PPARTICULATE EMISSIONS EMISSION STANDARDS Allowable levels of particulate emissions are specified in several different ways, having somewhat different meth-odologies of measurement an
Trang 1P
PARTICULATE EMISSIONS
EMISSION STANDARDS
Allowable levels of particulate emissions are specified in
several different ways, having somewhat different
meth-odologies of measurement and different philosophies of
important criteria for control Permissible emission rates are
in a state of great legislative flux both as to the definition
of the suitable measurement and to the actual amount to be
allowed This section summarizes the various types of
quan-titative standards that are used in regulating particulate
emis-sions For a detailed survey of standards, the reader should
consult works by Stern, 1 Greenwood et al , 2 and the Public
Health Service. 3
A recent National Research Council report proposes
future studies on the nature of particulate emissions, their
effect on exposed populations and their control 4 Friedrich
and Reis 5 have reported the results of a 10-year multinational
European study on characteristics, ambient concentrations
and sources of air pollutants
The following paragraphs give an overview of standards
for ambient particulate pollution and source emission The
precise and practical methodology of making accurate and/
or legally satisfactory measurements is beyond the scope of
this article Books such as those by Katz, 6 Powals et al , 7
Brenchly et al , 8 and Hawksley et al 9 should be consulted
for detailed sampling procedures In the Federal Register
USEPA announced the implementation of the PM-10
regu-lations (i.e., portion of total suspended particulate matter of
10 µ m or less particle diameter). 40,41
Ringlemann Number
Perhaps the first attempt at quantifying particulate
emis-sions was developed late in the 19th century by Maximilian
Ringlemann He developed the concept of characterizing a
visible smoke plume according to its opacity or optical
den-sity and originated the chart shown in Figure 1as a
conve-nient scale for estimation of opacity The chart consists of
four grids of black lines on a white background, having
frac-tional black areas of 20, 40, 60 and 80% which are assigned
Ringlemann Numbers of 1–4 (Ringlemann 0 would be all white and Ringlemann 5 all black.) For rating a smoke plume, the chart is held at eye level at a distance such that chart lines merge into shades of grey The shade of the smoke plume is compared to the chart and rated accordingly The history and use of the Ringlemann chart is covered by Kudlich 8 and by Weisburd. 9
In actual practice, opacity is seldom determined by use
of the chart, although the term Ringlemann Number persists
Instead, observers are trained at a “smoke school.” 10 Test plumes are generated and the actual percentage of light atten-uation is measured spec-trophotometrically within the stack
Observers calibrate their perception of the emerging plume against the measured opacity Trained observers can usu-ally make readings correct to ⫾ 1/2 Ringlemann number. 11,13
Thus, with proper procedures, determination of a Ringlemann Number is fairly objective and reproducible
The Ringlemann concept was developed specifically for black plumes, which attenuate skylight reaching the observ-er’s eye and appear darker than the sky White plumes, on the other hand, reflect sunlight and appear brighter than the background sky so that comparison to a Ringlemann chart is meaningless The smoke school approach is quite applicable, however Observations of a white plume are calibrated against the measured light attenuation Readings of white plumes are somewhat more subject to variation due to relative locations
of observer, plume, and sun It has been found that observa-tions of equivalent opacity taken with the observer facing the sun are about 1 Ringlemann number higher 13 than those
FIGURE 1 Ringlemann’s scale for grading the density of smoke.
