Exit Gas Composition Research Articles

Blast Furnace Slag Formation Prediction Model Using Classical Thermodynamics

Blast furnace (BF) ironmaking is the most widely used technology for hot metal production. In steelmaking industry, 80% of the steel in the world is produced in the BF‐basic oxygen furnace route. It is well known that poor quality of the raw material i.e., high gangue content in the iron ore affects the BF process performance and the cohesive zone formation, which is the most critical zone in the BF operations. Increased gangue content in the iron ore causes variation in the slag formation and slag volume thus affecting the fuel rate and BF performance. Therefore, in this study, the slag formation is studied to understand the slag properties at different locations inside the BF. The model is based on classical thermodynamics and is implemented using ChemApp linked with FactSage databases. The model aids in understanding the slag formation in the BF for various burden chemistry, fuel, and flux inputs. The final hot metal and slag composition along with the exit gas volume and composition predicted from this model are compared with industrial BF plant data operating across different conditions.

Computational Modelling on Gasification Processes of Municipal Solid Wastes Including Molten Slag

The formulation of the CFD-DEM model, CD-MELT, is established in this study to include three-phase non-isothermal processes with simultaneous combustion and melting for gasification simulations. To demonstrate the model capability, CD-MELT is used to assess the need for slag recycling for the non-isothermal melting of municipal solid wastes (MSW) in a prototype waste-to-energy research facility. The simulation encompasses the full fixed-bed slagging gasification process, including chemical reactions and melting of MSW and slag. In order to assess the need for slag recycling, comparisons are made for the two cases of with and without, in terms of the slag mass, liquid slag volume fraction, exit gas composition, and temperature distribution in the gasifier. The prediction results enable the tracking of liquid molten slag as it permeates through the solids-packed bed for the first time in the literature as far as we are aware, which is crucial to address design considerations such as distribution of bed temperature and optimal location for slag-tap holes at the bottom, as well as potential slag clogging within the porous media. The model also predicts an uneven and intermittent slag permeation through the packed bed without the recycling, and provides a plausible explanation for the operators’ experience of why slag recycling is important for process stability. Finally, the predicted slag outlet temperature using the proposed CFD approach also agrees well with the measurement data published in an earlier case study for the same facility.

INVESTIGATION OF MICROALGAE GASIFICATION UNDER STEAM ATMOSPHERE IN DOWNDRAFT GASIFIER BY USING ASPEN PLUS®

Energy production is facing the environmental and economic issues due to growing population and uncertainties about the fossil fuels. These concerns prompt the researchers to find widely available and renewable alternative such as biomass instead of the fossil fuels. Microalgae is one of the promising biofuels owing to its rapid growth speed and higher calorific value. Steam gasification is an alternative way converting biomass to syngas with higher H2 and lower CO2 content compared with the other thermochemical conversion processes. In the present work, the downdraft gasifier model was developed by using Aspen Plus® program that has the capability to investigate the performance of microalgae gasification. Before the performance evaluation of the gasification, validation of the model successfully completed and exit gas compositions of H2, CO2, CO and CH4 were found very close for experimental study and the developed model. Effects of the main parameters of the process such as steam/biomass ratio and gasification temperature were assessed on the syngas composition and higher heating value (HHV) of syngas. The obtained results were stated that the increment in the temperature showed great effect on the H2 and CO compositions of syngas, they increased from 50.72% to 56.47% and 28.11% to 28.84% respectively. The simulation results also illustrated that the rising of the S/B ratio was favored the steam related reactions and increased the H2 content in syngas. However decreasing trend of the CH4 caused reducing of the HHV of syngas as a function of temperature and steam as well.

