X
SEP A
United States Control Technology EPA-450/3-90-002
Environmental Protection Center October 1989
Agency Research Triangle Park NC 27711
Evaluation of Emission
Control Devices at
Waferboard Plants
control ^ technology center
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EPA-450/3-90-002
FINAL REPORT
EVALUATION OF EMISSION CONTROL DEVICES
AT WAFERBOARD PLANTS
CONTROL TECHNOLOGY CENTER
SPONSORED BY:
Emission Standards Division
Office of Air Quality Planning and Standards
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
Air and Energy Engineering Research Laboratory
Office of Research and Development
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
Center for Environmental Research Information
Office of Research and Development
U. S. Environmental Protection Agency
Cincinnati, OH 45268
October 1989
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DISCLAIMER
This document presents an engineering evaluation of control options
for wood chip dryers. Specifically, the document discusses the use of
electrified filter beds and wet electrostatic precipitators for control of
wood chip dryer effluents. Also, emission reduction by reduced
temperature drying is discussed. The EPA does not represent that this
document comprehensively sets forth all of the procedures for wood chip
dryer and control device operation, or that it describes applicable legal
requirements which vary among the States.
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
11
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ACKNOWLEDGEMENT
This engineering assistance report for wood chip dryers was prepared
for EPA's Control Technology Center by Mr. C. C. Vaught of Midwest
Research Institute. Mr. Leslie Evans of EPA's Office of A1r Quality
Planning and Standards was the Work Assignment Manager.
111
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PREFACE
The wood chip dryer engineering assistance project was funded by
EPA's Control Technology Center (CTC). The CTC was established by EPA's
Office of Research and Development (ORD) and Office of Air Quality
Planning and Standards (OAQPS) to provide technical assistance to State
and local air pollution control agencies. Three levels of assistance can
be accessed through the CTC. First, a CTC HOTLINE provides telephone
assistance on matters relating to air pollution control technology.
Second, more in-depth engineering assistance can be provided when
appropriate. Third, the CTC can provide technical assistance through
publication of technical guidance documents, development of personal
computer software, and presentation of workshops on control technology
matters.
The engineering assistance projects, such as this one, focus on
topics of national or regional interest that are identified through
contacts with State and local agencies. In this case, the CTC was
contacted by the State of Colorado Department of Health, Air Pollution
Control Division, with a request for information about control of wood
chip dryer emissions from waferboard plants. Specifically, the agency
requested available information on the use of the electrified filter bed
and wet electrostatic precipitator for control of wood chip dryer
effluents. As a result, EPA's Emission Standards Division (ESD)
contracted with Midwest Research Institute (MRI) to conduct an engineering
evaluation of these control options. This report presents the results of
that evaluation. The report discusses the composition of wood, design and
operation of the control devices, costs, and factors affecting
performance.
iv
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TABLE OF CONTENTS
Page
LIST OF FIGURES v11
LIST OF TABLES v111
SECTION 1.0 INTRODUCTION 1
SECTION 2.0 SUMMARY AND CONCLUSIONS 3
2.1 CHARACTERIZATION OF EMISSIONS 3
2.2 EMISSION CONTROLS 3
2.3 PRESS VENT EMISSIONS 4
SECTION 3.0 GENERAL PROCESS DESCRIPTION 5
SECTION 4.0 EXTRACTABLE ORGANICS IN WOOD 7
SECTION 5.0 CHARACTERIZATION OF WOOD CHIP DRYER EFLUENTS 11
5.1 TURPENES 11
5.2 RESINS AND FATTY ACIDS 13
5.3 PRODUCTS OF THERMAL DECOMPOSITION 14
SECTION 6.0 AEROSOL FORMATION 15
SECTION 7.0 EMISSION CONTROLS 18
7.1 ELECTRIFIED FILTER BED 19
7.1.1 General Description 19
7.1.2 Pollutant Removal Efficiencies 26
7.1.3 Factors Affecting Performance and
Suitabi 1 ity 26
7.1.4 Costs 30
7.2 WET ELECTROSTATIC PRECIPITATORS 30
7.2.1 General Description 30
7.2.2 Pollutant Removal Efficiencies 32
7.2.3 Factors Affecting Performance and
Suitability 37
7.2.4 Costs 39
SECTION 8.0 LOW/REDUCED TEMPERATURE DRYING 41
8.1 DRYER TEMPERATURE VERSUS EMISSIONS 41
8.2 DRYER LOADING VERSUS EMISSIONS 43
8.3 PRODUCTIZATION 3PHV DRYER 43
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TABLE OF CONTENTS (continued)
SECTION 9.0 PRESS VENTS 48
SECTION 10.0 REFERENCES 52
APPENDIX A. EFB AND ESP USER LIST A-l
APPENDIX B. WEYERHAUSER'S EFB TEST DATA B-l
APPENDIX C. GEORGIA-PACIFIC'S ESP TEST DATA C-l
APPENDIX D. PRODUCTIZATION 3PHV DRYER PATENT D-l
APPENDIX E. MEMORANDUM: FORMALDEHYDE FROM WAFERBOARD PRESS
OPERATIONS E-l
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LIST OF FIGURES
Page
Figure 1. Minimum theoretical particle size formed for
olelc add at various supersaturatlons 16
Figure 2. Theoretical vapor pressure of small particles of
olelc acid 16
Figure 3. Electrified filter bed system 20
Figure 4. Ionizer and gravel bed assembly 21
Figure 5. Gravel bed schematic 22
Figure 6. Gravel bed flow controller 24
Figure 7. Disengagement chamber 25
Figure 8. Bag filter 27
Figure 9. Wet ESP module equipped with traveling spray system . 33
Figure 10. Product 1zat1 on 3PHV rotary drum dryer 44
Figure 11. Flow comparison of conventional triple pass dryer
and 3PHV drum dryer 45
vi 1
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LIST OF TABLES
Page
TABLE 1. ETHER-SOLUBLE EXTRACTIVES CONTENT OF COMMON HARDWOODS.... 8
TABLE 2. ETHER-SOLUBLE EXTRACTIVES CONTENT OF COMMON SOFTWOODS.... 9
TABLE 3. TURPENTINE CONTENT OF WOOD SPECIES 12
TABLE 4. EFFICIENCY SUMMARY OF WEYERHAEUSER'S EFB IN MONCURE,
NORTH CAROLINA, FOR CONTROL OF WOOD PARTICLE DRYER
EXHAUST TEST PERFORMED OCTOBER 20, 1988 28
TABLE 5. EFFICIENCY SUMMARY OF EFB FOR CONTROL OF WOOD PARTICLE
DRYER EXHAUST TEST PERFORMED FEBRUARY 14-17, 1989 29
TABLE 6. EFB COST EVALUATION 31
TABLE 7. EFFICIENCY SUMMARY OF GEORGIA-PACIFIC'S WET ESP IN
DUDLEY, NORTH CAROLINA, FOR CONTROL OF WOOD CHIP
DRYER EXHAUST TEST PERFORMED SEPTEMBER 1983 34
TABLE 8. EFFICIENCY SUMMARY OF GEORGIA-PACIFIC'S WET ESP IN
SKIPPERS, VIRGINIA, FOR CONTROL OF WOOD CHIP DRYER
EXHUAST TEST PERFORMED APRIL 20, 1989 -35
TABLE 9. EFFICIENCY SUMMARY OF GEORGIA-PACIFIC'S WET ESP IN
WOODLAND, MAINE, FOR CONTROL OF WOOD CHIP DRYER
EXHAUST TEST PERFORMED OCTOBER 25, 1988 36
TABLE 10. CAPITAL AND OPERATING COST OF WET ESP 40
TABLE 11. INCREASE OF PARTICULATE MASS RATE WITH INCREASING INLET
TEMPERATURE 42
TABLE 12. VOC EMISSION FACTORS FOR PRESS VENTS 50
viii
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1.0 INTRODUCTION
The U. S. Environmental Protection Agency (EPA), Office of A1r
Quality Planning and Standards (OAQPS), 1s Involved 1n responding to
requests from EPA Regional Offices and from State and local air pollution
control agencies to Investigate air pollutant emission sources and the
control technologies that can be applied to reduce these air pollutants.
These requests are sometimes received at the Control Technology Center
(CTC) and require quick evaluations of air pollution emission sources and
the control technologies that can be used to reduce the emissions from
these sources. These emission sources may be significant enough to
warrant national standards or guidelines. Accordingly, OAQPS studies
these sources to determine whether they warrant further review and
possibly national standards development.
The State of Colorado Department of Health, A1r Pollution Control
Division, has received complaints of eye and lung irritation from
residents near a waferboard manufacturing plant located outside of Olathe,
Colorado. The State requested assistance from the CTC 1n determining
possible emission sources within the plant and assessing potential
controls for those emissions. The CTC report published in September 1987
recommended that additional work be done in determining the effectiveness
of a wet electrostatic precipitator (ESP), a dry type of control system
such as an electrified filter bed (EFB), and any other promising control
methods.
Recently, the State of Colorado Air Pollution Control Division
requested additional assistance from the CTC in determining the
effectiveness of control devices for emissions from wood chip dryers in
waferboard plants. The pollutants of concern are particulate matter,
formaldehyde, other wood decomposition products, and volatile organic
compounds (VOC). The review conducted by Midwest Research Institute (MRI)
for the CTC focuses on the evaluation of EFB's and wet ESP's. Colorado
and several other States also have expressed an interest in a review of
press vent emissions.
This report presents a general process description of waferboard
production (Section 3.0), an analysis of the extractable organics in wood
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(Section 4.0), a characterization of wood chip dryer effluents
(Section 5.0), a discussion on aerosol formation (Section 6.0), an
evaluation of emission control options (Section 7.0), and a review of the
available Information on press vent emissions (Section 8.0).
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2.0 SUMMARY AND CONCLUSIONS
2.1 CHARACTERIZATION OF EMISSIONS
It 1s difficult, with the limited data available, to characterize
wood chip dryer effluents. Emissions from wood chip dryers are composed
of organic compounds from the extractable portion of the wood, wood dust,
products of combustion, and fly ash. Wood species, dryer temperature,
dryer loading rate, previous drying history of the wood, and other factors
significantly affect the composition of wood chip dryer effluents. An
understanding of the relationships between these factors and the
composition of wood chip dryer exhaust emissions would require
comprehensive parametric test data that currently are not available.
2.2 EMISSION CONTROLS
The two devices used to control wood chip dryer effluents are the
electrified filter bed (EFB) and the wet electrostatic precipitator
(ESP). These are the devices most likely to be considered in a best
available control technology analysis.
The EFB has been a popular control device in the wood products
industry for controlling dryer effluent gases. Approximately 40 units are
1n use to control emissions from waferboard and other composite material
dryers. Because the EFB is a dry control device, it offers the
convenience of producing a dry waste stream that requires disposal but no
further treatment. The current data show EFB particulate removal
efficiency to be 79 to 94 percent. Total hydrocarbon removals are
expected to be much lower (10 to 20 percent) because the EFB cannot
electrostatically remove any material that 1s not a solid or that it
cannot condense. One of the more prevalent problems associated with the
EFB 1s the difficulty it sometimes has with the extremely sticky,
hydrocarbon-laden gas streams generated from the drying of pine and other
softwood species. Hydrocarbons condensing in the unit collect on the
ionizer and on the surface of the gravel, reducing the efficiency of the
unit and requiring frequent shutdowns and cleaning of the unit. For this
reason, the EFB is more suited for controlling effluents generated from
the drying of hardwoods and other low-resin-content species.
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Wet ESP's are used to control effluent gas streams containing
particulate and sticky, condensible hydrocarbon pollutants. These devices
have been used extensively in various industrial applications (e.g.,
aluminum pot lines, carbon anode baking furnaces, and wool fiberglass
plants) to control particulate matter. Five wet ESP's are in service to
control wood chip dryer effluents in the waferboard and other wood
composite material Industries. Tests indicate that the particulate
collection efficiency of a wet ESP 1s between 90 and 98 percent. Wet
ESP's have a demonstrated removal efficiency of 70 percent for total
gaseous nonmethane organic (TGNMO) compounds. Wet ESP's are better than
EFB's for the control of sticky, hydrocarbon-laden wood chip dryer
effluent streams. A disadvantage of wet ESP's is that their capital and
operating costs are higher than for EFB's. Also, plants using wet ESP's
must have the ability to dispose or consume within the plant their spent
spray water.
2.3 PRESS VENT EMISSIONS
Emissions from the press vents result as the resinated chips are
heated 1n the press. Formaldehyde and other VOC's contained 1n the resin
and wood chips evaporate and exit through the press vents. Three factors
were Identified that affect formaldehyde emissions from press vents:
(a) the excess formaldehyde content of the resin, (b) the amount of resin
used, and (c) the press temperature. The data indicate that from 5 to
15 percent of the excess formaldehyde in a panel board is emitted during
the pressing and board cooling operations. Analysis of the available data
on press vent emissions suggests that use of methyldlisocyanate resins
(MDI) instead of phenol/formaldehyde resins would result 1n a 50 percent
reduction of VOC emissions and a 90 percent reduction of formaldehyde
emissions.
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3.0 GENERAL PROCESS DESCRIPTION
The fundamental processing steps involved 1n the production of
waferboard, oriented strandboard (OSB), and related panelboard products
are described below. Some processing techniques will vary among different
plants and product lines.
Logs that go to the waferboard plant are cut to 100 inches in length
by a slasher saw and put into a hot pond. The hot pond, maintained at a
temperature between 80° and 120°F (18° to 43°C), pretreats the logs for
waferizing by thawing them during winter operations. The logs are
debarked and carried to stationary slasher saws where they are cut into
33-inch lengths in preparation for the waferizer. The waferizer slices
the logs into wafers about 0.028 inch thick. The wafers are then conveyed
to the wet wafer storage bin to await processing through the dryer(s).
The dryer(s) is normally fired by wood wastes from the plant and occasion-
ally by oil. When methylenediphenyldiisocyanate (MDI) resin is utilized
in the blending process, the wafers are dried until their moisture is 8 to
10 percent. When phenolic resin is used in the blending process, the
wafers are dried to 4 to 5 percent moisture. The dried wafers are
pneumatically conveyed from the dryer, separated from the gas stream at
the primary cyclone, and transferred onto a rotary screen. The gas stream
continues through a multiclone, I.D. fan, and sometimes a tertiary pollu-
tion control device (i.e., EFB, wet ESP) and then is discharged through a
.stack into the atmosphere. A rotary screen further classifies the
wafers. Undesired material is sent to a fuel preparation system for the
dryer burner and the screened wafers are stored in dry bins. The wafers
are then conveyed to the blender where they are blended with the resin.
The resinated wafers then go to the formers where they are metered out on
a continuously moving screen system. The continuous formed mat is then
separated into desired lengths by a traveling saw, passed to the accumu-
lating loader, and sent to the press. The press applies heat and pressure
to activate the resin and bond the wafers into a solid sheet of waferboard.
The bonded sheet is then trimmed to final dimensions, sprayed on the edges
with a protective coating, and packaged for shipping.
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For the purposes of this study, the emission points of interest are
the wood chip dryers and the presses.
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4.0 EXTRACTABLE ORGAN ICS IN WOOD
It 1s customary 1n the wood products Industry to differentiate the
wood tissue components from the extractive components of wood. The
extractive components Include the substances that are soluble 1n neutral
organic solvents or are volatile with steam. The term extractive
components embraces a wide range of chemical compounds. No single species
of wood contains all the possible compounds or even all the different
classes of compounds. This discussion will focus on the rather large
group of materials generally referred to as "resins." Wood resin will be
generally defined as those hydrophoblc substances soluble in neutral,
nonpolar organic solvents. This will Include terpenes, resin acids, fatty
adds and esters, and various alcohols, hydrocarbons, and other neutral
compounds associated with these materials.
As shown 1n Table 1, the resin content of hardwoods varies greatly
from one species to another. The majority of the hardwoods listed contain
considerably.less than 1 percent resin by weight. From Table 2, it is
apparent that softwoods contain considerably more resin than hardwoods.
Resin contents of at least 1 percent have been reported for almost every
species of softwood listed; however, the pines have by far the highest
resin content. The most striking difference between hardwood and softwood
resin is the almost complete absence of resin acids in hardwood resins.
In contrast, resin adds are a major component of pine and spruce resin,
generally accounting for 30 to 40 percent of the weight of the extract.1
The major component of both hardwood and softwood resin is fatty
acid. In softwoods, the fatty acids make up 40 to 65 percent of the
resin, while in hardwoods they account for 60 to 90 percent.1 In fresh
wood samples, the bulk of the fatty acids are usually present as esters.
