Bleaching of Wastepaper Technology and Economics

Swaroop Iyengar Deinking Feasibility Manager

Brown &Root Forest ProducrS

Bleaching of Wastepaper Technology and Economics

Swaroop Iyengar Brown & Root

Abstract

The technologies to bleach wastepaper have moved from the basic peroxide and hydrosulfite methods to sophisticated multistage techniques. Many of these strategies have been in response to the use of wastepaper with increasing levels of fibrous "contaminants" and the use of unbleached grades such as OCC. Equipment and systems to bleach and/or color strip wastepaper are briefly reviewed and the tradeoffs between wastepaper costs, operating costs and capital costs are explored.

Introduction

This report explores some of the technical and cost impacts of using bleaching methods with different grades of wastepaper. This is important since mills are often confionted with producing a high quality product using a low cost wastepaper while not impacting capital and operating costs. A variety of reasons have led to the large number of "ledger" grade deink plants in installed the last five years and ones planned for. Investments in ledger grade deink facilities, often project financed, have ranged between $250,000 to $360,0OO/daily ton. The variation in price reflecting scope of the project - wastewater treatment, dry-lap machine etc. An essential part of the these deink facilities is a sophisticated bleach system to handle the increasing amount of colored fibrous

costs for bleaching has in some cases become comparable to that in virgin fiber facilities, as discussed below.

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It is not the intent of this paper to be a compendium or text for all bleaching techniques or methods but rather an overall review of the options available and the costs associated with their installations. Total installed costs consist not only of the major process equipment that is often advertised as the "tool" for a particular unit operation, but also the ancillary hardware associated with it. As a perspective the list below indicates all equipment that must be bought in order to install an oxygen delignification step. Associated with this purchase cost, is construction cost for its installation as well as civil/structural, electrical, instrumentation and piping costs. The total installed cost is often three times that of the major process equipment cost.

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Equipment Name Standpipe, Oxygen Reactor MC Pump Pump, Oxygen Reactor MC Motor, Pump, Oxygen Reactor MC Pump, Oxygen Reactor MC Pump Degasifier Motor, Oxygen Reactor MC Pump Degasifier Mixer, Oxygen Reactor High Shear Drive, Oxygen Reactor High Shear mixer Motor, Oxygen Reactor High Shear mixer Heater, Static Pulp Distributor, Static Oxygen Reactor Oxygen Reactor Discharger, Oxygen Reactor Drive, Discharger, Oxygen Reactor Motor, Discharger, Oxygen Reactor Tank, Oxygen Reactor Blow Agitator, Oxygen Reactor Blow Tank Drive, Agitator, Oxygen Reactor Blow Tank

The alternative processes were evaluated in terms of capital costs, quality benefits, operating costs and maintainability/operability. The methods provide a basis for making decisions on which bleaching methods to use for a given wastepaper grade and the relative operating vs. capital costs.

The design of the bleach system is part of the overall deink facility. The primary objective of the facility is to remove ink by means of various unit operations - flotation, washing etc. Bleaching is incorperated to either decolorises high lignin content fibers or dyed fibers. Bleach chemicals do not bleach ink. Image analysis provides an on-going quality control tool in a deink plant monitoring ink particle size and distribution on a continuous basis. It provides a method for identifjing if brightness problems are related to poor bleaching or poor ink removal. The deink facility must be designed to handle the large variety of ink types that are present in wastepaper today. More importantly, the facility must be engineered so that non-fibrous components do not accumulate in the system and that there is flexibility in control of the process. The best method to produce a good quality product is thus to design a good deink system which removes ink and which includes bleach sequenceh appropriate for the wastepaper utilized.

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This report covers bleaching techniques used in deink facilities that use brown grades, wood containing grades and ledger type grades. A scale has been recently developed that provides a method for examining the bleach response of various chemicals ( 5 ) The Sharpe-Lowe scale provides a means to evaluate different bleaching options with regard to brightness and shade. The latter is particularly important in the use of deink pulp for fine paper grades.

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Brown Grades

Delignification of processed OCC has for the past few years been investigated (1) and installed at several sites (2). The process produces a pulp which is classified as 100% post-consumer and which is comparable to bleached virgin fiber in strength with a brightness in excess of 85 GE. The impetus for this process was the low cost of OCC prevalent two or three years ago ($10-50/ton) and the ability to use unit operations in an existing virgin pulp line. Today with OCC prices over %l2O.ton, some of the same rational may not make economic sense.

