Iron and steel for sunflower and soya

By Eamonn Ryan

The civils and builders’ work on this project is approximately R100-million alone, amounting to about 30% of the entire development budget, comprising reinforced concrete pits, foundations, and housing for three high-pressure boilers; reinforced concrete foundations for 23 silos; 16 000m2 of concrete hardstands and roads; a truck-holding facility for 22 trucks; and foundations for a host of other manufacturing and storage structures.

Casting the reinforced concrete.

Casting the reinforced concrete.

Central Edible Oil (CEOCO) previously leased the premises from the previous holding company on the adjacent site, but following a management decision by CEOCO, proceeded to purchase the real estate and subsequently expand the operation through considerable investment. Once complete, CEOCO will be ready to ramp up and centralise scattered production and storage facilities at its Boksburg site, and increase its Boksburg offering with soya meal and soya crude oil production. CEOCO is involved in the processing of sunflower seed, with the primarily yield comprising crude sunflower oil, whereby sunflower husk and meal are by-products once the oil has been extracted from the sunflower seed. The meal is sold as farm feed to industry and the husk used as biofuel for the steam-generating boilers, currently under construction.

The processing of soya beans, a facility previously based in Delmas, centres around a primary yield of soya meal, with the soya crude oil being a by-product in the processing operation. Storage of soya beans was previously located in silos across the country near farming supply points, but this storage is now being centralised on the CEOCO property.

Paul Maitre, a director of the project’s consulting civil and structural engineering firm, ADA Consulting Engineers, says: “The financial logic behind this, and what sparked the development, was that the new owners looked at the situation of paying an extraordinary amount of money for storage around the country between farm and plant. They realised they could finance and build their own silos and take the capex knock but after a fixed period, they would be paid for and would thereafter contribute to profit.”

Scope of work

The main contractor is Iguana Projects. Maitre says the firm was appointed for its competence in concrete, for (in addition to all the concrete work) the project involves constructing a road network entirely in concrete. The structural steel component is being done by Distinctive Trading, both firms being direct contractors to CEOCO. The project management and professional quantity surveying is being undertaken by ProAfrica Property Services.

The project consists of establishing 23 silos comprising an aggregate storage capacity of circa 42 000 metric tons (t); road network and concrete hardstand equivalent to approximately 16 000m2; 8.5m-deep reinforced concrete intake pits for soya bean and sunflower seed offloading; concrete foundation for the silos and boilers; a 5 000t crude oil storage farm as well as a massive truck stacking area capable of holding 22 articulated vehicles; and a seed sampling and weighbridge facility. Maitre explains the rationale for all this infrastructure: “The sunflower seeds and soya beans are harvested during the short three to four months harvest season. Processing, nonetheless, has to continue all year round, so substantial storage facilities are required, both as a buffer for production and to manage distribution.”

The project will absorb approximately 750t of reinforcing steel and 350t of structural steel.

CEOCO is establishing their own boilers, which will secure the business’s independence. At present, CEOCO is supplied with steam by the previous holding company on the adjacent site. The site separation required business autonomy, whereby the reduced long-term cost of steam was driven by the availability of husk, which has a high calorific value; thus, a biofuel ideal for steam production. In addition, a 750m bulk water supply and 1.1km 7.5MVA MV reticulation has been completed by the team on behalf of the City of Ekurhuleni as part of the project.

At the moment, the husk from the sunflower crude oil process is being sold as animal feed and to the poultry industry, but once the boilers have been commissioned, the husk will be used as biofuel for the boilers. The boilers they’ve ordered are configured to be able to burn husk and coal to fire the boilers. The soya facility is an upgrade of the business’s current capacity (located in Delmas) and re-establishing it on the Boksburg site. The soya production facility was designed from scratch using the client’s technical and practical knowledge and 40 years of exposure and experience in the industry.

Trucks arrive directly from source of the raw material (sunflower seed or soya bean). Initial OH&S checks are undertaken at the main guardhouse, whereafter articulated vehicles proceed to a seed sampling station where samples are taken and immediately analysed, giving permission for trucks to proceed, or rejected. A fully automated weighbridge system will guide the vehicles through the offloading and/or loading process, right through to obtaining the final waybill ticket.

Sunflower husks, soya meal, and sunflower meal are transported on overhead gantries via conveyors to either the nine silos for meal storage and distribution, or to another seven silos for husk storage as fuel for the boilers. Sunflower and soya crude oil is pumped via the overhead gantries to ten 12m-high tanks, each with a capacity of 500 000ℓ. The oil, says Maitre, either gets piped to the adjacent business for manufacturing purposes or delivered to customers using oil tankers for the distribution. Overhead gantries housing crude oil pipelines and conveyors ensure transport of all product around the site.

The meal silos are conical elevated structures — the only way meal can be preserved and shifted to conveyors to be loaded onto trucks. “They are quite a challenging construction build,” says Maitre. The base is a solid reinforced concrete (RC) raft supported onto the dynamically compacted in situ soils. This base in turn supports the RC columns, above which a 17.5-degree sloped RC slab accommodate the loading channels.

