Removal of PCDD/F from Incinerator Flue Gases by Entrained-Phase Adsorption

Abstract

The emission abatement of polychlorinated dioxins and furans (PCDD/F) issued from municipal solid waste incineration is growing in importance because of more stringent emission standards and general concern about their toxic characteristics. These substances cannot be separated by conventional gas cleanup processes but are successfully removed through adsorption onto carbonaceous materials. The simplest technique is the entrained-phase injection of pulverized adsorbents in the flue gas, followed by fabric filter separation. The various related techniques are briefly reviewed here. Operating conditions and results obtained from Flemish MSWIs are given. The results illustrate the excellent overall removal efficiency. Furans are adsorbed to a slightly higher extent than dioxins.

PCDD/F removal by carbonaceous adsorbents is thereafter modeled from first principles for the contribution of both entrained-phase (η₁) and cake filtration (η₂) to the overall efficiency (η_T). Application of the model equations and comparison of measured and predicted overall efficiencies for the Flemish municipal solid waste incinerators (MSWIs) demonstrate that the approach is meaningful and that the dominant parameters are the operating temperature, the dosage and activity of adsorbent, and the fraction of adsorbent in the filter cake. The model equations enable the MSWI operators to predict the adsorption efficiencies for any combination of operating parameters and to assess the sensitivity of the process to varying operating conditions.     

Removal of SO2 from Simulated Flue Gases Using Non-Thermal Plasma-Based Microgap Discharge

Abstract

The removal of sulfur dioxide (SO₂) from simulated flue gases streams (N₂/O₂/H₂O/SO₂) was experimentally investigated using microgap discharge. In the experiment, the thinner dielectric layers of aluminum oxide (Al₂O₃) were used to form the microgap discharge. With this physical method, a high concentration of hydroxyl (OH·) radicals were produced using the ionization of O₂ and H₂O to further the conversion of SO₂ into sulfuric acid (H₂SO₄) at 120° C in the absence of any catalysts and absorbents, which were captured with the electrostatic precipitator (ESP). As a result, the increase of discharge power and concentrations of O₂ and H₂O increased the production of OH· radicals resulting in enhanced removal of SO₂ from gas streams. With the test and analysis, a number of H₂SO₄ droplets were produced in experiment. Therefore, a new method for removal of SO₂ in semidry method without ammonia (NH₃) additive was found.     

Studies on the Removal of Sulfur Dioxide from Hot Flue Gases to Prevent Air Pollution

The pollution of the atmosphere by sulfur dioxide is one of the gravest of all in public nuisance problems, especially in the industrial regions. A practically applicable method in industry for the removal of sulfur dioxide has been studied. The Kiyoura-T .I .T. process utilizes the oxidation method to convert S0₂ of the flue gas to S0₃ in the presence of vanadium oxide. A limited amount of water vapor present in the flue gas reacts with S0₃ to form H₂SO₄. Ammonia is then introduced to the gaseous mixture, which is now at the suitable temperature, to form ammonium sulfate. Conditions are controlled to produce ammonium sulfate of the right size to produce aggregate that may be removed by a dry cyclone separator.     

Removal of SO2 From Flue Gases Using Carbon at Elevated Temperatures

The interaction of a typical flue gas with active charcoal and bituminous coal char at temperatures between 600 and 800°C and atmospheric pressure has been studied. The SO₂ in the flue gas interacts with the carbon to form primarily H₂S, COS, and a carbon-sulfur surface complex. H₂S and COS break through the carbon bed much in advance of SO₂. At 800°C, sulfur retention on the bed exceeds at least 11% before SO₂ breakthrough occurs. The reaction of H₂S and COS with O₂ over active charcoal at 100–140°C to produce sulfur, which deposits on the carbon, has also been studied and found to be feasible. As a result of this study, a new process is outlined for the removal of SO₂ from flue gas, with the ultimate conversion     

燃煤倒焰窑烟尘污染的治理

燃煤倒焰窑烟尘治理，因其本身结构特点，若单纯采用末端治理，则投资大，治理效果不稳定，在治理上存在一定难度。通过实践，采用炉头增氧，尾部喷淋的治理工艺可以达到好的治理效果，而且投资少，工期短，运行费用低，易于操作。     

