Pressurized Thermogravimetric Analyzer Research Articles

Methane formation mechanism during pressurized pyrolysis of coal core in the context of deep underground coal gasification

Deep underground coal gasification (UCG) is characterized by high reaction pressure (dependent on hydrostatic pressure of coal seam) and high CH4 content. The formation mechanism of CH4 in product gases has always been an interesting topic. In this paper, pressurized pyrolysis characteristics of coal core were studied through a pressurized pyrolysis device. The formation mechanism of CH4 and structural evolution of semi-coke during the pressurized pyrolysis process were identified by X-ray diffractometer (XRD), pressurized thermogravimetric analyzer coupled with Fourier transform infrared spectrometer (TG-FTIR) and carbon-13 nuclear magnetic resonance (13C NMR). The results indicate that the yield of pyrolysis gas and carbon emission rate rise with an increase of pyrolysis pressure, while the yield of tar decreases. Compared with atmospheric pressure, the pyrolysis gas yield increases from 148.6 L/kg to 172.6 L/kg at 3.0 MPa, the CH4 yield increases from 32.6 L/kg to 77.3 L/kg. The CH4 begins to be released at around 400 °C at different pyrolysis pressures, and the generation rate reaches its maximum at around 500 °C. The analysis of 13C NMR shows that the relative content of the oxy-quaternary carbon in the aliphatic group decreases significantly from 9.2% to 1.8% with an increasing pyrolysis pressure. Therefore, pressure promotes the reaction of aliphatic carbon with hydrogen radicals to form CH4, which is one of the main reactions for the generation of CH4 by pressurized pyrolysis.

Study on pressurized isothermal pyrolysis characteristics of low-rank coal in a pressurized micro-fluidized bed reaction analyzer

In order to investigate the pressurized isothermal pyrolysis characteristics of coal, the effect of pressure on gas release characteristics and the kinetics of pressurized isothermal pyrolysis are explored for the first time in a pressurized micro-fluidized bed reaction analyzer (P-MFBRA). This work finds that the yields of CO2, CO, CH4, and H2 increases with temperature and pressure. The difference in the order of gas-releasing reduces as temperature and pressure rises, but that of gas-ending first decreases and then increases with pressure. The most probable mechanism functions of CO2, CO and CH4 change from shrinking core model to homogeneous model at 1 MPa, 0.8 MPa and 0.5 MPa, respectively, showing that reaction is controlled by chemistry under low pressure but affected by diffusion effect with elevating pressure. The rate constant and activation energy (Ea) of each gas appear an increasing-decreasing tendency and the difference between Ea of each gas reduces with pressure. Compared with non-isothermal experiments, the Ea (20.8–475 kJ mol−1) and pre-exponential factor in P-MFBRA are less than those (70–150 kJ mol−1) in the pressurized thermogravimetric analyzer (P-TGA), indicating P-MFBRA can effectively reduce the diffusion inhibition, and the kinetics obtained is close to the reaction in industrial fluidized bed reactor.

Kinetic modeling of gasification reactions of CO2 and H2O for Thar lignite char at elevated pressures

Gasification reactions of Thar coal chars with CO2 and H2O have been investigated, using pressurized thermo-gravimetric analyzer (PTGA). A quartz fixed-bed reactor was used to prepare coal char at 900 °C with a nitrogen environment. Dynamic heating segments were maintained with a constant heating rate during all experiments. The temperature was raised from room temperature to 1000 °C, at different pressures 1 atm., 5 atm., and 10 atm. using pure reacting gases (CO2 and H2O). The weight loss data obtained from PTGA results were used to study the kinetic behavior of Thar lignite char for gasification reactions with CO2 and H2O as gasifying reacting species. It was observed that gasification reactions of char with reacting gas CO2 and char with reacting gas steam (H2O) initiated at 750 °C and completed after reaching 950 °C, at atmospheric pressure, but the occurrence of reactions was slightly delayed at high pressures. Volumetric Model and Grain Model were used to develop a kinetic model for Thar lignite. The direct plot and integral methods were used to calculate Arrhenius parameters such as the pre-exponential factor (A) and activation energy (E). An increase of A and E was also observed in increasing pressures. The activation energy (E) was investigated from 244.64 to 317.6 kJ/mol at atmospheric pressure; whereas, it is lying in the range of 286.13–356.67 kJ/mol at a pressure of 10 atm.

