Denitration Efficiency Research Articles

Experimental Study on Simultaneous Desulfurization and Denitrification by DBD Combined with Wet Scrubbing

A dielectric barrier discharge (DBD) reactor combined with a wet scrubbing tower was used to carry out an experimental study on desulfurization and denitrification. The effects of the packing type, packing height, spray density, mass fraction of the NaOH solution, discharge power in the DBD reactor, and simulated flue gas flow rate on the desulfurization and denitrification efficiency were analyzed, along with the influence weight of each factor, using orthogonal testing. The experimental results showed that SO2 was easily absorbed by the scrubbing solution, while the desulfurization efficiency remained at a high level (97–100%) during the experiment. The denitration efficiency was between 12 and 96% under various operating conditions. Denitration is the key problem in this system. The influence weights of the DBD power, simulated flue gas flow rate, mass fraction of the NaOH solution, spray density, packing type, and packing height on the denitration efficiency were 56.96%, 18.02%, 11.52%, 5.02%, 4.33%, and 4.16%, respectively. This paper can provide guidance to optimize the desulfurization and denitrification efficiency of this DBD reactor combined with a wet scrubbing system.

Hydrochloric Acid‐Assisted Regeneration of Cobalt Ethylenediamine for NOx Remediation in Flue Gas

AbstractCobalt ethylenediamine ([Co(en)3]3+) is widely used for NOx remediation in flue gas. However, its industrial applications are limited due to the lack of an efficient regeneration method that converts Co3+ to Co2+. Here, hydrogen chloride is applied as an additive and the performance of cobalt ethylenediamine under variable flue gas compositions is analyzed. The results demonstrate that low pH values favor the conversion of Co3+ to Co2+. Further, a reaction temperature of 100 °C and more than three minutes reaction time were found to accelerate the reduction of Co3+. The NOx removal efficiency could reach more than 70 % after the first regeneration. After 23 consecutive days of continuous experiments, the denitration efficiency of flue gas could be as high as 60 % or more.

CFD analysis of influencing factors on SCR denitration efficiency of sintering flue gas based on response surface methodology

Selective catalytic reduction（SCR） technology is the key technology of flue gas denitration. SCR reactors are the systems contributing to pollution-free emission if they function properly. In order to study SCR denitration chemical reaction simulation and optimize the denitration effect, the CFD analysis of SCR reactor was carried out. The realizable k-ϵ turbulence model, component transport model and chemical reaction model were used to simulate the SCR denitration reactor. Based on the response surface methodology (RSM), the effects of three factors on the denitration efficiency were studied, including catalyst inlet gas velocity, reaction temperature and NH3/NO molar ratio. The quadratic multinomial regression model of three factors affecting the denitration efficiency was established. In addition, the structure of hot air duct and guiding plate were optimized based on the non-uniform inlet temperature. The results showed that: three factors had a significant impact on the denitration efficiency, and the interaction of catalyst inlet gas velocity and reaction temperature is the most significant; the structure optimization of hot air duct and guiding plate can improve the denitration efficiency and reduce outlet NO concentration relative standard deviation, and avoid catalyst abrasion. In this paper, a suitable numerical simulation model is proposed for SCR denitration reaction, and the consideration of non-uniform inlet temperature and the proposition about taking relative standard deviation of NO concentration at the outlet as an optimization index contribute to a more practical and more reasonable structure optimization.

Heavy metals impregnated TiO2 catalysts for the multi-pollution reduction of coal-fired flue gas

