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.     

Supercritical water gasification of black liquor with wheat straw as the supplementary energy resource

Supercritical water gasification (SCWG) is a new treatment of black liquor (BL) for both energy recovery and pollution management. To provide more energy for the pulp mill, it is proposed to use the pulping raw material as supplementary energy source because it is readily available, inexpensive and renewable. In this study, co-gasification of BL and wheat straw (WS) in supercritical water was investigated. The synergistic effect was observed in the co-gasification because the addition of wheat straw can make better use of the alkali in BL. The maximum improvement of the gasification by the synergistic effect was obtained with the mixing ratio of 1:1. The influences of the temperature (500–750 °C), reaction time (5–40 min), mixture concentration (5.0–19.1 wt%), mixing ratio (0–100%) and the wheat straw particle diameter (74–150 μm) were studied. It was found that the increase of temperature and reaction time, and the decrease of concentration and wheat straw particle size favored the gasification by improving the hydrogen production and gasification efficiency. The highest carbon gasification efficiency of 97.87% was obtained at 750 °C. Meanwhile, the H₂ yield increased from 12.29  mol/kg at 500 °C to 46.02  mol/kg. This study can help to develop a distributed energy system based on SCWG of BL and raw biomass to supply energy for the pulp mill and surrounding communities.     

Hydrogen enriched syngas production via gasification of biofuels pellets/powders blended from olive mill solid wastes and pine sawdust under different water steam/nitrogen atmospheres

In this work, we study the gasification of pellets produced, after densification, by blending olive mill solid wastes, impregnated or not by olive mill waste water, and pine sawdust under different steam/nitrogen atmospheres. The charcoals necessary for the gasification tests were prepared by pyrolysis using a fixed bed reactor. The gasification technique using steam was chosen in order to produce a hydrogen-enriched syngas. Gasification tests were performed using macro-thermogravimetric equipment. Tests were carried out at different temperatures (750 °C, 800 °C, 820 °C, 850 °C and 900 °C), and at different atmospheres composed by nitrogen and steam at different percentages (10%, 20% and 30%). Results show that the mass variation profiles is similar to the usual lingo-cellulosic gasification process. Moreover, the increase of temperatures or water steam partial pressures affects positively the rate of conversion and the char reactivity by accelerating the gasification process. The increase of the gasification yields demonstrates the promise of using olive mill by-products as alternative biofuels (H₂ enriched syngas).     

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.     

The development of a real-time thermogravimetric analyzer on the gasification of pine sawdust in a simulated fluidized bed gasifier

In this study, a real-time thermogravimetric analyzer was developed for providing insight into the reactivity and gasification process of pine sawdust. The mass loss rate of pine sawdust, syngas composition, and tar compounds in the gasification process were analyzed at different gasification conditions. According to the real-time thermogravimetric analysis, 800°C of the gasification temperature, 0.25 of the equivalence ratio, and 600 kg/(m²·h) of the gasification throughput were regarded as an optimum conditions for the gasification of pine sawdust in a fluidized bed gasifier.     

Co-gasification between coal/sawdust and coal/wood pellet: A parametric study using response surface methodology

This study had compared raw biomass and pre-treated biomass co-gasified with coal with the aim of investigating the reliability of pre-treated biomass for enhancing gasification performance. Sawdust (SD) and wood pellet (palletisation form of sawdust - WP) and blends of these two feedstocks with sub-bituminous coal (CL), were gasified in an air atmosphere using an external heated fixed-bed downdraft gasifier system. Response surface methodology (RSM) incorporating the central composite design (CCD) was applied to assist the comparison of all operating variables. The three independent variables were investigated within a specific range of coal blending ratios from 25% to 75%, gasification temperature from 650 °C to 850 °C and equivalence ratio from 0.20 to 0.30 against the dependent variables, namely the H₂/CO ratio and higher heating value of the syngas (HHVsyngas). The results revealed the H₂/CO ratio and a higher heating value of the syngas of more than 1.585 and 6.072 MJ/Nm³, respectively. Findings also showed that the H₂/CO ratio in the syngas from CL/WP possessed a higher value than the CL/SD. In contrast, CL/SD possessed a higher heating value for syngas with about 1% difference compared to the CL/WP. Therefore, co-gasified coal with wood pellets could potentially be a substitute for sawdust.     

