Proper wood handling and sorting from the beginning of the process is the key to the mill's pulp stability - and important to customers
October 2007
By Graeme Rodden, Editor, Pulp & Paper
As Chile's largest forest products company, Celulosa Arauco y Constitucion S.A. ("Arauco") is well known for its massive Valdivia and Nueva Aldea pulp mill projects. However, its pioneer mill from whence the company name was taken has also had its share of improvements over its 30+ years of life and can now produce close to 770,000 tonnes/yr of bleached softwood (pine) and hardwood (eucalyptus) pulp on its two lines. Arauco Arauco is part of the Horcones industrial complex, which also includes a plywood facility and sawmill.
The pulp mill uses two species of eucalyptus, globulus and nitins; the latter has a shorter fiber length. The mill uses 1.2 million m3/yr of softwood chips, half of which are purchased. The mill uses 2.1 million m3/yr of roundwood, of which 1.2 million m3 is softwood. Again, 50% of the softwood logs are purchased. The remaining 900,000 m3/yr of roundwood is purchased hardwood logs.
Logs arrive at the mill and are sorted for use in the pulp mill or the adjacent plywood/sawmill complex. The solid wood facilities also supply the pulp mill with chips and biomass while the pulp sends treated water, steam and electrical power back.
Besides supplying the solid wood complex with power, the pulp mill is also able to send 30 MW back to the national grid. There are three turbo-generators at the pulp mill, two attached to Line 1. All of the company's mills have a surplus of electrical power, produced by biomass. The pulp mill also produces more than 800 tonnes/yr of tall oil and 6,000 tonnes/yr of turpentine, which is sold to the USA.
Starting at 300 tonnes/day
Line 1 is a swing line, able to produce both hardwood and softwood pulp in campaigns, but in late 2006 the line was making only hardwood pulp. Built in 1971 with a capacity of 300 tonnes/day, this line uses the batch pulping process. A first modernization project was done in 1988. Eucalyptus use started in 1998 following the Arauco 21 retrofit. The work included a new woodyard and chipping line from Metso Paper for hardwood. Eucalyptus pulp production increased every year until it reached 100% in 2006. Metso also supplied Delta screens, three twin-roll presses and vacuum filters in the bleach plant of Line 1.
Installed in 1991, Line 2 produces softwood pulp. This newer line produces the bulk of the mill's pulp, more than 500,000 tonnes/yr. Line 2 features a Kvaerner (now Metso) fiber line including a continuous digester that was designed at 1,000 tonnes/day but which now produces 1,400-1,450 tonnes/day. Arauco was able to hit design capacity within nine months of startup. The line also has a five-stage bleaching sequence, one of the last ones built. It was designed for minimal chemical consumption. Line 2 also has a GL&V screening system.
Other than the digesters, the two lines are very similar. The mill is very pleased with the efficiency of its continuous digester, especially how it relates to the liquor makeup process from the evaporators, recovery boiler and causticizing system.
One of the strengths of the mill's pulp is its stability. The mill can boast of consistent high brightness (90+ ISO), strength and cleanliness. This is a result of the care taken in wood handling and preparation. The wood (logs and chips both internally and externally sourced) is carefully combined to obtain consistent moisture content. The chips are the same all the time. This prevents upsets in the cooking process.
Yield is about 46% for pine, 50-51% for eucalyptus. It takes approximately 3.4 tonnes of eucalyptus to make one tonne of pulp and about 5.4 tonnes of pine for each tonne of pulp.
There are two oxygen delignification units on each line, giving a positive effect on effluent levels. Arauco Arauco was the first mill to install Metso's two-stage OxyTrac oxygen delignification system.
In the future, the mill hopes to install a new wash press for the softwood line, increasing consistency from 3.5% to 5.5-6%. Currently, there is one main control per line with smaller satellite control rooms. The mill hopes to be able to change the distributed control systems (DCS) on both lines within two years.
There are three baling lines, two for pine pulp and one for eucalyptus. They are designed so that two lines can handle production from the entire mill. There are different parameters for pine and eucalyptus pulp regarding the amount of time needed to press a bale.
More on the environment
Arauco plans to spend close to $60 million on projects related to the environment at the mill. For example, water consumption currently runs about 60 m3/tonne of pulp. The mill does recycle water already but plans to add a cooling tower to increase the level and bring fresh water consumption down to 40-50 m3/tonne. Other environmental projects will also help reduce odor.
A new effluent treatment system was installed in 1991 when Line 2 was added. Effluent from both lines is combined. There is an aerated lagoon with 5-6 day retention that provides a good reduction in temperature, BOD and COD levels.
Basic effluent from both lines passes through a bar screen and goes to a primary clarifier and then passes to a mix tank where it is combined with acid effluent from the two lines. From here it is conveyed to the aerated lagoon prior to its outlet 1 km out in the Arauco Gulf. Sludge from the primary clarifier is pressed and then burned in a power boiler.
The pulp mill operates throughout the year but there is an annual nine-day maintenance shutdown. The pulp mill employs 480 people, with 232 of these on shift (four-shift system, eight hours per shift). Altogether, the Horcones complex employs some 3,000 people.
There has been an interesting shift in Arauco's markets over the years. In 1975, Europe represented 65% of the company as a whole's market. Now, Asia accounts for 65% of its wood pulp exports and Europe only 27%. The Americas buy the remaining 8%. Mill officials do not see markets changing in the foreseeable future. Asia will remain Arauco's largest customer.
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