Study Group Problems 

Industry:

Sugar Cane Processing

Industrial Representative:

Richard Loubser, Sugar Milling Research Institute NPC,

c/o University of KwaZulu-Natal, Durban.

Moderator:

Student Moderators:

Problem Statement:

In South Africa, the diffuser is a popular method for extracting sugar from sugar cane. It is a counter current washing machine with shredded cane added at one end and imbibition added at the other end of a chain (ladder) conveyor system. The water percolates through the cane bed and is pumped forward and reintroduced to the cane bed closer to the end where the cane is added. This is how the counter current effect is achieved.

The system relies on the free percolation of the water or juice through the cane bed. It was found during the development of the cane diffuser, however, that fine particles tend to form a layer in the bed which retards the free flow of the juice through the bed.

To ensure that the flow through the bed is restored, lifting screws are used. These are arranged across the diffuser bed as shown in Figure 1.

Figure 1. Lifting screws in a diffuser

Most lifting screws rotate at 40 revs per minute and are of a similar design regardless of make of diffuser.

As the cane passes the screws, they churn up the cane to disrupt any layers of fine particles that may have formed on the cane bed. Adjacent screws turn in opposite directions to enhance the effect of the screws.

The mounting of the lifting screw is designed with a shear pin that fails to protect the screw itself from failure. Given the design of the screw, it is possible to determine the strength of the pin.

Many factories are operating with lifting screws that are not working because the shear pin has failed. There is very little in the literature to guide the design of the lifting screw to handle the forces experienced in churning up the bed.

It is tempting to replace the pin with stronger components. This, however, has disastrous consequences. It would be far more acceptable if the lifting screws could be designed according to the maximum forces that would be experienced.

It would be useful if a method for estimating the load on the lifting screw could be determined. A typical cane preparation is shown in Figure 2. It consists of long strands with lengths in the order of 7 cm and thickness of a few millimetres. In between the long strands are shorter, thinner strands and then there is the fines and pith component. To churn this up, it is required that the bed is torn apart as it passes the lifting screws.

Figure 2. Prepared cane

Anecdotal evidence indicates that the effort required by the lifting screws reduces with increasing the amount of juice held up in the bed. Does the lubricating and buoyancy effect outweigh the mass effect? Is there a balance point?

The desired output from this study would be a way of estimating the worst-case design load for the lifting screw. The model would need to estimate how factors such as strand length, packing density and juice hold-up would interact and influence the design load.

Supporting Material

First-day Presentation

Report-back Presentation

A dream to come true, or irreversible damage about to hit Coastal-Marine Tourism & Biodiversity and threaten Climate Change Resilience

Industry: Tourism Sector (Coastal & Marine Tourism), Robotics

Industry Representative: Dr Lombuso Precious Shabalala,

Department of Applied Management, UNISA

Student Moderators:

Problem Statement:

The sea or ocean hosts a unique, largely unexplored biodiversity that is incredibly fragile. The impacts of deep-sea mining could be irreversible, resulting in habitat destruction, species extinction, climate disruption, and disruption of oceanic food chains, as well as an impact on tourism activities.  Fast-advancing technologies have now granted access to even the deepest parts of the ocean, fuelling interest in commercial exploration of deep-sea resources, such as metals and rare earth elements. Deep-sea mining (DSM) activities are currently planned in the economic zones of several national jurisdictions, particularly Pacific Island States, and in areas beyond national jurisdiction (Kaikkonen & van Putten, 2021). Ma et al. (2022) define Deep-sea mining as the utilisation of hydrodynamic or mechanical methods to transport mineral ores from the seabed to the ocean surface and then transport the ores to land-based processing plants by ship. The scholars further note that, despite the vast amount of research and development that has made significant progress, there are still many obstacles to its industrial development activities, which include concerns about environmental pollution and sustainable development issues, regardless of the employment of technological advancements such as ore exploration, robotics, and hydrodynamic lifting (See Figure 1). 

Figure 1:  Schematic diagram of the mining system. Source: Yao et al., 2025.

Additionally, these activities have garnered attention from governments, companies, and scientific research institutions.  Figure 2 presents the multifaceted impacts of plume generation. A deep-sea plume is a cloud of fine sediment suspended in the water, primarily caused by human activities like deep-sea mining or natural events like storms. These plumes can spread over large areas, reduce water clarity, and potentially smother or poison marine life by burying them or releasing toxic compounds.

