Saiccor - The First 50 Years 5.8 MB - Sappi

The Cantacuzene Period (1952–1965)
The first plant to prove troublesome was the digesters�
In May 1956 the carbon brick lining of No 5 digester collapsed and
had to be rebuilt� The other digesters soon followed� It became
apparent that rebuilding digester linings was a fulltime occupation�
Solutions to the collapse of the brick linings were being sought when
it became necessary to order No 6 digester� It was decided to buy an
improved type of digester from the German company Esseners,
consisting of a mild steel shell clad with stainless steel� No 6 digester
was commissioned in January 1960 and operated at 6,6 bar (10 per
cent higher than No’s 1-5)�
Between December 1960 and June 1962 the brick linings on No’s
1-5 digesters were replaced with loose stainless steel linings – a vacuum
between the stainless steel and the mild steel shell had to be
maintained� The stainless steel linings were a great improvement on
the bricks, but also collapsed from time to time� No 7 digester, a repeat
of No 6, was commissioned in May 1961� When the order was ready
to be placed for No 8 digester, Avesta (Sweden) were making cold
stretched digesters, but Lloyds of London would not approve the
design of these vessels� An order was consequently placed on Canzler
of Germany for another clad stainless steel one� No 8 digester was
commissioned in January 1962�
From No�9 digester onwards all digesters were Avesta coldstretched
stainless steel� Ingemar Johanssen of Avesta,
the patent holder of the cold stretching process, was
a regular visitor during the construction of these
digesters� No 9 was commissioned in 1963, No 10 in
1964, No 11 in 1967, No 12 in March 1969, No 13 in
December 1969, and No 14 in 1973� No’s 15-17 were
bought secondhand (11 years old) from Vallvik in
Sweden in 1975� These digesters were cut in half,
across the centre, and transported to South Africa� A
piece was welded in to make the digester 1,2 m longer
(the same volume as the others, 285 m 3 )� No’s 18-20
digesters were commissioned with the magnesium
plant in May 1985� No’s 21-23 were commissioned
with the Mkomazi plant in January 1995�
A programme to replace No’s 1-8 digesters was
started in 1980; they were commissioned as follows:
No 1 – 1983 No 2 - 1982 No 3 - 1981
No 4 – 1982 No 5 – 1980 No 6 – 1990
No 7 – 1987 No 8 - 1989
No’s 9 and 10 operated at 6 bar, while from No 11 on
the operating pressure was increased to 10 bar, the
higher pressure giving a better quality pulp, particularly Construction of digesters 18, 19 and 20 in 1984
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