Showing papers in "Industrial & Engineering Chemistry Research in 2008"

Natural Gas Processing with Membranes: An Overview

Abstract: Every year, the world uses close to 100 trillion scf (standard cubic feet) of natural gas. All of this gas requires treatment before it enters the pipeline, making natural gas processing by far the largest market for industrial gas separation processes and equipment. Of this huge market, membranes have less than a 5% share, but this is changing; membrane-based removal of natural gas contaminants is growing faster than any other segment of the membrane gas separation business. This paper gives an overview of the membrane technology in current use for natural gas treatment and outlines the future prospects.

Formula for the Viscosity of a Glycerol−Water Mixture

Abstract: An empirical formula is proposed for the calculation of the viscosity of glycerol−water mixture for mass concentrations in the range of 0−100% and temperatures varying from 0 to 100 °C. It compares well with three databases available in the literature, and its application procedure is also simpler than other previously developed correlations.

Sorption-Enhanced Hydrogen Production: A Review

Abstract: In the sorption-enhanced hydrogen production process, hydrocarbon reforming, water gas shift, and CO2 separation reactions occur simultaneously in a single reaction step over a reforming catalyst mixed with a CO2 sorbent. Transferring CO2 as it is formed from the gas to the solid phase shifts the normal equilibrium restrictions and allows both the reforming and water gas shift reactions to approach completion. Depending on reaction conditions, the product (dry basis) may contain as much as 98% H2 and only ppmv levels of CO and CO2, thereby minimizing the final H2 purification step or even eliminating it for some applications. A number of CO2 sorbents have been studied including calcium-based oxides, K-promoted hydrotalcite, and mixed metal oxides of lithium and sodium. The sorbent is consumed during H2 production so that the process is intrinsically unsteady state. Process economics requires that the sorbent be regenerable and used in many reaction−regeneration cycles. Regeneration may occur via temperatu...

Reducing the Cost of CO2 Capture from Flue Gases Using Pressure Swing Adsorption

Abstract: Pressure swing adsorption (PSA) processes have been used extensively for gas separation, especially in the separation of hydrogen from CO2, and in air purification. The objective of this paper is to examine the economic feasibility of pressure swing adsorption (PSA) for recovering CO2 from postcombustion power plant flue gas. The analysis considers both high-pressure feed and vacuum desorption using commercial adsorbent 13X, which has a working capacity of 2.2 mol/kg and CO2/N2 selectivity of 54. The results show that using vacuum desorption reduces the capture cost from US$57 to US$51 per ton of CO2 avoided and is comparable in cost to CO2 capture using conventional MEA absorption of US$49 per ton of CO2 avoided. In this paper, a sensitivity analysis is also presented showing the effect on the capture cost with changes in process cycle; feed pressure and evacuation pressure; improvements the adsorbent characteristics; and selectivity and working capacity. The results show that a hypothetical adsorbent wi...

Room-Temperature Ionic Liquid−Amine Solutions: Tunable Solvents for Efficient and Reversible Capture of CO2

Abstract: Solutions of room-temperature ionic liquids (RTILs) and commercially available amines were found to be effective for the capture of CO2 as carbamate salts. RTIL solutions containing 50 mol % (16% v/v) monoethanolamine (MEA) are capable of rapid and reversible capture of 1 mol of CO2 per 2 moles MEA to give an insoluble MEA−carbamate precipitate that helps to drive the capture reaction (as opposed to aqueous amine systems). Diethanolamine (DEA) can also be used in the same manner for CO2 capture in RTILs containing a pendant hydroxyl group. The captured CO2 in the resulting RTIL−carbamate salt mixtures can be readily released by either heating and/or subjecting them to reduced pressure. Using this unprecedented and industrially attractive mixing approach, the desirable properties of RTILs (i.e., nonvolatility, enhanced CO2 solubility, lower heat capacities) can be combined with the performance of amines for CO2 capture without the use of specially designed, functionalized “task-specific” ionic liquids. By ...

