U.  S,              OF HEALTH,            AND WELFARE

            AIR POLLUTION

                AND  THE


        An Annotated Bibliography
                  Paul A. Kenline
                  Jeremy M. Hales
                Field Studies Branch
        Robert A. Taft Sanitary Engineering Center
                Public Health Service
               Division of Air Pollution
                 November 1963

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

ABSTRACT                                          v
INTRODUCTION                                     1
     Digester Blow System Emissions                      4
     Smelt Tank Emissions                              5
     Lime Kiln Emissions                              5
     Recovery Furnace Emissions                         5
     Multiple Effect Evaporator Emissions                  6
     Control of Particulate Emissions                      7
     Control of Gaseous Emissions                        8
INDEX  TO BIBLIOGRAPHY                           9
ANNOTATED BIBLIOGRAPHY                        15
SELECTED PAPERS                                 77

    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.

                 AIR  POLLUTION
                       AND    THE

    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.

                                                     AIR POLLUTION
"Brew ton 300
Cooso Pines 300
Demopolis 350
Tusca loosa 500
Mobile 1,015
Mobile 550
Naheola 310
Snowfioke 150
Crasseit 575
Crossett 80
Pine Bluff 170
P,ne Bluff 745
Antioch 215
Foley 800
Jacksonville 500
Jacksonville 1,370
Polatka 810
Panama City 1 620
Pensacola 580
Pensacola 450
Port St Joe 1,200

Augusta 350
Brunswick 525
Mocon 700
Rome 725
St Marys 800
Savannah 2,100
Voldosta 700
Port Wentworth 625
Lewtslon 500

Bastrop 580
Bogalusa 1,180
Elizabeth 240
Hodge 500
Sprmghill 150
West Monroe
Lincoln 180
Old Town 140
Rumfard 350
Luke 515
Filar City 165
Muskegon 125
Cloquet 130
International Falls 125
Lumberton 100
Moss Point 650
Natchez 900

Berlin 450

Ticonderoga 150
Acme 700
Canton 930
Plymouth 950
Roonoke Rapids 650
Albany 250
St Helens 375
Springfield 400
Toledo 600
Roaring Spring 120
Spring Grove 190
Tyrone 140'
Williamsburg 85
Catawba 400
Charleston 1,250
Georgetown 1,455
Calhoun 450
Counce 500
Evadale 360
Lufkin 300
Pasadena 670
Covington 660
Franklin 690
Hopewell 800
West Point 600
Camas 700

Everett 80
Everett 325
Longview 825
Longview 575
Port Townsend 420
Tocoma 400
Wallula 200
Kaukouno 250
Mosmee 165

                     DESCRIPTION  OF


    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)  lies
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 tanklthe 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 sn

Kraft Pulping Industry
                               PULP ••
         WOOD CHIPS
                                         MUD (CALCIUM CARBONATE)
                                        KILN  GASES
                    Figure  2.  The kraft 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.

  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 dissoivea
 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.*
condition s
Cook time 3.75 hr
Temp 172 °C
Sulfidity 22%
Ib /ton dry pulp

0 to 0.10

0 to 0.88

0.01 to 0.94

       Hydrogen sulfide

       Methyl mercaptan

       Dimethyl sulfide

       Dimethyl di sulf ide

       Su I fur dioxide
                                               Concentration, mg per liter




 * The values in Tables 2 through 8 were calculated from data in the Bibliography and from the
forthcoming PHS 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 '

 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.
Influent particulate
loadings, ton/day
Efficiency of
mesh demister
Effluent particulate
emissions, tons/day
 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.
      Particle concentration,
Particulate emissions,
Ib /ton dry pulp
Recovery Furnace Emissions
    The recovery furnace is  a major source of particulate and gaseous
pollution (Tables 6 and  7).

