Addition Of Char Research Articles

Co-combustion characteristics of coal with invasive alien plant chars prepared by torrefaction or slow pyrolysis

Lignocellulosic samples of Lantana camara (LC) and Mimosa pigra (MP) were pre-treated by torrefaction (300 °C) or pyrolysis (>500 °C) in order to study their potential use as co-fuels with coal. Combustion of the resultant chars, three coals and some blends was investigated by thermogravimetric analysis (10 °C min−1). The effects of biomass composition, pre-treatment temperature of char and blending ratio, on combustibility parameters of ignition, burnout and combustion indices were determined. The addition of reactive char in the fuel mixture consistently resulted in the reduction of ignition temperature, while lowered burnout temperatures of the blends indicated interactions between char and coal during co-combustion. Blends up to 15% showed similar combustion characteristics as those of the parent coals, with co-combustion occurring within the coal combustion zone. Most of the lowest combustion indices were obtained at 30% blends, mainly due to combustion occurring over a wider temperature range, while for blends ≥60%, co-combustion took place in the char combustion zone, with better co-combustion efficiencies, by up to 244% for 90% blend when compared with parent coal. Comparatively, pyrolysed char blends recorded higher combustion indices than torrefied sample blends. The results also showed that lignocellulosic composition of the precursor influenced the combustion mechanisms.

Efficient drying and oxygen-containing functional groups characteristics of lignite during microwave irradiation process

ABSTRACTTo remove the high moisture of ZhaoTong lignite, the efficient drying characteristics and oxygen-containing functional groups changes in lignite during microwave irradiation process were highlighted in this study. As the microwave absorbers, lignite char and NaNO3 were added to microwave drying of ZhaoTong lignite. The minimum chemical oxygen demand of waste water generated from microwave drying process of lignite was 99.89 mg O2 L−1. The effects of microwave power, lignite mass, the weight ratio of lignite char to lignite and NaNO3 content on the drying rate, and moisture diffusion coefficient of lignite were investigated during lignite microwave irradiation process. It was found that the drying rate and moisture diffusion coefficient of lignite increased with increasing microwave power, the weight ratio of lignite char to lignite and NaNO3 content, but decreased with increasing lignite mass. Lignite char and NaNO3 were mixed with lignite that can enhance the instantaneous surface temperature of lignite sample under microwave irradiation. Compared with addition of lignite char to lignite, the addition of NaNO3 to lignite can decrease the unit electric power consumption of moisture evaporating. And the minimum unit electric power consumption of moisture evaporating was 9.44 Wh g−1. The FTIR technology was used to investigate the oxygen-containing functional groups changes in lignite during microwave drying process. The oxygen-containing functional groups of lignite were effectively removed with increasing microwave power.

Microwave Torrefaction of Moist Municipal Solid Waste (MSW) Pellets with the Addition of Char from Agricultural Residues

An investigation of the effect of the addition of char from agricultural residues on the torrefaction of moist municipal solid waste (MSW) pellets (40 wt.% moisture) was carried out in a microwave oven (500-800 W for 4-12 minutes). Char from agricultural residues, including corncob, palm shell, straw, and bagasse, was used as the microwave absorbers to enhance the absorption of microwave irradiation. It was found that the addition of char from bagasse yielded the lowest remaining mass (or mass yield) and volatile matter (VM) content, but the highest temperature and heating value, of the torrefied MSW pellet. Moisture in the MSW pellet with or without the addition of microwave absorber was completely removed after being torrefied for 8-12 minutes. The VM contents remained in the MSW pellets with the addition of microwave absorbers were lower than that in the MSW pellet without the addition of microwave absorber. The addition of microwave absorbers led to an increase in carbon (C) content but a decrease in oxygen (O) content of the torrefied MSW pellets, compared to those of the raw MSW pellet. The heating values of the torrefied MSW pellets with the addition of microwave absorbers were equivalent to that of sub-bituminous coal, enhanced from that of the raw MSW pellet, which was lower than that of lignite.

