生物质活性炭烟气脱硫脱硝的研究进展

烟气脱硫脱硝技术是燃煤电厂烟气污染物控制的主流技术,其中生物质活性炭烟气脱硫脱硝以其新颖、高效、经济、资源化的特点成为近年来的研究热点。生物质活性炭烟气脱硫技术以吸附脱硫为主;生物质活性炭烟气脱硝技术根据烟气温度窗口划分为低温吸附脱硝（包括NO吸附与NO氧化吸附）、中温NH₃-SCR脱硝技术及高温异相还原脱硝技术。综述了孔隙结构、表面化学性质、表面改性等因素对生物质活性炭脱硫脱硝性能的影响,总结了提高生物质活性炭脱硫脱硝性能的途径与方法。最后指出,生物质活性炭异相还原脱硝反应建立更为通用的动力学模型、NH₃-SCR脱硝技术中生物质活性炭催化剂效率的进一步提升、生物质活性炭脱硫脱硝制备生物缓释肥、生物质活性炭改性与担载催化剂实现多污染物一体化脱除等方向可做深入探索与研究。     

SO2 and NO selective adsorption properties of coal-based activated carbons

The aim of this paper is to study binary gas adsorption on the activated carbon in the fixed-bed reactor. Coal-based granular activated carbons can selectively adsorb SO₂ and NO. Physically adsorbed NO is replaced and desorbed by SO_2. Chemically adsorbed NO can promote the absorption of SO₂. The presence of SO₂ and NO can enhance the chemical adsorption of NO and SO₂, respectively. When the diameter of granular activated carbon decreases and the specific surface area increases, both the penetration time of the activated carbon bed and SO₂ removal efficiency increase. The whole removal efficiency of SO₂ is more than 99% in the penetration time, but the whole removal efficiency of NO is only 55% in the coexistence of SO₂ and NO. SO₂ adsorption capacity of HNO₃ dipped granular activated carbon is higher than that of non-treated one. The two experimental results are agree with each other.     

Cobenefit of SO3 reduction on mercury capture with activated carbon in coal flue gas

Parametric experiments were carried out to study the interactions of mercury, SO₃, and injected activated carbon (AC) in a coal flue gas stream. The levels of SO₃ vapor in flue gas were altered by individually varying flue gas temperature, moisture, or sodium fume injection in the flue gas. Meanwhile, mercury emissions with AC injection (ACI) upstream of an electrostatic precipitator (ESP) were evaluated under varied SO₃ concentrations. SO₃ measurements using a condensation method indicated that low temperature, high moisture content, and sodium fume injection in flue gas shifted SO₃ partitioning from the vapor to particulate phase, subsequently improving mercury capture with ACI. 0.08 g/m³ of DARCO^® Hg-LH injection only provided approximately 20% mercury reduction across the ESP in a bituminous coal flue gas containing 28 ppm SO₃, but mercury capture was increased to 80% when the SO₃ vapor concentration was lowered less than 2 ppm. Experimental data clearly demonstrate that elevated SO₃ vapor is the key factor that impedes mercury adsorption on AC, mainly because SO₃ directly competes against mercury for the same binding sites and overwhelmingly consumes all binding sites.     

Development of Catalyst-Sorbents for Simultaneous Removal of SO2 From Flue Gas by Low Temperature Ozone Oxidation

One technological process employing ozone and heterogeneous catalyst-sorbents was proposed for removal of SO₂ from flue gas. The catalyst-sorbents were developed and tested especially for adsorption and oxidation of SO₂. Alternative catalyst-supporters including γ-Al₂O₃, permutite, silica gel, activated carbon and diatomite combined with different metal oxides (MnO₂, Cr₂O₃, Fe₂O₃, CuO, CoO and NiO) were evaluated and tested. It was found that γ-Al₂O₃ doped with MnO₂ can be considered as removal-effective sorbent for adsorption and oxidation of SO₂. The synergetic effect between ozone and catalyst was found to be dominated. Effects of catalyst preparation parameters like calcination temperature, metal loaded and reaction temperature, etc. were investigated based on the MnO₂/Al₂O₃ catalyst-sorbents. Results show that γ-Al₂O₃ combined with 8% Mn, calcinated under 573 K and reacted at 413 K are the optimal parameters for removal of SO₂. Extra NO in flue gas can slightly enhance the capture efficiency of SO₂.     

