Spray dryer of NIIStrikeramik design

Contents

Introduction

1 Literature and Patent Analysis

1.1 Drying basics

1.2 Classification of dryers

1.3 Dryer Class Selection

1.4 Patent Analysis

2 Process section

3 Process calculation of the process and design parameters of the apparatus

3.1 Initial data

3.2 Determination of chamber dimensions

3.3 Thermal calculation

Conclusion

List of sources used

Appendix A (mandatory)

Introduction

The degree of depreciation of fixed assets in industry reaches 54%. Their annual attrition is 1.7%, with the introduction of new ones - 1.1%, which leads to the aging of fixed assets, especially their active part. The average age of machinery and equipment is 17 years.

Domestic developments in the field of production technologies for efficient types of construction materials, due to the inability to offer the consumer immediately complete technological equipment with its installation and commissioning services, remain not always in demand. Scientific and technological progress in the Russian construction materials industry is based on foreign scientific and technical developments and purchases of imported technological equipment.

Due to lack of funding, the development and formation of a system of national standards is lagging behind, which hinders the development of the production of modern high-performance products and structures and their introduction into construction practice.

Solving the problems facing the industry of building materials, products and structures should be carried out in 2 stages:

At the first stage (20092012 years) it is necessary to :

- attract the necessary investments for modernization of existing production facilities;

- Update the fixed assets of the construction materials industry to a higher level of equipment;

- reduce resource consumption, energy and labor costs for production;

- attract private investment and loans from commercial banks, development of sources of extrabudgetary financing from stock markets, income

from financial, economic and entrepreneurial activities on the basis of an integrated programmatic approach to organizing investments and introducing innovations, mobilizing the entire key potential of the region to reduce dependence on the import of construction products and products from other regions and organizing new production of building materials;

b) at the second stage (20132020 years) it is necessary to:

- ensure the production of competitive high-quality materials and products;

- increase labor productivity due to maximum mechanization and automation of production processes;

- Ensure the rational use of mineral natural resources and the involvement of various industries in the production of man-made wastes.

The main sources of financing for the construction of new production facilities and the modernization of existing enterprises in 200112014 will be extrabudgetary funds.

The purpose of this work is to design a cost-effective and least energy-intensive continuous spray dryer.

To achieve this goal, the following objectives were achieved:

- Study of types of dryers;

- Study of spray dryers and drying processes of materials therein;

- Consideration of process schemes using spray dryers;

- performance of thermal calculation of the apparatus and calculation of its dimensions;

- design of this apparatus.

1 Literature and Patent Analysis

1.1 Drying basics

Drying - thermal process of moisture removal (evaporation) from solid materials. As a result of evaporation of moisture from the material surface, a gradient of moisture concentrations occurs, which is the driving force of its internal movement from the material depth layers to the evaporation surface. This movement of moisture is associated with a violation of its connection with the solid material and with an appropriate energy consumption, so the speed (intensity) of the drying process depends on the form of the connection of moisture with the dry substance of the material [3].

According to the method of heat communication, convective, contact, thermal radiation, sublimation and high-frequency dryers are distinguished. Convective dryers are mainly used for drying mineral materials, in which heat for evaporation of moisture is transferred to the material from a gaseous drying agent (heated air, flue gases or their mixture with air) with its direct contact with the surface of the material.

In its simplest form, the drying process is carried out in such a way that the drying agent heated to the temperature maximum allowed by the dried material is once used in the drying apparatus.

During the drying process, heat is consumed not only for evaporation of moisture, but also for heating of the dried material, transport devices, loss to the environment and loss of heat with the spent drying agent (air or flue gases). Therefore, reducing heat loss is an important technical and economic task when using dryers.

Convective dryers are widely used in industry and are carried out in the following most typical designs: drum, spray, pneumatic and belt dryers. The designs of these devices are discussed below.

1.2.3 Pneumatic dryers

Dryers of this construction are mainly used to remove surface moisture from loose materials such as sand, crushed minerals, powders.

Drying is carried out in a vertical pipe with a length of up to 20 m. The material particles move in a stream of heated air (or flue gases), the speed of which exceeds the rate of rotation of the particles, and ranges from 10 to 30 m/s. In such dryers, the drying process lasts seconds and in such a short time only part of the free moisture can be evaporated from the material.

The energy consumption in pneumatic dryers is significant, and it decreases with a decrease in the particle size of the material, which should not exceed 10 mm. Air dryers are combined with other types of dryers to dry coarse particulate materials and to remove bound moisture from the material. Thus, despite the compactness and simplicity of the apparatus, the application of pneumatic dryers is limited to the conditions mentioned above.

However, pneumatic dryer pipes are often used due to the simplicity of the design, and in them the drying of the product can be combined with pneumatic transport. Multi-tube dryers, classifier pipes are also used for drying and simultaneous separation of material into two fractions [2].

1.3 Dryer Class Selection

Spray dryers are discussed in this paper.

Spray dryer includes drying chamber, gas equipment, ventilation system, suspension supply system, instrumentation and automation.

The drying chamber is a tower welded from 4-5 mm metal sheet, covered by a metal cover. Chamber bottom is made in form of cone hopper and welded to body. In the manufacture of ceramic tiles for the body, stainless steel of type X13 or X25T is used. Outside, the side and upper surface of the body is insulated by mineral-wool plates 200 mm thick, and the bottom - by mineral-wool plates 60-100 mm thick. The coating layer of thermal insulation is thin sheet metal - aluminum or galvanized steel. Chamber bottom ends with central hole for powder discharge. A leak with a petal gate is attached to the hole, which reduces air suctions. In the cover of the drying chamber there is an explosive valve in the form of a membrane made of asbestos cardboard with a thickness of 10 mm. To monitor the operation of burners and nozzles in the walls of the drying chamber, there are hatches with viewing windows and devices for illuminating the working space. Outside, one or more standard vibrators are mounted on the cone bottom with a disturbing force of not more than 1000 N. Vibrators are designed for short-term actuation during "hanging" of powder on the bottom.