Certain conifers secrete a viscous liquid called oleoresin
(essentially of a solution of a resin in a volatile oil) when the tree is
wounded. In the case of pine oleoresin, the volatile oil, or turpentine,
constitutes about 25 percent of the weight of the oleoresin.1 The
nonvolatile part of the oleoresin consists mainly of resin acids. Both
the volatile oil and the resin acids belong to the terpenoids, a group of
compounds derived from a family of hydrocarbons known as the terpenes. As
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TABLE 1. ETHER-SOLUBLE EXTRACTIVES CONTENT OF COMMON HARDWOODS1
Species
Sugar maple
Red maple
Yellow birch
Paper birch
American beech
White ash
Black tupelo
Water tupelo
Sweetgum
Eastern cottonwood
Blgtooth aspen
Yellow poplar
White oak
Black willow
American basswood
American elm
Ether-soluble,
percent (w/w)
of whole wood
0.22-0.89
—
0.43-1.43
1.5-3.52
0.3-0.86
—
0.27-0.40
0.34
0.22-0.49
0.3-0.4
0.86-2.7
—
—
0.3
0.89-13.2
0.28
Sapwood
0.23-0.26
0.16-0.51
0.36-0.88
0.79-2.97
0.19-0.26
0.88-1.17
0.44
0.95
—
—
—
0.13-0.27
0.46-0.65
—
—
^ mm
Heartwood
0.25-0.33
0.21-0.31
0.30-1.18
2.19-3.89
0.38-0.57
0.45-0.46
0.54
0.88
—
—
—
0.43-0.58
0.62-0.71
—
—
__
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TABLE 2. ETHER-SOLUBLE EXTRACTIVES CONTENT OF COMMON SOFTWOODS1
Species
Balsam fir
White fir
Douglas fir
Eastern hemlock
Western hemlock
Eastern larch
Western larch
Western redcedar
Incense cedar
Yellow cedar
White spruce
Black spruce
Red spruce
Jack pine
Short! eaf pine
Long leaf pine
Ponderosa pine
Monterey pine
Eastern white pine
Slash pine
Ether-soluble,
percent (w/w)
of whole wood
1.0-1.8
0.23
0.3-2.6
0.2-1.2
0.3-1.3
1.3
0.72-0.93
0.3-2.5
3.33-4.90
1.36-3.34
0.4-2.1
0.6-1.0
—
1.9-4.3
1.1-2.3
2.1-9.2
6.5-9.6
—
5.9
1.4-15.2
Sapwood
0.95
0.20
0.4
—
0.2-0.5
—
—
—
0.67
1.00
—
—
0.6-1.2
1.6
2.6-3.8
1.4-2.7
3.2-4.8
0.5-1.2
5.46
—
Heartwood
0.74-1.18
0.25
1.0
—
0.2-1.0
—
—
—
4.78
1.32
—
—
0.8-1.5
5.2
3.9-13.3
3.6-20.3
2.7-9.9
2.0-6.8
3.62
—
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might be expected, the volatile oils of the pines have been studied more
than oils of other species because of their commercial importance. Gum
turpentine is obtained by steam distillation of the oleoresin, and wood
turpentine is usually obtained by steam distillation or solvent extraction
of pine heartwood. Gum and wood turpentine may have very different
compositions. For example, the gum turpentine from pine was found to
contain approximately 65 percent a-pinene and 35 percent s-pinene, while
the wood turpentine consisted of 80 percent a-pinene, 10 percent limonine,
8 percent a-terpinene, and very little s-pinene.1 Most of the pines from
the southeastern United States produce turpentines comprised chiefly of
a-pinene and 8-pinene, the former predominating.
10
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5.0 CHARACTERIZATION OF WOOD CHIP DRYER EFFLUENTS
Emissions from direct-fired wood chip dryers are composed of organic
compounds evaporated from the extractable portion of the wood, wood dust,
products of combustion, and fly ash. The organic portion of the emissions
can be categorized as: (1) turpentine, (2) resin and fatty adds, and
(3) combustion and pryolysis products. Wood species, dryer temperature,
dryer loading rate, previous drying history of the wood, and other factors
significantly effect the composition of wood chip dryer effluents. An
understanding of the relationships between these factors and the
composition of wood chip dryer exhaust emissions would require
comprehensive parametric test data that currently are not available.
5.1 TERRENES
Turpentine is a major constituent of many softwood species. The
amount present in numerous softwood species can be found in Table 3. The
actual amount of turpentine present in the wood being dried depends on the
wood species and on the amount of drying the wood has undergone. Green
softwood contains the most turpentines. The amount of turpentine in the
wood will decrease as it dries, either in a drying process or during
storage. A 50 percent loss of turpentine from wood has been reported
during storage of wood chips in an open pile for 1 week.2
Terpenes have boiling points of about 155°C (311°F). Nearly all of
the turpentine material contained in green wood chips is removed during
drying because the boiling points of the terpenes are below the dryer air
temperatere. Terpenes will remain 1n the vapor state in the dryer and
when emitted to the atmosphere and, thus, will not contribute to
particulate emissions or the opacity of dryer plumes.
Terpenes are among the most photochemically reactive compounds.
Although terpenes have been shown to react rapidly in the presence of NO,
and ultraviolet light to form ozone, they are inefficient ozone
producers. Secondary reactions with ozone result in oxidation of terpenes
that block further photochemical reactions. Although the reaction rates
for terpenes are high, the net ozone yield is low.
x
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TABLE 3. TURPENTINE CONTENT OF WOOD SPECIES'
Species
Bahama pine
Balsam fir
Black spruce
Douglas fir
Washington
Canada
Eastern white pine
Engelman spruce
Grand fir
Jack pine
Hemlock
Eastern
Mountain
Western
Loblolly pine
Lodgepole pine
Long leaf pine
Pacific silver fir
Noble fir
Pitch pine (yellow
or Southern pine)
Pond pine
Turpentine,
gal /ton
dry wood
1.09
0.93
0.08
1.05
0.19
1.05
0.18
NO
0.81
. ND
ND
ND
0.97
0.54
4.06
ND
NO
1.12
0.92
Species
Ponderosa pine
Red pine
Sand pine
Short leaf pine
Sitka spruce
Splash pine
Spruce pine
Subalplne fir
Sugar pine
Tamarack
Virginia pine
(scrub pine)
White fir
Western larch
Western red cedar
Western white pine
White spruce
Turpentine,
gal /ton
dry wood
0.98
0.99
0.48
0.89
0.12
1.40
1.17
0.15
0.66
0.12
5.86
ND
0.66
ND
0.24
0.16
ND = None detected.
12
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5.2 RESINS AND FATTY ACIDS
Resins and fatty acids, otherwise known as pitch, are also natural
constituents of wood. The amount of pitch in the wood varies with
species, with softwood species containing a large amount and hardwood
species containing very little. Fatty adds contained 1n southern wood
species consist primarily of oleic and Unolelc adds. The resin acids
are principally levoplmaratic, palustratic, and abletic acids.2
As with the terpenes, resin and fatty adds also vaporize during
drying. Fatty acids have boiling points between 320°C and 370°C (608° to
698°F). Resin acid boiling points are even higher.2 Vaporization of
pitch Increases with higher drying temperatures, higher airflow through
the dryer, and higher pitch content of the wood. Unlike the terpenes,
vaporized resins and fatty acids cool and condense as they exit the dryer
to form an aerosol that produces the blue haze associated with wood
product dryer emissions. Aerosol formation is discussed further in
Section 6.0. Analyses of the condensible fractions of veneer dryer
emissions have been conducted. The same fatty and resin acids found in
wood extractives were found in the veneer dryer emissions. The amount of
each chemical species varied greatly depending upon the wood species dried
and the point at which the dryer was sampled. Slightly more resin acids
than fatty acids were found in most of the samples.2
A study was done recently by the National Council of the Paper
Industry for Air and Stream Improvements (NCASI) at eight panelboard
plants whose dryers produced furnish for particleboard, waferboard, OSB,
and fiberboard manufacture. Emissions of condensable organic material,
defined as the material capable of passing a filter at 250°F and
condensing at 70°F, ranged between 0.04 and 2.5 Ib/ton of product.3 Total
particulate and condensable organic material emission rates ranged from
0.8 to 6.5 Ib/ton of product. The concentration of these materials in the
exit gas and hence the emission rate was influenced by the temperature of
the gases entering the dryer, the species being dried, and the amount of
drying the wood had undergone.
13
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5.3 PRODUCTS OF THERMAL DECOMPOSITION
The reactions that occur during the thermal decomposition of wood
result 1n the formation of a large number of chemical compounds. More
than 200 compounds Isolated after pyrolysis of resinous woods have been
identified, and, undoubtedly, many others not yet identified are
present. Although the origin of all the products of thermal decomposition
cannot be assigned to individual components of the original wood, it 1s
known that each of the major components yields characteristic decomposi-
tion products. Thus, furans result from pyrolysis of pentoses, and an
assortment of aromatic substances from pyrolysis of lignin. The origin of
much of the acetic acid is attributed to the acetyl groups in the wood.
At the elevated temperatures, secondary reactions of many types take
place. The final products represent not only a wide variety of
substances, but also the varying proportions of these substances depend
upon the conditions during the decomposition reactions.
Wood remains stable when heated up to about 100°C (212°F), except for
loss of hydroscopic water. As the temperature increases further, carbon
dioxide, carbon monoxide, hydrogen, and water are formed by the chemical
decomposition of the wood constituents. Between 100° and 250°C (212° to
480°F) decomposition causes the wood to darken. At higher temperatures,
up to 500"C (850°F), carbonization occurs and additional volatile
materials are lost.1*
The products resulting from the thermal decomposition of wood can be
classified as noncondensable pyroligneous liquor, insoluble tar, and
charcoal. The products obtained by laboratory pyrolysis over the range of
250° to 350°C (480° to 610°F) were approximately 27.5 percent water,
10 percent noncondensable gases, 2 percent acids and methanol, 5 percent
dissolved tar, and 8 percent settled tar. Over the range of 350° to 450°C
(610° to 770°F) the products were 4 percent water, 3 percent nonconden-
sable gases, 2 percent settled tar, and 0.5 percent acids and methanol."*
The noncondensable gases consisted largely of carbon dioxide and carbon
monoxide, with smaller quantities of hydrogen and hydrocarbons.
14
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6.0 AEROSOL FORMATION
Some of the organic materials in wood chip dryer emissions form
aerosols upon cooling. These particles form on condensation nuclei,
mainly fly ash and other solid part icu late, and grow rapidly as the gases
are cooled. As these particles exit the stack and are cooled further,
they are visible as a blue haze that is characteristic of wood chip dryer
emissions. The behavior of small aerosols as they enter the atmosphere is
important. Extremely small aerosols are likely to revaporize due to their
high vapor pressures. Larger aerosols would be expected to exist for much
longer time periods allowing coagulation, agglomeration, and surface
chemical oxidation effects to take place.
The size of the smallest aerosol particle possible is given by the
equation.2
p " RT In S
where:
dp » smallest stable aerosol particle size
o » surface tension of compound
v = molar volume of compound
R = gas law constant
T » absolute temperature
S = degree of supersaturation. This can be taken as the actual
vapor pressure of the material in the gas (as a particle)
divided by the vapor pressure of the material over a flat
surface (bulk liquid).
Particles smaller than dp will tend to evaporate while particles larger
than dp will tend to grow in a supersaturated gas stream. Figure 1 shows
the theoretical minimum particle size produced at different degrees of
supersaturation for oleic acid.2 Rapid cooling of wood chip dryer
emissions either by mixing with ambient air or by cooling with water
sprays should produce high supersaturations and, thereby, produce
submicron aerosol particles. Reference to Figure 2 will show that it is
unlikely that any oleic acid particles less than 0.003 ym will form.
15
-------
0
CT>
UJ
UJ
_l
CJ
h-
o:
01
OOI
0
_L
-J-
5 10 15 20
SUPER SATURATION
25
I
O
to
a
E
o.
a.
»\
UJ
DC
UJ
or
Q.
o:
O
o_
<
500
100 -
40 80 120 160
TEMPERATURE °C
200
Figure 1. Minimum theoretical particle size formed
for oleic acid at various supersaturations.
Figure 2. Theoretical vapor pressure of small
particles of oleic atid.
-------
Once the wood chip dryer emissions have been cooled and condensation
has taken place, the supersaturation of the organics will be reduced
because of transfer of material from the gas phase to the liquid phase.
Small particles formed under high supersaturation are no longer stable.
They will revaporlze, and the evaporated organics will tend to recondense
on larger particles.2
The vapor pressure of a material in a very small diameter particle is
much higher than the vapor pressure of that same material over a flat
surface. This 1s known as a the Kelvin effect. A relationship between
vapor pressure of a small particle to the vapor pressure over a flat
surface 1s given by:2
Pd 4 v a
where Pd and PS are the vapor pressures of the material 1n particle form
and over a flat surface (bulk liquid), respectively. Figure 2 shows the
Kelvin effect for various particle sizes and temperatures for oleic
add.
No studies have been undertaken to determine the fate of these
aerosols in the atmosphere. However, It is known that typically
75 percent of the particulate matter found in uncontrolled wood chip dryer
exhaust streams is less than 1 micron in aerodynamic diameter with
65 percent being less than 0.5 microns. More information is needed on
wood chip dryer emission particle size distributions from controlled
sources to comment on the possibility of revaporization of small
aerosols. Furthermore, aerosol behavior in the stack bears no
relationship to what might be expected to occur in the atmosphere.
17
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7.0 EMISSION CONTROLS
As discussed In the previous section, wood chip dryer exhaust streams
contain dry participate, products of combustion and pyrolysis, and
aerosols formed from the condensation of hydrocarbons volatilized from the
wood chips. Study of the particle size distribution indicates that
75 percent of the particulate matter is less than one micron in
aerodynamic diameter. The submicron size of this pollutant suggests that
wet scrubbers would have to operate in the 60- to 70-inch of water column
range to be effective.
Baghouse systems for control of wood chip dryer exhaust streams have
been tried and abandoned because of the extreme fire hazards and also
because very large air-to-cloth ratios were required due to the 15 percent
to 30 percent moisture in the wafer dryer gas stream making the baghouse
susceptible to blinding. This makes baghouse systems economically
unfeasible and very undependable. No baghouse manufacturer could give a
reasonable guarantee that the fire hazard problem or the problems
resulting from high moisture could be solved at this time. Resolution of
these problems is necessary before baghouse systems offer a long-term
dependable solution to controlling partlculate matter from a wafer dryer
gas stream.
Electrostatic control devices have been demonstrated to be highly
efficient at controlling the submicron particulate streams. The two
devices currently used to control wood chip dryer effluents are the EFB
and the wet ESP. These are the devices that are most likely to be
considered in a best available control technology analysis and are
discussed in the sections that follow. In addition to controlling
emissions using add-on controls, attempts are being made by States and
waferboard facilities to reduce the amount of pollutant formed in the
dryer. This may be accomplished by reducing dryer inlet temperatures,
reducing the load on the dryer, and/or redesigning the dryer flow path.
7.1 ELECTRIFIED FILTER BED
7.1.1 General Description
The EFB fine dust collector is an air pollution control device which
serves to remove fine dust and smoke particles from flue gas streams.
18
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Eighty-four units are currently in use for a variety of pollution control
applications (see Appendix A). Half are in use to control emissions from
waferboard and other composite material dryers.
In the system, the fine dust particles in the exhaust gases are given
an electrostatic charge 1n the corona formed by the Ionizer, then are
deposited on an electrically polarized filter bed of pea gravel. The pea
gravel 1s removed from the filtration region and cleaned externally 1n a
pneumatic conveyor. The dust removed from the gravel 1s conveyed to a
small bag filter, and the cleaned gravel 1s returned to the filter. The
following sections detail the operation of the various components. A
general view of the system and the location of system components are
presented in Figure 3.
7.1.1.1 Ionizer. The exhaust gas stream laden with dust enters the
system as shown in Figure 4. It turns downward and passes through an
annular region formed by two concentric cylinders. Centered in this
annulus are four rings spaced vertically 5 inches apart. Sharp-pointed
needles protrude from the ring edges. The cylinders are electrically
grounded while the rings are held at a high DC negative voltage. Corona
discharge from the needle points creates Ions, which stream from the
needle points toward the adjacent cylinder wall. These Ions attach to
and, as a result, electrostatically charge the dust particles as they
pass.
A set of blowdown nozzles removes dust that accumulates on the
needles and tube, impeding the ionization process. Compressed air is
supplied to these nozzles periodically on a timed cycle. The ring hanger
assembly is rotated slowly (continuously) by a motor drive, cleaning dust
from the entire circumference of the wall and needles.
7.1.1.2 Filter Bed. As shown 1n Figure 5, pea-shaped gravel is held
between front and rear louver sets to form the filter bed. The louver
structure provides large, nonfouling passages for the gas while retaining
gravel by its angle of repose. The louvers are electrically grounded. A
cylindrical, expanded metal sheet is suspended between the louver sets and
held at a high DC positive voltage. The voltage polarizes the gravel,
inducing regions of positive and negative charge on the stones.
