Experimental investigations of hydrogen production from CO catalytic conversion of tar rich syngas by biomass gasification

State-of-the-art review on hydrogen's production, storage, and potential as a future transportation fuel

Global energy consumption is expected to reach 911 BTU by the end of 2050 as a result of rapid urbanization and industrialization. Hydrogen is increasingly recognized as a clean and reliable energy vector for decarbonization and defossilization across various sectors. Projections indicate a significant rise in global demand for hydrogen, underscoring the need for sustainable production, efficient storage, and utilization. In this state-of-the-art review, we explore hydrogen production methods, compare their environmental impacts through life cycle analysis, delve into geological storage options, and discuss hydrogen's potential as a future transportation fuel. Combining electrolysis to make hydrogen and storing it in porous underground materials like salt caverns and geological reservoirs looks like a good way to balance out the variable supply of renewable energy and meet the demand at peak times. Hydrogen is a key component of our sustainable economy, and this article gives a broad overview of the process from production to consumption, touching on technical, economic, and environmental concerns along the way. We have made an attempt in this paper to compile different methods for the production of hydrogen and its storage, the challenges faced by current methods in the manufacturing of hydrogen gas, and the role of hydrogen in the future. This review paper will serve as a very good reference for hydrogen system engineering applications. The paper concludes with some suggestions for future research to help improve the technological efficiency of certain production methods, all with the goal of scaling up the hydrogen economy.

Reflecting on the environmental impact of the captured carbon feedstock

Climate change mitigation potentials of carbon capture and utilization (CCU) closely depend on the energy and chemicals used to capture the chemically inert CO2. The potential environmental benefits of CCU are typically assessed using Life Cycle Assessment (LCA) methodology. Although LCA is a standardized method, modelling CO2 as a carbon feedstock instead of an emission introduces an ambiguous "multifunctionality issue". Inconsistent multifunctionality practices have been applied to deal with this methodological complexity in LCAs of CCU technologies. Using one method instead of another can lead to highly positive or negative carbon footprints for the same carbon source and CO2 capture process. A comprehensive guideline to clarify the best practices to conduct LCAs of CCU technologies was published in 2020 (and updated in March 2022) in a collaborative process involving over 40 experts. In this guideline and linked scientific articles from experts involved in its development, a so-called "substitution method" is recommended to avoid suboptimal choices of CO2 sources, improve comparability and harmonize decision-making. This article critically reviews the methodological formulation of the recommended method and suggests corrections to possible inaccuracies in a future update of the guideline. Furthermore, various illustrative examples of common CO2 feedstocks were used to illustrate the meaning of adopting such a method in practice. Economic-based benchmarking of the environmental impacts of CO2 feedstocks calculated with such a method was also broadly illustrated.

Valorization of fluid petroleum coke for efficient catalytic destruction of biomass gasification tar

Large volumes of waste petroleum coke stockpiled in open yard not only represent a huge loss of valuable material but also pose a significant risk to the environment. This work proposed an innovative strategy for waste petroleum coke valorization by exploring its catalytic performance of biomass gasification tar destruction. Waste petroleum coke was firstly activated by potassium hydroxide (KOH) to obtain high specific surface area as well as low sulfur and ash contents. Petroleum coke derived catalyst showed superior performance than a commercial activated carbon derived catalyst for destruction of naphthalene as the tar model compound. The petroleum coke derived catalyst exhibited 99.1% naphthalene destruction efficiency at 800 °C but deactivated quickly under N₂ atmosphere. Under H₂ and steam atmospheres, the catalytic activities were 98.6% and 96.5% for 8 h, respectively. To study the correlation between catalytic performance and the structure of carbon catalyst, elemental analysis, scanning electron microscope (SEM) analysis, transmission electron microscope (TEM) analysis, X-ray powder diffraction (XRD) analysis, Brunauer-Emmett-Teller method (BET) analysis, Fourier transform infrared (FTIR) spectroscopy, temperature programmed oxidation (TPO) analysis and Raman spectroscopy were performed on both fresh and spent catalysts. Results demonstrated that the hydrogen-rich groups (small rings and amorphous carbon) and oxygen-containing groups may account for the good resistance to coke deposition under H₂ and steam atmospheres.