                                                    AIR POLLUTION
Pollutant generated by
furnace (with primary
stack gas scrubber),
Ib /ton dry pulp
Hydrogen sulfide:
Final emissions with
venturi scrubber,
Ib /ton dry pulp
Final emissions with
electric precipitator,
Ib /ton dry pulp
  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



   Hydrogen sulfide

   Methyl mercaptan

   Dimethyl  sulfide

   Sulfur dioxide
 10 to 40 tons / day

100 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

Ib /ton dry pulp


Oxidation tower

95 to 100%
Emissions from
Ib /ton dry pulp

0 to 0.06

                       MEASURES  FOR


 Control of Participate Emissions
     Attempts to curb the smoke  and odors issuing from  pulp mills have
 been nearly as long lived as the kraft 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 air 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,

  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
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 with
this method  arises from  tremendous  periodical  surges of gas that  occur
when the digesters are blown. One company has attempted to  solve this

 Kraft Pulping Industry                                                 °

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 "Inka
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-
    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,  12.7,  128, 130, 132, 138, 147, 154
    Liquid absorption
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

  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 Stack Gases
Major pollutants:
I.  Particulate: fly ash, sodium sulfide, sodium sulfate, sodium oxide, sodium
     Corrective measures:
     Electrostatic precipitators
     6, 9, 10,  14, 24, 50, 61, 81,  103, 104
     43, 81, 87, 114, 124
     Venturi  scrubbers
     29, 41, 43, 45, 48, 81, 87, 88, 101,  114, 136, 137
     Condensation methods
     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
     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,
    14, 81, 90, 114,
    Wet scrubbers
    90, 114,

Kraft Pulping Industry

Dissolver Vent Gases
Major pollutants: sodium carbonate, sodium sulfide.
Corrective measures:
    Integrated  operations




1.      Adams, D. F. and R. K. Koppe: Application of instrumentation to
          pulp  mill  atmospheric  discharges. TAPPI,  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,  mercaplans, and alkyl sulfides
        and   disulfides. TAPPI, 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


                                                 AIR POLLUTION
   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 heal 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
                            GAS TO ATMOSPHERE
                  WATER AND
                  CHEMICAL  MAKE-UP
   Figure  3.  Schematic flow diagram of chemical and heat recovery process.
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  Kinasoorl
Paper Trade J., ,141:48-50. Oct.  7, 1957.  Since install;™
   r                                    omce installing recovery

Annotated Bibliography                                                '7

        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: HOW Weyerhaeuser controls kraft odor with the yaporsphere.
        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 materials! 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

   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 t^S, Na2S, and mercaptans.  Na2S
       will yield H^S in presence of  an acid.  If Na^S is converted  to
       Na2SC>4 by oxidation  it does not form t^S. 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  tha 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
       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.

Hydrogen sulfide
Dimethyl disulfide
Methyl mercaptan
Dimethyl sulfide
Volume, %
vi ru lence
      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.

dry distillation
in smelter
mg per liter










18.    Bergstrom, H., and K.  G.  Trobeck: Sulfur losses  in the production
       of sulfate  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.  1,406,581. 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.




   Figure  4.  Schematic flow diagram of a process for utilizing black liquor.
20.    Bernhardt,  A. A.,  and J. S. Buchanan: Recovery of dissolve! vent
      stack  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.

Before use of
mi st eh mmotor
After use of
mi st el i minator
Salt cake loss,
Ib per ton of pulp


dol lars per day

68 90


 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.     Bialkowsky,  H.  W.,  and G. G. DeHaas: Stabilization of Douglas Fir
        krafi black liquor.  Paper Mill News,  74:14-22. Sept. 1,  1951. Work
        on  the  development 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 precipitalor 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.,   122.'
       (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
 26.    British  Columbia Research  Council discovers new methods to re-
       duce krafi 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  oi  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
    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  samole
     2. Time required for collection and analysis of a sample-     '

 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 IVz 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 the 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  vemuri scrubber  at Balhurst.   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 2'3
      Baume higher than  would  otherwise be  obtained. Although  it has
      been claimed that oxidation prior  to evaporation is the cause of re-

 Pufp 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 Baurfie, hot

 Salt cake  in stack gas

 Salt cake  recovered per day

 260 tons per day

 58,000 cfm


 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



 9.9 Ib/ft3

 27 to 29 Bourne

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

 15.480 Ib


 Annotated  Bibliography

       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 Na2iS—*•  Na2 82O 3 .
         Generation  of H^S 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.
  27-FOOT STEEL                             FLAME    (FLOW              KILN
                       SCRUBBER           ARRESTER CONTROL)