Trang 2taken in the prescribed method with the sun at the observer’s
back Nevertheless, when properly made, observations of
Ringlemann numbers are reproducible among observers and
agree well with actual plume opacity
Opacity regulations specify a maximum Ringlemann
number allowable on a long-term basis but often permit
this to be exceeded for short prescribed periods of time For
instance, a typical requirement specifies that emissions shall
not exceed Ringlemann 1, except that for up to 3 min/hr
emis-sions up to Ringlemann 3 are permitted This allowance is of
considerable importance to such operation as soot blowing
or rapping of electrostatic precipitator plates, which produce
puffs to smoke despite on overall very low emission level
Federation regulations of the Environmental Protection
Agency 14 specify that opacity observations be made from a
point perpendicular to the plume, at a distance of between
two stack heights and one quarter of a mile, and with the sun
at the observer’s back For official certification, an observer
under test must assign opacity readings in 5% increments
(1/4 Ringlemann number) to 25 plumes, with an error not
to exceed 15% on any single reading and an average error
(excluding algebraic sign of individual errors) not to exceed
7.5% Annual testing is required for certification In view of
previous studies, 11,13 this is a very high standard of
perfor-mance and probably represent the limits of visual
quantifica-tion of opacity
Perhaps the greatest advantage of the Ringlemann Number
approach is that it requires no instrumentation and very little
time and manpower Readings can usually be made by
con-trol authorities or other interested parties without entering the
premises of the subject source Monitoring can be done very
frequently to insure continual, if not continuous, compliance
of the source Finally, in terms of public awareness of
par-ticulate emissions, plume appearance is a logical candidate
for regulation Air pollution is, to a great extent, an aesthetic
nuisance affecting the senses, and to the extend that plume
appearance can be regulated and improved, the visual impact
of pollution is reduced
The Ringlemann Number concept has drawbacks reflecting
its simple, unsophisticated basis Most serious is that, at
pres-ent, there is no really quantitative relationship between stack
appearance and the concentration of emissions Additional
factors; such as particle size distribution, refractive index,
stack diameter, color of plume and sky, and the time of day,
all have a marked effect on appearance On a constant weight
concentration basis, small particles and large smoke stacks will
produce a poor Ringlemann Number Plumes that have a high
color contrast against the sky have a very strong visual impact
that does not correspond closely to the nature of the emissions
For example, a white plume may be highly visible against a
deep blue sky, but the same emission can be practically
invis-ible against a cloudy background As a result, it is often
dif-ficult to predict whether or not proposed control devices for a
yet unbuilt plant will produce satisfactory appearance Certain
experience factors are presented in Table 1 for emissions,
mea-sured on a weight concentration basis, which the Industrial Gas
Cleaning Institute has estimated will give a Ringlemann 1 or
a clear stack
A second objection is that Ringlemann number is a purely aesthetic measurement which has no direct bearing
on physiological effects, ambient dirt, atmospheric corro-sion, or any of the other very real and costly effects of par-ticulate air pollution There is some concern that regulations
of very low Ringlemann numbers will impose very costly control measures upon sources without producing a com-mensurate improvement in the quality of the environment
Thus a high concentration of steam will produce a visually prominent plume, but produce virtually no other undesirable effects Opacity restrictions are usually waived if opacity is due entirely to steam but not if any other particles are pres-ent, even if steam may be the major offender
Instrumental Opacity
Many factors affecting the visual appearance of a smoke plume are external variables, independent of the nature of the emissions In addition, visual reading cannot be taken at all
at night; and manpower costs for continuous daytime moni-toring would be prohibitive For these reasons, instrumental measurements of plume opacity are sometimes desirable
A typical stack mounted opacity meter is shown in path traversing the smoke stack, and a phototube receiver which responds to the incident light intensity and, hence,
to the light attenuation caused by the presence of smoke
Various techniques including beam splitting, chopper stabi-lization, and filter comparison are used to maintain stable baselines and calibrations At present, however, there is no way to distinguish between dust particles within the gas stream and those which have been deposited on surfaces in the optical path Optical surfaces must be clean for mean-ingful measurements, and cleanliness is difficult to insure for long periods of time in dusty atmosphere The tendency, therefore, is for such meters to read high, indicating more smoke than is actually present For this reason, and because
of reluctance to have a continuous record of emissions, there has not been a very strong push by industries to supplant Ringlemann observations with opacity meters
