Experimental Analysis of Low-Temperature Bed Drying of Wooden Biomass Particles

This report investigates the low-temperature bed drying of biomass particles for use in a gasification process. Experimental drying equipment capable of drying up to 0.25 m³ of biomass batchwise was constructed. The experimental result indicates that the drying equipment and applied method are appropriate to evaluate different drying parameters and their influence on the drying course. Drying parameters such as air temperature, air velocity, bed height, and type of wood are studied regarding the drying rate, final moisture content in the material, and bed pressure drop. The constant-rate and falling-rate drying period are studied to obtain an energy efficient drying process. Measurements show that the drying zone (where the actual drying occurs) progresses irregularly through the bed.     

Experimental Analysis of Low-Temperature Bed Drying of Wooden Biomass Particles

This report investigates the low-temperature bed drying of biomass particles for use in a gasification process. Experimental drying equipment capable of drying up to 0.25 m³ of biomass batchwise was constructed. The experimental result indicates that the drying equipment and applied method are appropriate to evaluate different drying parameters and their influence on the drying course. Drying parameters such as air temperature, air velocity, bed height, and type of wood are studied regarding the drying rate, final moisture content in the material, and bed pressure drop. The constant-rate and falling-rate drying period are studied to obtain an energy efficient drying process. Measurements show that the drying zone (where the actual drying occurs) progresses irregularly through the bed.     

Pneumatic Drying of Iron Ore Particles in a Vertical Tube

The drying and hydrodynamic characteristics of iron ore particles in a vertical pneumatic conveying dryer (0.078 m ID × 6.0 m high) have been determined. The pressure drop decreases along the height at the acceleration region, while it remains constant irrespective of the height in the fully developed region. The degree of particle drying in the dilute pneumatic region increases with increasing superficial inlet gas velocity at constant inlet gas temperature and solid injection rate. However, it decreases with increasing solid injection rates at identical superficial inlet gas velocity and inlet gas temperature. The degree of particle drying increases from 48.6 to 82.5% as the inlet gas temperature increases from 100 to 400 °C.     

Simulation of hydrodynamic behaviour and mass transfer efficiency of reduced pressure distillation

A random packing hydrodynamic simulator is designed specially to carry out experiments under reduced pressures with a counter-current flow air/water system. The simulator results (air/water system) compared to those obtained in a real packed distillation column (benzylchloride/ ethylbenzene system) show a good agreement between hydrodynamic parameters like pressure drop, flooding flow rate, and total liquid hold-up. Empirical relationships derived from the simulator experimental results are proposed allowing the calculation of the pressure drop in a packed distillation column, operating in the pressure range between 10 kPa and atmospheric pressure. The influence of reduced pressure on the HETP in the distillation column and interfacial area in the simulator was also investigated.     

Pneumatic Drying of Iron Ore Particles in a Vertical Tube

Abstract

The drying and hydrodynamic characteristics of iron ore particles in a vertical pneumatic conveying dryer (0.078 m ID × 6.0 m high) have been determined. The pressure drop decreases along the height at the acceleration region, while it remains constant irrespective of the height in the fully developed region. The degree of particle drying in the dilute pneumatic region increases with increasing superficial inlet gas velocity at constant inlet gas temperature and solid injection rate. However, it decreases with increasing solid injection rates at identical superficial inlet gas velocity and inlet gas temperature. The degree of particle drying increases from 48.6 to 82.5% as the inlet gas temperature increases from 100 to 400 °C.     

粮仓搅拌干燥装置的试验研究

低温筒仓和自然通风干燥是常用的玉米干燥方式,但存在物料降水、降温不均匀和效率低等问题。针对低温筒仓干燥存在的问题,深入研究了仓内螺旋搅拌器的工作原理,设计了搅拌干燥试验台,研究了螺旋搅拌器结构参教和运动参教对搅拌器性能的影响,对七种不同尺寸的螺旋和两种粮食的干燥均匀性进行了对比试验,选出了较好的结构参数,为搅拌器的设计和应用提供了理论依据。     

Effect of stirring on cellulose graft copolymerization. V. Influence of reaction parameters

