Production of hydrogen-rich syngas from absorption-enhanced steam gasification of biomass with conch shell-based absorbents

In this study, steam gasification of pine sawdust is conducted in a fixed-bed reactor in the temperature range 650–700 °C with calcined conch shell (CS) serving as a starting absorbent. The CS is further subjected to hydration (HCS) and calcination (CHCS) to prepare a modified absorbent. It is found that the hydration-calcination treatment of CS causes smaller CaO crystal grains with a larger BET surface area and more porous surface. As a consequence, CHCS exhibits higher catalytic activity for tar reforming, faster reaction rate for CO₂ absorption and better performance for H₂ selectivity than CS. Elevating the temperature contributes to tar reduction but results in lower H₂ content and higher CO₂ content, while an increase in Ca/C leads to higher H₂ content. And the H₂ content can reach approximately 76% with the use of CHCS when temperature and Ca/C ratio are 650 °C and 2, respectively.     

Catalytic decomposition of biomass tars: use of dolomite and untreated olivine

Although biomass is getting increased attention as a renewable energy source, one of the remaining problems still to be solved is the reduction of the high level of tar present in the product gas from gasification of biomass. The purpose of the present work is to study the activity of olivine and dolomite for tar destruction. Some researchers investigated olivine as bed material for biomass gasification. But it is not yet known how tars behave in the presence of olivine and whether olivine has some activity towards tar destruction. A slipstream from a lab-scale atmospheric bubbling-fluidised-bed gasifier (located at ECN) is passed through a secondary fixed-bed reactor where the additives are placed. For easy understanding, the results are represented in terms of the following tar classes; GC-undetectable tars (class 1), heterocyclic compounds (class 2), aromatic compounds (class 3), light polyaromatic compounds (class 4), heavy polyaromatic compounds (class 5). The general observation is that the conversion of all tar classes increases as the temperature was raised from 800 to 900 °C for both additives. The water-soluble heterocyclic compounds can be easily converted by thermal treatment. At the temperature of 900 °C, the water-soluble heterocyclic compounds are completely converted. A 48% decrease in heavy PAHs is observed with pure sand. Addition of 17 wt% olivine to the sand leads to a 71% decrease of PAHs at 900 °C, whereas addition of 17 wt% (pre-calcined) dolomite converted 90%. Also improvement in conversion of other tar classes is observed when olivine and dolomite are added during hot gas cleaning. A total tar amount of 4.0 g m₀⁻³ could be reduced to 1.5 and 2.2 g m₀⁻³ using dolomite and olivine, respectively, at a temperature of 900 °C. Inspite of this reduction in total tar concentration, a limited impact on the tar dewpoint is observed.     

Catalytic steam reforming of complex gasified biomass tar model toward hydrogen over dolomite promoted nickel catalysts

The complex mixture of gasified tar model (phenol, toluene, naphthalene, and pyrene) was steam reformed for hydrogen production over 10 wt% nickel based catalysts. The catalysts were prepared by co-impregnation method with dolomite promoter and various oxide supports (Al₂O₃, La₂O₃, CeO₂, and ZrO₂). Steam reforming was carried out at 700 °C at atmospheric pressure with steam to carbon molar ratio of 1 and gas hourly space velocity of 20 L/h·g_cat. The catalysts were characterised for reducibility, basicity, crystalline, and total surface area properties. Dolomite promoter strengthened the metal-support interaction and basicity of catalyst. The Ni/dolomite/La₂O₃ (NiDLa) catalyst with mesoporous structure (26.42mn), high reducibility (104.42%), and strong basicity (5.56 mmol/g) showed superior catalytic performance in terms of carbon conversion to gas (77.7%), H₂ yield (66.2%) and H₂/CO molar ratio (1.6). In addition, the lowest amount of filamentous coke was deposited on the spent NiDLa after 5 h.     

