Treatment Of Off-gas Research Articles

Self-sustained stable combustion of off-gas from Solid Oxide Fuel Cell in a cone-shaped porous burner with preheaters

A divergent porous medium burner with three embedded preheaters has been numerically studied in this paper. The burner can be used to recover heat from Solid Oxide Fuel Cell for burning extremely low calorific off-gas. The developed burner consists of a conical section filled with porous media in the upper part and three preheaters located downstream through which the fresh mixture recovers heat from exhaust gas. A coupled solution method is used to study the structure of the preheater, and the feasibility of the method is verified. The results show that the burner can use the heat recovered from the exhaust gas to burn mixtures without the need for any external heating. The burner is capable of dealing with extremely low calorific off-gas, it can stabilize the combustion of a mixture with a heating value of 0.908 MJ/kg. The results also show that the mass flow ratio has a great influence on the recovery efficiency. When the mass flow ratio is less than one, the recovery efficiency increases sharply with the increase of mass flow ratio. With the further increase of mass flow ratio, the recovery efficiency decreases. This study provides the guidance for the treatment of low-grade off-gas without additional energy consumption.

An Overview of Electron Accelerator Applications in Environmental Protection with an Emerging Pollutants Decomposing approach

Bachground: In recent years, problems related to environmental damage and natural resource degradation are receiving increased attention from researchers throughout the world. This occurs mostly, through un-eco-friendly technology used to produce industrial products. Therefore, eco-friendly science and technology (green technology) which can empower and control the existing coal power plant for the virtue of society and the earth is required. Today, the design and application of electron accelerator has been well developed due to reliability, larger capacity, greater energy range, and cost reduction. Technologies that use particle accelerators are considered critical to advance high-tech processes in various economic fields, including material processing, sterilization of medical products, environmental protection, medicine, cargo inspection, chemical analysis, nuclear energy, etc. High-energy and high-power beams pose the ability to alter the physical, chemical, and biological properties of materials on an industrial scale. This technology has received more attention than other conventional treatment methods due to the need for smaller areas, high electrical efficiency, and production of by-products such as fertilizers. The electronic beam process in the treatment of off-gas, wastewater, and sludge, as well as the decomposition of emerging contaminants, is mentioned as a non-chemical, additive-free process that uses radiolysis to effectively decompose contaminants. The literature addresses various applications of electron accelerators in order to modify the physical, chemical, or biological properties of industrial pollutants in the liquid, solid, and gas phases through treatment by ionizing radiation to control environmental pollution. Many advantages can be achieved through this method, which is known as radiation processing.

Off-gas detection and treatment for green air-plasma process

Abstract Thermal plasma is a promising technology widely used in materials processing and waste treatment due to its unique properties including high temperature, high energy density, high chemical activity, and high quench rate. Air-plasma is preferentially used because air is of low price as plasma gas. The content of NO x in off-gas from air-plasma was determined using a gas analyzer, and a treatment unit was designed for the green air-plasma process. Results show that the concentration of NO x in off-gas from air-plasma was 2,489 and 9,112 ppm when the plasma input power was 50 and 150 kW, respectively. O2 in the off-gas would act as an oxidant to promote NO x absorption; thus, alkali absorption method was directly used for the treatment of the present off-gas from air-plasma. The absorption efficiency could be increased to 62.2% when additional O2 was provided into the off-gas to change its O2 content from 20% to 50%. The absorption rate was estimated based on the experimental data and a multistage absorption unit design, which could be reduced below 100 ppm and meet the emission standard. This article presents the feasibility of thermal plasma off-gas purification, so as to truly realize the green plasma process.

Air classification: Potential treatment method for optimized recycling or utilization of fine-grained air pollution control residues obtained from dry off-gas cleaning high-temperature processing systems.