The equipment associated with the system involves a conventional OCC processing line consisting of the following:

Pulper Detrashing HD Cleaning Coarse screening Fine screening Forward cleaning Lightweight cleaning Thickening Rejects handling Water clarification

The objective of these unit operations is to produce a pulp that is fiee of non-fibrous contaminants. The product at this stage has a Kappa number of 85 or higher which is deligdied in a digester with chemicals (kraft, sulfite), oxygen treatment follows with a two or three stage bleach sequence. The requirements for brightness drive the decision on number of delignification stages. For a high brightness pulp a chlorine dioxide stage followed by peroxide and a second chlorine dioxide stage may be used. A two stage system could be a chlorine dioxide stage followed by a Eop stage. The issues on operating costs are related to the Kappa number of the OCC and the brightness required of the end product.

The quality issues of bleached OCC pulp have been presented by several investigators (3) and indicate that a quality superior to that fiom deinking mixed office waste is obtained. Bench scale studies of ECF methods without the digesting stage, indicated earlier, have been reported with strength preservation by acid activation with Carols acid (peroxymonosulphuric acid), peracetic acid or a mixture of the two (2).

The major benefit of producing this type of pulp is that there are no "stickies" issues, to impact on the paper machine (critical to fast, commodity fine paper machines) and that the unit operations and equipment are well understood by the operating and maintenance staff. The mill must however have excess capacity in the evaporators to handle the liquor from the washing operations and excess capacity in chlorine dioxide or oxygen generation. Other consumables such as

i Bleaching of Wastepaper Page 3

peroxide are operating costs that do not require a substantial amount of capital expense if not already in place at the mill. '-1 The total installed cost for the OCC plant varies between $25,000 and $40,000 /daily ton. The variation in costs is a direct hnction of system complexity and is driven in a inverse relationship with raw materiallpulp quality. The total installed cost for the delignification and bleaching varies between $90,000 and $15O,OOO/daily ton. The capital costs for ECF sequences is difficult to quantifl at present.

The economics of using this process thus involves a cost for the production of bleached pulp fiom OCC, (which currently hovers around $15O/ton) and the price of bleached hardwood kraft, with which the recycled fiber competes - all other things being equal (that is federal and state mandates not withstanding). Currently NBHK is selling at about $770/ton and even with today's OCC prices, bleached pulp fiom OCC, is not cost competitive with virgin fiber. However, bleached OCC pulp is cost competitive with ledger grade deink pulp.

Wood containing grades

Bleaching systems for news and magazine systems are well documented (4). Peroxide and or hydrosulfite are usually used at different stages in the system. Brightness of 65% IS0 with 1% hydrogen peroxide are easily achieved at 12% consistency after a good washing stage. The trend is to use peroxide at the dispersion stage so that the disperser can act on the high consistency (about 30%) stock as a mixer. The challenge is to handle unbleached fibers which are invariably found in commingled curbside collections. And as producers are aiming for higher quality value- added products this has become an important issue. One approach is to use an oxygen stage with peroxide. The installation cost is approximately $1 5,OOO/daily ton. There are increasing numbers of bleaching sequences of peroxide and hydrosulfite which are being augmented by this oxygen system. An example of this is the production of light weight coated grades with 100% O W , where a blade metering size press is instaiied.

Peroxide, hydrosulfite or FAS bleaching can all be undertaken at 12-15% consistency at 70 deg C for about an hour (4). Wood containing finishes (OW, OMG) may benefit an additional 2 points by sequential Peroxide - FAS sequences (6). Operating costs are about $23/ddy ton However, the approximately $500,000 in capital cost for a two stage bleach sequence for a 300 TPD system requires a cost/risk review. The impact on brightness can be offset by addition of a dewatering device ahead of the peroxide retention tower so that a high consistency bleach stage (20%) is achieved.

E a two stage sequence is justified, although there is no significant capital impact, the order of bleach addition can have a significant impact on brightness in a two stage sequence - FAS followed by peroxide has about 6 points higher brightness than the reverse sequence (7).

