Elevated Flare Stack Pilot Assembly Ignition Design
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Solution Overview
Problem
Existing pilot assemblies for elevated flare stacks face reliability issues due to the poor durability of hot surface ignition (HSI) elements exposed to extreme heat and weather conditions, and spark igniter systems that require frequent maintenance from soot buildup, leading to pilot flame failures and regulatory fines for unburned gas emissions.
Innovation Solution
A pilot assembly design featuring dual lines, a fire path tubing with an HSI element positioned below the nozzle, and a pilot tubing with a venturi mixer, where the HSI element generates flame segments that ignite a premixed fuel/air mixture in the nozzle, improving durability and reliability by shielding the HSI from heat and weather, and using a thermocouple to sense flame temperature effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the HSI element is positioned at the nozzle to ignite the fuel/air mixture, then the ignition reliability is improved, but the durability of the HSI element deteriorates due to exposure to extreme heat and weather conditions
Solution Approach 1:
The pilot assembly is divided into two separate tubing lines: a fire path tubing that contains the HSI element and generates flame segments, and a pilot tubing that delivers the fuel/air mixture to the nozzle. This segmentation allows the HSI element to be positioned away from the nozzle, protecting it from extreme heat and weather conditions while still enabling reliable ignition of the fuel/air mixture at the nozzle location.
Solution Approach 2:
Flame segments generated in the fire path tubing act as an intermediary between the protected HSI element and the fuel/air mixture at the nozzle. These flame segments travel through the fire path tubing and ignite the fuel/air mixture at the nozzle, allowing the HSI element to remain shielded from direct exposure to extreme conditions while maintaining ignition functionality.
2Reliability
If a spark igniter is used to ignite the fuel/air mixture, then the ignition capability is achieved, but maintenance frequency increases due to soot buildup on sparking tips
Solution Approach 1:
The mechanical spark ignition system is replaced with a hot surface ignition element that generates flame segments through controlled combustion in the fire path tubing. This substitution eliminates the sparking tips that accumulate soot, thereby reducing maintenance frequency while maintaining reliable ignition capability through the flame segments that ignite the fuel/air mixture at the nozzle.
3Measurement precision
If the thermocouple is positioned to sense flame temperature at the nozzle, then the flame detection accuracy is improved, but the thermocouple durability deteriorates due to exposure to extreme heat
Solution Approach 1:
The flame segments generated in the fire path tubing serve as an intermediary that allows the thermocouple to be positioned away from the nozzle while still accurately sensing flame temperature. The thermocouple can be placed in the fire path tubing where it detects the temperature of the flame segments, which accurately reflects the combustion conditions without exposing the thermocouple to the extreme heat and weather conditions at the nozzle location.
Data Source
AI summary
Pilot assemblies comprising a fire path tubing and pilot tubing in fluid communication through a pilot nozzle for elevated flare stacks are disclosed. A plurality of flame segments is generated using a hot surface ignition element or a spark igniter in the fire path tubing and ignites fuel/air mixture flowing through the pilot tubing into a pilot nozzle to produce a reliable pilot flame. The pilot flame ignites the waste gases flowing out of the flare tip of elevated flare stacks. Methods for operating the pilot assemblies are also disclosed.