FUNDAMENTAL ASPECTS OFCOAL-WATER FUEL DROPLET COMBUSTION AND

SECONDARY ATOMIZATION OF COAL-WATER MIXTURES

FINAL REPORT, Volume II

by

T.U. Yu, S.W. Kang, J.M. BedrJ.D. Teare and A.F. Sarofim

MIT EL 87-003 February 1987

DOE/PC/70268-F2

FUNDAMENTAL ASPECTS OFCOAL-WATER FUEL DROPLET COMBUSTION

ANDSECONDARY ATOMIZATION OF COAL-WATER MIXTURES

FINAL REPORT

Professor J.M. BeerProfessor A.F. SarofimPrincipal Investigators

Volume II

The Energy Laboratoryand

Department of Chemical EngineeringMassachusetts Institute of Technology

Cambridge, Massachusetts 02139

Date Prepared - November 1986

Prepared for

United Stated Department of EnergyPittsburgh Energy Technology Center

Fossil Energy Program

Under Grant Number: DE-FG22-84PC70268

i

DISCLAIMERS

This report was prepared as an account of work sponsored by an agency

of the United States Government. Neither the United States nor any agency

thereof, nor any of their employees, makes any warranty, expressed or

implied, or assumes any legal liability or responsibility for any third

party's use of the results of such use of any information, apparatus,

product or process disclosed in this report, or represents that its use by

such third party would not infringe privately owned rights.

ii

FOREWORD

Grant Number DE-FG22-84PC70268 covered research carried out at the

Massachusetts Institute of Technology during the period October 1984-

September 1986. All of this research related to combustion of coal-water

fuels, but the workscope covered two entirely separate tasks which involved

experimental work in three different facilities at MIT.

The Task 1 investigations dealt with Fundamental Aspects of Coal-Water

Fuel Droplet Combustion, and the experiments were carried out in Laminar

Flow Reactors. The Technical Monitor at the DOE Pittsburgh Energy

Technology Center for this portion of the work was Dr. James D. Hickerson.

The Task 2 research was on Secondary Atomization of Coal-Water

Mixtures, and this involved measurements on a Spray Test Rig to characterize

spray atomization quality of fuels with various treatments, followed by

combustion tests in a 1-3 MWth Combustion Research Facility. The Spray Test

Rig was also used to characterize the nozzle used in the Task 1 work. The

Task 2 Technical Monitor was Mr. Charles McCann, who was also the Project

Manager for the Grant.

Because of the disparate nature of these separate-but-related Tasks,

this Final Report is issued in two volumes; Volume I covers the Fundamental

Aspects and Volume II deals with Secondary Atomization.

iii

RESEARCH TEAK

Principal Investigators

Professor J.M. Be6rProfessor A.F. Sarofim

Research Group Tasks

Prof. J.M. Be6r 1, 2

Dr. D. Froelich 1

Mr. S.9. Kang 1, 2

Mr. S.G. Kang 1

Prof. A.F. Sarofim 1, 2

Dr. S. Srinivasachar 1

Dr. J.D. Teare 1, 2

Mr. L.D. Timothy 1

Dr. M.A. Toqan 2

Dr. P.M. Walsh 2

Dr. T.U. Yu 2

Reports Prepared by:

Volume I Volume II

S.W. KangA.F. SarofimJ.D. TeareJ.M. Be6r

T.U. YuS.W. KangJ.M. Be6rJ.D. TeareA.F. Sarofim

ACKNOWLEDGEMENTS

The contributions of the members of MIT-CRF group to the experimental

program, and of Ms. Bonnie Caputo in the report preparation, are gratefully

acknowledged.

ABSTRACT

This Final Report is issued in two volumes, covering research into the

combustion of Coal Water Fuels (CWF). Two separate but related tasks are

discussed; Volume I contains results obtained under Task 1 - Fundamental

aspects of Coal-Water Fuel Droplet Combustion in which the experiments were

carried out in Laminar Flow Reactors. The present report, Volume II, covers

experiments under Task 2 - "Secondary Atomization of Coal-Water Mixtures".

Three methods of improving spray fineness by fuel treatment were

investigated - 1) the heating of the CWF under pressure to produce steam as

the pressure drops during passage of the CWF through the atomizer nozzle 2)

the absorption of CO02 gas in the CWF to produce a similar effect, and 3) the

addition of a chemical additive which will cause microexplosions in the

droplets upon heating. These treatments are expected to produce disruptive

atomization, i.e., the disintegration of slurry droplets subsequent to their

leaving the atomizing nozzle, and therefore to yield better burnout and

finer fly ash particle size distribution upon combustion. The effects of

disruptive atomization upon CWF spray size distribution were studied using a

spray test chamber equipped with a laser diffraction particle size analyzer;

the data were fitted to the Rosin-Rammler particle size distribution

function. The combustion characteristics of the treated CWFs were

investigated in the MIT Combustion Research Facility.

The spray chamber tests established that thermally-assisted atomization

produced reductions both in the mean droplet size and in the mass fraction

of large particles in the spray. For fuel delivery temperatures up to 100*C

this effect is attributable to lowered fuel viscosity, while further heat of

the CWF (to 1500C in these experiments) produces disruptive atomization

In-flame measurements and high speed cine pictures made during

combustion tests provided detailed information for comparisons of treated

and untreated CWF. Thermally-assisted atomization was the most effective of

the methods studied for improving carbon conversion efficiency and reducing

fly ash particle size. CO02 and picric acid addition techniques showed

substantial improvements but they were less effective.

v

Table of Contents

Page

Disclaimers i

Foreword ii

Research Team iii

Acknowledgements iii

Abstract iv

Table of Contents v

1. Introduction 1

2. Experimental Apparatus and Conditions 3

2.1 Spray Test Rig and Optical Spray Measurement 32.2 Experimental Equipment, Measurement Methods and 6

Experimental Variables2.3 Fuel Treatments 11

3. Experimental Results and Discussion 11

3.1 Spray Tests 113.1.1 Thermally-Assisted Atomization 113.1.2 C02 -Assisted Atomization 20

3.2 Combustion Tests 24

4. Summary and Conclusions 36

References 38

Appendix A A-IAppendix B B-1Appendix C C-l

1. Introduction

During coal water slurry combustion there is a tendency for the coal

particles to agglomerate within individual droplets while the water is

evaporating; the agglomerates are then dried out and undergo thermal

decomposition in the flame. Hence the resulting coal particle size

distribution (p.s.d.) will be determined more by the size distribution of

the atomized fuel spray than by the initial particle size of the coal.

Large particles formed through agglomeration have increased burnout times

and produce large fly ash particles which accelerate convective tube bank

erosion. Such erosion can be reduced if the fly ash particles are

sufficiently small that they follow the gas streamlines around tubes rather

than impact on them.

In pulverized coal combustion it is known that finer grinding of the

coal will yield reduced fly ash p.s.d. The relationship between coal

particle size and fly ash size, however, is less straight-forward for CWF.

If finer coal p.s.d. in the slurry could permit use of smaller atomizer

nozzle orifices, this might lead to finer fly ash p.s.d. via improved

atomization, with the fineness of atomization being related to the orifice

dimensions of the atomizer. Unfortunately, finer solids p.s.d. leads to

increased slurry viscosity for a given CWF solids loading, and this, in

turn, may lead to coarser atomization unless the viscosity is reduced by

means of an additive or by diluting the slurry with water.

An alternative route to finer p.s.d. of the spray droplets and of the

fly ash is the use of fuel treatment to produce disruptive atomization; the

atomizer would deliver as fine a spray as readily achievable, but fuel

treatment or additives would cause further disintegration of the atomized

droplets, yielded finer droplet p.s.d. for combustion.

