And Alkaline Earth Metals Research Articles

Catalytic Biomass-Derived Tar Decomposition Using Char from the Co-pyrolysis of Coal and Giant Leucaena Wood Biomass

In this study, the catalytic effect of chars from the co-pyrolysis of Indonesian coal and biomass [giant leucaena wood (LN)] on the biomass-derived tar decomposition was investigated using a two-stage fixed-bed reactor. The catalytic performance of the coal char (CC), LN biomass char (LNC), and coal/LN blended chars (C/LN) at three different weight ratios on the catalytic tar cracking under nitrogen (N2) and tar steam reforming under a steam/N2 mixture was studied. The C/LN showed a better catalytic role for tar decomposition than the CC and LNC. The high coal fraction [3:1 (w/w) C/LN] blended char had a good catalytic effect on both tar catalytic cracking and tar steam reforming because of its high surface area and silicate forms of the alkali and alkaline earth metals (AAEM) on the char. On the other hand, char with a high biomass ratio [1:3 (w/w) C/LN] also had a good catalyst activity in tar steam reforming because of the high steam activation of the char surface and the AAEM would be in the form of p...

Upgrading and multistage separation of rice straw by degradative solvent extraction

Upgrading and multi-stage separation (UMSS) of rice straw was conducted at different temperatures using 1-methylnaphthalene (1-MN) as solvent. Three main solid products were obtained: low molecular weight extract (soluble), high molecular weight extract (deposit) and extraction residue (residue). The elemental composition, chemical structure and physicochemical characteristic of each component were analyzed in detail. Alkali and alkaline earth metal (AAEM) contents of solid products and rice straw were also measured by ICP-MS. The results showed the yield of soluble increased with temperature, and the carbon-based yield of soluble reached 33.48% at 350°C. The carbon content and oxygen content of three solid products (soluble, deposit, and residue) increased and decreased with temperature, respectively. The carbon content of soluble and deposit reached up to 82.36% and 80.59% respectively. Meanwhile the oxygen contents of them were as low as 9.50% and 12.03% respectively. More than 86.99% oxygen of rice straw was removed as H2O and CO2. Soluble was almost free from ash, and the ash content of deposit was also less than 1.50%. The higher heating values (HHV) of three solid products were significantly higher than that of rice straw. The FT-IR results indicated that not only dehydration reaction and decarboxylation reaction occurred, but also including obvious aromatization reaction. The contents of Na, Mg and K of soluble and deposit were extremely low, and they decreased with temperature gradually. In conclusion, the degradative solvent extraction method realized dehydration, deoxygenation and multistage separation of biomass under mild condition, and obtained a variety of products of low ash and oxygen content as well as high carbon content and HHV.

Bioslurry as a Fuel. 6. Leaching Characteristics of Alkali and Alkaline Earth Metallic Species from Biochar by Bio-oil Model Compounds

In a bioslurry fuel system, inherent alkali and alkaline earth metallic (AAEM) species can be leached from biochar into the bio-oil phase because of the interaction between biochar and bio-oil [as ...

Microwave-assisted gasification of rice straw pyrolytic biochar promoted by alkali and alkaline earth metals

A novel microwave assisted gasification technique was developed whereby pyrolytic biochar obtained from rice straw was used as the feedstock. The conversion efficiencies and gas composition obtained at 800°C by conventional heating method were similar to that obtained at 550°C by microwave-assisted gasification. At 550°C using microwave heating, the CO+H2 yields were over 90vol.% and H2 content was 60vol.%. The effects of alkali and alkaline earth metals (AAEM) on microwave-assisted gasification activity of biochar were also investigated. The results indicated that 5% K2CO3 and 5% KOH increased the carbon conversion efficiency from 74.39% to 79.95% and 85.04%, respectively, but CO2 content increased remarkably. Ca(OH)2 was a suitable gasification catalyst and excellent CO2 absorber. 10% Ca(OH)2 reduced CO2 percentage from 21.92vol.% to 10.83vol.% and shortened reaction time from 90 to 60min. Based on the AAEM catalytic mechanisms and microwave heating function, the intermediate C(O) and dipole rotation of materials molecules played a crucial role in the microwave-assisted gasification of biochar. This study proves that microwave heating coupled with the addition of AAEM result in low-temperature microwave-assisted gasification of biochar.

