Multi-pollutants simultaneous removal from flue gas

The multi-stage humidifier semi-dry flue gas cleaning technology, the CRS plasma flue gas cleaning technology and oxidative additive flue gas cleaning technology were investigated for multi-pollutants removal. The semi-dry flue gas cleaning technology using multistage humidifier and additive can improve oxidation and absorption, and it can achieve high multi-pollutants removal efficiency. The CRS discharge can produce many OH radicals that promote NO oxidation. Combining NaOH absorption can achieve high deSO2 and deNOx efficiencies. It is very fit of the reconstruction of primary wet flue gas desulfurization (WFGD). In addition, Using NaClO2 as additive in the absorbent of WFGD can obtain very high removal efficiency of SO2 and NOx.     

Simultaneous removal of SO2 and NO by wet scrubbing using aqueous chlorine dioxide solution

The present study attempts to generate chlorine dioxide (ClO(2)) gas continuously by chlorate-chloride process and to utilize it further to clean up SO(2) and NO(x) gases simultaneously from the flue gas in the lab-scale bubbling reactor. Experiments were carried out to examine the effect of various operating parameters like input SO(2) concentration, input NO concentration, pH of the reaction medium, and ClO(2) feeding rate on the SO(2) and NO(x) removal efficiencies at 45 degrees C. Complete oxidation of NO into NO(2) occurred on passing sufficient ClO(2) gas into the scrubbing solution. SO(2) removal efficiency of about 100% and NO(x) removal efficiency of 66-72% were achieved under optimized conditions. NO(x) removal efficiency decreased slightly with increasing pH and NO concentration. Input SO(2) concentration had marginal catalytic effect on NO(2) absorption. No improvement in the NO(x) removal efficiency was observed on passing excess of chlorine dioxide in the scrubbing solution.     

Effects of sodium modification, different reductants and SO(2) on NO reduction by Rh/Al(2)O(3) catalysts at excess O(2) conditions

Although many catalysts of NO reduction have been developed, the presence of excess O(2) and SO(2) significantly inhibits their performance when they are used to treat the incineration flue gas. To solve such problem, this study prepared new Rh/Al(2)O(3) catalysts and investigated the effects of Na modification, SO(2) and different reductants. Experimental results indicated that the average removal efficiency of NO at such high O(2) concentrations exceeded 80% when the Rh/Al(2)O(3) catalysts were used. CO was a better reductant than C(3)H(6) and the best concentration ratio of reductant/NO was equal to 1. Adding Na to modify Rh/Al(2)O(3) catalysts significantly enhanced the removal efficiency of NO from 80 to 99% at 250-300 degrees C, especially at relative high SO(2) concentrations. Unfortunately, Rh-Na/Al(2)O(3) catalysts do not have long-time activities for NO reduction, possibly because of the formation of NaNO(3). Both Rh/Al(2)O(3) and Rh-Na/Al(2)O(3) catalysts have good performance for NO reduction, they can feasibly be used to reduce NO in the flue gas from waste incineration.     

Interactions between mercury and dry FGD ash in simulated post combustion conditions

Two different flue gas desulfurization (FGD) ash samples were exposed to a simulated flue gas stream containing elemental mercury vapor to evaluate the interactions and determine the effects of gas components, dry FGD ash samples, and temperature on adsorption and heterogeneous oxidation of mercury. Both samples were characterized for surface area, unburned carbon content, element content, and mineralogical composition. Mercury speciation downstream from the sample was determined using Ontario Hydro Method. Results showed that higher levels of mercury oxidation were associated with higher levels of mercury capture. The NO(2), HCl, and Cl(2) promoted mercury oxidation, while SO(2) and NO had inhibitory effects on mercury oxidation. Unburned carbon of dry FGD ash sample played an important role in mercury capture. Whether the surface area was caused by unburned carbon or by calcium-based sorbents might be more significant than the level of surface area. Extent of mercury oxidation and capture increased slightly and then decreased as the temperature rising due to the interaction of mass transfer and reaction rates control.     

