High-temperature Entrained Flow Reactor Research Articles

A collection of model parameters describing the gasification behavior of different fuels under entrained flow conditions

Entrained flow gasifiers can be fed with a variety of fuels. However, each fuel has its own gasification behavior resulting in different operating conditions and ideal design configurations. The optimum can be determined by e.g. modelling and simulating their gasification behaviors. Therefore, models and their parameters are necessary, which consider the processes involved. A collection of model parameters describing results of experimental investigations under entrained flow gasification is included in the presented “Solid Fuel Entrained Flow Gasification Database”. The database contains information about devolatilization, surface area development, thermal deactivation and the reaction kinetics including product gas inhibition of five lignites, five bituminous coals, one anthracite, two pretreated biomasses and one blend. Their determination in a wire mesh reactor, a pressurized high temperature entrained flow reactor, a structural analyzer and thermogravimetric balances is exemplary presented by four investigated fuels. Further the content of the database is explained and visualized by comparing the results with ten other fuels. Overall, the presented database is unique in its kind as it summarizes these insights and supplements it with further information. There is no other fuel database available, which covers model parameters and refers to validation data of such a broad range of fuels considering entrained flow gasification.

Determination of the Intrinsic Gasification Kinetics of a Bituminous Coal Including Product Gas Inhibition and Char Deactivation Under Entrained Flow Conditions

Abstract This work provides experimentally obtained data concerning the gasification of bituminous coal under entrained-flow conditions. The main focus lies on the determination of reaction kinetics with and without product gas inhibition as well as on thermal deactivation behavior. For this reason, experiments were carried out in a pressurized high-temperature entrained-flow reactor. The reactor is designed for temperatures of up to 1800 °C and pressures of up to 50 bar. In this study, char samples with different residence times at temperatures between 1200 °C and 1600 °C and a pressure of 10 bar were obtained. Pyrolysis experiments were performed in pure nitrogen, while an O/C ratio of one was selected for the gasification. In addition to ultimate, proximate, and structural analyses of the char samples, e.g., to calculate conversion according to the ash tracer method, intrinsic reaction kinetics of the pyrolysis chars with carbon dioxide and steam were determined in a high-pressure thermogravimetric analyzer. The influence of carbon monoxide inhibition on carbon dioxide gasification and of hydrogen on steam gasification was quantified using the Langmuir–Hinshelwood equation. Further, the deactivation behavior of the pyrolysis chars was analyzed by measuring their reactivities under constant reaction conditions and plotting them as a function of residence time. The presented results give an overview about factors like temperature, pressure, gas composition, and residence time affecting fuel conversion. Furthermore, constants describing the reaction behavior of the fuel were determined, which can be used for future simulation of gasification processes.

Comparison of entrained flow CO2 gasification behaviour of three low-rank coals – Victorian brown coal, Beulah lignite, and Inner Mongolia lignite

This study compared the entrained flow CO2 gasification behaviour of three lignites from around the world. The coals include Victorian brown coal-Yallourn, one American lignite-Beulah, and one Chinese lignite-Inner Mongolia. The comparison is made through gasification performance-gas composition and carbon conversion, pollutant gas emission, char characterization, and mineral matter transformation. The gasification experiments were carried out at a wide range of temperatures (1000–1300 °C), input CO2 concentrations (10–40% CO2), and residence times (5–7 s) using a high-temperature entrained flow reactor. The increase in temperature, input CO2 concentrations, and residence time increased the CO concentration and carbon conversion. The three coals had a very similar gas composition on N2 and CO2 free basis with high CO concentration (approximately 92–96%) at 1200 °C. Beulah lignite obtained nearly 100% carbon conversion at 1100 °C and 20% CO2, Yallourn coal at 1200 °C and 20% CO2, and Inner Mongolia lignite at 1300 °C and 20% CO2 or at 1200 °C and 40% CO2. Yallourn coal released the least HCN, NH3, and H2S, Beulah lignite released the most NH3, and Inner Mongolia released the most H2S. At high carbon conversion of 99%, the particle size of D(0.9) was still high (∼50 µm) because of particle agglomeration. The inorganic mineral matter behaviour of each coal at high temperature varied markedly due to the significant differences in coal ash composition. However, the common mineral transformation found for all three coals was the decomposition of CaSO4. Mineral transformations during CO2 gasification tended to increase ash fusion temperature and enhance gasification reactivity.

