Steam gasification of selected energy crops in a fixed bed reactor

The increasing world's energy demand and environmental concerns related to GHG emissions as well as depleting fossil fuel resources and unstable prices of crude oil and natural gas have caused a renewed interest in renewable energy sources, and in particularly in biomass, as an alternative to fossil fuels. In the paper the results of steam gasification of Salix Viminalis, Miscanthus X Giganteus (MXG), and Andropogon Gerardi in a laboratory-scale fixed bed reactor in the temperature range of 650–900 °C are presented as well as the procedure and results of biomass chars reactivity testing in the process of steam gasification. The highest reactivity R₅₀ in the whole temperature range was observed for MXG. Hydrogen content in the synthesis gas was comparable for MXG and Andropogon Gerardi and lower for Salix Viminalis, while the volumes of the synthesis gas and hydrogen were highest for MXG at all temperatures.     

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.     

Sorbent enhanced hydrogen production from steam gasification of coal integrated with CO2 capture

In this work, CO₂ capture and H₂ production during the steam gasification of coal integrated with CO₂ capture sorbent were investigated using a horizontal fixed bed reactor at atmospheric pressure. Four different temperatures (650, 675, 700, and 750 °C) and three sorbent-to-carbon ratios ([Ca]/[C] = 0, 1, 2) were studied. In the absence of sorbent, the maximum molar fraction of H₂ (64.6%) and conversion of coal (71.3%) were exhibited at the highest temperature (750 °C). The experimental results verified that the presence of sorbent in the steam gasification of coal enhanced the molar fraction of H₂ to more than 80%, with almost all CO₂ was fixed into the sorbent structure, and carbon monoxide (CO) was converted to H₂ and CO₂ through the water gas shift reaction. The steam gasification of coal integrated with CO₂ capture largely depended on the reaction temperature and exhibited optimal conditions at 675 °C. The maximum molar fraction of H₂ (81.7%) and minimum CO₂ concentration (almost 0%) were obtained at 675 °C and a sorbent-to-carbon ratio of 2.     

Enhanced hydrogen-rich gas production from steam gasification of coal in a pressurized fluidized bed with CaO as a CO2 sorbent

Steam gasification of a typical Chinese bituminous coal for hydrogen production in a lab-scale pressurized bubbling fluidized bed with CaO as CO₂ sorbent was performed over a pressure range of ambient pressure to 4 bar. The compositions of the product gases were analyzed and correlated to the gasification operating variables that affecting H₂ production, such as pressure (P), mole ratio of steam to carbon ([H₂O]/[C]), mole ratio of CaO to carbon ([CaO]/[C]) and temperature (T). The experimental results indicated that the H₂ concentration was enhanced by raising the temperature, pressure and [H₂O]/[C] under the circumstances we observed. With the presence of CaO sorbent, CO₂ in the production gas was absorbed and converted to solid CaCO₃, thus shifting the steam reforming of hydrocarbons and water gas shift reaction beyond the equilibrium restrictions and enhancing the H₂ concentration. H₂ concentration was up to 78 vol% (dry basis) under a condition of 750 °C, 4 bar, [Ca]/[C] = 1 and [H₂O]/[C] = 2, while CO₂ (2.7 vol%) was almost in-situ captured by the CaO sorbent. This study demonstrated that CaO could be used as a substantially excellent CO₂ sorbent for the pressurized steam gasification of bituminous coal. For the gasification process with the presence of CaO, H₂-rich syngas was yielded at far lower temperatures and pressures in comparison to the commercialized coal gasification technologies. SEM/EDX and gas sorption analyses of solid residues sampled after the gasification showed that the pore structure of the sorbent was recovered after the steam gasification process, which was attributed to the formation of Ca(OH)₂. Additionally, a coal-CaO–H₂O system was simulated with using Aspen Plus software. Calculation results showed that higher temperatures and pressures favor the H₂ production within a certain range.     

