AKTIEBOLAGET ATOMENERGI

STUDSVIK, NYKÖPING, SWEDEN 1974

AE-40K

THE DEPOSITION KINETICS OF CALCIUM HYDROXY APATITE

ON HEAT TRANSFER SURFACES AT BOILING

by

T Kelén, R Gustafsson

ABSTRACT

An experimental investigation was performed to study the deposi-

tion of calcium hydroxy apatite in boiler furnace tubes and on nuclear

steam generator tubing. The investigation was run in a high-pressure

loop at pressures up to 10 MPa. The heat transfer surface was run

at densities of heat flow rates up to 0. 9 MW- m" and boiling. The

deposition rate constants thus recorded were in the range 0. 1-1 00

urn- s~ . Increments in the density of heat flow rate and in the water

temperature increased the deposition rate sharply. No clear

dependence of electrical conductivity or pH were traced. Sodium

polyacrylate had a marked inhibiting effect on the deposition. The de-

position was recorded by measuring the gamma radiation from Ca-47,

which was used as a tracer isotope.

Printed and distributed in September 1 974

CONTENTS

1. INTRODUCTION

page

3

2. EXPERIMENTAL 3

2. 1 Loop construction 3

2.2 Determination of the deposition rate constant 4

2.3 Water chemistry control 5

3. RESULTS 6

3.1 General remarks 6

3.2 Magnitude and reproducibility of the deposition rateconstants 6

3.3 Influence of steam quality 7

3.4 Influence of temperature 7

3. 5 Influence of density of heat flow rate 7

3.6 Influence of pH 7

3.7 Influence of electrical conductivity 8

3. 8 Influence of concentration of calcium- and silica-species 8

3. 9 Influence of polyacrylate dosing 8

4. DISCUSSION 8

4. 1 Range of the deposition rate constants 8

4. 2 Influence of density of heat flow rate 9

4.3 Influence of temperature 10

4. 4 Influence of chemistry 1 1

5. CONCLUSIONS 11

ACKNOWLEDGEMENTS 12

REFERENCES 13

TABLES 14

FIGURES

APPENDIX 1

- 3 -

1 . INTRODUCTION

The deposition of contaminants on heat transfer surfaces is awell-known but disturbing phenomenon which may cause trouble inconventional steam boilers as well as in nuclear reactor systemsif it is not properly controlled. Typical of the operational disturb-ances to which this phenomenon leads are rise of temperature, fallin pressure» hide-out and, in nuclear primary systems, conta-mination with radioactive corrosion products.

Phosphate conditioning of the feed water involves special depo-sition problems, since in the presence of metal ions such as thoseof the alkaline earths, phosphate precipitates may be formed. Acommon contaminant in phosphate treated boilers and nuclear steamgenerators is calcium hydroxy apatite, which is generally attributableto calcium present in the make-up water. The aim of the present in-vestigation was to study the deposition of this contaminant on heattransfer surfaces under boiling conditions and to elucidate the para-meters which determine the deposition rates.

2. EXPERIMENTAL

2.1 Loop construction

The investigation was run in the high-pressure loop Maggan.The loop consists of a primary circuit with pressure regulation,

a dosage section and a drainage section. Operational data are asfollows:

Pressure:

Temperature:

Circulation flow:Dosage flow:

Power:

Density of heat flow rate:Volume of water in the primarycircuit:

max 10 MPa (100 bars)max 31 0°C (saturation tem-perature)

max 1 kg* s2-20 g-s"1

max 2-20kW

-1

max 1. 5 MW- m

5 dm"

-2

A schematic diagram of the loop is presented in Fig 1.

The test section was electrically heated using an AC-source

operating between 0-10 V. The power supply was regulated in a

- 4 -

preheating section by an adjustable transformer and in the test sec-

tion by a Variac transformer. The power in each part could be varied

between 0 and 20 kW corresponding to a range of density between 0-1.5

MW- m~ for the heat flow rate.

