首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
基于NiO载氧体的煤化学链燃烧实验   总被引:2,自引:2,他引:2  
高正平  沈来宏  肖军 《化工学报》2008,59(5):1242-1250
采用流化床反应器并以水蒸气作为气化-流化介质,研究了以NiO为载氧体在800~960℃内的煤化学链燃烧反应特性。实验结果表明,载氧体与煤气化产物在反应器温度高于900℃体现了高的反应活性。随着流化床反应器温度的提高,气体产物中CO2的体积浓度(干基)呈单调递增;CO、H2、CH4的体积浓度(干基)呈单调递减;煤中碳转化为CO2的比率逐渐递增,碳的残余率逐渐递减。反应器出口气体CO2、CO、H2、CH4的生成率随反应时间呈单峰特性,H2生成率的峰值远小于CO的峰值;且随反应器温度升高,CO2生成率升高,CO、H2、CH4的生成率降低。反应温度高于900℃时,流化床反应器NiO载氧体煤化学链燃烧在9 min之内就基本完成,CO2含量高于92%。  相似文献   

2.
Kinetic data of a promising oxygen carrier of NiO/NiAl2O4 have been established from experiments in a small fluidized bed batch reactor using methane. The particles were prepared by spray-drying using commercially available raw material and selected as the best candidates from an earlier screening study. The particles clearly showed high reactivity, with a maximum gas yield between 86% and 93% in the temperature interval 750 °C to 950 °C when using a bed mass and a gas flow corresponding to only 6 kg/MWfuel. A comparison of the reactivity with data from TGA experiments showed that the reactivity generally was faster in the batch fluidized bed in the investigated temperature interval. A simple reactor model using kinetic data from the batch fluidized bed reactor and the TGA predicted a minimum mass of 9–24 kg/MWfuel of oxygen carrier particles for full gas yield of methane to carbon dioxide in the fuel reactor. Comparison with experiments performed in a 10 and 120 kW CLC reactor with the same type of oxygen carrier showed that even when employing 13 to 50 times the amount of oxygen carrier theoretically needed for complete gas conversion, full gas yield was not obtained in the circulating systems. Hence it is of great importance to consider the fluid dynamics and gas-solid contact when modeling the fuel reactor of a chemical-looping combustor.  相似文献   

3.
The naturally occurring mineral ilmenite, FeTiO3, has been examined as oxygen carrier for chemical-looping combustion. NiO-based particles have been used as an additive, in order to examine if it is possible to utilize the catalytic properties of metallic Ni to facilitate decomposition of hydrocarbons into more reactive combustion intermediates such as CO and H2. Firstly, ilmenite was examined by oxidation and reduction experiments in a batch fluidized-bed reactor. These experiments indicated moderate reactivity between ilmenite and CH4, which was used as reducing gas. However, adding 5 wt.% of NiO-based particles to the ilmenite improved the conversion of CH4 greatly, resulting in an increase in combustion efficiency with a factor of 3. Secondly, 83 h of chemical-looping combustion experiments were conducted in a small circulating fluidized-bed reactor, using ilmenite as oxygen carrier and natural gas as fuel. A wide range of process parameters and different levels of NiO addition were examined. Occasionally, there were problems with the circulation of solids between the air reactor and fuel reactor, but most of the time the experiments worked well. The products were mostly CO2, H2O and unconverted CH4. Adding small amounts of NiO-based particles to the reactor increased the conversion of the fuel considerably. For the base case conducted at 900°, the combustion efficiency was 76% for pure ilmenite and 90% for the corresponding experiments with 1 wt.% NiO-based particles added to the reactor. The properties of ilmenite were found to change considerably during operation. Used particles had lower density, were more reactive and more porous than fresh particles. These changes appear to have been physical, and no unexpected chemical phases could be identified.  相似文献   

