Steam co-gasification of coal and biomass derived chars with synergy effect as an innovative way of hydrogen-rich gas production

The main results of the experimental work on steam co-gasification of Polish hard coal and Salix Viminalis blends in a fixed bed reactor under atmospheric pressure and at the temperature of 700, 800 and 900 °C are presented in the paper. The effectiveness of co-gasification of coal/biomass blends of 20, 40, 60 and 80% w/w biomass content was tested in terms of gas flows, composition, carbon conversion and chars reactivity. A synergy effect in the co-gasification tests, consisting in increase in the volume of hydrogen produced, when compared to the tests of coal and biomass gasification, was observed at all tested temperatures. The observed synergy effect was attributed to the catalytic effect of K₂O present in blend ash (6-10% wt). Moreover, in co-gasification of blends of 20 and 40% w/w biomass content, increase in the total gas yield was observed, when compared to the tests of coal and biomass gasification at all tested temperatures. In tests of co-gasification of blends of higher biomass content (i.e. 60 and 80% w/w), a slight decrease in the total volume of product gas was observed, when compared to the tests of coal and biomass gasification. Nevertheless, higher ratio of biomass in co-gasification makes it still an attractive option in terms of CO₂ emission reduction and increase in hydrogen production.     

Experimental study on syngas production by co-gasification of coal and biomass in a fluidized bed

The main results of an experimental work on co-gasification of a Chinese bituminous coal and two types of biomass in a bench-scale fluidized bed are reported in the present study. Experiments were performed at different oxygen equivalence ratio, steam/carbon ratio and biomass/coal ratio. In addition, stabilization of co-gasification process was investigated. It was found that a relatively low oxygen equivalence ratio favors the increase of syngas yield (CO + H₂). There is a maximum value in the curve of syngas yield versus steam/carbon ratio. Moreover, the content of H₂ in gas increases with the increase of biomass ratio while that of CO and syngas yield decrease. A continuous stable operation can be gained.     

Petrographic and chemical reactivity assessment of Indian high ash coal with different biomass in fluidized bed co-gasification

The reactivity of coal and biomass has been evaluated by comparing the optical and chemical changes in feed material prior and after the co-gasification. The proximate, ultimate, GCV, low-pressure N₂ sorption isotherm, micropetrography, SEM and EDX spectroscopy analyses are carried out to assess the reactivity of blends of high ash Indian coal and biomass. The relative changes in parameters like surface area, pore size, and pore volume have been correlated with reacted percentage area of coal macerals and cellulose-lignin cellular structures of biomass. The Optimas image processing software is being used to mark the reacted portion of organic constituents and calculated the reactivity percentage. The bottom ash of pure coal has shown the least reacted organic matters, indicating inefficiency of high ash coal due to a large amount of inorganic and inertinite contents that is resisting the oxidation. The reactivity percentage is determined by the petrographic and SEM images, and varies from 36.34 to 99.64% and 6.61–96.22%, respectively. It is summarised that the estimation of percentage alteration of macerals and other micro-organic constituents can be used as one of the practical approaches for the assessment of the reactivity of coal and biomass. The blending ratio 6:4 of coal and press mud has shown the highest reactivity (>99.64%). The values of petrographic and SEM reactivity have shown good correlations with the carbon contents, unreacted vitrinites, mineral matters and biomass remnants. These relations have been taken into account to formulate the proposed petrographic empirically calculated reactivity (R_PEC). The focus has also been made to investigate the influence of feed composition on carbon conversion and heating value of the product gas.     

Assessment of flexible energy vectors poly-generation based on coal and biomass/solid wastes co-gasification with carbon capture

This paper evaluates biomass and solid wastes co-gasification with coal for energy vectors poly-generation with carbon capture. The evaluated co-gasification cases were evaluated in term of key plant performance indicators for generation of totally or partially decarbonized energy vectors (power, hydrogen, substitute natural gas, liquid fuels by Fischer–Tropsch synthesis). The work streamlines one significant advantage of gasification process, namely the capability to process lower grade fuels on condition of high energy efficiency. Introduction in the evaluated IGCC-based schemes of carbon capture step (based on pre-combustion capture) significantly reduces CO₂ emissions, the carbon capture rate being higher than 90% for decarbonized energy vectors (power and hydrogen) and in the range of 47–60% for partially decarbonized energy vectors (SNG, liquid fuels). Various plant concepts were assessed (e.g. 420–425 MW net power with 0–200 MW_th flexible hydrogen output, 800 MW_th SNG, 700 MW_th liquid fuel, all of them with CCS). The paper evaluates fuel blending for optimizing gasification performance. A detailed techno-economic evaluation for hydrogen and power co-generation with CCS was also presented.     

