EPA 340/1-76-007
FEBRUARY 1975
Stationary Source Enforcement Series
ANALYSIS OF CONTROL STRATEGIES
AND COMPLIANCE SCHEDULES FOR
WOOD PARTICLE ANDHBER DRYERS
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office Of Enforcement
Office of General Enforcement
Washington, D.C. 20460
-------
ANALYSIS OF CONTROL STRATEGIES
AND COMPLIANCE SCHEDULES FOR
WOOD PARTICLE AND FIBER DRYERS
Contract No. 68-01-3150
Technical Service Area No. 1
Task Order No. 19
EPA Project Officer
Norman Edmisten
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Region X, Air Compliance Branch
Portland, Oregon
July 1976
-------
Errata Sheet for EPA Publication EPA 340/1-76-007, ANALYSIS OF CONTROL
STRATEGIES AND COMPLIANCE SCHEDULES FOR WOOD PARTICLE AND FIBER DRYERS
Cover: Release date is July 1976
Page ii was inadvertantly dropped from manuscript. It should read:
This report was furnished to the U.S. Environmental Pro-
tection Agency by PEDCO-Environmental Specialists, Inc.,
Cincinnati, Ohio, in fulfillment of Contract No. 68-01-3150
(task 1-19). The contents of this report are reproduced herein
as received from the contractor. The opinions, findings, and.
conclusions expressed are those of the author and not neces-
sarily those of the U.S. Environmental Protection Agency.
The Enforcement Technical Guideline series of reports is issued by the
Office of Enforcement, Environmental Protection Agency, to assist the
Regional Offices in activities related to enforcement of implementation
plans, new source emission standards, and hazardous emission standards
to be developed under the Clean Air Act. Copies of Enforcement Technical
Guideline reports are availableas supplies permitifrom Air Pollution
Technical Information Center, Environmental Protection Agency, Research
Triangle Park, North Carolina 27711, or may be obtained, for a nominal
cost, from the National Technical Information Service, 5285 Port. Royal
Road, Springfield, Virginia 22161.
"Eechnical Report Data Page: Point number 1: correct document number is
EPA 340/1-76-007
Point number 6: correct release date is
July 1976
-------
ACKNOWLEDGMENT
This report was prepared for the "U.S. Environmental
Protection Agency, Region X, Air Compliance Branch, by
PEDCo-Environmental Specialists, Inc. Mr. N. Steve Walsh
was the PEDCo Project Manager. The principal author of
this report was Dr. David C. Junge with support provided by
Dr. Richard W. Boubel,
Mr. Norman Edmisten was the Project Officer for the
U.S. Environmental Protection Agency. The author is appre-
ciative of the assistance and advice extended by Mr. Edmisten.
Cooperation by the many participating firms within the
industry was essential to the timely completion of this
proejct and is very much appreciated.
111
-------
TABLE OF CONTENTS
Page
1. INTRODUCTION 1-1
Purpose 1-1
Scope 1-2
2. SUMMARY: STATUS OF CONTROL TECHNOLOGY FOR 2-1
PARTICLE AND FIBER DRYERS
3. THE PRODUCTION PROCESS 3-1
4. PARTICLE AND FIBER DRYING SYSTEMS 4-1
Energy Input Systems 4-1
Particle/Fiber Feed Systems 4-2
Dryer Designs 4-5
Particle Separation Systems 4-14
Fan Systems 4-15
Dryers Connected in Series 4-16
Dryers Equipped with Partial-Air-Recirculation 4-17
Systems
Dryers Equipped with Full Exhaust Gas Recircula- 4-17
tion Systems
Energy Sources for Dryers 4-22
5. EMISSIONS OF POLLUTANT MATERIALS FROM PARTICLE 5-1
DRYER SYSTEMS
Pollutant Emissions from Particle Dryers 5-1
IV
-------
TABLE OF CONTENTS (continued)
Page
Measurement of Particle Dryer Emissions 5-6
Selection of Measurement Technique 5-9
Opacity 5-10
Factors Affecting Emissions from Uncontrolled 5-10
Dryers
6. REGULATIONS PERTAINING TO PARTICLE DRYER EMIS- 6-1
SIGNS
Process Weight Regulations 6-1
Regulations Pertaining to Concentration of 6-5
Pollutant Emissions
Regulations Pertaining to Opacity 6-6
Other Applicable Regulations 6-9
7. APPLICATION OF CONTROL TECHNOLOGY TO MEET 7-1
EMISSION REGULATIONS
Wet Scrubber Emission Control Devices 7-1
Full-Recirculation Control Systems 7-7
Partial-Recirculation Control Systems 7-12
Medium- and High-Energy Secondary Cyclone Control 7-16
Devices
Multiple-Cyclone Control Systems 7-20
Fabric-Filter Emission Control Systems 7-22
Other Systems for Controlling Dryer Emissions 7-24
Safety Considerations Relative to Dryer Emission 7-26
Control Devices
v
-------
TABLE OF CONTENTS (continued)
Page
8. INDUSTRY-WIDE COMPLIANCE STATUS SUMMARY 8-1
9. REFERENCES 9-1
APPENDIX A INTRODUCTORY NOTES ON THE THEORY OF A-l
PARTICLE DRYING
APPENDIX B TERMINOLOGY OF WOOD-BASED FIBER AND B-l
PARTICLE PANEL MANUFACTURING
APPENDIX C PATENT ON FULL-RECIRCULATION DRYER C-l
SYSTEM
APPENDIX D SUMMARY DATA SHEETS FOR 76 PARTICLE AND D-l
FIBER DRYERS
APPENDIX E PARTICLEBOARD AND MEDIUM-DENSITY FIBER- E-l
BOARD MANUFACTURING PLANTS
APPENDIX F HARDBOARD MANUFACTURING PLANTS F-l
APPENDIX G PLANTS WHOSE PRODUCTS ARE NOT VERIFIED G-l
VI
-------
LIST QF FIGURES
Figure Page
3-1 Flow Diagram of a Typical Particleboard 3-4
Plant
4-1 Steam Heat Exchanger Used to Heat Air 4-3
Stream for Drying Particleboard Feedstock
4-2 Direct-Combustion Energy System Used to 4-4
Heat Ambient Air Stream for a Particle
Dryer
4-3 Typical Particle Feed System 4-6
4-4 Schematic Diagram of a Typical Tube-Type 4-8
Fiber Dryer
4-5 Typical Flash Dryer for Particle and Fiber 4-9
Drying
4-6 Schematic Diagram of a Typical Single-Pass 4-11
Stationary Drum Dryer
4-7 Schematic Diagram of a Single-Pass Rotary 4-12
Drum Dryer
4-8 Schematic Diagram of a Triple-Pass Rotary 4-13
Drum Dryer
4-9 Schematic Illustration of a Typical Two- 4-18
Stage Particle Dryer System
4-10 Schematic Illustration of a Typical Dryer 4-19
Equipped for Partial Recirculation of the
Gas Stream
4-11 Schematic Diagram of a Particle Dryer 4-21
Equipped with Full Exhaust Gas Recircula-
tion System
vii
-------
Figure
LIST OF FIGURES (continued)
8-1 Distribution of Particleboard and Hardboard 8-12
Plants in the United States
A-l Sensible Heat Imparted to Wood and Water to A-6
Raise it to the Evaporation Temperature
A-2 Energy Required to Evaporate Water from A-8
Wood as a Function of Moisture Content
A-3 Energy Exhausted to Atmosphere in a Single- A-10
Pass Particle Dryer
Vlll
-------
LIST OF TABLES
Table Page
7-1 Summary of Wet-Scrubber Control Devices for 7-5
Particle Dryers
7-2 Summary of Full Recirculation Control 7-9
Systems for Particle Dryers
7-3 Summary of Partial Recirculation Control 7-14
Systems for Particle Dryers
7-4 Summary of Medium and High-Energy Secondary 7-19
Cyclone Control Devices for Particle Dryers
8-1 Compliance Status Summary: Particleboard 8-3
and Medium-Density Fiberboard Plants
8-2 Compliance Status Summary: Hardboard Plants 8-8
8-3 Plants in Questionable Status 8-10
A-l Density and Moisture Content of Some A-3
Typical North American Wood Species
A-2 Range of Approximate Energy Use for Drying A-11
Particles
IX
-------
1. INTRODUCTION
Under Section 113 of the Clean Air Act, as amended in
1970, the Administrator of the Environmental Protection
Agency (EPA) is required to initiate Federal Enforcement
Action against sources known to be in violation of any
control strategy provisions of a State Implementation Plan
(SIP). The EPA Regional Offices have primary responsibility
for implementation of the Federal Enforcement Program.
Policy development and guidance with respect to enforcement
is furnished by EPA's Division of Stationary Source Enforce-
ment. This report is concerned with control of pollutant
emissions from dryers in the wood products industry to
achieve compliance with regulations.
The wood products industry includes manufacturers of
wood-based fiber and particle panel materials. The produc-
tion processes usually include drying of the wood raw mate-
rials to control moisture content. Particle dryers used for
this purpose have been identified as significant potential
sources of atmospheric pollutant materials. The nature of
the emissions in terms of type, quantity, and effect on the
environment is variable. Similarly, the factors that in-
fluence emissions are complex and variable.
PURPOSE
The major objectives of this project are to define the
state of the art in applied control technology for particle
dryers in the wood-based fiber and particle panel manufac-
turing industry and to define the status of compliance on a
nationwide basis for particle and fiber dryer installations.
1-1
-------
SCOPE
Information for this study has been obtained from many
sources. Field investigations were made of 76 particle and
fiber dryer installations at 19 manufacturing plants in the
states of Oregon, North Carolina, South Carolina, Virginia,
and Georgia. These plants represent a cross section of the
production of these products in the United States. In the
course of the investigation, information was obtained from
plant managers, production foremen, plant operators, equip-
ment vendors, and regulatory agencies on the Federal, state,
and local levels. An intensive literature search was
carried out, and valuable insight was gained from discus-
sions with consultants who have worked in this aspect of
emission measurement and control technology.
To ascertain the compliance status and compliance
schedules of the industry, data reports of the Compliance
Data System (CDS) and National Emission Data System (NEDS)
were reviewed. Directories of the Forest Products Industry,
the National Particleboard Association, and Acoustical and
Board Products Association were utilized to verify iden-
tities, locations, and production levels of the various
board producers. All EPA regional offices were contacted
for supportive information, and some local agencies were
contacted.
The report is organized so as to present briefly the
basic operations of wood and fiber panel production (Section
3) and the specific functions of the several major dryer
configurations (Section 4) .
Pollutant emissions from dryer systems are character-
ized in Section 5, with a brief discussion of emission
measurement techniques. Regulations pertaining to particle
dryer emissions are summarized in Section 6.
1-2
-------
The balance of the report deals with control technology
currently applied in the industry, describing (in Section 7)
for each major control option the degree of success achieved
in meeting regulations, any major problems, approximate
costs, and recommended applications. Section 8 summarizes
the current known compliance status of dryer units, indus-
try-wide .
For readers unfamiliar with the wood-based fiber and
particle panel manufacturing industries, substantial sup-
portive information is presented in the appendices. Ap-
pendix A provides introductory notes on the theory of par-
ticle drying, and Appendix B identifies the terminology of
the industry, including definitions, classifications of
particleboards, raw materials used, and finished products of
the industry.
1-3
-------
2. SUMMARY: STATUS OF CONTROL TECHNOLOGY
FOR PARTICLE AND FIBER DRYERS
A major purpose of this study was to summarise the
state of the art of technology for control of emissions from
particle and fiber dryers. In the course of the effort, 76
dryers were evaluated during visits to 19 manufacturing
facilities in Oregon, North Carolina, South Carolina,
Virginia, and Georgia. Evaluation of each dryer include?
assessment of important parameters regarding temperatures,
flow rates, species and moisture content of process feed,
dryer design, fuel sources, type of control (if any) ap-
plied, and degree of success in meeting regulations. The
following comments and conclusions are based on discussions
with regulatory officials, plant managers, plant operators,
and equipment suppliers, and on review of the literature
regarding particle dryer emissions and emission control
technology.
1. Emissions from particle dryers can be categorized
in terms of three typical classes of particles: (1) large
particles, principally fibers larger than 10 microns; (2)
small, solid particles (the inorganic, noncombustible
materials that come primarily from direct combustion of
energy sources connected to the dryers); (3) small volatile
organic particles, which are the condensation products of
volatile materials evaporated from the dryer furnish.*
* 'Furnish1 denotes the material furnished to the process,
i.e., the process feed or input.
2-1
-------
2. Selection of a system for control of dryer emis-
sions will be based on numerous considerations, including
the following:
0 What regulations are to be met (grain loading,
opacity, mass emission rate, or other)?
0 What classes of particles must be controlled in
order to meet the requirements?
0 What are the capital and operating costs of alter-
native collection or control devices?
0 What are the space requirements?
0 What are the energy requirements?
0 What are the potential maintenance and operational
problems?
0 What are the safety considerations (e.g., fire
hazard, explosion potential)-?
0 Will the systems considered operate under fluc-
tuating flow rates?
0 If sanderdust is to be used as a fuel for direct
combustion, what is its inorganic ash content? Is
the sanderdust treated to make it noncombustible?
Is the supply sufficient for use on a year-around
basis?
Items (1) and (2) concern broad or general considera-
tions. Following are more specific comments:
3. Control of emissions of large-fiber particles is
technologically proven and is not particularly difficult.
Control can be accomplished with well-designed and operated
cyclone systems provided that the furnish is of reasonable
mean particle size. For furnish with very small mean par-
ticle size, control can be accomplished with wet scrubbers,
full-recirculation systems, partial-recirculation systems,
secondary medium-energy cyclones, multiple cyclones, or
2-2
-------
fabric filters. Cost of installation of these systems
ranges from $3/cfm to $7/cfm.
4. Control of inorganic, noncombustible ash can be
accomplished with medium-energy scrubbers and probably with
fabric filters, although use of the latter has not been
demonstrated relative to particle dryers. Because the
particles are both small and noncombustible, devices such as
low-energy wet scrubbers, recirculation systems, secondary
medium-energy cyclones, or multiple cyclones are not appro-
priate for control of these emissions. A change of the fuel
to reduce the ash content would be a reasonable alternative
if replacement fuels are available and are not prohibitively
expensive.
5. Controlling emissions of inorganic ash content to
meet grain loading or mass emission requirements will not
necessarily meet opacity requirements. The small particles
are particularly visible in a characteristic blue haze.
6. Control of organic volatile components of the wood
furnish is possible by two alternative methods. The most
widely used and most successful method is to limit the dryer
inlet temperatures to levels at which organic materials are
not evaporated from the furnish. If this approach is not
feasible in light of plant production requirements, then
only one of the control methods investigated appears to be
acceptable: full recirculation of exhaust gases from the
primary cyclone to the combustion chamber on the dryer
energy source. Because of the concern over emissions of
volatile organics, some elaboration is in order.
Wet scrubbers have been used to control opacity related
to volatile organic emissions, but without success. In some
cases and under some atmospheric conditions scrubber plumes
2-3
-------
will mask the blue haze for a long enough period that the
system may be judged to be in compliance; under other con-
ditions, however, opacity will exceed the restrictions.
Even high-energy scrubbers have not proved successful in
controlling submicron particles such as those that cause the
classic blue-haze problem.
Partial recirculation systems do not circulate all of
the combustible haze-forming particles back to the combus-
tion chamber. The nonrecirculated portion of the exhaust
gases creates the opacity, and the systems are ineffective.
Medium-energy secondary cyclone systems and multiple cy-
clones cannot collect submicron size particles and thus are
also ineffective.
A single baghouse installed to reduce dryer emissions
emits a noticable blue haze from its base. Dilution air
that circulates under the fabric filter helps to disperse
the condensation particles. Collection of the organic
materials in the filter may plug the filter and make it
inoperative. This should be recognized as a limitation of
filter systems. For control of large fibers and of in-
organic emissions, a well-designed and operated fabric
filter may be feasible.
It appears that only full-recirculation systems can
control opacity caused by volatile organic materials in the
submicron size range. As long as temperatures in the com-
bustion zone are maintained at levels high enough to burn
the combustible organic materials, opacity due to these
materials will be controlled. But an energy penalty is
incurred. Full-recirculation systems require significantly
higher energy input per pound of water evaporated than does
any alternative system. This requirement results from very
2-4
-------
high exit temperatures of the exhaust gas stream as it
enters the atmosphere. The energy requirement may be met by
burning inexpensive sanderdust; the use of fossil fuels
would be prohibitively expensive. Sanderdust from the
manufacture of particleboard may have high ash content.
Although some of the fly ash will be captured on the par-
ticles in the dryer, most will be recirculated through the
dryer and out the exhaust stack. Because of the predomi-
nance of fine particles, these fly ash emissions may result
in both high grainloading and high opacity.
Test results show that emissions from full-recircula-
tion systems are between 0.10 and 0.20 gr/sdcf* under some
operating conditions.
7. Although there is considerable development of
technology for control of volatile organic emissions from
veneer dryers, transfer of this experimental technology has
not been great. Applicability of this technology will be
determined by the classes of particles that leave the
dryers. Devices for control of blue haze from veneer dryers
will not necessarily be successful in control of blue haze
due to inorganic fly ash produced in a particle dryer energy
source. Low-temperature operation of particle and fiber
dryers (as with veneer dryers) will limit organic emissions.
8. No control system is universally applicable.
Application at a specific plant is governed by variations in
species, particle size, and moisture content of the furnish
and in manufacturing processes.
9. Success in meeting emission regulations depends
somewhat on the measurement techniques used to determine
* When grain loadings are expressed under actual non-
standard conditions, they may be considerably smaller
(i.e., order of magnitude).
2-5
-------
compliance. The measurement techniques often are selected
at the discretion of the control agency. For sources in-
volving high levels of volatile organic materials, the
measurement technique is crucial.
10. Most, but not all, particle dryers have been
tested to determine emission levels. Dryers generating low
levels of visible emissions receive less pressure from the
agencies for emission testing. In addition, most plants are
either operating in compliance With emission limits or are
making changes that will bring them into compliance. The
industry has made large capital investments specifically for
emission control.
There is no doubt that particle dryers can be operated
in compliance with most current regulations, particularly
those related to concentration, mass emission rates, and
opacity. At some plants the changes required in current
production practices and/or the capital requirements for
purchase and installation of control devices may create
serious problems. Operators of dryers that receive a sub-
stantial input of energy from boiler exhaust gases generated
by fuels having high ash content may be faced with extreme
difficulty in meeting regulations. In the interest of
energy conservation, it may be warranted to consider revi-
sions to regulations governing emissions from such dryers
unless, of course, the regulations are essential for the
attainment and/or maintenance of air quality standards.
2-6
-------
3. THE PRODUCTION PROCESS
Processes for manufacturing wood-based fiber and par-
ticle panel products are briefly summarized in this section.
Raw materials are received at the plant site in a wide range
of sizes and moisture contents. Since manufacturing re-
quires uniform size and moisture levels, the initial proc-
esses are (1) refining of raw materials to yield the re-
quired size of fibers or particles, and (2) drying of the
fiber or particles. These processes may be performed in
reverse order depending on the products. Production of some
particleboard products requires two discreet size ranges for
the particle furnish. Coarse particles may be used to form
the center or core of the panel, and fine particles may be
used to form exterior surfaces, which require a very smooth
finish. Thus, the furnish for particleboard is often clas-
sified as "surface" and "core" materials.
The amount of drying required depends on two major
factors: the production process and the initial moisture
content* of the raw material. In manufacture of hardboard
as well as some insulation board and fiberboard, the moisture
content of the material delivered to the board manufacturing
machine may be in excess of 15 percent on a dry basis. For
* Moisture content (MC) may be discussed on a wet basis or
a dry basis. The fiber and particle panel industries use
the dry basis. The two bases are related as follows:
MC (wet) = 100 * MC (dry) ( . = 100 x MC (wet)
MC iwet) 10Q + MC (dry) MC vary) IQQ _ MC (wet)
Where MC is expressed in percent.
3-1
-------
most particleboard operations, the moisture levels must be
held between 4 and 6 percent (dry basis). (Appendix B
provides definitions of board products and associated
terminology.)
The initial moisture level for raw materials, discussed
later in greater detail, typically varies from high values
of 200 percent to low values of 6 to 8 percent. Raw mate-
rials whose initial moisture content exceeds 60 percent may
entail two stages of drying, particularly when moisture
levels in the different components of the furnish vary over
a wide range.
Particles including wood chips, planer shavings, saw-
dust, and flakes are normally dried on a continuous basis in
rotary drum dryers. Wood fiber, being much lower in bulk
density, is normally dried in a tube dryer with signifi-
cantly higher volumes of air and lower inlet temperatures.
Appendix A presents a discussion of particle drying theory.
After the raw materials are dried and particle size
distributions are controlled within acceptable limits,
resins are added in a blending machine. The prepared
furnish is then carried to the mat former, where it is built
up into a uniformly thick layer of uncompressed, loose
particles. The mats may be formed on individual backing
sheets (cauls) or they may be formed on a continuously
moving screen wire bed. The loose mat is usually subjected
to moderate compaction and is then placed in a steam-heated
press. The high temperature and pressure in the press sets
up the bonding resins to give the required strength char-
acteristics. The smooth surfaces of the press leave the
panels with correspondingly smooth surfaces.
When the press cycle is completed, the panels are
removed and allowed to cool. Preset saws trim the edges and
3-2
-------
ends to meet size requirements. If the surface requires
sanding, the individual panels are routed to automatic high-
speed surface sanders. Packaging and shipping operations
complete the basic manufacturing process. Figure 3-1 de-
picts process flow in a typical particleboard plant.
Approximately 75 plants are manufacturing particleboard
in the U.S., with annual production exceeding 5 billion
square feet, on the basis of 3/4-inch-thick product. Twenty
hardboard plants produce 3.5 billion square feet of products
on a 1/8-inch-thick basis.
3-3
-------
RAM MAT'L
STORAGE
REFINER
PRESSES
OFF - STACKER
COOLER
STACKER
TRW SAWS
6
I
PARTICLE DRYER
MAT FORMERS
T
I
SANDER
CYCLONE
SEPARATOI
BLENDER
-^- TO PACKAGING AND
SHIPPING
Figure 3-1. Flow diagram of a typical particleboard plant,
-------
4. PARTICLE AND FIBER DRYING SYSTEMS
Particle and fiber dryers are integrated into complex
production systems. At most plants the dryer systems con-
sist of five principle components: (1) a heat-energy input
system, (2) a particle or fiber feed system, (3) the dryer,
in which particles (fibers) are subjected to sufficient
residence time and turbulence at elevated temperatures to
separate moisture from the particles, (4) a system to
separate the dried particles (fibers) from their carrier gas
stream, and (5) a fan system for moving the particles and
gas stream through the dryer. Certain dryer systems include
components whose purpose is to provide turbulence, mechan-
ical mixing, separation of particles (fibers), or other
functions to aid in separating moisture from the wood feed
stock.
ENERGY INPUT SYSTEMS
In most dryer systems, the particles are carried
through the various components by a carrier gas stream
(air). The air must be heated from its incoming temperature
level (ambient in most cases) to a level high enough to
evaporate the moisture from the wood. Energy required to
heat the air is provided by a variety of sources. The
preheat temperature of the air stream is generally con-
trolled by the temperature of the gas stream leaving the
dryer, since this has proved to be the most efficient means
of controlling the discharge moisture content of the wood
particles (fibers).
4-1
-------
Temperature of the incoming air may be raised by direct
or indirect contact heat exchangers. Indirect contact
exchangers are used only when steam or hot water serves as
the energy source (see Figure 4-1). For all other energy
sources, one or more fuels are burned and the resulting
high-temperature combustion products are mixed directly with
the incoming air stream. As a precaution against potential
fire or explosion, design of combustion-based energy systems
must ensure that all of the fuel is completely oxidized
before it comes in contact with the feed stock of particles
or fibers. Typical combustion systems include a long,
cylindrical, stationary chamber to ensure complete combus-
tion and thorough mixing of the incoming air stream before
it contacts the feed stock (see Figure 4-2).
Several plants have combined the use of steam-heated
systems and direct combustion systems to provide energy
input to the dryer(s). This procedure is based on the
availability of steam capacity at the plant and the relative
cost and availability of alternate energy sources for direct
combustion.
PARTICLE/FIBER FEED SYSTEMS
The rate of flow of moist wood particles or fibers to
the drying system must be regulated to bring about uniform
drying and control of the exit moisture content. The rate
of feed is based on production needs and is limited by the
operating parameters of the dryer system. Another approach
would be to monitor and control the rate of water input to
the dryer (.i.e., the water contained in the particles).
This would ensure more uniform evaporation rates in the
dryer and therefore more uniform exit moisture levels of the
wood particles or fibers. However, continuous monitoring of
4-2
-------
WET FURNISH
INLET
FEEDER VALVE
I
U)
AIR
INLET
?
y
/
e o o o o o
o o o o o
STEAM HEAT
EXCHANGER
ROTARY DRUM DRYER
D
Figure 4-1. Steam heat exchanger used to heat air stream
for drying particleboard feedstock.
-------
WET FURNISH
INLET
FUEL BURNER
COMBUSTION ZONE AND DIRECT
CONTACT AIR HEATER
Figure 4-2. Direct-combustion energy system used to heat
ambient air stream for a particle dryer.
-------
the input moisture to the dryer is difficult to accomplish.
Furthermore, because of variations in size and morphology of
the particles, the rate of drying is highly variable.
Control of feed rate therefore seems adequate for production
purposes.
A typical feed system is illustrated in Figure 4-3. A
material transfer mechanism, usually a pneumatic system
culminating in a cyclone separator, carries the moist feed
stock to a storage hopper. From the hopper the stock is
dropped into a rotary (star) feed valve. The rpm of the
rotary feed valve controls the rate of flow of the wood feed
stock to the dryer. Flow rate is directly influenced by the
bulk density of the feed stock, and any abrupt changes in
bulk density will alter the exit moisture level. For most
systems, this is not a severe limitation. The rpm of the
rotary valve is generally controlled by a DC drive or a
variable-speed reducer coupled to an AC drive.
DRYER DESIGNS
Particle dryers are manufactured in a variety of con-
figurations, sizes, and material handling capacities to meet
specific production requirements. The basic purpose of the
dryer is to subject wood particles or fibers for a suf-
ficient time period to physical conditions conducive to
evaporation of water from the wood. The dryer therefore
must be large enough to allow sufficient residence time and
must provide for movement of particles to increase the rate
of evaporation. Tumbling action, jets of high-temperature
air, rakes or paddles, and other methods are used to bring
about movement of particles relative to each other and to
the drying air stream. Beyond these basic requirements,
4-5
-------
INLET FOR
WET FURNISH
EXHAUST
CYCLONE
SEPARATOR
WET FURNISH
FEED BIN
FEEDER VALVE
WET FURNISH TO
DRYER INLET
Figure 4-3. Typical particle feed system.
4-6
-------
dryer design entails considerations of energy requirements,
reliability, maintenance, and capital costs.
The two principal design categories are tube dryers and
drum dryers. Drum dryers may incorporate fixed or rotary
drums, and rotary drum dryers may entail one or three
passes. These basic designs are briefly described in the
following paragraphs.
