INDUSTRIAL PROCESSES
REFERENCE MANUAL
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TABLE OF CONTENTS
SECTION
1 FURNITURE FINISHING
2 ELECTROPLATING
3 PRINTED CIRCUIT BOARDS
4 WOOD PRESERVATION
5 ROCK CRUSHING AND CEMENT PRODUCTION
6 INJECTION MOLDING
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CHAPTER 1
FURNITURE FINISHING
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TABLE OF CONTENTS
Chapter Page
1 FURNITURE FINISHING 1-1
1.1 INDUSTRY DESCRIPTION 1-1
1.2 PROCESS DESCRIPTION 1-2
1.2.1 Cleansing and Pretreatment 1-5
1.2.2 Primecoat, Flashoff Area, and Oven 1-5
1.2.3 Topcoat Application 1-6
1.2.4 Flashoff Area 1-11
1.2.5 Ovens 1-11
1.3 IDENTIFICATION AND CHARACTERIZATION OF EMISSION
POINTS AND WASTE STREAMS 1-11
1.3.1 Cleansing, Pretreatment, and Rinsing 1-13
1.3.2 Coating Application 1-14
1.3.3 Flashoff Area 1-19
1.3.4 Bake Oven 1-19
1.3.5 Equipment Cleaning 1-20
1.4 POLLUTION PREVENTION, WASTE TREATMENT, AND
CONTROL SYSTEMS 1-20
1.4.1 Material Substitution 1-22
1.4.2 Process Modifications 1-28
1.4.3 Modified Operating Practices 1-29
1.4.4 Add-On Controls/Treatment 1-31
EXHIBITS
Number Page
1-1 Schematic Drawing of Typical Spray Coating Line 1-3
1-2 Common Techniques Used in the Coating of Metal Furniture Pieces 1-4
1-3 Furniture Finishing Spray Application Methods 1-8
1-4 Schematic Drawing of a Roll Coating Operation 1-12
1-5 Estimated Hydrocarbon Emissions Reduction Potential 1-16
1-6 Emission Factors for Typical Metal Coating Plants 1-18
1-7 Summary of Furniture Finishing Waste Streams 1-21
1-8 Summary of Furniture Pollution Prevention Options 1-23
1-9 Summary of Coating Categories 1-25
BIBLIOGRAPHY 1-38
APPENDIX
A Contacts A-l
A92-214.1 1-i
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CHAPTER 1
FURNITURE FINISHING
1.1 INDUSTRY DESCRIPTION
Furniture manufacturing facilities vary in size based on the type of furniture manufactured,
the range of materials employed in the manufacturing processes, the number of manufacturing
and coating lines, and the amount of assembly required. While there are many manufacturing
operations, this discussion deals with finishing operations related only to metal and wood
operations. This distinction has been drawn because the predominant number of emission
points from the industry come from manufacturing (finishing) operations of metal and wood.
The coatings applied at a manufacturing facility vary with personal preference, type of
furniture, application technique, pretreatment, and end use. Most of the coatings applied to
metal furniture are enamels, with the most common consisting of alkyds, epoxies, and acrylics
containing various mixtures of ketones, aromatic, aliphatic, terpene, ester, ether and alcohol
solvents. Other metal furniture facilities use lacquer, metallic coatings, and powder coatings.
The majority of wood furniture manufacturing facilities use traditional nitrocellulose coatings
with high solvent contents. Typical solvents used in wood furniture finishes are alcohols,
aliphatics, aromatics, esters, glycol ethers, and ketones. Some wood manufacturing facilities
use waterbome or radiation-curable coatings.
Metal furniture is manufactured for both indoor and outdoor use, and may be divided into two
general categories: business and institutional, and household. Business and institutional
furniture is manufactured for use in hospitals, schools, athletic stadiums, restaurants,
laboratories and other types of institutions, and government and private offices. Household
metal furniture is manufactured primarily for home and general office use. Items often
considered to be metal furniture include tables, chairs, waste baskets, beds, desks, lockers,
benches, shelving, file cabinets, lamps, and room partitions and other fixtures.
A92-214 1 1-1
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Wood furniture is generally categorized as high, medium, or low end with the quality of the
furniture correlating closely with the number of finishing operations performed on the piece.
A low end piece might undergo from six to 12 finishing operations, while a high end piece
could require up to 30 finishing steps. Much of the low end furniture is constructed of
medium density fiberboard (MDF) with some plastic and natural wood components. Low end
furniture is often painted rather than finished. Manufacturers of low end furniture will
frequently use high-speed production techniques to apply a coating of plastics, laminated
vinyl overlays, and lower quality veneers. High end furniture manufacturers construct their
products of solid wood and wood veneers with the wood grain showing through the finish.
These manufacturers finish their products with more topcoats and intermediate handcraft steps
than medium and low end furniture manufacturers. The number of finishing steps involved in
the manufacture of high end furniture makes it a very labor intensive industry. Medium end
furniture combines the techniques used in both low and high end facilities. The finishing
practices for exposed wood surfaces are similar for all household wood furniture, including
television and other cabinets. Exhibit 1-1 illustrates a typical spray coating line in a wood
furniture facility.
Furniture, regardless of type, is finished in essentially the same manner. Both metal and
wood furniture parts may be finished while they are unassembled, partially assembled, or
completely assembled. Furniture may also be finished either manually or by automatic
methods.
1.2 PROCESS DESCRIPTION
A schematic of the steps in metal furniture finishing is found in Exhibit 1-2. With the
exception of the cleaning and pretreatment step, this is the same process used in finishing
wood furniture which is illustrated in Exhibit 1-1. The arrows rising from the individual
steps indicate emissions of volatile organic materials.
A92-214 1 1-2
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Key to Rooms
1) Toner
Toner
Wash Coat
Dry Booth
Stain
Sealer
1st Lacquer
(8 2nd Lacquer
- Topcoat
Exhibit 1-1. Schematic Drawing of a Typical Spray Coating Line.3
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FROM
MACHINE SHOP
ELECTROSTATIC, OR
CONVENTIONAL AIR OR
AIRLESS SPRAY COATING
FLASHOFF
AREA
TO FINAL
ASSEMBLY
PRIME COAT, FLASHOFF AREA
AND OVEN
(OPTIONAL)
CLEANSING AND
PRETREATMENT
FLOW COATING
TOPCOAT OR SINGLE
COAT APPLICATION
Exhibit 1-2. Common Technir * Used In The Coating of Metal Furniture Pieces.
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1.2.1 Cleansing and Pretreatment
The cleansing and pretreatment employed in metal furniture manufacturing consists of a three-
to five-stage process. In general, the process contains the following steps:
Process Stage Three-Stage* Five-Stage
Alkaline cleaner wash 1 1
Iron phosphate treatment 2a 2
Hot water rinse 2b 3
Chromic rinse 2c 4
Cold water rinse 3 5
* Only one of the treatments or rinses (2a, 2b, 2c) are utilized in the three-stage process.
The alkaline cleaner wash removes mill scale, grease, and oil. Iron phosphate treatments, hot
water rinses, and/or chromic rinses are employed to improve coating adhesion and rust
prevention. The furniture pieces are then rinsed with cold water. Following a cold rinse,
pieces of metal furniture are dried at 130*-180*C (250'-350T).1
In some manufacturing facilities, the entire wash section is omitted and the metal pieces are
cleaned in a shot blasting chamber or organic solvent cleaning operation.
The pretreatment employed in wood furniture manufacturing consists of initial planing and
sanding to prepare the surface for coating applications.
1.2.2 Primecoat, Flashoff Area, and Oven
Although most metal furniture is finished in a single-coat operation, some pieces require a
prime coat application due to the topcoat formulation or the end use of the furniture. Prime
coats may be applied by spray methods, flow or dip coating techniques. These methods are
discussed under top coat application (Section 1.2.3). The substrate with the prime coat then
goes through a flashoff period to avoid popping of the film when the prime coat is baked.
The prime coat is usually baked in an oven at 160°-200"C (300'-400'F).'
A92-214.1 1-5
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Before a topcoat can be applied to wood furniture, several "primers" must be applied. The
finishing sequence of wood furniture varies considerably, but the main priming steps include
staining, applying a washcoat, filling, sealing, glazing, and shading. Some of these steps may
be omitted in the manufacture and finishing of low and medium end furniture.
• Stains: Stains add initial color to the wood. They serve to even out and accent the
natural wood grain.
• Washcoats: Washcoats aid in coating adhesion, filling, and color uniformity. They
also help seal the wood from subsequent staining operations. In addition, washcoats
prepare the wood surface for sanding after stain applications.
• Fillers: Fillers are highly-pigmented wiping stains containing oil which are use to
"fill" open pore woods such as oak and mahogany.
• Sealers: Sealers, like washcoats, provide adhesion, enable sanding, increase build, and
seal the wood.
• Glazes: Glazes, shading stains, and spatter add highlights or character to wood.
In most cases, the furniture is allowed to air dry, or "flash off," in between each priming
application step. Ovens are increasingly used for this operation. After washcoats and sealers
are applied and prior to topcoat application, the furniture is sanded.
1.2.3 Topcoat application
Topcoats (like the primers previously described) may be applied by spraying, dipping, or roll
or flowcoating. Manufacturing facilities applying a variety of paints (metal furniture) or
stains (wood furniture) usually use spray coating methods. If a plant manufacturers furniture
using only one or two paints/stains, they may use flowcoating, dipping, or rollcoating.
7.2.3.7 Spray Coating
Spray coating is the most widely used method of coating application for both metal and wood
furniture. Spray systems are often characterized by their transfer efficiency, or the ratio of
A92-214.1 1-6
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the weight of coating solids deposited on an object to the total weight of coating solids used
in a coating application step. The material that is not deposited on the object is lost to the
surrounding air and is often referred to as overspray. Systems with high transfer efficiencies
deliver significantly more material to the substrate than to the surrounding air.
Spray guns operate on the principle of atomization, the process whereby coating materials are
separated into particles. The quality of finish improves as the particle diameter decreases.
This is partly because film thickness is directly proportional to the diameter of the particle.
Thinner films are associated with better quality finishes. However, as particle size decreases,
so does transfer efficiency.
Spray coating is normally performed in a booth to contain overspray and prevent surface
contamination. Two kinds of spray booths are commonly employed; down draft and side
draft. Spray booth air flow rates vary depending on human occupation, the type of booth, and
the size of the spray booth and its openings.
The five most common spray application methods are discussed below and summarized in
Exhibit 1-3. All of these spray technologies attempt to reduce overspray and waste by
increasing transfer efficiency and maintaining quality of finish. Once the finish has been
applied, the coated furniture is transferred to a flash-off area or oven for curing.
1.2.3.1.1 Conventional Air
Conventional air spray guns use compressed air to atomize the coating material at pressures
ranging from 35,000 to 70,000 kgs/m2 (ksm) (50 to 100 psi). Although compressed air results
in very fine particle atomization and high quality finishes, it also causes inefficient
A92-214 1 1-7
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EXHIBIT 1 -3. FURNITURE FINISHING SPRAY APPLICATION METHODS
oo
Application Method
Conventional Air Spray
Airless Spray
Air-Assisted Airless
Electrostatic
HVLP
(High-volume, low-pressure)
Transfer Efficiency Atomization Quality Industry Application
30 - 60 Very Fine Decorative
40 - 50 Coarse Primarily Maintenance
45 - 65 Fine Functional
Decorative
80 - 95 Fine Functional
Decorative
65 - 90 Fine Functional
Decorative
Industrial
Coatings Applied
Nitrocellulose
Waterbome
Nitrocellulose
Waterbome
Nitrocellulose
Waterbome
High-Solids
Nitrocellulose
High-Solids
Powder Coatings
Waterbome
Radiation-Curable
Radiation-Curable
Nitrocellulose
Waterbome
High-Solids
Cost for Base
Unit
$250
$1,700
$2,800
$2,500
$1,500
A97-214.1
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material transfer. Approximately 30 to 60 percent of the material sprayed is delivered to the
substrate. The remaining 40 to 70 percent of the material is wasted through overspray or
fogging.2
1.2.3.1.2 Airless
Airless units use fluid or hydraulic pressure instead of air to atomize the coating material.
They have an average transfer efficiency of 40 to 50 percent and produce less fog than
conventional air spray systems.3 The quality of the particle atoraization is coarse and the
process is used basically for maintenance purposes.
1.2.3.1.3 Air-Assisted Airless
Air-assisted airless units combine the best features of conventional compressed air atomization
and airless atomization. The nozzle tip acts to atomize approximately 85 percent of the
material by employing the airless methods of fluid or hydraulic pressure.4-5 Atomization is
then completed with compressed air that is introduced at the nozzle tip. The spray would be
coarsely atomized and the pattern poorly defined without the compressed air. The addition of
the air allows for a finely atomized coating that approaches that of compressed air
atomization. The transfer efficiency for air-assisted airless spray ranges from 45 to 65
percent. The quantity of overspray and fog is similar to that of airless spraying.6'7
1.2.3.1.4 Electrostatic
Electrostatic spraying uses the basic principle of electrostatics, similar or like electrical
charges repel each other while unlike charges attract. The atomized paint particles are
positively charged and the piece to be coated is grounded or negatively charged. The strength
of the attraction not only pulls the coating to the substrate but also causes the spray to wrap
around the piece of furniture being finished, and cover all sides including most indented and
recessed areas. Spraying from many angles is unnecessary because of this wrap-around
effect. The result is fewer spraying passes and a reduction in both labor and material.
A92-214.1 1-9
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Electrostatic systems have an average transfer efficiency of 80 to 95 percent.8 While metal
furniture is naturally conductive, wood is not. To use electrostatic spray methods with wood
furniture, the furniture must first be coated with a sensitizing agent which renders it humidity
sensitive and, therefore, conductive.
1.2.3.1.5 High-volume, low-pressure (HVLP)
HVLP units atomize material at less than 7,000 ksm (10 psi) by using a high volume of
warm, dry, atomizing air. The low pressure air passes through large passages in the spray
gun with few restrictions. The air in HVLP systems contains enough energy and atomization
potential to carry the coating to the substrate instead of rapidly expanding as it does when
released from most spray systems. This enables HVLP systems to coat a substrate without
significant fog, resulting in less overspray. Consequently, HVLP units deliver a consistently
high transfer efficiency between 65 and 90 percent.9
7.2.3.2 Dip Coating
After spray coating, dip coating is the most common method of finish application. Conducted
either manually or automatically, items to be coated are loaded onto an overhead conveyor
which lowers them into a tank containing the finish. Once coated, the pieces are raised from
the tank and suspended in a flash-off area over a drainboard.
7.2.3.3 Flow Coating
Flow coating involves conveying the furniture pieces to be coated into an enclosed flow
coating chamber. In the chamber, the coating material is directed at the object from all
angles through many nozzles. The spray from the nozzles forms a curtain through which the
furniture must pass. Once the furniture has been coated, it is held over a drainboard in a
flash-off area. The excess coating drains back into the chamber where it is filtered and
eventually pumped back into a coating holding tank.
A92-214.1 1-10
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1.2.3.4 Roll Coating
Roll coating involves transferring the finish to a substrate by a roller or a series of rollers.
Roll coating techniques may be used to coat flat furniture components prior to assembly.
Because the majority of furniture consists of non-flat pieces, roll coating is not a frequently
used coating method. A roll-coating diagram is schematically illustrated in Exhibit 1-4.
1.2.4 Flashoff Area
The flashoff area is defined as the area between two spray booths or between a booth and an
oven. Facilities may have one or several flash-off areas in which the volatiles in the coating
are allowed to evaporate and the film is allowed to cure or partially cure before the next
finishing step. Some flashoff areas utilize forced air circulation or a separate exhaust system
which removes the volatiles (fumes) from the working area.
1.2.5 Ovens
Once the coated pieces have passed through the flashoff area, they enter the baking oven.
Baking ovens are used in the metal furniture industry to bake or cure the coatings that have
been applied, and may contain several zones with temperatures ranging from 160° to 230°C
(300° to 450°F)1. The ovens that are used in the wood furniture industry operate at lower
temperatures (typically less than 55°C (130°F)) because at higher temperatures, the natural
moisture in the wood may be driven out resulting in damage to the coating. These ovens are
used mainly to flash off and dry the solvent since the oven temperature is not hot enough to
bake or cure the coating.
1.3 IDENTIFICATION AND CHARACTERIZATION OF EMISSION POINTS AND
WASTE STREAMS
The primary waste streams generated at furniture finishing facilities using traditional solvent-
based coatings include solvent cleaning wastes and volatile organic compound (VOC)
A92-214.1 1-11
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-^T
I
H-«
K)
I tTBiiX
tatrU
r-rrn~
•niMiia
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emissions. In furniture facilities with an "open" finishing department, sources of air
emissions are difficult to define as there are often no official spray booths or separate
ventilation systems. Typically, only small furniture facilities have this type of layout
The four main sources of VOC emissions are spray booths, flashoff areas, ovens, and cleanup
operations.
1.3.1 Cleansing, Pretreatment, and Rinsing
The preparation of metal furniture is an involved process requiring chemical treatment. This
complicated preparation process also generates wastes that require treatment prior to disposal.
The cleaning processes that are involved in the preparation of metal furniture may include
between 3 and 5 steps. These are:
1. Alkaline cleaner wash
2. Iron phosphate treatment
3. Hot water rinse
4. Chromic rinse
5. Cold water rinse
The alkaline cleaner is used to remove oil and grease, while the iron phosphate treatment
improves the adhesion characteristics of the surface of the metal. Most facilities utilize a
preparatory process which involves these two steps and a water rinse.
This preparatory process produces a wastewater stream containing several constituents which
must undergo treatment before disposal. The likely contaminants and the expected average
concentrations include:
Average Concentration
Phosphates (total) - 9.5 mg/L
Hexavalent chromium - 1.5 mg/L
Total chromium - 20.1 mg/L
Oil and grease - 550 mg/L
A92-2141 1-13
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The cleansing, pretreatment, and rinsing steps apply only to metal furniture. An in-depth
discussion of these wastes, minimization measures, and treatment options involved in the
metal furniture pretreatment processes is found in Section 2.5 and 2.7 of the Electroplating
chapter.
The preparation of wood furniture is far simpler than that of metal furniture and consists of
initial planing and sanding to prepare the surface for the application of coalings. The wastes
produced from these processes include wood chips, filings, and sawdust, which are non-
hazardous and may be disposed of along with any other non-hazardous solid waste (e.g.,
garbage) that may be generated at the facility.
1.3.2 Coating Application
In the furniture industry, coatings are usually applied in spray booths using various types of
spray equipment. Spray booths generally do not have any temperature or humidity control
and are maintained at ambient conditions. Finishing operations may use either manual or
automatic spray booths. In order to control particulates, many booths are equipped with dry
filters, typically made of paper material. In the past, water curtains were used to control
particulates; however, since the spent water was a hazardous waste, hazardous waste disposal
costs had to be considered. As these costs increased, the cost effectiveness of water curtain
filtration decreased. Therefore, most new and modified spray booths that use filters are
equipped with dry filters.
The furniture industry uses a variety of sizes and types of spray booths. Residential furniture
manufacturers usually apply coatings manually in booths that are approximately 2.4 meters (8
feet) high, 5.8 m (19 ft) wide, and 2.7 m (9 ft) deep. Typical exhaust rates from these booths
range between 283 and 850 cubic meters per minute (mVmin) (500 cubic feet/sec (cfs), with
an average exhaust rate of 540 m3/min (315 cfs). Most booths used by residential furniture
manufacturers consist of only a backside.
A92-2141 1-14
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Spray booths used by office/cabinet manufacturers applying coatings manually to
preassembled furniture are approximately 2.1 m (7 ft) high, 6.1 m (20 ft) wide, and 3.6 m
(12 ft) deep. Typical exhaust rates from these booths range between 198 and 566 mVmin
(115 and 330 cfs), with an average exhaust rate of 397 mVmin (232 cfs). These booths often
consist of only a backdrop. If, however, pieces are coated prior to assembly, they can enter a
four-sided booth through slots in the sides. Manufacturers using the more efficient automatic
spray equipment can use smaller spray booths with an average exhaust rate of 105 mVmin
(61 cfs).
The waste streams generated in the coating application/spray booth area are solvents, excess
paint, and waste filters. Exhibit 1-5 compares VOC emissions from conventional and
waterbome coatings in a sampling of North American furniture manufacturing facilities.
Suppliers of the furniture finishes are also indicated in the table.
7.3.2.7 Filters
The filters in spray booths provide a mechanical means of filtering the air by passing it
through a form of filter media. As the filter removes the paint particulates in the air stream,
the buildup will gradually restrict the air flow and require a change in the filter media. Paper
or pad type filters with accumulated paint or varnish solids are often disposed of in a
dumpster as solid waste. Cloth filters may be washed and reused. The wash water may then
require proper treatment.
Water wash spray booths flush paint particulates out of an air stream by drawing the air
through a continuous curtain of moving water. The solid paint particles are flung off of the
water curtain and into a collecting pan. The water is then treated by compounding causing
the paint particles to coagulate and float on the surface where they are then skimmed off of
the top.
Neither the water wash spray booth systems nor the dry filter booths remove any solvent
vapors.
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EXHIBIT 1-5. ESTIMATED HYDROCARBON EMISSIONS REDUCTION POTENTIAL
Estimated kg of Hydrocarbon Emitted
per 100 m2 of Surface Covered1
Furniture Manufacturers-Finish Supplier
Drexel Heritage-Inmont
Bassett-Spniance
Bassett-Guardsman
Bassett-Mobil
Broyhill-Mobil
Bemhardt-Reliance
Bemhardt-Guardsman
Stanley-Reliance
American-Lilly
American-Inmont
American -Guardsman
Henredon-Reliance
Thomas ville-Guardsman
Conventional
99.8
120
87.1
43
71.4
98.8
-
160
136
-
.
120
81.2
Waterborne
5.9
89.0b
34
30.0e
12.0"
7.3
58.7s
12
29
.11
24
16
36
Potential
Percent
Reduction
94
26
61
30
83
92
.
93
79
-
.
87
55
"Average values taking into account supplier-estimated overspray values and different furniture pieces.
'Trial goal was to replace wash coat and sealer only with waterbome substitutes and keep the balance conventional.
Trial goal was to replace color coats only with waterbome substitutes but keep conventional clear coats.
•"Calculated values based on actual finish usages.
'Values appear high, based on other trial data.
Source: Participating finish suppliers.
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7.3.2.2 Solvents
Because the coatings employed in furniture finishing contain a wide variety of volatile
substances with a wide range of concentrations, the solvent streams emitted during the
finishing process also contain a variety of VOC concentrations and components. The organics
in these streams consist of alcohols, ketones, cellosolves, acetone, toluene, xylene, and other
volatile compounds. Some of the coating organics volatilize as the material is being applied.
An additional amount volatilizes once the spray reaches the substrate or the spray booth filter.
It is estimated that 85 percent of the VOC emissions in the wood furniture coating process
occur in the spray booths. The remaining 15 percent of the emissions are released during
curing operations in the bake ovens and flashoff areas. The emissions from a variety of metal
coating plants is provided in Exhibit 1-6. The majority of VOC emissions from metal
furniture coating operation occurs in the application and flashoff areas.
i
Spent solvents are also produced during the finishing of furniture. The two major sources of
spent solvents in furniture finishing are the stripping, or "wash off", of wood furniture and the
cleanup of finishing equipment and spray booths. In the wood furniture stripping process,
improperly finished furniture is stripped of its defective finish using a lacquer thinner or
"stripper" which is reused until it becomes too contaminated for further use. Spray guns, feed
lines, and spray booths are cleaned on a regular basis using a lacquer thinner which is
discharged into storage containers after being used in the cleanup. In addition, some spent
solvent also results from the occasional batch of defective finishing materials.
The virgin stripper that is used in these processes is usually composed of a mixture of
toluene, xylene, acetone, ethanol, butanol, isopropyl alcohol, naphtha, methyl ethyl ketone,
and esters. The spent solvents from the stripping of furniture and spray booth cleanup may
become contaminated with stains, fillers, glazes, and nitrocellulose. The solvents that are
used in the furniture industry are normally non-halogenated and have high BTU values and,
therefore, are usually much easier to dispose of than spent solvents from industries that use
A92-214.1 1-17
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EXHIBIT 1-6. EMISSION FACTORS FOR TYPICAL METAL COATING PLANTS
Type of Plant
Large appliances
Prime and topcoat spray
Metal furniture1
Single spray*
Single dip0
Miscellaneous metal'
Conveyor single flow0
Conveyor dip
Conveyor single sprayd
Conveyor two coat, flow and spray
Conveyor two coat, dip and spray
Conveyor two coat, spray
Manual two coat, spray and air dry
Production Rate
768,000 units/yr
48 x 106 ftj/yr
23 x 106 fl2/yr
16 x 106 ftVyr
16 x 106 ftVyr
16 x 106 ft2/yr
16 x 106 ft'/yr
16 x 106 ftVyr
16 x 106 ft2/yr
8.5 x 106 ftVyr
Emissions
Hg/hr
315
500
160
111
HI
200
311 .
311
400
212
ton/yr
347
550
176
122
122
220
342
342
440
233
Estimated Emissions (%)
Application
and
Flashoff
80
65-80
50-60
50-60
40-50
70-80
60-70
60-70
70-80
100
Ovens
20
20-35
40-50
40-50
50-60
20-30
30-40
30-40
30-30
0
I
H-"
oo
Source:
A92-214 1
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halogenated solvents or produce low BTU wastes. In the past, these spent solvents were
disposed of in secure landfills. However, landfilling liquid wastes is prohibited in the United
States under RCRA. Due to these restrictions, furniture manufacturing facilities have had to
explore other means by which to manage their spent solvents. One of the options commonly
practiced by furniture companies in managing their spent solvents is recycling, both onsite
and offsite. Other options exercised by some furniture manufacturing facilities in the
management of their spent solvents is the incineration of these spent solvents onsite or using
them as fuel. Recycling, however, has proven to be a more economical means of managing
the spent solvents than incinerating these wastes or using them as a fuel.
1.3.2.3 Coating waste
Most of the coating waste generated during the coating application process is captured by the
spray booth filters and is handled as described in Section 1.3.2.1.
1.3.3 Flashoff Area
The wastes generated in flashoff areas are solvents. The flashoff area serves as a staging area
between two finishing steps where volatiles in the coating are allowed to evaporate and the
film is allowed to cure or partially cure before the next finishing step. Some flashoff areas
have forced air circulation which forces the excess coating solvent to evaporate.
1.3.4 Bake Oven
Solvents are also the primary waste stream resulting from the oven curing process. The
elevated temperatures in the oven cause any remaining solvent in the coating to volatilize
from the furniture surface. Oven temperatures can range from 38° to 121° C (100° to 250°F)
depending on the type of coating used, while the exhaust rate can range from 21.2 to 425
mVmin (750 to 15,000 ftVmin).
A92-214.1 1-19
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1.3.5 Equipment Cleaning
The primary process waste generated from equipment and spray booth cleaning is spent
solvents which are usually contaminated with paints, stains, fillers, glazes, and nitrocellulose.
1.4 POLLUTION PREVENTION, WASTE TREATMENT, AND CONTROL
SYSTEMS
Much of the waste generated in furniture finishing is a result of using solvent based coatings.
Exhibit 1-7 summaries the finishing processes and their corresponding waste streams. If
finishers moved to alternative product formulations (i.e., high-solids, waterbornes, radiation
curables, or powder coatings), then a significant amount of waste would be eliminated
(pollution prevention). VOC emissions would be reduced as would equipment cleaning
wastes. Spray guns, dip tanks, and roller mills used to apply solvent based material must be
cleaned with solvents thereby generating solvent cleaning wastes. However, when applying
waterbornes and many other finish formulations, alkaline or water washes can be used
effectively in cleaning equipment. In many cases, the treatment and handling measures for
these wastes are simpler and more cost effective than actions taken for solvent cleaning
wastes.
If solvent based materials must be used, air emissions and finishing wastes can be reduced by
increasing the transfer efficiency of the application equipment. Increased transfer efficiency
results in more material on the substrate and less in the air or on spray booth filters.
In addition to reformulating products and increasing transfer efficiency, furniture
manufacturers can reduce waste by improving operating procedures and implementing
recycling and good housekeeping techniques.
Add-on control devices should serve as a last means of reducing wastes. In the furniture
industry, add-on control devices to control air emissions are not always applicable because of
A92-214.1 1-20
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EXHIBIT 1-7. SUMMARY OF FURNITURE FINISHING WASTE STREAMS
Waste Stream Constituents
Process Stream
Industries Using
System Constituents
Cleansing and Pretreatment Metal Furniture
Acid solutions
Alkaline solutions
Abrasives
Organic compounds
Chelating agents
Low or high pH
Dissolved metals
Compiexed metals
Metal chips and fines
Rinsing
Metal Furniture
Water
Low or high pH
Dissolved metals
Organic compounds
Waste chemicals
Chelating agents
Coatng Application
Flashoff Area
Bake Oven
Equipment Cleaning
Wood and Metal
Furniture
Wood and Metal
Furniture
Wood and Metal
Furniture
Wood and Metal
Furniture
Coating materials
Organic vapors
Water
Organic vapors
Organic vapors
Organic vapors
Liquid organics
Coating materials
Participates
Organic compounds
Organic compounds
Organic compounds
Organic compounds
Waste chemicals
Coating particulates
A92-214 1
1-21
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the low concentration of VOCs and the varied constituents in the emission streams. Many
traditional control devices such as carbon absorption (scrubbers) and condensation are most
efficient in removing higher concentration, single component waste streams. As such, they are
not be very efficient in controlling the low concentrations and varieties of VOCs found in
furniture finishing emissions. In addition, some of the constituents in the finishing waste streams
could act as poisons to catalysts used in catalytic incinerators.
1.4.1 Material Substitution
Pollution prevention opportunities for reducing waste and emissions through material substitution
and process modifications are summarized in Exhibit 1-8 and described in the following section.
1.4.1.1 Coatings
The most effective way to eliminate or reduce solvent waste generated during the coating
application process is to change to alternative coating formulations with lower solvent contents.
Although low solvent coatings exist and are successfully used in many facilities, other furniture
finishing plants are reluctant to invest the time and effort required to change to new and
developmental technologies. The following sections discuss several low solvent coating
alternatives. A summary of these options is presented in Exhibit 1-9.
1.4.1.1.1 High Solids
The normal solids content for conventional coatings ranges from eight to 30 percent, while high-
solids coatings typically contain 40 to 100 percent solids.10'11 Because high solids coatings
contain less solvent and more solids, they help to lower VOC emissions. In addition, less
material must be shipped, stored and sprayed to achieve the desired film build. In short, this
means less potential to generate waste. Two coatings which fall into the high solids category are
radiation-curable and powder coatings.
A92-214.1 1-22
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EXHIBIT 1-8. SUMMARY OF FURNITURE POLLUTION PREVENTION OPTIONS
10
Coating/Process
Type
UV-Curable Coatings
Waterbome Coatings
Powder Coatings
High-Solids
Coatings
High Volume/Low
Pressure Units
Penetration within
Industries Using Industry
Wood and Metal Slight
Furniture
Wood and Metal Currently used
Furniture
Metal Furniture Currently used
Wood and Metal Currently used
Furniture
Wood and Metal Currently used
Furniture
Plant Size
Large
Medium
Large
Medium
Large
Small
Medium
Large
Small
Medium
Large
Advantages
Durable, less material used,
low VOC emissions
Low VOC emissions, H20
clean-up, reduce fire hazard
Quality finish, durable, low
VOC emissions, less material
required to coat, excess
recyclable
Low VOC emissions, less
material required to coat, good
color matching, potential
energy reduction
Low VOC emissions, quality
finish, increased transfer
efficiency, minimized waste
disposal
Disadvantages
Application problems,
toxicity problems, cost
Wood surface raising,
quality of finish, longer
drying time, Increase oven
temp., need humidity
control
Faraday effect, cost,
difficult touch-up, requires
oven curing, color change
Reduced shelf-life, short
pot-life, Faraday effect
No electrostatic wrap,
difficult to use on parts
with many open spaces
Potential for Furniture Use
(Issues)
Possible (application difficulties,
equipment and coating costs)
Currently used in larger
facilities
Possible
(application and cure
difficulties-high cure temps.)
Yes
(currently used)
Yes
(currently used)
Flat Line Finishing Wood and Metal Currently used
Furniture
Large Efficient, good material
utilization, low VOC emissions,
good transfer efficiency, quality
finish
Can use only with long,
flat stock
Yes
(currently used in some
industries)
A92-214.1
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EXHIBIT 1-8 (CONTINUED)
Potential for Furniture Use
Coating/Process
Type
Industries Using
Penetration within
Industry
Plant Size
Advantages
Disadvantages
Electrostatic Units
Wood and Metal
Furniture
Common in metal
furniture, not as
frequent in wood
Small Increased transfer efficiency,
Medium good material utilization,
Large quality finish, low VOC
emissions
Wood requires sensitizing
agent, difficult to use in
low humidity, not good
with case goods, parts
must be grounded
Yes
(currently used)
Pressure Atomized
Units
(Airless)
Wood and Metal Currently used in Small Low VOC emissions, reduced
Furniture many facilities Medium material consumption, less
Large coating rebound
Limited coat thickness,
high pressure requires
increased operator care
Yes
(currently used)
Air-Assisted Airless
Units
Wood and Metal
Furniture
Currently used
operations
Small Operates at low pressure, less
Medium rebound, low VOC emissions,
Large reduced material consumption
Yes
(currently used)
A92-214.1
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EXHIBIT 1-9. SUMMARY OF COATING CATEGORIES
to
Coating Category
High-Solids Coatings
Radiation-Curable
Coatings
Powder Coatings
Waterbome
Coatings
Nitrocellulose Based
Coatings
Volume Volume VOC
Percent Percent Content
Solids Solvent (Ibs/gal)
40-100 0-60 0-5
20-100 0-80 0-5
98 - 100 0 0
25-80 5-20 1-3
8-30 70-92
Quality of Finish
High Quality
Very Durable
High Quality
Very Durable
High Quality
Very Durable
Varies
High Quality
Durable
Cure Temperature
Required
(»f)
Air Dry - 400
UV-Cure
EB-Cure
350 - 400
66 • 241
Air Dry -165
Available Film
Thickness
(mils) Method of Application
0.5 - 2.0 Electrostatic
Air Assisted Airless
HVLP
2-10 Rollcoating
Electrostatic
HVLP
< 1 Electrostatic
1 .0 Conventional Air Spray
Air-Assisted Airless
Electrostatic
Airless
HVLP
1.0 Conventional Air Spray
Air-Assisted Airless
Airless
HVLP
Electrostatic
A92-214 1
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1.4.1.1.2 Radiation Curables
Radiation curable coatings are coatings formulated to cure at room temperature with the
assistance of a radiation source, either an ultraviolet (LTV) light or an accelerated electron
beam (EB). The electromagnetic radiation energy effects a chemical and physical change in
the coating materials by forming cross-linked polymer networks. Radiation-curable coatings
typically have higher solids contents than their conventional solvent-borne counterparts. The
majority of current radiation-curable systems contain none of the organic solvents found in
conventional coatings. The film-forming components in a radiation-curable system may be
considered 100 percent reactive, which means all of the material is converted into the
polymer network and nothing evaporates before the coating or ink is considered dry. The
coatings are most often applied to the substrate by a roll coating station, although spray
devices may be used with some types of radiation-curable components. Radiation curable
coatings have been used successfully in both metal and wood furniture applications. Some
disadvantages associated with radiation curable systems are the initial start-up and conversion
costs and toxicity classifications of the materials utilized.
1.4.1.1.3 Powder
Powder coatings are mixtures of dry synthetic resins, pigments, solid additives, and from zero
to ten percent entrapped volatiles. The application of powder coating is based on the
principle that charged particles attract. Negatively charged atomized powder particles are
sprayed onto the positively charged (grounded) part to be coated. The powder is
pneumatically fed from a supply reservoir to a spray gun which renders a low amperage, high
voltage charge to the powder fragments. These particles, which have become negatively
charged, are readily attracted to the positively coated surface of the part. This attraction
results in a wrap-around effect which not only pulls the coating to the substrate but also
causes the spray to wrap around the piece and cover all sides, including most indented and
recessed areas. The powder particles are then held on the surface of the part until melted and
fused into a smooth coating in the baking ovens.
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Any overspray resulting from the coating process can be collected and recycled using a
powder recovery system. These systems range in size depending on user needs, but all
operate by separating unused powder from its carrying air stream by incorporating vacuum
and filtration methods to return the powder to a feed hopper for reuse. Employing this
method allows the user to approach a 100 percent efficiency-use rate.
Although powder coatings may be used in coating wood furniture, they are better suited to
metal furniture as metal is naturally conductive.
1.4.1.1.4 Waterbornes
Waterbome coatings contain water as the main solvent or dispersant, although most contain
five to 20 percent organic solvent for coating property enhancement. Waterborne formulations
reduce or eliminate solvent emissions and improve worker and operation safety. Waterborne
formulations reduce fire hazards and explosion potential in storage and application areas
which lowers insurance rates. Hazardous waste handling is minimal because water is used for
clean-up. Waterbome coatings allow for rapid color changes and quick and simple clean-up
because of their solubility in water.
Waterbome coatings are a very feasible waste reducing alternative in the metal furniture
industry, but somewhat less feasible for wood furniture finishing. The application of
waterbome finishes to wood substrates may result in grain raising. Although quality
waterbornes for wood furniture are produced, they may be difficult to find or of limited
availability.
1.4.1.2 Cleaning materials
Like coatings, cleaning materials may be reformulated to reduce solvent waste and air
emissions. Air VOC emissions may also be reduced if high boiling point solvents are used
A92-214.1 1-27
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instead of highly volatile materials. Although materials with high boiling points and low
volatility will eventually evaporate when exposed to air, they will not volatilize during
pouring and agitating to the extent that highly volatile materials will. In some instances,
aqueous, detergent-type cleaners can be substituted for solvent-based materials.
1.4.2 Process Modifications
1.4.2.1 Coaling application
The wastestreams generated during the coating application process include waste solvent and
waste paint. One way to effectively reduce these wastes is to reduce the amount of overspray
produced. This can be accomplished by increasing the transfer efficiency of the application
equipment either by using more efficient equipment or by moving to automatic spray devices.
Because spray technologies are the most common application techniques used in furniture
finishing, the two most efficient spray application methods are discussed below.
1.4.2.1.1 Electrostatic
Electrostatic systems have an average transfer efficiency of 80 to 95 percent.8 Electrostatic
methods may be used to apply conventional solvent-based coatings, powder coatings, and
high-solids materials. Recent equipment developments also make the application of
waterborne coatings possible. In the past this method was unsafe because the conductivity of
the materials presented a shock hazard. Current practices isolate material supplies to prevent
physical contact with this part of the system and allow for quality coating.
1.4.2.1.2 HVLP
HVLP systems produce considerably less overspray than conventional systems with transfer
efficiencies measured between 65 and 90 percent. This can result in significant waste
reduction. Water-wash booths may be replaced by dry filter media reducing water pollution
A92-214.1 1-28
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and hazardous waste generation. Less overspray and migration also reduce necessary booth
and equipment cleaning, sludge removal, and filter changing while increasing material usage.
HVLP systems may be used to apply radiation curable, waterborne, and high-solids coatings.
1.4.2.2 Spray booth modifications
The most common spray booths in the furniture industry are used to apply a finish with
manual spray equipment. These booths, which are open on all sides, require large volumes of
ventilating air which are normally supplied by a side draft system. Side draft booths
incorporate a fan which moves air past the operator, over the piece being coated, and through
the spray booth filters. The_filters remove the overspray (i.e., particulates) and direct the air
out of the booth stack (usually to the atmosphere). Enclosing the spray booth by minimizing
the openings needed for furniture to enter and exit would allow recirculation ductwork to be
installed. Recirculating spray booth air reduces uncontrolled emissions and reduces the
amount of fresh air which is required to be supplied to the operator.
1.4.2.3 Enclosed finishing lines
Enclosing finishing lines allows for a higher capture efficiency of the organics released during
the finishing sequence (e.g., emissions from spray booths, flash-off areas, and ovens). Total
enclosures may be constructed over a spray booth, an oven, or over the entire finishing line.
Total enclosures are very important if add-on control equipment is used. The emissions from
these enclosed areas are captured and exhausted through a stack or a duct to a control device.
1.4.3 Modified Operating Practices
1.4.3.1 Reduction and recycling in cleanup solvent use
Modified operating practices are often considered by industry to be the lowest-impact
approach to reducing waste. Because no change in solvent is involved, there is no
A92-214.1 1-29
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compromise in cleaning efficiency. The idea is to restrict the movement of air across
containers of solvent and to limit the amount of solvent exposed to air. Containers of
cleaning materials (i.e., rags and towels) saturated with solvents must be closed tightly to
prevent solvent evaporation.
To be an effective pollution prevention technique, the cleaning of small parts should be
conducted in a closed unit to prevent splashing and spraying which creates emissions.
Equipment is currently being manufactured which will clean spray equipment without
requiring the operator to spray cleaning solvent through the air. Cleansing of the internal
parts is accomplished by submerging the gun in a tank which is able to pump solvent through
the gun. The solids in the cleaning solvent settle out and the solvent is recycled. The solids
are removed for disposal.
Another method to limit the use of cleanup solvents is to issue a limited amount of solvent to
each operator during a shift. This administrative action limits the total solvent consumption
and requires the operators to monitor solvent use, but may adversely affect equipment
conditions if equipment cleanliness is not properly monitored. Such administrative actions
require a good operator training session prior to implementation.
A third waste minimizing method is to use countercurrent rinsing sequences. This method
uses recycled "dirty" solvent to initially clean equipment. Following this step, "clean"
recycled or virgin solvent is used to rinse away the "dirty" solvent. The countercurrent
sequence extends the life of cleaning solvents and, in some cases, permits the spent solvent
can be used as a thinner for the finishing material.