A review on reactivity characteristics and synergy behavior of biomass and coal Co-gasification

Co-gasification is a promising approach to the clean and high-efficiency co-utilization of biomass and coal with syngas (H₂+CO) production. Gasification reactivity is an important factor influencing the operation conditions choice, carbon conversion efficiency and syngas production performance. Coal-biomass interaction during co-gasification will directly result in the synergy behavior of different forms and intensities on co-gasification reactivity. Due to the fuel origin diversity, structural property difference and reaction process complexity of biomass and coal, a clear understanding of reactivity characteristics and synergy behavior of co-gasification is very essential for revealing co-gasification reaction mechanism and providing theoretical support for actual application. In this paper, the influences factors (such as feedstock type, blended ratio, gasification temperature, co-pyrolysis process, gasification reactor and biomass pretreatment) for co-gasification reactivity and the synergy behavior on co-gasification reactivity are summarized in details, and non-catalytic/catalytic synergy mechanisms for co-gasification are discussed. Previous researchers have acquired a plenty of meaning data, providing important reference for industrial application of co-gasification technology. However, volatile matter-char interaction mechanism during co-pyrolysis was still unclear, AAEM migration and transformation route during co-gasification are lack of in-situ analysis, transfer route and interaction of free radicals during co-gasification process were unknown, and co-gasification kinetics model containing dynamic synergistic/inhibition factors hasn't been established.     

A review on exergy analysis of biomass based fuels

Renewable energy sources can be a good substitute of the fossil fuels which are being terminated fast. Nowadays biomass and biofuels are considered because of their environment friendly characteristics and their ability of supplying much more energy. An alternative means to select the most efficient and convenient biomass, is exergy analysis. The present paper has reviewed the existent surveys on the exergy analysis of different kind of biomass included the woody biomass, herbaceous and agricultural biomass, aquatic biomass, contaminated biomass and industrial biomass. The most common thermochemical processes are investigated and the efficiency of the different process and various kinds of biomass are determined.     

Effect of fuel blend composition on hydrogen yield in co-gasification of coal and non-woody biomass

In this study, torrefaction of sunflower seed cake and hydrogen production from torrefied sunflower seed cake via steam gasification were investigated. Torrefaction experiments were performed at 250, 300 and 350 °C for different times (10–30 min). Torrefaction at 300 °C for 30 min was selected to be optimum condition, considering the mass yield and energy densification ratio. Steam gasification of lignite, raw- and torrefied biomass, and their blends at different ratios were conducted at downdraft fixed bed reactor. For comparison, gasification experiments with pyrochar obtained at 500 °C were also performed. The maximum hydrogen yield of 100 mol/kg fuel was obtained steam gasification of pyrochar. The hydrogen yields of 84 and 75 mol/kg fuel were obtained from lignite and torrefied biomass, respectively. Remarkable synergic effect exhibited in co-gasification of lignite with raw biomass or torrefied biomass at a blending ratio of 1:1. In co-gasification, the highest hydrogen yield of 110 mol/kg fuel was obtained from torrefied biomass-lignite (1:1) blend, while a hydrogen yield from pyrochar-lignite (1:1) blend was 98 mol/kg. The overall results showed that in co-gasification of lignite with biomass, the yields of hydrogen depend on the volatiles content of raw biomass/torrefied biomass, besides alkaline earth metals (AAEMs) content.     