19
-------
DISENGAGEMENT CHAMBER
COLLECTED DUST
OUT TO
'SAG FILTER
GRAVEL RESERVE
OOWNCOMEP. PIPE
LOW GRAVEL LEVEL SENSOR
DIRTY GAS
INLET
GBWEL GATE
CLEAN GAS
»> OUTLET
INFEEQ PIPE
. ADJUSTABLE VENTURl NOZZLE
AIR
RESSURE BLOWER
Figure 3. Electrified filter bed system.
20
-------
PURGE AIR
BLOWER
DISC SLOWDOWN AIR IN -\ |,
CLEAN GRAVEL IN
UPPER
HOPPER -T_
:ONIZER DISCS
INNER LOUVERS
I3EO ELECTRODE-
OUTER LOUVERS
OUTLET PLENUMS
BOTTOM HOPPER
CUST AND GKAVEL OUT
Figure 4. Ionizer and gravel bed assembly.
21
-------
-HIGH VOLTAGE
-BCD ELECTRODE
I (EXPANDED METAL)
INNER LOUVERS
Figure 5. Gravel bed schematic.
22
-------
After passing through the ionizer, the exhaust gas flows down the
chamber inside the inner louvers and then outwardly through the annular
filter bed. As it does, the negatively charged dust particles are
attracted and attached to the positively charged regions on the gravel.
Cleaned gas collects in the outlet plenum and exits the system.
As dust accumulates in the filter bed, it fills the pore spaces and
increases the filter's resistance to flow. To maintain constant gas flow
pressure drop across the system, the gravel is slowly and continuously
removed from the filter bed. The bottom hopper assures uniform gravel
flow around the annulus of the filter. Clean gravel is provided to the
upper hopper, which is operated in a flooded condition. Gravel feed rate
is determined by removal rate from below.
7.1.1.3 Gravel Cleaninq/Recirculation. Figures 6 and 7 show the
gravel cleaning and recirculatlon system. The purpose of this system is
to clean the gravel and elevate it to the top of the filter bed for
reuse. Gravel travels from the bottom hopper to the feeder via the infeed
pipe. The Infeed pipe, flooded with gravel, acts as an air pressure seal
between the feeder and the filter bed. The feeder regulates the gravel
recycle rate and carries gravel to the base of the lift line. The lift
line blower supplies lift air through a venturi nozzle to the lift line.
The venturi creates negative pressure in the feeder, which aspirates dust
into the lift line through a slot in the side of the pipe. Gravel rate is
set by the nozzle position. Lowering the nozzle opens more slot area and
allows more gravel to be pneumatically elevated to the disengagement
chamber.
Violent agitation in the lift line, as the gravel is pneumatically
conveyed, dislodges dust. The lift line discharges into the disengagement
chamber, which decreases air velocity. The cleaned gravel falls into the
gravel reserve hopper while the dust is conveyed with the lift air out to
the bag filter. The overflow pipe is primarily utilized in loading or
unloading of the system with gravel. Under normal operation, the gravel
level in the storage pile remains below the overflow level.
Clean gravel returns to the filter as required through the downcomer
pipes. The downcomer pipes also act as air pressure seals between the
disengagement chamber and the filter.
23
-------
LIFT PIPE
GRAVEL FEED
CONTROLLED
FROM
LIFT SLOWER —-
Figure 6. Gravel bed flow controller,
24
-------
1FT
L ••!•: i
• BOUNCE PAD
DISENGAGEMENT
CHAMBER
INSPECTION PORT
•O
LIFT AIR CONVEYS
DUST TO BAG FILTER
PRESSURE
EQUALIZING
TAP
LIFT &IRCONVFX?
GRAVEL AND OUST
LOW GRAVEL
LEVEL INDICATOR
. DOWNCOMER PIPE
\ RETURNS CL EA N GRA VEL
ro FILTER BED
Figure 7. Disengagement chamber.
25
-------
The dust collector shown In Figure 8 1s a conventional pulse jet bag
filter. It is equipped with a fan to provide draft from the disengagement
chamber to the bag filter. Oust collects on the bags and, at timed
Intervals, the bags are pulsed with compressed air to dislodge the
accumulated dust layer. The agglomerated dust falls to the bag filter
bottom hopper where 1t 1s discharged through a rotary airlock feeder to
the customer's receptable. A hopper vibrator on a timed cycle helps dust
flow out of the baghouse hoppers.
7.1.2 Pollutant Removal Efficiencies
With the exception of one test program, all of the testing done to
date on EFB systems controlling wood chip dryers has focused on
particulate measurements (see Appendix B). Tables 4 and 5 summarize the
available Information for capture efficiency of particulate matter in an
EFB. The data show that average capture efficiencies range from 79 to
94 percent for particulate. Data from a plant desiring to remain
anonymous indicates the EFB controls approximately 20 percent of the total
hydrocarbon emissions (see Table 5).
7.1.3 Factors Affecting Performance and Suitability
The EFB has been a popular control device 1n the wood products
industry for controlling dryer effluent gases. Because the EFB is a dry
type of control, it offers the convenience of producing an effluent stream
that requires no further treatment. The unit is also relatively small and
does not require a large amount of floor space.
One of the more prevalent problems with the EFB is the sticky
hydrocarbon coating that accumulates on the ionizer and gravel during the
drying of pine and other high resin content softwood species. According
to EFB, Inc., experience has shown that the major factor contributing to
the hydrocarbon glaze in their units is condensed moisture. Captured
particulate matter laden with hydrocarbon adheres to the gravel. The
hydrocarbon dissolves in moisture droplets occasionally formed on the
gravel. This produces a glazing of hydrocarbon that is not readily
removed by agitation in the disengagement chamber. Over time, the glazing
builds up and reduces the efficiency of the unit forcing frequent shutdown
and cleaning. According to EFB, Inc., this occurrence can be virtually
eliminated by insulating the unit and operating the unit at temperatures
26
-------
CUTLET-,
?!LOT SOLENOID
VALVE CONTROLLER —
Figure 8. Bag filter.
27
-------
TABLE 4. EFFICIENCY SUMMARY OF WEYERHAEUSER's EFB IN
MONCURE, NORTH CAROLINA, FOR CONTROL OF WOOD
PARTICLE DRYER EXHAUST
TEST PERFORMED OCTOBER 20, 1988
Run No.
Inlet
part1culate,
Ib/h
Outlet
part1culate,
Ib/h
Efficiency,
percent
1
2
3
AVERAGE
21.7
20.4
15.4
19.2
1.52
1.40
0.775
1.23
93.00
93.14
94.97
93.70
28
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TABLE 5. EFFICIENCY SUMMARY OF EFB FOR CONTROL OF WOOD
PARTICLE DRYER EXHAUST3
TEST PERFORMED FEBRUARY 14-17, 1989
Run
No.
1
3
4
5
10
AVERAGE
Part 1cu late
Inlet,
Ib/h
15.4
16.4
10.6
12.0
13.7
13.6
Outlet,
Ib/h
7.6
1.4
1.3
2.8
1.5
2.9
Efficiency,
percent
51
91
88
77
89
79.2
Total hydrocarbon
Inlet,
Ib/h
24.2
33.6
29.4
26.2
20.8
26.8
Outlet,
Ib/h
21.6
27.4
18.5
19.0
19.8
21.3
Efficiency,
percent
11
18
37
27
5
19.6
aPlant desires to remain anonymous
29
-------
above the dewpoint cf the incoming gas stream. A thermal oxidation unit
has been used at one plant to burn the resin from the surface of the
gravel. It was apparently successful at removing the sticky material but
the Intense heat caused the gravel to fracture, creating the need for
greater amounts of makeup gravel. The gravel used 1n the EFB is a special
basaltic rock mined only in Washington State. A certain number of the
rocks will be destroyed in the unit over time and will need to be replaced
periodically. The "banging" action in the disengagement chamber is the
primary cause of rock destruction.
The EFB has a relatively narrow temperature operating range. The
temperature inside the unit must never approach the dew point of the gas
stream being treated since condensation of water within the system will
result in an electrical short in the gravel bed. As a result, the
manufacturers suggest that the unit be operated at 30°F above the dew
point temperature. To maintain temperature, some units use a preheater to
heat the incoming gas stream. Also, the unit must be preheated before
each startup to allow the system components to warm so they do not collect
condensation. Units are insulated to minimize heat loss. The need to
maintain an elevated temperature in the unit is diametrically opposed to
the enhancement of hydrocarbon aerosol formation, which increases the
removal efficiency of these compounds.
7.1.4 Costs
Table 6 presents the estimated capital and operating cost for three
EFB's for a waferboard plant operating three wood chip dryers and with a
projected production rate of 488 tons/day of finished product. These
costs were quoted by EFB, Inc., to the Michigan Department of Natural
Resources, Air Quality Division, in 1988.5
7.2 WET ELECTROSTATIC PRECIPITATORS
7.2.1 General Description
An ESP is a particulate control device that uses electrical forces to
move entrained particles out of the flowing gas stream and onto collector
plates. Particle collection in an ESP involves three steps: the
electrical charging of particles in the gas stream, the collection of the
particles on the collection plates or electrodes, and the removal of the
collected particulate matter. Wet ESP's are used on effluent gas streams
30
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TABLE 6. EFB COST EVALUATION9
I. Installed Capital Costs
Included:
1. Basic units (3)
2. Add booster fan (3)
3. Gravel hoppers (3)
4. Bucket elevators (3)
5. Gravel
6. EFB startup supervision
7. Freight
8. Stacks
9. Ducting, dampers with actuators
10. Platforms and catwalks
11. T.O. piping, Insulation
12. MCC's, wiring, CE panel
13. Foundations
14. Installation
15. Crane rental
II. Operating Costs (yearly)
TOTAL: $1,050,000
Yearly, $
Electrical 300 HP @ 0.04/kw 75,000
Rock replacement 15,000
General maintenance 30,000
Bag replacement 5,000
125,000
III. Annual Costs
Capital* $1,050,000x0.1627 170,835
Operating 125,000
Total annual costs 295,835
Calculated for 10 year life at 10 percent interest.
31
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containing sticky, condensable hydrocarbon pollutants. These devices have
been used extensively in various industrial applications (e.g., aluminum
pot lines, carbon anode baking furnaces, and wool fiberglass plants) to
control particulate. Five wet ESP's are 1n service to control wood chip
dryer effluents 1n the waferboard and other wood composite material
Industries.
Figure 9 presents a diagram of a Un1ted-McG1ll wet ESP. Electric
fields are established by applying a direct-current voltage across a pair
of electrodes, a discharge electrode, and a collection electrode.
Particulate matter and water droplets suspended 1n the gas stream are
electrically charged by passing through the electric field around each
discharge electrode (the negatively charged electrode). The negatively
charged particles and droplets then migrate toward the positively charged
collection electrodes. The particulate matter is separated from the gas
stream by retention on the collection electrode. Earlier designs of wet
ESP's specified that water sprays be located above the electrodes to
create a continuous film of water on the collector plates to wash the
collected particulate matter from the plates. The most recent installa-
tions have replaced this continuous spray system with an intermittent
traveling header system equipped with multiple high-pressure spray
nozzles. The high-pressure spray dislodges and removes any remaining
organic and particulate buildup from the plates. Use of intermittent high
pressure sprays instead of continuous sprays results in a decreased water
requirement and reduced voltage degredation in the wet ESP.
7.2.2 Pollutant Removal Efficiencies
At this time, data indicating the efficiency of the wet ESP in
removing pollutants from wood chip dryer exhaust streams are limited. To
date, only five wet ESP's are on-line to control wood chip dryer
exhaust. Georgia-Pacific, which operates three Un1ted-McG1ll wet ESP's,
has conducted particulate matter testing on each. These tests, conducted
at the inlet and outlet of each precipitator, show an average particulate
collection efficiency of from 90.5 to 94.8 percent (see Tables 7 through
9). Georgia-Pacific has also tested for formaldehyde and total gaseous
nonmethane organics (TGNMO) at their Woodland, Maine, and Skippers,
Virginia, plants. At Woodland, Maine, the wet ESP averaged 70 and
52 percent removal of TGNMO and formaldehyde, respectively (see
32
-------
Quick-disconnect spray nozzles
Drive cable
Module
Flexible hose
Swivel connection
Alternating high-voltage and
grounded collection plates
Variable-speed drive
Self-cleaning casters
Access door
Inlet for purge air
Inlet for water
Figure 9. Wet ESP module equipped with traveling spray system.
33
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TABLE 7. EFFICIENCY SUMMARY OF GEORGIA-PACIFIC'S WET ESP IN
DUDLEY, NORTH CAROLINA, FOR CONTROL OF WOOD CHIP
DRYER EXHAUST
TEST PERFORMED SEPTEMBER 1983
Run No.
1
2
4
AVERAGE
Inlet
part 1cu late,
Ib/h
81.70
61.13
79.29
74.04
Outlet
part 1cu late,
Ib/h
7.712
7.219
5.820
6.917
Efficiency,
percent
90.56
88.19
92.66
90.47
Test report does not account for Run No. 3.
34
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TABLE 8. EFFICIENCY SUMMARY OF GEORGIA-PACIFIC'S
WET ESP IN SKIPPERS, VIRGINIA FOR CONTROL OF
WOOD CHIP DRYER EXHAUST
TEST PERFORMED APRIL 20, 1989
Run No.
Inlet, Ib/h
1
2
3
AVERAGE
Outlet. Ib/h
1
2
3
AVERAGE
TGNMO
98.1
286.2
177.4
187.2
22.3
168.5
84.6
91.8
Formaldehyde
9.6
10.0
11.4
10.3
8.0
11.2
11.5
10.2
Part icu late
131.5
46.6
303.4
160.5
11.7
14.6
10.8
12.4
Efficiency, percent
1
2
3
77.2
41.1
52.3
16.7
-12.0
-0.9
91.1
68.7
96.4
AVERAGE
56.9
1.3
85.4
35
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TABLE 9. EFFICIENCY SUMMARY OF GEORGIA-PACIFIC'S WET ESP IN
WOODLAND, MAINE, FOR CONTROL OF WOOD CHIP DRYER EXHAUST
TEST PERFORMED OCTOBER 25, 1988
Run No.
Inlet, Ib/h
1
2
3
4
AVERAGE
Outlet, Ib/h
1
2
3
4
AVERAGE
Efficiency.
1
2
4a
AVERAGE
TGNMO
83.52
143.21
60.99
95.91
37.99
18.77
19.25
25.34
percent
54.51
86.89
68.45
68.45
69.95
aPlant ran out of chips. Data
Formaldehyde
0.1084
0.0978
0.1294
0.0817
0.1043
0.596
0.0495
0.0490
0.931
0.0628
45.02
49.39
62.13 ,
(-13.95)°
52.18
represents partial
Dry catch
80.27
54.36
55.95
78.28
67.22
3.65
3.70
4.31
5.86
4.38
95.46
93.20
92.30
92.52
93.37
run.
Dry /wet
combination
189.81
126.38
142.73
118.17
144.27
6.45
6.68
7.65
7.97
7.19
96.60
94.72
94.64
93.26
94.81
36
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Table 9). At Skippers, Virginia, the wet ESP averaged 57 and 1.3 percent
removal of TGNMO and formaldehyde, respectively (see Table 8). Appendix C
contains more detailed information on the data collected from the Georgia-
Pacific tests.
7.2.3 Factors Affecting Performance and Suitability
There are several performance factors that must be considered when
determining the appropriateness of a wet ESP for control of wood chip
dryer effluents. Certainly of utmost concern, next to the precipitator's
ability to control emlslons, is the plant's ability to treat, consume, or
discharge the spent spray water and sludge generated by the unit. Spray
water used to clean the collection plates 1s recycled. Each time the
spray water 1s redrculated through the preclpltator, more sol Ids become
suspended and dissolved 1n it. It 1s known that a total solids content of
greater than 2 percent will cause spray nozzles 1n the precipitator to
plug. Plugged nozzles must be manually cleaned, resulting in excessive
down time of the unit.
Suspended solids are removed relatively easily by flocculation and
mechanical removal (I.e., filtration and/or settling). Dissolved solIds
are not so easily removed. They remain 1n solution and become more
concentrated with each pass through the preclpltator. As the total solids
content approaches 2 percent, it becomes necessary to remove all of the
spent spray water, replacing it with fresh water, or to blow down or
remove a portion of the spent spray water on a continuous basis, replacing
it with makeup water to reduce the dissolved solids content.
As mentioned earlier, a plant operating a wet ESP must have the means
to treat, consume, or discharge the spent spray water and sludge generated
by the precipitator. Most waferboard plants are located in rural areas
without the services of a local municipal wastewater treatment system to
receive their spent spray water. These are plants typically designated as
zero discharge facilities and cannot obtain an NPDES permit to release the
spent spray water to nearby streams or rivers. As a result, plants using
the wet ESP must treat their own spent spray water and/or consume some or
all of it internally.