1.4.3.2 Housekeeping
One waste-reducing housekeeping method which has been used successfully in many plants is
the segregation of waste streams. After use, rather than combining all cleaning materials,
such as solvents or cleaning materials from a single or variety of finish lines, the waste
A92-214.1 1-30
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materials are separated and stored by type. This increases the useful life of the cleaner and
reduces ultimate disposal or off-site recycling costs.
1.4.3.3 Proper spray techniques
The least expensive way to reduce overspray and VOC emissions generated during the
coating application process is to practice proper spray techniques. These techniques can
improve transfer efficiency without incurring the cost of new or modified equipment.
Implementing a spray techniques program involves adjusting equipment to the proper settings,
training the operators on proper techniques, and developing a system for inspecting and
maintaining the spray equipment at maximum efficiency. The basic fundamentals of a good
spray technique include the following:
0 A 50 percent overlap of the spray pattern
0 A distance from gun to workpiece of 16 to 20 cm (6 to 8 in.)
0 A gun delivery volume of approximately 7.1 mVmin (250 ftVmin.)
8 Holding the gun perpendicular to the surface
0 Triggering the gun at the beginning and end of each pass
A training program that incorporates these techniques, if implemented correctly, can reduce
finishing material usage, reduce waste generated from overspray, reduce air emissions, and
improve the quality of the product
1.4.4 Add-On Controls/Treatment
The two add-on control techniques which are considered to be technically feasible for both
the metal and the wood furniture industry are carbon adsorption and thermal incineration.
A92-2141 1-31
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1.4.4.1 Carbon adsorption
Almost 50 to 80 percent of the volatile organic compounds from furniture finishing are
released during the application and flashoff processes. Carbon adsorption techniques can
reduce emissions from these areas by 75 to 90 percent depending on the capture efficiency of
the control device.
In the carbon adsorption process, VOC emission streams are passed through a bed of
activated carbon in which the VOC molecules are captured on the porous carbon surfaces by
non-chemical Van der Waals forces. The adsorptive capacity of the carbon bed tends to
increase with the gas phase VOC concentration, molecular weight, diffusivity, polarity, and
the boiling point of the VOC. After the working VOC capacity of the carbon is reached, the
VOC can be desorbed from the carbon and collected for reuse.
Desorption of the VOC from the used carbon bed is typically achieved by passing low-
pressure steam through the bed. In the regeneration cycle, heat from the steam forces the
VOC to desorb from the carbon where it is entrained in the steam. After the carbon bed has
been sufficiently cleared of VOC, it is cooled and replaced on line with the emission stream.
Meanwhile, the VOC-laden steam is condensed, and the VOC is separated from the water by
decanting or, if necessary, by distillation. If the VOC is not recovered for reuse or
reprocessing, it may be incinerated.
The size of a carbon adsorption unit is dependent on the exhaust flow rate, its desorption
period, and VOC concentration. The flow rates and volatile organic concentrations will vary
in each furniture facility because of the wide variety of coatings employed in the finishing
process. In order to optimize the efficiency of the carbon adsorber, the finishing line should
be enclosed.
Carbon adsorption is considered a viable control option for the application and flashoff areas
because exhaust gases are at ambient temperature and contain only small amounts of
paniculate matter that could contaminate the carbon bed.
A92-214.1 1-32
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1.4.4.2 Thermal incineration
Thermal incinerators pass the emission stream through a combustion chamber where the
VOCs are burned at temperatures typically ranging from 700 to 1,300°C (1,300 to 2,370°F).
Initially, burning is started with the assistance of a natural gas flame or similar heat source.
If the VOC in the emission stream has a sufficient heating value and
concentration, ignition temperatures can be sustained by the combustion of the VOC, and the
auxiliary heat can be turned off. If the ignition temperature cannot be maintained by
combustion only, the auxiliary heat must be left on. Auxiliary heat can be provided by fuels
such as natural gas and from recovery of heat released during combustion. The waste gases
from the thermal incinerator are usually vented to the atmosphere.
Incinerators are more efficient than carbon adsorbers for reducing VOC emissions from
furniture finishing operations. The concentration of organic vapors is usually higher in the
oven exhaust (5 to 15 percent of the lower explosive limit (LEL)) than in the application and
flashoff areas and provides some fuel for the incinerator.
Thermal incineration is widely used to control continuous, dilute VOC emission streams with
constituents from a number of compounds. Thermal incinerators can achieve VOC removal
efficiencies of 98 percent or a 20 ppm exit concentration. For safety considerations, VOC
concentrations are usually limited to 25 percent of the LEL (lower explosive limit) for the
VOC. If the VOC concentration is higher in the waste gas, dilution may be required.
Thermal incinerators remove particulates and other organics in addition to VOCs, thus
enhancing their utility.25
1.4.4.3 Solvent Stills
For those solvents that have become too soiled for reuse, some manufacturing facilities have
determined that it is cost effective to install stills that will recycle their spent solvents.
A92-2I4 1 1-33
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The installation of solvent stills allows manufacturers to lengthen the life of cleaning solvents
and to reduce the purchase of virgin solvent by implementing in-house recycling. Spent
solvent is pumped or poured into the boiling chamber where it is boiled. Vapors form
and pass through the vapor tube into a water-cooled condenser. The vapors are condensed
into a liquid state and flow into a container or drum. When a visual check through a sight
glass indicates that no additional distillate is available, the unit is allowed to cool. Once
cooled the material remaining in the boiling chamber is removed and disposed of as
hazardous waste.
By recycling spent solvents in-plant, out-of-plant recycling costs can be avoided. These costs
can include recycling fees, transportation charges, and insurance premiums. In addition, in-
plant recycling eliminates the risk of any spills or accidents that could occur during
transportation of these wastes.
Recycling solvents presents some limitations. Because the composition of the solvent
changes with distillation, it is not possible to reuse the reclaimed solvent in stripping, or
"wash-off operations. Acetone is added to this reclaimed solvent and this reconstituted
mixture is then used for thinning coatings in the facility's spray operations. This reuse results
in a reduction in the quantity of virgin solvent that is purchased for the spray mix.
There are several types of distillation equipment available that handle a wide variety of
solvents with varying capacities. Perhaps the most important design parameter to be
considered in selecting a still to recover spent solvents is the type(s) of solvent(s) that are to
be recycled. The presence of nitrocellulose lacquer residues, which many furniture industry
solvents contain, poses special problems because nitrocellulose can become explosive when
heated. The manufacturers of these stills recommend that special design features be included
in those stills that will be utilized to recover spent solvents containing nitrocellulose. These
features may include vacuum distillation, a water-flush quick cooldown mechanism, a caustic
neutralizing flush, or explosive protection casings with the still placed in an isolated location.
A92-214.1 1-34
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When recycling solvents, efforts should be made to keep solvents segregated. In facilities
that utilize several different solvents in various stages of their operation, these solvents should
be kept segregated in order to be able reclaim them for reuse. If solvents are not kept
segregated, the material that is reclaimed will be a mixture of the various solvents that are
used, which may render it unsuitable for reuse in any of the facility's processes thereby
leaving disposal as the only remaining alternative of handling this material. Segregation of
solvents is, therefore, always required for those facilities that wish to recycle their spent
solvents in-house, or offsite.
One of the disadvantages to solvent recycling through distillation is the still bottoms that
remain after the solvent has been reclaimed. These still bottoms are usually composed of
unrecovered solvents and any contaminants that soiled the solvent, including paints, stains,
fillers, glazes, and nitrocellulose. The types and levels of constituents present in these still
bottoms vary depending on production processes. These still bottoms must be managed as a
hazardous waste and disposed of accordingly. In the United States, some solvent recyclers
have discovered that it is more cost effective to send these wastes to RCRA-type facilities
that practice fuel blending programs (e.g., to cement kilns and industrial boilers), rather than
sending the resulting bottoms to commercial incinerators.
When a facility has determined that in-house recycling is not feasible, it may opt to send its
spent solvents to outside recyclers for distillation. Most outside recyclers will reclaim spent
solvents for approximately three-quarters the cost of virgin solvents. Two basic types of off-
site or commercial solvent recycling are available: custom toll recycling and open market
recycling.
In custom toll recycling, the generator's spent solvents are kept segregated, batch processed to
the generator's specification, and then returned for reuse. The custom toll system reduces the
chances of the recycled solvent being contaminated with substances foreign to the
manufacturing process of the generator.
The second form of commercial reclamation is known as open market recycling, where the
A92-214 1 1-35
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spent solvents are co-mingled with like or similar wastes from many generators, and
processed for resale and reuse in the marketplace as refined solvent This option is available
to virtually all generators of spent solvents, so long as the recycling facility offers the service
(some companies specialize only in custom toll recycling), and there is a resale market for the
refined product. One of the potential limitations to this type of recycling involves waste
segregation. If a generator is using several different solvents in the various steps of its
operation, and co-mingles the waste, it is likely that the refined solvent from the waste may
be unsuitable for resale, leaving disposal as the only alternative.
The disadvantages of outside recycling are the transportation costs and the damages and
cleanup liability associated with a possible spill. Also to be considered is the possibility of
liability the generator may assume from any actions the recycler may take that lead to
liability. One such problem of particular concern is the means of disposing of still bottoms,
which may be classified as a hazardous waste.
1.4.4.4 Pretreatment of Waste Water
The only significant water-based waste stream associated with furniture manufacturing is that
from the prefinishing operations of metal furniture. The wastewater stream that is generated
during the preparation of the metal furniture must undergo pretreatment before discharge into
the sewage system to protect public-owned treatment works (POTW) from the adverse
impacts that may occur from hazardous or toxic wastes. Pretreatment is conducted to prevent
interference with the POTW, "pass-through" of contaminants, and contamination of municipal
sludges, and improve opportunities to recycle and reclaim industrial wastewaters and sludges.
The spent alkaline solution that may be discharged to the wastewater stream requires
neutralization. Any salts that are precipitated during this neutralization step must be separated
and, subsequently, dewatered. For more information regarding the treatment of this waste,
refer to the Electroplating chapter.
Any hexavalent chromium that is present in the waste stream must be reduced to the trivalent
A92-214.1 1-36
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form before precipitation out of solution. The Electroplating chapter also presents a detailed
discussion of the treatment technologies that are available to accomplish this reduction and
removal.
Any other solids (e.g., oil, grease, particulates, etc.) that are present in the waste stream
produced by these prefinishing processes can be removed through microfiltration (see Section
2.8.4 of the Electroplating chapter) and subsequently treated for disposal. Disposal options
include stockpiling (temporary), incineration, or landfilling. Prior to disposal, wastes that are
classified as hazardous may be encapsulated or stabilized by the addition of binders, as
described in Section 2.8.
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BIBLIOGRAPHY
Economic Analysis of Proposed Effluent Guidelines - Wooden Furniture & Fixture Processing
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Control of Volatile Emissions from Existing Stationary Sources, Volume HI: Surface Coating
of Metal Furniture. U.S. EPA, Office of Air and Waste Management, Research Triangle
Park, North Carolina 27711. EPA-450/2-77-032. December 1977.
Wood Furniture Coating: Summary Report for Technical Support in Development of a
Revised Ozone State Implementation Plan for Memphis, Tennessee. Pacific Environmental
Services, Inc., Durham, NC. Prepared for the U.S. EPA. PB86-157583. June 1985.
Seminar Publication - Solvent Waste Reduction Alternatives. U.S. EPA, Center for
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Reducing Emissions from the Wood Furniture Industry With Waterborne Coatings. U.S.
EPA, Industrial Environmental Research Laboratory, Cincinnati, Ohio. EPA-600/2-80-160.
Managing and Recycling Solvents, North Carolina Practices, Facilities, and Regulations.
Prepared by Jerome Kohl, Phillip Moses, and Brooke Triplet!, Industrial Extension Service,
School of Engineering, North Carolina State University, Raleigh, North Carolina. December
1984.'
U.S.-Mexico Trade - Some U.S. Wood Furniture Firms Relocated From the Los Angeles Area
to Mexico. U.S. General Accounting Office. GAO/NSIAD-91-191. April 1991.
Surface Coating of Metal Furniture - Background Information for Promulgated Standards.
U.S. EPA, Office of Air Quality Planning and Standards, Research Triangle Park, NC.
EPA/450/3-80-007b. October 1982.
Managing and Recycling Solvents in the Furniture Industry. Pollution Prevention Program,
North Carolina Department of Environment, Health, and Natural Resources. May 1986.
Guide to Solvent Waste Reduction Alternatives. Alternative Technology and Policy
Development Section, Toxic Substances Control Division, California Department of Health
Services. Prepared by ICF Consulting Associates, Incorporated, 707 Wilshire Boulevard, Los
Angeles, CA. October 10, 1986.
Engineering Bulletin - Solvent Extraction Treatment. U.S. EPA, Office of Emergency and
Remedial Response, Washington DC. EPA/540/2-90/013. September 1990.
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Solvent Waste Reduction Symposia, Conference Proceedings. Sponsored by California
Department of Health Services. Produced by ICF Consulting Associates, Incorporated, Los
Angeles, CA. October 20-21, 1986 - Santa Clara, CA, October 23-24, 1986 - Los Angeles,
CA.
Compilation of Air Pollution Emission Factors, Third Edition Update Package. U.S. EPA,
Office of Air and Radiation, Office of Air Quality Planning and Standards, Research Triangle
Park, NC 27711.
Surface Coating of Metal Furniture - Background Information for Proposed Standards. U.S.
EPA, Office of Air Quality Planning and Standards,Research Triangle Park, NC. EPA-450/3-
80-007a. September 1980.
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DRAFT
APPENDIX A
CONTACTS
Reprinted from Guideline Series on Control of Volatile Organi'c
Compound Emissions from Wood Furniture Coating Operations. Draft
Chapters 1-4. U.S. Environmental Protection Agency, Research
Triangle Park, NC. October 1991.
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COATING SUPPLTERS
AEXCEL Corporation
7373 Production Drive
Mentor, OH 44061-0780
Mr. Richard Milhem
Akzo-Reliance, Inc.
1431 Progress Street
High Point, NC 27261
Mr. Gerry Currier
Ameron Corporation
P. O. Box 192610
Little Rock, AR 72219-2610
Mr. Mike Harris
Amity Finishing Products
P. O. Box 107
Sun Prairie, WI 53590
Mr. George Cash
Avery—Decorative Films Div.
65O West 67th Place
Schererville, IN 46375
Mr. Greg Emily
C. E. Bradley Laboratories, Inc.
P. O. Box 811
Battleboro, VT 05301
Mr. Rasheed H. Kanaan
Cardinal Industrial Finishes
1329 Potrero Avenue
South El Monte, CA 91733
Mr. Sam Ortolono
Chemcraft Sadolin International,
Inc.
P. O. Box 669
Walkertown, NC 27051
Mr. Gary Marshall
Crown Metro, Inc.
P. O. Box 2910
Lenoir, NC 28645
Mr. Greg Sprole
Guardsman Chemicals, Inc.
2147 Brevard Road
High Point, NC 27261-1029
Mr-. Ron Tucker
Hood Products, Inc.
P. 0. Box 163
Freehold, NJ 07728
Mr. Eric Kasner
James B. Day & Company
Day Lane
Carpentersville, IL 60110
Mr. Steven J. Plumley
Lawrence McFadden ConiDany
7430 State Road
Philadelphia, PA 19136
Mr. Peter Beck
PPG Industries, Inc.
7601 Business Park Drive
Greensboro, NC 27409
Mr. Andy Riedell
Pratt & Lambert
Industrial Coatings Division
16116 East 13th Street
Wichita, KS 67230
Mr. Wallace A. Steele
Radcure, Inc.
217 Freedman Drive
Port Washington, WI
Mr. Keith Clark
53074-0247
Reneer Films Corpora-ion
Old Hickory Road"
Auburn, PA 17922
Ms. Wendy Steed
Snyder Brothers
Avon Street
Toccoa, GA 30577
Mr. Len Snyder
Spruance Southern, Inc.
Old Highway 52 South
Winston-Salem, NC 27107
Mr. David King
The Lilly Company
P. 0. Box 2358
High Point, NC 27261
Mr. William Dorris
A-l
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U. S. Cellulose
520 Parrott
San Jose, CA
Ms. Jennifer O'hara
Valspar Corporation
1647 English Road
High Point, NC 27261
Mr. James Bohannon
A-2
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RESIN SUPPLIERS
Cargill
2301 Crosby Road
Wayzeta, MN 55391
Mr. Al Heitkamp
Ciba Geigy
3 Skyline Drive
Hawthorne, NY 10532-2188
Mr. William Collins
Dow Chemical Company
2040 Willard H. Dow Center
Midland, MI 48674
Ms. Karen Krigbaum
Eastman Chemicals
Eastman Road
Kingsport, TN 37660
Mr. Jeff Powell
ICI Resins
1717 Rivermist Drive
Lilburn, GA 30247
Mr. Edward Elkins
Mobay Corporation
Mobay Road
Pittsburgh, PA 15205-9741
Dr. Bernd H. Riberi
Mobil Oil Corporation
3225 Gallows Road
Fairfax, VA 22037
Mr. Bill Press
Reichhold Chemicals, Inc.
525-T North Broadway
White Plains, NY 10603
Mr. Jeffrev Dannerman
Rohm and Haas
Independence Mall West
Philadelphia, PA 19105
Mr. Nick Roman
Sanncor Industries
300 Whitney Street
Leominster, MA 01453
Mr. Henry Merken
A-3
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FURNITURE MANUFACTURERS
Allied Wood Industries
P. O. Box 1823
Southern Pines, NC 28387
Mr. David Allen
American Woodmark Corporation
Rt. 220 South, Industrial Pk.
Moorefield, WV 26836
Mr. Bob Taylor
Aristokraft, Inc.
1 AristoKraft Square
Jasper, IN 47546
Mr. Dave Hurst
Basset Furniture Industries,
Inc.
Main St., P. O. Box 626
Bassett, VA 24955
Mr. Mike Nelson
Bernhardt Furniture Company
P. O. Box 740
Lenoir, NC 28645
Mr. Buck Deal
Broyhill Furniture Industries,
Inc
1 Broyhill Park
Lenoir, NC 28633
Mr. William Sale
Corrections Industries
Penitentiary of New Mexico
Santa Fe, NM
Mr. L. D. Alexander
Daniel Peters Woodworking
2056 Lock Haven Drive
Roanoke, VA 24019
Mr. Daniel Peters
Elite Furniture Restoration
P. O. Box 623
Toluca, IL 61369
Mr. Don Scrivner
Fieldstone Cabinetry, Inc.
Highway 105 East
Northwood, IA 50459
Mr. Steve Teunis
Florida Furniture Industries,
Inc.
P. O. Box 610
Palatka, FL 32177
Mr. Fount Rion, Jr.
Henkel-Harris Company, Inc.
P. O. Box 2170
Winchester, VA 22601
Mr. Rex Davis
Henrendon
'P. O. Box 70
Morgantown, NC 28655
Mr. Paul (Buck) Smith
Herman Miller, Inc.
8500 Byron Road
Zealand, MI 49464
Mr. Paul Murray
Hickory Chair
37 9th St. PI. S.E.
Hickory, NC 23603
Mr. Richard Mosley
Kitchen Kompact
P. O. Box 868
Jeffersonville,
Mr. Walt Gahm
IN 47131
A-4
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KraftMaid Cabinetry
16052 Industrial Paarkway
Middlefield, OH 27711
Mr. Byron Bombay
Masco Corporation
21001 Van Born Road
Taylor, MI 48180
Dr. Paul Eisele, PhD
Merillat Industries, Inc.
P. O. Box 1946
Adrian, MI 49221
Mr. Gary Butterfield
Mills Pride, Inc.
423 Hopewell Road
Waverly, OH 45690
Ms. Debra Hannah
O'Sullivan Industries, Inc.
1900 Gulf Street
Lamar, MI 64759
Mr. Ralph Williston
Platform Beds, Inc.
400 North First Street
Grants, NM 87020
R. T. Miller
Stanley Furniture
Highway 57 West
Stanleytown, VA 24168
Mr. Alex Teglas
Steelcase
P. O. Box 1967/CS-2S08
Grand Rapids, MI 49501
Mr. Phil Schneider
Stow & Davis Wood Division
Cane Creek Industrial Park
Fletcher, NC 28732
Mr. L. T. Ward
Terra Furniture
17855 Arenth Avenue
City of Industry, CA 91744
Mr. Gary Stafford
The Bartley Collection, Ltd
3 Airpark Drive
Easton, MD 21601
Mr. Joe Layman
The Lane Company, Altavista
Operations
Box 151
AltaVista, VA 24517-0151
Mr. Jon Parish
Thomasville Furniture
Industries, Inc.
P. O. Box 339
Thomasville, NC 27361
Ms. Sherry Stookey
Vaughn Furniture
P. O. Box 1489
Galax, VA 24333
Mr. Pres Turbyfill
Vintage Piano Company
P. 0. Box 51347
Chicago, IL 60651
Mr. John Gonzalves
Virginia House Furniture Corp,
P. 0. Box 138
Arkins, VA 24311
Mr. Randall Sparger
Wambold Furniture
6800 Smith Road
Simi Valley, CA 93063
Mr. Mark Trexler
WCI Cabinet Grouo
701 South N Street
Richmond, IN 47374
Mr. Bob Livesay
Wood-Mode Cabinetry
1 Second Street
Krearner, PA 17833
Mr. Gronlund
WoodCo Incorporated
5225 Quast Avenue. N.E.
Rodgers, MN 55374
Mr. Rick Wood
WoodMark Manufacturing
No.-4, Sapona Business Park
Lexington, NC 27292
Mr. Ellis Murphy
A-5
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APPLICATION SYSTEMS VENDORS
Air Power, Inc.
P. O. BOX 41165
Raleigh, NC 27629
Mr. Ron Lowe
Apollo Sprayers International,
Inc.
10200 Hemstead Highway
Houston, TX 77092
Mr. Paul McClure
Binks Manufacturing Company
9201 W. Belmont Avenue
Franklin Park, IL 60131
Mr. Rick Campobasso
CAN-AM Engineered Products, Inc.
30350 Industrial Road
Livonia, MI 43150
Mr. M. H. Bunnell
DeVilbiss Company
300 Phillips Avenue
Toledo, OH 43692
Ms. Nancy Lieber
Graco, Inc.
24775 Crestview Court
Farmington Hills, MI 48335
Mr. Peter Bankert
Graco, Inc.
4050 Olsen Memorial Highway
Minneapolis, MN 55440-1441
Mr. Glenn Muir
Graco, Inc.
9451 W. Belmont
Franklin Park, IL 60131-2391
Mr. Steven Kish
High Point Pneumatics
Box 5802
High Point, NC 27262-5802
Mr. Wayne Roach
Kremlin, Inc.
211 South Lombard
Addison, IL 60101
Mr. Ken Ehrenhofer
Nordson Corporation
1321 Cedar Drive
Thomasville, NC 27360
Mr. John Collett
Paint-0-Matic
Box 1426
Willits, CA 65490
Mr. Ron Budish
Ransburg, Inc'.
3939 West 56th Street
Indianapolis, IN 46208
Mr. Loren Simonson
S. A. Services
P. O. Box 129
Dudley, NC 28333
Mr. Fred McLeod
Speedflo Manufacturing
Corporation
4631 Winfield Road
Houston, TX 77039
Mr. Dave Masterson
Stiles Machinery
3965 44th Street Southeast
Grand Rapids, MI 49508
A. J. Stranges
The DeVilbiss Co.
300 Phillips Ave., P. O. Box 913
Toledo, OH 43692-0913
Mr. John Truschill
Union Carbide Chemicals
6230 Fairview Road
Charlotte, NC 28210-3297
Ms. Renee Morgan
Volstatic, Inc.
7960 Kentucky Drive
Florence, KY 41042
Mr. James Baugh
Wagner Spray Tech Corporation
1770 Fernbrook Lane
Minneapolis, MN 55447
Mr. Gale Finstad
A-6
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ADD-ON CONTROL VENDORS
ABB Flakt Alpha
29333 Stephenson Hwy.
Madison Heights, MI 48071
Mr. Steven Blocki
Baron-Blakeslee
2003 North Janice Avenue
Melrose Park, IL 60160
Mr. Sherman McGrew
Calgon Carbon Corporation
P. O. Box 717
Pittsburgh, PA 15230-0717
Mr. Mark Weissert
Classic Air Systems
P. 0. Box 6130, Buffalo Shoals
Road
Statesville, NC 28677
Mr. Chuck Campbell
Combustion Engineering
Andover Road, Box 372
Wellsville, NY 14895
Mr. Brian Cannon
CVM Corporation
402 Vandever Avenue
Wilmington, DE 19802
Ms. Roxanne Pietro
DCI International
1229 Country Club Road
Indianapolis, IN 46234
Mr. Bob Zopf
Durr Industries
40600 Plymouth Road
Plymouth, MI 43170-4297
Mr. Dinesh Bhushan
George Koch Sons, Inc.
10 S. Eleventh Avenue
Evansville, IN 47744
Mr. Don Miller
Global Environmental
P. O. Box 2945
Greenville, SC 29602
Mr. John Hatcher
Hirt Combustion Engineers
931 South Maple Avenue
Montebello, CA 90640
Mr. Chris Oakes
Hoyt Manufacturing Corp.
251-T Forge Road
Westport, MA 02790
Mr. Steven Rooney
Huntington Energy Systems
1081 Briston Road
Mountainside, NJ 07092
Mr. Ray Elsman
Industrial Technology Midwest
P-. O. Box 626
Twin Lakes, WI 53181
Mr. William Nowack
M & W Industries
P. O. Box 952
Rural Hall, NC 27045
Mr. Jim Minor
Met-Pro Corporation
160 Cassell Road
Harleysville, PA 19438
Dr. Robert Kenson
Moco Fume Incinerators
First Oven Place
Romulus, MI 43174
Mr. Bill Diepenhorst
Nucon International, Inc
P. O. Box 29151
Columbus, OH 43229 -
Mr. Joseph Enneking
Ray-Solve, Inc.
100 West Main Street
Boundbrook, NJ 08805
Mr. Jules Varga
Reeco, Inc.
6416 Carmel Road
Charlotte, NC 23226
Mr. George Yundt
A-7
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Salem Industries
245 South Mill Street
South Lyon, MI 48178
Mr. Lyman Thornton
Smith Engineering Company
P. O. Box 359
Broomhall, PA 19008-0359
Mr. Roy Mcllwee
Stiles Machinery, Inc.
3965 44th Street Southeast
Grand Rapids, MI 49508
A. J. Stranges
Terr-Aqua Enviro Systems, Inc.
700 East Alosta, Unit 19
Glendora, CA 91740
Mr. Lynn Shugarman
Tigg Corporation
Box 11661
"Pittsburgh, PA 15228
Mr. John Sherbondy
VARA International, Inc.
1201 19th Place
Vero Beach, FL 32960 -
Mr. Jerald Mestemaker
VIC
1620 Central Avenue, NE
Minneapolis, MN 55413
Mr. Tom Cannon
Weatherly, Inc.
1100 Spring St.,NW, Suite 800
Atlanta, GA 30309
Mr. Rick Daeschner
A-8
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GOVERNMENT AGENCIES
Bay Area Air Quality Mgmnt.
District
939 Ellis Street
San Francisco, CA 94109
Ms. Carol Lee
Mr. Dan Belik
Ms. Sandra Lopez
City of Dallas, Env. Health Div.
320 E. Jefferson, Rm. LL 13
Dallas, TX 75203
Mr. Gary Burlbaw
FL Dept. of Environmental
Regulation
2600 Blairstone Rd.-Twin Towers
Tallahassee, FL 32399-2400
Mr. James K. Pennington
GA Department of Natural
Resources
205 Butler St., Suite 1162
Atlanta, GA 30334
Mr. Bill Mitchell
Illinois Environmental
Protection Agency
Div. of Air Pollution Control
2200 Churchill Road
Springfield, IL 62794-9276
Mr. David A. Asselmeier
Mr. John Reed
Indiana Dept. of Environmental
Mgmnt.
105 S. Meridan Street
Indianapolis, IN 46206-6015
Mr. David Mclver
Ms. Ann Keighway
Mr. Andy Knott
Mr. Paul Dubenetzky
Maryland Air Management Division
2500 Broening Highway
Baltimore, MD 21224
Mr. Frank Courtright
MI Dept. of Natural Resources
P. O. Box 30028
Lansing, MI 48909
Mr. Bob Irvine
Mr. D'ave Yanochko
Mr. David Ferrier
Mr. Ray Gray
Mr. Greg Edwards
Mr. Tom Julian
Ms. Linda Davis
NC Dept. of Env., Health, & Nat.
Res.
8025 N. Point Blvd., Suite 100
Winston-Salem, NC 27106
Mr. Myron Whitely
NC Dept. of Environment, Health,
& Natural Resources,
P. O. Box 950
Moresville, NC 28115
Mr. Keith Overcash
NC Dept. of Environment, Health,
& Natural Resources
P. O. Box 27687
Raleigh, NC 27611
Mr. Mike Sewell
Mr. Sammy Amerson
Mr. Bob Wooten
NJ Dept. of Environmental
Protection
Bureau of Engineering and
Regulatory Support
Trenton, NJ 08625
Ms. Beth Raddy
NJ Dept. of Environmental
Protection
New Source Review
Trenton, NJ 08625
Mr. Mike Sabol
NY State Dept. of Env.
Conservation
50 Wolfe Road
Albany, NY 12233-3254
Mr. Jim Coyle
A-9
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Occupational Safety & Health
Admin.
200 Constitution Avenue
Washington, D. C. 20210
Mr. Joe Bodie
Mr. Sangi Kanth
Occupational Safety & Health
Administration
Route 1, Box 259-C
Black Mountain, NC 28711
Mr. Don Jackson
Ohio EPA Southeast District
2195 Front Street
Logan, OH 43138
Ms. Susan Clay
Mr. Glen Greenwood
Ohio EPA Northeast Regional
Office
2110 East Aurora Road
Twinsburg, OH 44087
Ms. Bridgett Burns
Ohio EPA, Div. of Pollution
Control
1800 Water Mark Drive
Columbus, OH 43266-0149
Mr. Mike Riggelman
Ohio EPA Southwestern District
40 South Main Street
Dayton, OH 45402
Mr. Lawrence Harrell
PA Div. of Environmental
Resources
Bureau of Air Quality
200 Pine Street
Williamsport, PA 17701
Mr. Richard Maxwell
PA Dept. of Environmental
Resources
101 S. 2nd St., 114 Executive
House
Harrisburg, PA 17120
Mr. Krishnan Ramamurthy
Mr. Terry Black
San Diego County APCD
9150 Chesapeake Drive
San Diego, CA 92123
Mr. Ben Hancock
South Coast Air Quality Mgmnt.
District
9150 Flair Drive
El Monte, CA 91731
Mr. Monty Price
Mr. Roger Oja
Texas Air Control Board
6330 Hwy 290 East
Austin, TX 78723
Mr. Lane Hartsock
TN Div. of Air Pollution Control
701 Broadway, Customs House 4th
Fl.
Nashville, TN 37247-3101
Mr. David Carson
U. S. EPA Region V
230 South Dearborn Street
Chicago, IL 60604
Mr. Steve Rosenthal
U. S. Environmental Protection
Agency
Emissions Standards Division
(MD-13)
Research Triangle Park, NC
27711
Mr. Dave Salman
U. S. EPA Region III
841 Chestnut Building
Philadelphia, PA 19107
Mr. Ray Chalmers
Ms. Eileen Glen
U. S. Environmental Protection
Agency-
AEERL, MD-62B
Research Triangle Park, NC
27711
Mr. Charles Darvin
A-10
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VA Dept. of Air Pollution
Control
7701-03 Timberlake Road
Lynchburg, VA 24502
Mr. Terry Moore
VA State Air Pollution Control
Board
P. 0. Box 10089
Richmond, VA 23240
Mr. Robert Mann
WI Dept. of Natural Resources
Box 7921
Madison, WI 53707
Mr. Robert Park
A-ll
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ASSOCIATIONS
American Furniture Manufacturers
Assn.
P. O. Box HP-7
High Point, NC 27261
Mr. Larry Runyan
Business & Instit. Furn. Mfg.
Assn.
2335 Burton S.E.
Grand Rapids, MI 49506
Ms. Susan Perry
Canadian Paint & Coatings Assn.
9900 Cavendish Blvd., Suite 103
Quebec St.Laurent, Quebec,
CANADA H4M2VZ
Ms. Karen David
Canadian Kitchen Cabinet Assn.
27 Goulburn Avenue
Ottawa, Ontario, CANADA K1N8C7
Mr. Marco Durepos
Kitchen Cabinet Manufacturers
Assn.
1899 Preston White Drive
Reston, VA 22091-4326
Mr. Richard Titus
Manufacturers of Emissions
Controls Assn.
1707 L Street, NW, Suite 570
Washington, DC 20036
Mr. Raymond Connor
National Paint & Coatings Assn.
1500 Rhode Island Avenue, NW
Washington, DC 20005
Mr. Bob Nelson
Southern CA Finishing & Fab.
Assn.
2552 Lee Avenue
S. El Monte, CA 91733
Mr. Ed Laird
Western Furnishings Mfg.-Assn.
12631 East Imperial Hwy., Suite
106F
Sante Fe Springs, CA 90670
Mr. Jay Walton
A-12
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OTHER
ENSR Consulting & Engineering
35 Nagog Park
Acton, MA 01720
Mr. Kevin Jameson
Ms. Vicky Putsche
EnvironTech Associates, Inc.
485 Juniper Street
Warminster, PA 18974
Mr. Pete Obst
Journal of Waterborne Coatings
1 Technology Plaza
Norwalk, CT 06854
Mr. Stewart Ross
Ron Joseph & Associates Inc.
12514 Scully Avenue
Saratoga, CA 95070
Mr. Ron Joseph
Southern CA Edison Company
2244 Walnut Grove Avenue
Rosemead, CA 91770
Mr. Martin Ledwitz
A-13
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-------
CHAPTER 2
ELECTROPLATING PROCESSES
-------
TABLE OF CONTENTS
Chapter Page
2 ELECTROPLATING PROCESSES 2-1
2.1 INDUSTRY DESCRIPTION 2-1
2.2 PROCESS DESCRIPTION 2-1
2.2.1 Surface Cleaning/Preparation 2-1
2.2.2 Surface Modifications (Electroplating Processes) 2-5
2.23 Workplace Rinsing and Finishing Operations 2-7
2.3 IDENTIFICATION AND CHARACTERIZATION OF EMISSION
POINTS AND WASTE STREAMS 2-10
23.1 Surface Cleaning and Preparation 2-10
23.2 Surface Modification 2-11
23.3 Workpiece Rinsing and Finishing Operations 2-17
2.4 SOLVENT AIR EMISSIONS - POLLUTION PREVENTION, WASTE
TREATMENT AND CONTROL SYSTEMS 2-17
2.4.1 Solvent Stills 2-17
2.4.2 Reducing Emissions from Solvent Cleaning Operations 2-17
2.5 WATER BASED POLLUTION PREVENTION AND WASTE
TREATMENT 2-23
2.5.1 Good Housekeeping 2-24
2.5.2 Reducing Water Usage 2-24
2.5.3 Material Substitution 2-27
2.5.4 Reducing Drag-out 2-28
2.5.5 Metal Recovery 2-30
2.5.6 Plating Bath Regeneration 2-47
2.6 WASTEWATER TREATMENT PROCESSES 2-49
2.6.1 Hexavalent Chromium Reduction 2-49
2.6.2 Cyanide Oxidation 2-51
2.6.3 Metal Precipitation 2-54
2.7 HAZARDOUS SOLID WASTE MANAGEMENT 2-57
2.7.2 Clarification 2-59
2.7.3 Sludge Dewatering 2-59
2.7.4 Ultrafiltration/MicroCltration 2-63
2.7.5 Stabilization/Solidification 2-68
2.7.6 Fixing Metals in Slags 2-68
2.7.7 Resmelting of Metals 2-68
Bibliography 2-71
A92-214.2 2-i
-------
TABLE OF CONTENTS (CONTINUED)
EXHIBITS
Number Page
2-1 Typical Cold Cleaner 2-3
2-2 Typical Vapor Degreaser "2-4
2-3 Electroplating Baths Containing Cyanide 2-6
2-4 Electroplating Operation and Associated Waste Streams 2-8
2-5 Hard and Decorative Chromium Plating Uses 2-9
2-6 Metal Parts Cleaning Wastes 2-12
2-7 Cold Cleaner Emission Points 2-13
2-8 Open Top Degreaser Emission Points 2-14
2-9 Process Wastes 2-15
2-10 Carbon Absorber 2-20
2-11 Adsorption Cycle 2-21
2-12 Desorption Cycle 2-22
2-13 Counter - Current Rinse System 2-26
2-14 Summary of Recovery Technology Application 2-31
2-15 Rising Film Evaporation 2-32
2-16 Flash Evaporation 2-34
2-17 Submerged Tube Evaporation 2-35
2-18 Atmospheric Evaporation 2-36
2-19 Double-effect Evaporation 2-37
2-20 Mechanical Vapor Compression 2-38
2-21 Chromic Acid Ion Exchange Recovery 2-40
2-22 Drag Out Recovery 2-41
2-23 Plating Drag-out Recovery 2-43
2-24 Reverse Osmosis: Mixed Wastewater Stream Recovery 2-44
2-25 Advanced Reverse Osmosis 2-45
2-26 Electrodialysis 2-46
2-27 Electrodialytic Ion Exchange Cell (EDIX) 2-48
2-28 Chromium Reduction 2-50
2-29 Cyanide Oxidation 2-52
2-30 Cyanide Oxidation: Wet Air Oxidation 2-53
2-31 Hydroxide Precipitation - Stream Neutralization 2-55
2-32 Metal Solubility as a Function of pH 2-56
2-33 Conventional Waste Treatment 2-58
2-34 Basic Settling Chamber 2-60
2-35 Mixed Clarifier 2-61
2-36 Inclined Plate Settler 2-62
2-37 Filter Press 2-64
2-38 Vacuum Filter 2-65
2-39 Basket Centrifuge 2-66
2-40 Pressure Belt Filter 2-67
2-41 Stabilization/Solidification 2-69
2-42 Metal Slag Recovery System '. 2-70
A92-214.2 2-ii
-------
CHAPTER 2
ELECTROPLATING PROCESSES
2.1 INDUSTRY DESCRIPTION
Electroplating operations are performed by many industries involved in forming and
finishing metal products. Plating involves altering the surface properties of a metal in
order to increase corrosion or abrasion resistance, alter appearance, or otherwise
enhance the utility of the metal product. Plating operations are normally batch processes
where metal objects to be coated (workpieces) are dipped into and then removed from
baths containing various reagents for achieving the required surface condition. The
workpieces may be transported through the process manually on racks or in barrels or
automatically by conveying racks.
Most plating operations have three basic process steps: surface cleaning or preparation,
surface modification, and workpiece rinsing and finishing. These sections are covered in
detail below, followed by a discussion of pollution prevention opportunities, waste stream
treatment and control technologies.
2.2 PROCESS DESCRIPTION
22.1 Surface Cleaning/Preparation
The preparation of a metal surface involves several stripping and cleaning operations
which are inherent steps in industries involved with the manufacture of metal parts and
equipment. Almost all fabricated metal products require some form of cleaning. Most
machined parts are cleaned with solvents, while paint and old plating materials are
stripped from workpieces using caustics and abrasives. During the plating process
workpieces are cleaned several times using water, acids, caustics, and detergents.
Most industries performing plating operations use one of five types of cleaning media:
solvents (halogenated and nonhalogenated)
alkaline cleaners (aqueous cleaners)
acid cleaners (aqueous cleaners)
nonchemical, abrasive materials
water
Other frequently used cleaning materials include mixtures of solvents and alkalines and
mixtures of water-immiscible solvent emulsified in water (i.e., emulsions).
Cleaning methods depend upon three factors: the nature of surface contamination, the
type of metal substrate, and the degree of cleanliness required. Cleaners, except for
abrasives, are normally contained in large open tanks. The parts to be cleaned are
mounted on racks or contained in perforated horizontal barrels.
A92-2142 " 2-1
-------
2.2JJ Solvent Cleaning
Solvents, the most widely used class of cleaners, are used in removing oil-based
contaminants, by either cold cleaning or vapor phase cleaning (vapor degreasing)
methods. A third, less common cleaning method is diphase cleaning.
22.7.7.7 Cold Cleaning
Cold cleaning is the simplest and least expensive method of solvent cleaning. As a
result, it is also the most common. The solvents used in cold cleaning are usually at
room temperature although they may be slightly heated, and always remain well below
the solvent's boiling point.
Cold cleaning solvents account for almost all of the aliphatic, aromatic, and oxygenated
degreasing solvents and about one-third of halogenated degreasing solvents. The average
cold cleaning unit generally emits only about one-third ton per year of organics, with
about one half to three-fourths of that emission resulting from evaporation of the waste
solvent at a disposal site.
The four types of cold cleaning are wipe cleaning, soak cleaning, ultrasonic cleaning, and
steam gun cleaning. A typical cold cleaner is illustrated in Exhibit 2-1.
2.2JJL2 Vapor Degreasing
The vapor degreasing process cleans parts through the condensation of hot solvent
vapors on colder metal parts. The cleaning cycle involves lowering parts into the vapor
zone (i.e., the vaporous area above the boiling solvent). The condensing solvent
dissolves surface contaminating oils and provides a washing action to clean the parts.
After condensation ceases, the parts are slowly withdrawn from the degreaser. The
residual liquid solvent on the parts quickly evaporates as the parts leave the vapor zone.
The cleaning action may be increased by spraying the parts with solvent or by immersing
them into the liquid solvent bath.
The solvents selected for vapor degreasing boil at much lower temperatures than do the
contaminants, thus the solvent/soil mixture in the degreaser boils to produce an
essentially pure solvent vapor. Most vapor degreasers are batch loaded, cleaning only
one work load at a time. A typical vapor degreaser is illustrated in Exhibit 2-2.
