出水回流对HABR处理印染废水效能的影响研究

文章采用中试规模复合式厌氧折流板反应器(HABR)对印染废水进行处理,研究了出水回流对HABR处理印染废水效能的影响,重点考察了回流比对污染物去除效果的影响和不同回流比下污染物的去除规律。试验结果表明,随着回流比(R)的增大,反应器中的污泥层高度逐渐增大,CODCr和色度去除率分别可达63.0%和55.6%。     

出水回流对HABR处理印染废水效能的影响研究

文章采用中试规模复合式厌氧折流板反应器(HABR)对印染废水进行处理,研究了出水回流对HABR处理印染废水效能的影响,重点考察了回流比对污染物去除效果的影响和不同回流比下污染物的去除规律。试验结果表明,随着回流比(R)的增大,反应器中的污泥层高度逐渐增大,CODCr和色度去除率分别可达63.0%和55.6%。     

撞击流反应器撞击面稳定性研究进展

撞击流技术因其良好的混合特性近些年用于强化制备超细粉体反应中的混合过程。撞击面的稳定影响反应器内的混合效果,所以本文对撞击面稳定性的研究进行了综述。撞击流反应器不同结构形式包括平面撞击流、轴对称撞击流和微型撞击流等。文中简述了撞击流稳定性的实验研究手段,分析轴对称撞击流反应器的径向偏转振荡的起止条件和不同喷嘴间距下的轴向偏移振荡规律,并且分析平面撞击流反应器的撞击面偏转周期以及偏转振荡的起止条件。得出轴对称撞击流与平面撞击流撞击面驻点的振荡对混合都有促进作用,并且偏移振荡周期不定,轴对称撞击面偏移振幅与喷嘴间距和雷诺数相关。平面撞击流的偏转振荡周期与进口流速成反比,反应器结构参数是撞击流稳定性的影响因素之一。根据轴对称撞击流偏移振荡对混合的促进作用,本文提出一种新型的预设流量波形双组撞击流反应器。新型撞击流反应器的独特结构克服了物料反应通道单一缺点,通过预设波形控制其进口流量,增大其撞击面偏移振幅,消除撞击面无序振荡,使流动轨迹扩展,扩大混合区域,并设计实验装置与方法讨论动态流量撞击流反应器撞击面稳定性对混合效果的影响。最后,本文对轴对称撞击流反应器的混合性能研究前景进行展望。     

ABR-好氧复合工艺处理生活污水条件优化研究

采用厌氧折流板反应器(ABR)-好氧复合工艺处理生活污水,该工艺以收集的曝气气体的提升作用取代回流泵实现混合液的回流,能有效节省动力消耗。在进水温度为25℃左右,p H为6.5~8.5的条件下对处理条件进行了优化,结果表明,该组合工艺脱氮除磷的最优条件:HRT为7.5 h,混合液回流比R1为200%、R2为50%,DO为3 mg/L。在最优条件下,处理出水水质稳定,处理效果良好。     

双循环两相生物处理工艺除磷试验

采用双循环两相生物脱氮除磷工艺（BICT）进行除磷试验研究。双循环两相生物脱氮除磷工艺由独立设置的前置厌氧反应器、悬浮生长的主反应器、附着生长的硝化反应器及介于主反应器和硝化反应器之间的沉淀池组成。在改变四种运行参数（泥龄、充水比、上清液回流比、运行时序）的条件下,对双循环两相生物处理工艺的除磷能力进行了实验室规模的试验研究。试验用反应器总体积为70L,连续运行210d。试验原水为市政污水。结果表明：BICT工艺通过缩短主反应区的运行泥龄,在不降低系统脱氮效率的基础上,强化了系统的除磷能力。当泥龄从20d降低至5d时,系统的除磷效率由76．5％提高至89．3％。缩短泥龄使主反应区的充水比得以提高,容积利用率增加;充水比可由最初的33％增加至60％。硝化液回流比由100％提高到200％时,系统的除磷效率几乎没有变化,这说明硝化液回流比对系统除磷能力影响较小;在循环周期中增加后曝气可进一步提高系统的过剩摄磷能力。     

