STRUCTURE OPTIMIZATION OF A CIRCULATING MOVING BED REACTOR

A stress distribution model for a liquid-solid circulating moving bed reactor that consists of a bottom reaction chamber, a top regeneration chamber, a coupling standpipe, a particle transportation system, and a bottom standpipe is established based on the equations of continuity and momentum balance. Simulations show that the stress concentration regions are at the bottom of the regeneration chamber and the coupling standpipe. To reduce the maximal stress and increase the operation flexibility in a reactor for the 2000-ton-per-year production of linear alkylbenzene, the regeneration chamber should have a low height-to-radius ratio (about 9), a suitable half-conical angle between 28° and 35°, and standpipe radius of about 0.05 m.     

Study on the stress distribution and modeling of the stand pipe in a circulating moving bed

The liquid-solid circulating moving bed reactor is a novel one, which consists of two reaction chambers and a particle transport system. Particles move down to the lower reaction chamber from the upper reaction chamber through a coupling standpipe and to the particle transport system through a bottom standpipe, and are then conveyed into the upper reaction chamber through a riser. A stress distribution model based on the equations of continuity and momentum balance in the reactor is established and used for simulations which shows that the stress concentration regions are at the coupling standpipe and the bottom of the regeneration chamber. To reduce the largest stress in the stress concentration regions and to minimize catalyst consumption, the regeneration chamber should be designed to give a low ratio of height to diameter. Zoning diagrams of the flow patterns in the bottom standpipe are proposed and the flow patterns can be readily deduced from the pressure gradient.     

循环流化床煤燃烧/热解双反应器系统稳定性分析

为了考察循环流化床煤燃烧/热解双反应器系统的稳定性,在冷态实验装置上以电厂锅炉灰为实验物料,其中提升管的内径为100 mm,高为6.7 m,与热解室相连立管的内径为44 mm,高3 m,热解室的截面积为200 mm×200 mm,高770 mm。分别考察了影响系统稳定运行的主要因素,并对系统中存在的几对平衡关系进行了分析。结果表明,旋风料腿内的固体料位高度、热解室内的料位高度以及热解室内的压力等是影响系统稳定运行的关键因素,尤其是热解室内压力的增加有可能使立管内料封破坏,最终导致系统瘫痪。而提升管与热解室立管之间压力的平衡以及提升管与旋风分离器料腿之间压力的平衡等在操作过程中必须保持稳定,否则也会发生窜气、架料、旋风分离器效率下降等现象,影响系统稳定运行。     

CFB煤燃烧／热解双反应器立管内气固流动模型分析

在循环流化床（CFB）煤燃烧／热解双反应器冷态实验装置上,以硅胶和电厂锅炉灰为实验物料,考察了立管内的气固流动特性,其中立管的内径44mm、高3m。研究结果表明,立管内的气固流动形态为移动床流动,Leung的立管流动模型适合对该系统中立管内移动床流动的描述,经拟合分别得到了立管内气、同速率以及气同相对速率与固体速率之间的经验方程,对热态实验过程中判断立管内的气固流动型态以及料封的稳定性均具有一定的参考价值。     

Reaction engineering studies of methane coupling in fluidised-bed reactors

The oxidative coupling of methane has been conducted in 30 and 60mm dia. fluidised-bed reactors. Methane conversions as high as 40% were achieved at isothermal conditions using methane/oxygen mixtures without diluents. At the same contact time the two reactors had similar selectivities to hydrocarbons. At 850°C the hydrocarbon selectivity decreased dramatically with increasing contact time but this effect was much less severe at lower temperatures. Axial gas concentration profiles through the catalyst bed in the 60mm reactor indicated that at 850°C there was a rapid consumption of oxygen and formation of products in the bottom section of the bed followed by a net loss of hydrocarbon in the oxygen-free zone. This loss was due to carbon formation on the catalyst which was circulated back to the oxygen-containing zone of the bed where the carbon was combusted.     

