O2/CO2气氛下木醋调质石灰石直接硫化反应动力学研究

采用热分析法研究了O₂/CO₂气氛下石灰石及木醋调质石灰石的直接硫化反应过程。结果表明,在实验温度1 023~1 173 K,经木醋废液调质的石灰石直接硫化钙转化率显著提高。在1 173 K时,木醋调质石灰石直接硫化反应50 min后钙转化率可达89.55%。木醋调质石灰石的主要成分为水合醋酸钙,调质使石灰石的结构更为疏松,有利于硫化反应的进行。采用缩核模型对反应过程进行了表征,得到石灰石及木醋调质石灰石直接硫化反应速率常数k_s和扩散系数D_eff的Arrhenius表达式。动力学计算结果表明,相比于石灰石,扩散对木醋调质石灰石直接硫化反应过程的影响较小,说明木醋调质石灰石直接硫化反应性能显著提升的原因为硫化反应扩散阻力的减小。     

用于流化床燃烧脱硫的石灰石的反应活性评价和测试研究

对用于燃煤流化床燃烧脱硫的脱硫剂石灰石的反应活性进行了研究，提出了易于进行数学处理的石灰石硫盐化模型，得出了评价石灰石反应活性的两个指标－最大转化率和反应速率常数。研究方法除采用了传统的热天平法和鼓泡流化床外，还根据循环流化床燃烧技术的特点，发展了提出了湍流床法和石英棉法，并进行了不同试验条件下的实验研究，对不同反应活性温度技术进行了试验比较。     

石灰石的孔隙结构特性及对固氟反应的影响

用三种石灰石为研究对象，应用高温管式炉、扫描电子显微镜和压汞仪对样品进行了一系列宏观与微观的对比实验，探讨了石灰石的孔隙结构特性及对固氟反应的影响。结果表明，通过扩大比表面积、增加孔隙率和减小粒径等途径可以改善石灰石的孔隙结构特性，提高钙基固氟剂高温下的利用率。     

O2/CO2气氛下石灰石煅烧与硫化反应研究

富氧燃烧技术是一种能够综合控制燃煤污染物排放的新型洁净燃烧技术。本文对O2/CO2气氛下煤燃烧流化床条件下的石灰石煅烧分解特性进行了热力学分析，并与热重试验结果进行了对比，得出石灰石的起始分解温度随O2/CO2气氛中CO2分压比的增大而增加，但增幅减小。结合小型流化床试验装置上煅烧与硫化反应过程中的石灰石样品的孔结构特性和可视化SEM分析，得出空气气氛和O2/CO2＝20/80气氛在煅烧与硫化反应过程中的孔结构特性差异很大：反应温度为1 123 K时，空气气氛下石灰石迅速分解，比表面积、孔隙率增大，硫化反应发生后孔堵塞导致比表面积、孔隙率减小；1 123 K的煅烧温度还不足以使O2/CO2＝20/80气氛下的石灰石分解，硫化反应过程中还伴随着石灰石的煅烧分解。     

添加剂对煤气化过程中石灰石固硫行为的影响

为了研究添加剂在石灰石固硫过程中的作用，选择了一系列添加剂对含不同氧化镁的二种石灰石进行改性，采用ＸＲＤ、ＸＰＳ及ＤＴＡＴＧ技术，研究了石灰石改性前后及煤气化过程中固硫反应前后钙基固硫剂的结构、表面组成及热性能，并与固硫特性相关联。实验得出：无机氯化物及一系列钠盐对石灰石的固硫能力具有不同程度的影响，其中氯化钠的促进作用最明显，其添加量有一最佳值；氯化镁及氢氧化钠具有负作用。添加剂通过影响石灰石的热分解性能及其气化残物的表面组成而起作用，对石灰石的结构影响较小。     

