Combustion Of Biochar Research Articles

Effect of Washing Pretreatment with Aqueous Fraction of Bio-Oil on Pyrolysis Characteristic of Rice Husk and Preparation of Amorphous Silica

Rice husk is an abundant agricultural by-product and the common disposal method of rice husk could cause serious environmental and human health problems. In this study, effects of washing with aqueous fraction of bio-oil on pyrolysis characteristic of rice husk and preparation of amorphous silica from combustion of biochar were investigated. Most metallic species in rice husk, especially alkali and alkaline earth metals (AAEMs), can be effectively removed by washing pretreatment with aqueous fraction of bio-oil. Thermogravimetric analysis indicated that aqueous fraction of bio-oil washing pretreatment prior to pyrolysis process obviously increased the value of pyrolysis characteristics parameters, such as the max decomposition rate, the temperature according to the max decomposition rate, and the mean decomposition rate. Meanwhile, the apparent activation energy was slightly increased after washing pretreatment. Furthermore, the high purity amorphous silica with a purity of 99.33% was obtained from combustion of biochar from pyrolysis of aqueous fraction of bio-oil washed rice husk. In addition, a novel method for utilization of rice husk via washing with aqueous fraction of bio-oil, pyrolysis and combustion of biochar was proposed. This method resolved the problem of pollution and waste aroused by rice husk and the whole process is known to be self-heating and environmentally friendly.

Performance of calcium manganate as oxygen carrier in chemical looping combustion of biochar in a 10 kW pilot

Chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) are carbon capture technologies which achieve gas separation by means of cycling oxidation and reduction of a solid oxygen carrier. In this study, the performance and CLOU properties of an oxygen carrier with perovskite structure, CaMn0.9Mg0.1O3−δ, were investigated in a 10kW pilot. The fuel consisted of biochar with very low sulphur content. Around 37h of operation with fuel were carried out in the 10kW chemical looping combustor. Previous operational experience in this unit has been achieved using different natural minerals as oxygen carrier – mainly ilmenite and manganese ore. Parametric studies performed in this work included variation of fuel flow, solids circulation rate, temperature and fluidization gas in the fuel reactor. The oxygen carrier was exposed to a total 73h of hot fluidization (T>600°C). No hard particle agglomerations were formed during the experiments. An oxygen demand as low as 2.1% could be reached under stable operating conditions, with a carbon capture efficiency of up to 98%. CLOU properties were observed at all fuel reactor temperatures, ensuring stable operation even without steam as gasification agent present in the fuel reactor. The results suggest that CaMn0.9Mg0.1O3−δ is suitable for the use as oxygen carrier in chemical looping combustion of solid biochar and offers higher gas conversion than previously tested materials without CLOU properties such as ilmenite. The experiments constitute the first successful operation using a non-copper CLOU oxygen carrier in combustion of solid fuel.

Combustion kinetics of pine sawdust biochar

The combustion kinetics of biochar derived from fast pyrolysis of pine sawdust was investigated by using nonisothermal thermogravimetric analysis under air atmosphere at different heating rates. The experimental conversion (α–T) curves contain some experimental errors, and the corresponding derivative conversion (dα/dT–T) curves have many fluctuations. Two strategies of obtaining the smooth dα/dT–T curves were used based on the robust locally weighted scatterplot smoothing method coupled with the corrected AIC smoothing parameter selection method. In the strategy of firstly smoothing α–T data and then differentiating smoothed α–T data, although the smoothed α–T data are relatively smooth, the dα/dT–T curves obtained from the differentiation of the smoothed α–T data have fluctuations. In the strategy of firstly differentiating α–T data and then smoothing dα/dT–T data, the obtained dα/dT–T curves with the optimal smoothing parameters are smooth enough, which indicates that the second strategy is effective. The isoconversional kinetic analysis of the smoothed dα/dT–T curves was performed by using the Friedman differential isoconversional method. The effective activation energies of biochar combustion were obtained and found to significantly vary with the conversion degree (from about 150 to 250 kJ mol−1 in the range of conversion degree from 0.05 to 0.95).

