REDUCTION OF TRS EMISSIONS
FROM LIME KILNS
Bahar Aminvaziri
A thesis submitted in conformity with the requirements
for the degree of Master‟s of Engineering
Graduate Department of Chemical Engineering and Applied Chemistry
University of Toronto
© Copyright by Bahar Aminvaziri (2009)
ii
Reduction of TRS Emissions from Lime Kilns
Master‟s of Engineering
Bahar Aminvaziri
Chemical Engineering and Applied Chemistry
University of Toronto
2009
ABSTRACT
The pulp and paper industry has been struggling to meet the new and stringent TRS
(Total Reduced Sulphur) emission compliance standards established in recent years.
However, a new approach by some regulatory bodies gives intricate operational parameters
a new and important role in achieving environmental compliance. TRS compounds that
cause the distinctive pulp mill odour, originate from sodium sulphide in white liquor used in
the kraft pulping process. Up to 20% of TRS emissions could originate from the lime kiln and
lime mud solids content is one of the operational parameters that could help reduce the TRS
emissions from the lime kiln. Residual sodium sulphide in the lime mud that results in TRS
gases, is dissolved in the moisture content of the mud. Although efficient lime mud washing
can remove most of the residual sodium sulphide, the remaining moisture content of the
mud still contains some sodium sulphide. Therefore, improved lime mud dewatering can be
effective in reducing the TRS emissions from the lime kiln. Data presented in this study
confirms that as the lime mud solids content increases, TRS emissions from the lime kiln
decrease. Data analysis demonstrates a negative linear correlation at 5% significance level
between TRS emissions and lime mud solids.
iii
ACKNOWLEDGEMENTS
This project would not have been possible without Professor
Honghi Tran‟s invaluable guidance, direction and patience.
I would also like to thank each and every staff member of the
Graduate Office at the Department of Chemical Engineering and
Applied Chemistry for their guidance and assistance throughout
this journey that started in 2004.
Bahar Aminvaziri
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TABLE OF CONTENTS
Page No.
ABSTRACT .................................................................................................................................. i
1. OBJECTIVES .................................................................................................................. 1
2. APPROACH .................................................................................................................... 2
3. INTRODUCTION ............................................................................................................. 3
4. LITERATURE REVIEW ................................................................................................... 6
4.1 TRS Compounds ................................................................................................. 6
4.1.1 Uses ......................................................................................................... 6
4.1.2 Environmental Fate .................................................................................. 7
4.1.3 Toxicology and Health Effects .................................................................. 8
4.2 Current Standards Regulating TRS ...................................................................... 9
4.2.1 Recent MOE‟s TRS Policies ................................................................... 10
4.3 Kraft Process ..................................................................................................... 12
4.3.1 Sodium Cycle ......................................................................................... 13
4.3.2 Calcium Cycle ........................................................................................ 17
4.3.3 Sulphur Recovery ................................................................................... 19
4.4 TRS Emission Reduction Measures ................................................................... 20
4.5 Reduction of Lime Kiln TRS Emissions .............................................................. 22
4.5.1 Excess Oxygen ...................................................................................... 23
4.5.2 Temperature ........................................................................................... 23
4.5.3 Fuel ........................................................................................................ 24
4.5.4 Lime Mud Washing ................................................................................. 24
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4.5.5 Lime Mud Dewatering............................................................................. 26
4.5.6 Scrubbing Flue Gases ............................................................................ 26
5. DATA ANALYSIS AND DISCUSSION ........................................................................... 28
5.1 Kiln A ................................................................................................................. 28
5.2 Kiln B ................................................................................................................. 30
5.3 Kiln C ................................................................................................................. 31
5.4 Statistical Analysis ............................................................................................. 32
6. CONCLUSIONS AND RECOMMENDATIONS .............................................................. 35
7. REFERENCES .............................................................................................................. 36
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LIST OF TABLES Page No.
Table 4-1: Odour thresholds of TRS Compounds (MOE, 2007) ........................................... 6
Figure 4-1: The Two Cycles of Kraft Pulping (Tran, 2008) ...................................................13
Table 4-2: Point Source Emission Estimates (Pinkerton, 1999) ...........................................20
Table 4-3: TRS Emissions Across U.S. Prior to 1979 (U.S. EPA 1979) ...............................20
Table 5-1: Parameters analyzed for each kiln .....................................................................28
Table 5-2: Regression Statistics for Kiln B Data ..................................................................34
Table 5-3: 95% Confidence Interval for Kiln B Data ............................................................34
LIST OF FIGURES Page No.
Figure 4-1: The Two Cycles of Kraft Pulping (Tran, 2008) ...................................................13
Figure 5-1: Flue Gas TRS Content vs. Mud Solids at Kiln A ................................................29
Figure 5-2: Flue Gas TRS Content vs. NCG Flowrate at Kiln A ...........................................29
Figure 5-3: TRS vs. Firing End Temperature at Kiln A .........................................................30
Figure 5-4: TRS vs. Lime Mud Solids at Kiln B ....................................................................31
Figure 5-5: TRS vs. Lime Mud Solids at Kiln C....................................................................32
Figure 5-6: Regression Analysis for Kiln B Data ..................................................................33
LIST OF APPENDICES Page No.
APPENDIX A – Sample Operational Data...............................................................................38
APPENDIX B – Jurisdictional Scan for TRS Emission Limits..................................................40
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ABBREVIATIONS
AAQC Ontario‟s Ambient Air Quality Criteria
ADP Air Dried Pulp
CCME Canadian Council of Ministers of Environment
DCE Direct contact Evaporators (DCE)
EC European Commission
IPPC Integrated Pollution Prevention and Control
MERAF Multi-pollutant Emission Reduction Analysis Foundation
MOE Ontario Ministry of the Environment
NCASI National Council of Paper Industry for Air and Stream Improvement Inc
NCG Non-Condensable Gases
NDCE Non-Direct Contact Evaporators
O.Reg 419/05 Ontario‟s Air Quality Regulation
POI Point of Impingement
TRS Total Reduced Sulphur
U.S. EPA United States Environmental Protection Agency
VOC Volatile Organic Compound
1
1. OBJECTIVES
The objectives of this study were to conduct a literature review on operational
parameters that affect the Total Reduced Sulphur (TRS) emissions from lime kilns and
suggest ways to reduce these emissions by confirming their effectiveness through data
analysis.
The study first reviewed the kraft pulping process and its main sources of TRS
emissions. As lime kilns were identified as one of the main sources, the focus was placed
on establishing the correlations between kiln operating parameters and TRS emissions.
2
2. APPROACH
The literature review for this study focused on various Best Available Techniques to
reduce TRS emissions from the pulping process, recommended by the European
Commission (EU), United States Environmental Protection Agency (U.S. EPA), Environment
Canada (EC) and various researchers around the world. Process optimization was
identified as one of most recent techniques that are practiced in order to reduce TRS
emissions. Since lime mud solids content was found to be one of the lesser researched
operational parameters that have been identified for process optimization of a lime kiln, this
parameter was then chosen as the subject of data analysis.
Operational data of three lime kilns were collected from two kraft pulp mills in
Canada and one in New Zealand and analyzed to examine for a correlation between lime
mud solids content and TRS emissions. Once a correlation was observed to support that an
increase in lime mud solids content results in decreased TRS emissions, other operational
parameters were investigated to rule out a similar trend between those and TRS emissions.
The absence of other correlations confirmed the hypotheses that link lime mud solids
contend and TRS emissions from a lime kiln.
Analysis of the data sets involved linear regression analysis and a 95% confidence
interval to confirm a negative correlation coefficient.