Fine particulate formation and ash deposition during pulverized coal combustion of high-sodium lignite in a down-fired furnace

The high-reserve Zhundong lignite, rich in Alkali and Alkaline Earth Metal (AAEM) elements, causes severe fouling and slagging problems in stationary combustion systems. In this paper, the ash deposition propensity as well as its relation to AAEM-rich fine particulates was investigated in a 25kW down-fired furnace possessing similar conditions to practical combustors. The high content AAEM (mainly calcium) species in Zhundong lignite results in the molten slag at the vicinity of the burner inlet, differing from other case burning high-ash-fusion (HAF) bituminous coal. The ash deposits were collected at a position with gas temperature of 800°C, whereas the fine particulates were sampled at the same position by a two-stage nitrogen-dilution isokinetic probe. The deposition tendency of ash particles from Zhundong lignite is apparently higher than those from contrast fuels and even herbaceous biomass. It is then related to the sticky surfaces of both bare deposition tube and bulk fly ash particles, forming from large amounts of AAEM species, which enhances the deposition propensity.

Kinetics and Mechanism of Steam Gasification of Char from Hydrothermally Treated Woody Biomass

Hydrothermal treatment (HTT) is a promising way of upgrading biomass as a solid fuel and precursor of carbon materials by eliminating or transforming carbohydrates and also leaching alkali and alkaline earth metallic (AAEM) species. This study investigated steam gasification of a woody biomass that had been upgraded by HTT at 250 °C. HTT removed 87–97% of AAEM species from the biomass. The char from the pyrolysis of the treated biomass underwent gasification, obeying first-order kinetics with respect to the mass of char over the entire range of conversion. This kinetics arose from non-catalytic gasification. AAEM species remaining in the char had no catalytic activity. The specific surface area of char increased monotonically with its conversion from 500 to well above 2000 m2/g. The non-catalytic nature of the gasification was responsible for such a significant surface area development. The surface area was, however, not a factor influencing the rate of gasification. The presence of the inherent AAEM cata...

Leaching of Alkali and Alkaline Earth Metallic Species from Rice Husk with Bio-oil from Its Pyrolysis

Removal of alkali and alkaline earth metallic (AAEM) species, in particular, that of potassium, is an effective way to upgrade rice husk, because its combustion and gasification often suffer from the formation of potassium silicate with a low softening or fusion temperature. This work has been investigating the leaching of AAEM species with a bio-oil (BO) from the pyrolysis of the parent rice husk. The leaching with BO, which had a pH of 2.59, gave removal rates of K and Na equivalent to or higher than those with an aqueous solution of hydrogen chloride (HCl aqueous) or acetic acid (AcOH aqueous) at pH of 2. The leaching abilities of BO in terms of the removal rates of Mg and Ca were equivalent to HCl aqueous at pH 0 and AcOH aqueous at pH < 2, respectively. Such performances of BO arose from the presence of not only AcOH with a concentration of 6 wt % but also phenolic compounds (phenol, alkylphenols, and methoxyphenols). The phenols permeated into the organic matrix of the rice husk, forming hydrophobic...