4.
《Fuel》2006,85(5-6):736-747
The feasibility of using NiO as an oxygen carrier during chemical-looping combustion has been investigated. A thermodynamic analysis with CH4 as fuel showed that the yield of CH4 to CO2 and H2O was between 97.7 and 99.8% in the temperature range 700–1200 °C, with the yield decreasing as the temperature increases. Carbon deposition is not expected as long as sufficient metal oxide is supplied to the fuel reactor. Hydrogen sulfide, H2S, in the fuel gas will be converted partially to SO2 in the gas phase, with the degree of conversion increasing with temperature, but decreasing as a function of pressure. There is the possibility of sulfide formation as Ni3S2 at higher partial pressures of H2S+SO2 in the reactor. The reactivity of freeze granulated particles of NiO with NiAl2O4, MgAl2O4, TiO2 and ZrO2 sintered at different temperatures was investigated in a small fluidized bed reactor by exposing them cyclically to 50% CH4/50% H2O and 5% O2 at 950 °C. During the reducing period, the NiO initially reacted with the CH4 to form CO2 and H2O. However, there were always minor amounts of CO from the outlet of the reactor even at high concentrations of CO2, which was due to the thermodynamic limitations. Here, the ratio CO/(CO2+CO+CH4) was between 1.5 and 2.5% at 950 °C for the oxygen carriers with alumina based inert. A small amount of CH4 was released from the reactor at high degrees of oxidation of the NiAl2O4 and MgAl2O4-based carriers. As the time under reducing conditions increased, steam reforming of CH4 to CO and H2 became considerable, with Ni catalyzing this reaction. Whereas the ZrO2 particles showed similar behavior as the alumina-based carriers, the TiO2-based particles showed a markedly different reaction behavior, likely due to the complex interaction between NiO and TiO2.  相似文献   

5.
利用1 kWth串行流化床反应器对钠修饰铁矿石载氧体进行试验研究,考察燃料反应器温度对煤化学链催化燃烧特性的影响。结果表明,钠在820~920℃温度下显著促进了煤气化反应的进行,随着燃料反应器温度的提高,使用Na-铁矿石时燃料反应器出口CO2浓度明显增大,CO浓度明显降低,在920℃时CO2捕集效率和碳捕集效率分别达到78.60%和80.54%,而使用纯铁矿石时CO2捕集效率和碳捕集效率仅为40.27%和45.65%。在高温950℃时Na-铁矿石活性下降,出现烧结和团聚现象,燃料反应器出现滞流态化现象,这可能是钠的化合物熔点较低和载氧体过度还原所导致的。XRD和SEM分析结果显示钠修饰铁矿石促使更多的Fe2O3被还原为Fe3O4。  相似文献   

6.
A. Abad  T. Mattisson  A. Lyngfelt  M. Rydén 《Fuel》2006,85(9):1174-1185
Chemical-looping combustion (CLC) is a method for the combustion of fuel gas with inherent separation of carbon dioxide. This technique involves the use of two interconnected reactors. A solid oxygen carrier reacts with the oxygen in air in the air reactor and is then transferred to the fuel reactor, where the fuel gas is oxidized to carbon dioxide and water by the oxygen carrier. Fuel gas and air are never mixed and pure CO2 can easily be obtained from the flue gas exit. The oxygen carrier is recycled between both reactors in a regenerative process. This paper presents the results from a continuously operating laboratory CLC unit, consisting of two interconnected fluidized beds. The feasibility of the use of a manganese-based oxygen carrier supported on magnesium stabilized zirconia was tested in this work. Natural gas or syngas was used as fuel in the fuel reactor. Fuel flow and air flow was varied, the thermal power was between 100 and 300 W, and the air ratio was between 1.1 and 5.0. Tests were performed at four temperatures: 1073, 1123, 1173 and 1223 K. The prototype was successfully operated at all conditions with no signs of agglomeration or deactivation of the oxygen carrier. The same particles were used during 70 h of combustion and the mass loss was 0.038% per hour, although the main quantity was lost in the first hour of operation. In the combustion tests with natural gas, methane was detected in the exit flue gases, while CO and H2 were maintained at low concentrations. Higher temperature or lower fuel flows increases the combustion efficiency, which ranged from 0.88 to 0.99. On the other hand, the combustion of syngas was complete for all experimental conditions, with no CO or H2 present in the gas from the fuel reactor.  相似文献   