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3. INTRODUCTION
TRS (total reduced sulphur compounds) consist of mainly hydrogen sulphide, methyl
mercaptan, dimethyl sulphide and dimethyl disulphide. In the pulp and paper industry, these
odorous compounds originate from sodium sulphide which is a necessary component of the
white liquor in kraft pulping process. In Ontario, approximately 74% of TRS emissions come
from the pulp and paper sector (MOE, 2007). In the last decade, environmental regulatory
bodies have moved to impose more stringent air compliance standards for these
compounds. In Ontario, many rounds of consultations with the pulp and paper sector have
uncovered economic and feasibility challenges that these new standards create for this
struggling industry. Therefore, the government is adopting a new approach that evaluates a
facility‟s compliance based on implemented operational improvements that result in a
reduction of air emissions rather than meeting the stringent air quality standards. This new
regulatory regime gives intricate operational parameters a new and important role in
achieving environmental compliance for the pulp and paper sector.
It has been reported that up to 20% of the ground level TRS concentration near a
kraft mill could originate from its lime kiln (Jarvensivu et al, 1999). Amongst the operational
parameters that could help reduce these emissions from the lime kiln, increasing the lime
mud solids content (i.e. dewatering) plays a major role and is the subject of this study.
Pulp and paper mills have continuously decreased TRS emissions by improving
process technologies and applying pollution prevention plans in the past two decades.
Data collected from a large number of pulp and paper mills across the United States show
that although pulp and paper production using the kraft process has increased dramatically
over the past two decades, the overall TRS emissions have been reduced by about 85%
(Das and Jain, 2001).
4
High concentrations of TRS gases cause serious health effects such as paralysis,
pulmonary oedema and respiratory irritation (MOE, 2005). However, TRS emissions from
kraft pulp mills are sufficiently low that don‟t cause adverse health impacts, but still produce
an unpleasant odour (MOE, 2005). Currently, most air quality standards worldwide for TRS
are odour-based.
The odour perception thresholds of compounds vary from person to person and
depend on age, gender and smoking habits. However, it is generally reported that the
odour threshold for hydrogen sulphide is about 5 µg/m3, 1.2 µg/m3 for methyl mercaptan, 28
µg/m3 for dimethyl sulphide and 66 µg/m3 for dimethyl disulphide (MOE, 2007). Research
has shown that hydrogen sulphide can react with paints containing heavy metals to make
them darker over time, which has a potential aesthetically negative socio-economic impact
on communities who live close to kraft mills (U.S. EPA, 1979).
In the kraft pulping process, lignin is separated from wood fibres in a process that
emits TRS gases, due to presence of sodium sulphide (Na2S) in the white liquor. Major
point sources of TRS gases are kraft recovery furnaces, smelt dissolving tanks, lime kilns,
black liquor oxidation systems, digesters, evaporators, brown stock washers, turpentine
recovery systems, tall oil systems, liquor storage tanks, and condensate strippers
(Pinkerton, 1999).
Numerous technology improvements have lead to a significant reduction in TRS
emissions from kraft pulp mills. The improvements include the installation of black liquor
oxidizers, replacement of direct contact evaporator furnaces with non-direct contact
evaporators, improved lime mud washing and installation of non-condensable gas collection
and combustion systems (Das and Jain, 2001). TRS emissions from lime kilns have
decreased mainly through improved kiln design and process modifications such as better
lime mud washing to remove sulphides (Pinkerton, 1999).
5
Residual sodium sulphide in the lime mud is responsible for the majority of TRS
emissions from a lime kiln. Sodium sulphide in lime mud reacts with water and carbon
dioxide to produce hydrogen sulphide in the lime kiln over the temperature range of 200 to
250 °C (Jarvensivu et al, 1999).
Data presented in this study verifies that as lime mud solids increase, TRS
emissions from the lime kiln decrease. It has been suggested that the residual sulphide in
the lime mud is dissolved in the moisture content of the mud. Although efficient lime mud
washing can remove most of the residual sodium sulphide, the remaining moisture content
of the mud still contains some sodium sulphide. Therefore, improved lime mud dewatering
can be effective in reducing the TRS emissions from the lime kiln. In a case study in 1994,
the use of dewatering aids increased the mud solids from 65% to 72%, while reducing lime
kiln fuel consumption, lowering TRS emissions and resulting in better quality lime production
(Ford, 1994).
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4. LITERATURE REVIEW
4.1 TRS COMPOUNDS
TRS compounds include mainly hydrogen sulphide, methyl mercaptan, dimethyl
sulphide and dimethyl disulphide. This mixture is colourless but has an unpleasant odour
that can be described as rotten egg and rotten cabbage. Table 4-1 shows the odour
threshold of each ingredient. TRS compounds are soluble in alcohol, ether and water,
except for dimethyl disulphide, which is insoluble in water.
TABLE 4-1: ODOUR THRESHOLDS OF TRS COMPOUNDS (MOE, 2007)
Compound Odour Threshold
Range (µg/m3) Odour Threshold
Mean (µg/m3)
Hydrogen Sulphide 1.6-270 5
Methyl Mercaptan 0.0003-81 1.2
Dimethyl Sulphide 2.58-51 28
Dimethyl Disulphide - 66
4.1.1 Uses
Hydrogen sulphide is used as a reagent and intermediate in the production of other
reduced sulphur compounds, sulphuric acid, and in the precipitation of sulphides from
metals. Other uses include additives in lubricants and oils, agricultural disinfectants, and
metallurgical applications. Large quantities of hydrogen sulphide are used in the production
of heavy water, for use in nuclear power reactors.
Methyl mercaptan has been used as a gas odourant for natural gas, as an
intermediate in the production of pesticides and jet fuel, and in the synthesis of plastics,
flavours and food additives.
Dimethyl sulphide is utilized as an intermediate product in the synthesis of dimethyl
sulphoxide, as a catalyst pre-activator, as a gas odourant, and as a solvent for anhydrous
7
mineral salts. Dimethyl disulphide is used as a sulphating agent for certain industrial
catalysts and also permitted by the U.S. Food and Drug Administration for direct use on
food as a flavouring agent.
4.1.2 Environmental Fate
Hydrogen sulphide exists as a vapour in the atmosphere, dissolves in water and
moist environments and could deposit on soil. This gas has a residence time of up to 40
days in the atmosphere, depending on several conditions such as ambient temperatures,
humidity, sunlight and the presence of other pollutants (MOE, 2007). It does not undergo
photolysis or photochemical reaction with oxygen but, it may be oxidized by hydroxyl
radicals to form sulph-hydryl radical (SH-), and eventually sulphur dioxide and sulphate
compounds (MOE, 2007).
Hydrogen sulphide is not expected to bioconcentrate or biomagnify in the food chain,
since it can be biologically degraded to elemental sulphur.
Unlike hydrogen sulphide, methyl mercaptan in air is degraded by photochemical
and nitrate radical reactions. In water, methyl mercaptan could volatilise, or be oxidized,
depending on the pH and the presence of oxidants and metal catalysts (MOE, 2007). This
compound has a low Bioconcentration Factor (BCF) and a low calculated octanol/water
partition coefficient (Kow) and is not considered to bioaccumulate (MOE, 2007).
Dimethyl sulphide and dimethyl disulphide exist primarily as vapours in the
atmosphere and degraded by photochemically produced hydroxyl and nitrate radical
reactions (MOE, 2007).
Dimethyl sulphide and dimethyl disulphide are not expected to bind to sediment or
solids in water to any significant degree and to bioconcentrate in aquatic organisms (MOE,
2007). They easily volatilize from water and soil.
