NBSIR 74-612

Building and Evaluation of a

Second Polluted Air Delivery System

G. P. Baumgarten

Fluid Meters Section

Mechanics Division

National Bureau of Standards

Washington, D. C. 20234

November 1974

Final Report on PADS 2

Prepared for Environmental Protection Agency

National Environmental Research Center

Quality Control Branch

Chemstrand BIdg.

Research Triangle Park, N. Carolina 27711

NBSIR 74-612

BUILDING AND EVALUATION OF A

SECOND POLLUTED AIR DELIVERY SYSTEM

G. P. Baumgarten

Fluid Meters Section

Mechanics Division

National Bureau of Standards

Washington, D. C. 20234

November 1974

Final Report on PADS 2

Prepared for Environmental Protection Agency

National Environmental Researcti Center

Quality Control Branch

Chemstrand BIdg.

Research Triangle Park, N. Carolina 27711

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

Building and Evaluat

Second Polluted

Delivery Syst em

ion of a Air

ABSTRACT

The building and evaluation of a second configuration of a prototype SO2

and CO polluted air delivery systejn (PADS) is discussed. The delivery

system was built to deliver sulfur dioxide (SO2) and carbon monoxide (CO)

at a rate of 5 liters per minute. The design concentrations by volume

were 1.0, 0.5, 0.1, and 0.04 parts per million (ppm) of SO2 in air and

50, 20, and 2 parts per million of CO in nitrogen. It consists of a diluent

air delivery system utilizing a critical flow sonic nozzle and three separate

pollutant flow systems utilizing laminar flow porous plugs, one plug for

each desired output concentration. The system is contained in a dispatch

case and the gases are delivered to it from pressurized containers through

detachable supply lines.

By maintaining specific upstream pressures on the critical flow nozzle and

the laminar flow porous plugs, PADS 2 produced average output concentrations

of; 0.95, 0.50, 0.117, and 0.057 ppm of SO2 ; and 52.9 and 18.1 ppm of CO.

These concentrations were determined by measurements with NBS calibrated

analyzers. The expected output concentrations were 0.93, 0.52, 0.103, and

0.05 ppm of SO2 and 51.2, 18.0, and 1.49 ppm of CO based on flow calibrations

of the individual components. The uncertainty of the output concentration

is estimated to be about 7 percent.

Polluted Air Delivery System 2

Introduction

This report covers the partial evaluation of a second flow configuration

of a polluted air delivery system (PADS) designed to produce known

concentrations of pollutants in air. The evaluation of the first PADS was covered in reference 1. The gas flow configuration of PADS 2 was designed to be sjnranetrical about a new gas mixing chamber constructed

of Teflon as opposed to stainless steel in PADS 1. This change was

to reduce the tube surface area to which the polluted mixture would be

exposed. These changes were expected to, and did, improve equilibration

time and reproducibility of performance.

The PADS

PADS 2 was designed to produce sulfur dioxide (SO2) pollutant

concentrations of 0.04, 0.1, and 1.0 parts per million by volume

(ppm) in air. These concentrations were produced by mixing air

containing an average initial concentration of 2240 ppm of SO2

with pure air flowing at a rate of 5.0 liters per minute. PADS 2 was also designed to produce carbon monoxide, CO, pollutant concentrations of 2, 20, and 50 ppm in air. CO concentrations were produced

by mixing nitrogen containing 42,100 ppm of CO with pure air flowing

at a rate of 5.2 liters per minute.

The dilute mixtures were produced as follows. The diluent air flow

of 5 liters per minute, Lpm, for SO2 and 5.2 Lpm for CO, was metered

with a critical flow nozzle having a throat diameter of 0.0396 cm. The nozzle was operated with an upstream pressure, P^, of 38 and 40

psig, (2.62 X 10^ and 2.76 x lO^n/m^ gage) for SO2 and CO respectively.

The pollutant was metered through one of three porous plug laminar

flow restrictors for any one of the desired output concentrations.

The porous plugs were operated at upstream pressures of 13, 14.3,

and 11.2 psig (^.96 x 10^, 9.86 x 10\ and 7.72 x lO'' n/m^ gag^ for SO2

and 12 psig(8.27 x 10^ n/m^ gage) for CO. Pollutant flow rates at

these pressures are 0.11, 0.23, and 2.1 cubic centimeters per minute,

cc/min, for SO2 and 0.19, 2.2, and 6.4 cc/min for CO.

Figure 1 is a schematic of PADS 2. This piping configuration was chosen in order to shorten the flow path of pollutant gas between

its flow restrictor and the mixing chamber. It was expected that

this reduction of surface area in contact with the metered pollutant

would reduce the amount of metered pollutant adsorbed. The mixing

chamber and outlet manifold is the only part of the system that is

made differently than in PADS 1. They are combined in a single piece

of Teflon. Improved mixing and reduction of SO2 adsorbed from the

outlet mixture was also expected from this change.
- 2 -

A detailed explanation for choosing the devices and parts used in

the PADS is covered on pages 1 and 2 of reference 1.

