Proceedings of the Tomsk Polytechnic Institute Named after S. M. Kirov, Holder of the Order of the October Revolution and the Order of the Red Banner of Labor

Volume 226　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1976

Improving the Efficiency of Thermal Power Plants by Steam-Turbine Units with Maximum Regeneration and Adiabatic Phase Formation in the Turbine Inlet Section

S. V. Polozhii

(Presented by the scientific seminar of the Department of TPP)

Technical progress in world and domestic power engineering over the past 15–20 years has been determined by the modern steam-power cycle, owing to the transition of thermal power engineering to superhigh and supercritical steam parameters, the use of complex regenerative heating of feedwater, steam reheating, with the broadest progress in the production of the main and auxiliary equipment of unit-type thermal power plants, and exceptionally high concentration and centralization of electric-power production in unit installations of enormous capacity. As a result, there has been a sharp improvement in the technical-and-economic indices of electricity production at thermal power plants—reduction in the specific fuel consumption, in the initial and current capital investments for the construction and operation of thermal power plants, and in the cost of producing electric power.

Within the framework of the existing steam-power cycle, the present direction in the development of thermal power engineering and the technical policy in this field are, unquestionably, correct and have been proven by the entire course of development of world and domestic power engineering over the past two decades. The low technical level of development of thermal power engineering in the preceding period especially clearly emphasizes the high technical-and-economic indices of powerful unit-type thermal power plants with superhigh and supercritical steam parameters. This latter circumstance is one of the reasons for satisfaction with this path of development of thermal power engineering, for an uncritical attitude toward the shortcomings of the modern steam-power cycle. This also largely explains the underestimation, by supporters of the modern steam-power cycle, of the work of the Tomsk Polytechnic Institute on steam-turbine installations with adiabatic phase formation, as well as the construction of unit-type thermal power plants in the initial period of world power engineering for practically unsuitable initial steam temperatures and pressures of 300–350 atm and 600–650°C. As a result, after 6–8 years of mastering and operating such high-temperature units at 600–650°C in the early 1960s, the U.S. power industry completely abandoned them and was forced to switch to the construction of units at a low temperature of about 538°C. The same occurred in the power industry of the FRG, and later the initial steam temperature also had to be lowered in the power industry of the USSR.

The Seventh World Energy Conference (Moscow, 1968) in fact summed up the discouraging results of the current state of powerful superhigh- and supercritical-pressure steam unit installations, gave an objective assessment of the modern steam-power cycle and of its limited possibilities for ensuring a further increase in the thermal efficiency of thermal power plants [1—4]. The work of the World Energy Conference in this respect must be regarded as positive for thermal power plants with adiabatic phase formation, as the most effective method of producing electric power [5—9]. Enormous efforts and material expenditures were required to master in our country units with a lower initial steam temperature than previously in U.S. units, 565°C, in the preceding seven-year period. Still greater efforts and additional material expenditures were required for the development and operation of 300 MW units at a steam temperature of 560°C at supercritical pressure, introduced into operation at the end of the preceding seven-year period as the principal units of the ninth five-year plan. As a result of the impossibility of attaining the design performance indicators of such units over many years, in 1971 a decision was made to reduce the steam temperature in supercritical-pressure units of 300, 500, 800 MW and higher capacity to 540°C. This decision in fact signified the transition of domestic power engineering, as had earlier occurred in U.S. power engineering, to the low, realistically attainable steam temperature in powerful supercritical-pressure units. An even more vivid example of the inadequacy of the modern steam-power cycle is the stagnation in the reduction of specific fuel consumption over the last 5–6 years in a number of the world’s leading capitalist countries, above all in the United States. The saturation of U.S. power engineering with the most powerful and advanced units in the world did not lead to the expected reduction of specific fuel consumption in the country. Over the last five years the specific fuel consumption in U.S. power engineering not only did not decrease, but even increased somewhat—from 361 g/kWh in 1963 to 363 g/kWh in 1967. In England, over the last six years the substantial commissioning of unit capacity likewise did not ensure a reduction in the country’s specific fuel consumption, which has remained stable at the level of 440—445 g/kWh. It is especially noteworthy that abroad there has been a reassessment of the capabilities of modern units. Many power engineers of the world now regard new units as the final stage in the development of classical thermal power engineering before its replacement by nuclear power plants, and have also come to the conclusion that there are limiting possibilities—a “ceiling”—for modern units at the modest steam temperature of 555–540°C. Enormous material expenditures, and many years of varied activity in developing, mastering, and operating units with superhigh steam temperature, were required in order to become convinced of the erroneousness of such a path of development of thermal power engineering toward a very high steam temperature. Such a steam temperature of the modern steam-power cycle in powerful installations has proved to be 90–110°C lower than that which began to be mastered a decade and a half ago, and 150–200°C lower than that which power engineers in the past predicted for the present time—1970–1975. This is the regression of the modern steam-power cycle in large-scale power engineering, its inability to ensure further substantial progress in thermal power engineering, and the objective conditions for transferring it to adiabatic phase formation as a means of technical progress in thermal power engineering.

