Mines in general, make use of compressed air systems for daily operational activities. Compressed air on mines is traditionally distributed in two typical fashions. Firstly, direct pipe feed systems for single shafts or compressed air ring networks where multiple shafts are supplied with compressed air from an integral system. These compressed air networks make use of number compressors feeding the ring from various locations in the network. While mines have sophisticated control systems to control these compressors they are not dynamic. Compressors are selected on static priorities for a chosen time period of the day. While this is acceptable for some days it is not always the ideal solution. The compressed air demand of the ring is dynamic and it is difficult to estimate the future need of the system. The Dynamic Compressor Selector (DCS) is described as a solution to this problem. DCS is a computer based control system featuring a Graphical User Interface (GUI). The aim of DCS is to dynamically calculate a control pressure set-point, given the demand for compressed air as well as choose the optimal compressors to supply the given compressed air. This will reduce the power requirement of the compressed air ring as well as reduce compressor cycling. DCS was implemented and tested on a single mine compressed air system. Achieved results were 1.8 MW in electricity savings as well as the added benefit of reduced cycling. This saving results in a cost saving of R3.7 million per annum. The problems and shortfalls of the system are also discussed as well as possible future directions for moving forward. / MIng (Computer and Electronic Engineering), North-West University, Potchefstroom Campus, 2014

The generation of compressed air comprises 20% of the total electricity usage in the mining industry, although compressed air is often seen as a free source of energy. There are however significant costs associated with generating compressed air and maintaining a compressed air system. There are several methods to optimise the electricity used to generate compressed air. The focus of this study is on one of these methods – the implementation of a dynamic air compressor selector. A Dynamic Compressor Selector (DCS) system was developed to fulfil this purpose. DCS is a system that combines demand- and supply-side management of a compressed air network. DCS calculates a pressure set point for compressors and schedules the compressors according to the demand from the end-users. End-users include shafts, plants, workshops and smelters. DCS takes all of the compressors and end-users into consideration while doing the calculations. This dissertation focuses on the DCS implementation process and on the problems encountered by previous authors while implementing the DCS technology. Additional problems were encountered while the DCS technology was implemented. DCS was however still successfully implemented. This study will expand the implementation procedure to ensure that the technology can be implemented successfully in the future. DCS was implemented at a platinum mine in South Africa where it was able to calculate pressure set points for the compressors. DCS was able to accurately match the supply of, and demand for compressed air closely, resulting in lower overall compressed air usage. DCS improved compressor scheduling and control, limiting compressor cycling. Improved compressor scheduling and control resulted in significant decreases in the electricity used to generate compressed air at the mine. A target average evening peak clip of 2.197 MW was simulated, set and achieved. Evening peak clip power savings in excess of an average of 3 MW were achieved. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

<div>Vapor compression cycles are the most common method used to provide cooling to environments. In the residential area, refrigerator/freezers as well as air conditioners/heat pumps almost exclusively use vapor compression cycles. The driving force behind a vapor compression cycle is the compressor, where a variety of compressor types are used in the same application. While reciprocating compressors are found in the majority of refrigerator/freezers, scroll compressors are predominantly used in residential air conditioners. Yet other compressors have emerged as replacements due to increased efficiency. A R134a oil-free prototype scroll compressor and a R134a reciprocating compressor are operated in a hot-gas bypass test stand under refrigerator/freezer conditions to compare performance. Additionally, a R407C scroll compressor and a R410A rotary compressor are operated in a compressor calorimeter under air conditioning/heat pump conditions to compare performance. Experimental results show that the reciprocating compressor far outperforms the prototype scroll compressor in the refrigerator/freezer application, while the performance between the scroll and rotary compressors are almost equal in the air conditioning application.</div><div>Pressure fluctuation at compressor discharge is also measured in the compressor calorimeter to determine feasibility of applying a novel muffling design to air conditioning compressors, although it was found that traditional muffling methods currently used are effective to a degree such that this new method is unwarranted. Data from the compressor calorimeter is also used to investigate the accuracy of the AHRI 540 10-Coefficient Correlation compressor map in predicting performance both inside and outside the tested operating conditions. The AHRI 10-Coefficient Correlation achieves high accuracy inside tested operating conditions but is inept in extrapolating performance, where other map correlations are more accurate.</div>

