The effect of H₂S on internal dry reforming in biogas fuelled solid oxide fuel cells

Internal dry reforming of methane is envisaged as a possibility to reduce on capital and operation costs of biogas fuelled solid oxide fuel cells (SOFCs) system by using the CO2 present in the biogas. Due to envisaged internal dry reforming, the requirement for biogas upgrading becomes obsolete, thereby simplifying the system complexity and increasing its technology readiness level. However, impurities prevailing in biogas such as H2S have been reported in literature as one of the parameters which affect the internal reforming process in SOFCs. This research has been carried out to investigate the effects of H2S on internal dry reforming of methane on nickel-scandia-stabilised zirconia (Ni-ScSZ) electrolyte supported SOFCs. Results showed that at 800°C and a CH4:CO2 ratio of 2:3, H2S at concentrations as low as 0.125 ppm affects both the catalytic and electric performance of a SOFC. At 0.125 ppm H2S concentration, the CH4 reforming process is affected and it is reduced from over 95% to below 10% in 10 h. Therefore, future biogas SOFC cost reduction seems to become a trade-off between biogas upgrading for CO2 removal and biogas cleaning of impurities to facilitate efficient internal dry reforming

Biohydrogen production through dark fermentation from waste biomass:Current status and future perspectives on biorefinery development

Green and clean hydrogen production has become a significant focus in recent years to achieve sustainable renewable energy fuel needs. Biohydrogen production through the dark fermentation (DF) process from organic wastes is advantageous with its environmentally friendly, energy-efficient, and cost-effective characteristics. This article elucidates the viability of transforming the DF process into a biorefinery system. Operational pH, temperature, feeding rate, inoculum-to-substrate ratio, and hydrogen partial pressure and its liquid-to-gas mass transfer rate are the factors that govern the performance of the DF process. Sufficient research has been made that can lead to upscaling the DF process into an industrial-scale technology. However, the DF process cannot be upscaled at the current technology readiness level as a stand-alone technology. Hence, it requires a downstream process (preferably anaerobic digestion) to improve energy recovery efficiency and economic viability. The article also discusses the possible hydrogen purification and storage techniques for achieving fuel quality and easy accessibility. The article further tries to unfold the opportunities, challenges, and current scenario/future research directions to enhance hydrogen yield and microbial metabolism, depicting the commercialization status for biorefinery development. Finally, the current progress gaps and policy-level loopholes from the Indian perspective are highlighted by analyzing the strengths, weaknesses, opportunities, and threats

Energy, exergy, and environmental analyses of renewable hydrogen production through plasma gasification of microalgal biomass

In this study, an energy, exergy, and environmental (3E) analyses of a plasma-assisted hydrogen production process from microalgae is investigated. Four different microalgal biomass fuels, namely, raw microalgae (RM) and three torrefied microalgal fuels (TM200, TM250, and TM300), are used as the feedstock for steam plasma gasification to generate syngas and hydrogen. The effects of steam-to-biomass (S/B) ratio on the syngas and hydrogen yields, and energy and exergy efficiencies of plasma gasification (ηEn,PG, ηEx,PG) and hydrogen production (ηEn,H2, ηEx,H2) are taken into account. Results show that the optimal S/B ratios of RM, TM200, TM250, and TM300 are 0.354, 0.443, 0.593, and 0.760 respectively, occurring at the carbon boundary points (CBPs), where the maximum values of ηEn,PG, ηEx,PG, ηEn,H2, and ηEx,H2 are also achieved. At CBPs, torrefied microalgae as feedstock lower the ηEn,PG, ηEx,PG, ηEn,H2, and ηEx,H2 because of their improved calorific value after undergoing torrefaction, and the increased plasma energy demand compared to the RM. However, beyond CBPs the torrefied feedstock displays better performance. A comparative life cycle analysis indicates that TM300 exhibits the highest greenhouse gases (GHG) emissions and the lowest net energy ratio (NER), due to the indirect emissions associated with electricity consumption.</p

Direct internal methane reforming in biogas fuelled solid oxide fuel cell; the influence of operating parameters

