Oxygen Transfer Material Research Articles

Techno economic comparison of combustor integrated steam reforming and sorption enhanced chemical looping steam reforming of methanol

Methanol steam reforming (MSR) has gained significant attention for in-situ hydrogen (H2) production. To overcome the high energy requirement in the process, two modified methods such as combustor integrated steam reforming (CISR), and sorption enhanced chemical looping steam reforming (SE-CLSR) are widely used for the production of H2. In the present work, a techno-economic comparison of CISR and SE-CLSR models has been carried out using Aspen Plus V11to assess the economic viability of hydrogen generation by MSR process. SE-CLSR model is developed considering NiO as an oxygen transfer material (OTM). Simulations have been performed to observe a strong dependence of methanol conversion, hydrogen yield, CO selectivity with different operating conditions like temperature, steam to methanol (S/M) ratio, catalyst weight to methanol molar ratio. The sensitivity analysis of the considered models is performed to obtain the optimum operating conditions. The hydrogen production cost is estimated as 2.66 $/kg and 2.79 $/kg from CISR and SE-CLSR processes, respectively.

Sorption enhanced–chemical looping steam methane reforming: Optimizing the thermal coupling of regeneration in a fixed bed reactor

Sorption enhanced–chemical looping steam methane reforming is a promising process for hydrogen production. In this process, the reformer contains, in addition to a solid CO2 sorbent, an oxygen transfer material (OTM). Ιn–situ CO2 capture by the sorbent shifts the overall reaction to the products' side, leading to high purity H2 production in a single step. The saturated sorbent is then regenerated in a second reactor at higher temperatures. The OTM is simultaneously reoxidized, generating significant amount of heat which is in–situ used for sorbent's regeneration. In this work, the optimization of heat coupling during the regeneration step of the intensified process was studied experimentally using a NiO/ZrO2 OTM–reforming catalyst, mechanically mixed with a CaZrO3–promoted CaO sorbent. The effect of two key operating parameters during regeneration was considered: the residence time of the feed stream and the type of oxidant (air, pure O2). Higher space velocities increased the percentage of CaCO3 decomposition without external heat supply. The use of pure O2 can provide in situ 47% of the heat requirements of the sorbent's regeneration, a value which is very close to the theoretical degree of autothermicity under the investigated conditions (57%), while producing a pure, ready for sequestration CO2 stream.

Hybrid catalytic materials with CO2 capture and oxygen transfer functionalities for high–purity H2 production

In this work, we report the development and performance evaluation of hybrid, multifunctional catalytic materials based on NiO and CaO for the Sorption Enhanced Chemical Looping Steam Methane Reforming process (SE–CL–SMR). The multifunctional materials with various NiO/CaO/inert ratios were prepared via the sol–gel auto–combustion method. Testing under SE–CL–SMR conditions was conducted in a fixed bed reactor unit. High CH4 conversion is achieved over all developed materials, resulting in the production of high–purity hydrogen (> 95 %) at 650 °C and steam/carbon ratio of 3. Compared to a mixed bed of sorbent and oxygen transfer material (OTM), operation with the multifunctional material allows for more efficient use of the heat generated by Ni reoxidation during regeneration due to the direct heat transfer between the OTM and sorbent phases. Although higher NiO and CaO content in the hybrid material translates to greater loss of autothermicity during regeneration with increasing number of cycles, the decrease of the inert fraction reduces up to ∼25 % the volume of the bed compared to the respective sorbent/OTM mixture. Such an outcome clearly demonstrates the benefit of using a multifunctional material for the intensified SE–CL–SMR process.