Evaluation of SO2 oxidation and fly ash filtration by an activated carbon fluidized-bed reactor: The effects of acid modification, copper addition and operating condition

It is expected that the simultaneous removal of acid gases and particles from flue gas, using a single process and at the same temperature, will become an economical, and thus, desirable option. Accordingly, this study investigates the potential for the utilization of a fluidized-bed adsorbent/catalyst reactor for the simultaneous removal of SO₂ and fly ash from simulated flue gas. The operating conditions for the evaluation include: (1) different pre-treatments of the adsorbent/catalyst, (2) the operating parameters of adsorption/filtration and (3) the effects of simultaneous adsorption/filtration through the fluidized-bed reactor. Based on the experimental data gathered, the Brönsted acid sites were formed on the surface of activated carbon (AC) support materials after modification with nitric or sulfuric acid and it acted as anchor. This characteristic accounts for the promotion of the effects of dispersion and adsorption of the adsorbent/catalyst. Moreover, the addition of copper facilitated the oxygen transfer of SO₂ to the carbon matrix. The concentration of SO₂ removed by the fluidized-bed adsorbent/catalyst reactor decreased from 17.9 to 14.2 mg SO₂/g of adsorbent after exposure to a high concentration of fly ash. Therefore, an acid-pre-treatment of the adsorbent/catalyst is required to hasten the removal of SO₂ in the simulated flue gas. Our result shows that the acidic groups may facilitate the adsorbent/catalyst removal of SO₂ when there exist high concentrations of fly ash in the flue gas.     

Enhancement of the denitrification efficiency over low-rank activated coke by doping with transition metal oxides

Low-rank activated coke (AC) is widely used for industrial flue gas purification due to its multipollutant cooperative removal capability. To enhance the denitrification capacity of AC for the selective catalytic reduction (SCR) of NO with NH₃, several transition metal (Fe, Mn, Ce, V) oxides were uniformly loaded into AC by solvent impregnation. Compared to untreated AC, modified AC showed excellent denitrification efficiency above 90%. N₂ adsorption-desorption and Raman spectroscopy techniques were used to characterize the pore size distribution and crystal structure of AC samples. The introduction of transition metal oxides had little effect on the pore structure of AC but increased the nitrogen-containing functional groups, which facilitated NO removal. Moreover, x-ray photoelectron spectroscopy (XPS) was used to analyze the valence changes of metal elements before and after denitrification. After the reaction, the content increase of the low-valence metal oxides indicated that the transition metal oxides were involved in the reaction of NO with NH₃. High-valence metal oxides oxidized NO to NO₂, which reacts more easily with NH₃, thereby increasing the denitrification efficiency. Importantly, in the presence of SO₂, modified AC still presented high denitrification performance. This transition metal oxides doping method can effectively improve the ability of low-rank AC to remove NO in multi-contaminant flue gas.     

改性活性炭的烟气脱硫脱硝性能研究

采用浸渍法改性活性炭,低温吸附模拟烧结机烟气中的SO2和NO,研究了质量分数3%的HNO3改性活性炭表面官能团的变化及其吸附烟气中SO2和NO的性能。Boehm滴定结果表明:浸渍时间6 h,干燥温度130℃,干燥时间2 h得到的活性炭碱性基团增加最多,与傅里叶变换红外光谱分析结果相符。改性后的最佳活性炭,前60 s的脱硫率维持在90%以上,脱硝率在前20 s也达90%以上,再生后改性活性炭脱硫脱硝能力基本不变。     

Study of SO2 adsorption and thermal regeneration over activated carbon-supported copper oxide catalysts

The mechanisms of SO₂ adsorption and regeneration over activated carbon-supported copper oxide sorbent/catalysts were analyzed. Studies were carried out in a fixed-bed reactor equipped with a non-dispersive infrared gas analyzer to detect the reaction products and by using X-ray powder diffraction (XRPD) and temperature-programmed desorption (TPD) experiments to characterize the nature of the sulfate species and surface oxygen complexes. The results indicate that SO₂ was catalytically oxidized to SO₃ over a copper phase in the presence of gaseous oxygen, and then reacted with a copper site to form a sulfate linked to copper without desorption into the gas phase. The activated carbon support did not participate in this sulfation reaction. After the adsorption of SO₂, the exhausted sorbent/catalysts could be regenerated by direct heat treatment in inert gas at temperatures between 260 and 480 °C, while the neighboring surface oxygen complexes on the carbon surface were acting as the reducing agents to reduce CuSO₄ to Cu. During the subsequent adsorption process, the copper is rapidly oxidized by oxygen in the flue gas.     

