Thermal characteristics of the combustion process of biomass and sewage sludge

The combustion of two kinds of biomass and sewage sludge was studied. The biomass fuels were wood biomass (pellets) and agriculture biomass (oat). The sewage sludge came from waste water treatment plant. The biomass and sludge percentage in blends with coal were 10 %. The studied materials were characterised in terms of their proximate and ultimate analysis and calorific value. The composition of the ash of the studied fuels was also carried out. The behaviour of studied fuels was investigated by thermogravimetric analysis (TG, DTG and DTA). The samples were heated from an ambient temperature up to 1,000 °C at a constant three rates: 10, 40 and 100 °C min^?1 in 40 mL min^?1 air flow. TG, DTG and DTA analysis showed differences between coal, biomass fuels and sewage sludge. 10 % addition of studied fuels to the mixture with coal changed its combustion profile in the case of sewage sludge addition. The combustion characteristics of fuel mixtures showed, respectively, qualitative summarise behaviour based on single fuels. Evolved gaseous products from the decomposition of studied samples were identified. This study showed that thermogravimetric analysis connected with mass spectrometry is useful techniques to investigate the combustion and co-combustion of biomass fuels, and sewage sludge, together with coal. Non-isothermal kinetic analysis was used to evaluate the Arrhenius activation energy and the pre-exponential factor. The kinetic parameters were calculated using Kissinger–Akahira–Sunose model.     

Effective direct chemical looping coal combustion with bi-metallic Fe–Cu oxygen carriers studied using TG-MS techniques

This paper contains the results of research on a promising combustion technology known as chemical looping combustion (CLC). The noteworthy advantage of CLC is that a concentrated CO₂ stream can be obtained after water condensation without any energy penalty for CO₂ separation. The objective of this work was to prepare novel bi-metallic Fe–Cu oxygen carriers and to evaluate the performance of these carriers for the CLC process with hard coal/air. One-cycle CLC tests were conducted with supported Fe–Cu oxygen carriers in thermogravimetric analyzer (TG) utilizing hard coal as a fuel. The effects of the oxygen carrier chemical composition, particle size, and steam addition on the reaction rates were determined. The fractional reduction, fractional oxidation, and the reaction rates were calculated from the TG data. Notably, the support had a considerable effect on the reaction performance. Moreover, bi-metallic Fe–Cu oxygen carriers exhibited significantly improved reactivity compared with monometallic Fe oxygen carriers. Furthermore, the addition of a second reactive metal oxide stabilized the oxygen carrier structure. The oxidation reaction was significantly faster than the reduction reaction for all supported Fe–Cu oxygen carriers. The TG data indicated that these oxygen carriers had stable performances up to 900 °C and may be effectively used for direct coal CLC reactions.     

Chemical looping combustion characteristics of coal with Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> oxygen carrier

Chemical looping combustion (CLC) by direct use of coal as fuel is promising with its prominent advantages, but insufficient conversion of coal in the CLC system is a great limitation. In this research, in order to explore the limiting factor inherent for coal conversion in the CLC system, from the perspective of chemical structure of coal, reaction of a selected Chinese typical coal (designated as LZ) with Fe₂O₃ was systematically investigated. Thermogravimetric investigation of LZ coal reaction with Fe₂O₃ at the oxygen excess number Φ = 1.0 indicated that after dehydration, there existed three discernible reaction stages as observed, which were attributed to the combined reactions of Fe₂O₃ with the primary and secondary gaseous products evolved from LZ coal. Meanwhile, the Fe₂O₃ provided should be controlled around Φ = 1.0 aiming at effective conversion of LZ coal and simultaneous proper utilization of Fe₂O₃. And then, both gaseous Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy analysis of the gaseous and solid products formed from reaction of LZ coal with Fe₂O₃ at Φ = 1.0 indicated that full conversion of LZ coal was not reached with a little unconverted CO occurring, though partial Fe₂O₃ was over reduced to lower valence of oxides than Fe₃O₄. Furthermore, in order to explore the insufficient conversion of LZ coal at the molecular scale, X-ray photoelectron spectroscopy analysis revealed the distribution and evolution of the carbon functional groups involved in LZ coal after its reaction with Fe₂O₃ and further found that effective conversion of the aromatic/aliphatic C=C/C–H groups in LZ coal was the rate-limited step at the molecular scale with the relative content of these groups still dominated around 59% after LZ coal reaction with Fe₂O₃. Finally, solid IR (infrared) analysis and quantitative evaluation of the solid products of LZ coal reaction with Fe₂O₃ indicated that the length of aliphatic C–H groups decreased due to its partial disintegration, while the aromatization of the residual char was aggravated with the higher relative IR intensity ratio of the aromatic C=C groups, which reduced the reactivity of LZ residual char and hindered the full conversion of LZ coal.     

