焦炭颗粒在不同控制区域中的燃烧特性

针对焦炭颗粒在煤粉炉内的复杂燃烧过程,建立相互耦合的导热、气相传质模型及改进的随机孔模型. 通过FORTRAN编程,研究了焦炭颗粒在不同控制区域中的燃烧特性,应用改进的随机孔模型,研究了焦炭颗粒在扩散-化学反应动力学控制区中的燃烧特性. 结果表明,在扩散-化学反应动力学控制区,碳基上的小孔内部存在O2浓度梯度,焦炭颗粒的转化速率在转化率约为0.39时出现最大值,随燃烧过程进行先增大后减小.     

钙和羟基影响焦炭还原N2O的量子化学研究

基于密度泛函理论(DFT),在M06-2X/6-311G(d)基组水平下，研究了钙和羟基在焦炭还原N₂O过程中的作用。采用了Zigzag焦炭模型及钙和羟基修饰后的焦炭模型对N₂O还原反应过程进行模拟。结果表明：整个反应过程分为三个阶段，N₂O的吸附、N₂的析出以及C(O)配合物的解吸，三种模型的决速步均位于C(O)配合物解吸阶段；动力学结果表明，随着反应温度升高，反应速率常数增大，温度升高对N₂O-C反应有促进作用；根据传统过渡态理论(TST)计算得到，原始Zigzag焦炭模型及钙和羟基修饰后的焦炭模型异相还原N₂O的反应活化能分别为450.1 kJ/mol, 420.4 kJ/mol和406.3 kJ/mol,表明钙和羟基对焦炭还原N₂O均有促进作用；钙和羟基促进焦炭还原N₂O反应的机理不同，钙吸附到焦炭表面，向焦炭转移电子使焦炭带有更多的负电荷，增加了焦炭边缘活性位点的反应活性，决速步的能垒降低，整个反应的放...     

C—N键催化氢解反应研究进展

叙述了非杂环类含氮化合物和杂环类含氮化合物C—N氢解反应常用催化剂,讨论了苄基型含氮化合物的底物结构、催化剂及反应条件对C—N氢解反应的影响,初步探讨了C—N键催化氢解反应机理。认为C—N键的催化氢解反应不仅与含氮化合物的分子结构有关,还与催化剂的性能有关,若要从根本上提高C—N键氢解活性还需深入对反应机理的研究。     

循环流化床燃烧条件下焦炭表面NO_x还原机理研究进展

为使CFB锅炉达到NO_x原始超低排放,需要更加深入地理解煤炭燃烧过程中NO_x生成和还原机理,其中焦炭对NO_x的还原(NO_x-char反应)被认为是CFB含氮反应体系中最重要的环节之一.综述了文献中对NO_x-char反应的研究结果 ,围绕基本反应过程、焦炭中矿物杂质作用和影响因素三个部分,较为全面地阐述了焦炭表面NO_x还原过程.研究表明,碳原子除可直接作为还原反应物外,还可为CO,H_2,NH_3等还原性气体提供吸附表面从而间接还原NO_x,同时焦炭中的K,Fe,Ca等具有催化活性的矿物杂质能明显促进NO_x-char反应.多种还原作用共同存在使得NO_x-char反应的影响因素众多,包括煤种、热解条件、反应温度、焦炭粒径、碳燃尽率、CO/O_2/H_2O/SO_2等环境气体、焦炭中矿物杂质含量和化学组成等.另外,很多情况下这些因素并非独立作用,而是相互影响,且常在不同条件下对NO_x还原表现出"促进-抑制"两重性质.未来还需更加深入地研究焦炭表面NO_x反应体系,特别是定量描述不同影响因素的作用,建立CFB全炉膛NO_x排放模型,从而为深度挖掘循环流化床技术的低氮燃烧潜力奠定理论基础.     