Reaction-based kinetic model for the reduction of supported NiO oxygen transfer materials by CH4

Abstract The focus of this study is to assess the reaction rate-based kinetics of three NiO-based oxygen transfer materials (OTMs) supported on ZrO2, Al2O3 and SiO2 under CH4 reduction. Both NiO weight change data and gaseous phase composition from TGA-MS tests are utilized for the elucidation of the reaction scheme. We show that mainly CH4, as well as CO and H2 (primary NiO reduction products by CH4), are involved in the reduction process under a varying extent that depends on the support used. The developed kinetic model is first order dependent on the concentration of the main reductant at each reaction and a function of the NiO/Ni concentration. On ZrO2, NiO is exclusively reduced by CH4 via both total and partial oxidation. On the other hand, in addition to CH4, CO and H2 also contribute to NiO reduction on Al2O3 and SiO2. Still, total and partial CH4 oxidation are the dominant routes. In the case of SiO2 in particular, the reduction rate of NiO by CO and H2 is the highest among all OTMs. The CH4 decomposition reaction, catalyzed by the metallic nickel sites, also takes place via the Langmuir-Hinshelwood mechanism after the completion of the NiO reduction. The rate of this reaction correlates with the surface area of the materials due to the higher population of active metallic nickel sites on the surface, leading to carbon deposition in the order NiO/Al2O3 > NiO/SiO2 > NiO/ZrO2.

Hydrogen production from bio-oil: A thermodynamic analysis of sorption-enhanced chemical looping steam reforming

The steam reforming of pyrolysis bio-oil is one proposed route to low carbon hydrogen production, which may be enhanced by combination with advanced steam reforming techniques. The advanced reforming of bio-oil is investigated via a thermodynamic analysis based on the minimisation of Gibbs Energy. Conventional steam reforming (C-SR) is assessed alongside sorption-enhanced steam reforming (SE-SR), chemical looping steam reforming (CLSR) and sorption-enhanced chemical looping steam reforming (SE-CLSR). The selected CO2 sorbent is CaO(s) and oxygen transfer material (OTM) is Ni/NiO. PEFB bio-oil is modelled as a surrogate mixture and two common model compounds, acetic acid and furfural, are also considered. A process comparison highlights the advantages of sorption-enhancement and chemical looping, including improved purity and yield, and reductions in carbon deposition and process net energy balance.The operating regime of SE-CLSR is evaluated in order to assess the impact of S/C ratio, NiO/C ratio, CaO/C ratio and temperature. Autothermal operation can be achieved for S/C ratios between 1 and 3. In autothermal operation at 30 bar, S/C ratio of 2 gives a yield of 11.8 wt%, and hydrogen purity of 96.9 mol%. Alternatively, if autothermal operation is not a priority, the yield can be improved by reducing the quantity of OTM. The thermodynamic analysis highlights the role of advanced reforming techniques in enhancing the potential of bio-oil as a source of hydrogen.

Kinetics of perovskite-like oxygen carriers for chemical looping air separation

Chemical looping air separation gives an energy-efficient choice for oxygen production. We performed kinetic analysis of YBaCo4O7+δ, Y0.95Ti0.05BaCo4O7+δ, Y0.2Ti0.05Dy0.75BaCo4O7+δ, and Y0.15Zr0.1Dy0.75BaCo4O7+δ oxygen carriers in a CLAS process. TG experiments were conducted with heating rates of 0.5, 1, and 2 °C/min in a thermogravimetric analyzer. Further exploration is required to develop an appropriate oxygen carrier. So, we used the model-free approach, Starink method, to evaluate the apparent activation energy. And, masterplots method was applied to determine the most probable mechanism function. The results show that the distributed activation energies of oxidation/reduction process are 189.42/286.22 kJ/mol, 197.70/324.87 kJ/mol, 195.41/310.4 kJ/mol, and 192.20/293.53 kJ/mol for YBaCo4O7+δ, Y0.95Ti0.05BaCo4O7+δ, Y0.2Ti0.05Dy0.75BaCo4O7+δ, and Y0.15Zr0.1Dy0.75BaCo4O7+δ oxygen carriers, respectively. Random nucleation and nuclei growth A model is the most suitable for oxidation process. The A model and D are the most suitable for the reduction process. Regarding YBaCo4O7+δ, Y0.95Ti0.05BaCo4O7+δ, Y0.2Ti0.05Dy0.75BaCo4O7+δ, and Y0.15Zr0.1Dy0.75BaCo4O7+δ kinetic, oxygen transfer materials are rate-determined by nucleation and nuclei growth. For reduction kinetic, the gas diffusion stage could also become a dominant step.