8
4.1.3 Toxicology and Health Effects
The U.S. EPA distinguishes between pollutants that could endanger public health
(health-related pollutants) and those for which adverse effects on public health have not
been demonstrated (welfare-related pollutants) (U.S. EPA, 1979). Very little information is
available on adverse health impacts of TRS emissions from kraft mills on animals, humans
and vegetation (U.S. EPA, 1979). Amongst the four compounds, hydrogen sulphide is the
only one with known impacts on human health. Others are only known to effect public
welfare and not human health.
At very high concentrations (over 10,000,000µg/m3) hydrogen sulphide can cause
acute death. At lower concentrations (30,000 to 500,000µg/m3) it causes serious health
effects such as nerve paralysis, pulmonary oedema and respiratory irritation (U.S. EPA,
1979). However, it is unlikely that such high concentrations occur near a kraft mill. In 1979,
U.S. EPA reported that the highest concentrations ever measured in the vicinity of a kraft
mill were in the order of 100 µg/m3. While it is believed that hydrogen sulphide impacts
animals the same as humans, adverse impacts on vegetation have not been documented.
In a Finnish study, excess mortality from cardiovascular diseases was observed in
kraft pulp mill workers who had been chronically exposed to TRS gases at concentrations
lower than 15 ppm (Jappinen and Tola, 1990). However, determining a valid dose-
response relationship with respect to hydrogen sulphide exposure is very difficult (MOE,
2007).
What has captured most attention about TRS compounds is their odour. Currently,
most of current air quality standards around the world for TRS are odour-based.
9
4.2 CURRENT STANDARDS REGULATING TRS
The Environmental Protection Agency (EPA)‟s New Source Performance Standards
that set guidelines for TRS emissions came into effect in 1976. States were given authority
to develop their regulations based on these guidelines with an effective date in early 1980s.
By 1990, most existing mills were in compliance with states regulation (Pinkerton, 1999). In
2003, EPA adopted a chronic inhalation Reference Concentration (RfC) of 2 µg/m3.
In Canada, the Canadian Environmental Protection Act does not regulate TRS
emissions and therefore, several provinces such as Ontario, Alberta, British Columbia,
Manitoba, Saskatchewan and New Brunswick have been imposing odour-based air quality
criteria on TRS emissions. These guidelines have been summarized in Appendix B.
Prior to the development and enforcement of Ontario‟s Local Air Quality Regulation
(O.Reg 419/05), Ontario Ministry of the Environment imposed guidelines on hydrogen
sulphide ½ hour point of impingement concentration (30 µg/m3) and one-hour odour-based
air quality criterion for TRS mixture (40 µg/m3). Currently O.Reg. 419/05 imposes sector-
based standards as stringent as 10 µg/m3 for a half hour period. However, a newly
proposed policy will evaluate a facility‟s compliance based on implemented operational
improvements that result in emission reduction rather than meeting the air quality standards.
A review of current available standards indicates that the majority of guidelines and
regulations impose limits on TRS concentration based on odour. Due to the lack of
toxicological data for methyl mercaptan, dimethyl sulphide and dimethyl disulphide, there is
no health-based air quality guidelines for a number of jurisdictions and agencies. Therefore,
proposing an effects-based air quality standard for TRS is only possible by using hydrogen
sulphide (H2S) as a surrogate.
10
4.2.1 Recent MOE’s TRS Policies
In 2006, with the introduction of a new policy proposal, TRS emission limits became
the subject of a new discussion in Ontario. The policy decision was finalized by the Ministry
of the Environment on August 31, 2007 and the new limits became part of Ontario
Regulation 419/05 (Local Air Quality). However, since many of the facilities could not
comply with the new standards, the Alteration of Standards process was introduced.
Facilities that prepared a Technical Benchmarking Report to demonstrate that the TRS point
of impingement concentrations are likely to be below the upper risk threshold at specified
receptors could be eligible for an alternative TRS standard. In June 2009, the Ministry of
the Environment proposed Sector–Based Technical Standards to manage air pollution for
the pulp and paper industry. Under this new policy proposal, the Minister will have the
authority to allow facilities in a sector to meet technical standards as opposed to
contaminant-based standards on a sector-basis as opposed to case-by-case under the
Alteration of Standards process.
Local Air Quality Regulation (O.Reg. 419/05)
Currently, under Ontario Regulation 419/05 (Local Air Quality), air quality compliance
criteria for TRS compounds emitted from pulp and paper facilities are as follows:
A 24-hour average Ambient Air Quality Criteria (AAQC) of 14 µg/m3 for TRS based
on the adverse effects on the respiratory system (nasal lesions) of this mixture,
which will be a standard; and
A 10-minute average AAQC of 13 µg/m3 for TRS based on odour effects, which will
be a standard; and
A half-hour standard of 10 µg/m3 for TRS based on both odour and health effects of
this mixture.
11
In addition, air quality standards for mercaptans (as methyl mercaptan) call for a 10-
minute limit of 13 µg/m3 and a half-hour standard of 10 µg/m3. Air quality criteria for
Dimethyl Sulphide (DMS) and Dimethyl Disulphide (DMDS) include a 10-minute limit of 30
µg/m3 for DMS; and a 10-minute AAQC of 56 µg/m3 for DMDS. These additional standards
are all odour-based.
Alteration of Standards Process
The alteration of standards process is intended to deal with facilities that are not able
to come into compliance with the new requirements by the phase-in period due to technical
or economic issues. It allows for altered standards to be set on a site specific basis using a
publicly transparent process.
If a facility indicates that results of the Technical Benchmarking Report demonstrate
that the TRS point of impingement concentrations are likely to be below the upper risk
threshold at specified receptors identified in O. Reg. 419/05, and therefore the Facility may
be eligible for the alternative standards process. A key objective of the Ministry‟s review of
the TBR is to ensure that “best efforts” have been made to identify and implement solutions
to control.
Sector–Based Technical Standards
Requests for altered standards are considered on a case-by-case basis. However,
new or updated standards can present common or similar implementation challenges for
more than one facility within a sector and therefore, the Ministry of the Environment (MOE)
is proposing amendments to O. Reg. 419/05 to allow the Minister to have the authority to
establish sector-specific technical standards, as opposed to contaminant-based standards.
The proposed Forest Products Sector Technical Standard is intended to identify
technical and operational practices and solutions to reduce air emissions. It would establish
12
consistent requirements across a sector, which a facility may choose to follow, rather than
the current compliance requirements in O. Reg. 419/05. Current proposal uses acrolein as
an example of a contaminant that creates compliance challenges in this industry, however;
this policy could be applied to TRS compliance issues across the sector as well.
4.3 KRAFT PROCESS
Today, about 80% of all the pulp in the world is produced through the sulphate or
kraft process (EC, 2000). Amongst a variety of chemicals that are emitted to the air, TRS
compounds stand out for this process. The kraft process is a versatile process applicable to
all wood species and produces high strength pulp (Smook, 2002).
Manufacturing paper and paper products is a complex process, involving two distinct
phases: the pulping of the wood and the manufacturing of paper. The kraft process starts
with cooking the pulp in large digester vessels and ends with chemical recovery.
In the kraft process, wood chips are immersed in white liquor (a mixture of NaOH
and Na2S) and cooked in a digester to break up the lignin in the wood and free the cellulose
fibre. The spent liquor (black liquor) is washed from the pulp in the brown stock washers and
recovered. The liquor is then concentrated in evaporators and burned in the recovery boiler.
The smelt in the bottom of the recovery boiler is removed and dissolved in water to form
green liquor (Na2CO3 and Na2S). The green liquor is contacted with lime to form white liquor
which can be reused in the process. Figure 4-1 better demonstrate this process.
