Pressurized Drop Tube Furnace Research Articles

Experimental study on the reaction kinetics of char combustion in a pressurized O2/H2O atmosphere

Pressurized O2/H2O combustion is a potential CCS technology. In this study, a pressurized horizontal furnace was used to prepare pyrolysis char under pressurized inert atmosphere, and then a pressurized drop tube furnace was used to carry out char combustion under pressurized O2/H2O atmosphere (5% O2, 20% H2O) at the same pressure and temperature as the pyrolysis process. The carbon conversion of char under different pressures (0.4/0.7/1.0 MPa), temperatures (900/950/1000 °C), and residence time (1.38/2.76/4.14 s) was studied by proximate analysis. The random pore model was used to calculate reaction kinetic parameters of char combustion at different pressures. The results show that when the pressure increased from 0.4 MPa to 0.7 MPa, the carbon conversion increased significantly, with the increment reaching up to 9.90 percentage points. The marginal diminishing effect became significant when the pressure was greater than 0.7 MPa. The reaction activation energy and pre-exponential factor at 0.4/0.7/1.0 MPa were 66.53/66.29/35.79 kJ/mol and 20.54/36.84/1.69 s−1, respectively.

Modification of extended chemical percolation devolatilization model for application to low-rank coals

For understanding coal gasification reactions, primary pyrolysis reaction is important as the first stage of the gasification reactions. Recently, the authors developed a primary pyrolysis model to predict tar formation behavior by extending the chemical percolation devolatilization (CPD) model which is often used to predict pyrolysis behavior. The extended CPD (Ex-CPD) model predicts gas and tar components as respective chemical species. Consequently, the secondary tar decomposition behavior can be calculated by elementary step-like reaction models. However, some of the coal structure parameters used in the model contradict the 13C NMR data. That is, the molecular weight of the aromatic ring clusters calculated by the original Ex-CPD decreases with the aromatic index obtained by 13C NMR. In this study, this problem was resolved by modifying the calculation procedure to determine the coal structure parameters. The recalculated aromaticity index agreed with that calculated from the 13C NMR data. The modified Ex-CPD model was validated through comparison with coal gasification experiments using a pressurized drop tube furnace. The calculation results successfully described the trend of light gases, soot, and char yield in the experiments.

Calcination and desulfurization characteristics of calcium carbonate in pressurized oxy-combustion

Pressurized oxy-combustion is one of the most promising and efficient CO2 capture technologies for coal-fired power plants, which could reduce energy consumption for carbon capture. However, due to the effects of pressurization and flue gas recirculation, the partial pressure of sulfur oxides (SOx) in pressurized oxy-combustion is significantly higher than that of air-combustion, which leads to the corrosion risks and environment hazards. It is essential to investigate the SOx control in pressurized oxy-combustion. In this paper, the in-furnace calcination and desulfurization characteristics of calcium carbonate in pressurized oxy-combustion were carried out in a pressurized drop tube furnace. The findings show that the sulfation reaction in pressurized oxy-combustion is direct sulfation and the sulfation rate increases with the increase of temperature and pressure. The desulfurization efficiency in pressurized oxy-combustion is lower than that in atmospheric air atmosphere below 950 °C, but it reverses above 950 °C, indicating that the minimum desulfurization temperature in the furnace of the pressurized oxy-combustion is higher than that of atmospheric air atmosphere. Therefore, limestone can still be used as a sorbent in the pressurized oxy-combustion furnace. This study could contribute to the design of dry desulfurization systems in pressurized oxy-combustion combustors that use fossil fuel energies with high efficiency and low SOx emissions.

Modeling Coal Swelling during Pyrolysis at Elevated Pressure by Using a Single Bubble Model: Validation and Application

ABSTRACT Pressurized oxy-coal combustion technologies are attracting more attention of researchers because of their advantages of carbon capture. While the ambient pressure could significantly influence the coal pyrolysis behavior. In this study, Yulin coal was used for the pyrolysis experiment in a pressurized drop tube furnace. Pyrolysis temperature of 1273 K, and pressures of 1, 4, 7, 10 atm were considered. The swelling behavior of produced char was analyzed by the scanning electron microscope (SEM). The char evolution process during pyrolysis at elevated pressure was simulated by a revised single bubble model, in which the volatile releasing rate and yield by residence time can be obtained from the CPD (chemical percolation devolatilization) model. Results show that the revised single bubble model is suitable for predicting the char evolution over a wide range of pressure and heating rate. Optimum pressure is present in the range of 7–15 atm, where the swelling ratio and porosity reach the maximum value. This model can predict the two regimes of coal swelling in varied heating rates, which is more obvious at high pressure. The porosity development by time can also be output, and the variation trends are similar to the swelling ratio.