New Insights into the Interactions of CO2 with Amine-Functionalized Silica

Abstract: The CO2−amine chemistry in gas−solid processes was investigated under both humid and dry conditions using aminopropyl-grafted pore-expanded MCM-41 silica (MONO-PE-MCM-41). To draw accurate conclusions, a set of conditions had to be met including (i) the use of an adsorbent with open pore structure and readily accessible adsorption sites, e.g. MONO-PE-MCM-41 with a mean pore size of 7.2 nm; (ii) the CO2 concentration in the feed should be high enough to achieve saturation via chemisorption, but low enough to avoid any additional physisorption, e.g., 5% CO2 in N2; (iii) the use of a reliable method for the accurate measurement of CO2/N ratio. Under such conditions, the obtained CO2/N ratios were reminiscent of those obtained in the CO2 scrubbing process using ethanolamine solutions. Under dry conditions, the CO2/N ratio was close to 0.5, consistent with the formation of carbamate. Streams with relative humidity (RH) of 27, 61, and 74% were studied as well. As RH in the feed increased, CO2/N ratio increased ...

Fast pyrolysis of Oil Mallee Woody Biomass : Effect of temperature on the yield and quality of pyrolysis products

Abstract: This paper presents an investigation of the production of crude bio-oil, char, and pyrolytic gases from the fast pyrolysis of mallee woody biomass in Australia. The feedstock was ground, sieved to several narrow particle size ranges, and dried prior to pyrolysis in a novel laboratory-scale fluidized-bed reactor. The effects of pyrolysis temperature (350−600 °C), and biomass particle size (100−600 μm), on the yields and composition of bio-oil, gas, and char are reported. In agreement with previous reports, the pyrolysis temperature has an important impact on the yield and composition of bio-oil, char, and gases. Biomass particle size has a significant effect on the water content of bio-oil. It is interesting to note that the temperature for maximum bio-oil yield, between 450 and 475 °C, resulted in an oil with the highest content of oligomers and, consequently, with the highest viscosity. Such observations suggest that the conventional viewpoint of pyrolyzing biomass at temperatures over 400 °C to maximize...

Room-Temperature Ionic Liquids: Temperature Dependence of Gas Solubility Selectivity

Abstract: This study focuses on bulk fluid solubility of carbon dioxide (CO2), methane (CH4), hydrogen (H2), and nitrogen (N2) gases in the imidazolium-based RTILs: 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]), 1-n-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]), and 1,3-dimethylimidazolium methyl sulfate ([mmim][MeSO4]) as a function of temperature (25, 40, 55, and 70 °C) at near-atmospheric pressures. The experimental behaviors are explained in terms of thermodynamic relationships that account for the negligible vapor pressure of the RTIL as well as the low solubilities of the gases. Results show that, as temperature increases, the solubility of CO2 decreases in all RTILs, the solubility of CH4 remains constant in [emim][Tf2N] and [hmim][Tf2N] but increases in [mmim][MeSO4] and [emim][BF4], and the solubility of N2 and H2 increases. Also, the ideal solubility selectivity (ratio of pure-componen...

Stoichiometry of Cr(VI) Immobilization Using Nanoscale Zerovalent Iron (nZVI): A Study with High-Resolution X-Ray Photoelectron Spectroscopy (HR-XPS)

Abstract: Remediation of chromium-contaminated sites presents both technological and economic challenges as conventional methods are often too expensive in removing chromium in the soil matrix such as chromium ore process residue (COPR). In this work, reduction and precipitation of hexavalent chromium [Cr(VI)] by nanoscale zerovalent iron (nZVI) are evaluated. Cr(VI) is rapidly reduced and immobilized on the iron nanoparticle surface. In the pH range of 4 to 8, the nZVI has a chromium removal capacity ranging from 180 to 50 mg Cr/g nZVI. Under similar conditions, microscale iron particles (100 mesh) typically have a capacity of less than 4 mg Cr/g Fe. Characterizations with high-resolution X-ray photoelectron spectroscopy (HR-XPS) indicate that Cr(VI) is reduced to Cr(III), which is subsequently incorporated into the iron oxyhydroxide shell of nZVI and form alloy-like Cr−Fe hydroxides with a representative formula approximating (Cr0.67Fe0.33)(OH)3 or Cr0.67Fe0.33OOH. The Cr−Fe hydroxide shell is relatively stable a...

Crystal Shape Engineering

Abstract: In an industrial crystallization process, crystal shape strongly influences end-product quality and functionality, as well as downstream processing. In addition, nucleation events, solvent effects, and polymorph selection play critical roles in both the design and operation of a crystallization plant and the patentability of the product and process. Therefore, investigation of these issues, with respect to a priori prediction, is (and will continue to be) an important avenue of research. In this review, we discuss the state-of-the-art in modeling crystallization processes over a range of length scales relevant to nucleation through process design. We also identify opportunities for continued research and specific areas where significant advancements are needed.

