不同生物质灰的理化特性

根据我国和美国国家标准,将稻草、松木屑和梧桐树叶3种生物质分别在815和600℃下制灰,此外也在500℃下制灰进行比较。测定了灰分量和灰成分,考察了灰成分中氧化物的含量变化以及生物质灰的积灰、结渣特性;利用X射线衍射方法和SEM对不同温度灰的物相和灰形态进行了分析;利用灰熔点仪测定了生物质灰的灰熔点。研究表明:灰分量、灰成分、物相变化、灰形态以及灰熔点均与灰化温度密切相关,600℃的灰化温度比较适合研究生物质灰分的性质。     

Ash deposition and sodium migration behaviors during combustion of Zhundong coals in a drop tube furnace

Zhundong coalfield is one super-large coalfield recently discovered in China. However, the utilization of Zhundong coal in power plants has caused serious ash-related issues mainly due to its high-sodium feature. The ash deposition problem on convection heat exchanger surfaces is still particularly difficult to resolve and its mechanism has yet to be fully understood. This study deals with the ash deposition and alkali metal migration behaviors on convection heat exchanger surfaces between 400 and 800 °C during combustion of Zhundong coal using a lab-scale drop tube reactor. Experimental results show that the sodium content in ash deposit of Zhundong coals increases obviously as the deposition temperature decreases from 800 to 600 °C, while it is almost unchanged below 600 °C. The contents of iron and calcium in ash deposits exhibit nonmonotonic variations as the deposit probe temperature varies between 400 and 800 °C. Quartz and calcium sulfate are main crystalline phases in ash deposit of Zhundong coals. Calcium is inclined to present as calcite and lime at low deposition temperature, while high temperature facilitates calcium sulfation. Sodium of crystalline phase is found as albite and sodium sulfate at low deposition temperature. Both condensation of gaseous alkali metals and formation of low-melting minerals were responsible for the ash deposition phenomenon on convection heat exchanger surfaces involved in combustion of Zhundong coal. The sodium content in ash deposit decreases considerably with the increasing combustion temperature while the case of iron variation is opposite due to its low-volatility. In addition, the Na content in ash deposits increases obviously with the access air ratio reduced from 1.2 to 1.05, but the local weakly reducing atmosphere leads to less iron within ash deposits. Clarification of sodium migration and evaluation of ash deposition behaviors during combustion of Zhundong coal is helpful for a better exploration of the functional mechanism of ash deposit and then large-scale utilization of high-sodium coals.     

Effect of ash on dielectric properties and micro-structure of high alkali coal at different temperature pyrolysis

The effect of ash on dielectric properties and micro-structure of high alkali coal at different temperature pyrolysis was studied, so as to provide theoretical basis for coal deep processing by microwave. An acid-washed method was adopted to remove ash in Zhundong coal for preparing coal chars at 700 °C–1300 °C. X-ray diffraction analysis was used to characterize the microcrystal structure. The thermal stability was characterized by thermogravimetric analyzer, and the dielectric properties were measured by a vector network analyzer. The results showed that when the pyrolysis temperature was below 1100 °C, the presence of ash hindered the development of carbon structure in raw coal char. The main reason is that the alkali metal oxides (K₂O and Na₂O) in the ash promoted the solution loss reaction during pyrolysis. The structure of the original carbon layer was damaged, thereby the graphitization degree, thermal stability and dielectric properties of raw coal char were weaker than the ash-free coal char. When the pyrolysis temperature reached 1300 °C, the minerals were completely melted. The reaction of phase transition of SiO₂ in ash played a catalytic role on raw coal char structure, resulting in tighter arrangement of adjacent carbon layers. The raw coal char showed stronger dielectric properties and thermal stability.     