Simultaneous thermogravimetric-mass spectrometric study on the co-combustion of coal and sewage sludges

To combust coal together with a small percentage (<10%) of sewage sludge may be an option for the management of these wastes. Combustion of two different sewage sludge, one semianthracite coal and several sludges-coal blends (containing different dried mass% of each of the two sewage sludges) were studied by simultaneous TG/MS dynamic runs carried out at 5°C min^–1 in the temperature range 100–800°C. No interactions have been observed between coal and sludge during the blends combustion. Neither the combustion process, neither the studied emissions have changed appreciably for the mass% of sludge in the blends considered in this work.     

Chemical looping combustion of high-sulfur coal with NiFe2O4-combined oxygen carrier

Chemical looping combustion (CLC) of coal has gained increasing attention as a novel combustion technology for its attractive advantage in the inherent separation of CO₂. In relative to the single metal oxide-based oxygen carrier (OC), combined OC owned superiority for CLC of coal. In this research, combined NiFe₂O₄ OC was synthesized using sol–gel combustion synthesis method, and its reaction with a typical Chinese high-sulfur coal as Liuzhi (LZ) coal was performed in a thermogravimetric analyzer (TG). And then, systematic investigation was carried out to explore the evolution of sulfur species and minerals involved in coal and their interaction with the reduced NiFe₂O₄ OC through different means, including fourier transform infrared (FTIR), field scanning electron microscopy/energy-dispersive X-ray spectrometry, X-ray diffraction, and thermodynamic simulation. TG–FTIR analysis of LZ reaction with NiFe₂O₄ indicated that two reaction stages were experienced at 350–550 and 800–900 °C, respectively, far different from LZ pyrolysis, and SO₂ occurred mainly related to oxidization of H₂S with NiFe₂O₄ over 550 °C. Meanwhile, lattice oxygen transfer rates of NiFe₂O₄ involved at the two reaction stages were higher than that of directly mixed NiO with Fe₂O₃ OC and thus more beneficial for LZ coal conversion. Both experimental means and thermodynamic simulation of the solid-reduced residues of NiFe₂O₄ with LZ coal indicated that the main-reduced counterparts of NiFe₂O₄ were Ni and Fe₃O₄. In addition, though good regeneration of the reduced NiFe₂O₄ was reached, the side products Ni₃S₂ and Ni₂SiO₄ should be noted as well for its detrimental effect on the reactivity of NiFe₂O₄ OC.     

添加煤灰及混合氧化物对石油焦CO2高温气化反应的影响

以化学组成相近的燃烧煤灰、气化煤灰和混合氧化物为添加剂,分别通过干混法和湿混法加入石油焦中,并借助热重分析仪在1200-1400 ℃下进行CO₂气化实验,研究高温下煤灰掺混方式、含量及物相组成对石油焦CO₂气化的影响,并使用混合氧化物替代实际煤灰研究其对石油焦的高温气化催化作用。结果表明,石油焦气化反应速率随煤灰添加量的增加而提升;气化温度为1200、1300 ℃时,使用干混法和气化煤灰对石油焦的气化促进作用较弱;但气化温度为1400 ℃时,改变煤灰和石油焦的掺混方式及其中活性金属存在方式,对石油焦气化反应几乎没有影响。这是高温下煤灰熔融,导致液态熔体与石油焦表面接触良好、活性金属自由度高以及传质阻力增加共同作用的结果。此时混合氧化物的催化指数与混合物中铁钙含量具有线性关系,即添加高铁钙含量的煤灰可以促进石油焦CO₂气化反应。     

