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=== Adsorption process ===
=== Adsorption process ===
[[File:Adsorbimento - layout rigenerazione.svg|thumb|upright=1.8|Process scheme of a pressure swing unit.]]
{{see|Adsorption}}
{{see|Adsorption}}
Adsorption is the phenomenon of [[sorption]] of gases or [[solutes]] on solid or liquid surfaces. The adsorption on solid surface occurs when some substances collide with the solid surface creating bonds with the atoms or the molecules of the solid surface. There are two main adsorption processes: physical adsorption and chemical adsorption. The first one is the result of the interaction of intermolecular forces. Since weak bonds are formed, the adsorbed substance can be easily separated. In chemical adsorption, chemical bonds are formed, meaning that the absorption or release of adsorption heat and the activation energy are larger respect to physical adsorption. These two processes often take place simultaneously. The adsorbent material is then regenerated through [[desorption]], which is the opposite phenomenon of sorption, releasing the captured substance from the adsorbent material.<ref>{{cite journal |last1=HaidongHu |last2=KeXu |title=Physicochemical technologies for HRPs and risk control |journal=High-Risk Pollutants in Wastewater |date=2020-01-01 |pages=169–207 |doi=10.1016/B978-0-12-816448-8.00008-3 |url=https://doi.org/10.1016/B978-0-12-816448-8.00008-3 |language=en}}</ref>
Adsorption is the phenomenon of [[sorption]] of gases or [[solutes]] on solid or liquid surfaces. The adsorption on solid surface occurs when some substances collide with the solid surface creating bonds with the atoms or the molecules of the solid surface. There are two main adsorption processes: physical adsorption and chemical adsorption. The first one is the result of the interaction of intermolecular forces. Since weak bonds are formed, the adsorbed substance can be easily separated. In chemical adsorption, chemical bonds are formed, meaning that the absorption or release of adsorption heat and the activation energy are larger respect to physical adsorption. These two processes often take place simultaneously. The adsorbent material is then regenerated through [[desorption]], which is the opposite phenomenon of sorption, releasing the captured substance from the adsorbent material.<ref>{{cite journal |last1=HaidongHu |last2=KeXu |title=Physicochemical technologies for HRPs and risk control |journal=High-Risk Pollutants in Wastewater |date=2020-01-01 |pages=169–207 |doi=10.1016/B978-0-12-816448-8.00008-3 |url=https://doi.org/10.1016/B978-0-12-816448-8.00008-3 |language=en}}</ref>

Revision as of 11:39, 18 June 2021

The sorption enhanced water gas shift (SEWGS) is a technology that combines a pre-combustion carbon capture process with the water gas shift reaction (WGS) in order to produce a hydrogen rich stream from the syngas fed to the SEWGS reactor.[1]

The water gas shift reaction converts the carbon monoxide into carbon dioxide:

CO + H2O ⇌ CO2 + H2

while carbon dioxide is captured and removed through an adsorption process.[1]

The in-situ CO2 adsorption and removal shifts the water gas shift reaction to the right-hand side completely converting the CO and maximizing the production of high pressure hydrogen.[1]

From the beginning of the second decade of 21th century this technology started gaining attention since it shows advantages over carbon capture conventional technologies and because hydrogen is considered the energy carrier for the future.[2][3]

Process

Ordinary water gas shift reaction on top. SEWGS concept on bottom.

The SEWGS technology is the combination of the water gas shift reaction with the adsorption of carbon dioxide on a solid material. Typical temperature and pressure ranges are 350-550°C and 20-30 bar. The SEWGS reactor inlet gas is usually a mixture of hydrogen, CO and CO2, where steam is added to convert CO into CO2.[4]

The conversion of carbon monoxide into carbon dioxide is enhanced shifting the reaction equilibrium through the adsorption and removal of CO2 which is one of the product species.[1]

The SEWGS technology is based on a multi-bed pressure swing adsorption (PSA) unit in which the vessels are filled with the water gas shift catalyst and the CO2 adsorbent material.  Each vessel is subjected to a series of processes. In the sorption/reaction step, a high pressure hydrogen rich stream is produced, while during sorbent regeneration a CO2 rich stream is generated.[5]

The process starts with the feeding of syngas to the SEWGS reactor, where the CO2 is adsorbed and a hydrogen-rich stream is produced. The regeneration of the first vessel starts when the sorbent material is saturated by CO2, directing the feed stream to another vessel. After the regeneration, the vessels are re-pressurized. A multi-bed configuration is necessary to guarantee a continuous production of hydrogen and carbon dioxide. The optimal number of beds usually varies between 6 and 8.[5]

Water gas shift reaction

Further information: Water-gas shift reaction

The water gas shift reaction is the reaction between carbon monoxide and steam to form hydrogen and carbon dioxide:

CO + H2O ⇌ CO2 + H2

This reaction was discovered by Felice Fontana and nowadays is adopted in a wide range of industrial processes such as in the production process of ammonia, hydrocarbons, methanol, hydrogen and other chemicals. In the industrial practice two water gas shift sectons are necessary, one at high temperature and one at low temperature with an intersystem cooling.[6]