Stack mounted opacity meters, of course, will not detect detached plumes, which may contribute to a visual Ringlemann observation Detached plumes are due to particles formed by condensation or chemical reaction after gas leaves the stack and are thus beyond detection of such a meter
At present, Texas is the only state with emissions control regulations based on use of opacity meters, 15 as described
by McKee. 11 The Texas regulations is written so that smoke
of greater optical density (light attenuation per unit length
of light path) is permitted from low velocity stacks or small diameter ones Basically, a minimum transmittance of 70%
is allowed across the entire (circular) stack diameter if the stack has an exit velocity of 40 ft/sec, and adjustment equa-tions are provided for transmittance and/or optical path length if non-standard velocity or path length is used
Perhaps the greatest dissatisfaction with emission regula-tions based either on visual observation number or on instru-mental opacity is due to the fact that there is presently no
Trang 3TABLE 1 Industrial process emissions expected to produce visually clear (or near clear) stack
Utilities and industrial power plant fuel fired boilers
Trang 4quantitative procedure for design of equipment to produce
complying plumes Equipment vendors will usually
guar-antee collection efficiency and emission concentrations by
weight, but they will not give a guarantee to meet a specified
opacity This is indeed a serious problem at a time when a
large precipitator installation can cost several million dollars
and take twenty months to fabricate and install Overdesign
by a very conceivable factor of two can be very expensive in
unneeded equipment Underdesign can mean years of delay
or operation under variance or with penalty payments
Some progress has been made in applying classical
theo-ries of light scattering and transmission to the problem of
predicting opacity This effort has been greatly hampered by
paucity of data giving simultaneous values of light
attenua-tion, particle size distribuattenua-tion, and particle concentration in
a stack Perhaps the most comprehensive work to date has
been that of Ensor and Pilat. 16
Weight Limits on Particulates
Perhaps the least equivocal method of characterizing and
specifying limits on particulate emissions is according to
weight, either in terms of a rate (weight of emissions per unit
time) or in terms of concentration (weight per unit volume)
Measurement of emission weights must be done by
iso-kinetic sampling of the gas stream, as outlined in the
follow-ing section on measurement Although the principles of such
measurement are simple, they are difficult and time
consum-ing when applied with accurate methodology to
commer-cial installations For this reason, such measurements have
not previously been required in many jurisdictions and are
almost never used as a continual monitoring technique
Limits on weight rate of emissions are usually dependent
on process size Los Angeles, for instance, permits emissions
to be proportional to process weight, up to 40 lbs/hr
particu-lates for a plant processing 60,000 lbs/hr of material Larger
plants are limited to 40 lbs/hr For furnaces, the determining
factor is often heat input in BTU/hr rather than process weight
In cases where a particular plant location may have several
independent units carrying out the same or similar processes,
regulations often require that the capacities be combined for
the purposes of calculating combined emissions
Concentration limits are usually independent of process
size For instance, the EPA specifies incinerator emission of
0.08 grains particulates per standard cubic foot of flue gas
(0.18 gm/NM 3 ) Dilution of the flue gas with excess air is
usu-ally prohibited, or else correction must be made to standard
excess air or CO 2
Ground Level Concentrations of Suspended Particulates
A limit on ground level concentration of particulates is an attempt to regulate emissions in accordance with their impact
on population A smoke stack acts as a dispersing device, and such regulations give incentive to build taller stacks in optimum locations
In theory, ground level concentrations can be measured directly Usually, however, emissions are measured in the stack, and plume dispersion equations are then used to cal-culate concentration profiles Plume dispersion depends on stack height, plume buoyancy (i.e density relative to ambi-ent air), and wind velocity, and wind patterns In addition, plumes are never stationary but tend to meander; and cor-rection factors are usually applied to adjust for the sampling time at a fixed location Dispersion calculations are usually easier than direct ground level measurements; and in cases where many different sources are present, calculation offers the only practical way to assess the contributions of a spe-cific source A recent evaluation of plume dispersion models
is given by Carpenter et al 15
In some states, a plume dispersion model is incorporated into a chart which gives an allowable weight rate of emissions
as a function of effective stack height and distance from prop-erty lines An example of this approach is shown in Figure 3
FIGURE 3 Emission requirements for fine particles
based on plume dispersion model (New Jersey Air Pollution Code).