Hydrogen production from coal gasification for effective downstream CO2 capture

The coal gasification process is used in commercial production of synthetic gas as a means toward clean use of coal. The conversion of solid coal into a gaseous phase creates opportunities to produce more energy forms than electricity (which is the case in coal combustion systems) and to separate CO₂ in an effective manner for sequestration. The current work compares the energy and exergy efficiencies of an integrated coal-gasification combined-cycle power generation system with that of coal gasification-based hydrogen production system which uses water-gas shift and membrane reactors. Results suggest that the syngas-to-hydrogen (H₂) system offers 35% higher energy and 17% higher exergy efficiencies than the syngas-to-electricity (IGCC) system. The specific CO₂ emission from the hydrogen system was 5% lower than IGCC system. The Brayton cycle in the IGCC system draws much nitrogen after combustion along with CO₂. Thus CO₂ capture and compression become difficult due to the large volume of gases involved, unlike the hydrogen system which has 80% less nitrogen in its exhaust stream. The extra electrical power consumption for compressing the exhaust gases to store CO₂ is above 70% for the IGCC system but is only 4.5% for the H₂ system. Overall the syngas-to-hydrogen system appears advantageous to the IGCC system based on the current analysis.     

The synergistic effect of Ca(OH)2 on the process of lignite steam gasification to produce hydrogen-rich gas

The synergistic effect of Ca(OH)₂ prepared by the wet-mixing method on lignite steam gasification process at different temperatures (700–900 °C) was analyzed in a spout-fluid bed reactor. Firstly, to avoid disturbance of volatile and tar, active carbon was used as a model compound. On the one hand, Ca(OH)₂ effectively catalyzed the water-gas shift (WGS) reaction to improve H₂ concentration, but the performance was weaker at higher temperature due to the enhancement of boudouard reaction and the weakening of WGS reaction. On the other hand, it was found that the (CO+2CO₂)/H₂ ratio of syngas produced at 700 °C in the presence of Ca(OH)₂ was 0.82, which was much lower than that of the other cases, owning to the absorption of CO₂. The synergistic effect was observed at this temperature, for the adsorption of CO₂ altered equilibrium of the WGS reaction and further improved H₂ concentration. Then two kinds of Chinese lignite (HLH and XM) were selected to further study the performance of Ca(OH)₂ on optimizing the lignite steam gasification process. In the presence of Ca(OH)₂, tar and char yields greatly reduced at the same reaction temperature, whereas the gas yields significantly increased. As a catalyst, Ca(OH)₂ can not only promote solid–gas reaction to decrease char yield, but also accelerate tar decomposition to reduce its yield in syngas. Based on GC–MS data, it can be deduced that Ca(OH)₂ has different catalytic activity on the steam reforming of tar with different molecular structures. Contrast to Class 4, tars of aliphatic hydrocarbons, Class 2 and Class 5 were clearly catalytic reformed. Hydrogen-rich gas can be produced at 800 °C and 900 °C owning to the catalytic effect of Ca(OH)₂, but the highest H₂ concentration was found at 700 °C due to the additional effect of CO₂ absorption, which was supported by the results of thermogravity experiments.     

Hydrogen production via steam gasification of ash free coals

The kinetics of the coal to hydrogen conversion can be significantly enhanced by introducing catalysts. The catalysts are, however, commonly deactivated by irreversible interaction with mineral matters in coal. This work addresses hydrogen production via steam gasification of ash free coals. Following the production of ash free coals (AFCs) derived from various raw coals (brown, bituminous, and coking coal), fixed-bed steam gasification of the AFCs was performed as a function of temperature and which was compared with one another and also with that of the matching raw coals. In the absence of a catalyst, AFCs produced from different parent coals exhibited similarly low gasification reactivity, comparable to a high rank coal (coking coal) at 700 °C. As expected, the reaction became faster with increasing temperature in the range, 700–900 °C. The steam gasification of AFCs was highly activated by K₂CO₃ above 700 °C. It was very likely that water–gas shift reaction associated with the gasification of AFCs was also catalyzed.     

