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Between “Living in South Africa” parts 1 and 2, a rather boringly technical article about my reason for being there. This will be the last Monday Memory for 2018 but I intend to increase the frequency from fortnightly to weekly when I return with “Living in South Africa” part 2 on January 7th 2019.
The principal agricultural product of the region where the SAICCOR (South African Industrial Cellulose Corporation) mill is located is sugar cane. This is harvested throughout nine months of the year, during which time a large fleet of road and rail trucks transports it to sugar mills. For three months of the year this fleet is idle – or would be, but for the eucalyptus plantations, SAICCOR and other timber conversion operations such as Masonite whose mill was and still is (though now operating as Evowood) in Estcourt.
The problem for these operators was that the bulk of the year’s supply of timber was delivered during this 3 month ‘closed season’ for cane. The wood yard at SAICCOR covered a vast area in which logs were stacked up to 15 feet high. A 9 foot wide trench filled with water (the canal) ran the length of the yard in its centre. Down this logs were floated to the point where they were transferred to the chipping machine. A team of African labourers used wooden poles with metal hooks to guide the logs along.
A couple of crawler cranes with grabs unloaded the trucks during the delivery period, dropping a proportion into the canal and stacking the remainder. The rest of the year the same cranes lifted logs from the stacks and dropped them into the canal.
The process operated 24/7 except for a single weekly 8 hour shift when everything was cleaned and necessary maintenance undertaken.
Similar undertakings in North America had converted from storing logs to storing chips. This took up less space but meant that chipping capacity, and the handling of timber, had to be doubled. That was the main task for our small team. It took all of 1974, running well into1975.
Taking our cue from similar installations in North America and at Estcourt, the canal was replaced by a flume – a fast flowing stream that carried logs down to the transfer point. This was served by a concrete storage tank the top of which was at ground level, a filtration system to remove sand, grit and bark shards from the water, a pump and a pipeline to return water to the top of the flume. All of this had to be designed and constructed whilst the normal operation of the plant continued.
The hydraulic design of the flume to achieve the desired combination of volume and velocity required the application of a complex formula involving a constant called the Reynolds Number, meant to represent the frictional resistance of the steel liner which was layed to a gradient.
Back then there was no computer programme available to do the calculation for me. The team were allocated one of the first electronic calculators. This was a fairly basic model. I’m not sure if the kind called ‘scientific’ even existed yet. Certainly ours would only do basic addition, multiplication/division and simple functions like square roots.
It was important that I got the calculation right because there was a lot of steel and skilled labour involved in the construction. If it did not work as intended the cost of rectifying it would have been considerable. Because of that my calculations were thoroughly checked by one of the in-house designers. I’m pleased to be able to report that we did get it right.
Another innovation concerned the unloading crane. This was intended to run on rails either side of the flume, with an articulated jib and grab that lifted logs from road or rail transports and dropped them between its ‘legs’ into the flume. The proposed machine had been designed in conjunction with a hydraulics engineer who had come from Italy as part of the original installation team in the mid 1950s, subsequently setting up his own business in Durban. The contract had been awarded before we arrived. Many months had elapsed since then and several trials in the works had failed to demonstrate that the machine was capable of performing its intended task.
SAICCOR’s managing director, an Irishman who was extremely supportive towards our team, was becoming increasingly frustrated by this failure of the supposed specialist to deliver. The route from Umkomaas to Durban passed through an industrial area on the south side of the city. One of the many businesses that lined the dual carriageway was Blackwood Hodge, the South African distributor for JCB. There was always an array of excavators of various sizes on display in their yard. One day the MD waltzed into my office and explained that he had just come back from Durban and had a brainwave as he passed Blackwood Hodge. Would I get in touch with them and see if it would be possible to come up with an adaptation of one of their machines? To cut a long story short, it was and we did.
A further design task which I undertook was the method for lifting logs from the flume and depositing them onto the final conveyor into the chipper. The canal terminated in a so called jack ladder – a chain conveyor that carried the logs up an incline and dropped them onto a conveyor belt running at right angles. With the flume, the logs would be the wrong way round for this so my new elevating chain conveyor had to end with a steel chute designed to turn the logs through 90 degrees before dropping them on to the conveyor belt.
Whilst I was designing the log handling part of the project, Walter was designing a system of pipes and blowers to distribute chips to the new storage area. This now had to be integrated with the existing chip handling which consisted of a very long inclined conveyor belt which transported chips from the base of the chipping machine to the top of the digester – a vertical cylinder in which the wood chips were dissolved in acid to create pulp. This conveyor had to be split about half way up the incline so that chips could be diverted to the blower system when required.
One aspect of the design for water cleaning was the final filtration to remove very fine particles. I had seen an article in a South African business journal which described how a centrifuge had been used to reclaim tobacco shreds from the water used in a tobacco processing facility in what was then Southern Rhodesia. It seemed to me this would be ideal for our application.
The team leader disagreed. He had already been in touch with a company that had supplied filtration equipment to Courtauld’s Derby factory and insisted we should have a cloth filter that would be cleaned by vibration. He contended that “you can’t separate organic materials (in our case small particles of bark and wood splinters) using a centrifuge” I argued that tobacco is organic and it reportedly works in the tobacco factory. Perhaps I could go up there and have a look. Anyway, I thought the splinters would get trapped in the fabric of the vibrating filter.
Of course I was over-ruled. I spent many hours over the Christmas and New Year period, when we were commissioning the plant, trying to get the vibrating filter to work without success. The manufacturer’s representative flew out to assist but had no success. At the end of January Freda, Ian and I returned to England. When Walter returned, a few weeks later, he told me that the vibrating filter had been abandoned and a centrifuge installed in its place.