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ABSTRACT
For some years after the change in political dispensation in South
Africa, Sappi Fine Paper's Stanger Mill had faced a market being eroded by imported papers of higher quality. During the isolation period, quality was not so much a determining factor in the local market as
competition was limited.
Although Stanger Mill began to make approaches for capital injection into the mill, Sappi
Group was globalising on a large scale and found less opportunity to spend capital in South Africa.
In 1999, a project proposal was developed and presented to the Sappi Fine Paper SA board
for a quality based upgrade to PM1 at Stanger Mill. The request was for funding to upgrade the approach flow system, replace the headbox, add a topformer, reduce the draws in the press section, increase stability
replace the pond size press with a film press with IR afterdrying and a new winder. In addition, control and drive systems would be almost totally upgraded.
In the coater area, improved IR drying, a new kitchen and upgrade of the rewinder were
proposed.
The benefits were to be improved sheet dimensional stability, reduced two sidedness and
improved surface from double coating. In addition, 33% additional capacity was proposed as the quality would improve market share.
This paper will look at the development of the project, the installation and start up and
the successes and disappointments of the upgraded paper machine including quality and quantity. The contribution of the major partners to the success of the project will also be discussed.
Rebuild at Sappi Fine Paper, Stanger Mill, August 2001
History of Stanger Mill
Stanger Pulp and Paper (SPP) was commissioned by a consortium of Reed Corporation and CG
Smith Sugar (now Illovo Sugar) in 1976. The basic concept of the mill was to make coated woodfree paper using the bagasse waste from the CG Smith mill Gledhow at Stanger on the North coast of KwaZulu Natal, South
Africa. Apart from the cost benefits, the product would consist of mainly post agricultural waste product, seen as an ecological advantage.
Initially, only the fine paper line, comprising a Beloit fourdrinier paper machine and
offline coater, was constructed but soon afterwards a pulpmill and tissue mill were added. No major developments were made on the paper line except changing the drive system, including infrared drying with profile
control and the headbox in the early nineties. Control systems were also upgraded from time to time.
So, the initial paper machine consisting of a fourdrinier forming table with a dandy roll
for heavier weights, the three nip press section and the drier section including the pond size press remained the basic production line for 25 years.
The blade coater was converted to Jagenberg CombiBlade and infrared drying was installed.
The finishing house received a major upgrade in the nineties.
Products made
Sappi Fine Paper's Stanger Mill forms an integral part of Sappi Fine Paper's leading
position in the coated woodfree market, supplying the South African section of that market. Prior to August 2001, Sappi Stanger produced single coated papers and during the era of political isolation was able to
maintain a significant market share
Developments in coated woodfree papers
In the eighties and nineties, significant advances were made in the quality of coated
paper. This was achieved through multiple coating of the paper and advances in coating technology and chemicals. Purpose designed lattices and pigments are produced by major chemical manufacturers and these raw
materials can be designed to suit the end user requirements exactly.
State of Stanger product and market prior to the rebuild
With the advent of the ''new'' South Africa came a wider range of imported coated paper
and increased quality through multiple coating technologies. Sappi Stanger was not able to compete against these papers in the market and moved to markets traditionally held by lightweight coated (LWC) papers (which
are not made in this country) at a much lower margin than Sheet Fed Offset Litho papers.
In addition, label papers, only coated on one side are produced.
Whilst the chemicals and pigments were available, the ability to apply additional
coatings was not as the capacity of the coating machine is only marginally greater than that of the paper machine.
Hence the management team of Sappi Stanger started to motivate for an upgraded paper
machine with online coating capabilities.
Scope of the project
The requirements of the upgrade were to produce a paper product which had properties
equivalent to the major portion of imported papers. The main properties targeted were better sheet stability, improved two-sidedness, a smoother printing surface, better gloss, higher whiteness and better printing
properties in general.
It was also decided that increased capacity was required to give a better return on the
investment. Initially this would be set at 33% increase in tonnage but new equipment would be installed to eventually achieve a machine speed of 1100 m min-1 where practicable. The first phase of the upgrade would be designed for 700 m min-1.
Equipment requirements
As is usual with this type of investment, the equipment aspirations of the mill
production teams far outweighed the available capital. This required some modification to the initial specifications.
The following configuration was decided as optimal within the financial constraint:
Stock Preparation
The stock preparation required a major overhaul to cope with the increased capacity and
to reduce the energy consumption and specific water usage. A broke deflaker/refiner was required.
Approach flow
The approach flow needed to be almost completely rebuilt in such a away as to reach the
goal of 1100 m min -1. For the most part the tankage would remain the same except for a new white water chest and a new white water tower; the latter installed to assist with the goal of maintaining the
current level of water consumption at the higher capacity.
Screening and cleaning systems required replacement to increase cleaning efficiency,
reduce air entrainment, reduce operational costs and improve machine runnability through cleaner stock. A four stage heavy reject cleaner system was required where the first stage included light weight rejects to be
processed in a light weight reject system. The screening system was seen to be an integral part of the short loop.
Forming Section
A new headbox would be required to achieve the increased quality demand and a dilution
headbox was envisaged. The forming table would require revamping and the dandy needed to be replaced by a hybrid former type top wire. Together with the press section requirements, the vacuum system needed a
complete overhaul and possible new capacity.
The main objectives being to improve two-sidedness improve formation and attain a better
sheet stability.
