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iiSIERGY

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DOE/PR/06010-T14 ' (DE83017239)

EVALUATION OF Oj AND CO MONITORING SYSTEMS

FOR COMBUSTION CONTROLS

Final Report

By

C. Presser H, G. Semerjian

M. Juberts

March 1983

Work Performed Under Contract No. AI01-76PR06010

National Bureau of Standards

U. S. Department of Commerce

Washington, D. C.

U. S. DEPARTMENT OF ENERGY
DISCLAIMER

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Price: Printed Copy A06

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address.
DOE/PR/06010-T14

(DE83017239)

Distribution Category UC-95f

Evaluation of 0

^ and CO Monitoring Systems

For Combustion Controls

Final Report

By

C. Presser

H. G. Semerjian

M. Juberts

Chemical Process Metrology Division

Center for Chemical Engineering

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

Prepared for the

U.S. Department of Energy

Office of Industrial Programs

Washington, D.C. 20585

Under Contract No. EA-77-A01-6010
mi,
ABSTRACT

A study has been carried out to provide a comparative evaluation of

in-situ O 2 and CO monitors used for combustion control. The

experiments have been carried out in the MBS experimental furnace, which is equipped with a complete on-line gas sampling and analysis

system used as a reference system. Chemical equilibrium calculations, carried out by the minicomputer based data acquisition system, also

provide an indication of the extent of reaction, and a means to detect

possible measurement errors. Specific areas of interest included

evalution of the performance of the instruments over a wide range of operating conditions, effect of higher inlet temperatures on the stack

gas composition, effect of furnace cavity pressure on the CO and 0?

measurements and the effect of variations in the stack gas temperature

The O2 stack gas monitor has a Zr02 Type sensor. The system

performed reliably and provided the capability to operate at high

process temperatures. The O 2 measurements, however, were found to be

quite sensitive to air leakage when the furnace was kept below

atmospheric pressure. On-line calibration of the instrument at the

process temperature was also found to be necessary, especially for an aspirating type probe which is used to control the gas sampling rate.

The in-situ CO monitoring system is based on infrared absorption

measurements across the stack. The CO measurements were found to be

quite sensitive to stack gas temperatures and this effect has been

quantified in a heated test cell. The findings indicate that accurate

measurements of CO concentration will require simultaneous measurement

of gas temperatures and compensation of the CO reading. The stack gas composition was found to be dependent upon furnace cavity temperature

and heat transfer processes which are influenced by physical geometry,

fuel /air mixing and heat extraction rate. Experimental results are presented for both natural gas and No. 2 fuel oil fired systems. The

results of this study indicate that stack gas monitoring is a valuable

combustion control method when utilized with pre-established setpoints which are unique for a particular installation and load.

1
ACKNOWLEDGEMENT

This work was partially supported by the Department of Energy,

Conservation and Renewable Energy, Office of Industrial Programs, under

Contract No. EA-77-A01-6010. The technical program manager was Mr.

Stanley F. Sobczynski . This support is gratefully acknowledged.
TABLE OF CONTENTS

Page

Abstract i

Acknowledgements ii

List of Figures v

Executive Summary ix

I. Introduction 1

II. Evaluation of In-situ O 2 and CO Monitors 5

a. Experimental Facility 5

b. Experimental Design 7

c. Measurements Below the Recuperator 8

d. Measurements Above the Recuperator 14

e. Heat Transfer Effects on Stack Gas Composition 19

f. In-Situ CO Monitor: Investigation of the Effect of Stack

Gas Temperatures 21

III. Conclusions 25

References 29

Appendices 31

Appendix A. Description of the Experimental Furnace Facility ... .33

a. The Experimental Furnace 33

b. Gas Sampling and Analysis System 38

c. Data Acquisition System (DAS) 42

Appendix B. Description of the In-Situ O2 and CO Monitors 45

a. In-Situ Oxygen Analyzer 45

b. In-Situ Carbon Monoxide Analyzer 48

Appendix C. Figures 51

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LIST OF FIGURES

Fig. 1 - NBS Experimental Furnace.

Fig. 2 - Typical results of equilibrium calculations for adiabatic

fl ames.

Fig. 3 - Location of gas sampling probe, in-situ O2 monitor, and

flange where CO monitor was installed below the recuperator.

Fig. 4 - Variation of CO2 concentration with equivalence ratio; Fuel

= Natural Gas; Sampling below recuperator.

Fig. 5 - Variation of O 2 concentration with equivalence ratio; Fuel = Natural Gas; Sampling below recuperator.

Fig. 6 - Variation of CO concentration with equivalence ratio; Fuel = Natural Gas; Sampling below recuperator.

Fig. 7 - Variation of COo concentration with equivalence ratio; Fuel

= No. 2 Fuel Oil; Sampling below recuperator.

Fig. 8 - Variation of O 2 concentration with equivalence ratio; Fuel = No. 2 Fuel Oil; Sampling Below recuperator.

Fig. 9 - Variation of CO concentration with equivalence ratio; Fuel = No. 2 Fuel Oil; Sampling below recuperator.

Fig. 10 - Variation of CO concentration with equivalence ratio; Fuel = No. 2 Fuel Oil; Sampling below recuperator; Included are CO

equilibrium levels based on flame temperature.

Fig. 11 - Variation of CO with excess O 2 for several boilers and

furnaces.

Fig. 12 - Variation of CO and O2 concentration with equivalence

ratio; Expanded Scale; Fuel = Natural Gas; Sampling below

recuperator.

Fig. 13 - Variation of CO and O2 concentration with equivalence

ratio; Expanded scale; Fuel = No. 2 Fuel Oil; Sampling below

recuperator.

Fig. 14 - Variation of Excess O 2 with equivalence ratio at different

furnace pressures; Fuel = No. 2 Fuel Oil.

Fig. 15 - View of the CO monitoring system as installed in the stack

above the recuperator.

Fig. 16 - Variation of CO2 concentration with equivalence ratio; Fuel

= Natural Gas; Sampling above recuperator; Dilution observed

due to CO monitor cooling air.

V
Fig. 17

Fig. 18

Fig. 19

Fig. 20

Fig. 21

Fig. 22

Fig. 23

Fig. 24

Fig. 25

Fig. 26

Fig. 27

Fig. 28

Fig. 29

Fig. 30

Variation of O 2 concentration with equivalence ratio; Fuel

= Natural Gas; Sampling above recuperator; Dilution observed

due to CO monitor cooling air.

Variation of CO2 concentration with equivalence ratio; Fuel

= No. 2 Fuel Oil; Sampling above recuperator; Dilution

observed due to CO monitor cooling air.

Variation of 0^ concentration with equivalence ratio; Fuel

= No. 2 Fuel Oil; Sampling above recuperator; Dilution

observed due to CO monitor cooling air.

Variation of CO 2 concentration with equivalence ratio; Fuel

= Natural Gas; Sampling above recuperator; With pilot flame

on; Minimum cooling air dilution.

Variation of O 2 concentration with equivalence ratio; Fuel

= Natural Gas; Sampling above recuperator; With pilot flame

on; Minimum cooling air dilution.

Variation of CO concentration with equivalence ratio; Fuel = Natural Gas; Sampling above recuperator; With pilot flame on; Minimum cooling air dilution.

Variation of CO 2 concentration with equivalence ratio; Fuel

= No. 2 Fuel Oil; Sampling above recuperator; Tp = 888°C;

Minimum cooling air dilution.

Variation of 0^ concentration with equivalence ratio; Fuel

= No. 2 Fuel Oil; Sampling above recuperator; Tp = 888®C;

Minimum cooling air dilution.

Variation of CO concentration with equivalence ratio; Fuel = No. 2 Fuel Oil; Sampling above recuperator; Tp = 888®C;

Minimum cooling air dilution.

Start-up transient test: CO 2 variation with time; <}) = 0.5;

Fuel = Natural Gas; Sampling above recuperator.

Start-up transient test: O2 variation with time; (p = 0.5;

Fuel = Natural Gas; Sampling above recuperator; In-si tu O2

monitor below recuperator.

Start-up transient test: CO variation with time; 4) = 0.5;

Fuel = Natural Gas; Sampling above recuperator.

Start-up transient test: CO variation with stack gas

temperature; (p = 0.5; Fuel = Natural Gas; Sampling above

recuperator.

Variation of COo concentration with equivalence ratio; Fuel

= No. 2 Fuel Oil; Sampling above recuperator; Tp = 920®C.
Fig. 31 - Variation of 0^ concentration with equivalence ratio; Fuel

= No. 2 Fuel Oil; Sampling above recuperator; Tp = 920°C.

Fig. 32 - Variation of CO concentration with equivalence ratio; Fuel = No. 2 Fuel Oil; Sampling above recuperator; Tp = 920®C.

Fig. 33 - Long-term transient tests: Cool Furnace; Tp = 870®C; T;^ = 177®C; Fuel = No. 2 Fuel Oil; Variation of CO2

concentration with equivalence ratio; Sampling below

recuperator.

Fig. 34 - Long term transient tests: Cool Furnace; Tp = 870®C; Ty^ = 177®C; Fuel = No. 2 Fuel Oil; Variation of O 2

concentration with equivalence ratio; Sampling below

recuperator.

Fig. 35 - Long term transient tests: Cool Furnace; Tp = 870®C; Ty^ = 177®C; Fuel = No. 2 Fuel Oil; Variation of CO concentration

with equivalence ratio; Sampling below recuperator.

Fig. 36 - Long term transient tests: Warm Furnace; Tp = 910®C; Ty^ = 249 ®C; Fuel = No. 2 Fuel Oil; Variation of COo

concentration with equivalence ratio; Sampling below

recuperator.

Fig. 37 - Long term transient tests: Warm Furnace; Tp = 910®C; Ty^ = 249®C; Fuel = No. 2 Fuel Oil; Variation of O 2

concentration with equivalence ratio; Sampling below

recuperator.

Fig. 38 - Long term transient tests: Warm Furnace; Tp = 910®C; Ty^ = 249®C; Fuel = No. 2 Fuel Oil; Variation of CO concentration

with equivalence ratio; Sampling below recuperator.

Fig. 39 - Long term transient tests: Hot Furnace; Tp = 945®C; Ty^ = 270®C; Fuel = No. 2 Fuel Oil; Variation of CO 2

concentration with equivalence ratio; Sampling below

recuperator.

Fig. 40 - Long term transient tests: Hot Furnace; Tp = 945®C; Ty^ = 270®C; Fuel = No. 2 Fuel Oil; Variation of O 2 concentration

with equivalence ratio; Sampling below recuperator.

Fig. 41 - Long term transient tests: Hot Furnace; Tp = 945 ®C; Ty^ = 270®C; Fuel = No. 2 Fuel Oil; Variation of CO concentration

with equivalence ratio; Sampling below recuperator.

Fig. 42 - Schematic of heated absorption test cell assembly.

Fig. 43 - View of heated absorption test cell assembly.

Fig. 44 - Absorption coefficient of CO as a function of temperature.

vii
Fig. 45

Fig. 46

Fig. 47

Fig. 48

Fig. 49

Fig. 50

Fig. 51

Fig. 52

Fig. 53

Fig. 54

Fig. 55

Fig. 56

Fig. 57

Fig. 58

Fig. 59

Fig. 60

Dependence of CO measurements on test cell temperature.

MBS Experimental Furnace Facility.

MBS Experimental Furnace: Si deview of furnace.

NBS Experimental Furnace and Burner.

NBS Experimental Furnace: The Recuperator.

Experimental furnace control and data acquisition system.

View of gas sampling and analysis system.

Water cooled gas sampling probe.

Location of water cooled gas sampling probe.

Schematic of gas analysis and sampling system.

DEC PDP 11/60 minicomputer based data acquisition and control

system.

Location of in-si tu O 2 monitor.

Schematic of O 2 probe.

Schematic of the in-si tu CO monitoring system.

Schematic of the rotating wheel and three sealed gas cells

inside the CO monitor.

Typical output from the CO detector.

vi ii
EXECUTIVE SUMMARY

Industrial efforts to improve the efficiency of boilers and

furnaces have led to the development of a number of automatic control

systems, which regulate the fuel and air flow rates and try to optimize

the combustion and energy transfer processes. Most of the combustion

control systems rely on measurement of the composition of flue gases,

which is then used to adjust the fuel /air mixture in the combustion

zone. In the past, gases have been sampled out of the exhaust stream,

either in a continuous manner or in batches, and analyzed for a number

of species. More recently, in-situ gas monitors have been developed to

provide a continuous reading of species concentration in the flue gases

with a faster response as compared to gas sampling systems. The

general goal is to keep the fuel /air mixture as close to the

stoichiometric mixture as possible, where the combustion and energy

transfer processes are optimized, without generating excessive amounts

of gaseous and particulate emissions.

