Bigging up Saiccor

Sappi is expanding the world's largest dissolving pulp facility

November 2007
By Justin Toland, Editor

The world's largest dissolving pulp mill is about to get even bigger. In May 2008, Sappi Saiccor mill in Umkomaas, near Durban, KwaZulu-Natal, South Africa, will startup a new pulp line to give a total capacity of some 810,000 tonnes/yr.

Fittingly, the name of the investment project in Zulu is Amakhulu, which translates as 'The Big One'.

Some 1,700 contractors are at working on the $460 million scheme. Sweden's ÅF Group and its local partner, Murray & Roberts, are handling the delivery on an EPCM basis. The investment includes 11 new magnesium (MgO2) batch digesters and associated chip loading, as well as the world's largest magnesium oxide and sulfur dioxide recovery boiler. "The new recovery boiler should increase energy self-sufficiency," believes technical dirtector, Sappi Saiccor, Derek Weightman.

Also part of the scope of supply: new roads within the mill, a weighbridge, the relocation and expansion of the log storage area, a new chipping line, the decommissioning of two calcium digesters, new evaporator plants, a new bleach plant and pulp machine, an upgrade to the existing chlorine dioxide plant, an addition to the Eskom Rayon substation, transformer yard and switchgear, new air compressors and dryers, new human resources and training facilities and a new canteen.

Andritz is supplying the bleaching, evaporation and pulp drying equipment for the new line and is responsible for basic and detail engineering, mechanical erection, supervision, startup and training.

The new pulp drying line will include an Andritz Twin Wire Former (working width: 4 m) as well as an Andritz Küsters calender to maintain uniform pulp sheet properties, an important parameter when it comes to dissolving pulp.The new six-effect 370-tonne/day evaporation plant will feature an advanced sulfite liquor evaporator equipped with a stripper and a methanol recovery unit for the cleaning of condensates.

Sappi is adding 300,000 tonnes/yr of new capacity at Saiccor, but also closing an older line, for a net gain of some 220,000 tonnes/yr

The new line – located in a new building known as Continua 5, situated where the mill's woodyard used to be – will churn out up to 300,000 tonnes/yr of chemical cellulose. At the same time, some older, calcium digesters (capacity: 75,000 tonnes/yr) are being decommissioned, to give a net increase in output of some 220,000-225,000 tonnes/yr. "It's not enough," says Weightman, such is the current and projected demand for chemical cellulose.

The mill's pulp is a blend of calcium-cooked and magnesium-cooked fibers. Currently the split is 60% calcium/40% magnesium. Following the Amakhulu Project, the ratio will be 70:30 in favor of magnesium.

Weightman explains that Sappi Saiccor has been able to continue using calcium because of its location next to the Indian Ocean. "The depth and current means the sea is able to assimilate the calcium." (Effluent is discharged 6.5 km out to sea at a depth of 50 m). By contrast, mills located around the Great Lakes or Baltic Sea have to make many other chemical products as a matter of course to avoid discharge. "Most calcium mills have had to shut down because you can't recover [calcium]," he says. "You can recover magnesium: the pulp is a byproduct almost of the magnesium recovery process."

According to Weightman, Sappi Saiccor has the most sophisticated SO2 monitoring system in the southern hemisphere (with a limit of 190 ppb for 15 minutes). Chip waste is sold to local farmers and hazardous waste is taken by a contractor to an approved site elsewhere.

The production process

Sappi Saiccor today uses 100% eucalyptus fibers to manufacture its pulp (acacia use was discontinued in October 2006). Wood is sourced from plantations in Zululand and the KwaZulu-Natal Midlands. The mill uses mainly eucalyptus grandis urofila and dunii smithii nitenes. There are separate chip piles for each species.

Chips are cooked in batch digesters at 140 °C, 10 bar pressure, for 5-7 hours. The bleaching sequence is either E-D-Eo-DP or E-D-Eo-DH (normally DH). The bleaching sequence will be the same for the new line, says technical support, Sappi Saiccor, Lester Van Groeningen.

Brightness after the final step is 93.5 to 94 ISO. The pulp is then screened to remove silicone, before it is fed onto the 'paper machine'. The web is formed at "one and a bit percent consistency" notes Van Groeningen.

Machine #4, a 5.6 m wide Metso unit can produce up to 1,000 tonnes/day of pulp at a running speed of 140 m/min. The pulp dryer (ABB Flakt) is of the flat airborne type, rather than cylindrical. It is followed by an 8-blade cutter/layboy.

A buffer warehouse can hold some 2,000 tonnes of output, with the main warehouse (80,000 tonnes capacity) located in Durban.

Pulp is sold in both bales and reels. Weightman explains that most European customers want bales and most US customers want reels. The rest of the world goes for a mix of the two.

The lignin plant

Saiccor is also home to one of the two largest lignin plants in the world. LignoTech South Africa (LTSA) is a 50/50 joint venture with Borregaard (The Norwegian firm is responsible for technology, R&D and export sales). The jv was signed in December 1997 and production of products derived from lignosulfanate began 12 months later. The initial capacity of 55,000 tonnes/yr was boosted to 155,000 tonnes/yr in 2003, with the addition of a second evaporation plant at a cost of ZAR 330 million ($38 million). "We are now talking about the next expansion," says engineering manager, LTSA, Diyan Botha. LTSA manufactures seven products in either powder or liquid form. Some 350 tonnes of powder and 80-100 tonnes of liquid "on a typical day", says Botha.

The lignin powder is packed in 600 kg bulk bags or 25 kg bags and stretch wrapped on 1.2 kg pallets. As of mid-2007, the product was selling for somewhere in the range of $300-350/tonne.

Some 90% of output goes to the construction industry, the remainder is used as a dust binder for dirt roads or as an animal feed binder. Some 90% of LTSA's output is exported, main markets being Southeast Asia, the Middle East and the Americas.

Some of the everyday products that contain chemical cellulose

R&D

The Saiccor mill started up on December 1, 1955 and was originally an integrated supplier of viscose to Courtaulds in the UK (and USA). After Sappi bought the facility in 1988, it remained reliant on Courtaulds for R&D for several years. Soon the mill began branching out into new product areas, for instance adding a new non-viscose line in 1995. In 2001, Sappi Saiccor built a new technology center specially to be able to do research into non-viscose applications. "The aim is to work out the impact of our wood furnish and process on the customer's process," explains the technology center's Tracy Wessels. "We have some pilot facilities to do this." The center's pilot digester can be used for both calcium and magnesium cooks.

Some 30 people work at the technology center, divided into a number of research zones. As well as a general lab for testing viscose and cellulose acetate, there is a shift laboratory for testing production pulp quality.

The center's viscose lab consists of a machine for spinning viscose SF and viscose filament and a preparation area. Trials can be either small-scale (with 200g of pulp) or large-scale (using 1 kg).

In addition, Saiccor has a lab for acetate and cellulose ethers R&D; a lab for microcrystalline cellulose (MCC) – a substance used in the pharmaceutical and food industries; and a cooking and bleaching research lab.

In areas such as MCC, softwoods have traditionally been used. "That's why we have to do a lot of research," notes Weightman. Saiccor also collaborates with a number of universities and research institutes with the target being to solve problems, to help customers optimize products, and to develop new products.

Weightman says that Sappi has had some success in developing an MCC product for tablet manufacturers and is now working on one for colloidal (food) applications. Acetate ToW is another focus. "The acetate market is growing because of the switch from unfiltered to filtered cigarettes, for example in China," the technical director points out.

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