Internal dry reforming (IDR) of methane for biogas-fed solid oxide fuel cell (SOFC) applications has been experimentally investigated on planar Ni-GDC (cermet anode) electrolyte-supported cells. This study focuses on the effect of CO2 concentration, current density, operating temperature, and residence time on internal methane dry reforming. A single cell is fed with different CH4/CO2 mixture ratios between 0.6 and 1.5. Extra CO2 recovered from carbon capture plants can be utilized here as a reforming agent. The I-V characterization curves are recorded at different operating conditions in order to determine the best electrochemical performance while the power production is maximized, and carbon deposition is suppressed. The outlet gas from the anode is analyzed by a micro gas chromatograph to investigate methane conversion inside the anode fuel channel and to understand its influence on the cell performance. Relatively long-term experiments have been performed for all gas mixtures at 850°C under a current density of 2000 A m−2. The results indicate that when the cell is fed with biogas with an equimolar amount of CH4 and CO2, carbon deposition is prevented, and maximum power density is obtained.Energy Technolog

Thermodynamic analysis of a novel integrated biomass pyrolysis-solid oxide fuel cells-combined heat and power system for co-generation of biochar and power

Biochar derived from pyrolysis or gasification has been gaining significant attention in the recent years due to its potential wide applications for the development of negative emissions technologies. A new concept was developed for biochar and power co-generation system using a combination of biomass pyrolysis (BP) unit, solid oxide fuel cells (SOFCs), and a combined heat and power (CHP) system. A set of detailed experimental data of pyrolysis product yields was established in Aspen Plus to model the BP process. The impacts of various operating parameters including current density ((Formula presented.)), fuel utilization factor ((Formula presented.)), pyrolysis gas reforming temperature ((Formula presented.)), and biochar split ratio ((Formula presented.)) on the SOFC and overall system performances in terms of energy and exergy analyses were evaluated. The simulation results indicated that increasing the (Formula presented.), (Formula presented.), and (Formula presented.) can favorably improve the performances of the BP-SOFC-CHP system. As a whole, the overall electrical, energy and exergy efficiencies of the BP-SOFC-CHP system were in the range of 8–14%, 76–78%, and 71–74%, respectively. From the viewpoint of energy balance, burning the reformed pyrolysis gas can supply enough energy demand for the process to achieve a stand-alone BP-SOFC-CHP plant. In case of a stand-alone system, the overall electrical, energy and exergy efficiencies were 5.4, 63.9 and 57.8%, respectively, with a biochar yield of 31.6%

Plasma gasification performances of various raw and torrefied biomass materials using different gasifying agents

Plasma gasification of raw and torrefied woody, non-woody, and algal biomass using three different gasifying agents (air, steam, and CO2) is conducted through a thermodynamic analysis. The impacts of feedstock and reaction atmosphere on various performance indices such as syngas yield, pollutant emissions, plasma energy to syngas production ratio (PSR), and plasma gasification efficiency (PGE) are studied. Results show that CO2 plasma gasification gives the lowest PSR, thereby leading to the highest PGE among the three reaction atmospheres. Torrefied biomass displays increased syngas yield and PGE, but is more likely to have a negative environmental impact of N/S pollutants in comparison with raw one, especially for rice straw. However, the exception is for torrefied grape marc and macroalgae which produce lower amounts of S-species under steam and CO2 atmospheres. Overall, torrefied pine wood has the best performance for producing high quality syngas containing low impurities among the investigated feedstocks.Energy Technolog

Energy, exergy, and environmental analyses of renewable hydrogen production through plasma gasification of microalgal biomass

In this study, an energy, exergy, and environmental (3E) analyses of a plasma-assisted hydrogen production process from microalgae is investigated. Four different microalgal biomass fuels, namely, raw microalgae (RM) and three torrefied microalgal fuels (TM200, TM250, and TM300), are used as the feedstock for steam plasma gasification to generate syngas and hydrogen. The effects of steam-to-biomass (S/B) ratio on the syngas and hydrogen yields, and energy and exergy efficiencies of plasma gasification (ηEn,PG, ηEx,PG) and hydrogen production (ηEn,H2, ηEx,H2) are taken into account. Results show that the optimal S/B ratios of RM, TM200, TM250, and TM300 are 0.354, 0.443, 0.593, and 0.760 respectively, occurring at the carbon boundary points (CBPs), where the maximum values of ηEn,PG, ηEx,PG, ηEn,H2, and ηEx,H2 are also achieved. At CBPs, torrefied microalgae as feedstock lower the ηEn,PG, ηEx,PG, ηEn,H2, and ηEx,H2 because of their improved calorific value after undergoing torrefaction, and the increased plasma energy demand compared to the RM. However, beyond CBPs the torrefied feedstock displays better performance. A comparative life cycle analysis indicates that TM300 exhibits the highest greenhouse gases (GHG) emissions and the lowest net energy ratio (NER), due to the indirect emissions associated with electricity consumption.Energy Technolog

