ON THE EXPECTED ELECTRICAL INDICATORS OF A LARGE METALLURGICAL PLANT

B. I. Kudrin, I. F. Antonov, R. G. Astratov

(Presented by the scientific seminar of the departments of electric power stations and electrical systems and networks)

Modern metallurgical plants under construction are the largest enterprises for the production of ferrous metal. As a rule, such enterprises have a complete metallurgical cycle. They include ore-, coal-preparation and agglomeration plants, coke-chemical, blast-furnace, steelmaking production, blocks of rolling shops, an enormous power economy (CHP plants, air-blower stations, etc.), and repair and auxiliary facilities. Ferrous metallurgy is characterized by high rates of growth in the electrical equipment of labor, exceeding the rates of growth of electrical equipment for industry as a whole, which determines the considerable magnitude of the consumed power. Such enterprises are characterized by the presence of many consumers of electric power assigned to the first category and by the presence of a special group of first-category consumers. Although a large part of the shops may be assigned to the second category (for example, the blooming mill, the agglomeration plant), nevertheless economic considerations, the possibility of massive underproduction, and the existence of a rigid technological connection within a shop and between individual productions make it necessary to ensure the reliability of the power supply of these consumers in the same way as for the first category. A certain number of third-category consumers does not influence the construction of the power-supply system. Among the special features of a metallurgical enterprise is the considerable built-up area (more than 20 sq. km). At the same time, the general plan, both in a scheme with a sequential arrangement of shops and in a single-cycle scheme with a parallel arrangement, is distinguished by a high building density and considerable saturation with above-ground communications. This complicates the construction of networks, especially during reconstruction of the plant.

When designing the power-supply system of a metallurgical enterprise, the maximum loads by shops and productions are determined; the voltage of the supply and distribution networks is selected; the location and number of the main step-down and distribution shop substations are determined; the schemes of energy distribution and substation schemes are selected; the method of transmitting electric power is chosen; and so on.

When constructing the power-supply scheme, certain features characteristic of metallurgical enterprises should be taken into account, namely:

1. The complexity of the electric-power supply system, the large number of substations of various purposes, and the extent of cable and overhead lines.

2. The need to ensure the reliability and uninterrupted operation of the electric-power supply scheme.

3. The concentration of electric-power consumers in small areas, i.e., in one building there may be consumers with a load of 15–20 thousand kW and more, while individual production facilities (buildings) are simultaneously dispersed.

4. Severe operating conditions for electrical installations and electrical equipment.

5. The possibility of organizing rational operation and repair.

6. The need for dispatching and telemechanization of the power facilities, with a transition to an automatic production-control system.

7. The high cost of the fixed assets of metallurgical production, with a relatively small percentage cost of external electric-power supply.

8. The rate of growth of electricity consumption for the plant as a whole and by districts when selecting the capacity of transformers for the main step-down substations. For example, for the West Siberian Metallurgical Plant, which is carrying out intensive construction, this growth by year is characterized by the following figures (1963 is taken as 1.00): 1964 — 3.32; 1965 — 6.23; 1966 — 10.1; 1967 — 19.6; 1968 — 28.8; 1969 — 33.6. In relation to the preceding year, the annual increase in electricity consumption averaged 60%.

In order to specify the magnitude of the expected basic electrical indicators, let us consider approximate loads for the principal production facilities and districts of a large metallurgical plant with an annual capacity on the order of 10–12 million tons of steel. As the basic electrical indicators in electric-power supply designs, the following should be adopted: maximum load—the half-hour calculated maximum load \(P_m\); maximum coefficient—the ratio of the maximum load to the average load \(k_m\); demand factor—the ratio of the maximum load to the installed capacity \(k_c\); annual number of hours of utilization of the maximum—the ratio of the enterprise’s annual electricity consumption to the maximum load \(T\). On the basis of experience in designing metallurgical plants in Siberia and the Far East, Table 1 gives the maximum loads and specific consumptions per unit of output for certain production facilities. The data for 1958–1960 characterize the maximum loads and specific consumptions adopted in developing design assignments for plants under construction and reconstruction, i.e., the situation with electricity consumption at that time; for 1968–1969, the loads actually achieved by production facilities and the specific consumptions; for 1975–1980, the expected consumptions and loads are given.

The increase in load and the rise in specific consumption by districts are explained, first, by general causes—measures aimed at improving working conditions; automation and mechanization of production processes; the need to reduce gas pollution and dustiness of the air basin, to reduce discharges, etc.; and, second, by causes specific to the given production facility.

The increase in load for coke-chemical production is explained by an increase in energy expenditures for coal preparation due to higher requirements for the charge, with a simultaneous expansion of the grades of coal used for coking; by an increase in the number, by volume and by quantity,

names of chemical products; the introduction of new technology for improving coke, for example formed coke; the commissioning of dry coke-quenching installations, etc.

Table 1

For blast-furnace shops, a continuous increase in furnace volume to 3000 and, in the future, to 5000 cubic meters is characteristic, with simultaneous improvement of blast-furnace production technology, improvement in burden preparation, application of increased gas pressure in the working space of the furnace, use of pulverized coal fuel and natural gas for injection into the hearth, and oxygen enrichment of the blast. Blast-furnace slag is planned for complete processing. Powerful gas-cleaning and slag-processing installations are being built at blast-furnace shops. To supply blast-furnace production with compressed air, steam-air stations (ABS) are being built near the blast-furnace shop; these are major consumers of electric power. ABS is being separated from the TPP.

