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            AIR POLLUTION

                AND  THE

    KRAFT  PULPING    INDUSTRY

        An Annotated Bibliography
                      by
                  Paul A. Kenline
                 Jeremy M. Hales
                Field Studies Branch
        Robert A. Taft Sanitary Engineering Center
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
                Public Health Service
               Division of Air Pollution
                 November 1963

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The  ENVIRONMENTAL HEALTH SERIES of reports  was established
to report the results of scientific and engineering studies of man's en-
vironment: The community, whether urban,  suburban,  or rural, where
he lives, works, and plays; the air, water and earth he uses and reuses;
and the wastes he produces and must dispose of in a way that preserves
these natural resources.   This SERIES  of reports provides for profes-
sional users a central source of information on the intramural research
activities of the Centers in the Bureau of  Disease Prevention and En-
vironmental Control, and  on  their cooperative activities with State and
local agencies, research institutions, and industrial organizations.  The
general subject  area of  each report is indicated by  the letters  that
appear in the publication number; the indicators are
                  AP - Air Pollution

                  RH - Radiological Health

                  UIH - Urban and Industrial Health
Reports in the SERIES will be distributed to requesters, as supplies
permit.  Requests for reports in the AP SERIES should be directed to
the Air Pollution Technical Information Center, National Center for Air
Pollution Control,  Public  Health Service, U. S. Department of Health,
Education, and Welfare, Washington, D.  C.  20201.
           Public Health Service Publication No. 999-AP-4

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                   CONTENTS
                                                Page
ABSTRACT                                         v
INTRODUCTION                                     1
DESCRIPTION OF THE KRAFT PULPING PROCESS     2
SURVEY OF PULP MILL PROCESS EMISSIONS          4
     Digester Blow System Emissions                      4
     Smelt Tank Emissions                              5
     Lime Kiln Emissions                              5
     Recovery Furnace Emissions                        5
     Multiple Effect Evaporator Emissions                  6
MEASURES FOR CONTROLLING EMISSIONS            7
     Control of Particulate Emissions                      7
     Control of Gaseous Emissions                        8
INDEX TO BIBLIOGRAPHY                           9
ANNOTATED BIBLIOGRAPHY                       15
SELECTED PAPERS                                 77
                         111

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                          ABSTRACT
    Since the first kraft mill came into existence in 1891, the potential odor
problem has been well recognized. Accordingly, a great deal of literature
has been published  describing practical and  theoretical  work in the field
of kraft mill odor control. Some progress has been made, but even  today
most kraft mills are faced with serious problems of atmospheric pollution.
    The following  work  provides an  annotated bibliography  of  articles
concerning  measurement and control of  kraft  mill air-borne pollution
currently available in the literature. It is  the authors' intention that this
should  provide  a retrospective view  of what has been  accomplished and
should form a sound basis for  further work in the field.  In  addition to  154
abstracts, this  bibliography contains a description of the kraft  pulping
process, a survey of mill emissions, and a consideration of control measures.

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                 AIR  POLLUTION
                       AND    THE
     KRAFT  PULPING    INDUSTRY
                    INTRODUCTION

    Cellulose, produced  by pulping processes, is one of the most versatile
and useful products of modern technology.
    The production of pulp in  the United States  amounted to  almost 22
million tons in 1957. This total  was produced by the following  processes:
Sulfate (kraft),  12 million tons; mechanical, 3 million tons; sulfite, 2%
million tons; soda, % million tons; all  others, 4 million tons.
    Thus, over half of the pulp  produced in the United States comes from
sulfate, or kraft, processing.
    When  the first kraft mill was built in 1891, the operators were well
aware of the air pollution problem involved. The first papers concerning
kraft mill  odor  problems appeared in  the literature  around 1900. Today,
despite the progress in recent years, most kraft pulp mills are still living
with this problem.
    The locations of kraft mills in the  United States, and their  capacities
are shown in Figure  1 and Table 1, respectively.
       Figure 1.  Location of sulfate (kraft) mills in the United States.
                                I

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                                                     AIR POLLUTION
 Table I.  SULFATE PULP MILLS IN THE UNITED STATES

       (The figure after the city name indicates production in tons of pulp per day)
ALABAMA (7)
Brewton 300
Coosa Pines 300
Demopolis 350
Tuscaloasa 500
Mobile 1,015
Mobile 550
Naheola 310
ARIZONA (1)
Snowflake 150
ARKANSAS (5)
Camden 615
Crossett 575
Crossett 80
Pine Bluff 170
Pine Bluff 745
CALIFORNIA (1)
Antioch 215
FLORIDA (9)
Fernandina Beach 650
Foley 800
Jacksonville 500
Jacksonville 1,370
Polatlto 810
Panama City 1,620
Pensacola 580
Pensacola 450
Port St. Joe 1,200
GEORGIA (8)
Augusta 350
Brunswick 525
Macon 700
Rome 725
St. Marys 800
Savannah 2,100
Valdosta 700
Port Wentworth 625
IDAHO (I)
Lewiston 500


LOUISIANA (6)
Bastrop 580
Bogalusa 1,180
Elizabeth 240
Hodge 500
Springhill 150
West Monroe
MAINE (3)
Lincoln 180
Old Town 140
Rumford 350

MARYLAND (1)
Luke 515
MICHIGAN (2)
Filar City 165
Muskegon 125
MINNESOTA (2)
Cloquet 130
MISSISSIPPI (3)
Lumberton 100
Moss Point 650
Natchez 900
MONTANA {))
Missoula
NEW HAMPSHIRE (1)
Berlin 450
NEW YORK (1)
Ticonderogo 150
NORTH CAROLINA (4)
Acme 700
Canton 930
Plymouth 950
Roanoke Rapids 650
OREGON (4)
Albany 250
St. Helens 375
Springfield 400
Toledo 600
PENNSYLVANIA (4)
Roaring Spring 120
Spring Grove 190
Tyrone 140'
Williamsburg 85
SOUTH CAROLINA (3)
Catawba 400
Charleston 1 ,250
Georgetown 1 ,455
TENNESSEE (2)
Calhoun 450
Counce 500

TEXAS (3)
Evadale 360
Lufkin 300
Pasadena 670
VIRGINIA (4)
Covington 660
Franklin 690
Hopewell 800
West Paint 600
WASHINGTON (8)
Comas 700
Everett 80
Everett 325
Longview 825
Longview 575
Port Townsend 420
Tacoma 400
Wallula 200
WISCONSIN (2)
Kaukauna 250
Mosinee 165






                    DESCRIPTION  OF

        THE  KRAFT  PULPING  PROCESS

    Pulp wood can be  considered to have two basic  components, cellulose
and lignin. The fibers of cellulose, from which the pulp is made, are bound
together in the wood owing to the presence of the lignin. To render cellulose
usable for pulp manufacture, any chemical pulping process must first re-
move the lignin.
    The major discriminating factor of the kraft process  (Figure 2) Ijfis
in its utilization of a solution of sodium sulfide and sodium hydroxide in
water to dissolve lignin from wood. This liquor is mixed with wood chips
in a large, upright pressure vessel, known as a  digester, and cooked for
about 3 hours with steam at a gauge pressure of approximately 110 pounds
per square inch.
    During the cooking period the digester is relieved periodically to reduce
the pressure build-up of various gases within.
    When cooking is completed, the bottom of the digester is suddenly
opened, and its contents forced into the blow  tank. Here the major portion
of the  spent cooking liquor  containing the dissolved  lignin  is drained and
the pulp enters the initial stage of washing. From the blow'tankl the pulp
passes  through the knotter, which removes the chunks of wood not broken
down during cooking. It then proceeds through various intermittent stages
of washing and bleaching, after which it is pressed and dried into the fin-
ished product.
    A major reason for the  economic success  of this type of pulping  oper-
ation lies  in its  ability to recover most  of the chemicals from the  spent

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 Kraft Pulping  Industry
                              PULP •*
         WOOD CHIPS
               WATER
                      CALCIUM f
                     I HYDROXIDE
MUD (CALCIUM CARBONATE)
SLAKER

"" \
                    Figure  2.  The krafr pulping process.
cooking liquor for re-use in subsequent cooks. The recovery process is in-
itiated by introducing  the spent ("black") liquor from the blow tank into
a multiple effect evaporator where it is  concentrated  into a mixture with
a density of about 25° Baume! The spent (or black) liquor, is further concen-
trated in a direct contact evaporator, which, by bringing the liquor into di-
rect contact with recovery furnace flue gases,  evaporates  an additional
portion of water.
    The combustible, concentrated, black liquor thus produced is then
forced through spray nozzles into the recovery furnace, where it is burned
to recover a portion of the heat by oxidation of the  dissolved lignin  and
to conserve the inorganic  chemicals, which fall to the floor of the furnace
in a molten state.

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  4                                                   AIR POLLUTION

     The resulting melt, which consists mainly of a mixture of sodium sul-
 fide  and sodium carbonate, is withdrawn from the furnace  and dissolved
 with water and weak liquor from the causticizing plant. The "green liquor"
 thus  produced is pumped into  a causticizer, where the sodium carbonate
 is converted to sodium hydroxide by the addition of calcium hydroxide. The
 calcium carbonate resulting from the reaction precipitates from the solution
 and is collected and introduced into a lime kiln, where it is converted  to
 calcium oxide. This is  slaked  to produce calcium hydroxide for  further
 use in the causticizer.
     The effluent solution produced  by the causticizing reaction with the
 green liquor contains sodium hydroxide, sodium sulfide, and  smaller quan-
 tities of sodium  sulfate and  sodium carbonate. Known as "white liquor,"
 this solution  is withdrawn and  re-used in the digestion  process.
               SURVEY  OF  PULP  MILL

                   PROCESS  EMISSIONS

Digester  Blow System Emissions
     The major pollutants from the blow system(Tables 2 and 3)are organic
mercaptans and  sulfides with lesser amounts of hydrogen sulfide. Sulfur
dioxide and  particulates are negligible.*
  Table 2.  BLOW SYSTEM EMISSIONS PRIOR TO TREATMENT
Digester
cooking
conditions
Cook time 3.75 hr
Temp 172'°C
Sulfidity 22%
Unknown
Hydrogen
sulfide
Methyl
mercaptan
Dimethyl
sulfide
Ib /ton dry pulp
0.45
0 to 0.10
2.50
0 to 0.88
1.37
0.01 to 0.94
Ref
66
18
      Table 3. GAS CONCENTRATIONS IN BLOW SYSTEM EMISSIONS
                    Gas
      Hydrogen sulfide

      Methyl mercaptan

      Dimethyl sulfide

      Dimethyl disulfide

      Sulfur dioxide
Concentration, mg per liter
       OtoO.4

       3 to 72

      0,5 to 35

      0.2

      0
 * The values in Tables 2 through 8 were calculated from data in the Bibliography and from the
forthcoming PUS Report, The Study of Air Pollution in the Interstate Region of Lewiston, Idaho,
and Clarkston, Washington. These are rough estimates and not typical of a particular mill.

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 Kraft Pulping Industry
 Smelt Tank Emissions
     Emissions from the smelt tank (Table 4) are primarily  participate.
 Uncontrolled particulate emissions may run about 20 pounds per ton of
 pulp. Use of a simple water spray may reduce this figure to 5 pounds per
 ton of pulp, while a mesh demister may further reduce this to 1 or 2 pounds
 per ton of pulp. Thus an average 600 tons per day mill may emit 6 tons of
 particulate if uncontrolled.
   Table 4.  PARTICULATE EMISSIONS FROM SMELT DISSOLVER TANKS
Influent particulate
loadings, ton/day
5.6
Efficiency of
mesh demister
80%
Effluent particulate
emissions, tons/day
1.1
 Lime  Kiln   Emissions
    The lime kiln is a major source of particulate emissions (Table 5);
gaseous emissions are not so pronounced- Particulate emissions reportedly
range from 5 to over 15 grains per cubic foot. This may represent up to 10
or more tons emitted per day.  Use of scrubbers reduces these  emissions to
about 0.5 grain per cubic foot, roughly 1 ton per day.
      Table 5. PARTICULATE EMISSIONS FROM LIME KILNS
      Particle concentration,
      grains/ft-^
Particulate emissions,
Ib /ton dry pulp
                     0.86
             18.7
Recovery Furnace Emissions
    The recovery furnace is  a major source of particulate  and gaseous
pollution (Tables 6 and 7).

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                                                   AIR POLLUTION
   Table 6. HYDROGEN SULFIDE AND PARTICULATE EMISSIONS FROM RECOVERY
          FURNACES
Pollutant generated by
furnace (with primary
stack gas scrubber),
Ib /ton dry pulp
Hydrogen sulfide:
3.59
Particulates:
150
Final emissions with
venturi scrubber,
Ib /ton dry pulp
0.72

12
Final emissions with
electric precipitator,
Ib /ton dry pulp
3.59

7
  Electrostatic precipitators remove 85 to 97 percent of the particulate. Ven-
  turi scrubbers remove 60 to 95 percent of the particulate and some of the
  gases.

   Table 7. RECOVERY FURNACE EMISSIONS
              Pollutant:
        Emission:
   Particulate

   Particulate

   Hydrogen sulfide

   Methyl mercaptan

   Dimethyl sulfide

   Sulfur dioxide
 10 to 40 tons/day

TOO to 400 Ib/ton of pulp

130 to 935 ppm

 60 to 1,400 ppm

     125 ppm

  1 to 350 ppm
Multiple  Effect Evaporator  Emissions
  Table 8. EMISSIONS FROM MULTIPLE EFFECT EVAPORATORS WITH AND WITHOUT
         PREVIOUS BLACK LIQUOR OXIDATION
Pollutant

Hydrogen
sulfide
Methyl
mercaptan
Dimethyl
sulfide
Potential
emissions,
Ib /ton dry pulp
1.2
0.04

Oxidation tower
efficiency
95 to 100%
95%
10%
Emissions from
evaporators,
Ib /ton dry pulp
0 to 0.06
0.003


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                       MEASURES  FOR

             CONTROLLING  EMISSIONS
 Control of Participate Emissions
    Attempts to curb the smoke  and odors issuing from pulp  mills have
 been nearly as long lived as the krafl process itself. This is exemplified
 by an article in a  1922 journal describing a process wherein  the smoke
 from the mill is passed through a pile of wood chips or straw to remove
 both the odors and the particulate matter.
    Subsequent  developments have included more  refined techniques of
 collection. One such technique,  electrostatic precipitation, utilizes an elec-
 tric field to effect the  collection of charged, air-borne, particulate matter.
 Particulates can be removed from gaseous streams  with efficiencies  of
 greater than 95 percent with such equipment.
    The cyclone is  another unit of equipment  successfully applied to re-
 move particulate matter from effluent streams,  though it is generally used
 in conjunction with other removal equipment because of its low efficiency
 for  small particulates. Cyclones effect  a centrifugal force  on suspended
 particles by causing the carrier gas to spin in a tight, helical path. The
 particles move outward, hit  the peripheral walls of the unit, and fall out
 of the stream into  a hopper below.
    Various  modifications of the cyclone have been put into  successful
 operation. One utilizes a continuous spray dispersed  inside the unit to in-
 crease efficiency by  impinging air-borne particles on liquid droplets. These
 units, known as wet cyclones,  have frequently been used in kraft mills
 as flue gas scrubbers. Here black liquor is dispersed as the scrubbing agent,
 and  simultaneously  concentrated by evaporation. The efficiencies of cy-
 clones vary over a wide range and are considerably lower than those norm-
 ally expected from  electrostatic precipitators.    '
    Filtration provides  a third effective means of particulate removal, but
 has been used only  to a limited extent in kraft mill ah* pollution control.
 Particulate  emissions from lime kiln and dissolver  stacks have been  ef-~
 fectively reduced, however, by  use of  mesh demisters,  which are screen
 filters located inside the stacks.
    Venturi scrubbers constitute a fourth type of removal equipment. These
 are employed mainly in cleaning the voluminous gas streams  issuing from
 the furnaces and lime kiln. Scrubbers of this type force the gases at high
velocity through the venturi,  simultaneously injecting a spray  of scrubbing
liquor at the throat.  Particles of suspended matter are impinged upon the
spray droplets, which are in  turn collected by a cyclone at  the outlet of
the unit. Standard venturi scrubbers may attain efficiencies of 85 percent,
                                  7

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 8                                                  AIR POLLUTION

 and recently developed, steam-atomized types have been observed capable
 of efficiencies slightly higher.
     The major disadvantage of the venturi scrubber is its high power re-
 quirement. This  is offset somewhat by its ability to recover a  portion of
 the heat  and odorous gases from effluent streams as well as by its lower
 maintenance requirements. Electrostatic precipitators, on the other hand,
 require little power for their operation and have slightly higher efficiencies.
 They are ineffective as gas removers, however, and require greater "down"
 times for maintenance.
     Installation of collection equipment is made attractive to pulp mill own-
 ers from  an economic as well as  from an air pollution control  standpoint.
 It has been estimated that the amount  of particulate salts issuing from the
 stacks is  about 150 pounds per ton of pulp produced. For  a 100-ton-per-day
 mill, a collection system  operating with 90 percent  efficiency will save
 approximately $200 per day  by recovering these chemicals—a  substantial
 amount, which should rapidly pay off any reasonable investment in such
 equipment.
Control of Gaseous  Emissions

    Owing to the high virulence of trace quantities of pulp mill pollutant
gases as well as to their capability of issuing from many points within a
mill, the control of gaseous emissions has been recognized as a much greater
problem than that of air-borne particulate matter. Attempts to solve this
problem have generally followed one of two paths: (1) Chemical conversion
of odorous sulfur compounds into ones that are not so objectionable, and
(2) retention of sulfur compounds within the system.
    Among the first developments to become  popular in commercial ap-
plication was the black liquor oxidation process. This involves oxidation  of
the sulfur compounds in weak black liquor by  contacting it with air prior
to its admission to the multiple effect evaporators. Oxidation effects a con-
version to  less volatile compounds, which are  less odorous and  have less
tendency to escape into the atmosphere.
    It is generally accepted that  the oxidation  process reduces the  odor  of
evaporator gases and retains in the black liquor the sulfur compounds that
would otherwise be  emitted to the atmosphere. This larger concentration
of sulfur compounds results, however, in a tendency for their emission from
the recovery furnace stacks upon  combustion of  the black  liquor. As a
corollary of odor reduction by black liquor oxidation, it is important, there-
fore, to exercise rigid control over furnace operating conditions to minimize
emission of reduced  sulfur compounds.
    Oxidation of black liquor has several economic  implications,  one  of
which is the retention of sulfur  in the recovery system  and a  resulting
reduction in the amount of elemental sulfur needed to maintain a constant
sulfidity in the cooking  liquor.  Of much  greater   importance,  however,
are the  markedly reduced  corrosion  rates found characteristic of evap-
oration equipment processing oxidized black liquor.
    Another method  of mitigating odors from sulfur gases is simply to col-
lect these gases and  dispose  of them by burning.  The main problem wijth
this  method  arises from  tremendous periodical surges of gas that occur
when the digesters are blown. One company has  attempted  to solve this

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 Kraft Pulping Industry                                                 9

problem by collecting the gases in a large spherical surge tank that evens
the flow and supplies a continuous stream to the furnace for burning.
    Absorption of sulfur gases in liquids has been of limited use, especially
for handling gases from the evaporators.  One such unit,  called  an  "Ink a
Tower," utilizes a sodium hydroxide  solution as an  absorbent. This method
has  been found  effective in deodorizing noncondensable gases from the
multiple effect evaporators.
    Oxidation of exhaust gases by  catalytic methods has also  been pro-
posed, but its use has been limited. Processes designed for catalytic oxida-
tion may be extensively used in  the future.
    More dubious methods of controlling pulp mill odors  have been those
of odor masking  and counteraction, which involve introduction of a specific
substance at a selected point within a mill for dispersal with the mill gases,
to render them less noticeable. These methods are attractive to mill owners
 because they are simple and inexpensive to incorporate into any pulp mill,
 and are not affected by any basic changes in the process.
    Results of odor masking and counteraction have been varied and diffi-
cult to evaluate. These methods also have the disadvantage  that,  in  most
cases, nothing is done to eliminate the  noisome  gases,  and any  adverse
effect, other than odor, will persist.


               INDEX TO  BIBLIOGRAPHY
    The following index serves as a key to the Annotated Bibliography. The
numbers refer to the  correspondingly  numbered abstract in the Biblio-
graphy.
    For example, for collection and combustion as corrective measures for
digester relief and blow gases, the reader  is referred to abstract 35 (among
others),  which is an article by A.  A.  Coleman on  "The  Combustion of
Noncondensable Blow and Relief Gases in the Lime Kiln."
Digester Relief and Blow Gases
Major pollutants: hydrogen  sulfide,  methyl  mercaptan, dimethyl  sulfide,
dimethyl disulfide.
    Corrective measures:
    Collection and combustion
    8, 11, 12, 35,  52, 54, 66, 95
    Catalytic oxidation
    83, 105,  106
    Oxidation  in liquor oxidation tower
    13, 26, 71, 103, 107, 124
    Odor masking and counteraction
    63, 64, 85,  89, 116,  127, 128, 130, 132, 138, 147, 154
    Liquid absorption
    64
Multiple Effect Evaporator Gases
Major  pollutants: hydrogen  sulfide,  methyl mercaptan,  dimethyl sulfide,
dimethyl disulfide.
    Corrective measures:
    Black liquor oxidation
    5, 10, 11, 13, 16,  19, 22, 23,  26,  28, 31, 33, 37, 38, 39, 44, 46,  53, 54, 59, 71, 77,
    79, 81,  95,  102, 105, 121, 130, 131, 141,  142, 144, 145,  146, 148,  153
    Collection and combustion
    8,  11, 12, 35,  52,  54, 66, 95
    Liquid absorption
    54

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 10                                                    AIR POLLUTION
    Catalytic oxidation
    54, 84, 105, 106
    Odor masking and counteraction
    86, 90, 116, 127, 128,  130, 132, 138, 147, 154
    Integrated operations
    129, 131
Recovery Furnace Slack  Gases
Major pollutants:
I.   Particulate:fly ash, sodium sulfide, sodium sulfate, sodium oxide, sodium
carbonate.
    Corrective measures:
    Electrostatic precipitators
    6, 9, 10, 14, 24, 50, 61, 81, 103, 104
    Cyclones
    43, 81, 87, 114, 124
    Venturi  scrubbers
    29, 41, 43, 45, 48, 81, 87, 88, 101,  114, 136,  137
    Condensation methods
    65
    Integrated operations
    5, 7, 40, 58, 101, 124
    Spray scrubbers
    66, 81, 83, 114
II.  Gaseous: hydrogen  sulfide,  methyl  mercaptan,  dimethyl  sulfide,
dimethyl disulfide.
     Corrective measures:
    Air oxidation
     65, 109
     Cyclone  scrubbers
     87
     Venturi scrubbers
     29,  87, 88, 136, 137
     Integrated operations
     58, 62, 124, 129
     Odor masking and counteraction
     62,  63, 86, 89, 114, 127, 128, 130,  132, 138, 147, 154
     Spray scrubbers
     66, 83
     Catalytic oxidation
    84, 105,
Lime Kiln Stack Gases
Major pollutants: calcium carbonate.
Corrective measures:
    Electrostatic precipitators
    81, 120,
    Venturi scrubbers
    47, 75, 81, 114,
    Cyclones
    14, 81, 90, 114,
    Wet scrubbers
    90, 114,

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Kraft Pulping Industry                                                  11

Diuolver Vent Gases
Major pollutants: sodium carbonate, sodium sulfide.
Corrective measures:
    Filtration
    20,
    Integrated  operations
    101,

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 ANNOTATED
BIBLIOGRAPHY

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                        ANNOTATED

                      BIBLIOGRAPHY
1.      Adams, D. F. and R. K. Koppe: Application of instrumentation io
          pulp  mill atmospheric  discharges.  TAP PI, 41:  366-377. July
        1958. Many different types of instrumentation are currently avail-
        able for the quantitative and qualitative study of atmospheric pollu-
        tants-  The importance  of  obtaining quantitative  information con-
        cerning atmospheric  discharges from  the pulping process  is cur-
        rently being realized. This  report describes the available instrumen-
        tation applicable to the  study  of pulping  emissions,  including
        instruments  for  (1)  collection of  field  and  source samples,  (2)
        laboratory analysis of  collected samples,  and (3)  automatic, con-
        tinuous analysis  and recording. Instruments having  immediate or
        potential  application in pollution  studies are critically reviewed.
        A new, versatile, automatic  analyzer with potential application in
        the analysis  of malodorous gases in parts per billion concentration
        range  is described. A preliminary report on  the  development of
        a gas-liquid  chromatographic procedure for the separation of mix-
        tures of malodorous sulfur-containing compounds is  included plus
        62 references
2.      Adams, D. F. and R. K. Koppe.  Gas chromatographic  analysis of
        hydrogen  sulfide, sulfur dioxide,  mercaptans, and alkyl sulfides
        and   disulfides. TAP PI, 42; 601-605. (1959). In view of analytical
        difficulties arising  from chemical  similarities among sulfur com-
        pounds commonly found in pulp  mill stream  samples, a technique
        based  solely on physical properties appears desirable. This article
        presents  such  a  method,  which  employs a  chromatographic de-
        termination to analyze for volatile  sulfur gases. This method, with
        adequate  column packings and carrier solvents, results in highly
        specific analyses  with little  interference from other compounds.
3.     Adams, D. F., R.  K. Koppe, and D.  M. Jungroth: Adsorption  samp-
       ling  and  gas chromatographic analysis of sulfur compounds  in
       waste process gases. TAPPI, 43:602-608. June 1960.  A new procedure
       for source sampling and analysis of malodorous,  sulfur-containing
       gases from  the kraft pulping process has been developed. The
       pollutants are adsorbed  and/or  condensed on activated silica gel
       at minus 78.5 ° C, desorbed under conditions of heat and vacuum,
       trapped at minus  195.8 °C, and transferred onto a gas-liquid chrom-
       atographic column for analysis in  a conventional manner by use
       of a rising column temperature technique. Water vapor,  more polar
       than  the malodorous vapors,  must be preferentially removed from
       the source sample prior to adsorption to prevent chromatographic
       elution of  less polar compounds. The major portion of the water is

                                 15

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   16
                                               AIR POLLUTION
  4.
  eliminated by condensation at 0°C, and additional water  vapor is
  subsequently removed  on a  solid desiccant,  such  as  anhydrous
  calcium sulfate.
  Anderson, E.: Some gas cleaning problems in pulp and paper mills.
  Pacific  Pulp and  Paper Ind., 13:23-26. Jan. 1939.  Problems  and
  methods of cleaning air-borne effluent streams are  discussed.  Em-
  phasis is placed upon Cottrell precipitators for particulate  collec-
  tion. A method of destroying odorous gases by passing them through
  an oxidation heat exchange tower is  described.
  Anon: The B & W Tomlinson chemical and heai recovery process.
  Paper Mill News,  69:98-99. Nov. 16,  1946. A process is described
  that oxidizes weak black liquor to eliminate odorous fumes.  The
  stabilized liquor is further utilized in a cyclonic evaporator  to en-
  train fumes of sodium salts from the  recovery furnace. Flow chart
  included.

                    GAS TO ATMOSPHERE

          WATER AND         |
          CHEMICAL MAKE-UP
 HOT WATER
  TO MILL
   Figure  3.  Schematic flow diagram of chemical and heat recovery process.
7.
Anon:Five precipitators at Union Bag to eliminate odor and smoke.
 Paper Mill News,  69:7. Aug. 10, 1946. An installation of the largest
series  of electrostatic  precipitator units in the  history of the pulp
and paper industry is  being completed at the Union Bag, and Paper
Corporation's Savannah  plant. These units are expected  to  elimi-
nate practically all the smoke and reduce odors  to a minimum. Cost
of the  installation was $500,000.
Anon:  How  Mead eliminated recovery stack  snow at Kingsport.
Paper  Trade  «/., ,141:48-50. Oct. 7, 1957.  Since  installing  recovery

-------
Annotated Bibliography                                               17

        furnaces, the Kingsport plant has been plagued with the problem
        of soda ash "snow" rising from their stacks and falling on the near-
        by business district. This fallout occurred in  spite of  the electro-
        static precipitator, which was about 90 percent effective in recover-
        ing  ash particles. To  combat  this problem, a fog  scrubber was
        purchased that was highly successful  in  eliminating snow  when
        placed  in  series following the precipitator.  With this  unit, an 88
        percent efficiency has been obtained at the expense of only a 0.75-
        inch  H£O pressure drop. This also enables the carbonate to be re-
        claimed. This  scrubber  has been in operation since 1956,  and no
        snow problem has arisen  since that time.
8.       Anon: rjow Weyerhaeuser controls kraft odor with the raporsphere.
        Paper  Trade  J., 139:12-13. Jan- 3,  1955. Twenty-five-foot spheres
        are being used in two of Weyerhaeuser's  plants to catch noncon-
        densable gases from the kraft process. These two units, located at
        Springfield, Oregon, and  Everett, Washington, are said to be at
        least  90 percent effective in removing odorous gases.  Their pur-
        pose is  to collect the gases and emit them continuously for burning
        or chlorination.
9.       Anon:  Koppers  precipitator  installed  to  control  air  pollution.
        Paper  Mill  News,  81:28.  June 9, 1958. The St.  Regis  Paper
        Company's Jacksonville Mill has added a third  electrostatic pre-
       cipitator to their recovery furnace system.  The combination of the
       new and older units will effect a 112-ton-per-day salt cake recovery.
10.    Anon: A new board mill - Springfield sets new standards.  Pulp &
       Paper Mag., 23:42. Nov. 1949. A new 150-ton-per-day kraft mill con-
       structed by Weyerhaeuser in Springfield, Oregon, has incorporated
       several measures to utilize materialsl further and decrease pollution.
       Among these is a Bergstrom oxidation tower,  which removes a large
       portion  of the malodorous  gases. Here 25,000  cfm  of stack gases cir-
       culate   countercurrentily  to  250  gallons per  minute of condensate.
       The tower is 10 feet in diameter and 28  feet high. It is packed with
       4-inch cross-partition rings.  The  recovery stack gases are passed
       through an electrostatic precipitator prior to  expulsion into the at-
       mosphere. The resulting ash is  conveyed  dry into the  salt  cake-
       mixing tank. Combination  of these with other operations helps the
       new mill to utilize a higher percentage of the raw materials and
       reduce the  emission of pollutants to  the atmosphere.
11.    Anon: New system controls dust and odor. Pulp &  Paper Mag., 33:77.
       1959.  A  gas washer, a black liquor oxidation tower,  a  gas holder,
       and a  high temperature furnace have been, added  to the air pollu-
       tion control equipment  of the San Joaquin Pulp  Mill. This equip-
       ment is  designed to process 14,000 cubic feet  of gas per minute. Its
       cost was $600,000.
12.    Anon:  A new way to reduce kraft odors.  Pulp & Paper Mag., 29:122.
       Mar. 1955. Weyerhaeuser has developed a new type of gas holder
       that collects odorous vapors arising from the kraft process and emits
       them in  a continuous stream for disposal. Called the "vaporsphere,"
       it consists of a 27-foot steel  sphere, inside  of which is  mounted a
       gas-tight diaphragm. The diaphragm  rises  and  falls with the rate
       of  gas flow and thereby  evens out the tremendous surges of gas
       that arise from the blowing of digesters. From the  vaporsphere, the
       gases are transferred to a  furnace and burned. Weyerhaeuser  also

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   18                                                  AIR  POLLUTION

        operates a black liquor oxidation process that reduces odors from
        the evaporation system. Besides being effective in odor control, this
        system has economized  the  sulfur balance of the process,  making
        addition of elemental sulfur unnecessary.
  13.    Anon:  Odor  abatement in pulp mills.  Pulp & Paper Mag. Can.,
        53:108. Dec. 1952. In 1951 a large-scale experiment was carried out
        in the Bloedel, Stewart, and Welch pulp  mill at Port Alberni, B. C-
        A black liquor pilot oxidation unit was constructed and tested, while
        15,000 gallons of oxidized black liquor were being continuously accum-
        ulated. This liquor was fed into the recovery furnace, and the efflu-
        ent  gases  were analyzed. Studies indicated that a  substantial de-
        crease in odor resulted from the substitution of the oxidized  liquor.
        Also encouraging were the results of  studies indicating that digester
        relief gases could be rendered innocuous by absorption in the oxida-
        tion tower. Plans are currently under way for installation of  a full-
        scale oxidation unit.
 14.    Anon: We  don't have all the answers.  Air Repair,  2 :52-59. Nov.
        1952. The over-all problem  confronting a pulp mill consists of two
       general parts: the fly ash carried in the flue gas from the chemical
       recovery furnaces, and odors emanating principally from the wood
       digestion system. In the cook, the primary reaction is  between the
       cooking chemicals and the lignin. The  product is soluble in water,
       and  is washed from the fibers  and sent to the recovery  furnace.
       Electrostatic precipitation was found to remove 90 to 95 percent of
       recovery furnace fly ash. Another dust source is the lime-producing
       system. Champion Paper and Fibre Company (Pasadena, Texas) has
       installed a  rotoclone scrubber on their lime kiln at a cost of $40,000.
       To combat  the odor problem, relief gases are vented and condensed.
       The noncondensable gases are  destroyed by burning. Reaction prod-
       ucts of digestion contain some  H^S, Na2S, and mercaptans.  Na£S
       will  yield H^S in  presence of an acid.  If Na2>S  is  converted to
       Na2SC>4  by oxidation it does not form H2S. For this reason Champ-
       ion oxidizes their spent liquor. Champion uses  scrubbers on vapors
       that  distill  off from the  multiple  effect  evaporators.  This  article
       contains general statements  concerning  air pollution by M.  D. May
       of the Champion Paper and Fibre Company at a public hearing in
       Houston,  Texas.
15.     Anon: West coast steps up water, air  controls.  Pulp & Paper  Mag.,
       35:9.  May 1, 1961.  Portland, Oregon — This  session  has produced
       increased activity in the legislation of controls over air and water
       pollution. It appears that the state sanitary authority will have more
       power and  will have the authority to  specify to cities and industry
       what must  be done, but shall  not specify  the means to these  ends.
       The demands specified by these committees are  believed by  some
       to be so stringent as to make the resulting costs exceedingly high.
16.     Anon: Western kraft deodorizing mill.  Paper Mill News, 83:28 Sept.
       12,  1960.  The Western Kraft Corporation has recently installed a
       Collins black liquor oxidation unit at their kraft mill in Albany,
      Oregon. It is too early to estimate accurately the reduction in pollu-
      tion potential resulting from the tower, but every indication is given
      that a marked  improvement  has  taken place.  The  Albany  Mill is
      the fifth  establishment to employ this  type  of tower.  The others
      are at Thilmany, Wisconsin; Bathurst, New Brunswick; Jacksonville,

-------
 Annotated  Bibliography
19
       Florida; and Longview, Washington. The Albany tower is, however,
       designed for greater oxidation capacity per ton of pulp than any
       of its predecessors.
 17.    Bergstrom, H.:  Pollution of water and air by sulfale mills.  Pulp &
       Paper Mag. Can.,  54:135-140. Nov. 1953. A discussion is  given  con-
       cerning the evolution of odorous substances and  their  control  in
       kraft pulp mill operations. Poisoning of mill personnel from efflu-
       ent gases has been a problem so  serious as  to cause death in  some
       instances. The following table indicates the concentrations of various
       compounds that could quickly cause death  to humans.

