The team and the technology defy the skeptics

Transcription

1 w ELL - THEY VE DONE rr! The Millar Western group has many exciting projects to its credit, and the completion of its Leroeffluent pulp mill in Meadow Lake, Saskatchewan, is another success story, The mill stands out like a ship in the rolling landscape as one approaches Meadow Lake, a small farming coinniunity north-west of Saskatoon. From the start, our intention was to be a visible part of the community, says John Eccleston, mill manager. Consulting with local community and environmental groups has been, and will continue to be, an important element in Millar Western s business process. The new niili site was chosen because it is close to extensive, Iiigliquality pulpwood. Road and rail access was good, there were good connections with power and natural gas supplies, and the area had a willing and able local labor force. The original plan back in 1989 was to build the tonnes/ycar (t/y) alkaline peroxide/bleached cheniithermomechanical pdp(api /BCTMP) mill with an effluent stream going out to the Beaver River. However, as the company looked at the technology in different ways, they scrapped the design that included a biological treatment system, and opted for a closedloop, zerclemuent system. So, in mid-january 1992, the mill started up, producing 100% aspen, chlorine-free APP/BCTMP - a pioneering endeavor which is proudly explained by the Millar Western team. OUlLD ON SUCCESS It is about four years since Millar Western entered the pulp business with a new APP/BCTMP pulp mill in Whitecourt, Aka. Before then, the 73-year old company had a long history in construction, lumber and chemicals. 2 g i/& /Bf WOW LAKE S ZERO-EFFLUENT IS GOOD NEWS FOR MILM WESTERN The team and the technology defy the skeptics BY SUSAN STEVENSON, MANAGING EDITOR The pulping process used at Wiitecourt was a patented alkaline bleaching system developed by Scott Paper Co., Philadelphia, PA. The process is based on a cycle of high compression chip squeezing using Hymac (4: 1 compression ratio) plug screw feeders, followed by impregnation of the fibre with chernicals. This cycle is repeated in three subsequent stages using different chemical combinations, and results in a largely destructured chip, free of debris, cheniically treated and ready for the refining process. The company has learned a lot about the process at Whitecourt according to Joe Costantino, corporate technical director, operations and projects. What we ve done at Meadow Lake is take the successes we ve had at Whitecourt and build on them. We learned from our experiences there, duplicated the best elements and made improvements wherever we could. he savs. A major part of the improvctnent is in the area of the zero effluent system and how that is achieved. The process for Meadow Lake was developed jointly by Millar Western and NLK-Consultants, the consulting engineers for the new mill and for the Whitecourt operation. According to Millar Western president Mac Millar, There isn t any magic involved in our zero-effluent process. We just looked at things a little differently. We took proven technology and put it together in a new configuration. The various options that were available for zero liquid effluent for Meadow Lake are outlined in a paper given by Doug Frornson, NLK, at the Technical Association of the Australian and New Zealand Pulp and Paper Industry (Appita) meetings in April These included biological treatment, evaporation, freeze crystallization - and evap oration was the route chosen. The final design was based on extensive laborato- PULP & PAPER CANADA 93:lO (1992) 13

2 ry testing, and several months of pilot plant results from Whitecourt. In brief. the total pulp mill effluent is collected, suspended solids are removed and the efflyent evaporated in a train of the largest mechanical vapor recompression (MVR) evaporators in the world. Distillate from the evaporation is treated to remove organics and then recycled to the CTMP mill. Concentrate from evaporation is oxidized in a chemical recovery boiler. While the overall Meadow Lake water purification and recycle system is unique, the individual unit operations are all well proven in the pulp and paper industry. Zeroeffluent is a fasiinating aspect of the Meadow Lake mill. However, making pulp is the name of the game - and Millar Western does that very well. Eccleston and Bob Leslie, operations manager, commented that startup went better than they could have hoped. There was surprising little offgrade pulp produced, and as Leslie put it. There