Gas Reactor Research Articles

Investigation of Bubble Properties in a Bubbling Fluidized-Bed Gasification Reactor Using a Computational Particle Fluid Dynamic Model

Investigation of Bubble Properties in a Bubbling Fluidized-Bed Gasification Reactor Using a Computational Particle Fluid Dynamic Model

Catalyzed oxidation of IG-110 nuclear graphite by simulated fission products Ag and Pd nanoparticles

To evaluate the stability of nuclear materials in high temperature gas reactors under air ingress conditions, catalytic oxidation of IG-110 graphite by two simulated fission products, metallic Pd and Ag, was studied in oxidative atmosphere and at temperatures up to 1000 °C using an integrated furnace, mass spectroscopy and infrared spectroscopy system. Transmission electron microscopy and X-ray diffraction studies show that Pd and Ag nanoparticles were successfully introduced onto powdery IG-110 graphite through an impregnation and subsequent heat-treatment process. The combined mass spectroscopy and infrared spectroscopy methods allow simultaneous analysis of two gaseous products, CO and CO2, and separate measurements of activation energy for their formation reactions. It was found that the introduction of Pd or Ag to IG-110 graphite substantially catalyzed the oxidation of graphite, characteristic of decreased onset temperatures for the oxidation of graphite. Moreover, the catalytic effects by Pd and Ag are considerably different based on measured concentration ratios of CO2 to CO as a function of oxidation temperatures. Ag makes the graphite oxidation commence at approximately 400 °C with CO2 being the dominant product. In contrast, Pd significantly increases the concentration ratio of CO2 to CO at temperatures higher than approximately 690 °C, although it decreases the onset temperature for the oxidation reaction to around 525 °C. To understand the catalytic difference, the mechanism of the graphite oxidation is discussed based on the changes of surface oxygen species on Ag and Pd.

Solid recovered fuel gasification in sliding bed reactor

This study examines a solid recovered fuel gasification process in the context of a regional, clean energy supply from an affordable source. The examination of this approach was performed under various equivalence ratios and load regimes. A unique cross/updraft gasification reactor with a fixed (sliding) bed over the circular grate with tangential gasification media intake was utilised. This technology is a perspective in waste-to-energy and waste-to-materials production. The investigated parameters included producer gas quality and purity, overall conversion efficiency and char material yield. It was found that a low material load is very beneficial in terms of gas purity and conversion efficiency, reaching up to 93%. Also, the formation of tar compounds was measured as low as 0.7 g/m3. However, when the equivalence ratio parameter was 0.14, the gas's lower heating value was only 2.4 MJ/m3. Also, a lower heating value equal to 5.0 MJ/m3 was reached in a low-efficiency regime (48%) when the fuel load was more significant (48.5 kg/h), and the equivalence ratio was only 0.04. The low tar content suggests a very clean process. Also, the material valorisation in the form of char is beneficial as this carbon-rich material no longer has a waste character and can be utilised in many fields.

Thermodynamic and environmental analysis of auto-thermal supercritical water co-gasification polygeneration system of sewage sludge with coal

An auto-thermal supercritical water (SCW) co-gasification polygeneration system has been developed to treat sewage sludge (SS) with coal addition for H2 and heat production. Thermodynamic analysis based on Gibbs free energy minimization and life cycle environmental impact assessment of the system was performed under different conditions. The sensitivity analysis results show that H2 yield increased first and then decreased with the increase of preheated water when the proportion of dry coal to dry SS was less than 1.75 but decreased monotonically when the proportion was over 2. It is necessary to add 21% dry coal of raw SS amount when the system was energy self-sufficient to treat SS directly for avoiding pretreatment energy consumption. The largest exergy destruction was in the SCW gasification reactor which could be over 11500 kW for a 10 t/h processing requirement under 650 °C. The energy and exergy efficiency of the SS SCW co-gasification system can be improved effectively by adding coal, which can reach 79.5% and 47.9% under the preheated water ratio of 1 and the dry coal ratio of 3, respectively. Under this condition, 347.1 kg/h H2 and 20.5 t/h steam could be produced. The global warming potential (GWP) of the system was only 1.10–2.5 kg CO2-eq by the life cycle assessment considering carbon capture and storage (CCS) at a dry coal ratio of 3 based on the natural enrichment of CO2-rich gas by the SCW gasification technology.

