Off-gas Stream Research Articles

Regenerative Adsorption and Removal of H 2 S from Hot Fuel Gas Streams by Rare Earth Oxides

Sorbent materials that allow for high-temperature, regenerative desulfurization of fuel gas streams for the anode of a solid oxide fuel cell have been developed. Reversible adsorption of H2S on cerium and lanthanum oxide surfaces is demonstrated over many cycles at temperatures as high as 800 degrees C, on both fresh or presulfided sorbents, and at very high space velocities. The adsorption and desorption processes are very fast, and removal of H2S to sub-parts per million levels is achieved at very short (millisecond) contact times. Any type of sulfur-free gas, including water vapor, can be used to regenerate the sorbent surface. Preferably, the anode off-gas stream is used to sweep the desorbed H(2)S to a burner.

Mass balance calculations in copper flash smelting by means of genetic algorithms

This paper presents mass balance calculations using genetic algorithms for copper smelting in an Outokumpu flash furnace. Based on the elemental composition of the copper concentrates being fed to the reactor, the mineralogical composition of the concentrate mixture is adjusted by means of genetic algorithms. The macroscopic mass balance equations for the species entering and leaving the furnace are solved and the compositions and flow rates of matte, slag, and the off-gas stream are computed. Good agreement between the predicted and plant data was obtained in terms of matte and slag flow rates, matte grade, and copper, iron, magnetite, and silica contents in the slag. Predictions are more suitable and faster to obtain with this method than a conventional method in which the mineralogical composition of the feed is not adjusted. Future applications of the formulation are discussed.

Regulatory Off-Gas Analysis from the Evaporation of Hanford Simulated Waste Spiked with Organic Compounds

After strontium/transuranics removal by precipitation followed by cesium/technetium removal by ion exchange, the remaining low-activity waste in the Hanford River Protection Project Waste Treatment Plant is to be concentrated by evaporation before being mixed with glass formers and vitrified. To provide a technical basis to permit the waste treatment facility, a relatively organic-rich Hanford Tank 241-AN-107 waste simulant was spiked with 14 target volatile, semi-volatile, and pesticide compounds and evaporated under vacuum in a bench-scale natural circulation evaporator fitted with an industrial stack off-gas sampler at the Savannah River National Laboratory. An evaporator material balance for the target organics was calculated by combining liquid stream mass and analytical data with off-gas emissions estimates obtained using U.S. Environmental Protection Agency (EPA) SW-846 Methods. Volatile and light semi-volatile organic compounds (<220 °C BP, >1 mm Hg vapor pressure) in the waste simulant were found to largely exit through the condenser vent, while heavier semi-volatiles and pesticides generally remain in the evaporator concentrate. An OLI Environmental Simulation Program (licensed by OLI Systems, Inc.) evaporator model successfully predicted operating conditions and the experimental distribution of the fed target organics exiting in the concentrate, condensate, and off-gas streams, with the exception of a few semi-volatile and pesticide compounds. Comparison with Henry's Law predictions suggests the OLI Environmental Simulation Program model is constrained by available literature data.

Activated-Carbon-Supported NaOH for Removal of HCl from Reformer Process Streams

An environmentally friendly method was developed to remove HCl from industrial waste gases, specifically the gas produced from a catalytic reforming process. The method uses activated-carbon-supported NaOH (NaOH/C) to treat the HCl-containing gas. A continuous-upflow fixed-bed reactor was used to test the performance of the prepared NaOH/C. Because chlorides contained in the off-gas stream of a reformer are normally less than 100 ppm, the cycle length of the NaOH/C will be expected to reach 1 year, and an accelerated aging test with a HCl concentration of 223 000 ppm was developed to shorten the test time. The accelerated aging test was confirmed to be reliable because the HCl treatment capacity of the NaOH/C for the accelerated aging test is almost the same as (within 15% deviation) that for standard tests with a gas stream containing 1000 ppm HCl. Effects of the water content on the performance of the NaOH/C were investigated by the accelerated aging test, and the results indicated that the HCl treatmen...