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Ledger grades

Pre-consumer

Collection and sorting system typically dictate the level of process needs for pre-consumer furnishes. The base requirement is peroxide followed by in some cases FAS. FAS use has grown since it is effective in color stripping many of the dyes typically found in colored printed grades which are prevelant even with the most diligent quality control. However even FAS is not effective on dark, deep shades like blues and reds.

There is a tradeoff between the grade of wastepaper used and the capital cost of the system to be installed. The "cleaner" the wastepaper, the lower the capital requirement, however the cleaner wastepaper comes to the user at a cost premium based on supply and demand. At present, hard white shavings(PSI-No.30), a pre-consumer grade, is averaging $530/ton, while sorted white ledger (pSI-No.40), a post consumer grade is averaging $380/ton.

One approach is to install a simple system (for example a pulping and screening system) and then augmenting it in phases(9). This would typically use a pre-consumer waste such as hard white shavings (PSI-N0.30). In a facility averaging 120,000 TPY and requiring a 40% recycled content that would correspond to a recycled fiber plant size of about 150 TPD. Initially, an investment of $10 million should be adequate to install a system capable of processing this pre-consumer type of waste. This would require typically only some simple unit operations such as a pulper, cleaners and screens together with warehouse and process buildings. Generally an economic evaluation of this phased approach of adding equipment with a corresponding decrease in wastepaper fbmish, should be conducted.

For simple systems such as this, bleaching costs - capital and operating costs - are minimal. Today, non-chlorine sequences - peroxide and hydrosulfite - are preferred. With most pre- consumer grades this translates to a capital expense of about $20,0OO/daily ton for a peroxide system. Generally it is also recommended to conceive of the bleach system as a phased process similar to the deink system so that additional systems may be added to allow lower quality waste to be processed by the system. For example initially only a tower for an hour retention time at 12% consistency may be installed. The next phase would allow addition of a dewatering system to allow bleaching at 30% and subsequently a phase where dispersion is added.

It is important that in the conceptual phase of the planning this type of approach is identified so that the building and systems are designed allowing future phases to be implemented cost effectively. The impact of scope on project costs is discussed below.

Post consumer mades

The most commonly targeted wastepaper for recycled fiber use by writing and printing producers is computer printout (CPO) paper. However, due the large demand for this wastepaper grade it is often difficult to procure and when available is high priced (laser free - $450/ton; laser containing - $390/ton). The requirements for a system using CPO are very similar to those for pre-consumer

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grades with the addition of a few additional unit operations which are dependent on the type of printing on the CPO. The more complex and expensive system design is to handle laser printed CPO. This will typically require flotation and dispersion in the system. As the quality of the CPO decreases due to less complete sorting, the requirement for additional unit operations increases - the addition of lightweight contaminant removal cleaners, fine slotted screens etc. In addition, the need to handle a larger amount of rejected material has to be addressed and consequently permitting issues for landfill and wastewater treatment.

Bleach sequences follow the trends that have been discussed in the previous section; HydrosuifiteEAS or peroxide. With more contaminated, lower cost wastepaper however, the impact on process control is significant. Waste paper quality by necessity is poorer and the system must handle these variations. Retention times, chemical dosage rates, consistency require close control and capital must be allocated to control these factors. A general rule is that for each control loop the total installed costs are about $20,000. Good control however cannot cure poor engineering, so if pumps are not sized right, piping is poorly designed or control valves are incorrectly located, the desired brightness gains developed on the bench or pilot plant will not be achieved. An example is that of an existing chest which has been converted to the retention of 12% peroxide treated dispersed stock, without modification resulting in dead stock, inadequate retention time and almost 100% residual peroxide.

Water management is also critical in achieving the brightness displayed in pilot planthench scale tests. Engineering in tightly closed water mills must not allow residual oxidizing components to destroy a reducing bleach chemical and vice versa.