Propylene epoxidation in a microreactor with electric heating

Gas phase propylene epoxidation on gold catalysts has attracted wide attention from industry and academia due to its high selectivity. However, it suffers from low propylene conversion and rapid catalyst deactivation. Experiments showed that propylene conversion could be increased by raising H₂, O₂, or C₃H₆ concentration in the feed, but the feed compositions were within the explosion limit. It was also shown that the activity of the used catalyst could be fully recovered, but the regeneration temperature was 280 °C, much higher than that for reaction. Therefore a microchannel reactor was devised to suppress explosion and was constructed with Fecralloy, to raise the temperature rapidly for catalyst regeneration by electric heating. In two minutes the temperature of the reactor could be raised from 50 to 300 °C. Catalysts were coated on the alloy belt by dip coating, and the performance of the reactor was evaluated under different operating conditions. Results showed that in the microreactor the overall reaction rate was controlled mainly by the intrinsic reaction rate, and also influenced by film diffusion to a certain extent. The deactivated catalyst was regenerated in the microchannel reactor and the activity was fully recovered.     

负压差立管内的气固两相流

在φ800 mm×12000 mm流化床实验装置上对150 mm×11500 mm负压差立管内气固两相流的轴向压力、空隙率和气体流动特性进行了测量和分析.立管出口无约束淹没在密相流化床内,颗粒质量流率范围G_s<1200 kg&#8226;m^-2&#8226;s^-1.立管内气固两相流态有两种存在形式,当颗粒质量流率G_s<200～250 kg&#8226;m^-2&#8226;s^-1时,流态是稀密两相共存形式;当G_s>200～250 kg&#8226;m^-2&#8226;s^-1时,流态是浓相输送流态.两种流态之间可以相互转换,主要取决于颗粒质量流率的变化.影响立管内气固两相流的轴向压力、空隙率分布、气相的流动特性和气固流态存在形式的主要参数是颗粒质量流率G_s、旋风分离器入口速度V_i、下端流化床流化速度u_f,质量流率G_s是主要的影响因素.     

Determination of standpipe pressure profiles and slide valve orifice discharge coefficients on synthol circulating fluidized-bed reactors

A Synthol Circulating Fluidized-Bed (CFB) reactor utilizes a finely divided, reduced iron oxide catalyst to convert (CO + H₂) to gaseous and liquid fuels. The reactor consists essentially of a fast-fluidized bed with a hopper and standpipe providing a pressure seal sufficient to maintain a high catalyst inventory in the reaction zone. For optimum reactor operation, the catalyst must flow down the standpipe in the dense-phase fluidized-flow regime so giving maximum pressure recovery.Tests carried out on the Sasol 1 commercial reactors showed that the dense-phase flow regime could be maintained with minimal use of added aeration. Work carried out on a large cold-model hopper and standpipe showed that added aeration was vital in maintaining dense-phase flow and in achieving a high pressure recovery. The relatively high pressure operation of the commercial reactors and consequent low compression effect going down the standpipe is such that the entrapped aeration entering the standpipe is sufficient to prevent a flow regime transition to a packed bed. Orifice discharge coefficients determined on the commercial reactors and the cold model agreed closely with values reported in the literature.     

Temperature dependence piezoelectric properties of 0.78PMN-0.32PT ceramics

The temperature dependence piezoelectric properties of 0.78PMN-0.32PT ceramics were studied. The results show that the planar coupling coefficient Kp keeps almost unchanged from room temperature to 90°C, and drops rapidly at temperature regions from 100°C to 130°C. It drops slowly at 130-150°C. Qm reaches minimum values at about 90-100°C, and maximum value at about 140-150°C. This phenomenon can be attributed to the phase transition in this composition. The rhombohedra1 phase changes to tetragonal phase at about 90°C, and tetragonal phase changes to cubic at about 150°C.     