Chemical looping gasification for hydrogen production: A comparison of two unique processes simulated using ASPEN Plus

The research compares the simulations of two chemical looping gasification (CLG) types using the ASPEN Plus simulation software for the production of H₂. The simulated biomass type was poultry litter (PL). The first CLG type used in situ CO₂ capture utilizing a CaO sorbent, coupled with steam utilization for tar reforming, allowing for the production of a CO₂-rich stream for sequestration. Near-total sorbent recovery and recycle was achieved via the CO₂ desorption process. The second type utilized iron-based oxygen carriers in reduction–oxidation cycles to achieve 99.8% Fe₃O₄ carrier recovery and higher syngas yields. Temperature and pressure sensitivity analyses were conducted on the main reactors to determine optimal operating conditions. The optimal temperatures ranged from 500 to 1250 °C depending on the simulation and reactor type. Atmospheric pressure proved optimal in all cases except for the reducer and oxidizer in the iron-based CLG type, which operated at high pressure. This CLG simulation generated the most syngas in absolute terms (2.54 versus 0.79 kmol/kmol PL), while the CO₂ capture simulation generated much more H₂-rich syngas (92.45 mol-% compared to 62.94 mol-% H₂).     

Biomass to hydrogen-rich syngas via tar removal from steam gasification with La1-XCeXFeO3/dolomite as a catalyst

Biomass gasification produces hydrogen, which is a clean and promising technology. One of the most important aspects of the biomass gasification process is choosing the right catalyst. In this study, 10% La_1-XCe_XFeO₃/Dolomite (X = 0,0.2,0.4,0.6,0.8) synthesized using the sol-gel method was used as a catalyst in biomass gasification for the production of hydrogen-rich syngas. Gasification tests were carried out in a fixed bed reactor. The effects of an elemental substitution in LaFeO₃, temperature on the product were examined. Ce-substitution boosted the activity of LaFeO₃/DOL according to the data. Among the prepared catalysts, La_0.8Ce_0.2FeO₃/DOL performed the best, yielding a greater H₂ production and tar with a higher naphthalene concentration. As the temperature rises, so does the H₂ yield, at 850 °C, the highest H₂ yield is 0.69Nm³/Kg. Furthermore, the aromatization of phenols in tar is more likely to occur at high temperatures.     

Enhancement of the quality of syngas from catalytic steam gasification of biomass by the addition of methane/model biogas

In this study, methane and model biogas were added during the catalytic steam gasification of pine to regulate the syngas composition and improve the quality of syngas. The effects of Ni/γ-Al₂O₃ catalyst, steam and methane/model biogas on H₂/CO ratio, syngas yield, carbon conversion rate and tar yield were explored. The results indicated that the addition of methane/model biogas during biomass steam gasification could increase the H₂/CO ratio to about 2. Methane/model biogas, steam and Ni/γ-Al₂O₃ catalyst significantly affected the quality of syngas. High H₂ content syngas with H₂/CO ratio of about 2, biomass carbon conversion >85% and low tar yield was achieved under the optimum condition: S/C = 1.5, α = 0.2 and using Ni/γ-Al₂O₃ catalyst. According to ANOVA, methane and catalyst were the key influencing factors of the H₂/CO ratio and syngas yield, and the tar yield mainly depended on the Ni/γ-Al₂O₃ catalyst. Biogas, as a more environmentally friendly material than methane, can also regulate the composition of syngas co-feeding with biomass.     

Hydrogen-rich gas from catalytic steam gasification of municipal solid waste (MSW): Influence of catalyst and temperature on yield and product composition

In the present study the catalytic steam gasification of MSW to produce hydrogen-rich gas or syngas (H₂ + CO) with calcined dolomite as a catalyst in a bench-scale downstream fixed bed reactor was investigated. The influence of the catalyst and reactor temperature on yield and product composition was studied at the temperature range of 750–950 °C, with a steam to MSW ratio of 0.77, for weight hourly space velocity of 1.29 h⁻¹. Over the ranges of experimental conditions examined, calcined dolomite revealed better catalytic performance, at the presence of steam, tar was completely decomposed as temperature increases from 850 to 950 °C. Higher temperature resulted in more H₂ and CO production, higher carbon conversion efficiency and dry gas yield. The highest H₂ content of 53.29 mol%, and the highest H₂ yield of 38.60 mol H₂/kg MSW were observed at the highest temperature level of 950 °C, while, the maximum H₂ yield potential reached 70.14 mol H₂/kg dry MSW at 900 °C. Syngas produced by catalytic steam gasification of MSW varied in the range of 36.35–70.21 mol%. The char had a highest ash content of 84.01% at 950 °C, and negligible hydrogen, nitrogen and sulphur contents.     