12! n —
  Figure  5.  Schematic flow diagram of a system for destroying odorous digester
             relief and blow gases.
36.    Collins, T. T.:  Comparison of methods for determination of sulfide
       in oxidized sulfate black liquor.  Paper Trade J.,  129:29-33. Aug. 25,
       1949.  Several analytical  techniques for determination of sulfide  in
       black  liquor were tested,  and their  relative  merits are discussed
       Experimental difficulties  owing  to  oxidation  of the black  liquor
       are bothersome to all  techniques,  and it  is highly desirable  to use
       an analytical method that can  be completed in a short period. For
       this  reason,  the Borlew-Pascoe  method  (Abstract  25),  which in-
       volves a potentiometric nitration  with silver nitrate, was  considered
       the most  adequate for the studies to be  conducted.
37     Collins, T. T., Jr.: The oxidation of  sulfate  black liquor. Paper Trade
       J.,  131 :  30-38. Oct.  12, 1950.   As  a  result of  extensive pilot plant
       and laboratory  investigations,  a full-scale  sulfate  black  liquor oxi-
       dation  system has been erected and  operated  at  Thilmany so that
       its effect upon  the  sulfur balance of  the recovery system could  be-
      determined. The oxidation unit at  Thilmany is not operating at pres-
      ent because an excess of sulfuric acid  in the chemical makeup main-
       tains the cooking liquor sulfidity  in the desired range  Although a
      high sulfidity level (33 percent, TAPPH) of white liquor was attained,
      no improvements in pulp quality  were observed  A high  degree of
      oxidation of black liquor resulted  in the reduction of sulfur loss by
      more than 90 percent  in the vacuum and direct contact evaporators.

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  sulfale black  liquor. A review
       of Ihe 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

      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-
Size in microns
Wt percent
       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-

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
        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 sulfale  recovexy
      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 for 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 :  1
          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.

                                                         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  J., 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
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 ,000 cfm

 300°F dry bulb
 163°F wet bulb

 20,000 Ib salt cake/day


 4,000 Ib/day

 400 Ib/day

 500,000,000 Btu/day


 Annotated  Bibliography                                              3'

           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 (r$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.
  Figure  6.  Schematic flow diagram for thilmany salt cake recovery process.
46.    Collins, T. T., and P. H. West: Some recent developments  in  krafl
      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  slack  gases.
      ?V1PP/,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

                                                       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 venluri
        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

Velocity of
entering gos m
throat, fps

Gal Ions of
liquor per
1,000 ft3 of gas
venturi atomizer
Liquid |et

AP across
atomi zer,
w g


       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  kilo watt-hours per ton.
        „ TO 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 the analytical  methods for mercaplan  and  sulfur  com-
       pounds. TAPP1, 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 the manufacture of krafl 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. TAPP1, 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-

     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.
  S3.     DeHaas,  G. G.: Stabilization of Douglas Fir krafi 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 6 to  8 feet high, and
         packed with V4-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   mato
 dorous gases issuing from evaporators.
 3. Inka Tower
      An "inka tower" may be used  to  treat stack
passed through the  precipitator,  to  remove

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. Dalle-Valle: A study of the odors generated
      in the manufacture of  kraft paper.  Tech. Assoc. Papers, 22:312-315.
      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 arid 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

  36                                                  AIR POLLUTION

      1S  the vast quantity of  material  blown  out  the  stacks.  From a
      plant manufacturing 300 tons per day  of kraft PW the smoke a
      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 (Cr^CgE^SH)  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.


Water-soluble organic matter
Ether-soluble organic matter
Free carbon
      Production of 300 tons of finished paper per 24 hours means a loss of
18,000 pounds of Na2SO4 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.
56.     Felicetta, V. F., Q. P. Peniston, and J. L. McCarthy: Determination
       of hydrogen sulfide,  methyl m-rcaptan, dimethyl  sulfide and disul-
       fid« in kraft 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                                              37

       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 Ihe 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  grams 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-


rticle size, fji
Efficiency, %
 59.    Fones, R. E., and J. E. Sapp: Oxidation of krafl 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 precipilators in air pollution control.  Proc.
       llth  Indus. Waste  Conf. May 1956. Purdue Eng.   Extension Dfpt. 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
       m 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 sulfate
      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  sulfaie 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-

  4Q                                                  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  flO.3 pounds] of  pulp). The digester condensate  also
      contained mercaptan.  After turpentine  removal, 2.1 kilograms of
      chlorine  per  metric  ton  (4.2 pounds per 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
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
66.    Hansen,  G. A.: Odor  and fallout control in a kraft pulp mill. J of the
      Air Pollution Control Assoc.,  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  to  sulfate  pulping  operations.  TAPPI, 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                                              41

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
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 A7HA, 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,)-

                                                      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.


