# Flare and off-gas recovery: Science and thermodynamics

Unburnt fuel, the richest waste stream of all

Source page: https://www.materialinsights.org/energy/e_flare_recovery/rc-sci/

What this tab covers The thermodynamics: the grade (temperature or pressure) of the energy being recovered, energy versus exergy efficiency, and how harsh the waste stream is on equipment.

Flared and vented gas is not waste heat but unburnt fuel, so it is the highest-grade stream in the recovery family. The hard parts are its location, its variable composition and its contaminants.

#### Grade of energy
Favourable

The resource is chemical energy: mostly methane and heavier hydrocarbons in associated gas, and hydrogen in refinery purge streams. Temperature does not matter, and the gas can be sold, burnt for power or reinjected. The World Bank's 2026 Global Gas Flaring Tracker found 167 billion cubic metres (bcm) flared in 2025, the highest since 2019 and the third rise in a row. It is up about 6% on a revised 157 bcm for 2024; the previous edition had reported 151 bcm. The World Bank says one bcm could make about 4 billion kWh, so 167 bcm is roughly 670 TWh (calculated). The coal sector adds about 43 Mt a year of methane, much of it in dilute ventilation air, which is far harder to use than drained gas.^[2](https://www.iea.org/reports/global-methane-tracker-2026/key-findings)^[3](https://www.iea.org/reports/global-methane-tracker-2025/understanding-methane-emissions)^[4](https://www.worldbank.org/en/programs/gasflaringreduction/publication/2026-global-gas-flaring-tracker-report)^[5](https://www.developmentaid.org/api/frontend/cms/file/2026/08/Global-Gas-FlaringTracker-June-23-2026.pdf)^[6](https://www.worldbank.org/en/news/press-release/2026/06/23/global-gas-flaring-rises-energy-security)
 Gas flared worldwide 167 bcm (2025)^[4](https://www.worldbank.org/en/programs/gasflaringreduction/publication/2026-global-gas-flaring-tracker-report)^[5](https://www.developmentaid.org/api/frontend/cms/file/2026/08/Global-Gas-FlaringTracker-June-23-2026.pdf) Change from 2024 about +6% (from a revised 157 bcm)^[5](https://www.developmentaid.org/api/frontend/cms/file/2026/08/Global-Gas-FlaringTracker-June-23-2026.pdf)^[6](https://www.worldbank.org/en/news/press-release/2026/06/23/global-gas-flaring-rises-energy-security) Power potential about 4 billion kWh per bcm; about 670 TWh for 167 bcm (calculated)^[5](https://www.developmentaid.org/api/frontend/cms/file/2026/08/Global-Gas-FlaringTracker-June-23-2026.pdf) Coal methane emissions about 43 Mt/y (coal sector)^[2](https://www.iea.org/reports/global-methane-tracker-2026/key-findings)

#### Exergy versus energy efficiency
Favourable

Recovered gas keeps nearly all its value as fuel, so energy and exergy recovery are both high when the gas is piped and sold. Hydrogen is a special case. Burning a hydrogen-rich purge stream as refinery fuel wastes most of its value. AIChE estimates that hydrogen used as fuel gas costs 11 to 15 times as much as natural gas for the same heat. Recovery units return hydrogen at very different recovery rates and purities: pressure swing adsorption (PSA) 75 to 92% at 99.9% purity or better, membranes 85 to 95% at 90 to 98%, and cryogenic separation 90 to 98% at 95 to 99%. Flaring itself is only partly effective. Of the 429 Mt CO2e from flaring in 2025, about 50 Mt CO2e came from unburnt methane (about 1.8 Mt of methane), about 12% of the total (calculated).^[5](https://www.developmentaid.org/api/frontend/cms/file/2026/08/Global-Gas-FlaringTracker-June-23-2026.pdf)^[9](https://www.aiche.org/resources/publications/cep/2018/january/recovering-hydrogen-and-profits-hydrogen-rich-offgas)
 H2 recovery, PSA / membrane / cryogenic 75-92% / 85-95% / 90-98%^[9](https://www.aiche.org/resources/publications/cep/2018/january/recovering-hydrogen-and-profits-hydrogen-rich-offgas) H2 purity, PSA / membrane / cryogenic 99.9%+ / 90-98% / 95-99%^[9](https://www.aiche.org/resources/publications/cep/2018/january/recovering-hydrogen-and-profits-hydrogen-rich-offgas) Flaring emissions about 429 Mt CO2e, of which about 50 Mt CO2e unburnt methane (2025)^[5](https://www.developmentaid.org/api/frontend/cms/file/2026/08/Global-Gas-FlaringTracker-June-23-2026.pdf) Cost of hydrogen burnt as fuel 11-15 times natural gas for the same use^[9](https://www.aiche.org/resources/publications/cep/2018/january/recovering-hydrogen-and-profits-hydrogen-rich-offgas)