Clean iron production through direct reduction of mineral iron carbonate with low-grade hydrogen sources; the effect of reduction feed gas composition on product and exit gas composition

Direct reduction of mineral iron carbonate with hydrogen is a high-potential candidate for carbon dioxide emission reduction in the iron and steel industry. This novel technology provides a new route for ‘clean’ iron production. For economic implementation, a sufficient supply of hydrogen is crucial. Up to now only highly pure hydrogen sources were used for the direct reduction. On the way to a sustainable, completely hydrogen-based iron production, low-grade hydrogen sources need to be considered. The effect of the hydrogen concentration and the impact of matrix constituents such as methane and carbon dioxide in the hydrogen source on the direct reduction of mineral iron carbonate with hydrogen at 873 K were investigated in this project. It was shown that complete iron carbonate conversion is possible at a metallization degree of 78 wt% with hydrogen concentrations as low as 55 vol%. Carbon dioxide in the feed gas (27–63 vol%) favors magnetite formation instead. Hydrogen is also consumed by the reverse water gas shift reaction in the formation of carbon monoxide. Methane in the feed gas (15–80 vol%) does not have a negative impact on the composition of the solid product. These results suggest that methane-rich hydrogen sources (e.g., coke oven gas) are viable options for direct iron carbonate reduction opening up a novel pathway for clean iron production from mineral iron carbonate with low-grade hydrogen sources.

Comparison of the Photoautotrophic Growth Regimens of Chlorella sorokiniana in a Photobioreactor for Enhanced Biomass Productivity

Microalgae have a wide industrial potential because of their high metabolic diversity and plasticity. Selection of optimal cultivation methods is important to optimize multi-purpose microalgal biotechnologies. In this research, Chlorella sorokiniana AM-02 that was isolated from a freshwater lake was cultured under various high photosynthetic photon flux density (PPFD) conditions and CO2 gas levels in standard Bold’s basal medium (BBM). Furthermore, a wide range of nitrate levels (180–1440 mg L−1) was tested on the growth of C. sorokiniana. Microalgae growth, pigment concentration, medium pH, exit gas composition, as well as nitrate, phosphate, and sulfate levels were measured during an experimental period. The preferred high PPFD and optimal CO2 levels were found to be 1000–1400 μmol photons m−2 s−1 and 0.5–2.0% (v/v), respectively. The addition of nitrate ions (up to 1440 mg L−1) to the standard growth medium increased final optical density (OD750), cell count, pigment concentration, and total biomass yield but decreased the initial growth rate at high nitrate levels. Our findings can serve as the basis for a robust photoautotrophic cultivation system to maximize the productivity of large-scale microalgal cultures.

Influence of burner nozzle configuration, and inlet gas composition on combustion, gas dynamics, temperature and concentration profile in a rotary hearth furnace

ABSTRACT A CDF model for simulating gas dynamics, heat and mass transfer in the freeboard of a pilot-scale Rotary Hearth Furnace (RHF) is developed in conjunction with an independent solid reduction model at the bottom of the hearth. The effect of air-inlet configuration and inlet fuel composition on the fuel requirement, exit gas composition, fluid flow, temperature, and gaseous composition distribution have been investigated using this model. The lower air-inlet tubes orientated at 5° upwards keeping remaining air and fuel tubes horizontal emerged as the most recommended burner configuration. Various alternative fuels categorized in terms of calorific values, demonstrated that the fuel with high calorific value required less fuel and produced less CO2 emission. Interestingly, it was found that for the same calorific value a combination of blast furnace gas and coke oven gas (BF+COG) produced less CO2 emission compared to a combination of COG+BF+NG (Natural gas).

Numerical simulation of gas-solid flows in fluidized bed gasification reactor

A numerical model for simulating a fluidized bed gasifier should include appropriate parameters to capture the dynamics of gas-solid flows, gasification kinetics and the interaction between these two. The focus of the present study is to analyze the effects of coal gasification chemistry models reported in literature on the prediction of product gas composition in a fluidized bed gasification reactor. Numerical results are validated against the experimental data available in literature. The validated model is used to examine the available chemical kinetics schemes for water gas shift reaction, steam methane reforming reaction and char heterogeneous reactions. It is also used to assess the effects of hydrodynamic models parameters such as drag model, particle-particle restitution coefficient and specularity coefficient on exit gas composition. Results show that the predictions of product gas composition are notably affected by the choices of the kinetics schemes for water gas shift and steam methane reforming reactions. Systematic analysis using the available choices to simulate initial processes such as moisture removal, volatile and tar cracking is reported. Drag models and the value of specularity coefficient are shown to have no effect on product gas composition, and the particle-particle restitution coefficient slightly influences the predicted gas composition.