FIGURE 2 Stack mounted opacity meter (Bailey Meter
Co.).
SPOTLAMP
LIGHT SOURCE
SPACED FLANGES FOR AIR INLET
SMOKE OR DUST PASSAGE
BOLOMETER SPACED FLANGES
FOR AIR INLET
Trang 5The particular regulation shown also accounts for differing
toxicity of certain particulates and allocates the emission
factors of Table 2 accordingly
Very often permissible ground level concentrations are
set according to other sources in the area Thus a plant would
be allowed greater emissions in a rural area than in a heavily
industrialized neighbourhood
Dust fall
A variant on the ground level concentration limit is a dustfall
limit This basically superimposes a particle settling velocity
on ground level concentration to obtain dustfall rates in weight
per unit area per unit time This is a meaningful regulation
only for large particles and is not widely legislated at present
Federal Clean Air Statutes and Regulations
The major federal statutes covering air pollution are PL 88– 206
(The Clean Air Act of 1963), PL 90–148 (The Air Quality Act
of 1967) PL 92–157, PL 93–115, PL 95–95 (The Clean Air
amendments of 1977), and PL 95–190, Administrative
stan-dards formulated by the Environmental Protection Agency
(EPA) are given in the Code of Federal Regulations Title 40,
parts 50, 51, 52, 53, 58, 60, 61, and 81
The EPA has established National Ambient Air Quality Standards (NAAQS) For suspended particulate matter the primary standard (necessary to protect the public health with
an adequate margin of safety) is 75 µ g/M 3 annual geometric
mean with a level of 260 µ g/M 3 not to be exceeded more than once per year All states have been required to file state implementation plants (SIP) for achieving NAAWS It is only through the SIP’s that existing pollution sources are regulated
The EPA requires no specific state regulations for limits on existing sources, but suggestions are made for
“emission limitations obtainable with reasonable available technology.” Some of the reasonable limits proposed for particulates are:
1) Ringlemann 1 or less, except for brief periods such as shoot blowing or start-up
2) Reasonable precautions to control fugitive dust, including use of water during grading or demo-lition, sprinkling of dusty surfaces, use of hoods and vents, covering of piles of dust, etc
3) Incinerator emission less than 0.2 lbs/100 lbs refuse charged
4) Fuel burner emissions less than 0.3 lbs/million BTU heat input
5) For process industries, emission rates E in lbs/hr and Process weight P in tons/hr according to the
relationships:
E = 3.59 P 0.62 for P ⭐ 30 tons/hr
E = 17.31 P 0.16 for P ⭓ 30 tons/hr
“Process weight” includes all materials introduced to the process except liquid and gaseous fuels and combustion air Limits should be set on the basis of combined process weights of all similar units at a plant
In considering what emission limits should be estab-lished, the states are encouraged to take into account local condition, social and economic impact, and alternate control strategies and adoption of the above measures is not manda-tory It is expected, however, that such measures will become the norm in many areas
For new or substantially modified pollution sources, the EPA has established new source performance standards The standards for particulate emissions and opacity are given in
EPA for technical advice They must provide ports, plat-forms, access, and necessary utilities for performing required tests, and the EPA must be allowed to conduct tests at rea-sonable times Required records and reports are available
to the public except where trade secrets would be divulged
The states are in no way precluded from establishing more stringent standards or additional procedures The EPA test method specified for particulates measures only materials collectable on a dry filter at 250°F an does not include so called condensables
TABLE 2 Pollution Control Code)
Fine Solid Particles
Chapter 1, Sub-chapter C, with regulations on particulates in
Trang 6In addition to new source performance standards, major
new stationary sources and major modifications are usually