Adsorption process

Process scheme of a pressure swing unit.
Further information: Adsorption

Adsorption is the phenomenon of sorption of gases or solutes on solid or liquid surfaces. The adsorption on solid surface occurs when some substances collide with the solid surface creating bonds with the atoms or the molecules of the solid surface. There are two main adsorption processes: physical adsorption and chemical adsorption. The first one is the result of the interaction of intermolecular forces. Since weak bonds are formed, the adsorbed substance can be easily separated. In chemical adsorption, chemical bonds are formed, meaning that the absorption or release of adsorption heat and the activation energy are larger respect to physical adsorption. These two processes often take place simultaneously. The adsorbent material is then regenerated through desorption, which is the opposite phenomenon of sorption, releasing the captured substance from the adsorbent material.[7]

In the SEWGS technology, the pressure swing adsorption (PSA) process is employed to regenerate the adsorbent material and produce a CO2 rich stream. The process is similar to the one conventionally used for air separation, hydrogen purification and other gas separations.[8]

Conventional technology for carbon dioxide removal

Process schemes for pre-combustion CO2 capture. Top: conventional scheme for a conventional technology. Bottom: scheme for the SEWGS concept.

The technology industrially used for carbon dioxide removal is amine washing technology based on chemical absorption of carbon dioxide. In chemical absorption, reactions between the absorbed substance (CO2) and the solvent are formed producing a rich liquid. The rich liquid then enters the desorption column where carbon dioxide is separated from the sorbent which is re-used for CO2 absorption. Ethanolamine (C2H7NO), diethanolamine (C4H11NO2), triethanolamine (C6H15NO3) mono-ethanolamine (C2H7NO) and methyl-diethanolamine (C5H13NO2) are commonly used for the removal of CO2.[9]

Advantages of SEWGS over conventional technologies

The SEWGS technology shows some advantages when compared to traditional technologies adopted for pre-combustion removal of carbon dioxide. The traditional technologies, indeed, need two water gas shift reactors (a high temperature and a low temperature stage) to have a high conversion of carbon monoxide into carbon dioxide with an intermediate cooling stage between the two reactors. In addition, another cooling stage is necessary at the outlet of the second WGS reactor for the CO2 capture with a solvent. Furthermore, the hydrogen rich stream at the outlet of SEWGS section can be directly fed into a gas turbine while the hydrogen rich stream produced by the traditional route needs a further heating stage.[2]

Applications

The importance of this technology is directly related to the problem of global warming and the mitigation of the carbon dioxide emissions. In hydrogen economy, hydrogen, considered a clean energy carrier, will replace the fuels with pollution problems, since it doesn't produce any pollutants and have a high energy content. Therefore, interest around hydrogen as an alternative to fossil fuel started increasing from the beginning of second decade of 21th century.[3]

The SEWGS technology, through which it is possible to produce high-purity hydrogen without need for further purification processes, finds a possible application in a wide range of industrial processes, such as in the production of electricity from fossil fuels or in the iron and steel industry.[2][5][10]

The integration of the SEWGS process in natural gas combined cycle (NGCC) and integrated gasification combined cycle (IGCC) power plants has been investigated since it would allow the production of electricity from natural gas or coal with almost-zero emissions. In NGCC power plant the carbon capture achieved is around 95% with a CO2 purity over 99%, while in IGCC power plant the carbon capture ratio is around 90% with a CO2 purity of 99%.[5][10]

The investigation of SEWGS integration in steel mills started during the second decade of 21th century. The goal is to reduce the carbon footprint of this industrial process that is responsible of the 6% of total global CO2 emissions and 16% of the emissions generated by industrial processes.[11]

The CO2 captured and removed can be stored or used for the production of high value chemical products.[11]

Sorbents for SEWGS process

The reactor vessels are loaded with sorbent pellets. Sorbent must have the following features:[5]

  • high CO2 capacity and selectivity over H2
  • low H2O adsorption
  • low specific cost
  • mechanical stability under pressure and temperature variation
  • chemical stability in the presence of impurities
  • easily regeneration by steam

Different sorbents materials have been investigated in order to be used in SEWGS. Some of them are:

  • K2CO3-promoted hydrotalcite[4][12]
  • potassium promoted alumina[12]
  • Na–Mg double salt[13]
  • CaO[14]

Potassium promoted hydrotalcite is the sorbent material that has been most studied for SEWGS application.[4]

Its principal characteristics are:[10]

  • low cost
  • sufficiently high CO2 cyclic working capacity
  • fast adsorption kinetics
  • good mechanical stability