Gases lea
to fur
Ib Na
elief gases to oxidation
(after dilution)
nsoble gases from evaporators
ving oxidation tower
quantity of sulfur returned
nace from oxidation tower (as
2SC>4 per ton pulp)
H2S and


di sulfides






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.


Gas temp, °F
Dew point, °F
GAS ANALYSES (equivalent
Ib Na2S04/ton pulp)
Smelt sulfidity, %
HoS and mercaptans
Organic disulfides
COS and C$2
Total sulfur compounds in gas
(Ib Na2S04/ton pulp)
Salt cake recovery in fume
system (Ib Na^O^j/ton pulp)
Entering Leaving











Sulfidity of smelt, percent Na^S in black
Entering tower: grams of Nc^S per liter
of black liquor
Leaving tower: grams of NaoS per liter of
black liquor
Oxidation efficiency, %
Run no.

                                                      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
Total sulfur compunds in gas
(Ib Na2SO^j/ton pulp)
Salt cake recovery in fume
system (Ib Na2S04/ton pulp)













74.    Kenline, P. A.: In  quest  of clean  air for Berlin.  New Hampshire.
      Sanitary Engineering Center   Technical Report A61-9.  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.
Suspended particulate, ug/m
Hydrogen sulfide, ppb
Sulfur dioxide, pch
Dustfall, tons/m^ per mo
Soiling, Cohs/1000 ft

Annotated Bibliography
          PULP MILL
Recovery furnace
Blow gases
Smelt tank
Lime kiln
Boiler plant (1 boiler only)
Emission of pollutants in Ib per hr
Hydrogen sulfide

Sulfur dioxide

      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.
7$.    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,

  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.
79.    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 kraft 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:
Recovery furnace exhaust
Electrostatic precfpitators a
Venturi scrubbers a
No equipment a
Lime ki In exhaust
Wet scrubbers
Dry dust collectors
No equipment
No lime kiln


    Three mills use both precipltators and scrubbers.
     The electrostatic precipitators were  from 90 to 98  percent efficient
     as compared with 85 to 90 percent for the venturi scrubbers 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
      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  installation (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  (T able 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.

                                                       AIR  POLLUTION

Furnace qas alone:
Hydrogen sulfid.e
Methyl mercaptan
Sulfur dioxide
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


57.2 to 181
78. 8 to 111.5
3.9 to 12.1
Cone after treatment, mg/m^

8 to 46


0.58 to 3.4
0.44 to 0.52
 85.    May,  B.  F.: Experiences in the abatement of kraft  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.     ?4ay, B. F.: Experiences in the abatement of krafi 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
       hmited success;  further  experimentation  is needed before it will
       be  possible  to  assess the real value  of  these  compounds A process

Annotated  Bibliography
       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.  Chew.  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-
   Black liquor flow

   Collection efficiency

   Saltcake loss

   Draft loss across venturi

   Draft loss across separator

   Pulp production

   Recovery furnace weight
venturi scrubber

Dust loading at standard conditions
dry gas, gr/ ft^
Dust loading, stack conditions,
90 %
To scrubber

From scrubber
  50,000 Ib/hr


   4,500 Ib/day

     30 in. water

      4 in. water

    165 tons / day

    120 tons
                  DIRTY FLUE GAS 485°F, 3.9 GRAINS
                  OF DUST PER CUBIC FOOT
       LIQUOR TO
                                                     CLEAN FLUE  GAS 180 F,
                                                     0.4 GRAINS OF DUST
                                                     PER CUBIC FOOT
   Figure  8.  Schematic flow diagrams of thilmany chemical recovery unit.

                                                     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 venturi 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

Venturi inlet diameter
Venturi throat diameter
Venturi outlet diameter
Cyclone diameter
Cyclone height
Fan power
4' 8"
3' 10"
450 hp
            FROM FURNACE
                                                       GASES TO STACK
                 SCRUBBING LIQUOR    (*)PUMP
  Figure  9.  Schematic flow diagram of venturi scrubber unit at Burnie

Annotated  Bibliography
       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.
89.    Meuly, W. C-,  and B. K.  Tremaine: Abatement of sulfale pulp mill
       malodors by  odor masking agents. TAPPI, 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 p.ulp- 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-
Digester relief
Multiple effect
"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. TAPPI, 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 (eO^F) cubic

  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>/2 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  speclrophotomeiric
      method for the determination of mercapians 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 kraft 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
       sulfale 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 chromaiographic  analysis of hydrogen sulfide, sulfur  dioxide,
       mercaplans, 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 coniamina-
       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
 94-11. Laboratory evaluation of  gas  sampling  procedure for  recovery
       furnace  slack 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.