BP型抑制剂抑制焦炭劣化反应动力学

为促进抑制焦炭劣化技术进步,用热重分析法测得不同温度下BP型抑制剂的抑制焦炭劣化反应动力学实验数据,用未反应核收缩模型对所得数据进行拟合,建立了基于BP型抑制剂的抑制焦炭劣化反应动力学模型,确定了模型参数。统计检验表明模型是显著和可信的。根据Arrhenius方程得到BP型抑制剂抑制焦炭劣化反应活化能Ea=285.0kJ·mol-1和有效扩散活化能ED=164.6 kJ·mol-1,均高于未添加抑制剂的空白焦炭试样S0的劣化反应活化能Ea=142.0kJ·mol-1和有效扩散活化能ED=96.3 kJ·mol-1。依模型算得的抑制焦炭劣化反应过程中的外扩散传质相对阻力ηG/∑η、内扩散传质相对阻力ηD/∑η和界面化学反应相对阻力ηC/∑η数据表明,试样S0的反应主要受界面化学反应和外扩散影响,而试样SBP因负载抑制剂,其反应主要受内扩散和界面反应影响。随着反应的进行,两者的劣化反应受内扩散、界面化学反应同时影响。在较低温度下,焦炭劣化反应主要受界面化学反应控制,随反应温度升高,界面化学反应的相对阻力ηC/∑η逐渐下降。     

煤基含氮合成气一步法制二甲醚工艺的模拟与优化

利用Aspen Plus化工流程模拟软件对煤基含氮合成气一步法合成二甲醚的工艺进行了模拟与优化,结合二甲醚合成的反应动力学方程选择了平推流反应器模型,探讨了反应压力、反应温度对二甲醚产量、CO转化率和产物分布的影响,并通过灵敏度分析对其进行了优化。研究了精馏塔的回流比、理论板数和进料位置等因素对二甲醚吸收和精馏过程的效果和能耗影响,得到了高纯度、低能耗二甲醚生产的最优操作条件。     

焦炭预存量数控模型的研发与应用

分析了干熄焦生产中与焦炭预存量有关的因素,建立了干熄炉内焦炭预存量的数控模型。利用迭代优化策略,使系统不断对公式进行计算、优化和迭代补偿,从而使模型失配、时变、干扰等引起的不确定性及时得到弥补,有效防止了红焦外溢和炽热红焦排出损坏设备等重大事故的发生。     

焦油渣对焦炭微观结构及反应动力学的影响

对一种工业废焦油渣的基本性质、结构组成及热稳定性进行了分析,并添加该种废焦油渣于配煤中,使用实验焦炉进行了炼焦实验.应用SCHERRER′S公式研究了焦炭微晶结构的变化,并探讨了添加焦油渣对焦炭微孔结构及碳溶反应动力学的影响.结果表明,添加焦油渣促进了焦炭微晶结构的生长,焦炭微晶结构的网状平面尺寸(La)及堆垛高度(Lc)明显增加,层间距d002减少.碳原子更加容易进行重排并向石墨结构进行转变,焦炭石墨化度增加.添加焦油渣的焦炭微孔结构发生了变化,孔径更细,表面积增加,孔体积下降.就焦炭的碳溶反应而言,焦炭的反应性和反应动力学变化不明显.     

基于区间模糊规划方法的炼焦配煤优化模型

在合理利用自然资源和保护环境的前提下,将两种及以上单种煤以合适比例均匀配合,可使各种煤之间取长补短,从而以最小经济成本得到符合技术性能要求的焦炭.然而受实际条件限制,单种原料煤的煤质和煤量等参数是变化的,优化配煤必须科学处理此类情况.建立了一种基于区间模糊规划的炼焦配煤优化模型,并应用到案例研究中.结果表明,以成本最小化为目标,基于区间模糊规划的炼焦配煤优化模型可以得到最优解,模型结果可为焦炭行业配煤技术人员提供参考.     

