EPA-600/2-79-026
January 1979
MULTIMEDIA ASSESSMENT OF POLLUTION POTENTIALS
OF NON-SULFUR CHEMICAL PULPING TECHNOLOGY
by
Victor Gallons
Food and Wood Products Branch
Industrial Environmental Research Laboratory
Cincinnati, Ohio 45268
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency5 and approved for publica-
tion. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on
our health often require that new and increasingly more efficient pollution
control methods be used. The Industrial Environmental Research Laboratory-
Cincinnati (IERL-Ci) assists in developing and demonstrating new and improved
methodologies that will meet these needs both efficiently and economically.
A severe odor problem is caused by reduced sulfur compounds in the kraft
process. The pulping industry has been developing new pulping technology to
replace the kraft process with processes that do not contain sulfur and thus
eliminate the odor problem. This report assesses the potential air, water,
and solid waste pollution and energy use of new and non-sulfur pulping tech-
nologies. A forward look to the potential pollution reductions or hazards
and energy use of these evolving pulping technologies will help the agency
make decisions on supporting research on specific technologies. Investiga-
tions can be implemented on problem areas before the processes are implemen-
ted.
All of the proposed new pulping processes reduce odor emissions, but
generally at the expense of greater SOp and particulate emissions. Expected
BOD, suspended solids, color, and toxicity are generally lower than expected
from a kraft mill. Some of the new processes will require less energy and
others will require more energy than does the kraft process.
For further information contact the Food and Wood Products Branch,
Industrial Environmental Research Laboratory-Cincinnati.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
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ABSTRACT
This report gives an estimate of the air, water, and solid waste pollu-
tion generated by developing and existing non-sulfur pulping techniques that
are potentially competitive with kraft pulping. Also developed were energy
use and needs estimates for these pulping processes. Processes investigated
were soda pulping, soda semi chemical pulping, soda pulping followed by oxygen
delignification, thermomechanical pulping followed by oxygen delignification,
oxygen pulping of wood wafers, chlorine dioxide pulping, solvent pulping and
the Rapson process.
All of the pulping processes considered develop less water pollutants
and less total reduced sulfur emissions than does the kraft process. Sulfur
dioxide and particulate emissions vary from process to process, some being
greater than that expected from kraft and some less. Sulfur dioxide and
particulate emissions largely originate from power boilers. Requirements for
power produced from power boilers vary considerably between mill types. Some
air pollutants presently not inherent to the production of pulp, such as
sodium iodide, hydrochloric acid, and carbon monoxide, are potentially emit-
ted from several of the new pulping processes.
IV
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CONTENTS
Foreword i i i
Abstract 1v
Figures vi
Tabl es vi i
1. Introduction l
2. Conclusions 3
3. Recommendations 5
4. Kraft Pulping 7
5. Soda Pulping n
6. Soda Semi chemical Pulping 17
7. Oxygen Alkali Pulping 22
8. Thermomechanical Pulping Followed By Oxygen Delignification 30
9. Oxygen Pulping of Chips 38
10. Chloride Dioxide Pulping 44
11. Solvent Pulping 49
12. Rapson Process 53
References 57
Appendices 61
A. Energy use calculations 61
B. Power boiler S0~ emissions 76
C. Particulate emissions 77
D. NO Emission calculations 80
E. Sulfur loading to non-sulfur pulping processes 82
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FIGURES
Number Page
1 Diagram of a kraft pulping process 8
2 Diagram of a soda pulping process 12
3 Diagram of a soda semichemical pulping process 18
4 Diagram of an oxygen alkali pulping process 24
5 Diagram of a thermomechanical pulping process
followed by oxygen delignification 33
6 Diagram of oxygen pulping of chips process 39
7 Diagram of a ci07 pulping process 46
8 Diagram of the Rapson process 53
9 Percent hydrochloric acid vs. sulfidity 55
vi
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TABLES
Number Page
1 Summary of Results 4
2 Toxicity and Color of Bleach Plant Effluents 28
A-l Black Liquor Compositions 63
A-2 Calculated Bomb Heat Values 64
A-3 Flue Gas Composition 65
A-4 Recovery Furnace Gas Mass Balance 66
A-5 Recovery Furnace Heat Balance 67
A-6 Pulping Energy Balance 68
A-7 Pulp Wash Energy Requirements 69
A-8 Evaporator Energy Requirements 70
A-9 Heat Requirements of a CEDED Bleaching Sequence 71
A-10 Heat Requirements of a C/DEDED Bleaching Sequence
with Full Countercurrent Water Reuse 72
A-ll Heat Requirements of a DED Bleaching Sequence with
Full Countercurrent Water Reuse 73
A-12 Mill Energy Balance 74
B-l Calculation of S02 Emissions 76
C-l Calculation of Particulate emissions 78
D-l Boiler NO Emissions 80
/\
D-2 Recovery Furnace and Lime Kiln NO Emissions 81
A
E-l Organosulfur Emissions 83
vii
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SECTION 1
INTRODUCTION
Environmental pressures have caused the pulp and paper industry to dev-
elop new pulping processes and significantly modify existing processes. The
changes proposed are often a result of specific pollution problems such as
color, BOD, or odor emissions. The reduction of one specific pollutant may
cause an increase in other pollutants. This paper evaluates the air, water,
and solid waste pollutants from some of the more promising new pulping tech-
nologies, as well as from some existing technologies that may gain in popu-
larity.
The goals of the processes being developed are generally aimed toward
the reduction of reduced sulfur compounds (odors), reduction of color from
the bleach plant, or elimination reduced sulfur emissions. Non-sulfur pro-
cesses include soda pulping, oxygen pulping, halogen pulping, thermomechani-
cal pulping, solvent pulping, and nitric acid pulping. Reuse of bleach plant
effluents and eventual disposal into the kraft recovery system is aimed at
elimination of colored effluents or the elimination of all effluents. These
processes include the Rapson process and electrostatic precipitator dust
catch leaching.
Pollutants investigated in this report are: 1) air-reduced sulfur com-
pounds (odors), sulfur dioxide, particulates, and chlorides; 2) water-BOD,
suspended solids, color, and toxicity; 3) and solid wastes. Some processes
generate nontypical pollutants particular to that process. These will be
discussed individually in the sections covering the particular process.
Energy requirements for the new processes are also discussed.
PROCESSES INVESTIGATED
Two soda pulping processes are discussed herein: full soda pulping,
and soda semichemical pulping. Although they are similar processes there are
enough differences between the two to result in different pollutional charac-
teristics. Although soda pulping is an old and well known process, it is in-
cluded because of its low-odor potential.
Several process configurations have been developed for oxygen pulping.
These processes include oxygen pulping of thin chips, soda pulping followed
by oxygen delignification, and thermochemical pulping followed by oxygen de-
lignification. An alkaline sulfite pulping-oxygen delignification process
and oxygen alkali semichemical process have also been proposed. The first 3
aforementioned processes will be examined separately since each has its dis-
tinctive pollution characteristics. The latter two are not examined in this
paper.
1
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Halogen pulping is of interest to the pulp and paper industry because
of the high strength pulps produced at high yields. Although there are pro-
blems to be solved, such as optimum process configuration and the high cost
of pulping chemicals, this process offers many potential advantages over the
kraft process.
An occasional journal article appears on solvent pulping indicating that
the process is still being considered for commercial development. The pro-
cesses are being designed with lignin by-product production in mind and with
air pollution control as a major side benefit.
Although the Rapson process is not a sulfur-free process it is included
because of some potential air pollution problems, it is a new development,
and because it does not produce a contaminated water discharge.
PROCESSES NOT INVESTIGATED
Nitric acid pulping is not included because of a lack of industry in-
terest due to high pulping chemical cost, corrosion, and cooking liquor dis-
posal problems. Emission of toxic nitrogen oxides is also a potential pro-
blem (1).
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SECTION 2
CONCLUSIONS
Each of the pulping processes studied in this paper has its own poten-
tial pollution problems, but they are generally less than would come from a
kraft mill. Some of the new pulping processes are designed to reduce air
pollution and some to reduce water pollution. The result is generally a de-
crease in most pollution parameters but an increase in a few other pollution
parameters, or in some cases, the creation of a new pollutant not indigenous
to the present pulping industry. The increased pollutants resulted from
power production in boilers due to the higher energy requirements of some of
the new pulping processes compared to kraft. All of the new processes re-
sult in the reduction of odors due to reduced sulfur, less BOD, less suspend-
ed solids, less color, and lower toxicity. The process that shows the lowest
air and water pollution problems is production of pulp by high pressure
thermomechanical defiberation followed by oxygen delignification. Table 1
lists the estimated pollution parameters for the processes investigated.
The values presented in Table 1 are estimates. Improvements in the pro-
bable process configurations assumed may alter the results presented. For
instance, pulping at higher consistencies in any of the oxygen pulping pro-
cesses will reduce evaporation energy requirements and hence may reduce total
energy requirements and, therefore, SOp and particulate emissions.
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TABLE 1. SUMMARY OF RESULTS
All values are given as kg/metric ton pulp (Ib/ton) except energy
Parameter
Kraft
Soda
Soda
Semi
Chem.
Oxygen
Oxygen
Soda
Therm.
Mech.
Oxygen
Chips
Chlorine
Dioxide
Solvent
Rapson
Air
Reduced
Sulfur
so2
Parti culates
NOX
Others
0.12
(0.25)
2.3
(4.6)
2.8
(4.6)
21.9
(43.8)
0.0002
(0.0004)
0.9
(1.8)
2.7
(5.4)
27.1
(54.2)
0.0002
(0.0004)
0.3
(0.6)
3.0
(6.0)
7.2
(14.4)
.0002
(.0004)
1.2
(2.4)
3.6
(7.2)
19.2
(38.4)
Nal
0.2
(0.4)
CO
0-0.05
(0-0.1)
0
(0)
0.5
(1.0)
1.5
(3.0)
3.4
(6.8)
0
(0)
0.6
(1.2)
1.8
(3.6)
3.4
(6.8)
0
(0)
0.8
(1.6)
2.6
(5.2)
8.9
(17.8)
Nal
0.2
(0.4)
CO CO
0-0.05 0-0.05
(0-0.1) (0-0.1)
0
(0)
..
-_
~
Organic
Vapors
0.12
(0.25)
2
(4)
5.1
(10.2)
21.9
(43.8)
HC1
10
Water
BOD
TSS
Color*
Toxicity*
Solid*
Wastes
Purchased
Energy
Requirements
KKcal/t
(1000 BTU/Ton)
Power boiler
Capacity
KKcal/t
(1000 BTU/Ton)
7
(14)
15
(30)
~
--
1349
(4857)
492
(1772)
7.1
(14.2)
13.2
(26.4)
—
Lower
Similar
1268
(4566)
492
(1772)
2
(4.0)
8.0
(16.0)
„
Lower
Similar
2501
(9006)
2401
(8646)
1.0
(2.0)
2.8
(5.6)
Lower
Lower
Lower
1548
(5574)
834
(3003)
0.7
(1.4)
2.8
(5.6)
1.0
(2.0)
2.8
(5.6)
Lower Lower
Lower
Lower
740
(2665)
740
(2665)
Lower
Lower
951
(3424)
951
(3424)
0
0
0
0
Little
1456
(5243)
1237
(4454)
1.0
(2.0)
2
(4)
Lower
Lower
Similar
Unknown
Unknown
0
0
0
0
Lower
1050
(3781)
198
(713)
*Compared to kraft mill discharges.
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SECTION 3
RECOMMENDATIONS
Development and implementation of several of the new pulping technolo-
gies will significantly reduce the amount of both air and water pollution
from new mills as well as their energy requirements. A long range research
and development program should be implemented to bring those new pulping
technologies which are advantageous to the environment and have lower energy
requirements into industrial practice.
The processes having the greatest potential for reducing overall pollu-
tion are chlorine dioxide pulping and oxygen delignification following high
pressure thermomechanical pulping. Halogen pulping has no effluent and
manageable air pollution problems. The air pollution problems could be re-
duced by lower yields or using supplemental fuels in the recovery furnace
instead of in separate power boilers.
There would be no toxic materials discharged from a halo pulping mill.
Halo pulping, once developed, should receive rapid and wide spread acceptance
by the pulping industry because of the high strength pulp produced.
To achieve commercial development of the halo pulping process several
problems need to be resolved. Halogen pulping processes need to be further
investigated to reduce fiber damage in the refining stage. A high termpera-
ture thermomechanical stage to reduce fiber damage should be investigated. A
cost analysis of a halo pulp mill should be prepared to determine if the pro-
cess is economically viable. Energy requirements for production of pulping
chemicals should be scrutinized.
Oxygen delignification following high pressure thermomechanical deligni-
fication shows the most promise as a pollution free, low energy consuming
pulping process. Although the process evaluation in this paper shows a water
discharge from the process, this discharge could be eliminated by the develop-
ment of the appropriate technology. The only discharge arises from the bleach
plant. Recycling bleach plant wastes back through the recovery furnace would
eliminate all discharges but result in a buildup of chlorides in the cooking
chemicals. Chlorides could be removed from the pulping chemicals by crystal-
lizing sodium carbonate from a white liquor side stream and returning the
solid to the process, and using the chloride containing stream for bleach
plant chemical production. The additional energy gained from the organic
materials in the bleach plant effluent may reduce mill energy requirements
and result in less air pollution from power boilers.
Work yet required for commercialization of the thermomechanical-oxygen
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pulping system is optimization of the thermomechanical stage to result in the
least fiber damage, optimization of the oxygen stage to result in the least
carbohydrate degradation, development of oxygen stage configuration, and de-
velopment of a process to dispose of bleach plant wastes in the chemical re-
covery system.
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SECTION 4
KRAFT PULPING
Comparison of non-sulfur pulping processes to existing kraft mills is
not a valid comparison. The non-sulfur pulping mills, as well as any new
kraft mills, will be built with environmental limitations and energy conser-
vation in mind. To reach a fair assessment of the comparative pollution loads
of non-sulfur pulping to kraft pulping, the comparisons should be between
mills employing the latest technology. For that reason, a model of a new
kraft mill designed with pollution control and energy conservation in mind is
used for comparative purposes.
Some of the major new features in a new kraft mill would be, for air
pollution control, black liquor oxidation and lime kiln mud oxidation; for
water pollution control, use of the decker effluent for brown stock washing
and counter current wash in the bleach plant. All new pulping processes will
likely use counter current washing in the bleach plant. Figure 1 is a dia-
gram of a kraft mill.
AIR EMISSIONS
Much work is being done to further the state-of-the-art on air emission
control. Use of the new control technologies can reduce present day emission
levels. The following air pollution estimates are made assuming up to date
control technology is being used.
Reduced Sulfur
Reduced sulfur emissions come from three main sources, digester relief
and blow gases, lime kiln exhaust, and black liquor burning. Other minor
sources are from washers, black liquor oxidation towers, smelt dissolving
tanks, black liquor evaporation, and the lime kiln slaker vent.
Non-condensible gases from digester relief and flash can be incinerated
in the recovery furnace or lime kiln. Reductions in odors from black liquor
evaporation and incineration can be reduced by black liquor oxidation. Odors
from washers can be eliminated by using diffusion washers. Lime kiln exhaust
odors can be reduced by oxidation of the lime mud. New point source standards
for new kraft mills require that total reduced sulfur emissions be less than
0.12 Kg/t (0.25 Ib/T).
Sulfur Dioxide
Sulfur dioxide emissions from a kraft recovery boiler depend upon the
operating conditions of the boiler. High sulfidities, low firing rates, low
7
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2.1 (2.5)
4.2
1.3 |
STEAM
CAUSTICIZING
f 0.0
COMBUSTION
1.-8
EVAPORATION
4.2
i
2.1
7.7
7.2
6.3
9.8
3.9
1 *"
DIGESTER
I
r7.4
WASH
H 6.7
KNOTTER
,
,
DECKER
r8'7
1.0
FLA
SH ,
9.1
25.9
4.1
CHLORINATION
>||r34.6
WASH
6.7
EXTRACTION
0.8
8.2
WASH
CI0
WASH
0.4
0.8
8.4?
EXTRACTION
WASH
jE
CIO.
WASH
;.9
35.8
11.8
0.8
0.8
9.6
Figure 1. Diagram of a kraft pulping process
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bed temperatures, and low primary air temperature will result in high sulfur
dioxide emissions. The opposite conditions will result in low or no sulfur
dioxide emissions from the recovery boiler. In a new or existing kraft mill
these variables can be controlled to minimize sulfur dioxide emissions (2)
(3).
Other S02 emissions are from the lime kiln and from power boilers. Lime
kiln SCL emissions are between 0 to 1.4 kg/t (2.8 Ib/T), depending upon the
sulfur Content of the fuel oil (46). Power boiler S02 emissions calculated in
appendix B are 0.3 kg/t (0.6 Ib/T). Total S09 emissions from a kraft mill are
between 0.3 to 1.7 kg/t (0.6 to 3.4 Ib/T). ^
Particulates
Particulate emissions occur wherever there are combustion processes,
particularly (excuse the pun) from the recovery boiler, lime kiln, and power
boilers. Incidental emissions of 0.01 to 0.5 kg/t (0.02-1.0 Ib/T) occur from
the smelt dissolving tank. Particulate emissions from the recovery furnace
can be controlled to 2.3 kg/t (4.7 Ib/T), and emissions from the line kilns to
0.5 kg/t (1.0 Ib/T) (31). Particulate emissions from the power boilers calcu-
lated in Appendix C are 0.52 kg/t (1.04 Ib/T). Total particulate emissions
from a bleached kraft mill are 3.3 kg/t (6.6 Ib/T) bleached pulp.