Figure 2:  Schematic of plume impacts. Source: Yao et al., 2025.

Coastal and Marine tourism are affected by deep-sea mining.  For instance, a study conducted in Fiji found that pristine coral reefs possess a tremendous potential for contributing to tourism and economic development (Folkersen et al., 2018).  In addition, the study revealed that its tourism economy relies heavily on diving and coastal activities. Unfortunately, despite the importance of coral reefs to the Fijian tourism sector, the Fijian Government has granted exploration licenses to mining companies to assess the viability of deep-sea mining (DSM). Understanding divers’ perceptions of coral reefs and environmental issues is, therefore, paramount to sustaining the tourism sector. There is concern that DSM may negatively impact reef-related tourism due to tourists’ perception that DSM activities degrade Fiji's coral reefs. A study by Kaikkonen and van Putten (2021) confirms that economic development and human activities in the ocean are accelerating, with maritime activities at the forefront of numerous government, research, and industry initiatives aimed at expanding the ‘Blue Economy’. The deep sea is being promoted as the new frontier for resource extraction (Kaikkonen & van Putten, 2021).

Tourism is one of the top sectors that contributes to Gross Domestic Product and creates jobs in South Africa and globally. A call to halt deep-sea mining in Africa (Greenpeace, 2025) before it begins has already garnered over 4,822,507 signatures (on petitions) opposing deep-sea mining. These individuals argue that the deep sea is a treasure trove of biodiversity and home to countless wonders and possibilities. It is also one of our best allies against climate change. Kaikkonen and van Putten (2021) concur regarding the deep sea as the largest ecosystem on the planet.

The problem to investigate

It is understood that oceans produce approximately 50% of the oxygen we breathe, absorb around 25% of global CO₂ emissions, and capture approximately 90% of the excess heat generated by those emissions (Greenpeace Africa, 2025). This suggests that oceans are our first line of defence against climate change. Destabilising such could lead to a disaster against humanity.

• Currently, there is no guarantee of a sustainable mining system that optimises the conservation of life forms (biodiversity) and tourism activities, including climate change resilience.
• Secondly, there is no assurance that benefits yielded from the blue economy will reach local communities and contribute to genuine sustainable development.

Building on the previously presented Figures 1 and 2, this problem seeks to develop:

1. Mathematical models for the creation and spread of plumes in deep-sea mining.
2. A mathematical model that supports a sustainable deep-sea mining system or method, which, upon its implementation, could optimise the conservation of life forms and tourism activities and contribute to climate change resilience.

References

Folkersen, M.V., Fleming, C.M. and Hasan, S., 2018. Deep-sea mining's future effects on Fiji's tourism industry: A contingent behaviour study. Marine Policy, 96, pp.81-89.

Greenpeace, 2025. Stop deep sea mining before it starts. Available from: https://www.greenpeace.org/international/act/stop-deep-sea-mining/ https://www.greenpeace.org/africa/en/blog/58872/deep-sea-mining-africa-cannot-stay-still/  . Access Date:10 Nov 2025.

Kaikkonen, L. and van Putten, I., 2021. We may not know much about the deep sea, but do we care about mining it?. People and Nature, 3(4), pp.843-860.

Ma, W., Zhang, K., Du, Y., Liu, X. and Shen, Y., 2022. Status of Sustainable Development of Deep-Sea Mining Activities. Journal of Marine Science and Engineering, 10(10), p.1508.

Yao, W., Tian, C., Teng, Y., Diao, F., Du, X., Gu, P. and Zhou, W., 2025. Development of deep-sea mining and its environmental impacts: a review. Frontiers in Marine Science, 12, p.1598584.

Additional Material

Greenpeace Africa. URGENT petition telling African Govts to deliver a firm NO’ to deep sea mining before it starts. https://www.facebook.com/share/p/1FZTrFPksA/. Access Date: 11 Nov 2025.

PHYS.ORG.  Deep-sea mining risks disrupting the marine food web, study warns. Available from:https://phys.org/news/2025-11-deep-sea-disrupting-marine-food.html. Access Date: 11 Nov 2025.