In the dust collected from the off-gas of high-temperature processes, usually components that are volatile at the process temperature are enriched. In the recycling of the dust, the concentration of these volatile components is frequently limited to avoid operation problems. Also, for external utilization the concentration of such volatile components, especially heavy metals, is often restricted. The concentration of the volatile components is usually higher in the fine fractions of the collected dust. Therefore, air classification is a potential treatment method to deplete the coarse material from these volatile components by splitting off a fines fraction with an increased concentration of those volatile components. In this work, the procedure of a sequential classification using a laboratory air classifier and the calculations required for the evaluation of air classification for a certain application were demonstrated by taking the example of a fly ash sample from a biomass combustion plant. In the investigated example, the Pb content in the coarse fraction could be reduced to 60% by separation of 20% fines. For the non-volatile Mg the content was almost constant. It can be concluded that air classification is an appropriate method for the treatment of off-gas cleaning residues.

Microbial biofilms: a concept for industrial catalysis?

Biofilm reactors have long been commercially used in the treatment of wastewater and off-gas. New opportunities are arising with the rapid expansion of our understanding of biofilm biology over the last few years. Biofilms have great potential as industrial workhorses for the sustainable production of chemicals because of their inherent characteristics of self-immobilization, high resistance to reactants and long-term activity, which all facilitate continuous processing. A variety of biofilm reactor configurations have been explored for productive catalysis and some reactors have been operated continuously for months. Sectors that might particularly benefit from this biofilm approach include synthetic chemistry (ranging from specialty to bulk chemicals), bioenergy, biologics and the food industry.

Removal of Methyl Parathion from Artificial Off-Gas Using a Bioreactor Containing a Constructed Microbial Consortium

Methyl parathion (MP), a highly toxic organophosphorus pesticide, was widely used for agriculture crop protection. During the production of MP and the process of MP-containing wastewater treatment, MP can release into the atmosphere and will do great harm to adjacent communities. A consortium comprised of an engineered microorganism and a natural p-nitrophenol (PNP) degrader was assembled for complete mineralization of MP. We genetically engineered Escherichia coli BL21 (DE3) enabling the overexpression of methyl parathion hydrolase (MPH). In addition, we isolated Ochrobactrum sp. strain LL-1 that utilized PNP, a product of MP hydrolysis, as the sole carbon, nitrogen, and energy source. The coculture effectively hydrolyzed 0.2 mM MP and prevented the accumulation of PNP in suspended culture. A laboratory-scale bioreactor containing the dual-species consortium was developed for the treatment of artificial off-gas containing MP. The bioreactor maintained over 98% of average MP removal efficiency over a 75 day period, and PNP produced from hydrolysis of MP was degraded completely, indicating that complete mineralization of MP was achieved. The strategy of linking degrading consortium to a bioreactor may provide an alternative to physicochemical abatement technologies for the treatment of waste-gas streams containing MP as well as other PNP-substituted organophosphates.

Performance of two biofilters with neutral and low pH treating off-gases

Two different functional biofilters were carried out and compared for the treatment of off-gas containing multicomponent odors and volatile organic compounds (VOCs) in this study. The effects of pH values and the empty bed retention time (EBRT) on the performance of the bioreactors were studied; and the characteristics of microbial populations in the two biofilters were also determined. The experimental results indicated that the removal efficiencies of hydrophilic compounds such as butyric acid and ammonia were higher in the neutral pH biofilter (NPB) than those in the low pH biofilter (LPB). In contrast, the removal efficiencies of the compounds with poor water solubility such as styrene and ethyl mercaptan were higher in the LPB than those in the NPB. The characteristics of microbial population in the two biofilters revealed that the heterotrophic bacteria, nonacidophilic thiobacteria, ammonia oxidizing bacteria, and nitrite oxidizing bacteria were major microorganisms in the NPB, whereas acidophilic thiobacteria and fungi were dominant in the LPB. Therefore, the performance of the biofilter depended on the characteristics of the compound being treated and the type of microorganisms.

