【作者】 王保文；

【导师】 郑楚光； 晏蓉； 郑瑛；

【作者基本信息】 华中科技大学 ， 热能工程， 2008， 博士

【摘要】 以煤为主的化石燃料在满足了电力生产和能源需求的同时，燃烧过程中排放的CO₂也引起大气中CO₂浓度不断增加，而CO₂等温室气体的排放是引起全球气候变暖的重要原因。因此减少以煤炭利用过程中CO₂的排放刻不容缓，非常必要。化学链燃烧技术是一种新颖的燃烧技术，由于具有较高的燃烧效率、彻底消除NOx排放以及CO₂内分离的特点而受到了广泛的关注。因此，研究以煤为燃料的化学链燃烧技术对于CO₂的减排和煤炭的高效利用具有重要的意义。本文依托华中科技大学煤燃烧国家重点实验室和新加坡南洋理工大学环境科学工程研究院的国际交流合作项目，对Fe₂O₃基氧载体与以煤为燃料的化学链燃烧技术进行了详细的研究，并对CO₂的化工利用进行了创新性的探索。主要研究内容与成果如下：采用热力学分析方法对煤合成气与构成氧载体的活性金属氧化物的反应进行了模拟计算，对减小氧载体碳沉积和固相硫组分的影响因素进行计算并发现，在相同条件下，压力的增加会导致更多沉积碳和固相硫组分的形成；而温度的增加则会抑制沉积碳的产生以及更多SO₂气体的产生；而煤合成气中水蒸汽和CO₂对碳沉积以及气相SO₂的产生的作用与温度的影响类似，尽管影响程度不同。采用质能平衡方程对不同类型的氧载体与煤合成气的反应系统进行计算，结果表明，NiO、CoO基氧载体会导致燃料反应器温度降低；而Fe₂O₃、Mn₃O₄则对燃料反应器温度的保持有利；对于CuO，由于其放热特性，CuO的含量增加会导致反应器温度急剧增加。进一步地，就各种惰性载体对燃料反应器温度的影响而言，其最优选择顺序为：MgAl₂O₄>Al₂O₃>SiO₂>TiO₂>ZrO₂。设计并建立以尿素为燃料、硝酸盐为氧化剂的溶胶一凝胶燃烧合成法（SGCS）制备Fe₂O₃／Al₂O₃氧载体，优化了SGCS法的工艺参数，并对其反应性能、抗烧结和碳沉积性能进行了详细的研究；进一步地，研究了惰性载体Al₂O₃的含量对Fe₂O₃／Al₂O₃氧载体性能的影响，发现质量比为8：2的Fe₂O₃／Al₂O₃氧载体不仅具有较好的反应性能，而且具有良好的抗烧结以及抗碳沉积能力。此外，以质量比为8：2的Fe₂O₃／Al₂O₃氧载体为基础，对添加CuO、MgO的复合氧载体的反应性能、抗烧结以及抗碳沉积能力进行研究，发现对Fe₂O₃-CuO／Al₂O₃复合氧载体，CuO的加入能够有效地提高氧载体的反应性和抗碳沉积能力，而MgO的加入则对氧载体的抗烧结和抗碳沉积能力有利。值得注意的是，CuO和MgO的加入量均以不超过Fe₂O₃以及Al₂O₃质量比的30％为宜。Fe₂O₃基氧载体与不同煤种的热重研究表明，Fe₂O₃的还原产物为不低于Fe₃O₄价态的氧化物；煤与金属氧载体的反应并不是氧载体与煤的直接反应，而是与其热解和气化产物的气固反应。因此，直接以煤为燃料的化学链燃烧技术是可行的，而且CuO-Fe₂O₃／Al₂O₃氧载体与煤反应具有一定的反应协同性。此外，由于CuO的放热反应特性，对于燃料反应器能量平衡非常有利。最后，对氢气活化的Fe₂O₃、CuFe₂O₄与CO₂的氧化反应制CO的可行性进行了初步的试验和热力学研究，发现该方法与化学链燃烧技术耦合用于CO₂分解是可能的。更多还原