Influence of different state alkali and alkaline earth metal on chemical structure of Zhundong coal char pyrolyzed at elevated pressures

The investigation on the evolution of coal char structure is the prerequisite in evaluating the catalytic action of alkali and alkaline earth metal (AAEM) during pressurized pyrolysis. In the study, Zhundong raw coal samples were first treated using the chemical fractionation method, and then pyrolyzed at 0.1 MPa–3 MPa in a pressurized thermogravimetric analyzer (PTGA). In order to understand the effect of AAEM on the chemical structure of the samples at elevated pyrolysis pressures, the Fourier transform infrared spectroscopy (FT-IR), the Raman spectroscopy and a series of original structure parameters were employed. It is indicated that over 1 MPa, water-soluble AAEM inhibited the decomposition of phenolic hydroxyl group, while ion exchangeable AAEM inhibited the decomposition of carboxyl functional groups and catalyzed the cracking of aliphatic long chains. The influence of pressure on conversion of functional groups was various at different pyrolysis temperatures. Under 1 MPa, the pressure had distinct influences on the carbon skeleton structure of coal char and mainly promoted the graphitization process of samples during pyrolysis. Besides, the ratios of phenolic hydroxyl, ether and aliphatic aromatic in char were not sensitive with elevated pressure.

Effects of H2S on the Reactivity of Ilmenite Ore as Chemical Looping Combustion Oxygen Carrier with Methane as Fuel

A series of experiments were carried out in a pressurized thermogravimetric analyzer to study the effects of H2S on the reactivity of ilmenite oxygen carrier under pressurized conditions. The total...

Effect of pressure and H2 on the pyrolysis characteristics of lignite: Thermal behavior and coal char structural properties

The aim of the present work was to investigate the effect of pressure and H2 on the pyrolysis characteristics of lignite. Thermogravimetric behavior during lignite pyrolysis was studied under different Ar or H2 pressures using a pressurized thermogravimetric analyzer (P-TGA). Structural properties of coal chars obtained from P-TGA were investigated by the application of elemental analyzer, Fourier transform infrared spectroscopy, X-ray diffraction analyzer, and gas sorption surface area and pore size analyzer. CO2 gasification reactivity of coal chars was also evaluated by TGA tests. The results demonstrated that the weight loss for lignite pyrolysis increased in the presence of H2 and it became more remarkable with rising pressure. Meanwhile, conversion of C and H during pressurized hydropyrolysis was promoted to a higher level considerably. Aromaticity as well as graphitization degree for coal chars were both intensified with addition of H2, especially under elevated pressures. As to the mesopore structure, BET specific surface area of coal chars from hydropyrolysis increased obviously in comparison with that of coal chars obtained in Ar atmosphere, especially under pressurized conditions. Moreover, coal chars from hydropyrolysis exhibited higher CO2 gasification reactivity.

