Dry Scrubbing Systems Research Articles

Mechanism of Dissolution Behavior of the Secondary Alumina

The study on dissolution of alumina in aluminum electrolyte has never been suspended. The raw materials used in aluminum smelter are made up of primary alumina and secondary alumina. The latter is the by-product of a dry scrubbing system. The differences in dissolution behavior of these two kinds of alumina are studied in this article. A see-through cell was used for observing the dissolution behavior of alumina. It was found that the dissolution rate of the secondary alumina was significantly faster than that of the primary alumina. The effect of possible impurities in the secondary alumina on the dissolution behavior, including carbon dust, hydrogen fluoride (HF), and other fluorides (Na5Al3F14, Na3AlF6, AlF3), was investigated. The carbon dust played an important role in improving the dissolution behavior. However, fluorides and chemisorbed HF have little effect on the dissolution behavior of the secondary alumina.

Crust and alumina powder dissolution in aluminum smelting electrolytes

Modern smelter potlines often undergo process excursions, which are attributed to “solubility problems” of the alumina used. Assigning the problem to a specific property is, however, a challenge, compounded by the fact that the alumina has usually undergone secondary treatments through a dry scrubbing system prior to arrival at the cell. With a better understanding there is the potential for avoiding some of the troubles experienced in these “alumina solubility” problems but there is a need to clarify what are the relevant chemical and physical properties of the alumina that are having the impact. Published and unpublished data are drawn together here to provide further insight into the alumina solubility issues.

The Utilization of Catalyst Sorbent in Scrubbing Acid Gases from Incineration Flue Gas

Catalyst sorbents based on alumina-supported CuO, CeO2, and CuO-CeO2 were applied to a dry scrubber to clean up the SO2/HCl/NO simultaneously from pilot-scale fluidized-bed incineration flue gas. In the presence of organic compounds, CO and the submicron particles SO2 and HCl removed by the fresh catalyst sorbents and NO reduced to N2 by NH3 under the catalysis of fresh and spent desulfurization/dechloridization (DeSO2/DeHCl) catalyst sorbents (copper compounds, Cu, CuO, and CuSO4) were evaluated in this paper. The fresh and spent catalyst sorbents were characterized by the Brunner-Emmett-Teller method (BET), X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), inductively coupled plasma-mass spectrometry (ICP-MS), and the elemental analyzer (EA). The study showed that the performances of CuO, CeO2, and CuO-CeO2/γ-Al2O3 were better than that of Ca(OH)2. The removal efficiency of SO2 and HCl was 80-95% in the dry scrubber system. Under NH3/NO = 1, NO could not be reduced to N2 because it was difficult to control the ratio of air/fuel in the flue gas. For estimating the feasibility of regenerating the spent catalyst sorbents, BET and EA analyses were used. They indicated that the pore structures were nearly maintained and a small amount of carbon accumulated on their surface.

Mercury control research: effects of fly ash and flue gas parameters on mercury speciation

Mercury Control Research: Effects of Fly Ash and Flue Gas Parameters on Mercury Speciation Chun Wai Lee and James D. Kilgroe U.S. Environmental Protection Agency National Risk Management Research Laboratory Research Triangle Park. NC S. Behrooz Ghorishi ARCADIS Geraghty & Miller, Inc. Research Triangle Park, NC In flue gas from combustion systems, mercury (Hg) is typically in the vapor phase at flue gas cleaning temperatures, and the control of Hg emissions is dependent on the specific Hg compounds that are present (speciation) and the type of air pollution devices employed. In dry and semi-dry scrubbing systems, the control of Hg emissions is dependent on the sorption of Hg by particulate matter (PM) which can be subsequently collected in a PM control device. In wet scrubbing systems, the principal mechanisms of control are the removal of soluble forms of Hg and the collection of particle-bound Hg. At combustion temperatures, Hg is believed to be predominantly in the form of elemental mercury (Hgo). As the flue gas is cooled, thermochemical equilibrium calculations indicate that Hgo is converted primarily to ionic mercury (Hg++) in the form of mercuric oxide (HgO) or mercuric chloride (HgCl2). Hgo is insoluble in water, but HgO has a low solubility while HgCl2 is highly soluble. The oxidation of Hgo to an ionic form depends on the temperature, the time-temperature proflle, the flue gas composition, the reaction kinetics, and the presence of solids that may catalyze reactions. Bench-scale experiments were conducted to study the effects of flue gas and fly ash parameters on the oxidation of HgOin simulated flue gases containing hydrogen chloride (Hel). Gas-phase studies indicated that the in-flight post-combustion oxidation of Hgo in the presence of HCI is very slow and proceeds at measurable rates only at high temperatures (>700 °C) and high HCI concentrations (>200 ppm). The presence of sulfur dioxide (S02) and water vapor in the simulated flue gas significantly inhibited the gas-phase oxidation of Hgo. On the other hand, a preliminary investigation indicated that the gas-phase reaction of Hgo with chlorine (Cl:z) is fast At 40°C and in the presence of 50 ppm C12, 100% of the input Hgo was oxidized to HgCl2 in less than 2 seconds, indicating that Cl2 is a much more active chlorinating agent than HCl. The effects of fly ash composition were investigated using a fixed-bed reactor containing different model fly ashes (simulated fly ash) consisting of mixtures of some major components found in coal and municipal waste combustor (MWC) fly ashes. Work to date has focused on the

