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Computational fluid dynamics (CFD) was applied to model industrial flares under low-Btu, low-flow rate conditions (stand-by mode). The modeled tests were conducted at the John Zink R&D facility in Tulsa, OK in September 2010, using propylene/Tulsa Natural Gas/nitrogen as vent gases under open-air conditions. This work focuses on CFD modeling using the EDC (Eddy Dissipation Concept) and PDF (Probability Density Function) models to predict the destruction and removal efficiency (DRE), combustion efficiency (CE), and speciated emissions with a reduced 50-species combustion mechanism. Generally, the EDC model underpredicts DRE/CE while the PDF model overpredicts DRE/CE, when compared with measurements. The sources of discrepancies and the challenges to the flare modeling in the stand-by mode are discussed. In view of the significant differences between the measured and modeled results, further investigations involving a better domain with a refined mesh, a different turbulence model, or a combination of EDC/P...

The natural gas liquefaction process is an important sector of the overall liquefied natural gas (LNG) value chain. In this article, a thermodynamic-analysis-based study of the minimization of the energy consumption of a typical natural gas liquefaction process is performed. First, a rigorous simulation of the natural gas liquefaction process is conducted. According to the simulation results, the operating states of the refrigerant and natural gas streams are revealed, along with the operating conditions of the entire liquefaction process. Then, the energy consumption roadmap is determined through in-depth thermodynamic analysis, where the opportunities for energy consumption minimization are identified. Based on the thermodynamic analysis, a rigorous optimization model is developed and solved for energy consumption reduction of the same natural gas liquefaction process. Finally, the optimization results are examined again through rigorous simulation to check the feasibility of the obtained optimal solution.

Ethylene plant upsets usually lead to flaring of off-spec products, resulting in significant losses of raw material and energy as well as to air emission problems. Under the premise of plant safe operation, establishing process recycles connecting off-spec streams to their upper-stream process can help to reduce flaring during plant upsets. Operational strategies for recycling the potential flaring sources, i.e., effluents from the acetylene reactor and ethylene tower overhead, under various process upsets are developed and analyzed based on rigorous plant-wide dynamic simulations. Safety considerations on the compressor system performance have been addressed by quantitative comparison of the effectiveness of various recycling strategies. Case studies demonstrate that the safety-considered flare minimization strategies can proactively reduce the flaring emission amount and upset time and thus have great potentials of economical and environmental benefits to ethylene plants.

Multilayer films with anionic phosphomolybidic acid (PMo(12)) clusters have been fabricated via the electrostatic layer-by-layer (LbL) method. The charged mass transport phenomena of these thin films have been studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+/2+) as the redox probes. By adding a film resistance and a film capacitance to the conventional Randles equivalent circuit, we can calculate the diffusion coefficient values that help understand the microscopic nature of the thin films. When the negatively charged probe [Fe(CN)(6)](3-/4-) was used, lower diffusion coefficients were obtained for multilayers deposited from higher ionic strength solutions. This relationship was less obvious when the positively charged probe [Ru(NH(3))(6)](3+/2+) was used, in which the electrostatic attraction between PMo(12) clusters and the probe ions complicates the mass-transfer process. It is believed that the addition of salt to dipping solutions increases the tortuosity of the films so the mass transport takes longer paths, inducing lower diffusion coefficients. Higher PMo(12) loading causes lower diffusion coefficients due to the polyoxometalate clusters blocking the paths for charged probe ions.

Flaring is an important but passive method in ethylene plants to protect plant personnel, facilities, and the ambient environment. However, excessive flaring emits huge amounts of CO, CO 2 , NO x , and hazardous volatile organic compounds (VOCs), which may cause locally transient air pollution problems and negative societal impacts. Flaring may also cause high losses of raw material and energy that could generate more desired products for the industry. Thus, flare minimization has great benefits to environmental, societal, and industrial sustainability. Based on current industrial practices, a general strategy for flare minimization under various ethylene plant events is presented.