Morphology of char particles from coal pyrolysis in a pressurized entrained flow reactor: Effects of pressure and atmosphere

A pressurized drop tube furnace was used to study the pyrolysis behavior of bituminous and lignite coal at elevated pressure. Experiments were conducted at the pressure range from 1 to 10 atm in 100% N2 or 100% CO2 atmosphere. The volatile yields, char morphology, swelling ratio, and pore structure were discussed in detail. The results show that the pressure, atmosphere and coal rank could effect on the volatile releasing and char evolution significantly. In N2 atmosphere, the total volatile yields of YL and NM coal decrease as the pressure elevated, while in CO2 atmosphere, the mass release of NM coal increases at high pressure contributed by the reaction of CO2 with organic macromolecule inside the particles; different with bituminous coal, no significant swelling behavior is found with the increase of pressure; the BET surface area of YL char decreases as the pressure increases, while for lignite coal, in N2 atmosphere and at high pressure, less macro pores are formed, which could contribute to the BET surface area. While in CO2 atmosphere, the CO2-macromocular organic reaction would promote the volatile releasing, and the BET surface area decreases significantly at high pressure.

The evolution characteristics of bituminous coal in the process of pyrolysis at elevated pressure

In the present study, we report the formation rules of gas products (CO, CO2, CH4, HCN, NH3) and the evolution characteristics of the physicochemical structure during the pyrolysis of Shenhua bituminous coal under evaluated pressure using pressurized drop tube furnace (PDTF). The operating pressure, temperature, and residence time were in the range of 1073 ∼ 1273 K, 0.3 ∼ 1.2 MPa, and 0.3 ∼ 3.0 s, respectively. During the experiments, the outlet flue gas was analyzed with an online Fourier Transform Infrared Spectroscopy (FTIR) gas analyzer, and the physicochemical structure of pyrolysis char were sampled and characterized with FTIR, X-ray Photoelectron Spectrometer (XPS), and nitrogen adsorption–desorption methods. The results show that the increasing pyrolysis pressure, temperature and residence time would all promote the release of carbon and nitrogen-containing light gases. The increasing pyrolysis pressure and temperature would promote the decomposition of aliphatic hydrogen content and oxygen-containing functional group. When the pyrolysis residence time is less than 0.6 s, the decomposition of the active structure would be promoted as the residence time increases. While, when the pyrolysis residence time is in the range of 0.6–3.0 s, the active structure of the char products tends to be stabilized. As the pyrolysis residence time increases, the carbon content in the char products first shows a rapidly increase from 69.89% to 87.78%, and then slowly up to 91.25%; however, the oxygen content in the char products first decrease from 28.38% to 10.08% rapidly, and then slowly down to 6.98%; the nitrogen content has an overall downward trend. The specific surface area of the pyrolysis char reached its peak at the pyrolysis residence time of 0.6 s. When the pulverized coal particles were pyrolyzed for 0.6 s under high temperature (1273 K), high pressure (0.9 MPa) and high heating rates, most of the volatiles in the pulverized coal particles have been released.

Effects of total pressure and CO2 partial pressure on the physicochemical properties and reactivity of pressurized coal char produced at rapid heating rate

Abstract The effects of the total pressure (0.1–1.3 MPa) and the CO2 partial pressure (0–0.45 MPa) on the physical structural properties, chemical structural properties and reactivity of Shenhua coal pressurized char at 1273 K were investigated in a pressurized drop tube furnace (PDTF). There were reverse-direction effects on char yield between total pressure and CO2 partial pressure for char preparation. Porosity characteristics were performed using an ASAP2020 instrument. It was found that same-direction increment effects on BET surface and porosity between total pressure and CO2 partial pressure for char preparation. Carbon structure and surface structure were performed by Raman and XPS methods. The results showed that both total pressure and CO2 partial pressure can promote the transformation of small aromatic structures to large aromatic structures and increase the graphitization degree of the char. With increasing total pressure and CO2 partial pressure, the unstable N-5 content decreased, while the N-6 and N-Q content increased.

