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The Formation Mechanism of Induced Draft Booster
Fan Scale in a Sulfite Pulp Mill
by
Ruzheng Wang
A thesis submitted in conformity with the requirements
for the degree of Masters of Applied Science
Department of Chemical Engineering and Applied Chemistry
University of Toronto
©Copyright by Ruzheng Wang 2019
ii
The Formation Mechanism of Induced Draft Booster Fan Scale in a Sulfite
Pulp Mill
Ruzheng Wang
Master of Applied Science
Department of Chemical Engineering & Applied Chemistry
University of Toronto
2019
Abstract
Pulp mills burn the spent pulping liquor in a boiler to recover pulping chemicals and to
generate electricity. At the sulfite mill in this study, an induced draft booster fan is between the
ammonia and caustic scrubbers. There is significant scale formation on the ID booster fan blades.
This results in fan vibration that is severe enough that the boiler needs to be shut down to remove
the scale. This leads to both maintenance costs and lost revenue.
The objective of this project is to understand the scaling mechanism. This work includes
mill sample analysis, field tests at the mill, laboratory studies and mill operating data analysis. The
ID booster fan scale mainly contains (NH4)2Mn2(SO4)3, CaSO4 and (NH4)2SO4. The work shows
that the key to scale formation is the formation and precipitation of (NH4)2Mn2(SO4)3 that is
formed from the reaction of ammonia scrubber carryover droplets and the particulate matters.
iii
Acknowledgements
I would like to express my thanks of gratitude to my supervisors Prof. Nikolai DeMartini and
Professor Honghi N. Tran for their guidance and support throughout this project. The professional
and personal skills and immense knowledge I have learned from them are valuable and I believe
will be helpful to my future career.
In addition, I would like to express my gratitude to Sue Mao, who always kindly resolve my
questions whenever I needed guidance with my research, and Dr. Georgiana Moldoveanu who is
always patient and kindly assist me with my laboratory issues. I am also thankful to my friends
and colleagues whom I have worked with over the past two years. Their great support in
deliberating over problems and findings is truly helpful to me.
I would like to thank the consortium members for their financial support as well as valuable
discussions and information regarding kraft and sulfite pulp mill, and scaling problems specific to
this work. I would like to thank Michel Monet, Les Kosiak, Lyle Biglow and other team members
of RayonierAM, for their contributions to my field studies. Their excellent cooperation and support
are essential to my successful sampling campaign and mill operating data analysis.
Finally, I must express my gratitude to my parents and for their wise counsel and being a good
listener. Their endless love and continuous encouragement are key to my years of study overseas.
This accomplishment would not have been possible without them.
iv
Table of Contents
Acknowledgements ........................................................................................................................ iii
Table of Contents ........................................................................................................................... iv
List of Tables ................................................................................................................................ vii
List of Figures .............................................................................................................................. viii
Chapter 1 ......................................................................................................................................... 1
1. Introduction ............................................................................................................................. 1
1.1. The Sulfite Process ........................................................................................................... 1
1.2. Sulfite Recovery Boiler and Flue Gas Cleaning .............................................................. 1
1.3. Induced Draft Booster Fan Scale Formation .................................................................... 4
1.4. Objectives ......................................................................................................................... 4
Chapter 2 ......................................................................................................................................... 5
2. Literature Review .................................................................................................................... 5
Chapter 3 ......................................................................................................................................... 7
3. Methodology ............................................................................................................................ 7
3.1. Mill Sample Analysis ....................................................................................................... 7
3.1.1. Analytical Techniques Used in Mill Samples Analysis ............................................ 7
3.1.2. Induced Draft Booster Fan Scale Analysis ............................................................... 8
3.1.3. Mill Solution Analysis .............................................................................................. 8
3.2. Sampling Campaign at the Sulfite Mill ............................................................................ 9
3.2.1. Equipment and Materials .......................................................................................... 9
3.2.2. Experimental Plan ................................................................................................... 11
3.3. Laboratory Experiments ................................................................................................. 11
3.3.1. Lab Studies of Deposit Formation Mechanism ...................................................... 11
v
3.3.2. Lab Studies of Powdered ID fan Scale and NH3 Scrubber Water .......................... 12
3.3.3. Experimental Investigation of (NH4)2Mn2(SO4)3 Solubility................................... 13
3.4. Multivariate Analysis ..................................................................................................... 14
Chapter 4 ....................................................................................................................................... 15
4. Results and Discussion .......................................................................................................... 15
4.1. Mill Sample Analysis ..................................................................................................... 15
4.1.1. Induced Draft Booster Fan Scale Analysis ............................................................. 15
4.1.2. Mill Solution Analysis ............................................................................................ 27
4.2. Sampling Campaign at the Sulfite Mill .......................................................................... 28
4.3. Laboratory Experiments ................................................................................................. 32
4.3.1. Laboratory Probe Studies ........................................................................................ 32
4.3.2. Role of Particulate Matter in Scale Formation ....................................................... 35
4.3.3. Experimental Investigation of (NH4)2Mn2(SO4)3 Solubility................................... 38
4.4. Multivariate Analysis ..................................................................................................... 40
4.4.1. Effect of Selected Parameters on Vibration Intensity ............................................. 40
4.4.2. Effect of Selected Parameters on ID Booster Fan Efficiency ................................. 44
Chapter 5 ....................................................................................................................................... 51
5. Conclusions ........................................................................................................................... 51
Chapter 6 ....................................................................................................................................... 53
6. Recommendations for future work ........................................................................................ 53
References ..................................................................................................................................... 54
Appendices .................................................................................................................................... 56
Appendix A: Spent sulfite liquor analysis................................................................................. 56
Appendix B: XRD profiles of the rest of the ID booster fan scales .......................................... 57
Appendix C1: List of process parameters selected for MVA analysis ..................................... 58
vi
Appendix C2: Score scatter plots from mill data in 2015-2017 ................................................ 60
vii
List of Tables
Table 1. Chemical analyses of the sulfite pulp mill ID fan ash deposits (wt.% >1% shown) ........ 5
Table 2. Compositions of coal ash and the deposits in the coal-fired power plant......................... 6
Table 3. XRF results for four scale samples (values given in wt.%) ............................................ 17
Table 4. Raw data from ICP-OES analysis on scale samples (values given in wt.%) .................. 17
Table 5. Results from SEM-EDS powder analysis (values given in wt.%) .................................. 18
Table 6. SEM-EDS surface scan compositions (values given in wt.%) ....................................... 19
Table 7. Elements and compounds with corresponding analytical techniques ............................. 23
Table 8. Complete composition of ID fan scale and ID Booster scales (values given in wt.%) .. 24
Table 9. Estimated amount of each phase in ID fan scale and ID booster scale .......................... 24
Table 10. Results of mill solution analysis (values given in ppm) ............................................... 27
Table 11. Particulate analysis at the inlet of ID booster fan ......................................................... 36
Table 12. Solid content of liquors ................................................................................................. 56
Table 13. Analysis of Anions........................................................................................................ 56
Table 14. Analysis of elements by ICP-OES (Based on the dry weight of solids)....................... 56
Table 15. List of process parameters selected for MVA analysis ................................................. 58
viii
List of Figures
Figure 1. Schematic diagram of the recovery boiler system ........................................................... 3
Figure 2. Clean fan blades (left) and fouling fan blades (right)...................................................... 4
Figure 3. Schematic diagram of coal-fired power plant ................................................................. 6
Figure 4. Surface of scale samples with two distinct colors ........................................................... 8
Figure 5. Experimental setup for deposit sampling ........................................................................ 9
Figure 6. Deposit probe design ..................................................................................................... 10
Figure 7. Experimental setup for gas sampling ............................................................................ 11
Figure 8. Experimental setup for drying NH3 scrubber water ...................................................... 12
Figure 9. Experimental setup for mixing particulates and NH3 scrubber solution ....................... 13
Figure 10. Experimental setup for investigating (NH4)2Mn2(SO4)3 solubility ............................. 14
Figure 11. Scale samples obtained from the sulfite pulp mill....................................................... 15
Figure 12. Sampling locations of ID booster fan .......................................................................... 16
Figure 13 (a). XRD profile of the ID fan scale ............................................................................. 20
Figure 14. Composite results of scale elemental compositions .................................................... 22
Figure 15. Thermal profile of the ID booster fan (Outside the fan blade) .................................... 26
Figure 16. Thermal profile of the MnSO4 ..................................................................................... 26
Figure 17. Probe surfaces after 3-hour exposure to the flue gas ................................................... 28
Figure 18. Probe surfaces after 1-day exposure to the flue gas .................................................... 29
Figure 19. Group of pictures showing the deposit buildup after 38-day exposure to the flue gas 29
Figure 20. Illustration of the locations where deposits were built on the probe ........................... 30
Figure 21. Composite elemental analysis of ID booster fan and probe deposit ........................... 30
Figure 22. XRF profiles of the probe deposit ............................................................................... 31
ix
Figure 23. Probe surfaces after drying the solution containing (NH4)2SO4 and MnSO4. ............. 32
Figure 24. XRD profiles of the solid sample collected from the probe after 1-day drying of
solution containing (NH4)2SO4 and MnSO4 ................................................................................. 33
Figure 25. Probe surfaces after 1-day NH3 scrubber water drying. .............................................. 33
Figure 26. XRD profiles of the solid sample from the probe after 1-day of NH3 scrubber drying.