The calcium hydroxy apatite was obtained by mixing streams

of CaNO, and phosphate solutions using two piston pumps. The for-

mation of the apatite was confirmed by X-ray diffraction analysis.

The feed water flow throughout the runs was held at a constant

rate of 2 g* s~ which gave an exchange constant for the loop water

of 4M0"4 s~\

The steam quality in the test section was calculated from values

for the coolant flow and the subcooling, the latter being recorded

continuously on a pen-recorder during the experiments.

The pH and the electrical conductivity of the loop water were

recorded in the drain water.

2.2 Determination of the deposition rate constant

The amounts of calcium in the test section and in the water were

monitored by measuring the gamma radiation from Ca-47 (half life

4. 5 d, obtained from Risö, Denmark) which was added as an isotopic

tracer.

Two Nal scintillation detectors were used; one of which was

mounted at the test section to measure deposited calcium. The sec-

ond measured the calcium concentration in the water, generally the3

drainage water, which was sampled in 25 cm aliqots with a Vogel

pipet and transferred to a plastic vessel placed on the detector.

The detectors were fed by separate HV-units but were alter-

nately switched to a common single channel analyzer connected to

a sealer.

The deposition rate constant was calculated from information

concerning the slope of the graph for deposited calcium vs time and

the calcium concentration in the water. The constant is defined as

follows:

dc,

-dT = k ' c w 0 )

where

- 5 -

t

k

c

= mass of deposit per unit area, kg* m

= time, s-1

w

s rate constant, m* s

= concentration in the water, kg*m -3

The detector located at the test section and that used for the

water samples were calibrated against each other in such a way

that k could be calculated from the values for the relative counting

rate. A detailed description of the method is given in the appendix.

2.3 Water chemistry control

The investigation was based on a water chemistry designed to

simulate the normal chemistry of drum boilers at medium pressures;

the significant parameters being

pH

conductivity

CaO

= 10-1

~ 100 U-S- cm

= 1 0 g- m" (1 0 ppm)

Stepwise changes of this chemistry were made in some runs by

changing the pH, the conductivity or the calcium concentration.

The pH was kept at 1 0 by feeding a solution with a specific con-

centration of Na,PO.. Increments of the pH were made by simply

increasing the phosphate concentration. The pH was lowered by

changning from Na-PO, to mixtures of Na^HPO, and NaHLPO..

The conductivity was increased by dosing with Na.SO.-solu-

tions.

Sudden changes between the various water chemistries were

made in order to obtain distinct transition points on the deposition

vs time plots. To achieve this, a special procedure was used as

follows. A 8mall volume of solution was fed into the loop in the space

of a few minutes. Although the volume concerned was too small to

displace any considerable part of the loop water, it contained che-

micals that produced the desired change in water chemistry on

mixing with the loop water. The feed water system was then switched

over to new supply-tanks containing solutions satisfying the require-

ments of the newly imposed water chemistry. This procedure per-

mitted adjustment of any chemical parameter to a new level within

- 6 -

the space of i 0 to 20 minutes. Relying only on a direct change of

supply tanks to affect a transition several hours would have been re-

quired to establish a new equilibrium.

The feed water was degassed by bubbling a stream of nitrogen

through it.

3. RESULTS

3.1 General remarks

The same test section of stainless steel SIS 2333 was used

throughout the investigation, the surfaces exposed to the water con-

sisting initially of stainless steel oxides. These surfaces, however,

were covered with deposits of calcium hydroxy apatite during the pre-

liminary running in of the loop. Accordingly the material of the test

section should be incapable of influencing the course of deposition

during the experimental runs.

The influences of the morphology, chemical condition and struc-

tural condition of the deposition surface were not investigated. It is

possible that if the test section had featured a different surface

roughness then a slight shift might have been observed for the set

of k-values. Furthermore a prolonged deposition run with constant

running data might have resulted in a deposit with a different surface

condition, which could in turn have influenced the deposition rates.

Although such long-term influences were not studied systematically

in this investigation, some preliminary runs of long duration indicate

that they are not very significant.

