM DUCT
'Fully welded
lonqitudmal seam)
DIMENSIONS:
8" minimum
90" maximum
GORED ELBOW
DIMENSIONS:
R - 1 5A
fot *
90* moa or* pcx« 'or e«cn
18* Of ti*ctK>n
STRAIGHT TEE
STRAIGHT 90° CROSS
T—
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J—
H
-I-
r^i
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jp
'• — !»-
"— ~x
— I — •"
\\
DIMENSIONS:
Maximum C = A '
n
j
i
4
i *. ""i
I U i DIMENSIONS:
!
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---
1 !
^
•^--
•=.
n
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-j- V - C * 2
Maximum C or 0 * A
_1
~T
HEAVY-DUTY
CONTROL DAMPER
CONCENTRIC
REDUCER
ECCENTRIC REDUCER
t Reference: "Single-Wall Round and Flat Oval Duct and
Fittings - in: Sheet Metal Division Catalog. Groveport, OH:
United McGill Corporation. 1990.
10-11
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With blast gate dampers, a second type, the flow is
controlled by sliding the damper blade in and out of the duct.
Blast gates are often used to control the flow of air streams
containing suspended solids, such as in pneumatic conveyors. In
these respects, butterfly dampers and blast gates are analogous,
respectively, to the globe valves and quick-opening gate valves
that are used to regulate liquid flow in pipes.
Multiblade (louvered) dampers operate by means of the same
principal. However, instead using a single blade or plate to
control the gas flow, multiblade dampers employ slats that open
and close like Venetian blinds.15 Louvered dampers typically are
used in very large ducts where a one-piece damper blade would be
too difficult to move.
Manually-controlled dampers simply have a handle attached to
the control rod which is used to adjust the gas flow by hand. If
automatic control is needed, a pneumatic or electronic actuator
is used. The actuator receives a pneumatic (pressurized air) or
electrical signal from a controller and converts it to mechanical
energy which is used, in turn, to open/close the damper via the
damper rod. In this respect, an actuated damper is analogous to
an automatic control valve.16 For example, an automatic damper
may be used to control the dilution air flow rate to an
incinerator combustion chamber. This flow rate, in turn, would
depend on the combustibles concentration (i.e., percentage of
lower explosive limit—%LEL) in the inlet waste gas stream. If
this concentration deviates from a predetermined amount ("set
point"), a signal is sent from the measuring device via the
controller to the automatic damper to increase/decrease the
dilution air flow rate so as to maintain the desired %LEL.
Expansion joints are installed, especially in longer metal
duct runs, to allow the ductwork to expand or contract in
response to thermal stresses. These fittings are of several
designs. One type, the bellows expansion joint, consists of a
piece of flexible metal (e.g., 304 stainless steel) that is
welded to each of two duct ends, connecting them. As the
temperature of the duct increases, the bellows compresses; as the
duct temperature decreases, the bellows expands.
Another commonly used expansion joint consists of two
flanges between which is installed a section of fabric. Like the
bellows expansion joint, it compresses as the duct temperature
increases, and vice-versa. The temperature dictates the type of
fabric used. For instance, silicone fiberglass and aramid fiber
cloth can be used for duct temperatures of up to 500°F., while
coated fiberglass cloth is needed to accommodate temperatures of
1, 000°F.17
The last component to consider is the ductwork support
system. However, it is far from being the least important. As
10-12
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the SMACNA (Sheet Metal and Air Conditioning Contractors'
National Association) HVAC Duct Construction Standards manual
states, "The selection of a hanging system should not be taken
lightly, since it involves not only a significant portion of the
erection labor, but also because [the erection of] an inadequate
hanging system can be disastrous." As a rule, a support should be
provided for every 8 to 10 feet of duct run.18 Ductwork can be
suspended from a ceiling or other overhead structure via hangers
or supported from below by girders, pillars, or other supports.
A suspension arrangement typically consists of an upper
attachment, a hanger, and a lower attachment. The upper
attachment ties the hanger to the ceiling, etc. This can be a
concrete insert, an eye bolt, or a fastener such as a rivet or
nailed pin. The hanger is generally a strap of galvanized steel,
round steel rod, or wire that is anchored to the ceiling by the
upper attachment. The type of hanger used will be dictated by
the duct diameter, which is proportional to its weight per lineal
foot. For instance, wire hangers are only recommended for duct
diameters up to 10 inches. For larger diameters (up to 36
inches), straps or rods should be used. Typically, a strap
hanger is run from the upper attachment, wrapped around the duct,
and secured by a fastener (the lower attachment). A rod hanger
also extends down from the ceiling. Unlike strap hangers, they
are fastened to the duct via a band or bands that are wrapped
around the circumference. Duct of diameters greater than 3 feet
should be supported with two hangers, one on either side of the
duct, and be fastened to two circumferential bands, one atop and
one below the duct.19 Moreover, supports for larger ductwork
should also allow for both axial and longitudinal expansion and
contraction, to accomodate thermal stresses.20
10.2.3 Stacks
Short stacks are installed after control devices to disperse
the exhaust gases above ground level and surrounding buildings.
As opposed to "tall" stacks, which can be up to 1000 feet high,
short stacks typically are no taller than 120 feet.
Certain packaged control devices come equipped with short
("stub") stacks, with heights ranging from 30 to 50 feet. But if
such a stack is neither provided nor adequate, the facility must
erect a separate stack to serve one or more devices.
Essentially, this stack is a vertical duct erected on a
foundation and supported in some manner. For structural
stability, the diameter of the stack bottom is slightly larger
than the top diameter, which typically ranges from 1 to 7 feet.21
A short stack may be fabricated of steel, brick, or plastic
(e.g., fiberglass-reinforced plastic, or FRP). A stack may be
lined or unlined. The material selection depends on the physical
10-13
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and chemical properties of the gas stream, such as corrosiveness
and acidity, as well as the temperature differential between the
gas stream and the ambient air. Liners of stainless steel,
brick, or FRP usually are used to protect the stack against
damage from the gas stream. They are much easier and less
expensive to replace than the entire stack. Alternatively, the
interior of an unlined stack may be coated with zinc
(galvanized), aluminum, or another corrosion-resistant material,
but a coating does not provide the same protection as a liner and
does not last as long.22
Short stacks are either self-supporting (free-standing),
supported by guy wires, or fastened to adjacent structures. The
type of support used depends on the stack diameter, height and
weight, the wind load, local seismic zone characteristics, and
other factors.
Auxiliary equipment for a typical stack includes an access
door, a sampling platform, ladders, lightning protection system,
and aircraft warning lights. The access door allows for removal
of any accumulated materials at the bottom of the stack and
provides access to the liner for repair or replacement. Local
and state air pollution control regulations also may require the
permanent installation of sampling platforms for use during
periodic compliance tests, while ladders are used both during
stack sampling and maintenance procedures. The lightning
protection system is needed to prevent damage to the stack and
immediate surroundings during electrical storms. Lastly,
aircraft warning lights are required by local aviation
authorities.23 Altogether, these auxiliaries can add a large
amount to the base stack cost.
10.3 Design Procedures
As stated above, a hood, ductwork, and a stack are key
elements in any air pollution control system. Because each of
these elements is different, both in appearance and function,
each must be designed separately. But at the same time, these
elements comprise a system, which is governed by certain physical
laws that serve to unite these elements in
"common cause". Thus, before the individual design procedures
for hoods, ductwork, and stacks are described, ventilation
fundamentals will be presented. These fundamentals will cover
basic fluid flow concepts and how they may be applied to air
pollution control ventilation systems. Nonetheless, these
concepts will be given as straightforwardly as possible, with the
aim of making the design parameters easy to understand and
compute.
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10.3.1 Design Fundamentals
10.3.1.1 The Bernoulli Equation
The flow of fluids in any hood, duct, pipe, stack, or other
enclosure is governed by a single relationship, the familiar
Bernoulli equation. Put simply and ideally, the Bernoulli
equation states that the total mechanical energy of an element "of
flowing fluid is constant throughout the system. This includes
its potential energy, kinetic energy, and pressure energy.
However, as no system is ideal, the Bernoulli equation must be
adjusted to take into account losses to the surroundings due to
friction. Gains due to the energy added by fans, pumps, etc.,
also must be accounted for. For a pound mass (lbm) of fluid
flowing in a steady-state system the adjusted Bernoulli equation
is:24
Jvdp + Az(g/gc) + A(u2)/2gc = W - F (10.1)
where: v = specific volume of fluid (ft3/lbm)
p = static pressure—gauge (lbf/ft2)
z = height of fluid above some reference point (ft)
u = fluid velocity through duct, hood, etc. (ft/sec)
g = gravitational acceleration (ft/sec2)
gc = gravitational constant (32.174 ( [lbm-ft/sec2]/lbf)
W = work added by fan, etc. (ft-lbf/lbm)
F = energy lost due to friction (ft-lbf/lbm)
Each of the terms on the left hand side of equation 10.1
represents an energy change to a pound mass of fluid between two
locations in the system—points "1" and "2". The work (W) and
friction (F) terms denote the amounts of energy added/lost
between points 1 and 2.
Note that the units of each term in equation 10.1 are "ft-
lbf/lbm," energy per unit mass. In the English system of units,
"lbf" and "lbm" are, for all intents, numerically equivalent,
since the ratio of the gravitational acceleration term (g) to the
gravitational constant (gc) is very close to 1. In effect,
therefore, the equation units are "feet of fluid" or "fluid head
in feet". In air pollution control situations, the fluid often
has the properties of air. That is because the contaminants in
the waste gas stream are present in such small amounts that the
stream physical properties approximate those of pure air.
Because air is a "compressible" fluid, its specific volume
is much more sensitive to changes in pressure and temperature
than the specific volume of such "incompressible" fluids as
water. Hence, the "vdp" term in the equation has to be
integrated between points 1 and 2. However, in most air
pollution control ventilation systems neither the pressure nor
10-15
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the temperature changes appreciably from the point where the
emissions are captured to the inlet of the control device.
Consequently, the specific volume is, for all practical purposes,
constant throughout the ventilation system, and one does not have
to integrate the vdp term. With this assumption, the first term
in equation 10.1 becomes simply:
fvdp = vjdp = vAp (10.2)
Illustration: VOC emitted by an open tank is captured_by a hood
and conveyed, via a blower, through 150 feet of 12-inch diameter
ductwork to a refrigerated condenser outdoors. The blower, which
moves the gas through the hood, ductwork, and condenser, is
located immediately before the inlet to the condenser. Thus, the
entire ventilation system is under vacuum. The stream
temperature and absolute pressure are 100°F and approximately 1
atmosphere (14.696 lbf/in2) , respectively. The elevation of the
refrigerated condenser inlet is 30 feet below that of the tank.
The air velocity at the source is essentially zero, while the
duct transport velocity is 2,000 ft/min. The static gauge
pressure increases from -0.50 in. w.c. (water column) at the
source to 4.5 in. w.c. at the blower outlet. Finally, the
calculated friction loss through the ductwork and hood totals
1.25 in. w.c. Calculate the amount of mechanical energy that the
blower adds to the gas stream. Assume that the gas temperature
remains constant throughout.