Total Reduced Sulphur compounds are generated and emitted to the air by the
digesters, pulp washers, evaporators and recovery furnaces.
The overall TRS emissions from kraft mills in the United States declined by about
100,000 tonnes from 1970 to 1995, despite the production increase of about 80%
(Pinkerton, 1999). Numerous technology improvements have lead to this significant
13
reduction. TRS emissions from lime kilns have decreased through improved kiln design and
process modifications such as better lime mud washing to remove sulphides.
FIGURE 4-1: THE TWO CYCLES OF KRAFT PULPING (TRAN, 2008)
4.3.1 Sodium Cycle
Cooking
Wood has two basic components, cellulose and lignin. The pulping process
removes lignin and recovers the fibres (the pulp) for manufacturing paper. In kraft pulping,
wood chips are cooked (digested) at an elevated temperature and pressure in a solution of
sodium sulphide and sodium hydroxide called white liquor (Grace and Malcolm, 1983). This
cooking process can be either batch or continuous.
Lime Kiln
Causticizing
Plant
Digester
Washing
Evaporators
Recovery
Boiler
Calcium
Cycle Sodium
Cycle
Lime Lime
Mud Weak Black
Liquor
Heavy
Black Liquor
Green
Liquor
Smelt
White
Liquor
Water
Wood
Pulp
14
The white liquor chemically dissolves the lignin and as the chips are “blown” from the
digester, the chips are broken into individual fibres. This mixture leaving the digester
contains dark liquor that is now called black liquor as well as pulp fibre. As the fibre is
filtered and washed with water, black liquor is collected for recovery of the chemicals. The
washed fibre pulp is eventually bleached, pressed and dried into pulp or paper.
The large vessels, in which the wood chips are cooked, are called digesters.
Digesters generally operate at an elevated temperature of 170-180°C and pressure of 690-
880 kPa, in either batch or the continuous mode (Grace and Malcolm, 1983).
The sulphur content of the white liquor will greatly affect the TRS emissions from the
digester. Lower sulphidity (sulphide content) results in less TRS emissions (MOE, 1995).
However, the desirable operating level for sulphidity is in the range of 25-35% on Total
Titrateble Alikali and the pulp quality and the cooking reaction rate diminish at a sulphidity
level below 15% (Smook, 2002). To adjust the sulphidity, the ratio of sulphur to sodium in
the make-up chemicals must be altered.
Washing
From the blow tank, the cooked pulp is pumped through a series of screens and
washers to separate the spent liquor and pulp. Modern pulp washing facilities normally
recover about 97% of the chemicals applied in the digester (Grace and Malcolm, 1983). The
washing system includes knot removal, screening, and washing to remove the dissolved
lignin from the pulp prior to bleaching. If the washed pulp needs more delignification, that
could be achieved using oxygen. The washed pulp that is still brown at this stage may go
through a bleaching process before being dried to yield paper.
15
Evaporation and Chemical Recovery
Upon completion of the cooking process, black liquor containing residual pulping
chemicals and dissolved organics, is concentrated in evaporators and burnt in the recovery
furnace, producing what is called smelt, a molten salt of Na2CO3 and Na2S.
The spent liquor (weak black liquor) removed from the digesters and extracted from
pulp is a dilute solution of dissolved solids (13 to 17%) that needs to be concentrated to 60
to 80% solids to realize its maximum fuel value for burning (Smook, 2002). Weak black
liquor is concentrated in multiple-effect evaporators, producing strong black liquor. Further
concentration of black liquor is typically achieved in a concentrator for modern recovery
boilers, or a direct-contact evaporator (DCE) in old recovery boilers.
The recovery boiler is at the heart of the kraft recovery process and is the most
expensive single equipment item in the pulp mill, performing the following functions:
Evaporating the remaining free water from the liquor solids
Burning the organic constituents and generating steam for the process
Reducing oxidized sulphur to sulphide
Recovering inorganic chemicals in molten form
Most old recovery furnaces had a direct-contact evaporator, in which hot combustion
gases were utilized to concentrate the liquor. The contact between black liquor and hot flue
gases allows the furnace gases to strip reduced sulphur from liquor and emit TRS gases
(Smook, 2002). However, the new furnaces, also called low odour recovery boilers, are
designed with non-contact evaporators that result in much lower TRS emissions.
The organic content of concentrated black liquor, derived from pulping the wood, is
burnt in the recovery furnace. The combustion produces molten smelt which consists of
mostly sodium carbonate and sodium sulphide, and heat which is used to generate steam
and power.
16
Smelt continuously flows through smelt spouts to a dissolving tank where it is
dissolved in water to produce green liquor. The smelt dissolving tank is an enclosed
agitated tank with its own vent stack. The shattering and violent interaction between molten
smelt and water generates large volumes of steam and air emissions including TRS.
The main sources of odour in older mills include black liquor combustion, weak black
liquor evaporation and the digestion process. Sulphur compounds from the digesters are
primarily dimethyl sulphide and dimethyl disulphide, while sulphur compounds from the
evaporators are primarily H2S with lesser amounts of dimethyl sulphide (CCME, 2002).
The vapour that comes off the digester and evaporators also includes some volatile
constituents. When the water vapour is condensed these volatiles will either condense and
contaminate the condensate or remain as non-condensable gases (NCGs) depending on
their boiling point.
Compared to new non-direct contact evaporators, direct contact evaporation in a
recovery boiler releases a large amount of TRS as a result of the following reaction:
Na2S + CO2 + H2O Na2CO3 + H2S (reaction 1)
This old technology of exposing the evaporated black liquor to the flue gases for
further concentration prior to firing was used during the 1930s to early 1970s by all kraft
recovery boiler manufacturers (CCME, 2002). In mills that still use this technology the
odour problem can be partly overcome by using black liquor oxidation before evaporation.
Smelt is discharged from the recovery boiler into the smelt dissolving tank. It is
generally dissolved in weak wash from the lime mud washing process to form green liquor.
This solution that is green because of some impurities, is then sent to a clarifier and then
mixed with lime is an agitated tank called slaker.
17
The process of dissolving smelt produces dissolved sodium salts such as NaHS in
water and contributes to H2S emissions. Studies have shown that liquors with higher
sulphidity and lower causticity results in higher H2S emissions (Fredrick et al, 1996).
4.3.2 Calcium Cycle
Causticizing
To produce white liquor, green liquor containing sodium carbonate is transferred to a
causticizing tank where calcium oxide is mixed with the solution. Sodium carbonate is then
converted into sodium hydroxide and calcium carbonate (lime mud). White liquor is
returned to the process, while lime mud is washed, dried and burnt in a lime kiln to
regenerate the calcium oxide or quicklime. This process is called calcination or lime burning
(reaction 4). Reactions 2 and 3 better define the steps leading to lime burning:
Slaking: CaO + H2O Ca(OH)2 (reaction 2)
Causticizing: Ca(OH)2 + Na2CO3 2NaOH + CaCO3 (reaction 3)
Calcination: CaCO3 + heat CaO + CO2 (reaction 4)
Lime Burning
Calcination or lime burning takes place at high temperatures (higher than 815°C) in a
rotary lime kiln, which functions as a chemical reactor and a heat transfer device (Green and
Hough, 1992). Lime kilns used in the kraft process are usually rotary kilns that consume
fossil fuels to generate heat.
Rotary lime kilns are large refractory lined steel cylinders which are slightly inclined
from the horizontal and are slowly rotated. Lime mud is introduced at the higher end and
slowly makes its way to the lower discharge end due to the inclination and rotation. A
burner is installed at the discharge end of the kiln. Heat transfer from this flame and the hot
18
combustion gases that flow up the kiln dries, heats, and calcines the counter-flowing lime
mud solids.
