Internal configurations for a multi-product dividing wall column

This paper addresses possibilities and peculiarities associated with establishing the most beneficial internal configuration of a complex dividing wall column (DWC), using as a base case the separation of a multicomponent aromatics mixture into four or five product streams. As expected, the V_min-diagram method proved to be an appropriate tool in such a study, as a means for identifying and assessing promising configurations and at the same time to provide the necessary inputs and reliable initial guesses for detailed simulation-based determination of energy and stage requirements. A new, energy efficient two-top product configuration is introduced that appears to be an interesting option for a four-product DWC.     

DRY COLUMN APPROXIMATION FOR PRESSURE DROP IN SPINNING CONE COLUMNS

A rotation-related normalization of variables has been introduced, and dimensionless fundamentally based correlations have been developed, for pressure drop in a spinning cone column (SCC) in the absence of liquid flow (dry column). The pressure drop is a sum of the dynamic and the centrifugal pressure components. Under typical SCC conditions, the correlation reduces to the form of ΔP _G  = 2N _st (k _reg R o ² + k _rot ), where N _st is a number of cone sets, Ro is the Rossby number (a rotation-normalized gas flow rate), and k _reg and k _rot are empirical coefficients characterizing the flow regime and the centrifugal efficiency of the rotor, respectively. This “dry column approximation” fits the data extremely well (the variation accounted for by the correlation is 98% of the total variation). It can be used as a theoretical limit for pressure drop prediction in an SCC at low liquid loads. The pressure regimes are classified as the centrifugal (Ro < 0.2), the intermediate (0.2 < Ro < 1.0), and the dynamic regimes (Ro > 1). Based on these dimensionless boundaries, dimensional diagrams of SCC operating regimes are constructed for laboratory and commercial-scale columns. The generality of the results is discussed in terms of the applicability of the correlations to larger scale equipment, the determination of empirical coefficients, and the linkage with CFD analysis of SCCs.     

SO2 SCRUBBING IN A TAPERED BUBBLE COLUMN SCRUBBER

SO₂ emissions from various sources are found to occur in various concentrations and quantities. Abatement of SO₂ emission, therefore, assumes significant importance over the decades. Wet scrubbers offer great advantage over other devices for gas cleaning. That is the reason that compliance with SO₂ standards will in many cases result in the installation of scrubbing devices. This article presents results of a study on the scrubbing of SO₂ (initial concentration ranging between 400 and 1780 ppm) in a tapered bubble column scrubber using water and dilute sodium alkali. Preliminary studies reveal that the tapered bubble column is capable of generating higher fractional gas holdup than a standard bubble column under similar situations. Moreover, the tapered bubble column has generated bubbles with less power consumption than the existing columns under comparable hydrodynamical conditions. Experimental results indicate that almost 100% SO₂ removal (i.e., zero penetration) can be achieved in the scrubber developed in alkali scrubbing at an optimum Q_L/Q_G ratio of 3.0 m³/1000 ACM. The selection of any gas-cleaning device is based on the performance of the system. In view of this, empirical and semi-empirical correlations are put forward for the prediction of the performance of the scrubber in terms of different pertinent variables of the system for water as well as alkali scrubbing. Experimental results fit extremely well with the correlations. The removal efficiency achievable in the present tapered bubble column scrubber has been found to be higher than that of a single-stage standard bubble column with some modification. The present tapered bubble column is, therefore, hydrodynamically, energetically, and efficiency-wise much better than a standard bubble column.     

Extraction of Caprolactam with an Alternative Benign Solvent in a Pulsed Disc and Doughnut Column

Abstract

Caprolactam is obtained by extraction using organic solvents like benzene, toluene, or chlorinated hydrocarbons. As an alternative solvent, the mixed solvent heptane‐heptanol (40 mass %) was selected in previous studies based on a relatively high distribution ratio of caprolactam, a low mutual solvent solubility, beneficial physical properties, and a low distribution ratio of impurities. Now, the hydraulic and mass transfer characteristics of the extraction of caprolactam in a pulsed disc and doughnut column (PDDC) were investigated using the benign solvent. The results were compared to those for toluene.

The PDDC showed qualitatively comparable operational characteristics for both solvents. In the hydraulic experiments the mixed solvent showed smaller drop diameters and hold‐ups, required lower pulsation intensities for regime transitions, but the operational windows are slightly smaller. For both solvents, mass transfer resulted in increasing drop diameters and pulsation intensities required for regime transition. In the forward extraction the mixed solvent was superior, where HETS/m=0.26 to 0.37, compared to 0.42 to 0.67 for toluene, while less theoretical stages are required as well. For the back‐extraction HETS/m=0.33 to 0.40 for the mixed solvent compared to 0.30 to 0.37, but toluene requires the lower amount of theoretical stages.

The hydraulic characteristics at equilibrium and concentration profiles in both the forward and back‐extraction were described accurately using the developed models.     

填料塔中磷酸钠缓冲溶液吸收低体积分数SO2的体积传质系数

为满足磷酸一钠和二钠缓冲溶液脱硫设计开发的需要,采用磷酸钠缓冲盐溶液为吸收剂,测定和计算了在鲍尔环填料塔中磷酸钠溶液吸收模拟烟气中SO2的体积总传质系数KYa.在常温常压下,考察了空塔气速、喷淋密度、入口SO2体积分数、吸收液磷酸根浓度和初始pH等工艺参数对KYa的影响.结果表明,KYa随着空塔气速、喷淋密度、初始pH和磷酸根浓度的增加而增大;随着入口SO2体积分数的增加先增加后减小;该体系的传质过程受气膜和液膜共同控制.     

PHENOL BIODEGRADATION BY RALSTONIA PICKETTII EXTRACTED FROM PETROLEUM REFINERY OIL SLUDGE

Phenol-degrading bacterial strains have been extracted from oil-sludge samples collected from a local refinery. A selective medium was used to isolate the active strain capable of utilizing phenol as a sole carbon source, which was identified as Ralstonia pickettii. The growth kinetics of mixed and isolated R. pickettii suspensions were investigated using different initial concentrations of phenol in the range of 25 to 200 g m^?3 at 35°C and pH of 8.5. The results were compared to those of a commercially available mixed bacterial suspension, which was either acclimatized to 100 g m^?3 phenol concentration, extracted from PVA particles that were subjected to real petroleum refinery wastewater containing phenol, or an isolated active strain grown on a selective medium that was identified as Pseudomonas putida. The effect of substrate inhibition was observed using all bacterial suspensions, and the growth results were used to determine the parameters of a suitable kinetic model. It was found that the phenol biodegradation ability of the indigenous bacteria, R. pickettii, isolated from refinery sludge was comparable to that of the commercially available bacteria.     

GENERALIZED PREDICTIVE CONTROL OF A PULSED LIQUID-LIQUID EXTRACTION COLUMN

This paper deals with the application of a general predictive controller to a pulsed liquid-liquid extraction column. The control purpose is to maintain the column in its optimal behaviour zone in spite or flowrates and physical properties of solvent and solute fluctuations. The complex dynamics of the column is modeled by a low order linear discrete model with time varying parameters which are recursively identified. Based on these estimates, the control policy is adapted on line.

The obtained results illustrate the successful application of such an adaptive algorithm.