Oxidative coupling of methane in fluidized- and packed-fluidized-bed reactors

Oxidative coupling of methane to higher hydrocarbons (C₂₊) using NaOH/CaO and pure CaO as catalyst was studied in fluidized- and packed-fluidized-bed reactors at 700°C to 800°C, partial pressures of methane from 0.5 to 0.7 bar and oxygen from 0.05 to 0.25 bar and a total pressure of ca 1 bar; oxygen conversion amounted generally to 50 to 100 %. C₂₊ selectivity depends for both reactors markedly on temperature and oxygen partial pressure. The optimum temperature ranges between 750 and 800°C. Highest selectivities (ca 76 %) were achieved at the lowest oxygen partial pressure (ca 0.06 bar); maximum yields (ca 13.5 %), however, were obtained at an oxygen partial pressure of ca 0.14 bar. The application of the fluidized-bed reactor is more favourable than the packed-fluidized-bed reactor with respect to operability and C₂₊ selectivity.     

Catalytic activity of pitch-based activated carbon fiber of large surface area heat-treated at high temperature and its regeneration for NO–NH3 reaction at ambient temperatures

The catalytic activity of a pitch-based activated carbon fiber (ACF) of very large surface area (OG-20A) was studied for NO–NH₃ reaction in a flow reactor at ambient temperatures. The ACF exhibited the highest activity in wet as well as dry gas among heat-treated ACFs so far examined by the present authors. The calcination at 1100°C was essential to exhibit the highest activity especially in wet gas. Although high humidity always retarded the reaction very markedly, its retardation was very much emphasized against NO of low concentration around 10 ppm. Sufficient amount of OG-20A-H1100 (3 g) allowed complete removal of 10–200 ppm NO by reduction and adsorption for initial 6 h even at least in wet gas at 25–30°C depending on NO concentration. The removal conversion decreased gradually for several hours following to the stationary one. The reactivity of adsorbed NO and NH₃ was examined in air to regenerate the period of complete NO removal over the ACF. The regeneration at 30°C was found optimum after the removal reaction at 25 or 30°C to provide the same period of complete removal by 3 h, leaking minimum amounts of adsorbed NO and NH₃. A higher reaction temperature of 35°C shortened the period of complete NO removal, and the successive regeneration at 30°C by 3 h failed in the complete NO removal in the second run. Oxygen appears necessary to regenerate the activity through enhancing the reaction of adsorbed NO and NH₃. NH₃ in the regeneration gas appears to inhibit the reaction of adsorbed species, increasing NH₃ leak.     

Competition between the gas and surface reactions for the oxidative coupling of methane 1. ‘Non-isothermal’ results in catalytic jet-stirred reactor

A catalytic jet-stirred reactor (CJS reactor) has been developed to investigate the interaction between gas-phase and surface reactions for the oxidative coupling of methane. This reactor allows the modification of the number of catalyst pellets (La₂O₃) for a fixed gas-phase volume. It permits also to set different temperatures for the gas-phase volume and the catalyst. The results of these ‘nonisothermal’ experiments are presented; they suggest that the contribution of the gas-phase reactions is rather significant and that the C₂₊ selectivity is improved by an increase of the gas-phase temperature up to 850°C.     

Adsorption of tetrachloroethylene (PCE) in gas phase on zeolites of faujasite type: Influence of water vapour and of Si/Al ratio

This study is focused on the adsorption of a chlorinated volatile organic compound, the tetrachloroethylene (PCE), on dealuminated faujasite type zeolites with framework Si/Al ratio between 5 and 100. PCE dynamic adsorption experiments with and without water vapour (relative humidity of, respectively, 50% and 0%) were carried out in a fixed bed reactor at 50 °C. Breakthrough curves were fitted by a model using the integral of a Gauss distribution. PCE adsorption capacities depend on the adsorbent microporous volume. However, in presence of water vapour, PCE adsorption is favoured on hydrophobic zeolites but also depends on the diffusional limitations inside the porous system. In order to have a better understanding of water molecules adsorption, isotherms were measured using thermogravimetric method at 25 °C. The presence of water vapour generally decreases PCE uptake but its influence decreases as the Si/Al ratio of the adsorbent increases. Experiments with various gases hourly space velocity (GHSV) and inlet PCE concentrations were also performed. PCE complete desorption was obtained on HFAU(Si/Al = 17) at 180 °C. This easy regeneration of the sample permitted adsorption/regeneration cycles maintaining good adsorption properties.     

