A complete woodchip conveying package supplied by TAKRAF Africa to Sappi’s Saiccor mill in Umkomaas, KwaZulu-Natal, South Africa, featured a unique four-conveyor, double-decker, walk-in type gallery, with the gantry bridge spanning 45 m, at a height of 24 m, over the existing Sulphur plant. The double-decker gantry houses the four conveyors in a 2 (top deck) + 2 (bottom deck) arrangement.
This double-decker design, together with other innovative design and technical features, enabled TAKRAF Africa to produce a successful solution within the severely confined space of the brownfields site and integrate it into the existing mill infrastructure.
The woodchip conveying package, the Sappi Saiccor Woodyard Upgrade (SSWU), handles increased production made possible by expansion to the Saiccor mill from 780 000 tpa to 890 000 tpa.
The package conveys woodchips from existing and new chipping lines to feed two new stockpiles at up to 680 tph. Using four screw reclaimers (from another OEM) and associated conveyors, woodchips are reclaimed from the stockpiles at a maximum 403 tph and conveyed to existing infeed digestor conveyors to feed existing silos.
The package covered design, engineering, installation and commissioning of 24 trough conveyors, 10 m to approximately 200 m long and some with incline angles of 19°; three Redler en-masse chain conveyors; transfer towers; and related systems. Conveying capacities range from 5 tph to 806 tph and belt speeds from 1.5 m/s to 2.8 m/s.
Technical and aesthetic highlights
The project incorporated ground-breaking steel structures, the most impressive being the double-decker gallery and large spanning stockpile gantries. Gantry G1 (weighing 72 tonnes), for example, spans 45 m over the plant. This is rarely done in conveying applications.
Consideration of structural framing and stability of gantries during engineering enabled lifting the double-decker gantries into position without interference with the existing plant. The head-end gantry G3, spanning over a Blower Building, was the largest lift, weighing over 85 tonnes.
The stockyard consists of A-frame support trestles, which transfer large forces from stockpile gantries to piled foundations. The trestle baseplates are considered as pinned connections to ensure that the A-frames only transfer axial forces to the foundations.
With reference to the cladding, while most of the 13 600 m2 used was fabricated from aluminium and painted blue to aesthetically match the existing plant, the double-decker conveyors were clad with stainless steel sheeting as protection from the corrosive environment. The structures were assembled, lifted and fixed into position without cladding to prevent damage to the latter. Most of the cladding was therefore installed at height, with structures reaching 35 m high.
Other innovative features include three reversible conveyors feeding two reversible shuttle conveyors to convey material to either of two stockpiles from the different chipping lines. Chutes were designed using DEM technology, as woodchips tend to exhibit airborne behaviour at certain velocities. Stockpile stacking is done by automated zone control with equal spreading of different wood species.
The bypass system from the stacking route to the reclaim conveyors, used if a reclaim machine is undergoing maintenance or in case of unplanned downtime, has a self-supported pipe design requiring no intermediate trestle support. A bypass plough mechanism diverts material temporarily from the existing chipping line to a newly supplied conveyor.
Redler conveyors convey fines generated by the screening system. Besides their ability to fit in with restricted layouts and space, their multiple discharges facilitate building of a “conshelled type” stockpile and assist in loading a truck evenly.
Structural steel fabrication is the norm in the bulk materials handling industry, providing conveying systems with the durability and strength to withstand harsh weather and heavy industrial use.
Structural steel also offers flexibility to the structural design engineer. This is evident in the various different framing systems that were utilized on the project to deliver intricate solutions in the restrictive constraints of the layouts and existing infrastructure.
Additionally, the strength per mass ratio of steel allows design of structures that can be lifted into position after pre-fabrication and assembly, as with the double-decker gallery and woodpile galleries.
In total, structural steel of approximately 1 700 tons was designed, fabricated and installed within a 12-month project duration. All hot-rolled structural steel profiles were rolled and fabricated in South Africa.
Due to the short timeline, fabrication was split between local South African fabricators. Structural detailing and fabrication companies were selected early in the project to assess their capabilities in manufacturing timelines and prevent ‘overloading’. Availability of certain section sizes was a key element, with four structural detailing, five structural fabrication and one dedicated flooring and hand railing company(ies) used.
