Height Equivalent To A Theoretical Plate Values Research Articles

HETP measurement using industrial-scale batch distillation

The height equivalent to a theoretical plate (HETP), representing the mass transfer efficiency, allows designers to determine the packed bed height. In this study, a novel methodology was proposed to evaluate the HETP using an existing industrial-scale batch distillation when designing the height of an industrial-scale continuous distillation column. Specifically, an existing batch distillation used for the reclamation of dichlorodifluoromethane CCl2F2 (R-12 or Freon-12) from a waste refrigerant mixture was employed to determine the HETP value. Prior to the simulation, a literature survey was investigated to determine the suitable property package for simulation. The simulation results were then compared with the experimental data to determine whether REFerence fluid PROPerties can be used as a suitable package for this study. Several batch distillation runs were carried out using industrial structured packing and random packing, which are candidates for the design and optimization of a continuous distillation column in this specific separation. The batch distillation was then rigorously simulated for a comparison with the experimental data, enabling us to calculate the HETP value. The simulated results agreed well with experimental data, demonstrating that the proposed methodology is effective and easy to apply.

Pressure drop behavior and mass transfer properties of a high specific area random type packing in a narrow packed column

In this paper, the comprehensive experimental examinations are conducted to investigate the mass transfer properties of Dixon ring packing. The main aspect of this study is to investigate the characteristics of Dixon ring packing using a narrow packed column. Firstly, the mass transfer properties of the packing were investigated using distillation experiments at total reflux. Afterwards, the pervasive experiments were conducted to plot the generalized pressure drop correlation chart. Finally, the variation of height equivalent to a theoretical plate (HETP) was determined at total reflux operations for various vapour loading factors. Our findings showed that increasing the vapour loading factor up to 0.62 Pa0.5 would eventually decrease the HETP. It was also shown that the further increase in the vapour loading factor results in a sudden increase in the HETP value. According to our findings, the selection of the optimum vapor loading factor would enhance the value of HETP up to more than 57 %.

Effects of Cross Linking on the Chromatographic Nitrogen Isotope Separation

The effects of cross linking with porous cation exchange resin were studied for nitrogen isotope separation. The displacement chromatography was conducted by the resin with cross linking rang from 20% to 40%. A sharp adsorbed ammonium band was maintained for each operation. Enriched 15N isotopes with 0.93% were obtained by 20% cross linking resin and two meters chromatographic operation which started from the natural abundance of ammonium molecule. The effect of cross linking percentage on the height equivalent to a theoretical plate (HETP) was evaluated in the present work and the HETP value is proportional to the cross linking percentage. HETP value of 0.036 cm was obtained at the present system by using 20% cross linking resin.

Impact of a pressure drop on a monolithic capillary column on the efficiency and separation ability of the column

The impact of inlet and outlet column pressures on column separation properties was investigated for monolithic capillary column in gas chromatography. It was demonstrated that the classical Van Deemter equation does not allow us to make a clear choice of the optimal separation conditions. More relevant data can be obtained from the dependence of the height equivalent to a theoretical plate (HETP) on the inlet and outlet column pressures. The dependence ensures that the minimum HETP value can be achieved at high values of inlet and outlet column pressures, but the ratio of the pressures must approach 1. The efficiency of the column under these optimal conditions can exceed by 25–35% the column efficiency under the optimal conditions found using the classical Van Deemter plot. It was shown that a decrease in inlet and outlet column pressures even at a relative pressure close to 1 leads to an increase in HETP and the loss of column separation ability.

The influence of pressure on the separating properties of columns in gas chromatography

The Giddings model taking into account the dependence of the coefficients of the van Deemter equation on pressure was used to study changes in the efficiency of a hollow capillary column as the inlet and outlet carrier gas pressures changed. The observed dependence of height equivalent to a theoretical plate (HETP) in the coordinates of inlet and outlet pressures can be approximated by a surface having the shape of a folded sheet of paper, when minimum HETP values are situated along the bend line. Any surface section is actually a van Deemter curve in the corresponding coordinates. The dependence of the minimum HETP on inlet and outlet pressures, which determines the optimum parameters of column service, is of the greatest interest. It was shown that, over the range of pressures studied, the minimum HETP should monotonically decrease as the pressure increases. Experimental model verification showed close correspondence between the inlet and outlet pressures and the values predicted by the model. At the same time, the experimentally found improvement of the efficiency of the column was smaller than that predicted theoretically. Possible reasons for the discrepancy between theory and experiment are considered.