Memory effect on the dioxin emissions from municipal waste incinerator in Taiwan

Evaluation of the dioxin removal efficiency of the air pollution control device (APCD) at an existing municipal waste incinerator (MWI) located in Taiwan is conducted via stack sampling and analysis. The MWI investigated is equipped with cyclones, dry lime scrubbing systems and fabric filters as APCDs. Results indicate that the patterns of dioxin isomers at APCDs' inlet and stack are similar. During the first year of carbon injection, the concentrations of emitted dioxin decreased greatly. The dioxin removal efficiency increased from 26.9% to 96.6% after injecting 115 kg/day activated carbon (AC). At the second year, the dioxin removal efficiency reaches 98.7% after injecting the same rate of AC continuously. The lower efficiency achieved with activated carbon injection (ACI) during the first year can be attributed to the memory effect, i.e. the dioxin or precursor desorbs slowly to the flue gas and increases the dioxin concentration at stack, resulting in a lower dioxin removal efficiency than expected.

Gas phase reactions of hydrogen peroxide and hydrogen peroxide/methanol mixtures with air pollutants

Hydrogen peroxide and its mixtures with methanol are capable of removing multiple air pollutants, NO, SO3, and carbon-containing compounds from combustion-generated flue gas. Chemical kinetic calculations and experimental data demonstrate that hydrogen peroxide can be injected into flue gas at temperatures of 700–1100 K to convert unreactive NO and corrosive SO3 to NO2 and SO2. Nitrogen dioxide is much moure reactive than NO and can be removed downstream simultaneously with SO2 by wet or dry scrubbing systems that are currently required for SO2 control. Hydrogen peroxide also promotes the oxidation of organic compounds to CO and CO2 and the oxidation of CO to CO2. The H2O2 molecules dissociate into two OH radicals, and four chain reactions of different types are involved in the pollutant emission removal process with the following main reactions: NO-to-NO2 conversion: OH+H2O2→H2O+HO2: HO2+NO→NO2+OH SO3-to-SO2 conversion: OH+H2O2→H2O+HO2; HO2+SO3→HSO3+O2; HSO3+M→SO2+OH+M RH oxidation: OH+RH→H2O+R; R+O2→ oxidation CO oxidation: OH+CO→CO2+H; H+O2→OH+O

Nitrogen Dioxide Reaction with Alkaline Solids

At conditions typical of a bag filter in a coal-fired flue gas, nitrogen dioxide (NO2) diluted with nitrogen was exposed to various alkaline and nonalkaline solids in a packed-bed reactor. On nonalkaline solids, 3 mol of NO2 reacted readily with water to produce 2 mol of nitric acid (HNO3) and 1 mol of NO. Alkaline solids such as calcium hydroxide or calcium silicate (from lime and fly ash) produced less NO and neutralized the nitric acid on the surface. A mathematical model developed to predict rates of NO2 removal on these surfaces successfully compared experimental and predicted rates. These results are relevant to technology for removal of NOx by addition of methanol to dry scrubbing systems for flue gas desulfurization.

Retrofitting an existing MSW waste-to-energy facility to meet emission requirements

In this article Brian Heap (Procedair Division, Stein Atkinson Stordy Ltd) reports on the design and installation of a dry scrubbing system for a municipal solid waste (MSW) incineration plant

PCDDs, PCDFs emission control by dry scrubbing system

Presently, in Japan there are no limitations on the emission of PCDDs or PCDFs, but in order to study the feasibility of dry type air pollution control, a pilot plant was constructed in 1988 and the removal efficiencies for PCDDs, acid gas and heavy metals were measured. At the same time PCDDs concentration was compared with that of a previously installed electrostatic precipitator (ESP) plus wet scrubber line. In this paper, the following two items are reported. 1. (1) The difference in the amounts of PCDDs and PCDFs produced due to differences in gas temperature and retention time in ESP and fabric filter (FF). 2. (2) Removal efficiencies of PCDDs and PCDFs of fabric filter. PCDDs concentration, generally 100–200 ng/Nm 3 at the boiler outlet (ESP inlet and/or Quench Reactor (QR) inlet), increased several times at the ESP outlet, but it showed almost no increase at the QR outlet due to a sudden temperature drop. The temperature was 280–310°C, and the gas retention time was 12 sec. during passage through ESP so that it is thought that PCDD was formed under these conditions. On the other hand, a removal efficiency of approx. 90% was obtained with the fabric filter, and the PCDD at the bag outlet was at a sufficiently low level.