Toluene and styrene removal from air in biofilters

Two identical sized laboratory-scale biofilters, filled with the same type of packing material, consisting of a mixture of peat and glass beads in a 4:1 volume ratio, are investigated for the purification of toluene and styrene-containing off-gas streams. One of the biofilters was inoculated with a toluene-degrading strain of Acinetobacter sp. NCIMB 9689, and the other with a styrene-degrading strain of Rhodococcus rhodochrous AL NCIMB 13259. For both pollutants, different sets of continuous experiments were conducted in the biofilter columns, varying both the inlet pollutant concentration and the superficial gas velocity. Maximum elimination capacities of 242 and 63 g m packing material −3 h −1 packing material were recorded for toluene and styrene, respectively. Furthermore, the deodorization (defined as the achievement of a pollutant concentration in the effluent gas below the pollutant olfactory threshold value) of toluene and styrene-containing waste-gases was also considered. This was achieved, operating at maximum inlet concentrations of 1.99 and 0.20 g m −3 and at superficial gas velocities of 17.8 and 122 m h −1, respectively.

WETFINE, a new gas cleaning technology for sinter and pellet plants

In connection with the increasingly severe environment regulation, VOEST-ALPINE Industrieanlagenbau (VAI) has developed the WETFINE system, which allows to reduce the emissions from sinter, pellet, waste incineration plants, etc. to previously unattained levels. The key element of this system, a wet electrostatic precipitator, removes not only fine dust particles from the offgas stream, but also dioxin and furan, as well as SO3 compounds.

A Fungal Vapor-Phase Bioreactor for the Removal of Nitric Oxide from Waste Gas Streams

ABSTRACT Ground-level O3 formation is becoming a major concern in many cities due to recent tightening of O3 regulations. To control O3 formation, more efficient treatment processes for O3 precursors, such as NOx and volatile organic compounds (VOCs), are needed. One promising new technology for removing both NOx and VOCs from off-gas streams is biofiltration, a simple process whereby contaminated air is passed through a biologically active packed bed. In this study, a toluene-degrading fungal bioreactor was used to treat an aerobic gas stream contaminated with NO. The fungal bioreactor removed 93% of the inlet 250-ppmv NO at an empty bed contact time (EBCT) of 1 min when supplied with 90 g/m3/hr toluene. The presence of NH4 + concentrations greater than 0.4 mg NH3/g dry packing medium, however, resulted in poor NO removal. The bioreactor achieved a maximum toluene elimination capacity of 270 g/m3/hr and maintained greater than 95% toluene removal efficiencies over the 175-day study period.

Aluminum Remelting using Directly Solar-Heated Rotary Kilns

To check the feasibility of solar thermal remelting of aluminum scrap a directly absorbing rotary kiln receiver-reactor was constructed for experimentation in a mini-plant scale in the DLR high flux solar furnace. Conventionally the high energy demand for heating rotary kilns is met by the combustion of fossil fuels. This procedure generates a big exhaust gas volume which is contaminated by volatiles if the technology is applied to treat waste materials. Application of concentrated solar radiation to provide the high temperature heat enables to substitute the fossil fuel. Thus smaller off-gas streams are generated and lower investment and O&amp;M cost are expected for the off-gas purification. In this paper market and environmental issues are discussed and pre-designs both for solar pilot and industrial scale applications are presented.