Mass transfer characteristics of a structured packing for ammonia rectification in ammonia–water absorption refrigeration systems

In ammonia–water absorption refrigeration systems a purification process of the vapours produced in the generator is required. One type of equipment to carry out the purification process is a packed column. However, detailed experimental studies at the normal operating conditions found in ammonia–water absorption refrigeration systems have not been found. An experimental facility has been designed and built to study the ammonia–water rectification in packed columns. Experimental tests have been performed at the normal operating conditions found in the high-pressure stage of a small power ammonia–water absorption refrigeration system. In this paper, the experimental set-up is described and experimental results of the height equivalent to a theoretical plate (HETP) and the volumetric mass transfer coefficient of a rectifying section with the Sulzer BX packing are presented. The HETP values and the experimental mass transfer coefficients are compared with different data and correlations proposed in the literature; it has been found that the differences are appreciable.

Hydrogen Isotope Separation by Combined Electrolysis Catalytic Exchange Under Reduced Pressure

At the National Institute for Fusion Science experimental studies on hydrogen isotope separation by a Combined Electrolysis Catalytic Exchange (CECE) process have been carried out in order to apply it to the system of water detritiation for D-D burning experiments of the Large Helical Device. As an improvement of the CECE process, we have developed a reduced-pressure method as a means of enhancing the separation factor. The feasibility of this method is examined through application to a CECE process using a prototype separation column. Hydrogen-deuterium isotope separation experiments are performed in the two cases where column pressures are 12 and 101 kPa, and the separation factors for hydrogen and deuterium are obtained as 6.8 and 5.6, respectively. It is confirmed that the present method is applicable and useful to the CECE process. The values of Height Equivalent to a Theoretical Plate (HETP) are estimated by analyses with the equilibrium stage model. The HETP values are 15 cm at 12 kPa and 13 cm at 101 kPa. The increase of superficial velocity with decreasing pressure may spoil the efficiency of the mass transfer.

Preliminary Experiments on Hydrogen Isotope Separation by Water-Hydrogen Chemical Exchange under Reduced Pressure

A pressure-reducing method is used effectively in a water distillation process to enhance the equilibrium separation factor. The feasibility of the technique is established through application to a water-hydrogen chemical exchange process using a prototype separation column. Isotope separation experiments examining the water-hydrogen chemical exchange reaction are performed for column pressures of 12–101 kPa, and the separation factors for hydrogen and deuterium are obtained. The HETP (Height Equivalent to a Theoretical Plate) values were distributed in the range of 6 to 15 cm. By reducing the pressure in the column, the process temperature can be lowered without reducing the molar fraction of water vapor in the gas stream. It confirmed that the separation factors under reduced pressure are larger than under atmospheric pressure. This fact demonstrates the effectiveness of reduced pressure in water-hydrogen chemical exchange processes.

Characterization of Horizontal Distillation Column Equipped with Rotating Non-woven Fabric Packing.

The performance characteristics of a horizontal column equipped with 36 non-woven fabric elements that could be rotated in a direction normal to the column-sectional area were evaluated. Separation efficiency and pressure drop were measured under atmospheric pressure at total reflux, using the cyclohexane-heptane system. The stable operation range for a horizontal orientation was limited to the restricted region of the F-factor. However, separation efficiency, which was expressed in terms of HETP (height equivalent to a theoretical plate), at inclinations of 5 and 10 degrees was found to be approximately equal to that for a brush packing system with a horizontal orientation described in a previous work. Particularly, HETP values at a 5 degree inclination ranged from 0.078 to 0.16 m when the F-factor ranged from 0.07 to 0.27 m/s(kg/m3)1/2 at rotation speeds of 50 to 200 rpm. The pressure drop at inclinations of 5 and 10 degrees was larger than that for the brush packing system oriented horizontally by a factor of between 2.5 and 4.