The synergistic conversion of VOCs and NO in SCR region of power plants is still a challenge and its catalytic redox mechanism needs to be further understood. Heavy metal oxide loading can effectively expand the low-temperature VOCs and NO potency of catalysts. Here, a series of single heavy metal oxide (CeOX, CrOX, and MnOX) modified TiO2 catalysts were prepared to study their performance of removing VOCs (benzene and toluene) and NO between 260 °C and 420 °C. The catalytic potency was thoroughly investigated, and their physicochemical properties were assessed by a variety of instruments. Performance evaluation of catalysts found that CrOX/TiO2 achieved over 99% VOCs removal and 78.20% denitration efficiency at 340 °C, which was hopeful to be applied to industrial SCR areas. The excellent performance of CrOX/TiO2 should be attributed to the strong redox capacity and abundant surface active oxygen. Also, the in-situ DRIFTS results verified that the NH3-SCR reaction of CrOX/TiO2 catalyst at 340 °C was governed by the combination of the Eley–Rideal mechanism and the Langmuir–Hinshelwood mechanism. More importantly, it confirmed that alkoxides, benzoates, and anhydrides are the main intermediates, indicating that the reaction pathway may be as follows: benzene → benzoquinone → … → CO2 and H2O, and toluene → benzyl alcohol → benzaldehyde → benzoic acid →…→ CO2 and H2O.

Research on precise ammonia injection technology in thermal power plant

Under the situation of ultra-low emission in China, SCR denitration system generally has the problem of high ammonia escape from the reactor outlet, and the escape ammonia reacts with SO3 in flue gas to generate NH4HSO4, which will aggravate the blockage of air preheater and affect the denitration efficiency, so the ammonia injection has a great impact on the NOx emission concentration of power plant. In this paper, how to accurately spray ammonia in SCR denitration system is introduced in detail, that is, after the flow field partition optimization of denitration system, the corresponding advanced measurement system, advanced control system and actuator are added combined with the partition.

Effect of TiO2 crystal form on the denitration performance of Ce–W–Ti catalyst

Abstract Titanium dioxide supports, which were prepared by roasting metatitanic acid under different conditions, were used to prepare a series of Ce–W–Ti catalysts. The structure and denitration properties of the catalyst were studied. The results showed that TiO2 had different crystal types (mixed crystal phases with different proportions of anatase and rutile) under different roasting conditions, and the denitration efficiency of mixed crystal was better than that of pure phase TiO2. Ce–W/200 °C-1 hTiO2 catalyst exhibited a prominent NO conversion rate, and it can reach higher than 90% at a temperature range from 250 to 500°C. The large specific surface area, low content of rutile TiO2 in the support, high content of chemical adsorbed oxygen and high surface acidity were favorable to denitration performance of Ce–W–Ti catalyst.

Low-medium temperature application of selective catalytic reduction denitration in cement flue gas through a pilot plant

Low-medium temperature application of selective catalytic reduction (SCR) denitration in cement flue gas was established and investigated in this study. The 2000 h continuous operation shows the concentration of NOx at the outlet can be maintained at 24 mg/Nm3 on average, while due to the increase of SO2 in flue gas, the NOx concentration increased to 57.5 mg/Nm3 after long time operation. The sulfur deposition is the main reason for catalyst deactivation, and SO2 is still a big obstacle for low-medium temperature SCR application in cement flue gas. The denitration efficiency was tested as fluctuated from 73.5% to 86.2%, and ammonia concentration after SCR was as still as high as 22.5–60.0 mg/Nm3 due to the excessive ammonia injection from selective non-catalytic reduction (SNCR), shows serious ammonia escape problem for SNCR, and the potential application of hybrid SNCR-SCR technology. In order to maintain the denitration efficiency above 85.0%, the gaseous hourly space velocity (GHSV) should not be exceeded 2800 h−1, the electrostatic precipitators (ESP) setting at 60 kV was relatively appropriate, the temperature of the flue gas should be kept at above 200 °C. The concentrations and toxic equivalent quantities (TEQs) of the PCDD/Fs congeners in the flue gas raised greatly after SCR reactor, indicating the PCDD/Fs concentration should be concerned during the application of low-medium temperature SCR, especially for the waste co-disposal processes.

