Side Stripper Research Articles

Energy-Efficient Designs of Thermally Coupled Distillation Sequences for Four-Component Mixtures

A design procedure for thermally coupled distillation sequences for the separation of four-component mixtures is presented. The schemes analyzed include a sequence with a side rectifier and a side stripper and a sequence with a prefractionator (Petlyuk-type column). Initial designs for the thermally coupled distillation sequences are obtained from the tray distribution of a conventional distillation sequence and then optimized for energy consumption using two interconnecting flows as search variables. Several tray arrangements for each thermally coupled design were analyzed, and the results show that the sequence with side columns can reach a lower energy consumption.

Design and Energy Performance of Alternative Schemes to the Petlyuk Distillation System

Three types of thermally coupled distillation systems, namely the sequence with side rectifier, the sequence with side stripper and the Petlyuk column, have been shown to provide significant energy savings for the separation of ternary mixtures with respect to the conventional direct and indirect sequences. Although the Petlyuk column in general is more energy efficient than the other options, its structure creates potential operating problems because of the bidirectional flow of the vapor interconnecting streams. Alternative options with potential operational advantages have been recently suggested. In this paper we analyze the energy performance of six alternative schemes to the Petlyuk system with thermal coupling. Two of them make use of two interconnections with unidirectional flow, while the other four show a reduction in the number of interconnections. It is shown that several of the alternate options provide similar energy savings to the Petlyuk column.

A crude distillation unit model suitable for online applications

A steady state, multicomponent distillation model particularly suited for fractionation of crude oil has been developed based on equilibrium stage relations. For a mixture of C components, the present formulation uses C+3 iteration variables namely the mole fractions of the components, temperature, total liquid and total vapor flow rates on each stage. This choice of variables makes the present model numerically stable and robust rendering a separate initial guess computation unnecessary. An improved scheme of numbering the equilibrium stages when side strippers are present, was found to be advantageous with respect to computation time. Selected example problems have been included from literature as well as industry to demonstrate the efficacy and usefulness of the method. The accuracy of predictions and speed of solution of the model equations are particularly suited for online applications such as online optimization.

The synthesis of thermally coupled distillation flowsheets for separations of five-component mixtures

The thermally coupled distillation flowsheets for separation of five-component mixtures are studied based on the total annual costs. Fourteen simple column sequences and some feasible thermally coupled configurations with side strippers and/or side rectifiers are considered. The costs of the flowsheets are calculated and compared for several real five-component mixtures with various relative volatility distributions and a wide range of feed compositions. Several heuristics are proposed for the synthesis of multicomponent thermally coupled distillation flowsheets.

Controllability Analysis of Thermally Coupled Distillation Systems

A comparison of the controllability properties of three thermally coupled distillation sequences (Petlyuk, sequence with side rectifier, and sequence with side stripper) using singular value decomposition is developed. Those properties are also compared to the energy consumption required for separating ternary mixtures. The parameters obtained via singular value decomposition show that sequences with a side rectifier or a side stripper have better control properties than the Petlyuk system, although the Petlyuk scheme has lower energy requirements than the systems with side columns.

Thermodynamically Efficient Systems for Ternary Distillation

In an earlier work (Agrawal, R.; Fidkowski, Z. T. Eng. Chem. Res. 1998, 37, 3444) it was shown that for the distillation of a ternary liquid mixture into pure component product streams the modified direct or indirect split configurations can have higher thermodynamic efficiencies than the conventional thermally coupled configurations. In this paper, thermally coupled column configurations are modified by incorporating intermediate temperature reboilers and condensers to accept/reject heat at the temperatures of boiling/condensing binary mixtures. The modified side rectifier or side stripper configurations retain the low vapor flow of the unmodified configurations. They have the same total number of reboilers and condensers as do the direct or indirect split but they provide higher thermodynamic efficiencies than the corresponding direct or indirect split. These new configurations also provide an additional degree of freedom to shift heat (cold) duty between the intermediate temperature reboiler (condenser) and the reboiler at the warmest temperature (condenser at the coldest temperature). Finally, a more complete ternary and quarterary superstructure is suggested that contains these new configurations as well as all earlier known superstructures and configurations.

