Ethylene Furnace Radiant Coil Decoking via COT Feedback Control
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Solution Overview
Problem
The decoking process in ethylene furnaces is difficult to control, leading to potential damage to radiant coils and increased downtime due to the lack of direct measurement of coke burning rate and detection of coke spalling, resulting in inefficient and potentially damaging decoking procedures.
Innovation Solution
Controlling steam and air flows to maintain predetermined coil outlet temperatures (COT) during the decoking process, allowing for monitoring of coke burning and adjustment of air and steam flow rates to achieve a controlled burn, reducing coil damage and decoking time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If air and steam flow rates are increased to accelerate coke burn rate, then decoking time is reduced, but radiant coil damage increases
Solution Approach 1:
The patent implements a feedback control system that continuously monitors CO2 levels in the effluent gas and uses this information to adjust air and steam flow rates dynamically. This closed-loop control allows the system to accelerate decoking when safe and slow down when approaching damage thresholds, resolving the contradiction between speed and safety.
Solution Approach 2:
The patent transitions from static, conservative flow rates to dynamic, adaptive flow rates that change based on real-time process conditions. By making the air and steam flow rates variable rather than fixed, the system can optimize decoking speed while preventing coil damage through continuous adaptation to changing coke burn rates.
2Loss of time
If air flow rate is increased to remove coke faster, then decoking time is reduced, but localized fast burning and coil erosion increase
Solution Approach 1:
CO2 analysis provides real-time feedback on the coke burn rate, enabling the control system to detect localized fast burning conditions and adjust air distribution accordingly. This prevents coil erosion by identifying and responding to problematic zones before significant damage occurs.
Solution Approach 2:
The patent applies different air and steam flow rates to different coils based on individual CO2 measurements and coke deposition patterns. Rather than uniform treatment, the system tailors the decoking conditions to each coil's specific needs, preventing localized overheating and erosion while maintaining overall efficiency.
3Object-affected harmful factors
If conservative air and steam flow rates are used to prevent coil damage, then coil safety is improved, but decoking time increases
Solution Approach 1:
The feedback control system using CO2 analysis allows the system to operate at higher flow rates when conditions permit, rather than being constrained by conservative fixed limits. This dynamic adjustment maintains safety while significantly improving decoking efficiency compared to always using conservative settings.
Solution Approach 2:
The system transitions from static conservative flow rates to dynamic flow rates that adapt to real-time conditions. This allows the system to exploit safe operating windows and accelerate decoking when conditions allow, while maintaining protection margins when approaching limits.
4Temperature
If initial air introduction is performed slowly to avoid coil overheating, then coil temperature control is improved, but decoking process time increases
Solution Approach 1:
The patent uses CO2 analysis to provide real-time feedback on the actual coke burn rate during initial air introduction. This allows the system to safely increase air flow rates faster than traditional conservative methods because the feedback provides direct information about thermal conditions and coke reactivity, enabling rapid yet controlled air introduction.
Solution Approach 2:
The patent replaces indirect temperature monitoring methods with direct chemical analysis of CO2 emissions. This substitution provides more immediate and accurate information about the decoking process state, enabling faster and safer air introduction rates compared to methods that rely on temperature lag or conservative estimates.
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 method enables a more efficient and controlled decoking process, reducing radiant coil damage and decoking time by maintaining precise control over steam and air flows based on monitored COTs, ensuring safe and rapid removal of coke.
Implementation Method 1
introduction of air and steam to the radiant coils in the furnace... allow coke on the radiant tubes to be burned
Implementation Method 2
heating the coils while monitoring the coil outlet temperature (COT) of the coils in the furnace... achieved by burning off the deposited coke
Data Source
AI summary
Methods are provided for decoking the radiant coils in an ethylene cracking plant. The decoking process is controlled by monitoring the coil outlet temperature to control the rate of burning of coke in the radiant coils. Air flow rates, steam flow rates and coil outlet temperatures are controlled during the decoking process to prevent tube damage, minimize decoking time and maximize coke removal.