A Review on the Potential Applications of Curved Geometries in Process Industry

Abstract: The potential industrial applications of curved tubes for single- and two-phase flow are reviewed within the context of physics of flow, trends in the development of technology, and its laboratory to industrial-scale commercialization. Comparison of the performance of curved tube configurations demonstrates its edge over the conventional motionless mixers, heat exchangers, and reactors. Alongside, their respective advantages and limitations are also highlighted. Further, a compendium of the available correlations for single- and two-phase friction factor and heat- and mass-transfer coefficient in curved tubes has also been presented. Key issues regarding the design parameters governing the performance of the curved tubes for mixing and heat- and mass-transfer that impact the research, development, and scale-up or scale-down of such devices are also analyzed. Emerging trends for the development of a new class of curved tubes, namely, inverters and serpentine and chaotic devices are also presented.

Critical Properties, Normal Boiling Temperature, and Acentric Factor of Another 200 Ionic Liquids

Abstract: The critical properties, the normal boiling temperature, and the acentric factor of 200 ionic liquids have been determined using an extended group contribution method, which is based on the well-known concepts of Lydersen and Joback and Reid, that was developed by the authors. The method does not require any additional data besides knowledge of the structure of the molecule and its molecular mass. Because experimental critical properties of ionic liquids are not available, the accuracy of the method is checked by calculating the liquid density of the ionic liquids considered in the study for which experimental data are available in the literature. The results show that the values determined for the critical properties, the normal boiling temperature, and the acentric factor are sufficiently accurate for engineering calculations, generalized correlations, and equation of state methods, among other applications.

Recent Advances and Applications of Statistical Associating Fluid Theory

Abstract: This review presents recent advances and applications of statistical associating fluid theory (SAFT), which has been extended in the past few years, conceptually and practically, to improve its performance and to represent thermodynamic properties of complex systems, such as associating polymers, polydispersed polymers, aqueous electrolytes, dipolar and quadrupolar systems, ionic liquids, near-critical systems, interfacial phenomena, crystallizable copolymers, gas hydrates, liquid crystals, biomaterials, and oil reservoir fluids, as well as dynamic properties such as viscosity.

Review of Fluid Slip over Superhydrophobic Surfaces and Its Dependence on the Contact Angle

Abstract: A review of the characteristics of hydrophobicity is presented, with the goal of investigating the relationship, if any, between the contact angle (a macroscopically observed property) and the slip length (a microscopic phenomenon). An analysis of simulations, and of their evolution through the years, sheds light on some inherent differences between contact angle and slip length behavior on flat and patterned surfaces. Previous studies lead to the conclusion that epitaxial layering of fluid near the solid is intricately related to the magnitude of fluid slip. Epitaxial layer data help to explain unexpected slip length behavior in relation to the contact angle, and reported inconsistencies between slip length experiments and simulations. Therefore, it seems that solids that can produce favorable epitaxial layering of the fluid will cause larger slip. Dimensional analysis is used to elucidate the contact angle−slip length relationship. Results can be applied to the development of artificial supersolvophobic...

Switchable Solvents Consisting of Amidine/Alcohol or Guanidine/Alcohol Mixtures

Abstract: Liquids that consist of a mixture of an alcohol and either an amidine or a guanidine have been developed to switch from a low-polarity form to a high-polarity ionic liquid upon treatment with CO2 at atmospheric pressure. Treatment with N2 and/or mild heat (50−60 °C) reverses the process. These liquids can be used as switchable solvents to dissolve and then precipitate a solute or to dissolve reagents for a chemical synthesis and then precipitate the product.

Experimental Investigation on CO2 Post−Combustion Capture by Indirect Thermal Swing Adsorption Using 13X and 5A Zeolites

Abstract: Experimental results of CO2 post-combustion capture for a TSA process including an internal heat-exchanger (indirect heating/cooling) are presented. The comparative experimental study is carried out on 13X and 5A zeolites, with a mixture 90% N2−10% CO2 modeling the flue gas. With 5A zeolite having given the best performances, we tested it with various operating conditions including one with nitrogen purge during desorption. This one showed a good compromise between CO2 capture rate, purity of the desorbate, volumetric productivity, and specific-heat consumption. We obtained a volumetric productivity of 37 kgCO2/m3ads·h and a specific-heat consumption of 6 MJ/kgCO2 at our laboratory scale and 4.5 MJ/kgCO2 for the adiabatic estimate (in the same order of magnitude as those obtained industrially with the reference MEA amine process). These results are promising because our process is not optimized yet and the scale-up on an industrial version involves a reduction in specific-heat consumption.