New thermally coupled schemes for ternary distillation

AbstractThe fully thermally coupled system of distillation columns for ternary separation has two, two‐way connections between the columns. New, simplified (and easier to control) systems of columns for ternary separations, with a reduced number of connecting streams, are proposed. The new systems contain one one‐way and one two‐way connection between the columns. Depending on which connection is located on top and which phase stream (liquid or vapor) is used in the one‐way connection, there are four possible configurations for these new systems. For certain feed compositions and relative volatilities of components, these new systems can replace the fully thermally coupled system of columns without any increase in energy demand. The optimum system selected from the four proposed configurations consumes no more, and frequently much less, energy than the side stripper or side rectifier configurations or than a system with a prefractionator.

Production of Ultrahigh-Purity Oxygen: A Distillation Method for the Coproduction of the Heavy Key Component Stream Free of Heavier Impurities

Use of a side stripper for the coproduction of the heavy key component stream free of undesirable heavier impurities has been suggested. A side stream containing the heavy key component is withdrawn from a column at a location that is sufficiently above the feed such that it is essentially free of the undesired impurities. This side stream is then distilled in a side stripper to remove lighter components. From a given feed, this method is capable of coproducing a significant fraction of the heavy key component with extremely high purities and with minimal additional energy usage. Coproduction of ultrahigh-purity oxygen, containing only ppb level impurities, along with standard-grade oxygen (99.5%) is presented. In comparison with earlier techniques, this method of distillation is simpler and more efficient and uses less equipment while maintaining a high recovery of oxygen from air

Temperature-heat diagrams for complex columns. 2. Underwood's method for side strippers and enrichers

The authors present insight into complex column heat flow which facilitates extension of Underwood's method to columns with side-stream strippers and side-stream enrichers. This presentation is much simpler than previous ones. The same insights show that, even though less configurations are more energy efficient, they require a larger temperature range for operation than analogous simple column sequences.

Simulation of large scale dynamic systems—II. A modulator simulator for the dynamics of distillation systems

A modular dynamic simulator has been developed to simulate the dynamics of interacting distillation columns. The dynamic simulator consists of a Fortran software package with dynamic modules to simulate distillation columns, reboilers, condensers and control systems. The modules can be modified to simulate special reboilers, condensers and control systems. User input to the simulator consists of the system description, constants, physical property data and an optional initial state. Two example problems have been used to test the simulator: (1) A 5 component, 29 stage distillation column with controllers, and (2) An atmospheric crude unit with 4 side strippers. Each of the side strippers and the main column are simulated independently. Steady-state conditions for the crude unit are computed by following a policy which approximates crude unit start-up procedures. We illustrate the type of results obtainable from the simulator by presenting several dynamic responses of the crude unit to step disturbances. Scope—We describe a modular simulator for distillation systems built around the coordinator concept described and analyzed in Part I. Simulation of 2 substantial problems, a 29 stage distillation column, and crude unit, demonstrate the methodology. Significance—The simulator and worked examples demonstrate the validity of reducing a complex simulation to an interconnection of independent simulations tied together by a coordinator. The advent of parallel processing should enable simulation of the dynamics of extremely large, and heretofore intractable, systems using the modular approach.

Analysis and prevention of metallurgical failures at a major direct coal liquefaction pilot plant

The H-Coal Pilot Plant in Catlettsburg, KY was the largest-capacity direct coal liquefaction project operating in the United States. Since the start of operations, performance of its components was carefully monitored and occasional failures were examined and documented. The results of the examinations were used to develop remedial steps and improve the design of scale-up units. In this paper, the metallurgical aspects of the following incidents will be described: 1) stress corrosion cracking of martensitic stainless steel bolting on the waterside of a heat exchanger; 2) stress corrosion cracking of a superalloy seal ring; 3) brittle failure of a low alloy nut in a block valve body; 4) corrosion damage in the fractionator and side stripper; 5) erosion/corrosion of a coal liquid transfer line in the atmospheric fractionation area; 6) pitting corrosion in a deaerator carbon steel inlet pipe; 7) brittle failure of a martensitic stainless steel ball in a block valve handling coal liquids; and 8) cracking of cobalt-base alloy seat rings in block valve applications. In addition, remedial steps and preventive measures leading to successful performance after repair will be briefly described.