Characterization of the ash deposits along deep-cooling of the exhaust gas in coal-fired power plants

Ash deposition and condensation of acid vapors under deep-cooling of exhaust gas in a 1000 MW ultra-supercritical power plant were investigated. X-ray diffraction, X-ray fluorescence and laser particle size analyzers were employed to characterize the components, elements and particle size distribution of deposits at different metal wall temperatures. The results show that the deposits formed at the metal wall temperatures of 40 °C–60 °C were much thicker than the deposits at 70 °C–90 °C from the perspectives of the morphology and thickness. Fluorides and chlorides were observed in deposits formed at the metal wall temperatures of 40 °C–60 °C. Thin deposits were composed of Al-Si oxides and simple sulfates when the metal wall temperatures were 70 °C–90 °C. The dew-point temperatures of water, HCl and HF vapors were around 40 °C, 60 °C, and 60 °C, respectively. Basic ferric, aluminum and calcium sulfates, which were acted as traps to absorb the condensate and fly ash. Hydration played an important role in the growth of deposits formed at the metal wall temperature of 40 °C–60 °C.     

Valorisation of vegetable market wastes to gas fuel via catalytic hydrothermal processing

Residues of leek, cabbage and cauliflower from the market places as representatives of lignocellulosic biomass were processed via hydrothermal gasification to produce energy fuel. The experiments were carried out in a batch reactor at temperatures 300, 400, 500 and 600 °C and corresponding pressures varying in the range of 7.5–43 MPa. Natural mineral additives trona, dolomite and borax were used as homogenous catalysts to determine their effects on the gasification. More than 70 wt% of carbon in vegetable residue samples were detected in the gas phase after the hydrothermal gasification process at 600 °C. The addition of trona mineral further promoted the gasification reactions and as a result, less than 5 wt% carbon remained in the solid residue at the same temperature, degrading the biomass samples into gas and liquid products. The fuel gas with the highest calorific value was recorded to be 25.6 MJ/Nm³, from the hydrothermal gasification of cabbage at 600 °C, when dolomite was used as the homogeneous catalyst. The liquid products obtained in the aqueous phase were detected as organic acids, aldehydes, ketones, furfurals and phenols. The gas products were consisted of hydrogen, carbon dioxide, methane, and as minors; carbon monoxide and low molecular weight hydrocarbons (ethane, propane, etc.). Above 500 °C, all biomass samples yielded 50–55 vol% of CH₄ and H₂ while the CO₂ composition was around 40 vol% as the gas product.     

Phosphorus recovery from sewage sludge char ash

Phosphorus was recovered from the ash obtained after combustion at different temperatures (600 °C, 750 °C and 900 °C) and after gasification (at 820 °C using a mixture of air and steam as fluidising agent) of char from sewage sludge fast pyrolysis carried out at 530 °C. Depending on the leaching conditions (extraction time, acid load and acid concentration, and type of acid) 90% mass of the original P was recovered. Regarding char combustion ash, higher phosphorus yields are obtained from ash obtained at 900 °C than at 600 °C and 750 °C when using sulphuric acid. Combustion temperature does not affect phosphorus leaching with oxalic acid. A contact time of 2 h and an oxalic acid load of 10 kg kg⁻¹ of P seem sufficient for phosphorus extraction. Almost all phosphorus present in gasification ash is leached after 2 h with both sulphuric and oxalic acid using an acid load of 14 kg kg⁻¹ of P. Char ash is a possible renewable source of phosphorus and it can be an alternative to rock phosphate in fertilizer production. The combination of sewage sludge pyrolysis, combustion or gasification of the char and phosphorus extraction from the final solid residue contributes to the integral exploitation of sewage sludge.     

Characterization and productivity of cassava waste and its use as an energy source

This study sought to quantify and characterize cassava waste as fuel. The wastes from three cultivars were collected to study and were divided into three distinct parts of the cassava plant: seed stem, thick stalks, and thin stalks. Physical and chemical analyzes were carried out to determine the elemental composition of the waste: volatile matter; fixed carbon; ash; moisture; lignin; cellulose; hemicellulose; ash composition and higher heating value were determined. We conducted a thermogravimetric analysis in oxidizing and inert atmospheres to study the behavior of the waste as fuel. The root productivity obtained ranged from 7.7 to 13.0 t ha⁻¹ yr⁻¹ on a dry basis (db), and the ratio between waste and roots varied from 0.36 to 0.91. The physical and chemical properties of cassava waste are analogous to those of woody biomass regarding the elemental composition, the higher heating value, and thermogravimetric analysis. Ash content varied from 2.5% to 3.5%, reaching around 6.0% in samples unwashed. Approximately 60% of the ashes are alkali oxides, especially P₂O₅, K₂O, and CaO, which have low melting points. The alkali index calculated suggests that there is a strong tendency that the combustion process leads to ash fouling and the formation of ash deposits.     