Hydrogen Production by Fluidized Bed Reactors: A Quantitative Perspective Using the Supervised Machine Learning Approach

The current hydrogen generation technologies, especially biomass gasification using fluidized bed reactors (FBRs), were rigorously reviewed. There are involute operational parameters in a fluidized bed gasifier that determine the anticipated outcomes for hydrogen production purposes. However, limited reviews are present that link these parametric conditions with the corresponding performances based on experimental data collection. Using the constructed artificial neural networks (ANNs) as the supervised machine learning algorithm for data training, the operational parameters from 52 literature reports were utilized to perform both the qualitative and quantitative assessments of the performance, such as the hydrogen yield (HY), hydrogen content (HC) and carbon conversion efficiency (CCE). Seven types of operational parameters, including the steam-to-biomass ratio (SBR), equivalent ratio (ER), temperature, particle size of the feedstock, residence time, lower heating value (LHV) and carbon content (CC), were closely investigated. Six binary parameters have been identified to be statistically significant to the performance parameters (hydrogen yield (HY)), hydrogen content (HC) and carbon conversion efficiency (CCE) by analysis of variance (ANOVA). The optimal operational conditions derived from the machine leaning were recommended according to the needs of the outcomes. This review may provide helpful insights for researchers to comprehensively consider the operational conditions in order to achieve high hydrogen production using fluidized bed reactors during biomass gasification.

New Methodological Approach for Performance Assessment in the Bioenergy Field

Bioenergy, along with other renewables, has always played its part in the world’s energy transition. Tracking the progress to meet specific goals has long been tackled and led to performance evaluation in the field. The present study aims to contribute to this area with a performance assessment framework in the bioenergy field. It comprises 16 European countries and 30 indicators assigned to three dimensions: innovation, efficiency, and sustainability and it follows a well-established methodology. For enabling country-to-country comparison, five maps are designed for better illustration. The country performance ranking is one of the main outputs of the analysis, revealing the outperformers and the weakest countries from its bottom half, as well as the particularities of countries scoring on each of the three dimensions. The policy recommendations and study limitations represent the most relevant part of the conclusions.

Experimental Parameter Study on Synthesis Gas Production by Steam-Oxygen Fluidized Bed Gasification of Sewage Sludge

The conversion of biogenic residues to fuels and chemicals via gasification and synthesis processes is a promising pathway to replace fossil carbon. In this study, the focus is set on sewage sludge gasification for syngas production. Experiments were carried out in a 20 kW fuel input bubbling fluidized bed facility with steam and oxygen as gasification agent. In-situ produced sewage sludge ash was used as bed material. The sensitivity of the key operation parameters gasifier temperature, oxygen ratio, steam to carbon ratio, and the space velocity on the syngas composition (H2, CO, CO2, CH4, CxHy, H2S, COS, NH3, and tars) was determined. The results show that the produced syngas has high H2 and CO concentrations of up to 0.37 m3 m−3 and 0.18 m3 m−3, respectively, and is thus suitable for synthesis of fuels and chemicals. By adjusting the steam to carbon ratio, the syngas’ H2 to CO ratio can be purposely tailored by the water gas shift reaction for various synthesis products, e.g., synthetic natural gas (H2/CO = 3) or Fischer–Tropsch products (H2/CO = 2). Also, the composition and yields of fly ash and bed ash are presented. Through the gasification process, the cadmium and mercury contents of the bed ash were drastically reduced. The ash is suitable as secondary raw material for phosphorous or phosphate fertilizer production. Overall, a broad database was generated that can be used for process simulation and process design.