Three treatments to produce microexplosions in atomized droplets have

been studied at MIT:

i) CWF heating, which was first studied in Germany (1) and

successfully tested (2) by Babcock & Wilcox; if a pressurized fuel

is heated to a value approaching its saturation temperature, the

water content of the slurry 'flash vaporizes' as its pressure is

rapidly reduced in the atomizing nozzle. The resulting volumetric

change from steam release causes the droplets initially formed by

the nozzle to shatter, yielding a substantial decrease in p.s.d.

ii) The absorption of CO2 in the slurry under pressure, as initially

proposed at MIT (3); CO2 is dissolved into the fuel by injection

into the line between the pump and fuel nozzle. During the

pressure release in the atomizing nozzle, the dissolved CO2 evolves

in gaseous form and disrupts CWF droplets.

iii) The use of picric acid as an additive as suggested by Dr. Kenneth

Olen (4); upon the injection of the CWF spray into the flame the

water-soluble and thermally unstable chemical produces

microexplosions on the surface of the coal particles in the hot

environment, resulting in separations of partially agglomerated

coal particles.

Some quantitative characteristics of these three treatment techniques

are presented in Appendix A.

In the following sections are reported the results of experimental and

analytical studies carried out at MIT to provide information on the effects

of disruptive atomization in reducing p.s.d. of droplet and fly ash

particles; the influence of the three types of fuel treatment is evaluated

in terms of the spray droplet p.s.d., the overall flame behavior including

flame stability and carbon burnout, the p.s.d. of particulates within the

flame and at exit from the combustor, and the fly ash deposition.

Experimental results showed that the fuel treatments were effective in

reducing p.s.d. of droplet and fly ash particles (5, 6, 7).

2. Experimental Apparatus and Conditions

2.1 Spray Test Rig and Optical Spray Measurement

A schematic diagram of a spray test rig is shown in Figure 1. CWF

droplet p.s.d. for a spray discharged into a 1.25 x 0.45 x 1.00 m chamber

was measured by means of a laser diffraction spray analyzer (8). Two sides

of the chamber have plexiglas walls for optical observation and measurement;

the other sides are fitted with honeycomb sections through which outside air

to be entrained by the spray can pass. This supply of outside air is

necessary to suppress any recirculation of small particles inside the

chamber. A description of the spray test rig and the laser diffraction

analyzer is given in Appendix B.

The measurement technique of the analyzer is based on the Fraunhofer

diffraction pattern superimposed on the geometrical image produced by

droplets in the path of a monochromatic light beam. The analyzer,

manufactured by Malvern Instruments Inc., comprises a laser light source

that passes light through the two plexiglas plates perpendicular to the fuel

spray flow, a 31-element photodetector that receives the light signal on the

other side of the chamber, and a minicomputer and a control terminal that

process output signals from the photodetector and print out droplet size

distribution parameters. In the processing of the signal a functional form

for the size distribution is fitted to the data; for example, the software

yields best-fit Rosin-Rammler (R-R) parameters from which other spray

characteristics, including mass median diameter (MMD), can be calculated.

EXHAUSTTOOUTSIDE AIR

EXHAUSTFAN

ROOM AIR

I I I I

FLOWMETER

ATOMIZINGAIR SUPPLY

AIR FLOWDAMPER

WATER

SPRAYCHAMBER

FILTER

P : PRESSURE GAUGE

T : TEMPERATURE GAUGE

V : VALVE

R : REGULATOR

TO STORAGE PUMPTANK

CO2

INJECTION

STIRRER

FUELMIXINGTANK

FILTER

STEAM OUT

STEAM IN

V WATER

FUEL PUMP

Schematic diagram of spray test facilityFigure i.

5

An assessment was made of the relative error due to our choice of this R-R

size distribution by comparison with fits based on a "model-independent"

size distribution. The index used to show the quality of the least-square

fit of the data was defined as

31Z Log [light intensity calculated - light intensity measured]2

1

had a value always less than 4.3, and its value did not improve (i.e.,

decrease) when the model-independent size distribution was used instead of

the R-R functional form.

The laser beam was aimed perpendicular to the spray axis, 30 cm

downstream from the nozzle tip. The transmissivity of the spray was

monitored, and multiple scattering effects were determined according to the

empirical calibration technique developed by Dodge (9). The error on MMD

due to multiple scattering was always less than 5%. A 300 mm focal length

lens was used for the laser-diffraction particle size measurements. This

gave an observable size range between 5 and 560 Mm.

During spray experiments the thermally-assisted and C02-assisted

atomization techniques were tested. The fuel flow rate was maintained at

163 kg/h, while the atomizing air/fuel mass flow ratio and the nozzle

diameter were varied. The atomizer nozzle used for spray tests was of the

OR-KVB dual fluid type developed by Occidental Research Corp. and KVB, Inc;

it is of internal mixing and has a single exit orifice.

Both the spray tests and the combustion studies were carried out with

Coal-Water Fuels Prepared by Atlantic Research Corporation to the same

specification (coal particle size, viscosity, and fuel additive). The coal

in the CWF used for the spray tests was "Montcoal", and that in the CWF

prepared for the combustion experiments was "Splashdam". The origins of

these coals were different, but in each case the coal type was bituminous;

the two coals were of the same rank and were similar in composition. There

is no reason to believe that differences in coal type used in the

formulation of the CWF caused any differences to exist in the qualitative

behavior of the CWF sprays used in the two types of experiments. Indeed,

experiments were subsequently carried out at MIT with a range of coal types

in CWFs, and these later spray tests have confirmed that the behavior of a

CWF under disruptive atomization is insensitive to the coal type (10).

2.2 Experimental Equipment, Measurement Methods and ExperimentalVariables

The MIT Combustion Research Facility (CRF) is a 1.2 m x 1.2 m cross-

section, 10 m long combustion tunnel equipped with a single burner capable

of up to 3 MW firing rate. The combustion tunnel, shown in Figure 2, is

comprised of a number of 0.3 m wide, watercooled, refractory lined or bare

metal interchangeable sections. The sections can be arranged to control

heat extraction along the length of the flame, and thus to simulate the

thermal environment of a wide range of industrial and utility flames. The

facility is extensively instrumented to permit accurate control of flame

conditions and detailed characterization of internal flame structures. The

experimental burner consists of an infinitely variable swirl generator (of

IFRF moveable block design). Combustion air from the swirl generator passes

through a 0.176 m diameter nozzle coaxial with a 0.06 m diameter fuel gun.

The fuel gun and atomizer are moveable along the axis of the burner,

permitting variation in the position of fuel injection relative to the

nozzle throat. Detailed descriptions of the burner and combustion chamber

have been given by Be6r et al. (11) and Farmayan et al. (12).

In-flame measurements were obtained with water-cooled probes which

could be inserted into the combustion chamber at various axial stations.

Solids sampling was carried out with probes in which the sampling lines were

Burner Experimental Cylindrical Cold-Wall ExhaustChamber Afterburner Chamber Section

Figure 2. Furnace assembly and air supply

either water-cooled or steam-heated. In the former case a water spray was

injected into the line at the sampling nozzle to quench reaction in the

collected sample, and in the latter case the probe was connected to a

cascade impactor where particulates could be classified aerodynamically into

several size ranges. The various techniques used for in-flame measurements

of temperature, gas composition and solids concentration have been reported

elsewhere (11, 12).

Fine and regular-grind CWFs supplied by ARC were used for the

combustion tests. Experiments were carried out to determine the effect of

addition of CO2 , picric acid, and the preheating of the fuel to 110*C prior

to atomization. Over this range of preheat, neither slurry caused any

plugging in the pipeline or nozzle. For each slurry a baseline study was

carried out using untreated fuel.

Specifications of the two ARC CWFs (Fine and regular-grind; Coal type:

- Splashdam) are included in Table 1. The experimental conditions

maintained constant during the combustion tests are given in Table 2. It

should be noted that the excess air in the flames studied was maintained at

a level unusually low for coal combustion (8-9%) to accentuate the

improvements due to the fuel treatments. However, the two types of CWF

(fine and regular-grind) were tested under different thermal inputs (1.0 and

1.3 MW, respectively). Thermal input was increased to raise the flame

temperatures in the regular-grind CWF experiments, but this would result in

improved combustion efficiency at a given axial location relative to the

corresponding fine-grind case. Thus quantitative comparisons between

equivalent fine and regular-grind cases are not available.

