气化炉液池内单个高温气泡传热、传质的数值模拟

建立了气、液间传热传质数学模型,对单个热气泡在上升过程中与处于蒸发阶段的水之间的传热、传质规律进行了数值研究,获得了气泡半径、气泡温度、水蒸发速率以及蒸发量随时间的变化规律.研究表明:在水恒温蒸发阶段,由于传热传质的共同作用,气泡半径随着气泡的上升而变小,并逐渐趋于稳定;随着气、液间温度差的增大,气泡半径缩小得越快;在气泡与水开始接触时,水的蒸发速率及气泡内的水蒸汽增量最大;气泡温度在较短时间内急剧下降,并趋于稳定;随着气泡半径的缩小,气泡冷却速率提高;但随着接触时间的继续增加,对气体的冷却效果却无明显作用.     

低水胶比大掺量多元复合胶凝体系水化特性研究

为了研究低水胶比条件下多元复合胶凝材料的水化反应规律及影响因素,设置梯度结构低水胶比,采用等温量热法、化学结合水量法,分别研究水胶比和矿物掺合料掺量对水泥-矿渣-粉煤灰三元复合胶凝体系水化放热、水化程度的影响。结果表明,与较高水胶比体系不同,水胶比为0.20～0.30时,降低水胶比均会增大样品的最大放热速率;水胶比为0.25、0.30时,复掺矿渣-粉煤灰会延长加速期持续时间,复掺40%时加速期持续时间最长,且体系第二放热峰出现的时间也有所延迟,但进一步降低水胶比至0.20,复掺矿渣-粉煤灰则会使第二放热峰出现时间略有提前,加速期持续时间随复掺量的增加而缩短;水胶比为0.20、0.30时,复掺掺量为30%的复合体系反应程度最大,水胶比为0.25时,复掺掺量为40%的复合体系反应程度最大,且低水胶比条件下硬化浆体的反应程度与水胶比几乎呈线性关系。     

中温条件下铝镁锂合金与水反应的动态过程

铝水反应是铝作为新能源的一种主要利用方式。为了探究熔融态下铝水反应的动态传递规律,利用自制的反应器,研究了中温条件下铝镁锂合金与水蒸气反应的动态过程,并对反应器内部的温度、压力、氢产率进行了实时监测。实验结果表明:启动温度为500℃时,通入水蒸气后,反应器内部温度迅速升高,最高温度为791℃;金属反应区的截面温度分布差异较大,存在局部的核心高温区;随着反应的进行,核心高温区自进水口处向外向下传递,传递速率约为0.33 mm/s,该速率主要是由水蒸气扩散速率和热传递速率共同决定的。     

大体积混凝土低热水泥与普通水泥基胶凝材料热学及力学性能对比研究

胶凝材料水化热是造成大体积混凝土温度裂缝的主因,工程中多采用低热水泥或掺加矿物掺合料的普通水泥基胶凝材料降低水化热,目前关于二者水化热降低机制及力学、热学综合性能的对比研究较少。系统测定不同粉煤灰、矿渣掺量下低热水泥和普通水泥基胶凝体系的水化热和抗压强度,对比分析二者在3、7d水化热条件下的热学、力学性能发展规律,建立热学、力学综合性能等值线图,为大体积混凝土胶凝材料选择提供参考。研究表明,在相同3、7d水化热条件下,掺加掺合料的普通水泥基胶凝材料早期水化热及放热速率低于纯低热水泥,适用于对早期强度要求较高的工民建大体积混凝土;低热水泥最终水化热低,后期强度增长率大,适用于设计龄期较长的水工大体积混凝土;根据温度控制或强度要求,通过综合性能等值线图,可直接确定水泥基胶凝材料的力学、热学最优性能及其组成,为大体积混凝土胶凝材料选择提供参考。     

Optimal analysis of the exothermic process of a Mg/MgH2 thermochemical heat storage system

基于镁/氢化镁热化学储热系统,建立了二维非稳态数学模型.对吸氢放热过程中的传热传质现象进行了数值模拟,主要研究了壁面温度和反应床当量导热系数对系统反应速率的影响.结果表明,放热过程中存在最佳的壁面温度使反应速率达到最快,过高或者过低的壁面温度都将使反应床的温度偏离理论上的最佳值,从而降低反应速率.针对不同当量导热系数的反应床,最佳壁面温度也不相同;反应床的当量导热系数并非越大越好,应该根据具体的边界温度以及氢气压力情况进行合理的选择以获得最佳的反应速率.     

