Studying the integration of solar energy into the operation of a semi-autogenous grinding mill. Part I: Framework, model development and effect of solar irradiance forecasting

Grinding is one of the most energy-demanding processes of copper mines. Declining ore grades and harder rocks will further intensify this demand. Periods of stressed copper prices, high energy costs and climate change mitigation targets additionally motivate the search for alternative energy sources in mining. In Chile, many copper operations are located in the Atacama Desert, hence solar energy systems are an attractive solution. However, the mineral hardness is variable and uncertain in time and space, which adds challenges to planning energy systems with high solar shares. More specifically, here a stochastic optimization model is developed. It sizes the solar photovoltaic (PV), battery energy storage system (BESS) and the contracted power, based on the solar radiation, mineral hardness, and costs. Using Markov Chains, different years of solar radiation are generated from historical records. These solar scenarios are used to test the impact of individual years with long periods of cloudy/rainy days on the sizing of the system, in contrast to planning with an average year or planning with many-year time horizons in a stochastic approach. The novelties lie in the developed model, and in understanding the impact of the uncertainty and variability of rock hardness and solar irradiation on the optimal sizing of the PV-BESS system and the power capacity contract. Furthermore, the impact of a larger variability of ore hardness is evaluated in one scenario. PV-BESS can cost-effectively provide energy to the grinding mill. Different planning approaches lead to significant differences in the recommended power supply. In contrast to planning with the average solar year, using a conservative solar year (many cloudy days) yields significantly smaller sizes of PV and BESS (20% and 55%) and a higher reliance on the grid (larger contracts and imports); and the stochastic approach follows a similar line (10% and 25% smaller). Despite its increased grid dependency, the one-year stochastic approach provides more robust solutions regarding costs and sizes (avoiding penalties). The variability of the rock hardness also impacts the size of all components of the PV-BESS system, especially the battery energy capacity. Its relevance for battery sizing motivates to perform further studies with a focus on the uncertainty and variability of the ore

Studying the integration of solar energy into the operation of a semi-autogenous grinding mill. Part II: Effect of ore hardness variability, geometallurgical modeling and demand side management

In the first part of this work, a solar photovoltaic system with battery storage (PV-BESS) and grid backup system to supply a SAG mill was modeled. There, the overall framework, the optimization model, and the model for the solar forecast were presented. Here, in the second part, the impact of ore hardness variability and uncertainty is studied. Demand side management strategies are modeled to improve the solar energy integration. This work starts by analyzing the impact of the mineral hardness variability and uncertainty (in the SAG mill's feed) on the sizing of the PV-BESS system. For this, several feed hardness variabilities are considered in order to understand the effects of the frequency, amplitude, and phase with sun hours. Second, for demand-side management, a feed hardness array is generated by mixing two normal distributions with different standard deviation and mean values, representing a hard and soft ore. And third, realistic SAG mill feeds are generated with geostatistical simulations. Different densities of the sampling grids in the geostatistical simulations generate estimated ore feeds with varying levels of uncertainty. These are used to propose a greenfield sizing methodology. The results show that the PV-BESS system proves to be an attractive solution under all scenarios considered, being able to reduce the total costs by over 30% (when considering a Chilean scenario). It allows decreasing the electricity imports by more than 80% and lowering the power capacity contracts by more than 15%. The frequency and phase of the hardness of the feed show the benefit of mineral management; the more prominent the amplitude and the standard deviation is, the more cost-effective the integration of renewable energy becomes. Managing the rock hardness assists in complying with the capacity contract during more extended periods of low solar irradiation and reduces the need for batteries. Models estimated from limited data are smooth and under estimate the hardness variability leading to smaller BESS results from the simulations showing its importance as an energy buffer. The sizing methodology using predicted feed showed that the model could be applied to a realistic mineral feed

Integrating photovoltaic solar energy and a battery energy storage system to operate a semi-autogenous grinding mill