Some plants may have the ability or capacity to consume some or all
of their spent spray water internally. Plants that operate boilers or
37
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other wet cell burners that produce steam for the presses, heat for the
buildings and hot ponds, or other uses can apply some of the spent spray
water to the fuel. Some or all of the remaining spray water may be used
as makeup water 1n the hot ponds and 1n the debarker for dust control.
The amount of spent spray water a plant can consume will vary. Current
estimates suggest that approximately 13 gallons per minute of spent spray
water will be required as blowdown water to keep the dissolved solids
content below 2 percent.
Because wood chip dryer effluents contain sticky organlcs and dry
partlculate matter, wet ESP collection plates are particularly succeptable
to fouling. If the collection plates are not thoroughly washed in the
spray cycle, they can become dry and caked with collected partlculate
matter. This will reduce the efficiency of the unit and lead to the
eventual shutdown and cleaning of the unit. Occasionally, a cake formed
on a plate will break loose and become lodged between an Ionizing and a
collection plate shorting the circuit between the two plates. This also
results in reduced efficiency and increased down time.
As discussed in Section 3.0, a major component of the extractable
portion of wood are adds. These adds significantly lower the pH of the
spray water, which creates a corrosive environment 1n the precipitator.
Caustic is added to the spray water to raise the pH to between 7 and 8.
The resulting alkaline pH will react with fats contained in the spray
water to produce surfactants (soap) that can cause foaming, thus,
antifoaming agents are also added to the spray water. Wood chip dryers
that are heated by suspension burners discharge an effluent gas that is
less acidic than that heated by a grate-type burner. Suspension burners
entrain considerably more fly ash in the dryer effluent than grate-type
burners. This fly ash is alkaline and serves to partially neutralize the
acidic hydrocarbons exiting the dryer. As a result, suspension burners
may reduce the corrosive nature of the effluent and decrease the amount of
caustic required to neutralize the spray water.
The most recent wet ESP constructed to control wood chip dryer
emissions is at Georgia-Pacific's facility in Woodland, Maine. Gases
exiting the dryer enter a prequench to cool and condense (saturate) gases
before they enter the precipitator. The prequench is essentially a low-
38
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energy scrubber that sprays water into the incoming gas stream. The gas
that exits the prequench is saturated (i.e., multicomponent hydrocarbons
here approached their vapor-liquid equilibrium), and, thus, further
cooling in the precipitator will condense and capture more of the
condensable hydrocarbon, mainly the sticky resins. Because the wet ESP
cannot collect by electrostatic removal any material that will not
condense, the prequench chamber increases removal efficiency by lowering
the gas temperature, thus, saturating the stream and maximizing the
condensation of hydrocarbon for removal.
The wet ESP operates well under a variety of conditions. The
operating window is usually wide enough that process upsets in the dryers
and increased production and airflows are not a problem. One properly
designed and sized unit should have the capacity to serve the pollution
control needs of a multidryer plant. To date no facility has required or
installed multiple wet ESP's for the control of wood chip dryer exhaust
streams. However, wet ESP's are large and require substantial space.
7.2.4 Costs
Table 10 presents the estimated capital and operating cost for a wet
ESP installed in a waferboard plant operating three wood chip dryers and
with a projected production rate of 488 tons/day of finished product.
These estimates were made for Louisiana-Pacific's plant in Sagola,
Michigan. These costs were reviewed by the Michigan Air Quality Division,
Louisiana-Pacific, and United McGill in April of 1988, and all parties
agreed that the costs appeared to be accurate.5
39
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TABLE 10. CAPITAL AND OPERATING COST OF WET ESP3
I. Installed Capital Cost
Base system installed 51,733.400
Fan with motor, starter, rigging, & wiring NAa
Foundation, floor, aprons, and roads 40,000
40 gal/min water supply (well)0 35,000
6EP stack, foundation, and platform 70,000
Enclosure heating and heat tracing 2,000
Power source (180 amp, 3 phase)0 5,000
Bleed off water and sludge handling 10 700
Water clarification system NAa
Total installed price 1,896,100
11. Operating costs S/year
A. Electrical demand
1. Precipitator
a. Transformer/rectifiers (14.5 kw) 5,080
b. Purge air (8.5 kw) 2,978
c. Controls (0.8) 280
d. Chamber lights (1.0 kw) 350
e. Traveling header (0.1 kw x 3) 105
2. Water treatment and circulation system
a. Controls (0.4 kw) ' 140
b. Pumps (39.2 kw) 13,736
c. Sludge dewater (1.5 kw) 526
d. Clarifier (1.5 kw) 526
Total kw (cost $0.04Aw) 23,721
B. Water supply (15,000 gal/day « $0.02/100 gal) 1,905
C. Operation and maintenance (assumed labor costs of S20/hour)
1. Fu11-time operator/supervisor (40 hours/week) 41,600
2. Plate and nozzle cleaning (2 people, 1 day every other week, 8,320
416 hours/year)
3. Weekend operation unscheduled repairs, etc. (16 hours/week)
4. Replacement parts
0. Chemical consumption
1. Polymer (50 Ib/day)
2. Caustic soda (110 gal/day)
Total annual operating costs
III. Annual Costs
Capital (1,896,100)(0.1175)c 222,792
Operating 195,342
Total annual costs S418 134
^Included.
^Figures provided by Louisiana-Pacific.
Calculated for 20 year life at 10 percent interest.
40
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8.0 LOW/REDUCED TEMPERATURE DRYING
Dryer configurations and operation vary from plant to plant. The
typical dryer, however, accomplishes a tremendous amount of work in a
relatively short time, 1n a relatively small space, and within rather
demanding limits. At the same time, unacceptable emissions can be
generated that can be characterized as solid particulate matter, which is
normally invisible, and liquid particulate (aerosol) or blue haze
condensable hydrocarbons, which are normally very visible. These
emissions are to a large degree a function of the wood species being
dried. However, dryer temperatures, dryer loading rates and dryer design
also affect pollutant emission rates.
8.1 DRYER TEMPERATURE VERSUS EMISSIONS
Most dryers in operation utilize high volumes of air to convey
material of varied size through one or more passes within the dryer and
then discharge the material pneumatically to a cyclone. The high material
flow rate through a cyclone handling a gas stream with a large proportion
of smaller sized material results in emissions even when the cyclone is
performing at a high removal efficiency. The blue haze condensable
hydrocarbons have been observed being emitted only from dryers removing
less than 10 percent of moisture and with operating temperature of greater
than 700°F (371°C).6
Table 11 presents data from diagnostic testing done on a particle
board dryer in Rapid City, South Dakota.7 Temperature increases
throughout the range of 550°F to 950°F (310°C to 560°C) showed that small
increases in the inlet temperatures produced relatively large increases in
the particulate mass rate. The study also showed that moisture content,
once thought to be a key variable in the entire opacity and particulate
equation, proved within a large range to be insignificant.
The report suggested that low temperature drying could be
accomplished through the addition of predryers for the green materials.
The additional dryers would alleviate the excessive loading of the
existing dryers and would allow them to operate at low temperatures while
achieving the desired moisture content in the product. In addition to the
production flexibility of having additional dryers, operating^and
41
-------
TABLE 11. INCREASE OF PARTICULATE MASS RATE WITH INCREASING
INLET TEMPERATURE
Cumulative
Target Part1culate Increase in Increase 1n
Inlet temp., mass rate, Ib/h mass rate, percent mass rate, percent
550
650
750
850
950
3.77
5.95
9.02
12.66
18.47
NAa
58
52
40
46
a
58
139
236
390
aNA = Not applicable.
42
-------
maintenance techniques for dryers and their associated equipment are
usually well-known to plant personnel.
8.2 DRYER LOADING VERSUS EMISSIONS
Another critical cause of blue haze Is overloading a dryer by
attempting to remove too much moisture within a given time. Overloading
results 1n the Introduction of green material to a high-temperature flame
or gas stream causing a thermal shock that results in rapid and excessive
volatilizing of hydrocarbons that condense upon release to ambient air,
causing the characteristic blue haze.
In conventional three-pass dryers, the velocity of the air slows
through the second and third passes, allowing larger particles to settle
out and smaller particles to pass through; however, this 1s not the case
at high material flow rates. Larger settled particles will interrupt the
flow of the smaller, faster moving particles with the result being that
all particles are traveling at a rate determined only by the forward
velocity of the larger particles. When smaller particles are held at
these slower velocities in the second and third passes for a prolonged
period of time, volatilization of their surfaces occurs, which results in
the formation of hydrocarbon and carbon monoxide emissions. Should
plugging occur in the second or third passes due to the material dropping
out of suspension, elevation of particle surface temperatures to their
flash points will result in combustion.
8.3 PRODUCTIZATION 3PHV DRYER
The conventional three-pass dryer is a rotating cylindrical drum that
consists of three, concentric, interlocked cylinders. Hot gases enter the
innermost cylinder with the wet wood chips and progress through the
Intermediate and then the outer drum shells in a serpentine flow path
while pneumatically conveying the wood chips through the dryer.
The 3PHV rotary dryer, shown in Figure 10, like the conventional
three-pass dryer, is a rotating cylindrical drum consisting of three,
concentric, interlocking cylinders. In the 3PHV dryer, hot gases enter
the outermost cylinder with the wood chips and progress through the
intermediate and then the inner drum shells in a serpentine flow path.
This flow path direction 1s the opposite of that in the conventional
three-pass dryer (see Figure 11). The reason the 3PHV dryer should reduce
emissions is described below.
43
-------
EXPANSIVE NATERIAL INFEEfl INTRODUCES
MATERIAL OUTSIDE Of HOI SAS FLOM STREAK
HOI GAS ENTRY
HIGH TEMPERATURE
MINERAL MOO. INSULATION
ALTERNATING FLIBHTS
PROVIDE BHEATEfl SHOWERING
LABYRINTH FRONT SEAL PERMITS
THERMAL EXPANSION AND
OELU6C HATER ESCAPE
KICKER FLIGHTS MOVE
NATERIAL AHAV FROM SEAL
(ULVANEALLEO SKIN
OUAOTRAK SUPPORTS'
KITH CRAPHITE BLOCK LUBRICATION
CHAIN DRIVE IS POSITIVE ACTING
REVERSIME SPROCKET
FOR AOOtO MEAR SURFACE
OHY Mtlllllil
MIT
Iff I OH SHU)1
CONTINUOltS MOTION SINSOA
FLIGHTS AND OlISSETS COMINUOUSLV
MEIOEO ON NATERIAL HANDLING SIDE
PRESSURE VESSEL QUALITY STRESS
RELIEVED TRACKS HEAT SHRUNK AND MfI OH)
TO MASSIVE BASEPLATES
PREHEATING AM) SEPARATION IONE
3PHV ROTARY DRUM DRYER
PRODUCTIZATION. INC.
Independence. Kansas 67301
U S. PATENT Ntt 472SI7I (7/B8-BROCHURE)
Figure 10. Productization 3PHV rotary drum dryer.
-------
MATERIAL INLET
HOT GASES
MATERIAL INLET
HOT GASES
PRODUCTIZATION. INC. 3PHV DRUM DRYER
CONVENTIONAL TRIPLE PASS DRUM DRYER
FLOW COMPARISON
PRODUCTIZATION. INC.
Independence. Kansas 67301
MATERIAL EXIT
\
'I
MATERIAL EXM
Figure 11. Flow comparison of conventional triple pass dryer and 3PHV drum dryer.
-------
A determinant 1n establishing a saltation (conveying) velocity for a
particle is the relationship between the density of the particle to the
density of the supporting gases. As wet particles dry, their density
decreases, and as gases cool (due to the transfer of heat), their density
increases. When the density of the particle decreases sufficiently due to
Us drying, and the density of the cooling gases Increases sufficiently,
the aforementioned relationship determining an Individual particle's
saltation velocity dictates that the saltation velocity will decrease. If
the gas velocities are greater than the particle's saltation velocity, the
particle will be pneumatically conveyed. Gas velocities 1n the primary
and secondary passes of the 3PHV are not capable of supporting
(pneumatically conveying) any but the least dense (dryest) particles. The
denser (still moisture laden) particles will undergo a showering action in
these passes while being propelled not at conveying velocities, but at
velocities determined by a combination of drag and gravity forces.
Because small particles have a higher surface area in proportion to
their mass, moisture 1s more rapidly evaporated from their surfaces.
Also, heat and, therefore temperature gradients traverse to the center of
smaller particles more rapidly than larger ones. As the moisture 1s
evaporated from the particle, the particle density 1s reduced. Once the
saltation velocity of the particle is reduced below the prevailing gas
velocity, the particle is picked up in the gas stream and conveyed through
the remaining drums.
Larger particles are retained in the outer drum where they undergo
showering action and are subjected to turbulent airflow. Once the
moisture of these larger particles is reduced to the desired moisture
content, particle densities are likewise reduced, which allows them to
reach their own saltation velocities. Larger particles will reach their
respective saltation velocities in either the outer (first pass) or
intermediate (second pass) drum depending upon their size, weight, and
moisture content.
In the first pass, the 3PHV dryer allows smaller, dried particles to
pass through the slower moving mass of larger, wetter particles in an area
bounded by the outer and intermediate drum cylinders, which is much larger
than the area of the inner drum of conventional triple pass dryers. As
46
-------
the larger particles are dried, they will "catch up" with the smaller
faster moving particles in an area bounded by the intermediate (second
pass) drum cylinder. Here, airflow velocities become high enough to
convey the entire mass of particles out of the drying portion of the drum
and Into the Inner (third pass) drum cylinder where they will be conveyed
out of the dryer.
In summary, as particles dry, they approach their saltation
velocity. As they reach saltation velocity, it 1s Important to provide a
gas velocity sufficient to pick up the particle and pneumatically convey
1t out of the drying environment. This action prevents the product from
reaching temperatures in excess of the wet bulb temperature, thus reducing
carbon monoxide and hydrocarbon emissions associated with pyrolysis and
combustion of the wood chips. Appendix D contains more detailed
information on the productization 3PHV dryer.
47
-------
9.0 PRESS VENTS
Emissions from the press vents result as compounds 1n the resin used
to bind the chips evaporate when heated. These emissions usually exit
through exhaust fans mounted on the roof above the presses. Georgia
Pacific's plant 1n Lebanon, Oregon, 1s the only plant 1n the country
attempting to control emissions from the press vents. A spray chamber
containing 80 spray nozzles continuously sprays the exiting press vent
gases with water to cool, condense, and adsorb some of the hydrocarbons.
The spray chamber, Installed 1n 1972, has never been tested so no
Information 1s available regarding pollutant removal efficiencies.
The type of resin used and, thus, the compounds present in Its
formulation vary depending upon the type of panel being manufactured.
Urea/formaldehyde (UF) resins are primarily used in the production of
particle board and medium density fiberboard. These panels typically
contain 8 to 9 percent (w/w) resin. The UF resin is used 1n applications
where the final product will not be subject to weathering.
Phenol/formaldehyde (PF) resins are used in the production of structural
particle board, waferboard (WB), and oriented standardboard (OSB).
Structural particle board contains approximately 6 percent (w/w) resin,
and WB and OSB contain approximately 2 percent (w/w) resin. The PF resins
are more resistant to moisture than UF resins.
In an effort to eliminate the potential for formaldehyde emissions,
MDI resins have been used by some manufacturers. The MDI resins produce a
higher strength panel than the UF or PF resins. Therefore, manufacturers
are able to use less MDI resin to meet the industry's product standards.
However, MDI resins are much more expensive than UF or PF resins, and
panels produced with MDI resins tend to stick to the presses. Two
approaches have been used to prevent the panels from sticking. One is to
spray the presses lightly with an antisticking agent between press
cycles. Another approach is to use UF or PF resins to bind the material
on the two outer surfaces of the panel. The core of the panel is bound
with the MDI resin. This reduces the amount of formaldehyde available to
volatilize and the panel retains the structural strength provided by the
MDI resin.
48
-------
In a recent study, three factors were identified that affected
formaldehyde emissions from press vents: (a) the excess formaldehyde
content of the resin, (b) the amount of resin used, and (c) the press
temperature.8 Excess formaldehyde is the amount of formaldehyde in the
resin 1n excess of the amount required for stoichlometric reaction with
the urea or phenol 1n the resin. The emission rates have been shown to
increase 1n proportion to the increase in the free formaldehyde content of
the resin. The excess or free formaldehyde contents of resins are often
held proprietary by resin manufacturers. The study showed that where such
Information was available, the data Indicated that 5 to 15 percent of the
excess formaldehyde in the panelboard was emitted during the pressing and
board cooling operations.8
New resin formulations use constituents other than urea to react with
the formaldehyde. Because of this, the stoichiometric ratio of
formaldehyde to urea cannot be used to predict the formaldehyde emission
rate.
A better method to compare resins for their potential to emit
formaldehyde during partlcleboard manufacture would be to use the excess
formaldehyde content of the resin calculated on the basis of the amount of
formaldehyde in excess of the amount needed to react stoichiometrically
with the urea and other reactive constituents in the resins. However,
resin manufactures will not divulge sufficient information about their
resins to allow these calculations to be made.
