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Process Safety Engineering

Flare System Design and Analysis

We design API 521, API 537 and API 14.10 compliant disposal networks with Aspen Flarenet and PIPENET hydraulics, Hajek and Ludwig radiation analysis and EPA 40 CFR 60.18 visibility compliance

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Technical overview

Flare System Design
and Analysis

Flare system design integrates the whole disposal network from the pressure relief devices through the collection headers, knockout drums, liquid seals, stack and flare tip, and our team makes sure your emergency and continuous relief loads are routed safely without violating backpressure limits, thermal radiation thresholds, noise constraints or environmental emission standards. The discipline operates under API 521 and ISO 23251 for sizing, under API 537 for flare tip selection and design, under API STD 14.10 for offshore flare and vent, under EPA 40 CFR 60.18 and 63.11 for environmental performance including 98 percent destruction efficiency, exit velocity and visible emission limits, and under the 2020 EPA refinery MACT amendments that tightened flare performance monitoring. We execute the work in Aspen Flarenet, PIPENET and Aspen HYSYS for hydraulic and thermodynamic modelling, in FLACS and FRED for radiation and dispersion, and increasingly with LIDAR based flare tip performance monitoring that reflects the post Texas City and post Buncefield era. The common audit findings we resolve include undocumented simultaneous relief assumptions, hot case radiation exceedance at maintenance walkways, water seal sizing that ignores low flow stagnation, and missing flare gas recovery integration where you have committed to zero routine flaring.

Flare System Design and Analysis Overview
Engineering process

Flare System Design and Analysis workflow

Simultaneous Relief Load Study

Identify and justify all simultaneous relief load cases per API 521 Section 5, develop case matrix with fire credit, blocked outlet simultaneity, and utility failure scenarios.

Knockout Drum & Liquid Seal Sizing

Size knockout drum for 500 µm droplet separation per API 521, size water seal for purge gas management and oxygen ingress prevention across all relief scenarios.

Header Hydraulic Modelling

Model disposal network in Aspen Flarenet / PIPENET, verify Mach number (<0.7 sustained), pressure profile, erosional velocity limits, and simultaneous flow distribution.

Flare Tip Selection & Stack Determination

Select flare tip type per API 537 (utility, steam assist, air assist, enclosed, sonic), determine stack height from radiation, dispersion, structural, and wind loading requirements.

Radiation & Environmental Compliance

Calculate thermal radiation iso contours per API 521 Annex D (Hajek Ludwig / Brzustowski Sommer), verify EPA 40 CFR 60.18 destruction efficiency and exit velocity compliance.

FGR Sizing & Deliverable Package

Size flare gas recovery compressor for routine flaring zero commitment, issue design basis, hydraulic model files, radiation contour plots, and environmental compliance package.

Flare System Design and Analysis Scope
Scope of work

Every deliverable from basis to handover

Complete Flare System Design and Analysis scope covering every calculation, drawing, specification, and construction support activity.

We develop the simultaneous relief load case under API 521 Section 5 with credit logic and case justification
We model the disposal network hydraulics in Aspen Flarenet and PIPENET across steady state and transient conditions
We size the headers with a Mach number and erosional velocity check, typically holding Mach below 0.7 sustained and below 1.0 short term
We size the knockout drum under API 521, typically for separation of 500 micron liquid droplets
We size the water seal to provide purge gas and prevent oxygen ingress
We select the flare tip under API 537 across utility, steam assisted, air assisted, enclosed ground and sonic types
We assess thermal radiation under API 521 Annex D using the Hajek and Ludwig method, the Brzustowski and Sommer method and a single point method
We determine the stack height from radiation, dispersion and structural and wind loading
We size the flare gas recovery compressor for your zero routine flaring commitment
We confirm EPA 40 CFR 60.18 compliance across destruction efficiency, exit velocity and visible emissions
Engineering outcomes

Outcomes of Flare System Design and Analysis

Thermal Radiation and Backpressure Control
  • We dispose of all simultaneous relief loads safely without exceeding backpressure
  • We set thermal radiation exclusion zones that protect your people and occupied buildings
  • We prevent flare liquid carryover and the potential for a ground level explosion
  • We make sure the flare ignites reliably in all weather conditions
API 521 and API 537 Flare Defence
  • We deliver API 521 backpressure compliance for all pressure relief devices
  • We provide the continuous flare compliance monitoring required under the Clean Air Act
  • We address OSHA 1910.119 mechanical integrity for the flare system
  • We meet the noise and radiation limits in your environmental permit
Flare Reliability and Smokeless Operation
  • We size the knockout drum correctly so liquid does not carry over to the tip
  • We calculate the minimum purge rate so you prevent flashback
  • We integrate flare gas recovery to reduce your routine flaring volume
  • We support your zero routine flaring commitments
Flare Sizing and Capacity Investment Value
  • We help you avoid a costly flare system redesign after startup
  • We optimise the flare tip size so you avoid unnecessary capital cost
  • We reduce your exposure to environmental penalties from excess flaring
  • We help your flare gas recovery generate a return on capital
Standards & references

Codes & standards we work to

API 521 / ISO 23251 (8th Ed., 2024)API 537 (3rd Ed., 2017) flare detailsAPI STD 14.10 (offshore)API 520 Pt I / IIEPA 40 CFR 60.18 / 63.112020 EPA Refinery MACT (Subpart CC)Energy Institute HEM 3NFPA 30World Bank EHS GuidelinesOISD STD 106 / 116 / 118 (Petroleum)PESO certification (India)CEA Regulations 2010 (India Electrical Safety)Indian Petroleum Rules 2002
When to engage

Triggers that signal the need

You are at FEED or detail engineering for a new plantYou are increasing capacity or adding new relief sourcesYou are replacing or upgrading a flare tipYou need a relief system review after an incidentYou face a Clean Air Act compliance evaluationYou have reached a periodic revalidation
Industries served

Where Flare System Design and Analysis applies

Oil & Gas, Upstream

Wellheads, separators, gas compression, FPSO topsides, produced water systems.

UpstreamOffshoreFPSO
Refineries & Petrochemicals

Distillation columns, reactors, heat exchangers, storage spheres, LPG handling.

RefiningPetrochemical
LNG & Gas Processing

Cryogenic exchangers, liquefaction trains, BOG compressors, storage and sendout.

LNGCryogenic
Specialty Chemicals

Reactive systems, batch reactors, solvent handling, runaway reaction scenarios.

ReactiveBatch
Power Generation

Boilers, HRSGs, steam headers, hydrogen systems, ammonia SCR units.

PowerHydrogen
Pharma & Food

Sterile vessels, CIP/SIP, pressure fermenters, solvent recovery, spray dryers.

PharmaFood & Bev
What we deliver

Tangible deliverables

  • Simultaneous relief load case study
  • Flare header hydraulic model
  • Flare tip selection and specification
  • Thermal radiation analysis and exclusion zone map
  • Stack height determination
  • Noise assessment report
  • Knockout drum sizing calculations
  • Flare system design basis document
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Speak with our team to scope an engagement tailored to your facility, regulatory context, and lifecycle stage.

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