Solution:
•^ First, develop a factor to convert "inches of water" to "feet
of air":
Feet of air = (Inches of water) (1 ft/12 in) (valoo/vwloo) (10.3)
where: vwloo = specific volume of water @ 100°F = 0.01613 ft3/lbm
valoo = specific volume of air @ 100°F, 1 atmosphere
Because the system absolute pressure is close to
atmospheric, the waste gas behaves as an ideal gas. Thus, the
specific volume can be calculated from the ideal gas law:
va = RT/pM (10.4)
where: R = ideal gas constant = 1,545 ft-lbf/(lbm-mole) (°R)
T = absolute temperature of gas = 100 + 460 = 560°R
M = molecular weight of gas (air) =
28.85 lbm/lbm-mole
p = absolute pressure = 2,116 lbf/ft2
Substituting, we obtain:
10-16
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va = 14. 17 ft3/lbm
Finally, substitution of these values for va and vw into equation
10.3 yields:
Feet of air (@ 100°F/ 1 atm.) = 73.207 x Inches of water
"S" Compute the changes in the mechanical energy terms and the
friction losses between the hood inlet (point 1) and the blower
outlet/condenser inlet (point 2):
Pressure: vAp = (4.5 - [-0.50] in. w.c.)(73.207 ft air/in, w.c.)
366.0 ft air
Potential: Az = -30 ft air (point 2 is below point 1)
Kinetic: Au2/2gc = ([2,000 f t/min] / [60 ft/min/1 ft/sec])2 x
(1/2) (32.174[lbm-ft/sec2]/lbf)-'
= 17.3 ft air
Friction losses: F = 1.25 in. w.c. x 73.207
= 91.5 ft air
"S" Substitute above results into equation 10.1 and solve for W,
the fan energy added:
366,0 + (-30) + 17.1 = W - 91.5, or
W = 444.6 ft-lbf/lbm air = 6.07 in. w.c.
To convert the fan energy input, W, to horsepower (hpf) , we.
would have to multiply it by the air mass flow rate (lbm/sec),
and divide the result by the horsepower conversion factor, 550
ft-lbf/sec-hp. However, the mass flow rate is just the volume
flow rate (Q, ftVsec) divided by the specific volume:
hpf = W(Q/v.) (1/550) = 0.001818WQ/va (10.5)
(The reader may wish to compare this equation to the fan
horsepower equation in Chapter 3 [page 3-55] of this manual.)
In turn, Q is a function of the duct velocity (u,, ft/sec) and
duct diameter (Dd, ft) :
Q = u,(7rDd2/4) (10.6)
Equation 10.6 applies, of course, only to circular ducts.
If we combine equations 10.5 and 10.6 and substitute the
inputs for this illustration, we obtain:
10-17
-------
hpf = (444.6) (2,000/60) (7T/4) (1) 2 (1/14 . 17) (1/550)
= 1.49 hp
Some observations about this illustration:
•®" Recall that the precise units for W and the other terms in
equation 10.1 are "ft-lbf/lbm air," which, for convenience, have
been shortened to "ft air". Thus, they measure energy, not
length.
"S" Compared to the pressure energy and friction terms, the
potential and kinetic energy terms are small. Had they been
ignored, the results would not have changed appreciably.
"^ The large magnitude of the pressure and friction terms clearly
illustrates the importance of keeping one's units straight. As
shown in step (1) , one inch of water is equivalent to over 73
feet of air. However, as equation 10.3 indicates, the pressure
corresponding to equivalent heights of air and water columns
would be the same.
ss' The fan power input depends not just on the total "head" (ft
air) required, but also on the gas flow rate. Also, note that
the horsepower computed via equation 10.5 is a theoretical value.
It would have to be adjusted to account for the efficiencies of
the fan and fan motor. As mentioned in Chapter 3, the fan
efficiency ranges from 40 to 70 percent, while the motor
efficiency is typically 90 percent. These efficiencies are
usually combined into a single efficiency (e, fraction), by which
the theoretical horsepower is divided to obtain the actual
horsepower requirement.
10.3.1.2 Pressure: Static, Velocity, and Total
Although it is more rigorous and consistent to express the
Bernoulli equation terms in terms of feet of air (or, precisely,
ft-lbf/lbm of air), industrial ventilation engineers prefer to
use the units "inches of water column (in. w.c.)." These units
were chosen because, as the above illustration shows, results
expressed in "feet of air" are often large numbers that are
cumbersome to use. In addition, the total pressure changes in
ventilation systems are relatively small, compared to those in
liquid flow systems. Total pressure changes expressed in inches
of mercury would be small numbers which are just as awkward to
work with as large numbers. Hence, "inches of water" is a
compromise, as values expressed in this measurement unit
typically range from only 1 to 10. Moreover, practical
measurement of pressure changes is done with water-filled
10-18
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manometers.
In the previous paragraph, a new quantity was mentioned,
total pressure (TP). Also known as the "impact pressure", the
total pressure is the sum of the static gauge (SP) and velocity
pressures (VP) at any point within a duct, hood, etc., all
expressed in in. w.c.25 That is:
TP = SP + VP (10.7)
where: SP = (cf)vp
VP = (cf)uY2gc
The "cf" in the expressions for SP and TP is the factor for
converting the energy terms from "ft air" to "in. w.c.", both at
standard temperature and absolute pressure (70°F, 1 atmosphere).
(Again, keep in mind that, regardless of what units SP or VP are
expressed in, the actual units are "energy per unit mass".) This
conversion factor would be obtained via rearranging equation
10.3:
cf = in. w.c./ft. air = 12 (vw70/va70) (10.8)
where: vw70 = specific volume of water at 70°F = 0.01605 (ft3/lbm)
va70 = specific volume of air at 70°F = 13.41 (ft3/lbm)
Thus: cf = 0.01436 in. w.c./ft air
Clearly, "cf" varies as a function of temperature and
pressure. For instance, at 100°F and 1 atmosphere, cf = 1/73.207
= 0.01366. Nevertheless, unless noted otherwise, all quantities
henceforth in this chapter will reflect conditions at 70°F and 1
atmosphere.
Conspicuously absent from equation 10.7 is the potential
energy term, "z(g/gc)". This omission was not inadvertent. In
ventilation systems, the potential energy (P.E.) is usually small
compared to the other terms. (For example, see illustration
above.) The P.E. is, of course, a function of the vertical
distance of the measurement point in question from some datum
level, usually the ground. At most, that distance would amount
to no more than 20 or 30 feet, corresponding to a P.E. of
approximately 0.3 to 0.4 in. w.c. Consequently, we can usually
ignore the P.E. contribution in ventilation systems without
introducing significant error.
The static gauge pressure in a duct is equal in all
directions, while the velocity pressure, a function of the
velocity, varies across the duct- face. The duct velocity is
highest at the center and lowest at the duct walls. However, for
air flowing in a long, straight duct, the average velocity (u,)
10-19
-------
approximates the center line velocity (ucl) .26 This is an
important point, for the average velocity is often measured by a
pitot tube situated at the center of the duct.
By substituting for "cf" in equation 10.7, we can obtain a
simple equation that relates velocity to velocity pressure at
standard conditions:
VP = 0.01436u2/2gc (10.9)
Solving:
ut (ft/sec) = 66.94 (VP) 1/2 (10.10)
Or:
u, (ft/min) = 4,016(VP)"2 (10.11)
Incidentally, these equations apply to any duct, regardless
of its shape.
As Burton describes it, static gauge pressure can be thought
of as the "stored" energy in a ventilation system. This stored
energy is converted to the kinetic energy of velocity and the
losses of friction (which are mainly heat, vibration, and noise).
Friction losses fall into several categories:27
o®1 Losses through straight duct
"3" Losses through duct fittings—elbows, tees, reducers, etc.
•S" Losses in branch and control device entries
•S" Losses in hoods due to turbulence, shock, vena contracta
°^ Losses in fans
"S" Losses in stacks
These losses will be discussed in later sections of this
chapter. Generally speaking, much more of the static gauge
pressure energy is lost to friction than is converted to velocity
pressure energy. It is customary to express these friction
losses (ASPf) in terms of the velocity pressure:
F = ASPf = kVP (10.12)
where: k = experimentally-determined loss factor (unitless)
10-20
-------
Alternatively, equations 10.11 and 10.12 may be combined to
express F (in. w.c.) in terms of the average duct velocity, ut
(ft/min):
F = (6.200 x 10'8)ku,2 (10.13)
10.3.1.3 Temperature and Pressure Adjustments
Equations 10.8 to 10.13 were developed assuming that the
waste gas stream was at standard temperature and pressure. These
conditions were defined as 70°F and 1 atmosphere (14.696 lbf/in2) ,
respectively. While 1 atmosphere is almost always taken as the
standard pressure, several different standard temperatures are
used in scientific and engineering calculations: 32°F, 68°F, and
77°F, as well as 70°F. The standard temperature selected varies
according to the industry or engineering discipline in question.
For instance, industrial hygienists and air conditioning
engineers prefer 70°F as a standard temperature, while combustion
engineers prefer 77°F, the standard temperature used in Chapter 3
("Thermal and Catalytic Incinerators").
Before these equations can be used with waste gas streams
not at 70°F and 1 atmosphere, their variables must be adjusted.
As noted above, waste gas streams in air pollution control
applications obey the ideal gas law. From this law the following
adjustment equation can be derived:
Q2 = Q,(T2/T,) (P,/P2) (10.14)
where: Q2,Qi = gas flow rates at conditions 2 and 1,
respectively (actual ft3/min)
T2,T, = absolute temperatures at conditions 2 and 1,
respectively (°R)
P2,P, = absolute pressures at conditions 2 and 1,
respectively (atm)
However, according to equation 10.6:
Q = ut(7rDd2/4)
If equations 10.6 and 10.14 were combined, we would obtain:
ut2 = u,,(T2/T,) (P,/P2) (Dd22/Ddl2) (10.15)
This last expression can be used to adjust u, in any
equation, as long as the gas flow is in circular ducts.
10-21
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10.3.2 Hood Design Procedure
10.3.2.1 Hood Design Factors
When designing a hood, several factors must be considered:28
os* Hood shape
BS> Volumetric flow rate
"& Capture velocity
°3" Friction
Each of these factors and their interrelationships will be
explained in this section.
As discussed in section 10.2.1, the hood shape is determined
by the nature of the source being controlled. This includes such
factors as the temperature and composition of the emissions, as
well as the dimensions and configuration of the emission stream.
Also important are such environmental factors as the velocity and
temperature of air currents in the vicinity.
The hood shape partly determines the volumetric flow rate
needed to capture the emissions. Because a hood is under
negative pressure, air is drawn to it from all directions.
Consider the simplest type of hood, a plain open-ended duct.
Now, envision an imaginary sphere surrounding the duct opening.
The center of this sphere would be at the center of the duct
opening, while the sphere radius would be the distance from the.
end of the duct to the point where emissions are captured. The
air would be drawn through this imaginary sphere and into the
duct hood. Now, the volume of air drawn through the sphere would
be the product of the sphere surface area and the hood capture
velocity, uc:29
Q = uc(47rx2) (10.16)
where: x = radius of imaginary sphere (ft)
Equation 10.16 applies to a duct whose diameter is small
relative to the sphere radius. However, if the duct diameter is
larger, the capture area will have to be reduced by the cross -
sectional area of the duct (Dd) , or:
Q = uc(47rx2 - 7rDd2/4) (10.17)
Similarly, if a flange were installed around the outside of
the duct end, the surface area through which the air was
drawn—and the volume flow rate—would be cut in half. That
occurs because the flange would, in effect, block the flow of air
from points behind it. Hence:
10-22
-------
Q = uc(27rx2) (10.18)
From these examples, it should be clear that the hood shape
has a direct bearing on the gas flow rate drawn into it. But
equations 10.16 to 10.18 apply only to hoods with spherical flow
patterns. To other hoods, other flow patterns
apply—cylindrical, planal, etc. We can generalize this
relationship between volumetric flow rate and hood design
parameters as follows:
Q = f(u,, x, Sh) ' (10.19)
where: "f(...)" denotes "function of..."