were no major surprises - mechanically, everything has run well. It is just a learning curve - a matter of adjusting chemical addition rate, of the steam plant getting used to the demands of the pulp mill. The adjustment is simply the interaction of the process, water recovery and the newly trained operators. Eccleston made special mention of the MOPS mill optimization system installed at Meadow Lake. Its been a godsend, he commented. All facets of a problem can be interrelated on a screen, with history, present data, control loops, all available to help in the diagnosis of a particular problem. And no-one is going to say that a mill start up has no GALORE The mill uses aspen for its fibre source, producing a high-brightness, high-yield pulp, in common with many of the new Alberta mills. Millar Western is supplied with timber under the Nor- Sask Forest Management License Agreement. Mistik Management Ltd., (Mistik is a Cree word for tree ), is the company created to manage the forest land base. Mistik uses an integrated resource management approach in conducting its forest operations, and involves local communities directly in forest management planning. About half of 1% of the productive land base will be harvested annually to supply both the Millar Western pulp mill and the nearby NorSask sawmill. An advisory committee has been established to include all the interested local stakeholders. Logged aspen is trucked to the mill, debarked, chipped on-site, and screened. Chips are then conveyed to a storage bin, and from there into the mill. Because start-up went remarkably well, chip demand was higher than expected in the spring months. A watchful eye is kept on the wood supply when the roads to the mill are not suitable for logging trucks during spring thaw. The mill has two pulping lines - one for tissue and towelling, and the other for printing and writing papers. In the pretreatment, chips are moved to an atmospheric pre-steaming bin, stored for 45 minutes at 90 to 95 C. then washed of debris and moved on to the three-stage impregnation system mentioned earlier. The plug screw feeders used at Meadow Lake are larger than those used at Whitecourt both in volume and in horsepower, providing better chemical action on the fibres. Next in the line are the primary hp, 64-in.diameter Hymac single-disc refiners. Line one features a single primary refiner, while line two has dual primary refiners, to refine the pulp before it reaches the wash chest. Another process improvement learned from Whitecourt experience is the addition at Meadow Lake of interstage washing on Hymac/Thune presses. After washing, the pulp is refined in the secondary refiners to the desired pulp freeness. Meadow Lake refiners all run at atmospheric pressure, since this improves the stability of residiual hydrogen peroxide in the the pulp and provides better bleaching eficiencies in the refiners. Pulp cleaning and screening comes next - Hooper screening systems, and five-stage Celleco cleaning. In the parallel bleaching lines, a solution of hydrogen peroxide and sodium hydroxide is added to a mixer ahead of the first bleaching tower, for two-hour retention at 60 to 70 C at 10% consistency. From the bleaching towers, post-bleach pulp washing follows, and then on to Sunds Defibrator twin-roll presses for final dewatering. The pulp is then flash dried in a Flakt two-stage tower to a moisture content of about 14%. In the cooling stage, the pulp temperature is reduced to 30 C to minimize brightness reversion. Finishing is on two Sunds Defibrator lines, with slab presses producing 250- kg bales, and bale presses where the pulp is tied, labelled, and packed in 16 PULP & PAPER CANADA 93:lO (1992)

3 units of four bales, ready for shipping. The Meadow Lake pulp was clearly marked "chlorine-free - Made in Canada" the day that PULP & PAPER CANADA was there. The highly successful marketing of the pulp around the world by the Millar Western team means the APP/BCTMP is a great ambassador for Canadian forest products abroad. The successful production of the pulp is contingent on a number of factors. Chief among them is the quality of the water used in the pulping process - which brings us back to the zeroeffluent system. OATER RECOVERY Process water for the mill comes from Meadow Lake which is shallow - and it brings with it high levels of organic material. When this water was used for flushing lines and chests in the early commissioning stages, it was of adequate quality. Its use as make up water in the mill is also satisfactory, after some primary