Fired Heater Positive Pressure Convection Efficiency
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Solution Overview
Problem
Conventional fired heaters in petroleum refineries and petro-chemical plants suffer from reduced efficiency and increased emissions due to ambient air ingress, requiring high excess O2 levels and resulting in suboptimal heat transfer and higher NOx and greenhouse gas emissions.
Innovation Solution
A fired heater unit operates under positive pressure with a vertically arranged convection section and longitudinally finned vertical tubes, utilizing forced convective heat transfer and eliminating the need for induced draft blowers, allowing for lower excess O2 operation and enhanced heat transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional balanced draft design with forced draft blower and induced draft blower is used, then ambient air can be supplied to preheater and flue gas can be withdrawn, but ambient air ingress occurs which reduces heater efficiency and increases emissions
Solution Approach 1:
The invention removes the induced draft blower from the conventional balanced draft design, extracting only the necessary function of maintaining positive pressure. This eliminates the source of ambient air ingress while retaining adequate air supply capability through the forced draft blower alone, thereby improving heater efficiency to 95% while maintaining operational stability
Solution Approach 2:
The invention changes the pressure parameter from balanced draft (near atmospheric) to positive pressure operation. By maintaining positive pressure throughout the heater using only the forced draft blower, the system prevents ambient air ingress and achieves higher efficiency with lower excess O2 levels (1-2%)
2Use of energy by moving object
If conventional horizontal convection tubes are used, then heat transfer can occur, but the heater requires larger size and longer heat transfer surface area
Solution Approach 1:
The invention transitions from horizontal convection tubes to vertical convection tubes with upward flow direction. This dimensional change in flow orientation enables more compact heat transfer surface arrangement and reduces the overall heater volume while maintaining effective heat transfer capability through forced convection
3Reliability
If higher excess O2 levels (3% or higher) are used to prevent combustion instabilities, then operational stability is maintained, but heater efficiency decreases and emissions increase
Solution Approach 1:
The invention changes the excess O2 parameter from conventional levels (3% or higher) to lower levels (1-2%). This is enabled by the positive pressure operation that prevents ambient air ingress, allowing the system to maintain combustion stability with reduced excess oxygen, thereby decreasing NOx and greenhouse gas emissions by approximately 3%
4Productivity
If induced draft blowers are used to withdraw flue gas, then flue gas removal is achieved, but maintenance problems increase
Solution Approach 1:
The invention removes the induced draft blower entirely from the system, extracting only the essential function of flue gas removal which is achieved through the forced draft blower creating positive pressure. This eliminates the maintenance problems associated with induced draft blowers while maintaining adequate flue gas withdrawal capability
Solution Approach 2:
The system uses the forced draft blower to serve multiple functions: supplying combustion air and creating positive pressure to drive flue gas flow through the heater. This self-service approach eliminates the need for a separate induced draft blower, reducing maintenance requirements
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 configuration achieves a potential thermal efficiency of 95%, reduces NOx and greenhouse gas emissions by 3%, and results in a compact, low-maintenance design with energy savings from reduced fuel consumption.
Implementation Method 1
The utilization of positive pressure operation permits forced convective heat transfer from the flue gas to the process fluid in the convection section of the heater
Implementation Method 2
The forced convective heat transfer decreases the effective convective heat transfer surface needed to heat the process fluid
Implementation Method 3
a twin cell vertical tube box type radiant section with a convection section of vertical tube orientation located between the two radiant cells
Data Source
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AI summary
A fired heater unit is disclosed having at least one radiant heating section with each of the at least one radiant heating section having a heating element located therein. The unit includes a convection section operatively connected to the at least one radiant heating section, wherein the convection section having at least one vertically oriented convection tube. Each of the at least one convection tube being operatively connected to the at least one radiant heating section. Each of the at least one convection tube includes an inner tube having process fluid flowing therethrough, wherein the process fluid being heated by the at least one radiant heating section, and an outer tube extending along a predetermined portion of the inner tube, wherein the outer tube is spaced from the inner tube to form a flow path therebetween.