Kinetics of gas-liquid reaction between NO and Co(NH3)6(2+)

Wet ammonia desulphurization process can be retrofitted for combined removal of SO2 and NO from the flue gas by adding soluble cobalt(II) salts into the aqueous ammonia solutions. The Co(NH3)6(2+) formed by ammonia binding with Co2+ is the active constituent of scrubbing NO from the flue gas streams. A stirred vessel with a plane gas-liquid interface was used to measure the chemical absorption rates of nitric oxide into the Co(NH3)6(2+) solution under anaerobic and aerobic conditions separately. The experiments manifest that the nitric oxide absorption reaction can be regarded as instantaneous when nitric oxide concentration levels are parts per million ranges. The gas-liquid reaction becomes gas film controlling as Co(NH3)6(2+) concentration exceeds 0.02 mol/l. The NO absorption rate is proportional to the nitric oxide inlet concentration. Oxygen in the gas phase is favorable to the absorption of nitric oxide. But it is of little significance to increase the oxygen concentration above 5.2%. The NO absorption rate decreases with temperature. The kinetic equation of NO absorption into the Co(NH3)6(2+) solution under aerobic condition can be written as.     

Efficient decomposition of NO by ammonia radical-injection method using an intermittent dielectric barrier discharge

Although many NO decomposition systems have been developed using plasmas such as dielectric barrier discharges (DBDs), corona discharges, surface discharges, glow discharges, and microwave discharges, the present system is unique on the viewpoint of the use of an intermittent one-cycle sinusoidal power source to generate DBD plasma. There are several features of the system: (1) easy control of the electric power consumed in the DBD plasma, and (2) DBD-plasma generation used only for the production of ammonia radicals. The system employs a radical injection system, where the radicals are produced in a separate discharge chamber, called radical injector, from NO flow field. This enables an efficient production of ammonia radicals being appropriate for DeNOx. It is shown from the temperature dependence of NO removal (DeNOx) characteristics that the present system is a low-temperature DeNOx system compared to a conventional thermal DeNOx system, and NO decomposition is performed over a wide range of gas temperature containing NO. Surveying parametric characteristics of DeNOx, the energy efficiency is improved by a factor of 30% compared to the previously obtained result.     

Reaction characteristics of Ca(OH)2, HCl and SO2 at low temperature in a spray dryer integrated with a fabric filter

The objective of this research was to evaluate the reaction characteristics of CaOH2, HCl and SO2 in the flue gas emitted by a laboratory incinerator. The amount of sulfur retained in the residues (including the spray dryer ash and baghouse ash) was also evaluated in this study. The experimental parameters included HCl concentration (500-2000 ppm), SO2 concentration (500-2000 ppm), relative humidity (40-80% RH), and the addition of CaCl2 (30 wt.%).The results indicated that an HCl concentration of 500-2000 ppm did not affect HCl removal efficiency in the spray dryer at 150 degrees C and 45+/-5% RH. On the other hand, increase in SO2 concentration from 500 to 2000 ppm enhanced SO2 removal at 150 degrees C and 75+/-5% RH. Moreover, increase in removal efficiency of SO2 was more obvious when the relative humidity was greater than 80%. When the flue gas contained both HCl and SO2 simultaneously, the removal efficiency of SO2 could increase from 56.7 to 90.33% at HCl concentration of 236 ppm. However, when the concentration of HCl exceeded 535 ppm, the removal efficiency of SO2 decreased with increasing concentration of HCl. The removal efficiency of SO2 could be increase to 97.7% with the addition of CaCl2.     