clarification. Further processing of the lake water is required to meet boiler feed-water standards. So, after clarification, the lake water goes to dual media filters, then to a reverse osmosis membrane Zeolite softeners are used to polish the water before de-aeration and subsequent use in the boiler. The mill has a 1.irgest train of the largest MVR evaporators in the world. The three KCC units are each 100 feet high and 24 feet in diameter at the base. Inside each vessel are 40 miles of stainless steel tubes. Scaling in these tubes has caused some plugging, not unexpectedly. However, it is not as bad as some critics had predicted, and with the investigative laboratory on-site, (see box), a close eye is kept on the matter. Centrifugal compressors, driven by 3500-lip electrical motors, are supplied by Roots. These remarkable units are checked regularly - a wise precaution when turbine blades are rotating at 3200 rpm. The mill's total waste water flow containing up to 2% dissolved solids and minimal suspended solids, is directed to these evaporators. A portion of the distillate is recycled hot directly to the pulp mill. The balance is cooled and biologically stabilized before it is recycled. The clean fraction of the distillate, or mids as it is known, is about 90% of the total. The other 10%. described as tops, is directed to a steam stripping column for the removal of volatile wood organics, chiefly methanol. The evaporation residue is a slurry of about equal parts of organic and inorganic material, at 35% solids. This move^ on to two RCC concentrators High level chemistry Most mills have a testing lab on-site. The Meadow Lake mill has one too. The difference is that it is more than a pulp testing lab. Because of the need to know as much as possible about the water recovery and the many chemical constituents in pulp mill waste water, it is a major research laboratory. Senior mill chemist Dr. Mark Hoddenbagh comments that "because our mill is a closed system, we face some special challenges. With no effluent going out, the chemicals in the process have the opportunity to build up and cause problems. We have to monitor things very closely, and so we're using some very specialized equipment, the kind you might only expect to find in university or research labs." There is a gas chromatograph coupled to a mas spectrometer, allowing the mill to identify and quantify up to different organic compounds. This has opened some very interesting avenues for research as well as for day-today monitoring of process streams and for troubleshooting. The ion chromatograph measures anionic species and has helped to track chlorides, sulphates and carbonates - leading to work on corrosion and scaling. There is an atomic absorption spectrophotometer, a Fourier transform infra red spectrophotometer for tracking compounds and for identifying unknown substances. For a mill in northern Saskatchewan, access to this kind of equipment, as well as more routine units, provides an immediate response to any problem that might arise. It is all part of Millar Western's innovative approach to business. Swan Stevenson which bring the solids to 70% concentration, prior to incineration. Approximately 95% of the energy required for evaporation is recovered, making the MVR evaporation very costeffective. In winter, waste water comes directly from the pulp mill at about 40"C, the feed pre-heaters take the water to 90 C while the mids lose about 40 C. During the summer, the system becomes energy-rich, so the waste water is diverted to the ponds to cool off before coming into the feed pre-heater system. Heat balancing from season to season is proving a challenge. The heart of the water storage system is in the ponds. These lie on the east side of the mill site, and are not visible from the road that passes the mill. The system, known affectionately as Serving the Pulp and Paper Industry NLK Consultants Inc. congr;itul:itcs Millar Western Pulp Ltd. on the successful completion of the blcaclicd chcini-tliermoiiicchatiical pulp inill at llieadow Lake, Sask;itclicw;in. NLK is proud to have been involved in the project; providing services for the feasibility study, detail design enginecring, procurement, construction ni;in;igement and start-up assistance. NLK has an exclusive agreement with Millar Western Pulp for commercialization of the Meadow Lxkc zero liquid effluent technology. NLK Consultants Inc. Vancouver, B C,I loiit real, PQ Edmontoii, AB *rei: (~60.1) IX (1)(514) rei: (i)(403) F~x: (l)(h04) (1)(514) I.'~x: (1)(403) FXY: Seattlr. 1WI Tcl: (1)(206) Fax (1)(206) Greeiivillr, SC Tcl: (1)(803) ';~: (1)(80.3) Additiorinl 0ficr.c England: l.ondon, hliinchcstcr Joirr t f4iituw 0jfirr.Y: S pili n, Sxudi Arabia, I ndonesi;i, Australia lieprrscii tritivrs: 1 pi 11, Argcn t i na, Iran PULP & PAPER CANADA 93:lO (1992) 19

