xvEPA
United States
Environmental Protection
Agency
Environmental Monitoring Systems
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-81-024 July 1981
Project Summary
Evaluation of Molecular
Sieves for Sampling NO,
Emissions at Electric
Utility Plants
Henry F. Hamil
A field study was conducted to
evaluate the use of molecular sieves
for collection of NOx (NO + NOa) emis-
sions from utility boilers. It was found
that NOx could be collected efficiently
(>99%) at sample flow rates of 1
L/min over 20- to 40-min sampling
periods at the NOx levels encountered
in modern utility boilers. The removal
of the stack gas moisture by use of an
impinger train or condenser ahead of
the sample trains was shown to be
necessary for efficient NOx collection.
This Project Summary was develop-
ed by EPA's Environmental Monitor-
ing Systems Laboratory, Research
Triangle Park. NC. to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The Source Branch (SB)of the Quality
Assurance Division (QAD), EMSL/EPA,
is involved in developing new methods
for N0« collection at a coal-fired electric
utility plant.
reason for undertaking this work is that
the present reference method (Method
7) for measuring these emissions is
restricted to a sampling time of only 15
seconds. This necessitates multiple
samplings to obtain a sample represen-
tative of the emissions.
The first phase of this work involve,d a
laboratory study to screen potential NOx
collection systems. (This work will be
published at a later date.) One of the
promising systems for this work utilized
-molecular sieves to collect the NOX. A
work assignment was then issued to
Southwest Research Institute to
conduct a field evaluation of this system
for NOx collection at coal-fired electric
utility plant.
The field sampling train utilized was
similar to an EPA Method 6 sampling
train with the following exceptions: the
molecular sieve containers (either a 2.0
x 14-cm glass tube, glass midget
impingers, or stainless steel midget
impingers) were used in place of the
standard midget impinger setup of
Method 6, and provisions were made to
monitor the effluent from the molecular
sieve bed with a continuous NOX moni-
tor to assess NOX collection efficiency
The variables studied included (1) the
type and amount of molecular sieve
used; (2) the type of molecular sieve
container used; (3) the effect of sample
flow rate on NOx absorption efficiency;
(4) the effect of uncondensed water
vapor in the sample on NOx collection
efficiency; and (5) the effect of cooling
the molecular sieve bed on NOx collec-
tion efficiency.
The NOx-molecular sieve samples
generated in this work will be used by
the SB to test and refine analytical
> US GOVERNMENT PRINTING OFFICE 1961 -757-012/7170
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recovery procedures developed in the
laboratory.
Conclusions
The data obtained in this study indi-
cate that molecular sieves provide a
sampling medium for high efficiency
collection of NO, from fossil fuel-fired
utility boilers.
Sample collection efficiency is direct-
ly proportional to the amount of
molecular sieve used in the sampling
train and inversely proportional to the
sample flow rate. Sampling can be
carried out for 40 minutes at a flow rate
of 1.0 L/min with 60 g of molecular
sieves with a 99+% collection efficiency
at NOx levels of 200 ppm.
The stack gas moisture content must
be removed ahead of the molecular
sieves. Failure to remove the moisture
rapidly depletes the capacity of the
sieves for NOx due to absorption of the
water vapor.
Henry F. Hamil is with the Southwest Research Institute, San Antonio. TX 78284.
John H. Margeson is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Molecular Sieves for Sampling NOx
Emissions at Electric Utility Plants," (Order No. PB 81-178 865; Cost: $6.50,
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
Recommendations
Since the moisture removal system
showed some NOX absorption, other
moisture removal systems, such as cold
traps, should be investigated in order to
minimize NOx absorption. Further tests
should be conducted on the molecular
sieve collection procedure at different
fuel-type boilers and after different
type control devices. Additional work is
needed to complete development of the
cadmium reduction-colorimetric and
nitrate-electrode-analytical recovery
procedures before a viable sampling
and analytical procedure is obtained.
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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Fees Paid
Environmental
Protection
Agency
EPA 335
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Penalty for Private Use $300
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