7.
The reactivity of a Ni-based oxygen carrier prepared by hot incipient wetness impregnation (HIWI) on α-Al2O3 with a NiO content of 18 wt% was studied in this work. Pulse experiments with the reduction period divided into 4-s pulses were performed in a fluidized bed reactor at 1223 K using CH4 as fuel. The number of pulses was between 2 and 12. Information about the gaseous product distribution and secondary reactions during the reduction was obtained. In addition to the direct reaction of the combustible gas with the oxygen carrier, CH4 steam reforming also had a significant role in the process, forming H2 and CO. This reaction was catalyzed by metallic Ni in the oxygen carrier and H2 and CO acted as intermediate products of the combustion. No evidence of carbon deposition was found in any case. Redox cycles were also carried out in a thermogravimetric analyzer (TGA) with H2 as fuel. Both tests showed that there was a relation between the solid conversion reached during the reduction and the relative amount of NiO and NiAl2O4 in the oxygen carrier. When solid conversion increased, the NiO content also increased, and consequently NiAl2O4 decreased. Approximately 20% of the reduced nickel was oxidized to NiAl2O4, regardless ΔXs. NiAl2O4 was also an active compound for the combustion reaction, but with lower reactivity than NiO. Further, the consequences of these results with respect to the design of a CLC system were investigated. When formation of NiAl2O4 occurred, the average reactivity in the fuel reactor decreased. Therefore, the presence of both NiO and NiAl2O4 phases must be considered for the design of a CLC facility.  相似文献   

8.
Behavior of ilmenite as oxygen carrier in chemical-looping combustion   总被引:1,自引:0,他引:1  
For a future scenery where will exist limitation for CO2 emissions, chemical-looping combustion (CLC) has been identified as a promising technology to reduce the cost related to CO2 capture from power plants. In CLC a solid oxygen-carrier transfers oxygen from the air to the fuel in a cyclic manner, avoiding direct contact between them. CO2 is inherently obtained in a separate stream. For this process the oxygen-carrier circulates between two interconnected fluidized-bed reactors. To adapt CLC for solid fuels the oxygen-carrier reacts with the gas proceeding from the solid fuel gasification, which is carried out right in the fuel-reactor. Ilmenite, a natural mineral composed of FeTiO3, is a low cost and promising material for its use on a large scale in CLC.The aim of this study is to analyze the behavior of ilmenite as oxygen-carrier in CLC. Particular attention was put on the variation of chemical and physical characteristics of ilmenite particles during consecutive redox cycles in a batch fluidized-bed reactor using CH4, H2 and CO as reducing gases. Reaction with H2 was faster than with CO, and near full H2 conversion was obtained in the fluidized-bed. Lower reactivity was found for CH4. Ilmenite increased its reactivity with the number of cycles, especially for CH4. The structural changes of ilmenite, as well as the variations in its behavior with a high number of cycles were also evaluated with a 100 cycle test using a CO + H2 syngas mixture. Tests with different H2:CO ratios were also made in order to see the reciprocal influence of both reducing gases and it turned out that the reaction rate is the sum of the individual reaction rates of H2 and CO. The oxidation reaction of ilmenite was also investigated. An activation process for the oxidation reaction was observed and two steps for the reaction development were differenced. The oxidation reaction was fast and complete oxidation could be reached after every cycle. Low attrition values were found and no defluidization was observed during fluidized-bed operation. During activation process, the porosity of particles increased from low porosity values up to values of 27.5%. The appearance of an external shell in the particle was observed, which is Fe enriched. The segregation of Fe from TiO2 causes that the oxygen transport capacity, ROC, decreases from the initial ROC = 4.0% to 2.1% after 100 redox cycles.  相似文献   

9.
The distribution of air oxygen atoms in the oxidation products of rich mixtures of syngas with air in flame and the under autoignition conditions at constant volume has been investigated by numerical simulation using the tracer method. It has been found that in rich mixtures, the oxidation of hydrogen and carbon oxide has a stepwise nature, which is clearly visible in the profiles of the rates of production of H2O and CO2. The observed stepwise nature inevitably results in the heat-release rate occurring in steps. The reaction pathways and the role of the oxygen atom of the CO molecule in the heat release in these flames has been investigated.  相似文献   