The approach generally used for combustion control is to monitor

the level of carbon monoxide (CO) and/or excess oxygen (O2) in the

flue gases, which are used as an indication of deviation from

stoichiometric conditions. Optimum combustion performance is usually

obtained with slightly fuel -lean flames, due to non-uniform fuel /air

mixing. The CO monitors are based on the measurement of infrared

absorption across the stack gases. The concentration of excess O2 is

determined by the electrochemical reaction occurring across a test-tube

shaped ceramic probe, made up of yttria stabilized zirconium oxide

IX
(Zr02). The current practice is to locate these monitoring systems

in the boiler stack, far downstream of the combustion zone, where the

gas temperatures are low and the chemical reactions are assumed to have

been frozen or completed. At this point, the wall and gas temperatures

are low enough so that any interference due to wall or gas radiation is

not expected, and the lifetime of the instruments is substantially

increased.

The objective of this study was to provide data on the performance

of in- situ O 2 and CO monitors over a wide range of operating

conditions, and to investigate the effect of heat transfer processes on

the relationship between the combustion zone properties and stack gas

measurements. Two stack gas monitoring systems, a Zr02 Type O 2 sensor and an in-si tu CO monitor based on infrared absorption, have

been evaluated in the MBS experimental furnace. These instruments are

typical of in-si tu flue gas monitors that are used for combustion

control in boilers and furnaces.

The experiments were designed to compare the measurements obtained

with the in-si tu CO and O 2 monitors to those obtained with the gas

sampling system and to theoretical equilibrium calculations. Furnace

conditions varied from a hot highly radiating environment,

representative of industrial furnaces, to a cooler environment,

representative of industrial boilers. Data were recorded over the

equivalence ratio range of 0.75 to 1.05 for both natural gas and No. 2

fuel oil. Interest was centered around the desired region for

X
automatic controls; viz., 100£C0_<300 ppmv, 0<P2£2% (excess) and

0 . 95£(^1 . 0 .

The Zr02 type O 2 monitor performed reliably over a long period

of time, and provided quite repeatable measurements with an accuracy of

0.25% O 2 over the full range and a sensitivity of about 2% O 2 tor a

change of 0.1 in equivalence ratio. The instrument, however, did not

have a provision for on-line calibration, and the O 2 measurements

were found to be quite sensitive to the air aspiration rate, which

controlled the gas sampling rate from the stack. The Zr02 sensor

provides the capability for operating at high temperatures, nominally

1540®C (2800®F) and below, which is valuable especially for high

temperature furnace applications. It also means that this sensor could

be located closer to the combustion zone, and provide better time

response.

Measurements with the in-si tu CO monitoring system could only be

carried out where the gas temperatures were more moderate, less than

370®C (700®F). In general, the readings obtained with the in-situ CO

monitor were less than half of those obtained with the gas sampling

system. This deviation was attributed primarily to the effect of gas

temperature on the CO absorption coefficient. This effect was

quantified in a set of experiments carried out in a heated cell. These

findings indicate that any accurate measurement of CO concentration in

the stack gases, using infrared absorption, will require a simultaneous

measurement of gas temperature and compensation of the CO measurements.

Additional effects due to CO2 and water vapor absorption may also be

important.

XI
A definite dependence of stack gas composition measurement upon

furnace temperature and heat transfer processes was displayed as the

furnace heated up over a long period of time. These results indicate

that the relationship between combustion fuel /air mixture and stack gas

composition is not unique. It will vary as a function of furnace

cavity temperature which is affected by physical geometry, burner

geometry (and its effect on fuel /air mixing), and by the rate of heat

extraction. The application of stack monitoring systems for combustion

control, over the narrow range desired for optimal operation, will

require static and/or dynamic allowances for these factors. The

characteristics of a particular system should be carefully analyzed

prior to implementation of a control system intended to optimize

combustion at or near stoichiometric conditions. The results of this

study indicate that stack gas monitoring is a valuable combustion

control method, when utilized with pre-established setpoints. These

setpoints can be expected to be unique for a particular installation

and load.

These observations also point towards the need for combustion

control systems, which do not necessarily rely on stack gas

measurements, but rather on measurements made directly in the

combustion zone.
I. INTRODUCTION

Industrial efforts to improve the efficiency of boilers and

furnaces have led to the development of a number of automatic control

systems, which regulate the fuel and air flow rates, and try to

optimize combustion and energy transfer processes [1]. Most combustion

control systems rely on measurement of the composition of flue gases,

which is then used to adjust the fuel /air mixture in the combustion

zone. In the past, gases have been sampled out of the exhaust stream,

either in a continuous manner or in batches, and analyzed for a number

of species. More recently, in- situ gas monitors have been developed to

provide a continuous reading of species concentration in the flue gases

with a faster response as compared to gas sampling systems. The

general goal is to keep the fuel /air mixture as close to the

stoichiometric mixture as possible, where the combustion and energy

transfer processes are optimized, without generating excessive amounts

of gaseous and particulate emissions.

The approach generally used for combustion control is to monitor

the level of carbon monoxide (CO) and/or excess oxygen (O 2

) in the

flue gases, which are used as an indication of deviation from

stoichiometric conditions. Excess air introduced into the combustion

zone can result in lower flame temperatures as well as increased energy

loss through the stack gases. A combustible mixture deficient of

oxygen (or air) produces large amounts of combustible products (CO,

hydrocarbons, particulates, etc.) and results in energy losses in the

form of unburned fuel [2-4]. Optimum combustion performance is usually

obtained with slightly fuel lean flames due to non-uniform fuel /air

1
mixing. For typical boiler configurations, automatic control is

desirable over the CO concentration range of 100-300 ppmv, and excess

oxygen range of 0-2% (about 0-10% excess air) [5-8].

The CO monitors are usually based on the measurement of infrared

absorption across the stack gases [9]. The concentration of excess

O 2 is often determined by the electrochemical reaction occurring

across a test-tube shaped ceramic probe, made up of yttria stabilized

zirconium oxide, Zr02 [10-12]. The current practice is to locate

these monitoring systems in the boiler stack, far downstream of the

combustion zone, where the gas temperatures are low and chemical

reactions are assumed to have been frozen or completed. At this point

the wall and gas temperatures are low enough, so that any interference

due to wall or gas radiation is not expected, and the lifetime of the

instruments is substantially increased.

The installation of these monitors in the stack may present

additional problems. The stack conditions being monitored may not be

entirely representative of conditions inside the combustion chamber.

Air infiltration and/or stratification of flue gases can significantly

influence the O 2 concentration, and to a lesser degree the CO level

[13]. Disturbances in the furnace chamber may also result in control

loop instabilities due to the increased response time of the monitoring

system.

The relative advantages of using CO or O 2 monitoring systems, or

both, for combustion control have been debated in the literature [14].

Depending on the particular combustor configuration, the type of fuel

utilized in the system and the range of fuel /air mixtures over which

control is desired, one of the two monitoring systems may be more

2
i

I applicable. A number of studies carried out by industrial, government

I and academic institutions have identified automatic on-line control of

I

I combustion processes as a generic technology, which can provide energy

savings and an improvement in process efficiency for a wide variety of

industries [15-19]. The suggested approach has been to encourage

increased and more efficient use of existing control technology, as

i well as development of new control techniques. CO monitoring systems

i have been cited often as a new technology, which is not fully

utilized.

The application of CO monitors for combustion control, especially

in high temperature processes, has been relatively limited, primarily

due to a lack of detailed and reliable data on their performance and

operating range. The purpose of this study was to provide such data by

comparative evaluation of an O 2 monitor and a CO monitor in the NBS

experimental furnace.

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II. EVALUATION OF IN-SITU O2 AND CO MONITORS

An evaluation of in- situ O2 and CO monitors was carried out in

the NBS experimental furnace. The objective of the experimental

program was to provide data to establish the suitability of oxygen and

carbon monoxide monitoring systems for combustion control over a wide

range of operating conditions. The facility is equipped with a

complete on-line gas analysis capability, which was used as a reference

system. Specific areas of interest were evaluation of the performance

of the instruments over a wide range of operating conditions; effect of

higher inlet temperatures (for installations with heat recovery

systems) on the stack gas composition; effect of furnace cavity (or

stack) pressure level on the CO and O 2 measurements; and the effect

of variations in the stack gas temperature.

Experimental Facility

The experimental furnace (Fig. 1) has a combustion chamber with

the internal dimensions of 80 cm (W) x 110 cm (H) x 240 cm (L). A

single burner fires horizontally through one end into the combustion

chamber. The combustion products exhaust from the opposite end of the

chamber, past a recuperator, and then up through the stack. The

recuperator is designed to preheat incoming combustion air before

reaching the burner. Several ports, located along the walls of the

furnace, permit visual observation of the flame and the introduction of

intrusive probes; viz., a water-cooled emission probe. A complete

on-line gas analysis system is used for combustion gas sampling and

5
analysis. The system has the capability to analyze the effluents for

the following species concentrations: CO, C02» 02» N0/N0x» SO 2

and total hydrocarbons (THC). The output of the gas analyzers, the

temperature, pressure and flow rate of all the input and output

streams, and other furnace parameters are continuously monitored by the

DEC PDP 11/60* minicomputer-based data acquisition and control system

(DAS). Removal of thermal energy from the furnace is achieved with a

variable thermal load heat exchanger. A high temperature damper

located in the stack is used to maintain positive furnace pressure

during experiments. A more detailed description of the experimental

facility is presented in Appendix A.

The in-si tu O 2 nionitor evaluated during this study utilizes an

yttria stabilized zirconia tube probe to measure the excess O 2

content of stack gases. The monitor is located at the far end wall of

the furnace in the plenum beneath the recuperator. The sensor probe

uses an aspirating extraction technique to transport the sample gas

from the probe inlet to the sensing cell which is kept at a constant

temperature of 700°C (1300°F). The in-si tu CO monitor selected for

evaluation is an infrared device that uses a high resolution absorption

*Certain commercial equipment, instruments or materials are

identified in this report in order to adequately specify the

experimental procedure. In no case does such identification imply

recommendation or endorsement by the National Bureau of Standards, nor

does it imply that the material or equipment is necessarily the best

available for the purpose.

6
Experimental Design

The experiments were designed so that the concentrations recorded

by the in-si tu O 2 and CO monitors could be compared with those

measured with the gas sampling system. The fuel /air equivalence ratio

derived from the latter [20] was then compared to the measured input

input fuel /air ratio, to check for internal consistency. In addition,

on-line chemical equilibrium calculations [21] were carried out based

on input fuel and air flow rates, and for selected temperatures; e.g.,

adiabatic flame temperature, measured furnace cavity temperature or

stack gas temperature. A typical set of calculations for methane/air

combustion, based on adiabatic flame temperatures, are shown in Fig.

2. The predicted gas composition can then be compared with measured

species concentrations to give an indication of the extent of reaction,

effect of local temperature, possible measurement errors, and dilution

effects.

The measurements were carried out at various furnace operating

conditions; i.e., high and low heat throughput rates, after different

periods of furnace preheating, with different rates of furnace heat

extraction, and with different burner inlet air temperatures.

Experiments were conducted with both natural gas and No. 2 fuel oil.

The fuel/air equivalence ratio (ratio of actual fuel to air ratio to

the stoichiometric fuel to air ratio) was varied from about 0.75 to

1.05, the region around =1.0 being the main area of interest,

spectroscopy technique. The CO concentration can be monitored over the

range of 0-1000 ppmv, in flue gases which are below 370®C (700®F). A

more detailed description of each monitor is given in Appendix B.

7
Measurements Below the Recuperator

For the first set of experiments, both the O 2 2nd CO in-si tu

monitoring systems were located in the region beyond the curtain wall

but below the recuperator (see Fig. 1). The gas temperatures

encountered in this zone (500-750®C) were more typical of conditions to

be found in an industrial furnace stack, where no recuperator existed.

The in-situ O 2 probe was located on the far end wall, 23 cm (9 in)

above the sighting port which is in line with the burner (see Fig. 3).

The in-situ CO monitoring system was located at the same height as the

O2 probe. The source and the analyzer units were located on the side

walls of the stack cavity (behind the curtain wall) such that the

infrared beam crossed the stack 31 cm (12 in) in front of the end wall.

The stack gas sampling probe was inserted into the stack through a port

23 cm (9 in) to the side of the O 2 probe, and 9 cm (3.5 in) above,

enabling gases to be sampled from the area immediately above the region

where the infrared beam traverses the stack cavity.

The results obtained in this region, below the recuperator, are

shown in Figs. 4-6 for natural gas and Figs. 7-9 for No. 2 fuel oil.

The furnace pressure was kept positive, thereby preventing air

infiltration into the furnace. The furnace was generally preheated for

3-4 hours (to about 900®C) before data acquisition was initiated.

