Low temperature physical absorption

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Category: Carbon capture (mature) Subcategory: Physical absorption Combustion type: Pre

DESCRIPTION

For low-temperature physical absorption, the Rectisol process is chosen due to its high commercial readiness. This process utilizes cold methanol (CH3OH) as a solvent to remove CO2 and acid gases (H2S, COS) from the feed gas, primarily in pre-combustion applications. However, physical absorption is not economical for processes where the CO2 concentration is below 15%.1 The Rectisol process can be configured in various ways to meet different process requirements (see figures).1,2 Specific layouts are designed for selective H2S removal, extensive CO2 removal, and comprehensive removal of both CO2 and H2S.3 The feed gas enters the absorption column, where it comes into contact with cold methanol (range: -20 to -50 °C)1,4 at high pressure. The methanol selectively absorbs CO2 and other acid gases (e.g., H2S, COS) from the feed gas. The CO2-rich methanol then undergoes a pressure reduction step in a flash tank, allowing a portion of the absorbed gases to be released. Further regeneration of the methanol is achieved through a combination of pressure reduction and heating, ensuring the complete removal of the remaining absorbed gases. The regenerated methanol is then cooled back to the required low temperature before being recycled to the absorption column. The Rectisol process enables the capture of high-purity CO2, making it suitable for storage or further processing, and is typically applied at industrial scales.

 

Rectisol CO2 Capture ProcessRectisol Co-Capture Process

TECHNICAL ASPECTS (all % are volume-based)

Point sources: Biomass/MSW-based applications, coal-based plants, IGCC, chemical plants, ammonia, and H2 production.5

CO2 concentration range: 20% – 30%5

CO2 capture efficiency: 99%5

CO2 purity: 95%5

Min. feed gas pressure: 20 bar6

Max. feed gas temperature: 35 °C7

Typical scale: Medium to large (0.36 – 3.6 MtCO2/yr)5

Primary energy source: Electricity5

Impurity tolerance: Solvent is chemically stable and does not form heat-stable salts when in contact with the flue gas.8

FUNCTION IN CCU VALUE CHAIN

  • Capture CO2 from feed gases.
  • Removal of other acid gases (e.g., H2S, COS).5

LIMITATIONS

  • High energy requirements due to low operating temperatures.
  • Less suitable for low CO2 concentration ranges.5
  • Requires substantial refrigeration infrastructure.
  • Higher selectivity for H2S over CO2.

ENERGY

  • Electricity is primarily used for cooling and compression of the gas streams.
  • Electricity is used in pumping solvent and refrigeration.

CONSUMABLES

  • Methanol for solvent preparation, minimal loss due to regeneration, and make-up is required.
Energy and Consumables
Parameter Value
Heat (GJ/tCO2) 0.352
Electricity (kWh/tCO2) 402 - 831
Cooling duty (GJ/tCO2) ** 0.0812
Solvent make-up (kg/tCO2) 4.71

1 CO2 removal only, flash based; flow rate: 180.4 t/h; inlet pressure:27.9 bar; inlet temperature: 6.6 °C; outlet pressure: 110 bar; outlet temperature: 30 °C; ~90% energy is for compression; ~10% energy is for pumps; no heat duty required.

2 IGCC plant; 2-stage Rectisol; CO2 and H2S removal; feed pressure – 32.3 bar; ~40% CO2; 179 t/h CO2; 90% capture efficiency.

** Cooling duty refers to the refrigeration.

COSTS

CAPEX: 9 €/tCO2 1

Main CAPEX: absorption column, cooling and refrigeration, pumps, and compressors.

OPEX: 38 €/tCO2 1

Main OPEX: electricity and maintenance.

CO2 capture cost: 47 €/tCO2 1

1 Rectisol process; IGCC plant; CO2 conc. – 38.6%; capacity – 1 MtCO2/yr; lifetime – 25 yrs; discount rate – 8%; 2015 euros; includes CO2 compression to 110 bar; electricity price – 96 €/MWh.

