Calcium Carbonate Scale Formation in Copper Pipes on Laminar Flow

Abstract

Calcium carbonate is commonly precipitated as a scale in the transportation pipes of water. The presence of this mineral deposit becomes problematic, because it can block the pipes and lead to a decline in piping performance. Calcium carbonate precipitation from the synthetic solution was experimentally investigated in the present study. The aim of research was to predict the occurrence of precipitates and characterize the scale precipitated from the solutions. The synthetic solutions were prepared using CaCl2 and Na2CO3, which was mixed with distilled water (H2O). The concentrations of Ca2+ at 2000, 3000, 4000 and 5000 ppm. in the solution were adjusted and the solution flow in the Cu pipes at the different flow rate of 30, 40 and 50 ml/min. It was found that in all the experiments, the conductivity decreased abruptly after a certain induction period. Higher temperature produced more mass of the scale indicating that the increasing temperature promote scale formation. SEM analysis showed that the scale was rhombohedral, while EDS revealed that the elemental composition of the scale consisted of Ca, C and O. The crystalinity of the scale was found to be mostly calcit as shown by the XRD

Full text

CALCIUM CARBONATE SCALE FORMATION IN COPPER PIPES ON
LAMINAR FLOW
Raharjo, S*, Bayuseno, Ab, Jamarib, Muryanto, Sc
*Department of Mechanical Engineering, Muhammadiyah University in Semarang, Indonesia
bDepartement of Mechanical Engineering, Diponegoro University, Semarang Indonesia
cDepartment of Chemical Engineering, UNTAG University in Semarang, Semarang Indonesia
*Corresponding author. Tel. +62-8164242537, +62-8445768
E-mail address: *samraharjo2@gmail.com; apbayuseno@gmail.com
ABSTRACT
Calcium carbonate is commonly precipitated as a scale in the transportation pipes of water. The presence of this mineral
deposit becomes problematic, because it can block the pipes and lead to a decline in piping performance. Calcium
carbonate precipitation from the synthetic solution was experimentally investigated in the present study. The aim of
research was to predict the occurrence of precipitates and characterize the scale precipitated from the solutions. The
synthetic solutions were prepared using CaCl2 and Na2CO3, which was mixed with distilled water (H2O). The
concentrations of Ca2+ at 2000, 3000, 4000 and 5000 ppm. in the solution were adjusted and the solution flow in the Cu
pipes at the different flow rate of 30, 40 and 50 ml/min. It was found that in all the experiments, the conductivity decreased
abruptly after a certain induction period. Higher temperature produced more mass of the scale indicating that the increasing
temperature promote scale formation. SEM analysis showed that the scale was rhombohedral, while EDS revealed that the
elemental composition of the scale consisted of Ca, C and O. The crystalinity of the scale was found to be mostly calcit as
shown by the XRD
Keywords: calcium carbonate, induction time, prototipe scale formation, scale morfology
INTRODUCTION
Scaling is one of the main serious engineering
problems in process industries as the scales my hinder
the flow of solution in industrial pipes or tubes. Accurate
estimation of scale formation is thus very important.
Calcium sulphate, carbonate potentionaly deposited add
clogged pipping system (Azimi and Papangelakis, 2010).
The calcium carbonate scale formation was
influenced by several aspects such as flow rate,
concentration of solution, pH value, temperature,
pressures, and ionic strength (Bahadori, 2010). In
laminar turbulence,the higher flow rates,the more
calcium carbonate scale mass indicating the fluid flow
enchances the scale formation (Muryanto et al., 2012).
Previous studies done by Gourdon, have shown that
CaCO3 scale formation can be found in fully laminar and
fully turbulent. In fully laminar the formation was in a
slow growth while in fully turbulent the formation was
easily found in the angels (Amor et al., 2004). The flow
of the fouling is described as having pronounced rippling
and surface waves of partially laminar and partially
turbulent nature.As the turbulent also will enhance the
mass transfer,the rate of crystal deposition can also be
promoted (Gourdon, 2011).
Other researchers indicated that scale growth does
not always remain linear with time,as higher velocity can
sometimes reduce scale deposition (Basim et al., 2012).
Crystallization occurs due to the lateral growth of the
scale deposit on the membrane surface, resulting in flux
decline and surface blockage (Zhang, 2002). Thus,the
scaling formation is actually the crystallization
phenomenon.Bulk crystallization arises when crystal
particles are formed in the bulk phase through
homogeneus crystallization and my deposit on
membrane surfaces as sediments/particles to form a cake
layer that leads to flux decline (Zhen et al., 2010). In
addition, supersaturated scale forming conditions leads
to scale growth and agglomeration (Rabizadeh et al.,
2014). This is due to the random collision of ions with
particles and secondary crystallization occurs on the
surface of these foreign bodies present in the bulk phase
(Alice et al., 2011).
In electrolyte solutions, the transition temperature
of calcium carbonate solubility may vary because of
variation in the water activity (Fathi et al., 2006). The
solubility of common scales in water is shown in Figure
1, solubility of CaCO3, BaSO4 and CaSO4 as a function
of temperature.
Figure-1. Solubility of Common Scalesas a function of
temperature (Amer, 2009).
The aim of the present research was to examine the
nucleation and growth of calcium carbonate crystals, and
identify calcium carbonate formation and the scaling
potential in pipes. In the present study, calcium sulfate
crystals were grown by the prepared solution containing
calcium carbonate composition and then characterized
by XRD for the mineral determination and SEM analysis
with EDX for elemental analysis and morphology.
,
Web of Conferences DOI: 10.1051/
conf/2016MATEC 58 matec 5
01029 (2016) 801029
BISSTECH 2015
© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative
Commons Attribution
License 4.0 (http://creativecommons.org/licenses/by/4.0/).