Table 1

Specifications on the ARC Coal-Water Fuels*

A. Montcoal (Used for Spray Tests)

- Solids p.s.d. in slurrySize (pm) 300 150 75 45 10 5 1% Passing 100 97 81 72 29 15 2

- Slurry Solids: 68.1%

-I- App. Viscosity (Haake): 800 ± 50 cp in interval 2000 - 8000 sec-

B. Splashdam (Used for Combustion Tests)

o ARC Regular (Runs 324 to 326)- Solids p.s.d. in slurry

Size (pm) 850 70 20 7.6% Passing 100 80 50 30

- Slurry solids: 70.3% -1- App. Viscosity (Haake): 616 cp at 70*F and 102 sec

o ARC Fine (Runs 320 to 323)- Solids p.s.d. in slurry

Size (pm) 600 75 30 9.9 4.6% Passing 100 96.9 80 50 30

- Slurry solids: 69.6%

-1- App. Viscosity (Haake): 416 cp at 70*F and 102 sec

o Characteristics of the Parent Coals- Proximate Analysis: As received Dry Basis% Moisture 1.07 -% Ash 5.50 5.56% Volatile 30.44 30.77% Fixed Carbon 62.99 63.67Btu/lb 14561 14718

- Ultimate Analysis (Dry)% Carbon 82.91% Hydrogen 5.06% Nitrogen 1.50% Chlorine 0.11% Sulfur 0.61% Ash 5.56% Oxygen (diff.) 4.25

*Analyses of experimental slurries provided by Atlantic Research Corp.

Table 2

Experimental Conditions of Combustion Tests (Runs 320 to 326)

Fixed Conditions

o Atomizer: Solid Cone 50* OR-KVB Nozzle, 3.175 mm Orifice Diameter

o Burner Type: 25* Half Angle Divergence, Refractoryo Combustion Air Swirl: S = 2.8o Burner Nozzle Diameter: 0.176 mo Atomizer Position: At the entrance of the divergent quarlo Combustion Chamber Configuration (from burner to outlet):

7 Water-cooled refractory lined sections2 Water-cooled bare metal sections5 Water-cooled refractory lined sections

ARC Fine (Runs 320 to 323)

o CWF Type: ARC Fine, Splashdam, 67.5%, Coal Loadingo Fuel Flow Rate: - 188 kg/h (-1.0 MW Firing Rate)o Fuel Pressure at Nozzle: -1.65 MPa (-1.20 MPa with Heating)o Fuel Temperature: -260C (-1100 C with Heating)o Atomizing Air Flow Rate: -35.9 kg/ho Atomizing Air Pressure: -1.20 Mpao Combustion Air Flow Rate: - 1119 kg/ho Combustion Air Preheat: -290*Co Excess 02: -2%

ARC Regular (Runs 324 to 326)

o CWF Type: ARC Regular, Splashdam, 69.5% Coal Loadingo Fuel Flow Rate: - 232 kg/h (-1.3 MW Firing Rate)o Fuel Pressure at Nozzle: -1.72 MPa (-1.40 MPa with Heating)o Fuel Temperature: -270C (-1100C with Heating)o Atomizing Air Flow Rate: -42.9 kg/ho Atomizing Air Pressure: -1.34 Mpao Combustion Air Flow Rate: - 1570 kg/ho Combustion Air Preheat: -310*Co Excess 02: -2%

2.3 Fuel Treatments

For the thermally-assisted atomization studies, steam-heated lines

connecting the fuel pump to the Spray Test Rig and to the CRF burner are

capable of raising the CWF temperature to about 150*C. Each line is about

12 m long and equipped with gauges for monitoring pressures and temperatures

of both steam and CWF.

For the study of fuel treatment by CO2 absorption, a 15 cm section

containing a CO2 injection assembly can be readily inserted into either main

fuel line at the high pressure side of the fuel pump. Figure 3 shows a

schematic diagram of the injection system. The maximum CO2 flow rate which

could be injected into the line without producing pulsating sprays or flames

was approximately 4 g/kg CWF. This is about 50% of the theoretical

saturation limit.

The chemical treatment of the CWF was effected by premixing picric acid

with CWF, with special care being taken to ensure uniform mixing. The

"nominal" picric acid concentration was chosen to be 0.35 g/kg CWF, which is

within a factor of two of that required to cover the CWF coal particles with

a monolayer of picric acid molecules. Several picric acid concentrations in

excess of the nominal were tested, but visual observation of the flames

showed no discernable improvement in atomization quality. Thus the in-flame

measurements were carried out with the nominal picric acid concentration.

3. Experimental Results and Discussion

3.1 Spray Tests

3.1.1 Thermally-Assisted Atomization

The mass median diameter (MMD) of the spray was calculated from the

laser diffraction measurement data and plotted in Figure 4 as a function of

P,T

ROTOMETER

ELECTRICALIIEATINGELEMENT

FUEL LINE SECTION

CO2 INJECTION ASSEMBLY

CO2 CYLINDER

Schematic diagram of CO2 injection systemFigure 3.

ARC CWF (68/32,OR-KVB NOZZLEFuel Flow Rate 2.72

standard)

kg/min

x X xA

400]

E

ZL

I-

U)U)2

xx *xxx

XX

o2 oo B

Nozzle OrificeDiameter (mm)

3.3023.1753.1753.1752.794

CoalMMD

0

Particles= 26.3km

I I I I I50

I I ~ ~ I

OC100 150

CWF TEMPERATURE

Effect of CWF temperature on mass median diameter of CWF spray(CWF - ARC Montcoal)

80

60 O- x0

Air/ FuelMass Ratio

0.3190.2730.2610.1330. 133

40

20

RunI

- 2345

Figure 4.

I I I I I I I I I I

CWF temperature. For both high (0.261 - 0.319) and low (-0.133) A/F ratios,

the MMD decreases monotonically with increasing CWF temperature. Up to

100*C the reduction in spray droplet size is due to the decrease of

effective viscosity of the CWF with increasing temperature. At higher

temperatures the continuing reduction in MMD may be partly due to further

decrease in viscosity, but it is also attributable to disruptive flash

vaporization of water in the droplets. It does not appear feasible to

quantify the relative roles of these two mechanisms without first obtaining

CWF viscosity data measured at high shear rate and high temperature (in the

range 100-150*C).

For the high A/F ratio it may be observed that the measured MMD

approaches the MMD of the parent coal particles in the CWF, indicating the

potential of thermally-assisted atomization for improvement of spray

quality. At the low A/F ratio of 0.133 there is a similar decrease in MMD

in the range 100*C to 150*C, but the smallest droplet MMD measured is still

much larger than that of the parent coal particles.

For Run 3 (0.261 A/F ratio and 3.175 mm orifice dia.), the experimental

data were further analyzed in the form of particle mass distribution.

Figure 5 shows the relative mass distribution of sprays for three different

temperatures (21*C, 100*C and 148*C) and of the parent coal particles used

in the formulation of the ARC CWF. The curves represent differential forms

of the cumulative Rosin-Rammler mass distribution.

The beneficial effect of heating CWF from room temperature to 100*C and

then to 148*C can be seen in Figure 5. As temperature increases not only

does the mean diameter decrease, but also the spray size distribution

becomes more uniform; i.e., the number of large droplets existing in the

spray diminishes. At room temperature (-21*C), for example, 13% of the

2.0

1.0

0

Size distribution of coal particles and CWF droplets

at various CWF temperature (CWF - ARC Montcoal)

0OO

I)O

100 200

PARTICLE DIAMETER (/.Lm)

Figure 5.

spray mass is contained in droplets greater than 100 microns, whereas at a

temperature of 148*C the corresponding percentage of the spray mass is 1.3.

Figure 5 also shows that the mass distribution of the spray at 148*C in the

large size range is close to that of the parent coal particles. Due to

forcing of the data to the Rosin-Rammler functional form, the size

distribution of 148*C CWF shows fewer large particles above 80 pm than the

parent coal. This error, however, is small ( < 1%) and does not change the

above conclusion.