催化裂化装置待生立管磨损原因分析及处理措施

对催化裂化装置同轴式沉降再生器待生立管磨损原因进行分析,认为原设计不合理是主要原因,对待生立管及密封结构进行了改进。     

PROTOTYPE HIGH TEMPERATURE/HIGH PRESSURE KILN FOR THE EVALUATION OF WOOD DRYING SCHEDULES

A new laboratory kiln was developed and built to perform over a very wide range of drying conditions. For example, the dry bulb temperature can vary from 30°C to 150°C and the dew point can be adjusted between 20°C and 130°C. Obviously, with such a high level of dew point, pressures over atmospheric pressure may be induced inside the chamber. For this reason, the kiln has been designed to withstand pressure of up to 3 bars. This kiln can also perform vacuum drying.

A programmable controller allows the temperature levels to be maintained within ± 0.2°C. Because the whole kiln can be heated only through the agitated water present at the bottom of the kiln, the load temperature can be increased up to 130°C in saturated conditions, without any change of moisture content.

The kiln has various sensors attached and is capable of withstanding severe conditions (high temperature, saturated vapour and elevated pressures). At present, air and water temperatures as well as temperature at different locations within the board can be collected during the drying process. A load cell and pressure gauges are also available. The first tests performed using this equipment are presented at the end of the paper.     

Hydrodynamic study of a toroidal fluidized bed reactor

Hydrodynamic behavior of a newly developed toroidal fluidized bed reactor is studied in this work. The reactor has a gas distributor consisting of angled blades in an annular ring at the reactor bottom. The driving force for particles to move over the distributing blades comes from the velocity head of gas jets accelerated upon entering the blade spacing. Relevant hydrodynamic behaviors are measured with various inert materials in a pilot scale 400-mm toroidal fluidized bed reactor. The observed hydrodynamic behavior is found to be essentially predictable at ambient temperature by conventional hydrodynamic models. Fine particle tracking on the reactor wall is clearly observed through oxidation of zinc dross at a bed temperature of around 1120°C, and is simulated on the basis of a simplified mathematical model. Hydrodynamic issues, such as particle flying trajectory and retention time in the reactor, are discussed based on the developed model.     

Experimental characterisation of high temperature creep resistance of mullite

The creep behaviour of mullite has been studied at temperatures between 1100 °C and 1450 °C. The two standard stages, primary and steady state are observed. The steady state strain creep rate may be represented by the standard relationship: with a stress exponent value n equal to about unity and an activation energy Q of about 410 kJ/mol at low temperatures and up to 731 kJ/mol for temperatures above 1300 °C. At high stress or temperature specimens failed. SEM observations of the fracture surface revealed that SCG played a major role in the failure process. The experimental lifetime values were compared to a simulation conducted by integration of V-K_I laws determined by Double Torsion technique at 1200 and 1300 °C. A fair agreement is observed suggesting that the creep duration is limited by SCG which causes the material failure, as assumed by Lange.     