石灰石/石膏法烟气脱氟反应的动力学研究

对石灰石/石膏湿法烟气脱氟反应过程进行了描述,建立了基于双膜理论的CaCO3 HF反应动力学模型,并对模型进行了计算和分析,考察了反应温度、反应时间、HF气相分压、Ca/F摩尔比等因素对反应的影响。结果表明,CaCO3颗粒的转化率和脱氟率随着反应温度、反应时间、HF气相分压的增加而增加,Ca/F摩尔比对脱氟率有重要影响,双膜理论模型可较好地描述石灰石/石膏湿法脱氟反应的动力学行为。研究结果对于典型的湿法烟气脱硫技术的气态氟化物的脱除机理研究和为开发统一的燃煤污染物控制技术具有指导意义。     

吸收增强式甲烷水蒸气重整制氢循环反应模拟

吸收增强式甲烷水蒸气重整制氢反应可以生成高浓度的H2和较低浓度的CO、CO2。研究建立了考虑钙基吸收剂活性下降对吸收增强式甲烷水蒸气重整制氢过程影响的多次循环反应模型,在实验数据验证的基础上,计算了三种吸收剂活性下降特性对吸收增强式重整制氢过程的影响。结果表明,对于石灰石吸收剂,产生高纯H2的时间随循环次数的增加而急剧下降;白云石循环反应活性提高,产生高纯H2的时间随循环次数的增加而缓慢下降;CaO/Ca12Al14O33的循环使用次数明显大于石灰石和白云石。     

热重分析法研究贝壳固硫反应动力学

采用热分析法研究了贝壳和石灰石固硫反应过程, 用等效粒子模型对固硫反应过程进行了表征, 计算分析了其固硫反应动力学参数. 结果表明, 贝壳比石灰石含有较多的碱金属盐, 其作用是提高了贝壳固硫反应速率常数和有效扩散系数. 贝壳固硫反应中存在补偿效应. 根据等动力学温度判别固硫剂活性适用于不同反应控制区的活性判断. 碱金属成分对钙基固硫剂活性有正负两个方面的影响, 含量过大或过小都会削弱固硫剂活性, 因而存在最适含量. 在1 073～1 273 K温区固硫时, 钙基固硫剂中碱金属离子与钙离子摩尔比为1∶50左右时固硫活性较高.     

稀硫酸与石灰石反应的巧妙设计

在初中化学教科书中,探究二氧化碳的实验室制法时,选用了稀盐酸与石灰石反应,但制得的二氧化碳气体中含有部分氯化氢气体,导致部分性质实验难以完成。     

燃煤过程中CaO对氟析出的固定作用

通过XRD和热力学分析探讨了煤燃烧过程中CaO燃烧固氟反应与反应平衡过程。固定床燃烧试验表明 :在燃烧温度 1173K时 ,CaO对煤中氟析出的抑制范围在 13 6 1W %～ 80 4 4W % ,平均为 4 7 5 3W %。d 15 0mm×10 0 0mm流化床燃烧试验表明 :流化床燃烧时 ,CaO对煤中氟析出的固定作用比固定床燃烧效果明显 ,石灰石的添加量和粒度对固氟效果有显著的影响。对于本试验 ,0 2mm～ 1 0mm粒度的石灰石固氟效果最佳 ,在Ca F =6 0～ 70时 ,脱氟率可达到 6 6 7W %～ 70 0W %。在燃煤过程中添加CaO或石灰石具有固氟固硫的双重作用。     

A model for the absorption of sulphur dioxide into a limestone slurry

A model has been developed for the removal of sulphur dioxide from flue gas by absorption into a limestone slurry. The flue gas desulphurization unit consists of an absorber tower and an oxidation tank. Flue gas enters the absorption tower at the bottom and meets the limestone slurry. There are five important chemical reactions with a finite rate. The rate-limiting reactions are limestone dissolution, calcium sulphite precipitation and dissolution, gypsum precipitation, sulphur dioxide absorption and sulphite oxidation in the slurry. The model also accounts for the presence of chloride ions, magnesium ions and organic acids in the limestone slurry. The absorption rates of sulphur dioxide and carbon dioxide in the tower are calculated according to the two-film model. A non-uniform set of limestone particles is also included in the model. The model was tested against literature data and the agreement between the data and the model was satisfactory. A sensitivity analysis of the desulphurization process was carried out, the inputs to the model were changed and the results from the calculations were compared with the expected results. The response to the change in the inputs agreed well with the expected results.     

