Main Operating Conditions Research Articles

Removal of phenyl-urea herbicides in natural waters by UF membranes: Permeate flux, analysis of resistances and rejection coefficients

The removal of four phenyl-urea herbicides (linuron, diuron, chlortoluron and isoproturon) dissolved in natural waters by UF membranes was studied in a cross-flow laboratory equipment in batch concentration mode (with recycling of the retentate stream). Two polyethersulfone UF membranes (PW and PT with MWCO of 20,000 and 5000 Da) and a thin film composite membrane (GK with MWCO of 2000 Da) were used. The influence of the main operating conditions (transmembrane pressure, initial concentration of herbicides and MWCO of the membranes) on the steady-state permeate flux was established. The fouling of the higher MWCO membrane (PW) was higher than that of the tight membranes (PT and GK). The analysis of the resistances to the permeate flux obtained revealed that the contribution of the fouling resistance to the total resistance was much lower than the inherent resistance of the clean membranes. In addition, the internal fouling resistance was more important than the external, due to irreversible adsorption on the membrane. The rejection coefficients of the phenyl-urea herbicides were evaluated, being the sequence linuron>diuron>chlortoluron>isoproturon. The herbicide mass adsorbed onto the membranes was also determined, being adsorption onto the membrane surface/pores the main mechanism of herbicides retention.

Supercritical water oxidation of coal in power plants with low CO2 emissions

Abstract In this paper, the application of Super Critical Water Oxidation (SCWO) to direct combustion at low temperature of coal fine particles with pure oxygen for power generation is presented, including also a novel method for capturing and storing carbon dioxide as liquid. A detailed simulation model of a 100 MW th coal-fired SWCO plant with low CO 2 emissions characterised by a steam cooled membraned SC reactor has been developed using Aspen Plus software. According to the well-known Semenov's thermal-ignition theory, the coal particle ignition temperature in SCW conditions has been also evaluated and the results have been integrated within the Aspen Plus model. This has been tested under different operating conditions. The simulation results are presented and the effects of the main plant operating conditions, such as ignition temperature, coal particle size and combustion pressure on the plant performances are discussed. The gross and net thermodynamic efficiencies of the power plant have been estimated to be around 44% and 28%, respectively. The pure oxygen production process results the main energy penalty.

Nanofiltration processes applied to the removal of phenyl-ureas in natural waters

Four phenyl-urea herbicides (linuron, diuron, chlortoluron and isoproturon) dissolved in a commercial mineral water and in reservoir water were subjected to nanofiltration (NF) processes in cross-flow laboratory equipment with recycling of the retentate stream. Three NF membranes of different nature, with molecual weigth cut-off (MWCO) in the range 150–300 Da, were used. The hydraulic permeabilities of the membranes were determined from filtration experiments of ultra-pure (UP) water. In the NF of the synthetic waters, the permeate fluxes were evaluated, the influence of the main operating conditions (transmembrane pressure, temperature, and MWCO of the membranes) on the steady-state permeate fluxes was established, and the different resistances found in the system, which are responsible of the flux declines, were deduced. The retention coefficients for each herbicide were also evaluated and discussed in view of the nature and characteristics of herbicides and membranes. Finally, the herbicides mass adsorbed on the membranes were also determined and the contribution of the adsorption mechanism to the global retention is pointed out.

Removal of phenyl-urea herbicides in ultrapure water by ultrafiltration and nanofiltration processes

Membrane filtration of four phenyl-urea herbicides (linuron, diuron, chlortoluron, and isoproturon) dissolved in ultrapure water was studied in a laboratory cross-flow device in batch concentration mode (with recycling of the retentate stream). Three UF (MWCO of 20 000, 5000 and 2000 Da) and three NF (MWCO of 150–300 Da) membranes were used. The influence of the main operating conditions (transmembrane pressure, tangential velocity, temperature, pH, and MWCO of the membranes) on the steady-state permeate fluxes and the retention factors of the phenyl-ureas was evaluated. The herbicide mass adsorbed onto the membranes was also determined, and the contribution of the fouling resistance to the total resistance to permeate flux was much lower than the inherent resistance of the clean membranes.