Typical CO2

, O2 and CO measurements as a function of fuel /air

equivalence ratio are shown in Figs. 4-9 (4)<1 is a fuel lean mixture,

(|)>1 a fuel rich mixture, and (J)=l is a stoichiometric mixture).

Included are results obtained with the gas sampling/analysis system.

8
with the Zr02 in-si tu O2 monitor, and from equilibrium calculations

based on stack gas temperature measurements. The C02» O2 ^nd CO

measurements obtained from the gas analysis system are "dry"

measurements, since all the water is removed from the gas sample before

analysis (see Appendix B). These readings are then corrected by using

the measured species concentrations of the flue gas to calculate the

corresponding amount of water formed during combustion [20]. The

measurements are then reported as the "wet" values. These are, of

course, the appropriate values for comparison with the in-si tu

measurements and the equilibrium calculations. The general trends show

that as the fuel /air mixture becomes richer (i.e., as increases) and

approaches a stoichiometric mixture, the maximum theoretical value of

CO 2 Concentration (wet) is attained (9.5% for natural gas and 13.3%

for No. 2 fuel oil) at approximately =1, and then starts decreasing

beyond that point due to lack of available oxygen. This is clearly

indicated in Figs. 5 and 8, where the excess O 2 falls steadily with

increasing <!>, until the stoichiometric mixture is reached, beyond which

point no more oxygen is detected. The CO concentration remains below

20 ppmv for fuel lean mixtures, and rapidly rises beyond <t>=^ (see Figs.

6 and 9). The equilibrium calculations are included in each case, and

the general trends agree with the measurements. Indeed, it is

surprising to see such good agreement between the CO concentrations and

the computed equilibrium values. It indicates that the CO oxidation

proceeds fast enough to reduce the CO concentration from the high

levels expected to exist in the combustion zone (see the CO equilibrium

levels based on flame temperature in Fig. 10) to the much lower levels

9
that correspond to an equilibrium at the lower stack temperature.

This behavior should be unique to systems where the overall

furnace cavity temperature remains high, and the amount of total heat

extraction is relatively modest; i.e., low enough not to quench the CO

oxidation. Indeed in most industrial applications, the CO

concentrations are found to be much higher, as reported by Gilbert [5].

Figure 4 of Ref. 5 is reproduced here as Fig. 11, which indicates that

automatic control of boilers, kilns and furnaces for maximum combustion

efficiency could be achieved over the range 120-250 ppmv CO and 0-2.2%

excess 02 *

To allow for a direct comparison, the experimental data obtained

in the furnace over the range 0.96£clKl.04 is expanded and shown in Fig.

12 for natural gas, and Fig. 13 for No. 2 fuel oil. A closer

examination of Figs. 11-13 shows that the measured CO and excess O2 curves intersect outside the limits proposed by Gilbert (i.e., less

than 100 ppmv CO at 0.1 -0.2% O 2

) for natural gas and just inside the

limits for No. 2 fuel oil, with the oil flame requiring more excess

O2

, as expected. These results indicate that, under certain

circumstances, the expected relationship between the conditions

existing in the combustion zone and those monitored in the stack could

be significantly different. They also suggest that the range of the

control parameters (i.e., CO and O 2 concentration) to be utilized may

strongly depend on the particular combustion system configuration and

heat extraction profile.

The O 2 nieasurements obtained with the Zr02 probe are also

shown in Figs. 5 and 8. For the fuel lean flames, these readings are

observed to deviate from the gas sampling measurements by more than

10
0.5% 02* As the flame becomes richer this difference is reduced;

however, the percent difference remains about the same. Part of this

discrepancy was attributed to a lack of a calibration procedure, except

at ambient air conditions. An attempt was made to pass calibration gas

over the Zr02 cell at normal furnace operating conditions in order to

check the instrument calibration and to verify that the Zr02 cell was

still functioning properly. The aspirator air hose was replaced by

tubing that was connected to calibration gas bottles. The open end of

the aspirator was blocked so that the calibration gases would flow back

past the sensor cell and out through the sampling pipe into the furnace

cavity. The monitored O2 level was checked with 2.09% and 3.94%

O2/N2 calibration gas and the agreement was good, thus indicating

that the Zr02 cell was working properly.

It was also realized that the readings could be affected by varying

the aspiration flow rate. Fig. 8 presents two sets of data taken at

different aspirator air flow rates for varying fuel /air ratio. It was

found that the in-si tu O2 >^eadings could be changed significantly

(compare open and solid symbols. Fig. 8) and be made to correspond with

the on-line analyzer measurements for an aspirator downstream pressure

of 2.5 KPa (10 in H2O gauge). This pressure was used throughout the

remaining reported tests. The discrepancy which developed during later

tests between the monitored O2 level and the gas sampling O2

analyzer shows that the aspirator air flow should be readjusted for

each furnace run, according to the furnace pressure.

These tests were all performed with a positive furnace pressure of

15-25 Pa (0.06 - 0.1 in H2O) in order to prevent any dilution

11
effects, through leakage of outside air into the furnace, which could

effect the Zr02 probe readings or influence the combustion processes

occuring upstream of the probe. The influence of varying the fuel /air

ratio, over the range 0 . 5_< (})£l . 1 , upon the furnace pressure was found to

be relatively small, and hence the effect on oxygen measurements to be

negligible. Any substantial variation in the furnace pressure,

however, could effect the flow rate of sampled gases over the Zr02

sensor. Figure 14 presents the variation of the excess O 2

concentration with equivalence ratio for both the in- situ O2 nionitor

and the on-line O 2 analyzer. The experiment, performed with No. 2

fuel oil, showed a definite increase in the O 2 i^eadings with a

negative furnace pressure, indicating air infiltration and dilution

effects.

Measurements with the in-si tu CO monitoring system were also

attempted at this location below the recuperator, where the gas

temperatures are at or above 500®C (930°F). This was considered to be

representative of typical industrial furnace-type applications. In the

experimental furnace, the high temperature gases from the combustion

zone flow past two large water tube heat exchangers, located upstream

of the curtain wall (see Fig. 1), where about 30-50% of the thermal

energy is removed.

The CO monitoring system was set-up for a nominal optical path of

91 cm (3 ft) across the stack cavity. This corresponded to the inner

wall dimensions, since the cooling air for the sapphire windows also

purged the circular passages between the external (source or analyzer)

units and the furnace inner wall. This air flow, however was assumed

to be small enough not to penetrate the central part of the stack, and

12
simply flow up along the walls with a minimum amount of influence on

the CO readings. This indeed may be the case for industrial

applications, where the in-si tu CO monitoring system is usually placed

on a boiler stack with a diameter several times that of the

experimental furnace, with correspondingly larger flow rates.

Unfortunately, because of the smaller size of the furnace, the

cooling air was found to penetrate into the stack gases, effecting not

only the CO readings, but also the measurements obtained with the

Zr02 probe and the gas sampling probe. Both of these probes were

located near the center of the stack, indicating substantial air

penetration. Attempts were made to minimize the cooling air flow;

however, the readings obtained from the in-si tu CO monitor were still

far lower than those obtained from the gas analysis system (see Fig.

9). In addition, it was also observed that radiation emitted from the

hot furnace walls, especially after several hours of heating, affected

the detector signal quite substantially. This radiant energy, however,

is emitted as a continuum and effects only the d.c. level. The

frequency discrimination capability of the monitor should therefore

compensate for this effect.

Based on these observations, it was concluded that our inability

to obtain reliable data at this location was primarily due to the

higher stack gas temperatures, which resulted in a reduced absorption

coefficient, and hence reduced the indicated CO levels. It was

therefore decided to relocate the in-si tu CO monitoring system in the

stack above the recuperator, where the gas temperatures are

substantially lower.

13
Measurements Above the Recuperator

The in-si tu CO monitor was fixed to the tapering portion of the

stack above the recuperator as shown in Fig. 15. This provided a 91 cm

(3 ft) separation between the source and analyzer units of the monitor.

The gas sampling probe drew effluent at a location 15 cm (6 in) above

the infrared beam so that one could detect dilution effects by the CO

monitor cooling blowers. The excess O 2 reading could then be

compared with the in- situ Zr02 monitor located below the recuperator.

A discrepancy in the two excess O 2 readings would indicate a change

in the effective path length through dilution. The absence of an

increase in the O 2 level would indicate that the air flow introduced

by the CO monitoring system does not perturb the flue gases and that

the stack readings could be assumed indicative of upstream combustion

processes.

The initial tests produced a large increase in the excess O 2 3s

illustrated in Figs. 16 and 17 (natural gas) and Figs. 18 and 19 (No. 2

fuel oil) where approximately 5% excess O 2 was recorded at

stoichiometric conditions. As expected this reduced significantly the

CO 2 concentration when compared to the equilibrium computations.

In an attempt to reduce the dilution effect of the cooling air and

match the O 2 reading in the stack with the value monitored below the

recuperator, the cooling air blower outlet was restricted with

2.54x10”^ cm (0.001 in) thick brass shim stock. After restricting

the blower output with several pieces of shim stock, it was found that

when the center of the restriction contained a 0.3 cm (1/8 in) diameter

opening the monitor output signal voltage would drop until the

instrument could no longer function. The monitor panel indicated an

14
increase in the beam opacity beyond 80%. Insufficient air cooling

allowed flue gases and soot particles to enter the instrument

connecting flanges. Consequently, the indicated CO level increased

until the monitor output went off-scale. The 0.3 cm (1/8 in)

restriction also induced excessive blower heating (operating at 540

watts) which caused an increase in the air temperature by 12-14°C

(20-25®F).

This problem was alleviated partially by replacing the blowers

with air-conditioned air from the room ventilation system. This

provided cooler air at lower flow rates and pressure than was achieved

with the in- situ CO monitor blowers. The cooler air was also used to

provide additional cooling for the instrument electronics. The best

operating conditions were obtained with the air-conditioned air and a

0.6 cm (1/4 in) restriction in the line, which caused a 0.5% increase

in the stack excess O 2 and a reduction in the detector electronic

signal from 2V to 1-1. 5V. It was impossible to produce a full 2V

signal (recommended operating level) without increasing significantly

the stack excess 02* The beam path length was not known accurately

since insufficient cooling air permitted effluents to enter the

instrument connecting flanges. Soot had been discovered on the inside

face of the 0.6 cm (1/4 in) restriction after using the No. 2 fuel oil,

which indicated reduced beam transmission near the sapphire windows.

The inability to obtain a strong detector signal without excess O 2

dilution may indicate that the cooling air does not pass through the

connecting flanges uniformly, and permits effluents to move into the

flanges at the same time. The air may pass into the flanges

15
tangentially and develop a swirling motion with a central recirculating

zone which draws flue gases toward the sapphire windows.

Another problem arose due to the heat rising from the recuperator

which increased the detector electronic's temperature above 49®C

(120®F). This problem was resolved by cooling the detector cabinet

with air-conditioned air and by insulating the detector cabinet from

the recuperator.

The measurements of CO 2

. CO and O 2 concentration for the range

0.8£(K1.04 are presented in Figs. 20-22 for natural gas and Figs. 23-25

for No. 2 fuel oil. These show the effect of the 0.5% excess O 2 in

the stack flue gases. The furnace was relatively warm; e.g., for the

No. 2 fuel oil case the furnace gas temperature (Tp) was

approximately 888°C (1630°F) and the stack gas temperature {T5j|<)

was about 290®C (550°F) at =1.

Figures 20-22 illustrate the effect of permitting the pilot light

to burn continuously in order to prevent flame outs. The extra natural

gas shifts the measured readings from both the gas sampling and in- situ

instruments to the lean side because the additional fuel is unaccounted

for in (}). The effective change in (p is 4%.

Data obtained without the pilot flame. Fig. 23, indicates that the

CO 2 peak is shifted to slightly larger than 4^1 because of the lower

furnace temperature. The maximum value attained is lower than the

theoretical maximum due to the 0.5% excess 02* The CO level will

consequently rise when the flame is slightly richer than expected and

the excess O 2 reaches its minimum past the stoichiometric point.

Comparison with the in- situ CO monitor in Figs. 22 and 25 shows that

16
the CO level remains at 10-40 ppmv for lean flames. Past

stoichiometric conditions both CO readings rise simultaneously, but the

in-si tu monitor readings generally remain at less than half the gas

sampling value (originally, with the cooling blowers, this ratio was

1:3-4). For automatic control purposes the in- situ instrument could be

used as an indicator of the presence of CO, but not necessarily to

provide an accurate measurement of the CO concentration. Good

agreement between in- situ O 2 monitor (Figs. 21 and 24) and the gas

sampling data is primarily due to the adjusted setting of the air

aspiration rate. Note that the minimum reading of excess O 2 is 1% on

the instrument. This monitor would be suited for automatic control of

boilers (Ref. 5, Fig. 4) where the desired control range is ^- 2 %

excess O 2 (at approximately 100-300 ppmv CO); however, for gas and

oil fired systems, the indications in the lower range need to be

improved since excess O 2 levels range from 0-0.6%.