2.2.LL3 Diphase System
Diphase systems use both water and solvent for cleaning purposes. The parts to be
cleaned pass through a water bath prior to passing through a solvent spray.
A92-214.2 2-2
-------
Exhibit 2-1
Typical Cold Cleaner
Top
Cleaner
Pump
A92-214.2
2-3
-------
Exhibit 2-2
Typical Open Top Degreaser
Safety Thermostat
Condensing Coils
Temperature
Indicator
Cleanout Door
Solvent Level Sight Glass
Freeboard
'.Vater Jacket
Concensate Trougn
Watar Separator
Heating Elements
Work Rest And Protective Grate
A92-214.2
2-4
-------
2.22.2 Aqueous (Add and Alkaline) Cleaning
Alkaline and acid cleaning are both accomplished using soak tanks similar to those used
with solvent cleaning. Aqueous cleaning serves to displace soils from metal surfaces
rather than dissolve them as is the case with solvent cleaners. Alkaline solutions contain
builders (sodium salts of phosphates, carbonates, silicates, and hydroxides) and
surfactants (detergents and soaps) and are used to remove soil as well as old plating and
paint. Acidic cleaning solutions may contain mineral acids (nitric, sulfuric, and
hydrochloric), organic acids (sulfamic, acetic, oxalic, or cresylic), detergents, and
chelating agents. Acid cleaners are used to remove rust scale and smut from metal
parts. The chelating agents reduce the chemical activity of metal ions while increasing
their solubility, thus allowing more ions to be held in suspension in a process bath.
2213 Abrasive Cleaning
Abrasive cleaners are designed for creating smooth surfaces and for removing rust,
oxides and burrs, and old plating and paint. Typical abrasives are aluminum oxide or
silicon carbide mixed with an oil or water based binder. This abrasive-binder mixture is
applied to a buffing wheel made from an absorbent material such as cloth. The metal
part is held against the spinning wheel until surface contamination is eliminated.
Other methods of abrasive cleaning involve blasting the part with either sand, plastic
media, or in some cases, crystallized sodium bicarbonate.
22.2 Surface Modifications (Electroplating Processes)
Electroplating is achieved by passing an electric current through a solution containing
dissolved metal ions and the object to be .plated. The metal object acts as a cathode in
an electrochemical cell and attracts metal ions from the solution. Ferrous and
nonferrous metal objects are typically electroplated with aluminum, brass, bronze,
cadmium, chromium, copper, iron, lead, nickel, tin, or zinc. Precious metals such as
gold, platinum, and silver are also used to plate ferrous and nonferrous pieces. A typical
electroplating process involves cleaning, stripping of old plating or paint, electroplating,
and rinsing between each of the previously mentioned steps. Several common
electroplating materials are discussed in the following sections.
2227 Cyanide Plating
There are many electroplating baths which contain cyanide as a component. The most
common are listed in Exhibit 2-3.
During the electroplating process cyanide dissociates from its metal ion. The metal ion
is attracted to the workpiece, while the cyanide is released in the waste stream. In some
facilities, the cyanide-containing plating solution is filtered continuously to ensure that
the plating baths remain free of the solids that form during the plating operation.
A92-214 2 2-5
-------
EXHIBIT 2-3. ELECTROPLATING BATHS CONTAINING CYANIDE
Electroplating Bath Name
Composition
Cadmium Cyanide
Copper Cyanide
Fluoride-Modified Copper Cyanide
Cadmium Cyanide
Sodium Cyanide
Copper Cyanide
Sodium Cyanide
Copper Cyanide
Potassium Cyanide
A92-214.2
2-6
-------
A general process flow diagram for cyanide plating is depicted in Exhibit 2-4. This
diagram also represents the typical process flow for most plating operations.
22.22 Chromium Plating
There are two types of chromium electroplating: hard, in which a relatively thick layer
of chromium is deposited directly on the base metal (usually steel) and decorative, in
which the base material is plated with a layer of nickel prior to the addition of a
relatively thin layer of chromium. The industrial or hard chromium coating processes
have desirable engineering properties such as heat, wear, corrosion, and erosion
resistance and a low coefficient of friction. Some of the uses of hard and decorative
chromium plating processes are listed in Exhibit 2-5.
Chromic acid anodizing, a second electroplating operation, consists of the immersion of
the base metal, usually aluminum, in a chromic acid solution. Electricity is applied to
produce a film of chromium deposit on the base metal. The uses of chromic acid
anodizing include aircraft parts and architectural structures that are subject to high stress
and corrosion.
Chromium coatings are deposited mainly from a highly toxic, chromic acid solution
containing chromic acid, sulfuric acid, and sometimes a fluoride catalyst.
2.2.3 Workpiece Rinsing and Finishing Operations
2.2.31 Water Rinsing
Water cleaning and rinsing is an integral part of every parts cleaning process. Most of
the cleaning operations previously mentioned require a water rinse before and after each
operation. Water washing is normally done in a soak tank or with a spray unit. Some
soak tanks are equipped with air or mechanical agitation devices which enhance the
effectiveness of the rinsing operations. The agitation is done either by spraying
compressed air at the bottom of the tank or by mechanical propellers.
Overflow from rinse tanks may be routed to a specific sump (i.e., a cyanide sump in rinse
tanks associated with cyanide plating) or to a general waste sump. The flow of make-up
water into the plating or stripping baths may be level-controlled which allows the water
to be continually replenished.
Typically the last rinse step in a plating sequence is done with a warm water bath 50-
60°C (120 to 140°F) to thoroughly clean the plated parts and to facilitate subsequent
drying operations.
A92-214.2 2-7
-------
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Exhibit 2-4. Electroplating Operation and Associated Waste Streams
A' <2
-------
EXHIBIT 2-5. HARD AND DECORATIVE CHROMIUM PLATING USES
Hard Electroplating Uses Decorative Electroplating Uses
Engine Components Automotive Trim
Marine Hardware Metal Furniture
Plastic Molds Bicycles
Zinc Die Castings Hand Tools
Industrial Rolls Plumbing Fixtures
Hydraulic Cylinders and Rods
A92-214 2 2-9
-------
223.2 Machining
Machining processes use cutting tools that shear metal from the surface of the
workpiece. Much of the power consumed in cutting is transformed into heat. Most of
this heat is carried away by the sheared metal chips while the rest is split between the
tool and the workpiece. Temperatures at the tool to workpiece surface interface may
reach 93°C (200<>F).
Machining operations involve a variety of metal cutting processes including turning,
drilling, milling, reaming, threading, broaching, grinding, polishing, planing, and cutting
and shaping. Many turning and some drilling processes are completed on lathes which
bold and spin the workpiece against the edge of the cutting tool. Drilling tools are used
both for making holes and for enlarging existing holes (reaming). Milling involves
cutting unusual or irregular shapes into the workpiece. Broaching is the finishing of
internal holes with a machine called a broach.
Machining operations also involve applying metalworking fluids to the workpiece and
cutting tool in order to facilitate the cutting process. These fluids act as lubricating,
cooling, finishing, and rinsing materials. They may be water (with or without an alkali),
emulsions of a soluble oil or paste, or oils (e.g., mineral, sulphurized, or chlorinated).
2.3 IDENTIFICATION AND CHARACTERIZATION OF EMISSION POINTS AND
WASTE STREAMS
All of the processes associated with plating operations have specific waste streams and
emission points. Most of the sources of air emissions occur during metal cleaning and
surface preparation operations. These emissions consist of organic vapors from solvent
cleaners and acid and alkali fumes from aqueous cleaning materials. In addition,
particulates are released during finishing and machining operations.
*
2.3.1 Surface Cleaning and Preparation
The primary waste streams associated with surface cleaning of metal parts are
summarized in Exhibit 2-6 and include abrasives, solvents, alkalines, acids, and rinse
water. The specific composition of these streams depends on the cleaning media used,
the type of substrate, and the type of surface contaminant removed (e.g., oils, greases,
waxes, metal particles, or oxides).
Cleaning solutions may be acidic or basic and may or may not contain organics.
Normally, significant levels of heavy metals are not present, although some aqueous
cleaning streams may contain cyanide. The pollutants expected from the acid/alkaline
cleaning waste stream might be as follows:
Copper 3 mg/1
Nickel 3 mg/1
Zinc 3 mg/1
Lead 3 mg/1
Iron 36 mg/1
A92-214.2 2-10
-------
Another waste stream from cleaning processes is stripping waste which results from the
stripping off of old plated material.
Rinse water waste streams are often combined with acid and alkaline cleaning solutions
(which tend to neutralize each other) and treated at wastewater treatment facilities. If a
facility employs blasting, the rinse water may be contaminated with sand, sodium
bicarbonate, or plastic pellets.
2.3JJ Emissions from Cold Cleaners
The sources of solvent emissions from cold cleaners include bath evaporation, solvent
carry-out, agitation, waste solvent evaporation, and spray evaporation. These are
depicted in Exhibit 2-7. Solvent emissions are estimated to be approximately 0.3 metric
tons (.33 tons) per year with a range from 0.17 to 0.5 metric tons (.19 to .55 tons) per
year.
2.3J.2 Emissions from Vapor Degreasers
Most of the emissions resulting from vapor degreasing operations are those vapors that
diffuse out of the degreaser. Unlike the cold cleaners, vapor degreasers do not lose
much solvent through waste solvent evaporation or liquid carry-out. The average open
top vapor degreaser emits about 2.5 kilograms (5.5 Ibs) per hour per meter2 of opening.
Assuming an open surface area of 1.67 m2 (18 ft2), a typical emission rate from a vapor
degreaser would be 4.2 kilograms (9.25 Ibs) per hour or 9,500 kilograms (20,950 Ibs) per
year. Emissions from a vapor degreaser are illustrated in Exhibit 2-8.
2.3.2 Surface Modification
Some of the common waste streams from surface modification processes are noted in
Exhibit 2-9 and described in more detail in the following sections. The exact
composition of the process wastes will depend on the specific plating process and the
removed surface contaminant. In certain cases, specific process waste streams, such as
concentrated cyanide wastes and filter sludges, may be combined.
Both spent alkaline cleaning solutions and spent acid cleaning solutions are generated by
the periodic replacement of contaminated process solutions. Rinse waters are generated
from overflow of rinse tanks and contamination by drag-out from cleaning baths. The
waste removed from plating tanks by the continuous filtering of the baths results in filter
sludges.
2.3.2.1 Meted Baths and Rinses
Most spent plating solutions contain high concentrations of metals. Because of this, the
plating solutions are not as easily disposed of or treated as are cleaning solutions. As
impurities build, the bath is purged. Wastewaters resulting from electroplating processes
also contain a variety of heavy metals and cyanide.
A92-2142 2-11
-------
EXHIBIT 2-6. METAL PARTS CLEANING WASTES
No. Waste Description Process Origin
Composition
Abrasive
Solvents
Alkalines
Acids
Rinse water
Removal of rust, scale
polishing of metal
Removal of oil-based soils
Removal of organic soils,
descaling
Removal of scale, smut
Removal of previous
Aluminum oxide, Silica
metal, water, grease
Halogenated and non-
halogenated solvents, oil-
based contaminants
Alkaline salts, additives,
organic
Acids, additives, dissolved
metal salt, water
Water with traces of cleaners
and cleaning material
additives
A92-214.2
2-12
-------
»WASTE
4 )SOLVENT
Exhibit 2-7. Cold Cleaner Emission Points
A92-214.2
2-13
-------
Up top.
exhaust
1 •*'' I *! -I 'I I K!' I •' %Vi •• '• V '•'i
I' /I . • '' • I-1 ii !'•' 'I 4-u» ' i i if I
).'/.*• (i VAPOR . |f •(';/ M {/\:| */|p
0
WASTE
rot vim
niniin
If
CONDENSER
COILS
Exhibit 2-8. Open Top Degreaser Emission Points
Af 2
-------
EXHIBIT 2-9. PROCESS WASTES
Waste Description
Process Origin
Composition
Spent process solutions Plating and chemical conversion
Filter sludges
Quench oils and
quench oil tank
cleanup wastes
Spent salt bath
Plating and chemical conversion
Case hardening
Carburizing, nitrating, cyaniding
Wastewater treatment Wastewater treatment
sludge
Vent scrubber wastes Vent scrubbing
Ion exchange resin
reagents
Specific to the process
solution
Silica, silicides,
carbides, ash plating
bath constituents
Oils, metal fines,
combustion products
Sodium cyanide and
cyanate. Potassium
cyanide and cyanate.
Metal hydroxides,
sulfides, carbonates
Similar to process
solution composition
Demineralization of process water Brine, HC1, NaOH
A92-214 2
2-15
-------
For example, in a chromium plating operation, the rinse water stream might contain the
following contaminants:
Chromium(6+) 12 mg/1
Chromium(total) 18 mg/1
Copper 3 mg/1
Nickel 3 mg/1
Iron 36 mg/1
The level of chromium could be significantly higher if multiple rinse streams are utilized.
The chromium 6+ ion is particularly hazardous and must be reduced to the 3+ ion.
2.3.2.2 Wastewaters from Spills
Wastes produced from spills and leaks are usually present to some extent in an
electroplating process. Water is used to wash away floor spills resulting from tank
leakage, from accidental overflow of the plating/stripping tanks, and from the dripping of
solutions from parts during their transfer between tanks. The resulting wastewater
contains all of the contaminants present in the original plating or cleaning solutions.
25.23 Metal Cyanides
The primary sources of cyanide waste come from operations associated with cadmium,
copper, and silver plating and stripping. These waste streams normally occur from the
overflow of associated rinse tanks.
For metal plating involving cyanide eg:cadmium, zinc or copper, the rinse water stream
would contain the metal contaminant and cyanide:
Metal 20 mg/1
Cyanide 25 mg/1
2.3.2.4 Chromic Adds
Emissions of chromic acid mist occur due to the inefficiency of the chromium plating
process. Only about ten to twenty percent of the electric current applied to the solution
is actually used in the deposition of the chromium on the item. The vast majority of the
electric current is consumed in the evolution of hydrogen gas, with the resultant
liberation of gas bubbles, which burst at the surface of the plating solution, forming a
fine mist of chromic acid droplets.
23.25 Tank Dumpings
Once a plating solution is spent, the process tank is often emptied or "dumped." The
chemical bath dumps containing heavy metals and sludges are another source of
hazardous waste.
A92-214.2 2-16
-------
23.26 Rinse Waters
Contaminated rinsewater accounts for the majority of plating process waste as numerous
rinsing steps occur during the plating operations. Rinse water is used to wash off the
drag-out or excess solution that remains on the workpiece surface after the workplace is
removed from the plating bath. Typically, more drag-out results from plating pieces in
perforated barrels than from rack plating. Drag-out that is carried into the next process
bath is treated as a contaminant and is referred to as drag-in.
2.3.3 Workpiece Rinsing and Finishing Operations
Like the electroplating rinse waters, the rinse water generated' during the finishing
operations contains heavy metals and cyanides.
2.4 SOLVENT AIR EMISSIONS - POLLUTION PREVENTION, WASTE
TREATMENT AND CONTROL SYSTEMS
2.4.1 Solvent Stills
The installation of solvent stills allows manufacturers to lengthen the life of cleaning
solvents and to reduce the purchase of virgin solvent by implementing in-house recycling.
Stills consist of a boiling chamber, a condenser, a reclaim container, and a ventilation
device. Spent solvent is pumped or poured into the boiling chamber where it is boiled.
Vapors form and pass through the vapor tube into a water-cooled condenser. The
vapors are condensed into a liquid state and flow into a container or drum. When a
visual check through a sight glass indicates that no additional distillate is available, the
unit is allowed to cool. Once cool, the material remaining in the boiling chamber is
removed and disposed of as hazardous waste.
2.4.2 Reducing Emissions from Solvent Cleaning Operations
Solvent cleaning operations are the primary source of volatile organic compound (VOC)
air emissions. The five main devices which are used to reduce these emissions include
covering the still, increasing the freeboard height, installing refrigerated chillers, using
safety switches, and using carbon adsorbers.
2.4.2.1 Covers
Covers are the most important control device for open top degreasers. Although most
degreasers already have covers, they can be more effectively and frequently used if they
are automated or assisted by mechanical devices.
For vapor degreasers, the cover should open and close in a horizontal motion so that the
air/vapor interface disturbance is minimized. These types of covers include rolled plastic
covers, canvas curtains and guillotine covers.
A92-2142 2-17
-------
The covers on cold cleaners are often mechanically assisted by means of spring loading
or counterweighing. In certain applications, submerged and water covers may be used.
The submerged cover is a horizontal sheet of material which is submerged approximately
two inches below the surface of a liquid solvent that is vigorously pump agitated. The
water cover is a layer of water between two and four inches thick over a halogenated
solvent. Water covers cannot be used in applications where the water would corrode the
metal surface of the parts to be cleaned or where it would degrade the solvent.
Covers are also used to control acid and alkali fumes resulting from aqueous cleaning
processes.
24.22 Freeboard Height
The freeboard reduces the drafts near the air/solvent interface. An acceptable
freeboard height is normally determined by the freeboard ratio, the freeboard height
divided by the width (not length) of the degreaser's air/solvent area. The freeboard
ratio is normally 0.5 to 0.6 for the open-top vapor degreasers, except for very volatile
solvents where a minimum freeboard ratio of 0.75 is used. Increasing the freeboard ratio
from 0.5 to 0.75 often reduces emissions by 25 to 30 percent, while increasing the
freeboard ratio from 0.5 to 1.0 may result in a 50 percent reduction in emissions. The
freeboard height does not have much effect on cold cleaners using low volatilizing
solvents, but it does benefit cold cleaners using higher volatility solvents.
2.4.2.3 Refrigerated ChiUers
Condenser coils and a freeboard water jacket can help prevent solvent vapors in a vapor
degreaser from overflowing. These primary condenser coils control the upper limit of
the vapor zone. The addition of refrigerated freeboard chillers above the primary
condenser coils impede the diffusion of solvent vapors from the vapor zone into the work
atmosphere by chilling the air immediately above the vapor zone and creating a cold air
blanket. The blanket of cold air results in a sharper temperature gradient which reduces
the mixing of air and solvent by narrowing the air/vapor mixing zone. The chilling also
produces a stable inversion layer which decreases the upward convection of solvent laden
air.
Another type of refrigerated chiller is the refrigerated condenser coil which replaces the
primary condenser coils. If the coolant circulating through the condenser coils is
refrigerated enough, it will create a layer of cold air above the air/vapor interface.
These coils are normally used only on small open-top vapor degreasers.
2,4.2.4 Safety Switches
Safety switches are devices used on vapor degreasers to prevent emissions during
malfunctions and abnormal operation. The five main types of safety switches are as
follows:
Vapor level control thermostat
Condenser water flow switch and thermostat
A92-214.2 2-18
-------
Sump thermostat
Solvent level control
• Spray safety switch
The first four safety switches turn off the sump heat while the fifth turns off the spray.
The most important safety switch is the vapor level control thermostat. This device is
activated when solvent vapor rises above the designated operating level. If the coolant
flow is interrupted and hot vapors are sensed, the sump heater is turned off thereby
minimizing vapor escape. The condenser water flow switch and thermostat turn off the
sump heat when either the condenser water stops circulating or the condenser water
becomes warmer than specified. The sump thermostat and the solvent level control
prevent the sump from becoming too hot resulting in solvent decomposition. Although
the safety spray switch is not used as often as the other devices, it can also help to
control solvent vapors. When the vapor level drops below a specified level, the pump for
the spray equipment will shut off until the normal level is attained.
24.2.5 Carbon Adsorbers
Carbon adsorbers are widely used to capture solvent emissions from metal cleaning
operations. A typical adsorber is illustrated in Exhibit 2-10. When applied correctly to
solvent cleaning processes, adsorbers can achieve high levels of emission control
capturing in excess of 95 percent of the organic material input to the system and
reducing total emissions by 40 to 65 percent. The actual and theoretical emission values
differ because the ventilation equipment in the adsorber cannot capture all of the solvent
vapors and deliver them to the adsorption bed. Solvent vapors occurring from parts
drag-out, leaks, spills, and waste solvent disposal, are not significantly affected by a
ventilation system. The effectiveness of the ventilation system (and the effectiveness of
the adsorber) can be improved by improving ventilation design and by using drying
tunnels or other devices to decrease the solvent losses due to drag-out. Additional
methods of reducing drag-out are discussed in Section 2.6.4.
In the carbon adsorption process, solvent emission streams are passed through a bed of
activated carbon in which the VOC molecules are captured on the porous carbon
surfaces by non-chemical Van der Waals forces. The adsorptive capacity of the carbon
bed tends to increase with the gas phase VOC concentration, molecular weight,
diffusivity, polarity, and boiling point of the solvent. After the working solvent capacity
of the carbon is reached, the VOC can be desorbed from the carbon and collected for
reuse. The adsorption and desorption cycles are illustrated in Exhibits 2-11 and 2-12.
Desorption of the VOC from the used carbon bed is typically achieved by passing low-
pressure steam through the bed. In the regeneration cycle, heat from the steam forces
the VOC to desorb from the carbon where it is entrained in the steam. After the carbon
bed has been sufficiently cleared of VOC, it is cooled and replaced on line with the
emission stream. Meanwhile, the VOC-laden steam is condensed, and the VOC is
separated from the water by decanting or, if necessary, by distillation.
A92-214.2 2-19
-------
Solvent Ladon Air Inlet
10
w
o
— Water
Separator
*— Steam Line
Clean Air Exhaust
Exhibit 2-10. Carbon Adsorber
A '2
-------
Exhibit 2-11. Adsorption Cycle
Solvent-Laden
Air Inlet
Activated Carbon
Bed •-
Clean Air
Exhaust
A92-214.2
2-21
-------
Exhibit 2-12. Desorption Cycle
Condenser
Recovered ^~
Solvent
Activated
Carbor
A92-214.2
2-22
-------
The principal advantage of carbon adsorption is that it is very cost effective with low
concentrations of VOCs. VOC recovery offsets operation costs, and operation of the
adsorber is relatively simple for both continuous and intermittent use.
Certain types of VOCs such as those which are difficult to strip from carbon or those
which are miscible with water may not be candidates for carbon adsorption. If the VOC
involved is miscible with water, additional distillation measures are necessary to recover
the VOC. If steam-stripping is conducted with chlorinated hydrocarbons, corrosion and
wastewater treatment problems may occur. Also, carbon adsorption is relatively sensitive
to emission stream humidity and temperature. Dehumidification is necessary if the
emission stream has a high humidity (relative humidity > 50 percent) and cooling may
be required if the emission stream temperature exceeds 49-54 degrees C (120-130
degrees F).
Two commonly used adsorption systems are the fixed-bed system and the fluidized-bed
system. In the fixed-bed system, non-moving beds of carbon are alternately placed on-
line and regenerated. In the fluidized-bed system, loose, clean carbon is constantly
metered into the bed while loose, VOC-laden carbon is removed for regeneration.
Fixed-Bed Systems. In a continually operating fixed-bed system, the VOC emission
stream is passed through two or more non-mobile carbon beds. In a two-bed system,
one bed is on-line with the emission stream while the other bed is being regenerated or
on standby. When the first bed reaches its working VOC capacity, the emission stream
is redirected to the second bed, and the first bed is regenerated. While two beds are
common, three or more beds can be used in a variety of configurations, with more than
one bed on-line at a time.
Fluidized-Bed Systems. The fluidized-bed adsorber system contains one or more beds of
loose, beaded activated carbon. The VOC emission stream is directed upward through
the bed where the VOCs are adsorbed onto the carbon. The flow of the emission
stream stirs the carbon beads causing it to "fluidize" and flow within the adsorber. The
VOC-cleaned air exiting the adsorber is passed through a dust collector and then
released into the atmosphere. Fresh carbon is continually metered into the bed while
VOC-laden carbon is removed for regeneration.
Fluidized-bed adsorbers can capture more VOC with a given quantity of carbon because
the fluidized bed mixes newly regenerated carbon and VOC more thoroughly, and
because the system continually replaces used carbon with regenerated carbon. This
increased VOC-capacity reduces costs for steam regeneration.
2.5 WATER BASED POLLUTION PREVENTION AND WASTE TREATMENT
There are numerous methods to reduce water based of pollution. The following
methods have been discussed:
2.5.1 Good Housekeeping
2.5.2 Reducing Water Usage
2.5.3 Alternative Sources of Materials
A92-214 2 2-23
-------
2.5.4 Reducing Drag-out
2.5.5 Metal Recovery
2.5.6 Plating Bath Regeneration
2.5.1 Good Housekeeping
The following housekeeping practices are generally easy to implement for any
manufacturer and require little or no capital investment:
Repair all leaking tanks, pumps, valves, et.
Inspect tank and tank liners on a regular basis to prevent liner failures that may
result in bath dumps.
Inspect steam coils and heat exchangers on a regular basis to prevent accidental
contamination of steam condensate and cooling water or leakage of condensate
and cooling water into the plating bath. Inspecting coils for scale buildup is also
important.
Install high-level alarms on all plating and rinse tanks to avoid accidental bath
overflows.
Maintain plating rocks and anodes to prevent contamination of baths. Remove
racks and anodes from baths when not in use.
Minimize the volume of water used during cleanup operations.
Properly train plating personnel so that they understand the importance of
minimizing bath contamination and waste generation, and preventing spills.
Properly clean and rinse parts prior to plating to minimize contamination of the
plating bath. Areas that are not to be plated should be masked or stopped off
with tape and wax to limit corrosion from these areas. Parts should be removed
from the bath at the optimum time.
2.52 Reducing Water Usage
Reducing water usage can be accomplished by various process changes or additional
control devices such as
multiple rinse tanks
surface evaporation
conductivity cells
flow regulators
water re-use
spray rinse
A92-214.2 2-24
-------
2.5.21 Multiple Rinse Tanks - see process Exhibit 2-13
2.5.2.1J Counter Current Flow
In a counter current system, the parts pass through the rinse tanks in a direction counter
to the flow of rinse water. Fresh water is fed into the final rinse tank to ensure the parts
are properly cleaned. The water then passes through the other tanks and progressively
becomes more concentrated with the contaminants. The volume of water required to
obtain the same concentration of contaminants in the final rinse as would be achieved
using only one rinse tank can be reduced by up to 99 percent using this simple process.
advantage: may reduce water usage by 99 percent
2.5.2.1.2 Parallel Flow
Fresh water is introduced to each rinse tank and the overflow is discharged to waste.
This flow system also significantly reduces the volume of water required although not to
the extent of counter current flow.
2.5.2.2 Surface Evaporation
Evaporation from the plating tank means that continual topping off is required. A
standard (2.8 sq m (30 square feet)) surface area tank could expect to lose 18.9
liters/hour (5 gallons/hour) through evaporation operating at a temperature of 65°C
(150° F). Agitation of the tank contents can double evaporation rates. Likewise,
temperature increases from (27° to 71° C (80° to 160° F) will increase evaporation by a
factor of 10.
If evaporation is significant, the waste rinse water can be used to top off the plating tank.
Indeed, if the rate of wastewater flow equals the rate of evaporation then all wastewater
can be used up in this way and no further treatment processes are required. The
temperature of
the plating tank can be raised in order to increase the rate of evaporation, but it is
necessary to ensure that the additives will not be degraded at the higher temperatures.
In the case of multiple rinse tanks, the upstream rinse tank contents may be recycled and
the final rinse would be a free rinse containing a much reduced level of contaminants
requiring little or no further treatment.
advantage: reduces wastewater
recycles valuable metals
A92-214.2 2-25
-------
Exhibit 2-13
TRIPLE STAGE COUNTER-CURRENT RINSE SYSTEM
10
Workpiece
Movement
PROCESS
TANK
RINSE
RINSII
Work
Product
RINSE
Rinse
Walni
In flu0111
t Effluent to
Recycle, Resource
Rec' ry or Irenlrnonl
-------
25.23 Conductivity Cells
The allowable maximum concentration for a rinse tank is known before the contents
must be subjected to treatment. A simple conductivity probe, controller unit and
automated valve can be utilized to automate the procedure of providing fresh solution.
When the level of contaminant reaches a preset level, the valve is automatically opened
and fresh water is introduced to the rinse tank until dilution reaches a preset minimum.
A reliable probe is required and the control box should be housed in a non-corrosive
material.
advantage: simple, cheap process
reduces excess water usage
2.5.2.4 Flaw Regulators
After establishing the appropriate flow rate into a rinse tank, this level can be accurately
maintained using flow regulators.
advantage: do not need to reset flow rate each time
valve is opened
25.25 Water Re-use
Final rinse water generally has a low level of contaminants and can therefore be re-used
as an intermediate rinse. Alternatively it can be used as rinse water for another process
step where the level and type of contaminants do not affect the rinsing operation e.g^,
rinse water from acid dipping can be used as rinse water for alkaline dipping.
advantage: reduces wastewater generation
25.26 Spray Rinse or Air Knives
As the work piece is removed from the plating tank, it is suspended above it while a
spray rinse or air knife (mounted on the lip of the plating tank) is sprayed over the work
piece. Up to 75 percent of chemicals can be returned to the tank in this manner. It is
especially suitable for lengthy plating processes where the work piece spends many hours
or days in the tank e.g., hard chromium plating.
advantage: reduces chemical drag-out and hence the need for large volumes of
rinse water.
2.5.3 Material Substitution
If the toxic substances found in waste streams can be prevented from entering the
system, wastewater treatment may not be required. Several alternative feed chemicals
can be utilized as described below.
A92-214.2 2-27
-------
2.5.3J De-ionized Water
De-ionized water can be substituted for tap or softened water for both rinsing and
topping up plating tanks.
advantages: reducing contaminants to the plating process, providing a better rinsing
function, reducing waste build up in the effluent stream.
2.5.3.2 Zinc Plating
In zinc plating, cyanide based solutions are conventionally used. An alternative is to use
a low cyanide bath, an alkaline bath or a proprietary neutral chloride bath. With the
latter, ammonium or potassium ions are required for complexing the zinc. While
substitution has the advantage of eliminating toxic cyanide from waste these methods
appear to reduce ductility and therefore are really only suitable for cosmetic zinc
applications.
25.3.3 Cadmium Plating
Chemical substitutes in cadmium plating can include acid baths consisting of cadmium
oxide, sulfuric acid, distilled water, and anionic compounds.
25.3.4 Copper Plating
Copper sulphate can be used as a substitute.
25.3.5 Tin Plating
Acid tin chloride can be used as an alternative.
25.3.6 Trivalent Chromium
Trivalent chromium can replace hexavalent chromium in some circumstances.
25.3.7 Cyanide
Cleaners can be replaced by ammonia or trisodium phosphate. Chromic acid used for
pickling purposes can be replaced by sulfuric acid or hydrogen peroxide.
2.5.4 Reducing Drag-out
Drag-out refers to the plating solution that adheres to the parts after they are taken out
of the plating bath and is carried-over into the rinsewater. Drag-out represents the
largest volume source of wastewater in electroplating operations. Minimizing drag-out
will reduce the amount of contaminants entering the next process bath or rinsewater,
thus reducing the volume of waste that must be treated and disposed.
A92-214.2 2-28
-------
Several techniques have been developed to control drag-out. These drag-out reduction
methods are inexpensive to implement and are repaid through savings in recovered
plating chemicals. Techniques to control drag-out include:
Modifying properties of the plating bath to improve drainage of the plating
solutions back into the plating baths or reduce the concentration of dissolved
metals in the drag-out. These methods include:
Decreasing bath viscosity: by reducing the chemical concentration of
the bath or by increasing the bath temperature.
Decreasing bath surface tension: by adding non-ionic wetting agents or
increasing bath temperature.
Lowering the withdrawal rate of parts from a bath. This method can reduce the
thickness of a drag-out layer because of surface tension effects.
Increasing the drain time over the plating tank.
Installing drain boards, drip bars, and drip tanks to capture the drag-out. The
collected drag-out can be fully or partially returned to the plating bath to make
up for evaporative losses. These devices save chemicals, reduce rinse
requirements, and prevent unnecessary floor wettings.
Proper racking: By careful racking and parts removal, entrapment of bath
materials on surfaces and in cavities is minimized. Methods to accomplish this
include:
parts should be racked with major surfaces vertical.
parts should not be racked directly over one another.
parts should be oriented so that the smallest surface area of the piece
leaves the bath surface last.
Designing parts to promote drainage, e.g, parts with no cups or shelves.
Designing plating racks with a minimum surface area, minimum horizontal
surfaces, no pockets, and an effective orientation to promote drainage.
Using air knives with oil-free compressed air to knock plating films off parts and
back into the plating tanks.
Using fog and spray rinses, parts can be spray rinsed with deionized water over
the plating tanks. This method is used when tank evaporation rates are sufficient
to accommodate the added volume of spray water.
A92-214.2 2-29
-------
In rack plating: Provide drain bars over the plating tank from which the rack can
be hung to drain for a brief period.
In barrel plating: Rotate the barrel over the plating tank to remove excess plating
solution.
2.5.5 Metal Recovery
Metals recovered from the waste stream can be recycled. The resulting detoxified (waste)
stream can then proceed to disposal, further minor treatment, or it can be recycled to
the rinse tanks if the required purity levels have been achieved. There are obviously two
major advantages to this type of treatment:- 1) expensive chemicals are recycled 2) the
wastewater volume is minimized or even eliminated. Several major methods for
recovering metals are available and are discussed below. The methods are:
2.5.5.1 Evaporation
2.5.5.2 Ion Exchange
2.5.5.3 Electrolytic Cell Process
2.5.5.4 Reverse Osmosis
2.5.5.5 Electrodialysis
2.5.5.6 Freeze Crystallization
Exhibit 2-14 identifies which metal recovery application is suitable for each electroplating
process.
2.5.51 Evaporation
This process is suitable for plating operations where high drag-out levels are experienced.
It is best used with multistage rinse tanks where the volume of water is reduced and the
concentration of contaminants is high. Such plating operations would include metal
cyanide baths, hot chromium baths, and ambient temperature nickel baths.
Wastewater entering the evaporator is distilled, the distillate is recycled to the third rinse
tank and the plating metals are returned to the plating tank. There are several types of
evaporators described in the following sections.
2.5.5JJ Rising Film Evaporators - see Exhibit 2-15
Wastewater enters the reboiler (a shell and tube heat exchanger with wastewater either
within the tubes or within the shell on the surface of the tubes) and forms a
vapor/droplet mixture. The mixture enters the separator and the water vapor passes to
the condenser and hence to the third rinse tank. The concentrate is recycled to the
reboiler until the concentration reaches a preset level. Once this level is attained, the
valve opens and passes the concentrate to the plating bath.
A92-214 2 2-30
-------
EXHIBIT 2-14. SUMMARY OF RECOVERY TECHNOLOGY APPLICATION
Metal
Recovery
Techniques
Evaporation
Reverse
Osmosis
Ion
Exchange
Electrolysis
Electro-
dialysis
Plating Baths
Decorative
Chromium
X
X
Hard
Chromium
Nickel
X
X
X
X
Electro-
less Nickel
X
Cadmium
(CN)
X
X
X
Zinc
(CN)
X
X
X
X
Zinc
(Cl)
X
X
X
Copper
(CN)
X
X
X
X
Tin (BF4)
X
X
X
Silver
X
X
X
X
10
Source: (U.S. Environmental Protection Agency, 1985. Environmental Pollution Control Alternatives - Reducing Water Pollution Control
Costs in the Electroplating Industry).
NOTE: An "X" identifies which metal recovery process is suitable for the noted electroplating process.
A92-214 2
-------
10
6
10
KEDOILER"
l.ic|iiid/va|>or
Steam or -
hot water
Cmidonsatu -^
or warm water
Waslcwater
Water vapor
SEPARATOR
no
Liquid rccirculation
-<- Deinister
Concentrate
CONOFNSER
VACUUM PUMP
The hcatimj iiKuliiiin and wastcwnter may Ix: interchatujed in the
shell inul tuhes, dcpcndiiH) on the iiiiiiuifatituror.
Exhibit 2-15. Rising Film Evaporation
-^-Cooling water
Coolinrj water
Distillate
A V2
-------
2.5.5.1.2 Flash Evaporators - see Exhibit 2-16
This process is very similar to the rising film evaporator except that some of the plating
bath is continuously recycled through the evaporation system. Some of the plating
solution flashes off in the separator and provides heat to the wastestream. This reduces
the overall energy
2.5.5J.3 Submerged Tube Evaporators - see Exhibit 2-17
This process involves only a single unit, which minimizes capital expenditure. The
submerged tube unit operates under a vacuum 492-914 kg/m2 (0.7 - 1.3 Ib/in2) created
by diverting some of the cooling water through an external educator. Heating coils are
immersed in the boiling wastewater. Distillate passes through a demister and is
condensed via the cooling coils. It is then passed to the final rinse tank. The
concentration of chemicals in the boiling wastewater becomes steadily more concentrated
until a preset level is achieved, at which time the solution is returned to the plating tank.
Unlike the rising film and flash evaporators, the wastewater is not continually
recirculated.
2.5.5.1.4 Atmospheric Evaporators - see Exhibit 2-18
Wastewater passes through a heat exchanger (shell and tube). The vapor mixes with
ambient air and is discharged to the atmosphere as saturated air. The contaminated rinse
water is recirculated until it reaches a preset concentration level, at which stage it is
returned to the plating tank. With this process, no condenser unit is required as the
water vapor is discharged to atmosphere. However because of this, water needs to be
added to the rinse tanks. De-ionized water should be used to avoid build-up of minerals
in the plating tanks.
2.5.5.7.5 Double Effect Evaporators - see Exhibit 2-19
The wastewater stream is split between two reboilers. The vapor from the first stream
enters the second reboiler and hence supplies thermal energy as it condenses. This
process requires extra capital expenditure, yet does provide a method of treating two
separate waste streams. The steam requirements are also reduced.
2.5.5.1.6 Mechanical Vapor Recompression - see Exhibit 2-20
The mechanical compressor superheats the vapor and increases pressure before it is
passed to the boiler. This process avoids the need for any external steam source.
In the case of all evaporators, careful choices need to be made for the material of
construction of the condenser and evaporator units, in order to resist the corrosive
properties of the plating chemicals eg: use titanium, tantalum, borosilicate glass, FRP
(fibre glass reinforced plastic), stainless steel, or PVC (polyvinyl chloride). Carbon steel
is suitable for use in alkaline cyanide recovery.
A92-214.2 2-33
-------
Sleam or -
hot water
Condcnsale -<
or warm water
Wastewater
Liquid/vapor
Witter viipor
Slil'ARATOR
Liquid rccirculation
Demislc-r
To bath
From b.i
U CONDIINSnil
VACUUM I'UMP
The huating medium und wastewater may l>e inturchoiKjed in the
shell and lubes, depending on the manufacturer.
Exhibit 2-16. Flash Evaporation
Cooling water
Cooling water
Distillate
A92-2
-------
EDUCTOft
Coolina water
DEMISTER
Nonccndensables
Hot water
or steam
Warm water or
condensate
Concentrate
Exhibit 2-17. Submerged Tube Evaporation for Chemical Recovery
A92-214.2 2-35
-------
Saturated air
PACKED
TOWER
EVAPORATOR
Air inlet
Wastewater
Concentrate
Steam
Steam
concensa:e
HEAT
EXCHANGER
RESERVOIR
REC1RCULATION
PUMP
Exhibit 2-18. Atmospheric Evaporation for Chemical Recovery
A92-214.2 2-36
-------
vapor
Vapor
SEPARATOR
Liquid/vapor
SI en in
S tea in
X
Wastewnlcr
REUOILER
First effect
SEPARATOR
l.i(|iiicl/vapor
KEHOILEK
Second effect
Vacuum
CONDENSER
Cooling water
Cooling Water
ACCUMULATOR
Distillate
Concentrate
Exhibit 2-19. Double-effect Evaporation for Chemical Recovery
A92-214.2
-------
Vapor
ro
(1)
00
COMPRESSOR
Desuperheating
Water —
ACCUMULATOR
Return
to rinse
VACUUM
PUMP
H
Distillate
r
Concentrate
SEPARATOR
Rt-BOILER
Liquid
recirculation
Wiistewater
Exhibit 2-20. Mechanical Vapor Recompression Evaporation for Chemical Recovery
'4.2
-------
2.5.5.2 Ion Exchange
This process is suitable for purification of spent plating baths, recovery of anodizing
baths and the recovery of plating materials from rinse water solutions (copper, zinc,
nickel, tin, cobalt and chromium).
Metals and impurities are removed by using polymeric resins which replace harmful or
valuable ions in solution with safe, inexpensive ones. The cations removed are generally
replaced by hydrogen ions and anions removed are replaced by hydroxide ions. This
method reduces the concentration of dissolved metals to less than 0.5 mg/1 and is
suitable for dilute solutions. The exchange resins are regenerated with acid (for cation
regeneration) and alkaline (anions). It is important that the rinse water is prefiltered to
remove grease, oil and solids which may foul the resins.
Chromic acid recovery (see Exhibit 2-21) represents a good example of ion exchange.
The rinse water from chromic acid plating is collected in a wastewater reservoir. It is
then passed through a cation and two anion columns. The cation column removes the
heavy metals from the solution. The anion columns remove the chromate ions. The anion
resin is regenerated by the addition of sodium hydroxide to the anion columns, resulting
in the formation of sodium chromate. The sodium chromate is transported to the second
cation column, where it is regenerated to chromic acid, by the addition of hydrochloric
acid. (The sodium ion is replaced with a hydrogen ion.)
25.5.3 Electrolytic CeU Process
This process is suitable for the recovery of metals, oxidation of cyanide (by addition of
sodium chloride to the rinse water), and the reduction of hexavalent chromium. It is also
suitable for the regeneration of ammoniacal and chloride etch solutions during metal
recovery. These systems recover 90-95 percent of the available metals.
