Single-step integrated CO2 absorption and mineralization (IAM) using fly ash and mixed amine can reduce high energy consumption of absorbent regeneration while enabling the treatment of solid waste, however, the mineralization performance and kinetics are still unclear. This study adopted monoethanolamine (MEA)/N-Methyldiethanolamine (MDEA) mixed amine solution (MAS) as CO2 absorbent and fly ash as mineralizing materials to complete the IAM process in single-step, while realizing the regeneration of mixed amine. The mineralization performance was studied, and the reaction kinetics were analyzed by surface coverage model. The results demonstrated that fly ash effectively mineralized the absorbed CO2 in MAS and mixed amine regenerated. The mineralization efficiency reached maximum of 64.8 % at 40 degrees C, solid-liquid (S/L) ratio of 100 g/L, stirring rate of 500 r/min and 90 min, reaching 60.3 % after 10 cycles. The kinetic results demonstrated that surface coverage model exhibited excellent predictive capability for mineralization process (correlation coefficient (R-2) > 0.99), with identification of surface reaction governed by calcium leaching as the primary rate-limiting factor. The regeneration of mixed amine was achieved by forming carbamate and protonated amine. The CO32-/HCO3- effectively reacted with the active Ca2+ ions in fly ash to realize mineralization, and the mineralization solid products was mainly CaCO3.

Char-bound nitrogen [char(N)] is confirmed to be the real intermediate in heterogeneous reduction during coal combustion. Aiming to have a deep insight into the interaction mechanism between NO and char(N) containing different functional forms of nitrogen, a comprehensive theoretical exploration with density functional theory at M06–2X/6–31G(d,p)//def-TZVP level is performed. The detailed electronic descriptions of char(N) surface based on spin density, Mulliken atomic charge and electrostatic potential exhibit the attack sites and electron donating capability during NO chemisorption in the following order: char(N-5) < char(N-X) < char(N-6). Oxygen surface complex, an intermediate for N2O formation and a catalyst for NO reduction, can weaken the connected CN bond and promote N2 separation. The migration of oxygen atoms to adjacent active sites is thermodynamically conducive to reduction reactions, leading to the preferred pathway of N2 release on char(N-5) and char(N-X) surfaces. Contiguous active sites remaining along char edge are unfavorable for N2O detaching, while beneficial to NO further chemisorption for consecutive reactions, resulting in the great contributions of char(N-5) in reducing NO. The lower energy barriers for NO reduction follow the sequence coincident with the results of electronic property analysis. The kinetically favorable temperatures and activation energies of different char(N) for reducing NO are determined, which is consistent with previous experiments. The theoretical results provide evidences to explain microscopic mechanism of NO-char(N) interaction, making contributions to effectively minimize NOx emissions in the future.

海水湿法烟气脱硫装置排放的脱硫废水在曝气过程中,由于脱硫废水中存在部分还原性离子(SO32-、Fe2+、Mn2+等),会将脱硫过程中捕集的汞、砷离子还原为气态汞和气态砷再次释放到大气中,降低湿法脱硫系统的汞、砷脱除效率.采用曝气反应器,通过模拟实际脱硫废水的曝气过程,重点考察了温度、Cl-质量浓度、SO32-浓度、SO42-质量浓度及曝气流量对汞、砷再释放特性的影响.结果表明:随着温度的提高和曝气流量的增大,会加速汞、砷离子的还原,促进汞、砷的再释放;随着SO32-浓度的提高,会显著抑制汞的再释放,但对砷的再释放影响较弱;汞、砷的再释放率呈现先增大后减小的趋势;Cl-和SO42-可与溶液中的汞离子形成性质稳定的络合物,也可与砷离子以更稳定的化合态相结合,从而有效抑制汞、砷的再释放,并且Cl-的抑制作用比SO42-更显著.

