No abstract

No abstract

Acidity (pH) has been realized to be the most important soil characteristic that modulates bioavailability of heavy metals by affecting both the chemical speciation of metals in soil and the metal binding to the active sites on biota.In this work, we show that besides soil pH, metal bioavailability also depends to a certain extent on the type of soil. A better understanding of the role of soil type in regulating metal availability can be achieved with the analysis of soil composition and with calculations using chemical speciation models. Results of pot experiments, in which three different soils were spiked with nickel, show that the EC 50 of total nickel in decreasing the biomass production of oats varies widely (0.7-22.5 mmol kg -1 soil, more than 30 times). pH (4.7-7.0) is the most important factor, explaining up to a factor of 14 difference of nickel bioavailability in the soils. The remaining variation is caused by other differences in soil composition (soil type). The bioavailability and toxicity of nickel in the organic matter-rich soil studied is less than half of that in the sandy and clay soil studied at a similar pH. The chemical calculations using a multi-surface speciation model show that soil organic matter binds Ni much stronger than clay silicates and iron (hydr)-oxides within the acidic pH range, which supports the experimental findings. In all three soils, the EC 50 of Ni expressed in terms of Ni in 0.01 M CaCl 2 soil extraction is rather stable (24-58 µM), suggesting the possibility to use this extraction as an estimation of metal availability in soil.

The main objective of this study is to predict the performance of an industrial‐scale (ID = 5.8 m) slurry bubble column reactor (SBCR) operating with iron‐based catalyst for Fischer–Tropsch (FT) synthesis, with emphasis on catalyst deactivation. To achieve this objective, a comprehensive reactor model, incorporating the hydrodynamic and mass‐transfer parameters (gas holdup, εG, Sauter‐mean diameter of gas bubbles, d32, and volumetric liquid‐side mass‐transfer coefficients, kLa), and FT as well as water gas shift reaction kinetics, was developed. The hydrodynamic and mass‐transfer parameters for He/N2 gaseous mixtures, as surrogates for H2/CO, were obtained in an actual molten FT reactor wax produced from the same reactor. The data were measured in a pilot‐scale (0.29 m) SBCR under different pressures (4–31 bar), temperatures (380–500 K), superficial gas velocities (0.1–0.3 m/s), and iron‐based catalyst concentrations (0–45 wt %). The data were modeled and predictive correlations were incorporated into the reactor model. The reactor model was then used to study the effects of catalyst concentration and reactor length‐to‐diameter ratio (L/D) on the water partial pressure, which is mainly responsible for iron catalyst deactivation, the H2 and CO conversions and the C5+ product yields. The modeling results of the industrial SBCR investigated in this study showed that (1) the water partial pressure should be maintained under 3 bars to minimize deactivation of the iron‐based catalyst used; (2) the catalyst concentration has much more impact on the gas holdup and reactor performance than the reactor height; and (3) the reactor should be operated in the kinetically controlled regime with an L/D of 4.48 and a catalyst concentration of 22 wt % to maximize C5+ products yield, while minimizing the iron catalyst deactivation. Under such conditions, the H2 and CO conversions were 49.4% and 69.3%, respectively, and the C5+ products yield was 435.6 ton/day. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3838–3857, 2015

A multiphase-Eulerian, three-dimensional (3-D), computational fluid dynamics (CFD) model was built to investigate the local hydrodynamics of a pilot-scale (0.29 m ID, 3 m height) Slurry Bubble Column Reactor (SBCR). The model was first validated against the gas holdup radial profiles in an air-water-glass beads system obtained in a 0.254 m ID and 2.5 m height column under ambient conditions at various superficial gas velocities by Yu and Kim (Bubble characteristics in the radial direction of three-phase fluidized beds. AIChE Journal 34, 2069–2072, 1988). The model was next validated against the gas holdup radial profile data for N2-Drakeol-glass beads system obtained in a 0.44 m ID and 2.44 m height reactor, including internals, operating under ambient conditions at various superficial gas velocities by Chen et al. (Fluid dynamic parameters in bubble columns with internals. Chemical Engineering Science 54, 2187–2197, 1999). The model was also validated against experimental data obtained in our lab for N2-Fischer Tropsch (F-T) reactor wax-Fe catalyst system obtained in a pilot-scale, Slurry Bubble column Reactor, SBCR (0.29 m ID, 3 m height) under pressures and temperatures up to 25.9 bar and 490 K, respectively. These three validations led to the selection of the turbulence and interphase drag coefficient models, and the optimization of the solution method, mesh size and structure and the step size. Moreover, the inclusion of RNG k-ε turbulence model coupled with the Wen-Yu (Mechanics of Fluidization. Chemical Engineering Progress Symposium Series 62, 100–111, 1966) / Schiller-Naumann (A drag coefficient correlation. Zeitung Ver. Deutsch. Ing 77, 318–320, 1935) drag correlations, and the mass transfer coefficients were found to provide the most accurate predictions of the experimental data. The CFD model was then used to investigate local gas holdup, liquid recirculation, local turbulence intensities, bubble diameters, and solids distribution throughout our pilot-scale SBCR, operating under typical F-T process conditions. The model predictions showed strong liquid recirculation and backmixing near the walls of the reactor, and the solid-phase velocity vectors closely followed those of the liquid-phase. A relatively high liquid turbulence intensities were observed in the vicinity of the sparger upon startup, however, after reaching a steady state, the liquid turbulence intensities became more evenly distributed throughout the reactor. The liquid turbulence intensities were slightly higher near the center of the reactor, and closely resembled the velocity vectors. Also, the Sauter mean bubble diameters increased, whereas the solids distribution decreased with reactor height above the gas distributor.