High-temperature irradiation-resistant thermocouple instability model for in-pile reactor use

This article presents an instability model for the high-temperature irradiation-resistant thermocouple (HTIR-TC). Here the term instability defines the superposition of both drift and inhomogeneity of TC thermoelements occurring simultaneously. The HTIR-TC is an advanced thermocouple (TC) that uses the refractory metals niobium and molybdenum as sensing thermoelements for generating electromotive force (EMF) in a field of neutrons and at temperatures upward of 1,600°C. In the Advanced Gas Reactor (AGR) 5/6/7 tests conducted at Idaho National Laboratory’s Advanced Test Reactor (ATR), the HTIR-TCs showed low to moderate instability throughout the life of the test. The instability model reveals that HTIR-TCs can, when the operating temperature of the reactor fuel is normal, maintain performance throughout an 18-month refueling cycle typical of nuclear power plants, reflecting an instability of less than ±1%. The HTIR-TC is also qualified for incorporation into a test fixture during the testing of new fuels.

Calculation method of friction coefficient on flat plate in supercritical water laminar boundary layer flow

In supercritical water (SCW) gasification reactor, understanding the interaction of SCW with wall surfaces and the boundary layer situation is significant to gasification efficiency improvement. This paper wishes to find a convenient way to calculate the friction coefficient on flat plate in SCW laminar flow with a pseudo-critical incoming state. The velocity profiles characteristics in the SCW boundary layer would be studied using direct numerical simulation (DNS) method, and they would be applied to variable separation of friction coefficient expression. Then, a semi-analytical formula for plate friction applied to the SCW fluid field would be derived, and it would be found to be the extended form of that derived from the Blasius's theory. In this formula, the effects of the unique properties variation around critical points had been isolated as dimensionless parameter Gμ*, dependent on pressure and temperature boundary conditions. The method of obtaining Gμ* by DNS will be given, and two details in the processes will be explained. Finally, the dependence between Gμ* and boundary conditions would be derived by numerical experiments. By the semi-analytical formula and diagram of Gμ*(Tw)|in, the friction coefficient on one side of the plate in SCW laminar flow could be quickly calculated. The applicable inflow states are five pseudo-critical points of 23–27 MPa, the wall temperature is 645–673 K, and the Reynolds number range is above 1×105. The accuracy of this method has been proved by comparing the results obtained by it with DNS results.

Comparative Study of Hydrogen Thermal Decompostion Characteristics According to Space Velocity Using Combustible Waste Plastics

This Study using combustibe waste plastic compared the pyrolysis Characteristics according to GHSV and the performance of various catalysts for hydrogen production reactor. pyrolysis synthetic oil and synthetic gas (H<sub>2</sub>/CO) of waste plastic are produced using a gasification reactor in a lab scale. HDPE, PP, PS, among the main components of waste plastic were selected as a sample. It was possible to produce high value added hydrogen by producing hydrogen and crude oil through the catalytic reforming reaction that is improved the pyrolysis in vapor. The production of crude oil without catalysts was high at 70.2 wt% and among oil with more 18 hydrocarbons wax’s hydrocarbons accounted for 70.47%. On the other hand in the case of producing crude oil using a catalyst the amount decreased, but the hydrocarbon percentage of increased C<sub>5</sub>~C<sub>14</sub>. As a result of the pyrolysis of each of the catalysts determined according to the GHSV. 10,000 hr-1, 8,000 hr-1, 5,000 hr-1, amount of synthetic oil produced in the case of the GHSV was higher than the other two conditions, but the hydrocarbon of C<sub>5</sub>~C<sub>14</sub> was 30~40%. Based on this it was confirmed that the caloric value of the pyrosis crude oil was up to 11.583 kcal/kg and the pyrolysis oil yield was 58%. In a lab-scale in ternal circulating pyolysis gasification reactor waste plastic is pyrolyzed into catalysts, heat and material resins pyrolyzed into catalysts, heat and material resins at isothermal temperature to produce plastic products such as PS, PE, PP and phthalate.