Formation and O2/CO2 combustion characteristics of real-environment coal char in high-temperature oxy-fuel conditions

Oxygen-fuel combustion is a promising technology for CO2 emission reduction. The high-temperature entrained flow reactor and high-temperature drop tube furnace were used to analyses the formation and O2/CO2 combustion characteristics of real-environment coal char in high-temperature oxy-fuel conditions. It proposed “inflection point standard” of high-temperature flame method for the preparation of real-environmental oxy-fuel coal char according to the flame method. The results show that the ratios of C=O/C-O and C=O/Car increase in the coal char compared with the raw coals. The trend of C=O/Car in oxy-fuel condition is opposite to that in the inert atmosphere, due to the effect of high-concentration CO2. To achieve the burnout rate similar to air combustion for coal char, with the increase of coal rank, the O2 concentration should be enhanced. The optimal O2 concentration for the oxy-fuel combustion of JC anthracite is 30%, while that of other low-rank coals could be lower than 30%. The combustion characteristic of JC anthracite is with the highest sensitivity to temperature and O2 concentration.

Rapid pyrolysis and CO2 gasification of anthracite at high temperature

Anthracite could be burnt efficiently at high temperature utilizing oxy-coal technology. To clarify the effects of temperature and atmosphere on char porosity characteristics, char morphology, fuel-N conversion, and reducing products release, rapid pyrolysis and CO2 gasification of anthracite was carried out in a high temperature entrained-flow reactor to simulate the condition in a pulverized coal furnace. Developed pore structure was formed in the gasification chars, which could be contributed to charCO2 reaction at high temperatures. More mesopores were formed in internal carbon skeleton and retained against collapse and coalescent for gasification chars than pyrolysis chars. Compared with pyrolysis char, smoother and denser surface was observed in gasification char with the irregular bulges disappeared due to the destruction of external carbon skeleton. Char-N could be oxidized to NO in CO2 atmosphere and then reduced to N2 by (CN) on the char surface. Char-N release was greatly promoted due to gasification reaction along with poly-condensation at high temperature; and the preact release of char-N would result in a larger portion of NOx reduction in the following reduction zone with the oxygen-staging combustion technology compared with that in air-staging combustion. Complementally, homogeneous reduction in NOx emission would play a minor effect for anthracite in oxy-coal combustion because of the deficiency of CH4 and HCN, especially at high temperature.

Influence of Torrefaction on Biomass Gasification Performance in a High-Temperature Entrained-Flow Reactor

In the present work, the gasification performances of two pairs of raw and torrefied biomasses, including raw forest residue and torrefied forest residue, and raw spruce and torrefied spruce in a high-temperature entrained-flow reactor, are numerically examined and compared to each other using a Eulerian–Lagrangian CFD model developed based on OpenFOAM. Moreover, the sensitivities of three important operating parameters (excess air ratio, steam/carbon molar ratio, and biomass particle diameter), which vary in the range of practical significance, are also tested. The calculated results are analyzed both qualitatively and quantitatively by five indicators: isothermal profiles, char consumption rate, gas compositions, species yield, and carbon conversion along the reactor length. The obtained results show that torrefied biomass can increase the maximum temperature in the reactor as compared to its raw parent fuel. During gasification, CO, H2, and CO2 are the major species in the product gas and CH4 accounts ...

Eulerian–Lagrangian Simulation of Biomass Gasification Behavior in a High-Temperature Entrained-Flow Reactor

In this paper, a multiscale Eulerian–Lagrangian CFD model based on OpenFOAM has been constructed, which takes into account heat and mass transfer, pyrolysis, homogeneous and heterogeneous reactions, radiation, as well as the interactions between the continuous gas phase and discrete particles. The proposed model is validated and applied to a laboratory-scale biomass entrained-flow reactor. The operating temperatures are high (1000–1400 °C) and influences of five operating parameters (reactor temperature, steam/carbon molar ratio, excess air ratio, biomass type, and particle size) on the gasification behavior are explored. Results show that an increase in the reactor temperature has a positive effect on both the H2 and CO productions; increasing the steam/carbon ratio increases the H2 production but decreases the CO production; increasing the excess air ratio decreases both the H2 and CO productions; the variations in the gas product for the four biomasses studied are not so significant, because of similar biomass nature and, hence, one type can be replaced by another without any major consequences in the gasification performance; and both the CO and H2 productions and carbon conversion decrease with an increase in particle size. Moreover, the predicted results follow the same trend as the experimental data available in the literature. Quantitative comparisons are also made, and the agreement is good.