Comparison of chromatographic methods for hydrogen isotope separation by Pd beds

Comparison among three chromatographic separation methods, i.e. hydrogen-displacement chromatography, self-displacement chromatography and frontal chromatography, is made in an experimental way using several gas mixtures of hydrogen and deuterium. There is small difference in the height equivalent to a theoretical plate (HETP) based on the plate theory among the three chromatographic techniques. The HETP value for the self-displacement chromatography is 3.9 cm, and that for the frontal or H 2-displacement chromatography is 3.0 cm at the same flow-rate. The self-displacement chromatography is more useful for the separation of a small amount of deuterium or tritium from other hydrogen isotopes under a moderate recovery ratio. Since the frontal chromatography uses no other gas than the sample, it is more convenient for the separation of deuterium from natural hydrogen even though a lower recovery ratio.

Neural Network Modeling of Structured Packing Height Equivalent to a Theoretical Plate

The height equivalent to a theoretical plate (HETP) of nine types of structured packing was successfully modeled using a neural network. The network was trained on data similar to that used to develop semiempirical mass-transfer models. The HETP was then predicted using the trained network. The neural network model yields a very accurate prediction of experimentally determined HETP values, and it is more accurate than a traditional semiempirical model. Using the neural network, it is also possible to rank the relative importance of input variables in determining the HETP. In particular, this work shows that the roughness of the structured packing surface is a very important input parameter.

Separative Analyses of Packed Water Distillation Column with Channeling Stage Model

In order to predict the HETP (Height Equivalent to a Theoretical Plate) values of packed water distillation columns, we developed the channeling stage model taking account of the effect of axial mixing in the liquid phase. The overall channeling coefficients were defined as in terms of the channeling coefficients ρ for the mass transfer through the phases and for the axial mixing in each phase. The coefficients ρ and ; were estimated for the packed column of 100 cm in length and 1.6 cm in inner diameter where Dixon gauze rings of 3 mm or 6 mm were packed. The HETP values calculated with the overall channeling coefficients ρ agreed well with the values obtained experimentally. By examining ρ and ;, we showed that the mass transfer efficiencies for 6 mm Dixon gauze ring per a unit length of the column were larger than those for 3 mm. On the other hand, the losses in degree of separation by the axial mixing for 6 mm were larger than those for 3 mm.

Basic design of distillation columns filled with metallic structured packings

This paper reports a comparison of several available correlations to calculate flooding velocity and mass transfer efficiency by using the concept of height equivalent to a theoretical plate (HETP) for distillation columns filled with metallic structured packings. It is found that there are more correlations for pressure drop or gas velocity at flooding than correlations to predict HETP values, and that most of the correlations need empirical constants or exponents for their calculation. Nevertheless, these values are not reported for all the packings and all the sizes available. A case study is made for application of the proposed methods, and the results are presented and compared. A brief comment is made on each method and its ease of application.

A study of isotopic exchange of hydrogen and deuterium in a LaNi 3Al 2 hydride bed

An experimental study was carried out on the isotopic exchange of hydrogen and deuterium in a LaNi 3Al 2 hydride bed. The exchange capacity of the LaNi 3Al 2 hydride for deuterium, the overall mass-transfer coefficient and the height equivalent to a theoretical plate (HETP) were obtained from the analysis of effluent curves for a pulse or step change of an influent deuterium concentration. The exchange capacity for deuterium was found to be almost constant between 200 and 300°C and was around 1.7 in a D/metal ratio. The rate of the isotopic exchange was independent of the total hydrogen pressure, and a value of 31.8 kJ/mol was obtained for its activation energy. The minimum HETP value obtained was 0.5 cm at 300°C and is smaller than that of a cryogenic distillation column for hydrogen isotopic separation.