     Table 9. RELATIVE VIRULENCE OF PULP MILL GASES
Gas
Hydrogen sulfide
Dimethyl disulfide
Methyl mercoptan
Dimethyl sulfide
mg/rnl
1.4
20
20
140
Volume, %
0.1
0.5
1
5.4
Relative
virulence
1
1:14
1:14
1:100
      The figures in this table can be better appreciated when it is noted
that hydrogen  sulfide  has about the same  toxicity  as  hydrogen cyanide.
The most practicable way of neutralizing  these substances is  by  burn-
ing them. This may be done  by conveying the vapors into the furnace.
      Examples of the quantity and concentration of volatile sulfur com-
pounds produced by a sulfate pulp mill are shown in the following table.

 Table 10.  QUANTITY AND CONCENTRATION OF VOLATILE SULFUR COMPOUNDS
          PRODUCED BY A SULFATE MILL
Source
Digester
condensate
gases
Diffusers
condensate
gases
Evaporators
dry distillation
in smelter
Hydrogen
sulfide,
Mercaptans,
Sulfides,
mg per liter

131
0

230
11.3

76.4
1.3

1,136
71.7

333
405

3.5
2.65

2,288
34.1

0
503

0
0.32

-------
 20
                      AIR  POLLUTION
18.    Bergstrom, H.,  and K. G. Trobeck: Sulfur losses in the production
       of  sulfaie  cellulose.  Translated  from  Svensk  Papper,  48(3):49-54.
       Feb. 15, 1945, by the Institute of Paper Chemistry, Appleton, Wis.
       The losses of sulfur in the manufacture of sulfate pulp occur mainly
       in the condensate; in noncondensable gases from the digester, dif-
       fusers, and multiple  effect evaporators;  and from the recovery fur-
       nace gases. Several investigations to determine the sulfur losses  at
       a given moment in the  manufacture of  sulfate pulp are reported.
19.    Bergstrom, H.,  and K. G. Trobeck: U. S. Pat. 2,406,581. Process  of
       utilizing black  liquors.  This  process utilizes  liquor  oxidation and
       subsequent evaporation to dryness by concentration to 80 or 90 per-
       cent solids prior to ejection through a flasher for final drying.
WASTE LIQUOR


O£
LLJ
N
Q
X
o


o£
o
i
2
2
UJ
« 	

1

FLASH
DRYER
SOLIDS ^
FURNACE
   Figure 4.  Schematic flow diagram of a process for utilizing black liquor.
20.   Bernhardt,  A. A.,  and J. S. Buchanan: Recovery of dissolver vent
      slack  soda  losses.  TAPPI,  43:191-A. June 1960.  The smelt  shatter
      system at the Nekoosa Mill was troubled with  the entrainment of
      small  particles in  the  air issuing from the dissolver stack. For this
      reason, the mill installed a collection system consisting of  a wire
      mesh  filter situated so that the vent gases pass through the filter
      medium.  The  droplets impinge on  the mesh, grow,  and fall  back
      against the  airflow. Cost of the unit  was $2,600. Its payback time,
      based  on salt cake recovery was about 6 weeks-
 Table 11. COLLECTION OF SODIUM SULFATE BY MEANS OF A MESH FILTER
Before use of
mist eliminator
After use of
mist eliminator
                             Salt coke loss,
                            Ib per ton of pulp
17.1
 0.5
                            Value,
                         dollars per day
6890
 2.50

-------
 Annotated Bibliography                                              21

 21.     Bialkowsky, H. W., and G. G. DeHaas: A catalytic oxidation  pro-
        cedure for  determining sulfur compounds  in  kraft mill gases.  Pulp
        & Paper Mag.  Can.,  53:99-105.  Oct. 1952.  Sources of atmospheric
        sulfur loss from kraft mills are reviewed together with various tech-
        niques  for  analysis of these sources.  Among these  techniques are
        the mercury and cadmium salt precipitation methods for differenti-
        ating between  hydrogen  sulfide, methyl mercaptan, and dimethyl
        sulfide; the bromine  oxidation  method of Siggia  and Edsberg for
        determining alkyl sulfides  and disulfides; and  the potentiometric
        titration method for sulfides and methyl mercaptan. A method for
        determination of total sulfur and sulfur dioxide is described in de-
        tail. This technique employs a  quartz tower operating at 1,000 °C
        for the catalytic Oxidation of the sulfur compounds to sulfur dioxide.
        The sulfur dioxide is  further oxidized  to sulfur trioxide in a hydro-
        gen  peroxide solution. The  amount of sulfur  present is then deter-
        mined by resulting changes  in pH. A single test requires only about
        1 minute, and the apparatus can also be used as a continuous mon-
        itoring  device.
 22.     Bialkcwsky, H.  W.,  and G.  G. DeHaas: Stabilization of Douglas Fir
        kraft black liquor.  Paper Mill News,  74:14-22. Sept. 1,  1951. Work
        on the  develop.ment of equipment and procedures for stabilization
        of black liquor  in an  oxidation tower  is described. Laboratory data
        are given describing  the surface requirements for  complete stabili-
        zation at various liquor flow and  airflow rates. A full-scale tower was
       constructed capable of handling 300  gallons of black liquor per
       minute. This installation has resulted in a marked decrease in hy-
       drogen  sulfide losses,  which has effected a corresponding decrease
       in air pollution-
23.    Blackerby, L. H.:  Improving liquor oxidation. Pulp & Paper Mag.,
       34:84-85. June 1960. William B. West of the Crown Zellerbach Corp-
       oration  won the 1960  Shipley Award  with his  paper  concerning
       black liquor oxidation. The author reported increasing oxidation
       of black liquor at the Elk Falls mill by changing the  flow of the
       two oxidation towers  from a parallel to a series arrangement.
24.    Blessing, W. H.: Three unit precipiiaior saves $1000 daily at Long-
       view. Paper Trade J.,  142:22-23.  Sept.  29, 1958. A three-stage, wet-
       bottom, electric  precipitator  installed at the Longview,  Washington
       plant has been successfully  operating  at an efficiency of 96.7 per-
       cent. About 38 tons of salt cake per day are recovered, representing
       a daily saving of over  $1,000.
25.    Borlew,  P. B-, and T.  A.  Pascoe:  Potentiometric determination of
       sodium  sulfide in sulfate  pulp black liquor.  Paper Trade J.,   1221
       (10):31.  1946. A high-sodium,  glass  electrode was  developed  that
       was successful in determining  the  concentrations of inorganic sul-
       fide in black liquor.  The half-cell was  prepared by mixing sodium
       hydroxide,  ammonia,  and  water in  such amounts  that  the final
       solution would contain a volume of  500 milliliters, and concentra-
       tions  of  NH4OH and NaOH of 0.05  and 1.0  N,  respectively. The
       sodium sulfide content of the black liquor was determined with
       this apparatus by a potentiometric titration with silver nitrate. This
       analysis  is subject to very little interference from other  compounds
       normally found  in  black liquor. It  exhibits  a  sharp endpoint,  and

-------
 22                                                  AIR POLLUTION

       represents a substantial improvement over the older, more involved
       techniques.
 26.    British Columbia Research Council discovers  new  methods  to re-
       duce kraft mill odors. Paper Trade J.,  134(2) :14. 1952. An apparatus
       is described that exposes black liquor to air in a concurrent absorp-
       tion  column. Some of  the odorous compounds are oxidized,  which
       reduces the  air pollution problems arising from  the  evaporators
       and the furnace. Gases from the digesters can  also  be added to the
       air supply of the unit and be oxidized in the column.
27.     British Columbia Research Council: A  manual  describing a method
       for  the  collection   and  analysis  of   pulp  mill  effluents.   Van-
       couver 8, Canada. Apr. 1959. In December, 1957, the Mead Corpora-
       tion  of Chillicothe, Ohio, commissioned the British Columbia  Re-
       search Council to develop a field method for the identification and
       measurement of the substances  responsible for kraft mill odors. One
       year  later, this manual describes  a method for the collection and
       subsequent laboratory analysis of  samples of  effluents from  kraft
       pulp  mills. The method should, with some changes, be applicable
       also to some other kinds of effluents, such as  those, perhaps, from
       petroleum refineries. The manual  was submitted  as  a  Progress
       Report—the seventh—to the  Mead  Corporation. They have agreed
       to make  it available to  other  laboratories. The British  Columbia
       Research  Council  was happy to arrange for the distribution, and
       will welcome criticisms and suggestions about  the manual. It is to
       be emphasized  that the  manual is in fact a Progress  Report. The
       method is not represented as being perfect, but then few entirely
      new methods  are.  For  example, the behaviour of  sulfur dioxide,
      particularly its influence  on the measurement of hydrogen sulfide,
      has not yet been completely studied. Besides, a smaller field  kit
      would be  advantageous; the one described in the manual is, in fact,
      the first to be  constructed. The methods prescribed are,  however,
      the result of extensive  laboratory  studies on  the quantitative re-
      covery of known kraft  mill pollutants  in the  trap train that  com-
      prises the sample collection device. These studies will be described
      in papers to be submitted for  publication. The field kit  and pro-
      cedure have been  used  successfully to  sample  and analyze all im-
      portant  kraft mill  effluents and process  streams.  Collection  of a
      sample from the duct leading to a lime kiln  stack was  found to
      be the one  unwieldy operation, because of the large  amount of
      rain continuously forming in the duct. It is believed that this appa-
      ratus  and method are good starting points for a smaller, modified
      field kit that  would collect  a  much  smaller  sample in  applying
      this new,  supersensitive  instrument to  the analysis  of malodorous
      effluents.
    The introduction contains  two  parts:
     1. Synopsis. Procedures  are described for:
       A. Collection of pollutants from a gaseous stream  by  use of the
          field kit,
       B. laboratory  concentration of the collected sample  by  use of
          fractionation apparatus,
       C. gas  chromatographic analysis of the concentrated  sample.
     2. Time required for collection and analysis of  a sample:

-------
                                                                     23
 Annotated  Bibliography

        It requires 1 full day for one operator to obtain a sample from an
        effluent or process stream and to complete the analysis for hydrogen
        sulfide in the field  laboratory.  This day  includes the periods  re-
        quired to transport the field  kit to the sampling site, to take the
        sample, to clean  the  kit, and transport it back to  its original  lo-
        cation. It is advisable to examine a new sampling  site a day or
        more  before the actual sampling operation. The exact arrangement
        of sampling tubes and means for their support can be devised. The
        location of a 110V a-c outlet,  the length of extension cord needed,
        the existence of a suitable hole in the duct for insertion of a sampling
        tube,  and other such matters can  be determined. The  laboratory
        concentration and  gas chromatographic analysis of a single sample
        requires about lYz days,  but if several samples are to be analyzed,
        the time  required is  about 1 day per sample.
 28	British Columbia  Research Council: A study of Ihe kinetics of oxi-
       dation of kraft black  liquor. Vancouver 8,  Canada. June  1959. The
       work described in this report is part of a continuing study  to acquire
       knowledge for the curtailment of  kraft pulp mill odors. It deals with
       the effects of sulfide  concentration, temperature, oxygen pressure,
       and liquor turbulence on  the rate of oxidation of black liquor.
 29.     Callaghan, C. V.: The  venturi scrubber at Bathurst.  Pulp & Paper
       Mag. Can., 54:106-107. Apr. 1953. A venturi scrubber  device is de-
       scribed that has been installed  at the Bathurst Mill. The unit  proc-
       esses gases given off from the recovery  furnace, issues  them into
       a cyclone, and then emits  them into the stack. The  scrubbing liquor
       caught  by the cyclone is collected in a slurry tank  and mixed  with
       make-up water for re-use  as a scrubbing agent. The cost of building
       the total  unit,  including   the  building  and chimney,  was about
       $125,000 (Table 12).
 30.     Gate, F. L.:Design of  chimneys for odor dispersion. TAPPI, 36:225-
       228. 1953.  The design of a chimney is a definite factor in the dis-
       persion of air pollutants, but does not provide a complete solution  to
       the problem. It has been suggested that the concentration of pollutant
       should  vary inversely as the square of distance for  locations farther
       than  50 chimney heights from  the stack.  It follows, therefore, that
       distant  places may be affected by pollution  regardless  of the height
       of the chimney. In view of these facts it must be acknowledged that
       various collection equipment may  be required, in addition to a  well-
       designed stack, for successful abatement of air pollution.
31.     Champion Paper, Inc.: Black liquor oxidation. Champion Paper,  Inc.,
       Texas Division.  Although black liquor  oxidation has become an in-
       tegral operation of many pulp mills, its use has been limited in south-
       ern pine mills owing to excessive foaming of black liquor in these
       plants.  Champion has  solved this  problem by placing the oxidation
      tower after the  multiple effect  evaporators, thereby processing the
      concentrated black liquor,  which  has  less tendency to  foam.  The
      evaporator gases are washed with a weak sodium  hydroxide  solu-
      tion, which further reduces sulfur losses to the atmosphere.  An addi-
      tional advantage of oxidizing strong black liquor is  that the heat of
      oxidation serves to evaporate the  mixture to a  concentration of 29
      Baume  higher than would otherwise be  obtained. Although it has
      been claimed that oxidation prior  to evaporation is the cause of re-

-------
 Table 12. PERFORMANCE DATA  FOR BATHURST GAS-SCRUBBING UNIT
Pulp production

Gas volume at stack

Gas temperature at stack

Gas temperature into venturi

Venturi fan motor current

Total  slurry flow

Gas velocity at venturi  throat

Slurry velocity at jets

Furnace draught,

     before venturi tube

     before throat

     before cyclone

     after cyclone

     after fan

Fan power consumption


Pump  power consumption


Slurry pH

Slurry temperature

Na20 in slurry

Slurry Baume, hot

Salt cake in stack gas


Salt cake recovered per day

Recovery
260 tons per day

58,000 cfm

165°F

290°F

75 amps

53.5 cfm

275 fps

20 to 25 fps

-0.2 in. H20

+ 0.5 in. H20

-0.8 in. H20

-19  in. H20

-22  in. H20

+ 0.5 in. H20

325 hP
22.4 kw-hr/ton

20 hp
1.4 kw-hr/ton

8.5

160°F

9.9 Ib/ft3

27 to 29 Bourne

17,200 Ib/day
6.6  Ib/ton of pulp

 15.480 'b

89.6%

-------
 Annotated Bibliography                                             ^5


       duced corrosion  of  evaporator  tubes, this was  not believed  to be
       the case with Champion's mill. Foam in the oxidation tower is con-
       trolled by spraying with heating oil. A foam breaker is being planned
       to replace  this method.
 32.    Chase, S.:  Control of air pollution at the Champion Paper and Fibre
       Company.  Proceedings  semi-annual  technical  meeting.  Air Pollution
       Control   Association.   Houston,  Texas.  Dec. 3, 1966. The  Pasadena,
       Texas, mill of Champion Paper and Fibre Company was  started in
       1937.  The first electrostatic precipitators were made for eliminating
       or collecting  into manageable quantities the  air pollutants  present.
       Around 1950  a special department was created solely  for the  pur-
       pose of dealing with problems of stream and  air  pollution.  This
       paper is a report of Champion's progress in the field of air pollution.
       Sources and  control  of solid pollutants  and  obnoxious  odors  are
       discussed. Solids  originate from the recovery furnace and the  lime
       kiln. Odors arise  from digester relief  gases, blow gases, and the re-
       covery furnace. Control equipment and techniques include  electro-
       static  precipitators, water sprays,  dust collectors, condensers;  com-
       bustion, absorption, scrubbing, and odor masking.
33.    Anon: Tower oxidizes odors  away. Chem. Eng., 59(9):232-235. Sept.
       1952. The Springfield, Oregon,  mill of the  Weyerhaeuser  Timber
       Company uses air oxidation of  black  liquor  in a  tower to reduce
       odors  and save sulfur. Some observations  on the operations are:
        Saves  1,000 tons of  sulfur  per  year.
        Black liquor: 300 gpm at a sulfur concentration of 3 grams per liter.
        Tower: 10 feet in diameter, 30 feet high, packed with  22  feet of 4-
                 inch partition rings;effective surface of 50,000 square  feet.
        Air: 10 cubic feet per minute for each gpm of liquor-
             No foaming problem.
        No H2S found  in air leaving the oxidation tower. Complex chem-
             ical reaction, but chiefly Na2^S—>•  Na£ 820 3 .
        Generation  of H«jS in evaporators has virtually  been eliminated;
       H2S  is  generated   in the  recovery furnace, and volatile  organic
       sulfur compounds are released from digesters and  evaporators.
34.    Chipman,  W. A.: Physiological  effects of  sulfate pulp mill wastes
       on shellfish. Paper Trade J.,  127:47-49. Sept. 16, 1948. Although it has
       been demonstrated many times that pulp mill effluents have adverse
       effects on aquatic life, no work prior to that of this paper  had been
       done on the effects of pulp mill wastes on shellfish. The experimen-
       tal work reported here involved  measurements of the effect of con-
      centration of  pulp mill  waste on  the  various normal activities of
      oysters. It was found that effluent concentrations of 50 ppm were
      sufficient  to depress activity in some cases. The waste material re-
      duced the time that oysters kept their shells open, and decreased
      their gill pumping and filtration rates. An unsuccessful attempt was
      made to isolate and determine the toxic compound responsible  for
      the observed physiological effects.  It was demonstrated,  however,
      that the toxic  compound can  be precipitated from the black liquor
      by salting out .
35.    Coleman,  A. A.: The combustion  of noncondensable blow and relief
       gases  in  the  lime kiln. TAPPI, 41(10):166A-168A.  Oct.  1958.  The
       burning of digester relief and blow gases in the lime kiln has been

-------
  26                                                   AIR POLLUTION

       found practical from an operational standpoint.  Over-all  odor re-
       duction has improved because of reduced downtime of the gas burn-
       ing system. Maintenance labor for experienced  mechanics has been
       reduced  by at least  35  hours per month.  A  fuel savings  of about
       $450 per month or $0.04 per air-dry  ton has been obtained  by  elim-
       ination of the  separate, gas-burning furnace.  At  Weyerhaeuser's
       Springfield, Oregon,  mill, a system  for destroying odorous digester
       relief and blow gases has been in operation for several years. This
       system is described by DeHaas and Hansen (TAPPI 38:732-738, 1955).
       The lime kilns are now successfully burning  blow and relief gases.
       The distance from scrubber to kiln is 350 feet. Rupture plates along
       the gas line will release pressure in case of an  explosion; water seals
       are below the vertical runs of piping. These catch any condensation
       in the gas line. The system was put into operation in  July  1957.
       Thirty cfm of gas  flows from sphere to kiln; dilution to beyond in-
       flammability is 20:1-
                                                                    KILN
27-FOOT STEEL
VAPORSPHERE s
Q
^/
GASES ROC
FLAME
CRUBBER ARRESTER

K-PAC
LU
I—J

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                                                                     27
 Annotated Bibliography

       The recovery furnace itself,  however, proved  to  be the source of
       a large quantity of hydrogen sulfide when.it was not properly oper-
       ated and lacked sufficient air. This was true even if the black liquor
       had been oxidized. As a complement  to black  liquor oxidation  and
       to a properly designed and operated  recovery  furnace, the venturi
       scrubber, with its remarkable ability for absorbing sulfur  dioxide,
       appears satisfactory for reducing both  sulfur and sodium losses from
       the kraft recovery system.
 38.    Collins,  T. T.,  Jr.: The oxidalion of sulfaie black  liquor. A review
       of the literature in two parts.  Paper  Trade J.,  136: 37-40.  Mar. 20,
       1953-  136:  19-22.  Mar. 27, 1953.  In his  introduction the author
       states: "Recently,  however,  considerable impetus has been given to
       research in the field  of black liquor  oxidation  and this may be at-
       tributed  to the pressing odor problem of sulfate  mills in some lo-
       calities.  Not  only is  the  odor  problem of some  consequence,  but
       there  seems  to be considerable complaint (and some  suits)  about
       the effect of sulfate  mill recovery fumes  in  staining house paint.
       The use  of black liquor oxidation systems to reduce  the sulfide con-
       tent of the waste gas is mentioned as  a partial  solution to the prob-
       lem."  This is a fine  review of the literature  and patents covering
       the subject of  black  liquor oxidation; there  are 67 references.
39.    Collins, T. T., Jr.: The oxidation of sulfate  black liquor and related
       problems. TAPPI, 38(8): 172A-175A. Aug.  1955. Within  the last 5
       years  there has been considerable interest in the  field  of sulfate
       black  liquor oxidation. Most of  the basic work  that  has been publi-
       cized has been carried on by a few  groups of investigators.  This
       work  is  listed. An article by the same  author  2 years  before,
       in which the  literature and patents  covering the  subject of black
       liquor oxidation were reviewed, is continued.  Collins  reports that,
       "the final requirements for a successful scrubber for the fume-heat-
       sulfur recovery process have now been met for over a year by the use
       of a black liquor venturi scrubber on  a 250-ton furnace at the Thil-
       many  mill at Kaukauna, Wisconsin."  Other items  discussed  in  this
       article include  foaming, analysis of black liquor for  its sulfide  con-
       tent, beneficial results to  the  kraft process from oxidation, savings
       achieved by oxidation, and redesign of the kraft recovery furnace.
40.     Collins, T. T., and R. H.  Collins: Recovery of  heal and chemicals
       in sulfate recovery furnace stack gases. Part I.  Paper Ind., 29:1608-
       11. 1948.  Part II. Ibid,  1766-71. An extensive  literature review is
       given concerning  the  quantities of heat  and materials lost through
       stacks  of recovery furnaces. The review also considers the  various
       methods of recovery used at the time and appraises their value.

41.    Collins, T. T., C. R. Seaborne, and A.  W. Anthony: Removal of  salt
       cake fume from sulfate recovery furnace stack gases by scrubbing.
       Tech. Assoc. Papers. 30:168-172. 1947. A new apparatus for scrubbing
       the fume of sodium salts  from  sulfate or  soda furnace stack gases
       has  been developed successfully on a  pilot plant scale. The equip-
       ment consists  essentially of a venturi through  which waste gases
       going to the stack pass at high velocity. At the same time, recirculated
       •water  injected into the  constriction  is  atomized by  the  energy
       of the gases  under  extremely turbulent conditions  existing  in
       the  throat and is then removed in  a dry cyclone following  the

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28
                                                    AIR POLLUTION
      venturi  atomizer.  Efficiencies  of  sodium  removal  as  high as  99
      percent  have  been attained by a  combination consisting  of  the
      venturi  atomizer  followed  by  the conventional  Pease-Anthony
      scrubber, instead of a cyclone. The combination of venturi atomizer
      followed by a dry  cyclone, called the venturi scrubber, has given 85
      to 94 percent sodium  recovery  on a pilot plant scale with  an esti-
      mated power consumption for large-scale operation of approximately
      43 killowatt-hours  per ton of pulp. Because of the easily attainable
      high efficiency,  low first cost,  and simplicity of operation of the
      venturi  scrubber, the  addition of any other equipment to the com-
      bination to improve the efficiency seems economically  unjustifiable.
      In the literature, reference is made  to four devices  for dust collec-
      tion: electrostatic  precipitator,  wet scrubber,  dry cyclone, and  bag
      filter. Only electrostatic precipitation has had extensive commercial
      use. Electrostatic precipitator: high initial  cost, high operating cost
      for  labor  and maintenance,  85  to  95 percent efficiency, very  low
      power costs. Wet  scrubbers:  used in Scandinavia, claimed  efficient
      in  heat and chemical recovery. Dry cyclones: ineffective  because
      of  small size  of sulfate fume.  Bag filters: have not  been  studied
      widely.  Dust from mill is principally soda ash, while sulfur gases
      contain  much H2S and little  SO2-
 Table. 13.  SALT CAKE FUME CAUGHT BY ELECTROSTATIC PRECIPITATOR:
          SIZE DISTRIBUTION
Size in microns
<0.1
0.1-0.2
0.2-0.3
0.3-0.4
0.4-0.5
0.5-0.6
0.6-0.7
0.7-0.8
0.8-0.9
0.9-1.0
1.1
1.2
1.3
1.4
1.5
Count
861
82
101
85
83
50
31
21
12
22
0
4
1
1
7
Wt percent
0.7
0.5
2.3
4.6
8.7
9.2
9.0
9.1
7.3
18.6
0
5.8
1.9
2.3
20.0
       Kleinschmidt and Anthony, at Thilmany Pulp and Paper Company,
     used a pilot plant scrubbing unit on sulfate recovery furnace fume
     with 65  percent fume recovery.  The plant used a 140-ton B & W-

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Annotated Bibliography

       Tomlinson  unit  with gas  conditions of  60,000 cfm at 300 °F dry
       bulb and  163 °F wet bulb. Losses  of salt cake were as low  as 60
       pounds per ton of pulp, but it is reasonable to estimate this  at 150
       pounds per ton. Tests at Thilmany averaged 183 pounds per ton
       of pulp  with  use  of  a Pease-Anthony cyclonic-spray  scrubber.
       Theory of operation of the venturi atomizer is discussed. It  has as
       high as 99  percent efficiency. Maximum  power  requirement for
       90 percent efficiency is 43 kilowatt-hours per ton of pulp. The
       venturi scrubber  consists of a venturi  atomizer followed  by a dry
       cyclone  and  induced draft fan. Scrubbing liquor  is  recirculated
       until almost  saturated,  then  returned  to  the pulping  system as
       make-up.
        Conclusions:
        1. Venturi scrubber can recover 90  percent of  salt  cake fume
           within reasonable cost limits.
        2. There  is economic  value  in low-level heat recoverable  from
           scrubbed gases.
        3. Gases may become  saturated and  may rain in cold weather.
        4. Low first cost  makes scrubbing  attractive.
42.    Collins, T.  T.:  The sampling  and analyzing  of sulfaie  recovery
      furnace stack gases. Paper Ind.. 29:1437-39. 1948. A  literature sur-
      vey is presented concerning stack sampling and analysis. The theory
      and conditions for  isokinetic stack sampling are discussed at length.
43.     Collins,  T. T.: The scrubbing of  sulfate  recovery furnace  stack
      gases. Part I.  Paper Ind.,  28:680-86.  1947.  A  pilot plant study of
      the operating characteristics of cyclonic  and venturi scrubbers for
      removing effluent  compounds  from kraft mills is described. A gen-
       eral description of sampling and analyzing techniques is also  given.
      Part II. Ibid,  28:830-34. 1947. Operating  curves, based upon the per-
       centage  of sodium salt  removal,  are  given fcr both  cyclone and
       venturi scrubbers. Emphasis  is placed  upon  the venturi scrubber
       owing to its high efficiency. The effects of various types  of injection
      patterns were also studied, and operating characteristics are given
      for each pattern. It is stated that 43 kilowatt—hours per ton of pulp
      would be  required  for  90 percent sodium salt removal by the
      venturi scrubber.
      Part III. Discussion of data. Ibid, 28:984-86.  1947. The characteristics
      of the cyclone scrubber are discussed in  terms  of the equation:

       Efficiency :
          where:
          D : diameter of scrubber
          W :  effective volume of  sprayed water
          d : diameter of  water droplets
          G - volume of gas  scrubbed.
      It is noted that  the efficiency of the cyconic  scrubber increased
     as  the temperature  of the inlet water was  lowered.  The  reverse
     of  this effect was observed for  the venturi scrubber. The following
     advantages of the venturi  scrubber are noted:
      1. The venturi scrubber has as high an efficiency  for small  par-
     ticles as any device presently known.  This is true from an economic
     as  well as  from  a  percentage  recovery  standpoint.

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 30
                                                       AIR POLLUTION
         2. This type of scrubber uses less water to recover a given amount
       of material than do other wet devices.
44.    Collins, T.  T-: Some aspects  of oxidizing sulfate black liquor.  Paper
       Trade  «/., 130:37-40. Jan.  19, 1950.  An outline of a study,  conducted
       at the Thilmany Mill, of the oxidation properties of black liquor
       is  given. The effects  of  air and peroxide oxidation  were  studied-
       It  was  concluded that commercial-scale oxidation by  peroxide is
       economically  unfeasible,  especially since equivalent  oxidation of
       the sulfur  can be accomplished by air.
                                                                    •
45.     Collins,  T.  T., and P.  H. West:Some recent  developments in kraft
       recovery. Part I. Paper Trade  J.,  129:19-22. Sept. 1,  1949. With the
       continued  interest  in recovering  more completely  the  heat  and
       chemicals given off by the kraft process, the reclamation of chem-
       icals other than  those composing  salt cake has become important.
       Of these,  sulfur  and  lime  losses  are  of special  interest. In  illus-
       tration,  the  following quantities  characteristic  of  the  Thilmany
       Pulp  and  Paper  Company's  operation  are  tabulated.
           The  quantities of salt  cake  recovered  by  the  new  venturi
       scrubber at the Thilmany mill  were  significant. An estimated 90
       percent recovery has  been  attained,  which  effects  a  reclamation
       of from 7 to  12 tons of salt cake per day. The present consumption
       of salt cake is  128 pounds  per ton of  pulp, as  compared  with a
       previous average of 291 pounds  per ton. This increase in  efficiency
       has been attributed  to  the venturi scrubber.  Although the  new
       equipment has  been  ineffective  in  lessening  odors arising  from
       noncondensable gases, emissions  of particulates from the  stack
       have  been visibly  reduced. Corrosion of the  removal  equipment
 Table 14.  QUANTITY AND VALUE OF HEAT AND CHEMICALS IN THILMANY
          SULFATE RECOVERY FURNACE STACK GASES
Pulp produced

Volume of stack gases

Temperature of stack gases



Stack dust equivalent to

Value  (@$25/ton)

Hydrogen sulfide + mercaptans from stack


Sulfur dioxide from stack

Stack gas heat above 140 F

Value  (@$0.80/1000 Ib steam)
150 ton/day

50,000cfm

300°F dry bulb
163°F wet bulb

20,000 Ib salt cake/day

$250/day

4,000 Ib/day

400 Ib/day

500,000,000 Btu/day

$383/day

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 Annotated Bibliography                                               31

   Table 15.  QUANTITY AMD VALUE OF CHEMICALS IN THILMANY LIME KILN
            STACK GASES
   Pulp produced                                  150 tons/day

   Volume of stack gases                           12,000 cfm

   Temperature                                    525 °F dry bulb

                                                163 °F wet bulb

   Dust in stack gases                              10,000 Ib/day

   Value (_-$2/ton)                                 $10/day
      has been somewhat of  a problem, especially when the gases were
      acidic. Stainless steel and protective coatings have been  employed
      as preventative measures.
                                                             STACK
  Figure 6.  Schematic flow diagram for thilmany salt cake recovery process.
46.    Collins, T. T., and P. H. West: Some recent developments in kraft
      recovery. Part II. Paper  Trade  J., 129:25-29- Sept. 8, 1949. Much  of
      the  original sulfur  of the kraft  process  is  lost out the  stacks  in
      gaseous  form. With the  advent of modern particulate  collection
      equipment, the problem of decreasing sulfidity of the liquor has
      arisen. The oxidation of black liquor has been employed  to reduce
      this tendency. This measure  has also proved effective in reducing
      corrosion and bad odors. The article also gives a review of the opera-
      ting experience with the venturi scrubber at Thilmany, Wisconsin.
47.     Collins,  T. T.:  The venturi  scrubber and  lime  kiln  stack gases.
      T.APP/,42(1):9-13. Jan. 1959. The literature on dust losses and scrub-
      bers for  lime kilns is reviewed. Comparative test data are given on
      a number of units, including the Pease-Anthony venturi scrubber and
      a  recent modification of that unit  called the Chemico S-F  venturi
      scrubber. Efficiencies of approximately 99 percent for removal of lime
      dust are achieved at relatively low pressure drops of 6 to 10 inches
      water gage across the unit. Heavy slurries are used as the  scrubbing
      liquor in the  Chemico unit. Tests showed 63 to 80 percent removal
      of soda fume, which is volatilized  at the hot  end  of the  kiln, and
      has  a smaller particle size than the larger lime dust mechanically

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  32
                                                      AIR POLLUTION
       entrained in the kiln gases. Because of the high soda content of the
       lime sludge burned in the kilns at Palatake, a further reduction of
       soda losses appears possible by improved washing of the sludge.
 48.    Collins, T. T., C. R. Seaborne, and A. W. Anthony: Use of the veniuri
       scrubber on sulfate recovery furnace gases. Paper Trade J., 126:45-49.
       Jan. 15, 1948. A description of the venturi scrubber employed  at the
       Thilmany, Wisconsin, Pulp and Paper  Company is given. This Scrub-
       ber was built and designed on the basis of pilot plant data, and has
       proved itself to be above 90 percent effective in salt recovery. Scrub-
       bing liquor is injected at the throat of the venturi by nineteen %-inch
       nozzles. The composition  of  the liquor is kept  constant, by  continu-
       ous bleeding  of  a  stream of  30 to  32° Baume' solution from the

   Table 16. PERFORMANCE OF VENTURI SCRUBBER
Velocity of
entering gas in
throat, fps


217
216
219
211
250
235
259
248
233
Gallons of
liquor per
1,000 ft3 of gas
entering
venturi atomizer
7.3
5.9
5.5
7.5
5.0
3.5
2.6
3.8
5.2
Liquid jet
velocity
fps


11.0
8.5
8.0
10.5
8.2
5.0
9.2
13.0
18.0
AP across
atomizer.
w g


18.6
20.9
15.8
19.4
18.0
13.9
12.7
16.1
18.7
Scrubbing
efficiency,
%


88
86
85
87
90
84
81
88
90
       scrubbing fluid. During the test runs the gas velocities at the throat
       of the scrubber were from 210 to 260 feet per second. For an average
       daily production of 150 tons of pulp, the power requirement, of the
       scrubber was  40  kilowatt-hours per ton.
    FROM
    FURNACE
                                                           • TO STACK
    Figure  7.  Schematic flow diagram of thilmany venturi scrubber process.
48.A    Collins, T. T.: Oxidation of kraft black liquor-where does it stand?
       Paper Trade J., July 23, 1962.  This  process  may well play  an even
       more vital role in odor control as increasing attention is focused on
       pollution. The author sets out to alleviate confusion in this field and

