7 replies to this topic

[ryn376]

Does anybody have any guidance on thermal oxidizer header design? We are working on preliminary stages of design and will have a company to do the relief evaluations, but before that I wanted to gather some basic information on design such as header pressures, header sizing, required controls and safety instrumentation. This header will tie into a flare in case of overpressure/high flow.

Edited by ryn376, 02 February 2026 - 09:15 AM.

[Pilesar]

The best guidance I can give is to have as many people check the design that you can. Very complicated -- high hazard. The thermal oxidizer company may offer guidance based on what they have seen in other installations. Web search may turn up something.

[ryn376]

I looked online and took a look through John Zink's Combustion Handbook, but it was more theoretical than practical regarding this. I also looked in GPSA. Unfortunately, I have not been able to find anything useful.

[breizh]

Hi,

Why don't you contact vendors directly and submit to them your query.

Attached one ref with a nice brochure:

Thermal Oxidizer Design - Process Combustion Corporation

The reference company should be John Zink.

my 2 cents

Breizh 

[latexman]

What standards are you using for the header design?

[ryn376]

Latexman, do you have any standards you would recommend looking at?

Edited by ryn376, 03 February 2026 - 09:59 AM.

[latexman]

When I ask Google AI, “what standards apply when designing a relief header to a flare?”, here’s what it said:

Designing a relief header to a flare involves adhering to key standards, most notably API Standard 521 (Pressure-relieving and Depressuring Systems), which covers system sizing, backpressure, and safe disposal of vapors. Other primary standards include API 520 (sizing/selection), API 537 (flare details), and regulations like OSHA 29 CFR 1910.119 and EPA 40 CFR 63.670. Key design factors include total relief load, allowable backpressure, and flow velocity, which must be carefully engineered to prevent overpressure. [1, 2, 3, 4, 5]
Key Standards and Regulatory Guidelines:

• API 521/ISO 23251: The primary standard for pressure-relieving and depressuring systems, providing guidelines for evaluating and designing the entire disposal system, including headers, subheaders, and knockout drums.
• API 520 (Parts I & II): Guidelines for the sizing, selection, and installation of pressure-relieving devices, which directly impact the header load.
• API 537: Covers the design and operation of flare tips and related equipment.
• EPA 40 CFR 63.670 (Subpart CC): Regulations regarding the design, operation, and monitoring of flares, including smokeless capacity, assist steam/air, and vent gas flow rates.
• OSHA 29 CFR 1910.119: Process Safety Management (PSM) standards requiring detailed documentation of relief systems. [1, 3, 4, 6, 7]

Key Engineering Design Criteria:

• Backpressure Limits: Relief headers must be sized to keep backpressure below allowable limits (e.g., <10% of set pressure for conventional PSVs) to ensure proper operation.
• Velocity (Mach Number): Typically, gas velocities should not exceed 0.5 Mach in the header, though higher velocities may be allowed in specific, non-critical segments.
• Header Sizing (Capacity): Headers must be designed to handle the peak discharge from all plausible, simultaneous relief scenarios.
• Fluid Phase and Flow: Headers must be designed to accommodate both liquid carryover and vapor, often requiring sloped piping toward a knockout drum to prevent liquid pockets.
• Material and Support: Piping design must account for large thermal movements, low-temperature brittle fracture risks from Joule-Thomson cooling, and massive reaction forces on elbows during high-capacity, sudden relief events. [2, 8, 9, 10, 11]

Key Components in System Design:

• Knockout Drums: Used to separate liquid from vapor before the flare tip.
• Seal Drums/Water Seals: Prevent air from entering the header and flashback from the flare.
• Purge Gas System: Ensures a positive pressure in the header to prevent air ingress. [1, 12, 13, 14, 15]

AI responses may include mistakes.

[1] https://www.atex-ene...es-from-api-521
[2] https://gushr.ai/api...ief-conditions/
[3] https://www.smithbur...f-flare-studies
[4] https://www.dorytest...dards-List.html
[5] https://www.scienced...ering/flare-tip
[6] https://www.ecfr.gov.../section-63.670
[7] http://www.jmcampbel...sign-pit-falls/
[8] https://www.cheresou...-header-sizing/
[9] https://www.gasproce...-flare-headers/
[10] https://engimates.co...-flare-systems/
[11] https://www.cheresou...eader-supports/
[12] https://www.ecfr.gov...section-60.103a
[13] https://www.emerald....-at-an-oilfield
[14] https://www.scribd.c...0/Flare-Package
[15] https://ureaknowhow....are-Systems.pdf

I recognize all those standards. Did that help you?

[breizh]

A google search

Thermal Oxidizer Design Code: Standards for Safety & Compliance - CADAIR

 

Breizh