Process simulation development of a clean waste-to-energy conversion power plant: Thermodynamic and environmental assessment

Waste-to-energy (WTE) conversion technologies for generating renewable energy and solving the environmental problems have an important role in the development of sustainable circular economy. This paper presents a novel high-efficiency WTE power plant using refuse-derived fuel (RDF) as feedstock by integrating torrefaction (T) pretreatment with plasma gasifier (PG), solid oxide fuel cell (SOFC), and combined heat and power (CHP) system. The combined impacts of torrefaction conditions (i.e. temperature and residence time) and steam-to-fuel (S/F) ratio on the energy and environmental performances of the proposed T-PG-SOFC-CHP power plant without CO2 capture (System I) is first evaluated. Results show that torrefaction of RDF prior to plasma gasification provides better syngas quality and therefore the system electrical efficiency (SEE) and CHP efficiency (CHPE) of System I can be markedly boosted compared to that of untreated RDF. However, the integration of torrefaction unit shows a negative effect on the energy return on investment (EROI) due to high energy demands for torrefaction and plasma gasification. Overall, the values of CHPE of System I range from 47.25% to 55.39% when the torrefaction temperatures of 200 and 250 °C are adopted. In contrast, the torrefaction of RDF at 300 °C is not a recommended condition for operation in the T-PG-SOFC-CHP power plant because of noticeably negative energy and environmental impacts. Moreover, to prevent the risk of carbon deposition on the SOFC anode, a recirculation ratio (RR) of the anode off-gas of 30% is required. Finally, the introduction of oxy-fuel combustion technology into the T-PG-SOFC-CHP system for CO2 capture (System II) allows to achieve a zero direct CO2 emission WTE power plant. However, this results in an energy penalty of about 5.40–6.77% associated with the CO2 capture and compression process.Energy Technolog

The effect of H₂S on internal dry reforming in biogas fuelled solid oxide fuel cells

Internal dry reforming of methane is envisaged as a possibility to reduce on capital and operation costs of biogas fuelled solid oxide fuel cells (SOFCs) system by using the CO2 present in the biogas. Due to envisaged internal dry reforming, the requirement for biogas upgrading becomes obsolete, thereby simplifying the system complexity and increasing its technology readiness level. However, impurities prevailing in biogas such as H2S have been reported in literature as one of the parameters which affect the internal reforming process in SOFCs. This research has been carried out to investigate the effects of H2S on internal dry reforming of methane on nickel-scandia-stabilised zirconia (Ni-ScSZ) electrolyte supported SOFCs. Results showed that at 800°C and a CH4:CO2 ratio of 2:3, H2S at concentrations as low as 0.125 ppm affects both the catalytic and electric performance of a SOFC. At 0.125 ppm H2S concentration, the CH4 reforming process is affected and it is reduced from over 95% to below 10% in 10 h. Therefore, future biogas SOFC cost reduction seems to become a trade-off between biogas upgrading for CO2 removal and biogas cleaning of impurities to facilitate efficient internal dry reforming.Sanitary EngineeringEnergy Technolog

Solid oxide fuel cells (SOFCs) fed with biogas containing hydrogen chloride traces: Impact on direct internal reforming and electrochemical performance

This study is particularly aimed at investigating the influence of hydrogen chloride traces in biogas on direct internal reforming in solid oxide fuel cells (SOFCs). The experiments are performed with simulated biogas containing methane to carbon dioxide ratio of 3:2, the usual average proportion in biogas. To the best of our knowledge, there are no reported studies that investigated the effect of hydrogen chloride on direct internal reforming by clearly establishing the effect of reforming with outlet gas composition measurements. The experiments at SOFC operating temperature of 850 °C reveals no negative effect on reforming or cell performance, with 4, 8, and 12 ppm(v) of hydrogen chloride in biogas. At 800 °C, there is no visible performance degradation, but a negligible amount of methane (∼ 1%) is detected in the anode off gas. Both the reforming and electrochemical performance are marginally affected at 750 °C. Further, post-test analyses (FESEM-EDS, XRD) of the used SOFC reveals no damage to the cell at microstructure level or chlorine poisoning. All the experiments are performed in the context of utilizing the biogas generated from sewage treatment plants in an SOFC system. The reported level of chlorine traces in biogas generated from sewage sludge is &lt; 10 ppm(v) and hence the limit set for experiments is at par with this value.Energy TechnologySanitary Engineerin