Partial oxidation of sewage sludge briquettes in a updraft fixed bed

The fixed bed reaction of sewage sludge briquettes was investigated to evaluate the potential applications to gasification, combustion, or production of biochar as soil ameliorator. The reaction had two distinctive stages: ignition propagation and char oxidation. The ignition front of the sludge briquettes propagated at a lower speed, which significantly increased the stoichiometric ratio of overall combustion reaction and peak temperatures. The ignition front also had irregular shapes due to the channeling effects. During the char oxidation stage, the sludge ash agglomerated because of the slow reaction rate and increased CO2 formation. Because of low energy content in the product gas, the large briquettes were not favorable for syngas production. In addition, the low burning rates and ash agglomeration could cause problems in the operation of a grate-type furnace for combustion. However, the char accumulated above the ignition front had similar properties with that from pyrolysis under inert atmosphere. Therefore, the fixed bed reaction under partial oxidation conditions can be applied to produce biochar as soil ameliorator from the sludge briquettes without external heat supply.

Combustion characteristics of moso bamboo (Phyllostachys pubescens)

This study was carried out to investigate combustion characteristics of moso bamboo, including outer layer (OB), middle layer (MB) and inner layer (IB) and bamboo leaves (BL), respectively. The results showed that combustion characteristics of moso bamboo were similar to other biomass materials. There were two separate peaks in the combustion process; the first peak corresponding to combustion of volatile matters and the second peak corresponding to combustion of biochar. Compared to OB, MB and IB, BL had a worse fuel quality with higher H/C and O/C value, N and S content, ash content and lower combustion efficiency. Furthermore, BL had a higher slagging index and MB had a higher fouling index. These combustion characteristics of bamboo should be taken into consideration to efficiently design and operate the combustion systems when directly used for fuel production.

Combustion Kinetics of Biochar from Fast Pyrolysis of Pine Sawdust: Isoconversional Analysis

Non-isothermal thermogravimetric data were used to evaluate the Arrhenius parameters (activation energy and the pre-exponential factor) of the combustion of biochar. The biochar was produced as a byproduct from the fast pyrolysis of pine sawdust particle. The isoconversional methods (Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa method) were used for evaluating the activation energy and the kinetic model function f(α), which was determined by using the master plot method. The effective activation energy for combustion of biochar was 212.524 kJ mol–1 in the conversion range of 0.15–0.85. The results showed that the most probable mechanism is the simple order reaction model function, f(α) = (1 – α)3.3, and A = 6.20 × 1012 s–1.

Continuous pyrolysis of pine sawdust at different pyrolysis temperatures and solid residence times

In this work, the continuous pyrolysis of pine sawdust is performed with a screw reactor to investigate the influence of pyrolysis temperature and solid residence time on products and energy distribution. Gas chromatograph/mass spectrometer (GC/MS) and Fourier transform infrared spectroscopy (FTIR) were used to confirm the identities of bio-oil. The combustion kinetics of bio-char had analyzed by thermo-gravimetric (TG). The results of gas chromatograph showed that carbon monoxide is the main component in produced gas, and the maximum gas yield of 54.5% was obtained at the temperature of 900°C. Compositional analysis of the oil products showed that phenols were the major components, and its proportion increased at higher temperatures and longer solid residence times. The activation energy of bio-char combustion is 461.10kJmol−1 and 108.45kJmol−1 in the ranges of 290–314°C and 314–518°C, respectively. The maximum of energy profit rate is 6.49% obtained at the temperature of 900°C with the solid residence time of 6min.

Production of solid fuel biochar from waste biomass by low temperature pyrolysis

Low temperature pyrolysis was employed to produce solid fuel biochars from woody (pine wood) and non-woody biomass (coconut fiber) in the present study. Chemical evolution of biomass under pyrolysis conditions was determined and fuel qualities of the biochars were evaluated including energy densities, ash-related problems and combustion behaviors. The results showed that dehydration reaction of the biomass had same preference with decarboxylation reaction under pyrolysis conditions. The hemicellulose and cellulose in non-woody biomass showed faster decomposition than those in woody biomass. The biochars derived from coconut fiber showed lower energy densities and energy yields than those from pine wood under identical conditions. All major ash forming metals originally contained in raw biomass were accumulated in the resultant biochars and more serious slagging and fouling problems were present during combustion of pyrolytic biochars compared to raw biomass. The reactivity of biomass decreased and the main mass loss shifted to elevated temperature zone with the increasing pyrolysis temperature, indicating increased thermal efficiency and environmental benefits were achievable during biochar combustion compared to raw biomass combustion. Taking into account combustion characteristics and energy yield, optimal pyrolysis temperatures for solid fuel production were around 300 degrees C for coconut fiber and 330 degrees C for pine wood. (C) 2015 Elsevier Ltd. All rights reserved.