Axial compressors are widely used in many aerodynamic applications. The design of an axial compressor configuration presents many challenges. Until recently, compressor design was done using 2-D viscous flow analyses that solve the flow field around cascades or in meridional planes or 3-D inviscid analyses. With the advent of modern computational methods it is now possible to analyze the 3-D viscous flow and accurately predict the performance of 3-D multistage compressors. It is necessary to retool the design methodologies to take advantage of the improved accuracy and physical fidelity of these advanced methods. In this study, a first-principles based multi-objective technique for designing single stage compressors is described. The study accounts for stage aerodynamic characteristics, rotor-stator interactions and blade elastic deformations. A parametric representation of compressor blades that include leading and trailing edge camber line angles, thickness and camber distributions was used in this study A design of experiment approach is used to reduce the large combinations of design variables into a smaller subset. A response surface method is used to approximately map the output variables as a function of design variables. An optimized configuration is determined as the extremum of all extrema. This method has been applied to a rotor-stator stage similar to NASA Stage 35. The study has two parts: a preliminary study where a limited number of design variables were used to give an understanding of the important design variables for subsequent use, and a comprehensive application of the methodology where a larger, more complete set of design variables are used. The extended methodology also attempts to minimize the acoustic fluctuations at the rotor-stator interface by considering a rotor-wake influence coefficient (RWIC). Results presented include performance map calculations at design and off-design speed along with a detailed visualization of the flow field at design and off-design conditions. The present methodology provides a way to systematically screening through the plethora of design variables. By selecting the most influential design parameters and by optimizing the blade leading edge and trailing edge mean camber line angles, phenomenon s such as tip blockages, blade-to-blade shock structures and other loss mechanisms can be weakened or alleviated. It is found that these changes to the configuration can have a beneficial effect on total pressure ratio and stage adiabatic efficiency, thereby improving the performance of the axial compression system. Aeroacoustic benefits were found by minimizing the noise generating mechanisms associated with rotor wake-stator interactions. The new method presented is reliable, low time cost, and easily applicable to industry daily design optimization of turbomachinery blades.

Eskom is under increasing pressure to provide reliable and sustainable electricity. Demand Side Management (DSM), offers a short– to medium–term solution to this problem. During 2009, the mining sector consumed approximately 16% of the domestic electricity supplied by Eskom. This made the mining sector one of the major targets for Eskom–initiated DSM programmes. The mining industry uses compressed air for a wide variety of applications and production purposes. This creates many opportunities to reduce electricity consumption and operating costs. Reducing the airsystem demand may however not result in significant electrical energy savings, unless the compressed–air supply is accurately managed to meet the reduced demand. Until recently, compressor control in the mining sector generally consisted of operating the compressors continuously, regardless of the actual demand for compressed air. Excessive compressed air is blown off into the atmosphere resulting in energy loss. This usually occurs when the compressors are operated manually. A computer–controlled compressor management solution, which optimises the efficiency potential of the compressed–air supply, is required to obtain significant electrical energy savings. The need for such a solution was addressed by the development of an energy management solution for mine compressor systems. This solution is referred to as Energy Management System (EMS) and is capable of starting, stopping, loading and unloading compressors. In addition to this, compressor output can be controlled to maintain a desired pressure set–point. In this study, the development and implementation of EMS on ten different mine compressor systems is presented. Automatic compressor capacity control was implemented, while an operator manually initiated compressor starting; stopping; loading and unloading, according to EMS control schedules. Centralised compressor control is one of the main advantages offered by EMS, especially for compressed–air systems with multiple compressor systems at different geographic locations. EMS facilitated effective and sustainable electrical energy reductions for all these compressed–air systems. / Thesis (M. Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2011.

