The next few months will be a time of toil and worry, but if all goes to plan, ultimately a time of pride and satisfaction for one of the biggest pulp producers in Latin America (and therefore the world). Chile's Celulosa Arauco y Constitución (Arauco) is starting to commission its 700,000 tonne/yr greenfield market pulp mill in the country's Valdivia province.
The new mill is located near San Jose de la Mariquina, 60 km northeast of Valdivia city. Arauco is making a total investment of $1,200 million in the project, which will boost its total pulp capacity to more than 2.2 million tonnes/yr. Around $300 million of this sum has gone on securing over 100,000 ha of plantations to supply raw material to the mill. The fiber line will be fed with 60% radiata pine and 40% eucalyptus. The mill will run the pine and eucalyptus in campaigns.
Groundbreaking work began in December 2001 and in February 2002 the company announced that it had awarded Metso Paper the contract for a complete pulp mill fiber line and pulp drying system, from cooking through baling.
By May 2002, Arauco had pulled together a 10-strong team of equipment and service suppliers for the plant on an EPS (engineering, procurement and supervision) basis. Alongside Metso Paper, other key suppliers include Metso Automation (more than 1,400 Neles control and automated on/off valves), Andritz (responsible for the woodyard and part of the recovery island), Kvaerner (the boilers), MAN (turbo generators) and Alstom (electrical precipitators). Aquaflow is providing the effluent treatment plant while Cellchem supplies the chlorine dioxide plant. Maestranza Iquique, Femesa, Edyce, Fat and Arrigoni are responsible for assembling the site's tanks and metal structures while HE Fiberglass is in charge of the main glass fiber tanks. Valdivia will be self-sufficient in energy and intends to sell its surplus to the Chilean national grid.
The pulping line
Metso Paper's scope of supply includes SuperBatch cooking, OxyTrac oxygen delignification amd TwinRoll washing in all stages of the fiber line. "The chosen technology has been especially designed for production of a high quality end product with minimum environmental impact," explains Alpo Tuomi, VP marketing, Metso Paper Chemical Pulping Business Line.
The cooking process
Arauco chose the SuperBatch-K cooking process for pulp digesting. Launched last year as an extension of SuperBatch displacement batch cooking (which was itself introduced in the late 1980s), this process is designed both to save energy and improve pulp quality. "The K-process enables a very simple tank arrangement," says Tuomi. This, he continues, "Results in both a less expensive installation and a simplified operation. All this is done without sacrificing any of the achieved advantages regarding pulp quality, process flexibility, etc."
Screening and delignification
Valdivia is implementing the Metso DeltaCombi screening system for brownstock screening, which carries out both knotting and fine screening in one unit. "The working principle features a rotating perforated basket for separation of larger particles and debris, and a rotor and slotted basket on top of the screen for separation of shives and smaller impurities," explains Tuomi. All necessary screening is done before the first washing stage.
Oxygen delignification prepares the fibers for final bleaching and can be carried out in a number of ways. At Valdivia, Metso Paper is installing a two-stage OxyTrac delignification process, which removes up to 70% of the remaining lignin after cooking when running softwood. This is achieved by concentrating the use of chemicals to the first stage of the process where they are able to provide a noticeably higher effect per unit added. "By working with a low temperature and higher pressure during the first stage when the alkali concentration is high, negative impacts on the fiber are avoided. The result is high pulp strength and high pulp yield," says Tuomi. Another benefit of efficient lignin removal prior to final bleaching is a reduction in the need for bleaching chemicals and a reduction in effluent from the bleaching process.
Washing, bleaching and re-screening
The pulp will be washed using a new generation of TwinRoll wash presses. These combine displacement washing and pressing in one unit. Traditionally used only in the brown stock area of a fiber line, Metso pioneered the introduction of wash presses into the bleach plant. The supplier says that the TwinRoll washer is able to form an effective barrier between different bleaching stages, enabling very sharp pH changes and further closure of the bleaching process without risk of scaling problems. The latest TwinRoll presses have been modularized to increase production efficiency and improve wear and spare part economy. Based on only two roll diameters, the new generation of presses is designed to enable output of up to 3,000 air-dried tonnes (adt)/day.
The bleaching sequence at Valdivia is D-EO-D-D and both radiata pine and eucalyptus pulps will have a brightness level of 91% ISO.
Bleached pulp will then be screened using four-stage DeltaScreen technology together with cleaners in the approach system of the pulp drying machine. Accepts from the primary stage will be taken straight to the machine chest while the reject flow is fed to following stages. DeltaCombi in quartenary stage configuration features both slot and hole baskets, thus operating also as a police screen for cleaners. Rejects from the quartenary stage screen will then be fed to the cleaners that include both heavy and light reject stages. Heavy reject cleaning comprises two-stage heavy reject cleaners followed by two-stage reverse cleaners for removal of lightweight impurities. The accepts from the first lightweight cleaner will be returned to the feed of the primary stage, while rejects from the final stages of the reject cleaners will be removed from the process.
The wet end
The pulp line's wet end (MB former) will feature a hydraulic-type closed headbox and a fourdrinier with the intention of creating gentle and progressive dewatering and thereby achieving high dryness at the end of the forming table and a good sheet structure for the final product.
The press section will consist of a two-nip CombiPress followed by a Symbelt shoe press with rubber covered SymZL counter roll and maximum linear load of 1.500 kN/m. The first open draw of the web comes after the CombiPress, where dryness will already exceed 40%. The extended nip will give more dwell time and together with a high nip load, there will be higher web dryness prior to the airborne dryer compared to traditional felt presses, explains Metso.
The dryer section
The DryWay airborne pulp dryer has a trim width of 8.0 m. It features a dryer section and a cooler section and utilizes medium pressure steam to dry the sheet. There are several drying decks where hot drying air is blown against both sides of the pulp sheet. Circulation air fans keep the drying air circulating. In front of each fan there is a steam coil for heating the drying air before blowing it to the nozzle sections.
A number of accessories have been added to the dryer section to make life easier for the operators, including a tail cutter with tail threading system; movable platforms with broke removal equipment; a vacuum cleaning system; a steam-operated fire extinguishing system; a web guiding system with guide roll; and web transfer and web tension control systems.
The pulp web will then be transferred from the dryer section to the tail-threading unit of the Cutter-Layboy (with fully-automated control system). The new DryWay Cutter design that will be used at Valdivia has an overlapping device for high speed runs (up to 300 m/min).
Bale handling
Two-line baling will be handled by Metso Paper's Robo-technology, which utilizes servomotors rather than conventional hydraulics and pneumatics. When a set of sheet stacks is ready on the Cutter-Layboy conveyor it is automatically delivered to a scale for weighing before being processed as follows:
• A Robopress compresses the sheet stack with a force up to 15 MN or to a preset bale height
• A Roboapplyer applies and folds a bottom and a top sheet of wrapper on the long sides of the bale
• A Robotyer puts the first wires around the bale
• An Ink Jet Marker applies required information such as sequence number, quality and weight on the bale
• A Folding Machine, turns the bale 90 degrees and folds the wrapper at the short sides
• A second Robotyer applies the remaining wires.
The bale will then proceed to the Robostacker for stacking prior to shipping by truck or train.
Tuomi is convinced that Arauco's investment in Valdivia, "Will strengthen [its] position as one of the leading suppliers using environmentally sustainable technology for the production of high quality pulps." Whatever happens to the market, the new mill certainly promises to make a splash in 2004.