Development of a high‐temperature two‐stage entrained flow gasifier model for the process of biomass gasification and syngas formation

This paper presents development of the Mitsubishi Heavy Industries (MHI) gasifier utilizing an analogy between a model with coal feedstock and the model with torrefied woody biomass. A computational fluid dynamics (CFD) model was primarily developed for coal gasification, and the simulation results were validated with similar published work and experimental measurements. The model was extended for the woody biomass to predict the gasifier performance under the gasification process. The results were used to compare the effect of fuel type on the gasifier performance and gaseous product compositions. The second-level injection nozzles were modified tangentially, and the flow characteristics, species yields, and temperature were evaluated. The possibility of reducing the gasifier length from 13 to 8 m is also evaluated for different total length. The results revealed that using woody biomass leads to a decrease in the mole fraction of CO and H2 at the gasifier outlet compared with coal. An opposite trend was observed for CO2 and CH4 compositions. The contributions of modified second-level nozzles to the total gas composition and exit temperature only account for less than 3%. Reducing the gasifier length from 13 to 8 m increased the exit temperature from 1289 to 1340 K, but the changes in the exit gas composition were less than 2%. The new design of the MHI gasifier can reduce the investment costs by reducing the gasifier length as well as using biomass instead of coal.

Net carbon-di-oxide conversion and other novel features of packed bed biomass gasification with O2/CO2 mixtures

Biomass thermo-chemical conversion under O2/CO2 conditions is experimentally investigated to establish its CO2 conversion potential. Packed bed configuration with counter-current flame propagation is chosen for this purpose and three different fuels are used (agro-residue pellets, coconut shells and wood pellets). For oxidizer streams containing 20, 25, 30, 40 and 50% O2 (v/v) (rest CO2) steady flame propagation is established at different superficial velocities and the following quantities are measured – temperature along the reactor, mass consumption rate and exit gas composition. Corresponding reference experiments with O2/N2 mixtures are performed for comparing the net CO2 conversion. The propagation regimes, similar to earlier studies with air, fall under the following two categories – (1) gasification – volatile oxidation accompanied by char reduction and (2) char oxidation dominated – simultaneous char and volatile combustion. Invoking equilibration of volatile oxidation under gasification conditions, a new procedure is established to estimate the net CO2 conversion (NCC). In general, NCC is significant around the volatile stoichiometric point (ϕv=1) and falls off on either side as the oxygen mass flux is decreased or increased. NCC is zero in very rich regime i.e. when ϕv≫1 due to low bed temperatures and also when ϕv<1 due to char oxidation. Maximum NCC of 627 g/kg of biomass is observed with 30% O2/70% CO2 (v/v) case at ϕv=0.96 for agro residue pellets. Cold gas efficiency (ηg) is as high as 85% for the maximum NCC case. Enhanced gasification efficiencies of O2/CO2 cases as compared to corresponding air cases is due to the additional conversion of CO2 to CO (predominantly C + CO2 → 2CO). The difference in the fraction of char left over with CO2 and N2 cases is consistent with this observation. Corrected fuel flux (CFF), proposed to address these variations in fuel heating value, oxygen fraction in the oxidizer etc., is shown to exhibit universality with respect to oxygen mass flux and fuel type.

Improved Kinetic Data Acquisition Using An Optically Accessible Catalytic Plate Reactor with Spatially-Resolved Measurement Techniques. Case of Study: CO2 Methanation

Modelling and optimization of chemical reactors require a good understanding of the reactions mechanism with the corresponding kinetic description. Therefore, high quality kinetic data are needed, which can be challenging to obtain, especially for fast and highly exothermic reactions such as the CO2 methanation. Traditionally, kinetic studies rely on measuring the exit gas composition (1 data point per species and experiment) using differential reactors with diluted catalyst beds and reactants to avoid temperature change. Therefore, an optically accessible catalytic channel reactor was designed, which allowed for the chance to gather spatially-resolved information on axial gas composition and catalyst surface temperature, specifically by means of a movable sampling capillary and shortwave infrared-thermography (SWIR), respectively. A catalyst coated plate was placed at the bottom of the channel, while a set of two quartz glass plates covers the top. In the current study 35 data points per gas species were collect for 1 experiment conducted under laminar flow conditions at 425 °C. Catalyst surface temperature determined via a SWIR camera was not influenced by polyatomic molecules partaking in the reaction and thus did not falsify the kinetic data. The catalyst mass distribution along the reactor axis was determined, enabling the development of a correct reactor model for kinetic parameter estimation and model discrimination.

