EFFECTS OF POTASSIUM AND CARBONATE ON THE DEPOSITION OF SYNTHETIC RECOVERY

BOILER CARRY OVER PARTICLES

Keyvan Rezvani Jorshari

A thesis subrnitted in conforrnity with the requirernents for the degree of Master of Applied Science

Graduate Department of Chernical Engineering and Applied Chemistry University of Toronto

O Copyright by Keyvan Rezvani Jorshari 2000

National Library m*m of Canada Bibliothèque nationale du Canada

Acquisitions and Acquisitions et Bibliographic Services services bibliographiques 395 Wellington Street 395. nie Wellington OttawaON K1A ON4 Ottawa ON K1A ON4 Canada Canada

The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sell reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la forme de rnicrofiche/film, de

reproduction sur papier ou sur format électronique.

The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or othemise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation.

To Setareh & Keyhan

Effects of Potassium and Carbonate on the Deposition of Synthetic

Recovery Boiler Carryover Particles

Master of Applied Science, 2000

Keyvan Rezvani Jorshari

Department of Chernical Engineering and Applied Chemistry

University of Toronto

ABSTRACT

Massive ç q o v e r deposit formation on superheater and boiler bank tubes in many kraft

recovery units c m cause a critical and production-timiting problem, which leads to an

unscheduled boiler shutdo wn. it is there fore crucial to understand the tendency o F moken

carryover particles ro accumulate on heat transfer surfaces in the upper furnace of

recovery boilers. Plugging of flue gas passages is strongly related to deposit composition.

Deposits accumulate as deposition exceeds the deposit removal capability of the

sootblowers.

Understanding the conditions that affect carryover deposition is important for better

control of deposits and for optimizing boiler operation. Of the many components in

deposiu. potassium and carbonate are of great important since they lower the Trst

melting temperature of carryover deposits.

This project studies the efkcts of potassium and carbonate in carryover deposits using the

Entrained Flow Reactor at the University of Toronto. The experimental results show that

potassium has an effect on the deposition rate of carryover panicles only when the

chloride content is between 1 and 5 mole% CV(Na+K).

The effect of carbonate in deposits containing various chloride and potassium cûntcnts on

deposition was also examined. The results show that carbonate has an insignifcant effect

on the carryover deposition even when carbonate content is as high as 60 mole%

C03/(Na2+&).

The deposition rate of particles is affected mainly by iiquid content. m d a minimum

liquid content of 15-20 wt% is essential for particles to deposit.

ACKNOWLEDGMENTS

1 wish to acknowledge the tremendous contribution of Professor Honghi Tran for his

wonderhl supervision. His excellent guidance and suggestions were very helpful and

appreciated.

Many thanks are due to Professor David Barham for his valuable comments.

I would Like to thank the faculty and staff of the Pulp & Paper Centre for [ostering a

pleasant environment.

I wish to express my gratitude to my dear parents for their encouragement and

inspiration.

Last but the most. I would iike to dedicate this work to my devoted wife. Mahshid for her

great support without which I could not complete this work.

TABLE OF CONTENTS

ABSTRACT

ACKNOWLEDGMENTS

TABLE OF CONTENTS

LIST OF FIGURES AND TABLES

1. INTRODUCTION

2. LITERATUFtE REViEW

2.1 De position in Recovery Boilers

2.2 Deposit Composition

2.3 Carryover Deposit Chemisiry

2.4 Characteristics of Carryover Deposits

2.4.1 Thermal Behaviour

2.4.2 Liquid Content

2.4.3 Stickiness

2.5 Effect of Chemistry on Deposit Chuacteristics

2.5.1 Et'fect of Potassium

2.5.2 Effect of Carbonate

3. METHODOLOGY

3.1 Equipment

3.2 Procedures

4. RlESULTS AND DISCUSSION

4.1 Experimental Reproducibility

4.2 EKect of Potassium on Deposiiion Rate

4.3 Effect of Carbonate on Deposition Rate

4.4 Efkct oELiquid Content on Deposition Rate

4.5 Implications

5. CONCLUSIONS

6. RECOMMENDATIONS

REFERENCES

APPENDICES

vi

LIST OF FIGURES

Figure 2- 1

Figure 2-2

Figure 2-3

Figure 2-4

Figure 2-5

Figure 3- 1

Figure 3-2

Figure 3-3

Figure 4- 1

Figure 4-2

Figure 4-3

Figure 4-4

Figure 4-5

Main sections of a kraft recovery boiler with the typical tlue gas

temperatures 4

Composition (wt8) of the deposits at different boiler locations 6

Composition (wt%) of a typical carryover deposit 8

Effect of Liquid content on adhesion efrciency of 150-420 pm particles at

800'~ EFR temperature f 1

Effect of carbonate on the FMT of deposits at different potassium contents

& 5 mole% CV(Na+K) 14

The Entrained Flow Reactor 15

Exit of the EFR 19

Top of the EFR 30

Deposit mass of particles on the probe for 3 repiicate experiments 22

Effect of potassium on the deposition rate of particies containing O to 4

mole% CV(Na+K) 24

Effect of potassium on the deposition rite of particles containing 5 to 20

mole% CV(Na+K) 25

Effect of poiassium on the deposition rate of particles at various chloride -'

leveis 36

Appearance of the deposits containing 2 mole% CV(Na+K) & three

different potassium contents; T ,b, = 50O0c. exposure time = 25 min 28

vii

Figure 4-6 Appearance of deposits containing 4 mole% CV(Na+K) & two different

potassium contents; T ,& = ~ 5 0 ~ ~ . exposure tirne = 25 min 29

Figure 4-7 Effect of carbonate on the deposition rate of particles containing 5 moLe%

CV(Na+K) and varying potassium levels 3 1

Figure 4-8 Effect of carbonate on the deposition rate of particles containing 5 mole%

K/(Na+K) and varying chloride levels 32

Figure 4-9 Effect of chloride on the deposition rate of particles containing 5 mole%

K/(Na+K) and varying carbonate levels 33

Figure 4- 10 Appearance of the deposits containing 1 mole% CV(Na+K). 5 mole%

W(Na+K) & and three different carbonate contents: T ,b, = 500'~.

exposure time = 25 min

Figure 4- 1 1 Appearance of the deposits containing 3 mole% CV(Na+K). 5 mole%

Kt(Na+K) & three different carbonate contents; TN, = 500'~. exposure

t h e = 25 min 36

Figure 4- L 2 Liquid content (wt%) of particles containing 5 mole% K/(Na+K) and

40 mole% COd(Na2+K2) as a Funçtion of tempenture. and chloride

content 38

Figure 4- 13 Effect of liquid content on the deposition rate of paiucles containing various

amounts of chioride, potassium and carbonate; assumed pahcle

temperature: 7 5 0 ~ ~ 40

Figure 4- 14 Effect of liquid content on the deposition rate of particles containing various

amounts of chloride, potassium and carbonate; assumed particle

tempenture: 770'~ 41

LISTS OF TABLES

Table 3- 1 Experimental conditions 18

Table 3-2 Composition rnatrix of syntheiic particles with 5 mole % CV(Na+K) and

20 mole % COJ(Na2+K2) 19

LISTS OF APPENDICES

Appendix A Photographs of deposits on the probe 49

Appendix B Liquid content (wtB) of typical deposits at a temperature between

50°c to 900'~ 54

Appendix C Graphs of Liquid content (wt%) of various deposits at a temperature

between 500'~ to 90°c

1. INTRODUCTION

A recovery boiler is often referred to as the heart of the knft recovery process. It is used

to recover the inoganic pulping chemicals and to produce steam and power for the pulp

mil1 (1).