The fusion characteristics of ashes from anthracite and biomass blends

Fusion characteristics of ashes from anthracite and biomass (pine sawdust and corn stalk) blends were investigated. These ashes were prepared in a muffle furnace (MF) and a drop tube furnace (DTF) at the temperatures of 815 °C and 1200 °C respectively. The fusion temperatures of ashes were measured in an ash fusion temperature analyzer, the morphological characteristics and element component of ashes were analyzed by means of SEM (Scanning Electron Microscope) fitted with EDS (Energy Disperse Spectroscopy). The minerals species and transformation characteristics were also detected using XRD (X-ray diffraction). The fusion temperatures of MF blends ashes were lower than those of DTF blends ashes because of the difference of ash preparation temperatures. The structures of ashes made in MF were dispersed and loose, but the ashes made in DTF were denser and larger resulting in obvious agglomeration. The fusion temperatures decreased with biomass addition ratio increasing due to large amounts of alkali and alkali-earth species in pine sawdust/corn stalk ash regardless the ash preparation method. K and Ca-bearing compounds can react with aluminosilicates in anthracite to create low temperature eutectics which can decrease the fusion temperatures of anthracite and biomass blends.     

An innovative strategy on co-production of porous carbon and high purity hydrogen by alkaline thermal treatment of rice husk

An innovative biomass conversion method was proposed to co-produce porous carbon and high purity hydrogen by alkaline thermal treatment (ATT). Hydrogen with purity over 80 vol % and porous carbon with a specific surface area of 2298.5 m²/g were co-produced at 500 °C for the first time. In this study, the effects of various reaction parameters on hydrogen production and the properties of porous carbon were investigated. The composition of gas products was tested, and the pore structure, morphology, graphitization degree and crystal structure of porous carbon were analyzed. The results showed that the optimum experimental conditions were alkali/rice husk mass ratio of 3:1, reaction temperature of 500 °C and reaction time of 60 min. A variety of characterization results showed that alkali etched the surface of rice husk at appropriate temperature, forming a large number of pore structures, and releasing volatile substances and hydrogen. The addition of alkali reduced the microcrystalline structure between graphite layers and increased the proportion of amorphous structure in porous carbon. Electrochemical test results showed that the specific capacitance of porous carbon prepared under the best reaction conditions reached 228.94 F/g at the current density of 0.2 A/g.     

Novel pretreatment pathways for dissolution of lignocellulosic biomass based on ionic liquid and low temperature alkaline treatment

Pretreatment, fractionation and hydrolysis remains costly and challenging process steps in biochemical conversion of softwoods. Here, ionic liquid pretreatment using 1-ethyl-3-methylimidazolium acetate (EMIM-OAc) at high temperature (100 °C, 6 h) and alkali based (NaOH/urea) pretreatment at sub-zero temperature (−18 °C, 24 h) were compared and combined in studies of Norway Spruce biomass deconstruction. Both treatments significantly improved the enzymatic digestibility of the biomass. EMIM-OAc gave higher glucan than mannan digestibility, indicating a more pronounced effect on the cellulose polymer than on the hemicellulose polymer. In contrast, low temperature alkali pretreatment using NaOH or NaOH + urea gave a more pronounced effect on mannan than on glucan digestibility. By combining the two methods the total monosugar yield after enzymatic hydrolysis was improved by 20–50% as compared to using ionic liquid or alkali based pretreatment alone. Lignin dissolution was low for both methods under the conditions studied.     

Photo-chemical property evolution of superior thin g-C3N4 nanosheets with their crystallinity and Pt deposition