....................................................................................................................................................... 34
Figure 27. Probe surfaces after 6-day NH3 scrubber water drying. .............................................. 34
Figure 28. XRD profiles of the solid sample from the probe after 6-day of NH3 scrubber drying
....................................................................................................................................................... 35
Figure 29. ID fan scale before and after mixing with NH3 scrubber solution .............................. 37
Figure 30. XRD profile of the solid sample collected from the mixture of ID fan scale and NH3
scrubber solution ........................................................................................................................... 37
Figure 31 (a). Concentration of soluble Mn2+ in NH3 scrubber solution (1000, 2000 and 5000
ppm NH4+) at 60℃ as a function of time ...................................................................................... 39
Figure 32. (NH4)2Mn2(SO4)3 solubility in various NH3 scrubber solutions at T = 60℃. ............. 40
Figure 33. Score scatter plot for mill data in 2018 ....................................................................... 41
Figure 34 (a). Coefficient plot for vibration intensity from mill data in 2018.............................. 42
Figure 35 (a). Airflow/Amps versus time from fragmental mill data in 2018 .............................. 45
Figure 36. Score scatter plot for fragmental mill data in 2018 ..................................................... 47
Figure 37 (a). Coefficient plot for Airflow/Amps from fragmental mill data in 2018 ................. 48
Figure 38. Thermal profile of the ID booster fan (Inside the fan blade) ...................................... 57
Figure 39. Thermal profile of the ID booster fan (On the duct wall) ........................................... 57
Figure 40 (a). Score scatter plot for mill data in 2017 .................................................................. 60
x
Figure 41 (a). Score scatter plot for fragmental mill data in 2017 ................................................ 61
1
Chapter 1
1. Introduction
1.1. The Sulfite Process
The sulfite process is one of the two major types of chemical pulping processes in the pulp and
paper industry, the other one is the kraft process, also referred to as the sulfate process. The main
aim in the chemical pulping process is to delignify wood in order to produce pulp. The history of
the sulfite process can be retraced back to 1857, when Julius Roth first treated wood chips with
sulfurous acid. The sulfite pulping process became the dominant pulping method by 1900 [1].
Today the kraft process is the predominant pulping method for the three following reasons: the
high strength of kraft pulp, the ability to handle almost all species of fiber sources, and the
favorable economics due to high chemical recovery efficiency (~99%) [2]. However, fine writing
paper is most often made by the sulfite process, which provides excellent whiteness, good stability,
and reasonable strength, but with a lower yield and higher cost [3]. Sulfite pulps now account for
less than 10% of the total chemical pulp production and the number of sulfite pulp mills is still
decreasing [1].
In the sulfite process, wood chips are first brought to a digester, where the wood chips are cooked
using the pulping liquor at a high temperature (120-150℃) and high pressure (75-100 psig). The
pulping liquor is a mixture of sulfurous acid and its salts (Na+, NH4+, Mg2+, K+, or Ca2+). This
digestion process dissolves lignin in the pulping liquor and produces wood pulp and weak spent
sulfite liquor (red liquor). The red liquor is washed from the pulp, which is sent to the bleaching
plant, and the weak red liquor is sent to the multiple-effect evaporators and recovery boilers for
chemical and energy recovery. Alternatively, lignin can be recovered as lingo-sulfonate and
hemicelluloses converted to ethanol.
1.2. Sulfite Recovery Boiler and Flue Gas Cleaning
Chemical recovery is a key component of the pulping process. It has three main functions: i)
minimizing the environmental impact of the waste streams; ii) recycling pulping chemicals; iii)
co-generating steam and power. Several different schemes have been developed for chemical
2
recovery in the sulfite process depending on the cation used. In calcium based systems, which are
mostly found in older mills, chemical recovery is not practical, and the spent liquor is usually
discharged or incinerated. In sodium or potassium based operations, the energy and pulping
chemicals can be recovered, however, due to the complex chemistry, the chemical recovery is
process is more complicated and less efficient than the kraft process. In ammonium-based
operations, the energy, and much of the sulfur, can be recovered by combusting the spent liquor,
but the ammonia is converted to H2O and N2 when the red liquor is burned. The magnesium sulfite
process has the most well-developed and efficient recovery cycle. The magnesium and sulfur are
recovered in their oxidized forms, MgO and SO2. The sulfite pulp mill that had been studied in
this work uses the ammonium based sulfite process. The ammonium recovery system is introduced
in more detail below.
A schematic diagram of the chemical recovery process is shown in Figure 1. The first step is
concentration of the red liquor to 50-52% dry solids using evaporators in which steam is condensed
on one side of the heat transfer surface and water is evaporated from the red liquor on the other
side. This is accomplished by evaporators in series in which the red liquor is concentrated in stages.
At 50-52% dry solids, the red liquor still contains too much water for combustion to be sustained,
so a support fuel such as natural gas must be used. The spent sulfite liquor is sprayed into the boiler.
Steam is used to atomize the liquor to ensure the liquor is fully combusted. The hot flue gas
generated in the boiler flows through heat exchangers in the convective zone (superheaters, boiler
bank and economizers) to convert the boiler feedwater to high pressure steam. This steam is used
to generate process steam and electricity in a back pressure turbine. Air is introduced into the boiler
through forced draft fans and an induced draft fan is used to pull the combustion air through the
boiler and to keep the boiler slightly below atmospheric pressure so that hot flue gases do not leak
out of the boiler.
3
Figure 1. Schematic diagram of the recovery boiler system
After passing through the induced draft fan, the flue gas passes through a number of steps to
recover sulfur. The flue gas passes through an ID fan and then is split into four parallel lines. Each
includes a quench tower, an ammonia scrubber, a caustic scrubber and a wet electrostatic
precipitator. The quench tower uses a co-current water spray to cool down the hot flue gas from
200 to 70℃. The ammonium scrubbers have two stages to absorb sulfur dioxide gas using
ammonia as a scrubbing solution to regenerate the acid for the sulfite pulping process. Ammonia
is injected to the inlet stream of the second stage and the scrubbing solution from the second stage
flows down to the first. The caustic scrubbers are designed to lower the level of sulfur dioxide in
the flue gas to meet the environmental regulations. Wet electrostatic precipitators are designed for
flue gases saturated with water vapor. They are used to remove both particulate matters and liquid
droplets. A second induced draft fan is installed between the ammonia scrubbers and caustic
scrubbers. The one fan draws from all four ammonia scrubbers and feeds all four caustic scrubbers.
It is used to help move the flue gas though the scrubbing process, therefore it is named as induced
draft booster fan.
4
1.3. Induced Draft Booster Fan Scale Formation
There is significant scale buildup on the induced draft booster fan blades and the scales are
removed with hammers and high pressure water. Figure 2 shows both the clean and fouled fan
blades. The scale varies in color and is a mixture of light orange, browns and dark green. It also
appears to have flow patterns.
Figure 2. Clean fan blades (left) and fouling fan blades (right)
The scale formation on the ID booster fan blades leads to a mass unbalance on the fan and
consequently, the fan starts to vibrate. The fan vibration intensity is measured by the mill. When
the vibration reaches a determined threshold, the mill slows down the fan. Eventually the mill
needs to shut down the boiler (and mill) for 2 to 3 days and clean the fan, resulting in lost
production.
1.4. Objectives
The objective of this study is to identify the likely cause of the induced draft booster fan scaling
so that the mill can find a means of reducing the rate of scaling. The main approaches are:
1. Sample collection at the mill, both liquid and solid, and analysis;
2. Deposit probe measurements and gas sampling at the pulp mill;
3. Laboratory studies to explore variables affecting scale formation independently;
4. Multivariate analysis of mill process data to determine if a correlation could be found
between mill operation and fan blade scaling.
5
Chapter 2
2. Literature Review
Induced draft fan scaling
Scaling and fouling are common to all types of industries. In a pulp mill, scaling issues in black
liquor evaporators [4], boilers [5], superheaters and economizers [6], and green liquor system [7]
have all be extensively studied. ID fan scaling is also common to pulp mills, but the researches
conducted to investigate it are very limited, because in most instances it does not limit production
or cause significant operational problems. Only two previous works on ID fan scaling were found
and discussed in this section.
One study of ID fan scaling in an ammonium-based sulfite recovery boiler was found [8]. Massive
scale buildup was found to form at ID fan housing sidewalls and reduced the fan capacity to the
point where the boiler had to be shutdown over a period of 7-14 days, which is extremely fast. The
chemical composition was determined and listed below in Table 1. Differential thermal analysis
showed that except for sulfate, the deposits contained both pyrosulfate and bisulfates. The
formation mechanism appears to be the volatilized potassium and sodium in flue gases reacted
with sulfur trioxide (SO3) and formed small amounts of low-melting bisulfate salts. The molten
bisulfate salts can bind and hold the high-melting sulfates, resulting in significant deposits on the
cold-end surfaces.
Table 1. Chemical analyses of the sulfite pulp mill ID fan ash deposits (wt.% >1% shown)
Elements Ca K Na Mg Mn Si S
1st stage ID fan 6.7 9.7 2.9 2.8 1.5 1.1 20.2
2nd stage ID fan 5.9 8.3 2.2 2.5 1.6 0.9 20.5
Wang et al. [9] studied severe ash fouling on an ID fan blades in a coal-fired power plant. The
boiler and its gas cleaning configurations are shown in Figure 3. The ID fan is installed after the
selective catalytic reactor (SCR), heat exchangers, a dry electrostatic precipitator (ESP), and before
the wet flue gas desulfurization (WFGD) tower. The chemical composition of the deposits and the
coal used in the boiler is listed in Table 2. The elements showed up in the coal ash are in agreement
6
with those in deposits. The major phases identified in the deposits are calcium sulfate (CaSO4) and
its dehydrate (CaSO4·H2O), ammonium sulfate ((NH4)2SO4), tschermigite ((NH4)Al(SO4)2·12H2O)
and quartz (SiO2). A likely formation mechanism is that due to the low temperature, sulfuric acid
condensed and reacted with ash particles in the flue gas, the mixture of sulfate products and silica
particles has superior sticking propensity and consequently built up on the fan blade.
