# Research and Development of the Combined Cycle Power Plants Working on Supercritical Carbon Dioxide

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

#### 1.1. Promising Methods to Increase the CCGT Plant Efficiency

#### 1.2. Replacing the Water Stream Circuit with Carbon Dioxide for CCGT Plants

_{2}power facilities resulted in the development of the five cycles presented in Figure 1. The simplest S-CO

_{2}cycle is a closed Brayton cycle with the heat utilization of the exhaust gases (Figure 1a). It contains a compressor (C), regenerator (RH), reactor (R), turbine (T), electricity generator (G), and pre-cooler (PC). The S-CO

_{2}Brayton cycle with reheating is shown in Figure 1b. Here, the turbine consists of a high-pressure turbine (HPT), and a low-pressure turbine (LPT). The S-CO

_{2}Brayton cycle with intermediate cooling is presented in Figure 1c. The introduction of intermediate cooling allows for an increase in the cycle efficiency due to a reduction in the compressor’s energy consumption. The S-CO

_{2}Brayton cycle with partial cooling is presented in Figure 1d. It differs from the simplest S-CO

_{2}Brayton cycle (Figure 1a) by application of a cooler (CR), pump (P), recompressing compressor (RC), high-temperature regenerator (HTR), and low-temperature regenerator (LTR). The use of partial cooling together with two sections of regenerators improves the regeneration system’s efficiency.

_{2}with recompression. Its net efficiency is 47.3% [20]. However, it should be noted that all the cycles under consideration are characterized by a high initial temperature of heat supply, which will certainly have a negative impact on the efficiency of the waste heat boiler. In this connection, additional measures are required to reduce the temperature of gases released into the atmosphere.

#### 1.3. Current State of Research on Carbon Dioxide Cycles

_{2}is expanded in the turbine and cooled in the regenerator. The cycle efficiency is 56% at the turbine inlet temperature of 1400 °C.

_{2}Brayton cycle with recompression and the basic option, allowing efficient utilization of low-potential heat.

#### 1.4. Approaches to Energy Cycle Optimisation

## 2. Materials and Methods

#### 2.1. Research Object

_{2}is sent to the high-temperature heat exchanger and, further on, to the high-temperature superheater 1.

_{2}is sent to the T3 carbon dioxide turbine, where the expanding working flow performs useful work. After that, the carbon dioxide gas is sent to the heat exchanger and, further on, to the precooler PC. The cooled carbon dioxide gas is sent to the C2 compressor for compression to the required pressure, after which the working flow is sent to the heat exchanger for utilization of the exhaust gas heat of the T3 carbon dioxide turbine [30].

#### 2.2. Modeling Method

#### 2.3. Validation of the Modelling

## 3. Results and Discussion

#### 3.1. Optimisation of the CO_{2} Brayton Cycle with Recompression

_{2}cycle, which can reach a maximum net efficiency of 25% [21].

#### 3.2. Optimisation of the Basic Version of the CO_{2} Brayton Cycle

## 4. Conclusions

- The thermal scheme and mathematical model for the gas turbine combined cycle working on CO
_{2}have been developed. The optimal values of the key thermodynamic parameters have been identified for the case of gas turbine unit GTE-160. It has been established, that at a temperature of 517 °C, the efficiency of the carbon dioxide Brayton cycle with recompression could be equal to 43.41% and achieve inlet and outlet turbine pressures of 24.0 and 8.5 MPa, respectively, and at the recompression percentage of 37.5%. - The maximum net power generation of 55.1 MW is achieved with a zero-recompression ratio with a net efficiency of 37.98% at a pressure of 30 MPa. This happens due to the fact that the temperature of carbon dioxide at the inlet to the waste heat boiler decreases, therefore, the heat supply to the highly efficient cycle increases.
- When optimizing the secondary circuit, it was found that during the operation of the main Brayton cycle, the highest efficiency of the combined cycle is observed at pressures at the inlet and outlet of the turbine equal to 32 MPa and 8 MPa, at which the efficiency reaches 19.6%.
- Based on the mathematical simulation, it was found that replacing the conventional steam power plant, which operates in combination with GTE-160 gas turbine plant and uses carbon dioxide Brayton cycles, with recompression and base version provides a 1.2% increase in the net efficiency of the combined power plant. Such an increase in efficiency can be explained by a high average integral temperature of the heat supply in the Brayton cycle, the carbon dioxide temperature upstream of HE1 being about 311 °C, whereas, in the conventional design, this value is about 100 °C (the temperature downstream of the atmospheric deaerator).