Eskom is under increasing pressure to provide reliable and sustainable electricity. Demand Side Management (DSM), offers a short– to medium–term solution to this problem. During 2009, the mining sector consumed approximately 16% of the domestic electricity supplied by Eskom. This made the mining sector one of the major targets for Eskom–initiated DSM programmes. The mining industry uses compressed air for a wide variety of applications and production purposes. This creates many opportunities to reduce electricity consumption and operating costs. Reducing the airsystem demand may however not result in significant electrical energy savings, unless the compressed–air supply is accurately managed to meet the reduced demand. Until recently, compressor control in the mining sector generally consisted of operating the compressors continuously, regardless of the actual demand for compressed air. Excessive compressed air is blown off into the atmosphere resulting in energy loss. This usually occurs when the compressors are operated manually. A computer–controlled compressor management solution, which optimises the efficiency potential of the compressed–air supply, is required to obtain significant electrical energy savings. The need for such a solution was addressed by the development of an energy management solution for mine compressor systems. This solution is referred to as Energy Management System (EMS) and is capable of starting, stopping, loading and unloading compressors. In addition to this, compressor output can be controlled to maintain a desired pressure set–point. In this study, the development and implementation of EMS on ten different mine compressor systems is presented. Automatic compressor capacity control was implemented, while an operator manually initiated compressor starting; stopping; loading and unloading, according to EMS control schedules. Centralised compressor control is one of the main advantages offered by EMS, especially for compressed–air systems with multiple compressor systems at different geographic locations. EMS facilitated effective and sustainable electrical energy reductions for all these compressed–air systems. / Thesis (M. Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2011.

<p>  </p> <p>The focus of this work was to characterize the overall performance effects due to altering the stagger angle of a variable inlet guide vane (VIGV) on a multistage axial compressor. Data were collected from the Purdue three-stage axial compressor (P3S). The stagger angle from the VIGV was varied thrice from the baseline configuration in increments of 5 degrees resulting in four configurations with angles of 4 deg, 9 deg, 14 deg, and 19, where the baseline configuration was 9 degrees. </p> <p>Compressor performance data were collected and analyzed for each stagger angle configuration along three corrected speeds (68%, 80%, 100%). Each speedline consisted of approximately six loading conditions for which the corrected mass flow rate was matched for each configuration to allow for a basis of comparison among the configurations. Stalling mass flow rates and stall inception were also investigated. Total pressure and total temperature rakes were installed throughout the compressor to investigate the performance at interstage locations for each loading condition. In addition to the rakes, static pressure taps were distributed along the compressor and unsteady pressure measurements were distributed circumferentially. Capacitance probes were installed over each of the three rotors to evaluate rotor tip clearance measurements during the tests. The effects of the stagger angle on the stability margin of the compressor were also characterized. Each speedline presented, thus, includes a representative stall point in addition to the six loading conditions where detailed flow field traverses were conducted. </p> <p>The results of this investigation showed that while the total pressure ratio (TPR) increased as the stagger angle decreased, the stability margin was reduced. The opposite trend was observed with a decrease in overall TPR across the compressor and an increase in stability margin for increased stagger angles. Based on findings from previous authors, this trend was anticipated. A similar metric for monitoring compressor performance is isentropic efficiency. This investigation utilized both temperature-based and torque-based isentropic efficiency. The greatest effect of the VIGV stagger angle on compressor isentropic efficiency occurred at the lowest loading conditions, and there was no discernible impact on isentropic efficiency at high loading conditions for this case. As VIGVs typically have the greatest impact on off-design conditions, this trend was expected. The varied stagger angle configurations had no discernible effect on the type of stall inception mechanism experienced by the compressor. The primary effect on stall that was consistent across the configurations was a noticeable increase in the duration and strength of modal oscillations present throughout the compressor with increased stagger angles, indicating an increase in stability. </p> <p>The data collected and presented herein provide a unique, robust dataset to improve understanding of the effects of changing stagger angles on variable inlet guide vanes on multistage axial compressors. These data correspondingly provide a unique training set and validation method for predictive technology. </p>

