Experimental study and mathematical modeling of industrial rotary dryer for dicalcium phosphate production

Dissertation

Master's degree

Chemical Engineering Department

Abstract:

The purpose of this thesis is the mathematical modeling of rotary dryer for drying dicalcium phosphate. In this project, with different temperature conditions and different number of cycles of the dryer, the moisture level of the product coming out of the dryer has been checked. As a result, 100 data have been obtained from the output of the rotary dryer, and transient analyzes have been performed on them. The humidity ratio in each cycle of the dryer has been obtained at different times, and by using the Table curve software and passing the curve from the experimental data, 7 mathematical models have been performed on the output data of this dryer, and the constants of these models, their coefficient of determination, the mean square error and the relative error percentage have been obtained. With the help of the information obtained by the models, the best model with the highest coefficient of determination and the lowest mean squared error and relative error percentage has been examined, and the best model compatible with the largest number of experimental data is the Modified Henderson and Pabis model. Finally, these experimental data were investigated with the help of neural networks, the obtained results have the minimum absolute error (0.06) and are highly generalizable.

Key words: rotary dryer, drying, modeling, dicalcium phosphate

Introduction

Dicalcium phosphate is one of the supplements that has a significant effect on increasing the growth and development, fertility and lactation and ossification of livestock and poultry, and improving the quality of this product is of great help to the livestock and poultry industry. The moisture in dicalcium phosphate is effective on its absorption percentage in the living body, so a dryer is used to bring its moisture to its desired level (maximum 3%). The dryer examined here is a rotary dryer.

The drying process in the rotary dryer in question has been investigated in 5 seasons. In the first chapter, we define the drying process. In the second chapter, we have a brief look at the background of the investigations carried out on drying and dryers. The review of the method of doing the work and description of the desired dryer is done in the third chapter. In the fourth chapter, mathematical models and neural network models are performed on different data, and finally, in the fifth chapter, the final summary and suggestions are presented.

Introduction

Drying is perhaps the oldest, most common and one of the most widely used operations in chemical engineering. More than 400 types of dryers have been reported in sources, while more than 100 types of them have the ability to be used in industry. The amount of energy consumed in dryers reaches 5% for chemical industry processes and 35% for papermaking industries. Drying occurs as a result of liquid evaporation by heat transfer to raw materials that are moist [1].

More than 85% of industrial dryers are convection type with hot air or contact with combustion gases. More than 99% of the goals of this operation are to remove water. The method of solid drying depends on the heat transfer mechanism, the drying material and the method of heat transfer in the form of conduction [1], convection [2] and radiation [3]. In most direct heat dryers, the heat transfer mechanism is usually convection, and in indirect heat dryers, the main heat transfer mechanism is conduction. In both cases, it is possible to transfer a significant part of the heat through radiation[2].

During the drying process, wet materials come into contact with unsaturated air, and as a result, the amount of moisture decreases and the air becomes humid. Usually, the drying process is done with air heating before the better process; Therefore, the drying process can be divided into two stages: heating the air and evaporating moisture from the material. A comprehensive study of drying requires familiarity with the factors that affect the movement of liquid and vapor under assumed thermal conditions. This topic will include the investigation of the internal structure of solid materials that are used to calculate the intensity of liquid and vapor flow based on physical properties and surface properties.This subject will include the examination of the internal structure of solid materials that are used to calculate the intensity of liquid and steam flow based on physical properties and surface properties. All these factors are not of equal importance. Some of them are more important in the drying stage with constant intensity and others in the drying stage with decreasing intensity [2]. Other characteristics are determined as much as possible only with the help of physical and chemical properties of the materials, while the dynamics of drying examines the changes in temperature and humidity curves in the body of the dryer. Heat transfer from the surrounding space to the materials causes evaporation of surface moisture. Moisture can be transferred from the inside of the body to the surface and then evaporate, or inside the product and in a vapor-liquid state, evaporate and transfer to the surface of the product in the form of vapor. In general, the normal course of drying consists of three stages: the food is heated to the drying temperature, then the moisture evaporates from the surface of the product at a rate suitable for the moisture content, when the moisture is close to the critical moisture, the drying speed is reduced. Critical moisture is a function of drying speed, high drying speed increases the speed of reaching the critical moisture point and low drying speed reduces it[4]. In conduction mode, wet solid materials are placed in a chamber that is heated from the outside, and the resulting vapors are released from the considered holes. In the convection mode, hot gas is blown on the surface of wet solid materials, as a result, both a heat source is provided and the possibility of removing steam is provided [2]. The main factor in drying is mass transfer from wet solids. From a theoretical point of view, there is little understanding of the mechanism of mass transfer from drying solids. Mass transfer in this case probably depends on the size, shape and state of the particles that make up the solid materials and how liquids and vapors exit from the pores and voids inside the solid materials and their external surface. This is the maximum that can be said in this case. In some types of dryers (especially conductive dryers) and in some stages, the intensity of drying is usually controlled by heat transfer to the material instead of mass transfer from the solids being dried. Under these conditions, the intensity of drying is determined by the clear rules of heat transfer and is somewhat independent of the properties of the material being dried, but in general, the intensity of drying depends on the mass transfer from the solid materials being dried [2].

In view of the above two factors, the following points should be paid attention to in practice:

- It is possible to determine the drying speed of a material by conducting experiments and obtain it It is very difficult from an experimental point of view.

-Experiments should be performed based on the type of dryer used [5].

1-3-1- Heat transfer in the drying process

The heat required in drying materials may be through radiation, convection, conduction, or by volumetric absorption of electromagnetic energy or Provide radio frequency. The method of drying solid materials depends on the mechanism of heat transfer to the drying material and which of the modes of conduction, convection and radiation are effective. In most direct heat dryers, the main heat transfer mechanism is usually convection, during which the drying process takes place by passing hot gas flow through or over the material. In indirect heat dryers, the main heat transfer mechanism is conduction, in which heat is transferred to the material through the wall. In both cases, it is possible for a significant part of the heat to be transferred by radiation.

Also, when the heat transfer is by convection, the thermal conductivity will have some effect and vice versa.