Surface Compositions of Carbon Sorbents Exposed to Simulated Low-Rank Coal Flue Gases

Abstract

Bench-scale testing of elemental mercury (Hg⁰) sorption on selected activated carbon sorbents was conducted to develop a better understanding of the interaction among the sorbent, flue gas constituents, and Hg⁰. The results of the fixed-bed testing under simulated lignite combustion flue gas composition for activated carbons showed some initial breakthrough followed by increased mercury (Hg) capture for up to ～4.8 hr. After breakthrough, the Hg in the effluent stream was primarily in an oxidized form (>90%). Aliquots of selected activated carbons were exposed to simulated flue gas containing Hg⁰ vapor for varying time intervals to explore surface chemistry changes as the initial breakthrough, Hg capture, and oxidation occurred. The samples were analyzed by X-ray photoelectron spectroscopy to determine changes in the abundance and forms of sulfur, chlorine, oxygen, and nitrogen moieties as a result of interactions of flue gas components on the activated carbon surface during the sorption process. The data are best explained by a competition between the bound hydrogen chloride (HCl) and increasing sulfur [S(VI)] for a basic carbon binding site. Because loss of HCl is also coincident with Hg breakthrough or loss of the divalent Hg ion (Hg²⁺), the competition of Hg²⁺ with S(VI) on the basic carbon site is also implied. Thus, the role of the acid gases in Hg capture and release can be explained.     

Bench-Scale Investigation on Removing Sulfur Dioxide from Flue Gases

The relationship between asbestos consumption and mesothelioma incidence in Connecticut has been investigated.

Asbestos has many industrial applications; however, several of these result in the dissipation of this material (e.g., vehicle brake and clutch lining erosion). In Connecticut, asbestos manufacturing operations contribute approximately 10 tons of airborne asbestos fibers each year, while vehicle brake and clutch lining erosion add another 2 tons. The demolition, especially the “explosive demolition” of buildings which have been fireproofed and/or insulated with asbestos-containing materials may be the most significant future source of asbestos emissions unless adequate precautions are taken.

Occupational asbestos fiber exposure has been known to cause asbestosis, lung cancer, and cancer of the lining of the stomach and lung (mesothelioma) for some time. Recently, the previously rare mesothelial malignancy has been linked to nonoccupational asbestos fiber exposure as well.

There were 133 Conneticut residents diagnosed with mesothelioma between 1935 and 1972. Although subject to diagnostic error, available statistics suggest that the combined sex age-adjusted mesothelioma incidence rate (AAR) per 100,000 Connecticut population has exhibited a possible 10-fold increase since 1935, rising from 0.02 during 1940 to 1949 to 0.25 from 1960 to 1969. The trends for both men and women also showed sharp increases over the same time period (1940 to 1970). The rapid rise in Connecticut's mesothelioma incidence rate closely follows the increase in the State's cumulative asbestos consumption and suggests a linearly increasing cause-effect relationship.     

Propane Removal from Propane-Air Mixtures by Soil Beds

Dilute concentrations of hydrocarbons are difficult and expensive to remove from air by conventional scrubbing methods. Propane removal from propane-air mixtures by soil beds was measured in laboratory experiments and in an industrial application. In closed containers in the laboratory, the time to reduce the initial 1–3 percent propane concentrations by half was 5 to 20 hours for soils at pH 6–8, moderate moisture contents, and temperatures ≥15°C. The propane removal rate was slower when the soil was air dry at 2°C temperature, or was pH 5.3. A test soil bed continuously removed 92-98 percent of the propane from an input air stream containing 0.6–1 percent propane.     

Application of the Active Soda Process for Removing Sulphur Dioxide from Flue Gases

The active soda process1 was applied for desulfurlzatlon of flue gases emitted by a plant burning heavy fuel oil In a rotary drum drier for stone aggregate. The flue gas capacity of the plant was about 6,7 m³/s at normal conditions. The SO₂ concentration varied between 400– 500 ppm. The solid, dry and fine-grained NaHCO₃ of good quality was fed directly into the hot gas stream at the outlet of the rotary drier In two variants—with and without grinding. The mean particle size was 0.180 m^-3 or 0.070 m^-3, respectively. The achieved desulfurizatlon degree was shown to be directly dependent on the flue gas temperature and on the grinding effect, as well as on the normalized stoichiometric ratio. The highest achieved desulfurization degree amounted up to 74 percent. During the design of the desulfurization process no pilot plant installations and tests were necessary, and for the final process no special chemical reactor was used.     

