Sorption-enhanced Chemical Looping Research Articles

Thermodynamic analysis on the coupling effects of operating parameters in sorption-enhanced chemical looping gasification with rice husk as feedstock

Sorption-enhanced chemical looping gasification (SECLG) has a favorable ability to produce H2-rich syngas without any extra separation process. To comprehensively investigate the performances, the temperature in the fuel reactor (FR) side TFR, molar ratio of steam or CaO to carbon (λsteam/C, λCaO/C), circulation ratio of oxygen carrier to carbon (λOC/C) are changed to test their effects on the products. Then the coupling effects on SECLG are deeply analyzed by changing two and three of the operating parameters. Results demonstrate that under fundamental conditions, the sorption enhancement becomes unavailable when the temperature is higher than 775 °C but decreasing λsteam/C and increasing λOC/C can elevate this critical temperature. Increasing the λOC/C or λsteam/C can enhance the H2 concentration first, then weaken H2 concentration. The maximum value of H2 concentration is 62.47% when λOC/C = 0.4 and λsteam/C = 1.9. When the FR temperature is lower than 775 °C, there is an optimal λOC/C for maximizing the H2 concentration at a specific temperature. When the temperature is 650 °C, λOC/C = 0.5 and λsteam/C = 1.9, the maximum value of H2 concentration can reach 95.73% in SECLG.

Sorption-enhanced chemical looping steam reforming coupled with water splitting for syngas and H2 coproduction using waste plastic as fuel

Chemical looping is a promising technology for hydrogen production. Achieving both high purity and yield is an ongoing challenge, due to low fuel conversion and carbon deposition. In this study, a sorption-enhanced chemical looping reforming coupled with water splitting (SE-CLSR-WS) process was proposed to co-produce syngas and H2 by using waste plastic as the fuel. The Ni-doped Ca2Fe2O5 brownmillerites were designed and employed as oxygen carriers (OCs) and CO2 sorbent. The introduction of Ni leaded to lattice distortion of brownmillerite, thereby enhancing the redox activity of lattice oxygen. In fuel reactor (FR), CaO in-situ captured CO2 and shifted reaction equilibrium towards PET pyrolysis gas reforming, enhancing both syngas yield and PET conversion rates. Adhere to the surface of OCs, CaO improved cyclic performance by inhibiting agglomeration of active metals. Calcination reactor (CR) was set between FR and steam rector (SR) to in-situ desorb CO2 and remove carbon deposition, enhancing hydrogen purity in SR. When Ca2Ni0.75Fe1.25O5-0.25CaO was applied to SE-CLSR-WS process, it exhibited synergistically strengthened performance in reaction activity, sorption capacity and cyclic stability, with a syngas purity of 82.71 % and H2 yield of 8.01 mmol/g OC with 93.26 % purity.

Synergistic promotions between high purity H2 production and CO2 capture via sorption enhanced chemical looping reforming

Hydrogen energy, a promising clean source, holds potential to combat global warming. To achieve efficient and low-carbon H2 production, we proposed an isothermal sorption-enhanced chemical looping reforming (SE-CLR) process to realize the high-purity hydrogen production and in-situ CO2 capture at mild temperatures (550–650 °C). For practical application, the process is characterized to use Fe-Ni double metal oxide particles as steam methane reforming oxygen carriers, and K2CO3-promoted Li4SiO4 particles as CO2 sorbent. The oxygen transfer capacity of metal oxide matintained high at 57.4%, and the K-Li4SiO4 absorbents remained at 22.5% CO2 absorption capacity over 200 isothermal absorption-regeneration cycles. Conducting a synergistic conversion mechanism within double metal oxides and absorbents, and adjusting the absorbent-to-metal oxide mass ratio to 7:4, enhanced hydrogen purity to 92% and CO2 uptake to 95%. Furthermore, in-situ CO2 removal in CLR processes achieved methane conversion and H2 production rates equivalent to conventional CLR processes under the same reaction conditions, but at temperatures ∼60 °C lower. The effects of the reaction temperature, pressure, steam-to-methane and methane-to-solid ratios on SE-CLR performance were studied systematically. Finally, stable hydrogen production with a purity of 91%–89% and CO2 uptake of 94%–91% were obtained over 25 CLR cycles, with minimal changes in mechanical strength of particles.