High purity hydrogen production from sorption enhanced chemical looping glycerol reforming: Application of NiO-based oxygen transfer materials and potassium promoted Li2ZrO3 as CO2 sorbent

Ni based oxygen transfer materials (OTMs) and Li2ZrO3 based sorbent have been synthesized for their potential use in a sorption enhanced chemical looping steam reforming (SE-CLSR) process. Ni based OTMs were firstly tested under chemical looping steam reforming (CLSR) process and the gaseous products with temperature variety during this process were measured and analyzed. Experimental results indicated that both of the OTMs exhibited good activities and stability during multiple glycerol reduction-air oxidation cycles towards H2 production. The desired maximum hydrogen selectivities of 87.9% and 84.7% were obtained for NiO/NiAl2O4 and NiO/ZrO2 for steam to carbon ratio of 3 at 550°C. The fuel feed step of reduction process could be divided into two periods with the OTMs possessing a dual function of oxygen carrier and catalyst. The decrease of conversions and selectivity for both OTMs was mainly due to the coke deposition, which reduced the catalytic effect in the reforming reaction as well as the oxygen transfer effect in the reduction reaction. Sorption enhanced chemical looping steam reforming (SE-CLSR) process for H2 production with in-situ CO2 removal was carried out with OTM/sorbent ratio of 1 and multi-cyclic reaction/regeneration processes under 550°C/850°C with a steam/carbon ratio of 3 was also achieved. H2 purity were both enhanced by the two OTMs and sorbent in SE-CLSR. Therefore, it is possible to utilize oxygen from NiO and steam to oxidize glycerol, while enhancing the water-gas-shift reaction by capturing CO2 at the same time.

Chemical equilibrium analysis of hydrogen production from shale gas using sorption enhanced chemical looping steam reforming

Detailed chemical equilibrium analysis based on minimisation of Gibbs Energy is conducted to illustrate the benefits of integrating sorption enhancement (SE) and chemical looping (CL) together with the conventional catalytic steam reforming (C-SR) process for hydrogen production from a typical shale gas feedstock. CaO(S) was chosen as the CO2 sorbent and Ni/NiO is the oxygen transfer material (OTM) doubling as steam reforming catalyst. Up to 49% and 52% rise in H2 yield and purity respectively were achieved with SE-CLSR with a lower enthalpy change compared to C-SR at S:C 3 and 800K. A minimum energy of 159kJ was required to produce 1mol of H2 at S:C 3 and 800K in C-SR process, this significantly dropped to 34kJ/mol of produced H2 in the CaO(S)/NiO system at same operating condition without regeneration of the sorbent, when the energy of regenerating the sorbent at 1170K was included, the enthalpy rose to 92kJ/mol H2, i.e., significantly lower than the Ca-free system. The presence of inert bed materials in the reactor bed such as catalyst support or degraded CO2 sorbent introduced a very substantial heating burden to bring these materials from reforming temperature to sorbent regeneration temperature or to Ni oxidation temperature. The choice of S:C ratio in conditions of excess steam represents a compromise between the higher H2 yield and purity and lower risk of coking, balanced by the increased enthalpy cost of raising excess steam.

