Prospects for the development of modern GTP and an alternative way of their development

Summary

ACTUALITY. Energy security is one of the main directions of society’s development, it is the most effective use of the potential of natural energy resources for stable economic growth, improvement of the population life quality and strengthening the country’s foreign economic and political positions. Thermal power plants (ТPP) in Russia consume 39,5 % of the gas used for domestic needs of the country, while generating approximately 67 % of electricity and 47 % of thermal energy. This means that in the next 15 years, thermal power stations will remain the main ones in the Russian electric power industry, and their energy weight in the total rated capacity will not change significantly.

PURPOSE. The search for alternative energy conversion schemes and their comparison with modern gas turbine plants (GTP).

METHODS. The tasks of calculating the parameters of the working process of power plants for an ideal and real approximation were studied based on thermodynamic analysis. When calculating the ideal plants, losses were not taken into account in order to identify their maximum degree of efficiency. Losses in the major units are taken into account in order to show the state-of-the-art technology and evaluate a possible transition to another energy conversion structural design.

RESULTS. The results showed that modern gas turbine plants (GTP) have approached to their maximum, and further energy efficiency improvement is associated with the transition to new energy conversion structural design.

CONCLUSION. As the analysis has shown, the modified Heron turbine (MHT) is the optimal structural design for converting thermal energy from gas combustion into mechanical rotational energy.

Introduction

At the present time the most common power plants in the energy sector are thermal power plants, where thermal energy released during the combustion of hydrocarbon fuels is converted into energy using gas turbine plants with an efficiency factor of 26-45% and steam turbines with an efficiency factor of 20-40%. They account for about 60% of the electricity generated on Earth and 66.8% [1] of the electricity produced in Russia [2], but due to the fact that their efficiency remains at a level up to 45%, it turns out that most of the energy resources are wasted, which, in turn, is associated with imperfections of the design of energy conversion plants [3, 4]. In this connection, one of the key priorities of Russia’s energy strategy for the period up to 2030 is the most efficient use of natural energy resources and the potential of the energy sector for sustainable economic growth, improving the quality of life of the country’s population and helping to strengthen its foreign economic position. The priority areas of development in the energy sector are as follows [5]:

– development of gas turbine plants with a capacity of 300-350 MW and on their basis — highly efficient condensing combined-cycle steam-gas plants with a capacity of 500-1000 MW, powered by natural gas and having an efficiency above 60%;

– development of standard modular cogeneration combined–cycle steam-gas plants with a capacity of 100 and 170 MW with an efficiency factor of 53-55 % at thermal power plants;

– development of environmentally friendly coal–fired condensing power units for super-supercritical steam parameters with an efficiency factor of 43 — 46 % and with a capacity of 660 — 800 MW;

– creation of environmentally friendly combined-cycle steam-gas plants with a capacity of 200-600 MW with gasification of solid fuels and with an efficiency factor of 50-52% and a combined–cycle steam-gas plant based on coal synthesis gas.

In connection with the above, the purpose of this study is to demonstrate a possible alternative design scheme with higher efficiency indicators compared to existing GTP design schemes, for which calculations and comparative analysis of the main characteristics of a single-shaft gas turbine plant and an alternative energy conversion scheme were carried out.

The scientific significance of the study consists in the fact that this study demonstrates a new approach to energy conversion [6], which opens up new aspects for research and experiments.

Literary review

Analysis of the scientific and technical literature shows that the interest in finding the most effective schemes for thermal energy conversion into mechanical energy still remains relevant. In this regard, the requirements for improving the efficiency of GTP are constantly increasing, but there is one related drawback. This is thermal energy conversion into mechanical energy, which is accompanied by large losses reaching 60-70% and more [7,8,9]. Such parameters of the GTP thermodynamic cycle as the gas temperature in front of the turbine and the degree of pressure increase in the compressor are the main ones to increase its efficiency. Many studies conducted by Russian [10,11,12,13] and foreign [14,15,16] scientists are related to the analysis of thermodynamic cycle parameters effect on the efficiency of GTP. But despite numerous scientific researches for improving the efficiency of GTP, their efficiency remains at the level of 26 – 45 % [17, 18], which indicates that the possibilities of their improvement are limited. In addition, this determines the need to search for new design schemes for converting thermal energy into mechanical energy, and then into electrical energy [19, 20, 21].