"Sh" indicates hood shape factors
u, = design velocity—capture, face, slot
Table 10.1 lists design equations for several commonly used
hood shapes. As this table shows, Q is a function of x, the hood
shape, and, in general, the capture velocity (uc). But in one
case (booth hood), the design velocity is the hood face velocity
(uf) . And in the case of slotted side-draft and back-draft
hoods, the slot velocity (us) is the design velocity. In
reality, both the hood face and slot velocities are the same, as
each measures the speed at which the gas passes through the hood
inlet opening(s).
When gas enters a hood, there is mechanical energy loss due
to friction. This friction loss is calculated using equations
10.1 and 10.2, assuming that the potential energy contribution
from gravity, Az(g/gc), and the work added to the system, W, are
both zero. Thus:
vp2 - vp, + u22/2gc - Ui2/2gc = - F (10.20)
Replacing these terms with the corresponding ones from
equations 10.7 and 10.12, we obtain:
SP2 - SP, + VP2 - VP, = - He = - khVP2 (10.21)
where: SP, = static gauge pressure at point i (in. w.c.)
VP; = velocity pressure at point i (in. w.c.)
Hc = hood entry loss (in. w.c.)
kh = hood loss factor (unitless)
In this equation, subscript 1 refers to a point just outside
the hood face. Subscript 2 denotes the point in the duct, just
downstream of the hood, where the duct static pressure, SP2 or
SPh, and the duct transport velocity, u2 or ut, are measured. At
point 1, the hood velocity pressure, VP,, is essentially zero, as
the air velocity there is negligible. -Moreover, the static gauge
10-23
-------
Table 10.1 Design Equations, Loss Factors, and Coefficients of
Entry for Selected Hood Types*
Hood Type
Duct end
(round)
Flanged duct
end (round)
Free - standing
slot hood
Slot hood
w/sides, back
Tapered hood
Booth hood with
tapered take-off
duct (round)
Canopy hood
Canopy hood
w/ insert
Dip tank hood
(slotted)
Paint booth
hood
Design
Equation*
Q = 47TX2UC
Q = 2irx2uc
Q = 27TXLUC
Q = 0.57rxLuc
Q = 2?rxuc
Q = uA,
Q = l,4Pxuc
Q = l,4Pxuc
Q = 125A,
Q = lOOAfc
Loss Factor
(*h)
0.93
0.50
1.78
1.78
0.06tf
0.25
0.25
1.0
1.78
0.25
Coefficient of
Entry (Ce)
0.72
0.82
0.55
n.a.§s
0.97
0.89
0.89
0.71
n.a.
n.a.
* Reference: Burton, D. Jeff. Industrial Ventilation Work
Book. Salt Lake City: DJBA, Inc. 1989.
In the equations: Q = flow rate drawn into hood (ft3/min)
= distance from hood to source (ft)
= hood capture velocity (ft/min)
= hood face velocity (ft/min)
= hood slot velocity (ft/min)
= hood face area (ft2)
= perimeter of source (ft)
= width of hood slot (ft)
= tank + drainboard surface area (ft2)
= booth cross -sectional area (ft2)
x
uc
uf
us
P
L
A,
A,,
§§ Nc-t applicable.
45
n Both kh and Cc pertain to round ducts and to hoods with a
taper. At other angles, kh and Cc will differ.
10-24
-------
pressure, SP,, will be zero, as the absolute pressure at point 1
is assumed to be at one atmosphere, the reference pressure.
After these simplifications are made, equation 10.21 can be
rearranged to solve for the hood loss factor (kh) :
kh = (-SPh/VP2) - 1 (10.22)
At first glance, it appears that kh could be negative, since
VP is always positive. However, as the air entering the hood is
under a vacuum created by a fan downstream, SPh must be negative.
Thus, the term "-SPh/VP2" must be positive. Finally, because the
absolute value of SPh is larger than VP2, kh > 0 .
The hood loss factor varies according to the hood shape. It
can range from 0.04 for bell mouth hoods to 1.78 for various
slotted hoods. A parameter related to the hood loss factor is
the coefficient of entry (cc) .30 This is defined as:
ce = {l/(l+kh) }1/2 (10.23)
ce depends solely on the shape of the hood, and may be used to
compute kh and related parameters. Values of kh and cc are listed
in Table 10.1.
Illustration: The static gauge pressure, SPh, is -1.75 in. w.c.
The duct transport velocity (ut) is 3,500 ft/min. Calculate the
loss factor and coefficient of entry for the hood. Assume
standard temperature and pressure.
Solution: First, calculate the duct velocity pressure. By
rearranging equation 10.11 and substituting for u,, we obtain:
VP = (ut/4,016)2 = (3,500/4,016)2 = 0.76 in. w.c.
Next, substitute for VP in equation 10.22 and solve:
kh = (-SPh/VP) - 1 = (- [-1.75] /0.76) - 1 = 1.30.
Finally, use this value and equation 10.23 to calculate the
coefficient of entry:
ce = {l/(l + 1.30) }"2 = 0.66.
Hood design velocities are listed in Table 10.2. Three
kinds of velocities are shown: (1) capture (defined in Section
10.2.1), (2) face, and (3) slot. As stated in Section 10.2.1,
the capture velocity is the air velocity induced by the hood to
capture contaminants emitted at some distance from the hood
inlet. The face velocity is the average velocity of the air
10-25
-------
passing through the hood inlet (face). A similar parameter is
the slot velocity, which is the average air velocity through the
hood slot openings, whose area is only a fraction of the entire
hood face area. Consequently, the slot velocity is usually much
higher than the face velocity.31
Note that these velocities range from 50 to 100 ft/min (tank
and degreasing hoods) to 2,000 ft/min, the recommended slot
velocity for slotted side-draft/back-draft hoods. As a reference
point, the velocity of air in industrial operations due to
thermal mixing alone is 50 ft/min. Thus, hood design velocities
must exceed this value if effective capture is to occur. 32
Two other velocities are also discussed in the industrial
hygiene literature, although they do not have as much bearing on
hood design as the capture, face, or slot velocities. These are
the plenum velocity and the transport velocity. The first is the
velocity of the gas stream as it passes through the tapered
portion of a hood (plenum) between the hood opening and the duct
connection. This plenum is a transition area between the hood
opening and duct. Consequently, the plenum velocity is higher
than the hood face velocity, but lower than the duct (transport)
velocity. The transport velocity—the gas velocity through the
duct—varies according to the waste gas composition. It is a
crucial parameter in determining the duct diameter, the static
pressure loss, and the sizes of the system fan and fan motor.
(For more on transport velocity, see Section 10.3.3.)
10.3,2.2 Hood Sizing Procedure
As witn many control devices and auxiliaries, there are
several approaches to sizing hoods. Some of these approaches are
quite complex, entailing a series of complex calculations that
yield correspondingly accurate results. For instance, one hood
sizing method in the literature involves first determining the
hood dimensions (length and width for rectangular hoods;
diameter, for circular). The next step is to estimate the amount
of metal plate area (ft2) required to fabricate a hood of these
dimensions, via parametric curves. (No curves are provided for
nonmetal hoods.) This plate area is input to an equation that
includes a "pricing factor" and the per-pound price of metal.
The cost of labor needed to fabricate this hood is estimated from
equations similar to the plate-area relationships. Finally, the
metal and labor costs are summed to obtain the total fabricated
hood cost.33
This method does yield reasonably accurate hood cost—or
rather, it did. Unfortunately, the labor cost data are
outdated—1977 vintage—which makes them unescalatabler (The
rule-of-thumb time limit for escalating costs is five years.)
Even if the costs were up-to-date, the procedure is cumbersome to
10-26
-------
use, especially if calculations are made by hand.
A simpler sizing method—yet one sufficiently accurate for
study estimating purposes involves determining a single
dimension, the hood face area (A,-) . This area, identical to the
hood inlet area, can be correlated against the fabricated hood
cost to yield a relatively simple cost equation with a single
independent variable. To calculate A,-, the following information
is needed:
•®" Hood type
"S" Distance of the hood face from source (x)
•®* Capture (uc) , face (uf) , or slot velocity (us)
•®" Source dimensions (for some hood types).
As the equations in Table 10.1 indicate, these same
parameters are the ones that are used to determine the volumetric
flow rate (Q) through the hood and ductwork. With most control
devices and auxiliaries being sized, Q is given. For hoods,
however, Q usually must be calculated.
Illustration: A circular canopy hood is being used to capture
emissions from a chromium electroplating tank. The hood face is
6 feet above the tank, an 8-foot diameter circular vessel. The
capture velocity for this example is 200 ft/min. Assuming that
the tank and surroundings are at standard conditions, calculate
the required volumetric flow rate drawn into the hood, the hood
face area, and the hood face velocity.
Solution: Obtain the canopy hood equation from Table 10.1:
Q = 1.4Pxuc (10.24)
where: P = perimeter of tank (ft)
x = distance of hood above tank (ft)
uc = capture velocity (ft/min)
Because the tank is circular, P = 7r(8) = 25.1 ft.
Therefore:
Q = (1.4) (25.1) (6) (200) = 42,200 ft3/min.
For this type of canopy hood, the hood diameter is 40%
greater than the tank diameter (hence, the "1.4" factor in
equation 10.24). Thus:
A,- = (7T/4) ( [1.4] [8] )2 = 98.5 ft2
Finally, the hood face velocity (uf) would be:
10-27
-------
Table 10.2 Hood Design Velocities**
Operation/Hood Type
Tanks, degreasing
Drying oven
Spray booth
Canopy hood
Grinding, abrasive
blasting
Slot hood
Velocity Type
Capture
Face
Capture
Capture
Capture
Slot
Velocity Range
(ft/min)
50 -" 100
75 - 125
100 - 200
200 - 500
500 - 2,000
2,000
** Reference: Burton, D. Jeff. Industrial Ventilation Work
Book. Salt Lake City: DJBA, Inc. 1989.
10-28
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Uf = Q/Af = 42,200/98.5 = 428 ft/min.
In this example, note that the hood face velocity is higher
than the capture velocity. This is logical, given the fact that
the hood inlet area is smaller than the area through which the
tank fumes are being drawn. The face velocity for some hoods is
even higher. For example, for slotted hoods it is at least 1,000
ft/min.34 In fact, one vendor sizes the openings in his slotted
hoods so as to achieve a slot velocity equal to the duct
transport velocity.35
10.3.3 Ductwork Design Procedure
The design of ductwork can be an extremely complex
undertaking. Determining the number, placement, and dimensions
of ductwork components—straight duct, elbows, tees, dampers,
etc.—can be tedious and time-consuming. However, for purposes
of making study-level control system cost estimates, such
involved design procedures are not necessary. Instead, a much
simpler ductwork sizing method can be devised.
10.3.3.1 Two Ductwork Design Approaches
There are two commonly used methods for sizing and pricing
ductwork. In the first, the total weight of duct is computed
from the number and dimensions of the several components. Next,
this weight is multiplied by a single price (in $/lb) to obtain
the ductwork equipment cost. To determine the ductwork weight,
one needs to know the diameter, length, and wall thickness of
every component in the system. As stated above, obtaining these
data can be a significant effort.