During each run the test section activity and the drain water

activity were plotted as a function of time. Examples of these plots

are given in Figs 2-5.

3 . 2 Magnitude and reproducibility of the deposition

rate constants

In Table 1 are gathered data concerning the operating conditions

and the resulting deposition rate constants. The values of the con--1 -1

stants range between zero (less than 0. 1 urn- s" ) and 80 unv s" .

The standard deviations of the constants obtained from inde-

pendent runs under steady state conditions are presented in Table 2.

In general they do not exceed 50 % except in the runs at 224°C, where

the constants were rear the detection limit.

- 7 -

3. 3 Influence of the steam quality

In one run the steam quality in the test-section was varied by-

altering the power supplied to the preheater section. The steam con-

tent at the inlet of the test section was kept initially at 1 . 2 % and at

the outlet at 2. 3 %. It was then increased to 3. 1 % at the inlet and

4. 2 % at the outlet by raising the preheating power from 1 0 to 1 7 kW.

The detector, which was placed half-way up the test section, recorded

the same deposition rate constant before and after the change. The

density of heat flow rate was held constant during the run.

The result indicates that the steam quality does not inflwence

the deposition rate within the range of steam contents used in this in-

vestigation.

3. 4 Influence of temperature

The deposition rate constant is plotted versus the temperature

in Figs 6 and 7. The plots show a strong positive dependence on tem-

perature in the range investigated, namely 224-310 C.

3. 5 Influence of density of heat flow rate

Linear plots of the deposition rate constant vs the density of heat

flow rate are given in Fig 8, while log plots are shown in Fig 9. These

plots show that an increase in the heat flow rate leads to a sharp in-

crease in the deposition rate.

The approximately linear relationship between deposition rate

constant and density of heat flow rate exhibited by the logarithmic

plot features slopes which lie between two and three for all the three

temperatures investigated. This demonstrates that the deposition rate

constant was approximately proportional to a value between the second

and the third power of the density of heat flow rate.

3. 6 Influence of pH

It was not possible to detect any definite influence of pH. Positive

changes were recorded after both reductions and increments of pH.

On the other hand sudden releases of deposit were recorded in some

cases. During one run no change was recorded of the deposition rate

although the pH was increased from 1 0 to 11.

- 8 -

It is possible that during long runs a change in pH will lead to

a variation in the deposition rate since the deposition seems to be

sensitive to pH changes. It is, however, more probable that the re-

corded changes were a direct result of disturbances of the water

chemistry itself rather than of changes in the actual value of the pH.

3.7 Influence of electrical conductivity

No significant influence was traced. In some cases an increase

in conductivity resulted in a sudden release of deposit. In other cases

nothing happened at all. There were no indications that the deposition

rate increased after dosing with Na^SO.-solution.

3.8 Influence of the concentration of calcium- and

silica-species

No significant influence was traced.

3. 9 Influence of polyacrylate dosing

Dosing with polyacrylate had a strong inhibiting influence on the

deposition. In the three runs in question a part of the deposit was re -

leased to the water immediately after dosing was started. No deposi-

tion was recorded as long as the polyacrylate remained in the system.

In two of the runs the deposit actually continued to decrease after the

initial shock-release.

4. DISCUSSION

The authors do not know of any literature data for the deposi-

tion kinetics of calcium hydroxy apatite on heat transfer surfaces under

conditions of high pressure boiling. The deposition of iron oxides is,

however, treated by several authors, of which Mankina et al [ i ] give

a good account for the deposition in fossil-fired boilers, while

Charlesworth [2] treats the deposition in nuclear boiling water sys-

tems.

4. 1 Range of the deposition rate constants

Deposition rate constants obtained in the present investigation

are compared with Mankind' s and Charlesworth' s in the table below.

- 9 -

Source

Mankinaet al1)

Charlesworth '

This work

Magnitude

deposition

constant, t

l 0 - 1 _ 1 (

102-1C

10" 1 -1C

of

r a t e-1

xm-s

)

, 4

Density of

heat

MW

0.