Tube Dryers
Tube dryers, which are used principally to dry fibers
rather than particles or small chips of wood feed stock, are
nothing more than long tubes through which the heated air
stream and the fibers pass. As illustrated in Figure 4-4,
the tube is designed to accommodate the carrier gas stream
at the minimum velocities required to keep the fibers en-
trained long enough that the moisture can evaporate to the
required level. The dryer includes no moving parts and
therefore is inexpensive to construct and maintain (relative
to the more complex rotary drum dryers). The tube dryer,
however, requires more energy to evaporate a pound of water
than does the drum dryer because larger volumes of heated
air are reuqired to carry the fibers through the tube dryer.
An interesting modification of the tube dryer is the
'flash' dryer (Figure 4-5). Whereas in the tube dryer all
of the particles move through the tube at approximately the
same rate, in a flash dryer the moist particles are injected
at the bottom and are suspended in an upward-flowing gas
stream. As the particles become dryer, their density de-
creases and they are carried upward and into the collector
system. The heavier, still-moist particles remain in sus-
pension until enough moisture is evaporated to allow the
carrier gas stream to remove them from the dryer. Thus, the
flash dryer involves considerable relative motion between
4-7
-------
WET FURNISH
INLET
STEAM HEAT EXCHANGER
\
CYCLONE
SEPARATOR
DRY FURNISH
EXIT
PULL THROUGH
FAN
Figure 4-4. Schematic diagram of a typical tube-type fiber dryer.
-------
WET FURNISH
STEAM HEAT EXCHANGER
FLASH DRYER
EXHAUST
CYCLONE
SEPARATOR
DRY FURNISH
PULL-THROUGH
FAN
Figure 4-5. Typical flash dryer for particle and fiber drying.
-------
the particles and the carrier gas stream. Flash dryers,
like tube dryers, are stationary units with no moving parts.
Drum Dryers
Drum dryers are the most commonly used in the wood
products industry. They were developed for drying agri-
cultural crops and are still used more extensively for crop
drying than for drying wood products. Drum dryers are
designed with stationary or rotating drums. Use of sta-
tionary drums requires some device or system to keep the
moist particles moving through the dryer and to maintain
turbulent motion of the particles with respect to the air
stream. Both of these requirements can be met with systems
of moving rakers inside the drum or with high-velocity air
jets. Manufacturers of stationary drum dryers advertise
competitive capital costs, since the drums do not rotate and
therefore do not require moving parts such as shafts, bear-
ings, and the like. Each of the stationary drum dryers
evaluated in this project was a single-pass design; that is,
moist particles enter the drum in one end and leave the drum
at the opposite end after a single pass through the system.
A single-pass, stationary dryer drum is illustrated'in
Figure 4-6.
Rotary drum dryers are large cylinders with horizontal
axes, having either single-pass or triple-pass design, as
illustrated in Figures 4-7 and 4-8. In either case, the
drums are externally supported on trunion mounts; as they
rotate about their axes, the rotary motion and the air
stream moving through the dryer transport the wood feed fronj
the inlet to the outlet. Residence time is controlled by
the size of the drum, the rate of revolution, and the rate
of gas flow through the drum.
4-10
-------
WET FURNISH
HOT AIR
INLET
FEED VALVE
STATIONARY DRUM
ROTATING PADDLES
I
6-
DRY FURNISH EXIT
Figure 4-6. Schematic diagram of a typical single-pass stationary drum dryer.
-------
WET FURNISH
INLET
HOT AIRf
INLETA
DRY FURNISH
EXIT
ROTARY DRUM
=U TRUNION MOUNTS
MATERIAL HANDLING
FAN
Figure 4-7. Schematic diagram of a single-pass rotary drum dryer.
-------
WET FURNISH
i
M
U)
DRY FURNISH
EXIT
FEEDER VALVE
ROTARY DRUM
c-
=4 ITRUNION MOUNTS
MATERIAL HANDLING
FAN
Figure 4-8. Schematic diagram of a triple-pass rotary drum dryer.
-------
The single-pass design is less efficient in terms of
space utilization than the triple-pass design. Although
this can be compensated for by installing "fill" in single-
pass drums, only two mills have used this procedure. The
triple-pass drum is by far the most common in wood products
industries. A typical triple-pass drum measures 90 inches
in diameter by 28 feet long.
PARTICLE SEPARATION SYSTEMS
After the particles leave the dryers, they are sepa-
rated from the carrier gas stream, usually in cyclone sepa-
rators. Most dryers are directly connected to a single
cyclone so that the entire gas stream from the dryer enters
the cyclone (see Figures 4-4 and 4-5). Centrifugal force
exerted on the particles inside the cyclone separates them
from the,gas stream. The particles are carried to the
bottom of the cyclone and are discharged into a bin or
receiving hopper. The carrier gas stream exits from the top
of the cyclone.
The phrase "primary cyclone" designates the first
cyclone in a system downstream from the particle dryer.
Emissions to the atmosphere of potentially pollutant mate-
rials from particle dryers occur principally at the gas exit
duct of the primary cyclone. At this point the gas stream
contains any fibers or wood particles that were not col-
lected in the cyclone. It also contains products of com-
bustion from the energy source for the dryer (unless the
dryer is heated by steam or hot water) and may contain
volatile organic materials evaporated from the wood particle
feed stock.
Because the exit duct of the primary cyclone is the
principle point of pollutant emission, design of the pri-
4-14
-------
mary cyclone is of critical importance in limiting these
emissions, particularly of wood fiber materials. The col-
lection efficiency of cyclones is influenced by many fac-
tors, including size distribution of the particles to be
separated, particle density, moisture content and tempera-
ture of the carrier gas stream, gas flow rate, and geometry
of the cyclone. Many technical papers regarding cyclone
9
design could be consulted in the event that emission
problems are traced to inefficient cyclone design.
FAN SYSTEMS
The principle means of moving particles through dryers,
associated duct work, and cyclones is by partial or total
suspension in a gas stream moving through the system. Large
industrial centrifugal fans used to move the gas through the
system may be placed between the dryer and the primary
cyclone or downstream from the primary cyclone. In the
latter case, the cyclone is said to be a "pull-through1
system whereas when the fan precedes the cyclone the gas
stream is 'pushed1 into the cyclone. In terms of overall
system efficiency, location of the fan makes no great dif-
ference. If the fan is placed downstream from the cyclone,
however, a rotary Cstar) discharge valve must be incor-
porated on the material exit from the cyclone.
Power requirements for fan systems vary over a wide
range, dependent on the size, flow rates, and differential
pressure requirements of the system. Systems equipped with
pollution control devices may require much more fan power
than systems without such devices. Typical fan power re-
quirements for uncontrolled systems range from 50 to 150
horsepower.
4-15
-------
For most dryer systems, the fans are constant-speed
units connected directly to 440-volt, 3-phase drives. Since
gas flow through a given dryer is held constant in most
operations, no dampers are used to vary the gas flow rates.
Following this discussion of the basic components of
particle dryer systems, attention is now given to common
modifications of dryer designs and to the principle energy
sources for dryer operation.
DRYERS CONNECTED IN SERIES
Moisture content of the furnish for wood panel products
must be controlled to close tolerances, usually within 1
percent of the average level required. If the raw materials
received at the plant site are of reasonably uniform mois-
ture content, the drying process can be accomplished in a
single stage. In practice, however, initial moisture levels
do vary over a wide range. Moisture content of sawdust may
be more than 200 percent (dry basis); that of green planer
shavings, about 100 percent, and of recycled edge and end
trim, about 6 percent. If these materials are fed to a
common dryer, it would be difficult to dry the sawdust to
the 6 percent level without burning the already dry edge and
end trim. This problem can be resolved in two ways. First,
raw materials with high initial moisture levels can be fed
to a 'green1 dryer, or predryer, which is the first dryer in
a series of two. Moisture levels at the exit from the green
dryer may range from 12 to 15 percent (dry basis). Another
solution is to mix the raw feed so that the resultant
average moisture level is reasonably uniform. Such mixing
may be done prior to a green dryer. Final drying is done in
a second-stage dryer, to which typical input moisture levels
4-16
-------
are 12 to 15 percent. Figure 4-9 illustrates a typical two-
stage particle dryer system.
DRYERS EQUIPPED WITH PARTIAL-AIR-RECIRCULATION SYSTEMS
Partial recirculation of the exit gases from the pri-
mary cyclone to the dryer can reduce the energy requirement
per pound of water evaporated. Another advantage is that
the gas stream to be recycled is picked up at the perimeter
of the primary cyclone exit duct, which is the zone of
highest concentration of escaping particles. The particles
are thus recycled to the dryer rather than added to the
system emissions. A typical system for partial recircula-
tion of air is illustrated in Figure 4-10.
In spite of the obvious energy and environmental bene-
fits of partial-recirculation systems, few have been in-
stalled in the industry. Such systems are of course more
expensive to install than nonrecycling systems. Further,
the strong incentives to reduce particle emissions and to
reduce energy requirements are relatively recent.
DRYERS EQUIPPED WITH FULL EXHAUST GAS RECIRCULATION SYSTEMS
The discussion of drying theory in Appendix A indicates
possible economic benefits of recirculating up to 60 percent
of the exhaust gas stream. An increasing number of dryers,
however, are designed to recirculate the entire exhaust gas
stream. This is being done, in spite of high energy costs
of operation and added capital costs for installation,
because of two significant advantages offered by a full-
recirculation system.
In the past, particle dryers have been heated with
steam or fired with fossil-based fuels, such as natural gas
4-17
-------
WET FURNISH
I
H1
CO
,FEED VALVE
STEAM HEAT
EXCHANGER
CYCLOUE
SEPARATOR!
f /EXHAUST
tL
'EXfWUST
FIRST-STAGE
TUBE DRYER OR
FIRST-STAGE
DRUM DRYER
STEAM HEAT
EXCHANGER
CYCLOKE
SEPARATOR
SECOND-STAGE
TUBE DRYER OR
SECOND-STAGE
DRUM DRYER
DRY FURNISH
Figure 4-9. Schematic illustration of a typical two-stage particle dryer system.
-------
EXHAUST GAS
PARTIAL EXHAUST GAS RECIRCULATION LINE
WET FURNISH
INLETi
\
DIRECT-COMBUSTION
HEAT EXCHANGER
~ ROTARY DRUM DRYER
~
1
CYCLONE
SEPARATOR
DRY FURNISH
II ^AN
^A
Figure 4-10. Schematic illustration of a typical dryer equipped
for partial recirculation of the gas stream.
-------
or propane. More recently, plants having sanding operations
that generate substantial quantities of sanderdust have been
using this material to replace high-cost fossil fuels. In
effect, plants with sufficient sanderdust for fuel can
ignore the added energy requirement for full exhaust gas
recycling on particle dryers. Several plants have justified
the capital cost of conversion to sanderdust firing on the
basis of fuel savings alone. There are, however, several
constraints on the use of sanderdust as fuel. Not all
plants sand their finished panel products. Of those that
do, not all generate enough sanderdust on a continuous basis
to provide adequate energy for particle drying. Further-
more, not all sanderdust is combustible. If panel products
are treated to make them fire resistant or nonflammable, the
sanderdust cannot be used as an energy source.
The second and perhaps the most important incentive for
use of full-recirculation systems is control of emissions
from particle dryers. Some portions of the dryer emissions
may be combustible, the percentage varying among dryer
systems and depending upon many factors. Where dryer emis-
sions must be reduced to meet regulations and these emis-
sions contain a high percentage of combustible materials,
the use of full exhaust gas recycle systems can be a prac-
tical means of emission control.
The design of these systems is relatively straight-
forward. As illustrated in Figure 4-11, the material exit-
ing from the primary cyclone is ducted back to the inlet
g
area of the dryer. In some installations the entire gas
volume is carried into the combustion chamber; in others, it
is split so that a portion enters the combustion chamber and
the remainder is used for dilution air on the inlet to the
4-20
-------
FULL EXHAUST 6AS RECIRCULATION LINE
NJ
CYCLONE
SEPARATOR
HIGH-TEMPERATURE
EXHAUST GASES
WET FURNISH
INLET
DIRECT-COMBUSTION
HEAT EXCHANGER
DRY |
FURNISH
ROTARY DRUM DRYER
MATERIAL HANDLING
FAN
A
Figure 4-11. Schematic diagram of a particle dryer equipped
with full exhaust gas recirculation system.
-------
dryer. The only exit gas stream from the system comes
directly from the combustion chamber exhaust. This stream
is at high temperature (typically 800 to 1600T) and con-
tains little, if any, combustible material. As a note of
interest, patents issued to the Stearns Rogers Co. for full-
recirculation systems are included in Appendix C.
It is important to note again the practical limits on
installation of full-recirculation systems. They require
significantly higher energy input than do partial-recir-
culation systems or nonrecirculating systems and therefore
are practical only for plants that have access to low-cost
fuels such as residual sanderdust. Second, they are prac-
tical in controlling emissions of combustible materials
only; they are of no value in controlling noncombustible
emissions. In addition, they can be used only in conjunc-
tion with direct-fired dryers. Dryers equipped exclusively
with steam heaters or hot water heaters are not advantageous
for use with full-recirculation systems.
ENERGY SOURCES FOR DRYERS
Energy requirements for particle or fiber dryers can be
high. For example, consider a dryer with a moderate through-
put rate of 30,000 pounds per hour of wet furnish. If the
material enters the dryer at 100 percent moisture (dry
basis) and leaves at 5 percent moisture, the energy input to
the dryer may be in the range of 25 million Btu per hour.
Sources of energy to the dryer may be grouped in four
principle categories:
0 Indirect heating with steam or hot water cir-
culating systems.
0 Direct heating with exhaust gases from nearby
boiler installations.
4-22
-------
0 Direct firing of fossil fuels or wood residue
fuels.
0 Combinations of two or more of the above systems.
Steam Systems
Figure 4-1 illustrates a typical steam heat exchanger
connected to a dryer. This system is commonly used where
steam is available and where drying does not require high
temperatures. The upper temperature limit for inlet air to
the dryer using steam as an energy source is generally
400°F. The cost of steam heat depends entirely on the fuel
used to generate the steam at the boiler. If wood residue
fuels are burned, the delivered cost of the energy may range
from $0.50 to $0.75 per million Btu. If oil is burned,
however, the delivered cost of the energy could easily
exceed $2.00 per million Btu. Steam-heated dryers are
installed both as single units and as units connected in
series. A distinct advantage of steam as an energy source
is that the dryer exhaust gases contain no combustion
products and emission levels will be lower than those from
any alternative system, all other factors being equal.
Boiler Exhuast Systems
A rather recent modification to dryer systems is to
connect them to the exhaust ducts from boilers. Typical
exit temperatures for exhaust gases from boilers in particle-
board/hardboard plants range from 400 to 625°F. The energy
input from these exhaust gases of course depends on the
temperature, moisture content, and flow rates of the gases.
Even a small boiler can contribute several million Btu per
hour to a particle dryer. A large boiler installation may
supply up to 100 percent of the required energy.
Connection to boiler exhaust ducts has both positive
and negative aspects. The primary advantage is in fuel
4-23
-------
savings at the dryers. A well-balanced system may save from
$50,000 to $100,000 per year in dryer fuel costs if the
boiler exhaust can be used to replace fossil fuels. On the
negative side, first the products of combustion from the
boiler stack will enter the dryer. Most of these leave in
the dryer exhaust system and add to the pollutant emissions.
The boiler (by itself) may be in compliance, as may the
dryer, but when these units are connected, the resultant
system will probably fail to comply with emission limits.
Most regulatory agencies make no provisions in the emission
regulations to promote such energy-conserving systems.
In addition to the emissions problem, other technical
problems are encountered in connecting boilers to dryers.
For most boilers the steam demands fluctuate, and thus so do
the stack gas flow rates. Auxiliary fuel systems may there-
fore be required to maintain the required energy input to
the dryers. Further, if the boiler is fired with wood and
bark residues, emissions from the boiler may contain sig-
nificant amounts of unburned carbon. This could reduce the
quality of the particles or fibers being dried, principally
through unwanted addition of carbon to the furnish. Also,
entry of burning carbon particles into the dryer could cause
fires and/or explosions.
Direct-Fired Dryers
The most common method of energy input to fiber and
particle dryers is through direct combustion of fuels in the
heat energy input system. Two principle types of fuels are
used: (1) fossil fuels, including natural gas, butane,
propane, diesel oil, and/or heavier residual oils; and (2)
wood residue fuels, including hogged wood and bark but
4-24
-------
principally sanderdust. Since these fuels undergo combus-
tion, their use results in the products of combustion
entering and leaving the dryer. These combustion products
are principally gases (C02, H20, N2, O2), but may also
include solid particles known as fly ash, the inorganic
component of the fuel that does not burn. Gaseous and
liquid fossil fuels produce neglible amounts of fly ash, but
emissions from some residual oils and certainly from wood
residue fuels may be significantly high.
Fossil fuels have become almost prohibitively expensive
for use in drying wood. Plants still using these fuels are
making every effort to find alternative energy sources ,
particularly those burning natural gas. Although it is the
least expensive of the fossil fuels, industrial curtailments
on interruptible contracts have been increasing, and in many
parts of the country natural gas is available less than 50
percent of the time.
There is a steady trend toward the use of sanderdust as
fuel for dryers. Where it is available in reasonable quan-
tities, it has proved economical and relatively easy to
handle on a continuous basis. Precautions must be taken to
limit dust emissions in transmission and storage of sander-
dust. Its explosive character is well documented. A pilot
light, usually with natural gas, must be maintained at all
times in the sanderdust burner to prevent flameout.
Use of wood residue fuels other than sanderdust is not
technically difficult but does require significant pretreat-
ment to control both moisture and particle size distribution
of the fuel. Problems in the use of wood residue fuels
result principally from lack of fuel preparation and/or lack
of control of the combustion process. Properly handled,
wood residues can provide an excellent alternative fuel
source.
4-25
-------
Combined Energy Sources
Since the energy "diet" for a plant is based on avail-
ability and relative costs of alternative energy sources,
each plant will attempt to maintain production with the
least overall cost. As a result, steam-heated dryers are
often used with natural gas as an auxilliary fuel and the
capability to burn propane or diesel oil as a standby.
Other combinations of energy sources for the dryer may be
feasible.
4-26
-------
5. EMISSIONS OF POLLUTANT MATERIALS FROM
PARTICLE DRYER SYSTEMS
This section describes the particulate and gaseous
emissions from particle dryers, the methods of measuring
emissions, and the factors that affect the pollutant emis-
sion levels.
Pollutant materials emitted to the atmosphere are
classed as gaseous and particulate pollutants. Common
gaseous pollutants include sulfur dioxide, oxides of nitro-
gen, reduced sulfur compounds, and carbon monoxide. Par-
ticulate pollutant materials occur in the solid or liquid
state and are defined as
"... any matter, except uncombined water, which exists
as a liquid or solid at standard conditions."12
Standard conditions* are defined as:
"... a temperature of 60° Fahrenheit and a pressure of
14.7 pounds per square inch absolute."^2
It is important to note that the definition of particu-
late pollutants to include "any matter" encompasses all
possible materials that might be emitted to the atmosphere,
with the exception of uncombined water.
POLLUTANT EMISSIONS FROM PARTICLE DRYERS
Emissions from particle dryers include both gaseous and
particulate materials. Gaseous materials include princi-
* There is considerable variability among various agencies
with respect to temperatures selected for "standard con-
ditions." Oregon DEQ uses 70°F., Lane Regional APA
(Eugene, Oregon) uses 60°F. Some agencies specify 60°F,
or 20°C.
5-1
-------
pally gaseous combustion products (CO, C00, NO, N00, N0 , 0.,,
« 22^
H20, etc.) plus the carrier air stream. These emissions are
not considered to represent an environmental hazard, and
regulatory agenices have taken no steps toward either mea-
surement or control.
Particulate emissions from particle dryers are regarded
by control agencies as a source of environmental concern.
Though not clearly defined in terms of collected data, these
emissions may be classified in two distinct groups: large
particles and small particles.
Large-Particle Emissions
Large particles may be loosely considered as any par-
ticles whose diameter is greater than 10 microns.* Almost
all large particles emitted from dryers are wood fibers.
These fibers enter the dryer as "fines" and are too small to
be collected in primary cyclones. Thus, they are emitted to
the atmosphere in the cyclone exhaust gas stream. Mean
particle size of typical fiber emissions ranges from 20 to
50 microns. When dryer systems are uncontrolled, most of
the materials emitted to the atmosphere consist of large
particles. Concern over fiber particles resulted in promul-
gation of Oregon's regulations pertaining to particleboard
7
and hardboard processing plants.
Small-Particle Emissions
Small particles, those of diameter less than 10 mi-
crons, can be conveniently discussed in terms of two sub-
groups: solid particles and volatile organic particles.
Solid Particles - Solid particles are products of two proc-
esses, combustion and use of additives. Dryers heated by
exhaust gases from boilers and dryers heated directly by
-6
* One micron is equal to 10 meters (or 1 micrometer).
5-2
-------
burning of fossil fuels or wood residue fuels both emit the
products of combustion. The particulate products of com-
bustion are inorganic fly ash (the noncombustible portion of
the fuel) and fixed carbon, which results from incomplete
combustion.
The second process that generates solid particles is
the addition of adhesive resins to the particle furnish
prior to the drying operation. In theory, small resin
particles passing through the dryer will escape from the
cyclone. This is speculative, however, since no definitive
measurements have shown that resin particles actually do
make up a portion of the solids emitted by dryers. Further,
the amount of such emissions is undoubtedly very small
relative to other emissions from the dryers.
Volatile Organic Particles - This second subgroup of small
particles emitted by dryers constitutes a very real problem,
which can be explained theoretically in terms of the three
principle components of wood:
0 Lignin - The characteristic cementing constituent
between the walls of the cells of woody tissues.
Lignin is a brownish substance whose exact chem-
ical composition is unknown.
0 Cellulose - The chief substance composing the cell
walls of wood. Cellulose is a carbohydrate repre-
sented by the empirical formula (CgH _05) .
0 Hemi-Cellulose - Any of a group of complex car-
bohydrates that surround the cellulose fibers of
plant cells. Hemi-celluloses have no chemical
relationship to cellulose.
When wood is placed in a high-temperature atmosphere for
drying, the volatile portion of these organic materials may
evaporate and enter the gaseous phase. In addition to the
physical process of evaporation, chemical changes may also
occur through pyrolysis and oxidation. The result is that a
5-3
-------
mixture of gaseous organic materials and inorganic water
vapor may be present in the dryer.
As the gas mixture proceeds through the dryer system,
the temperature gradually decreases. High-molecular-weight
gases begin to condense when the temperature reaches 360 to
400°F. Lower-molecular-weight gases condense at lower
temperatures. Very light molecules may remain in the
gaseous state as the dryer exhaust enters the atmosphere and
is cooled to ambient temperatures.
The condensation products of the organic gases are
thought to be principally in the liquid state. This is not
clearly defined, since the substances having very high
molecular weight may condense to form a viscous liquid,
which approaches the physical characteristics of a solid at
ambient temperatures. Whether liquid or solid, the con-
densation products are presumed to be submicron in size,
perhaps about 0.5 micron in diameter. They are further
presumed to be essentially spherical and subject to the
classical laws of physics. These comments, as noted ear-
lier, are theoretical. Laboratory work has shown that wood
constituents are definitely volatile in part. Volatility is
species-dependent and, of course, highly temperature-de-
pendent. In any case some of the organic components of wood
are known to be volatile.
It is also known that organic materials in the gaseous
state can condense to form discreet particles. Again, there
is considerable temperature dependency as well as functional
dependence upon the molecular weight and concentration of
the gaseous substance. Thus, one can conclude from con-
sideration of these known physical phenomena that small
particles of condensed organic materials can be expected in
the exhaust gas streams of some wood particle dryers.
5-4
-------
Supporting evidence for this conclusion was provided in
a study of emissions generated in the drying of sheets of
wood in veneer dryers, which demonstrated the presence of
volatile organic materials. In that the process of drying
veneer is similar to the process of drying wood particles or
fibers, one could conclude that emissions from wood particle
dryers may, under certain conditions, contain condensed or
condensable organic compounds.
Emission tests of particle dryers have demonstrated the
presence of condensable materials, other than water, in some
exhaust gas streams. These condensable materials are sol-
uble in organic solvents. No accurate determinations of
their molecular structures have been made.
Although it is common practice within industry and
regulatory agenices to refer to the volatile organic con-
stituents of particle dryer exhaust gases as "hydrocarbons,"
this is a misnomer. There is no theoretical basis for
assuming the presence of organic materials whose molecular
structures are limited to atoms of hydrogen and carbon.
Further, there are no test data that suggest that these
materials are either principally or exclusively hydrocarbons
or even that they contain trace amounts of hydrocarbons.
By way of summary, dryer emissions may be of three
different categories: 1) large particles composed princi-
pally of fibers; 2) small inorganic particles; 3) small
organic particles. Both the inorganic and the organic small
particles may form the characteristic blue haze associated
with fiber and particle dryers. Attention is now focused on
the methods of measuring emissions.
5-5
-------
MEASUREMENT OF PARTICLE DRYER EMISSIONS
Measurement of emissions from particle dryers involves
several techniques specific to the parameters being mea-
sured. The primary parameters of concern are:
Concentration (gr/sdcf)
Mass emission rate (Ib/hr)
Opacity (%)
Occasionally, size distribution of the particles is deter-
mined.
Measurements of concentration and mass emission rates
are closely related. Determination of the mass emission
rate is based on knowing the concentration of particles and
the flow rate of gases from the system in accordance with
the formula:
Mass emission _ n noon-? concentration gas flow rate
rate (Ib/hr) ~ °-uuyi)/ x (gr/sdcf) X (sdcfm)
Techniques for determination of concentration have been
the source of considerable disagreement. The methods and
their limitations are briefly summarized below.
The Hi-Volume Method
In April 1972 the Oregon DEQ issued a document entitled
Standard Sampling Method for Determination of Particulate
Emissions from Cyclones. The procedure described involves a
noncondensing sampling train in which the sample is col-
lected isokinetically and is drawn through a large glass-
fiber filter. Gas flow rates through the hi-volume sampler
typically range from 20 to 50 cfm. Particles collected on
the filter are analyzed gravimetrically, and emission con-
centrations are calculated on the basis of the mass of
collected sample and the volume of air sampled.
In most particle dryers exhaust gases leave the primary
cyclone, particularly in uncontrolled systems. Since the
5-6
-------
emissions emanate from cyclones, the hi-volume method was
considered to be applicable.
Advantages of the hi-vol method include the ability to
gather large samples in a relatively short period of time
and the ability to gather several samples from the same
source and thus to facilitate statistical analyses to deter-
mine normal variations about the mean concentration. In
terms of application to particle dryers specifically, the
greatest limitation of the method is that it involves a
noncondensing train. Regulatory agencies define particles
as materials that exist as liquids or solids at standard
conditions. The temperatures at the filter in a hi-vol
train may well be above standard temperatures. Thus,
agencies are concerned that condensable organic materials
may not have condensed by the time they pass through the
filter. Since they would not be caught in the train and
included in the measured concentrations, results would tend
to indicate lower-than-actual concentrations, considering
the definition of the term "particulate."
The S-8 Method
In September 1972 the S-8 Source Test Committee of the
Pacific Northwest International Section of the Air Pollution
Control Association published a Source Test Procedure for
Determination of Particulate Emissions from Veneer Dryers.
This procedure utilizes a condensing sampling train.
Isokinetically collected samples are passed through an
initial filter, a set of condensing impingers, and a final
filter to collect all of the condensable materials that
might be emitted from the dryers. The procedure was de-
veloped in response to the recognition that emissions
specific to veneer dryers consist principally of condensable
water vapor and volatile organic materials.
