Variant – 7

1. Dry Dust removal equipment

Removal of particulate pollutants.

The dust removal equipment available may be divided into two large groups: Dry dust removal equipment and wet dust removal equipment. For both groups: A few representative examples will be discussed.

Dry Dust removal equipment

In dry dust removal equipment dust separation from the carrier gas is achieved directly i.e. in the dry state, without the use of a special dust collection agent like water drops. The collected dry dust can be directly disposed of. The use of dry dust removal equipment involves however the danger of dust explosion. Therefore, special measures have to be taken to prevent dust explosion and pressure release in case of explosion.

The separation of dust particles from a gas is mainly due too the action of three forces: inertia force, surface or adhesion force, and electrical force. In most of the dry dust separators, one force dominate over the other thus determines the separation process. According to the prevailing force there are three groups of the dry dust removal equipment:

1. Mass force separator.

2. Adhesion force separator.

3. Electrical force separator.

A typical mass force separator is the cyclone. Under the action centrifugal forces, the dust particles are separated from the gas phase. Conventional adhesion force separators are bag and pocket filters. A typical electrical force separator is the plate precipitator. The three types of dry dust separators are schematically illustrated in Fig. 1.

The cyclone consists of entrance chamber, vortex chamber, dust collection chamber and gas exit tube, the letter extending into the interior of the cyclone. The gas is introduced tangentially so that a rotational movement of gas and dust particles is obtained. Due to this rotational motion, centrifugal forces result which carry the dust particles toward the wall entrance and vortex chamber. The cyclone separates the dust continuously.

2. Normalization of the harmful substances, disposal with sewage.

Before disposal in a pond sewage should be cleaned up to the highest degree because under effect of natural factors the secondary products of decomposition may be formed, negatively influencing quality of water.

To carry out process it is necessary, firstly, after sewage disposal, the presence in the pond of the soluble oxygen. Chemical or bacterial oxidation of the organic substances contained in the sewage, results in decrease in concentration of oxygen, dissolved in water. (1 liter of H2O contains 8-9 sm3 of O2. Organic substances interacting with dissolved O2 are oxidized to СО2 and Н2О. Therefore, the parameter was entered allowing estimating the total quantity of pollution in water according to absorption of О2. Such parameter is biochemical demand of oxygen (BOD). BOD is equaled to quantity of O2. Depending on time there are BOD5 (five-day), BOD20 (twenty-day), BOD (full), in this case the oxidation is finished.

According to « Rules of surface waters protection from pollution » the water quality of a reservoir after sewage disposal should meet to the following basic requirements: quantity of dissolved О2 should be not less than 4 mg / l; BOD (full) at 20 С is not higher than 3 mg/l. The contents of weighed substances in water after sewage discharge should not be increased more than in 0,25 and 0,75 mg /l for reservoirs I and II correspondently, a mineral sediment is no more than 100 mg /l; including chlorides is 350, sulfates is 500 mg / l; odour and smacks of water should absent; a surface of water should not contain the floating impurities, films, spots, oils, oil products, poisonous substances.

3. The elementary evolutionary phenomenon

Genetic structure is a relationship of various genotypes and equilocal genes in the community. Totality of genes of all community species is called genofund. The genofund is characterized with frequencies of equilocal genes and genotypes. Frequency of equilocal genes is its share in all totality of equilocal genes of the given gene. The sum of frequencies of all equilocal genes is equal to unit.

The long and directed change of genetic structure of community, its genofund is called the elementary evolutionary phenomenon. Without change of the community genofund, evolutionary process is impossible.

The factors changing genetic structure of community are following:

1) Mutation is a source of new equilocal genes appearance;

2) Unequal capable of living of species (species are subjected to action of selection);

3) Not casual interbreeding;

4) Drift of genes is a change of equilocal genes frequency, which are casual and independent of selection action (for example, flashes of diseases);

5) Migrations are outflow of available genes and (or) inflow new ones