An Eco-Friendly Fluidizable FexOy/CaO-γ-Al2O3 Catalyst for Tar Cracking during Biomass Gasification

The present study deals with the development, characterization, and performance evaluation of an eco-friendly catalyst, using 2-methoxy-4-methylphenol (2M4MP) as a surrogate tar. The 2M4MP was selected due to its chemical functionalities and the fact that it is a good model compound to represent the tar formed during biomass low temperature gasification. The eco-friendly catalyst was prepared using the typical Fe and Ca minerals which are present in ash. These ash components were added to a fluidizable γ-Al2O3 support using a multistep incipient impregnation, yielding Fe oxides as an active phase and CaO as the promoter. The prepared catalyst displayed a 120 m2/g BET specific surface area, with few γ-Al2O3 bulk phase changes, as observed with XRD. TPD-NH3 and pyridine FTIR allowed us to show the significant influence of CaO reduced support acidity. A TPR analysis provided evidence of catalyst stability during consecutive reduction–oxidation cycles. Furthermore, catalyst evaluation vis-à-vis catalytic steam 2M4MP gasification was performed using the fluidized CREC riser simulator. The obtained results confirm the high performance of the developed catalyst, with 2M4MP conversion being close to 100% and with selectivities of up to 98.6% for C1-C2 carbon-containing species, at 500 °C, with a 7.5 s reaction time and 1.5 g steam/g 2M4MP. These high tar conversions are promising efficiency indicators for alumina catalysts doped with Fe and Ca. In addition, the used catalyst particles could be blended with biochar to provide an integrated solid supplement that could return valuable mineral supplements to the soil.

Fluidised Bed Gasification of Diverse Biomass Feedstocks and Blends—An Overall Performance Study

The aim of this work is to investigate the fluidised bed gasification of several pure and blended feedstock prepared in the form of pellets: oak bark, two bark/wheat straw blends (85/15 and 50/50 wt%) and lignin residue remaining from bioethanol production. Gasification conditions were defined to be representative of dual fluidised bed ones (steam gasification at 850 °C, followed by air combustion of the char). The cold gas efficiency (77–81%), gas composition and tar content (0.9–2.3 g/kgdaf) are close for the gasification of bark and the two bark/wheat straw blends. For lignin residue, the cold gas efficiency is lower (71%), and the tar content is 9.1 g/kgdaf. The agglomeration propensity is much higher for lignin residue than for the other feedstock. This was put into evidence with in-bed temperature measurements at different levels, and confirmed with post-test size screening of the bed material particles. The 50/50 wt% bark/wheat straw blend seems to undergo defluidisation in combustion, however followed by refluidisation of the bed. These findings were also well correlated with a predictive model for defluidisation.

Biomass Availability in Europe as an Alternative Fuel for Full Conversion of Lignite Power Plants: A Critical Review

Biomass has been demonstrated as a capable source of energy to fulfill the increasing demand for clean energy sources which could last a long time. Replacing fossil fuels with biomass-based ones can potentially lead to a reduction of carbon emissions, which is the main target of the EU climate strategy. Based on RED II (revised Renewable Energy Directive 2018/2001/EU) and the European Green Deal, biomass is a promising energy source for achieving carbon neutrality in the future. However, the sustainable potential of biomass resources in the forthcoming decades is still a matter of question. This review aims at estimating the availability of biomass for energy reasons in the EU, and to evaluate its potential to meet the coal power plant capacity of the main lignite-producer countries, including Germany, Poland and Greece. Plants in line with the sustainability criteria of RED II have been selected for the preliminary estimations concerning their full conversion to the biomass power concept. Furthermore, the various barriers to biomass utilization are highlighted, such as the stranded asset risk of a future coal phase-out scenario, biomass supply chain challenges, biomass availability in main lignite-producer EU countries, the existing full conversion technologies, and biomass cost. A variety of challenges in the scenario of lignite substitution with biomass in a plant are investigated in a SWOT (strengths, weaknesses, opportunities, and threats) analysis. Technological risks and issues should be tackled in order to achieve the coal phase-out EU goal, mainly with regard to the supply chain of biomass. In this direction, the development of logistics centers for the centralized handling of biomass is strongly recommended.