针对某电厂300 MW燃煤机组超低排放条件下电除尘器极线出现的严重裹灰、板结现象,通过分析积灰样品烧失量、可溶性离子浓度、灰成分、粒径以及比电阻特性,结合锅炉超低排放运行特点,研究了电除尘器极线裹灰形成的关键影响因素.结果表明,低低温电除尘器极线上裹灰样品的NH+4、SO24-及灰样中SO3含量均较高,证实了电除尘器极线裹灰的主要原因是SCR脱硝系统逃逸氨与烟气中SO3反应生成硫酸氢铵,且由于低低温电除尘器工作温度较低,烟气中硫酸氢铵一旦形成后难以分解,造成电除尘器极线裹灰严重.同时由于除尘器入口烟气湿度过大,导致飞灰黏性增加,加剧了电除尘器极线裹灰与板结现象.硫酸氢铵使飞灰性质发生改变,飞灰粒度降低,同时硫酸氢铵的附着会影响电除尘器荷电,导致电除尘器除尘效率下降,进一步加剧极线积灰现象.因此,为减少电除尘器裹灰、板结现象,必须有效控制电除尘器入口烟气含水率,同时严格控制脱硝系统氨逃逸及SO3生成浓度等关键影响因素.

Amine CO 2 capture is an effective post-combustion carbon capture (PCC) technology, while CO 2 mineral carbonation is a safe and stable method for CO 2 storage. In this paper, these two methods were combined, and the CO 2 absorption-mineralization performance of mixed amine solution coupled with CaO under different ratios of mixed amine solution, temperature, reaction time and CaO addition ratio were studied by using MEA/MDEA mixed amine solution as the CO 2 absorbent and using CaO as the CO 2 mineralizing raw material. The results show that CaO could effectively mineralize the CO 2 absorbed in MEA/MDEA solution, realizing the regeneration of MEA/MDEA solution simultaneously under normal temperature and pressure. Meanwhile, the MEA/MDEA solution can still maintain a high CO 2 conversion rate (77.4%) and CO 2 cycle loading (1.03 mol/L) after five cycles of absorption-mineralization experiments. The FT-IR and XRD analyses reveal that the addition of CaO makes a large amount of Ca 2+ and OH − into the MEA/MDEA solution, which could react with and protonated amine in the solution to form calcium carbonate precipitate and free amine respectively, thus realizing the mineralization of CO 2 and the regeneration of MEA/MDEA solution. The main component of solid products obtained is calcium carbonate, and calcite is its main crystal form.

The catalytic mechanism of Na during NO reduction on char surface is proposed to provide fundamental information for minimizing NOx emissions. A molecular modeling study was carried out using density functional theory to clarify the NO reduction and CO release pathways on char surface. The calculation results explain the promotion phenomenon caused by Na catalysis, and the fluctuation of the CO release curve in the experiment. Under H2O/Ar atmosphere, besides the NO-char heterogeneous reaction, simultaneous occurrence of the NO homogeneous reaction with lower energy barrier improved the NO reduction rate. According to the simulation results, the catalytic effect of Na is manifested in that it can weaken the conjugated components of the aromatics structure, and form a stable H-C-O-Na structure to weaken the connected C-C bond, thereby facilitating the CO release. Mayer bond order and RDG analyses indicate that the participation of Na can prevent the C-O bond from being stretched, and generate the strong attractive interaction to promote the NO reduction.

为避免温室效应带来的负面影响,CO2减排已成为目前的当务之急.CO2矿物碳酸化作为一种有潜力的CO2减排技术,受到了学者们的广泛关注.CO2矿物碳酸化方法主要包括直接干法碳酸化、直接湿法碳酸化以及间接碳酸化等不同工艺过程.目前,CO2直接或间接碳酸化方法面临的关键挑战是提升CO2碳酸化反应动力学特性;反应速率慢、碳酸化效率较低是当前该技术的主要问题.传统CO2胺类化学吸收法具有吸收速率快、吸收容量大和吸收剂能循环再生的优点,但能耗和运行成本较高.将CO2胺类化学吸收法与CO2碳酸化过程结合而开发的CO2吸收-矿化一体化技术(IAM)不仅解决了传统工艺高能耗、低转化率的问题,而且使工艺流程简化、成本降低,有利于应用于工业化.本文主要综述了近年来CO2矿化技术的研究进展,对比了各种工艺技术路线的不同特点,并分析指出加强对IAM工艺反应机理的研究以及开发出高效、经济的吸收剂和矿化原料,将是该工艺未来研究的重点和关键.