Press section
The main changes required at the press section were to reduce the length of draw between the second and third press and to modify rolls to increase dewatering capacity, particularly of the second press.
These modifications were to improve runnability through reduced sheet breaks.
Drying section
In the first part of the dryer section, sheet stabilisation would be required for the
higher speeds. This would improve runnability.
The pond size press would be replaced with a film press with on machine coating
capability followed by infrared drying. This would require sophisticated coating and size preparation systems.
This change was considered the most economical means to achieved double coating
capability.
The reel-up
The pope reel-up would be modified to increase runnability, including a magazine for
empty spools and increased automation.
Machine control
The control systems would be completely converted to DCS with Profibus data transfer.
Other equipment requirements
In addition to the requirements on the paper machine, a new coater kitchen would be
required as well as an upgrade on the winder on the coated paper winder.
Very little would be required at the first stage of the rebuild to the off-machine coater.
The selection of suppliers of equipment
For project engineering co-ordination and training, the supplier selected was Remy of
Sweden with CTS of Finland providing the engineering consultant component of the alliance.
In selection of the primary paper machine, there were only two major equipment suppliers
remaining in the market place and both were invited to tender. After much rigorous technical and financial debate and comparison, the main equipment supplier selected was Voith Paper.
Other important suppliers selected were GAW of Austria for the coater kitchen and
ancillaries, GL& V for the cleaner system and Jagenberg to upgrade the winder.
The important equipment to be supplied by Voith were approach flow and screening system,
a ModuleJet dilution headbox, a Duoformer D hybrid former and a SpeedFlow film press. The pope reel-up was also redesigned by Voith.
Shut down
The machine was shut down in mid July 2001 for the main rebuild; some minor modifications
had been achieved prior to the main shut to improve the shut duration.
Start up
The machine was started up a little late due to hold ups with piping contractors. Some of
the main problems encountered at the start up were:
Lifting of the Duoformer top wire on the run.
This was caused by differential speed between the top and bottom wire and after
modifications to the speed control and the wire tensions, this has not given problems again.
The draw modifications in the press section and at the film press required a little
learning to allow for easy tail feed. In particular, the draw at the film press requires careful setting each time the machine is restarted. The draw is very long, approximately 20 meters, and the differences
between tail and full sheet, and high and low steaming rates make a big difference to the sheet at this stage of the process.
These problems and many smaller ones being overcome the machine started to produce paper
on 17 August 2001. In reality, the long haul had just begun.
Judging from the experiences of other rebuilds, the start up journey of PM1 at Sappi
Stanger was comparatively good. Obviously, some difficult periods were experienced and indeed there were some very dark days.
One major setback was the change from using the film press for starch application to the
objective use of on machine coating. This caused serious changes to the nature of the paper produced, resulting from reduced base paper, reduced bulk, increased operating speed and the lack of the internal bonding
achieved from the application of surface starch.
This is a view from the operating deck.
However, the investor perspective is quite different. Having invested the capital into
the mill, quite simply, they wanted a return and this was not forthcoming at the anticipated rate. In retrospect, it may be argued that the capital return on these types of investment should have a latent phase in
terms or payback. If one looks at previous projects of this nature and extent, there was always a period of regret after the start up but invariably this has turned to such an extent that the project has repaid
itself handsomely.
The achievements of the project
Primarily, from a financial point of view, the cost of the project was brought in on
target. This was directly due to excellent control on behalf of the project management.
The technical objectives have been mostly achieved. On the heaviest grade
(300 gsm coated paper) the machine run is not satisfactory yet. The difference in sheet quality was visibly noticeable in the coater and finishing sections.
Formation was improved for all grammages. It is anticipated that
formation on heavyweights can be further improved with modifications to the forming table.
Scott-Bond was expected to decline as a result of the action of the hybrid former. However, the action taken to counteract this, application of cationic starch, has resulted in higher z-direction strength.
TSO angles have been reduced to the level required for coated art paper, or office papers, of less than 2 as was predicted before the project.
The MD/CD ration is also better than expected. Basis mass profiles are in line with expected values at 2-F of ~0,5%.
What should we have done differently?
White water chest
The spatial constraints required a small white water "chest". In retrospect, it would have been prudent to increase the size at the expense of some other item of equipment.
Operators have however adapted to the conditions at start up and the large white water external silo does assist.
Carbonate loss
The loss of carbonate through the cleaner system is relatively high. Although this was not
anticipated it will require rectification at some stage.
Forming table elements
It was a deliberate decision to only modify the forming table after the start up. The reasons
for this are that it was not clear as to how the forming would change and it would be better understood after running for a while and that it was intended to install ceramic elements
which may have been damaged in the start up period.
A new set of forming table elements has been purchased and will be installed prior to
delivery of this paper.
The press section
This will have to be rebuilt with full sheet support if the machine speed is to be increased
any further. The open draw between the second and third press, although reduced during the project, is one of the most constraining areas on the machine. The number of sheet
breaks traceable back to the press section is excessive although lubrication of the centre roll has improved sheet release and hence the draw.
Film press pulper
The need for a film press pulper was considered during the project design stage but was not
included in the project for a number of reasons, despite the change in the feed system to include a Fibron unit. A sheet break at the film press requires the sheet to be broken at the
press section to avoid full sheet being turned into the basement. This must then be manually removed. This has been found to be totally unsatisfactory and a film press pulper has been
ordered within the capital project and will be installed by the time this paper is delivered. This will improve uptime on the machine and reduce the risk of paper web in the basement.
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