Calcium looping gasification for high-concentration hydrogen production with CO2 capture in a novel compact fluidized bed: Simulation and operation requirements

The coal/CaO/steam gasification system is one of the clean coal technologies being developed for hydrogen production with inherent carbon dioxide separation. A novel reactor configuration for the system is proposed in this paper. It consists of three major counterparts: a gasifier, a riser and a regenerator. A regenerable calcium-based sorbent CaO is used to remove carbon dioxide. In the gasifier, the coal-steam gasification reaction occurs with in situ carbon dioxide removal by carbonation reaction. The removal of carbon dioxide favors the gasification and water-shift reaction equilibrium and enables the production of a hydrogen-rich gas stream. CaO is regenerated in the regenerator by burning the unreacted char with oxygen, and a pure stream of carbon dioxide is separated after a cyclone. The regenerated CaO then flows into the riser above the gasifier, and removes the carbon dioxide in the outlet gases from the gasifier and drives the water-gas shift reaction forward, further improving the hydrogen purity. In this work, the feasibility and optimum process conditions of the proposed system were described. The hydrogen purity can reach 96 vol% at a steam flow 80 mol/s and CaO recycle rate 30 mol/s when the carbon conversion rate is 0.50. Increasing the steam flow and CaO recycle rate can enhance the hydrogen yield and purity. With the rise of operation pressure from 1 bar to 10 bar, the hydrogen yield and purity decrease and methane yield increases. High pressure leads to higher calcination temperature. At 10 bar, the temperature for CaCO₃ decomposition is approximately 1100 °C, at such temperature, the sorbent is easy to deactivate. The appropriate temperatures in the gasifier and the riser are 700 and 600 °C, respectively. An analysis of heat integration is conducted. The maximum carbon conversion rate is ∼0.65. A hydrogen production efficiency of 58.5% is obtained at a carbon conversion rate 0.50, steam flow 60 mol/s and CaO recycle rate 30 mol/s, with a hydrogen purity of 93.7 vol%.     

Lime enhanced biomass gasification. Energy penalty reduction by solids preheating in the calciner

Hydrogen is expected to be one of the most important energy carriers in the future. Gasification process may be used to produce hydrogen when joined with carbon capture technologies. Furthermore, the combination of biomass gasification and carbon capture presents a significant technical potential in net negative greenhouse gas emissions. Lime enhanced biomass gasification process makes use of CaO as a high temperature CO₂ carrier between the steam biomass gasifier and an oxy-fired regenerator. Important energy penalties derive from the temperature difference between the reactors (around 250–300 °C). A cyclonic preheater similar to those used in the cement industry may improve the energetic efficiency of the process if the particles entering the regenerator reactor are heated up by the gas leaving this reactor. A lime enhanced biomass gasification system was modelled and simulated. A cyclonic preheater was included to evaluate the improvement. Results show an increase of the gasification chemical efficiency and a reduction of the energy consumption in the regenerator.     

Comparative studies on steam gasification of ash-free coals and their original raw coals

Catalytic gasification of raw coals at mild condition is not realized yet mainly due to deactivation of catalysts via their irreversible interaction with mineral matters in coal. As a means to achieve repeated use of catalysts, four different ash-free coals (AFCs) containing less than 0.2 wt% ash are produced in this work. Steam gasification of ash-free coals (AFCs) and their parent raw coals of various ranks ranging from lignite (Eco) to coking coal (Posco) is performed in a fixed bed reactor at 700–900 °C. Regardless of the rank of the parent raw coals, all the AFCs behave like a highly carbonized coal such that their gasification rate are similarly slow and they exhibit relatively low H₂/CO ratio. The steam gasification and associated CO to CO₂ conversion of the AFCs are, however, significantly enhanced by K₂CO₃, resulting in the higher H₂/CO and CO₂/CO molar ratio.     

