The Converts: North American Mills Make the Switch to ECF Pulp Production
by Papermaker Staff and Douglas C. Pryke
Canadian Papermaker *
If the development in the last five years is any indication, elemental chlorine-free (ECF) pulp is here to stay - at least in North America.
ECF is proving to be the fastest growing bleaching method in the North. America bleached chemical pulp market. Some 42 bleaching lines in the US and Canada have replacedchlorine with chlorine dioxide, says Tony Johnson, technical director, Simons Engineering of Appleton, Wis. This year alone. North American mills are estimated to,produce more than 15.2 million tonnes of ECF pulp. In Canada, 60% of all bleached chemical pulp production is ECF; in the US, that figure is about 30 per cent.
Of the kraft mills that bleach pulp, about 25% of the Canadian mills and 21% of the US mills have installed an oxygen delignification system. And while one wouldn't expect so many different bleaching sequences, in fact there are. Some 38 different bleaching sequences are being used in the 52 bleaching lines in Canada. In the United States, there are 115 sequences and 164 lines.
The Avenor Experience
Avenor Inc.'s mill in Dryden, Ont., is one of the latest to convert to ECF pulp production.
The mill produces 300,000 tpy of uncoated woodfree papers used for copying, envelopes, forms bond, and offset printing. Its production also includes 150,000 ADtpy of bleached market softwood pulp, which is sold mainly to US lightweight coated paper producers.
Dryden operates a single-fibre line with a Kamyr continuous digester operating with wash-modified continuous cooking. The Kappa number of the pulp entering the bleach plant is 28. The mill does not have an oxygen delignification installation because the available savings did not justify the cost of a retrofit. Current and future environmental limits are achievable without oxygen delignification, says Mike Ford, manager of technical services at Dryden.
Quite simply, the mill converted to ECF pulp production because of the demand from US customers and the projected AOX and chloroform regulation limits in Ontario.
Although the mill switched over to ECF pulp production less than a year ago, it has already achieved significant environmental benefits, Ford says. The AOX in final treated effluent fell from 2.8 kg/air-dry ton (ADt) to between 0.3-0.4 kg/ADt. Chloroform levels in the mill effluent are currently below those of the local drinking water, Ford says.
The Avenor mill currently uses a bleaching sequence of DEopDED. Pulp quality is stable and there are no problems associated with the ECF conversion and machine runnability, says Ford. Boise Cascade
Perhaps the most important question to ask about converting to ECF pulp production is whether it affects paper machine performance.
Pulp mill day supervisor Dave Gallagher says the conversion at Boise Cascade's Wallula, Wash. mill, has not had any effect on the market pulp it ships to customers, or on the bleached pulp used to produce fine paper that is converted to xerographic, offset, and forms bond grades.
Boise Cascade's Wallula mill produces 825 ADtpd of bleached softwood pulp, 350 ADtpd of which is market pulp. The primary destination of the market pulp is the US, but some of it is destined for Europe.
The fibre line consists of a Kamyr two-vessel vapor phase digester and M&D digester for sawdust pulp, without oxygen delignification. The kappa number of the pulp entering the bleach plant is between 27 and 29 on average. The mill's bleaching sequence is DEopDEpD.
Before the mill converted to ECF pulp production, the paper machine group expressed concerns about adverse effects on machine performance and paper quality. Although the pulp group tried to allay the paper group's concerns, it wasn't until after the conversion that doubts disappeared.
Indeed, the ECF pulp met standard brightness requirements and was even able to produce a higher brightness that a customer requested. The paper machine set monthly production records with ECF pulp.
Gallagher says that one of the keys to Boise's success with ECF pulp was the extra training sessions given to operators. Along with giving them a better understanding of the pulp bleaching process, the sessions also fostered a sense of ownership and responsibility.
Gallagher says that ECF bleaching costs were comparable to 60% chlorine dioxide substitution costs. At the same time, the mill noted that adsorbable organic halides (AOX) and color decreased with 100% substitution compared to 60% chlorine dioxide substitution. The mill had average AOX loadings in the range of 0.3-0.5 kg/ADt, Gallagher says.
Bob Cicale, manager of pulp manufacturing for Champion International Corp.'s Canton, NC mill, said that ECF pulp production has been an integral component in helping his mill meet not only state environmental regulations, but also the Environmental Protection Agency's (EPA) proposed "Cluster Rules."
Champion's mill at Canton faced serious water problems in the late 1980s regarding the impact of the mill's wastewater discharge on the Pigeon River, which flows near the mill and into Tennessee. The relationship between North Carolina, Tennessee and the mill became strained as the color of the water became a major source of concern.
Champion worked with the state and federal regulatory agencies to resolve the wastewater problem, which threatened the mill's water permits. The result was a modernization project at the mill whose goal of decreasing the environmental impact on the Pigeon River depended to a large extent on implementing ECF technology.
Canton is a large mill, producing about 1,300 ADtpd of bleached kraft pulp, about 680 tpd of uncoated free sheet printing and writing papers, and some 680 tpd of paperboard. It has 18 conventional batch digesters followed by oxygen delignification on its hardwood and softwood fibre lines. Champion installed the oxygen delignification systems to decrease the color impact of effluent on the Pigeon River, along with achieving lower BOD, COD, and AOX levels.