The crystallinity and composition of superior thin g-C₃N₄ nanosheets were adjusted at different temperature settings to study property evolution via a two-step thermal polymerization procedure. g-C₃N₄ sample prepared at 600 °C shows high N/C ratio and amorphous structure while a crystalline g-C₃N₄ sample with C/N ratio of nearly 0.75 was obtained at 750 °C. The band gap varies for each type of g-C₃N₄ sample and photodegradation kinetics were examined to be related to the crystallinity of the g-C₃N₄ sample. The RhB photocatalytic degradation plots for g-C₃N₄ nanosheets samples prepared at more than 600 °C are fitted using the pseudo-first-order model while the reaction for bulk g-C₃N₄ sample prepared at 550 °C follows zero-order kinetics. This phenomenon is ascribed to the varying surface states of the g-C₃N₄ samples. g-C₃N₄ nanosheets prepared at 700 °C showed the best photocatalytic performance, in which the sample with both amorphous and crystalline structural features is assumed to be amorphous/crystalline homojunctions. Moreover, Pt deposition confirms that g-C₃N₄ nanosheets prepared at 700 °C reveal the highest photocatalytic H₂ evolution rate of 4892 μmol/hg which is about 21 times high compared with amorphous g-C₃N₄ nanosheets prepared at 600 °C.     

TG-GC-MS study of pyrolysis characteristics and kinetic analysis during different kinds of biomass

In this paper, TG-GC-MS was used to study the pyrolysis characteristics and kinetic parameters of the atypical biomass such as traditional Chinese medicine residues, livestock and poultry wastes, fungus planting sticks, bagasse and the typical biomass such as bark. It was found that the activation energies of the five kinds of biomass were significantly different. The activation energies of the mixed kinds of traditional Chinese medicine residues and livestock and poultry waste were lower. The mixed biomasses could reduce the initial pyrolysis temperature and accelerate the pyrolysis speed. The water released in the whole process of the atypical biomasses mass loss process. There were two peaks of HR at ∼78 °C and ∼367 °C respectively. The second peak value is significantly higher than the first one, and the peak intensity is 2.44 times of woody biomasses. The peak intensities of non-condensible gas during the atypical biomass pyrolysis are CO + C₂H₄ > CO₂ > H₂ > CH₄. The proportion of CO + C₂H₄ pyrolysised by HR is 39.45%, the H₂ is 16.47%, and the CH₄ is 5.17%.     

Pyrolysis analysis of different Cuban natural fibres by TGA and GC/FTIR

In this work, the pyrolysis of different Cuban biomass such as: sugar cane bagasse, coffee, residue of tobacco and sawdust of pine has been studied. The pyrolysis was carried out at different temperatures in a small furnace placed at the injection port of a gas chromatograph coupled to a Fourier transform infrared spectrometer (Py-GC/FTIR). Thermogravimetric analysis (TGA) was also carried out using a thermobalance. For tobacco residue, pyrolysis yield of charcoal and liquid products decreases with pyrolysis temperature (300–600 °C). When the pyrolysis is carried out at 300 °C charcoal yield is similar for tobacco residue, sawdust of pine and husk of coffee (≈40%) while for husk of coffee and sugar cane bagasse the charcoal yield is lower but the yield of the liquid product is higher.     

Optimization of hydrogen production in in-situ catalytic adsorption (ICA) steam gasification based on Response Surface Methodology

The present study investigates the optimization of hydrogen (H₂) production with in-situ catalytic adsorption (ICA) steam gasification by using a pilot-scale fluidized bed gasifier. Two important response variables i.e. H₂ composition (in percent volume fraction, %) and H₂ yield (in g kg⁻¹ of biomass) are optimized with respect to five process variables such as temperature (600 °C–750 °C), steam to biomass mass ratio (1.5–2.5), adsorbent to biomass mass ratio (0.5–1.5), superficial velocity (0.15 m s⁻¹–0.26 m s⁻¹) and biomass particle size (350 μm–2 mm). The optimization study is carried out based on Response Surface Methodology (RSM) using Central Composite Rotatable Design (CCRD) approach. The adsorbent to biomass mass ratio is found to be the most significant process variables that influenced the H₂ composition, whereas temperature and biomass particle size are found to be marginally significant. For H₂ yield, temperature is the most significant process variables followed by steam to biomass mass ratio, adsorbent to biomass mass ratio and biomass particle size. The optimum process conditions are found to be at 675 °C, steam to biomass mass ratio of 2.0, adsorbent to biomass mass ratio of 1.0, superficial velocity of 0.21 m s⁻¹ that is equivalent to 4 times the minimum fluidization velocity, and 1.0 mm–2.0 mm of biomass particle size. The theoretical response variables predicted by the developed model fit well with the experimental results.     