 54                                                   AIR POLLUTION

94-13.  A manual for adsorption sampling and gas chromalographic analy-
       sis of kraft 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  chromatcgraphic 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  chromatography 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 been 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
       noncondensabls 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 oxiaation 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 ih« krafi
       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  in 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 sludy,  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 discoloia-
      -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  krafl 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  control of 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
                                                 TO ATMOSPHERE
               TO GREEN   _
              PRECIPITATOR   I

-_ P



      Figure 10.  Schematic flew diagram of recovery system at Rosen lew mill.
       Measures  taken to control these effluents  at  the  Maryvale  Mill  are
 as follows:
       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.

Furnace flue
Oily condensate from
digester gas
Aqueous condensate
from digester gas
Digester foul water



Threshold odor di-
lution, 1 part in



           20%       40%

                                        DIGESTER  DRAIN

                                        DECKER DRAIN

                                        WASHING AND SCREENING DRAIN


                                        RECOVERY FLOOR


                                        DIGESTER FOUL WATER

                                        DIGESTER GAS

                                        EVAPORATOR FOUL GAS

                                        EVAPORATOR GAS

       Figure 1 1 .
                 SODIUM I        I

Relative sodium and sulfur losses at Maryvale,

Annotated  Bibliography
Evaporator 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-
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.
250 to 300
980 to 1,120
Make-up salt cake, Ib/ton pulp
Prior to in-
stallation of


After installa-
tion of pre-


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

106.  Schneider, F.:  Deodorizalion of krafl  mill exhaust TAPPI, 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).
                                                            TO ATMOSPHERE
         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
















gos flow,








feed, Ib/Jir








Na?S content
of Slack liquor,














11 -24 to 11:35

14: 34 to 14:44


9:33to 9:43

11:37 toll:49

14:25to 14:36

15:42 10 15:52

17:15 to 17:27

11:1110 11:13
1:30 to 11:33
4:28 to 14:29
4:33 to 14:34
4:41 to 14:42
9:25to 9:27
9:32lo 9:33
9:36to 9:37
9:42to 943
lt'42 to 11:43
14:26 to 14:27
14:29 to 14:31
14:33 to 14:35
15:41 to 15:42
15:44 to 15:45
15.48 to 15:49
17:08 to 17:10
17 15to 17:17
17:19lo 17:20
17:22lo 17:24

To lower




From to,e,





, 16





 108.  Schoening, M. A., and R. H. Wright: Intensity of the odor release  at
      various points in  the kraft pulping  process. TAPPI, 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.




Muni lock


11 52


Sample token
ll.lBto 11:26
11. 26 to 11. 35
953io 9:58
9 58 10 10:03
12-10to 12.13
12 13)o 12 16
12.16to 12-21
12 21 to 12.27
1? 27io 12:34
12 34to 12:42
10-53 to 10: 58
10. 58io 11-04
11-04 rol 1-10
15 10)o 11-17
11-17)0 1 1.23
11 23)oll.29




methyl mer-
coplan, ftg/\


na/m \



den sate
Methyl mer-

Digester charge included 200 Ib sulfur

Digester charge included 200 Ib sulfur

No sulfur added to digester charge

No sulfur added to digester charge




















Samp e la on
0:32 to 10:35
0.36to 10: 39
1:03 to 11 06
I 06 to 11 13
l:13toll 19
4.33lo 4-37
4-37(0 442
4-42)0 4-47
4-47ra 4-51
9:26lo 9:29
9:29to 9-32
9.32)o 9:35
9:35io 9:38
9:38to 9:41
mercop an,
^9 ml