Thermal analysis of fluidised bed combustion residues containing limestone scavenger

A method has been developed using thermoanalytical techniques for the analysis of residues from coal-burning fluidised bed plant where limestone is used as a sulphur scavenger. This completely eliminates the need for lengthy wet chemical analyses and allows the derivation of parameters necessary for efficient plant operation, such as limestone addition rate, calcium utilisation efficiency and calcium to sulphur mole ratio. The method also gives values for the unburned carbon content and the ratio of coal ash to limestone derivatives in the sample.     

流化床煤气化炉内脱硫的研究Ⅰ．台式流化床煤气化的炉内脱硫试验

采用台式流化床煤气化装置，研究了影响炉内脱硫效率的因素。炉内脱硫对高硫煤特别有效，脱硫效率可达９０％以上。所采用的二种石灰石和一种白云石脱硫效率相近，按Ｃａ／Ｓ比比较则白云石稍好些。虽然脱硫效率随Ｃａ／Ｓ比增加而增加，但当Ｃａ／Ｓ比达到３后几乎不再增加。存在一个最佳脱硫操作温度。在非焙烧区，脱硫率随压力增加而下降，而在焙烧区脱硫率和压力几乎无关。测定了脱硫剂脱硫前后的孔容积分布，发现脱硫之后１～３０ｎｍ的孔容显著减少。     

SO2 retention by highly cycled modified CaO-based sorbent in calcium looping process

The limestone modified by pyroligneous acid has been proved to have good CO₂ capture behavior in the calcium looping process. In this work, SO₂ retention of the highly cycled modified limestone in the carbonation/calcination cycles was investigated in a thermogravimetric analyzer (TG). The cyclic carbonation/calcination of the modified limestone was performed in a dual fixed-bed reactor and then the cycled modified limestone was sent for sulfation in TG. The effects of sulfation temperature, cycle number, and prolonged carbonation on SO₂ retention of the cycled modified limestone were discussed. The optimum temperature for sulfation of the cycled modified limestone should be in the range of 900–950 °C. The effect of sulfation temperature on SO₂ retention of the modified limestone drops with increasing cycle number. With increasing cycle number from 20 to 100, the sulfation conversion of the cycled modified limestone is stable and can reach ~0.4. The cycled modified limestone exhibits obviously higher SO₂ retention than the cycled raw one for the same number of cycles. The prolonged carbonation increases SO₂ retention of the modified limestone and the raw one after the subsequent cycles. The sulfation conversions of the modified limestone and the raw one at 118 min after 9-h carbonation in the 20th cycle increase 43 and 56 %, respectively. The cycled modified limestone shows a greater SO₂ retention than the cycled raw one after the same prolonged carbonation treatment. The prolonged carbonation increases the pores in 5–20 nm range which is considered the optimum pore size for sulfation of CaO-based sorbent, so it results in an improvement in SO₂ retention of the cycled sorbents.     

Thermogravimetric analysis of sulfation kinetics of calcined limestones or dolomites

Experiments have been conducted with a thermogravimetric analyzer for sulfation of various calcined limestone or dolomite sorbents under reaction conditions similar to those in a fluidized bed coal combustor. The volume reaction model has been utilized to account for the heterogeneous sulfation reaction of calcined limestone or dolomite. Effects of particle size and SO₂ concentration on the extent of sulfation have been analyzed on the basis of the model. Also numerical simulation has been made of the effect of wearing off the particle outer surface during sulfation. The applicability of the model has been verified with experimental data for the sulfation reaction obtained in this study and other data available in the literature.     