Rinse water is passed through the electrolytic cell. The metal ion is plated onto the
cathode. Once a certain thickness has been reached, the metal is removed (usually by
scraping). Good agitation is required. The rinse water concentration should generally be
in the range of 2 - 10 g/1 for homogenous metal deposition. This process, known as
electrowinning, is illustrated in Exhibit 2-22.
High surface area cathodes can be utilized for more dilute concentrations (10-50 mg/1).
Strips of metal up to a half inch thick are formed on the cathode. In this situation the
treated rinse water can be disposed to the sewer.
Planar cathodes are flexible and as such the deposited metal can be removed simply be
flexing the cathode.
A92-214 2 2-39
-------
Exhibit 2-21
ION EXCHANGE SYSTEM FOR CHROMIC ACID RECOVERY
Plotlng
Both
toni.
H««KVuW
ID tJolkig fcolh
-- •..—..»-»-^^«__
s: 3
boo Car
„ fit
X 3
j 3
IT Ml
L__J
_M
[
\
IkMI
w .
'
-------
PLATING BATH
RECIHCULATED
muse
RUNNING RINSE
WORK
10
\
ELECTROLYTIC
CELL
Rinse
water
To Drain
Exhibit 2-22. Drag Out Recovery From A Recirculated Rinse: Electrolytic Cell
A92-2142
-------
A fluidized bed electrochemical reactor is also suitable for dilute solutions of cadmium,
nickel, nickel-iron alloy, copper and zinc. The cell has a set of apertured, expanded-
metal-mesh electrodes immersed in a bed of small beads. The bed is fluidized to twice
its original depth. The glass beads continually scrub the surface of the electrode and thus
promote mixing, ensuring fresh solution is continually brought to the surface of the
electrode.
2.5.5.4 Reverse Osmosis
This process is suitable for recovery in many different electroplating applications - acid
nickel plating; cyanide copper, zinc and cadmium plating; copper sulfate. It is not
suitable for solutions with a high oxidation potential eg: chromic acid or extreme pH
solutions where the membrane can be destroyed.
The process employs a semi-permeable membrane (tubular, spiral wound or hollow
fibre) within a pressure vessel The feed stream enters under pressure 281,200 - 562,500
kg/m2 (400 - 800 Ib/in2). Selective permeation of the ions produces a purified permeate
stream and a concentrated stream. The concentrated stream can then be recycled to the
plating tank, while the purified stream can be re-used as a rinse stream.
This can be used for either plating drag-out recovery (see Exhibit 2-23) or wastewater
stream metal recovery illustrated in Exhibit 2-24. It is expected that 90 percent of metals
should be recovered in this manner, which greatly reduces any end-of-pipe treatment.
The unit generally functions continuously and has low operating costs with electricity the
only operating cost. The membrane can however become plugged up by suspended solids
or precipitate products. This can be avoided by upstream filtration prior to reverse
osmosis processing.
A modification of the typical reverse osmosis process is advanced reverse osmosis. This
process can achieve concentration ratios of up to 10,000 : 1 using lower performance
membranes. The difference is that while the clean water is returned to the rinse tanks,
the concentrate is held in a storage tank for further passes in order to achieve the
required concentration. The system is fully automated and controlled by a
microprocessor which directs the flow of the various streams without operator assistance.
The membrane materials and system components are specially designed to suit the
environment and thus enhance the life of the membrane.
Exhibit 2-25 illustrates the concentration ratios that can be achieved with advanced
reverse osmosis, the number of passes required and the life of the membrane for various
plating operations.
25.5.5 Electrodiafysis - see Exhibit 2-26
This process is suitable for recovering drag-out plating constituents from rinsewater eg:
from nickel, acid zinc, zinc cyanide and chromium plating operations and also for
regenerating chromic acid etchant.
A92-214 2 2-42
-------
Surface
Evaporation
to
J^
OJ
Make-Up
Water
Dr«ig-0ul
Drag-Out
PLATING
BATH
(I)
Parts
Filter
I
1
FIRST
RINSE
'
R.O.
UN
330 SQ
T
.FT.
fcfe
SECOND
RINSE
Parts
Permeate Recycle
(T)
To Waste
Treatment
Concentrate Recycle
Note: Reverse Osmosis Unit Performance Rased on
Solids Rejection and 951 Product Recovery
Flux Rate = 0. 10 C;il/h/Fl2
Drag-Out Recovery =
90%
Stream
No.
1
2
3
'1
5
6
7
8
Flow Rate
gp»
3.0
1.0
t.O
15.0
15.0
57.0
GO.O
3.0
Total Dissolved
Solids--Mfj/l
_-
252.500
'1,300
30
300
06
1.300
8 '1,000
Exhibit 2-23. Plating Dragout Recovery Using Reverse Osmosis
-------
Make-Up
WASTE WATER
HOLDING TANK
Permeate Recycle
Concentrate
f
Secondary Batch
Treatment Tank
Notes: Stage 1 R.O. Unil--Solicls Rejection = 95%
Product Recovery = 90%
Stage 2 R.O. Unit — Solids Rejection • 90%
Pioducl Recovery = 90%
Purified Rinse Water Savlnns - 13G5C.nI/h
Hascd on 99% Recycle
Si cam
No.
1
2
3
'1
5
G
7
B
Flowrate
«!>»
13G5
1500.
1350
13G5
150
US
15
15
Total Dissolved
Solids--M(]/l
1,00'I.S
1.000
50
50
9.550
955
UG.900
30
Exhibit 2-24. Mixed Waste Water Recycle Via Reverse Osmosis
A92-2
-------
EXHIBIT 2-25. ADVANCED REVERSE OSMOSIS
Plating
Acid Copper Sulfate
Copper Pyrophosphate
Tin/Lead Fluoborate
Bath
pH
0
8
0
Concentration
Ratios
40
200
10
Passes to
Required Strength
3
2-3
4
Membrane
Life (mos)
6+
6+
6+
Tin and Tin/Lead Methane
Sulfonic
Electroless Copper
Electroless Nickel
Bright Nickel
Nickel Sulfamate
Watts Nickel
Zinc Chloride
Zinc Cyanide
Copper Cyanide
Cadmium Cyanide
Hexavalent Chrome
Etchants
Peroxy-Sulfuric
Ammonium Chloride
Chromic-Sulfuric Acid
Sulfuric Acid
Hydrochloric Acid
3.6
12
10
4.3
4
4.4
4.9
12
13.5
12
-.14
0
8
-.5
0
.5
100
1000*
250
110
250
100
30
25
30
25
100
30
60
70
40
20
2-3
1*
2
2-3
2-3
2-3
3
3
3
3-4
2-3
4
3
2-3
3-4
4
6+
6+
6+
6+
6+
6+
6+
6+
6+
6+
1
1-2
6+
1
6+
6+
Coatings/Sealers/
Passivators/Cleaners
Chelated Lead
Brightener
Chrome Iridite
Nickel Acetate
Nitric Acid
Sodium Hydroxide
13.5
2
5.5
1
13.5
80
10.8
150
30
20
2
2-3
2
4
4
4 +
1 +
6+
1
3 +
"Special membrane, selective separation.
A92-214.2
2-45
-------
to
L
Cs
WO II K
V X
*'*'-V:» if !
PLATING
CONC. PLATING
D n A Q O U T
FILTER
oj
V.
RIN3E TANKS
r T
PUR IF IE I) RINSE
A = ANION-SELECTIVE MEMBRANE
C = CATION-SELECTIVE MEMBRANE
M + = CATIONS
X- = ANIONS
CATHODE
LA_
c
DILUTING
CIRCUIT
A
:;i.
Q
•^
M <
t
{
y
<
>
|
M -
/
X -
|
/
<
\
1
M i
/
X7
M
/
^
#
ANODE
CONCENTRATING
/ CIRCUIT
Exhibit 2-26. Electrodialysis System
A92-
-------
Anion-permeable or cation-permeable membranes are employed. Electrodes create an
electrical potential which causes anions and cations to move across the respective
membranes. The ions move from the dilute circuit to the concentrating circuit. Multiple
passes may be required. It is important to maintain turbulent flow for efficiency. A high
recovery rate of up to 95 percent is expected. There is no residual to be disposed of as
both streams are recycled.
25.5.5J Electrodiafytic Ion Exchange Cell (EDIX) - see Exhibit 2-27
In this process, wastewater enters the regenerate chamber. The hydrogen and metal ions
migrate across the cation-permeable membrane to the concentrate chamber. There now
remains an excess of negative ions in the regenerate chamber. Water is broken down to
a hydrogen and hydroxide ion. The hydrogen replaces the migrating ions and the
hydroxide is discharged at the anode as oxygen with further formation of water.
The concentrate chamber now has an excess of positive ions. Again water breaks down
into the hydrogen and hydroxide ions. Hydrogen migrates to the cathode and is released
to the atmosphere, while the hydroxide ion neutralizes the positive ions that have
migrated across the membrane. More than one pass is usually required in order to
achieve the desired concentration levels.
2.5.5.6 Freeze Crystallization
In this process, wastewater is mixed with an immiscible refrigerant eg: Freon. As the
refrigerant evaporates, the solution forms a mixture of pure ice water crystals and
concentrated contaminants. The crystals are separated, washed and melted to give pure
water. The contaminant stream containing the metals can be recycled to the plating tank.
This process has both high capital and operating costs and is therefore only suitable for
treatment of a very small volume of water.
2.5.6 Plating Bath Regeneration
Plating tank solutions become spent due to a build up of impurities. This is a major
source of hazardous waste. The plating bath can be regenerated using activated carbon
or dummying.
2.5.6J Activated Carbon
Activated carbon absorbs the products from the breakdown of organic brighteners,
polymeric photoresist additives and inorganic impurities. Hydrogen peroxide is added to
oxidize the volatile organic contaminants. The used carbon from this process is disposed
of at a hazardous waste landfill. Typically, a copper bath needs to be treated every 3
months and a solder electroplating bath needs treatment every month.
A92-2142 2-47
-------
K)
-k
CC
ANODE
FROM RINSE TANK
I
0
OH
REGENERATE
CHAMBER
(R)
H
TO FINAL TREATMENT
FROM CONCENTRATE TANK
II
XDNCENTRATE
CHAMBER
(C)
CATIONS
OH
CATHODE
H
TO CONCENTRATE TANK
-• DIPOLAR MEMBRANE
CATION
.l!: VflUMRRANE
Exhibit 2-27. Schematic diagram of the electrodialytic ion exchange (EDIX) cell.
-------
2.5.6.2 Dummying
This method selectively removes a particular impurity. For example: copper can build
up in a zinc or nickel bath. In order to remove the copper, an electrolytic panel is added.
A low (trickle) current is applied and the copper is deposited on the electrode. The bath
needs to be taken out of process during this operation - usually 1 or 2 days, but the life
of the bath can be substantially extended using this simple technique.
2.6 WASTEWATER TREATMENT PROCESSES
Unless one of the previously mentioned metal recovery processes or wastewater
elimination methods is employed, the waste stream will require some treatment before
disposal. The main toxic contaminants that require removal include hexavalent
chromium, cyanide and heavy metals. The treatment processes described below deal with
the removal of these three components.
2.6.1 Hexavalent Chromium Reduction
2.6JJ Sulfur Dioxide Reduction - see Exhibit 2-28
In order to remove the chromium from the waste stream, it is necessary to precipitate
the insoluble hydroxide. To achieve this, any hexavalent chromium present in the waste
must first be reduced to the trivalent state. Sulfur dioxide or sodium bisulfite is used as
the reducing agent. The pH must be kept low in order to optimize the oxidation
reduction potential (ORP), which is achieved by the addition of sulfuric acid. The
hydroxide is then precipitated by raising the pH.
This is proven, reliable technology with easy operator control, although it does increase
the volume of sludge produced. Hexavalent chromium is reduced to less than 0.05 mg/1
26.7.2 Ferrous Sulfate Reduction
The process is very similar to sulfur dioxide reductions discussed above, except ferrous
sulfate is added instead of sodium bisulfite. The conditions can be acidic or alkaline. The
advantage of using ferrous sulfate is that it is a natural byproduct of steel pickling and as
such is readily available. The disadvantage of the process is that it produces additional
sludge as the result of the precipitation of the ferrous hydroxide. The advantage of
alkaline conditions is that the neutralization step following acidification is no longer
required. The residual of hexavalent chromium is reduced to less than 0.05 mg/1.
26.13 Sacrificial Iron Anodes
A consumable iron electrode is used up in this process. An electric current generates
ferrous ions which reduce the chromium to the trivalent form. The reaction proceeds at
neutral pH. It is an inexpensive technology, but does increase sludge volume due to the
addition of ferrous hydroxide.
A92-214 2 2-49
-------
NaHSO3
SUPPLY
Waslewater
T T
- PR PC
SUPPLY
t o
'•jtraliration
O
-------
2.62 Cyanide Oxidation
2.6.2J Alkaline Chlorination - see Exhibit 2-29
This two stage process to reduce cyanide in the waste stream operates as follows:
1. Sodium hypochlorite or chlorine gas and sodium hydroxide are added. (The
latter is cheaper but chlorine gas requires careful handling) The pH is
maintained at 10 or above. In this reaction the cyanide is converted to the
cyanate form in only two minutes.
2. Further sodium hypochlorite is added at pH of 8.0 - 8.5 with a residence
time of between 30 - 60 minutes. The cyanate forms nitrogen gas and the
carbonate.
The cyanide concentration in the waste stream is reduced to less than 1 mg/1. In order to
properly control the reaction, it is important to recognize the end point of the cyanide to
cyanate reaction and therefore a reliable ORP control system is required. Continual
agitation is required to avoid the precipitation of solid cyanides. The process cannot
oxidize stable cyanide complexes (e.g., ferrocyanides), which should be separated
upstream.
2.6.2.2 Electrolytic Oxidation
This process is suitable for high levels of cyanide waste. A 20,000 mg/1 solution can be
reduced to 0.5 mg/1 - ie: a reduction of 99.99 percent. The cyanide waste stream is
subjected to electrolysis at 93°C (200°F) for several days. The cyanide is broken down via
the cyanate to carbon dioxide and ammonia. The reaction slows down as the electrolyte
is used up and also as the current flow is reduced by scaling on the anode.
2.6.2.3 UV Light/Ozonation
This process is generally used for aqueous wastes that contain a high proportion of
oxidizable constituents e.g., the final treatment step of a waste stream. It is also suitable
for complexed cyanides. The cyanide stream is mixed with ozone and enters a reaction
chamber. The stream passes several UV lamps. The UV radiation enhances oxidation of
the cyanide to nitrogen and hydrocarbonate. The destruction rate can be improved by
elevating temperatures to 65°C (150°F), increasing the ozone concentration and
introducing a catalyst metal ion, such as copper.
2.6.2.4 Wet Air Oxidation - see Exhibit 2-30
This process is suitable for a wastestream concentration of greater than 1 percent, which
can be reduced to less than 1 mg/1 - a cyanide destruction rate of over 99 percent. The
wastewater is combined with oxygen at temperatures and pressures up to 326°C (620°F)
and 2.2 million kg/m2 (3000 psig) respectively. A feed chemical oxygen demand (COD)
concentration of 2 percent is sufficient to cause a temperature rise and liberate volatile
A92-2142 2-51
-------
NaOU
STORAGE
Cyanide
Waslewater
r
(OKP
NaOH
NaOCI
M
T
I
I
NaOCI
SIOUAGI:
^— j_
lL- i
Neutralization
Exhibit 2-29. Two-Stage Cyanide Oxidation System
-------
F-007 CYANIDE RUN
to
L/i
DILUTION
WATCH
HICM-
PftESSURE
PUUP
HIGH
PRESSURE
PUUP
RCACTOR
HIGH
RECIRCULATION Pfl|1^1S1U,'
PUUP PUMP
AIR
AIR
COMPRESSOR
C
•*
n
i
•
PREHCATCR
OXIDIZCO
UOUOK
Exhibit 2-30. Cyanide Oxidation: Schematic Diagram of Zimpro/Passavant Wet Air Oxidation Process
A92-214.2
-------
components. The solubility of oxygen is enhanced by the elevated pressure and the
oxidation is encouraged by higher temperatures. The wastewater/oxygen stream enters
the reactor where it is oxidized to the carbonate and ammonium ions. The oxidized
liquor proceeds to neutralization and metal precipitation.
There are two main types of reactors: a) the tower reactor is a vertical vessel, where air
is introduced from atmosphere to interface with the feed; b) the cascade of completely
stirred tank reactors is a series of horizontal chambers within a horizontal cylinder. Air is
injected into each chamber as the feed progresses through the chambers.
2.6.2.5 Thermal Oxidation
The thermal oxidation process uses a heated reactor to destroy the cyanides by thermal
decomposition. This is ideal for high concentrations of cyanides - e.g., spent baths,
cleaners, strippers, and concentrated rinse water.
26.26 Ozone Oxidation
This process is used as an alternative to alkaline chlorination of cyanides. In this process,
the wastewater is shattered into a fine mist within a rotary vacuum filter. The resulting
particles have a greater surface area for contact with the ozone gas. When the smaller
wastewater droplets are exposed to the ozone, it oxidizes the cyanide content of the
waste stream.
2.6.3 Metal Precipitation
26.3J Hydroxide Precipitation - see Exhibit 2-31
After the chromium stream has been segregated and reduced, the cyanide stream has
been segregated and oxidized, all streams are collected and neutralized, at which stage
the metals are precipitated and the solid wastes separated.
Hydrated lime (calcium hydroxide) or sodium hydroxide can be utilized for metals
precipitation. This is accomplished by control of the pH level in order to minimize the
solubility of the metals present. Exhibit 2-32 illustrates the different pH levels for
minimum solubility of various metals.
Hydrated lime vs Sodium hydroxide
longer reaction time short reaction time
(30 mins) (15 mins)
high solids content light, fluffy floe
(1,370 mg/1) (230 mg/1)
faster settling rate
A92-214.2 2-54
-------
NaOH
SUPPLY
Wastewater
SUPPLY
V"?
i
_!
To Flocculation/
Clarification
Exhibit 2-31. Hydroxide Precipitation - Stream Neutralization
A92-214.2 2-55
-------
EXHIBIT 2-32. METAL SOLUBILITY AS A FUNCTION OF PH
Dissolved Metal Concentration (mg/1)
Raw pH pH pH
Metal Wastewater 8.4 8.8 9.2
Chromium (total) 45.0 0.1 0.11 0.1
Cadmium 1.0 0.02 0.02 0.02
Copper 25.0 0.02 0.02 0.03
Nickel 10.0 0.20 0.20 0.20
Iron 20.0 NM NM NM
Note: NM = not measured.
A92-214.2 2-56
-------
Each of these neutralizing agents (hydrated lime or sodium hydroxide) has benefits. The
comparison above illustrates the differences. A denser floe is desirable as it reduces
sludge dewatering requirements.
A one or two stage neutralizer can be utilized. A single stage involves the addition of
both acid and base to the same tank. Two stages are utilized for wider swings in reagent
demand.
2.6.3.2 Sodium bomhydride
Sodium borohydride is a strong reducing agent, capable of precipitating metal ions to
elemental metals. Ninety-five percent reduction in total metals can be achieved from a
complex waste stream. It also produces a low volume of sludge. The precipitated metals
can then be reclaimed. The operating and capital costs are higher than for conventional
hydroxide precipitation.
2.6.3.3 Sulfide Precipitation
In this process, the sulfides are precipitated instead of the hydroxides. Sodium sulfide or
ferrous sulfide can be utilized. This method is expensive and creates additional sludge
volumes. The main advantage of this method is that metal chelates can be removed.
Metal ions form chelates with certain other compounds present in the waste stream such
as: ammonia, phosphates, and tartrates. The chelates are soluble under alkaline
conditions and as such will not precipitate out under hydroxide treatment.
2.7 HAZARDOUS SOLID WASTE MANAGEMENT
During the neutralization step in the waste treatment cycle, many metals will precipitate
out. Other suspended solids will also be contained in the waste stream such as: large
organic molecules, complexed heavy metals, oil and grease. In order to separate out the
solids, coagulation or flocculation need to occur, after which the waste stream will be
clarified. The separated solids or sludge will only be between 0.5 - 3.0 percent by weight.
In order to reduce the amount of water in the sludge (concentrate it), the sludge needs
to be dewatered. See Exhibit 2-33 for a simple schematic of the whole waste treatment
process.
For example, the typical levels of pollutants in the sludge from a nickel, chromium and
zinc plating operation were found to be:
oil & grease 93,000 mg/kg
nickel 155,600 mg/kg
iron 84,400 mg/kg
chromium 24,620 mg/kg
zinc 11,900 mg/kg
copper 7,100 mg/kg
lead 270 mg/kg
cadmium 7 mg/kg
other 623,103 mg/kg
A92-214 2 2-57
-------
Bisulphite
ciilonnu
Acid
F'olyinai
Clarification
Cyanide Oxidation
Flocculalion
Precipitation
Sludge
Thickening
Cr Reduction
Acid/>
Riueo Waters
Filter Press
•"•/•
Wnatewater
Discharge
Collection
Exhibit 2-33. Conve nal Waste Treatment
-------
There are a variety of processes employed to thicken (concentrate) the sludge. These
processes are described in the following text.
Coagulation is the process of mixing coagulants with wastewater and then creating large
particles which will settle through the process of flocculation. Initially, coagulants are
added to the wastewater to form small particles with the wastewater constituents.
Coagulants are generally inorganic chemicals such as: alum, lime or ferrous sulfate.
Flocculation occurs through the growth of larger, more dense particles that have good
settling characteristics. Floe builders are conventionally organic polyelectrolytes and are
added after the neutralizing step ie: after precipitation. Gentle tank agitation is required.
2.72 Clarification
A clarifier is a settling chamber where the solids are separated from the waste stream
solution. The resulting wastewater stream should only contain 5-50 mg/1 solids, while
the resulting sludge stream should be between 0.5 - 3.0 percent solids by weight. Three
types of clarifiers utilized in the industry are described below:
27.27 Rectangular Clarifier - see Exhibit 2-34
Basic settling chambers are usually rectangular tanks. The wastewater stream is fed into
one end of the tank and overflows at the other. The solids settle to the base of the unit
and are raked to a sludge well at regular intervals by a travelling scraper bridge.
27.22 Circular Clarifiers - see Exhibit 2-35
In the circular clarifier, the incoming feed is mixed with a sludge blanket that is
maintained within the chamber. The new solids join the sludge blanket and the clean
effluent is removed from the tank.
27.23 Plate Settlers - see Exhibit 2-36
A plate settler consists of angled plates. As the solid particles settle due to gravity
through the solution, they impinge on one of the angled plates and then slide down to
the bottom of the tank. This accelerates the rate of settling. This unit is the smallest and
hence most suited to applications where there is limited space available.
2.7.3 Sludge Dewatering
Sludge waste from plating operations is normally considered hazardous, due to the
possibility of leaching metals. As such, it requires careful disposal. It is therefore
desirable to reduce the volume in order to reduce disposal costs. Sludge dewatering can
be carried out using different filter techniques is noted below.
A92-214.2 2-59
-------
10
c\
o
INFLUENT SURFACE SKIMMER
MIXING CHAMBER ULADL
SCUM TROUGH
\
CQ
i^- i _
V
\
(1:
t
^ —
-?. »-
TRAVELING rilUOGE
AMI) TRACTION DUIVE
EFFLUENT
WEIR I'LATE
"7°"%^ 3_Sl
_
BAFFLES
:LUF.NT PIPC
SLUDGE WELL
SLUDGE DRAWOFF PIPE SLUDGE SCRAPER HLADE
Exhibit 2-34. Rectangular Clarifier Basin
-------
EFFLUENT COLLECTOR FLUME
AGITATOR
CHEMICAL I-EIED INl.HTS
X
IIIFI.UENT
V SKIMMIMG
-•--
00000000 0 O O O/..•:..
OO 00 00 0000
p--i
SLUDGI:
BLOW OFF
LINE
SAMPl.H -
PORTS
SLUDGE
CONCENTRATOR
MIXING HAFf
AGITATOR 20NIZ
ARM
PRECIPATOR
DRAIN
SWING
SAMPLE
INDICATOR
Exhibit 2-35. Solids Contact Clarifier with Sludge Blanket Filtration
(Courtesy of the Permutit Co.)
-------
Influent
— -V Effluent
£.'>'$:?:( *S-ir^:W^ Sludcje •:g^i&{;ffff&<
Exhibit 2-36. Inclined Plate Settler
2-62
-------
2.7.31 Filter Press- see Exhibit 2-37
The filter process is generally a simple plate and frame construction. The sludge is fed
into the cavities between the plates. When the cavities are full, the hydraulic ram applies
pressure. The filtrate is forced out through the filter media and ports in the plate. When
the filtrate starts to become concentrated with solids, the ram pressure is released. The
dried cake falls onto a conveyor or directly into a hopper. The solids content ranges from
20 - 50 percent by weight.
27.5.2 Vacuum Filters - see Exhibit 2-38
The sludge slurry is placed in a basin which is placed on a rotary drum consisting of
panels of filter material. A vacuum is applied to the panels and the sludge adheres to
the panel surface. Water and air are drawn through the panel by the vacuum and are
discharged to the filtrate outlet. The solids, adhering to the panel, are discharged in the
discharge area by air blown through the panel. Efficiency can be improved by precoating
the drum with diatomaceous earth, which acts as a filter medium. This technique is most
suitable for dilute sludges. The resultant solids content of the sludge cake is 15 - 40
percent by weight.
27.3.3 Basket Centrifuges - see Exhibit 2-39
The sludge slurry enters the centrifuge and the heavier sludge is rejected to the inner
wall while the clarified liquid is decanted from the top. When the basket is full, sludge
solids begin to overflow from the top. At this stage, the centrifuge is decelerated and a
rake pushes the sludge downwards off the inner walls. A solids content of 10 - 25 percent
by weight can be expected.
27.3.4 Pressure Belt Filter - see Exhibit 2-40
This method is ideal for treating highly compressible polymer treated sludges. This type
of sludge tends to collapse against the filter medium and block the transport of water.
The belt filter is made up of a series of belts, each applying more compression to reduce
the water content. The throughput can be accelerated by increasing the speed of the
belts, but with subsequent degradation.of solids content.
2.7.4 Ultraflltration/Microfiltration
Ultrafiltration/Microfiltration is an alternative to clarification and is an effective means
of removing suspended solid particles, oil, grease, large organic molecules and complexed
heavy metals. The concentrate is passed over a porous structure until the desired
concentration level is achieved. Turbulent flow is required to avoid build up of solids on
the surface.
Ultrafilters have a pore size of 0.001 - 0.1 micrometers which is suitable for metal
hydroxide precipitates.
Microfilters have a pore size of 1 - 5 micrometers.
A92-214.2 2-63
-------
Exhibit 2-37. Plate and Frame Filter Press
Solids Collect
in Frames
Plate
Fixed Head
Filtrate
Frame Movable Head
y_ Closing Device
-
Sludge -i
Feed
Under
Pressure
ii^JjLlLJ
Filter Cloth
A92-214.2
2-64
-------
Exhibit 2-38. Rotary Vacuum Filter
Dewatering Zone (cake Drying)
Rotation
Discharge Zone
Discharged Filter CaUe
Filtering Zone
A92-214.2
2-65
-------
Exhibit 2-39. Basket Centrifuge
Basket
Motor
Polymer Feed
Pipe
Sicht Class
Centrate
Discharge
Feed Inlet
A92-214.2
2-66
-------
Exhibit 2-40. Pressure Belt Filter
Gravity Drninage
Sludge
Sludge clumps to new belt
Internal water released
Flocculated
Sludge
iludge dumps to new bell:
• nteriinl wntor released —-"jL-
Low Pressure
Stncje
^ llitjli Pressure
Stjiye
Medium Pressure
Stage
A92-214.2
2-67
-------
2.7.5 Stabilization/Solidification - see Exhibit 2-41
The final sludge cake treated by any of the above processes, can de disposed of at a
chemical landfill or can be further treated. One such method of further treatment is to
stabilize or solidify the waste. A binder is used to form a concrete mix which is
chemically stable and prevents leaching of contaminants, is able to withstand a great
force and can resist crushing.
Stabilization is a chemical reaction which converts inorganic waste to the least soluble,
most environmentally inert form. Solidification improves handling, decreases surface
area and encapsulates the material in a monolithic solid of high structural integrity.
The waste is added to water and the binder (typical binders are cement, pozzolan,
thermoplastic). The stream is mixed, cured at room temperature for over 48 hours and
then cooled. It is important to determine the correct ratio of binder-water-waste at the
start of each batch to ensure the integrity of the concrete mix.
2.7.6 Fixing Metals in Slags - see Exhibit 2-42
Metal oxides can be bonded to silica to form silicates (or glass). The components are
fused into an homogenous liquid and then allowed to solidify. Other chemicals such as
soda (sodium oxide), need to be added to achieve fusion at low temperatures. The
residual slag can be crushed and sold as aggregate.
/
Further advantages of this technology are:
1. Hexavalent chromium can be dissolved in slags to about 6 percent and
remains resistant to leaching.
2. Dried sludges with nickel and iron oxides can be recovered as ingots by
addition of carbon which acts as a reducing agent.
example: 2450 g dried sludge + 1232 g additives
= 1079 g iron-nickel alloy ingots + 857 g slag
2.7.7 Resmelting of Metals
The waste sludge can be sent to a smelting facility in order to extract the metal content.
A92-214.2 2-68
-------
WASTE TO
BE
STABILIZED/'
SOLIDIFIED
N>
c\
VO
WATER BINDER
LJ.
WATER BINDER
WATER-TO-
WASTE AND
BINDER-TO-
WASTE RATIO
SELECTION
hM
BATCH
PREPARATION
CURING
to-
DETERMINATION
OF CONFINED
COMPRESSIVE
STRENGTH AT 7.
H. 21 AND 28 DAYS
TOXICfTY
CHARACTERISTIC
LEAGUING
PROCEDURE
(AFTER 28 DAY
CURE)
ANALYSIS
OF
LEACMATE
INITIAL SCREEN TESTING
UCS TESTING
TCLP TESTING
Exhibit 2-41. Flowchart for WES Stabilization/Solidification Processing
A92-214 2
-------
Additives
Dried
sludge
Blender
Tilt
Furnace
Hot
Metal
Metal
Moulds
ro
Cooler
to Resale
Cool
Metal
Crusher
Excess slag
to resale
Slag
Storage
Slag to
additives for
recycle
Exhibit 2-42. Metal Slag Recovery System
-------
Bibliography
Electroplating Wastewater Pollution Control Technology - George C. Cushnie, Jr.
Characterization and treatment of wastes from metal finishing operations EPA/600/2-
90/055. November 1990.
Waste minimization audit report: case studies of minimization of solvent wastes and
electroplating wastes at a DOD installation. EPA/600-52-88/010. March 1988.
Guidelines for waste reduction and recycling - metal finishing, electroplating. Printed
circuit board manufacturing hazardous waste reduction program of Oregon, July 1989.
Waste audit study - metal finishing industry PRC Environmental Management, Inc. San
Francisco, CA May 1988.
Recovery of rinse water and plating both from process rinses using advanced reverse
osmosis. Ronald R. Rich and Thomas von Kuster Jr. Water Technologies Inc.
Symposium Proceedings - September 1989. Metal waste management alternatives:
minimizing, recycling and treating hazardous metal wastes.
Process options for waste minimization and metal recovery for the metal finishing
industries by C.W. Walton, A.C. Hillier, and G.L. Pope University of Nebraska - Lincoln,
Department of Chemical Engineering. The Environmental Challenge of the 1990's
Proceedings. June 1990. International conference on pollution prevention: clean
technologies and clean products.
Source reduction opportunities in the plating industry by Terry Foecke (MNTAP) -
Metal Waste Management Alternatives: minimizing, recycling and treating hazardous
metal wastes - Symposium proceedings - September 1989.
Solids detoxification - Metals recovery by C.T. Philip, Enviroscience Inc. and William
Rostockes and J. Dvovsek, Rostoke Inc. - same symposium proceedings as ref. 8.
Other references consulted:
An electroplating case study of structuring information and modeling to produce more
with less: by P.M. Ros Cleaner Production, Canterbury, September 1990. EPT,
Department of the Environment (UK)
Closed loop plating system for waste minimization Larry Foss - Foss Plating Company -
same as symposium as ref. 8
Case study of a minimum discharge, heavy metal waste reduction system at Aeroscientific
Corporation, Anaheim, CA. Gary Hulbert and Bernard Fleet Toxic Recovery Systems
International. - symposium ref. 8
A92-214.2 2-71
-------
Recovery of metals in circuit board and metal plating manufacturing - Al Crane General
Dynamics, Pomona Division. - symposium ref. 8
Cal-tech management. Final Report
A92-214.2 2-72
-------
-------
CHAPTER 3
PRINTED CIRCUIT BOARDS
-------
TABLE OF CONTENTS
Chapter Page
3 PRINTED CIRCUIT BOARDS 3-1
3.1 Industry Description 3-1
3.2 Process Description 3-1
3.2.1 Raw Materials 3-1
3.2.2 Basic Processes 3-2
3.2.3 Subtractive Processing 3-2
3.2.4 Additive Processing 3-7
3.2.5 Alternative Process 3-7
3.3 Identification and Characterization of Emission Points and Waste
Streams 3-7
3.3.1 Air Emissions 3-8
3.3.2 Waste Streams 3-8
3.4 Pollution Prevention, Waste Treatment, and Control Systems 3-13
3.4.1 Cleaning and Board Preparation 3-13
3.4.2 Pattern Printing and Masking 3-19
3.4.3 Electroplating and Electroless Plating 3-21
3.4.4 Etching 3-26
3.4.5 General Wastewater and Sludge Treatment 3-28
Exhibits Page
3-1 Raw Materials Used in the Manufacture of Printed Circuit Boards 3-3
3-2 Printed Circuit Board - Manufacturing Process 3-4
3-3 Row Sheet and Waste Generation Points 3-9
3-4 Waste Streams from the Manufacture of Printed Circuit Boards 3-10
3-5 Estimated Waste Generation Levels of Copper for Typical Printed Circuit Board
Manufacturer 3-11
Bibliography 3-30
A92-214.3 3-i
-------
CHAPTER 3
PRINTED CIRCUIT BOARDS
3.1 INDUSTRY DESCRIPTION
Printed circuit boards are electronic circuits created by mounting electronic components on a
non-conductive board, and creating conductive connections between them. The creation of
circuit patterns is accomplished using both additive and subtractive methods. The conductive
circuit is generally copper, although aluminum, nickel, chrome, and other metals are
sometimes used. There are three basic types of printed circuit boards: single sided, double
sided, and multi-layered. The manufacturing processes for each type are very similar, with
multi-layered boards requiring the additional step of laminating.
3.2 PROCESS DESCRIPTION
There are two common methods of manufacturing printed circuit boards, additive and
subtractive. The additive method uses a non-conductive board and deposits conductive
material in a circuit pattern by electroless plating. The subtractive method uses a conductive
copper-clad board and deposits additional conductive material in a circuit pattern using both
electroless plating and electroplating. These two methods collectively are known as pattern
plating. An alternative method known as panel plating is described briefly in Section 3.2.4.
The additive method generally produces less metal waste, however it is a less common
process than the subtractive method. The following discussion focuses on the subtractive
method: however, the differences between the two methods are identified.
3.2.1 Raw Materials
The raw materials used in the manufacture of printed circuit boards include process chemicals
as well as items that constitute the end product The primary product materials are board
materials, copper and other conductive metals, tin/lead, and electronic components.
A92-2143 3-1
-------
Subsidiary processes which require additional raw materials include cleaning, electroless
plating, printing of resists and sensitizer, electroplating, and etching. Exhibit 3-1 illustrates
the raw materials used in the manufacture of printed circuit boards.
3.2.2 Basic Processes
There are five basic processes common to the manufacture of all printed circuit boards. They
are cleaning and surface preparation, electroless plating, pattern printing, electroplating, and
etching. These processes are completed in different sequences for the additive and
subtractive methods. Exhibit 3-2 illustrates the sequence of operations for both the additive
and subtractive manufacturing processes.
3.2.3 Subtractive Processing
3.2.3. J Board Cleaning and Preparation
The subtractive process uses a copper clad board. The copper material is fixed to the non-
conductive board with adhesive, screws, or pressure/heat bonding. These boards are
sometimes baked to ensure complete curing of the lamination. The process of making a
printed circuit board begins with the preparation of the circuit surface. The holes needed to
mount the electronic components are drilled, deburred, and sanded, and the board is cleaned
prior to the plating process. Cleaning is accomplished by immersing the boards in a bath of a
mild etchant, such as a peroxide/sulfuric acid solution which cleans the copper and removes
oxides.
3.2.3.2 Electroless Copper Plating
After cleaning, the boards are electroless plated with copper to provide a conductive layer
through the drilled mounting holes. Electroless plating involves the catalytic reduction of a
metallic ion in an aqueous solution containing a reducing agent, resulting in deposition
A92-2143 3-2
-------
EXHIBIT 3-1. RAW MATERIALS USED IN THE MANUFACTURE OF PRINTED CIRCUIT BOARDS
PROCESS
Cleaning and Prep
Electroless Plating
Pattern Printing and Masking
Electroplating
Etching
CATEGORY
Board Materials
Cleaners
Electroless Copper Bath
Catalysis
Screens
Screen Inks
Resists
Sensitizers
Electroplating Baths
Resist Solvents
Etchants
MATERIALS
glass-epoxy, ceramics, plastic, phenolic paper, copper Toil
sulfuric acid, fluoroacetic acid, hydroflouric acid, sodium hydroxide,
potassium hydroxide, trichloroethylcne, perchloroethylene, methylene chloride
copper sulfate, sodium carbonate, sodium gluconate, Rochelle salts, sodium
hydroxide, formaldehyde
stannous chloride, palladium chloride
silk, polyester, stainless steel
composed of oil, cellulose, asphalt, vinyl or other resins
polyvmyl cinnamate, allyl ester, resins, isoprenoid resins, methacrylate
derivatives, polyolefin sulfones
Thiazoline compounds, azido compounds, nitro compounds, nitro aniline
derivatives, anthones, quinones, diphenyls, azides, xanthone, benzil
copper pyrophosphatc solution, acid-copper sulfate solution, acid-copper
fluoroborate solution, tin, lead, gold, and nickel plating solutions
ortho-xylene, meta-xylene, para-xylene, toluene, benzene, chlorobenzene,
cellosolve and cellosolve acetate, butyl acetate, 1,1,1-trichloroethane, acetone,
methyl ethyl ketone, metliyl isobutyl ketone
Sulfuric and chromic acid, ammonium persulfate, hydrogen peroxide, cupric
chloride, feme chloride, alkaline ammonia
A92-2I43
-------
Order Entry
Job Planning/Eng.
Inspection
Incoming Documentation
Drill Programming
Shear Laminate
Drilling
L
Elactroless Copper
Through Hole Plating
Dry Film/
Screen Image for Plating
L
Touch Up
Pattern Plata
Copper, Tin-Lead
Resist Strip/Etch
Contact Finger Plating
Nickel/Gold
R«flow (Solder Fusing)
Inspection
Solder Mask/Legend
Fabrication (Routing)
Final Inspection &
Electrical Testing
Package & Ship
Photo
1. Programming Film
2. Inner Layer Film
3. Outer Layer Film
4. Solder Mask A Legend
S. Step and Repeat
6. Touch Up
7. Circuit Spread & Choke
Shear Thin Clad Laminate
Dry Film
Image for Etcher
Touch Up
Etch Copper
Resist Strip
Black Oxide
Inner Layer Inspection
Cut Prepreg
Inner Layer/
Prepreg Booking
Press Books into
Multilayer Panels
Exhibit 3-2. Printed Circuit Board PCB Manufacturing Process
3-4
-------
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without the use of external electric energy. The deposited layer is very thin, covers the
substrate uniformly, but is too thin to constitute a final circuit. To build the thickness and
strength of the circuit, additional layers of conductive material must be applied to the board.
3.2.3.3 Pattern Printing and Masking
Building up the thickness of the individual circuit is done with a selective deposition of
conductive material rather than the overall deposition practiced in the electroless setup. To
add metal on just the circuit areas, a layer of plating resist is applied to the non-circuit area of
the board, using screen printing or photolithography methods. This resist prevents the
adherence of electroplated metal to the non-circuit areas of the board. The circuit areas then
receive multiple layers of electroplated metals.
3.2.3.4 Electroplating of the Circuit Area
Electroplating is accomplished by immersing the board in a copper plating solution such as
acid-copper sulfate along with a pure metal anode. The anode is then electrically charged,
causing it to dissolve and be deposited on the board. The plating resist prevents the
deposition of metal on the non circuit areas. Several layers are deposited in this manner,
including a final layer of tin/lead to act as an etching resist.
3.2.3.5 Etching
Once the circuit has reached the desired thickness, the plating resist is stripped from the non-
circuit area exposing the non-circuit areas. The boards are then run through an etching bath
to remove the copper from the non-circuit areas. The circuit areas are protected from this
etching process by the final layer of tin/lead deposited during electroplating. The resulting
board has a strong electronic ckcuit, with conductive metal in the mounting holes and along
the circuit path. The electronic components are subsequently mounted to complete the board.
A92-214.3 3-6
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3.2.4 Additive Processing
The additive process uses a plain board, so the baking step is not required. It also reverses
the electroless plating/print resist steps. In the additive method the plating resist is printed on
non-circuit areas, defined by pattern printing and masking, before the electroless plating. This
prevents any copper from adhering to the non-circuit areas of the plain board and, most
significantly, eliminates the need to etch copper away from the non-circuit areas. Finally, the
circuit is built up to the desired thickness using electroless plating rather than electroplating.
3.2.5 Alternative Process
Both the additive and subtractive methods described above are pattern plating methods. In
pattern plating copper or other conductive metals are deposited only on the circuit areas, and
in the board's component mounting holes. An alternative method is panel plating. In this
method, the entire board is electroplated with copper to the desired circuit thickness, and an
etching resist is applied to the circuit areas. The board is then etched to remove copper from
the non-circuit areas. This method results in the production of more metal waste than pattern
plating, since a greater amount of copper is deposited on, and then removed from, the board.
