ASSESSMENT OF THE INFLUENCE OF THE THERMODYNAMIC FACTOR ON THE CRYSTALLIZATION PROCESS IN A VACUUM APPARATUS

Особенность состояния системы жидкость–твердое тело в метастабильном растворе вещества состоит в том, что она (система) претерпевает два фазовых превращения в вакуум-аппарате (ВА) – кристаллообразование и растворение, требующие экспериментального изучения и описания в силу их важности при совершенствовании технологии производства кристаллического сахара. Однако и теоретическое обоснование фазовых превращений в метастабильном растворе разработано недостаточно. В статье предпринята попытка количественно поставить и решить проблему учета возникающего при проведении обработки метастабильного сахарсодержащего раствора повышения температуры в результате конденсации молекул на центре концентрации при пересыщении в ВА. В качестве основы численного моделирования поставленной задачи использовали программные продукты информационной среды Mathcad. С использованием модели диффузионного массопереноса сахарозы в пересыщенном растворе к затравке был разработан алгоритм расчета зависимости массы сахарозы от времени проведения процесса кристаллизации. На примере сахарозы дана оценка влияния физического фактора – выделяющейся при кристаллообразовании теплоты на расчет теплового баланса и производительности ВА. The peculiarity of the state of the liquid-solid system in a metastable solution of a substance is that it (the system) undergoes two phase transformations in a vacuum apparatus (VA) – crystal formation and dissolution, requiring experimental study and description due to their importance in improving the technology of production of crystalline sugar. However the theoretical justification of phase transformations in a metastable solution has not been sufficiently developed. The article attempts to quantify and solve the problem of taking into account the temperature increase that occurs during the processing of a metastable sugar-containing solution as a result of condensation of molecules at the concentration center during supersaturation in VA. Software products of the Mathcad information environment were used as the basis for numerical modeling of the task. Using a model of diffusive mass transfer of sucrose in a supersaturated solution to the seed, an algorithm was developed for calculating the dependence of the sucrose mass on the time of the crystallization process. On the example of sucrose, an assessment of the influence of a physical factor – the heat released during crystallization on the calculation of the thermal balance and the productivity of the VA is given.

Experience of using a vacuum extractor

The idea of creating a vacuum apparatus was put forward about 150 years ago (McKay, Zeman, Simpson, etc.). However, the method received wide application only after the creation of Finderle (Yugoslavia, 1952) and, independently of him, Malmstrm (Sweden, 1953) of more advanced models of vacuum extractors.

Improving the massecuite crystallization in sugar production

The article discusses the concepts of continuous vacuum apparatus operation: vertical VKT (VKT – Verdampfungs-Kristallisations-Turm) and horizontal cascade of VKH vacuum apparatus (VKH —horizontal vacuum pan) from BMA (Germany). The advantages and features of the vertical continuous vacuum apparatus VKT are shown, as well as the possibilities for increasing the efficiency of the product department of sugar factories. Thanks to the special design of the crystallization chambers, the low massecuite level above the heating chamber and the use of mechanical stirrers in each chamber, the VKT apparatus can operate without difficulty with a very small temperature difference between heating steam and massecuite, as well as with an absolute heating steam pressure well below 1 bar. With optimal use of VKT vacuum apparatus, a variety of energy-saving schemes can be implemented, for example, double-effect evaporation in the crystallization section. Part of the secondary crystallization steam is used to heat one of the VKT units, which saves the heating steam of the evaporator unit used for this purpose. With an increase in the productivity of the sugar factory, it is possible to quickly equip the VKT apparatus with an additional chamber. The device works continuously throughout the season, especially with products with massecuite purity of more than 94%. The chambers are cleaned without stopping the entire apparatus. The boiling of massecuite of all stages of crystallization in VKT devices ensures a uniform operating mode of the food compartment, allows to achieve an increase in sugar yield and helps to reduce steam consumption at the plant.

Formation of sucrose crystallization centers and their growth in a vacuum apparatus

The article considers sucrose crystallization as a mass transfer process, which is a phase transition from a liquid phase to a solid phase, and includes two main stages: the formation of crystallization centers and the growth of crystals to the desired size. The scientific novelty of the work lies in the development of existing theoretical and practical ideas about the formation of centers of crystallization of sucrose and their growth in the massecuite mass, the analysis of the main factors affecting this process. On the basis of the studies obtained, a method has been developed to improve the efficiency of the technology for boiling the massecuite of the first crystallization, which refers to the methods of boiling the massecuite I crystallization with intermediate centrifugation of the massecuite. A feature of the method is the formation of crystallization centers in the massecuite by their spontaneous formation. The analysis of the obtained research results showed that the work on the proposed method makes it possible to increase the efficiency of boiling massecuite I crystallization, to ensure an increase in the yield and quality of crystalline white sugar.

Thermal - Vacuum dehydration and dispergation of dispersed materials

Scientific and technical studies on the intensification of removal moisture from dispersed materials and their simultaneous dispergation in the hollow heating element of a thermo-vacuum apparatus is researched. Continuous thermo-vacuum dehydration and dispergation process of zirconium hydroxide, brown coal, graphite, sawdust, biological materials is considered. Based on conducted studies was made conclusions about perspective to use this technology. Thermo-vacuum technology is different from the other by low-temperature heating, low time processing, humidity indicators controlling and nano-dispersion grinding. Keywords: dehydration, dispergation, energy saving