subject to a “Prevention of Significant Deterioration” review
If a particulate source of more than 25 tons/year is located
in an area which attains NAAQS or is unclassifiable with
respects to particulates, the owner must demonstrate that the
source will not violate NAAQS or PSD concentration
incre-ments This requires modelling and preconstruction
moni-toring of ambient air quality If the new or expanded source
is to be located in an area which does not meet NAAQS, then
emission from other sources must be reduced to offset the
new source The regulation regarding emission offsets and
prevention of significant deterioration are relatively recent
A summary of federal regulations as of 1981 has recently
been published as a quick guide to this rapidly changing
field. 18
In recent years, regulation of particulate emissions from
mobile sources has been initiated The burden is essentially
on manufacturers of diesel engines Because the emission
requirements and test procedures are quite complex and
because the target is highly specific, a comprehensive
discus-sion is beyond the scope of this article Some representative
standards are: Diesel engines for urban buses, 0.019 grams/
megajoule, and other diesel engines for road use, 0.037 grams/
megajoule: 19 Non-road diesel engines, 1 gram/kilowatt-hour
for sizes less than 8 kilowatts in tier 1 down to 0.2 grams/
kilowatt-hour for units larger than 560 kilowatts in tier 2. 20
Locomotives, 0.36 grams/bhp-hr for switching service in tier
1 down to 0.1 grams/bhp-hr for line service in tier 3. 21 Marine
diesel engines, 0.2 grams/KwH to 0.5 grams/KwH, depending
on displacement and tier. 22 Note that the emission units above
are as specified in the printed regulation
Particulate emission standards are also being promulgated
by agencies other than the Environmental Protection Agency
In general, these are workplace standards An example
would be the standard for mobile diesel-powered
transporta-tion equipment promulgated by the Mine Safety and Health
Administration This specifies that the exhaust “shall not
con-tain black smoke.” 23
MEASUREMENT OF PARTICULATE EMISSIONS
As a first step in any program for control of particulate
emis-sions, a determination must be made of the quantity and
nature of particles being emitted by the subject source The
quantity of emissions determines the collection efficiency
and size of required cleanup equipment The particle size and
chemical properties of the emitted dust strongly influence
the type of equipment to be used Sampling for this purpose
has been mainly a matter of industrial concern A last step
in most control programs consists of measuring pollutants
in the cleaned gas stream to ensure that cleanup equipment
being used actually permits the pertinent emission targets to
be met With increasing public concern and legislation on air
pollution, sampling for this purpose is increasingly required
by statute to determine compliance with the pertinent
emis-sion regulations To this end the local pollution control
authority may issue a comprehensive sampling manual which sets forth in considerable detail the procedures to be used in obtaining raw data and the computations involved in calculating the pertinent emission levels
Complete and comprehensive source testing procedures are beyond the scope of this paper References 24–28 give detailed instruction for performance of such tests
Sampling of gas streams, especially for particulates, is simple only in concept Actual measurement require special-ized equipment, trained personnel, careful experimental and computational techniques, and a considerable expenditure
of time and manpower Matters of technique and equipment are covered in source testing manuals as mentioned above and are briefly summarized later in this paper Two addi-tional complicating factors are usually present First is the frequent inaccessibility of sampling points These points are often located in duct work 50–100 ft above ground level
Scaffolding must often be installed around the points, and several hundred pounds of equipment must be lifted to that level Probe clearances are often critical, for in order to make