For furnace gas temperatures below 540®C (1000®F), along with heat

removal by the two combustion chamber heat exchangers and the

recuperator, conditions in the stack may be considered similar to that

of a boiler except for the effect of the high temperature flame and

furnace wall radiation on completion of combustion processes. In order

to simulate boiler conditions where wall incident energy is removed by

heat exchangers, an attempt was made to keep the furnace gas

temperature below 540®C by minimizing the thermal energy content of the

flame. The flame was stabilized by keeping the pilot on continuously.

The procedure did not prove to be successful since, for the oil flame,

the furnace gas temperature (Tp) rose above 540°C almost immediately.

17
and for the natural gas flame, the fuel /air ratio was altered 4% due to

the extra pilot gas.

Another approach was attempted in which data were recorded during

the furnace transient start-up. Although long tests with rich flames

could not be attempted, some data could be acquired for lean flames

under quasi -steady conditions.

Several tests were performed for different equivalence ratios.

The results presented in Figs. 26-29 are for(j)=0.5 with gas sampling in

the stack. The length of each test was approximately 30 minutes which

depended upon our ability to keep the stack gas temperature between

150-190®C (300-375®F). The furnace gas temperature rose to 685®C

(1265®F) during this trial. Upon flame ignition the cold furnace walls

produced an initial surge of CO (Figs. 28 and 29) for the very lean

flame due to the poor fuel /air mixing and freezing of chemical

reactions. The CO level peaks after several minutes and then drops

exponentially as the stack gas temperatures grow. During the initial

startup (the first 100 sec) the CO 2 concentration (Fig. 26) increases

and the O 2 concentration (Fig. 27) decreases rapidly. The rate of

change in CO2 and O2 is then reduced as the rate of change in CO

decreases. The CO concentrations recorded from the in-situ device are

also shown in Figs. 28 and 29. CO readings above 1000 ppmv (beyond the

panel meter scale) were also measured by connecting the analog output

signal (linear) to a strip chart recorder. It is again observed that

the in-situ CO monitor provides readings which are about half the value

obtained with the gas analysis system throughout its operating range.

The Zr02 sensor reading stayed within 0.5% of the gas sample

measurements. When the air-conditioned air flow across the sapphire

18
windows of the in-si tu CO monitor was slightly increased there were no

significant changes. However, when the fuel /air ratio was increased to

(|)=0.56, the initial surge of CO was reduced and vanished for the richer

flames. The increase in combustion air inlet temperature was

insignificant.

Heat Transfer Effects on Stack Gas Composition

Figures 30-32 present data taken during the same experiment shown

in Figs. 23-25; however, the furnace gas temperature had risen from a

temperature of Tp = 888®C to Tp = 920®C at cj)=l. A shift in the

experimental curves toward the lean side was realized due to increased

furnace gas temperature and higher combustion air inlet temperature.

Figs. 33-41 illustrate this heat transfer effect for a 7 hour test

using No. 2 fuel oil. Three sets of data were obtained over a 2 hour

interval each, with one hour of furnace preheating which ensured flame

stability. Presented are the C02» O

2 and CO concentrations for

0.78£4>£l .04. The furnace gas temperature (Tp) for the 3 tests (ie.,

cold, warm and hot, respectively) were 870, 910 and 945®C at (}) - 1

,

along with combustion air inlet temperatures ilf^) of 177, 249 and

270°C. Gas samples were extracted from the plenum beneath the

recuperator, where the gas temperatures were 588, 677 and 717®C,

respectively, at cj) - 1 . The in- situ CO monitor was inoperable for this

experiment.

For the "cold" test (Figs. 33-35) the CO2 concentration is lower

than the equilibrium values (based on the stack gas temperatures) on

the lean side of stoichiometric mixture indicating reduced combustion

19
efficiency which may be, in part, due to poor fuel evaporation and

nonuniforin fuel /air mixture. As the flame becomes richer the CO2

concentration reaches the same maximum value as predicted

theoretically, but on the rich side of the stoichiometric fuel /air

value. The CO level similarly does not grow until the flame is fuel

rich, and the amount of excess O 2 remains greater than the

equilibrium value until it is depleted on the fuel rich side of the

fuel /air stoichiometric point. The discrepancy in the readings by the

Zr02 sensor is again due to the incorrect adjustment of the

aspiration rate.

For the "warm" test (Figs. 36-38) the furnace temperatures are

somewhat higher. The CO2 concentration appears to reach its maximum

value at the fuel /air equivalence ratio predicted by the equilibrium

calculations, with the two curves almost overlapping one another. The

CO and excess O 2 concentrations are also in better agreement with the

equilibrium calculations.

For the "hot" test (Figs. 39-41), gas temperatures are generally

higher than the above cases. The maximum CO2 level is attained for

fuel lean mixtures, contrary to the earlier observation with the cooler

flame, which may be an indication of improved combustion processes.

Less excess O 2 is available as compared to the theoretical values.

Correspondingly, the CO level is observed to start increasing at a

leaner fuel /air mixture.

Goldman and Timnat [22] tend to support these findings for No. 2

fuel oil (refer to Fig. 7 of Ref. 22). The variation of C02» CO and

O 2 Concentration is presented for two burner tunnels. Effluent was

sampled 94 cm (37 in) downstream of the burner. One tunnel has a

20
relatively large volume whose ability to develop hot combustion gas

recirculation in the sudden expansion region is much less than a second

smaller tunnel which utilizes its internal volume more effectively.

The latter tunnel develops a strong recircul ation zone which enhances

fuel droplet evaporation. Their results show that higher tunnel gas

temperatures associated with the smaller tunnel enhance combustion

efficiency and appear to shift the concentration curves to leaner

flames. A similar phenomenon is occurring for the NBS furnace as it

approaches steady state conditions.

In-situ CO Monitor: Investigation of the Effect of Stack Gas

Temperatures

It was pointed out earlier that the relatively low CO

concentrations measured in the stack gases, with the in-situ CO

monitor, were primarily attributed to the higher temperatures

encountered in the stack. In order to clearly identify and quantify

this effect, an absorption cell was fabricated, where the gas

temperature, pressure and composition could be carefully controlled,

and CO measurements could be made using the CO monitoring system. A

sketch of the experimental set-up, and a picture of the test cell are

shown in Figs. 42 and 43, respectively.

The cell was 91.5 cm (3 ft) long and was encased by high vacuum

flanges. Two sapphire windows, located on the end flanges, allowed

optical access into the cell. The sapphire windows were identical to

the ones used in the CO monitoring system, so that the spectral

response of the system would not be altered. The cell was made of 12

cm (4 3/4 in) I.D. steel tube. The end flanges were made of stainless

21
steel. The cell was heated with a 0.63 mm (0.025 in) Nichrome wire

which was wrapped around the steel tube. The temperature was

controlled with three powerstat variable transformers and measured with

three T-type thermocouples inserted into the cell. The temperatures

were monitored with a digital LED meter and a multi pen strip chart

recorder. The cell pressure was kept constant throughout the tests at

near atmospheric pressure. The source and analyzer units of the CO

monitoring system were then mounted on the two sides of the cell.

Before the tests, the test cell was flushed with dry N 2 for

several hours in order to remove any residual gases. Then a

calibration gas mixture of 779 ppmv CO/N 2 was introduced into the

cell from one end, and the gases exiting from the other end were fed

into the gas sampling/analysis system, where the CO concentration was

continuously monitored with the non-dispersive infrared (NDIR) CO

analyzer. The concentration measurements provided by both the in-si tu

stack monitoring system and the NDIR analyzer were recorded, and these

values agreed relatively well (the in-si tu monitor gave a reading of

730 ppmv instead of 779 ppmv). The calibration provided by the

manufacturer for the in- situ monitor was not altered, which could have

been done to obtain an exact agreement. But this was not considered to

be critical for this set of experiments.

The cell was then gradually heated, and the results obtained with

both the in- situ monitor and the NDIR analyzer were shown in Fig. 44.

The experiments were limited to temperatures below 275®C (530®F),

because of the sealant used to fix the sapphire windows to the

stainless steel flanges. It can be seen that, while the reading from

the NDIR analyzer stayed constant, the measurements obtained with the

22
in-si tu monitor decreased by more than twofold as temperature increased

from 20°C to 260°C. This cycle was repeated as the cell was allowed to

cool down to room temperature, and the values obtained duplicated very

closely those obtained during the heating cycle. It should be noted

that the NDIR analyzer measurements are carried out at a constant

temperature within the instrument itself, and therefore are not

expected to be effected by ambient temperature variations.

The results obtained during these experiments document the

sensitivity of the CO concentration measurements, obtained with the

in-si tu monitor, on the stack gas temperature. This dependence on

temperature is due to the variation of the absorption coefficient

K = NQ, which then affects the infrared light transmission through

Beer's Law:

T = I/Iq = exp (-KL)

where T is the transmittance, I and Iq are transmitted and incident

intensities, respectively, and L the optical path. The absorption

coefficient could change either due to changes in the molecular number

density, N (cm"^), or the absorption cross section, Q (cm^). The

observed reduction in measured absorption, with increasing temperature,

could be attributed, to a large extent, to a decrease in the number

density, since the pressure was kept constant. This does not, however,

account completely for the observed effect. When the data (see Fig.

14) are corrected for density effects, using the ideal gas law, the

measured curve still shows a significant drop (18%) in the CO

concentration at 260®C. The remaining change has to be attributed to

changes in Q, with temperature, over the spectral bandwidth of the

absorption measurements. A typical variation of the absorption

23
coefficient and spectral features are shown in Fig. 45, which has been

reproduced from Ref. 23. It can be seen that the dependence on

temperature could be quite significant, and it will depend on the

bandwidth used for the measurements. This bandwidth was not available,

and therefore an accurate estimate of this effect could not be made.

Results obtained with this simple experiment suggest that accurate

measurements of CO concentration in stack gases, using line-of-sight

infrared absorption techniques, will require an appropriate correction

for changes in the stack gas temperature. Even if the temperature does

not change over a large range, the instrument has to be calibrated for

the appropriate mean gas temperature. Hence, an on-line temperature

correction, based on actual stack gas temperature measurements, would

be most appropriate to realize the full potential of in- situ CO

monitoring systems.

24
III. CONCLUSIONS

The objective of this study was to provide data on the performance

of the two stack gas monitoring systems over a wide range of operating

conditions, and to investigate the effect of heat transfer processes on

the relationship between the combustion zone properties and stack gas

measurements. Two in-si tu monitoring systems, a Zr02 type O

2

sensor and a CO monitor based on infrared absorption, have been

evaluated in the NBS experimental furnace. These instruments are

typical of in-si tu flue gas monitors that are used for combustion

control in industrial boilers and furnaces.

The experiments were designed to compare the measurements obtained

with the in-si tu CO and O2 nionitors to those obtained with the gas

sampling system and to theoretical equilibrium calculations. Furnace

conditions varied from a hot highly radiating environment

representative of industrial furnaces to a cooler environment

representative of industrial boilers. Data were recorded over the

equivalence ratio range of 0.75 to 1.05, for both natural gas and No. 2

fuel oil. Interest was centered around the desired region for

automatic controls; viz., 100£C0_<300 ppmv, 0<P2£2% (excess) and

0 . 95^

<1^1 . 0 .

The Zr02 type O 2 monitor performed reliably over a long period

of time, and provided quite repeatable measurements with an accuracy of

0.25% O 2 over the full range and a sensitivity of about 2% O 2 for a

change of 0.1 in equivalence ratio. The instrument, however, did not

have a provision for on-line calibration, and the O 2 measurements

25
were found to be quite sensitive to the air aspiration rate, which

controlled the gas sampling rate from the stack. The Zr02 sensor

provides the capability for operating at high temperatures, nominally

1540°C (2800°F) and below, which is valuable especially for high

temperature furnace applications. It also means that this sensor could

be located closer to the combustion zone, and provide better time

response.

Measurements with the in-si tu CO monitoring system could only be

carried out where the gas temperatures were more moderate, less than

370®C (700®F). In general, the readings obtained with the in-situ CO

monitor were less than half of those obtained with the gas sampling

system. This deviation was attributed primarily to the effect of gas

temperature on the CO number density, but also partly to the effect of

gas temperature on the the CO absorption coefficient. This effect was

quantified in a set of experiments carried out in a heated cell. These

findings indicate that any accurate measurement of CO concentration in

the stack gases, using infrared absorption, will require a simultaneous

measurement of gas temperature and compensation of the CO measurements.

Additional effects due to CO2 and water vapor absorption may also be

important.

