MICROMIXING EFFECTS ON BARIUM SULFATE PRECIPITATION IN AN MSMPR REACTOR

The Effects of non-ideal and nonhomogeneous mixing on barium sulfate precipitation in an MSMPR reactor were observed experimentally and analyzed theoretically. To generate nonhomogeneous mixing the unmixed feed streams were fed to the reactor at the same location (joint feeding mode) or a plug flow reactor was connected to the MSMPR reactor. These nonhomogeneous mixing conditions resulted in significant reductions in particle size and increases in particle numbers. These non ideal mixing effects were dependent on the impeller speed, feed stream velocity and residence time in the connected plug flow reactor and are believed to result from elevated supersaturation levels in a premixing zone which are controlled by turbulent micromixing

To model the effect of nonhomogeneous mixing (premixing) in the MSM PR reactor a plug flow-stirred lank reactor series model was developed. The plug flow reactor represents the premixing region of the MSMPR reactor in which turbulent micromixing is important, and the stirred tank reactor describes the homogeneous mixing region of the MSMPR reactor where particle growth is important. The model predicts that the premixing effect is strongly dependent on micromixing of the feeds in the premixing region, and thus, as the turbulent mixing intensity in this region is increased, the particle size in the product suspension is reduced and the particle population is increased. These predictions of the model arc in good agreement with the experimental data. An interesting prediction of the model is that as the impeller speed increases, the precipitation of barium sulfate in an MSMPR reactor deviates increasingly from the precipitation in a perfectly mixed (ideal) reactor.     

间歇搅拌反应器的微观混合特性

<正> 1 引言 微观混合是指流体分子尺度上的混合,而化学反应过程又是反应物分子间相互有碰撞作用的过程,微观混合对搅拌槽内进行化学反应有直接影响,因此开展对间歇搅拌反应器微观混合状况的研究十分必要。但微观混合的机理和模型较复杂,测定方法较困难,过去20年来集中于机理与模型研究,实际应用报道较少。本文对乙酸乙酯不可逆二级皂化间歇反应器中搅拌转速、介质粘度对微观混合状况的影响进行研究。 2 微观混合状态的描述 2.1 微观混合模型概述 从Danckwerts提出一整套混合统计概念和微观混合的2种极限理想状态后,许多研究者力求把这2种状态结合起来描述实际的微观混合状态,并通过大量实验,从工程和机理角度提出了不少微观混合模型。但这些工程模型都是单参数模型,经湍流类比分析,其微观混合参数都与理想混合时间有关,具有共同的结构特征。     

EFFECT OF PVA AND GELATIN ADDITIVES ON BARIUM SULFATE PRECIPITATION IN AN MSMPR REACTOR

The effect of high molecular weight additives (PVA and gelatin) on barium sulfate precipitation in an MSMPR reactor is investigated. The impeller speed is varied from 0 to 1200 rpm and the additive concentration in the bulk solution is increased up to 5.0 g/1. As the additive concentration is increased, the particle growth rate decreases and the nucleation rate increases. However, the particle morphology is not changed by the additives. The experimental results are explained qualitatively by supposing that the additive is adsorbed on the particle surface and inhibits the mass transfer to the surface.

To explain the additive effect quantitatively a diffusion limitation model is developed. The diffusion limitation model predicts the effects of additives over the entire range of additive concentrations and impeller speeds set in the experiments. The model predicts very high supersaturation levels in the reactor which is consistent with a mass transfer controlled particle growth. Furthermore, the model results are consistent with simple theories of polymer adsorption and diffusion in polymer solutions     

铬酸钡比色法测定垢样中硫酸盐含量的探讨

对垢样中硫酸盐含量测定方法进行改进,建立铬酸钡比色测定法.通过精密度实验和回收率实验,验证该测定方法准确可靠,缩短分析时间,降低分析成本.     

DYNAMIC OPTIMISATION OF THE SELECTIVITY IN A BATCH ELECTROCHEMICAL REACTOR

In a stirred batch electrochemical reactor where a series of cathodic reactions ABD takes place, the optimal profiles of electrode potential required to reduce the concentration of A from C_AO to C_Af in a specified batch period t_f, while maximising the final concentration of product B, were determined by means of Pontryagin's maximum principle. The influence of the liquid/solid mass transfer coefficient and the desired final conversion rate of A was investigated. In this paper, the reaction studied was the electroreduction of oxalic acid (A) to glyoxilic acid (B) followed by the reduction of glyoxilic acid to glycollic acid (A). The results obtained by applying optimal profiles were compared to those resulting from constant electrode potentials. It was shown that in realistic operating conditions, the final concentration of Scan be improved up to 25% when electrode potential is optimised.     

生物优势菌种对SBBR除磷性能的影响

通过投加聚磷菌与未投加聚磷菌的对比试验,研究投加优势菌种后淹没序批式生物膜法(SBBR)除磷性能。试验结果表明:SBBR反应器中投加生物优势菌种后,厌氧段总磷释放和好氧段总磷吸收的效果明显增加,提高了除磷效率,缩短了停留时间。在填料装填密度为30%,水力停留时间为7h(其中厌氧3h,好氧4h),pH值在6.5～8.5时,进水COD在0.2～1.5kgCOD/m3.d时,投加菌种的反应器中COD和TP去除率均明显高于未投加菌种的反应器,去除效率提高5%以上,反应器对COD和TP的变化具有更强的适应性。     

INTERPRETATION OF MICROMIXING EFFECTS ON FAST CONSECUTIVE-COMPETING REACTIONS IN SEMI-BATCH STIRRED TANKS BY A SIMPLE INTERACTION MODEL