Optimization of a Pilot‐Scale Amine Scrubber to Remove SO2: Higher Selectivity and Lower Solvent Consumption

A pilot‐scale study of flue gas desulfurization based on an amine‐based solvent using applicable industrial values was carried out for sulfur dioxide (SO₂) removal. The plant consisting of absorption and desorption columns was operated with different working parameters such as solvent flow rate, inlet concentration of SO₂, temperature of desorption column, and pH of absorption agent. The Taguchi method was utilized to obtain the best combination of working parameters for the most efficient reduction of SO₂ outlet concentration. The industrial gas‐to‐liquid ratio could be optimized by applying a defined SO₂ concentration, stripper temperature, and solvent pH value. The achieved efficiency is much better compared to our previous study while the gas‐to‐liquid ratio is higher in this work.     

Removing H2S from Biogas Using Sorbents for Solid Oxide Fuel Cell Applications

Desulfurization of biogas is essential for its application in solid oxide fuel cells. The influence of CH₄, CO₂, H₂, and O₂ as well as the effect of moisture onto desulfurization performance of an activated carbon, an adsorbent based on a CuO‐MnO mixture, and a zeolite adsorbent were analyzed. The use of moisturized gas had no negative influence on the H₂S adsorption performance of activated carbon. The CuO‐MnO sorbent showed the best performance, but the presence of moisture had a negative influence. The performance of zeolite dropped for three gas mixtures, while for two other mixtures moisture had little to no influence on H₂S adsorption performance.     

改性桑树枝焦对模拟烟气中汞的吸附性能

采用固定床热解、蒸汽活化和改性剂(H₂O₂、ZnCl₂和NaCl)浸渍等方法制得不同的桑树枝焦。在固定床吸附实验台上,研究了蒸汽活化、改性剂、吸附温度和烟气组分等对改性桑树枝焦汞吸附性能的影响。结果表明:蒸汽活化显著提高了桑树枝热解焦的比表面积,H₂O₂改性可进一步提高桑树枝蒸汽活化焦比表面积并改善其孔隙结构参数,ZnCl₂和NaCl改性则降低了桑树枝蒸汽活化焦的比表面积、D-R微孔容积和总孔容。10%H₂O₂和30%H₂O₂浸渍改性桑树枝焦的单位汞吸附量分别是蒸汽活化焦的2.02倍和1.77倍;相同改性剂浓度下,ZnCl₂改性焦的单位汞吸附量比NaCl改性焦稍好;随着ZnCl₂浓度增大,改性桑树枝焦的汞吸附性能增强,MT600-A-ZnCl₂(5%)桑树枝焦的单位汞吸附量达到29.55 μg·g^-1,是蒸汽活化焦的3.37倍。在吸附温度为60～120℃范围内,H₂O₂改性焦的汞吸附效率及单位汞吸附量随着吸附温度的升高而下降,而ZnCl₂改性焦的单位汞吸附量则随着吸附温度提高呈现先增大后减小的趋势,最佳吸附温度为90℃。烟气中SO₂和NO组分对汞吸附性能有一定的抑制作用,随着SO₂和NO浓度的增加,汞吸附效率和单位汞吸附量均稍有下降。     

The use of rice hulls for sustainable control of NOx emissions in deep space missions

The use of the activated carbon produced from rice hulls to control NOx emissions for future deep space missions has been demonstrated. The optimal carbonization temperature range was found to be between 600 and 750 degrees C. A burnoff of 61.8% was found at 700 degrees C in pyrolysis and 750 degrees C in activation. The BET surface area of the activated carbon from rice hulls was determined to be 172 m2/g when prepared at 700 degrees C. The presence of oxygen in flue gas is essential for effective adsorption of NO by activated carbon. On the contrary, water vapor inhibits the adsorption efficiency of NO. Consequently, water vapor in flue gas should be removed by drying agents before adsorption to ensure high NO adsorption efficiency. All of the NO in the flue gas was removed for more than 1.5 h when 10% oxygen was present and the ratio of the carbon weight to the flue gas flow rate (W/F) was 15.4 g min/L. Reduction of the adsorbed NO to form N2 could be effectively accomplished under anaerobic conditions at 550 degrees C. The adsorption capacity of NO on the activated carbon was found to be 5.02 mg of NO/g of carbon. The loss of carbon mass was determined to be about 0.16% of the activated carbon per cycle of regeneration if the regeneration occurred when the NO in the flue gas after the carbon bed reached 4.8 ppm, the space maximum allowable concentration. The reduction of the adsorbed NO also regenerated the activated carbon, and the regenerated activated carbon exhibited an improved NO adsorption efficiency.     

