New pressure drop correlation for sieve tray distillation columns

Abstract

Pressure drop data for distillation sieve trays have been obtained with experimental trays with small outlet weir heights, including zero, and for trays with small perforations which exhibit large pressure drops due to surface tension. These data have been added to literature data to form a large composite data base with extensive variations in fluid and gas properties, flow rates, and tray designs.A new pressure drop correlation has been developed which retains the use of the dry tray pressure drop, but provides new procedures for estimating liquid inventory and the resistance to vapor flow due to surface tension forces. This correlation gives a mean absolute error of 6.0% and an average error of -0.6%. These errors are significantly less than the errors between measurements and preldictions from two other correlations using the same composite data base. D. L. BENNETT SCOPEPressure drops across distillation column sieve trays should be estimated accurately as part of column designs to determine downcomer backup, column pressure drop, and tray efficiency. These pressure drop calculations become more important in designs for nonfouling service, where small tray spacings are used and flooding limits tray capacity.The objectives of this paper are: a. To determine whether the liquid inventory on a sieve tray can be measured by a tray-mounted manometer, or whether the inventory should be estimated from the total measured pressure drop by subtracting the other pressure drop components.b. To report sieve tray pressure drop data from trays with low outlet weir heights, including zero, and for trays with small perforations which exhibit large surface tension pressure drops.c. To develop a composite data base, consisting of the above data and literature data, which has large variations in fluid and gas properties, flow rates and tray designs.d. To develop a simple pressure drop correlation for sieve trays based on this composite data base, and to compare the accuracy of this correlation with that of several other correlations, using the same data base. CONCLUSIONS AND SIGNIFICANCETray-mounted manometers had been suggested as possible tools for direct measurement of clear liquid head on aerated sieve trays. Time-average measurements made on special trays with fixed liquid inventories showed large discrepancies with known average liquid heads, dependent upon vapor flow rates and clear liquid heads. Therefore, clear liquid heads were determined from total pressure drop measurements from an independent evaluation of surface tension resistance and conventional dry hole pressure drops.Pressure drop data are reported in Table 1 for trays with small weir heights and small perforation sizes. These data were added to literature data to develop a large composite data base with the extensive range of fluid and gas properties, flow rates, and tray designs summarized in Table 2. A pressure drop correlation has been developed using this composite data base. The total pressure drop is assumed to consist of the dry tray component, the liq...

Enhancement of Sieve Tray Efficiency using Computational Fluid Dynamics

“…12 in this work), at a given gas flow rate the use of the Bennet et al [1] correlation amounts to using a constant multiplier as a drag coefficient. This constant factor is inversely proportional to the average liquid holdup fraction, but it is proportional to the second power of the average gas holdup fraction.…”

“…System geometry: Based on trays specification [1], sieve trays, that is, both circular and rectangular are created in Gambit and boundary conditions are defined for system. Design is also created on ProE (Figure 1) for proper visualisation and solid or wireframe is exported to gambit.…”

“…Tray design heavily relies on experience [1] because little is known about the flow behaviour and heat-and mass-transfer on the tray. The main reason for this is the poor understanding of the complex behaviours of the multiphase flow inside the tray.…”

“…In this paper a three-dimensional transient CFD model is developed, within the two-phase Eulerian framework, for hydrodynamics of a circular and rectangular tray. The required interphase momentum exchange coefficient is estimated on the basis of the correlation of Bennett et al [1] for the liquid holdup. In this work a model is developed using CFD tool to give the predictions of the fluid flow patterns, and heat and mass transfer over sieve tray.…”

Metodologias de análise de dados para um sistema de otimização em tempo real.

“…Existem correlações complexas para o cálculo da queda de pressão em pratos de orifício (BENNETT et al,1983), nas quais seria preciso estimar parâmetros diferentes com as configurações dos pratos, vazões de líquido e vapor e as propriedades das fases, sendo necessário então um detalhamento mais rigoroso do modelo.…”