Figure 3. Schematic diagram of coal-fired power plant
Table 2. Compositions of coal ash and the deposits in the coal-fired power plant
Elements (wt.%) Si Al Ca Fe S Mg
Coal ash 18.0 7.8 12.3 8.3 4.6 0.8
Deposits 14.6 12.2 8.4 3.4 6.9 0.7
The sulfite pulp mill being studied in the first literature (earlier case) has the ID fan built right after
the boiler, which has a much higher operating temperature (200℃ minimum) than in the sulfite
mill in this study (about 60℃, current case). At this temperature, the condensation of sulfuric acid
is unlikely to occur, indicating that the molten salts can be contributing to this scale formation by
altering the physical behaviour of the ash.
The gas cleaning configuration in the second literature is similar to the one in the sulfite pulp mill
in this study. The ID fan investigated is located in the middle of the gas cleaning units, which
means that the temperature in the two cases are low, condensation of wet flue gas may play a role
7
in scale formation and deposition. In addition, ammonia (NH3) is involved in both two ID scale
formations, it can be a important reactant in scale formation and therefore determine the properties
(physical and chemical) of the products. However, the fuel in recovery boiler (red liquor) in the
sulfite pulp mill has a more complex chemistry (more elements from the wood), therefore the ID
booster fan scale formation in the sulfite pulp mill is still different from the literature and needs to
be investigated.
Chapter 3
3. Methodology
3.1. Mill Sample Analysis
3.1.1. Analytical Techniques Used in Mill Samples Analysis
X-Ray Fluorescence (XRF) was used to determine the elemental composition (mostly inorganics)
of solid samples, it was performed by S2 Ranger energy dispersive X-ray fluorescence
spectrometry (Bruker). Power X-Ray diffraction (XRD) was performed using a Philips XRD
system with a PW 1830 HT generator, a PW 1050 goniometer, PW3710 control electronics and
X-Pert system software, to identify the phases of the bulk material. XRD profiles were compared
and matched with the International Centre for Diffraction Data (ICDD) database.
Thermogravimetric Analysis (TGA) was performed on solid samples using a TA Instruments
STD-Q600 Simultaneous Thermogravimetry and Differential Scanning Calorimeter (TGA/DSC).
The sample was equilibrated in a N2 environment at 20°C then the temperature was ramped at
20°C/min to 1000 °C.
The concentration of metal ions was determined using an Agilent 700 Series Inductively Coupled
Plasma Optical Emission Spectrometer (ICP-OES), which was calibrated and calculated using
reference solutions prepared with a standard solution (Fisher Chemical, 1000 ppm ± 1%). For
sample preparation, the samples (solid and liquid) were digested using 70% nitric acid at 95℃ for
two hours in digestion block (SCP Science). Then the solutions were filtered using 0.2 μm nylon
filter (Basix), and the filtrate was diluted with 5% nitric acid. Concentrations of ammonium (NH4+),
8
sulfate (SO42-) ions were determined using DionexTM AquionTM ion chromatography (IC) system
(Thermo Scientific). For IC analysis, solid samples were dissolved in deionized water at 95℃ for
two hours and the filtrate was diluted with deionized water as well since nitrate ions can affect the
peak position of cations.
3.1.2. Induced Draft Booster Fan Scale Analysis
A total of four scale samples (one from the ID fan, three from the ID booster fan) were collected
from the sulfite mill during a mill visit in November, 2017. To prepare the samples, a small amount
of scale (approximately 5g) was collected from each of the samples, ground into fine powders
using a mortar and pestle, dried at 110 ℃ for 12 hours (to remove water content before analysis)
and kept in a re-sealable zipper storage bags for storage. The powdered scale samples were then
analyzed by XRF, XRD, TGA/DSC, ICP-OES, IC and SEM-EDS. SEM-EDS has been used to
perform two analyses, one is elemental analysis of powdered scale samples and the other is surface
scan on two areas with distinct color differences (from one piece of scale) as is shown below, in
Figure 4.
Figure 4. Surface of scale samples with two distinct colors
3.1.3. Mill Solution Analysis
Three liquid samples (quench tower solution, 1st and 2nd stage NH3 scrubber solutions) were
collected from the sulfite pulp mill on Feb 1, 2018 and Oct 12, 2018, respectively. The analytical
techniques used are ICP-OES and IC analysis.
9
3.2. Sampling Campaign at the Sulfite Mill
A mill sampling campaign was conducted at this sulfite pulp mill in October 2018 to understand
the recovery boiler system and to study the ID booster fan scale formation. Two main experiments
were:
1. Setting up a deposit probe in a sampling port located at the inlet of ID booster fan to know
the chemical composition of fresh particles in the flue gas and to gain insights into the
deposition mechanism.
2. Sampling of the flue gas in the same sampling port to understand the environment of scale
formation.
3.2.1. Equipment and Materials
The deposit sampling campaign was conducted using a 316L stainless steel probe, Figure 6. The
probe has a 1-inch O.D. and is 80 inches long. This put the end of the probe about 5 inches away
from the wall of the gas duct upstream of the ID booster fan, Figure 5. The end of the probe was
threaded, allowing a 4-inch metal ring to be threaded on. For a new run to start, the metal ring can
be simply replaced by a new one and the probe will be reinserted. Both two ends of the probe were
sealed by rubber stoppers to prevent gas leaking from the pipe. A Teflon sleeve was used at the
insertion point. An adjustable metal support was used to keep the probe steady supported.
Figure 5. Experimental setup for deposit sampling
10
Figure 6. Deposit probe design
The gas sampling was conducted by using a vacuum pump (Model DOA-P704, GAST) to extract
flue gas through a 3/8 inch O.D., 80 inches long 304L stainless steel tubing, Figure 7. All the
equipment was connected by 1/4 inch I.D., PVC tubing (McMaster-Carr). An acetal plastic, push-
to-connect adapter (McMaster-Carr) was installed to connect stainless steel tubing and plastic
tubing. Four 125mL impingers were connected in series. A 0.1N sulfuric acid (H2SO4) solution
was used to capture ammonia (NH3) and a 3% hydrogen peroxide (H2O2) solution was used to
capture sulfur dioxide (SO2) [10, 11]. An empty tube was used first to capture droplets/condensate
from the gas. A drying tube with drierite (CaSO4) was connected to the impingers in order to
absorb potential liquid carryover from the impingers to protect the vacuum pump. A flowmeter
(Model Air 605, MATHESON) was used to measure the flow rate of extracted flue gas.
During the ammonia collection, preparation of the four impingers are: The first and second
impingers are filled with 50mL of 0.1N sulfuric acid, the third impinge is filled with 50mL of 3%
hydrogen peroxide in order to clean the flue gas and prevent inhaling sulfur dioxide and the last
one was left empty to condense water content. The sulfur dioxide sampling train was using the
same setup but switching the two impinger solutions. The solutions were diluted with deionized
water and analyzed by IC to measure the concentrations of ammonium (NH4+) and sulfate (SO4
2-).
11
Figure 7. Experimental setup for gas sampling
3.2.2. Experimental Plan
There are three runs in total for deposit sampling. The first run took 3 hours and it followed by a
1-day and a 38-day run. This was done to understand the aging effect on scale formation by
exposing the deposit probe to flue gas for different periods of time. All the sampling rings with
deposits (if any) were kept in zippered plastic bags and taken to the lab at the university for analysis.
XRD, ICP-OES and IC analysis were carried out as outlined in Section 3.1.1.
For gas sampling, two runs were performed (one for capturing NH3 and one for SO2). Each run
took 5 mins and the impinger solutions were collected using sample bottles. IC analysis were
carried out as outlined in Section 3.1.1.
3.3. Laboratory Experiments
3.3.1. Lab Studies of Deposit Formation Mechanism
Experiments were carried out using a piece of galvanized steel gas duct (4 inches I.D. and 1 ft.
long), Figure 8. A 316 L stainless steel probe was inserted through the wall of gas duct. A beaker
contains NH3 scrubber solution was placed in the gas duct and the solution was transferred by a
12
FisherbrandTM variable-flow peristaltic pump (Fisher Scientific), droplets that are not dried on the
probe would drop to the beaker for recirculation. Supplied air was humidified by bubbling water
and preheated to 60℃ and to simulate the flue gas in the duct, it passed through a glass tubing and
dried the NH3 scrubber water on the probe. The temperature inside the gas duct was set at 60℃
and controlled by heating tape. The deposit formed on the probe was collected by spatula and
analyzed by XRD analysis.
Three experiments were conducted to study the connection between NH3 scrubber solution and the
ID booster fan scale formation. The first experiment is adding 1g MnSO4 to 20mL deionized water
to make MnSO4 solution, then mixing it with 20mL NH3 scrubber solution. The second experiment
is using 300mL NH3 scrubber solution to recirculate in the experimental setup and it was a one-
day run. In the third experiment, 3L NH3 scrubber solution was dried for six days with a rotating
probe (same experimental setup but a longer run than the second trial).
Figure 8. Experimental setup for drying NH3 scrubber water
3.3.2. Lab Studies of Powdered ID fan Scale and NH3 Scrubber Water
Experiments were run to identify the reaction products between particulate in the flue gas and
ammonia scrubber solution. Since the particle samples in the flue gas were not collected during
the mill visit, ID fan deposits (which were powdery) was selected as a substitute of particulate
13
matter due to similar chemical compositions. One gram powdered ID fan scale was scattered in
the aluminum tray and 1mL NH3 scrubber solution was added in droplets by pipette, Figure 9. The
tray with mixture was then put in an oven and dried at 60℃. After the liquid was totally evaporated,
the remaining solids were collected and analyzed by XRD analysis.
Figure 9. Experimental setup for mixing particulates and NH3 scrubber solution
3.3.3. Experimental Investigation of (NH4)2Mn2(SO4)3 Solubility
Equilibrium experiments were carried out to determine the solubility of Mn in ammonia scrubber
water at different levels of dilution, Figure 10. This was done to vary the concentration of NH4+
and SO42-. Five 100mL Erlenmeyer flasks with magnetic stirrers were held at a fixed temperature
in a water bath. Silicone oil was added to the top of the water bath to reduce water evaporation.
The heating plate underneath has both temperature and stirrer speed control for the magnetic
stirrers.