a sample traverse on 12 ft dia stack, a 14 ft probe is needed, and clearance must be available for insertion into the sam-pling port as well as a means for suspending the probe from above At least one professional stack sampler is an ama-teur mountain climber and puts his hobby to good use on the job A second complicating factor is the adverse physical conditions frequently encountered A somewhat extreme but illustrative example is a refinery stream recently sampled Gas temperature was 1200°F requiring special probes and gas-kets and protective clothing for the workers The gas stream contained 10% carbon monoxide creating potential hazards
of poisoning and explosion especially since duct pressure was slightly above that of the atmosphere Temperature in the work area was in excess of 120°F contributing further to the difficulty of the job
In preparation for a sampling program, work platforms
or scaffolding and valved sample ports must be installed
All special fittings for adapting the sampling probes to the ports should be anticipated and fabricated Arrangements must be made with plant operating personnel to maintain steady operating conditions during the test The test must
be carefully planned as to number and exact location of tra-verse sample points, and probes should be premarked for these locations Flow nomographs for sampling nozzles should be made; and all filters, impingers, and other ele-ment of sampling trains should be tared With that advance preparation a 3 man sampling team would require 1–2 days
to position their equipment and make gas flow measure-ments and 2 sample transverses at right angles in a large duct or stack
Measurement of Gas Flow Rates
A preliminary step in determination of emission rates from
a stack is measurement of the gas flow rate Detailed pro-cedures in wide use including the necessary attention to technique have been published by the ASME, 20 ASTM, 19
the Environmental Protection Agency, referred to as EPA, 21
Trang 7TABLE 3 Federal Limits of Particulate Emissions from New Stationary Sources (Through 2004 Codified in CFR, Title 40 Chapter 1/Part 60)
(27% for 6 min/hr)
(27% for 6 min/hr)
(6 min/hr exception)
(20% once per production cycle)
(continued)
Trang 8TABLE 3 (continued)
calcium silicon or silicomanganese zirconium alloys
tap period
smelt dissolving tank lime kiln, gas fired
10 g/dscm 0.1 g/kg black liquor solids 0.15 g/dscm 0.30 g/dscm
35
—
—
—
pressed & blown glass, borosilisate pressed & blown glass, soda lime & lead pressed & blown glass, other compositions
Gas fuel
l0.1 g/kg glass 0.5 g/kg 0.1 g/kg 0.25 g/kg 0.25 g/kg 0.225 g/kg
Oil fuel
l0.13 g/kg glass 0.65 g/kg 0.13 g/kg 0.325 g/kg 0.325 g/kg 0.225 g/kg
—
—
—
—
—
— Glass manufacture, modified process
container, flat, pressed, blown glass, soda lime container, flat, pressed, blown glass, borosilicate textile and wood fiberglass
0.5 g/kg 1.0 g/kg 0.5 g/kg
*
*
*
column dryer, plate perforation >2.4 mm rack dryer, exhaust screen filter cans thru 50 mesh
fugitive, truck unloading, railcar loading/unloading fugitive, grain handling
fugitive, truck loading fugitive, barge or ship loading
—
— 0.023 g/dscm
—
—
—
—
0 0 0 5 0 10 20
0.05 g/dscm
—
7 10
dyer calciner, unbeneficiated rock calciner, beneficiated rock
0.03 g/kg rock 0.12 g/kg rock 0.055 g/kg rock 0.0006 g/kg rock
10*
10*
10*
0*
(continued)
Trang 9TABLE 3 (continued)
shingle of mineral-surfaced roll saturated felt or smooth surfaced roll Asphalt blowing still
with catalyst addition with catalyst addition, #6 oil afterburner
no catalyst, #6 oil afterburner Asphalt storage tank
Asphalt roofing mineral handling and storage
0.04 g/kg 0.4 g/kg 0.67 g/kg 0.71 g/kg 0.60 g/kg 0.64 g/kg
20 20
—
—
—
— 0 1
with catalytic combustor
no catalytic combustor
4.1 g/hr 7.5 g/hr
—
—
stack or transfer point on belt conveyors
0.05 g/dscm
—
—
7 10 15
*Continous monitoring by capacity meters required
The above standards apply to current construction Existing unmodified units may have lower standards.