See also

References

  1. ^ a b c d Jansen, Daniel; van Selow, Edward; Cobden, Paul; Manzolini, Giampaolo; Macchi, Ennio; Gazzani, Matteo; Blom, Richard; Heriksen, Partow Pakdel; Beavis, Rich; Wright, Andrew (2013-01-01). "SEWGS Technology is Now Ready for Scale-up!". Energy Procedia. 37: 2265–2273. doi:10.1016/j.egypro.2013.06.107. ISSN 1876-6102.
  2. ^ a b c Manzolini, G.; Giuffrida, A.; Cobden, P.D.; van Dijk, H.A.J.; Ruggeri, F.; Consonni, F. (2020-03-01). "Techno-economic assessment of SEWGS technology when applied to integrated steel-plant for CO2 emission mitigation". International Journal of Greenhouse Gas Control. 94: 102935. doi:10.1016/j.ijggc.2019.102935. ISSN 1750-5836.
  3. ^ a b Chan Hyun Lee; Ki Bong Lee (2014-10-22). "Application of one-body hybrid solid pellets to sorption-enhanced water gas shift reaction for high-purity hydrogen production". International Journal of Hydrogen Energy. 39 (31): 18128–18134. doi:10.1016/j.ijhydene.2014.04.160. ISSN 0360-3199.
  4. ^ a b c Bakken, Egil; Cobden, Paul D.; Henriksen, Partow Pakdel; Håkonsen, Silje Fosse; Spjelkavik, Aud I.; Stange, Marit; Stensrød, Ruth Elisabeth; Vistad, Ørnulv; Blom, Richard (2011). "Development of CO2 sorbents for the SEWGS process using high throughput techniques". Energy Procedia. 4: 1104–1109. doi:10.1016/j.egypro.2011.01.161.
  5. ^ a b c d e Manzolini, Giampaolo; Macchi, Ennio; Binotti, Marco; Gazzani, Matteo (March 2011). "Integration of SEWGS for carbon capture in natural gas combined cycle. Part A: Thermodynamic performances". International Journal of Greenhouse Gas Control. 5 (2): 200–213. doi:10.1016/j.ijggc.2010.08.006.
  6. ^ Baraj, Erlisa; Ciahotný, Karel; Hlincík, Tomas (2021-03-15). "The water gas shift reaction: Catalysts and reaction mechanism". Fuel. 288: 119817. doi:10.1016/j.fuel.2020.119817. ISSN 0016-2361.
  7. ^ HaidongHu; KeXu (2020-01-01). "Physicochemical technologies for HRPs and risk control". High-Risk Pollutants in Wastewater: 169–207. doi:10.1016/B978-0-12-816448-8.00008-3.
  8. ^ Manzolini, Giampaolo; Macchi, Ennio; Binotti, Marco; Gazzani, Matteo (March 2011). "Integration of SEWGS for carbon capture in natural gas combined cycle. Part A: Thermodynamic performances". International Journal of Greenhouse Gas Control. 5 (2): 200–213. doi:10.1016/j.ijggc.2010.08.006.
  9. ^ Li Xie; Jun Xu; Yidie Zhang; YingyingHe (2020-01-01). "Biogas upgrading". Advances in Bioenergy. 5: 309-344. doi:10.1016/bs.aibe.2020.04.006. ISSN 2468-0125.
  10. ^ a b c Gazzani, Matteo; Macchi, Ennio; Manzolini, Giampaolo (2013-03-01). "CO2 capture in integrated gasification combined cycle with SEWGS – Part A: Thermodynamic performances". Fuel. 105: 206–219. doi:10.1016/j.fuel.2012.07.048. ISSN 0016-2361.
  11. ^ a b (Eric) van Dijk, H. A. J.; Cobden, Paul D.; Lukashuk, Liliana; de Water, Leon van; Lundqvist, Magnus; Manzolini, Giampaolo; Cormos, Calin-Cristian; van Dijk, Camiel; Mancuso, Luca; Johns, Jeremy; Bellqvist, David (2018-10-01). "STEPWISE Project: Sorption-Enhanced Water-Gas Shift Technology to Reduce Carbon Footprint in the Iron and Steel Industry". Johnson Matthey Technology Review. 62 (4): 395–402. doi:10.1595/205651318X15268923666410. ISSN 2056-5135.
  12. ^ a b Coenen, Kai; Gallucci, Fausto; Hensen, Emiel; van Sint Annaland, Martin (2018-05-01). "CO2 and H2O chemisorption mechanism on different potassium-promoted sorbents for SEWGS processes". Journal of CO2 Utilization. 25: 180–193. doi:10.1016/j.jcou.2018.04.002. ISSN 2212-9820.
  13. ^ Chan Hyun Lee; Ki Bong Lee (2017-11-01). "Sorption-enhanced water gas shift reaction for high-purity hydrogen production: Application of a Na-Mg double salt-based sorbent and the divided section packing concept". Applied Energy. 205: 316–322. doi:10.1016/j.apenergy.2017.07.119. ISSN 0306-2619.
  14. ^ Zivkovic, Luka A.; Pohar, Andrej; Likozar, Blaz; Nikacevic, Nikola M. (2016-09-15). "Kinetics and reactor modeling for CaO sorption-enhanced high-temperature water–gas shift (SE–WGS) reaction for hydrogen production". Applied Energy. 178: 844–855. doi:10.1016/j.apenergy.2016.06.071. ISSN 0306-2619.

Projects in which SEWGS technology is investigated:

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