10.
Chemical-looping combustion (CLC) has emerged as a promising option for CO2 capture because this gas is inherently separated from the other flue gas components and thus no energy is expended for the separation. This technology would have some advantages if it could be adapted for its use with coal as fuel. In this sense, a process integrated by coal gasification and CLC could be used in power plants with low energy penalty for CO2 capture. This work presents the results obtained in the combustion of syngas as fuel with a Ni-based oxygen carrier prepared by impregnation in a CLC plant under continuous operation. The effect on the oxygen carrier behaviour and the combustion efficiency of several operating conditions was determined in the continuous CLC plant. High combustion efficiencies (~99%), close to the values limited by thermodynamics, were reached at oxygen carrier-to-fuel ratios higher than 5. The temperature in the FR had a significant influence, although high efficiencies were obtained even at 1073 K. The syngas composition had small effect on the combustion, obtaining high and similar efficiencies with syngas fuels of different composition, even in the presence of high CO concentrations. The low reactivity of the oxygen carrier with CO seemed to indicate that the water gas shift reaction acts as an intermediate step in the global reaction of the syngas in a continuous CLC plant. Neither agglomeration nor carbon deposition problems were detected during 50 h of continuous operation in the prototype. The obtained results showed that the impregnated Ni-based oxygen carrier could be used in a CLC plant for the combustion of syngas produced in an integrated gasification combined cycle (IGCC).  相似文献   

11.
Chemical looping gasification (CLG) provides a novel approach to dispose the sewage sludge. In order to improve the reactivity of the calcined copper slag, NiO modification is considered as one of the good solutions. The copper slag calcined at 1100 ℃ doped with 20 wt% NiO (Ni20-CS) was used as an oxygen carrier (OC) in sludge CLG in the work. The modification of NiO can evidently enhance the reactivity of copper slag to promote the sludge conversion, especially for sludge char conversion. The carbon conversion and valid gas yield (Vg) increase from 67.02% and 0.23 m3·kg-1 using the original OC to 78.34% and 0.29 m3·kg-1 using the Ni20-CS OC, respectively. The increase of equivalent coefficient (Ω) facilitates the sludge conversion and a suitable Ω value is determined at 0.47 to obtain the highest valid gas yield (0.29 m3·kg-1). A suitable steam content is assigned at 27.22% to obtain the maximum carbon conversion of 87.09%, where an acceptable LHV of 12.63 MJ·m-3 and Vg of 0.39 m3·kg-1 are obtained. Although the reactivity of Ni20-CS OC gradually decreases with the increase in cycle numbers because of the generation of NiFe2O4-δ species, the deposition of sludge ash containing many metallic elements is beneficial to the sludge conversion. As a result, the carbon conversion shows a slight uptrend with the increase of cycle numbers in sludge CLG. It indicates that the Ni20-CS sample is a good OC for sludge CLG.  相似文献   

12.
The feasibility of using three different solid fuels in chemical-looping combustion (CLC) has been investigated using NiO as oxygen carrier. A laboratory fluidized-bed reactor system for solid fuel was used, simulating a chemical-looping combustion system by exposing the sample to alternating reducing and oxidizing conditions. In each reducing phase 0.2 g of fuel was added to the reactor containing 20 g oxygen carrier. The experiments were performed at 970 °C. Compared to previously published results with other oxygen carriers the reactivity of the used Ni-particles was considerably lower for the high-sulphur fuel and higher for the low-sulphur fuel. Much more unconverted CO was released and the fuel conversion was much slower for high-sulphur fuel such as petroleum coke, suggesting that the nickel-based oxygen carrier was deactivated by the presence of sulphur. The NiO particles also showed good reactivity with methane and a syngas mixture of 50% H2 and 50% CO. For all experiments the oxygen carrier showed good fluidizing properties without any signs of agglomeration.  相似文献   

13.
基于热重和红外联用进行等温实验,探讨了化学链燃烧载氧体CaSO4在CO气氛下的还原反应特性.研究发现:温度对CaSO4还原反应历程和速率有显著的影响,在10%CO气氛下,温度低于900℃时,发生单一反应,CaSO4的还原产物只是CaS,气相产物为CO2;当温度高于950℃后,发生平行反应和连串反应组合成的多重反应,固体产物为CaS和CaO,而产物气中除了有CO2,还存在SO2和COS,且气相硫化物的析出以COS为主;随着反应温度的升高,CaSO4与CO反应速率显著增加,而目标产物CaS在固体产物中所占的摩尔分数呈下降趋势;基于钙基载氧体化学链燃烧中燃料反应器温度不宜高于950℃.  相似文献   