Kinetics and reaction mechanism of isothermal oxidation of Iranian ilmenite concentrate powder

Thermal oxidation of commercial ilmenite concentrate from Kahnouj titanium mines, Iran, at 500–950 °C was investigated for the first time. Fractional conversion was calculated from mass change of the samples during oxidation. Maximum FeO to Fe₂O₃ conversion of 98.63 % occurred at 900 °C after 120 min. Curve fit trials together with SEM line scan results indicated constant-size shrinking core model as the closest kinetic mechanism of the oxidation process. Below 750 °C, chemical reaction with activation energy of 80.65 kJ mol^?1 and between 775 and 950 °C, ash diffusion with activation energy of 53.50 kJ mol^?1 were the prevailing mechanisms. X-ray diffraction patterns approved presence of pseudobrookite, rutile, hematite, and Fe₂O₃·2TiO₂ phases after oxidation of ilmenite concentrate at 950 °C.     

Combustion study of HTPB–sugar hybrid fuel with gaseous oxygen

In the present investigation, some combustion studies have been carried out with 50 % HTPB + 50 % sugar fuel grain, burning in the gaseous oxygen stream using swirl and showerhead injectors, and the regression rate has been compared. The combustion of fuel grain has been carried out for burning duration of 10 ± 1 s at four different oxidizer injection pressures, viz 1.52, 2.21, 2.76 and 3.24 MPa. The regression rates were found to increase with increasing injection pressure. Use of swirl injector exhibited higher regression rate compared to the showerhead injector. The average regression rate and fuel mass consumption rate in case of swirl injector were found to be higher than that of showerhead injector. The average regression rate for the fuel with swirl injector has been found to be 18.81, 15.11, 17.73 and 20.23 % more than that of shower head injector. The exhaust plume was also found out to be brighter and longer for a swirl injector compared to that of the showerhead injector. The thermal decomposition characteristic of fuel has been determined using differential thermal analysis and thermo gravimetric analysis techniques. The decomposition study was carried out at heating rate of 10 °C min^?1 in an oxygen atmosphere. The exothermic peak indicating that major decomposition takes place at a higher temperature of 483.3 °C. Mass loss have been found using TG analysis. Residual mass of 1.262 % has been obtained in the heating range of 30–500 °C. Heat of combustion of fuel is found to be 6972.41 Cal g^?1.     

Properties and performance of metakaolin pozzolanic cement pastes

The heating rate effect on the thermal behavior of clays from Arumetsa and Kunda deposits (Estonia) and an illitic clay from Füzérradvány (Hungary) was studied. Experiments were carried out under dynamic heating condition up to 1050 °C at the heating rates of 1.25, 2.5, 5 and 10 °C min^?1 in a stream of gas mixture containing 79 % of Ar and 21 % of O₂ with Setaram Labsys 1600 analyzer. Two different ashes were used as additives: the electrostatic precipitator ash from the first field and the cyclone ash formed, respectively, at circulating fluidized bed combustion (temperatures 750–830 °C) and pulverized firing (temperatures 1200–1400 °C) of Estonian oil shale at Estonian Power Plant. For calculation of kinetic parameters, the TG data were processed by the differential isoconversional Friedman method. The results of thermal analysis and the variation of the value of activation energy E along the reaction progress α indicated the complex character of decomposition of clays and their blends with Estonian oil shale ashes, and the certain differences in thermal behavior of different clays depending on their origin.     

Crystallization study of SrSnO3:Fe

Alkaline earth stannates have recently become important materials in ceramic technology due to its application as humidity sensor. In this work, alkaline earth stannates doped with Fe³⁺ were synthesized by the polymeric precursor method, with calcination at 300 °C/7 h and between 400 and 1100 °C/4 h. The powder precursors were characterized by TG/DTA after partial elimination of carbon. Characterization after the second calcination step was done by X-ray diffraction, infrared spectroscopy, and UV?Cvis spectroscopy. Results confirmed the formation of the SrSnO₃:Fe with orthorhombic perovskite structure, besides SrCO₃ as secondary phase. Crystallization occurred at 600 °C, being much lower than the crystallization temperature of perovskites synthesized by solid state reaction. The analysis of TG curves indicated that the phase crystallization was preceded by two thermal decomposition steps. Carbonate elimination occurred at two different temperatures, around 800 °C and above 1000 °C.     