The extent of disruptive atomization can be estimated using the area

enclosed by two mass distribution lines of 100*C and 148*C. These two lines

intersect each other at a particle diameter of approximately 43 microns.

The enclosed area to the right of this abscissa represents the total amount

of large particle mass lost due to disruptive atomization, and it is equal

to the area to the left of 43 microns, which is the total amount of fine

particle mass gained. The area is calculated to be 0.2, i.e., it can be

said that as much as 20% of the total mass of spray droplets is converted

into finer droplets.

The strength of flash vaporization from a sudden expansion of high

temperature pressurized water into atmospheric pressure can be related to a

"volume change". The volume change occurs because some of the water will

vaporize to steam as it undergoes a sudden pressure drop below its

saturation pressure, typically to 1 atm. The bulk liquid must cool down to

the saturation temperature corresponding to the reduced pressure, and the

heat released is available for the production of steam, which results in a

greater total volume. The values of enthalpy of saturated water between 373

K and 500 K, obtained from Steam Tables (13), can be reasonably well

represented by a linear function of temperature given by

h - 4.32 x 103 Ts - 1.193 x 106, (J/kg) for 373 K < Ts < 500 K,

where Ts is the saturated water temperature in K. Therefore, the change of

enthalpy of the water from its value at 373 K is

Ah - 4.32 x 103 Ts - 1.612 x 106, (J/kg), (1)

and this is available for steam production. If it is assumed that the

saturated water at high temperature can be passed through a rapid pressure

drop to atmospheric pressure without any transient process of vaporization,

the volume change compared to its original volume could be represented by

Ah

AV v vfh- fg 3.20 Ts - 1.194 x 103V- 1 1 3 1 ((2)

vfv + 1 1.043 + 1- ( )Y

with h = 2.255 x 106 J/kg (heat of vaporization of water,1 atm & 373 K).

vg = 1.672 m3/kg (specific volume of steam, 1 atm & 373 K)

vf- 1.043 x 10-3 m3/kg, (specific volume of water, 373 K)

Pc 1.3 x 103 kg/m3 (density of coal),

and where 7 is the mass fraction of water in the CWF.

In addition, the mass fraction of vaporized steam is

Am Ah -3m h 7 = (1.916 x 10 Ts - 0.715) 7 (3)

fg

These relationships are approximately linear with temperature and are

displayed in Figure 6 as a function of water mass fraction of the CWF. For

example, if the water heated to 150*C in a pressurized line undergoes sudden

expansion to atmospheric pressure through the atomizing nozzle, the water

temperature should decrease to -100*C, liberating an "excess" enthalpy of

2.15 x 105 J/kg. This is sufficient to vaporize 10% of the water and

produce a 150-fold increase in specific volume. If the water forms part of

a 70/30 coal-water slurry, the instantaneous flash vaporization produces

Absolute Pressure

500

(kpa)

1000 1500 2000

150°C 200

I I I , 1400

I I I I

450

Saturation Temperature

Volume and mass fraction of steam generated from CWF as a functionof saturation temperature. y: Water mass fraction in CWF

100300 r--

200

I00

>,

0

o

0.15

El

E

0.1

-0

0°-

0.05

100

I I I

Figure 6.

- 0.03 kg of steam per kilogram of CWF, representing a net 55-fold increase

of specific volume.

For the present case of the CWF atomization shown in Figure 4 the fuel

flow rate at 2.72 kg/min and at 150*C (corresponding to a fuel volume flow

rate of 4 x 10-5 m3/s) will result in a vaporized steam flow rate of -2.3 x

10-3 m3/s. This in turn corresponds to 36% of the atomizing air volume flow

rate (6.4x10-3 m3/s) at the A/F ratio of 0.133. Assuming that the vaporized

steam flow acts like atomizing air flow, the effective A/F mass ratio

changes from 0.133 to (0.133 + 0.03)/(1.0-0.03) - 0.168, which is a 26%

increase due to 0.03 kg of steam per CWF kilogram. The assumption is

conservative, because the specific volume of the steam produced is 58%

larger than that of the atomizing air, thus calling for higher flow

velocities to maintain a given volumetric flow rate.

One question which arises is whether the heating of CWF from 100*C to

150*C provides better atomization quality than would be obtained by directly

increasing the atomizing air mass flow by 26% at 100*C. As of this time,

there have been no direct experimental comparisons to clarify such a

question.

However, the data in Figure 4 show the extent of improvement achievable

with CWF at 100*C when the A/F ratio is doubled (from 0.133 to 0.261).

Since this A/F increase actually quadruples the momentum of the atomizing

air, it is reasonable to postulate that a 41% increase in A/F ratio, or a

doubling of momentum, would yield approximately half as much improvement

relative to the data at A/F - 0.133; i.e., would yield an improvement

roughly equivalent to that obtained by increasing fuel temperature to 150*C

while maintaining A/F ratio unchanged at 0.133.

From an operational viewpoint it can be argued that the cost of

achieving a given improvement in atomization quality should be lower when

the fuel heating technique is used than when the same improvement is

obtained by increase in flowrate of the atomizing medium. The compression

work for pressurized air is usually provided by electrically-driven motors,

while use of steam as the atomizing medium will significantly increase the

requirement for demineralized make-up water supplied to the boilers; these

factors make use of high atomizing-to-fuel mass flow ratios prohibitively

expensive.

The experimental tests on thermal atomization have provided new

information on the effectiveness of flash vaporization on CWF atomization.

However, better understanding of the phenomena associated with flash

vaporization, both upstream and downstream of the nozzle orifice, is

required to provide an improved way of controlling and optimizing thermally-

assisted atomization.

3.1.2 CO02 -Assisted Atomization

The role of dissolved CO2 in spray atomization has been studied by

measuring spray droplet size distributions obtained using CWF with a range

of CO2 concentrations. The experimental measurements of MMD as a function

of CO2 concentration indicate that CO2 by itself produces a more modest

improvement in atomization quality (Figure 7).

One possible explanation for these results can be seen from the

comparison of volume expansion between CO2 atomization and thermally-

assisted atomization. Since the solubility of CO2 in water at 31*C is

-3AV = 6.38 x 10 P scc/g H20, (4)

where P is the nozzle fuel pressure in kPa, the ratio of the volume of

maximum soluble CO02 to the CWF volume becomes

OR CWS (standard, 70/30)OR - KVB NOZZLE

NOZZLE ORFuel Flow RA/F Moss RFuel Nozzle

Run22

IFICEate =atio =

DIA. 3.175mm2.27 kg/min0.151

Pressure 720 KPa

E

C

a)

aL

Er

In0

C

0aa"3

U)U)

I I I I I I I

0.1 0.2

C0 2 /CWS Mass0.3

Ratio (%)

Effect of CO2 concentration on mass median diameterof CWF spray

120

I 10 -

00 --

o

Xo

90-

80

60 1-

5010.4

Figure 7.

)

-3AV 6.38 x 10 3Py (5)

V 10- + - (l-y)PC

where - is the mass fraction of water in CWF, and Pc is the coal density

which is approximately 1.3 x 103 kg/m3 . The mass fraction of CO2 is

Am -5-m - 1.15 x 105 PY (6)

m

Equations (5) and (6) are graphically displayed in Figure 8. At 1000 kPa,

the volume change achieved from an expansion of CO2 in water is 6.4.

However, the corresponding volume change when the CO2 is dissolved in

(70/30) CWF is only 2, which is about 25 times smaller than the volume

expansion achievable by heating to the saturation temperature of 150*C.

This relatively weak volume change is probably the primary reason why the

C02 -assisted atomization did not show significant improvement in spray

quality.

One problem noted during the CO2 experiments was that whenever the

injected mass of CO2 exceeded approximately 50% of its maximum soluble

amount, the resulting sprays from the nozzle became non-uniform and

pulsating. This phenomenon is probably due to CO2 gases left undissolved in

the fuel line. Since in our case the residence time for dissolution of CO2

is finite, it is to be expected that the calculated value of CO2 solubility

in H20 would be larger than the actual value.