面向反应再生过程的量子粒子群多目标优化

针对催化裂化反应再生过程难以有效解决提升效率、降低损耗、减少排放的多目标优化问题,利用改进的多目标量子粒子群算法进行求解。建立轻油收率、焦炭产率和硫化物排量的多目标优化模型;引入拥挤熵排序更新外部档案,精确估计非支配解集分布性;构造自适应因子以动态调整吸引子,平衡算法的收敛性和多样性;再引入高斯变异进行分段式扰动,增强算法的局部搜索精度,最后求解该优化模型。对某厂催化裂化进行实验,得到轻质油吸收率76.22%,焦炭产率5.72%和硫化物排放量626 mg/m~3的结果,均优于其他比较算法,表明改进后的算法可以快速、准确地获得分布均匀的Pareto最优解,能有效解决反应再生过程多目标优化问题。     

介孔二氧化钛固载γ-谷氨酰转肽酶的制备及性质

γ-谷氨酰转肽酶（GGT）在临床诊断和生物催化方面具有重要的应用价值。本文以介孔氧化钛晶须为载体进行GGT的固定化,考察了载体结构特性、吸附时间和给酶量对固定化效果的影响,并对固定化酶的催化特性及其稳定性进行了研究。结果显示,以最可几孔径为30 nm的介孔TiO₂为载体,载体载酶量可达5.07mg·g^-1。在给酶量为18.99 U·g^-1时,经室温吸附2.5 h,固定化酶活性回收率可达73.05%。固定化酶的pH稳定性和热稳定性均显著优于游离酶,在4℃下保温贮藏60 d、转化22个批次后,固定化酶活力仍可保持初始值的71.30%。经测定,游离酶和固定化酶的米氏常数K_m分别为0.79 mmol·L^-1和1.05 mmol·L^-1,酰基化反应活化能分别为13.59 kJ·mol^-1和15.42 kJ·mol^-1;固定化GGT的失活反应活化能E_d为92.80 kJ·mol-1,相比于游离酶（49.61 kJ·mol^-1）有明显的增加。     

Adsorbed species and reaction rates for NO-CO-O2 over Rh(111)

We have studied the NO-CO-O₂ reaction over a Rh(111) catalyst by monitoring the reaction products (CO₂, N₂O, and N₂) and the infrared (IR) intensity of surface CO and NO at various partial pressures of NO, CO and O₂, and sample temperatures. The selectivity for N₂O formation, apparent activation energy for product formation, and NO consumption rate during NO-CO-O₂ are identical to those measured during the NO-CO reaction. The IR measurements show that during NO-CO-O₂ the same two adsorbed species, NO at 1640 cm^-1 and linear CO at ~2040 cm^-1, are present in the same surface concentrations as during NO-CO. For this reason the NO-CO-O₂ kinetics are dominated by the NO-CO kinetics, the NO consumption is rate limited by dissociation of adsorbed NO, and the N₂O selectivity is dominated by surface NO coverage. In contrast, O₂ consumption is adsorption rate limited with the NO-CO adsorption-desorption equilibrium controlling the vacant sites required to dissociatively adsorb O₂. These kinetic and IR data of the CO-NO-O₂ reaction and our interpretation of them agree with previous studies over supported Rh catalysts and thus confirm the previously proposed explanation. From RAIRS and kinetic data we estimate the rate constant for the CO+O→CO₂ elementary step. The pre-exponential factor for this rate is 2×10¹⁰ s^-1, a factor of 50 smaller than previous estimates. This rate constant is important to the NO-CO-O₂ kinetics because it affects O coverage, which, under certain conditions, inhibits NO consumption. This revised version was published online in July 2006 with corrections to the Cover Date.     

