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Hydrogen Production by Sorption-Enhanced Methane Steam Reforming

Hydrogen Production by Sorption-Enhanced Methane Steam Reforming

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Fossil fuels will continue to be a major source for energy in the near future and techniques for reducing greenhouse gases, while still producing energy from such sources must be implemented. Sorption-enhanced methane steam reforming (SE-SMR) is one possible economical viable route for hydrogen production with simultaneous CO2 capture [1, 2]. In such a process, reforming of natural gas is carried out while a sorbent is co-present with the catalyst in the reactor. CO2 produced in the reactor reacts with the sorbent to make a solid carbonate, thus driving the reforming reaction towards products and exceeding the sorbent free thermodynamic equilibrium for the reactions. The sorbent is regenerated in a subsequent process step. The main reaction equations for the SE-SMR process are given below:

 

CH4(g) + H2O(g)             CO(g)  + 3H2(g)        Reforming               (1)

CO(g) + H2O(g)              CO2(g)  + H2(g)        Water-gas shift        (2)

MO(s) + CO2(g)              MCO3(s)  Sorption (MO=metal oxide)   (3)

CH4(g) + 2H2O(g)           MCO3(s)  + 4H2(g) Overall                      (4)

Reaction 1 and 2 take place during the catalytic steam reforming and is around 600 °C. Equation 3 describes the exothermic reaction between CO2 and the sorbent (calcined dolomite in our case) while the reverse of eq. 3 describes regeneration of the sorbent, typically carried out at 800-900 °C if calcined dolomite is used. Eq. 4 describes the total reaction that takes place in the reformer reactor in the SE-SMR reaction. Equation 4 is close to thermoneutral, while the regeneration is strongly endothermic and thus needs significant amount of heat to progress. The sorbent (MO) used in SE-SMR needs to be regenerated, preferably continuously, and this may be taken care of by using two connected reactors where the powder is transported between the two units. For the TCCS-5 conference, we will present our continuation work and reactor development for the SE-SMR process using our circulating fluidized bed reactor. Several experiments have been carried out to investigate various aspects of continuous hydrogen production by SE-SMR in our lab reactor system. As operating experience with the system has increased we have improved the performance of the reactor. However, more work has still to be done in order to reach optimum reaction conditions and process control. The system can potentially be applied for studying many different aspects of SE-SMR. The presented reactor system is modular and hence facilitating change of components and modifications for future experiments, both for SE-SMR and other chemical looping processes.

 

[1]       D.P. Harrison, Ind. Eng. Chem. Res. 47 (2008) 6486

[2]        E. Ochoa-Fernandez, G.Haugen, T. Zhao, M. Rønning, I. Aartun, B. Børresen, E. Rytter, M. Rønnekleiv, D. Chen, Green Chem. 9 (2007) 1

 

 

Emneord
Sorption enhanced steam methane reforming
Språk
Engelsk
Presentert på
5th CCS Conference
Sted
Trondheim
Dato
2009-06-16 - 2009-06-17
Arrangør
SINTEF-NTNU
Publikasjons-id
SINTEF S14090