External Adiabatic Burner Combustion System for High-Temperature Heat Transfer
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Solution Overview
Problem
Existing high-temperature heat transfer systems in industrial reactors face challenges such as high capital costs, heat leaks, and NOx production due to large burner flames and inefficient heat distribution, particularly in fuel processors for hydrogen production and other endothermic reactions.
Innovation Solution
A combustion system where only combustion air is preheated to a temperature consistent with the fired heater's thermal rating, using an external adiabatic burner for partial combustion, and additional fuel is injected via spray nozzles to maintain temperature, optimizing heat transfer and reducing the size of the radiant box.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fuel is injected in the combustion air and a monolithic oxidation catalyst is installed on the external surface of the catalyst tubes, then combustion of the fuel is obtained without installing any burner, but this solution is not suitable for industrial plants because of the higher reforming temperatures and presents safety concerns due to the presence of fuel mixed with combustion air before oxidation starts
Solution Approach 1:
The invention extracts the combustion process from the internal catalyst tube system and relocates it to an external adiabatic burner. This separation eliminates the safety issue of fuel mixed with combustion air inside the catalyst tubes while maintaining the ability to achieve high reforming temperatures through the external burner's concentrated heat source.
Solution Approach 2:
The external adiabatic burner acts as an intermediary device that converts fuel and air into high-temperature combustion products, which then serve as the heat source for the reforming process. This intermediary approach allows controlled combustion outside the catalyst system while transferring heat efficiently to the reforming reactions.
2Device complexity
If the combustion of the fuel is performed in the shell outside the reaction tubes with auto ignition, then the need for separate ignition devices and burner structures is eliminated, but serious mechanical problems occur because of the high flame temperature and different thermal expansion of the shell and the tubes
Solution Approach 1:
The invention extracts the combustion process from the shell space and relocates it to an external adiabatic burner positioned outside the reactor vessel. This eliminates the mechanical stress problems caused by high flame temperatures and differential thermal expansion between the shell and tubes, while still providing the necessary heat for auto-ignition of the reforming process.
Solution Approach 2:
The system is segmented into distinct functional zones: an external adiabatic burner for combustion, a radiant section for heat transfer, and a catalyst tube section for reforming reactions. This segmentation allows each component to be optimized independently, with the burner handling combustion and the reactor handling chemical reactions, thereby avoiding mechanical compatibility issues.
3Productivity
If a large number of burners are installed in the radiant box walls to provide uniform heat distribution, then heat transfer efficiency is improved, but capital costs and heat leaks increase
Solution Approach 1:
The heating function is segmented between the external adiabatic burner and the internal spray nozzles. The external burner provides the majority of heat through the radiant section, while the internal spray nozzles provide localized supplemental heating only where and when needed, eliminating the requirement for numerous burners in the radiant box walls and reducing associated heat leaks and capital costs.
Solution Approach 2:
The process fluid or reactants themselves serve as the cooling medium for the external adiabatic burner through the convection section, and the spray nozzles use the process stream to provide localized heating. This self-service approach eliminates the need for separate burner systems in the radiant box walls, reducing capital costs and heat leaks while maintaining efficient heat transfer.
4Power
If consistent amounts of fuel are fired in all burners with very high flame temperature, then sufficient heat is provided for endothermic reactions, but NOx production increases and heat distribution becomes inefficient
Solution Approach 1:
The invention applies different combustion strategies to different locations: the external adiabatic burner operates with controlled air-fuel ratios to minimize NOx while providing bulk heat, and the internal spray nozzles provide localized heating with precise fuel injection. This local quality approach replaces the uniform high-temperature combustion of conventional burners, reducing NOx production while maintaining sufficient heat generation for endothermic reactions.
Solution Approach 2:
The system changes the combustion parameters by using an external adiabatic burner with controlled excess air ratios and supplemental fuel injection through spray nozzles. This allows the combustion process to operate at lower peak temperatures in the main burner while maintaining sufficient overall heat input, thereby reducing NOx formation through parameter optimization rather than uniform high-temperature combustion.
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 efficient high-temperature heat transfer with reduced capital costs, minimized radiant box size, and lower NOx production by using small, low-cost flames and precise control of heat distribution, enhancing the efficiency of processes like hydrogen production and fluid preheating.
Implementation Method 1
carry out a partial combustion in an external adiabatic burner to increase the temperature of the combustion air to a higher temperature close to that of the flue gas inside the fired heater itself
Implementation Method 2
the flue gas transfers heat at a temperature much higher than the auto ignition temperature
Implementation Method 3
additional fuel is injected with spray nozzles and burned
Implementation Method 4
the mixture of flue gas and pre-combusted air, with all the oxygen required to complete the combustion, is cooled in the heater because of the heat transfer to the process fluid in the coils or in the catalyst tubes
Implementation Method 5
a fuel processor to produce hydrogen by steam reforming of hydrocarbons
Implementation Method 6
The catalyst was installed inside the tubes and the combustion of the fuel was performed in the shell
Implementation Method 7
The inside and outside wall temperatures of the reaction tubes are maintained at acceptably level even though the flame temperature of the combustion gases reaches a very high level
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
In a combustion system to transfer heat at high temperature in heaters comprising a radiant box where the fuel is fired, the combustion air, available at ambient temperature or after preheating using an external source of heat or the sensible heat of the flue gas of the heater itself, is sent to one or more external adiabatic burners where a partial combustion is performed before said combustion air is introduced into the radiant box to be mixed with the fuel.