Evaluation of a novel coupling process for the simultaneous production of syngas and ultra-pure hydrogen from natural gas with in situ utilization of carbon dioxide

Recently, with the aim of developing clean and efficient energy systems, various designs based on chemical looping combustion and reforming have been suggested. This study proposed and investigated the production of ultra-pure hydrogen in dual-purpose integrated zero-emission reforming (UPH2-DPIZER) process based on the sorption-enhanced chemical looping steam methane reforming (SECLSMR). This process is proposed on the basis of reduction in the emissions of carbon dioxide as well as the simultaneous generation of pure hydrogen and syngas for use in a wide range of applications. One of the most novel aspects of this research is that the proposed UPH2-DPIZER process can reduce or eliminate carbon dioxide emissions because all the produced and chemisorbed CO2 can be applied directly in the reforming process without any additional purification. Furthermore, the synthesized 30 wt%NiO-5wt.%CeO2/Al2O3 oxygen carrier was examined using the X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) techniques along with evaluation in SECLSMR process. The attained results of experimental tests are applied to adapt and validate the simulations of novel proposed process. The other objectives of this study are the reduction in required energy for the whole process along with reduction in the direct consumption of fossil fuels. The experiments showed high H2/CO molar ratio of 36 at 550 °C with appropriate methane conversion of about 74 %, while at 750 °C, nearly a complete conversion of CH4 occurs. The obtained results from the simulation of proposed UPH2-DPIZER showed the production of ultra-pure hydrogen along with syngas with H2/CO molar ratio of about 1 with negligible CO2 release.

Green hydrogen production from biomass – A thermodynamic assessment of the potential of conventional and advanced bio-oil steam reforming processes

Steam reforming of bio-oil derived from biomass pyrolysis is one of the most promising methods for the production of green hydrogen with minimal carbon footprint. In this context, this work investigates the thermodynamic potential of hydrogen production from bio-oil steam reforming. Four routes – conventional steam reforming (CSR) and three advanced reforming processes – sorption-enhanced steam reforming (SESR), chemical looping steam reforming (CLSR) and sorption-enhanced chemical looping steam reforming (SE-CLSR) - were modeled for this purpose. Bio-oil was modeled as a complex mixture of model compounds belonging to all major oxygenate families in order to have a closer resemblance with raw bio-oil. CaO was selected as the sorbent, while NiO was selected as oxygen carrier. Furthermore, the effect of process parameters such as steam to carbon, sorbent to carbon, oxygen carrier to carbon ratios, and reforming temperature was explored. H2 purity and yield along with energy demand, served as the parameters for comparing the performance of the four processes. SESR provided the highest H2 yield (0.216 kgH2 kgBio-oil−1) among all the processes under optimum conditions along with a purity greater than 99 %. CLSR, meanwhile, had the lowest H2 yield and purity (0.178 kgH2 kgBio-oil−1 and 64.6 %, respectively). The combined SE-CLSR process had H2 yield greater than both CSR and CLSR (0.197 kgH2 kgBio-oil−1) and a H2 purity greater than 99 %. High in-situ heat generation was noted in the reforming reactor for both SESR and SE-CLSR, pointing towards a good potential for auto-thermal operation. Overall, SE-CLSR process is a highly intensified process with substantially lower energy requirements than all the other processes. The results highlight that by combining CO2-sorption and chemical looping with traditional reforming, H2 can be obtained in higher yields and purity and lower energy consumption.