Manganese sulfate (MnSO4) was used as the source of manganese and the solvent is the NH3
scrubber solution acquired from the pulp mill in Oct. 2018. To prepare the solutions, NH3 scrubber
solutions from the pulp mill were diluted to five different levels (20000, 10000, 5000, 2000, 1000
ppm NH4+) and 1g MnSO4 was added to 100 mL of each solution. One sample was taken for the
first four sample collections and two samples were taken starting from the fifth sample collection.
Liquid sample was taken from the flask using a 3mL syringe (with needle) and immediately filtered
using 0.2 µm nylon syringe filter. The filtrate was then diluted with 5% nitric acid (HNO3) and
manganese concentration was determined using ICP-OES.
14
Figure 10. Experimental setup for investigating (NH4)2Mn2(SO4)3 solubility
3.4. Multivariate Analysis
Multivariate analysis was carried out to determine if one or more process parameters could be
identified as the root causes of the ID Booster fan scaling. Four years of hourly average operating
data was collected for the boiler and from other recovery processes. To quantify ID booster fan
scale formation, two values were considered: one is ID booster fan vibration intensity; the other is
ID booster fan air flow rate over fan amps (a calculation on the fan efficiency, which is expected
decrease with increasing scale formation).
Multivariate analysis is an effective statistical method to summarize data tables with multiple
variables by creating several new variables containing most of the information. These new latent
variables are then used for problem solving and display (i.e., classification, correlations and more).
The new variables, called the scores, denoted by t, are created as weighted linear combinations of
the original variables and each observation has a t value.
In this study, a commercially available software package SIMCA 14 (Umetrics; Umeå, Sweden)
was used to construct an MVA model using mill operating data. The program uses PCA and OPLS
and to summarize the information from the observations.
15
Chapter 4
4. Results and Discussion
4.1. Mill Sample Analysis
4.1.1. Induced Draft Booster Fan Scale Analysis
Four scale samples in total were collected and tested (one from the ID fan (Sample A), three from
the ID booster fan). Photographs of the four scale samples from the sulfite pulp mill are shown in
Figure 11. The first scale sample was obtained from the ID fan, the sample was soft (mostly powder;
the chunks are relatively easy to break apart) and light grey in color. Three samples were collected
from different locations on the ID booster fan: Inside the fan blade (Sample B), outside the fan
blade (Sample C) and on the duct wall (Sample D), Figure 12. They share the similar physical
properties: light orange and dark green in colour and are both hard and difficult to remove from
the fan blade.
Figure 11. Scale samples obtained from the sulfite pulp mill
16
Figure 12. Sampling locations of ID booster fan
In order to determine the chemical composition of the scale samples, multiple analytical techniques
were applied. XRF, ICP-OES, IC & SEM-EDS analysis were used to perform elemental analysis
while XRD analysis was done to identify the phases in the fan scales. A complete chemical
composition was established by gathering all the analytical results.
XRF, ICP-OES, IC and SEM-EDS analysis
Table 3 shows raw XRF results of the four powdered scale samples. The elements in this analysis
are listed as oxides. It is because the standards used in this analysis are geological standards, where
metals are usually present in oxides, therefore, any metals detected will be reported as oxides.
Table 4 and Table 5 show the raw results from ICP-OES and SEM-EDS analysis, respectively.
They are both elemental analysis. After compared with results from XRF analysis, some findings
were observed. The concentration of most metal ions from the three analysis methods are similar,
indicating that the results of the elemental analysis are accurate, XRF result were taken for the
following composite analysis because it is measured in wt% and easy for calculation in the
composite analysis. The amount of sulfur and manganese are significantly lower in the XRF results
than as determined by SEM-EDS and ICP-OES analysis, while SEM-EDS and ICP-OES are
reporting similar results. Therefore, measurements of sulfur and manganese from ICP-OES
analysis were used in this composite analysis, rather than the results from XRF.
17
Table 3. XRF results for four scale samples (values given in wt.%)
Oxides ID fan Inside Outside Wall
MgO 5.75 0.43 0.37 0.27
Al2O3 1.57 0.44 0.34 0.4
SiO2 1.29 1.35 1.34 0.81
SO3 39.07 38.93 39.26 39.29
Cl 0.27 0.25 0.24 0.22
K2O 6.25 0.68 0.64 0.65
CaO 14.18 13.11 13.37 12.31
MnO 1.79 4.04 4.09 4.40
Fe2O3 1.01 3.09 3.06 3.17
ZnO 0.28 2.64 2.43 2.19
BaO 0.22 1.42 2.33 1.37
Sum 75.73 75.89 74.87 72.69
Table 4. Raw data from ICP-OES analysis on scale samples (values given in wt.%)
Elements ID fan Inside Outside Wall
S 24.6 24.0 22.6 23.2
Ca 12.4 10.4 9.64 9.19
Mn 1.90 9.95 9.92 9.33
N 0.06 7.90 7.18 8.80
K 6.25 0.68 0.64 0.65
Mg 5.33 0.25 0.23 0.21
Zn 0.28 2.64 2.43 2.19
Fe 1.01 1.75 1.72 1.90
Ba 0.22 1.42 2.33 1.37
Al 1.57 0.44 0.34 0.40
18
Table 5. Results from SEM-EDS powder analysis (values given in wt.%)
Elements ID fan Inside Outside Wall
O 44 40 40 41
S 22 26 26 25
Ca 14 11 14 10
Mn 2.3 12 10 12
K 9.6 0.6 0.6 0.7
Mg 3.3 N.D. N.D. N.D.
Surface scan of scale sample by SEM-EDS
Area analysis by SEM-EDS was conducted in order to determine if the various colors on the
deposits were the result of significant different compositions. Two areas (one dark green and one
light orange area) from one scale sample were analyzed. Two area scans were performed of each.
Table 6 shows the results of compositions from SEM-EDS. The elements with the largest
differences are given in bold.
From the table, it can be found that the piece with light color (orange area) has higher oxygen,
sulfur and nitrogen. Based on the possible compounds, it has a higher amount of ammonium sulfate.
The one with dark color has significantly higher calcium content and no nitrogen, so it is largely
calcium sulfate. The amount of manganese is similar in all samples. One possible explanation is
that the N, Ca, Mn are from different sources (e.g. gas, water and particles). The deposit probe
measurements and laboratory experiments in the following sections helped clarify the sources of
these elements.
19
Table 6. SEM-EDS surface scan compositions (values given in wt.%)
Elements Light_1 Light_2 Dark_1 Dark_2
O 47 46 52 51
S 28 27 22 22
N 8.9 7.5 N.D. N.D.
Ca 4.6 3.7 12 15
Mn 6.9 13 9.3 7.6
K 2.0 1.6 0.5 0.5
Zn 2.1 6.0 N.D. 1.9
Fe 0.5 1.1 1.0 1.1
XRD Analysis
XRD analysis was done to identify the phases in the four fan scales. Figure 13 (a) - (d) are the
XRD peak patterns generated. After matching the peak patterns with the ICDD Powder Diffraction
database, potential chemical phases were matched and shown in the same graph. All peaks in ID
fan and ID booster fan scale patterns were identified.
Different phases were found in ID fan and ID booster fan scales. In the profile from ID fan scale,
the major peaks of calcium sulfate (CaSO4) can be found at 25.4º, 31.4º, 38.6º, 40.8º, and the rest
of the major peaks (21.9º, 28.3º and 33.6º) were identified as a potassium and magnesium double
salt, K2Mg2(SO4)3. In the profile from ID booster fan scale, major peaks at 20.9º, 27.6º, 29.4º,
32.8º, 35.6º and 43º were identified as two different phases of a double salt, manganese ammonium
sulfate, (NH4)2Mn2(SO4)3 and (NH4)2Mn(SO4)2·H2O. Peaks of calcium sulfate (CaSO4) and
ammonium sulfate ((NH4)2SO4) were also identified.
20
Figure 13 (a). XRD profile of the ID fan scale
Figure 13 (b). XRD profile of the ID booster fan scale (Outside the fan blade)
0
400
800
1200
1600
20 25 30 35 40 45 50 55 60
Co
un
ts
Position 2θ
CaSO4
K2Mg2(SO4)3
0
100
200
300
400
20 25 30 35 40 45 50 55
Co
un
ts
Position 2θ
(NH4)2SO4
(NH4)2Mn(SO4)2·H2O
(NH4)2Mn2(SO4)3
CaSO4
21
Figure 13 (c). XRD profile of the ID booster fan scale (Inside the fan blade)
Figure 13 (d). XRD profile of the ID booster fan scale (On the duct wall)
0
100
200
300
400
20 25 30 35 40 45 50 55
Co
un
ts
Position 2θ
(NH4)2SO4
(NH4)2Mn(SO4)2·H2O
(NH4)2Mn2(SO4)3
CaSO4
0
100
200
300
400
20 25 30 35 40 45 50 55
Co
un
ts
Position 2θ
(NH4)2SO4
(NH4)2Mn(SO4)2·H2O
(NH4)2Mn2(SO4)3
CaSO4
22
Composite Elemental Analysis and Phase identification
The values in Figure 14 are composite elemental analysis based on results from XRF, SEM-EDS,
ICP-OES and IC analysis (Only elements with wt% > 1% are shown). Elements and ions with their
corresponding analytical techniques are shown in Table 7. The analysis used for each element in
the composite composition is in bold. Sulfur and calcium are the two major elements in all four
scale samples (close to 23% and 10%, respectively). The ID booster fan scales contain more
manganese (close to 10%), nitrogen (about 7%, in the form of ammonium), iron, zinc and barium
than the ID fan deposit, and less potassium and magnesium. The concentration differences between
three ID Booster fan scales are small, suggesting that the source of deposition is the same for all
locations in the ID Booster fan.