TG measurement of reactivity of candidate oxygen carrier materials

This study examined several candidate raw materials for use as the reactive agents in developing new oxygen carriers for chemical looping combustion. A thermogravimetric analyzer, Mettler TGA/DSC1, was used to measure oxygen capacity and relative reaction rates during oxidation and reduction cycles. The reactive gases used were 4 % hydrogen in inert gas for the reduction cycle and air for the oxidation cycle, with a nitrogen purge between reduction and oxidation cycles. Samples were typically tested for at least ten cycles to study any change in reactivity or oxygen capacity. Reaction temperatures tested ranged from 700 to 900 °C. Materials tested included an iron oxide ore, iron-based tailings from a metals extraction process, a nickel oxide supported on nickel aluminate and a copper oxide plus inert material system. The materials varied in their oxygen capacity, reactivity and the change in properties with repeat cycles. Of the samples tested, the NiO–NiAl₂O₄ oxygen carrier demonstrated the fastest reaction in reduction and oxidation and had stable properties over ten cycles. The iron oxide ore sample performance declined significantly with repeat cycles. The performance of the iron-based tailings declined slightly over the ten cycles. The addition of inert second phase materials to CuO improved the performance by inhibiting sintering of the oxide at the operating temperature. Although the reactivity of the tailings and iron hydroxide samples was not as high as the NiO based oxygen carrier, they are promising carrier materials due to their low cost and lower toxicity relative to nickel. Future experiments will look at CO and CH₄ reduction reactions using the TG, surface characterization using SEM, XRD, and cyclic testing in a batch fluidized bed reactor.     

基于水泥修饰的赤铁矿载氧体污泥化学链燃烧特性研究

采用水泥修饰赤铁矿来提高载氧体的反应活性。实验在1kW_th串行流化床上进行,研究了添加水泥对污泥化学链燃烧特性的影响,考察其长期运行的物化性能。结果表明,在实验工况下,赤铁矿添加水泥后,出口的未燃气体浓度明显下降。燃料反应器温度低于870℃时,水泥的添加使污泥的碳转化率和燃烧效率显著升高。在10h长期运行后,一部分污泥灰沉积在载氧体表面。虽然在反应过程中部分的Fe₂O₃被深度还原,但在长期运行中未出现流化问题和烧结现象。     

A double-stage tube furnace—acid-trapping protocol for the pre-concentration of mercury from solid samples for isotopic analysis

High-precision mercury (Hg) stable isotopic analysis requires relatively large amounts of Hg (>10 ng). Consequently, the extraction of Hg from natural samples with low Hg concentrations (<1–20 ng/g) by wet chemistry is challenging. Combustion–trapping techniques have been shown to be an appropriate alternative [1]. Here, we detail a modified off-line Hg pre-concentration protocol that is based on combustion and trapping. Hg in solid samples is thermally reduced and volatilized in a pure O₂ stream using a temperature-programmed combustion furnace. A second furnace, kept at 1,000 °C, decomposes combustion products into H₂O, CO₂, SO₂, etc. The O₂ carrier gas, including combustion products and elemental Hg, is then purged into a 40 % (v/v) acid-trapping solution. The method was optimized by assessing the variations of Hg pre-concentration efficiency and Hg isotopic compositions as a function of acid ratio, gas flow rate, and temperature ramp rate for two certified reference materials of bituminous coals. Acid ratios of 2HNO₃/1HCl (v/v), 25 mL/min O₂ flow rate, and a dynamic temperature ramp rate (15 °C/min for 25–150 and 600–900 °C; 2.5 °C/min for 150–600 °C) were found to give optimal results. Hg step-release experiments indicated that significant Hg isotopic fractionation occurred during sample combustion. However, no systematic dependence of Hg isotopic compositions on Hg recovery (81–102 %) was observed. The tested 340 samples including coal, coal-associated rocks, fly ash, bottom ash, peat, and black shale sediments with Hg concentrations varying from <5 ng/g to 10 μg/g showed that most Hg recoveries were within the acceptable range of 80–120 %. This protocol has the advantages of a short sample processing time (～3.5 h) and limited transfer of residual sample matrix into the Hg trapping solution. This in turn limits matrix interferences on the Hg reduction efficiency of the cold vapor generator used for Hg isotopic analysis.     