掺混比例对生物质和煤流化床共气化特性影响的试验研究

采用新型床料在鼓泡流化床中进行了2种典型的木本和草本生物质与烟煤的空气-水蒸气气化试验,研究了生物质掺混比例对燃气组分和热值、气化效率及碳转化率等参数的影响规律.结果表明:当松木屑的掺混比例从0%增大到100%时,H2和CO的体积含量分别增加了4.6%和4.4%,CO2的体积含量减少了3%,CH4和CnHm的含量也有所增加;当稻秸的掺混比例从0%增大到100%时,CO的体积含量先从25.8%上升至27.5%,再下降至25.3%,其他燃气组分的变化趋势与松木屑和煤气化的相类似;随着生物质掺混比例的增加,2种生物质和煤共气化的气化效率和碳转化率均有所提高,且在共气化过程中存在协同效应.     

Iron ore as oxygen carrier improved with potassium for chemical looping combustion of anthracite coal

Chemical looping combustion (CLC) is an innovative combustion technology with inherent separation of CO₂ without energy penalty. When solid fuel is applied in CLC, the gasification of solid fuel is the rate-limiting process for in situ gasification of coal and reduction of oxygen carrier. The K₂CO₃-decorated iron ore after calcinations was used as oxygen carrier in CLC of anthracite coal, and potassium ferrites were formed during the calcinations process. The experiments were performed in a laboratory fluidized bed reactor with steam as a gasification medium. Effects of reaction temperature, K₂CO₃ loading in iron ore and cycle on the gas concentration, carbon conversion, gasification rate and yields of carbonaceous gases were investigated. The carbon gasification was accelerated during the fast reaction stage between 860 °C and 920 °C, and the water–gas shift reaction was significantly enhanced in a wider temperature range of 800 °C to 920 °C. With the K₂CO₃ loading in iron ore increasing from 0% to 20% at 920 °C, the carbon conversion was accelerated in the fast reaction stage, and the fast reaction stage became shorter. The yield of CO₂ reached a maximum of 94.4% and the yield of CO reached a minimum of 3.4% when use the iron ore loaded with 6% K₂CO₃. SEM analysis showed that the K₂CO₃-decorating in iron ore would cause a sintering on the particle surface of oxygen carrier, and the K₂CO₃ loading in iron ore should not be too high. Cycle experiments indicate that the K₂CO₃-decorated iron ore has a relative stable catalytic effect in the CLC process.     

Modelling co-gasification of plastic waste and lignin in supercritical water using reactive molecular dynamics simulations

Supercritical gasification is a promising technology for the utilisation of biomass and plastic wastes. To further understand the synergistic effect of lignin and plastic co-gasification under the influence of supercritical water, the microscopic mechanism of the co-gasification of lignin and plastic in supercritical water was studied using reactive molecular dynamics simulations. The influence of temperature on the evolution behaviour of the carbon chains was also analysed. At low temperatures (≤2000 K), lignin cracks slowly, whereas most polyethylene does not crack, and gas production yield is low. The quantity of supercritical water participating in gasification increases with increasing temperature, but there exists an upper limit to this increase. At high temperatures (3000 K–5000 K), the main gasification products include H₂, CH₄, CO, and CO₂.     

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.     

Experimental study of torrefied pine as a gasification fuel using a bubbling fluidized bed gasifier

Torrefied biomass has higher C/O ratio, resulting in improved heating value and reduced hygroscopic nature of the biomass, thus enabling longer storage times. In the southeastern United States, pine is has been identified as a potential feedstock for energy production. The objective of this study was to understand the performance of torrefied pine as a gasification fuel in a bench-scale bubbling fluidized bed gasifier. The gasification of torrefied pine was carried out at 790, 935 and 1000 °C and three equivalence ratios (ERs: 0.20, 0.25 and 0.30). The effect of process variables were studied based on i) products yield, ii) syngas composition iii) syngas energy content, and iv) contaminants. The mean concentration of CO increased with an increase in temperature, but was not statistically significant. On the other hand, H₂ concentration increased whereas CH₄ concentration decreased significantly with an increase in temperature from 790 to 935 °C. Further, with an increase in ER from 0.20 to 0.30, only CO₂ concentrations increased in the syngas. Results from torrefied pine were compared with raw pine gasification, and it was observed that torrefied pine gasification led to much higher char yield (more than twice) than pine; however, it produced less than half as much tar.     