柴油燃烧颗粒碰撞凝并过程

以柴油机后燃期颗粒的初期碰撞凝并过程为研究对象,在KF模型基础上,通过结合矩方法和颗粒尺寸分布模型,建立了柴油机颗粒碰撞凝并数学模型.探讨了柴油机燃烧过程中,自由分子区中的初级颗粒碰撞频率、凝并速率和剩余表面积的变化规律以及对颗粒尺寸生长的影响作用.结果表明:随着滞留时间增长,初级颗粒的碰撞频率逐渐降低;颗粒粒径分散性的增加能够提高碰撞频率;在同一粒径下,随着凝并特征时间增加,凝并速率明显降低;当粒径小于12.6,nm时,凝并速率对凝并特征时间变化的敏感性较高;初始凝并特征时间越大,表面积减小越慢;颗粒表面积随着滞留时间的增加而减小.     

富钙生物油的脱硫性能研究

利用自制热重装置分别考察了富钙生物油与传统钙基脱硫剂的性能和温度、CO2,SO2浓度对富钙生物油煅烧产物脱硫性能的影响。试验结果表明,富钙生物油的脱硫速率优于氢氧化钙和乙酸钙。在SO2体积分数低于0.4%时,富钙生物油的脱硫速率在整个脱硫过程中变化很小,由此推断在脱硫过程中其表面以及孔道不会被CaSO4堵塞,整个反应受SO2在其表面的扩散控制。温度对富钙生物油的脱硫性能影响显著,经900℃煅烧,富钙生物油生成的煅烧产物CaCO3/CaO在800～850℃条件下获得最大脱硫速率;CO2的浓度对其脱硫速率无显著影响。烟气中SO2体积分数高于0.4%时,提高SO2浓度会导致富钙生物油脱硫速率增加值显著下降。     

钒基SCR催化剂动态反应及氨存储特性的试验研究

试验研究了温度和空速对催化还原反应速率、NOx转化效率、氨存储、氨泄漏的影响,分析了氨存储释放过程以及氨存储量与NOx转化效率的关系。试验结果表明:温度对催化还原反应速率的影响非常大,在20 000/h空速下400℃时的平均反应速率是200℃时的17倍;而空速对反应速率的影响很小,在同一温度下空速从20 000/h变化至50 000/h时,平均反应速率基本保持不变;但增大空速加快了氨泄漏,使得氨泄漏出现的时间提前,从而限制了NOx转化效率的进一步提高,温度对氨饱和存储量的影响比空速的影响大,在200℃和240℃时NOx转化效率基本与氨存储量呈线性关系,在大于320℃时氨存储量对NOx转化效率的影响较小。     

基于复合胶凝材料的CO2矿化养护实验研究

研究了粉煤灰-钢渣-水泥复合胶凝材料的水固比、原料配比、养护时间、CO2压力等因素对固碳率和抗压强度的影响.实验结果表明,采用50％钢渣与10％粉煤灰掺比的试件,在剩余水固比w/s=0.25时达到了最高的固碳率和抗压强度.当CO2养护压力由0.2 MPa上升到2 MPa时,固碳率提高了45％.XRD分析表明与自然养护对...     

铜基分子筛SCR催化剂活性及NH3存储特性

对比反应温度对大孔Cu/beta和新型小孔Cu/SSZ-13催化剂新鲜和老化样的平均反应速率、NO_x转化率、NH_3存储量和NH_3泄漏的影响;分析了NH_3存储、释放过程以及NH_3存储量与瞬时NO_x转化率的关系;研究了Cu/SSZ-13在空速为3×10~4h~(-1)和5×10~4h~(-1)下NH_3存储特性.结果表明:温度对催化还原反应速率影响显著,空速影响次之;温度升高,两种催化剂平均反应速率升高.两种Cu基催化剂显示出相似的NH_3存储、释放过程.随着温度升高或者空速增加,催化剂的饱和NH_3存储量变小、饱和NH_3存储时间变短;标称NO_x转化率随着温度的增加而增加,随着空速增加而降低.低温下瞬时NO_x转化率随着NH_3存储量的增加而增加;300℃时NH_3存储量对NO_x转化率影响减小.两种催化剂中Cu/SSZ-13对NH_3存储量依赖度更低,且水热稳定性能更优.     