Evaluation of PADS 2

It was hoped that PADS 2 could be evaluated considering all of the

performance characteristics as performed for PADS 1 and listed In

reference 1, pages 2 and 3. However, due to inadequate time and

resources, it was not possible to complete the program. A limited

amount of data was obtained using the unit with both SO2 and CO

which will be the basis for the evaluation.

The purchased pollutant gases used in the tests, SO2 and CO, and

the SO2 analyzer were calibrated by the Air Pollution Analysis

Section, Analytical Chemistry Division of NBS. The SO2 pollutant

was analyzed twice by titration with standarized sodium hydroxide.

On August 1, 1973, the concentration was 2230 ppm at a bottle

pressure of 2000 pounds per square inch (psi) (1.379 x 10 n/m^ gage)

and on February 27, 1974, the concentration was 2250 ppm at a bottle

pressure of 1300 psi. (8.963 x 10^ n/m^ gage). The CO pollutant

was analyzed by comparison with two standards containing 3.95 and

A. 06 percent of CO in Nitrogen. The analysis was made by gas

chomatography which yielded a concentration of 4.21 percent. Both

gas analyses have a relative uncertainty of 1 percent of concentration.

The calibration of the SO2 analyzer was performed by using air

containing known amounts of SO2, supplied by NBS standard reference

material permeation tubes, and measured flows of air. The

concentration indicated by the voltage output, not the visual

dial, was within ± 2 percent full scale of the calibration values.

The CO analyzer was a gas chromatograph , which was calibrated at

least twice each day, whenever data was taken for PADS 2, with two

standard samples of 8.29 and 50.1 ppm of CO in N2

Referring to Section 3.1 of reference 1, the characteristics

evaluated are numbers 1 and 4, kinetic behavior (equilibration time)

and reproducibility. The results for PADS 1 for the remaining

performance characteristics, except factor number 3, would apply

equally well to PADS 2.

1. The time required for PADS 2 to achieve an equilibrium state was 30 minutes or less for all concentrations with either pollutant.

The time period for 95 percent of final concentration varied from

20 minutes down to one. The higher concentrations gave shorter

equilibration times. An insert was installed in the mixing

section, figure 2 and 3, to improve equilibration time and mixing

efficiency. Although it did not shorten the equilibration time

for PADS 2, it did improve the uniformity of concentration across

the outlet flow.
- 3 -

Reproducibility was based on the standard deviation of the constant

K, (equation 3, in reference 1) as determined from the measurements,

where

Ci P2(1+P2/2B) ^ " C~ Pi+B

and Ci is the known inlet concentration of SO2 in air

supplied to the porous plugs, ppm.

C is the output concentration of the system, ppra.

?! is the inlet gage pressure for the critical nozzle in psig.

P2 is the inlet gage pressure for the porous plugs in psig.

B is the barometric pressure in psia.

These values for the constant K apply only at the conditions

which existed during evaluation at NBS. Any other evaluation

of the unit at different conditions would need different values

of K derived by application of equation 1 page 3 of reference 1.

The average barometric pressure during evaluation of PADS 2 was

14.55 ± 0.02 psia (1.003 x 10^ ± 138 n/ra^) and the temperature

was 24.9 ± 2.2°C. Barometric pressures and temperatures for each

concentration are included in table 1. The gages used for measuring

Pi and P2 were calibrated and are accurate within the readability

of the gage. The pressures used and mentioned in this report were

in a range where no correction to the readings was necessary.

For the desired output concentrations of 0.04, 0.1, and 1.0 ppm

of SO2 the value of K is 14000, 7770, and 693 with actual output

concentrations of 0.057, 0.117, and 0.95 ppm. The estimate of

standard deviation, S, for each of these K values is ± 3.3, ± 3.9,

and ± 0.8 percent, of K, respectively. An extra concentration and

K value was determined by operating the highest concentration porous

plug flow restrictor at 1/2 of the original pressure. The desired

concentration was 0.5 ppm and it had K and S values of 647 and ± 0.7

percent of K and the actual concentration was 0.50.

For the desired output concentrations of 2, 20 and 50 ppm of CO,

the values of K and S are; 8685 ±0.3 percent of K, 723 ±4.6

percent of K, and 247 ± 2.9 percent of K. The value of K at the

lowest concentration is based on flow calibrations of the porous

plug and nozzle because a standard sample of low CO concentration

was not available at the time the tests were run for calibration

of the CO analyzer.
- 4 -

A comparison can be made between the resulting output concentration

chemically measured and the expected output concentration based on relative flow rates through the porous plugs and nozzle as determined

by flow calibrations and equation 2, page 4 of reference 1. The

average output concentrations of SO2, measured chemically, were 0.95,

0.50, 0.117, and 0.057 ppm, compared to expected concentrations of

0.93, 0.52, 0.103, and 0.050 ppm. The average output concentrations

of CO were 53 and 18 ppm, compared to expected outputs of 51 and 18 ppm.