One of such possible design schemes is a modified Heron turbine (MHT) [22]. The peculiarity of this scheme is that jet engines located on the impeller, rather than rotor and stator equipped with working blades and nozzle devices, are used to convert thermal energy from gas combustion into mechanical rotational energy.

Such a design scheme is not new and has already been tested on the example of a hydro-steam turbine (HST) [23, 24], where it has demonstrated its efficiency, reliability and simplicity. But despite all its advantages, the HST has some disadvantages, and the main problem is the low efficiency of the nozzle and the sliding of the liquid phase at its outlet, as well as a high dependence on the capacitor.

Materials and methods

Two power plants, respectively shown in Fig. 1 and 2, were taken for comparison. Initially, it is necessary to describe the main advantages and disadvantages of GTP.

Fig.1. Schematic diagram of GTP: 1 — air supply to the compressor; 2 — compressor; 3 — compressed air supply to the combustion chamber; 4 — supply of combustible gas; 5 — combustion chamber; 6 — supply of combustion products to the turbine; 7 — turbine; 8 — exhaust gases withdrawal; 9 — generator;

Fig.2. Schematic diagram of MHT: 1 — air supply to the compressor; 2 — compressor; 3 -compressed air supply to the jet engine chamber; 4 — supply of combustible gas; 5 — combustion chambers of jet engines; 6 – working wheel; 7 — generator;

The main advantages of GTP [25, 26]:

• compact size and weight;

• various types of fuels, liquid and gaseous, can be used;

• environmental damage is minimized, emissions of harmful substances are within 25 ppm;

• mobility of plants and quick access to the operating mode compared to GTP.

The main disadvantages of GTP [25, 26]:

• the electrical efficiency is low 26-45%, since two thirds of the total output power is used to drive the compressor;

• high temperatures of internal processes impose serious restrictions on the operating conditions of the plant;

• turbine blades require special cooling methods due to high operating temperatures of 1100 — 1260 °C and high pressure at the turbine inlet.

The low efficiency factor of the GTP is due to a lot of local losses in the main units, such as the axial compressor, combustion chamber (CS) and turbine.

Losses in the compressor and turbine of the GTP [27]

The two main groups of losses in the blade mechanism are the losses in the inter-blade channels and terminal losses, consisting of many other types of losses that are widely represented in modern literature. The efficiency of the blade mechanisms is 83-92%, which indicates a high degree of their effectiveness [28, 29, 30].

Losses in the combustion chamber

The ideal combustion process differs from the real one, since it does not take into account the losses consisting of hydraulic [31] and thermal [32] losses. Hydraulic losses can be divided into the following types of losses:

• losses due to the air leakage into the holes of the CC (combustion chamber) and the elements of the front device;

• losses in the diffuser;

• losses due to mixing of jets of the fuel mixture components;

• losses in the ring channels.

Heat losses are associated with the processes in the CC, which are accompanied by heat losses due to heat dispersion into the surrounding space and incomplete combustion of fuel. The total pressure loss in the CC is 1-3 %.[33]

Overview of the modified Heron turbine

This scheme is based on the Heron turbine [34], which was modified as follows [35]. The components, passing through the compressor, enter the impeller, where they flow through sealed channels into collectors, after which they are evenly distributed over the CC of jet engines, where they are mixing and entering into a chemical combustion reaction, forming a high-temperature gas jet directed tangentially to the outer diameter of the impeller. With this scheme, the thrust of jet engines creates torque on the plant shaft, and the flow rate of combustion products provides the required revolutions. This scheme allows for more efficient conversion of energy resulting from gas combustion compared to modern GTP schemes, which will be demonstrated below.

The MHT scheme (see Fig.2) differs from the GTP scheme (see Fig.1) in the absence of a turbine, which is replaced by an impeller with jet engines. For the purpose of comparative analysis of these plants, a number of assumptions were made: losses in the compressor are the same; the advantages and disadvantages of MHT are the same as for single-shaft GTP; specific impulse losses are zero.

Losses in jet engines

-thrust reduction coefficient

-coefficient of thermal resistance

 -the coefficient of excellence of processes in CC

-the coefficient of excellence of processes in the nozzle

-the coefficient of non-adiabatic processes

-the coefficient of non-calculation of the nozzle

As a result, the total thrust losses in the liquid rocket engines are from 3 to 17 %, taking into account the above values of the individual components.[36]

All of the above losses were taken into account in the calculations of GTP and MHT.