Now the erroneousness of the recommendations made as early as the beginning of the 1950s for transferring domestic power engineering to superhigh initial steam parameters of 580—650°C is especially evident. In this conne-

It is also worth recalling the unjustified optimism of the participants in the 1965 conference at ENIN in Moscow on steam-turbine plants with adiabatic steam formation, who asserted the broad prospects and possibilities for increasing the initial parameters and the thermal economy of domestic high-power units and, on this basis, denied the need to develop TTI work on steam-turbine plants, as well as the relevance of these studies. The basis for converting power engineering to unit installations, both abroad and in our country in the past, was the high thermodynamic efficiency—technically and economically unjustified, as subsequently became obvious—of the modern steam-power cycle with an ultra-high initial steam temperature, the calculated (theoretical) performance indicators of such units under base load on the assumption of high operating reliability and short commissioning periods. The introduction of such units was not preceded by a profound analysis of the real possibilities of achieving, and of the expediency of realizing, such calculated and design performance indicators for the units; nor by scientifically grounded forecasts or knowledge of the new problems and ways of solving them, both for the units themselves and for the power systems and the country’s power engineering as a whole.

To provide for this new stage in the development of power engineering in the highly developed countries of the world, enormous work was carried out, before which the scale and scientific achievements of the preceding period in the development of thermal power engineering pale. However, neither the high level of organization of scientific research, nor the unprecedented intensity and scale of this research, nor the great efforts of the operating personnel of thermal power stations and power systems, erection, commissioning, and other organizations and of the power industry, made it possible to overcome the shortcomings of the modern steam-power cycle and to realize the theoretical possibilities of such a cycle with an ultra-high steam temperature of 600–650°C and pressures of 300–350 atm, with which the new stage in the development of thermal power engineering began 15–20 years ago in the most developed countries of the world. The periods for attaining the design indicators of units with ultra-high temperature stretched out over many years, which had been anticipated and accepted in the designs. Units with a steam temperature above 570°C, however, proved to be economically unjustified, operationally unreliable, and technically unprepared. The commissioning and operation of such units were accompanied by a degree of operating unreliability and an accident rate unprecedented in the history of power engineering, by a small number of hours of utilization of installed capacity, by the underproduction of an enormous amount of electric power, required large annual additional capital investments, and also by low thermal economy in the operation of such units for many years. The complete unsuitability and inexpediency of operating the units under variable conditions leads to a sharp deterioration in the economy of power systems, to the widespread use, in the variable portion of loads, of uneconomical thermal power stations and peaking installations. As a result of the action of these contradictory factors, in recent years there has been stagnation in the reduction of specific fuel consumption in the United States, England, and other developed countries, despite the annual introduction of large capacities of unit installations.