All of the evaluation results are presented in table 1. The results

are the averages of from four to ten separate tests.

4. Conclusions ,

-

The changes in the design of the PADS did make an improvement.

Improvement in equilibration time appears at the highest and lowest

concentrations of SO2 in air. The time required to attain 95 percent

of the equilibration value reduced from 4 minutes to 1 minute at 1 ppm

and from 25 to 11 minutes at the lowest concentration. Of course

the lowest concentrations are not the same for both PADS. The low

concentration in PADS 2 was designed to be higher than in PADS 1

to improve total performance.

Comparing the standard deviations of the value K for PADS 1 and 2 indicates a marked improvement for PADS 2: from ± 4.4 percent

to ± 0.8 percent at 1 ppm; ± 4.6 percent to ± 0.7 percent at 0.1 ppm;

and from ± 61 percent to ± 3.3 percent at the lowest concentration.

Comparing the output concentration obtained with expected output

concentration gives an average uncertainty of about 7 percent.

No comparisons can be made for CO, since PADS 1 was not used with CO.

5. Reference 1

Building and Evaluation of a Polluted Air Delivery System, NBSIR

73-414, April 1974.

NBS

213.06

G. P. Baumgarten

11/12/74
- 5 -

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- 6 -
MIXING CHAMBER SHOWING INSERT, POLLUTANT CONNECTOR,

AND CRITICAL NOZZLE POSITIONS

Critical

flow Nozzle

Figure 2
- 8 -

TEFLON INSERT INTO MIXING CHAMBER

5 +

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7^ CIV,

Figure 3

TEFLON POLLUTANT CONNECTOR-VALVE TO MIXING CHAMBER

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Figure 4

USCOMM-NBS-DC
I NBS-1 l^A <nc:v. 7-73)

U .-3. CZPT . OF COMM . BIBLIOGRAPHIC DATA

SHEET

1. IMUl.ICATIdN OK K1:P0K I' NO.

NBSIR 74-612

2. Ciov 't Ac t e s s 1 on

N.i.

3. I< r ( 1 p I cll t

' s Ac Cl- - 1.111 .\ w .

4. 1111.1. A.-.i) -^l HI ITLl-:

Building and Evaluation of a Second Polluted Air Delivery

System

5. 1 'u M u .1 1 loll Dai ( November 1974

6. Pcrlormm^ Or^an i /.itum ( cdc

7. Ai rilOKi^' G. P. Baumgarten

8. Per 1 or n'li n < Or^aii. Kcport No. NBSIR 74-612

9. PI-.Ki-OKMl.W; <)l<t,A.\ I/.ATION \A.MI-: ANO Al)I)Ri:SS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proii-ct lask/Uork L'ni: No. 2130468

11. f .ontracl ' (irant No.

12. ~-p.>n -...r i IV. ( V>;an iz at lun N'amc and CompU tc Address (Street, City. Stole, ZIP)

Environmental Protection Agency

Xacional Environmental Research Center

Quality Control Branch

Chenstrand Bldg., Research Triangle Park, N. Carolina 27711

13. Type of Kcport & l-'criod Cov crtd Final Report on PADS 2

14. Sponsoring Agency Code*

15. .sri'i^i.!-. v,i N l AK"*' .\ori-;s

16. Ai'"- IK A( r (A 200-\\orJ or less factual summory o( most si^ificant information. If documcnf includes a significant

hihUnp,rul,hv or litcr^iturt- survey, mention it here.)

The building and evaluation of a second configuration of a prototype SO2 and CO polluted

air delivery system (PADS) is discussed. The delivery system was built to deliver

sulfur dioxide (SO2) and carbon monoxide (CO) at a rate of 5 liters per minute. The

design concentrations by volume were 1.0, 0.5, 0.1, and 0.04 parts per million (ppm)

of SO2 in air and 50, 20, and 2 parts per million of CO in nitrogen. It consists of a diluent air delivery system utilizing a critical flow sonic nozzle and three separate

pollutant flow systems utilizing laminar flow porous plugs, one plug for each desired

output concentration. The system is contained in a dispatch case and the gases are delivered to it from pressurized containers through detachable supply lines.

By maintaining specific upstream pressures on the critical flow nozzle p.ud the laminar

flow porous plugs, PADS 2 produced average output concentrations of; 0.95, 0.50, 0.117, and 0.057 ppm of SO2 ; and 52.9 and 18.1 ppm of CO. These concentrations were determined

by measurements with NBS calibrated analyzers. 'The expected output concentrations were

0.03, 0.52, 0.103, and 0.05 ppm of SO2 and 51.2, 18.0, and 1.49 ppm of CO based on flow

calibrations of the individual components. The uncertainty of the output concentration

is estimated to be about 7 percent.

17. KI.'l' \SORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

I

j Air pollution; critical flow; laminar flow; nozzle; porous plug; sulfur dioxide

t concentration; carbon dioxide concentration.

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