在燃煤烟气中选择性催化还原(SCR)技术由于脱硝效率高、选择性好被广泛应用,然而SCR催化剂的催化作用会使烟气中的SO2氧化成SO3,SO3会与NH3等反应生成硫酸氢铵(ABS)和硫酸铵(AS),当烟气温度低于硫酸铵盐的凝结温度时,其会沉积在催化剂、空预器及其附属设备上,引发诸多严重的问题,对电厂的运行和环境造成了不利影响.本文综述了燃煤烟气中SO3与硫酸氢铵的生成特性及其控制方法最新进展,分析了SO3在锅炉和SCR系统中的形成机理、迁徙转化特性,阐述了控制SO3与硫酸氢铵生成的方法,介绍了不同活性组分对催化剂表面SO3和硫酸氢铵生成的影响.最后提出了开发新型催化剂是燃煤烟气中SO3与硫酸氢铵生成控制的重点研究方向.

选择性催化还原(SCR)技术由于脱硝效率高、选择性好而被广泛应用于烟气氮氧化物排放控制;然而,目前广泛采用的钒钛系SCR脱硝催化剂会使烟气中SO2氧化成SO3,烟气中过高的SO3对电厂安全运行会造成严重影响,也会对环境造成污染.以典型V2O5-WO3/TiO2催化剂为研究对象,系统研究了SCR脱硝过程中烟气流量、温度、O2浓度、SO2浓度等对催化剂表面SO3生成特性的影响,并进一步对SO3生成的反应动力学特性进行了分析.研究表明:催化剂表面SO3生成反应中SO2的反应级数为0.59,当O2浓度大于3％时,O2的反应级数为0,该反应的表观活化能为70.39 kJ/mol;实验条件下,烟气中SO2浓度增加会使SO3生成的反应速率提高;O2浓度对催化剂表面SO3生成影响并不显著;烟气温度对催化剂表面SO3生成具有显著影响,高温会促进SO3的生成.

以不同热解条件下制取的陕西烟煤(YL)半焦为原料,使用预糊化淀粉为黏结剂冷压成型制取成型燃料,分析不同热解条件下获得的煤焦成型后的物理特性,研究热解条件对半焦挥发分和表面含氧官能团的影响规律,揭示热解半焦特性对其成型的影响机理.结果表明:热解停留时间和热解终温对半焦成型特性具有显著影响.热解停留时间增加和热解终温升高会降低半焦挥发分含量和表面含氧官能团,影响黏结剂颗粒和半焦颗粒之间的黏结作用,从而会降低半焦成型后的冷压强度和跌落强度.结果表明:挥发分质量分数在16％以上的半焦成型后冷压强度大于450 N,适宜成型;热解终温小于600℃且热解停留时间小于5 min的半焦表面含氧官能团含量较高,成型后冷压强度大于450 N,可用于成型.半焦的成型特性受其挥发分含量和表面含氧官能团的综合影响.

以国内某600 MW墙式切圆燃烧锅炉为研究对象,在炉膛关键区域布置了高温CO在线监测系统,通过试验与数值模拟计算,研究了炉膛CO生成特性与锅炉效率及NOx排放的关联特性,并建立了低氮综合燃烧指数,以平衡锅炉高效燃烧与低氮排放之间的矛盾.研究结果表明,该锅炉效率随监测的炉膛CO浓度增大呈现先增大后减小的趋势,炉膛NOx排放浓度随炉膛CO浓度的增大而逐渐降低;锅炉CO生成特性与锅炉效率及NOx排放均表现出了显著相关性,优化炉膛CO生成特性能够使得锅炉燃烧效率与氮氧化物排放的综合性能实现优化.锅炉实际运行中,可通过监测与调控炉膛CO浓度,获得低氮综合燃烧指数最大值,以有效平衡锅炉效率与NOx排放之间的矛盾,实现锅炉的高效、低氮运行.