Nitrogen Oxides
Nitrogen oxide emissions are calculated in Appendix D, and are 21.9 kg/t
(43.8 Ib/T) for a kraft mill.
WATER DISCHARGES
Estimates for the BOD and total suspended solids discharges from a kraft
mill were taken from BPCTCA Effluent Limitations for the Bleached Kraft Indus-
try (4). The maximum 30 day average for bleached kraft BOD is 7.1 kg/t
(14.2 Ib/T), and the maximum 30 day average for suspended solids is 12.9 kg/t
(25.8 Ib/T). Newly built mills should achieve at least half these values
through planning for better pulp washing and spill containment.
Color
Color in a kraft mill effluent arises mainly from black liquor spills,
decker effluents, and caustic stage bleach plant effluents. In a well design-
ed new kraft mill, black liquor spills should be eliminated or drastically re-
duced and decker effluents recycled back to brown stock washing. Bleach plant
effluents would contain about 140 color units (5).
Toxicity
Toxicity in kraft mill effluents is largely attributed to the fatty acids
and to chlorinated lignin fragments in the bleach plant effluent. Fatty acids
should be of minor concern in a well designed kraft mill because of a lack of
spills and lack of decker effluent. Bleach plant toxicity would remain at
about 0.9 toxicity units (5).
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SOLID WASTES
Solid wastes from a kraft mill occur from 4 main sources: process loss-
es including wood preparation, green liquor dregs, washing and screening
losses, bleach plant wastes, drying wastes and spills; water treatment
sludges; fly ash; and biological solids developed from treatment of effluents.
Process losses can be estimated by assuming they are 90% of the raw
waste load suspended solids, or that which would be removed in the primary
clarifier. Knots and shives are not included because they can be refined or
repulped. Process loss solid wastes are estimated to be 22 kg/t (44 Ib/T)
(6). Water treatment waste solids depend upon the quantity and quality of
water treated. The variables are too numerous to attempt an estimate of
solids from that source. Fly ash generation will depend upon the quantity of
energy required and the type of fuel used in the boiler. Bark and coal will
produce the greatest quantity of fly ash, whereas gas or oil will produce
none.
Biological solids derived from secondary treatment of effluents are the
largest solid waste disposal problem. They have a high volume to dry weight
ratio when wet and are difficult to dewater. The quantity of biological
solids produced depends upon the quantity and quality of the effluent and the
detention time of the secondary treatment. Activated sludge systems will
produce more solids than will an aerated lagoon.
ENERGY
The major energy uses in a kraft mill are pulping, evaporation, brown
stock washing, bleaching, and lime production. Most of the energy used in a
kraft mill is derived from burning the black liquor which contains dissolved
wood materials. Appendix A gives calculations for deterimining energy use
for a kraft mill.
A new kraft mill would keep its energy requirements low by recycling as
much water as possible. In older kraft mills much process heat is used once
in heating fresh water, and then discharged. Recovery of low temperature
waste heat may be designed into new mills.
The total energy required from external sources in a kraft mill is 1349-
KKcal/t (4856 x lO*3 BTU/T). Of that energy required, 852 KKcal/t (3067 x ~\0^
BTU/T) is used for causticizing lime mud, and 492 KKcal/t (1171 x 103 BTU/T)
is used for producing electricity or process steam.
10
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SECTION 5
SODA PULPING
PROCESS DESCRIPTION
Alkaline pulping originally used sodium hydroxide as the active pulping
chemical. Small amounts of sulfur compounds found their way into the cooking
chemical system so that the original soda mills had a sulfidity of around 5%
or less. It was found that the presence of the sulfide in the cooking liquor
improved the yield and strength of the pulp. The kraft industry developed
when Dahl used sodium sulfate as the make-up chemical in place of soda.
The equipment and processes used in soda pulping are essentially the same
as that used in the kraft industry. A model of a soda pulping mill was de-
veloped by using a typical kraft type process without use of sulfur compounds.
Chips at 45% moisture are pulped to a 47% yield using 18% chemical on
wood and at a liquor to wood ratio of 3:1 in a continuous digester. The cook-
ing chemical is sodium hydroxide. The pulp is washed counter currently using
water from the knotters. The pulp is then bleached in a CEH sequence.
Bleaching losses are assumed to be 8%. The black liquor is evaporated and
burned in a recovery furnace. The resulting green liquor is causticized.
Figure 2 is a block diagram of the model mill.
Some work is being done using potassium hydroxide as the base in place
of sodium hydroxide. Potassium hydroxide is a more selective pulping agent
than sodium hydroxide and, therefore, produces greater yields (7). If potas-
sium hydroxide is to be used in a mill, washing efficiency of the pulp will
have to be greatly increased to reduce losses of cooking chemicals. Potas-
sium hydroxide is considerably more expensive than sodium hydroxide or sodium
sulfate.
Recent work has shown that with a 0.1 to 1% anthraquinone addition to
soda pulping liquors an increase in pulp yields of a given liquor content can
be achieved (8,g). There is insufficient information available as to whether
higher pulp strengths can be achieved. If higher pulp strengths can be
achieved, anthraquinone could be used to replace sulfur in existing kraft
mills to keep odors under control.
Bleached soda pulps are normally used in specialty papers such as offset,
book, bond, memo, duplicator, tablet, writing, and envelope grades. Soda pulp
strength characteristics are weaker than those of sulfite pulps but have de-
sirable properties of high bulk, good formation, high opacity, high degree of
softness, and a smooth surface. The advantage of soda pulping over sulfite
pulping is that the soda process can pulp resinous soft woods whereas the
11
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1.9 (2.3)
4.b
±» PAN ^T
'
ICIZING
1
COMBUSTION
1
1.3
— L_ V A 1 U 1
',.7
NATION
4.8 6
2.1
7.9
.y
-
10.0
2
29
..4
— ^
7.5
.5
DIGESTER
,
,8.8
WASH
,
,7.9
KNOTTER
,
,(1.08)
DECKER
,
8.7
CHLORINATION
\
' 34.6
1.0
9.1
WASH
0.7
EXTRACTION
0.8
WASH
HYPOCHLORITE
WASH
6.7
31.5
10.4
2.0
9.6
Figure 2. Diagram of a soda pulping process
12
-------
sulfite process cannot. Soda pulping may be able to compete with the sulfite
pulp market, but would be unable to compete with the kraft pulp market due to
inferior strength properties. There are presently three mills making pulp
from wood chips in the United States. Mills pulping other materials than
wood often use a soda cook.
AIR EMISSIONS
Reduced Sulfur Compounds
The lack of sulfur as a pulping chemical allows emissions from a soda
pulping mill with greatly reduced odor compared with kraft. Some reduced
sulfur odors do occur because of an unintentional buildup of sulfur in the
cooking chemical cycle. The sulfur compounds are converted to their reduced
state in the recovery furnace. The reduced sulfur compounds are then emitted
to the air at various localities in the mill. A number of sources contribute
sulfur to a soda pulping mill. Appendix E discusses the sulfur contributions
to and escapes from non-sulfur pulping processes.
Uncontrolled reduced sulfur emissions are about 0.01 kg/t (0.02 Ib/T).
Odors from a soda mill can be effectively controlled by chemically scrubbing
the gases containing malodorous compounds with oxidants. Controlled emissions
would be about 0.0002 kg/t (.0004 Ib/T) reduced sulfur compounds.
Sulfur Dioxide
There should be no sulfur dioxide emissions from the recovery boiler at
a soda mill. Small amounts of sulfur dioxide form in the recovery boiler at
the low sulfidities present in a soda pulp mill. The sulfur dioxide reacts
with sodium carbonate fumes and oxygen is completely removed as sodium sulfate
in the electrostatic precipitator.
Sulfur dioxide can be expected in the lime kiln flue gas. The quantity
present will depend upon the sulfur content of the fuel and the quantity of
CaO required. About 60% more NaOH on wood is required for soda pulping than
for kraft pulping. Therefore, soda mills should emit about 60% more S0? from
their lime kilns than do kraft mills. Sulfur dioxide from the lime kiln will
range between a trace and 0.32 kg/t (.64 Ib/T) (10).
Sulfur dioxide will be present in the power boiler fuel gas. The quan-
tity present will depend upon the sulfur content of the fuel and the amount of
steam required by the mill. Power boiler capacities required to operate a
soda pulping mill are calculated in Appendix A. Appendix B shows sulfur
dioxide emission calculations from power boilers for different fuels. Sulfur
dioxide emissions from power boilers based on the use of wood wastes are used
in the summation of the total mill S02 emissions because wood wastes are the
lowest cost fuel. S02 emissions from the power boiler are 0.3 kg/t (0.6 Ib/T)
pulp.
A soda pulping mill will emit approximately 0.94 kg/t (1.88 Ib/T) pulp
sulfur dioxide.
13
-------
Particulates
Particulate emissions from the soda process are shown in Appendix C.
They are much higher than kraft participate emissions because sodium hydrox-
ide and sodium oxide volatilize at a considerably lower temperature in the
recovery furnace than does sodium sulfide and sodium sulfate. These volatil-
ize at a considerably lower temperature in the recovery furnace than does
sodium sulfide and sodium sulfate. These volatilized sodium compounds con-
dense and react with flue gases to form particulates. In summary, emissions
are: from the recovery furnace, 1.55 kg/t (3.0 Ib/T) pulp; from the smelt
tank, 0.25 kg/t (0.54 Ib/T) pulp; and from the lime kiln, 0.5 kg/t (1.0 Ib/T)
pulp; from the power boiler, 0.5 kg/t (1.0 Ib/T) pulp, for a total of 2.8 kg/t
(5.2 Ib/T) pulp.
Nitrogen Oxides
Nitrogen oxide emissions are calculated in Appendix D and are 21.1 kg/t
(42.2 Ib/T) for a soda pulping mill.
WATER DISCHARGES
The major effluent sources from a soda pulp mill are decker seal pit
water, digester relief condensates, evaporator condensates, bleach plant
effluent, spills, and miscellaneous wastewaters including recovery plant
discharge, boiler plant blowdown and water treatment wastes. Pollutional
compounds present are BOD, suspended solids, color, and toxicity.
Biochemical Oxygen Demand
Raw waste BOD values from soda mills range between 20 and 30 kg/t
(40-60 Ib/T) of pulp produced. Half of the BOD originates from the bleach
plant (11). After treatment the maximum 30 day average BOD values will be
less than 7.1 kg/t (14.2 Ib/T), which is the Best Practicable Control Techno-
logy Currently Available effluent guidelines limitation for the soda sub-
classification.
Total Suspended Solids
Raw waste total suspended solids from a soda mill range between 20 and
30 kg/t (40-60 Ib/T) of pulp produced (11). Solids in the raw waste are re-
moved sufficiently in primary and secondary treatment and have little effect
on the treated effluent. Suspended solids are generated by biological treat-
ment. Suspended solids after treatment are less than 13.2 kg/t pulp (26.4
Ib/T), the Best Practicable Control Technology Currently Available effluent
guidelines limitation for the soda subcategory.
Color
Little information on color discharges from soda mills is available.
14
-------
Toxicity
Soda pulping effluents contain compounds that are toxic to aquatic life.
Toxic compounds contained in soda mill effluents are resin acid soaps and
turpene derivatives. Since sulfur is not used in the process the effluents
appear to have a slightly lower toxicity level than kraft mill effluents (5)
Another paper repcr's that soda mill white water is considerably less toxic
than kraft mill white water (12).
SOLID WASTES
Solid wastes from a soda mill occur from 4 main sources: 1) process
losses including wood preparation, green liquor dregs, washing and screening
losses, bleach plant wastes, drying wastes and spills; 2) water treatment
sludges; 3) fly ash; and 4) biological solids developed from treatment of
effluents.
Process losses can be estimated by assuming they are 90% of the raw
waste load suspended solids, or that which would be removed in the primary
clarifier. Knots and shives are not included because they could be refined
or repulped. Process loss solid wastes are estimated to be 22 kg/t (44 Ib/T)
(6). Water treatment waste solids depend upon the quantity and quality of
water treated. The variables are too numerous to attempt an estimate of
solids from that source. Fly ash generation will depend upon the quantity
of energy required and the type of fuel used in the boiler. Bark and coal
will produce the greatest quantity of fly ash, whereas gas or oil will pro-
duce none.
Biological solids derived from secondary treatment of effluents are the
largest solid waste disposal problem. They have a high volume to dry weight
ratio when wet and are difficult to dewater. The quantity of biological
solids produced depends upon the quantity and quality of the effluent and the
detention time of the secondary treatment. Activated sludge systems will pro-
duce more solids than will an aerated lagoon. Overall, a soda mill will pro-
duce about the same quantity of solids as a kraft mill.
ENERGY
The energy use in a soda mill is quite similar to that found in a kraft
mill. There are two major differences; the amount of energy produced in the
recovery furnace is greater for soda mills than for kraft mills, and a soda
mill uses more fuel oil in the lime kilns. Kraft mills produce less energy
in the recovery furnace than do soda mills because large quantities of energy
are required to reduce sulfates to sulfides. Soda mills have no sulfur com-
pounds in their cooking liquors. The sulfide in kraft mill liquors supplies
some of the active alkali during digestion. Because of the lack of sulfides
in a soda mill more sodium hydroxide is required to provide the active alkali
and more lime is required for caustization of the green liquor.
The soda process requires a total purchased energy of 1268 KKcal/t
(4,566 KBTU/T) bleached pulp. Of that energy, 1117 KKcal/t (4,022 KBTU/T)
15
-------
is contained in fuel oil to fire the lime kiln. The remaining 151 KKcal/t
(544 KBTU/T) will most likely be produced by burning bark and wood residues,
16
-------
SECTION 6
SODA SEMICHEMICAL PULPING
PROCESS DESCRIPTION
Semi chemical pulping was developed to produce high yield chemical pulps.
The chips are cooked in a digester with chemicals for a shorter time than a
full chemical cook, then are refined to produce pulp. Most semichemical
pulping uses neutral sulfite pulping chemicals.
A model of a soda semichemical pulp mill was used to calculate pollution
loads and energy requirements. Chips at 45% moisture are pulped to a 75%
yield in a continuous digester. PUlping conditions were: 10% chemical on
wood, 3:1 liquor to wood ratio, and 20% NaOH and 80% Na2C03 as chemical on
wood. The cooking temperature was 170 C (338 F). After blowing the chips
are passed through a refiner, then washed and screened. If the pulp is to be
used for making paper it is bleached in a CEH sequence. The black liquor is
evaporated and burned. The resulting green liquor is partially causticized.
The process is shown in Figure 3.
Pulp Properties and Uses
The pulps produced are similar to those produced by NSSC. These pulps
are most suitable for production and corrugating media, braille, duplicator,
envelope, ledger, and offset type papers where high strengths are not re-
quired.
State of Development
Many mills producing semichemical corrugating medium by the NSSC process
are converting to sulfur free processes. Eight mills made the conversion in
1977 and four more are considering the change (13). The conversion is being
made for three reasons. 1) poor markets for the salt cake by-product pro-
duced by NSSC pulping via fluidized bed incinerators; 2) high chemical costs
because sodium sulfate and soda ash can not be recycled and 3) reduced sulfur
emissions leading to odor problems.
AIR EMISSIONS
Reduced Sulfur Compounds
The lack of sulfur as a pulping chemical greatly reduced odor emissions
from a soda semichemical pulping mill. Some reduced sulfur odors do occur
because of an unintentional build up of sulfur in the cooking chemical cycle.
17
-------
1.2(1.45)
1.3
6.U
i
COMBUSTION
fo.5
EVAPORATION
3.U
6.4
4.4
1.4
^—
7.8
4.7
7.2^
29.5
DIGESTER
1
REF
i
,5.6
NER
4.6
WASH
i
6.7
KNOTTER
,
,
DECKER
,
8.7
CHLORINATION
\
-36.4
WASH
1.0
9.8
31.5
0.7
0.8
EXTRACTION
8.9
WASH
II
10.4
HYPOCHLORITE
2.0
WASH
9.6
6.7
Figure 3. Diagram of a soda semichemical pulping process
-------
The sulfur compounds are converted to their reduced state in the recovery
furnace. A number of sources contribute sulfur to a soda pulping mill.
Appendix E discusses the sulfur contributions and losses in non-sulfur pulp-
ing processes.
Uncontrolled reduced sulfur emissions are about 0.01 kg/t (0.02 Ib/T).
Odors from a semichemical soda mill can be removed by chemically scrubbing
the gases containing malodorous compounds with oxidants. Controlled emis-
sions would be about 0.0002 kg/t (.0004 Ib/T) reduced sulfur compounds.
