THE DESIGN AND DEVELOPMENT OF A NOVEL TRANSDUCER FOR THE MONITORING OF PROCESS PARAMETERS UNDER AGGRESSIVE ENVIRONMENTS

This paper describes the design and development of a novel vibrating reed transducer capable of providing routine and on line measurements of various process parameters. The system is driven and detected remotely under ambient conditions by transmitting transverse vibrations through a stiff elastic rod which is securely clamped at an intermediate point along its length. This allows operation under aggressive environments as only one free span of the vibrating element enters the test medium. The unit, when employed in the form of a gas densitometer can provide density measurements with ±1 × 10^-3 g/cm³ resolution when tested with the gases N₂, C0₂ and He up to a maximum pressure of 150MPaand70°C.

A mathematical analysis is also developed which successfully predicts some of the design criteria required for developing systems which are stable and whose response is governed predominantly by the conditions prevailing at the sampling or the remote span of the reed.     

A MONTE-CARLO APPROACH TO THE INTERPRETATION OF BUBBLE PROBE SIGNALS IN FREELY BUBBLING FLUID BEDS†

The interpretation of the signals generated by a double probe may be done by the three characteristic times method:

t₁ the time duration of the pulses;

t₂ the time shift between the signals of the two probes;

t₃ the time interval between two pulses on one channel.

Each of these times is largely dispersed and the corresponding histograms may be constructed.

The present work is a trial to go over from the time histograms to physical properties of the bubbles combining a Monte-Carlo simulation and a flexible simplex optimisation procedure.

As a result, the percentage of oblique bubbles cutting just one level, the bubble size distribution, the average velocity-size relation, and the individual dispersion around it may be defined.

The procedure is finally applied to experimental results obtained with a light probe in a fluid bed of glass beads.     

INVITED REVIEW ABSORPTION OF NOX GASES

Oxidation of nitric oxide is an important step in NO_x absorption. Recent advances namely catalytic oxidation and the use of slrong oxidizing agents have been reviewed. The refinements which have been made in the kinetics of NO oxidation have been discussed. Several liquid phase absorbents have been suggested for the NO removal, particularly for the purpose of pollution abatement. Different models for NO oxidation using nitric acid have been analysed and the limitations of published information have been brought out.

Absorption of tetravalent nitrogen oxide (NO₂ and N₂O₄) has received considerable attention. The absorbents include water, nitric and sulfuric acids, sodium hydroxide, sodium sulfite and sodium chlorite. Absorption in water and nitric acid is important in the manufacture of nitric acid. The published information on the mechanism of NO₂ and N₂O₄ absorption in water has been critically analysed. The problem of nitrous acid decomposition has been analysed on the basis of film theory. The predictions agree favourably with the available experimental data.

A new mathematical model has been developed for a packed column. Performance charts have been prepared which take into account the effects of concentration of nitric acid, superficial liquid velocity, temperature and the partial pressures of various components. A simplified model on the basis of NO oxidation has also been presented.

Various process design aspects have been discussed in detail. Optimum values for various operating parameters exist and basis for their selection has been explained. Some engineering aspects such as the selection of equipment and material of construction have also been discussed. A comparison between semi-batch and continuous modes of operation has been presented. The problem of the manufacture of pure nitrites has been analysed

Specific recommendations have been made regarding the use of equations and procedures in design. The knowledge gaps have been clearly brought out and suggestions have been made for future work     

EVALUATION OF CONDUCTIVE HEAT TRANSFER MECHANISMS BETWEEN AN IMMERSED SURFACE AND THE ADJACENT LAYER OF PARTICLES IN BUBBLING FLUIDIZED BEDS

The evaluation of the heat transfer coefficient h_wp between a heat exchanging surface immersed in a gas fluidized bed and the adjacent layer of dense phase particles is analyzed in this contribution. Gas convective and radiant effects are not included in the present analysis.

The inclusion of h_wp, or an equivalent formation, in mechanistic models describing heat transfer has been necessary because the sudden voidage variation close to the immersed wall restrains significantly the heat transfer rate. However, there is not at present a widely accepted expression to evaluate h_wp.