Alkali and alkaline earth metallic (AAEM) species leaching and Cu(II) sorption by biochar

Alkali and alkaline earth metallic (AAEM) species water leaching and Cu(II) sorption by biochar prepared from two invasive plants, Spartina alterniflora (SA) and water hyacinth (WH), were explored in this work. Significant amounts of Na and K can be released (maximum leaching for Na 59.0mgg−1 and K 79.9mgg−1) from SA and WH biochar when they are exposed to contact with water. Cu(II) removal by biochar is highly related with pyrolysis temperature and environmental pH with 600–700°C and pH of 6 showing best performance (29.4 and 28.2mgg−1 for SA and WH biochar). Cu(II) sorption exerts negligible influence on Na/K/Mg leaching but clearly promotes the release of Ca. Biochars from these two plant species provide multiple benefits, including nutrient release (K), heavy metal immobilization as well as promoting the aggregation of soil particles (Ca) for soil amelioration. AAEM and Cu(II) equilibrium concentrations in sorption were analyzed by positive matrix factorization (PMF) to examine the factors underlying the leaching and sorption behavior of biochar. The identified factors can provide insightful understanding on experimental phenomena.

Promoting effect of various biomass ashes on the steam gasification of low-rank coal

Application of biomass ash as a catalyst to improve gasification rate is a promising way for the effective utilization of waste ash as well as for the reduction of cost. Investigation on the catalytic activity of biomass ash to the gasification of low rank coal was performed in details in the present study. Ashes from 3 kinds of biomass, i.e. brown seaweed/BS, eel grass/EG, and rice straw/RS, were separately mixed with coal sample and gasified in a fixed bed downdraft reactor using steam as the gasifying agent. BS and EG ashes enhanced the gas production rate greater than RS ash. Higher catalytic activity of BS or EG ash was mainly attributed to the higher content of alkali and alkaline earth metal (AAEM) and lower content of silica in it. Higher content of silica in the RS ash was identified to have inhibiting effect for the steam gasification of coal. Stable catalytic activity was remained when the amount of AAEM in the regenerated ash was maintained as that of the original one.

Effect of minerals on surface morphologies and competitive reactions during char gasification in mixtures of O2 and CO2

This study aims to investigate the effect of minerals on surface morphologies and competitive reactions during char gasification in mixtures of O2 and CO2. Char gasification experiments were performed in O2/Ar, Ar/CO2, and O2/CO2 environments to study char structure evolution and competitive reactions between char-O2 and -CO2 gasification. Chars gasified under Ar/CO2 or O2/CO2 were observed to have large pores on their surface, while chars gasified under O2/Ar did not have them. The reaction between catalyst/carbon interfaces was key in explaining the difference in surface morphologies of chars gasified under O2 and CO2. High specific surface area and large pores produced by gasification in CO2 increased char gasification rates in the internal diffusion-controlled regime. Then, two coals of different ash composition (including high alkali and alkaline earth metallic (AAEM) and low AAEM species) were used to study competitive reactions between O2 and CO2 on the active sites. When chars prepared from coals including a low AAEM species were used, the char gasification rate in O2/CO2 environments was almost 60% of the sum of those in O2/Ar and Ar/CO2 environments, regardless of specific surface area. This indicated that char-O2 and -CO2 reactions were competitive. However, when chars prepared from coals including a high AAEM species were used, higher Ca and Na concentrations were detected on the char surface, and the char gasification rate in O2/CO2 environments was almost the same as the sum of gasification rates in O2/Ar and Ar/CO2 environments, implying that Ca and Na played an important role as active sites. Unlike air environments, all surrounding gases were reactive in the O2/CO2 environments. Therefore, a sufficient active site, mainly consisting of catalyst in this study, was important not only to enhance char gasification reactions but also to prevent competitive reactions between char-O2 and CO2 gasification.

Effect of biomass type on the performance of cogasification of low rank coal with biomass at relatively low temperatures

Cogasification of low rank coal with three kinds of biomass, i.e., Japanese cedar, rice straw, and seaweed, at relatively low temperatures were performed in a fixed bed downdraft reactor. The effect of different biomass addition on the coal gasification performance was investigated by comparing the experimental char and gas yields with the calculated prediction data. Effect of the blending ratio was also investigated. It was found that the mixing of coal with biomass revealed a synergy effect. Biomass promoted the coal gasification rate, but the extent of promoting effect was depended on the characteristics of biomass themselves. Alkali and alkaline earth metal (AAEM) content played an important role in this synergy effect. Seaweed which contained high AAEM content promoted the coal gasification significantly. Structure of coal was also found to have great effect on the cogasification performance. The results indicated that cogasification of coal with biomass is feasible at relatively low temperatures.