Reducing acid leaching of manganiferous ore: Effect of the iron removal operation on solid waste disposal

The process of reducing acid leaching of manganiferous ore is aimed at the extraction of manganese from low grade manganese ores. This work is focused on the iron removal operation. The following items have been considered in order to investigate the effect of the main operating conditions on solid waste disposal and on the process costs: (i) type and quantity of the base agent used for iron precipitation, (ii) effective need of leaching waste separation prior to the iron removal operation, (iii) presence of a second leaching stage with the roasted ore, which might also act as a preliminary iron removal step, and (iv) effect of tailings washing on the solid waste classification. Different base compounds have been tested, including CaO, CaCO3, NaOH, and Na2CO3. The latter gave the best results concerning both the precipitation process kinetics and the reagent consumption. The filtration of the liquor leach prior to iron removal was not necessary, implying significant savings in capital costs. A reduction of chemical consumption and an increase of manganese concentration in the solution were obtained by introducing secondary leaching tests with the previously roasted ore; this additional step was introduced without a significant decrease of global manganese extraction yield. Finally, toxicity characteristic leaching procedure (TCLP) tests carried out on the leaching solid waste showed: (i) a reduction of arsenic mobility in the presence of iron precipitates, and (ii) the need for a washing step in order to produce a waste that is classifiable as not dangerous, taking into consideration the existing Environmental National Laws.

Experimental study and optimization of the agglomeration of acerola powder in a conical fluid bed

The aim of this work was to study the physical property modifications of acerola powder produced by a wet-agglomeration process in a fluid bed. A 2 2 full experimental design was used to evaluate the influence of the main operational conditions and to optimize the agglomeration process. The product transformations were determined by an analysis of the particle diameter, size distribution, morphology, moisture content and solubility. The agglomeration of small granules results in an increase in the instant properties, increasing particle solubility.

Gasification and co-gasification of biomass wastes: Effect of the biomass origin and the gasifier operating conditions

Air gasification of different biomass fuels, including forestry (pinus pinaster pruning) and agricultural (grapevine and olive tree pruning) wastes as well as industry wastes (sawdust and marc of grape), has been carried out in a circulating flow gasifier in order to evaluate the potential of using these types of biomass in the same equipment, thus providing higher operation flexibility and minimizing the effect of seasonal fuel supply variations. The potential of using biomass as an additional supporting fuel in coal fuelled power plants has also been evaluated through tests involving mixtures of biomass and coal–coke, the coke being a typical waste of oil companies. The effect of the main gasifier operating conditions, such as the relative biomass/air ratio and the reaction temperature, has been analysed to establish the conditions allowing higher gasification efficiency, carbon conversion and/or fuel constituents (CO, H 2 and CH 4) concentration and production. Results of the work encourage the combined use of the different biomass fuels without significant modifications in the installation, although agricultural wastes (grapevine and olive pruning) could to lead to more efficient gasification processes. These latter wastes appear as interesting fuels to generate a producer gas to be used in internal combustion engines or gas turbines (high gasification efficiency and gas yield), while sawdust could be a very adequate fuel to produce a H 2-rich gas (with interest for fuel cells) due to its highest reactivity. The influence of the reaction temperature on the gasification characteristics was not as significant as that of the biomass/air ratio, although the H 2 concentration increased with increasing temperature.

Experimental study of fluidized bed agglomeration of acerola powder

The aim of this work was to study the main effects of acerola powder on fluidized bed agglomeration. A 2(4-1) fractional factoring design was used to evaluate the main operating conditions (fluidizing air temperature, fluidizing air velocity, atomizing air flow and height of nozzle in the bed). The mechanical and physicochemical product changes were determined by analysis of particle diameter, moisture content, wetting time and bed porosity. The particle enlargement by agglomeration occurred when the relative humidity in the bed increased and, thus, the moisture of the product increased. However, the excessive increase in relative humidity resulted in a decrease in yield, caused by caking and product incrustation. The consolidation of small granules resulted in an increase in the instant properties, decreasing the wetting time and increasing the solubility in a short period of agitation.