The study also showed that the emission rate of formaldehyde
increased in proportion to the amount of resin used in the panelboard and
the press temperature. The formaldehyde emission factors ranged between
0.30 and 0.75 Ib/thousand square feet of product using UF resin.8
The results of the study show that the formaldehyde emissions from
partlcleboard press vents are related to the amount of excess formaldehyde
in the unpressed boards loaded into the press. It would appear that
formaldehyde emission rates could be reduced by using less excess
formaldehyde in the resin. The industry has already decreased the amount
of excess formaldehyde in resins in order to reduce the emissions of
formaldehyde from the finished product into the living or work space.
This reduction of excess formaldehyde in the resin also resulted in longer
press times and, hence, reduced production rates.
49
-------
Two recent tests for VOC emissions at Louisiana Pacific plants shed
some light on the level of VOC emissions that might be expected from press
vents.
TABLE 12. VOC EMISSION FACTORS FOR PRESS VENTS10
VOC emission
Interpoll Labs factor, Ib
Plant
Hayward, Mis.
Sagola, Mich.
Report No.
7-2405
8-2552
Resin VOC /ton product
100 percent MDI
50 percent liquid PF for
surface and 50 percent
MDI for the core
0.36
0.56
The above results can be used to estimate VOC emissions for 100 percent PF
resin, since data collected by Interpoll Labs has shown that the MDI 1s
not volatilized. This being the case, the 100 percent MOI test VOC
emission factor is Indicative of the VOC's emitted from the wood itself
(Ew) and the 50:50 test correspond to the VOC's emitted from the wood and
from the PF resin in the surface (Es). The general relationship is shown
below:
Et - Ew+Ec+Es+EMDI
where:
Et * total VOC emission factor;
Ew = VOC emission factor due to VOC's emitted from the wood;
Ec = VOC emission factor due to VOC's emitted from PF resin in the
core;
Es = VOC emission factor due to VOC's emitted from PF resin on the
surface; and
EMDI a VOC emission factor due to volatilization of MDI = 0.
In the case where 100 percent MDI was used:
Ec = Es = EMDI s °
and thus:
0.36 » Ew+0+0+0
Ew = 0.36 Ib VOC/ton product
50
-------
This is equivalent to saying that the use of 100 percent MOI allows
estimation of the base VOC emission factor for the wood 1n the board. A
plant using 50 percent MDI (1n the core) and 50 percent P/F resin (on the
surface) 1s represented 1n terms of the general equation as follows:
0.56 = EW+EC+ES
Since Ew = 0.36 and Ec = 0 because MDI was used 1n the core, then:
0.56 = 0.36+0+ES
Es - 0.20 Ib VOC/ton product
Now if 1t may be assumed that EC < ES (which is a very safe assumption,
since loss of PF from the core 1s much less likely than loss of PF from
the surface of the waferboard, then the total VOC emission factor where
100 percent PF 1s used may be calculated as follows:
Et ' EK+EC+ES
where
Ew = 0.36
Es = 0.20
Ec < 0.20, then
Et = 0.36+0.204*0.20
Et < 0.76 Ib VOC/ton product
This analysis suggests that use of MDI resins instead of PF resins
would result in a 50 percent reduction 1n VOC emissions. Other estimates
(see Appendix E) suggest that changing from PF resins to MDI resin will
result in a 90 percent decrease in formaldehyde emissions from the press
vents.
51
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10.0 REFERENCES
1. Hni1s, W. E. Wood Extractives and Their Significance to the Pulp
and Paper Industries. Academic Press, New York. 1962.
2. A Study of Organic Compound Emissions from Vendor Dryers and Means
for Their Control. NCASI Technical Bulletin No. 405. August 1983.
3. A Survey of Emissions from Dryer Exhausts in the Wood Panel board
Industry, NCASI Technical Bulletin No. 504. September 1986.
4. Browning, B. L. The Chemistry of Wood, Interscience Publishers, New
York. 1963.
5. Letter. Wardell, L. L., Michigan DNR to Dimmick, F., CTC. June 2,
1988.
6. Maloney, T. M. Modern Particleboard and Dry-Process Fiberboard
Manufacturing. MUler Freeman Publications, Inc. San Francisco,
California. 1977.
7. Kandaras, C. "Diagnostic Tests Result 1n Low Temperature Drying for
Particulate Emission Controls." .Proceedings of the Twenty-Fifth
Washington State University International Particleboard/Composite
Materials Symposium. March 1987.
8. A Survey of Formaldehyde and Total Gaseous Nonmethane Organic
Compound Emissions from Particleboard Press Vents. NCASI Technical
Bulletin No. 483. June 1986.
9. Formaldehyde, Phenol, and Total Gaseous Nonmethane Organic Compound
Emissions from Flakeboard and Orlented-Strand Board Press Vents.
NCASI Technical Bulletin No. 503. September 1986.
10. Friedman, J. N., Lonnes, P. PSD Applicability Analysis of the
proposed plant expansion of the OSB plant in Bemidji, Minnesota.
Interpoll Laboratories, December 4, 1988.
52
-------
APPENDIX A.
EFB AND ESP USER LIST
-------
EFB USER LIST
Company
Location
Application
Flo\v,acfm Start Up
Louisiana-Pacific
Louisiana-Pacific
Louisiana-Pacific
Louisiana-Pacific
Allegheny Particleboard
Allegheny Particleboard
Allegheny Particleboard
Kronospan
Mason Chamberlain
Louisiana-Pacific
Packwood-Hurst
VA Hospital
Schenck-Weyerhaeuser
Schenck-Weyerhaeuser
Sverdrup
Weyerhauser Co.
Weyerhauser Co.
Northern States Power
Northern States Power
Willamette Ind.
Louisiana-Pacific
Louisiana-Pacific
U.S. Plywood
Louisiana-Pacific
Louisiana-Pacific
Weyerhaeuser Co.
Weyerhaeuser Co.
Weyerhaeuser Co.
Weyerhaeuser Co.
Badger Foundry
Louisiana-Pacific
Potlatch
Potlatch
Potlatch
Houlton, ME
Houlton, ME
Hayward, WI
Hayward, WI
Mt. Jewett, PA
Mt. Jewett, PA
Mt. Jewett, PA
Sandebeck, D
Picayune, MS
Sand Point, ID
Packwood, WA
Seattle, WA
Elkin, N.C.
Elkin, N.C.
Nashville, TN
Springfield, OR
Springfield, OR
Ashland, WI
Ashland, WI
Foster, OR
Hayward, WI
Hayward, WI
Gaylord, MI
Hayward, WI
Hayward, WI
Grayling, MI
Grayling, MI
Grayling, MI
Grayling, MI
Winona, WI
Sagola, MI
Bemidji, MN
Bcmidji, MN
Bemidji, MN
OSB Dryer 50,000 June 1989
OSB Dryer 50,000 June 1989
Wood Fired Boiler 40,000 May 1989
Wood Fired Boiler 32,000 May 1989
Particleboard Dryer 77,000 Nov 1989
Particleboard Dryer 77,000 Nov 1989
Particleboard Dryer 77,000 Nov 1989'
Chipboard Dryer 130,000 Apr 1989
Steel and Alum. Forging 120,000 May 1989
Wood Fired Boiler 70,000 Feb 1989
Wood Fired Boiler 30,000 Jan 1989
Hospital Incinerator 10,000 Jan 1989
OSB Dryer 60,000 Eng Contr
OSB Dryer 60,000 Eng Contr
Wood Fired Boiler 70,000 May 1988
Particleboard Dryer 50,000 Jan 1989
Particleboard Dryer 50,000 Jan 1989
Wood/Coal Fired Boiler 160,000 Sept 1988
Wood/Coal Fired Boiler 160,000 Sept 1988
Plywood Veneer Dryer 40,000 June 1988
OSB Dryer 50,000 Mar 1988
OSB Dryer 50,000 Mar 1988
Particleboard Dryer 70,000 Apr 1988
OSB Dryer 50,000 Feb 1988
OSB Dryer 50,000 Feb 1988
OSB Dryer 50,000 Sept 1987
OSB Dryer 50,000 Sept 1987
OSB Dryer 50,000 Sept 1987
OSB Dryer 50,000 Sept 1987
Grey Iron Foundry 13,000 Aug 1987
Wood Fired Boiler 50,000 Jan 1988
OSB Dryer 30,000 Aug 1987
OSB Dryer 30,000 Aug 1987
OSB Dryer 30,000 Aug 1987
A-l
23 January 1989 - Page 1
-------
EFB USER LIST
Company
Location
Application
Flow.acfm Start Up
Potlatch
Boise-Cascade
Boise-Cascade
Louisana-Pacific
Louisana-Pacific
Louisana-Pacific
Northern States Power
Seaman Paper Co. •
Weyerhaeuser, Co.
BP Canada
Weyerhaeuser, Co.
First Aroostook
Pinetree Power .
Potlatch
Potlatch
Northwood Panelboard
International Paper
Potlatch
Potlatch
J.M. Huber
Northwood Panelboard
Louisiana-Pacific
Louisiana-Pacific
Louisiana-Pacific
Louisiana-Pacific
Louisiana-Pacific
Vanguard Products
Proctor & Gamble
Northwood Panelboard
DuPont
Northwood Panelboard
G2S Constructors
Kelley Co.
Chamberlain Mfg. Co.
Bemidji, MN
Lagrande, OR
Lagrande, OR
Sagola, MI
Sagola, MI
Sagola, MI
OSB Dryer
Particleboard Dryer
Particleboard Dryer
OSB Dryer
OSB Dryer
OSB Dryer
French Island, WI RDF/Wood Fired Boiler
Baldwinville, MA Wood Fired Boiler
Particleboard Dryer
Asphalt Saturator
Particleboard Dryer
MSW Incinerator
Wood Fired Boiler
OSB Dryer
OSB Dryer
OSB Dryer
Moncure, NC
Montreal, PQ
Moncure, NC
Sydney, NS
Bethlehem, NH
Cook, MN
Cook, MN
Bemidji, MN
Nacogdoches, TX Wood Fired Boiler
Cook, MN OSB Dryer,
Cook, MN OSB Dryer
Easton, ME Wood Fired Boiler
Bemidji, MN OSB Dryer
Two Harbors, MN OSB Dryer
Chilco, ID OSB Dryer
Dungannon, VA OSB Dryer
Kremmling, CO
Montrose, CO
Danbury, CT
Greenbay, WI
Bemidji, MN
Washington, WV
Bemidji, MN
Lewiston, ME
L.A., CA
OSB Dryer
OSB Dryer
Silicon Rubber Curing
Wood Fired Boiler
Wood Fired Boiler
Plastic Extrusion
Wood Fired Boiler
Wood Fired Boiler
MSW Incinerator
New Bedford, MA Steel Forging
30,000
35,000
35,000
60,000
60,000
60,000
120,000
40,000
70,000
50,000
70,000
70,000
120,000
30,000
30,000
50,000
35,000
30,000
30,000
50,000
50,000
50,000
50,000
50,000
50,000
50,000
5,000
75,000
25,000
5,000
27,000
80,000
8,000
200,000
Aug 1987
July 1987
July 1987
July 1987
July 1987
July 1987
Sept 1987
Apr 1987
Mar 1987
Mar 1987
Mar 1987
Dec 1986
Dec 1986
Dec 1986
Dec 1986
Dec 1986
Nov 1986
Nov 1986
Nov 1986
July 1986
Sept 1986
Apr 1986
Mar 1986
Feb 1986
Oct 1985
Sept 1985
Nov 1985
Dec 1985
Oct 1985
Sept 1985
Aug 1985
May 1985
Apr 1985
May 1985
A-2
23 January 1989 - Page 2
-------
EFB USER LIST
Company
Location
Application
Flo'.v,acfm Start Up
General Electric
Bio-Energy
Alcoa
Domtar
CHR Industries
Coatings Engineering
Voltck
GM Co.-Chevrolet Div.
3M Co.-Chemolite Div.
Shaw Pipe
Bay State Smelting
Airco Speer
Schlage Lock
Canadian Gypsum
Domtar
Globe Roofing
Canadian Johns-Manville
ERCO
Quality Aluminum
Rumford Nat'l Graphics
Ballston Spa, NY
Concord, NH
Cleveland, OH
Lachine, QE
New Haven, CT
Sudbury, MA
Lawrence, MA
Livonia, MI
St. Paul, MN
Vancouver, B.C.
Somerville, MA
St. Mary's, PA
Denver, CO
Winnipeg, MB
Vancouver, B.C.
Vancouver,B.C.
Toronto, ON
Cambridge, MA
Milwaukee, WI
Concord, NH
PFB Coal Combustor 1,000 Sept 1984
Wood Fired Boiler 100,000 June 1984
Aluminum Forging 100,000 Sept 1983
Asphalt Saturator 20,000 Aug 1983
Silicone Rubber Curing 8,000 June 1983
PVC Curing Oven 8,000 Dec 1982
Polyethylene Curing 16,000 July 1982
Metal Polishing 20,000 June 1985
Glass Bubble Former 20,000 Dec 1981
Coal Tar Pipe Coating 20,000 Nov 1981
Brass Smelting 20,000 Nov 1981
Carbon Electrode Mfg. 8,000 Dec 1980
Brass Foundry 8,000 Nov 1980
Asphalt Saturator 20,000 Sept 1980
Asphalt Saturator 20,000 Mar 1980
Asphalt Saturator 20,000 Oct 1979
Fiberglass Curing 30,000 Apr 1979
FB Coal Combustor 20,000 Aug 1981
Aluminum Foundry 20,000 May 1981
Lithography Press 18,000 May 1981
A-3
23 January 1989 - Page 3
-------
McGiJi Preci* ator Systems
7G6/P/01t it'
Order Date/
No. Startup Date Cu s t ome r/Locat i on
1. 7/82-7/83
2. 5/84-9/85
3. 12/84-4/86
4. 8/87-
i
-P.
Georgia Pacific
Dudley, NC
Georgia Pacific
Skippers, VA
Collins Pine
Chester, CA
Georgia Pacific
Woodland, Maine
INSTALLATION LIST BY APPLICATION
in chronological order by purchase date
CHIP DRYERS (HEP)
EP Model No. Application/Emission No. of Sources
3-600 (HEP) Green Flake Chip Dryers/ 3
Plyash, Condens. Organics
3-900 (WEP) Green Flake Chip Dryers 4
Plyash, Condens. Organics
2-550 (WEP) Wood Boiler/Chip .Dryer 3
(Dutch oven) flyash,
Condensing organics
3-525 (WEP) Green Flake Chip Dryer 2
Flyash, Condens. Organics
Performance Guarante<
Design Vol. Flow - dust concentration
(std. cfm, dry) (grains/scfd)
121,429
170,736
86,084
66,600
0.017
0.017
0.023
0. ill 4
No.
1.
2.
i.
Dates:
Start/Finish
8/12-9/19/81
9/29-10/30/81
7/28-8/28/84
MOBILE PRECIPITATOR* TESTS
Customer/Local ion
Champion Int >M national
Gayloard, MI
Georgia Pacific Corp.
Dudley, NC
Collins Pine
Chester, CA
Primary Emission
Flyash, Condens. Organics
Flyash, Condens. Organics
Wood Boiler flyash,
Condensible organics from
dryer
Numhoi "I .1 ack To ;t :,
f.l
-------
APPENDIX B.
WEYERHAEUSERS1 EFB TEST DATA
• Moncure, North Carolina
-------
ENVIRONMENTALISTS INC
c
POST OFFICE BOX 12291
RESEARCH TRIANGLE PARK
NORTH CAROLINA 27709-2291
919-781-3550
STATIONARY SOURCE SAMPLING REPORT
REFERENCE NO. 6041A
WEYERHAEUSER COMPANY
MONCURE, NORTH CAROLINA
PARTICULATE EMISSIONS AND PLUME OPACITY TESTING
SURFACE LINE ELECTRIFIED
FILTER BED INLET AND STACK
Performed For: Carl Schenck, AG
OCTOBER 20. 1988
B-l
-------
INTRODUCTION
1.1 Outline of Test Program. Stationary source sampling was performed
for Carl Schenck, AG at Weyerhaeuser Company in Moncure. North Carolina, on
October 20. 1988. Three sets of concurrent EPA Method 5 runs were performed
at the surface line electrified filter bed (EFB) inlet and stack to determine
the particulate emissions. The particulate emissions results were used to
determine the EFB capture efficiencies. Along with the Method 5
testing, concurrent EPA Method 9.testing was performed at the stack to
determine the plume opacity. The testing was conducted for compliance and
guarantee purposes.
1.2 Test Participants. Table 1-1 lists the personnel present during
the test program. '
TABLE 1-1
TEST PARTICIPANTS
Carl Schenck, AG
Laboratoriua Himmelheber
GmbH & Co. , KG
Schenkmann & Piel
GmbH 4 Co . , KG
Clarke's Sheet Metal, Inc.