The second method is a variation of the first. In this
technique, the ductwork components are sized and priced
individually. The straight duct is typically priced as a
function of length, diameter, and wall thickness, as well as, of
course, the material of construction. The elbows, tees, and
other fittings are priced according to all of these factors,
except for length. Other variables, such as the amount and type
of insulation, also affect the price. Because it provides more
detail and precision, the second method will be used in this
chapter.
10.3.3.2 Ductwork Design Parameters
Again, the primary ductwork sizing variable are length,
diameter, and wall thickness, ~Another parameter is the amount of
insulation required, if any.
10-29
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•*" Length: The length of ductwork needed with an air pollution
control system depends on such factors as the distance of the
source from the control device and the number of directional
changes required. Without having specific knowledge of the
source layout, it is impossible to determine this length
accurately. It could range from 20 to 2,000 feet or more. It is
best to give the straight duct cost on a $/ft basis and let the
reader provide the length. This length must be part of the
specifications of the emission source at which the ductwork is
installed.
•*" Diameter: As discussed in Section 10.2.2., circular duct is
preferred over rectangular, oval, or other duct shapes.
Therefore:
A,, = 7TD//4 (10.25)
where: AJ = cross-sectional area of duct (ft2)
Dd = duct diameter (ft)
The duct cross-sectional area is the quotient of the volumetric
flow rate (Q) and the duct transport velocity (ut) :
AJ = Q/u, (10.26)
Combining equations 10.25 and 10.26 and solving for Dd:
Dd = 1.128(Q/u()1/2 (10.27)
As Q is usually known, the key variable in equation 10.27 is
the duct transport velocity. This variable must be chosen
carefully. If the u( selected is too low, the duct will be
oversized and, more importantly, the velocity will not be high
enough to convey the particulate--matter in the waste gas stream
to the control device. However, if ut is too high, the static
pressure drop (which is proportional to the square of ut) will be
excessive, as will be the corresponding fan power consumption.
Cost is also a consideration when determining the optimum
duct diameter. The equipment cost increases with increasing duct
diameter. However, the fan power cost changes inversely with
diameter. Nonetheless, for study-estimating purposes, the
optimum duct diameter does not have to be determined. It is
sufficient to calculate the duct diameter merely by using the
transport velocity values contained in this section.
The transport velocity typically varies from 2,000 to 6,000
ft/min, depending on the waste gas composition. The_ Tower duct
velocity would be adequate for a waste gas containing gaseous
pollutants or very fine, light dusts, while the higher velocity
would be needed to convey a stream with a large quantity of
10-30
-------
metals or other heavy or moist materials. The following
velocities may be used as general guidance:36
Material (s) Conveyed
Gases; very fine, light dusts
Fine, dry dusts and powders
Average industrial dusts
Coarse dusts
Heavy or moist dust loading
Minimum Transport Velocity
(ut, ft/min)
2,000
3, 000
3,500
4,000 - 4,500
> 4,500
Table 10.3 supplements these values with recommended duct
velocities for a variety of conveyed materials.
**" Wall thickness: The wall thickness of a duct depends on
several factors—internal pressure, diameter, material of
fabrication, and other structural parameters. Nonetheless, duct
of a given diameter can be fabricated of a range of wall
thicknesses, and vice-versa. For instance, 24-in. diameter 304
stainless steel "fully-welded longitudinal seam duct" is
fabricated in thicknesses ranging from 22 to 14 gauge (0.0313 to
0.0781 in.). This same range of gauges is used with duct
diameters ranging from 3 to 36 in.37
Note that the gauge number decreases with increasing wall
thickness. This measure, which is traditionally used in the
metal fabricating industries, is more convenient to deal with
than the thickness expressed in inches, as the latter are usually
small numbers less than 0.25. Moreover, the gauge number varies
according to the metal used—carbon steel (galvanized or
nongalvanized), stainless steel, or aluminum. Gauges for these
metals are given in Table 10.4 for a wide range of nominal
thicknesses.
The gauge measure is not used with plastic duct, as the wall
thickness is typically expressed in inches. In any event, the
wall thickness usually does not need to be known to estimate duct
cost, as this parameter is already accounted for in the cost
equations. (See Section 10.4.)
•S" Insulation: As discussed in Section 10.2.2., insulation can be
either installed on the outer surface of ductwork or the ductwork
itself can be fabricated with built-in insulation. In the "first
case, the amount of insulation required will depend on several
heat transfer variables, such as: the temperature, velocity,
10-31
-------
composition, and other properties of the waste gas; the ambient
temperature; the duct diameter, wall thickness, and thermal
conductivity; and the desired surface ("skin") temperature.
Determining these variables involves making a series of complex
calculations that, while well-established, are beyond the scope
of this chapter. Such standard references as Perry's Chemical
Engineers' Handbook and Plant Design and Economics for Chemical
Engineers present these calculations, as do heat transfer
bibliographies.38-39
The second approach is to select pre-insulated ductwork. As
mentioned previously, it can be equipped with any type and
thickness of insulation. However, 1, 2, or 3 inches is typical.
(Prices for these are presented in Section 10.4.)
10.3.3.3 Ductwork Pressure Drop
As mentioned in Section 10.3.1, ventilation system energy
losses due to friction are traditionally computed as fractions of
the velocity pressure, VP. In most cases, equation 10.12 can be
used to estimate these losses. Technically, though, these
equations apply only to those regions in the ventilation system
where there are no changes in the velocity pressure (i.e., where
the duct diameter is constant). These regions would include
straight duct, hoods, and such fittings as couplings and simple
elbows. But, with tees, wyes, and other divided flow fittings,
the velocity—and velocity pressure—are .not constant between the
fitting inlet and outlet. The corresponding friction loss (Fb)
is a function of both the upstream (inlet) and branch VP's, as
the following equation indicates:40
Fb = VPu(kh-l) + VPb (10.28)
where: VPU, VPb = upstream and branch velocity pressures,
respectively (in. w.c.)
kb = branch loss coefficient
However, divided flow fittings generally are not used with simple
pollution control ventilation systems, except in those cases
where a tee might be needed, say, for purposes of adding dilution
air.§
As any fluid mechanics textbook would attest, the friction
loss for ductwork is a complex function of several variables:
§ Divided flow fittings are needed with more-complex
control systems that collect waste gases from several emission
points. The design of such ventilation systems is beyond the
scope of this chapter, however.
10-32
-------
Table 10.3 Minimum Duct Velocities for Selected Materials5
Material
Aluminum dust (coarse)
Brass turnings
Cast iron boring dust
Clay dust
Coal dust (powdered)
Cocoa dust
Cotton dust
Flour dust
Foundry dust
Grain dust
Lead dust
Limestone dust
Magnesium dust (coarse)
Metal turnings
Plastics dust (buffing)
Rubber dust
Silica dust
Soap dust
Soapstone dust
Spray paint
Starch dust
Stone dust
Tobacco dust
Minimum Transport Velocity
(ft/min)
4,000
4,000
4, 000
3,500
4,000
3,000
3,000
2,500
3,000 - 5,000f
2,500 - 3,000
4,000
3,500
4,000
4,000 - 5,000
3,000
2,500 (fine) - 4,000 (coarse)
3,500 - 4,500
3,000
3,000
2,000
3,000
3,500
3,500
§ Reference: Burton, D. Jeff. Industrial Ventilation Work
Book. Salt Lake City: DJBA, Inc. 1989.
1 Transport velocity varies with foundry operation.
10-33
-------
Table 10.4 Wall Thicknesses of Steel and Aluminum Duct5
Gauge
Number
28
26
24
22
20
18
16
14
12
10
Nominal Thickness (inches)
Carbon Steel
Galv*
0.0187
0.0217
0.0276
0.0336
0.0396
0.0516
0.0635
0.0785
0.1084
0.1382
Nongalv*
0.0149
0.0179
0.0239
0.0299
0.0359
0.0478
0.0598
0.0747
0.1046
0.1345
Stainless Steel
(304 or 316)
0.0156
0.0188
0.0250
0.0313
0.0375
0.0500
0.0625
0.0781
0.1094
0.1406
Aluminum
3003-H14t
0.025
0.032
0.040
0.050
0.063
0.080
0.090
§ Reference: Engineering Design Reference Manual for Supply
Air Handling Systems. Groveport, OH: United McGill Corporation.
1992.
f To provide equivalent strength and stiffness, the nominal
thickness of aluminum is approximately 150% of the nominal
thickness of galvanized carbon steel of the same gauge.
* Galvanized and paintable galvanized carbon steel.
* Nongalvanized carbon steel.
10-34
-------
duct diameter and length, transport velocity, and gas viscosity
and density. Specifically, the Darcy-Weisbach and Colebrook
equations are typically used to make this calculation, the latter
being used to compute the .Reynolds number.41 Traditionally, the
friction loss has been obtained from a nomograph or, more
recently, computer programs. A typical nomograph is found in
Burton. 2 Also, to simplify the calculation, empirical equations
have been derived for certain kinds of commerically-available
ductwork. For instance, to estimate the friction loss per 100 ft
(Fd/100 ft) at standard conditions for round, spiral, galvanized
ductwork having 10 joints per 100 ft, use the following
equation:
43
Fd/100 ft = 0.136 (l/D)L!8(ul/l,000)L8
where: Dd = duct diameter (ft) , and: 0.25 < Dd < 5
(10.29)
Clearly, this equation provides the total friction loss, not the
loss factor (k). However, the reader may compute k for a given
diameter (Dd) and flow rate (Q) by simply dividing the equation
10.29 results by VP and multiplying by 100.
To estimate the friction loss for other duct materials,
multiply the value from equation 10.29 by a roughness correction
factor, approximate values of which are:
Material
Non- spiral -wound galvanized
Fiberglass (smooth finish)
ABS and PVC plastic
Concrete
Corrugated flex duct
Roughness Correction Factor
0.9
0.8
0.8
1.4
2.3
Loss factors for fittings have also been compiled, based on
experimental data. Mainly of interest are those for 90° elbows,
arguably the most commonly used fitting in air pollution control
systems. The "k90" values for elbows vary according to the
diameter and radius of curvature, which is expressed as a
multiple of the elbow diameter. Typical ranges of these values
are as follows:45
10-35
-------
Radius of
0.
1.
1.
1.
2.
2.
Curvature
50
00
25
50
00
50
Friction
0.
0.
0.
0.
Loss Factor (k90)
0
0
30
27
24
22
.80
.35
- 0
- 0
- 0
- 0
.55
.39
.27
.24
As these values indicate, the higher the radius of
curvature, the lower the friction loss. This stands to reason,
as the higher the radius of curvature, the more gradually the gas
stream changes direction. For an elbow having of angle less than
90°, multiply the above k^ value by an adjustment factor (6/90),
so that:
k, = (0/90)k90
where: k« = loss factor for 6 < 90°
(10.30)
Illustration: A control device at a cosmetic factory is connected
to a source by 250 feet of round spiral duct. The duct run
includes three 90° elbows and two 45° elbows, each with a 1.50
radius of curvature. The volumetric flow rate (Q) of the waste
gas (which contains entrained face powder) is 15,000 ftVmin at
standard conditions. Calculate the friction loss for the
ductwork.