During the burning of black Liquor in a recovery boiler, massive deposits may accumulate

on tube surfaces in the superheater and boiler bank regions. The deposits are composed

principally of sodium sulfate and sodium carbonate. They reduce heat transfer rates. plug

the gas passages. and Iead to the formation of a corrosive environment at tube surîàces.

Deposits are derived from three distinct sources: canyover. fume, and intemediate-sked

particles (2. 35). Canyover particles result from mechanical entrainment of black iiquor

droplets or fragments OC burning droplets. Carryover particles range in size from about 20

pm to about 3 mm. The chernical composition of particles is an important parameter

affecting the rate of deposition on tube surfaces.

Of the inorganic components in deposits. chloride and potassium salts are the

components which cause the most concern because they can signifcantly alter the

thermal properties of the deposits. Chloride affects the amount of the Liquid phase in

deposits while potassium lowers the fïst melting temperature of deposits from 6 1 0 ' ~ at

O mole% to a value of about 5 2 0 ' ~ at 8 mole% K/(Na+K) and higher (1).

The amount of the liquid phase in the carryover particle can determine the rate of deposit

accumulation, which depends on the concentration of chloride and potassium salts in the

partic le (6).

The rate of canyover deposition is generaily govemed by two principal factors: the

quantity and the stickiness of carryover particles in the rlue gas, Le., a high deposition

rate occurs when there is a large quantity of sticky carryover particles (4).

Shenassa (29) studied the dynarnics of deposition of carryover particles. and the eftècts of

chloride, temperature and size of the particles on deposition. using an Entrained Flow

Reactor (EFR). She round that at a given temperature, the deposition occurs only ai a

critical chloride content. and above this chloride content. the deposition increases until il

reaches its maximum. The effect of other components, such as potassium and carbonate.

was no t exarnined in Shenassa's work

Since potassium and carbonate greatly affect the melting tempenture of carryover

particles, they are expected to play a role in the deposition of the particles on tube

surfaces.

The aim of this study is to investigate the effects of potassium and carbonate on the

carryover deposition using the Entrained Flow Reactor.

2. LITERATURE REVIEW

2.1 DEPOSITION IN RECOVERY BOILERS

Black liquor. a by-product of the chemical puiping process. is concentrated from 15-20%

to 65%- 85% dry solids. before k i n g burned in a recovery boiler. The two main

functions of recovery boilers are to recover the pulping inorganic chemicals. and to

recover energy from the combustion of the organic portion of the black Liquor in order to

generate s t e m and power ( 1). Due to the high inorganic (ah) content (about 40% on a

dry basis). and the low melting temperature of the ash aHer combustion. many recovery

boilers expenence severe tly-ash deposition problems (14). The accumulation of deposits

in the upper section of a recovery boiler can cause serious problems. such as a decrease in

the boiler thermal efficiency. acceleration of tube corrosion. and plugging of the flue gas

passages. which rnay Iead to costly, unscheduled shutdowns of boilers. The accumulation

of non-process rnaterials. such as chloride and potassium. tends to worsen the iouling

conditions in recovery boilers (15).

Recovery boilers have two main sections: a furnace section and a convective heat transfer

section, The convective heat transfer section contains four sets of tube banks: the screen

tubes. the superheater, the boiler bank. and the economizer. In the lower superheater

region, where the flue gas temperature is usually higher than 80O0c, fly-ash particles may

still be burning and therefore be at a higher temperature than the surroundhg tlue gas.

They strike the tubes as molten droplets and form hard, hsed deposits. In the upper

superheater, where the Hue gas temperature is about 70O0c, massive deposition can occur

and result in severe plugging. Ar the inlet of the boiler bank. where the flue gas

temperature is between 550'~ and 700'~. plugging rnay occur as a result of elevated

chloride and potassium concentrations and/or high flue $as temperatures caused by

severe fouling in the superheater region (13). Figure 2-1 shows rypical the gas

temperatures at different locations in a kraft recovery boiler.

Figure 2-1. Main sections of a kraft recovery boüer with the typid flue ges tempemtures (29)

Tran (14) investigated the occurrence of plugging and its potentiai causes at various

locations in a boiler. He showed that plugging mostly occurs at the boiier bank inlet. and

is often a result of high flue gas temperature caused by severe cmyover fouling in the

superheater regio n

Carryover particles result tiom mechanical entrainmenr oE black iiquur druplers or

fragments of burning droplets. Canyover deposits are smelt-like; usually pink. fused and

very dense. They range in size from about 20 pm to about 3-mm. (1). In the lower

superheater where most alkali vapors do not condense, carryover is dominant. fonning a

hard. hsed and srnelt-iike deposit. In the upper superheater and regions downstrearn from

the generating bank. the flue gas temperature is lower. allowing some inorgmic vapors tu

condense and form turne (20). Fume particlcs are rnuch smdler than carryover particles.

2.2 DEPOSIT COMPOSITION

The major chemicai components are basically the same t'or ail recwery boibr deposits,

however, the deposit composiiion depends on the composition of black liquor. tüining

conditions in the lower furnace, location in the boiler. and the CI input to the mil1 (1).

Since deposits are a mixture of carryover and fume in proportions that Vary with location

in the boiler. their composition is determined by both the chemistry and relative

proportions of the carryover and hme.

Figure 2-2 shows composition (wt%) of the deposits at different boiler locations.

LOWER FüRNACE

SUPER- HEATER

BOILER BANK

1 i

ECONO- MIZER

ESP

Figure 2-2. Composition (wt%) of the deposits at different boiler locations (10)

The deposits in the lower furnace generally contain more Na2C03 and Na2S. and les

Na2S04. NaCl and potassium salts than deposits in the upper furnace. As carryover

particles travel to the upper fumace. most of the Na2S is oxidized to Na2S04. It should be

noted that in recent years, a trend towards higher solid f h g rates and hot bed operation

has resulted in higher concentrations of Na2C03 in the upper furnace deposits.

2.3 CARRYOVER DEPOSIT CHEMISTRY

Carryover deposits are composed typically of 40-50 w t% sodium carbonate (Na2COs).

40-50 wt% sodium sulphate (Na2S04). small amounts of sodium sulphide (Na2S). sodium

chloride (NaCl). potassium salts. and unbumed organic material (char). As carryover

paniclcs move 10 the upper section of the hoiler. Na2CO?. NaCl. and other aikali

compounds react with suifur compounds in the tlue gas to forrn Na2S04. Aller

deposition, Na2C03 may react with SOI/S03 in the tlue gas to also produce Na2S04. In

addition, some chlorides may slowly be convened to sulfate by reaction with S 0 2 and

water vapor tiom the [lue gas at high ternperatures.

