High pressure water supply strategy for mine bulk air coolers 34
transfer and psychometry – the approaches followed by Markov and Bayes to successfully develop maintenance policies and formulate thermal and production relations.
Van Rooyen used nine case studies to test the proposed method on underground bulk air- cooling systems. The results revealed that the actual cooling performance deviated from the optimal performance by approximately 29%, which resulted in a 2 °C increase in outlet air temperature. This was due to external and internal foulants being present on the heat transfer areas. Furthermore, the model predicted that internal fouling (18% of 29%) increased the BAC outlet air temperature by 1.3 °C, while external fouling (11% of 29%) increased the BAC outlet air temperature by 0.7 °C. Van Rooyen removed the external and internal foulants, which improved the mining revenue by R58 million and R30 million, respectively. Temperature reductions for the removal of external and internal foulants were expected to be 0.7 °C and 1.3 °C, respectively.
Although Van Rooyen improved the cooling of the CBAC by managing foulants, he did not focus on the water flow through these systems to reduce temperatures even further.
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1.4.2 Research conducted on water management
Conradie: Reconfiguring mine water reticulation systems for cost savings [11]
Conradie’s study concluded that significant energy and cost savings could be achieved by decreasing the cold water supply to underground end users. He investigated whether reconfiguring a mine WRS would decrease the water demand throughout the entire day. This reconfiguration entailed removing inefficient CWCs and replacing them with CBACs, which were installed on the entrance of each active mining level. Conradie developed a methodology to accurately evaluate the energy and cost savings associated with the reconfiguration. He used calculations and simulations to verify the actual data obtained from the specific mining operation. This verified data was used as inputs to accurately evaluate the energy consumption of the original and reconfigured WRS.
The strategy proposed to decrease the cold water consumption substantially throughout the day. The total water reduction was calculating by multiplying the amount of CWCs removed by their specific water flow rate. The reduction obtained was subtracted from the scaled water consumption of the original system. Conradie predicted an annual energy reduction of 49.1 GWh with an annual cost saving of R31.8 million.
Conradie’s study did not include the control of cold water through underground cooling systems while ensuring energy efficiency.
Van der Wateren: Optimising energy recovery on mine dewatering systems [22]
Van der Wateren’s study investigated the optimal use of ERDs to reduce energy consumption on deep-level gold mines. He found that previous studies conducted in the field of ERDs overlooked certain difficulties associated with the control of these systems. This entailed that certain technologies used were outdated. Therefore, Van der Wateren identified the need to develop a methodology to ensure that maximum energy reduction is achieved by means of ERDs. This methodology proposed to integrate ERDs into the dewatering system.
Van der Wateren decided to implement his strategy on a South African gold mine with a complex dewatering system. This system had four 3CPFSs and a closed-loop high pressure u-tube system. Although potential WSO initiatives showed a water flow reduction of 40 ℓ/s during the blasting period, the strategy was not implemented as temperatures were affected negatively. A high pressure u-tube system was used to redirect 15 ℓ/s from the 102 level (L) hot dam to the 77L hot dam. By integrating ERDs into the mine’s dewatering system, a total power saving of 3.5 MW was achieved, which resulted in a R1.7 million annual cost saving.
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Van der Wateren used a high pressure u-tube system to redirect water from one hot dam to another. However, he did not utilise this high pressure water to its full advantage. No cooling improvements were achieved by this study.
Taljaard: Analytical control valve selection for mine water reticulation systems [28]
Taljaard found that only a few people are underground during blasting periods, yet a large amount of water is consumed due to a lack of control. He proposed that minimising the water sent underground would result in significant energy savings on dewatering pumps. Taljaard’s study included developing and implementing an analytical control valve selection method to manage the water flow and pressure at appropriate positions throughout the WRS. This method was applied to a case study, which realised a 3.1 Mℓ water saving and a 3.55 MW power saving.
Taljaard’s study controlled water flow by reducing pressure. Even though energy savings were realised, underground cooling systems were affected negatively by a decrease in cold water.
Taljaard did not improve underground conditions by increasing water flow through cooling systems. However, these control valves can be used to develop a strategy to increase water flow through cooling systems.
Schoeman: The integrated effect of DSM on mine chilled water systems [39]
Schoeman investigated the effects that arise when reducing the amount of cold water sent underground to reduce the electrical energy used by dewatering pumps to pump water from underground operations. This was done by means of WSO projects. Schoeman used simulation models to determine the influences of reducing cold water. The research was implemented on two case studies.
Schoeman’s research concluded that reducing cold water underground could realise an energy saving of R8 million for Case Study A and R14 million for Case Study B. However, it was found that ERDs were operationally affected and underground cooling systems, such as BACs and CWCs, experienced a reduction in cooling duty. Case Study A experienced an average cooling reduction of 884 kW and Case Study B a reduction of 870 kW during non- entry periods.
Schoeman controlled the water flow to underground end users by means of WSO valves. He reduced the total amount of water and did not increase the water flow to achieve increased cooling duty for underground cooling systems.
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Buys: Optimising the refrigeration and cooling system of a platinum mine [51]
Buys investigated different optimisation strategies for implementation on a platinum mine’s surface refrigeration and cooling system as well as on the underground WRS. It was found that by optimising both the supply and demand of service deliveries, larger energy savings may be realised.
The strategies were identified to address possible inefficiencies in the refrigeration and cooling systems. This entailed to match the cooling supply with demand by means of water flow control. This was done by implementing variable speed drives (VSDs) and equipment to reduce cold water wastages on secondary spot coolers. Buys proposed installing mechanical valves (three-way high pressure valves) on CWCs to reduce wastages, but this could not be implemented due to strikes. However, VSDs were installed on cooling auxiliaries and BAC pumps. By doing this, Buys achieved an annual cost saving of R12.5 million as these VSDs improved the efficiency of the cooling auxiliaries by controlling the water flow rate based on the cooling supply. This was done without affecting the service delivery.
Buys used VSDs to control the water flow through surface cooling systems. Three-way high pressure valves were proposed to minimise water wastages on CWCs. However, none of these strategies can be implemented on secondary cooling systems as they do not use pumps to supply cold water.