North Carolina Department of
Natural Resources and
Community Development
Entropy Environmentalists, Inc.
Fritz Bossier
Test Coordinator
Gerhard C. Trutter,
Dipl. Ing. FH
Test Coordinator
Alfred H. Schenkmann
Test Observer
Bill Firneisz
Test Observer
David Y. Daniel
Test Observer
Neill M. Harden
Project Manager
Barry F. Rudd
Sampling Team Leader
W. Todd Langdon
Sampling Team Leader
Dennis D. Holzschuh
Engineering Technician
Leslie C. Murray
Engineering Technician
Keith R. Hazel
Plume Opacity Observer
ENTROPY
-------
SUMMARY OF RESULTS
2.1 -Presentation. Table 2-1 presents test results and EFB/baghouse
capture efficiencies for the testing performed October 20. 1988. at the
surface line EFB inlet and stack. Run-by-run summaries for the EFB inlet and
stack particulate tests are presented in Tables 2-2 and 2-3, respectively.
The plume opacity summary is presented in Table 2-4. Detailed test results
are presented in Appendix A; field and analytical data are given in
Appendix B.
2.2 Guarantee Allowable Emissions. The allowable filterable
particulate concentration is 0.065 and 0.004 grains per actual cubic foot
(Gr/ACF) for the EFB inlet and stack, respectively. The allowable plume
opacity is 20*.
c
ENTROPY
-------
c
TABLE 2-1
TEST RESULTS AND EFB/BAGHOUSE CAPTURE EFFICIENCIES
Surface Line EFB Inlet and Stack
EFB Inlet
Concentration, Gr/ACF
Filterable
Emission Rate, Ib/hr
Filterable
Stack
Concentration, Gr/ACF
Filterable
Emission Rate, Ib/hr
Filterable
Plume Opacity
Highest 6-min. Average, %
Highest Single Reading, %
EFB
Capture Efficiency. %*
21.7
1.52
7
10
93-00
Test- Set
2
20.4
1.40
1
5
93-14
0.775
5
15
94.97
Capture efficiency (CE) calculated as follows:
Average
0.0398 0.0371 0.0289 0.0353
19.2
0.00279 0.00254 0.00142 0.00225
1.23
93.70
100
Inlet Emission - Stack Emission
CE = — »
Inlet Emission
21.7 - 1.52
CE = * 10o = 93.00 %
21.7
Note: Capture efficiencies calculated using filterable
emission rates.
ENTROPY
-------
TABLE 2-4
SIX-MINUTE AVERAGE PLUME OPACITY OBSERVATIONS SUMMARY
Surface Line Stack
Run Number
Highest 6-Minute Average Opacity, %
Highest Single Opacity Reading, %
M9-SL-0-1
7
10
M9-SL-0-2
1
5
M9-SL-0-3
5
15
C
Set
No.
1
2
3
4
5
6
7
8
9
10
Set
No.
1
2
3
4
5
6
7
8
9
10
-- Hun My-bL-o-:
Time
Start
1133
1139
1145
1151
1157
1203
1209
1215
1221
1227
End
1139
1145
1151
1157
1203
1209
1215
1221
1227
1233
•>_£•? n t
nun pry— ju>— \j— ^
Time
Start End
1442
1448
1554
1600
1606
1612
1618
1624
1630
1636
1448
1554
1600
1606
1612
1618
1624
1630
1636
1642
Avg. %
Opacity
0
1
1
D
7
4
4
4
4
2
Avg. %
Opacity
0
0
P
P
0
0
5
P
P
3
Run M9-SL-0-2
Set — Time --- Avg. %
No- Start End Opacity
1 1306 1312 i
2 1312 1318 0
3 . 1318 1324 0
<* 1324 1330 o
5 1330 1336 0
6 1336 1342 o
7 1342 1348 o
8, 1348 1354 o
9 1354 1400 o
10 1400 1406 0
D = Interference from dust cloud emitted from device at
base of stack.
P = Interference from plume emitted from other stack.
ENTROPY
-------
c
PROCESS DESCRIPTION. AND OPERATION
3-1 General. Weyerhaeuser Company in Moncure. North Carolina operates
surface line and core line sander dust burners for drying wood chips. For
this program, the surface line was tested.
The primary fuel for the surface line burner is 100* sander dust.
Potential emissions include the products of complete and incomplete
combustion of the fuel and any extraneous materials present. The emissions
are controlled by four cyclones, an electrified filter bed,
3-2 Source Air Flow. Figure 3-1 is an air flow schematic showing the
passage of the flue gases through the surface line.
3-3 Operation During Testing. The method for determining the system
feed rate is accompished by measuring the dryer conveyor belt speed.
According to Weyerhaeuser Company, the surface line was operated at an
average setting of 80* during testing, which is the maximum capacity
setting. The maximum load is 17,000 pounds per hour. Thus, the feed rate
during testing is calculated as follows:
(0.80 / 0.80) * 17,000 = 17,000 pounds per hour
ENTROPY
-------
SAMPLING AND ANALYTICAL PROCEDURES
4.1 General. All sampling and analytical procedures were those
recommended by the United States Environmental Protection Agency and the
North Carolina Department of Natural Resources and Community Development
Descriptions of the sampling equipment and procedures (extracted from
40 CFR 60) are provided in Appendix D.
4.2 Sampling Points. The number and location of the sampling points
were determined according to EPA Method 1. -ft. EPS inlet cross section was
divided into 2k equal areas with 12 sampling points on each of two traverse
axes, as shown in Figure 4-1. The stack cross section was divided into 12
equal areas with six sampling points on each of two traverse axes, as shown
T n w^ fv*«v*«<* h __ *>
,- in Figure 4-2.
4.3 Volumetric Air Flow Rates
4.3.1 Flue Gas Velocity. EPA Method 2 was used to take the velocity
measurements during the traverses of the EF* inlet and stack cross sections.
4.3-2 Flue Gas Composition. Multipoint, integrated flue gas samples
were collected at the stack and analyzed using EPA Method 3 to determine the
flue gas composition and molecular weight for each run. The results were
also used for the EFB inlet.
the s * ^ •"•*•*»- by analyzing
EPA "n
4.4 Emissions Determinations. EPA Method 5 sampling procedures were
used to determine the particulate emissions. At the EFB inlet, each of the
poznts was sampled for 2.5 minutes, resulting in a net run time of 60
-nutes. At the stack, each of the 12 points was sampled for five minutes
also resulting in a net run time of 60 minutes.
4.4.1 Filterable. EPA Method 5 analytical procedures were used to
analyze the filterable particulate.
B-7
ENTROPY
-------
4-2
c
TRAVERSE POINTS
2 AXES
12 POINTS/AXIS '
24 TOTAL POINTS.
TO ELECTRIFIED
FILTER BED
3.51
50" ID.
SECTION M-M
ABORT
GATE
FROM
CYCLONES
FIGURE 4-1 . SURFACE LINE ELECTRIFIED FILTER BED INLET TEST LOCATION.
B-8
-------
TRAVERSE POINTS
2 AXES
6 POINTS/AXIS
12 TOTAL POINTS
4-3
33.3" I.D.
B
SECTION N-N
25'
t
N
42'
« «
A
t
FROM EXHAUST FAN
N
FIGURE 4-2. SURFACE LINE STACK TEST LOCATION.
ENTROPY
-------
C
4.A.2 Condensable. The sapling r.rain distilled water reagent and
acetone rinses were analyzed to determine the condensable particulate
emissions. For each run, the impingers• water was extracted three times with
chloroform and then extracted three times with ether. TTie acetone rinses and
the pooled chloroform and ether phases were evaporated to dryness at room
temperature and desiccated. After extraction, the water phase was evaporated
to dryness on a steam bath and desiccated. Following desiccation a
gravimetric analysis was performed on each phase to determine the weight of
the residue.
4.5 Plume Opacity. The procedures outlined in EPA Method 9 were
followed in determining the plume opacity.
4.6 Equipment Calibration. Pertinent calibration data are provided in
Appendix C.
B-10
ENTROPY
-------
APPENDIX C.
GEORGIA-PACIFIC'S ESP TEST DATA
• Dudley, North Carolina
• Skippers, Virginia
• Woodland, Maine
-------
9/20/83
108.48
1016.5
9/20/83
102.54
1117.0
9/21/83
101.83
861.6
TABLE C-l. PARTICULATE SAMPLING AT INLET OF WET ESP.
GEORGIA-PACIFIC - DUDLEY, NORTH CAROLINA
Run Number
Date
% Isokinetcs
% Excess Air
Volume of Gas Sampled,
SCF* Dry " 25.825 24.977 25.312
Stack Gas Flow Rate,
SCFM* Dry 96,543 96,583 97,454
Stack Gas Flow Rate,
ACFM 135,560 132,430 137,230
Particulates: **
Catch, mgrams 165.59 119.79 156.03
Concentration, grains/
SCF* Dry 0.0988 0.0739 0.0949
Emission Rate, Ibs/hr 81.70 61.13 79.29
* 68°F, 29.92 in. Hg.
** Front half only
C-l
-------
9/20/83
98.83
1016.5
9/20/83
95.03
1117.0
9/21/83
101.76
861.6
TABLE C-2. PARTICULATE SAMPLING AT OUTLET OF WET ESP
GEORGIA-PACIFIC - DUDLEY, NORTH CAROLINA '
Run Number
Date
% Isokinetic
% Excess Air
Volume of'Gas Sampled
SCF* Dry 67.224 66.688 68.054
Stack Gas Flow Rate,
SCFM* Dry 87,589 88,277 88,882
Stack Gas Flow Rate,
ACFM 117,810 118,003 118,470
Particulates: **
Catch, mgrams 44.85 41.32 33.79
Concentration, grains/
SCF* Dry 0.0103 0.0095 0.0077
Emission Rate, Ibs/hr 7.712 7.219 5.824
* 68°F, 29.92 in. Hg.
** Front half only
C-2
-------
TABLE C-3. TEST SUMMARY AT GEORGIA-PACIFIC'S PLANT IN SKIPPERS, VIRGINIA.
SYSTEM
TEST DATE
6EOR6IA PACIFIC CORPORATION
SKIPPERS, VIRGINIA
ESP FOR CHIP DRYING PROCESS
APRIL 20, 1989
INLET
OUTLET
PARAMETER
GENERAL
6s, FLOW, ACFK
Bs dry, FLOW SCFN
Vi std, CUBIC FT.
XI
RUN tl-IRUN 12-1 RUN I3-IAVERAGE
191240 199280 197975 196165
114227 123895 114814 117645
44.95 48.45 44.75
100.1 99.5 99.2
PARTICULATE MATTER
PUR AV6, LB/HR 131.5 46.6 303.4 160.5
Cs, GR/SCF .1342 .0440 .3096 .1626
EFFICIENCY, X (BY HEIGHT)
FORMALDEHYDE
P«R AV6, LB/HR 9.6 10.0 11.4 10.3
CSi 6R/SCF .0098 .0095 .0116 .0103
EFFICIENCY, X BY HEIGHT)
VOLATILE ORGANIC COMPOUNDS
PUR AV6, LB/HR 98.1 286.2 177.4 187.2
EFFICIENCY, X (BY HEIGHT)
RUN 11-0 RUN 12-ORUN 13-0 AVERAGE
175481 196836 176021 182779
114528 121743 113318 116529
46.50 50.38 46.08
103.3 105.3 103.5
11.7 14.6 10.8 12.4
.0117 .0137 .0109 .0121
91.1 68.7 96.4 85.4
8.0 11.2 11.5 10.2
.0080 .0104 .0117 .0100
16.7 -12.0 -0.9 1.3
22.3 168.5 84.6 91.8
77.2 41.1 52.3 56.9
C-3
-------
TABLE C-4. TEST SUMMARY AT GEORGIA-PACIFIC'S PLANT IN WOODLAND, MAINE.
SYSTEM
GEORGIA PACIFIC
CHIP DRYER INLET
WOODLAND, MAINE
TEST DATE
OCTOBER 25, 1988
PARAMETER
Qs, FLOW, ACFM
Qs dry. FLOW SCFM
Vm std, CUBIC FT.
%I
PMR AVG, LB/HR
DRY CATCH
DRY AND WET
Cs, GR.SCF
DRY CATCH
DRY AND WET
TGNMO LB/HR
FORMALDEHYDE LB/KR
RUN 1-1
88135
62735
24.01
122.2
80.27
189.80
0. 134
0.317
83.52
. 1084
RUN 2-1
88387
60425
14.99
110.2
54.36
126.38
0.0998
0.232
143.21
.0978
RUN 3-1
86270
59797
15.01
110.3
55.95
142.73
0.1038
0.265
60.99
.1294
AVERAGE
87597
60986
63.53
152.97
0.1126
0.271
. 111S
C-4
-------
TABLE C-4. CONTINUED.
SYSTEM
TEST DATE
GEORGIA PACIFIC
CHIP DRYER EXHAUST
WOODLAND, MAINE
OCTOBER 25, 1988
PARAMETER
Qs, FLOW, ACFM
Qs dry,
FLOW SCFM 56278.9
Vm std, CUBIC FT.
PMR AVG, LB/HR
DRY CATCH
DRY AND WET
RUN #1-0
87660.7
52692.9
RUN #2-0
83307.7
54024.9
RUN #3-O
83186.0
54332.2
AVERAGE
84718.14
44.12
108.1
3.65
6.45
41.84
109.5
3.70
6.68
42.62
105.7
4.31
7.65
3.88
6.93
Cs, GR/SCF
DRY CATCH .0073 .0078
DRY AND WET 0.0128 0.0141
ALLOWABLE, LB/HR (DRY CATCH ONLY)
TGNMO LB/HR 37.99 18.77
FORMALDEHYDE LB/HR .0596 .0495
.0090
0.0160
19.25
.0490
.0080
0.0143
8.6*
.0527
*based on limiting total waferboard plant particulate emissions to 50
Tons/Year or less, and deducting other waferboard plant emissions
C-5
-------
TABLE C-4. CONTINUED.
SYSTEM
GEORGIA PACIFIC
CHIP DRYER EXHAUST
WOODLAND, MAINE
TEST DATE
PARAMETER
Qs, FLOW, ACFM
Qs dry, FLOW SCFM
Vm std, CUBIC FT.
PMR AVG, LB/HR
DRY CATCH
DRY AND WET
Cs, GR/SCF
DRY CATCH
DRY AND WET
OCTOBER 25,1988
RUN 4-1
92199
69788
7.81
107.8
78.28
118.17
0.126
0.190
FORMALDEHYDE LB/HR .0817
RUN 4-0
80824
58344
15.69
108.9
5.86
7.968
0.011
0.015
.0931
C-6
-------
United States Patent :-i
Shinn et aL
[nj Patent Nmnben
[45] Date of Patent:
4,729,176
Mar. 8, 1988
both of Independence,
[54] ROTARY DRUM DRYER AND METHOD
[73]
[21]
[22]
[51]
[52]
Ma
AppL No.: 33J44
FDed: Apr. 1.1997
IntCL*
U.S.O.
[58] FlaUaf
F26B 3/lft F26B 11/04
34/33; 34/128;
34/129; 34/136
34/33. 108. 109, 127.
34/128. 129. 130, 132, 134, 136; 432/103. 105.
106. 107. 111. 112
[56]
idtad
U.S. PATENT DOCUMENTS
U71.407
1.641.101
1471.934
1.9U.677
1.9M.67I
1.996J47
2476473
2.1134*7
2.13X972
2^93.911
2J16.4S9
2JI9.673
2.6IU43.
3.097433
3.137.346
3.41O233
3.713.763
3.906.961
3.916.107
3/1921 Frawr .
1/1927 Wo* .
1/1932 W€B 0 aL .
Arnold
Arnold
Reppcn
1/1935
1/1935
4/1935
4/1937 Arnold
V193S Fi
10/1931
9/1942
4/1943
3/1943
11/1932
34/24
213/10
•3/27
Schmidt «*L
Preach
Araoid
7/1963
6/1964
11/1961 Sekr
1/1974
9/1973
11/1973
Ham«aL
110/15
RoweUctaL
RowcUctaL
3.993.9U 12/1976
4037.622 12/1910
4O39.0S1 3/1911
4J76J43 V19C3
4.477.914 IO/19M
Fn
FTI
ctaL
.... 432/71
.... 34/147
..„ 23/293
„ 34/109
_ 34/121
, Jr.