As a result of the above reactions. a typical carryover deposit in the superheater repion

has the composition as shown in Figure 2-3. [t contains less suKde and carbonate,

slightly less chloride. and more sulphate than oxidized smelt. Since potassium does not

change as a result of either oxidation or sukàtion, the potassium content of the çarryover

deposit is essentially the same as in oxidized smelt.

Other (0.5) %

Figure 2-3. Composition (wt % ) of a ty pical carryover deposi t ( 1 )

2.4 CHARACTERISTICS OF CARRYOVER DEPOSITS

2.4.1 THERMAL BEHAVIOUR

The melting behavior of carryover deposits plays a ptimary role in determining the extent

of superheater and boiler bank deposit buildup. Deposit thermal propenies vary greatly

since their c hemicai compositions change with locations in boilers.

Four characteristic temperatures have ken identified to describe the formation of

deposits on tube surfaces: the frst meltiog temperature (FMT). the sticky temperature

(Tsnr). the radical deformation (TRD), and the complete melting temperature (CMT) (1).

At the fïst melting temperature. the fïsst liquid phase appears in the deposit. The

cornplete melting temperature is the temperature at which the deposit is completely

molten. The two other tempentures (TSTK and Tm) play the most important role in

determining deposit accumulation: these temperatures lie between the FMT and CMT:

the sticky temperature is the temperature above which deposits contain enough liquid ( 15

to 20 wt%) to become sticky; the radical deformation temperature is Jeiïned as thc

temperature above which the iiquid content of deposits rnakes deposits slag. Le.. about 70

wtQ. Deposition occurs when the deposit temperature ranges between TsTK and TRD.

Deposits ;iccumulate and do not stop growing if the temperature is between the sticky

temperature and the radical deformation temperature. Outside of this temperature range.

deposits either do not have enough liquid phase to be sticky or their liquid content is high

enough that they tlow and therefore do not build up (1).

Tran (3) teported thai the complete melting tempenture of the system Na2S04-Na2C03-

Na2Ch decreases dmost linearly from 860'~ when no chloride is present to 6 2 5 ' ~ as the

amount of sodium chloride increases to about 33 mole56 Na2C12. However. adding more

sodium chloride increases the complete melting temperature of the system.

2.4.2 LIQUID CONTENT

The rate of canyover deposition in recovery boilers is a function of liquid content of

deposits since the iiquid content is responsible for the adhesion between particles and the

surtace (24). The amount of the liquid content in canyover deposits influences

significantly the deposit stickiness, which is directly related to particle composition and

temperature (6. 16). While the iiquid content is the main cause of stickiness. the other

factors include particle CO mposition. surface tension. viscosity, surface c haracterist ics.

tube and deposit temperature. size and velocity of carryover deposits.

2.4.3 STICKINESS

The stickiness of carryover deposits has been studied extensively in the context of the

melting characteristics of deposits (4. 12. 13). Issak et al. ( 1 1) developed a technique to

simulate the adhesion of a carryover pmicle to a metai surîàce. The presence of Liquid

content was found to be essential for strong adhesion to occur. The adhesion strength was

minimal under conditions where both the deposit and the substrate surfaces were solid.

A minimum liquid content of 18 to 20 wtQ For rough surFices. and 7 wt% for smooth

surfaces was detemined for strong adhcsion to take place ( 17).

Shenassa (29) reported that the particle adhesion etficiency (the ratio of particle mass

deposited on the probe to the particle mass that coilide with the probe) was strongly

affected by both chloride content and tlue gas temperature. For particles between 150 and

300 Pm. the minimum liquid content required to make them sticky is about 20 wt% at

800'~ EFR temperature (Figure 2-4).

O 20 40 60 80 100

Liquid content, %

Figure 2-4. Effect of liquid content on adhesion efficiency of 150-420 pm particles at

8 0 0 O ~ & 880% EFR temperatures (29)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

2.5 EFFECT OF CHEMISTRY ON DEPOSIT CHARACTERISTICS

Deposits in recovery boilers have a reiatively simple chemistry. They consist of more

than 99 wt% water-soluble aikaii compounds and Iess than 1 wt% p u y burned black

liquor residue and water-insoluble impurities. The deposition rate of particles increases

with decreasing FMT. As a result. particles with higher chioride and potassium content or

lower FMT deposit more readily (8).

Chloride has a significant effect on deposit melting temperature, and hence on the deposit

stickiness (4). Previous studies (4. 27, 29) showed that ai a given temperature between

the FMT and the CMT, increasing the chloride content increases the Liquid content in the

deposits.

2.5.1, EFFECT OF POTASSIUM

The potassium content in deposits varies from boiler to boiler, depending on the type of

wood pulped and the degree of mil1 dosure. It ranges from 4 to 8 mole% KJ(Na+K) for

softwood mills. and from 8 to 15 mole% for hardwood rniils. With input tFom other

sources such as seaborne logs and make-up chemicals, the potassium content çan be as

high as 20 mole% W(Na+K) (14.22-32).

Shivgulam (5) reponed that the tcmary eutectic temperature for the phase system NaCl-

Na2CO+Na2S is decreased by the replacement of sodium with potassium from 5 9 8 ' ~ to

530'~.

Tran (3) investigated the effect of potassium salu on the Tist and complete melting

temperatures of deposits by substituting &CO3 Cor the equivalent amount of Na2C03 on

a molar basis. The tlrst melting temperdture of the system NazSO&Ia2C03-Na2C' 7 was

lowered frorn 625'~ to 560'~ as 5 mole % of Na2C03 was substituted by K2CO3, and to

5 3 5 ' ~ as 10 mole % of N a c 0 3 was substituted by K2C03. Further substitution had a

lesser effect. Furthemore. the fxst melting point of the mixtures (35.5 mole% Na$&)

was lowered to 520'~ as 15 mole % &COr was substituted. and leveled offat 5 2 0 ' ~ for

hieher K2C03 substitution. Based on this result. Tran concluded that potassium c m lower

the complete melting point of the system by about 50 '~ when 15 mole% Na2C03 is

substituted by K2C03.

2.5.2 EFFECT OF CARBONATE

The carbonate content in deposits varies widely. depending on the sulphidity of the

liquor. the amount of carryover. and the bed temperature. It may be as low as O mole%

C03/(Naz+Kr) in fume deposits from a high sulphidity-low bed temperature boiler. and as

high as 60 mole% C03/(Nar+K2) in smelt-Iike carryover deposits. Carbonate is a major

component in deposits. which has an eiTect on the deposit tlrst meltinp temperature

because of the tendency of alkali carbonates to form so lid solutions with aikali sulphares.

Increasing the carbonate content from 10 to 50 moie8 COd(Na2+K2) decreases the tîrst

rnelting temperature t'rom 570 '~ to 5 2 3 ' ~ for softwood mills. and iiom 545'~ to 5 1 [OC

for hardwood rnills (23). It is expected that for overloaded boilers and/or boilers

operating at high bed temperatures at hardwood mills. the combination of high carbonate

and high potassium contents c m result in a FMT as Iow as 5 1 1°c (23).

