• Energy Research

Abstract 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 ( η E n , P G , η E x , P G ) and hydrogen production ( η E n , H 2 , η E x , H 2 ) 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 η E n , P G , η E x , P G , η E n , H 2 , and η E x , H 2 are also achieved. At CBPs, torrefied microalgae as feedstock lower the η E n , P G , η E x , P G , η E n , H 2 , and η E x , H 2 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.

La gazéification au plasma de la biomasse ligneuse, non ligneuse et algale brute et torréfiée à l'aide de trois agents de gazéification différents (air, vapeur et CO2) est effectuée par une analyse thermodynamique. Les impacts de la matière première et de l'atmosphère de réaction sur divers indices de performance tels que le rendement du gaz de synthèse, les émissions de polluants, le rapport énergie plasmatique/production de gaz de synthèse (PSR) et l'efficacité de la gazéification du plasma (PGE) sont étudiés. Les résultats montrent que la gazéification au plasma de CO2 donne le PSR le plus bas, conduisant ainsi à la PGE la plus élevée parmi les trois atmosphères réactionnelles. La biomasse torréfiée présente un rendement accru en gaz de synthèse et en PGE, mais est plus susceptible d'avoir un impact environnemental négatif des polluants N/S par rapport à la biomasse brute, en particulier pour la paille de riz. Cependant, l'exception concerne le marc de raisin torréfié et les macroalgues qui produisent des quantités plus faibles d'espèces S dans des atmosphères de vapeur et de CO2. Dans l'ensemble, le bois de pin torréfié présente les meilleures performances pour la production de gaz de synthèse de haute qualité contenant de faibles impuretés parmi les matières premières étudiées. La gasificación por plasma de biomasa leñosa cruda y torrefactada, no leñosa y de algas utilizando tres agentes gasificantes diferentes (aire, vapor y CO2) se realiza a través de un análisis termodinámico. Se estudian los impactos de la materia prima y la atmósfera de reacción en varios índices de rendimiento, como el rendimiento de gas de síntesis, las emisiones contaminantes, la relación de producción de energía de plasma a gas de síntesis (PSR) y la eficiencia de gasificación de plasma (PGE). Los resultados muestran que la gasificación con plasma de CO2 da el PSR más bajo, lo que conduce al PGE más alto entre las tres atmósferas de reacción. La biomasa torrefactada muestra un mayor rendimiento de gas de síntesis y PGE, pero es más probable que tenga un impacto ambiental negativo de los contaminantes N/S en comparación con los crudos, especialmente para la paja de arroz. Sin embargo, la excepción es para el orujo de uva torrefactado y las macroalgas que producen menores cantidades de especies S en atmósferas de vapor y CO2. En general, la madera de pino torrefactada tiene el mejor rendimiento para producir gas de síntesis de alta calidad que contiene bajas impurezas entre las materias primas investigadas. 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. يتم تغويز البلازما للكتلة الحيوية الخشبية وغير الخشبية والطحالب باستخدام ثلاثة عوامل تغويز مختلفة (الهواء والبخار وثاني أكسيد الكربون) من خلال تحليل ديناميكي حراري. يتم دراسة تأثيرات المواد الخام وجو التفاعل على مؤشرات الأداء المختلفة مثل إنتاج غاز التخليق وانبعاثات الملوثات وطاقة البلازما على نسبة إنتاج غاز التخليق (PSR) وكفاءة تغويز البلازما (PGE). تظهر النتائج أن تغويز بلازما ثاني أكسيد الكربون يعطي أقل نسبة PSR، مما يؤدي إلى أعلى نسبة PGE بين أجواء التفاعل الثلاثة. تعرض الكتلة الحيوية Torrefied زيادة إنتاج غاز التخليق و PGE، ولكن من المرجح أن يكون لها تأثير بيئي سلبي على ملوثات N/S مقارنة بالملوثات الخام، خاصة بالنسبة لقش الأرز. ومع ذلك، فإن الاستثناء هو لمارك العنب والطحالب الكبيرة التي تنتج كميات أقل من الأنواع S تحت أجواء البخار وثاني أكسيد الكربون. بشكل عام، يتمتع خشب الصنوبر المغطى بأفضل أداء لإنتاج غاز صناعي عالي الجودة يحتوي على شوائب منخفضة بين المواد الأولية التي تم التحقيق فيها.

In the face of the rapidly dwindling carbon budgets, negative emission technologies are widely suggested as required to stabilize the Earth’s climate. However, finding cost-effective, socially acceptable, and politically achievable means to enable such technologies remains a challenge. We propose solutions based on negative emission technologies to facilitate wealth creation for the stakeholders while helping to mitigate climate change. This paper comes up with suggestions and guidelines on significantly increasing carbon sequestration in coffee farms. A coffee and jackfruit agroforestry-based case study is presented along with an array of technical interventions, having a special focus on bioenergy and biochar, potentially leading to “negative emissions at negative cost.” The strategies for integrating food production with soil and water management, fuel production, adoption of renewable energy systems and timber management are outlined. The emphasis is on combining biological and engineering sciences to devise a practically viable niche that is easy to adopt, adapt and scale up for the communities and regions to achieve net negative emissions. The concerns expressed in the recent literature on the implementation of emission reduction and negative emission technologies are briefly presented. The novel opportunities to alleviate these concerns arising from our proposed interventions are then pointed out. Our analysis indicates that 1 ha coffee jackfruit-based agroforestry can additionally sequester around 10 tonnes of CO2-eq and lead to an income enhancement of up to 3,000–4,000 Euros in comparison to unshaded coffee. Finally, the global outlook for an easily adoptable nature-based approach is presented, suggesting an opportunity to implement revenue-generating negative emission technologies on a gigatonne scale. We anticipate that our approach presented in the paper results in increased attention to the development of practically viable science and technology-based interventions in order to support the speeding up of climate change mitigation efforts.

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 < 10 ppm(v) and hence the limit set for experiments is at par with this value.

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 (j), fuel utilization factor (Uf), pyrolysis gas reforming temperature (Treformer), and biochar split ratio (Rbiochar) on the SOFC and overall system performances in terms of energy and exergy analyses were evaluated. The simulation results indicated that increasing the Uf, Treformer, and Rbiochar 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%.

AbstractInternal 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.

AbstractInternal 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.