In order to reach a final conclusion on the effectiveness of this CO2 -

assisted atomization technique, further studies are needed. How the

absorbed CO2 escapes from the water during a sudden expansion and/or after

primary atomization remains unanswered.

1000Absolute Pressure (kpa)

22

EE

O

1.5 u

oI0.5

0.5

0,

2000

Volume and mass fraction of CO2 dissolvable into CWF as afunction of absolute pressure-y: Water mass fraction in CWF

I;>1>>

00U

)E030

I0

5

Figure 8.

3.2 Combustion Tests

Experimental data of gas composition, solids concentration and carbon

conversion efficiency for the baseline case and for three fuel treatments

are compared in Tables 3 and 4 for the ARC fine and regular-grind CWFs,

respectively. The carbon conversion efficiency improvements due to fuel

treatments are accompanied by corresponding reductions in 02 concentration

at the furnace exit. The lower 02 concentrations are concomitant with

increased CO2 concentrations and lower final concentration of CO. The data

show that the thermally-assisted atomization is the most effective method in

improving the carbon conversion efficiency. CO2 injection is slightly more

effective than picric acid addition.

Photographs of the flames of ARC fine CWF taken during the four scoping

trials (Runs 322 -0 to -3) are shown in Figure 9. It can be seen from a

close observation of the still photos that the different treatments yield

varying improvements in flame stability and fuel-air mixing. A fuller

flame length was especially evident when the CWF was heated, consistent with

the measurements of more complete carbon burnout.

The effect of fuel treatments was studied further in terms of the

particle size distribution (p.s.d.) of flame solids, as determined by a

cascade impactor. Particles larger than 20 pm were captured by a cyclone

upstream of the impactor and sieved manually. Particle size distributions

of particulates taken in flames of fine and regular-grind CWFs at a distance

of X/D - 17.1 (D - 0.176 m is the combustion air nozzle diameter) are

plotted in Figures 10 and 11. In Figure 11 mass percentage of unburned

carbon as a function of particle size is also plotted for the thermally-

assisted and baseline cases, indicating substantial reduction in the amount

of unburned carbon in the larger particles for the former case. With the

Table 3

Summary of Experimental Data from Scoping Tests withVarious Secondary Atomization Treatments for ARC Fine CWF (Run 322)

322-0

Base

27°C

322-1

CO2

322-2

Picric Acid

3.9 g/kg CWF 0.35 g/kg CWF

322-3

Heating

1080C

Axial PositionX/D, D - 0.176 m

Temperature K

02 %

CO %

CO2 %

Solid Concentration*

(g/m3 , NTP)

3.3 17.1 3.3 17.1

- 1352

3.52

0.0202

- 14.57

- 1353

- 2.70

- 0.0067

15.57

63.9 20.1 58.8 8.7

3.3 17.1

- 1354

- 3.30

- 0.0076

14.98

57.0 8.8

3.3 17.1

1353

0.71

0.0035

- 17.21

22.7 2.6

Ash (%)

Carbon Conversion*Efficiency (%)

5.7

3.7

7.9

- 32.1

CWF Type: ARC Fine Splashdam

* Water-quench solids sampling probe (X/D - 3.3)Steam-heated solids sampling probe (X/D - 17.1)

t Carbon conversion efficiency at combustion exit (X/D - 28) for all cases was >99%.

Run No.

Treatment

7.4

26.3

11.0

52.9

Table 4

Summary of Experimental Data from Scoping Tests withVarious Secondary Atomization Treatments for ARC Regular CWF (Runs 325)

Run No.

Treatment

Axial PositionX/D, D = 0.176 m

Temperature K

02%

CO %

CO2 % 1

Solid Concen- 9tration*

(g/m3 , NTP)

Ash (%)

Carbon ConversiontEfficiency (%)

325-1

Base

270C

3.3 17.1

1727

0.8

0.8

6.0

9.0

325-1

CO2

3.9 g/kg CWF

3.9 17.1

1459 - 1486

2.56 - 2.46

0.0071 - 0.0071

16.5 - 16.6

2.3 79.01 1.9

5.8 39.0 7.4 47.6

325-2

Picric Acid

0.35 g/kg CWF

3.3 17.1

- 1490

- 2.22

- 0.0072

- 16.8

80.78 2.2

6.7 44.0

325-3

Heating

1100

3.3 17.1

1771

0.8

15.9

52.2

1496

1.92

0.0057

18.2

1.5

8.0 71.5

4.4 90.8 26.3 93.5 18.0 92.5 32.3 97.7

CWF Type: ARC Regular Splashdam

* Water-quench solids sampling probe (X/D - 3.3)Steam-heated solids sampling probe (X/D - 17.1)

t Carbon conversion efficiency at combustion exit (X/D = 28) for all cases was >99%.

BASE (Run 322-0)

CO2 (Run 322-1)

PICRIC ACID (Run 322-2)

HEATING (Run 322-3)

Photographs of CWF flames with various treatments(Run 322, CWF - ARC Fine Splashdam)

Figure 9.

4.5 - CO2 ASSISTED

- PICRIC ACID

o 1.5 a BASELINE

x

ARC-FINEzoH

1.0H

4

MI

0.5

0 100 200 300

PARTICLE DIAMETER ( / M )

Figure 10. Fly ash and residual char (unburned carbon) particle sizedistribution for the effect of different fuel treatments(CWF - ARC Fine Splashdam; Flame thermal input - 1.0 MW)

1002,5

2.0

E o

0

m

B

100 200 300

PARTICLE

Figure 11. Fly ash and residualdistribution for the

DIAMETER d(/Am)

char (unburned carbon) particle size

effect of different fuel treatments

(CWF: ARC Regular Splashdam; Flame thermal input - 1.3 MW)

0z0

5050wzmZ:3:Qz

0,5

fuel treatments, improvement in size distribution by reduction of the large

particle mass fraction and corresponding increase in the small particle mass

fraction can be seen for both the fine and the regular-grind CWFs. CO2 and

picric acid addition resulted in appreciable improvement in p.s.d. However,

the technique of CWF heating produced the best p.s.d. observed.

Trimodal distributions of particle size seen on Figures 10 and 11

indicate that several mechanisms may contribute to the production of fly ash

and residual char particles during CWF combustion. As small and

intermediate size particles are formed through the partial disintegration of

coal agglomerates, these may continue to burn, with each producing a single

fly ash particle; this is roughly equivalent to a yield of one fly ash

particle per original coal particle in the CWF, and it creates the middle

peak of the p.s.d. Alternatively several very small fly ash particles can

be produced through fragmentation of a single parent coal particle, which

corresponds to the left-most peak of p.s.d., while some of the large

particles formed initially through agglomerations may still exist at the

axial station at which sampling was carried out (X/D - 17.1). Disruptive

atomization causes effects of coal particle size on char burn-out and fly

ash particle size to become more important. This is evidenced by the number

of large particles surviving to the axial location of X/D - 17.1 (see Figure

10 and 11 - the right-most peaks); the number is higher for the flames of

the regular-grind CWF than for those of the fine-grind CWF. The middle

peaks of these trimodal distributions are centered at 45 pm and 20 Mm for

the fine and regular-grind cases, respectively. In the latter case the

unburned carbon content of the 20 pm particles was very small, but carbon

content was not measured at X/D - 17.1 for the fine-grind flames. No direct

comparison of the relative extents of burnout for these two fuels can be

made, because (as indicated earlier) the regular-grind CWF was burned in

flames with higher thermal input than the fine-grind.

Detailed measurements (see Appendix C) on the centerline of the flames

of both fine and regular-grind CWFs were made for the case of thermally-

assisted atomization for comparison with the baseline data; some radial

traverses were also carried out for one flame (Table C-2). The centerline

distributions of flame velocity and temperature are plotted in Figure 12.

Figure 13 shows that solids concentrations from each thermally-assisted

flame are lower than those of the corresponding baseline case and,

furthermore, the carbon burnout is better.