Gas burners are installed uniformly around the perimeter to burn gas in the walls of the drying chamber, approximately in the middle along the height. Exhaust umbrella for exhaust gas removal is installed in cone bottom. Exhaust branch pipe of umbrella is connected to dust collecting cyclone, which, in its turn, is connected to suction fan. The umbrella section is 2 m, which provides a small (not more than 24%) removal of material with exhaust gases. The dryer is equipped with a system of instrumentation showing temperature and vacuum in the upper part of the drying chamber ,

in discharge cone, before and after cyclones. The gas pressure and the slurry pressure in the delivery line are also controlled. Mechanical tangential nozzles operating at a pressure of 12 atm are used to spray the suspension. The diameter of the nozzles is 2.1 or 1.5 mm.

Nozzles with nozzles of small diameter are clogged faster. Therefore, much attention is paid to cleaning the slurry. At joint grinding of plastic and dewatering materials suspension is passed through vibrating sieve with 400 otv/cm2 and at pumping into service pool through sieve with 900 otv/cm2. Compliance with the rules of suspension preparation and serviceability of its cleaning system practically exclude clogging of nozzles.

Structurally, the spray dryer includes a drying chamber with a bottom and systems: suspension supply and spraying, heat supply, extraction and cleaning of exhaust gases, instrumentation and automation, as well as structural building elements.

In accordance with GOST 1890680, general-purpose spray dryers, depending on the method of spraying the suspension, are divided into two types:

RF - spray dryers with spraying of source material by mechanical or pneumatic nozzles;

RC - spray dryers with spraying of initial material by centrifugal nozzles.

Execution of dryers can be: N - not explosion-proof, Vvzryvozashchishchenny, P - with the fire extinguishing device.

Materials of the following groups can be used to manufacture dryer structural elements in contact with the obtained powder or initial suspension during operation: U - carbonaceous steels and cast iron, K - corosyonic-resistant steels and alloys, T - titanium and its alloys, M - colored alloys, E - enamels.

This standard establishes 6 modifications of spray dryers depending on their design features (location of the sprayer and coolant supply, bottom design):

1 - with lower coolant supply, conical bottom and sprayer arrangement at the top of drying chamber;

2 - with upper coolant supply, conical bottom and sprayer arrangement at the top of drying chamber;

3 - with upper coolant supply, conical bottom and sprayer arrangement at the bottom of drying chamber;

4 - with upper coolant supply, flat bottom and sprayer arrangement at the top of drying chamber;

5 - with upper supply of heat carrier, flat bottom and arrangement of sprayer at the bottom of drying chamber;

6 - with lower and upper supply of heat carrier, conical bottom and arrangement of sprayer at the top of drying chamber. [3]

The main disadvantage of the upper slurry dryers is the significant difference in humidity between the large and fine granules, whereby the large particles adhere to the conical bottom and prevent the powder from evenly leaving the dryer. In the lower slurry feed, the moisture content of the powder at different distances from the axis of the dryer is substantially the same as the average. The noted drawbacks of the upper slurry dryers are eliminated in the lower slurry dryers.

In addition to gas-fuel spray dryers, liquid-fuel dryers, preferably fuel oil, are used. A distinctive feature of such dryers is the use of a remote furnace installed at zero elevation and a connecting pipeline between the furnace and the ceiling of the dryer.

The developed spray dryer designs have the following features:

- application of a group of mechanical nozzles close to each other, operating at a pressure of 0.8 to 1.2 MPa, installed along the axis of the dryer from the bottom up, or installed from the top and directed vertically downwards, for spraying the suspension;

- Combustion of gas in metal tunnels located inside the drying chamber at the middle height;

- exhaust gas extraction in the lower part of the drying chamber through the exhaust umbrella;

These features provide the following advantages.

Combustion of gas inside the drying chamber eliminates heat losses by furnace devices and gas ducts, provides extremely high initial temperature of heat carrier, allows to conduct the process with minimum air flow rate and, as a result, provides minimum possible specific heat consumption - up to 3.18 MJ and electric power - up to 0.004 kVt∙ch per 1 kg of evaporated moisture.

Spraying the suspension with a group of nozzles creates a high concentration of material in the flare volume, allows to reduce the size of the drying chamber and in this regard provides a high specific moisture removal - more than 25 kg/( m3∙ch). Due to the low flow rate of the heat carrier, the removal of the dried product does not exceed 4%. The required low slurry pressure allows the use of wear-resistant membrane pumps.

The spray drying process is usually divided into three stages: mass spraying; heat and mass exchange between mass droplets (particles) and the environment; and separating the dried product from the gas stream. Such division of the process is somewhat conditional, since it is impossible to outline a clear boundary between these stages due to their overlapping [3].

Most generally, spraying refers to the process of crushing a liquid jet into a large number of droplets and distributing these droplets in space. In spray dryers, liquid crushing is carried out due to the kinetic energy of the liquid (mechanical spraying) or the kinetic energy of the gas (pneumatic spraying).

The dynamics of the sputtered jet movement are very complex. There are attempts to describe its motion by solving the differential equilibrium equation of forces acting on individual liquid droplets. However, the flight of the isolated liquid drop cannot reflect the dynamics of the spray as a whole [3].