MEROS®: an improved dry-type gas-cleaning process for the treatment of sinter offgas

VAI has developed the MEROS® process (Maximized Emission Reduction Of Sintering) in which dust and harmful metallic and organic components present in sinter offgas are removed in a series of treatment steps to levels previously unattained with conventional gas-treatment techniques. In a number of test campaigns, the technical and economical advantages of this innovative sinter offgascleaning process were verified. voestalpine Stahl subsequently placed an order with VAI for the installation of an industrial MEROS facility to be started-up in August 2007.

Off‐gas Treatment in De‐chlorination Process of PVC

Waste polyvinyl chloride (PVC), which is used as oil substitute in blast furnaces, contains a large amount of chlorine. In the case of pyrolyzing PVC, it produces hydrochloric gas (HCl) which can damage plant equipment and pollute the environment. Hence it must be de‐chlorinated before it is injected into the blast furnace. This paper studied the treatment of off gas in the de‐chlorination process of PVC, and its influence on the environment. The results showed that a multi‐stage absorption system for HCl could recover up to 10% of the hydrochloric acid, which could then be used directly in galvanizing processes. It also reduced the emission of HCl to 0.0066 ~ 0.0068 mg/m3, which is far less than the 0.030 mg/m3 allowed by the national environmental standard [1].

Decomposition Mechanism for Electron Beam Irradiation of Vaporized Trichloroethylene−Air Mixtures

Decomposition of trichloroethylene (TCE) in electron beam irradiation was examined in order to get information on treatment of industrial off-gas. Air containing vaporized TCE was sealed into a glass vessel and irradiated with an electron beam. The concentration of TCE exponentially decreased with dose (air-absorbed energy). The doses necessary to decompose 90% of input TCE molecules had a value of 3.6 kGy independent of an initial concentrations ranging from 50 to 1800 ppmv. Between G values of decomposition and initial concentrations, the following equation was obtained: G(−TCE) [μmol J-1] = 1.5 [μmol J-1] + 0.020 [μmol J-1 ppmv-1] × conc [ppmv]. The equation shows that concentrations of Cl radicals remained constant at 6.3 × 10-4 ppmv (at 298 K and 1 bar) independent of concentrations of TCE and products under a dose rate of 2.1 kGy/s. Termination reactions in the decomposition mechanism for EB irradiation of TCE and tetrachloroethylene (PCE) were also clarified on the basis of the relation of G value of decomposition and the initial concentrations. Dichloroacetyl chloride, which was identified as a primary product, was decomposed and oxidized to give CO and CO2. Phosgene was also identified as a primary product. From the proportion of DCAC to COCl2 concentrations, a branching ratio was calculated to be 5.3 in the Cl radical chain reaction of TCE. Formation of HCl and/or Cl2 was analyzed and the collection of the products from the gas phase was examined with alkaline solution. The effect of water (400−25 000 ppmv) on decomposition efficiency was examined. The decomposition efficiencies had the same value as that in dry air.

Decomposition of chloroethenes in electron beam irradiation

Abstract Decomposition of tetrachloroethylene and other chloroethenes in electron beam irradiation were examined in order to get information on treatment of industrial off-gas. The G-values of decomposition were larger in the order of tetrachloro->trichloro-> trans -dichloro-> cis -dichloro->monochloro-ethylene. For tetrachloroethylene, the effect of initial concentration on G-value of decomposition was also examined. The G-values of decomposition increased with the initial concentration. Decomposition mechanism and the difference in G-values of decomposition between trans - and cis -dichloroethylene were discussed.