Effects of hydrogen peroxide, sodium carbonate, and ethanol additives on the urea-based SNCR process

The issue of secondary pollutants represents a classic problem in the urea-based selective non-catalytic reduction (SNCR) process. Therefore, this study took to investigate the evolutions of secondary pollutants when including additives during the urea-based SNCR process. Results indicated that additives, namely hydrogen peroxide, sodium carbonate, and ethanol, clear improved denitration efficiency between 750 °C - 925 °C due to the increase of OH groups. Compared to rates without any additives, the “temperature window” width of hydrogen peroxide, sodium carbonate, and ethanol increased by 30%, 30%, and 52%, respectively. The temperature at the maximum denitration efficiency was decreased by 25 °C with the addition of ethanol. The addition of hydrogen peroxide, sodium carbonate, and ethanol decreased the amount of ammonia leakage at 725 °C - 900 °C. Besides, the emissions of HNCO and N2O were decreased by adding sodium carbonate during 725 °C - 900 °C. Therefore, the addition of sodium carbonate proved to be beneficial for reducing the secondary pollutant emissions in SNCR. This study aims to provide a deeper understanding of the urea-based SNCR process in combustion.

Core-shell nanostructure α-Fe2O3/SnO2 binary oxides for the catalytic oxidation and adsorption of elemental mercury from flue gas

In this study, core-shell nanostructure α-Fe2O3/SnO2 binary oxides were prepared to for gaseous elemental mercury (Hg0) removal. The composites were characterized and the results showed that α-Fe2O3/SnO2 was created with the SnO2 core and α-Fe2O3 shell nanostructure. α-Fe2O3/SnO2 had both 76% of Hg0 removal efficiency and 80% of denitration efficiency during 120 min at 350 ℃, which was much higher than the Hg0 removal efficiency of α-Fe2O3 or SnO2 nanospheres. The O2 played an active role in the Hg0 removal over α-Fe2O3/SnO2 at high temperature, however, the SO2 and H2O vapor could reduce the Hg0 removal efficiency of α-Fe2O3/SnO2 to 35% and 40%, respectively. The HCl in flue gas can greatly promote the Hg0 removal efficiency to 95% interpreted as Deacon Reaction mechanism. When HCl is absent in flue gas, the mechanism of Hg0 removal is concluded to catalytic oxidation and adsorption. The gaseous Hg0 is oxidized by Fe3+ and surface-chemisorbed O2- to form HgO adsorbed on the surface and in the void of α-Fe2O3/SnO2. Meanwhile, the Fe2+ is re-oxidized by Sn4+ to form Fe3+ and Sn2+, and the Sn2+ is re-oxidized by O2 in the flue gas.

Influence of cerium doping on Cu-Ni/activated carbon low-temperature CO-SCR denitration catalysts.

In this study, to evaluate the effects of two methods for activation of nitric acid, air thermal oxidation and Ce doping were applied to a Cu–Ni/activated carbon (AC) low-temperature CO-SCR denitration catalyst. The Cu–Ni–Ce/AC0,1 catalyst was prepared using the ultrasonic equal volume impregnation method. The physical and chemical structures of Cu–Ni–Ce/AC0,1 were studied using scanning electron microscopy, Brunauer–Emmett–Teller analysis, Fourier-transform infrared spectroscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, CO-temperature programmed desorption (TPD) and NO-TPD characterisation techniques. It was found that the denitration efficiency of 6Cu–4Ni–5Ce/AC1 can reach 99.8% at a denitration temperature of 150 °C, a GHSV of 30 000 h−1 and 5% O2. Although the specific surface area of the AC activated by nitric acid was slightly lower than that activated by air thermal oxidation, the pore structure of the AC activated by nitric acid was more developed, and the number of acidic oxygen-containing functional groups was significantly increased. Ce metal ions were inserted into the graphite microcrystalline structure of AC, splitting it into smaller graphene fragments, whereby the dispersibility of Cu and Ni was improved. In addition, many reaction units were formed on the catalyst surface, which could adsorb more CO and NO reaction gases. With the increase in Ce doping, the relative proportions of Cu2+/Cun+, Ni3+/Nin+ and surface adsorbed oxygen (Oα) in the Cu–Ni–Ce/AC0,1 catalyst increased. In addition, after the introduction of Ce into Cu–Ni/AC, the amount of weak and medium acids significantly increased. This may be due to the Ce species or its influence on the Cu/Ni species. Further, the active sites of the acid were more exposed. According to the results of the study, a composite metal oxide CO-SCR denitration mechanism is proposed. Through the oxidation–reduction reaction between the metals, the reaction gas of CO and NO is adsorbed and the incoming O2 is converted into (Oα), which promotes the conversion of NO into NO2. The CO-SCR reaction is accelerated, and the rate of low-temperature denitration was increased. Overall, the results of this study will provide theoretical support for the research and development of low-temperature denitration catalysts for sintering flue gas in iron and steel enterprises.