Integrated catalytic adsorption (ICA) steam gasification system for enhanced hydrogen production using palm kernel shell

This paper investigates the integrated catalytic adsorption (ICA) steam gasification of palm kernel shell for hydrogen rich gas production using pilot scale fluidized bed gasifier under atmospheric condition. The effect of temperature (600–750 °C) and steam to biomass ratio (1.5–2.5 wt/wt) on hydrogen (H₂) yield, product gas composition, gas yield, char yield, gasification and carbon conversion efficiency, and lower heating values are studied. The results show that H₂ hydrogen composition of 82.11 vol% is achieved at temperature of 675 °C, and negligible carbon dioxide (CO₂) composition is observed at 600 °C and 675 °C at a constant steam to biomass ratio of 2.0 wt/wt. In addition, maximum H₂ yield of 150 g/kg biomass is observed at 750 °C and at steam to biomass ratio of 2.0 wt/wt. A good heating value of product gas which is 14.37 MJ/Nm³ is obtained at 600 °C and steam to biomass ratio of 2.0 wt/wt. Temperature and steam to biomass ratio both enhanced H₂ yield but temperature is the most influential factor. Utilization of adsorbent and catalyst produced higher H₂ composition, yield and gas heating values as demonstrated by biomass catalytic steam gasification and steam gasification with in situ CO₂ adsorbent.     

Characteristics of cardboard and paper gasification with CO2

Evolutionary behavior of syngas chemical composition and yield have been examined for paper and cardboard at three different temperatures of 800, 900 and 1000 °C using CO₂ as the gasifying agent at constant flow rate. Specifically the evolution of syngas chemical composition with time has been investigated. Pyrolysis of the sample was dominant at the beginning of the gasification process as observed from the high initial devolatilization of the sample followed by char gasification of material to form syngas for a long period of time. Results provided the role of gasification temperature on kinetics of the CO₂ gasification process. Increase in gasification temperature provided increased conversion of the sample material to syngas. Thus the sample conversion to syngas was low at the low temperature of 800 °C while at elevated temperatures of 900 and 1000 °C substantial enhancement of the kinetics process occurred. The evolution of extensive reaction rate of carbon-monoxide was calculated. Results show that increase in temperature increased the extensive reaction rate of carbon-monoxide. The global behavior of syngas chemical composition examined at three different temperatures revealed a peak in concentration of H₂ to exhibit after few minutes into the gasification that changed with gasification temperature. At 800 °C gasification temperature peak in H₂ was displayed at 3 min into gasification while it decreased to only 2 min, approximately, at gasification temperatures of 900 and 1000 °C. The effect of reactor temperature on CO mole fraction has also been examined. Increase in the gasification temperature enhances the mole fraction of CO yields. This is attributed to the increase in forward reaction rate of the Boudouard reaction (C+CO₂2CO). The results show important role of CO₂ gas for the gasification of wastes and low grade fuels to clean syngas.     

Low temperature sugar cane bagasse pyrolysis for the production of high purity hydrogen through steam reforming and CO2 capture

Biomass pyrolysis offers a fast route to produce elevated yields towards highly valued liquid products. This research aims the determination of optimal experimental conditions for a slow and low temperature pyrolysis to produce the highest yield towards condensable (CVM) and non-condensable (NCVM) volatile matter from Mexican cane bagasse and to quantify and characterize the compounds that constitute CVM and NCVM obtained. Results indicate that yield towards volatiles is strongly dependent on temperature. The highest yield was achieved at temperatures greater than 500 °C at a heating rate of 10 °C/min, residence time of 60 min and a particle size between of 420 and 840 μm. Product quantification under isothermal conditions determined that at 550 °C the NCVM, CVM and solid residue was of 26, 57 and 16%, respectively. Preliminary thermodynamic analysis of steam reforming and CO₂ absorption reactions using one of the main CVM products resulted in a potential high hydrogen production yield.     

Hydrogen-rich gas from catalytic steam gasification of biomass in a fixed bed reactor: Influence of temperature and steam on gasification performance

The catalytic steam gasification of biomass was carried out in a lab-scale fixed bed reactor in order to evaluate the effects of temperatures and the ratio of steam to biomass (S/B) on the gasification performance. The bed temperature was varied from 600 to 900 and the S/B from 0 to 2.80. The results show that higher temperature contributes to more hydrogen production.     