Styrene was grafted onto dissolving pulp by the cellulose xanthate–Fe²⁺–H₂O₂ system. Reaction parameters were found to have strong influence on conversion to both copolymer and total polymer, as well as on the dependence of polymerization on stirring. The formation of polymer was almost completely inhibited by pure oxygen, while air only slowed down the reaction. Under inert atmosphere, the effect of agitator speed was found to be strongly dependent on monomer and substrate concentration as well as on the concentration of emulsifier. The location of the maximum on the conversion vs. agitator speed curve was strongly affected by the shape of the stirrer. The presence of emulsifier had a relatively small effect on copolymer formation in the case of acrylamide, a water-soluble monomer. Also the effect of stirring was less marked in the case of acrylamide. In all the systems investigated, the conversion to copolymer and total polymer was found to drop rapidly above a certain limiting agitator speed. The latter was different and characteristic for each system. No polymer formation was observed beyond 1000 rpm regardless of all other reaction conditions.     

A Model for Through Drying of Tissue Paper at Constant Pressure Drop and High Drying Intensity

A mathematical model for through drying of paper at constant pressure drop was developed. The model is based on physical properties; hence, basis weight, pressure drop, drying air temperature, pore size distribution, initial gas fraction, and tortuosity are important input parameters to the model. The model was solved for different combinations of the variables basis weight, drying air temperature, and pressure drop corresponding to industrial conditions and the results were compared with data from bench-scale experiments. The simulations show that the drying rate curve is very sensitive to the air flow rate and that correctly modeling the correlation between pressure drop and air flow rate is the most important factor for a successful model for through drying. The model was tuned by adjusting the parameters initial gas fraction and tortuosity in order to give the best possible fit to experimental data. For a given basis weight and pressure drop, different drying air temperatures resulted in relatively constant values of the fitted parameters. This means that the model can well predict the effects of changes in drying air temperature based on a tuning of the model performed at the same basis weight and pressure drop. However, for a given basis weight, an increase in pressure drop yielded fitted parameters that were somewhat different; i.e., a lower initial gas fraction and a higher tortuosity, a change that increases the resistance to air flow. This implies that the correlation between pressure drop and air flow rate in the model does not quite capture the nonlinear relationship shown by the experiments.     

A Model for Through Drying of Tissue Paper at Constant Pressure Drop and High Drying Intensity

A mathematical model for through drying of paper at constant pressure drop was developed. The model is based on physical properties; hence, basis weight, pressure drop, drying air temperature, pore size distribution, initial gas fraction, and tortuosity are important input parameters to the model. The model was solved for different combinations of the variables basis weight, drying air temperature, and pressure drop corresponding to industrial conditions and the results were compared with data from bench-scale experiments. The simulations show that the drying rate curve is very sensitive to the air flow rate and that correctly modeling the correlation between pressure drop and air flow rate is the most important factor for a successful model for through drying. The model was tuned by adjusting the parameters initial gas fraction and tortuosity in order to give the best possible fit to experimental data. For a given basis weight and pressure drop, different drying air temperatures resulted in relatively constant values of the fitted parameters. This means that the model can well predict the effects of changes in drying air temperature based on a tuning of the model performed at the same basis weight and pressure drop. However, for a given basis weight, an increase in pressure drop yielded fitted parameters that were somewhat different; i.e., a lower initial gas fraction and a higher tortuosity, a change that increases the resistance to air flow. This implies that the correlation between pressure drop and air flow rate in the model does not quite capture the nonlinear relationship shown by the experiments.     

Drying of a Porous Material in a Pulsed Fluid Bed Dryer: The Influences of Temperature,Frequency of Pulsation,and Air Flow Rate

In this work, a four-section pulsed fluid bed apparatus with a 0.18 m² cross-section area was used to investigate the influence of pulsed-fluidization variables on the drying process of molecular sieves, a test material that was chosen because it presents an initial constant drying rate period. A two-level factorial design was developed to evaluate the influences of the inlet gas temperature—40 and 70°C—the frequency of pulsation—250 and 900 rpm—and the air flow rate—500 and 600 m³(STP)/h—on the drying rate. In addition, a comparison was made between the drying rates achieved with conventional and pulsed fluidization. Results showed that all the investigated variables affect the drying rate. Moreover, drying rates with conventional fluidization are considerably higher, which shows that one must expect a lower drying rate when pulsation is used in a drying process controlled by the external evaporation. Concerning fluid dynamics, this work also analyzed the influence of the frequency of pulsation on the pressure drop across the bed. The higher the frequency, the higher the pressure drop. That result can be explained by the reduction of channeling.     