Ion-drift reactor™ concept

This paper will focus on one of the advanced air pollution control (APC) technologies currently under development at MSE Technology Applications (MSE-TA). This technology, which has a patent pending, is an ion-drift reactor™ (IDR™). One of the applications of this reactor is to remove low-concentration fine particulate and hazardous pollutants, such as mercury vapor, products of incomplete combustion (PICs), and dioxins/furans from the air or incineration offgas. The pollutants are electrically sensitized by reagent ions by means of charge-exchange, hydrogen transfer, electron and ion attachments, hydrogen abstraction, and other reactions initiated by injection of reagent ions into the contaminated offgas or airstream. Selectively sensitized pollutant particles, clusters and molecules are then removed from the airstream by their drift in the electric field. In contrast to electrostatic precipitators and different types of other non-thermal plasma (NTP) technologies, the reagent ions are generated separately in the ion source of this new device and then injected into the contaminated offgas stream. This is thought to allow much better control over the discharge parameters and to allow much higher reaction selectivity than that of conventional NTP technologies. In comparison with conventional APC technologies, such as adsorption, heterogeneous catalysis, or absorption, an IDR™ utilizes ion-drift together with diffusion as the mechanisms of mass transfer, which reduces the reactor residence time and the differential pressure drop across the reactor in analogous conditions. These advantages are especially important for removal of mercury, other trace elements, and fine respirable particulate (PM 2.5) from the incineration offgas and air.

00/01118 Survey of aircure experience on dust control system for PRB coal

This paper will focus on one of the advanced air pollution control (APC) technologies currently under development at MSE Technology Applications (MSE-TA). This technology, which has a patent pending, is an ion-drift reactor™ (IDR™). One of the applications of this reactor is to remove low-concentration fine particulate and hazardous pollutants, such as mercury vapor, products of incomplete combustion (PICs), and dioxins/furans from the air or incineration offgas. The pollutants are electrically sensitized by reagent ions by means of charge-exchange, hydrogen transfer, electron and ion attachments, hydrogen abstraction, and other reactions initiated by injection of reagent ions into the contaminated offgas or airstream. Selectively sensitized pollutant particles, clusters and molecules are then removed from the airstream by their drift in the electric field. In contrast to electrostatic precipitators and different types of other non-thermal plasma (NTP) technologies, the reagent ions are generated separately in the ion source of this new device and then injected into the contaminated offgas stream. This is thought to allow much better control over the discharge parameters and to allow much higher reaction selectivity than that of conventional NTP technologies. In comparison with conventional APC technologies, such as adsorption, heterogeneous catalysis, or absorption, an IDR™ utilizes ion-drift together with diffusion as the mechanisms of mass transfer, which reduces the reactor residence time and the differential pressure drop across the reactor in analogous conditions. These advantages are especially important for removal of mercury, other trace elements, and fine respirable particulate (PM2.5) from the incineration offgas and air.

00/01120 Zero-emission plant on the drawing board

This paper will focus on one of the advanced air pollution control (APC) technologies currently under development at MSE Technology Applications (MSE-TA). This technology, which has a patent pending, is an ion-drift reactor™ (IDR™). One of the applications of this reactor is to remove low-concentration fine particulate and hazardous pollutants, such as mercury vapor, products of incomplete combustion (PICs), and dioxins/furans from the air or incineration offgas. The pollutants are electrically sensitized by reagent ions by means of charge-exchange, hydrogen transfer, electron and ion attachments, hydrogen abstraction, and other reactions initiated by injection of reagent ions into the contaminated offgas or airstream. Selectively sensitized pollutant particles, clusters and molecules are then removed from the airstream by their drift in the electric field. In contrast to electrostatic precipitators and different types of other non-thermal plasma (NTP) technologies, the reagent ions are generated separately in the ion source of this new device and then injected into the contaminated offgas stream. This is thought to allow much better control over the discharge parameters and to allow much higher reaction selectivity than that of conventional NTP technologies. In comparison with conventional APC technologies, such as adsorption, heterogeneous catalysis, or absorption, an IDR™ utilizes ion-drift together with diffusion as the mechanisms of mass transfer, which reduces the reactor residence time and the differential pressure drop across the reactor in analogous conditions. These advantages are especially important for removal of mercury, other trace elements, and fine respirable particulate (PM2.5) from the incineration offgas and air.

