Sorption-enhanced Methane Reforming Research Articles

Model validation of the Ca-Cu looping process

In this work an experimental demonstration and validation of a 1-D pseudo homogeneous reactor model for the Ca-Cu looping process is presented. The Ca-Cu looping process is a highly integrated process based on sorption-enhanced reforming of methane using CaO as sorbent, combined with chemical looping of a Cu-based oxygen carrier to provide the energy for the regeneration of the sorbent. Experiments were carried for all three involved process steps. The sorption-enhanced reforming step was studied at two different scales under different conditions. The effects of different bed compositions, operating temperatures, methane residence times and different steam-to-carbon ratios on the hydrogen production rate have been evaluated. A methane space velocity of 2.26 kgCH4h−1 kgcat−1 and a temperature range of 600–650 °C were found to be the most appropriate for optimal performance of the SER step and when increasing the steam-to-carbon ratio the hydrogen fraction produced increased.Moreover, complete cycles (consecutive steps of sorption-enhanced steam reforming, oxidation and reduction/calcination) have been performed in a medium-scale packed bed reactor (0.6 m length), where the three functional materials needed for this process were physically mixed. The Ca-Cu process was successfully demonstrated experimentally, forming 90% of H2 in the sorption enhanced reforming stage and regenerating well the sorbent in the reduction/calcination step.The experimental results obtained from the experimental campaign have been used to validate a packed bed reactor model and a good agreement between the model and the experimental data was found.

Modeling of sorption enhanced steam methane reforming in an adiabatic fixed bed reactor

Sorption enhanced methane reforming (SER), employing a CaO-based solid as a high temperature CO2 sorbent, is generally considered to be a promising route for H2 production. In this paper we present a dynamic pseudo-homogeneous model to describe the operation of a packed bed reactor in which the SER reaction is carried out under adiabatic conditions. This reactor can be implemented according to several process schemes, including a novel Ca/Cu looping process for hydrogen generation with inherent CO2 capture. The proposed SER model is based on the well-established principles of gas–solid contact and heat transfer in fixed-bed reactors and on the kinetic expressions published in the literature that describe the main reactions involved in the process. The resulting model describes the transient performance of the SER reaction and confirms the theoretical viability of this critical reaction stage in a large scale H2 production facility. It is demonstrated that the SER process can yield a CH4 conversion and H2 purity of up to 85% and 95%, respectively, under operating conditions of 923 K, 3.5 MPa, a steam/carbon ratio of 5 and a space velocity of 3.5 kg/m2 s.

Sorption properties of lithium carbonate doped CaO and its performance in sorption enhanced methane reforming

In-house prepared lithium carbonate doped CaO was tested for its CO 2 sorption properties and suitability as a CO 2 sorbent for sorption-enhanced reforming of methane. The new material demonstrated CO 2 capacity at the temperatures above the equilibrium for CaO recarbonation reaction. However, the capacity was unstable and decreased during carbonation–regeneration cycles. After sufficiently large number of cycles Li dopant escaped from the sorbent and its sorption behavior resembled to that of CaO. The main route of escape is, probably, a crossover of liquid Li 2CO 3 onto crucible in TG experiments and onto catalyst in SER tests. Sorption enhanced methane reforming at 2 bar pressure, 750 °C and H 2O to CH 4 ratio of 4 using novel sorbent yielded as high as 99.8 vol% pure hydrogen during the first cycle. In subsequent cycles the hydrogen purity drastically decreased as a result of severe catalyst poisoning by Li.