CO2 avoidance cost: 67 €/tCO2 avoided 9

9 Rectisol process; IGCC plant; CO2 & H2S capture; CO2 conc. – 39.85%; feed pressure – 32.3 bar; capture efficiency – 95%; capacity - 2 MtCO2/yr; lifetime – 35 yrs; fixed charge factor – 17.21%; 2014 euros; includes CO2 compression to 120 bar; electricity price – 142 €/MWh.

ENVIRONMENTAL

CO2 footprint: 294 kgCO2eq/tCO2 10,11*

                       26 kgCO2eq/tCO2 10,11**

*Emissions considered for materials and energy; includes IGCC plant, CO2 capture, liquefaction, transport, and storage.

**Emissions only for capture and liquefaction.

Spatial footprint: Not available.

Environmental issues: Minimal process emissions and effluents.

ENGINEERING

Maturity: Commercial (TRL 9)5

Commercial-scale Rectisol® units are operated worldwide.

Retrofittability: Moderate

Relatively retrofittable into facilities that already have syngas or gas processing units, but it requires significant cooling and infrastructure.

Scalability: High

The Rectisol process can be adapted to various capacities (modular system).5

Process type: Liquid solvent-based without chemical reactions.

Deployment model: Centralized or Decentralized.

Decentralized CO2 absorption at point sources with centralized desorption.

Technology flexibility: Hybridization with other capture technologies is feasible. Other technologies, such as membranes or PSA, can be used to increase CO2 concentration.

TECHNOLOGY PROVIDERS

INNOVATIONS

Recticap™ is an enhanced version of Rectisol™ specifically designed for energy transition projects focused on low-carbon hydrogen production.

Multi-stage Rectisol process for improved selectivity and higher CO2 capture rates.

BENCHMARK

  • Amine-based absorption methods like MEA processes (chemical absorption).
  • High-temperature physical absorption, such as Selexol.

CONTACT INFO

Mohammed Khan (mohammednazeer.khan@vito.be)

Miet Van Dael (miet.vandael@vito.be)

ACKNOWLEDGEMENT

This infosheet was prepared as part of the MAP-IT CCU project funded by VLAIO (grant no. HBC.2023.0544).

REFERENCES

1.    Roussanaly S, Vitvarova M, Anantharaman R, et al. Techno-economic comparison of three technologies for pre-combustion CO2 capture from a lignite-fired IGCC. Front Chem Sci Eng. 2020;14(3):436-452.

2.    Padurean A, Cormos CC, Agachi PS. Pre-combustion carbon dioxide capture by gas-liquid absorption for Integrated Gasification Combined Cycle power plants. Int J Greenh Gas Control. 2012;7:1-11.

3.    Liu K, Song C, Subramani V. Hydrogen and Syngas Production and Purification Technologies. (Liu K, Song C, Subramani V, eds.). John Wiley & Sons, Inc.; 2010.

4.    Ma Y, Liao Y, Su Y, et al. Comparative investigation of different CO2 capture technologies for coal to ethylene glycol process. Processes. 2021;9(2):1-19.

5.    Barlow H, Shahi SSM. State of the Art: CCS Technologies 2024.; 2024.

6.    Kohl AL, Nielsen R. Gas Purification. 5th ed. Gulf Pub; 1997.

7.    Wang J, Shen Y, Zhang D, Tang Z, Li W. Integrated VPSA and Rectisol Process for CO2 Capture from UCG Syngas. SSRN Electron J. Published online 2022.

8.    Zaman M, Lee JH. Carbon capture from stationary power generation sources: A review of the current status of the technologies. Korean J Chem Eng. 2013;30(8):1497-1526.

9.    Porter RTJ, Fairweather M, Kolster C, Mac Dowell N, Shah N, Woolley RM. Cost and performance of some carbon capture technology options for producing different quality CO2 product streams. Int J Greenh Gas Control. 2017;57:185-195.

10.  Cuéllar-Franca RM, Azapagic A. Carbon capture, storage and utilisation technologies: A critical analysis and comparison of their life cycle environmental impacts. J CO2 Util. 2015;9:82-102.

11.  Viebahn P, Nitsch J, Fischedick M, et al. Comparison of carbon capture and storage with renewable energy technologies regarding structural, economic, and ecological aspects in Germany. Int J Greenh Gas Control. 2007;1(1):121-133.

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