Effects of Pressure on the Characteristics of Bituminous Coal Pyrolysis Char Formed in a Pressurized Drop Tube Furnace

Abstract: To investigate pyrolysis characteristics of Shenhua bituminous coal under pressurized conditions, the effects of pressure (0-1.2 MPa) on the physicochemical structure and combustion reactivity of pyrolysis char samples prepared at 1073 and 1273 K were studied in a pressurized drop tube furnace (PDTF). The low temperature nitrogen adsorption test was used to characterize the physical structure of char samples. The results showed that, the increase of pyrolysis pressure is conducive to formation of mesopores, and the specific surface area is larger at 1273K. Raman and XPS analysis were used to characterize the chemical structure of char samples. The results showed that, the increase of pressure can promote the transformation of smaller aromatic structure into larger aromatic structure, and the graphitization degree are more obvious at 1273K. With the increase of pressure, the proportion of C=C/C-C bond in char structure increases and the proportion of C-H bond decreases. It indicates that the unst...

Particle residence time measurement in a pressurized drop-tube reactor with radioactive tracer

Particle residence time measurements were carried out in a pressurized drop-tube furnace (PDTF) using char particles marked with the isotope technetium-99 m. The effect of variations in the particle size (63–200 µm), gas temperature (673–1223 K), pressure (10–40 bar (g)) and superficial gas velocity (14–264 mm/s) was investigated, under reactive and inert atmosphere (CO2). The experimental method described in this work allowed the particle position to be determined experimentally as a function of time in a reactor that is otherwise not suited for the direct observation of the particles. This data can be correlated to the particle velocity and residence time. It was found that for the range of particle Reynolds numbers considered in this work (0.8–15.4), the experimental results can be described via the sedimentation velocity in combination with a drag force term based on the correlation by Haider and Levenspiel. An evaluation of the results revealed further insights into the correlation between the particle size distribution and the particle’s residence time distribution, RTD.

Extension of the chemical percolation devolatilization model for predicting formation of tar compounds as soot precursor in coal gasification

This paper proposed and validated a new coal devolatilization model that can predict yields of respective gas and tar components, and be directly coupled with an elementary step-like reaction model. The new model was an extension of the chemical percolation devolatilization (CPD) model. The CPD model is one of the existing primary pyrolysis models that consider the coal chemical structure. The mole fraction of labile bridges, cross links, peripheral groups, and average molecular weight of monomer in coals examined in this study were determined by a 13C NMR analysis. The aromatic ring clusters size distribution was determined by a coal pyrolysis test using a Curie point pyrolyzer. The thermal decomposition process of the coal chemical structure was expressed by nine elementary reactions. From the above, the extended CPD model can predict gas and tar components as respective chemical species (H2O, CO2, CO, CH4, benzene, naphthalene and phenanthrene) and consequently capture the secondary decomposition and polymerization in gas phase by coupling the detailed gas-phase chemistry. The proposed model was validated by comparing with experiments using a pressurized drop tube furnace (PDTF). The results showed that the trend of light gases and soot yield in the experiments could be successfully reproduced by the extended CPD model.

Proposal of a new soot quantification method and investigation of soot formation behavior in coal gasification

Coal gasification is one of the key technologies for utilization of coal. Coal gasification mainly consists of coal pyrolysis, char gasification, and gas-phase reactions. Soot is made up of fine solid carbon particles formed by volatile matter decomposition and has lower gasification reactivity than char. Since the solid products of coal gasification contain both char and soot, it is difficult to quantify the amount of soot produced by this process. In this study, a novel soot and char quantification method utilizing a laser diffraction particle size analyzer is proposed. Coal gasification experiments were performed using a pressurized drop tube furnace (PDTF). The soot and char yields were quantified by the new method. During CO2 gasification, char was selectively gasified and the amount of soot barely decreased. Hence, the carbon conversion initially increased, but remained around 0.8 even at 1673K. In the case of other gasifying agents, O2 or H2O, different behavior was found. During O2 gasification, the soot yield considerably decreased as the O2 concentration increased. The main reason was not soot gasification, as presumed, but rather the reaction of tar components with O2. In the H2O gasification, the soot yield slightly decreased as the H2O concentration increased.