Effect of acid on morphology of calcite during acid enhanced defluoridation

Fluoride removal from water by lime materials is a promising defluoridation process. Acid enhanced limestone defluoridation (AELD) technique involves precipitation of CaF₂ as well as adsorption of fluoride on the surface of limestone which is capable of reducing fluoride concentration to below the WHO guideline value of 1.5 mg/L. Acids such as acetic acid and citric acid are added to the fluoride water before filtration through limestone column to enhance the Ca²⁺ activity in solution for precipitation of fluoride as CaF₂. This paper describes the effects of these acids on the quality of the limestone during the AELD process, which has been studied to evaluate the reusability of the limestone. The reaction products that formed during the AELD process have also been analyzed. The detail study of the morphology of the limestone before and after use have been done using various analytical techniques, viz., X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy combined with energy dispersive X-ray spectroscopy. The study reveals that the limestone degrades to some extent in the process due to dissolution of calcium carbonate by the acids and adsorption of fluoride by the limestone. While appreciable quantity of the citrate salt of calcium was formed in the column, the acetate salt mostly remained dissolved in the water. Since mainly the surface of the limestone particles take part in the reaction, the limestone particles can be reused for the defluoridation process after cleaning the outer surface. The limestone after use remains also suitable as raw material for cement.     

Experimental studies using a single pellet high temperature diffusion cell reactor

It is very important to know the effective diffusivities of reactant gases through the porous solid matrices for a diffusion limited reaction. The single pellet high temperature diffusion cell reactor is used to measure the effective diffusivities of argon and nitrogen during the sequence of calcination, sintering, salt addition and sulfation of Greer limestone. This system can be used to study and gas—solid reaction systems where the solid phase undergoes changes between 25 and 1200°C.     

Sulfation behavior of white mud from paper manufacture as SO<Subscript>2</Subscript> sorbent at fluidized bed combustion temperatures

The calcination characteristics, sulfation conversion, and sulfation kinetics of a white mud from paper manufacture at fluidized bed combustion temperatures were investigated in a thermogravimetric analyzer. Also, the comparison between the white mud and the limestone in sulfation behavior and microstructure was made. Although the white mud and the limestone both contain lots of CaCO₃, they are different in the alkali metal ions content and microstructure. It results in a marked difference in sulfation behavior between the white mud and the limestone. The CaO derived from white mud achieves the maximum sulfation conversion of 83% at about 940 °C which is 1.7 times higher than that derived from limestone at about 880 °C. The shrinking unreacted core model is appropriate to analyze the sulfation kinetics of the white mud. The chemical reaction activation energy E _a and the activation energy for product layer diffusion E _p for the sulfation of the white mud are 44.94 and 55.61 kJ mol⁻¹, respectively. E _p for the limestone is 2.8 times greater than that for the white mud. The calcined white mud possesses higher surface area than the calcined limestone. Moreover, the calcined white mud has more abundant pores in 4–24 nm range which is almost optimum pore size for sulfation. It indicates that the microstructure of the white mud is beneficial for SO₂ removal.     

Synthesis of isoamyl acetate usin NaX and NaY zeolites as catalysts

A liquid phase esterification reaction between glacial acetic acid and isoamyl alcohol has been studied using NaX and NaY zeolites as catalysts. The influence of calcination temperature, the amount of catalysts, reaction temperature, time of esterification and the molar ratio of the reactants has been investigated. Water insoluble products have been isolated from the reaction mixture and analyzed for the ester. Both NaX and NaY are found to be active as catalysts in the reaction. However, their catalytic activity varies with the reaction conditions and their calcination temperature. The reaction has been found to be 100% selective to ester formation. Catalytic activity of the zeolites has been correlated with their surface acidity.