Lime kiln is divided into four functional zones, each representing a stage in the
conversion of lime mud to reburned lime (Green and Hough, 1992):
- Drying: water is evaporated from lime mud that typically enters the kiln at a solids
content of 68%;
- Heating: lime mud at 95% solids content or higher is mixed well with hot flue gases;
- Calcination: calcium oxide pellets begin to form at temperature above 800°C; and
- Cooling: hot lime pellets cool down, while exchanging heat with the incoming
secondary air flow.
Modern kilns are equipped with precoat mud filters that deliver lime mud with solids
content as high as 80% (Green and Hough, 1992). This has greatly improved fuel economy
for lime kilns.
The TRS emissions, mainly hydrogen sulphide, may originate from two sources in
the lime kiln. The incomplete combustion of fuel that contains sulphur, due to a lack of
oxygen, is one source. The flue gases then will contain carbon monoxide and hydrogen
sulphide. The second source is the unwashed sodium sulphide in the lime mud fed into the
kiln. The likelihood of this source depends on the degree of lime mud washing and its state
of oxidation.
The lime mud is fed to the feed end of the kiln. As the mud dries, the reaction
between of carbon dioxide in the kiln gas and sodium sulphide and water in the lime mud
results in the formation of hydrogen sulphide or TRS. Due to the low temperature in this
region of the lime kiln, the majority of TRS cannot be oxidized, resulting in emissions.
The installation of a wet scrubber followed by an electrostatic precipitator can reduce
the TRS emissions from the flue gas. However, fresh water should be used as the
19
scrubbing medium to avoid the stripping of odorous gases from the scrubbing water. If
process condensates are used, they should be steam stripped first, or sodium hydroxide
should be added to the scrubber water to raise the pH. The scrubber water is recycled to
the causticizing system (MOE, 1995).
4.3.3 Sulphur Recovery
The majority of sulphur in the kraft process goes through the recovery cycle, but
some sulphur reacts with wood components for form TRS emissions. Methanol and TRS
emissions that are collected throughout the process are also called Non-Condensible
Gases. Studies have shown that TRS compounds could make up about 20% of NCGs (on
a dry basis) with methyl mercaptan accounting for more than half of that amount, hydrogen
sulphide and dimethyl sulphide for about a quarter and dimethyl disulphide less than 2%
(Zhang et al, 2006).
The most common method of treating NCGs is collection and combustion in the
power boiler, lime kiln, a recovery boiler or a stand-alone incinerator. Sulphur is then lost as
sulphur dioxide (SO2) from the combustion process. The SO2 can be captured in an alkali
scrubber (Green and Hough, 1992).
A portion of the sulphur introduced into the kiln could react with lime to form CaSO4
and enter the sodium cycle through the causticizing plant as Na2SO4 (reaction 5), which may
be captured in an electrostatic precipitator.
CaSO4 + Na2CO3 Na2SO4 + CaCO3 (reaction 5)
If the sulphur loss is significant, sulphur make up of some kind may be required in
the process (Green and Hough, 1992).
20
4.4 TRS EMISSION REDUCTION MEASURES
Major point sources of TRS gases are kraft recovery furnaces, smelt dissolving
tanks, lime kilns, digesters, evaporators and brown stock washers, as demonstrated in
Table 4-2 and Table 4-3. The TRS content of different emission streams could also vary as
a function of liquor sulphidity (MOE, 1995).
Area sources of TRS include Wastewater Collection and Treatment System and
Landfilling. However, due to their fugitive nature, it is difficult to estimate TRS emissions
from the area sources.
TABLE 4-2: POINT SOURCE EMISSION ESTIMATES (PINKERTON, 1999)
Source Unit 1970 1980 1990 1995
Recovery Furnaces lb/ton ADP* 71.1 15.2 8.9 8.2
Smelt Dissolving Tanks lb/ton ADP 2.9 3.9 1.3 0.9
Lime Kilns lb/ton ADP 11.8 3.9 2.0 2.1
Black Liquor Oxidation Systems lb/ton ADP 0.1 0.4 0.5 0.4
Digesters and Evaporators lb/ton ADP 29.4 5.5 1.0 0.5
Washer Systems lb/ton ADP 4.4 5.9 6.0 5.8 *ADP: Air Dried Pulp
TABLE 4-3: TRS EMISSIONS ACROSS U.S. PRIOR TO 1979 (U.S. EPA 1979)
Source Average National Emissions
(g/kg ADP*)
Recovery Furnace 1.25
Digester System 0.32
Lime Kiln 0.31
Multiple-Effect Evaporator System 0.22
Brown Stock Washer System 0.15
Condensate Stripper System 0.11
Smelt Dissolving Tank 0.1
Black Liquor Oxidation System 0.05 *ADP: Air-Dried Pulp
21
Data collected from a large number of pulp and paper mills across the United States
show that although pulp and paper production using kraft process has increased
dramatically in the last 25 years, the overall TRS emissions have been reduced by about
85% (Das and Jain, 2001). Numerous technology improvements have lead to a significant
reduction in TRS emissions from kraft pulp mills:
Change of Direct contact Evaporators (DCE) to Non-Direct Contact Evaporators
(NDCE)
Installation of black liquor oxidation systems at mills with DCEs
Improved design and operation of recovery furnaces, especially by maintaining
stable and efficient combustion conditions
Reduced use of TRS-containing condensate for washing the pulp, as well as
improved low-emission washer design
Collection and incineration of NCGs throughout the whole process
Installation of improved limes kilns with more advanced process control
Black liquor oxidation minimizes TRS emissions from recovery furnaces in which
vent gases come into direct contact with black liquor. Non-DCE furnaces eliminate contact
between flue gases and black liquor and generally better combustion control. The new
evaporators generate 75% less emissions.
However, it has been reported that burning NCGs could result in ring formation in the
lime kiln and accelerated corrosion in the bark boiler. Therefore many mills have installed
scrubbers to remove TRS before incineration of methanol in NCGs. White liquor can
effectively remove TRS gases from NCGs before combustion in the lime kiln, which
eliminates a major disturbance to their operation (Zhang et al, 2006). Non-condensable
gases from digesters and evaporators contain high levels of TRS. When these gases are
collected and burned the TRS gases are oxidized to SO2, resulting in odour reduction. The
22
SO2 is then captured generally in alkaline scrubbers and returned to the process. (Das and
Jain, 2001)
Installation of more efficient shatter jet nozzles and lowering the pressure of the
steam delivered to the shatter jets have proven effective in reducing TRS emissions from
the dissolving tank (Fredrick et al, 1996).
TRS emissions from lime kilns have decreased mainly through improved kiln design
and process modifications such as better lime mud washing to remove sulphides.
4.5 REDUCTION OF LIME KILN TRS EMISSIONS
TRS emissions from the lime kiln originate either from the incomplete combustion of
fuel or the residual sodium sulphide in the lime mud. Improving mud washing and
dewatering and introducing process control can reduce the TRS emissions from the lime kiln
by more than 80% (MOE, 1995).
The multi-variable nature of the calcination process that involves non-linear kinetics
and time delays makes the control of a lime kiln a difficult task. During the operation,
several variables need to be considered and controlled while disturbances such as change
in lime mud composition or fuel characteristics could occur (Jarvensivu et al, 2000). Models
based on process fundamentals have been used to estimate the temperature of the solids,
flue gas and refractory along the length of the kiln; however, in the last decade, the attention
has been shifted toward empirical models for developing supervisory-level control systems
(Jarvensivu et al, 2000). The major process control variables for a lime kiln include excess
oxygen, temperature, lime mud composition, fuel characteristics and NCGs that may be fed
into the kiln.