A performance comparison of heat pumps using a scroll (Sanden) and a reciprocating (Bitzer) compressor was conducted experimentally. The refrigerant used was R600a (isobutane). The heat pump components were evaluated performance-wise through: volumetric and isentropic efficiency of the compressors; the UA-value of the condensers and evaporators; sensible enthalpy differences between the liquid and the suction line in the internal heat exchanger; and overall heat pump system comparison as the coefficient of performance. The Bitzer heat pump had existing measuring devices and equipment installed, and it was already filled with refrigerant. The Sanden heat pump required installation of equipment and measuring devices and a refrigerant refill. The refrigerant charge was decided according to the criteria of the lowest compressor speed, which had an effect of overcharge for higher speeds. The measurements included the temperature of water and refrigerant, pressure of the refrigerant, water volume flow, and compressor power. The heat pumps performances were then evaluated based on these parameters. The Sanden compressor showed higher volumetric efficiency than the Bitzer compressor, for the two lower (out of three) speeds of the compressor. The isentropic efficiency of the Bitzer compressor proved to be higher for all pressure ratios out of the three speeds respectively. The condenser in the Bitzer heat pump showed proper UA-values based on the temperature differences between refrigerant and heat sink. The UA-values of the Sanden heat pump condenser did not increase with compressor speed which then gave a larger temperature difference between refrigerant and heat sink, for the two higher compressor speeds. The evaporators had a similar issue with the temperature difference between refrigerant and heat source, which also showed on the UA-values. The internal heat exchanger in the Bitzer heat pump had a larger sensible enthalpy difference on the suction side compared to the liquid side, when condenser subcooling was low, indicating that some fraction of refrigerant was being condensed instead. The Sanden heat pump instead had higher condenser subcooling and the sensible enthalpy difference showed to be very low in the internal heat exchanger. Finally, the coefficient of performance showed to be slightly higher in the Bitzer heat pump for almost all evaluated condensation and evaporation temperatures. / En jämförelse av prestandan för två värmepumpar, en med scroll- (Sanden) och en med kolvkompressor (Bitzer) har gjorts. Köldmedlet som användes var R600a (isobutan). Komponenterna och hur deras prestanda blev utvärderad följer här: kompressorernas volymetriska och isentropisk verkningsgrad; kondensorns och förångarens UA-värden; den sensibla entalpiskillnaden mellan gas- och vätskeledning i den interna värmeväxlaren; en övergripande jämförelse av värmepumparna i form av deras värmefaktor. Värmepumpen med Bitzerkompressor utvärderades med befintliga komponenter och mätutrustning, och en redan fylld mängd köldmedium. Värmepumpen med Sandenkompressor installerades med mätutrustning och komponenter, och fylldes med köldmedium. Mängden köldmedium bestämdes utifrån kriterier för det lägsta varvtalet på kompressorn, vilket visade sig ge en för stor mängd köldmedium vid de högre varvtalen. Mätningarna inkluderade temperatur på vatten och köldmedium, köldmediets tryck, vattnets volymflöde samt kompressorns effektbehov. Prestandan för värmepumparna är sedan utvärderad utifrån dessa data. Sandenkompressorn visade en högre volymetrisk verkningsgrad för de två lägre (av tre) hastigheterna utvärderade i experimenten, jämfört med Bitzer. Den isentropiska verkningsgraden var högre i Bitzerkompressorn för samtliga tryckförhållanden för de tre respektive hastigheterna. Kondensorn i Bitzervärmepumpen uppvisade goda UA-värden, baserat på temperaturskillnaderna mellan köldmedium och värmesänka. Kondensorn i Sandenvärmepumpen visade ingen förbättring av UA-värden när kompressorns hastighet ökade, vilket i sin tur gav upphov till stora temperaturskillnader mellan köldmediet och värmesänkan. Förångarna i båda värmepumparna uppvisade liknande problem med höga temperaturskillnader mellan värmekälla och köldmedium, vilket även deras UA-värden visade. Den interna värmeväxlaren i Bitzervärmepumpen visade större skillnad i den sensibla entalpin på sug- jämfört med vätskesidan, när underkylningen i kondensorn var låg, vilket indikerade på att en del av köldmediet istället kondenserade. I Sandenvärmepumpen var kondensorns underkylning högre vilket då uppvisade en liten skillnad i den sensibla entalpin mellan de båda sidorna. Slutligen så visade Bitzervärmepumpen en något högre värmefaktor än Sandenvärmepumpen för nästan alla utvärderade kondenserings- och förångningstemperaturer.