Reduction and oxidation kinetic modeling of NiO-based oxygen transfer materials

Abstract This study investigates the redox kinetics of four NiO-based oxygen transfer materials (OTMs) supported on Al 2 O 3 , TiO 2 , SiO 2 and ZrO 2 . The OTMs were tested and evaluated under twenty consecutive methane reduction/air oxidation cycles. Several solid-state kinetic models were consecutively and optimally screened for each OTM at different redox cycles. The use of different supports resulted in different forms of the redox kinetics. NiO/Al 2 O 3 and NiO/TiO 2 reduction kinetics were rate-determined by chemical reaction and fitted via the Unreacted Shrinking Core Model. On the other hand, NiO/ZrO 2 and NiO/SiO 2 reduction was found to proceed via nucleation and subsequent nuclei growth and was suitably described with Avrami-Erofeev models. The use of different types of kinetic models is attributed to differences in strength of metal-support interactions. Specifically, the strong interaction between NiO and Al 2 O 3 and TiO 2 creates NiO-support interfaces where Ni nuclei are formed very fast, rendering the chemical reaction the governing step of the reduction process. When NiO is supported on SiO 2 and ZrO 2 , the interaction is weak and NiO basically behaves like free NiO, reducing via the slow formation of homogeneous nuclei on the surface and the subsequent faster growth of Ni domains. Regarding Ni oxidation kinetics, all OTMs were rate-determined by nucleation and nuclei growth. NiO/Al 2 O 3 and NiO/TiO 2 OTMs followed an Avrami-Erofeev model approach for all considered cycles, while NiO/ZrO 2 oxidation kinetics were described via a Prout-Tompkins model that considered a short but still, significant nucleation period.

Energy efficient sorption enhanced-chemical looping methane reforming process for high-purity H2 production: Experimental proof-of-concept

High purity H2 was produced by a novel low-energy sorption enhanced steam methane reforming process by introducing a second loop in order to provide part of the required heat for the endothermic sorbent calcination in the regeneration stage. The feasibility of the intensified reforming process was demonstrated experimentally over a mixture of a bifunctional NiO-based oxygen transfer material/reforming catalyst supported on ZrO2, and a ZrO2-promoted CaO-based CO2 sorbent. The experiments were performed in a bench-scale fixed bed reactor unit. The influence of operating parameters, such as reformer’s temperature, steam/methane and NiO/CaO molar ratios and space velocity of the feed stream, was investigated in order to determine the optimum operating conditions and assess the full potential of the combined process over the two solids. The presence of the CO2 sorbent in the reactor facilitated H2 production of high purity. Equilibrium concentrations were obtained over all studied conditions, even at very high space velocities. The process was further demonstrated with a continuous cyclic test of 20 reforming/regeneration cycles at a temperature of 650°C. The CO2 sorbent and the oxygen transfer material exhibited excellent stability without deterioration in performance for 20 consecutive cycles, corresponding to more than 60h of testing. H2 concentration over 95% was achieved throughout the sorbent’s prebreakthrough region during the reduction/reforming/carbonation stage. During the reoxidation/calcination step, the highly exothermic Ni oxidation provided adequate heat to raise the temperature of the solids and decompose up to 45% of the saturated sorbent without external heating.

메탄을 이용한 매체 순환 개질 시스템을 위한 Ni-YSZ 촉매에서의 Y에 따른 촉매 반응 특성 연구

Nickel based oxygen transfer materials supported on two different YSZs were tested to evaluate their performance in methane chemical-looping reforming. The oxygen transfer materials of YSZs were selected with different amount of the doped yittrium in the <TEX>$ZrO_2$</TEX> structure. The yittrium of 8 mol% stabilized the zirconia oxide to a cubic structure compare to the 3 mol% doping, which is known to be a good for oxygen transfer. Various nickel amounts (16wt.%, 32wt.%, 48wt.%) were loaded on the selected supports. The nickel amount of 32% shows the optimized catalyst structure with good physical properties and reducibility from the XRD, BET and H2-TPR analysis, especially when the support of 8YSZ was used. From the methane chemical-looping reforming, hydrogen was produced by methane decomposition catalyzed by Ni on both YSZs. Comparing two YSZ supports of 3YSZ and 8YSZ during the cycling tests, the catalyst with 8YSZ (Ni 32%) exhibits not only the higher methane conversion and hydrogen production but also a faster reaction rate reaching to the stable point.