Comparative study on combustion and oxy-fuel combustion environments using mixtures of coal with sugarcane bagasse and biomass sorghum bagasse by the thermogravimetric analysis

Biomass and coal have different physicochemical properties and thermal behavior. During the co-combustion of coal-biomass mixtures, their thermal behavior varies according to the percentage of each fuel in the mixture. Thereby, this research aims to characterize the thermal behavior of mixtures of coal, sugarcane bagasse, and biomass sorghum bagasse as biomass in simulated combustion (O₂/N₂) and oxy-fuel combustion (O₂/CO₂) environments. Experiments have been performed in duplicate on a thermogravimetric analyzer at heating rate of 10 °C/min. A uniform granulometry was considered for all materials (63 μm) in order to ensure a homogeneous mixture. Four biomass percentages in the mixture (10, 25, 50 and 75%) have been studied. Based on thermogravimetric (TG) and thermogravimetric (DTG) analyses, parameters such as combustion index, synergism, and activation energy have been determined, as well as the combustion environment influence on these parameters. The results indicate that, although sugarcane bagasse has the lowest activation energy, the thermal behavior of both types of biomass is similar. Thus, biomass sorghum bagasse can be used as an alternative biomass to supply the power required during sugarcane off-season. For both mixtures, optimal results were obtained at 25% of biomass. By analyzing the environment influence on combustion behavior, the results indicate that when N₂ is replaced with CO₂, it is observed an increase in reaction reactivity, a higher oxidation rate of materials and an improvement in evaluated parameters.     

Comparative exergy analysis of sorption enhanced and conventional methane steam reforming

Exergy efficiency analysis tool is used to evaluate sorption enhanced steam reforming in comparison with the industrial hydrogen production route, steam reforming. The study focuses on hydrogen production for use in high pressure processes. Thermodynamic sensitivity analysis (effect of reforming temperature on hydrogen yield and reforming enthalpy) was performed to indicate the optimum temperature (650 °C) for the sorption enhanced reforming. The pressure was selected to be, for both cases, 25 bar, a typical pressure used in the industrial (conventional) process. Atmospheric pressure, 1000 °C and CO₂ as inert gas were specified as the optimum operating parameters for the regeneration of the sorbent after performing exergy efficiency analysis of three realistic case scenarios. Aspen Plus simulation process schemes were built for conventional and sorption enhanced steam reforming processes to attain the mass and energy balances required to assess comparatively exergy analysis. Simulation results showed that sorption enhanced reforming can lead to a hydrogen purity increase by 17.3%, along with the recovery of pure and sequestration-ready carbon dioxide. The exergy benefit of sorption enhanced reforming was calculated equal to 3.2%. Analysis was extended by adding a CO₂ separation stage in conventional reforming to reach the hydrogen purity of sorption enhanced reforming and enable a more effective exergy efficiency comparison. Following that analysis, sorption enhanced reforming gained 10.8% in exergy efficiency.     

Catalytic steam co-gasification of biomass and coal in a dual loop gasification system with olivine catalysts

A dual loop gasification system (DLG) has been previously proposed to facilitate tar destruction and H₂-rich gas production in steam gasification of biomass. To sustain the process auto-thermal, however, additional fuel with higher carbon content has to be supplied. Co-gasification of biomass in conjunction with coal is a preferred option. Herein, the heat balance of the steam co-gasification of pine sawdust and Shenmu bituminous coal in the DLG has been analyzed to verify the feasibility of the process with the help of Aspen Plus. Upon which, the co-gasification experiments in the DLG have been investigated with olivine as both solid heat carriers and in-situ tar destruction catalysts. The simulation results show that the self-heating of the DLG in the co-gasification is achieved at the coal blending ratio of 28%, gasification circulation ratio of 19 and reforming circulation ratio of 20 when the gasifier temperature 800 °C, reforming temperature 850 °C, combustor temperature 920 °C and S/C 1.1. The co-gasification experiments indicate that the tar is efficiently destructed in the DLG at the optimized reformer temperature and with olivine catalysts.     