Sorption-enhanced chemical looping steam reforming of glycerol with CO2 in-situ capture and utilization

Hydrogen production from chemical looping steam reforming using an oxygen transport catalyst is definitely enhanced by CO2 in-situ capture, which shifts the chemical equilibrium and reduces the energy demands. The utilization of CO2 from this process as a reactant for chemicals and fuels could help to improve economic reasons and mitigate its impact on climate. In this study, we proposed a sorption-enhanced chemical looping steam reforming of glycerol to realize the synergetic capture and conversion of CO2 in one integrated chemical looping hydrogen production process. The process is characterized to usethe oxidized NiO/NiAl2O4 as a steam reforming catalyst, the reduced NiO/NiAl2O4 as a CO2-CH4 dry reforming catalyst, and the inexpensive dolomite as a CO2 sorbent. The surface carbon that would deactivate the catalyst is combusted by air after CO2-CH4 dry reforming and the Ni on the catalyst is re-oxidized. The coupling of these different processes of chemical looping steam reforming, CO2 in-situ capture, dolomite decomposition and CO2 in-situ utilization, results in simultaneous generation of high purity hydrogen and syngas. The results demonstrated that hydrogen of above 92.5% was one-step generated and CO2 was decreased to zero in the pre-CO2 breakthrough periods. The reduced NiO/NiAl2O4 catalysts favored the CO2-CH4 dry reforming at 850 °C. The syngas of H2-to-CO molar ratios of 0.8–1.1 through the conversion of CO2 from in-situ extraction of the absorbed CO2 dolomite, was produced. The NiO/Al2O4 with 15 wt% NiO gave the highest hydrogen and syngas yields, and maintained high performance for the proposed system. The catalysts and dolomite exhibited good stability with no obvious loss of activity in 10 cycles.

Advanced Steam Reforming of Bio-Oil with Carbon Capture: A Techno-Economic and CO2 Emissions Analysis

A techno-economic analysis has been used to evaluate three processes for hydrogen production from advanced steam reforming (SR) of bio-oil, as an alternative route to hydrogen with BECCS: conventional steam reforming (C-SR), C-SR with CO2 capture (C-SR-CCS), and sorption-enhanced chemical looping (SE-CLSR). The impacts of feed molar steam to carbon ratio (S/C), temperature, pressure, the use of hydrodesulphurisation pretreatment, and plant production capacity were examined in an economic evaluation and direct CO2 emissions analysis. Bio-oil C-SR-CC or SE-CLSR may be feasible routes to hydrogen production, with potential to provide negative emissions. SE-CLSR can improve process thermal efficiency compared to C-SR-CCS. At the feed molar steam to carbon ratio (S/C) of 2, the levelised cost of hydrogen (USD 3.8 to 4.6 per kg) and cost of carbon avoided are less than those of a C-SR process with amine-based CCS. However, at higher S/C ratios, SE-CLSR does not have a strong economic advantage, and there is a need to better understand the viability of operating SE-CLSR of bio-oil at high temperatures (>850 °C) with a low S/C ratio (e.g., 2), and whether the SE-CLSR cycle can sustain low carbon deposition levels over a long operating period.

A natural gas-based eco-friendly polygeneration system including gas turbine, sorption-enhanced steam methane reforming, absorption chiller and flue gas CO2 capture unit

