The socioeconomic development of any country is directly associated with an increase in power consumption. The traditional power industry development worldwide and in Russia is based on the use of fossil fuels. Nowadays, the main fuels used are coal, oil, and natural gas. It is worth mentioning that the tendency of hydrocarbon fuel consumption increase is constant (Figure 1a) [1,2], which leads to their exhaustion, environment pollution, and irreversible climate changes. Prospectively, it is a problem that slows down economic growth and threatens mankind’s stable development. Figure 1b shows that more than 40% of electricity production comes from coal fuels and less than 10% is based on nuclear fuels. Steam turbine units are widely used for both nuclear and thermal power plants: they produce about 50% of the world electricity. This emphasizes the high actuality of the problem of increasing the efficiency of steam turbine power plants. Therefore, the problem of increasing the efficiency of coal-fired power plants is a topical one, especially considering the widespread of steam turbine units.

The considered equipment has reached its utmost perfection, so the cycle efficiency may be considerably improved only by an increase in the thermodynamic cycle’s initial parameters. Natural-gas-fired power plants have passed to combined cycles that allow heat supply temperatures of up to 1200–1500 °C and, thus, reach a thermal efficiency of over 60% [3,4,5,6]. Yet, there is no solution for the problem of thermodynamic efficiency enhancement by an increase in initial parameters in coal-fired and nuclear power plants. Nowadays, the most advanced steam turbine coal-fired facilities have reached a thermal efficiency level of 42–43% [7,8]. It is worth mentioning that the total installed power of coal-fired steam turbine facilities every year demonstrates a stable increase (Figure 2) [9,10]. This may be explained by the use of large resources of hard fuels in many countries and the coal price staying constant for many years. Thus, the power industry has a goal to increase the efficiency of coal-fired power plants, which will save fossil fuel resources and reduce the contribution of more expensive fuels, natural gas, and oil products. In addition, it allows environmental harm reduction by the mitigation of toxic NO_x and SO_x and greenhouse CO₂ emissions. Therefore, it is important to find promising ways to improve steam turbine power units.

The next step is the transition from the currently widespread supercritical (SC) initial parameters of 24 MPa and 540 °C to the ultra-supercritical (USC) ones of around 30 MPa and 600 °C. The main drawback of the transition to USC steam parameters is a remarkable increase in the expensive structure materials’ contribution to the total metal expenses. These materials are used for the boiler super-heater, direct and intermediate steam pipelines, and the turbine high-temperature compartments.

Figure 3 shows the changes in applicable structure materials that follow the transition from SC to USC parameters. Heat-resistant alloys with high nickel contents predominate [11] over the martensite steels that have better thermo-physical performance and are used in SC conditions.

Figure 4 shows the heat-resistant materials’ distribution over the steam turbine facility elements in a USC facility. The main elements that need a transition from the traditional materials to the new heat-resistant and heat-proof ones are the steam superheating surfaces, especially the superheater exit panels, boiler steam collectors, high-temperature live and superheated steam pipelines, check and control valve blocks, turbine internal housings, first stages, and rotors. Therefore, an increase in the initial parameters of steam turbine power units requires a whole range of new alloys and equipment production technologies.

Works on thermal efficiency improvement in the coal-fired power plants are actively being undertaken in many countries [12,13,14,15]. World leaders have already put into operation steam facilities with ultra-supercritical steam parameters of p₀ = 32 MPa initial pressure and t₀ = 600–620 °C initial temperature [16,17]. These facilities with an efficiency level of 43% are being introduced in large scales in European Union countries, Japan, the USA, and China [18]. The next step in the efficiency improvement needs a transition to a higher level of the initial steam parameters, USC with p₀ = 34–36 MPa initial pressure and t₀ = 700–760 °C initial temperature. The same leading countries of the EU, Japan, USA, and China actively developed this direction of USC power facilities’ improvement [19,20,21]. The main equipment manufacturers, power production, and research companies have taken part in these programs. The new operation conditions require the development of new materials. In addition to this, the financial factor slows down the introduction of high-temperature power plants, which is due to an increase in the contribution of expensive heat-resistant materials to the metal consumption expenses. The ratio of traditional turbine materials’ cost to that of the heat-resistant steels and alloys cost is 1/5 regarding SC and 1/43 regarding USC. The increase in heat-resistant materials’ contribution is a source of increase in power facilities’ price that results in problems regarding the improvement in financial efficiency despite the remarkable thermal efficiency increase and better environmental performance. The straight steam parameters’ increase from 540 to 720 °C in temperature, together with the pressure rise from 23.5 to 35 MPa, increases the power facility’s price to 20–25% [22]. Figure 5 shows the price increase in the main and auxiliary equipment that follows the SC to USC transition. The main steam pipeline price grows more than three times, the turbine and auxiliary equipment are 30% and 10% more expensive, respectively, and the boiler price is more than two times higher. Therefore, the current methods for increasing the coal-fired power plants’ efficiency require a significant increase in the unit price and may not be economically viable in regions with lower fuel prices.

Thus, one of the key directions of high-temperature power facility improvement and provision of their competitiveness is the reduction in heat-resistant steels’ and materials’ consumption for main equipment manufacturing.

2. Competitiveness Improvement of High-Temperature Steam Turbine Power Plants

5. Conclusions