Ethylene oxide (EO) is an important chemical intermediate for the production of various chemical products. The manufacturing of EO involves critical exothermic reactions at high temperature and high pressure, whose failure may cause catastrophic personal injury, severe air pollution, and tremendous economic loss. Thus, an EO plant must be well controlled under various situations, especially during its start-up operations. In this paper, a general methodology for improving chemical plant start-up operations through plant-wide dynamic simulation has been developed. It undergoes modeling and validations for steady-state, dynamic, and historian start-up operations. On the basis of the validated dynamic simulation model, the original plant start-up strategy is further examined and optimized to speed-up the plant start-up operation with enhanced safety considerations. A case study on an EO plant start-up has demonstrated the significant operational and economic benefits of the proposed methodology.

Multistage compression systems (MSCS) are the most important and valuable facilities in chemical plants, whose failure may cause severe accidents and/or tremendous economic loss. Thus, operation for MSCS needs sufficient care under various situations, especially during plant startup. This paper employs rigorous pressure-driven dynamic simulations to examine and improve operation safety of the cracked gas compression system during an ethylene plant startup. For safety consideration, antisurge process design and control strategies are dynamically evaluated along with startup procedures. Operating point trajectory for each compressor and their potential safety problems are identified. Assisted by the rigorous dynamic simulation, the plant startup procedure is improved with better safety performance.

Flaring is crucial to chemical plant safety. However, excessive flaring, especially the intensive flaring during the chemical plant start-up operation, emits huge amounts of volatile organic compounds (VOCs) and highly reactive VOCs, which meanwhile results in tremendous industrial material and energy loss. Thus, the flare emission should be minimized if at all possible. This paper presents a general methodology on flare minimization for chemical plant start-up operations via plantwide dynamic simulation. The methodology starts with setup and validation of plantwide steady-state and dynamic simulation models. The validated dynamic model is then systematically transformed to the initial state of start-up and thereafter virtually run to check the plant start-up procedures. Any infeasible or risky scenarios will be fed back to plant engineers for operation improvement. The plantwide dynamic simulation provides an insight into process dynamic behaviors, which is crucial for the plant to minimize the flaring w...

This study investigates the products, kinetics, and reactor design of atrazine photolysis under 254-nm ultraviolet-C (UVC) irradiation. With an initial atrazine concentration of 60 microg/L (60 ppbm), only two products remain in detectable levels. Up to 77% of decomposed atrazine becomes hydroxyatrazine, the major product. Both atrazine and hydroxyatrazine photodecompose following the first-order rate equation, but the hydroxyatrazine photodecomposition rate is significantly slower than that of atrazine. For atrazine photodecomposition, the rate constant is proportional to the square of UVC output, but inversely proportional to the reactor volume. For a photochemical reactor design, a series of equations are proposed to calculate the needed UVC output power, water treatment capacity, and atrazine outlet concentration.

Photocatalysis utilizes near-UV or visible light to break down organic pollutants into innocuous compounds at room temperatures. This paper introduces the use of semiconducting optical crystals as an additive to a photocatalyst. The perovskite optical material BaTiO 3 (band gap of 3.7-3.8 eV) is found to increase VOC destruction when black light is used. The best composition found is 0.1 wt% BaTiO 3 with the balance being TiO 2 . This photocatalyst increases tetrachloroethylene (PCE) conversion by 12% to 32% for space times between 1.4 and 17.2 seconds and inlet concentrations of 40 to 130 ppm with a 4 W black light. The average enhancement is approximately 25 %. For butyraldehyde conversion the maximum enhancement is 20 % at 130 ppm in 3.6 seconds. The UV/VIS spectroscopy data indicate a lower absorbance with the additive. The reaction parameters studied are space velocity, inlet concentration and light source. Oxidation by-products are identified using a GCMS.