Combustion characteristics of biomass fuels in a fixed bed micro-gasifier cook stove

This paper deals with the effect of different biomass fuels used in a fixed bed advanced micro-gasifier cook stove’s combustion process. Combustion of different biomass fuels like coconut shells, Prosopis Juliflora and wood pellets were investigated in an advanced cook stove for an air velocity of 3 m/s. The actual testing procedure followed to evaluate full performance characteristics of the stove was as per the world standard protocol WBT 4.2.3, and the results were analyzed in terms of thermal efficiency. The measured variables like bed temperatures, mass loss and exit gas composition were used to estimate the combustion characteristics of each fuel in terms of flame propagation, fuel burning rate and the combustion quality. The two mode operations of combustion processes namely flaming and char mode of the fuels were also studied. The experimental outcomes provide a clear idea on the impact of the different fuel properties on flame propagation, burning rate and indoor air quality. Thus, the flame propagation rates are 0.063, 0.071 and 0.05 mm/s with an average fuel burning rate of 16, 12 and 10 g/min are achieved. Also the thermal efficiency of fixed bed micro-gasifier is found to be about 36.7±1 % for coconut shell, 36±1 % for Prosopis Juliflora and for wood pellets it is about 38.5±1 %.

Coal particle and bed physical transformational behaviour after thermochemical conversion in a fixed bed

This paper examines the physical transformational behaviour that coal particles and the bed structure undergo in a fixed bed reactor. The transient overfeed configuration is used with feed gas entering from the bottom of the 1.2m reactor with an inner diameter of 104mm. The fuel bed loading, of 3.3kg on average, consisted of non-devolatilized seam two coal of 4, 6 and 8mm particles from the Highveld region in South Africa and was inertinite-rich. Transient exit gas composition and temperature profile inside the fixed bed of particles, is presented along with a full chemical and physical characterisation of the feed coal and the partially converted bed contents consisting of coal, char and ash particles. The bed dissection method implemented was designed to limit mechanical fragmentation by minimizing particle handling and bed structural disturbance during sampling. Particle size distribution and the particle size distribution width showed a significant variation in the oxidation zone and the ash bed which was not previously quantified on industrial scale experiments. The bulk, true as well as the apparent (measured by hydrostatically weighing in mercury) densities are reported for the different reaction zones of pyrolysis, reduction, oxidation and the ash bed, and showed significant variation in each zone. The particles and the fixed bed structural change were established by the measured particle porosity and the fixed bed voidage. The extensive role of particle agglomeration in the lower sections of the fixed bed was demonstrated in the bed voidage data and is evidently tracked as the reaction front moves up through the fixed bed of particles. The mode of operation simulated the transient start-up procedure and subsequent particle and bed transformational behaviour during industrial fixed bed combustion and gasification.

Coal particle chemical transformational behaviour after thermochemical conversion in a fixed bed

This paper examines the chemical transformational behaviour that coal particles undergo during conversion in deep packed beds, typically found in industrial combustion and gasification operations. Experiments were performed in a transient overfeed packed bed laboratory scale reactor fed with 4, 6 and 8mm coal particles. The reactor was operated at atmospheric pressure and is 1.2m in length and has an inner diameter of 104mm. The coal loading was 3.3kg and resulted in a bed height of 520mm. A typical inertinite-rich South African seam four coal from the Highveld region was used as fuel in the reactor. The transient temperature profile in the descending bed as well as the exit gas composition is presented here. A post experiment dissection of the bed contents along with full chemical characterisation was undertaken. Care was taken to ensure that the dissection method, specifically designed for minimal disturbance to the fixed bed structure, could provide an accurate representation of the characteristic reaction zones. The residual volatile matter and the overlap in the reduction and pyrolysis zones were insensitive to particle size variation and mainly determined by the maximum temperature in each zone. Where it was found useful, these reaction zone profiles are compared to industrial and pilot operations. The reaction front velocity and heating rates that particles experience in the different reaction zones was obtained and showed significant variation during the transient start-up stage, but are remarkably comparable once the stable reaction front is formed. This current mode of operation represents fixed bed combustion and gasification operations particularly during the transient start-up stages.