Conveyor gantries and galleries have trussed sides and tops and bottoms. Each conveyor gantry is portalized at the trestles to transfer lateral forces in the top chords to the trestles.
Two types of trestles support the 45 m spanning woodpile galleries in the stockyard: Type A trestles resist vertical, horizontal and longitudinal forces on the galleries, while Type B trestles resist vertical and horizontal forces to reduce the effect of thermal movement.
Due to constrained interfaces and limited space, a conventional transfer tower at the head-end was not possible. A transfer gantry concept was therefore developed to ensure conveyor system stability by transferring all longitudinal belt and wind forces on the conveyor back to an anchor trestle. This is typical on the reclaim, double-decker and incline conveyors. The incline conveyors have sliding joints at the top trestle joining to the gallery to ensure longitudinal forces are transferred to the anchor trestle and not the gallery. The transfer towers are traditional braced and portalized structures.
As this was an operational plant, certain tie-ins had to be completed during limited shutdown windows, while also interfacing with new and existing Civils and LPS power supply services. Client involvement in construction meetings ensured access for pre-assembly and lifting with minimal disruption to other construction activities. More than 50 % of construction was completed next to existing plant operations. Some big lifts were completed early morning or late afternoon to reduce impact on other construction activities.
As the fast-track contract called for precise planning, the project team was aligned at the project start. Dedicated teams were set up for the basic design and the project was internally planned in three areas to allocate engineering responsibilities to mechanical and structural teams and drawing office section leaders. ‘Design base / criteria’ ensured that the structural team worked on the same baseline for the relevant loading criteria.
The quality assurance and control team provided effective communication with workshops to ensure no repeat inspections, while inclusion of the project manager in the engineering team’s daily meetings facilitated project scheduling.
Safety was a critical consideration from the start, and particularly so during execution, with challenges such as working at height and working in a very confined, brownfields site. Due to the project team’s safety focus, the project was closed out successfully with only one lost time injury (LTI).
Project motivation editorials are provided by the project nominator. If any technical details, company names or product names are incorrect, please notify the SAISC so that the error can be corrected.
|Physical address of the project Street Address |
|Google Maps link||https://www.google.co.za/maps/place/Sappi+Saiccor+(Pty)+Ltd/@-30.180527,30.7709497,15z/data=!4m5!3m4!1s0x0:0xf89ed4af015a3a0f!8m2!3d-30.180527!4d30.7709497|
|Completion date of steelwork||MARCH 2019|
|Completion date of full project||MAY 2019|
|Tonnage and steel profiles used||1600|
|Client/ Developer||Sappi Pty Ltd – Saiccor Operations|
|Architect / Clients Engineer / Owners Engineer||SIVEST|
|External Drawing office||Atomic Projects|
|External Drawing office||Cad House|
|Steelwork Contractor||QR Steel|
|Steelwork Contractor||Impact Engineering|
|Steelwork Contractor||Avellini Brothers|
|Steelwork Contractor||FP Engineering|
|Steelwork Contractor||Coertzen Engineering Consultants|
|Cladding Manufacturer||Global Roofing Solutions – A division of Consolidated Steel Industries (Pty) Ltd|
|Cladding Supplier||Global Roofing Solutions – A division of Consolidated Steel Industries (Pty) Ltd|
|Corrosion Protection||Rand Sandblasting Projects|
|Paintwork Contractor||Rand Sandblasting Projects|
|Paintwork Contractor||Louwill Engineering (Pty) Ltd|
|Paintwork Contractor||QR Steel|
|Paintwork Contractor||Impact Engineering CC|
|Paintwork Contractor||Coertzen Engineering Consultants|
|Photographer, Photo competition||UNPRECEDENTED Pictures|
|Photographer, Other submitted images||UNPRECEDENTED Pictures|
|CLADDING (If applicable)|
|Completion date of cladding||MARCH 2019|
|Cladding profile/ type used||IBR686|
|Cladding area coverage||13600m²|
|Cladding tonnage||84,76 tonne|
If you were a part of this project, and your company details are incorrect or missing – please notify the SAISC so that the error can be corrected.