Socio-economic impacts of energy crops for heat generation in Northern Greece

Bioenergy is considered to be an attractive option mainly due to driving forces of an environmental nature (e.g. climate change and sustainability issues). This is particularly the case for energy crops, which show higher productivity per land unit than their conventional counterparts. In addition, by comparison, such crops are more homogeneous in terms of their physical and chemical characteristics than residual resources that are often described as the biomass resource of the future. However, despite the long-term research and the considerable efforts to promote them, implementation is still rather slow across Europe. In this paper, two perennial energy crops, cardoon and giant reed, are evaluated in Rodopi, northern Greece, as alternative land use, through comparative financial appraisal with the main conventional crops.

Based on the output of this analysis, the breakeven for the two energy crops is defined and an economic and socio-economic evaluation of a biomass district heating system is conducted.

Results prove that energy crops can be attractive alternatives if they are properly integrated into existing agricultural activities and complement the current cropping options. As such, they provide raw material for local heat applications, thus resulting in increased income for the region and an increase in the number of jobs.     

A two phase model of high temperature steam-only gasification of biomass char in bubbling fluidized bed reactors using nuclear heat

A two phase biomass char steam gasification kinetic model is developed in a bubbling fluidized bed with nuclear heat as source of energy. The model is capable of predicting the temperature and concentration profiles of gases in the bubble, emulsion gas and solid phases. The robust model calculates the dynamic and steady state profiles, as well as the complex parameters of fluidized bed. Three pilot scale gasifiers were simulated in order to see the effect of the H/D ratio and the bed heating dynamics in the gasification kinetics, these parameters are found to be really important in order to enhance the water-gas shift reaction, and consequently, the hydrogen production. For the system modeled, hydrogen is the principal product of the steam-only gasification, as reported in the literature data. The carbon dioxide yield seems to be smaller than the ones in other works, but these differences are due principally to the energy source (no combustion is conducted) and that char (no oxygen in the solids) was used as the carbon source.     

Combined production of hydrogen and power from heavy oil gasification: Pinch analysis,thermodynamic and economic evaluations

Integrated Gasification Combined Cycle (IGCC) represents a commercially proven technology available for the combined production of hydrogen and electricity power from coal and heavy residue oils. When associated with CO₂ capture and sequestration facilities, the IGCC plant gives an answer to the search for a clean and environmentally compatible use of high sulphur and heavy metal contents fuels, the possibility of installing large size plants for competitive electric power and hydrogen production, and a low cost of CO₂ avoidance.     

Optimization-based planning of a biomass to hydrogen (B2H2) system using dedicated energy crops and waste biomass

The utilization of biomass for hydrogen production is one of the promising options for a sustainable energy system. In this paper, we develop a new optimization-based approach for design and analysis of the B2H2 system including production, storage, and distribution using dedicated energy crops as well as various resources of waste biomass. To achieve this goal, we first develop an optimization model using mixed-integer linear programming technique that includes practical variables and constraints for decision-making about the usage of dedicated energy crops. We then conduct a case study of the B2H2 system for the road transportation sector of future Korea. As a result, we identify an optimal system configuration that includes the utilized biomass types, occupied land sizes, the number and location of facilities, and the biomass and hydrogen flows between regions. We also analyze the cost distributions and the sensitivity of the main cost drivers on the total annual cost (TAC). The results reveal that the proposed B2H2 system is economically competitive with some of the other renewable-based hydrogen supply systems (wind and solar) in Korea.     

Hydrogen-rich gas from catalytic steam gasification of biomass in a fixed bed reactor: Influence of particle size on gasification performance

The catalytic steam gasification of biomass was carried out in a lab-scale fixed bed reactor in order to evaluate the effects of particle size at different bed temperatures on the gasification performance. The bed temperature was varied from 600 to 900 °C and the biomass was separated into five different size fractions (below 0.075 mm, 0.075–0.15 mm, 0.15–0.3 mm, 0.3–0.6 mm and 0.6–1.2 mm). The results show that with decreasing particle size, the dry gas yield, carbon conversion efficiency and H₂ yield increased, and the content of char and tar decreased. And the differences due to particle sizes in gasification performance practically disappear as the higher temperature bound is approached. Hydrogen and carbon monoxide contents in the produced gas increase with decreasing particle size at 900 °C, reaching to 51.2% and 22.4%, respectively.