A precise formulation for h_wp accounting for transient conduction inside spherical particles, the Smoluchowski effect, the concentration of particles in the adjacent layer (N_p) and an effective separation gap (l₀) is developed here.

Although N_p can be estimated, in principle, from experimental evidence in packed beds, and it is reasonably expected that l₀ = 0, the analysis of experimental heat transfer rates in moving beds, packed beds, and bubbling fluidized beds indicate that values of h_wp are, in general, smaller than expected from these assumptions. Appropriate values of l₀ and N_p are then stimated by fitting the experimental data.

The probable effect of surface asperities is also discussed by analyzing a simplified geometrical model. It is concluded that the parameter l₀ can be also effective to account for particle roughness, independently of thermal properties.     

IMPORTANCE OF DISPERSED SOLIDS IN BUBBLES FOR EXOTHERMIC REACTIONS IN FLUIDIZED BEDS

Ignition of activated carbon particles were measured in a vertical tube reactor of 4 cm ID, where single particles fell consecutively through a gas mixture containing oxygen.

A two dimensional fluidized bed reactor 24 cm wide, 51 cm high and 2.5 cm in thickness was used for visual observation through a wide front window 24 cm × 35 cm covered with a silica glass plate 1 cm thick. Activated carbon particles were fluidized incipientiy by air, and a gas mixture containing oxygen was injected upwards into the bed through a nozzle positioned 5 cm above the distributor, forming single bubbles intermittently.

It was observed that carbon particles dispersed in rising bubbles were ignited abruptly at emulsion phase temperatures above 550°C. Experimental findings from the fluidized bed were compared with those from the tube reactor, suggesting that the igniting conditions for particles dispersed in bubbles are nearly the same as for single particles falling in the tube reactor.     

泡沫薄膜液在直管内的流变学特性

针对泡沫液在多孔介质内的流动特点,对泡沫薄膜液在直管内的流变学特性进行了实验研究。按单相幂律流体假设,获得二氧化碳及氮气泡沫薄膜液的表观黏度数据。结果表明：泡沫薄膜液具有较大表观黏度并呈现剪切变稀的非牛顿流体特性。由于水溶性影响,二氧化碳泡沫液的表观黏度要小于氮气泡沫液。利用量纲分析法确定量纲1参数,对泡沫薄膜液的流变学特性进行了量纲1分析并给出基于两相流动分析的阻力模型。     

泡沫薄膜液在变径管内的流变学特性

针对泡沫流体在储层介质内的流动特点,对泡沫薄膜液在变径管内的流变学特性进行实验研究。基于两相流动假设,利用量纲分析法确定量纲1参数ΔpD/δ及（3μU/σ）^2/3。通过CO₂及N₂泡沫的实验结果发现泡沫薄膜液在变径管内流动时需克服启动压力,量纲1参数间呈明显的线性关系,而且N₂泡沫与CO₂泡沫相比具有更大的流动阻力。与直管相比,泡沫薄膜液在变径管内具有更大的流动压差。实验结果表明,对于揭示泡沫液在多孔介质中的流动机理,Herschel-Bulkley模型优于幂律模型。     

基于TiO2溶胶杂化的分子筛炭膜制备及其结构与性能

以聚酰亚胺为前体,TiO₂溶胶为掺杂剂,经成膜和炭化制得杂化炭膜。采用热失重、电子显微镜、X-射线衍射、红外光谱和渗透法对前体的热性能、炭膜的微观形貌、微结构、表面官能团和气体分离性进行了表征。考察了TiO₂溶胶用量、渗透温度和渗透压力对炭膜的结构与性能影响。结果显示,掺杂TiO₂溶胶显著提高了最终炭膜渗透性和选择性;采用TiO₂溶胶量为10%前体所制备的杂化炭膜对H₂、CO₂、O₂渗透性分别为1993.8、1555.6、266.9 Barrer,同时H₂/N₂、CO₂/N₂、O₂/N₂选择性分别为93.6、73.0、12.5。     