5-7
-------
Because the procedure involves low rates of sample gas
flow, in the range of 1 cfm, only small volumes of gas can
be sampled during a normal run. Further, the train involves
many components and often is difficult to seal against
leakage in field operations. Because of the sample time
required and complexity of the equipment, few replicative
tests are taken to determine variations about the mean.
Although it is difficult to collect representative samples
from cyclone exhaust systems, the system is adequate for
sampling of veneer dryer vents.
The EPA Method 5
The U.S. Environmental Protection Agency, in the
Federal Register of December 23, 1971, published the much-
used "Method 5." This procedure was designed for deter-
mination of concentration of particulate materials specific
to large, fossil-fuel-fired steam generating boilers.
Through an evolutionary process it has come to be accepted
by many regulatory agencies as appropriate for determination
of particulate concentrations from a wide variety of sources.
It involves isokinetic collection of the sample gas stream
in a heated probe. Gases are passed through a heated glass-
fiber filter and then to a series of impingers. There is no
final filter downstream from the impingers. The system
entails low gas flow rates, similar to those of the S-8
Method.
The heated probe and filter prevent condensation of the
volatile organic constituents of the sample in the probe and
the filter. The aerosol condensates are collected in the
impinger portion of the sampling train. The analytical
procedures would have to be modified to include an extrac-
tion for organic determination (i.e. , option available in
the S-8 Method).
5-8
-------
SELECTION OF MEASUREMENT TECHNIQUE
Selection of a measurement technique for particle dryer
emissions is somewhat discretionary. Requirements of the
12
Oregon DEQ under OAR 20-040 are as follows:
1) Any sampling, testing or measurement performed
under this regulation shall conform to methods on
file at the Department of Environmental Quality or
to recognized applicable standard methods approved
in advance by the Department.
2) The Department may approve any alternative method
of sampling provided it finds the proposed method
is satisfactory and complies with the intent of
these regulations and is at least equivalent to
the uniform recognized procedures in objectivity
and reliability, and is demonstrated to be repro-
ducible, selective, sensitive, accurate, and
applicable to the program.
On October 18, 1974, the Director of the DEQ issued a
letter to all consultants stating as follows:
"In January 1973 the Department developed a standard
Source Test Procedure for Veneer Driers. Some con-
sultants have used this method on wood particle dryer
tests, while others have used the boiler test method.
To assure comparable results in the future, the Veneer
Dryer Method will be required on all of bark and wood
particle dryers, since a large percentage of the emis-
sions is expected to be hydrocarbons."
Of the source test results made available to this study
on particle dryers located in Oregon, 60 percent of the
tests were made with the hi-vol method, 35 percent with the
S-8 Method, and 5 percent with the EPA Method 5.
The Department of Natural and Economic Resources,
Office of Water and Air Resources, the State of North
Carolina, regulates selection of the testing method as
follows:
Regulation No. 6, Paragraph 6.4:
"Testing to determine compliance shall be in accordance
with methods approved by the Board of Water and Air
Resources."
5-9
-------
OPACITY
Visual determination of compliance with applicable
opacity regulations is made by following procedures first
published in this country by the U.S. Bureau of Mines,
Information Circular 8333. This method entails the use of
the Ringelmann chart for discriminating the degree of shade
or density of visible emissions. The opacity concept
evolved from the effective, use of the Ringelmann chart in
quantitating dense smoke emissions. Opacity regulations are
commonly enforced throughout this country. The principles
and procedures are stipulated in EPA Test Method Number 9,
Federal Register, Volume 36, Number 247, Thursday, December
23, 1971.
Under atmospheric conditions and production methods
that promote condensation of water vapor in the exhaust gas
stream, the gas stream frequently appears as billowing white
plumes. The presence of significant quantities of condensed
water vapor often makes it difficult to obtain accurate
estimates of the opacity of the exit gas stream. The large
particles in the gas stream are typically light brown or
beige, the color of wood fibers. The small particles,
because of their effect on the scattering of incident light
rays, typically appear as blue. "Blue haze" is the prin-
cipal source of opacity in particle dryer plumes.
FACTORS AFFECTING EMISSIONS FROM UNCONTROLLED DRYERS
Large-Particle Emissions
Fiber emissions from particle dryers are influenced by
a variety of parameters, some related to the drying process
and some to system design. Some of the more significant
factors are listed and discussed briefly below.
5-10
-------
1. Percentage of fines in the particle furnish to the
dryer. Cyclone collection efficiency depends on the size
distribution of materials handled in the system. If a large
percentage of fine materials enter the cyclone, then one
would expect a significant portion of those fines to be
entrained in the exhaust gas stream from the cyclone.
2. Feed rate of materials through the dryer and cy-
clone. The total amount of material handled by the cyclone
also strongly affects fiber emissions. As feed rate of
material through the system increases, so does the con-
centration of materials in the exhaust gas stream.
3. Gas flow rates through the cyclone. Cyclone col-
lectors are designed to operate at optimum efficiency within
a certain range of gas flow rates. If the flow rates exceed
the design range or fall significantly below it, collection
efficiency will be reduced, with greater amounts of fibers
being entrained in the exhaust gas stream.
4. Moisture content of the exhaust gases. High levels
of moisture in exhaust gases tend to add to the collection
efficiency of cyclones handling fine materials, perhaps
because of an agglomerating effect of the moisture. Not all
materials, however, are affected beneficially, as are wood
fibers.
5. Addition of adhesive resins to the particle furnish
prior to drying. Agglomeration of the fiber particles to
prevent entrainment in the cyclone exhaust gas stream can
also be effected by the addition of resins before the dryer.
Since the cost of resins is a major business expense, how-
ever, loss of 1 percent of the resins through entrainment in
the dryer exhaust can be very expensive.
6. Design of the cyclone. Design of the cyclone system
is perhaps the most important of the variables affecting
5-11
-------
emissions of large particles. A well-designed system will
provide significantly higher collection efficiency on fiber
particles than a poorly designed system.
7. Design of the fan system. Uniformity of gas flow
through a cyclone is influenced by a fan design. A cen-
trifugal fan with only four or six blades sends a pulsating
gas flow through the system, tending to make the return
vortex in the cyclone unstable and consequently to increase
entrainment of particles in the exhaust gas stream. Cen-
trifugal fans with 12 to 16 blades greatly reduce the pulsa-
tions in the system. The rpm of the fan system also in-
fluences the degree of pulsation.
Small-Particle Emissions
The primary cyclones in dryer systems are designed to
separate wood fibers and particles from the carrier air
stream. These units are generally effective for collection
of particles whose mean size is larger than 50 to 100
microns. They are not effective, however, for particles
whose size range is less than 10 microns. Any small par-
ticles that enter the dryer or that are generated in the
dryer or in the energy source for the dryer will leave the
primary cyclone in the exhaust gas stream as pollutant
materials. The factors that influence the quantity of small
particles are as follows.
1. The energy source for the dryer. If the dryer is
heated with exhaust gas from a boiler or is direct-fired,
the products of the combustion process will include small
particles.* The inorganic ash content of the fuels is most
* The amount of small particles generated by the combustion
of natural gas, propane, or butane probably is negligible
because of the lack of inorganic, noncombustible materials
in these fuels. Any incomplete combustion of the fuels,
however, generates fixed carbon particles.
5-12
-------
significant. Wood, for example, contains up to 2.5 percent
inorganic ash.* If sanderdust is burned as an energy
source, the concentration of particles prior to dilution
will be more than 2.0 gr/sdcf. With normal dilution, the
fly ash from sanderdust combustion can still exceed 0.20
gr/sdcf at the cyclone exit.
2. Species of furnish. The volatile organic materials
that contribute to the presence of small particles vary
significantly with wood species. Douglas fir contains
significant amounts of haze-forming volatile materials,
whereas white firm emits small amounts of such materials
when processed in the same manner. No summary data are
available concerning the influence of species on volatile
organic emissions.
3. Rate of moisture removal. The drying rate depends
principally on the amount of moisture to be removed and on
residence time. If the furnish is fed to the dryer at 12
percent moisture (dry basis) and must be dried to 5 percent,
the amount of water to be evaporated is relatively small and
correspondingly low inlet temperatures to the dryer can
bring about the required results with little or no evapora-
tion of the volatile organic components of the wood. Con-
versely, if the inlet moisture level is 200 percent and must
be reduced to 5 percent in a single step, very high inlet
temperatures are required. These high temperatures cause
evaporation of significant amounts of volatile organic wood
g
components.
Rate of moisture removal is also a function of resi-
dence time. A very large dryer handling a small mass flow
of material can provide enough residence time for the
* The ash content of wood can range from 0.5 to 1.0 percent.
Bonding resins used in particleboard production may increase
the inorganic ash content of sanderdust to 2.5 percent.
5-13
-------
materials to dry at moderate temperatures. Small dryers
receiving as much furnish as the pneumatic or mechanical
systems can push through provide little residence time for
any single particle. Under these conditions, high tempera-
tures are required to dry the materials quickly, with re-
sulting high concentrations of haze-forming emissions.
Although there is a tendency to conclude that the
temperature is the key to organic emissions, temperature of
the system is a dependent variable. Moisture differentials
and feed rates through the dryers are relatively independent
process variables. The average temperature does influence
the amount of blue haze formed, but temperature cannot be
adjusted arbitrarily. The operator can, however, adjust the
process in terms of the required changes in moisture levels
per dryer stage and in terms of the feed rates through the
dryers and thereby can control the temperature requirement
for drying.
The factors that influence the emission of particles
from dryers may be summarized in terms of the elements of an
effective dryer system:
0 The furnish consists of large particles only.
0 The furnish is fed at nominal rates through the
primary cyclone.
0 Gas flow rates through the cyclone are kept within
the design range.
0 Moisture levels of the gas stream in the cyclone
are kept relatively high.
0 The cyclone is designed as a high-efficiency unit.
0 The fan is designed for minimum pulsation of air
flow through the cyclone.
0 The dryer energy source is steam-heated coils.
5-14
-------
0 The species to be dried is white fir.
0 Moisture levels of the furnish are kept relatively
constant.
0 The residence time in the dryer is adequate for
drying at low temperatures.
In an installation like this, emission levels for the
"uncontrolled" cyclone were measured at less than 0.02
gr/sdcf and the opacity was 0 percent. Dryer Nos. 30
through 33, as listed in Appendix D, incorporate these
performance characteristics.
5-15
-------
6. REGULATIONS PERTAINING TO PARTICLE DRYER EMISSIONS
Several categories of regulations pertaining to par-
ticle and fiber dryers are currently in effect. The regula-
tions promulgated by the various states may vary signifi-
cantly; specific regulations are cited herein as examples,
but are not to be construed as typical of or applicable to
other jurisdictions. It is recommended that the appropriate
state regulations be consulted to determine emission limits
applicable to the jurisdiction in which a plant is located.
PROCESS WEIGHT REGULATIONS
On March 5, 1971, the Oregon Environmental Quality
Commission (EQC) adopted process weight emission standards
for particleboard and hardboard plants located within the
jurisdiction of the Department of Environmental Quality
(DEQ). The levels adopted were based on the following
approach:
"After evaluating a considerable amount of data, sam-
pling results from three fully-tested Oregon (particle-
board) plants were selected for detailed analysis. For
each one, the high-emitting cyclones and their existing
emissions were grouped and totalled. The emissions for
the 6-8 highest emitters were reduced by 90% and a new
plant-site total calculated. The resultant emission,
divided by the plants' hourly production capacity,
represented a Ibs/M sg. ft. emission level achievable
by the hypothetical control program ... the range of
controlled emissions ranges from 1.9 to 2.8 Ibs/M sq.
ft. ... The emission standard of 3.0 Ibs/M sq. ft. was
adopted by the ... Commission..."^
In the account of development of the regulation, no
mention is made of haze or blue haze; neither is there
6-1
-------
mention of organic materials, volatile organics, condens-
ables, or hydrocarbons. The primary emphasis in promulga-
ting Oregon's regulations for emissions based on process
weight of plant production is on controlling fiber emis-
sions, principally from cyclones handling sanderdust and
from particle dryers.
OAR 25-320 (2) (a) (for particleboard):12
No person shall cause to be emitted particulate matter
from particleboard plant sources including, but not
limited to, hogs, chippers, and other materials size
reduction equipment, process or space ventilation
systems, particle dryers, classifiers, presses, sanding
machines, and materials handling systems, in excess of
a total from all sources within the plant site of three
(3.0) pounds per 1000 square feet of particleboard
produced on a 3/4 inch basis of finished product
equivalent.
OAR 25-320 (2) (b):
Excepted from subsection (a) are truck dump and storage
areas, fuel burning equipment, and refuse burning
equipment.
OAR 25-325 (2) (a) (for hardboard):
No person shall cause to be emitted particulate matter
from hardboard plant sources including, but not limited
to hogs, chippers, and other material size reduction
equipment, process space ventilation systems, particle
dryers, classifiers, presses, sanding machines, and
materials handling systems, in excess of a total from
all sources within the plant site of one (1.0) pound
per 1000 square feet of hardboard produced on a 1/8
inch basis of finished product equivalent.
OAR 25-325 (2) (b)
Excepted from subsection (a) are truck dump and storage
areas, fuel burning equipment, and refuse burning
equipment.
6-2
-------
It is important to note that the process weight regula-
tions are not applied directly to individual dryers. The
dryer emissions are included in the total of emissions from
all sources within the process plant. Thus, even though the
dryers could be well-controlled in every respect, the plant
could still fail to meet process weight limitations because
of emissions from sources other than dryers.
When the Oregon EQC adopted the standards for particle-
board and hardboard plants, they also adopted standards for
veneer and plywood processing plants. Emissions from veneer
dryers are not included in the process weight limitations
placed on plywood operations. Particle dryer emissions,
however, are included in the limitations for particleboard
and hardboard plants. Undoubtedly this difference results
from the recognition at that time that veneer dryers do not
contribute to emissions of fibers, whereas particle dryers
do.
Information supplied by the U.S. EPA indicates that the
Oregon regulations are not typical of most states with
respect to process weight restrictions. California, Georgia,
Kentucky, Mississippi, North Carolina, and South Carolina
have adopted process weight emission standards patterned
after those set originally in California. The North Carolina
regulations, perhaps the most typical, are indicated be-
13
low:
2.30 Control and Prohibition of Particulate Emissions
From Miscellaneous Industrial Processes
No person shall cause, suffer, allow, or permit par-
ticulate matter caused by industrial processes for
which no other emission control standards are appli-
cable to be discharged from any stack or chimney into
the atmosphere in excess of the rates shown in Table I.
6-3
-------
Table I. NORTH CAROLINA REGULATION 2.30
ALLOWABLE RATE OF EMISSION BASED ON
ACTUAL PROCESS WEIGHT RATE
Process weight
rate
Lb/hr
100
200
400
600
800
1,000
1,500
2,000
2,500
3,000
3,500
4,000
5,000
6,000
7,000
8,000
9,000
10,000
12,000
Ton/hr
0.05
0.10
0.20
0.30
0.40
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.50
3.00
3.50
4.00
4.50
5.00
6.00
Rate of
emission
Lb/hr
0.551
0.877
1.40
1.83
2.22
2.58
3.38
4.10
4.76
5.38
5.96
6.52
7.58
8.56
9.49
10.4
11.2
12.0
13.6
Process weight
rate
Lb/hr
16,000
18,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
120,000
140,000
160,000
200,000
1,000,000
2,000,000
6,000,000
Ton/hr
8
9
10
15
20
25
30
35
40
45
50
60
70
80
100
500
1,000
3,000
Rate of
emission
Lb/hr
16.5
17.9
19.2
25.2
30.5
35.4
40.0
41.3
42.5
43.6
44.6
46.3
47.8
49.0
51.2
69.0
77.6
92.7
Interpolation of the data in this table for process
weight rates up to 60,000 Ibs/hr shall be accomplished
by use of the equation E = 4.10 p°(-67), ana inter-
polation and extrapolation of the data for process
weight rates in excess of 60,000 Ibs/hr shall be accom-
plished by use of the equation:
E = [55.0 P°(>11)] - 40
Where E = rate of emission in Ib/hr and
P° = process weight rate in ton/hr.
6-4
-------
Process weight per hour means the total weight of all
materials introduced into any specific process that may
cause any emission of particulate matter. Solid fuels
charged are considered as part of the process weight,
but liquid and gaseous fuels and combustion air are
not. For a cyclical or batch operation, the process
weight per hour is derived by dividing the total proc-
ess weight by the number of hours in one complete
operation from the beginning of any given process to
the completion thereof, excluding any time during which
the equipment is idle. For a continuous operation, the
process weight per hour is derived by dividing the
process weight for a typical period of time.
It may be seen that North Carolina's process weight
regulations for emissions from miscellaneous processes
covers a broad spectrum within which particleboard and
hardboard plants and particle dryers may be included;
whereas Oregon maintains a regulation specifically directed
toward particleboard and hardboard manufacturing opera-
tions.
REGULATIONS PERTAINING TO CONCENTRATION OF POLLUTANT
EMISSIONS
In addition to process weight limitations for particle
and fiber panel production facilities, individual particle
dryers are subject to limits on the concentration of par-
ticle emissions. On February 15, 1972, the Oregon DEQ
12
adopted the following regulation:
OAR 21-030 PARTICLE EMISSION LIMITATIONS FOR SOURCES
OTHER THAN FUEL BURNING AND REFUSE BURNING
EQUIPMENT
(1) No person shall cause, suffer, allow or permit the
emission of particulate matter, from any air
contaminant source other than fuel burning equip-
ment or refuse burning equipment in excess of:
(.a) 0.2 grains per standard cubic foot for ex-
isting sources, or
6-5
-------
(b) 0.1 grains per standard cubic foot for new
sources.
These restrictions are typical of concentration regula-
tions of most states. An additional set of restrictions is
placed on particle dryers whose energy source systems in-
clude direct combustion of fuels. The Oregon DEQ adopted
12
the following regulation on May 22, 1970:
OAR 21-020 FUEL BURNING EQUIPMENT LIMITATIONS
No person shall cause, suffer, allow, or permit the
emission of particulate matter, from any fuel burning
equipment in excess of:
(1) 0.2 grains per standard cubic foot for existing
sources, or
(2) 0.1 grain per standard cubic foot for new sources.
Few states consider direct-fired dryers to be in the
category of fuel burning equipment. At present North
Carolina has no regulation pertaining to concentrations of
particulate emissions.
REGULATIONS PERTAINING TO OPACITY
Within the regulations of the Oregon DEQ, opacity is
12
covered by the following provisions:
OAR 21-015 VISIBLE AIR CONTAMINANT LIMITATIONS
(1) Existing Sources Outside Special Control Areas.
No person shall cause, suffer, allow, or permit
the emission of any air contaminant into the
atmosphere from any existing air contaminant
source located outside a Special Control Area for
a period or periods aggregating more than 3
minutes in any one hour which is:
(a) As dark or darker in shade as that designated
as No. 2 on the Ringlemann Chart, or
(b) Equal to or greater than 40% opacity.
6-6
-------
(2) New Sources in All Areas and Existing Sources
Within Special Control Areas: No person shall
cause, suffer, allow or permit the emission of any
air contaminant into the atmosphere from any new
air contaminant source, or from any existing
source within a Special Control Area, for a
period or periods aggregating more than 3 minutes
in any one hour which is:
(a) As dark or darker in shade as that designated
as No. 1 on the Ringelmann Chart, or
(b) Equal to or greater than 20 percent opacity.
(3) Exceptions to 21-015 (1) and 21-015 (2).
(a) Where the presence of uncombined water is the
only reason for failure of any emission to
meet the requirements of Section 21-015 (1)
and 21-015 (2), such sections shall not
apply.
(2) Existing fuel burning equipment utilizing
wood wastes and located within Special Con-
trol Areas shall comply with the emission
limitations of Subsection 21-015 (1) in lieu
of Subsection 21-015 (2).
Note that, with the exception of uncombined water
vapor, this regulation applies to any material emitted to
the atmosphere that results in opacity levels in excess of
the standards. The following opacity regulations promul-
gated by North Carolina, although similar to those of
Oregon, may be somewhat more representative of the format of
typical requirements.
Regulation Ho. 2 - Control and Prohibition of Visible
Emissions
2.0 Purpose
The intent of this regulation is to promulgate
rules pertaining to the prevention, abatement and
6-7
-------
control of emissions generated as a result of fuel
burning operations and other industrial processes
where an emission can be reasonably expected to
occur, except during startups made in accordance
with procedures approved by the Board.
2.1 Scope
This regulation shall apply to all fuel burning
installations and such other processes as may
cause a visible emission incident to the conduct
of their operations.
2.2 Restrictions Applicable to Existing Installations
No person shall cause, suffer, allow or permit
emissions from any installation which are:
(1) Of a shade or density darker than that
designated as No. 2 on the Ringelmann Chart
for an aggregate of more than 5 minutes in
any one hour or more than 20 minutes in any
24-hour period or
(2) Of such opacity as to obscure an observer's
view to a degree greater than does smoke
described in paragraph 2.2, subparagraph 1.
(3) All existing sources shall be in compliance
with the provisions of Paragraph 2.3 within 5
years.
2.3 Restrictions Applicable to New Installations
No person shall cause, suffer, allow or permit
emissions from any installation which are:
(1) Of a shade or denisty darker than that
designated as No. 1 on the Ringelmann Chart
for an aggregate of more than 5 minutes in
any one hour or more than 20 minutes in any
24-hour period, or
(2) Of such opacity as to obscure an observer's
view to a degree greater than does smoke
described in paragraph 2.3, subparagraph 1.
6-8
-------
2.4 Where the presence of uncombined water is the only
reason for failure of an emission to meet the
limitations of paragraph 2.2 and 2.3 those re-
quirements shall not apply.
OTHER APPLICABLE REGULATIONS
The primary regulations applied to particle and fiber
dryers are those already outlined (process weight, con-
centration, and opacity). Other regulations that might be
applied but are not generally considered in regard to these
process industries include nuisance regulations, general
"catch-all" regulations, and regulations pertaining to the
size of particles that may be emitted from a process or
plant.
Two additional classes of regulations that could have
considerable impact on the particle and fiber processing
industries are those pertaining to emission sampling and to
"general provisions." With respect to emission sampling,
most agencies require that upon request the owners or
operators of process equipment shall make or have made a
source test and shall submit a report to the agency direc-
tor. Because of the high cost often entailed in performing
the prescribed test procedures, such regulations can result
in significant costs to industry. Most agencies have
applied these regulations carefully and have required tests
only when they were believed necessary. As a result, some
of the particle and fiber dryers having very low visible
emissions have not been tested, whereas others whose visible
emissions indicate potentially significant contaminant input
to the atmosphere have been tested.
Regulations identified as "general provisions" also can
have a large impact on particle and fiber drying processes.
12
The Oregon DEQ under OAR 25-310 (4) states as follows:
6-9
-------
Upon adoption of these regulations, each affected
veneer, plywood, particleboard, and hardboard plant
shall proceed with a progressive and timely program of
air pollution control, applying the highest and best
practicable treatment and control currently available
The phrase "...highest and best practicable treatment
and control..." is fairly common in control agency regula-
tions. Some agencies have been accused of misusing the
concept. It is admittedly difficult to apply to technically
complex systems. However, it is an effective way of ad-
vancing the universal application of the state-of-the-art of
control technology.
North Carolina's emission control standards contain a
similar requirement:
13
Section IV, paragraph 1:
..."All sources shall be provided with the maximum
feasible control."
6-10
-------
7. APPLICATION OF CONTROL TECHNOLOGY TO MEET
EMISSION REGULATIONS
In responding to the regulations relative to particle
and fiber dryers, industry members have applied several
types of emission control devices. In this section these
devices are described and evaluated in terms of effective-
ness, cost, and operational problems.
WET SCRUBBER EMISSION CONTROL DEVICES
One of the first control devices to be applied in the
industry was a wet scrubber system installed in southern
Oregon. This system was successful in reducing emissions to
acceptable levels. All of the 19 wet scrubbers presently
installed on fiber and particle dryers visited during this
study were manufactured by the same company, and 18 of the
19 are of the same design and construction.
Success in Meeting Regulations
In terms of percentage, 95 percent of the scrubbers
installed (18 of 19) are effectively keeping the dryer
emissions in compliance. There are some important reasons
for the high degree of success and for the single 'failure.1
The scrubber installations, designated according to dryer
numbers on the data sheets in Appendix D, are described in
some detail in the following pages.
Dryers 4 through 7 are heated with steam in combination
with natural gas. The input of small particles from the
energy source is thus effectively zero. The normal input
temperatures to the dryers range from 250 to 300°F, a range
7-1
-------
that precludes the formation of small particles due to
volatile organic components of the wood. Therefore, the
only particles that must be controlled are the large par-
ticles, the fibers, which are easily handled by any well-
designed scrubber. As a result, operating opacity is zero
and the particle concentrations are in compliance.
Dryers 13 through 20 are equipped with scrubbers that
are not now in operation. The scrubbers have been demon-
strated to be effective in controlling emissions, but emis-
sion levels are normally too low to justify the cost of
operating the scrubbers. The emission levels are low be-
cause, as with dryers 4 through 7, these are low-temperature
units heated with steam and natural gas. Since the maximum
operating temperature is 480°F, volatile organic components
are not released from the furnish. The primary cyclones are
effectively engineered and operated within their design
ranges. Thus the need for the wet scrubbers has not yet
materialized. Should the plant decide to increase produc-
tion levels and "push" the dryer capacity, operation of the
scrubbers may be required.
Dryer 26 uses sanderdust, natural gas, and propane as
its energy sources. With inlet temperatures of 550°F, some
small particles are evaporated from the furnish. The sander-
dust combustion generates other small particles but the
scrubber is effective in controlling the combined input of
small particles. The large fiber particles are easily
caught in a scrubber, and the result is that the unit does
meet the regulations. Under normal operation the opacity
observed is less than 5 percent. There are occasional
excursions opacity exceeds 20 percent; moisture content of
the furnish requires higher inlet temperatures or when the
furnish is predominantly wet Douglas fir. Generally, the
unit is in compliance.
7-2
-------
Dryer 27 uses the same energy sources as Dryer 26 but
operates at lower inlet temperatures. As a result, less
volatile material is evaporated from the wood and opacity is
lower. Again, the scrubber is effective in keeping the
emissions in compliance.
Dryers 40 and 41 are heated with steam and natural gas.
Dryer 43 is heated with steam and hot water only. Inlet
temperatures for these dryers seldom exceed 200°F. With
these temperatures and energy sources, the only particles
entering the scrubber are fibers that are easily controlled.
Dryer 42 receives all of its energy input from a boiler
fired with wood and bark residues. Inlet temperatures range
from 450 to 500°F. Under these conditions, fine particles
from the boiler represent a significant input to the system
and the heat drives off some volatile organic components.
With this combined input of fine particles plus the input of
large particles, the scrubber must be highly efficient to
keep the whole system in compliance. Although emissions
from this scrubber are the highest in terms of concentration
of any of the installed units (0.071 gr/sdcf), the require-
ments are met. Opacity is not a problem since the input
temperatures are not sufficiently high to drive off ex-
cessive amounts of volatile organic components.
Dryer 9 is equipped with a scrubber that is not com-
pletely effective and fails consistently to keep the dryer
emissions in compliance. The energy source is a sanderdust-
fired boiler, which produces fine particles in significant
quantities. Further, the inlet temperatures to the dryer
range from 400 to 700°F. Since most of the furnish is
Douglas fir, the combination of high temperatures and high
content of volatile organic compounds common to Douglas fir
results in generation of many fine particles.