Combining Biomass Gasification and Solid Oxid Fuel Cell for Heat and Power Generation: An Early-Stage Life Cycle Assessment

Biomass-fueled combined heat and power systems (CHPs) can potentially offer environmental benefits compared to conventional separate production technologies. This study presents the first environmental life cycle assessment (LCA) of a novel high-efficiency bio-based power (HBP) technology, which combines biomass gasification with a 199 kW solid oxide fuel cell (SOFC) to produce heat and electricity. The aim is to identify the main sources of environmental impacts and to assess the potential environmental performance compared to benchmark technologies. The use of various biomass fuels and alternative allocation methods were scrutinized. The LCA results reveal that most of the environmental impacts of the energy supplied with the HBP technology are caused by the production of the biomass fuel. This contribution is higher for pelletized than for chipped biomass. Overall, HBP technology shows better environmental performance than heat from natural gas and electricity from the German/European grid. When comparing the HBP technology with the biomass-fueled ORC technology, the former offers significant benefits in terms of particulate matter (about 22 times lower), photochemical ozone formation (11 times lower), acidification (8 times lower) and terrestrial eutrophication (about 26 times lower). The environmental performance was not affected by the allocation parameter (exergy or economic) used. However, the tested substitution approaches showed to be inadequate to model multiple environmental impacts of CHP plants under the investigated context and goal.

Catalytic conversion of gaseous tars using land, coastal and marine biomass-derived char catalysts in a bench-scale downstream combined fixed bed system

The catalytic activity of biochar for tar removal was evaluated in a bench-scale combined fixed bed reactor by comparison of gaseous tar catalytic cracking behaviors over land (Corn stalks, Cs), coastal (Reed, Re) and marine (Sargassum horneri, Sh) char catalyst. The experiments demonstrated that the tar yield after addition of the biochar was reduced significantly; the tar conversion efficiency reached to 94.6% for catalytic at 850 °C with 50 mm char bed length using Re char. And the yield and composition of gas also changed markedly. The percentage of H₂ and CO in the product gas were obviously increased. Sh has a higher H₂ content (49.3% of the total gas content), whereas, CO dominated in the gas products for Cs (45.4%) and Re (48.1%). The results from GC-MS analysis illustrated that the increase in temperature promoted the tar cracking and also promotes the polymerization of some tar components.

Influence of Raw Material Drying Temperature on the Scots Pine (Pinus sylvestris L.) Biomass Agglomeration Process—A Preliminary Study

For biomass compaction, it is important to determine all aspects of the process that will affect the quality of pellets and briquettes. The low bulk density of biomass leads to many problems in transportation and storage, necessitating the use of a compaction process to ensure a solid density of at least 1000 kg·m−3 and bulk density of at least 600 kg·m−3. These parameters should be achieved at a relatively low compaction pressure that can be achieved through the proper preparation of the raw material. As the compaction process includes a drying stage, the aim of this work is to determine the influence of the drying temperature of pine biomass in the range of 60–140 °C on the compaction process. To determine whether this effect is compensated by the moisture, compaction was carried out on the material in a dry state and on the materials with moisture contents of 5% and 10% and for compacting pressures in the 130.8–457.8 MPa range. It was shown that drying temperature affects the specific density and mechanical durability of the pellets obtained from the raw material in the dry state, while an increase in the moisture content of the raw material neutralizes this effect.

Influence of Pyrolysis Temperature on Product Distribution and Characteristics of Anaerobic Sludge

