Wet Scrubber System Research Articles

Oxidation Removal of Elemental Mercury from Flue Gas by K<sub>2</sub>S<sub>2</sub>O<sub>8</sub>

The important step for increasing gaseous elemental mercury (Hg0) removal in wet scrubber systems is altering the chemical form of the Hg0to a water-soluble oxidized species. This work focuses on the removal of elemental mercury from simulated flue gas by aqueous K2S2O8in a bubble reactor. In the system of K2S2O8oxidize Hg0, the reaction velocity of K2S2O8and Hg0is soon. Reached a higher removal rate after 10min. Increase the concentration of K2S2O8can remarkably improve the removal rate of Hg0to 85% With the rise of import mercury concentration has increased mercury removal rate to 89.5%.

Removal of ammonia and particulate matter using a modified turbulent wet scrubbing system

Conventional scrubbers are typically modified to serve the needs of modern industries that discharge effluents that cause synergetic, adverse effects on the environment. We designed and developed a modified turbulent wet scrubber (MTWS) to remove air pollutants as they emerge from a coal furnace. Experiments were conducted to estimate the pressure drop and the efficiencies of ammonia gas and particulate removal via the MTWS. The optimum water levels and gas flow rates for effective scrubbing of ammonia gas at different concentrations and particulate matter at different feed rates were estimated. For ammonia gas at a concentration of 45ppm, a gas flow rate of 3.5m3/s and a water level of 58cm in MTWS and position B (central position of the nozzle) in the water level of the nozzle yielded efficient ammonia gas removal for the given time. Similarly, for a fly ash feeding rate of 140mg/min, the same gas flow rate and water level in the MTWS yielded high efficiencies even for particles at the submicron level.

Effect of sewage sludge content on gas quality and solid residues produced by cogasification in an updraft gasifier

In the present work, the gasification with air of dehydrated sewage sludge (SS) with 20wt.% moisture mixed with conventional woody biomass was investigated using a pilot fixed-bed updraft gasifier. Attention was focused on the effect of the SS content on the gasification performance and on the environmental impact of the process. The results showed that it is possible to co-gasify SS with wood pellets (WPs) in updraft fixed-bed gasification installations. However, at high content of sewage sludge the gasification process can become instable because of the very high ash content and low ash fusion temperatures of SS. At an equivalent ratio of 0.25, compared with wood pellets gasification, the addition of sewage sludge led to a reduction of gas yield in favor of an increase of condensate production with consequent cold gas efficiency decrease. Low concentrations of dioxins/furans and PAHs were measured in the gas produced by SS gasification, well below the limiting values for the exhaust gaseous emissions. NH3, HCl and HF contents were very low because most of these compounds were retained in the wet scrubber systems. On the other hand, high H2S levels were measured due to high sulfur content of SS. Heavy metals supplied with the feedstocks were mostly retained in gasification solid residues. The leachability tests performed according to European regulations showed that metals leachability was within the limits for landfilling inert residues. On the other hand, sulfate and chloride releases were found to comply with the limits for non-hazardous residues.

Mineralization of Gaseous Acetaldehyde by Electrochemically Generated Co(III) in H2SO4 with Wet Scrubber Combinatorial System

Electrochemically generated Co(III) mediated catalytic room temperature incineration of acetaldehyde, which is one of volatile organic compounds (VOCs), combined with wet scrubbing system was developed and investigated. Depending on the electrolyte's type, absorption come removal efficiency is varied. In presence of electrogenerated Co(III) in sulfuric acid, acetaldehyde was mineralized to CO2 and not like only absorption in pure sulfuric acid. The Co(III) mediated catalytic incineration led to oxidative absorption and elimination to CO2, which was evidenced with titration, CO2, and cyclic voltammetric analyses. Experimental conditions, such as current density, concentration of mediator, and gas molar flow rate were optimized. By the optimization of the experimental conditions, the complete mineralization of acetaldehyde was realized at a room temperature using electrochemically generated Co(III) with wet scrubber combinatorial system.

