Triple-Cycle Power Generation with CO2 Separation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for reducing CO2 emissions in power generation, such as fuel de-carbonization and post-combustion capture, are costly and inefficient, and existing gas turbines cannot operate in oxyfuel cycles, leading to low thermal efficiency and high energy requirements for CO2 extraction and sequestration.
Innovation Solution
A triple-cycle power generation system integrating a gas turbine, exhaust gas recirculation, and CO2 separation, where stoichiometric combustion with recycled exhaust gas produces a CO2-rich stream for capture and a nitrogen-rich stream for expansion, generating additional power and reducing emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If stoichiometric combustion with exhaust gas recirculation is used, then CO2 concentration in the flue gas is increased, but the temperature of the discharge stream becomes too high for direct expansion
Solution Approach 1:
A heat exchanger is introduced as an intermediary component between the combustion chamber discharge and the expander inlet. The heat exchanger transfers thermal energy from the hot CO2-rich discharge stream to a recycle stream, cooling the discharge stream to a temperature suitable for expansion while preheating the recycle stream, thus resolving the temperature incompatibility without compromising CO2 concentration
Solution Approach 2:
The system changes the temperature parameter of the discharge stream through controlled heat exchange with the recycle stream. By adjusting the heat exchanger operation, the discharge stream temperature is modified from combustion temperatures (typically >1000°C) to expander-suitable temperatures, enabling the expansion process to proceed efficiently while maintaining high CO2 concentration
2Temperature
If conventional NGCC systems use excess air for combustion, then combustion is moderated, but excess oxygen is generated which is difficult to remove and reduces efficiency
Solution Approach 1:
The system discards the harmful excess oxygen by using stoichiometric or slightly fuel-rich combustion conditions that minimize oxygen in the flue gas. Simultaneously, it recovers the valuable CO2 by concentrating it through the exhaust gas recirculation approach, where the limited air intake (40% of total gas turbine intake) ensures that CO2 becomes the predominant remaining gas after combustion, eliminating the need for expensive oxygen removal equipment
Solution Approach 2:
The oxygen concentration parameter in the combustion air is fundamentally changed from the conventional 21% (ambient air) to a controlled stoichiometric ratio with recirculated exhaust gas. This parameter change transforms the combustion products from an oxygen-rich mixture to a CO2-rich mixture, solving both the temperature control and excess oxygen removal problems simultaneously
3Quantity of substance
If post-combustion CO2 extraction equipment is added to NGCC systems, then CO2 capture is achieved, but the equipment is large and expensive and requires multiple compression stages
Solution Approach 1:
The system performs preliminary concentration of CO2 during the combustion process itself by using exhaust gas recirculation. This preliminary action creates a CO2-rich flue gas stream directly at the combustion chamber outlet, eliminating the need for complex post-combustion separation equipment. The CO2 is concentrated before any extraction or separation steps would be required, simplifying the overall system architecture
Solution Approach 2:
The system extracts only the necessary amount of air (40% of total intake) for stoichiometric combustion, rather than using full ambient air. This selective extraction of air components ensures that the combustion products are naturally CO2-rich, and the recirculated exhaust gas further concentrates CO2, making subsequent CO2 extraction or utilization straightforward without requiring large, complex separation equipment
4Quantity of substance
If CO2 is extracted from low pressure flue gas, then CO2 capture is possible, but a fraction of produced power must be used for compression and extraction
Solution Approach 1:
The system performs preliminary pressurization of the CO2-rich stream by utilizing the high-pressure environment created during stoichiometric combustion with recirculated exhaust gas. The combustion chamber operates at elevated pressure, and the recirculation system maintains this pressure, so CO2 is concentrated and available at high pressure before any extraction or utilization step, eliminating or minimizing the need for additional compression power
Solution Approach 2:
The system merges the CO2 concentration function with the combustion process itself. By combining exhaust gas recirculation with stoichiometric combustion, the system achieves both temperature control and CO2 concentration in a single integrated process, rather than requiring separate compression and separation stages. This merging of functions eliminates the energy penalty associated with dedicated CO2 extraction equipment
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system achieves low emission, high efficiency power generation and CO2 capture, reducing the cost of CO2 production and enhancing oil recovery processes by utilizing the synergies between nitrogen and CO2 production, while minimizing oxygen byproducts and energy consumption.
Implementation Method 1
a combustion chamber configured to stoichiometrically combust a first compressed oxidant and a first fuel
Implementation Method 2
The discharge stream from the combustion chamber is expanded in an expander
Implementation Method 3
exhaust heat from the gas turbine Brayton cycle is captured to make steam and produce additional power in a Rankin cycle
Data Source
AI summary
Methods and systems for low emission power generation in combined cycle power plants are provided. One system includes a gas turbine system that stoichiometrically combusts a fuel and an oxidant in the presence of a compressed recycle stream to provide mechanical power and a gaseous exhaust. The compressed recycle stream acts as a diluent to moderate the temperature of the combustion process. A boost compressor can boost the pressure of the gaseous exhaust before being compressed into the compressed recycle stream. A purge stream is tapped off from the compressed recycle stream and directed to a C02 separator which discharges C02 and a nitrogen-rich gas which can be expanded in a gas expander to generate additional mechanical power.