This elevated slab also supports the steel silo and a state-of-the-art flooring system that has been sourced and imported from abroad to facilitate movement of the meal within the silos.

A new office block will also be built adjacent to the soya plant to accommodate the employees required for the expanded soya plant. There is substantial open space in reserve for future expansion.

Erecting

Steel erection to the new soya plant against the soya silos in the background.

Project challenges

One major challenge is coordinating timelines: the seven 30m-high steel seed silos are being manufactured in Turkey (but branded a tongue-soothing MySilo). They are currently being erected; however, they required storage on site until completion of the civils work for each silo. The foundation, circular reinforced concrete retaining walls, and complex fluted reinforced concrete surface beds with extensive aeration channels, bore with them a construction complexity in itself. “The silo top structures are a very efficient steel corrugation assembly, and it is amazing to think how much concrete would have to be used to achieve the same purpose,” says Maitre.

The boilers are being imported from the Philippines. “Everything’s on the water, so to coordinate delivery and construction has proven to be a challenge,” he adds.

“The foundations were problematic, as a second challenge. Right from the onset, we knew we had difficult geotechnical conditions. The geology is loose-to-medium-dense sands, which cannot support conventional foundations. We had two options: piling the whole site, which would be quite costly (albeit adjacent industrial sites were piled, but those structures are more substantial), though we eventually went with dynamic compaction below all the silos, the boilers, and the new soya processing plant. This wasn’t necessary for the roads.”

Maitre explains this process: “We used large cranes to lift a 12.5t block of steel and repeatedly dropped it from a height of 22m. That gives you good foundation bearing for a depth in excess of 12m. We were looking for good bearing for 8m to 12m and they achieved it. This adds considerably to the costs — it took two rigs and was time-consuming. The result was that a lot of the silos arrived before we were ready and had to be stored in warehouses until we had the concrete bases in readiness. We have avoided this aspect with the boilers, despite the rains we have been having recently [February/March].”

An unexpected plant shutdown required maintenance of the solvent plant. This was scheduled at short notice and was under way at the time of the Civil Engineering Contractor visit. Maitre says this presented an ideal opportunity to commence work on the solvent plant and surrounds — but also required ADA to complete all its design work and client briefings within three weeks to facilitate work during the plant downtime.

“This made it a project within a project, as we had to complete all this work within the four-week shutdown window,” he says.

Concrete roads for longevity

Of interest is that the developers have opted for an entirely concrete road. “Because the site will be extensively developed, the high traffic load of trucks will be using hydraulics and manoeuvring in tight spaces — putting extra wear on the road surface. Hence, we preferred heavy-duty concrete to asphalt or paving. The loss of any downtime due to road wear and tear would cost the production process far in excess of any additional upfront cost of road surfacing.”

Coincidentally, says Maitre, concrete roads are one of his personal particular interests, having written his university thesis on the subject and he liaised with The Concrete Institute’s Bryan Perrie on it many years ago. “Ever since then, I’ve had a passion for concrete slabs on the ground. The failures are extensive and well documented. I interacted closely with Bryan on ultra-thin concrete layers they’ve been investigating of late, and after thorough discussion, we went for conventional un-reinforced concrete. We’re casting right now in the harshest of climatic and weather conditions: in the heat of summer and also during high rainfall, both of which can compromise concrete road construction. We concentrate on testing of the factors that can compromise concrete — making sure it has as low a water content as possible, the lowest slump as practically possible, but at the same time still practical from a workability point of view. We dictated that the ready-mix supplier takes a slump test of every single ready-mix concrete truck coming in, and any truck that was in excess of 100mm was sent away.”

Ready-mix suppliers have standard mixes that have been tested, but conditions of rain and temperature can cause variances, causing variable slump results due to wet sand and stone in the mix. Too much moisture can cause shrinking and cracks in the concrete — “We want to avoid that upfront. Often people don’t fully realise that concrete on the ground has a very high risk of failure.

“Innocuous as pouring concrete on the ground may seem, there’s a whole range of factors which influence the outcome: moisture on the ground, the weather, your concrete type, saw cutting at the correct time (if you don’t do that you will get cracking), depth and spacing of saw cuts; that’s all defined. This was all agreed upfront with each role player, so we were all on the same page. The result is that on our roads, what’s been cast to date is of a really high quality.

“Concrete roads are forever. It’s well documented in the US where roads built over 100 years ago are still around — and the technology of those days was a lot more crude than today’s, but they’re still in good nick.”

Maitre

Paul Maitre, a director of the project’s consulting civil and structural engineering firm, ADA Consulting Engineers.

Conclusion

Maitre says, contrary to the general state of the civil engineering business, his firm is extremely busy. “Last year was the busiest in the history of the company,” something he attributes to the fact that, unlike contracting firms that are wedded to the state of infrastructure roll-out by government, a consulting engineering firm can diversify.

Professional team

 Client    Central Edible Oil (CEOCO)
 Main contractor    Iguana Projects
 Structural steel engineers    Distinctive Trading
 Quantity surveyor    ProAfrica Property Services
 Project management    ProAfrica Property Services
 Consulting engineers    ADA Consulting Engineers
 Ready-mix cement provider    AfriSam

 

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