0.

0.

flow-2

• m

03-0.

26-1 .

3 -0 .

rate,

2

40

9

Temperature

TP-1 70-boiler

~ 285°C

-224-310°C

Type of

deposition

iron oxides oncarbon steel

iron oxideson zircaloy

apatite onstainless steel

1) Calculated from Mankinas data.

2) Roughly estimated from Charlesworth' s data on the concentra-

tion of Fe in the water and the surface concentration of deposit

by assuming equilibrium between deposition and release and a

release probability of 1 • 1 0 s

4. 2 Influence of the density of heat flow rate

Both Mankina f1 "J and Charlesworth [2J report a strong dependence

of deposition on the density of heat flow rate, rp. Mankina proposes

an empirical proportionality to cp .

Charlesworth' s exponents range between 1 . 0 and 5. 5 When all

the data are considered, however, he estimates the best overall

value to be about 2.

In Fig 9 the slopes corresponding to the exponents 2 and 3 are

shown for comparison. The present data seem to fit in somewhere

between these two slopes.

Although the dependences on the density of heat flow rate ob-

tained in this investigation are not strictly quadratic, the Mankina

constants have been calculated from the plots in Fig 9. The constant

is defined by

dt M w«p

o -

where

= concentration of contaminant on the surface, kg-m-2

w

5 -1 -2= Mankinas constant, m -s -kW

= concentration of contaminant in the water, kg-m

= density of heat flow rate, kW-m"

-3

In the table below the Mankina constants obtained in this work

are compared with Mankinas own data.

Source

Mankina et al

This work

Mankinas constant,5 -1 , w - 2m • s «kW

1.7. ID"10

Remarks

224°C250°C310°C

It was mentioned earlier that alterations made to the steam con-

tent did not have any effect on deposition. This observation is in

good agreement with the results of other investigations.

4.3 Influence of temperature

The influence of temperature is appreciable, as can be seen from

Figs 6 and 7. The mechanism behind this is not known.

Kelén and Arvesen[3] report the value 1 . 0 m4-°C-kW~1 -kg"1 as

the thermal resistance number for a typical calcium hydroxy apatite

deposit obtained under boiling conditions. This value was used in com-

bination with the mean values for the deposition rate constants given

in Table 2 to estimate rates of temperature rise on heat transfer sur-

faces at different pressures. The results are listed in the table below.

Pressure

MPa

2.5

4.0

10.0

Density of heat

flow rate, MW-m"2

0. 3

0.4

0.9

Rate of

temperature rise

2 C* month"

5°C-week"1

3°C«hour"1

i ) assuming 10 rng-kg calcium hydroxy apatite in

the water and no release of deposited material

. 11 .

The above values indicate the magnitude of the problem produced

by the rapid rise in temperature in steam generating equipment which

follows an increase in the pressure and in the density of heat flow

rate. The indications are that it becomes practically impossible to

run a unit at 10 MPa and 0.9 MW-m with phosphate conditioning,

a fact which agrees well with normal water chemistry specifications.

4.4 Influence of chemistry

The calculation of deposition rate constants using the formula

(1) in section 2.2 presumes that the deposition rate is proportional

to the contaminant concentration, or in other words, that the deposi-

tion rate constant is independent of the contaminant concentration. To

check this, the concentration of apatite in the water was increased

during the course of a number of runs. Since no definite alteration

of the constant was detected, it was concluded that the equation, on

which the calculation was based, was valid in the ppm-range. It is,

however, probable that concentration effects will appear at low con-

centrations, where an appreciable part of the calcium is in solution.

Changes in pH and electrical conductivity or the addition of sili-

ca-species did not affect the deposition to a significant degree. The

only significant chemical influence which was observed was that pro-

duced by sodium polyacrylate, which acted as a deposition inhibitor.

This agrees with Ahrnbom' s L4J observations on a number of Swedish

drum boilers that have been conditioned with polyacrylate.