Reducing the Cost of CO2 Capture from Flue Gases Using Membrane Technology

Abstract: Studies of CO2 capture using membrane technology from coal-fired power-plant flue gas typically assume compression of the feed to achieve a driving force across the membrane. The high CO2 capture cost of these systems reflects the need to compress the low-pressure feed gas (1 bar) and the low CO2 purity of the product stream. This article investigates how costs for CO2 capture using membranes can be reduced by operating under vacuum conditions. The flue gas is pressurized to 1.5 bar, whereas the permeate stream is at 0.08 bar. Under these operating conditions, the capture cost is U.S. $54/tonne CO2 avoided compared to U.S. $82/tonne CO2 avoided using membrane processes with a pressurized feed. This is a reduction of 35%. The article also investigates the effect on the capture cost of improvements in CO2 permeability and selectivity. The results show that the capture cost can be reduced to less than U.S. $25/tonne CO2 avoided when the CO2 permeability is 300 barrer, CO2/N2 selectivity is 250, and the membr...

Fuels from Waste Plastics by Thermal and Catalytic Processes: A Review

Abstract: Feedstock recycling of plastic waste by thermal and catalytic processes is a promising route to eliminate this refuse (which is harmful to the environment) by obtaining, at the same time, products that are useful as fuels or chemicals. During the past decade, this option has undergone an important evolution from a promising scientific idea to an alternative that is very close to reality with commercial opportunities. Thus, several commercial processes have been developed worldwide, most of them especially addressed toward the preparation of diesel fuel. The present review highlights the most remarkable achievements of the field, providing a fundamental insight into this fascinating area and highlighting the main milestones that should be achieved in the next future for this alternative to become applied commercially on a large scale.

Modeling Liquid−Liquid Equilibrium of Ionic Liquid Systems with NRTL, Electrolyte-NRTL, and UNIQUAC

Abstract: Characterization of liquid−liquid equilibrium (LLE) in systems that contain ionic liquids (ILs) is important in evaluating ILs as candidates for replacing traditional extraction and separation solvents. Although an increasing amount of experimental LLE data is becoming available, comprehensive coverage of ternary liquid-phase behavior via experimental observation is impossible. Therefore, it is important to model the LLE of mixtures that contain ILs. Experimental binary and ternary LLE data that involve ILs can be correlated using standard excess Gibbs energy models. However, the predictive capability of these models in this context has not been widely studied. In this paper, we study the effectiveness with which excess Gibbs energy models can be used to predict ternary LLE solely from binary measurements. This is a stringent test of the suitability of various models for describing LLE in systems that contain ILs. Three different excess Gibbs free energy models are evaluated: the non-random two-liquid (N...

Desulfurization of Fuel by Extraction with Pyridinium-Based Ionic Liquids

Abstract: The pyridinium-based ionic liquids (ILs) N-butylpyridinium tetrafluoroborate ([BPy][BF4]), N-hexylpyridinium tetrafluoroborate ([HPy][BF4]), and N-octylpyridinium tetrafluoroborate ([OPy,][BF4]) were found to be effective for the selective removal of aromatic heterocyclic sulfur compounds from diesel at room temperature. The results suggested that the structure and size of the cation greatly affect the extractive performance of ILs. The extractive performance using pyridinium-based ILs followed the order [BPy][BF4] < [HPy][BF4] < [OPy][BF4], and for the IL, the sulfur removal selectivity of sulfur compounds followed the order thiophene (TS) < benzothiophene (BT) < dibenzothiophene (DBT) under the same conditions. The pyridinium-based ILs would not contaminate the diesel due to their insolubility. On the other hand, diesel has a certain solubility in pyridinium-based ILs, varying from 0.49 wt % for [BPy][BF4] to 1.97 wt % for [OPy][BF4]. According to the results, [HPy][BF4] and [OPy][BF4] might be used as promising solvents for the extractive desulfurization of diesel.

