The equilibrium concentrations of SiHCl3 and SiCl4 in the SiCl4–H2 system are investigated on the basis of thermodynamic data for the corresponding pure compositions under specified thermodynamic parameters. Eight independent reactions in the SiCl4–H2 system for hydrogenation of SiCl4 to SiHCl3 are obtained. Furthermore, the factors (such as temperature, pressure, and feed mole ratio) influencing the equilibrium concentrations of SiCl4 and SiHCl3 are studied. Diagrams of the equilibrium concentrations of SiCl4 and SiHCl3 as a function of temperature, pressure, and feed mole ratio are presented. Finally, the optimal thermodynamic conditions in the SiCl4–H2 system for hydrogenation of SiCl4 to SiHCl3 are determined to be 1,100°C, 0.3 MPa, and a feed molar ratio of 4. Under these conditions, the conversion ratio of SiCl4 to SiHCl4 is about 25%, compared to a value of less than 20% in actual production.
In this article, computational investigation of the gas–liquid flow in stirred tank with multiple Rushton impellers was carried out. Experimental results of average and local details of gas–liquid flow characters were reported, including gas–holdup, bubble Sauter diameter, specific area and mass transfer coefficient. Thoroughly interphase momentum transfer models including drag and non-drag models were investigated, together with four mass transfer coefficient models using commercial CFD software ANSYS CFX 12.0. Among the drag models tested, the modified Brucato model showed more accurate results than others, while non-drag models showed slight effects on the average flow and local flow characters. For accurate local flow simulation, the population balance model (PBM) showed quite sensitive effect on the local gas distribution. Simulation of interphase mass transfer with eddy cell model showed the most agreement with experimental measured data. Additionally, two advection schemes were employed and compared with each other to test their ability to get more accurate simulation result.
Due to the depletion of high-grade manganese ore, much attention has turned to recover manganese from low-grade ores; however, these are usually associated with high-iron content. Moreover, the conventional process of extracting Mn from iron-rich low grade manganese oxide ore focused on recovery of Mn, while ignoring the leaching characteristics of Fe. Hence, simultaneous investigations on leaching behavior and separation efficiency of both manganese and iron were carried out for attaining high recovery of manganese with low iron content from the high-iron low-grade pyrolusite ore using simulated flue gas as the reductant. The effects of leaching parameters, flue gas components and initial particle size on the leaching efficiency of Mn and Fe were studied, and the results indicated that higher separation efficiency of Mn from iron was achieved at lower SO2 concentration, O2 concentration and suitable pulp density. The experimental validation revealed that 93.12% Mn and only 2.57% Fe were extracted under the optimal operating conditions: SO2 percentage of 5%, O2 percentage of 1%, reaction temperature of 35°C, solid-to-liquid ratio of 250 g/L, and more than 120 min. Kinetic modelling has indicated that the Mn leaching rate is controlled by the rate of diffusion of SO2/O2 from the gas phase to the liquid phase, and the rate of diffusion of product or reactants to the ore surface through an inert product layer is the rate-limiting step for Fe dissolution.
As a natural refrigerant, carbon dioxide (CO2, R744) is proposed to be used in chillers and heat pumps. Generally, CO2 in chillers and heat pumps is a trans-critical cycle. CO2 is super-critical in the evaporator of trans-critical cycle, which is called gas cooler. The CO2-water gas cooler of helix tube was designed and studied in the paper. An experimental research was conducted in range of CO2 temperature (373.15–393.15 K) and CO2 pressure (8–10 MPa). The numerical simulation was conducted to investigate the temperature distribution and flow velocity distribution in the gas cooler. Based on the experimental and numerical study, the results showed that the helix tube gas cooler had a good field coordination between the temperature gradient and flow velocity. The experimental results show that the Fc (field coordination number) of fluids in the helix tube gas cooler was less than other gas coolers, especially in the water side. The numerical results show that the distribution of cooling water temperature in the helix tube gas cooler was more complex and inhomogeneous than the straight tube gas cooler. The heat transfer performance of the helix tube gas cooler was investigated experimentally. An increase of CO2 bulk temperature deteriorated the heat transfer performance due to a decrease of thermal properties (e.g., specific heat and thermal conductivity). The exergy loss rate was used to evaluate the irreversibility of gas cooler. The results show that the order of irreversibility is straight tube, single helix tube, followed by double helix tube.
The process and plant design stages, in particular the preliminary process design (PPD) stage, are performed repeatedly to cope with environmental changes at a plant during its lifecycle. The stages after the original design are called revamp design stages. As the PPD is repeated, operational flexibility is decreased. As a result, slight deviations from the intended critical process conditions during operation can lead to problems. However, in many cases, the causes of an operational problem are not identified, leading to safety issues. To overcome this, a framework including two Business Process Models (BPMs) is developed and modeled using IDEF0 with a hierarchical nature and ability to describe the PDCA engineering cycle. One BPM is developed to acquire the information on critical process conditions generated in the PPD stage. The other BPM is developed to systematize the acquired generated information into technology for the PPD by associating the information with design variables. The former BPM must first be developed as a reference model for the latter as a requirement. Furthermore, the framework is clearly divided into the above-mentioned two BPMs to manage the technology throughout the plant lifecycle while keeping consistent linkage to each other. Finally, it is confirmed that the developed framework has the necessary structure to systematize the technology of the PPD throughout the plant lifecycle by tracing a practical example problem of a distillation column in the framework.
The present study evaluates the lipase (Novozym 435)-catalyzed transesterification of triolein and methanol mixtures to generate fatty acid methyl esters (FAMEs) using dimethyl ether (DME) in a batch reactor and a continuous pipe reactor. The addition of DME facilitated the preparation of homogeneous mixtures of triolein and methanol. The effect of the Novozym 435 and DME contents in the feed mixtures on the time–course of FAME production was analyzed. With increasing contents of Novozym 435 and DME in the feed mixtures, the FAME concentration increased more rapidly in the batch reactor than in the continuous reactor. The feed flow rate and DME content were varied, and the FAME concentration at the outlet of the pipe reactor was measured with variation of the residence time and DME content. Increasing the DME content in the feed mixtures and the residence time led to a more rapid increase in the FAME concentration for the batch reactor than that in the continuous pipe reactor.