3.3 IDENTIFICATION AND CHARACTERIZATION OF EMISSION POINTS AND
WASTE STREAMS
Each of the five common processes associated with the manufacture of printed circuit boards
results in specific emissions and waste streams. Air emissions customarily occur as part of
the board preparation process. Although rinse water is not the primary waste stream of any
one process, taken in total, it is the largest source of hazardous waste in the manufacture of
printed circuit boards.
A92-214.3 3-7
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3.3.1 Air Emissions
The emissions of air pollutants from the manufacture of printed circuit boards are
predominantly part of the board cleaning and preparation process while other emissions are
generally of much less significance. The majority of the emissions are acid fumes and
organic vapors from the cleaning processes. Some particulates are also emitted in the drilling
and finishing of the boards. Proper ventilation and exhaust of all process baths, rinse
operations, and mechanical operations is essential to managing the air emissions of a printed
circuit board manufacturing operation and can also contribute to reduction in liquid and metal
waste generation.
3.3.2 Waste Streams
Each manufacturing process may generate multiple waste streams. Rinse water and other
rinse solutions are usually the largest streams by volume but are generally lower in
concentration of hazardous chemicals than spent process baths. Exhibit 3-3 illustrates the
origins of each waste stream in the manufacturing process. Exhibit 3-4 contains a detailed
listing of the constituents of each waste stream. To put in perspective the rate of waste
generation for the critical streams of waste water, acid copper wastes, and total sludge from
metal bearing waste streams, Exhibit 3-5 has been developed to illustrate typical waste
generation rates. Contamination of rinse streams can be minimized by strategies that reduce
drag-out of process solutions. Treatment and reuse of rinse streams is also effective in
reducing overall waste generation. Such strategies are summarized in Section 3.4. Detailed
discussion of many of these strategies is found in the Electroplating chapter of this manual.
3.3.2.1 Cleaning and Preparation
Spent acid and alkaline solutions, flouride, and spent halogenated solvents from the cleaning
steps compose the primary wastes from this process. In addition, the wastewater stream from
the rinsing operation can contain suspended metals and paniculate board materials.
A92-2143 3-8
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COPPER-CLAD
BOARD
BOARD
PREPARATION
SURFACE
PREPARATION
CATALYST
APPLICATION
ELECTHOLESS
PLATING (FLASH)
IMAGE
TRANSFER
L_
ELECTROPLATING
(COPPER)
ELECTROPLATING
(SOLDER)
ETCHING
ELECTROPLATING
(TABS)
FINISHED BOARD
WASTEWATER WITH SOLIDS
WASTE ORGANIC SOLIDS/DETERGENTS
ACID OR ALKALINE RINSEWATERS
.+. RINSEWATERS CONTAINING TRACE
PRECIOUS METALS
.», SPENT PLATING SOLUTION
RINSEWATER CONTAINING COPPER
^ WASTEWATER WITH PHOTORESIST
SOME ORGANICS
SPENT PLATING SOLUTION
RINSEWATER CONTAINING COPPER
•*• SPENT PLATING SOLUTION
RINSEWATER CONTAINING TIN AND LEA3
SPENT ETCHANTS
RINSEWATER CONTAINING METALS
RINSEWATER CONTAINING NICKEL
SOME CYANIDES
MULTILAYER
BOARD
APPLICATION
c
FINISHED
MULTILAYER
BOARDS
j
Exhibit 3-9. Printed Circuit Board Production Flowsheet and Waste Generation (15)
3-9
-------
EXHIBIT 3-4. WASTE STREAMS FROM THE MANUFACTURE OF PRINTED CIRCUIT BOARDS
WASTE SOURCE
WASTE STREAM
DESCRIPTION
WASTE STREAM COMPOSITION
Cleaning/Surface Preparation
Spent acid/alkaline solution
Spent halogenated solvents
metals, flouride, acids, halogenated solvents, alkali, board materials,
sanding materials
Waste rinse water
Electroless Plating
Spent electroless copper bath
Spent catalyst solution
acids, stannic oxide, palladium, complexed metals, chelating agents,
copper
Spent acid solution
Waste rinse water
Pattern Printing and Masking
Spent developing solution
vinyl polymers, chlorinated hydrocarbons, organic solvents, alkali
Spent resist removal solution
Spent acid solution
Waste rinse water
Electroplating
Spent plating bath
Waste rinse water
copper, nickel, tin, tin/lead, gold, flouride, cyanide, sulfate
Etching
Spent etchant
Waste rinse water
ammonia, chromium, copper, iron, acids
A9M14.3
-------
EXHIBIT 3-5. ESTIMATED WASTE GENERATION LEVELS OF COPPER FOR TYPICAL PRINTED CIRCUIT
BOARD MANUFACTURER
* '$K" ^C^-^^Cf^^^%^^^fi^^^^^^^^^^^^^^^^^|f>^^^
Yi&^^^^^'^^^^^^^m^^^^^R^^^^^^^^^^^^S^^^^
PC Board Production Volume MVday (sq.ft./day)
Water Usage and Discharge litres/day (gal/day)
Acid Copper Plating Tank
Volume of Drag-out llr/day
Copper Metal Produced Kg/day
Equivalent to Kg/year
Percentage of Total Acid Copper Wastes
Total Copper Sources
Metal Produced Kg/day
Metal Produced Kg/year
Total Copper in Untreated Waste mg/kg
Sludge Generation @ 3% Copper metric tons/year (tons/year)
PRINTED CIRCUIT BOARD FACILITY
23 (250)
47,313 (12,500)
3
.08
18.75
10%
.75
187
15
5.44 (6)
371 (4,000)
757,000 (200,000)
48
1.2
300
10%
12
3,000
15
907 (100)
A92-214.3
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3.3.2.2 Electroless Plating with Copper
The waste streams in this operation are spent catalyst solutions, spent electroless copper bath,
spent acid cleaning solution, and waste rinse water. These streams contain acids, stannic
oxide, palladium, complexed metals, and chelating agents, but the major component of waste
is copper.
3.3.2.3 Pattern Printing and Masking
This process uses developing solution, resist removal solution, and acid cleaning solutions.
The process' waste streams are comprised of these spent solutions, and waste rinse water.
The streams contain vinyl polymers, chlorinated hydrocarbons, organic solvents, and alkali.
3.3.2.4 Electroplating and Electroless Plating
Spent plating bath (containing copper, nickel, tin, lead, and gold) is the major waste stream
from this process. This waste stream can also contain flouride, cyanide, and sulfate. Waste
rinse water is a secondary waste stream (in terms of the concentration of hazardous waste) but
is the highest volume stream and requires extensive treatment. Contamination of this rinse
water is a direct result of drag-out, and can be greatly reduced by drag-out reduction
strategies.
3.3.2.5 Etching
The majority of waste from this process is in the spent etchant, which contains ammonia,
chromium, copper, iron, and acids. The quantity of waste rinse water is also an important
factor in this process, and once again represents a high volume stream.
A92-214.3 3-12
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3.4 POLLUTION PREVENTION, WASTE TREATMENT, AND CONTROL
SYSTEMS
The methods of controlling waste from the manufacture of printed circuit boards vary from
proactive pollution prevention (waste minimization) techniques to reactive waste treatment.
Each of the five subsidiary processes in board manufacture can be subjected to: 1. product
substitution; 2. process modification including recycling and resource recovery; and 3. waste
treatment strategies. While these technologies are discussed in detail in Chapter 2 -
Electroplating, the significant features of the descriptions and process flow diagrams from that
part of the manual are summarized below.
The industry has two significant production method substitutions available which can have a
very positive effect on the volume of wastes produced in printed circuit board manufacturing.
The first, the use of Surface Mounted Devices (SMD), can reduce the overall size of a printed
circuit board by more than 50%, leading to lower raw material usage rates. The second,
Injection Molding of substrate materials coupled with additive plating methods, can cut the
generation of metal waste significantly. Each of these methods has defined drawbacks which
must be carefully considered, especially the increased use of chloroflourocarbons in SMD
technology.
The following discussion focuses on strategies appropriate to each of the subsidiary processes
for substitution, recycling and waste treatment. Some relative advantages and disadvantages
of the available options are also presented.
3.4.1 Cleaning and Board Preparation
This process includes the preparation and cleaning of boards and the cleaning and
maintenance of manufacturing equipment such as electroplating racks. The primary sources
of hazardous waste streams in this process are spent cleaning bath and waste rinse water. A
number of proactive methods can be utilized to minimize these waste streams, and reactive
waste treatment and recycling strategies can reduce their impact
A92-214.3 3-13
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3.4.1.1 Material Substitutions
Reduction of wastes can be achieved by substituting abrasive or non-chelated cleaning agents
for traditional aqueous cleaning methods. Non-hazardous abrasives can be used in blasting or
vibratory cleaning techniques that generate less waste than chemical cleaning processes. The
disadvantage is that they can only be used prior to the insertion of electronic components into
the board. Non-chelated cleaning chemicals, such as alkaline cleaners, are less effective than
chelated chemicals. However, if they provide adequate cleaning they eliminate the need for
treatment chemicals that are required to counteract the effect of chelating compounds on the
waste stream. Chelating compounds improve the solubility of metal ions, but they also inhibit
precipitation of the ions in the waste stream. To counteract this effect, a reducing agent such
as ferrous sulfate must be used to break down complex ions, resulting in a significant increase
in iron precipitation in the waste stream. Non-chelated cleaners will reduce the overall
volume of sludge by eliminating the presence of chelating compounds and treatment
chemicals in the waste stream. Similar, although less dramatic, reductions can be obtained by
using mild chelators that require lower concentrations of reducing treatment chemicals. One
drawback to the use of non-chelated cleaners is the need for increased filtration to remove the
solids that form in the bath.
3,4.1.2 Process Modifications
3.4.1.2.1 Extending Bath Life
The most important process modifications that can be introduced in the cleaning operations
result in an extension of the cleaning bath life. Bath life can be extended by reducing
impurities and reducing solvent loss due to drag-out. Several factors influence the drag-in of
particle contamination in the cleaning operation. Impurities enter the bath from three sources:
racks, drag-in, and water, chemical, or air quality.
A92-214.3 3-14
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Rack Design and Maintenance
Proper rack design and maintenance can minimize corrosion and salt buildup on racks that
leads to contamination of the bath. Fluorocarbon coatings can also be applied to racks to
prevent corrosion, with the added effect of reducing drag-out on the racks. Another process
modification recommended for the reduction of cleaning bath contamination is the use of a
multi-stage cascading rinse system to clean electroplating racks. These racks are generally
cleaned with a nitric acid bath. This type of system circulates rinse solution through a series
of tanks, counter to the flow of the work. In this arrangement, the work is first rinsed in the
least clean tank, and then in successively cleaner baths. The spent solution from each bath is
continuously moved forward to replenish the previous bath, with the effluent from the first
bath used to replenish the process bath if possible. Such a system has the potential to reduce
the generation of waste nitric acid by as much as 75% over a single tank system. The multi-
tank arrangement will slow the degradation of the total volume of nitric acid used for rack
cleaning. Furthermore, by having the effluent from each stage flow counter to the direction
of travel of the racks, and serve as makeup for the previous stage, less bath makeup will be
used. This type of rinsing system is described in detail in the Electroplating chapter section
2.5.2 of this manual.
Board Rinsing Between Operations
Efficient rinsing of boards between process steps will help reduce drag-in of paniculate
contaminates from the board drilling and finishing step. Rinse efficiency can be improved by
increasing the turbulence between the board and the rinse water, increasing the contact time
of the rinse water, and ensuring that sufficient volume of rinse water is used. A variety of
methods for accomplishing these improvements are available. They include the use of: closed
circuit rinses, supplementary spray rinsing, fog nozzles, increased agitation, multiple-stage
counter current rinsing, and rinse water controls to manage flow in rinsing baths. Two very
effective rinse control technologies are flow regulators, which maintain a predetermined
optimal flow rate of rinse water, and conductivity probes, which can detect increased levels of
dissolved solids in the rinse stream and trigger a greater rinse flow to compensate for the
A92-214.3 3-15
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increased solids levels. Immersion rinsing can be effectively combined with spray and fog
methods to reduce overall rinse water usage, and reduce drag-in at subsequent operations.
Counter flow systems such as the one described for rack cleaning can be very effective.
Total rinse water used can be reduced by having the rinse flow counter to the work. This
flow will concentrate the contamination of the rinse water in the early tanks. The effluent
from the first rinse tank can be further concentrated by evaporation and used as influent for
the bath. Exhibit 2-_ shows such a rinse system.
Water, Chemicals and Air Makeup
The use of deionized or distilled makeup water to compensate for evaporation will help
reduce the introduction of minerals and other solids into the bath. Such contamination can
lead to impurity buildup, requiring a change of the bath solution. Proper chemical storage
can help reduce impurities as well, by avoiding unwanted chemical reactions that result in the
generation of bath contaminants. All cleaning chemicals should be stored in non-reactive
mixtures, or each chemical used in the cleaning baths should be stored separately. The
introduction of airborne particulates into bath solutions can lead to premature exhaustion of
the bath. Proper ventilation and exhaust of board preparation areas will help reduce this
source of contamination.
Filtering
Reducing the introduction of contaminants into the bath provides dramatic improvement in
bath life. Further increases can be gained through the use of effective filtering devices to
remove contaminants that do find their way into the cleaning solution.
Active filtering can be accomplished by circulating the solution past a variety of available
filtering devices, and passive filtering can be accomplished by removing settled particulates
from the bath after prolonged shut down periods.
A92-214.3 3-16
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3.4.1.2.2 Reducing Chemical Drag-out
Once sources of bath contamination have been reduced as much as possible, additional bath
life can be gained by reducing solvent loss from the effects of drag-out. Reducing drag-out
has the double effect of prolonging cleaning bath life, and reducing the contamination of rinse
water. Several factors lead to increased drag-out including large board size, high solution
viscosity, high surface tension, and other factors affecting the drainage of fluid from the
board, such as its withdrawal from the cleaning bath. Board size is a design issue, and
frequently beyond the control of the manufacturer. Whenever possible, board size should be
reduced to help minimize waste generation. The following discussion focuses on the methods
more readily subjected to the manufacturer's control.
Chemical bath concentration
Drag-out can be reduced by controlling the bath chemical concentration. This technique can
cut drag-out in two ways: 1. lowering the concentration of chemicals reduces the waste
present in any drag-out that does occur; 2. reduced chemical concentrations will lower the
viscosity of the bath solution, allowing the fluid to drain off the boards more rapidly upon
withdrawal. Initial bath mixtures can be of lower concentration because of their freshness.
Further chemicals can be added to the solution as the bath ages to maintain its level of
effectiveness. Manufacturers should run experiments to determine the minimum effective
chemical concentration for the bath, and the rate at which further chemicals should be added
to compensate for chemical age and degradation. Minimum adequate concentrations are
frequently lower than those recommended by the chemical manufacturer.
Operating the bath at higher temperatures
In addition to making changes in chemical concentration, viscosity can be further reduced by
operating the bath at a higher temperature. The viability of this option must be carefully
examined because of increased energy costs, increased rate of evaporation, and the need for
additional air pollution controls.
A92-214.3 3-17
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Wetting agents
The use of wetting agents can reduce the surface tension of the bath solution, allowing greater
drainage of the solution from the boards upon withdrawal from the bath. This option has
some potential problems, particularly the tendency to cause foaming problems in the bath. It
should be evaluated carefully, and if appropriate agents can be identified, the technique has
the potential to yield drag-out reductions of up to 50%.
Board withdrawal and drainage
Proper withdrawal of the boards from the bath is very important to drag-out reduction. The
boards should be withdrawn slowly, and should be allowed to drain sufficiently to minimize
the amount of solution that adheres to their surface. Of the two requirements, slower
withdrawal can have a more beneficial effect than increased drainage time, and will better
avoid the possibility of adverse chemical oxidation effects on the board. The minimum
recommended drainage time is 10 seconds.
3.4.1.3 Waste Treatment
A variety of treatment techniques, leading to neutralization or recycling of wastes, are
available in the cleaning processes. Rinse water in particular is easily subjected to reuse and
recycling strategies that can significantly reduce their volume and chemical concentration.
Recycling cleaning agents and recovering metal contaminants. Waste from the cleaning of
boards can be treated to recover both the cleaning acid and the metal particles removed by the
cleaning operation. Boards are cleaned using a peroxide/sulfuric acid solution, a mild etchant
that removes oxides and cleans copper prior to plating. There are two methods that can be
used to treat the spent acid bath. The spent cleaning bath can be brought off line and cooled,
causing the suspended copper to crystalize as copper sulfate. These crystals can be dissolved
into solution and treated with activated carbon to remove the organics. They can then be
A92-2143 3-18
-------
used to top off the copper electroplating bath. The supernatant from the cooled spent
cleaning bath can then also be returned to the bath. Alternatively, ion exchange can be used
to regenerate the solution, or it can be returned to the tank and replenished with oxidizers.
Recycling rinse solutions. Rinse solutions can also be reused for a variety of purposes. One
option is to use the effluent from a rinse that follows an acid cleaning bath as the influent for
a rinse following an alkaline cleaning bath. If both systems require the same flow rate, 50%
less rinse water would be used to operate them. This system can actually improve rinse
efficiency for two reasons. First, the chemical diffusion process is accelerated by the reduced
concentration of the alkaline material at the interface of the drag-out film and the surrounding
water. Second, the neutralization reaction reduces the viscosity of the drag-out film. These
methods have some potential problems. For example, unwanted precipitation of metal
hydroxides onto the cleaned boards can occur. For this, and other reasons, careful
investigation prior to combining acid and alkaline rinses is warranted.
Other recycling options include using acid cleaning rinse effluent as a rinse for pieces that
have undergone a mild acid etch process. Rinses containing a high level of process chemicals
can be concentrated through evaporation and returned to the process baths. As previously
discussed, closed circuit rinsing can dramatically reduce the hazardous chemical content of
the waste stream. Effluent from a critical or final rinse can be used for influent in rinses that
do not require high efficiencies. This is the same principle that closed circuit, counter flow
rinsing systems utilize, but can be applied in situations where such systems are not cost
effective.
3.4.2 Pattern Printing and Masking
The techniques available to minimize waste in this process are very similar to those used in
the photoprocessing industry. For general information on these methods, see the Waste
Minimization Opportunities Assessment Manual (USEPA, 1988). The procedures discussed
below have demonstrated high potential for improvement
A92-214.3 3-19
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3.4.2.1 Material Substitutions
Aqueous resist formulas. Water based resists are currently being substituted for solvent based
resists throughout the printed circuit board industry. The benefits of such a substitution
include the elimination of toxic spent solvents from the processing and application of resists.
3.4.2.2 Process Modifications
Two significant process modifications, screen printing and use of dry resist, can be used in
the pattern printing and masking process. Each of these opportunities is limited by the
effectiveness of the technology in special, high-demand situations, but should be explored and
implemented when feasible.
3.4.2.2.1 Screen-Printing
Transition of photolithography operations to screen-printing offers the opportunity to eliminate
the use of developers in applying resist. Screen-printing technology has advanced sufficiently
to overcome the major obstacle to this transition, resolution of the image. Screen-printing
techniques resulting in 0.025 cm (.01 inch) resolution are now available, but were not
previously achievable.
3.4.2.2.2 Dry Photoresist Removal
The Asher dry photoresist removal method can be used to eliminate the use of organic resist
stripping solutions. This method is very common in the semiconductor industry, but has not
gained widespread use in the printed circuit board industry as yet. This may be due to the
greater thickness of resists used to manufacture printed circuit boards.
A92-214.3 3-20
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3.4.2.3 Waste Treatment
3.4.2.3.1 Recycle Photoresist Stripper
Photoresist stripper can be reused following a simple filtering operation. Photoresist is a
polymer material that remains in the stripper tank in small flakes that slowly settle to the
bottom. These flakes can be actively filtered out of the tank, or the resist stripper solution
can be filtered into a clean tank and reused. Residue buildup will degrade stripper
performance before chemical degradation in most cases. Multi-stage stripper tanks can also
help reduce this problem. Flakes of polymer that adhere to the board in the first tank can be
removed in the second tank, leaving less waste to enter the rinse water stream.
3.4.3 Electroplating and Electroless Plating
Source reduction efforts associated with the electroplating and electroless plating processes
center on reducing the hazardous nature of the materials used, extending process bath life,
improving rinse efficiency, and recovering/reusing spent materials. Many of the techniques
are similar to those discussed for the cleaning and board preparation processes. There is
potential to avoid the use of chemical plating operations altogether. Low volume
manufacturers can use mechanical etching of copper clad boards for prototype and specialty
boards. This method uses computer design of the circuit pattern and a stylus etching
apparatus. It is not a viable process for high volume production, but should be considered for
prototyping and low volume production.
3.4.3.1 Material Substitutions
Use of non-cyanide plating baths and stress relievers. Water soluble cyanide compounds of
many metals are frequently added to electroless copper plating baths to relieve internal stress
in the deposited layer. Polysiloxanes may be substituted for cyanides to reduce the hazardous
nature of spent bath solutions.
A92-214.3 3-21
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Use of purer anode materials. During the plating process, impurities in the anode matrix are
frequently left in the plating bath, contributing to the degradation of the solution. The use of
purer anode materials will reduce this problem.
3.4.3.2 Process Modifications
Use of anode bags. Anode bags, wrapped around the anode, can be used to further reduce
the contamination of the plating bath by trapping impurities. These bags will also prevent
pieces of decomposed anode from falling into the plating bath.
Position the workpiece properly on the plating rack. When racks are removed from the
plating bath, plating solution will adhere to the surface of each board on the rack. Boards
should be placed to minimize this drag-out. Optimal placement should be determined
experimentally, but the following guidelines may prove useful:
• Orient the plated surface as close to vertical as possible.
• Rack with the longer dimension of the board oriented horizontally.
• Rack with the lower edge tilted slightly from the horizontal so runoff will be
from a comer rather than an edge.
Use computerized/automated control systems. Computerized process control systems can
reduce the chance of unexpected decomposition of the plating bath. Board handling and bath
monitoring systems are available but require significant capital outlays and improved worker
training.
Recover drag-out from baths. Some drag-out will occur despite the best efforts to avoid it
The drag-out solution can be partially recovered by placing drainage boards, tilted towards the
process bath, between plating operations and following rinses. The use of such drainage
boards can capture and return solution that might otherwise fall to the floor and enter the
waste water system on washdown.
A92-2143 3-22
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Use of drag-out tanks. Another method for recovering drag-out is the use of static rinse tanks
called drag-out tanks. Such tanks do not have a continuous inflow of rinse water, so the
chemical concentration of the rinse solution increases as more work passes through it
Eventually the concentration reaches a level suitable for re-use in the process bath.
This is most advantageous for baths that are operated at an elevated temperature. Such baths
suffer evaporative losses that can be restored by using the spent rinse water. Since these
tanks do not have a continuous flow of water to create turbulence, air is sometimes used to
create an agitation effect that improves rinsing although mechanical agitation may introduce
fewer impurities. Manufacturers should carefully examine the potential for drag-out tanks
before using them.
Maintain bath solution quality. In addition to the techniques used to extend bath life
discussed in earlier sections, the quality of the solution in a process bath will have a distinct
impact on its ability to perform, and thus to extend the effective life cycle of the bath. The
methods to extend bath life outlined in Section 3.4.1.2 are applicable to the extension of
plating baths. It is important to focus attention on maintaining optimum bath conditions.
Many facilities use drag-out as a means of purging process baths of impurities that degrade
their performance. From an environmental standpoint, this is a poor technique since it does
not directly address the issue of impurity formation, results in a high loss of valuable process
solutions, and moves the problem downstream to the treatment unit By maintaining optimum
bath conditions, the useful life of a bath can be extended. For example, frequent monitoring
of the solution can lead to timely additions of reagents and stabilizers that will prolong bath
life. Good bath temperature control can maximize bath performance and proper maintenance
and cleaning of cooling/heating coils improves the heat transfer needed to maintain bath
temperatures. Mechanical agitation rather than air agitation should be used when feasible.
Air can introduce oil and carbon dioxide into process baths, shortening their life. Continuous
filtering and treatment with activated carbon will prevent surface roughness on the plated
boards. Since filters can seldom remove solids at the same rate as they are introduced into a
bath, the filtering flow rate should be kept as high as possible, and the filter should be run
A92-214.3 3-23
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even when the bath is not in use. In general, any strategy that leads to the removal of
impurities from the bath should be pursued. Innovative approaches, such as temporarily
reducing the bath temperature to encourage the crystallization of metallic salts, and improve
their removal by filtration, should be applied to all process baths.
Improve rinse efficiency. The discussion in Section 3.4.1.2 identifies a number of methods
for improving rinse efficiency. These methods are equally applicable to the electroplating
operation.
One additional issue which should be investigated to improve rinse efficiency is the design
of rinsing systems." Many systems create excess rinse water because of poor design.
Oversizing of pipes, the inability to turn systems off easily when not needed, lack of effective
flow and pressure controls, and other design problems can lead to a significant increase in
waste stream volume.
3.4.3.3 Waste Treatment
Segregate waste streams to promote recycling. In many printed circuit board manufacturing
facilities rinse streams, and even process waste streams, are mixed and treated together. This
approach places limits on the treatment strategies which can be employed, and on the types of
reusable byproducts that can be obtained from treatment. The segregation of waste streams
can alleviate this problem and promote efficient individualized treatment of specific waste
streams.
3.4.3.3.1 Recover Metal Value From Bath Rinses
Historically, metal recovery has not been an economical option for manufacturers of printed
circuit boards. However, new regulations governing effluent pretreatment have made
recovery a more attractive approach. Increased regulatory requirements for sludge disposal
have also led to renewed focus on recovery/reuse of the metal content of waste streams. As a
A92-2143 3-24
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result, manufacturers may now find it advisable to recover copper, other metals, and metal
salts lost due to drag-out of process chemicals. Chemical metal recovery costs are dependent
on a variety of variables. Unit size, space available, production down time, and layout of
equipment should all be considered before selecting and implementing a strategy.
Evaporation. Waste rinse water can be evaporated, using single or multiple effect
evaporators, yielding a concentrated solution with a high metal content Once the metal
concentration is equal to that of the process bath, the solution can be used to top off the bath.
Well designed evaporative systems can even recapture the water vapor, condense it, and reuse
it as rinse water. Despite its relatively high energy requirements, this technique is simple and
easy to use. A distinct disadvantage of this approach is the tendency of calcium and
magnesium salts present in the original rinse water to contaminate the process bath, resulting
in rapid deterioration of the bath quality. Deionization or softening of influent rinse water
can alleviate this problem.
Reverse osmosis. Semipermeable membranes can be used to selectively filter rinse solutions,
reconcentrating those constituents of the rinse stream that can pass through the membrane,
and leaving a regenerated rinse solution behind. Such membranes cannot fully recover all
process bath constituents, therefore the makeup concentrations achieved are not always equal
to original bath concentrations. The membranes are also subject to wear from pH extremes
and prolonged exposure to pressure. This approach has proven to be particularly effective for
nickel plating baths and rinses.
Liquid membranes. Liquid membranes, composed of polymeric materials loaded with ion-
carrying solution, can be used to remove chromium from rinse waters and spent etching baths.
The solution drawn through the membrane forms a tertiary araine metal complex, which can
be treated with sodium hydroxide solution.
Ion exchange. Ion exchange recovers metals from a dilute rinse stream by passing the
solution through a bed containing a resin material. The resin replaces the organics in the
solution with ions. The metals can then be recovered from the resin by cleaning it with an
A92-2143 3-25
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acid or alkaline solution. This type of system is very complex and requires careful operation
and maintenance, but may prove less delicate than reverse osmosis systems, and better for use
on dilute rinse streams.
Electrolytic recovery. The metallic content in the rinse water can be collected in a solid slab
by passing current between a submerged anode and cathode. As the current passes through
the solution, metallic ions collect on the cathode forming a solid slab that can be reclaimed,
or used as a plating anode.
This method has been successfully used to recover gold, silver, tin, copper, zinc, solder alloy,
and cadmium. The process works best on solutions with a greater than 100 mg/1
concentration of metal ions.
Electrodialysis. In this method, an electric current and selective membranes are used to
separate the positive and negative ions from a solution into two streams. Feeding the solution
through successive cation and anion membranes, charged with current, will segregate the
streams, and concentrate salts or metal ions. This process has not been used as widely as
other metal recovery techniques.
High surface area electrowinning/electrorefinaig. Using the same principle as electrolytic
recovery, a metal containing solution can be passed through a carbon filter cathode. The
metal will plate out on the cathode, which can be placed in an electrorefiner. The
electrorefiner reverses the current, removing the metal fibers from the cathode and plating
them on a stainless steel starter sheet.
3.4.4 Etching
3.4.4.1 Material Substitutions
Use differential plating instead of conventional electroless plating. The correct use of certain
stabilizers in the electroless plating bath can cause copper to plate on the board's through
A92-214.3 3-26
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holes three to five times faster than on the surface. This differential plating leaves much less
copper on the surface of the board that ultimately has to be etched away. Differential plating
is not a fully developed technique, but has high potential for reducing the rate of metal
contamination in etching baths.
Use non-chelated etchants. Non-chelate mild etchants such as sodium persulfate and
hydrogen peroxide/sulfuric acid can be used to replace ammonium persulfate chelate etchant.
Use thinner copper foil to laminate board. Thinner foil reduces the amount of copper which
must be etched away, and thus reduces the amount of waste generated. Many manufacturers
are switching to thinner laminates on their boards.
Use non-chrome etchants. Ferric chloride or ammonium persulfate etchants are preferable to
chromic-sulfuric etchants. Non-chromic etchants reduce the toxicity of spent etchant baths.
3.4.4.2 Process Modifications
Use pattern instead of panel plating. Panel plating requires plating of the entire board
surface. Pattern plating, whether additive or subtractive, involves much less application of
metal to the board. Some computer, microwave, and other applications requiring uniform
cross section of circuitry may demand panel plating, however, most other applications can be
satisfactorily manufactured using the pattern method.
Use additive instead of subtractive method. The additive method eliminates etching
altogether. By printing the resist on a non-laminated board's non-circuit area prior to
electroless plating the first layer of the circuit pattern, additive processing eliminates
deposition of copper on the non-circuit area. While this technique does require the use of
solvent based resists, it is gaining popularity because it creates less waste and results in lower
manufacturing costs. Additive processing eliminates spent etchant waste and cuts down on
the generation of metal hydroxide sludge.
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3.4.4.3 Waste Treatment
Recycle spent etchant. Electrolytic diaphragm cells have been used to regenerate spent
chromic acid from etching operations. The electrolytic cell oxidizes trivalent chromium to
hexavalent chromium and removes contaminants. This can result in regenerated solution of
equal or higher quality than fresh etchant.
Direct chlorination. Cupric chloride, a strong etchant used to produce patterns on board base
material, can be regenerated through direct chlorination. The etchant becomes spent as
copper reduces the cupric chloride (CuClj) to cuprous chloride (CuCl). The spent etchant can
be oxidized, and reused.
3.4.5 General Wastewater and Sludge Treatment
In the processes described, wastewater treatment generates hazardous waste in the form of
sludge. The volume of sludge generated is proportional to the level of contamination of spent
rinse streams. These streams are contaminated through the drag-out of process chemicals.
The major methods of reducing the waste found in sludge include waste stream segregation,
use of alternative treatment chemicals, and alternative treatment technologies.
3.4.5.1 Waste Stream Segregation
Segregating waste streams can improve the efficiency of a waste treatment stream. The
isolation of various waste streams creates a broader variety of treatment options. As an
example, segregating streams containing chelating agents reduces the amount of ferrous
sulfate that must be added to the stream to break down the chelators. This in turn minimizes
the precipitation of iron in the sludge generated by the non-chelator streams.
Another volume reduction strategy is to isolate non-contact cooling streams from
contaminated streams. Cooling streams can be redirected in a closed loop, without any
A92-2143 3-28
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treatment, thereby reducing the total water discharge and the total volume of wastewater
requiring treatment.
3.4.5.2 Use of Alternative Waste Treatment Chemicals
The selection of chemicals used in the treatment process can affect the volume of sludge
generated. For example, lime and caustic soda are two common chemicals used for
neutralization and precipitation. Although lime costs less per unit, it can generate as much as
ten times more dry weight of sludge than caustic soda.
Alum and ferric chloride are coagulating agents used to improve floe formation, but they
increase sludge generation by converting to hydroxides in use. Polyelectrolyte conditioners,
which are more expensive, can be used without adding to sludge volume, and thus may be
less expensive to use when the cost of sludge disposal is factored into the decision. These
substitutions, and others, must be made after consideration of waste characteristics and
removal efficiency in any given plant environment
3.4.5.3 Alternative Treatment Technologies
Ion exchange can be used to treat the entire waste stream prior to discharge to the publicly
owned treatment works. This treatment, coupled with an activated carbon filtering treatment
system, can enable the recycling of rinse water, although process chemicals cannot be
recovered after mixing of the various waste streams. Economic justifications for such a
system must be developed if an ion exchange system is to be installed, but experience
indicates payback can be achieved in three to four years.
3.4.5.4 Sludge Treatment
A full discussion of sludge dewatering and hazardous sludge disposal is presented in the
Electroplating section. The methods detailed include filter pressing to dewater the sludge and
final stabilization/solidification of the dried sludge cake.
A92-2143 3-29
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Bibliography
Waste reduction at a printed circuit board manufacturing facility using modified rinsing
technologies by Paul Pager MNTAP.
Case Study: total employee involvement helps the bureau of engraving meet pollution
abatement goals. John C. Buckbee ffl. Pollution Prevention review/Winter 1990-1991.
EPA/600/M-91/022 - July 1991 - Waste Minimization Assessment for a manufacturer of
printed circuit boards by F. William Kirsch and Gwen P. Looby.
EPA/600/M-91/021 - July 1991 - Waste minimization assessment for multilayered printed
circuit board manufacturing.
A92-214.3 3-30
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CHAPTER 4
WOOD PRESERVATION
-------
TABLE OF CONTENTS
Chapter Page
4 WOOD PRESERVATION .4-1
4.1 Industry Description 4-1
4.2 Process Description 4-2
4.2.1 Seasoning 4-2
4.2.2 Incising 4-2
4.2.3 Pressure Treating 4-2
4.2.4 Treatment Chemicals 4-4
4.3 Identification and Characterization of Emission Points and Waste Streams . 4-8
4.3.1 Seasoning 4-8
4.3.2 Pressure Treating 4-8
4.4 Pollution Prevention, Waste Treatment, and Control Systems 4-9
4.4.1 Pollution Prevention 4-9
4.4.2 Waste Treatment and Control Systems 4-12
WOOD PRESERVATION REFERENCES 4-16
EXHIBITS
Number Page
4-1 Stages in Pressure Treatment 4-5
4-2 Principle Constituents of High-Temperature Creosote 4-6
4-3 Principle Fractions from a Typical Coke-Oven Tar 4-7
4-4 Analytical Data for Wastewaters from Creosote and Penta Treatments 4-10
4-5 Analytical Data for Wastewaters Containing CCA Salts 4-11
A92-214.4 4-i
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CHAPTER 4
WOOD PRESERVATION
4.1 INDUSTRY DESCRIPTION
The purpose of wood preservation is to improve the utility of wood by keeping it dry or by
preventing its decay. By impregnating fibers with preservative, wood is made toxic to fungi,
termites and other insects, marine borers, and bacteria which would use the wood as a food
source.
Preservation techniques are used when the wood will come in contact with soil or water.
Marine and land pilings, crossties, and telephone poles are only a few of the end-uses of
treated wood. The preservation action is believed to begin with the movement of toxic
material from the preserved timber to the surrounding environment. The movement of the
preservative establishes a zone of defense against potential invading organisms. Over time,
the preservative in the environment is leached away from the area and is replaced with more
preservative from the treated wood. Although the goal of wood preservation is to achieve
maximum fixation of the preservative within the wood, many factors influence this objective
including the type of preservative used, the soil and moisture condition, and the microbial
activity of the immediate ecosystem.
The cell structure of wood is important to the preservation process. Wood is composed of
millions of hollow cells which are filled with air. These cells run both longitudinally from
root to crown and radially from center to bark. Most of the cells in the center of a tree (i.e.,
the heartwood) are dead, their purpose being to provide support The live, newly formed cells
(i.e., the sapwood) located just inside the bark and cambium of the tree contain pits and a
series of vertical flow channels through which nutrients flow. Some softwoods (e.g., pines,
spruces, larches, and the Douglas fir) also contain resin canals which form another network
within the tree. These natural passageways also serve as the transport method by which
preservation chemicals are moved throughout the timber. The most common species of wood
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used in preservation processes are the Southern Pine, the Ponderosa Pine and the Red Pine.
Most other wood species do not readily accept chemical preservatives.
4.2 PROCESS DESCRIPTION
4.2.1 Seasoning
Because the most effective treating results are obtained with dry wood, wood is often subject
to seasoning prior to treatment. Although air seasoning, or allowing the wood to air dry, is
the easiest method of drying wood, it can also be very time consuming. Several of the
commercial artificial seasoning methods include boultonizing, steam conditioning, and kiln
drying. Boultonizing involves evaporating water from wood by heating the wood in a
creosote or an oil-type preservative while simultaneously subjecting it to a vacuum. This
method of conditioning varies in time from 6 to 40, hours depending on the type of wood
being conditioned. Steam conditioning subjects wood to live steam at temperatures of 104° to
118°C (219° to 244°F) for periods of 1 to 20 hours. Immediately after steaming, a vacuum is
applied to remove moisture. The kiln drying method involves placing wood in a drying kiln
and evaporating the internal moisture.
4.2.2 Incising
After wood has been seasoned, it is often incised to obtain optimum treating results. Incising
consists of making shallow slit-like holes in the surface of the material to be treated so that
deeper and more uniform preservative penetration may be obtained.
4.2.3 Pressure Treating
Pressure treatment of wood with preservatives is the most effective method of protecting
wood against attack by decay, insects, fire, and other wood-destroying agents. Pressure
treatment allows deep, uniform, and controlled preservative penetration.
2144 4-2
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The pressure treating process involves two primary steps: loading and reloading a cylindrical
retort with lumber while the preservation solution is prepared, and conducting the treatment
cycle. The loading stage involves placing bundles of lumber on tram cars and rolling them
into a retort which is normally 1.8 meters (6 feet) in diameter and 15.2 meters (50 feet) long.
The retort cylinder is normally mounted on saddle blocks which allow for the slight
expansion and contraction that occurs during processing at elevated temperatures. The
cylinders are also frequently equipped with steam-heating coils to maintain the temperature of
the preservative solution during the processing cycle. The cylinder is also equipped with an
array of pipelines which transport preservative, water, air, and/or vacuum as necessary during
the process.
A plant operator controls each treatment sequence according to the specific type of wood
which is to be treated. The six stages of the treatment cycle, as illustrated in Exhibit 4-1, are
initial vacuum, cylinder flood, pressure applied, initial drain, final vacuum, and final drain
and unload. The entire pressure treating process may be completed in approximately one
hour.
The initial vacuum removes air from the naturally occurring passageways within the lumber,
allowing the subsequent penetration of preservative. The greater the quantity of air removed,
the greater the percentage of treatment chemicals allowed to penetrate the lumber. The plant
operator can control the time of vacuum and, therefore, the amount of preservative
penetration. In most cases, 85 percent sapwood penetration is recommended. However, the
penetration level does vary with the species and thickness of the wood. After the initial
vacuum is complete, the retort is flooded with preservative and a secondary vacuum is
applied at this time.
Pressure application begins after the preservative fills the retort. The preservative solution is
pumped into the cylinder until the pressure reaches 150 psi. Once this pressure is reached, it
is maintained for the time necessary to yield the required penetration. At the end of the
pressure period, the pressure is released and the preservative is drained from the retort.
214.4 4-3
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Some of the preservative solution remains trapped between the lumber in the packs of wood
after the initial draining period. Another vacuum is applied to dry the lumber and to remove
excess preservative solution.
The final drain serves to remove any excess preservative released as a result of the final
vacuum. The preservative solution is drained from the retort and returned to a storage tank.
Once the retort is drained, the treated lumber is unloaded.
4.2.4 Treatment Chemicals
4.2.4.1 Chromated Copper Arsenate (CCA)
One preservative commonly used in the pressure treating process is Chromated Copper
Arsenate (CCA). As the name implies, this preservative consists of three active ingredients,
each toxic to wood-destroying organisms, and each with its own function. Copper and
arsenic prevent decay by a variety of fungi. The arsenic also prevents attack by insects and
termites. Chrome ensures the safety of humans and animals that come into contact with the
treated wood while still protecting against wood-destroying organisms by chemically fixing
the copper and arsenic into the wood.
Although CCA is a waterbome preservative, it will not leach from wet wood. Copper,
arsenic, and chrome begin reacting with the wood cells immediately after being forced into
the lumber. The chromium salts react to form insoluble compounds, which subsequently
render the CCA non-leachable.
4.2.4.2 Creosote, Coal-Tar, and Related Materials
The preservatives used in creosote treatment methods consist of creosote, coal-tar, and related
materials. All of these preservatives are mixtures of organic materials resulting from the
pyrolysis of natural organic materials and/or subsequent distillation of the resulting tars. The
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Initial Vacuum Cylinder Flood Pressure Applied Initial Drain Final Vacuum
Final Drain
& Unload
EXHIBIT 4-1. Stages in Pressure Treatment
-------
primary preservatives in this class are coal-tar creosote and mixtures of creosote with crude
coal-tar.
Coal-tar creosote is a residual product from the distillation and processing of coal-tar. It is a
blend of naphthalene drain oil, wash oil, anthracene drain oil, and heavy distillate oil. These
oils are blended to meet specifications as required by certain wood species. The resulting
constituents of creosote coal-tar preservatives and their corresponding weight percentages are
listed in Exhibit 4-2.