【Abstract】 Fossil fuels, especially coal, are used as fuel to generate electricity and meet energy demand, but they also emits a large amount of CO₂ and causes the great increase of CO₂ concentration in the atmosphere along with ever-increasing effect from the CO₂-related greenhouse effect. Therefore, it is of great necessity to decrease CO₂ emission into the atmosphere from fossil combustion. Compared to various kinds of present existing technologies to combat CO₂ emission from fossil combustion, chemical looping combustion receives great attraction and intensive research for its three distinguished advantages, such as high combustion efficiency by decreasing the combustion irreversibility, eradication of NOx formation as well as CO₂ inherent separation without extra instrument and energy consumption. Obviously, it would be greatly meaningful and advantageous if fossil fuels, especially coal were adopted as the fuel for chemical looping combustion. Under the project of the related research cooperation between State Key Laboratory of Coal Combustion in Huazhong University of Science and Technology and Institute of Environmental Science and Engineering in Nanyang Technological University （Singapore）, a detailed research on chemical looping combustion with coal as the fuel and Fe₂O₃-based oxides as the oxygen carriers are performed. Meanwhile, the chemical utilization of CO₂ emitted from the system of chemical looping combustion were also innovatively explored. Based on all the related researches, the meaningful results are summarized as follows:The reaction of active metal oxides （the main component for oxygen carriers） with syngas derived from coal gasification are simulated by means of thermodynamics on the principle of the minimization of Gibbs energy, with focus on the various influencing factors on the carbon deposition and the formation of solid sulfur compounds. The simulation results indicated that under the fixed condition, the increase of pressure would lead to more carbon and solid sulfur compounds deposited on the oxygen carriers. On the contrast, the increase of temperature can inhibit carbon deposition and produce more SO₂ in gas state. In terms of H₂O and CO₂ function in the syngas, similar to the function of temperature, the increase of the two gas fractions will decease the formation of solid carbon and produce more gas SO₂, though the inhibition function of carbon deposition and the oxidization capacity of the two fractions in the syngas are different. The investigation of the effect on the temperature of fuel reactor （FR） from the reaction between different oxygen carriers （including various active metal oxides and inert supports） and syngas using mass and energy balances demonstrates, NiO and CoO based oxygen carriers lead to the decrease of FR temperature, while the Fe₂O₃ and Mn₃O₄ based oxygen carriers are beneficial to maintain the FR temperature, but due to the exothermal specialty, the increase of CuO content in CuO based oxygen carriers will cause dramatical increase of FR temperature. With regard to the supports’ effect on FR temperature, the optimal selection option in descending order should be: MgAl₂O₄ > Al₂O₃> SiO₂ > TiO₂ >ZrO₂.Oxygen carrier preparation is the basis of the investigation and application of chemical looping combustion. The novel sol-gel combustion synthesis method （SGCS） for the preparation of Fe₂O₃/Al₂O₃ oxygen carrier is designed and optimized. Different mass ratios of Fe₂O₃ to Al₂O₃ oxygen carriers are produced and experimentally researched, indicating the mass ratio of 8 to 2 for Fe₂O₃/Al₂O₃ is the best whether for the reactivity or the resistance to sintering and carbon deposition. Furthermore, the CuO and MgO stabilized Fe₂O₃/Al₂O₃ oxygen carrier were synthesized and indicated that the addition of CuO was conductive to the improvement of the reactivity and resistance to carbon deposition, while MgO-stabilized oxygen carrier is better in its resistance to sintering and carbon deposition.The reaction of variety of coals with Fe₂O₃ based oxygen carriers performed on TGA indicates that the product of the reduction of Fe₂O₃ with coals is oxides with valence no lower than Fe₃O₄.Oxygen carriers actually react with the products from the pyrolysis and gasification of coal instead of coal in itself when coal is directly used as the fuel. Furthermore, CuO-Fe₂O₃ mixed oxygen carriers really demonstrate the synergistic effect on the oxidization of coal along with less heat demand for the CuO exothermal specialty.Finally, preliminary experimental and thermodynamic research of reduction between the hydrogen-activated Fe₂O₃ and CuFe₂O₃ with CO₂ emitted from the chemical looping combustion to produce CO are performed. The feasibility of producing CO from such process is validated to reach the decrease the goal of emission of CO₂.更多还原