Catalytic coal hydrogasification by cobalt-calcium catalyst in a pressurized fluidized bed: Role of hydropyrolysis and catalysis process

Coal pyrolysis, hydropyrolysis and hydrogasification were performed in a lab-scale pressurized fluidized bed with or without cobalt-calcium bimetallic catalyst (Co-Ca) to preliminarily discern the role of hydropyrolysis, Co-Ca catalyst and H2 in the course of coal catalytic hydrogasification (CCHG). The hydrogasification reactivity and chemical structure of the coal chars generated after hydropyrolysis were also analyzed by means of pressurized thermogravimetric analyzer (P-TGA), FT-Raman and FT-IR, etc. Results indicate that Co-Ca catalyst possesses catalytic depolymerization and hydrogenation effect on coal during hydropyrolysis, which resulted in the promoted yield of CH4, tar and the high hydrogasification reactivity of the generated char. Co-Ca catalyst alone and H2 alone are hardly to fracture the CC bonds in condensed aromatic rings of coal, but the union of them yields a superior bonds cleavage ability. The catalytic cleavage of CC bonds is the crucial step of CCHG at the temperature above 800 °C with the hydrogen pressure above 1 MPa. Moreover, the CCHG process over Co-Ca catalyst is discussed and the probable pathways of the catalytic cleavage of CC bonds are proposed.

Measurement of CO2 Diffusivity in Phase-Changing Aminosilicone CO2 Capture Solvent

The mass transfer performance of a phase-changing aminosilicone CO2 post-combustion capture absorbent has been characterized. The aminosilicone, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (GAP-0), rapidly transforms from a low-viscosity liquid into a friable solid upon exposure to gaseous CO2. Mass transfer performance of this absorbent was studied to inform design and scaleup of a CO2 capture process. The long-term mass transfer rate of CO2 gas through a solid GAP-0 carbamate salt layer into a quiescent pool of liquid GAP-0 was characterized using pressurized thermogravimetric analysis. This experiment led to an estimate of the CO2 permeability of the carbamate salt solid of 1.46 × 10–9 mol of CO2 m–1 s–1 atm–1. Given literature-reported values of CO2 solubility in silicone polymers, the CO2 diffusivity through GAP-0 carbamate salt was inferred to be approximately 4.39 × 10–11 m2/s. In parallel, the CO2 absorption rate into a spray of GAP-0 droplets was studied in a laboratory spray reactor. Wh...

Reduction Kinetics of Ilmenite Ore for Pressurized Chemical Looping Combustion of Simulated Natural Gas

Reduction kinetics of ilmenite ore as an oxygen carrier for the chemical looping combustion of a simulated natural gas mixture under elevated pressure was studied using a pressurized thermogravimetric analyzer (PTGA). The fuel gas is a mixture of hydrocarbon, carbon dioxide, and nitrogen to simulate an actual combustion environment. The oxidation phase of the experiments was carried out in air. Effects of temperature (1023–1223 K), total pressure (0.6–1.6 MPa), fuel partial pressure (0.126–0.34 MPa), and CO2 partial pressure (pFuel/pCO2 = 0.5–1) were studied. The results showed that the presence of small amounts of ethane and propane clearly led to a higher ilmenite reactivity at temperatures below 1123 K, but this effect became less significant as temperature increased and completely disappeared above 1123 K. The results also showed that increasing CO2 partial pressure had little effect on ilmenite conversion rate, though it did have some slightly negative influence on ilmenite oxygen carrying capacity t...

Kinetics of steam and CO2 gasification with high ash fusion temperature coal char under elevated pressure

ABSTRACTA high ash fusion temperature (AFT) coal char was gasified with steam and CO2 under elevated pressure in a modified pressurized thermogravimetric analyzer. The ambient pressure varied from 0.5 MPa to 3 MPa. It was found that activation energy Ea (char-CO2 reaction) was from 214.19 kJ/mol to 240.35 kJ/mol, and activation energy Ea (char-steam reaction) was from 170.02 kJ/mol to 174.02 kJ/mol by using shrinking core model. The factor of partial pressure influence (n) was 0.44 and 0.54 for CO2 and steam gasification, respectively. The results proved that the high AFT coal (LJ coal) has poor gasification reactivity by comparing with other research and provided complete kinetic data for developing the entrained flow gasification technology using high AFT coal.