Study on denitration and sulfur removal performance of Mn–Ce supported fly ash catalyst

Nitrogen oxides (NOx) are the main pollutants of air, which mainly come from the combustion of coal and fossil fuels. In this paper, with fly ash used as the catalyst carrier, the effects on the denitration and sulfur resistance of Mn–Ce loading sequence and molar ratio were studied. The catalyst was characterized and analyzed by XRD, XPS, SEM. The results show that when Mn–Ce bimetal is loaded at the same time, Mn ions enter the CeO2 lattice to form a solid solution of Mn–O–Ce fluorite structure, which makes the catalyst has the best denitration and sulfur resistance. The catalyst denitration performance increases first and then decreases with the increase of Mn–Ce molar ratio. When Mn–Ce is 1:1, the denitration efficiency is higher, the total conversion rate of NO is the highest and the deactivation time is the longest, the catalyst is resistant to sulfur performance is also the best.

Highly efficient MnOx/biochar catalysts obtained by air oxidation for low-temperature NH3-SCR of NO

In this study, a novel air oxidation treatment strategy was proposed to modify Mn-doped biochar catalysts for enhanced removal of NO at low temperature. The pre-oxidation at 400 °C and post-oxidation at 250 °C under air atmosphere was applied respectively before and after impregnating biochar with Mn-containing solution (BC-OMO). The results showed that, after pre-oxidation the specific surface area and total pore volume of the sample increased to 734 m2/g and 0.440 cm3/g respectively in comparison with those without pre-oxidation (557 m2/g and 0.353 cm3/g). After further post-oxidation, the contents of Mn4+ and chemisorbed oxygen (Oα) in BC-OMO increased to 36.2% and 49.8% respectively from those without air oxidation (25.4% and 38.7%), which could enhance the surface acidity and redox capabilities of the catalysts. The denitration results showed that the conversion efficiency of NO for BC-OMO catalyst reached as high as 97.0% at 150 °C, which was significantly higher than that without air oxidation (61.8%). The mechanisms for improving denitration efficiency of MnOx/biochar catalysts by pre- and post-air oxidation were also discussed.

O3 oxidation excited by yellow phosphorus emulsion coupling with red mud absorption for denitration

Directing to unwieldiness NOx emitted by the industry, the removal of NOx was implemented using yellow phosphorus (P4) emulsion and red mud slurry as composite absorbent. Where yellow phosphorus is considered to stimulate formation of the ecological ozone (O3) from O2, the oxidation of insoluble NO into water-soluble NOx species by O3, and the red mud as a pH buffer can be used to maintain the pH of the absorption liquid in a range that better absorbs NOx. NO is finally converted into NO2− and NO3−, whereas the yellow phosphorus is mainly PO43−. Single-factor influencing on the efficiency of denitration include the concentration of yellow phosphorus, reaction temperature, stirring intensity, gas flow rate, O2 content, and red mud solid-liquid ratio were investigated. Response surface methodology (RSM) was used to optimize the process parameters. It was indicated that the removal rate of NOx can reach 99.3% under the optimal conditions. Moreover, the possible denitration reaction mechanism was also discussed.