#### Media compatibility and corrosiveness
Mixed

Associated gas is often wet and sour. It carries liquids, hydrogen sulphide and carbon dioxide, so recovery needs separation, compression and corrosion-resistant metals. A refinery flare gas analysed in Iran was about 77% methane and 11% ethane, with traces of hydrogen sulphide that had to be cut below 4 ppm in the products. An Italian refinery recovery unit used a liquid-ring compressor, which tolerates liquids and dirty gas, plus chemical treatment for hydrogen sulphide and inert gases. Membranes need feed above about 300 psig and PSA above about 150 psig. Membranes also need at least 25 to 50% hydrogen in the feed, and PSA at least 40%. Coal mine ventilation air is mostly air, so its methane is usually destroyed by oxidation rather than used as fuel.^[7](https://ideas.repec.org/a/eee/energy/v109y2016icp1-12.html)^[8](https://www.mdpi.com/1996-1073/11/7/1868)^[9](https://www.aiche.org/resources/publications/cep/2018/january/recovering-hydrogen-and-profits-hydrogen-rich-offgas)^[10](https://ember-energy.org/latest-insights/global-coal-mine-methane-review-2026/cutting-cmm-this-decade-is-urgent-and-feasible)
 Refinery flare gas methane content (case) 76.88 mol%^[8](https://www.mdpi.com/1996-1073/11/7/1868) Product H2S target below 4 ppm^[8](https://www.mdpi.com/1996-1073/11/7/1868) Minimum H2 in feed, PSA / membrane over 40% / over 25-50%^[9](https://www.aiche.org/resources/publications/cep/2018/january/recovering-hydrogen-and-profits-hydrogen-rich-offgas)

#### Variants compared^[4](https://www.worldbank.org/en/programs/gasflaringreduction/publication/2026-global-gas-flaring-tracker-report)^[7](https://ideas.repec.org/a/eee/energy/v109y2016icp1-12.html)^[8](https://www.mdpi.com/1996-1073/11/7/1868)^[9](https://www.aiche.org/resources/publications/cep/2018/january/recovering-hydrogen-and-profits-hydrogen-rich-offgas)^[10](https://ember-energy.org/latest-insights/global-coal-mine-methane-review-2026/cutting-cmm-this-decade-is-urgent-and-feasible)

| Variant | Main stream | Typical use | Economics indicator |
|---|---|---|---|
| **Upstream flare gas recovery and associated gas use** | Associated gas at oil fields | Pipeline sales, power, reinjection, LNG or LPG | USD 70-100 billion upfront to end routine flaring worldwide |
| **Refinery off-gas (flare gas) recovery** | Flare header gas | Back into refinery fuel gas, or LNG/NGL | Payback about 1.6-3 years in two case studies |
| **Purge gas hydrogen recovery** | Hydrogen-rich purge or off-gas | Recycled hydrogen via PSA, membrane or cryogenic | Hydrogen as fuel costs 11-15 times gas |
| **Coal mine methane** | Drained gas and ventilation air | Power and heat, or flaring/oxidation | 62% of drainage potential at negative net cost (IEA via Ember) |

#### Sources

1. [Global Methane Tracker 2026: Key findings](https://www.iea.org/reports/global-methane-tracker-2026/key-findings) International Energy Agency, 2026
2. [Global Methane Tracker 2025: Understanding methane emissions](https://www.iea.org/reports/global-methane-tracker-2025/understanding-methane-emissions) International Energy Agency, 2025
3. [2026 Global Gas Flaring Tracker report (publication page, covering 2025)](https://www.worldbank.org/en/programs/gasflaringreduction/publication/2026-global-gas-flaring-tracker-report) World Bank, 2026
4. [Global Gas Flaring Tracker 2026 (full report, covering 2025; copy hosted by DevelopmentAid)](https://www.developmentaid.org/api/frontend/cms/file/2026/08/Global-Gas-FlaringTracker-June-23-2026.pdf) World Bank, Global Flaring and Methane Reduction Partnership, 2026
5. [Global gas flaring rises, undermining energy security (press release, 23 June 2026)](https://www.worldbank.org/en/news/press-release/2026/06/23/global-gas-flaring-rises-energy-security) World Bank, 2026
6. [Energy efficiency improvement in oil refineries through flare gas recovery technique to meet the emission trading targets (Comodi, Renzi and Rossi), Energy 109](https://ideas.repec.org/a/eee/energy/v109y2016icp1-12.html) Elsevier (abstract via RePEc/IDEAS), 2016
7. [Thermo-economical evaluation of producing liquefied natural gas and natural gas liquids from flare gases (Barekat-Rezaei et al.), Energies 11(7) 1868](https://www.mdpi.com/1996-1073/11/7/1868) MDPI (peer-reviewed), 2018
8. [Recovering hydrogen, and profits, from hydrogen-rich offgas (Chemical Engineering Progress)](https://www.aiche.org/resources/publications/cep/2018/january/recovering-hydrogen-and-profits-hydrogen-rich-offgas) AIChE, 2018
9. [Global Coal Mine Methane Review 2026: cutting CMM this decade is urgent and feasible (reporting IEA Global Methane Tracker 2025, UNEP and UNECE figures)](https://ember-energy.org/latest-insights/global-coal-mine-methane-review-2026/cutting-cmm-this-decade-is-urgent-and-feasible) Ember, 2026

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_flare_recovery/index.md)
- [Overview](https://www.materialinsights.org/energy/e_flare_recovery/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_flare_recovery/correlation/index.md)
- [Engineering and integration](https://www.materialinsights.org/energy/e_flare_recovery/rc-eng/index.md)
- [Economics and contracts](https://www.materialinsights.org/energy/e_flare_recovery/rc-econ/index.md)
- [Impact and additionality](https://www.materialinsights.org/energy/e_flare_recovery/rc-impact/index.md)
- [What to track](https://www.materialinsights.org/energy/e_flare_recovery/tracking/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_flare_recovery/links/index.md)