Two-dimensional fluid simulation of plasma reactors for the immobilization of krypton

Direct current glow discharge plasma sources are being developed as reactors for immobilization of radioactive krypton gas recovered from the off-gas stream of a nuclear fuel reprocessing plant. In order to design these reactors, two-dimensional simulations have been performed using a fluid model coupled with Poisson's equation. Nonlinear governing equations were expressed by a fully implicit scheme and the equations were solved using the Newton–Krylov method. We investigated algorithm performance of two methods from the Krylov projection techniques, namely the Bi-CGSTAB method and the transpose-free quasi-minimal residual (TFQMR) method. The results showed that the Bi-CGSTAB method converged considerably faster than the TFQMR method. Direct current glow discharge plasmas in three types of krypton immobilization apparatus were simulated to study the differences in electrode geometry. Simulation results agreed qualitatively with measurements of electron density.

State space sensitivity to a prescribed probability density function shape in coal combustion systems: Joint β-PDF versus clipped Gaussian PDF

The turbulent transport of three coal off-gas mixture fractions is coupled to a prescribed joint β -probability density function ( β -PDF) mixing model. This physical transport and subgrid joint β -PDF mixing model is used to explore the incorporation of coal off-gas compositional disparities between the devolatilization and the char oxidation regime in detailed pulverized-coal combustion simulations. A simulation study of the University of Utah pulverized-coal research furnace is presented to evaluate the sensitivity of different mixing model assumptions. These simulation studies indicate that using a variable composition to characterize the process of coal combustion does not appreciably change the predicted gas-phase temperature field. Moreover, neglecting fluctuations in the char off-gas stream was found to change gas-phase temperature predictions by approximately 15%. State space variable sensitivity to the assumed shape of the PDF (clipped Gaussian vs. joint β ) is presented. Simulation results indicate differences in temperature profiles of as much as 20% depending on the chosen shape of the PDF. Integration accuracy issues for the joint β -PDF are presented and are found to be acceptable. A robust β -PDF function evaluation procedure is presented that accommodates arbitrarily high β -PDF distribution factors. This robust algorithm simply transforms the joint β -PDF function evaluation into a logarithmic form. The assumption that a joint PDF, as rigorously required within a prescribed subgrid mixing model, can be written as the product of N − 1 statistically independent probability density functions is quantified and shown to be less accurate.

Assessment of Changes in Microbial Community Structure during Operation of an Ammonia Biofilter with Molecular Tools

Biofiltration has been used for two decades to remove odors and various volatile organic and inorganic compounds in contaminated off-gas streams. Although biofiltration is widely practiced, there have been few studies of the bacteria responsible for the removal of air contaminants in biofilters. In this study, molecular techniques were used to identify bacteria in a laboratory-scale ammonia biofilter. Both 16S rRNA and ammonia monooxygenase (amoA) genes were used to characterize the heterotrophic and ammonia-oxidizing bacteria collected from the biofilter during a 102-day experiment. The overall diversity of the heterotrophic microbial population appeared to decrease by 38% at the end of the experiment. The community structure of the heterotrophic population also shifted from predominantly members of two subdivisions of the Proteobacteria (the beta and gamma subdivisions) to members of one subdivision (the gamma subdivision). An overall decrease in the diversity of ammonia monooxygenase genes was not observed. However, a shift from groups dominated by organisms containing Nitrosomonas-like and Nitrosospira-like amoA genes to groups dominated by organisms containing only Nitrosospira-like amoA genes was observed. In addition, a new amoA gene was discovered. This new gene is the first freshwater amoA gene that is closely affiliated with Nitrosococcus oceanus and the particulate methane monooxygenase gene from the methane oxidizers belonging to the gamma subdivision of the Proteobacteria.