Mixed ofiTce waste

Increasingly, customers have wanted to use the lowest cost wastepaper on the market - mixed office waste, which can be as low as $90/ton. The problems associated with using mixed office waste to produce an acceptabie quaiity puip are due to the type and ievei of contaminants that it typically contains. Some commonly found objectionable materials include:

0 Browngrades 0 Newsprint and wood-containing grades 0 Non-fibrous materials

In order to incorporate this type of waste into a fine paper sheet, additional unit operations must be included in a pre-consumer waste deink process. This negatively impacts both operating and capital costs. Some examples of costs necessary to handle mixed waste and their impact include:

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System Impact cost Sort system Capital cost $10,00O/ton

Deink systemB1eaching Additional $1 00,00O/ton Operating cost $SO/ton

Capital cost Additional $3 O/ton Operating cost

Capital cost Additional $1 O/ton Operating cost

Rejects Additional $30,00O/ton

A wastepaper supplier can handle the sorting stage and, at a price, deliver a wastepaper product . within one of the PSI classifications ( e.g. PSI 40 - sorted white ledger). In general this reduces both operating and capital costs but this should be evaluated within the context of the company philosophy (Should we be in the wastepaper collection business? How important is quality control?) and overall economics. To maintain quality, many deinked newsprint producers who use wastepaper from municipal collection programs, have found it advisable to install sort facilities.

) Multiple stage bleach sequences are generally required for these systems. The same chemicals discussed earlier have been utilized in these systems. An option is the use of chlorine dioxide, if the deink system is integrated within an existing bleached grades complex and has the availability of chlorine dioxide. With chlorine dioxide the range of chromophores decolorised are comparable to all other oxidizing agents at a much lower operating cost. A multiple stage bleach sequence may include oxidative and reductive steps and can also include oxygen and/or ozone. An example is OZPF (oxygen, ozone, peroxide, FAS). The impact of higher wastepaper prices is that "contaminants" in the deink system and these sequences become a necessity rather than an option. The impact on the operating cost is often over $SO/ton which has to be passed on to either the customer or absorbed by the mill. Integrated mills often have a better ability to handle some of these costs than market deinked mills. The latter typically may not have pass through costs incorporated in the off-take contracts or may have a price structure pegged to the cost of virgin pulp.

Ozone has gained popularity in the processing of mixed office waste due to its strong oxidizing ability and its "environmentally-fiiendly" posture (8). In a multi-stage sequence ozone appears to provide both strength and optical benefits. Manufacturers of ozone are using a similar approach to the producers of PCC with a self-financed "over the fence'' fackty. A facility fee is incorporated in the cost of ozone to cover this and their operating cost The manufacturing facility costs are borne by the ozone supplier due to the proprietary nature of the facility design and gas generation. Operating costs are typically associated with oxygen costs, electricity and a facility fee averaging $30/ton of end product .

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The benefits on brightness of pressurized peroxide have not been found to be sigrzlficant over un- pressurized method, however the benefits of capital costs are that the size of the retention tower is halved fi-om about two hours to one hour.

)

There are many reports in the literature of $/Delta brightness point for a particular chemical bleach /addition rate or multistage sequence (lo), which may not provide the proper analysis. Using the Sharpe Lowe index an objective assessment can be made on the most cost effective sequence of Chlorine dioxide, hydrosulfite, FAS, peroxide, oxygen and ozone.

- Yield

Bleaching with the types of oxidative and reductive agents discussed does not negatively impact yield. The exception is bleached OCC wherein the lignin remaining in the pulp is removed. The economics of a deink facility is based on the yield from the recycled fiber facility. Typically for pre-consumer grades a yield of over 98% is possible. For post consumer grades beginning with CPO, the yield depends on the quality control and the sorting operation. Higher quality post consumer grades such as CPO may have a yield of 95% if relatively clean and free of laser printing, but may be as low as 90% if contaminated. Mixed ledger grades (colored and white) use will result in yields of 80% or lower, with mixed waste usage resulting in yields in the high 60's and low 70's. The major factor in determining yield in all other grades is contaminant content of the wastepaper, the quality required and the system design. For example, quality specifications for wastepaper quality may be the following:

Target Not to Exceed I Wastepaper YO YO

Coated Paper 10 20 Colored Paper 15 20

White Ledger 60 100

Unbleached 0 2 NewsDirectory 0

Contaminants Non-impacts 0 40 Stickies 0 1 Ash 10 10

Increasingly, the deinked pulp quality specifications have become tighter with requirements for paper machine runnability as well as brightness, shade and dirt count.