Standard method of single-shaft GTP calculation was used to calculate the characteristics. The temperature in front of the turbine, the stoichiometric coefficient, the heat capacity of the combustion products, the adiabatic index of the combustion products were taken as the input data, and a number of values for the parameter «degree of pressure increase in the compressor» were selected to obtain a wider range of data. The essence of the method is to determine the ratio of useful work to the supplied heat.

To determine the air and gas flow characteristics, the value of the electrical power of the plant was assumed to be 32 MW. The total power of the plant corresponds to the ratio of the electrical power to the efficiency factor, which clearly reflects the difference between the results of calculations carried out with and without losses.

The input data for calculations are shown in Table 1. Calculations of the GTP and MHT parameters were carried out for two options. The first option is idealized plants, that have no losses and the efficiency of the components corresponds to one (Tables 2, 3). This calculation was carried out in order to show the physical limits of modern GTP and MHT.

The second option is real plans, in which ones we take into account the presence of losses and the real efficiency of the components (Tables 4, 5). The results of these calculations allow us to demonstrate a possibility of increasing the generated power by changing the energy conversion scheme.

Results

Calculations using this method were carried out in the Excel program with rounding the value to the third and fourth digits.

Discussion

The difference Пc in the input data is due to the fact that in real conditions at high values of Пc , the ratio of useful work and supplied heat will tend to zero, which is clearly shown in Tables 2, 4.

Analysis of the design parameters of the gas turbine plant has demonstrated the presence of the efficiency extremum depending on the degree of pressure increase in the compressor. The maximum efficiency values for the ideal approximation (see Table 2) and for the calculation with the losses taken into account (see Table 4) correspond to Пc = 100 and Пc = 40. There is no maximum efficiency value depending on the pressure in the CC in the design values of the MHT parameters, at the same time there is a continuous increase in the examined range.

The changes in the calculated values of the stoichiometric coefficient at the beginning and at the end of Tables 2.4 are caused by an idealized approach to GTP calculations based on the set values of the heat capacity of combustion products and the lowest heat of combustion of natural gas.

According to the data [37] and to the presented calculation results (see Table 4), the efficiency of the most efficient modern turbines is close to or already within the range of gas turbine plants operating without losses (see Table 2), which shows the high level of design and technological solutions used in the design and development of these plants. This makes it clear that these designs have reached their limit and a further increase in the efficiency of plants will require more complex solutions and greater material costs that are not comparable with the value of the increase in efficiency. For example, one of the most efficient turbines in the world, 9HA-01, whose declared efficiency is 42.9% in a simple cycle [38], was first launched in 2015. In 10 years, only one modification of this turbine was developed — 9HA-02, declared efficiency of this modified turbine is 44%, which is the highest value among companies involved in turbines design and development. A further increase in the efficiency of gas turbine plants is associated with plants operating in a combined cycle [39, 40, 41], which increases the efficiency to 54-64%, depending on the power of the gas turbine plant. From this we can conclude that for further development of energy efficiency it is necessary to change the method of converting primary energy into mechanical energy.

According to the data obtained (see Table 5), the efficiency factor of the modified Heron turbine tends to 65%, which is comparable to the value for plants operating in a combined cycle [42, 43]. This allows us to declare its high prospects.

Also, when calculating the MHT characteristics (see tables 3, 5), an assumption was made for more correct comparison of the MHT and GTP, for this purpose the data obtained in the calculations of the GTP were used (see tables 2, 4). It should be noted that the characteristics adopted for MHT calculations, such as pressure in the chamber, the stoichiometric coefficient, which affect the temperature in the combustion chamber, have different values in the rocket engines, and since there is no turbine in the MHT scheme, this removes some of the temperature limitations, which the gas turbine has, and which can further increase the efficiency of the modified Heron turbine.

Conclusions

It was demonstrated based on the calculations that it is possible to have an alternative energy conversion scheme different from modern gas turbine plants and having higher efficiency indicators and prospects. This study did not take into account the influence of the exhaust device on the efficiency of the alternative scheme, since losses in the exhaust device can be caused by various factors such as the geometric features of the nozzle, the number of jet engines, the shape of the exhaust device, as well as parameters of the operating environment, which requires separate examination and analysis.

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Authors of the publication

Danil A. Lyukshin – Kazan, Russia. https://orcid.org/0009-0008-8297-4453. E-mail: danil-la84@mail.ru.

Denis A. Lyukshin – Kazan, Russia. https://orcid.org/0009-0001-0378-7916. E-mail: luksindenis@gmail.com.