Poly-generation systems have attracted a lot of attention due to the increment of efficiency as well as reducing energy penalties, costs and pollutants. Extensive research has been done on these systems in recent years. The current work is done with the aim of simulating an environmentally friendly poly-generation system in the power plant of Shahrood city in Iran. In this way, a poly-generation system is simulated in Aspen Plus software which consists of: I) a gas turbine (GT) for power generation with natural gas fuel of Shahroud power plant, that its flue gas is utilized to supply heat for other cycles and streams, II) a sorption-enhanced chemical looping reforming (SECLR) which simultaneously generates H2 by steam methane reforming (SMR) and uptakes produced CO2 by calcium adsorbent during the carbonation/calcination reactions. In this section, there is also a chemical looping combustion (CLC) based on redox reactions of Ni/NiO to provide heat of the reactors, III) a NH3/H2O absorption refrigeration system to yield the cooling demand, IV) a high-pressure steam generation unit and V) a MEA-based post-combustion CO2 capture unit (PCC) for flue gas. In this system, an attempt has been made to prevent heat loss by internal streams, especially gas turbine exhaust gas, so that energy loss is minimized. Moreover, environmental issues are also prioritized to reduce the CO2 emissions as much as possible. The proposed process is capable of producing 133.3 MW power, 9.875 MW cooling, 50 kg/s high-pressure steam and 0.384 kg/s hydrogen. The mass flow rates of CO2 captured in the SECLR and PCC sections are 2.6 kg/s and 15.35 kg/s, respectively. Moreover, the total energy efficiency of the integrated system is 68.74%. Ultimately, a sensitivity analysis was performed to identify the key parameters and their influence on the process performance.

Optimisation of a sorption-enhanced chemical looping steam methane reforming process

An intensified hydrogen production steam reforming process named ‘Sorption-Enhanced Chemical Looping Steam Methane Reforming’ (SE-CL-SMR) was studied. Aspen Plus was used to carry out a thermodynamic investigation into the influence of various operating conditions on hydrogen production and process thermal efficiency. The steam to carbon molar ratio (S/C), the CaO to carbon molar ratio (CaO/C), the metal oxide to carbon molar ratio (MeO/C), the metal oxide composition (NiO:CuO), and the oxidising agent species were all shown to influence the process performance.The main findings were that; (1) the introduction of CaO reduces the potential for coke formation with predicted zero coke formation for CaO/C ratios > 0.4; (2) increasing amounts of metal oxide (MeO/C) and steam (S/C) enhance the hydrogen production yield and purity; (3) due to its involvement in an exothermic reaction, the presence of CuO allows for the reforming reactor to operate as an adiabatic reactor with an operating temperature within the range of 600 °C–700 °C; (4) an increase in the NiO:CuO ratio leads to an increase in methane conversion.With the operating conditions of S/C = 3, CaO/C = 1, MeO/C = 1, NiO:CuO = 0.9 and air as the oxidising agent, a hydrogen purity as high as 98% was predicted for the SE-CL-SMR process, along with the lowest observed CO2 production rate. Under the same conditions and using pinch analysis, the thermodynamic model prediction of the thermal process efficiency is reported as ca. 86%. This is significantly higher than the reported efficiency of 79% for the ‘Sorption-Enhanced Steam Methane Reforming’ (SE-SMR) process, predicted using similar thermodynamic models.

Performance of sorption-enhanced chemical looping gasification system coupled with solid oxide fuel cell using exergy analysis

Coal gasification system integrated with solid oxide fuel cell (SOFC) provides a promising energy conversion way owing to its high efficiency. To get a deep insight into the energy performance of this system, a thermodynamic evaluation is implemented. Meanwhile, the technologies of chemical looping and CO2 sorption are introduced into this integration system. It is found that the addition of oxygen carrier and sorbent into coal gasification system can promote the output power of the SOFC with a higher exergy destruction, where the exergy efficiency of most modules in the system can reach 80% except tar separation. The results also reveal that a suitable improvement of gasifying agent amount is beneficial to the energy performance of the system. When the H2O/C molar ratio is increased to 3.0, the SOFC exergy efficiency of 97% can be achieved.