With the exception of the polyacrylate it seems as if the water

chemistry has played a secondary role in the deposition process

studied here. The determining parameters for the deposition rate

constant seem to be largely the temperature and the density of heat

flow rate.

5. CONCLUSIONS

1 . The order of magnitude of the deposition rate constant was

0.1 -1 00 p,m» s" under the conditions investigated

2. The steam content did not influence the deposition rate in the

nucleate boiling regime.

3. The deposition rate constant was roughly proportional to a func-

tion between the second and third power of the density of heat

flow rate.

4. The deposition rate constant was appreciably larger at higher

temperatures.

5. No clear dependence of pH and electrical conductivity was traced,

nor f̂ id the addition of silica influence the deposition rate.

6. Sodium polyacrylate showed a strong inhibiting effect on the df o-

sition.

7. The results indicate that the deposition rate can be restricted

by limiting one or more of the parameters temperature, density

of heat flow rate and calcium hydroxy apatite concentration.

Another possibility is to add polyacrylate.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the advice and suggestions

offered by Lars Ahrnbom at the Swedish Steam Users Association.

We also wish to thank those of our colleagues at AB Atomenergi

who were involved in the investigation, and in particular Mr Mac

Arnell for his help with the experimental equipment and the evalua-

tion of the data and Mr Marian de Pourbaix whose group was respon-

sible for the construction and servicing of the Maggan-loop.

The investigation was carried out at the Section for Corrosion

and Reactor Chemistry, Aktiebolaget Atomenergi, Stud svik, and was

financed by grants from the Swedish Board of Technical Development.

REFERENCES

MANKINA, N.N. et al. ,Teploenerg. 6 (1^9) ' 2p . 79.Transl. by J. Jackson:Formation of iron deposits in recirculation steam boilers.Brit. Power Eng. 2 (1 961 ):4 p. 60.

CHARLESWORTH, D.H. ,The deposition of corrosion products in boiling-water systems.Chem. Eng. Progr. Symp. Ser. 66 (197O):1O4 p. 21.

KELÉN, T. , andARVESEN, J . ,Temperature increments from deposits on heat transfer sur-faces: the thermal resistivity and thermal conductivity of de-posits of magnitite, calcium hydroxy apatite, humus and copperoxides. 1972.(AE-459).

AHRNBOM, L. ,Adding of polyacrylate for reduction of the phosphate content inthe boiler water and of the water side deposits in the tubes. 1 974.(SVF-14) (in Swedish).To be published in Svensk Papperstidn.

- 14 -

Table 1 Operating conditions

Run No

Date

Pressure, MPa

Temperature, C

Coolant flow, kg« s

Inlet steam content, %

Outlet steam content, %

Density of heat flowrate, MW.m"2

pH in drain

n in drain, u-S* cm

Concentration of «additives, mg- kg

Deposition rate .constant k, \irr\- s

1

7306

2 . 5

224

0.

2 .

3.

0 .

10

13

8.0

294

18

1

5

4

. 1

110

CaO

0 .2

10

2 . 2

2

7306

4 . 0

250

CaO

1.3

14

6 .4

280

0. 17

2. 1

3 . 5

0.4

10. 1

110

10

1.9

10.0

310

13.1

3

7306

2 . 5

224

CaO

0 .7

15

4.0 8.0

250 294

0.17

2.1

3 .5

0.4

10.1

120

10

0.7 5.5

4

730618

3.2

0.3

CaC

0.8

2 . 5

224

0. 18

2. 1

5.3 2.1

0.9 0

10.0

110

) 10

0.3 0.9

Run No

Date

Pressure, MPa

Temperature, C

Coolant flow, kg* s"

Inlet steam content, %

Outlet steam content, %

Density of heat flowrate, MW-m"2

pH in drain

H in drain, uS-cm"

Concentration ofadditives, mg.kg"

Deposition rate .constant k, u,m« s

5

7:

3.

0.