Activity study of NiO-based oxygen carriers in chemical looping steam methane reforming

This study evaluates the performance of NiO-based oxygen carriers supported on ZrO2, TiO2, SiO2, Al2O3 and NiAl2O4 as conventional reforming catalysts at low temperature (650°C) as well as oxygen transfer materials (OTMs) for chemical looping steam methane reforming. Conventional reforming experiments with pre-reduced OTMs demonstrated satisfactory performance of NiO/Al2O3, NiO/ZrO2 and NiO/NiAl2O4 at 650°C, with less than 8% relative decrease in conversion after 10h time-on-stream. On the other hand, NiO/SiO2 and NiO/TiO2 were found to have low activity (<50% initial CH4 conversion) and deactivated rapidly, eventually dropping to less than 10% CH4 conversion after 2h on stream. The three most promising materials were tested under chemical looping steam methane reforming conditions for twenty consecutive redox cycles in a fixed bed flow unit. NiO/ZrO2 exhibited good activity with initial CH4 conversion higher than 80% and had very good stability. Deactivation was minimal after 20 consecutive redox cycles, corresponding to 20h exposure to CH4/steam. NiO/Al2O3 and NiO/NiAl2O4 demonstrated similar high initial activity, but also high deactivation, leading to methane conversion of 59 and 63% conversion respectively at the end of the test.

NiO supported on Al2O3 and ZrO2 oxygen carriers for chemical looping steam methane reforming

Two nickel based oxygen transfer materials (OTMs) supported on alumina and zirconia were tested for their potential use in chemical looping reforming. Zirconia supported (Ni–Zr) OTM exhibited good redox activity and stability during multiple CH4 reduction-air oxidation cycles in a thermogravimetric unit. Alumina supported OTM (Ni–Al) showed increasing degree of reduction during the first 12 cycles, due to reduction of NiAl2O4 species, followed by stable performance during the last 8 redox cycles. Hydrogen was produced by methane decomposition catalyzed by Ni on both OTMs. Decrease in carbon deposition and hydrogen production with increasing number of cycles is attributed to sintering of nickel during redox cycles. Steam methane reforming experiments in a fixed bed reactor showed that Ni–Zr OTM is superior to the Ni–Al OTM in terms of stability during 20 cycles of reduction/reforming and reoxidation at 650 °C and 850 °C respectively.

Thermodynamic analysis of hydrogen production via chemical looping steam methane reforming coupled with in situ CO2 capture

In this study, a detailed thermodynamic analysis of the sorption enhanced chemical looping reforming of methane (SE-CL-SMR), using CaO and NiO as CO2 sorbent and oxygen transfer material respectively, was conducted. The effect of different parameters, such as reactor temperature, pressure, H2O/CH4 ratio, CaO/CH4 ratio and CaO/NiO ratio was investigated. Moreover, the use of different sweep gases and oxidants for the re-oxidation/calcination cycle, like pure oxygen, air, steam and CO2, was specifically addressed. Conventional steam reforming (SMR) and sorption enhanced steam reforming (SE-SMR) were also investigated for comparison reasons.The results of thermodynamic analysis show that there are significant advantages of both sorption enhanced processes compared to conventional steam reforming. Presence of CaO sorbent in the reformer leads to higher methane conversion, hydrogen purity and yield at low temperatures (∼650°C). Addition of the oxygen carrier, in the chemical looping reforming concept, minimizes thermal requirements of the process, and results in superior performance compared to SE-SMR and SMR processes. A negative effect from NiO addition is reduction in hydrogen production (due to the reaction of part of methane with NiO to form CO/CO2). Hydrogen yield is up to 11% lower compared to SE-SMR for a NiO/CaO ratio of 0.7. It was found that only pure O2 can be used for re-oxidation/regeneration in order to reduce the energy requirements of the SE-CL-SMR process up to 26% compared to SE-SMR and up to 55% compared to conventional SMR.