An experimental study for a combined system of tar sand, oil shale, and olive cake as a potential energy source in Jordan

Jordan is an example of a third world country that is non-oil producing but contains huge reserves of other energy sources such as tar sand, oil shale, and olive cake. Some limited research is available about how to utilize these energy sources in pure form. However, available research does not deal with combinations of these energy sources. This experimental study investigates combinations of these energy forms as potential energy sources in Jordan. The experimental procedure involves characterization of samples by proximate analysis, calorific value determination of different combinations, and a compacting process of the different particles. The best combination, with respect to calorific value, is found to be 20% tar sand, 20% olive cake, and 60% oil shale. Compacting materials either with starch or with heated tar sand up to 110°C for 1 h indicates a feasible process for handling, packaging, and transporting.     

Syngas yield during pyrolysis and steam gasification of paper

Main characteristics of gaseous yield from steam gasification have been investigated experimentally. Results of steam gasification have been compared to that of pyrolysis. The temperature range investigated were 600–1000 °C in steps of 100 °C. Results have been obtained under pyrolysis conditions at same temperatures. For steam gasification runs, steam flow rate was kept constant at 8.0 g/min. Investigated characteristics were evolution of syngas flow rate with time, hydrogen flow rate and chemical composition of syngas, energy yield and apparent thermal efficiency. Residuals from both processes were quantified and compared as well. Material destruction, hydrogen yield and energy yield is better with gasification as compared to pyrolysis. This advantage of the gasification process is attributed mainly to char gasification process. Char gasification is found to be more sensitive to the reactor temperature than pyrolysis. Pyrolysis can start at low temperatures of 400 °C; however char gasification starts at 700 °C. A partial overlap between gasification and pyrolysis exists and is presented here. This partial overlap increases with increase in temperature. As an example, at reactor temperature 800 °C this overlap represents around 27% of the char gasification process and almost 95% at reactor temperature 1000 °C.     

Air gasification of dried sewage sludge in a two-stage gasifier. Part 2: Calcined dolomite as a bed material and effect of moisture content of dried sewage sludge for the hydrogen production and tar removal

In order to produce a clean producer gas, the air gasification of dried sewage sludge was conducted in a two-stage gasifier that consisted of a bubbling fluidized bed and a tar-cracking zone. The kind and amount of bed materials, the kind of additives in the upper-reactor, and the moisture content in the sewage sludge were selected as operating variables in order to investigate their effects on the development of the producer gas characteristics. In our experiments, the gasification of a dried sewage sludge sample containing 30 wt.% of moisture with a combination of calcined dolomite as the bed material and activated carbon in the tar-cracking zone removed the most tar and produced the highest hydrogen concentration. The total tar removal efficiency and the H₂ content in the producer gas from the sample noted above reached 88.4% and 32.1 vol.%, respectively. The LHVs of all the producer gases were high with values above 7 MJ Nm⁻³.     

Absorption-enhanced steam gasification of biomass for hydrogen production: Effect of calcium oxide addition on steam gasification of pyrolytic volatiles

The effect mechanism of calcium oxide (CaO) addition on gasification of pyrolytic volatiles as a key sub-process in the absorption-enhanced steam gasification of biomass (AESGB) for H₂ production at different conditions was investigated using a two-stage fixed-bed pyrolysis–gasification system. The results indicate that CaO functions as a CO₂ absorbent and a catalyst in the volatiles gasification process. CaO triggers the chemical equilibrium shift to produce more H₂ and accelerates volatile cracking and gasification reactions to obtain high volatile conversion rates. Increasing the gasification temperature could improve the reaction rate of cracking and gasification of volatiles as well as the catalytic effect of CaO, which continuously increase H₂ yield. When the gasification temperature exceeds 700 °C, the sharp decrease in CO₂ absorption capability of CaO drastically increases the CO₂ concentration and yield, which significantly decrease H₂ concentration. The appropriate temperature for the absorption-enhanced gasification process should be selected between 600 °C and 700 °C in atmospheric pressure. Increasing the water injection rate (represented as the mass ratio of steam to biomass) could also improve H₂ yield. The type of biomasses is closely associated with H₂ yield, which is closely related to the volatile content of biomass materials.     