The influence of different chemical compositions in biomass on gasification tar formation

To elucidate the relationship between biomass composition and tar formation, forest residue sawdust, rich in lignin, and agriculture waste cornstalks, rich in cellulose, were gasified in a spout-fluidized bed reactor from 700 °C to 900 °C. Gel permeation chromatography (GPC) coupled with a photodiode array detector (PDA) and gas chromatography – mass spectrometry (GC–MS) were used to analyze the tar character. The GPC results showed that the molecular mass distribution of the gasified tars were unchanged, only the amount of each component changed when the temperature increased during gasification. The amount of heaviest molecular mass components decreased, while the lighter components increased with temperature. Sawdust tar and cornstalks tar both showed aromatic character, while cornstalks tar contained more aliphatic compounds than sawdust tar. The tar formation mechanism has been proposed from the experimental data analysis.     

Fast pyrolysis of date palm biomass using Py-GCMS

Pyrolysis of Date Palm Petiole (DPP) and Date Palm Seed (DPS) biomass was conducted by fast pyrolysis and on-line analysis of the outlet stream by gas chromatography connected to mass spectrometry (Py-GCMS) at different temperatures (450, 500 and 600 °C) in order to study the effect of this variable on the product distribution. The concentration of the components in the volatile stream (bio-oil and non-condensable gases) was greatly influenced by temperature and, to a minor extent, by the content of the biomass components (cellulose, hemicellulose and lignin). The most abundant compound families quantified are acids, anhydrosugars, ketones, furans and phenols. The most abundant compound identified was levoglucosan, which is mainly derived from the degradation of cellulose, with its relative content being as high as 18.3% for DPS pyrolysis at 450 °C and considerably lower for DPP pyrolysis (12.2%). The relative content of acetic acid was as higher as 10.2% at 450 °C for DPP pyrolysis. The knowledge of product composition is crucial for the development of large scale fast pyrolysis units for the valorization of these Tunisian agricultural wastes.     

Hydrothermal gasification of xylose: Effects of reaction temperature,pressure, and K2CO3 as a catalyst on product distribution

The hydrothermal gasification of xylose, as a model substance for the main polysaccharide in hemicelluloses, was carried out at high temperatures (up to 600 °C) and high pressures (up to 42.5 MPa) in the presence of an alkali catalyst with a constant reaction time of 3600 s. The comparison of the experimental results, such as the volume of the gas phase, composition of the gas, and the liquid products together with the total organic carbon content (TOC) provides the knowledge of the chemical reaction pathways of the xylose and their dependence on the reaction conditions, temperature, pressure, and catalyst. Both the gas and liquid phases were analyzed using chromatographic techniques. The major gaseous compounds produced were hydrogen, methane, carbon dioxide, carbon monoxide and C₂C₄ hydrocarbons. The carbon gasification efficiencies were improved by increasing the temperature and decreasing the pressure and reached their maximum value (86%) at 20 MPa and 600 °C with the addition of K₂CO_3. The highest measured concentration of the retro aldol reaction product was acetic acid and the dehydration product was 5-methyl furfural.     

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.     

Sustainable biohythane production from algal bloom biomass through two-stage fermentation: Impacts of the physicochemical characteristics and fermentation performance

Algal bloom biomass, sourced from a freshwater lake in Chongqing, was pre-treated by hydrothermal pre-treatments with or without acid/alkali catalysts, and subsequently used as a substrate for sustainable biohythane production via fermentation. Fourier transform infrared (FTIR) spectroscopy analyses suggested hydrothermal acid/alkali pre-treatments significantly changed peak intensities of chemical compositions in algal bloom biomass. Derivative thermogravimetric (DTG) analyses showed more macromolecular substances hydrolysed after hydrothermal acid/alkali pre-treatments. When bloom algae were pre-treated with 1% HCl at 140 °C for 10 min, an optimal specific hydrogen yield (SHY) of 39.4 mL/g volatile solid (VS) was obtained, which is 38.2% higher than raw biomass. However, a 34.4% decrease in SHY occurred under hydrothermal pre-treatment with 1% NaOH due to the enhancement of Maillard reaction. When using the effluents in methane fermentation, specific methane yields (SMYs) were 177.1–276.8 mL/g VS. Two-stage process effectively reduced the total fermentation time by 22.7% compared with single-stage fermentation.     

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.