Development and verification of helium–xenon mixture cooled small reaction system

Although Helium–Xenon mixture cooled small reactor has been widely concerned, there is no mature thermal calculation software that can be applied to Helium–Xenon mixture cooled small reactor in China. In this paper, a semi empirical formula used to predict the physical properties of binary inert gas mixtures is used to establish a physical property calculation model of Helium–Xenon mixture gas mixtures, and the flow and heat transfer calculation model, turbine model and compressor model are modified and improved, so as to achieve the calculation of the Brayton cycle system. The function of the original system analysis program is expanded and improved, and the simulation program for he xenon mixed gas reactor system is developed. At the same time, the closed Brayton cycle system is established by using the system analysis program developed in this paper, and the calculation results are compared with the design values. The maximum relative error is 6.9%. The steady-state operation results of the model are in good agreement with the design operation parameters, which proves the applicability of the improved simulation model. The steady-state response characteristics analysis, the introduction of positive and negative reactivity accidents and the calculation of transient conditions such as step load drop of the reactor were carried out. The overall trend is the same as the literature survey results. The results show that the system analysis program developed in this paper is suitable for the analysis of the Brayton cycle system of Helium–Xenon mixture cooled small reactor.

Determination of the Optimum Operating Conditions for Integrated Methanol and Ethanol Plant from Natural Gas Reactors

Methanol and ethanol can be produced from many kinds of feedstock. One of the most preferred methods to synthesize methanol is from natural gas, which is reformed to form synthesis gas (syngas) and converted by a catalyst to form methanol. Conversely, ethanol production mostly comes from biomass, which competes with human food fulfilment. Several pieces of literature conduct syngas transformation to ethanol to solve this problem. However, the experiment is conducted on a lab scale or pilot scale. Before the technology can be mass-produced on a plant scale, we must determine the most suitable operating condition for the reactor to escalate the reactor's productivity. This study is aimed to determine the optimal operating condition for the integrated methanol and ethanol plant, which is the reactors. The software used for the study is Aspen Plus V12.1. The independent variables for all the reactors in this study are the pressure (P) and the temperature (T). We add the feed molar flow ratio as the independent variable for the Steam Methane Reforming (SMR) and the ethanol synthesis reactor. The dependent variable that will be used for the determination of the optimal operating condition of the reactors is the reactant conversion and the product yield. The data validation between the experimental data conducted by other authors and the process modeling result is in good agreement with less than 6% of error for all three reactors. After performing the process simulation and sensitivity analysis to determine the optimal operating condition for the reactors, it is found that the optimal operating condition for the reactors is as follows: (1) SMR reactor: 25 bar pressure, 1,223 K temperature, feed molar flow ratio (H2O/CH4 ratio) of 3, (2) methanol synthesis reactor: 100 bar pressure and 503 K temperature, and (3) ethanol synthesis reactor:110 bar pressure, 583 K temperature, and feed molar flow ratio (H2/CO ratio) of 0.75.

Modeling Biomass Particle Evolution at Pyrolysis Conditions Considering Shrinkage and Chemical Kinetics with Conjugate Heat Transfer

Biomass pyrolysis is an attractive method to produce renewable biofuel in a short time scale. This paper discusses a computational study considering particle shrinkage and reaction kinetics to characterize biomass particle evolution under pyrolysis conditions. A representative elementary volume (REV) scale simulation was conducted in three dimensions to resolve the gas and solid domains. The interface was modeled using the conjugated heat transfer (CHT) and the adapted partially saturated method (PSM) in the lattice Boltzmann (LB) framework. A sufficient gas thickness was considered to simulate the interface physics, such as the thermal boundary layer and product gas outflux. The current simulation was validated using three different experiments. The particle conversion time, temperature, and shrinkage were well predicted. A parametric study investigated the effect of different modeling approaches and operating conditions. Results show that the internal heat transfer is affected by the particle size, inlet gas velocity, reactor temperature, and geometry. The Fourier number decreases to a nearly constant value as the particle size increases. The Péclet number increases linearly with the reactor temperature. Sub-particle scale simulation results reveal that the CHT model and permeability need to be considered when simulating gaseous product efflux out of the biomass particle. Three regimes are identified based on the particle permeability: diffusion-limited, mixed, and advection-limited. The gaseous product efflux delays the overall conversion in the mixed regime. A modified heat transfer coefficient is formulated based on the current numerical study.