Figure 2-5 shows the effect of carbonate on the fîrst melting temperature of deposits

which contain 5 mole% Cl/(Na+K) and different potassium contents.

Figure 2-5. Effect of carbonate on the FMT of deposits at different potassium

contents & 5 mole% CV(Na+K) (33) - - - - - - - - - - - - - - -

For particles with potassium contents below 7.5 mole% W(Na+K), increasing the

carbonate content, up to about 50 mole% COd(Nat+Kz). decreases signififantly the FMT

of deposits. A funher increase in carbonate content results in a higher FMT. The results

also show that the effecc of carbonate is significant only when the potassium content is in

the range of 2.5 to 7.5 mole% W(Na+K). At high potassium levels. > 15 mole8

W(Na+K), the effect of carbonate becomes minimal (33).

3. METHODOLOGY

3-1 EQUIPMENT

In order to rneasure the rate of deposit formation from carryover particles under

conditions similar to those in recovery boilers, the Entrained Flow Reactor (EFR) at the

University of Toronto was used to simulate the conditions experienced by canyover

particles in the upper section of a recovery boiler (Figure 3- 1).

Part lc le i e e d e r - Prim ary air

Corn bustion B u r n c r chnm be

\ - S atu ra l p a s - S c c o n d a r y

a i r - D l l u t l o n

a l r

Furnace

Cam e r n

i1i F luc gas to e x h n u s t

Figure 3-1. The Entrained Flow Reactor (29)

The EFR is made up of five high temperature tubular furnaces which have a maximum

openting temperature ol 1350~~. The reactor consists of the following: a particle feeding

section, a gis combustion unit, a long vertical heating section, a test section with an air-

cooled probe, a gas exhaust blower, and a data acquisition and control system.

The particle feeder consists of a 0.3 m wide &y 1.2 m long belt conveyor that transports

particles to the top ofa particle injector. A tlow of pressurized carrier air ensures the ilow

of the particles into the injector which passes through the gas combustion unit. A cerarnic

honey comb provides a uniforrn gas ilow. and introduces the puticles into the first zone

of the heated section at the top of the reactor.

The gas combustion unit located at the top of the reactor is equipped with a natural gas

burner. The combustion gases are mixed with dilution air to produce a gas of desired

volume whüe the tempenture and the tlow rate of the inlet gas to the heated section are

controlled through two independent control loops.

The heated section is an assembly of five split-shell tube furnaces that forrn a 6.1 m long

vertical unit. The temperature of each furnace is monitored by two R-type themocouples.

The non-heated sampling section located between the bottom of the heated section and

the exhaust system is provided to facilitate sarnple collection of deposits. This section

consists OC an insulated chamber which minimizes heat lost by convection. It is placed on

a stainless steel base located above the well mouth of the exhaust system.

A control panel is provided for the gas combustion unit in order to control the

temperature and the tlow rate of the gas leaving the combustion chamber. A data

acquisition program is used to monitor the particle ked rate, the bumer combustion gas

temperature and flow rate, five furnace zone ternperatures. the probe surface temperature

and the deposit weight.

3-2 PROCEDURES

In this study. the EFR was operated at an average gas velocity of between 0.5 and 1 mis

to pmvide a maximum laminar gas tlow velocity between 1 to 2 rnk. The heating

chamber was operated at a constant temperature between 3 0 0 ' ~ to 110O0c so that the

gas and particle temperatures at the heating chamber exit could mach a preset

temperature of 900'~ or lower. In order to estimate the desired experimental conditions

of the EFR, the velocity and temperature of the particles were calculated. The tlue gas

was assumed to be at 8 0 0 ' ~ with a velocity of 1.8 m/s. The initial temperature of the

panicles was assumed to be 20% and the reactor was assurned to have a wall

temperature of 800'~.

The experimentd conditions are summarized in Table 3- 1.

Table 3-1. Expenmental conditions used in this investigation

L

PARAMETERS

1

EFR hrnace temperature

Bumer Temperature

Fiue Gas Velocity

RANGES

800'~

80ooc

Probe Temperature

Particle Feeding Rate

5 0 0 ~ ~

2.0 gmin

Natural Gas Flow Rate

Combustion Air Flow Rate

Synthetic deposits of desired compositions were prepared by mixing pure chernicals

including NarS04. Na2C03, NaCl and K s 0 4 . The mixtures were melted in a rnuffle

tùmace at about 1 1 0 0 ~ ~ then the cooled melts were ground and sieved into the size range

from 150 prn to 300 Pm. The units of K. Cl and CO3 concentration in deposits ;ire used as

fractional units such as CV(Na+K), C03/(Na2+K2) and W(Na+K) as mole percent

assuming the anions are bound proportionally to Na and K. The charges of the ionic

components of the deposits are also omitted. Le.. ~03'' is expressed as CO3. Na' as Na.

etc.

1.7- 1.8 m'th

20.1-20.2 m31h

Dilution Air Flow Rate

For example, to make 100 moles samples that contain 5 mole% CV(Na+K), 20 mole %

CO$(Na2+K2) and various K levels, the amounts of the chernicals used in the mixtures

are as shown in Table 3-2.

22.1-22.6 m3/h

Table 3-2. Composition rnatrix of synthetic particles with 5 mole % CU(Na+K) and

20 mole % COJ(Na+K2)

I Na2C03, moles

Na2S04, moles

&SOI, moles

NaCI, moles

The deposition rate of the particles were deterrnined using an air-cooled probe placed at

the exit of the EFR (Figure 3-2).

Figure 3-2. Exit of the EFR

For each run, 50 g of the synthetic particles was introduced into the top of the EFR at a

feed rate of 2 g/min, using the conveyor belt at a speed of 2.5 cm/min as shown in Figure

3-3.

Figure 3-3. Top of the EFR

As particles traveled d o m the reactor, they were heated and deposited on the probe. The

probe was 1.6 cm in diameter and made of stainless steel 316 equipped with a type-K

thennocouple embedded under the surfàce.

During the experirnents. the probe temperature was controiled at 500 f 15%, by

regulating an appropriate amount of air through the probe.

To determine the arnount of the deposits, a magnetic force compensation weight ce11 was

used which provided dynamic mass data continuously throughout the experiment. The

overail length of the collected deposits on the pmbe surfice was 17 cm. which wiis the

inside diameter of the EFR. Mer each experiment. the probe surface was cleaned and

then polished using 180 and 320 gnt emery cloths.

4. RESULTS AND DISCUSSION

4-1. EXPERIMENTAL REPRODUCIBILITY

The reproducibiiity of the experiments was examined by measuring the deposition rate of

synthetic carryover particles of identical chernical composition at 800'~ EFR temperature

and 1.8 m/s gas velocity in three experiments. Figure 4- 1 shows the deposit mass of 150-

300 pm particles as a function of time for ail the experiments. The deposition rate for these

experiments has an average of 0.14 f 0.01 rng/(g-crn2-min) with a coefficient of variation

of 6.0%. This coefficient of variation is used in determining the error associated with each

deposition measurement. and in interpreting the results of the effect of examined variables

on pmicle deposition.