改性半焦脱除烟气中SO2的研究

对内蒙工业副产褐煤半焦（比表面积49.187m^2／g,孔容0.0351cm^2／g）,采用加压水热化学活化法,HNO3活化法和高温煅烧相结合的方法制备出半焦烟气脱硫剂,并对脱硫剂的脱硫性能进行固定床活性评价。分析表明,其脱硫效果比较好,转化率维持在50％以上的累计硫容可达24．30％,脱硫时间长达35h,远远高于原料半焦的脱硫效果（硫容为0．68％,时间为1．5h）;同时采用水洗法对脱硫剂进行再生,其再生液可用来制备浓度为9.01％的稀硫酸。     

非平衡放电等离子体治理有害气体

重点分析了常温常压下非平衡放电等离子体产生的条件及其物理和化学性能，综合评述了放电技术的理烟气中有害气体ＳＯ２，ＮＯｘ，ＣＯ２的机理和研究现状。     

Reduction of Greenhouse Gases from Anaerobic Piggery Wastewater Treatment by Bromochloromethane in Taiwan

Abstract

This work establishes methods of reducing the amount of methane produced from the anaerobic treatment of piggery wastewater by either reducing the storage time before solid/liquid separation or inhibiting the activity of methanogens in anaerobic wastewater treatment system. Experimental results showed these two methods can be adopted effectively to reduce methane production resulting from anaerobic piggery wastewater treatment. First, the wastewater must be processed using solid/liquid separation immediately after washing pig houses. This process can reduce by 62% the biogas production and indirectly decrease the methane production from the anaerobic wastewater treatment reactor. Second, adding 10 mg L^?1 bromochloromethane (BCM) daily into the anaerobic wastewater treatment reactor can significantly reduce the amount of biogas and methane produced during the anaerobic fermentation process. Furthermore, biogas production can be completely inhibited after 4 days. Adding BCM (≤10 mg L^?1) to wastewater only slightly affected the efficiency of the anaerobic wastewater treatment process. Results in this study can provide the basis for further research on reduction of the amount of methane produced from anaerobic wastewater treatments.     

Silica-Enhanced Sorbents for Dry Injection Removal of SO2 from Flue Gas

Novel silica-enhanced lime sorbents were tested in a bench-scale sand-bed reactor for their potential for SO₂ removal from flue gas. Reactor conditions were 64°C (147°F), relative humidity of 60 percent [corresponding to an approach to saturation temperature of 10°C (18°F)], and inlet SO₂ concentration of 500 or 1000 ppm. The sorbents were prepared by pressure hydration of CaO or Ca(OH)₂ with siliceous materials at 100°C (101 kPa) [212°F (14.7 psi)] to 230°C (2793 kPa) [446°F (405 psi)] for 15 min to 4 h. Pressure hydration fostered the formation of a sorbent reactive with SO₂ from fly ash and Ca(OH)₂ in a much shorter time than did atmospheric hydration. The conversion of Ca(OH)₂ in the sand-bed reactor increased with the increasing weight ratio of fly ash to lime and correlated well with B.E.T. surface area, increasing with increasing surface area. The optimum temperature range for the pressure-hydration of fly ash with Ca(OH)₂ was between 110 and 160°C (230 and 320 °F). The pressure hydration of diatomaceous earth with CaO did not offer significant reactivity advantages over atmospheric hydration; however, the rate of enhancement of Ca(OH)₂ conversions was much faster with pressure hydration. Scanning electron microscope (SEM) and x-ray diffraction studies showed solids of different morphology with different fly ash/lime ratios and changing conditions of pressure hydration.     

Soil and Compost Filters of Malodorant Gases

Removing low concentrations of pollutant gases from air streams is difficult and expensive.^1,2 Removal techniques include water scrubbing (with and without permanganate, hypochlorite, or lime), burning, and sorption by activated charcoal. The shortcomings of these techniques are that they require fuel, maintenance, water, high capital costs, they pollute the wash water, and/or some concentrate only, rather than remove the offender.