Co-gasification of palm kernel shell and polystyrene plastic: Effect of different operating conditions

Palm kernel shell (PKS) biomass has great potential for power generation via gasification as it contains high energy content. However, abundant it may be, the source of PKS is scattered throughout the country, thus the consistency of feedstock supply may be hard to maintain. Co-gasifying with another source, such as plastics, can be seen as one of a solution to mitigate the supply chain problem. Polystyrene (PS) plastics have potential as a plastic feedstock because of its high domestic and industrial usage. As PS is also hard to recycle, using PS as a co feedstock for gasification is a way for PS waste management. However, the study on the performance of air co-gasification of PKS and PS has not been done before. It is essential to investigate the performance before it is utilized in the real world. In this work, the performance co-gasification of PKS and PS with different operating conditions was investigated. The gasification experiment was done in an electrically heated downdraft gasifier with a diameter of 8 cm. The reaction temperature was varied from 700 to 900 °C, with the equivalence ratio varied from 0.07 to 0.27. The PS weight percentage of the total feedstock was varied from 0 to 30 wt%. It was found that the vol% of CO and H₂ on the producer gas increased with temperature while reducing the vol% of CO₂ and CH₄. HHV and the amount of gas produced were also increasing with increasing temperature. Increasing ER reduced the HHV of the gas but increased the amount of gas produced. Adding more PS to the feedstock blend increased the percentage of the produced gas at 900 °C, however, at the lower temperature of 800 °C, the percentage of gas produced decreased with increasing PS wt%.     

Experimental study on hydrogen-rich syngas production via gasification of pine cone particles and wood pellets in a fixed bed downdraft gasifier

The main objective of this research is to investigate gasification of pine cones particles and wood pellets in a pilot scale 10 kWth downdraft fixed bed gasifier using air as an oxidizing agent. In this work, it was found that syngas produced by gasification of pinecones particles is rich in environmentally friendly hydrogen and that would be a clean alternative energy carrier for the production of clean energy. In addition, the effect of gasification temperature and equivalence ratio on the composition of syngas and gasification performance for pine cones and wood pellet were analysed comparatively. During the experimental works gasification took place with air, in a temperature range of 701–1046 °C, for various air equivalence ratios (0.14–0.37) and under atmospheric pressure. It is found that H₂ and CO production increased by increasing reactor temperature. Another finding is that the mean cold gas efficiency was 65% for pinecone particles and 80% for wood pellet gasification.     

水蒸气气氛下生物质与聚丙烯共气化产气特性数值分析

搭建生物质与废塑料共气化动力学模型,并用实验数据对其进行验证。选用6种生物质和聚丙烯作为共气化反应物,以水蒸气为气化剂,计算气化温度在300～1000℃之间、气化压强在0.1～0.8 MPa之间、聚丙烯和松木锯末质量比例在0.5～2.5之间,以及不同生物质类型等对生物质和聚丙烯共气化产气特性的影响。结果表明：松木锯末气化中添加聚丙烯后,最高产气量和最大产气速率增加,最高产气总流量提高21.46%,最高产气速率提高4.64%,H₂和CO最高产量分别提高54.27%和79.51%;压强增加不利于提高共气化产气的H₂和CO含量,有利于提高CH₄含量;6种常见生物质和聚丙烯共气化产氢量大小顺序为：果皮>棉花秆≈玉米秸秆>杨树木屑>稻秆>条浒苔;聚丙烯掺混比率增加有利于提高H₂、CO和CH₄等组分产量。     

Syngas production by integrating CO2 partial gasification of pine sawdust and methane pyrolysis over the gasification residue

The aim of this work was to study syngas production by integrating CO₂ partial gasification (for CO production) of pine sawdust (PS) and methane pyrolysis (for H₂ production) over the gasification residue. Effect of the gasification conditions (including CO₂ flow rate, reaction temperature, mass ratio of PS:Ni and reaction time) was investigated on properties of the gasification residue. Besides CO-rich gas released from the gasification process with CO₂ conversion up to about 92%, the gasification residue could serve as robust catalyst for H₂ production by methane pyrolysis. Thanks to the nickel crystallites formed with high reduction degree and high dispersion on the surface after the gasification process, the gasification residue was competent for high and stable methane conversion (about 91%) at 850 °C. In addition to the flexible syngas output (in theory, with an arbitrary ratio of H₂/CO), valuable filamentous carbons can be achieved by regulating the process parameters.     

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.     