From these positions it is necessary to approach the evaluation of steam-turbine plants with adiabatic phase formation, as well as the fundamental reconsideration of the existing situation with the aim of carrying out the task of converting power engineering to adiabatic phase formation. The conversion of domestic power engineering to adiabatic phase formation is fully prepared by the present state of development of thermal power engineering and can be carried out on a broad front and at a rapid pace with...

with a significant reduction in material costs and with high efficiency in operation. The conversion of thermal power plants to adiabatic phase formation is based on well-mastered power equipment for moderate steam pressures (steam turbines of industrial thermal power plants, the medium-pressure cylinders and low-pressure cylinders of modern units, steam pipelines and superheaters of moderate pressure, auxiliary equipment), on the organization of production of inexpensive elements for such installations [5, 7, 9] (turbines with adiabatic phase formation, low-temperature boilers with a low-pressure superheater), with the cessation of production of straight-through expensive supercritical-pressure boilers, ultra-high-pressure steam-turbine cylinders, and other elements associated with ultra-high and critical steam parameters. Such a conversion of power engineering to adiabatic phase formation eliminates the shortcomings of the modern steam-power cycle in unit installations and industrial thermal power plants [5—9]. The degree of preparedness and justification for introducing APF units is at present incomparably higher than was the case for units with the traditional steam-power cycle when they were introduced in the USA, the FRG, the USSR, and other countries.

In steam-turbine installations with APF, all the basic properties of adiabatic phase formation are used: the production of a new phase, the kinetic energy of the flow, and the dispersity of the flow. This determines the distinctive character of the cycles and heat-flow diagrams, the technological process, and the elements of such power installations [5—9]. At the same time, in installations with APF of the initial modification, the fortunate feature is the use of modern power equipment in its simplest and cheapest part, while preserving the station-wide and auxiliary equipment, as well as the construction, layout, and other solutions of modern thermal power plants.

The APF turbine is a fundamentally new and progressive element of steam-turbine installations with adiabatic phase formation of the initial modification and, according to the final result of the APF process, may be implemented either as an evaporator-generator or as a condenser-generator (when the working medium is supplied somewhat above the critical state—230—250 ata, 380—385°C). In the latter case, saturated steam for the steam part of the cycle is obtained by condensation of the steam phase in the “CG” turbine. This type of APF turbine ensures higher thermal economy for such installations, reduces the final moisture content of the flow in the flow passage and the energy consumption of the boiler circulating pump in comparison with “EG” turbines. The APF turbine as a power unit has significant advantages over

Table 1

Comparison of design indicators for a modern boiler and an APF boiler

steam turbines, especially ahead of the superhigh-pressure and high-pressure cylinders, which it replaces in modern units.

The boilers of steam-turbine units with APF do not have the shortcomings of modern once-through boilers for supercritical parameters and drum boilers for subcritical steam pressures \[5, 8\].

For some comparison of the advantages of the boilers of APF units, Table 1 gives the design data for a modern boiler for supercritical pressure \[11\] of a 1200 MW unit and the boiler of an APF unit of 200 MW \[5\].

The thermal efficiency of a TPP with APF and its comparison with a K-300-240 unit of 300 MW are given in Table 2. The boiler of the APF unit of 200 MW has a metal consumption 15% lower than the boiler of a 1200 MW unit for supercritical steam parameters. The consumption of pearlitic steels is 6.8 times lower, and of austenitic steels 4.5 times lower, in the APF boiler than in the boiler of the 1200 MW unit.

Table 2

Comparison of design performance indicators of the K-300-240 and APF-300 units

The high operating reliability of APF units and their flexibility, low accident rate, and other positive characteristics of such units, predicted in the past on the basis of theoretical studies, are now being confirmed by the practice of bringing into service and operating modern units in world and domestic power engineering.

The low cost of power equipment and the high efficiency of TPPs with APF, along with the high operating performance of APF units, make it possible to recommend the introduction of adiabatic phase formation into the country’s power industry and, above all, for improving the efficiency of thermal power engineering in Siberia—for the construction of powerful, reliable, and inexpensive units using Siberian open-pit coals, for the mass production and transmission of electric power to the western regions of the country.

REFERENCES

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3. V. G. Zhilin, A. M. Nekrasov, A. S. Pavlenko. The power industry of the USSR and the nearest prospects for its development. Elektricheskie stantsii, No. 8, 1968.

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7. S. V. Polozhii. On the kinetics of the process of steam condensation in a turbine stage. Izv. TPI, vol. 137, 1965.

8. V. S. Patychenko, S. I. Mochan, M. Z. Gudkin, B. M. Shleifer, L. M. Khristich, V. I. Sheptun, S. I. Zaraiskii. Development of a boiler unit for a 1200 MW unit. Energomashinostroenie, No. 7, 1968.