EXHIBIT 4-2. Principle Constituents of High-Temperature Creosote
Compound Percent by Weight
Naphthalene 7-28
Phenanthrene 9-14
Acenaphthene 2-5
Fluoranthene 2-5
Fluorene 2-4
Methylnaphthalenes 1-4
Pyrene 2-3
Carbazole 1.8-2.7
Anthracene 1.2-1.8
Diphenylene oxide 0.5-1.0
9,10-Dihydroanthracene 0.1 -0.3
Source. Nicholas, Darrel D.T ed., Wood Deterioration and Its Prevention by Preservative Treatments, Volume II-
Preservatives and Preservative Systems, Syracuse University Press, Syracuse, NY. 1973.
Creosotes and coal-tars are produced by the high-temperature carbonization of bituminous
coal. The carbonization process takes place in a pusher-type oven with vertical flues. The
coal is charged into the oven on the pusher side. The oven is heated by the combustion of
coke-oven gas. The coal at the wall of the oven immediately softens and forms a plastic zone
which moves toward the center of the oven as the coking continues. Coking is complete
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when the two plastic zones meet in the center of the oven and the temperature has reached
900° to 1000°C (1,652° to 1,832°F). The molten liquid is then pushed from the oven in
pieces three to six inches in cross section and about half of the oven width in length. A
normal oven is 12.2 meters (40 feet) long, 4.3 meters (14 feet) high, and about 43 centimeters
(17 inches) wide.
Almost 32.2 to 34 liters (8.5 to 9.0 gallons) of tar are recovered per ton of coal carbonized.
Most of this is shipped to a distillation plant for further processing. Several of the fractions
resulting from the distillation of coal-tar, including wash oil, anthracene oil, and heavy oil, are
useful to the wood preserver. Upon cooling, the anthracene oils deposit crude anthracene
crystals. The oil which is drained from this crystallization is used in blending creosote.
These and other coal-tar fractions are listed in Exhibit 4-3.
EXHIBIT 4-3. Principle Fractions from a Typical Coke-Oven Tar
Compound
Benzol light oil
Naphtha light oil
Naphthalene oil
Wash oil
Anthracene oil
Heavy oil
Medium-soft pitch
Percent
0.6
2.9
14.6
2.8
8.0
9.5
56.6
Boiling Point
Range, °C (°F)
99-160 (210-320)
168-196 (334-385)
198-230 (388-446)
224-286 (435-547)
247-355 (477-671)
323-372 (613-702)
—
Source: Nicholas, Darrel D, ed., Wood Deterioration and Its Prevention by Preservative Treatments, Volume II-
Preservatives and Preservative Systems, Syracuse University Press, Syracuse, NY. 1973.
214.4 4-7
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4.3 IDENTIFICATION AND CHARACTERIZATION OF EMISSION POINTS AND
WASTE STREAMS
4.3.1 Seasoning
Steam conditioning is the most common method of seasoning and is a major source of water
contamination. After steam conditioning, the excess preservative in the cylinder is returned to
storage. A thin film of the preservative is left on the walls of the cylinder and is washed
down by steam condensate during the succeeding steaming cycle. The steam condensate then
leaves the cylinder through the steam trap. The condensates contain entrained oil,
preservative, and other organic material such as sugar, which is extracted from the wood
during the steaming operation.
4.3.2 Pressure Treating
The waste streams resulting from pressure treating operations are similar to those originating
from steam conditioning. Between batch operations, the retort is rinsed, resulting in
wastewater streams containing oil, preservatives, and sugars.
Other sources of wastewater resulting from the pressure treating process include cooling
water, vacuum water, wash water, storm water, boiler blow-down water, and heating-coil
condensate. The boiler blow-down water and condensate from heating coils may or may not
contain contaminates, depending on the use and nature of the boiler water treating compounds
and whether or not the heating coils contain leaks through which the preservative can enter.
Specific contaminants in the waste streams depend on the type of preservative used during the
treatment process. Exhibits 4-4 and 4-5 relate effluent characteristics of facilities using CCA
and creosote preservatives.
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4.4 POLLUTION PREVENTION, WASTE TREATMENT, AND CONTROL SYSTEMS
4.4.1 Pollution Prevention
There are several in-plant process changes which can be made that will reduce the total flow
and organic loading of wastewater streams. Several of these process modifications include
closed steaming, modified-closed steaming, reduction in steam conditioning, reuse of cooling
water, and recovery of free oils. Additional preventative maintenance measures can also be
implemented which will reduce total water flow and water contamination.
4.4.1.1 Closed Steaming
Closed steaming aids in altering the characteristics of the wastewater streams and in reducing
the volume of plant wastewater. The process consists of the following steps:
• Drawing water from a reservoir into the treating cylinder at the start of a steaming
cycle to a depth sufficient to cover the heating coils
• Applying steam to the coils to generate more steam within the cylinder
• Returning the water to the reservoir for future use
The number of times that the water can be reused depends on the type and quality of the
preservative and the characteristics of the water itself. In addition to reducing the volume of
wastewater, closed steaming reduces the oxygen demand of the cylinder effluent by reducing
the content of emulsified oils in the effluent. After die closed steaming cycle, the water in
the cylinder is returned to the reservoir through a pipe sized to reduce agitation, thus
preventing emulsification. The free oil can then be removed by gravity separation and
skimming.
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EXHIBIT 4-4. Analytical Data for Wastewaters from Creosote and Penta
Treatments
Waste Concentration Range
Characteristic (mg/1 - except pH)
Pentachlorophenol 40-100
Phenols 150-350
Chemical oxygen demand 3,000-60,000
Biochemical oxygen demand 1,500-25,000
Oil content 80-6,000
Total solids 2,000-20,000
pH 4.0-5.5
Total free sugars 1,800
Arabinose 460
Xylose 287
Glucose 213
Galactose 517
Mannose 403
Source. Nicholas, Darrel D., ed.. Wood Deterioration and Its Prevention by Preservative Treatments, Volume II.
Preservatives and Preservative Systems, Syracuse University Press, Syracuse, NY 1973.
Some of the advantages of closed steaming over conventional steaming include the following:
• Reducing the volume of wastewater that must be treated
• Improving the quality of steam-conditioning cylinder effluents by reducing oxygen
demand
• Increasing oil recovery by eliminating the emulsion problem
• Reducing the cost of treating wastewater by reducing the total organic loading that
must be removed by conventional wastewater treating methods
One of the difficulties associated with closed steaming is that the process adds approximately
30 minutes to steaming time.
214.4 4-10
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EXHIBIT 4-5. Analytical Data for Wastewaters Containing CCA Salts
Waste ' Concentration Range
Characteristic (mg/l - except pH)
Chemical oxygen demand 1,700
Arsenic 300
Copper 170
Chromium (hexavalent) 375
Phenols <1
_pH 5.0
Source- Nicholas, Darrel D, ed, Wood Deterioration and Its Prevention by Preservative Treatments, Volume II
Preservatives and Preservative Systems, Syracuse University Press, Syracuse, NY. 1973
4.4.1.2 Modified-Closed Steaming
Modified-closed steaming charges live steam to the cylinder as in open steaming, but retains
the condensate in the cylinder. When the condensate reaches a depth slightly higher than the
heating coils, open steaming is stopped and the remaining steam required for the process is
generated within the cylinder using the heating coils. After the steaming cycle is complete,
the oil is recovered and the water is discharged. Modified-closed steaming adds little or no
time to the steaming cycle, which reduces boiler operating time and reduces fuel costs.
4.4.1.3 Reduction in Steam Conditioning
Much of the wastewater flow from a wood treatment plant comes from the steaming of green
(not fully aged) stock. If the amount of wood to be steamed can be reduced, a significant
reduction in wastewater flow will occur. One way to reduce the flow is to use kiln-drying
rather than steaming.
214.4 4-11
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4.4.1.4 Reuse of Cooling Water
Reusing cooling water will also reduce the total wastewater flow. Cooling water recirculation
will require that a cooling pond or holding tank be constructed to act as a staging area prior
to the water reentering the condensers.
4.4.1.5 Recovery of Free Oils
One difficulty in treating wastewater from wood treatment plants is handling the oils that
often become entrained in wastewater from steaming condensate. Free oil can be recovered
from wastewater by gravity separation. Creosote separation is normally accomplished in a
sump equipped with a series of baffles to decrease turbulence and permit the heavier-than-
water fractions to settle to the bottom of the sump. The lighter fractions then rise to the
water's surface.
4.4.1.6 Preventative Maintenance
Cylinders, pipes, and sumps should be monitored, and repaired if necessary, on a regular basis
to prevent preservative losses which can contaminate both process wastewater and stormwater.
The preservative which is lost from treatment cylinders can be collected and returned to a
preservative storage tank for future use.
4.4.2 Waste Treatment and Control Systems
The degree to which wastewater is treated depends on the outfall of the wastewater effluent
and the permit requirements. More treatment is necessary for effluents terminating in
receiving streams than for plant effluents which will be further treated by municipal treatment
plants. Assuming complete on-site processing, both primary and secondary treatments are
normally required to meet minimum treatment standards. Some of the secondary methods
which may be used to treat wood preservation waste streams include biological treatments,
chemical oxidation, and activated carbon filtration. The most effective method, or
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combination of methods, will vary with the preservative mix, the flow rate, and the degree of
automation.
4.4.2.1 Primary Treatments
Creosote waste streams often contain entrained oils which must be removed prior to
secondary treatment methods. The methods used to capture the oils usually include
flocculation and sedimentation. Flocculating agents include metallic hydroxides, alum, ferric
chloride, and polyelectrolytes. Flocculation treatments normally generate a volume of sludge
equal to five to ten percent of the volume of wastewater. The sludge often has a high water
content and should be dewatered. The recovered water should then be sent to the secondary
treatment operations.
The CCA salts, copper, chromium, and arsenic are not biodegradable and will stay in the
environment for indefinite periods of time if not removed. Because they are toxic to the
microorganisms found in biological treatment operations, the salts must be removed in
primary operations. Many of the procedures used by the wood preservation industry for
treating waters containing inorganic salts have been adapted from the electroplating industry.
A detailed discussion of metal recovery options is found in Section 2.5.5 in the electroplating
material. Information specific to reducing hexavalent chromium is located in Section 2.6.1.
and Section 2.6.3 contains additional information concerning metal precipitation.
4.4.2.2 Secondary Treatments
The main purpose of secondary treatment is to remove dissolved organic material from
wastewater. Biological processes are generally the most effective secondary treatment
methods, but chemical oxidation and activated-carbon adsorption have also been successful.
These processes are discussed in more detail in Section 2.7.
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4.4.2.2.1 Biological Treatments
The four most commonly used methods of biological treatment are trickling filtration,
activated sludge, and oxidation lagoons. Trickling filters consist of a cylindrical tower filled
with crushed stone, slag, or plastic media. The media is covered with a layer of slime formed
by aerobic bacteria. Wastewater is uniformly applied to the top of the cylinder by a rotating
distributor arm equipped with nozzles. The wastewater trickles down through the media
coming into contact with the slime layers. The contaminants in the water are then destroyed
by the aerobic bacteria which form the slime.
Activated sludge units consist of an aeration basin and a settling tank. The wastewater enters
the aeration basin at one end and leaves at the other. As the water moves through the basin,
contaminants are destroyed by biologically active sludge. The water and some of the sludge
is discharged into a settling tank or clarifier where the activated sludge is settled out and
returned to inlets of the aeration basin. The treated water can then be discharged.
Oxidation ponds simulate the natural biological oxidation and sedimentation that occurs in
lakes and streams. As with other biological treatment methods, the contaminants in the
wastewater are destroyed by microorganisms, principally bacteria.
4.4.2.2.2 Chemical Oxidation
Creosote wastestreams contain phenol contaminants which can be successfully destroyed by
chlorine and ozone. Chlorine gas and calcium or sodium hypochlorite are often used for
chlorination treatments. The chlorine-containing materials may be added manually, as is often
the case with the powdered calcium and sodium hypochlorite salts, or with a continuous-flow
system for chlorine gas. In order to destroy the phenols, chlorine treatments must operate
with the following restrictions:
• The proper amount of chlorine must be added to the wastewater
2144 4-14
-------
The temperature of the wastewater must be maintained below 43"C (HOT) to
prevent the formation of chlorates
The pH must be adjusted to 7.0 or higher to prevent the formation of
chlorophenols
Sufficient reaction time must be allowed (1 to 2 hours) to ensure complete
oxidation of phenols
4.4.2.2.3 Activated-Carbon Adsorption
Carbon has a strong affinity for nonpolar compounds such as phenol. As such, phenol and
other organic materials in the wastewater are adsorbed to the carbon surface. Once spent, the
carbon should be disposed of at a hazardous waste landfill. The process wastewater may be
treated further or discharged.
2144 4-15
-------
WOOD PRESERVATION REFERENCES
Lumber: Basic Engineering Principles & Wood Preservation, Universal Forest Products, Inc.,
Grand Rapids, ML 1984.
Nicholas, Darrel D., ed., Wood Deterioration and Its Prevention by Preservative Treatments,
Volume I: Degradation and Protection of Wood, Syracuse University Press, Syracuse, NY.
1973.
Nicholas, Darrel D., ed., Wood Deterioration and Its Prevention by Preservative Treatments,
Volume II: Preservatives and Preservative Systems, Syracuse University Press, Syracuse, NY.
1973.
Stranks, D.W., Wood Preservatives: Their Depletion as Fungicides and Fate in the
Environment, Department of the Environment, Canadian Forestry Service, Forestry Technical
Report 10, Ottawa, Canada. 1976.
Environmental Protection Service. Literature Review of Wastewater Characteristics and
Abatement Technology in the Wood and Timber Processing Industry. EPS 3-WP-77-2.
Fisheries and Environment Canada. Minister of Supply and Services, Canada. 1977.
Thompson, Warren S., ed., Pollution Abatement and Control in the Wood Preserving
Industry. Mississippi State University, Forest Products Utilization Laboratory, State College,
MS. 1970.
A92-214.4 4-16
-------
-------
CHAPTERS
ROCK CRUSHING AND CEMENT PRODUCTION
-------
TABLE OF CONTENTS
Chapter Page
5 ROCK CRUSHING AND CEMENT PRODUCTION 5-1
5.1 INDUSTRY DESCRIPTION 5-1
5.1.1 Rock Crushing 5-1
5.1.2 Cement Production 5-1
5.2 PROCESS DESCRIPTION 5-2
5.2.1 Rock Crushing 5-2
5.2.2 Cement Production 5-5
5.3 IDENTIFICATION AND CHARACTERIZATION OF EMISSION
POINTS 5-13
5.3.1 Rock Crushing 5-13
5.3.2 Cement Production 5-20
5.4 EMISSION REDUCTION METHODS 5-27
5.4.1 Rock Crushing 5-27
5.4J2 Cement Production 5-34
BIBLIOGRAPHY 5-48
EXHIBITS
Number Page
5-1 Flow Diagram of a Typical Crushing Plant 5-3
5-2 Portland Cement Process Flow Diagram 5-6
5-3 Crushing and Grinding Processes for Portland Cement Production 5-8
5-4 Finish Mill Grinding and Shipping 5-12
5-5 Emission Factors for Uncontrolled Paniculate Emissions from Crushing Operations
at Rock Crushing Facilities 5-14
5-6 Emission Factors for Uncontrolled Paniculate Emissions from Fugitive Dust Sources
at Rock Crushing Plants 5-15
5-7 Potential Emission Sources from Portland Cement Plants 5-21
5-8 Size-Specific Paniculate Emission Factors for Cement Kilns 5-23
5-9 Size-Specific Emission Factors for Clinker Coolers 5-24
5-10 Control Options for Paniculate Emission Sources in the Non-Metallic Minerals
Industry 5-28
5-11 Wet Dust Suppression System 5-30
5-12 Dust Suppression Application at Crusher Discharge 5-31
5-13 Potential Sources of Paniculate Emissions and Typical Control Technologies 5-35
5-14 Application of Emission Control Devices to Portland Cement Processes 5-36
5-15 Controlled Paniculate Emission Factors for Cement Manufacturing 5-37
5-16 Typical Fabric Filter Arrangement With Shaker for Dust Removal 5-39
5-17 Flow Diagram of a Dry Cyclone Collector 5-41
5-18 Gas Flow Diagram for a Gravel-bed Filter 5-43
5-19 Dust Suppression Practices 5-46
-------
CHAPTERS
ROCK CRUSHING AND CEMENT PRODUCTION
5.1 INDUSTRY DESCRIPTION
5.1.1 Rock Crushing
Rock crushing, one of many non-metallic mineral processing industries, produces crushed rock
in a wide range of quantities. The end uses of this rock are many and diverse. The minerals
may be used in their natural state or processed into a variety of manufactured products. The
construction and lime manufacturing industries use rock and crushed stones in their natural state.
Major rock types processed by the crushed and broken stone industry include limestone,
dolomite, granite, trap rock and sandstone, quartz and quartzite. Dolomite production constitutes
the widest and most important end use of crushed and broken stone in the United States. Minor
types include calcareous marl, marble, shell, and slate. Classifications used by the industry vary
considerably and in many cases do not reflect actual geological definitions.
Non-metallic mineral processing, including rock and crushed stone, generally involves product
unloading, conveying, crushing, screening, milling, size classifying, material handling, and
storing. All of these processes can be significant sources of dust emissions if uncontrolled.
Some mineral processing operations may also require washing, drying, calcining, or floating
operations. The operations performed depend on the rock type and the desired product.
5.1.2 Cement Production
Most of the hydraulic cement produced in the United States is portland cement, a cementitious,
crystalline compound composed of metallic oxides. Portland cement is used in the construction
of many kinds of structures including buildings, bridges and highways, and in products such as
concrete masonry, concrete piping, and many precast components for constructions such as
A92-214J 5-1
-------
prestressed concrete. The primary process in portland cement manufacturing is the calcining or
sintering of carefully ground and mixed raw materials in an inclined rotary kiln fired by fossil
fuel. The raw materials are clay, sand, iron ore, limestone shale, feldspar, etc., which contain
calcium carbonate, silica, alumina, ferric oxide, and other elements. The following five types of
Portland cement are manufactured in the United States. Each type differs in composition of raw
materials and production methods.
• Type I is used for general concrete construction when the special properties of the other four
types are not required.
• Type n is used in general concrete construction exposed to moderate sulfate action or where
moderate heat of hydration is required.
• Type m is used when high early strength is required.
• Type IV is used when a low heat of hydration is required.
• Type V is used when high sulfate resistance is required.
Chemical reactions that occur during calcining result in the formation of a clinker. Pulverizing
these clinkers with gypsum yields a powder called portland cement. Mixed with water, portland
cement forms a slowly hardening paste. When sand and gravel are added to the mixture, it
becomes concrete. Approximately 1.6 tons (1454 kg) of raw materials are required to produce
1 ton (909 kg) of cement.
5.2 PROCESS DESCRIPTION
5.2.1 Rock Crushing
Rock and crushed stone products are generally first loosened by drilling and blasting, then loaded
by power shovel or front-end loader and transported by heavy earth-moving equipment.
Techniques used for extraction vary with the nature and location of the deposit. A general
process flow diagram for a typical crushed rock and stone processing plant is shown in
Exhibit 5-1.
5-2
-------
TRUCK DUMP
I
PRIMARY
SCREEN
LO
SECONDARY
vSCREEN
BAGGING
OPERATION
FINISHING
SCREENS
FINE ORE
STORAGE BIN
o
TRUCK OR RAILCAR
LOADING
Exhibit 5-1. Flow Diagram of a Typical Crushing Plant
-------
5.2 J.I Primary Crushing and Screening
Quarried stones are normally delivered to the processing plant by truck and dumped into a
hoppered feeder, usually a vibrating grizzly type, or onto screens. These screens separate or
scalp larger boulders from finer rocks that do not require primary crushing, thus minimizing the
load to the primary crusher. Crushing is the process by which coarse material is reduced by
mechanical energy and attrition to a desired screening size. The mechanical stress applied to
rock or stone fragments during crushing may be accomplished by either compression or impact.
Compression crushers slowly squeeze the fragment and force a fracture, while an impact crusher
applies an abrupt breaking force. Compression crushers produce relatively closely graded
products with a small proportion of fines. Impact crushers produce a wide range of sizes and
a high proportion of fines. Compression crushers, such as jaw or gyratory crushers, are usually
used for initial production, although impact crushers are gaining favor for crushing low-abrasion
rock, such as limestone and talc, and where high reduction ratios are desired. The crusher
usually reduces the rock to between 3 and 12 inches (8 and 30 cm). The crusher product and
the grizzly troughs (the undersize material) are discharged onto a belt conveyor and normally
transported to either secondary screens and crushers, or to a surge pile or silo for temporary
storage.
5.2.1.2 Secondary Crushing and Screening
The secondary screens generally separate the process flow into either two or three fractions
(oversized, undersized, and troughs) prior to entering the secondary crusher. The oversized
particles are discharged to the secondary crusher for further reduction. The undersized, which
require no further reduction at this stage, normally by-pass the secondary crusher. The third
fraction, the troughs, is separated when processing some minerals. Troughs contain unwanted
fines that are usually removed from the process flow and stockpiled as crusher-run material. For
secondary crushing, gyratory or cone crushers are most commonly used, although impact crushers
are used at some installations.
A9Z-214.S 5-4
-------
5.2.1.3 Tertiary Crushing and Screening
The product from the secondary crushing stage, usually 1 inch (2 cm) or less in size, is
transported to tertiary screens for further sizing. Sized material from this screen is either
discharged directly to a tertiary crushing stage or conveyed to a fine-ore bin which supplies the
milling stage. Cone crushers or hammermills are commonly used for tertiary crushing. Rod
mills, ball mills, and hammermills are normally used in the milling stage. The product from the
tertiary crusher or the mill is usually conveyed to a type of classifier such as a dry vibrating
screen system, an air separator, or a wet rake or spiral system. Oversized materials are returned
to the tertiary crusher or mill for further reduction. At this point, some mineral end products of
the desired grade are conveyed directly to finished product bins or stockpiled in open areas by
conveyors or trucks.
5.2.1.4 Additional Crushed Rock Processing
Most crushed rock and stones require additional processing depending on the rock type and
product specifications. In certain cases, stone washing may be required to meet particular end
product demands like concrete aggregate processing. Some minerals, especially light-weight
aggregates, are washed and dried, sintered, or treated prior to primary crushing. Others are dried
following secondary crushing. Crushed and broken stone normally are not milled and are
screened and shipped to the consumer after secondary or tertiary crushing.
5.2.2 Cement Production
The portland cement production process involves three basic steps. First, raw materials are
crushed and mixed. Second, the mixture is heated to high temperatures in a kiln where chemical
reactions take place and a rock-like substance called clinker is formed. The clinker is then
cooled in a clinker cooler. Finally, the cooled clinker is crushed, and ground gypsum or other
materials are added to obtain the properties desired in the finished cement. The various steps are
shown in Exhibit 5-2.
A92.214 S 5-5
-------
QUARRYING
RAW
MATERIALS
-
PRIMARY AND
SECONDARY
CRUSHING
-
RAW
MATERIALS
STORAGE
in
o\
DRY MIXING
AND
BLENDING
STORAGE
SLURRY MIXING
AND
BLENDING <
-
STORAGE
i
DUST
COLLECTOR
FUEL
i
CLINKER
COOLER
STORAGE
AIR
SEPARATOR
STORAGE
SHIPMENT
Exhibit 5-2. Portland Cement Process Flow Diagram
-------
5.2.2.1 Raw Material Handling
The basic raw materials in portland cement manufacturing contain calcium carbonate, silicone
oxide, and ferric oxides, with minor amounts of sulfate, alkali, and carbonaceous materials.
Limestone is the most common source of calcium. Limestone can also have naturally high
amounts of clay or shale, which contain aluminum silicates or free silica. Usually, raw materials
such as clay, shale, or iron ore must be added to adjust the chemical composition of the clinker.
Processing of these raw materials into kiln feed involves quarrying and crushing phases and
mixing and grinding phases. Limestone is usually obtained from an open quarry located on or
near the plant site. Raw materials not quarried at the site are typically brought to the plant by
truck or rail and stored in stockpiles near the crushing machinery. The raw materials are crushed,
screened, and ground to the appropriate size for mixing and blending before they are charged to
the kiln. Crushing sometimes take place in two or three stages, as shown in Exhibit 5-3.
5.22.1.1 Crushing and Screening
Crushing reduces the size of rock obtained from the quarry. Crushing equipment typically
consists of primary and secondary crushers, and occasionally uses tertiary crushers. Primary
crushers may be of the gyratory, jaw, roll, or hammer type. Secondary crushers, often
hammerrnills, crush the rock to smaller than 1 inch (2.5 cm) in diameter. Crushed raw materials
are stored in silos or stockpiles.
Occasionally, a tertiary crusher is necessary, in which case the material is sent through a finer
hammermill operation, which reduces it to about 5/16 inch (0.8 cm). After each crushing
operation, the rock enters a screening operation. After the last crushing step, a bucket elevator
transports each type of raw material to separate compartments for storage prior to fine grinding.
A92-2W.5 5-7
-------
TRUCK BARGE
n
RR CAR
CO
RAW MATERIAL
UNLOADING
COAL. LIMESTONE. CLAY
GYPSUM. SAND. IRON ORE
LIMESTONE. CLAY
SAND. IRON ORE
FUEL FOR HEATING KILN
LIU
TRUCK BARGE
Exhibit 5-3. Crushing and Grinding Processes for Portland Cement Production
-------
5.22.12 Fine Grinding, Mixing, and Blending
Raw materials are drawn from their separate storage compartments and proportioned to the proper
composition before being charged to the kiln. Composition of the feed material depends on
whether a "wet process" or a "dry process" is to be used. Exhibit 5-3 illustrates each of these
techniques.
In the wet grinding process, ball mills or compartment mills (a ball mill combined with a tube
mill) are used, and water is added to the mill with the crushed raw materials. The resulting
slurry, which is about one-third water, is discharged from the mill and stored in open tanks where
additional mixing takes place. From the tanks, the slurry may be fed directly to the kiln, may
first be dewatered to form a cake containing about 30 percent moisture, or may be dried in a
dryer heated by exhaust gases from the kiln or the clinker cooler.
In the dry grinding process, ball mills, roller mills, or compartment mills are also used, but the
materials are ground without water. Crushed raw materials are dried in the mill itself or in a
direct-contact rotary dryer until the free moisture content is less than one percent. Heat for the
mill or dryer can be supplied by direct firing, although it is usually supplied by recirculation of
hot exhaust gases from the kiln or clinker cooler. If a roller mill is used, all kiln exhaust gases
can be directed through the mill for drying and preheating; if a ball mill is used, only a portion
of the exhaust gases can be directed to the mill.
5.2.2.2 Clinker Production
The rotary kiln is the major potential source of atmospheric emissions at portland cement plants.
Raw feed (wet slurry or dry feed) is fed into the upper end of an inclined rotary kiln and
conveyed slowly toward the lower end of the kiln by gravity and rotation of the kiln cylinder.
Kilns are fired from the lower end so that the hot gases pass countercurrent to the descending
raw feed material. As it travels downward, the feed becomes exposed to increasing heat. First,
the water is evaporated with the aid of various types of heat exchangers. As the temperature of
the charge increases, organic compounds are volatilized, sulfates are decomposed, and chlorides
A92-214.5 5-9
-------
and alkali salts are partially volatilized. At about the mid-section of the kiln, calcium and
magnesium carbonates are decomposed, and carbon dioxide is liberated. Calcium oxide and
magnesium oxide are also formed. In the hot zone of the kiln (2700°F/1480°C), about 20 to 30
percent of the charge is convened to liquid. It is through this medium that the chemical reactions
proceed.
5.22.2.1 Wet Process of Clinker Production
In the wet process of clinker production, feed material enters the kiln in a wet slurry form. Wet
process kilns are either short kilns with cyclone preheaters or long kilns with internal chain
preheaters. In the United States, rotary kilns are used, and most new plants use long kilns with
chains or some other type of preheating system. The chains, which are suspended in the
preheating zone of the kiln and arranged to help break up clumps of raw materials, aid in heat
transfer and improve fuel consumption.
5.2222 Dry Process of Clinker Production
Using a dry process kiln in the calcination process requires that less moisture be evaporated from
the feed material than if a wet process kiln were used: this is the only difference between the wet
process and dry process. Dry process kilns are short rotary units (either with or without
preheaters), rotary kilns with a suspension preheater, or long rotary kilns with a built-in preheater.
Dry process kilns can be 20 to 25 percent shorter than wet process kilns because little or no kiln
residence time is needed to evaporate water from dry feed. Adding a preheater to a dry process
kiln is more efficient, permitting use of a kiln one-half to two-third shorter than a dry kiln
without a preheater. Also, because of the increased heat transfer efficiency, a preheater kiln
system requires less energy than a wet kiln or a dry kiln without a preheater to achieve the same
amount of calcination.
A92-2145 5-10
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522.23 Clinker Cooling
Clinker is discharged from the kiln to a clinker cooler. The clinker cooler serves a dual purpose:
it reduces the temperature of the clinker so that processing can continue; and it provides a means
of recovering the heat from the clinker to preheat primary or secondary combustion air. Ambient
air is passed through a moving bed of hot clinker, cooling the clinker from about 2700°F
(1480°C) to about 150°F (66°C). Clinker coolers can be the planetary, (multicylinder), grate or
vibrating type. The planetary cooler consists of a series of tubes located around the
circumference of the discharge end of the kiln which rotates around the kiln. The material flows
from the kiln into the tubes containing internal baffles that transfer the heat from the material to
the cooling air being pulled in. This heated air is returned to the kiln as preheated combustion
air. In a greater cooler, the hot clinker is cooled by passing air upward through the moving bed
of clinkers on a perforated grate. The exhaust gases from a grate-type cooler can either be routed
to an emission control device or recycled to the kiln or preheater.
Cooled clinker can be stored in silos, storage halls, or outdoor stockpiles. Clinker cooler exhaust
gases can be ducted to emission control equipment or can be recycled to the kiln, the preheater,
the raw mill, or a raw feed dryer.
5.2.2.3 Cement Manufacture and Shipment
Exhibit 5-4 is an illustration of finished cement grinding and shipping. The process consists of
grinding the clinker with about 5 percent gypsum to regulate the setting time of the cement The
finishing mills are sometimes sprayed with water to keep them sufficiently cool and to minimize
dehydration of the gypsum. Depending on the type of cement being made, other additives such
water proofing and air-entraining agents may be mixed at this time. The finish mill can be an
open circuit, where the material passes through the mill regardless of particle size, or a closed
circuit, where air classifiers send over-sized clinker back through the mill for further grinding.
The finished cement is packaged in bags or bulk loaded and delivered by rail, truck, or ship.
The uncontrolled finish grinding operation can contribute substantial amounts of particulate
emissions. If control devices are used, the collected dust, which represents about 15 percent of
A92-214J 5-11
-------
AIR
CLASSIFIER
CEMENT
COLLECTOR „. ^
S3tm» 'rt^PS
V1
St. GYPSUM
ADDED
BULK STORAGE
BULK BULK BOX PACKAGING TRUCK
TRUCK CAR CAR MACHINE
Exhibit 5-4. Finish Mill Grinding and Shipping
-------
the feed, is usable product Transfer of the material after grinding can also generate fugitive
emissions.
5.3 IDENTIFICATION AND CHARACTERIZATION OF EMISSION POINTS
5.3.1 Rock Crushing
Essentially, all mineral processing operations are potential sources of particulate emissions.
Emissions may be categorized as either process fugitive emissions or open fugitive dust
emissions. Process fugitive emission sources include those sources for which emissions are
amenable to capture and subsequent control. Sources of process fugitive emissions include
crushing, screening, grinding, loading, and conveying. Open fugitive dust sources are not
amenable to control using conventional control systems and would require strategies that prevent
entrainment of settled dust by wind or machine movement. Fugitive dust sources include
hauling, haul roads, stockpiles, and plant yards. Some fugitive dust sources, like emissions from
silos, can be effectively controlled by conventional control strategies such as baghouses.
Dust emissions occur from many operations in rock and stone quarrying and processing. A
substantial portion of these emissions consists of heavy particles that may settle within the plant.
Factors affecting emissions from either source category (process fugitive source and fugitive dust
source) include the type of ore (rock), quantity and surface moisture content of the ore processed;
topographical and climatic factors; and the type of equipment and operating practices employed.
Available emission factors for uncontrolled emissions from process fugitive and fugitive dust
sources are provided in Exhibits 5-5 and 5-6, respectively.
The type of ore processed is important. Soft rocks produce a higher percentage of fine-grained
material than do hard rocks because of their greater friability and lower resistance to fracture.
Thus, the processing of soft rocks results in a greater potential for uncontrolled emissions than
the processing of hard rock. Major rock types arranged in order of increasing hardness are talc,
A92-214J 5-13
-------
Exhibit 5-5. Emission Factors for Uncontrolled Particulate Emissions
from Crushing Operations at Rock Crushing Facilities
Type of
crushing1*
Primary or
secondary
Dry material
Wet material'
Tertiary dry
material11
Particulate <
30pm
kg/Mg (Ib/ton)
0.14 (0.28)
0.009 (0.018)
0.93 (1.85)
Particulate <
10pm
kg/Mg Ob/ton)
0.0085 (0.017)
-
-
Emission factor rating
D
D
E
"Based on actual feed rate of raw material entering the particular operation. Emissions will vary by rock
type, but insufficient data are available to characterize these phenomena. Dash = no data.
Typical control efficiencies for cyclone, 70 - 80%: fabric filter, 99%; wet spray system, 70 - 90%.
'Refers to crushing of rock either naturally wet or moistened to 1.5-4 weight % with wet suppression technique.
"Range of values used to calculate emission factor is 0.0008 - 1.38 kg/Mg.
A92-214.5
5-14
-------
u\
i—«
LA
Exhibit 5-6. Emission Factors for Uncontrolled Particulate Emissions
from Fugitive Dust Sources at Rock Crushing Plants
Operation
Wet quarry drilling
Batch drop
Truck unloading
Truck loading
Conveyor
Front end loader
Conveying
Tunnel belt
Dust Sources
Unfractured stone
Fractured stone
Crushed stone
Crushed stone
Crushed stone
Emission
g/Mg
4 x lO'2
8 x 10'3
5 x lO'2
NAb
1.1 x 10'1
Factor
Ib/ton
1 x irr*
2 x 10'5
1 x 10'4
NA
2x 10-4
'Expressed as g/Mg (Ib/ton) of material through primary crusher, except for front end loading, which is g/Mg
(Ib/ton) of material transferred.
"NA = Not available.
-------
clay, gypsum, barite, limestone and dolomite, feldspar, and quartz. Thus, talc could be expected
to exhibit the highest uncontrolled emissions and quartz the least
The moisture content of the material processed can have a significant effect on uncontrolled
emissions. This is especially evident during quarrying, initial material handling, and initial plant
process operations such as primary crushing. Surface wetness causes fine particles to adhere to
the faces of larger stones, with a resulting dust suppression effect However, as new fine
particles are created by crushing and attrition, and as the moisture content is reduced by
evaporation, this suppression diminishes and may disappear. Since moisture content is usually
expressed as a basis of overall weight percent, the actual moisture amount per unit area will vary
with the size of the rock being handled. On a constant mass fraction basis, the per-unit-area
moisture content varies inversely with the diameter of the rock. Therefore, the suppressive effect
of the moisture depends on both the water content (mass) and the size of the rock product
Typically, a wet material contains 1.5 to 4 percent water.
The primary geographic and seasonal factors affecting uncontrolled paniculate emissions are wind
and material moisture content. Wind parameters vary with geographical location, season and
weather. It can be expected that the level of emissions from unenclosed sources (principally
fugitive dust sources) will be greater during periods of high winds. The material moisture
content also varies with geographic locations, season and weather. Therefore, uncontrolled
emissions from both process emission sources and fugitive dust sources generally will be greater
in arid regions than in temperate ones and greater during the summer months because of a higher
evaporation rate.
A large number of material, equipment, and operating factors influence emissions from
processing plants. Principal processing facilities include crushers, screens, and material handling
and transfer equipment All these units are potential sources of paniculate emissions. Emissions
are generally emitted from process equipment at feed and discharge points and from material
handling equipment at transfer points.
A92-214J 5-16
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53.1.1 Crushing Operations
Generating paniculate emissions is inherent in the crushing process. The most important element
influencing emissions from crushing equipment is the type and moisture contect of the rock being
crushed. The crushing mechanism employed also has a substantial impact on the size reduction
that a machine can achieve. The crushers used in the rock crushing industry are jaw, gyratory,
roll, and impact crushers. Jaw crushers are principally applied for primary crushing. There are
three types of gyratory crushers: pivoted spindle, fixed spindle, and cone crushers. The fixed and
pivoted spindle gyratories are used for primary and secondary crushing, and cone crushers for
secondary and tertiary crushing. Roll crushers are utilized primarily at intermediate or final
reduction stages and are often used at portable plants. Crushing units using impaction rather than
compression generally produce a larger proportion of fines. In addition to generating more fines,
impact crushers generate larger quantities of uncontrolled paniculate emissions per ton/kilogram
of material processed than any other crusher type.
The level of uncontrolled emissions from jaw, gyratory, cone and roll crushers closely parallels
the reduction stage to which they are applied, with emissions increasing progressively from
primary to secondary to tertiary crushing.
Insufficient data are available to present a matrix of rock crushing emission factors detailing the
different rock types and variables discussed above. Available data for preparing emission factors
also vary considerably for extractive testing and plume profiling. Emission factors from
extractive testing are generally higher than those based on plume profiling tests, but they have
a greater degree of reliability. Some test data for primary crushing indicate higher emissions than
from secondary crushing, although factors affecting emission rates and visual observations
suggest that the secondary crushing emission factor, on a throughput basis, should be higher.
Exhibit 5-5 shows single factors for either primary or secondary crushing which were derived
from a combined data base. An emission factor for tertiary crushing is also given, but it is based
on extremely limited data. All factors are rated low because of the limited and highly variable
data base.
A92-214J 5-17
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5.3.1.2 Screening Operations
Screening is the process by which a mixture of stones is separated according to size. Screening
surfaces may be constructed of metal bars, perforated or slotted metal plates, or woven wire
cloth. Screening equipment commonly used in the non-metallic minerals processing industry
includes grizzlies, shaking screens, and vibrating screens. Grizzlies are used to remove tines
prior to primary crushing, thus reducing the load on the primary crusher. Shaking screens are
generally used for screening coarse material, one-half inch (1.3 cm) or larger. "Vibrating screens
are by far the most commonly used screen type in the rock crushing industry. Where large
capacity and high efficiency are desired, the vibrating screen can be used in place of all other
screen types.
Dust is emitted from screening operations as a result of the agitation of dry material. The level
of uncontrolled emissions depends on the quantity of fine particles contained in the material, the
moisture content of the material, and the type of screening equipment. Generally, the screening
of fines produces higher emissions than the screening of coarse materials. Also, screens agitated
at large amplitudes and high frequency emit more duct than those operated at small amplitudes
and low frequencies.
Screening emission factors are not available for crushed rock and stone processing however,
screening emission factors for sand and gravel processing (0.16 Ib/ton [0.08 kg/Mg] for TSP and
0.12 Ib/ton [0.06 kg/Mg] for PM-10) should be similar to those expected from screening of
crushed stones.
5.3.1.3 Conveying Operations
Material handling devices are used to convey materials from one point to another. The most
common devices include feeders, belt conveyors, bucket elevators, and screw conveyors. Feeders
are used to receive material and deliver it to process units, especially crushers. Belt conveyors
are the most widely used means of transporting, elevating, and handling materials in the non-
metallic minerals processing industry. Elevators are utilized where substantial elevation is
A92-214J 5-18
-------
required within a limited space. Screw conveyors are usually used with wet classification, thus
preventing significant emissions.
As with screening, the level of uncontrolled emissions from conveying operations depends on the
material being handled, its size, moisture content, and the degree of agitation. Perhaps the largest
emissions occur at conveyor belt transfer points. Depending on the conveyor belt speed and the
free fall distance between transfer points, substantial emissions may be generated. Emission
factors for transfer operations are included in Exhibit 5-6.
5.3.1.4 Grinding Operation
Grinding further reduces material to particle sizes smaller than those attainable by crushers.
Grinding mills generally utilize impact rather than the compression mechanism. The principal
types of mills used are hammer, roller, rod, and fluid energy. Hammermills are used for
nonabrasive materials and can accomplish a size reduction up to 12:1. Roller mills can produce
material ranging from 20 mesh to 325 mesh or finer. Rod mills are principally used for handling
a maximum feed size of 1 to 2 inches (2.5 to 5 cm) and grinding to a maximum of 65 mesh.
Fluid energy mills are used when the desired material size is in the range of 1 to 20 pm.
Grinding mills usually produce a larger proportion of fines. Paniculate emissions are generated
from grinding mills at the grinder's inlet and outlet. Gravity-type grinding mills accept feed from
a conveyor and discharge product into a screen or classifier or onto a conveyor. These transfer
points are sources of paniculate emissions. The outlet has the highest emissions potential
because of the finer material. Air-swept mills include an air conveying system and/or an air
separator. The air separators are generally cyclone collectors. In some systems, the air merely
conveys the material to a separator for deposit into a storage bin, with the conveying air escaping
through the cyclone vent. In other grinding systems, the air is continuously recirculated.
Maintaining this circulating air system under suction keeps the operating mill dustless, and any
surplus air drawn into the system due to the suction created by the fan is released through a vent.
In both cases, the vent gases will contain a certain amount of paniculate matter.
