A holistic approach to evaluate the feasibility of implementing ice thermal storage on deep mines
Over the past decade, the mining industry has been faced with several challenges that have contributed towards dwindling profit margins across many South African deep-level mines. One of the major, if not the most significant contributing factor has been attributed towards ever-increasing operating costs, primarily resulting from escalating prices in electricity. Refrigeration systems have been identified as one of the largest single energy consumers in the mining sector, contributing up to 24% of a mine’s total electrical energy consumption. To assist in offsetting low commodity prices and reducing margins for profit, optimising cooling systems on existing mining operations has become critical for the current and future sustainability of gold mining operations in South Africa. Although a wide variety of load management initiatives have already been extensively implemented on mine refrigeration systems, the subsequent load-shifting capability and cost-saving potential remains limited. The sustainability and profitability of deep-level gold mining in South Africa remains under threat. To alleviate financial strain prompted by ever-increasing electricity tariff rates, a need was identified to implement more effective load management strategies and techniques capable of maximising the cost-saving potential of mine refrigeration systems. Ice thermal storage has the potential to make up the shortfall. Ice thermal storage systems represent a relatively new technology utilised on mines and as a result, studies are limited. Through widespread utilisation in the building industry, ice thermal storage systems have revealed countless benefits, of which the most instrumental is the cost-saving potential. By storing energy in the form of ice during periods when electricity tariffs are cheapest and releasing it during periods when electricity is most expensive, lucrative cost savings can be achieved. The aim of the study is to prove whether it is worthwhile to implement ice thermal storage on mines as an alternative, more effective cost-saving solution. Therefore, extending the knowledge in the field of ice based thermal storage, contributing to the development and wider utilisation of such systems in the mining industry. To accomplish this, a generic methodology that can be utilised to evaluate and sustainably implement ice thermal storage as an alternative cost-saving technique within the mining industry was developed. Through application of a simulation strategy incorporating analytical approaches, a feasibility analysis was incorporated to predict system behaviour and determine project feasibility without capital expenditure. Improved implementation strategies and operation approaches are also provided to assist in the sustainability of future installations within the mining industry. A South African deep-level gold mine was chosen as the case study mine. Mine P was selected as it represents one of the only mines in South Africa currently employing ice thermal storage to capitalise on a variable time-of-use electricity tariff structure. Due to extended periods of downtime throughout the 2018/2019 financial year, Mine P’s ice thermal storage system afforded a unique opportunity for this study to analyse the operational and financial impact on the holistic cooling system, with and without the use of ice thermal storage. Through case study implementation, the analytical approaches in constructing an accurate predictive simulation model on the use of ice thermal storage on mines was verified and validated. Validation results revealed an average percentage error of 6.5%. Actual implementation results with and without the use of ice thermal storage were critically analysed and compared, quantifying the financial impact and benefits gained by incorporating ice thermal storage on a mine cooling system. A holistic approach was adopted. Actual implementation results revealed significant load reduction and cost-saving potential. An average hourly load shift of 6.0 MW was achieved for the morning Eskom peak period during weekdays. Whereas, for Eskom’s evening peak period, an average hourly load shift of 7.1 MW was achieved. This translates to an annual cost-saving potential of R 4.5 million. A reduction of R 502 per megalitre of water cooled was revealed when comparing a conventional refrigeration system to that incorporating the use of ice thermal storage. In addition, an average decrease of 42 kWh per megalitre of water cooled was realised. Consequently, service delivery requirements were compromised, with an overall deterioration of 7.1%. Represented by the global systems coefficient of performance, a reduction in the performance of the holistic refrigeration system of 14.3% was revealed. Comparing estimated cost savings to-date to that of the initial capital investment, a return on investment of just under 123 months (10.3 years) has been approximated. Based on the findings obtained throughout this study, it is clear that ice thermal storage systems remain expensive with an unfavourable payback period. Since the majority of deep-level gold mines across South Africa are suffering with dwindling profit margins, ice thermal storage does not pose a feasible cost-saving strategy for many mining operations. However, ice thermal storage systems should be considered for implementation on profitable mines with a life of mine greater than 10 years. Not only does ice thermal storage offer significant cost-saving potential, but with mines planning to dig deeper in search of gold-rich ore deposits, ice thermal storage allows for expansion without the need to invest in additional refrigeration units.
- Engineering