界面聚合法制备用于脱氮提纯CH4的N2优先渗透ZIF-90/聚酰胺混合基质膜

作为一种高效的分离方法,膜法分离非常规天然气具有较理想的应用前景。相较CH₄优先渗透膜,N₂优先渗透膜优势在于分离N₂/CH₄混合气后CH₄处于高压侧,利于后续处理。以均苯三甲酰氯为油相单体,间苯二胺为水相单体,采用界面聚合法在聚砜基膜上制备致密超薄聚酰胺分离层,并通过向其中引入孔径可允许N₂分子通过而不允许CH₄分子通过的纳米颗粒ZIF-90,在膜内形成固定的N₂传递通道,成功制备了用于脱氮提纯CH₄的N₂优先渗透混合基质膜。膜渗透选择性能测试结果显示当混合基质膜中纳米颗粒掺杂量为0.30 g·L^-1时,2 bar（1 bar=0.1 MPa）进料压力下,N₂渗透速率达1.16×10^-9 mol·m^-2·s^-1·Pa^-1,N₂/CH₄分离因子达16.6,分离因子比未掺杂ZIF-90的聚酰胺膜提高46.5%,具有一定的处理非常规天然气脱氮提纯甲烷的应用潜力。     

界面聚合法制备用于脱氮提纯CH4的N2优先渗透ZIF-90/聚酰胺混合基质膜

作为一种高效的分离方法,膜法分离非常规天然气具有较理想的应用前景。相较CH₄优先渗透膜,N₂优先渗透膜优势在于分离N₂/CH₄混合气后CH₄处于高压侧,利于后续处理。以均苯三甲酰氯为油相单体,间苯二胺为水相单体,采用界面聚合法在聚砜基膜上制备致密超薄聚酰胺分离层,并通过向其中引入孔径可允许N₂分子通过而不允许CH₄分子通过的纳米颗粒ZIF-90,在膜内形成固定的N₂传递通道,成功制备了用于脱氮提纯CH₄的N₂优先渗透混合基质膜。膜渗透选择性能测试结果显示当混合基质膜中纳米颗粒掺杂量为0.30 g·L^-1时,2 bar（1 bar=0.1 MPa）进料压力下,N₂渗透速率达1.16×10^-9 mol·m^-2·s^-1·Pa^-1,N₂/CH₄分离因子达16.6,分离因子比未掺杂ZIF-90的聚酰胺膜提高46.5%,具有一定的处理非常规天然气脱氮提纯甲烷的应用潜力。     

ABSORPTION AND DESORPTION TO AND FROM LIQUID FILMS ON INCLINED PLANES

Two published theoretical models are examined and applied to experimental results for absorption and desorption. The system used was CO₂/H₂O and studies were made for liquid film flow down inclined planes. Experimental results give “Reduced” values of mass ransfer rates.

Interferometric studies give interfacial concentration, penetration and film depths, and take-up of carbon dioxide. In the case of desorption the interferograms are distorted by “deflections.”

All the experimental values for absorption and desorption differ from those calculated from theoretical models.

Desorption is not a mirror image of absorption, and it is approximately 75% of the transfer rate of absorption over a wide operating range.

A comparison is made of the behaviour of static pools and flowing liquid films.     

THE CHARACTERIZATION OF KINETICS BY SINGULAR POINTS: COMPARISON OF SUPPORTED VS. UNSUPPORTED AND ISOTHERMAL VS. NONISOTHERMAL Pt CATALYSTS IN AMMONIA OXIDATION

Similar multiplicity features were observed during ammonia oxidation on supported or unsupported Pt catalysts, whether in the isothermal or nonisothermal modes of operation. Two types of isothermal multiplicity patterns were observed upon varying ammonia concentration. The simplest model predicting the transition between the two must have a pitchfork singularity. The same singularity accounts also for the diagrams observed with varying oxygen concentration. The singularities of the isothermal kinetics are inferred also from nonisothermal experiments

These similarities suggest that identical kinetic models are responsible for multiplicity in supported and unsupported catalysts. The dependences on either reactant is used to characterize the kinetics by defining the highest order singularity in the temperature-concentrations space. This information is utilized to develop the simplest rate expression which accounts for the observations

The two simultaneous reactions, producing N₂ and N₂O, were found to ignite and extinguish simultaneously.     

TRANSITION OF FLOW REGIME IN FLUIDIZED BEDS WITH SLANTING BLADE BAFFLES

A flow model is proposed to investigate the transition of flow regime from bubbling to turbulent fluidization postulating that the flow in the emulsion phase follows the Richardson-Zaki equation.