-------
 Annotated Bibliography                                              33

       point out the latest advances. He discusses early studies on oxidation,
       control of the foam  problem, economic return, the Bergstrom - Tro-
       beck systems, British Columbia Research Council systems,  Weyer-
       haeuser system, and other aspects of black liquor oxidation. The
       article cites 113 articles in the literature  and lists  41 patents.
 49.    Colombo, P., D. Corbetta,  A. Pirotta, and  A.  Sartori: Critical dis-
       cussion on Ihe  analytical methods for mercaptan and sulfur  com-
       pounds. TAPPI, 40:490-498.1957. A short discussion of previous analy-
       tical methods is given as an introduction to the presentation of a new
       technique for analysis of combustion gases  from recovery furnaces.
       With this method, the sample is absorbed in a sodium acetate solu-
       tion, where  the sulfur  dioxide undergoes  chemical reaction. The
       hydrogen sulfide is then precipitated in a solution of 5 percent cad-
       mium  chloride. The final steps involve absorption of methyl mercap-
       tan in  a methanol trap at minus 75 °C. The sulfur dioxide is analyzed
       by a gravimetric determination of sulfuric acid produced by oxidation
       of the  cadmium sulfide precipitate. Methyl mercaptan and hydrogen
       sulfide are determined by the standard potentiometric titration with
       silver nitrate. The precision of this determination is about 20 percent
       for mercaptan concentrations of 20 milligrams per cubic meter. It
       becomes better, however, for samples of larger concentration.
50.    Copcutt, V.  W.: A  report  on  precipitator  applications.  Air  Eng.,
       1:44,46.  Apr. 1959.  A summary is given of recent industrial appli-
       cations of precipitators for process  improvement, material recovery,
       and  air pollution control in the  chemical  field.  Paper  mills (all
       types)  have  167 precipitators in use, with  a total capacity of 18.9
       million cubic feet per minute. A typical 1-day  collection at an in-
       stallation  (one or more precipitators per installation) is 50  tons of
       sodium sulfate per recovery furnace.
51.    Dalla-Valle, J. M.,  and H. C.  Dudley: Evaluation  of  odor nuisance
       in ihe manufacture of kraft paper. Public Health Reports, 54(2):35-43.
       Jan. 13, 1939. also Tech. Assoc.  Papers, 22:312-315. 1939. This article
       contains a large table of odor threshold levels, some of which are
       as  follows (in mg/liter)  Hydrogen sulfide,  .0011;  dimethyl  sulfide,
       .0011; methyl mercaptan,  .0011;   ethyl  mercaptan, .00019;  diethyl
       mercaptan, .00025.
52.     DeHaas, G. G., and G. A. Hansen: The abatement of kraft pulp mill
       odors by burning. TAPPI, 38(12):732-738.  Dec.  1955. This paper dis-
       cusses the methods used to improve the recovery of sulfur  and to
       reduce  the odor nuisance, particularly the digester relief  and blow
       gases, associated with kraft mills. The highest losses occurred in the
       recovery furnace stack gases.  These losses were practically elimina-
       ted  by  installing a black  liquor oxidation tower and improving the
       operation of the  recovery  furnace.  The  hydrogen  sulfide.  released
       with the  lime kiln gases is not significant when the kiln is operated
       with a slight excess of air. An analytical method, based on a modified
       Orsat-type apparatus for the volumetric gas analysis of digester relief
       and blow gases, is described.  This  analysis  is suitable to determine
       oxygen, hydrogen sulfide, and the total amount of organic compounds.
       The chemical tests made show the efficiencies of black liquor oxida-
       tion. Use of combustion  at  different temperatures and of chlorina-
       tion as means of rendering the  digester and blow  gases harmless is
       discussed. A detailed description is given of pilot plant tests of col-

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    34                                                 AIR POLLUTION

        lecting the blow gases and digester relief gases in barrage balloons.
        The large-scale installations now in operation include a vaporsphere
        and a combustion  chamber in one mill. In the other mill  a  vapor-
        sphere and an arrangement to mix the digester relief and blow gases
        with chlorination effluent is used. Details of operation and equipment
        are given. The results of chemical tests to eliminate possible causes
        of explosions are indicated.
 53.    DeHaas,  G. G.: Stabilization of Douglas Fir kraft black liquor. Pulp
        & Paper  Mag., 25:70-72. Dec. 1951. For the purpose of studying the
        oxidation characteristics of Douglas Fir kraft black liquor, the author
        employed a series of laboratory steel towers 8 to 8 feet high, and
        packed with %-to  %-inch raschig rings. Extreme foaming difficulties
        were encountered with these towers, so a glass tower was constructed
        for visual observation. Results of these tests showed that  1,000 square
        feet of packing surface will handle 10 pounds of sulfide ion  per hour.
        A stainless steel pilot tower was then built for further investigation.
        The packing consisted of 3-inch cross-partition rings having a total
        effective  surface area of 5,750 square feet. Observed  efficiencies were
        about 97 percent  for flow rates of 29-9  gallons per minute. A full-
        scale tower was then constructed, 10 feet in diameter. 30 feet high,
        and packed to a height of 22 feet, with 4-inch cross-partition rings.
        With this unit in operation, it became possible  to eliminate  the addi-
        tion of sulfur and yet observe an increase of  black liquor sulfidity
        to 20  percent from  the  16 percent normally found  under previous
        operating conditions.
 54.    Dexter, G. M.: Elimination of kraft mill odors. Paper Trade J., 129:78-
        81. Nov.  17,  1949. Perhaps the greatest  disadvantage of the kraft
        process is the nauseating odor it produces. This has been stated by
        some  to  be unavoidable,  the cost of control  equipment being too
        great. The following analysis shows, however, that these waste odors
        can be eliminated  economically,  particularly in new mills. The odor,
        resulting mainly from hydrogen sulfide and mercaptans, varies sig-
        nificantly with the type  of wood used, and with the ratio of sodium
        sulfate to caustic in the cooking liquor. Generally, the odor increas-
        es with  the concentration of sulfate  in  the liquor.  Pulp quality
        requires, however, that the sulfate concentration be kept about one-
        third that of the caustic.
 Analysis  of Operation
 1.  Scrubbing

      The incondensable gases from the various sources may be  introduced
 into a  tower  for scrubbing  with a weak oxidizing agent, such  as sodium
 hypochlorite,  or  air. This method has proved  successful in the partial elim-
 ination of odors  from several kraft mills.
 2. Oxidation Towers
      A process has been introduced in which black liquor is passed  through
 an  air oxidation  tower before it is taken into the evaporators. This process
 has been  claimed to be 90 to 100  percent effective in eliminating malo-
 dorous  gases issuing from evaporators.
 3. Inka Tower
      An  "inka tower" may be used to treat stack gases, after they have
passed  through the precipitator, to  remove  incondensable  gases with .90

-------
 Annotated  Bibliography                                             35

 percent  effectiveness. This tower operates  by passing the  gases  upward
 through a series of perforated plates containing a sodium hydroxide solution.
 4. Recovery Furnace
       The operating conditions of a furnace  have been shown to have  a
 direct consequence on the amounts of sulfur compounds in the stack gases.
 For this reason, it is recommended that the furnace be slightly larger than
 mill capacity, to avoid overloading. New furnace designs have been capable
 of reducing sulfur gases to a large extent.
 5. Direct Contact Evaporators
       The direct contact evaporators tend to  vaporize the  odorous  gases
 contained by the  black liquor. They  thereby serve  as  a  pollution source,
 thought  by many to be much greater than is the furnace  itself.  For this
 reason it is suggested that these evaporators be replaced  with  multiple
 effect units.
 6. Burning Incondensable Gases
       The incondensable gases from the various sources may be collected
 and burned in an oxidizing furnace. A burner located outside the immediate
 plant is  recommended, to avoid explosion hazards.
 7. Catalyst Chambers
       Catalytic conversion of sulfur  compounds presents  a  definite possi-
 bility for the abatement of pulp mill odors. Although this type of operation
 can be highly effective, prohibitive costs make it currently unfeasible.
 8. Chimneys
      Increased  chimney heights  would reduce odors to some extent in
 some cases.
 9. Waste Effluents
      Effluents pumped from the mill to settling ponds are also a source of
 odor. A possible solution would be to pipe in the stack gases from the lime
 kiln.  This would cause rapid precipitation of the sludge and  release the
 sulfur gases, which could be collected and  introduced  into the  furnace
 for burning.
55.     Dudley, H. C.,and J. M. Dalla-Valle: A study of the odors generated
       in the manufacture of kraft paper. Tech. Assoc. Papers, 22:312-31?.
       1939. This report deals with the results of a study made on obnoxious
       odors generated in the manufacture of kraft paper. There are three
       sources of obnoxious odors owing to processes in the  plant studied:
      (1) Production of hydrogen sulfide, (2) production of volatile organic
       sulfur compounds, and (3) release  of  large quantities of chemical
       smoke, which contains sodium sulfate, sodium sulfide, traces of hydro-
       gen sulfide, and large  quantities  of carbon and organic matter. In
       evaluating the sources of odors and their contribution to the generally
       disagreeable conditions that arise downwind from the plant, it may
       be stated that: (1) The amount of  hydrogen sulfide released from the
       plant is relatively small and may be  considered of no consequence
       in causing any odor except at the  point of origin in certain buildings.
       (2) The odor produced by the release of organic sulfur vapors from the
       pulp digesters and the vapors from the turpentine condensers  is very
       disagreeable  at the  point  of release;  the quantity  of such  vapors,
       however, is probably not sufficient to cause marked  odors under
       normal operating conditions at any great distance from the plant.
       (3) The greatest and, probably, the only major contributing factor
       to the obnoxious conditions arising within a mile radius of the plant

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  36                                                 AIR  POLLUTION

      is  the vast quantity of material blown out  the  stacks. From  a
      plant manufacturing 300 tons per day of kraft paper,  the smoke is
      estimated to contain,  under  normal  operating  conditions,  18,000
      pounds of sodium sulfate per 24 hours.  In addition, there is much
      carbon and partially carbonized organic matter, as well as a mixture
      of somewhat volatile oils.  This smoke, of rather low temperature,
      soon reaches the ground and spreads over an area of several square
      miles. The peculiar sweetish and somewhat sickening  odor seems to
      arise  from the organic constituents. Methods of study  are recom-
      mended  that may lead to  control of  the odor-generating processes.
      The possibilities that electrical  precipitators offer to prevent an ex-
      cess of chemical smoke are stressed.
        The concentrations of materials causing odors, are:  Ethyl mercap-
      tan 0.00019  mg/liter—odor of  decayed  cabbage; hydrogen sulfide
      0.0011 mg/liter—odor of rotten eggs; methyl sulfide 0.0011 mg/liter-
      odor  of  decayed  vegetables; propyl mercaptan 0.000075 mg/liter—
      unpleasant odor;  thiocresol (CH3C6H4SH)  0.0001 mg/liter—rancid,
      skunk-like odor. Hydrogen sulfide is formed and released (1) at the
      smelt tanks where molten  sodium carbonate and sodium sulfide are
      dropped into water, and (2) in the  separator building where this
      solution  is filtered. Digestion brings about the formation of  many
      unknown volatile organic sulfur compounds.  At nearly all points
      of the process  where the pulp  is handled after digestion, certain of
      these ill-smelling compounds are released, mainly from the turpen-
      tine condenser and as blow gas from  the digester.


  Table  17.  ANALYSIS OF AIR-DRIED SAMPLE  FROM RECOVERY
            FURNACE STACK
Material %
Moisture
NaoSOx
Na2S
Water-soluble organic matter
Ether-soluble organic matter
Free carbon
7.8
75.1
(Trace)
9.8
1.8
5.5
      Production of 300 tons of finished paper per 24 hours means a loss of
18,000 pounds of Na2SO£ per 24 hours. Stack gases amount to 88,000 cubic
feet per minute. Thus the total solid concentration is 0.003 ounce per cubic
foot (3 mg/1). In addition, great amounts of moisture, some traces of hydro-
gen sulfide, and large quantities of volatile organic matter are  released.
Twelve tons of solids per 24 hours pour out the stacks.
58.     Felicetta, V. F., Q. P. Peniston, and J. L. McCarthy:  Determination
       of hydrogen sulfide. methyl marcaptan,  dimethyl sulfide and disul-
       fide in  krafi pulp mill process streams.  TAPPI, 36(9) :425-432. Sept.
       1953. Mass spectrometric examination of the volatile components in
       the condensate from kraft pulp digester blow gas has confirmed the

-------
 Annotated  Bibliography                                              3'

       presence of hydrogen sulfide,  methyl mercaptan,  dimethyl sulfide,
       and dimethyl disulfide, and has shown that the corresponding ethyl
       compounds and other sulfur-containing derivatives are not present
       in significant concentration.  A relatively simple and rapid method
       for quantitative determination of each of the four above-named com-
       ponents in gas or condensate streams has been evolved and  is set
       forth. The two  acidic substances  are batch-absorbed  into aqueous
       sodium  hydroxide solution while the  two thio-ethers are simultan-
       eously taken up in benzene. The liquid phases are then separated.
       Quantitative determination of hydrogen sulfide and methyl mercap-
       tan in the alkaline aqueous solution is carried out by potentiometric
       titrations with silver nitrate-  Quantitative determination of dimethyl
       sulfide and disulfide in the benzene solution is carried out by means
       of bromate-bromide titrations  of  the components after they have
       been partly separated by a  single-stage batch distillation. Results
       obained on  known mixtures are set forth. The method has given
       reasonably satisfactory analyses of  two gases and two  condensate
       process streams in a  kraft  pulp mill.
 57.    Felicetta,  V. F.  and J. L. McCarthy: The pulp mill research  pro-
       gram at the University of Washington. TAPPI, 40:851-866. 1957. Es-
       tablished on January 1,  1944, the  pulp mills  research  program  has
       received grants  to date  of about $500,000-  Chemical  investigations
       have been conducted dealing with problems arising from pulp mill
       effluent streams. Processes for utilization, control, and analysis of
       these streams are now being studied. It  is believed that, owing to
       the contributions of  this program, the by-products of the pulp and
       paper industries are presently being utilized to a greater extent. This
       program is helping to bring  nearer the day when complete use  can
       be made of all the materials consumed in the kraft process.
58.    First, M. W., H. E. Friedrich,  and R- P. Warren: Reduction of emis-
      sions from a recovery boiler. TAPPI, 43(6):182A-185A. June  1960.
      This paper describes  recent  pilot studies conducted at large paper
      mills and  reviews the performance of full-scale  installations with
      gas-handling capacities of up. to 160,000 cfm. The spent digestion
      liquor contains  about one-half the weight of the original wood plus
      almost all the original pulping  chemicals. From the boiler, particu-
      Jate loading of the furnace gas runs 3 to 6 grains per cubic foot. The
      electrostatic  precipitator  removes approximately 90 percent of this
      loading.  Soda Process  Plant  at Kingsport, Tennessee: Recovery by
      an electrostatic  precipitator  averages 90  percent.  A  Buffalo  Forge
      Company TE Washer  was installed downstream of  the precipitators.
      The gas flow to the  washer  is  57,000 cubic feet per minute with a
      dust loading of 0.21 grains per standard cubic foot. The  effluent dust
      loading is 0.027 grains per standard  cubic foot for a recovery of 88
      percent. Soda ash recovered  is 1.7 pounds per minute. An analysis
      of the particle size efficiency curve shows that the washer does  not
      collect material that the precipitator is incapable of collecting,  but
      captures instead agglomerated  particles blown off the precipitator
      plates. Kraft Process Plant at Everett, Washington: Tests on a pilot
      scale TE Washer gave efficiencies of up to 95 percent depending upon
      furnace operation. Kraft Process Plant at San Joaquin, California: A
      full-scale TE Washer, of  160,000 cubic foot per minute capacity, was

-------
  38                                                  AIR POLLUTION

        installed downstream of an electrostatic precipitator. Dust  loadings
        to the washer normally  ranged between 0.05  and  0.15 grains per
        cubic foot,  but rose  to greater than 3 grains per cubic foot when
        the precipitators were down. This  washer met  the guarantee to re-
        move  88.5  percent  by weight of dust  discharged  from the pre-
        cipitators.

    Table 18. RELATION OF PARTICLE SIZE TO RECOVERY EFFICIENCY
Particle size, jx
20
15
10
5
2
1
Efficiency, %
95
92
85
65
30
20
 59.    Fones, R. E.,and J. E. Sapp: Oxidation of kraft black liquor with pure
       oxygen. TAPPI, 43:369-373. 1960. Black liquor oxidation has  many
       attributes that  make it an attractive measure to incorporate into  a
       kraft  mill. The high degree of foaming of southern black liquor,
       however, makes this process difficult to operate. For this reason, in-
       vestigations were carried  out to determine whether oxidation in a
       pressurized vessel would be economically practical.  Addition of oxy-
       gen to the digester toward the end of a normal kraft cook was found
       to  reduce the amount  of  sodium sulfide present, but the resulting
       pulp was of reduced strength and brightness. Furthermore, the cost
       of  adding the oxygen was found to be prohibitive.  Reduction of the
       price of oxygen, however,  would make a process of  this type worthy
       of  further investigation.
 60.    Freudenberg, K., and M. Reichert:  Sulfate pulp mill odors. TAPPI,
       38(8):165A-166A. Aug.  1955. This letter to  the  editor refers to per-
       sonal  experience concerning the  existence of the well-known odor
       around the Vita Mayer Mill near Tradate Varese, Italy  (see article
       by P. Ghisoni, TAPPI, 37:201. 1954. Abstract 62). It also contains
       information on  the threshold value  of methyl mercaptan.
 61.    Gaudette, P. R-: Electrical  precipitators in air pollution control.  Proc.
       llth Indus. Waste Conf. May 1956. Purdue Eng.  Extension Dept. Eng.
       Bull. Vol. XLI. June  1957. Precipitators are  90 to 98  percent efficient.
       Recoveries of chemicals in kraft mills run 100 to 150 pounds per ton
       of pulp,.
62.    Ghisoni, P.:  Elimination of odors  in a  sulfate pulp mill. TAPPI,
       37(5):201-205. May 1954. A description of a  plant,  at Cartiera Vita
       Mayer & Company of Milan, Italy, for the elimination of the mercap-
       tans from a sulfate pulp mill is given.  The main operations are: (1)
       Condensation of all relief  and blow gases with indirect  condensers;
       (2)  use of the condensed water as  dilution water in  a chlorination
       tower of the bleaching plant; (3)burning of the ncncondensable  gases
       in one boiler together with natural gas;  (4) cooling of the smoke  from
       the recovery  boiler to the dew point, followed by oxidation  with
       chlorine and reheating to  avoid corrosion in  the chimney.

-------
Annotated  Bibliography                                              39

63.    Gordon, W. O., and E. E. Creitz: Chlorine as a deodorant in sulfale
      paper pulp manufacture. Paper Trade J., 106:81-85. Apr. 28, 1938. The
      characteristic odor  of kraft pulp manufacture has been attributed to
      methyl and ethyl mercaptans and sulfides.  These are produced (1)
      during the digestion process, (2)  from the discharging of the digesters,
      (3) from the condensate from the evaporators, and (4) from the burn-
      ing of  black liquor in the furnace. To test the odor-reducing  capabil-
      ities of chlorine, a 2.5-cubic foot digester was constructed.  Experi-
      ments  were conducted  by charging the digester with 35 pounds of
      chips, and adding cooking liquor consisting of 6.0 pounds of sodium
      hydroxide and 3.0 pounds of sodium sulfate added to 120 pounds of
      water. Cooks  were allowed  to  proceed at 169 °- C for periods of 3
      hours,  during which the digesters were relieved continually.  Relief
      gases were led to a condenser and passed through a spray chamber
      containing 20 liters of hypochlorite solution of known chlorine con-
      tent. Two alcohol traps were added to the end of the train as  a safety
      measure. It was found that the average amount of chlorine consumed
      per run was 1.29 grams. The odor-reducing capabilities of the  chlorine
      were highly significant. The effect of chlorine on the condensed re-
      lief gases was also  studied. It was observed that chlorine was fairly
      effective in reducing odors of these liquids, although much of the
      odor reappeared when  the mixtures were  allowed  to stand over-
      night. From this study it was concluded that approximately 25 pounds
      of chlorine per ton of pulp is necessary for the elimination  of odor.
      The cost of such a measure is prohibitive and can be justified only
      in special cases.
64.    Gordon, W. O., and E.  E.  Creitz:  Elimination  of obnoxious  gases in
      the  sulfate pulping process.  Ind. Eng. Chem...  26:565-567.  May, 1934.
      During the kraft  cooking process,  some  of  the sulfur combines
      with part of the organic constituents of the work to form  mercap-
      tans, alkyl sulfides, and similar compounds. Mercaptans and alkyl
      sulfides can be  removed from noncondensable relief gases from the
      digesters of the kraft pulping process  by means of a solution of hypo-
      chlorite sprayed  into the gases.  The aqueous  layer of the  conden-
      sate  from these relief  gases, as well as that from the evaporation
      of the black liquor,  is also  treated with hypochlorite. The odor
      of  the  organic  sulfur  compounds  in  these  distillates   is  re-
      moved, but  the liquors  are  not rendered  entirely odorless  by
      this  treatment.  The   condensate   from   the  digester  relief
      gases  consumed  about  21  kilograms   of   active   chlorine per
      metric  ton  (4.2   pounds  per  ton)  of  pulp  produced,   while
      the  distillate  from  the  black  liquor  consumed  several  times
      this amount. It is believed impractical to destroy all the mercaptans
      by the chlorine treatment, and  other means are suggested for elim-
      inating these obnoxious odors. This article gives the results obtained
      from an experimental  sulfate mill, with a capacity of 16 kilograms
      (35 pounds)  of chips per batch.  The chips  are  cooked at 100 pounds
      per square inch for 4 to 8 hours. Sources of gases  were digester re-
      lief, blow-off pit, wash water used to wash pulp (which in older mills
      may be discharged into a nearby stream), black liquor evaporator,
      and  black liquor furnace  (recovery  furnace). Gases  from  cooking
      (relief and blow) were collected by dissolution in alcohol, and  titrated
      with iodine solution. Results indicate  0.0603 grams of mercaptan pro-

-------
  40                                                 AIR  POLLUTION

      duced per 15.96 kilograms  (35 pounds) of chips. Later  experiments
      with hypochlorite spray  showed  about 15 times as much chlorine
      was necessary to oxidize the gases as would  be  required by this
      amount  of mercaptan. Chlorine  evidently oxidizes the mercaptan
      further than iodine does, and also oxidizes other gas  constituents,
      such as methanol. The average amount of chlorine necessary to de-
      odorize the gas was 1.3 grams per cook. Hence chlorine consumption
      amounted  to 0.25 kilograms per metric ton (0.5 pounds per ton) of
      pulp (each cook  of  15.96  kilograms of  air-dried wood produced 4.67
      kilograms   £10.3  pounds}  of pulp). The digester  condensate also
      contained  mercaptan. After  turpentine removal,  2.1 kilograms  of
      chlorine per metric ton (4.2 pounds p,er ton)  of pulp were needed
      to deodorize the condensate. Vapors from the evaporation of black
      liquor require much larger quantities of chlorine. The mercaptan
      odor can be removed,  but other odors remain. It is recommended
      that  the liquors containing mercaptans be used for washing  pulp
      and for making up cooking liquor. They should not be discharged;
      gases  containing  mercaptans  should  be  burned  in the  recovery
      furnace.
65.    Haegglund, E.: The odor question in sulphate pulp manufacture. Paper
      Trade J.,  83:50. Dec. 16, 1926.  A critical review of the theories and
      proposed methods of control of kraft mill air pollution is given. Em-
      phasis is placed upon the procedure of Wislicenus, which involves the
      mixing of stack gases with air to promote oxidation on the way  up
      the flue, and  Schwalb's process, which utilizes wood chips for gas
      absorption.
66.    Hansen, G. A.: Odor and fallout control in a kraft pulp mill. J. of  the
      Air  Pollution Control Assoe., 12(9):409-413. Sept. 1962. A description
      is given of the air  pollution control measures  used at the Weyer-
      hauser mills. Emphasis is placed  upon the vaporsphere surge tank,
      which holds digester gases prior to their combustion in the lime kiln,
      and the spray scrubber,  which collects the sodium salts that  pass
      through the electrostatic  precipitators.  These measures  have caused
      an estimated 90 percent reduction in odors and  particulate fallout.
67.    Hendrickson, E. R.:  Air pollution sampling and  analysis  with special
      reference to sulfate pulping operations. Report to the National Coun-
      cil for Stream Improvement. Unpublished. 1958. This is a report  on
      techniques and procedures for sampling materials  emanating from
      kraft mills, which have been  under laboratory investigation at the
      University of Florida, and also investigated in the field. It describes
      stack-sampling equipment, analytical procedures, areal sampling, and
      simplified techniques. While it is believed that  these techniques and
      procedures will provide adequate information at minimum cost, they
      are  not yet ready for routine use.
68.    Hendrickson, E. R.: Air pollution sampling and  analysis  with special
      reference io sulf ate pulping operations.  TAP PI, 42:173-176A.  May
      1959. In view of the present public interest in  air  pollution,  it may
      be a sound idea for the individual pulp mill to initiate; its own samp-
      ling programs. Such programs must be well-designed,  however, to
      provide meaningful data  at a reasonable cost. A summary is given
      of some analytical techniques available for determination of various
      gases emitted by kraft mills.

-------
 Annotated Bibliography                                              4'

 69.   Hendrickson, E. R.: Atmospheric improvement activities of the pulp
      industry. TAPPI, 43:193A-195A. Mar. 1960. Because of increased pub-
      lic concern, the pulp  industry has been conducting research on con-
      trol  of its  air-borne'emissions. This has been difficult  because con-
      trol  measures and restrictions are demanded even  before research
      can be conducted to provide for them. Frequently research is  hamp-
      ered by the lack of reliable techniques for  analytical determination
      of pollutant compounds. Study is therefore  in progress  to determine
      new ways  of analysis. Control of particulate emissions  has been  ac-
      complished by equipment such as venturi  scrubbers,  cyclones, and
      electrostatic precipitators. Gaseous emissions are more difficult  to
      control. Oxidation of black liquor prior to evaporation has been used
      to curb gases issuing from the evaporators. Partially  successful  at-
      tempts to eliminate digester gases by burning or chlorinating have
      also been made. A few mills have constructed gas holders to  reduce
      surges in the line from the blowing  of the digesters.
70.    Hendrickson, E. R.: Technical procedures for determining pulp mill
      stack losses. Report to the National Council for Stream Improve-
      ment. Unpublished. 1959. This report describes research work being
      done at the University  of Florida on sampling and analysis tech-
      niques for the National Council for Stream Improvement. Initial work
      was  in the area of stack sampling, with the recovery furnace as the
      first target. Sampling is done for particulates, sulfur dioxide,  hydro-
      gen sulfide, and total sulfur as sulfur dioxide. It is believed that this
      program provides necessary information at the  least cost  consistent
      with providing reliable data- The laboratory work is reported  nearly
      complete, and additional field evaluation is being conducted. Basic
      techniques of sampling and analysis  are reviewed. The work being
      done at Washington  State for the National Council is also briefly
      reviewed.
71.    Hendrickson, E. R., C. G. Walker,  and V. D. Chapnerkar: Identifica-
      tion  of the nonsulfur organic compounds in stack gases from pulp
      mills. Paper presented at the annual meeting of A1HA, Washington,
      D. C, May 1962. In the manufacture of wood  pulp by the sulfate
      or kraft process, the noncellulosic portions of the wood are dissolved
      away by the cooking liquor. The cooking liquor consists essentially
      of sodium  hydroxide and sodium  sulfide. This  liquor is added  to
      wood chips, and the combination is cooked  at high temperature and
      pressure for several hours. The result is a mixture of wood pulp and
      black liquor. The black liquor is washed from the pulp before further
      processing.  For the process to be economically feasible the cooking
      chemicals must be recovered from the black liquor. This  is accom-
      plished in a reducing atmosphere  in the recovery furnace. Heat,  as
      well as  chemicals, is  recovered. Because of the  nature of  the fuel,
      many and various combustion products are formed. Some of these are
      odorous sulfur compounds that, together with some nonsulfur com-
      pounds, result  in the typical kraft odor.  The  sulfur-bearing com-
      pounds have been reasonably well  identified. The objective of this
      study was to identify some of the nonsulfur organic compounds.  By
      means of mass spectrometry, ultraviolet absorption photometry, gas
      chromatography, and more conventional analytical  procedures, the
      following compounds were identified: Pyrene, fluoranthene, benz(a)-
      anthracene, chrysene, benzo(3)pyrene, benzo(a)pyrene,  benzo(g,h,i,)-

-------
  42
AIR POLLUTION
      perylene, coronene, and vanillin. Phenanthrene, anthracene, and an-
      thanthrene have been tentatively identified on the basis of compari-
      son of their absorption spectra with those published in the literature.
      None of the pure, polynuclear,  aromatic  hydrocarbons tested gave
      an odor. Benzo(a)pyrene has been indentified as a strong carcinogen
      and  benz (a) anthracene has mild carcinogenic properties. It is to be
      emphasized that the  results  presented are merely qualitative.  No
      quantitative  data have yet been obtained.
71 A.  Hendrickson,  E.  R.: Air pollution  control activities associated with
      alkaline pulping, ca 1960. Unpublished: 18pp. This is a good, general
      paper on the emission of pollutants from kraft pulping, their effects,
      and control. It describes alkaline (kraft) pulping, sources of air pollu-
      tants, effects of pollutants, control of particulates, odor reduction,
      and other controls. Thirteen  articles in the literature are cited.
72.   Hisey, W. O.: Abatement of sulfate pulp mill odor and effluent nui-
      sance. TAPPI, 34:1-6. Jan. 1951. A description is given of the recovery
      system in the South  African  Pulp and Paper  Industries' mill. This
      plant utilizes a black liquor oxidation tower as a sulfur trap, where
      all odorous sulfur gases are diluted with air and passed through the
      oxidation tower. Residual  gases from the tower are burned in  the
      furnace. Digester  condensates are  blown  with air into  a packed
       tower, and the effluent is  used  as make-up water in a spray cooling
      pond- This creates a  negligible odor.  Fume recovery towers and a
      cyclonic evaporator were installed in the recovery furnace. So far
      it has been shown that 90 percent of the  sulfur gases leaving the
      furnace is recoverable. The low odor of  the stack  gases is reduced
      even further by injection of small amounts  of chlorine. These efforts
      have resulted in the  maintenance  of an  exceedingly low degree of
      odor in the atmosphere, and in the requirement of relatively small
      amounts of new chemicals to make up the  cooking solution. Operation
      data are presented in Tables  19 through 22.

   Toble 19. ANALYSIS OF SULFUR COMPOUNDS IN GAS STREAMS (Ib sulfur/million ft3qos)

Digester relief gases to oxidation
tower (after dilution)
Noncondensable gases from evaporators
Gases leaving oxidation tower
Estimated quantity of sulfur returned
to furnace from oxidation tower (as
Ib NaoSO^ per ton pulp)
H2Sand
mercaptans

1.78
575.9
3.55


...
Organic
disulfides

2.40
99.2
7.42


...
Inorganic
sulfur

Nil
Nil
Nil



Total
sulfur

4.18
675.1
10.79


8.3
73.    Institute of Paper Chemistry. Bibliographic Series No. '178. Alkaline
      processes. II. Black liquor.  1952. Unpublished.  An annotated bibli-
      ography, consisting of 108 references to foreign and domestic publica-
      tions and patents concerning odors from the kraft process, covering
      both relief gases and black liquors.  This document makes a good
      reference piece.

-------
  Table 20. FUME RECOVERY SYSTEM OPERATING TESTS

Gas temp, °F
Dew point, °F
GAS ANALYSES (equivalent
Ib Na2S04/ton pulp)
Smelt sulfidity, %
hUS and mer cap tans
Organic disulfides
COS and CS2
so2
so3
Na2S204
Na2S04
Na2C03
NaCI
Total sulfur compounds in gas
(Ib Na2S04/ton pulp)
Salt cake recovery in fume
system (Ib Na2S04/ton pulp)
Entering Leaving
1
195
170


14
19.0
1.9
Nil
Nil
Nil
Nil
148.0
2.9
27.3

168.9
...
2
193
157


16.5
8.8
Present
2.7
8.9
Nil
14.1
124.0
Nil
14.7

158.5
...
1
157
156


...
2.8
2.0
Nil
Nil
Nil
Nil
12.5
2.2
8.5

17.3
151.6
2
154
153


...
0.5
Present
1.6
Nil
Nil
3.5
4.0
2.0
8.9

9.6
148.9
Table 21. BLACK LIQUOR OXIDATION TOWER DATA

Sulfidity of smelt, percent Nc^S in black
liquor
Entering tower: grams of Na2S per liter
of black liquor
Leaving tower: grams of Ha^S per liter of
black liquor
Oxidation efficiency, %
Run no.
1
14
3.4
0.58
83
" II
18.7
5.4
0.45
92
III
25.5
8.2
1.28
84

-------
 TABLE 22. CYCLONIC EVAPORATOR OPERATING TESTS
                                                      AIR  POLLUTION

Gas temp, °F
Dew point, «F
Black liquor concentrations,
% solids
Smelt sulfidity, %
Gas Analyses (equivalent Ib
Na2S04 ton of pulp)
H2S and Mercaptans
Organic disulfides
COS and CS2
S02
S03
Na2S204
Na2SC4.
Na2C03
NaCI
Total sulfur compunds in gas
(Ib Na2SO^/ton pulp)
Salt cake recovery in fume
system (Ib Na2SO^/ton pulp)
Entering
1
420
51.5
19.5

17.4
Nd
1.2
58.0
Nil
Nil
153.0
34.8
38.1
229.6


2
440
54.0
25

2.6
Nd
0.8
10.0
Nil
Nil
136.0
Nil
30.0
149.4


3
400
54.7
14

52.5
3.2
Nil
5.3
Nil
Nil
234.5
5.4
74.3
295.5


Leaving
i

62.5


9.1
Nd
0.9
5.5
Nil
18.8
86.0
11.4
20.8
120.3
109.3
2
189
169
65.6


10.6
Nd
0.8
2.0
Nil
6.0
82.0
Nil
Nil
101:4
48.6
3
195
170
64.1


19.0
1.9
Nil
Nil
Nil
Nil
148.0
2.9
27.3
168.9
126.6
74.    Kenline, P. A.: In quest of clean air for  Berlin, New  Hampshire.
      Sanitary Engineering Center  Technical Report  AG'2-9. U. S. Dept. of
      Health, Education, and Welfare, Public Health Service, Cincinnati,
      Ohio. 1962- An appraisal of the nature, sources, extent,  and effects
      of air pollution in Berlin, New Hampshire, concludes that the situa-
      tion warrants corrective  action. Pollutants of concern include par-
      ticulates, sulfur dioxide,  hydrogen sulfide, and malodorous organic
      sulfur gases. The major source of these pollutants is a pulp mill.
       On the basis of this survey corrective measures are recommended.
  Table 23. AIR QUALITY MEASUREMENTS
Pollutant
o
Suspended particulate,u.g/m°
Hydrogen sulfide, ppb
Sulfur dioxide, poh
Dustfall, tons/m^ per mo
Soiling, Cohs/1000 ft
Average
183

16
35
0.5
Maximum
309
23
33
68 -
1.9

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 Annotated Bibliography
                                                                    45
   Toble 24. MEASUREMENTS OF POLLUTION FROM VARIOUS SOURCES IN THE KRAFT
          PULP MILL
Source
Recovery furnace
Blow gases
Smelt tank
Lime kiln
Boiler plant (1 boiler only)
Emission of pollutants in Ib per hr
Hydrogen sulfide
332
3.
1.7
9.7

Sulfur dioxide
50
0.1
0.06
0.6
248
Particulate
97
65
106
740
      Some  of  these measures are attractive because  of  resulting eco-
      nomic   advantages. Community  good will,  too,  must  be weigh-
      ed  with the   other  advantages of the  installation  of  additional
      control  equipment.  Sampling  procedures are  included, and the
      report  gives  an over-all  status of air  pollution from kraft mills.
75.    Klason.P-'- Malodorous substances in sulfate. Paper Trade J.,  79:30.
      July 10, 1924.  Investigations  concerning  the nature of malodorous
      compounds formed during the kraft process are described. Methods
      of analysis for these compounds and suggestions for preventing their
      formation are given.
76.    Kopita, R.: The use of an impingement baffle scrubber in gas cleaning
      and absorption. Air Repair, 4:219-222. Feb. 1955. In many paper mills,
      gases vented from rotary lime kilns contain up to 15 grains of dust
      per cubic foot of gas. Combination venturi  slot and impingement
      plate scrubbers are  operating in many mills.  The scrubber achieves
      over 97 percent recovery and  reduces the amount of dust in the dis-
      charge  to less than  0.3 grains per cubic foot of  gas.
77.    Kraft,  F.:  Marathon in Canada. TAPPI, 32:14-A.  Sept.  1949. The
      chemical recovery system of the new Marathon pulp mill in Canada
      employs an air oxidation system for the black liquor that has ob-
      tained oxidation  efficiencies of up to 80  percent. Upon leaving this
      system, the liquor goes to the  multiple effect evaporators, after which
      it is further concentrated in furnace gas cyclone scrubbers,  which
      clean the stack gases as well as evaporate black liquor.
78.    Kress, O., and J. W. Mclntyre: The  distribution of  sulfur during the
      kraft pulping operation.  Paper Trade J., 100:43-45. May  2, 1935.  A
      laboratory scale  investigation  was  conducted  to determine the
      stoichiometry of  the  sulfur  compounds throughout  the stages  of
      the kraft process. Both stationary and  rotary  autoclaves were used.
      The rotary units  had a capacity of about  14 pounds  air-dry wood
      chip's,  while the stationary  units had capacities of about 625 grams.
      Because preliminary  experiments with  the rotary autoclaves re-
      sulted in high sulfur losses,  it  was decided that the smaller, sta-
      tionary units were more  adaptable to  the  requirements of this
      project. The gas relief lines  from the autoclaves were  fitted with
      three  glass absorption towers, packed with glass wool  and filled
      with nitric acid.  When the  autoclaves were  relieved through this
      system, no odor  characteristic of mercaptans could be detected.  It
      was therefore assumed that all the  effluent sulfur compounds were
      trapped out. Two types of experiments were  made, those in which
      the cooks were discontinued  and analyzed after given time periods,

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  46                                                 AIR  POLLUTION

      and those in which the cooks were allowed to run  continuously, the
      liquor being  sampled  and  analyzed at various  times throughout
      the run. Screened spruce chips and prescribed quantities of cooking
      liquor were used in the  experiments to  simulate mill operations.
      The sulfide and hydroxide in the cooking  liquor, and the total sul-
      fur in the white liquor were determined, as well as the total sulfur
      in the black liquor. Analytical techniques  are given in  the  text.
      It was concluded  from the data that the loss in sulfur arising from
      the blowing of digesters is very small  (about 0-05 percent). About
      3 to 4 percent of the sulfur is retained by the cooked wood chips.
73.    Kress, O.: U. S. Patent 2,570,460. Oxidizer for black liquor. The tower
      consists of  an  enclosed  series of downward inclined  shelves that
      distribute the downward  flow of black liquor in a continuous, even
      pattern. Air is passed into the tower from below, which gives a
      thin gas-liquid contact area for mass transfer.
80.    Landsberg,  H-, and E. E- Escher: Poteniiometric instrument for sul-
      fur determination. Ind. Eng. Chem.,  46(7):1422-1428.  July 1954.  An
      automatic instrument continuously records trace  quantities of  oxi-
      dizable sulfur compounds in the range of  one-tenth to several hun-
      dred  parts  per million by volume  of gases in  atmospheres. Colori-
      metric titration  with  electrolytically  generated bromine  is  used.
      Titration is  electronically  controlled at  a potentiometric balance
      point. Various applications  in the  natural gas.  process,  and  air
      pollution fields are  discussed.
81.   Lardieri, N. J.: Present treatment practice  of krafi  mills on air-borne
      effluents.  Paper  Trade J.,  142:28-33. Apr.  14, 1958. A survey  of 58
      U. S. kraft mills  was taken to determine the extent of air pollution
      control  being exercised. The  results indicated  the following equip-
      ment was being  used:
  Table 25.  CONTROL EQUIPMENT ON RECOVERY FURNACE AND LIME KILN EXHAUST
  Recovery furnace exhaust
  Electrostatic precipitators
  Venturi scrubbers a
  No equipment
          a
a
50
 9
 2
  Lime kiln exhaust
  Wet scrubbers
  Dry dust collectors
  No equipment
  No lime kiln
                                           54
                                            1
                                            1
                                            2
  ° Three mills use both precipitators and scrubbers.