$0627

2 . 5

224

0. 18

2. 1

2 4.3

3 0.6

10.0

100

CaO 10

0. 6 1.4

7

730629

10.0

310

0. 17

2. 1

3.2 5.3 2.1

0.3 0.9 0

-10

100

CaO 10

4.4 73 r e l ea se

8

730702

0. 17

3 .5

10

100

CaO

1 1

10.0

310

0.17

2 . 1

3 .5

0.4

11

500

10

11

0.21

3.2

11

500

1 5

- 1 5 -

Table 1 cont

Run No

Date

P r e s s u r e , MPa

Temperature, C

Coolant flow, kg* s

Inlet steam content, %

Outlet steam content, %

Density of heal flowra te , MW-m

pH in drain

K in drain, nS» cm"

Concentration ofadditives, mg-kg"

Deposition ra te .constant k, jim* s"

9

730703

0.18

3 .5

10

100

CaO

0 . 5

2 . 5

224

0.18 0.22

2 . 1

3.5 3.2

0.4

11 11

450 450

10

0.4 release

10

730704

4.0

250

10.1

100

CaO

0.9

6.4

280

0.

2 .

3 .

0.

10.

100

10

3.0

6.4 6.4

280 280

18

1

5

4

1 ~7 -10

120 350

7.7 18

12

730808

4 . 0

2 50

0.17

1.2 3.1

2.3 4.2

0 . 3

10.0

85

CaO 10

0.5 0.5

Run No

Date

P r e s s u r e , MPa

Temperature , C

Coolant flow, kg- s~

Inlet steam content, %

Outlet steam content, %

Density of heat flowra te , MW-m"2

pH in drain

H in drain, nS» cm"

Concentration of .additives, mg*kg"

Deposition ra te ,constant k, y,m» s~

13

730809

2.5

224

0.18

2.1

3.2 4 .3

0.3 0.6

10.0

90

CaO 10

0 .3 0 . 9

14

730810

10.0

310

0. 17

2.1

2.1 3.2 4.3

0 0.3 0.6

10.0

100

CaO 10

0 .8 6.0 50

15

730813

10.0

310

0.17

2.1

2.1 4.3 5.3

0 0.6 0.9

10,0

90-100

CaO 10

0 52 82

- 16 -

Table 1 cont

Run No

Date

Pressure, MPa

Temperature, C

Coolant flow, kg* s

Inlet steam content, %

Outlet steam content, %

Density of heat flowrate, MW-m"2

pH in drain

H in drain, y,S* cm

Concentration of -additives, mg-kg

Deposition rate ,constant k, urn* s

16

730814

10.0

310

0. 17

2 . 1

4 . 3

0 .6

10.0

100 500

CaO 10

56 5.3

17

730815

10.0

310

0. 17

2 . 1

4 . 3

0 .6

9.7-10.0 9.7

100 500

CaO 10

36 11

18

730816

4 . 0

250

0. 17

2 . 1

4 . 3

0 . 6

9.8

95 550

CaO 10

3.5 3.5

19

730826

4 . 0

250

0. 17

2. 1

3. 5

0 .4

9.8-10.0

90-100

CaO 5 - 1 0

1.6 1. 1

Ir

Ca

rc

Run No

Date

Pressure, MPa

Temperature, C

Coolant flow, kg* s

Inlet steam content, %

Outlet steam content, %

Density of heat flowrate, MW-m*2

pH in drain

H in drain, (j,S*cm

Concentration ofadditives, mg-kg"

Deposition rate .constant k, urn. s

20

730822

4 . 0

250

0. 17

2. 1

3 ,5

0 .4

10, 1

110 220

CaO 5 - 5 0

3. 3 0

21

730823

4 . 0

250

0. 17

2. 1

3 .5

0.4

10.1

110 140

CaO 10acrylate 600

4. 4 release

22

730827

4 . 0

250

0. 17

2 . 1

3.5

0.4

9.9

110

CaO 10acrylate 600

2.2 release

23

730828

4 . 0

250

0. 17

2 . 1

3.5

0 . 4

10.0

100

CaO 10SiO2 50

3.1 2.9

- 17 -

Run No

Date

Pressure, MPa

Temperature, C

Coolant flow, kg»s~

Inlet steam content, %

Outlet steam content, %

Density of heat flowrate, MW.m"2

pH in drain

H in drain, u,S« cm

Concentration ofadditives, mg« kg"