Characteristic of hydrogen and syngas evolution from gasification and pyrolysis of rubber

The characteristics of syngas evolution during pyrolysis and gasification of waste rubber have been investigated. A semi-batch reactor was used for the thermal decomposition of the material under various conditions of pyrolysis and high temperature steam gasification. The results are reported at two different reactor temperatures of 800 and 900 °C and at constant steam gasifying agent flow rate of 7.0 g/min and a fixed sample mass. The characteristics of syngas were evaluated in terms of syngas flow rate, hydrogen flow rate, syngas yield, hydrogen yield and energy yield. Gasification resulted in 500% increase in hydrogen yield as compared to pyrolysis at 800 °C. However, at 900 °C the increase in hydrogen was more than 700% as compared to pyrolysis. For pyrolysis conditions, increase in reactor temperature from 800 to 900 °C resulted in 64% increase in hydrogen yield while for gasification conditions a 124% increase in hydrogen yield was obtained. Results of syngas yield, hydrogen yield and energy yield from the rubber sample are evaluated with that obtained from woody biomass samples, namely hard wood and wood chips. Rubber gasification yielded more energy at the 900 °C as compared to biomass feedstock samples. However, less syngas and less hydrogen were obtained from rubber than the biomass samples at both the temperatures reported here.     

A study on the effect of the CO2/steam mixtures and the addition of natural minerals on the reactivity of Adaro coal gasification

The synergetic effect in reactivity and gas yield on the various ratio of CO₂/steam mixtures was investigated. The isothermal gasification was conducted at three different temperatures. The synergy effect was evaluated on the ratio of CO₂/steam mixtures and reaction temperatures. In order to analyze the synergy quantitively, two reaction indexes were calculated from carbon conversion. The effect of natural minerals like Dolomite and Kaolin was investigated as well. The influence of synergy was varied upon the ratio of CO₂/steam mixtures and the optimal synergy was observed when the ratio of CO₂/steam mixtures was 1:2. The best synergy in reactivity and gas yield was shown at 800 °C and at 900 °C, respectively. By adding Dolomite, the synergetic effect in both reactivity and H₂ yield was promoted at 800 °C. Conclusively, the ratio of CO₂/steam mixtures and Dolomite played an important role to facilitate the synergy in the coal gasification.     

High temperature steam-only gasification of woody biomass

We have studied a high temperature steam gasification process to generate hydrogen-rich fuel gas from woody biomass. In this study, the performance of the gasification system which employs only high temperature steam exceeding 1200 K as the gasifying agent was evaluated in a 1.2 ton/day-scale demonstration plant. A numerical analysis was also carried out to analyze the experimental results. Both the steam temperature and the molar ratio of steam to carbon (S/C ratio) affected the reaction temperature which strongly affects the gasified gas composition. The H₂ fraction in the produced gas was 35–55 vol.% at the outlet of the gasifier. Under the experimental conditions, S/C ratio had a significant effect on the gas composition through the dominant reaction, water–gas shift reaction. The tar concentration in the produced gas from the high temperature steam gasification process was higher than that from the oxygen-blown gasification processes. The highest cold gas efficiency was 60.4%. However, the gross cold gas efficiency was 35%, which considers the heat supplied by high temperature steam. The ideal cold gas efficiency of the whole system with heat recovery processes was 71%.     

Inhibition of steam gasification of biomass char by hydrogen and tar

The influence of hydrogen and tar on the reaction rate of woody biomass char in steam gasification was investigated by varying the concentrations in a rapid-heating thermobalance reactor. It was observed that the steam gasification of biomass char can be separated into two periods. Compared with the first period, in the second period (in which the relative mass of remaining char is smaller than 0.4) the gasification rate is increased. These effects are probably due to inherent potassium catalyst. Higher hydrogen partial pressure greatly inhibits the gasification of biomass char in the first and second periods. By calculating the first-order rate constants of char gasification in the first and second periods, we found that the hydrogen inhibition on biomass char gasification is caused by the reverse oxygen exchange reaction in the first period. In the second period, dissociative hydrogen adsorption on the char is the major inhibition reaction. The influence of levoglucosan, a major tar component derived from cellulose, was also examined. We found that not only hydrogen but also vapor-phase levoglucosan and its pyrolysates inhibited the steam gasification of woody biomass char. By mixing levoglucosan with woody biomass sample, the pyrolysis of char proceeds slightly more rapidly than with woody biomass alone, and gas evolution rates of H₂ and CO₂ are larger in steam gasification.     