23
Even though some kilns are operated with excessive amount of oxygen and higher
than normal temperature for the purpose of burning TRS gases, this increases the fuel
requirement of the kiln and reduces its fuel economy (Green and Hough, 1992).
4.5.1 Excess Oxygen
The presence of excess oxygen is critical in the operation of the lime kiln, especially
if NCGs are collected and also burned in the kiln. Excess oxygen results in lower TRS
emissions by oxidizing the residual sulphide in the lime mud into sulphur dioxide.
The residual sodium sulphide in the lime mud reacts with water and carbon dioxide
to produce hydrogen sulphide in the lime kiln over the temperature range of 200 to 250 C
(Jarvensivu et al, 1999). At higher temperatures in presence of excess oxygen the formed
hydrogen sulphide oxidizes to sulphur dioxide (reaction 6).
H2S + 3/2 O2 SO2 + H2O (reaction 6)
The amount of excess oxygen varies for different kilns, depending on the design and
air leak. A study conducted in 1999 observed that any increase in excess oxygen up to
3.5% would result in less hydrogen sulphide and more sulphur dioxide, as oxidation rate
increases (Jarvensivu et al, 1999). Others recommend an excess oxygen levels of 4% by
volume or greater (CCME, 2002).
Molecular oxygen can be added to the combustion air to control H2S generation from
the lime mud in the combustion zone.
4.5.2 Temperature
Lime kiln is generally used for the combustion of NCGs such as digester relief
gases, digester blow gases, evaporator vent gases and stripper vent gases. The
24
temperature of hot end of the kiln has a great impact on the oxidation rate of the NCGs and
TRS, similar to excess oxygen. As the temperature increases, the oxidation rate of TRS
gases and NCGs increases (Jarvensivu et al, 1999).
Laboratory studies show that the oxidation reaction of H2S occurs very slowly at low
temperatures, but at temperatures over 550 °C, it takes less than a second to oxidize H2S
(Tran, 2007). At temperatures below 350 °C, little oxidation takes place even at 5% oxygen.
4.5.3 Fuel
Various fossil fuels could be used in lime kilns. In kilns that burn high sulphur oil or
petroleum oil, H2S is formed as a result of reactions between sulphur and hydrocarbon in
the fuel under local reducing conditions caused by poor burner performance (Tran, 2007).
Therefore, one of the measures recommended for reducing TRS emissions is the use of
low-sulphur fuel such as natural gas (EC, 2001). The higher the sulphur content of the fuel,
the higher are the chances of incomplete combustion of reduced sulphur.
4.5.4 Lime Mud Washing
Inadequate washing and dewatering leaves residual white liquor in the lime mud,
which includes water soluble sodium compounds such as NaOH, Na2S and Na2CO3 and
Na2SO4 (Tran, 2007). As lime mud moves through the kiln, the chemistry of these
compounds changes. In the chain section of the lime kiln, Na2S reacts with CO2 and H2O to
form H2S and Na2CO3 (reaction 7), while in the higher temperature zone Na2S will be
oxidized to Na2SO4 (reaction 8) (Tran, 2007):
Na2S + CO2 + H2O H2S + Na2CO3 (reaction 7)
Na2S + 2O2 Na2SO4 (reaction 8)
25
Improving lime mud washing could decrease the washable sodium sulphide
concentration to less than 0.01 wt% in the mud and therefore the TRS emissions to 5 ppm
(MOE, 1995). Recommended measures to increase the efficiency of lime mud washing
include:
Maximizing the slurry concentrations in the white liquor clarifier and the lime mud
washer or pressure filter (MOE, 1995);
Using clean wash water instead of contaminated condensate at the last washing
point;
Increasing the temperature of the wash water on the lime mud precoat filter to about
80°C to improve the performance of the filter (MOE, 1995);
Applying lime mud recycle to improve lime mud washing (MOE, 1995);
Increasing the lime mud washing capacity; and
Installing a lime mud precoat filter to obtain a high solids content.
In the lime mud filter a small amount of air is sucked through the lime mud cake to
oxidize the rest of sodium sulphide left on the surface of lime mud particles to sodium
thiosulphate. Sodium thiosulphate does not result in TRS emissions (EC, 2001).
Lime mud washing on the precoat filter can be accomplished with clean water or with
condensate from the evaporator system. However, the use of contaminated condensate is
not recommended, since it could introduce reduced sulphur compounds and VOCs into the
lime mud to be released in the lime kiln. Use of clean wash water, a high degree of lime
mud washing and obtaining a relatively dry filter cake with about 80% solids will remove the
TRS and VOCs which could enter the lime kiln (MOE, 1995).
26
4.5.5 Lime Mud Dewatering
Generally, 20 to 40% of the material entering the precoat filter is mud solids and the
rest include three types of water: free water, sorbed and crystallized water (Ford, 1994).
Improved dewatering reduces residual sodium sulphide in the mud, stabilizes the
combustion and reduces lime kiln fuel consumption. Chemicals used for dewatering have
improved lime mud washing and dewatering on the precoat filter (Ford, 1994).
About 60% of the water in the lime mud is free water held in capillaries between the
calcite particles, which can be easily drained by a vacuum filter (Ford, 1994). Another 10 to
15% of the water in the mud is attached to the surface of the calcite particles through
hydrogen bonding and cannot be removed without a dewatering aid (Ford, 1994).
Dewatering chemicals are chemicals with both hydrophobic and hydrophilic
functional groups on their molecules. These molecules can detach the sorbed water
molecules from the surface of lime mud particles, which is then removed by the precoat
filter. In addition, since these chemicals attach themselves to the mud, the mud particles
change from hydrophilic to hydrophobic and lose the tendency to stick together and to the
equipment (Ford, 1994).
In a case study conducted at a 2000 tpd linerboard mill the use of dewatering aids
increased the mud solids content from 65% to 72%, reducing the fuel consumption by
$800,000 per year (Ford, 1994).
4.5.6 Scrubbing Flue Gases
Newer lime kiln designs have an electrostatic precipitator to remove particulate from
the kiln flue-gas. Old kiln designs have scrubbers. However, the choice of scrubbing liquid
is very important. While caustic solution absorbs hydrogen sulphide and methyl mercaptan
27
it does not absorb dimethyl sulphide and dimethyl disulphide. When TRS has high organic
content, an oxidizing agent such as sodium hypochlorite is more effective (MOE, 1995).
28
5. DATA ANALYSIS AND DISCUSSION
Data from three kilns were analyzed in search of a correlation between TRS
emissions from the lime kiln and solids content of the lime mud. Each set of data presented
various parameters that were measured and recorded continuously during the operation of
the kiln. Therefore, the relationship between various parameters and TRS were also
investigated as a comparison. Table 5-1 lists the parameters that were studied for a visible
relationship with TRS emissions for each kiln.
TABLE 5-1: PARAMETERS ANALYZED FOR EACH KILN
Parameter Mill A Mill B Mill C
Mud Solids X X X
Firing End T X X
NCG Flow X X
Sulphidity X
Mud Flow X
Flue Gas Oxygen X
5.1 KILN A
Kiln A is a natural gas kiln at a kraft mill in Alberta. The Kiln A data set was collected
from December 1, 2006 to December 1, 2007. Several parameters were recorded in this
period, including lime mud solids, lime mud feed rate, TRS emissions and NCG flow rate.
Figure 5-1 shows a graph of flue gas TRS content as a function of lime mud solids
for this kiln. As expected, with the increase in mud solids, TRS emissions decline.