Sulfur Dioxide
There should be no sulfur dioxide emissions from the recovery boiler at
a soda semichemical mill. Small amounts of sulfur dioxide that form in the
recovery boiler at low sulfidities react with sodium carbonate fumes and are
removed as sodium sulfate in the electrostatic precipitator.
Sulfur dioxide can be expected in the lime kiln flue gas. The quantity
present will depend upon the sulfur content of the fuel and the quantity of
CaO required. Since the cooking liquor Na^CO-, to NaOH ratio is between 2:1
and 4:1, and 10% Na^O on wood is used (14), much less calcium oxide is re-
quired than in a kraft mill. A kraft mill needs to produce 188 kg (376 Ib/T)
CaO per ton of pulp. A semichemical soda mill will require less than 47 kg
(97 Ib/T) CaO per ton pulp, or about 25% of a kraft mill lime requirement.
Sulfur dioxide emissions from the lime kiln would be between a trace and
0.05 kg/t (0.10 Ib/T). These values were computed by taking 25% of emissions
expected from a kraft lime kiln.
Sulfur dioxide will be in the power boiler flue gas. The quantity pre-
sent will depend upon the sulfur content of the fuel used and the amount of
steam required by the mill. Appendix B shows that S0? emissions from a soda
semichemical mill to be about 0.5 kg/t (1.0 Ib/T) pulp for oil fired boilers,
0.8 kg/t (1.6 Ib/T) pulp for coal fired boilers, and 0.3 kg/t (0.6 Ib/T) for
waste wood fired boilers.
Particulates
Particulate emissions from the soda semichemical process are shown in
Appendix C. In summary, emissions are: from the recovery furnace, 0.29
kg/t (0.38 Ib/T) pulp; from the smelt tank, 0.1 kg/t (0.2 Ib/T) pulp; from
the lime kiln, 0.11 kg/t (0.22 Ib/T) pulp; and from the power boiler, 3.0
kg/t (6.0 Ib/T) pulp, for a total of 3.5 kg/t (7.0 Ib/T) pulp.
Nitrogen Oxides
Nitrogen oxide emissions are calculated in Appendix D and are 7.2 kg/t
(14.4 Ib/T) for a soda semichemical pulp mill.
WATER DISCHARGES
The major effluent sources from a soda semichemical pulp mill are decker
seal pit water, digester relief condensate, bleach plant wastes, spills, and
19
-------
miscellaneous waste water including recovery plant discharge, boiler plant
blowdown, and water treatment plant wastes.
Biochemical Oxygen Demand
Raw waste loads from a soda semichemical pulping mill are about 18-19
kg BOD per t (36-38 Ib/T) pulp (11). Nearly 80% of this BOD comes from the
pulp mill consisting largely of digester relief condensate and spills. The
remaining 20% comes from carryover in the evaporators. The BOD is reduced to
2 kg BOD per t (4 Ib/T) pulp with biological treatment.
Total Suspended Solids
Raw waste total suspended solids from a soda semichemical mill are about
40 kg/t (80 Ib/T) pulp (11). About 60% of the suspended solids come from the
pulping area, largely from spills. The remaining 40% of the suspended solids
come from the liquor recovery area and water plant discharges (15). Solids
in the raw waste are removed sufficiently in primary and secondary treatment
and have little effect on the solids discharged. Suspended solids are gen-
erated by biological treatment and make up the bulk of the solids in the dis-
charge. Suspended solids discharge from this type of mill is estimated to be
8 kg/t (16 Ib/T) pulp. This estimate was arrived at by dividing the BOD from
a soda mill by the ratio of BOD in the inlet to the suspended solids in the
effluent from a kraft mill.
Color
Little information on color discharges from a soda semichemical mill is
available.
Toxicity
Soda mill effluents are reported to be less toxic than kraft mill efflu-
ents (12). Toxic materials such as dimethyl sulfide are not present, al-
though the resin acids are.
SOLID WASTES
Solid wastes from a semichemical soda mill occur from 4 main sources:
process losses including wood preparation, green liquor dregs, washing and
screening losses; drying wastes, and spills; water treatment sludges, fly
ash; and biological solids developed from treatment of effluents. Process
losses can be estimated by assuming they are 90% of the raw waste load sus-
pended solids, or that which would be removed in the primary clarifier.
Knots and shives can be refined or repulped to reduce solids loss. Process
loss solid wastes are estimated to be 36 kg/t (72 Ib/T). Water treatment
waste solids are dependent upon the quantity and quality of water to be treat-
ed. The variables were too numerous to attempt an estimate. Fly ash genera-
tion will depend upon the quantity of energy required and the type of fuel
used in the boiler. Bark and coal will produce the greatest quantity of fly
ash, whereas gas and oil will produce none. Biological solids derived from
secondary treatment of effluents are the largest solid waste disposal problem.
20
-------
They have a high volume to dry weight ratio when wet and are difficult to de-
water. The quantity of biological solids produced depends upon the quantity
and quality of the effluent and the detention time of the secondary treat-
ment. Activated sludge systems will produce more solids than will an aerated
lagoon. Overall, a soda mill will produce about the same quantity of solids
as a kraft mill.
ENERGY
Energy requirements for the various pulping processes are calculated in
Tables 6 through 16 in Appendix A. Energy requirements from sources external
to the mill are 91 KKcal/t pulp (328 KBTU/T) for causticizing and 2401 KKcal/t
pulp (8646 KBTU/T) for other mill power requirements for a total of 2501
KKcal/t (9006 KBTU/T) pulp. Electrical energy is assumed to be produced on
site from high pressure steam from either the recovery furnace or auxiliary
power boiler. Either gas, oil, or coal was assumed to be burned in the auxil-
iary power boiler.
Purchased energy requirements per ton pulp in a soda semichemical mill
are high because of the high yield. High yield results in less organic ma-
terials to be burned in the recovery furnace and thus in less energy produc-
tion. A semi-bleaching sequence saves some energy.
21
-------
SECTION 7
OXYGEN ALKALI PULPING
PROCESS DESCRIPTION
Oxygen pulping is being developed as a means of producing a high
strength chemical pulp without the odor problems associated with the kraft
pulping process. Oxygen alkali pulping is essentially a soda pulping pro-
cess followed by an oxygen delignification or oxygen bleach stage. The com-
bination of the soda pulping and oxygen delignification yields a pulp suit-
able for bleaching by a DED sequence.
Comparison of Process Alternatives
Yield
In oxygen-soda pulping delignification takes place in two stages, in the
soda stage and in the oxygen stage. The relative amount of delignification
occurring in each stage has a strong effect upon the pulp strengths when com-
pared at the same overall final yield. Pulps produced with a low amount of
delignification in the soda stage and the major portion of delignification in
the oxygen stage produced low strength pulps and required long detention
times in the oxygen stage (16). Pulps produced by delignification to the
fiberization point in the soda stage and further delignification in the
oxygen stage produced the strongest pulps (17) (18). For purposes of pollu-
tant calculations in this paper a soda yield of 55% and a soda-oxygen yield
of 50% were assumed. An additional 5% yield loss during bleaching was also
assumed.
Cooking Conditions
To achieve a full chemical pulp in the soda stage sodium hydroxide is
required. Pulping with NaHCO., results in a high shives content (19). The
chips are cooked with 8-13% NSOH as Na?CO, on wood depending on the yield de-
sired (16), (17), (20), (21). 16% NaOR on wood in the soda stage was used
for the calculations in this paper. The liquor to wood ratio was assumed to
be 3:1 in the soda stage. The cook temperature was assumed to be 160 C.
Sodium hydroxide, sodium carbonate, and sodium bicarbonate have been
investigated for use as active alkali in the oxygen stage. The active alkali
acts primarily as a buffering agent in oxygen delignification (18). High
pH's lead to excessive degradation of the cellulose while low pH's result in
slow reaction rates. The pH should ideally be held between 8.0 and 9.5.
Production of organic acids and carbon dioxide by the oxidation reactions re-
sults in consumption of active alkali.
22
-------
Addition of NaOH at once causes too high an initial pH. The addition of
Na~CO, results in a satisfactory oxygen cook. The pH of the cook can be con-
trolled by the digester relief rate, that is by control of the C0? content of
the gases (22).
Alkali dosages above 7% are reported to result in weak pulps (17). An
alkali dosage of 5% was used in the oxygen stage. Oxygen consumption has
been reported to be 15 to 18% on the soda stage pulp (16). Bleed off of
gases produced during delignification will result in a loss of oxygen, bring-
ing the oxygen requirement to 20 to 30% of the weight of wood. The consis-
tency in the oxygen stage was assumed to be 10%. Oxygen consumption will in-
crease with higher recycle rates of black liquor to the digester due to oxi-
dation of black liquor solids. This will also result in a loss of heating
value of the black liquor (23).
In choosing a temperature in the oxygen stage the degradation of cellu-
lose must be balanced by delignification rate or reactor size. At oxygen
stage temperatures above 120°C (248°F) to 140°C (284°F) the pulp strength
properties deteriorate rapidly (17). At lower temoeratures the delignifica-
tion rate drops off rapidly. For the calculations, 120°C (248°F) was used.
Fiqure 4 shows the process.
Products
Oxygen pulps can be used in the same applications as kraft pulps except
where tear and fold are critical. Oxygen pulps typically have low tear and
fold properties. Oxygen pulps would be well suited to use as linerboard.
They may also be used in register, bond, and memo papers. Tissue could not
be made from oxygen pulp because of the low tear.
State of Development
The first full scale mill using soda pulping followed by oxygen delig-
nification has just been built and is presently going through start up and
shake down. No details are available to date about the mill and its charac-
teristics. If this mill is a commercial success, more pulping mills of the
soda-oxygen type may be expected in the future.
AIR EMISSIONS
Reduced Sulfur Compounds
Oxygen pulping mills are not entirely sulfur free and therefore the pos-
sibility of reduced sulfur odor emissions exists. Although all sulfur present
in the oxygen stage will be in the oxidized form, reduced sulfur compounds
will be present at other locations in the mill. The soda stage will contain
reduced sulfur compounds and could have an odor problem. Appendix E shows
possible odor emissions from a soda pulping mill. Since pure oxygen will be
available in the mill, small quantities could be introduced into the soda
stage to oxidize the sulfur compounds and eliminate odors.
23
-------
1.7
2.5
CAUSTICIZING
1.3
6.3
1.7 (2.08)
COMBUSTION
1.3
EVAPORATION
9.0
9.0
2.0
SODA DIGESTER
2.1
9.1
4.1
2.1
4.1
7.4
6.5
3.5
1.9
1.0
7.0
REFINER
WASH
8.0
6.5(1.14)
02 DIGESTER
,(1.04)
WASH
12.1
5.9
KNOTTER
DECKER
8.5(1.04)
CIO-
11.6
0.4.^
0.8
9.6
WASH
U
EXTRACTION
(
WASH
{
F
CI02
i
\
WASH
15. IO
,_0.8
T0.40
6.9(1.0)
Figure 4. Diagram of an oxygen alkali pulping process
24
-------
Sulfur Dioxide
There should be no sulfur dioxide emissions from the recovery boiler at
an oxygen-soda mill. Small amounts of sulfur dioxide form in the recovery
boiler due to the low sulfur content of the pulping liquors. The sulfur di-
oxide reacts with the sodium carbonate fumes in the flue gas and is removed
as sodium sulfate in the electrostatic precipitator.
Sulfur dioxide can be expected in the lime kiln flue gas. The quantity
present will depend upon the sulfur content of the fuel and the quantity of
CaO required. About 5% more NaOH on wood is required for oxygen-soda pulp
than for kraft pulp so SCL emissions should be about 5% more than from kraft
mills. Emissions will range between a trace to 0.21 kg/t ADP (0.42 Ib/T ADP)
(10).
Sulfur dioxide will be in the power boiler flue gas. The quantity pre-
sent will depend upon the sulfur content of the fusl and the amount of steam
required by the mill. Calculations for S02 emissions from the power boiler
are in Appendix B. SOg emissions for oil Tired furnaces are 2.8 kg/t (5.6
Ib/T) pulp; for coal fTred furnaces, 4.4 kg/t (8.8 Ib/T); and for waste wood
fired boilers, 0.6 kg/t (1.6 Ib/T) pulp.
Particulates
Calculations for particulate emissions are in Appendix C. Emissions
from the recovery furnace are 2.33 kg/t (4.6 Ib/T) pulp which includes the
contribution due to sodium iodide if iodide is used as a carbohydrate protec-
tor during pulping. If sodium iodide is not present, particulate emissions
from the recovery furnace would be slightly less. Another contribution to the
total particulate emissions from a soda oxygen mill is 0.21 kg/t (0.42 Ib/T)
from the power boilers. The total particulate emissions from a soda oxygen
mill is estimated to be 3.85 kg/t (716 Ib/T).
Nitrogen Oxides
Nitrogen oxide emissions are calculated in Appendix D and are 19.2 kg/t
(38.4 Ib/T).
Iodide
If iodide is used as a cellulose degradation inhibitor in the oxygen
delignification stage, there is a possibility of iodide emissions from the
recovery furnace. Sodium iodide vaporizes at 1304 C (2379 F). well above
the bed temperature of a normal recovery furnace of about 982 C (1800 F),
however, at 982 C (1800 F) sodium idodide has a vapor pressure of 28 mm Hg,
which means a considerable quantity of sodium iodide can be vaporized. Sodium
chloride (which has a vapor pressure lower than sodium iodide), is known to
readily vaporize from kraft mill recovery furnaces. Condensation of the io-
dide will form a fume. The fumes can probably be removed from the flue gas
via an electrostatic precipitator with other particulates, although electro-
static precipitators are not as efficient on sodium chloride as they are on
other sodium salts, and therefore may show a poor performance on sodium iodide.
25
-------
About 60 kg/t (120 Ib/T) Nal on pulp is projected. About 40% of the Nal
in the black liquor will be vaporized, of which 50% will be captured in the
direct contact evaporator and 98% of the remainder removed by the electro-
static precipitator. Nal emissions would be about .24 kg/t (0.48 Ib/T) pulp.
If pulping chemicals are to be recovered by a wet oxidation method,
there would be no air emission of sodium iodide.(24).
Carbon Monoxide
The formation of carbon monoxide in oxygen bleaching mills has been
observed. At low consistencies between 0 to 50 g (0.1 Ib/T) carbon monoxide
per ton was measured, and at high consistencies (20-30%) 300 to 500 g (0.6 to
1.0 Ib/T) carbon monoxide per ton pulp was observed in the degasing line
(25). Similar formation of carbon monoxide was found in an oxygen pulping
system (26). Carbon monoxide formed during oxygen pulping can be handled by
venting the pressure relief gases to the recovery furnace or lime kiln air in-
take, as is done in kraft mills for odor control. There should be no carbon
monoxide emissions allowed from an oxygen pulping mill.
WATER DISCHARGES
New pulp mills will have the advantage of being able to install the new-
est technology for control of water effluents. Materials of construction can
be chosen so that corrosion is minimized. Old equipment would not require
modification or need to be replaced and plant layout can maximize the effi-
ciency of recycle. Water pollution discharges will be lower than existing
mills, disregarding the oxygen pulping. Oxygen pulping itself offers several
advantages, largely that the chlorination and first extraction stages in the
bleach plant are no longer required. Nearly 80% of the bleach plant BOD is
contained in the chlorination and first extraction stages of the bleach plant.
With new technology such as that used in the Rapson process, chlorides
may be removed from the cooking liquor enabling bleach plant effluents to be
recycled to the pulping cycle. These mills would have no discharge.
Biochemical Oxygen Demand
BOD discharges from an oxygen pulp mill are much lower than from a kraft
mill. Practices that result in reduced BOD are reuse of decker water on the
brown stock wash and elimination of the chlorination and first extraction
stage in the bleach plant. The evaporator condensate waters are recycled to
the screen and causticizing department. The only pollutant from the pulping
stage would be from the relief gas concentrate turpentine separation, minor
flows from the causticizing department, and from leaks and spills. Digester
condensate from a continuous digester contains 2.6 Kg/t (5.8 Ib/T) BOD (15).
Spills and miscellaneous flows may amount to 3 Kg/t (6.0 Ib/T) (15).
Bleach plant effluents from an oxygen pulp mill will be much less than
that from a kraft mill. The oxygen pulping stage eliminates the need for the
chlorine and first extraction step leaving a DED sequence. The largest flow
will be from the chlorine dioxide stage wash. BOD from the DED bleaching se-
26
-------
quence in a kraft mill is between 2 and 3 Kg/t (4-6 Ib/T) (27), (28). Raw
BOD loadings from an oxygen pulping mill bleach plant will be slightly higher
than a kraft mill DED portion of bleach plant because of carry over of black
liquor solids from the decker into the bleach plant which are normally washed
out in the chlorination stage. BOD loading from an oxygen bleach plant
should be about 3 to 4 Kg/t (6-8 Ib/T) pulp.
Total BOD raw waste loading from an oxygen pulp mill is about 8.6 to
9.6 Kg/t (17.2-19.2 Ib/T) oulp. Assuming a 90% efficient waste treatment
system, final iJOiJ discharges will be in the range of .86 to .96 Kg/t (1.72-
1.82 Ib/T).
Suspended Solids
Because of the reduced discharges due to recovery of decker effluents
and short bleaching sequences, suspended solids discharges will be less than
expected from a kraft mill. Suspended solids would enter the sewer through
spills, lime kiln dregs, water treatment plant sludges, and bleach plant
effluents. Spills will contribute about 5 Kg/t (10 Ib/T) suspended solids.