Review of CO2 recovery methods from the exhaust gas of biomass heating systems for safe enrichment in greenhouses

Abstract Novel approaches to practice CO 2 enrichment in greenhouses from the exhaust gas of a biomass heating system are reviewed. General CO 2 enrichment benefits for greenhouse plant production are described along with optimal management strategies to reduce fuel consumption while improving benefits. Alternative and renewable fuels for CO 2 enrichment, landfill biogas and biomass, are compared with traditional methods and fuels. Exhaust gas composition is outlined to address the challenges of CO 2 enrichment from biomass combustion and leads to a comparison between combustion and gasification to improve boiler efficiency. In terms of internal modifications to a biomass heating system, syngas combustion, following biomass gasification, presents good potential to achieve CO 2 enrichment. Regarding external modifications to clean the exhaust gas, CO 2 can be extracted from flue gases via membrane separation that has shown a lot of potential for large industries trying to reduce and isolate CO 2 emissions for sequestration. Other research has optimized wet scrubbing systems by extracting SO 2 and NO emissions from flue gases to form ammonium sulphate as a by-product valuable to fertilizer markets. The potential of these techniques are reviewed while future research directions are suggested.

Simultaneous removal of gaseous pollutants with a novel swirl wet scrubber

In recent years, researchers have put a considerable effort to decrease the emission of harmful gaseous pollutants to the atmosphere. Although conventional wet scrubbers are being widely used to remove harmful gases, they have low removal efficiencies. This study reports the effect of some operating conditions on simultaneous removal of NO, NO 2, SO 2, and CO 2, using a novel swirl wet scrubber system. The gaseous pollutants were absorbed into NaOH solution. As the absorbent media was circulated continuously for removal purpose, therefore the production of chemical wastes were minimized. The effect of absorbent concentration, gas flow rate, and liquid flow rate were investigated. The best efficiencies of NO, NO 2, SO 2, and CO 2 simultaneous removal were 77, 88, 100 and 80%, respectively, with 2%, w/v NaOH as the scrubber medium. A comparison between this study and literature data shows that the liquid–gas flow rate ratio ( F L/ F G) in the novel scrubber of this work is much smaller than other gaseous pollutant removal systems. Therefore higher removal efficiency is obtained based on the same liquid flow rates.

Cold DeNOx development for oxyfuel power plants

Flue gas purification is a necessary method to avoid emission of sour gases like SO x and NO x into the environment. Another important aspect is the zero CO 2 emission from coal-fired power plants. Oxyfuel technology is one of the processes to reach this goal. LINDE KCA Dresden in cooperation with Vattenfall Europe is operating a pilot plant producing liquefied CO 2. Product specification and material requirements make flue gas purification for the removal of SO x and NO x unavoidable. The new oxyfuel technologies offer new process conditions for flue gas purification which are not available at atmospheric conditions. At Linde laboratories, catalytic and non-catalytic DeNOx and DeSOx processes have been screened for oxyfuel application. After first feasibility studies, laboratory experiments and economic evaluations, it was decided to develop a process based on wet scrubber systems to remove NO x from flue gas, simultaneously producing ammonia nitrites which can be thermally decomposed into nitrogen in a second step. After demonstration of the single process steps on laboratory scale, a pilot scrubber was erected and commissioned in 2010 at Schwarze Pumpe Oxyfuel Pilot Plant. In September 2010, the successful completion of the pilot tests demonstrated the NO x removal efficiency of this technology. The data from the pilot plant tests have been used to finalise a kinetic model describing the NO x absorption behaviour regarding NO x removal rate and nitrite selectivity for demonstration of plant scale up. This DeNOx-process is now marketed under the name “LICONOX”.

Risk Assessment as a Decision-Making Tool for Treatment of Emissions at a New Aluminum Smelter in Iceland: 1. Background and Introduction

ABSTRACT Protection of human health and ecosystems is gaining importance in corporate decision- making regarding industrial development. During the design phase for an aluminum smelter in East Iceland, it became necessary to determine whether a wet scrubber system should be installed to reduce sulfur dioxide emissions. Predictive risk assessment was used to determine whether there would be a consequential difference in the level of risk to human and ecological receptors from constituents in air emissions from the aluminum smelter, either with or without wet scrubbers. Benchmark exposure concentrations were established for avian, mammalian, and plant receptors and were compared to air modeling predictions to develop risk estimates. Benchmark concentrations were derived using plant uptake models for fluoride and polycyclic aromatic hydrocarbons (PAHs), and food-web modeling for birds and mammals. Exposure models were developed for all receptors, and population-level effects were modeled for plant, bird, and mammal receptors. Results indicated that exposures under both scenarios are lower than risk thresholds, and overall risk was lower for a smelter without wet scrubbers. Thus, although mass loading of sulfur dioxide (and other constituents) would be reduced using wet scrubbers, the corresponding risk to ecological receptors would actually be higher because of higher exposure-point concentrations in air.