Removal of SO2and NOXfrom Stack Gas by Reaction with Calcium Hydroxide Solids

Previous workers have shown that simultaneous SO2/NOX removal can be obtained in a dry scrubbing system with Ca(OH)2 promoted by an additive such as NaOH, and that fly ash and product recycle improve the reactivity of the solids toward SO2. To test SO2/NOX removal with fly ash and product recycle, bench-scale experiments with a packed bed reactor were performed at bag filter conditions. The most reactive solid for NOX removal was prepared by slurrying Ca(OH)2 with fly ash, CaSO3, and NaOH. The best conditions for NOX removal were the greatest temperature (125°C) and greatest concentrations of SO2 (1500 ppm) and O2 (20 percent). At the best conditions, NOX removed in 1 hour was 3-4 moles per 100 moles Ca(OH)2, compared to 5-10 moles SO2 removed per 100 moles Ca(OH)2. The best SO2 removal was obtained at the highest relative humidities/lowest temperatures (55% RH/ 65°C) with solids prepared by slurrying Ca(OH)2 with fly ash and NaOH. At these conditions, SO2 removed In 1 hour was 60-80 moles per 100 moles C...

The Feasibility of Wet Scrubbing for Treating Waste-to-Energy Flue Gas

The selection of Hue gas treatment processes in the waste-to-energy industry has generally followed the trend of the coal-fired power industry. The highly favored process for both industries is the dry scrubber (spray absorber) followed by a fabric filter. As more attention is focused upon increasingly greater efficiencies, lower outlet concentrations, heavy metals emissions, and toxic organic pollutant emissions, the advantages of wet scrubbing become more pronounced. This paper provides an objective technical and economic evaluation of selected wet scrubbing and dry scrubbing systems for a generic waste-to-energy facility. The advantages and disadvantages of wet scrubbing are discussed and translated into cost benefits or penalties.

Canada's National Incinerator Testing and Evaluation Program (NITEP) Air Pollution Control Technology Assessment

In order to address the many concerns associated with emissions from municipal energy-from-waste facilities, Environment Canada established the National Incinerator Testing and Evaluation Program (NITEP). In recognition of the absence of a useful data base on incinerator emission control systems, Environment Canada, in co-operation with Flakt Canada, constructed a pilot plant to evaluate a dry scrubber system and a spray-dryer (wet-dry) system, each followed by a fabric filter (baghouse). Extensive sampling was done before and after each reactor, as well as in the stack. All particulate material collected in the bottom of the scrubbers and the fabric filter were analysed and subjected to leaching tests to determine the suitability of subsequent disposal alternatives. All samples taken were analysed for dioxins, furans, other organic substances, metals and acid gases. Many different operating conditions were tested to identify optimum removal efficiency for all pollutants of concern. The final results were very significant. Flue gas temperature was found to be an important operating variable for achieving high removal efficiency for many of the pollutants measured. Appropriate operating conditions were identified to obtain extremely high removal efficiencies for dioxins and furans (>99%), other trace organics (up to 98%), heavy metals, including mercury, arsenic, lead (>99%) and up to 97% for mercury. Excellent removal (>95%) was also obtained for acid gases, i.e. HCl and SO2.

Production and disposal of wastes from dry and wet flue-gas cleaning systems

The design of a flue-gas cleaning system for the removal of particulates and sulfur dioxide contaminants must take into account many factors for there to be successful operation and no secondary environmental impacts. One of the factors which must be taken into account is the production of wastes and the procedures to be put into place for proper disposal. For many years, Argonne has had a high-sulfur dry scrubbing system in operation as the means of emissions control from its largest coal-fired boiler. During this period thousands of tons of a dry powdery waste have been produced and landfilled without any adverse environmental effects. This paper reviews the theory of operation of a dry scrubbing system, and briefly details the performance of the Argonne system over several years. Among the performance details given are the results of an experimental program utilizing a high-sulfur ( s>4.2%) coal, done in co-operation with the Consol Coal Company, and the findings from a study on the leachate, toxicity, and disposal of the dry wastes. The experimental programs, to date, have shown that a dry scrubbing system can technically and economically remove sulfur dioxide and particulates from flue gas produced from the combustion of high-sulfur coal. In addition, mixtures of dry scrubber wastes and fly ash have been subjected to the standard U.S. Environmental Protection Agency toxicity tests. The results of these tests indicate that while the ash composition of the coal will have a bearing upon test results, for the most part mixtures of this waste and coal fly ash can be declared non-hazardous.