METHODOLOGY
Materials and Apparatus
All solutions used in this study were prepared
by dissolving reagent grade chemicals directly without
further purification. The solution was prepared under
saturated calcium sulfate by mixing directly into glass
containers two equimolar solutions of calcium chloride
dihydrate (CaCl2•2H2O, minimum assay 99%, Sigma)
and anhydrous sodium carbonate (Na2CO3, analytical
grade, Sigma). Both reactants were dissolved in aqueous
solutions containing 10 L of water and the solution
concentration of Ca2+ was adjusted to be 2000, 3000,
4000 and 5000 ppm respectively. The selected range of
temperatures was 30 to 40 °C. Each solution was then
poured into a tube made of stainless and stirred at low
speed. Two of the tube is connected with two brands of
Iwaki magnetic pump long and trial test was conducted
for 8 hours for each treatment with different flow rates.
Experiments using a scaling simulator are shown in
Figure 2.
Further, induction time of precipitation was
measured by a conductivity method. This method was
employed in the present study to measure the induction
time for nucleation of calcium sulfate precipitation. The
conductometer with a Consort C831 analyzer was used
for each experiment at specified condition of the
repeated three times. Therefore, the induction times and
precipitation results presented in this study are the
average of three values. In order to minimize costs of
EDX analysis, the three samples were mixed and
analyzed for crystal shape, crystal structure, and density.
Each stock solution was then filtered through 0.22 μm
paper filters to eliminate the presence of impurities, and
stored at room temperature before subsequently analyzed
by SEM/EDX.
Figure-2: Experimental setup used in the CaCO3 precipitation
Materials Characterization
The characterization of the precipitating scales was
conducted through scanning electron microscopy
coupled with energy dispersive X-ray analysis (SEM-
EDX). SEM apparatus equipped with an EDX was used
for characterizing the microstructure and morphology.
For the observation, the powder crystals were mounted
on a circular metallic precipitate holder and finally
sputtered with gold.
RESULTS
Induction Time of crystallization
Induction time can be defined as the time required
for between the generation of supersaturation and
appearance of nucleic detected through concentration
change. This can be seen since the onset of nucleation
showing a reduction in the concentrations of
crystallizing ion and molecules take place due to their
association into the solid phase, thus the conductivity
which is proportional to the concentration will undergo a
reduction. This reduction in conductivity could be
measured as the induction time. However, the measured
induction time presents the sum of the nucleation time
for appearance of critical size nuclei. Additionally,
growth time of nucleic from critical size to the size
possessing enough mass at solid phases makes a
reduction of the solute concentration in the solution at
the detectable extent through conductometry.
In the present study, the reaction was continued for
about 25 minutes after the induction time until the nuclei
were formed into the coupon and observed in computer
monitors. Figure 3 shows the changes in conductivity
during the course of nucleation experiment at room
temperature and flow rates of 30, 40, and 50 ml/min.
Figure-3 Variations of conductivity during the course of
precipitation
Experimental results showed that the induction
time was essentially under the influence of carbonate
concentration. As Figure 3 shows, the induction time
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Web of Conferences DOI: 10.1051/
conf/2016MATEC 58 matec 5
01029 (2016) 801029
BISSTECH 2015
2