     The electrostatic  precipitators were  from 90 to 98  percent efficient
     as compared with 85 to 90 percent for the venturi scrujbberp. In ad-
     dition,   the  scrubbers required  more power  for  their  operation.
     These disadvantages may  be  offset somewhat,  however, by the rel -
     ative simplicity of the venturi and its ability to trap some of  the  o-
     dorous noncondensable gases.

-------
Annotated Bibliography                                             47

      Odorous gases occur primarily in the digestion and  recovery sys-
      tems. Digester gases are sometimes collected and burned or chlor-
      inated.  Recovery gases have been passed through oxidation towers
      or wet scrubbers. Odor masking has also been employed.   Money
      spent by the mills in the survey was broken  down as follows:
      Electrostatic  precipitators   and venturi  scrubbers  for  recovery
           furnace  Stack  gases 	 $24,142,000
      Lime kiln exhaust  equipment  	$2,661,000
      Black liquor oxidation towers, chlorination towers, and other control
           methods  for sulfur compounds 	  $1,885,000
      Stack gas cleaning equipment for fuel and bark burners
            	$1,973,000
      Total	 $30,661,000.
82.    Lardieri, N. J.:Pulp and paper  industry progress  in atmospheric
      pollution control.  Paper  Trade J.,  143:42-46. 1959.  The significant
      progress made by the pulp and paper industry in the control of air-
      borne effluents  has  fortunately preceded the current  rise  of public
      interest in the subject.  Although the research program  is proceed-
      ing along several  lines,  it has two divisions:  measurement and con-
      trol. Recent studies  of measurement techniques have involved work
      with gas chromatography  and various chemical methods, such  as
      the ADAK analyzer; and the device for sampling hydrogen sulfide,
      sulfur  dioxide,  and total  sulfur developed  by  the  University  of
      Florida research project. Black liquor oxidation has become of con-
      siderable interest as a  means of reducing emissions. This method
      has  been applied  mainly  in the northern  regions  of the  frorth
      American continent, because foaming difficulties have been encoun-
      tered in the south. Other important developments in emission control
      are sulfur dioxide recovery systems, venturi  scrubbers, and electro-
      static precipitators.  With these and  other developments,  the pulp
      industry should be  able to meet the requirements of  the rapidly
      increasing regulatory  activity in the air  pollution  field.
83.    Maksimov,  V.  F., et  al.: Purification of kraft  mill  waste  gases.
      Bumazh. Prom.,  34(5):14-16. 1959.  Chem. Abs., 54:1778.  Jan. 25,  I960.
      Waste  gases from the  recovery  furnace  of  the  Svetogorsk kraft
      mill were treated in an experimental foam-type  scrubber. Results
      of this experiment are  given  in Table 26.  Furnace gas velocity  was
      3.2 meters per second, and the scrubbing solution contained 20  to
      30 grams of NaOH  per liter. In a full-scale  insta?lation (4,700  mm
      high, 2,200  mm diameter  scrubber,  with a  capacity of  30 cubic
      meters per  hour of  black liquor  and 800  cubic meters per hour  of
      gas), using  black liquor as the scrubbing medium, the content  of
      sulfur  gases contained in mixed gases was reduced (Table 26),
84.    Marsch,  J.  D. F., and  W. B.  S. Newling:  British Patent 7M.996
      (1957). Oxidation  of hydrogen sulfide  to sulfur dioxide. A process
      is discussed for  treating hydrogen sulfide-containing gases by cata-
      lytic oxidation of the hydrogen sulfide to sulfur dioxide. This process
      comprises heating the gases that contain  at  least sufficient oxygen
      to oxidize the  hydrogen sulfide to  sulfur dioxide (180 to 450 ° C), and
      bringing them into contact with a catalyst consisting of one  or
      more sulfates of  heavy  metals  superficially  converted  to sulfates
      of metal oxide  cations.

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  48
AIR POLLUTION
  Table 26. PURIFICATION OF RECOVERY FURNACE GASES

Furnace gas alone:
Hydrogen sulfide
Methyl mercaptan
Sulfur dioxide
Furnace and evaporator
gases, mixed:
Hydrogen sulfide
Methyl mercaptan
Sulfur dioxide
Furnace, evaporator, and
digester gases, mixed:
Hydrogen sulfide
Methyl mercaptan
Sulfur dioxide
Dimethyl sulfide
Dimethyl disulfide
Hydrogen sulfide
Methyl mercaptan
Sulfur dioxide
Cone pretreat, mg/m
34 to 1,200
12 to 204
15 to 937
792
149
254
529
2,560
87.8
330
166
57.2 to 181
78.8 to 111.5
3.9 to 12.1
Cone after treatment, mg/m''
10 to 40
8 to 46
2tol20
41
22
7.4
42
335
7.3
26
26
3.5
0.58 to 3.4
0.44 to 0.52
85.    May, B. F.: Experiences in the abatement of krafi mill odors. Un-
       published. Gulf States Paper Corporation. Tuscaloosa, Alabama.  16
       pp.  The  experiences  at the  Braithwaite,  Louisiana, mill of Gulf
       States  Paper Corporation with the odor  problem since the mid-
       1920's are presented. A historical presentation is given, in the hope
       that the  rest of the  industry may learn  from the experiences  of
       this mill. Use of a direct condenser for digester blow gases brought
       the  first success in odor abatement. Chlorine was tried for deodor-
       izing the condenser effluent,  but was  found ineffective. Until  1951
       all attempts at  odor abatement were made with condensers, water
       spray scrubbers and improved processing equipment. Trials of odor-
       masking aromatic  compounds began in the fall of 1951. Efforts  to
       effect a milder and less obnoxious odor by use of these compounds
       has  produced a slight trend toward  abating odors.  Positive con-
       clusions, however,  await extended trials. Trial of a scrubber system
       employing bleach plant waste liquors is under consideration. Eval-
       uation of results is the most  difficult  aspect of this field of study.
       A practical yet accurate  means of odor measurement is needed.
86.     $lay, B. F.: Experiences in the abatement of kraft mill odors. TAPPI,
       36:374-378. 1953. A retrospective account of experiences of the Gulf
       States Paper Corporation's problems in air pollution control is given.
       A digester  blow gas  condenser was  the first successful piece  of
       equipment used for odor control. Chlorine gas was also used, but
       was  ineffective. The use  of odor-masking compounds has been  of
       limited success; further experimentation  is needed before it will
       be possible to assess the real value of these compounds. A process

-------
 Annotated Bibliography
                                                                        49
       utilizing bleach plant waste liquors in a scrubber system is currently
       under study.
87.    Meinhold, T. F.: Thilmany reclaims 90%  of  chemicals  from flue
       gas.  Chem. Proc.,  19:14-15.   Mar.  1956. Thilmany installed  a 250-
       ton B & W  recovery  unit  equipped with a  black liquor venturi
       scrubber. It has been in operation  over 2  years. A schematic dia-
       gram  and operating  characteristics are given  below.  The one dis-
   Toble 27   OPERATING CHARACTERISTICS OF B 8. W RECOVERY UNIT
   Black liquor flow

   Collection efficiency

   Saltcake loss

   Draft loss across venturi

   Draft loss across separator

   Pulp production

   Recovery furnace weight

   Recovery of soda from furnace gas by
       venturi scrubber
   Dust loading at standard conditions
       dry gas, gr/ ft"3

   Dust loading, stack conditions,
       gr/ft3
                                            50,000 Ib/hr

                                               89%

                                             4,500 Ib/day

                                               30 in. water

                                                4 in. water

                                               165 tons /day

                                               120 tons
                                               90%

                                       To scrubber
                                          5.87


                                          3.90
                                                              From scrubber
0.66


0.40
                  DIRTY FLUE GAS 485°F, 3.9 GRAINS
                  OF DUST PER CUBIC FOOT
    LIQUOR TO VENTURI
    THROAT, 62 PERCENT SOLIDS
LIQUOR TO
CYCLONE WALL
62 PERCENT SOLIDS
LIQUOR TO MIXING  ~*~
TANK AND FURNACE,
62 PERCENT SOLIDS
                                                  CYCLONE
                                                      CLEAN FLUE GAS 180 F,
                                                      0.4 GRAINS OF DUST
                                                      PER CUBIC FOOT
                                                  LIQUOR FROM EVAPORATORS,
                                                  42 PERCENT SOLIDS
   Figure  8.  Schematic flow diagrams of thilmany chemical recovery unit.

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 50
AIR POLLUTION
      advantage—high power requirements—is more than offset by good
      heat recovery (saves 3,000 pounds of steam per hour), good chemical
      recovery  (90  percent), low  cost, and  low space  requirements.
88.    Mellor, D., and P. G. Stevens: Use of the veniuri scrubber on alkali
      fume.  Australian  Pulp & Paper Ind..  9:222-248.  1955.  To reduce
      economic losses and air pollution from effluent particulate matter,
      the Burnie Pulp Mill has conducted laboratory tests on various types
      of collection equipment to determine the one most suitable for in-
      dustrial use. Pilot plant  experiments with bubble cap towers,  cy-
      clones, packed towers, spray chambers,  and venturi scrubbers were
      conducted with varying degrees of success. On the basis of favor-
      able  pilot data  and encouraging  results published  by  earlier  in-
      vestigators, a full-scale venturi  scrubber was selected.
      The full-scale unit operated with a  recovery efficiency of 85 per-
      cent or more when the injected cleaning liquor flow rate was  not
      less than  3  gallons  per  1,000  cubic  feet of stack  gas. The  gas

 Table 28.  STRUCTURAL SPECIFICATIONS  OF THE  VENTURI SCRUBBER
Part
Venturi inlet diameter
Venturi throat diameter
Venturi outlet diameter
Cyclone diameter
Cyclone height
Fan power
Spec
4' 8"
26"
3' 10"
12'
35'
450 hp
            FROM FURNACE
  BLEED OFF<
                                     CY-
                                    :LONE
                                                      GASES TO STACK
                                                 -•{FAN	
                 SCRUBBING LIQUOR
                                        I PUMP
  Figure  9.  Schematic flow diagram of venturi scrubber unit at Burnie mill,

-------
Annotated Bibliography
                                                                   51
       flow rates through  the venturi  were  from 53,000 to 64.000  cfm.
       Approximately 15  to  17  inches pressure water  gauge was lost
       across the venturi, and 2.0 to 2.5 inches were lost across the cyclone.
       Meuly, W. C-,  and B. K. Tremaine: Abatement of sulfate pulp mill
       matadors by odor masking  agents. TAPPl, 36:154-161.  1953.  The
       results of an attempt to mask sulfate pulp mill odors are described.
       Masking compounds were added directly to the digester charge, and
       allowed to flow through the plant equipment and remain with the
       source  of odor at all times.  Laboratory tests  were made to deter-
       mine the relative amounts of odor produced by the various opera
       tions of the kraft process.  The results  are presented  in terms of
       "Gram  Sense Values" per ton  of pulp. These results  are given in
       Table 29. The  cost of applying the masking agent was from 12 to 24
       cents per ton pulp for the usual concentrations. Results of full-scale
       tests indicated that  this type  of  odor masking was definitely ef-
       fective.
    Table 29.  RELATIVE AMOUNTS OF ODOR PRODUCED BY VARIOUS OPERATIONS
            OF THE KRAFT PROCESS
Location
Digester relief
Digester
blowdown
Multiple effect
evaporators
Cascade
evaporators
Total
"CSV" /ton of pulp
Total liberated
20,000 x 106
Min 27,000 x 106
102,000 x 106
38, 000 x 106
187,000 x 106
Air-borne portion
20,000 x 106
Min 27,000 x 106
10, 000 to 30,000 x 106
Max 38,000 x 106
50,000 to 100,000 x 106
90.    Mockridge, P. C.: The use of Peabody scrubbers on lime kiln stack
      gases. TAP PI, 38(4) :255-256. Apr. 1955.  A cyclone  is unsuited for
      control  of lime kiln gases because there is a considerable quantity
      of material below  10 microns in size. Fines not collected  by cy-
      clones may run 2 to  4 grains per standard (60 °F) cubic foot.  Bag-
      houses are at a disadvantage because of high moisture and temper-
      ature. A Peabody scrubber in use at the Chesapeake Corporation
      is described. The kiln is 11 feet  in diameter with  a rating of 250
      tons of calcine per day; gas low is 26,000  standard (60?F) cubic

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   52                                                AIR POLLUTION

       feet per minute.  Temperature  of  gases  leaving scrubber  is  150°F
       and the pressure drop across the  scrubber is  4%  to  5%  inches of
       water.  Dust load from kiln  is  16  grains  per  standard cubic foot;
       from the scrubber is 0.3 to 0.4 grains per  standard cubic foot. This
       corresponds to an efficiency of 97 percent.
91.    Moon, D. G.: Practical aspects  of  recent  kraft mill developments.
       Paper Trade J., 104:103-107. Feb. 25, 1937.  Since the depression the
       construction of new mills has  created  interest in the application
       of some of the new improvements.
       These have  generally  been  found to apply  to:
         1. Improved  cooking techniques,
         2. recovery and utilization of heat from blow-off steam,
         3. use of more efficient evaporation systems,
         4. improved  recovery furnace units,
         5. continuous  causticizing  systems and  lime  recovery,
         6. reduction of odors.
       Condensing the  blow-off steam  has probably been   the greatest
       help  in reducing  offensive  odors.   The  noncondensables can  be
       exhausted  through  a  fan  and readmitted   to the furnace,  which
       reduces much of the odor  that  would otherwise be emitted-
92.    Moore,  H.,  H. L. Helwig,  and  R.  J. Graul:  A specirophotometric
       method for the determination of mercaptans in air. Am. Ind. Hyg.
       Assoc. J., 21:466. I960-. With  this method,  mercaptans  are collected
       in  5 percent  mercuric  acetate solution  and reacted  with  N,N-
       dimethyl-p-phenylenediamine to form a red  complex that can be
       quantitatively determined with  a  spectrophotometer.  The sensitiv-
       ity of this  method is  about 0.00023 micromole  of mercaptan per
       cubic centimeter. There is  no interference from H2S. Interferences
       from SO 2 and NO 2 are present, but are  slight in the concentrations
       normally encountered  in air pollution  studies.
93.    Murray, F. E.,  and H. B.  Rayner: A procedure for sampling and
       analysis of hydrogen sulfide in krafl mill stack gases. TAPPI, 44:219-
       220. 1961. A description is given of a method of determining hydro-
       gen sulfide  in  stack  gases.  The hydrogen sulfide content of the
       gas  is  analyzed by absorption in  zinc  acetate solution and  subse-
       quent colorimetric observation  by  Lauth's  violet method.  This pro-
       cedure  permits rapid  sampling and analysis for hydrogen sulfide
       concentrations of 20 to 800 micrograms per liter.
94.    National Council for Stream Improvement: Air pollution  Technical
       Bulletins. Unpublished. A series of bulletins relates to air pollution
       and the pulp and paper industry.  To date there are  16:
  94-1. Sampling and analysis of air-borne gaseous effluents resulting from
       sulfate pulping. Sept.  1957. 28 pp. A literature review  of available
       methods of  sampling for atmospheric  effluents  from  the sulfate
       pulping  industry. 54  references.
   94-2 Present  treatment practice of air-borne  effluents  in; the  United
       States kraft industry. Nov.  1957. 18 pp.  Results  are, given of a
       survey of  the  kraft pulping industry in the United States. It was
       the purpose of this survey, with respect  to which most mills were in-
       dividually  visited by Council engineers, to obtain  information
       concerning the disposal of air-borne effluents within the industry.
       A total of  58  mills participated in the survey.

-------
Annotated  Bibliography

  94-3. Applied meteorology for the pulp and paper industry.  Mar. 1958.
       21  pp. General.
  94-4. Application of instrumentation to pulp mill atmospheric  discharges.
       Mar. 1958. 17 pp.. A literature review of instruments for the samp-
       ling, analysis, and automatic sampling and recording of  particulate
       and gaseous atmospheric  pollutants.  48  references.
  94-5. Methods  for the determination of sulfur  compounds in pulp  mill
       effluent gases. Sept. 1958. 13 pp. Report of research at Washington
       State University on a gas chromatographic procedure for  the  sep-
       aration and identification of  sulfur-containing malodorous  com-
       pounds. This procedure has potential application to the study  of
       gaseous pulp mill  effluents at  the sources and in  the atmosphere
       in  the vicinity  of the sources.
  94-6. Gas chromatographic  analysis of hydrogen sulfide, sulfur dioxide,
       mercaptans, and alkyl sulfides and  disulfidss. Apr. 1959.14 pp. A
       gas  chromatographic  technique  is  presented for  the  separation
       and identification of complex mixtures of volatile sulfur-containing
       compounds of the type found in kraft pulp digester blow gas and
       black liquor combustion products. Research  at  Washington State
       for the NCSI.
  94-7  Studies on the analysis of kraft mill gases. Apr. 1959. 9 pp. A  con-
       tinuation  of Bulletin 5-
  94-8. Manual of methods for the determination of atmospheric  conlamina-
       ination (tentative). May 1959. 18  pp. Intended for the use of local
       mills  this  manual  has  sections on:  meteorological  instrumenta-
       tion and  observations, recommended  units for reporting air pollu-
       tion measurements, recommended standard method for  particulate
       fallout, and recommended standard  method  for  the  determination
       of  hydrogen sulfide.
  94-9. Progress report  on studies on the analysis of  pulp mill  gases.  July
       1959.  17 pp. A progress report on the gas chromatographic tech-
       nique, and on research at Washington State.
 94-10- Progress report on studies on the analysis of  pulp mill  data. Sept.
       1959. This  summarizes the research work  at Washington State Uni-
       versity on methods for collection and analysis of gaseous pulping
       emissions.
 94-11. Laboratory evaluation of  gas sampling procedure  for  recovery
       furnace stack gas. Dec.  1959. 25 pp.  Research at  the  University
       of  Florida for the NCSI to determine the concentration  of gases
       of  interest that result  from sulfate pulping operations is described.
       Stack sampling  is  done for particulates,  sulfur dioxide, hydrogen
       sulfide, and total sulfur as sulfur dioxide. This method is believed
       to  provide  the necessary information  at  the  least  cost consistent
       with providing  reliable data-  The analytical techniques are  rea-
       sonably standard, and in all  cases  a colorimetric procedure  has
       been adopted.
 94-12. Manual: Air pollution  control combustion processes.  Apr. 1960. This
       manual, prepared for the  NCSI at  New York  University, deals
       with the legislative aspects of air pollution (particularly solid  fuel
       combustion) and methods of complying with various control codes
       that have been promulgated.  A section on measurement of atmos-
       pheric pollutants and  incineration is also enclosed, together with
       a state air pollution control agency directory.

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 54                                                 AIR POLLUTION

 94-13. A manual for adsorption sampling and gas chromatographic analy-
       sis of krafl mill source gases. Sept. 1960. This bulletin presents de-
       tailed methods for sampling and chromatographic analysis of kraft
       mill gases developed at Washington State University.  The method
       is based upon  the condensation  and/or adsorption of the gaseous
       effluents on  activated silica followed by desorption and subse-
       quent  gas  liquid chromatographic  analysis.
 94-14. Manual for the sampling and analysis of kraft mill recovery stack
       gases. Oct. 1960. This bulletin describes a method for  the sampling
       and  analysis  of kraft mill  recovery stack gases developed at  the
       University  of Florida.  It is intended as  an alternate  to the  pre-
       viously described chromatographic technique. This method samples
       for  particulates, hydrogen sulfide, sulfur  dioxide, and total com-
       bustible sulfur gases.
 94-15. Survey of kraft mill emission using gas chromaiography techniques.
       Oct. 1962. 23 pp. This bulletin presents the results of the survey
       of gaseous emissions conducted  at  nine  specific  northwest kraft
       mills by the National Council  Research  Projects at Washington
       State University. This  study was designed to  evaluate gas chrom-
       atographic sampling  and analytical techniques developed at Wash-
       ington  State University and also to attempt to define the ranges
       of emissions  from typical operations and various pollution abate-
       ment processes used in the industries. This report illustrates the
       variation in  gases discharged  and  gives evidence  to  indicate  the
       efficiencies of  various abatement procedures.  This study is  con-
       cerned  primarily with the concentration of hydrogen sulfide, meth-
       yl mercaptan,  dimethyl sulfide,  and dimethyl disulfide. The pres-
       ence  of many other gaseous  components is established and  two
       of these are identified.  Tests were run on  digester gases, oxidation
       towers,  recovery furnace gases,  lime  kilns, smelt tanks,  evapor-
       ators, and  miscellaneous  sources.
 94-16. Identification of non-sulfur  organic compounds in the stack gases
       from pulp mills. Dec.  1962. 19 pp. (Qualitative but not quantita-
       tive) identification  of a number of polynuclear, aromatic hydro-
       carbons is made, as  well as a tentative identification of vanillin.
       The  following have beeri identified or tentatively identified in the
       recovery furnace stack gas:  benz(a)anthracene,  benzo(a)pyrene,
       benzo(e)pyrene, benzo(g,h,i,)perylene,  chrysene,  coronene, fluor-
       anthene, pyrene, anthanthrene,  and  phenanthrene. None  of  the
       compounds identified were  found to have  an odor, except vanillin.
       Some of these  compounds are considered  carcinogens.
95-    National Council for Stream Improvement: A critical review of the
      literature on  black liquor oxidation and the burning  of kraft  mill
      noncondensabl® gases. Unpublished, ca 1959.  19 pp. The  literature
      on the  oxidation  of sulfate  black liquor and the burning of non-
      condensable gases produced  in the kraft process has been reviewed.
      The  theoretical aspects of  oxidation, existing  treatment  systems,
      and the  patent aspects of black liquor oxidation are discussed.  The
      published results  on  oxidation  indicate that, from  an  air pollution
      standpoint, a  considerable reduction in the amounts of  reduced  sul-
      fur compounds from evaporation and recovery furnace operation can
      be obtained. Evidence is also presented suggesting that the emission
      of odorous sulfur  compounds from the digestion phases of the kraft

-------
Annotated  Bibliography

      process  can be greatly curtailed if these noncondensable gases are
      passed through the black  liquor oxidation unit. Other benefits at-
      tributed to  black  liquor oxidation include chemical savings in the
      form of lessened  sulfur make-up and  decreased lime usage in the
      causticizing stage. Black liquor  oxidation also results in increased
      sulfidity in the cooking liquor.  The  patent aspects  of black liquor
      oxidation are rather confused at the  moment but  it appears that
      the  Bergstrom-Trobeck  patents have priority in the United States-
      Successful  burning  of  noncondensable  gases  from digesters  and
      multiple effect evaporators in units such as lime kilns, bark  burners,
      separate furnaces, and recovery furnaces has been  reported. There
      has  been an apparent  decrease in this  practice in the United States
      during  the  past 20 years, since only 2 of 60 kraft mills surveyed
      in 1957 engaged  routinely in burning as  compared with 14 of 30
      mills in 1939. This may be attributed to  the  difficulties experienced
      in the combustion of  these highly explosive mixtures. This review
      concludes that both black liquor oxidation and the burning of non-
      condensable gases offer possibilities for greatly reducing the amounts
      of reduced  sulfur compounds emitted to  the atmosphere from  kraft
      operations.  Capital expenditures required for both processes would
      appear  to be moderate and operating costs low. In burning of non-
      condensable gases, the use of existing  combustion equipment seems
      not  only economical but desirable. Operating costs for  nonconden-
      sable burning are negligible, and may be more than met by chem-
      ical  and heat savings  in the case of black liquor oxidation. It does
      not  appear from  the  previous  literature on this subject that the
      possible techniques for oxidizing foamy-type black liquor have been
      exhausted.  Additional research  on this  problem seems fully  war-
      ranted. There are 27  references.
96.   National Council  for  Stream Improvement.  A review of th«  kraft
      odor problem and control processes. Unpublished.  Oct. 16, 1951. 8 pp.
      This paper  updates the  Institute of Paper Chemistry's bibliography;
      it contains  29  entries.
97.    Organization for European Economic Co-operation (Paris):  The po-
      sition in Europe and in the United States. Air and Water Pollution.
      132-137. Feb. 1957. Papermaking itself  is not a serious cause of air
      pollution. The production, by the sulfite and  sulfate  processes of the
      pulp industry,  of  the  cellulose it requires is the  real source of the
      trouble. Both processes  are liable  to emit salts jn the form of fly
      ash  and sulfur dioxide, while  from the  sulfate  process come the
      obnoxious odors  of hydrogen  sulfide, mercaptans,  and analogous
      sulfide  compounds. The operations that cause pollutants to escape are
      classified for the sulfate and the sulfite processes. The chief methods
      for  reducing  air  pollution are listed.  A  flow diagram  (schematic)
      is included to show  where air polluting substances arise from a
      sulfate  mill. A  very brief description  of the air  pollution situation
      is given for four mills—two Swedish  and two German.
98.   Pate, J.: Air pollution in  area of Snohomish River  Bridge, Everett,
      Washington. Unpublished. Extreme corrosion observed on the bridge
      across  the  Snohomish River at Everett, Washington, prompted a
      study to determine  its cause.  Since  corrosion rates were decidedly
      higher  on  the  western side of the bridge, a pulp mill  situated

-------
 56                                                  AIR POLLUTION


      immediately to the west was suspected to be the major factor con-
      tributing to the problem.  The ensuing  study indicated that the
      bridge was being exposed to large quantities of air-borne particu-
      late matter issuing from the mill, and that this was the prime cause
      of the high corrosion rates.
99.    Pate, J.: Air-borne effluent study,  Longview. Unpublished. An  in-
      vestigation was carried out to study the sources and characteristics
      of air-borne particulates issuing from a  pulp mill at  Longview,
      Washington. For this purpose, dustfall jars were placed  at various
      strategic locations surrounding the mill, and samples were obtained
      from the outlets of the  lime  kiln  and the recovery furnace. The
      results were analyzed from air pollution and corrosion standpoints.
      It was found that calcium salts did not present a serious corrosion
      problem. The major source  of  calcium deposits was  the causticizer-
      slaker operation. It was concluded that the lime kiln and recovery
      furnace stacks  provided the majority of  the corrosive compounds.
      An unexpectedly high concentration of sulfur compounds  was found
      issuing from the lime kiln stack.
100.   Pate J.:  Dispersion and fallout project, Longview  paint discolora-
      -tion • Episode II. Unpublished. A description is given of the air pollu-
      tion outbreak in Longview, where the paint on several houses showed
      severe discoloration. Upon consideration of the location of the  dam-
      age and the meteorological aspects, it was concluded that the pollu-
      tion must have  arisen from a pulp  mill. Suggestions for  preventive
      action  against further occurrences are  given.
101.   Perttula, A. E.:  Novel ideas in kraft recovery reduce  losses, odors for
      Finnish mill.. Paper   Trade. J., 145:20-28. June  26,  1961. The  re-
      covery system of the Rosenlew  kraft pulp mill has incorporated some
      unique ideas that significantly add  to  its effectiveness. This system
      has reversed the position of the boiler, placed the electrostatic pre-
      cipitator before the economizer, and added a double venturi scrubber
      to the system to provide a  final cleansing of the  gases before they
      are emitted to the stack. This  arrangement necessitates operation of
      the precipitator  at the abnormally high temperature  of 600 to 800° F-
      This temperature range, however, is above the "back corona" region,
      and reasonably  high  efficiencies are obtained. Resulting high heat
      transfer  coefficients,  owing  to  the  lack  of dirt  deposition on  the
      economizer, demonstrate a marked advantage of this type of system.
      The temperature of the gases  issuing from the economizer is about
      250° F. Green liquor is used as a cleansing agent in  the venturi scrub-
      bers,  which is  advantageous because the  sodium carbonate in  the
      liquor induces  the absorption  of  the sulfur  compounds  in the flue
      gas. This system removes, on the average, 38 pounds of  sulfur and
      7.5 pounds of sodium per short ton of pulp; the efficiency is greater
      than 97 percent.
102.   Reid,  H. A.: The odor  problem at Mary vale.  Proc.  Australian Pulp
      & Paper Ind.,  3:479-500. 1949. The evolution and controlol odorous
      gases at  the Maryvale pulp mill are discussed. Emissions from var-
      ious locations in the plant were estimated; the results are presented
      in Table 30 and Figure 11.

-------
  Annotated Bibliography
57
                                                 TO ATMOSPHERE
       FIRST VENTURI      SECOND VENTURI
         STAGE              STAGE
V.
x^
HOT, CLEAN
WATER

*s V-
•s. S
^
f

1 HEAT U 	 1
f| EXCHANGER P
1 t,
COLD, CLEAN
WATER
TO GREE
LIQUOR
PLANT
^
N

•C
\
)
|_
-J
T
d
1

J~OVERFLOW
n TANK
i
N ^
CAUSTIC1ZING
P
t
]
31
DISSC
T
c
FLUE GAS
                                          FORCED DRAFT FAN
              ELECTROSTATIC
              PRECIPITATOR~
           FURNACE
                            N
r
j
— >
STACK
      Figure 10.  Schematic flow diagram of recovery system at Rosenlew mill.
       Measures taken to control these effluents at the Maryvale Mill are
 as follows:
 Digesters
       Digester  blow  gases have  been  vented through an air oxidation
 tower. Various methods have  been suggested to "even out" the sporadic
 flow of the blow gases.

-------
 Table 30. NUISANCE VALUE OF MARYVALE EFFLUENTS
Source
Gases
Digester
Evaporator
Furnace flue
Liquids
Oily condensate from
digester gas
Aqueous condensate
from digester gas
Digester foul water
Evaporator
Volume,
ft3/hr

1,000
300
3,000,000


0.05

2.0
240
8,000
Threshold odor di-
lution, 1 part in

10,000
2,000
4


20,000,000

300,000
10,000
1,500
0%
20%
40%
                               60%
                    LEGEND:
                                       PULP






                                       DIGESTER DRAIN






                                       DECKER DRAIN






                                       WASHING AND SCREENING DRAIN






                                       CAUSTICIZING





                                       RECOVERY FLOOR






                                       CLEANING






                                       DIGESTER FOUL WATER






                                       DIGESTER GAS





                                       EVAPORATOR FOUL GAS





                                       EVAPORATOR GAS
                                   SULFUR
       Figure 11.  Relative sodium and sulfur losses at Mar/vale.

-------
Annotated Bibliography
                                                                    59
           Gas
      A tower packed with blue metal has been utilized for oxidation of
black liquor. This has reduced the odor potential  of the resulting evapor-
ator gas  about 30 percent.  A much  larger tower  for this purpose is pro-
posed.
103-  Roberts,  L.  M-, and C. E. Beaver: Application of electrical precipi-
     tation equipment for  the reduction  of atmospheric pollution.  Proc.
     Air Pollution  Control Assoc..  50-59. 1951. As  of 1951, Research Corp-
     oration had in operation 67 precipitators handling 6.5 million  cubic
     feet  of gas per  minute. The  gas has  acidic  constituents;  particles
     are of extremely fine size. Collected dust is extremely light, weighing
     9 pounds  per  cubic  foot. A recent survey indicated recoveries  of 88
     to 145 pounds of salt cake  per ton of pulp  produced, the average
     being  118 pounds.  At the  average precipitator  availability  of 95
     percent, a 250-ton pulp mill recovers 4,900 tons of re-usable material
     per year.
104.  Roberts, L. M., C. E. Beaver, and W. H. Blessing: Operating experi-
     ences with Cottrell  precipitators  on sulfate recovery  furnace gases.
     Paper Trade J., 127:45-49. Oct. 28, 1948.  A general discussion is given
     on the theory and construction of Cottrell electrostatic precipitators.
     These precipitators are built in multiple units, and are rated on the
     basis of 90 percent removal for a flow rate of 2,000 cfm. The pressure
     drop between  inlet and outlet is less than 1 inch of water. A summary
     of operating experiences was prepared from questionnaires sent to var-
     ious  plants  currently  operating precipitators  of  the  Cottrell  type.
     These results  are  summarized in Table 31.
  Table 31.  AMOUNT OF PRECIPITATE COLLECTED WITH COTTRELL PRECIPITATOR
Plant
1
2
3
4
5
6
7
8
9
Production,
tons/day
225
250 to 300
630
300
288
230
450
980 to 1,120
225
Collected
precipitate,
Ib/tonpulp
88
100
145
117
135
135
130
110tol20
94
Make-up salt cake, Ib/ton pulp
Prior to in-
stallation of
precipitator
246

307

316
300
300
225
350
After installa-
tion of pre-
cipatator
158

163

193
180
170
132
256
 105.  Sands, A. E., and L. D. Schmidt:  Recovery of sulfur from synthesis
     gas. Ind. Eng.  Chem., 42(11):2277-2287. Nov.  1950.  This  article de-
     scribes process for H2S removal and sulfur recovery using dry box
     (iron oxide)  and activated carbon  catalyst.

