Flue Gas Scrubber Segmentation for Below-Dew-Point Heat Recovery
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Solution Overview
Problem
The existing district heating plants face poor heat recovery efficiency due to the inability to cool flue gas below its dew point in the flue gas scrubber, leading to inefficient heat transfer and associated corrosion, pressure drop, and condensation issues with combustion air humidifiers.
Innovation Solution
A method involving a heat pump system that divides district heating water into portions, where one portion is cooled and passed through a heat exchanger to lower the scrubbing liquid temperature, allowing flue gas to be cooled further, and transferring heat from this portion to another portion using a heat pump, enhancing heat recovery efficiency and reducing operational costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If flue gas is cooled in a flue gas scrubber with scrubbing liquid, then heat is recovered into the scrubbing liquid, but the flue gas cannot be cooled under its dew point leading to poor heat recovery efficiency
Solution Approach 1:
The system divides the fluid stream into two separate portions and processes them through different heat exchange paths. The first portion is cooled in a first heat exchanger, while the second portion is cooled in a second heat exchanger, allowing independent temperature control to achieve below-dew-point cooling without compromising heat recovery efficiency
Solution Approach 2:
The first portion of the fluid is cooled before being mixed with the second portion. This preliminary cooling action enables the combined fluid to absorb more heat from the flue gas, allowing the flue gas to be cooled below its dew point while maintaining high heat recovery efficiency
2Loss of energy
If a combustion air humidifier is used to increase moisture content of flue gas, then heat recovery capacity is improved, but corrosion problems occur in the heating boiler
Solution Approach 1:
The system converts the harmful effect of moisture condensation (which causes corrosion) into a beneficial heat recovery mechanism. By cooling the flue gas below its dew point in a controlled manner through the two-portion fluid system, water vapor condenses and releases latent heat that is captured in the scrubbing liquid, improving heat recovery while avoiding corrosion in the heating boiler
Solution Approach 2:
The scrubbing liquid acts as an intermediary medium that facilitates heat transfer from the flue gas without introducing moisture into the heating boiler. The condensed water vapor is captured in the scrubbing liquid rather than being reintroduced to the combustion process, eliminating corrosion while maintaining heat recovery capacity
3Loss of energy
If a combustion air humidifier is used to cool flue gas further, then heat recovery efficiency improves, but pressure drop over the combustion air system increases
Solution Approach 1:
The system extracts the humidification function from the combustion air system. Instead of adding moisture to the combustion air through a humidifier (which causes pressure drop), the moisture is introduced directly into the flue gas stream in the scrubber, achieving the same heat recovery effect without affecting combustion air pressure
4Temperature
If a combustion air humidifier is used to increase moisture content, then flue gas cooling is improved, but condensation problems occur in the combustion air system
Solution Approach 1:
The system converts the potential harm of condensation in the combustion air system into a beneficial process by moving the condensation to occur in the flue gas stream. Water vapor condenses in the flue gas within the scrubber where it is captured by the scrubbing liquid, rather than condensing in the combustion air system where it would cause problems
Solution Approach 2:
The scrubbing liquid serves as an intermediary that captures condensed water vapor directly from the flue gas. This prevents condensed water from entering the combustion air system and causing condensation problems, while still achieving the desired flue gas cooling effect
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 allows for improved heat recovery efficiency by enabling flue gas to be cooled to a lower temperature, increasing condensation heat recovery and reducing operational costs through high COP values and lower heat pump capacity requirements.
Implementation Method 1
transferring heat from the first portion of the fluid into the second portion of the fluid with a heat pump
Implementation Method 2
The flue gas is cooled by spraying scrubbing water over the packing bed 107, as a result of which heat is released from the flue gas and recovered into the scrubbing water
Implementation Method 3
the water vapour contained in the flue gas condenses and the released condensing heat may be utilised
Data Source
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AI summary
A method and an arrangement are provided for transferring heat from flue gas into fluid. The flue gas is passed through a flue gas scrubber (205, 305) in which the flue gas is cooled with scrubbing liquid. The scrubbing liquid is circulated from the flue gas scrubber (205, 305) into a heat exchanger (210, 310) and back to the flue gas scrubber (205, 305). A first portion of the fluid is passed through the heat exchanger (210, 310) whereby heat from the scrubbing liquid is transferred into the first portion of the fluid. Before the first portion of the fluid is passed through the heat exchanger (210, 310), heat from the first portion of the fluid is transferred into a second portion of the fluid.