Experimental study on kinetics of coal char\u2013CO2 reaction by means of pressurized thermogravimetric analysis

Comprehensive kinetic studies were performed to establish the validity of many kinetic expressions that describe the behavior of char samples during pressurized gasification toward CO2. The gasification experiments were carried out isothermally in a high-pressure thermogravimetric analyzer (TG-HPs, TA Instruments, USA). Two char samples derived from Turów lignite B and Janina sub-bituminous C were used for the studies. The models that were employed are regarded as the most popular: the volumetric (VM); the modified volumetric (MVM); the grain (GM); the random pore (RPM); and the Langmuir–Hinshelwood model. The models were validated at 850, 950, and 1050 °C, and at CO2 pressures of 0.4, 1, 11, and 21 bar. The effects of temperature and pressure were significant and increased the reaction rate. The calculated values of activation energy were similar for the various models employed and ranged from 169 to 212 kJ mol−1 for the Turów sample and 182 to 238 kJ mol−1 for the Janina coal char sample. The GM, RPM, and MVM fit the experimental data well, in contrast to the VM and LH models.

Reduction Kinetics of Ilmenite Ore as an Oxygen Carrier for Pressurized Chemical Looping Combustion of Methane

Reduction kinetics of ilmenite ore as an oxygen carrier for methane chemical looping combustion under elevated pressures was studied using a pressurized thermogravimetric analyzer (PTGA). The reduction phase of the experiments was carried out in a mixture of methane and nitrogen with carbon dioxide and/or steam to simulate an actual combustion environment. The oxidation phase of the experiments was carried out with air. Effects of the temperature (1123–1223 K), total pressure (0.6–1.6 MPa), methane partial pressure (0.23–0.64 MPa), and particle size (45–300 μm) were studied. Tests were also carried out to examine the effect of higher redox cycle numbers on the performance of ilmenite ore. The results showed that increasing the total pressure reduced the rate of conversion during ilmenite ore reduction, e.g., when the total pressure increased from 0.9 to 1.6 MPa, the reduction conversion rate decreased by 6–14% depending upon the reaction temperature because the negative effect of the pressure was less pro...

Kinetic study on metallurgical coke gasification by steam under various pressures

Kinetics of metallurgical coke gasification by steam has been researched via a pressurized thermogravimetric analyzer under elevated pressures. The influences of total pressure and steam partial pressure upon gasification reactivity have been investigated. Three typical kinetic models, i.e., grain model, homogeneous model, and random pore model, have been used to simulate the reaction behavior. Concluded to be the model supplying the optimal fit to experimental data, the RPM was selected to obtain kinetic parameters. The nth-order equation is fit to depict the relationship between the gasification reactivity and the partial pressure of steam. That activation energies evaluated under various pressures are approximate to each other suggests that reaction mechanisms corresponding to these activation energies are alike.

Pressurized chemical looping combustion with CO: Reduction reactivity and oxygen-transport capacity of ilmenite ore

Ilmenite ore has shown promise as an oxygen-carrier in chemical looping combustion operation. Since operating at higher pressures has been proven to hold important benefits for chemical looping combustion, this study aims to investigate the performance of ilmenite ore under pressurized conditions. The reduction reactivity and oxygen-transport capacity of Canadian ilmenite ore in pressurized chemical looping combustion during redox cycles were investigated in a pressurized thermogravimetric analyzer, using carbon monoxide and air as reductant and oxidant respectively. While increasing the CO partial pressure from 0.32 to 0.80MPa (at a constant total pressure) led to higher rates of reaction and higher oxygen-transport capacity, increasing the total pressure up to 2.4MPa (at a constant CO partial pressure while varying the pCO2) had the reverse effect. Furthermore, increasing the temperature from 1123 to 1323K resulted in a pronounced increase in the reduction rate. Although increasing the particle size from 75–125μm to 300–425μm resulted in a slower rate of reduction, the effect was minor. A kinetic grain model with a changing grain size was fitted to reduction rate data obtained at 1.6MPa. The order of reaction with respect to the CO partial pressure was calculated as 0.67, while the activation energy was determined to be 115kJ/mol.