Causticizing and boiler room effluents will contribute about 3 Kg/t (6 Ib/T)
suspended solids.
Most of the suspended solids in the raw waste load will be removed by
primary and secondary treatment. Solids produced by biological activity
during secondary treatment will make up the bulk of suspended solids in the
effluent, and is directly related to the BOD and the method of treatment.
Assuming a concentration of 100 mg/1 suspended solids escaping in the efflu-
ent and a flow of 28,000 1/t (1679 gal/T) pulp, suspended solids leaving with
the treated effluent are 2.8 Kg/t (5.2 Ib/T) pulp.
Color
Oxygen pulping liquors have about one fourth the color of kraft or soda
liquors (12), (29). Spills from screening and deckers would thereby contain
relatively little color. The strongly colored chlorine extraction stage
effluent would also not be present. The DED bleaching effluent has 1.5% of
the color of the full CEDED bleaching sequence (5).
Toxicity
Conditions present during oxygen pulping destroy resin and fatty acids
that are responsible for toxicity in many pulp mill discharges (30). Other
toxic materials such as methyl sulfides are not present because of the ab-
sence of reduced sulfur. Bio-assay tests have shown that oxygen pulping
liquors are non-toxic (12). The chlorination stage bleach plant effluent
which contributes to effluent toxicity is not present in oxygen pulping mills.
Chlorine dioxide bleaching effluents have been shown to be less toxic than
chlorine stage effluents (5). Toxicities resulting from the bleach plant
effluent are shown in Table 2.
27
-------
TABLE 2. TOXICITY AND COLOR OF BLEACH PLANT EFFLUENTS
Stage Toxicity Units Color Units BOD
c
E
D
.5
.2
.13
140
338
7.3
9.0
7.0
1.9
SOLID WASTES
Solid wastes from an oxygen-soda mill come from several sources: 1)
process losses, including wood preparation, green liquor dregs, washing and
screening losses, bleach plant wastes, drying wastes, and spills; 2) water
treatment sludges; 3) fly ash; 4) anH biological solids developed from treat-
ment of effluents.
Process solids losses can be estimated by assuming that 90% of the sus-
pended solids in the effluent are removed in the primary clarifier. Knots
and shives are re-refined. Process solids losses are estimated to be 8 Kg/t
(16 Ib/T) so that clarifier solids to be disposed of are estimated to be
9 Kg/t (18 Ib/T). Addition of metal salts to retard cellulose degradation
will result in extra green liquor dregs of about 2.0 Kg/t (4.0 Ib/T).
Water treatment waste solids are dependent upon the quality and quan-
tity of the water to be treted. Water quality is highly variable, depending
upon plant location and season, and thereby making estimates of sludges pro-
duced difficult. Water use in an oxygen-soda mill would be less than that of
kraft, so the solids produced by this source are less.
Fly ash generation will depend upon the quantity of energy required and
the type of fuel used in the boiler. Bark and coal will produce the great-
est quantity of fly ash, whereas gas or oil will produce none. Use of ex-
ternal energy is greater for oxygen soda pulping than for kraft, so fly ash
generation will be greater.
Biological solids derived from secondary treatment of effluents are the
largest solids waste disposal problem. They have a high volume to dry weight
ratio when wet and are difficult to dewater. The quantity of biological
solids produced depends upon the quantity and quality of the effluent and the
detention time of the secondary treatment. Activated sludge systems will
produce more solids than will an aerated lagoon. Overall, an oxygen-soda
mill will produce less biological solids than a kraft mill because of the
lower raw BOD loading to the treatment plant.
ENERGY
The major energy uses in an oxygen-soda mill are for heating the diges-
ters, evaporating the black liquor, bleaching, and causticizing. Digester
28
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heating is a major energy user because pulping is by a two stage process with
washing in between. In each stage high value steam is used to heat the di-
gestors, and hot water is produced when the pulp is blown. A well designed
mill should be able to recover this heat for other uses in the mill such as
wash water in the bleach plant. Black liquor evaporation uses more energy
than other pulping processes because of the high loading to the evaporators.
The two digesters in sequence produce more liquors to be evaporated than other
processes. To reduce the evaporator energy requirements, higher consisten-
cies can be used in the oxygen stage or a higher degree of black liquor re-
cycle used so as to reduce the ev?r>orator loading.
The amount of energy recovered from burning the black liquor is not as
great as in a kraft mill because of the higher unbleached yield and the oxi-
dation of some of the organics in the oxygen pulping stage. Higher yields
result in less organic materials to be burned in the recovery furnace. De-
struction of organics in the oxygen stage also results in less organics to
be burned in the recovery furnace. Oxidation of organics in the digester
liberates heat in the digester, so digestor heating requirements are reduced.
Production of tonnage oxygen consumes energy but is partically offset by a
reduction in energy required to produce bleach plant chemicals. The oxygen
delignification stage replaces the first chlorination and extraction steps
in the bleach plant, realizing energy savings in the bleach plant.
For an oxygen soda pulp mill the energy required from sources external
to the mill is 1287 Kcal/t (4634 KBTU/T). Of that energy, 714 Kcal/t (2570
KBTU/T) is required for causticizing and 561 Kcal/t (2020 KBTU/T) is used to
fire power boilers.
29
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SECTION 8
THERMOMECHANICAL PULPING FOLLOWED BV OXYGEN DELIGNIFICATION
Process Description
Because oxygen pulping is diffusion limited (20), different means are
employed to expose the lignin directly to the pulping liquors. In thermo-
mechanical pulping the chips are reduced to fibers by refining. High tempera-
tures are used to reduce the damage to pulp fibers. The lignin is then readi-
ly available to attack by oxygen in the pulping liquor.
Chips are first cooked with steam under high pressure for about 5 min-
utes, then refined while under pressure. The pulp then passes into the
oxygen stage where active alkali and oxygen are added. Following the oxygen
stage the pulp is washed, screened, and bleached if desired. The bleaching
sequence is DED since the oxygen stage replaces the chlorine and extraction
stages of a normal full bleaching sequence. The cooking liquors are evapora-
ted and the solids incinerated for chemical recovery. If NaOH is the pulping
chemical, the green liquor passes through a causticizing plant. If NaCO-, is
the pulping chemical, the causticizing plant is unnecessary.
Comparison of Process Alternatives
Thermomechanical Stage
The significant process variables in the thermomechanical stage are the
cook time, cook temperature, and refiner rpm and clearance. Sufficient time
in the preheater is required to raise the chips to a uniform temperature.
Less than 5 minutes are required for heating the chips. The preheating tem-
perature governs the amount of lignin softening that occurs.
When wood chips are heated the lignin and hemicelluloses between the
cell walls becomes soft. The softening of the lignin begins at specific tem-
peratures referred to as t'ie glass point. The glass point for each species
of wood is different. During cooking the lignin is heated to the glass point
so the fibers can be easily separated upon refining. At temperatures below
the glass point the wood fractures through the outer layer of the secondary
cell wall. At temperatures above the glass point the wood fractures through
the lignin layers between the cells. When wood has been fiberated above the
glass point the fibers will be coated with a layer of lignin (31). The tran-
sition between spruce fracturing in the cell wall or fracturing between the
cell wall occurs between 120°C (248°F) and 135°C (275°F) (31).' The therrno-
mechanical pulps will be stronger if the fibers have not been torn. A thermo-
mechanical stage temperature of 160 C (320 F) was used.
30
-------
Oxygen Stage
The majority of the delignification takes place in the oxygen stage of
oxygen thermomechanical pulping. Critical parameters are time, temperature,
active alkali concentration, pH, stirring rate, and oxygen pressure.
The amount of time required in the oxygen stage is a function of all the
other parameters mentioned. Pulps with kappa numbers below 15 can be pro-
duced in less than 2 hours (32). The time required may be shortened by opti-
mizing the other variables. Stirring, which increases oxygen availability,
is of prime importance. The conditions in most laboratory oxygen pulping in-
vestigations are that of oxygen starvation. All the oxygen is added at the
beginning of the reaction and is rapidly consumed. About 20% oxygen on
beechwood is required (16). Other types of wood require different amounts of
oxygen.
Higher temperatures lead to faster delignification rates. Temperatures
above 150 C (302 F) are suitable to produce a pulp with a brightness above
30% and a yield of less than 60% in about 60 minutes. A temperature of 160 C
(320 F) is used in these calculations since that is the temperature of the
pulp leaving the refiners. When the same temperature is used in both stages
there is no loss of energy between staqes.
Cooking chemicals are either sodium hydroxide or sodium carbonate. The
use of sodium carbonate in the oxygen stage as active alkali results in pulp
of higher brightness, a higher breaking length, and a lower tear factor at
the same yields than pulps made with sodium hydroxide as the active alkali
(32). The use of sodium carbonate as active alkali also eliminates the need
for the energy intensive causticizing plant. 2% Na^CO., on wood was used for
calculation purposes.
Oxygen consumption will be greater than 350 Kg/KKg (700 Ib/T) pulp pro-
duced. High oxygen pressures are used to maintain an excess of oxygen in the
reactor liquors. Easily available oxygen in the digester speeds the lignin
destruction leaving less time for the slower cellulose depolymerization re-
actions to degrade the pulp strength.
Bleaching to high brightness can be accomplished with a DED sequence.
Full countercurrent washing would be used. It would not be possible to re-
use bleach plant wash water for washing black liquor from the pulp after the
oxygen stage because of the difficulty of separating chlorides from the
sodium carbonate. In the Rapson process the sodium carbonate is taken out of
the white liquor along with the sodium chloride.
The consistency of the pulp during the oxygen reaction affects the pulp-
ing rate due to the quantity of dissolved oxygen in the pulping liquor avail-
able for reaction. Low consistencies result in high delignification rates
(20). A likely method of achieving low consistencies without having to heat
large volumes of white liquor is to have a high recirculation rate of black
liquor with reoxygenation of the liquor while outside the digester. This
high recirculation rate would cause an increase in oxygen consumption due to
further attack of the dissolved wood solids in the liquor (23). Fresh white
31
-------
liquor would be slowly added, the bleed off going to the pulp wash. Figure 5
shows the process.
Products
The pulps produced by this method are somewhat lower in strength than
kraft pulps. The lower strength is due to the mechanical damage to the
fibers in the thermomechanical stage. Higher steaming pressures would lead
to less fiber damage and thereby stronger pulps. If the thermomechanical
step can be optimized and problems of chemical damage of the fiber resolved,
the pulps should have strengths comparable to kraft pulps and, therefore,
have similar uses.
State of Development
Thermomechanical pulping followed by oxygen delignification is still in
the laboratory bench scale stage. Much work is required on process optimi-
zation, especially on the thermomechanical stage, before a pilot plant can be
built.
The advantage of thermomechanical pulping followed by oxygen delignifi-
cation over other oxygen pulping methods is that wood residues from other
forest products can be used. Chip uniformity or thin chips are not required.
AIR EMISSIONS
Reduced Sulfur Compounds
Although small amounts of sulfur compounds may be present in the cooking
liquor, reduced sulfur emissions should not occur from a thermomechanical-
oxygen pulping mill. Sulfur compounds will be reduced in the recovery fur-
nace. Since no lime kiln is needed, there are no lime kiln emissions.
Oxygen in the pulping stage will immediately oxidize all reduced sulfur com-
pounds. Little reversion of oxidized compounds should occur during black
liquor evaporation.
Sulfur Dioxide
Sulfur dioxide emissions should not occur from the recovery furnace at a
thermomechanical-oxygen pulping mill. The small quantities of S0? that form
in the recovery furnace react with the fumes and are removed by tne electro-
static precipitators as sodium sulfate. Since there is no lime kiln there
will be no sulfur discharge from that potential source.
Sulfur dioxide emissions will occur from the power boiler, the quantity
emitted depending upon the sulfur content of the fuel and the amount of
energy required. Calculation for S0? emissions from a thermomechanical-
oxvqen pulping mill are contained in Appendix B. Emissions are 2.5 Kg/t
for coal fired
Fers.
u A y M t-11 |.'u i |j i ? 114 INI i i u i c ^u 11 UCL i i icu ill nppci iu i A u.i~iiii-J-»(v/ii^ w i *-
(5.0 Ib/T) S0? for oil fired boilers, 3.9 Kg/t (7.8 Ib/t) S02
boilers, or 075 Kq/t (1.0 Ib/T) S00 for waste wood fired boiT<=
32
-------
0.7
1.74(2.12)
STEAM
STEAMING
2.6
2.6
7.2
COMBUSTION
1.3
EVAPORATION
7.2
2.5
REFINER
9.8
2.5
OXYGEN PULPING
14.4
6.6
5.9
12.3
WASH
8.0
5.9
SCREENING
DECKER
8.5(1.04)
1.9
11.6
0.4^
0.8
9.6.^
CI02
{
.
WASH
1
EXTRACTION
J)
WASH
1),
Cl
02
jj,
WASH
15.1
0.8
10.4
6.9(1.0)
Figure 5. Diagram of a thermomechanical pulping process
followed by oxygen delignification
33
-------
Particulates
Quantities of participate emissions from oxygen-thermomechanical pulping are
listed in Appendix C. Particulates from the recovery furnace should be very
low or non-existent due to the low heating value of the black liquor. If
supplemental fuel is fired with the black liquor to increase steam produc-
tion, a higher particulates emission would be expected. Smelt tank particu-
late emissions are 0.21 Kg/t (0.42 Ib/T) pulp. There are no lime kiln emis-
sions since there is no lime kiln. Nearly all of the particulates from an
oxygen-thermomechanical mill will result from the power boiler. Particles
from a waste wood fired power boiler are estimated to be 0.78 Kg/t (.56 Ib/T).
The total particulate emissions from an oxygen-thermomechanical mill are
estimated to be 1.5 Kg/t (3.0 Ib/T) bleached pulp.
Carbon Monoxide
The formation of carbon monoxide in oxygen bleaching mills has been
observed. At low consistencies, between 0 and 50 g carbon monoxide/t
(0.0-1.0 Ib.T) were measured, and at high consistencies (20-30%), 300 to 500
g carbon monoxide/t (0.6-1.0 Ib/T) pulp was observed in the degassing line
(25). Similar formation of carbon monoxide can be expected in an oxygen
pulping system (26). Carbon monoxide formed during oxygen pulping can be
handled by venting the pressure relief gases; to the recovery furnace or lime
kiln air intake, as is done in kraft mills for odor control. There should be
no carbon monoxide emissions allowed from an oxygen pulping mill.
Nitrogen Oxides
Nitrogen oxide emissions are calculated in Appendix D and are 3.4 Kg/t
(6.8 Ib/T) for an oxygen-thermomechanical pulp mill.
WATER DISCHARGES
New pulp mills will have the advantage of being able to install the
newest technology for control of water effluents. Materials of construction
can be chosen so that corrosion is minimized. Old equipment would not re-
quire modification or need to be replaced and plant layout can maximize the
efficiency of recycle. Water pollution discharges will be lower than exist-
ing mills, disregarding the oxygen pulping. Oxygen pulping itself offers
several advantages, largely that the chlorination and first extraction stages
in the bleach plant are not longer required. Nearly 80% of the bleach plant
BOD is contained in the chlorination and first extraction stages of the
bleach plant.
A no discharge mill does not appear possible with oxygen-thermomechanical
pulp mills. Disposal of the bleach plant waste through the recovery furnace
would not be possible as with the Rapson process in a kraft mill. During
crystallization of the sodium chloride in the Rapson process sodium carbonate
is also precipitated (33). Separation of the carbonate from the chloride by (
leaching would be extremely difficult.
34
-------
Biochemical Oxygen Demand
BOD discharge from an oxygen pulp mill is much lower than from a kraft
mill. Contributing to the reduced BOD are reuse of decker water on the brown
stock wash and elimination of the chlorination and first extraction stage
in the bleach plant. Evaporator condensate waters are recycled to the screen
and causticizing department. Spills and miscellaneous flows are the only BOD
contributions from the pulping area and contain about 3 Kg/t (6.0 Ib/T) (43).
Bleach plant effluents will be much less than from kraft mills. The
oxygen pulping stage eliminates the need for the chlorine and first stage ex-
traction step. The largest flow will be from the chlorine dioxide stage wash.
BOD from the DED bleaching sequence in a kraft mill is between 2 and 3 Kg/t
(4-6 Ib/T) pulp (33), (34). Raw BOD loadings from an oxygen mill bleach
plant will be slightly higher than a kraft mill DED portion of the bleach
plant because of carry over of black liquor solids from the decker into the
bleach plant. BOD loading from an oxygen bleach plant should be about 3 to 4
Kg/t (608 Ib/T) pulp.
Total BOD raw waste loading from an oxygen pulp mill is about 6 to 7 Kg/t
(12-14 Ib/T) pulp. Assuming a 90% efficient waste treatment system, final BOD
discharges will be in the range of .6 to .7 Kg/t (1.2-1.4 Ib/T).