Nitric oxide removal from flue gas with a biotrickling filter using Pseudomonas putida

The development of an effective biotrickling filter (BF) system to inoculate a newly isolated strain of Pseudomonas putida SB1 for the effective treatment of nitric oxide (NO) is described. The experiments were carried out in a bench-scale BF under high concentrations of O(2) and NO in simulated flue gas. A method including alternating aeration in screening and rescreening based on the pH changes for cultivating natural aerobic denitrifying bacteria was employed. The SB1 showed a denitrifying capability of 95% nitrate removal rate over a 24h period in an aerobic environment, with no nitrite accumulation. The BF system was able to consistently remove 82.9-94.2% NO when the inlet NO was 400ppm in an enriched oxygen stream of 2-20%. The oxygen had no negative effect on the aerobic denitrifier SB1, but rather enhanced the total efficiency in part by chemical oxidation and in part by the strain activities. A kinetic relation between the oxygen concentration and biological NO removal was developed to confirm that the microbial metabolism played the main role. 79.3% of the total NO removal can be attributed to bio-denitrifying at 20% oxygen, and most chemical oxidation occurred concurrently. Overall, the study demonstrates that NO removal by the aerobic denitrifying process in BF is feasible in flue gas.     

气-液膜接触器结构优化及其传质性能研究

以海水作为吸收剂,采用模拟烟气,对气-液膜接触器进行传质性能评价试验,考察其工艺结构参数、气液介质流动速率及方式、气液压差、烟气SO2浓度等因素对传质系数、脱硫率及膜效用的影响.试验表明,在气相压力较低情况下,气液流速、气液压差对总气相传质系数影响明显,而烟气SO2浓度的影响可忽略不计.适当提高膜接触器的填充密度,增加膜吸收级数,采用错流模式的气液流动方式,均可改善烟气流场分布,增大有效传质面积,提高膜效用.与传统吸收塔相比,新型膜气体吸收装置的气液两相独立控制,可灵活应对烟气浓度变化对脱硫稳定性的影响,同时具有低气阻、耐污染、规模可线性放大等优点,工业化应用前景广阔.     

Simultaneous desulfurization and denitrification by microwave reactor with ammonium bicarbonate and zeolite

Microwave reactor with ammonium bicarbonate (NH(4)HCO(3)) and zeolite was set up to study the simultaneous removal of sulfur dioxide (SO(2)) and nitrogen oxides (NO(x)) from flue gas. The results showed that the microwave reactor filled with NH(4)HCO(3) and zeolite could reduce SO(2) to sulfur with the best desulfurization efficiency of 99.1% and reduce NO(x) to nitrogen with the best NO(x) purifying efficiency of 86.5%. Microwave desulfurization and denitrification effect of the experiment using ammonium bicarbonate and zeolite together is much higher than that using ammonium bicarbonate or zeolite only. NO(x) concentration has little effect on denitrification but has no influence on desulfurization, SO(2) concentration has no effect on denitrification. The optimal microwave power and empty bed residence time (EBRT) on simultaneous desulfurization and dentrification are 211-280 W and 0.315 s, respectively. The mechanism for microwave reduced desulfurization and denitrification can be described as the microwave-induced catalytic reduction reaction between SO(2), NO(x) and ammonium bicarbonate with zeolite being the catalyst and microwave absorbent.     

Application of TiO2-coated alumina beads to dielectric barrier discharge-photocatalyst hybrid process for NO and SO2 removals

NO and SO2 removal by dielectric barrier discharge-photocatalyst (DBD-P) hybrid process was examined for various conditions of process variables. Alumina beads were coated with TiO2 thin film by a rotating cylindrical PCVD reactor and they were packed inside the cylindrical reactor. The NO and SO2 removal efficiencies can be enhanced by using a combination of dielectric barrier discharge and photodegradation by TiO2. The stronger the applied voltage is, the higher the pulse frequency is, or the longer the gas residence time is, the higher the NO and SO2 removal efficiencies become. By applying additional photocatalytic effect, NO removal efficiency increased more significantly than SO2 removal efficiency, because SO2 removal efficiency was already high by dielectric barrier discharge only. In this study, we found that the alumina beads coated with TiO2 thin film by a rotating cylindrical PCVD reactor could be used effectively to remove NO and SO2 by DBD-P hybrid process.     