Solution: Because the material being conveyed in the ductwork
(face powder) is light, an appropriate transport velocity (u,) in
this case is 2,000 ft/min. (See text table above.) Upon
substituting this value and the volumetric flow rate into
equation 10.27 we obtain the duct diameter (Dd) :
Dd = 1.128 (15, 000/2, OOO)0'5 = 3.09 ft
Next, substitute the diameter and velocity into equation 10.29 to
compute the straight duct friction (static pressure) loss, Fd:
Fd = 0.136 (1/3 .09) K18(2, 000/1,000) L8(250/100)
= 0.313 in. w.c.
The 250/100 factor in this expression adjusts the friction loss
from 100 feet (the basis of equation 10.29) to 250 feet (the
length of the duct system in this illustration).
10-36
-------
The rest of the friction loss occurs through the five elbows
(three 90°, two 45°), each with a 1.50 radius of curvature.
These losses (Fe) are computed via equation 10.12:
Fe =
where: VP = (2 , 000/4, 016) 2 (equation 10.11, rearranged)
= 0.248 in. w.c.
For the 90° elbows, ks = k90 = 0.33 (average of table range) , and
Fe = 3 x 0.33(0.248) = 0.246 in. w.c.
For the 45° elbows, k# = (45/90)k90 = 0.165 (equation 10.30),
and:
Fe = 2 x 0.165(0.248) = 0.0818 in. w.c.
The total friction loss is, therefore:
F = 0.313 + 0.246 + 0.0818 = 0.641 in. w.c.
From this illustration, two observations may be made: (1)
the static pressure loss through the straight duct is not large,
even at this length (250 ft.) and (2) the losses through the
elbows—which total 0.328 in. w.c.—are larger than the straight
duct loss. Though it may be tempting to neglect fittings losses
for the sake of expediency, doing so can cause a significant
underestimation of the ventilation system static pressure loss.
10.3.4 Stack Design Procedures
As with ductwork, the design of stacks involves a number of
stream, structural, and site-specific parameters.46'47 These
include:
"3° Waste gas variables: inlet volumetric flow rate, temperature,
and composition;
"S" Site-specific data: elevation above sea level, ambient
temperature fluctuations, topographic and seismic data,
meteorological records, and building elevations and layout;
t®" Structural parameters: thickness of stack wall and liner,
location of breeching opening, type of supports, load capacity of
foundation, modulus of resistance, and natural vibration
frequency.
10-37
-------
Fortunately, for study cost-estimating purposes, the only
two stack design parameters that need to be determined are: (1)
the stack diameter and (2) the stack height. The other variables
(e.g., wall thickness) are incorporated into the equipment cost
correlations. The stack diameter is relatively easy to
determine, as it depends primarily on waste stream conditions.
The stack height is more difficult to arrive at, as it is
influenced by several site-specific variables. Nonetheless,
ample guidance has been developed to allow the estimator to
determine an acceptably accurate stack height.
10.3.4.1 Calculating Stack Diameter
Because most stacks have circular cross-sections, the stack
diameter (Ds, ft) can be calculated via the duct diameter formula
(equation 10.27):
Ds = 1.128(Qe/uc)1/2 (10.31)
where: uc = stack exit velocity (ft/min)
Qc = exit volumetric flow rate (actual ft3/min)
It should be noted that the stack diameter in this formula
is measured at the stack exit, not at the entrance. That is
because, for structural reasons, the diameter at the bottom of
the stack typically is larger than the top diameter. Also note
that the stack exit velocity does not necessarily equal the duct
transport velocity. Finally, Qe may be different from the
volumetric flow rate used to size the ductwork. Because the
stack always follows the control device, the flow rate entering ••
the device may not equal the flow rate entering the stack, either
in standard or actual ft3/min terms. For instance, in a thermal
incinerator, the outlet standard waste gas flow rate is almost
always higher than the inlet flow rate due to the addition of
supplemental fuel.
The stack exit velocity, ue, affects the plume height, the
distance that the plume rises above the top of the stack once it
exits. In a well-designed stack, ue should be 1.5 times the wind
speed. Typically, design exit velocities of 3,000 to 4,000
ft/min are adequate.48 This range corresponds to wind speeds of
34 to 45 mi/hr.
10.3.4.2 Calculating Stack Height
Estimating the stack height is more difficult than
calculating the stack exit diameter. The stack height depends on
several variables: the height of the source; the stack exit
velocity; the stack and ambient temperatures; the height, shape,
and arrangement of the nearby structures and terrain; and the
composition of the stack outlet gas. Some of these variables are
10-38
-------
straightforward to determine, while others (such as the
dimensions and layout of nearby structures) are difficult to
determine without performing on-site modeling and monitoring
studies.
This height has two components: the height of the stack
itself (Hs) and the plume rise height (Hpr) . Together these
components comprise the effective stack height (He) . That is:
He = Hs + H,,r (10.32)
However, the cost of the stack is a function of Hs alone.
(See Section 10.4.) As discussed above, the plume rise is a
function of the stack exit velocity. It also depends on the
temperature differential between the stack gas and the ambient
air. Specifically, a 1°F temperature difference corresponds to
approximately a 2.5-ft. increase in Hpr.49
For those sources subject to State Implementation Plans
(SIPs) , the stack height (Hs) should be determined according to
"good engineering practice" (GEP). GEP is defined as "the height
necessary to insure that emissions from the stack do not result
in excessive concentrations of any air pollutant in the immediate
vicinity of the source as a result of atmospheric downwash,
eddies, or wakes which may be created by the source itself,
nearby structures, or nearby terrain obstacles."50 In this
respect, GEP establishes the maximum allowable stack height
credit for purposes of calculating the ambient air quality impact
of the emitting source. A source may build a stack to any
height, but only a certain amount of stack height will be allowed
in determining environmental impacts.51
For stacks constructed after January 12, 1979, the GEP stack
height shall be the greater of: (1) 65 meters (213 ft); (2) the
height demonstrated by an approved fluid model or field study
that ensures that stack emissions do not cause excessive
pollutant concentrations from atmospheric downwash, wakes, eddy
effects., etc; or (3) the height determined by the following
equation:52
Hs = Hh + 1.5L (10.33)
where: Hs = GEP stack height, measured from the ground level
elevation at the stack base (ft)
Hb = height of nearby structure(s) measured from this
ground level elevation (ft)
L = lesser dimension (height or projected width of
nearby structure(s))
10-39
-------
10.3.4.3 Calculating Stack Draft
As discussed previously, waste gas flowing through hoods and
ductwork loses static pressure due to friction. In the case of
stacks, however, the gas stream can actually gain static
pressure, as a result of stack draft, which is the draft created
by the stack gas-ambient air temperature differential. Stack
draft (SPS, in. w.c.) can be calculated as follows:53
SPS = 0.034(HS - HJIICL/T^,, - 1/TJ (10.34)
where: Hhr = height of stack breeching (inlet duct
connection)
above stack base (ft)
II = barometric pressure (in. w.c.)
Tamb = ambient temperature (°R)
Tsa = average stack gas temperature (°R)
Illustration: The waste gas from a thermal incinerator has an
outlet flow rate and temperature of 21,700 actual ftVmin. and
550°F, respectively. The maximum wind speed in the vicinity is
42 mi/hr, while the stack exit and ambient temperatures are 450 °F
and 70°F, in turn. The barometric pressure is 1 atm. (29.92 in.
Hg) . The incinerator is near a 35-ft tall brick building, while
the "projected width" of an adjacent building is 40 ft. For a
stack to disperse the incinerator off gas, calculate the required:
(1) exit velocity, (2) diameter, (3) height, and (4) draft.
Solution:
n®" Exit velocity: According to the above guideline, the velocity
should be 1.5 times the wind speed, or:
ue = 1.5 x 42 mph x 88 fpm/mph = 5,540 ft/min.
"S" Stack diameter: The exit volumetric flow rate is measured at
the stack exit temperature, namely 450 °F. However, the above
flow rate was measured at 550 °F, the incinerator outlet
temperature. Correcting to the stack exit temperature, we
obtain:
Qe = 21,700 x (450 + 460)/(550 + 460) = 19,600 actual
Substituting this value into equation 10.31:
Ds = 1.128 (19, 600/5, 540)"2 = 2.12 ft.
"^ Stack height: As a first approximation, estimate the GEP stack
height from equation 10.33, where the variables Hh and L are 35
ft and 40 ft, respectively:
10-40
-------
Hs = 35 + 1.5 (40) = 95 ft.
Clearly, this Hs is less than the GEP maximum height (213 ft) , so
it will be used in this example.
DS=> Stack draft: All of the inputs needed to compute the stack
draft via equation 10.34 are known except the stack breeching
height, Hbr. However, a minimum of 5 ft is recommended for this
parameter.54 This value will be used in this calculation. Also,
the average stack temperature is:
Tas = (450 + 550)/2 + 460 = 960°R.
Finally, the barometric pressure expressed in inches of water is:
II = 29.92 in. Hg x 13.6 in. water/in. Hg = 407 in. w.c.
Upon substitution, we obtain:
SPS = 0.034(118 - 5) (407) (I/[70 + 460] - 1/960) = 1.32 w.c.
10.4 Estimating Total Capital Investment
This section presents the information needed for estimating
the total capital investment (TCI) for hoods, ductwork, and
stacks. The TCI includes the equipment cost (EC) for the hood,
ductwork, or stack; taxes; freight charges; instrumentation (if
applicable); and direct and installation costs. All costs are
presented in second quarter 1993 dollars, and are of "study"
estimate accuracy (+ 30 percent). Moreover, the costs are for
new facility installations; no retrofit costs are included.
The equipment costs are presented in Section 10.4.1, while
the installation costs are shown in Section 10.4.2. In each of
these sections, the three categories of equipment are covered in
separate subsections.
10.4.1 Equipment Costs
Several vendors provided costs (prices) for each of the
three equipment categories. Their responses reflected a range of
sizes, designs, and materials of construction. These prices have
been correlated against some easy-to-determine design (sizing)
parameter via least-squares regression analysis. Each of these
correlations pertains to a certain type of equipment (e.g.,
circular canopy hoods) within a specified size range of the
parameter in question (e.g., 2 to 200 ft2 inlet area). For that
reason, a cost correlation should not be extrapolated outside the
10-41
-------
parameter range specified.
Some of the prices the vendors provided pertain to stock
("off-the-shelf") items, while other costs are for custom-
fabricated equipment. Vendors tend to specialize in either stock
or custom items. Most hoods and stacks are custom-made, either
fabricated in the vendor's factory or erected on-site.
Conversely, ductwork components usually are stock items, though
larger pieces have to be custom-made. (Of course, there are
exceptions to this.) Finally, all prices given in the following
section are "F.O.B. (f ree-on-board) vendor," meaning that they
include neither freight nor taxes.
10.4.1.1 Hood Costs
In all, four vendors provided prices for hoods.55 These
prices covered the following types of hoods:
"S" Canopy — circular
"S" Canopy — rectangular
os" Push-pull
«®" Side-draft
"®" Back-draft (slotted)
Descriptions and design procedures for these hoods are given
in Sections 10.2.1 and 10.3.2, respectively. As explained in
Section 10.3.2, hood costs have been found to correlate well with
the hood inlet or face area (Af, ft2) . Furthermore, the
functional form that best fits the cost- face area correlation
(equation) is the "power function", or:
Ch = aAfb (10.35)
where: Ch = hood cost ($)
a,b = equation regression parameters
The values of the equation parameters vary according to hood
type and material of construction. These parameters are shown in
Table 10.5.