Flue-Gas Carbon Capture on Carbonaceous Sorbents: Toward a Low-Cost Multifunctional Carbon Filter for "Green" Energy Producers †

Abstract: A low-pressure Carbon Filter Process (patent pending) is proposed to capture carbon dioxide (CO2) from flue gas. This filter is filled with a low-cost carbonaceous sorbent, such as activated carbon or charcoal, which has a high affinity (and, hence, high capacity) to CO2 but not to nitrogen (N2). This, in turn, leads to a high CO2/N2 selectivity, especially at low pressures. The Carbon Filter Process proposed in this work can recover at least 90% of flue-gas CO2 of 90%+ purity at a fraction of the cost normally associated with the conventional amine absorption process. The Carbon Filter Process requires neither expensive materials nor flue-gas compression or refrigeration, and it is easy to heat integrate with an existing or grassroots power plant without affecting the cost of the produced electricity too much. An abundant supply of low-cost CO2 from electricity producers is good news for enhanced oil recovery (EOR) and enhanced coal-bed methane recovery (ECBMR) operators, because it will lead to higher o...

Aqueous Solubility of Some Natural Phenolic Compounds

Abstract: In this work, the aqueous solubilities of two hydroxybenzoic acids (gallic and salicylic acid) and three phenylpropenoic acids (trans-cinnamic, ferulic, and caffeic acids) are addressed. Measurements were performed, as a function of temperature, between 288.15 and 323.15 K, using the shake-flask method for generating the saturated aqueous solutions, followed by compositional analysis by spectrophotometric and gravimetric methods. The pH values of the saturated aqueous solutions were measured by potentiometry. Additional thermodynamic properties, which are fundamental for a better understanding of the solubilization process, as well as necessary for the modeling studies, such as melting temperatures and fusion enthalpies were determined by differential scanning calorimetry (DSC). Apparent acid dissociation constants (Ka) were obtained by potentiometry titration. The measured data were modeled with the cubic-plus-association (CPA) equation of state (EoS). This EoS is applied, for the first time, for multifunctional associating molecules, and the results indicate that it can adequately be used to represent the measured and other literature data with satisfactory accuracy. 1. Introduction Fruits, vegetables, spices, and aromatic herbs are a natural source of phenolic compounds. These can be raw materials for the synthesis of different molecules with industrial interest, such as some drugs, cosmetics, antioxidants, antiseptics, and flavors; they also can be used in the preparation of resins, plasticizers, dyes, inks, and pharmaceutical products. 1 Many of these phenolic compounds have potential chemical and biological properties, such as antioxidant, chelating, free-radical scavenging, anti-inflammatory, antialergic, antimicrobial, antiviral, anticarcinogenic, chemoprevention (interfering with a disease process), and ultraviolet (UV) filtering properties. Most of them are phytochemical (they are not required for the normal functioning of the body, but they do have a beneficial effect on health, or an active role in the treatment of a disease). Because of their hydrogen-bonding ability and aromaticity, phenolic compounds can frequently act as free-radical scavengers, forming aryloxyl radicals (ArO ·). The stabilization of these radicals by other functional groups enhances the antioxidant

One-Part Geopolymer Mixes from Geothermal Silica and Sodium Aluminate

Abstract: In geopolymer technology, silicate solutions are frequently used as alkali activators to dissolve the solid aluminosilicate precursor and aid in binder formation. These corrosive and often viscous solutions are not user-friendly and would be difficult to use for bulk production. Developing geopolymers as a one-part mixture (“just add water”), similar to Portland cement, increases their commercial viability. Here, for the first time, the geopolymer system consisting of geothermal silica and solid sodium aluminate (providing the solid silica, alkali, and alumina sources) is studied. The effects of water content, high early silica, and high early alumina in the formation of one-part mix geopolymers are also investigated. This system demonstrates that making geopolymers from solid sources by “just adding water” is possible. XRD shows that the formulation with less water has an unexpected greater extent of crystallinity. It is also observed that a high early Al concentration inhibits geopolymerization, while a...

Carbon Dioxide Capture Using a CO2-Selective Facilitated Transport Membrane

Abstract: A novel CO2-selective membrane with the facilitated transport mechanism has been synthesized to capture CO2 from the industrial gas mixtures, including flue gas. Both mobile and fixed amine carrier...