7-3
-------
The input of fibers or large particles to the scrubber
is relatively small, indicating a well-designed and -operated
primary cyclone system. The resultant input to the scrubber
then, is predominantly small particles, less than 1 micron
in diameter and likely in the 0.5-micron range. Collection
of submicron particles is difficult for mechanical collection
devices. The scrubber performs consistently at the 70 to 75
percent level of efficiency. In doing so, it meets the
requirements for concentration and for process weight, but
does not consistently meet the requirements for opacity.
The burden of fine particles to the system is too great, and
the resultant blue haze is evident.
Summary data on wet scrubber control devices are given
in Table 7-1.
Problems With Wet Scrubbers
Most industry representatives who operate wet scrubbers
would rather not, for the following reasons:
1) The cost of installation and operation. Of the 19
units, 18 are low-energy systems with pressure
differentials in the range of 3 to 8 inches H2O.
Even this relatively low level of energy input
entails operating expense. By contrast, the
system that fails to achieve compliance is a high-
energy scrubber requiring 50 inches E^O pressure
drop, an energy input requiring costly electric
usage.
2) Wet scrubbers usually convert an air pollution
problem into a water treatment problem. With
today's restrictions on wastewater discharge,
operation of a typical scrubber system may entail
as much capital for cleaning and recycling the
water as for initial purchase of the scrubber.
Unless the liquid handling system is well-engi-
neered and properly installed, the liquid slurry
generated in the scrubber can create a significant
disposal and water pollution problem.
7-4
-------
Table 7-1. SUMMARY OF WET-SCRUBBER CONTROL DEVICES FOR PARTICLE DRYERS
1
ui
Dryer
No. »
4
5
6
7
8
9
13
14
15
16
17
18
19
20
26
27
40
41
42
43
Energy source*
Primary
Steam
Steam
Steam
Steam
Steam
Sander dust
Steam
Steam
Steam
Steam
Steam
Steam
Steam
Steam
Sanderdust
Sanderdust
Steam
Steam
Bark-fired
Steam
Secondary
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Boiler
Hot H20
Inlet
temp. , °F
250-300
250-300
250-300
250-300
250-300
400-700
480 max
480 max
480 max
480 max
480 max
480 max
480 raax
480 max
550
350
200
200
450-500
200
Primary
species
D. Fir/
hemlock
D. Fir/
hemlock
D. Fir/
hemlock
D. Fir/
hemlock
D. Fir/
hemlock
D. Fir/
hemlock
D. Fir/pine
D. Fir/pine
D. Fir/pine
D. Fir/pine
D. Fir/pine
D . Fir/pine
D. Fir/pine
D. Fir/pine
D. Fir /pine
D. Fir/pine
Pine
Pine
Pine
Pine
Exit cone.,
gr/sdcf j
Unknown
Unknown
Unknown
Unknown
Unknown
0.049
Unknown
Unknown
Unknown
Unknown
0.08
Unknown
Unknown
Unknown
0.02
0.02
0.023
0.018
0.071
0.002
Opacity,
%
0
0
0
0 .
0
10- ao
<10
<10
<10
<10
<10
<10
<10
<10
<5
<5
<5
<5
<5
<5
Status
Complies
Complies
Complies
Complies
Complies
Fails in
opacity
Complies
w/o scrubber
Complies
w/o scrubber
Complies
w/o scrubber
Complies
w/o scrubber
Complies
w/o scrubber
Complies
w/o scrubber
Complies
w/o scrubber
Complies
a/o scrubber
Complies
Complies
Complies
Complies
Complies
Complies
Additional information on these dryeri ii given in Appendix
D.
-------
3) Maintenance of the system can be costly. Liquid
systems tend to corrode, erode, and most of all,
to plug with great regularity. Some plant opera-
tors claim that as much as 1 1/2 man years per
year are required to keep the scrubbers in opera-
tion.
Costs of Wet Scrubbers
Costs for installation of wet scrubbers cover a wide
range. The first units installed were inexpensive, since
the engineering and installation were done in-house. Cost
is estimated at less than $l/cfm, based on early-1971
3
prices.
In 1974 installations cost approximately $2.50/cfm. It
is not known, however, whether this value includes all of
the costs, i.e., engineering, purchasing, construction
management, materials, startup, etc.
Typical costs reported by EPA for 1976 are $3 to $5 per
cfm for turnkey jobs. Industrial estimates of the cost for
a complete wet scrubber system including pumps, pipes, water
recirculation system, water cleanup system, fiber handling
system, engineering, purchasing, construction management,
materials, and startup range from $5 to $7/cfm. For a
typical particle dryer with gas flow rates of 30,000 cfm,
this might represent a capital investment of $150,000 to
$210,000.
Recommended Application of Wet Scrubbers
Experience to date indicates that wet scrubbers can be
used effectively to control large particles and limited
amounts of small particles. Their use for control of blue
haze is not promising. With dryers whose energy sources are
limited to natural gas, propane, butane, steam, and/or hot
water, and whose maximum inlet temperatures do not exceed
500 to 550°F, wet scrubbers apparently can be used effectively
7-6
-------
to keep the system in compliance with regulations. Even
with systems fired with sanderdust or the exhaust gases of
boilers, wet scrubbers appear to be effective so long as the
inlet temperatures are kept to reasonably low levels (less
than 500°F) and/or the species dried is not high in volatile
organic components (i.e., white fir). For systems operated
outside of these restrictions, the success of wet scrubbers
in controlling small particles is doubtful. Even with high-
energy scrubbers, enough small particles may pass through
the system to result in high opacity levels. Nevertheless,
an important advantage inherent in control with scrubbers
is their resistance to fire hazards.
FULL-RECIRCULATION CONTROL SYSTEMS
Seven full-recirculation systems have been installed on
fiber and particle dryers in Oregon, with mixed results.
Dryers 1 and 2 are equipped with full-recirculation
units. Dryer 2 is not yet complete. The performance of
Dryer 1 is considered satisfactory and in compliance with
all of the pertinent regulations.
Although Dryers 10 and 12 also are complying with the
regulations, the concentration of emissions from Dryer 10 is
closely approaching the limit of 0.1 gr/sdcf. Because full-
recirculation units are considered as fuel burning devices,
the control agency requires that emission levels be corrected
to 12 percent C02-*
Dryer 11 has not yet demonstrated compliance and is
faced with two independent problems. First, the sanderdust
* Many dryers employ direct combustion of fuels as an energy
source. The control agencies have not considered these
devices to be "fuel burning devices" nor required the cor-
rection to 12 percent C02 until the full recirculatdon
systems came into use. At present at least one agency re-
quires that the correction be made. In all probability,
this does not result in a major adjustment to the emission
concentration levels, since full-recirculation systems
normally operate with low levels of excess air. The reasons
for requiring the C02 correction on full-recirculation
systems are not clear.
7-7
-------
used to fire the system contains significant amounts of
incombustible inorganic ash. The high ash levels result
from the addition of salt compounds to the bonding resins in
the panel products. These resins are picked up in the
sanding operation and are incorporated into the sanderdust
along with its normal inorganic ash content. When the
sanderdust is burned, the ash becomes fly ash and increases
the emission concentrations. Several plants using sander-
dust as fuel have met the same situation. One plant solved
the problem by changing the chemical makeup of their bonding
resins. The change, however, increased the cost of the
resins and therefore increased the product cost.
The second problem in operation of Dryer 11 entails
high turndown ratios. Because this dryer is somewhat over-
sized, it must operate at low percentage rates of maximum
capacity and cannot always maintain high temperatures in the
combustion zone. At low levels of production, the system
becomes unbalanced and incomplete combustion results. Plans
are under way to improve the combustion controls to handle
low-level production situations.
Dryers 28 and 29 also suffer from high ash content of
the sanderdust and from high turndown ratios (wide flow-rate
variations). During normal production they are considered
to be in compliance with the regulations. They emit a blue
haze because of the incombustible fly ash in the sanderdust,
but the levels of opacity are typically in compliance (less
than 20 percent). Table 7-2 presents summary data on full-
recirculation control systems.
Success in Meeting Regulations
As noted above, full-recirculation systems enable dryer
operators to meet the regulations of the agencies. The
7-8
-------
Table 7-2. SUMMARY OF FULL RECIRCULATION CONTROL SYSTEMS
FOR PARTICLE DRYERS
Dryer
No.a
1
2
10
11
12
28
29
Energy sources
Primary
Sanderdust
Sanderdust
Sanderdust
Sanderdust
Sanderdust
Sanderdust
Sanderdust
Secondary
Hogged wood
Hogged wood
Propane
Propane
Propane
Natural gas
Natural gas
Inlet
temp. , °F
800
550
800-1000
800-1000
800-1000
800
600
Primary
species
D. fir
D. fir
D. fir
D. fir
D. fir
D. fir/pine
D. fir/pine
Exit cone. ,
gr/sdcf
0.072
0.121
0.152
0.08
0.09
0.08
Opacity,
%
0
0
<10
<10
<3
<5
<5
Status
Complies
Unknown
Unknown
Unknown
Complies
Complies
Complies
^Additional information on these dryers is given in Appendix D.
-------
concentration regulations may be more restrictive for these
systems if they are corrected for C02. Since all all of the
full-recirculation systems are fired principally with
sanderdust, which contains appreciable amounts of resin-
based salts, the systems do emit substantial quantities of
fine particles that form blue haze. Concentrations for each
system tested closely approach the limit of 0.1 gr/sdcf.
Under some operating conditions, such as high turndown
ratios, the concentration limits may be exceeded.
Problems with the Systems
Full-recirculation systems are cost-effective only for
mills that sand enough panels to generate the required
sanderdust fuel. One of the systems is equipped with fuel
preparation facilities that permit the use of hogged fuel
(wood and bark residues) and the use of agricultural resi-
dues such as straw. Under these circumstances full recir-
culation may be economically attractive. The systems re-
quire additional capital investments for fuel preparation
equipment.
Opacity in the exhaust gas stream is a major difficulty
for at least one plant. Fine particles generated in the
combustion process (fly ash) are not circulated through any
other control devices; thus they contribute directly to
opacity and also to borderline levels of concentration.
None of these systems has logged enough operating time
to indicate the major operational problems. One might
expect, however, that problems will be related to material
handling of the fine-particle fuels and to control of the
combustion system.
Dryers 24 and 25 are equipped with full-recirculation
systems that are not used. These dryers are fueled with
7-10
-------
propane and natural gas. The cost of operating the systems
as full-recirculation units is prohibitive.
Costs of Full-Recirculation Systems
Only two plants can provide information regarding costs
of full-recirculation systems. Based on the number of
dryers involved and the total package costs/ it appears that
conversion to this system costs $125,000 to $150,000 per
dryer. At the installations evaluated, this cost was
balanced by the high cost of fqssil fuels, the alternative
energy source. Conversion to wood residue fuels provided
substantial returns on the investments.
Recommended Applications of Full-Recirculation Systems
Use of these systems is recommended only when there is
an adequate supply of low-cost fuels such as sanderdust.
They are prohibitively expensive to operate using fossil
fuels.
For proper operation, high temperatures must be main-
tained in the combustion zone and the levels of dilution air
fed to the dryer must be held low to minimize fuel usage.
This results in high temperatures at the dryer inlet and
correspondingly high levels of volatile organic emissions
from the furnish. These high temperatures may further limit
application should they result in degradation of particular
furnishes or species.
Probably the most important potential limit on future
application of full-recirculation systems is opacity due to
inorganic fly ash from salt based bonding resins. For
installations using sanderdust or other fuels containing
high levels of inorganic ash, opacity will be a persisting
problem. Pressure on the part of control agencies for
nonvisible plumes may eventually require the use of bag-
houses, high energy scrubbers, or other control devices to
7-11
-------
collect the fine particles. Changing to salt free resins
to limit the input of inorganic fly ash may be a practical
solution.
PARTIAL-RECIRCULATION CONTROL SYSTEMS
Partial recirculation of exhaust gases from the primary
cyclone to the combustion chamber on direct-fired dryers is
done as much for economy as for emission control. The
system can be effective for emission control, however, and
should not be overlooked as a control alternative. Of the
76 dryers investigated in this study, 7 are equipped with
what might be considered partial-recirculation systems
installed for emission control purposes.
Dryers 49 and 50 can recycle up to 30 percent of the
exhaust gases from the cyclones. The systems are identical
in design and size and are used as predryers to reduce the
moisture content of wet Douglas fir to the 15 to 18 percent
level (dry basis). Inlet temperatures range from 600 to
900°F. At these high temperature levels one would expect
significant amounts of fine particulate generated by the
volatile organic components in the furnish. Both units are
fired with sanderdust, with natural gas as an auxiliary
fuel. The sanderdust also generates fine-particle fly ash.
The point of entry for the recirculated gas is down-
stream from the combustion chamber, where the oxygen con-
centrations are relatively low, probably less than 10 per-
cent. Under these conditions, the potentially combustible
volatile organic fine particles will not burn quickly, if at
all. The result of this design is that opacity levels of
emissions from these dryers frequently rise above 20 per-
cent. Emission data on grain loading show values ranging
from 0.09 to 0.20 gr/sdcf.
7-12
-------
Dryers 59 and 60 are designed to recycle up to 40 per-
cent of the exhaust gases from the cyclones; however, the
gases do not return to the dryer combustion chamber. These
dryers are fired with sanderdust, receive heat energy from
boiler exhaust stacks, and have fuel oil backup. The dryer
exhaust gases are passed through "skimmers," which remove
most of the entrained particles. The pneumatic line from
the skimmers carries up to 40 percent of the total dryer
exhaust back to the boilers, where the combustible portion
of the entrained particles is burned. Inlet temperatures to
the dryers are 800°F. The furnish, however, is southern
pine, which does not contain appreciable amounts of haze-
forming volatile compounds. Opacity from the nonrecycled
portion of dryer exhaust gas is typically 5 to 10 percent.
No data are available regarding grain loadings. Regulatory
agencies consider that the dryers are in compliance.
Dryers 67, 68, and 69 are steam-heated units whose
furnish is "mixed hardwoods," principally of southeastern
species. Since the inlet temperatures are 300°F, no fine
particles are generated by volatility of the wood. With
steam heaters, no fine particles are formed by combustion of
the energy source. Twenty percent of the exhaust gases from
each of the three dryers is separated in a "skimmer," a
centrifugal separator unit designed to remove large par-
ticles. This 20 percent portion of the exhaust gas stream
is carried back to the dryer input. The remaining 80 per-
cent is vented to the atmosphere. No grain loading data are
available. Opacity is 0 percent, and the dryers are con-
sidered to be in compliance.
Table 7-3 presents summary data on partial-recircula-
tion control systems.
7-13
-------
Table 7-3. SUMMARY OF PARTIAL RECIRCULATION CONTROL SYSTEMS FOR PARTICLE DRYERS
Dryer
No.a
49
50
59
60
67
68
69
Energy sources
Primary
Sanderdust
Sanderdust
Sanderdust
Sanderdust
Steam
Steam
Steam
Secondary
Natural gas
Natural gas
Boiler stack
Boiler stack
Boiler stack
Boiler stack
Boiler stack
Inlet
temp., °F
600-900
600-900
800
800
300
300
300
Primary
species
D. fir
D. fir
Pine
Pine
Hardwoods
Hardwoods
Hardwoods
Exit cone . ,
gr/sdcf
0.18
0.09
Unknown
Unknown
Unknown
Unknown
Unknown
Opacity,
%
10-20
10-20
5-10
5-10
0
0
0
Status
Fails
Fails
Complies
Complies
Complies
Complies
Complies
-4
1
Additional information on these dryers is given in Appendix D.
-------
Success in Meeting Regulations
Two of the seven dryers equipped with partial-recircula-
tion systems are borderline with respect to compliance. The
combination of high-temperature drying of Douglas fir and
firing of sanderdust generates significant amounts of fine
particles, some of which are combustible. Even the com-
bustible fraction has little opportunity to oxidize when
recycled, because of low oxygen levels at the point of
entry. For the other five dryers, which do not generate
small particles, recycling works effectively to control
large particles.
Problems With the Systems
From an operational standpoint the partial-recircula-
tion systems present no apparent problems. They do conserve
energy, as noted earlier.
Costs of Partial-Recirculation Systems
The only data available on costs of such systems are
probably not at all representative of "normal" industrial
applications. Dryers 59 and 60 required major revisions of
the energy sources, the system piping, and numerous sub-
systems in addition to installation of the partial-recir-
culation subsystems. Total cost of revisions was estimated
at $500,000 for each dryer.
For Dryers 49 and 50, the partial-recirculation sub-
systems were designed into the entire dryer system before
construction. No information is available on the cost of
the recirculation portion of the dryer system.
No data are available on costs for dryers 67, 68, and
69.
Recommended Applications of Partial-Recirculation Systems
Partial-recirculation systems cannot control fine
particles effectively. They can be used very effectively
7-15
-------
for large particles when "skimmers" are used to concentrate
the large particles in the recycled gas handling system.
Therefore, these systems are recommended only for dryers in
which fine particles are not generated either by the energy
source or by the high-temperature evaporation of volatile
organic components in the furnish. The chief benefit of
partial recirculation is energy conservation.
MEDIUM- AND HIGH-ENERGY SECONDARY CYCLONE CONTROL DEVICES
Medium- to high-energy cyclone separators have been
used on 9 of the 76 dryers evaluated in this study. These
cyclones are provided in several air flow configurations,
requiring use of one or two secondary fans as energy inputs
to increase the collection efficiency. The cyclones are
used as both primary and secondary collectors. Their use as
primary collectors has met with limited success because of
plugging. For purposes of this study, the cyclones are
discussed in terms of use as secondary collectors. Exhaust
gases from the primary cyclones are fed to these cyclones,
which remove a portion of the remaining entrained particles
from the gas stream.
Dryer 48 is a moderately low-temperature dryer (300 to
400°F inlet) drying Douglas fir from the 18 percent moisture
level to the 5 percent level. It is sanderdust-fired and
therefore generates fine particles as fly ash. Natural gas
is used as auxiliary fuel. Rates of gas flow and material
flow through the system are high (44,000 cfm and 40,000 to
50,000 Ib/hr). As a result, significant amounts of large
particles leave the primary cyclone in the exhaust gas
stream. The secondary cyclone system works effectively to
control these large particles (fibers). Emission levels are
7-16
-------
in the range of Q.Q6 gr/sdcf. Opacity, due principally to
fine particles of fly ash from combustion of sanderdust,
typically ranges from 10 to 15 percent.
Dryer 51 is very similar to Dryer 48. Although no
exact data on inlet temperatures are available, they are
expected to be moderately low, probably less than 400°F.
The furnish is Douglas fir, and the moisture differential
from inlet to exit is only 10 percent. Like Dryer 48 it is
sanderdust-fired with natural gas backup. Large fibers are
the primary problem in the primary cyclone exhaust, and:.the
secondary cyclone controls these emissions effectively.
Exit loading on the system is 0.05 gr/sdcf. Opacity, due
again to fly ash-based fine particles in the sanderdust
firing system, is typically 10 to 15 percent.
Dryer 53 is equipped with a cyclone as a secondary
collector. In operation, the cyclone routinely plugged and
interrupted operation of the plant. The dryer is now shut
down completely. No emission data are available.
Dryer 54 is identical to Dryer 53 and is operating
satisfactorily. The major difference in the two dryer
systems is the furnish. Dryer 53 was set up to dry southern
pine from 100 percent moisture to 22 percent (dry basis).
The high moisture content of the exhaust gases undoubtedly
acted to agglomerate the fines picked up in the secondary
collector. Dryer 54 handles dry furnish only, typically
drying from 22 percent moisture to 5 percent. No informa-
tion is available concerning inlet temperatures to the dryer.
At the temperatures used, however, the southern pine furnish
presents no apparent difficulty by formation of fine par-
ticles due to volatile organic components. The energy
source is primarily natural gas, with oil as auxiliary fuel.
7-17
-------
The secondary cyclone handles large particles well. Exit
grain loadings are 0.029 gr/sdcf. Opacity is 0 percent.
Dryers 57 and 58 are large, identical units equipped
with medium-energy cyclones as secondary collectors. Both
dryers are fired with natural gas, with propane as standby
fuel. The furnish is "mixed hardwoods." Inlet temperatures
are not known. No fine particles are formed, and opacity is
9 percent for the system. Fiber emissions are well con-
trolled by the secondary cyclones. The grain loadings are
0.035 and 0.063 gr/sdcf, respectively from Dryers 57 and 58.
Horsepower requirements of the secondary cyclones are high,
450 each. The gas flow rate through each .system is 46,000
scfm.
Dryers 70, 71, and 72 are natural-gas-fired tube dryers
handling mixed hardwoods. Since inlet temperatures are kept
to 375°F, few if any fine particles are formed either by
combustion or by evaporation of volatile components of the
furnish. Opacity readings on the exhaust stacks are zero.
Secondary cyclones were installed to control large-particle
emissions from the systems. Grain loadings are about 0.05
gr/sdcf.
Table 7-4 presents summary data on the medium- and
high-energy cyclone control systems.
Success in Meeting Regulations
Eight of the nine dryers equipped with secondary
cyclones are operating within the emission limitations.
(The ninth is shut down.) Dryers 48 and 51 are occasionally
borderline with respect to opacity limits. Although cyclone
systems are ineffective in controlling particles in the size
range less than 10 microns, the secondary cyclones are per-
forming well where large particles are the principle emis-
sion problem.
7-18
-------
Table 7-4. SUMMARY OF MEDIUM AND HIGH-ENERGY SECONDARDY
CYCLONE CONTROL DEVICES FOR PARTICLE DRYERS
Dryer
No.a
48
51
53
54
57
58
70
71
72
Energy sources
Primary
Sanderdust
Sander dust
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Natural gas
Secondary
Natural gas
Natural gas
Fuel oil
Propane
Propane
?
?
?
Inlet
temp. , °F
300-400
<400
-
?
?
?
<375
<375
<375
Primary
species
D. fir
D.. fir
NOT OPERABLE
Pine
Hardwoods
Hardwoods
Hardwoods
Hardwoods
Hardwoods
Exit cone. ,
gr/sdcf
0.06
0.05
-
0,029
0,035
0.063
~0.05
~0.05
~0.05
Opacity,
%
10-15
10-15
0
0
0
0
0
0
Status
Complies
Complies
Complies
Complies
Complies
Complies
Complies
Complies
I
M
VO
Additional information on these dryers is given in Appendix D.
-------
Problems with: the System
As noted earlier, secondary cyclones are prone to
plugging in some circumstances. Very high moisture contents
in the exhaust gases in combination with high concentrations
of fiber particles may cause excessive plugging. Plant
operators who have attempted to use these systems as primary
cyclones have experienced some plugging difficulties.
The greatest limitation inherent in these systems is
the high level of energy input required. Of the nine
systems studied, power requirements ranged from 0.002 to
0.013 hp/cfm. The combined electricity bills for Dryers 57
and 58 (450 hp each) exceed $110,000 per year.
Cost of Medium-Energy Secondary Cyclone Control Systems
Cost data for installation of secondary control systems
on Dryers 48, 51, 70, 71, and 72 show a range from $3.00
to $5.00/cfm. The other plant modificatons involved in
retrofitting Dryers 57 and 58 raised the cost to $11.00/cfm.
Accounting for inflationary factors, a reasonable range for
installation costs today would be about $6/cfm, including
engineering, materials, construction management, startup,
and associated costs.
Recommended Applications of the Systems
Medium- and high-energy secondary cyclone control
devices have proved successful in controlling large par-
ticles, in the size range above 10 microns. For dryers
whose emissions include substantial quantities of small
particles that result in the formation of visible blue haze,
these systems are not adequate to control opacity.
MULTIPLE-CYCLONE CONTROL SYSTEMS
Success in Meeting Regulations
Only two dryers, 62 and 63, were equipped with multiple
cyclones for secondary control systems. Both dryers are
7-20
-------
fired with fuel oil and have high inlet temperatures. Dryer
62 typically operates with inlet temperatures of 800 to
1000°F. Southern pine is the principal species of furnish.
Apparently, organic material from the furnish collected in
the multiple cyclone, and eventually a major fire occurred.
The dryer is now shut down and is not expected to operate in
the near future. The control device is beyond repair.
Dryer 63 operates with lower inlet temperatures (600 to
800°F). It is used to dry southern pine from the 20 percent
to the 5 percent moisture level. The multiple-cyclone
secondary collector works effectively to control large-
particle emissions. The exit grain loading is 0.028 gr/
sdcf. Although no information is available regarding
opacity, the installation is said to be in compliance with
regulations.
Problems with the Systems
Multiple cyclones may have a high energy requirement.
For Dryer 63 the energy requirement per cfm is as high as
that for the most demanding medium-energy secondary cyclone
(0.013 hp/cfm) , which amounts to 200 hp for the 15,000 cfm
dryer.
Multiple cyclones may be subject to fires, as demon-
strated by Dryer 62. With the exception of wet scrubber
systems, however, all other secondary control devices have
the same limitation. The difficulty is not so much the
equipment design, but rather that the fibers collected in
the systems are explosive and flammable.
Cost of Multiple-Cyclone Systems
Accurate cost information is not available for the two
installations of multiple cyclones. A conservative estimate
for complete installation including engineering, materials,
7-21
-------
construction management, installation, and startup is in the
range of, $4 to $6/cfm.
Recommended Applications of Multiple Cyclones
If judged on the basis of their use among the 76 dryers
investigated, multiple cyclone control devices might not be
recommended for dryer emission control purposes. They are
useful in controlling particles of about 10 microns but are
not recommended for control of fine particles that generate
visible blue haze.
FABRIC-FILTER EMISSION CONTROL SYSTEMS
Success in Meeting Regulations
Of the 76 dryers investigated, only Dryer 44 is equipped
with a fabric filter control device. This dryer is fired
with natural gas, drying Douglas fir from the 50 percent
moisture level to the 8 percent level. Inlet temperatures
range from 385 to 550°F. Large-particle (fiber) emissions
exceeded the allowable limits before the baghouse was in-
stalled, and the unit effectively controls the large-par-
ticle emissions.
At the higher emission temperature ranges, particularly
with Douglas fir, opacity is a major concern. The fabric
filter is not insulated and operates at approximately 175°F,
somewhat below the expected condensation temperatures for
most of the haze-forming organic materials. Surprisingly,
condensation of these materials has not resulted in plugging
or blinding of the filter cloth. Since the dryer is fired
with natural gas, the energy source contributes no fine
particles of fly ash. Blue haze can be seen leaving the
bottom exit duct of the baghouse, but because the cross-
sectional area of the exit duct is so large the system is
subject to sufficient dilution from normal circulating air
currents and therefore does not exceed the opacity limits of
20 percent.
7-22
-------
Problems with the Fabric-Filter System
This system had operated only a few months at the time
of evaluation for this study and has caused no unexpected
problems or operational difficulties. Although there has
been concern that condensation of the water vapor in the gas
stream would tend to blind or plug the filter materials,
this has not occurred. The short operational experience
jindicates that the fabric filter systems may provide a
reasonable solution to control of particles.
Costs of the Fabric-Filter System
The installed cost of the system is $65,000 to handle
22,000 cfm, yielding a rate of about $3/cfm, which is a most
competitive figure. Since this is a recent installation,
the price should reflect current costs. The pressure drop
across the baghouse is approximately 7 inches H20.