Figure 14. Composite results of scale elemental compositions
0
5
10
15
20
25
S Ca Mn N K Mg Zn Fe Ba Al
Co
nce
ntr
atio
n(w
t.%
)
Tested elements
ID fan
Inside
Outside
Wall
23
Table 7. Elements and compounds with corresponding analytical techniques
Elements and compounds Techniques
Ammonium IC
Sulfur XRF, ICP-OES
Calcium XRF, ICP-OES
Manganese XRF, ICP-OES, SEM-EDS
Potassium XRF, ICP-OES
Magnesium XRF, ICP-OES
Aluminum XRF, ICP-OES
Iron XRF, ICP-OES
Zinc XRF, ICP-OES
Barium XRF, ICP-OES
Table 8 provides a complete calculated chemical composition based on results from all analytical
techniques applied to the scale samples. The pH of a 5 wt% d.s. solution of each sample and the
calculated cation to anion ratio are listed as well. The pH tells the acidity or basicity of the solids
in solution and the cation/anion ratio was used to check the charge balance in the solid.
The concentration of sulfur (sulfate) is high enough, that most of the Ca, Mg and K likely exist as
sulfates although there might be small amounts of oxides and the low pH of the 5 wt.% solution
of the ID fan scale sample indicates presence of bisulfate. Manganese ammonium sulfate
((NH4)2Mn2(SO4)3) was the salt containing Mn found using XRD analysis. Ammonium ions may
also be present as ammonium sulfate ((NH4)2SO4). Iron, zinc, aluminum are assumed to be present
as oxides. For the ID fan scale, the sum of all components is close to 100%, which suggests that
most of the scale is known. Carbon (char) appeared to be present in the ID scale sample. CHNS
analysis was used to determine carbon content and the amount of carbon is about 0.9% in the ID
fan scale. For the ID Booster fan, the sum of compositions are all close to 100%.
The charge balances in all ID booster fan scales are close to one, but the charge balance on the ID
fan scale has a cation to anion ratio as 0.75, which indicates that there are more cations existing.
Part of the sulfate can be in the form of bisulfate, but the presence of bisulfate does not fully explain
the small ratio, a missing cation is likely to exist.
24
Table 8. Complete composition of ID fan scale and ID Booster scales (values given in wt.%)
In wt.% ID fan Inside Outside Wall
Ca2+ 12.43 10.35 9.64 9.19
Mn2+ 2.51 9.94 9.92 9.33
NH4+ 0.06 7.90 7.17 8.80
K+ 5.19 0.56 0.53 0.54
Mg2+ 3.47 0.25 0.23 0.21
Na+ 0.37 0.17 0.16 0.13
SO42- 73.92 65.98 62.15 63.70
Al2O3 1.6 0.4 0.3 0.4
Fe2O3 0.9 2.6 2.6 2.7
ZnO 0.3 2.6 2.4 2.2
BaO 0.2 1.4 2.3 1.4
SiO2 1.3 1.4 1.3 0.8
C%+H% 0.9% N.D. N.D. N.D.
Total 102% 104% 98% 99%
Cations to anions ratio 0.75 1.01 1.02 1.02
pH 2.7 5.4 5.7 6.0
Table 9. Estimated amount of each phase in ID fan scale and ID booster scale
ID fan scale ID booster scale
CaSO4 ~ 42% (NH4)2Mn2(SO4)3 ~ 39%
K2Mg2(SO4)3 ~ 29% CaSO4 ~ 33%
Sulfates (Mn, Na) ~ 8% (NH4)2SO4 ~ 17%
Oxides ~ 5% Oxides ~ 8%
Organics ~ 1% Sulfates (K, Mg) ~ 2%
Sum ~ 85% Sum ~ 99%
25
TGA/DSC Analysis
TGA/DSC analysis was performed to study the weight loss and melting of fan scales which can
be used to identify the presence of certain species. Figure 15 is the TGA curve generated for ID
booster fan scale (Outside the fan blade). The rest two of them are shown in Appendix B. All three
have similar weight loss profiles and thermal reactions, and are therefore discussed collectively.
There are two major weight losses. Between 200 and 400℃, the weight loss is about 30%. This is
likely the decomposition of ammonium sulfate [12, 13]. A typical thermal profile of ammonium
sulfate shows a two-step decomposition: The first step occurs at 200-300℃, in which (NH4)2SO4
will convert to (NH4)2S2O7 and release NH3 and H2O (Rxn. 1). The second step is a total
decomposition of (NH4)2S2O7, which takes place at 300-400℃ (Rxn. 2).
2(𝑁𝐻4)2𝑆𝑂4(𝑠)→ (𝑁𝐻4)2𝑆2𝑂7(𝑠)
+ 2𝑁𝐻3(𝑔)+ 𝐻2𝑂(𝑔) (Rxn. 1)
3(𝑁𝐻4)2𝑆2𝑂7(𝑠) → 2𝑁𝐻3(𝑔)
+ 6𝑆𝑂2(𝑔)+ 2𝑁2(𝑔)
+ 9𝐻2𝑂(𝑔) (Rxn. 2)
The thermal events of ID booster fan scale decomposition between 200 and 400℃ are consistent
with the literature, but the weight loss for each step does not match. From the literature, the weight
loss is larger in the second stage since the salt is totally decomposed in this stage, but the TGA
weight loss profile shows the opposite. It should also be noted that the literature reports the thermal
decomposition of pure ammonium sulfate but the scale sample in this study contains
(NH4)2Mn2(SO4)3, (NH4)2SO4 and little bisulfate, which is a more complex mixture. Therefore, the
literature is only contributing to the speculation of the phases in the scale. The second weight loss
of the ID booster fan scale decomposition is seen between 800 and 900℃ and corresponds to
manganese sulfate decomposition, resulting in a 12.5% weight loss. A reference curve for MnSO4
decomposition is provided in Figure 16. A 10% weight loss at 250℃ is likely the dehydration of
MnSO4 salts and MnSO4 decomposes between 800 and 900℃, resulting in a 45% weight loss (loss
of SO3 and SO2). The TGA/DSC results also implied that when (NH4)2Mn2(SO4)3 is ramp heated,
it is likely to decompose to (NH4)2SO4 and MnSO4 first between 200-400℃.
26
Figure 15. Thermal profile of the ID booster fan (Outside the fan blade)
Figure 16. Thermal profile of the MnSO4
-4
-3
-2
-1
0
1
2
0
10
20
30
40
50
60
70
80
90
100
0 200 400 600 800 1000
Wei
gh
t p
erce
nta
ge
(%)
Temperature (℃)
Weight
Heat Flow
(Normalized)
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
1
2
0
10
20
30
40
50
60
70
80
90
100
0 200 400 600 800 1000
Wei
gh
t p
erce
nta
ge
(%)
Temperature (℃)
Weight
Heat Flow
(Normalized)
27
4.1.2. Mill Solution Analysis
The concentrations of three mill solutions received in early 2018 were summarized in Table 10.
Multiple solution samples were pulled from the three locations during the sampling campaign in
Oct 2018. It is noticed that the variation in NH4+ concentration is significant and it can go up to
30000 ppm. However, the concentrations of metal ions were constant and extremely low compared
to NH4+. It was found that both the quench tower solution and the NH3 scrubber water have all the
ionic species found in the scale, indicating that these solutions can be the source of the scales. The
quench tower solution has much higher metal ions and little sulfur and ammonium compared to
the NH3 scrubber solution. The two NH3 scrubber solutions have similar concentrations for all the
metal ions and the 2nd stage NH3 scrubber has more ammonium (NH4
+) dissolved in the solution.
It can be expected because liquid ammonia is injected at the second stage. From the calculation, it
can be determined that the NH3 scrubber solution has approximately 2.1g/100mL NH4+, which is
around 7.7g/100mL (NH4)2SO4.
Table 10. Results of mill solution analysis (values given in ppm)
Quench tower NH3 scrubber 1st stage NH3 scrubber 2nd stage
Ca 560 11 9.6
Mn 140 1.6 1.1
K 400 53 59
Mg 220 3.4 2.9
Fe 26 0.5 0.7
Si 320 6.6 23
S 1100 9000 13000
NH4 150 21000 22000
pH (without dilution)
pH 2.5 6.1 6.5
28
4.2. Sampling Campaign at the Sulfite Mill
Field test at the pulp mill was a starting point of investigating the scaling mechanism. Deposit
probe measurements were performed for different lengths of time. This was done to gain
information on the aging effect and to understand how fast the scales built up. Figure 17 is the
picture of the deposit ring after 3 hrs exposure to the flue gas. White solids was seen on the probe
surface and there is very little deposit. The solids show drag marks, which suggests that the flue
gas in the duct has high water content and the small droplets spread out and dried out on the probe.
The solid is too little to be analyzed by XRD, but after being dissolved in deionized water, NH4+
can be detected. A reasonable speculation is that the solid is mostly (NH4)2SO4 precipitated from
the drying of droplets of the ammonia scrubber solution. After only three hours, there was no clear
deposit similar to the ID booster fan scale.
Figure 17. Probe surfaces after 3-hour exposure to the flue gas
Figure 18 is a photograph taken of the probe surfaces after 1-day exposure to the flue gas. Some
white solids were observed on the surface. It appears to be that the flue gas impinged the probe
and salts started to nucleate at the edge of the tube. However, only a thin layer of solids (orange in
colour) was built up at the edge of the probe and the solids was still not enough for XRD analysis.
The observation suggests that the deposit is slow growing, therefore, a long-term experiment was
carried out.
29
Figure 18. Probe surfaces after 1-day exposure to the flue gas
Figure 19 is a group of pictures depicting the deposit buildup after 38 days exposure to the flue
gas. Clear deposits were observed on the probe. Scales formed at two locations only but not
uniformly distributed. The scales appear to have nucleated at several locations and then grown
from there. The deposits are mostly orange with dark green areas, which is similar in appearance
to the scale samples collected from the ID booster fan blades. Based on measurements, the two
spots are both about 5 inches away from the two facing ducting walls, Figure 20.