Void fraction of the whole bed ε_f and the mean velocity of bubbles U_b were measured in fluidized beds of 0.3 and 0.5 m ID, in which slanting blade baffles were positioned. Mo-catalyst, silica gel, sand and glass beads with size between 135-443 μm were fluidized by air.

Void fraction of the emulsion phase ε _e was calculated on the basis of the above model. Correlating ε _e with superficial gas velocity U_ƒ, we found that ε _e was very close to ε _mƒ in the bubbling regime and that e, increased with increasing U_ƒ in the turbulent regime.

Calculated values of the volume fraction of bubble phase δ were correlated with U_ƒ, from which apparent transition point from bubbling to turbulent regime was estimated. Combining information obtained, transition of flow regime in the above type of fluidized beds is discussed     

A SIMPLE APPLICATION OF MURPHREE TRAY EFFICIENCY TO SEPARATION PROCESSES

Vapor-liquid equilibrium is predicted by using the Soave modification of the Redlich-Kwong equation of state (EOSrpar;. The concept of equal fugacities is used to calculate the equilibrium constant, K₁ = y₁/x₀, then, it is shown how the Murphree tray efficiency can be applied on the liquid or the vapor phases to modify that constant. The derivatives needed are calculated numerically, and it is shown that for absorbers and distillation columns, Murphree tray efficiency applied this way can be used to simulate the actual number of stages

Murphree tray efficiency values can be specified for one, several or all of the components on any stages of a column

A dehydration example is shown, the dew point depression values of a mixture of water-gas, using a triethylene glycol solution for dehydration purposes, are calculated by incorporating the method into a process simulator program called PROSIM® and compared with the values reported in the literature.     

HEAT TRANSFER IN SPOUTED BEDS

Experiments were carried out in order to analyse the wall-to-bed and fluid-to-particle heat transfer coefficients in spouted Beds. wall-to-bed heat transfer coefficients were determined in cylindrical-conical and conical spouted beds for various gas flow rates, particle sizes and bed heights for spouted beds with and without draft tubes.

A new definition for wall-to-bed transfer coefficient was proposed baaed on experimental observations.

The heat tranefer area was also studied to ensure that a physically significant fluid-to-particle heat transfer coefficient was achieved.     

KINETIC AND STRUCTURAL STUDIES OF REGENERATION OF SULFIDED DOLOMITE IN CARBON DIOXIDE I THE FIRST CYCLE REGENERATION

(Communicated by H. L. Toor)

Half-calcined dolomite (CaCO₃ · MgO) is one of the most promising sorbents for desulfurizing fuel gas at high temperatures. For environmental reasons, the spent dolomite must be capable of regeneration for cyclic use. Regeneration by a mixed gas of H₂O/CO₂ has not met with success due mainly to the deterioration of sorbent reactivity with cycling. This research investigates an alternative method of regeneration using CO₂ alone and its application to cyclic use.

Kinetic data for first cycle regeneration are collected in a TGA system at 500 to 950°C and 1 to 21.4 atm. The effects of gas-composition, preconditioning and solid structure are also studied. The results show that regeneration by CO, is equally effective as by H₂O/CO₂ in terms of sorbenl reactivity. More significantly, the sorbent has shown a much slower deterioration upon cycling. Examination of solid structure by SEM and compositional profile of sulfur by XES reveals that the reaction proceeds topochemically above 700°C and homogeneously below 650°C. A transport-reaction model is developed and shown to agree closely with experimental results.     

A Method to Obtain Gas-PDMS Membrane Interaction Parameters for UNIQUAC Model

The recovery or capture of one or more components from gas mixture by membrane separation has become a research focus in recent years. This study investigates the gas-membrane solution equilibrium, for which Henry’s law is not applicable if the gas phase is a mixture. This problem can be solved by using UNIQUAC model to calculate the activity coefficient of gas dissolved in the membrane. A method was proposed in this study to obtain the gas-membrane interaction parameter for UNIQUAC model. By the experiments of gas permeation through polydimethylsiloxane PDMS membrane, the solubility coefficients of some gases (N₂, CO₂, CH₄) were measured. Through non-linear fitting UNIQUAC model to the experimental results from this study and in literature (H₂, O₂, C₃H₈), the gas-membrane interaction parameters for these gases were obtained. Based on these parameters, the activity coefficients of the dissolved gas were calculated by UNIQUAC model, and their values agree well with the experimental data. These results confirm the feasibility and effectiveness of the proposed method, which makes it possible to better predict gas-membrane solution equilibrium.     