-------
  60
                     AIR  POLLUTION
106.  Schneider, F.: Deodorization of kraft mill exhaust. TAP PI, 41:70/A.
     Jan. 1958. The most offensive emissions from  the kraft process are
     in the form  of terpenes,  mercaptans, and sulfides. Furthermore, the
     operation most responsible for air pollution is the blowing of the di-
     gesters. A process for collection and  elimination  of terpenes, mer-
     captans, and sulfides arising from digester blow gases is  therefore
     suggested. The process first condenses out high boiling terpenes from
     the  blow  gases  in  a preliminary  condenser.  The  gases  then pass
     through a continuous filter into an adsorbing unit where the sulfur
     compounds  are  removed. From  the adsorbing  unit  the gases are
      issued  into  the stack.  Since the digester  blows are discontinuous
      the absorber can be intermittently  steam-cleaned, and the resulting
      liquid can be  separated and  processed (Patent applied for).
 BLOW  GAS
     TERPENES
3
o
                        u
                                                     STEAM
                                DILUTION AIR
r
    MIXING
    CHAMBER]
                              DIMETHYL
                              SULFIDE
                               WATER
                         TO ATMOSPHERE
                               t
        Figure 12.  Schematic flow diagram of deodorization process.
107.  Schoening, M. A., L. W. Shemilt, and  R.  H. Wright:  Black liquor
      oxidation and the absorption of noncondensable digester gases. TAPPI,
      36:176-179. 1953.  A pilot scale  oxidation tower was constructed to
      study black liquor stabilization.  The packing consisted of  vertical
      asbestos sheets, the surfaces of which were imprinted with a pattern
      of raised diamonds. Black liquor was allowed to flow over the sheets
      and was oxidized by concurrently flowing  air. The spent air from
      the  column contained none of the odors characteristic of hydrogen
      sulfide or  mercaptans.  In further studies,  noncondensable  digester
      gases were allowed to flow through the column with the air supply-
      With  correct operating conditions, all the odor was again eliminated.
      This  type  of tower provides a method of  continuous black liquor
      oxidation  that  practically eliminates problems with foaming. It is
      also compact.

-------
Annotated Bibliography
                                                                      61
  Toble 32. ABSORPTION OF NONCONDENSABLE GASES IN BLACK LIQUOR OXIDATION UNIT
Chip>
Hemlock





Cedar



1-ir



Hemlock



F,r

Hemlock


Fir


Fir



Average
Air
Mow,
elm
21.2





31



21.5



21



30.2

19.4


28.7


19.4




Non
conden-
soble
gas flow,
elm
7.5





13.4



7.3



7.0



13.5

3-0


13.8


3-6




Block liquor
lead, Ib/kr
6,100





0,020



5,860



5,350



Nil

5,380


5,360


5,290




No^S content
ol Slock liquor,
5/1
To
tower
2.7





2.9



2.3



2.3





2.4


2.7


3.0




From
tower
0.7





0.6



0.4



0.3





0.4


0.6


0.6




Digester
blown
ll:24toll:35





14: 34 to 14:44



20:53 to21:07



9:33lo 9:43



11:37 to 11:49

14:25 to 14:36


15:42 to 15:52


17:15 to 17:27




Sampled
11:111011:13
Il:l4toll:l6
11:1810)1:20
11:221011:24
11:26 to 11:27
11:301011:33
14:18tol4:l9
14:28 to 14:29
14:33 to 14:34
14:41 to 14:42
20: 50 to 20:51
20:55to20:56
20:59 to 21:00
21:06 to2l:07
9:25to 9:27
9:32to 9:33
9:36 to 9:37
9:42 to 9:43
11:37 to 11:38
ll:42to 11:43
14:26 to 14:27
14:29 to 14:31
14:33lo 14:35
15:41 to 15:42
15:44 to 15:45
15:48 to 15:49
17:08 to 17:10
17: 15 to 17:17
17: 19 to 17:20
17:22 to 17:24

Gos
To lower
H^,
(.0/1
19


3



u

n
10
24
28
32
8
20
16
16
96
140
52
52
^

216
300
16
8
16
32
39
MeSH,
in/1
6,240
6,000
6,560
1.280
320
3,480
3.520
4,960


1,940
9,440
9,920
15,760
9,840
12.800
12,600
6,400
3.680
7,840
4.480
5,200
4,240
240
9,920
8,800
4,320
2,820
2,160
5,040
5,693
From
Hf.
Afl'l


















96
92
10

10





2
2

ower
MeSH,
Co/I





.16
24











1,840
1,690
192

152



60

48
448

108.  Schoening, M. A.,  and R. H. Wright: Intensity of Ihe odor release at
     various points in the kraft  pulping process. TAP PI, 35:564-569.  1952.
     A study was carried out at the Bloedel, Stewart, and Welch pulp mill
     to determine the concentrations of hydrogen  sulfide and mercaptan
     issuing from various sources. The sources investigated were:
        1. Digester relief,
        2. blow gases,
        3. evaporator effluents,
        4. furnace  gases,
        5. stack gases,
        6. washer room ventilators,
        7. green liquor  tank vapors,
        8. sewer outfall,
        9. lime sludge filter.
     Results are summarized in  Tables 33 through 39.  It was concluded
     that the blow tank and stack gases were the  major sources of odor,
     while the other effluents were minor in comparison.

-------
 Table 33. DIGESTER GAS-OFF
Chips
F.r


Hemlock


t-ir





H.-mlock





Digester
charged
10:54


9:15


11:52





10-46





Sample token
11:121011:18
11:181011:26
11:261011:35
9:50 to 9:53
9:5310 9:58
9:5610 10:03
12: lOto 12:13
12:13tol2:16
12-16tol2:21
12 21 to 12:27
12.27t« 12:34
12:34 to 12:42
10:53 to 10:58
10: 58 to 11:04
ll:04to 11:10
11.101011:17
11: 17 to 11:23
ll:23toll:29
Noncondensable gas
H2S,
cs/l
104
96
112
192
40
120




16





' 8

methyl mer-
caplan, ftg/\
13.600
14,600
6,300
6,000
9,800
7,300


920
280
1,240
1,040
120
1,000
440
400
1,230

Condeniote
HjS,
,,9/ml
18
19
14
32
41
38

'i
1
3
6
7
9
8


'2
4
Methyl mer-
captan,0g/ml
304
64
32
224
176
144












Remarks
Digester charge included 200 lt> sulfur


Digester charge included 200 Ib sulfur


No su Ifur odded'to digester charge






No sulfur added to digester charge




Table 34.  DIGESTER RELIEF
Chips
Fir


Hemlock


F,r



Hemlock




Digester
filled
7.50


7:45


11. -42



6:41




Digester
relieved
10:23


11:00


4:27



9:20




Digester
blown
10:50


11:19


4:51



9:41






10:27tolO:30
10:321010:35
10:36to 10:39
11:03 to 11:06
11:06.011:13
11:131011:19
4:33la 4:37
4:37to 4:42
4:42to 4:47
4:47 to 4:51
9:26 to 9:29
9:29lo 9:32
9:32lo 9:35
9:35to 9:38
9:38to 9:41
Noncondensoble gas
H2S,

60
76
104
16
32
64
160
93
147
73
84
104
124
32
72
Methyl
U9/I
18,300
19,600
20,400
13,400
14,700
13,500
17,300
17,500
20,800
19.500
15,200
14,600
13,500
12,000
14,000
Condensote
"#',

108
140
151
166
165
124
73
49
46
56
16
22
42
43
71
Methyl
US/ml
1,308
812
816
1,170
916
760
178
136
128
140
456
444
436
244
312
Remarks
Digester charge included 200
Ib sullur

Digester charge included
200 Ib sulfur

No sulfur adderl la digester
charge


No sulfur added to digester
charge



 Table 35. DIGESTER BLOW GASES
Chips
Fir






Frr







Hemlock





Fir


Fir

Hemlock


Hemlock


Digester
1:45






9:30







9:52





9:09


1:10

10:37


3:34


Sample taken
1-.47 to 1:49
1:49 la 1:50
1:50 to 1:52
1:52 to 1:S2>1
l:52bto I:53!i
l:53!jto 1:55
1:55 lo 1:57
9:31 to 9:33
9:33 to »:3i
9:35 to 9:36!]
9:36l]to 9:38
9:38 to 9:40
9:40 to 9:42
9:42 la 9:43!i
9:43tito 9:45
9:53 to 9:55
9:55 lo 9:57
9:59 lo 10:00
10:00 lo 10:01
10:01 lo 10:02
10:02 to 10:03
10:03 to 10:05
9:10 lo 9:14
9:14 to 9:18
9:18 lo 9:23
1:10 to 1:14
1:14 to 1:18
1:18 lo 1:22
10:37 1010:42
10:42 la 10:46
10:46 to 10:50
2:35 to 2:40
2:40 to 2:44
2:44 to 2:47
Noncondensoble gas
H,S.
»«VI
Nd°
Nd
Nd
Nd
Nd
Nd
NrJ
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd




80






Methyl
mercopton,
*g/l
12,500
31,700
49,000
93,100
99.900
102,700
51.400
5,680
11,400
12,800
16,800
23,200
19,200
30,000
22,000
11,200
33,600
36,400
49,800
29,600
38,400
16,800
4,600
3,800
19,800
3,800
3,800
30,800
800
6,200
3,300
6,600
10,400
11,700
Condensote
&
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
13
28
20
16
34
29
2
12
21
22.
31
1
Methyl
mercaptan,
*g/rnl
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
188
356
344
228
428
524
120
188
356
112
2IJ
8
Total vapor
Methyl mer-
copton, *.g/
ml at 10OC
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
Nd
198
281
578
206
424
892
85
228
272
191
322
227
Remarks
Digester charge included
200 Ib sulfur





Digester charge included
200 Ib sulfur






Digester charge included
200 Ib sulfur





No sulfur added to di-
gester charge

No sulfur added to di-
gester charge (blown
from higher than usual)
No sulfur added la di-
gester charge

No sulfur added to
digester charga

1 Notts:  Nd m«oni not doturminod.

-------
 Table 36.  EVAPORATOR JET CONDENSER EFFLUENT



May
May
May
June

25
30
31
2
Liquid effluent

H2S,
Ag/ml
2
Tr°
Tr
Tr
Methyl
mercaptan,
jig/ml
24
12
Tr
Tr
Air above liquid surface

H2S,
*9/l
Tr
4. . .

Tr
Methyl mercoptan,
*g/i
120
28
20
16
a Tr means trace.
Table 37, FURNACE GAS

Date, 1950

May 27
May 29
May 30
June 1
June 9
June 12
June 15
June 20
Noncondensable gas

H2S,

390
84
52
1
2
3

Methyl
mercaptan,
A9/I
7







Condensable gas

H2S,
•A g/m 1
2
49
52
10
3
2
9
27
Methyl mercopton,
^g/m 1
40
56
112
40
4
10
78
24
Table 38. STACK GAS

Date, 1950
June 9
June 9
June 12
June 15
June 20
Noncondensable gas,
depth 6 ft
H2S,
A9/I
3
326
119
370
460
Methyl
mercaptan,
A9/I

...

. . .
15
Noncondensable gas.
depth 12 ft
H2S,
Ag/i
42
195
204
536
420
Methyl
mercaptan,

...

36
...
Condensate combined,
6 and 12 ft
H2S,
/i g/m 1
1
7
5
15
46
Methyl
mercaptan,
It g/ml

30
10
25
28
    Schwalbe, C. G.: Removal of ihe odors in sulfate pulp mills.   Paper
    Trade J., -75:51. Nov. 23, 1922. A process  is described that utilizes  a
    tower, packed with wood chips or  straw, to  absorb the obnoxious
    gases produced  in  the  kraft  process. Since wood  has the property
    of absorbing various organic sulfur compounds, it is hypothesized
    that these products in their absorbed form react with oxygen to form
    relatively  less  obnoxious compounds.  This type of absorbent  also
    provides a surface for condensation of  the sodium salts of the stack
    gases. These solids can be washed off and re-used, and the wood chips,

-------
  64
                                                 AIR POLLUTION
 Table 39. MISCELLANEOUS OPERATION DATA
Sampling
Roof vent over knotter


Roof vent over green
liquor smelt tank

Hood over lime sludge
filter
Sewer outfall
Date, 1950
May 10,
May 24,
May 30,
May 18,
May 30,
June 1,
May 18,
May 26,
May 31,
Noncondensable gas
H2S,


...

...

a
Tr
a
Tr
Methyl
mercaptan,
32
20
4

...
16
Tr
Liquid
H2S,
/ig/m 1


...
...
...

2
Methyl
mercaptan,
/ig/ml
...

...
...
...

12
10
    o Tr means trace.
no.
111.
112.
 thereby regenerated, may be  replaced in the tower for further use.
 After use, the wood chips can be  burned as boiler  fuel. When the
 chips  are  used to purify digester  gases  only,  they  can be  cooked
 for pulp with no  adverse effects.
 Schwalbe,  C. G.:  Removal of offensive odors in sulfate  pulp mills.
 Paper  Trade J., 74:52. Jan.  19, 1922. The  amounts  of mercaptans,
 methyl sulfide, and  methyl disulfide emitted per ton of  pulp are
 stated,  and a discussion of the pollution problem, with various meth-
 ods  of contaminant treatment, is  given.
 Segal, W.:  Quantitative determination of methyl mercapian, dimethyl
 disulfide,and dimethyl sulfide  in a gas mixture. Anal. Chem.,  25(11):
 1645-1648. Nov. 1953. Studies were undertaken to determine the sulfur
 products arising from microbial decomposition of organic sulfur com-
 pounds. Evidence  was obtained that volatile sulfur compounds  such
 as methyl mecaptan and alkyl sulfide were  produced from  methion-
 ine.  No satisfactory methods were  available for the quantitative de-
 termination of these products, formed slowly  during  the  decomposi-
 tion process.  The method described provides a means of quantitatively
 determining  methyl  mercaptan, dimethyl  disulfide,   and  dimethyl
 sulfide  occurring as mixtures in gas. The method should  find appli-
 cation  where quantitative determination of  mercaptans and alkyl
 sulfides is  needed.
 Segerfelt, B.  N.: The bad odor  from  sulphate pulp mills. Paper Trade
 J., 74:95 June 8, 1952. Sources of odor and  operating conditions for
 their minimization in the  kraft process are discussed. It  is stated
 that odors  arising from the cooking  process can be  almost elimin-
ated by cooling the gases and  diluting the condensate  with  water.
 It is recommended that the operating temperature of  the  furnace be
kept high to  reduce odorous compounds further,

-------
Annotated Bibliography

113.  Segerfelt, B. N.: Method of removing malodorous gases formed in the
     sulfate and soda pulp manufacture. U.S. Patent /.£.">'/,'/?£. Apr.  19,
     1932. This method  removes malodorous gases  formed in pulp manu-
     facture by bringing them to their dew points, and treats them with
     hydrocarbons belonging to the terpene and camphor groups.
114.  Semrau, K. T..et al.: Influence  of power input on efficiency of dust
     scrubbers. Ind. Eng. Chem., 50:1615-1620. Nov. 1958. The performance
     of venturi, cyclonic spray, and  pipeline scrubbers on dust and fume
     from a black liquor  recovery furnace  and a  lime  kiln  was investi-
     gated on a pilot plant scale. Cold water was used as  scubbing liquid
     in the first two devices, and hot recirculated solution in the third.
     Efficiency data were  correlated  on the basis of total theoretical power
     input per unit of gas flow rate.
115.  Sensenbaugh, J. D., and W. C.  L. Hemeon: A low cost sampler for
     measurement of low concentration of  hydrogen sulfide.  Air  Repair,
     4:5-25.  1954. The AISI hydrogen sulfide  tape sampler is described.
     This unit operates  by forcing the sample  air by means of a vacuum
     through a paper filter  impregnated with lead  acetate. Any  hydrogen
     sulfide in the sample reacts to form lead acetate, the amount of which
     can  be determined  by photoelectric techniques.
116.  Sherwood, P. K.: Odor removal  improves public reactions. Paper Ind.,
     42:784-787. 1961.  There are several general methods of solving the
     odor problems of kraft mills. Among these are the methods of cata-
     lytic combustion,  absorption, and odor masking and counteraction.
     Odor masking and  counteraction are attractive because of their rela-
     tively low cost. A specific counteracting  compound,  however, may
     be required for each different odor.
117.  Siggia, S., and R.  L. Endsberg: Determination of alkyl sulfides  and
     disulfides. Anal.  Chem., 20:938-939. 1960.  A method  for analysis of
     alkyl sulfides, disulfides, and mercaptans is described. The procedure
     involves titration  with bromine water, the endpoint  being determ-
     ined by the appearance of the characteristic bromine color. The meth-
     od is precise  to about 0.3 percent in the best  cases.
118.  Stevens, R. H.: Report  of committee on sulfate pulp.  Paper Trade J.,
     84:142-145. Feb. 24, 1927.  (Section on  sulfate  mill  odors.) The com-
     mittee has made no direct progress on the  problem of odor abatement.
     A process has recently been proposed to eliminate digester odors by
     adding disodium phosphate. This has proved effective in experiments
     but  has yet to be  proved on a  full-scale basis. It was reported that
     a  Nordstrom drying  tower constructed  in the  Crown-Williamette
     Mill in Camas, Washington, was highly effective in reducing effluent,
     malodorous gases.
119.  Stone, J.  E.:  Progress  in  alkaline pulping—1953.  Southern  Pulp &
     Paper  Manufacturer.  Oct.  1, 1954. This  is a literature review  on
     progress in alkaline  pulping for 1953.  It  covers  the  following sub-
     jects: expansion, modernization, new mills, the cooking process, sul-
     fate  liquor cycle (including black liquor oxidation and odor control),
     stream pollution, and digester  corrosion. It has 200 references".
120.  Sultzer, N. W., and C.  E. Beaver: Alkali recovery by electrical pre-
     cipitation.  Paper Trade J., 102:33-35. Jan.  23,  1936. Losses of sodium
     salts through the stacks of recovery furnaces of both  soda and kraft
     pulp mills may cause a serious economic  loss. Tests  for the magni-
     tudes of these losses have resulted in the following data:

-------
  66
AIR POLLUTION
   Table 40. LOSS OF SODIUM SALTS a
Plant
1
2
3
4
5
6
7
8
9
10
11
12
Process
Kraft
Kraft
Kraft
Kraft
Kraft
Kraft
Kraft
Kraft
Soda
Soda
Soda
Soda
Type of
recovery
furnace
Kiln
Kiln
Spray
Spray
Kiln
Kiln
Kiln
Spray
Spray
Kiln
Kiln
Kiln
Capacity,
tons /day
60
220
110
60
100
125
38
72
50
37.5
35
100
No20 loss,
Ib /ton pulp
57
68
69
85
20
22
32
40
59
31
67
30
 a On the assumption that salt cake costs $15 per ton, this indicates that a 100-ton kraft
   mill would save $24,800 annually by collecting these compounds.
         A variety of equipment is used for particulate collection in pulp
   mill stack gases, but the  combined advantages of the  Cottrell electro-
   static precipitation equipment  seem to outweigh those of  other  types
   Electrostatic precipitators  can collect  particulate salts either as  dry
   solids, as wet  salts, or  solution.  Their efficiency is high  over a wide
   variety  of operating conditions. The electric power consumption aver-
   ages about 8 killowatt hours  per million  cubic feet  of  gas  treated.
   The pressure drop  is only about  Vz inch of water,  and labor costs are
   low. Corrosion can become a problem with  steel precipitators  handling
   Na2SC>4, and  it is  suggested that all steel  parts exposed  to the stack
   gases be  continuously  wetted  with an alkaline solution.
121.  Sylwan, O.: Practical results obtained  with black liquor oxidation.
      Paper  Trade  J., 137:14.  Sep,t. 4, 1953. A  description  is given of the
     operation  of  a black liquor oxidation plant of the  B-T  type. It is
     suggested that this  type of unit should  have many important  ad-
     vantages, even in older mills.  With the oxidation unit,  a 34 percent
     increase in capacity  of  the recovery system was observed. Important
     savings were also made because of reduced corrosion and fuel con-
     sumption owing to  the presence of the oxidation plant.

-------
Annotated  Bibliography
122.  Tomlinson, G. H., G. H. Tomlinson II, J. N. Swartz, H. D. Orloff, and
     J. H. Robertson: Improved heat and chemical recovery in the alkaline
     pulping processes. Pulp & Paper Mag. Can., 47:71-77. 1946. A progress
     report is given on the development of  additional heat  and chemical
     recovery equipment with descriptions of the various units involved.
     These are as follows: cyclones, cyclonic evaporators, oxidation towers,
     and packed columns. This material is presented with emphasis on
     economic  advantages.  It is  acknowledged, however,  that the  air
     pollution aspect is  of  extreme importance.
123.  Tomlinson, G. H., and J. M. Ferguson: Odor abatement  in an akaline
     pulp mill. 'Pulp & Paper Mag. Can., 57:119-122. Dec.  1956. The  prin-
     cipal measures employed to overcome the problem of odorous emission
     at  the Cornwall Mill have consisted  of  cooling and condensation of
     the digester blow and  relief steam, chlorination  of the nonconden-
     sable  gases, and  complete  fixation of the black liquor. These  mea-
     sures,  combined  with  control of the  sulfidity of the  black liquor,
     have  significantly reduced the "kraft odors" in the area surrounding
     the plant.
124.  Tomlinson, G. H., and H. R. Douglas: A progress report on the second-
     dary recovery of heat and chemicals in the alkaline pulp  mill.  Pulp
     & Paper Mag. Can.,  53:96-104. Mar. 1952. The  TBT recovery process
     is described, which employs  a  conventional Bergstrom-Trobeck oxi-
     dation system in the fixation of black liquor. Upon leaving the oxida-
     tion unit,  the liquor is passed through multiple effect and  cyclonic
     evaporators and then burned in the furnace. The  resulting gases are
     scrubbed in the cyclonic evaporator, two deluge towers,  and a cooling
     tower before being emitted to the  atmosphere. Resulting  hot water
     is used for  washing the brown stock. It is noted that in  former appli-
     cations  of  the B-T oxidation process the resulting minimization of
     sulfur losses at the evaporators  was offset  by  corresponding greater
     losses (as  SO 
-------
  68                                                 AIR POLLUTION


125.  Tomlinson,  G. H.,  and G.  H.  Tomlinson  II: Recovery of heat and
     chemicals from black liquor. U. S. Patent 2,840,454. Paper Ind., 40:550.
     1948. A new recovery cycle process  has been developed capable  of
     recovering almost  all the sodium sulfate fume in  the  stack  gases
     and eliminating the noxious odors emitting therefrom.
126-  Thompson, C. J., H. J. Coleman, C." C. Ward, and H.  T. Rail:  Separa-
     ation of organic sulfur compounds of liquid thermal diffusion.  Anal.
     Chem.,  29:1601-1611. 1957. The apparatus and procedure  for  thermal
     separation of sulfur compounds  from  petroleum products is given.
     Varying separation efficiencies were found for  the  different sulfur
     compounds  from  other  sulfur compounds and  from  hydrocarbons.
     In  some cases no separation  could be obtained with  the apparatus
     described.
127.  Tremaine, B. K.: Masking air-borne malodors; utilization of aromatic
     chemicals in industrial odor abatement. TAP PI, 36:143A. Aug. 1953.
     Recently, several products intended for  the masking of industrial
     odors have become available. These may be used in pulp mills in the
     following ways: Spray them into effluent  streams,  add them  directly
     to  the process,  add them to  scrubbing liquors, or  spread them on
     contaminated surfaces. The cost of  this type of measure was said
     to be about 10 to 25 cents per ton of pulp.
128.  Trobeck, K. G., W. Lenz, and A.  A. Tirade: Air  pollution  control.
     Pulp & Paper Inter., Apr. 1959. This article is a report  on the new
     TLT method of control of kraft mill odors, used at the  Loreto and
     Pena Pobre mills near Mexico City. The  method makes use of the
     conversion of mercaptans into hydrogen  sulfide,  which is  further
     oxidized by means of air. From 1  to  3  kilograms of chlorine  per ton
     of pulp is added to supplement the chemical treatment.  Odor-mask-
     ing agents are reported  only partially  effective.  Black liquor oxida-
     tion eliminates several sources of noxious odors. The digester heat
     recovery system is an  effective  control  for  offensive  compounds.
     The TLT system is described. Results of odor  measurements are
     given.
129.  Trobeck, K. G.: The B-T system for soda and heat recovery in sulfate
     pulp mills.  Paper  Trade  J., 130:40. Apr. 20, 1950.  The lT-T  process,
     successfully used for  over 6  years,  is described. This system  takes
     liquor from the evaporators  and  concentrates  it  with  superheated
     steam at 400°  C  and 10 atmospheres pressure.  The  resulting sat-
     urated steam is recirculated  to  a superheater  and  repeatedly used
      as a drying  agent. The  concentrated  liquor is  then ejected into a
     vessel at 1  atmosphere. The resultant "steaming off' creates a solid
     containing only 15 percent water,  which is then burned in the fur-
     nace. Advantages  of  this method are:

         1. Less  stack  loss from steam in flue gases,
         2. reduction of heating surfaces in the boiler.

-------
Annotated Bibliography

                   Q
                                                                    69
                                  PUMP
 LIQUOR FROM
  EVAPORATOR"
                  CONCENTRATOR
                     10 ATM
                  0
                  UJ
                  at
                  £
K^JE
                                      VAPORATION
                                         ESSEL
                                              §J,
                                                         1
                                                           SUPERHEATER
      Figure 14.  Schematic flow diagram of soda and heat recovery process.

130.  Trobeck, K. G., W. Lenz, and A. Tirado: Elimination of malodors in
     a kraft pulp mill. TAPPI, 42(6): 425-432. June 1950. Experiences in the
     Ixaft pulp mill of Loreto and Pena Pobre  indicate that only three
     sources of malodor wiH remain  if the black liquor is properly oxi-
     dized. These are:  Gases produced by the  digesters, condensates also
     produced by the digesjers, and  gases delivered by the stack of the
     recovery  boiler. An  installation for the  elimination of odors from
     gases and condensates from  digesters,  and  one similar  installation
     for handling gases going to the stack of the recovery boiler have been
     successfully  operated in  Loreto  and Pena Pobre  for about 1 year.
     Use is made of the  reaction between  chlorine and gaseous sulfur
     compounds. A preliminary treatment of the sulfur compounds with
     air in presence of water produced  a definite saving of chlorine as
     well  as some  additional  benefits.  Results of tests to improve and
     clarify the different stages of the odor elimination system, including
     black liquor oxidation, are discussed.
131.  Trobeck,  K.  G.: Some  data on the  oxidation of black liquor. Paper
     Trade  J.,  135:27-31-  July 4, 1952.  It has  been  found that  the  high
     sulfur losses as hydrogen sulfide and mercaptans  that occur in the
     evaporators of a kraft mill can be reduced by oxidation of the black
     liquor prior  to its evaporation. For  this purpose,  several air oxida-
     tion units were set up in various Swedish  plants to combine black
     liquor with air and produce a foam. This foam was then separated
     with  a cyclone and  converted to its normal liquid form by means
     of "foam-breaking" equipment.  The black liquor,  thereby  oxidized,
     was then sent on to the  evaporation units.  Besides  being  effective
     in retaining sulfur, the  oxidation systems  have markedly reduced
     corrosion in  various  parts of  the operations, especially in the evap-
     orators.  The sulfidity of the resulting white liquor was raised to an
     average  of 28.74 percent. This is compared to a previous average of
     26.16 percent. Trobeck  believes that  increased  sulfur emissions from
     other operations,  owing to the presence of the  oxidation equipment,
     prevented the  sulfidity from becoming  even higher than  the value
     obtained.

-------
70                                                   AIR POLLUTION
 Table 41. AVERAGE TUBE LIFE IN EVAPORATOR (IN MONTHS)
Effect
1
2
3
4
Unoxidized
22.0
33.4
25.3
29.2
Oxidized
More than 115
More than 103
More than 55
More than 48
   Table 42.  EXPERIMENTAL DATA ON OXIDATION SYSTEM
   Liquor temperature,  before oxidation
                      after oxidation

   Air temperature, before oxidation
                  after oxidation

   Concentration, before oxidation (% solids)
                after oxidation (% solids)

   Sulfide content,  before oxidation
                  after oxidation

   Air used, per short ton

   Black liquor solids per ton of pulp

   Total black liquor per ton of pulp
 190.4 °F
 185 °F

  68 °F
 183.1  °F

  16.1
  17.6

   0.35%
   0.07%

 1,520 Ib

 2,800 Ib

17,400 Ib
                                AIR OUT
     BLACK LIQUOR
                                      CYCLONE
                                                          TO EVAPORATORS
     Figure 15.  Schematic flow diagram of black liquor oxidation unit.

-------
 Annotated Bibliography                                              ''

 132.  Von Bergen, J. M.: Odor counteraction in kraft mill operations. Paper
     Mill News,  77:120-158. July 3, 1954.  A  general discussion of public
     relations is given with special reference to the aspects of air pollu-
     tion. The field of odor counteractant study is described, the present
     state of the art is indicated, and an experiment with a full-scale
     kraft  mill   is  cited. The  advantages  and   applicability  of  odor
     counteraction  systems are  discussed briefly. The author notes that
     a combination of two normally obnoxious odors may tend  to counter-
     act each other so  that no  strong smell is apparent. The chief advan-
     tage of odor counteraction  is that it requires  little expense  and is
     relatively simple  to apply.
 133.  Wagner, C. L.:  Alkali recovery from pulp liquors. Ind. Eng.  Chem.,
     22(2) -.122-121. Feb.  1930.  A  new  process for  the  recovery of alkali
     from wood  pulp manufacture  is described. This unit (furnace, boiler,
     induced draft fan, and scrubber)  is almost identical in  design to the
     soda and  sulfate processes.  Its function  is to burn the  volatiles  and
     fixed carbons, secure absolute combustion, return the chemicals, re-use
     them in the most  available  form,  and eliminate  wastes,  labor,  dirt,
     smoke,  and  odors.  The water scrubber  was  87 percent efficient at
     loadings less than 1 grain per cubic foot and 69 percent  efficient at
     loadings up to 2 grains per cubic foot. Emissions from furnace per ton
     of pulp amounted to: 30,400  pounds of air,  1,560 pounds of water,
     and 400 pounds of salt cake (sodium  sulfate).
134.  Wagner, C.  L.: Modern recovery  in sulfate  and soda  mills.  Paper
     Trade J., 89:82-83.  Oct. 3,  1929. In the author's  opinion, the Wagner
     recovery furnace  is one   of the most outstanding developments in
     pulp mill operations in the last decade. Developed by the J. O. Ross
     Engineering Corporation,  this  furnace utilizes several  principles,  i.e.,
     centrifugal  force,  countercurrent sprays, and  wet  contact  surfaces to
     remove and  recover 97 to  98 percent of the effluent particulate mat-
     ter.  It is also successful  in  eliminating  odor problems  arising from
     hydrogen  sulfide  and mercaptans, which are destroyed upon intro-
     duction to  the secondary  combustion  unit. The payback time of this
     unit, based  on recovery savings is stated to  be about 2 years.