Sorption-enhanced chemical looping oxidative steam reforming of methanol for on-board hydrogen supply

Hydrogen is an indispensable energy carrier for the sustainable development of human society. Nevertheless, its storage, transportation, and in situ generation still face significant challenges. Methanol can be used as an intermediate carrier for hydrogen supplies, providing hydrogen energy through instant methanol conversion. In this study, a sorption-enhanced, chemical-looping, oxidative steam methanol-reforming (SECL-OSRM) process is proposed using CuO–MgO for the on-board hydrogen supply, which could be a promising method for safe and efficient hydrogen production. Aspen Plus software was used for feasibility verification and parameter optimization of the SECL-OSRM process. The effects of CuO/CH3OH, MgO/CH3OH, and H2O/CH3OH mole ratios and of temperature on H2 production rate, H utilization efficiency, CH3OH conversion, CO concentration, and system heat balance are discussed thoroughly. The results indicate that the system can be operated in auto-thermal conditions with high-purity hydrogen (99.50 vol%) and ultra-low-concentration CO (< 50 ppm) generation, which confirms the possibility of integrating low-temperature proton-exchange membrane fuel cells (LT-PEFMCs) with the SECL-OSRM process. The simulation results indicate that the CO can be modulated in a lower concentration by reducing the temperature and by improving the H2O/CH3OH and MgO/CH3OH mole ratios.

Fe2O3/CaO-Al2O3 multifunctional catalyst for hydrogen production by sorption-enhanced chemical looping reforming of ethanol

Sorption-enhanced chemical looping reforming of ethanol for hydrogen production was investigated using Fe2O3 as oxygen carrier and modified CaO-based Al2O3 as CO2 sorbent. Combined Fe2O3/CaO-Al2O3 multifunctional catalysts were demonstrated and prepared by different methods including sol-gel, mechanical mixing, and impregnation at different Fe contents (5, 10, and 15 wt%). The results showed that the multifunctional catalyst prepared by impregnation method with 5 wt% Fe loading provided the highest H2 purity of 70% in the pre-breakthrough period which lasted for 60 min at 600 °C. This was attributed to the preserving of Ca12Al14O33 inert support in the structure during the preparation as shown by XRD results, leading to higher surface area as determined by N2 physisorption and to prevention of particle agglomeration as evidenced by SEM-EDX. Although the H2 production was inhibited by the presence of Ca2Fe2O5 phase, a stable performance was found for at least 5 repeated cycles both for sorption capacity and oxygen carrier. The ease of decarbonation was also observed with this material as confirmed by DSC-TGA analysis. This highlighted the mutual advantages of Fe in CaO sorption stability and Ca in Fe oxygen carrier stability which could offset their intrinsic weak robustness.

Thermodynamic evaluation of sorption-enhanced chemical looping gasification with coal as fuel

Chemical looping gasification (CLG) is regarded as an efficient way for the utilization of solid fuel and hydrogen-enriched syngas production. In this work, a thermodynamic analysis is carried out to evaluate the CLG performance of coal on the basis of Gibbs free energy minimization. In order to enhance the gasification process, CO2 sorption is employed and sorbents are circulated in the whole system. The influence of operating parameters on the CLG performance as well as heat requirement of the system is further examined. The results reveal that the addition of sorbent can promote the hydrogen production and provide the heat for the reaction in the fuel reactor (FR), whereas additional energy input is still required for the whole system. A proper increase of oxygen carrier circulation rate can achieve the auto-thermal condition of the system.

Analysis of the sorption-enhanced chemical looping biomass gasification process: Performance assessment and optimization through design of experiment approach

Abstract In this study, the performance of high-purity hydrogen production through the sorption-enhanced chemical looping gasification (SECLG) process, involving a gasifier, calciner, and air reactor, was investigated. In this process, the biomass feedstock was wood residue, and steam, calcium oxide (CaO), and nickel oxide (NiO) were used as a gasifying agent, CO2 sorbent, and oxygen carrier, respectively. First, the influences of key operational parameters (i.e., steam to carbon (S/C) molar ratio, gasifying temperature, and NiO to carbon (NiO/C) molar ratio) on product gas yields and net energy consumption of the process were studied. According to the first and second laws of thermodynamics, performance indicators of the SECLG process demonstrated that increases in energy and exergy efficiencies occurred with increases in S/C molar ratio and/or gasifying temperature. Then, mathematical models indicative of correlations between energy efficiency, exergy efficiency, and major operating parameters (e.g., S/C molar ratio and gasifying temperature) were developed through the design of experiment (DOE) method and used for process optimization. The optimal conditions offering maximum energy (70%) and exergy (56%) efficiencies were a S/C molar ratio of 4.5 and gasifying temperature of 700 °C, under which all reactors operated at thermal self-sufficient conditions.