O 5 10 15 20 25 30

Time, min

Figure 4-1. Deposit m a s of particles on the probe for 3 repücate experiments

The deposition rate is expressed as mg of the deposit coiiected on the probe per g of

particles introduced into the EFR per square centimeter of the probe projected area per

minute. The foilowing formula is used for determinhg the deposition rate of the particles:

where DR is the deposition rate of particles. Whtieir and WD,,, respectively are the

weights of the particle and deposit. A is the projected area of the probe. and T is the

exposure time of particle deposition.

4-2. EFFECT OF POTASSIUM ON DEPOSITION RATE

The effect of potassium on the deposition rate of particles at various chlonde levels is

shown in Figure 4-2. It should be noted that in these experiments. there was no carbonate

in the partic les.

CI/(Na+K), mole % B

O and 1

Figure 4-2. Effwt of potassium on the deposition rate of particles containing O to 4

mole % CV(Na+K)

For particles containing chloride content of 1 mole% CY(Na+K) or less. no deposition was

observed even when the potassium content was as high as 20 mole% K/(Na+K). At a

chloride content between 2 and 4 mole% CV(Na+K). potassium appeared to have some

effect. Le., increasing potassium content in the particles resulted in an increase in

deposition rate. At 5 mole% CV(Na+K). however. the effect was minimal.

Figure 4-3 shows the effect of potassium on the deposition rate for panicles containing

more than 5 mole% CV(Na+K).

Figure 4-3. Effect of potassium on the deposition rate of particles containing 5 to 20

mole % CV(Na+K)

The deposition rate of particles containing 5 to 20 mole8 CV(Na+K) was about the same

for al1 tests. This suggests that once the chloride content exceeds 5 mole% CV(Na+K), the

deposition rate is intluenced by chloride only; potassium has no additional effect on

deposition raie.

Figure 4-4 shows the deposition rate at different potassium levels, re-plotted as a function

of chloride content.

K/(Na+K), mole % - -0 -5 - -10 - -15 -4- 20

O 5 10 15 20 25 CI/(Na+K), mole %

Figure 4-4. Effwt of potassium on the deposition rate of particles at various chloride

leveis

The graph clearly illustrates the effect of potassium in three regions of chloride content: in

the first region where chloride content is l e s than I mole% CV(Na+K), no deposition

occurs; in the second region where particles contain 1 to 5 mole% CV(Na+K). significant

deposition is observed. This increase in deposition is presumably due to the high liquid

content of particles. In the third region where particles contain more than 5 mole%

CV(Na+K), potassium has no further effect on the deposition rate. These results suggest

that for a given particle composition. particles start to deposit only when a minimum level

of liquid content of deposits is reached. Since the tiquid content increases with chloride

concentration. the rate of deposition increases as the chloride concentration increases up to

a maximum level.

It is interesthg to note that although the liquid content of deposits containhg 20 mole%

CY(Na+K) is much higher than that of 5 mole% CV(Na+K). the deposition rate remains

constant at chloride concentration above 5 mole% CV(Na+K) to 2U mole% Ci/tNa+Kj.

This suggests that at a chloride level of 5 mole% CU(Na+K), particles have sufficient

liquid for maximum deposition to occur.

Figures 4-5 and 4-6 ülustrate the appearance of the deposits on the probe after each test.

It was found that deposits containhg a high potassium content are more tenacious and

difficult to remove from the tube surface than oncs with a lower potassium content.

Figure 4-5. Appearanee of the deposits containing 2 mole% CU(Na+KJ & three

different potassium contents; T ,h = 50O0c, exposure time = 25 min

Figure 4-6. Appearance of the deposits containing 4 mole% CU(Na+K) & two

different potassium contents; T ,,k = 500'~ and exposure time = 25 min

4-3. EFFECT OF CARBONATE ON DEPOSITION RATE

In order to examine the effect of carbonate. appmpriate arnounts of Na2C03 were added to

the synthetic mixtures before the 150 to 3M) pm sized particles were prepared. Other

experimental parameters were kept at the same values.

As discussed earlier. potassium has no additional effect on deposition once the chloride

content exceeds 5 mole% CII(Na+K) (Figures 4-3 and 4-4). Since carbonate has a lesser

effect on the f i s t melting temperature of deposits compared to potassium. it is expected to

have a lesser effect on deposition. Therefore. in this study. the effect of carbonate w u

examined only for particles that have a chloride content between O and 5 mole%

CV(Na+K) .

Figure 4-7 shows the effect of carbonate on the deposition rate for particles containing 5

mole% Ci/(Na+K) and different potassium contents. The deposition rate was constant at

about 0.065 mg/gcm2-min. This, along with the results shown in Figure 4-3, suggests that

carbonate has no measurable effect on deposition for particles containing more than 5

mole% CV(Na+K).

Figure 4-7. Effect of carbonate on the deposition rate of particles containing 5 mole%

For particles containing les than 5 mole% CU(Na+K). the effect of carbonate on the

deposition rate is also examined.

Figure 4-8 shows the effect of carbonate on the deposition rate for particles contaîning 5

mole% W(Na+K), the typical potassium content of carryover deposits in recovery boilers.

Figure 4-8. Effect of carbonate on the deposition rate of partides containing

5 mole% K/(Na+K) and varying chloride levels - - - - - - - - - - - - - -

For particles with no chloride. no deposition was observed as the carbonate content was

increased to 40 mole% CO$(Naz+&). This is consistent with the results obtained earlier

for particles that contained little or no chloride. At 60 mole% CO$(Na2+K2). the

deposition rate appeared to increase markedly h m O to 0.055 mg/g-cm'-min. However.

the deposit in this case was found to have an appearance different from that of deposits

o btained from other tests: it was powdery, t'uffy and very easy to remove.

For particles containing 1 up to 3 mole% CV(Na+K), increasing carbonate content resulted

markedly in an increase in deposition rate. At a higher chloride level. ix.. > 3 mole%

CV(Na+K). the e ffect of carbonate was insignificant.

Figure 4-9 shows the sarne data as Figure 4-8, except that it is plotted as deposition rate at

various carbonate levels against chloride content.

/ / COJ(Na2+K2), mole %

O 1 2 3 4 5 6 CV(Na+K), mole %

Figure 4-9. Effect of chloride on the deposition rate of particles containing 5 mole%

K/(Na+K) and varying carbonate levels

It should be noted that in the recovery boiler superheater region, the chloride and

potassium contents in carryover particles are typically higher than 1 mole% CV(Na+K) and

5 mole% W(Na+K) respectively, while the carbonate content typicdiy ranges from 40 to

60 mole% CO3/(Na2+K2).

It may be concluded therefore &rom Figures 4-1. 4-8 and 4-9 [hot ~hc: rCkci OC clubonatz on

carryover deposition in the recovery boiler superheater region is insigni ficant.

