Project Type
Project Team Zoom Interview Case Study
Project Summary Case Study
Location
Steel Profiles Used
  • Date of Steelwork Completion
    2023-05-31
  • Tonnage
    165
  • Hot Rolled Structural Sections
    Universal Beams (I Sections)
  • Plates
    High Strength and Special Structural Plates
Project Overview

PROJECT OBJECTIVE & REQUIREMENTS
Viva’s scope was part of a larger flue gas desulphurization project for a coal boiler in Ngodwana
• To design a 500 m3 capacity silo to store lime with a bulk density of 1700 kg/m3
• To design the silo as a fully welded structure
• Geometry to suit constraints on site due to neighbouring existing structures

ENGINEERING
• Design of the silo considered permanent loads, roof loads, material loads, wind loads as well as loads due to both
asymmetric and symmetric flow of material.
• Since the silo was to be transported and erected as one element and due to its shear size, a comprehensive lift study had to be performed.
• Some of the engineering considerations included in the lift study were:
• Selecting the most appropriate lifting methodology (in this case, tandem lift with spreader beams)
• Sizing the lifting lugs, pins, shackles, etc
• Strengthening the silo at the lifting points
• Designing steel transport saddles

Project Details
The Lime Silo was certainly the focal point of the project. This silo was 5,892m in diameter, 25,6m High and weighed 61T! Due to the shear size of the silo, the roof of the workshop had to be removed for the silo to be rigged out of the workshop. onto waiting abnormal transport.
There was a fair amount of site work required (like removing the internal transport supports) before the Silo could be lifted into position. With tremendous support from our Client and our Engineering partners, RMCE, we could finally start lifting the Silo into position. The Lime Silo was finally lifted into position by a tandem lift with a 140T and a 550T mobile crane. The Silo access walkway had to tie into an existing platform at level 23.470m
Getting the Silo onto site was equally as challenging as the fabrication and transport This was achieved with many trips to site measuring, measuring and measuring again to ensure what we were manufacturing would fit between the many existing structures. Abnormal transport having to carefully manoeuvre its way onto site between existing structures and a working plant.
Benefits of Steel in this Application

Steel provides a smooth interface between with the ensiled material and this relatively low surface roughness aids the flow of stored material.
The cylindrical walls and a steep hopper of steel is is designed to generate mass flow - Figure (a)
A shallow hopper with a rough surface is prone to forming dead zones that result in reduced
live capacity, as depicted for pipe flow conditions – Figure (c).
Mass flow conditions are a requirement for this project. There was an option to manufacture this tank on site - Transporting piece small panels to site, installing, site building and welding the Silo in situ.
Steel has lent itself to the incredible amount of work that can be done off site in a controlled and safe environment while site civil works can be completed concurrently. The steel silo was fully welded in the workshop for this application provides for better fabrication control and quality assurance than a site bolted structure.
The manufacturing process of steelwork can be monitored closely to ensure that all materials used in the silo construction are of the specified quality and workmanship is to the desired standard.
Fabrication in steel allows any corrections, if needed, to be made before the silo leaves the workshop.
For this application a fully fabricated silo allowed for rapid deployment within an operating facility that would not have been possible if the silo were to have been site bolted or constructed in concrete. Steel silos are ductile and resilient to pressure variations in the ensiled material resulting from the static and flow load conditions
Ring stiffeners are provided for buckling resistance due to non-uniform hoop tension load effects
At the hopper transition (from cylindrical form to conical form) the ring stiffener resists substantial compression forces and together with the stiffened wall, acts as a girder spanning between support columns
The benefit of steel for this application is a lightweight structure, transportable and rapidly deployed. The steel mass: ensiled mass is as low as 13%

Testimonials

"We are proud of the innovation demonstrated during fabrication of the silo, where for example, the workshop roof was removed to accommodate the structure of such large size
We are proud of managing the logistics of transporting an abnormal load with the challenge of negotiating obstructions enroute and legal issues
We are proud of the way in which difficulties arising from lifting the silo within the tight constraints of the plant were overcome, thanks to the cooperation and support from our client
We are proud of the quality of workmanship and design of this silo, which illustrates the substantial benefit of fabricating a fully welded steel structure off-site which made it possible to be deployed and commissioned within a tight delivery programme
The benefit of steel in this application is that the in-plane stresses in the silo walls are primarily tensile for which steel is a most appropriate construction material. Out of plane load effects due to buckling and flexure are catered for by stiffeners
A low structural mass : ensiled material mass was achieved by using steel in this application" - Collen Gibbs, Viva Engineering.