Modeling of coal char gasification in coexistence of CO2 and H2O considering sharing of active sites

In a coal gasifier, CO2 gasification and H2O gasification occur at the same time. Many researchers have constructed CO2 gasification model and H2O gasification model separately. Only a few models explain the competition between CO2 gasification and H2O gasification. These models are divided into two types according to the properties of the active sites. Some models assume that CO2 gasification and H2O gasification occur at separate active sites, whereas others assume that all of the active sites are shared and are common to both CO2 and H2O gasification. There are some coals whose gasification reaction rates, with CO2 and H2O in coexistence, cannot be described by the conventional models. In this study, a Langmuir–Hinshelwood type gasification model was modified to explain the char gasification by CO2 and H2O. In the proposed model, CO2 gasification and H2O gasification partially share active sites. Coal chars, which were prepared through pyrolysis using a drop tube furnace at ambient pressure and 1673K, were gasified with CO2 and H2O using a pressurized drop tube furnace (PDTF) and a thermogravimetric analyzer (TGA) at various temperatures. The proposed model was found to describe the gasification reaction rates of the experiments more accurately than the conventional models.

Analysis of gasification reaction of coke formed using a miniature tubing-bomb reactor and a pressurized drop tube furnace at high pressure and high temperature

Coal gasification to produce gaseous fuel such as CO and H 2 is well-known as one of the key technologies for utilization of coal. Coal gasification mainly involves two steps: the initial rapid devolatilization of coal to produce char, tar and gases and the subsequent gasification of the char produced. Char gasification, being the slower step, is believed to control the overall conversion process. It is, however, known that solid carbon called coke (soot) is formed from the volatiles produced during the initial devolatilization at high temperature above 1000 ∘ C. Since the gasification reactivity of the coke is expected to be rather low, it is important to examine if the coke is really formed and to estimate the gasification reactivity of the coke if it is formed. In this study it was clarified that the coke is actually formed at high temperature and high pressure from the equilibrium calculation and experiments using a miniature tubing-bomb reactor (mini-TBR) and a pressurized drop tube furnace (PDTF). The ratio of coke to char was roughly 1 to 1 for the solid carbons prepared by the PDTF. The gasification reactivity of the coke was found to be 1 20 – 1 6 of the char when compared at 1200 ∘ C. SEM and TEM observations also clarified that the solid carbon obtained by PDTF was the mixture of char and coke.

Gasification rate analysis of coal char with a pressurized drop tube furnace

Two coal chars were gasified with carbon dioxide or steam using a Pressurized Drop Tube Furnace (PDTF) at high temperature and pressurized conditions to simulate the inside of an air-blown two-stage entrained flow coal gasifier. Chars were produced by rapid pyrolysis of pulverized coals using a DTF in a nitrogen gas flow at 1400°C. Gasification temperatures were from 1100 to 1500°C and pressures were from 0.2 to 2 MPa. As a result, the surface area of the gasified char increased rapidly with the progress of gasification up to about six times the size of initial surface area and peaked at about 40% of char gasification. These changes of surface area and reaction rate could be described with a random pore model and a gasification reaction rate equation was derived. Reaction order was 0.73 for gasification of the coal char with carbon dioxide and 0.86 for that with steam. Activation energy was 163 kJ/mol for gasification with carbon dioxide and 214 kJ/mol for that with steam. At high temperature as the reaction rate with carbon dioxide is about 0.03 s −1, the reaction rate of the coal char was controlled by pore diffusion, while that of another coal char was controlled by surface reaction where reaction order was 0.49 and activation energy was 261 kJ/mol.

