Oxy-Fuel Boiler Recirculation Using CO2 Refrigeration at Low Load
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The oxy-fuel process in combustion plants is inefficient in terms of energy consumption and component utilization, with oversized apparatuses and high energy demands for air separation and CO2 capture, necessitating a method to enhance flexibility and reduce overall energy consumption.
Innovation Solution
Implementing a load-dependent heat transfer system that recirculates a carbon dioxide-rich stream from the CO2 compression unit to the air separation unit, utilizing the recirculated stream as a refrigerant to transfer heat energy and reduce external energy input, controlled by a regulating device to optimize energy allocation based on boiler system load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an air separation unit is used to provide oxygen gas for oxy-fuel combustion, then oxygen supply is achieved, but a large amount of energy is required for refrigeration and compression
Solution Approach 1:
The patent combines the air separation unit with the CO2 compression unit, allowing them to share common infrastructure including refrigeration systems, compressors, and control mechanisms. This integration enables the ASU to operate more efficiently by utilizing the CO2 compression infrastructure, thereby reducing overall energy consumption while maintaining reliable oxygen supply for oxy-fuel combustion
Solution Approach 2:
The integrated system performs multiple functions: the air separation unit provides oxygen for combustion while simultaneously producing a nitrogen-lean gas stream that is fed to the CO2 compression unit. The refrigeration system serves both the air separation process and the CO2 compression cooling requirements, reducing duplicate energy expenditure and improving overall system efficiency
2Reliability
If CO2 capture involves cooling and compression of flue gas, then CO2 separation is achieved, but energy consumption increases
Solution Approach 1:
The system performs preliminary cooling of the flue gas in the air separation unit's refrigeration system before the gas enters the CO2 compression unit. This pre-cooling reduces the energy burden on the CO2 compression unit, as the gas enters already at a lower temperature, requiring less additional cooling and compression energy to achieve the desired CO2 separation and liquidification
Solution Approach 2:
The nitrogen-lean gas stream acts as an intermediary medium, carrying the flue gas through the air separation unit where initial cooling and partial separation occur. This intermediary process prepares the gas for more efficient final CO2 separation in the compression unit, reducing the overall energy requirement by distributing the separation work across two stages
3Productivity
If components are designed for full boiler capacity, then maximum output is achieved, but components are oversized during low load operation
Solution Approach 1:
The patent implements dynamic operation of the air separation unit and CO2 compression unit, allowing their capacity to be adjusted according to the boiler's actual load. During low load periods, these units operate at reduced capacity rather than at fixed maximum capacity, thereby avoiding the energy waste associated with oversized component operation while still maintaining the capability to handle maximum boiler output when required
4Reliability
If CO2 compression unit operates during low load, then CO2 capture continues, but surge conditions may damage equipment
Solution Approach 1:
The air separation unit serves as an intermediary stage that conditions the flue gas before it enters the CO2 compression unit. By performing preliminary cooling and separation in the ASU, the system ensures that the gas entering the compression unit is at optimal temperature and composition, preventing surge conditions that could damage the compression unit while maintaining continuous CO2 capture operation during low load periods
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 approach decreases overall energy consumption and operational costs by effectively utilizing heat energy within the process, particularly during low load periods, and prevents equipment damage from surge conditions.
Implementation Method 1
the recirculated carbon dioxide rich stream is passed through an air separation unit where it is acting as a refrigerant by transferring heat energy from streams within the air separation unit to the carbon dioxide rich stream which then is evaporated
Data Source
Figure 1
Figure 2
AI summary
The present disclosure relates to a method of operating a boiler system (27) comprising an oxy-fuel boiler (7) in which an oxygen stream (6) and a fuel stream (2) are combusted to generate a flue gas stream (8), an air separation unit (4) producing the oxygen stream (6) for the oxy-fuel boiler (7), and a gas processing unit (25) for cleaning and compressing at least a portion of the flue gas stream (6) generated in the oxy-fuel boiler (7) producing a pressurized carbon dioxide stream (18), the method comprising: operating the boiler system (27), at least for a period of time, in a recirculation mode, during which a carbon dioxide stream (20) from a CO2 compression unit (17) within the gas processing unit (25) is evaporated in the air separation unit (4) and forwarded as a stream (24) to the gas processing unit (25). The present disclosure further relates to a boiler system for an oxy-fuel process as well as to a power plant comprising such a system. The present disclosure also relates to the use of a carbon dioxide containing stream as a refrigerant.