Co-gasification of biomass and coal for methanol synthesis

In recent years, a growing interest has been observed in the application of methanol as an alternative liquid fuel, which can be used directly for powering Otto engines or fuel cells achieving high thermodynamic efficiencies and relatively low environmental impacts. Biomass and coal can be considered as a potential fuel for gasification and further syn-gas production and methanol synthesis. In the near future, the economy of methanol production through coal and biomass gasifications can be achieved by their linking with modern gas-steam power systems. The essence of linking is the full utilisation of the capacity of coal/biomass gasification installations. The up-to-date experience of coal and biomass gasification, including gas processing towards syn-gas and methanol production, is described and discussed. A conceptual flow diagram of pressurized and oxygen feeded co-gasification of biomass and coal integrated with combined cycle and parallel methanol production is evaluated. The effect of methanol production rate on the economy of power production is assessed.     

Thermodynamics research on hydrogen production from biomass and coal co-gasification with catalyst

A model comprises two sub-models, i.e. combustion and gasification models, is developed to simulate a single fluidized bed two-step gasification process and to predict H₂ production under different conditions. The combustion sub-model which consists of volatile precipitation and char combustion sub-models. The combustion sub-model is used to forecast residual char. The gasification sub-model, based on the mass and energy balance, is used to examine thermodynamically the effect on the hydrogen production of calcium oxide as the catalyst. Moreover, the effects of the operational conditions on the hydrogen production such as biomass/coal (mass ratio), temperature, steam/coke, and calcium/coke, are simulated. The results indicate that the addition of calcium oxide at certain conditions can significantly improve hydrogen production and lower the required temperature for gasification. The model predicts that the maximum hydrogen production of 60% can be achieved under the conditions of temperature in the range of 800-850 °C, calcium/coke, steam/coke, and coal/biomass (mass ratio) are 0.5, 1.8, and 1/4, respectively. The model predictions are in good agreement with the experimental data.     

Exergy analysis of hydrogen production plants based on biomass gasification

Biomass gasification is a promising option for the sustainable production of hydrogen rich gas. Five different commercial or pilot scale gasification systems are considered for the design of a hydrogen production plant that generates almost pure hydrogen. For each of the gasification technique models of two different hydrogen production plants are developed in Cycle-Tempo: one plant with low temperature gas cleaning (LTGC) and the other with high temperature gas cleaning (HTGC). The thermal input of all plants is 10 MW of biomass with the same dry composition. An exergy analysis of all processes has been made. The processes are compared on their thermodynamic performance (hydrogen yield and exergy efficiency). Since the heat recovery is not incorporated in the models, two efficiencies are calculated. The first one is calculated for the case that all residual heat can be applied, the case with ideal heat recovery, and the other is calculated for the case without heat recovery. It is expected that in real systems only a part of the residual heat can be used. Therefore, the actual value will be in between these calculated values. It was found that three processes have almost the same performance: The Battelle gasification process with LTGC, the FICFB gasification process with LTGC, and the Blaue Turm gasification process with HTGC. All systems include further processing of the cleaned gas from biomass gasification into almost pure hydrogen. The calculated exergy efficiencies are, respectively, 50.69%, 45.95%, and 50.52% for the systems without heat recovery. The exergy efficiencies of the systems with heat recovery are, respectively, 62.79%, 64.41%, and 66.31%. The calculated hydrogen yields of the three processes do not differ very much. The hydrogen yield of the Battelle LTGC process appeared to be 0.097 kg (kg_{(dry biomass)})⁻¹, for the FICFB LTGC process a yield of 0.096 kg (kg_{(dry biomass)})⁻¹ was found, and for the Blaue Turm HTGC 0.106 kg (kg_{(dry biomass)})⁻¹.     

Sorption enhanced steam hydrogasification of coal for synthesis gas production with in-situ CO2 removal and self-sustained hydrogen supply

The in-situ removal of CO₂ and the increase of the energetic gas yield, including hydrogen and methane, by sorption enhanced steam hydrogasification (SE-SHR) process were investigated. Lignite was used in this study as the feedstock to the steam hydrogasification reaction (SHR) with the addition of calcined dolomite as a sorbent. CO₂ was reduced dramatically with the introduction of the sorbent into the reactor. The production of hydrogen and methane was increased simultaneously. The hydrogen yield was increased by 60% when the calcium oxide to carbon molar ratio was increased to 0.86 as compared to the results without the sorbent. The hydrogen in the product gas was sufficient to maintain a self-sustained supply back to the SHR when the calcium oxide to carbon molar ratio was over 0.29. The performance of the SE-SHR was determined at different temperatures ranging from 650 °C to 800 °C and at different steam to carbon molar ratios. Additionally, the char conversion was also enhanced in all cases with the sorbent introduction. The synthesis gas production using SE-SHR coupled with steam methane reforming was also modeled by Aspen Plus. The simulation results showed that the H₂/CO ratio of the synthesis gas generated based on SE-SHR process was 6 with higher overall energy efficiency of 74.5%. Summarily, the main findings of this study were that the overall performance of the SE-SHR was substantially improved compared to the conventional operation of the SHR and the quality of synthesis gas produced based on SE-SHR process was more flexible for the downstream processing.     