Torrefaction of Municipal Solid Waste (MSW) Pellets using Microwave Irradiation with the Assistance of the Char of Agricultural Residues

In this study, the effects of the addition of char of agricultural residue (corncob, palm shell, straw, and bagasse) as a microwave absorber on the microwave torrefaction of municipal solid waste (MSW) pellets at 500-800 W for 4-12 minutes were investigated. The experimental results revealed that the torrefied MSW pellets with the addition of microwave absorbers had lower mass yields but higher temperatures than did the torrefied MSW pellet without the addition of microwave absorber. The addition of char of bagasse resulted in the lowest mass yield and the highest temperature of the torrefied MSW pellet. Moisture was completely removed from the MSW pellets after being torrefied for 8-12 minutes. The addition of microwave absorber and the increases in torrefaction time and microwave power caused the mass yield and the remaining amount of volatile matter (VM) of the torrefied MSW pellet to decrease. However, the remaining amount of fixed carbon (FC) was found to be relatively constant, approximately at the amount of FC in the raw MSW pellet. A decrease in VM content was found to be highest for the torrefied MSW pellet with the addition of char of bagasse. The amount of carbon (C) was found to be highest, whereas the amount of oxygen (O) was found to be lowest, for the torrefied MSW pellet with the addition of char of bagasse. The heating values of the torrefied MSW pellets with the addition of microwave absorbers were found to increase from that of the raw MSW pellet, and the heating values of the torrefied MSW pellets with the addition of char of straw and bagasse were equivalent to that of sub-bituminous coal. The use of microwave power of 650 W and the addition of char of bagasse were the most suitable combination, as they yielded the torrefied MSW pellet with the highest heating value, a reasonably high energy yield, and an appropriate amount of VM.

The calcification potential of cryogel scaffolds incorporated with various forms of hydroxyapatite for bone regeneration

Cryogels are advantageous scaffolds for bone regeneration applications due to their high mechanical stability and macroporous structure. Anatomically, bone is composed of collagen and hydroxyapatite and during remodeling, these structural components are replaced. However, early forms of mineralization include calcium salts which take up to months to be converted to the desired hydroxyapatite form. Thus, it is beneficial to provide a primary source of hydroxyapatite within the scaffold, expediting the process of mineralization during bone regeneration. In this study, chitosan–gelatin (CG) cryogels were incorporated with various forms of hydroxyapatite to evaluate effects on the standard characteristics of cryogels, as well as the potential for increased mineralization. Testing included the comparison of porosity, swelling, mechanical integrity, cellular infiltration, and mineralization potential between all types of cryogels. The addition of bone char to CG cryogels produced scaffolds with appropriate porosity and interconnectivity. Additionally, the bone char cryogels exhibited an adequate swelling potential, suitable mechanical properties, excellent cell attachment, and increased mineralization. These properties support this cryogel for such an application in tissue engineering.

Investigation of novel naturally occurring manganocalcite for CO2 capture under oxy-fuel calcination

The rapid capacity decay of CaO-based sorbents from limestone is one of the key issues for post-combustion CO2 removal using calcium looping process. Finding other naturally occurring Ca-containing minerals instead of limestone has been proved to be an effective way to acquire sorbents with highly improved cyclic CO2 capture performance. In the current work, a novel naturally occurring manganocalcite mineral was employed to produce CaO-based sorbent. EDS mapping has demonstrated that the inert solid support of Ca2MnO4 are homogeneously dispersed among the ultrafine active specie of CaO particles. As a result, calcined manganocalcite exhibits an obviously enhanced 20-cycle performance compared to calcined limestone when pure N2 calcination is used. Even under oxy-fuel calcination atmosphere, the sorbent still holds a surprisingly high conversion of ∼40% at the 20th cycle, 3.1 times as high as that of calcined limestone. Besides, the calcined manganocalcite is superior to calcined limestone for capturing CO2 under SO2-presence carbonation and oxy-fuel calcination. Coal combustion process during calcination stage was also investigated through employing synthetic char to simulate coal to burn with manganocalcite. It has been found that 0.5wt.% addition of synthetic char is the optimal ratio for manganocalcite in this study.