Suspended Solids
Because of the reduced discharges due to recovery of decker effluents
and shortened bleaching sequences, suspended solids discharges will be much
reduced. Suspended solids would enter the sewer through spills, water treat-
ment plant sludges, and bleach plant effluents. Spills will contribute about
5 Kg/t (10 Ib/T) suspended solids.
Most of the suspended solids in the raw waste load will be removed by
primary and secondary treatment. Solids produced by biological activity
during secondary treatment will make up the bulk of suspended solids in the
effluent and are directly related to the BOD and the method of treatment.
Assuming a concentration of 100 mg/1 suspended solids escaping in the efflu-
ent and a flow of 28,000 1/t (6717 gal/T) pulp, suspended solids leaving with
the treated effluent are 2.8 Kg/t (5.6 Ib/T) pulp.
Color
Oxygen pulping liquors have about one fourth the color of kraft or soda
liquors (12), (29). Spills from screening and deckers would thereby contain
relatively little color. The strongly colored chlorine extraction stage
effluent would also not be present. Color would be much less than found in
kraft mill effluents.
Toxicity
Conditions present during oxygen pulping destroy resin and fatty acids
that are responsible for toxicity in many pulp mill discharges (30). Other
toxic materials, such as methyl mercaptan and methyl sulfide, are not present
35
-------
because of the absence of reduced sulfur. Bio-assay tests have shown that
oxygen pulping liquors are non-toxic (12). Chlorination stage bleach plant
effluents, which contribute a large amount of toxicity to kraft mill efflu-
ents, are not present in oxygen pulping mills. Chlorine dioxide bleaching
effluents have been shown to be less toxic than chlorination stage effluents
(5).
SOLID WASTES
Solid wastes from an oxygen-thermomechanical mill derive from several
sources: process losses including wood preparation, green liquor dregs,
washing and screening losses, bleach plant wastes, drying wastes, and spills;
water treatment sludges; fly ash; and biological solids developed from treat-
ment of effluents.
Process solids losses can be estimated by assuming that 90% of the sus-
pended solids in the effluent are removed in the primary and secondary clari-
fier. Process solids losses are estimated to be 8 Kg/t (16 Ib/T) and process
solids to be disposed of to be 7.2 Kg/t (14.4 Ib/T).
Water treatment waste solids are dependent upon the quality and quantity
of the water to be treated. Water quality is highly variable depending upon
location and season and thereby making estimates of sludges produced diffi-
cult. Water use in an oxygen-thermomechanical mill would be less than that of
kraft so the solids produced by this source are less.
Fly ash generation will depend upon the quantity of energy required and
the type of fuel used in the boiler. Bark arid coal will produce the greatest
quantity of fly ash, whereas gas or oil will produce none. Use of external
energy is greater for oxygen-thermomechanical pulping so fly ash generation
will be greater.
Biological solids derived from secondary treatment of effluents are the
largest solids waste disposal problem. They have a high volume to dry weight
ratio when wet and are difficult to dewater,. The quantityof biological solids
produced depends upon the quantity and quality of the effluent and the deten-
tion time of the secondary treatment. Activated sludge systems will produce
more solids than will an aerated lagoon. Overall, an oxygen-soda mill will
produce less biological solids than a kraft mill because of the lower raw BOD
loading to the treatment plant.
ENERGY
The major energy using operations in an oxygen-thermomechanical mill are
pulping, evaporation, bleaching, and oxygen production. Oxygen-thermomechani-
cal pulping differs in energy usage from typical kraft mills in several as-
pects. Since sodium bicarbonate is used as the active alkali, there is no
need to causticize the green liquor, resulting in considerable energy savings.
The oxidation of organics in the oxygen stage results in less energy produced
by the recovery furnace, but the energy produced by the oxidation reactions
helps heat the digestor. There is enough heat produced in the reactor by
lignin oxidation to make the pulping stage a net exporter of energy. Although
36
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the wood processing takes place in two reactor steps there is no energy loss.
All of the heat applied in the precooking and refining stage is transferred
to the oxygen stage. Oxygen-thermomechanical pulping requires a short bleach
sequence resulting in an additional energy savings. The production of high
pressure pure oxygen requires a considerable amount of energy.
The total energy required from external sources to an oxygen-thermomecha-
nical mill is 617 KKcal/t (2221 KBTU/T) bleached pulp. All of the external
energy requirements will be for electrical power. Some excess power boiler
capacity may be required for electricity production, with process steam being
available in excess.
37
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SECTION 9
OXYGEN PULPING OF CHIPS
PROCESS DESCRIPTION
Wood is cut into shavings or wafers parallel to grain to a thickness of
1 mm. The chips are cooked at 130 C for 16 hours with oxygen and 20 to 22%
sodium carbonate on wood. The carbonate is added as the cook progresses and
carbon dioxide is relieved several times during the cook to maintain a pH of
8.0. High pH's are avoided (34). Screen rejects are 3.6%, giving a yield
of 54% (35). Yields can be increased by lower cooking temperatures and
shorter times. Carbohydrate stabilizers (30 g/1 KI) are added to improve
pulp quality and yield.
The pulp is washed and screened. The liquors are evaporated and inci-
nerated or wet oxidized for recovery of chemicals. If KI is used in the pro-
cess, wet oxidation is a likely chemical recovery means because of the high
volatility of KI (24). No causticizing plant is required. The pulp can be
bleached in a DED sequence. Figure 6 shows the process.
Products
Oxygen pulps that use potassium iodide in the cook as a carbohydrate
inhibitor have breaking lengths equal to that of kraft, superior burst factors,
but lower tear factors than kraft pulps. The pulp would be good for produc-
ing liner board, bag, and construction paper.
State of Development
Oxygen pulping of chips is still in the bench scale stage. The process
should be ready for a pilot scale trial.
AIR EMISSIONS
Reduced Sulfur Compounds
Although small amounts of sulfur compounds may be present in the cooking
liquor, reduced sulfur emissions should not occur from an oxygen chip pulping
mill. Sulfur compounds will be reduced in the recovery furnace. Since no
lime kiln is needed, there are no lime kiln emissions. Oxygen in the pulping
stage will immediately oxidize all reduced sulfur compounds. Little reversion
of oxidized compounds should occur during black liquor evaporation. There
should be little sulfur in the system because the only source of sulfur is
raw water makeup and chemical impurities.
38
-------
1.6 (1.96)
2.8
I >, 3.9 7.8
TT3
1
COMBUSTION
fu
£& EVAPORATION
1
8.0
3.9
7.6
5.2
1.5
c
>.9
— »>
OXYGEN PULPING
1
9.4
WASH
,
5.9
SCREENING
i
DECKER
i
8.5
8.0
1.9
CI02
11.6
WASH
EXTRACTION
WASH
CIO.
WASH
15.1
0.8
6.9 ( 1.0)
10.4
Figure 6. Diagram of oxygen pulping of chips process
39
-------
Sulfur Dioxide
Sulfur dioxide emissions should not occur from the recovery boiler at
an oxygen chip pulping mill. The small quantities of SCL that form in the
recovery furnace react with the fumes and are removed by the electrostatic
precipitators as sodium sulfate. Since there is no lime kiln, there will be
no sulfur discharge from that potential source.
Sulfur dioxide emissions will occur from the power boiler, the quantity
emitted depending upon the sulfur content of the fuel and the amount of
energy required. As shown in Appendix B, SO^ emissions from the power boiler
at an oxygen chip pulping mill are 3.2 Kg/t (6.4 Ib/T) pulp for oil fired
boilers, 5.0 Kg/t (10.0 Ib/T) pulp for wood waste fired boilers.
Particulates
Particulate emissions are shown in Appendix C. Particulate emissions
from an oxygen chip pulp mill total 4.8 Kg/t (9.6 Ib/T) pulp. Particulate
emissions from the recovery furnace are 1ow--0.59 Kg/t (1.18 Ib/T) pulp be-
cause of the low heating value of the black liquor. Smelt tank emissions
are 0.23 Kg/t (0.46 Ib/T) pulp. The lack of a lime kiln precludes lime kiln
emissions. Power boiler emissions of 1.3 Kg/t (2.6 Ib/T) pulp from a waste
wood fired boiler make up the bulk of the emissions. Total particulate emi-
ssions from an oxygen chip pulping mill is estimated to be 2.12 Kg/t (4.24
Ib/T).
Nitrogen Oxides
Nitrogen oxide emissions are calculated in Appendix D and are estimated
to be 3.4 Kg/t (6.8 Ib/T) for an oxygen chip pulping mill.
Iodide
If iodide is used as a cellulose degradation inhibitor in the oxygen
delignification stage, there is a possibility of iodide emissions from the
recovery furnace. At the normal recovery furnace bed surface temperature of
928 C (1800 F), sodium iodide has a-vapor pressure of 28 mm Hg. At this high
vapor pressure considerable amounts of sodium iodide will be vaporized.
Sodium chloride, which has a vapor pressure lower than sodium iodide is known
to varporize from kraft mill recovery furnaces. Condensation of the iodide
will form a fume. The fumes can probably be removed from the flue gas via an
electrostatic precipitator with other particulates. Electrostatic precipi-
tators do a poor job of removing sodium chloride, so they may do a poor job of
removing sodium iodide.
About 60 Kg Nal/t (120 Ib Nal/T) pulp is projected. Assuming 98% effi-
ciency for the brown stock washers, and about 40% of the Nal in the black
liquor being vaporized, of which 50% will be captured in the direct contact
evaporator and 98% of the remainder removed by the electrostatic precipitator,
Nal emissions would be about 0.24 Kg/t pulp.
40
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Carbon Monoxide
The formation of carbon monoxide in oxygen bleaching mills has been ob-
served. At low consistencies, between 0 to 50 g carbon monoxide per ton
(0-0.1 Ib/T) were measured, and at high consistencies (20-30%), 300 to 500 g
carbon monoxide per ton (0.6-1.0 lb/T) were observed in the degassing line
(30). Similar formation of carbon monoxide can be expected in an oxygen pul-
ping system. Carbon monoxide formed during oxygen pulping can be handled by
venting the pressure relief gases to the recovery furnace or lime kiln air
intake as is done in kraft mills for odor control. There should be no carbon
monoxide emissions allowed from an oxygen pulping mill.
WATER DISCHARGES
New pulp mills will have the advantage of being able to install the new-
est technology for control of water effluents. Materials of construction can
be chosen so that corrosion is minimized. Old equipment would not require
modification or need to be replaced, and plant layout can maximize the effi-
ciency of recycle. Water pollution discharges will be lower than existing
mills disregarding the oxygen pulping. Oxygen pulping itself offers several
advantages, largely that the chlorination and first extraction stages in the
bleach plant are no longer required. Nearly 80% of the bleach plant BOD is
contained in the chlorination and first extraction stages of the bleach plant.
A zero discharge mill does not appear possible with oxygen chip pulp
mills. Disposal of the bleach plant waste through the recovery furnace would
not be possible as with the Rapson process in a kraft mill. During crystalli-
zation of the sodium chloride in the Rapson process, sodium carbonate is also
precipitated (33). Separation of the carbonate from the chloride by leaching
would be extremely difficult.
Biochemical Oxygen Demand
BOD discharges from an oxygen pulp mill are much lower than from a kraft
mill. Contributing to reduced BOD are reuse of decker water on the brown
stock wash and elimination of the chlorination and first extraction stage in
the bleach plant. The evaporator condensate waters are recycled to the
screen and causticizing department. Only pollutants from the pulping stage
would be from leaks and spills. Spills and miscellaneous flows amount to
about 3 Kg/t (6 Ib/T) (15).
Bleach plant effluents will be much less than compared to kraft mill
bleach plants. The oxygen pulping stage eliminates the need for the chlorine
and first extraction step. The largest flow will be from the chlorine dio-
xide stage wash. BOD from the DED bleaching sequence in a kraft mill is
between 2 and 3 Kg/t (4-6 Ib/T) pulp (27), (28). Raw BOD loadings from an
oxygen mill bleach plant will be slightly higher than a kraft mill DED portion
of the bleach plant because of carry over of black liquor solids from the
decker into the bleach plant. BOD loading from an oxygen bleach plant should
be about 3 to 4 Kg/t (6-8 Ib/T) pulp.
41
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Total BOD raw waste loading from an oxygen pulp mill is about 6 to 7
Kg/t (12-14 Ib/T) pulp. Assuming a 90% efficient waste treatment system,
final BOD discharges will be in the range of .86 to .96 (kg/t (1.72-1.92
Ib/T).
Suspended Solids
Because of the reduced discharges due to recovery of decker effluents
and short bleaching sequences, suspended solids discharges will be much re-
duced. Suspended solids would enter the sewer through spills, water treat-
ment plant sludges, and bleach plant effluents. Spills will contribute about
5 Kg/t (10 Ib/T) suspended solids, and boiler room effluents will contribute
about 1 Kg/t (2 Ib/T) suspended solids.
Most of the suspended solids in the raw waste load will be removed by
primary and secondary treatment. Solids produced by biological activity
during secondary treatment will make up the bulk of suspended solids in the
effluent and are directly related to the BOD removed and the method of treat-
ment. Assuming a concentration of 100 mg/1 suspended solids escaping in the
effluent and a flow of 28,000 1/t (6717 gal/T) pulp, suspended solids leaving
with the treated effluent are 2.8 Kg/t (5.6 Ib/T) pulp.
Color
Oxygen pulping liquors have about one fourth the color of kraft or soda
liquors (12), (29). Spills from screening and deckers would thereby contain
relatively little color. The strongly colored chlorine extraction stage
effluent would also not be present. Color would be much less than that in
the effluent from a kraft mill.
Toxicity
Conditions present during oxygen pulping destroy resin and fatty acids
that are responsible for toxicity in many pulp mill discharges (30). Other
toxic materials such as methyl mercaptan and methyl sulfides are not present
because of the absence of reduced sulfur. Bio-assay tests have shown that
oxygen pulping liquors are non-toxic (12). Chlorination stage bleach plant
effluents, which contribute a large amount of toxicity to kraft mill efflu-
ents, are not present in oxygen pulping mills. Chlorine dioxide bleaching
effluents have been shown to be much less non-toxic than chlorination stage
effluents (5).
SOLID WASTES
Solid wastes from an oxygen pulping mill derive from 4 main sources: 1)
process losses; including wood preparation, green liquor dregs, washing and
screening losses, bleach plant wastes, drying wastes, and spills; 2) water
treatment sludges; 3) fly ash; and, 4) biological solids developed from treat-
ment of effluents.
Process solids losses can be estimated by assuming that 90% of the sus-
pended solids in the effluent are removed in the primary clarifier. Knots
42
-------
and shives are re-refined. Process solids losses are estimated to be 6 Kg/t
(12 lb/T), and process solids to be disposed of to be 5.4 Kg/t (10.8 lb/T).
Water treatment waste solids are dependent upon the quality and quantity
of the water to be treated/ Water quality is highly variable, depending upon
location and season, thereby making estimates of sludges produced difficult.
Water use in an oxygen pulping mill would be less than that of kraft, so the
solids produced by this source are less.
Fly ash generation will depend upon the quantity of energy required and
the type of fuel used in the boiler. Bark and coal will produce the greatest
quantity of fly ash, whereas gas or oil will produce none. Use of external
energy is much greater for oxygen pulping, so fly ash generation will be much
greater.
Biological solids derived from secondary treatment of effluents are the
largest solids waste disposal problem. They have a high volume to dry weight
ratio when wet and are difficult to dewater. The quantity of biological
solids produced depends upon the quantity and quality of the effluent and the
detention time of the secondary treatment. Activated sludge systems will
produce more solids than will an aerated lagoon. Overall, an oxygen pulping
mill will produce less biological solids than a kraft mill because of the
lower raw BOD loading to the treatment plant.
ENERGY
The major energy uses in an oxygen pulp mill are evaporation of black
liquor, oxygen manufacture, and bleaching. Digester heating would normally
require a large amount of energy, but the oxidation reaction within the di-
gestor should be able to provide more than the required amount. Oxidation
of organics in the digestor leaves less organics to be burned in the recovery
furnace. The energy produced by the recovery furnace is considerably less
than found in kraft mills. The higher yield of oxygen pulping also decreases
the amount of energy produced in the recovery furnace. The manufacture of
high pressure oxygen requires 1820 KKcal/t (6553 KBTU/T) Op. At 20% oxygen
on wood, oxygen manufacture is a major energy consumer. Oxygen pulps are
easily bleached, thus requiring short bleaching sequences and thereby result-
ing in some energy savings over a kraft bleach sequence. No energy is used
in causticizing green liquor because sodium carbonate is used as the active
alkali in the digestor.
Oxygen pulping will require additional power production facilities to
produce 951 KKcal/t (3424 KBTU/T) pulp. Power boilers for electricity pro-
duction would be the most likely additional energy source.
43
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SECTION 10
CHLORIDE DIOXIDE PULPING
PROCESS DESCRIPTION
Pulping with halogens has long been considered as a pulping process be-
cause of the high selectivity of chlorine compounds in their attack on lignin
while leaving the cellulose compounds intact. The major obstacle to halogen
pulping has been its cost. New interest has developed for halogen pulping
because of its pollution free potential. Energy use remains a prime consid-
eration.