Effect of coal type on gasification in pressurized drop tube furnace

In order to understand the effect of coal type on coal gasification process at 15 atmospheric pressure of pressurized drop tube furnace (PDTF), a numerical study was conducted. Eulerian approach is used for the gas phase, whereas Lagrangian approach is used for the solid phase. Turbulence is modelled using the standard k–ε model. The turbulent gas-phase combustion model incorporates the eddy dissipation model. One-step two-reaction model is employed for the devolatilization. Effect of coal type on carbon conversion at the same coal feed rate and gas flow rate cannot be verified due to the variation of equivalence ratio according to coal composition. Therefore, the same equivalence ratio is chosen to evaluate the effect of coal type on gasification. It is found that the volatile release based on experimental results should be taken in computations to predict accurate carbon conversion, especially in coal gasification due to the low gasification reaction. Even at over 1500 K and 15 atmospheric pressure, at which reactions are primarily diffusion-controlled, the exit carbon conversion varies with the coal type. The temperature gradient in near-burner region becomes gentle with increasing proximate volatile and moisture contents, but the volatiles released can make the temperature gradient steep by means of the fast reaction with oxygen. Copyright © 2001 John Wiley & Sons, Ltd.

Pressurized drop tube furnace tests of global coal gasification characteristics

Pressurized drop tube furnace tests of global coal gasification characteristics

The Effect of Pressure on Ash Formation during Pulverized Coal Combustion

A bituminous coal with a size faction of 63−90 μm was combusted under oxidizing atmosphere (air) in a drop tube furnace (DTF) and a pressurized drop tube furnace (PDTF) at a gas temperature of 1573 K and pressures of 0.1, 0.5, 1.0, and 1.5 MPa. Ash generated at high pressure was found to be much finer than ash generated at low pressure due to the differences in char structure. Pressure influcences ash formation by its effect on the structure of char particles after devolatilisation. Char samples produced at high pressure have higher proportions of porous char particles which fragment to form finer ash particles. This study confirms and elaborates upon previous studies relating the structure and morphologies of char to ash formation.

An Experimental Study on the Effect of System Pressure on Char Structure of an Australian Bituminous Coal

A 63−90 μm size fraction of an Australian bituminous coal sample was fed into a drop tube furnace (DTF) and a pressurized drop tube furnace (PDTF) to generate chars. A gas temperature of 1573 K and system pressures of 0.1, 0.5, 1.0, and 1.5 MPa were considered. Particle size analysis, scanning electron microscopy (SEM), and image analysis were employed to analyze the chars produced in order to investigate the effect of system pressure on the resultant char structure and morphology. The char character was found to be influenced significantly by the system pressure. Results obtained indicated that the coal and char fragmentation might have occurred during devolatilization at high pressure. The char size (as characterized by the swelling ratio) was also observed to increase with system pressure. The cross-sectional characterization of the char particles indicated that at high pressure the majority of the char particles are of high porosity with thin walls or network (the group I type) rather than of medium porosity with thicker walls or network (the group II type) and of low porosity (the group III type). Char particles generated at high pressure were also observed to have a higher internal and surface porosity.

Pressurized drop tube furnace tests of global coal gasification characteristics

Pressurized drop tube furnace (PDTF) tests were performed with an Indonesian sub-bituminous coal while temperature, oxygen/coal ratio, steam/coal ratio and pressure were systematically varied. The tests were designed to investigate the effects of these experimental parameters on the pulverized coal gasification characteristics at elevated pressure. The results showed that the gasification at elevated pressure is more productive than that at atmospheric pressure, considering the carbon conversion and cold gas efficiency. The oxygen/coal ratio at the maximum cold gas efficiency ranged between 0.5 and 0.7 g/g. Only when the temperature was sufficiently high, did the increase of steam/coal ratio result in the improvement of cold gas efficiency. As the pressure increased, the contribution of carbon conversion by heterogeneous reactions increased while the conversion by pyrolysis decreased. Copyright © 2000 John Wiley & Sons, Ltd.

97/04401 Devolatilization of Yallourn coal in a pressurized drop-tube furnace: Yeasmin, H. et al. Proc. Annu. Int. Pittsburgh Coal Conf., 1996, 13, (1), 8–13

A pressurized drop-tube furnace has been built to study the details of the kinetic behavior of low rank coal during devolatilization, gasification and combustion at the Cooperative Research Centre (CRC) for New Technologies for Power Generation from Low-Rank Coal. The facility can be operated at pressures and temperatures up to 1,600 kPa and 1,673 K respectively. The reaction time can be varied from about twenty milliseconds to several seconds. A fluidized bed coal feeder is capable of a coal feed rate from 20 to 90 g/h. The facility is also capable of using various atmospheres from inert to oxidizing and reducing. Devolatilization of Yallourn coal at various pressures and temperatures has been carried out. Preliminary results are presented in this paper.