氧化铁石墨固相还原非等温反应动力学

准确测试固固反应,如铁矿炭还原反应的动力学在科学研究和实际应用中均具有重要意义。利用热重程序升温的方法研究了氧化铁石墨还原的固固反应特性,在惰性气氛下分别考察了研磨与浸渍混合后焙烧制得的Fe₂O₃/C样品的失重曲线,采用Flynn-Wall-Ozawa公式和Coats-Redfern公式相结合的方法分别求算了两种混合样品的固固反应动力学参数,研究发现氧化铁在炭表面的聚集形态与其活化能变化规律直接相关,且浸渍焙烧法所得样品的活化能符合强吸热反应活化能变化规律。结合固体原位XRD表征与气体产物在线分析手段,发现在初始阶段Fe₂O₃即可与C直接反应生成Fe₃O₄和CO₂。该反应的活化能约为530 kJ·mol^-1,反应机理为二级化学反应模型。     

MnOx-WO3/TiO2NH3选择性还原NOx的催化性能与动力学

研究了Mn-W/TiO2用于NH3选择性催化还原NOx体系的催化反应性能,在很宽的温度范围和各种气体条件下,该催化剂显示了较高的催化活性.在GHSV 18900 h-1、100～350℃条件下,NOx转化率高达80.3%～99.6%,Nz选择性达98.7%～100%;当反应气体中有0.01%SO2(分压比,下同)和6%...     

烷基吗啉在氯化钠和氯化钾表面的吸附

采用密度泛函理论(DFT)的PW91方法,研究了十二烷基吗啉(DMP)分子在带缺陷的NaCl(100)和KCl(100)上的吸附情况.缺陷引入后晶体表面离子电荷发生较大变化,使得NaCl(100)表现出正电性,而KCl(100)则表现出负电性.DMP在NaCl(100)的Na顶位发生吸附,吸附能约为-157.00 kJ...     

Kinetic relationship between NO/N2O reduction and O2 consumption during flue-gas recycling coal combustion in a bubbling fluidized-bed

Flue-gas recycling combustion of a sub-bituminous coal and its rapid pyrolysis char at 1120 K has been simulated experimentally in a bubbling fluidized-bed. O₂, CO₂ and H₂O, and NO or N₂O were pre-mixed and fed into the bed together with coal/char particles with the O₂ concentration in the exit gas maintained at 3.5 vol%. Increasing the inlet O₂ concentration, thus increasing the O₂ consumption rate and decreasing the flue-gas recycling ratio, caused the once-through conversion of fuel-bound nitrogen into N₂O to decrease while the conversion to NO to remain unchanged. The in-bed reductions of NO and N₂O were both first order with respect to the respective nitrogen oxide, with the rate constants to increase linearly with the rate of O₂ consumption in the bed and thus also with that of char/volatiles consumption. This finding, which indicated linear increase in the concentrations of reactive species involved in NO/N₂O reduction with the rate of O₂ consumption, enabled consideration that the homogeneous and heterogeneous reduction rates of NO and N₂O were proportional to the consumption rates of O₂ by the volatiles and char, respectively. The rate analysis of the kinetic data revealed the relative importance of burning volatiles and char as the agents for the reduction of NO and N₂O. While the reduction in the gas phase was fully responsible for the NO-to-N₂O conversion, the reactions over the char surface governed the NO-to-N₂ reduction. The volatiles and char had comparable contributions to the reduction of N₂O to N₂. The NO-to-N₂ and N₂O-to-N₂ reductions over the char surface were, respectively, accelerated and decelerated by increasing the H₂O concentration.     

Interactions of CO and NO with the perovskite-type oxide larho3

Some aspects of the interactions of CO and NO with LaRhO₃ have been studied. The reduction of this oxide with CO occurs where the contracting sphere model is of perovskite structure stable up to a concentration of anion vacancies of ca. 2e^? per molecule. By reduction of LaRhO₃ at 817 K, rhodium was obtained, highly dispersed on a matrix of La₂O_3. After a reduction-oxidation cycle at 871 K the particle size of the perovskite decreased drastically. The activation energy of the reduction (67 kJ mol^?1) was significantly lower than that of other LaMO₃ oxides of group-VIII metals. Coverages of CO(θ_CO) and NO(θ_NO) at room temperature were lower than 3%, θ_NO being substantially higher than θ_CO. The reversibly adsorbed fractions of CO and NO underwent a remarkable decrease after preadsorbing NO and CO, respectively. This competitive adsorption is assumed to be associated with the adsorption of CO and NO on metallic sites. NO preadsorption inhibited the total adsorption of CO more severely than the reverse, indicating that NO is bound more strongly than CO to the LaRhO₃ surface.     