倒锥形填料筐精馏塔板的性能研究

提出了一种新型高效塔板——倒锥形填料筐新型精馏塔板(RTPLT),在冷模塔内对该塔板的流体力学性能和塔内液体停留时间分布情况进行了研究。由实验数据关联得到了干板压降、湿板压降和漏液率的经验式。结果表明:RTPLT具有塔板压降低、雾沫夹带小、处理能力大等优点,其塔内液体停留时间分布的主要因素是液体流量。     

新型规整填料的性能及其在硫酸工业中的应用

针对硫酸干吸塔研制出了TJ160X型陶瓷规整填料，通过试验研究和分析证明该填料比传统的散堆填料具有更大的比表面积、更大的通量，其效率高、压降低。该填料在相同的条件下，压降是散堆填料的1／3，通量提高2倍以上。结合先进的液体分布器，模拟设计了一套硫酸干吸塔。探讨了将先进的陶瓷规整填料塔技术用于硫酸干吸系统的途径和方法。     

超超临界锅炉垂直水冷壁水动力特性

针对超超临界锅炉水冷壁系统水动力特性,建立了适用于复杂串并联回路系统的水动力特性计算模型,基于POWERSTATION4.0平台研制了水动力计算程序。按出口工质温度相等的原则计算节流补偿压降;以给定热负荷和节流方式进行流量分配和压降特性校核计算,用Chebyshev多项式拟合法拟合水动力特性曲线方程。并数值研究了1000 MW超超临界锅炉垂直水冷壁水动力特性,计算结果表明:U形叉管有利于垂直水冷壁节流调节,低负荷率下炉膛回路具有较强的正流量特性,而在超临界负荷具有弱的负流量特性。上炉膛回路在不同负荷率下均具有负流量特性。水冷壁水动力特性曲线呈单值性。研究结果为超超临界直流锅炉垂直水冷壁的工程设计及运行监测提供了可靠的理论依据。     

Trickle Flow Multiplicity: The Influence of the Prewetting Procedure on Flow Hysteresis

The existence of multiple hydrodynamic studies (MHS) in trickle flow is a well-known phenomenon. It is also known that different prewetting procedures result in major differences in MHS when the hydrodynamic variables pressure drop, liquid holdup and gas–liquid mass transfer are considered. Given a certain prewetting procedure one still has the option to perform flow hysteresis cycles to achieve an even wider variety of MHS. Although numerous studies have been performed on trickle flow hysteresis, none have attempted to decouple the hysteresis behaviour from the prewetting procedure followed. Accordingly there are numerous hysteresis possibilities that have not been investigated. In this work a single liquid and gas cycle were performed for four distinct prewetting procedures described here as a dry bed, a Levec type prewetted bed, Kan prewetted bed (achieved by increasing either the liquid or the gas flow rate until the pulsing flow regime is reached) and a Super prewetted bed. Pressure drop, liquid holdup and gas–liquid mass transfer are the hydrodynamic parameters studied to quantify the various MHS. It is shown that the shape and extent of the hysteresis cycle are strongly dependant on the prewetting procedure. In terms of flow structure, similar hysteresis trends on the Kan Liquid and Super prewetting modes indicate that these modes are hydrodynamically similar. The additional measurement of the hysteresis behaviour of gas–liquid mass transfer proofs that neither holdup nor pressure drop can be used as an indicator of the distribution uniformity.     