Experimental Analysis of the Operation of Quantum Dot Intermediate Band Solar Cells

With a 63.2% theoretical efficiency limit, the intermediate band solar cell (IBSC) is a new photovoltaic device proposed to overcome the 40.7% efficiency limit of conventional single gap solar cells. Quantum dot technology can be used to take the IBSC concept into practice. In this respect, the results of experiments carried out recently to characterize IBSC solar cells containing different numbers of InAs quantum dot layers as well as the theoretical models used to describe and analyze the related experimental data are summarized here. Electroluminescence and quantum efficiency measurements confirm that the main operating conditions for IBSCs are complied with in structures with a low number of QD layers. These conditions include the production of photocurrent from absorption of below band gap energy photons and the formation of distinctive quasi-Fermi levels associated with each electronic band (i.e., the conduction, valence, and intermediate bands).

Industrial batch crystallization of a plate-like organic product. In situ monitoring and 2D-CSD modelling. Part 2: Kinetic modelling and identification

The batch seeded cooling solution crystallization of a fine organic material, exhibiting a platelet-like habit, was investigated and a model of the time variations of the crystal size distribution (CSD) was designed using two-dimensional population balance equations. Activated surface secondary nucleation and attrition secondary nucleation mechanisms were considered, coupled with growth mechanisms of two main dimensions of the crystal, resulting in a set of eight kinetic parameters. The model relates the effects of the main batch operating conditions: seeding temperature, cooling rate and total area of the seed particles, on both the supersaturation profile and bi-dimensional CSD. Surface secondary nucleation occurs first since it is promoted by the introduction of seeds and remains active as long as the relative supersaturation exceeds a threshold value of about 16%. It vanishes below which could be expected as we deal with an activated mechanism. Contact secondary nucleation occurs later when the concentration of solid is sufficient. It is spread over time until supersaturation disappears at the end of the batch process. This contact secondary mechanism is assumed to be the dominant nucleation mechanism as it generates about two-thirds of the final crystal number. Sharp desupersaturation profile following the introduction of seeds, which was observed experimentally, is shown to be quantitatively described through the growth of seed particles. The termination of the batch process is more difficult to represent. Due to crystal attrition, distinct growth rates between initial and secondary crystals or growth rate dispersion might explain such difficulty.

Micellar Enhanced Ultrafiltration for Arsenic(V) Removal: Effect of Main Operating Conditions and Dynamic Modelling

In this work arsenic removal by micellar enhanced ultrafiltration (MEUF) was investigated using cetylpyridinium chloride (CPC) in ceramic membrane apparatus. Permeability tests and discontinuous diafiltration tests were performed in different operating conditions to evaluate the effect of membrane pore size (20 and 50 nm), transmembrane pressure, pH, surfactant concentration (1-3 mM), and arsenic concentration (10-40 mg/L) on permeate flux decline, arsenic, and CPC rejections. These preliminary experimental results showed that a ceramic membrane with large pore size allows treament of high fluxes of concentrated arsenic-bearing solutions even by using low surfactant concentrations. Arsenic concentration in the permeate was at the 1 ppm level, with feed As concentrations (10 ppm) that are larger than those generally used in MEUF studies and with CPC amounts that are lower than the usual ones. In addition, operating conditions adopted in these tests obtained CPC concentrations in the permeate always lower than its critical micellar concentration (0.9 mM). Dynamic simulations of discontinuous two-step diafiltration tests allowed a simple and adequate representation of the performance of the process especially for 1 mM CPC, while discrepancies for 2.5 mM CPC level denoted complex interactions between CPC and As.

Energetic, exergetic and thermoeconomic analysis of Bilkent combined cycle cogeneration plant

This paper is a case study of thermodynamics and economics related analyses applied to an existing gas/steam combined cycle cogeneration plant. Basic thermodynamic properties of the plant are determined by energy analysis utilizing main operation conditions. Exergy destructions within the plant and exergy losses to environment are investigated to determine thermodynamic inefficiencies and to assist for guiding future improvements in the plant. Cost balances and auxiliary equations are applied to several subsystems in the plant, hence, cost formation in the plant is observed. Additionally, cost rate of each product of the plant is calculated. Copyright © 2005 John Wiley & Sons, Ltd.