电子束半干法烟气净化试验装置

电子束烟气净化技术因能对烟气同时进行脱硫脱硝处理而备受关注。清华大学核能技术设计研究院建立了烟气处理量为 10 0 0 0m3/h的电子束半干法烟气净化实验装置。实验装置由烟气调节系统、喷雾干燥系统、注氨系统、烟气辐照系统、收集系统 5个子系统组成。本文介绍了电子束半干法烟气净化工艺流程 ,并对各子系统的组成和功能进行了描述。在试验装置上进行的大量实验表明 ,电子束半干法烟气净化工艺为电子束烟气净化提供了良好的反应条件 ,比传统电子束烟气净化工艺的能耗大大降低。累计15 0 0h的运行情况表明 ,电子束半干法烟气净化工艺系统的工作可靠性和稳定性很好。     

Emission control of SO2 and NOx by irradiation methods

Microwave discharges at 2.45 GHz frequency and accelerated electron beams operated at atmospheric pressure in synthetic gas mixtures containing N(2), O(2), CO(2), SO(2), and NO(x) are investigated experimentally for various gas mixture constituents and operating conditions, with respect to their ability to purify exhaust gases. An original experimental unit easily adaptable for both separate and simultaneous irradiation with microwaves and electron beams was set up. The simultaneous treatment with accelerated electron beams and microwaves was found to increase the removal efficiency of NO(x) and SO(2) and also helped to reduce the total required dose rate with approximately 30%. Concomitant removal of NO(x) ( approximately 80%) and SO(2) (>95%) by precipitation with ammonia was achieved.     

Ammonia removal in electrochemical oxidation: mechanism and pseudo-kinetics

This paper investigated the mechanism and pseudo-kinetics for removal of ammonia by electrochemical oxidation with RuO(2)/Ti anode using batch tests. The results show that the ammonia oxidation rates resulted from direct oxidation at electrode-liquid interfaces of the anode by stepwise dehydrogenation, and from indirect oxidation by hydroxyl radicals were so slow that their contribution to ammonia removal was negligible under the condition with Cl(-). The oxidation rates of ammonia ranged from 1.0 to 12.3 mg N L(-1)h(-1) and efficiency reached nearly 100%, primarily due to the indirect oxidation of HOCl, and followed pseudo zero-order kinetics in electrochemical oxidation with Cl(-). About 88% ammonia was removed from the solution. The removed one was subsequently found in the form of N(2) in the produced gas. The rate at which Cl(-) lost electrons at the anode was a major factor in the overall ammonia oxidation. Current density and Cl(-) concentration affected the constant of the pseudo zero-order kinetics, expressed by k=0.0024[Cl(-)]xj. The ammonia was reduced to less than 0.5 mg N L(-1) after 2h of electrochemical oxidation for the effluent from aerobic or anaerobic reactors which treated municipal wastewater. This result was in line with the strict discharge requirements.     

Multi-functional sorbents for the simultaneous removal of sulfur and lead compounds from hot flue gases

A multi-functional sorbent is developed for the simultaneous removal of PbCl(2) vapor and sulfur dioxide from the combustion gases. The sorbent is tested in a bench-scale reactor at the temperature of 700 degrees C, using simulated flue gas (SFG) containing controlled amounts of PbCl(2) and SO(2) compounds. The removal characteristics of PbCl(2) and SO(2), individually and in combination, are investigated. The results show that the mechanism of capture by the sorbent is not a simple physical adsorption process but seems to involve a chemical reaction between the Ca-based sorbent and the contaminants from the simulated flue gas. The porous product layer in the case of individual SO(2) sorption is in a molten state at the reaction temperature. In contrast, the combined sorption of lead and sulfur compounds generates a flower-shaped polycrystalline product layer.     