The mining sector in Chile is facing a steady increase of energy consumption, which is mainly explained by the lower grades, the increase in rock hardness, and deeper mines. Although much of the mining activity in Chile is located in the Atacama Desert, where the solar radiation is high, the integration of solar energy in mining remains elusive. This work explores, through simulation, the use of a solar photovoltaic energy system (PV) and a battery energy storage system (BESS), combined with energy from the grid, to operate a semi-autogenous grinding mill (SAG). For this, a novel mixed-integer linear programming model was developed to optimize the operational costs of the joint SAG-PV-BESS operation, after which the best sizes of PV and BESS components are found through scenario inspection. Further, the implementation of a demand side management (DSM) option is considered by a proper sequencing of the SAG feed to make a more efficient use of the solar energy. The results show an interdependent behavior of the SAG-PV-BESS system and a strong influence of DSM. The use of both PV and BESS allows reducing the contracted power for the SAG, without incurring into overconsumption penalties. If DSM is implemented, the system allocates the higher consumption, associated to harder ore, during daytime to use the available PV energy. Overall, the combined effect of PV and BESS operation of SAG mills allows reducing the energy-associated operational costs. This effect is exacerbated when DSM is implementedThe Chilean National Commission for Scientific and Technological Research (CONICYT), through the Solar Energy Research Center SERC-Chile (FONDAP 15110019) and the Solar Mining project (CONICYT-BMBF 20140019), and the German Academic Exchange Service (DAAD)

One-year treatment with ethyl esters of n-3 fatty acids in patients with hypertriglyceridemia and glucose intolerance Reduced triglyceridemia, total cholesterol and increased HDL-C without glycemic alterations

n-3 Fatty acids in the form of ethyl esters (EE) allow lower daily doses and improved compliance. Administration of n-3 fatty acids to patients with glucose intolerance has led to controversial findings, some studies indicating worsening of the disorder, others no effect, or an improvement. A total of 935 patients with hypertriglyceridemia, associated with additional cardiovascular risk factors, i.e. glucose intolerance, NIDDM and/or arterial hypertension were entered a double blind (DB) protocol lasting 6 months with n-3 EE versus placebo, followed by a further 6 months of open study (n = 868) on 2 g a day of n-3 EE. At the end of the DB period, triglyceridemia in the total group was reduced significantly more by n-3 EE, without alterations in glycemic parameters. In the 6 months open follow up, patients on n-3 EE with type IIB hyperlipoproteinemia showed a significant reduction of total cholesterol, both in cases with (-4.15% vs. the 6 month levels) and without NIDDM (-3.8%). HDL-cholesterol had an overall mean rise of 7.4%, maximal in type IV patients with (+9.1%) and without (+10.1%) NIDDM. No alterations in glycemic parameters were detected in treated patients. Administration of n-3 EE to patients with hypertriglyceridemia associated with NIDDM or impaired glucose tolerance appears safe and effectiv

Indobufen versus warfarin in the secondary prevention of major vascular events in nonrheumatic atrial fibrillation. SIFA (Studio Italiano Fibrillazione Atriale) Investigators.

The results of a large prospective randomized trial have shown the efficacy of oral anticoagulation in the secondary prevention of major vascular events in patients with nonrheumatic atrial fibrillation (NRAF); less well established is the role of antiplatelet agents. The present study compared the effects of indobufen, a reversible inhibitor of platelet cyclooxygenase, with those of warfarin in this setting. A total of 916 patients with NRAF and a recent (< or = 15 days) cerebral ischemic episode were admitted to this multicenter, randomized study, during which they were treated with either indobufen (100 or 200 mg BID) or warfarin (to obtain an international normalized ratio of 2.0 to 3.5) for 12 months. The two groups (462 on indobufen and 454 on warfarin) were well balanced in terms of their main baseline characteristics. The primary outcome of the study was the combined incidence of nonfatal stroke (including intracerebral bleeding), pulmonary or systemic embolism, nonfatal myocardial infarction, and vascular death. At the end of follow-up, the incidence of primary outcome events was 10.6% in the indobufen group (95% confidence interval, 7.7% to 13.5%) and 9.0% in the warfarin group (95% confidence interval, 6.3% to 11.8%), with no statistically significant difference between treatments. The frequency of noncerebral major bleeding complications was low: only four cases (0.9%) of gastrointestinal bleeding were observed, all of them in the warfarin group. We conclude that, within the limitations of its design, this study may help the medical community in devising appropriate antithrombotic strategies for NRAF patients for whom oral anticoagulants are contraindicated or do not represent a feasible approach to treatment