Recommended Applications of Fabric Filters
With limited operational experience on only one in-
stallation, there is little basis for endorsement of this
approach to emission control of particle dryers. Fires and
explosions have occurred on fabric filters used to control
wood fiber emissions. These potential hazards should be
considered.
Experience with fabric filters on other equipment
indicates that they are very effective in controlling fiber
emissions. With proper selection of the fabric, they can
also be effective in controlling fly ash-type emissions such
as those generated in combustion of wood-residue fuels.
Observation of Dryer 44, however, indicates that the filters
are not entirely effective in collecting volatile organic,
haze-forming emissions. Thus, for high-temperature drying
of Douglas fir, they are not necessarily an appropriate
selection.
7-23
-------
OTHER SYSTEMS FOR CONTROLLING DRYER EMISSIONS
LoW-Temperature Operation
In review of the technology that has been applied to
control emissions from dryers, emphasis to this point has
been on tail-end control devices. Recognizing the impor-
tance of temperature in formation of small particles of
organic matter, some companies have chosen to design and
operate their dryers at temperatures below those at which
haze is formed. In some instances this is accomplished by
reducing the rate of flow of furnish to the dryers. In
other cases, the same result can be achieved by drying very
wet furnish in two stages rather than in a single step. Of
the 76 dryers surveyed, 17 were not equipped with tail-end
control devices but were maintained in compliance with
opacity regulations by operating at low inlet temperatures
(below 450°F). The dryers in this category are numbers 3,
21, 22, 24, 25, 30 through 39, 47, and 52. Dryers 3, 34,
and 47 were fired with sanderdust, which provided an input
of haze-forming fly ash. Opacity on these three dryers was
estimated to be typically less than 10 percent, but emis-
sions were visible. Opacity on the remaining 14 dryers was
estimated to range from 0 to less than 10 percent.
Managers and operators agree that low-temperature
operation is effective in meeting opacity requirements and
also offers the advantage of minimizing fires. Offsetting
these positive benefits is the additional capital cost
required to permit this type of operation. Low feed rates
of furnish to the dryer and/or staged drying both require
more drying equipment than is needed for high feed rates to
single-stage dryers. If low feed rates are used without
additional equipment, production is reduced. In the highly
7-24
-------
competitive board and panel markets, reduced production
could affect competition cost operations.
The maximum temperature on the inlet to the dryer is
not easily specified, since formation of blue haze is very
species-dependent. Many plants use mixed species in their
furnish, and the upper limit for one species may not be the
same as that for another. The situation is further com-
plicated by lack of knowledge about the volatile organic
content of selected species and their temperature-depen-
dence. Experience with Douglas fir suggests that if the
maximum inlet temperature is below 450°F, blue haze forma-
tion will be within current opacity restrictions. This is
purely a rule of thumb, however, which does not take into
account the fuel used, type of dryer, particle size, and
other factors that affect opacity. With southern pine,
inlet temperatures might go as high as 600°F without appre-
ciable haze formation, as demonstrated by Dryer 61, which
has no tail-end control device, is fired with sanderdust,
and is considered to operate at 0 percent opacity.
Energy use for low-temperature drying is about the same
as for higher temperatures on the basis of Btu per pound of
water evaporated (see Figure A-2, Appendix A). If high
inlet temperatures result in the need for energy-consuming
tail-end control systems to reduce opacity, the overall
energy use may be significantly greater than in lower-
temperatures operation. Energy balances should be con-
sidered in evaluating alternative approaches to opacity
control.
The alternative of reducing drying temperatures to meet
emission regulations entails a space requirement for addi-
tion of more dryers. Since particle and fiber dryers are
fairly large installations, many plants may not be able to
provide enough space for additional dryers.
7-25
-------
Installation of 'Short Fall
Of the 76 dryers considered in this report, 2 were
designed with single-pass rotating dryer drums. This drum
design has been retrofit with internal steel' structures
called 'short fall fill1 at two plants in the U.S.
(Neither plant was visited during this study.) 'Short fall
fill' is a descriptive term meaning that internal baffles
have been placed in such a fashion that the particles
passing through the dryer can 'fall1 only a short distance
before coming into contact with a baffle. The direct con-
tact of the particles with the baffles assists in drying the
particles, in part through conductive heat transfer and in
part through the greater turbulence around each particle as
it comes into contact with and then separates from the
internal baffles. For those dryers that have been so
modified, the initial production rates have been maintained
while the inlet temperatures were reduced and blue haze was
eliminated in operation at design capacities.
No cost data are available concerning installation of
short fall fill. It is, however, designed only for use on
single-pass rotating dryer drums. As noted in Appendix A,
the vast majority of plants are using triple-pass rotary
dryers, for which installation of this baffle system would
not be appropriate. Patents on this system are held by
Steams-Rogers Co. of Denver.
SAFETY CONSIDERATIONS RELATIVE TO DRYER EMISSION CONTROL
DEVICES
Manufacturers of wood-based particle and fiber panel
products are highly safety conscious. The handling of
small, dry wood particles makes these manufacturing facil-
ities prone to fires and occasional major explosions. On
7-26
-------
March 23, 1976, a major fire destroyed a northern California
plant. Six men were killed in the holocaust.
The potential for fires and explosions, particularly in
and around dryer systems, is of significant concern to plant
owners and operators. Their concern has increased as the
complexities of the operations have expanded to include
dryer emission control. Consideration must be given to
these potential hazards in the design, installation, and
operation of control devices.
Wet scrubbers present few hazards. Because they in-
volve water sprays and designs to trap the small fibers in
water, fire is not a problem. Full-recirculation systems,
however, present a serious potential hazard. They are
typically operated with high inlet temperatures that drive
off volatile, combustible, organic materials from the wood
furnish. As these are recirculated to the high-temperature
combustion unit, they are burned along with any fibers that
were not collected by the primary cyclone. The high tem-
peratures at the dryer inlet could easily set the furnish on
fire, except that the combustion products are low in oxygen.
The low oxygen concentration prevents rapid oxidation of the
dryer furnish. If an inspection port is left open or is
opened during operation, however, the oxygen concentration
could increase enough to result in a major fire. Partial
recirculation control systems are subject to the same
hazards.
Secondary cyclones are not without fire and explosion
potential. In some units installed in the southeastern .
U.S., condensation of the volatile organic materials on
interior surfaces has built up a layer of combustible
materials several inches thick. A serious fire that de-.
7-27
-------
stroyed a unit emphasizes the need for proper design and
operation of these systems.
As noted earlier, Dryer 62 is not functional. A fire
destroyed the dryer and the multiclone collector, which had
accumulated significant quantities of combustible, condensed
organic materials in the interior.
Of all the control devices, fabric filters are most
feared for their fire and explosion potential. These
filters may collect explosive concentrations of combustible
wood fibers. One northwestern plant finally removed a
baghouse installed on a particle transfer system after the
fifth fire in the system destroyed the bags.
Decisions concerning installation of any type of emis-
sion control equipment in a wood-based particle or fiber
manufacturing plant, must be based on consideration of the
safety aspects of the alternative devices. Particular
attention should be given to "upset" conditions, plugging of
primary cyclones, variations in material flow rates, and
other process variables that could result in extreme hazards.
7-28
-------
8. INDUSTRY-WIDE COMPLIANCE STATUS SUMMARY
Information was compiled and developed to ascertain the
compliance status and compliance schedules for wood particle
dryers operated in each plant in the U.S. manufacturing
particleboard, medium-density fiberboard, and hardboard.
Source data reports from CDS and NEDS were accessed for the
requisite data. For most regions, detailed compliance
information within these data systems was limited, incom-
plete, and/or unknown. The information sought included
number of dryers operated, dryer compliance status, and
dates of scheduled incremental actions in accordance with a
State Implementation Plan (SIP). Directories of the Forest
Products Industry, the National Particleboard Association,
and the Acoustical and Board Products Association were used
to verify the list of board producers and to provide produc-
tion data. All EPA regional offices were contacted for
supportive information, as were several local control
agencies having particle dryers under their jurisdiction.
It was beyond the scope of this task to contact individual
plants or all local control agencies to obtain detailed
supportive or missing data.
The data were assembled and tabulated by firm for the
following categories:
0 Number of dryers.
0 Facility identifications (state, county, CDS
number,' NEDS number, state registration number).
0 Dates of SIP incremental scheduled actions.
0 General compliance status and method of deter-
mination.
8-1
-------
Seventy-five plants were identified under Standard
Industrial Classifications (SIC's) 2492 and 2499 as manu-
facturers of particleboard or medium-density fiberboard. Of
these, 35 demonstrated full dryer compliance and/or entire
source compliance (which indicates complete individual point
compliance). It was not possible in all cases to identify
the exact number of dryers operated by each plant or spe-
cific compliance status, since these data were missing in
some of the CDS sumamries. The dates of SIP scheduled
incremental actions were recorded where available. Table 8-
1 tabulates the aforementioned for each identified plant
alphabetically by state. A listing of each plant with its
address, numerically arranged to correspond with the listing
in Table 8-1, is included in Appendix E.
Table 8-2 presents, in the same format as Table 8-1,
the data for all verified hardboard manufacturing plants in
the United States, a total of 20. All plants were iden-
tified under SIC's 2490 and 2499. Of the 20 plants, 13
demonstrated full dryer compliance and/or entire source
compliance (indicating complete individual point compli-
ance) . As with the particleboard plants, it was not always
possible to identify the number of dryers operated by each
plant or to obtain complete compliance schedules. A listing
of each plant with its address, numerically arranged to
correspond with the listing in Table 8-2, is presented in
Appendix F.
Table 8-3 lists plants that probably include particle-
board or hardboard operations but could not be verified,
either through one of the wood products industry directories
or through the CDS or NEDS data summaries. The correspond-
ing list of addresses is presented in Appendix G, alpha-
betically by plant, arranged sequentially by state.
8-2
-------
Table 8-1. COMPLIANCE STATUS SUMMARY: PARTICLEBOARD AND MEDIUM-DENSITY FIBERBOARD PLANTS
Facility
1. Giles & Kendalld
2. Louisiana Pacific3'
3. Louisiana Pacific
4. MacMillan Bloedel
Particleboarda'b/d
5. Olinkrafta'b'd
6. Southwest Forest
Industries*'3
7. Georgia Pacifica'b/d
8. International Papera' '
9. Singerc'd'e
10. Wynnewood Products
11. American Forest
Products13 »d
12. Big Bear Board
Products13 »d
13. Champion . ,
International '
14. Collins Pineb/d
15. Fiberboard
16. Georgia Pacifica'
17. Hambro Forest
Products* »d
No. U
dryers
J
2
1
Facility identification
State
01
01
01
01
01
03
04
04
04
04
05
05
05
05
05
05
05
County
0280
3460
2420
0200
0080
1160
1100
0220
6700
7580
6020
4540
2000
CDS #
00014
produc
00004
00004
00400
00002
00005
00001
00005
00035
00002
00003
produc
00013
00002
NEDS
X ref
0014
ition t
0004
0010
0005
0001
0001
tion £
0045
0005
State
reg. #
o start
tarted ]
SIP schedule
Type
none
6/7J6
none
none
pend
appr
975
none
Submit
plan
3/14/74
2/28/74
Final compliance
Sched
3/24/75
6/74
Achiev
2/19/7!
Status
unknown
variance
achieved
Dryer
Compliance
Status
In
X
X
e
X
X
X
X
X
xe
xe
X
Out
Eval.
nethod
'Unknown
X
unknown
insp
:
(
unknown
X
on
sched
L
insp
insp
on
sched
insp
Data source: CDS Source Data Summary, CDS "quick look," or NEDS
b EPA Regional Office
. Local Control Agency
Listed in at least one directory: Forest Products Industry, Acoustical & Board Products Association, National
Particleboard Association
^ Compliance status of entire source
Where data is indicated as "unknown," it was listed as such in CDS and/or NEDS summaries
-------
Table 8-1 (continued). COMPLIANCE STATUS SUMMARY: PARTICLEBOARD
AND MEDIUM-DENSITY FIBERBOARD PLANTS
oo
I
Facility
18. Humboldt Flakeboarda/d
19. Louisiana Pacific
20. Sequoia Board3
21. Georgia Pacific
22. Temple Industries
23. Weyerhaeuser '
24. Pctlatch Forest3 'd
25. Swain Industries
26. Tenn-Flakea/d
27. Duraflake South3 'd
28. Louisiana Pacific3
29. Olinkraft-Pa.rticle3'd
30. Champion ,
International
31. Blandin Wood
Products15 'd
32. Cladwoodd
33. Champion ,
International
34. Georgia Pacific3'
n
n
0)
d&
Z 13
1
^
1
1
1
Facility identification
State
05
05
05
11
11
11
13
15
18
19
19
19
23
24
24
25
25
County
3300
4320
1340
0860
0200
1720
1680
2920
1660
2980
CDS t
00522
00010
00001
00010
01405
00004
00001
00003
00001
00004
TJEDS^
X ref
0047
0017
0001
0004
0001
0003
0001
0004
State
reg. #
OT-73-14
SIP schedule
Type
none
none
Enf/
Adm
pend
appr
none
none
none
appr
Submit
plan
F Final compliance
Sched
4/1/74
Achiev
Status
unknown
Dryer
Compliance
Status
In
X
e
X
e
X
x°
xe
Out
X
X
unknowr
X
xe
Eval.
method
NEDS
insp
cert
off
sched
f
cert
cert
cert
off
sched
Data source: CDS Source Data Summary, CDS "quick look, or NEDS
b EPA Regional Office
d Local Control Agency
Listed in at least one directory: Forest Products Industry, Acoustical & Board Products Association, National
Particleboard Association
^ Compliance status of entire source
Where data is indicated as "unknown," it was listed as such in CDS and/or NEDS summaries
-------
00
I
(Jl
Table 8-1 (continued). COMPLIANCE STATUS SUMMARY: PARTICLEBOARD
AND MEDIUM-DENSITY FIBERBOARD PLANTS
Facility
35. Georgia Pacific3'3
36. Kroehler ,
Manufacturing3 '
37. Evans Products3 /d
38. Plum Creek Lumber3'3
39. Ponderosa ,
Products3 >a
4 0. Carolina Forest
Products'1
41. Evans Products3'3
42. Georgia Pacific3'
43. International Paper3'
4 4. Nu-Woodsd
4 5. Permaneer
4 6. Surecorec/d
4.7. Weyerhaeuser3 'd
4 8. Bohemia3 'd
in
M
a
>,
Q M,
55 .3.
4
3
3
2
Facility identification
tate
25
25
27
27
32
34
34
34
34
34
34
37
37
38
County
2500
1460
1100
0480
0140
0720
0880
3180
2280
1760
1020
CDS #
00002
00031
00002
10002
00902
09001
00050
00007
00001
00002
00051
NEDS
X ref
0002
0020
0007
0002
0529
State
reg. #
20-0529
SIP schedule
Type
un-
known
un-
known
un-
known
none
none
Enf
ord
Submit
plan
Final compliance
Sched
12/74
5/73
6/30/76
Achiev
12/9/5
Status
variance
variance
achieved
Compliance
Status
In
xe
xe
Out
xe'
xe
e
X
unknown
X
xe
X
xe
X
Eval.
method
off
sched
off
sched
on
sched
cert
f
off
sched
no
sched
cert
on
sched
Data source: CDS Source Data Summary, CDS "quick look," or NEDS
° EPA Regional Office
j Local Control- Agency
Listed in at least one directory: Forest Products Industry, Acoustical & Board Products Association,
National
Particleboard Association
Se'lata
.- it wa. listed »« ,uch in CDS and/or NEDS series
-------
CD
I
Table 8-1 (continued). COMPLIANCE STATUS SUMMARY: PARTICLEBOARD
AND MEDIUM-DENSITY FIBERBOARD PLANTS
Facility
49. Boise Cascade3'
50. Brooks-Willamette3 'd
51. Publishers' Paper
52. Duraflake3'd
53. Fiberboarda/d
54. Medforda'd
55. Permaneer3'
56. Penr.aneer '
57. Roseburg Lumber3
58. Timber Products3'
59 . Weyerhaeuser3 ' a
60. Weyerhaeuser3'
61. Georgia Pacific3'
62. Georgia Pacific3'3
63. Holly Hill Lumber3'6
m
n
ID
>,
O U
Z T3
4
;
6
2
1
2
10
6
11
Facility identification
State
38
38
38
38
38
38
38
38
38
38
38
38
42
42
42
County
1800
0500
1080
0880
0840
0520
0840
0520
0840
0920
1020
0420
0680
1860
CDS #
00003
00004
00014
00001
00011
00034
10009
00030
00019
00008
00023
00005
00003
00002
NEDS
X ref
0002
0002
0143
0013
0027
0063
0032
0034
8866
State
reg. #
31-0002
09-0002
22-0143
10-0013
15-0027
10-0063
15-0032
18-0034
20-8866/
67/68
SIP schedule
_
Type
pend
pend
Enf
ord
none
pend
pend
pend
Submit
plan
1/15/75
7/1/75
'3/75
Final compliance
Sched
6/30/75
11/1/74
7/31/75
12/76
9/30/79
11/1/75
12/31/73
Achiev
6/1/75
2/1/75
t in op
9/75
12/31/73-
5/12/75
Status
achieved
achieved
vio-
lation
on schec
on sched
eration
achieved
ach'vd
achieved
Dryer
Compliance
Status
In
X
X
X
xe
X
X
X
x°
X6
X6
Out
X
X
X
X
Eval.
method
»
cert
S.test
off
sched
insp
cert
cert
S. test
cert
cert
cert
Data source: CDS Source Data Summary, CDS "quick look," or NEDS
k EPA Regional Office
, Local Control Agency
Listed in at least one directory: Forest Products Industry, Acoustical & Board Products Association, National
Particleboard Association
e Compliance status of entire source
-------
00
Table 8-1 (continued). COMPLIANCE STATUS SUMMARY: PARTICLEBOARD
AND MEDIUM-DENSITY FIBERBOARD PLANTS
Facility
64 International
Paper a»d
65. Tenn-Flakea/d
66. Kirby Lumber0 'd
67 . Louisiana Pacific '
68 . Permaneerc '
69. Temple Industries0 'd
70 . Champion ,
International '
71. Masonitea'd
72 . Union Camp '
73. International Papera'c
74 . Rodman Industries '
75. Weyerhaeuser3'
No.
dryers
1
1
1
1
1
1
1
Facility identification
State
42
44
45
45
45
45
48
48
48
49
51
51
County
1140
1260
2310
0870
0110
1420
3120
2940
0480
1960
4060
CDS i
00002
00021
00002
00011
00002
00002
00001
00004
00013
00008
00004
NEDS
X ref
0021
0002
0003
0002
0001
0013
0003
0003
State
reg. #
32-0021
107-
625-6
111-
292-9
115-
229-7
104-
0003-1
SWAPCA
73-7
380006
SIP schedule
Type"
none
Enf
ord
Submit
plan
6/1/71
Final compliance
Sched
6/1/72
Achiev
12/31/73
12/31/7-
12/31/72
8/6/14
Status
ach'vd
"A"
ach'vd
"A"
ach'vd
"A"
ach ' vd
Dryer
Compliance
Status
In
X*
jP
X
X
X
X
Out
X
X
xe
xe
xe
X
Eval.
method
cert
cert
insp
insp
insp
insp
insp
on
sched
on
sched
cert
on
sched
on
sched
Data source: CDS Source Data Summary, CDS "quick look," or NEDS
° EPA Regional Office
, Local Control Agency
Listed in at least one directory: Forest Products Industry, Acoustical & Board Products Association, National
Particleboard Association
, Compliancy status of entire source
Where data is indicated as "unknown," it was listed as such in CDS and/or NEDS summaries
-------
Table 8-2. COMPLIANCE STATUS SUMMARY: HARDBOARD PLANTS
oo
I
00
Facility
1. Chicago Hardboard
2. Abitibib'd
3. Boise Cascade '
4. Superwooda/
5. Superwooda/b'd
6. Celotexb'd
7 . Georgia Pacific '
8. Masonitea'd
9. Weyerhaeuser3
10. Georgia Pacifica'd
11. Pope & Talbota'd
12. U.S. Plywooda/d
13. Weyerhaeuser3'
14. Masonitea'
15. Celotex Sellers a'b'd
16. Champion ,
International '
vt
M
O
0&
Z t3
3
7
4
1
4
Facility identification
State
14
23
24
24
24
33
34
34
34
38
38
38
38
39
42
42
County
0220
1780
0240
3260
1520
2940
2840
0720
0320
1020
1080
0920
1000
1660
2440
CDS #
00002
00001
00001
00031
00001
00041
00039
00020
00007
00049
00016
00011
00009
00006
00026
NEDS
X ref
0001
0004
0031
0041
0039
0011
6403
5195
0035
State
reg. t
B-1476
123000
-0017
06-0011
20-6403
/01/04
22-5195
18-0035
SI
Type
Enf/
Adm
Enf/
Adm
Enf/
Adm
none
none
pend '
pend
none
Submit
plan
11/1/74
12/31/3
P schedule
Final compliance
Sched
3/30/75
-12/31/5
Achiev
8/75
11/19/5
12/9/75
6/12/75
Status
achieved
achieved
achieved
resched
achieved
Dryer
Compliance
Status
In
xe
xe
X
xe
e
X
X
X
xe
xe
xe
xe
Out
unknown
e
X
xe
e
X
X
Eval.
nethod
f
cert
cert
on
sched
cert
off
sched
cert
cert
insp
cert
off
sched
cert
cert
cert
Data source: CDS Source Data Summary, CDS "quick look," or NEDS
b EPA Regional Office
d Local Control Agency
Listed in at least one directory: Forest Products Industry, Acoustical & Board Products Association,
Particleboard Association
£ Compliance status of entire source
Where data is indicated as "unknown," it was listed as such in CDS and/or NEDS summaries
National
-------
Table 8-2 (continued). COMPLIANCE STATUS SUMMARY: HARDBOARD PLANTS
Facility
17. Celotexa'd
18. Temple Industries
19. Evans Products3 'd
20. Evans Products '
No. |
dryers f
Facility :
State
44
.45
48
51
County
1460
1460
2860
identification
CDS *
00008
00002
00003
NEDS
X ref
0008
0003
0003
State
reg. t
510003
SIP schedule
Typ°e
Submit
plan
Final compliance
Sched
6/75
Achiev
Status
Dryer
Compliance
Status
In
xe
e
X
Out
X
Eval.
method
off
sched
cert
cert
Data source: CDS Source Data Summary, CDS "quick look," or NEDS
b EPA Regional Office
5 Local Control Agency
Listed in at least one directory: Forest Products Industry, Acoustical & Board Products Association, National
Particleboard Association
e Compliance status of entire source
00
-------
00
I
Table 8-3. PLANTS IN QUESTIONABLE STATUS
(Exact Product Unverified)
Facility
1. American Forest
Products3
2. Fiberite West Coasta
3. Georgia Pacific3 /e
4. Louisiana Pacific3'
5. U.S. Plywood3
6. Pack Rivera
7. Georgia Pacific3
8. International Paper3
9. Georgia Pacific
10. Georgia Pacific3
11. Georgia Pacific
12. Masonite3
Facility identification
State
05
05
05
05
05
13
18
25
34
34
34
34
County
5940
5440
4540
0960
7580
0240
2540
1940
1060
CDS #
00505
00002
00513
00006
00002
00007
00003
00047
00040
00030
00130
NEDS
X ref
0013
0009
0033
0003
0047
0130
State
reg. #
T-2329
SIP schedule
Type
none
appr
none
none
Enf/
Adm
none
Submit
plan
Final corrroliance
Sched
Achiev
Status
uryer
Comoliance
Status
In
e
X
e
X
e
X
xe
e
X
e
X
i
I
X
Out
Xs
unknown
Xs
xe
x°
Eval.
method
insp
insp
insp
insp
cert
off
sched
cert
cert
Data source: CDS Source Data Summary, CDS "quick look, ' or NEDS
b EPA Regional Office
, Local Control Agency
Listed in at least one directory: Forest Products Industry, Acoustical & Board Products Association, National
Particleboard Association
Compliance status of entire source
-------
Figure 8-1 shows the distribution of all verified
plants summarized in Tables 8-1 and 8-2 (total 95) by state.
The greatest concentration (approximately 29 percent) occurs
in Oregon and California; the Region IV (southeastern)
states account for an additional 32 percent.
In summary, the data from the individual plant surveys
and the compliance status survey both indicate an industry-
wide average of about three or four wood particle dryers per
plant. Of the 95 particleboard and .hardboard plants veri-
fied, about 47 percent had dryers in compliance, 25 percent
were not in compliance, and no data were available to deter-
mine the status of the remaining 27 percent. Twelve plants
were identified that could not be verified as either par-
ticleboard or hardboard producers. No data are available to
indicate the average period of time required for dryers to
achieve full compliance from the original scheduled date of
control plan submission.
8-11
-------
00
I
M
NJ
Figure 3-1. Distribution of particleboard and hardboard plants in the
United States (number of verified plants per state).
-------
9. REFERENCES
1. Adams, D. F., et. al. Volatile Emissions from Wood.
Proceedings of the 5th Annual Particleboard Symposium.
Washington State University, Pullman, Washington. 1971.
2. Buikat, E. R. Operating Problems with Dryers and
Potential Solutions. Proceedings of the 5th Annual
Particleboard Symposium. Washington State University,
Pullman, Washington. 1971.
3. Buntrock, K. Scrubbers in Particleboard Plants.
Proceedings of the 5th Annual Particleboard Symposium.
Washington State University, Pullman, Washington. 1971.
4. Comstock, G. L. Energy Requirements for Drying - Lumber,
Veneer, Particles. Proceedings No. P-75-13. Forest
Products Research Society, Madison, Wisconsin. 1975.
5. Junge, D. C. Boilers Fired with Wood and Bark Residues.
Research Bulletin No. 17. Forest Research Laboratory,
Oregon State University, Corvallis, Oregon. 1976.
6. Junge, D. C. Energy Alternatives for the Forest Products
Industry. Proceedings No. P-75-13. Forest Products
Society, Madison, Wisconsin. 1975.
7- Odell, F. G. Air Quality Standards for Particleboard
Plants. Proceedings of the 5th Annual Particleboard
Symposium. Washington State University, Pullman, Washington.
1971.
8. Porter, S. M. Gas Recycling and Dryer Modifications to
Reduce Smoke Emissions. Proceedings of the 5th Annual
Particleboard Symposium. Washington State University,
Pullman, Washington. 1971.
9. Shumate, R. D. Design and Operation of Dry Centrifugal
Dust Collectors. Proceedings of the 5th Annual Particle-
board Symposium. Wasington State University, Pullman,
Washington. 1971.
10. Smith, K. T. The Drying of Wood Residue for Use in Hogged
Fuel-Fired Boilers. Masters Thesis, Oregon State University,
Dept. of Mechanical Engineering, Corvallis, Oregon.
June 1974.
11. Surdyk, L. V. Dryer Modifications to Reduce Smoke Emissions
and Improve Drying. Proceedings of the 5th Annual Particle-
board Symposium. Washington State University, Pullman,
Washington. 1971.
9-1
-------
9. REFERENCES (Continued)
12. Oregon Administrative Rules, Chapter 340. Dept. of
Environmental Quality. Air Quality Division.
13. Rules and Regulations Governing the Control of Air
Pollution. State of North Carolina, Dept. of Natural
and Economic Resources, Office of Water and Air Resources,
9-2
-------
APPENDIX A
INTRODUCTORY NOTES ON THE THEORY
OF PARTICLE DRYING
-------
INTRODUCTORY NOTES ON THE THEORY OF PARTICLE DRYING
In the manufacturing of wood-based fiber and particle
panel products, control of the .moisture content of the raw
materials is critical. Moisture affects the quality of the
finished products and the bonding abilities of the resins.