Bi-metallic CuO-NiO based multifunctional material for hydrogen production from sorption-enhanced chemical looping autothermal reforming of ethanol

Bi-metallic CuO-NiO based multifunctional materials were developed and employed for H2 production via sorption-enhanced chemical looping autothermal reforming (SE-CLAR) of ethanol. The effects of adding copper oxide (CuO) as a co-oxygen carrier and material preparation method on H2 production performances, including activity, reusability, and energy penalty, were studied. The results revealed that adding CuO into one-body multifunctional material provided positive impacts on H2 production performances. The use of multifunctional material could reduce reforming temperature to milder temperature at 500 °C. The key finding is that position of CuO in the multifunctional material showed a significant effect. Placing of CuO on the surface could enhance catalytic property whereas placing NiO closed to CaO could reduce heat for CaO regeneration. For the SE-CLAR operating temperature at 500 °C and steam to ethanol ratio (S/E) = 3, impregnation of NiO on the surface of homogeneous CuO-CaO-Ca12Al14O33, NiO/CuO-CaO-Ca12Al14O33, produced 83% H2 purity for 30 min while impregnation of CuO on the surface of homogeneous NiO-CaO-Ca12Al14O33, CuO/NiO-CaO-Ca12Al14O33, produced 89% H2 for 45 min. Sol-gel one-pot synthesis method of NiO-CuO-CaO-Ca12Al14O33 produced 91% H2 purity for 60 min. Complete regeneration temperature of CaO was achieved at 800 °C, which accounts for 14% thermal energy reduction for the CuO/NiO-CaO-Ca12Al14O33. The NiO/CuO-CaO-Ca12Al14O33 could maintain its performance on producing high H2 purity for at least five consecutive operating cycles.

Effect of calcination/carbonation and oxidation/reduction on attrition of binary solid species in sorption-enhanced chemical looping reforming

The effects of chemical reactions on the attrition of oxygen carrier particles and CO2 sorbent based on a chemical looping reforming (CLR) process with intrinsic CO2 capture were analyzed. Iron/hematite as an oxygen carrier, and limestone/lime as a CO2 sorbent were tested in a jet attrition apparatus. Attrition tests were conducted with particles of a single species and with binary solid mixtures, for different temperatures, different gas species and ranges of gas concentrations, varied to the reactions. Material properties were measured to investigate how the chemical conversion of particle species affects the attrition in both single-species, and two-species environments. Iron oxidation decreased the particle crushing strength, forming a porous iron oxide layer on the surface. When hematite was reduced with CH4, the proportions of reduced iron oxides increased the intrinsic crushing strength on the surface. For limestone, calcination increased the attrition due to a decrease in the intrinsic particle crushing strength. Lime carbonation reduced attrition because of increasing ductility and sintering, as well as the formation of a limestone surface layer of carbonate. Particle attrition increased when two solid species were mixed together, due to the increasing frequency of inter-particle collisions.

Thermodynamic equilibrium analysis of H2-rich syngas production via sorption-enhanced chemical looping biomass gasification

In this study, thermodynamic equilibrium analysis of the sorption-enhanced chemical looping biomass gasification (SE-CL-BG) using Fe2O3 as the oxygen carrier, CaO as the CO2 sorbent, and CO2 or H2O as the gasifying agent for producing H2 rich syngas was conducted. Based on the amount of OC introduced, highly selective syngas can only result when a small amount of oxygen carrier is introduced. Due to carbon and hydrogen oxidations, the yields of CO and H2, cold gas efficiency, and the second-law efficiency of SE-CL-BG case were found to be lower than the conventional biomass gasification case in which no oxygen carrier and CO2 sorbent were introduced. Compared with conventional biomass gasification, the advantage of SE-CL-BG is that biomass gasification can be operated at lower temperatures (500–750 °C) with higher H2 yield due to the enhanced water-gas shift reaction and lower heat duty due to heat release from the CO2 absorption reaction. The computed results indicated that CaO loses the ability to absorb CO2 as the temperature becomes higher than 800 °C.