Heat storing/releasing characteristics of a chemical heat storage unit of electricity using a Ca(OH)2/CaO reaction

The applicability of the Ca(OH)₂/CaO thermochemical reaction for heat storage derived from night-time electricity was studied. The heat releasing rate, heat output, and thermal efficiency were investigated experimentally by using a laboratory/scale heat storage unit incorporated with a fin-type heat exchanger. It was found that, during the heat-releasing step, when water vapor at an ambient temperature of around 300K was introduced into the reactor, the temperature of the CaO reactant bed was increased to around its equilibrium temperature of 610 K. The hydration heat was then recovered by the heat exchanger medium (city water) the temperature of which was rapidly increased to above 343 K. The amount of the heat recovered from the CaO packed bed was about four times higher than that which might be recovered if the energy storage was carried out by the latent heat of water of the same volume. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(6): 400–409, 1996     

Experimental study on pore distribution characters and convert rate of CaO

During the reaction between calcium sorbents and SO2, calcium sorbents are first calcined and converted into CaO. CaO can be obtained by calcining Ca(OH)2or CaCO3. The porosity of the sorbent is increased because of calcination and is decreased because of sulfurization. In the calcination process H2O or CO2 is escaped from the particles and pores are formed in particles. The reaction or convert rate of CaO is influenced strongly by the pore structure characters. From Ca(OH)2 to CaO the escape velocity of H2O or its mass transfer is one of the key factors influencing the pore forming. During calcination process different healing velocity, different heating time and temperature were suggested. The temperature rising rate and calcining temperature play important role to the pore structure. The convert rates of CaO obtained through different calcining conditions were investigated experimentally. Some interesting results were showed that the calcium utilization of CaO particles is determined not only by the special surface area and total pore volume, but also by pore-size distribution. The main factor influencing the sulfation is the pore diameter distribution at lower sulfation temperature. For higher reaction temperature specific volume is the important reason. But pore-size distribution is strongly influenced by heat flux and temperature in the calcining process.     

Heat recovery from a thermal energy storage based on the Ca(OH)2/CaO cycle

Thermal energy storage is very important in many applications related to the use of waste heat from industrial processes, renewable energies or from other sources. Thermochemical storage is very interesting for long-term storage as it can be carried out at room temperature with no energy losses.Dehydration/hydration cycle of Ca(OH)₂/CaO has been applied for thermal energy storage in two types of reactors. One of them was a prototype designed by the authors, and in the other type conventional laboratory glassware was used. Parameters such as specific heats, reaction rate and enthalpy, mass losses and heat release were monitored during cycles. Although in the hydration step water is normally added in vapour phase, liquid water, at 0 °C has been used in these experiences.Results indicated that the energy storage system performance showed no significant differences, when we compared several hydration/dehydration cycles. The selected chemical reaction did not exhibit a complete reversibility because complete Ca(OH)₂ dehydration, was not achieved. However the system could be used satisfactorily along 20 cycles at least. Heat recovery experiments showed general system behaviour during the hydration step in both types of reactors. The designed prototype was more efficient in this step.Main conclusions suggested carrying out one complete cycle at a higher dehydration temperature to recover total system reversibility. A modification of the prototype design trying to enhance heat transfer from the Ca(OH)₂ bed could also be proposed.     

CFB-FGD 工艺中Ca(OH)2颗粒悬浮液最大分散度的实验研究

CFB-FGD工艺中的CaO颗粒粒径偏大，CaO转化率比较低．降低CaO颗粒粒径的途径之一是优化脱硫剂制备工艺．为此，研究了用5种不同制备工艺得到的Ca(OH)2颗粒悬浮液和悬浮液中Ca(OH)2颗粒的算术平均粒径．实验结果表明，采用0．006mol／L的六偏磷酸钠溶液与CaO水合反应得到的Ca(OH)2颗粒悬浮液的分散度增加了6．62倍，Ca(OH)2颗粒的算术平均粒径降低到了1053nm．这是一种简单、有效、经济的脱硫剂制备工艺．     

Dynamic simulation of CaO/Ca(OH)2 chemical heat pump systems

Using energy and exergy analyses, a dynamic simulation is carried out with a CaO/Ca(OH)₂ chemical heat pump system for heating and cooling applications. The system consists of hydration/dehydration reactor connected to condenser/evaporator with a control valve in between. During the dehydration process, heat is supplied at 700 K for dehydration of Ca(OH)₂ and steam is condensed at 293 K. During evaporation/hydration process, heat is supplied at 290 K for evaporation of water at 273 K and heat of hydration is supplied to a load at 353 K. Duration of one cycle takes about 12 hours. Two subsystems are used to provide for heating/cooling demands in a continuous manner. Using synthetic demands of a residential dwelling, various performance parameters have been calculated for a 24 hour period. The results showed that CaO/Ca(OH)₂ chemical heat pump system could satisfy heating and cooling demands of a typical dwelling. Its energy and exergy efficiencies were 58.7% and 61.6% for heating and 12.7% and 4.5% for cooling respectively.     