管式振荡流反应器的流动模式研究(Ⅰ)PIV和RTD实验研究

采用粒子成像可视化（PIV）技术研究了管式振荡流反应器（OFR）内的流场形态和混合特点,并采用脉冲进样法测定了OFR在不同振荡条件下的停留时间分布函数。实验结果表明,OFR的混合特性十分复杂,并随振荡强度的变化呈现出不同的特征。振荡强度较低时,振荡使得OFR径向混合加强,减少了滞留区,流体的流动趋于平推流;振荡强度较高时,腔室内布满数目、尺寸和位置不断变化的漩涡,使每个腔室趋向于全混,腔室问的返混增大。实验数据与多级串联全混釜模型的比较结果显示,OFR的混合特性远非简单流动模式模型所能表征。     

背包式反应器与精馏塔耦合合成醋酸甲酯的模拟

针对背包式反应器与精馏塔耦合过程循环流股多,模拟计算收敛难度大的缺点,在Aspen P lus的RadFrac模型中引入Murphree板效率,仅用一个精馏塔模型就描述了这个复杂耦合过程的模拟模型。在固定精馏塔塔板数的情况下,讨论了背包反应器个数和间隔位置、进料位置、回流比和催化剂量等因素对醋酸甲酯合成的影响。初步探索了反应能力和分离能力的匹配问题。模拟结果表明,当采用5个背包反应器,反应器之间间隔4块分离塔板的配置时,在适宜条件下醋酸总转化率可达到96.3%。     

三股对撞式撞击流反应器微观混合性能研究

采用高速数码相机对三股对撞式撞击流反应器不同入口雷诺数下的流场特征进行了研究,并采用碘化物-碘酸盐平行竞争反应体系,考察了不同喷嘴直径下的入口雷诺数、不同溶液体积流量比对离集指数的影响。结果表明:入口雷诺数、溶液体积流量比对离集指数有明显的影响。增大入口雷诺数,三股流体高速撞击破碎成的液滴粒径逐渐减小,液滴雾化程度增加,离集指数减小,微观混合效果增加;增大体积流量比,溶液局部浓度增大,导致混合不均匀,离集指数增大。与传统撞击流反应器相比,三股对撞式撞击流反应器离集指数为传统撞击流反应器的2/5,表现出了较好的微观混合性能,更适用于不等溶液体积流量比的液液快速混合反应。     

T型反应器内非稳态吞噬流机理

运用激光诱导荧光（PLIF）技术和大涡模拟方法对T型反应器内的流动特性进行了研究。发现随着Reynolds数（Re）的增大,T型反应器中依次出现分离流（Re<120）、稳定吞噬流（120≤Re<190）、非稳态吞噬流（190≤Re≤300）、非稳态对称流（Re>300）四种流动模式。通过大涡模拟重点考察了非稳态吞噬流的振荡特性。结果表明,在非稳态吞噬流型下,T型反应器内撞击面上会周期性地出现旋涡合并现象,合并的涡向下传递,产生自持振荡。此时撞击区的压力、速度和涡量也发生周期性变化,且变化周期与旋涡合并周期相同,这种振荡是由速度和压力的周期性转换引起的。     

撞击流反应器内流场特性研究进展

综述了国内外撞击流反应器内流场速度和脉动振荡特性的研究进展。目前,对非限制撞击流反应器内撞击流体的径向速度发展及轴向速度与撞击驻点的脉动特性都有了系统研究,对撞击驻点的振荡模式进行了划分,并得出大量适用于不同喷嘴间距的速度关联式,但对驻点振荡模式的产生机理还没有明确解释。层流状态下随着雷诺数增大,众多学者对受限撞击流反应器内流型的流动模式进行了划分,提出了出现吞噬流模式的临界参数关联式,由于结构等参数的变化当前还没有普遍适用控制流型模式变化的关联式。在浸没撞击流反应器内用非线性分析法确定撞击区并划分了流场区域,但目前尚不能揭示湍流状态下流场能量分布与速度信号等的变化规律。最后作者对撞击流反应器内部流场结构的研究前景进行了展望。     

振荡流通过内插螺旋翅片管传热特性的数值模拟

振荡折流换热器广泛应用在包含传热传质过程的化工过程中,本文对管内插入螺旋翅片的振荡折流换热器进行了三维非稳态数值模拟,模拟在斯特劳哈尔数St=2,4,8和振荡雷诺数Reo=20,40,80范围内进行。通过作出瞬时三维流线,以观察流动状态随时间变化规律,发现其中有纵向涡和横向涡的周期性形成和脱落;得到了圆管周向局部传热系数随时间变化规律,以及不同振荡参数（St和Reo）下周向平均传热系数随时间的变化规律。结果表明：局部传热系数沿周向不均匀分布,并在翅片斜对面达最大;周向平均传热系数随时间周期性变化,时间平均传热系数随振幅增大而增大,但受频率影响却不明显;在本文讨论的参数范围内,平均传热系数最大可达圆管层流的4倍。     