Pyrolysis of anaerobically digested sludge can serve as an efficient biomass for biofuel production. Pyrolysis produces products like char, bio-oil, and combustible gases by thermochemical conversion process. It can be used for sludge treatment that decreases sludge disposal problems. Sludge produced from anaerobic co-digestion (microalgae, cow dung, and paper) waste has high carbon and hydrogen content. We investigated the candidacy of the anaerobic sludge having high heating value (HHV) of 20.53 MJ/kg as a reliable biomass for biofuels production. The process of pyrolysis was optimized with different temperatures (400, 500, and 600 °C) to produce high quantity and improved quality of the products, mainly bio-oil, char, and gas. The results revealed that with the increase in pyrolysis temperature the quantity of char decreased (81% to 55%), bio-oil increased (3% to 7%), and gas increased (2% to 5%). The HHV of char (19.2 MJ/kg), bio-oil (28.1 MJ/kg), and gas (18.1 MJ/kg) were predominantly affected by the amount of fixed carbon, hydrocarbons, and volatile substance, respectively. The study confirmed that the anaerobic sludge is a promising biomass for biofuel production and pyrolysis is an efficient method for its safe disposal.

Thermal Analysis of Nigerian Oil Palm Biomass with Sachet-Water Plastic Wastes for Sustainable Production of Biofuel

Nigeria, being the world’s largest importer of diesel-powered gen-sets, is expected to invest in bio-fuels in the future. Hence, it is important to examine the thermal properties and synergy of wastes for potential downstream resource utilization. In this study, thermal conversion as a route to reduce the exploding volume of wastes from sachet-water plastic (SWP) and oil palm empty fruit bunch (OPEFB) biomass was studied. Thermogravimetric (TGA) and subsequent differential scanning calorimeter (DSC) was used for the analysis. The effect of heating rate at 20 °C min−1 causes the increase of activation energy of the decomposition in the first-stage across all the blends (0.96 and 16.29 kJ mol−1). A similar phenomenon was seen when the heating rate was increased from 10 to 20 °C min−1 in the second-stage of decomposition. Overall, based on this study on the synergistic effects during the process, it can be deduced that co-pyrolysis can be an effective waste for energy platform.

Techno-Economic Analysis of a Small-Scale Biomass-to-Energy BFB Gasification-Based System

In order to limit global warming to around 1.5–2.0 °C by the end of the 21st century, there is the need to drastically limit the emissions of CO2. This goal can be pursued by promoting the diffusion of advanced technologies for power generation from renewable energy sources. In this field, biomass can play a very important role since, differently from solar and wind, it can be considered a programmable source. This paper reports a techno-economic analysis on the possible commercial application of gasification technologies for small-scale (2 MWe) power generation from biomass. The analysis is based on the preliminary experimental performance of a 500 kWth pilot-scale air-blown bubbling fluidized-bed (BFB) gasification plant, recently installed at the Sotacarbo Research Centre (Italy) and commissioned in December 2017. The analysis confirms that air-blown BFB biomass gasification can be profitable for the applications with low-cost biomass, such as agricultural waste, with a net present value up to about 6 M€ as long as the biomass is provided for free; on the contrary, the technology is not competitive for high-quality biomass (wood chips, as those used for the preliminary experimental tests). In parallel, an analysis of the financial risk was carried out, in order to estimate the probability of a profitable investment if a variation of the key financial parameters occurs. In particular, the analysis shows a probability of 90% of a NPV at 15 years between 1.4 and 5.1 M€ and an IRR between 11.6% and 23.7%.

Low-Carbon Energy Planning: A Hybrid MCDM Method Combining DANP and VIKOR Approach

With the development of urbanization, people’s living standards have improved. Simultaneously, the growing aggravation of resource shortages and environmental pollution have also gradually attracted widespread attention. Low-carbon energy planning can effectively reduce dependence on fossil resources and carbon emissions to the atmosphere, as well as improve the utilization of resources. Therefore, the formulation and evaluation of low-carbon energy planning have become the focus of attention for related colleges and institutions. This paper puts forward a hybrid multi-criteria decision making(MCDM) method combining decision making trial and evaluation laboratory(DEMATEL), analytical network process(ANP), and VIKOR to obtain the weight of each criterion and evaluate each alternative about low-carbon energy planning for building. A hierarchy structure of criteria involving cost, safety, reliability, and environment protection is built. Afterwards, a case of four alternatives is applied for testifying this methodology. Lastly, a comparison with prior methodologies serves as proof of the raised ranking. The presentation has proved that this methodology offers a more precise and effective foundation for decisions about low-carbon energy planning evaluation.