Heterogeneous reduction of nitric oxide on synthetic coal chars

Model compounds, with a controlled heteroatoms content and well-defined functionalities, were used to study the release of nitrogen compounds from char combustion. In the present work, the mechanisms involved in NO-char heterogeneous reduction were studied with a synthetic coal (SC) char as carbon source. Another synthetic char (SN) without any nitrogen in its composition was also employed in these studies. Temperature programmed reduction (TPR) tests with a gas mixture of 400 ppm NO in argon and with isotopically labelled nitric oxide, ¹⁵NO (500 ppm ¹⁵NO in argon), were carried out. The gases produced were quantitatively determined by means of MS and FTIR analysers.Under the conditions of this work the main products of the NO-C reaction were found to be N₂ and CO₂. The main path of reaction involves the formation of surface nitrogen compounds that afterwards react with nitrogen from the reactive gas to form N₂. It was observed that fuel-N also participates in the overall heterogeneous reduction reaction, although to a lesser extent.     

A Study of the Activated Decomposition of CO2 on the Cu Component of a Cu/ZnO/Al2O3 Catalyst

The decomposition of CO₂ over the Cu component of two ZnO/Al₂O₃ supported Cu catalysts, having different Cu areas, has been studied over the temperature range 393–513 K. The time dependence of the evolution of CO from a CO₂/He stream (10% CO₂, 101 kPa) which was dosed continuously over the catalyst showed two peak maxima, the first of which moved to shorter times on raising the temperature. The activation energy for the decomposition of CO₂ on the ZnO/Al₂O₃ supported polycrystalline copper was obtained from a plot of the logarithm of the time to the peak maximum of the first peak against the reciprocal of the dosing temperature. The value so obtained was 83±10 kJ mol^-1 (catalyst A) and 86±10 kJ mol^-1 (catalyst B) for fresh catalysts reduced in H₂ at 513 K. This value fell to 49 ±4 kJ mol^-1 (catalyst A) and 55±5 kJ mol^-1 (catalyst B) after CO reduction at 473 K of the Cu which had been oxidised by the decomposition of the CO₂. This lowering of the activation energy for the second CO₂ decomposition is considered to be due to the original morphology of the Cu not being restored by reduction in CO after the oxygen-driven reconstruction of the Cu deriving from the decomposition of the CO₂.     

Nitric oxide emissions and temperature evolution during the char grate‐fired process

Understanding the char grate‐fired process is key to developing a low‐nitric oxide (NO) technology for industrial boilers. In this work, char combustion and NO emissions during a grate‐fired process were studied in a small‐scale one‐dimensional fixed‐bed system by adjusting the char/oxygen (O₂) ratio. Evolution of the surface temperature of the char bed was measured using an infrared temperature measurement system. As the char/O₂ ratio increased, a reaction layering of the char bed occurred. The char bed can be divided into oxygen‐absent and ‐present parts in time, and into reduction and oxidation layers in space. This kind of division was determined by the complete oxidation layer that could deplete all O₂. The reduction layer could reduce NO emissions well. With the increase of the char/O₂ ratio, the char mass proportion of the oxygen‐absent part increased, while that of the oxygen‐present decreased; and the NO emissions and conversion rate of char nitrogen decreased. When combustion began, char started to burn and released a large amount of heat, and the surface temperatures of both the oxidation and reduction layers increased, with a larger rise of the former of about 260 °C. As the reaction proceeded, the surface temperature of the oxidation layer gradually decreased, while that of the reduction layer increased until the char bed was burnt through.