Moisture can create special problems in the hot presses as
it expands in the vapor state and causes "blows". Raw
materials for the manufacture of panel products are received
with a wide range of moisture contents. Table A-l indicates
typical moisture contents for "green" material of some north
4
American species. Note, that moisture levels vary widely
among species and within species. In most softwoods the
moisture content of the sapwood is typically much higher
than that of the heartwood. Since smaller trees have a much
larger percentage of sapwood than heartwood, they tend to
have high moisture levels. Moisture content of old, large
trees is therefore lower than that of small young trees.
Moisture content of particle furnish for panel products
may be different from the values in Table A-l because of
these variations. It may vary also with the manufacturing
operations that generate the furnish. Planer shavings, for
example, may be predried in a kiln, whereas sawdust may be
wetted by the water added from sawguides.
Furnish for particle products is dried by raising the
temperature of the wood to a level high enough to evaporate
(
the undesirable moisture fraction. When a wet solid under-
goes thermal drying, two processes occur simultaneously:
A-2
-------
Table A-l. DENSITY AND MOISTURE CONTENT OF SOME TYPICAL
NORTH AMERICAN WOOD SPECIES
Species
Softwoods
Douglas fir
Old growth
Second growth
Englemann Spruce
Ponderosa Pine
Southern Yellow Pine
Western Hemlock
Hardwoods
Northern Red Oak
Red Alder
Yellow Birth
Yellow Poplar
3.
Green moisture
content, % ^0
by wt. (dry basis)
45
60
60
100
100
100
80
100
75
90
Water per
Unit Vol,
Ib/ft3
12.6
16.8
12.0
23.7
29.3
23.7
27.9
23.1
25.7
22.5
Green moisture content refers to the moisture content
of fresh cut wood samples.
A-3
-------
1. Heat Transfer - Transfer of heat energy to the wet
solid to raise the temperature high enough for
evaporation to take place;
2. Mass Transfer - Transfer of the moisture contained
in the interior of the wood to its surface, from
which the moisture evaporates.
Heat energy transfer in a drying process can occur by
convection, radiation, conduction, or any combination of
these. Mass transfer of moisture from the solid to the
gaseous environment is dependent on the internal movement of
moisture from the interior to the surface, and the diffusion
of evolved water vapor away from the surface. Either of
these two factors may be limiting in the drying process.
The internal movement of moisture is a function of physical
characteristics of the solid and its moisture content;
removal of water vapor from the surface depends on external
conditions such as temperature, humidity, flow rate of the
surrounding air, and area of exposed solid surface.
In a particle dryer, the energy requirements are re-
lated to five factors:
1. Heat energy imparted to raise the temperature of
the wood and the water.
2. Heat energy required to vaporize the water.
3. Loss of heat energy by venting or exhausting of
the gas stream to atmosphere.
4. Loss of heat energy by radiation and convection
from the dryer.
5. Loss by other mechanisms such as leaks, faulty
steam traps, etc.
A significant amount of drying energy (AH ) is expended
s
in raising the temperature of the wood and water from ambi-
ent to the evaporation temperature. Assuming that all other
A-4
-------
energy losses could be eliminated, the minimum energy re-
quirement for evaporation drying would be:
AHmin = AHv + AHs (1)
Expressed in terms of Btu/lb of water evaporated:
AHv = 1000 Btu/lb (2)
t Cwd + (Jj^x C )] AT (3)
AH = Q IPlF Wa
[ Mi - Mf ]
100
where :
Cwd = sPecific heat of wood (0.3 Btu/lb°F)
= specific heat of water (1.0 Btu/lb°F)
M. = initial moisture content (%) , dry basis
Mf = final moisture content (%) , dry basis
AT = temperature change from ambient to
evaporation temperature (°F)
From the above, Eq. 1 easily reduces to:
AT . = 1000 + [3° + Mi] AT (4)
min tM± - Mf]
AT is shown in Figure A-l for a range of initial
s
moisture contents, final moisture contents, and temperature
increases. It is clear that this value for drying energy
becomes quite high, particularly with low initital moisture
contents and large temperature increases. This energy added
to AH gives the minimum energy required exclusive of vent-
ing and other dryer losses. This can range from 1100 Btu/lb
to more than 1500 Btu/lb (See equations 1 & 2) .
A-5
-------
^ 800-
g 700-
i
o
5 600H
I
i CQ
kU
500-
400-
300-
200-
100-
AT = TEMPERATURE RISE FROM
AMBIENT TO EVAPORATION
POINT
15% MOISTURE CONTENT
20
AT « 150*F
AT - 75*F
40 60 80 100 120
INITIAL MOISTURE CONTENT, X (DRY BASIS)
Figure A-l. Sensible heat imparted to wood and water to
raise it to the evaporation temperature.
A-6
-------
The energy required to convert water from the liquid to
the gaseous phase is called the heat of vaporization. For
wood at initial moisture contents above 30 percent the "heat
of wetting" becomes a significant part of the total energy
and must be added to the heat of vaporization. This is
illustrated in Figure A-2. In most drying processes, the
heat of wetting can be ignored. Heat of vaporization varies
only slightly in the range of normal drying temperatures
from 1037 Btu/lb at 100°F to 970 Btu/lb at 212°F.
Venting or exhausting of air from a dryer represents
another major source of energy loss. As a rough approxima-
tion, energy use in drying is proportional to the tempera-
4
ture drop in the air as it passes through the dryer.
AH . a (T_ - T_) (5)
mm E L
where
Tp = Temperature entering
T = Temperature leaving
Energy loss in venting is proportional to the difference
between ambient air temperature T and vented air, usually
4
T , and the fraction of vented air X :
AHv a (TL - V (V
The ratio of vented energy to minimum drying energy is:
AHv = (TL - V (V
AHmin (TE - V
A-7
-------
1400
HEAT OF WETTING
(SHADED AREA)
HEAT OF VAPORIZATION (AHy)
20 40 60 80 100
MOISTURE CONTENT, % (DRY BASIS)
Figure A-2. Energy required to evaporate water from
wood as a function of moisture content.
A-8
-------
Vented energy may amount to less than 10 percent of total
energy in dryers where the proportion of air vented is small
or the temperature of vented air is near ambient. It may be
well over 50 percent of the total energy in some nonrecir-
culating particle dryers. Figure A-3 shows the amount of
energy lost through venting in a nonreciculating dryer from
which all the air is exhausted to the atmosphere. As enter-
ing air temperature goes up and exhaust temperature goes
down, the amount of energy lost through venting decreases.
The loss through venting is reduced in direct proportion to
the amount of air recycled through the dryer.
Adding the amount of heat lost through venting to AH .
provides a fair approximation of the minimum drying energy
requirement. It typically ranges from 130 Btu/lb of water
evaporated to as much as 3000 Btu/lb. Actual drying energy
will be somewhat above these values because of other energy
losses, dryer design, or maintenance deficiencies.
Particles, including wood chips, planer shavings,
sawdust, and flakes are normally dried on a continuous basis
in rotary drum dryers. Fibers, because of the low bulk
density, are normally dried in a tube dryer with signifi-
cantly higher volumes of air and somewhat lower inlet.tem-
peratures. Most particle and fiber dryers are single-pass
in the sense that the air is exhausted after passing through
the dryer. Because of this, thermal efficiency is highly
sensitive to the entering and exhaust air temperatures and
the ambient air conditions as indicated above. As a general
rule, drum dryers require 1500 to 1900 Btu/lb of water
evaporated for wet material (starting at 100 percent mois-
ture content on a dry basis) and 1900 to 2300 Btu/lb of
water evaporated for particles in the 20 to 30 percent
moisture range. Tube dryers are somewhat less efficient
A-9
-------
1500-
o
W t*
X fc*J
Ul ft-
g $ 1000-
fc; «
500-
AMBIENT AIR - 70°F
250*F EXH.
160CF EXH.
4-
400
-8-
4-
300 400 500 600 700 800
TEMPERATURE ENTERING DRYER, °F
Figure A-3 Energy exhausted to atmosphere
in a single-pass particle dryer.
A-10
-------
because of the large volumes of air required; these dryers
typically require 2200 to 2400 Btu/lb for wet fiber and 2800
to 3000 Btu/lb for particles with initial moisture contents
in the range of 20 to 30 percent. Typical ranges of energy
consumption for particle dryers are shown in Table A-2.
Table A-2. RANGE OF APPROXIMATE ENERGY
USE FOR DRYING PARTICLES
(unit production ion volume basis)
Inlet Exit Energy use. Energy use,
oisture, moisture, Btu/lb H20 million Btu/1000
%a %a evaporated sq. ft on 3/4" basis
Particleboard
Dry wood residues 25 5
Wet wood residues 100 5
Green chips (fiber 100 5
type board)
* Dry basis.
2000-3000 1.1 - 1.7
1600-2000 4.2 - 5.2
2000-25000 5.2 - 6.5
A-11
-------
APPENDIX B:
TERMINOLOGY OF WOOD-BASED FIBER AND
PARTICLE PANEL MANUFACTURING
B-l
-------
TERMINOLOGY OF WOOD-BASED FIBER AND
PARTICLE PANEL MANUFACTURING
Because there is some confusion regarding use of terms
describing the basic products of the industry, definitions
of ASTM are provided here. Note that the board and panel
products are grouped in two basic categories: (1) those
manufactured from ligno-cellulosic fibers and fiber bundles,
wherein interfelting of the fibers and a natural bond are
characteristic; (2) those manufactured from particles that
range in size from fine elements approaching fibers to large
flakes, which are blended with synthetic resin adhesive and
consolidated into boards known as resin-bonded particleboards
or more commonly as particleboards.
GENERAL DEFINITIONS
Wood-base fiber and particle panel materials - a generic
term applied to a group of board materials manufactured
from wood or other ligno-cellulosic fibers or particles
to which binding agents and other materials may be
added during manufacture to obtain or improve certain
properties. Composed of two broad types, fibrous-
felted and particleboards.
Fibrous-felted boards - a felted wood-base panel
material manufactured of refined or partly refined
ligno-cellulosic fibers characterized by an integral
bond produced by an interfelting of fibers and in the
case of certain densities and control of conditions of
manufacture by ligneous bond, and to which other
materials may have been added during manufacture to
improve certain properties.
B-2
-------
Particleboards - a generic term for a panel manufactured
from lignocellulosic materials (usually wood) primarily
in the form of discrete pieces or particles, as distin-
guished from fibers, combined with a synthetic resin or
other suitable binder and bonded together under heat
and pressure in a hot-press by a process in which
entire interparticle bond is created by the added
binder, and to which other materials may have been
added during manufacture to improve ce'rtain properties.
Particleboards are further defined by the method of
pressing. When the pressure is applied in the direction
perpendicular to the faces, as in conventional multi-
platen hot press, they are defined as flat-platen
pressed, and when the applied pressure is parallel to
the faces, they are defined as extruded.
Wood-cement board - a panel material where wood usually
in the form of excelsior is bonded with inorganic
cement.
Classification of Fibrous-felted Boards
Structural insulating board - a generic term for a
homogeneous panel made from lignocellulosic fibers
(usually wood or cane) characterized by an integral
bond produced by interfelting of the fibers, to which
other materials may have been added during manufacture
to improve certain properties, but which has not been
consolidated under heat and pressure as a separate
stage in manufacture, said board having a density of
less than 31 Ib/ft3 (specific gravity 0.50) but having
a density of more than 10 Ib/ft3 (specific gravity
0.16).
Hardboard - a generic term for a panel manufactured
primarily from inter-felted lignocellulosic fibers
(usually wood), consolidated under heat and pressure in
a hot-press to a density of 31 lb/ft3 (specific gravity
0.50) or greater, and to which other materials may have
been added during manufacture to improve certain
properties.
Medium-density hardboard - a hardboard as previously
defined with a density between 31 and 50 lb/ft3
(specific gravity between 0.50 and 0.80).
High-density hardboard - a hardboard as previously
defined with a density greater than 50 lb/ftJ (specific
gravity 0.80).
B-3
-------
Classification of Particleboard
Low-density particleboard - a particleboard as pre-
viously defined with a density of less than 37 lb/ftj
(specific gravity 0.59).
Medium-density particleboard - a particleboard as
previously defined with a density between 37 and 50
lb/ft3 (specific gravity between 0.59 and 0.80).
High-density particleboard - a particleboard as pre-
viously defined with a density greater than 50 lb/ft3
(specific gravity 0.80).
NOTE: It is the industry practice to measure density
of particleboards on the basis of moisture content and
volume at time of test.
TERMS RELATED TO RAW MATERIALS
The materials used for manufacturing of board and panel
products differ in both species and physical characteristics
of the furnish material. The species vary with geographical
location. In the northwestern states, typical species
include Douglas fir/ white fir, ponderosa pine, red alder,
Englemann spruce, and western hemlock. In the southeastern
states, typical species are Southern yellow pine, red oak,
yellow birch, and other hardwoods. Care is taken with all
species to remove bark from the process raw material.
The physical characteristics of the furnish vary
according to the manufacturing processes that produce it;
e.g., the furnish may take the form of chips, flakes, planer
shavings, or sawdust. Each of these forms has a character-
istic size, shape, and moisture content. As an aid in
distinguishing the various kinds of feed stock, the fol-
lowing definitions of the ASTM are provided.
Terms Relating to Wood-Base Fiber and Particle Panel Materials
Air-felting - forming of a fibrous-felted board from an
air suspension of damp or dry fibers on a batch or
continuous forming machine (sometimes referred to as
the dry or semi-dry process).
B-4
-------
Binder - an extraneous bonding agent, either organic or
inorganic, used to bind particles together to" produce a
particle board.
Chips - small pieces of wood chopped off a block by ax-
like cuts as in a chipper of the paper industry, or
produced by mechanical hogs, hammermills, etc.
Curls - long flat flakes manufactured by the cutting
action of a knife in such a way that they tend to be in
the form of a helix.
Fibers - the slender threadlike elements or groups of
wood fibers or similar cellulosic material resulting
from chemical or mechanical defiberization, or both,
and sometimes referred to as fiber bundles.
Flat-platen pressed - a method of consolidating and hot
pressing a panel product in which the applied pressure
is perpendicular to the faces.
Flake - a small wood particle of predetermined dimen-
sions specifically produced as a primary function of
specialized equipment of various types, with the
cutting action across the direction of the grain
(either radially, tangentially, or at an angle between),
the action being such as to produce a particle of
uniform thickness, essentially flat, and having the
fiber direction essentially in the plane of the flakes,
in over-all character resembling a small piece of
veneer.
Heat treating - the process of subjecting a wood-base
panel material (usually hardboard) to a special heat
treatment after hot pressing to increase some strength
properties and water resistance.
Hot-pressing - process for increasing the density of a
wet-felted or air-felted mat of fibers or particles by
pressing the dried, damp, or wet mat between platens of
hotpress to compact and set the structure by simultaneous
application of heat and pressure.
Particle - the aggregate component of a particle board
manufactured by mechanical means from wood or other
ligno-cellulose material (comparable to the aggregate
in concrete) including all small subdivisions of wood
such as chips, curls, flakes, sawdust, shavings, silvers,
B-5
-------
strands, wood flour, and wood wool. Particle size may
be measured by the screen mesh that.permits passage of
the particles and another screen upon which they are
retained, or by the measured dimensions as for flakes
and strands.
Sawdust - wood particles resulting from the cutting and
breaking action of saw teeth.
Shaving - a small wood particle of indefinite dimensions
developed incidental to certain woodworking operations
involving rotary cutterheads usually turning in the
direction of the grain; and because of this cutting
action, producing a thin chip of varying thickness,
usually feathered along at least one edge and thick at
another and usually curled.
Size - asphalt, rosin, wax, or other additive introduced
to the stock for a fibrous-felter board, prior to
forming, or added to the blend of particles and resin
for a particle board, to increase water resistance.
Slivers - particles of nearly square or.rectangular
cross-section with a length parallel to the grain of
the wood of at least four times the thickness.
Strand - a relatively long (with respect to thickness
and width) shaving consisting of flat long bundles of
fibers having parallel surfaces.
Tempering - the manufacturing process of adding to a
fiber or particle panel material a siccative.material
such as drying oil blends of oxidizing resin which are
stabilized by baking or other heating after introduction.
Wet-felting - forming of a fibrous-felted board mat
from a water suspension of fibers and fiber fundles by
means of a deckle box, fourdrinier, or cylinder board
machine.
Wood flour - very fine wood particles generated from
wood reduced by a ball or similar mill until it resembles
wheat flour in appearance, and of such a size that the
particles usually will pass through a 40-mesh screen.
Wood wool (excelsior) - long, curly, slender strands of
wood used as an aggregate component for some particle-
boards.
B-6
-------
The resins used to manufacture board products affect
both the quality of the finished product and the environ-
mental emissions. Two types of resin, urea-formaldehyde and
phenol-formaldehyde, are used for most manufacturing opera-
tions involving particleboard and medium-density board.
Urea-formaldehyde is the most common and is suitable for
interior use. Phenol-formaldehyde is used where the panel
is subjected to extreme heat or humidity or for exterior
applications. The resins are carefully "engineered" to meet
the specific needs of the manufacturing operation in terms
of the wood species and the specifications for strength,
fire resistance, moisture resistance, etc., of the finished
product.
TERMS RELATED TO FINISHED PRODUCTS
The finished products of the board and panel products
industry cover a wide range. The following list includes
the categories recognized by the ASTM.
Terms Describing Wood-based Fiber and Particle Panel
Products
Acoustical board - a low-density, sound absorbing
structural insulating board having a factory-applied
finish and a fissured, felted-fiber, slotted or per-
forated surface pattern provided to reduce sound
reflection. Usually supplied for use in the form of
tiles.
Building board - a natural finish multi-purpose struc-
tural insulating board.
Decorative hardboard - hardboard that is scored or
engraved after manufacture or by pressing during manu-
facture on a patterned caul to produce a decorative
surface.
Extruded particleboard - a particleboard manufactured
by forcing a mass of particles coated with an extraneous
binding agent through a heated die with the applied
pressure parallel to the faces and in the direction of
extruding.
-------
Hardboard underlayment - a service-grade hardboard made
or machined to close thickness tolerances for use as a
leveling course and to provide a smooth surface under
floor covering materials.
Insulating formboard - a specially fabricated structural
insulating board designed for use as a permanent form
for certain poured-in-place roof construction.
Interior finish boards - structural insulating board
with a factory-applied paint finish, fabricated in the
form of plank, board, panels, or tile for interior use.
Intermediate fiberboard sheathing - a high-density
structural insulating board sheathing product used in
frame construction under masonry veneer, siding,
shingles, and stucco.
Insulating roof deck - a structural insulating board
product designed for use in openbeam ceiling roof
construction. The product is composed of multiple
layers of structural insulating board laminated to-
gether with water-resistant adhesive.
Mat-formed particleboard - a particleboard in which the
coated particles are formed first into a mat having
substantially the same length and width as the finished
board from being flat-platen pressed.
Nail-base fiberboard sheathing - a specially manu-
factured, high-density structural insulating board
product designed for use in frame construction to
permit the direct application of certain exterior
siding materials such as wood or cement-asbestos
shingles.
Particleboard corestock - common name given to particle-
board manufactured for use as a core for overlaying.
Particleboard panel stock - common name given to
particleboard manufactured primarily for use as panel
material, and in which the surfaces may be treated to
obtain decorative effects.
Particleboard underlayment - an underlayment-grade
particleboard made or machined to close thickness
tolerances for use as a leveling course and to provide
a smooth surface under floor covering materials.
B-8
-------
Perforated hardboard - hardboard with closely spaced
factory punched or drilled holes.
Planed-to-caliper hardboard - hardboard that is machined
to a close thickness tolerance.
Prefinished wall panels - hardboards with a factory-
applied finish, such as baked-on enamel, lacquer, or
similar finish.
Prefinished particleboard - particleboard with a factory-
applied finish, such as lacquer, baked-on enamel, or
similar finish.
Roof insulation board - structural insulating board
fabricated for use as above-deck roof insulation.
Service hardboard - a hardboard of about 55 Ib/ft
(specific gravity 0.88) density intended for use where
standard strength board is not required and better
dimensional stability is desired.
Screen-back hardboard (SIS) - hardboard with a reverse
impression of a screen on the back produced when a damp
or wet mat is hot-pressed into a board and dried in the
press.
Sheathing - structural insulating board for use in
housing and other building construction, which may be
integrally treated, impregnated or coated to give it
additional water resistance.
Shingle backer - a specially fabricated sheathing-grade
structural insulating board used as a backer strip in
coursed shingle construction.
Sound-deadening board - a specially manufactured
insulating board product for use in building construc-
tion in wall and floor assemblies to reduce sound
transmission.
Smooth - two-side hardboard (S2S) - hardboard produced
from a dry mat pressed between two smooth hot platens.
Standard hardboard - hardboard substantially as manufac-
tured at the end of hot pressing, except for humidifica-
tion to adjust moisture content, trimming to size, and
other subsequent machining, and having the properties
associated with hardboard meeting specifications for
that quality product.
B-9
-------
Tempered hardboard - a hardboard subjected to tempering
as previously defined or specially manufactured with
other variation in usual process so that the resulting
product has special properties of stiffness, strength,
and water-resistance associated with boards meeting
specifications for that quality product.
Tempered service hardboard - service hardboard, as
previously defined, which as been given a tempering
treatment to improve such properties as stiffness,
strength, and water resistance.
Subcategories of Particleboard Products
Following is a summary list of particleboard subcate-
gories, based on both end use and on physical parameters of
the products.
Corestock - products of flakes or particles, bonded
with ureaformaldehyde or phenolic resins with various
densities and related properties. For furniture,
casework, architectural paneling, doors, and laminated
components.
Wood-veneered particleboard - Corestock overlaid at the
mill with various wood veneers. For furniture, panels,
wainscots, dividers, cabinets, etc.
Overlaid particleboard - particleboard faced with
impregnated fiber sheets, hardboard or decorative
plastic sheets. For applications such as furniture,
doors, wall panelings, sink tops, cabinetry, and store
fixtures.
Embossed particleboard - surfaces are heavily textured
in various decorative patterns by branding with heated
roller. For doors, architectural paneling, wainscots,
display units, and cabinet panels.
Filled particleboard - particleboard surface-filled and
sanded ready for painting. For painted end-products
requiring firm, flat, true surfaces.
Exterior particleboard - Made with phenolic resins for
resistance to weathering. For use as an exterior
covering material. See FHA UM-32 or consult manu-
facturer.
B-10
-------
Toxic-treated particleboard - particleboard treated
with chemicals to resist insects, mold, and decay
producing fungi. For tropical or other applications
where wood products require protection against insect
attack or decay.
Prime or undercoated - factory-painted base coat on
either filled or regular board - exterior or interior.
For any painted products.
Floor underlayment - panels specifically engineered for
floor underlayment. Underlay for carpets or resilient
floor coverings.
Fire-retardant particleboard - particles are treated
with fire retardants. For use where building codes
require low flame spread material, as in some schools,
office buildings, etc.
B-ll
-------
APPENDIX C
PATENT ON FULL-RECIRCULATION
DRYER SYSTEM
-------
f-!".*3&'$&!l£' tt'-.TT
3538614
5i~^r--r±^sss>
tenth
s .
sijs November,
'*v.
seventy,
nine ty-f i f th .
SS'ljCrCflS, THERE HAS BEEN PRESENTED TO THE
Coiuii*!l»»Sonov» of I^ntoniH
A PETITION PRAYING FOR THE GRANT OF LETTERS PATENT FOR AN ALLEGED
NEW AND USEFUL INVENTION THE TITLE AND DESCRIPTION OF WHICH ARE CON-
TAINED IN THE SPECIFICATION OF WHICH A COPY IS HEREUNTO ANNEXED AND
MADE A PART HEREOF, AND THE VARIOUS REQUIREMENTS OF LAW IN SUCH CASES
MADE AND PROVIDED HAVE BEEN COMPLIED WITH, AND THE TITLE THERETO IS,
FROM THE RECORDS OF THE PATENT OFFICE IN THE CLAIMANT (S) INDICATED
IN THE SAID COPY, AND WHEREAS, UPON DUE EXAMINATION MADE, THE SAID
CLAIMANT (S) is ADJUDGED TO BE ENTITLED TOAPATENT UNDER THE LAW.
NOW, THEREFORE, THESE liCtflftoM* a»«l«Owl ARE TO GRANT UNTO
THE SAID CLAIMANT (S) AND THE SUCCESSORS, HEIRS OR ASSIGNS OF THE SAID
CLAIMANT (S) FOR THE TERM OF SEVENTEEN YEARS FROM THE DATE OF THIS
GRANT, SUBJECT TO THE PAYMENT OF ISSUE FEES AS PROVIDED BY LAW, THE
. RIGHT TO EXCLUDE OTHERS FROM MAKING, USING OR SELLING THE SAID INVENTION
ROUGHQUT THE UNITED STATES.
C-2
-------
Nw. 10,1970 E. c WEIMER ETAL 3,538,614
HETHOD AND APPARATUS FOR RECYCLING DRYER STACK OASES
Flltd Sept. 9. 1968
INVENTORS
ERVIN C. WEIMER
HAROLD W. SHIDELER
STUART M. PORTER
ATTORNEYS
C-3
-------
United States Patent Office
3,538,614
Patented Nov. 10, 1970
3,538,614
KMTHOD AND APPARATUS FOR RECYCLING
DRYER STACK CASES
Ercfa C Welmcr and Harold \V. Shidelcr, Wheat Ridge,
Bill Stuart M. Porter, Denver, Colo., assignors to The 5
Stcofas-Koger Corporation, Denver, Colo., a corpora-
fiai ef Colorado
Filed Sept. 9, 1968. Ser. No. 758,412
Int. CL F2«b 3/32
US. Ct 3418 < Claims
ABSTRACT OF THE DISCLOSURE
Tfeito invention relates to an improved method and ap-
jsswiBJ for recycling dryer stack oases wherein said gases, 15
sSffloj with the solids entrained therein, are drawn off tan-
gwa&Hly from ths product-recovery cyclones and re-
Mlmd !o the system at a point within the combustion
SBae ssar the discharge end of the latter where these oxy-
JpB-Ssaa recycled stack: gases will not inhibit combustion 20
£e» S!t« ftimace, yet will combine with the primary com-
bssUiOE i;ases to produce a pre-warmed gas mixture for
define the wet pulp in the dryer that will not support com-
SittSCkra therein and is essentially inert in the sense that it
wfil aot bring about oxidative degradation of the product. 25
At She same tims, the solids are being burned to eliminate
Stem as atmospheric contaminants and their combustion
feieat fa reclaimed to assist in the drying of the oroduct.
As cwaitial fcMure of the system is that all components
Sbsrsot, together with the stack gases flowing there- 30
titfougb, to& ft'tamtained at a temperature above the dew
joint v« been abandoned. One of the most serious problems
^countered was that of (he ducts becoming clocged with
'"p dust. Undoubtedly, other problems were encoun- 00
""I to which no solution was readily apparent and.