Primary Exanuiur Liny L Schwartz
AaortHf. AgtM. of /Inn—Schmidt. Johnson. Hovey A
Williams
[57]
ABSTRACT
An improved, high efficiency rotary drum dryer and
method is disclosed which achieves outstanding ther-
mal efficiencies by provision of • multiple-pass rotary
dryer designed JO that the product to be dried is first
conveyed through an outermost drum of relatively
large cross-sectional area and then through succeeding
internal drums of progressively smaller cross-secnonal
areas. In this way. the velocity of induced air currents
traveling through the dryer increases from pass to pass.
with the result that the net velocity of product through
successive passes also increases. The preferred dryer
also includes bousing structure in surrounding relauon-
110/14
relativeiy tow humidity ambient-derived air into the
central drum so as to tower the partial pressure of mois-
ture in the drying atmosphere, thus promoting tbe final
of drying. The preferred dryer also includes an
' for selective introduction of a liquid or solid
product treating agent into the final central drum. The
dryer of the invention is capable of drying a greater
volume of material with a shorter dryer and increased
efficiencies are obtained because of increased airflow
without •«•*•"?•"* settling out of larger particles and
possible dryer plugging.
11 Claims, 5 Drawing Flgana
.^.....r..^..tl
* -?L4*-1*' f*'
** I / ml 79
0-1
-------
US. Patent Mar. 8.1988
Sheet 1 of 3 4,729,176
10
'46
68
-------
US. Patent Mar. 8,1988
Sheet 2 of 3 4,729,176
-------
US. Patent Mar. 8,1988
Sheet 3 of 3 4,729,176
fi
f
D-4
-------
4,729,176
the innermost, smallest diameter drum, whereupon t.ie
ROTARY DRUM DRYER AND METHOD product a conveyed vu induced draft currents utrou?n
the outer drams uaol it reaches a passageway defined
BACKGROUND OF THE INVENTION by tbe outer dram aad tbe next adjacent inboard drum.
I pjgjd of tog invention 3 At tm* P0""* toe product is ia in final dried condition
The pin mveaooa • broadly imnCTwd with aa •** » delivered for Author baadhag or_cotieeaon,
improved mnlopta-oaas dryer useful for drying a van* ' HUB, *n™ "T^V. " ^^
ery of particulars such sswc^foraisa aad agricultural compaiattvaly mgh an-'
products. Mora particularly, it • concerned with such a ditiooj in tbe amermost drum (first pass) when the
10 y»r««.g products an tbe heaviest aad tbe wettest.
i use of an ••'*••••> flow path arrange* Lower air veJootiea aad lower fT^TTT™****'"? obtain in
; todavct incoming, initially wet product the imeimediate dram (second peas), and even lower
and imiufiamns exist m the outer drum
anol dried product ai removed from the conventional dryeis a) employed becaase it is believed
within the drying appentas increases as the cnrrems relaovdy small ooas leiranal area central drum where
peas through tbe dryer, whereby the velocity differeD- the highest air current velocity aad temperature condi-
tiai betweea such air currents aad the saltation veloo* •** ti««»« exist* In thg succeeding, larger «*»••«••'•• outer
t*0 of parocies
dram to reduce tbe partial pressure of water vapor of ,n p««, thtr^g**. « tmtt nntil tbf larger pemcto SIT
dried enough to be picked up and conveyed by prevail-
- _:.. ,„••,•-,*•
IflK BIT CflcTCB^B*
• ^^
Ia practice though, the relatively high air current
velocity conditions ia the first peas of a coaveaaoaal
dryer caaa» the wet partides to be quicUy driven away
aPOBi the beat source, and then • consepuently a re-
able fpn¥r ^wtH^ dryer coan^uru^on**and fuels velocity of tbe product (Le^ the minimum air current
beiag employed. CoasKknbie nseaicta baa been con- vdodtv ****** *** °P •* convey product at s
ducted ia the past toward achieving maximum dryer 40 Pven mooture level). Thus, plugging of the dryer may
efficiency, bmn view of fe relative* complex aatare occar. perticulariy at high pioduct flow rates, and at
Tf the profrHa. the H"<1 dryer h«f yf *•»*"» ru^up^i best the produa only moves at a rate determined by the
In general however, tbe drying process involves sev- forward velocity of tbe slowest moving (largest) parn-
eimlds«ineti»aaesOTatages.Tnatato«y.iiio«hysro. dt* The result is that tbe flow rate must be decreased
iconic materials *»!»«•* several 4**~* drymg rate 43 and this inevitably has aa adverse effect oa drymg effi-
periods as they peas through a multiple pan dryer. Ini- ciency.
ti^dryiagisaceompainedbyawarmmgofthematerial SUMMARY OF THE INVENTION
aad ID anrnrtam moisture. The drymg rate iauesici
during this «•"*««' pffiml. whue thf moisture content The present invention overcomes the problems de-
dmp« to m Ming w>^n mf~mi* t^, K^MH.MJ tfi« «». » scribed above and provides a unique dryer construction
staat rate period of drying. During tbe constant rate •«* method providing high drymg cfBrirnrin and the
penc^inowiire.evmpofmied from the wri*ce of prod- conjeaneat abuity to dry relatively large quantities of
act parades as a steady rate until tbe wrffrr*t are no product in a small dryer untiring reduced amounts of
longer entirely wet. Thereafter, a fattmgotiT period fueL
obtains when tbe drying rate decreases because of the 33 Broadly speaking, the multiple-peas dryer of the in-
mcnasmg difficulty of moving internal product mois- veatioa reverses the normal dryer flow path and pro-
be ««l"ff up and vides that bif***™^ initially wet product is directed to
moved away. Finally, the product moisture is reduced an outer drum having a relatively large effective cross-
to a point when aa emuuorium a »«»«Mi.k~> with the sectional area, whereupon the product and attendant air
surrounding atmosphere. 60 cuiieuu pass inwardly through drums of successively
Conventional three pass dryers mdude an elongated. smaller effective cmai ifrrionsl areas, so that the prod-
horizontal, axially rotatabk body having aa outer drum act exits from the smallest diameter central drum.
aad a series of concentric, smaller diameter drums In more detail, the preferred dryer includes an eion-
withia the outer drum. The respective drums are in gated, normally horizontally disposed, axially rentable
communication with each other and define a serpentine 63 body having means defining a plurality of elongated
flow path to the dryer. Without known exception, such internal passageways in communication with each other
dryers are provided with a product inlet oriented for to present a cononnous. serpentine flow path through
directing initially wet product and hot drying air into the body. Advantageously, these passageways are sub-
D-5
-------
4,729,176
3 *
runnaily concentric and eacn presents a different effec- drymg air u> the dryer 12. In addition, the fystem 10
GV« cross secuonal area. A product inlet is oriented for includes a cyclone separator assembly 16 having an
initially directing product to be dried into an outer induced draft fan unit IS aad a conduit 20 leading from
having a relatively large effective cross- the outlet of dryer 12 to the inlet of the assembly 16.
area. Further, in HIM si provided for creanng 3 Tuning now to FIGS. 2-5, it will be seen that the
of frtmtTd air withm the body aad along the dryer 12 broadly mciadta aa outer dram 22 together
flow aan far conveying the prodact aioag the flow with a pair of internal, concentrically disposed drams
path throagh the relatively large effective cross-sec- 24, 2a. It will be aotad in tha respect that the dram 22
banal ana passageway, and *frri toward and through is mhaianriailr longer than the intermediate dram 24
tha amaiiar effective croeB*eacooaai ana passageways. 10 aad ueuuai dram 3a> aad the anponaace of this feature
A prodact outlet is provided in commanicaooa with a win be rrnlainail harainaftar.
havmg a relatively small effective cross- toaay eveat.ow«dram22»m theformof aaeloo-
i. generally tat nr"lv*** «<«••«•••> ceuual I*****- fn^*ftmr metallic body made up of a pan* of area-
. _—,. Thorn, the dryer of the invent-on effec- lar in uuas aauiion. etegased members 21 aad 30 ori-
avery employs the novel principle of "outer dram to 13 entad in end-to-cad relationship. As best seen m FIG. 2.
inner dtoBT operation, the right-hand cad of member 21 is beveled as at 32. aad
In trthtr aspgrn of th* nr^nmm, »««"««« provide correspondingly the lefthand end of member 30 is bev-
for iatrodBaag quantities of relatively dry ambient- eled as a* 34. A relatively short, circular in cross-section
derived air imp the ""-—•"-* passageway of the dryer nywmiffg ring 34 of iiiuesani thickness is intercon-
body. so as to lower the paroai pressare of water within 20 nected with the respective adjacent beveled eads 32.34
thf air cnmms try^^g •'"•regf **** **y**- «*«"« «- uf ilii ilniin di fining mrmhrn 7t Tft si mil trr mriih"
KM^-|. »IM. fc..i pm~m of drying. Preferably, an gion. seen. Each of the members 2a. 30 is covered by external
tm4, rmstt^t ftt*"*^ ttomnn v ««iMMJie*iiy di». thermal aamiaaoaaa at 31, 40. Ring 34 ia provided with
posed about the in-mmm dram of the dryer to define a pair of laterally spaced apart, outwardly extending
therewith aa elongated, aaaalar zone; and an annular. 23 inetailic tracks cc ores 42.44, the funcnon of which will
arcuate, infvrufd air-directing flange is located at the be described.
entnace of the inner dram so as to direct the ambient The kfthaad or miet end of outer dram 22 is provided
sir into sad along tfae length trf thr passagmfiy i1f final with an annalar angle flange 4< (see FIG. 2) which is
by the «•••» dram. affixed to the ememe cad of the dram mcmorr 21. A
The present invention also provides apparatua for the 30 statiooary circntar head 41 • recerved by flange 4« as
tntrodacboB of a liquid or solid additive (eg* water, illustrated, and coven the cad of outer rotatabie drum
wax. resim a* oiganicbind^mto tfae inneriiiost drum 22. Head 41 ia provided with a large, rectangular prod-
pssisgrwsy. Soch appannss is advantageoosly m the oct inlet opeamg SO and aa integral, upwardly and
fonn of an ekmgated. rigid, aoa-fotating tube extending obliquely enmrting prodact inlet chute 5Z Moreover.
into the inner pea-airway adjacent the entrance end 33 bead 40 iadodes a lower, circular iniet opening 54 for
thereof. the introduction of heated drymg a» ia» the dryer. For
In practice, dryers in —~~«—— with the present this purpose, a tabular collar-type connector 54 is af-
mveatioB achieve measurably increased drying efficaen- fixed to head 41 m icgisuy with opening 54, and is
cies. This obtains by virtne of the -outer dram to inner designed to mate with the outlet of boner 14. Finally.
drum" operation thereof which serves to successively 40 the head 41 includes a central opening 57 therethrough
increase the velocity of the air currents travenmg the sized to aixijuimnrtatr a liquid additive conduit.
serpentine dryer flow path. This ensures that the prod- The opposite end of dram 22 is provided with a
o« has aa increased averas^ net vekxary in each of the mouaong ring 51 similar to the ring 34. Thus, tfae ring
mi 11 su¥S 'f-^m pasiagrnfays ft t riplshurl rhii is irrry 51 is of circBiar arms sucrion, bat has a rhtrlmns
different from coaveaoonal dryers, wherein the aver- 43 greater than that of the adjaceat drum-defining member
age act velocity of the product decreases from passage- 30, Farther, the extreme righthaad cad of the member
way to passageway. 30 is beveled to facilitate conngrrirm of ring 51 thereto;
md the ring 51 ia provided with a pair of annular, out-
BRJEF DESCRIPTION OF THE DRAWINGS ^^^^ZLii., ^^t r^ aTta. The outennost
FIG. laasideeievaamalviewo/acompieiaprod- 30 righthaad end of tfae ring 51 is beveled as at 44. and the
act drying annaratas in accordance with the present end of the dnmi 22 • m pan closed by provision of a
aveatsoa. semMorroidai end wall s35 affixed to the beveled end of
FIG. 2 is a fragmentary view in vertical section Olas- the beveled righfhand end of ring 51.
trating the consuuniuu of the ureferred dram dryer of The dram-defining member 21 ia provided with three
the invention; 33 series of laterally adjacent, carcum/erenoaily spaced
FIG. 3 is a sectional view taken aioag line 3—3 of span internal flights. Referring pamcaiariy to FIGS. 2
FIG. 2; and 3. it will be seen that a series tt of flights is pro-
FIG. 4 is a sectional view taken along line 4—4 of vided adjacent head 41 and includes a plurality of in-
FIG. 2; and wardly extending flight members 41 spaced about the
FIG. 5 is a sectional view takes aioag line 5—5 of 60 interior of the member 21. In a similar fashion, flighting
FIG. 2. series 70 and 72 are provided, respecnveiy having ctr-
DESCRIPnON OF THE PREFERRED
EMBODIMENT flighting within drum-defining member 21 is to initially
Turning now to the drawings, aad particularly FIG. 63 separate and "shower" incoming, initially wet product
1. a drying system 10 is illustrated which broadly in- to tfae dryer.
eludes a three-pass drum dryer 12 of unproved con- On the other hand, the adjacent drum-defining mem-
stracoon. together with a burner 14 for supplying hot ber 30 has a single series of elongated, orcumterennally
D-6
-------
4,729,176
5 *
. awartly extending (lights Tl which are relationship to • similarly dimensioned rmg
respecsveiy affusd to me inner face of the member 30 to the extreme iefthana end of bousuig n Howevs-
(tee FIGS. 2. 4 *nd 5V tbere •* °° »nfrhinint counecaon berw«ea the »dj*crnt
The tacermedMue dram 24 is in the form of an elon- rings 112. 114.
r,^ circular m urjMinunn metallic dement extend- 3 The outer face of housing M carries i plurality of
ing cssenoaily the entire axial length of nog 36, member reinforcing angle ribs 11* which extend between the
30 aa*i»g 58, b«* of a smaller dian»er. An arcuate m struts 104,110 as depicted. These ribs IK are oriented
wall 71 is attached in an evenly drcaauercnaaliy spaced fashion about
to the ierttraad and of drum 24 as seen in FIG. 2. with boosmg 98. Abo. the inner circular margm of end wad
cad way 78 bemt provided with a central aperture 80 10 65 is affixed » limiting M as illustrated.
therethroe*h7Ind wall 78 tether has a snxxxhlyaroH The inboard end of housmg M mdades a circular.
ate divcrter 82 affixed to the face thereof remote from arcuate m cross section divenar 118 which is affixed to
head 48 and —•—•"-g toward the opposite end of the the bousing and extends inwardly beyond dram 26 so
dryer 1Z The divenerC includes an apertured bearing that air passing through the tone 102 is diverted for
84 adjacent the apex timwt which is important for 15 passage into aad along the length of central dram 26.
piifpoms to be i»m riHif A drive sprocket 120 having a remforcmg angle 121
IntermedaUB dram 24 »tnypff^ within the dram- bolted thereto is secured by means of welding to the
**b»-i luimtmr M bj miani nf it r*—"T ** —'""T waU 65. m order to rotate the central drum 26 and. by
extending, eaxnauenaomUy spaced apart struts 86 to- virtue of the described mterconnecoom. the entirety of
~«-rt adjacent the right-hand cad of the dram 24 as 20 drum 12. For this purpose, the overall dram assembly
viewed m FIG. 2. In particular, it will be seen that a includes a chain 122 trained around sprocket 120. with
circular i-r-f-i--g platf 88 • secured to the extreme the chain being operanvdy coupled to a drive motor.
fight-**—•* fitft ^rftht 4r™» ^4. with the «tmtm 86 being The extreme righthand end of dram 26 terminates
welded to and ^*r^*"*g radially outwardly from plate adjacent a stationary plenum box 124. The box 124
88. TTie outboard ends of the struts «6 are weided to the 23 includes a heavies drop-out chute 126, and is coupled to
«tiM» face of guide ring 58. In Older to provide further conduit 20. Further, a flexible seal 128 is provided be-
frmgth and rigrtfty. Hrmn'*^ fT*"y -™—^"g "ig«* tween the end of dram 20 aad the into of stationary box
ribs 90 are affixed to the outer nee of drum 24 and are 124 to effect a rotating seal between these members.
oriented in a cacamferentiaily spaced rdntionship (see An enlarged secondary plenum box 130 is disposed in
FIG. 5). In this irtpmt, it will be noted that the angles 30 surrounding relationship to box 124 and is- provided
90 are oriented with the struts 86. with a tower ambient air mtet 132. A flexible semi 134 is
The opposite end of dram 24 adjacent cad wall 78 is provided between the extreme righthand end of housing
Ulewke supported by meam of radially outwardly ex- 9i and the outlet of plenum box 130. A blower assembly
•••nfoig, fir^f^effmanmny rp**^ apart «wr M- Th«g 136 (see FIG. 1) is situated below box 130 and is opera-
struts are weided to end wail 78 as shown and extend 33 tively coupled to air inlet 132. Finally, box 130 is
outwardly therefrom. The outboard ends of the struts equipped with a water injection port 138 so as to permit
92 are ako weided to a circular ring 94 which is situated selective injection of moisture into air currents within
adjacent the inner face of mounting ring 36. However. the outer plenum box.
th^. in BO mt-p^Hvp..^ between the imp Tl. Hi hi The complete dryer 12 is mounted for axial rotation
order to if***™****^ thermal •*!**-*» and contrac- 40 by means of a pair of mounting assemblies 140, 142
tion of the components making up the dryer 12. respectively located beneath the rings 36, 58. Each of
The inner face of dram 24 has a series of lifting and the mounting assemblies 140, 142 includes a pair of
separating flights 96 which are oriented m drcnmferen- spaced apart, axially rotatabie tnmntoas 144 and 146.
tially tptprd —«-*t-«*>fr and i-*"-»rf inwardly toward The trunnions 144,146 are respectively in engagement
the center of dram 12. *3 with the tires 42. 44 and 60. 62. The pie/erred drum
Central drum 26 is in the form of a tubular metallic mounting structure used in the preferred embodiment of
body m"Tir*imt substantially the length of the member the invention is fully described in copeadtng Appiica-
30 but projecting beyond the end of the latter for a short tion for U.S. patent Ser. No. 877.531, tiled June 23.1986
distance as illustrated in FIG. 2. A circular in cross-sec- and entitled "Mounting Structure for Rotary Drum
tion. radially enlarged bousing 98 » concentrically dis- 30 Dryer." This application is incorporated by reference
posed about dram 26. •*"< is fixedly trmmi thereto by herein.
means of a series of spacers 100. Thus, an elongated. Dryer 12 is also provided with an elongated addition
annular zone 102 is defined between the exterior face of conduit 148 which extends from a point outside of the
drum 26 and the interior face of housing 98. dryer through opening 57 of bead 48 and member 28.