Comparative exergoeconomic analyses of the integration of biomass gasification and a gas turbine power plant with and without fogging inlet cooling

Inlet cooling is effective for mitigating the decrease in gas turbine performance during hot and humid summer periods when electrical power demands peak, and steam injection, using steam raised from the turbine exhaust gases in a heat recovery steam generator, is an effective technique for utilizing the hot turbine exhaust gases. Biomass gasification can be integrated with a gas turbine cycle to provide efficient, clean power generation. In the present paper, a gas turbine cycle with fog cooling and steam injection, and integrated with biomass gasification, is proposed and analyzed with energy, exergy and exergoeconomic analyses. The thermodynamic analyses show that increasing the compressor pressure ratio and the gas turbine inlet temperature raises the energy and exergy efficiencies. On the component level, the gas turbine is determined to have the highest exergy efficiency and the combustor the lowest. The exergoeconomic analysis reveals that the proposed cycle has a lower total unit product cost than a similar plant fired by natural gas. However, the relative cost difference and exergoeconomic factor is higher for the proposed cycle than the natural gas fired plant, indicating that the proposed cycle is more costly for producing electricity despite its lower product cost and environmental impact.     

Comparative analysis of hydrogen production systems from biomass based on different absorbent regeneration processes

Hydrogen production through single-step process has been proposed for a long time. The process can produce H₂ in gasifier, and simultaneously, achieve integration of exothermic and endothermic as well as gas production and separation in one reactor. The process consists of mainly twin fluidized beds—a gasifier and a CO₂ absorbent regenerator. In this paper, two modes are suggested for absorbent regeneration. One case named PCC process is partial carbon conversion in the gasifier, and the carbon residue acts as a fuel for the regenerator; the other case named NO process is nickel oxidation in the regenerator to supply heat for absorbent regeneration. The mass and energy balances and cold gas efficiency were analyzed by thermodynamic calculation for the two different processes. When the feedstock is same, PCC process gives a higher cold gas efficiency of 0.74 than NO process of 0.67.     

Exergy analysis of biomass staged-gasification for hydrogen-rich syngas

Using Aspen Plus simulations, exergy analyses of hydrogen-rich syngas production via biomass staged-gasification are carried out for three configurations, namely, staged-gasification with pyrolysis gas combustion and char gasification (C-1), staged-gasification with pyrolysis gas reforming and char gasification (C-2), and staged-gasification with pyrolysis gas reforming and char combustion (C-3). The results show that, for the gasification and reforming processes, the exergy loss of pyrolysis gas with tar reforming is less than that of char gasification. As for the system, it is conducive to generating hydrogen by making full use of the hydrogen element (H) in biomass instead of the H in water. The benefits of C-1 are that it removes tar and produces higher yield and concentration of hydrogen. However, C-2 is capable of obtaining higher exergy efficiency and lower exergy loss per mole of H₂ production. C-3 theoretically has greater process performances, but it has disadvantages in tar conversion in practical applications. The appropriate gasification temperature (T_G) are in the range of 700–750 °C and the appropriate mass ratio of steam to biomass (S/B) are in the range of 0.6–0.8 for C-1 and C-3; the corresponding parameters for C-2 are in the ranges of 650–700 °C and 0.7–0.8, respectively.     