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**Supercritical CO

_{2}Brayton cycles: (

**a**) S-CO

_{2}Brayton cycle with regeneration; (

**b**) S-CO

_{2}Brayton cycle with reheating; (

**c**) S-CO

_{2}Brayton cycle with intermediate cooling; (

**d**) S-CO

_{2}Brayton cycle with partial cooling; (

**e**) S-CO

_{2}Brayton cycle with recompression. C—compressor, RH—regenerator, R—reactor, T—turbine, G—electricity generator, PC—pre-cooler, HTP—high-pressure turbine, LPT—low-pressure turbine, CR—cooler, P—pump, RC—recompressing compressor, HTR—high-temperature regenerator, LTR—low-temperature regenerator, MC—main compressor, and IC—intermediate cooler.

**Figure 5.**Dependence of the useful efficiency of the cycle on the power of the turbine and the power of auxiliary needs at the pressure at the change outlet of the carbon dioxide turbine in the cycle with the base set.

**Figure 10.**Investigation of the influence of pressure changes at the inlet to a carbon dioxide turbine. (

**a**) Net efficiency. (

**b**) Net power.

**Figure 11.**Dependence of the efficiency of the combined cycle on the pressure in the carbon dioxide turbine of the second cycle.

Parameter | Value |
---|---|

GT flue gas massflow, kg/s | 509 |

GT inlet temperature, °C | 1200 |

GT inlet pressure, MPa | 12 |

GT pressure ratio | 10.9 |

Heater the first cycle hot end temperature difference, °C | 20 |

Heater the second cycle hot end temperature difference, °C | 10 |

Regenerator temperature difference, °C | 10 |

Turbine outlet temperature (GTE-160), °C | 537 |

Exhaust gas mass flow (GTE-160), kg/s | 509 |

Electrical net efficiency (GTE-160), % | 34.4 |

The cycle minimal temperature, °C | 30 |

Cooler circulation water pressure, bar | 1.3 |

Turbine specific internal efficiency, % | 90 |

Compressor specific internal efficiency, % | 85 |

Mechanical efficiency, % | 99 |

Power generator efficiency, % | 99 |

Power motor efficiency, % | 99 |

Heat transportation efficiency, % | 99 |

Tmin, °C | Tmax, °C | Pmax, Bar | rcopt | Xopt | ηth, % [31] | ηth, % (This Work) | Delt |
---|---|---|---|---|---|---|---|

50 | 550 | 200 | 2.39 | 0.1837 | 36.71 | 36.93 | 0.599 |

50 | 550 | 300 | 2.8 | 0.254 | 38.93 | 39.021 | 0.234 |

32 | 550 | 200 | 2.64 | 0.3337 | 41.18 | 41.5 | 0.777 |

32 | 550 | 300 | 3.86 | 0.3549 | 43.32 | 43.17 | 0.346 |

Optimized Cycle | Initial Temperature, °C | Initial Pressure, MPa | Share of Recompression, % | Final Pressure, MPa | Net Efficiency, % |
---|---|---|---|---|---|

Recompression cycle | 517 | 30 | 0 | 8.5 | 37.91 |

Basic cycle version | 311 | 32 | - | 8.0 | 21.98 |

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**MDPI and ACS Style**

Rogalev, A.; Rogalev, N.; Kindra, V.; Komarov, I.; Zlyvko, O.
Research and Development of the Combined Cycle Power Plants Working on Supercritical Carbon Dioxide. *Inventions* **2022**, *7*, 76.
https://doi.org/10.3390/inventions7030076

**AMA Style**

Rogalev A, Rogalev N, Kindra V, Komarov I, Zlyvko O.
Research and Development of the Combined Cycle Power Plants Working on Supercritical Carbon Dioxide. *Inventions*. 2022; 7(3):76.
https://doi.org/10.3390/inventions7030076

**Chicago/Turabian Style**

Rogalev, Andrey, Nikolay Rogalev, Vladimir Kindra, Ivan Komarov, and Olga Zlyvko.
2022. "Research and Development of the Combined Cycle Power Plants Working on Supercritical Carbon Dioxide" *Inventions* 7, no. 3: 76.
https://doi.org/10.3390/inventions7030076