Dryer Calculation Project Drawings + Explanatory Note

Contents

1. Introduction

2. Justification of drying unit selection

3. Process Diagram Description

4. Material characteristic

5. Drying unit calculation (general procedure)

6. Material Balance

7. Determination of air flow rate

8. Heat balance

9. Pipe Diameter Calculation

10. Calculation of additional equipment

11. Current status of the question

12. List of used literature

Introduction.

Many chemical products are dispersed with any liquid carrier (water, organic solvent or diluent). Convective drying in a suspended state, where the gas is not only a heat carrier but also a transporting agent, is mainly used to produce dispersed products in dry form. Dryers with a suspended layer of dispersed material form a significant part of chemical equipment. These include fluidized bed dryers, pneumatic, spray, aerial, vortex, drum dryers. A distinctive feature of these dryers is a more or less uniform distribution of material in the gas coolant.

The modern trend in the development of the chemical industry is characterized by the creation of both large-tonnage and low-tonnage industries with a wide range of products. Under these conditions, the accuracy of calculations when designing newly created dryers of high unit capacity is of particular importance. At the same time, the tendency to unify and normalize known types of dryers requires an accurate assessment of their effectiveness in drying new products.

DRYING - removal of liquid (most often moisture, less often other liquids, for example volatile organic solvents) from substances and materials by thermal methods. It is carried out by liquid and removing formed vapors when heat is supplied to the dried material, most often with the help of so-called drying agents (heated air, flue gases and their mixtures with air, inert gases, superheated steam). Wet bodies are dried: hardcolloid, granular, powdered, lumped, granulated, sheet, woven and others (this group of dried materials is most common); paste-like; liquid suspensions, emulsions, solutions.

The purpose of drying, widely used in the production of the chemical and forestry complex, agriculture, the food industry, building materials, leather, light and other sectors of the national economy, is to improve the quality of substances and materials, prepare them for processing, use, transportation and storage. This process is often the last process step prior to the release of the finished product. The liquid is previously removed by cheaper mechanical methods, finally thermal.

Natural drying in the open air due to the significant duration is used extremely rarely and mainly in areas with a warm climate. In chemical industries, as a rule, artificial drying is used, carried out in special drying plants, which include: a dryer, or a dryer, where the process directly proceeds; auxiliary equipment-heat exchangers (heaters), a traction device (fan, blower) and a dust cleaning system used to heat the drying agent, pass it through a dryer and separate it from the dried product.

Drying is one of the most energy-intensive processes, so in the field of drying technology, saving energy resources is an urgent problem. The creation of high-efficiency and economical standard devices and installations will significantly reduce the energy consumption of drying. For the development of such devices and installations, methods of integrated analysis of wet materials and their classification as drying objects are necessary .

Justification of drying unit selection.

The choice of dryers depends on a number of factors. These include time C., aggregate state, allowed heating temperature, explosion and fire hazard, toxicity, shrinkage, contamination and other properties of the material to be dried; requirements for uniformity of drying; requirements for dust collection system and so on. In choosing, preference should be given to continuous dryers; drying with flue gases is more economical than air drying., However, it is not always possible due to contamination of the material. If no acidic or alkaline medium is formed when the material to be dried reacts with moisture, dryers, often large, should be made of ordinary steel, otherwise stainless steel, sometimes titanium.

The choice of dryers is related to the problem of material classification. A classification is currently being developed to allow a quick assessment of kinetics and to select the most rational type of dryer. Example classification of capillary porous materials. According to this, the wet materials are differentiated according to the internal structure, and the critical pore diameter dcr is taken as its characteristic, i.e. the diameter of the thinnest pores from which it is necessary to remove moisture before reaching the final moisture content; dcr parameter allows evaluating the vehicle and choosing an economically feasible drying device.

Industrial dryers.

According to the variety of materials to be dried, their properties and processing conditions, the dryer structures are also very diverse and different :

1. according to the method of heat supply (convective, contact, special );

2. by type of drying agent (air, gas, steam);

3. by the pressure in the drying chamber (atmospheric, vacuum );

4. the method of organizing the process (periodic or continuous);

5. in the mutual direction of movement of the dried material and the drying agent (in convective equipment, counter current, cross current);

6. by the state of the wet material layer in the apparatus (fixed, moving or suspended).

Dryers used in chemical industries, which are combined according to the method of heat supply, are described below.

With a significant decrease in the mass of particles of dispersed material during drying, free spilling and passing fluidized bed modes are used. Among these dryers, the most common are pneumatic, vortex chambers, devices with a boiling and fountain layer, vibratory.

Pneumatic dryers.

Pneumatic dryers (Figure 5) are one or more sequential dryers

about connected vertical pipes with a length of 1520 m. Wet material is supplied through the feeder and air heated in the heater is pumped by the fan from below. The material is carried away by the air flow moving at a speed of 1525 m/s. In the cyclone, the dry material is separated from the air and removed through the discharge device; air is discharged to atmosphere through filter. Turbulators (expanders, deflecting plates, swirlers, etc.) are inserted into the dryer tubes to activate the drying mode. Due to short contact times (1-5 seconds), such dryers are suitable for treating thermally unstable materials even at high drying agent temperatures; they are also distinguished by compactness, simplicity of design, but at the same time increased power consumption and heat (up to 8.4 kJ/kg of moisture).

Swirling drying chambers are the most interesting representatives of apparatus with swirled drying agent flows. These chambers are disk devices resembling a centrifugal fan with a tangential supply of coolant. Wet loose or fibrous material is loaded by feeder through side part of chamber and is swirled under action of gas jets to form annular rotating layer in apparatus. The gas flow rate is 5080 m/s, the residence time in the material chamber is 1020 s and 2-3 minutes for particles of size 0.10.2 and 3-4 mm, respectively.