"icrefore, further use of the recycling system became un-
Jt
-------
8,638,614
3 4
reduction in fuel obsts, and a unit of die type aforemen- tially free of entrained dust. A second induced draft fa
tuned diat results In a better quality and more consistent 44 connected into these stack ducts 42, sucks the stack
P1"**'' .. ' gases and entrained solids from the cyclones 24 before
Other oojecU will be in part apparent and in part they can enter the atmosphere and returns them to the
pointed out specifically hereinafter in connection with the . furnace 12 through a return duct 4ft at a point adjacent
detailed description of the single figure of the drawings ° the downstream end oi the combustion zone, but ahead
diat shows, somewhat schematically, a conventional ro- of the drying zone and the point at which the wet pulp
tary-drum-type pulp dryer installation equipped with the is introduced. Ducts 42 include dampers 48 that control
Hack gas recycling system of the present invention, to- the volume of gas recycled to the furnace.
fether with means for effecting automatic control thereof. 10 It has been mentioned previously that the recycled
Reference numeral 10 designates in a general way a gas and entrained solids are returned to the furnace ad-
icpresentative pulp-drying installation of the type having jacent the downstream end of the combustion zone. Since
furnace 12 connected to receive gaseous fuel through this is a critical factor in the proper operation of the
fad line 14 and discharge the hot gaseous products of recycle system, it would, perhaps, be wise to amplify
combustion into rotary-drum dryer 16 that contains the 15 some on this point
p«lp (not shown) which is to be dried. The dried product To begin with, one of the main objectives of die re-
b discharged from the dryer, in the particular installa- cycle system is to eliminate the solid pollutants whkh
tkM illustrated, into a primary product-recovery vessel would otherwise be discharged to the atmosphere. If, as
IS where it is collected from the bottom thereof. The aforementioned, we are going to get rid of these solids
moisture-laden gas from the dryer, carrying somewhere 20 by incinerating them, then, obviously, they must be re-
JB the neighborhood of 10% of the dried product, is turned to the system at a point where this will occur;
socked from die discharge end of the dryer through otherwise, they would merely continue to circulate through
damper 20 and delivered tangentially to the hollow cylin- the system in ever-increasing quantities. Thus, it becomes
drteal midsections 22 of cyclone separators 24 by in- imperative that the solids be returned to the system with-
doced draft fan 26. Most of the product remaining en- 25 in the combustion zone where it is still hot enough to
trained in the moving gas stream is separated centrifugally incinerate same. On the other hand, the stack gases carry-
m die cyclones 24 and is recoverd from the bottom there- ing these solid pollutants are substantially devoid of ozy-
cf lit die outlets of conical sections 28. Ordinarily, the gen, the oxygen content thereof running generally some-
fases, together with whatever solids remain suspended where around Vi to ITc. If, therefore, this stack gas were
flKrein diat have escaped separation in both the recovery 30 returned to the combustion zone near the upstream end
fasti 18 and the cyclones 24, are discharged to the at- thereof where the fuel and oxygen-rich primary combus-
moiphere through cyclone stacks 30. tion air enters the system, its effect would be to retard
b is to just such a pulp-drying installation as that combustion in the very area where excellent combustion
which has been described above that the recycle system is essential. Furthermore, the recycled stack gases would
of die present invention is added. The furnace section 35 tend to cool the combustion-zone if introduced near the
II la, of course, stationary and it houses the "combustion "lead" or upstream end thereof and it is essential for
sane" of the unit. The hollow cylindrical dryer drum proper combustion that the fuel flames remain quite hot
1C fa mounted for slow rotational movement about its Accordingly, it is essential that the stack gases and re-
loocltudinal axis upon trunnion blocks 32 which, in the tained solids be returned to the system far enough down-
particular form shown, lie spaced on opposite sides of 40 stream in the combustion zone where they will not re-
die fear drive therefor which has been designated by tard combustion or cool off said zone appreciably. On
numeral 34. the other hand, these recycled components must reenter
The intake end of the dryer drum telescopes over sta- the system where there is enough heat left to incinerate
tiooary tubular throat 36 at the discharge end of the the solids and, as previously stated, these requirements
*m«f* and rotates relative thereto. This tubular throat 45 are met by bringing the stack gases back into the system
is provided with a wet pulp intake tube 38 that receives adjacent the downstream or discharge end of the corn-
die wet pulp to be dried from some sort ci transport bustion zone.
mechanism (not shown) like, for example, a screw con- It so happens that returning the gases and entrained
veyor. The pulp, therefore, enters the system downstream solids to the system at this point also has distinct advan-
of die combustion zone where, as will be shown presently, so tages in terms of fuel savings. While the temperatures
the hot undiluted products of primary combustion in in the 'furnace should be quite hot to insure proper com~-
the furnace have been cooled considerably by mixing bustion, the gases used to dry the wet pulp must be con-
same with cooler stack gases preparatory to delivering siderably cooler for bca results. Therefore, in the con-
mid mixture to the drying zone within the dryer. ventional rotating-drum-type dryer installations, second-
At die discharge end of the dryer drum, a primary 55 ary air from the atmosphere is mixed with the hot gaseous
product recovery vessel 18 has been shown which, as products of combustion from the furnace to cool off the
aforesaid, separates somewhere around 90% of the dried latter preparatory to indroducing same into the drying
product from the system. While such a primary product zone. This air from the atmosphere is, of course, rich in
recovery step is desirable to reduce the cyclone load oxygen when compared with the recycled stack gases,
and thereby increase their efficiency, vessel 18 can be e!im- go and it is also a great deal cooler.
mated and the entire output fed directly to the cyclones. Use of the recycled stack gases at a temperature of
In either case, a small proportion of finely-divided solids, somewhere between approximately 240° F. and 290* F.
noaUy in the form of charred product which is not as the secondary cooling air instead of air drawn from
worth recovering, passes out the cyclone stacks with the the atmosphere at, say, 70° F., brings about significant
moisture-laden waste gases. 65 savings in fuel costs. Also, the combining of the hot
Now, die present invention contemplates the addition gaseous primary combustion products with the oxygen-
of a dryer gas recycle system to the above-described con- lean recycled stack gases results in a mixture which is
rational pulp-drying installation, said recycle system hav- substantially inert in that it will not support combustion
fag been indicated in a general way on the drawing by in the drying zone, nor will it contribute to an oxidative
reference numeral 40. Ducts 42 are connected tangential- 70 degradation of the pulp. To accomplish these ends, the
ry into die stack 30 of each cyclone 24 so as to draw recycled gases must enter the syslem ahead of the drying
off die stack gases spiralling circumferentially upward zone and ahead of the point where the wet pulp is intro-
on die inside periphery thereof that contain substantially dueed in order to cool off the primary products of com-
all of die left-over solids, that portion of the stack gas bustion to a temperature of about 1200° F. before they
circulating nearer die center of the stack being substan- 75 enter the dryer or come into contact with the pulp.
-------
3,538,614
6
Having thus described the several useful and novel fea-
tures of the instant method and apparatus for recycling
dryer stack gases, it will be apparent that the several worth-
while objectives for which the device was developed have
been achieved. Although but a single embodiment of the
invention has been illustrated and described, we realize
that certain changes and modifications therein may well
occur to those skilled in the art within the broad teaching
herein: hence, it is our intention that the scope of protec-
tion afforded hereby shall be limited only insofar as said
limitations are expressly set forth in the appended claims.
What is claimed is:
I. In combination in a pulp-drying plant: of the type
having a gas-fired furnace connected to deliver the hot
Existing drum-type pulp-drying installations commonly
provide for automatic control of the system by regulating
the amount of fuel fed to the furnace with an automatic
flow control valve 50 connected into fuel line 14. A tem-
perature responsive element 56 located in the primary
product recovery vessel in position to measure the tem-
perature of the stack gases leaving the dryer, sends infor-
mation on the temperature at this point to a suitable con-
trol mechanism that has been designated schematically by
box 54 and which functions to regulate the fuel flow so as
to keep the exhaust gas at a predetermined temperature.
Thus, an increase in wet feed material to the dryer tends
to reduce the temperature of the exhaust gases, and the
control as described functions to open the fuel valve to
satisfy the new conditions. A temperature element 52 15 gaseous products of combustion generated therein to the
housed inside the throat 36 sends information on the intake end of a drum dryer rotating about its longitudinal
temperature at this point to the control mechanism 54. This axis, means for delivering wet pulp to the intake end of
signal will act to override the basic control of the fuel. the dr.yer drum, means comprising a cyclone separator
valve should there* be a "malfunction or if. for any other for centrifugally separating the major portion of the solid
reason, the temperature in the throat exceeds a preselected 20 constituents into' a recovery vessel at the bottom thereof
value. In addition, the temperature of the moisture-laden while exhausting the gaseous constituents along with the
exhaust gases ordinarily discharged through the stacks can solids remaining suspended therein through a stack at the
be maintained at a level above the dew point until it re- top, a pneumatic convenor means including a damper-
enters the combustion zone of the system so that no con- controlled duct containing an induced draft fan connected
densation of the condensible fractions contained therein 25 to receive the gaseous products along with the solids eo-
will take place in the recirculation ductwork. Such tern- trained therein from the discharge end of the dryer drum
and deliver same tangentially to the cyclone separator, and
means for recycling the stack gases containing the major
portion of residual solids and removing the latter there-
30 from, said means including duct means having the inlet
end thereof connected tangentially into the cyclone stack
in position to draw off that portion of the exhaust gases
spiralling upwardly therein containing the major portion
of the residual solids and its outlet connected to return the
the latter. In the particular form shown herein, recirculat- 35 latter to the furnace at a point downstream of its combus*
ing fan dampers 20 and 48 control the volume of recycled tion zone where the hot gaseous products of combustion
gas returned to the furnace injesponse to a pressure-sens- will incinerate the solids and be cooled by the recycled
ing element 58 housed inside the combustion zone of the stack gases preparatory to contacting the wet pulp at the
furnace near the point at which the recycled gases enter intake end of the dryer drum, induced draft fan means
the latter. In the particular form shown, automatic damper 40 mounted in the duct means operative to draw the stack
drives 60 and 62 connected to dampers 29 and 48, respec- gases and entrai" id residual solids from the cyclone stick
lively, operate the latter in response to signals fed thereto and deliver same to the furnace, damper means mounted
from the control mechanism 54 which acts in accordance within the duct means operative upon actuation to control
with information fed thereto by the temperature and pres- the flow of recycled gas, and control means responsive 10
sure sensors. The system can,.of course, be controlled 45 the temperature of the moisture-laden gases leaving the
manually based upon this same temperature and pressure dryer drum operative to actuate the damper-controlled
perature measurement and fuel flow control is desirable
in existing pulp-drying installations, whether controlled
manually or automatically, tc maintain a uniformly dried
product
In a system like that of the instant invention where the
recycled stack gases are used as the source of secondary
air to mix with and cool the primary combustion products
from the furnace, means must be provided for regulating
50
information, and no particular novelty resides in doing
so automatically; therefore, no useful purpose would be
served by going into a detailed explanation of the auto-
matic control circuitry, especially when the apparatus nec-
essary to accomplish mannal control thereof has already
been described and illustrated.
As previously stated, the gas recirculated back through
the system will ordinarily have a temperature between ap-
proximately 240° F. and 290° F. but, in all cases, its tern-
pcrature must be above its dew point to eliminate un-
wanted condensation in the ductwork. The dew point tem-
perature, of course, varies with the pressure and degree
of saturation of the exhaust gases, a fact well-known to
any competent engineer and one, therefore, that is readily
determined under existing operating conditions.
Finally, a few words about the ductwork shown in the
^ccompanyinp drawing. The illustra'^d dryer installation
including two cyclone separators is, of course, intended as
^*'ng merely representative of many different arrange-
ments that can be used including only one or several such
"Waters, the stack cases from which are combined and
'"limed to the combustion zone. Alternatively, there is no
°°
03
duct so as to regulate the gas flow to the cyclone separator.
2. In a process for drying wet pulp of the type wherein
the hot dry gaseous products of primary combustion gen-
erated within the combustion zone of gas-fired furnace
are first cooled and passed in heat-exchange relation to wet
pulp being tumbled in a rotary drum dryer, then sucked
from the discharge end of the dryer drum and delivered
tangentially by an induced draft fan to a cyclone separator
where the major portion of any suspended solids ire
separated therefrom centrifugally and collected and finally
discharged by circulating same up the cyclone stack, the
improved method for removing any residual solids left in
the exhaust gases while using the latter to cool the hot
gaseous products of primary combustion which comprises:
drawing off the exhaust gases tangentially from the cyclone
stack so as to divert that portion thereof containing most
of the residual solids suspended therein and delivering
same to the furnace downstream of .the combustion zone,
said exhaust gases being allowed to cool to a temperature
no less than the dew point thereof before reentering the
furnace, said exhaust gases being mixed with the hot dry
gaseous product of primary combustion to cool the latter
*'«J for introducing the recirculated gases through a sin- -n and form a substantially inert oxygen-lean mixture there-
^< return duct 46. In fact, a better balanced system would with that will not support combustion in the dryer drum.
nly result if the flow of recycled gases was split and
| I'oJuced into opposite sides of the furnace, the return
---i on the back side being hidden by the one shown, but
""! functionally identical thereto.
and said suspended residual solids being incinerated by
said hot gaseous products of primary combustion.
3. The method as set forth in claim 2 in which: the
75 exhaust gases arc cooled to a temperature between ap-
-------
3,538,614
proximately 240* F. and 290* F. but no lower than the
dew point thereof before reentering the furnace.
4. The method as set forth in claim 2 in which: volume
and temperature of the exhaust gases are controlled in
relation to the volume and temperature of the hot gaseous
products of primary combustion such that the mixture
thereof enters the dryer drum at a temperature of approxi-
.mttely 1200* F.
5. The method as set forth in claim 4 in which: the
exhaust gases are allowed to cool to a temperature no less
than the dew point thereof before reentering the furnace.
f. The method.as set forth in claim 4 in which: the
exhaust gases are cooled to a temperature between approxi-
8
mately 240* F. and 290* F. but no lower than the dew
point thereof before reentering the furnace.
References Cllcd
5 UNITED STATES PATENTS
2,129,673 9/1938 Burns 1 34131 X
2,143,505 1/1939 Arnold 3428
2,715,283 8/1955 Halldorsson 3479
10 EDWARD J. MICHAEL, Primary Examiner
3479.131
US. CL XR.
07
-------
IN THE UNITED STATES PATENT OFFICE
Applicant : Ervln C. Welmer et ol Examiner i EJ. Michael
Serial No. : 758,412 " Pope- No. i 3
Filed t September 9, 1968 Group i 344
For j METHOD AND APPARATUS FOR Denver, Colorado
RECYCLING DRYER STACK GASES February 9, 1970
Hon. Commissioner of Patents
Washington, D.C. 20231
Sir:
AMENDMENT
Responsive to the Office action of November 12, 1969, please enter
the following amendments:
In the Claims;
Rewrite claim 4 In Independent form as follows.
4. (Amended) In combination In a pulp-drying plonf: of the type
having a gas-fired furnace connected to deliver the hot gaseous products of combustion
generated therein to the Intake end of a drum dryer rotating about Its longitudinal axis,
means for delivering wet pulp to the Intake end of the dryer drum, means comprising a
5 cyclone separate for centrlfugally separating the major portion of the solid constituents
Into a recovery vessel at the bottom thereof while exhausting the gaseous constituents
*"* T
along with the solids remaining suspended therein through a stack at the top, 'and' a
pneumatic conveyor means Including a damper-controlled duct containing an induced draft
fan connected to receive the gaseous products along with the solids entrained therein
10 from the discharge end of the dryer drum and deliver same tangentially to the cyclone
separator, 'the Improved apparatus] and means for recycling the stack gases
%* «4 ^^^"^i^^^*""
containing the major portion of residual solids and removing the latter therefrom,
r- -t
[which comprises:; sold means Including duct means having the Inlet end thereof
connected tongentlally Into the cyclone stack In position to draw off that portion of
08
-------
Applicant i Ervln C. Welmer et al
Serial No. t 758,412
-2-
15 the exhautt gases spiralling upwardly therein containing the major portion of the
reitdual solid* and Its outlet connected to return the latter to the furnace at a point
downstream of Its combustion zone where the hot gaseous products of combustion
will Incinerate the solids and be cooled by the recycled stack gases preparatory to
contacting the wet pulp at the Intake end of the dryer drum, Induced draft fan means
20 mounted in the duct mean* operative to draw the stack gases and entrained residual
wilds from the cyclone stack and deliver same to the furnace, [and'damper means
mounted within the duct means operative upon actuation to control the flow of
recycled gas, and The improved stack gas recycling apparatus as set forth In
^m B^^H ^M>
Claim 1 which includes: 1 control means responsive to the temperature of the
25 moisture-laden gases leaving the dryer drum operative to actuate the damper-controlled
duct so as to regulate the gas flow to the cyclone separator.
6. (Amended) In a process for drying wet pulp of the type wherein
the hot dry gaseous products of primary combustion generated within the combustion
zone of a gas-fired furnace are first cooled and passed in heat-exchange relation to
wet pulp being tumbled In a rotary drum dryer, then sucked from the discharge end
5 of the dryer drum and delivered tangent lolly by an -induced draft fan to a cyclone
separator where the major portion of any suspended solids are separated therefrom
centrlfugally and collected and finally discharged by circulating same up the cyclone
stack, the Improved method for removing any residual solids left in the exhaust gases
while using the latter to cool the hot gaseous products of primary combustion which
10 comprises: drawing off the exhaust gases tangcntlally from the cyclone stack so as
to divert that portion thereof containing most of the residual solids suspended therein
and delivering same to the furnace downstream of the combustion zone, nhe method
C-9
-------
Applicant t Ervln C. Weimer etal
SwlalNo. t 758,412
-3-
ei Ml forth in Callm 5 In whlch:?the| Mid exhaust gases[are! being allowed to
cool to a temperature no leu than the clew point thereof before reenterlng the
15 furnace, said exhaust gates being mixed with the hot dry gaieous product of primary
combustion to cool the latter and form a substantially inert oxygen-lean mixture
therewith that will not support combustion In the dryer drum, and said suspended
residual solids being Incinerated by said hot gaseous products of primary combustion.
Claim 8, line 1;
Delete "Claim 5" and substitute Claim 6 .
Cancel claims 1-3 and 5 without prejudice.
REMARKS
Claim 4 has been rewritten In Independent form as suggested and
claim 6 has also been rewritten as an Independent claim. Claims 1-3 and 5 have
been cancelled without prejudice.
.Amended claim 4 Is essentially original claim 1 plus old claim 4.
The form was changed to a combination claim to provide a better antecedent basis
for the words of old claim 4. Since old claim 4 was Indicated allowable if rewritten
In Independent form, amended claim 4 should now be allowable.
Claim 6 as rewritten is essentially original claim 5 plus the words of
Original claim 6. The method claimed in amended claim 6 Is not anticipated by an/
of the three cited references.
The method as now claimed definitely requires the recycled gases to
remain at all rimes above the dew point temperature. Neither Halldorsson, Arnold
nor Burns disclose this requirement. In fact, In Halldorsson It Is specifically
provided that the recycled gaset will condense In the wash tower W. Column 6,
lines 24-39. Furthermore, none of the references even touches on the problems
O10
-------
Applicant i Ervln C. Welmer et ol
total No. t 758,412
ouoclated with condensate fanning on the Inside wallt of the return duct
work.
At stated by the Examiner, there will obviously be tome cooling of
MM recycled gates In all of the devices disclosed by the cited references. The value
to which cooling Is permitted In applicants' device, however, Is very critical and,
contrary to the Examiner's statement, Is one of the primary novel features of
applicants' Invention. It was the exact problem of condensate forming on the inside
of the ductwork, not at all considered in Halldorston, Arnold or Burns, which applicants
Mf out to solve. It Is submitted that applicants' Invention has solved this problem In
a manner not taught or anticipated by the references.
Claims 7-10 are re-submitted for consideration in view of the above
remarks and Inasmuch as they ore merely narrower limitations on amended claim 6.
Based on the above remarks, it Is believed that amended claims 4,
6 and 8 and original claims 7, 9 and 10 ore in condition for allowance and prompt
action to this end will be appreciated.
Respectfully submitted,
ANDERSON, SPANGLER & WYMORE
Edwin I. Spongier, Jr.
Area Code 303
292-9292
ELS>»8
C-ll
-------
APPENDIX D
SUMMARY DATA SHEETS FOR 76
PARTICLE AND FIBER DRYERS
D-l
-------
a
1
to
DRYER NO.
PROCESS: HARDBOARD (FIBERS)
PARTICIEBOARD (PARTICLES)
DRYER TYPE: TUBE (INLINE)
FLASH
STATIONARY DRUM
ROTARY SINGLE PASS DRUM-
ROTARY TRIPLE PASS DRUM-
DRYER SYSTEM: SINGLE DRYER
1st DRYER IN SERIES
2nd DRYER IN SERIES
YEAR INSTALLED:
FURNISH: SURFACE
CORE
MATERIAL FEED RATE (LBS/HR DRY BASIS)
INLET MOISTURE (2)
EXIT MOISTURE (?)
EXIT GAS TEMP. (°F)
EXIT GAS FLOW RATE (ACFM x 1000)
MOST COW-ION SPECIES
MATERIAL SIZE RANGE
PRIMARY ENERGY SOURCE
SECONDARY ENERGY SOURCE
BACKUP ENERGY SOURCE
NON RECYCLE SYSTEM
PARTIAL RECYCLE SYSTEM
FULL RECYCLE SYSTEM
UNCONTROLLED SYSTEM: LBS/HR
gr/SDCF
OPACITY (%)
CONTROLLED SYSTEM: WET SCRUBBER
FULL RECYCLE
PARTIAL RECYCLE
MED. EN. SECONDARY CYC.
MULTIPLE CYCLONES
FABRIC FILTER
OTHER
COST OF CONTROLLED CAPITAL (1000 $)
SYSTEM: OP. EXPENSE (1000 $)
ANNUAL KAINTEHANCE (S)
ENERGY REQUIREMENTS: (HORSEPOWER)
CONTROLLED EMISSIONS: gr/SDCF-
EMISSION TEST KETHOO: HI-VCLUKE
EPA METHOD 5
S - 8 VENEER DRYER
/
^_
**
Hono.
HO. 5 '00
to -HO
10 -if
3C.S
O. Ft*
*»*>«,
itotero «
67>MlO
*-
39S n
0.072.
v*~~
e
^
is
~
Hono.
10.500
IO
SiO
ZOO +
P. Ml
*t->"
3
,^-
*
/torro
to, foo
/O
P.F/f
S/WA a»tr
aef.iaoao
< 10
t
£=
^
fc±
HOMO.
,5ltoo
'$'_'/
ZSO - too
its
P.Fl*.
srn
*1AT. CIS
^
10 "
21S" TV1
f
tZ=~
«^-
*""""
ff, 1 00
*"- 5
P.Fl*
57V,
t~~
i^
n
«.-«04ye<5
£
7^
i*
*~~
-
/5V too
/1-/S
/tf
O.F/4,
vr,,
-
^
*y.*.<7
t.f.f.p?
7
7^
«^
HOMO.
15. too
it-is
V-f
ISO- too
I&S
O.FiH
STSAff
Ai*7. MS
^-
iC *V^«.<
6
£=
t~-
4=^
Hono.
3l^oo
te-so
ite-ito
it.e
O. f/A.
U4T. i,A3
&J*. STK.
:n*
1
z^
t
*" ""
Horro.
v seo
40- fO
a.F/*
M7.44S
ALA. S7K.
OlESEL
0./67
^,
0.011
1C
1^-
t^~
fc^
Hone.
10,000
36- 60
H- 5"
o. fin.
SftuQ. OrST
^~
ffO TO
a.it-1
4*-
//
-^
*-^
1^
Ho no.
f.OOO
i-5
O.f/t
MiM. OViT
^^
f1
O.I'S'L
*»-
/2
1^.
«"
*^I
riono.
/ti.OOO
H-/S
S.t> SCfft
P.FI/l
S4AM /Wir
&^
0.08
*^-
-------
a
1
OJ
DRYE.R NO.
PROCESS: HARDBOARD (FIBERS)
PARTICLEBOARD (PARTICLES)
DRYER TYPE: TUBE (INLINE)
FLASH
STATIONARY DRUM
ROTARY SINGLE PASS DRUM-
ROTARY TRIPLE PASS DRUM-
DRYER SYSTEM: SINGLE DRYER
1st DRYER IN SERIES
2nd DRYER IN SERIES
YEAR INSTALLED:
FURNISH: SURFACE
MATERIAL FEED RATE (LBS/HR DRY BASIS)
INLET MOISTURE (2)
EXIT IIOISTURE (%)
INLET GAS TEMP. (°F)
EXIT GAS TEMP. (°F)
EXIT GAS FLOW RATE (ACFM x 1000)
KOST COW-ION SPECIES
MATERIAL SIZE RANGE
PRIMARY ENERGY SOURCE
SECONDARY ENERGY SOURCE
BACKUP ENERGY SCURCE
NON RECYCLE SYSTEM
PARTIAL RECYCLE SYSTEM
FULL RECYCLE SYSTEM
UNCONTROLLED SYSTEM: LBS/HR
gr/SDCF
OPACITY (£)
CONTROLLED SYSTEM: WET SCRUBBER
FULL RECYCLE
PARTIAL RECYCLE
MED. EN. SECONDARY CYC.
MULTIPLE CYCLONES
FABRIC FILTER
OTHER
COST OF CONTROLLED CAPITAL (1000 $)
SYSTEM: CP. EXPENSE (1000 $)
ANNUAL MAINTENANCE (S)
ENERGY REQUIREMENTS: (HORSEPOWER)
CONTROLLED EMISSIONS: gr/SDCF
EMISSION TEST METHOD: HI-VOLUHE
EPA METHOD 5
S - 8 VENEER DRYER
Ai
*^-
*
!^f~
IS~
ti. OOO
so
25-T>O
t&O
tea
O.F/A
sr//
MAT. 6/U
PAOPAUZ
l**~
1
^y
«
**-
* -
^
1L.O0O
S~O
is- yo
VBO
/BO
O.F,*.
57V/
XW. 6*1
fAOPAUC.
i
^
/}
fc
i, '
4^
*-
fl.OOO
GO
Z.S- Jtf
f&O
tQO
£>.?/*
sr/r
MA7. <*/lS
fAopAum.
t^
**-
/*
t^-
*--
fc^-
«^
ll.OOO
ff(3
zr-3tf
t&o
/e>o
O.Fl*.
yrn
A/47, sas
f>Aj>pnan.
i^~
t^-
17
A*~
fc*-
<*
HI. ooo
15- 30
f
VBO
ieo
30.t Sfiffi
f>. Ft*.
yrn
*»t7. 64A
tAOfAue.
4-^-
t
0.0&
1^
/B
*-
i
i^~
11. ooo
ts-so
5~
fBO
teo
O.&*.
>Tft
*J/t7. 6tS
MOPHUG.
t^-
~-
/7
f
1^-
&~-
HI. 000
Z"i-T>0
tr
tBO
l 8>O
0-P/4
srrt
UKT.iAS
1
IS*
10
«-~
I-
l^-
VI, ooo
15- SO
5
V9O
/BO
O.f/*
STfl
NAT.
Q.Fi*.
STM
U*~
23
t
*^-
4^-
/1T/
HOrfO.
20-30,000
2O- dO
5-6
lfea-/6OO
il-j-LiS
li.iscrti
O.FIA.
