A systematic approach to evaluate in-stope compressed air inefficiencies in deep-level mines

Abstract

The current decreasing production trend in South Africa and the role of compressed air inefficiencies in pipe networks are introduced in this study. Compressed air distribution systems that supply mining equipment have low mechanical efficiency. Various factors contribute to this low efficiency such as undersized pipes, poor control valve set-point control, and inactive sections that are not sealed off. A detailed literature survey revealed the initiative to investigate in-stope compressed air inefficiencies and the effect thereof on drilling pressure. The study provides a verified method for identifying compressed air inefficiencies inside the stoping area and evaluating the viability and efficacy of various approaches to address in-stope compressed air inefficiencies. A method is developed that systematically evaluates in-stope inefficiencies by establishing the flow and pressure baselines for the supply, demand and reticulation network of a compressed air system. The severities of the inefficiencies of the different compressed air sections are compared and prioritised using a Likert scale. After the compressed air system has been characterised by means of flow and pressure baselines, the method is used to develop a baseline simulation of a deep-level mine stoping area. The method addresses simulation time, parameters, components and accuracy. The method provides a theoretical approach for verifying the stope simulation model against the pressure and flow baseline, using the mean absolute error method. Using the verified simulation, the method applies literature studies and theory to highlight how a typical compressed air inefficiency will present itself in a stope network. The method is used to practically verify a compressed air inefficiency inside a stope network using measurement instrumentation. Finally, the method discusses generic simulation strategies that aim to mitigate compressed-air-related inefficiencies.

The method was implemented on a case study mine where it was used to analyse different sections of a compressed air system, aiming to identify in-stope inefficiencies. A Likert scale was used to assess various sections to ensure accurate representation of stope inefficiencies. Through this method, it was determined that the stoping section emerged as the top priority area for improvement in the case study mine. A baseline simulation of a case study stope was developed using simulation software. The characterisation curves showed the case study stope experienced a total pressure loss of 75 kPa from the travelway to the stope face. The 4" pipe section exhibited a pressure loss of 32 kPa over its length, while a pipe reduction (4" to 2") inside the case study stope resulted in a pressure loss of 43 kPa. To verify the identified inefficiencies, pressure sensors were installed throughout the stope. The case study stope experienced a total pressure loss of 80 kPa from the cross-cut intake to the face. During the drilling period, the 4" pipe experienced a 37 kPa pressure loss from the cross-cut intake while the 2" section experienced a further 43 kPa pressure loss. These results aligned with the simulated pressure loss. Six mitigation strategies were developed using a combination of theoretical principles and simulation software. The simulated strategies indicated that the identified inefficiencies can be mitigated by increasing the pipe size of the compressed air network to accommodate the flow demand of the network.