Exergy analysis of hydrogen-reduction based steel production with coal gasification-shaft furnace-electric furnace process

Carbon-free energy utilization in steel production is an effective way for China's iron and steel industry to achieve low carbon development. Thus, coal gasification-shaft furnace-electric furnace (CSE) technology, which use hydrogen-enriched gas for steel production, has recently become a sustainable topic of great concern. In the current study, the material flow analysis (MFA) and exergy assessment of the CSE process are conducted to investigate the material consumption and energy efficiency of this new steelmaking process. The exergy efficiency of the CSE process is calculated to be 50.11%, indicating a great potential for energy-saving. The results indicate that the coal gasification & gas purification that responsible for hydrogen-enriched gas production is the system with the largest exergy loss (account for 23.13% of the total exergy input), while the pelletizing system has the lowest efficiency (13.33%) due to heat loss. The key to further improve the thermal performance of this process lies in the heat recovery of the coal gasifier and pelletizing. It is also found that when the H₂ content in reducing gas rise from 57.00% to 100.00%, the exergy efficiency of the shaft furnace is only increased by 1.58%, while the demand volume of reducing gas significantly increases from 1326.30 Nm³/t to 2201.50 Nm³/t. The environmental benefits of hydrogen reduction based steelmaking must be considered together with energy utilization and production cost. The present work should do helpful effort for the application and further improvement of the CSE process in China.     

Hydrogen and power co-generation based on coal and biomass/solid wastes co-gasification with carbon capture and storage

This paper investigates the potential use of renewable energy sources (various sorts of biomass) and solid wastes (municipal wastes, sewage sludge, meat and bone meal etc.) in a co-gasification process with coal to co-generate hydrogen and electricity with carbon capture and storage (CCS). The paper underlines one of the main advantages of gasification technology, namely the possibility to process lower grade fuels (lower grade coals, renewable energy sources, solid wastes etc.), which are more widely available than the high grade coals normally used in normal power plants, this fact contributing to the improvement of energy security supply. Based on a proposed plant concept that generates 400–500 MW net electricity with a flexible output of 0–200 MW_th hydrogen and a carbon capture rate of at least 90%, the paper develops fuel selection criteria for coal blending with various alternative fuels for optimizing plant performance e.g. oxygen consumption, cold gas efficiency, hydrogen production and overall energy efficiency. The key plant performance indicators were calculated for a number of case studies through process flow simulations (ChemCAD).     

Performance analysis of support vector machine,Gaussian Process Regression,sequential quadratic programming algorithms in modeling hydrogen-rich syngas production from catalyzed co-gasification of biomass wastes from oil palm

The quest to attain net-zero emissions has increased the drive for more renewable energy potential from the co-gasification of biomass. The co-gasification of coconut shell and oil palm wastes is a potential technological route to produce hydrogen-rich syngas. However, the complexity of the gaseous-phase reaction often results in process uncertainties which could lead to energy and material wastage. Taking advantage of the data generated from the process, this study explores the performance of twelve machine learning algorithms built on the support vector machine (SVM), the Gaussian process regression (GPR), and the non-linear response quadratic model (NLRQM) using Sequential quadratic programming, and the Levenberg-Marquardt algorithms. The co-gasification of coconut shell and oil palm wastes blend catalyzed by Portland cement, dolomite, and limestone resulted in the maximum syngas production of 42 mol.%, 38 mol.%, 45 mol.%, respectively. The co-gasification process was modeled using SVM regression incorporated with linear, quadratic, and cubic kernel functions, GPR incorporated with rotational, squared, Matern 5/2, and exponential kernel functions, and non-linear response quadratic model (NLRQM) using sequential quadratic programming (SQP), and Levenberg-Marquardt (LM). The performance analysis of the models revealed that the SVM incorporated with linear kernel had the least performance with R² in the range of 0.3–0.7. Whereas the best performance in terms of prediction of the syngas composition was obtained using the NLRQM algorithm with an inbuilt SQP and LM algorithms. The observed syngas composition was consistent with predicted values with R² > 0.97 for the three catalyzed co-gasification processes. The low RMSE (<1) and MAE (<1) obtained from the models are indications of the robustness of the accurate prediction of the NLRQM-LM and NLRQM-SQP algorithms. The sensitivity analysis revealed that the co-gasification temperature, catalysts loading, and the blending amount play a significant role in the predicted syngas composition. However, the co-gasification temperature had the highest influence as indicated by the level of importance values.