External Combustion Air Preheating With Heat Transfer Fluid
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Solution Overview
Problem
Existing methods for preheating air in large furnaces, such as steam cracking furnaces, require significant structural alterations and increase fuel consumption, leading to high CO2 emissions and inefficiencies, making them impractical for retrofitting existing installations.
Innovation Solution
A furnace system utilizing a heat transfer fluid to indirectly heat combustion air within the convective heating section, allowing heat extraction from multiple sections of the furnace, with flexible placement and minimal structural changes, and incorporating a heat transfer fluid circulation system to preheat air and regulate flue gas temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If combustion air is preheated by indirect heat exchange with flue gas in the convection section, then radiant efficiency is increased and CO2 emissions are reduced, but the temperature of heat transfer surfaces may fall below the acid dew point causing condensation and corrosion
Solution Approach 1:
The patent introduces a heat transfer fluid as an intermediary medium between the flue gas and the combustion air. The heat transfer fluid is heated by flue gas in the convection section and then circulates to an external air preheater where it heats the combustion air. This intermediary approach allows heat recovery without exposing the combustion air path to corrosive flue gas, and the heat transfer surfaces remain above the acid dew point due to the controlled temperature of the heat transfer fluid.
2Use of energy by moving object
If a heat transfer fluid circulation system is implemented for air preheating, then fuel consumption is reduced by 5-30%, but the device complexity increases
Solution Approach 1:
The heat transfer fluid circulation system serves multiple functions: it recovers heat from flue gas in the convection section, preheats combustion air in an external air preheater, and can be integrated with existing furnace systems. The same heat transfer fluid loop performs both heat extraction from flue gas and heat transfer to combustion air, reducing the need for separate systems and minimizing overall complexity despite the circulation requirements.
3Object-generated harmful factors
If existing furnace installations are retrofitted with air preheating systems, then CO2 emissions are reduced by 8-20%, but significant structural alterations are required
Solution Approach 1:
The patent extracts the air preheating function from the internal convection section and places it in an external air preheater. The heat transfer fluid circulation system connects the external air preheater to the furnace convection section, allowing the preheating function to be added without modifying the internal structure of the furnace. This extraction approach enables retrofitting of existing installations with minimal structural alterations while achieving CO2 emission reductions.
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
Reduces fuel consumption by 5-30% and CO2 emissions by 8-20%, maintains thermal efficiency, and allows flexibility in feed preheating without significant modifications to the convection section.
Implementation Method 1
heating air by indirect heat exchange with a hot heat transfer fluid received via the heat transfer fluid inlet
Implementation Method 2
A heat transfer fluid circulation system is also included, having a flow line for circulating the cooled heat transfer fluid from the heat transfer fluid outlet to an inlet of the heat transfer fluid heating coil
Data Source
AI summary
Systems and processes for external combustion air preheating for providing preheated combustion air to a furnace. The furnace systems convective heating section includes multiple heating coils for waste heat recovery. The heating coils may be used for preheating a feed (feed preheat coils), heating a boiler feed water, superheating steam, or heating or superheating a feed stream prior to the feed being fed to the radiant coil. The waste heat in the combustion gas is also used to heat a heat transfer fluid, which may be used to pre-heat combustion air or for other purposes within the plant.