Continuous screening of base-catalysed biodiesel production using New designs of mesoscale oscillatory baffled reactors

Base-catalysed biodiesel production was continuously screened using new designs of mesoscale oscillatory baffled reactors. Experiments were carried out at very low flow rates, less than 2 ml/min, which would be in the laminar flow regime in non oscillatory, steady state. Initially central disc baffles and helically wound wires were used, but provided insufficient mixing at this scale as demonstrated by glycerol settling. A new design of sharp-edged, helically baffled reactor was developed specifically for this application, which exhibited homogeneous mixing in the two-phase liquid reaction even at these low flow rates and low oscillatory Reynolds numbers. Methyl ester (biodiesel) was produced at a consistent quality and there were clear responses to variations in input conditions. A clear step-change between various steady state molar ratios of methanol to oil and dynamic screening was observed in these mesoscale oscillatory baffled reactors. Rapid screening technique such as this has the potential to significantly reduce process development, operating costs and environmental impact.     

The axial dispersion performance of an oscillatory flow meso-reactor with relevance to continuous flow operation

A laboratory scale continuous oscillatory flow meso-reactor was developed and residence time distribution (RTD) studies were carried out in order to establish certain process characteristics of the system. In particular, the dispersion coefficient as a function of the primary variables was established. Using optical probes the axial dispersion was investigated by monitoring the response of a pulse dye tracer at different locations within the meso-reactor. Three cases, net flow without oscillation, oscillation without net flow, and oscillation plus net flow were studied over a range of oscillation frequencies, amplitudes, and net flow rates. Both the imperfect and the perfect pulse injection methods were used to determine the axial dispersion coefficient for the system with and without net flow. The axial dispersion coefficient and the dimensionless dispersion number were analysed in the context of different flow conditions. A correlation was established and demonstrated that the axial dispersion within the meso-reactor could be quantified as a function of flow conditions. The results showed that the laboratory continuous flow meso-reactor was able to produce plug flow with modest axial dispersion over a wide range of parameter space, thereby indicating efficient mixing and effective RTD performance.     

三维翅片管外螺旋流动传热强化

流体在螺旋隔板换热器的壳程类似于塞状流流动,几乎没有返混和流动死区.在相同压降下,其传热系数比普通的弓形隔板换热器高得多.以润滑油作为实验介质,研究了润滑油在螺旋隔板单管换热器的壳程传热和压降性能,并与光滑管进行了性能对比.采用Wilson图解法分别分离出了螺旋隔板花瓣管和光滑管单管换热器的管程传热系数,并计算出各自的壳程传热系数,壳程传热系数相对误差为±3％.实验结果表明,在相同Reynolds数下,螺旋隔板花瓣管单管换热器的Nusselt数和压降Δp分别是螺旋隔板光滑管单管换热器的2～2.7倍和1.3～1.4倍.与螺旋隔板光滑管单管换热器相比,螺旋隔板花瓣管单管换热器的传热性能的提高远高于压降的提高,证明在螺旋流条件下,花瓣管具有很好的传热强化性能.     

Characterisation of fluid mixing in novel designs of mesoscale oscillatory baffled reactors operating at low flow rates (0.3-0.6 ml/min)

For the first time two mesoscale oscillatory baffled designs (central and integral baffles with their volumes of 5.2 ml and 4.4 ml, respectively) were experimentally characterised at net flow rates as low as 0.3 ml/min (Re_n ∼ 1.25), giving a residence time of around 15-17 min over a wide range of oscillation conditions. The purpose was to identify the lower limits of operability, thereby determining the maximum residence time per unit reactor volume for these mesoscale units. The characteristics of fluid flow were found to be strongly affected by Strouhal number at these low net flows. For the integral baffles, the oscillation conditions exhibited little influence on the fluid mixing. For the central baffles, there were three distinct flow regimes, depending on Strouhal numbers which affect the fluid characteristics differently. At two regimes of Sts, St ≥ 0.8 and 0.13 ≤ St ≤ 0.2, an increase in frequency did not alter the axial dispersion. At St ≥ 0.8, the fluid experienced less uniform mixing, representing by right-skewed residence time distribution (RTD) curves. At 0.20 ≤ St ≤ 0.13, the fluid mixing was significantly improved, indicated by narrow and symmetrical RTD curves with Re_o up to 700. At 0.4 ≤ St ≤ 0.27 and St ≤ 0.1, the degree of plug flow was a function of Re_o. The maximum number of tanks achieved at these low flow rates was in the range 30-35, occurring at a velocity ratio (Re_o/Re_n) of 39-40.     

