Abstract
The heat costs in distillation columns were determined for the purpose of separating a four-component gas mixture in gas fractionators with various component selection sequences. A method for selecting the optimal scheme was developed. It is based on the concept of “internal energy saving” upon rectification. Internal energy saving means multiple steam operation on the plates of a distillation column, namely, its condensation on each plate with the release of the heat of condensation, which is used for the evaporation of the liquid entering the plate to obtain a new steam composition. It was shown that when binary and three-component mixtures are separated and products of equal purity are obtained, the heat costs are related to the internal energy saving. The calculation of the internal energy saving in a three-column system for the separation of a four-component mixture was carried out. The calculation confirms that, as the internal energy saving increases and, accordingly, the average internal energy saving in the system of columns increases, the total heat consumption is reduced. The results of calculating three separation schemes of the four-component mixture were compared using the program Aspen Plus with different methods for describing the phase equilibrium (NRTL, Peng-Robinson, Chao-Seader) was carried out. It was shown that the calculations with the use of Peng-Robinson and Chao-Seader methods match.
Highlights
The heat costs in distillation columns were determined for the purpose of separating a four-component gas mixture in gas fractionators with various component selection sequences
A method for selecting the optimal scheme was developed. It is based on the concept of “internal energy saving” upon rectification
Internal energy saving means multiple steam operation on the plates of a distillation column, namely, its condensation on each plate with the release of the heat of condensation, which is used for the evaporation of the liquid entering the plate to obtain a new steam composition
Summary
ВЫБОР ОПТИМАЛЬНОЙ СХЕМЫ РАЗДЕЛЕНИЯ СМЕСИ УГЛЕВОДОРОДНЫХ ГАЗОВ МЕТОДОМ РЕКТИФИКАЦИИ. Что затраты теплоты при разделении бинарных и трехкомпонентных смесей с получением продуктов разделения одинаковой чистоты связаны с величиной внутреннего энергосбережения. Выбор оптимальной схемы разделения смеси углеводородных газов методом ректификации the average internal energy saving in the system of columns increases, the total heat consumption is reduced. Показано [15], что выбор оптимальной схемы разделения многокомпонентных смесей методом ректификации может быть выполнен с учетом внутреннего энергосбережения в колоннах. При ректификации смеси бензол–толуол разного состава с получением 98% бензола в дистилляте и 98% толуола в кубовом остатке при коэффициенте избытка флегмы σ = 1.1 отмечено, что при одинаковой степени разделения исходных смесей разного состава затраты теплоты в кипятильнике существенно меньше в режимах с большим флегмовым числом R и, соответственно, с большим внутренним энергосбережением Эн в колонне. Колонна Число тарелок Номер тарелки питания Флегмовое число R Энергосбережение в колонне Потоки пара в колоннах, кмоль/ч Среднее внутреннее энергосбережение в двух колоннах Затраты теплоты, кВт Суммарные затраты, кВт
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