Impact of chars and readily available carbon on soil microbial respiration and microbial community composition in a dynamic incubation experiment

The carbonisation of biomass and organic residues is discussed as an opportunity to store stabilised carbon compounds in soil and to reduce mineralisation and the emission of CO2. In this study, pyrolysis char (600°C, 30min) and hydrothermal carbonisation char (HTC char; 210°C, 23bar, 8h), both derived from maize silage, were investigated in a short-term incubation experiment of soil mixtures with or without readily available carbon (glucose) in order to reveal impacts on soil microbial respiration and community composition. In contrast to pyrolysis char, the addition of HTC char increased respiration and enhanced the growth of fungi. The addition of glucose to soil-char mixtures containing either pyrolysis or HTC char induced an additional increase of respiration, but was 35% and 39% lower compared to soil-glucose mixtures, respectively, providing evidence for a negative priming effect. No significant difference was observed comparing the soil mixtures containing pyrolysis char+glucose and HTC char+glucose. The addition of glucose stimulated the growth of most microbial taxa under study, especially of Actinobacteria at the expense of fungi. Adding pyrolysis or HTC char to soil induced a decline of all microbial taxa but did not modify the microbial community structure significantly. Addition of pyrolysis or HTC char in combination with glucose however, increased the abundance of Actinobacteria and reduced the relative abundance of Acidobacteria and Betaproteobacteria while fungi were further increased in case of HTC char. We conclude that both chars hold the potential to bring about specific impacts on soil microbial activities and microbial community structure, and that they may compensate the variations induced by the addition of readily available carbon.

Copper ions removal from liquid phase by polyethersulfone (PES) membranes functionalized by introduction of carbonaceous materials

The method of synthesis of polymeric membranes based on polyethersulfone (PES) and modified by addition of carbonaceous materials (char or activated carbon) is presented and their potential application for removal of copper ions from liquid phase are examined. The addition of carbon brings about changes in the content of the surface oxygen group but has no significant effect on the chemical character of the groups, and acidic groups dominate. After filtration of a copper solution the total content of surface oxides considerably increases but the acidic groups remain dominant. Modification of PES membrane by addition of carbonaceous materials was found to strongly increase the membrane effectiveness in copper ions removal. The membrane with addition of char is the most effective at low copper concentrations, while the membrane with addition of activated carbon is the best at high concentrations of copper ions.

Application of char products improves urban soil quality

AbstractUrban soils are a key component of the urban ecosystem but little research has considered their quality and management. The use of char or partially combusted char products as a soil amendment is becoming popular worldwide because of perceived benefits to fertility and the potential for increasing carbon sequestration. In this study, we assessed the effect of applying coarse and fine char material on the quality of four different types of soil‐based root‐zone mixes typically used for turfgrass and general landscaping in Singapore: clay loam soil, approved soil mix (ASM, 3 soil:2 compost:1 sand), 50:50 (sand/soil) and 75:25 (sand/soil). Char briquettes made from sawdust were mixed thoroughly at rates of 25, 50 and 75% by volume with the soil mixes. Results showed that addition of char (both coarse and fine) significantly enhanced the carbon content of the mixes, with the largest increase being associated with the 50% and 75% additions. Soil nutrients (total N, extractable P, K, Ca and Mg) and mean weight diameter of aggregates were also significantly increased following the application of char. The clay loam and the 50:50 and 75:25 soil mixes were more responsive to the addition of char than was ASM.