A92-2145 5-19
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5.3.13 Bagging and Bulk Loading Operations
In the nonmetallic minerals industry, the valve-type paper bag is widely used for shipping fine
materials. The valve bag is "factory closed," that is, the top and bottom are closed either by
sewing or by pasting, and a single small opening is left in one comer. Materials are discharged
into the bag through the valve. The valve closes automatically due to internal pressure as soon
as it is filled. Bagging operations are a source of paniculate emissions. Dust is emitted during
the final stages of filling when dust-laden air is forced out of the bag. The process fugitive
emissions due to bagging operations are generally localized in the area of the bagging machine.
Fine product materials that are not bagged for, shipment are either bulk-loaded in tank trucks or
enclosed in railroad cars. The usual method of loading is gravity feeding through plastic or
fabric sleeves. Bulk loading of the fine material is a source of paniculate emissions because
dust-laden air is forced out of the truck or railroad car during the loading operation.
5.3.2 Cement Production
The potential sources of emissions from portland cement plants are illustrated in Exhibit 5-7.
Particulate, NOX, SO2, CO and CO2 are the primary emissions in the manufacture of portland
cement, and emissions may also include minute particles from the fuel and raw materials. Many
of the emission areas are at the ends of material conveying devices, called "transfer points."
Uncontrolled emissions at transfer points are reduced by lightly spraying the feed with water or
an aqueous chemical solution.
Exhaust gases from kilns, clinker coolers and dry milling systems constitute the larger emission
sources. In the wet process plants, raw materials are not dried but are ground with water to form
a slurry; therefore, the only dust is liberated from the transfer point at which rock is fed into the
grinding mill.
A92-214J 5-20
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TRUCK BARGE
RAW MATERIAL
UNLOADING
COAL, LIMESTONE. CLAY
GYPSUM. SAND. IRON ORE
LIMESTONE. CLAY
SAND. IRON ORE
LEGEND.
——POTENTIAL PM10 SOURCE
—•- PROCESS FLOW
(?) PROCESS EMISSIONS
(PP) PROCESS FUCmVE
(SB) OPEN DUST FUGITIVE
r
COAL
PILE
FUEL FOR HEATING KILN
012
TRUCK BARGE
013
Exhibit 5-7. Potential Emission Sources from Portland Cement Plants
-------
5.3.2.1 Particulate Emissions
Particulate matter is the primary pollutant from the manufacture of portland cement. The most
significant sources of participate emissions at a cement plant are the kiln and clinker cooler.
Kilns controlled by a cyclone dust collector for product recovery purposes can emit as much as
45 Ibs (20 kg) of particulate matter per ton (900 kg) of raw material, and clinker coolers
controlled by a cyclone dust collector can emit as much as 30 Ib/ton (15 kg/Mg) of raw material.
Approximately 50 percent of the particles in exhaust gases from a dry process kiln with a
preheater are smaller than 1.5 to 3.5 micrometers in diameter (i.e., the mass median diameter
[MMD] is 1.5 to 3.5 micrometers), and 85 to 99 percent of the particles are smaller than 10
micrometers. Similarly, for wet process kiln exhaust gases, the MMD is 7 to 40 micrometers,
and 20 to 60 percent of the entrained particulate matter is smaller than 10 micrometers in
diameter. However, the clinker cooler exhaust gas particles are larger; the MMD is from 30 to
over 100 micrometers, and less than 20 percent of the clinker cooler dust is smaller than 10
micrometer. Exhibit 5-8 presents size-specific emission factors for wet, dry, and uncontrolled
cement kiln operations. Exhibit 5-9 presents emission factors for uncontrolled and controlled
clinker coolers.
Quarrying, raw material storage, grinding and blending (in the dry process only), finish grinding,
and packaging operations can be vented to the atmosphere, and all are potential sources of
particulate emissions. The emission rate depends on the kind of raw material and its moisture
content, characteristics of the crusher, the kind of control equipment, and its operation and
condition. Particulate emissions also result from the open transporting of the crushed material
and from the crushing and screening operations that are vented to the atmosphere.
5.3.2.2 Gaseous Emissions
The exhaust streams from cement kilns and clinker coolers contain a number of gaseous species
in addition to the particulate matter. The following paragraphs discuss those emissions of carbon
monoxide, sulfur oxides and nitrogen oxides which remain in a gaseous state and therefore
A92-214.5 5-22
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I
£ Exhibit 5-8. Size-Specific Particulate Emission Factors for Cement Kilns
to
Cumulative mass % < stated sizeb
Uncontrolled
Particle
size
(urn)
2.5
5.0
10.0
Wet
process
kiln
7.0
20
24
Dry
process
kiln
18
NA
42
Wet
process
kiln with
ESP
64
83
85
Baghouse
Wet
process
kiln
NA
NA
NA
Dry
process
kiln
45
77
84
*ESP = electrostatic precipitator. NA = not available.
"Aerodynamic diameter. Percentages rounded to two significant figures.
-------
Exhibit 5-9. Size-Specific Emission Factors for Clinker Coolers
Particle
size"
(pm)
2.5
5.0
10.0
15.0
20.0
Cumulative
< stated
Uncontrolled
0.54
1.5
8.6
21
34
mass %
size"
Gravel
bed
filter
40
64
76
84
89
Cumulative emission factor
< stated sizec
Uncontrolled
kg/Mg
0.025
0.067
0.40
0.99
1.6
Ib/ton
0.050
0.13
0.80
2.0
3.2
Gravel bed filter
kg/Mg
0.064
0.10
0.12
0.13
0.14
Ib/ton
0.13
0.20
0.24
0.26
0.28
'Aerodynamic diameter
"Rounded co two significant figures.
°UniC weight of pollutant/unit weight of clinker produced. Rounded co cwo significant figures.
A92-214.3
5-24
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uncontrolled. Fluorides, hydrocarbons and hydrogen sulfide may also be emitted.
5.32.2.2 Carbon Monoxide
Carbon monoxide emissions are generally negligible due to the excess air present in the kiln.
A typical analysis of the kiln exhaust gas would have zero to two volume percent carbon
monoxide.
5.32.22 Sulfur Oxides
Emissions of sulfur oxides from portland cement kilns are caused by fuel combustion and clinker
formation. Sulfur oxide emissions are almost solely in the form of sulfur dioxide (SO^, although
small quantities of sulfuric acid (H2SO4) and S03 may exist in kiln exhaust gases.
The SO2 emissions result from both sulfur in the fuel and sulfur in the raw materials. Direct
correlation of these factors with S02 emissions is difficult because of the complex chemistry of
sulfur in the kiln. Sulfur can be absorbed into the clinker, raw feed, or dust collected in a control
device or emitted as a gas. In addition, the amount of sulfur found in the fuel and the feed can
vary significantly from plant to plant Wet process kilns tend to emit larger quantities of SO2
than dry process kilns because they require more heat per Mg of clinker produced than do dry
process plants.
Emissions of SO2 from the kiln are reduced significantly by the production process because the
SO2 is absorbed into the clinker. About 75 percent of the SO2 formed in the kiln reportedly is
absorbed into the clinker. Data on reduction of SO2 emissions in the production process vary
widely because of differences in process parameters and in sulfur content of raw feed material
and fuel.
A92-214.S 5-25
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5.3223 Nitrogen Oxides
Parameters that affect emissions of NOX from cement kilns include the nitrogen content in the
fuel and raw materials, the flame and kiln temperature, the residence time that combustion gases
remain at this temperature, the rate of cooling of these gases, and the quantity of excess air in
the flame. As flame temperature increases, the amount of thermally generated NOX increases,
and the amount of NOX generated from fuel increases with the quantity of nitrogen in the fuel.
NOX can form in portland cement kilns at temperatures of 2600° to 3000°F (1427° to 1649°C).
Because clinkering occurs at about 2700T (1482°C), temperatures favorable for NOX formation
are reached in routine kiln operation.
5.32.2.4 Fluorine
Fluorine can be released in the kiln from the raw materials and fuel during the formation of
clinker. Tests performed on the cleaned gas from 11 cement kilns in the United States found no
gaseous fluorides. This is expected since calcium fluoride is produced in the presence of excess
calcium oxide and can be removed by fabric filters or electrostatic precipitators.
5.3225 Hydrocarbons
Hydrocarbons, principally aldehydes, can result from the discharge of the products of incomplete
fuel combustion. This would ordinarily only occur during start-up or malfunction.
5.32.2.6 Hydrogen Sulfide
Hydrogen sulfide and other odiferous sulfides can be emitted from a cement plant if certain raw
materials such as marl, clay, shale, and marine shells are used in a wet process kiln. Establishing
excess air conditions by reducing the fuel supply and increasing the air supply will control this.
A92-214.5 5-26
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5.4 EMISSION REDUCTION METHODS
5.4.1 Rock Crushing
5.4.1.1 Available Particulate Control Technology
The diversity of the paniculate emissions sources involved in mining and processing non-metallic
minerals requires use of a variety of control methods and techniques. Dust suppression
techniques designed to prevent particulate matter from becoming airborne are applicable to both
process fugitive and fugitive dust sources. Where particulate emissions can be contained and
captured, particulate collection systems are used. Emission sources and applicable control options
are listed in Exhibit 5-10.
Methods used to reduce emissions include wet dust suppression and/or dry collection. In a wet
dust suppression system, dust emissions are controlled by applying moisture in the form of water
or water plus a wetting agent sprayed at critical dust-producing points in the process flow. This
causes fine particulate matter to be confined and remain with the material flow rather than
becoming airborne. Dry collection involves hooding and enclosing dust-producing points and
exhausting emissions to a collection device. Combination systems utilize both methods at
different stages throughout the processing plant In addition to these control techniques, the use
of enclosed structures to house process equipment may also be effective in preventing emissions
to the atmosphere.
5.4.1.1.1 Wet Dust Suppression
In a wet dust suppression system, dust emissions are controlled by applying moisture in the form
of water or water plus a wetting agent sprayed at critical dust-producing points in the process
flow. This causes dust particles to adhere to larger mineral pieces or to form agglomerates too
heavy to become or remain airborne. Thus, the objective of wet dust suppression is not to fog
an emission source with a fine mist to capture and remove particulates emitted, but rather to
prevent emissions by keeping the material moist at all process stages. However, no actual
A9Z-214.5 5-27
-------
Exhibit 5-10. Control Options for Particulate Emission Sources
in the Non-Metallic Minerals Industry
Operation or Source
Control Option
Hauling
Crushing
Screening
1) Water wetting of haulage roads
2) Treatment of haulage roads with surface
agents
3) Soil stabilization
4) Paving
5) Traffic control
1) Wet dust suppression systems
2) Capturing and venting emissions to a control
device
1) Wet dust suppression systems
2) Capturing and venting emissions to a control
device
Conveying (Transfer points)
Stockpiling
Grinding
Storage Bins
1) Wet dust suppression systems
2) Capturing and venting emissions to a control
device
1) Stone ladders
2) Stacker conveyors
3) Water sprays at conveyor discharge
4) Pugmill
1) Wet dust suppression systems
2) Capturing and venting emissions to a control
device
1) Capturing and venting emissions to a control
device
Conveying (other than
transfer points)
Windblown dust from stockpiles
Bagging
Loading (product into rail cars,
trucks, ships)
1) Covering
2) Wet dust suppression systems
1) Water wetting
2) Surface active agents
3) Covering (i.e.. silos, bins)
4) Windbreaks
1) Capturing and venting emissions to a control
device
1) Water wetting
2) Capturing and venting emissions to a control
device
A92-214.5
5-28
-------
paniculate emission measurements have been made to estimate the attainable control efficiency
of wet dust suppression systems at rock crushing plants.
The wet dust suppression method has been used on a wide variety of stones including limestone,
granite, shale, dolomite, sand, and gravel. It can generally be considered to have a universal
application to stone handled through a normal crushing and screening operation. In some cases,
however, water sprays cannot be used since the moisture may interfere with further processing
such as crushing, screening, or grinding, where blinding problems may occur. In addition, the
capacity of the dryers used in some of the processing steps limits the amount of water that can
be sprayed onto the raw materials. Once the materials have passed through the drying operations,
water cannot be added and other means of dust control must be utilized.
In order to enhance the effectiveness of the wet suppression technique, wetting agents are added
to the water to lower its surface tension and consequently improve its wetting efficiency. The
dilution of such an agent in minute quantities in water (1 part wetting agent in 1,000 parts water)
is reported to make dust control practical throughout an entire crushing plant. In a crushed stone
plant, this may amount to as little as 1/2 to 1 percent total moisture per ton (900 kg) of stone
processed.
A typical wet dust suppression system is illustrated in Exhibit 5-11. Exhibit 5-11 shows the basic
components and features of the wet dust suppression system including a dust control agent,
proportioning equipment, a distribution system, and control actuators. A proportioner is
necessary to proportion the wetting agent and water at the desired ratio and to provide moisture
in sufficient quantity and at adequate pressure to meet the demands of the overall system.
Distribution is accomplished by spray headers fitted with pressure spray nozzles. One or more
headers are used to apply the dust suppressant mixture at each treatment point at the rate and
spray configuration required to effect dust control. A variety of nozzle types may be used
depending on the spray pattern desired. Exhibit 5-12 shows a typical arrangement for the control
of dust emissions at a crusher discharge. As for spray actuation, it is important to prevent waste
and undesirable muddy conditions, especially when the material flow is intermittent. Spray
headers at each application point are normally equipped with an on-off controller which is
A9Z-214.5 5-29
-------
TRUCK DUMP
SECONDARY
CRUSHER/
SCREENS
PRIMARY
CRUSHER
INCOMING
WATER LINE
i
PROPORTIONER
DUST CONTROL
AGENT
Exhibit 5-11. Wet Dust Suppression System
-------
SUPPRESSANT
FILTER
COKTROL
VALVE
Exhibit 5-12. Dust Suppression Application at Crusher Discharge
A92-214.5
5-31
-------
interlocked with a sensing mechanism so that sprays will be operative only when there is material
actually flowing.
In adding moisture to the process material, several application points are normally required; The
initial application point is commonly made at the primary crusher truck dump. Applications are
also made at the discharge of the primary crusher and at all secondary and tertiary crushers where
new dry surfaces and dust are generated by the fracturing of stone. In addition, treatment may
also be required at feeders located under surge or reclaim piles if this temporary storage results
in sufficient evaporation. The amount of moisture required at each application point is dependent
on a number of factors including the wetting agent used, its dilution ratio in water, the type and
size of process equipment, and the characteristics of the material processed (type, size
distribution, feed rate and moisture content).
5.4.1.12 Dry Collection Systems
Paniculate emissions generated at plant process operations (crushers, screens, grinders, conveyor
transfer points, fine product loading operations and bagging operations) may be controlled by
capturing and exhausting potential emissions to a collection device. Depending on the physical
layout of the plant, emission sources may be manifolded to a single centrally located collector
or ducted to a number of individual control units. Collection systems consist of an exhaust
system utilizing hoods and enclosures to capture and confine emissions, dusting and fans to
convey the captured emissions to a collection device, and a collection device for paniculate
removal prior to exhausting the air stream to the atmosphere.
Exhaust Systems and Ducting. If a collection system is to effectively prevent paniculate
emissions from being discharged to the atmosphere, local exhaust systems including hooding and
ducting must be properly designed. Process equipment should be enclosed as completely as
practicable, allowing for access for operation, routine maintenance and inspection requirements.
For crushing facilities, recommended hood capture velocities range from 61 to 150 meters per
minute. A well designed enclosure can be defined as a housing which minimizes open areas
between the operation and the hood and contains all dust dispersion action. Good duct design
A92-214 5
5-32
-------
dictates that adequate conveying velocities be maintained so that the transported dust particles
will not settle in the ducts along the way to the collection device. Based on information for
crushed stone, recommended conveying velocities range from 1,100 to 1,400 meters per minute.
Collection Devices. The most efficient collection device used in the non-metallic mineral
processing industry is the fabric filter or baghouse. Fabric filters will be discussed in detail in
Section 5.4.2.1. Other collection devices include wet capture. The principle of collection in wet
capture devices involves contacting dust particles with liquid droplets and then having the wetted
and unwetted particles impinge upon a collecting surface where they can be flushed away with
water. The major types of wet collectors are cyclone, mechanical, mechanical-centrifugal, and
Venturi scrubbers.
Wet cyclones impart a centrifugal force to the incoming gas stream causing it to increase in
velocity. Atomized liquids are introduced to contact and carry away dust particles. The dust
impinges upon the collector walls, with clean air remaining in the central area of the device.
Efficiencies in this type of equipment average in the vicinity of 98 percent
Mechanical scrubbers have a water spray created by a rotating disc or drum contacting the dust
particles. Extreme turbulence is created which insures this required contact Efficiencies are
about the same as cyclone wet scrubbers.
Mechanical centrifugal capture devices with water sprays are similar to their dry counterparts
with the exception that a water spray is. located at the gas inlet so that the particulate matter is
moistened before it reaches the blades. The water droplets containing particulate are impinged
on the blades while the clean air is exhausted. In this case, the spray not only keeps the blades
wet causing dust to impinge upon them, but it also serves as a medium to carry away particles.
Venturi scrubbers rely on an impaction mechanism and extreme turbulence for dust collection.
The extreme turbulence causes excellent contact of water and particulate. The wetted panicles
travel through the Venture tube to a cyclone spray collector. Efficiencies are very high,
averaging 99.9 percent These high efficiencies are also evidenced in the low particle size ranges
A92-214J 5-33
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collected (less than 1 micrometer in diameter). This design is best suited to applications
involving removal of 0.5 to 5 micron size.
5.4.1.13 Combination Systems
Wet dust suppression and dry collection techniques are often used in combination to control
particulate emissions from crushing plant facilities. Wet dust suppression techniques are
generally used to prevent emissions at the primary crushing stage and at subsequent screens,
transfer points and crusher inlets. Dry collection is generally used to control emissions at the
discharge of the secondary and tertiary crushers, where new dry surfaces and fine particulates are
formed. In addition to controlling emissions, dry collection results in the removal of a large
portion of the particulates generated with the resultant effect of making subsequent dust
suppression applications more effective with a minimum of added moisture. Depending on the
product specifications, dry collection may also be necessary at the finishing screens.
5.4.2 Cement Production
5.4.2.1 Available Particulate Control Technology
Typical methods used for control of particulate emissions from potential sources at portland
cement manufacturing facilities are listed in Exhibits 5-13 and 5-14. The kiln and clinker cooler
are the first and second largest sources, respectively, of particulate emissions at a cement plant.
Particulate emissions also occur during material handling, transfer, and storage. Particulate
emissions from kilns are controlled by fabric filters, electrostatic precipitators (ESP), or cyclones.
Particulate emissions from clinker coolers and other facilities (mills, storage facilities, and
transfer facilities) are typically controlled by fabric filters.
Exhibit 5-15 includes controlled particulate emission factors for the different processes in cement
manufacturing. The types of controls listed in Exhibit 5-15 are discussed below.
A92-214.5 5-34
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Exhibit 5-13. Potential Sources of Particulate Emissions
and Typical Control Technologies
Operation or Source
Control Option
Raw material system
(including crushing
and grinding)
Raw material dryer
Crushed raw material storage
(except coal piles)
Raw blending
Kiln (including preheater/
precalciner systems)
Clinker cooler
Clinker storage
Finish mill system
Finished product storage
Conveyor transfer points
(e.g., to primary crusher,
secondary crusher, elevators,
materials storage, grinding
mill)
Packaging (i.e., bagging)
1) Fabric filter
1) Fabric filter
1) Fabric filter
2) Capturing and venting
emissions to a control
device
1) Fabric filter
2) Capturing and venting
emissions to a control
device
1) Fabric filter
2) Electrostatic precipitator
1) Fabric filter
2) Electrostatic precipitator
3) Gravel bed filter
1) Capturing and venting
emissions to a control
device
2) Fabric filter
3) Enclosure
4) Cover
5) Windbreaks
1) Fabric filter
2) Electrostatic precipitator
1) Fabric filter
1) Fabric filter
2) Capture to control device
3) Wet suppression
4) Work practice
1) Fabric filter
A92-214.5
5-35
-------
Exhibit 5-14. Application of Emission Control Devices to Portland Cement Processes
Effectiveness of Emission control device8
Process
Raw material crushing and grinding
Calcining
Clinker cooling
Product storage packaging and loadout
General housekeeping and fugitive controls
Cyclone separator
Unsatisfactory
Successful1"
Successful
Unsatisfactory
Impractical
ESP
Impractical
Successful
Successful
Impractical
Impractical
Fabric
filter
Successful
Successful
Successful
Successful
Successful
Gravel bed filter
Impractical
Impractical
Impractical
Impractical
Impractical
Y1 "Wet collectors are generally not used for portland cement processes.
<*> 'Preliminary cleaning only; used with ESP or fabric filter.
-------
Exhibit 5-15. Controlled Particulate Emission Factors for
Cement Manufacturing
Paniculate
Type of source
Wet process kiln
Dry process kiln
Clinker cooler
Control
Baghouse ESP
Multiclone
Multicyclone
+ ESP
Baghouse
Gravel bed
filter
ESP
Baghouse
kg/Mg
clinker
0.57
039
130"
0.34
0.16
0.16
0.048
0.010
Ib/ton
clinker
1.1
0.78
260"
0.68
0.32
0.32
0.096
0.020
Emission
Factor
Rating
C
C
D
C
B
C
D
C
Primary limestone
crusher*
Primary limestone
screen'
Secondary
limestone screen
Baghouse
Baghouse
0.00051
0.00011
0.0010
0.00022
D
and crusher*
Conveyor transfer*
Raw mill system*1*1
Finish mill system"
Baghouse
Baghouse
Baghouse
Baghouse
0.00016
0.000020
0.034
0.017
0.00032
0.000040
0.068
0.034
D
D
D
C
factors are tor kg paniculate/Mg (Ib pamculate/ton) of clinker produced, except as noted.
ESP = electrostatic precipitator.
"•Based on a single test of a dry process kiln fired with a combination of coke and natural gas.
Not generally applicable to a broad cross section of the cement industry.
'Expressed as mass of pollutant/mass of raw material processed.
'Includes mill, air separator and weight feeder.
'Expressed as units of cement produced. Includes mill, air separator(s) and one or more material transfer operations.
A92-214.5
5-37
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5.42.1.1 Kiln
Fabric Filters. A fabric filter system consists of a woven textile material, usually in the shape
of a cylindrical bag, housed in a metal enclosure having inlet and outlet gas connections, a dust
discharge hopper, and a means for periodic cleaning of the fabric. Exhibit 5-16 illustrates a
fabric filter system. The particulate-laden gas enters the filter through the inlet gas connection
and passes through the filtering medium, where the paniculate matter is retained. The gas then
leaves the filter via the outlet gas connection. The efficiency of a fabric filter is directly
proportional to the fabric area. Design efficiencies of greater than 99.9 percent are typical. The
filter is sized in terms of cloth area as a function of the amount of gas handled and the method
of filter cleaning. The area is determined from the air-to-cloth ratio, which is arrived at by
dividing total air flow by the cloth area. The air-to-cloth ratio of fabric filters ranges from about
1.3:1 to 2:1 for kilns and alkali bypass systems. The bags are typically made of fiberglass and
cleaned by reverse air. Bag life is affected by the abrasiveness of the paniculate matter in the
exhaust gases, temperature of the gases, and maintenance practices.
Advantages of fabric filters include high efficiencies, simplicity in operation, reliability, and the
ability to isolate compartments for repairs. Disadvantages of fabric filters include the need for
a high pressure drop (necessitating high energy consumption), a low resistance to temperatures
above 600°F (316°C), and the potential for blinding of the bags at temperatures below the dew
point.
Electrostatic Precipitators. Electrostatic precipitators can operate economically and at high
control efficiencies on exhaust gas streams with high-volume flow rates (> 2,000 cfm/> 56.6
mVmin) and temperatures in the 300° to 600°F (149° to 315°C) range. In the portland cement
industry, ESP are mainly used to control particulates in the exhaust gas flow streams from cement
kilns. Cleaning of exhaust gases using electrostatic precipitators involves three steps: (1) passing
the suspended particles through a direct-current corona to charge them electrically; (2) collecting
the charged panicles on a grounded plate; and (3) removing the collected paniculate from the
plate by a mechanical process. Design efficiencies greater than 99.9 percent are typical of ESP.
A9Z-214J 5-38
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SHAKER ^^h-
MOTOR
BAFFLE
PLATE
DIRTY AIR
INLET
DUST CONVEYING
SYSTEM
HANGERS
CLEAN AIR
SIDE
OUTLET
PIPE
FILTER
BAGS
TUBE
SHEET
HOPPER
Exhibit 5-16. Typical Fabric Filter Arrangement With Shaker
for Dust Removal
(Courtesy of Wheelabrator-Frye Corporation)
A92-214.5
5-39
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The high resistivity of particles in cement kiln exhaust gases requires that the gases be
conditioned prior to entering the ESP. Resistivity is about a factor of 10 lower for wet process
kilns than for dry process kilns because of the moisture in the gases; however, the resistivity of
exhaust gases from the dry process kilns can be lowered by spray cooling. Exhaust gases from
dry process kilns with preheaters have higher resistivity than those from dry process kilns without
preheaters. ESP can1 operate at high temperatures and at temperatures below the dew point
Cyclones. Use of cyclone separators has been limited in the portland cement industry. Cyclone •
collection systems consist of one or more conically shaped vessels in which the gas stream
follows a circular motion prior to outlet (typically at the bottom of the cone). As shown in
Exhibit 5-17, the dust-laden gas enters the upper cylindrical section tangentially, which produces
a centrifugal force that preferentially throws the larger, heavier particles outward to the walls of
the cylinder. The gas spirals downward into the conical section, where the gas velocity increases
and greater centrifugal force is generated. The particulate matter collected at the walls is swept
to the bottom of the cone section, where it is discharged into a collection hopper or drum. The
cleaned gas exits from the unit through an outlet at the top center of the cylindrical section.
Cyclones are easy to operate but cannot readily achieve high efficiencies in the removal of small
particles. Collection efficiency is a function of (a) size of particles in the gas stream, (b) particle
density, (c) inlet gas velocity, (d) dimensions of the cyclone, and (e) smoothness of the cyclone
wall. In the cement industry, cyclone-type collection systems are used for product recovery.
Cyclones are typically used as precollection systems in combination with fabric filters and ESP.
5.42.12 Clinker Cooler
Fabric Filters. Most of the fabric filters used for control of clinker cooler emissions are the
negative-pressure type. The bags in fabric filters controlling clinker coolers are typically cleaned
by a pulse jet cleaning mechanism and have air-to-cloth ratios ranging from about 4:1 to 9:1.
The bags may be made of fiberglass. Clinker cooler exhaust gas temperatures range from about
200° to 450°F (93° to 232°C).
A9Z-214.5 5-40
-------
CLEAN-AIR
OUT
DIRTY AIR
IN
TOP VIEW OF CYCLONE
CLEAN AIR OUT
!
£' U
, % *
• - / !
. .
W PIT PTY ATP
:-V "•:'.. • • INLET
OUTLET PIPE EXTENDS
INTO THE CYCLONE
TO PREVENT INLET AIR
FROM SHORT-CIRCUITING
DIRECTLY TO THE OUTLET
SLEEVE TO
PREVENT
PARTICULATE
FROM BLOWING OUT
THE SPINNING AIR FORCES Tl
PARTICULATE TO THE WALL-
OF THE CYCLONE
A SLOW-SPEED MOTOR TURNS
THE "STAR" VALVE THAT SEALS
THE COLLECTION HOPPER FROM
THE CYCLONE
PARTICULATE
COLLECTION
HOPPER
OR DRUM
Exhibit 5-17. Flow Diagram of a Dry Cyclone Collector
A92-214.5
5-41
-------
Electrostatic Precipitators. In the portland cement industry in North America, ESP are rarely
used to control particulates in the exhaust gas streams from clinker coolers. If exhaust gas
streams contain a large amount of moisture, care must be taken to maintain the gas temperature
well above the dew point to prevent condensation in the precipitator.
Advantages of ESP include the ability to handle large volumes of gas with very little pressure
drop, the relatively lower power requirements (as compared to fabric filters) due to the low
pressure drop, and the ability to handle high temperature gases and corrosives. However, ESP
have disadvantages: sulfur oxides in the exhaust gas corrode the metal parts causing reduced
efficiency, sulfur acids can diffuse into concrete casings and eventually destroy them, and alkalies
can coat high-voltage components and cause short circuits.
Gravel Bed Filter. Gravel-bed filters have been used successfully in the portland cement industry
for many years, although their application is limited. A gravel-bed filter control system consists
of 6 to 20 modules, each of which may contain from 1 to 3 gravel beds.
The gravel-bed filter applies the principles of centrifugal force and impingement to the removal
of particulates from an exhaust gas stream. As shown in Exhibit 5-18, as the particulate-laden
gas enters the filter, it is subjected to centrifugal forces which move the larger particulates
outward to the walls, from which they eventually fall to the bottom for removal via an air lock.
The partially cleaned gas first flows up through a riser to one or more filter chambers located
above and then passes down through gravel beds supported on wire mesh screens. The
paniculate in the gas impinges upon the gravel surface and is captured by deposition. The
cleaned gas stream from the beds is exhausted through a clean-gas chamber into an exhaust duct
that conveys it to a stack for discharging to the atmosphere. Modules must be removed from
service at regular intervals and subjected to cleaning by backflushing them with air.
The one process point in a portland cement plant where the gravel-bed filter has been widely
used is the clinker cooler. The cooler is frequently subjected to process upsets that cause high-
temperature-gas excursions, a condition that is easily accommodated by the gravel-bed filter. The
filter does an excellent job of removing the abrasive paniculate from the cooling exhaust gases.
A92-214.5 5-42
-------
BACKFLUSH DUCT
BACKFLUSH
CONTROL VALVE
EXHAUST
PORT
DIRTY
GAS
DUCT
VALVE
CYLINDER
STIRRING RAKE
MOTOR/REDUCERS
GAS CHAMBER
STIRRING RAKE
GRAVEL BED
CLEAN GAS
CHAMBER
SCREEN
SUPPORT
FOR BED
RISER TUBE
PRIMARY
COLLECTOR
(CYCLONE)
DOUBLE TIPPING GATE
(DUST DISCHARGE)
Exhibit 5-18. Gas Flow Diagram for a Gravel-bed Filter
(Courtesy of Rexnord Corporation)
A92-214.5
5-43
-------
Stack tests show that the gravel-bed filter has paniculate removal efficiencies averaging 99.85
percent. Because of the inherent ability of the gravel-bed to withstand temperatures in excess
of 1,000°F (538°C), inlet gas streams require no cooling. The gravel-bed is also resistant to
attrition and therefore can be used to filter abrasive paniculate materials.
5.42.13 Other Facilities
Affected facilities other than the kiln and clinker cooler include feeding, transfer, and discharge
operations; raw material, clinker, and finished product storage; loading and unloading of raw and
final products; and disposal of material collected by the control devices. Because of the volume
of material processed, these sources have the potential of contributing significant amounts of
emissions. Containment and dust suppression practices prevent these sources from generating
excessive emissions, however.
Feeding, transfer, and discharge operations are all sources of emissions problems, and spilled
product and wind are responsible for entrainment of the dust. Most of the entrained dust results
from spillage and agitation of material at the transfer points. Such emissions are contained by
either enclosing (totally or partially) or hooding these transfer points with exhaust gases directed
to fabric filters. The air-to-cloth ratios of fabric filters controlling these facilities range from 4:1
to 8:1. The bags are less heat resistant than those used to control kilns or clinker coolers.
Loading and unloading operations of both raw materials and final product create an emission
problem because of the mechanical agitation of the material as it strikes the sides and bottom of
the receiving vessel and because of displaced air during loading and unloading. Various
containment practices are used in combination. Such practices include enclosing the operation,
choke-feeding or using a telescoping chute to limit the free-fall distance of the material, and
using movable hoods ducted back into the unloading vessel.
Dust emissions from storage piles occur when the material is dumped onto the pile and when
wind blows across the pile. Containment methods are enclosure of the storage area or the
application of dust suppressants to the material. Wet suppression methods include the application
A92.2I4 5 5-44
-------
of water, chemicals, and foam. The point of application is most commonly at the conveyor feed
and discharge points, but some applications are at conveyor transfer points and equipment
intakes. A wet suppression system is shown in Exhibit 5-19. The type of material stored
determines which containment method should be used (e.g., the application of water is not a
suitable containment method for stored finished cement). The use of telescoping chutes is also
an effective containment practice during the dumping of material onto storage piles.
Finally, the disposal of material collected by the control devices also can be a source of
emissions. The disposal process consists of loading, unloading, and transporting of the waste.
Containment methods for loading include enclosing the loading area and reducing the free-fall
distance into the disposal vehicle. Containment in transport can be accomplished by the use of
an enclosed vehicle. Containment during the unloading of the waste at the disposal site can be
accomplished by reducing the free-fall distance and covering or chemically stabilizing the
material at the site to prevent wind erosion. Exhibit 5-19 summarizes the various containment
practices.
5.4.2.2 Available Gaseous Emissions Control Technology
5.42.2.1 Carbon Monoxide
Currently, there are no methods available for reducing CO or CO2 except process control for CO
and reduced production for CO2.
5.4222 Sulfur Oxides
Sulfur dioxide may be generated both from the sulfur compounds in the raw materials and from
sulfur in the fuel. The alkaline nature of the cement, however, provides for direct absorption of
SO2 into the product. Using a baghouse that allows the SO2 to come into contact with the
cement dust provides inherent reduction of 75 percent or more of the raw material and fuel sulfur
A92-2145 5-45
-------
Exhibit 5-19. Dust Suppression Practices
Telescoping or Chemical or
Operation Enclosing Hooding choke-feeding water spray
Transfer and conveying X X
Loading and unloading XXX
Paved and unpaved roadways X
Storage piles X XX
Disposal X XX
A92-214.5 5-46
-------
content The percent reduction will vary with the alkali and sulfur content of the raw material
and fuel.
5.4223 Nitrogen Oxides
Currently, there are data to support only two types of NOX reduction in the cement industry in
the United States. First, for conventional wet and dry process kilns, NOX emissions are reduced
by fuel conversion, with coal producing the least NOX. For new construction, the data are not
yet clear. Some preheater/precalciner systems have low emissions and others have high
emissions.
There are at least ten different preheater/precalciner systems used in the cement industry in the
United States and each appears to have unique emission properties. However, it is evident that
for a single system, burning oil in the calciner produces less NOX than coal. The NOX emissions
from preheater/precalciner appear to relate to design'. Some have very low emissions and others
have emissions in a mid range of some conventional or wet processes.
A92-214.5 5-47
-------
BIBLIOGRAPHY
Non-Metallic Mineral Processing Plants - Background Information for Proposed Standards.
EPA-450/3-83-001a, U.S. Environmental Protection Agency, Office of Air Quality Planning and
Standards, Research Triangle Park, NC, April 1983.
Air Pollution Control Techniques for Non-Metallic Mineral Industry. EPA-450/3-82-014, U.S.
Environmental Protection Agency, Office of Air Quality Planning and Standards, Research
Triangle Park, NC, August 1982.
Emissions from the Crushed Granite Industry: State of the Art. EPA-600/2-78-021, U.S.
Environmental Protection Agency, Industrial Environmental Research Laboratory, Cincinnati, OH,
February 1978.
Source Assessment: Crushed Stone. EPA-600/2-78-004L, U.S. Environmental Protection
Agency, Industrial Environmental Research Laboratory, Cincinnati, OH, May 1978.
Research Triangle Institute. Characterization of Particulate Emissions from Stone-Processing
Industry, Research Triangle Park, NC, EPA Contract No. 68-02-0607, May 1975.
Cement and Concrete Reference Book. Portland Cement Association, Chicago, Illinois, 1964.
Kreichelt, T., D. Kemnitz, and S. Cuffe. Atmospheric Emissions From the Manufacture of
Portland Cement. Publication No. AP-17, U.S. Department of Health, Education, and Welfare,
Cincinnati, Ohio, 1967.
Industrial Process Profiles for Environmental Use: Chapter 21 - The Cement Industry. EPA-
600/2-77-023u, U.S. Environmental Protection Agency, Research Triangle Park, NC, 1977.
Multimedia Assessment and Environmental Research Needs of the Cement Industry. EPA-600/2-
79-111, U.S. Environmental Protection Agency, Research Triangle Park, NC, May 1979.
Background Information for Proposed New Source Performance Standards: Portland Cement
Plants. APTD-0711, U.S. Environmental Protection Agency, Office of Air Quality Planning and
Standards, Research Triangle Park, NC, August 1971.
Portland Cement Plants - Background Information for Proposed Revisions to Standards. EPA-
450/3-85-003a, U.S. Environmental Protection Agency, Office of Air Quality Planning and
Standards, Research Triangle Park, NC, May 1985.
Portland Cement Plant Inspection Guide. EPA-340/1-82-007, U.S. Environmental Protection
Agency, Office of Air Quality Planning and Standards, Research Triangle Park, NC, June 1982.
A92-214.5 5-48
-------
A Review of Standards of Performance for New Stationary Sources - Portland Cement Industry.
EPA-450/2-79-012, U.S. Environmental Protection Agency, Office of Air Quality Planning and
Standards, Research Triangle Park, NC, March 1979.
F. Bergman. Review of Proposed Revision to AP-42 Section 8.6, Portland Cement
Manufacturing. EPA Contract No. 68-02-4395, Midwest Research Institute, Kansas City, MO,
September 30, 1990.
J.S. Kinsey. Lime and Cement Industry - Source Category Report, Volume II. EPA Contract No.
68-02-3891, Midwest Research Institute, Kansas City, MO, August 14, 1986.
Control Techniques for Particulate Emissions from Stationary Sources: Volume 1. EPA-450/3-
81-005a, U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards,
Research Triangle Park, NC, March 1981.
Compilation of Air Pollutant Emission Factors, Volume I, Fourth Edition and Supplements. U.S.
Environmental Protection Agency, Office of Air Quality Planning and Standards, Research
Triangle Park, NC, September 1985 through September 1991.
T. E. Kreichelt, et al., Atmospheric Emissions from the Manufacture of Portland Cement, AP-17,
U.S. Environmental Protection Agency, Cincinnati, Ohio, 1967.
A92-214.5 5-49
-------
6
-------
CHAPTER 6
PLASTIC INJECTION MOLDING
-------
TABLE OF CONTENTS
Chapter Page
6 PLASTIC INJECTION MOLDING 6-1
6.1 INDUSTRY DESCRIPTION 6-1
6.2 PROCESS DESCRIPTION 6-11
6.2.1 Heating/Injection Systems 6-11
6.2.2 The Injection Molding Process 6-18
6.3 IDENTIFICATION AND CHARACTERIZATION OF EMISSION POINTS
AND WASTE STREAMS 6-29
6.4 POLLUTION PREVENTION, RECYCLING, AND POLLUTION
CONTROL SYSTEMS 6-34
6.4.1 Pollution Prevention 6-34
6.4.2 Recycling Operations 6-37
6.4.3 Pollution Control Systems 6-39
6.5 REFERENCES 6-41
EXHIBITS
Number Page
6-1 Injection Molding Input Materials and Products 6-3
6-2 Typical Injection-Molding Machine, with its major elements identified 6-12
6-3 Typical Injection Rates 6-13
6-4a Conventional Injection Molding Machine 6-14
6-4b Piston Type Preplastifying Machine 6-16
6-4c Screw Type Preplastifying Machine 6-17
6-4d Reciprocating Screw Injection Machine 6-19
6-5 Cyclical Injection Molding Process for Thermosets 6-20
6-6 Cyclical Injection Molding Process for Thermoplastics 6-21
6-7 Manpower Requirements for Operating an Injection Molding Machine 6-22
6-8 Typical Processing Temperatures for Commonly Used Thermoplastics and
Thermosets 6-24
6-9 Injection-Molding Cycle-Melt Ready for Injection 6-25
6-10 Injection-Molding Cycle—Melt Being Injected 6-26
6-11 Injection-Molding Cycle-Mold Closed for Part Cooling; Melt Being Plasticized .... 6-27
6-12 Injection-Molding Cycle—Part Ejection - 6-28
6-13 Sources and Types of Emissions From Injection Molding Operations 6-30
6-14 Possible Injection Molding Decomposition Products 6-32
6-15 Styrene Emitted From Thermooxidative Degradation 6-33
6-16 Model Injection Molding Plant Machine Layout 6-35
6-17 Anderson Tool and Plastics Corp - Work Order 6-42
6-i
-------
CHAPTER 6.0
PLASTIC INJECTION MOLDING
6.1 INDUSTRY DESCRIPTION
The plastics industry is one of the world's largest and fastest growing manufacturing enterprises
whose products are used worldwide. The plastics industry processes raw materials into finished
goods by several methods, the most common being injection molding and extrusion. These two
methods comprise more than 64 percent of the total plastics production. This discussion will
concentrate on injection molding, which accounts for 23 percent of plastics production.
A large number of items used in daily life are produced through injection molding. Typical
product categories include housewares, toys, automotive parts, building supplies and household
furnishings. Plastic molding facilities range from small plants with a single process and a few
employees to large plants with several hundred employees.
Injection molding is used to produce intricate plastic parts with excellent dimensional accuracy.
Injection molding has the advantage that molded parts can be manufactured with little or no need
for finishing operations such as polishing or other surface treatments. The products of injection
molding adopt the surface characteristics of the mold in which they were formed (i.e. smooth or
textured). Injection molding involves the plasticizing of pelletized or granular plastic with heat
and the subsequent injection of the melt into a mold cavity. Most mold cavities are comprised
of multiple cavities, allowing for very high production rates. The high production rates make
injection molding a very economical method for producing plastic products.
Plastic is a generic term for a group of synthetic or natural organic materials composed of high
molecular weight, long chain molecules. The molecular composition, in combination with the
pattern and amount of branching in the molecule and the degree of crosslinking between chains,
determines the characteristics of the material Plastic materials include many types of resins,
resinoids, organic polymers, cellulose derivatives, casein derivatives, and proteins. Except for
A92.214.6 6-1
-------
some specialty applications, the majority of plastic materials used in consumer and industrial
products is made of synthetically produced organic polymers and copolymers.
