The protection of nature has become one of the most burning problems of the 21st century. The Earth provides people with mineral resources, forest, fields – everything that makes the foundation of industrial and agricultural production. Why does all this want protection? Because people often do things which pollute land and waters greatly. It’s very dangerous because it damage health of the people.
There are a lot of industrial enterprises in our country, that’s why we can’t ignore the problem of the protection of our environment. Our plants and factories put their waste materials into water and atmosphere and pollute the environment. There are many kinds of transport in our big cities, that’s why we must pay attention to the protection of our nature and the health of people.
All metallurgical plants have to have a gas cleaning equipment. Donetsk steel plant has different kinds of the gas cleaning equipment: gas scrubbing, cyclones, bag filters and aerodynamic filters. Preparing pulverized coal section includes three degrees of cleaning:

1. cyclone,
2. aerodynamic filter,
3. fabric filter.

Cyclon

Cyclones provide a low-cost, low-maintained method of removing larger particulates from gas streams. On their own, they are not usually sufficient to meet stringent emissions standards, but they serve well as precleaners for other, more expensive control devices and for dry-product recovery. Common uses are collection of grinding and machining dust in woodworking plants and tool rooms and in industrial materials handing. A cyclone reduces dust loading and removes larger abrasive particles, in this way extending the life of the fabric filter, which is usually used as the final collector. Multiple-tube cyclone arrangements are used on fossil fuel boilers, where they handle the larger volumes effectively as precleaners. Particles enter the cyclone suspended in the gas stream, which is forced into a vortex by the shape of the cyclone. The inertia of the particles resists the change in direction of the gas and they move radially outward across the gas streamlines. The gas inlet is usually at the top of the cyclone, and the gas is forced into a cyclonic path by the shape of the inlet itself, the outer wall of the device and the cylindrical tube extending down from the top to the cyclone known as the vortex finder. The gas spirals in the cylindrical section of the cyclone, and the particles move outward under the influence of centrifugal force until they strike the body of the cyclone. There they are caught in the thin laminar layer of air to the wall and are carried down-ward by gravity to be collected in the dust hopper. When the gas reached the cone-shaped section, increased rotational gas velocity helps to keep the dust against the wall. The direction of the vortex reverses near the bottom of the cone and cleaned gas rises to exit through the central tube of the vortex finder.

Fabric filters

The primary way to categorize a fabric filter is by the method used to clean it. In general, accumulated dust is separated from the fabric by some combination of the following effects.

1. Deflection on the fabric / dust cake, tending to fracture the cake and separate it from the fabric.
2. Acceleration of the fabric/dust cake, yielding separation forces.
3. Gas flow in the reverse direction, yielding aerodynamic forces that separate the dust from the fabric and subsequently move the dust toward the collecting hopper.

Four cleaning methods have evolved, each of which generates some combination of these fabric-dust-cake separation effects. The majority of bag houses currently in use employ one or more of these cleaning methods.

1. Shaker-cleaned baghouses. In shake cleaning, the tops of the bags are shaken, preferably horizontally, resulting in deflections and acceleration forces throughout the bag. Zero or reverse flow is normally combined with the shaking.
2. Reverse-air-cleaned baghouses. In reverse-air cleaning, a combination of bag deflection and reverse flow is used to remove dust from the fabric. This process, which results in very low stresses on the fabric, was developed specifically for easily damaged fabrics such as fibreglass.
3. Pulse-jet-cleaned baghouses. Pulse-cleaned baghouses use outside - in flow, where the fabric collapses against a wire cage during filtration. During cleaning, a pulse of high-pressure air is directed into the bag (the reverse flow direction), inflating the bag and causing fabric/ cake deflection and high inertial forces that separate the dust from the bag.
4. Sonic cleaning. Sonic cleaning, if used, usually augments another cleaning method. Sonic energy is normally introduced into the baghouse by air-powered horns. Although the process is not well understood, the sonic air shock waves apparently generate acceleration forces that tend to separate the dust from the fabric.

Filtration fabrics made of natural fibers such as cotton or wool is still employed for many filter applications; the development of synthetic fibres, however, has greatly extended the possible range of applications for fabric filters. Continuing developments in fiber and fabric technology may be anticipated. Synthetic fibres are widely used for filtration fabrics because of their low cost, better temperature- and chemical resistance characteristics, and small fiber diameter. Synthetics used include acetates, acrylics, polyamides, polyesters, polyolefin, and polyvinyl chlorides. Specialty fibers for high-temperature use such as Teflon, Ryton and carbon fibres have been developed; however, the synthetic fiber most used for high-temperature applications is glass. The properties of glass fiber, such as good acid resistance, good heat resistance, and high tensile strength, solve many of the problems inherent in baghouses. Fiberglass has the following characteristics.It is non-combustible because it is completely inorganic.

1. It has zero moisture absorption; therefore, is not subject to hydrolysis.
2. It has dimensional stability (low coefficient of linear expansion).
3. It has very high tensile strength, but poor resistance to flex and abrasion. There are some chemical surface treatments that improve the flex-abrasion characteristics of glass.
4. It has good resistance to acids, but is attacked by hydrofluoric, concentrated sulphuric and hot phosphoric acids.
5. It has poor resistance to alkalis; hot solutions of weak alkalis; hot solutions of weak alkalis attack glass.
6. It has poor resistance to acid anhydrides and metallic oxides. For this reason, glass baghouses should not be operated at or below the dew point.