CASE STUDY # 79
Purpose of this Case Study: The development and
utilization of ozone treatment technology in the
bleaching process for full chemical pulps in the pulp and
paper industry has allowed recycling of waste streams
from the bleach plant, producing dramatic reductions in
the volume of liquid effluent and with pollutants, such
as biological oxygen demand (BOD), chemical oxygen demand
(COD), color, and chlorinated organics.
1. Headline: A submission of ozone bleaching for bleach
plant closeup
2. Background: The new bleach plant begun startup in mid-
August, 1992. The switch to full-time use of ozone
bleaching was made on September 19, 1992.
Further details: see description of cleaner production
application
3. Cleaner Production Principles:
- Process modification:
It was necessary to develop a successful bleaching stage
utilizing ozone as a bleaching agent for chemical pulp by
substituting the ozone stage for a chlorine gas bleaching
stage. Numerous past ozone bleaching studies performed by
others encountered problems which prevented commercialization
and modification of the process.
- Equipment Modifications:
For the successful use of ozone bleaching, it was
necessary to develop, from first principles, new
equipment to substitute for conventional equipment
normally used for bleaching.
- Recycling and Reuse:
The opportunity of eliminating the discharge of the
normal bleach plant effluent was created by the process
change that eliminated chlorine treatment and, therefore,
chlorine contamination made the wash water too corrosive
to recover. By devising recycle methods, it became
possible to reuse these recovered waters for replacing
fresh water required for wash water, and ultimately to
recover formerly sewered contaminated wash waters back
into the closed cycle liquor recovery system already in
existence for pulping liquors.
4. Description of Cleaner Production Application:
Process and Waste Information
The original manufacturing process is in use at Union
Camp's Franklin, Virginia for the bleaching of the total
mill's requirement of southern kraft pine pulp was a
conventional 5-stage bleaching sequence using chlorine as
a bleaching agent in the first treatment state (C),
caustic extraction for the second stage (E), chlorine
dioxide for the third stage (D), followed by a repeated
caustic extraction for the fourth stage (E), and a
repeated chlorine dioxide treatment for the fifth stage
(D). This CEDED process is the most common and one of the
most economical bleaching process for the pulp. For each
stage, the dissolved organics and the inorganic bleaching
chemicals must be washed out of the pulp before entering
the next stage. Although the amount of wash water and
resulting effluent could be minimized by reuse of the
washings as wash water for the prior stage in a
countercurrent fashion, eventually it was necessary to
sewer all the washings for treatment in the plant's
effluent treatment system. This occurred because the
utilization of chlorine and chlorine dioxide contaminated
the washings with chloride, causing corrosion problems
when washings were recovered in the mill's existing
closed cycle cooking liquor system. The result is a high
volume of bleach plant effluent containing large amounts
of BOD, COD, color, and chlorinated organics (which are
formed principally from the reaction of chlorine with the
pulp).
The replacement manufacturing process, developed after
more than a decade of research and development including the
erection and operation for several years of a US$ 6,5 million
pilot plant for several years, is a pioneering 4-stage
bleaching sequence, using oxygen with caustic as bleaching
agents in the first stage (O), followed by ozone treatment in
the second stage (Z), caustic extraction augmented by oxygen
in the third stage (EO), and a final chlorine dioxide stage
(D). Since there is no use in the O, Z, or EO stages of
chemicals that are incompatible with recycle and recovery in
the mill's existing pulping liquor closed-cycle system,
virtually all of the washings from these three stages are
recovered without sewering. The only significant effluent from
the bleach plant is the small amount of contaminated washings
coming from the final chlorine dioxide stage. Reduction in
effluent losses that must go to the mill's treatment system
are very significant, as the following table illustrates:
Liquid Effluent from the Bleach Plant
CEDED bleaching OZ(EO)D Bleaching %
Before Change After Reduction
Volume of Effluent 55.1 7.5 86
M3/AD Tonne
BOD5, Kg/AD Tonne 16 1.8 89
COD, Kg/AD Tonne 65 5.6 91
Color, Kg/AD Tonne 185 3.5 99+
Chlorinated Organics 5.7 0.076 98
Kg/AD Tonne (1)
(1) Total Organics Halides Test Method
Raw material effects are as follows:
% of Chemical Usage on O.D.Pulp
CEDED2 Bleaching OZ(EO)D Bleaching
Before Change After
Chlorine 7.1 0
Total Caustic 5.9 5.0
Total Chlorine Dioxide 2.2 1.0
Total Oxygen 0 7.0
Ozone 0 0.8
Sulphuric Acid 0 3.4
The newer, more state-of-the art bleach plant did
increase the electrical power demand locally at the mill:
Running Power Requirements