Properties change of activated coke for sintering flue gas purification in cyclic removal of SO2 and NOx

The properties of activated coke (AC) for sintering flue gas purification greatly affect the efficiency of desulfurization and denitration, but they gradually change during cycles. The change in properties of coal-based AC during cycles was studied to clarify the change law and AC optimization index. The AC oxygen content rapidly increases from 13.49 to 17.87 wt.% in the early cycles to form phenol, which promotes the denitration rate from 55.63% to 78.20%. The denitration performance slowly increases in subsequent cycles because of the generation of quinone from AC slow oxidation. However, the oxygen-containing groups are not conducive to adsorption capacity of AC for NO. The adsorbed NO species which can be replaced by SO2 is the main NO species on AC, and its amount decreases with the decrease in C=C content of AC. The AC chemical loss leads to the opening of closed pores, expansion of original pores and formation of new pores, causing micropore volume to increase from 0.085% to 0.152%, compressive strength to decrease from 472 to 336 N, and abrasive resistance to decrease from 97.87% to 94.16% during cycles. The low oxygen content and high micropore volume are favorable to the initial desulfurization performance, and the former is more decisive. After a while, the desulfurization rate is linearly positively correlated with the micropore volume regardless of the chemistry. 4-h desulfurization rate increased from 69.03% to 85.91% during 25 cycles due to the increasing micropore volume. The AC properties change in cycles will greatly affect the desulfurization and denitration rate in the height direction of the flue gas purification system. Selecting the coal-based AC with moderate micropore volume, easy oxidation surface and less original oxygen-containing groups facilitates the better purification efficiency at lower cost for sintering plants.

Comparative Study on NH3-SCR of High Entropy Mineral Catalytic Materials for Different Ratios of Rare Earth Concentrate/Rare Earth Tailing

Abstract A series of high-entropy mineral catalytic materials were obtained by mixing rare earth tailings containing Fe oxide and rare earth concentrate rich in Ce in Baiyun Obo in different proportions, and by acid-base leaching and microwave roasting. The effects of different proportions of mixed rare earth minerals on the denitrification activity of the samples were analyzed by various techniques, including XRD, EDS and SEM. The mineral phase structure and surface morphology of the catalysts were analyzed. The surface properties of the samples were tested by TPD and XPS methods. The denitrification activity of the sample was simultaneously evaluated and compared in the microreactor. The results show that the denitration efficiency of the active powder is the best when the mixing ratio of rare earth tailings/rare earth concentrate is 1:1, the denitration rate can reach 82%. In summary, different proportions of optimization are extremely effective methods to improve catalyst performance.

Effect of F, V and Mn co-doping on the catalytic performance of TiO2-pillared bentonite in the photocatalytic denitration

F, V and Mn co-doped TiO2-pillared bentonite was prepared by the sol-gel method and characterized by XRD, nitrogen sorption, UV-vis spectroscopy, SEM, etc.; its performance in the photocatalytic denitration of NO was investigated under visible light irradiation at room temperature. The results indicate that the photocatalytic denitration efficiency of F-V-Mn co-doped TiO2-pillared bentonite for NO at a concentration of 661 μg/m3 is approximately 100%; when the concentration of NO increases to 1657 μg/m3, the photocatalytic efficiency decreases to 81.9%, which is however 33.8% higher than that over the unpillared F-V-Mn co-doped TiO2. The reaction rate constant over the F-V-Mn co-doped TiO2-pillared bentonite is twice as high as that over the V-Mn co-doped TiO2 pillared bentonite; moreover, the F-V-Mn co-doped TiO2-pillared bentonite also displays improved resistance against water and SO2 poisoning. TiO2 pillars can not only retain the flaky crystal structure of bentonite, but also increase the distance between bentonite layers from 0.667 to 0.710 nm and enhance the adsorption capacity. Meanwhile, the doping elements can inhibit the growth of TiO2 rutile and reduce the band gap of TiO2, which is effective in improving the response to visible light, prolonging the service life, and broadening the application range of TiO2 for the photocatalytic denitration.