As shown in the following pictures. increasing carbonate contents increased the deposit

m a s on the probe surface (Figure 4- 10 and 4- L 1). More pictures are shown in Appendix

A.

Figure 4-10. Appearance of the deposits containing 1 mole% CV(Na+K) & 5 mole% KI(Na+K) and three different carbonate contents; T ,,k= 5 0 0 ~ ~ . exposure time = 25 min

Figure 4-11. Appearance of the deposits containing 3 mole% Cl/(Na+K) & 5 mole% W(Na+K) and three different carbonate contents; T pmh= 500°c, exposure time = 25 min

4-4. EFFECT OF LIQUID CONTENT ON DEPOSITION RATE

Previous studies (1 1.29) suggested that the Liquid content in carryover pmicles is the main

parameter goveming the particle deposition process. Since the Iiquid content increases with

chloride concentration, the rate of deposition increases as the chloride concentration

increases until it reaches a maximum Ievel at a chloride content between 1 and 5 mole%

Cl/(Na+K). Above this point the deposition remains constant or decreased siightly (29).

In thû study. the effect of tiquid content on particle deposition was examined. The

deposition data shown in Figures 4-2, 4-3, 4-7 and 4-8 were plotted against the iiquid

content. This theoretical liquid content was calculated by Dr. Mikko Hupa's research group

at the Abo Akademi University in Turku, Finland, using MELTEST. a thermodynarnic

mode1 for liquid and solid solution phases in the system Na2SO~-NaCl-KrC03.

The temperature and liquid content data for typical deposits containing 5 mole% K/(Na+K)

and 40 mole% COd(Na2+K2) are summarized in Appendix B, md the graphs of liquid

content versus temperature for 200 different compositions are illustrated in Appendix C.

In order to understand the correlation between liquid content and deposition, the iiquid

contents of typicai particles containing 5 mole8 W(Na+K), 40 mole% CO3,(Naz+Kz) and

difkrent chloride contents are plotted against particle temperature (Figure 4- 12).

500 600 700 800 900

Temperature (OC)

Figure 4-12. Liquid content (wt%) of particles containing 5 mole% K/(Na+K) and

40 mole % C03/(Na2+Kr) as a unction of temperature, and chloride

content

As shown, the liquid content of particles increases with both temperature and chloride

content. This implies that in recovery boilen, increasing the tlue gas temperature in the

superheater region causes carryover deposition to occur at a lower chiotide content. On the

other hand, increasing the chloride content in black liquor causes carryover deposition to

occur at a lower flue gas temperature in the superheater region. The Liquid content is

directly related to particle temperature. which is a hnction of tlue gas tempenture and

tube surface temperature.

Shenassa (29) reported the estimated impact temperature for particles with different

chloride contents. The results suggested that panides traveiing through iha EFR ai 8 0 0 ' ~

and the non-heated section reached the EFR temperature pnor to exit: however. they

decreased in temperature once they entered the non-heated section. Although the particle

temperature is expected to be somewhat lower at the EFR exit. the exact temperature is not

known. and thus the üquid content c m not be calculated.

In order to calculatc the iiquid content. it is assurned that the particles were ai 750'~ when

they hit the probe surtàce. Figure 4-13 shows the correlation between the deposition rates

obtauied in this study, and the liquid content of dilferent particles at 7 5 0 ~ ~ using graphs in

Appendix C.

O 20 40 60 80 100 120

Liquid Content, wt%

Figure 4-13. Effect of liquid content on the deposition rate of particles containhg

various ernounts of chloride, potassium and carbonate; assurneci

particle temperature: 7 5 0 ' ~

The data clearly show the importance of the üquid content in particle deposition. Particles

begin to deposit as the liquid content reaches about 15 wt%. Increasing the liquid content

causes particles to deposit at a higher rate untii the rate reaches the maximum level at about

0.08 mg/gcrn~min. The requirement of 15 wt% liquid content is consistent with results

obtained in previous studies ( 1 1, 29).

As shown in Figure 4-13. when the liquid content of panicles is Iess than 15 wt%. there is

no deposition. Only one data point at 0% liquid content (arrow sign) does not fit weii with

the rest. The deposition rate was 0.057 rne/g-cm'-min. instead of zero. However. if the

assumed particle temperature was 770'~. the minimum liquid content of particles required

to deposit would be about 20 wt% (Figure 4-14). and the above data point at 0 8 iiquid

content would tjt better with other data points. This implies that if the calculated liquid

content data are reliable. the particle temperature was more kely to be 7 7 0 ' ~ than 750'~.

Liquid Content, w t %

Figure 4-14. Effect of iiquid content on the deposition rate of particles containing

various amounts of chloride, potassium and carbonate; assumed particle

temperature: 7 7 0 ~ ~

4-5. IMPLICATIONS

The results of this project cm have relevance to the operational problems regarding

particle deposition in kraft recovery boilers. The knowledge of the factors influencing

deposit formation can assist in the better operation of the recovery boiler.

The change in thermal conditions of particles in the non-heated section of the EFR

resembles the conditions prevailing in recovery boilers. In the EFR, the particle

temperature decreases at the EFR exit before they hit the probe surface controiled at

500'~. In the recovery boiler. as carryover particles pass through the superheater region.

the temperature decreases from 850-900'~ to about 550-600'~ at the boiter bank inlet.

The tube surface temperature in the superheater region typically varies lrorn 170'~ near

the boiler drum to 4 8 0 ~ ~ at the final superheüter outlet.

It is important to recognize the Limitations of the application of the îïndings of the present

study. In this work carryover deposition in kraft recovery boiters was simulated in the

Entrained Flow Reactor. However. there are several differences between a kraft recovery

boiler and the EFR. These differences could cause discrepancies in the de position results

obcaîned from the experiments in the EFR and the canyover deposition in recovery boilers.

In a kraft recovery boiler. in-tlight canyover particles are cooled down by the surrounding

Bue gases, white in the EFR, particles are heated by the hot surrounding gases. The in-

flight canyover particles may react with the chernicals in the flue gases and hence

experience changes in theû chemistry; this does no t occur for the synthe tic carryover

particles in the EFR.

The maui results of this study are the effects of potassium and carbonate on the carryover

deposition. Since the formation of carryover deposits on a solid surface is determined by

the quantity of liquid phase, the presence of the liquid phase is essential for particles to

deposit on the tube surface. The tenacity and the amount of liquid content present in

deposits depend on its composition and temperarure.

This study shows that in mills. with more than 5 mole% CV(Na+K). lowering potassium

content through precipitator catch purging is unlikely to minimize the plugging problem. It

is noted that while çhloride content of the deposit is higher thm 5 mole% CV(Na+K). the

increased potassium content has no funher effect on the deposition rate. This is important

since it suggests that for mills that have chloride content l es than 5 mole% CV(Na+K),

purging precipitator catch would help to alleviate the fouling problern.

For a typical potassium level. such as 5 mole% K/(Na+K), increasing the carbonate content

resulted in an increase in the deposition rate only when the chloride content is between 1

and 3 mole% CV(Na+K).