Effects of Oxygen Enrichment in Air Oxidants on Biomass Gasification Efficiency and the Reduction of Tar Emissions

This study applied oxygen-enrichment conditions to remove tar (the main problem in biomass gasification) and increase gasification efficiency. Experiments on oxygen-enrichment conditions were conducted at oxygen concentrations of 21%, 25%, 30%, and 35% in oxidants. This was expected to increase the partial oxidation reaction in gasification reactions, thus leading to thermal decomposition of tar in producer gas. The decomposed tar was expected to be converted into syngas or combustible gases in the producer gas. The results were as follows: Tar-reduction efficiency was 72.46% at 30% oxygen enrichment compared to the standard 21% enrichment condition. In addition, the concentrations of syngas and combustible gases in the producer gas tended to increase. Therefore, the 30% oxygen-enrichment condition was optimal, resulting in 78.00% for cold gas efficiency and 80.24% for carbon conversion efficiency. The application of oxygen enrichment into the lab-scale gasification system clearly reduced the concentration of tar and tended to increase some indexes of gasification efficiency, thus suggesting the usefulness of this technique in large-scale biomass gasification operations.

Characterization of Recycled Wood Chips, Syngas Yield, and Tar Formation in an Industrial Updraft Gasifier

In this study, the moisture content, calorific value, and particle size of recycled wood chips were measured. The wood chips were used to fuel an 8.5 MWth updraft gasifier to produce syngas for combustion in a steam-producing boiler. In-situ syngas composition and tar concentrations were measured and analyzed against biomass fuel properties. No efforts were made to adjust the properties of biomass or the routine operating conditions for the gasifier. A sampling device developed by CanmetENERGY-Ottawa (Ottawa, ON, Canada) was used to obtain syngas and tar samples. Wood chip samples fed to the gasifier were taken at the same time the gas was sampled. Results indicate that as the fuel moisture content increases from 20% to 35%, the production of CO drops along with a slight decrease in concentrations of H2 and CH4. Tar concentration increased slightly with increased moisture content and proportion of small fuel particles (3.15–6.3 mm). Based on the findings of this study, biomass fuel moisture content of 20% and particles larger than 6.3 mm (1/4″) are recommended for the industrial updraft gasifier in order to achieve a higher syngas quality and a lower tar concentration.

Supercritical Water Gasification of Scenedesmus Dimorphus µ-algae

The aim of the paper is based on the experimental tests of Gasification in supercritical water for humid biomass, Scenedesmus dimorphus. In this work, experimental tests were carried out in order to understand the main parameters of the SCWG process and their influence varying the total solids content, GGE and CGE gas yield and energy recovery. Based on experimental test and considering literature data about energy demand for microalgae growth and energy required for SCWG process it was possible to evaluate that with minimum total solid content necessary for setting-up a self-sustainable process considering the only energy recovery from the condensation of the water outlet the process. At the same time these simulation were repeated considering of use the enthalpy of water in SCW condition for turbine expansion instead heat recovery obtained not only syngas production usable for biofuels synthesis but also power production.

An experimental approach aiming the production of a gas mixture composed of hydrogen and methane from biomass as natural gas substitute in industrial applications

This work presents an experimental approach aiming the production of a gas mixture composed of H₂ and CH₄, which should serve as natural gas substitute in industrial applications. Therefore, a lab-scale process chain employing a water gas shift unit, scrubbing units, and a pressure swing adsorption unit was operated with tar-rich product gas extracted from a commercial dual fluidized bed biomass steam gasification plant. A gas mixture with a volumetric fraction of about 80% H₂ and 19% CH₄ and with minor fractions of CO and CO₂ was produced by employing carbon molecular sieve as adsorbent. Moreover, the produced gas mixture had a lower heating value of about 15.5MJ·m^-3 and a lower Wobbe index of about 43.4MJ·m^-3, which is similar to the typical Wobbe index of natural gas.