High speed cine pictures and photographs of the flames show a wider

spray angle for the thermally-assisted case relative to that of the

baseline, and corresponding improved flame stability is manifested by

reduced ignition distance and absence of low frequency fluctuations in flame

front position. The improvement in combustion conditions can be further

illustrated by SEMs (Scanning Electron Micrographs) taken for the solid

particles captured from the centerlines of the thermally-assisted and

baseline flames at X/D - 17.1. Comparison of the SEMs of 250 - 355 pm

particles in Figure 14 shows that the state of oxidation is more advanced in

the flame with thermally-assisted atomization.

For the baseline and thermally-assisted cases further comparisons were

made by determining deposition rates of fly ash on ceramic tubes inserted

perpendicular to the flame axis and thermally equilibrated with the flame

gases. The transverse distribution of deposition rate was determined from

the total amount of fly ash deposited per unit length of deposition probe

during a period of 20 minutes. Effects of CWF heating on the deposition

rates for tube diameters of 25.4 and 6.35 mm are shown in Figure 15. The

o BASELINE

• * THERMALATOMIZATION

ARC-REGULAR

I I I L I20 30

2000

1500

10000

I I10 20 3

Figure 12. Comparison of gas velocity and temperature at the centerlineof CWF flames for baseline and thermal atomization cases

Left:CWF - ARC Regular Splashdam

Right:CWF - ARC Fine Splashdam

Flame thermal input - 1.3 MW Flame thermal input - 1.0 MW

40

1000

I I I I i

o BASELINE

STHERMALATOMIZATION

ARC-FINE

4 V%,%

I00

I-

E

z0

I-

0aC3

,)

- TIIERMALAIOMIZATION -

I BASELINE

0 10 20

X/D, DISTANCE FROM BURNER

I 0°

0I I I I I

20

X/D, DISTANCE FROM BURNER

Figure 13. Solids concentrations and unburned carbon percentageon the centerline of CWF flames for baseline and thermalatomization cases

Left:CWF - ARC Regular Splashdam

Right:CWF - ARC Fine Splashdam

Flame thermal input - 1 3 MW Flame thermal input - 1.0 MW

SIO

'10E

z

I-g

zaUjzo 10

CJ

0(n

(A) BASELINE

(B) THERMALLY ASSISTED ATOMIZATION

Figure 14. SEM photographs of particles collected from the centerlineof the flame at X/D = 17.1, 250 - 355 pm size range(CWF - ARC Regular Splashdam)

101

X/D= 17.1 IBASELINE THERMAL

ATOMIZATION

_ O TUBE DIA. 6,35 mm

C U0 TUBE DIA. 25.40 mmE

t 100

O

-

W

0

100 20 40 60

DISTANCE FROM FLAME AXIS (cm)

Figure 15. Transverse distributions of fly ash deposition rate per unitarea of ceramic tubes at X/D - 17.1, for thermally-assistedand baseline cases (CWF - ARC Regular Splashdam)

deposition rate with CWF heating for a 25.4 mm tube is less than that

withoug heating (baseline) case at all transverse locations, by a factor of

about 0.5 - 0.6.

As would be expected, the smaller tube has higher capture efficiency by

particle impaction which results in higher normalized deposition rates.

However, for this tube the CWF heating produces increased deposition rates

relative to the baseline case in the region close to the flame axis. The

reason for this could be related to the reduction of the mass fraction

larger particles which are capable of eroding the deposited material upon

their impaction. Thus by their removal the risk of tube erosion is reduced

but the heat exchange surface might collect more of the fine particle

deposits.

4. Summary and Conclusions

Three methods of inducing disruptive atomization to improve the quality

of spray droplet p.s.d., and thereby yield finer fly ash p.s.d., have been

studied using the MIT Spray Rig and CRF. They include 1) thermally-

assisted, 2) C02 -assisted and 3) chemically-assisted atomization. The spray

rig studies involved measurements of droplet p.s.d. and mass median diameter

of sprays using a laser diffraction analyzer. In-flame measurements made

during combustion experiments in the CRF served to determine the influence

of these three methods of disruptive atomization on flame stability, carbon

burnout, and resultant fly ash p.s.d.

During the spray tests the thermally-assisted atomization of CWFs was

found to improve spray quality. This improvement was probably due to a

decrease in viscosity at temperatures lower than 100*C, and to disruptive

atomization at temperatures higher than 100*C. Compared to normal

atomization the CO02-assisted method had a more modest effect upon reduction

of CWF spray particle size. This can be explained by the differences in the

volume expansion due to flash vaporization and the evolution of gaseous CO2

in the CWF droplet.

During combustion experiments the characteristics of the three modes of

disruptive atomization studied to identify the effectiveness of each method

in reducing the fly ash p.s.d. The most effective method was the thermally-

assisted atomization, judged by reduction of solids concentration and p.s.d.

determined along the length of the flames. While not as effective as

thermal atomization, CO2 and picric acid additions to the slurry have also

given beneficial results. The improvement in atomization quality due to CO2

absorption was slightly greater in the flame than in sprays introduced into

a cold environment. The chemically-assisted atomization was in the third

place in ranking behind thermal and CO02 -assisted atomization.

38

References

1. Merten, M. and Homer, M., Section in Final Report on "Combustion of

Coal/Water Suspension Power Plants," Steinkohlen bergbauvereim (LigniteMining Association), Essen, Germany, January, 1972.

2. Daley, R.D., Farthing, G.A., Jr. and Vecci, S.J. Coal Water SlurryEvaluation, Vol. 2, Final Report CS-3413, Research Project 1895-3 EPRIPalo Alto, CA 1984.

3. Reid, R.C., Sarofim, A.F., and Be6r, J.M., MIT, Cambridge, MA., privatecommunication (1983).

4. Olen, K.R., "Chemically Enhanced Combustion of Water-Slurry Fuels,"U.S. Patent No. 4,445,150, June 19, 1984.

5. Yu, T.U., Kang, S.W., Toqan, M.A., Walsh, P.M., Be6r, J.M., andSarofim, A.F., "Secondary Atomization of Coal-Water Slurry Fuels,"Seventh International Symposium on Coal Slurry Combustion andTechnology, New Orleans, Louisiana, May 22-24, 1985.

6. Yu, T.U., Kang, S.W., Toqan, M.A., Walsh, P.M., Teare, J.D., Beer, J.M.and Sarofim, A.F., "Disruptive Atomization and Combustion of CWF," 8thInternational Symposium on Coal Slurry Preparation and Utilization,Orlando, Florida, May 27-30, 1986.

7. Yu, T.U., Kang, S.W., Toqan, M.A., Walsh, P.M., Teare, J.D., Be6r, J.M.and Sarofim, A.F., "Effect of Fuel Treatment on Coal-Water FuelCombustion," 21st Symposium (International) on Combustion, WestGermany, August, 1986.

8. Swithenbank, J., Bear, J.M., Taylor ,S.S., Abbot, D. and McCreath,G.C., "A Laser Diagnostic Technique for the Measurement of Droplet andParticle Size Distribution," AIAA 14th Aerospace Sciences Meeting, AIAApaper No. 76-69, 1976.

9. Dodge, L.G., "Change of Calibration of Diffraction-Based ParticleSizers in Dense Sprays," Optical Engineering, Vol. 23, No. 6, 1984.

10. Beer, J.M., Toqan, M.A., Teare, J.D., "Reduction of Fly Ash ParticleSize in Coal-Water Fuel Flames" Phase IV Final Report September, 1986.

11. Be6r, J.M., Jacques, M.T., Farmayan, W.F., and Teare, J.D., "DesignStrategy for the Combustion of Coal-Derived Liquid Fuels," EPRI InterimReport, (RP1412-6), Palo Alto, California, 1982.

12. Farmayan, W.F., Srinivasachar, S., Monroe, L., Ditaranto, F., Teare,J.D. and Beer, J.M., "NOx and Carbon Emission Control in Coal-WaterSlurry Combustion," Proceedings Sixth International Symposium on CoalSlurry Combustion and Technology, p. 165, U.S. DOE, Pittsburgh EnergyTechnology Center, 1984.