The transfer characteristics and removal capability of Hg in ultra-low emission facilities such as selective catalytic reduction (SCR), low temperature electrostatic precipitator, seawater desulfurization and wet electrostatic precipitator in a 300 MW coal-fired boiler of a power plant were studied under different working conditions and different types of coal. The results show that under different working conditions, the total emission concentration of mercury is basically 1.16-2.90 μg/m3. The final release of mercury into the atmosphere is mainly composed of elemental mercury and a small amount of oxidized mercury, the particulate mercury was completely removed. Most mercury is removed in seawater flue gas desulfurization. The overall removal efficiency of mercury of low temperature electric precipitator, a seawater flue gas desulfurization scrubber and wet electric precipitator is 25%, 62% and 37% respectively on average. The proportion of Hg2+ is the key to affect the efficiency of mercury removal in flue gas, and the higher proportion of Hg2+ in flue gas is beneficial to obtain higher efficiency in electrostatic precipitators and seawater flue gas desulfurization devices. In the 300 MW coal-fired boiler of a power plant equipped with a selective catalytic reduction unit, a low temperature electrostatic precipitator, a seawater flue gas desulfurization scrubber, and a wet electrostatic precipitator and other ultra-low emission facilities, the average removal rate of total mercury is about 83%, which can achieve greater levels of mercury removal.

The char samples were prepared from the coal impregnated with NaCl under different steam concentrations and temperatures. The mode of occurrence of sodium and the contents of sodium in different chars with the same conversion ratio were analyzed by inductively coupled plasma mass spectrometry. The effects of steam and temperature on the migration and transformation of sodium in the coal during the thermal conversion processes were studied. The results showed that the increase of steam concentration enhanced the release of water-soluble sodium during the thermal conversion of coal and promoted the transformation of water-soluble sodium into ammonium acetate, hydrochloric acid and insoluble sodium. As a result, the release of sodium was suppressed to a certain extent. It was also observed that increasing the reaction temperature could promote the release of water-soluble sodium and promote the transformation of water-soluble sodium to the other soluble forms of sodium. The evolution of char structure was an important influence on the release of sodium. The results revealed that the degrees of char condensation increased with the steam gasification reaction. The formation of large aromatic ring structures from the condensation of the small aromatic rings played the important role in the encapsulation of sodium, which would inhibit the release of sodium.

With the comprehensive promotion of ultralow emissions and world-class energy consumption standards, the disposal of the spent SCR (selective catalytic reduction of NOx with NH3) catalyst and fly ash has become a new challenge for coal power plants. In this study, a new method of simultaneous utilization of the spent SCR catalyst and fly ash in concrete preparation was developed. The working performance and heavy metal leaching characteristics of concrete prepared by replacing some cement with the spent SCR catalyst/fly ash were investigated. Results suggested that the addition of fly ash could improve the deterioration of concrete fluidity caused by the addition of the spent SCR catalyst. Better working performance was evidenced at 5% of the spent SCR catalyst and less than 10% of fly ash addition. When more than 10% of the spent SCR catalyst was added into concrete, the compressive strength and impermeability of the concrete were significantly worsened, but those could be improved by adding fly ash due to its pozzolanic activity. Leaching characteristics showed that the solidification efficiency of V and As could reach more than 96 and 97%, respectively, which mainly comes from the generation of C-S-H gels by the hydration reaction of cement in the concrete curing process. Results revealed that the method proposed in this study can achieve high-efficiency solidification of heavy metals in spent SCR catalysts. In general, the simultaneous utilization of the spent SCR catalyst and fly ash to replace some parts of the cement for preparing concrete is a promising method for harmless disposal of spent SCR catalysts.