Critical equipment plays an essential role in industry because of its lack of redundancy. Failure of critical equipment results in a major economic burden that will affect the profit of the enterprise. Lack of redundancy for critical equipment occurs because of the high cost of the equipment usually combined with its high reliability. When we are analyzing the reliability of such equipment, as a result, there are few opportunities to crash a few pieces of equipment to actually verify component life. Reliability is the probability that an item can perform its intended function for a specified interval of time under stated conditions and achieve low long-term cost of ownership for the system considering cost alternatives. From the economical standpoint, the overriding reliability issue is cost, particularly the cost of unreliability of existing equipment caused by failures. Classical questions about reliability are: · How long will the equipment function before failure occurs? · What are the chances that a failure will occur in a specified interval for turnaround? · What is the best turnaround interval? · What is the inherent reliability of the equipment? · What are the risks of delaying repair/replacements? · What is the cost of unreliability? · … We will try to answer these questions for a critical reciprocating compressor, which has been in service for only 4 years and has undergone only few failures. Professionals in all industries are faced with the problems of performing maintenance actions and optimizing maintenance planning for their repairable systems. Constructing stochastic models of their repairable systems and using these models to optimize maintenance strategies require a basic understanding of several key reliability and maintainability concepts and a mathematical modeling approach. Therefore, our objective is to present fundamental concepts and modeling approaches in the case of a critical reciprocating compressor. We developed a stochastic model not to simulate a reciprocating compressor with a complete set of components but mainly to optimize the overhaul period taking into account the main failure modes only. How to lower the cost? How to reduce or remove maintenance actions that are not strictly necessary? How to improve the long-term profitability of ageing plants with the strict respect of Health-Safety-Environment HSE requirements? A reciprocating compressor is a complex machine that cannot be described with a single reliability function. A compressor has several failure modes. Each failure mode is assumed to have its own Weibull cumulative distribution function. The compressor is then a system with several Weibull laws in series. We will extend the usual procedure for minimizing the expected total cost to a group of components. Different components may have different preventive maintenance “needs”, but optimizing preventive maintenance at the component level may be sub-optimal at the system level. We will study also the reliability importance indices that are valuable in establishing direction and prioritization of actions related to a reliability improvement plan, i.e. which component should be improved to increase the overall lifetime and thus reduce the system costs. When considering a large system with many items that are maintained or replaced preventively, it is advantageous to schedule the preventive maintenance in a block such that the system downtime is kept as small as possible. This requires that the resources are available so that the maintenance of components can be performed simultaneously or according to a well-defined sequence. The result of the stochastic model optimization came as a surprise. We thought to find a new mean-time-between-failure MTBF, larger than the actual overhaul period. Actually, the model showed that there is no economical interest to schedule a systematic preventive maintenance for this reciprocating compressor. Nevertheless, we cannot wait for a failure (and the associated corrective maintenance) because the loss-of-production cost is too high and this compressor has no spare. Preventive maintenance is not the optimum strategy, but predictive maintenance is. But what means predictive maintenance? It is a maintenance policy to regularly inspect equipment to detect incipient changes or deterioration in its mechanical or electrical condition and performance. The idea behind this is to perform corrective maintenance only when needed, before the occurrence of failure. We need to find how to detect performance deterioration of the compressor with a couple of weeks or days notice before failure. So it is possible to schedule a right maintenance activity at the optimum moment. To summarize, the main findings of this thesis are · a new method to estimate the shape factor of a Weibull distribution function, · a stochastic model demonstrating that we have to move from systematic preventive maintenance to predictive maintenance, · a low cost system based on thermodynamic approach to monitor a reciprocating compressor, · an automatic detection of performance deterioration.

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