高初始含湿多孔介质喷雾干燥过程的热质耦合传递

多孔介质是大量干燥过程的主体,由于实际多孔介质干燥过程的复杂性,建立通用的干燥过程传热传质模型十分困难。通过分析喷雾干燥过程中高初始含湿多孔介质与干燥介质之间的传热传质机理以及各因素对传热传质的影响,根据马歇尔方程探讨了干燥介质与料雾之间的水蒸汽分压差在干燥过程中的变化情况,反映了多孔湿介质在喷雾干燥操作中的传热传质过程的几种特性,为确定实际生产中喷雾干燥器的操作条件指明了新的出路。     

Étude expérimentale sur le court-circuit de l'alimentation dans un réservoir imparfaitement agité en régime continu

The influence of various parameters on the degree of channeling of the feed is shown for a continuous, imperfectly mixed, stirred tank. Various forms of agitators have been used, more particularly the marine propeller type. In general, the amount of channeling decreases as the agitator speed increases. However, more channeling is often observed at low speeds than when the agitator is stopped. The nature of the maximum short-circuit observed at a given agitator speed is explained. Channeling usually decreases as the agitator diameter increases and as the distance between inlet and outlet increases. Channeling becomes more important as the flow rate increases. When baffles are present, the degree of channeling is hardly affected by their width, their position or whether they are slanted.     

Ecoulement de fluides newtoniens et non newtoniens à travers des lits fixes stratifiés

Fixed beds of plate shape particles have been studied in two different “flow-particle” configurations. From pressure drop measurements performed for a Newtonian fluid flow, two characteristic structural parameters have been determined by using a capillary - type model. The differences concerning the hydrodynamic behaviour of the two configurations are discussed and a factor characterizing the bed anisotropy is proposed. A dimensionless equation allowing the pressure drop determination for Newtonian and non-Newtonian purely viscous fluid flow in the two configurations, for a large range of Reynolds numbers, is proposed and tested with experiments.     

立式聚合釜气液传质特性的研究

本文旨在开发新一代聚四氟乙烯立式反应釜。分别在纯水-氧、乳化剂水溶液-氧两个体系中,用纯氧物理吸收法测定了H/D=1.27的釜的传质容量系数K_La,分析了两体系K_La差别的原因,并对实验结果进行了关联。研究表明,水体系的K_La,是乳液体系的2.5倍,桨型、安装位置等参数对传质有明显影响。在H/D≤1.27的釜中以单层三叶船舶推进器为最佳桨型。     

Pressure-drop predictions in a fixed-bed coal gasifier

In the Sasol Synfuels plant in Secunda, Sasol-Lurgi fixed-bed dry-bottom gasifiers are used for the conversion of low-grade bituminous coals to synthesis gas (syngas). The gasifiers are fed with lump coal having a particle size in the range from 5 to 100 mm. Operating experience shows that the average particle size and particle-size distribution (PSD) of feed coal, char and ash influence the pressure drop across the bed and the gas-flow distribution within the bed. These hydrodynamic phenomena are responsible for stable gasifier operation and for the quality and production rate of the syngas. The counter-current operation produces four characteristic zones in the gasifier, namely, drying, de-volatilization, reduction and combustion. The physical properties of the solids (i.e. average particle size, PSD, sphericity and density) are different in each of these zones. Similarly, the chemical composition of the syngas, its properties (temperature, density and viscosity) and superficial velocity vary along the height of the bed. The most popular equation used to estimate the pressure drop in packed beds is that proposed by Ergun. The Ergun equation gives good predictions for non-reacting, isothermal packed beds made of uniformly sized, spherical or nearly spherical particles. In the case of fixed-bed gasifiers, predictions by the Ergun equation based on the average or inlet values of bed and gas flow parameters are unsatisfactory because the bed structure and gas flow vary significantly in the different reaction zones. In this study, the Ergun equation is applied to each reaction zone separately. The total pressure drop across the bed is then calculated as the sum of pressure drops in all zones. It is shown that the total pressure drop obtained this way agrees better with the measured result.     

Pressure drop hysteresis in trickle bed reactors

An understanding of the hydrodynamics of trickle bed reactors (TBR) is essential for their design and prediction of their performance. Flow variables, packing characteristics, physical properties of fluids and operation modes influence the behavior of the TBR. The existence of multiple hydrodynamic states or hysteresis (pressure drop, liquid holdup, catalyst wetting, gas-liquid mass transfer) is due to the different flow structures in the packed bed and can be attained by a set of different operating procedures. Experiments were performed to study the effect of liquid and gas velocity, liquid surface tension, liquid viscosity and the particle diameter of the packing on two-phase pressure drop hysteresis. The parallel zone model for pressure drop hysteresis in the trickling flow was used for analysis of experimental data and flow structure. Theoretically predicted pressure drop hysteresis loop is in satisfactory agreement with experimental data.