The important role of microwave receptors in bio-fuel production by microwave-induced pyrolysis of sewage sludge

Microwave receptor plays an important role in the microwave pyrolysis of sewage sludge in view of its significant influence on the yield and property of bio-fuel products. The yield and the chemical compositions of bio-fuels (gases and oils) obtained from sewage sludge mixed with different receptors (graphite, residue char, active carbon or silicon carbide) were investigated in this study by Gas Chromatography (GC), Gas Chromatography–Mass Spectrometry (GC–MS), and Fourier Transform Infrared Spectroscopy (FTIR). The results showed that the use of silicon carbide gave rise to the highest final temperature of 1130 °C, resulting in the highest yield of gas fraction (up to 63.2 wt.%). The low heating rate (200 °C/min) which was attributed to the addition of residue char promoted condensation reactions and resulted in an increase in solid yield. The existence of active carbon could prolong the resistance time of volatiles in the hot zone owing to its porous structure, generating the maximum concentration of H 2 + CO (60%) in the pyrolysis gas. When graphite was used, the final low temperature favoured the cyclization of the alkenes, giving rise to a higher concentration of mononuclear aromatics in the pyrolysis oils. The model established in this study revealed that the quantity and quality of the products obtained from the microwave pyrolysis highly depended on the process conditions, which were influenced by the receptor significantly.

Pyrolysis of coal-tar asphaltene in supercritical water

Pyrolysis of coal-tar asphaltene, the main active component of coal tar in supercritical water (SCW), is investigated to further understand the upgrading mechanism of coal tar. It is found that coal-tar asphaltene convert to gas, maltene and char both in N 2 and in SCW, but the conversion of coal-tar asphaltene and the yield of maltene in SCW are significant higher than those in N 2. The effect of maltene and char in coal tar on the pyrolysis of coal-tar asphaltene is also studied. The results indicate that the presence of maltene could suppress the formation of char. And the addition of char could reduce the maltene yield. The analysis of pyrolysis product indicates the aromatic nucleus of asphaltene molecule is mainly composed of 2–4 rings aromatic hydrocarbons. Based on these results the pyrolysis mechanism of asphaltene in SCW was discussed.

Immobilization of Heavy Metal Ions (CuII, CdII, NiII, and PbII) by Broiler Litter-Derived Biochars in Water and Soil

Chars, a form of environmental black carbon resulting from incomplete burning of biomass, can immobilize organic contaminants by both surface adsorption and partitioning mechanisms. The predominance of each sorption mechanism depends upon the proportion of organic to carbonized fractions comprising the sorbent. Information is currently lacking in the effectiveness of char amendment for heavy metal immobilization in contaminated (e.g., urban and arms range) soils where several metal contaminants coexist. The present study employed sorbents of a common biomass origin (broiler litter manure) that underwent various degrees of carbonization (chars formed by pyrolysis at 350 and 700 degrees C and steam-activated analogues) for heavy metal (Cd(II), Cu(II), Ni(II), and Pb(II)) immobilization in water and soil. ATR-FTIR, (1)H NMR, and Boehm titration results suggested that higher pyrolysis temperature and activation lead to the disappearance (e.g., aliphatic -CH(2) and -CH(3)) and the formation (e.g., C-O) of certain surface functional groups, portions of which are leachable. Both in water and in soil, pH increase by the addition of basic char enhanced the immobilization of heavy metals. Heavy metal immobilization resulted in nonstoichiometric release of protons, that is, several orders of magnitude greater total metal concentration immobilized than protons released. The results suggest that with higher carbonized fractions and loading of chars, heavy metal immobilization by cation exchange becomes increasingly outweighed by other controlling factors such as the coordination by pi electrons (C=C) of carbon and precipitation.

Combinations of synergistic interactions and additive behavior during the co-oxidation of chars from lignite and biomass

The aim of this study is to investigate the co-combustion behavior of two different pyrolytic chars. For this purpose, Elbistan lignite and woody shells of hazelnut were pyrolysed in a tube furnace by heating to 900 °C with a heating rate of 40 °C min−1 under dynamic nitrogen flow of 400 mL min−1 to obtain pyrolytic char. These chars were mixed to obtain blends having the biomass char in the ratios of 5, 10, and 20 wt.%. Non-isothermal DTA and TGA profiles of the chars were obtained from ambient to 900 °C with a heating rate of 40 °C min−1 under the static ambient atmosphere. DTA and TGA profiles of the blend chars were interpreted considering the thermal characteristics such as ignition point, burnout at a given temperature, maximum burning rate, the end of combustion etc. Relations between the fraction of the biomass char in the blends and the thermal behavior of the blends were evaluated according to the synergistic approach. It was found that addition of biomass char led to important variations in some thermal properties which can not be explained by the additive behavior. However it can be concluded in general that the combinations of synergistic interactions and additive behavior govern the thermal properties of the blend chars during co-oxidation.