Figure 19. Group of pictures showing the deposit buildup after 38-day exposure to the flue gas
30
Figure 20. Illustration of the locations where deposits were built on the probe
The chemical analysis of probe deposits is shown in Figure 21, along with the composition of ID
booster fan scale that was presented earlier in Figure 15. The elemental compositions of ID booster
fan scale and probe deposit are similar. The probe deposit has lower calcium, nitrogen (ammonium)
and barium, but the differences are small. XRD analysis also indicates that the probe deposit
contains the same phases as those ones shown in ID booster fan, Figure 22.
Figure 21. Composite elemental analysis of ID booster fan and probe deposit
0
5
10
15
20
25
S Mn Ca N Zn Ba Fe K Al Mg
Wei
gh
t p
erce
nta
ge
(in %
)
Tested elements
ID booster fan
Deposit
31
Figure 22. XRF profiles of the probe deposit
The deposit probe sampling indicates that the scale formation occurs over weeks and the carryover
droplets from NH3 scrubber hit the fan and dry out and nucleate at a certain location, results in
scaling. Furthermore, the chemical composition of probe deposit is similar to the ID booster fan
scale, which indicates that the source for the two deposits is the same and factors such as pressure
gradients in the ID booster fan pressure are not key to the mechanism of scale formation. Thus it
was concluded that a simple laboratory probe set-up could be used to consider some variables
independently.
The concentration of NH3 and SO2 was determined by analyzing and calculating the NH4+ and
SO42- in the impinger solutions combined with the measured gas flow through the impingers. The
SO2 level was 440 and 370 ppmv, NH3 level was 330 and 300 ppmv on the two days of the
measurements, which are in good agreement. However, there is no clear indication that the gas
phase is critical to scale formation.
0
500
1000
1500
10 20 30 40 50 60 70 80
Co
un
ts
Position 2θ
(NH3)2Mn2(SO4)3
(NH4)2Zn(SO4)2
CaSO4·0.5H2O
32
4.3. Laboratory Experiments
4.3.1. Laboratory Probe Studies
The chemical analysis of ID booster fan scale and NH3 scrubber water show that the NH3 scrubber
water has all the species found in the scale. That said, the concentrations of Ca2+ and Mn2+ in the
scrubber water are low compared to NH4+ and SO4
2- in the scrubber water. The source of Mn found
in the scale was not obvious.
In the first trial, MnSO4 was added to the NH3 scrubber water to see if (NH4)2Mn2(SO4)3 would
precipitate. When adding the 20mL MnSO4 solution to 20mL of NH3 scrubber solution, significant
amount of white salt precipitated. In order to fully dissolve the salts, 360mL deionized water was
added to the mixture (400mL in total) to dilute the solution. This diluted solution was then used in
the laboratory probe study. Droplets were dropped on the probe surface in the presence of
humidified air at 60 °C. The probe surface after the experiment is shown in Figure 23. The
precipitated salts had to be scraped from the probe surface. The XRD profile of the solid is a great
match to the double salt (NH4)2Mn2(SO4)3, indicating that this was the primary salt precipitated
from the initial solution of dissolved MnSO4 and (NH4)2SO4, Figure 24. The deposits are hard and
adhesive to steel surface, meaning that (NH4)2Mn2(SO4)3 is likely to cause hard scale formation
on the ID booster fan.
Figure 23. Probe surfaces after drying the solution containing (NH4)2SO4 and MnSO4.
33
Figure 24. XRD profiles of the solid sample collected from the probe after 1-day drying of solution
containing (NH4)2SO4 and MnSO4
Figure 25 is the photograph of the probe after a trial with ammonia scrubber water from the mill
with no other additions. The precipitated salt is wet, soft, and easy to remove. The XRD profiles
match to (NH4)2SO4’s pattern in ICDD database. The major peak of (NH4)2SO4 can be found at
16.9º, 20.4º, 20.6º, 23º, 28.6º, 29.4º, Figure 26. This is likely the source of the (NH4)2SO4 found in
the ID booster fan scale, but it does not form the hard scale found on the ID booster fan blades.
Figure 25. Probe surfaces after 1-day NH3 scrubber water drying.
0
1000
2000
3000
4000
5000
10 20 30 40 50 60 70 80
Co
un
ts
Position 2θ
(NH4)2Mn2(SO4)3
(NH4)2SO4
34
Figure 26. XRD profiles of the solid sample from the probe after 1-day of NH3 scrubber drying.
The observations from the second trial were expected since the concentration of Mn in NH3
scrubber is only 2 mg/L, if all precipitated from the 300 ml of solution used, only 2.4 mg
(NH4)2Mn2(SO4)3 would precipitate along with 22g (NH4)2SO4, which is still below 2% of the
solids and cannot be detected by XRD analysis. A longer experiment was carried out using a
rotating probe, which could allow the (NH4)2SO4 to fall off. Figure 27 is the picture of the probe
after a 6-day run. The observations are similar to the first trial. A small amount of white solids
were collected, and the XRD profile indicates that all the peaks are from (NH4)2SO4, Figure 28.
Figure 27. Probe surfaces after 6-day NH3 scrubber water drying.
0
5000
10000
15000
20000
25000
10 20 30 40 50 60 70 80
Co
un
ts
Position 2θ
(NH4)2SO4
35
Figure 28. XRD profiles of the solid sample from the probe after 6-day of NH3 scrubber drying
The results from the three experiments showed that the double salt (NH4)2Mn2(SO4)3, which is a
major component of the ID booster fan scale, can form through crystallization from an aqueous
solution containing NH4+, Mn2+ and SO4
2-. It has a low solubility and is likely to precipitate in
(NH4)2SO4 solution, which is the main cause for scale formation on the ID booster fan blade and
gas phase composition does not seem to be crucial. However, evaporation of NH3 scrubber solution
produces mostly (NH4)2SO4 because there is much more NH4+ than Mn2+ in the solution, therefore,
NH3 scrubber water may not be the main source of Mn, indicating that a source of Mn plays a role
in the hard scale formation.
4.3.2. Role of Particulate Matter in Scale Formation
Another factor considered is particulate matter flowing in the flue gas. A report on the particulate
analysis (analyzed and written in 2016) at the ID booster fan was provided by the pulp mill and
this was used as no particulate samples were collected. The results were summarized in Table 11.
Comparison to ID fan scale’s composition shows that the ratio of the metals are close, except for
a very high potassium and sodium in the particulates. Therefore, ID fan scale was chosen as a good
substitute of particulate matter in the following experiments.
0
1000
2000
3000
4000
5000
10 20 30 40 50 60 70 80
Co
un
ts
Position 2θ
(NH4)2SO4
36
Table 11. Particulate analysis at the inlet of ID booster fan
Metals (in wt.%) Particulate matters ID fan scale
Potassium 82 0.6
Sodium 5.8 0.4
Calcium 4.7 12
Manganese 3.3 2.0
Magnesium 1.3 3.5
Iron 1.0 0.9
Zinc 0.2 0.3
Barium 0.1 0.2
Color changes can be observed visually. Figure 29 shows the picture of ID fan scale before and
after mixing with NH3 scrubber solution at 60℃ in the laboratory. After the mixture was totally
dried, the precipitated salt is both orange and dark green, which has a similar appearance to the ID
booster fan. The XRD profiles were matched to the phase patterns of CaSO4 and (NH4)2Mn2(SO4)3
found in ICDD database, Figure 30. The results suggested that mixing the ID fan scale and NH3
scrubber water can form the double salt (NH4)2Mn2(SO4)3. Since the ID fan scale and the
particulate matter flowing in the flue gas share similar chemical composition, it can be concluded
that a mixture of particulate matter and NH3 scrubber solution can form (NH4)2Mn2(SO4)3 and the
particulates flowing in the duct can be the main source of Mn.
37
Figure 29. ID fan scale before and after mixing with NH3 scrubber solution
Figure 30. XRD profile of the solid sample collected from the mixture of ID fan scale and NH3
scrubber solution
0
500
1000
1500
2000
10 20 30 40 50 60 70 80
Co
un
ts
Position 2θ
(NH3)2Mn2(SO4)3
CaSO4
38
4.3.3. Experimental Investigation of (NH4)2Mn2(SO4)3 Solubility
The laboratory experiments showed that the formation of (NH4)2Mn2(SO4)3 is key to ID booster
fan scaling and it appears that the partial dissolution of solid particles and the subsequent
precipitation of the double salt is the key to the hard scale formation. Therefore this experiment
was to investigate the solubility of double salt (NH4)2Mn2(SO4)3 in the NH3 scrubber solution at
60℃ and the effect of NH4+ concentration on the (NH4)2Mn2(SO4)3 solubility. The ammonia
scrubber water was diluted to give NH4+ concentrations of 20,000, 10,000, 5,000, 2,000, 1,000
ppm NH4+). One gram of MnSO4 was added to 100 ml of the 5 solutions with differing NH4
+
concentration. Samples were taken at regular time intervals and analyzed for Mn concentration
using ICP-OES. From the experiment discussed in 4.3.1, it can be concluded that the main product
after adding MnSO4 to NH3 scrubber solution is (NH4)2Mn2(SO4)3, so one assumption made in this
experiment is that all Mn2+ ion added were reacted and were existing as (NH4)2Mn2(SO4)3.
The observation for the solution with 1000 ppm NH4+ is slightly different. During the solution
preparation, the solution was clear at first when MnSO4 was added, more salts were precipitated
after stirring for about 5 minutes. It indicates that the reaction between (NH4)2SO4 and MnSO4
take place in aqueous phase and forms (NH4)2Mn2(SO4)3. This double salt then crystallizes and
the amount of precipitation is affected by the concentration of NH4+. Figure 31 (a) and (b) give the
concentration of Mn in solution as a function of time for the solutions with different NH4+
concentrations. From the figure, all five systems appear to reach the equilibrium in 2 hours.