不同煤种对混煤自固硫的影响

以平朔煤作为中硫煤,选用三个典型低硫煤与其进行不同比例掺配,并研究了煤种对混煤固硫效果的影响.结果表明：混煤固硫率的大小与（Ca＋Mg）/S摩尔比和灰中（CaO＋MgO）的含量有关;低、低（Ca＋Mg）/S摩尔比煤掺配后,混煤的（CaO＋MgO）利用率随（Ca＋Mg）/S摩尔比的增大呈整体下降趋势,降硫效果主要取决于配煤对硫分的稀释作用;低、高（Ca＋Mg）/S摩尔比煤掺配后,混煤的（CaO＋MgO）利用率在（Ca＋Mg）/S摩尔比为0.8～1时达到最大值,降硫效果取决于配煤对硫分的稀释作用和自身固硫作用.     

CaO和Fe（N03）3复合催化锦界煤焦-C02气化的实验研究

在搭建的固定床实验台上对CaO和Fe（NO3）3复合催化锦界煤焦-CO2常压等温气化的反应特性进行了研究．结果表明：复合催化剂最佳质量添加比例为1％Ca、29／6Fe,且在最佳添加量下气化时间比原煤焦和单组分催化剂下的气化时间分别缩短了103rain和18rain,催化强度系数分别是原煤焦、单组分催化剂CaO和Fe（N03）3的5．71倍、1．65倍和2．04倍,气化温度降低了100K,气化温度降低程度介于单组分催化剂CaO和Fe（NO3）3之间;复合催化过程生成的部分Ca（NO3）2与CaO的活性不同,即Ca的催化强度与其前驱物的形式有一定关系;添加单组分催化剂的煤焦活化能与原煤焦的活化能基本相同,不同添加比例的复合催化剂的煤焦活化能增加的程度不同,且在最佳添加比例下增加程度最小,其值为15．4％．     

Effect of CaO hydration and carbonation on the hydrogen production from sorption enhanced water gas shift reaction

Sorption enhanced water gas shift reaction (SEWGS) based on calcium looping is an emerging technology for hydrogen production and CO₂ capture. SEWGS involves mainly two reactions, the catalytic WGS reaction and the bulk carbonation of CaO with CO₂, and the solid product is CaCO₃, and the Ca(OH)₂ may be formed from the reaction of CaO with H₂O with the presence of steam in gas phase. The effect of Ca(OH)₂ and CaCO₃ on the catalytic WGS reaction and carbonation reaction was studied in a fluidized bed reactor. It was found that the hydrated sorbent and CaCO₃ did not show any catalytic reactivity toward WGS reaction at 400 °C. When the temperature was increased to 500 °C and 600 °C, the catalytic reactivity of hydrated sorbent was recovered partially, but this will depend on the steam fraction in gas phase, the recovery of fresh CaO surface from dehydration of Ca(OH)₂ may be the reason of catalytic reactivity recovery. CaCO₃ can catalyze the WGS reaction at the high-temperature (>600 °C), this may due to the CaCO₃ decomposition and recarbonation processes in which the CaO is transiently formed. The possible mechanism was discussed.     

Behavior of Ca(OH)2/CaO pellet under dehydration and hydration

With construction of a thermochemical energy conversion prototype system to store solar heat, thermal dissociation of pellets of Ca(OH)₂ and hydration of CaO have been investigated in some detail for its application to the system. The inorganic substance is very attractive as a material for long term heat storage, but molar density changes associated with the reaction are fairly large. Therefore, this factor has been taken into account in the kinetic equation. The importance of additives and pellet size has been discussed considering reactivity and strength of pellets. An analysis has been attempted when chemical reaction is important. The deformation of pellets was observed during hydration.     

Biodiesel production over lime. Catalytic contributions of bulk phases and surface Ca species formed during reaction

Lime is pointed out as an effective catalyst for biodiesel production by oil methanolysis. Several Ca phases are formed during reaction. Each Ca phase has different contribution to the catalyzed process.Using CaO as a catalyst, S shape kinetics curve was observed and the induction period can be ascribed to the Ca(OH)₂ formation. When Ca(OH)₂, prepared by contacting CaO with H₂O, is used as catalyst the initial period with a slow rate of transesterification has almost vanished. Besides, if the catalyst surface is totally converted into methoxide species the induction period is longer than the analogous obtained with CaO. This is an indication that the methoxide species strongly bonded to Ca are less reactive.The calcium diglyceroxide material (CaO_diglyc), prepared by contacting CaO with a mixture of methanol and glycerol, displays a totally different kinetics curve with no induction period. The faster kinetics and the Ca species detected in the glycerin phase seem to underline a non-negligible homogeneous process contribution.The characterization of the post-reaction catalysts underlines the relevance of the surface and bulk catalyst modifications. Calcium hydroxide can be pointed out as the active phase whereas calcium diglyceroxide is responsible for the catalyst deactivation due to calcium leaching.