54AU7. 0uS7
UffT. 6*1
FUKL. at.
l**"
i3.5O
too
*^
2V
*^
I*-"
t*~
/ns
r^
tt-l6,»9O
1S-BS
/O
*fO
no
v
-------
D
WTER TO
PROCESS: HARD50ARD (FIBEPS)
PARTICLEBOARD (PARTICLES)
DRYER TYPE: TUBE (IMI',1)
FLASH
STATIONARY DRUM
ROTARY SINGLE PASS DRUM-
ROTARY TRIPLE PASS DRUM-
DRYER SYSTEM: SINGLE DRYER
1st DRYER I'l SERIES
2nd DRYER IN SERIES
YEAR INSTALLED:
FURNISH: SURFACE
MATERIAL FEED RATE (LBS/HR DRY BASIS)
INLET MOISTURE (?)
EXIT MOISTURE (I)
INLET GAS TEMP. (°F)
EXIT MS TEKP. (°F)
EXIT GAS FLOW RATE (ACFM x 1000)
MOST COMMON SPECIES
MATERIAL SIZE RANGE
PRIMARY ENERGY SOURCE
SECONDARY ENERGY SOURCE
BACKUP ENERGY SOURCE
NON RECYCLE SYSTEM «
PARTIAL RECYCLE SYSTEM
FULL RECYCLE SYSTEM
UNCONTROLLED SYSTEM: LBS/HR
gr/SPCF
OPACITY (2)
CONTROLLED SYSTEM: WET SCRUBBER
PARTIAL RECYCLE
MED. EN. SECONDARY CYC.]
MULTIPLE CYCLONES ]
FABRIC FILTER ......
OTHER
COST OF CONTROLLED CAPITAL (1000 S)
SYSTEM: OP. EXPENSE {1000 $)
ANNUAL Itt I [ITERANCE (S)
ENERGY REQUIREMENTS: (HORSEPOWER)
CONTROLLED EMISSIONS: gr/SDCF
EMISSION TEST METHOD: hi -VOLUME
EPA METHOD 5
S - 8 VENEER DRYER
Z»
^
t*-
*s~
I1T5
/V-/i,0o0
Hf-Bf
&-H
HSO
HO
s/ SCFH
£>./=/*
urn. m
PKOPAUL
rn»7 aieo
O.It
<.IO
Z6
4^
\s
lit?
H3>
!2-oO
Zo S~
2V
Af/4.
SAuo.eon
0147. 6A£
#IOMJ£.
l^-
t^~
21
SOOO
O.Oi
io
. *
1*-
I*-
V3
/1-lS
&OO
/&o
8.7 xfn
O.F/H.
ST
NtST. C9S
flAoMJJi
V
1000
0.0. fJUK.
IfTfAft
*^-
;
Q
31
^
t^
1170
i---
ZO.ooo
B-IO
f-&
2.1.0
P. fine.
«tT£AM
/
o
1^-
3Z.
l^~
r-
is-
/47O
l^~ '
2tf, ooo
*-5
3-V
/7 "=T
f>. 0JAJ&
yns-An
2.
0
**
J±
t^
t^
is'
1170
^-~
2,O,OOO
t-&
a-v
/7S-
f. />/*/£.
ST£Aff
1
a
*^
jv
f
^~
V
I17O
)S,eoo
0-/0
3-y
3>00
I&O
P. PiUK.
an. STX.
OIL,
L^
2.
.fr*je.
OIL.
l*~
2.
s
\^
f
JfOHO.
3. OOO
i>sr
/6
3iS- 3VC
/as-
/3
0, PttJC.
S>T£4ff
O.OH
O
...^
-------
a
1
BRYw NO. 37 ZB 31 HO yy
PROCESS: HARDBOARD (FIBERS)
PARTICLEBOARD (PARTICLES)
DRYER TYPE: TUBE (INLINE)
FLASH
STATIONARY DRUM
ROTARY SINGLE PASS DRUM-
ROTARY TRIPLE PASS DRUM-
DRYER SYSTEM: SINGLE DRYER
1st DRYER IN SERIES
2nd DRYER IN SERIES
YEAR INSTALLED:
FURNISH: SURFACE
MATERIAL FEED RATE (LBS/HR DRY BASIS)
INLET MOISTURE i)
EXIT MOISTURE %}
INLET GAS TEMP. °F)
EXIT GAS TEMP. °F)
EXIT GAS FLOW RATE ACFM x 1000)
MOST COMMON SPECIES
MATERIAL SIZE RANGE
PRIMARY ENERGY SOURCE
SECONDARY ENERGY SOURCE
BACKUP ENERGY SOURCE
NO'N RECYCLE SYSTEM
PARTIAL RECYCLE SYSTEM
FULL RECYCLE SYSTEM
UNCONTROLLED SYSTEM: LBS/HR
gr/SDCF
OPACITY (%)
CONTROLLED SYSTEM: WET SCRUBBER
PARTIAL RECYCLE
MED. EN. SECONDARY CYC.
MULTIPLE CYCLONES
FABRIC FILTER
COST OF CONTROLLED CAPITAL (1000 $)
SYSTEM: OP. EXPENSE (JOOO $)
ANNUAL MAINTENANCE (S)
ENERGY REQUIREMENTS: (HORSEPOWER)
OPACITY (!}
EMISSION TEST METHOD: HI-VOLUME
EPA METHOD 5
S - 8 VENEER DRYER
v
f
«-"
Mono,
3,000
is"
J6S
/3
P. AAHI
^^^
a ^s
a
^^
ir
*<-
t^
Hona,
3. coo
-^j-
Ai?6~?°
/*J
P. PitJS.
S7fl
O.OS
^^
K^
JX-
<*-
//«»*.
£, 10O
35"
ZVO -36O
//
/*. PifJ&
37/T
o.o z.
a
^*"
£=
t^~
t
it&H
liOHO.
20*5.000
3-S"
160-2.00
33
P. f. f/4
M*6**
10-ZO
^*"
l^-
1371
Horto.
'i.i.^ffO
8
?/0'."°0
1.1
P.Fl*.
»«* ^
IO-LO
^
t^'
*~
/97/
i
IS- So. eeo
tS--/8
S-7
leO-HOO
/SO -/iO
7/
D.Fl*.
SA*>fi DtifT
ItT. C«S
O-06 - 041
< IO
"
^
^^
""
/ 97/
*o-fo.ooo
/S-s0
ff-7
zoo -v
-------
D
I
CTi
DRIER NO. m SO 5Y 5Z 53 5t »5 A 6 57 -=» » 37 6O
PROCESS* HARDBOARD (FIBERS)
PARTICLEBOARD (PARTICLES)
DRYER TYPE: TUBE (INLINE)
FLASH '
STATIONARY DRUM
ROTARY SINGLE PASS DRUM-
ROTARY TRIPLE PASS DRUM-
DRYER SYSTEM: SINGLE DRYER
1st DRYER Id SERIES
2nd DRYER IN SERIES
YEAR INSTALLED:
FURNISH: SURFACE
MATERIAL FEED RATE (LBS/HR DRY BASIS)
INLET KOISTUPE (")
EXIT HOISTURE (£)
INLET GAS TEMP. (°F)
EXIT GAS TEMP. (°F)
EXIT GAS FLOW RATE (ACFM x 1000)
HOST COMMON SPECIES
MATERIAL SIZE RANGE
SECONDARY ENERGY SOURCE
BACKUP ENERGY SCURCE
NON RECYCLE SYSTEM
PARTIAL RECYCLE SYSTEM
FULL RECYCLE SYSTEM
UNCOMTROLLED SYSTEM: LBS/HR
gr/SDCF
OPACITY (%)
CONTROLLED SYSTEM: WET SCRUBBER
PARTIAL RECYCLE
MED. EN. SECONDARY CYC.
MULTIPLE CYCLONES
FABRIC FILTER
OTHER
COST OF CONTROLLED CAPITAL (1000 $)
SYSTEM: CP. EXPENSE (1000 $)
ANNUAL I-'AINTENANCE ($}
ENERGY REQUIREMENTS: (HORSEPOWER)
CONTROLLED EMISSIONS: gr/SDCF
EMISSION TEST METHOD: HI-VOLUKE
EPA METHOD 5
S - 8 VENEER DRYER -1
*^
«-
^
(ITi
Pte. p«yeti
09, ceo
so
/S--/8
£00 ~ 9ta
220 -11.5
17
e.Fte.
SA*J0. OJi.7
MT. 6AS
r~
fM. necve.
O./d
- i^~
«^
^
l^~
J97f
ntwn
(tO, OO O
A O
'?-/e
660-100
iia-i
«8
0.f/X
s*-a.ojsr
tjft,-. &as
*-^
fan nntyc.
O.01
**""
*-^
*--
*^-
lltf
2O-5O, OOQ
S-7
Ilt-Jtff
2.2.
P.F-S*
stue. Mil
#4T, 6AS
^
9S"
SO
a.of
i**
^
i**
t-
as-o
ISO
l.f scfri
PifJK
yrtAH
i^
O.O Si
O
^
fc^
1^-
l*~
/* '73
i^^
Sooo
2Z.
6(7
^7
f>j*)e.
snwauiT
attr. Ms
FUEL ait.
t^-
^
*~
t-
t*-
/?73
*-- .
LO, OOO
\ \
s-
tss-
t/.3 scfff
fwt
tnrlscAUt
*")7. C/&
FU&L OIL
t
t^
ISO
0-OZ1
l^
*-
IS~
*--
/»/J7
i
2V, OOO
Ji.
9
llf
3V.$~
0/*J£
ID fTe&N
Ufff. 6/IS
Fi/Ei. Oft.
Sf&jo. acn
l^-
-
o.ooi
~~ zo
v^
t^
*--
4.^
/9&7
i^
iV. 000
*?
/if
S7.S-
f/AJf.
t /res*
A>/)7. 6AS
fjei- an.
z&oe, omT.
t
o.ooS"
-v T.Q
i^"
i^
^
'
t-*'
US')
HOHO
if. OOO
G n
n o
7
/5~1
ft.OSlff,
Mteuoto
UHT.tAS
PAOfAfJZ
^
^
soo
7f00
HSQ
o.ozf
^
r
»^-
f-
115 t
Mono.
15,000
,£/)
7
tBO
«6.0 SCfft
HMeuo&s
nor, CAS
PAOPAat
t^-
V
foo
75~OO
t?0
O, O6Z
i^-
i*~
<--
*--
HT4
ti, ooo
fif
3
Sao
2.OO
f>i*ie.
< »/t "
Mae- Olli T
fJaf. fvCL.
am. S7A
H0?o
S-/0
n /SIA.
foo
/!«-
*-
*-^
t^
/97f
It. 000
& C?
3
&00
z.o a
fj/jt.
< Vi"
tA^o.aan
ttm. fvej.
OL.1. 37X
*O?t
5-/0
Te &LX
5V 0
/zr
-------
D
1
DHHS HO. / 62 fj *T *» if, 67 6« 67 7O 7/ 72.
PROCESS: HARDBOARD (FIBERS)
WRTICLEBOARO {PARTICLES)
DRYER TYPE: TUBE (INLINE)
FLASH
STATIONARY DRUM
ROTARY SINGLE PASS DRUM-
ROTARY TRIPLE PASS DRUM-
DRYER SYSTEM: SINGLE DRYER
1st DRYER IH SERIES
2nd DRYER IN SERIES
TEAR INSTALLED:
FURNISH: SURFACE
MATERIAL FEED RATE (LES/HR DRY BASIS)
INLET MOISTURE S)
EXIT MOISTURE *)
INLET GAS TEKP. °F)
EXIT GAS TEKP. °F)
EXIT GAS FLOW RATE ACFM x 1000)
MATERIAL SIZE RAt.'GE
PRIMARY ENERGY SOURCE
SECONDARY ENERGY SOURCE
BACKUP ENERGY SOURCE
NON RECYCLE SYSTEM
PARTIAL RECYCLE SYSTEM
FULL RECYCLE SYSTEM
UNCONTROLLED SYSTEM: LBS/HR
gr/SDCF
OPACITY (£)
CONTROLLED SYSTEM: WET SCRUBBER
PARTIAL RECYCLE
KED. EN. SECONDARY CYC.
MULTIPLE CYCLONES
FABRIC FILTER
OTHER
COST OF CONTROLLED CAPITAL (1000 $)
SYSTEM: OP. EXPENSE (1000 $)
ANNUAL KAIIITEMANCE (S)
ENERGY REQUIREMENTS: (HORSEPOWER)
OPACITY (J}
EMISSION TEST METHOD: HI-VOLUME
EPA METHOD 5
S - 8 VENEER DRYER
*«
i**
*<
1110
*
6.S-OO
10
iS
6OO
ZOO
Pjut.
<^a"
MiJO.aasT
HOG. n>et
AIM. STA.
*^
0
CXC-LOHG.
100
SO
H*
^~
t^
/17i
Mono.
S,OOO
BO
f
too -/ooo
as
a.o se&i
SHUiOttT
fae.L. OIL.
i^
^
2.OO
**
^
*^-
/?7i
MOttO.
t.ooo
f.O
S
too - BOO
//O
/S4 sefff
PlM4. SMAV
£U£lr 4V4
t^
l^'
?t)O
.ai.B
"
i^
t^
i^
/<»73
HOHb.
ll.ooo
si
5-
6Zf
220
s-»
ffafQu>eaai
~P/*J£S "
UV,6AJ
FVBL OIL.
^*"
£l- &l-
t^
0.6M
iOO
&>^
.K-
*^
IS '
/*7J
HOM0.
/Z.OOD
5V
S
tfz.r
ZZd
s-f
/fMfioeooS
"FMJCS "
U4T. 6AS
fU£L &t.
!**
I.SZi.
/oo
^
r~
t^
*»
int
/JOffO.
n.soo
0i
*i2>
ZOO
no
/dr. 7
HtoOUOtOS
<>/l"
STfl
Z0>o
SKirfrl&t
SO
o
*- 1 *^
* -
f
ino
Horfa.
IZ. fOO
82-
ts
300
z?a
/f. 7
yafoiyaaa;
< '/*"
S7VT
ZO Ja
SXtrtire*
SO
O
*--
»^-
I17O
Hofia.
12., soo
Bi.
yj
34O
1.70
/s~.y
^M*M»a*.
STf
W?o
sKittirex
fo
0
i^-
f
tS
1110
HOMO.
IZ, S~00
H2i
5~
37T
17 O
If. 7
<'/£"
Ufff. 6fiS
PRoPAAlf
}/
l*-
,
62.
l?0
F LAj/M*
0
*^
V
V~
I17O
Horfd.
n. foo
V3
5-
375"
/7O
/S.7
< '/i"
?/tOffrJ£
1^-
t
Bi.
/s-c
-luuSu*
0
»*~
ts-
r
/17O
Mont.
/Z* FOO
V3
S
37S"
/7ff
/S~.7
Hinouteoas
MffT.OU
AtaMtU.
k*
i^-
&2-
/SO
7 UK/44
0
-------
o
J
oo
PROCESS: HARDBOARD (FIBERS)
PARTICLEBOARD (PARTICLES)
DRYER TYPE: TUBE (INLINE)
FLASH
STATIONARY DRUM
ROTARY SINGLE PASS DRUM-
ROTARY TRIPLE PASS DRUM-
DRYER SYSTEM: SINGLE DRYER
1st DRYER III SERIES
2nd DRYER IN SERIES
YEAR INSTALLED:
FURNISH: SURFACE
CORE
MATERIAL FEED RATE (LBS/HR DRY BASIS)
EXIT IIOISTURE («)
INLET GAS TEMP. (°F)
EXIT GAS Te^P. (°F)
EXIT GAS FLOW RATE (ACFH x 1000)
MATERIAL SIZE RANGE
PRIMARY ENERGY SOURCE
SECONDARY ENERGY SOURCE
BACKUP ENERGY SOURCE
HON RECYCLE SYSTEM
FULL RECYCLE SYSTEM
UNCONTROLLED SYSTEM: LBS/HR
gr/SDCF
OPACITY (%)
CONTROLLED SYSTEM: WET SCRUBBER
FULL RECYCLE
PARTIAL RECYCLE
MED. EN. SECONDARY CYC.
MULTIPLE CYCLONES
FABRIC FILTER
OTHER
COST OF CONTROLLED CAPITAL (1000 $)
SYSTEM: OP. EXPENSE (1000 $)
ANNUAL KAIFITENAKCE (S)
ENERGY REQUIREMENTS: (HORSEPOWER)
OPACITY (X)
EMISSION TEST METHOD: HI-VOLUME
EPA METHOD 5
S - 8 VENEER MYEft
*»
fr
i^-
ll&O
HOMO.
12.000
25 '-*0
60O
/A
r< v*"
MO. & OIL
*---
/*
o
**
Ir-
t*~
f
!<)&O
tfOHO.
tl.o&O
ZS--VO
&OO
/S
*%'!%?
A/9. & 61 i.
l*~
/v
0
«-
*
*»-
<^-
it&S
Harta
li.OOO
6
no -loo
ww^qal
tan. 6 a/t.
i~-
/7
£>
*^-
^~
**
t^-
/9A5"
HOrtO
12,000
&>
no -too
<»/y"
100.6 OIL.
\^
11
o
^
-------
APPENDIX E
PARTICLEBOARD AND
MEDIUM-DENSITY FIBERBOARD
MANUFACTURING PLANTS
E-l
-------
1. Giles & Kendall/ Incorporated
Maysville, AL
2. Louisiana Pacific Corporation
Post Office Box 246
Clayton, AL 36016
3. Louisiana Pacific Corporation
Eufalla, AL
4. MacMillan Bloedel Particleboard, Incorporated
Pine Hill, AL
5. Olinkraft, Incorporated
Monroeville, AL
6. Southwest Forest Industries, Incorporated
Box 1809
Flagstaff, AZ 86001
7. Georgia Pacific Corporation
Post Office Box 520
Crossett, AR 71635
8. International Paper Corporation
Post Office Box 610
Malvern, AR 72104
9. Singer Company
Main Street
Trumann, AR
10. Wynnewood Products Company
Division of Permaneer Corporation
Post Office Box 685
Hope, AR 71801
11. American Forest Products
Highway 49
Martell, CA 95654
12. Big Bear Board Products
Division of Golden State Building Products
Box 1028
Redlands, CA 92373
13. Champion International
Box 2317
Redding, CA 96001
E-2
-------
14. Collins Pine Company
Box 796
Chester, CA 96020
15. Fibreboard Corporation
4300 Dominguez Road
Rocklin, CA
16. Georgia Pacific Corporation
2163 North State Street
Ukiah, CA 95482
17- Hambro Forest Products
Post Office Box 129
Crescent City, CA 95531
18. Humboldt Flakeboard
Drawer CC
Arcata, CA 95521
19. Louisiana Pacific Corporation
Arcata, CA
20. Sequoia Board, Incorporated
Post Office Box 906
Chowchilla, CA 93610
21. Georgia Pacific Corporation
Box 187
Vienna, GA 31092
22. Temple Industries, Incorporated
Thompson, GA
23. Weyerhaeuser Company
Box 547
Adel, GA 31620
24. Potlatch Forest Corporation
Post Office Box 786
Post Falls, ID 83854
25. Swain Industries, Incorporated
1001 West Second Street
Seymour, IN 47274
E-3
-------
26. Tenn-Flake Corporation
Industrial Park
Middlesboro, KY 40965
27. Duraflake South, Incorporated
Division of Willamette Industries, Incorporated
Simsboro, LA 71275
28. Louisiana Pacific Corporation
Box 26
Urania, LA 71480
29. Olinkraft Particle
Lillie, LA 71256
30. Champion International
Gaylord, MI 49735
31. Blandin Wood Products Company
Box N
Grand Rapids, MN 55744
32. Cladwood Company
Division of Forest Products Sales Company
Box 3
Virginia, MN 55792
33. Champion Internation
Route 7-N
Oxford, MS 38655
34. Georgia Pacific Corporation
Box 309
Louisville, MS 39339
35. Georgia Pacific Corporation
Box 627
Taylorsville, MS 39168
36. Kroehler Manufacturing Company
Box 4176, West Station
Meridian, MS 39301
37. Evans Products, Incorporated
Drawer L
Missoula, MT 59801
38. Plum Creek Lumber Company
Post Office Box 160
Columbia Falls, MT 59901
E-4
-------
39. Ponderosa Products, Incorporated
1701 Bellamah, N.W.
Box 813
Albuquerque, MM 87103
40. Carolina Forest Products, Incorporated
King Street
Wilmington, NC 28402
41. Evans Products, Incorporated
Box 168
Moncure, NC 27559
42. Georgia Pacific Corporation
Box 727
Whiteville, NC 28472
43. International Paper Company
Box 229
Farmville, NC 27828
44. Nu-Woods, Incorporated
747 Harrisburg Drive, S.W.
Lenoir, NC 28645
45. Permaneer Corporation
Division of Wynnewood Products Company
Box 756
Black Mountain, NC 28711
46. Surecore Corporation
(formerly Ward Industries, Incorporated)
2400 Industrial Park
Miami, OK 74354
47. Weyerhaeuser Company
Division of Craig Box
Craig Plant, Highway 70
Broken Bow, OK 74728
48. Bohemia, Incorporated
Particleboard Division
50 North Danebo Avenue
Eugene, OR 97402
49. Boise Cascade Corporation
Post Office Box 1087
LaGrande, OR 97850
-------
50. Brooks-Willamette Corporation
(Affiliate of Willamette Industries, Incorporated)
Hill Street
Bend, OR 97701
51. Publisher's Paper Company
Philomath, OR
52. Duraflake Company
Division of Willamette Industries, Incorporated
Old Pacific Highway
Albany, OR 97321
53. Fibreboard Corporation
Clear Fir Products Division
1116 South A Street
Springfield, OR 97477
54. Medford Corporation
North Pacific Highway
Medford, OR 97501
55. Permaneer Corporation
Division of Forest Products Industries, Ltd.
Oillard Garden Road
Dillard, OR
56. Permaneer Corporation
Division of Forest Products Industries, Ltd.
Post Office Box 178
White City, OR 97501
57. Roseburg Lumber Company
Highway 99
Roseburg, OR 97432
58. Timber Products Company
McAndrews Road
Medford, OR 97501
59. Weyerhaeuser Company
Post Office Box 9
Klamath Falls, OR 97622
E-6
-------
60. Weyerhaeuser Company
Wood Products Division
Post Office Box 275
Springfield, OR 97477
61. Georgia Pacific Corporation
Russellville, SC 29476
62. Georgia Pacific Corporation
Sumter, SC
63. Holly Hill Lumber Company
Box 128
Holly Hill, SC 29059
64. International Paper Company
Southern Kraft Division
Box 3189
Greenwood, SC 29646
65. Tenn-Flake Corporation
2525 Trade Street
Morristown, TN 37814
66. Kirby Lumber Company
Post Office Box 1566
Silsbee, TX 77656
67. Louisiana Pacific Corporation
Corrigan, TX 75939
68. Permaneer Corporation
Division of Wynnewood Products Company
Box 1088
Jacksonville, TX
69. Temple Industries, Incorporated
Diboll, TX 75941
70. Champion International
Drawer 250
South Boston, VA 24592
71. Masonite Corporation
West Main Street
Waverly, VA 23890
72. Union Camp Corporation
Edgehill Drive
Franklin, VA 23851
Ei-7
-------
73. International Paper Company
Longbell Division
Box 579
Longview, WA 98032
74. Rodman Industries
Resinwood Division
Box 76
2601 Cleveland Avenue
Marinette, WI 54143
75. Weyerhaeuser Company
1401 East Fourth Street
Marshfield, WI 54449
E-8
-------
APPENDIX F
HARDBOARD MANUFACTURING PLANTS
F-l
-------
1. Chicago Hardboard
2561 West Madison
Chicago, IL
2. Abitibi Corporation
416 Ford Avenue
Alpena, MI
3. Boise Cascade Corporation
Second Street
International Falls, MN 56649
4. Superwood Corporation
Post Office Box 518
Bemidji, MN 56601
5. Superwood Corporation
1400 West W and Waterfront
Duluth, MN 55802
6. Celotex Corporation
Subsidiary of Jim Walter Corporation
Laurel Bank Avenue
Box 67
Deposit, NY 13754
7. Georgia Pacific Corporation
Box 348
Conway, NC 27820
8. Masonite Corporation
U.S. 64
Springhope, NC 27882
9. Weyerhaeuser Company
Moncure, NC 27559
10. Georgia Pacific Corporation
Hardboard Division
Post Office Box 869
Coos Bay, OR 97420
11. Pope & Talbot
Box 426
Oakridge, OR 97463
12. U.S. Plywood
Division of Champion International
Post Office Box 547
Lebanon, OR 97355
F-2
-------
13. Weyerhaeuser Company
Post Office Box 9
Klamath Falls, OR 97601
14. Masonite Corporation
Box 311
Towanda, PA 18848
15. Celotex-Sellers Corporation
Marion, SC
16. Champion International
Catawba Manufacturing Division
Box 66
Catawba, SC 29704
17. Celotex Corporation
Route 4, Box 1090
Paris, TN 38242
18. Temple Industries, Incorporated
Diboll, TX 75941
19. Evans Products, Incorporated
Box 135
Doswell, VA 23047
20. Evans Products Company
Fiber Products Division
Philips, WI 54555
F-3
-------
APPENDIX G
PLANTS WHOSE PRODUCTS ARE NOT VERIFIED
G-l
-------
1. American Forest Products
Stockton Box Plant
Forest Hill, CA 95631
2. Fiberite West Coast Corporation
690 North Lemon
Orange, CA
3. Georgia Pacific Corporation
Lenore and Commercial Streets
Willits, CA 95490
4. Louisiana Pacific Corporation
Oroville, CA
5. U.S. Plywood
Post Office Box 2317
Anderson, CA
6. Pack River Company
Dover, ID
7. Georgia Pacific Corporation
Route 38
Evarts, KY
8.- International Paper Company
Box 37
Wiggins, MS 39577
9. Georgia Pacific Corporation
Box 507
Ahoskie, NC 27910
10. Georgia Pacific Corporation
Box 666
Enfield, NC
11. Georgia Pacific Corporation
Plymouth, NC
12. Masonite Corporation
Box 459
Thomasville, NC 27360
G-2
-------
TECHNICAL REP03T DATA
i ''.Vcse rcaJ /ussfM'fions on the revfl-sc before completing)
3. RECIPIENT'S ACCESSION NO.
EPA 340/1-75-007 __J
TiTL = AND 3-J3TITL.5
Analysis of Control Strategies and Compliance Schedules
for Wood Particle and Fiber Dryers
5. .REPORT DATE
..Issue: February
6. PERFORMING ORGANIZATION CODE
7. AUTHOR-3)
David C. Junge & Richard W- Boubel
3. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Protection Agency
Office of Air and Water Programs
Research Triangle Park, North Carolina 27711
13. TYPS OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT j
The state of the art of technology for control of emissions from wood particle and fiber!
dryers has been summarized and the status of compliance for such installations in the
United States defined. Operational aspects of wood and fiber panel production are
discussed. Pollutant emissions from dryer systems are characterized and emission
measurement techniques are reviewed. For each major control option, the degree of
success achieved in meeting regulations, major problems, approximate costs, and
recommended applications are summarized. It has been concluded that particle dryers
can be operated in compliance with most regulations, particularly those related to
concentration, mass emission rates, and opacity, although no control system is univer-
sally applicablei
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
bJDENTIFIERS/OPEN ENDED TERMS
CO3ATI Held/Group
wood products
wood wastes
Enforcement
Emission testing
13 B
14 D
. DlSTRl'3UT!O\ STATEMENT
Release unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. Or PAGES
169
20, SECURITY CLASS (Tillspage)
Unclassified
22. PRICE
orm 2220,1 (9-71)
------- |