8 2
8 6
1,1 0
9 6
7 0


Digester charge included 200
Ib sulfur

Digester charge included
200 Ib sulfur

No sulfur added to digcsler

No sulfur added to digester








1 45






Somple taken
1:47 lo :49
1:49 to :50
1.50 lo :52
1 52 to .52!;
l:52hto :53b
1-53'jto .55
1 55 to .57
9:31 to 9:33
9:33 to 9-:>l
9:35 to 9 36! 3
9-36!3to 9 38
938 lo 9:40
9 40 lo 9:42
9:42 to 9 43! i
9.43'ito 9-45
9:53 lo 55
9.55 to 57
9:59 to 1 00
10-00 io 1 01
10-01 lo 1 02
10-02 to 1 03
10-03 tol 05
9:10 to 9:14
9:14 lo 9:18
9:18 lo 9.23
1-10 lo 1-14
1:14 to 1 18
1:18 to 1 22
10:37 Id 10:42
10-42 to 10:46
10:46 to 10 SO
2:35 lo 2:40
2:40 lo 2:44
2:44 to 247


1 1,700

Total vapor
Methyl mer-
capton, Jig/
ml at 10OC



Digester chorge included
200 Ib sulfur

Digester charge included
200 Ib sulfur

No sulfur added to di-

No sulfur odded to di-
gester charge (blown
From higher than uiJal)
No sulfur added to di-
gester chorge
No sulfur added to
digester charge


Dote, 1950

May 25
May 30
May 31
June 2
Liquid effluent

(tg/m 1
Air above liquid surface


Methyl mercaptan,
 a Tr means trace.
 Table 37, FURNACE GAS

Dote, 1950

May 27
May 29
May 30
June 1
June 9
June 12
June 15
June 20
Nonconden sable gas




Condensable gas

£ g/m 1
Methyl mercaptan.
/ig/m 1
 Table 38. STACK GAS

Date, 1950
June 9
June 9
June 12
June 15
June 20
Noncondensable gas,
depth 6 ft

Noncondensable gas,
depth 12 ft
A 9/1


Condensate combined,
6 and 12 ft
/t g/m 1

109.   Schwalbe, C. G.:  Removal of the 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,

                                                      AIR  POLLUTION
Roof vent over knotter

liquor smelt tank

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



ftg/m 1

/ig/m 1

    a Tr means trace.
     thereby regenerated, may be replaced in the tower for further use.
     After  use, the wood chips can be  burned as boiler  fuel. When the
     chijps  are  used to purify digester  gases  only,  they  can be  cooked
     for pulp with no  adverse effects.
110.  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.
111.  Segal,  W.:  Quantitative determination of methyl mercaptan, 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.
112.  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 SHTSnL  eSJ
     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          lurnace be

Annotated Bibliography                                              °^

113.  Segerfelt, B. N.: Method of removing malodorous gases formed in the
     sulfate  and soda pulp  manufacture. U.S. Patent l.S.'i'j.'rIft.  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 eificiency 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:

                                                       AIR POLLUTION
1 UUIC *tw.
Type of
Na20 loss,
Ib /ton pulp
  1 On the assumption that sa
   mill  would save $24,800 a
It cake costs $15 per ton, this indicates that a 100-ton kraft
nnually 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 % 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 2 and SOg) in the furnace. With the present  system,
     however, such furnace  losses  are greatly eliminated.

         TO  STACK



         Figure 13.  Schematic flow diagram of TBT recovery process.

  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
127.  Tremaine,  B. K.:  Masking air-borne malodors; utilization of aromatic
      chemicals  in industrial odor abatement.  TAPP1, 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. Tirado: 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
129.  Trobeck, K. G.: The B-T system for soda and heat  recovery in sulfale
     pulp mills. Paper  Trade  J.,  130:40. Apr.  20, 1950.  The  B-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
LU *—
"* h-

,„. , ,l^~~— iF



      Figure 14.  Schematic flow diagram of soda and heat recovery process.

130.  Trobeck, K. G., W. Lenz, and A. Tirade: Elimination of malodors in
     a kraft pulp mill. TAPPI, 42(6): 425-432. June 1950. Experiences in the
     tj-aft pulp mill  of Loreto and Pena Pobre  indicate that only three
     sources of malodor wiU 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

70                                                   AIR POLLUTION

More than 1 15
More than 103
More than 55
More than 48
   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




 2,800 Ib

17,400 Ib
                                AIR OUT
                                                          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):122-127.  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  1953, 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 veniuri 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 colorimetric
      determination of hydrogen  sulfide and  methyl mercapian  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,
, *n   ™ PyeVented by addition of a cationic wetting agent to  the reagent.
140.   Wright, R  H.: The  dissemination of odors  from  kraft 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                                             73

      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  effect of
      black liquoi  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  liquoi
      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-
143.  Wright, R. H.: It is possible to build  and operate a completely odor-
     less kraft 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 sulfale 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

  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  kraft 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 krafl 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   2,115,83:).  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  + 20 2  +  H2O = Na2S2O3  + 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'7  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.