Deposition rate ,constant k, |jim»s~

Table 1

24

730829

4.0

250

0. 17

2. 1

3 . 5

0 . 4

9.9

100 400

CaO 10SiO2 50

3.1 2.9

c ont

25

7 30904

8.0

294

0. 17

2. 1

3. 5

0.4

10.0 10.5

120 300

CaO 10SiO2 50

7.3 8.2

26

730905

2 . 5

224

0. 18

2 . 1

2.1 3.2 5.3

0 0.3 0.9

10.0i 00

CaO 1 0

0 0 7.8

27

2. 1

0

1

120

2 . 5

224

0. 18

2. 1

3.2

0 . 3

0 .0

135

CaO 10

0 0

4

0

1

0

. 3

.6

40

. 2

Run No

Date

Pressu re , MPa

Temperature, C

Coolant flow, kg*s~

Inlet steam content, %

Outlet steam content, %

Density of heat flowrate, MW.m'2

pH in drain

H in drain, JAS* cm"

Concentration ofajditives, mg-kg

Deposition rate <constant k, ii,m«s"

28

730907

2.5

224

0.18

CaO

0

6.4 10.0

280 310

0. 17 0. 17

2 . 1

3 .5

0.4

10.0

100

10

5.1 22

29

730910

2 . 1

0

4.0

250

0.17

2 . 1

3.2 4.3

0.3 0.6

10.0

150

CaO 10

0 1.0 U

30

730911

2 . 1

0

130

4.0

250

0. 17

2 . 1

3 .3

0.6

10.0

110

CaO 10

re-lease 4.

5.3

0 . 9

120

2 15

31

730912

4. 0

250

0.

2 .