Investigation on SO2, NO and NO2 release characteristics of Datong bituminous coal during pressurized oxy-fuel combustion

The release behaviors of SO2, NO and NO2 of Datong bituminous coal during the pressurized oxy-fuel combustion were studied by pressurized thermogravimetric analyzer combined with Fourier transform infrared spectroscopy, which mainly focused on the effect of pressure to the emission characteristics. The experimental results demonstrated that more pyrite could be converted to the sulfur precursors and then oxidized to SO2 with increasing pressure up to 2 MPa. However, because the conversion of SO2 to SO3 probably was accelerated at 3 MPa, the conversion rate of fuel-S to SO2 decreased to some extent. Along with the increase of volatiles yield at elevated pressure, more volatile-N released during devolatilization converted into NO which led to an increase of NO emission. With increasing pressure from 0.1 to 2 MPa, the conversion value of fuel-N to NO2 increased gradually due to the elevated oxygen partial pressure. But the NO2 emission declined somewhat at 3 MPa due to the accelerated decomposition rate of NO2 at higher combustion temperature. The NOx (NO and NO2) emission under pressurized oxy-fuel atmosphere monotonously increased with increasing pressure.

Thermogravimetric analysis of hydrogen production of Al–Mg–Li particles and water

Hydrogen is a renewable and environmentally friendly fuel with high calorific value. Aluminum is a good option for working as hydrolyzing metal, and aluminum–water reactions at medium–high temperature serve as a good energy supply in the use of both hydrogen and released heat, which leads to high energy efficiency. This study focused on hydrogen production characteristics and the chemical kinetics of aluminum particles with the addition of magnesium and lithium below 1030 °C. The experiments were conducted with THERMO CAHN's Thermax500 pressurized thermogravimetric analyzer. The Al content was settled at 85%, and the Mg and Al contents were adjusted from 0% to 15%. The addition of Li and Mg into Al resulted in good hydrolysis performance, and the ratio of the reacted Al to the total Al was over 50% and even reached up to 89%. The reaction process showed an obvious three-stage feature, and the three stages primarily corresponded to the reactions of Li, Mg, and Al. The products of hydrolysis in our tests were LiAlO2, Li2Al4O7, Al2O3, and MgO. The different promotion mechanism of Li and Mg on the reaction of Al–H2O resulted in a hydrolysis performance that did not change monotonously with Li content.

Characterization of an ilmenite ore for pressurized chemical looping combustion

This work presents the characterization results of a Canadian ilmenite ore tested in pressurized chemical looping combustion cycles. The ilmenite ore was isothermally cycled in a pressurized thermogravimetric analyzer using carbon monoxide as a reducing fuel and air as an oxidizing gas. All samples were calcined prior to submission to cycles. X-ray diffraction (XRD) comparing raw and calcined ore samples indicate the disappearance of ilmenite crystals and the formation of rutile and ferric pseudobrookite. Cycled ilmenite ore surface morphology was found to be insensitive to the total pressure (up to 51bar) and CO partial pressure (3.2–8.0bar). These findings are in agreement with thermodynamic equilibrium predictions using FactSage. SEM images reveal the development of cracks in the oxidized particles after 4 redox cycles at 950°C and 16bar, which was correlated to the original lamellar structure of the raw ilmenite ore. Increasing the number of redox cycles from 3.5 to 19.5 resulted in large cracks near iron-rich lamellae. Furthermore, the average grain size was smaller after 19.5 cycles. Increasing the reaction temperature from 850°C to 1050°C resulted in similar surface morphologies, but increased grain size. Despite being below melting temperatures, the sample cycled at 1050°C did agglomerate. Local temperature excursions during sample oxidation may have led to melting. This study provides insights into the phase transformations and morphological changes accompanying the use of this type of ilmenite ore in a pressurized chemical looping combustion process, highlighting the need for proper adjustments to the design and operation of the process.