To explore if a similar correlation with other process control parameters is present,
the TRS content of the flue gas was plotted as a function of NCG flowrate (Figure 5-2) and
the lime kiln excess oxygen (Figure 5-3). However, as demonstrated by the figures, no
visible correlation between these parameters and TRS emissions can be observed.
29
FIGURE 5-1: FLUE GAS TRS CONTENT VS. MUD SOLIDS AT KILN A
FIGURE 5-2: FLUE GAS TRS CONTENT VS. NCG FLOWRATE AT KILN A
30
FIGURE 5-3: TRS VS. FIRING END TEMPERATURE AT KILN A
5.2 KILN B
This set of data was collected from March 2006 to July 2007 at a pulp mill in New
Zealand. As Figure 5-4 shows, a simple direct correlation is observed between TRS
emissions and lime mud dryness. To search for other correlations, the TRS emission rate
was also plotted as a function of mud sulphidity. No visible correlation between TRS
emissions and this process parameter was apparent.
31
FIGURE 5-4: TRS VS. LIME MUD SOLIDS AT KILN B
5.3 KILN C
The final set of data analyzed was collected at another kraft mill in Alberta from
August 2002 to January of 2006. A direct correlation between TRS emissions and mud
solids content was confirmed in Figure 5-5, similar to observations at kiln A and kiln B.
Other process control parameters that were plotted for this kiln include the firing end
temperature, NCG flowrate and mud flowrate. As seen in previous cases, these parameters
failed to show a correlation with TRS emissions, as easily spotted as mud solids content.
32
FIGURE 5-5: TRS VS. LIME MUD SOLIDS AT KILN C
5.4 STATISTICAL ANALYSIS
The visible correlation that was observed between TRS emissions and lime mud
solids was put to test using statistics. For each set of data, linear regression analysis was
conducted to find an equation (y=ax+b) that best describes the correlation between lime
mud solids and TRS emissions. A 95% confidence interval was then calculated for the
correlation coefficient „a‟. In addition, p- value was also calculated for the null hypothesis
(Ho), that is the correlation coefficient could be zero, or in other words there is no particular
correlation between lime mud solids and TRS emissions.
In all three cases, the linear regression analysis resulted in a negative coefficient „a‟
(the slope), due to the observed negative relationship between the two variables. Figure 5-6
demonstrates the linear regression analysis for Kiln B data. The correlation coefficient in this
case is -3.32 and the intercept is 266.91. However, as shown in Table 5-2 the value
33
calculated for R2 is very low due to a lot of noise in the data. The fitted line through Kiln A
and Kiln C data showed similar equations.
FIGURE 5-6: REGRESSION ANALYSIS FOR KILN B DATA
To reject the null hypothesis, a 95% confidence interval was calculated for the
correlation coefficient of each data set. Table 5-3 shows the result for Kiln B data. The lower
and upper bound of the confidence interval are both negative and the p-value is 3.13 x 10 -
41, well below the 5% error margin. This confirms that the probability of null hypothesis is
within 5% error margin. Statistical analysis on Kiln A and C demonstrate similar results with
negative confidence intervals and p-values in the order of 10-30.
34
TABLE 5-2: REGRESSION STATISTICS FOR KILN B DATA
Regression Statistics
Multiple R 0.568
R Square 0.323
Adjusted R Square 0.321
Standard Error 15.789
Observations 467
TABLE 5-3: 95% CONFIDENCE INTERVAL FOR KILN B DATA
Coefficients Standard
Error t Stat P-value
Lower 95%
Upper 95%
Intercept 266.91 15.71 16.99 1.03E-50 236.04 297.79
X Variable 1 -3.32 0.22 -14.88 3.13E-41 -3.76 -2.88
As demonstrated by statistical analysis on all three sets of data, the correlation found
between lime mud solids and TRS emissions is a negative linear correlation at 5%
significance level. However, due to the wide dispersion of the data, R2 value calculated for
each correlation is lower than 0.4, as a result of other parameters fluctuating while data
collection takes place. These parameters include sulphidity (of the white liquor), amount
and quality of water used to wash the lime mud, as well as the temperature of water, which
collectively impact the amount of residual sodium sulphide in the lime mud.
35
6. CONCLUSIONS AND RECOMMENDATIONS
Data presented in this study confirms that generally as lime mud solids content
increases, TRS emissions from the lime kiln decrease. Therefore, improving lime mud
dewatering could result in lower TRS emissions from a lime kiln.
As demonstrated by statistical analysis on all three sets of data, the correlation found
between lime mud solids and TRS emissions is a negative linear correlation at 5%
significance level. However, due to the wide dispersion of the data, R2 value calculated for
each correlation is lower than 0.4, as a result of other parameters fluctuating while data
collection takes place. These parameters include sulphidity (of the white liquor), amount
and quality of water used to wash the lime mud, as well as the temperature of water, which
collectively impact the amount of residual sodium sulphide in the lime mud.
To further explore the relationship between lime mud solids and TRS emission rate
from the lime kiln, it is recommended to collect data during periods where other operating
parameters have minimum fluctuations.
36
7. REFERENCES
Canadian Council of Ministers of Environment, Multi-pollutant Emission Reduction Analysis
Foundation Summary Report for the Pulp and Paper Sector, 2002
Das, T.K. and Jain A.K.. “Pollution Prevention Advances in Pulp and Paper Processing.”
Journal of Environmental Progress, Vol 20, Issue 2, July 2001, pp.87-92
European Commission, Reference Document on Best Available Techniques in the Pulp and
Paper Industry, Integrated Pollution Prevention and Control, 2001
Ford, W. “Dewatering chemistry helps solve problems in lime kiln operation” Pulp and
Paper, Volume 68, Issue 4, April 1994, pp. 115-117
Fredrick, W. J., Joseph P. D and Russell J. A. “Controlling TRS emissions from dissolving-
tank vent stacks.”, TAPPI Journal, June 1996, pp. 144-148
Grace, T. M., and Malcolm, E. W., 1989, Pulp and Paper Manufacture -Alkaline Pulping
Volume 5, 3rd Ed. The Joint Textbook Committee o the Paper Industry, 1989.
Green, R.P. and Hough, G., (1992), Chemical Recovery in the Alkaline Pulping Processes,
1992 TAPPI Press.
Jarvensivu, M., J. kivivasara and K. Saari. “A field survey of TRS emissions from a lime
kiln”, Pulp and Paper Canada, Volume 100, 1999, Issue 11, pp. 28-31
Jarvensivu, M., K. Saari and S. L. Jamsa-Jounela, “Intelligent control system of an industrial
lime kiln process.” Control Engineering Practice, Volume 9, 2001, pp. 589-606
Ministry of the Environment, Technical Cost Assessments of Potential Control Options for
TRS Emissions from Ontario Sources, 1995
Ministry of the Environment, “Ontario Air Standard for Total Reduced Sulphur”, Standards
Development Branch, 2007
Pinkerton, John E. “Trends in U.S. Kraft Mill TRS Emissions”, TAPPI Journal, April 1999, pp.
166-169
37
Smook, Gary. Handbook for Pulp and Paper Technologies. 3rd Edition. Vancouver: Angus
Wilde Publications Inc., 2002.