Application of Dry Flue Gas Scrubbing to Hazardous Waste Incineration

Dry scrubbing of the flue gas from chemical waste incineration is becoming an increasingly viable alternative to wet scrubbing. This paper discusses the relative advantages and disadvantages of wet and dry scrubbing systems and compares the relative capital and operating costs. The design parameters of the dry scrubbing process are discussed, including reagent atomization, gas dispersion, gas temperatures, and particulate removal. The history of dry scrubbing process applications is discussed, including the successful European hazardous waste systems. Finally, a comparison is made among three very different hazardous waste incinerators in the U.S. that will utilize dry scrubbing systems.

Emissions control through dry scrubbing

AbstractConcern with operating problems, and the desire for system simplicity, has resulted in the development of dry scrubbing systems for flue gas cleanup, and their acceptance by industry as an alternate to the conventional wet scrubbers. These dry scrubbing systems incorporate two commonly used pieces of equipment; spray dryers, which have been used for many years to manufacture everything from detergents to powdered milk, and a particulates removal device (either a fabric filter or an electrostatic precipitator). The first application of this technology to removal of sulfur oxides from high sulfur coal combustion gases occurred when Argonne National Laboratory installed a system in 1981 as the control device on its main coal‐fired boiler. To date, this type of pollution control system has shown itself capable of meeting state emission standards and, in a special test run, of removing over 90% of the sulfur oxides produced from combustion of a coal with over 4% sulfur.

Heavy Metals From "Energy From Waste" Plants-Comparison of Gas Cleaning Systems

Municipal waste incinerators produce more heavy metals calculated per usable energy unit (g MWh-1 ) than other solid fuel fired plants, e.g. coal, peat and wood waste. This paper presents a comparison of some modern proven gas cleaning methods including an electrostatic precipitator (ESP) followed by a scrubber with condensation or an electrostatic scrubber, and a dry scrubbing systems using slurry injection followed by ESP or powder injection followed by fabric filter. The comparison shows that the system with fabric filter has a lower emission of many heavy metals than the other methods.

Dry Scrubbing of Aluminum Cell Gases: Design and Operating Characteristics of a Novel Gas/Solids Reactor

Engineering details of a pilot plant reactor are described. It comprises a vertical cylindrical vessel with a tangential bottom gas entry. Countercurrent spiraling gas-solids flow is achieved. Reacted solids can be withdrawn from the bottom or the top using a rising axial gas jet. The reactor was evaluated by testing in a dry scrubber system treating 14,000 m3/h of gas from prebake cells. At inlet concentrations of 30–60 mg/m3 it achieved 99.5% scrubbing efficiency with aluminas of a surface area of 45–80 m2/g at feed rates considerably less than cell requirements. Potential benefits are: 1) control of metal purity by segregation of scrubber catch to selected cells, 2) scrubbing high HF inlet concentrations at full feed rate, and 3) meeting more stringent working environment and stack emission requirements.

Dry Scrubbing of Aluminum Cell Gases: An Index for System Performance

To evaluate the effectiveness of HF/alumina contact in a dry scrubber, the conventional scrubbing efficiency is inadequate because of its dependency on many parameters, including alumina feed rate. A semi-empirical expression called the “scrubbing index” is shown to be an appropriate measure. The scrubbing index expresses the extent of scrubbing achieved per unit of alumina feed rate. For a given alumina type and scrubber contacting design, the index appears to be constant and independent of alumina feed rate and hydrogen fluoride concentration in the raw cell gas. It can thus be used to characterize a given scrubbing system and predict its performance with a given alumina type. The derivation of the index and its application to a vertical-stud Soderberg dry scrubbing system is described.

Alumina: Calcination Control and Smelting Use

Specific surface area should be used as the standard method for qualifying the degree of calcination of smelter-grade alumina. It is a property which is sensitive to temperature change in the calciner. The analytical method is precise, rapid, and operator-insensitive. It is thus a practical method for use in calciner control. Furthermore, for the smelter operator it is a direct measure of the performance of the alumina in a dry-scrubbing system. It is, however, a one number average property. Aluminas can vary in the spread of the degree of calcination and this can have significant effects on its behavior in use. Smelter operators should be aware of this fact and attempt to determine if the alumina is as uniform as they expect.

Dry scrubber system uses electron beams

Dry scrubber system uses electron beams