Drawing Scrubber Venturi for Course Design

Contents

Introduction

1. BRIEF DESCRIPTION OF THE ENTERPRISE

1.1 History of development of OJSC "Virage" enterprise

1.2 1.2 Environmental Impact of OJSC "Superage"

2. ENVIRONMENTAL PART

2.1 Characterization of the plant as a source of pollution

3 WET GAS PURIFIERS

3.1 Hollow and nozzle devices

3.2 Bubbling and foam devices

3.3 Percussion-inertial type devices

3.4 Centrifugal type devices

3.5 Venturi scrubber

3.6 Electrical filters

4. DUST COLLECTION EQUIPMENT CALCULATIONS

Literature

Introduction

Relevance. A large number of modern chemical and technological processes are associated with the crushing, grinding and transportation of bulk materials. At the same time, inevitably, part of the materials goes into an aerosol state, forming dust, which with process or ventilation gases is released into the atmosphere .

Dust particles have a large total surface, as a result of which their chemical and biological activity is very high. Some substances in the aerodispersed state acquire new properties, for example, the ability to explode. Industrial dust particles have different shapes and sizes. The concept of particle size due to the large variety of shapes is conditional. In dust collection, it is customary to characterize the particle size with a value that determines its deposition rate. Such a value is the sedimentation diameter (the diameter of the ball, the deposition rate and the density of which are equal to the deposition rate and the density of the particle being compared). In this case, the particle itself can have an arbitrary shape. Dust particles of different shapes at the same mass settle at different rates. The closer their shape is to spherical, the faster they settle. The largest and smallest particle sizes characterize the dispersion range of a given dust.

At present, several hundred different designs of apparatus for purifying gases from dust are known. Despite their diversity, they are all hardware options that use few basic principles of deposition or suspension.

Gravity and diffusion are the natural drivers of the dust particle deposition process in the stream. These forces, however, are insufficient for spontaneous cleaning of gases. Although the largest particles are sometimes captured by natural deposition in the gravitational field, most modern dust cleaning machines use a more intensive force field created artificially.

Thus, for dust collection, inertial forces manifested by changing the direction and speed of the dust-gas flow, as well as the electric attraction force of pre-charged particles to the precipitation electrode, are widely used.

It finds use in dust collection and a process of coagulation, as a result of which the formation of enlarged aggregates consisting of several dust particles occurs. This process is intensified by inertial, electrical or thermal forces. In dust collecting devices, the main particle deposition process is often accompanied by side-by-side undesirable processes. So, for example, already deposited particles can again be entrained in the gas flow, and the aggregates of particles formed during the coagulation process can collapse, etc.

To suppress secondary processes that interfere with dust collection, special measures are taken - wetting precipitation surfaces, reducing the gas velocity, increasing the electrical conductivity of particles, introducing liquid into the gas to increase the strength of particle aggregates, etc.

To extract dust-like particles from gases, gases are filtered through porous partitions. In this case, an inertial, electrical or diffusion particle deposition mechanism is used. The choice of the deposition mechanism depends on the size of the dust particles, the gas flow rate and other factors.

Depending on the nature of the forces used in dust collecting apparatuses for separating dust particles from the gas flow, they are divided into four main groups of dust settling chambers and cyclones, wet gas cleaning apparatuses, porous filters, electric filters.

The purpose of the work is to provide an overview of the main dust collection methods:

- gravitational and inertial dust cleaning methods;

- to consider the basic principles of construction and operation of the VTI scrubber located on the territory of the asphalt plant of OJSC "Virage"

2. environmental part

2.1 Characterization of the plant as a source of pollution

The object of the study is the asphalt plant of OJSC Virage in the Aksubaevsky district. For trapping solid particles from flue gases, a CVTI is used, where particles are deposited on a film of liquid flowing along the inner surfaces of the apparatus - walls and rods, and on liquid droplets in the volume.

3. gas wet cleaning devices

One of the simple and efficient methods of cleaning industrial gases from suspended particles is the wet method, which has been widely used in recent years in domestic industry and abroad.

Wet gas purifiers are characterized by high particulate trapping efficiency and low cost compared to dry purifiers.

Some types of wet cleaning apparatus (turbulent gas washers) can be used to clean gases from particles up to 0.1 μm in size.

In addition to competing successfully with high-efficiency dust collectors such as bag filters, wet gas cleaners can be used in cases where bag filters cannot be used due to the high temperature, high humidity or explosive nature of the gases being cleaned.