Gasification behavior of coal and woody biomass: Validation and parametrical study

The entrained flow gasification of two feedstocks (Kentucky coal and woody biomass) have been investigated in this study both numerically and experimentally. Previously, there had been no study that investigated the centerline parameters during the experimental gasification of Kentucky coal and biomass utilizing drop tube reactor (DTR). These high quality centerline experiments provide enough data for high fidelity model development and used for an innovative gasifier design. This work investigates the gasification behavior of Kentucky coal and wood waste under different gasification parameters including equivalence ratio, pressure and temperature. The experimental study was conducted in the air-blown atmospheric DTR experimental facility at the Waste-2-Energy Laboratory at Masdar Institute. The measured centerline temperature, exit gas composition, and SEM images was obtained for model validation and to gain better insight into the gasification of the two different feedstock particles. The Lagrangian–Eulerian based numerical model predicted the experimental results reasonably. The effect of the fuel type on the gas composition along the centerline of the gasifier indicated that Kentucky coal attained higher gasification efficiency when compared to that of wood waste. Moreover, the gasification efficiency was most sensitive to the equivalence ratio.

Production of Synthesis Gases from Ethanol Steam Reforming Process

In this study, the production of synthesis gases has been purposed under between 250oC - 700oC and 1 - 2 bars pressures. The research was conducted over a commercial BASF catalyst and a laboratory prepared catalyst. The catalyst has a content of different substances including basically NiO/Al2O3 and some additionals (Ca, Mg, Cr, Si). The experimental measurements were carried out within a recently developed experimental equipment which can be operated up to 1200o and 1 to 3 bars pressures. The study was conducted over a commercial BASF catalyst and a laboratory prepared catalyst under different ethanol/water ratios, temperatures, and catalyst loads. Under the condition when ethanol/water ratios were decreased from 1/2 to 1/10, it was observed that hydrogen ratios increased in exit gas composition of the reactor. With increments in catalyst loads from 1 to 5 grammes, hydrogen ratios in exit gas composition gradually increased. Reaction of ethanol-steam reforming started nearly at 300oC, and when temperature increments continued further up to 700oC, hydrogen yields in exit gas compositions of the reactor increased significantly to a range of 70% - 80%. In the case of using commercial BASF catalyst, hydrogen ratios in exit gas composition were found slightly higher than laboratory prepared catalyst. According to our observations, life time of laboratory prepared catalyst was found higher than the commercial BASF catalyst. In this study which kinetic measurements were applied, some kinetic parameters of ethanol-steam reaction were calculated. The mean activation energy of ethanol consumptions at 573oK - 973oK was found as 26.87 kJ/mol, approximately. All kinetic measurements were analyzed with a first order reaction rate model. In this study, some diffusion limitations existed, however, overall reaction was chemically controlled.

Study of particle size distribution and oxygen mass balance in a bubbling fluidizing combustor using cotton stalk

AbstractFluidized bed combustor is one out of the most popular techniques to utilize biomass wastes in agricultural states like Punjab, India. In this work, a three‐phase mathematical model, considering bubble growth along bed height, has been developed. The mathematical model has been used to find out certain key performance parameters like carbon utilization efficiency, bed carbon load and exit gas composition in a bubbling fluidized bed combustor using tuyre‐type distributor plate. The model predictions have been compared with 7.5 MW fluidized bed power plant using cotton stalk and are found to be in good agreement with plant data. © 2015 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

A study of the gasification of carbon black with molten salt of Li2CO3 and K2CO3 for application in the external anode media of a direct carbon fuel cell

The characteristics of gasification reactions for carbon–carbonate mixtures were experimentally investigated at high temperatures up to 900 °C, considering the application of the mixtures to the external anode media of a direct carbon fuel cell. A thermo-gravimetric analysis (TGA) was conducted in either a nitrogen or carbon dioxide ambient environment for Li2CO3, K2CO3 and a mixture of these two substances with carbon black. Changes in the exit gas composition were also monitored during the heating process. It was shown that gasification in the mixture media occurs much more rapidly than carbonate decomposition at elevated temperatures, even for low concentrations of CO2. It was also shown that the loading of carbonates to carbon significantly affects the global gasification reaction; it increased the reaction rate by an order of magnitude and decreased its activation energy. Based on the experimental observations, a simplified reaction model of gasification was suggested for the anode media of a DCFC, regarding carbonate-catalysed and metal-catalysed pathways of Boudouard reactions.