Steam reforming of tar derived from Fallopia Japonica stem over its own chars prepared at different conditions

In order to understand the promoting effect of char in different states on the steam reforming of biomass-derived tar during the gasification process, Fallopia Japonica stem (FJS) chars were prepared at different pyrolysis temperatures with different pyrolysis time, and used as the catalyst for the reforming of tar derived from FJS itself in a fixed-bed reactor. As-prepared FJS chars were characterized using Scanning Electron Microscope (SEM), Fourier Transform Infra Red spectroscopy (FT-IR), and Brunauer–Emmet–Teller (BET) surface area measurement for clarifying the relationship between the promoting effect and the physical and chemical structures of the char. It was found that BET surface area, chemical structure, and the contents of alkaline and alkaline earth metals (AAEM) in the char, which were obviously affected by pyrolysis temperature and time, had significant effect on char reactivity as well as the catalytic activity on tar reforming. The char obtained at lower temperature (<700°C) had lower BET surface area but higher active chemical components, thus showed higher gasification reactivity but lower promoting property on tar reforming. With the increase of BET surface area, the reactivity of char itself decreased at first due to the decrease of active chemical components, and then increased to some extent due to the increase in BET surface area. On the contrary, the promoting effect of char on the tar reforming increased at first and then decreased due to the decrease of AAEM species in the char and the shrinkage of old larger pores in char which could hinder the contact between FJS-derived tar and char.

A Review of Thermal Co-Conversion of Coal and Biomass/Waste

Biomass is relatively cleaner than coal and is the only renewable carbon resource that can be directly converted into fuel. Biomass can significantly contribute to the world’s energy needs if harnessed sustainably. However, there are also problems associated with the thermal conversion of biomass. This paper investigates and discusses issues associated with the thermal conversion of coal and biomass as a blend. Most notable topics reviewed are slagging and fouling caused by the relatively reactive alkali and alkaline earth compounds (K2O, Na2O and CaO) found in biomass ash. The alkali and alkaline earth metals (AAEM) present and dispersed in biomass fuels induce catalytic activity during co-conversion with coal. The catalytic activity is most noticeable when blended with high rank coals. The synergy during co-conversion is still controversial although it has been theorized that biomass acts like a hydrogen donor in liquefaction. Published literature also shows that coal and biomass exhibit different mechanisms, depending on the operating conditions, for the formation of nitrogen (N) and sulfur species. Utilization aspects of fly ash from blending coal and biomass are discussed. Recommendations are made on pretreatment options to increase the energy density of biomass fuels through pelletization, torrefaction and flash pyrolysis to reduce transportation costs.

The Influence of Alkali and Alkaline Earth Metals and the Role of Acid Pretreatments in Production of Sugars from Switchgrass Based on Solvent Liquefaction

This study investigated the influence of alkali and alkaline earth metals (AAEM) and the role of acid pretreatments in the production of sugars during solvent liquefaction of lignocellulosic biomass using 1,4-dioxane and water as solvents. The present study found that removal of AAEM by acid washing/water rinsing did not enhance sugar production during solvent liquefaction of pretreated switchgrass nearly to the extent observed for fast pyrolysis nor did it inhibit lignin decomposition, suggesting that AAEM play less of a role in determining product yields in solvent liquefaction. On the other hand, acid infusion greatly enhanced the yields of sugars during solvent liquefaction, presumably because the strong acid catalytically promoted both the depolymerization and the dehydration of polysaccharides. The main monomeric sugars formed were levoglucosan, glucose, and xylose. Levoglucosan was the predominant sugar when 1,4-dioxane was the solvent, whereas glucose was the major sugar when water was the solvent...

Continuous production of sugars from pyrolysis of acid-infused lignocellulosic biomass

Although pyrolysis of carbohydrate-rich biomass should theoretically yield large amounts of sugar, the presence of alkali and alkaline earth metals (AAEMs) in most biomass prevents this from happening.