Comparison of Extractive Distillation and Pressure-Swing Distillation for Acetone-Methanol Separation

Abstract: Two of the most common methods for separating a binary homogeneous azeotrope are pressure-swing distillation and extractive distillation. The former is effective if the composition of the azeotrope changes significantly with pressure. The latter method is effective if a suitable solvent can be found. This paper compares the steady-state design and the dynamic control of these two methods when applied to the acetone-methanol binary system. The minimum-boiling azeotrope at 1 atm contains 77.6 mol % acetone at 328 K. At 10 atm the azeotropic composition is 37.5 mol % acetone at 408 K, so pressure-swing separation is feasible. Extractive distillation is also feasible using water as the solvent. Both systems require two distillation columns. Purities of the two products are set at 99.5 mol %. Results show that the extractive distillation system has a 15% lower total annual cost. However, a third component (water) is introduced that appears as trace impurities in both the acetone and methanol products. It is also much more difficult to attain higher purities in the extractive distillation system than in the pressure-swing system because of ternary vapor-liquid equilibrium constraints. The dynamic controllabilities of the two alternative processes are quite similar. Steady-state designs and control structures are also developed for the two methods when the columns are heat integrated. Heat integration is straightforward in the pressure-swing system because the condenser temperature in the high-pressure column is 60 K higher than the base temperature in the low-pressure column. In the extractive distillation system, the pressure in the second solvent recovery column must be increased from 1 to 5 atm to provide the necessary temperature differential driving force.

Solid looping cycles: A new technology for coal conversion

Abstract: This article examines both oxygen looping cycles (otherwise known as chemical looping combustion), and lime-based CO2 looping cycles, where calcined limestone is used for in situ CO2 capture. There...

Properties of a Nano CaO/Al2O3 CO2 Sorbent

Abstract: This project studied the properties of nano CaO/Al2O3 as a high-temperature CO2 sorbent for its use in an adsorption enhanced reforming reaction. The sorbent containing nano CaCO3 precursors and aluminum oxide was prepared, and evaluation of the CO2 adsorption properties by a thermogravimetric analyzer, the results show that nano CaO/Al2O3 has a faster decomposition rate and has a higher CO2 adsorption ratio than micro CaO/Al2O3. The maximum adsorption ratio occurs at temperatures of 650 °C under a CO2 partial pressure of 0.33 atm. Durability studies show that the CO2 adsorption ratio remains at 68.3% after 50 cyclic runs under a carbonation temperature of 650 °C and calcination temperature of 800 °C, respectively. XRD, SEM, and BET were used for studying the change of micro characteristics of the CO2 sorbents before and after multiple carbonation−calcination runs. The results showed that the pore size of CaO/Al2O3 sorbents was enlarged and that a new substance (Ca12Al14O33) was formed even under a temper...

Metal Organic Framework Adsorbent for Biogas Upgrading

Abstract: The discovery of new materials with enhanced selectivity or capacity will boost adsorption applications, especially for environmental control. In particular, it was mentioned that metal-organic frameworks (MOF) with different tailored properties may be prepared for desired separations. To promote industrial application of MOF materials, up-scaling and process design still must be completely developed. In this work, we report adsorption equilibrium data of methane and carbon dioxide on Cu-MOF extrudates. The most important properties observed are the high-capacity for CO2 and the small nonlinearity of the isotherms. In this context, this adsorbent can be used for biogas upgrading to produce biomethane and reduce fossil-fuel CO2.

Accounts of Experiences in the Application of Artificial Neural Networks in Chemical Engineering

Abstract: Considerable literature describing the use of artificial neural networks (ANNs) has evolved for a diverse range of applications such as fitting experimental data, machine diagnostics, pattern recognition, quality control, signal processing, process modeling, and process control, all topics of interest to chemists and chemical engineers. Because ANNs are nets of simple functions, they can provide satisfactory empirical models of complex nonlinear processes useful for a wide variety of purposes. This article describes the characteristics of ANNs including their advantages and disadvantages, focuses on two types of neural networks that have proved in our experience to be effective in practical applications, and presents short examples of four specific applications. In the competitive field of modeling, ANNs have secured a niche that now, after two decades, seems secure.

Simultaneous Removal of SO2, NOX, and Hg from Coal Flue Gas Using a NaClO2-Enhanced Wet Scrubber

Abstract: A bench-scale study was conducted on the simultaneous removal of SO2, NOX, and mercury (both Hg0 and Hg2+) from a simulated coal flue gas using a wet calcium carbonate scrubber. The multipollutant capacity of the scrubber was enhanced with the addition of the oxidizing salt, sodium chlorite. The results showed a maximum scrubbing of 100% for SO2 and Hg species and near complete NO oxidation with about 60% scrubbing of the resulting NOX species. The chlorite additive was less effective as an oxidant in the absence of SO2 and NO in the flue gas. Oxidation of NO and mercury were only about 50% and 80%, respectively, in the case of no SO2 in the simulated flue gas. The mercury oxidation was similarly affected by the absence of NO in the flue gas.