Tran, H.N. “ The Kraft Recovery Process”, TAPPI Kraft Recovery Course, TAPPI Press
(2008)
Tran, H.N. “Lime Kiln Chemistry and Effects on Kiln Operations”, Tappi Kraft Recovery
Short Course, Tappi Press, 2007, pp 2.3-1 – 2.3-9
U.S. EPA, “Kraft Pulping: Control of TRS Emissions from Existing Mills”, March 1979
U.S. EPA, “Pulp and Paper and Paperboard Industry – Background Information for
Promulgated Air Emission Standards”, October 1997
Zhang, Z., C.Q Jia, H. Tran, P. Rouillard and B. Adams. “Scrubbing NCG with white liquor to
remove reduced sulphur gases.” Pulp and Paper Canada, Vol. 107, Issue 12, 2006,
pp. 74-79
38
APPENDIX A
SAMPLE OPERATIONAL DATA
39
TABLE A.1 - SAMPLE OF DAILY OPERATIONAL DATA (Kiln A)
Date/Time
Natural Gas Flow
NCG Flow
Primary Air Flow
Firing End T
Flue Gas Oxygen
Lime Mud Feed Flow
Lime Mud Solids to
Kiln
scm/hr Acm/min scm/min C % l/sec %
02/11/2006 7:00 2942.52 0.00 124.05 830.28 0.97 30.84 80.71
03/11/2006 7:00 2830.16 15.16 114.82 749.31 1.38 27.37 76.87
04/11/2006 7:00 3208.12 0.96 120.99 776.80 0.40 29.54 76.03
05/11/2006 7:00 3093.28 4.89 120.15 763.42 0.48 28.91 76.37
06/11/2006 7:00 3142.63 0.00 120.76 771.61 0.40 28.88 75.67
07/11/2006 7:00 3017.79 0.00 120.37 775.69 0.63 29.77 76.51
08/11/2006 7:00 2785.56 0.00 110.96 755.79 1.46 24.88 75.63
09/11/2006 7:00 1343.35 1.39 57.22 732.81 5.72 12.11 75.49
10/11/2006 7:00 2875.34 2.69 117.88 890.93 0.95 26.32 74.57
11/11/2006 7:00 2935.40 17.80 120.41 847.77 0.54 28.08 72.26
12/11/2006 7:00 2983.47 0.69 120.53 849.66 0.49 28.27 76.69
13/11/2006 7:00 3031.38 0.00 119.97 848.18 0.40 28.57 76.45
14/11/2006 7:00 3043.68 0.20 119.52 833.11 0.37 29.42 78.06
15/11/2006 7:00 3107.53 11.09 120.46 830.15 0.40 29.99 79.09
16/11/2006 7:00 655.45 8.26 62.35 676.72 8.20 4.90 80.10
17/11/2006 7:00 3.13 0.00 34.59 644.78 10.04 -0.20 80.10
18/11/2006 7:00 2067.36 6.15 102.37 788.32 3.28 20.17 82.53
19/11/2006 7:00 2968.34 1.12 120.18 807.45 0.69 29.26 76.74
20/11/2006 7:00 2945.29 0.00 118.39 816.31 0.76 28.69 75.96
21/11/2006 7:00 2963.32 0.10 118.65 808.64 0.89 28.85 77.70
22/11/2006 7:00 3063.53 0.13 119.91 833.71 1.12 28.60 77.86
23/11/2006 7:00 3397.93 0.00 121.10 801.66 0.81 29.86 77.97
24/11/2006 7:00 3523.22 0.00 120.41 800.23 0.57 31.05 78.60
25/11/2006 7:00 3488.81 0.00 120.59 799.12 0.54 30.56 80.70
26/11/2006 7:00 3441.86 0.00 120.61 806.69 0.73 29.55 80.23
27/11/2006 7:00 3509.66 0.58 120.60 817.05 0.64 29.91 78.99
28/11/2006 7:00 3574.10 0.00 120.74 805.57 0.48 30.13 74.41
29/11/2006 7:00 3548.84 0.00 121.04 825.65 0.46 30.08 77.88
30/11/2006 7:00 3421.30 3.50 120.13 836.87 0.60 29.84 78.18
01/12/2006 7:00 3296.51 0.00 118.89 856.33 0.46 30.07 75.98
02/12/2006 7:00 3146.47 0.00 119.93 895.67 0.66 30.05 76.50
03/12/2006 7:00 3084.58 0.00 119.60 887.71 0.73 30.11 76.33
04/12/2006 7:00 2959.32 0.00 118.12 877.60 1.15 29.73 76.88
05/12/2006 7:00 3058.01 0.05 117.01 904.24 0.60 29.34 75.74
06/12/2006 7:00 3137.14 0.00 116.97 912.83 0.67 29.35 76.32
07/12/2006 7:00 3051.54 0.00 116.95 914.74 1.11 29.82 76.58
08/12/2006 7:00 2982.98 3.49 116.15 946.76 1.00 29.03 76.64
09/12/2006 7:00 2995.61 1.12 115.80 859.09 0.98 29.19 74.88
10/12/2006 7:00 3062.53 0.00 116.71 788.38 0.70 29.51 75.36
11/12/2006 7:00 3118.43 0.00 116.70 846.76 0.75 29.49 75.98
40
APPENDIX B
A Jurisdictional Scan of TRS Emission Standards
41
TABLE B.1: A JURISDICTIONAL SCAN OF TRS EMISSION STANDARDS
Province Regulation/Guideline
Value Basis of
Guideline/Regulation Value Last
Update
Alberta
H2S 14 µg/m3 (1-hr AQG)
Odour Ambient Air Quality Criterion
1975
H2S 4 µg/m3 (24-hr AQG)
Odour Ambient Air Quality Criterion
1975
Static H2S 0.10 mg/SO3
(equivalent/day/100 cm2 as a 1-month
accumulated loading)
N/A Ambient Air Quality Criterion
N/A
British Columbia
TRS 7 µg/m3 (for forest industry)
(1-hr average)
Odour Maximum Desirable Criterion
1977
TRS 28 µg/m3 (1-hr average)
Odour Maximum Acceptable Criterion
1977
TRS 3 µg/m3 (24-hr average)
Odour Maximum Desirable Criterion
1977
TRS 6 µg/m3 (24-hr average)
Odour Maximum Acceptable Criterion
1977
H2S 7.5-14 µg/m3 (1-hr average)
N/A Maximum Desirable Criterion
1974-1975
H2S 28-45 µg/m3 (1-hr average)
N/A Maximum Acceptable Criterion
1974-1975
H2S 42-45 µg/m3 (1-hr average)
N/A Maximum Tolerable Criterion
1974-1975
H2S 4 µg/m3 (24-hr average)
N/A Maximum Desirable Criterion
1974-1975
6-7.5 µg/m3 (24-hr average)
N/A Maximum Acceptable Criterion
1974-1975
7.5-8 µg/m3 (24-hr average
maximum tolerable criterion)
N/A 1974-1975
42
Province Regulation/Guideline
Value Basis of
Guideline/Regulation Value Last
Update
Manitoba
H2S 1400 µg/m3
(1 hour average)
Undue annoyance from odour
Maximum Tolerable Level Concentration Guidelines
1985
15 µg/m3 (1 hour average)
Undue annoyance from odour
Maximum Acceptable Level Concentration Guidelines
1985
5 µg/m3 (24-hour average)
Undue annoyance from odour
Maximum Acceptable Level Concentration Guidelines
1985
1 µg/m3 (1-hour average)
Undue annoyance from odour
Maximum Desirable Level Concentration Guidelines
1985
New Brunswick
H2S 15 µg/m3
(1-hour average)
Odour Air Quality Objectives
1979
5 µg/m3 (24-hour average -
Ground Level Concentration)
Odour Air Quality Objectives
1979
Saskatchewan
H2S 15 µg/m3
(1-hour average)
Odour Clean Air Regulations
1989
5 µg/m3 (24-hour average)
Odour Clean Air Regulations
1989