                          SELECTED PAPERS
The following  papers  are  reprinted with  permission:
      Odor and fallout  control in a krafl 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 krafi mill  odor  control. R. H.  Wright  Paper 62-99.
      Presented at the annual meeting of the Air Pollution Control Assn.,
      Chicago,  111. May 1962.


               IN  A  KRAFT  PULP  MILL

                            G.  A. Hansen *


      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.


      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 odor"
 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.


                                                     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  (CH3SSCH3),  and  small  amounts  of similar ethyl
sulfide compounds . i In addition, hydrogen sulfide is formed in  consider-
able amounts.  To give  you an  idea of  the  quantities involved,  Table  1
shows the pounds of 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.



      Until  the recent introduction of the continuous digester, wood pulp-
ing had been a batch process. Generally, all kraft pulping processes follow

Selected Papers
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.
                                                       TO RETENTION

                                           BLACK LIQUOR      PONI>
                                             TO RECOVERY * STAGE BLEACH «*!"
           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.

 Q2                                                   AIR POLLUTION

 Chicago Bridge  and Iron Works  had available a low-pressure  gas con-
 tainer called a "Vaporsphere." 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
      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  CO2, SO2 and H2O took place.  Only when the furnace temp-
 erature dropped below 900° F. did any odorous compounds pass through
      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. Coleman3  has described  this system in detail in the
 October  1958 issue of TAPPI 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

Selected Papers
              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. 1 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  (Na2SC>4) 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

                                                      AIR  POLLUTION
wfth the  exception  of the odor control systems
haeuser mills.
                                                         by our Weyer-
    METER \
                 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 evapprate 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                                                     85

been known  for some time. However, attempts to apply the conventional
countercurrent 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 ether  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.
                    FLY ASH 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.

                                                      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
      Figure 4.  Stepwise removal of flyash from recovery furnace flue gas.

Selected Papers
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 on  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  ID. fan ahead  of  the scrubber accounts
 for the improvement  in 1958 over 1957.


Recovery stock emission, Ib /day
Fallout ot filter plant, oz /ItVday °
Sodium loss
44 x 10'5
3.6 x ID'5
Reduction, %
  0 Includes a background fallout of 1 .6 X 10'5 01 /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.

                                                        AIR  POLLUTION
OZ NA/FT2 /DAY X 10"5 )
— '
                             ~- SCRUBBER
             MILL DOWN AVERAGE
            ' ~    i"~	T ~
                  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  have 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.

Selected  Papers                                                   89

     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.

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 Kiln,",TAPP/, 41, 166-168A (October 1958).
4.  J. .S. Murray, "Scrubbing Kraft Recovery Furnace Gases,"TAPP7,43,
   899-902 (November  1960).


                     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

                                                  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

         BLOW TANK

           PULP WASHER
 '"    A '
,'     ^Ifrvl
V    f,ccOi.
                                                 ^S_ NEW
                                                       SALT CAKE
               Figure  1 .   Odor release in the kraft process.

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  sullate 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 white 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 suMate 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
       (c)  Power  plant, consisting of sulfur dioxide if  the furnace is
           being operated  properly.

 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.

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.

     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

 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-

Selected Papers
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
                               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-

  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. It 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,an all  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 gases 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

Selected Papers
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.
                                   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.

 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.
 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, TAPP/43, 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,
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).
12.   Bialkowsky, H. W., and G. G. DeHaas, 'Paper Mill News, 74, 14 (Sep-
     tember 1, 1951").
13.   Schneider, F., TAPPI, 41, 70A,  (January 1958).

Selected Papers
           IS  IT  POSSIBLE   TO  BUILD

                  AND  OPERATE   A


                         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


     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

 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.

      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
that the  odor control programme can impose an  indirect cost by limiting

Selected Papers                                                   101

production musi be  squarely  faced  and accepted at every level of the
      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 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 mercapian 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.