Illustration: What would be the cost of the electroplating tank
canopy hood sized for the illustration in Section 10.3.2.? Assume
that the hood is fabricated of FRP.
Solution: Recall that the face area (A,-) calculated for that hood
was 98.5 ft2. Because this is a circular canopy hood, the equation
parameters from Table 10.5 are: a = 123 and b = 0.575. (Note that
10-42
-------
Table 10.5 Parameters for Hood Cost Equation5
Type of
Hood
Canopy -
circular
Canopy -
rectangular
Push-pull
Side-draft
Backdraft
(slotted)
Backdraft
(slotted)
Backdraft
(slotted)
Backdraft
(slotted)
Backdraft
(slotted)
Fabrication
Material
FRPf
FRP
FRP
FRP
PVC*'*
PVCft
pp*t
FRP
Galvanized
Steel
Equation Parameter
a
123
294
595
476
303
789
645
928
688
b
0.575
0.505
0.318
0.332
1.43
0.503
0.714
0.516
0.687
Equation
Range
(Af, ft2)
2-200
2-200
2-200
2-200
0.6-2.0§§
1.1-2.1
1.1-2.1 -
1.1-2.1
0.5-1.3.
§ Based on data received from hood vendors. (See Reference
52.)
^ Fiberglass-reinforced plastic.
* Polyvinyl chloride.
* Each hood is equipped with two rows of slots, but no
dampers.
§§ For each slotted hood, "equation range" denotes the range
in the area of the slot openings, which is much less than the
total hood face area.
n Each hood is equipped with manual slot dampers and four
rows of slots.
** Polypropylene.
10-43
-------
this hood area falls within the equation range of 2 to 200 ft2.)
Substituting these parameters into equation 10.35, we obtain:
Ch = 123 (98.5)0575 = $1,720.
10.4.1.2 Ductwork Costs
Several vendors provided ductwork prices, also for a range of
sizes, materials, and designs.56 These prices covered the
following equipment items:
os* Straight ductwork:
* Circular
A Steel sheet (galvanized carbon, w/ & w/o
insulation; 304 stainless;)
A Steel plate (coated carbon; 304 stainless)
A Plastic (FRP; PVC)
* Square
A Steel (aluminized carbon; w/ & w/o insulation)
•S" Elbows (90°) :
4 Steel (galvanized carbon, w/ & w/o insulation;
304 stainless)
4 Plastic (FRP; PVC)
"S" Dampers:
4 Butterfly
A Steel (galvanized carbon, w/ & w/o insulation)
A Plastic (FRP; PVC, w/ & w/o actuators)
4 Louvered
A Steel (aluminized carbon w/ & w/o actuators)
4 Blast gate
A Steel (carbon)
A PVC
These prices were regressed against the diameter of the
equipment item (straight duct, elbow, or damper). The regression
correlations were of three forms: power function (primarily),
exponential, and linear. Equation 10.35 depicts the power
function, while the other forms are:
10-44
-------
Exponential: C, = aebD (10.36)
Linear: C, = a + bD (10.37)
where: Cj = cost of equipment item in question
a,b = regression parameters
The regression parameters are listed in Tables 10.6 to 10.-8,
along with the size applicability ranges for the respective
correlations. (Note: The correlations should not Jbe extrapolated
outside these ranges.) The following paragraphs contain additional
information about the price data and the correlations:
H Straight duct: As indicated above, vendors provided prices for
steel plate, steel sheet (spiral-wound and longitudinal seam), and
plastic straight duct. The major difference between the two steel
duct types lies in the wall thickness. Steel plate duct typically
has wall thicknesses of from 3/16 in. to 1/2 in., while steel sheet
duct wall thicknesses usually range from 28 gauge to 10 gauge. As
Table 10.4 shows, this range corresponds to thicknesses of 0.0149
in. to 0.1406 in., respectively, although the exact thicknesses
will vary with the type of steel used (e.g., carbon vs. stainless).
Also, as discussed in Section 10.3.3.2, each duct diameter can be
fabricated with a range of wall thicknesses.
Most of the steel duct vendors supplied prices for a minimum
and a maximum wall thickness for a given diameter. However, to
simplify matters for cost estimators, these "low" and "high" prices
first were averaged, and then the average prices were regressed
against the diameters. This averaging was necessary, because those
making study cost estimates usually do not have enough information
available to predict duct wall thicknesses.
Prices for both circular and square insulated steel sheet duct
were among the data received. The insulated circular steel duct is
"double-wall, spiral-wound" in construction, wherein the insulation
is installed between the inner and outer walls. Costs were
provided for both 1-in. and 3-in. fiberglass insulation
thicknesses. For the square duct, prices were given for a 4-in.
thickness of mineral wool insulation applied to the outer surface
of the duct. The correlation parameters in Table 10.6 reflect
these specifications.
Prices for both carbon steel (galvanized, painted, or
aluminized) and 304 stainless steel duct were received. The carbon
steel duct is used in situations where "mild" steel is suitable,
while the stainless steel duct is required whenever the gas stream
contains high concentrations of corrosive substances.
Vendors gave prices for plastic (FRP and PVC) duct also (Table
10.8). However, for a given diameter this duct is fabricated in a
10-45
-------
Table 10.6 Parameters for Straight Steel Ductwork Cost Equations1
Duct
Type
Circular-
spiral '
Circular-
spiral
Circular-
spiral
Circular-
spiral
Circular-
longitudinaps
Circular-
longitudinal
Circular-
longiludinal
Circular-
longitudinal
Square
Square
Material
Sheet -
galv CS*
Sheet -
304 SS*
Sheet -
galv CS
Sheet -
galv CS
Sheet -
galv CS
Sheet -
304 SS
Plate-
coat
csn
Plate-
304 SS**
Sheet -
alum
CS"
Sheet -
alum CS
Insulation
Thickness
(in.)
None
None
1
3
None
None
None
None
None
4
Equation
Type
Power
function
Power
function
Power
function
Power
function
Power
function
Power
function
Power
function
Power
function
Linear
Linear
Equation
Parameter
a
0.322
1.56
1.55
2.56
2.03
2.98
2.49
6.29
0.254
21.1
b
1.21
1.00
0.936
0.937
0.784
0.930
1.15
1.23
2.21
5.81
Equation
Range
(D, in.)
3 - 84
3 - 84
3 - 82
3 - 82
6 - 84
6 - 84
6 - 84
6 - 84..
18 - 48
18 - 48
§ Based on data from ductwork vendors. (Reference 53.
f Spiral-wound and welded circular duct.
* Galvanized carbon steel sheet.
* 304 stainless steel sheet.
H Circular _duct welded along the longitudinal seam.
TT Carbon steel plate with one coat of "shop paint".
** 304 stainless steel plate.
** Aluminized carbon steel sheet,
10-46
-------
Table 10.7 Parameters for Steel Elbows and Dampers Cost Equations8
Ductwork
Item
Elbows*
Elbows
Elbows -
insulated81
Damper s-
butterfly*1'
Dampers-
buOerfly /insulated^
Dampers -
louvered**
Dampers-
louvered
w/actuatorsm
Dampers -
blast gates
Material
Galv CS*
304 SS*
Galv CS
Galv CS
Galv CS
Alum
cs§§§
Alum CS
Carbon
steel
Equation
Type
Exponential
Exponential
Exponential
Exponential
Exponential
Power
function
Power
function
Power
function
Equation
Parameter
a
30.4
74.2
53.4
23.0
45.5
78.4
208.
17.2
b
0.0594
0.0668
0.0633
0.0567
0.0597
0.860
0.791
0.825
Equation
Range
(D, in.)
6-84
6 - 60
3 - 78
4 - 40
4 - 40
18 - 48
18 - 48
3 - 18
§ Based on data received from ductwork vendors, (See Reference
53.)
1 Single-wall "gored" 90° elbows, uninsulated.
* Galvanized carbon steel sheet.
* 304 stainless steel sheet.
§§ Double-wall "gored" 90° elbows with 1-inch fiberglass
insulation.
ft Single-wall "opposed blade" type manual butterfly dampers.
** Double-wall "opposed blade" butterfly dampers with 1-inch
fiberglass insulation.
** Louvered dampers with 95-98% sealing.
§§s "Aluminized" carbon steel sheet.
tn Louvered dampers with electric actuators (automatic
controls).
10-47
-------
Table 10.8 Parameters for Plastic Ductwork Cost Equations5
Ductwork
Item
Straight
duct
Straight
duct
Elbows -90°
Elbows -90°
Dampers -
butterfly
Dampers -
butterfly
Dampers-
butlerfiy w/acluators
Dampers -
blast gate
Material
PVCf
FRP*
PVC
FRP
PVC
FRP
PVC
PVC
Equation
Type
Power
function
Exponential
Power
function
Exponential
Power
function
Power
function
Exponential
Power
function
Equation
Parameter
a
0.547
11.8
3.02
34.9
10.6
35.9
299.
8.14
b
1.37
0.0542
1.49
0.0841
1.25
0.708
0.0439
1.10
Equation
Range
(D, in.)
6 - 48
4 - 60
6 - 48
4 - 36
4 - 48
4 - 36
4 - 48 .
4 - 48
§ Based on data received from ductwork vendors. (See Reference
53.)
f Polyvinyl chloride.
* Fiberglass-reinforced plastic.
* Butterfly dampers with pneumatic actuators (automatic
controls). All other dampers listed in this table are manually-
controlled.
10-48
-------
single wall thickness, which varies from approximately 1/8 in. to
1/4 in. Consequently, the estimator is not required to select a
wall thickness when costing plastic duct.
K Elbows: Prices for steel sheet and plastic 90° elbows were also
submitted. The steel sheet elbows were "gored" (sectioned) elbows
fabricated from five pieces of sheet metal welded together. Like
the straight duct, the steel elbows were priced at two wall
thicknesses: "minimum" and "maximum". These prices were averaged
before being regressed against the elbow diameter. Prices were
also given for both galvanized carbon steel elbows (with and
without 1-in. fiberglass insulation) and 304 stainless steel
elbows. Correlation parameters for steel elbows are listed in
Table 10.7.
Costs for both PVC and FRP 90° elbows were also given. The
PVC ells were fabricated from three sections ("three-piece
miter"), while the FRP elbows were one-piece molded fittings. As
with the plastic straight duct, each elbow of a given diameter was
fabricated in a single wall thickness. Table 10.8 contains
correlation parameters for plastic elbows.
t Dampers: Prices were obtained for three types of dampers:
butterfly, louvered, and blast gates. The galvanized carbon steel
butterfly dampers were priced with and without 1-in. fiberglass
insulation, while prices for the aluminized carbon steel louvered
dampers were based on either manual or automatic control (via
electric actuators). Similarly, the PVC butterfly dampers were
manual or equipped with pneumatic actuators. Both the carbon steel
and the PVC blast gates were manual. Correlation parameters for
the steel and plastic dampers are shown in Tables 10.7 and 10.8, in
turn.
Illustration: A fabric filter handling 16,500 ft3/min of 200°F.
waste gas laden with noncorrosive cocoa dust is located 95 ft
across from and 20 ft above, the emission source (a drying oven).
Straight duct with four 90° elbows (all fabricated from spiral-
wound, galvanized carbon steel sheet) and a butterfly damper (also
galvanized CS) will be required to convey the gas from the source
to the control device. Assume that the ductwork is insulated to
prevent condensation. Estimate the cost of these items.