13. Keehan, J.H., Keyes, F.C., Mill, P.G. and Moor, J.G., "Steam Tables,"John Wiley & Sons, Inc., 1969.

A-i

Appendix A - Characteristics of Fuel Treatment Techniques

Al. Thermal Atomization

If water is heated to 200*C (saturated vapor pressure then being 1550

kPa, or - 15 atm) its enthalpy in the liquid state is 0.853 MJ/kg. On

sudden expansion to atmospheric pressure the water temperature must decrease

to -1000 C, which represents a drop on enthalpy of -0.43 MJ/kg H20. This is

sufficient to vaporize -0.2 kg/kg H20, since the heat of vaporization of

water at 100*C is 2.26 MJ/kg. Thus the net result of a sudden expansion of

water at 200*C is the conversion of -20% of the water into steam, with a

300-fold increase in specific volume.

If the water forms part of 70/30 coal/water slurry, the instantaneous

flash vaporization produces -0.06 kg of steam per kg of CWF, representing a

net specific volume change of the mixture of -100-fold increase. Transfer

of the heat stored in the coal particles (initially at -2000 C) to the

remaining water would add to the extent of flash vaporization and enhance

the specific volume increase.

A2. Carbon Dioxide Injection

At 310 C the solubility of CO2 in water is -0.65 P cc (NTP) per gram of

H20, with P in atmospheres. Thus at a nozzle pressure of -7atm the

saturation level would be -4.5 cc/g H20, or -0.009 g/g H20, corresponding to

-0.0027 g/g CWF (for a 70/30 slurry), or -0.0045 g/g CWF (for a 50/50

slurry). It was expected that pronounced secondary atomization effects

would be observed with lesser amounts of dissolved C02 , at levels on the

order of 0.1% by weight of the CWF.

Provision must be made to prevent freezing of the CWF as a result of

temperature drop in the CO2 as it is expanded from storage pressure. This

A-2

was accomplished by making the injection section a part of the heated fuel

line discussed in Al.

A3. Picric Acid

An upper limit estimate of the 'desirable' amount of picric acid to be

added can be made by assuming a monomolecular coating for the coal particles

in the slurry. For instance, for spherical coal particles of diameter d,

the picric acid mass per particle would be rd2WM/ANA kg, where WM - 0.229

kg/mole, A = 20 x 10- 2 0 m2 (molecular 'area'), and NA = 6.02 x 1023/mole.

The particle mass would be rpd 3 /6 kg, with p - 1200 kg/m3 , so that the

picric acid requirement would be 6WM/pdANA kg/kg of coal, or (for a 70/30

slurry) 4.2 WM/pdANA - 3.3 x 10.4 kg/kg CWF for d - 20 pm. This corresponds

-3to 1.1 x 10 kg/kg H20 in the slurry, which is in turn approximately 10% of

the room temperature saturated solution concentration.

Picric acid dissolves rapidly in water, but its concentration at

saturation is too low (- 1%) to permit addition to the CWF by metering a

saturated solution, since this would cause excessive dilution of the CWF.

For the CRF experiments the most practicable method of introducing the

additive to the fuel was by premixing.

B-I

Appendix B. - Spray Test Rig and Optical Analyzer

B-1. Spray Test Rig

A schematic of the spray test facility is shown in Figure 1. Figure B-

1 is a photograph of the spray test rig. The atomizing air supply and fuel

pump systems are shared with the 3 MW combustion facility. The atomizing

air is supplied at pressures up to 2200 psig. It passes through a 1/2 inch

diameter line equipped with a pressure regulator, flow meter and a flexible

stainless steel hose, to a SPC[y nozzle. Atomizing air pressure and

temperature are measured at the- entrance of the fuel gun. The CWF is

delivered by a Moyno pump which can provide pressures up to 550 psig. On

its path to the spray nozzle the fuel passes through a flow meter (Micro

Motion Model C 25). Fuel pressure and temperature are measured at the gun

entrance.

A spray gun transporting the CWF and the atomizing air can be adjusted

vertically and horizontally to permit the traversing of different segments

of the conical spray by the laser beam of the optical spray analyzer.

The spray rig test chamber is 49" x 18" x 40". Two sides of the

chamber have plexiglas walls for optical observation and measurement. About

half of the area of the other sides of the chamber is comprised of honeycomb

sections through which air to be entrained by the spray can pass. The

supply of outside air is necessary to suppress the recirculation of small

particles into the path of the laser beam. Air at room temperature enters

through the honeycomb sections when the exhaust fan is switched on. At exit

from the spray chamber this entrained air and the atomizing air stream are

separated from the CWF, and then flow through a filter and a flexible hose

en route to the exhaust system of the CRF. The used CWF is collected in a

storage tank through a pump.

I I --~~-iL-i--~--=rr=2=~f;-re=~-~-L-----L-- - ~-~-mm~-

B-2

JEL LINE

f"

1-ILASER LIGHTSOURCE

ATOMIZINGAIR LINE

I: r;*~u

f~IT~I2

HEATED FUELSUPPLY LINE

, _ = .~a~i

EXHAUSTHOSE

S (

Photograph of spray test facility

SPRAYCHAMBER

I

Figure B-1.

B-3

B-2. Optical Analyzer

Figure B-2 shows a schematic diagram of a Laser Diffraction Spray Analyzer.

This analyzer (Malvern Instrument) consists of a He-Ne laser light source

that passes light through the two plexiglas plates perpendicular to the fuel

spray flow, of a 31 multi-element photodetector that receives the light

signal from the other side of the chamber, and of a minicomputer and a

control terminal that process output signals from the photodetector.

The operational principle of the laser diffraction spray analyzer is

based on the Fraunhofer diffraction pattern superimposed on the geometrical

image, produced by the droplets in the path of the monochromatic coherent

light beam. The diffraction pattern is large compared with the image. The

resulting light energy distribution is collected through a lens by a multi-

element detector consisting of 31 semi-circular rings. The lens acts

effectively as a Fourier transform lens by bringing all the scattered light

from droplets at various locations in the beam into the focal plane of the

lens. For monosize particles the light distribution pattern at the focal

plane would consist of alternate bright and dark fringes, the position of

which would depend upon the size of the droplets. When droplets of many

different sizes are present an aggregate light energy distribution is

obtained from which the drop size distribution can be calculated. The light

energy falling on one ring of the photo-detector located between radii si

and sj can be expressed (8) according to

M 2 2 2 2 2E.i - C M Nkk [(J + J ) - (J 0 + J1 ) ] B-Ii k Z1 0 1 si 0 1 s

where C is a constant, N is the number of droplets of size X, J0 and J1 are

Bessel functions, and M is the number of drop size ranges. The total light

energy distribution is also the sum of the product of the energy

B-4

A TD

NOZZLE

COLLIMATED ,, DIFFRACTEDBEAM B EAM

.ET SPRAY , I.

LIQUID

He - NeLASERI

SIZE

DISTRIBUTION

PRINT OUT

Figure B-2. Schematic diagram of laser diffraction analyzer

MULTIELEMENT

LIGHT

DETECTOR

MINICOMPUTER

CONTROL

TERMINAL

DROPL

I

B-5

distribution for each size range and the weight or volume fraction in that

range. This can be expressed in the form of a matrix equation

E - TW B-2

where W is the weight fraction and T contains the coefficients which define

the light energy distribution curves for each droplet. Rewriting the above

equation as W = T-1E, then with the knowledge of the inverse matrix T-1 the

weight distribution can be calculated from the measured light energy E. An

approach to the solution of Equation B-2 is to assume a form for W and

adjust the parameters by iterative means until the sum of the squared errors

Z(E-TW)2 is a minimum. The Malvern Instrument software is capable of using

various weight distributions for W, including Rosin-Rammler, normal

distribution, or "model independent". To determine the diffraction pattern

the 31 semi-annular detectors are scanned sequentially by a solid state

switch controlled by a microprocessor, both with and without the droplets

present in the beam.