Thermodynamic Analysis of Hydrogen Production via Chemical Looping Steam Methane Reforming Coupled with in Situ CO2 Capture

Abstract A detailed thermodynamic analysis of the sorption enhanced chemical looping reforming of methane (SE-CL-SMR), using CaO and NiO as CO 2 sorbent and oxygen transfer material (OTM) respectively, was conducted. Conventional reforming (SMR) and sorption enhanced reforming (SE-SMR) were also investigated for comparison reasons. The results of the thermodynamic analysis show that there are significant advantages of both sorption enhanced processes compared to conventional reforming. The presence of CaO leads to higher methane conversion and hydrogen purity at low temperatures. Addition of the OTM, in the SE-CL-SMR process concept, minimizes the thermal requirements and results in superior performance compared to SE-SMR and SMR in a two-reactor concept with use of pure oxygen as oxidant/sweep gas.

Thermodynamic Analysis of Glycerol Steam Reforming using Calcium Oxide and Iron Oxide for High-Purity Hydrogen Production

Abstract A thermodynamic analysis of glycerol steam reforming in the presence of a CO2 adsorbent (CaO) and solid oxygen transfer material (Fe2O3) for high-purity hydrogen production was performed using the Gibbs free energy minimization method. CO in reformate gas was reduced via CO oxidation by Fe2O3 into CO2 coupled with in situ CO2 capture by CaO. The high-purity hydrogen produced without using a downstream reactor has potential application in proton exchange membrane fuel cells (PEMFCs). The influence of temperature (300–1000 °C), pressure (0.1–1.0 MPa), and mole ratios of H2O/glycerol (1–10), CaO/glycerol (0–6), and Fe2O3/glycerol (0–6) on equilibrium gas compositions and carbon formation was evaluated. The produced gas (99.8 mol% H2 and 12.8 ppm CO) was obtained without carbon formation under the optimal conditions (450 °C, 0.1 MPa, CaO/glycerol mole ratio of 3, Fe2O3/glycerol mole ratio of 3 and H2O/glycerol mole ratio of 10), and can be directly used in PEMFCs. However, further optimizations are needed.

Separation of hydrogen from syngas using a chemical-looping cycle

A novel, modified CaO for use as a CO2 sorbent was prepared by dipping 2.0wt.% V2O5 in CaO. A vanadate, Ca2V2O7, was generated in the modified CaO and analyzed via X-ray diffraction. The experiments show that Ca2V2O7 neither adsorbed CO2 nor improved the microstructure of the sorbent; however, it accelerated the CO2 capture rate of CaO, as well as the decomposition rate of CaCO3, during the carbonation/calcinations cycles, thereby improving the CO2 capture capacity of the CaO-based sorbent and reducing the energy consumption of calcination. A process that separates hydrogen from syngas has been investigated by combing the chemical looping of a Fe-based catalyst (as the oxygen-transfer material) and that of the modified CaO (as the CO2 sorbent) in a fixed-bed reactor. Two operational stages, one for hydrogen enrichment and the other for solid regeneration, were alternately implemented under atmospheric pressure. The effects of the gas flow velocity, temperature, solid composition, and steam concentration on the hydrogen yield during the enrichment stage were investigated. The obtained information was used to optimize the operational conditions of the enrichment stage, and a hydrogen purity above 99.5% and a hydrogen yield reaching 27.91mmol/gFecatalyst were achieved. A total of 13 cycles were completed using the same solids. The regeneration of iron oxide during each regeneration stage reached 98% and that of the modified CaO was above 94%; however, a gradual decline in the performance of the solids after the third cycle occurred because of sorbent sintering.