5. CONCLUSIONS

Based on the research of this study. the lollowing conclusions may be drawn:

O Potassium has no rneasurable eft'ect on the deposition rate when the chloride content is

Iess than 1 mole% CV(Na+K).

r Increasing the potassium content results in an increase in the particle deposition rate

when the chloride content increases from 1 to 5 mole% CV(Na+K).

r At a chloride content higher than 5 mole% CV(Na+K), potassium shows no additional

effect on the deposition rate.

O For puticles containing 1 to 3 mole% CV(Nü+K). increasing the carbonate content

resulted in an increase in deposition rate. However. carbonate has no measurable eflect

on deposition for particles containing more than 3 mole% Ci/(Na+K).

e Since carryover particles in the superheater region of recovery boiiers typically contain

more than L mole% CV(Na+K), 5 mole% K/(Na+K) and 40 mole% COS(Na2+K2), the

eftect of carbonate on carryover deposition in this region of the boilers is insignificant.

O Liquid content is the dominant factor affecting curyover deposition. and chloride has

the greatest effect on üquid content. followed by potassium. and then carbonate.

O In order for carryover particles to deposit, they must have a Liquid content higher thm

15-20 ~ t % .

6. RECOMMENDATIONS

Based on the results obtained from the present study. the following recommendations can

be made for further investigation on particle depositio n:

Since deposits in recovery boilers consist of a small amount of NazS which may

influence the amount of liquid phase of deposits. the effect of sulphide on the particle

deposition rate needs to be studied.

In order io estimate the minimum liquid content necessary for deposition. an

experimental apparatus needs to be developed to meüsure puticle temperaiures ptior to

deposition on the probe surface.

A preheating device should be developed to increase particle temperature to a desired

temperature prior to feeding to the EFR.

REFERENCES

1,

2.

- 3.

4.

5.

6 .

7.

8.

9.

1 o.

I I .

12.

13.

Tran, H.N., "Kraft Recovery Boiler". Edited by Adams, T.N., Tappi press, Atlanta, 1997.

Tran, H.N., " How Does a Knft Recovery Boiler Become Plugged?", Tappi Journal, 69 (1 1). 102- 106 (1986).

T r i , H.X.. "A Study ùC Superheater Finsidc Dcposits Li Knf t Rccovcry Boüers". Ph.D. Thesis, Department of Chemical E n g i n e e ~ g and Applied Chemistry, University of Toronto, 1982.

rssak, P., Tran, H.N., Barham. D. and Reeve, D.W., "Stickiness of Fireside Deposits in Kraft Recovery Units, Part II. The Elfect of Potassium and Surface Treatment". Journal of Pulp and Paper Science. 13 (5): J 154 ( 1987).

Shivgulam, N., M.A.Sc. Thesis. Depmment of Chemical Engineering and Applied Chemistry, University of Toronto. 1977.

Tran. H.N., Reeve, D.W., Barharn. D.. "Formation of Kraft Recovery Boiler Superheater Fireside Deposits". Pulp and Paper Canada, 84 ( 1): T l 1 ( 1983).

Shenassa, R.. Tran, H.N., Kuhn, D.. "Dynarnic Study of Canyover Deposition Using an Entrained Flow Reactor". Research Consortium. 1997.

Mao, T.. "Impact of Liquid Droplets on Solid Surfaces and Its Applications to Cmyover De position in Kraft Recovery Bo ilers". Ph.D. Thesis. Department of Chemical Engineering and Applied Chemistry. University of Toronto. 1997.

Tran, H.N., Mao, X., Barharn, D., 'Thermal Analysis of the First Melting Temperature of Fireside Deposits", Presentation at the Recovery Boiler Consortium Meeting at the University of Toronto. Unpubüshed (1994).

Bergman, AG. and Sementsova, k K., ' n i e Temary Systems KrCi2-Na2S04- Na2C03 and Na-Ch-KtS04-&CO< Zhurnal Neorganicheskoi Khimü." 3 (2) 20 1 (1958).

Issak, P., M. A. Sc. Thesis. Department of Chemical Engineering anri Applied Chemistry, University of Toronto. 1986.

Tm, H.N., " Kraft Recovery Boiler Plugging and Prevention". Proceedings of 199 1 Kraft Recovery Operations, P. 18 1 (199 1).

Tran, H.N.. "Kraft Recovery Boiler Plugging and Prevention". TAPPI Kraft Recovery Short Course, P. 6.1.1 (1995).

Tran. H.N.. Elliott. M.. Barham, D.. and Reeve. D.W.. "Recovery Boiler Operation and Plugging in Canada". Pulp and Paper Canada 87: 7. P.T 278 ( 1986).

Mannisto, H.. and Mannisto, E.. b'Impact of Current Environmental Trends on Kraft Recovery Boiler", Proceedings of 1995 International Chemical Recovery Conkrence, p. Ag. Aprii 24. Toronto, Ontario ( 1995).

Reeve. D. W.. Tran H.N.. and Barham D.. 'The effluent-Free Bleached Kraft Pulp Mill. Pan XI; Chemical and Thermal Propenies of Recovery Boiier Superheater Fieside Deposits", Pulp and paper Canada. 82 (9). p. T3 15 ( 198 1).

Issak, P., Tran, H.N., Barharn, D. and Reeve, D.W., "Stickiness of Fireside Deposits". Journal of Pulp & Paper Science, 12 (3), May, p. J84 (1986).

Backman. R.. Hupa M., and Uppstu, P., "FouLing and Corrosion in Recovery Boiler Superheater AmT'. Tappi Journal. 70 (6): 123- 127 (1987).

Reeve. D. W.. Tm, H.N.. and Barham D. "Sintering of Deposits and Its Impact on Plugging in Kraft Recovery Units". Tappi Journal. 70 (4). p. 109 ( 1988).

lokiniemi. J., J. Pyykonen. P. Mikkancn. E.I. Kauppinen. "Modelling Alkali sait Deposition on Kraft Reco very Boiler Hcat exchangers". Proceedings of 1995 International Chemical Recovery Conference. p. B77. April 24. Toronto. Ontario ( 1995).

Backman. R.. Skrifvars, B . 4 , Hupa, M.. Süskonen. P.. and Matynierni. J., "Flue Gas and Dust Chemistry in Recovery Boilers with High Levels of Chlorine and Potassium". Journal OC Pulp and Paper Science, 22 (4): J 1 19- 126 ( 1996).

Tran. H.N., Barharn, D., and Reeve. D.W.. b'Chloride and Potassium in Kraft Chernicd Recoveiy Cycle", Pulp and Paper Canada. 9 1 5 . T 185-T L9O (1990).

Tran, H.N.. Barham, D., Mao, S. and Gonsko, M. "Effect of Carbonate on Deposit First Melting Temperature", Tappi Engineering 1999.

Wake, W. C., "Adhesion and the Formation of Adhesives", Applied Science Publishers, Ltd. London (1982).

Tran, H.N., Barham. D., Hupa M., "Fieside Corrosion in Kraft Recovery Boilers- An Overview of Chemistry", Tappi Kraft Recovery Operations Short Course. 28 1-287 (1990).

