Flare Gas BTU Control via Supplemental Fuel Injection
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Solution Overview
Problem
Oil and gas facilities face challenges in maintaining compliance with BTU Net Heating Value (NHV) requirements for flare combustion due to nitrogen purge streams diluting gas, leading to non-compliance and the need for expensive supplemental fuel gas connections, restricted natural gas supply, and inadequate fuel gas availability.
Innovation Solution
A method to control the BTU content of flare gas by introducing a nitrogen stream and combining it with supplemental fuel gas, adjusting the flow rates to maintain a minimum BTU content at the flare tip, using a portable and temporary supplemental fuel gas supply and automatic control systems based on real-time monitoring of HAP, pressure, and LEL levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If nitrogen purge streams are used to purge hydrocarbons and hazardous air pollutants, then the purification of process equipment is improved, but the BTU content of flare gas falls below regulatory NHVs
Solution Approach 1:
The system applies preliminary anti-action by introducing supplemental fuel gas to the flare stream before combustion occurs. This preemptive addition of hydrocarbons counteracts the diluting effect of nitrogen purge streams, ensuring the flare gas maintains sufficient BTU content (typically above 100-200 BTU/scf) to meet regulatory NHV requirements while still allowing effective purging of hazardous air pollutants.
2Reliability
If supplemental fuel gas connections are installed to maintain BTU content, then regulatory compliance is improved, but the project cost increases significantly
Solution Approach 1:
The system uses an intermediary approach by introducing supplemental fuel gas through a controlled injection point in the flare feed line. This mediator substance (fuel gas) bridges the gap between nitrogen-diluted flare gas and the required BTU content, achieving regulatory compliance without requiring expensive infrastructure changes or permanent connections between distant fuel gas sources and flare locations.
Solution Approach 2:
The system applies parameter changes by dynamically adjusting the flow rate of supplemental fuel gas based on real-time monitoring of flare gas composition and BTU content. This allows the system to maintain compliance with NHV requirements while optimizing fuel gas consumption, thereby reducing operational costs and avoiding the need for oversized, expensive infrastructure.
3Quantity of substance
If high volumes of supplemental fuel gas are drawn from natural gas utilities, then the BTU content requirement is met, but other critical users on the line are adversely affected
Solution Approach 1:
The system implements dynamics by using variable speed compressors and controllable fuel gas injection rates that can be dynamically adjusted based on flare demand and utility supply availability. This allows the system to optimize fuel gas consumption in real-time, drawing only the necessary volume to maintain BTU requirements without adversely impacting other critical users on the natural gas utility line.
4Adaptability or versatility
If process generated fuel gas is used as supplemental fuel, then the availability of external fuel gas is reduced, but the surplus fuel gas from process sources is inadequate
Solution Approach 1:
The system applies universality by designing a flexible fuel gas injection system that can accept multiple fuel gas sources including process-generated gases (hydrogen, propane, propylene, butane, light ends fuel gas) and external natural gas. This multi-functional approach allows the system to adapt to varying process conditions and utilize available fuel gas sources without being constrained by a single supply source, thereby overcoming the limitation of inadequate surplus fuel gas from any single process source.
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
Ensures regulatory compliance by maintaining the BTU content of flare gas streams at or above the required minimum, reducing project costs and logistical challenges through efficient use of supplemental fuel gas, even during high flow or supply limitations.
Implementation Method 1
combining the first gas stream with the supplemental fuel gas stream, thereby obtaining a flare gas stream comprising a final Btu content
Implementation Method 2
Flares are regularly used to combust hydrocarbons and hazardous air pollutants in refineries, chemical plants and other oil and gas related operations
Data Source
AI summary
A method for controlling the Btu content of a flare gas to combusted in a flare stack comprising a flare tip is provided. The method includes, introducing a first gas stream including nitrogen to be flared, the first gas stream having an initial Btu content, providing a supplemental fuel gas stream, and combining the first gas stream with the supplemental fuel gas stream, thereby obtaining a flare gas stream having a final Btu content measured at the flare tip.