Following oxygen delignification, the kappa number of the pulp entering the bleach plant is 17 for softwood and 11 for hardwood. The ECF bleaching sequence is DEoD, with the capability of using hydrogen peroxide in the extraction stages. In practice, the mill uses hydrogen peroxide for softwood bleaching. The mill produces softwood and hardwood with 86 ISO brightness.
Cicale says Champion has achieved major environmental results thanks to the modernization project and the implementation of ECF pulp bleaching. Through the use of oxygen delignification, more efficient pulp washing, spill control, and ECF bleaching, the mill has reduced its effluent flow to less than 110 million litres/day from 170 million litres/day. In addition, color has dropped to as low as 30 kg/t from 120 kg/t, COD to 15 kg/t from 40 kg/t, and AOX was down to 0.16 kg/t.
Champion's Canton mill will also be the demonstration site this year of new technology designed to virtually eliminate bleach plant effluent. The Bleach Effluent Recycle (BFR) process was designed by Champion's research and development personnel in West Nyack, NY, and Pensacola, Fla., and is the next step in closing up the pulp mill.
For Northwood Pulp & Timber Ltd., Prince George, BC, which produces 1,500 ADtpd of bleached kraft pulp, the driving force behind the mill's switch to ECF bleaching was its European customers.
The mill has two Kamyr continuous digesters and two, five-stage bleach plants. The Kamyr continuous digesters produce unbleached pulp at 27 Kappa number. The two identical DEopDEpD bleach plants produce 90 ISO brightness pulp, of which more than 65% is converted to printing and writing papers. About 40% of the mill's production is sold in North America, 30% to Europe, and the balance to Asia.
One European customer requested that Northwood ship a high brightness pulp with an AOX/ADt level of 0.4 kg. In addition, the customer was actually wondering whether it was possible for the mill to deliver pulp with an AOX level of 0.30 kg/ADt, says James Gordon, process engineer.
In response to this request the mill initiated a trial in which it made a 100% substitution of chlorine dioxide for chlorine, says Gordon.
As a result the mill achieved the low AOX levels by lowering the first stage Kappa factor to 0.11-0.14 and adding 0.45% hydrogen peroxide in the Eop stages. By lowering the Kappa factor to 0.06-0.08 levels, increasing the hydrogen peroxide in the Eop stages to I% on the pulp, and raising the Eop temperature to 86 Celsius from 77 Celsius, the mill was able to decrease AOX levels to 0.3kg/ADt. Bleaching costs rose 15% to achieve these low AOX, 90 ISO brightness pulps.The Future
If ECF pulps virtually
eliminate dioxins and furans in mill effluent, reduce AOX levels, and
help mills maintain quality standards for their pulp, shouldn't mills
be looking to move into totally chlorine-free pulps so that they can achieve
even greater environmental benefits? "No," according to the four mill
representatives cited in this article. They believe that there are no
significant additional environmental benefits to be gained from TCF pulps
and the attendant costs are higher.
Supplement: Trends in World Bleached Chemical Pulp Production: 1990-1995
Elemental chlorine-free (ECF) pulp bleached with chlorine dioxide is now and should continue to be the fastest growing sector of the world bleached chemical pulp (BCP) market, according to a survey by the Alliance for Environmental Technology (AET), based in both Washington, DC and Erin, Ont.
By the end of 1995, ECF pulp production is expected to surpass 28.5 million tpy, which means that it will have a 40% share of the world BCP market. The United States is the largest producer and user of ECF pulp. Although much has been written about totally chlorine-free (TCF) pulps, which are pulps bleached without chlorine or chlorine dioxide, their penetration of the marketplace has been confined mainly to northern Europe. TCF pulp production accounts for only seven per cent of all world markets. TCF pulp production will be about five million tonnes in 1995, according to the latest figures available to the AET. Of this amount, Scandinavian mills produce more than 60 per cent. Although the demand for TCF pulp and paper products is greatest in northern Europe, the demand for TCF pulps outside this area has been less significant.
The demand for ECF pulps has risen considerably in the five-year period studied by the AET, particularly in North America. In the United States, regulatory proposals such as the EPA Cluster Rules favor the adoption of ECF pulp production. The same holds true for the provinces of Ontario and Quebec, where current regulations encourage the conversion to ECF pulp production.
In British Columbia, where the provincial government has implemented a "Zero AOX" discharge requirement for 2002, the pulp bleaching picture remains unclear. The ministry of the environment recently indicated its willingness to reconsider the "total ban on chlorine pulp production," in light of recent scientific research.
The question of whether the market will choose ECF or TCF pulp production is not easy to answer. Although the market should ultimately prevail in the selection of either ECF or TCF pulp production, the two methods are currently vying for validity.
In North America, the majority of mills have selected ECF pulp production as a mainstay because the capital investment needed to retrofit an existing mill for totally chlorine-free production may be prohibitively high and may not achieve any significant additional environmental benefit.