Shenassa R.. Tran. H.N.. and Kuhn, D.. "Effect of Chloride on Deposition rate in Kraft Recovery Boilers" . Fireside Deposits and Corrosion, Research Consortium, Novernber 1997.

Gitlesen. G., and Motzfeldt. K, "Phase Diagrams by the Conductance Method in the System NazS04-Na2C0,", Acta. Chem. Scand. 8 1 (2). 488 ( 1964).

Hupa M.. Backman, R., Skrifvars, B . 4 , Forssen, M.. 'Liquor-to-Liquor Differences in Combustion and Gasikkation Processes: Dust Composition and Melting Properties", Proceedings of International C hemical Recovery Conference, 6 15-628 ( 1998).

Shenassa. R. Ph. D. Thesis. Department of Chernical Engineering and Applied Science, University of Toronto. 2000.

Bergeron. C. G., and Risbud. S.. "Introduction to Phase Equilibria in Ceramics". The Amencan Ceramic Society Inc. (1984).

Bama, J.L.. Mattie, R.J., Rogan. J.B.. Allison. S . " Fireside Corrosion inspections of Black Liquor Recovery Boilers", Kraft Recovery Operations Shon Course (1993).

Virkola. N.-E.. Keitaiinniemi. O.. "Undesirable Elements in Causticizing Systems". Tappi Journal. 65(7): 89-92 ( 1982).

Tran. H. N.. Gonsko. M., Mao. X.. "Effect of Composition on the First Melting Temperature of Fireside Deposits in recovery Boilers". Proceedings of Tappi Engineering Conférence ( 1996).

Reisman. A. "Phase Equilibria. Basic Principles Applications Experimental Techniques". Academic Press Inc.. Vol. 19 ( 1970).

Vedl, C. L.. Nichols, K. M.. "Fume Formation During Black Liquor Droplet Combustion: The Importance of Sodium Release During Devolatiiization". Paroceedings of Tappi International C hemical Recovery Conference. 609-6 14 (1992).

Cook, L.P. and McMurdie, H. E. Eds., " Phase Diagrarns for Ceramists, Vol. VF'. Am. Cemmic Soc.. Westerville. OH ( 1989).

Appendix A : Photographs of deposits on the probe

Appearance of the deposits containing 2 mole% CI /(Na+K), 5 mole% K/(Na+K) and three different carbonate contents; Tpmk = SM%, exposure time = 25 min

Appearance of the deposits containhg 5 mole% Cl /(Na+K), 5 mole% K/(Na+K) and three different carbonate contents; Tpma = 500°c, exposure time = 25 min

Appearance of the deposits containing 5 mole% Cl /(Na+K), 10 mole% K/(Na+K) and three different carbonate contents; Tpmbe = 5 0 0 ~ ~ ~ exposure time = 25 min

Appearance of the deposits containing 5 mole% Cl /(Na+K), 15 mole% K/(Na+K) and three different carbonate contents; T,,k = 500°c, exposure time = 25 min

Appearance of the deposits containing 60 Cw(Na2+K2), 5 mole% KI(Na+K) and three different chloride contents; Tpmk = 500O~, exposure time = 25 min

Appendix B: Liquid content (wt%) of typical deposits containing 5 moleoh K/(Na+K), 40 mole% C03/(Na2+K2) and various chloride contents at a temperature between 5 0 0 ~ ~ to 900'~

Appendix C: Graphs of liquid content (wt%) of various deposits at a temperature between 5 0 0 ~ ~ to 9 0 0 O ~

600 700 800

Temperature (OC)

Liquid content (wt %) of deposits contai~ng 5 mole% K/(Na+K) with no carbonate at a temperature between 500'~ to 90°c

500 600 700 800 900

Temperature (OC)

Liquid content (wt%) of deposits containing 5 mole% W(Na+K) and 20 mole% COJ(Na2+K2) at a temperature between 5 0 0 ~ ~ to 9 0 0 * ~

Liquid content (wt % ) of deposits containing 5 mole % W(Na+K) and 40 mole% C03/(Na2+K2) at a temperature between 5 0 0 ~ ~ to 9 0 0 O ~

Liquid content (wt%) of deposits containing 5 mole% K/(Na+K) and 60 mole% C03/(Na2+K2) at a temperature between 5 0 0 ' ~ to 90°c

Temperature (OC)

Liquid content (wt%) of deposits with no potassium and carbonate contents at a temperature between 5 0 0 ~ ~ to 90°c

Liquid content (wt%) of deposits containing 10 mole% K/(Na+K) at a temperature between 5 0 0 ~ ~ to 900'~

Liquid content (wt%) of deposits containing 20 mole% W(Na+K) at a temperature between 5 0 0 ' ~ to 900'~

600 700 800 Temperature (OC)

Liquid content (wt%) of de osits containing 30 mole% K/(Na+K) at E a temperature between 500 C to 90°c

700 800

Temperature (OC)

Liquid content (wt %) of de osits containing 20 mole % CO31(Na2+K2) at s a temperature between 500 C to 900'~

600 700 800

Temperature (OC)

Liquid content (wt%) of deposits containing 10 mole% K/(Na+K) and 20 mole% COJ/(Na2+K2) at a temperature between 5 0 0 * ~ to 900'~

Liquid content (wt %) of deposits containing 20 mole% K/(Na+K) and 20 mole% COd(Na2+K2) at a temperature between 5 0 0 ' ~ to 9 0 0 ~ ~

500 600 700 800 900

Temperature (OC)

Liquid content (wt%) of deposits containing 30 mole% W(Na+K) and 20 mole% COJ/(Na2+K2) at a temperature between 5 0 0 O ~ to 90O0c

700 800

Temperature (OC)

Liquid content (wt %) of de osits containing 40 mole % COJ(Na2+K2) at 8 a temperature between 500 C to 9 0 0 ' ~

Liquid content (IV~%) of deposits containhg 10 mole% W(Na+K) and 40 mole% C03/(Na2+K2) at a temperature between 5 0 0 ~ ~ to 9 0 0 O ~

Temperature (OC)

Liquid content (wt%) of deposits containing 20 mole% K/(Na+K) and 40 mole % COJ(Naz+K3 at a emperature between 500 '~ to 9 0 0 ~ ~

Liquid content (wt%) of deposits containhg 30 mole% W(Na+K) and 40 mole % COJI(Na2+K2) at a temperature between 5 0 0 * ~ to 9 0 0 O ~

Liquid content (wt %) of deposits containing 60 mole % COJ(Na2+K2) at a temperature between 50O0c to 90O0c

Liquid content (wt %) of deposits containing 10 mole% W(Na+K) and 60 mole% COJ(Na2+K2) at a temperature between 50O0c to 9 0 0 O ~

Temperature (OC)

Liquid content (wt%) of deposits containing 20 mole% W(Na+K) and 60 mole% C03/(Na2+K2) at a temperature between 500 '~ to 900 '~

Liquid content (wt % ) of deposits containing 30 mole % K/(Na+K) and 60 mole% COJ(Na2+K2) at a temperature between 50°c to 90°c