Modeling and Simulation of a Pilot-Scale Bubbling Fluidized Bed Gasifier for the Gasification of High Ash Indian Coal Using Eulerian Granular Approach

Abstract The present work deals with modeling and simulation of a pilot-scale bubbling fluidized bed gasifier (BFBG) for the gasification of high ash Indian coal. Taking into account different stages of coal gasification, such as drying, volatilization, gasification and combustion processes, a two-dimensional model with quadrilateral cells is developed using FLUENT 12.0 software. The model incorporates exchange of mass, momentum and energy between gaseous phase (phase 1) and solid phase (phase 2) using Eulerian–Eulerian approach. The solid phase is described by kinetic theory of granular flows. Four heterogeneous and four homogeneous reactions covering six species in gaseous phase (CO, CO2, H2, N2, O2 and H2O) and coal in solid phase are considered for the above process. The kinetics for the homogeneous reactions are described using eddy dissipation model available in FLUENT while that for heterogeneous reactions, a user-defined function (UDF) with Arrhenius kinetics is written in C language. The validation of the above model has been done using experimental data generated in a pilot-scale BFBG at Center Institute of Mining and Fuel Research (CIMFR), Dhanbad, India. The computed exit gas compositions as well as temperature profile inside the gasifier are in good agreement (within an error band of ±10%) with experimental data. The flow behaviors and volume fraction profiles of gas and solid phases in the bed zone and freeboard zone of the gasifier have also been predicted using this model.

Modeling of the entrained flow gasification: Kinetics-based ASPEN Plus model

In this study, the entrained flow gasification (EFG) of Kentucky coal and wood waste had been investigated using detailed kinetics-based ASPEN Plus model and experimental diagnostics. The experimental investigation was conducted in the air-blown atmospheric drop tube experimental facility furnace. The exit gas composition at different equivalence ratios was obtained to validate the developed ASPEN Plus model. In addition, the scanning electron microscopy (SEM) images of the char were observed along the gasifier to determine the behavior of the feedstock subjected to gasification and to select proper char gasification models. The model takes into account the passive heating through moisture release, devolatilization, volatile combustion and char gasification. It made the investigation of the gasification process and running sensitivity studies practically feasible as current equilibrium and high fidelity coupled thermo-chemical-flow models are insufficient or pertaining much complexity to use. The model compares reasonably well with the experimental data obtained in this work and is been used to carry out sensitivity study. A rise in the diameter and height sizes lead to an increase in the mole fraction of CO and H2 throughout the length of the gasifier, an opposite trend was observed for the CO2 and H2O composition. It was also observed that the mole fraction of the syngas was lower for the biomass waste compared to the baseline coal as this is attributed to the higher oxygen content (43.62%) and lower carbon content (49.41%) of the waste biomass compared to coal.

CO2 Adsorption: Experimental Investigation and CFD Reactor Model Validation

The National Energy Technology Laboratory is investigating a new process for CO2 capture from large sources such as utility power generation facilities as an alternative to liquid amine based adsorption processes. Many of these advanced dry processes are based upon sorbents composed of supported polyamines. In this analysis, experiments have been conducted in a laboratory-scale fluidized bed reactor and compared to CFD reactor predictions using kinetics obtained from TGA tests. Batch experiments were conducted by flowing a mixture of CO2, H2O, and N2 (simulated flue gas) through a fluidized bed of sorbent material. The exit gas composition time series data is compared to CFD simulations using a 3-dimensional nonisothermal reacting multiphase flow model. The effects of the gas flow rate, distributor design, and particle size are explored through the CFD simulations. It is shown that the time duration for CO2 adsorption decreased for an increase in the gas flow. Fluid bed hydrodynamics indicated that there were regions in the reactor where the inert FCC particles segregated and defluidized; without adversely affecting the capacity of the sorbent to adsorb CO2. The details of the experimental facility and the model as well as the comparative analysis between the data and the simulation results are discussed.