United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-85-005 Jan. 1985
Project Summary
Technical Assistance
Document for Monitoring
Sulfuric Acid Vapor from
Stationary Sources
William T. Winberry, Jr.
This document has been prepared for
the purpose of providing guidance on
the selection and use of source emission
monitoring techniques for monitoring
sulfuric acid vapor from stationary
sources. The different types of moni-
toring principles are discussed with
their advantages and limitations. Sec-
tions providing statistical evaluation of
different monitoring techniques - both
laboratory and field evaluation - are in-
cluded in the document. Also included
is a section dealing with generating
known concentration of sulfuric acid
vapor used in evaluating monitoring
techniques.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
When fuels containing sulfur are
burned, almost quantitative formation of
sulfur dioxide (S02) occurs. As much as 5-
8% of the sulfur dioxide emitted may be
converted to sulfur trioxide either by
Atomic oxygen in the combustion zone or
by efficient catalysis of heavy metal
contaminants in the fuel oil. At moisture
levels above four percent and temperatures
below 300°F (149°C), theoretical models
indicate that the sulfur trioxide quickly
combines with the water vapor present to
form sulfuric acid vapor. This newly
formed sulfuric acid vapor sorbs onto
particulate matter, causing "acid smut."
Excess amounts of sulfuric acid vapor or
acid smut can cause corrosion within the
flue gas ductwork. Once emitted, the
condensed sulfuric acid increase can also
cause plume opacity of an affected
industrial process.
Sulfuric acid in the flue gas can be
found as:
(1) A gas phase component at stack
temperature and water vapor concen-
tration;
(2) A condensed liquid droplet at
temperatures below the acid dew
point; or
(3) Absorbed on particulate matter at
stack gas temperature. In addition,
the free acid may react with metal
oxides formed in the combustion
flame to yield sulfates as Na2SO4,
MgS04, and FeafSCUh.
The composition and concentration
of the chemical species emitted are
influenced by fuel characteristics, boiler
design and operation, and emission
controls. It is precisely this combination
of emissions of different species of
sulfates that has hindered the characteriza-
tion and measurement of sulfuric acid
vapor from combustion sources.
EPA Federal Reference Method 8 was
established as a standard procedure for
monitoring SOa and HaSO* vapor from
acid production plants. Because of
sulfuric acid plant emissions (low particu-
late matter). Federal Reference Method 8
is applicable to only that source. Unlike
Method 8, those sampling techniques
associated with monitoring SO3 and
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H2S04 vapor from combustion sources
have had the problem of distinguishing
S03 HzSCU emissions from paniculate
sulfate emissions. Many analytical
techniques have been developed in order
to distinguish between paniculate matter
and sulfuric acid emissions.
The primary objectives of this technical
document are to present a detailed
summary of those analytical techniques
presently in use to monitor sulfuric acid
vapor from stationary sources. The
document is to provide guidance to users
concerning the advantages, limitations,
and performance characteristics of each
available technique. The author's experi-
ence with each technique serves as the
basic background material for this docu-
ment.
In particular. Section 7 of this document
summarizes the performance characteris-
tics of each of the reviewed monitoring
techniques, including advantages and
disadvantages. Table 1 illustrates those
findings.
Table 1. Sulfuric Acid Monitoring Systems: Advantages and Disadvantages
Method Abbreviation
Deposition Rate Probe (DRPj
Dew Point Meter (DPM)
Controlled Condensa- (CCS)
tion System
Modified Federal (MM6)
Reference Method 6
Severn Science Ltd. (SSL)
Continuous SOs/H-gO*
Analyzer
Variable Time
Measured Required
Rate of acid 3 to 5 hr.
deposition including
set-up &
lab work
Temperature 1/2-2 hr.
at which acid
condenses on
probe. Rate
of acid depo-
sition
S03/«2SO«/S02 1-2hr.
and other ap-
propriate
gases
Total Water 1/2-2 hr.
Soluble Sul-
fates (TWSS)
&S02
SOz/HzSO* 2 min.
Advantages
• Can determine
acid dew point
& rate of acid
deposition
• Can run addi-
tional analy-
sis
• Quick and easy
• Measures
rate of
buildup
and dew point
• Portable; (can
go to many
locations in
one day)
• Direct
measure-
ment of
sulfuric
acid vapor
• Sulfur balance
can be deter-
mined
• Compact, sim-
ple to oper-
ate
• Limited ex-
perience to
operate
• Portable, com-
pact
• Umbilical cord
allows for
flexibility.
adaptability
• Monitor simple
to operate
• Can visit many
locations at
one source
Disadvantages
• Good analytical *
techniques needed
• Paniculate build- «
up causes inter-
ference t
• Warmup error
• Dirty gas stream t
interferes
• HzSO* aerosol t
interferes
Low acid con- <
centration may
require several
hours to get dew
point
• Collection effi- t
ciency questionable t
• Temperature
control critical t
• Flow rate critical
• SO 2 oxidation may t
occur
• Paniculate/gas
separation
questionable
• Complete sample
recovery needed
• SOz oxidation may t
occur
• Paniculate/ 'gas
separation <
• Artifact forma-
tion
• Metal interference
• Equilibrium time <
required
• Artifact forma-
tion may occur
• Solution reservoir
needs periodic
refills
• Minimum moisture
required for
proper operation
O4%)
Comments
t Data scattered.
hard to interpret
> Distinct acid dew
point hard to find
\ Limited number of
data points can be
taken
> Calibration diff-
icult
> Reproducibility
poor
> No sample
collected for
further analysis
» Bulky
> Reproducibility
problems
> Long probe re-
quired
> Recovery crit-
ical; laboratory
techniques must
be good
t Only gives
TWSS & SOi
values
> Requires good
laboratory tech-
nique
> Frequent ad-
justments of
flow rates
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Table 1. (Continued)
Variable Time
Method Abbreviation Measured Required
Miniture acid con- (MACS) SOz/HiSOt 1 -2 hr.
densation system
Sulfuric acid fSAMMj SOs/HiSOt 1 -999 sec
mist monitor
Federal Reference (RMS) SOa/tf jSO4/S02 1 -2 hrs
Method 8
Laser Analytics 4%)
• Bulky, heavy
• Undetected leaks
in gas sampling
system may cause
problems
• Paniculate
interference
• Metal inter-
ference
• Isokinetic
sampling re-
quired
• Not a field
instrument
• High technical
capability requir-
ed to operate
• In-situ monitor.
therefore, can't
move around easily
• Field instru-
ment, but a high
level of techni-
cal background
needed to operate
Comments
• Much better
than larger
controlled
condensation
version
• Not commercially
available
• Satisfactory
degree of
reproducibility
• Extreme care
in handling
because of
glassware
• Not commercially
available
• Laboratory
techniques must
be good
• Bulky
• Applicable to
sulfuric acid
plants only
• Research tool
• Expensive
• Need high level
of technical
experience to
operate
• Research tool
• Expensive
• Need technical
experience to
operate
• Not commercially
available
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William T. Winberry, Jr., is with Engineering-Science, Durham, NC 27701.
Tom Logan is the EPA Project Officer (see below).
The complete report, entitled "Technical Assistance Document for Monitoring
Su If uric A cid Vapor from Stationary Sources." (Order No. PB 85-143 261; Cost:
$14.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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