Numerical study of the flow pattern and heat transfer enhancement in oscillatory baffled reactors with helical coil inserts

Oscillatory baffled reactors (OBRs) are a means of process intensification as they allow processes with long residence time to be converted from batch to continuous processing. Helically baffled OBRs have only been developed at “mesoscale” so far, but at this scale have displayed significant advantages in terms of the increased range of conditions over which plug flow is achieved. Scale-up studies are underway to determine whether this is replicated at larger scales. This paper reports fluid mechanical modeling of a helically baffled oscillatory flow for the first time. Time-dependent flow structures induced in tubular reactors have been analyzed on the basis of periodic, laminar flow numerical simulation. A reversing swirled core flow and its interaction with the unsteady mechanism of vortex shedding downstream of the wires has been described. This has allowed greater understanding of the flow structures, which will underpin optimal design and scale-up. The potential for heat transfer enhancement is discussed, considering the compound effect of oscillatory motion and helical coil inserts. The results show that the heat transfer for the helical baffled tube could be enhanced by a factor of 4 compared to a smooth tube in the tested range of oscillation conditions.     

Characterization and optimization of an oscillatory baffled reactor (OBR) for ozone-water mass transfer

Ozone-water mass transfer was investigated using an oscillatory baffled reactor (OBR) operated as a semi-batch and as a co-current up flow continuous reactor. The effects of input ozone concentration, input gas and water flow rates, and oscillation conditions on gas hold up, volumetric mass transfer coefficient and mass transfer efficiency were determined. The same reactor was operated as a baffled column (without oscillation) and as a bubble column to assess the effect of the reactor arrangement on the mass transfer. The results show that the OBR was 5 and 3 times more efficient for ozone-water mass transfer than the baffled and bubble columns, respectively. The enhancement obtained with OBR over the baffled column reactor was found to decrease with gas flow rate due to changes in bubble flow pattern from homogenous to heterogeneous. Under continuous flow conditions, the performance of the baffled reactor and the OBR were found to be twice efficient for ozone-water mass transfer than when operating under semi-batch conditions. The mass transfer effeciency (MTE) was found to increase from 57% using the baffled reactor to 92% with OBR under continuous flow at water and gas superficial velocities of 0.3 and 3.4 cm s⁻¹, respectively.     

Approximate residence time distribution of fully develop laminar flow in a straight rectangular channel

For microfluidic applications the residence time distribution (RTD) of laminar flow in rectangular channels is of interest. The exact velocity profile for this type of flow consists of an infinite series and does not allow analytical evaluation of the RTD curve. In this paper we adopt a simpler binomial product profile which was proposed in literature and serves as good approximation. This allows us to determine in an analytical manner approximate expressions for the diffusion-free RTD of fully developed laminar flow in a straight rectangular channel of arbitrary aspect ratio. Since the evaluation of this RTD is computationally elaborate because it involves the Gauss hypergeometric function, we fit it by an empirical model which is suitable for engineering applications. We find that for a Newtonian fluid there is a narrowing of the RTD as the aspect ratio decreases from unity (square channel) to zero (parallel plates). We investigate the range of applicability of the diffusion-free RTD and show that it is a good estimation for liquids in a certain range of Reynolds numbers. The actual limits of this range depend on the Schmidt number and on the aspect ratio and length-to-hydraulic-diameter ratio of the channel.     

Residence time distribution measurements in a pulsed baffled tube bundle

Experimental flow pattern and associated residence time distribution measurements are reported for a tube bundle where periodic baffles and fluid oscillation may be present. When there is no fluid oscillation, high Reynolds number flow conditions are required to give sharp residence time distributions. When baffles are present, fluid oscillation can give sharp residence time distributions for modest low net flow Reynolds numbers. These observations extend our previous results and also show the viability of the system, for example in use as a reactor or heat exchanger where a multi-tube configuration might be required.