Of the halogen compounds, ClO^ is one of the faster acting and more
selective compounds available. Chlorine dioxide pulping processes that have
been investigated are of two types: pulping of chips, and delignification of
thermomechanical pulp. Pulping of chips has the problem of uneven pulping.
The action of chlorine dioxide on the chips is very rapid. The reaction on
the exterior of the chip is complete before the chlorine dioxide can diffuse
to the interior of the chip, resulting in high chemical usage. Several in-
vestigations have been made concerning chlorine dioxide pulping of thin chips
to reduce the above problems (36), (37).
When thermomechanical pulp is delignified by C102> the lignin coating
the separated fibers is readily available to attack by the ClOp. Only
enough C102 is used to render the lignin soluble, resulting in substantial
savings in chemical costs.
Thermomechanical Stage
When preparing the thermomechanical pulp, care must be taken so as not
to damage the individual fibers during refining. The significant process
variables in the thermomechanical stage are the cook time, cook temperature,
and refiner rpm and clearance. Sufficient time in the preheater is required
to raise the chips to a uniform temperature. Less than 5 minutes are required
for heating the chips. The preheating temperature governs the amount of
liqnin softening that occurs.
When wood chips are heated, the lignin and hemicelluloses between the
cell walls becomes soft. The softening of the lignin begins at specific tem-
peratures referred to as the glass point. The glass point for each species
of wood is different. During cooking the lignin is heated to the glass point
so that fibers can be easily separated upon refining. At temperatures below
the glass point the wood fractures through the outer layer of the secondary
cell wall. At temperatures above the glass point the wood fractures through
the lignin layers between the cells. When wood has been fiberated above the
44
-------
glass point, the fibers will be coated with a layer of lignin. The transi-
tion between refined spruce fracturing in the cell wall or fracturing between
the cell wall occurs between 120°C (248°F) and 135°C (275°F) (31). The ther-
momechanical pulps will be stronger if the fibers have not been torn. A
thermomechanical stage temperature of 160 C (320 F) was used in the calcula-
tions for this paper.
Lignin modification with about 8% CIO-, or with a mixture of 77% ClOn
and 38% Cl?, takes place at 60 C for about 60 minutes in the chlorine dioxide
delignification reactor. Lignin is separated from the pulp with 7.5% sodium
hydroxide in an extraction step. Pulp yield is 59%. The pulp is then ready
for bleaching to a TAPPI brightness of 85 with a D/CED sequence (28), (39),
(40).
Pulping chemicals can be recovered by evaporation and burning the pulp-
ing liquor. A mixture of sodium chloride and sodium carbonate are produced.
The smelt is causticized and the NaOH and NaCl separated by crystallization.
Chlorine, hydrogen, sodium hydroxide, and sodium chlorate are produced by
electrolysis of the sodium chloride. Chlorine dioxide is produced with HC1,
from burning of hL and C1-, and sodium chlorate (36).
There is no effluent from halo pulping as evaporator condensates can be
used for washing of the final bleached pulp. Bleach plant effluents are re-
cycled through the screening room to the brown stock washers so that bleach-
ing chemicals are recovered. Since there is no chlorine stage in the bleach
plant, bleach plat water use will be low. The process is diagrammed in
Figure 7.
Products
Chlorine dioxide pulping produces a very strong bleached pulp but has
poor tear properties. Semibleached pulps are possible. Pulp can be sold in
direct competion with bleached kraft market pulp where tear is not a critical
property. Paper products would include specialty papers, tissue and towel-
ing, wrapping papers, bags, towels, linerboard, boxboard, and newsprint stock.
State of Development
Chlorine dioxide pulping is in different stages of development in differ-
ent parts of the world. In the United States the process is at the bench
scale level (38), (39). In Japan a 10 ton per day pilot plant has been built
(36), (41).
AIR EMISSIONS
Reduced Sulfur Compounds
Reduced sulfur compounds should be non-existent in a chlorine dioxide
pulping mill. Sulfur in any form should not exist in the process. Small
amounts of sulfur that enter the process as contaminants should be purged
or removed.
45
-------
1.5(1.72)
0.8
0.9
ELECTF
u.u
>ni YQI ^
t
CAUST
P 1 7 1 M C
ulZJIMb
f
COMBUSTION
fo.9
EVAPOF
3.2J
5.2
,
.4
_/
U.6
9.4
14.6
\
f
0.5
0.3
9.2
X0.3
0.5^
B.4
STEAMING
,
2.1
REF NER
>
CI02/CI PULPING
i
, 11.5
WASH
i
r 8.8
EXTRACTION
/
i
\
-9.3
WASH
i
,6.5
ClOg/CI
^28.3
WASH
^6.9
EXTRACTION
ty 7.2
WASH
^ 6.9
CI02
$ 7.4
WASH
11.9
L-9-1
21.5
30.6
8.9
>.9(1.0)
Figure 7.
Diagram of a CIO,, pulping process
46
-------
Sulfur Dioxide
As there are no sulfur compounds in the pulping chemicals, there should
be no sulfur dioxide emissions from the recovery furnace. Small quantities
of S0? may be emitted from the lime kiln due to sulfur in the fuel oil. Sul-
fur dioxide will also be emitted from the power boiler at a rate of 0.8 Kg/t
(1.6 Ib/T), according to Appendix B.
Particulates
Particulate emissions from various sources are listed in Appendix C.
Nearly all of the particulate emissions from a halogen pulping mill are
chlorides from the recovery furnace. Two factors cause the high particulate
emissions: a high rate of fume formation in the recovery furnace, and a re-
duced electrostatic precipitator collection efficiency for sodium chloride.
Fume formation in the recovery furnace will be accelerated because of the
high heating value of the black liquor and the high concentration of sodium
chloride in the black liquor. The high heating value will result in a high
temperature in the furnace. The high furnace temperature will increase the
volatilization of sodium chloride. Sodium chloride boils at a much lower
temperature than do other pulping chemicals. About 60% of the chloride may
be vaporized resulting in 121 Kg/t (242 Ib/T) pulp fumes. About 50% will
be adsorbed in the direct contact evaporators leaving about 60 Kg/t (120
Ib/T) to the electrostatic precipitator.
Collection efficiencies of electrostatic precipitators for NaCl are less
than for salt cake (42). Salt fumes fail to agglomerate and will pass through
the electrostatic precipitator (43). Furthermore, the volume of gas to be
treated in a C102 pulp mill will be greater than that for a kraft mill.
Assuming an electrostatic precipitator with an efficiency of 98%, particulate
emissions from a chlorine dioxide pulping mill would be about 1.2 Kg/t (2.4
lb/T) pulp. Emissions are lower than might be expected because of the smaller
quantity of non-organic solids per ton pulp that are fired in the recovery
furnace.
Particulate emissions from other sources are listed in Appendix C. Total
particulates from a chlorine dioxide mill are approximately 2.6 Kg/t (5.2
Ib/T) bleached pulp.
Nitrogen Oxides
Nitrogen oxide emissions are calculated in Appendix D and are estimated
to be 8.9 Kg/t (17.8 Ib/T) for a chlorine dioxide pulping mill.
WATER DISCHARGES
The chlorine dioxide pulping process recovers all of the process streams
for pulping chemical and energy production. Flows from the mill would consist
of spills and wash downs. Assuming that a modern mill would be constructed
with sufficient storage capacity to collect spills, there should be very
little discharge from a chlorine dioxide pulping process. Those flows result-
ing from washup could be evaporated in the process. A small amount of in-
47
-------
organic blowdown would be required to prevent the buildup of impurities in the
system.
SOLID WASTES
Solid wastes from chlorine dioxide pulping mills will derive from wood
preparation, green liquor dregs, drying wastes, spills, and fly ash,, The
solid wastes will consist of primarily inorganic material and will, thereby,
be fairly easy to dispose of.
Wood preparation solids wastes will consist mainly of sand, grit, and
bark fines from washing of logs, or of sand and clays from washing of chips.
Green liquor dregs may be difficult to dispose of by themselves because they
are quite hydrous and difficult to thicken (44).
Since chlorine dioxide pulping has no effluent, there will be no biologi-
cal solids produced. Reuse of most internal water streams will greatly reduce
the need for water treatment, and thereby greatly reduce the quantity of water
treatment solids to be disposed of. Overall, the chlorine dioxide pulping
processes will have little solids to dispose of.
ENERGY
The major detriment to the commercialization of chlorine dioxide pulping
has been the energy required for production of the pulping chemicals. Of all
the pulping alternatives considered in this paper chlorine dioxide pulping
will require the most auxilliary power production. Examination of Table 17
will show that the chlorine dioxide pulping process, including production of
chlorine chemicals, requires 107 KKcal/t (385 KBTU/T) pulp more purchased fuel
heat value than does kraft pulping. The large energy requirement for chlorine
dioxide production is largely offset by energy savings due to less causticiz-
ing capacity, lower digester temperatures and the shorter bleaching sequence.
The real reason that chlorine dioxide pulping has an overall high energy re-
quirement is the high yield of 58%. The high yield results in less organics
to be burned in the recovery furnace and thus in less internal energy produc-
tion. A decrease in the overall yield to 50% would provide an extra 850
KKcal/t (3060 KBTU/T) pulp, making chlorine dioxide pulping energy require-
ments compare favorably with the other pulping sequences. In an actual mill,
the yield will probably be kept high because of the high value of wood and
because of the loss of pulp strength observed at the lower yields.
The chlorine dioxide pulping process requires 1456 KKcal/t (5242 KBTU/T)
pulp purchased energy of which 1237 KKcal/t (4454 KBTU/T) is from power boil-
ers.
48
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SECTION 11
SOLVENT PULPING
PROCESS DESCRIPTION
Solvent pulping uses low molecular weight organic compounds to dissolve
lignin from wood chips and thereby affect fiberization. Solvents that have
been investigated for use in solvent pulping are ethanol, butanol, methyl
ethyl ketone, acetone, and cyclohexanone (45), (46). These solvents can be
recovered and produced on site. Ammonia can be added to the solvent to aid
in dissolving the lignin.
Chips enter the digester from the top where the temperature is 180 to
210°C (356 to 410 F). The high temperatures necessitate high pressure equip-
ment. The chips move through the digester counter currently to the solvent.
Fresh solvent entering at the low end of the digester serves as a wash for
the pulp. The used solvent leaves the top of the digestor, and is flashed
into a rectifying column, where the solvent is separated from the organics
and water that was in the wood. The solvent is condensed, heated and returned
to the digestor. The lignin separates from the water phase as a thick viscous
liquid, and can be dried to a powder. Hydrogenation of the powder produces
alcohols and ketones. The pulp is washed and bleached. The optimum bleach-
ing sequence has not been determined.
Products
Pulp produced by solvent pulping has strengths ranging from those similar
to sulfite to those similar to kraft, depending upon the solvent used. The
higher strength solvent pulps have lower tear than kraft because of the higher
hemicellulose content of the solvent pulps. The pulps could be used in place
of kraft pulps except where high tear strength is required.
State of Development
Solvent pulping is still in the laboratory stage of development. Because
of its early stage of development it is difficult to determine what its efflu-
ent and emission characteristics will be.
AIR EMISSIONS
Reduced Sulfur Compounds
As there are no sulfur containing chemicals in a solvent pulping mill
there will be no reduced sulfur emissions.
-------
Sulfur Dioxide
Since there are no sulfur containing chemicals used in a solvent pulping
mill there will be no sulfur dioxide emissions from the process. Sulfur dio-
xide emissions can be expected from the power plant if sulfur containing fuels
are used. The amount of sulfur dioxide emissions from a solvent pulping mill
will be determined by the energy requirements of the process. The process is
not at a stage of development where the energy requirements can be determined.
Particulates
The black liquor will contain no inorganic materials; when fired in the
recovery furnace there will be no formation of difficult to remove inorganic
fumes. Pyrolysis solids can be expected to be carried out of the recovery
furnace, but these are easily removed.
Some particulates may be expected from power boilers if coal or hog fuel
is used. The quantity of this material will depend upon the fuel used and the
energy required by the mill.
Organic Vapors
The use of volatile organic pulping liquor could lead to the escape of
organic vapors to the atmosphere. All pulping and washing operations would
need to be totally enclosed. Prevention of vapor leaks at the chip high pres-
sure feeder would be difficult. Scrubbing of organic vapors with water sprays
should remove organic fumes because of their high solubility in water.
WATER DISCHARGES
Discharges from a solvent pulping mill could consist of wash water and
bleach plant effluents. The brown stock wash water will require stripping to
remove residual volatile organic pulping liquors. Lignin materials dissolved
during pulping of the pulp are washed first with solvent to remove soluble
wood materials. Bleach plant effluents should be about the same as those ex-
pected from the kraft pulping process.
Biological Oxygen Demand
Raw BOD from the bleach plant will be about 10-15 Kg/t (20-30 Ib/T).
There should be no decker wash water since this water should be totally col-
lected for solvent recovery. After secondary treatment, the BOD in the efflu-
ent would be 1 Kg/t (2 Ib/T) pulp.
Total Suspended Solids
Suspended solids in the raw effluent should be removed by primary and
secondary treatment. Solids in the effluent would be comprised largely of
biological solids produced during secondary treatment. Suspended solids in
the effluent should be less than 2 Kg/t (4 Ib/T), depending upon the type
of secondary treatment and the effluent flow. The 2 Kg/t (4 Ib/T) number
was arrived at by assuming flows and BOD strengths from the solvent process
50
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to be similar to those from the kraft or soda process.
Toxicity
The toxicity of the effluents from a solvent pulping mill are difficult
to assess because of lack of information. Toxicity due to the bleach plant
would still be present. Resin acids probably will not be a problem in a sol-
vent pulping mill. There will be no turpentine separation or relief gas con-
densates. In summation, toxicity of the effluent from a solvent pulping mill
should be less than that from a kraft mill.
Color
Color will be present from the bleach plant chlorine extraction stage.
Decker color will not be present. The color in the effluent from a solvent
pulping mill should be less than from a kraft mill.
SOLID WASTES
Solid wastes from a solvent pulping mill will derive from 4 main sources:
1) process lossess including wood preparation, washing and screening losses,
bleach plant wastes, drying wastes, and spills; 2) water treatment sludge;
3) fly ash; and 4) biological solids developed from treatment of effluents.
Process losses are estimated by assuming they are 90% of the raw waste
load suspended solids, that which would be removed in the primary clarifier.
Process solids losses are estimated at 11 Kg/t (22 Ib/T) pulp. Water treat-
ment sludges will depend upon the quantity and quality required for the pro-
cess. There is no substantial difference in water requirements between kraft
and solvent pulping. The large water usage area, bleaching, is common to
both processes.
Biological solids derived from secondary treatment of effluents are the
largest solid waste disposal problem. They have high volume to dry weight
ratio when wet, and are difficult to dewater. The quantity of biological
solids produced depends upon the quantity and quality of the effluent and the
detention time of the secondary treatment. Activated sludge systems will pro-
duce more solids than will an aerated lagoon. Because of the slightly lower
BOD from a solvent pulping mill as compared to a kraft mill, biological solids
production will be less.
ENERGY
There is insufficient process information to make energy use calculations
for the solvent pulping process.
It may be possible for a solvent pulping mill to be nearly energy self
sufficient. The black liquors will not contain inorganic materials which
serve to reduce energy recovery in the recovery furnace. Also, the weak
black liquor will contain mostly organics, which have lower heats of evapora-
tion than does water. Major energy consumers will be heating the large vol-
umes of cooking liquors to high temperatures and production of hydrogen for
hydrogenation of dried lignin to produce pulping chemicals.
51
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SECTION 12
RAPSON PROCESS
PROCESS DESCRIPTION
The Rapson process was developed to remove chlorides from the kraft re-
covery system specifically so that bleach plant effluents could be disposed
of by incineration in the recovery boiler. Bleach plant effluents are to be
added to the chemical recovery cycle at the appropriate locations, specific-
ally to the screening room, brown stock washers, green liquor dissolving tank,
and lime mud washing. Chlorides are to be removed by crystallization from
concentrated white liquor, thus maintaining a sodium chloride concentration
in the white liquor of 30 g/1. Evaporator condensate will be stripped and
returned to the bleach plant as wash and makeup water. Extensive water reuse
in the bleach plant will be required to keep water volumes low. The Rapson
process has no effluent. Figure 8 shows the process.
Products
The Rapson process is a modification of the kraft process. The same pro-
ducts would be produced by the Rapson process as would be produced by the
kraft process.
State of Development
Parts of the process have been developed through pilot plant work. A
full scale mill is being constructed by Great Lakes Paper Co. in Ontario,
Canada.
AIR EMISSIONS
Reduced Sulfur Compounds
No difference in reduced sulfur emissions are expected between the Rapson
process and a normal kraft process. Kraft pulp mills located near the coast
which use salt water transported logs and have high sodium chloride; levels
in their cooking liquor have about the same total reduced sulfur emissions
from the recovery boiler as do kraft mills which do not contain salt in their
cooking liquors (47). When bleach plant effluents are used as brown stock
wash water, care will need to be taken to be sure that the wash water is alka-
line. Acidic wash water would cause the release of H2S from the residual
Na?S in the brown stock. Total reduced sulfur emissions should be 0.25 Kq/t
(075 Ib/T) from the recovery furnace and 0.125 Kg/t (0.25 Ib/T) from the pulp
washers resulting in a total of 0.375 Kg/t (0.75 Ib/T) pulp reduced sulfur
emissions from the Rapson pulping process (48).
