INTERNATIONAL CLEANER PRODUCTION INFORMATION CLEARINGHOUSE

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.