A definite dependence of stack gas composition measurement upon

furnace temperature and heat transfer processes was displayed as the

furnace heated up over a long period of time. These results indicate

that the relationship between combustion fuel /air mixture and stack gas

composition is not unique. It will vary as a function of furnace

cavity temperature which is affected by physical geometry, burner

geometry (and its effect on fuel /air mixing), and by the rate of heat

26
extraction. The application of stack monitoring systems for combustion

control, over the narrow range desired for optimal operation, will

require static and/or dynamic allowances for these factors. The

characteristics of a particular system should be carefully analyzed

prior to implementation of a control system intended to optimize

combustion at or near stoichiometric conditions. The results of this

study indicate that stack gas monitoring is a valuable combustion

control method, when utilized with pre-established setpoints. These

setpoints can be expected to be unique for a particular installation

and load.

These observations also point towards the need for combustion

control systems which do not necessarily rely on stack gas

measurements, but rather on measurements made directly in the

combustion zone.

27
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REFERENCES

1. Robertson, J.L. and Clarke, P.R., "f^icroprocessors and Instrumentation in

Furnace Control," Industrial Heating , Vol. 48, No. 5, pp. 9-12, May 1981.

2. Richardson, D.M., "Combustion Efficiency through Use of Flue Gas

Analyzers," Industrial Heating , Vol. 45, No. 5, pp. 20-21, May 1978.

3. Anson, D., Clarke, W.H.N., Cunningham, A.T.S. and Todd, P., "Carbon

Monoxide as a Combustion Control Parameter," Combustion , Vol. 43, No. 9,

pp. 17-20, March 1972.

4. Pruce, L.M., "Maximum Boiler Efficiency and Save Fuel with CO Monitoring,"

Power , Vol. 124, No. 1, pp. 70-72, January 1980.

5. Gilbert, L.F., Sr., "CO Control Heightens Furnace Efficiency," Chemical

Engineering , Vol. 87, No. 15, pp. 69-73, July 1980.

6. Spanbauer, J.P., "Energy Savings Through Advanced Boiler Control," paper

presented at the 1980 Annual Meeting of the Technical Association of the

Pulp and Paper Industry, 1980.

7. Jutila, J.M., "Guide to Selecting Stack Gas Monitors," Industrial

Technology , Vol. 27, No. 11, pp. 43-54, November 1980.

8. Gilbert, L.F., "Precise Combustion-Control Saves Fuel and Power," Chemical

Engineering , Vol. 83, No. 13, pp. 145-150, June 1976.

9. McArthur, L., Lord, H.C. and Gilbert, L.F., "Efficient Combustion Through

Boiler Air-Fuel Ratio Control," Final Control Elements, Vol. 3, 3rd Control

Valve Symposium and Process Control Technology, Instrument Society of

America, Pittsburg, pp. 101-106, 1977.

10. Hoffman, A.R., "Nature of Platinum-Zirconia Oxygen Sensor," Industrial

Heating , Vol, 47, No. 7, pp. 32-33, July 1980.

11. "Considerations for Energy Savings in Design and Use of Continuous Heat

Treating Furnaces - Part I - Role of Controls," Industrial Heating , Vol. 48, No. 6, pp. 33-37, June 1981.

12. Shafer, R.V., "Oxygen Measurement and Control for More Efficient Operation

of Soaking Pits," Industrial Heating, Vol. 48, No. 8, pp. 14-19, August

1981.

13. Opel, A.E. and Gilbert, L.F., "Closed Loop Source Monitoring Saves Energy

and Money," ASME Paper No. 78-WA/APC-6, December 1978.

14. Molloy, R.C., "Microprocessor Based Combustion Monitoring and Control

Systems Utilizing In-Situ Opacity, Oxygen, and CO Measurements," presented

at the 4th World Energy Engineering Conference in Atlanta, Georgia, Oct.

12-15, 1981 and also presented at the 3rd Annual Industrial Energy

Conservation Technology Conference and Exhibition, Houston, Texas, April

26-29, 1981.

29
15. Hall, E.H., et al , "Evaluation of the Theoretical Potential for Energy

Conservation in Seven Basic Industries," Battel le Columbus Laboratory,

Report to FEA, January 1975.

16. Hamm, J.R., et al , "Energy Conversion Alternatives Study (ECAS) - Vol . Ill:

Combustors, Furnaces and Low Btu Gasifiers," Westinghouse Electric Corp.

Research Laboratories, NASA CR-134941, February 1976.

17. Resource Planning Associates, "Implementation of Energy Conservation

Technology in the Pulp and Paper Industry," Report for Office of Industrial

Programs, Dept, of Energy, September 1980.

18. Fam, S.S., "Impact on Energy Conservation of Automatic Control Systems

Utilization in the U.S. Pulp and Paper Industry," Thermo Electron Rpt.

No. TE4265-20-80, 1980.

19. "Basic Research in Engineering - Workshop on Fluid Dynamics and Thermal

Processes," Engineering Societies Commission on Energy, Inc., February

1980.

20. "Procedure for the Continuous Sampling and Measurement of Gaseous Emissions

from Aircraft Turbine Engines," Society of Automotive Engineers, Inc., ARP

1256, October 1971

.

21. Brinkley, S.R., "Computational Methods in Combustion Calculations,"

Combustion Processes, Sect. C., High Speed Aerodynamics and Jet Propulsion , Vol. 2, edited by B. Lewis, R.N. Pease and H.S. Taylor, Princeton University

Press, Princeton, N.J., 1956.

22. Goldman, Y. and Timnat, Y.M., "Study of Liquid Fuel Combustion in

Tunnel Burners," Israel Journal of Technology, Vol. 14, Nos. 4-5,

pp. 179-186, 1976.

23. "Handbook of Infrared Radiation from Combustion Gases," eds. R. Goulard,

and J.A.L. Thompson, NASA SP-3080, 1973.

24. Young, S.B., "High Temperature Waste Heat Recovery Systems for Forge

and Other Furnaces," Industrial Heating, Vol. 47, No. 7, pp. 16-18, July

1980.

30
APPENDICES
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APPENDIX A

DESCRIPTION OF THE EXPERIMENTAL FURNACE FACILITY

The experimental facilities installed at the National Bureau of

Standards include a pilot-scale industrial furnace (see Fig. 46), a

complete gas sampling/analysis system and an automatic data acquisition

and processing system.

The Experimental Furnace

The experimental furnace has a combustion chamber, with the

internal dimensions of 80 cm (W) x 110 cm (H) x 240 cm (L). A single

burner fires horizontally through one end into the combustion chamber.

The combustion products exhaust from the opposite end of the chamber,

past a recuperator, and then up through the stack. The furnace walls

are made up of lightweight castable refractory and insulation

materials, anchored to a steel outer wall. The exit of the furnace is

formed by a curtain wall, which is perforated to allow for passage of

the gases. The plenum between the curtain wall and the insulated side

and end walls serves as a passage for exhaust gases to the recuperator

(Fig. 1 )

.

The experimental furnace has a rated capacity of 300 kw (1x10^

BTU/hr). At steady state, the outer wall temperature is designed to

stay below 70®C (160®F) when the chamber temperature reaches 1350®C

(2460®F). The furnace is sealed with high temperature RTY silicone

caulking compound in order to reduce furnace leakage. Several ports

33
are located along both furnace side walls and the downstream end wall

(Fig. 47). These ports permit visual observation of the flame, the

introduction of intrusive probes and provides an optical path across

the furnace. Fig. 1 indicates the location of each access port.

A Transjet burner, designed by Hague International [24], is fitted

into a 32.5 cm (12.8 in) diameter corbel which is cast from high

temperature alumina and sits normal to the front end face of the

furnace. The burner is capable of withstanding a combustion air inlet

temperature of 900®C (1650®F). The burner (Fig. 48) is designed to

recirculate and entrain combustion products with incoming fresh

combustion air, thereby enhancing flame stability. The burner air

passageways are thermally insulated in order to accomodate the high

inlet air temperatures.

Either natural gas or No. 2 fuel oil can be supplied to the

burner. An exchange of nozzles and fuel feed lines is required to

convert the burner from one fuel to another. The central core of the

burner serves to house the fuel and atomizing air lines, the electric

spark ignited pilot flame and the Fireye ultraviolet flame sensor.

The atomizing compressed air is regulated to a pressure of 100

KPa (15 psig) and a volumetric flow rate of approximately 450 1/min (16

ft^/min). This air is mixed with the liquid fuel, externally,

immediately downstream of the nozzle head. The No. 2 fuel oil is

supplied at approximately 55 KPa (8 psig) and can reach a maximum

volumetric flow rate of 0.48 1/min (7.6 gph). There are 8 fuel outlets

in the nozzle head which allow the atomizing air to flow tangentially

around the adjacent fuel openings. For natural gas, fuel is expelled

radially outward through 8 openings which are located around the head

34
of the gas supply line. Natural gas is supplied at 14 KPa (2 psig)

with a maximum volumetric flow rate of 510 1/min (18 ft^/min).

Cooling air is bled from the combustion air blower and passed

around the fuel injector in order to reduce thermal decomposition of

the fuel. The cooling air flow is 255 1/min (9 ft^/min) at a

pressure of 2. 5-3. 5 KPa (10-14 in H 2O), which accounts for about 1%

of the air blower capacity. A refractory stabilizer plate, which

surrounds the cooling air passageway inside the burner, provides a

separation between the preheated combustion air and the fuel supply

line.

Combustion stability is enhanced by holes located on the

downstream face of the stabilizer plate which generate hot combustion

gas recirculation. An electrically ignited pilot is used to fire the

main flame. The Fireye sensor is used to check for flame ignition and

continued combustion. During flame shutdown, compressed purge air is

provided at 21 KPa (3 psig) in order to remove any residual fuel in the

fuel line.

The recuperator is designed to preheat incoming combustion air

before reaching the burner. A ceramic heat exchanger, containing 30

silicon carbide tubes, is the main component of the recuperator which

is capable of withstanding long term exposure to gas temperatures of

1550®C (2820®F), (see Fig. 49). The heat transfer elements of the

recuperator are of a tubular configuration with an enhanced heat

transfer surface on both the exterior and interior of the tube. The

external surface area is increased by means of a spiral wound fin and

the internal bore is enhanced by longitudinal fins. The tubular

35
elements are nested together and arranged to provide the optimum

transfer of heat between the outgoing flue gases and the incoming

combustion air. The tubes are provided with seals to minimize incoming

combustion air losses due to leakage.

The ceramic elements are arranged to provide one cross- flow pass

on the exhaust gas side and one pass through the tubes on the

combustion air side. Metal tubes are used to bring the combustion air

to the ceramic elements inside the recuperator which are held in place

by adapters and compression springs. At the exit, heated combustion

air is passed from the ceramic elements through short metallic tubes to

an insulated header. Inlet temperatures of 274®C (525®F) have been

achieved for furnace gas temperatures of approximately 882®C (1620®F).

This corresponds to flue gas temperatures of 735®C (1355®F) entering

the recuperator and 404°C (760°F) leaving the recuperator. The furnace

gas temperature is measured by a Pt-Pt/10% Rh (S-type) thermocouple

stationed in front of the furnace load probes. Chromel-alumel (K-type)

thermocouples are located at several sites along the recuperator' s 28

cm diameter exit duct. This passageway is insulated so that heat

losses from the combustion air are minimized.

A pneumatically controlled stainless steel high temperature damper

located inside the stack is used to maintain positive furnace pressure

during experiments. Typical furnace overpressures of 0-50 Pa (0-0.2 in

H2O) are required to prevent air infiltration into the combustion

chamber.

A 4kw (5hp) turbo-blower supplies combustion air from the

surroundings to the burner. The blower has a rated maximum capacity of

23,100 1/min (49,100 ft^/hr) at 6.9 KPa (16oz/in^) gauge pressure.

36
copper-constantan (T-type) thermocouple and the line pressure is

measured by a pressure transducer in order to correct the oil flow for

viscosity effects.

Commercially supplied natural gas (96.9% CH4 , 2% 62^ 5

, 1.1%

others) is pressure regulated down to 14 KPa (2 psig). Some of this

gas is tapped off to the pilot burner before the gas reaches a manual

reset and motorized shut-off valve train which is used for gas flow

control. As a safety feature, low and high gas pressure switches set

pressure limits for the shut-off valve. The volumetric flow rate is

read from a rotameter (max: 510 1/min CH4 at 21 ®C, 100 KPa) while a

laminar flow device (max: 565 1/min at AP = 2 KPa, for flow conditions

at 21 and 100 KPa) and a pressure transducer provide the output

signal to the DAS. Flow control is accomplished in the same way

described for the No. 2 fuel oil supply; i.e., with a prove switch,

motorized valve and cam, and a solenoid valve. The line gas

temperature is measured with a T-type thermocouple.

