IMPROVING THE EFFICIENCY OF INDUSTRIAL POWER PLANTS THROUGH THE USE OF ADIABATIC VAPORIZATION

S. V. Polozhii

(Presented by Prof. I. N. Butakov, Doctor of Technical Sciences)

Improving the operating efficiency of industrial power plants is of great importance for the national economy, owing to the low thermal efficiency and the large absolute fuel consumption of industrial power plants. Table 1, by way of illustration, presents the structure of the industrial power plants of ferrous-metallurgy works.

Table 1

As can be seen from the table, more than 80% of the electric power at the industrial power plants of ferrous-metallurgy works was generated at low and medium pressures. More than half of the power plants were equipped with turbines of up to 6 thousand kW. The remaining power plants had unit capacities of 10–25 thousand kW. In the chemical, machine-building, food, and other branches of industry, power plants have still lower performance indicators than in the metallurgical industry. The share of power plants with capacities up to 5 thousand kW amounted, for example, in 1958, to 20% of the total installed capacity. These power plants produced about 10% of all electric power in the country, with costs ten or more times higher than at large regional power plants. The average capacity of district thermal power plants in 1958 was 25–35 thousand kW, while that of industrial thermal power plants was only 3–5 thousand kW. The capacity

the capacity of back-pressure turbines did not exceed 5% of the total capacity of heat-and-power turbines. The structure of electricity production and the actual state of district heating in the recent past are presented in Table 2. The total generation of electricity at CHP plants by the uneconomical condensing cycle exceeded 65% of all electricity produced at CHP plants during that period, while more than 35% of all heat supplied from CHP plants was simultaneously supplied in live steam. This means that

Table 2

about 60% of CHP plants operated as the worst condensing stations of small capacity, with low parameters, uneconomical turbines, and under off-design conditions. More than 30% of CHP plants operated as central boiler houses with expensive and complex power boilers and with a complex system of district-heating equipment. At a number of CHP plants, the supply of heat from boilers in live steam exceeded 80%. The effect of district heating in 1958 was expressed in a total fuel saving of 16.5 million tons of standard fuel. Of this, only 4.1 million tons of fuel was saved through electricity production by the district-heating cycle [2]. Seventy-five percent of the fuel saving was obtained through the centralization of heat supply and the supply of steam from CHP boilers, owing to the displacement of less economical industrial and building boiler houses.

Table 3

The structure of electricity production and fuel consumption at industrial CHP plants can be judged from the data in Table 3. The average specific fuel consumption at industrial CHP plants exceeded by 33% the average fuel consumption at state district power stations of the Ministry of Electric Power Stations, while the specific fuel consumption at industrial CHP plants when operating by the condensing cycle was almost

was twice as high as the fuel consumption at state district power plants. Industrial condensing power plants operated even less economically. The operation of all types of thermal power plants in 1962 was also characterized by a low share of electricity generation on the basis of external heat consumption: 42% of the total electricity output of thermal power plants, while at public power stations only 33% of the electricity produced by all public thermal power plants was generated by the district-heating cycle [3]. The share of combined production based on external heat consumption is increasing slowly. For example, in 1958 it amounted to 10.5%, and in 1962 to 12.5%—an annual increase of 5%. More than 65% of public thermal power plants in 1962 operated as condensing stations, less economically than state district power plants with the same steam parameters. At present, and in the prospective construction of modern thermal power plants, operation of condensing power plants, district boiler houses, and thermal power plants on solid fuel may be justified when the capacity of the thermal power plant is 50 thousand kW or more. When condensing power plants, district boiler houses, and thermal power plants operate on gas, district heating on the basis of the modern steam-power cycle may be justified only when the capacity of the thermal power plant is 100 MW or more [3]. This is the reason for the development in our country of centralized heat supply from district boiler houses. In 1970 it is planned to supply about 20% of heat to consumers from central boiler houses. Modern steam-power installations of small capacity are a heavy burden on the national economy. A considerable portion of funds is spent on the construction of modern small-capacity thermal power stations with isobaric steam generation. Such power installations are built not only in regions remote from power systems, but also in regions within the sphere of action of power systems. Over the decade 1951–1961 the number of small and medium isolated power stations increased threefold, from 57,000 in 1950 to 171,000 in 1961. In 1961 all these power stations generated 12% of the total quantity of electricity in the country. The annual relative loss to the national economy from the operation of small power stations, in comparison with the operation of state district power plants, is estimated at 1.5–2.0 billion rubles. In addition, up to 3 million tons of standard fuel are overconsumed per year. The cost of producing electricity at these stations was tens of times higher than for large state district power plants, and the specific capital investment was 4–5 times higher than for large state district power plants.