If, for example, the Rosin-Rammler distribution is postulated, then in

the processing of the signal the microprocessor assumes that the size

distribution is a good approximation to:

R = 1 - v - exp [-(X/X)n] B-3

where R is the weight fraction contained in particles of diameters greater

than X, X is the Rosin-Rammler mean diameter (for which R - 36.8%), and the

exponent n indicates the spread of diameters about the mean. For a fuel

spray typical values of n will be in the range 1.1 to 3, but n can increase

to 15-20 for near monosize droplets.

B-6

The microprocessor selects initial values of X and n and the light

energy distribution corresponding to the Rosin-Rammler distribution is

calculated through Equation B-2. A least squares error criterion is used to

determine the quality of fit between calculated and measured light energy

distribution. The parameters X and n are then iteratively adjusted to give

the best fit with minimum error. The Rosin-Rammler distribution in 15 size

ranges together with the calculated and measured light energy distribution

is printed by the microprocessor using the appropriate values of X and n.

Using X and n, the mass median diameter (MMD), which is the droplet

diameter below or above which lies 50 percent of the mass of the droplets

(i.e., R - 0.5), can be calculated by

MMD - X [In 2] 1/n B-4

The Sauter mean diameter, SMD, also can be related by

SMD - X/ r(l-1/n) B-5

where r is the gamma function. The SMD is the diameter of a droplet having

the same volume/surface ratio as the entire spray.

The mass distribution of a spray as the weight fraction in any size

increment is given by the derivative of Equation B-3, i.e.,

v n X ndv n exp[-(X/X)n] B-6dx

iXX

C-1

Appendix C - Experimental Data

The following four tables summarize the experimental data obtained by

in-flame measurements in the Combustion Research Facility. Centerline

distributions of flame temperature, velocity, gaseous species concentrations

and particle concentrations are tabulated. Some radial distributions are

included in Table C-2.

Table C-1

Experimental Data, Run 320 (ARC Fine, Base)*

Distance from

Air Nozzle

X(m) X/D

Gas

Temp.

T(K)

Gas

Velocity

u (m/s)z

Mole Fractions

(as measured, dry basis)

X2 XCO2 XCO XNO XSO2

(%) (%) (%) (ppm) (ppm)

Particle

Concentration

(g/m3 , NTP)

0.4 16.2 2.300 497 875

0.3 17.6 1.000 457 750

1.7

2.5

2.3

2.0

2.0

2.1

16.7

16.1

16.3

16.7

16.6

16.6

0.111

0.651

0.028

0.019

0.006

0.003

500

492

495

2.7 15.9 0.002 489

*Centerline Measurement

0.17

0.27

0.42

0.57

0.74

0.88

1.19

1.49

1.80

2.09

3.00

3.61

4.22

4.52

1.0

1.5

2.4

3.3

63.67

4.2

5.0

36.02

6.8

8.5

10.3

11.9

17.1

20.6

24.1

25.8

103.0

23.1

16.0

7.5

4.0

2.3

1.9

2.4

2.6

2.9

2.5

2.5

5.4

6.7

1515

1638

1681

1620

1580

1538

1450

1390

1309

1301

1297

1289

625

600

500

0

5.61

3.03

3.20

3.21

3.23

Table C-2

Experimental Data, Run 323 (ARC Fine, Heating)

Radial Distance from Gas Gas Mole Fractions ParticleDistance Air Nozzle Temp. Velocity (as measured, dry basis) Concentration

R(m) X(m) X/D T(K) u (nVs) X X XO 2 (g/m 3 , NTP)

(%) (%) (%) (ppm) (ppm)

0 0.17 1.0 - 106.00 0.27 1.5 1645 38.20 0.42 2.4 1719 33.0 - - - - -0 0.57 3.3 1697 14.3 1.6 14.9 1.150 700 525 26.210.1 1641 -4.1 6.4 12.5 0.056 580 513 9.47

CN0.2 1581 14.5 7.1 11.9 0.025 535 525 6.900.3 1570 11.8 6.1 12.9 0.012 550 538 4.360.4 1555 5.0 6.0 13.2 0.010 560 713 -0 0.88 5.0 1600 0.0 1.8 16.1 0.320 590 650 7.240.1 1602 -3.9 2.9 15.5 0.073 610 625 5.030.2 1619 -2.9 3.7 14.8 0.017 600 625 4.780.3 1618 2.0 4.4 14.4 0.014 610 563 4.780.4 1593 7.1 5.0 13.7 0.015 600 550 -0 1.19 6.2 1583 -3.4 3.0 15.5 0.040 590 650 -0 1.49 8.5 1566 -3.0 3.3 15.3 0.040 570 620 2.890.2 1584 2.1 3.2 15.3 0.011 590 638 -0.4 1589 2.8 3.6 14.9 0.008 600 650 2.530 1.80 10.3 1541 -1.8 3.4 15.1 0.015 - 625 -0 2.09 11.9 1500 1.5 3.2 15.3 0.016 - 625 3.550 3.00 17.1 1377 2.1 2.9 15.7 0.007 505 663 2.600 3.61 20.6 1356 2.1 2.6 16.3 0.007 - 575 -0 4.22 24.1 1326 2.8 2.6 15.9 0.008 - 675 3.33

C-3

Table C-3

Distance fromAir NozzleX(m) X/D

0.17

0.27

0.42

0.57

0.74

0.88

1.19

1.49

1.80

2.09

3.00

3.61

4.22

1.0

1.5

2.4

3.3

4.2

5.0

6.8

8.5

10.3

11.9

17.1

20.6

24.1

G

TerT(

Experimental Data, Run 324 (ARC Regular, Base)

as Gas Mole Fractions

np. Velocity (as measured, dry basis)K) uz(m/s) X0 XCO XCO XNO XSO

(%) (%) (%) (ppm) (ppm)

1393

1620

1771

1760

1757

1706

1667

1623

1576

1459

1450

1439

55.6

44.6

12.4

-6.9

-4.3

-4.2

-3.7

-3.7

-2.6

-0.9

0.7

0.8

0.5

0.4

1.8

3.6

3.1

2.8

2.4

2.5

2.2

15.7

17.0

17.7

18.1

17.2

15.5

16.1

16.3

16.9

16.7

17.1

3.300

1.600

0.800

0.900

0.093

0.027

0.016

0.011

0.007

0.006

0.005

740

750

690

630

710

740

740

720

700

710

680

1125

775

763

788

600

525

538

575

575

588

600

ParticleConcentration

(g/m3 , NTP)

423.73

99.00

28.66

6.92

4.30

3.04

2.36

2.34

*Centerline Measurements

C-4

Experimental Data,

Distance from

Air Nozzle

(m) X/D

Gas

Temp.

T(K)

Gas

Velocity

u (m/s)z

Table C-4

Run 326 (ARC Regular, Heating)*

Mole Fractions

(as

XO2

(%)

measured, dry basis)

XCO2 XCO XNO SO2

(%) (%) (ppm) (ppm)

43.6

14.0

10.4

-7.3

-8.3

-7.8

-7.0

-6.4

-5.7

-5.5

-4.0

-2.1

0

2.2

1.1 15.2

0.8 15.9

0.9

0.9

0.7

2.1

2.9

2.5

2.4

2.2

1.8

*Centerline Measurement

Particle

Concentration

(g/m3 , NTP)

166.48

0.17

0.27

0.34

0.42

0.57

0.63

0.74

0.88

0.94

1.19

1.49

1.80

2.09

3.00

4.22

1.0

1.5

1.9

2.4

3.3

3.6

4.2

5.0

5.4

6.8

8.5

10.3

11.9

17.1

24.1

1543

1664

1688

1727

1736

1748

1775

1739

1708

1681

1655

1610

1490

1460

4.000

3.500

1.300

0.900

0.700

0.175

0.037

0.025

0.013

0.006

0.007

700

670

700

690

670

710

710

710

720

710

670

16.9

17.3

17.8

17.4

15.9

16.8

16.9

16.8

17.4

700

1150

525

575

575

575

600

625

588

638

638

52.25

19.29

5.84

2.52

1.44

2.00

1.50