Heat extraction from the furnace is achieved with a variable

thermal load heat exchanger consisting of two water-cooled 25.4 cm (10

in) diameter stainless steel tubes, passing vertically downward through

the furnace roof at a station 170 cm downstream of the burner. Water

is supplied to the system at a pressure of 210 KPa (30 psig) before

passing through a filter. The volumetric flow rate is controlled

downstream of the filter with a pneumatic actuator and valve. The flow

rate is measured by a stainless steel orifice plate with a 1.3 cm

(0.527 in) bore. The output is read by a flow gauge having a maximum

flow of 38 1/min (10 gpm).

37
The water supply is split into 2 segments, one supply line for

each heat exchanger probe. Each leg contains a ball valve, a turbine

flowmeter which provides a flow reading for the DAS, and

copper-constantan (T-type) thermocouples which are placed on both the

upstream and downstream sides of the thermal load cells.

Gas Sampling and Analysis System

A complete on-line gas analysis system is used for combustion gas

sampling and analysis (Fig. 51). A water-cooled sampling probe was

fabricated as shown in Fig. 52. The probe has a 1.27 cm (0.5 in)

diameter hemispherical stainless steel head and shaft, with a

water-cooled jacket covering the gas collection channel. The 0.11 cm

(0.043 in) inlet diameter is designed to choke the flow at temperatures

above 260°C (500®F) for gas suction at 0.2 1/min (0.5 ft^/hr). The

84 cm (33 in) long probe which is situated at the far end furnace wall

below the recuperator (Fig. 53), is designed to reach the curtain

wal 1

.

The gas sample is delivered to a heated metal bellows vacuum pump

through a 460 cm (15 ft) section of heated line. The vacuum pump

operates at 14 1/min (0.5 ft^/min) for a bellows speed of 1725 rpm.

A second uncooled probe was also used to sample effluents below the

recuperator and inside the stack. The gas sample is then delivered

through a 1070 cm (35 ft) section of heated line to the analyzer

manifold. The heated lines and the vacuum pump are maintained above

150°C (300®F) in order to prevent condensation of hydrocarbons and

water vapor. The line and pump temperatures are continuously monitored

38
and controlled by temperature controllers (max: 300®C). The pump

manifold temperature is measured with a bi-metallic thermometer (max:

300®C) and the pump pressure is read from a 76 cm Hg (30 in Hg) vacuum

gauge. A nitrogen purge system is used to clear the probe, heated

lines and the analyzer manifold of large particulates whenever the gas

sample flow is significantly reduced. Two electro-mechanical valve

actuators are used to control the flow of gases through the manifold

(see Fig. 54).

The gas sample is delivered to the gas analyzers which are

connected in parallel. The sample first enters a flame ionization

detector (F.I.D.) type total hydrocarbon analyzer which provides a wet

reading. The manifold then leads into a stainless steel gas dryer

(Permapure) used to remove any water vapor present in the sample by

permeation distillation through a plastic tube bundle, and to prevent

the interference of water vapor inside the non-dispersive infrared CO

and CO2 analyzers. Compressed air is introduced into the dryer and

used to carry the water vapor out of the system via an 8 1/min

rotameter. The resulting dry gas is then introduced into the CO,

C02» O2

, NO/NO)^ and SO 2 analyzers. The flow rates through each

analyzer are carefully monitored by rotameters placed upstream of each

instrument. Unused sample gas is finally bypassed into the sample dump

manifold.

The Beckman Model 402 hydrocarbon analyzer utilizes the flame

ionization method of detection (F.I.D.) for determining total

hydrocarbon concentration. The sensor is a burner in which a regulated

flow of sample gas is passed through a H 2 /O2 flame sustained by

regulated flows of compressed air and 40% H 2 /N 2 fuel. The fuel and

air pressures are adjusted to 172 KPa (25 psig) and 103 KPa (15 psig).

39
respectively. Seven ranges of concentration are provided with the

instrument; viz., 10, 25, 100, 250, 1000, 2500, 10000 ppmv. Both speed

and magnitude of the analyzer response are affected by the type of

hydrocarbon being sampled. The system is therefore calibrated with

hydrocarbons that are representative of those to be sampled. Propane

is used as the reference span gas and compressed air is used to zero

the instrument. The sample gas is supplied to the burner at a

regulated pressure of 21 KPa (3 psig) and a flow rate of 1.9 1/min (4

ft^/hr) as measured by the F.I.D. sample bypass rotameter.

A Thermo Electron (TECO) Model lOAR chemiluminescent NO/NO^ gas

analyzer is used to determine the concentration of nitrogen oxides (NO,

NO2

) in the sample. The monitor provides 8 linear, full-scale ranges

including 0-2.5, 0-10, 0-25, 0-100, 0-250, 0-1000, 0-2500 and 0-10,000

ppmv. Calibration gases include compressed air for zero gas and

NO/N2 mixture for calibrating the instrument. The sample and

calibration gas flow rate is 1.2 1/min (2.5 ft^/hr).

The Beckman Model 755 oxygen analyzer measures the paramagnetic

susceptibility of oxygen. This susceptibility is much higher for

oxygen than other common gases. The instrument measures the total

magnetic susceptibility of the sample. This total is almost entirely

due to the oxygen present, so the measurement gives an accurate

indication of oxygen content. The unit is supplied with 4

switch-selectable ranges, 0-1, 0-2.5, 0-5 and 0-10% oxygen. The

calibration is accomplished with O 2 /N 2 span gas mixture and

nitrogen is used to zero the instrument. Calibration and sample gases

flow through the analyzer at 0.3 1/hr and are monitored using a

rotameter (max: 0.9 1/min at 21 °C and 100 KPa).

40
A Thermo Electron (TECO) Model 40 SO2 pulsed fluorescence

analyzer is available to carry out measurements of S02» when

necessary. The instrument provides 5 ranges; 0-50, 0-100, 0-500,

0-1000 and 0-5000 ppmv S02* Zero adjustment of the analyzer is

accomplished with nitrogen, and SO2/N2 span gas mixture is used to

calibrate the instrument. Recommended sample and calibration gas flow

rates are 0.9-3. 8 1/min (2-8 ft^/hr).

Two Beckman Model 865 non-dispersive infrared (NDIR) analyzers are

used to measure CO and CO2 concentrations in the sample gas. The CO

analyzer has one sampling cell and provides 3 scales, 0-1000, 0-2000,

and 0-5000 ppmv CO. The instrument is zero adjusted with nitrogen and

calibrated with CO/N2 span gas mixture. The CO2 analyzer is also a

single cell unit having 3 ranges which include 0-5, 0-10 and 0-20%

C02‘ It uses nitrogen for zero gas and CO2/N2 mixture for span

gas. Each range on both instruments has a nonlinear response and are

used with appropriate calibration curves. Required sample and

calibration gas flow rates are 0.5-0. 9 1/min (1-2 ft^/hr) which is

measured using a rotameter.

Response characteristics and linearity of the individual analyzers

are investigated using a Thermo Electron Model 900 heated sampler.

This dilution apparatus provides a means for filtering and diluting a

gas of known concentration at a specific rate and then introducing the

diluted gas to the analyzers. The instrument accurately blends dry air

with the sample in order to reduce the dew point and prevent

condensation at room temperature. The sample flow rate is

approximately 3.3 1/min (7 ft^/hr) at 69 KPa (10 psig). This is an

especially useful diagnostic tool because it enables the determination

41
of instrument response characteristics over a wide concentration

range.

All analyzers are checked and calibrated prior to start of and

during a test sequence. The calibration gases are brought to a patch

panel located near the analyzers. The various gases are connected to

the analyzers with quick disconnects and eliminate the need for

intricate valving. Excess dry sample gases are bypassed from the

system through a rotameter (max: 8 1/min).

Data Acquisition System (DAS)

The Digital Equipment Corp. (DEC) PDP 11/60 minicomputer based

data acquisition and control system (Fig. 55) is used to monitor and

record the many instrument variables involved in operating the furnace

during experiments which often run several hours. Since the computer

facility is located 610 m (2000 ft) away from the furnace, a Remote

Industrial Control (ICR) I/O subsystem is used to interface the process

instrumentation and control signals to the minicomputer. The ICR

contains an analog to digital converter board and has multiplexing for

40 differential input channels. System gains of 1000, 200, 100, 50,

20, 10, 2 and 1 are available to the user. The A/D converter has a

scan rate of 200 samples per second when scanning all the channels. The

following furnace input and output parameters are converted and entered

into the computer mass storage: coolant water flow, air flow, natural

gas and oil flows, and stack emissions by the gas sampling system (CO,

C02» O2, S02> NO/NO^ and total hydrocarbons).

A Fluke Model 2240B data logger is used to process and record the

various furnace temperatures. It presently uses 40 channels for analog

input data. With the A/D converter the data acquisition rate is

42
approximately 13-15 channels/sec when remotely connected to the

minicomputer. A high performance A/D converter is used for the

temperature measurements to obtain 1 uv resolution on the 40 mv range

for low level S-type thermocouples.

The Fluke data logger is compatible with T, K, R and S type

thermocouples. Automatic reference junction compensation corrects over

the temperature range 0®-50®C (0-120°F). Typical system accuracy for

fast scan temperature measurements is: jp.6®C for K-type, jHD. 5®C for

T-type, j^l.4®C for R-type and j^l.4®C for S-type thermocouples.

During an experiment the acquired data is temporarily stored on

the DAS disk system. After completion of the test the raw data is

processed and transferred to a Kennedy 75 ips, 9 track, 800 or 1600 bpi

magnetic tape transport system. A Versatec high speed printer/plotter

is used for hard copy listings of program files and for plotting

experimental results.

43
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APPENDIX B

DESCRIPTION OF THE IN-SITU 0?__AND CO MONITORS

In-Si tu Oxygen Analyzer

An in-situ O 2 monitor, with an yttria stabilized zirconia tube

probe, is located at the far end wall of the furnace and is used to

monitor excess oxygen content of the stack gases (see Fig. 56). The

probe consists of zirconium oxide (Zr02 ) high temperature solid

electrolyte ceramic material shaped like a test tube. Two porous

platinum electrodes coat the inside and outside surfaces of the

zirconia substrate and conduct electricity by means of oxygen ion

transport across the cell. The platinum acts as a catalyst to help

promote the electrochemical reaction. A cross section of the monitor

is shown in Fig. 57.

The monitor continuously measures excess O 2 in the stack and, if

desired, trims the concentration to a preset level that ensures maximum

combustion efficiency and fuel savings. The oxygen concentration of

stack gases is sensitive to naturally varying conditions in the fuel

and air flows such as fuel and air temperature, pressure, specific

gravity, calorific value, barometric pressure and humidity. In order

to ensure that no unburnt fuel is carried through the stack, most

combustors operate with excess air. This air leaves the stack,

however, at high temperatures, thereby wasting useful energy. Improved

efficiency can be achieved by reducing the level of excess O 2 ^nd by

maintaining this level within strict limits. A Readout/Control cabinet

45
provided with the Zr02 cell enables one to compare the stack O 2

content to the desired preset level and maintain this level by trimming

the fuel /air ratio.

Oil -free air is generally used as a reference gas since the oxygen

content of air is normally constant at sea level (20.9% O 2

). When

this air comes in contact with the inner probe surface, the oxygen is

converted to 0“ while removing electrons from the Zr02 J

O 2 2 0

2 0 + 4 e" ^ 2 0".

The ions travel through the probe to the outer surface where oxygen

from the flue gases is at a lower concentration. A similar but

opposite reaction occurs on this surface where 0“ changes back to

oxygen and free electrons;

2 0= ^ 2 0 + 4 e"

2 0 -> O2 •

As the oxygen concentration on both surfaces varies, so do their

reaction rates. The differential transport of ions and electrons give

rise to an electrical potential between the two surfaces. As the ions

deposit their electric charge on the inner and outer surfaces a voltage

builds up between the two electrodes and inhibits the flow of ions

through the cell wall. An equilibrium is reached when the voltage

across the electrodes exactly balances the driving force caused by the

difference in oxygen concentration across both faces of the probe. The

resulting voltage is given by the Nernst equation;

E = kT In (P 2 /Pi)

where k = 2.15x10-^ (V/°K)

46
T = temperature (®K)

Pz

~ oxygen partial pressure on the reference side of the

cell

(20.9% for air)

P-| = oxygen partial pressure on the sample side of the

cell

.

In addition to the O 2 concentration on both surfaces of the

probe, the voltage is also dependent upon the absolute temperature of

the sensor. In order to ensure good ion conduction across the cell,

the sensor temperature must be in the range 650-1 000®C ( 1 200-1 900®F )

.

At lower temperatures, operation can be sluggish and at higher

temperatures, operating life can be significantly reduced due to

reduced chemical stability of the electrodes. The probe is designed to

withstand temperatures of 1500®C (2800®F) for extended periods.

The operating temperature of the probe is 704®C (1300®F). This

temperature is maintained by a ceramic oven which surrounds the cell.