Improvement of fuel qualities of solid fuel biochars by washing treatment

Raw biomass washing prior to pyrolysis treatment has been employed to mitigate the ash-related problems encountered during resultant biochar combustion. However, wide-spread application of this approach is limited by high energy consumption and low washing efficiency. In the present study, the biochar washing instead of raw biomass washing was attempted to overcome aforementioned problems, and fuel qualities of washed biochars were investigated for the first time. The results showed that major ash forming metals can be efficiently removed by all tested washing agents (de-ionized water (DW), acetic acid (AA) and citric acid (CA)), especially for acid washing agents AA and CA. As a consequence, the ash content of the biochars decreased, and the slagging and fouling issues were dramatically mitigated. Due to metal removal, the washed biochars exhibited improved combustion properties, especially for the biochars derived from agricultural biomass. In addition, noticeable decreases in nitrogen and sulfur contents were observed following washing treatment, suggesting the additional benefit of reducing emissions of nitrogen and sulfur pollutants during washed biochar combustion.Compared to raw biomass washing prior to pyrolysis, the significantly increased washing efficiency and fuel quality and decreased hydrophilicity of the biochars indicate that pyrolysis combined with subsequent biochar washing is more suitable to produce solid fuel biochars with high fuel quality from different source of waste biomass.

Kinetics investigation on the combustion of biochar in O2/CO2 atmosphere

Oxy‐biomass combustion produces negative CO2 emissions. This study investigated the combustion kinetics of biochar in O2/CO2 atmosphere using a thermo‐gravimetric analyzer. The effects of atmosphere, O2 concentration, and fuel type were considered in this investigation. Results show that the reaction order of biochar combustion ranges from 0.5 to 1. Furthermore, the kinetic compensation effect can be observed between the apparent activation energy E and the frequency factor A. This relation is given by lnA = 0.181E − 14.618. Compared with O2/N2 atmosphere, O2/CO2 atmosphere delays biochar ignition and reduces activation energy. The ignition temperature of straw char is significantly lower than that of wood and coal char. The apparent activation energy of char combustion follows the inequality wood char > straw char > coal char. This result indicates that biochar combustion is more sensitive to temperature than coal char combustion. The reactivity of char combustion improves with increasing O2 concentration, but biochar has a lower degree of improvement than coal char. The change from air combustion to oxy‐fuel combustion and the increase in O2 concentration exert minimal effects on biochar combustion than on coal char combustion. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 923–932, 2015

Short- and long-term flammability of biochars

Biochar is becoming a commercial biomass-derived product that is transported, stored, and applied to land for environmental management. However, no information is available about its flammability that significantly affects how biochar can be handled. Given that biochar can have very different properties depending on how and from what it is produced, flammability may also vary significantly. The flammability of biochar and its dependency on biochar properties were quantified for a range of biochars produced at different pyrolysis temperatures and as a function of time after production. None of the studied biochars (34 samples stored for at least two years under argon gas) qualified as flammable substances, assessed using the applicable UN method. The majority of biochars (67%) had no combustion front propagation distance at all. Almost all of the studied fast pyrolysis biochars (71%) had higher combustion distances, whereas most slow pyrolysis samples (80%) did not combust. The combustion of stored biochars increased with the amount of volatiles (r2 = 0.27, p < 0.05, n = 11; dominated by fast pyrolysis biochars: r2 = 0.62, p < 0.05, n = 5), typical of biochars produced at lower temperatures. In contrast, the combustion of biochars within minutes of production was higher for biochars made at 723 K (450 °C) than 623 K (350 °C), but decreased to negligible levels within 1 h. Short-term flammability may be a function of the amount of free radicals and surface areas that can react with oxygen, whereas long-term flammability after storage may be a result of the potentially flammable volatile matter and some still weakly explained mechanisms for high-ash dairy feedstock.

Influence of particle fragmentation and non-sphericity on the determination of diffusive and kinetic fluidized bed biochar combustion data

In several studies of batch combustion of mineral or vegetal coal in fluidized bed reactors, it is assumed that the fragmentation of the fuel particles is meaningless and also that these particles are spheres. None of these assumptions is corrected although they are commonly accepted in many design and calculation procedures. Here the influence of the above mentioned phenomena on the experimentally obtained diffusive and kinetic data are compared with the equivalent results previously obtained by ignoring such occurrences. Four chars made from typical woods from the Portuguese forest were tested. The results show that for the studied chars, ignoring the phenomenon of fragmentation, diffusive and kinetic data are overestimated by about 5–10%, whereas not taking into account the actual shape of the particles overestimates the diffusive data between 45% and 50% and the kinetic data between 25% and 30%. This highlights the extreme importance of particle shape in the study and modeling of char combustion in fluidized bed reactors.

