MANUFACTURE OF PAPER AND PAPER PRODUCTS # 70

Background

The new bleach plant begun start-up in mid-August, 1992. The switch to full-time use of ozone bleaching was made on September 19, 1992.

The development and utilisation 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.

Cleaner Production Principle

Process modification.

Cleaner Production Application

Process modification: It was necessary to develop a successful bleaching stage utilising 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.

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 utilisation 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 (EOM), and a final chlorine dioxide stage (D). Since there is no use in the O, Z, or EOM 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(EOM)D Bleaching %

(1) Total Organics Halides Test Method

Raw material effects are as follows :

% of Chemical Usage on O.D.Pulp

CEDED2 Bleaching OZ(EOM)D Bleaching

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(EOM)D Bleaching

There was a slight reduction in the amount of steam used with the new process:

Steam Use, Kg/AD Tonne

CEDED Bleaching OZ(EOM)D Bleaching

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(EOM)D Bleaching

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.

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.

The new ozone bleaching process implemented at Franklin was the first commercial utilisation 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 co-operative 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 world-wide 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.

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(EOM)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:

Environmental and Economic Benefits

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

B. Conversion to pressurised screening

C. Conversion of decker to specialized 4th stage brown stock washer

D. General facilities for new bleach plant

E. Distributed Control System (DCS) for all new equipment

F. High Consistency 900 AD Ton/day oxygen stage

G. Two 450 A.D. ton/day high consistency ozone stages

H. Ozone gas generation and recycle system

I. 900 AD ton/day extraction stage

J. 900 AD Ton/Day Chlorine Dioxide Stage

K. Finished Product Storage and Distribution

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

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(EOM)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 sulfate and a chelant), the current bleaching chemical cost is $25.50/AD ton.

E. Total changes in annual operational and maintenance costs

Payback Times

In the calculation of the payback time for the "Cleaner Production Technique", it is not appropriate to use the $113 million total capital cost for the project since the major portion of the cost was a necessary replacement cost for ageing bleach plants. The two bleach plants in service for pine bleaching were nearing 40 years of use and needed replacement in the near future. We estimate that the capital cost over what would have been needed for a simple replacement is US$ 21 million. Thus, discounting the necessary replacement costs, the payback would be:

Benefits

There are a number of additional benefits that are not reflected in the above payback calculation. Among these are:

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

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(EOM)D process.

Additionally, we believe there are marketing advantages to our having eliminated the use of chlorine in the production of our pine pulp.

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.

The significant favourable 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.

The major driving force for our research efforts to develop the new technology was the realisation 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 ageing bleach plants became necessary.

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.

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).

Review Status

This case study was submitted to UNEP IE from the UN World Food Organization. It was edited for the ICPIC diskette in July 1995.

Subsequently the case study has undergone a technical review by Dr Prasad Modak at Environmental Management Centre, Mumbai, India, in September 1998.