Different Modeling Approaches for a Heterogeneous Liquid−Liquid Reaction Process

Multivariate linear regression (MLR) techniques were used to develop empirical models which are able to predict the formation of the main product and byproducts of the adiabatic benzene nitration process, as a function of the main operating conditions. Experiments carried out in a pilot plant enabled us to reproduce the operating conditions of the industrial process, providing experimental data in the intermediate and fast reaction regimes. The nitrobenzene (MNB) formation was modeled according to the film and Danckwerts mechanistic models, and the results were compared with a MLR model, showing that both approaches are suitable for describing this reaction. Nevertheless, the results stress an improved performance of the MLR model when compared to the mechanistic models, despite its structural simplicity. The statistical models developed for the nitrophenols (NPs), namely for the dinitrophenol and trinitrophenol (DNP and TNP, respectively), describe accurately the formation of these byproducts, overcoming...

Longitudinal and transverse mixing in rotary kilns: A discrete element method approach

Longitudinal and transverse mixing in horizontal rotary kilns has been studied, using a three-dimensional Discrete Element Method approach. The focus is on the effect of the main operating conditions, i.e., the filling degree and the rotational speed of the rotary kiln, on quantitative measures of longitudinal and transverse mixing. Discrete Element Method simulations have been performed for various values of the main operating conditions. Flow regimes have been determined from visualisations of the simulations. It is shown that the mixing in the longitudinal direction can be described by a diffusion equation. The dependence of the diffusion coefficient on the operating conditions has been determined from the results of the simulations. It is found that the diffusion coefficient increases linearly with rotational speed, while the influence of the filling degree is relatively small. The mixing in the transverse plane is quantified by an entropy-like mixing index. The results of the simulations show that this mixing index varies exponentially with the number of revolutions of the rotary kiln. The dependence on the operating conditions of the transverse mixing speed, as determined from the exponential behaviour of the mixing index, has been determined. This mixing speed decreases with increasing rotational speed and with increasing filling degree. The transverse mixing speed that has been determined from the results of additional two-dimensional simulations is generally larger than that observed in the corresponding three-dimensional simulations.

An instrumented pilot scale oven for the study of French bread baking

A static oven designed for French bread baking has been instrumented to monitor the processing conditions and record variables responsible for dough changes. Thermocouples are inserted at fixed position in the dough, mass loss is continuously weighed whereas expansion is measured by CCD video camera. Internal pressure and ambient humidity are controlled. Standard conditions for acceptable bread are checked and variable profiles measured in order to define the different sequences of variables related to the main macroscopic changes: expansion, scars opening and crust setting. This scheme is confirmed by modifying main operating conditions (temperatures and vapour injection), showing that water vapour favours expansion, reaching its maximum up to 1.7, at a crumb temperature close to 90 °C, in relation with internal pressure (90 kPa). Vault and hearth temperatures mainly influence crust, the setting of which stops loaf volume decrease (20%).

Circulating fluidised bed co-combustion of coal and biomass

Circulating fluidised bed combustion (CFBC) is receiving wide research attention in view its potential as an economic and environmentally acceptable technology for burning low-grade coals, biomass and organic wastes, and thereby mixtures of them. Designs of the existing fluidised bed boilers for biomass combustion are mainly based on experience from coal combustion because the mechanism of combustion of biomass in fluidised beds is still not well understood. A good understanding of the combustion and pollutant formation processes and the modelling of the combustor can greatly avoid costly upsets of the plants. In this paper, the performance of CFBC burning coal and biomass mixtures was analysed. Experimental results were obtained from the combustion of two kinds of coal with a forest residue (Pine bark) in two CFB pilot plants (0.1 and 0.3 MW th). The effect of the main operating conditions on carbon combustion efficiency was analysed. Moreover, a mathematical model to predict the behaviour of the co-combustion of coal and biomass wastes in CFB boilers has been developed and validated. The developed model can predict the different gas concentrations along the riser (O 2, CO, CH 4, etc.), and the carbon combustion efficiency. The experimental results of carbon combustion efficiencies were compared with those predicted by the model and a good correlation was found for all the conditions used.

