Film type evaporator vacuum

Contents

Contents

Introduction

Thermal calculation of the apparatus

Calculation of evaporated solution concentrations

Determination of boiling points of solutions

Calculation of heat transfer coefficients

Refinement of boiling points

Defining Heat Loads

Defining Heat Transfer Surfaces

3. Structural calculation

Calculation of pipe grids and methods of arrangement and fixation of heat exchange pipes in them

Calculation of cylindrical shell

Heat exchanger bottoms and covers

Calculation of nozzle diameters, selection of flanges, gaskets

Apparatus supports

Separator Calculation

Literature

Introduction

Evaporation is the process of thickening the solutions by removing part of the water from them by evaporation. By evaporation, supersaturated solutions are also obtained, in which crystallization is then carried out.

The evaporation process is carried out under excessive pressure or under vacuum. In overpressure evaporation, the secondary steam has a high temperature, so it is often used for heating in various heat exchangers operating at a lower pressure. In this case, the efficiency of the evaporator is improved. However, the increase in temperature and pressure of secondary steam is associated with a corresponding increase in heating steam pressure and installation cost. In addition, as these parameters increase, the quality of many food media, especially in their concentrated form, deteriorates.

When evaporated under vacuum, the boiling point of the solution decreases, which allows the use of low-pressure steam for heating vacuum evaporators. This method is widely used to evaporate solutions decomposing at elevated temperatures and solutions having a high boiling point at atmospheric pressure. The advantages of vacuum evaporation are also the reduction of heat losses to the environment and the increase of the useful temperature difference between heating steam and boiling solution. This reduces the heat exchange surface and overall dimensions of the apparatus.

Evaporation of the solution can be carried out in one apparatus (single-hull unit) or in a number of series-connected evaporators (multi-hull unit). In a single-hull apparatus, heat of heating steam is used once, and heat of secondary steam leaving the apparatus is usually not used. A single hull evaporator is used to thicken relatively small amounts of solution when heat savings are not important.

In a multi-hull evaporator, the secondary steam leaving any previous housing is heating steam for the subsequent steam, in which it boils at a lower pressure. This method of conducting the process provides significant heat savings, so it is widespread in industry.

Multihull evaporator plant consists of several single-hull evaporators connected in series both by thickened product and by heating steam. In it, the first housing is heated by steam coming from turbines or steam boilers, and for heating each subsequent housing, the secondary steam of the previous housing is used. Heat exchange in each housing is ensured due to temperature difference between heating steam and boiling product. This temperature difference is created by reducing the pressure in each subsequent housing compared to the previous one, which also facilitates the gravity transition of the thickened product from one housing to another. When moving from the previous housing to the next housing, i.e. to a space with a lower pressure and a lower temperature, the solution, having a higher temperature, is superheated and some water is removed from it as a result of self-evaporation. Thus, the self-evaporation process reduces the vapour consumption for evaporation.

The secondary steam leaving the last housing has a low temperature and is practically unsuitable for heating other heat exchangers, so it is sent to a condenser. Here, as a result of direct contact of cold water with steam, it is condensed and a vacuum is created that provides the necessary mode of operation.