Gasification kinetics during entrained flow gasification – Part I; Devolatilisation and char deactivation

The devolatilisation behaviour of solid fuels and the reactivity of the resulting char are important design parameters for entrained flow gasifiers. The volatile yield and devolatilisation rate of two coals are measured in a pressurised high temperature entrained flow reactor at up to 1600°C and 4.0MPa and in a wire mesh reactor. A pyrolysis model is derived that describes the influences of temperature, pressure, and residence time on devolatilisation.During the entrained flow pyrolysis experiments char samples are collected from the hot reaction zone and their reactivity and surface area are measured. A significant char deactivation is observed when the chars are exposed to a high temperature for a longer time during pyrolysis. This loss of reactivity is caused by a loss of specific surface area, but also by a decrease in intrinsic reactivity. Based on the experimental data set, a char deactivation model is derived that describes the loss of active sites by the continuous transformation of fresh reaction sites to deactivated sites.The experimental data and the models indicate that the devolatilisation rate is significantly faster than the char deactivation rate. Therefore char deactivation also occurs during the heterogeneous char reactions and should be considered in a char conversion model for entrained flow gasification.

Coal and char properties in high temperature entrained flow gasification

With the objective to measure coal conversion at realistic operation conditions the Pressurised High Temperature Entrained Flow Reactor (PiTER) is developed. The pyrolysis of Rhenish lignite is studied at temperatures up to 1600 °C and pressures up to 2.5 MPa. At longer residence time (above 1.5 s) volatile yield is 68 wt% and independent of temperature and pressure.Char samples are extracted from the hot reaction zone and their reactivity is analysed by weight loss in TGA experiments at defined conditions. Furthermore, specific char surface area is measured. At 1200 °C the intrinsic reactivity of char decreases by a factor of almost 7 from 0.5 s to 2 s residence time, but surface area (approximately 500 m2/g) is hardly affected. At 1400 °C and 1600 °C, the intrinsic reactivity also decreases, but simultaneously the surface area is reduced to below 300 m2/g. The difference in deactivation can only be explained by two different mechanisms: (i) experiments at 1200 °C are below the ash fusion temperature and graphitisation at the char surface may lead to a reorganisation of carbon atoms; (ii) above the ash fusion temperature, the melting of mineral matter additionally blocks the micropore structure and results in a loss of specific surface area.

Experimental investigation of high temperature and high pressure coal gasification

Pyrolysis and gasification behavior is analyzed at operation conditions relevant to industrial scale entrained flow gasifiers. A wire mesh reactor and the Pressurized High Temperature Entrained Flow Reactor (PiTER) are used to measure volatile yield of Rhenish lignite, a bituminous coal and German anthracite at high temperature and high pressure. In the wire mesh reactor at 1000 °C a significant influence of pressure on volatile yield is observed. For lignite the volatile yield (daf) decreases from 57 wt% at atmospheric pressure to 53 wt% at 5.0 MPa. In the same pressure interval the volatile yield of the bituminous coal strongly decreases, whereas no significant influence of pressure on the volatile yield of anthracite is detected. In entrained flow experiments (PiTER) at higher temperature and 0.5 MPa an enhanced devolatilization of the lignite is observed. At 1200 °C, the maximum volatile yield is 62 wt% and it increases to 67 wt% at 1400 °C. In entrained flow gasification experiments with Rhenish lignite a high level of conversion is measured at atmospheric pressure and at 0.5 MPa. At both pressures, coal conversion increases with temperature and residence time. The highest conversion of 96 wt% is achieved at a particle residence time of 1.3 s, at a temperature of 1600 °C, and a pressure of 0.5 MPa. The experimental results show a large influence of operation parameters on pyrolysis and gasification behavior of Rhenish lignite. The volatile release in the pyrolysis stage and the high level of conversion after a short residence time indicate that Rhenish lignite is suitable for gasification in an entrained flow reactor. The reactivities of char samples that are collected from the hot reaction zone of the PiTER are measured in a pressurized thermogravimetric analyzer (PTGA) at lower temperature (600–850 °C). The pyrolysis temperature in the entrained flow experiments significantly influences the reaction rate in the PTGA at lower temperature. With increasing pyrolysis temperature (1200–1600 °C) a continuous loss of reactivity is observed.