Plastic materials are generally classified into two basic groups: thermoplastics and thermosets.
Thermoplastics become soft when exposed to specific amounts of heat and harden when cooled.
The heating and cooling process can be repeated several times. Thermoplastic materials can be
processed by a large number of forming processes, the most common being injection molding
and extrusion. Some common thermoplastic materials include: acrylonitrile-butadiene-styrene
(ABS), high and low density polyethylenes (HDPE and LDPE), polypropylene, polystyrene, and
polyvinyl chloride (PVQ.
Therrnosetting plastics are set into permanent forms by applying heat and pressure during
molding or forming. Unlike thermoplastics, thermoset products cannot be softened or reformed
after they are set into a shape. Thermoset plastic products are usually formed by processes such
as compression molding, transfer molding and casting. However, some thermosets are also used
by injection molders. Thermoset plastic materials include alkyd resins, nylons, epoxy resins,
phenolic resins, and silicon.
Exhibit 6-1 lists a variety of the thermoplastic and thermoset resins used in injection molding.
Formulation criteria and typical end uses are also included.
A92-214.6 6-2
-------
EXHIBIT 6-1. INJECTION MOLDING INPUT MATERIALS AND PRODUCTS
Polymer Formulation Products
Acrylic Resins
Acrylonitrile-
Butadiene-Styrene
(ABS)
Usually requires desiccant
drying
Antistatics
Colorants
Flame Retardants
Lubricants
UV Stabilizers
Resin must be dried 2-4 hours
at 82-93°C (180-200°F) in a
dehumidifying air hopper drier
Antioxidants
Antistatics
Blowing Agents
Colorants
Flame Retardants
Lubricants
Reinforcers
Stabilizers
UV Stabilizers
Thin wall, complex parts for
household, optical, and
technical applications
Automotive lenses
Decorative escutcheons
Nameplates
Lighting louvers
Lighting lenses
Video disk products
Medallions
Typewriter buttons and bars
Pump parts
Piano keys
Appliance housing
Bobbins and spools
Bores, containers, carry cases, tackle
boxes
Flashlight housings
Football helmets
Furniture parts
Household items
Machine housings
Pipe fittings
Radio cabinets
Suitcases
Automotive components for
instrument panels, consoles, ducts,
door post covers, door locks, knobs,
radiator grills, and headlight
housings
Toys
Sporting goods
Hobby kits
Canoe parts
(continued)
A92-214.6
6-3
-------
EXHIBIT 6-1. INJECTION MOLDING INPUT MATERIALS AND PRODUCTS
(Continuted)
Polymer
Formulation
Products
Fluoroplastics
Ethylene-
Tetrafluoroethylene
Copolymer
ETFE (Teflon®)
Fluorinated Ethyl-
ene Propylene
Copolymer
FEP (Tefzel@)
Polyvinylidene
Fluoride
PVDF (Kynar@)
Palletized Resins
Fillers
Palletized Resins
Reinforcers
Pelletized Resins
Activators
Blowing Agents
Colorants
Crosslinking Agents
Curing Agents
Fillers
Plasticizers
Processing Aids
Reinforcers
Pump components
Process equipment parts
Tower packings
Process equipment parts
Electrical insulators
Valve fittings
Pumps for corrosove fluids
Bearing seals and rings
Valves
Pumps
Impellers
Seals
Gaskets
Electrical Connectors
(continued)
6-4
-------
EXHIBIT 6-1. INJECTION MOLDING INPUT MATERIALS AND PRODUCTS
(continued)
Polymer
Formulation
Products
Nylon 6 and Nylon
6/6
Polymer must be dried 4-10
hours at 110°C (230°F)
Antioxidants
Antistatics
Blowing Agents
Colorants
Fillers
Lubricants
Plasticizers
Reinforcers
UV Stabilizers
Medical items
Precision moldings
Shoe heels
Military items
Cases
Cookware
Valve caps
Automotive parts for fuel vapor
recovery, canisters, emissions
control components, fan blades,
distributor parts, cable ties, dome
light covers, and speedometer gears
Electrical components for connectors,
housings, battery boxes, small motor
casings, relay covers, wire ties,
switch housings, fuse holders,
terminal boxes, grommets, and clips
Machine parts for small gasoline
engine parts, starter gears, air
silencers, carburetors, cams, roller
bearings, small gears, sprockets,
pulleys, bushings, bearings, and
impellers
Fasteners
Drapery hardware
Pluming hardware
Furniture
Fixtures
Door hardware
Tool parts
Shower heads
Irrigation devices
Suspension mechanism for file
cabinets
Valves for aerosol cans
Marine deck fittings
Golf club parts
Gun stocks
Cigarette lighter
Spatulas bodies
(continued)
A92-214.6
6-5
-------
EXHIBIT 6-1. INJECTION MOLDING INPUT MATERIALS AND PRODUCTS
(continued)
Polymer
Formulation
Products
Phenolics
Polyacetal
Polycarbonate
Polyester
Polybutylene
Terephthalate
(PBT)
Polyethylene
Terephthalate
(PET)
Colorants
Fillers
Lubricants
Reinforcement
Antioxidants
Colorants
Reinforcers
UV Stabilizers
Resin must be dried 2-4 hours
at 127°C (260°F) in a
dehumidifying hopper drier
Antioxidants
Blowing Agents
Colorants
Flame Retardants
Lubricants
Mold Release Agents
Reinforcers
UV Stabilizers
Resin must be dried 2-4 hours
at 121°C (250°F)
Reinforcers
Crystalline resin must be dried Containers
2-4 hours at 150-180°C (302-
350°F)
Antioxidants
Antistatics
Colorants
Flame Retardants
Reinforcers
Bearings
Conveyors
Gears
Office supplies
Ballcocks
Pushbuttons for telephones
Pens
Tape cartridges
Toys
Zippers
Aerosol valves
Turn signals for autos
Specialty electrical parts
Molds
Automotive parts
Battery cases
Electrical parts
Household items
Petri dishes
Printed circuit boards
Safety shields
Templates and slide rules
Lenses
Electrical parts
Automotive parts
Housewares
(continued)
A92-214.6
6-6
-------
EXHIBIT 6-1. INJECTION MOLDING INPUT MATERIALS AND PRODUCTS
(continued)
Polymer
Formulation
Products
Polyethylene
Low Density
Polyethylene
(LDPE)
High Density
Polyethylene
(HOPE)
Ethylene Vinyl
Acetate
(EVA)
Polyphenylene Oxide
Antiblocking Agent
Antioxidants
Antistatic Agents
Blowing Agents
Colorants
Fillers
Flame Retardants
Impact Modifiers
Remforcers
UV Stabilizers
Antiblocking Agents
Antioxidants
Antistatic Agents
Blowing Agents
Colorants
Flame Retardants
Impact Modifiers
Remforcers
Stabilizers
UV Stabilizers
Antioxidants
Antistatics
Colorants
Corrosion Inhibitors
Crosslinking Agents
Fillers
Flame Retardants
Mold Release Agents
Remforcers
Thermal Conductors
Bobbins
Containers
Packaging
Lids for coffee cans, margarine tubs,
shortening, nuts, and pipe tobacco
Toys
Novelties
Housewares
Ice cream containers
Pails
Paint cans
Seating components
Tote boxes
Toys
Catsup and mustard containers
Ice cube trays
Canisters
Butter dishes
Hard hats
Furniture
Plates and sheets
Blocks
Rods and tubes
TV parts
Filter stacks
Filter discs
Valve seats
Surgical instruments
Food trays
Small appliance housings
Dashboard electrical connectors
Knobs and handles
Cases
Pumps
Shower heads
(continued)
A92-214.6
6-7
-------
EXHIBIT 6-1. INJECTION MOLDING INPUT MATERIALS AND PRODUCTS
(continued)
Polymer
Formulation
Products
Polyphenylene
Polyph
Sulfide
Polypropylene
Colorants
Mineral Fillers
Reinforcers
Antiblocking Agents
Antioxidants
Antistatic Agents
Blowing Agents
Colorants
Fillers
Flame Retardants
Lubricants
Plasticizers
Reinforcers
Stabilizers
UV Stabilizers
Bearings and cams
Electronic parts
Hair dryer parts
Small cooking appliances
Range components
Valves
Battery cases
Closures, lids, caps, and containers
Luggage and carry cases
Packaging
Tables
Toys and novelties
Washing machine agitators
Clothes drier filter housings
Dishwasher pump components,
silverware baskets, detergent
dispensers, inlets and drains
Refrigerator ice maker components
Room air conditioner air deflectors,
condensate pans, filter frames and
impellers
Television set parts
Butter dishes
Light shield
Ice cube trays
Tupperware®
Seats
Furniture frames
Sports equipment
Syringes
Labware
Medical tubing and connectors
Automotive door panels, fender
aprons, glove comportments, interior
trim
(continued)
A92-214.6
6-8
-------
EXHIBIT 6-1. INJECTION MOLDING INPUT MATERIALS AND PRODUCTS
(continued)
Polymer
Formulation
Products
Polystyrene
Polyvinyl Chloride
(PVC)
Antioxidants
Antistatics
Blowing Agents
Colorants
Fillers
Flame Retardants
Lubricants
UV Stabilizers
Antiblocking Agents
Antioxidants
Antistatic Agents
Blowing Agents
Colorants
Fillers
Flame Retardants
Fungicides
Impact Modifiers
Lubricants
Plasticizers
Heat Stabilizers
UV Stabilizers
Appliance parts
Cups, lids, dishes, and cutlery
Containers, boxes, vials, jars, and
tubs
Housewares
Refrigerator trays and covers
Toys and hobby kits
Produce trays
Cocktail glasses
Sporting goods
Soap dishes
Handles for kitchen utensils
Salt and pepper shakers
Coffee servers
Watering cans
Room dividers
Picture frames
Letter trays
Calendar bases
Toilet seats
Architectural trim moldings
Calculators
Tape reels, reel covers, and cassettes
furniture
Combs
Boots
Building and construction supplies
Bumper parts
Business machines and appliance
parts
Footwear, sandals, heels, and soles
Hospital and health care supplies
Pipe fittings
Plugs and connectors
Refrigerator gaskets
Toys
Filler strips
Rear view mirror housings
Window winder knobs
Bicycle grips
(continued)
A92-214.6
6-9
-------
EXHIBIT 6-1. INJECTION MOLDING INPUT MATERIALS AND PRODUCTS
(continued)
Polymer Formulation Products
Styrene-Acrylonitrile Resin must be dried for a Appliance parts
(SAN) minimum of 2 hours at 71- Automotive parts
82°C (160-180°F) Cosmetic containers
Tumblers
Fillers Automotive instrument lenses
Lubricants Blender jars and covers
Reinforcers Dishes and trays in appliances
Medical instruments and utensils
Tape reels
Picnic ware
Vinylidene Chloride Antioxidants Gasoline Filters
Heat Stabilizers ' Valves
UV Stabilizers Pipe fittings
Containers
Chemical process equipment parts
A9Z-214.6 6-10
-------
6.2 PROCESS DESCRIPTION
Injection molding is a cyclical process in which granular plastic feed is melted and injected into
a mold. After cooling, the product is ejected from the mold and finished. Injection molding
units consist of three principal parts, the heating/injection system, the clamp unit, and the
removable mold. There are several types of heating/injection units which are described in
Section 6.2.1. The clamp unit has two platens, one movable and one fixed, which support the
mold as well as absorbing some of the pressure applied to the injected plastic during the injection
stage of the molding cycle. The movable platen allows the two halves of the mold to be
separated and the product removed. Molds typically have two halves, although some special-
purpose molds have more parts. Exhibit 6-2 illustrates a typical injection molding machine. A
detailed description of the injection molding process is provided in Section 6.2.2.
6.2.1 Heating/Injection Systems
An injection machine can mold parts weighing from a few ounces to many pounds. The majority
of machines mold parts weighing from an ounce to a pound.2 The rate at which the plastics are
injected into the mold can vary. Generally, faster rates permit reducing cycle times but require
molding thinner parts. For example combs may be produced in a mold containing 12 comb
cavities. The mold may receive two shots per minute, resulting in a total production rate of 24
combs per minute. Typical injection rate specifications are presented in Exhibit 6-3.2
The four basic types of heating/injection systems used for commercial injection molding include:
Conventional injection molding machines
• Piston-type preplasticizing machines
• Screw-type preplasticizing machines
• Reciprocating-screw injection machines
A92-214.6 6-11
-------
ON
H
A. Oil reservoir D. Tie rod G. Hydraulic drive
B. Movable/)la(en E. Injection cylinder H, Control cabinet
C. Fixed platen F. Hopper I. Base with pumps
Exhibit 6-2. A typical injection-molding machine, with its major elements identified.1
(reprinted with permission from Weir, Clifford, Introduction to Injection
Molding, Society of Plastics Engineers, Inc., Greenwich, Connecticut, 1975.)
-------
EXHIBIT 6-3. TYPICAL INJECTION RATES
Machine Size (ton) Injection Rate (inVsec) Shot Capacity (ounces)
150 8-16 6-12
500 25 - 45 48 - 76
1000 70-90 ' 160 - 180
Two of the injection molding machines, the piston-type and the screw-type preplasticizers, have
an auxiliary heating cylinder, known as the preplasticizer. This cylinder is used to melt the
plastic feedstock and then transfer the melt to the injecting cylinder from which it is injected into
the mold.
Conventional Injection Molding. The plastic granules or pellets are poured into the machine
hopper and feed into the chamber of the heating cylinder, which is heated by conduction and
convection from the electrically heated walls. A plunger compresses the material, forcing it
through progressively hotter zones of the heating cylinder. Because there is little mixing within
the cylinder, a torpedo-shaped spreader is usually located in the heating cylinder to force the
polymer to flow against the heated metal surface of the cylinder. The presence of a spreader
makes the molten resin more uniform. The material flows from the heating cylinder through a
nozzle into the mold. This type of molding machine will produce mottled-colored molded parts
since colorants are not thoroughly mixed with the plastic material in the heated cylinder unless
pre-colored polymers are used as feed. Exhibit 6-4a illustrates a conventional injection molding
machine.
Piston-Type Preplasticizing. In a piston-type preplasticizing machine the plasticizing is
performed in a separate unit An auxiliary chamber is used to heat the plastic material by
conduction. A plunger pushes the melted plastic material into a second stage injection unit. This
injection unit serves as a combination holding, measuring, and injection chamber. During the
A92-214.6 6-13
-------
NOZZLE
MOLD
^-TORPEDO \ ~7^_FE£D HOPPER
~ A — — — W%£ [-PISTON
/V\A'L1>'X x \ fefe^- t I.
N \\\ \ \\ \ \ \\ \ \ \ \|
CONVENTIONAL IN'JECTIDN
MOLDING MACHINE
Exhibit 6-4a. Conventional injection molding machine.
A92-214.6
6-14
-------
injection cycle the shooting plunger forces the plastic melt from the injection chamber through
the nozzle and into the mold cavity. This machine produces pieces faster than a conventional
machine because the holding chamber can be filled to the proper volume (called a "shot") while
a part is cooling in the mold. This process is used to produce large molded parts (e.g., flower
parts, garbage pails, and automobile fenders and body parts), but is not in wide commercial use.1
Exhibit 6-4b illustrates a piston-type preplasticizing injection molding machine.
Screw-Type Preplasticizing. Screw-type preplasticizing systems use an extruder to plasticize the
plastic feedstock. A rotating screw feeds the pellets forward to the heated interior surface of the
extruder barrel (auxiliary heating chamber). The molten plastic is then driven from the extruder
into the injecting chamber and is forced into the mold by an injection plunger. The extruder
screw rotates backwards to begin the next cycle, while the screw in the shooting cylinder injects
the plastic melt into the mold. The use of a screw in the heating cylinder allows the following
advantages over other types of injection equipment:
• Better mixing and shear action of the plastic melt
• Better color blending
•
• Less stress in the molded part
Exhibit 6-4c illustrates a screw-type preplasticizing injection molding machine.
Reciprocating-Screw Injecting. This type of injection molding uses a horizontal, rotating screw
in place of the piston used in the heating chamber of conventional injection molding machines.
The rotating screw moves the plastic material forward under pressure to the front of the injection
cylinder, while the screw itself is pushed backwards by the accumulating melt. The shearing
action of the screw on the resin is the principal source of the melt healing. Back pressure inside
the heating cylinder is adjustable, thereby varying the amount of internal heat transmitted to the
melt Increased back pressure raises the melt temperature without requiring an increase in
heating cylinder temperatures by external electrical heating. As the molten plastic material
moves forward, the screw backs up until it reaches a limit switch which indicates that the
A9Z-214.6 6-15
-------
STUFFING PISTON
MOLD
PISTON TYPE
PREPLASTIFYING MACHINE
Exhibit 6-4b. Piston type preplastifying machine.
A92-214.6
6-16
-------
STUFFING SCREW
MOLD
SCREW TYPE
PREPLASTIFYING MACHIN:
Exhibit 6-4c. Screw type preplastifying machine.
A92-214.6
6-17
-------
cylinder contains enough melt. Once the limit has been reached, the screw stops turning and moves
forward, injecting the plastic material through the injection nozzle into the mold cavity. The
advantages of the reciprocating-screw injection system include:
• More efficient plasticizing of heat sensitive materials
• Rapid color blending
• Lower heat requirements
The reciprocating-screw injection machine is the most common machine for modern plastics
processing due to its fast cycles, low melting temperature requirements, and efficient mixing.
Exhibit 6-4d illustrates the typical reciprocating screw injection molding machine.
622 The Injection Molding Process
The basic operations of the cyclical injection molding process encompass the following step:2
• Drying
• Blending
• Plasticizing the feed
• Injecting the melt into the mold
• Molding - solidification of the melt
• Ejecting the finished part
• Finishing processes
These operations are the primary determinants of the productivity of the process and are discussed
in greater detail in the remainder of this section. Manufacturing speed will depend on the rate at
which the plastic can be heated to the molding temperature, the time required to inject the melted
plastic, and the cooling period before the product can be ejected from the mold. Exhibits 6-5 and
6-6 show the cyclical injection molding processes for thermosets and thermoplastics. The time
required for an injection molding cycle varies according to the design of the product and the
polymer formulation being utilized. Typical injection molding cycles
6-18
-------
SCREW DRIVE
MOTOR
MOLD
RECIPROCATING SCREW
INJECTION MACHINE
Exhibit 6-4d. Reciprocating screw injection machine.
A92-214.6
6-19
-------
HOPPER
<
'|
HEATING/
INJECTION
SYSTEM
;
Polymers
He
NOZZLE
MOLD
I
TRIMMING
1
Injection
Port
1 t
. Heat Scrap
Additives
Exhibit 6-5. Cyclical injection molding process for thermosets.5
-------
I
10
Additives
Thermoplastic
Scrap
Injection
Molded
Part
Polymers
Exhibit 6-6. Cyclical injection molding process for thermoplastics.5
-------
range from 10 to 35 seconds; however they can be as short as 1 second for very small parts (e.g.,
gumball containers) and as long as 120 seconds for larger, more intricate parts (e.g., garbage
cans).
Injection molding operations are relatively automated and require minimal manpower. Except for
scrap grinding and recycle of thermoplastics, employee manpower requirements are similar for
both thermoset and thermoplastic molding processes. Exhibit 6-7 lists estimated manpower
requirements to operate a typical injection molding machine.
EXHIBIT 6-7. MANPOWER REQUIREMENTS FOR OPERATING AN
INJECTION MOLDING MACHINE
Unit Workers/Unit/8-hr Shift
Mixing/Blending 0.5
Molding 0.5
Trimming 0.25
Scrap Grinding (Thermoplastics Only) 0.25
Plasticizing the feed. The feed hopper of the injection machine can be loaded by mechanical
machinery or manually by the machine operator. The polymer feed is usually granular or in the
form of small pellets. In addition to the raw polymer, additives are also included in the feed to
create desired characteristics in the polymer melt and the final molded product (such as color or
ultra-violet resistance). Plasticizing entails raising the temperature of the pelletized or granular
plastic feed to the point where it will flow under pressure. This is accomplished by
simultaneously heating and pulverizing the granular solid until it forms a melt at an elevated and
uniform temperature and pressure with uniform viscosity.2 This process step takes place in the
heating (plasticizing) cylinder, which is a simple heat exchanger. Most cylinders have heavy
steel walls with highly polished and hardened inner surfaces, and are typically surrounded by
variable electric heating elements. The size of the heating cylinder on any given machine is
usually determined by the volume of the parts to be molded. The heating cylinder of the
A92-214.6 6-22
-------
injection-molding machine is the primary element, since it is responsible for conditioning the
melt before its injection. Exhibit 6-8 presents typical processing temperatures for thermoplastics
and thermosets often used in injection molding processes.
Injecting. During the injection step, the molten plastic from the injection cylinder is transferred
through various flow paths (i.e., runners) into the cavity of the mold, where it takes the shape
specified by the mold cavity. The melt in the cylinder is forced out through the injection nozzle
by a reciprocating screw, an injection plunger, or a combination of both, depending on the type
of machine. The injection of the molten resin occurs at pressures as high as 20,000 psi. Molten
resin from the injection nozzle enters the mold through a system of runners. The runner system
for a single-cavity mold is simply a straight sprue (a hole leading to the mold cavity), but for
multicavity molds, the system may be complex in order to distribute the material to each cavity.
Exhibits 6-9 through 6-12 show the typical cycle of the injection process.
Molding. Molds, made of high-quality, non-porous steel, are vented to allow air, moisture, and
other gases to be forced out by the incoming melt, thereby avoiding bubbles and gaps in the
molded product1 Molding allows the plastic to solidify in the mold, which is kept closed by the
clamped platens of the machine. The molds are held together with great pressure to ensure that
the mold halves are not separated by the force exerted by the pressurized injection of the melt
The molds remain closed until the molded product has cooled sufficiently. The cooling period
is the most time consuming segment of the injection molding cycle. Thermoset materials require
that heat be applied to the mold during the molding period to complete polymerization.
Sometimes thermoplastic materials are cooled within the mold by the circulation of non-contact
cooling water.
Mold Ejecting. Mold ejection takes place after the clamping unit is opened. The ejection of the
molded part is usually accomplished by knockout pins or springs in the mold activated
mechanically or hydraulically by the machine. Some operations use jets of air to eject the
molded part Once the product is ejected, the mold finishing cycle can begin, commencing with
the plasticizing step.2
A92-214.6 6-23
-------
EXHIBIT 6-8. TYPICAL PROCESSING TEMPERATURES FOR
COMMONLY USED THERMOPLASTICS AND
THERMOSETS
Polymer Processing Temperature (°C)
Thermoplastics
Acrylic Resins 180 - 250
Acrylonitrile-Butadiene-Styrene (ABS) 180 - 250
Fluoroplastics
Ethylene-Tetrafluoroethylene Copolymer (ETFE) 260 - 330
Fluorinated Ethylene Propylene Copolymer (FEP) 200 - 260
Polyvinylidene Huoride (PVDF) 260 - 330
Nylon 6 260 - 290
Nylon 6/6 270 - 300
Polyacetal 185 - 225
Polycarbonate 280 -310
Polyester
Polybutylene Terephthalate (PBT) 232 - 260
Polyethylene Terephthalate (PET) 27 - 300
Polyethylene
Low Density Polyethylene (LDPE) 160 - 240
High Density Polyethylene (HOPE) 200 - 300
Ethylene Vinyl Acetate (EVA) 200 - 280
Polyphenylene Oxide 280 - 340
Polyphenylene Sulfide 315 - 330
Polypropylene 200 - 275
Polystyrene 180 - 260
Polyvinyl Chloride 160 - 210
' Styrene-Acrylonitrile (SAN) 180 - 240
Thermosets
Diallyl Phthalate 170 - 180
Melamine Formaldehyde 160 - 170
Unsaturated Polyesters 232 - 260
Urea Formaldehyde 150 - 160
A92-214.6 6-24
-------
Exhibit 6-9. Injection-molding cycle-melt ready for injection.1
•
-------
I
B
0V
A- Hyd r*u.l!c clump
cylinder
B,
C
ft
E. Injection notzie
F. Heating c
reciprocating tcrtw
(3. Hopper
,-4
(. Scrmy drive
J. Screw forw
L. Clamp otosing
N.
ibit 6-10. Injcction-molding cycle-melt being injected.1
Exhibit
-------
a\
i—L
A Hj4.r4.ulic
B Movable platen
C. Mold
D. fixed platen
E. Injee&ion nozzle
F. Heating cylinder And
reciprocating sen***
G. Ho/»p*r
H. Screw drive
Oilfrttfure
L Serf *j drive
L. Clamp closure
/V. No pressure.
Exhibit 6-11. Injection-molding cycle-mold closed for part cooling; melt being plasticized.1
(reprinted with permission from Weir, Clifford, Introduction to Injection
Molding, Society of Plastics Engineers, Inc., Greenwich, Connecticut, 1975.)
-------
s
oo
B
N
K—jf
C.
P. Fixed plate*
f. ln)*ct/bn nozzle
Mo y«We />/«&« r- ^eatmr «J/M*r *"rf
reciprocating ccr*»
6. h
Exhibit 6-12. Injection-molding cycle-part ejection.
H.
Oi/ pressure
K Clamp
N No pressure
-------
Mold Finishing. Depending upon the end use of the molded pan, some means of finishing
and/or decorating may be required. The finishing of a molded product may consist of removal
of sprues resulting from solidification of plastic in the runners, trimming excess plastic (flash),
decoration of the product, or the assembly of two or more pieces. Flash is excess plastic attached
to the product caused by worn or misaligned mold components, the use of improper cycle
conditions (i.e., excessive temperature or pressure), or the use of an improper grade of plastic
material. Decoration includes post-molding treatments such as application of color, trim, and/or
labels.1
6.3 IDENTIFICATION AND CHARACTERIZATION OF EMISSION POINTS AND
WASTE STREAMS
The primary waste streams generated at injection molding facilities include the following:
Solid Waste
• Air emissions
Operating fluid leaks
• Coolant fluids
• Noise pollution
Exhibit 6-13 summarizes the probable point sources and contaminants (indicated by X) from
injection molding operations.
Solid Waste. A large volume of solid waste is generated by rejected products, sprues, flash, and
other excess plastic produced by the injection molding process. Fortunately, most thermoplastic
waste can be recycled back into the feed. Thermoset plastic waste must be disposed of or ground
up and used as a filler to increase the viscosity of other polymers.
A92-214.6 6-29
-------
EXHIBIT 6-13. SOURCES AND TYPES OF EMISSIONS FROM INJECTION MOLDING OPERATIONS
Hopper
Heating/Injection
Mold
Trimmer
Grinder
Air Emissions
Participates
Polymer
X
X
X
Additives
X
X
X
Volatiles
Monomer
X
X
Additives
X
X
Decomposition
Products
X
X
Solid Waste
Polymer
X
Plnsticizer
X
Additives
X
o\
k
o
AVZ-214.6
-------
Air Emissions. Injection molding operations have the potential to release particulate and
hydrocarbon emissions to the atmosphere. Particulates are released during the addition and
mixing of polymer feed in the hopper. Particulates are also created by trimming the product and
grinding thermoplastic sprues, runners, and other scrap to be recycled. These particulates consist
of particles of polymer and additives.
Emissions of volatile organic compounds are liberated from vents in the heating/injection
cylinders and the molds. These emissions consist of traces of monomers, additives, and
decomposition products. Decomposition products occur when the processing temperature reaches
the decomposition temperature, which varies according to the type of plastic being molded.
Exhibit 6-14 presents those decomposition products which could be formed during injection
molding operations. Because styrene is a commonly used compounding material, specific
decomposition data is presented in Exhibit 6-15.
Operating fluid leaks. Oils, greases, hydraulic fluids, etc. may leak from equipment if it is not
maintained properly.
Coolant Fluids. Typically, water is used as a cooling agent to hasten the molding process. The
cooling water may become contaminated with greases from the mold. Thermal pollution is
another difficulty, as the coolant will absorb a great deal of heat and should not be returned
directly to a river or lake to prevent detrimental effects to biota.
Noise Pollution. Operating injection molding equipment (especially the grinders used to recycle
thermoplastic scrap) produces a great deal of noise which can result in accelerated worker fatigue
and hearing loss. The level of noise pollution often depends on the age and condition of the
molding and grinding equipment
A92-214.6 6-31
-------
EXHIBIT 6-14. POSSIBLE INJECTION MOLDING DECOMPOSITION PRODUCTS
Polymer
Acrylic Resins
ABS
Diallyl Phthalate
Fluoroplastics
Melamine Formaldehyde
Nylon 6 and 6/6
Phenolic
Polyacetal
Polybutylene
Polycarbonate
Polyester (thermoplastic)
Polyester (thermoset)
LDPE
HDPE
EVA
Polyphenylene Sulfide
Polypropylene
Polystyrene
PVC
SAN
Urea Formaldehyde
Highest t
Processing
Temp. (°C)
250
240
175
330
170
290
205
225
190
310
300
260
240
300
2870
330
275
260
210 •
240
160
Decomposition
Temp. (°C) +
320
300
285
300
182
300
300
250
300
330
300
275
100
100
100
700
300
300
100
300
182
Decomposition
*
*
*
HF
*
*
*
*
*
*
Acetaldehyde
*
Ketone Carbonyl
Groups form
Due To Oxidation
*
*
*
HCL
*
*
* Decomposition products are not formed at or near injection molding temperatures.
t The highest possible temperature readied by the normal injection molding of all formulations
of the polymer listed.
The lowest temperature at which decomposition products begin to form.
A92-2146
6-32
-------
EXHIBIT 6-15. STYRENE EMITTED FROM THERMOOXIDATIVE DEGRADATION
, lb/ton)a
Temperature
<°C)
197
200
208
218
224
240
250
Polystyrene
__b
Trace
--
~
--
520, 1.04 (8.0)
740, 1.48(7.0)
Impact
Polystyrene
-
~
--
~
310, 0.62 (3.4)
—
280, 0.56 (3.8)
Acrylonitrile-
Butadiene-Styrene
7800, 15.6 (68)c
-
2300. 4.6 (32)
--
-
—
-
Styrene-
Acrylonitrile
—
—
--
2700, 5.4 (32)
—
—
--
Uncontrolled emissions.
"--" Not measured.
Styrene yield is given in parenthesis as the percentage of total loss in weight.
-------
6.4 POLLUTION PREVENTION, RECYCLING, AND POLLUTION CONTROL
SYSTEMS
6.4.1 Pollution Prevention
Most of the pollution associated with injection molding operations can be avoided or minimized
through proper plant operations. Many potential pollution problems can be avoided if care is
taken to address the following topics:
• Proper plant layout
• Employee training
• Scheduling of work orders and jobs
• Inventory control
• Equipment maintenance
Segregation of waste streams
Proper plant layout. If a plant is laid out inefficiently, the operators are forced to constantly
relocate to monitor the machines for which they are responsible. This may prevent necessary
adjustments from being made at the proper time because the operators are busy elsewhere.
Problems may develop and remain unchecked for several days or longer. If the problems are
severe, the product run may be ruined, resulting in wasted raw materials and unusable off-
specification products. An operation that is efficiently arranged with easy operator access to all
important machine controls will help to prevent errors of this type by allowing operators to
perform all their tasks within a relatively small area. Exhibit 6-16 shows an example of a
properly laid out operation, with arrows indicating controls/Indicators which must be monitored
by an operator.
Employee Training. A solid employee training program will have beneficial effects on operation
efficiency of the plant. Workers who are well trained in the operation of their machines and in
troubleshooting procedures will produce more product in less time with less waste. Poorly
A92-2M.S 6-34
-------
^
U)
NO. 1
t
1
NO. 7
NO. 12
1
1
NO. 17
NO. 2
1
1
NO. 8
NO. 13
I
I
NO. 18
NO. 3
t
I
NO. 9
NO. 14
1
1
NO. 19
1
NO. 23
NO. 4
I
1
vJO. 20
NO. 5
r~
i
NO. 10
NO. 15
1
1
NO. 21
NO. 6
1
1
NO. 11
NO. 16
1
1
NO. 22
Exhibit 6-16. Model injection molding plant machine layout.
-------
trained workers will take longer to recognize potential problems in the molding process, and may
not understand hovy to deal with the problems once they are identified. This will result in more
frequent waste from rejected products. Well-trained employees are also more likely to request
maintenance for malfunctioning equipment, and thereby avoid serious mechanical problems
through preventive maintenance.
Scheduling of work orders and jobs. The order in which jobs are completed should be
determined by two significant factors: product color and raw materials availability. The color
being applied to the plastic must be considered during production scheduling decisions to ensure
first quality end products. Progressing from light colors such as yellow or pink to darker ones
like blue or black will prevent the lighter colored resins from being discolored by residues from
darker ones. Darker resins will not usually show discoloration from small amounts of resins
having lighter hues.
The second aspect of scheduling involves ensuring that correct amounts of raw materials are on
hand by requiring work orders from customers which define the amount of product desired. This
is especially important if the job requires special or proprietary raw materials. Excess raw
materials remaining after a job is completed may be wasted unless they can be used for
something else. Preferential treatment should be given to customers who commit to long runs,
as large batches make it possible to avoid purging the machines often, which causes large
amounts of waste plastic and downtime.
Waste plastic can also be minimized by using a purging foam for equipment cleaning. The foam
is fed through the molding system like the plastic feedstock. It shortens the cleaning process and
eliminates solvent cleaning waste.
Inventory control. In addition to careful ordering of raw materials and additives according to
work orders, any inventory left over should be carefully catalogued and stored in an orderly
fashion. This will facilitate use of any leftover materials and prevent waste. If records of excess
A92-214.6 6-36
-------
raw materials and additives are not maintained, the inventory will not be used efficiently and
valuable materials may be entirely wasted.
Equipment maintenance. A regular program of equipment maintenance is essential. Poorly
maintained equipment is more likely to malfunction and result in rejected parts and waste.
Machines that are not regularly maintained are also likely to develop leaks of oil and hydraulic
fluid. These leaks are an environmental hazard and may cause low fluid levels in the machines,
producing equipment breakdown and failure. The blades on grinders of recycling scrap
thermoplastics should be sharpened regularly to prevent unnecessary strain on the motor due to
difficulty in shredding the plastic. A regular program of maintenance on operating equipment
has the goal of keeping all machines in prime operating condition and stopping potential
problems before they happen.
Segregation of waste streams. The current technology has not produced an economical method
of separating mixtures of different polymers. For this reason, waste from machines using
different feedstocks should be kept separate. If waste thermoplastics are segregated, they can be
recycled and returned to the same process that they resulted from. Thermoset plastic wastes
which cannot be recycled should not be mixed with reusable products so they can be disposed
of. Careful waste segregation is an important part of a good recycling program, and is essential
for an economically sound plastics molding operation. Similarly, all waste maintenance liquids
(e.g., hydraulic oils, greases, and degreasers) should be separated. Another waste minimization
option for maintenance liquids is to consolidate maintenance liquids. Rather than using five
lubricating oils, a facility may be able to use two.
6.4.2 Recycling operations
Thermoplastic sprues, runners, and scrap generated by the trirnming of product flash can usually
be ground and recycled to the hopper feed. Virgin resin and regrind are usually mixed in a 4:1
ratio. As previously mentioned, it is important to segregate waste streams to avoid mixing
different polymers.
A9X-214.6 6-37
-------
Typically, scrap grinders are used to reduce runners, sprues, and reject parts to uniform small-size
particles that can be blended back into the molding material in the hopper. In small molding
facilities granulators are installed alongside or beneath each molding machine to regrind material
from the individual machines. This provides for a mechanical or manual feedback to the hopper.
Larger injection molding facilities may have a centralized area for all scrap grinding and
recycling.
A typical scrap grinder consists of three blades, two rotating and one stationary, housed in a
suitable chamber with a feed hopper at the top and a screen beneath which permits material to
pass through when it has been reduced to the proper size. There are numerous types of blades
designed for grinding of different types of plastics. Blades will operate more effectively if
sharpened on a regular basis. Blade maintenance should also be included in the maintenance
•
scheduls. Sharp blades allow for easier grinding (both in the cutting of the plastic material and
by causing less strain on the grinder). In addition, sharp blades yield a finer regrind which can
be incorporated more easily into the molding process. Plastics can be categorized into three main
categories with respect to their behavior in grinding operations:2
Energy-Absorbing Plastics. Most thermoplastics (e.g., low density polyethylene) are considered
to be energy-absorbing plastics. These plastics are somewhat flexible, impact resistant, and easily
granulated.
High Impact Plastics. These plastics (e.g., ABS) are extremely hard and are not easily broken.
/
These plastics will tend to shatter when exposed to great stress.
Friable Materials. These plastics (e.g., Phenolic resins, styrenes, etc.) break apart easily without
• application of extreme stress. Granulation of friable materials usually causes large amounts of
dust and airborne particulates.
Important topics to consider in choosing recycle granulators include2:
A92-214.6 6-38
-------
The general type of granulators- under-the press, beside the press, or a central recycling
system (this will depend on the size and arrangement of the overall operation)
Throughput requirements- what hourly production rate is required
Physical properties of the plastic to be recycled- this will determine the type of blades
that must be used
Choice of screens- this will depend on the size of the machines and the size of regrind
granules desired
6.4.3 Pollution Control Systems
Pollution resulting from injection molding operations is mostly minor and easily controlled. The
remainder of this section discusses control strategies for the emissions described in Section 6.3:
Solid Waste
• Air emissions
• Operating fluid leaks
• Coolant fluids
• Noise pollution
Solid Waste. The most efficient way to deal with thermoplastic waste is to recycle it Thermoset
scrap may not be recycled directly because it cannot be remelted, although it may be ground up
and used as filler material to increase the viscosity of other resins. However, because any plastic
waste which cannot be recycled is comprised of inert plastic material, it poses limited
environmental disposal problems.
Air emissions. The quantities of VOC released by the injection molding process depend largely
on the speed of the molding cycle and the polymers being molded. For instance, polystyrenes
operating at fast cycles will emit more fumes than polyethylenes operating at the same speeds.
Normally, emissions rates are relatively low resulting in more health and safety concerns than
A9Z-214.6 6-39
-------
environmental concerns. For this reason good ventilation of the manufacturing area is essential,
with hoods containing fans over each molding machine.
Paniculate emissions from the feed hoppers and grinding of scrap must also be controlled. Use of
exhaust fans and a baghouse Will effectively and cheaply alleviate this problem.
Operating fluid leaks. Use of catch pans with drain plugs will allow for easy removal of any fluids
that leak from the machines. The fluids may be collected and removed for disposal by a licensed
disposer.
Coolant fluids. If water is used to cool the molds, itrmay be contaminated by greases etc. from the
molds. The water will also be carrying waste heat and should not be returned to a river or lake
because of the possibility of thermal pollution harming biota. Cooling water should be returned to
ambient temperature and reused. A cooling tower may be used to remove waste heat from coolant
water. The plant water should also be consistently monitored for calcium (i.e., hard water) and
algae "growth. Hard water may result in scale deposits throughout the piping system. Scale will
cause inefficient machine operation and degradation of hydraulic fluids.
tfpise Ppttutioin. The nqi§e resulting from the operation of molding machines and recycle grinders
can be reduced by use of a system of baffles surrounding the machines. Baffle systems constructed
of wood and acoustical insulation are highly effective, however, simple systems made from sheets
of heavy canvas will usually suffice.
6-40
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6.5 REFERENCES
1. Weir, Clifford, Introduction to Injection Molding, Society of Plastics Engineers, Inc.,
Greenwich, Connecticut, 1975.
2. Rosato, D.V., Injection Molding Handbook, Van Nostrand Rsinjipld Company, Inc., .New
York, NY, 1986.
3. de Cleir, P.V. Polymers in Injection Molding, ^T/C Press, Los Angeles, CA, 108&
4. Dym, Joseph B. Injection Molds and Molding, Second edition, Van Nostrand Reinhold
Company, Inc., New York, NY, 1987.
5. U.S. Environmental Protection Agency, Industrial Process Profiles for Environmental
Use. Chapter 10A. The Plastics and Resins Processing Industry. EPA-"60d/2-85-0-8'6'.
6. U.S. Environmental Protection Agency. Development Document for Effluent Limitations,
Guidelines, and Standards for the Plastics Molding and Forming Point Source Category.
EPA-440/l-84-069b. Effluent Guidelines Division. Was#uig&ti, DC. February 19M.
7. Personal communication with Kare Anderson, Blasland & Bouck Engineers, T5}jpsset, .NY
by B. McMinn, TRC Environmental Corporation. "Injection Molding Processes." August
and September 1992.
8. U.S. Environmental Protection Agency. Economic Impact Analysis ofEffluen^Limitafions
and Standards for Plastics Molding and Forming Industry. EPA-440/2-84-025. Office
of Water Regulations and Standards. December 1984.
A92-214.6 6-41
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EXHIBIT 6-17
ANDERSON TOOL AND PLASTICS CORP.
WORK ORDER
JOB INFORMATION
Customer-
Pan Description No.-
Job No.-
MoldNo. - -Cav._ -K.O.-
Machine No.-
Dimension-
TIME .
Job Start-
Hts. Required-
Days Required-
Job Completion-
WEIGHT
Shot Weight- - ozs.
Pan Weight- - ozs.
, \,
Pieces per Ib.- -/sets
Lbs. per hour-
Parts per hour-
Material-/Blend No.
Machine Time
Inj. forward-
Inj. Hold-
Mold Open-
Inj. Delay-
Mold Qose-
Overall Cycle
Pressure Inj.-
Accumulaior-
CARTON INFORMATION ,
Carton No.-
.Ojiantity Required-
Pieces Per Carton-
Existing Cartons in Stock-
TEMPERATURE
Front-
Spare Front-
Rear-.
Spare Rear-
Nozzle-
Adapter-
REMARKS 1
,
•
.
.... 1
6-42
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