We have synthesized an annealed porous aerogel titania (LUAG2), which demonstrates a very high photocatalytic activity for aldehydes and perchloroethylene (PCE) photocatalytic oxidation (PCO) in gas phase under blacklight and fluorescent light irradiation. LUAG2 has a BET surface area of 237 m2/g and a porosity of 0.31 (volume fraction). X-ray diffraction (XRD) analysis shows LUAG2 is nearly pure anatase. It has improved the destruction of PCE and aldehydes as a group by 10–34% with black light compared to Degussa P-25. The optimum water vapor to butyraldehyde molar ratio is around 1/3. LUAG2 also shows better mineralization to CO2 than Degussa P-25 TiO2 does. Under irradiation of a 4 W fluorescent lamp LUAG2 gives a consistently higher conversion than that of Degussa P-25. The highly active photocatalyst indicates potential applications in indoor and outdoor environmental pollution control. A visible-light-responsive TiO2, NTB 200, is also investigated for comparison purposes.

Photocatalytic oxidation (PCO) of nitric oxide (NO) over TiO 2 catalyst was studied at source levels (5–60 ppm). The PCO process involves a series of oxidation steps by the OH radical: NO→HNO 2 →NO 2 →HNO 3 . The product NO 2 can be collected in an adsorbent bed and either recycled back to the combustion chamber or recovered as nitric acid. The ratio of NO 2 − to NO 3 − from spent catalyst liquor drops with irradiation time until a steady state is reached. The reactions are limited by thermodynamic equilibrium after ∼12 s space time. The steady-state experimental data from space time and inlet concentration effects can be described with the Langmuir–Hinshelwood (L–H) kinetic model with R 2 =0.9208.

In this study, gas phase photocatalytic oxidation (PCO) of n-butyraldehyde was carried out in a packed-bed reactor (titania supported on an inert packing). An on-line system consisting of two collection columns (one glass bead and one activated carbon) and a GC/MS was used for by-product identification. Various temperature levels (50, 90, 115, 170, 270, 320°C) were used in the by-product desorption from the activated carbon column. The oxidation yielded carbon dioxide as the end product. The by-products revealed many reaction pathways of the photocatalytic process. The major by-products (propionaldehyde, 1-propanol, ethanol, and acetaldehyde) were believed to undergo a C-C bond cleavage followed by hydrolysis. Secondary by-products (propyl formate, di-n-propyl ether, and 3-heptene) were caused by esterification, dehydration, and reductive coupling. Aldol condensation of the vapor phase aldehydes on TiO 2 surfaces followed by cyclization may be partially responsible for the formation of some minor by-produ...

This paper is the first to investigate photocatalysis using a cutting-edge and energy-efficient solid-state light source: Ultraviolet (UV) Light Emitting Diodes (LED's). UV LED's do not involve mercury vapor, can be driven with direct current (DC), and have a long lifetime of 100000 hours. UV LED's with a peak wavelength of 375 nm were tested for perchloroethylene (PCE) photocatalytic oxidation over Degussa P-25 TiO 2 . At a UV light output of only 49 μW/cm 2 , the designed reactor delivers a PCE conversion of up to 43 %. If the UV LED price continues to drop, it is very likely that UV LED's will replace UV lamps as the favored light source in photocatalysis applications.

The oxygen uptake process in a respirometer was analyzed by a mathematical model consisting of oxygen transfer accompanied with oxygen consumption reaction. The criterion to avoid an oxygen-transfer limitation was derived on the basis of the ratio of the maximum biochemical reaction rate to the maximum possible oxygen-transfer rate. The maximum biochemical reaction is described by the first-order rate equation, whereas the maximum possible oxygen-transfer rate is calculated by multiplying the oxygen-transfer coefficient with the solubility of oxygen in water. An oxygen-transfer coefficient in a respirometric reactor was estimated as 1.8 h -1 , by using the model analysis of an oxygen uptake data from the same reactor. A simplified criterion for respirometer without oxygen-transfer limitation is then obtained as XS? 16.51/ K 1 , where X and S represent concentration of biomass and substrate, respectively, and K 1 is the first-order rate constant, (L/mg VSS)/h.