Avvroach

An approach to analyzing a particular deink facility design including the bleaching sequence appropriate is shown below:

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Recycled fiber usage - project approach

Raw material Sourcing by grade Transportation Qualitylcost

1 Requirementlcapabllities Mill location

Grade mix Market needs Tonnage Location 1 I

Large Smiall Multiple vs. single

Permitting Needs

development Pro forma Sensitivity

analysis

Operating cost Capital cost Costlrisk Quality

I rrocess aesign

General arrangement Layout of small vs large

I

E o f M a M t d e I I I 1 MIU location analysk

Pulp mill impaci UtUitieshpart Papermachine impact Emuent system impart

estimate TIC for each option I 1 Schedule r I I I

1

I t i o n I

To following project phases Le. conceptual, d e t d etc.

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L d

c-

Options analysis Operating cost Capital cost Costlrisk Quality Raw material I

Options analysis Bleaching *Sequences *Stages *Operating cost

Capital cost Costlrisk Quality

4 6 harpellowe *Brightness #)Strength

Raw material *Brown 4,W hite *Colored

Options analysis Deink plant . Unit operations

*Pulping *Ink removallmodification *Contaminant removal .Clarification *Rejects handling

*Operating cost Capitial cost Costlirisk Qualiity Raw material

Bleaching of Wastepaper

Recycled fiber usage - project approach Options analysis

Page 10

Project Execution

In general, the choice of a particular equipment supplier for a particular unit operation, does not have as much impact on the project cost as the overall operations and maintenance philosophy and the number of unit operations. The impact on total project costs of different factors during the life of the project is shown in Fig 1. It is particularly important that for a deink project the scope in both the deink plant and the bleaching areas are defined with all project participants involved in the early stages of the project. For example, if as suggested above, a phased approach is to be used this must be identified early.

A typical spending curve/schedule for a deink project is shown in Fig 2. If a pre-engineered design is used, the customer can save time and money in preliminary investigations and in preparing an estimate (approximately 0.3-1% of TIC) and this will have the potential of saving additional engineering costs in the detail design phase (average 8% of total direct cost). On the basis of past projects a potential saving of 20-25% is possible in engineering costs when a pre-engineered plant is used.

A bigger impact of using a pre-engineering approach will be the savings in time, with construction beginning, in some cases, six months earlier. This assumes that the permitting required has been addressed. Cash flow can thus positively impact interest payments -- an impact that may be significant particularly if project financing has been used.

Financial impacts

Typically chemical costs are about 15-20% of the operating costs in a mixed office waste type of facility as show below. Of this chemical costs bleach costs are about 75%. In contrast the largest variable cost is that of the wastepaper - about 46% of the operating cost.

Wastepaper Chemicals Utilities Maintenance Labor Other - Sludge, water etc.

46 18 13 3 6 14

A typical debt coverage ratio for such a facility averages 2.5. A sensitivity that is often run after a financial model is constructed is the impact of variable costs (Wastepaper, chemicals, disposal, energy) rising by 15%. The impact is that the average debt coverage ratio drops to about 2.3. So the impact of chemical price increases are thus relatively small. If however the deink pulp price (if a market pulp producer or if accounting requires the deink facility to be a profit center) decreased by 15% the average debt service coverage ratio drops to below 1.7.

i

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References

1. Nguyen, X.T. U.S. Patent No. 5,302,244 2. Haywood, S.T. Pulp & Paper Feb. 1995 3. Nguyen, X.T., ShaS, A., Earl P.F., Earner, R.J. Progress in Paper Recycling May 1993

Bisner, H.M., Campbell, W.T., McKean W.T. Progress in Paper Recycling Nov. 1993 4. Heimburger, S.A. & Meng,T. Pulp & Paper Jan 1992 5. Sharpe, P.E., Lowe, R.W. TAPPI Pulping Conference 1993 6. Ortner, H. and Fischer S., TAPPI Pulping Conference 1990 7. Berger, M., Meier, J., and Eul W., Pacific Paper Expo 1990 8. Van Lierop, B., Liebergott, N. Journal of Pulp & Paper Science Vol20, No.7 1994 9. Iyengar, R.S. Wastepaper III Proceedings, Chicago 1992 10. Kogan, J., Perkins, A., Muguet, M., TAPPI Recycling Symposium 1995

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