52
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2.4
CRYSTALIZATION
5.0
7.5
r.4
CAUSTICIZING
la.
COMBUSTION
1.3
—*•
STEAM
1.2
EVAPORATION
1.7
8.5
7.6
1.2
ELECTROLYSIS
2.5
11.0
7.4
0.9
17.6
0.7
1.9
7.6
8.0
0.8
9.6
2.1 (2.50)
PULPING
8.6
WASH
1.0
9.1
I 6.7(1.18)
KNOTTER
DECKER
8.7
CI/CI02
WASH
EXTRACTION
WASH
JL
CIO-
WASH
EXTRACTION
WASH
CI02
WASH
9.4
22.0
7.0
8.2
3.0
8.4
lie.9(1.0)
Figure 8. Diagram of the Rapson process
53
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Sulfur Dioxide, Participates, and Hydrogen Chloride
Sulfur dioxide, particulates, and hydrogen chloride emissions are con-
sidered together because they are interrelated. Sulfur dioxide formation at
the furnace bed and combustion zone is dependent upon the sulfidity of the
black liquor. Higher sulfidities result in greater S02 formation. Higher
bed temperatures will also cause greater S00 formation. Particulate forma-
tion is also dependent on the furnace temperature. Higher temperatures re-
sult in more sodium vaporization from the furnace bed. Sodium chloride is
more volatile than other sodium compounds, so the presence of sodium chloride
will increase the quantity of sodium vaporized.
Vaporized sodium then reacts with S0~ and C0? to form sodium sulfate and
sodium carbonate fumes (49). The fumes consist of about 90% Na^CO., depending
upon the recovery system operation and the sulfidity (3). If tne sulfidity
is high, the amount of NaoCCU will be small and there will be an excess of
SCL in the flue gas. In the Rapson process, NaCl will be present in the flue
gas. If there is excess SCL in the flue gas, the following reaction takes
place to form hydrochloric acid (50).
S02 + 2NaCl + 02 + H20 Na2S04 + 2HC1
Two Swedish mills, with white liquor salt contents of 10 and 17 Kg
NaCl/ton solids in the black liquor and sulfidities of 37% and 35%, reported
200 and 350 ppm HC1 in their flue gas, respectively (50). Figure 9 shows
the percent HC1 of the total chloride in the flue gas as a function of sulfid-
ity (50). It should be noted that most U.S. mills do not have the high sul-
fidities that Swedish mills have, but range between 20% and 30% sulfidity.
The Rapson process can expect to have lower S02 emissions and higher
particulate and hydrogen chloride emissions from tne recovery boiler than
kraft mills would have. Assuming a sulfidity of 25%, S0? emissions should be
around 150 ppm, or 2 Kg SCL/t pulp (4 Ib/T). From Appendix C, particulate
emissions from the recovery furnace are 2 Kg/t (41b/T) pulp. HC1 emissions
are estimated by assuming 20% of the chloride fired to the furnace being
vaporized, 25% of the vaporized chloride being converted to HC1, arid about
50% of the HC1 being adsorbed in the direct contact evaporator. The estimat-
ed HC1 emission is 10 Kg/t (20 Ib/T).
Nitrogen Oxides
Nitrogen oxide emissions are calculated in Appendix D and are estimated
to be 21.9 Kg/t (43.8 Ib/T) for a Rapson process pulp mill.
WATER DISCHARGES
The Rapson process was developed to specifically eliminate any contami-
nated water discharge from a kraft mill. Minor discharges will occur from
blowdown of cooking chemicals, boiler blowdown, water treatment, and runoff
from wood or chip piles and cooling water. These flows contain little organic
material, hence BOD will be minimal. Suspended solids of the aforementioned
streams should be readily settlable and kept to a minimum.
54
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20 30 40
SULFIDITY
50
60
Figure 9. Percent hydrochloric acid vs. sulfidity
55
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SOLID WASTES
Solid wastes from the Rapson process occur from 3 main sources: 1) pro-
cess losses including wood preparation, green liquor dregs, drying wastes,
and spills; 2) water treatment sludges; and 3) fly ash.
Process losses will largely be made up of sand, silt, and bark fines from
wood preparation, and green liquor dregs. Green liquor dregs will present
a dewatering problem as they are quite hydrous (44). Fly ash production will
be less than that of kraft because of the lower energy requirements.
Because the Rapson process has no process effluent, and thereby no need
for a biological treatment plant, there will be no biological solids generat-
ed to be disposed of. Reuse of process waters within the mill will reduce
the amount of fresh water required by the mill and thereby result in a de-
crease in the quantity of water treatment solids produced.
Overall, the Rapson process will have a decreased solids handling problem
in comparison with the kraft process.
ENERGY
The addition of the Rapson process to a kraft mill changes energy use
patterns throughout the mill. Evaporation of white liquor to affect crystal-
lization of sodium chloride requires 940 KKcal/t (3384 KBTU/T) bleached pulp.
White liquor evaporation energy requirements are offset by the additional
organic load to the recovery furnace from the bleach plant effluent and from
the energy savings due to counter current water use in the bleach plant.
Organic materials recovered from the bleach plant result in an additional
710 KKcal/t (2556 KBTU/T) being produced in the recovery furnace. Energy
savings due to counter current washing in the bleach plant are 452 KKcal/t
(1627 KBTU/T) bleached pulp. Overall the Rapson process requires less pur-
chased energy than does a kraft mill, but if a new kraft mill were to use
many of the energy saving processes proposed for the Rapson mill, the kraft
mill would be more energy self reliant.
A Rapson process mill will need to purchase 1050 KKcal/t (3780 KBTU/T)
worth of fuel, of which 852 KKcal/t (3067 KBTU/T) will be in the form of
oil or gas to fire the lime kiln. The remainder of 198 KKcal/t (712 KBTU/T)
will come from hog fuel or other purchased fuel. Energy calculations are
presented in Appendix A.
56
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REFERENCES
1. Cox, L. A., and Worstor, H. E. "An Assessment of Some Sulfur Free
Chemical Pulping Process." TAPPI, 54:11. Nov. 1971.
2. "Environmental Pollution Control Pulp and Paper Industry, Part I, Air."
U. S. Environmental Protection Agency, Technology Transfer. EPA-625/7-
76-001. October 1976.
3. Lang, C. J., De Haas, G. G., Gommi, J. V., and Nelson, W. "Recovery
Furnace Operating Parameter Effects on S0? Emissions." TAPPI, 56:6.
June 1973. *
4. Development Document for Effluent Limitations Guidelines (BPCTCA) for
the Bleached Kraft, Groundwood, Sulfite, Soda, Deink and Non-Integrated
Paper Mills Segment of the Pulp, Paper, and Paperboard Point Source
Category. U.S. EPA. Dec. 1976.
5. "Identification and Determination of the Toxicity Contribution of the
Toxic Materials in Each Kraft and Sulfite Process Effluent Prepared in
a Pilot Plant." CPAR Project Report 360-1.
6. Gehn, H. "State of the Art Review of Pulp and Paper Waste Treatment."
Environmental Protection Technology Series, EPA-R2-73-184. April 1973.
7. Conners, W. J. and Sanger, N. "High Concentration Alkali Pulping of
Southern Pine." TAPPI 58:2, Feb. 1975.
8. Lowendhal, Lars and Samuel son, 01 of. "Carbohydrate Stabilization During
Soda Pulping with Addition of Anthraquinone." TAPPI, 61:2. Feb. 1978.
9. Lowendhal, Lars and Samuel son, 01 of. "Carbohydrate Stabilization During
Kraft Cooking with Addition of Anthraquinone." Svensk Papperstidning
80(12) 549 1977.
10. NCASI, EPA Cooperative Study, "Atmospheric Emissions From the Pulp and
Paper Manufacturing Industry." EPA 450/1-73-002.
11. Development Document for Interim, Final, and Proposed Effluent Limita-
tions Guidelines and Proposed New Source Performance Standards for the
Bleached Kraft, Groundwood, Sulfite, Soda, Deink, and Non-Integrated
Paper Mills. EPA 440/1-76-047a, Jan. 1976.
12. Worstor, H. E., Pudek, M. F., "The Effects of Oxygen Pulping on Toxicity
and Color of Effluent." Pulp and Paper Magazine of Canada, 74(3):95
\ i y / o i.
57
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13. Hanson, James P. "No-sulfur Pulping Pushing Out NSSC Process at Corru-
gating Medium Mills." Pulp and Paper. March, 1978.
14. Hanson, James P. and Kukolich, S. I. "Semichemical Pulping With NaCO,
and NaOH Combinations." 1974 Non-Sulfur Pulping Symposium, TAPPI,
Madison, WI.
15. An unpublished study by ECONO prepared for EPA.
16. Nakamura, M., and Matoura, H. "Oxygen-Alkali Pulping of Beechwood."
1974 Non-Sulfur Pulping Symposium, TAPPI, Madison, WI. TAPPI 58:44.
17. Saukkonen, M., and Palenius, I. "Soda-Oxygen Pulping of Pinewood for
Different End Products." 1974 Non-Sulfur Pulping Symposium, TAPPI,
Madison, WI.
18. Samuel son, 0., and Sjoberg, L. A. "Oxygen-Alkali Cooking of Wood Meal."
Svensk Papperstidning 75(1972) 583-588.
19. Phillips, R. B., and Mclntosh, D. G. "Microscopic Characterization of
Paper and Fiber Properties of Linerboard Yield Soda-Oxygen/Alkali and
Kraft Pulps." 1974 Non-Sulfur Pulping Symposium, TAPPI, Madison, WI.
20. Nagano, T., Migao, S., and Takeda L. "HOPES Oxygen Pulping Process--
Its Basic Concept and Some Aspects for the Reaction of Oxygen Pulping."
1974 Non-Sulfur Pulping Symposium, TAPPI, Madison, WI.
21. Change, H., Gratzl, J. S., and McKean, W. T. "Delignificatiori of High
Yield Pulps with Oxygen and Alkali." TAPPI 57:5, Nov. 1974.
22. Abrahamsson, Kjell and Samuel son, 01 of "Oxygen-Alkali Cooking of Wood
Meal, Part III, Influences of Oxygen Pressure, Carbon Dioxide, and Metal
Compounds". Svensh Papperstidning 76(1973) 480.
23. Samuelson, Olof and Sjoberg Lars-Arne "Wet Combustion of Dissolved Solids
During Oxygen Bi Carbonate Cooking." Svensk Papperstidning 80(12) 1977.
24. Minor, J. L., and Bormett, D. W. "Recovery of Iodide from Oxygen Pulping
Liquors." TAPPI 60:4. April 1977.
25. Kleppe, P. J., Backlund, A., and Schildt, Y. "Oxygen/Alkali Delignifi-
cation at Kaymr Digester Blowline Consistency—Status Report." TAPPI
1976 International Pulp Bleaching Conference, Chicago, IL. May 1976.
26. Abrahamsoon, Kjell and Samuelson, Olof. "Oxygen-Alkali Cooking of Wood
Meal, Part II. Experiments with Sodium Bicarbonate Solution." Svensk
Papperstidning 75(1972) 869.
27. Rowlandson, G. "Continuous Oxygen Bleaching in Commercial Production."
TAPPI, 54:6 (1971).
58
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28. Carpenter, W. L., McLoan, W. T., Berger, H. F., and Gellman, I. "A Com-
parison of Effluent Characteristics from Conventional and Oxygen Bleach-
ing Sequences, Results of a Laboratory Study." Preprint of a paper pre-
sented at the 1973 International Pulp Bleaching Conference, June 3-7,
1973. Vancouver, B.C.
29. McKean, W. T. "Potential Pollution Loads from Oxygen Pulping." 1976
TAPPI Environmental Conference, Atlanta, GA. April 26-28, 1976.
30. Erickson, M., and Dence, C. "Yield and Composition of Tall Oil from
Oxygen-Alkali Pulped Thermomechanical Fiber."
31. Attack, D. "On the Characterization of Pressurized Refiner Mechanical
Pulps." Svensk Papperstidning, 75(1972) 89.
32. Marton, R., Brown, A., and Granzow, S. "Oxygen Pulping of Thermo-
mechanical Fiber." 1974 Non-Sulfur Pulping Symposium, TAPPI, Madison,
WI.
33. Rapson, W. H., and Reeve, D. W. "The Effluent-Free Bleached Kraft Pulp
Mill, The Present State of Development" TAPPI 56:9, Sept. 1973.
34. Minor, J. D., and Sanyo, W. "Oxygen Pulping of Wood Chips with Sodium
Carbonate." 1974 Non-Sulfur Pulping Symposium, TAPPI, Madison, WI.
35. Minor, J. L., and Sanger, N. "Factors Influencing Properties of Oxygen
Pulps from Softwood Chips." TAPPI 57:5, May 1974.
36. Asaoka, H. "Pollution Free Pulping Process..." 1974 International
Symposium on Pulp and Paper, Tokyo, Japan.
37. Seletonga, Toga, and McGovern, J. N. "Experimental Halopulping of
Several Temperate and Tropical Hardwoods."
38. Nicholls, G. A., Jamieson, R. G., and Van Dronen, V. J. "The Oxidative
Pulping of Hardwoods." 1974 Non-Sulfur Pulping Symposium, TAPPI, Madi-
son, WI.
39. Anon. "Halopulping to Cost Chemicals a Market." Chemistry and Engineer-
ing News. May 19, 1969.
40. Nicholls, G. A., Jamieson, R. G., and Van Dronen, V. J. "Oxidative
Pulping of Softwoods." TAPPI, 59:5. May 1976.
41. Asaoka, H., Nagasawa, T., and Morita, M. "Pilot Plant Test for Pollu-
tion Free Pulping." TAPPI Environmental Conference, Chicago, IL. April
1977.
42. Karjalainen, P. 0., Lofkrants, J. E., and Christie, R. D. "Chloride
Buildup in Kraft Liquor Systems." Pulp and Paper Magazine of Canada,
73:12, Dec. 1972.
59
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43. Bosch, J. C., Pilat, J. J., and Hrutfiord, B. J. "Size Distribution of
Aerosols from Kraft Mill Recovery Furnace." TAPPI 54:11. Nov. 1971.
44. Stephenson, J. N., Ed. Pulp and Paper Manufacture, Vol. 1, Preparation
and Treatment of Wood Pulp.McGraw-Hill Book Co., Inc., New York, 1950.
45. Kleinert, T. N., "Organosolvent Pulping with Aqueous Alcohol." TAPPI
57:8. August 1974.
46. De Haas, G. G., and Lang, C. J. "Delignification with Ketones and
Ammonia." TAPPI 57:5. May 1974.
47. A Brief Submitted to the Provensial Pollution Control Board for Presen-
tation at the Public Inquiry on Pollution Control Practices in the
Forest Products Industry, held March 2, 1976.
48. Roberson, J. E., Hendrickson, E. R., arid Tucken, W. G. "The NAPCA Study
of the Control of Atmospheric Emissions in the Wood Pulping Industry."
TAPPI, Vol. 54, No. 2. February 1971.
49. Borg, A., Tender A., and Warnquist, B. "Inside a Kraft Recovery Furnace-
-Studies on the Origins of Sulfur and Sodium Emission." TAPPI Environ-
mental Conference. May 1973.
50. Warnquist, Bjorn. "Chlorides in the Kraft Recovery System, Part 1.
Chlorides in the Recovery Boiler, and Mechanism for Chloride Removal."
1976 International Bleaching Pulp Conference, May 2, 1976. Chicago, IL.
51. Gullichsen, J. "Heat Values of Pulping Spent Liquors." Proceedings of
the Symposium on Recovery of Pulping Chemicals, Helsinki. 1968.
52. Mullen, W. P., and Dence, C. W. "Characterization and Composition of
Spent Oxygen-Alkali and Soda Pulping Liquors." 1974 Non-Sulfur Pulping
Symposium, TAPPI, Madison, WI.
53. Histed, J. A. "Water Re-use and Recycle in Bleacheries." CPAR Project
Report 47-1 Environment Canada Forestry Service.
54. Bhada, R. K., Lange, H. B., and Markant, H. P. "Air Pollution From
Kraft Recovery Units—The Effect of Operational Variables." 1972 TAPPI
Environmental Conference.
55, Graig, A. V. "Some Aspects of Recovery Unit Operation." Pulp and Paper
Magazine of Canada. July 1965.
56. Galeano, S. T., and Leopold K. M. "A Survey of Emissions of Nitrogen
Oxides in the Pulp Mill." TAPPI, Vol. 56, No. 3. March 1973.
57. Brown, R. W., Di Luzio, J. W., Kuhn, D. E., and Rapp, G. G. "Black Liquor
Evaporation and Odor Control in Sulfur Free Alkaline Pulping." 1974 Non-
Sulfur Pulping Symposium, TAPPI, Madison, WI.