Many applications require continuous monitoring of operating variables for process and control equipment.
the Lost Angeles Air Pollution Control district, referred
to as APCD, 21 and the Western Precipitation Division,
referred to as WP. 21 This article will only treat the general
procedures and not significant differences between
popu-lar techniques
Velocity Traverse Points Because of flow non-uniformity,
which almost invariably occurs in large stacks, the stack
cross section in the sampling plane must be divided into a
number of smaller areas and gas velocity determined
sepa-rately in each area Circular ducts are divided by concentric
circles, and 2 velocity traverses are made at right angles
Figure 4shows a typical example Location of the sample
points can be determined from the formula
N
n⫽ 2 ⫺1
2
where
R n = distance from center of duct to the “ n th” point
from the center
D = duct diameter
n = sample point number, counting from center
N = total number of measurement points in the duct The number of sample points along one diameter is N /2
For rectangular ducts the cross section is divided into
N equal rectangular areas such that the ratio of length to
width of the areas is between one and two Sample points are
at the center of each area
The number of traverse points required is usually speci-fied in the applicable test code as a function of duct area or diameter Representative requirements are shown in Table 4
S-6 S-5
S-4
E-4 E-5
EAST
S-3
S-2 S-1
SOUTH
R3
R2
R1
FIGURE 4 Velocity and sampling traverse positions
in circular ducts.
Trang 10Very often more points are required if the flow is highly
non-uniform or if the sampling point is near an elbow or other
flow disturbance Figure 5shows the EPA adjustment for
flow nonuniformity
Velocity Measurement Velocity measurements in dusty
gases are made with a type S (special or staubscheibe) pitot
tube, shown in Figure 6,and a draft gage manometer Gas
velocity is given by
V⫽C 2gh L r r L/ g where
V = gas velocity
C = pitot tube calibration coefficient This would be
1.0 for an ideal pitot tube, but type S tubes deviate con-siderably
g = acceleration of gravity
h L = liquid height differential in manometer
L = density of manometer liquid
g = gas density
It is necessary to measure the temperature and the
pres-sure of the gas stream and estimate or meapres-sure its molecular
weight in order to calculate density
Gas Analysis For precise work gas composition is needed
for three reasons (1) so that molecular weight and gas density
may be known for duct velocity calculations, (2) so that duct
flow rates at duct condition can be converted to
standard-ized conditions used for emission specifications Standard
conditions are usually 70°F, 29.91 in mercury barometric
pressure, moisture free basis with gas volume adjusted to
TABLE 4 Required traverse points
More according to Figure 2 if near flow disturbance
4 12
20 or more
and
1–2 ft dia.
2–4 ft 4–6 ft
>6 ft
4 6–24 24 12 16 20
24 or more These numbers should be doubled where only 4–6 duct
diameters of straight duct are upstream.
8–12 12–20 Double or triple these numbers for high nonuniform flow.
NUMBER OF DUCT DIAMETERS DOWNSTREAM*
(DISTANCE B)
DISTURBANCE SAMPLING
DISTURBANCE
*FROM POINT OF ANY TYPE OF DISTURBANCE (BEND, EXPANSION, CONTRACTION, ETC.)
NUMBER OF DUCT DIAMETERS UPSTREAM*
(DISTANCE A)
SITE A
B
0 10 20 30 40
50
FIGURE 5 Sampling points required in vicinity of flow
distur-bance (EPA).
TUBLING ADAPTER PIPE COUPLING
STAINLESS STEEL TUBLING
FIGURE 6 Type S Pitot tube for use in dusty gas
stream.
12% CO 2 Some codes differ from this, however (3) For iso-kinetic sampling moisture content at stack conditions must
be known in order to adjust for the fact that probe gas flow is measured in a dry gas meter at ambient conditions