 135.  Wells,  S.  D., and  K. A.  Arnold:  Kraft  pulping with  low sulfidity.
     Tech. Assoc.  Papers, 24:156-159. 1941. The benefits derived from the
     buffering  action of the sulfide in  a normal kraft  liquor may be  ob-
     tained  by  continuous injection of a  liquor of  low sulfidity  during
     cooking. A  marked reduction in  mercaptans and other  substances
     causing objectionable odors  was noted during a cook  with a liquor
     of low sulfidity.
 136.  West, P. H.: Chemical and heat recovery with  the venturi scrubber
     at Thilmany. TAPPI, 38(7):399-402. July 1955. In  1946,  a  pilot plant
     venturi scrubber, using water to clean the recovery furnace flue gases,
     was  tested  at  Thilmany;  it showed  chemical  recovery efficiencies
     of about 90 percent. A similar full-scale unit, installed in 1947 follow-
     ing the  then existing 120-ton recovery unit, substantiated these find-
     ings. Further pilot studies, employing concentrated black liquor in-
     stead of water, indicated  improvement  in heat recovery efficiency
     over that of conventional  kraft recovery systems and maintenance oi

-------
  72                                                 AIR POLLUTION

      a high degree of  chemical recovery. In mid-1951,  because of  greatly
      increased pulp production and the demand for 600-psi  steam,  Thil-
      many purchased a new 250-ton B  & W recovery unit equipped with
      a black liquor venturi scrubber. The decision to include the  venturi
      as an integral part of the unit was based on several years of highly
      satisfactory performance  from the  water scrubber,  the  black liquor
      pilot unit, and from other considerations such as capital investment,
      space requirements, operation, and  chemical and heat recovery. This
      entire unit, in operation  since May 'l953, shows chemical collection
      efficiencies of approximately  90 percent  and heat  recovery  greater
      than normal.
137.   West, P. H., H. P. Markant, and J. H. Coulter: New venluri scrubber
      developments. TAPPI, 44:710-715.  Oct.  1961. In the interest  of im-
      proving recovery of  particulates  from  stack gases, the authors did
      extensive pilot level  investigation of  the operating characteristics
      of steam-atomized venturi scrubbers. This type of scrubber differs
      from  those of the  conventional  type  in that  it  utilizes steam to
      atomize the  scrubbing   liquor in  the  venturi  throat.  After  the
      pilot test program, a  plant-scale scrubber of a similar type was in-
      stalled at the Thilmany Plant. This unit gave a 90  percent scrubbing
      efficiency for a conventional scrubber.  This  required 700 pounds of
      steam per hour,  at a  pressure of  50 psi, for a 100-ton-per-day pulp
      operation. Owing to  the  addition  of this unit, the power require-
      ments of the venturi fan  and the scrubbing liquor pumps have drop-
      ped. The thermal efficiency of the  boiler-scrubber combination has
      increased because of the reduction in temperature from 190 to 175° F
      as the gases passed through the venturi. The unit has operated sat-
      isfactorily since it was installed in 1960.
138.  Woodward,  E. R.: Chlorine dioxide for  odor  control. TAPPI, 36:216-
     221.  1953. It has been well established  by other odor-producing in-
      dustries that chlorine  dioxide is a much more effective odor counter -
      actant than either chlorine or oxygen. This compound has been suc-
      cessfully used to  remove  odorous  compounds such as amines,  mer-
      captans, and  hydrogen  sulfide.  In  view of these  properties,  it is
      suggested that chlorine dioxide be employed  in the abatement of
      kraft mill odors.
139.   Wright, R. H., M. A. Schoening, and A. M- Hay ward: The colorimeiric
      determination of  hydrogen sulfide  and methyl mercaptan in sulfate
      pulp mill  effluents and  of sodium  sulfide in  black liquor. TAPPI,
      34:289-294. July 1951.  A quantitative determination  of hydrogen sul-
      fide  and methyl mercaptan has been developed that makes use of
      the  reaction with Bindschedler's green, which forms methylene blue
      and a pink substance,  respectively. There is little interference caused
      by the mercaptans in the determination of hydrogen sulfide.  All hy-
      drogen sulfide interference is eliminated in the  methyl  mercaptan
      determination by addition of cadmium chloride and use of a filter be-
      fore the color is  developed. A colorimetric determination of  sodium
      sulfide in black liquor is  also possible by this  same general method.
      Adsorption of methylene  blue by  black liquor solids must, however,
      be prevented by addition of a cationic wetting agent to the reagent.
140.   Wright, R.  H.: The dissemination  of odors  from  krafi  mill smoke
      stacks. Pulp & Paper Mag..Can.,  56:131-134. Apr.  1955. Marked im-
      provements have been  made in  our  capabilities  to  control gases

-------
 Annotated  Bibliography                                             '**

      emitting from  digesters and evaporators. There still exists, however,
      the problem of emissions from the  recovery  furnace, which becomes
      largely one of   atmospheric  dispersion.  Because of the logarithmic
      relationship  between  concentration and the relative odor of pollu-
      tants, the problem of odor reduction is difficult. It should be realized,
      however,  that the fewer the pollutants  emitted, the smaller the area
      that will be  affected. The  atmospheric dispersion equation  of Button
      was used to analyze the behavior of  smoke issuing from chimneys.
      From this study it was concluded that  chimney design alone should
      rarely be sufficient to eliminate  odor problems. The relative  effec-
      tiveness of a stack  is  highly dependent  upon surrounding terrain
      and weather conditions.
 141.  Wright, R. H., M. A.  Schoening,  and  L. W. Shemilt: The effecl of
      black liquor fixation on the release of kraft odors. TAPPI, 36:180-183-
      1953. An experiment was conducted  in which the normal black liquor
      supply of a kraft mill recovery system was replaced  with  oxidized
      liquor. Samples were taken at various locations throughout the proc-
      ess, and appropriate analyses of  sulfur compounds were  made.  In
      spite of various  operational difficulties encountered during the ex-
      periment, it was concluded that black  liquor fixation is an effective
      factor in odor  control.
142.   Wright, R. H.: The effect of packing type on the rate of black liquor
      oxidation. TAPPI, 36:85. 1953. Oxidation of black liquor flowing over
      various  types of packing was studied,  and a method of  scale-up to
      large columns from  these data was  proposed. The packing  consisted
      of vertical sheets with various surface patterns  designed to  break up
      the  flow pattern and increase the residence  time in the column. It
      was stated that  this type  of packing  possessed significant advan-
      tages in that it decreased foaming and improved the oxidation effec-
      tiveness.
143.  Wright, R. H.: It is possible to build and operate a completely odor-
     less  krafi  mill?   Can. Pulp and Paper: Ind., Sept. 1957. The answer
     to the question of whether  building and operating an odorless kraft
     mill is  a realizable objective is only partly a technical  one. Techni-
     cally, a  completely odorless mill  is  possible  if  management is  pre-
     pared to pay the price. In discussing  the technical aspects of building
     a  completely odorless  kraft  mill, the  author  describes the  kraft
     operating sequence, sources  of dust emission, sources of odor release,
     and  measures for the  control of odors, and gives an outline of the need-
     ed research. Sources of dust  emission listed are recovery furnace, lime
     kiln, and dissolving  tank; control  methods include electrostatic  pre-
     cipitators,  bag filters, and scrubbers. Odor sources are digester gases,
     evaporator  gases, furnace  gases,  and  miscellaneous gases  (digester
      loading, vents and pressure release valves,  oxidation tower, brown
      stock washers, and others);  measures for odor control include scrub-
     bing, black  liquor oxidation, condensation,  burning, and oxidation
      with chlorine or  ozone.
144.  Wright, R. H.: Kinetics of the oxidation of sulfate black liquor. TAPPI,
      35:276-280.  June 1952.  The oxidation  rates  of black  liquor  were
      studied  at various temperatures between 40  and 90° C,  and the re-
      action kinetics were  analyzed on the assumption that oxidation occurs
      through several first-order  reactions. The data were  explained by
      the  suggestion  that  one of  these reactions has a relatively large rate

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  74                                                  AIR POLLUTION

      constant and goes to completion rapidly. When this  reaction is almost
      completed, the slower  reactions become more significant and dom-
      inate the conversion process from- then on. Since reaction rates are
      relatively slow,  it was suggested that,  for a system exhibiting a
      moderate surface area,  diffusion should become relatively unimport-
      ant  as  a rate-controlling factor. It was  therefore hypothesized that
      any attempt to raise the surface area of contact equipment  beyond
      a certain value  should not  appreciably increase black  liquor oxi-
      dation rates.
 145.  Wright,  R. H.: New  work  in krafi  mill odor control. Paper 62-99.
      Presented at the  annual meeting of the Air Pollution Control Assoc-,
      Chicago, 111. May  1962. The first significant progress in  the odor
      control field was made about 20 years ago when it was discovered
      that the oxidation of black liquor rendered its volatile gases relatively
      odorless. This operation has been studied extensively in recent years.
      Recovery furnaces may also be a major emission source. This depends
      largely upon the operating conditions of the furnace. The common
      situation  is the  overloaded furnace  that  emits hydrogen sulfide in
      high concentrations.  Several other substantial advances have been
      made in the  field of pulp mill contaminant  control, but these methods
      are  by no means fully effective. Difficulties, such  as the  foaming
      tendency of black liquor,  have  reduced the  applicability of some
      processes to  below the point that  might otherwise  be expected. One
      encouragement is the increasing demand for  the chemicals that  are
      the  by-products  of recovery processes. The profitable sale of these
      chemicals may well give  rise to a  positive  incentive  for  further
      control of pulp mill emissions.
146.  Wright,   R. H.: Odor control in  Canada. Pulp & Paper,  26:89. Jan.
      1952. In  1948 the  British Columbia Research  Council undertook an
      investigation  of kraft mill  odor  control.  Of special interest in this
      investigation  was the black liquor  fixation  process,  discovered some
      years earlier  by Bergstrom  and Trobeck. In kinetic studies of black
      liquor oxidation,  it has  been shown that chemical reaction rate  is
      the controlling step of the process when  the gas-liquid contact area
      is  large.  Also, a  new type  of tower  packing has been designed for
      this process  that  is inexpensive  and highly effective. A  pilot-scale
      tower has been built and operated successfully  for liquor rates  of
      5,000 pounds per hour. Noncondensable gases from the digesters have
      also been introduced to this tower, and have undergone a high de-
      gree of oxidation. This process has been investigated mainly for odor
      control purposes.  But the increased sulfur retention of  the black
      liquor, owing to the presence of the fixation tower,  presents another
      attractive feature.
147.   Wright, R. H-: Odor counteraction. Chemistry in Canada,  Apr. 1958.
      The purpose of this paper is  to examine  evidence for  the phenomenon
      of odor counteraction and to  inquire whether, in the light  of current
      theories of olfaction, it is a real effect. It is concluded that no sig-
      nificant evidence for the existence of a phenomenon  of odor counter-
      action exists,  and that current theories  of the olfactory process lead
      one to expect that it would  exist.
148.   Wright,  R. H.,  and R. W.  Klinck: What Port Alberni has done to
      control kraft  mill odors.  Paper Trade J.  139:22-24.  Oct.  10,  1955.
      On the basis  of prior fundamental work  on black liquor  oxidation,

-------
 Annotated Bibliography

      the British  Columbia  Research Council  undertook the  design  of a
      full-scale unit for installation at the Port Alberni kraft mill of  Mac-
      Millan and Bloedel Company, Ltd.  This  apparatus has been in  oper-
      ation  for over  a year,  during which it has produced a marked  re-
      duction  in the  odor and, at  the same  time, has benefitted the mill
      operation in  other  ways, for example, by  improving the  sulfur re-
      covery.  The purpose of this  paper is to give a short  account of the
      equipment and  the results it has secured. This is the  first published
      report  on the operation of this new odor reduction  system, which
      not only controls recovery  system  odors  but successfully absorbs
      objectionable digester  gases.
 149.  Wright,  R. Ho Pulp mill odor control. Pulp & Paper Mag. Can., Dec.
      1961. This short  article reviews some  of the more successful  mea-
      sures  of odor control now in use. With  black liquor oxidation, the
      release  of odor from the  multiple  effect evaporators is practically
      eliminated.  The  first step toward  control  of digester  gases is the
      installation  of  a heat recovery system that reduces  the volume of
      uncondensed gas to manageable  proportions. Several processes are
      now in  use  for  treating both digester  and furnace gases.  These are
      discussed. It is  clear  from  this  discussion  that  no single, simple
      method of controlling  and eliminating emission of odors  exists. It
      is worth considering the cost of not containing the malodoous gases-
      Flue gases  from a recovery furnace may carry 500 ppm or  more
      of hydrogen sulfide.  If 250  ppm is taken as  a middle value,  and
      reasonable assumptions as to gas  flow and cost of chemical make-
      up are  made, the odor from the flue gas alone represents a loss of
      $0.57 per ton of pulp produced.
 150.  Wright,  R. H.: Black liquor oxidation: View in '62. Paper Mill News,
      Mar. 26, 1962. Black liquor contains alkali, lignin residues, sodium
      sulfide, and various organic sulfur  compounds. Black liquor oxidation
      is a process  in which the liquor is made to react with air to destroy
      the sodium sulfide and  methyl mercaptan. The process reduces odors
      from the  evaporators,  conserves  sulfur, and reduces  corrosion  in
      the evaporators. It is not a cure-all, but  it does offer advantages in
      chemical economy and  odor  reduction that make it an integral part
      of  a modern kraft mill. At present,  the main obstacle to the univer-
      sal adoption of  the process is the problem  of foaming that arises in
      mills cooking highly resinous woods such  as  pine. This problem is
      being actively studied and it will not be long before practical methods
      of dealing with it are found-
151.   Wright,  R.  H.:  The reduction of odors from kraft pulp mills. British
      Columbia Research Council,  Technical Bulletin  No, 27.  12  pp.  This
      short report  discusses making pulp by the kraft process, the malod-
      orous  substances  and where they originate,  the  dispersal  of odors
      in the atmosphere, and  the principles of  odor control. It emphasizes
      black liquor oxidation.
 152.  Young,  D.  J.:  U. S.  Patent   2,115,835.  Sulfate  pulp process.  This
      process  involves  sweeping all  air out  of the digester prior to  the
      cook, and then  bleeding the air-free  gases  fom  the digester and
      burning them while cooking is in progress.
153.   Ziegelmeyer, F., and O.  Feischl:  Oxidation of sodium sulfide in black
      liquor. Paper Ind., 40:324. 1958. The oxidation reaction of black liquor
      was studied,  and the results indicated that the hypothetical equation.

-------
 76                                                AIR  POLLUTION
       2Na2S  -1-202  +  H2° =BNa2S2O3  + NaOH (minus 215 K cal)
     is valid- It was shown that the organic substances present in black
     liquor increase the oxidation rate 20- to 30-fold.
154.  Zimm, F.  P.: Abatement of kraft mill odors. Paper Mill News, 77:20-
     22.  Aug.  14.  1954. The use of "reodorants" to counteract kraft  mill
     odors is discussed. For normal operation,  a kraft mill emits  from 4
     to 6 pounds  of foul  vapors per ton of pulp  produced. The DuPont
     Alamasic  line of reodorants has been about  70  percent effective in
     reducing these odors. Meteorological factors play an  important  role
     in the effectiveness of reodorants, and more or less of the deodorizing
     compound would be  expected  to be effective, depending on weather
     conditions and the time of day.

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                           SELECTED  PAPERS
The following papers are reprinted with permission:
      Odor  and fallout control in  a krafi pulp  mill. G. A. Hansen. Jour.
      Air Pollution  Control Assn.  12:409-413.  Sept.  1962.
      Air pollution  control activities associated with alkaline  pulping.
      E. R.  Hendrikson.  18 pp. Unpublished, qa.  1960.
      Is it possible to build and operate a completely odorless kraft mill?
      R. H.  Wright. Can. Pulp and Paper Ind.,  Sept. 1957.
      New work in kraft mill odor  control.  R. H. Wright  Paper 62-99.
      Presented at the annual meeting of the Air Pollution Control Assn.,
      Chicago, 111. May 1962.

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        ODOR AND  FALLOUT  CONTROL


                IN A KRAFT PULP  MILL


                             G. A. Hansen *



                              ABSTRACT

      A brief description of  the source and  nature  of odors and fallout
 released in the kraft pulping process is  presented. Development and  in-
 stallation of operating equipment to reduce both odor and fallout around
 a modern kraft pulp mill are described. Among the processes for control are
 (1) collection and destruction of relief and  blow gases,  (2) black liquor
 oxidation, and (3) recovery  furnace and lime kiln control  to suppress odor
 release. Flyash  control  with  an electrostatic  precipitator followed by  a
 Venturi-type, water-spray scrubber  is also described.


                         INTRODUCTION

      If this paper on kraft pulp mill air pollution control had been written
 10 years ago, the discussion would have  been quite  limited. As a matter
 of fact, there would have been no paper because none of the techniques
 and processes presented here were being used on a mill scale by the Weyer-
 haeuser Company or any other company at that time; some were not even
 in the laboratory stage  yet.
      Since the  time the first kraft mill was  built back in 1891, the men
 who operated these  mills were well aware of the fact that they had an
 air pollution problem. The  first  papers concerning kraft mill odor prob-
 lems appeared in the literature around 1900.  Today,  even with  all of the
 progress in recent years, most kraft pulp mills are  still living with this
 problem. We  at  the Weyerhaeuser Company are the first to admit that
 our  various  systems  will not completely eliminate the kraft mill odors
 or fallout. However,  they will  reduce by up to 90 percent or more all odof
 and  flyash released  to  the  atmosphere. We feel that this is a  significant
 improvement. Through constant research, we are continuing our efforts
 to further reduce that  remaining  10  percent. This  will  not be easy, I
 can  assure  you.
      Before  discussing the actual plant installations,  a brief  discussion
 of the scope of  the problem is in order as there are actually two phases
 to our  Kraft Mill air pollution problem: (1)  odor and (2) flyash. In the
Technical  Director,  Weyerhaeuser Company, Pulp  and Paperboard Di-
vision, Kraft Mill, Everett, Wash.

                                 79

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 80
AIR POLLUTION
case of the Weyerhaeuser Kraft Mill  at Everett,  Washington, these prob-
lems were made doubly acute because,  over the  years, a residential area
encroached upon the industrial area where  our sawmills  are located. For
efficiency  of operation, it is essential  to locate  a  pulp  mill adjacent to its
wood supply, which, in this case, was our two sawmills.  This meant that
we had private homes within one block of our  Kraft Mill  building site.
Therefore, when the Kraft Mill  was built  in  1953, the  latest  and  most
efficient air pollution control equipment was  installed.  Furthermore, as
new techniques  and new  equipment were  developed they  were  put to
use immediately.
                          SOURCES OF ODOR

      The kraft mill odor problem arises  from the use of sodium sulfide
        as one component of the pulping liquor. This normally  amounts
to  about one-third  of  the active pulping chemical charge; caustic  soda
(NaOH)  constitutes the other two-thirds. In the digesters,  the sulfide ion
from the sodium  sulfide combines with various organic side-chain radicals
from the cellulose  and  the  lignin of wood chips to form such organic
sulfides  as  methyl  mercaptan  (CH3SH), dimethyl  sulfide (CH3SCH3),
dimethyl  disulfide   (CHaSSCHg),  and  small   amounts  of similar  ethyl
sulfide compounds.1 In addition, hydrogen sulfide is formed in consider-
able amounts.  To give  you an  idea of the quantities  involved, Table  1
shows the pounds o£ the three major odorous  compounds released per ton
of wood  for various  cooking conditions. Since the yield of unbleached  pulp
is about 45 percent  based on Cook No. 2 from Table 1, we can see that
there would be about 6-2 pounds of combined sulfur compounds released
per ton of pulp produced. Since all of these compounds  are objectionable
in concentrations as low as  1 ppm, a 300-ton-per-day kraft mill pollutes
a lot of  air if  these are released to the atmosphere. In mills  using  black
liquor oxidation  and with closely controlled recovery furnace operations,
these digester blow  and relief gases are the major sources  of odor release.
 Table 1. VOLATILE SULFUR COMPOUNDS FROM PILOT PLANT COOKS
Cook
no.
1
2
3
4
5
6
7
8
9
Mm
T-
172
172
172
172
150
160
170
182
172
Total
cooking
time,
hr:min.
3:45
3:45
3:45
3:45
5:30
4:00
4:00
3:00
3:00
Active
olkali,
•a
18
16
16
19
20
20
10
16

Sulfidity,
0
22.5
18
18.5
20
20
20
20

Sulfur compounds °
H2S
0
0.29
0.25
0.18
Traces
Traces



CH3SH
0
1.60
1.29
1.25
0.29
0.35
1.15
1.49
0.15
(CH3)jS
0
0.88
0.99
0.88
0.17
0.35
0.74
1.25
0.05
Total
0
2.77
2.53
2.31
0.46
0.70
1.89
2.84
0.2
  Lb ton 0 0 wood.
      Until the recent introduction of the continuous  digester, wood pulp-
ing had been a batch process. Generally, all kraft pulping processes follow

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 Selected  Papers
                                          81
 essentially the same steps as shown in Figure 1,  which  is a flow  sheet of
 the batch process used at the Weyerhaeuser Company's  Kraft Mill in Ev
 erett, Washington. As a  result, release of blow and relief gases  is inter-
 mittent and  somewhat erratic. Attempts to burn  these gases directly from
 their points  of  discharge have met with limited  success. Relief gases  are
 released at  irregular intervals throughout the 3-hour cooking  cycle.  Al-
 though the amount of relief gas is relatively small, it contains most of  the
 odorous gases. In addition it normally carries with it a substantial  quantity
 of turpentine from the wood  resins. All  of these materials  are  extremely
 flammable. Mixed with the proper ratio of air, they  are explosive.  Without
 a proper collection system, burning of  these organic-rich gases has proved
 hazardous. The  blow gases,  on the other  hand,  contain less of  the  foul
 gases but are released in large volumes. In our Everett plant, we blow
 a digester approximately every 40 minutes, with a total release  of about
 8,000 cubic feet of blow  gases, relief gases and steam.  To successfully "de-
 odorize" the  kraft  pulping process,  these gas streams must be contained
 and  treated.
RELIEF
CONDENSER
      WATER
   JO
 TURPENTI
  STORAGE
WHITE LIQUO
                                         BLOW STE,
                                                               .VAPORSPHERE
      [I
     LIQUOR
  MEASURING TANKS
        *"
                                           TO RETENTION
                                             POND
           VACUUM WASHERS
    KNOTTERS  X (3 STAGE)    -SCREENS  THICKENER UNBLEACHED
      f   «^» f          /         '
     £ i /BLA
     ;   ~Y ST
—        L=_
    =1    I -
             BLACK LIQUOR
              STORAGE
               TO RECOVERY 6 STAGE BLEACH PIANT
                ' ' •••••'           CHLORINATOR
                                                                   1
          •ALES TO    -^
          SHIPPING   r "~jg
            Figure  1 .  Everett kraft mill pulping and bleaching system.
      As indicated above, early attempts at  burning these gases met with
limited  success  to say the  least.  Many  recovery furnaces and lime  kilns
have  been severely jolted with gas explosions,  some  resulting in  serious
damage, when these gases were introduced directly  to  the firing zones of
these units.
      In spite of such setbacks, Weyerhaeuser approached the odor problem
from  the theory that the only logical answer was to  destroy  the  odorous
materials, not to mask them with costly perfumes. After much experimen-
tation, including  a full-scale pilot plant trial using  World War II  surplus
barrage  balloons  as  gas collectors, a suitable gas container was selected.

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 82                                                  AIR  POLLUTION

 Chicago Bridge  and Iron Works  had available  a low-pressure gas con-
 tainer called a "Vap(orsphere." This gas accumulator is a steel sphere with
 a lightweight fabric diaphragm  attached  inside  at  the  middle.  The  gas
 enters  through the bottom  and is retained under the diaphragm  which
 "floats" up and down on the gas  cushion.  Both the blow  gases and relief
 gases are  collected  in this system. As the  Vaporsphere fills, an automatic
 valve opens to discharge just enough gas to equal the net flow generated
 for each cooking cycle;  it then  closes again.  The entire system is care-
 fully sealed to keep out all air  dilution.  In  other  words,  we  eliminate
 the explosion hazard by  keeping  oxygen out of the gas mix  in the storage
 system.
      Our main problem has been to find  a diaphragm fabric that  would
 resist the conglomeration of organic chemicals  discharged  into the Vapor-
 sphere. Plastics,  rubber,  miracle  fabrics—none of these would withstand
 the attack, until Du Pont developed Mylar. With a  film of Mylar sand-
 wiched  between  two layers of  cotton  ticking,  we  have now  had  dia-
 phragms which have lasted over  27  months. The  cost on  this basis  is  but
 a fraction of a cent per ton of pulp produced.  This low cost factor is  im-
 portant when comparing this system to the cost of some of the reodorants
 and  masking  chemicals  being offered which are  only  partially  effective
 in eliminating objectionable odors in the first place.
      Containing these obnoxious  gases  is  only the  first  step in solving
 our problem. Next,  we must dispose of the  gases safely and  economically.
 While we were experimenting with the barrage balloons as gas containers,
 a local  airplane pilot volunteered  to haul them up into the  sky  to  dump
 them. Although he was apparently quite serious in his offer,  we felt there
 was a better way.
      Since the initial work on  this problem was  done at Springfield,
 Oregon, where we operate an  unbleached board mill, I will  first describe
 their system for  burning the accumulated  gases. Originally,  the  collected
 relief and blow gases were piped to an Anthony furnace designed to with-
 stand relatively severe explosions. Just before  discharging the gases into
 this furnace, they were diluted with  air at  a ratio of  more than 50:1. This
 transition from no air to an excess of air kept the gas-air mixture from
 being in the explosive range except for just the instant when the air was
 added. When the gas-air mixture entered the furnace, which  was operated
 at 1400 ° F., complete combustion of the organic sulfides and  the hydrogen
 sulfide to CO 2, SO2 and H2O took place.  Only when the furnace temp-
 erature dropped below 900° F. did any odorous compounds  pass  through
 unburned.
      After several  years' experience with the  Anthony furnace, the sys-
 tem was shown to be practical and  safe. Today,  these combined  digester
 gases are being piped to the combustion  chamber  of the lime kiln, where
 they are burned (Figure 2). Since  the firing end of the lime  kiln operates
 at a temperature exceeding 2000° F., it is more than adequate for incin-
 erating  the foul gases.  Moreover,  the heat  value of these  gases,  although
 small when compared to the total requirements  of the lime kiln, is put
 to a useful purpose. Coleman^ has described this system in  detail in the
 October  1958 issue of TAPP1 magazine.
      Where bleached kraft pulp  is  being  produced,  a  simple, safe, wet
oxidation of the combined relief and blow  gases  can  be  practiced. Nor-
mally, the  first step in bleaching wood pulp is a chlorination stage.  With

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 Selected Papers
             83
                      SCRUBBER
                              J~|  FLAME
                               |   ARRESTER
           GAS
                                              FLOW
                                              CONTROL
                                               FAN
                                   U   V^
                                FLAME
                               ARRESTER
KILN
               Figure 2.  Burning of digester blow and relief gases.


 kraft pulps it  is customary to use 10 to 20 pounds excess  chlorine per
 ton of pulp in this stage. Being a powerful oxidizing agent, chlorine readily
 oxidizes organic sulfides and hydrogen sulfide to free sulfur, sulfonyl or
 sulfoxy compounds. * The threshold of detection for these compounds  is
 several hundred times  as  great  as the original sulfides.  Thus,  by  judi-
 ciously bleeding our foul  gases  from  the  gas-accumulation  system  into
 the dropleg of the chlorination washer we  can utilize the excess chlorine
 to destroy the obnoxious  gases, as shown  in Figure 1. This system has
 been used with success in  our Everett mill since we first went into opera-
 tion in 1953.
                        RECOVERY FURNACE

      Odor release is not confined to the pulping operation in a kraft mill.
The superior economy of the kraft process  is based  on recovery of the
pulping chemicals for re-use. During the cooking cycle virtually all of
the caustic is used up in the digesters, but only about  two-thirds of the
sodium  sulfide is used—with  one-third remaining in the spent liquor.
When I say "used up," I should say that these chemicals have reacted with
acidic groups or phenolic radicals of lignin to make these lignins soluble.
To reclaim these chemical components, it is necessary to concentrate the
spent liquor  and  then  burn the organics (lignin  and wood sugars) for
fuel. Salt cake (Na2SO4)  is added to  the  concentrated black liquor be-
fore it is sprayed  into the furnace. Carbon  from the organics reduces the
sodium sulfate to sodium sulfide  in the furnace bed. Thus, the "ash" from
the furnace is a molten mixture  of sodium  carbonate and sodium sulfide,
which is drained  off and dissolved in water. Lime is added to the solution
to convert the sodium carbonate  to sodium hydroxide. We then  have our

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84                                                   AIR POLLUTION

cooking liquor components again. This, of course, is a simplified explana-
tion of what  goes on in a  recovery  system; however, it  will  serve  our
purpose here.  Figure 3 is a  schematic presentation of the system used at
the Everett Kraft Mill,  which  is virtually the  same in  every kraft mill
with the  exception  of the odor control systems  utilized by  our Weyer-
haeuser mills.
                           EVAPORATORS, 7
     BLACK LIQUOR
   OXYGEN
    METER \
   BOILER
                Figure 3.  Everett kraft mill recovery system.
      In  evaporating the  spent  liquor,  multiple  effect evaporators  can
be  used effectively to go  from around  15 percent solids up to approxi-
mately 50 percent. For efficient furnace  operation, it is necessary  to  fur-
ther evaporate  the black liquor  to  60 percent solids or more.  Normally,
this is  accomplished with  some  type  of surface-contact evaporator using
hot flue  gas  for  the  evaporating medium. We use a cyclone-type evap-
orator at Everett, while a cascade-type evaporator is used at Springfield.
      As  you know, carbon  dioxide is  one of the principal products of
combustion. When this comes in contact with sodium sulfide in water—
such as happens in the contact evaporators described above—sodium  car-
bonate is formed  and hydrogen sulfide is released.  This is precisely what
happens in any kraft mill  recovery unit not  using oxidized  black  liquor.
In a 300-ton-per-day kraft  recovery  furnace, this escapement of hydrogen
sulfide might approach 5,000  pounds per day.
      Two techniques are  practiced in Weyerhaeuser kraft mills to pre-
vent loss  of sulfur from black liquor, both in the contact evaporators  and
in the furnace itself. The principle of  oxidizing residual sulfides in black
liquor  through contact with  oxygen from the air  in a  packed tower  has

-------
 Selected Papers                                                    35

 been known for some time. However,  attempts to apply the conventional
 counter-current flow  of air up, through a packed tower generated uncon-
 trollable foam problems as the black liquor was discharged from the bot-
 tom  of  the tower. Modifying the oxidation tower to  pass  both  the  black
 liquor and the air concurrently down through the packed tower, as  de-
 scribed  by  Bialkowsky  and  DeHaas,2 reduces  foam  formation  to  the
 point where a simple foam tank suffices to allow the foam to decay.  Al-
 though  the oxidation product has not been identified to my knowledge,
 the important thing  is that the oxidized sulfur compound  is retained in
 the black liquor until it is again reduced to sodium sulfide in the reducing
 zone of  the recovery furnace.
       In addition to  black liquor oxidation, our recovery furnace is equip-
 ped with a two-pen, Bailey recording  instrument to monitor both oxygen
 and combustibles continuously in the flue gas leaving  the furnace.  DeHaas
 and  Hansen 1 have  shown that where  furnace  drafts are controlled to
 maintain 2 to  3  percent oxygen  and less than 0.5 percent combustibles in
 the flue gas, malodorous  sulfur compounds can  almost be eliminated.
       The combination of black liquor  oxidation and controlled  oxygen
 in the flue gas has reduced sulfur emission from around 5,000 pounds per day
 to less than 500 pounds.  Under  ideal conditions, we have been below  100
 pounds  per day.
                             LIME KILN

      One other  source of odor release  in a  kraft mill is the lime  kiln.
When  the recovery  furnace  "ash," or smelt,  is  dissolved in water, one
main product is sodium carbonate; the other is sodium sulfide. The sodium
carbonate is  converted to  sodium hydroxide  by  adding quicklime (CaO)
to the  dissolved smelt. In the resulting reaction,  calcium carbonate forms
and  precipitates.  In  some  older mills this  may  be discarded; but,  most
modern mills feed the wet lime mud into a rotary lime kiln and reburn
the calcium carbonate to calcium oxide and carbon dioxide. A small amount
of sodium sulfide from the smelt carries into the  kiln  in the lime  mud.
Again, the carbon dioxide  in  the kiln  gases (released from both the lime
mud and the kiln fuel) will release hydrogen  sulfide  from the sodium
sulfide unless care is taken  to prevent  it.  The  control technique is the
same as for the  recovery furnace: keep an excess of oxygen in the flue
gas.  Therefore, the kiln operator is also equipped with a recording oxygen
meter  to  monitor the oxygen  level in the  exit  gas  from the kiln.
                     FLYASH FALLOUT PROBLEM

     The second phase  of a kraft  mill  air pollution  problem concerns
particulated material—in other words, flyash which is discharged with the
flue gas. Even though the Everett Kraft Mill was built with the best com-
bination flyash removal system available in 1953, there  was still a notice-
able  emission  of flyash  in  our flue gas. In 1955 we turned our attention
toward either adapting  an existing  system or  developing a new system
to further reduce air-borne flyash from our recovery  furnace stack.

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 86
                       AIR POLLUTION
      When the Everett Kraft Mill was built, it  came equipped with  a
cyclone-type, surface-contact evaporator.  This was followed  by a  Cot-
trell  precipitator manufactured  by the Western  Precipitation  Corpora-
tion. As illustrated in Figure 4, this arrangement removed about  97.5 per-
cent of the flyash leaving the furnace. Under normal operating conditions
in a 300-ton-per-day recovery furnace,  this  would mean  roughly 150,000
pounds of flyash entrained in the flue  gas  leaving the furnace unit. Of
this, about 75,000  pounds  would  be retained  in  the cyclone  evaporator,
71,250  pounds would be removed by the  Cottrell  precipitator and,  if no
other treatment were made, 3,750 pounds would be lost to the atmosphere.
Fortunately,  kraft mill fallout consists  primarily  of sodium sulfate and
sodium bicarbonate, with minor  amounts  of sodium chloride and sodium
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 Selected Papers
87
 carbonate,  all of which are nontoxic  in  the  amounts present. They did,
 however,  constitute a  nuisance in the immediate area  around the  mill.
 Even though the adjacent residential area had developed within a zoned
 industrial area, the presence of our Kraft Mill flyash was generating some
 loss  of  community good will.  We  decided  to see what  could reasonably
 be done about the problem.
       Other mills were facing the same  problem. One kraft  mill at An-
 tioch, California, put in a second electrostatic precipitator in the gas stream
 following the first unit. As far as I know, this has been  effective; how-
 ever, this  unit is quite expensive.  Other mills  have added Venturi-type
 mixers  to bring black liquor in intimate contact with  the flyash and,  thus,
 remove it.  This is also effective  but, in addition to being expensive to
 install,  this unit  has a high power  requirement for operation. After con-
 sidering various existing techniques for the removal of flyash, we decided
 to evaluate gas-scrubber systems en a pilot plant scale.
       Ultimately,  we  developed our own version of  a  Venturi-throated
 scrubber, which operates on water. Murray 4 described the  evaluation and
 selection of this unit in the November 1960 issue of  TAPPI.  This system
 provides no chemical recovery and  it  requires about  2 million gallons  of
 water daily. It is, however,  much  less expensive  to build  and to  operate
 than systems designed to salvage the small  amount of chemicals involved.
 The  value  of the flyash could not  justify  the installation of the larger,
 more complex recovery systems. Figure 4 illustrates flyash removal from
 the furnace through the scrubber.
       That our installation is  effectively reducing flyash losses to a min-
 imum has been shown in two.  ways. As part of our program, we installed
 a permanent sample  line to the top of the recovery  furnace  stack. Dur-
 ing each shift, recovery plant personnel test  stack gases for  sodium salt
 losses. Since virtually all of our flyash components are  sodium salts, we
 have  found it convenient to  compare our  losses in  terms of pounds  of
 sodium  per day. On this basis, sodium losses before the scrubber-installa-
 tion  are compared in  Table 2 with sodium losses after  the scrubber in-
 stallation. Per cent removal is also indicated. Figure 5 shows  graphically,
 by year, the average sodium  fallout at  the filter plant  station. As indi-
 cated by the dotted line, there is a  background fallout of about 1.6 x 10"^
 ounces per square foot  per day even when the Kraft Mill is not operating-
 The  addition of a supplementary I.D. fan ahead of the scrubber  accounts
 for the  improvement in 1958  over  1957.

  Toble 2. EFFECT OF RECOVERY STACK SCRUBBER ON FLYASH DISCHARGE

Recovery stock emission, Ib /doy
Fallout at filler plant, 01 /ft /day "
Sodium loss
Before
3,000
44 x 10'5
After
300
3.6 x 10'S
Reduction, %
90
92
   Includes a background fallout of 1.6 x 10"5 02 /ft2 per day, which is present even when the Kraft Mill is not operating.
      With the recovery stack scrubber effectively controlling flyash from
that source, there was another, less severe, problem at the lime kiln stack.

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88
AIR POLLUTION
   2
   2 x
         25
   O M
   < O
   Q£ •—'
                             -- SCRUBBER
                                INSTALLED
                 1956       1957       1958       1959       1960       1961

         Figure  5.  Effect of scrubber on sodium fallout, filter plant station.
  Our lime kiln has been equipped with a Peabody scrubber from the very
  beginning of operations. However, periodic tests showed that the Peabody
  unit  removed virtually 100 percent of the lime  dust but there was an
  appreciable  escapement  of sodium salts.  Without  too much  effort,  we
  could add the lime kiln stack gas to the existing recovery stack scrubber.
  It was felt that the extra  11,000 cubic feet per minute could  be handled
  without upsetting the  effectiveness of the unit. This was done, and with
  gratifying results. Normal sodium losses  through the Peabody scrubber
  had been  in the  neighborhood of 1,000 pounds per day. The  addition of
  these gases  to  the recovery stack only increased sodium losses from  the
  main stack  from 300 to 400 pounds  per day. This resulted in a  further
  net gain of  900 pounds of sodium removed from the atmosphere.
        Prior  to  the scrubber installation, we were losing 3,000 pounds of
  sodium per  day from the recovery furnace system and about 1,000 pounds
  per  day from the  lime  kiln. The scrubber  reduced these  losses to  a
  total  averaging about 400 pounds per day. This amounts  to approximately
  90 percent reduction in flyash. After we  have completed installation of
  a  heat  exchanger to recover  waste heat from the  scrubber recirculation
  water, we hope to improve  this efficiency somewhat. Tests haye  shown
  that  the colder the scrubber water is, the more effectively it operates. We
  hope  to squeeze our sodium emissions to less  than  200 pounds per day.