Vapour and gaseous components can be trapped in the wet gas purification apparatus simultaneously with the suspended particles. The disadvantages of wet treatment include the need to treat the resulting wastewater, increased splash and the need to protect the devices from corrosion during the treatment of aggressive media. Despite these disadvantages, wet gas treatment machines are successfully used in the chemical industry.

Wet cleaning devices are often used in gas cleaning systems for simultaneous cooling and humidification of gases. In this case, the gas purifiers also serve as mixing heat exchangers where the cooled gas stream is in direct contact with the cooling liquid.

Among the apparatus for cleaning gases from dust, wet dust collectors are characterized by the greatest variety, which is due to forces acting on gas and liquid flows. The liquid phase is present in the apparatus in the form of a film, jet, droplets, foam or various combinations.

According to the principle of operation, gas wet cleaning devices are divided into the following groups: hollow and nozzle, bubbling and foam, impact-inertial type, centrifugal type, dynamic and turbulent washers.

3.1 Hollow and nozzle devices

In hollow and nozzle devices, dust gases are passed through a stream of liquid sprayed, sprayed or flowing along the nozzle. At the same time dust particles are captured by flows of washing liquid and deposited in apparatus, and purified gases are released into atmosphere.

In hollow scrubbers, washing of gases is performed by spraying of liquid towards moving cleaned flow. Coarse spraying nozzles are used to irrigate scrubbers. High efficiency of gas cleaning is achieved if the washing liquid is sprayed to form drops of 0.5-1 mm. Typically, the scrubber is a circular or rectangular vertical apparatus. Nozzles are installed in one or several sections along height of apparatus.

To reduce splash, the gas velocity in the apparatus should not exceed 1-1.2 m/s. The hydraulic resistance of the hollow scrubber is small and usually does not exceed 250 Pa. The water flow rate is 5-10 m3/h per 1 m2 of cross-sectional area. Dust particles of more than 10 μm are most fully captured in these devices.

A characteristic feature of nozzle scrubbers is that the process of dust extraction occurs on the wetted surface of the nozzle as a result of numerous changes in the gas flow in the apparatus. Nozzle scrubbers are filled with nozzle elements of different configuration, which are retained on support grids. Erratic nozzle includes annular (when loaded in bulk), saddle-shaped, lump; in the regular - chord, block, corner.

The disadvantages of nozzle scrubbers are the frequent clogging of the nozzle in the treatment of dusty gases, which limits the scope of their application in the dust collection technique. Packing columns are useful only when collecting well-wetted dust, especially when the collecting processes are accompanied by cooling or cleaning of gases from other components.

3.2 Bubbling and foam devices

In bubbling apparatus, the bubble gases to be cleaned pass through the liquid bed; Note here that gas cleaning from suspended particles takes place due to large surface of gas contact with liquid. The gases to be cleaned are bubbled into the liquid through tubes lowered into the liquid layer. To crush gases into small bubbles, the edge of the bubble tube is often made toothed. The efficiency of such devices is quite high, however, due to the complexity of manufacture, they have limited industrial applications.

In foam apparatuses, the dust collecting effect is achieved by moving the gas to be cleaned through the foam bed. Foam in these devices can be formed in various ways: on the grid, where liquid is supplied, purged from below by air flow or when air flow strikes the liquid mirror.

Foam dust collectors are widespread in the chemical industry. They are simple in design and quite effective. Unlike bubblers in foam dust collectors, gases pass through the liquid at a rate higher than the rate of free bubble surfacing, which creates conditions for the formation of highly urbulized foam.

Foam gas washers are vertical apparatus of round or rectangular section, in internal cavity of which perforated or slotted grids are installed. The gases to be cleaned are supplied to the grates from below. As a result of intensive mixing of gas with liquid in the foam layer, dusty particles are wetted and separated from the flow, which are discharged from the apparatus in the form of sludge, and purified gases are discharged through a branch pipe located in the upper part of the apparatus.

There are foam dust collectors with failed and overflow grates. In the first of them, the liquid, as it were, "falls" through the holes in the grid through which the purified stream enters. Devices with overflow grids can operate with free drain of foam through the drain threshold. For efficient operation of devices with both failed and overflow grids, it is important that the liquid and gas are evenly distributed over the surface of the grids.

In foam devices with overflow grids, approximately three times less liquid is consumed and significant fluctuations in gas and liquid load are permissible than in devices with failed grids. However, grates of the failed type are less clogged with dust, since the water flowing into the holes washes away the sediment from the grates.