CEDED Bleaching OZ(EO)D Bleaching
Before Change After
Bleach Plant, MW 3.8 6.8
Ozone Generator Power, MW 0.0 4.5
Total MW 3.8 11.3
There was a slight reduction in the amount of steam used
with the new process:
Steam Use, Kg/AD Tonne
CEDED Bleaching OZ(EO)D Bleaching
Before Change After
413 KPa Steam 545 75
1034 KPa Steam 0 350
However, these steam and power comparisons are only in
terms of the extra energy required at the mill proper,
including the generation of the bleaching chemical ozone, and
does not account for reductions in the off-site energy
required to produce bleaching chemicals reduced by the use of
ozone. On a global basis, considering the power and steam
costs to run the bleach plant and produce the bleaching
chemicals (including those produced off-site), the comparison
is:
Total Energy Consumption, KWH/AD Tonne
CEDED Bleaching OZ(EO)D Bleaching
Before Change After % Reduction
1807 792 56% less
Scale of Operation
The original CEDED process being replaced was composed of
two identical bleach plants, each capable of producing
fully bleached pulp product at a rate of 450 air dried
tonnes per day each or a total of 900 AD tonne/day. The
single plant replacing them also has a capacity of 900 AD
tonne/day. This, of course, is a world class facility in
size.
Stage of Development
The process development followed the classical stages of
laboratory , bench scale exploration for a 7-8 year period,
followed by the erection and operation for three years of a
US$ 6,500,000, 23-tonne/day pilot plant. The full size 900 AD
tonne per day commercial facility was erected from April, 1991
through August, 1992. It has been in routine commercial
operation using ozone since September 19, 1992, or for more
than a year.
Level of Commercialization
The new ozone bleaching process implemented at Franklin
was the first commercial utilization of high consistency ozone
bleaching of pulp in the world and was the world's first
commercial use of ozone bleaching of any type for softwood
pulp. Union Camp has formed a cooperative marketing agreement
with Sunds Defibrator AB, a major, a major Swedish provider of
bleaching machinery and processes, to supply the new process
to others. The combination process and equipment package is
available worldwide to interested licensees. Union Camp and
Sunds Defibrator have worked together to adapt Sunds
Defibrator's existing standard equipment line of machinery for
the new application, and to design and fabricate new equipment
for the ozone reactor. Ozone generators were purchased from
commercial ozone generator manufacturers, but for this
specific application, the reactor off-gas cleanup and recycle
system was designed by Union Camp and the ozone generator
vendor.
Material/Energy Balances
The changes in raw material usage, energy usage, and
waste materials produced are well detailed in the above
"process and waste information" section. There are two
effects in other parts of the pulp mill that should be
documented. One of these is that part of the caustic used
in the OZ(EO)D bleaching is not required to be purchased
as a raw material. Since essentially all of the caustic
used in the oxygen stage treatment is recovered and
recycled back to the cooking liquor closed recycle
system, one is able to use caustic for the oxygen stage
when caustic makeup is needed for the cooking liquor
cycle, without the additional cost of an additional
caustic purchase. However, for the times when no caustics
makeup is required (or wanted), one can oxidize with
oxygen the product from the cooking liquor recycle -
white liquor - and use the oxidize white liquor for the
alkali requirement. This results in an extra load on the
cooking liquor recycle equipment's capacity. Calculations
show that this use of oxidized white liquor has resulted
in an extra regeneration load of about 5% more cooking
liquor for the pine pulp than would have been required
merely for cooking.
A second significant effect is that the recovery and
recycle of organic and inorganic solids purged in the
bleach plant effluents is about 7% more solids than
normal for pine production in the feed to the recovery
boiler in the cooking liquor closed cycle. While it is
true that this is an extra use of recovery capacity, it
also results in extra solids which may be used as fuel
for producing steam in the recovery boiler. About 6% more
steam per ton of pine pulp is being produced.
( The following three assumptions were made:
- Data is presented for the most part based on
results with southern pine produced with the kraft
process. Other pulp sources would produce different
numbers, but generally the same trends.
- Economic calculations are based on 1992-1993
typical construction and raw material costs for the
Southern United States.
- High consistency ozone treatment performance
is used as base. Ozone treatment at other
consistencies will produce different results.)
5. Economics:
Investment Costs
The total installed cost for the completely new bleached
line replacing the two old bleach lines was US$ 113 million.
Major items included in this project.