Solution: First, determine the diameter of the straight duct,
elbows, and damper. From Table 10.3, the minimum transport
velocity (u,) for cocoa dust is 3,000 ft/min. Substituting this
value and the gas volumetric flow rate into equation 10.27, we
obtain:
Dd = 1.128 (16,500/3,000) "2 = 2.65 ft = 31.7 in-.
Next, obtain the costs of the ductwork items as follows:
10-49
-------
ss' Straight ductwork: From Table 10.6, select the equation
parameters for galvanized circular spiral-wound duct (1-in.
insulation) and substitute them and the diameter into the
appropriate equation type (power function, equation 10.35) .
Straight duct cost ($/ft) = 1 . 55 (31 . 7) °'936 = $39.4/ft.
However, a total of 115 ft (95 + 20) of duct is required, so:
Straight duct cost = $39.4/ft x 115 ft = $4,531. "
es' Elbows: The Table 10.7 correlation parameters for galvanized
carbon steel, insulated elbows are 53.4 (a) and 0.0633 (b) .
However, the regression correlation form is exponential (equation
10.36) . Thus:
Elbow cost ($) = sa^e0-0633*31-7' = $397 ea .
For four elbows, the cost is: $397 x 4 = $1,588.
B3" Damper: Also from Table 10.7, select the correlation parameters
for galvanized carbon steel "dampers-butterfly/insulated" and
substitute into equation 10.36:
Damper cost ($) = 45 . 5e°-0597(31-7) = $302.
After summing the above three costs, we obtain:
Total ductwork cost = $6,421 <= $6,420.
10.4.1.3 Stack Costs
Prices for steel and PVC short stacks were obtained from four
vendors.57 The steel stack costs were for those fabricated from
carbon and 304 stainless steels, both plate and sheet metal. As
with ductwork, the difference between steel sheet and plate lies in
the thickness. For these stacks, the sheet steel thickness ranged
from 18 to 16 gauge (0.05 to 0.06 in., approximately) . Steel plate
thicknesses were considerably higher: 0.25 to 0.75 in, a fact that
makes them more resistant to wind and other loadings than stacks
fabricated of steel sheet. This is especially true for taller
stacks. The major drawback is that plate steel stacks are more
costly than those fabricated from steel sheet.
Another feature that increases costs is insulation. As the
correlation parameters show (Table 10.9), insulated stacks cost as
much as three times more per foot than uninsulated. With or
without insulation, a typical short (15- ft) steel stack consists of
the following components:58
10-50
-------
"^ Longitudinal seam duct (12-ft section)
"3" Reducer fitting (3-ft)
•S" Drip pan
•®" Support plate (1/4-in, welded to stack)
"S" Rectangular tap (for connecting to fan discharge)
"®" Ring (for attaching guy wires)
Taller stacks may require additional components, such as ladders
and platforms, guy wires or other supports, and aircraft warning
lights. (See Section 10.2.3.)
Table 10.9 lists the parameters and applicable ranges of the
stack cost correlations. The correlations cover short PVC stacks,
and taller stacks fabricated from plate steel (carbon and 304
stainless types) and sheet steel (insulated and uninsulated).
Except for three double-wall sheet steel designs, these stacks are
of single-wall construction.
Note that all of the correlations are power functions. Also
note that the equations apply to various ranges of stack height.
In all but one of these equations the cost is expressed in $/ft of
stack height. The exception is the cost equation for insulated
carbon steel sheet stacks of heights ranging from 30 to 75 f eet .-
In this equation the cost is expressed in $.
This last cost equation is different in another respect. The
other six equations in Table 10.9 correlate stack cost ($/ft) with
stack diameter (Ds, in.). However, this seventh equation correlates
stack cost with stack surface area (Ssl ft2) , a variable that
incorporates both the stack diameter and the stack height (Hs) . The
surface area is calculated via the following equation:
Ss = (7T/12)DSHS (10.38)
where: 1/12 = stack diameter (Ds) conversion factor
Illustration: Estimate the cost of the stack sized in the Section
10.3.4.3 illustration.
Solution: Recall that the stack dimensions were: Hs = 95 ft and
Ds = 2.12 ft = 25.4 in. Both dimensions fall within the ranges of
the cost correlations for steel plate stacks. Because the previous
illustration did not indicate whether the waste gas was corrosive,
we will estimate the prices for both carbon steel and 304 stainless
10-51
-------
Table 10.9 Parameters for Stack Cost Equations§
Material
pvc§§
Plate- coated CSn
Plate- 304 SS**
Sheet -galv CS"
Sheet-304 SSM
Sheet -insul CS/DWm
Sheet -uninsul CS/DW**
Sheet -insul
CS/DW*"
Equation Parameter4
a
0.393
3.74
12.0
2.41
4.90
143.
10.0
142.
b
1.61
1.16
1.20
1.15
1.18
0.402
1.03
0.794
Equation Range
Ds (in)*
12 - 36
6 - 84
6 - 84
8 - 36
8 - 36
18 - 48
18 - 48
24 - 48
Hs (ft)V
< 10
20 - 100
20 - 100
< 75
< 75
< 15
< 15
30 - 75
Based on data received from stack vendors. (See Reference
54.
f All cost equations are power functions. (See equation
10.35.) Except where noted, costs are expressed in terms of $/ft
of stack height.
* Stack diameter range to which each equation applies.
* Stack height range to which each equation applies.
§§ Polyvinyl chloride.
tf Carbon steel plate with one coat of "shop paint".
** 304 stainless steel plate.
** Galvanized carbon steel sheet.
§§§ 304 stainless steel sheet.
ftt Aluminized carbon steel sheet covered with 4 inches of
fiberglass insulation (double-wall construction).
*** Uninsulated aluminized carbon steel sheet (double-wall
construction).
*** Costs for these stacks are expressed in $, and are
correlated with the stack surface area (Ss, ft2) .
10-52
-------
steel plate stacks.
Upon substituting the equation parameters and stack dimensions
into equation 10.35, we obtain:
Price (carbon steel) = 3.74(25.4)U6 ($/ft) x 95 ft
= $15,100.
Price (304 stainless) = 12 . 0 (25 .4) L2° ($/ft) x 95 ft
= $55,300.
Notice that the price of the stainless steel stack is nearly
four times that of the carbon steel stack. In view of this
difference, the estimator needs to obtain more information on the
waste gas stream properties, so that he/she can select the most
suitable stack fabrication material. Clearly, it would be a poor
use of funds to install a stainless steel stack where one is not
needed.
10.4.2 Taxes, Freight, and Instrumentation Costs
Taxes (sales, etc.) and freight charges apply to hoods,
ductwork, and stacks, as they do to the control devices that these
auxiliaries support. As discussed in Chapter 2, these costs vary,
respectively, according to the location of the ventilation system
and the site's distance from the vendor. Typical values are 3%
(taxes) and 5% (freight) of the total equipment cost.
Unlike the control devices, ventilation systems generally are
not instrumented. The exception would be an electric or pneumatic
actuator for a butterfly or louvered damper. In such a case,
however, the cost of the instrument (actuator and auxiliaries)
would be included in the damper price. Thus, no supplementary
instrumentation cost is included.
10.4.3 Purchased Equipment Cost
With ventilation systems, the purchased equipment cost (PEC,)
is the sum of the equipment, taxes, and freight costs.
Incorporating the typical values listed in Section 10.4.2, we
obtain:
PECt = EC, + 0.03EC, + 0.05EC,
= 1.08 (EC,) (10.39)
where: EC, = total cost of hood(s), ductwork, and stack(s)
10--53
-------
10.4.4 Installation Costs
When making a cost estimate for an air pollution control
system according to the procedure in this manual, the estimator
first determines the cost of the control device, then estimates the
costs of -such auxiliaries as the hood, ductwork, stack, fan and
motor, and other items. To these items he/she adds the costs of
instrumentation, taxes, and freight, to obtain the PEC. Finally,
the estimator multiplies the PEC by the installation factor
appropriate to the control device (e.g., 2.20 for gas absorbers) to
obtain the total capital investment. In these cases, the
installation factor incorporates all direct and indirect costs
needed to install and start up the control system equipment,
including, of course, the hood, ductwork, and stack. (See Chapters
3 to 9 for more information about these factors.)
For this reason, it usually is unnecessary to estimate the
installation cost of the ventilation system separately. However,
there may be occasions where a hood, a stack, or ductwork has to be
installed alone, either as replacement equipment or to augment the
existing ventilation system. In those instances, the estimator may
want to estimate the cost of installing this item.
As might be imagined, these installation costs vary
considerably, according to geographic location, size and layout of
the facility, equipment design, and sundry other variables.
Nonetheless, some of the vendors (and a peer reviewer59) provided
factors for hoods and ductwork, which, when multiplied by their
respective purchased equipment costs, will yield approximate
installation costs. These are:
OS" Hoods: 50 to 100%
OS* Ductwork: 25 to 50%
If one or both of the latter factors is used, the total
capital investment (TCI) of the hood and/or ductwork would be:
TCI = (1 + IFh/d) x PECh/d (10.40)
where: IFh/d = installation factor for hood (h)/ductwork (d)
PECh/d = purchased equipment cost of hood (h)/ductwork (d)
10-54
-------
10.5 Estimating Total Annual Cost
10.5.1 Direct Annual Costs
Ventilation systems incur few, if any, direct annual costs, as
they function to support control devices. There are no costs for
operating or supervisory labor, operating materials, or waste
treatment/disposal allocated to ventilation systems. Maintenance
costs would also be minimal, except for such minor expenses as
painting, insulation repair, or calibration of automatic damper
controls. The only utilities cost would be the incremental
electricity needed for the waste gas stream to overcome the static
pressure loss in the hood, ducting, and stack.13 The incremental
electricity cost (Cc, $/yr) can be calculated as follows:
Ce = (1.175 x 10-4)peQFd6/e (10.41)
where: pe = electricity price ($/kwh)
Q = waste gas flow rate (actual ft3/min)
F = static pressure drop through ventilation
system (in. w.c.)
6 = operating factor (hr/yr)
e = combined fan-motor efficiency
Illustration: In the cosmetic factory ventilation system
illustration above (Section 10.3.3.3), what would be the cost of
the electricity consumed by the fan needed to convey the gas
through the ductwork? Assume an electricity price of $0.075/kwh, a
combined fan-motor efficiency of 0.6, and an 8,000-hr/yr operating
factor.
Solution: Recall that the pressure drop and gas flow rate for this
illustration were 0.313 in. w.c. and 15,000 actual ft3/min,
respectively. Upon substituting these values and the other
parameters into equation 10.40, we obtain:
Ce = (1.175 x ID"4) (0.075) (15,000) (0.313) (8,000)/0.6
= $552/yr.
13 Technically, this direct annual cost should be allocated to
the ventilation system fan, not to the hood, ductwork, and stack.
The fan power cost equation will be included in the Manual chapter
on fans. However, as the fans chapter has yet to be written, this
equation has been provided as a temporary convenience to Manual
users.
10-55
-------
10.5.2 Indirect Annual Costs
The indirect annual costs for ventilation systems include
property taxes, insurance, general and administrative (G&A), and
capital recovery costs. (Overhead—a fifth indirect annual
cost—is not considered, because it is factored from the sum of the
operating, supervisory, maintenance labor and maintenance materials
costs, which is negligible.) When a ventilation system is part of
a control system, these costs are included in the control system
indirect annual cost. However, if the ventilation equipment has
been sized and costed separately, these costs can be computed from
the total capital investment (TCI) via standard factors, as
follows:
Indirect Annual Cost
Property taxes
Insurance
General and Administrative
Capital recovery
Computation Equation
0.01 x TCI
0.01 x TCI
0.02 x TCI
CRF x TCI
The "CRF" term in the capital recovery equation is the capital
recovery factor, which is a function of the economic life of the
ventilation system and the interest rate charged to the total
capital investment. (See Section 2.3 of this manual for more
discussion of the CRF and the formula used for computing it.)