4 water world by the Millar Western team, consists of five major ponds which hold a total of 185 OOO ins of water. Tim Evans, technical superintendent, explained that two settling ponds and one water recovery pond (WRP) hold all the waste water. The distillate equalization pond and the water storage reservoir (WSR) hold all the clean water. The WRP and the WSR are the major storage basins that fluctuate in level according to pulp mill production rates and evaporator flow rates. They have level scnsing equipment that can be monitored or trended on thc Bailey millwide information system. According to Evans, The pond system allows maximum flexibility of operation. Having the large storage basin for waste water gives the pulp mill two days of run time with the water plant completely shut down. Eccleston told PULP & PAPER CANADA that to replace the small amount of water lost to h e atmosphere in process steam and evaporation from the ponds, make up water runs at about 1800 ins daily. This is extremely low compared to standard BCTMP and kraft mills. If this make up water is not available from the lake, tlie pulp mill can run for 20 days from clean water inventory in the WSR. Also, if there is a recovery boiler outage for any reason,< the pulp mill and evaporators can continue to run for 30 days without being affected. Settleable solids drop out of solution in the settling ponds which are concrete lined to make dredging simpler. MONTREAL TORONTO VANCOUVER Aquatic Toxicity Testing Trout Ce rio da p h n ia 0 Daphnia Fathead Minnow Microtox Algae Environmental Services Plant Compliance Operational Permit Audits Emissions Monitoring Impact Assessments Industrial Hygiene Site Characterizations Effluent Decommissioning Characterization Accredited Laboratories 121 Blvd. Hymus, Pointe Claire, Quebec H9R 1E6 Tel.: (514) Fax: (514) B.C. Tel.: (604) Fax: (604) I The WRP is strictly a holding basin, clay-lined to prevent seepage into the local ground water system. The distillate equalization pond is where the wood organics are consumed by biological action, and finally the WSR holds all the clean distilled water for reuse at the mill. It makes an excellent cup of coffcc, quite apart from anything else! The recovery boiler is another first for Millar Western. It is said to be the smallest of its kind in the world, designed by Babcock 8c Wilcox, and proven effective in similar ser- vice. It has a firing rate of 175 t/d of solids and a capacity of 236 t/d solids. Steam production is 25 t/h. The smelt runs out of the bottom through a spout onto a conveyor with ingot pans. The smelt solidifies quickly and sodium carbonate ingots move on tlie conveyor to drop in a small pile outside the back of the mill along side a bunker that stores ash from the flue gases collected by the elcctrostatic precipitator. The company is deciding whether to market the ingots, or to build a recaust plant to convert the sodium carbonate back into sodium hydroxide. With the rising price of caustic, this latter option is looking good. In present world markets, making pulp is one story, selling it is another. The Millar Western team have made a particular effort to know all the capabilities of the Meadow Lake product - and they sell it very carefully. The company s marketing group works closely with the pulp makers and with the paper makers, making sure that customers are provided with the type of product and technical services they need. Says Mac Millar, Our product development and technical sales approach has paid off in dollars and in sales volume. I think our customers came for the price and stayed for the quality. They re finding 100% aspen really works. The enthusiasm and energy throughout the Millar Western company is remarkable. The sense of belonging to an exciting, successful team appears to lie very strong. Peter Knorr, executive vice president, commented that one of the prerequisites of employees is that you don t mind working with them on a problem at two in the morning. Considering the progress of the company over the past five years, watch its activities - with NLK Canada it is coniinercializing the zero effluent technology on a royalty basis. Millar Western is an industry leader. P&PC 20 - PULP & PAPER CANADA 93:lO (1992)

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