Wood Bio-Oil Noncatalytic Gasification: Influence of Temperature, Dilution by an Alcohol and Ash Content

Biomass gasification is gaining attention as a route for biomass energy production. When large scale units are considered, bio-oil shows lots of advantages compared to solid biomass such as high energy volume density and easy handling and storing. Syngas (H2 and CO) can be produced from bio-oil by two gasification processes, also called reforming processes: catalytic reforming at medium temperature and noncatalytic reforming at high temperature. In the literature, most of the works focus on the catalytic reforming and mainly concern the aqueous fraction of bio-oil or model compounds. Only very few works can be found on the noncatalytic reforming of crude bio-oil. The objectives of this work were to perform experimentally the injection and gasification of nondiluted bio-oil in a lab-scale High Temperature Entrained Flow Reactor (HT-EFR) and to determine the syngas composition and yield. The influence of temperature on the gasification process has been investigated over a wide range from 1000 to 1400 °C. Hydrogen yield increases with temperature via steam reforming of CH4 and C2H2 and with water gas shift reaction. A thermodynamic equilibrium calculation was conducted. It shows that equilibrium is reached within several seconds at the temperature of 1400 °C. After that, experiments of gasification were realized at 1400 °C with pure ethanol and with ethanol added bio-oil and in order to study the impact of dilution on the syngas yield. The influence of ash on the gasification process has also been evaluated. The ash seems to cause a decrease in the total amount of gas produced.

Impact of torrefaction on syngas production from wood

Torrefaction is a way to treat biomass before transportation or thermochemical conversion. It can be used to increase the energy content of wood or to facilitate grinding. The purpose of this paper was to quantify the impact of such a treatment on the behaviour of wood during gasification by steam at high temperature to produce syngas. The aspects of both gas yields and reaction kinetics were considered. Beechwood was submitted both to light torrefaction and severe torrefaction, using a specially designed crossed fixed bed reactor. The initial wood and the torrefied woods were first characterised, then gasified in a new laboratory high-temperature entrained flow reactor (HT-EFR) at 1400 °C for 2 s in an atmosphere containing 20 vol% steam in N 2. The syngas produced was then analysed. The experiments were modelled using a thermo-dynamical equilibrium approach. It was confirmed that torrefaction decreased the O/C ratio. The quantity of syngas produced increased with the severity of the torrefaction. The equilibrium approach describes the results satisfactorily. Gasification experiments carried out at a lower temperature – 1200 °C – indicated that the chars from torrefied woods are less reactive towards steam than the char from wood.

The intrinsic combustion reactivity of pulverised coal chars: The use of experimental pore diffusion coefficients

This paper reports the intrinsic reactivity to oxygen (the rate of reaction per unit surface of pore area, ρi) of fine particles of three coal chars. The chars were prepared from a swelling low-volatile bituminous coal, a non-swelling low-volatile bituminous coal and a brown coal. Rate measurements were made under two conditions: in a low-temperature fixed-bed reactor where chemical processes alone controlled burning rates; and in a high-temperature entrained flow reactor, where pore diffusion had a strong effect on rates. The intrinsic reactivities at high temperature were determined using measured values of the pore diffusion coefficient (De) and other measured properties without the need to use any structural model of the chars' pore systems. The diffusion coefficients were measured using a non-isobaric chromatographic technique, the resulting coefficients being much smaller and having a higher temperature dependence than the corresponding Knudsen diffusion coefficients calculated using Wheeler's ‘average pore size’ structural model. It is concluded that these independent measurements of pore diffusivity, at moderately high temperatures give values which are more relevant to the kinetic processes involved in coal combustion than those determined using simplistic structural models. For the samples considered here, intrinsic reactivities, determined from measured diffusion coefficients and reaction rates, were in close agreement with those predicted on the basis of earlier models.