A. General high voltage electrical supply system upgrade
- New purchased power tie line to local utility
- New 15 KW bus room, ac and chemical filtered
makeup
- New 15 KW sync bus reactor, zig-zag grounding
transformer and switch gear
B. Conversion to pressurized screening
- Two knotters
- Two knot drainers
- Two primary screens
- Two secondary screens
- Two tertiary screens
- One quaternary screen
- One rejects dewatering press
- Associated tanks, pumps, conveyors, electric
equipment
C. Conversion of decker to specialized 4th stage brown
stock washer
- Modification of decker for split showers
- Converted to air doctor and improved wire cleaning
- New decker filtrate tank
D. General facilities for new bleach plant
- New 6-story building to house bleach plant, 33m x
55m x 40m high
- Licensee training center office complex in bleach
plant, including two offices, conference center, with
simulator and distributed control access facilities
- HVAC systems for building, including AC and
chemical filtered makeup for all electric/electronic
rooms, cooling tower
- Scrubber and fan for all bleach plant vent gases
E. Distributed Control System (DCS) for all new equipment
- 5 DCS computer systems
- General instrumentations and controls (750 +
loops)
- Data logging computer system
F. High Consistency 900 AD Ton/day oxygen stage
- Feed tank
- Magnesium sulphate tank addition system
- System for oxidizing white liquor with oxygen
- Liquid oxygen storage and vaporization system
- Twin roll feed press with pressate tank
- Steam mixer
- Plug screw feeder
- Fluffer
- Oxygen reactor and blow-tank
- Two twin roll wash presses with interstage tank and
pressate tank
- Oxygen off-gas venting system
G. Two 450 A.D. ton/day high consistency ozone stages
- Feed tank
- Two twin roll thickening presses
- Pressates tank with chilled water cooling, pH
adjustment recirculation system
- Two plug screen feeders
- Two disc fluffers
- Two ozone reactors with gas separators
- Two ozone reactor receivers
- Surge tank/tower
- Rotary drum washer with filtrate tank
- Chelate storage and addition system
H. Ozone gas generation and recycle system
- Five ozone generators with associated power
supplies capable of producing 6800 Kg/day of ozone at
6% concentration.
- Chilled water system with two mechanical chillers
and two cooling towers
- Recycle gas fibre scrubber
- Two recycle liquid ring compressors
- Economizer
- Thermal destruct unit
- Catalytic destruct unit
- Recycle gas cooling via chilled water and
refrigerative dryer
- Desiccant dryer
I. 900 AD ton/day extraction stage
- Steam mixer
- Thick stock pump
- Chemical mixer
- Oxygen addition system
- Upflow/downflow tower
- Rotary drum washer with filtrate tank
J. 900 AD Ton/Day Chlorine Dioxide Stage
- Steam mixer
- Thick stock pump
- Chemical mixer
- Upflow/downflow tower
- Rotary drum washer with filtrate tank
K. Finished Product Storage and Distribution
- 450 A.D. ton high density storage tank
- Miscellaneous pumps to feed tank, dilute and
distribute stock from tank
Changes in Operational and Maintenance Costs
A. Maintenance costs for the new facility are felt to be
essentially the same as for the two older, retired bleach
plants.
B. Operator manning has been inflated by one person per
shift (4 people total) for the initial shakedown of the totally
new system. This is an increase cost of about US$ 150,000 per
year, but we anticipate that this will be cut soon to produce
no change in the before and after crewing.
C. Energy costs
The net additional cost of power and steam is estimated to
be about $400,000 per year.
D. Savings from reduced bleaching chemical costs
Using 1993 raw material costs for the Franklin Mill and
the bleaching chemical requirements listed in the "Process and
Waste Information" section for the CEDED bleaching replaced by
the new process, the bleaching chemical costs would have been
about $36/AD ton. Using the bleaching chemical requirements
listed in the above stated section for the new OZ(EO)D process,
making the correction for substituting oxidized white liquor
for caustic, and adding the cost of miscellaneous bleaching
chemicals now being used (such as magnesium sulphate and a
chelant), the current bleaching chemical cost is $25.50/AD ton.