14.
The use of ilmenite as an oxygen carrier in chemical-looping combustion   总被引:2,自引:0,他引:2  
The feasibility of using ilmenite as oxygen carrier in chemical-looping combustion has been investigated. It was found that ilmenite is an attractive and inexpensive oxygen carrier for chemical-looping combustion. A laboratory fluidized-bed reactor system, simulating chemical-looping combustion by exposing the sample to alternating reducing and oxidizing conditions, was used to investigate the reactivity. During the reducing phase, 15 g of ilmenite with a particle size of 125–180 μm was exposed to a flow of 450 mLn/min of either methane or syngas (50% CO, 50% H2) and during the oxidizing phase to a flow of 1000 mLn/min of 5% O2 in nitrogen. The ilmenite particles showed no decrease in reactivity in the laboratory experiments after 37 cycles of oxidation and reduction. Equilibrium calculations indicate that the reduced ilmenite is in the form FeTiO3 and the oxidized carrier is in the form Fe2TiO5 + TiO2. The theoretical oxygen transfer capacity between these oxidation states is 5%. The same oxygen transfer capacity was obtained in the laboratory experiments with syngas. Equilibrium calculations indicate that ilmenite should be able to give high conversion of the gases with the equilibrium ratios CO/(CO2 + CO) and H2/(H2O + H2) of 0.0006 and 0.0004, respectively. Laboratory experiments suggest a similar ratio for CO. The equilibrium calculations give a reaction enthalpy of the overall oxidation that is 11% higher than for the oxidation of methane per kmol of oxygen. Thus, the reduction from Fe2TiO5 + TiO2 to FeTiO3 with methane is endothermic, but less endothermic compared to NiO/Ni and Fe2O3/Fe3O4, and almost similar to Mn3O4/MnO.  相似文献   

15.
《Fuel》2007,86(1-2):113-122
Chemical-looping combustion is a two-stage process proposed as an alternative for the combustion of carbonaceous materials, such as natural gas or coal gas, for almost complete CO2 capture. In the reduction stage, the structural oxygen contained in the lattice of a reducible inorganic oxide, is used for combustion of the carbonaceous material. In the regeneration stage the oxygen carrier, found in a reduced state after the reduction stage, is regenerated with pure air to recover the physical and chemical properties of the carrier, ready to reinitiate a new cycle reduction-regeneration. In a typical multicycle reactor test, the carriers are subjected to accumulative chemical and thermal stresses and the performance will, probably, decay progressively with the number of cycles. The occurrence of some side reactions may limit the efficiency of the overall process in CO2 capture. In this paper, titania-supported iron oxides with different iron loadings have been tested in multicycle tests in a fixed-bed reactor at 900 °C and atmospheric pressure, as oxygen carriers for the chemical-looping combustion of methane. The study shows that the available oxygen for methane combustion in the reduction stage is lower than expected since the active phase interacts with the support forming FeTiO3 ilmenite. The reactivity of these iron based carriers in the reduction stage is independent on the iron oxide content but lower than that exhibited by other tested carriers, such as CuO or NiO. However, iron carriers are cheaper no showing any tendency to carbon deposition.  相似文献   

16.
Influence of time-on-stream (0.5–15 h), CH4/O2 ratio in feed (1.8–8.0), space velocity (6000–510,000 cm3 g−1 h−1), catalyst particle size (22–70 mesh), and catalyst dilution by inert solid particles (diluent/catalyst weight ratio=4) on the performance at different temperatures (600–900°C) of the NiO/MgO solid solution deposited on SA-5205 [which is a low surface area macroporous silica-alumina catalyst carrier] in the oxidative conversion of methane to syngas (a mixture of CO and H2) has been investigated. The dependence of conversion and selectivity on the space velocity is strongly influenced by the temperature. Both the conversion and selectivity for H2 and CO are decreased markedly by increasing the CH4/O2 ratio in the feed. The catalyst dilution resulted in a small but significant decrease in both the conversion and selectivity for H2 and CO. The increase in the catalyst particle size had also a small but significant effect on both the conversion and selectivity in the oxidative conversion process. Both the heat and mass transfer processes seem to play significant roles in the oxidative conversion of methane to syngas at a very low contact time or very high space velocity (5.1×105 cm3 g−1 h−1).  相似文献   