Exergy analysis of hydrogen production from steam gasification of biomass: A review

Exergy analysis of hydrogen production from steam gasification of biomass was reviewed in this study. The effects of the main parameters (biomass characteristics, particle size, gasification temperature, steam/biomass ratio, steam flow rate, reaction catalyst, and residence time) on the exergy efficiency were presented and discussed. The results show that the exergy efficiency of hydrogen production from steam gasification of biomass is mainly determined by the H₂ yield and the chemical exergy of biomass. Increases in gasification temperatures improve the exergy efficiency whereas increases in particle sizes generally decrease the exergy efficiency. Generally, both steam/biomass ratio and steam flow rate initially increases and finally decreases the exergy efficiency. A reaction catalyst may have positive, negative or negligible effect on the exergy efficiency, whereas residence time generally has slight effect on the exergy efficiency.     

Steam and supercritical water gasification of densified canola meal fuel pellets

In this research, canola meal was densified using bio-additives including alkali lignin, glycerol, and l-proline. The fuel pellet's formulation was optimized. The best fuel pellet demonstrated relaxed density and mechanical durability of 1015 kg/m³ and 99.0%, respectively. Synchrotron-based computer tomography technique indicated that lack of water in pellet formulation resulted in a twofold increase in pellet porosity. Thermogravimetric analysis showed that ignition temperature (240 °C) and burn-out temperature (640 °C) for fuel pellet were smaller than those for coal. Impacts of process parameters were evaluated on the quality of the gas product obtained from pellet's steam gasification and hydrothermal gasification. The gasification experiments showed production of untreated syngas with a suitable range of H₂/CO molar ratio (1.3–1.6) using steam gasification. Hydro-thermal gasification produced a larger molar ratio of H₂/CO (1.8–51.2) for the gas product. Modeling of pellet's steam gasification showed an excellent agreement with experimental results of steam gasification.     

Sorption-enhanced steam gasification of woody biomass assisted by Ca/Na/FS (fine slag) composite sorbents

In this research, composite sorbents with high activity in promoting H₂ production during sorption-enhanced steam gasification of pine sawdust (PS) were developed by doping coal gasification fine slag (FS) and NaOH into calcined conch shell (CS). The tests performed in a laboratory-scale fixed bed reactor demonstrated that the composite sorbents greatly improved H₂ concentration and yield over that achieved with CHCS (CS after hydration and calcination), reaching 73.5% and 600.7 mL/g-PS, respectively. This promotion effect on H₂ production was not influenced by the unburned carbon in FS. To obtain high H₂ concentration and yield with as little NaOH and as much FS as possible, the optimum sorbent was found to be 3CS-2FS-0.32Na (in mass ratio of CS:FS:NaOH = 3:2:0.32). Under this condition, the H₂ concentration and yield reached 74.3% and 572.3 mL/g-PS, respectively. In five cycles of experiment, although the H₂ yield of 3CS-2FS-0.32Na decreased from 572.3 mL/g-PS to 416.6 mL/g-PS, it was always higher than with CHCS alone by at least 28%. The results in this study indicate that FS has potential to be an effective inert support material that endows CaO with high activity in H₂ production during sorption-enhanced steam gasification. This might help to provide a new approach to minimizing the negative environmental impact of FS.     

Process simulation and techno-economic assessment of SER steam gasification for hydrogen production

In the SER (sorption enhanced reforming) gasification process a nitrogen-free, high calorific product gas can be produced. In addition, due to low gasification temperatures of 600–750 °C and the use of limestone as bed material, in-situ CO₂ capture is possible, leading to a hydrogen-rich and carbon-lean product gas. In this paper, results from a bubbling fluidised bed gasification model are compared to results of process demonstration tests in a 200 kW_th pilot plant.Based upon that, a concept for the hydrogen production via biomass SER gasification is studied in terms of efficiency and feasibility. Capital and operational expenditures as well as hydrogen production costs are calculated in a techno-economic assessment study. Furthermore, market framework conditions are discussed under which an economic hydrogen production via SER gasification is possible.