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Pavese V.,Polytechnic University of Turin | Millar D.,Rehabilitation and Applied Research Corporation MIRARCO | Verda V.,Polytechnic University of Turin
ECOS 2015 - 28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems | Year: 2015

The process of gas compression in the downcomer shaft or pipe of a hydraulic air compressor is nearly isothermal due to: i) the mass flow rate of water being typically of three orders higher than that of the gas it compresses, ii) water having a heat capacity approximately four times that of air, and iii) the intimate contact and large heat transfer area between the gas phase and the liquid phase of the bubbly flow. A formulation for estimation of the efficiency of a closed or open loop hydraulic air compressor, expressed in terms of the principal hydraulic air compressor design variables, is presented. The influence of a hitherto underappreciated factor affecting the performance of these installations, such as the solubility of the gas being compressed in the water, is explored. A procedure for estimating the yield of compressed gas, accounting for these solubility losses, is explained and used to determine the mechanical efficiency of historical hydraulic air compressor installations from reported performance data. The result is a significant downward revision of hydraulic air compressor efficiency by approximately 20 percentage points in comparison to most reported efficiencies. However, through manipulation of co-solute concentrations in the water, and the temperature of the water (through regulation of the ejection of compression heat), the mechanical efficiency can be increased to the formerly reported levels. The thermo-economic implication of these efficiency determinations is that in a modern context, hydraulic air compressors may be able to outperform conventional mechanical gas compression equipment. Source


Romero A.,Rehabilitation and Applied Research Corporation MIRARCO | Carvalho M.,Federal University of Paraiba | Millar D.,Rehabilitation and Applied Research Corporation MIRARCO
ECOS 2015 - 28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems | Year: 2015

Mining operations are located in increasingly remote areas to search for relatively high grade mineral deposits, despite the challenges that arise. These challenges are fundamentally logistic and directly impact the profitability of the remote operation. One of the main challenges is energy supply, since locations that lack of a power grid, fuel pipelines or adequate - if existing - road access, have substantially increased energy-related operating costs. Today, a remote mine's energy costs add up to 40% of total operating expenses; this is in contrast with grid connected, accessible mines, where energy costs seldom reach 20%. In searching for more cost effective energy supply options, the present work uses the Optimal Mine Site Energy Supply (OMSES) concept to optimize the design and operation schedule of a remote underground mine's energy supply system. Energy demand, weather, and economic data were collected and processed, emulating a remote mine in the Northwest Territories, Canada. The optimal energy system minimized the total cost of the energy supply, which included not only the operation cost, but also the annuitized capital investment in equipment. Subsequently, the optimal system's design for the considered demands and environmental factors was subject to simulation and control optimization. Wind power was included in the formulation. Issues such as the necessary spinning reserve, and the penetration curtailment, among others, were analyzed, both in the design and the control problems. The work identified potential improvement for the integrated design and control of a remote mine's energy system, in particular when including a renewable energy resource with a considerable level of variability, i.e. wind. The optimal solution included the installation of two wind turbines, achieving 3% diesel savings with a 20% increase of investment compared with the conventional design. The model was validated with a real project - The Diavik Diamond Mine energy supply system, which included a wind farm with four turbines. A Model Predictive Control (MPC) approach was chosen to optimize scheduling in a simulation with variable conditions of wind speed and ambient temperature; this proved to be a convenient method to assess the robustness of optimal designs. Results also confirmed the limitations of design optimization when uncertainties related to wind energy were ignored. Source


Trapani K.,Laurentian University | Trapani K.,Rehabilitation and Applied Research Corporation MIRARCO | Millar D.L.,Laurentian University | Millar D.L.,Rehabilitation and Applied Research Corporation MIRARCO | Smith H.C.M.,University of Exeter
Renewable Energy | Year: 2013