Material processing furnaces are the key component of the manufacturing industries. The burners used in these furnaces require precise control over the flame structure such as flame shape, height, and width. This study mainly focused on the simulation of the flame structure with Computational Fluid Dynamics (CFD) approach. ANSYS Fluent 13.0 was used to predict the flame characteristics in an enclosed cylinder. Non-premixed combustion model was applied to this combustion phenomenon. To control the flame structure, a micro jet at the centre of the burner is introduced. The effect on flame parameters with varying flow rates of micro jet, fuel jet and co-flow jet is examined. This study confirms the experimental study by Sinha et al. [1], which concluded that an air micro jet at the center of a non-premixed flame can control the flame height and luminosity. Moreover, this paper visualizes the thermo chemistry and transport phenomenon of non-premixed combustion process. Emissions from the combustion are monitored for different boundary conditions. This study shows that innovative strategies can be developed for the precise control over the different types of flames with the help of numerical modeling.Copyright © 2012 by ASME

ABST R AC T Flaring emission during chemical plant turnaround operations generates huge amounts of air pollutants and also results in tremendous raw material and energy loss. This paper addresses near-zero aring studies for chemical plant turnaround operation to advance current endeavors on are minimization. Since off-spec products are inevitable during plant turnaround operations, they must be either recycled to the upstream process for online reuse or stored somewhere temporarily for future reprocessing when the plant manufacturing becomes stable, such that the off-spec products can be saved instead of being ared. A dynamic simulation based general methodology framework has been developed. The efcacies of the development are demonstrated by a virtual plant startup test.

Publisher Summary This chapter presents the solubility parameter and liquid volume for organic compounds in tabular form. The tabulation is arranged by carbon number such as C, C2, and C3, to provide ease of use in quickly locating the data by using the chemical formula. The compound name and chemical abstracts registry number (CAS No) are also provided in columns. Values for solubility parameter and liquid volume are given in the adjacent columns. The next column provides the code for the tabulation. For the tabulation, the results for solubility parameter are ascertained from heat of vaporization and liquid volume. In preparing the tabulation, a literature search is conducted to identify data source publications. Both experimental values for the property under consideration and parameter values for estimation of the property are included in the source publications. The publications are screened, and copies of appropriate data are made. These data are keyed into the computer to provide a database of values for compounds for which experimental data are available. The database also serves as a basis to check the accuracy of the estimation methods. Upon completion of data collection, estimation of values for the remaining compounds is performed. The compilations of CRC, Daubert and Danner, TRC, and Yaws are used extensively. Estimates for the enthalpy of vaporization at the boiling point are primarily based on the Kistiakowsky rule and Riedel method. The Joback method is used for estimating critical temperature. Estimates of liquid density are primarily based on the Schroeder correlation, Le Bas method, and Tyn-Calus equation. Liquid volume is ascertained from molecular weight and liquid density (molecular weight/density).

To demonstrate the development of an oxygen atom microreactor in the form of liquid-helium-cooled solid argon matrix deposited on an infrared (IR) window, the oxidation of ethylene by mobile O atoms has been investigated. O atom diffusion through the argon matrix is confirmed and used to examine ethylene–oxygen atom reactions. In a bench-scale matrix isolation system probed with a Fourier transform infrared (FT-IR) spectrometer, matrices of solid Ar at 8–10 K doped with NO2 and ethylene have been prepared on a ZnSe window within an evacuated cryostat. The matrices have been photolyzed using 350–450 nm photons, and the reaction products resulting from the reaction of O(3P), one of the photolysis products of NO2, with ethylene have been identified using FT-IR and a Gaussian 98W simulation program. These products include oxirane, acetaldehyde, ethyl nitrite radical, and ketene. The temperature effect in the range of 10–30 K on the products formed has also been investigated. The reaction mechanisms are discussed and the viability of the solid Ar matrix being a low temperature microreactor to examine reaction mechanisms of mobile oxygen atoms is elaborated.