Evaluation of persulfate oxidative wet scrubber for removing BTEX gases

Soil vapor extraction (SVE) coupled with air sparging of groundwater is a method commonly used to remediate soil and groundwater contaminated with volatile organic petroleum contaminants such as gasoline. These hazardous contaminants are mainly attributable to the compounds—benzene, toluene, ethylbenzene, and xylenes (known collectively as BTEX). Exhaust gas from SVE may contain BTEX, and therefore must be treated before being discharged. This study evaluated the use of iron-activated persulfate chemical oxidation in conjunction with a wet scrubbing system, i.e., a persulfate oxidative scrubber (POS) system, to destroy BTEX gases. The persulfate anions can be activated by citric acid (CA) chelated Fe 2+ to generate sulfate radicals (SO 4 −, E° = 2.4 V), which may rapidly degrade BTEX in the aqueous phase and result in continuous destruction of the BTEX gases. The results show that persulfate activation occurred as a result of continuous addition of the citric acid chelated Fe 2+ activator, which readily oxidized the dissolved BTEX. Based on initial results from the aqueous phase, a suitable Fe 2+/CA molar ratio of 5/3 was determined and used to initiate activation in the subsequent POS system tests. In the POS system, using persulfate as a scrubber solution and with activation by injecting Fe 2+/CA activators under two testing conditions, varying iron concentrations and pumping rates, resulted in an approximate 50% removal of BTEX gases. During the course of the tests which in corporate activation, a complete destruction of BTEX was achieved in the aqueous phase. It is noted that no removal of BTEX occurred in the control tests which did not include activation. The results of this study would serve as a reference for future studies into the practical chemical oxidation of waste gas streams.

Removal of Elemental Mercury by Sodium Chlorite Solution

AbstractThe important step for increasing gaseous elemental mercury (Hg0) removal in wet scrubber systems is altering the chemical form of the Hg0 to a water‐soluble oxidized species. This work focuses on the removal of elemental mercury from simulated flue gas by aqueous sodium chlorite in a bubble reactor. The effects of initial oxidizing solution concentration, reaction temperature, pH and mercury concentration in the inlet of the reactor on mercury oxidative absorption in sodium chlorite were investigated. The results indicate that higher concentrations of sodium chlorite favor Hg0 removal, with a greater efficiency observed in acidic than in alkaline solution. High temperature inhibits Hg0 absorption in aqueous sorbent when the reaction temperature is lower than ca. 40 °C, and the removal efficiency increases when the temperature is higher than that value. In conclusion, the major influencing factors on the levels of Hg0 removal are pH and chlorite concentration in solution.

Pilot Plant Testing of Elemental Mercury Reemission from a Wet Scrubber

This paper is to discuss the recent observations of elemental mercury (Hg0) reemissions from a pilot-scale limestone wet scrubber. Simulated flue gas was generated by burning natural gas in a down-fired furnace and doped with 2000 ppm of sulfur dioxide (SO2). Mercuric chloride (HgCl2) solution was delivered to the scrubber at a controlled rate to simulate the absorption of ionized mercury (Hg2+). Testing results have shown that, after Hg2+ was injected, elevated Hg0 concentrations were soon detected both in the scrubber effluent flue gas and the hold tank air, which reflected the occurrence of Hg0 reemissions in both places. When the HgCl2 feed was stopped, the Hg0 reemission continued for more than 2 h. In addition, a significant Hg0 reemission was also detected outside the scrubber loop. In an attempt to understand the Hg0 reemission increase across the wet scrubber system under transient and steady states and to understand the underlying relationship with the mercury complexes retained in the wet scrub...