3. 1

0 . 3

10

100

CaO

0.6

17

1

4 . 3

0 .6

. 0

150

10

3.7

Table 2 Mean value and standard deviation of k at various

pressures and densities of heat flow rate

T"1

°c

224

250

280

295

310

PMPa

2 . 5

4 . 0

6 .4

8.0

10.0

No of values

Mean, urn* s

Dev, j^rrr s

Dev, %

No of values

Mean, urn- s

Dev, p,m* s

Dev, %

No of values

Mean, urn- s

Dev, |i,m* s

Dev, %

No of values

Mean, (im* s

Dev, y,m« s

Dev, %

No of values

Mean, u,m« s

Dev, \in\' s

Dev, %

v, MW • m

0 . 3

5

0. 3

0 . 3

100

2

0 . 6

0. 1

17

2

5.2

1. 1

21

0 . 4

4

0 . 4

0 . 3

75

10

2. 1

1.2

57

3

3 .3

1.6

48

3

5 .0

2.6

52

3

15.4

5 .8

38

0 .6

3

0 .8

0 . 6

75

3

3 .8

0 . 4

11

4

48. 5

8.7

6

0.9

2

4 . 1

5 . 3

130

1

15

-

-

2

78

6

8

X

Spray-flowcircuit

Spray-condenser

tTest section

Preheating section

•mm —-> . ...^ ,^ J

I

' F e e d water; I

, preheatfr i

L _

i . ._

Primary circuit B-

Y

ö5

D r a i n a g e r i t c n i l

Feed w.ii'i fcu i L

Fig 1 Schematic diagram of the high-pressure loop Maggan

(O

a,

8wQ

O

H

DO

noo

1000

900

800

700

600

500

224

0

280

I I

310°C

I I8 10

TIME, h

OJWH

W

15

2Oi—•

H<oi

Wu

10 —

5

0

0 8 10

TIME, h

Fig 2 Deposition at various temperatures. Run 28

CONCENTRATION IN THEWATER, cps

AMOUNT OF DEPOSIT, cps

Oc

CL

A«OK

2

o

tSJO

wET

ex-

00

OO

O i—

oo o

o

3*

oo

T

00oo

roo

ooo

oo

oo

o

3

1000

09

O<

O

h

8WQ

O

h

O

900 _

800 -

700 _

600 _

500

30WXH

§< , (Q

H u

20

10 __

8 10

TIME, h

Fig 4 Influence of silica on deposition. Run 25

1150

CA04U

H>-<WO

u

Q

O

1100 —

1050

1000 —

950 —

900

acrylate 600 ppm

0 8 10

TIME, h

WÄ

n

100

50 —

8

TIME, h

Fig 5 Influence of poly aery Ute on deposition. Run 21

PRESSURE, MPa /non-linear scale)

2 .5 4 .0 6.4 8.0 10.0

CD•

XH

uw

§

8WQ

90

80 1-

70

60

50

40

30

20

10

0

200 250 300

TEMPERATURE, °C

Fig 6 Influence of temperature

PRESSURE, MPa (non-linear scale

(0

<HCO

§Uw

§t-*HO

10"

10

10

10-1

200

2 . 5 4 .0 6.4 8 .0 10.0

T~~ I"

1 i i i i i i

250

TEMPERATURE, °C

300

y i g 7 Influence of temperature, k in log-scale

90

(O

ZO

w

8WQ

80 _

70 _

60 U

50 _

40

30 -

20 -

10

0

O 0.2 0.4 0.6

DENSITY OF HEAT FLOW RATE, MW-m

0.8 1.0

" 2

Fig 8 Influence of density of heat flow rate

2.0

(OIC

o

1.5 —

1.0 —

0.5 —

0.0 —

-0.5 -

-1.0-0.6 - 0 . 4

log cp (cp in MW* m~ )

-0.2 0.0

Fig 9 Influence of density of heat flow rate, logarithmic scale

APPENDIX

CALIBRATING OF THE DETECTORS

The two detectors may be characterized by their respectivecalibration constants kA and k , defined by

t wk = P/p and

k = Q/qw ' n

where

-3P = specific activity in the test section, dps*m

p = counting rate of the test section detector, cpsQ = specific activity measured on the water sample detectors,

dps* m~3

q = counting rate of the water sample detector, cps

The deposition rate constant k is defined by

-sr- = k • cdt w

where

c, = surface concentration of deposit, dps-m-1k = deposition rate constant, m* s

c = concentration in the water, dps# mw r

k may then be expressed as

-2

k = dt 0)w

The surface concentration c , is obtained from the recordingd

made of p by assuming that the activity would give the same count-ing rate both homogenously dispersed in the solution and depositedon the tube wall. This assumption is justified by the fact that thedetector sees the test section approximately as a straight line.

The counting rate p is transformed to specific volume activityP by the calibration constant:

= P

APPENDIX i :Z

The transformation to specific surface activity, c , is then

achieved by multiplying by that volume of the test section seen by

the detector and dividing by the corresponding inner area:

c , = •=d Z

—• . • P = - • p • k*TT . r« 1 2 t

(2)

where

r = inner radius of test section, m

1 = length of test section in view of the detector, m

The disappearance of the tube length "1" in the formula signifies

that the exact field of view of the detector need not be known.

c is obtained from the recordings of q by

c = Q = qw n w

(3)

Substituting the expressions for c and c into (1) gives

k =d fT

dT (2w

dt1q

I2

w

The determination of k from the counting rates of the respective

detectors thus leads to an acquisition of knowledge of the radius of the

test section and of the ratio kVk .t' w

The values of r was 4 mm during all the runs.

The ratio k /k was determined by filling the loop with a gamma

active solution and recording the counting rate p. The same solution

was then measured on the water sample detector, giving the counting

rate q. Since the specific activity was the same in both c?ses, k /k

could be determined from the expressions

w

P ' w

w