Steelmaking production is developing along the path of constructing oxygen-converter shops, with the abandonment of construction of new open-hearth shops. Converter capacity is increasing, and converters of chiefly 200–300 t capacity will be built. Vacuum treatment, installations for producing synthetic slags to improve metal quality, briquetting of slags, and the introduction of continuous steel casting, with entire shops oriented toward it, cause a considerable increase in loads in converter shops. To obtain high-quality and special-quality steels, construction is planned of electric steelmaking shops with furnaces of 100 and 200 t capacity (300 t), respectively, with trans-

transformers of 25 and 40 thousand kVA (50 thousand kVA), and in the future with transformers of unit capacity 100 thousand kVA.

Rolling shops are the most powerful consumers of electric power, with a large number of large electric motors, up to 20,000 kVA per unit. The introduction of continuous rolling and measures to improve the quality of rolled products—for example, thermal strengthening—lead to an increase in specific costs and maximum loads.

At present, all the main shops are switching to a closed circulating water-supply cycle in order to eliminate the discharge of industrial wastewater. Maximum loads at pumping stations become comparable with the loads of certain production operations. The expected distribution of electric-power consumption for individual production operations of a metallurgical plant is characterized by Table 2.

Table 2

When constructing the main power-supply scheme of a plant with the maximum load of 1,200 thousand kW indicated in Table 1, the question of the capacity and location of the CHP plant must first of all be resolved. At present, the capacity of the CHP plant is determined not by electric-power requirements, but by the heat requirements of the plant and of nearby consumers. The location of the CHP plant is determined by the general plan, according to which the CHP plant is placed not at the center of the electrical loads, but on the outskirts of the plant and even at a distance of 3–5 km from its boundary. The main argument is the preservation of territory for the further development of the plant over the next 10–15 years. At modern plant CHP stations, turbogenerators of 100–300 MW are installed, and the total installed capacity of the CHP plant becomes of the same order as the enterprise’s maximum load.

However, the difficulties of transmitting electric power to distribution substations at generator voltage—for example, 10 kV—over distances of several kilometers necessitate transformation to a voltage of, for example, 110 kV.

The requirements of uninterrupted operation and reliability of power supply make it necessary to connect the plant to the power system; in this case,

the total installed capacity of the TPP generators and the transformers connected to the power system exceeds the enterprise’s maximum power by more than a factor of two. Connection to the power system should be carried out at a voltage of 500 kV or by several lines at a voltage of 220 kV, depending on the configuration of the power-system networks and the location of the sources of electric power. It is advisable to provide the main step-down substations for groups of rolling shops with a maximum capacity of 120–240 thousand kW as deep inputs at a voltage of 220 kV with transformers of 100 and 160 thousand kVA. The main step-down substations for consumers with a maximum load of 30–40 thousand kW and higher, located several kilometers from the supply sources, should be built at 110 kV as deep inputs with transformers of 25, 40, and 63 thousand kVA (Fig. 1). Taking into account atmospheric pollution and the need to maximize reliability and continuity of supply, it is apparently necessary to return to the installation of power circuit breakers on the high-voltage side. The main step-down substations are, as a rule, constructed with two transformers. The load on the substation buses is taken as not more than 120% of the capacity of one transformer. The number of main step-down substations at the plant will be 12–14.

Fig. 1. Schematic plan of the power supply of a metallurgical plant

The main step-down substations feed shop distribution, converter, and step-down substations. Distribution substations (DS) are of enclosed design, using complete switchgear. Most DS have two sections and two incoming feeders, each of which is rated for the full load or for 70% when consumers of the third category are present. For the most critical consumers, DS are made according to the so-called “one-and-a-half” scheme—three incoming feeders, three sections, with the middle one consisting of two half-sections. Each of the incoming feeders is rated for 70% of the maximum substation load. The total number of DS at the plant reaches 160–200.

At present, metallurgical plants have been built at which the following rated voltages are used: 3, 6, 10, 35, 110,

150, 220 kV. Experience has shown the need for careful selection of the voltage of the plant’s high-voltage network. The distribution of capacities shown in Table 1 from the MDS and the CHPP is possible only at 10 kV. The question of using 20 kV at the present time cannot be resolved favorably because of the absence of serially manufactured equipment. The use at the plant of a voltage of 10 kV for supplying power transformers and high-capacity motors, and of 3 kV for medium-capacity motors, creates great difficulties in operation and design. The choice of distribution voltage (10 and 3 kV, 10 and 6 kV, or only 6 kV) must be the result of a thorough techno-economic calculation.

From the standpoint of reliability and continuity of supply, the question of choosing the method of channeling electric power throughout the plant becomes very important. The radial scheme used for supplying the DS by power cables laid in cable blocks and cable tunnels becomes unreliable when the cable tunnels throughout the plant are 20–30 km long and the number of cables in a cross-section is 40–80 or more. It is necessary to return to consideration of the ring scheme widely used abroad, with the use of 10 kV mains for currents of 5000 A and more.

Table 3

From analysis of the data presented and the data of Table 3, it follows that for a metallurgical plant with a maximum electrical load of 1200 thousand kW the demand coefficient will be somewhat below the average for the plants. In our opinion, this coefficient has a tendency to decrease. The annual number of hours of utilization of the maximum should increase in connection with the improving regularity of the enterprise’s operation.

Conclusions

For a large metallurgical plant with a complete metallurgical cycle and an annual production capacity on the order of 10–12 million tons of steel, a maximum load of 1200 thousand kW is expected, with an annual number of hours of utilization of the maximum of 6900 hours and a demand coefficient of 0.3.