Biomass pyrolysis oils for hydrogen production using chemical looping reforming

This study considers the feasibility of using highly oxygenated and volatile pyrolysis oils from biomass wastes as sustainable liquid fuels for conversion to a hydrogen-rich syngas using the chemical looping reforming process in a packed bed. Pine oil and palm empty fruit bunches oil- ‘EFB’- were investigated with a Ni/Al2O3 catalyst doubling as oxygen transfer material (OTM). The effect of molar steam to carbon ratio (S/C) and weight hourly space velocity were investigated at 600 °C and atmospheric pressure on the fuel and steam conversion, the H2 yield and the H- and C-products distribution. With a downward fuel feed configuration and using a H2-reduced catalyst, maximum averaged fuel conversions of ∼97% for pine oil and 89% for EFB oil were achieved at S/C ratios of 2.3 and 2.6 respectively (on a water-free oil basis). This produced H2 with a yield efficiency of approximately 60% for pine oil and 80% for EFB oil notwithstanding equilibrium limitations, and with little CH4 by-product. Both oils exhibited very similar outputs with varying S/C. Upon a short number of cycles, i.e. starting from an oil-reduced catalyst, the fuel conversion dropped slightly but the steam conversion was constant, resulting in a slow decrease in H2 yield. Despite their high level of oxygen content, the pyrolysis oils were shown to maintain close to 90% reduction of the oxidised catalyst upon repeated cycles, but the rate of reduction decreased with cycling.

Waste Lubricating Oil as a Source of Hydrogen Fuel using Chemical Looping Steam Reforming

Initial results are presented for the production of hydrogen from waste lubricating oil using a chemical looping reforming (CLR) process. The development of flexible and sustainable sources of hydrogen will be required to facilitate a 'hydrogen economy'. The novel CLR process presented in this paper has an advantage over hydrogen production from conventional steam reforming because CLR can use complex, low value, waste oils. Also, because the process is scalable to small and medium size, hydrogen can be produced close to where it is required, minimising transport costs. Waste lubricating oil typically contains 13-14% weight of hydrogen, which through the steam reforming process could produce a syngas containing around 75 vol% H , representing over 40 wt% of the fuel. The waste oil was converted to a hydrogen rich syngas in a packed bed reactor, using a Ni/ Al O catalyst as the oxygen transfer material (OTM). An oil conversion rate based on carbon species (CO, CO and CH 4) of up to ~95% was achieved. The steam to hydrogen conversion of 53%, accounted for 63% of the total H produced, compared to the theoretical ideal of 67.4%. The syngas composition was initally >65 vol% H , 15 vol% CO, 15 vol% CO , and <5 vol% CH . Deterioration of the reactants conversion, specifically steam, was observed over repeated cycles indicating fouling of the catalyst. This was not by carbonaceous deposits, which were eliminated during the cycle's alternated oxidation steps, but could be by trace additives within the lubricating oil. Further work is planned in order to overcome this issue.

Enhanced coal gasification heated by unmixed combustion integrated with an hybrid system of SOFC/GT

For clean utilization of coal, enhanced gasification by in situ CO 2 capture has the advantage that hydrogen production efficiency is increased while no energy is required for CO 2 separation. The unmixed fuel process uses a sorbent material as CO 2 carrier and consists of three coupled reactors: a coal gasifier where CO 2 is captured generating a H 2-rich gas that can be utilized in fuel cells, a sorbent regenerator where CO 2 is released by sorbent calcination and it is ready for capture and a reactor to oxidize the oxygen transfer material which produces a high temperature/pressure vitiated air. This technology has the potential to eliminate the need for the air separation unit using an oxygen transfer material. Reactors' temperatures range from 750 °C to 1550 °C and the process operates at pressure around 7.0 bar. This paper presents a global thermodynamic model of the fuel processing concept for hydrogen production and CO 2 capture combined with fuel and residual heat usage. Hydrogen is directly fed to a solid oxide fuel cell and exhaust streams are used in a gas turbine expander and in a heat recovery steam generator. This paper analyzes the influence of steam to carbon ratio in gasifier and regeneration reactor, pressure of the system, temperature for oxygen transfer material oxidation, purge percentage in calciner, average sorbent activity and oxidant utilization in fuel cell. Electrical efficiency up to 73% is reached under optimal conditions and CO 2 capture efficiencies near 96% ensure a good performance for GHG's climate change mitigation targets.