Petroleum Environmental Research Forum Field Study on Biofilters for Control of Volatile Hydrocarbons

A field study on the treatment of volatile petroleum hydrocarbons (PHC) by biofiltration was conducted by the Petroleum Environmental Research Forum (PERF) between 1992 and 1994. Its objective was to assess the technical, regulatory, and economic feasibility of biofiltration for off-gases from petroleum processing and soil remediation equipment. It involved three small-scale biofilters provided by U.S. vendors, treating off-gas from two soil vapor extraction sites and a source of refinery wastewater. Comprehensive monitoring of biofilter operating parameters and performance was conducted. The results suggest that biofilters remove major petroleum hydrocarbon classes to strongly varying degrees. Typically more than 95% of aromatic compounds such as benzene, and odorous reduced sulfur compounds can be removed at residence times of one minute or less, while removal of more than 70% of light aliphatics will require residence times of several minutes, and will thus require correspondingly large filter volumes and higher capital expenditure. This indicates that off-gas composition and regulatory control objective will largely determine whether biofiltration is economically feasible for a given off-gas stream. The high percentage removal of aromatic hazardous air pollutants (HAP) and odors can generally be accomplished at comparatively short residence times (one minute or less) while the need for high-percentage removal, particularly of light aliphatics (<C5) will generally render biofiltration noncompetitive. Results from the field tests also showed that biofilter performance and operational reliability depend on the selection of filter material, the reliability of the moisture control system, and the level of fluctuation in PHC concentrations. This agrees with the findings from other full-scale biofilter projects. Finally, a preliminary economic comparison of biofilters and established control technologies suggested that biofiltration may, for a representative design case involving off-gas from a refinery wastewater treatment operation, offer considerable savings in total cost of air pollution control for petroleum hydrocarbon streams if regulations require the control of aromatic HAP or odors.

VOCs in Fixed Film Processes. I: Pilot Studies

Stripping of volatile organic contaminants (VOCs) during wastewater treatment is of concern due to the potential of these compounds to contribute to stratospheric ozone depletion, ground-level smog formation, chronic toxicity to exposed workers, and odors. A study of the fate of volatile organic contaminants (VOCs) in trickling filters (TF) and rotating biological contactors (RBC) was performed. Of the target compounds investigated, tetrachloroethylene was volatilized to the greatest extent, while 1,1,2,2-tetrachloroethane was the least volatilized in the TF and bromoform was least volatilized in the RBC. Toulene, o-xylene and 1,3,5-trimethylbenzene were biodegraded to the greatest extent and 1,1,2,2-tetrachloroethane was least biodegraded. Increasing the hydraulic loading tended to increase the proportion of influent VOCs found in the TF effluent. Imposing effluent recycle on the TF increased the fraction of influent VOCs found in the effluent, but also decreased the fraction stripped and increased the fraction that was biodegraded. Increasing hydraulic loading to the RBC tended to increase the proportion of influent VOCs found in the effluent and off-gas. Increasing the RBC disc rotational speed increased the fraction that was biodegraded and decreased the fraction of VOCs found in the effluent and off-gas streams. The TF tended to have greater losses to volatilizationmore » than the RBC while the RBC maintained a greater fraction of the candidate VOCs in the process effluent than the TF. Differences between the processes with respect to biodegradation could not be inferred.« less

Buffer gas effect on the detection of iodine by laser induced fluorescence

Laser-induced fluorescence (LIF) coupled with photon-counting technique to detect molecular iodine at ultratrace level is reported. Electronic quenching rate constants for N2, NO2 and H2O, as well as for the mixture of NO2 and H2O has been measured. The application of the LIF method to monitoring129I2 in spent fuel reprocessing off-gas streams is evaluated.