A nanoscale model for characterizing the complex pore structure of biochars

The development of a novel nanoscale model that can accurately describe the reactivity of solids consisting of multiple components and having ordered and random pores is presented. Domains of multiple solid phases are distributed on a computational grid to simulate reactants with different specific reactivities and dispersions. Sub‐nanometer slit pores and larger cylindrical pores with given size distributions are also distributed on the grid in regular and random arrangements respectively. The generated solids are then eroded using rules that simulate a gas‐solid, non‐catalytic reaction occurring in the kinetic control regime. A parametric study is first carried out to demonstrate how key pore structural parameters affect the reactivity patterns. Model predictions are found to be in excellent agreement with experimental thermogravimetric data for the combustion of biochars, both when the slit and random cylindrical pores are fully accessible to the reactant and when diffusional limitations appear in the smaller slit pores. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3412–3420, 2013

Biochar as a Fuel: 4. Emission Behavior and Characteristics of PM1 and PM10 from the Combustion of Pulverized Biochar in a Drop-Tube Furnace

Six biochar samples were produced from both slow and fast pyrolysis of mallee bark at 400–550 °C, respectively; such temperatures are typically used for biochar and/or bio-oil production in practice. Under the pyrolysis conditions, the biochar yields range from 26.7 to 37.0% and the majority (78.5–100.0%) of alkali and alkaline earth metallic (AAEM) species (mainly Na, K, Mg, and Ca) in biomass are retained in the biochars, while the retention of Cl in biochars is only 2.0–33.4%. The raw biomass and its derived biochar samples were then combusted in a laboratory-scale drop-tube furnace (DTF) at 1300 °C to investigate the emission behavior and characteristics of sub-micrometer particulate matter (PM1) and PM with an aerodynamic diameter less than 10.0 μm (PM10). The particle size distribution (PSD) of PM10 from raw biomass combustion has a bimodal size distribution, while the PSDs of PM10 from biochar combustion generally show a unimodal distribution. Although most inorganic species are retained in the biochar during pyrolysis, it is interesting to note that the combustion of biochars leads to a substantial reduction in the emission of PM1 (and the mass of Na, K, and Cl in PM1) that dominantly consists of PM with a size less than 0.1 μm (PM0.1) in comparison to biomass combustion, apparently because of the removal of volatiles and Cl from the raw biomass during pyrolysis for biochar preparation. The results imply that the combustion of volatiles (including the released inorganic species), which is particularly important during biomass combustion, is mainly responsible for PM1 emission. Meanwhile, considerable increases in the emission of coarser particulate matter with an aerodynamic diameter between 1 and 10 μm (PM1−10) and the mass of Mg and Ca in PM1−10 are also evident during biochar combustion, most likely as a result of more porous structure and increased ash loading of biochars.

Catechol and Humic Acid Sorption onto a Range of Laboratory-Produced Black Carbons (Biochars)

Although the major influence of black carbon (BC) on soil and sediment organic contaminant sorption is widely accepted, an understanding of the mechanisms and natural variation in pyrogenic carbon interaction with natural organic matter (NOM) is lacking. The sorption of a phenolic NOM monomer (catechol) and humic acids (HA) onto BC was examined using biochars made from oak, pine, and grass at 250, 400, and 650 degrees C. Catechol sorption equilibrium occurred after 14 d and was described by a diffusion kinetic model, while HA required only 1 d and followed pseudo-second-order kinetics. Catechol sorption capacity increased with increasing biochar combustion temperature, from pine < oak < grass and from coarse < fine particle size. At lower catechol concentrations, sorption affinity (Freundlich constant, K(f)) was directly related to micropore surface area (measured via CO(2) sorptometry) indicating the predominance of specific adsorption. In contrast, HA exhibited an order of magnitude less sorption (0.1% versus 1%, by weight) due to its exclusion from micropores. Greater sorption of both catechol and HA occurred on biochars with nanopores, i.e. biochars made at higher temperatures. These findings suggest that addition of BC to soil, via natural fires or biochar amendments, will sequester abundant native OM through sorption.