An original proposal for the deployment of photovoltaic (PV) systems in offshore environments is presented in this paper. Crystalline PV panels are considered where they are deployed on pontoon type structures and there are six case study examples precedent practise of such deployments in lakes and reservoirs (but not seas). The authors put forward an alternative based on flexible thin film PV that floats directly on the waterline. The paper then concentrates on the techno-economic appraisal of offshore PV systems in comparison to conventional marine renewable energy technologies. The difficulties of comparing offshore technology projects developed in various countries, using different currencies and in different years are overcome so that such comparisons are made on an equitable basis. The discounted cost of electricity generated by each scheme is determined, including capital expenditure (CAPEX) and yearly operation and maintenance (O&M) costs.Actual wind, tidal (current turbines and barrages) and wave projects were considered in the analysis alongside crystalline and thin film PV. Thin film PV was found to be economically competitive with offshore wind energy projects for latitudes ranging from 45°N to 45°S. The specific yield, assessed in terms of GWh/km 2 was higher for thin film PV than for wind, wave and tidal barrage systems. In addition the specific installed capacity, expressed in MW/km 2 was also higher than the other conventional technologies considered (excluding tidal current turbines). © 2012 Elsevier Ltd. Source


Romero A.,Rehabilitation and Applied Research Corporation MIRARCO | Romero A.,Laurentian University | Romero A.,BESTECH Ltd | Millar D.,Rehabilitation and Applied Research Corporation MIRARCO | And 4 more authors.
Applied Thermal Engineering | Year: 2015

Mine dewatering can represent up to 5% of the total energy demand of a mine, and is one of the mine systems that aim to guarantee safe operating conditions. As mines go deeper, dewatering pumping heads become bigger, potentially involving several lift stages. Greater depth does not only mean greater dewatering cost, but more complex systems that require more sophisticated control systems, especially if mine operators wish to gain benefits from demand response incentives that are becoming a routine part of electricity tariffs.This work explores a two stage economic optimization procedure of an underground mine dewatering system, comprising two lifting stages, each one including a pump station and a water reservoir. First, the system design is optimized considering hourly characteristic dewatering demands for twelve days, one day representing each month of the year to account for seasonal dewatering demand variations. This design optimization minimizes the annualized cost of the system, and therefore includes the investment costs in underground reservoirs. Reservoir size, as well as an hourly pumping operation plan are calculated for specific operating environments, defined by characteristic hourly electricity prices and water inflows (seepage and water use from production activities), at best known through historical observations for the previous year. There is no guarantee that the system design will remain optimal when it faces the water inflows and market determined electricity prices of the year ahead, or subsequent years ahead, because these remain unknown at design time. Consequently, the dewatering optimized system design is adopted subsequently as part of a Model Predictive Control (MPC) strategy that adaptively maintains optimality during the operations phase.Centralized, distributed and non-centralized MPC strategies are explored. Results show that the system can be reliably controlled using any of these control strategies proposed. Under the operating conditions considered, total annualized cost savings in the range of 50%, in comparison with non-optimized designs, can be achieved through design optimization and the use of predictive control. © 2015 Elsevier Ltd. Source


Levesque M.,Rehabilitation and Applied Research Corporation MIRARCO | Levesque M.,Laurentian University | Millar D.,Rehabilitation and Applied Research Corporation MIRARCO | Millar D.,Laurentian University | Paraszczak J.,Laval University
Journal of Cleaner Production | Year: 2014

Energy consumption rises as mines extract ore from deeper levels. Rising energy costs, increased public scrutiny and enhanced awareness of carbon emissions are factors which can influence mining companies to examine and reduce their energy use. A comparison of best practice energy management initiatives of the 1970's with more recent activities revealed that several measures reported for both periods were similar. After best practice measures have been adopted, the lack of reliable data will impede a continuous improvement approach. Mining companies routinely report on sustainability issues via corporate sustainability reports, for which several frameworks exist. An assessment of the energy-related reporting requirements of these guidelines determined that the development of transparent, standardized reporting on energy matters from the mining industry is essential to stimulate progress. Mining-specific energy data was also available from Statistics Canada, Natural Resources Canada and the Canadian Industrial Energy End-use Data and Analysis Centre, as well as in two Canadian and one U.S benchmarking studies. However, these resources were reviewed and found to be problematic. Examples of best practice as well as research and development initiatives in the mining industry are presented. A novel benchmarking approach, specific to mines, is proposed that could be used to demonstrate continuous improvement in energy efficiency within the mining industry. © 2014 Elsevier Ltd. All rights reserved. Source

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