     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

                                                         AIR  POLLUTION
                                                              I. DIGESTER
                                                              IA. DIGESTER RELIEF
                                                              IB. DIGESTER BLOW
                                                              2. BLOW TANK
                                                              3. ACCUMULATOR
                                                              4 OXIDATION TOWER
                                                              5. MULTI EFFECT
                                                              6. DIRECT CONTACT
                                                              7. ELECTRIC
                                                              8. MAKE - UP
                                                              9. FURNACE
                                                             10. CONTAMINATED
                                                                HOT WATER
                                                             II. SEWER
                                                             12. SEWER OUTFALL
                                                             13. DISSOLVING
                                                             14. CAUSTICIZING
                                                             15. MUD FILTER
                                                             16. LIME KILN
                                                             17. SLAKING
                                                             18. KNOTTER
                                                             19. WASHER
                                                             20. SCREENS
                                                             21. DRIER
                                                             22. TAILINGS
                                                             23. FOAM TANK
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 soluvion  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:

Selected Papers                                                      103

                                NaCl                 17.6%
                                NasCO»                36.4
                                Na2Sb,                33.6
                                Na2SO3                 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-

 |04                                                   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

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
     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.

     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
fallout 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-
iator, 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 heal 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-

 |06                                                  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.

      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 thai  when black  liquor is  properly oxidized the release
of  odors in  the multiple-effect evaporator  and furnace is  very greatly
      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),

Selected Papers
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 ihe air is passed countercurrent io 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).

I08                                                   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 in 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










* )


> O









0"s KJ4 IO'3 I0'z 10"' 10° 10' 10' 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.

                                                      AIR  POLLUTION
                                DOWNWIND ODOR
                                WIND 5 M.P.H.
                                SMOOTH LEVEL GROUND
                               MINIMUM PERCEPTIBE ODOR I X IO'12 g/l
                                    THRESHOLD WHEN SOURCE 0.05 g/sec.
            SOURCE AT
            GROUND LEVEL
                       SOURCE AT
                       225 FEET
                                SOURCE AT
                                450 FEET
                                                WHEN  SOURCE 0.5 g/sec.
                                     THRESHOLD WHEN SOURCE 5 g/sec. i
                              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.

 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 ah- 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.

     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.

 N2                                                  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.
                     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


 Selected Papers
                              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 simp.le 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.
S \

                               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.

 ,14                                                  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:

                2Na2S + H20 + 202 = Na2S203 + 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 Na2S prevents H^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 E ^.
      The smell  from the multiple-effect evaporator E'} 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  Ej- 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
                              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.
      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

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

      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,
2Xa.,S +  2H,0
                                      =  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

                 6XaOH  4- 3S = 2Xa,S + Xa2SO3 + 3H?<)

Selected  Papers                                                     117
The regenerated  sodium sulfide can then liberate H2S 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 reaction taking place in the oxidation tower effectively prevents
the release of H2S in the discharge gases. Dimethyl sulfide  (CH3>2S,  is
chemically neutral and has a boiling point  of only 38 °C so that it can be
partially stripped from the liquor, and its smell is objectionable. Dimethyl
disulfide, (CH^^ 82, which  is formed by the oxidation of methyl  mercap-
tan has a boiling point of 117°C and is much less volatile than  the mono-
sulfide, but it, too, can be carried off to  some extent by the exhaust gases,
and is somewhat  objectionable.
     It is known in a general way that these substances can be destroyed
by oxidation using solutions containing active chlorine, in forms which are
often available as wastes from a pulp bleaching  plant. However,  only re-
cently have the correct conditions for the effective  utilization  of  these
solutions been found.
     It turns out that the oxidation proceeds at a sufficiently fast rate
when the pH is low — in the range one to three — and is much slower at
higher pH values  of six to eight. However, at the low pH values there is a
considerable liberation of chlorine gas from the solutions and this can mask
the smell of the sulfur compounds. Many  past attempts to deodorize these
gases with bleach plant wastes or other chlorine  solutions have  turned out
to be unsatisfactory because the reaction was judged to be  complete when
only chlorine could be smelled in  the effluent gas. This was incorrect.  The
fact was that sulfur compounds were still present and their odors became
noticeable at some  distance down wind, when the chlorine was too  dilute
to mask their odor.
      A two-stage process has now been  developed  for the absorption and
oxidation of the malodorous substances  in the oxidation tower exhaust gas,

 ,I8                                                  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
               (CH3)2S + 2C12 + 2H20 = (CHOzSOj + 4 HC1


              (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 it 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
    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
                              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 unproved 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.


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 chromatographing 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.
                              Figure 11 .


 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.

      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