Simultaneous removal of SO2 and NOx by microwave with potassium permanganate over zeolite

Simultaneous sulfur dioxide (SO₂) and nitrogen oxides (NO_x) removal from flue gas can be achieved with high efficiency by microwave with potassium permanganate (KMnO₄) over zeolite. The experimental results showed that the microwave reactor could be used to oxidation of SO₂ to sulfate with the best desulfurization efficiency of 96.8% and oxidize NO_x to nitrates with the best NO_x removal efficiency of 98.4%. Microwave accentuates catalytic oxidation treatment, and microwave addition can increase the SO₂ and NO_x removal efficiency by 7.2% and 12.2% separately. The addition of zeolite to microwave potassium permanganate increases from 16.5% to 43.5% the microwave removal efficiency for SO₂, and the NO_x removal efficiency from 85.6% to 98.2%. The additional use of potassium permanganate to the microwave zeolite leads to the enhancement of SO₂ removal efficiency up from 53.9% to 95%, and denitrification efficiency up from 85.6% to 98.2%. The optimal microwave power and empty bed residence time (EBRT) on simultaneous desulfurization and denitrification are 259 W and 0.357 s, respectively. SO₂ and NO_x were rapidly oxidized in microwave induced catalytic oxidation reaction using potassium permanganate with zeolite being the catalyst and microwave absorbent.     

Impacts of acid gases on mercury oxidation across SCR catalyst

A series of bench-scale experiments were completed to evaluate acid gases of HCl, SO₂, and SO₃ on mercury oxidation across a commercial selective catalytic reduction (SCR) catalyst. The SCR catalyst was placed in a simulated flue gas stream containing O₂, CO₂, H₂O, NO, NO₂, and NH₃, and N₂. HCl, SO₂, and SO₃ were added to the gas stream either separately or in combination to investigate their interactions with mercury over the SCR catalyst. The compositions of the simulated flue gas represent a medium-sulfur and low- to medium-chlorine coal that could represent either bituminous or subbituminous. The experimental data indicated that 5–50 ppm HCl in flue gas enhanced mercury oxidation within the SCR catalyst, possibly because of the reactive chlorine species formed through catalytic reactions. An addition of 5 ppm HCl in the simulated flue gas resulted in mercury oxidation of 45% across the SCR compared to only 4% mercury oxidation when 1 ppm HCl is in the flue gas. As HCl concentration increased to 50 ppm, 63% of Hg oxidation was reached. SO₂ and SO₃ showed a mitigating effect on mercury chlorination to some degree, depending on the concentrations of SO₂ and SO₃, by competing against HCl for SCR adsorption sites. High levels of acid gases of HCl (50 ppm), SO₂ (2000 ppm), and SO₃ (50 ppm) in the flue gas deteriorate mercury adsorption on the SCR catalyst.     

铁水脱硫渣-生物质活性炭的烟气脱硫性能研究

以农业废弃物核桃壳为原料,以及炼钢副产品铁水脱硫渣作为添加剂,采用共混法制备铁水脱硫渣-生物质活性炭。采用固定床反应器对铁水脱硫渣-生物质活性炭进行脱硫实验,考察入口SO2含量、床层温度、水蒸气含量、空速和氧气含量等工艺参数对其脱硫性能的影响。结果表明,随着入口SO2含量和空速的增加,铁水脱硫渣-生物质活性炭的穿透硫容和脱硫穿透时间均减小,床层温度是显著因素,水蒸气和氧气有利于铁水脱硫渣-生物质活性炭的化学吸附,铁水脱硫渣-生物质活性炭的脱硫最优工艺参数：即入口SO2含量、空速、床层温度、水蒸气含量和氧气含量分别为0.25%、750 h-1、85℃、9%和12%,其穿透硫容为274.1 mg/g和脱硫穿透时间为31 h。     