Thermal analysis of soil amended with sewage sludge and biochar from sewage sludge pyrolysis

The main objective of the present study is to study the behaviour of sewage sludge and biochar from sewage sludge pyrolysis after addition to soil in a context of a temperate agricultural soil. For this, an incubation experiment was designed during 200 days. Carbon mineralization of soil amended with sewage sludge and biochar at two different rates (4 and 8 wt%) was evaluated. Differential thermal analysis, thermogravimetry and the first derivate of the TG were performed in oxidizing conditions on soil samples before and after incubation. Biochar obtained from sewage sludge pyrolysis at 500 °C was more stable in soil than original sewage sludge. After incubation experiment, the reduction of soil organic matter content was significantly lower in soil amended with biochar than in soil amended with sewage sludge. The thermostability index WL₃/WL₂ decreases after incubation in soil amended with biochar, however it increases in case of soil treated with sewage sludge.     

Experimental study of Fe–C–O based system below 1000 °C

The paper deals with the study of phase transformation temperatures of Fe (Fe–C–O) based metallic alloys. Six model alloys with graded carbon and oxygen content were used for experimental investigation. Low-temperature region (<1000 °C) was the investigated area. Phase transformation temperatures were obtained using Differential thermal analysis and Setaram Setsys 18_TM laboratory system. Controlled heating was conducted at the rates of 2, 4, 7, 10, 15, 20 °C min^?1. Region of eutectoid transformation (Fe_α(C) + Fe₃C → Fe_γ(C)), alpha–gamma (Fe_α(C) → Fe_γ(C)) and transformation Fe_α(O) + Fe_0.92O → Fe_γ(O) + Fe_0.92O was studied. New original data (phase transformation temperatures) were obtained in this study. The relationship between shift of phase transformation temperatures and chemical composition (mainly carbon and oxygen content) is investigated in this paper. To achieve good approximation to the equilibrium conditions, the extrapolation of the obtained phase transformation temperatures to the zero heating rate was performed. The influence of experimental conditions (heating rate) on temperatures of phase transformations was studied as well. Comparison of the obtained experimental data with the data presented in the accessible literature and IDS calculations (Solidification Analysis Package) was carried out. It follows from literature search that there is a lack of thermo-physical and thermo-dynamical data on Fe–C–O system.     

Cu修饰的Fe2O3/Al2O3氧载体的循环反应稳定性研究

采用冷冻干燥法制备了经Cu修饰（10%）的Fe₂O₃/Al₂O₃氧载体。利用热重分析仪分别在850、900和950 ℃等温环境下,使氧载体交替接触还原气体和氧化气体,来模拟氧载体在化学链燃烧中的循环过程。结果表明,经Cu修饰的Fe₂O₃/Al₂O₃氧载体在850和900 ℃下的等温循环过程中反应性能都很稳定,在950 ℃时的循环反应前期有微量烧结,但在循环后期反应性能也很稳定。随着反应温度的升高,氧载体氧化速率增大,还原速率和载氧率先减小后增大。与未经修饰的Fe₂O₃/Al₂O₃氧载体相比较,在900 ℃下作等温循环实验,经Cu修饰的Fe₂O₃/Al₂O₃氧载体具有较高的载氧能力和还原速率,但氧化速率较低;两者都具有较好的循环稳定性。     

A rapid polyol combustion strategy towards scalable synthesis of nanostructured LiFePO4/C cathodes for Li-ion batteries