Figure 32 shows the soluble manganese at 60℃ in solutions with various NH4+ concentrations
(1000 to 20000 ppm). The solubility was found to decrease with respect to increasing NH4+
concentration. The values decreased from 1.22g/100g solution to 0.004g/100g solution. When the
NH4+ concentration is below 10000 ppm, there is a linear relationship between Mn solubility and
the NH4+ concentration. And the solubility of (NH4)2Mn2(SO4)3 is close to zero when there is more
than 10000 ppm NH4+ in the solution. This indicates the double salt has a extremely low solubility
in NH3 scrubber solution.
This observation can be helpful in determining the amount of wash water necessary should the
mill decide use sprays on the ID booster fan to keep it clean. A higher water flow rate will lower
the chance of (NH4)2Mn2(SO4)3 double salt formation.
39
Figure 31 (a). Concentration of soluble Mn2+ in NH3 scrubber solution (1000, 2000 and 5000 ppm
NH4+) at 60℃ as a function of time
Figure 31 (b). Concentration of soluble Mn2+ in NH3 scrubber solution (10000, 20000 ppm NH4+)
at 60℃ as a function of time
0
0.3
0.6
0.9
1.2
1.5
0 20 40 60 80 100 120
(NH
4)2
Mn
2(S
O4)3
So
lub
ilit
y
g/1
00
g s
olu
tion
Time (h)
1000 ppm
2000 ppm
5000 ppm
0
0.005
0.01
0.015
0 20 40 60 80 100 120
(NH
4)2
Mn
2(S
O4)3
So
lub
ilit
y
g/1
00
g s
olu
tion
Time (h)
10000 ppm
20000 ppm
40
Figure 32. (NH4)2Mn2(SO4)3 solubility in various NH3 scrubber solutions at T = 60℃.
4.4. Multivariate Analysis
4.4.1. Effect of Selected Parameters on Vibration Intensity
Vibration intensity is the measurement the mill follows to determine if the ID booster fan needs to
be slowed down or stopped and cleaned. Vibration intensity is measured at multiple points in the
ID booster fan. Therefore it is used as the target parameter in the first trial.
Hourly average operating data from the pulp mill was used in this study to build a statistical model.
Table 15 in Appendix C1 lists the parameters selected. For MVA, an OPLS model was built, where
vibration intensity was first set as the output (Y variables) and all other process parameters were
set as inputs (X variables). The model uses all X variables to explain and predict the changes in Y
variables.
Figure 33 shows the score scatter plot for the OPLS model built from mill data in 2018 with 8208
observations. Each data point on the scatter plot represents one instance for all variables, in this
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.5 1 1.5 2 2.5
(NH
4)2
Mn
2(S
O4)3
So
lub
ilit
y
g/1
00
g s
olu
tion
Concentration of ammonium (ppm)x 10000
41
case hourly average value for all operating parameters. The ellipse represents a 95% confidence
interval of the data and the origin of the graph represents the average value across all variables.
The further away a point is from the origin (shown by X), the greater it deviates from the average.
Points clustered together on the scatter plot on each quadrant have similar collective characteristics
and can be connected back to specific operating conditions. It can be seen from Figure 33 that
most of the data points in year 2018 fit within the 95% CI, meaning that the model explains the
data moderately. The graphs for 2015-2017 were shown in Appendix C2. There are still many
observations outside the ellipse. The spread of the data points on the scatter plot demonstrates there
are many instances where operating parameters are far from average.
Figure 33. Score scatter plot for mill data in 2018
To determine the correlation of each X variable on the Y variables separately, a coefficient plot is
used where the contribution of each X variable on the corresponding Y variable is determined by
a positive or negative coefficient. Figure 34(a) shows the coefficient plot for the 2018 data from
the OPLS model for vibration intensity set as the Y variable. ID booster fan speed, vacuum to ID
booster and boiler burner temperature have the highest positive coefficients, whereas natural gas
42
flow and oxygen in flue gas have the most significant negative effect on vibration intensity. The
positive effects of ID booster fan speed and vacuum to ID booster fan on vibration intensity are
reasonable since more vibration happens if the fan speed is higher; the negative coefficients are
difficult to explain by process characteristics. However, the observations from year 2015-2017 do
not agree well with those from 2018, Figure 34(b)-(d). For instance, oxygen content in flue gas
was negatively correlated to vibration intensity from 2017 and 2018 data, but it has a strong
positive correlation to vibration based on data in 2015 and 2016. More process parameters were
found to have a positive correlation in some years and negative correlation in others. For one single
process parameter, it is impractical to have two opposing influences on ID booster scale formation.
Therefore, it can be concluded that vibration intensity may not be a good indicator of the amount
of scale formed on the fan blade. This is reasonable as vibration intensity is not directly a measure
of scale formation, but rather is an indication of an imbalance in the scale.
Figure 34 (a). Coefficient plot for vibration intensity from mill data in 2018
43
Figure 34 (b). Coefficient plot for vibration intensity from mill data in 2017
Figure 34 (c). Coefficient plot for vibration intensity from mill data in 2016
44
Figure 34 (d). Coefficient plot for vibration intensity from mill data in 2015
4.4.2. Effect of Selected Parameters on ID Booster Fan Efficiency
Another output that was considered was ID booster fan air flow rate divided by the fan current,
which is an expression of fan efficiency. With more scales attached to the fan blade, it should take
more energy for gas flow. Additionally, the presence of scale likely reduces the amount of air that
can be moved through the fan. Therefore, the fan efficiency may be proportional to the amount of
scale formed on the fan blades, which should be a good indicator of scale formation. Plotting the
fan efficiency (airflow/amps) versus time, it can be found that after a cleanup in May, the efficiency
tends to decrease for a month and half, indicating the scales was building up during this time period,
Figure 35(a)-(d). However, more variables can affect this number (Airflow/Amps). For example,
increasing the ID booster fan rotational speed increases the flow of air and reduces the load of the
ID booster fan. No clear way was found to incorporate the affect of these other factors and reduce
the fluctuation in the data. Therefore, MVA was performed using the data from the month and half
following a fan cleaning.
45
Figure 35 (a). Airflow/Amps versus time from fragmental mill data in 2018
Figure 35 (b). Airflow/Amps versus time from fragmental mill data in 2017
y = -5.2915x + 233342
3000
3500
4000
4500
5000
5500
6000
5/15/2018 5/25/2018 6/4/2018 6/14/2018 6/24/2018 7/4/2018
Air
flow
/Am
ps
y = -2.9034x + 129169
3000
3500
4000
4500
5000
5500
6000
5/16/2017 5/26/2017 6/5/2017 6/15/2017 6/25/2017 7/5/2017
Air
flow
/Am
ps
46
Figure 35 (c). Airflow/Amps versus time from fragmental mill data in 2016
Figure 35 (d). Airflow/Amps versus time from fragmental mill data in 2015
y = -2.9325x + 129252
3000
3500
4000
4500
5000
5500
6000
5/10/2016 5/20/2016 5/30/2016 6/9/2016 6/19/2016 6/29/2016
Air
flow
/Am
ps
y = -5.6903x + 244111
3000
3500
4000
4500
5000
5500
6000
5/15/2015 5/25/2015 6/4/2015 6/14/2015 6/24/2015 7/4/2015
Air
flow
/Am
ps
47
Figure 36 shows the score scatter plot for the new OPLS model built from mill data in 2018 with
895 observations. It can be seen from Figure 38 that most of the data points in year 2018 fit within
the 95% CI, meaning that the model explains the data well. The graphs for 2015-2017 exhibit the
same distribution and are shown in Appendix C2.
Figure 36. Score scatter plot for fragmental mill data in 2018
Figure 37(a) shows the coefficient plot for the ID booster fan efficiency. The positively correlated
parameters with fan efficiency for all four years are ID fan air flow and natural gas flow rate,
Figure 37(b)-(d). The ID booster fan efficiency was calculated by ID fan air flow, so the strong
positive correlation with this variable was expected. For natural gas flow rate, one possible
explanation is that the total gas flow increased. This is directly related to air flow rate and probably
no connections with the scale formation. The conclusion was that the correlations found cannot be
associated with ID booster fan scaling, so Airflow/Amps is not a good target parameter either.
48
Figure 37 (a). Coefficient plot for Airflow/Amps from fragmental mill data in 2018
Figure 37 (b). Coefficient plot for Airflow/Amps from fragmental mill data in 2017
49
Figure 37 (c). Coefficient plot for Airflow/Amps from fragmental mill data in 2016
Figure 37 (d). Coefficient plot for Airflow/Amps from fragmental mill data in 2015
50
From the MVA results, it can be found that the statistical models built can explain the observations
well (observations mostly within the 95% confidence interval and good R2 values). However, the
process parameters found to be correlated with scale formation were hard to be practically
explained by the process. There are three possible causes: 1. The two outputs selected to perform
MVA are not good indicators of ID booster fan scaling. ID booster fan vibration intensity in the
first trial measures instant fan blade movement, which means that a change in vibration intensity
can be also caused by a piece of scale falling off instead of scale formation. And changes in fan
speed may cause vibrations as well. Airflow/Amps seems to correlate well with scale formation in
first a month and half after fan cleaning, but then fluctuate in the following months, which is not
likely correlated to scale formation. 2. Some process parameters are manually controlled by the
mill operators to respond certain incidents (for instance, slowing down the ID booster fan speed
when there is violent fan vibration.). Then the correlations between process parameters and scale
formation were interfered and therefore difficult to find. 3. The mill data still needs more
preprocessing (for example, identifying outliers and data selection).
51
Chapter 5
5. Conclusions
A fundamental study was performed to investigate ID booster fan scale formation in a sulfite pulp
mill, first by collecting and analyzing mill samples (solid and liquid), and then by sampling
campaigns (setting up deposit probe and sampling flue gas) and laboratory experiments to study
scale formation mechanism. Lastly, multivariate analysis was used to find potential correlations
between mill operations and scale formation.
