Denise Blanc

On nonlinear distributed parameter model predictive control strategy: On-line calculation time reduction and application to an experimental drying process

It is now recognized that model predictive control (MPC) is an interesting alternative for real-time control of industrial processes. In the meantime, some problems do still remain in progress: for theoretical aspects, the a priori guarantee of the stability and for the practical aspects, the guarantee of sufficient time to solve to optimization problem at each sampled time positions. In this paper, we propose a global method that aims to reduce the on-line calculation time due to the PDE model based optimization task resolution. It is addressed for a particular class of systems not very often studied in this context: systems described by partial differential equations (PDEs) which are, in the present case, nonlinear and parabolic. In order to decrease the computational burden, the nonlinear PDE system is solved off-line. Then, a linearized PDE model around the previous off-line behavior is used to find the optimal variations for the on-line predictive control. The real-time control application given is concerned with a infrared drying process of painting film.

Arsenic stability in arsenopyrite-rich cemented paste backfills: A leaching test-based assessment

Arsenic (As) is a toxicant in tailings from sulphur deposits. It represents an environmental risk because of its high solubility. Tailings can be mixed with water (typically 25%) and a low proportion of hydraulic binder (3-7%) to produce a cemented paste backfill (CPB), stored in underground mine openings. CPB is a tailings storage technique, but it could also provide environmental advantages by stabilization of polluting elements such as As. Tailings from Casa Berardi mine (QC, Canada) contain As (3800 ppm), mainly in arsenopyrite form. For this study, three different CPBs were synthesized in laboratory using Casa Berardi tailings and three different binders. These pastes were submitted to various leaching tests after 28 days of curing. The results indicate that As is released at higher concentration for a fly ash-based CPB than for slag- and Portland cement-based CPB. However, at lower pH, As is better stabilized in fly ash-based samples. These differences can be explained by a variation of solubility of As-compounds in each CPB. Several mechanisms of As release occur, as diffusion and/or dissolution/precipitation. The accelerated weathering test results show that sulphide reactivity is buffered by the neutralizing minerals contained in CPB, and influence the As release behaviour by decreasing the oxidation of As-bearing sulphides.

Infrared drying process of an experimental water painting: Model predictive control

Abstract This article deals with the experimental control of an infrared drying process of a water based epoxy-amine painting. This approach is based on a unidirectional diffusional modeling of infrared drying phenomena where both heat and mass transfers under shrinkage conditions are accounted for. The control problem is concerned with the tracking of any given trajectory for one of the characteristics (i.e., the temperature or the mean water content) during the drying cycle. This is solved using the well-known model predictive control framework where the nonlinear diffusional model is directly used in the control formulation. Experimental results show the efficiency of the trajectory tracking. This method can be extended for more general constrained control problem.

Assessment of arsenic immobilization in synthetically prepared cemented paste backfill specimens

Mine tailings coming from the exploitation of sulphide and/or gold deposits can contain significant amounts of arsenic (As), highly soluble in conditions of weathering. Open mine voids backfilling techniques are now widely practiced by modern mining companies to manage the tailings. The most common one is called cemented paste backfill (CPB), and consists of tailings mixed with low amounts of hydraulic binders (3-5%) and a high proportion of water (typically 25%). The CPB is transported through a pipe network, to be placed in the mine openings. CPB provides storage benefits and underground support during mining operations. Moreover, this technique could also enhance contaminant stabilization, by fixing the contaminants in the binder matrix. CPB composites artificially spiked with As were synthesized in laboratory, using two types of hydraulic binders: a Portland cement, and a mix of fly ash and Portland cement. After curing duration of 66 days, the CPB samples were subjected to several leaching tests in various experimental conditions in order to better understand and then predict the As geochemical behaviour within CPBs. The assessment of the As release indicates that this element is better stabilized in Portland cement-based matrices rather than fly ash-based matrices. The As mobility differs in these two matrices, mainly because of the different As-bearing minerals formed during hydration processes. However, the total As depletion does not exceed 5% at the end of the most aggressive leaching test, indicating that As is well immobilized in the two types of CPB.

Heat transfer study and modeling during Emmental ripening

Firstly, thermal properties were determined on various Emmental cheese samples in order to check the literature empirical relationships for dairy products. Thermal conductivity or diffusivity values were in good agreement with the predicted data considering the temperature effect and the cheese composition in terms of water, fat and non-fat concentrations. Furthermore, the external convective heat transfer coefficients values were experimentally determined by using the psychrometric method with different air flow patterns similar to industrial round cheese ripening conditions. These coefficients are globally higher than published data concerning heat exchange between air and cylindrical bodies. For a temperature change step from 5 to 16 °C applied in our ripening cellar, the experimental temperature profiles measured in the round cheese were in good agreement with the data predicted by numerical simulation by using a 2-D finite difference method. For the temperature step higher than 16 °C, the model could be improved by taking into account the endothermic source terms corresponding probably to melting enthalpies of cheese fat fractions.

Determining the experimental leachability of copper, lead, and zinc in a harbor sediment and modeling

The potential leaching of pollutants present in harbor sediments has to be evaluated in order to choose the best practices for managing them. Little is known about the speciation and mobility of heavy metals in these specific solid materials. The objective of this paper is to determine and model the leachability of copper, lead, and zinc present in harbor sediments in order to obtain essential new data. The mobility of inorganic contaminants in a polluted harbor sediment collected in France was investigated as a function of physicochemical conditions. The investigation relied mainly on the use of leaching tests performed in combination with mineralogical analysis and thermodynamic modeling using PHREEQC. The modeling phase was dedicated to both confirm the hypothesis formulated to explain the experimental results and improve the determination of the main physico-chemical parameters governing mobility. The experimental results and modeling showed that the release of copper, lead, and zinc is very low with deionized water which is due to the stability of the associated solid phases (organic matter, carbonate minerals, and/or iron sulfides) at natural slightly basic conditions. However, increased mobilization is observed under pH values below 6.0 and above 10.0. This methodology helped to consistently obtain the geochemical parameters governing the mobility of the contaminants studied.

Geochemical characterization and modeling of arsenic behavior in a highly contaminated mining soil

The environmental assessment and management of historical mining sites contaminated with various inorganic species require a better knowledge of pollutant-bearing phases. Among elements present in mining soils, arsenic is a toxic metalloid with potential high content and high mobility capacity into the environment. The objective of this paper was to investigate the mobility and fractionation of arsenic (As) in a highly As contaminated soil (ca. 3 wt%). The soil was collected from an old gold mining site in France, where mining activities and smelting processes of gold ores took place. Single and sequential chemical extraction procedures were firstly conducted. These leaching tests were used to assess the potential mobility of As depending on its fractionation in the contaminated soil, and also on the portion of As sorbed onto soil particles. Additionally numerical simulations were performed using the USGS software PHREEQC-3 in order to evaluate the role of adsorption on As mobilization. This multidisciplinary approach provided information on the nature of As fixation in this mining soil. Moreover the role of adsorption in the control of dissolved As was evidenced by geochemical modeling. Results showed that As appeared to be mainly (ca. 72 wt%) reversibly sorbed to iron (Fe) compounds in the soil, in particular Fe oxyhydroxides. Consequently a potential risk of As mobilization exists especially under acidic and/or reducing conditions, which frequently occurs in mining environments.