ABSORPTIVE SEPARATION OF NO FROM DILUTE OFF-GAS

ABSTRACT With regard to its negligible absorption properties, the separation of nitrogen monoxide from dilute off-gas is limited to bench-scale experiments. Investigation has been centered on improving the rate of absorption by the use of complex-forming additives based on iron(II) compounds. Further efforts have been made to improve the separation efficiency by the use of reactive additives. Due to the low reactivity of nitrogen monoxide, these attempts did not succeed. The oxidation of moderately concentrated off-gas with ozone and the absorption of the so-formed nitrogen dioxide have been reported. Technical as well as economical considerations do not permit the application of the process to the treatment of dilute off-gas. The principle underlying this process led to the investigation of direct oxidation of the off-gas under electrical discharge followed by absorption with aqueous diamide solution. Temperature and moisture of the off-gas have been considered, in addition to various feed contents of nitrogen monoxide. The results of this investigation show that direct oxidation of nitrogen monoxide by corona discharge is possible. The rate of conversion increases with increasing gas velocity, accompanied by a decreasing specific energy consumption. Applied to tunnel off-gas purification, the direct oxidation route seems to offer promising technical boundaries as it is accompanied by efficient particle separation.

Decomposition of Volatile Organic Compounds in Air by Electron Beam and Gamma Ray Irradiation

AbstractRadiation decomposition and aerosol formation of various volatile organic compounds (VOCs) were examined to get information on a treatment of industrial off-gas. Model gases, air containing aromatic VOCs, chloroethenes and 1,2-dichloroethane, were sealed in batch reactors and irradiated with electron beam (EB) and gamma ray. For aromatic VOCs, G-values of decomposition in gamma ray irradiation were about 1.5 times larger than those in EB irradiation. The ratios of aerosol formation to decomposed aromatic VOCs were ranged from 30 to 66% on the basis of carbon. For chloroethenes except monochloroethylene, G-values of decomposition were 6 to 45 times larger than those of aromatic VOCs and the irradiated product was mainly gaseous compound. The G-values of decomposition in EB irradiation increased markedly with increase of chlorine atom in a molecule, while those in gamma ray irradiation were almost kept constant.

Endako Roasting Practice

The molybdenum conversion facility at Endako processes in excess of 14 million pounds of molybdenum (Mo) per year. Current practice exploits procedures and experience developed since the commencement of operations during 1965. This paper describes the current roasting practice and facilities as well as several associated processes, i.e. concentrate leaching to remove calcium from the roaster feed, concentrate drying in a multi-hearth dryer, the packaging of calcine into metal containers, the production of briquettes, and the treatment of roaster off-gas to recover dust and remove sulphur oxides.The Endako operation consists of two Nichols roasters - a 16-foot-diameter, 10-hearth unit and an 18-footdiameter, 12-hearth unit. Operating time of these units is in excess of 97%. The major influences responsible for achieving this availability are improved rabble design, scheduled on-line plowing of hearths and an aggressive preventive maintenance program.Endako is a prime producer of technical-grade molybdenum trioxide, the product having very low concentrations of minor-element irnpurities. Résumé La méthode de conversion du molybdène à Endako permet d'obtenir plus de 14 millions de livres de molybdène (Mo) par an. La pratique actuelle utilise les procédés et les expériences qui ont été développés depuis le commencement des opérations en 1965. Get article décrit les méthodes et la pratique actuelle de grillage ainsi que plusieurs proécédes connexes, à savoir: la lixiviation du concentré afin d'eliminer le calcium de la charge du four de grillage, le séchage du concentré dans un secheur à plar teaux multiples, l'emballage des produits de calcination dans des récipiants métalliques, la production de briquettes et le traitement des gaz de grillage afin de recuperer la poussiere et d' éliminer les oxydes de soufre. L'installation d'Endako est constituée de deux fours de grillage Nichols, un de 16 pieds de diamètre avec une unité de 10 plateaux et l'autre de 18 pieds de diamètre avec une unité de 12 plateaux. Les unités sont en opération pendant plus de 97% du temps. Les principaux lacteurs permettant d' obtenir cette disponibilité sont: une amélioration de la conception des bras d'agitation, un horaire precis pour le nettoyage des plateaux et un programme d'entretien preventif efficace.Endako est un des premiers producteurs de dioxyde de molybdène de calibre technique, le produit ayant une concentration trés laible en innpuretes d'elements mineurs.