Photolysis (350–450 nm) of NO2 molecules trapped in argon matrices at 10 K has been studied using Fourier transform infrared (FT-IR) spectroscopy to examine the mobility of the photolysis products, O(3P) and NO, and their subsequent reactions. The formation of N2O5 and N2O3 from reactions of these mobile species with immobilized NO2 and N2O4 is confirmed. Water molecules from the background gases in the vacuum have been found to be isolated in the argon matrix during deposition of diluted NO2 in Ar. The entrapped water molecules along with some of their NO2 adducts have been characterized. Exposure of the matrix to photons to photolyze NO2 resulted in not only internal matrix reactions, but also an enhanced deposition of ice over the surface of the argon matrix. This is caused by photodesorption of water molecules from the walls of the matrix isolation chamber and their subsequent condensation on the matrix surface. This ice overlayer has been found to give a very significant dangling OH band and a substantial librational band in the FT-IR spectra, indicating substantial surface area and internal porosity, respectively. The potential of using photodesorbed water to establish high surface area ice interfaces with dangling OH groups for heterogeneous photoreaction studies is discussed.

Nine glass concentric reactors (LD. from 19 to 94 mm) were constructed with a 4-watt UV lamp (1.5 cm O.D. × 11 cm length) located at the center. TiO

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Poly(p-phenylene vinylene) mulilayers have been prepared from its cationic precursor via the layer-by-layer deposition. The photoluminescence (PL) and film thickness of the multilayers have been examined via fluorimetry and atomic force microscopy. The PL of the multilayers has been observed that is consistent with the literature results. When phosphomolybdate PMo12 is incorporated into the multilayer structure, PL quenching is detected that is proportional to the amount of PMo12 used. The quenching is interpreted as exciton diffusion through the polymer multilayers, followed by exciton dissociation at the polymer/PMo12 interface. We show that the modeling used for calculating the PL intensities derived from inorganic semiconductors is also applicable to conjugated polymers. According to the model, an exciton diffusion length is found to be 11.5±0.4nm.

This paper describes a project of flare minimisation during plant startup by using dynamic simulation. Dynamic simulation was developed for recovery area in an olefin plant and used to examine startup procedures: • approaching shutdown • startup with recycle ethane • starting the cracked feed and increasing the feed to normal production rate. The dynamic simulation gives an insight into the process dynamic behaviour that is not apparent through the use of steady state simulation. This information is crucial for plant startup in order to minimise the flaring. This project demonstrated a feasibility of pollution prevention through flare minimisation for an olefin plant.

New technologies for producing polysilicon are being developed to provide lower cost material for solar cells which convert sunlight into electricity. This article presents results for the BCL Process, which produces the solar-cell silicon by reduction of silicon tetrachloride with zinc vapor. Cost, sensitivity, and profitability analysis results are presented based on a preliminary process design of a plant to produce 1000 metric tons/year of silicon by the BCL Process. Profitability analysis indicates a sales price of $12.1-19.4 per kg of silicon (1980 dollars) at a 0-25 per cent DCF rate of return on investment after taxes. These results indicate good potential for meeting the goal of providing lower cost material for silicon solar cells.

Theoretical effect of mass transfer by reversible cyclic chemical reactions is studied in this paper. On the basis of the film theory, an analytical equation has been derived to express the enhancement factor of gas absorption with first-order reversible cyclic chemical reactions. The finite difference method has been used to study the enhancement of gas absorption with second-order reversible cyclic reactions. The results indicate that the gas absorption rate is enhanced by the forward reaction rate, while is suppressed by the backward reaction. Although the diffusivity has some effects on enhancement factor, the influence is not as much as that of reaction rate. The theoretical equations are used to predict the enhancement factors for absorptions of carbon dioxide in acidic solution and l-butene in liquid phosphoric acid.

A reduction in the cost of silicon for solar cells is an important objective in a project concerned with the reduction of the cost of electricity produced with solar cells. The cost goal for the silicon material is about $14 per kg (1980 dollars). The process which is currently employed to produce semiconductor grade silicon from trichlorosilane is not suited for meeting this cost goal. Other processes for producing silicon are, therefore, being investigated. A description is presented of results obtained for the DCS process which involves the production of dichlorosilane as a silicon source material for solar energy silicon. Major benefits of dichlorosilane as a silicon source material include faster reaction rates for chemical vapor deposition of silicon. The DCS process involves the reaction 2SiHCl3 yields reversibly SiH2Cl2 + SiCl4. The results of a cost analysis indicate a total product cost without profit of $1.29/kg of SiH2Cl2.