17.
流化床铁基载氧体辅助富氧燃烧下传统石英砂床料被铁基载氧体替代,铁基载氧体扩展了传统床料的“热载体”的功能,另承担了“氧载体”的角色,为调节炉内氧分布与煤燃烧过程匹配提供了新思路。本文在热重实验平台探究了10%O2/90%CO2气氛下分析纯Fe2O3、赤铁矿及钢渣三种铁基载氧体辅助无烟煤焦燃烧特性及动力学。结果表明,相较于纯无烟煤焦燃烧,铁基载氧体辅助燃烧下无烟煤焦的燃烧特性得到显著改善,其中燃烧速率提高29%以上,燃尽温度降低65℃以上,综合燃烧指数提升2倍以上,活化能与指前因子同步增加且表现出“补偿效应”。三种铁基载氧体中分析纯Fe2O3对无烟煤焦燃烧特性的改善略优于赤铁矿和钢渣,钢渣可作为流化床铁基载氧体辅助富氧燃烧的床料替代石英砂。  相似文献   

18.
彭松  曾德望  陈超  邱宇  肖睿 《化工学报》2018,69(1):515-522
采用燃烧法合成了具有尖晶石结构的CoFeAlO4载氧体材料,通过表征手段和实验研究考察了不同温度下CoFeAlO4载氧体的化学链燃烧反应特性和循环稳定性,并对CoFeAlO4载氧体晶相结构和表观形貌的变化规律进行了分析。结果表明,温度升高有利于提高CoFeAlO4载氧体转化还原性气体CO的能力,使得还原反应速率更快,但高温下经“还原-氧化”会造成CoFeAlO4载氧体相态分离,难以保持稳定的自载体尖晶石结构。对反应前后CoFeAlO4载氧体晶相结构的分析表明,高温条件下经过“还原-氧化”后生成的CoFe2O4和CoAl2O4是导致CoFeAlO4载氧体烧结和循环稳定性下降的主要原因。  相似文献   

19.
化学链燃烧是一种具有CO2内分离特性的燃烧方式。以赤铁矿为载氧体,在1 kWth级串行流化床上进行了煤化学链燃烧试验。讨论了燃料反应器温度对气体产物组分的影响;比较了各反应参数对煤气化效率、煤气化产物的转化效率及碳捕集效率的影响情况,分析了煤中硫的排放问题。试验结果表明:温度由900℃升高到985℃,燃料反应器中CO体积份额逐渐增加,CO2体积份额逐渐减小,空气反应器中CO2浓度呈线性下降。燃料反应器温度的升高促进煤气化效率及碳捕集效率大大提高。载氧体量和系统负荷是煤气化产物转化效率的主要影响因素,载氧体量的增加和负荷的增加分别会使煤气化产物转化效率提高和下降。燃料反应器中的硫主要以SO2形式存在于燃料反应器,随温度的升高,SO2浓度由515×10-6逐渐增加到562×10-6相似文献   

20.
提出一种铁基氧载体(Fe3O4/FeO)化学链CO2重整CH4方法制备合成气。为评价该系统的性能,采用Aspen Plus软件对其进行过程模拟和热力学分析。以CH4转化率、CO2转化率、能源利用效率和产气氢碳比(H2/CO)为评价指标,得到系统的优化运行条件,并研究各操作参数(包括各反应器的温度和压力、氧载体甲烷比和CO2甲烷比)对系统性能的影响。结果表明:当系统处于优化工况时,得到CH4转化率为97.91%、CO2转化率为32.76%、能源利用效率为93.77%及产气氢碳比为0.93。该系统能有效利用CO2和CH4这两种温室气体获得较低氢碳比的合成气,利于二甲醚的高效合成。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号