A model is proposed for interpreting micromixing experiments in a semi-batch reactor. In these experiments, a fast consecutive-competing reaction system is used A + B → R, R + B → S, B being added either dropwise or as a pulse into an excess of A. A segregation index X_s = 2n_s/n_B0 is measured after completion of the reaction for various locations of the injection point. The macroscopic flow pattern is assumed to be known, essentially characterized by the recirculation time t_c. Micromixing then takes place within the cloud via a mechanism of interaction with the mean environment (IEM model, micromixing time t_m). Experimental results published by Barthole et al. (precipitation of barium sulphate) and Bourne et al. (diazo coupling) are successfully interpreted by this model. The influence of stirring speed, injection volume, concentration of species and mode of injection (pulse or dropwise) are especially well accounted for. This model provides a simple method for predicting the influence of mixing on selectivity in semi-batch reactors.     

EFFECTS OF pH,INITIATOR, SCAVENGER,AND SURFACTANT ON THE OZONATION MECHANISM OF AN AZO DYE (ACID RED-151) IN A BATCH REACTOR

In this study, an initiator (Fe²⁺) and a scavenger (CO₃ ^2?) were used at different concentrations in a batch reactor to investigate the reaction mechanism of ozonation of a model azo dye, namely Acid Red-151 (AR-151). Also, the effect of a nonionic surfactant known as a major pollutant in many industrial wastewaters, namely polyethylene glycol (PEG), was observed on the degradation rate of AR-151. The experimental parameters and their ranges were: pH (2.5–10), initiator (0.8–50 mg/L of Fe²⁺), surfactant (10–200 mg/L of PEG), and scavenger (10–500 mg/L of CO₃ ^2?); the initial concentration of the azo dye was kept constant at 20 mg/L in all the experiments. Results showed that decomposition of ozone was enhanced with increasing pH and increasing initiator (Fe²⁺) concentration at a scavenger concentration of 100 mg/L, when there is no dye in the medium. A scavenger concentration of 100 mg/L CO₃ ^2? was not sufficient to terminate the chain reactions of ozone decomposition. It was concluded that the dominant mechanism in the degradation of AR-151 was its direct oxidation with ozone molecules in water. The data obtained for the dye and chemical oxygen demand (COD) removals and total oxidation rate constants at different operating conditions were assessed in order to estimate the possible contribution of dye-oxidation by free radicals.     

ORIGINAL TITLE: INTERPRETATION OF MICROMIXING EFFECTS ON FAST CONSECUTIVE-COMPETITIVE REACTIONS IN SEMI-BATCH STIRRED TANKS BY A SIMPLE INTERACTION MODEL

Liquid-liquid equilibrium data for two ternary systems were obtained. The experimental data were measured for cyclohexane-toluene-sulfolane at 17, 25 and 50°C, and for hexane-toluene-sulfolane at 18 and 25°C. The NTRL and UNIQUAC models were used to correlate the experimental results and to calculate the phase compositions of the ternary systems. The agreement between the experimental results and the fitted values was equally good with both of the models.     

EFFECTS OF TURBULENT SHEAR STRESS ON THE GROWTH OF SUSPENDED PLANT CELLS IN A BUBBLE COLUMN REACTOR

In this paper,effects of increasing the height of column,bubble size and gas flow rate onthe growth of suspended Catharanthus roseus plant cells in a 1.5 litre bubble column were studied.Statistical characteristics of turbulence such as auto-correlation function,and auto-power spectral den-sity function of the nuctuating liquid velocity were measured in a bubble column employing pseudo-cell-granulated agar.Calculations of turbulent shear stress were carried out.From these studies it is sug-gested that in plant cell suspension culture sparged with large bubbles.turbulent shear stress is prob-ably one of the most important reasons for the inhibited cell growth and cell damage.Larger bubblesor higher gas flow rates lead to the increase in shear stress and are more detrimental to plant cells.     

人工配水和实际污水(AO)2SBR同步脱氮除磷比较研究

在污泥停留时间为15d、HRT为1.5h和DO的质量浓度约为2.5 mg·L-1条件下,分别对人工配水和实际生活污水进行了(AO)2SBR法同步脱氮除磷试验,并对处理效果进行了对比.结果表明,人工配水和实际污水的(AO)2SBR工艺好氧和缺氧脱氮除磷过程几乎全部以厌氧阶段合成的胞内聚羟基烷酸为碳源,说明反硝化脱氮除磷确实可实现“一碳两用”;人工配水和实际污水的好氧吸磷率分别为67.49％和93.42％、缺氧除氮率分别为58.22％和77.98％,实际污水驯化得到的反硝化聚磷菌和聚磷菌具有更强的反硝化能力和好氧吸磷能力.     

ON THE EFFECTS OF SYNGAS COMPOSITION AND WATER-GAS-SHIFT REACTION RATE ON FT SYNTHESIS OVER IRON BASED CATALYST IN A SLURRY REACTOR

Water gas shift reaction plays an important role in the Fischer-Tropsch synthesis reaction over iron-based catalysts. A slurry reactor model which accounted for the kinetics of both Fischer-Tropsch synthesis and water gas shift reaction was used to investigate the effects of hydrogen to carbon monoxide ratio, water vapor concentration and reactor temperature on synthesis gas conversion. The model was used to determine optimum concentration of water in the feed gas. For a given reactor temperature, the optimum concentration of water in the feed gas was found to increase with decreasing hydrogen to carbon monoxide ratio. The optimum concentration of water in the feed gas was found to decrease with increasing reactor temperature. Increasing the water gas shift reaction rate improved syngas conversion for low reaction temperatures.