Study on the performance of a hydrocyclone used for recycling the waste SCR catalyst

The selective catalytic reduction (SCR) catalyst has been widely used for de-nitrification processes of flue gas from coal-fired power plants because of its high de-nitration efficiency and low operating cost. But the SCR catalyst will lose efficacy in few years and its discharge would cause pollutions. A 20 mm hydrocyclone was used to separate TiO2 from SiO2 for the recycling of waste SCR catalysts based on lab tests and the simulation with Fluent in this paper. Results showed that both the pressure drop and separation efficiency increased with the increase of feed flow rate, the pressure drop almost levelled off when the swirl number exceeded 15.49, and the Newton efficiency increased with the increase of the swirl number as well and reached 83 % at the swirl number of 16.3. The purity of TiO2 could reach 95.53 %.

Study on the influencing factors of removal of NOX from cement kiln flue gas by sewage sludge as a denitration agent

Experimental study on the influencing factors of using sewage sludge as a denitration agent for cement industry was carried out on a self-made laboratory-scale fluid-bed reactor. Results indicate that sludge combustion at 900°C shows an ideal NOX (the sum of NO and NO2) removal activity under simulated working conditions of cement precalciner. The optimal removal efficiency of NOX can reach 70.36 ± 3.59% in the presence of cement raw meal (CRM) at a sludge particle size range of 0.18-0.25mm and the sludge dosage of 0.75g/min. Besides, the NOX removal efficiency increases to 76.94 ± 5.02% in the absence of CRM, indicating that cement raw meal inhibits the NOX removal. This phenomenon may be attributed to the fact that CRM has promotion effect on NH3 produced and obvious inhibitory effect on CO produced; while NH3 and CO play a leading role in NOX reduction, the combined effect leads to the decrease of NOX removal. Moreover, the relationship between the composition of CRM on the inhibition of NOX removal is MgO < CaCO3 < CRM < Al2O3 <Fe2O3. Meanwhile, the effect of additive variety on the sludge denitration activity indicates that urea significantly promotes the NOX removal, which is attributed to the decomposition of urea to form NH3. The stability experiment shows that sludge denitration efficiency remains stable above 70% in the presence of CRM and can reach over 80% when adding appropriate urea. This method can realize the removal of NOX in the cement kiln flue gas and the resource utilization of sludge. It is a promising method for sludge disposal.

An efficient and economic denitration technology based on fuel pretreatment for cement cleaner production

Nitrogen oxide (NOx) emission from cement industry has caused severe atmospheric pollution for low denitration efficiency of existing denitration technologies. To tackle down this problem, an innovative NOx reduction method exhibiting a higher denitration efficiency was developed in this study to satisfy the requirement of cleaner production. Besides, its specific mechanism was clarified in a bench scale experimental setup while its commercial viability was verified in a demonstration project. In accordance with the method, the pulverized coal was first pretreated in a specially designed pretreater where partial fuel nitrogen was in-situ reduced to N2. Subsequently, products of pretreatment that exhibited higher chemical activity were injected to the precalciner to further reduce formed NOx in the kiln gas. As revealed from the results, the denitration efficiency of the novel method can reach to 60%∼80%. Besides, it is promising in industrial application for the easy on-site implementation, high denitration efficiency and incomparable cost advantage. Under the premise of NOx that dropped largely, the costs of initial investment and operation were overly small. It is therefore revealed that the proposed approach outperforms many of the existing denitration technologies in technological and environmental indicators, as well as from the economical perspective.

Effect of Combustible Gas Components on SNCR Reaction with Reducing Agent in Ceramic Kiln

Selective non-catalytic reduction (SNCR) is a denitration method used in NOx process-control of ceramic kiln. In this study, the effect of combustion gas components (CO, H2, CH4) on NOx removal in the SNCR process was investigated, using ammonia and urea as reducing agent in a lab-scale experimental platform. The results showed that the addition of CO slightly promoted the NOx removal efficiency when ammonia was used as reducing agent, while when urea was used as reducing agent, the addition of CO inhibited the denitrification. The increase of H2 and CH4 addition ratio in the simulated flue gas reduced the de-NOx efficiency. With the same addition ratio, the effect of CH4 on the reduction of denitration efficiency was much more obvious than that of H2. When ammonia was used as reducing agent, the ammonia escape was much greater than that of urea.