Current Fully Bleached Chemical Savings
($36 - 25.50)/AD ton x 900 AD ton/day x 360 days/year = $
3,402,000/year
E. Total changes in annual operational and maintenance
costs
Current Total Savings = $3,002,000/year
Payback Times
In the calculation of the payback time for the "Cleaner
Production Technique", it is not appropriate to use the $113
million total capital cost for the project since the major
portion of the cost was a necessary replacement cost for aging
bleach plants. The two bleach plants in service for pine
bleaching were nearing 40 years of use and needed replacement
in the near future. We estimate that the capital cost over what
would have been needed for a simple replacement is US$ 21
million. Thus, discounting the necessary replacement costs, the
payback would be:
$21,000,000 capital = 7.0 years
$ 3,002,000/year annual savings
Benefits
There are a number of additional benefits that are not
reflected in the above payback calculation. Among these are:
A. Additional Savings If 100% Substitution Is Required -
It is becoming increasingly clear that, as a minimum, the
environmental control agencies and/or the marketplace is going
to require elimination of elemental chlorine as a bleaching
agent. Converting the CEDED bleach lines to DEDED by 100%
substitution of chlorine dioxide for chlorine is estimated to
elevate the bleaching costs from $35/AD ton to $45/AD ton.
Accordingly, the current total savings would be increased to
$5,918,000 per year and the incremental payout would become:
$21,000,000 capital = 3.5 years
$ 5,918,000/year annual savings
B. Marketing Enhancements
In the competitive environment where higher brightness is
a marketing asset, it was decided that the Franklin Mill
would increase its pulp brightness about two units (from
83 to 85 ISO). We believe there would have been
substantially more costs for accomplishing this with the
CEDED than with the current OZ(EO)D process.
Additionally, we believe there are marketing advantages to
our having eliminated the use of chlorine in the production of
our pine pulp.
C. Improved Environmental Position - There is significant
value in our having completely eliminated any concerns
about meeting current or future regulations in chlorinated
compounds, particularly the 2,3,7,8 dioxin stream
standard. The reduced volume and biological demand of the
bleached plant effluent enhances our effluent treatment
system's ability to meet current limits. Additionally, the
significant reduction in color of our bleach plant
effluent lowers any color impact on our receiving streams
and reduces the prospect of adverse comments by others who
share the receiving waterway.
Clearly, if we had been in the position of having to build
an effluent treatment system (as with a greenfield mill)
or greatly enlarging the effluent system (as with a major
expansion), the reduced volume and biological oxygen
demand concentration of the treated effluent would make
the bleach plant investment very attractive.
D. Public Relations - The significant favorable publicity
accorded to Union Camp as a result of its proactive
efforts to create a breakthrough in bleaching technology
that produces cleaner production, is a very large positive
benefit. Numerous awards have been received, including
TAPPI Pulping Conference's High Impact Paper Award, the
Thomas Edison Award for Patent Quality, the Virginia
Governor's Award for an Outstanding Environmental Project,
a Resolution by the Georgia Legislature praising Union
Camp's environmental concerns (sponsored by the Sierra
Club), and the American Forest & Paper Industry's Award
for Water Pollution Control. Feature articles about Union
Camp's environmental accomplishments have been published
in literally dozens of publications, including The New
York Times, Paper Age, Paper, PPI, Papermaker, Equipment,
Machinery & Materials, and Pulp & Paper.
E. Decision Driving Force
The major driving force for our research efforts to
develop the new technology was the realization that bleach
plant effluents were the major source of pulp mill
environmental missions and our desire to eliminate this
problem. The major driving force for implementing the new
technology was our desire to install the very best
possible process for cleaner production during pulp
bleaching, when replacement of aging bleach plants became
necessary.
6. Advantages: see Description of Cleaner Production
Application and Economics sections.
7. Constraints:
Technical Restraints: Thus far, we have not encountered
any wood source, or end of product need that would limit use of
the new technology. There may be some cases in which the use of
oxidized white liquor as an alkali source, overloads the white
liquor regeneration capacity of a facility. Similarly, there
may be some cases where the capacity of the recovery boiler in
the cooking liquor recycle system does not have the excess
capacity to process the extra solids recovered by recycling the
bleach plant washings.
8. Contacts:Union Camp Corporation
P.O.Box 178
Highway 58
Franklin, VA 23851
USA
Tel: 1-804-569-4321
Wells E. Nutt, President
Union Camp Technology, Inc
P.O.Box 178
Franklin, VA 23851
USA
Tel: 1-804-569-4431
Fax: 1-804-569-5166
Citations:
- Types of source material: Technical papers in journals,
conference proceedings, unpublished documents belonging to
Union Camp, news media articles (newspapers, trade
magazines).
9. Keywords: United States, USA, pulp and paper, bleaching,
new technology, ozone, BOD, chlorine, caustic, process
modification, recycling, ISIC 2611, ISIC 2621, ISIC 2631
10. Reviewer Comments: This case study was submitted to UNEP
IE from the UN World Food Organization. It was edited for the
ICPIC diskette in July 1995. It has not undergone a formal
technical review.