From laboratory-scale experiments to industrial-scale CFD simulations of entrained flow coal gasification

In this work advanced gasification models of four Australian coals were calibrated using laboratory-scale experiments with the aim of extrapolating these information for simulating large-scale gasification processes using CFD. In particular, the four studied coals, ranging from semi-anthracite to sub-bituminous, were extensively characterized using high-pressure bench and laboratory scale techniques.Coal devolatilization is modeled using the empirical competing two-step models, whose parameters are calibrated in a pre-processing step by means of the advanced CPD, FG-DVC and FLASHCHAIN®pyrolysis models. The results of the advanced pyrolysis models are at first validated against true volatile yield data obtained at high pressures and heating rates from wire-mesh reactor experiments.Char gasification is modeled using a nth-order intrinsic kinetics model. At first, intrinsic char kinetics was measured in kinetic regime from experiments in pressurized thermogravimetric analysis. Then, gasification experiments in a laboratory-scale pressurized entrained flow reactor have been used for estimating the reactivity in pore-diffusion regime, defining the diffusivity inside the particle pores.Finally, the calibration of the same coals have also been tested in a 5MW pilot-scale gasifier, offering a unique opportunity to apply our model over the continuum of laboratory and pilot scales. The model results again show good agreement with the experimental data of syngas composition and carbon conversion evaluated at the exit of the gasifier. The simulations of the pilot-scale gasifier demonstrates that industrial-scale gasification processes can be accurately predicted using advanced coal conversion models, adequately calibrated through laboratory-scale experiments.

Investigation of the Kinetics of Carbonation Reaction with Cao-Based Sorbents Using Experiments and Aspen Plus Simulation

The intrinsic kinetics of the carbonation reactions for two limestones (Havelock and Cadomin) were studied using an atmospheric thermogravimetric analyzer (ATGA) and a pressurized thermogravimetric analyzer (PTGA). A grain model was applied to measure the kinetic parameters. The order of the carbonation reaction was related to the carbon dioxide (CO2) partial pressure, changing from the first order to the zero order when the CO2 partial pressure exceeded ~0.7 atm for both limestones. The rate of carbonation reaction increased with increasing temperature up to 675°C and decreased with further increases. No significant effect of particle size was found on the rate of carbonation reaction. Thermodynamic and kinetic simulations of the carbonation reaction using the Aspen Plus simulator was performed, obtaining the optimal temperature of 650°C. The activation energies were 32.1 and 20.3 kJ/mol for the tested Havelock and Cadomin limestones, respectively. The simulation results from the kinetic model were in good agreement with the experimental data, showing the reversible characteristic of the carbonation reaction. The shift in the mechanism of the carbonation reaction with temperature and the shift in the reaction order with CO2 partial pressure were demonstrated by both the experiments and simulation.

Pressurized Thermogravimetric Study on the Hydropyrolysis and Hydrogasification Kinetics of a Bituminous Coal

Coal hydropyrolysis (CHP) and coal hydrogasification (CHG) are two important processes during coal conversion in a hydrogen atmosphere. Much attention has been paid on this clean coal conversion technology because of its advantages. In this work, the CHP and CHG kinetic characteristics of a bituminous coal are studied in a pressurized thermogravimetric analyzer (P-TGA). The effects of the pressure on the CHP and CHG kinetics of the bituminous coal are detected with the non-isothermal thermogravimetric method. In addition, the kinetic compensation effect (KCE) and isokinetic points of the two processes are investigated. Besides, the kinetic triplets, including the pre-exponent factor, the activation energy and mechanism function are also calculated and defined for all of the cases during the CHP and CHG processes. Meaningful and interesting conclusions are finally obtained from this study. The initial pyrolysis temperature will increase with the reaction pressure when the pressure is within 3 MPa. The appe...