CO2 absorption and regeneration of alkali metal-based solid sorbents

Potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO₂, Al₂O₃, MgO, SiO₂ and various zeolites. The CO₂ capture capacity and regeneration property were measured in the presence of H₂O in a fixed-bed reactor, during multiple cycles at various temperature conditions (CO₂ capture at 60 °C and regeneration at 130–400 °C). Sorbents such as K₂CO₃/AC, K₂CO₃/TiO₂, K₂CO₃/MgO, and K₂CO₃/Al₂O₃, which showed excellent CO₂ capture capacity, could be completely regenerated above 130, 130, 350, and 400 °C, respectively. The decrease in the CO₂ capture capacity of K₂CO₃/Al₂O₃ and K₂CO₃/MgO, after regeneration at temperatures of less than 200 °C, could be explained through the formation of KAl(CO₃)₂(OH)₂, K₂Mg(CO₃)₂, and K₂Mg(CO₃)₂·4(H₂O), which did not completely converted to the original K₂CO₃ phase. In the case of K₂CO₃/AC and K₂CO₃/TiO₂, a KHCO₃ crystal structure was formed during CO₂ absorption, unlike K₂CO₃/Al₂O₃ and K₂CO₃/MgO. This phase could be easily converted into the original phase during regeneration, even at a low temperature (130 °C). Therefore, the formation of the KHCO₃ crystal structure after CO₂ absorption is an important factor for regeneration, even at the low temperature. The nature of support plays an important role for CO₂ absorption and regeneration capacities. In particular, the K₂CO₃/TiO₂ sorbent showed excellent characteristics in CO₂ absorption and regeneration in that it satisfies the requirements of a large amount of CO₂ absorption (mg CO₂/g sorbent) and fast and complete regeneration at a low temperature condition (1 atm, 150 °C).     

SPATIAL DISTRIBUTION OF GAS AND SOLID PHASES IN CONICAL SLURRY BUBBLE COLUMNS

In this work we perform an experimental study of the spatial distribution of phases in slurry bubble columns with conical distributors that have a volume comparable to that of the cylindrical section. Three different distributors were used whose apex angles were 13°, 22° and 34°. In gas-liquid operation, the gas holdups are axially uniform in the cylindrical section and decrease towards the wall, whereas in the conical section they increase towards the inlet. These trends are observed in the three cones for all the operating conditions explored. The solids distributions in the conical sections are qualitatively different depending on whether the operation is semibatch or continuous with respect to the flow of solid-liquid suspension: in semibatch operation, the concentration monotonically increases towards the bottom of the cone and exhibits a slight increase as the wall is approached; in continuous operation, an absolute maximum in solids concentration is obtained at a point located on the wall of the cone and intermediate height. The location of this maximum moves upwards as the total solids content in the column increases and as the apex angle decreases. The maximum in solids concentration signals the most probable site for the onset of solids sedimentation and the presence of low mixing levels and reduced mass transfer rates in a slurry reactor. In the range of conditions explored in the present work, the lowest apex angle (13°) yields a more uniform solids distribution throughout the system     

High-pressure reaction and emissions characteristics of catalytic reactors for gas turbine combustors

The reaction and emissions characteristics of catalytic reactors comprising noble metal catalysts were investigated using homogeneous mixtures of natural gas and vitiated air at pressures up to 2.9 MPa. The mixture temperatures at inlet ranged from 500 to 700°C and the fuel-air ratio was increased till the exit gas temperature reached about 1200°C. Values of combustion efficiency greater than 99.5% and nitrogen oxides emissions for all catalytic reactors tested were less than 0.2 g NO₂/kg fuel (2 ppm (15% 0₂) ) for all reactors at reactor exit gas temperatures higher than about 1100°C. Combustion efficiency decreased with increasing pressure in the heterogeneous-reaction controlled region, though a pressure increase favored homogeneous, gas phase reactions. Appreciable reactivity deterioration by aging for 1000 h at 1000°C was observed at lower mixture temperatures. A two-stage combustor comprising a conventional flame combustion stage and a catalytic stage was fabricated and its NO,_x emissions and performance were evaluated at conditions typical of stationary gas turbine combustor operations. About 80% reduction in NO,_x emissions levels compared with flame combustion was attained at 1 MPa pressure and 1180°C exit gas temperature, together with complete hydrocarbon combustion.