Preparation and gas permeation of composite carbon membranes from poly(phthalazinone ether sulfone ketone)

Composite carbon membranes were prepared from poly(phthalazinone ether sulfone ketone) (PPESK) by incorporating with polyvinylpyrrolidone (PVP) or zeolite (ZSM-5) through stabilization and pyrolysis processes. The thermal stability of composite polymeric membranes was measured by thermal gravimetric analysis. The resultant composite carbon membranes were characterized by scanning electron microscopy, X-ray diffraction and gas permeation technique, respectively. The results illustrated that the thermal stability of composite polymeric membranes was enhanced by addition of ZSM-5 or reduced by PVP. For ZSM-5 or PVP composite carbon membranes prepared at 650 °C, the O₂ permeability is 199.70 Barrer or 124.89 Barrer, and the O₂/N₂ selectivity is 10.3 or 4.2, respectively. Compared with carbon membranes from pure PPESK, the O₂ permeability of ZSM-5 or PVP composite carbon membranes increases by 18.5 or 11.6 times, together with the O₂/N₂ selectivity decreasing by 35.2% or 73.6%, respectively. The gas separation mechanism of composite carbon membranes is molecular sieving. Adsorption effect also plays a significant role for CO₂ permeating through ZSM-5 composite carbon membranes.     

二氧化碳泡沫稳定性及聚合物对其泡沫性能的影响

基于CO₂气体性质的特殊性以及CO₂泡沫在多孔介质中表现出不同于其他气体泡沫的现象,利用气流法,选用十二烷基苯磺酸钠（SDBS）作为起泡剂,研究了CO₂泡沫的稳定性和衰减规律,以及聚合物部分水解聚丙烯酰胺（HPAM）对CO₂泡沫性能的影响。结果表明,在相同条件下,CO₂泡沫的稳定性比N₂泡沫差,并且CO₂泡沫的稳定性基本不受表面活性剂浓度的影响;CO₂泡沫的衰减曲线近似一条直线,泡沫形成后体积迅速减小。CO₂在水中具有较大的溶解度,泡沫的液膜渗透率系数大,因而泡沫稳定性差,也是造成CO₂泡沫在岩心内渗流规律区别于N₂泡沫的一个重要原因。HPAM的加入可以在一定程度上增强CO₂泡沫的稳定性,但同时也会使溶液起泡性能降低,所以实际应用时需要综合考虑泡沫特性,选择最佳的聚合物浓度。     

EFFECTS OF GEOMETRY ON HYDRODYNAMICS IN EXTERNAL-LOOP AIRLIFT REACTORS

Experimental investigations were carried out in model external-loop airlift reactors. Two reactors of laboratory scale (riser liquid height ranged between 1.16-1.56 m, riser diameter 0.03 m, A_D/A_R ratio between 0.111-1,000, total liquid volume V_T = (1.189-2.446).10^-3m³) and pilot-plant scale (riser liquid height of 4.4 and 4.7 m, respectively, riser diameter 0.200 m, A_D/A_R ratio of 0.1225 and 0.040 m, total liquid volume, V_T = (0.144-0.170) m³) were used.

The influences of reactor geometry characterized by some parameter as: A_D/A_R ratio, liquid height in riser and downcomer and liquid height in gas separator, together with the amount of introduced air, on the basic hydrodynamic design parameters: gas holdup and liquid circulation velocity were analysed.

The influence of gas sparger design on gas holdup and liquid velocity was found to be negligible.

The experimental liquid circulation velocity was correlated using a simplified form of the energy balance in airlift reactors, valid for external-loop airlift reactors with almost complete phase separation at the top.

An original dimensionless correlation for gas holdup prediction involving superficial velocities of gas and liquid, cross sectional areas, dispersion height, riser diameter, as well as Froude number, was obtained.