Experimental investigation of improved calcium-based CO2 sorbent and Co3O4/SiO2 oxygen carrier for clean production of hydrogen in sorption-enhanced chemical looping reforming

In this study, highly pure hydrogen is produced in sorption enhanced chemical looping steam methane reforming (SE-CLSMR) using cobalt-based oxygen carrier (OC) and cerium promoted CaO-based sorbent. In addition, the CO2 removal from a gas stream at high temperatures is investigated via calcium looping process prior to SE-CLSMR process. The prepared samples are characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and energy dispersive X-ray spectroscopy (EDX) techniques. The effect of Ca/Ce molar ratio (100/0.00–0.91/0.09), sorption temperature (550–650 °C) and sorbent lifetime are studied to find the optimal sorbent. The characterization results show the uniform and orderly CeO2 dispersed sorbent nanoparticles that notably improved the sorbent morphology compared with blank CaO. The sorption results revealed the negative effect of temperature on CO2 uptake of all the samples. In addition, the CO2 sorption evaluations indicate that the molar ratio of cerium to calcium plays a significant role in the stability of sorbent and improved the CO2 sorption capacity significantly. The high CO2 removal efficiency in the cerium modified sorbents could be due to decrease in diffusion resistance of CO2 through the sorbent structure during the carbonation reaction. Furthermore, results show that the addition of cerium to the sorbent structure, effectively improves the thermal resistance of synthesis sorbents. The SE-CLSMR results showed that the H2 purity could be increased up to about 95% considering Co3O4/SiO2 oxygen carrier and cerium promoted calcium-based sorbent at relatively low temperature of 550 °C, which is comparable with 84% in CLR process.

Thermodynamic analysis of the novel chemical looping process for two-grade hydrogen production with CO2 capture

The integrated sorption-enhanced chemical looping reforming and water splitting (SECLR-WS) process was proposed for hydrogen (H2) production from biogas using iron oxide as an oxygen carrier and calcium oxide (CaO) as a carbon dioxide (CO2) adsorbent. In the SECLR-WS process, the biogas feed is partially oxidized using iron oxide and CO2 is captured by CaO in the fuel reactor (FR) to produce H2-rich syngas. The iron oxide is re-oxidized in the steam reactor (SR) to generate a high-purity H2 stream and CaO is regenerated in the calcinator. The simulation of the SECLR-WS process was based on a thermodynamic approach and was performed using an Aspen Plus simulator. The effects of key parameters such as the steam feed to the FR to methane (SFR/CH4) and iron (II, III) oxide (Fe3O4) to CH4 (Fe3O4/CH4) molar ratios on the process performance in terms of H2 yield and purity, and CH4 conversion were investigated. The results showed that the H2 yield, H2 purity in the FR, and CH4 conversion could be improved by increasing the SFR/CH4 and CaO/CH4 molar ratios. A total H2 yield of 3.8 and a H2 purity in the FR of 97.01 mol% can be obtained at the FR and SR temperatures of 610 and 500 °C, and SFR/CH4, CaO/CH4, Fe3O4/CH4, and SSR/CH4 molar ratios of 2.2, 1.66, 1, and 2.87, respectively. The molar concentration of carbon monoxide (CO) in the high-purity H2 stream could be reduced by increasing the pressure in the SR and the amount of CO2 in the biogas feed stream negatively affected the performance of the system. In addition, increasing the Fe3O4/CH4 molar ratio can improve the heat demand in the FR.

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.