Removal of SO2 in Semi‐Dry Flue Gas Desulfurization Process with a Powder‐Particle Spouted Bed

Semi‐dry flue gas desulfurization was investigated with several kinds of SO₂ sorbents, such as slaked lime, limestone, Mg(OH)₂ and concrete pile sludge, in a powder‐particle spouted bed. Slurry droplets including sorbent fine particles were fed to a spouted bed of coarse inert particles spouted with hot gas containing SO₂. SO₂ removal efficiency was strongly affected by the approach to saturation temperature, Ca/S molar ratio and particle size of sorbent. Slaked lime showed the highest desulfurization efficiency. In this process, despite very short gas residence time, more than 90% SO₂ removal was easily achieved by choosing appropriate conditions.     

天然矿物共混活性焦联合低温脱硫脱硝

以P1/Ti2-15@AC天然矿物共混改性活性焦,模拟研究移动床反应器系统中活性焦联合脱硫脱硝反应过程。研究结果表明,采用新型天然矿物共混改性活性焦,结合加热再生设计,可以很好地将烟气脱硫和脱硝过程结合,从而实现高效率、低成本的一体化联合脱硫脱硝。研究表明,循环脱硫再生后P1/Ti2-15@AC-Rn的脱硝活性得到显著提升,P1/Ti2-15@AC-R1和P1/Ti2-15@AC-R2的脱硝NO转化率接近100.0%,第三次再生后降低至85.0%左右并保持基本稳定。这主要是因为脱硫再生后活性焦表面酸性C—O、C—S等酸性官能团增加,增强了脱硝时活性焦表面NH₃的吸附过程,从而提升脱硝反应效率。     

Catalytic removal of SO2, NO and HCl from incineration flue gas over activated carbon-supported metal oxides

Activated carbon-supported copper, iron, or vanadium oxide catalysts were exposed to incineration flue gas to investigate the simultaneous catalytic oxidation of sulfur dioxide/hydrogen chloride and selective catalytic reduction of nitrogen oxide by carbon monoxide. The results show that AC-supported catalysts exhibit higher activities for SO₂ and HCl oxidation than traditional γ-Al₂O₃-supported catalysts and the iron and vanadium catalysts act as catalysts instead of sorbents, and can decompose sulfate with evolution of SO₃ and then regenerate for more SO₂ adsorption to take place. The AC-supported catalysts also display a high activity for NO reduction with CO generated from a flue gas incineration process and the presence of SO₂ in the incineration flue gas can significantly promote catalytic activity. Using CO as the reducing agent for NO reduction is more effective than using NH₃, because NH₃ may be partially oxidized in the presence of excess O₂ (12 vol%. in the incineration flue gas used) to form N₂, which can decrease the overall extent of NO reduction.     

A Novel Dry Process for Simultaneous Removal of SO2 and NO from Flue Gas in a Powder‐Particle Fluidized Bed

A novel sorbent, potassium carbonate impregnated on porous fine alumina, was produced, and its reactive and regenerative properties were evaluated for dry‐type simultaneous removal of SO₂ and NO from flue gas under stack temperatures, by using a powder‐particle fluidized bed (PPFB) with I.D. of 53 mm as the reactor. High removal efficiencies for SO₂ and NO were achieved simultaneously. An apparent beneficial effect of SO₂ on the enhancement of NO removal was found based on a large amount of data. The alumina carrier was successfully regenerated and used repeatedly for the production of fresh sorbent particles. With no ammonia, low temperature, high removal efficiency, and no second waste emission as main characteristics, this dry process can be a competitive technology for pollution control of flue gas from power plants in the future.     

烟气水蒸汽含量对变温吸附烟气脱硫过程的影响

通过动态吸附实验,考察了水蒸汽含量对SO2在脱硫脱硝活性炭上变温吸附过程的影响,分析了其含量0~0.20(摩尔比或体积比,下同)条件下的吸附规律,并基于吸附模型对实验数据进行了讨论. 对Bangham吸附模型进行改进以包含水蒸汽的影响,并应用该模型进行了预测,在不同水蒸汽含量时,模型的模拟值与实验值吻合较好. 结果表明,在所研究的体系和条件范围内,烟气中的水蒸汽增大了脱硫率、SO2吸附量、平衡吸附量和吸附速率,其含量在0.07~0.10范围内效果较优,此时最大SO2平衡吸附量为73.00 mg/g.