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 Selected Papers                                                  69
                            SUMMARY

      To summarize, I have  described the  general odor-control systems
 currently being used in two  Weyerhaeuser  kraft mills. The systems are
 practical from a  cost standpoint and  are reasonably effective, although
 we do not  claim  them to  be  the ultimate answer to the problem. These
 systems are based on collecting and destroying the malodorous compounds
 by burning or by chlorine oxidation in the case of digester blow and relief
 gases.  In the recovery furnace and  evaporators, release of odors is pre-
 vented through black liquor oxidation and by carrying excess oxygen in
 the recovery furnace flue  gas.
      Flyash at the Everett Kraft Mill  has  been reduced  effectively by
 combining  lime kiln and recovery furnace flue gases before passing them
 through  a  modified Venturi  scrubber. Particulate matter  discharged, as
 measured by sodium concentration in the flue gas at the top of the stack,
 has been reduced over 90 percent. This is confirmed by fallout samples
 taken in the vicinity of the  mill itself.
      Perhaps the most effective evaluation of odor or fallout abatement
 programs  is  the  complaint department.  Inasmuch as the installation of
 the systems described has  reduced complaints to  the vanishing point, we
 feel reasonably certain that they are effective.


                           REFERENCES
 1.  G. G. DeHaas  and G.  A. Hansen,"The Abatement of Kraft Pulp Mill
    Odors," TAPPI, 38, 732-738 (December 1955).
 2.  H. W. Bialkowsky and G. G. De Haas,  "Stabilization of Douglas-Fir
    Kraft Black Liquor," Paver Mill  News, 74, 14-22 (September 1, 1951).
 3.  A. A. Coleman, "The Combustion of Non-Condensable Blow  and Relief
    Gases in the Lime KUn,",TAPP/, 41, 166-168A (October 1958).
 4.  J. S. Murray,  "Scrubbing Kraft Recovery  Furnace  Gases,"TAPP/,43,
    899-902  (November 1960).
 AIR  POLLUTION CONTROL ACTIVITIES

ASSOCIATED  WITH  ALKALINE PULPING


                     E. R. Hendrickson, Ph.D.*

                      ALKALINE PULPING
      Of the nearly 25 million tons of wood pulp produced in this country
each year, somewhat more than half is manufactured by an alkaline process.
The original alkaline process for producing pulp from wood was the so-called
soda process developed in England about  1854. Essentially  this method

*Air Pollution Research Laboratory^ University of Florida

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 90
                                                     AIR  POLLUTION
consisted of cooking wood chips  in a solution  of sodium hydroxide under
high pressure. A modification of the soda process is still practiced in this
country to a limited extent. Dahl, about  1890,  began investigations to im-
prove on  the basic soda  process. His studies  led  to the development  of
what is known as the sulfate process, in which a cooking liquor consisting
essentially of sodium hydrosulfide and  sodium hydoxide reacts with the
wood chips in a high-pressure  digester.  At the present time  by far the
majority of wood pulp produced in this country is  manufactured by the
sulfate  process.  Both of these alkaline  pulping  methods have  one  thing
in common,  in  order to be  economically feasible the  cooking chemicals
must be recovered. Recovery of the spent cooking liquors, while reducing
those materials  commonly discharged to a stream, may result in an in-
crease  of those materials discharged to the air. Gases and  vapors,  as well
as solid and liquid particulates discharged into  the  air in the vicinity  of
pulp mills,  have resulted  in numerous  complaints  from people living  in
the vicinity.  The industry,  through its organization known  as the National
Council for  Stream Improvement, has  undertaken  support of an  exten-
sive program of research into  the air  pollution problems which face  the
industry.  These  research programs are presently underway  at the  Uni-
versity  of Florida  and at Washington  State  University. Because of  the
relative importance of  sulfate pulping  and because  of  the peculiar  prob-
lems involved, this portion of the industry is being studied  first.
     Briefly (Figure  1), the process of  producing pulp  by   the sulfate
method consists  of placing wood  chips  into  large  digesters  along with
the cooking liquor  and heating to  about 350° F  and 115 pounds pressure
              CHIPS
          DIGESTER
          BLOW
           PULP WASHER
              PULP
                                                    PRECIPITATOR
                                                    ^/ NEW
                                                          SALT  CAKE
                Figure  1.  Odor release in the kraft process.

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Selected Papers                                                      91

for up to 8 hours. Following the digestion period,  the material is dumped
into a blow pit or blow tank,  where the liquor is drained from  the pulp.
This liquid, together with the first wash water is known as weak black
liquor and contains  the spent  reagent and  about half of the wood consti-
tuents. As mentioned previously, an essential part of the sulfate process
is recovery of chemicals from the  cooking liquors. Modern day practice
calls for concentrating the weak black liquor in  multi-effect evaporators
and direct-heat evaporators before burning in a recovery furnace to gen-
erate steam and to recover the cooking chemicals for re-use in the process.
Make-up and recovered saltcake is  added prior to the direct-heat evap-
orators. Reducing conditions are maintained in the lower part of the  fur-
nace and the carbonaceous materials are burned  off. The resulting smelt
consists  essentially  of  sodium  sulfide and sodium carbonate. When  this
smelt is  dissolved in water it results  in a green liquor in which the sodium
sulfide is converted to sodium hydroxide and sodium hydrosulfide. Since
the sodium carbonate is inert as far as the cooking liquor is 'concerned,
it is causticized by  the addition of lime to convert the sodium  carbonate
to sodium hydroxide and  precipitate calcium  carbonate. The calcium  car-
bonate is recovered in a  lime kiln for re-use in  the causticizing process.
The causticized solution, called while liquor, is  ready for use in cooking.
Before the digester  is charged with  the white liquor,  a quantity of black
liquor is frequently  added to it.
                       AIR POLLUTANTS

      From this brief description of the process, it would appear that the
three  major sources of air-borne  emissions are from liquor  preparation,
cooking,  and chemical recovery, and  that  both particulates and  odorous
gases  might be involved. Actually the air-borne wastes from sulfate pulp-
ing consist mainly of:
   1.  Solids from the:
       (a)   Recovery furnace,  composed of sodium  sulfate and  sodium
           carbonate plus carbon particles.
      (b)  Lime kiln, composed essentially of lime dust.
      (c}  Power plant, composed of  flyash, soot, or unburned bark, de-
           pending on the fuel used.
   2.  Mists from the:
       (a)   Recovery furnace.
       (b)   Lime kiln.
       (c)   Dissolving tank.
       (d)   Causticizer.
       (e)   Digester.
       (f)  Blow tank.
   3.  Odorous  and nonodorous gases from the:
       (a)   Recovery furnace,  composed essentially of sulfur dioxide and
           hydrogen sulfide.
       (b)   Lime kiln,  containing smaller  quantities of the  same  two
           gases.
       (c)  Power plant,  consisting of sulfur dioxide if the furnace  is
           being operated properly.

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 92                                                  AIR POLLUTION

         (d)  Digester relief, containing inorganic and organic sulfur com-
             pounds, such as hydrogen sulfide, methyl mercaptan, dimethyl
             sulfide, and dimethyl disulfide.
         (e)  Blow tank, containing the same  compounds.
         (f)  Turpentine recovery.
         (g)  Evaporators, consisting of hydrogen sulfide, methyl mercap-
             tan, dimethyl  sulfide,  and dimethyl disulfide.
 Other sources are  active,  but those  mentioned  are believed to be  the
 major ones.  In terms of volume, the off-gases from the recovery furnace
 make this the major source.  Digester relief gases, blow  gases, and  the
 off-gases from the  evaporators represent  a considerable  smaller volume,
 but have a potentially higher nuisance value.
                     EFFECTS OF POLLUTION

      The  possible effects  of air-borne emissions  from sulfate  pulping
are numerous (1). In  the  immediate  vicinity of mills, objections  are fre-
quently raised  about the effects of  fallout  from recovery furnaces, lime
kilns, and bark burners. Vegetation damage has been attributed to fallout
and  sulfur dioxide. Damage to structural materials and painted  surfaces
has been reported  from  air-borne saltcake particles and various sulfur-
containing gases. Lead base paint may be blackened in  the presence of a
sufficient concentration  of  hydrogen  sulfide  under  specific conditions.
Fallout, of course,  may be in the form of saltcake, flyash, soot, burned
bark  and wood  particles, and lime. As mentioned,  some of these actually
do damage to materials,  vegetation,  and painted surfaces. Others merely
contribute to the general dirtiness  of the  surrounding area. The larger
particles are usually deposited  close to the source, but smaller  particles
may  be  carried  several  miles.  Those which remain suspended in the  air
contribute to  visibility  interference,  sky  darkening,   interference with
transportation services, and may help to carry odors long distances.
      Health hazards from concentrations of gases found in the area around
sulfate pulping operations are not considered to be  of serious consequence.
Of the compounds which might be involved, the toxicity of sulfur dioxide
and  hydrogen sulfide are well known, but  little  is known about  the true
air  pollution signatures  of sulfate pulping: mercaptans, dimethyl sulfide,
and  dimethyl disulfide. The  limited  data presently available indicate that
hydrogen sulfide is about ten times  as toxic to rats as  disulfide and mer-
captan. From observations on  the concentration of hydrogen sulfide  in
the vicinity  of  sulfate pulping operations, it  has  been tentatively con-
cluded that toxic gases are not at sufficient concentration in  the vicinity
of such operations to justify air  pollution control  on the basis of health
hazards.  Although no disease or infirmity has  been proved to be directly
caused by odors per se,  odors  in the vicinity of  pulping operations are
considered unhealthy by the uninformed.  At least they are considered
obnoxious by many people, and as such, they might be held  to constitute
a nuisance. If a  recent court decision starts a  trend in  this  direction, the
encroachment of odors on private property could  be considered  trespass-
It is  known  that under appropriate  weather conditions,  which fortunately
are not present all the time, the odor from  sulfate  pulping may be notice-
able many miles away.

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 Selected Papers                                                     93

       Paint  damage in the form of discoloration by hydrogen sulfide is
 one of the most  common  complaints around sources of  this gas. Recent
 investigations by  the paint industry have  thrown some additional  light
 on the blackening effects of hydrogen sulfide. It might be well  to point
 out that many  master painters, paint  salesmen,  and paint manufacturers
 still hold  that  a  lead-pigmented paint is necessary for the best outdoor
 coating. Most fume-resistant paints contain titanium  oxide as the main
 pigment, but many of the best outdoor paints contain some quantity of
 lead  pigment to  improve  weathering. The major  conclusion  reached in
 the study  by the  paint industry (2) can be summed  up  by saying that any
 concentration of  hydrogen sulfide  present  in the atmosphere will pro-
 duce darkening of paint containing  lead pigments in time if the paint sur-
 face  is actually wet  with water. The researchers found,  however, that
 blackening is considerably  delayed  if the lead content  of  the paint is  low
 and if the paint  film remains  glossy and  unweathered.
       Solutions to some of the problems of  air pollution  facing the  in-
 dustry are not easily forthcoming. Research on projects  at universities
 and at individual mills is slowly producing results. The objectives of the
 two university  projects previously mentioned were  originally aimed at
 immediate investigation of control activities through a multiple approach.
 It was soon  found, however, that one of the first needs was adequate and
 accurate sampling methods and the original objectives  thus  had  to  be
 postponed while  sampling was investigated. Work on  the two  projects
 has been  reported  previously  in the  technical  bulletins of the National
 Council for  Stream Improvement (3). Research activities in the individual
 mills have been more directly aimed  at control. Unfortunately, many of
 these  developments never  appear in the literature.
                  CONTROL OF  PARTICULATES

     Many activities of the industry which  result in a lessening  of air
pollution potential, fortunately result also  in economic recovery of raw
materials or  product.  In fact, the units most responsible  for reducing
particulate  air  pollution from sulfate  pulping were originally installed
and later improved to reclaim valuable saltcake. For some time, practi-
cally all sulfate mills have been designed with cyclones and high-efficiency
electrostatic precipitators or Venturi  scrubbers on the  recovery  furnace.
Twenty years ago, the process required an average  of  about  300 pounds
of make-up saltcake per ton of pulp.  Today many  mills  operate  on 80
pounds or  less. At a  mill  producing  500 tons of  pulp a day, this  repre-
sents not only a savings  of  the cost of some 55 tons of saltcake daily, but
this amount  is no longer  spread  around in  the environment. For many
years, other important savings have been realized by appropriate scrubbers
on lime kilns, by  condensing digester relief  and  blow  gases  from  which
turpentine  and other compounds can be reclaimed, and by converting from
disc-type evaporators to  multiple-effect  units. Discharges to the  environ-
ment also have been reduced by improved  combustion practices in  power
boilers utilizing waste wood residues and in recovery  furnaces.
      More recently the  industry, stimulated  by an increase in air pollu-
tion  legislation  and encouraged by  improved sampling techniques, has

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 94                                                 AIR POLLUTION

developed new  ways of reducing  air-borne emissions to an  even lower
level. Some of the procedures are  not  yet  in  widespread use, but have
been quite successful in plants where they are practiced.  At present, three
general approaches are being used  for reducing odors and reducing fall-
out from recovery  furnace particulates.  To improve saltcake recovery,
secondary scrubbers have been installed in  some instances following pri-
mary collection devices such as electrostatic precipitators.  In general, it
is  not the purpose  of  these  secondary  scrubbers  to collect particles too
small to be collected by the  primary devices, but rather to reduce losses
caused by carry-over. An added dividend is  obtained since these scrubbers
also collect some gaseous material and thus reduce the amount of make-up
sulfur required. The secondary scrubbers may take any of several forms
although most of  them are commercially available devices. Venturi scrub-
bers  as  well as spray-type washers are popular (4).  Although the  Ven-
turi unit is most  effective in some  respects, the pressure loss through the
device may be as high  as 25 inches  of water. Loss  in the spray-type scrub-
ber, on the other  hand, may be only 0.5 to 6 inches  of water.  Water,  weak
black liquor, or both are used as scrubbing liquid. Generally, the scrubbing
solution is recirculated to a fixed salt  content. Normal  loads to the sup-
plemental scrubbing devices  are said to be 0.05 to 0.15  grains per  cubic
foot. This compares with 3 to 5 grains per cubic  foot as the  load on the
primary collectors. Since the secondary units  are not intended for high
dust loading, they will clog readily if the primary device stops functioning.
The soda ash in the effluent is probably recovered as  sodium carbonate
because  of the carbon dioxide content of the  flue gases. In order to  function
properly and  eliminate environmental problems rather than merely trans-
fer their location,  it is essential that some effective  type of mist  elim-
inator be installed  on the effluent line before discharge. A number of
commercial devices are available,  but frequently a tall  stack will  serve
as a mist eliminator. In mills where secondary  scrubbers are installed,
they reportedly are performing with satisfaction.
      Mist losses  from dissolving tanks have been  a  source  of local an-
noyance in pulp mills. The  most recent  attempts to control such emissions
have made use  of mesh demisters.  The mesh fibers are usually of stain-
less steel or  plastic and frequently are backwashed with water.  At one
installation (5), it is reported  that  99 percent  of all droplets  over 5ju di-
ameter are recovered.
                        ODOR REDUCTION

      One recent  approach to odor control  is collection and oxidation of
blow gases and digester relief gases. The most satisfactory way of collec-
tion appears to be removal of the  condensable fractions followed  by stor-
age in a floating-cover or diaphragm-type gas holder. The gas holder floats
on  the line  to take care of surges that  occur  during a  blow. Oxidation
of the collected gases  has been accomplished by burning and by mixing
with  bleach plant effluent. Several mills  have installed equipment in-
tended  to oxidize the sulfur  compounds by burning. Pure  digester relief
and blow gases are reportedly nearly free of oxygen. According  to De
Haas and Hansen (5)  the  gases should not contain more than 5 percent
oxygen, or a mixture of gas and air should  contain no more than 0.5 per-

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 Selected Papers
95
cent total organic compounds- All organic sulfides are reported  to be  de-
stroyed at 1200° F. The flame propagation rate in mixtures of these  gases
is less than 90 feet per second. In one early installation of this type, an
Anthony furnace  was used  as the combustion unit and was  operated at
1400° F.  This  furnace was fueled with  turpentine, fuel oil, or gas. The
non-condensable fraction  was  stored in  a gas holder  and metered into
the furnace. Operating difficulties, as well as potential  fuel savings, promp-
ted a change  about 2 years  ago. The  gases are  now  burned  in the lime
kiln. Coleman (7) reports  that the gas. now flows  through a rock scrubber
to remove turpentine mist,  through  a flame  arrester,  a flow  controller,
and  another flame  arrester before being diluted  in the primary air-duct
to the kiln. This arrangement is shown in Figure 2. The noncondensables
require dilution with  19  or more volumes of air  so the flow controller is
set to provide a fixed rate. Both the primary air fan and the induced draft
                                      MIXER
                                                     ADSORBER
 §
 o
                  CONTINUOUS
                   WET FILTER
                               Figure  2.
fan on the kiln are  electrically interlocked with the  flow controller to
shut off the gas if either fan stops. Rupture plates have been placed along
the gas lines in several locations. Noncondensable digester relief and  blow
gases  are readily oxidized with bleach plant effluent. For the usual con-
centration of chlorine in this waste, about  four volumes of  effluent are
required to each volume of gas. The simplest method of contact is to in-
troduce the gas flow into the dropleg of the bleaching unit. Combustion
of these gases has the advantage of possible recovery of heat and sulfur.
It has the  disadvantage, however, of requiring  elaborate  precautions to
prevent explosion. When the gases are oxidized with bleach  plant effluent,
neither heat nor sulfur can be recovered.
      Another recent approach to  assist in odor reduction has been under-
taken in a number of  mills in the northwest where  black liquor oxida-

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  96                                                 AIR POLLUTION

 tion units are installed. In theory, oxidizing the sulfur compounds in the
 liquor before evaporating and burning will prevent the formation of many
 of the odorous compounds  which are otherwise  released. Actually,  black
 liquor oxidation  is effective only  on the release of odorous gases from
 vacuum and direct-contact  evaporators.  Some improvement may be noted
 in the recovery  furnace  where  combustion may result  in  less hydrogen
 sulfide production, ft is reported that in some types of furnaces, oxidized
 black liquor burns better than unoxidized. Black liquor oxidation also has
 no  appreciable effect on  digester relief and blowgases.  Collins (8) reports
 that a high degree of black liquor oxidation results in a  reduction of  sul-
 fur losses     from evaporators of  more than  90 percent. Sulfur losses
 according  to  various   investigators,   may   average   from  1  to 15
 pounds per ton  of pulp  where black liquor oxidation  is  not practiced.
 Wright et  al  (9)  pointed  out, however,  that black liquor oxidation is no
 cure-all for odors since odor control  must be judged on,anall or nothing
 basis. The  public generally is  concerned more  with the presence or  ab-
 sence of odors than their intensity.
       Black liquor oxidation units take three  general forms: packed towers,
 thin-film oxidizers, and porous-plate aerators. These  various types of units
 have the advantages and disadvantages well-known to chemical engineers.
 Air  is used as the source of oxygen and  except in those cases where pine
 is pulped, no excessive foam is  produced. As you progress eastward across
 the  country, more and more severe foam  problems are found  until they
 reach  their peak  in the pine pulped in the southeast. Because of the ad-
 vantages of black liquor oxidation, a special  study is underway at the  re-
 gional  laboratory  of the  National  Council  for  Stream  Improvement in
 Baton Rouge. This study is  aimed specifically at  the application of black
 liquor oxidation to  southern pulping conditions. The thin-film unit devel-
 oped by the British Columbia Research  Council reportedly has been suc-
 cessfully applied  to southern operation.  The use of tonnage oxygen has
 been reported by several investigators <10,11), but  under the  conditions
 of the studies  pure oxygen  was not found to be suitable. The Air Pollu-
 tion Research  Laboratory at the University of  Florida is undertaking a
 study  of black liqour oxidation  using tonnage oxygen which appears feas-
 ible. In addition to no foam formation, potential heat recovery  is promis-
 ing.  Several mills on the west  coast which  utilize packed towers for black
 liquor oxidation have attempted the destruction of odorous gases  from
 the digester and blow  tanks in  the oxidizing  unit  (12). DeHaas (6) reports
 that while  nearly all of  the hydrogen  sulfide  was destroyed, about 45
 percent of the mercaptans and  90 percent  of the  dimethyl sulfide passed
 through unchanged.
                        OTHER CONTROLS
      The recent literature contains a proposal for treating blow and re-
lief gases to  recover salable chemicals  (13). It is not known whether the
complete process is in  full-scale use in any mill in this country. Schneider
proposed the condensation of the condensable fractions of the ^ases to re-
cover terpenes. A wet filter would remove any fibers present in the offgas
following which outside air would be mixed with the stream to cool  it to
about 100° F. Activated carbon is suggested as an adsorption medium  from
which mercaptans and sulfides could be recovered. It is proposed that the
adsorbers be regenerated and stripped by steam with the steam condensed

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 Selected  Papers
97
 to  remove  water and  dimethyl sulfide. Any mercaptan and sulfides in
 the water maybe decanted and fractionated. The gaseous mercaptan  which
 would pass through  the condenser would be  contaminated with dimethyl
 sulfide, but could be liquified and fractionated.  A scheme for accomplish-
 ing this proposal is seen  in Figure 3. The  author reports that  at present
 prices,  the  cost of the proposed installation would be  low enough  to  re-
 cover the capital investment in two years- The value of recovering sul-
 fide alone for a 300-ton-per-day plant would  amount to tens  of thousands
 of  dollars each year.
  O
  O
  ef.
               PRIMARY
                AIR
                                   LIME KILN
                               Figure  3.
     Several practices  to  remove  odo.rs  have been in vogue abroad for
a number of  years  but  have not yet found favor in  this country. Many
of them have been investigated here but  they have not yet been put into
practice.  For  example, Collins  (8)  reports that oxidation of  black liquor
by the addition of peroxides and  other  chemical oxidizers  was  studied
but was found to be impractical economically. Reduction  of odorous com-
pounds in the gas stream has been attempted by  using chlorine  dioxide,
chlorine,  ozone,  catalyst,  and adsorption  of  wood chips. Work  was re-
cently  completed at the University of Florida on catalytic  oxidation  of
some of the organic sulfur compounds  found in pulping  operations. With
further investigation, the results of this  basic research may  soon be ap-
plied to plant operation.

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 98                                                  AIR POLLUTION
      In  most sulfate mills, improved design and improved  operation  of
 the  recovery furnace can  pay large dividends.  The recovery  furnace  is
 intended  to serve as a  reclaiming  unit  for  cooking chemicals in a re-
 ducing  zone near the  bottom and a heat-recovery  unit in  a  secondary
 combustion zone  near  the top.  Adequate secondary air and sufficiently
 high temperatures can result  in greater  heat recovery by oxidizing the
 hydrogen sulfide  to  sulfur dioxide.  The  sulfur dioxide can then  be ab-
 sorbed  from the gas stream in a  wet scrubber and  the sulfur losses re-
 duced still  further.
      This  paper  has been able to cover only briefly,  some  of the steps
 being taken to control  air pollution from  alkaline pulping operations.
 Further research  into many of  the  problems of air pollution  which po-
 tentially face the pulp industry is urgently needed.  Some of the investi-
 gative work can best be undertaken at  individual mills. Other problems
 should represent a group effort and  be logically handled at existing proj-
 ects  established at universities and research institutes. This industry  is
 developing  sound approaches to the solution of its air  polution problems.
 From my personal experience with air  pollution, control activities, con-
 trol  agencies  look with considerably more favor on industries having  a
 planned program of attack on  their air pollution problems and a research
 program in existence before they encounter serious  trouble.
                           REFERENCES
 1.  Hendrickson,  E.  R., TAPPI, 43, 193A (March  1960).
 2.  Ward, G. B.,  Official  Digest of the Federation of Paint and Varnish
    Production Clubs,  28, 1089 (1956).
 3.  Atmospheric Pollution Technical  Bulletin Series, Nos.  1-14, National
    Council for Stream Improvement,  Inc., New York.
 4.  First, M. W., H. E. Friedrich,  and R.  P. Warren, TAPPI, 43, 182A
    (June 1960).
 5.  Bernhardt, A. A., and J. S. Buchanan, TAPP143, 191A (June 1960).
 6.  DeHaas,  G. G., and G. A. Hansen, TAPPI, 38,732 (1955).
 7.  Coleman, A. A., TAPPI, 41,  166A  (October  1958).
 8.  Collins, T. T., Paper Trade J. 130, 37 (January 19,  1950).
 9.  Wright, R. H., M. A. Schoening, and  L. W. Shemilt,TAPP7, 36, 180,
    (1953).
10.  Fones, R. E.,  and J. E.  Sapp, TAPPI, 43,  369 (1960).
11.  Murray,  F. E.  Project Report 59-36, British Columbia Research Council,
    Vancouver (June 9, 1959).                               I
12.  Bialkowsky, H. W., and G. G. DeHaas,  'Paper Mill  News, 74,14 (Sep-
    tember 1, 1951).
13.  Schneider, F.,TAPP/,41, 70A,  (January 1958).

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 Selected Papers
99
            IS  IT POSSIBLE  TO BUILD

                  AND  OPERATE   A

 COMPLETELY  ODORLESS KRAFT MILL?

                          R. H. Wright *


                          PART  1.
     A COMPLETELY odorless mill is 100 percent free from odor,  not
99 percent or even  99.9  percent free, but 100 percent odorless. The  an-
swer to the question of whether this is a realizable objective is only partly
a technical  one. Technically,  the answer is  that a completely  odorless
mill is possible if management is prepared to pay the price. But the price
is made up of three parts and all three parts must be paid in full.
                  THE ECONOMIC APPROACH

               TO BE FACED BY MANAGEMENT

     The first part  of the price consists of an initial down  payment
for odor control equipment, including enclosures and collecting ducts and
decontaminating apparatus to treat all the effluents leaving the mill. Some
of these, like the smoke stack, will be needed anyway, others  will not

* Head, Division of Chemistry, B C Research Council

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 100                                                 AIR POLLUTION

 be normal adjuncts to mill operation, but will be  especially designed for
 the purpose  of containing an odor which  has heretofore been allowed to
 escape uncontrolled.
      After  the down payment has  been made  there  will be instalment
 payments  which will go on as long as the mill  continues to operate. The
 instalment payments are partly direct and  partly  indirect.
      The direct instalment payments are the costs of maintaining all the
 odor control equipment  at  top  efficiency. This does  not present  much
 difficulty in the cases  where the  equipment directly  assists the process
 of making pulp: it is usually not very difficult to  convince the  operators
 of the importance of keeping a chemical and heat recovery system in first-
 class condition. It  may  be more  difficult to ensure the same  degree of
 maintenance on a  duct  and fan intended to collect a few cubic feet of
 foul gas from a tailings  chest or foam breaker But if  a completely odor-
 less operation is to be achieved, all the odor control equipment must be
 kept at top  efficiency. Several technically excellent odor control systems
 which have  been built  at one time or  another have failed primarily for
 this reason. It is therefore most important that the odor  control  measures
 shall interfere  as little  as possible with normal  mill  operation,  and that
 they shall give  a minimum of trouble and require a minimum  of main-
 tenance. Unless this requirement is met they are not  likely to be  ade-
 quately served and maintained  by the operators whose primary respon-
 sibility is, after all,  production. Odor control equipment must be acceptable
 to  and accepted by the operators, and must be designed accordingly-
      Even more important than the  direct instalment  payments are the
 indirect instalment  charges. These arise whenever it is necessary to  limit
 production to prevent odor emission.
    DESIGNED  CAPACITY AND  ODOR-FREE OPERATION

      For example a mill designed to produce 300 tons of pulp daily could
probably turn out  425 tons if everything were run at maximum overload,
but the operation  might cease to  be odorless at anything over 350 tons.
Under these  conditions, odor-free  operation would require that  the  mill
never be operated  at more  than 50 tons per day above its designed capac-
ity. This is a very real situation inasmuch as the most common limiting
factor in output is the amount of overload that  can be heaped on the re-
covery furnace, and when overdriven the furnace may generate unmanage-
able amounts of odor. The difference in output between the odor-free level
and the absolute maximum level at which the plant can be driven is dif-
ficult to estimate in advance, but it is probably  the largest charge against
the odor  control system.  Indirect payments must also  be  made  when-
ever it is  necessary to shut down the whole mill on account of some pos-
sibly  quite minor breakdown in the odor control equipment (in an extreme
case,  perhaps, nothing more than a  broken window).
      Breakdowns in odor •controlling apparatus  can be minimized (though
not wholly eliminated) by  good design and in some  case's duplication  of
equipment, and it may be possible to over-design the odor control' facilities
to a point where the limiting factor  may be somewhere else, but the fact
thai the odor control programme can impose an indirect cost by limiting

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 Selected Papers                                                  101

 production must be squarely faced  and accepted at  every level of the
 organization.
      If this is accepted, then an odorless mill can be realized.
      If this is not accepted, then there is little point in making detailed
 estimates of the initial down payment and direct instalment payments on a
 "completely odorless mill" because the mill will not be  completely odorless.
      A preliminary consideration of the technical problems suggests that
 the direct costs of a complete odor control system would not be excessive
 nor would they all be pure outgo. The release of dusts and odors repre-
 sents a loss of material  whose recovery (possibly with the simultaneous
 recovery of heat) would  constitute an operating economy. Moreover, some
 of  the odor control measures may be directly beneficial  to the process, as
 for example, when black liquor oxidation gives smoother evaporator opera-
 tion,  less corrosion, and  reduced carry-over  of  chemicals into the  hot
 condensate  which can then be used on the brown stock washers with the
 production of cleaner pulp.
                           PART   2.



        THE  TECHNICAL ASPECTS   OF

A  COMPLETELY  ODORLESS  KRAFT MILL

     THE  UNPLEASANT, cabbage-like odor,  which is characteristic of
the  kraft process and is commonly called the "kraft odor," is due mainly
to a group of organic sulphur compounds of which  the most important are
methyl mercaptan and its oxidation products, dimethyl disulfide and dime-
thyl sulfide. These and possibly other malodorous substances are formed in
the  digester by  chemical reactions between the  cooking  chemicals, es-
pecially sodium sulfide, and certain constituents of the wood. They are,
therefore, inseparable from the  kraft process  and its odor-free operation
will depend on methods  for retaining them in the system or converting
them to innocuous substances before allowing them to escape.
     Certain parts of the process may also give rise to an emission of dust
and it is generally desirable that this form of air  pollution be minimized
if possible by the same equipment as that used to contain the odors.
                KRAFT OPERATING  SEQUENCE

     Figure 1 shows the usual sequence of operations in producing kraft
pulp. Wood chips are  cooked at about 175° C with a solution containing
sodium sulfide and sodium hydroxide. When cooking is complete the digest-
ers are blown into a blow tank and the steam which flashes off  may be
passed into some form of heat recovery system. The pulp is then separated
from knots and incompletely-cooked chips and washed more or less free

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 102
AIR POLLUTION
                                                             I. DIGESTER
                                                             IA. DI6ESTER RELIEF
                                                             IB. DIGESTER BLOW
                                                             2. BLOW TANK
                                                             3. ACCUMULATOR
                                                             4 OXIDATION TOWER
                                                             5. MULTI EFFECT
                                                             •   EVAPORATOR
                                                             6. DIRECT CONTACT
                                                                EVAPORATOR
                                                             7. ELECTRIC
                                                                PRECIPITATOR
                                                             8. MAKE . UP
                                                             9. FURNACE
                                                            10. CONTAMINATED
                                                               HOT WATER
                                                            II. SEWER
                                                            12. SEWER OUTFALL
                                                            13. DISSOLVING
                                                            14. CAUSTICIZING
                                                            IS. MUD FILTER
                                                            16. LIME KILN
                                                            17. SLAKING
                                                            18. KNOTTER
                                                            19. WASHER
                                                            20. SCREENS
                                                            21. DRIER
                                                            22. TAILINGS
                                                            23. FOAM TANK
                 Figure  1.  Odor release in the kraft process.

from the spent  cooking liquor, or "black liquor," and the  latter is then
concentrated  by  evaporation first in the multiple-effect evaporator  and
then in  a direct contact evaporator using hot flue gas from the recovery
furnace- The  concentrated black liquor is burned  in the recovery furnace,
after adding the necessary make-up, chemicals. In the furnace carbonaceous
matter is burned, sodium hydroxide is converted to sodium carbonate, and
sulphur  compounds  are converted as far as possible into sodium sulfide.
The molten "smelt"  from the furnace consists mainly of sodium carbonate
and sodium sulfide and is  dissolved in water to give "green liquor"  which
is then recausticized with a soluxion of slaked lime to give white liquor,
which is then  sent  back  into  the  digester. The  calcium carbonate  that
is formed in  the recausticizing may be collected on a filter  and  reburned
to calcium  oxide which is then slaked and  used to recausticize a further
lot of green liquor. The furnace gas, besides containing the usual products
of combustion, also carries a substantial load of particulate matter, mainly
sodium sulfate and sodium carbonate which  is usually collected by an elec-
trostatic  precipitator and  returned to the system.
       Thus, two types  of  air pollution may result from  this sequence of
operations: pollution by solid particles and pollution by objectionable odor.