Control of nitric oxide, nitrous oxide, and ammonia emissions using microwave plasmas

The subject of this paper is mitigation of the undesirable side-effects of selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR): ammonia slip, residual NO(x), and N(2)O emissions. The use of microwave-plasma discharge within the flue gas was explored as a potential pollution-control method. The key issues addressed were: (1) N(2)O, NH(3), and NO removal efficiencies; and (2) sustaining a stable plasma at atmospheric, or close to atmospheric, pressure. In non-oxidizing atmospheres, removal efficiencies were always close to 100% for all species. In the presence of oxygen, however, appreciable amounts of nitric oxide and ammonia were formed. Methods leading to preventing these undesirable effects were examined. In a number of runs, stable plasma operation was attained at pressures close to atmospheric.     

Removal of ammonia from gas streams with dielectric barrier discharge plasmas

We reported on the experimental study of gas-phase removal of ammonia (NH3) via dielectric barrier discharge (DBD) at atmospheric pressure, in which we mainly concentrated on three aspects--influence of initial NH3 concentration, peak voltage, and gas residence time on NH3 removal efficiency. Effectiveness, e.g. the removal efficiency, specific energy density, absolute removal amount and energy yield, of the self-made DBD reactor had also been studied. Basic analysis on DBD physical parameters and its performance was made in comparison with previous investigation. Moreover, products were detected via ion exchange chromatography (IEC). Experimental results demonstrated the application potential of DBD as an alternative technology for odor-causing gases elimination from gas streams.     

Experimental determination of equilibrium constant for the complexing reaction of nitric oxide with hexamminecobalt(II) in aqueous solution

Ammonia solution can be used to scrub NO from the flue gases by adding soluble cobalt(II) salts into the aqueous ammonia solutions. The hexamminecobalt(II), Co(NH3)6(2+), formed by ammonia binding with Co2+ is the active constituent of eliminating NO from the flue gas streams. The hexamminecobalt(II) can combine with NO to form a complex. For the development of this process, the data of the equilibrium constants for the coordination between NO and Co(NH3)6(2+)over a range of temperature is very important. Therefore, a series of experiments were performed in a bubble column to investigate the chemical equilibrium. The equilibrium constant was determined in the temperature range of 30.0-80.0 degrees C under atmospheric pressure at pH 9.14. All experimental data fit the following equation well: [formula: see text] where the enthalpy and entropy are DeltaH degrees = - (44.559 +/- 2.329)kJ mol(-1) and DeltaS degrees = - (109.50 +/- 7.126) J K(-1)mol(-1), respectively.     

Simultaneous control of acid gases and PAHs using a spray dryer combined with a fabric filter using different additives

The purpose of this research was to simultaneously evaluate the removal efficiency of acid gases and PAHs from the flue gas emitted by a laboratory incinerator. This flue gas contained dust, acid gases, organics and heavy metals. A spray dryer combined with a fabric filter was used as the air pollution control device (APCD) in this study. The operating conditions investigated included different feedstock additives (polyvinyl chloride (PVC) and NaCl) and spray dryer additives (SiO2, CaCl2 and NaHCO3).The removal efficiency for SO2 could be enhanced by adding inorganic additives, such as SiO2, CaCl2 and NaHCO3. The presence of PVC in the incinerator feedstock also increased the removal efficiency of SO2in the spray dryer. The improved removal of PAHs could be attributed to the addition of feedstock additives (PVC and NaCl) and spray dryer additives (SiO2, CaCl2 and NaHCO3).     

Broadband spectroscopic sensor for real-time monitoring of industrial SO(2) emissions

A spectroscopic system for continuous real-time monitoring of SO(2) concentrations in industrial emissions was developed. The sensor is well suited for field applications due to simple and compact instrumental design, and robust data evaluation based on ultraviolet broadband absorption without the use of any calibration cell. The sensor has a detection limit of 1 ppm, and was employed both for gas-flow simulations with and without suspended particles, and for in situ measurement of SO(2) concentrations in the flue gas emitted from an industrial coal-fired boiler. The price/performance ratio of the instrument is expected to be superior to other comparable real-time monitoring systems.