Environmental context Free ion concentrations determine the effects of nutrients and pollutants on organisms in the environment. The Donnan membrane technique provides a measure of free ion concentrations. This paper presents clear guidelines on the application of the Donnan membrane technique for determining free ion concentrations in both synthetic and natural samples. Abstract The Donnan membrane technique (DMT) can be applied to measure free ion concentrations both in laboratory and in situ in the field. In designing DMT experiments, different strategies can be taken, depending on whether accumulation is needed. (1) When the free ion concentration is above the detection limit of the analytical technique (e.g. ICP-MS), no accumulation is needed and no ligand is added to the acceptor. Measurement can be based on the Donnan membrane equilibrium. (2) When an accumulation of less than 500 times is needed, an appropriate amount of ligand can be added to the acceptor and measurement can be based on the Donnan membrane equilibrium. (3) When an accumulation factor of larger than 500 times is needed, a relatively large amount of ligand is added to the acceptor and measurement can be based on the transport kinetics. In this paper, several issues in designing the DMT experiments are discussed: choice of DMT cell, measurement strategies and ligands and possible implication of slow dissociation of metal complexes in the sample solution (lability issue). The objective of this paper is to give better guidance in the application of DMT for measuring free ion concentrations in both synthetic and natural samples.

The gas‐solid flow behavior and dust distribution in four rough‐cut cyclones was numerically simulated on the platform of FLUENT 6.2. The Reynolds stress model and stochastic particle tracking model were used to describe the gas flow and particle motion. The calculation results indicated that the particle distribution patterns of the four rough‐cut cyclones were similar. Adding solid particles into the gas phase weakened the gas swirling intensity inside the cyclones. Data of rough‐cut cyclone down‐flow ratios were gained by simulation for the first time. Rough‐cut cyclones with wider diplegs were found to have a massive gas down‐flow through the dipleg which might cause serious coke generation inside the disengager. The simulated cyclone structure with its vortex finder wider than the dipleg and a hopper installed behaved the best. The results may provide indications for industrial anti coke research and rough‐cut cyclone design.

China is currently the world's top coal consumer and the largest oil importer to sustain its rising economy and meet the mounting demand for transportation fuels. However, the increasing emissions due to the huge fossil fuels consumption, coupled with oil market instability, could derail China's economic growth and jeopardize its national energy security. To face such a hurdle, China has been aggressively supporting low-carbon businesses opportunuties over the past decade, has recently announced several plans to cap coal utilization, and is currently the biggest investor in clean energy technologies. Coal-to-Liquid (CTL) is one of the most promising clean coal technologies, offering an ideal solution that can meet China's energy demands and environmental expectations. It is widely known that the Shenhua Group has pioneered and is currently leading the commercialization of the Direct Coal Liquefaction (DCL) process in China.This paper highlights a part of the joint research effort undertaken by the National Institute of Clean-and-Low-Carbon Energy (NICE) and University of Pittsburgh in order to develop and commercialize the Indirect Coal Liquefaction (ICL) process. In this mission, NICE has built and operated an ICL plant including a large-scale (5.8-m ID and 30-m height) Slurry-Bubble-Column Reactor (SBCR) for Fischer-Tropsch synthesis using iron catalyst. The research, conducted at the University of Pittsburgh over the past few years, allowed building a user-friendly Simulator, based on a comprehensive SBCR model integrated with Aspen Plus and is validated using data from the NICE actual ICL plant. In this paper, the Simulator predictions of the performance of the NICE SBCR, operating with iron and cobalt catalysts under four different tail gas recycle strategies: (1) direct recycle; (2) using a Pressure Swing Adsorption (PSA) unit; (3) using a reformer; and (4) using a Chemical looping Combustion (CLC) process, are presented. It should be mentioned also that our joint research effort has laid the foundation for the design of a commercial-scale SBCR for producing one-million tons per annum of environmentally friendly and ultraclean (no sulfur, no nitrogen and virtually no aromatics) transportation fuels, which could greatly contribute to ensuring China's national energy security while curbing its lingering emission problems.