decreased as the pH solution decreased from 9 to 6.5.
This effect was assumed to be due to an increase in
supersaturation through an increase in hydrogen
concentration. However, pH of the solution was higher
than 9, a longer induction time was observed. The
experimental results of the present study showed that the
induction time for precipitation increased from 20
minutes to 25 minutes. At higher supersaturations, a
lower value of induction time is expected; however, the
temperature will be more influential than supersaturation
due to its order and logarithmic function of effectiveness
(Mullin, 2004).
Flow rates influence on the mass of precipitates
The mass of precipitated calcium sulfate particles
per kg of water at different flow rates and concentration
is presented in Figure-4. As the Ca+2 concentration of
2000 ppm is fixed and the flow rates for the solution
increases in 30 to 50 ml/minutes. An increase in Ca+2
concentration will increase the supersaturation in the
solution due to the removal of free water from the
availability of the solute species. This will increase the
precipitation yield of calcium cabonate. However, the
trend of reduction in precipitation is similar to occur to
the different flow rates
Figure-4. velocity of deposit formed graph
Characteristics and morphology of precipitates
SEM examination of the CaCO3 scale exhibited a
wide images of calcite and the scales reveal crystalline,
there are scales in the structures rhombhohidral is shown
in figure 5. Morphology pyramid formed a) and
Compositions chemistry b).
Figure-5. Morphology feature is pyramid formed a),
and Compositions chemistry b).
According to theoretical calculations on the
percentage of weight of CaCO3 Ca content should be
40%, while the results of the analysis of micro Ca
content = 39.8 % so as to have difference of 0.2 % . For
levels of carbon (C) shall be 12 wt % while result of
analysis of micro C 10.5 % of micro analysis results that
have a difference of 1.5% . For oxygen levels should 64
%, while the results of the analysis of micro direct 60.06
% so as to have difference of 3.94%.From the analysis of
SEM-EDX test is concluded, its crust really crystal
CaCO3.
DISCUSSIONS
The EDX analysis of calcium carbonate as found in
this study of precipitates in Cu pipes is probably
rhombohidral. It should be considered here that
precipitates samples to be observed by SEM provides
strong intensities of Ca, O and C elements which is more
frequently found in SEM studies of calcium carbonate.
However, the conditions used for EDX analysis in the
present study and the detected amount of impurities
produced a difference in mineral speciation. It is also
important the observations of morphologies by SEM in
the study of a calcium carbonate with apparent
rhombohedral habit in the crystal. It can be assumed
from SEM morphology and EDX analysis (Ca, C) to be.
In contrast, the EDX analysis alone cannot distinguish
whether the analyzed crystals observed by SEM are
calcit, i.e. calcium carbonate valerite, aragonite and only
by additional XRD techniques could be identified these
minerals. In this case, the precipitation mechanisms of
calcium carbonate mineral phases (calcit, valerite and
aragonite) remain large unexplored. Therefore the role
and implications of valerite as a stable precursor phase to
calcit precipitation observed using XRD method, will
provide interesting results to natural and industrial
processes.
0
50
100
150
200
250
25 30 35 40 45 50 55
Deposit mass (mg)
Velocity (ml/min)
2000 ppm 3000 ppm 4000 ppm 5000 ppm
(a)
(b)
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CONCLUSIONS
It was found that in all the experiments, the
conductivity decreased abruptly after a certain induction
period. Higher temperature produced more mass of the
scale indicating that the increasing temperature promote
scale formation. SEM analysis showed that the scale was
rhombohedral, while EDS revealed that the elemental
composition of the scale consisted of Ca, C and O. The
crystalinity of the scale was found to be mostly calcit as
shown by the XRD.
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