The heater also serves to keep the flue gas hot and to burn away any

combustible material around the cell. Uncontrolled sooting can be

detrimental to proper sensor operation. The cell temperature is sensed

by a K-type thermocouple. When the temperature falls 3®C (5®F) below

the specified oven temperature, the heater is turned on and power is

supplied to the cell heater element. A light on the Readout/Control

panel is used to indicate when the heater is operating.

The sensor probe uses an aspirating extraction technique, based on

the Venturi principle, to transport the sample gas from the probe inlet

to the sensing cell. Air at 25.4 cm (10 in) H 2

O gauge pressure flows

past a tube leading from the cell cavity. This draws air up through

47
the tube to the aspirating air outlet which in turn causes flue gas to

flow down the sampling tube to the sensor. The silicon carbide

sampling tube is a straight passageway lined with mullite capable of

withstanding the high flue temperatures.

The Readout/Control cabinet has 4 major functions. It gives a

readout from the sensor in % volume excess O 2 on a wet gas basis,

controls the sensor cell temperature as indicated by the panel light,

generates a process control signal by comparing cell output to the

setpoint and permits selection of setpoints and modes of operation.

Printed circuit boards in the cabinet are used to provide power for all

the electronics, to amplify the probe signal, to control the probe

heater and to determine fuel /air ratio trim control. A meter zero knob

on the cabinet panel compensates for the small off-set voltage from the

cell when it is exposed to air on both surfaces. When the unit is

switched to calibrate mode, the control function is disabled and the

meter can then be corrected with the zero knob in order to match the

O2 concentration with the calibration gas (generally atmospheric air

= 20.9% O 2

).

In-Si tu Carbon Monoxide Analyzer

The in-situ CO monitor (Fig. 58) is an infrared device that uses a

high resolution absorption spectroscopy technique to measure CO in the

range of 0-1000 ppmv. An infrared beam of light is transmitted from a

light source compartment across a stack or duct to a detector

compartment on the opposite side. The minimum required beam path

length is 91 cm (3 ft). An infrared globar light source emitting a

wide beam of polychromatic light is mechanically chopped at a frequency

48
of 63 Hz and collimated before being transmitted through a sapphire

window interface and across the furnace stack to a duplicate sapphire

window and collecting mirror on the detector side. Blowers with a flow

capacity of 1450 1/min (51 ft^/min) protect the sapphire windows from

combustion products, soot and high stack temperatures. The detector

cell collecting mirror directs the attenuated beam into a wavelength

discrimination module which employs a gas cell correlation technique.

The light beam is passed through a rotating wheel containing three

sealed gas cells (Fig. 59). One chamber contains 100% CO, the second

has 100% N 2

» and the third is filled with approximately 10% CO. A

narrow band filter (transmitting at approximately A = 4.7 ym) located

in front of the beam detector allows only the CO sensitive portion of

the infrared spectrum that is not absorbed by the stack emissions to

pass. The intensity at this wavelength from each discriminator gas

cell is transmitted to an electronically cooled lead-selenide detector.

Each signal is amplified and transmitted via a signal cable to the

control room module. After the signals are again amplified and fed

into an analog/digital converter, the resulting digital signal is

passed into an Intel 8085 microprocessor. The microprocessor is

programmed to measure the difference between the signal level from the

nitrogen cell and the signal from the CO chambers. The flue gas CO

concentration is then computed from the ratio.

The instrument calibration is checked by comparing the indicated

CO level to a preset check value of 780 ppmv CO which is based on a 91

cm (3 ft) path length. The zero adjustment must be set initially for

no measurable CO concentration. The calibration can be checked at any

49
time by adding 780 ppmv to the present CO level as long as the sum is

below 1000 ppmv and the zero setpoint has not been changed.

Using an oscilloscope the peak to peak signal voltage from each

cell can be monitored as illustrated in Fig. 60. The voltage level

should be 2. 0^0. 5 V, through the 100% N2 chamber (cell#l). The

voltage can be adjusted with the detector amplifier located above the

cell discriminator wheel. When the signal level drops below 1.0 V the

opacity in the stack is 80% or greater and insufficient light is

transmitted across the stack. The CO level will then read off scale.

Warning lights will also indicate when data from the detector or to the

microprocessor are invalid.

50
APPENDIX C

FIGURES

51
52
Equivalence Ratio

Fig. 2 - Typical results of equilibrium calculations for adiabatic flames.

53

Mole

Fractions
54

Fig.

3

-

Location

of

gas

sampling

probe

(A),

in-situ

Op

monitor

(B),

flange

where

CO

monitor

was

installed

below

the

recuperator

(C),

and

porthole

of

the

furnace

end

wall

(D).
ooo

*6 0‘6 S '8 S’

L O’L S • 9°

fO

i~Z3 4-> fO E

=J

L.

J=i

II ^

(U3 I o

•r" <1

+-> • #» <T3 S- CT

•r~ O)o a. c E (U «o in > </) •r* <o • 3 O'-'

CT O)

0) 1 S-3

x:

O 4-> +j

•r* &- 2

s- Q. c o E o +-> CU

•r“ <TJJ—

+-> s- (O O)^

s. Q.O

4-> 3 <0 C U +-> O) o>oo u s- c c o 5 O u o

•—•a

(>0 <u <u o J3 CO

c_> (O cncQ

»4- c o •rC

1—

O c Q.-1- o E+->

rO fO -M (/1r—

fO 3 •1— • o

&. 00 1

(O (0 > oo

sf

cn

0*8

(•/] 503

55
COo

{'/.] ^!D

56

Variation

of

Oo

concentration

with

equivalence

ratio;

Fuel

=

Natural

Gas;

Sampling

Below

recuperator;

(o

-

Gas

Sampling;

A

-

Equilibrium

Calculation

Based

on

Stack

Temperature;

-

In-Situ

Monitor).
COo

57

Fig.

6

-

Variation

of

CO

concentration

with

equivalence

ratio;

Fuel

=

Natural

Gas;

Sampling

below

recuperator;

(o

-

Gas

Sampling;

A

-

Equilibrium

Calculation

Based

on

Stack

Temperature).
=1

*

(/] 203

58

ly

Variation

of

CO2

concentration

with

equivalence

ratio;

Fuel

=

No.

2

Fuel

Oil;

Sampling

below

recuperator;

(0

-

Gas

Sampling;

A

-

Equilibrium

Calculation

Based

on

Stack

Temperature).
=r E

Z3 .«<

S_

c\j

CL) Q- • :3 (o o o~oo

II I i~ I— < o

(U 4-> 3 • »v •r—

Ij- C7)

C c o O r—

•r- Q_ 3

+-> e 4-> fo fO T—

S- (/) COI (U t/> E U ITJ • C CU

O) I > O' 3

cr ••v O) s-o ^ 4-> ^ fO

•r- S_ 2 <uQ. C 3 o o

•I- OJ -M i- (O

sX

+-> o c —

<U O) U CO co cn o c

CVJn- o Q.

o>

s-3

4-> roS_

<u • Q.^ E CM

(U I— OJ ^ "q. o E

ro (O -M 00 CO I EO EO

O A-* ^

.r- <0 I

-t-> o rz ^

rO 3 ' -r- I— CJ ' "3 3 « > U. ^

00

(7J 20

59
(ANdd) 03

60

I

Variation

of

CO

concentration

with

equivalence

ratio;

Fuel

=

No.

2

Fuel

Oil;

Sampling

below

recuperator;

(o

-

Gas

Sampling;

A

-

Equilibrium

Calculation

Based

on*Stack

Temperature;

-

In-Si

tu

Monitor).
o

.95

1.00

1.05

1

itio;

Fuel

=

No.

2

'e

CO

equilibrium

ing;

+

-

Equilibrium

ibrium

• Calculation ; ; i

d:b:ri''^''b::bt|.

gpT|

•

.

:±;m

.4.4...i4.4..44..-.f*> %

{

> ! 1 A

...44.^i.4..4..j...i...|...

'b'-f-ff-fj-

...4.i..i.4..i.4.4.4 |.g

.

90

0

uivalence

n

Included

ar

-

Gas

Sampl

e; A

-

Equil

2 : : \

p-

—

.

85

0

PHI

tion

with

eq

recuperator;

perature;

(o

k

Temperatur

e).

' 2 i : : 1 i : : :

iLj:"|"r;tr4;t:r

-

: 2 : : k i : j : /

lo E 5“

F ^ s- S <u 13 +j o -M C OO <0 <u OJ OJ ^5“ U JD E C OU c rtJ O D- o W, O ^

CO o >— c

j. . O Cl. O fO O)

-

EEE[±to±F^|0F 14_ (T3 E

"O m

o t/0 a»

1/1 co ^u_

s= .• <o o - -Q tlra So

+J O (/) '— ^

Ln ^ aj cj OJ

s_ OJ >

rd 3 CL) <0 fC

‘

,

o > O CO

1 o

°

r- u_

1 i ] : ; : i

• : t

........

a

5 COm

D’OOOfig 0’00002 0*0

(AWdct) 03

61
lO

LU

QC

Q

LU

N LU

CD

CD

Lf) O

C>

CO

d

CsJ CD

LU

CD

>

X

o

CO

CO

LU

O

X

LU

CT>

(AlAldd) 3QIX0N01AI NOadVO

62

Variation

of

CO

with

excess

O2

for

several

boilers

and

furnaces.
CO ( P P M

V ] 4J

<o

<L) Uc

a>

ro>

O)

s-3

S- 4-> •" O n3 ^ C M- t. O o CU +£ -r- CD CL P -*-> C E

CLE — fO t_) to LO ITS O -(-> in to E to 3 Ci3 C

IO

S- I •a a1 yv-O •<^0) (/) <1> _

-Q j3

CT CDr— "V (/) ^ C "t— • « fO ^ 3 S- CQ

-C r— o- 0» +J cllu N

C S fO I ,— .1—

I/) fO +j c < C (TJ O • r- in _

S- CM

O

OJ

O I—

N to >1 S- C_3 ^ O

(T3 4- E

-M (O

ns C3

S-

+-> c

<DOco

(J

fO

s-3

4-> to

CM II Ooc

fO

<c 0) •!- s- s_ CM 3 J2 O 4-> -r- tO I

S- S- o a;

CU M- CL 3 E

CD O) E hO • •> C_J QJ I— ^

r— Qa

1|_ ns E <T3 O O CO +j

1/0 CO CO cO TS CO

•I— o>

+-> -o

ns c -O

•I- ns I a.X O

Lu ^ 3

cr

s-ns

S- + <uN • " >,

S- I—

CU ns N E c >,«a: O I—

ns

O

_

C (J

CU <c

in ins o o

CQ

O M- I CM

CD

63
6Q0. 0

500.0

CG [PPMV]

UOO.O 300.0 200.0 100.0 0. oS

i-o

4-S « C • 0i 5r. o 03 -r- o ^ 03 +J 03 ,— t P 3

(U

i-34->

O IT3 sOJ O) Q. C E

•r- <U Q.

u E -iC r— (T3 O ^ 5 rO 00 <0 O O (_j 4J

<u OJ E »o r— 3 c 'O •!— O > cn s- I c -Q . -o cr.— r-N/oi ^ •!“ • (O E 3 1- OQ .C <tS Q- (U

-*-> OO LU

NC

>1

O I I— f- >— <o +J

C •>- < C 03 O O <C'—

•I— .M 3

-M CVJO

<0 <U <1) O I—

I- 3 N fd -M U. >) S- O 3 r- O

03 <\J 03 <4- E O C 3 C • eC <1) T- O O S- 5- U Z CM 3 X> O 4-> T- CM II 03 I— O S- i- •>- .— O 03 3

"O 03 *— Q- ^ C 3 EUJ

fO Li_ g'^03 ^ s. + 01N

>,

S- I o • O , 03 r- Q- O

<4_ (d E fO O O 03

(/) t/> OO 03 10 3 N C 0 "O c/1 c >>^

•f— <U »0

O rTQ CD 03

O

»0

C "O

C <J .,-03 ( 03 cC O- ^ b

03

X

O 03

O

O > ill ^CD C_) <4- 1 CO

CT>

64
EXCESS

OXYGEN

(%)

EXCESS

OXYGEN

(%)

IN-SITU O2 MONITOR

EQUIVALENCE RATIO

Fig. 14 - Variation of Excess O 2 with equivalence ratio at different furnace

pressures; Fuel = No. 2 Fuel Oil.
66

Fig.