It should be noted that at a gas velocity of more than 1.0-1.2 m/s in foam apparatuses, strong entrainment of water drops is possible. Therefore, a drop catcher must be installed in the cross section of the apparatus above the foam layer. Recent studies in the field of improving foam devices have found that a special rectifier with a height of 60 mm in the form of cells with cells (35x35 mm) should be located above the main grid. The honeycombs align the foam layer over the entire grid area and allow increasing the gas velocity in the section of the apparatus body to 3 m/s .

In order to intensify mass and heat exchange processes, in recent years, an apparatus has become widespread in which hollow and continuous balls of polyethylene, polystyrene and other plastic masses serve as a movable nozzle.

A layer of hollow balls is placed in the apparatus body between the lower support-distribution grid and the upper limiting grid. These devices were successfully used to wet-dump gases in processes accompanied by the formation of suspensions and precipitation, when other devices turned out to be unsuitable.

With hydraulic resistance from 1500 to 2000 Pa, up to 99% particles of size from 2 μm and more are caught in a fluidized ball nozzle apparatus.

LTI foam dust collectors are used for fine cleaning of process, smoke and exhaust gases, as well as ventilation air from dust, mists and other contaminants, providing a higher degree of cleaning compared to other types of wet dust collectors.

3.6 Electrical filters

One of the most advanced methods of cleaning industrial gases from dust and mists is electrical cleaning in electrofilters.

The wide use of electrofilters for collecting solid and liquid particles is due to their versatility and high degree of gas purification at relatively low energy costs. The efficiency of electric gas treatment plants reaches 99%, and in some cases 99.9%. Such filters are capable of capturing particles of various sizes, including submicron particles, at a particle concentration in the gas of up to 50 g/m3 and higher.

Industrial electrostatic filters are widely used in the temperature range up to 400-450 ° C or more, as well as in conditions of exposure to corrosive media.

Electrofilters can be operated under vacuum and pressure of gases to be cleaned. They differ in relatively low operating costs, but the capital costs for the construction of electrofilters are quite high, since these devices are metal-intensive and occupy a large area, and are also supplied with special units for power supply. At the same time, with a decrease in gas productivity, unit capital costs increase significantly.

A preferred application of electrofilters from the viewpoint of economic feasibility is the cleaning of large volumes of gas.

The disadvantages of electrofilters along with their high cost include the high sensitivity of the process of electric cleaning of gases to deviations from the given technological mode, as well as to mechanical defects of internal equipment.

Sometimes the properties of the gas-dust stream are a serious obstacle to the electric gas cleaning process (for example, with high dust resistivity or when the gas to be cleaned is an explosive mixture).

Dust trapping in electrofilters is based on the known ability of differently charged bodies to attract to each other. The dust particles are first supplied with an electric charge, after which they are deposited on an oppositely charged electrode.

When gas with suspended dust particles passes in the interelectrode space, gas ions are adsorbed on the surface of the dust, so that the dust is charged and becomes able to move under the influence of an electric field to the precipitation electrodes. Dust settled on electrodes is periodically removed. Thus, electrogas cleaning includes processes of ion formation, charging of dust particles, their transportation to settling electrodes, periodic destruction of a layer of dust accumulated on electrodes and its removal into dust collecting bins.

As the electric field strength and the amount of charge produced by the particles increase, the velocity of the charged particles to the electrode increases. The electrostatic filter will be better at collecting dust, the longer its length, higher field strength and lower gas velocity in the apparatus.

Different designs of electrofilters differ in the direction of travel of gases (vertical, horizontal), the shape of settling electrodes (plate, compact, tubular, hexagonal), the shape of coronating electrodes (needle, round or bayonet section), the number of parallel working sections (single and multi-section). Electrofilters are divided into dry and wet.

In dry electrostatic filters, solid particles are usually trapped, which are removed from the electrodes by shaking. The gas to be cleaned in the dry precipitator shall have a temperature above the dew point to avoid condensation of moisture which may cause corrosion of the apparatus.

In wet electrostatic filters, solid and liquid particles washed off the surface of the electrodes by an irrigating liquid (usually water) can be trapped. The temperature of the gas entering the wet precipitator shall be close to or equal to the dew point. If liquid particles independently drain from the electrodes as they accumulate, then wet electrofilters may not have special washing devices.

There are two main types of precipitation electrodes - plate and tubular. Plate electrodes are used in both horizontal and vertical electrofilters, and tubular electrodes are used only in vertical ones. Tubular precipitating electrodes are preferable to plate electrodes due to better electric field characteristics. However, it is difficult to provide good shaking of tubular electrodes, and therefore they are rarely used in dry electrostatic filters and quite widely in wet ones.