Residence time distribution and dispersion of gas phase in a wet gas scrubbing system

Residence time distribution (RTD) of exhaust gas in a wet scrubbing system was investigated for application to the removal of SOx, NOx or dust included in exhaust gas. The mixing of gas phase in the wet scrubbing system was also examined by considering the axial dispersion coefficient of gas phase. Effects of gas amount (velocity), liquid amount (velocity) and solid floating materials on the residence time distribution (RTD) and axial dispersion coefficient of exhaust gas were discussed. The addition of solid floating materials could change the RTD and thus dispersion of exhaust gas in the scrubbing system. The mean residence time and axial dispersion coefficient of exhaust gas were well correlated in terms of operating variables.

폐기물소각시설의 유해대기오염물질 배출특성 연구

In this study, we have investigated waste incinerators which are one of the major HAPs emission sources. In order to obtain more reliable HAPs emission data from waste incinerators, direct sampling for the possible pollutants from the stack was carried out and the analysis was performed. The purpose of study was to understand the emission status from waste incinerators and recognize the problems and finally to set up a strategy to reduce the HAPs emissions from waste incinerators. The emission concentrations of 8 species of heavy metals and 16 species of PAHs have been analyzed for the first time in Korea. Not only the emission characteristics of HAPs from waste incinerators were identified, but also the analysis of reduction efficiencies for control devices such as BF and wet scrubbing systems was carried out.

Effect of raw materials on emissions of polychlorinated dibenzo- p-dioxins and dibenzofurans from the stack flue gases of secondary aluminum smelters

The present study was undertaken to investigate the effect of raw materials on PCDD/F emission from secondary aluminum smelters (ALS). Four plants each of aluminum ingot smelters (over 50% ingot) and secondary ALS (over 70% waste or recycled aluminum) were selected and the results compared. The secondary ALS yield much higher PCDD/Fs than the aluminum ingot smelters, or 7.94–22.76 ng/Nm 3 versus 0.57–2.67 ng/Nm 3, due to the large percentage of waste or recycled aluminum used. As for air pollution control devices (APCDs), the wet scrubber system in one of the aluminum ingot smelters exhibits an adverse effect on PCDD/F removal, due to the continuous recycle of the contaminated water through the scrubber system. Another ingot plant equipped with cartridge filter, there is a significant reduction in PCDD/F TEQ (52%). The powdered activated carbon injection at 2 kg/h (110 mg/Nm 3) in one ALS reduces 70% of the total PCDD/Fs. The average emission factor of four secondary ALS is much higher than that of aluminum ingot smelters, or 20-fold higher based on either raw materials or product. Consequently, more attention should be paid to the emission reduction of PCDD/Fs from the secondary ALS, including installation of a secondary burner, additional APCDs and the pre-cleaning of raw materials.

Mercury Oxidization in Dielectric Barrier Discharge Plasma System

The pronounced volatility of elemental mercury (Hg0) and some of its compounds, coupled with their extreme toxicity, makes these substances extremely hazardous. Conversion of Hg0 to HgO would significantly enhance mercury removal from flue gases. This investigation is focused on studying the effect of some of the constituents such as O2, H2O, CO2, and NOx present in flue gases on elemental mercury oxidation in a dielectric barrier discharge (DBD) reactor. The results show that Hg vapors (6 ppbv) in a stream of 0.1% O2 and N2 are effectively oxidized at the energy density of up to 114 J/L. Hg conversion of over 80% is achieved when present in a gas mixture of 8% O2, 2% H2O, and 10% CO2 in N2 balance. The presence of NOx enhanced mercury oxidation in the DBD reactor. The oxidation chemistry is discussed. Studies show that Hg can be simultaneously removed along with the other two major pollutants, NOx and SO2, in one DBD reactor followed by a wet scrubber system. This avoids the need of three techniques for the removal of major gaseous pollutants from coal-fired power plants.

Dioxin emissions after installation of a polishing wet scrubber in a hazardous waste incineration facility

Dioxin levels measured after wet scrubbing systems have been found to be higher than levels measured before the scrubber. It is believed that there is an adsorption of PCDD/Fs on plastic materials in the scrubber. The PCDD/F levels after a polishing wet scrubber were followed continuously for 18 months using long-time sampling equipment at a hazardous waste incineration facility in Sweden. Each sampling period lasted two weeks. It was found that the levels during and shortly after start-up periods were elevated. The decline was very slowly, which supports a memory effect in the scrubber. Further, a multivariate model showed that the relation between different homologues changed over time, which is in agreement with a desorption model, taking into account the vapour pressures for different congeners.