The ID booster fan scale is slightly acidic and consists of about 40% (NH4)2Mn2(SO4)3, 33%
CaSO4, 17% (NH4)2SO4, 8% metal oxides and 2% metal sulfates (mostly K, Mg). The source of
all three ID booster fan scales collected from different locations is the same. The key reactions for
the formation of the tenacious deposit appears to be the partial dissolution of MnSO4 in the ash
particles from the boiler in NH3 scrubber water and the subsequent precipitation of manganese
ammonium sulfate. This appears to bind the other deposit components such as ammonia sulfate
and calcium sulfate and is the component responsible for the hard nature of the deposit.
The probe study during sampling campaign indicates that ID booster fan scaling takes place over
weeks. Analysis of the air flow/amps ratio also indicated that scale build-up occurs over four to
six weeks after cleaning.
While the MVA analysis results showed that statistical models built can explain the observations
well (observations mostly within the 95% confidence interval and good R2 values), the results are
not consistent for all four years (2015-2018) indicating that the MVA may not be a good tool for
identifying the process parameters leading to scaling. This is because the scaling rate is slow,
taking place over weeks. Vibration intensity represents an unbalance in the scale, but not scale
build-up directly; and while airflow/amps is correlated to scaling, it is also influenced by other
factors that result in variability over short time intervals that are not related to scaling.
Ultimately, the scaling appears to be caused by too much particulate and ammonia scrubber
solution being carried over to the ID booster fan. Possible solutions include checking that air flow
distribution between the four sets of condensers and ammonia scrubber towers is even, confirming
there isn’t channeling in the ammonia scrubber tours and improving the system for removing
52
droplets from the gas exiting the ammonia scrubber towers. It may also be possible to go to a wet
ID booster fan arrangement in which the blades are continuously washed in order to prevent the
precipitation of salts on the surface. Our results would tend to indicate that such a system would
need to be very thorough as once the manganese ammonium sulfate deposit starts to form, it cannot
be washed. Anything that can be done upstream to limit carryover of scrubber water and particulate
should be done first.
53
Chapter 6
6. Recommendations for future work
Through the various analytical techniques, the overall composition of ID booster fan scale was
determined. However, more work is still needed to clarify some details regarding the ID booster
fan scale.
Surface scan on areas with different colors (light and dark) was performed. The
dark area has similar amount of Mn but no N (NH4+) comparing to the light area.
The form of Mn in the darker area will be worthy to investigate since it is unlikely
to be (NH4)2Mn2(SO4)3 and no more Mn compounds was found through bulk
analysis.
TGA analysis supported the idea that (NH4)2Mn2(SO4)3 decomposes to (NH4)2SO4
and MnSO4 at lower temperature and then the two chemicals decompose separately.
But the weight loss profile of (NH4)2SO4 was different from the literature, which is
needed to be investigated and explained. An experimental setup includes: Glass
tube (holding the scale samples), Bunsen burner (heating), thermometer (measuring
temperature), impingers (collecting gas products for analysis).
A reasonable scaling mechanism of ID booster fan was proposed in this work. But
the actual scale formation was still unknown because it occurs inside the ID booster
fan and cannot be seen. A fiber optic camera is recommended to put into a deposit
probe and insert into the sampling port at the ID booster fan inlet. This will help
the mill understand the scale formation visually.
Study of the washing solution that will be sprayed on the fan blades and used to
prevent (NH4)2Mn2(SO4)3 formation.
54
References
[1] Biermann, C. J., Essentials of pulping and papermaking. San Diego, CA: Academic Press,
1993.
[2] H. N. Tran and E. K. Vakkilainnen, “The Kraft Chemical Recovery Process,” in TAPPI
Kraft Recovery Short Course, St. Petersburg, FL, 2012.
[3] R. J. Hernandez and S. E. Selke, “Packaging: papers for sacks and bags,” in Encyclopedia
of Materials: Science and Technology, East Lansing: Elsevier Ltd., 2001, pp. 6642-6646.
[4] W. Schmidl and J. Frederick, “Controlling soluble scale deposition in black liquor
evaporators and high solids concentrations,” The Institute of Paper Science And
Technology, Atlanta, Georgia, Project F016-02, May 1999.
[5] M. Hupa, “Recovery boiler chemical principles,” TAPPI Kraft Recovery Short Course. St.
Petersburg, FL: TAPPI PRESS, 2012.
[6] A. F. Stam, K. Haasnoot, G. Brem, “Superheater fouling in a BFB boiler firing wood-based
fuel blends,” Fuel, vol. 135, Jun., pp. 322-331, 2014
[7] A. Giglio, “Calcite Scale Formation in the Green Liquor Handling System of the Kraft
Chemical Recovery Process” M.A.Sc thesis, University of Toronto, Toronto, ON, 2018.
[8] J. J. Leithem, R. J. Engen, M. W. Folsom and T. L. Pulliam, “Control of fireside ash
deposits in an ammonia-base sulfite recovery furnace,” Tappi, vol. 61, no. 10, Oct., pp. 37-
40, 1978.
[9] Y. Wang, H. Tan, K. Dong, H. Liu, J. Xiao and J. Zhang, “Study of ash fouling on the
blade of induced fan in a 330 MW coal-fired power plant with ultra-low pollutant emission,”
Applied Thermal Engineering, vol. 118, May, pp. 283-291, 2017
[10] United States Environmental Protection Agency, “Method 6C - Sulfur Dioxide -
Instrumental Analyzer Procedure,” United States Environmental Protection Agency, 2017.
[online] Available: https://www.epa.gov/sites/production/files/2017-08/documents/
method_6c.pdf [Accessed: Apr. 1, 2018].
55
[11] United States Environmental Protection Agency, “Field Test of Ammonia
Collection/Analysis Method,” United States Environmental Protection Agency, 1995.
[online] Available: https://www3.epa.gov/ttnemc01/ctm/NH3validation.pdf [Accessed:
Apr. 1, 2018]
[12] R. Kiyoura and K. Urano, “ Mechanism, Kinetics, and Equilibrium of Thermal
Decomposition of Ammonium Sulfate,” Industrial & Engineering Chemistry Process
Design and Development, vol. 9, no. 4, pp. 489-494, 1970.
[13] W. D. Halstead, “Thermal Decomposition of Ammonium Sulphate,” Journal of Applied
Chemistry, vol. 20, no. 4, pp. Apr., 1970.
56
Appendices
Appendix A: Spent sulfite liquor analysis
Table 12. Solid content of liquors
Liquor Solid content, %
Heavy liquor (2018-3-23) 50.04
Heavy liquor (2018-4-12) 44.68
Table 13. Analysis of Anions
liquor chloride Sulfite Sulfate Thiosulfate
mg/L mg/L mg/L mg/L
Heavy liquor (2018-3-23) 492 2281 18992 139
Heavy liquor (2018-4-12) 219 2962 17997 472
Table 14. Analysis of elements by ICP-OES (Based on the dry weight of solids)
Elements (in ppm) Heavy liquor Heavy liquor Heavy liquor
3/23/2018 4/12/2018 2/1/2018
S 75810 79130 72146
Ca 972 978 963
K 814 843 818
Mg 240 250 252
Mn 144 132 165
P 62 65 66
Fe 16 61 22
Zn 19 17 20
57
Appendix B: XRD profiles of the rest of the ID booster fan scales
Figure 38. Thermal profile of the ID booster fan (Inside the fan blade)
Figure 39. Thermal profile of the ID booster fan (On the duct wall)
-4
-3
-2
-1
0
1
2
0
10
20
30
40
50
60
70
80
90
100
0 200 400 600 800 1000
Wei
gh
t p
erce
nta
ge
(%)
Temperature (℃)
Weight
Heat Flow
(Normalized)
-4
-3
-2
-1
0
1
2
0
10
20
30
40
50
60
70
80
90
100
0 200 400 600 800 1000
Wei
gh
t p
erce
nta
ge
(%)
Temperature (℃)
Weight
Heat Flow
(Normalized)
58
Appendix C1: List of process parameters selected for MVA analysis
Table 15. List of process parameters selected for MVA analysis
List of process parameters
ID fan and ID booster fan NH3 scrubbers
ID booster fan vibration - Non-driving end NH3 injection rate at 1st stage
ID booster fan vibration - Driving end NH3 injection rate at 2nd stage
Vacuum to ID booster fan Recirculation stream flow rate at 1st stage
SO2 concentration in ID booster fan Recirculation stream pH at 1st stage
ID Booster fan temperature Recirculation stream temperature at 1st stage
ID booster fan speed Recirculation stream conductivity at 1st stage
Oxygen in the stack Recirculation stream flow rate at 2nd stage
Carbon monoxide in the stack Recirculation stream pH at 2nd stage
Stack gas temperature Recirculation stream temperature at 2nd stage
ID fan speed Recirculation stream conductivity at 2nd stage
Boilers NH3 scrubber 2nd stage outlet temperature
Oxygen in boiler Water levels in 1st stage NH3 scrubber
Liquor injection rate Caustics injection rate
Primary air flow rate Filtered mill water flow rate
Atomizing steam pressure Quench tower
59
Atomizing steam flow rate Recirculation stream flow rate
Natural gas burner temperature Recirculation stream pH
Natural gas injection rate Recirculation stream turbidity
Liquor tanks Filtered mill water flow rate
Red liquor temperature Quench tower inlet temperature
Red liquor dry solids Quench tower HX outlet temperature
Acid wash temperature Water levels in quench tower
Acid wash dry solids
NH3 injection rate
60
Appendix C2: Score scatter plots from mill data in 2015-2017
Figure 40 (a). Score scatter plot for mill data in 2017
Figure 40 (b). Score scatter plot for mill data in 2016
61
Figure 40 (c). Score scatter plot for mill data in 2015
Figure 41 (a). Score scatter plot for fragmental mill data in 2017
62
Figure 41 (b). Score scatter plot for fragmental mill data in 2016
Figure 41 (c). Score scatter plot for fragmental mill data in 2015