60
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APPENDIX A
ENERGY USE CALCULATIONS
Many factors determine a pulp mill's energy balance. Many of the major
ones can be determined. Many minor factors, such as those differences in
energy usage among individual pieces of equipment or usage of secondary
steam, will create variations from basic energy consumption for any type of
process. The energy balances presented here are to determine basic energy
use of each type of pulping process. Actual energy usage will vary somewhat
depending upon the process options taken.
The pervading factor in the quantity of energy that must be provided for
a pulp mill by burning purchased fuels is the quantity of energy recoverable
from the dissolved wood constituents contained in the b.lack liquor. Low
energy production at the recovery furnace will require that power boiler cap-
acity be added to take up the energy slack. The quantity of energy produced
in the recovery boilers will depend both upon the heat value and the quantity
of the black liquor. The black liquor heat value and quantity are determined
by the yield and the quantity and type of cooking chemicals used. There are
widely varying types of cooking chemicals and yield in the processes consid-
ered in this paper and, therefore, widely varying energy productions in the
recovery furnaces.
Other major energy users in pulp mills are the energy required for pulp-
ing, evaporation of black liquor, pulp washing, preparation of pulping and
bleaching chemicals, and heat used in the bleach plant. Oxygen pulping
systems are unique in the energy requirements for pulping in that the oxida-
tion of lignin to carbon dioxide liberates substantial quantities of energy.
The oxygen digesters will probably liberate more heat than they consume.
Evaporation of black liquor will require similar quantities of energy for
each of the pulping processes considered in this paper.
Bleaching chemicals can be produced either in plant or outside the plant.
The production of pulping and bleaching chemicals was included in the report
because this energy would be consumed somewhere and the impact on the environ-
ment displaced. The amount of heat used in the bleach plant will depend upon
the bleaching sequence used and the amount of countercurrent washing practic-
ed.
The approach taken in the calculations is to determine the steam pro-
duction expected from the recovery furnace and balancing that against steam
61
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and electrical energy consumption throughout the mill. Liquor heating values
are estimated and a heat balance around the recovery furnace is made. Steam
usage in pulping, black liquor evaporation, pulp washing, chemical prepara-
tion, bleaching, and miscellaneous and auxiliaries are estimated.
62
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Bleach Plant Energy Calculations
Three bleach plant models were chosen by which to calculate steam re-
quirements of the bleach plant: 1) a full CEDED sequence with no water re-
use, 2) a full C/D-EDED sequence with direct counter current water reuse (53),
and 3) a DED sequence with water reuse. The first sequence is to represent
the energy use in a bleach plant at a standard kraft, soda, or soda thermo-
chemical mill. The second sequence applies to the Rapson process, and a
standard kraft mill utilizing bleach plant water reuse. The third sequence
applies to oxygen and halogen pulping processes. In each case the energy
required was caluclated from the energy to heat the wash water from 35 to
the temperature required in the subsequent bleach or extraction stage. Tables
4-9 through A-ll show the calculations.
TABLE A-9. HEAT REQUIREMENTS OF A CEDED BLEACHING SEQUENCE
Schedule
W D
W
W D W
Consistency, %
Temperature, °C
Wash water flow/KKg/t
Wash water temperature
3 10 10 10 10
15 50 60 50 70
11.5 11.5 11.5 11.5 11.5
55 65 50 75 50
req. C
AT 40
Heat required, KKcal/t 460
Total heat required, KKcal/t = 2524
50
570
35
402
60
690
35
402
71
-------
TABLE A-10. HEAT REQUIREMENT OF A C/DEDED BLEACHING SEQUENCE WITH FULL
COUNTER CURRENT WATER REUSE
Schedule C/D W E W D
Consistency, % 3 10 10
Temperature, °C 25 50 60
Wash water flow, KKg/t 13.5 11.3
Temperature of water
from Previous stage, C 50 50
Wash water temperature
required, C 55 65
AT, °C 5 15
Heat required, KKcal/t 68 120
W E
10
50
10.5
50
60
0
0
W D W
10
70
10.5 11.3
45 15
75 50
30 35
315 395
Total heat required = 948 KKcal/t
72
-------
TABLE A-ll. HEAT REQUIREMENTS OF A DED BLEACHING SEQUENCE WITH FULL
COUNTER CURRENT WATER REUSE
Schedule D W
Consistency, % 10
Temperature, °C 60
Wash water flow, KKg/t 10.5
Temperature of water from previous
stage, C 50
Wash water temperature
required, C 50
AT, °C 0
Heat required, KKcal/t 0
Total heat required =710 KKcal/t
E W D W
10 10
50 70
10.5 11.3
45 15
75 50
30 35
315 395
-------
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Chlorine and Chlorine Dioxide Production Energy Requirements
Between 2,400 KWH to 3000 KWH is required to produce a ton of chlorine
in diaphragm cells. Normally about 10,000-12,000 Ib of steam is required
to concentrate each ton of caustic from 10-12% to approximately 50% NaOH.
Concentration of caustic won't be necessary for on-site production of chlo-
rine because shipping is not required.
Chlorine dioxide requires 5,425 KWH per metric ton of NaClO., produced
in a Krebs cell. Chlorine dioxide is produced from NaClO^ in a R3 generator,
using HC1 as the reducing agent. HC1 is available from chlorine production;
1.08 tons per ton of chlorine dioxide will be required. Chlorine dioxide
generators produce a mixture of chlorine dioxide and chlorine in about a
65:35 weight ratio. In chlorine dioxide pulping, this chlorine dioxide is
used as the total mixture with the chemical requirement expressed as total
chlorine.
For one metric ton of C^ + C12 as chlorine, 1.50 tons of NaClO^ and
1.03 tons of HC1, or 1.0 tons of chlorine and hydrogen are required. Pro-
duction of 1.50 tons of sodium chlorate will require 8137.5 KWH and produc-
tion of 1.0 tons of chlorine will require 3304 KWH. Burning of the chlorine
and hydrogen will provide considerable energy that can be used for the gen-
eration of some of the electrical power needed. Each ton of C102 + C12 as
chlorine will require 11,442 KWH or 9847 KKcal. Halogen pulping will require
0.15 tons Cl per ton pulp produced, or 1480 KKcal of energy per ton pulp.
75
-------
APPENDIX B
POWER BOILER S02 EMISSIONS
1. Assume use of oil containing 1.8% sulfur in the power boiler. Oil has a
heating value of 149,000 BTU/gal. Assume oil weighs 8 Ibs per gallon.
The quantity of sulfur dioxide produced in a power boiler fired with oil
is 3.4 g/KKcal.
2. Assume use of coal containing 1.9% sulfur and with a heating value of
13,000 BTU/lb. The quantity of sulfur dioxide produced in a power
boiler fired with coal is 5.3 g/KKcal.
3. Waste wood has a sulfur content such that it will produce 0.67 Kg/KKcal
of energy produced.
TABLE B-l. CALCULATION OF S00 EMISSIONS
Soda
Semi-
Kraft Soda Chem Soda Therm Chip ClOp Rapson
Energy required
KKcal/KKg pulp 492 151 2401 834 740 951 1237 198
S02 emissions for:
Oil fired
Kg/KKg pulp 1.7 0.5 8.2 2.8 2.5 3.2 4.2 0.7
Coal fired
Kg/KKg pulp 2.6 0.8 12.7 4.4 3.9 5.0 6.6 1.0
Waste wood
Kg/KKg pulp 0.3 0.1 1.6 0.6 0.5 0.6 0.8 0.1
76
-------
APPENDIX C
PARTICULATE EMISSIONS
Participate emissions from a recovery furnace are affected by a number
of recovery furnace operations such as firing rate, heating value of the
black liquor, water content of the black liquor, furnace temperature, pri-
mary and secondary air temperature, black liquor chemical makeup, excess
air, particulate control equipment efficiency, chemical and physical nature
of the particulates, and process configuration (54). Prediction of parti-
culate emissions from a soda mill recovery furnace is difficult, although
some trends are evident.
Particulate emissions from a recovery furnace originate in the volati-
lization of sodium and sodium compounds from the smelt on the furnace bed,
and from carryover of fine ash particles resulting from spraying of the black
liquor (49), (55). The larger particules resulting from carryover of ash are
easily removed. Volatilized sodium and sodium compounds condense and react
with available carbon dioxide and sulfur dioxide to form a fume. The amount
of fume formed depends upon the amount of sodium vaporized, which is in turn
governed by the bed temperature and the sulfidity of the black liquor. The
higher the bed temperature, the more volatilization of particulates. Low
sulfidities, or the lack of sulfur altogether, causes higher particulate
emissions.
Assuming all conditions other than the heating value of the black liquor
are held constant in the recovery furnace for each pulping process, a com-
parison of the expected particulate emissions can be made from those pro-
cesses.
If halogens, either the chloride or iodide, are present in the black
liquor, greater particulate emissions can be expected. Halogens vaporize
at a much lower temperature (1413 C for chlorides and 1304 C for sodium
iodide) than do other recovery furnace sodium compounds, hence the quantity
of fumes is much larger. The quantity of halogens vaporized in the recovery
furnace depends upon the proportion of halogens present and the bed tempera-
ture (42).
Table C-l lists the various sources of particulates from a pulp mill as
well as some of the operating parameters affecting particulate emissions.
Calculations for the smelt tank emissions are made by comparing the quantity
of smelt processed in each pulping process to the quantity used in kraft
pulping and adjusting the average particulate emissions for kraft mills re-
ported in Reference 54 accordingly. The same procedure was used for cal-
culating lime kiln emissions, using the quantity of NaOH required for com-
77
-------
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parison. Power boiler emissions are calculated from the energy requirements
of each type of mill for the fuels, gas, oil, coal, and wood waste.
79
-------
APPENDIX D
NO EMISSIONS CALCULATIONS
/\
The quantities of nitrogen oxides emitted from a power boiler is depend-
ent upon the flame temperature, and hence the fuel used. NO emissions for
various fuels as a function of power produced for power boilers are: bitumi-
ous coal, 0.00163 g/Kcal; residual fuel oil, 0.00096 g/Kcal; natural gas,
0.00067 g/Kcal; and waste wood 0.0018 g/Kcal (2), (56).
TABLE D-l. POWER BOILER NO EMISSIONS
Kraft Soda
Soda
Semi
Chem.
Oxy.
Soda
Oxy.
Therm.
Oxy.
Chip ClO^ Rapson
Energy required
KKcal/t pulp
No emissions
pulp for:
492
151 2401
834
740
951 1237 198
Oil fired
Coal fired
Natural gas
Waste wood
.47
.80
.33
.89
.14
.25
.10
.27
2.30
3.91
1.61
4.32
.80
1.36
0.56
1.50
.71
1.21
0.50
1.33
.91
1.55
0.64
1.71
1.19
2.02
0.83
2.23
0.19
0.32
0.13
0.36
Nitric oxides are also formed in the recovery furnace and in the lime
kiln. Nitric oxide concentrations in the recovery boiler are relatively
low because of the low flame temperature, High flame temperatures result
in higher NO formation. Lime kilns have higher flame temperatures and con
sequently result in higher nitric oxide emissions. Table D-2 shows calcula
tions for NO emissions from the recovery furnace and lime kiln. The esti-
mates were mcide by using a NO emission of 3 kg/t (6 Ib/T) from a kraft
furnace, and 18 kg/t (36 Ib/Tj NO from a kraft lime kiln, and scaling
the other types of mills according to the energy production in the recovery
furnace, or the energy consumption in the lime kiln, respectively.
80
-------
TABLE D-2. RECOVERY FURNACE AND LIME KILN NOX EMISSIONS
Soda
Semi Oxy. Oxy. Oxy.
Kraft Soda Chem. Soda Therm. Chip C102 Rapson
Recovery furnace
energy production,
KKcal/t 4172 4487 1367 3582 2862 2430 2961 4882
Recovery furnace
NOX emissions,
Kg/t 3.0 3.2 1.0 2.6 2.1 1.7 2.1 3.5
Lime kiln energy
use, KKcal/t 852 1117 91 714 0 0 219 852
Lime kiln NOX
emissions, Kg/t 18.0 23.6 1.9 15.1 0 0 4.6 18.0
81
-------
APPENDIX E
SULFUR LOADINGS TO NON-SULFUR PULPING PROCESSES
Although no sulfur compounds are intentionally added to non-sulfur
pulping processes, sulfur compounds are inadvertantly introduced into the
cooking liquors and recovery process. Sulfur compounds accumulate in the
cooking liquors until they are purged from the system. Sulfidities of about
5% can result from sulfur accumulations. Reduced sulfur emissions from pulp
mills result even at the low sulfur levels found in non-sulfur pulping.
Sulfur is introduced into the pulping chemical cycle from several
sources. Sulfur dioxide, produced by burning sulfur containing fuel oil in
the lime kiln, reacts with the lime to produce calcium sulfate. During the
causticizing step, the sulfate is transferred to the pulping liquor. About
0.5 pounds of sulfur per ton pulp is added to the cooking liquor from fuel
oil via causticizing. About 0.021 Ibs sulfur per ton pulp enters the mill
via purchased limestone (57). Sulfur enters a mill through the mill raw
water supply. The amount of sulfur added by the water supply will vary by
location, depending upon water quality. Some waters are naturally high in
sulfates. Treatment of surface waters with alum will contribute additional
sulfur to the mill.
The level to which sulfur accumulates in the cooking liquor depends upon
a balance between the sulfur input and sulfur losses. As the concentration
of sulfur in the cooking cycle increases, the quantity of sulfur lost in-
creases. Sulfur losses are through the chemical recovery flue gas, malodor-
ous emissions, losses through the brown stock washer system, losses in the
green liquor clarification dregs, and losses in the causticizing department.
Sulfur accumulation in a non-sulfur pulping mill cooking cycle may re-
sult in odor emissions from various sources. Table E-l lists sources and
quantities of reduced sulfur emissions from a soda mill prior to odor control
measures (57).
Odors from a non-sulfur mill can be effectively controlled by chemically
scrubbing the gases containing the malodorous compounds with oxidants. Col-
lection and scrubbing of the low pressure feeder and S.V. relief condenser
gases would eliminate 98% of the odor. These gases can be scrubbed with
hydrochlorite filtrate, chlorine filtrate, spent acid, and bleach plant
effluent (57).
82
-------
TABLE E-l. ORGANOSULFUR EMISSIONS
Low
S.V
#2
15%
Source
pressure feeder
. rel ief condenser
Diffusion washer
Black liquor tank
Compound
DMS*
DMDS
DMS
DMDS
DMS
DMDS
H9S
DMS
DMDS
Ibs S/ADTP
0.01618
0.00124
0.00200
0.00026
0.00006
0.00002
0.00008
0.00002
0.00016
%
86.90
11.21
0.43
1.40
DMS and DMDS stand for dimethyl sulfide and dimethyl
disulfide, respectively.
83
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TECHNICAL REPORT DATA
'Please read Instructions on the reverse before completing)
1 REPORT NO 2
EPA-600/2-79-026
4 TITLE AND SUBTITLE
MULTIMEDIA ASSESSMENT OF POLLUTION POTENTIALS OF NON-
SULFUR CHEMICAL PULPING TECHNOLOGY
7 AUTHOR(S)
Victor Dallons
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Food and Wood Products Branch
Industrial Environmental Research Lab.
Cincinnati, Ohio 45268
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Lab. - Cinn, OH
Office of Research and Development
U. S. Environmental Protection Agency
Cincinnati, Ohio 45268
3 RECIPIENT'S ACCESSIOONO.
5. REPORT DATE
January 1979 issuing date
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1BB610
11. CONTRACT/GRANT NO.
Inhouse
13. TYPE OF REPORT AND PERIOD COVERED
Final, 1/77 to 12/77
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report gives an estimate of the air, water, and solid waste pollution generated
by developing and existing non-sulfur pulping techniques that are potentially com-
petitive with kraft pulping. Also developed were energy use and needs estimates for
these pulping processes. Processes investigated were soda pulping, soda semichemical
pulping, soda pulping followed by oxygen delignification, thermomechanical pulping
followed by oxygen delignification, oxygen pulping of wood wafers, chlorine dioxide
pulping, solvent pulping and the Rapson process. All of the pulping processes
considered develop less water pollutants and less total reduced sulfur emissions
than does the kraft process. Sulfur dioxide and particulate emissions vary from
process to process, some being greater than that expected from kraft and some
less. Sulfur dioxide and particulate emissions largely originate from power
boilers. Requirements for power produced from power boilers vary considerably
between mill types. Some air pollutants presently not inherent to the production
of pulp, such as sodium iodide, hydrochloric acid, and carbon monoxide, are
potentially emitted from several of the new pulping processes.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Pulping, Pulp mills, Pollutions
Chemical pulping , Air pollution,
Water pollution, Odor Control
13 DISTRIBUTION STATEMENT
Release to Pub! ic
b. IDENTIFIERS/OPEN ENDED TERMS
Non-Sulfur Pulping
U SECURITY CLASS IThis Report)
UNCLASSIFIED
20 SECURITY CLASS /This page!
UNCLASSIFIED
c. COSATI Field/Group
138
21 NO OF PAGES
92
22 PRICE
EPA Form 2220-1 (9-73)
84
»US GOVEWMENT PRINTING OFFICE 1979-657-060/1595
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