Experimental study on the key factors affecting the gasification performance between different biomass: Compare citrus peel with pine sawdust

This work aims to reveal the advantages of citrus peel gasification and investigate the key factors affecting gasification performance. The gasification performance of citrus peel and pine sawdust are compared in a fixed bed reactor, and the reactivity and properties of biochar were investigated. The results showed that the H₂ yield and carbon conversion efficiency of citrus peel gasification were 34.35 mol/kg_biomass and 66.30%, respectively, which were higher than those of pine sawdust. Due to the high reactivity of citrus peel char, it only takes 100 min for the citrus peel to complete the gasification reaction, which is significantly faster than pine sawdust. Although the specific surface area of citrus peel char is lower than that of pine sawdust char, both the low degree of graphitization and the high catalytic index (2426.96) are favorable for the conversion of char, which ultimately lead to the high reactivity of citrus peel char.     

Product distribution from solar pyrolysis of agricultural and forestry biomass residues

Solar pyrolysis of pine sawdust, peach pit, grape stalk and grape marc was conducted in a lab-scale solar reactor for producing fuel gas from these agricultural and forestry by-products. For each type of biomass, whose lignocellulose components vary, the investigated parameters were the final temperature (in the range 800°C–2000 °C) and the heating rates (in the range 10–150 °C/s) under a constant sweep gas flow rate of 6 NL/min. The parameter influence on the pyrolysis product distribution and syngas composition was studied. The experimental results indicate that the gas yield generally increases with the temperature and heating rate for the various types of biomass residues, whereas the liquid yield progresses oppositely. Gas yield as high as 63.5wt% was obtained from pine sawdust pyrolyzed at a final temperature of 2000 °C and heating rate of 50 °C/s. This gas can be further utilized for power generation, heat or transportable fuel production.     

Sewage and textile sludge co-gasification using a lab-scale fluidized bed gasifier

This research aims to evaluate the hydrogen production and removal ability of impurity (e.g. tar and NH₃) generated from sewage and textile sludge co-gasification using lab-scale fluidized-bed gasifier with an integrated hot-gas cleaning system. The gasification temperature and equivalence ratio (ER) were controlled at 850 °C and 0.2, as well as the hot gas cleaning system operated at 250 °C with the combination of zeolite, calcined dolomite, and activated carbon. Experimental results indicated that the H₂ and CO yield in co-gasification of the tested sludge ranged from 2.12 to 2.45 mol/kg and from 2.83 to 3.98 mol/kg, respectively. The overall energy content of produced gas ranged between 2.40 and 2.63 MJ/kg, and cold gas efficiency (CGE) was nearly 15%. The impurities of produced gas were effectively mitigated by the hot-gas cleaning system, which could remove approximately 90% of the heavy fraction tar, up to 77% of total tar, and about 35% of ammonia. In summary, the combination of the fluidized-bed gasifier and the hot-gas cleaning system had been well developed for purifying the syngas produced from the tested sludge, and it could be applied to other organic wastes in the future.     

Evaluation on hydrothermal gasification of waste tires based on chemical equilibrium analysis

Massive amounts of waste tires are produced globally, which brings great challenges to the disposal and recycling of used tires. Hydrothermal gasification is a promising option for recycling waste tires. The hydrothermal gasification of waste tires was evaluated based on the chemical equilibrium analysis along with the response surface methodology (RSM) in terms of subcritical temperature range (250–300 °C), transition temperature range (350–400 °C), supercritical temperature range (550–600 °C), supercritical pressure (22.5–30.5 MPa) and feedstock concentration (5–20 wt%). CH₄ yield at 350 °C reached a maximum, 41.575 mmol/g. H₂ yield increased from 0.0283 to 53.602 mmol/g with increasing the temperature from 250 °C to 600 °C. CH₄ yield at the supercritical temperature increased with lifting the feedstock concentration, while H₂ yield decreased. The optimal parameters regarding maximum H₂ and CH₄ yields in the subcritical temperature range were 300 °C, 22.5 MPa and 12.5 wt%, respectively, while they in the supercritical temperature range were 550 °C, 30.5 MPa and 5.4 wt%, respectively. RSM was more suitable for predicting H₂ yield in the hydrothermal gasification of waste tires at subcritical and supercritical temperature ranges, but it was available for predicting CH₄ yield in three temperature ranges. This study can provide basic data for the hydrothermal treatment of waste tires.