Emissions Characterization and Off-Gas System Development for Processing Simulated Mixed Waste in a Plasma Centrifugal Furnace

Plasma arc technology is a high temperature process that completely oxidizes organic waste fractions: inorganic hazardous and radionuculide waste fractions are oxidized and encapsulated in a highly durable slag. The robust nature of the technology lends itself to application of diverse mixed and hazardous wastestreams. Over 500 hours of testing have been completed at the Department of Energy's Western Environmental Technology Office with a pilot-scale system. This testing was designed to demonstrate operability over a wide range of wastes and provide the data required to evaluate potential applications of the technology on both a technical and economic basis. In addition to characterization of the off gas for typical combustion products, the fate of radionuculide surrogates and hazardous elements within the Plasma Arc Centrifugal Treatment (PACT) system has been investigated extensively. Test results to date demonstrate that cerium, a plutonium surrogate, remains almost exclusively in the slag matrix. Hazardous elements such as chromium and lead volatilize to a greater extent and are captured by the off-gas system. Preliminary design work is underway to develop a minimum emissions off-gas system for demonstration on a engineering-scale plasma unit. The proposed system will filter particulate matter from the hot gas stream and treat them in an electric ceramic oxidizer, which replaces the conventional afterburner, prior to quenching and acid gas removal. Potential future work would use a liquid monoethanolamine system and membrane filter to separate carbon dioxide and nitrogen from the off-gas stream. The remainder of the gas stream, primarily oxygen, would be recycled back to the combustion chamber. This paper will provide: 1) a summary of the design, development, and performance of the PACT off-gas system and 2) results of radionuculide surrogate and hazardous element portioning.

Diagnostics for a waste processing plasma arc furnace (invited) (abstract)a)

Maintaining the quality of our environment has become an important goal of society. As part of this goal new technologies are being sought to clean up hazardous waste sites and to treat ongoing waste streams. A 1 MW pilot scale dc graphite electrode plasma arc furnace (Mark II) has been constructed at MIT under a joint program among Pacific Northwest Laboratory (PNL), MIT, and Electro-Pyrolysis, Inc. (EPI)c) for the remediation of buried wastes in the DOE complex. A key part of this program is the development of new and improved diagnostics to study, monitor, and control the entire waste remediation process for the optimization of this technology and to safeguard the environment. Continuous, real time diagnostics are needed for a variety of the waste process parameters. These parameters include internal furnace temperatures, slag fill levels, trace metals content in the off-gas stream, off-gas molecular content, feed and slag characterization, and off-gas particulate size, density, and velocity distributions. Diagnostics are currently being tested at MIT for the first three parameters. An active millimeter-wave radiometer with a novel, rotatable graphite waveguide/mirror antenna system has been implemented on Mark II for the measurement of surface emission and emissivity which can be used to determine internal furnace temperatures and fill levels. A microwave torch plasma is being evaluated for use as a excitation source in the furnace off-gas stream for continuous atomic emission spectroscopy of trace metals. These diagnostics should find applicability not only to waste remediation, but also to other high temperature processes such as incinerators, power plants, and steel plants.

Immobilization Index of Liquid LLW in Cementitious Grouts

AbstractThe ability of grouts formulated from mixtures of cementitious materials and attapulgite clay to immobilize various chemical species in the projected off-gas waste stream from vitrification of Hanford low level tank wastes was studied. Three different solid blends were evaluated, with cement :fly ash : slag clay weight ratios of 3:3:3:1, 3:0:6:1, and 0:0:9:1. The blended solids were mixed with a simulated low level liquid waste solution containing Na+, NO2-, NO3-, PO43- and OH- ions, in the proportion of 1 liter of solution to 1 kg of solid blend, and were cured either at 22°C (room temperature), 50°C or 90°C. Pore solutions were expressed at various ages and were analyzed to determine the reductions in concentrations of the individual ionic species. The results were expressed in the form of immobilization index (I) calculated for each species. The immobilization indices for Na+ (I Na+ ) and for OH- (IOH-)were similar in each case, and were found to be highest when only slag and clay was present (blend 0:0:9:1). The immobilization index for phosphate, , was 1 in all cases, i.e. phosphate was completely removed from solution. On the other hand removal of NO2- and NO3- ions was generally ineffective.