In the present study, carbon-coated lithium iron phosphate (LiFePO₄/C) is prepared directly by a polyol-assisted pyro-synthesis performed under reaction times of a few seconds in open-air conditions. The polyol solvent, tetraethylene glycol (TTEG), acts as a low-cost fuel to facilitate combustion and the released exothermic energy promotes the nucleation and growth processes of the olivine nanoparticles. In addition, phosphoric acid (used as the phosphorous source) acts as a catalyst to accelerate polyol carbonization. The structure analysis of the as-prepared LiFePO₄/C using X-ray, neutron diffraction and ⁷Li NMR studies suggested the efficacy of the rapid technique to produce highly crystalline phase-pure olivine nanocrystals. The electron microscopy and particle-size distribution studies revealed that the average particle diameters lie below 100 nm and confirmed the presence of a surface carbon layer of 2–3 nm thickness. The thermal and elemental studies indicated that the carbon content in the sample was approximately 5 %. The prepared LiFePO₄/C cathode delivered capacities of 162 mA h g^-1 at 0.1 °C rates with impressive capacity retention for extended cycling. The polyol-assisted pyro-synthesis, which evades the use of external energy sources, is not only a straightforward, simple and timely approach but also offers opportunities for large-scale LiFePO₄/C production.     

The kinetics of gasification of char derived from sewage sludge

Gasification of char derived from sewage sludge was studied under different oxidizing atmospheres containing CO₂, O₂ or H₂O. The gasification tests were carried out in thermobalance at different temperatures and oxidizing reagent concentrations. The most efficient were the gaseous mixtures containing oxygen. The reaction took place at temperature 400–500 °C, whilst in the case of CO₂ and steam much higher temperatures (700–900 °C) were necessary to complete the conversion. Two rate models for gas–solid reaction were applied to describe the effect of char conversion on reaction rate. The shrinking core model for reaction-controlled regime was found to be the best for predicting the rate of char gasification in CO₂ and O₂ atmosphere. The experimental data for steam gasification of the char were fitted best by the first-order kinetics. The kinetic parameters estimated from the experimental data are in accordance with the literature for lignocellulosic char gasification and are the first published for sewage sludge char gasification.     

Thermal reaction characteristics of the boron used in the fuel-rich propellant

High pressure DSC and simultaneous TG/DSC were used to study the different kinds of boron that was used in the fuel-rich propellant and the amorphous boron in different gases and different pressure. Also, some of the samples before the experiment and after the experiment were analyzed by the SEM. The results show that: (1) there is a big exothermic peak between 550 °C and 850 °C for all the samples because the combustion heat of boron is very high, and the exothermic peak appears in advance when the pressure or the oxygen concentration increases. (2) Although the reaction process of all the samples with air or oxygen could be divided into five stages, the reaction characteristics are different from each other. Especially, amorphous boron is much more active than the boron used in the fuel-rich propellant. (3) The exothermic peak at about 700 °C appears in advance, and the percentage conversion of boron decreases when the content of magnesium increases and boron–magnesium compound is used as the raw materials. (4) Some samples start to lose their mass for the sake of the evaporation of the (BO)_n.     

Thermal behavior of cashew gum by simultaneous TG/DTG/DSC-FT-IR and EDXRF

Cashew gum, an exudate polysaccharide from Anacardium occidentale L., was purified by alcohol precipitation. Thermal behavior of this polysaccharide was investigated by simultaneous TG/DTG/DSC-FT-IR analysis performed under nitrogen and air atmospheres and heating rate of 10 K min^?1. TG/DTG curves under oxidative atmosphere were similar to the curves under N₂ atmosphere until 340 °C, however, it was observed a profile difference due to the presence of two DTG peaks at 430 and 460 °C. DSC results showed endothermic and exothermic events corroborating with TG/DTG curves. The Simultaneous TG/DSC-FTIR analysis revealed that evolved gases from the decomposition of cashew gum sample were CO₂, CO, and groups: O–H, C–H, C=O, C–C, and C–O, in nitrogen and air atmospheres. Energy dispersive X-ray fluorescence analysis from the ash showed that the elements in larger amounts are CaO, MgO, and K₂O.