Influences of heating rate during coal char preparation and AAEMs on volatile–char interaction with different sources of biomass volatile

Volatile–char interaction is important for the operation of co-gasification of coal and biomass. Biomass generally produces large amount of volatiles while char is mainly produced from coal. Hence, in this study, the interaction between coal char and volatiles from biomass samples (xylan, cellulose and rice straw) was examined using a rapid-heating thermobalance reactor. Three types of coal char, consisting of slow pyrolyzed-coal char (Ex-char), fast pyrolyzed-coal char (In-char), and acid washed-coal char (Ac-char), were employed to reveal influences of heating rate during char preparation and retention of alkali and alkaline earth metallic (AAEM) species on char surface. The steam gasification rates of all coal chars in both cases with and without volatile contacting were investigated from the gas evolution rate and remaining char analyses. The results indicate that the steam gasification rates of Ex-char and In-char were significantly diminished by the volatiles derived from all sources, especially rice straw. However, in the case of Ac-char, the reduction of steam gasification rate was less important. Moreover, the Ex-char exhibited the catalyst for the decomposition of biomass volatiles, resulting in the increase in gas production rate. Porous structure and the AAEM over char play crucial roles on the volatile–char interaction.

A Method for the Quantification of Alkali and Alkaline Earth Metallic Species in Bioslurry Fuels

This study reports a method for the quantification of alkali and alkaline earth metallic (AAEM) species in bioslurry fuels. The so-called evaporation–ashing–digestion–ion chromatography (IC) method consists of four steps, including evaporation that converts bioslurry into solid-like residue, ashing that converts the residue into ash, acid digestion that dissolves the ash into a solution, and IC analysis that quantifies the AAEM species in the solution. The novelty of the method is the combination of the evaporation step with the existing ashing–digestion–IC method that is developed for solid fuels but not suitable for bioslurry fuels. The evaporation step consists of multi-steps of slow heating and holding at various segment temperatures corresponding to the boiling points of the major compounds in bio-oil, resulting in progressive evaporation of bio-oil vapors with little carry-over of biochar particles. The method has been successfully applied for quantifying AAEM species in bioslurry fuels with various biochar loading levels (5–20 wt %), with small relative standard errors (within ±3%) and low limitations of quantification (0.4–3.0 ppm). It also overcomes the biochar incomplete oxidation issue associated with the microwave–digestion-based methods, which considerably underestimate the concentrations of AAEM species in bioslurry fuels.

Effect of sulfuric acid on the pyrolysis of Douglas fir and hybrid poplar wood: Py-GC/MS and TG studies