15

-

View

of

the

CO

monitoring

system

as

installed

in

the

stack

above

the

recuperator.
ooo o^ c

0.0

O)

II

Fue' |S • ^o

S3 1

-Q

4-> fO ° P Scu c in

•r—_

u -M Q- c LU

OJfO

Q ' > <

i- .« cr O ct; (U

<T3 i- r—

-M

O Q.E 2 =3 to U 00 c O) o i- t/) •r— <T3 • +-> O) C3^ fO > 0>

sO 1 S-

+-> -Q 3 c «3 o +J

O) (T3 a C7> S- c C CU o r- i. Q. u

Q. 'O OJ

c\j E h- O to cn o oo C -5^

•<- o

^- • #' ' rO o i/) O +-> to o OO c CD U o c

i— 4-

O

+-> to o

<T3 s_ +j -a

•r— 3 0) +J c to

to <o o to > Z E QQ I

O)

U-

(7J EDO

67
GOO

m sg

68

>— j_

lO

O

i- 4-> 3 •!-

+-»

C

«J

O

T3

<U

</) ^ la

II o “

OJ o 3 4-) "o,:? o -a 3

'5-sS s- > ^1- E OJ (U 3 (J (/> . r- S c ,11 > o .,-

•-- 3

O’

O’ 3 UJ O) I— X S-o C 4-> o <o

•<- s-

-l-> (UQ. 3U

(U

SIT3

i- 4-> (O W)

(/) -—.

ro

O

CSJ-3 I -«-> (O o s- ^ (1) Q. •« E S- (U

C CL <0 > 0 E ••-(0 0)0

+J LO

C (O (O ••- -P • r— • ^ I— (/> i. Ut O

(O (O o c > ca o o 1

c: <u o > o oX) CM (O o O) M- C O
69 co -3

I— > ^

<U i_ c 3 O) E

U- </) S- o•>- c

O-r-

(O -I-

_

S- ^

(U r— o •>- C Q

<u rTM • 9t m $_ > o

•r- +J

Z3 IT3 O- i- OJ O)Q. jC 3

+j o

‘5 t! C (U o >

••- o

(O (O

s.

+-> cn

c: c: <U -r- u —

£= Q. O E u iS on

C\J o •» .—

MOOC 0) O 3

•I- u_

+-> CM

CJ> £=O O)

s-3+J

I- (tJ r- ^

(O <Uo.

cn E c <Uo

(O +JCO

c:o

T3

_ OJ

S- • CO

(O

OO <C S» Z CJ C3Q

00

C71
=r

0.2

<0

II 3

'^•oo

U- -o c ->.l

•2

+J

iq

1/1 ^_Q 5- 0:2

<u c o- O Oil) C 'r- 0) 4-> I I— 3

iq> (“-f— < 03 oi cr •" c (U S- .f- 0,—

tJ Q.

+j 2 E 4- <0 3 CO

0.

C0 0 rtj • *r“ <1) O'-'

+J i- (U

<o 1 si. (U 3

+J > 0 c O'— (0

(U ^ i- u iq 0> c s- 0. 0 E c <q <u

•r- h- CMi— 01 O Q. C ^ S ..- O

<+- IC I— (O O t-o O 4J O (/> c ••> o o .— c

•<- -I- S- o

+J o o

<0 +j

T3

•I— r— .r— fl> S. (U C (/I fO 3 O fO =» Li- E ca i

(T» !*) m ZQ

70
ooo f

-2 E fd

II

cu3 <U

<a o

(O O'*- s. M<o o ^

cu a. oc ^cu +J

'fO 3>3 S- CD

O' o

(U 4-3 (O r-

-c s- a.

4-> cu e •I- Q. 5 3o c cu o s4_> (U

CO >

s- o

-l-> -Q c <o

cuo o> c c: o •>- O I—C3. CM E O <d

CJ> C/) O c/3 ns C CD o

4_> rO

rO i-

•I- 3

i- -M

<o <d oCM

fO

c/1

(/) rd C3 • I cu

£-

O 3 -— +J

fd •" s- c cu O Q.

•>- E 4-> CU O t-

•I- -i«C "O o

fd

s- +J

•rC/1

fd

£= O) o c

•I- -a — cu O 10 o fd U CQ

O)

71
ooo

72

ITJ S- +J §2

TO 8 js li II (1) c 3 -i- O C

•r- o 4-> TO OJ

s- e

TO <U I— O vi_ C

O) 4-> t— o

TO f— > -r- •>- Q. 3

CTx:

<u -M X $-o C 4J o TO

-l-> TO

$- MC

(Uocou

<u>o

CVJ TO o cn

»4- c o -1-

•r- i. 3 O 0- 4-> LlI f-c I o <

Z3

criT- c in

•r- I r— C 0.*-i E

TO I

TO •*

CJ3 Q)

S. I 3

+J

O 10 w S-0) .t. a c E o <v Q. 4-> E 3-^

TO ^ U

c/) T— (0 3 -P .« CO

lO i- TO

C . TO O I

CM

cn
(X) o

cn

I— c

<0 -r-

<T3 rJ ^ O ^ ^ ^ CQ

II

0)3

4-> (O

•'- O cTO ^« M<0 (U o^

t- <oe E§ o) .— .;z O >4- s_

<U -M I— O r-

<0 rQ. O" 3 LxJ KTSZ

4> +-> I S i.o co c C (U o > u o o <aCD

<4-

C

O -r- C 0.4-4 O E O

•I- fO 1

4-> OO -r-

<tJ XJ

5- (/) S.

rt3 *r- > CD <0

CMCM

(AWdd) 03

73

on

Stack

Temperature; QIn-Situ

Monitor).
CMOz

II

(U3 e

U. 3

.. ^ o c

CT O) = lO

fO o“o C <-> o

+j

re3O

(O

<_) (O

i. ^ E QJ o 3 U 00 -r- C CO S_

(1) 00 XI

<0 II I— > •!-

•r- Ll_ 3 3 »— OO" LU

OJ .•

S. I ^ o

+J -M <

•r- (d X s_ •«

<1) CT> C3. C ^ E

<o

dj </> c > _

O) o o ^ ,<2 C (O ts o

(_) C7) '

CM-iO

O'O Q. O OO

O

•MO ••- (O -o

S- (U S. nJ 3 -r- > Li_ <0 co

(O

icn

CM

74

on

Stack

Temperature).
CM

CD • C O •>- Z I—o

II oo

'Z E 3 3

••

C o •»-

fo « A

S- oe

OJ CO O 00 c 00

O) «— II <d> U- I— 3

O- •*

<u o

J= +-> 4-> <0 co

-M

fO

S-O)Q.3o

(U

<v>o 0) ^ <j fO coo c

CMr— O Q.E

M- lO Oco o I 4-> <1 EO • 5^

cn- c 3

•I— •!-> Q.CO E I <o c

OO I—I

CO I ^ i 1 c^D I •»> O) O E3

-M • n fO C S- o ^

•r- Q-

•M £ 3 .<U +J O >o -o

(-> S- QJ E «5

<0 3 .r- 4-> > U. fd C/1 I

CM

on

75

Equilibrium

Calculation

Based

on
o

JO.O

A A

o

JQL

IT

A. A:. A A

o -©I 0

A A

CDO

(\J O

O'OOOe 0'00S2 O'OOOS O’OOSI O'OOOI O’OOS

(ANdd) 03

. ? <U 0-- 53 o “

II O £- ^ ^ O

<u e T;

12 1 ^ 013

(_>E

3

S- XI

fO • •

1- oo

lU 00 U 00 C 00

(U r— It <a> Li. •.- I— 3

oO) J_o ^ -M

4-> <0

•I- J- 2 <UQl

3 O

cr+J

UJ -r-c

I o

s; <

3

• ~X>

3>T- coo

I =r Q_ o o

<U f— c

0.1—• cn -!-> J- E

, to to t o i- 0)

+-> >

CO c o in

a; ^ nj • o <o C5 (U c s. o o> 1 3 u c +J o <0 o o — s. CD O Q. <u

, E • #v a.

<4- (O c E O (/I o (U h- c •« M

O I— 3

•r* ‘r* r— o

+J o (0 <0 TO 4-> CD

P-* 00

s. a> s. CD <0 3 c

• > li_ o

ir>

CVJ

o>

76
o

r/J EQ3

II

(U

77

Fig.

26

-

Start-up

transient

test:

CO2

variation

with

time;

<p

=

0.5;

Natural

Gas;

Sampling

above

recuperator;

(0

-

Gas

Sampling).
o

o

o

(!

I

CVJ

I

O)

78

Start-up

transient

test:

O

2

variation

with

time;

<p

=

0.5;

Fuel

=

Natural

Gas;

Sampling

above

recuperator;

In-situ

O

2

monitor

below

recuperator;

(o

-

Gas

Sampling;

-

In-Situ

Monitor).
o

o

(ANdd) 03

79

200.0

UOO.O

600.0

800.0

1000.0

1200.0

1400.0

1600.

TIME

[SEC]

Fig.

28

-

Start-up

transient

test:

CO

variation

with

time;

<j>

=

0.5;

Fuel

=

Natural

Gas;

Sampling

above

recuperator;

(o

-

Gas

Sampling;

-

In

-Situ

Monitor).
o

o

A]

m^0

; Jb

/ °

' i

f a

0

O

y t

0

o

]

J

9 ^

^

Q

0

C? i 1 1 i i i 1 i n

c

i !

: M M Q

3

pU

® o

o

( o

o’ooee 0’0082 o'ooea o'ooBT o’ooei

tANdcl) 03

r\j .r^ oo

.CO cn

CD

.cn oo

oo

oo

o

.rr oo

o

. I CM

.00 OO

.CM OO

is:: hCO

o

CD

'oo

oo .o

oo

o'ooe o’ooe

o

o

fo

II

-e-

<T» CM

80

Start-up

transient

test:

CO

variation

with

stack

gas

temperature;

0.5;

Fuel

=

Natural

Gas;

Sampling

above

recuperator;

(o

-

Gas

Sampling;

-

In-Situ

Monitor).
I oCO

o>

(X) 203

81

Variation

of

CO2

concentration

with

equivalence

ratio;

Fuel

=

No.

2

Fuel

Oil;

Sampling

above

recuperator;

Tp

=

920*C;

(0

-

Gas

Sampling;

A

-

Equilibrium

Calculation

Based

on

Stack

Temperature).
CM

•r— ^

o 'o.^ ^ ^ c

II I— (/» <U <0 SD

•*o o t*:

• «k i- CJ

0) o P U CM 5 c cn iz

0)

<0 ^J >^n •Z >- +j HOJ $. c _ 9 o f "o

S- (1) <u w

Q. nj 3 cfl u

o> «J c o

CMr— £ O Q. 3 ,

14- <0 $. I O 1/1 XI , = ..;: .( O I— ^ , -r- 3 i. 4J O CTO I <o Ul +J '

S. (1) I c

(0 3 0 > Ul < 2

I

CO

cn
o

C75 C\J C

•r— , • o "q. ' z E 1 II CO ' ,

to

<v <a 1 3 C3 1 u. 1 •o o

>w>^ -M

fO • ^

f- oo

(U oo CM c CTl 0) r— II ic> Lu

•r— 1— 3

CT • •> (U O

jC +J

4J <o

s-cua.

C 3 o O

•r“ <u +J s- <o

0) -M > C o

0>u sco a> u c o Q.

<4- § o </> c • A o r—

r* •1“ +J o

r—

S- (U

:3 u.

$-(Uc.E

<uo

(O

-»-» CO

c:o > ll. <i s;

C\J ro

Ul.

(ANdd) 03

83
zi* o Oi • c r-% r—

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93

Fig.

42-

Schematic

of

heated

absorption

test

cell

assembly.
94

View

of

heated

absor^ption

test

cell

assembly.
006

o

CO

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O

o

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oo

LU

QC3

I-

<

GC

LU

0-

LU

95

Fig.

44

-

Dependence

of

CO

measurements

on

test

cell

temperature.
cofcm'*'!

Fig. 45 - Absorption coefficient of CO as a function of temperature.

96
97

NBS

Experimental

Furnace

Facility.
Fig. 47 - NBS Experimental Furnace: Sideview of furnace.

98
Fig. 48 - NBS Experimental Furnace and Burner.

99
100

NBS

Experimental

Furnace:

The

Recuperator.
STACK

o »- z 05 Q.

(/) Q.(O

101

Experimental

furnace

control

and

data

acquisition

system.

103

Fig.

52

-

Water

cooled

gas

sampling

probe.
104

Location

of

water

cooled

gas

sampling

probe.
PROBE

105

Schematic

of

gas

analysis

and

sampling

system.
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a S < C3

UJ o o

n

00<

ii! ^

=>

Q- s^

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XLU —

U.=)< 5^

u

z

a

CQ<

cc

h—oo u

106

I

Fig.

55

-

DEC

PDP

11/60

minicomputer

based

data

acquisition

and

control

system.
107

Location

of

in-situ

O2

monitor.
CERAMIC HEATER

OXYGEN

SENSING

CELL
109

Fig.

58

-

Schematic

of

the

in-situ

CO

monitoring

system.
I a\

in

\

no

Schematic

of

the

rotating

wheel

and

three

sealed

gas

cells

inside

the

CO

monitor.
s>«0T

111

Fig.

60

-

Typical

output

from

the

CO

detector.