Effect of char on the melting characteristics of coal ash

The effect of char on the melting characteristics of coal ash was studied in the argon atmosphere using an ash fusion determinator connected with a camera and a computer. The results show that the coal char in ash has remarkable influence on the ash melting points as well as the ash melting behavior. The effects are related to the coal rank and the char content addition. For the coal ashes investigated, the deforming temperatures (DT), the softening temperatures (ST), and the flowing temperatures (FT) of all samples with the addition of coal char are higher than those of corresponding initial ashes. The ash melting points increase with the addition of coal char. When the content of coal char is 20% and when the temperature reaches or exceeds the corresponding original ash melting point, an infusible skeleton can be formed because of the sticking interaction between char and ash. When the skeleton formed, the softening temperature and flowing temperature of the sample are difficult or impossible to occur.

Effect of bone char application on Pb bioavailability in a Pb-contaminated soil

The effects of bone char (BC) application on the bioavailability of Pb in a polluted soil from Hunan Province, China were examined. The Pb-contaminated soil was treated with two types of bone char, one from the UK and the other from China. The bioavailability of Pb was determined in terms of the uptake by Chinese cabbage ( Brassica chinensis L.), sequential extraction and X-ray diffraction analysis. The results indicate that the Pb concentrations in both shoots and roots decreased with increasing quantities of added bone char, and the application of BC from the UK at the rate of 1.6% (w:w) had the largest effect. Lead Pb concentrations in the shoots and roots decreased by 56.0% and 75.9%, respectively, whereas the application of BC from Zhejiang Province, China at the rate of 1.6% (w:w) reduced Pb concentrations in the shoots and roots to 2.04 mg kg −1 and 8.42 mg kg −1, respectively, only 45.8% and 30.2% compared to the control treatment. Sequential extraction results indicate that the addition of bone char, as a metal-immobilizing agent, substantially transforms soil Pb from non-residual fractions to the residual fraction. The transformation was further confirmed using X-ray diffraction studies.

The fate of char-N at pulverized coal conditions

The fate of char-N (nitrogen removed from the coal matrix during char oxidation) has been widely studied at fluidized bed conditions. This work extends the study of char-N to pulverized coal conditions. Coal chars from five parent coals were prepared and burned in a laboratory-scale pulverized coal combustor in experiments designed to identify the parameters controlling the fate of char-N. The chars were burned with natural gas (to simulate volatiles combustion) in both air and in a nitrogen-free oxidant composed of Ar, CO 2, and O 2. In some experiments, the char flames were doped with various levels of NO or NH 3 to simulate formation of NO x from volatile-N (nitrogen removed during coal devolatilization). The conversion of char-N to NO x in chars burned in the nitrogen-free oxidant was 50–60% for lignites and 40–50% for bituminous coals. In char flames doped with NO x, the apparent conversion of char-N to NO x (computed using the NO x measurements made before and after the addition of char to the system) decreased significantly as the level of NO x doping increased. With 900 ppm NO x present before the addition of char, apparent conversion of char-N to NO x was close to 0% for most chars. While there is no clear correlation between nitrogen content of the char and char-N to NO x conversion at any level of NO x in the flame, the degree of char burnout within a given family of chars does play a role. Increasing the concentration of O 2 in the system in both air and nitrogen-free oxidant experiments increased the conversion of char-N to NO x. The effects of temperature on NO x emissions were different at low (0 ppm) and high (900 ppm) levels of NO x present in the flame before char addition.