For a ventilation system, the economic life varies from at
least 5 to 10 years to 15 to 20 years or more.60'61 In general, the
ventilation equipment should last as long as the control system it
supports. As discussed in Section 2.3, the interest rate to use in
the CRF computation should be a "pre-tax, marginal (real) rate of
return" that is appropriate for the investor. However, for those
cost analyses related to governmental regulations, an appropriate
"social" interest (discount) rate should be used. For these kinds
of analyses, the Office of Management and Budget (OMB) directs that
a real annual interest rate of 7% be used.62 (This replaces the
10% rate OMB previously had mandated.)
10.5.3 Total Annual Cost
The total annual cost (TAC) is calculated by adding the direct
(DC) and indirect (1C) annual costs:
TAC = DC + 1C
;i0.42)
10-56
-------
10.6 Acknowledgements
Several firms and individuals provided very useful technical
and cost information to this chapter. Foremost among these was
Todd N. Stine of United McGill Corporation (Raleigh, NC), who
submitted current prices for a variety of ductwork items, as well
as a comprehensive product catalog and engineering design manual.
In addition, Mr. Stine patiently replied to the author's many
questions, providing supplemental data when requested. Samir
Karandikar of EPCON Industrial Systems (The Woodlands, -TX) and
Gregory P. Michaels of Piping Technology & Products (Houston, TX)
also were very helpful in submitting data and responding to
inquiries.
The author also would like to thank the following firms for
their valuable contributions:
«3" Air Plastics, Inc. (Mason, OH)
«®" General Resource Corporation (Hopkins, MN)
"S" Harrington Industrial Plastics, Inc. (Chino, CA)
«®" Intellect Systems & Marketing, Inc. (Bohemia, NY)
«®" Wer-Coy Metal Fabrication Co. (Warren, MI)
In addition, several individuals reviewed the draft chapter
and provided valuable suggestions, supplemental information, or
both. The EPA peer reviewers, all located at Research Triangle
Park, NC, were:
"®" James C. Berry (OAQPS/ESD)
«S" Peter A. Eckhoff (OAQPS/TSD)
"^ Norman Kaplan (ORD/AEERL)
»5" James H. Maysilles (OAQPS/ESD)
«®" Larry Sorrels (OAQPS/ESD)
Finally, Howard Goodfellow of Goodfellow Consultants, Inc.
(Mississauga, Ontario, Canada) also reviewed the chapter and
supplied helpful comments.
10-57
-------
References
1. Goodfellow, H.D. "Ancillary Equipment for Local Exhaust
Ventilation Systems". In: Air Pollution Engineering Manual. New
York: Van Nostrand Reinhold/Air and Waste Management Association.
1992, pp. 155-205.
2. Burton, D. Jeff. Industrial Ventilation Work Book. Salt Lake
City: DJBA, Inc. 1989.
3. The Measurement Solution: Using a Temporary Total Enclosure
for Capture Efficiency Testing. Research Triangle Park, NC: U.S.
Environmental Protection Agency. August 1991 (EPA-450/4-91-020),
pp. 3,11.
4. The Measurement Solution, pp. 11-29.
5. Heinsohn, Robert Jennings. Industrial Ventilation:
Engineering Principles. New York: John Wiley & Sons, Inc. 1991. -
6. Telephone conversation between William M. Vatavuk, U.S.
Environmental Protection Agency (Research Triangle Park, NC) and
Todd N. Stine, United McGill Company (Raleigh, NC), May 24, 1993.
7. Thermoplastic Duct (PVC) Construction Manual. Vienna, VA:
Sheet Metal ar>d Air Conditioning Contractors' National
Association, Inc. (SMACNA). May 1987, pp. 61-85.
8. Thermoplastic Duct Construction Manual, p. 64.
9. Burton, p. 6-7.
10. Dust Control System Accessories Price List. Huntington Park,
CA: Murphy-Rodgers, Inc. July 1992.
11. Price and Data Catalog: Standard Ductwork Components.
Warren, MI: Wer-Coy Metal Fabrication Co. 1992-93.
12. Letters from Samir Karandikar, EPCON Industrial Systems
(Woodlands, TX) to William M. Vatavuk, U.S. Environmental
Protection Agency (Research Triangle Park, NC). May 21 and June
9, 1993.
13. "Double'Wall Insulated Duct and Fittings." In: Sheet Metal
Division Catalog. Groveport, OH: United McGill Corporation.
1990.
10-58
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14. "Single-Wall Round and Flat Oval Duct and Fittings." In:
Sheet Metal Division Catalog. Groveport, OH: United McGill
Corporation. 1990.
15. HVAC Duct Construction Standards: Metal and Flexible.
Vienna, VA: Sheet Metal and Air Conditioning Contractors'
National Association, Inc. (SMACNA). 1985, pp. 2-15 to 2-17.
16. Wherry, T.C. and Peebles, Jerry R., "Process Control". In:
Perry's Chemical Engineers' Handbook, Sixth Edition. New York:
McGraw-Hill, Inc. 1984.
17. Product catalog. Rio, WI: Gaskets, Inc. 1994.
18. HVAC Duct Construction Standards, pp. 4-2 to 4-3.
19. HVAC Duct Construction Standards, pp. 4-2 to 4-7.
20. Letter from Howard D. Goodfellow, Goodfellow Consultants
(Mississauga, Ontario, Canada) to William M. Vatavuk, U.S.
Environmental Protection Agency (Research Triangle Park, NC).
February 23, 1994.
21. Guide for Steel Stack Design and Construction. Vienna, VA:
Sheet Metal and Air Conditioning Contractors' National
Association, Inc. (SMACNA). 1983.
22. Goodfellow, pp. 192-193.
23. Goodfellow, p. 193.
24. Peters, Max S. and Timmerhaus, Klaus D. Plant Design and
Economics for Chemical Engineers, Third Edition. New York:
McGraw-Hill,.Inc., 1980, pp. 508-510.
25. Burton, pp. 2-10 to 2-11.
26. Burton, p. 2-11.
27. Burton, pp. 4-5 to 4-8.
28. Burton, p. 5-12.
29. Burton, pp. 5-15 to 5-16.
30. Burton, p. 5-5.
31. Burton, pp. G-2, G-5.
32. Burton, p. 5-18.
10-59
-------
33. Vatavuk, William M. and Neveril, Robert B., "Estimating Costs
of Air-Pollution Control Systems, Part III: Estimating the Size
and Cost of Pollutant Capture Hoods," Chemical Engineering,
December 1, 1980, pp. Ill to 115.
34. Telephone conversation between William M. Vatavuk, U.S.
Environmental Protection Agency (Research Triangle Park, NC) and
Dennis Woll, Air Plastics, Inc. (Mason, OH), August 10, 1993.
35. Telephone conversation between William M. Vatavuk, U.S.
Environmental Protection Agency (Research Triangle Park, NC) and
Pat Caputo, Intellect Systems & Marketing, Inc. (Bohemia, NY),
October 22, 1993.
36. Burton, "Chart 9".
37. Letter from Todd N. Stine, United McGill Corporation
(Raleigh, NC) to William M. Vatavuk, U.S. Environmental
Protection Agency (Research Triangle Park, NC). June 10, 1993.
38. Green, Don W. and Maloney, James O. Perry's Chemical
Engineers' Handbook, Sixth Edition. New York: McGraw-Hill, Inc.
1984.
39. Peters, Max S. and Timmerhaus, Klaus D. Plant Design and
Economics for.Chemical Engineers, Fourth Edition. New York:
McGraw-Hill, Inc. 1991.
40. Engineering Design Reference Manual for Supply Air Handling
Systems. Groveport, OH: United McGill Corporation. 1992, pp. 3-
4.
41. Engineering Design Reference Manual, p. 8.
42. Burton, "Chart 5".
43. Engineering Design Reference Manual, p. 7.
44. Burton, p. 6-6.
45. Burton, "Chart 13".
46. Goodfellow, p. 193.
47. Guide for Steel Stack Design and Construction, pp. 39 to 50.
48. Goodfellow, p. 193.
49. Carlton-Jones, Dennis and Schneider, H.B., "Tall Chimneys,"
Chemical Engineering, October 14, 1968, p. 167.
10-60
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50. Guideline for Determination of Good Engineering Practice:
Stack Height (Technical Support Document for Stack Height
Regulations) (Revised). Research Triangle Park, NC: U.S.
Environmental Protection Agency. June 1985 (NTIS PB-85-225241),
p.l.
51. Guideline for Determination of Good Engineering Practice, pp.
50-51.
52. Guideline for Determination of Good Engineering Practice, pp.
1-2.
53. Goodfellow, p. 194.
54. Guide for Steel Stack Design and Construction, p. 4.
55. Hood cost data request responses from four hood vendors to
William M. Vatavuk, U.S. Environmental Protection Agency
(Research Triangle Park, NC). June-July 1993.
56. Ductwork cost data request responses from six vendors to
William M. Vatavuk, U.S. Environmental Protection Agency
(Research Triangle Park, NC). May-July 1993.
57. Stack cost data request responses from four vendors to
William M. Vatavuk, U.S. Environmental Protection Agency
(Research Triangle Park, NC). May-July 1993.
58. Op. cat., Stine-Vatavuk letter, June 10, 1993.
59. Goodfellow-Vatavuk letter.
60. Goodfellow-Vatavuk letter.
61. Telephone conversation between William M. Vatavuk, U.S.
Environmental Protection Agency (Research Triangle Park, NC) and
Todd N. Stine, United McGill Company (Raleigh, NC), December 10,
1993.
62. Darman, Richard. Guidelines and Discount Rates for Benefit-
Cost Analysis of Federal Programs (OMB Circular No. A-94,
Revised). Washington, DC: Office of Management and Budget.
October 29, 1992.
10-61
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Abstract (Item #16) for EPA Form 2220-1
This is the third supplement to the OAQPS Control Cost
Manual (Fourth Edition). The supplement consists of a new Manual
chapter, Chapter 10 ("Hoods, Ductwork, and Stacks"). Like the
other chapters in the Manual, Chapter 10 is self-contained. It
discusses: (1) the types and applications of hoods used to
support add-on air pollution control devices; (2) the theory
underlying their operation and design; (3) basic sizing
procedures; and (4) procedures and current (1993) data for
estimating study-level (± 30%-accurate) capital and annual costs.
In particular, the chapter contains equipment costs for canopy,
push-pull, side-draft, and backdraft hoods; straight ductwork
(circular and square); 90o elbows; butterfly, louvered, and blast
gate dampers; and short (up to 100-foot) stacks. In addition,
the prices of each type of equipment reflect at least two kinds
of fabrication materials, such as carbon and 304 stainless steel
(plate and sheet types), FRP (fiberglass-reinforced plastic), and
PVC (polyvinyl chloride). These prices have been correlated with
appropriate sizing parameters (e.g., duct diameter). Finally,
Chapter 10 includes several example problems that illustrate the
various sizing and costing procedures; a table of contents; and a
list of references.
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