From this brief review of the development of industrial condensing power plants and thermal power plants and other types of small-capacity steam-power installations, it becomes clear how urgent is the task of increasing the efficiency of this group of steam-power installations. It is also obvious that the technical level of development of this group of steam-power installations does not correspond to the contemporary achievements in the development of productive forces, science, and technology. Such installations have no prospects for further improvement in thermal economy. The prolonged existence of this type of steam-power installation is now leading to an enormous overconsumption of fuel, metal, and other material resources; it is an archaism without which, it turns out, it is impossible to manage even in the long term. This is the essence of the crisis in the development of the modern steam-power cycle in this branch of heat-power engineering. This state of development of steam-power installations is determined by the existing method of steam generation, by the physical and thermodynamic properties of steam and of the cycles of such installations, under which a substantial increase in the thermal efficiency and unit capacity is impossible without increasing the initial steam pressure to superhigh values, and also by the contradictions that arise between the thermodynamic efficiency of the cycle and the efficiency of using the working fluid in the steam ...

turbine and, finally, by techno-economic contradictions in attaining an expedient level of utilization of fuel energy. Industrial condensing power stations and thermal power plants, having small capacity, do not permit the use of superhigh steam pressures and are forced, with modern steam generation, to operate at uneconomically low steam pressures and to retain the shortcomings of such steam parameters.

Table 4

Table 5

Note to Tables 4 and 5:
“net”—allowing for the energy consumption of the boiler circulating and feed pumps. The table data are without regenerative heating of the feedwater. The relative changes in the indices of installations with adiabatic steam generation were compared with an ordinary installation of the same pressure and superheat temperature of the steam. The feedwater pressure for all variants is 226 bar; the temperature is 374°C.

Accepted: the relative internal efficiency of the turbine stages is 0.72, of the steam turbines is 0.83; the mechanical efficiency and the generator efficiency are 0.96; the boiler efficiency is 0.90.

A successful solution to the problem of technical progress in industrial condensing power stations and combined heat-and-power plants is the conversion of such installations to adiabatic vaporization. Adiabatic vaporization, as is already known, makes it possible to preserve the favorable properties of low-pressure steam and to avoid the negative properties of superhigh pressure, to ensure high thermal efficiency of the cycle and the operation of steam in the turbine and of the entire installation of small capacity as a whole [4].

The design indices of steam-power installations with adiabatic vaporization at low and medium steam pressure are given in Tables 4 and 5. The data of Tables 4 and 5 were calculated without regenerative heating of the feedwater. The relative changes in the indices of installations with adiabatic vaporization were compared with a conventional installation of the same pressure and steam superheat temperature. The pressure of the heated water for all variants was 226 bar, the temperature—374°C. The relative internal efficiency of the turbines of the evaporator-generators was 0.72, of the steam turbine—0.83, the mechanical efficiency—0.96, of the generator—0.96, and the boiler efficiency—0.90. Table 6 gives the design indices of an isolated low-capacity condensing power station with adiabatic vaporization. The conversion of industrial thermal power plants to adiabatic vaporization, as these comparisons show, considerably increases thermal efficiency and reduces the specific consumption of fuel, steam, and water.

Table 6

As an illustration of the techno-economic advantages of the power equipment of low-capacity installations with adiabatic vaporization, Table 7 gives the main characteristics of water-

... of the generator boiler and a comparison of it with a boiler of the Biisk Boiler Plant of the DKV type. In accordance with the reduction in the specific consumption of fuel, cooling water, and steam, there is a reduction in the consumption of metal and in the cost of the elements of TPP equipment associated with the consumption of fuel—

Table 7

—fuel, air, combustion products, the condensing installation and water supply, the system of regenerative feedwater heating, and also reduces the specific metal consumption and cost of steam turbines with an evaporator-generator.

LITERATURE

1. V. N. Yureev. Improving the Economy of Industrial Power Plants. Teploenergetika, No. 4, 1958. Industrial Power Plants. GEI, Moscow, 1963.

2. L. A. Melent’ev. The direction of development and the tasks of improving the economy of district heating. Elektricheskie stantsii, No. 5, 1959.

3. E. Ya. Sokolov. Efficiency and appropriate areas of use of district heating, centralized heat supply, and electric methods of heating. Teploenergetika, No. 5, 1964.

4. S. V. Polozhii. Izv. vuzov SSSR—Energetika, No. 1, 1965.