Experimental Study for Separation Characteristics of Cryogenic Distillation Columns with An H-D-T System

This paper reports on cryogenic distillation experiments that have been performed with an H- D-T system (1.5 g of tritium) by using two columns with different inner diameters (1 and 2 cm) and different size packings (a 3-mm Dixon ring for the larger column and a 1.5- mm Dixon ring for the smaller column). The height equivalent to a theoretical plate (HETP) values measured during total reflux operation ranged from 4 to 6 cm for both columns and showed no apparent dependence on vapor velocities. The HETP values under total recycle operation, which varied from 3 to 6 cm, gradually decreased with increasing reflux ratios. The feed flow rates also had influenced the HETP. Consequently, the HETP values were correlated by the flow rates of the feed and vapor streams of the column and by the reflux ratio.

The rate of an exchange reaction of hydrogen and deuterium in a Mg 2Ni bed

Hydrides of intermetallic compounds of Mg 2Ni have a comparatively large isotopic effect in the equilibrium isotherm between hydrogen and deuterium or tritium. An experimental and analytical study is made on the isotopic exchange reaction of hydrogen and deuterium in a Mg 2Ni bed for isotope separation. Values of the first moment, the second moment and a height equivalent to a theoretical plate (HETP) are obtained on the basis of a pulse or a step change of an influent deuterium concentration. It is found that the HETP values have the least at an optimum temperature and linear velocity, and the value is about 3 cm. The activation energy of the isotopic exchange reaction of Mg 2Ni is 18.5 kJ mol −1. Thus the Mg 2Ni bed serves as an effective method for the isotopic separation of hydrogen isotopes.

Determination of gas chromatographic plate heights for hydrocarbon adsorption by superactivated carbon AX21

Values of the height equivalent to a theoretical plate (HETP) were determined for the adsorption of several hydrocarbons by the petroleum pitch-based superactivated carbon AX21 over the temperature range 90–120°C. It was found that the HETP values were independent of both the adsorptive and the temperature of measurement. This surprising result is interpreted in terms of a very high degree of interconnectivity of the micropore structure of AX21. It is also concluded that considerable caution is required in interpreting micropore diffusivities determined from gas chromatographic measurements.

Hydrogen isotope separation characteristics of cryogenic distillation column

Abstract Cryogenic distillation is a promising method for a hydrogen isotope separation system in the fuel cycle of nuclear fusion reactors. However, sufficient experimental information has not yet been obtained to enable us to achieve the cascade operation of cryogenic distillation columns. The present study aims to obtain such information. The experimental apparatus used in the present study is composed of a cryogenic distillation column, gas chromatographs and a helium refrigerator. The cryogenic distillation column can be operated in three modes; the total reflux mode, the total recycle mode and the total recycle mode with a feedback stream. In each experiment, the gas in the condenser and the gas or liquid in the reboiler are sampled and analyzed with gas chromatographs after the column pressure, the pressure drop in the packed section, and other operating conditions reach a steady state. The experimental results are arranged with the pressure drop in the packed section and the height equivalent to a theoretical plate (HETP). As a result of the total reflux experiments, it should be noted that the pre-flooding operation of the distillation column before the total reflux operation improves the separating efficiency of the distillation column and reduces the HETP value. The experimental results also show that the pressure drop increases with vapor velocity. The flooding point or the loading point is not observed with vapor velocity lower than 20 cm/s. As a result of the total recycle experiments, the HETP value is observed to decrease with reflux ratio.

Sample loading and efficiency in adsorption, partition and bonded-phase high-speed liquid chromatography

With the advent of liquid chromatography columns of extremely high efficiency the effect of sample load on the height equivalent to a theoretical plate (HETP) of the column can be more clearly studied. Previously, the inefficiency of the columns masked the peak broadening due to sample load and deterioration of performance from this cause was only seen to occur at loadings of the order of 100 μg/g of adsorbent. It has now been found that the HETP is a linear function of sample load above about 1 μg/g for microparticulate silica adsorbents which have been slurry packed to give columns with minimum HETP values of between 0.02 and 0.05 mm. The degree of dependence has been found to be a function of both the capacity ratio of the solute and the surface area of the adsorbent. The effect of linear velocity and particle size will be indicated and the relevance of this to the design of preparative liquid chromatography columns will be discussed. Addition of both physically and chemically bonded stationary phases to silica adsorbents is common place in high-speed liquid chromatography and the effect of these changes on the capacity of the columns is an important consideration which will also be outlined.