This paper reports results on the effect of sulfuric acid addition on the pyrolysis of raw and acid washed Douglas fir wood (DFW) (a softwood) and hybrid poplar wood (HPW) (a hardwood). Nitric acid (0.1%) was used to remove the alkali and alkaline earth metals (AAEMs) from the feedstock studied. Sulfuric acid concentrations of 0.05, 0.1, 0.3, and 0.5wt.% were applied to the ash free and raw feeds prior to pyrolysis tests in Py-GC/MS and TGA. Our results show that the effect of sulfuric acid addition can be explained by the existence of two reaction regimes. In the first reaction regime the content of ash exceeds the amount of sulfuric acid added. Under these conditions, the sulfuric acid is completely neutralized by the AAEMs; as a result, the char yield decreases and the levoglucosan yield increases as the sulfuric acid concentration increases due to the passivation of the catalytic effect of AAEMs. The second reaction regime is where the content of sulfuric acid exceeds the ash content; un-neutralized free sulfuric acid is available to catalyze dehydration, crosslinking, and polycondensation reactions responsible for the formation of extra char. In this regime the charcoal yield increases as sulfuric acid is added. The products detected by Py-GC/MS were classified into four groups: small molecules, small ring molecules, anhydrosugars, and phenolic compounds. The yield of small molecules (ethanedial, methylyinyl acetate, hydroxyacetaldehyde, methyl vinyl ketone, acetic acid, acetol, 2-hydroxyethyl acetate and methyl pyruvate) decreased as the concentration of sulfuric acid increased. The yield of furfural, a product of hemicelluloses dehydration reactions, increased as the content of sulfuric acid increased. The supplementary addition of sulfuric acid to acid washed samples further increased levoglucosan production in more than 50% compared with the control acid washed material. This result suggests that the sulfuric acid could also play a role mitigating undesirable interactions between cellulose and the other constituents in ash-free lignocellulosic materials. Levoglucosenone, a product of levoglucosan dehydration reactions, increased as more sulfuric acid was added. The yield of most methoxylated phenols (2-methoxy-4vinyl-phenol, isoeugenol, eugenol, 2-methoxy-4-propyl-phenol, vanillin, 2,6-dimethoxy-4-(2-propenyl)-phenol, 4-hydroxy-2-methoxycinnamaldehyde, syringaldehyde, 3,5-dimethoxy-4-(2-propenyl)-phenol, 1-(4-hydroxy-3,5-dimethoxylphenyl)-ethanone) in acid washed materials decreased as the content of sulfuric acid increased. Overall sulfuric acid has several major effects on the pyrolysis of lignocellulosic materials: passivation of AAEMs, mitigation of undesirable cellulose interactions in lignocellulosic materials, acceleration of dehydration and polycondensation reactions, mitigation of cellulose fragmentation reactions, and reduction of the formation of methoxylated mono-phenols from lignin.

Experimental and Kinetic Investigations of CO2 Gasification of Fine Chars Separated from a Pilot-Scale Fluidized-Bed Gasifier

The CO2 gasification behaviors of two fine chars separated from a pilot-scale fluidized-bed gasifier were studied in a thermogravimetric analyzer (TGA) within the temperature range of 1000–1300 °C. The physical properties of fine chars were examined by scanning electron microscopy (SEM), N2 adsorption, and X-ray diffraction (XRD). The differences in gasification reactivity and related properties between the fine chars and the corresponding experimental-produced coal chars were also compared. The results show that the fine chars have higher ash content, larger Brunauer–Emmett–Teller (BET) surface area, and better gasification reactivity than the corresponding coal chars. The gasification reactivity of fine chars was promoted by the catalytic alkali and alkaline earth metals (AAEMs) but inhibited by the enrichment of the ash layer in a higher carbon conversion range or the ash melting at a higher temperature. In addition to the AAEMs, the reactivity of different fine chars is mainly influenced by their pore and carbon crystalline structures. The kinetic investigation reveals that the modified random pore model (MRPM) and shifted-modified random pore model (S-MRPM) perform more reasonably than the random pore model (RPM) in some special conditions. Moreover, the reactivity of fine chars increases, and the reaction shifts from chemical reaction control to gas diffusion control as the gasification temperature increases.

Contribution of Volatile Interactions During Co-Gasification of Biomass with Coal

Thermo-gravimetric behavior during steam co-gasification of Japanese cedar and coal was investigated. The difference between co-gasification behavior and the average gasification behavior of cedar and coal indicates two synergetic peaks. The first peak occurred between 300 °C and 550 °C while the second peak was observed above 800 °C. The first peak coincides with volatile release and therefore associated with volatile interactions while the second peak is linked with catalytic effect of alkali and alkaline earth metal (AAEM). Acid washed cellulose and Na rich lignin chemicals were used as artificial biomass components. In reference to Japanese cedar, mixture of cellulose and lignin i.e. simulated biomass, was also investigated. Co-gasification of cellulose with coal and co-gasification of lignin with coal, demonstrates contribution of volatile interactions and AAEM catalysis respectively. Morphology of partially gasified blends, shows hastened pore development and physical cracking on coal particles. Brunauer−Emmett−Teller (BET) surface area of the charred blend was lower than the average surface area for charred biomass and coal.