Application of continuous chromatographic separation in sugar processing

The work deals with application of continuous counter-current chromatographic separation station in sugar technology. There are two main targets in this study: (1) Changes in sugar technology: simplification of sugar processing by sucrose crystallization from chromatographic extract without any previous demanding chemical processing and (2) higher valorisation of waste material and intermediates from sugar processing by isolation of high-quality substances. The chromatographic pilot plant KCHS-SMB-8, which was developed by the Department of Carbohydrate Chemistry and Technology ICT Prague and the firm MIKROPUR Hradec Kralove, was used for this purpose. Experiments deal with suggestion and verification of main operation conditions during chromatographic separation of technical sugar solution. The process was focused on separation of various model mixtures of sucrose/salt and sucrose/betaine. Results provide a basic data for further research and development for industrial use.

Whey ultrafiltration in a tubular membrane: effect of selected operating parameters

A study of whey ultrafiltration in a tubular membrane with a centrally inserted rod is reported in this work. Effects of the main operating conditions such as pH, temperature, and whey concentration on the ultrafiltration process have been investigated in a lab-scale tubular membrane. In particular, the mass-transfer resistance through the membrane (due to fouling and polarization), the flux decline vs. time, and the membrane-retention properties have been considered as representatives of the ultrafiltration process' performances. The study has been performed by using full factorial experiments, and results have been elaborated by the analysis of the variance (ANOVA). From permeability tests, the lowest value for the mass-transfer resistance (corresponding to the highest permeate flux) has been estimated at 5.8±0.3 MPa hr m−1, under the following operating conditions: pH 6, temperature 25°C, whey concentration factor (CF) 1. The ANOVA suggested that pH and whey concentration were significant factors, while temperature resulted not to influence the mass-transfer through the membrane in the investigated range (25–40°C). Flux declines have also been monitored during time and profiles have been fitted by an empirical model. In this case, the highest temperature (40°C) favored the decline kinetics and it determined the highest difference between initial and stationary fluxes. As concerns the membrane-retention properties, the highest proteins-rejection coefficient (which means the highest retention) was 0.90 (under pH 4, temperature 25°C, CF 5). Furthermore, pH was demonstrated to affect significantly the membrane-retention properties. In fact, the chromatogram of permeates showed that some native proteins pass through the membrane at pH 6, while just peptides pass at pH 4.

Experimental study on gas–liquid interfacial area and mass transfer coefficient in three-phase circulating fluidized beds

The gas–liquid mass transfer behavior is studied in a three-phase circulating fluidized bed reactor of 140 mm i.d. and 3.0 m height. Using the oxygen dissolution method, the volumetric mass transfer coefficient k L a is obtained from the measured bulk concentration of the liquid phase by fitting to the axial dispersion model (ADM). The gas holdup and the distribution of bubble size in the bed are measured by a fiber optical probe system, then the gas–liquid interfacial area a and the mass transfer coefficient k L are calculated. The influences of the main operating conditions, including superficial gas velocity, superficial liquid velocity and solid circulating rate, are studied systematically.

EXPERIMENTAL STUDY ON GAS-HOLDUP AND GAS-LIQUID INTERFACIAL AREA IN TPCFBs*

A new fiber optic probe system has been developed for measuring the gas-holdup εg and bubble size distribution Ps(db) in multiphase reactors. Experiments have been carried out in a gas-liquid-solid three-phase circulating fluidized bed (TPCFB) with 140mm inner diameter and 3 m height, in which air, tap water and 0.4 mm glass beads are used as the gas, liquid and solid phase, respectively. Based on the measured data, the gas-liquid interracial area a, one or the most important parameters concerning the mass transfer, has been derived. The radial profile of the gas holdup and the gas-liquid interracial area, and the influence or main operating conditions have been studied experimentally in TPCFBs.