                           DUST  EMISSION
      The following is a fairly representative analysis of the  particulate
matter entrained  in the flue gas:

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 Selected Papers                                                    103

                                 Nad                 17.6%
                                 Na:COs               36.4
                                 Na^O,                33.6
                                 Na^Oa                 4.4
                                 NaOH                 2.0
                                 Na,S                   0.7
                                 Carbon + undetermined  5.3

 The sodium chloride in this sample was derived from  the pulping of logs,
 which had been floated in salt water, and  it would be practically absent in
 an inland mill.  The rest of the components, with the exception of sodium
 sulfate, tend to  be markedly caustic and can damage or kill vegetation and
 mar the paint on automobiles for  distances of from  1  to 2  miles  down-
 wind  from the mill. The  control  of  this type of  pollution is therefore
 important, when a  pulp mill is  located near a built-up area or a farm-
 ing region.
      In addition to the fall-out of dust from the main stack,  there may be
 additional  fall-out  of particulate matter  from two  other  sources.  If the
 lime kiln which produces quick-lime  for  the recausticizing process  is op-
 erating wholly or in part on the precipitated calcium carbonate filter cake,
 there will generally be some entrainment of lime dust contaminated with
 a small proportion  of sodium salts  unless the lime kiln stack is provided
 with an efficient scrubber, in which case the dust load is usually negligible.
      The other source of dust is the dissolving tank. In many mills the red-
 hot smelt from the recovery furnace is  allowed to flow in a relatively mas-
 sive stream into the  dissolving  tank.  This  usually  results in very noisy
 operation with a copious liberation  of steam and occasional  explosions in
 the dissolving tank,  but there is usually very little loss of chemicals.  In re-
 cent years it has become a common practice to disintegrate the stream of
 molten material with a high pressure steam jet so  as to eliminate both the
 noise and the danger of  explosions in the dissolving  tank. However, the
 use of steam jets may increase the loss of  chemicals  by atomization and
 entrainment in the  steam leaving the  dissolving tank.
                         ODOR RELEASE
      In Figure 1 the places where odors may be released are shown by
clouds of vapor. Not  all these odor emissions are equally important, how-
ever,  some being much larger  or  more concentrated than others. Yet if  a
substantially odor-free process  is to be secured, all must  be brought under
control. The places where the largest amounts of odor  are released and
therefore those which  have received  the most attention up till now  are
the following:
        Digester Gases—The gases  given off when the digesters are relieved
and blown contain particularly high  concentrations of mercaptans  along
with steam and possibly other substances such as methanol. (This last may
have been the  substance responsible for occasional reports of  eye damage
following exposure to heavy concentrations of digester gas. It is an unusual
hazard inasmuch as most mills today  possess blow heat  recovery systems
which condense the greater part of the steam in the digester gas and with
it the very soluble  methanol.)  It is a fairly  common practice  to discharge
all these gases into the blow  tank from which they pass into the  heat
recovery system. There they distribute themselves between the vapor phase
and the contaminated  hot  water  in  the accumulator tank.  The uncon-

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 104                                                 AIR POLLUTION

 densed part constitutes a very serious source of odor because the volume is
 substantial and the concentration of malodorous material is very high  in-
 deed. The contaminated water usually finds its way eventually to the sewer
 where its ill-smelling constituents may be released at a greater or lesser rate
 depending upon the temperature,  the amount of exposure to the atmos-
 phere,  and the degree  of dilution  with other  liquid effluents.
         The Evaporator Gases—The weak black liquor containing about 15
 percent solids, after separation from the pulp, is normally evaporated  to
 about 50 percent solids  in a multiple-effect evaporator. In this process there
 may be a substantial production of foul gases which commonly include
 substantial amounts of  hydrogen sulfide. These gases are carried out  of the
 evaporator in  the  barometric leg  of the jet condenser. The  black  liquor
 leaving the multiple-effect evaporator is usually further evaporated to about
 65 percent solids in some  form of direct  contact evaporator where it is
 exposed to hot flue gas  from the recovery furnace.  The amount of odor
 picked up by  the  furnace  gases may be quite small, or it may  be very
 great, depending upon the  way  the equipment is operated. If Ihe viscous
 film of strong liquor builds  up a  cake which is subject to destructive distill-
 ation, then a  large quantity  of foul gas  may be  generated and carried
 into the atmosphere with the flue gas.
        The Furnace Gases—The operation  of the recovery furnace may be
 a  critical factor  in the odor producing process. The  primary function of
 the  recovery furnace is  to generate heat  by  oxidizing  the carbonaceous
 material in the strong black liquor, and  to regenerate the cooking chemi-
 cals by reducing  sulphur compounds to sodium sulfide which is a principal
 constituent of the smelt.  The problem of reducing  one constituent of the
 black liquor while  oxidizing another is solved  in part by correct design of
 the furnace and in part  by correct control of the combustion conditions, and
 in particular the primary and secondary air supply.  Inasmuch as the main
 purpose of the  furnace is  to generate heat and  chemicals, there may be cir-
 cumstances when,  for example,  the demand for steam may require that
 the  furnace be operated in  such  a  way that it generates substantial  quan-
 tities of foul-smelling  substances  (mainly partial  oxidation  products of
 methyl mercaptan), usually because there  is insufficient secondary  air or
 because the furnace is forced beyond its proper capacity. Generally speak-
 ing, the furnace  plus the direct contact evaporator constitute a significant
 source  of odor comparable  in importance to the digester gases.
        Miscellaneous Gases—In  addition to the foregoing, Figure 1 shows
a number of other points of  odor  emission, which individually may be rela-
tively unimportant, but which in the aggregrate are sufficient to produce
a significant odor problem  over  distances of a mile or two even though
the major  sources may be  completely controlled.
      For  example Figure  1 shows an intermittent  odor release from the
 top of the digester itself when it is  opened to admit a fresh charge of  chips,
 and occasional puffs of odor from the blow tank and accumulator  vents.
 The blow tank  is not usually designed as a pressure vessel, and is therefore
 fitted with pop valves, which allow steam  to escape if for  any reason the
 condenser  on the heat recovery apparatus fails or is slow to start up. The
 prevention of this kind of emission is mainly an operating problem,  but a
 comprehensive  odor control system  would make provision for some  ad-
 ditional condensing measures  to take care of abnormal operating condi-
 tions. In the same  way there  is normally no  emission of vapor from the

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 Selected Papers                                                    105

 accumulator tank vent when connected to the oxidation system in the way
 shown in Figure 1, but if the heat recovery system fails for any reason to
 condense the greater part of the steam when a digester is blown, then the
 volume may be greater than the oxidation  tower can handle and the ex-
 cess will escape via the vent pipe. Under  these conditions  large quanti-
 ties of malodorous material  may be released from both the  accumulator
 vent and the oxidation tower exhaust. This again is an abnormal but by no
 means an  unknown event and a  complete odor control system  would in-
 clude additional condensing  capacity on the  lower end of the  accumulator
 vent.
      Again, when the mixture of pulp and black liquor from  the digester
 is separated on the brown stock washer the hot mixture releases substantial
 quantities of water vapor and malodorous material which are commonly
 collected in a hood and discharged to the atmosphere. The concentration of
 mercaptan is normally quite small but the total volume of exhausting air is
 so large that the aggregate amount of odor is quite significant  from  this
 source. In general there will be some odor release wherever black liquor of
 incompletely washed pulp is  exposed to the atmosphere.
       MEASURES  FOR THE CONTROL OF DUST EMISSION

      The dust content of the furnace gas is  fairly large,  in  the order of
about 100 pounds per ton of pulp produced, and it is normally made up of
very minute particles less than a micron in diameter. The installation of an
electrostatic precipitator serves to retain 85 to 97 percent of this material,
but the operation is  not  100 percent and the balance escapes to the atmos-
phere. During its  passage through the precipitator, however, the  dust  is
largely flocculated so that the solid material which escapes from the stack
consists partly of  fluffy aggregates up  to a millimeter in  diameter  which
fall out within a mile or two of the mill and partly of fine particles which
are comparable  to those found in ordinary industrial smoke.  It is mainly
the large aggregates which damage paint and  vegetation.
      To remove the dust which passes through the electrostatic precipi-
tator, bag filters have been recommended. They are reported to provide an
effective solution,  though possibly  a costly and  troublesome  one  because
of short bag life. An alternative, and on the face of it, an attractive solution,
is the  use  of  a  system  of scrubbers designed to recover both heat  and
chemicals from the  furnace gases.  Of these the two best  known are the
Inka System and more recently the Tomlinson-B-W System.  In the latter
the electrostatic precipitator is eliminated completely and the furnace gases
are passed" through  a system of deluge  towers  or  more recently  cyclonic
scrubbers. These are  arranged so that the hot gases are first brought in con-
tact with black liquor from the multiple-effect evaporators whereby addi-
tional moisture is removed from the black liquor while the flue gases are
cooled nearly to the  dew point. Later, scrubbers take the flue gases through
the dew point so as to recover  the latent heat of the  water  vapor while
at the  same time scrubbing out  a large proportion of the  remaining  solid
material. The cooling  and condensation of the  moisture reduce the  total
volume of the gas  to a point where a smaller and lower stack can be used
to carry it off.
      Earlier  attempts to use processes of this sort were frustrated by the
fact that the flue gases normally contained both sulphur dioxide and hydro-

-------
 106                                                 AIR POLLUTION

 gen sulfide, and this combination in conjunction with water makes an ex-
 cessively corrosive mixture. Hence  it was necessary to make sure that the
 electrostatic precipitator and ancillary ducting were always maintained at
 a temperature above the dewpoint. The position was changed when it was
shown that the process of black liquor oxidation (to be more fully discussed
below) largely eliminates the hydrogen sulfide from the furnace gases and
 so overcomes the greater part of the corrosion problem. It also enables the
sensible and latent heat of the stack to be recovered without excessive cor-
rosion of  the equipment.
      The initial scrubbing of the flue gas with strong black liquor must be
 carefully  controlled. The  black liquor  is strongly alkaline because  of its
 sodium hydroxide and sodium sulfide content, and in contact with flue gas
 it absorbs carbon dioxide  which neutralizes the alkali and displaces hydro-
 gen sulfide from the sodium sulfide. The displacement of hydrogen sulfide
 can be prevented by the black  liquor oxidation process already mentioned,
 but the carbonation of the alkali, if allowed to go too far, may lower the pH
 to a point where the organic material (present as  sodium salts of lignin
 fragments) is precipitated with the formation of a solid cake in the scrubber.
      The power required to operate this system is  substantially greater
 than that  required to operate a disc evaporator and electrostatic precipitator
 but it is claimed that the improved heat and  chemical recovery justify the
 cost and the process can be operated with little difficulty  and with a major
 reduction in air pollution by both particulate matter and odors.
      At the present time there do not appear to be any standard or ready-
 made solutions to the  problem of solid material from the dissolving tank
 though technically the matter is not difficult.  The lime kiln dust is usually
 well taken care of by  a  scrubber  of standard design which  is normally
 integral with the burning equipment.
           MEASURES FOR THE CONTROL OF ODORS

      The emission of odors from the recovery plant is claimed to be sub-
stantially controlled  by the  Tomlinson-B-W  System already described-
Short of this a substantial degree of reduction may be effected in plants
equipped with the more conventional electrostatic precipitators by the pro-
cess of black liquor oxidation. In this process,  the weak black liquor after
separation from the pulp and before entering the multiple-effect evaporator
is exposed to an oxidizing gas, usually  air,  in such a way that the sodium
sulfide in the liquor is  destroyed by  conversion to other compounds  of
sodium  and sulphur.  (The precise chemical details of what happens have
not been fully worked out. It is generally agreed that the sodium sulfide
and mercaptan content is reduced by oxidation, but whether the main pro-
duct is  sodium sulfite or sodium thio-sulfate, or some other compound is
not yet known.) Experience  in  a number of mills in various parts of the
world has  shown  that when black liquor is properly oxidized  the release
of  odors in  the  multiple-effect evaporator and furnace is  very greatly
curtailed.
      Several kinds of black liquor oxidizing apparatus have been  reported.
Generally speaking,  they fall into two types:  those  which secure contact
between air and liquor by intentionally making foam  (and then breaking it),

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Selected  Papers
107
and those which avoid foam production as far as possible. In view  of the
powerful froth-forming characteristics of black liquor from resinous types
of wood, the non-foaming oxidation processes (if they can be made to work)
have much to recommend them on the score of simplicity and freedom from
operating troubles.  Generally  they consist of a tower  of some  sort con-
taining a refractory packing over  which the  liquor trickles in  good con-
tact with air which is passed  through the tower.
      If the air is passed countercurrent to the  black liquor, it tends to strip
malodorous material and carry it out into the  atmosphere. If, however, the
air and black liquor flow concurrently, any fbul smelling substances which
may escape from the  fresh black  liquor that enters  the  tower are re-
absorbed by the oxidized liquor farther down. This principle can also be
used to absorb the non-condensable digester gases, which otherwise  would
continue to be formed and escape during the relieving and blowing opera-
tions. If the oxidation  equipment is built close to  the  equipment that  is
used to condense the steam and vapors from the digesters, a very simple ar-
rangement serves to ensure that any uncondensed gases  are mixed with air
and drawn  into the  towers where  their foul smelling components are ab-
sorbed  and oxidized in the  black liquor. This procedure was  developed
and patented by the British  Columbia Research Council.
      A typical installation embodying the process  is shown in Figure  2.
Steam and vapors from the blow tank (A) pass via the duct (B) to the  direct
contact  condenser (C)  and into the  hot water accumulator  tank  (D). The
noncondensable  (and very malodorous)  gases would normally  escape  to
the atmosphere via the  stack (E) but are, instead, drawn through the duct
(F) into the  oxidation towers  (G) by fans mounted on  top  of the towers.
The additional air required for the oxidation is drawn downward through
the stack (E). The success of this process depends  on the fact that  black
    Figure  2.  Showing the blow tank (a), the accumulator tank (d), and the
              oxidation tower (g).

-------
 108                                                 AIR POLLUTION

liquor contains substances which strongly catalyze the oxidation of mer-
captan and that the tower design permits a very high ratio of air to black
liquor to be passed through the towers.  In this way the peak  emissions of
digester gas  which occur when digesters are blown can  be taken into the
towers  without  impairing their oxidizing  capacity.   This  makes  it  un-
necessary  to  provide  storage in vapor spheres  or otherwise of  the ex-
tremely foul and, on occasion, explosive digester gases. They are handled
 automatically as they come.
      It has sometimes been suggested that sulphur compounds which have
 been absorbed and oxidized  in this  way would later be stripped out again
 in the recovery plant, and especially in the direct contact evaporator. Ex-
 perience with several  installations  now in  operation has  not borne out
 this prediction.
      The measures thus far described,  namely, black  liquor oxidation
 (with absorption  of digester gases) plus scrubbing and condensation of stack
 gases, are capable of bringing about a very great diminution of the amount
of malodorous and  particulate  material released into the atmosphere. In
order to understand what  effect  these measures will have on the mill odor
it is  necessary to understand certain  characteristics of the sense of smell
and of the way  gases are diffused through  the atmosphere.
      Figure 3 shows the relation between the concentration of ethyl mer-
captan and the "strength" of the odor expressed on a zero to five scale esti-
mated subjectively by each of a number of observers whose separate  assess-
ments were averaged and plotted as points on the graph. It is  evident that
the strength of intensity of the odor sensation, insofar as it can be given a
numerical rating, is proportional to the logarithm of  the  concentration of
odorous material. This means  that, for example,  a  90 percent reduction
of malodorous material at any  point, i.e. a  reduction by a factor of 10,
may make a  scarcely perceptible reduction in the strength  of the odor
and a 99 percent reduction in concentration would be required to  reduce
the odor from, for example,  "faint" (strength 2) to "very faint" (strength
1). At first sight this would seem to preclude the possibility of really elim-
inating the odor, but the situation is redeemed by the  fact that as soon as
the odor is released it begins to mix with air until it becomes diluted to a
concentration that is below the threshold of perception. Hence if the quan-
tity of malodorous  material that is released at the source can be reduced
by, say, 90 percent,  the quantity of air required  to dilute it  will  also be
reduced by 90 percent, which in practice means a reduction in the radius
over which the smell will be noticed.
      The dilution of gases released  into the  atmosphere has been analyzed
mathematically by  Button, who has taken  into  account  such factors as
wind  strength, atmospheric turbulence, height and strength of the point of
emission, and other relevant factors. His formulae have been tested experi-
mentally in connection with the travel of war gas clouds and chimney stack
plumes  and have been shown to afford a reasonably  accurate account of
what  actually happens over short distances. For greater distance the postu-
lates tend to become artificial: for example it may be calculated that for a
source of given strength the  odor would be perceptible at distances ini the
order of 50 miles with a wind of 2 miles per hour velocity. But this would
imply that the wind blew in a constant direction and  with a  constant ve-
locity for  25  hours, which is somewhat unlikely, at least in the temperate
zone. However, taking Button's formulae at their face value, the downwind

-------
Selected  Papers
109
b
ODOR STRENGTH
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1
O"3 IO"2 10"' 10° I01 IOZ 10
                       ETHYL MERCAPTAN
                       MICROGRAMS PER LITER

                               Figure  3.
travel of odor from a source releasing five grams of odorous material per
second has been calculated for average conditions, over level ground cover-
ed with short grass, and for a wind velocity of five miles per hour. Figure
4 shows three curves, one for a point source of the specified type at ground
level  and the other for point sources  of  equal  strength at heights of 225
and 450 feet.
      Even  discounting any absolute numerical  accuracy  in these curves
they nevertheless  afford some interesting qualitative information.
      Thus  the downwind range  of an odor from a source at ground level
is relatively much less than that from an elevated source. This is because
there  is a high rate of shear in the  wind near the ground which induces
very rapid mixing. The effect of a tenfold reduction in the strength of the
source, say from five grams per second to 0.5 grams per second, is to dis-
place  the horizontal axis  (which represents the threshold of  perception)
upward as shown by the  dotted line. This reduces the downwind travel
by a factor  of about 4.  A further tenfold reduction in the strength of the
source would completely eliminate the odor from the 450-foot stack, would
almost eliminate  it from  the  225-foot stack except for  a zone  on the
threshold  of perceptibility two miles  downwind, but from the source at
ground level the  odor  would be appreciable for distances  out  to about
half a mile from the source.
      Thus  it may be concluded that the effect of every reduction in the
amount of odor released is to contract  the area within which the odor will
be perceived- When it is necessary to prevent odors very near the mill, ex-
cessively high stacks are not as necessary as stringent measures to prevent
any odor from being released anywhere and especially to  prevent  it from
being released near the ground.

-------
  no
                      AIR POLLUTION
            SOURCE AT
            GROUND LEVEL
 DOWNWIND ODOR
 WIND 5 M.P.H.
 SMOOTH LEVEL GROUND
MINIMUN PERCEPTIBE ODOR I X ICT12 g/l
                       SOURCE AT
                       225 FEET
                                    THRESHOLD WHEN_ SOURCE0.05 j/*ec.
                                SOURCE AT
                                '450 FEET
                                                THRESHOLD
                                                WHEN SOURCE 0.5 g/sec.
                                    THRESHOLD WHEN SOURCE 5 g/»ec.|
                             10
           15
20
25
                              Figure  4.
      Figure 1 shows that there are a multiplicity of such odor release
points. Many of them are quite minor and by themselves would probably be
quite unimportant. Taken altogether however they account in the aggre-
gate for a substantial part of the whole mill odor problem and must there-
fore be suitably cared for if completely odor-free operation is to be secured.
The manner in which they can be cared for is not yet subject to a ready-
made solution. The points of odor release are widely distributed through the
plant so  that some could be vented into  a common duct and treated to-
gether, while  others because of their location  or nature  might better  be
treated by themselves. The nature of the deodorizing treatment will not al-
ways be the same everywhere as some  will be more suitable  for some
effluents than others, and the most practical treatment  will have  to  be
worked out for each odor source.
    The  following are some  of the possible procedures.
        Burning—When  malodorous sulphur compounds are  completely
burned the sulphur is converted to sulphur dioxide  which has a relatively
faint odor. A  large volume,  low. intensity, and fairly constant stream of
contaminated  air can be passed into the  recovery furnace,  but only if it
does not create an explosion hazard or otherwise interfere with the  estab-
lished pattern of furnace operation, and  if the amount of ducting  is' not
excessive.  The use of  small furnaces especially for odor destruction has
been reported but they seem to involve considerable trouble and expense
and should be used only as a last resort.

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 Selected Papers                                                    III

         Scrubbing—Scrubbers can be set up to absorb and destroy malod-
 orous materials by means of solutions of chlorine  or  hypochlorite. Such
 solutions may be available as spent liquors from the bleach plant,  or they
 may be especially  prepared using chlorine purchased for the purpose.  If
 the volume of gas to be treated is small the scrubbers will be small and in-
 expensive. It may also be possible to operate existing scrubbers partly  or
 wholly  on spent bleach  or  other  oxidizing solutions.  For example, if a
 Peabody scrubber is used in the final stage of stack gas treatment, it may
 be operated partly  or wholly on an oxidizing solution.
         Destruction in the Gas Phase—Large volume, low intensity sources
 may be deodorized by adding small amounts of ozone,  or possibly  gaseous
 chlorine or by the action of deodorizing lamps.
       It is probable that many and perhaps  all of  these measures would
 have to be invoked in one place or another before the release of odors and
 particulate air contaminants could be brought, down to  an acceptable level.
 What is not known at present is  the  volume of contaminated air to be
 expected from each of the residual release points, nor  the precise chem-
 ical identity of the contaminants, nor their concentration. Further research
 and  study are therefore necessary  to secure the data on which specific rec-
 ommendations  for odor-free  operation can be based.
            AN OUTLINE OF THE NEEDED RESEARCH

      It is first of all necessary to make a detailed survey of several opera-
ting kraft mills so as to establish  as exactly as possible the volumes of con-
taminated air which are released and where they are released and with
what frequency, and what  concentration of malodorous material they con-
tain. The measurement of gas volumes is not usually a very difficult matter,
as it normally reduces to a flow measurement. Around sewer gratings and
similar low velocity emission points it may  be necessary to  build some
sort of confining box, but the measurement  of gas volume will not in gen-
eral call for the  development of  any new technique. The measurement of
the nature and concentration of the malodorous contaminant may present
more difficulty. Chemical tests (usually colorimetric) have been devised for
methyl mercaptan, and a few of the other substances, but the sensitivity of
these  tests falls far short  of that of the  nose.  It is possible  that the re-
cently developed process of vapor phase  chromatography may be applied
to the problem so that the malodorous materials may be identified more pre-
cisely than ever before and also their quantities. The techniques necessary
for this  work are,  however, not available  ready-made  at this time,  and
difficulty may be encountered as a result of the high content  of moisture
in many  of the  air streams to be analyzed. Some work  on  the method
will therefore be necessary. An alternative  method  of analysis, which can
be used if the  vapor phase chromatographic method cannot be developed
or is otherwise unsuitable,  is a simple measurement  of the total amount of
sulphur in the gas stream. This is a relatively simple test requiring merely
a filter to remove solid material,  an oxidizing operation to convert the sul-
phur into sulphur dioxide, and an absorber of  appropriate type. This has
the virtue of simplicity and the defect of being non-specific and of lumping
together substances with powerful and substances with quite weak odors.

-------
 112                                                 AIR POLLUTION

      Coupled with this identification and evaluation of the significant
points of odor release, experiments to test the efficacy of various methods of
odor destruction will have to be carried out. In a mill which already oper-
ates a bleach plant it would be a relatively simple matter to set up a small-
scale scrubber fed with actual spent bleach liquor and use  it to treat actual
effluent air streams. By analysis of gases entering and leaving the scrub-
ber the quantitative data needed for the design of full-scale deodorizing ap-
paratus would be secured. In the same way, the usefulness of free chlorine
or  ozone  in destroying residual traces of malodorous material in flue gas
from the  recovery  plant  or elsewhere could be established by  actual trial
using part of all of the  gas issuing from the mill.
      These methods of securing the required design data and of  testing
out the proposed odor absorption or destructive methods have obvious ad-
vantages  over an  exclusively  laboratory study. It is hoped that such a
comprehensive study can be  undertaken in the near future.
           NEW WORK  IN  KRAFT  MILL
                     ODOR  CONTROL


                           R.  H.  Wright *
      The problem of kraft  smells is as  old as the kraft pulping process.
The smells are mainly organic sulfur compounds, which are unavoidable by-
products of the pulping reaction, and which are released in varying  but
substantial amounts at many widely separated parts of the process. For the
benefit of those not  familiar with the pulp industry, Figure 1 shows the
bare  outlines of the  kraft process.
      Wood and chemicals are put into the reaction vessel, or digester, D,
where a reaction takes place which dissolves the noncellulosic part of the
wood and leaves the cellulose fibers undissolved. From the digester,  one
obtains pulp, spent  chemical solution  (called  weak  black  liquor),  and
smelly  gases.
      The weak black liquor  is passed to a series of evaporators E j and E2
where water is progressively removed to a point  where the residue can be
burned  in a furnace F to generate steam and regenerate the cooking chem-
icals.  The mill depicted in Figure 1 has no provision for odor control, so
that there are substantial amounts of odor released  from the digesters, the
evaporators, and the chemical recovery furnace. Unless special precautions
are taken, a mill making some hundreds of tons of pulp daily will easily re-
lease  some hundreds  of pounds of smelly material in the same time, and
as the threshold of perceptibility is not far from 10 parts per billion,'the
smell  can travel a long way before  it is dissipated.
       'British Columbia Research Council, Vancouver, Canada.
        Presented at the  55th Annual Meeting of APCA, Sheraton-Chicago
 Hotel,  May  20-24,  1962, Chicago,  Illinois.

-------
 Selected  Papers
                                                                113
WOOD
                   W.B.L
           1
           PULP
          CHEMICALS
                              Figure  1.
      Any odor control system must meet certain stringent but  common-
 sense requirements, which are  represented diagrammatically in Figure 2.
 First, the control system must be simple and it must not interfere with the
 basic process or operation of the mill. If  it does, the operators—who are
 human—will not make the best use of  it, and under those conditions even
 a technically sound system will  soon become discredited.
    BASIC
  PROCESS
                               Figure  2.
      As  an example, there have been various  attempts to  collect  the
smelly gases by means of ducts and then burn them at some central place
such as the recovery furnace. Apart from the cost and inconvenience of the
ducts,  the malodorous gases are often inflammable  or explosive, and  the
ducts tend to  ice up in cold weather. Understandably, few  such systems
have worked.

-------
 114                                                 AIR POLLUTION

      If the odor  control system  can contribute  some  additional fringe
 benefits, then it will be welcomed rather than tolerated, and the operators
 will be more inclined to maintain and even  improve it.
      The first substantial advance toward an acceptable system of smell
 control was made about 20 years ago as a result of studies by Bergstrom
 and Trobeck in Sweden and by G. H. Tomlinson in Canada. These led to
 the black liquor oxidation process. The weak black liquor from the digesters
 is an alkaline solution containing various organic and inorganic substances,
 including sodium sulfide and methyl mercaptan. If the hot liquor is brought
 in contact with air, the sodium sulfide is oxidized to sodium thiosulfate:

                2NaS +  H20 + 202 = Na&O, + 2NaOH


 and the methyl mercaptan is  oxidized  to dimethyl  di sulfide :

                    4CH3SH + 02 = 2(CH3)2S2 + 2H20
                     b.p. 7.6°C       b.p. 117°C

 These reactions have several beneficial effects. The chemical destruction of
 the Na£S prevents K^S from being formed by hydrolysis in the evapor-
 ators, the extra NaOH generated by the  reaction helps to maintain a high
pH, and the methyl mercaptan is converted into the disulfide which is much
 less volatile and  also less objectionable.  All  this helps to prevent sulfur
being lost and  makes for better chemical  economy.
      Figure 3 shows how black liquor oxidation affects the odor released
 from the mill. The oxidation tower, O.T.,  is situated so that the black liquor
 passes through it before going to the evaporator Ej.
      The smell  from the multiple-effect evaporator  Ej is eliminated  or
 very greatly reduced,  and, if the oxidation is sufficiently complete,  there
 will be very little pick-up of odor in the direct contact evaporator £2- Also,
 with properly designed apparatus it is possible to pass the  smelly digester
 gases into the towers where they are largely absorbed and deodorized.
      Thus, in a mill  using  black liquor  oxidation, the  most serious  re-
 maining sources of odor are, in order of decreasing importance, the recovery
 furnace, the direct contact evaporator, and the air exhausting from the oxi-
 dation towers.  The "problem of coping with these odors has been  studied
 intensively in recent years and is the main theme of  this paper.
                        FURNACE  ODORS

      By itself, black liquor oxidation has no effect on the  generation of
odors in the furnace. The prime function of the furnace is to oxidize and
burn away the organic matter in the black liquor and  at the same time to
chemically reduce the sulfur compounds  to Na2S. These seemingly incom-
patible functions  are brought about by maintaining reducing conditions at
the bottom of  the furnace and, by introducing enough secondary air higher
up to finish off the oxidation of the organic matter.                  '

-------
 Selected  Papers
115
                   O T
                    AIR
                               Figure  3.

      With a properly designed and operated  furnace these functions  are
fulfilled and the flue gas should contain no significant amounts of H^S or
other reduced sulfur compounds.  However, at high furnace loadings it is
often necessary to reduce the supply of secondary air in order to prevent
overheating  of the furnace, and the immediate result of this is incomplete
oxidation and the release of H2 S  and other malodors. Typical behaviour is
shown in  Figure 4, which also indicates  that at  the other extreme, when the
furnace is underloaded, it runs cool and the liquor is destructively distilled
without being fully burnt.
                                 LOAD

                                Figure  4.
      Since the recovery furnace is the most expensive piece of equipment
in a pulp mill, there are obvious incentives  to load it as fully as possible.
      Figures 5 and 6 show an experimental  H2 S meter which is now under
development  at  the British Columbia Research  Council  for the  purpose

-------
 116
                        AIR  POLLUTION
     Figure  5.  Flue gas analysis.
                H S analysis unit.
            Figure 6.  Flue gas analysis.
                      HLS recorder unit.
of monitoring the flue gas so that maximum loading can  be made consist-
ent with minimum  production of smell.
              THE  DIRECT CONTACT EVAPORATOR

      In principle,  a sufficiently  complete prior oxidation of the black
liquor will prevent the furnace gases from picking up any malodors in the
evaporator, apart from substances like dimethyl sulfide, which are not acidic
and therefore not retained by the alkali. In practice,  however, the direct
contact evaporator does tend  to contribute odors of which the most  import-
ant is hydrogen sulfide. For one thing, if the black liquor oxidation is incom-
plete so as to leave  a small residue of  sodium sulfide in the weak liquor,
this becomes magnified as a result of the evaporation of water and may
amount to a significant quantity  by the time the liquor reaches  the  re-
covery plant.
      Again, if the oxidation of the weak liquor is done at too low  a temp-
erature, then instead of the sodium sulfide  being oxidized to sodium thio-
sulfate, it is  oxidized only as far as elemental sulfur,  by the reaction,

                  2Na£ + 2H,0 + 02  = 4NaOH + 2S

When free sulfur is heated with alkali it is unstable with respect to sodium
sulfide and may undergo an auto-oxidation of the type
6NaOH
= 2Na,S
                                                3H2()

-------
 Selected Papers                                                     |)7
 The regenerated sodium sulfide can then  liberate H^S both by hydrolysis
 and by  reaction with carbon dioxide in the flue gas.
      Since it is not aways possible to  maintain a sufficiently high temp-
 erature in the oxidation towers to prevent this, one may be forced to carry
 out the  black liquor oxidation  in two stages, using a partial oxidation of
 the weak  liquor and finishing off the reaction after the liquor  has been
 partially evaporated. This is  likely to be  complicated and inconvenient.
      An alternative is to do away with the direct contact evaporator en-
 tirely and  to make a corresponding increase in the capacity of the  multiple-
 effect  evaporators.  This means an increase in complication, but  can  be
 made to yield some useful fringe benefits  also, over and above the im-
 proved control of odors.
      For  example the direct  contact evaporator involves  only a  single
 effect, and so requires about 1,000 Btu per Ib of water evaporated. Mills us-
 ing direct  contact  evaporators  also use a substantial amount of  steam to
 pre-heat the furnace air supply. If this steam is diverted to the extra mul-
 tiple-effect evaporators, the flue gas can be  used to heat the air.  Thus the
 elimination of the direct contact evaporators can confer an over-all opera-
 ting benefit in the form of heat economy, but at  the cost of a substantial
 increase in complexity. The  balance of advantage  from this has  to  be
 worked  out by each mill  for itself.
           THE OXIDATION TOWER EXHAUST GAS

      The reaction taking place in the oxidation tower effectively prevents
the release of H^S in the discharge gases- Dimethyl sulfide (CH3)2S, is
chemically neutral and has a boiling point of only 38°
-------
  118                                                  AIR POLLUTION
 using a gas-liquid reactor of conventional design. In the first stage the gases
 are exposed to chlorine solutions of low pH so as to absorb and oxidize the
 sulfur compounds to innocuous  products by  such reactions as
                       + 2C12 + 2H20 = (CH8)2SO2 + 4 HC1

                                   and

              (CH3)2S2 + 5C12 + 6H20 = 2CH3S03H + 10 HC1
 The second  stage of the scrubbing uses a solution of pH about eight to
 absorb any  residual chlorine or acid products of the oxidation.
       The process is particularly useful to mills producing  semi-bleached
 or bleached  kraft pulp because these normally have bleach plant effluents
 containing residual chlorine,  hypochlorous acid, and calcuim hypochlorite,
 and also large quantities of spent caustic solutions with an appreciable
 residue of sodium hydroxide. Naturally, the  oxidants must be used  in a
 chemically  adequate amount, and  if bleach  effluents  with only a small
 residue of chlorine are employed,  the  total  volume will be large. Thus,
 the scrubbing apparatus will be rather big, but  it is  inherently simple
 and need not be  overly expensive either to build or  operate.  Provided
 the necessary ducts are not too troublesome,  the scrubber can  be used to
 deodorize other gas streams as well.
                       SOME DIFFICULTIES

      Despite what has been said, kraft mill odor control measures are still
by no  means complete or fully effective. Black liquor  oxidation is not a
complete answer, though it would be difficult to imagine an effective con-
trol system that did not include it. Figure 7 depicts a mill equipped with an
oxidation tower arranged to absorb digester gases and  fitted with an ex-
haust gas scrubber, and with the direct contact evaporator eliminated. Such
a mill would be expected to give off a minimum of odor provided the load
on the furnace was not excessive. One or two  new mills using this system
are now nearing completion.
      The greatest single obstacle to the general introduction of oxidation
towers is the tendency of the black liquor derived from  resinous species of
wood to foam  enthusiastically and with the  slightest  encouragement—or
no  encouragement at all.  The foam handling  problems are  sufficiently
serious to create substantial operating difficulties.
      The surface  active substances responsible for the foam  are largely
soapy  or  soap-like  products formed by  the action of  the alkaline cooking
liquors on the  resinous constituents of the wood. Neutral extractable sub-
stances, including turpentine, are also present and  may contribute  to  the
problem.
    As long as no substantial markets exist for these chemical by-products
of the pulping reaction, they are best disposed of by burning  and  so  the
temptation is to process them through to the recovery plant with the rest
of the black liquor if this is at all  possible, even though it means a con-
stant battle with the foam.

-------
 Selected Papers
119
       BLEACH—•-
                              Figure  7.


      Fortunately there is a growing  demand for at  least some of these
 substances,  so that a few mills are beginning to install equipment for re-
 covering them from the weak black liquor. This is bound to improve the
 situation with regard to foaming,  and  together with improved methods of
 foam handling,  such as ultrasonic breakers, it is likely that black liquor
 oxidation will  soon find its way  into  mills where it  has  been heretofore
 regarded  as impractical.
                        ODOR ANALYSES

      As long as the nose remains the only instrument for detecting  the
odorous materials  at the  low concentrations at  which  they are found in
the open air at  some distance from their origin, the objective evaluation
of control measures  will be difficult.
      Developments  in analytical methods, and especially in gas chromato-
graphy, give some promise of replacing subjective appraisal by instru-
mented measurement.
      Figure 8 shows a convenient type of stainless steel  collecting tube,
which has been developed for collecting samples in the  open air. The pro-
cedure is  quite  simple. In Figure 9  a small pump operated  from  a  car
battery is used to  draw the air first through a  drying  train  and then
through the collecting tubes. The tubes can then be capped  and packed
in dry ice for shipment to the laboratory, where they are connected to a

-------
                   Figure  8.  Stainless steel collecting tube.
Figure  9.  Collecting samples in the field. Apparatus consists of a drying tube,
            three collectors in parallel, and a battery-operated pump, together
            with a foamed plastic refrigerator for the samples.

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                                                                     121

gas chromatograph  and the  sample transferred as shown  in  Figure 10.
Figure 11 shows the chromatogram of a sample collected  about a quarter
of a mile down wind from a pulp  mill  at  a point where  the odor was
Figure 10.  Apparatus for chromotographing the samples. The collecting tube  K
           is warmed by the heater N and the sample is swept into the top of the
           chromatographic column through the tap L.
                                              START
                              Figure 11 .

-------
122


noticeable but by no means strong. The pulp mill was located in the east-
ern United States and the sample was shipped by air 3,000 miles to British
Columbia to  be analyzed  in the chromatograph.
      Unfortunately, the  technique is  still  not  fully  perfected  because
samples collected in urban areas or in the vicinity of major highways con-
tain so many extraneous  substances  derived mainly from  motor vehicle
exhausts (though in at least one case a manure pile  made its contribution),
that the chromatograms are too cluttered to be very useful. The problem
is not insurmountable, and could, for  example, be nicely  taken care of
by  equipping the chromatograph  with a sufficiently sensitive  detector
that responded only to compounds containing sulfur.
                     ACKNOWLEDGMENTS

      My name is given as author of this paper, but it should more properly
be given as compiler.  To my colleagues, past and  present at the British
Columbia Research Council and especially to F. E. Murray, G. C. B.  Cave,
J. B.  Risk, and I. H. Williams must go the credit for whatever is  novel
in what I have said.
                           *U. S. GOVERNMENT PRINTING OFFICE : 1968 O - 307-332

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