The dram/housing composite made up of the inter- 33 Tbe inner end of the condnh 148 a received by bearing
connected dram 26 and housing 98 • supported adja- 84, and extends to a point just inside the lefthand end of
cent the righthand end of dryer 12 as seen in FIG. 2 by central dram 26 (see FIG. 2). Conventional metering
mesas of plural orcam/eretmafly spaced, radiallyout- equipment may be coupled to the exterior end of con-
wardly extendmg struts 104. The struts 104 are weided dnit 148 for the purpose of metering liquid or solid
to a narrow, circular remforcmg ring 106, the latter 60 additives into drum 26 as desired.
being in tun weided to the outer face of bousing 98. From the foregoing discussion, it will be appreciated
Tbe opposite ends of the struts 104 are weided to the that the overall drum assembly 12 presents an eion-
inner face of drum 24 as at 108. gated, normally horizontally disposed, axially rotatabie
The inner, lefthand end of drum 26 is supported by body with the drums 22.24 and 26 cooperatively defin-
piuraL drcumferencuuly spaced apart, radially out- 63 ing a plurality of internal passageways intercommuni-
wardly extending struts 110. In this rur. the respective cated to present a continuous serpentine flow path. In
struts 110 are weided to a narrow circular ring 112 particular, it will be seen that dryer 12 includes an elon-
which is positioned in closely adjacent, surrounding gated, annular in croswecnon outermost flow passage-
D-7
-------
4,729,176
8
way 150 having an entrance end 152 aad aa exit end 154
which is defined between the memocr 30 ana drum 34,
an elongated, annular i
mtermeoiaie p*»-
sageway 156 having an entrance end 151 and an exn end
160 and bemg defined buweaadram 24 and housmggt;
sageway 162 presenting an catnace cad 164 aad aa cxu
end 166. Moreover, the member 21 aad head 41 cooper-
1*1 for jsoenlty
I air. As wflba readily apprect-
^ iOfwalhaSaadTlenpMeathatflowof
pfOOOCt 4aOQ AUsf CflRCettLI tiHOIIfft tDkt QTyCT 12 BIQttt
proceed through the passsgfways ISO, 156 and 162.
rather thaa bemg abort aroat direcdy to any of the
oner passageways. IB general therefore, pioduct to be
16S and thence m serial order through
and central pasaageway 162 before kaviag the dryer via
exit end 166.
DC my ooc of & «wno of ir^nB*****1^*"^ •vwl*
able bonen. In general, the boner 14 would mdade an
air inlet 170 leading to a feet-fired burner chamber 172
i§fi|M~tf, •^•*aa*aemjt*aiBM«a»^aBm ajjiffh MtneMaf^VW San. a^lM
by GueUeUUy PerforaaDce Co* of Independence*
asa-ROEMMC-
product increase* aa the product moves to and through
the successive passageways.
Provuion of the blower aasembiy 136. plenum box
130, annular zone 102 aad divener flange 111 also per-
mm ready mtrodacooa of relatively low humidity,
Tana, if desired relatively dry air from toe atmosphere
may be directed into catnace end 164 of the paaaage-
way 162 for mixing with tbc heated. homid air currents
paaarag threat* the final dryer puiagtway. Inaamach
at a radacoon ia the '"•"'rfi«y of the ainueaiu within
10
penal pressure of the water vapor ia the combined
aimnan. eahaacad drying • obtained, becaaae a
" greater differential vapor pressure between moisture in
the product and moisture in the surrounding atmo-
sphere • developed, to will be noted ia this respect that
tost •BWMOC^CflVVO ttf V pRDCattaSQ WlCJUB ZOO6 102 by
virtue of indirect acaaaf through the wails of housing
n 99 and drum 26. Farthennore, provision of toe divener
119 CDMaVES (OeU CDC OCnVPd ttT CHftffff pttUfC*
way 162 at a subsiaatial velocity and with sufficient
turfaolence to promote proper mixing between the tow
humidity ambient air and the relatively high humidity
tor 174 haviac aa mlet 176 and • lower prod
30
box 134 and
taoeeskiQedm the an wul readily appreci-
mlet to nmlMk
174 by means of
fin ISO having
grade aad includes a large
air outlet stack 1S2. The
to the apper end of cyclone
hnt 144. In operation, an
««
If it is desired to add a treating agent in the final
passageway 162. sach it accomplished through use of
the conduit MS. It will be observed m this respect that
the outlet end of the conduit 14t ia strategically located
relative to divener flange lit so that the turbulent
to —*-**» mixing of the treating agent with the air/-
prodnct etream.
The present invention provides a number of opera-
tional advantages which cannot be duplicated in the
prior art. In order to iDustrate certain of these advaa-
provided which compares the drying characteristics of
unit IS serves to draw ambient air into burner "h""*""- 40 a 12 foot diammr by 60 foot long dryer in accordance
172 through inlet 170, whereupon sach air is heated and with the present invention versus a 12 foot diamter by
pulled through the previously docribcd internal flow 60 foot long three-peas dryer of convendonai design.
path of a dryer 12. T««—«t. aa product is shnulta- Table 1 presents die ralmlatrri data for the dryer m
aeouaiy delivered to dryer 12 (advantageously in a dia- accordance widi the mvenode, whereas Table 2 pres-
persed aheet-like Csshioa through the targe opening 50), 43 enta corresponding data for the conventional dryer.
it will be appreciated that sach product is conveyed TABLE 1
through the dryer by
------ « * — JW^ •• f* .i
createa oy mn la. r urtner
of the induced air currents
• -• ______
h negative pressure
carrena convey dried product from dryer 12 through
for ultimate separaooa m cyclone 174 and
,_. .. ^
IOC • 12 11.
50
advantages m operanoa. As is evident from
the foregomg. the dryer first of an provides a product
flow path which • the reverse of convendonai mua. 33
fT.> (%>
> CF.)
t>ywt>
VtkOOff
»
passageway 190 and thence through the
inner passageways 156 and 162. The outer passageway
150 has a maxanam. effective qoas iiitimial area,
whereas the inboard passageways 156. 162 have pro-
gressivciy smaller effective cross ncnonsl areas. As a
conseqaence. a will be appreciated that induced air
corrents passmg along the dryer flow path increase in
velocity as they proceed from the outer to the inner
passageway. This "«*«««t «<«•» the act velocity of the 63
product conveyed along the dryer flow path increases.
Thus, while the velocity of product may decrease or
vary within a given passageway, the net velocity of the
1.109 00*412
tu ooni4
tw oon«7
4n ai2tf*
zs4 aisiw
273 nistzz
z«i oi647i
230 oi7i3t
2I2 a,7JJt
2io 013011
201 013131
U7«
us»
1119
1411
uii
2J7I
us*
2J43
7.163
7.131
3S
iu
212
2U
221
230
2«
24«
2U
210
20S
asisu
0.0239
-------
4,729,176
10
TABLE 1-continued
4SOO 20* a 1326* 7.131
206 0.04001
4.111
1.00010
OO400I
l.*90
41.400
3M04
fTJOl ACFM
3MUUI9 BTU/fer
IJJ7 BTU/ferap
the parude (Table 2, coiuma 6). Even though the veioc-
ity differaoal is treat, the duration
1109
Vftff
4109
O09
1109
43JOO
1.100
1.024
HI
t*3
*74
'333
411
O04M2 3JM4
00*231
0070*5
00*342
OI1744
O14042
OI332*
4,70*
4J30
2411
14*1
2JOU
33
S3
121
1*3
210
223
230
23*
1.00010
O933IO
OI732I
0110*7
O«3344
O43027
027313
OI3I7*
632,1
61X4
373.2
333.1
13J4
_ to completely tuimvc then* mmtiiue. The al-
ready'dry pmrtictea an being conveyed because their
saltation iniquities an leas than the air velocity.
In the conventional dryer, the bulk of the material is
dried in the imennrdiaie (second paaa) drum (Table 2.
column •). Notice that air velocities an below the mini-
mon saltation velocity for both the dry and partially
column 4). Hen parades "settle on" and -drifting"
occurs. Then it a •""•*—« material flow which will
rr**t ft»« p^fTt if a material flow greater than this is
ff\mtn»^ imo this region, plugging will occur with
possible disastrous effects. Volatizmg of the surface
of dry parades may result in either their
air pollution control
23.41
37.13
ODD
13.00
3009
4100
J7I
JX
2t*
290
0.1*023
O164I7
016476
0.170*6
IJI3
IJ23
1.2*1
1.203
240
244
24*
230
012023
0.09002
O070IO
004001
22.il
21J3
2O02
1SJ3
Th. EOcincy' .
1.00010 004001
27.000 27.000
27JOJ IJMO
3*003 • 210JBO
23.«3
43.730 ACFM
4X1I7.71I BTU/hr
I.6M BTU/Ibcnp
OJ9J*
23
problem, or the elevation of their surface temperatures
pf i}***r
-------
11
4,729,176
the invention accomplishes this whereas • conventional
drum allow* the material to "settle out" which may
result m "blue haze", plugging, or s dryer fire.
Increased efficiency is posaoie because of greater
airflow through the dryer of the invenaoa. On the other
airflow through a conventional
esoita in more rapid advancement of the
away from the heat source and more
I "drop out" from
anally
fining a plurality of 13
ommuni-
flow path
8. A multiple-pass dryer, comprising:
an elongated, normally horizontally disposed, axiaily
rotauble body having an outermost drum and s
plurality of substantially concentric internal drums
of piugiissmly smaller diameter, said drums co-
operatively A^«"«g a plurality of riongit«1. sub-
stantially concentric internal passageways each
having aa entrance end and an cut end and being in
communacaooB with each other to present a con-
flow path through said body.
sys hiving a different
t respectively; 20
; inlet oriented for initially
t to be treated into a selected one
I a relatively large effec*
a product outlet in communication 23
of said passageways having a rela-
30
said other passageway being disposed within and
radially inboard of said one passageway; and
along said flow path for conveying said.product m
a cocurrent fashion with said air currents atong the
n^M.r.«htk«».tf,T^4^»r....,^.»yh.vil.t«»id
relatively large effective LI mi uctinnsl area, into 33
•iuj tKrr^gh nid other passageway having said
relatively small 0988*400110081 area, and out said
product outlet
1 The device of claim 1. ""-.H^iHg means for heating
said air currents. ^0
3. The device of claim 1. said passageway-defining
"*"•**•' compnsmg a plurality of elongated, concentric
drums, said one passageway being denned between the
outermost and next adjacent inboard drum, and said
other passageway being defined by the iuueiuiost drum. 43
4t The 4"?virft of claim !• including means for im*»^
tmuousi
ntermost drum having an axial length substan-
tiaily longer than the lengths of said internal drums
to define, at one end of said body, a premixing
zone, said zone being in communication with the
outermost passageway defined between said outer-
most drum and the next adjacent inboard drum;
means defining a wet product inlet m communication
means for aH*"4"*! a flow of heated air currents
within said body and proceeding from said premix-
ing zone and into and along said flow path first
along said outermost paasageway and then along
radially inner passageways for conveying said ini-
tially wet product from said premixing zone into
and along said flow path white simultaneously
drying the product; and
means
-------
APPENDIX E.
MEMORANDUM: FORMLADEHYDE EMISSIONS FROM WAFERBOARD PRESS OPERATIONS
-------
MEMORANDUM
To: Leslie B. Evans, EPA/CPB (MO-13)
From: John H. E. Stalling and Katherine L. Wertz, Rad1an/RTP
Date: 7 July 1987, 17 July 1987 Rev. 1
Subject: Formaldehyde Emissions from Waferboard Press Operations
Summary, At your request we have examined formaldehyde emissions from Dress
operations at the wafer-board facility In Olathe, Colorado. We haV Ssed
Ifi t^r! f ^r* nanufa
-------
Memorandum to L. Evans
7 July 1987, 17 July 1987 Rev. 1
Page 2
only. No correlation was found between the amount of formaldehyde emitted
and process parameters The data presented in the following table ??d1ca?e
that emissions vary with the resin formulation, but no data are available on
the excess formaldehyde content of the resins or on the degree of
polymerization.
Table 1. Press Emissions of Formaldehyde.
BJH Press Temperature. °F Percent Resin Ib/MSF HCHQ
B J US 4'8 0:33
C J J22 4'8 0-56
C A , :. 40° 4.8 0.53
v The
emission rate for press operations determined from emission testlna
tst rtOlSK iSi.SJS*^^1111* ?!"?• da1ly e$tinate- TJS Tunl 98S9
1nd
s ii. -
w*ro J%2 i J5J, 1ndicat?d *** the combined emissions from both press vents
The f!;2ii!h22 r !h6 Plant W?S °P«rat1n9 Wlt" »I •« the binding resin.
The formaldehyde emissions from the press vents during the March 1985 tests
were approximately an order of magnitude higher at 62.2 Ib HCHO/day Thf
plant "W litv. been opera^ng
eraissions rate
/.»..---• AyW
HCHO/day emission rate, the change from P-F resins to MOI
r«uii.ea in a s»u percent decline In formaldehyde emissions from th«%,£«*
vents. Conversely, if P.P rocin, LL e»K.*4*y*L 5]?s;rns..irom the Pf655
r«
use irt l2 o« af?^ Jre "Jj"4"^ ^r the MDI currently in
use, press emissions of formaldehyde might Increase ten fold.
" ^ also important to compare
indra h* ?fir dryer «*«1ons. Our review of the 01 athe facility
fSUidlhJta * P %Hryer rfiPresents the highest single emission point for
formaldehyde. Furthermore, an olfactory check of press steaming indicated
Pr?56i;C! °f fo""*ldehyde's acrid, astringent quality We comwJe
r°r±?^em1" -^SoS tSu-siw.rsiSidJM1
Ons rfur,nn fha most recent te$t Effl1ssions ranged from j^^
:h 1985 test to 205.8 Ib HCHO/day during the Junt ..„„
ooeramna w^h .ith-^ o f comPar1son «f formaldehyde emissions from plants
SSWSffil c^J cr£2Ur ^y. ™S " 4 h»°th«<«> e«^r1...
E-2
-------
Memorandum to I. Evans
7 July 1987, 17 July 1987 Rev. 1
Page 3
Table 2. Plantwide Formaldehyde Emissions
(Ib HCHO/day)
Equipment P-F Resins MDI Resin
Dryer 155 155
Press 65 - 6.6
TOTAL 220 161.6
Using the values in Table 2's hypothetical example, press emissions of
formaldehyde represent about 30 percent of total formaldehyde emissions
plantwide. In shifting to MDI resin, the percentage of total plantwide
formaldehyde emissions attributable to the press operations is reduced to
about 4 percent. An overall reduction of almost 27 percent 1s achieved for
formaldehyde emitted from the plant when considering the change from P-F
resins to MDI.
E-3
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TECHNICAL REPORT DATA
"ease read tnsmtcttons on me reverie le'cre i'
1 P6PCRT NO. :2. J =. IDENTIFIERS/OPEN ENDED TERMS
Air pollution control
i.. COSATi 1 icia.'Cirouo
Release unlimited
i
19. StCURITY CLASS / Hia Kqparii . : Z\. NO. OF PAfleS''-'
""c^ffEji.t ,;;;.:;:;!,... :..: ;...... • •
20. SECUHI
Unclassified
SPA Form 2220-1 (R«». 4-771 -SEVIOUS EDITION IS OBSOLETE
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U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard, 12th FloOf
Chicago, II 60604-3590
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