Gas-liquid multiphase computational fluid dynamics (CFD) of amine absorption column with structured-packing for CO2 capture
Abstract The gas−liquid multiphase Eulerian computational fluid dynamics (CFD) model was used to investigate hydrodynamics and CO2 removal efficiency of a pilot-scale amine absorber with structured-packing. The structured-packing was represented by a porous media zone having porous resistance, gas−liquid interfacial drag force, and liquid dispersion force. This study aimed to find a reasonable way to identify four modification factors of the Ergun coefficient that determine the hydrodynamic characteristics of structured-packing. The two modification factors (a and b) for porous resistance were mainly related to the liquid holdup (hL) with respect to the liquid load. The other two factors (c and d) for gas−liquid interfacial drag force depended on the specific wet pressure drop (ΔPwet/L) versus the gas load factor. The hL and ΔPwet/L increased in parallel with the increase of a and c, respectively, while the slopes of hL and ΔPwet/L increased with b and d, respectively.
CFD Modeling of Structured Packings at Small- and Meso-scale
This article presents a CFD model of the multiphase flow inside structured packings for amine-based post-combustion carbon capture. In the literature, simulations are performed at three scales due to computational limitations: small-, meso- and large-scale. This work focuses on small- and meso-scale, introducing interface tracking at both. The interfacial tracking is accomplished by using the Volume of Fluid (VoF) method. Small-scale allows studying the reaction kinetics of the absorption process in 2D geometries. Meso-scale has been used in the literature to describe the dry pressure drop of the packing (single-phase simulations). The interface tracking allows obtaining the relationship between the liquid load and both the liquid hold-up and the interface area. Data from the simulations are compared against experimental results found in the literature. The accurate modeling of the interface area, liquid hold-up and reaction kinetics allows utilizing this CFD model as a design tool for novel packings or to optimizing geometries already in use.
Cytoplsmic uridine phosphorylase of rat liver. Characterization and kinetics.
Abstract Uridine phosphorylase (uridine:orthophosphate ribosyltransferase, EC 2.4.2.3) of rat liver cytoplasm has been purified 1900-fold. Initial velocity patterns of the phosphorolysis of uridine or deoxyuridine and of the synthesis of uridine indicated a sequential mechanism. Product inhibition patterns with uracil or ribose 1-phosphate as inhibitors were consistent with an "ordered Bi Bi" reaction in which inorganic phosphate is the first substrate to bind to the enzyme and ribose 1-phosphate the last product to leave the enzyme. The most highly purified enzyme fractions still retained uridine-, deoxyuridine-, and thymidine-cleaving activities in the ratio of 10:7:1 at pH 7.4. The fractions separated into a major and a minor band of protein on electrophoresis in phosphate buffer. Aging of the enzyme with loss of activity resulted in an increase in the proportion of the minor band. The pH optimum of the enzyme for uridine cleavage was 8.2, for deoxyuridine cleavage, 6.5, and for uridine synthesis, 8.5. Uridine or deoxyuridine synthesis was inhibited 50% in the presence of 1 mm uracil. The enzyme did not catalyze the direct transfer of ribose from uridine to uracil in the absence of phosphate. Uridine protected the enzyme to a greater degree than phosphate against inhibition by o-iodosobenzoate. Thus, at least one sulfhydryl group and possibly three are present at or near the active site. Uridine cleavage, uridine synthesis, and deoxyuridine cleavage were inhibited by deoxyglucosylthymine. The phosphorolysis of deoxyuridine and thymidine by thymidine phosphorylase, also purified from rat liver cytoplasm, was not inhibited by deoxyglucosylthymine. The molecular weights of both uridine and thymidine phosphorylases were estimated to be 110,000.