The behavior of PCDD/Fs, PCBs, chlorobenzenes and chlorophenols in wet scrubbing system of municipal solid waste incinerator

Though some researchers have already reported polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) concentration in flue gas at inlet and outlet of wet scrubber (WS) in municipal solid waste incinerator (MSWI), there are few investigations about scrubbing water, suspended solid (SS) in scrubbing water and sludge. In order to understand the behavior of PCDD/Fs in WS and to make clear the effect of the residence time of scrubbing water in WS on the PCDD/Fs concentrations in scrubbing water and at the outlet gas of WS, PCDD/Fs, polychlorinated biphenyls (PCBs), chlorobenzenes (CBzs) and chlorophenols (CPs) concentrations in various media around WS were investigated at two MSWIs. PCDD/Fs concentration in flue gas at outlet of WS was higher than that at inlet of WS in both MSWIs. In WS A, it was observed that the homologue profiles changed considerably and the concentration of higher chlorinated compounds such as H7CDD/Fs and O8CDD/F increased remarkably at outlet gas of WS A. Only CPs were transferred from flue gas to scrubbing water in both WSs. As for scrubbing water, a large amount of their chlorinated aromatic compounds was detected in SS particles. According to the results, it was found that not only flue gas conditions but also operational and structural conditions in WS had great influence on minimizing the memory of chlorinated aromatic compounds in WS.

凝集沈殿処理によるダイオキシン類の形態別除去特性

Coagulation-precipitation treatment using ferric chloride was carried out in wastewater taken from a solid waste incinerator wet scrubbing system. The treated wastewater was fractionated with 1 μm and 0.1μm filter, and the dioxin concentration in each fraction was determinde. The isomer profiles indicated that 1) dioxin concentration in the “<0.1μm” fraction decreased, and 2) dioxin in the “≥0.1,<1μm” fraction between temproary increased by the conagulation process. Hence, it become clear that dioxin particle size increases and dioxin can be removed with conagulation-precipitation treatment. The relationship between dioxin isomer concentrations in montreated warte (X) and treatde water (Y), and Flocculant concentration (A) is expressed by the following regression formula. Y=2.3×1010×(X/A)+1.8 This result suggests that a dioxin concentration of more than 1,000 pg TEQ·l-1 in highly contaminated wastewater can be reduced to below the wastewater effluent regulation value (10 pg TEQ·l-1) by a combination of coagulation-precipitation treatment and membrane filtration.

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

海水の電解水による舶用排煙ＳＯｘ，ＮＯｘ，ＣＯｘとＰＭの処理システムの開発

In marine air pollution control, only SCR (Selective Catalytic Reduction) is estimated at a variable method to control NOx, but on the other hand, seawater scrubber applying the basic characteristic that is naturally alkaline (pH typically around 8.1) is viewed as an economical SOx removal system at present. Especially, seawater scrubber would not be necessary to follow any of the various land based flue gas desulfurization methods, i.e. wet, dry or alkali scrubbing. However, these methods are not readily adaptable to marine conditions due to the quantities of consumables required, i.e. lime or limestone, the means of operation and the commercial availability.This research is undertaken to develop a new method as the main target of eliminating all exhaust emissions, particularly onboard, because the vessel can easily use seawater and be apt to apply a wet scrubber system. First, with using only seawater, the SOx are absorbed by relatively high solubility compared to other components of exhaust pollutants, and PM (Particulate Matter) is removed through direct contact with sprayed seawater droplets. Besides, the electrolyzed alkaline seawater by electrolysis, which contains mainly NaOH together with alkali metal ions (i.e. Na+, K+, Mg2+, Ca2+), is used as the absorption medium of NOx and CO2. Especially, to increase NOx absorption rate into the alkaline seawater, nitric monoxide (NO) is adequately oxidized to nitric dioxide (NO2) in the acidic seawater, which means both volume fractions are adjusted to identical proportion. The results found that the SOx removal could be achieved nearly perfectly and also led to a sufficient reduction of PM without regard to the pH values of reaction seawater. However, it may be also necessary to do a trial for NOx and CO2absorption with using the electrolyzed seawater.