Comparison of unirradiated and irradiated AGR-2 TRISO fuel particle oxidation response

The silicon carbide (SiC) coating in a tristructural isotropic (TRISO) particle acts as a barrier to fission product release during reactor operation and accident scenarios. Oxidation and subsequent failure of the SiC layer during a rare air ingress event is a proposed mechanism for fission product release in a high-temperature gas-cooled reactor (HTGR). Although previous oxidation studies have analyzed unirradiated TRISO particle response, this study compared the oxidation behavior of irradiated and unirradiated TRISO particles from the second Advanced Gas Reactor Fuel Development and Qualification Program irradiation experiment (AGR-2). Particles with exposed SiC were subjected to six varying oxidizing tests in the Furnace for Irradiated TRISO Testing (FITT), examined for failure fraction with the Irradiated Microsphere Gamma Analyzer (IMGA) and characterized with focused ion beam and scanning/transmission electron microscopy techniques to analyze the oxide layer. Uncorrelated unirradiated particle failures throughout the series of exposures suggests that external factors inherent to the experiment increased particle failure sensitivity. However, irradiated particle observations indicated an increased failure response at 400 h 1400 °C in both 2% and 21% O2 atmospheres above failure associated with external factors. Oxide thickness measurements after 400 h at 1400 °C revealed a greater oxidation rate than predicted by parabolic growth, which was attributed to the increased complexity of the oxide structure at longer exposure times. Altering the atmosphere from 21% to 2% O2 reduced the average oxide thickness by approximately 12%–14% in both irradiated and unirradiated particles at 400 h 1400 °C. Overall, the minor variations observed between irradiated and unirradiated particles in this study led to the conclusion that unirradiated TRISO particles can be used to approximate irradiated TRISO oxidation kinetics.

Study of biomass gasification in an industrial-scale dual circulating fluidized bed (DCFB) using the Eulerian-Lagrangian method

Dual circulating fluidized bed (DCFB) has emerged as an efficient reactor for biomass gasification due to its unique feature of high gas-solid contact efficiency and separated reactions in two reactors, yet the understanding of complex in-furnace phenomena is still lacking. In this study, biomass gasification in an industrial-scale DCFB system was numerically studied using a multiphase particle-in-cell (MP-PIC) method featuring thermochemical sub-models (e.g., heat transfer, heterogeneous reactions, and homogeneous reactions) under the Eulerian-Lagrangian framework. After model validation, the hydrodynamics and thermochemical characteristics (i.e., pressure, temperature, and species) in the DCFB are comprehensively investigated. The results show that size-/density-induced segregation makes solid fuels concentrate on the bed surface. Interphase momentum exchange leads to the continuous decrease of the gas pressure axially. In the gasifier and combustor, the lower heating value (LHV) of the gas products is 5.56 MJ/Nm3 and 0.2 MJ/Nm3 and the combustible gas concentration (CGC) is 65.5% and 1.86%, respectively. The temperature in the combustor is about 100 K higher than that in the gasifier. A higher solid concentration results in a smaller value of particle heat transfer coefficient (HTC). The HTCs range from 50 to 150 W/(m2 K) for a solid concentration larger than 0.3 in the combustor while the HTCs range from 100 to 200 W/(m2 K) in the gasifier. The Reynolds number of biomass particles is two orders of magnitude larger than that of the sand particle. The numerical results shed light on the reactor design and process optimization of biomass gasification in DCFBs.

Mixing in Low Reynolds Number Reacting Impinging Jets in Crossflow

AbstractPrevious efforts to model uranyl fluoride formation in an impinging jet gas reactor underpredicted spatial mixing and overpredicted chemical conversion into particulates. The previous fluid dynamics model was based on the solution of the Reynolds Averaged Navier Stokes equations. After simulating fluid dynamics, aerosol dynamics were superimposed onto CFD-simulated gas reactant species concentrations. The current work explores the influence of complex unsteady flow features on the overall flow physics and chemistry for a low Reynolds number, opposed flow, impinging jet gas reactor where there is a low Reynolds number cross flow. The objective of this study was to assess the impact of model formulation on scalar mixing and transport. Transient flow simulations were performed using Scale Resolving Simulations. Large-Eddy Simulations with the dynamic Smagorinsky turbulence model were performed along with simulations which directly resolved the flow. Average and root-mean-square (RMS) velocities and species concentrations were computed along with modeled and resolved turbulence kinetic energy (TKE), modeled turbulence dissipation, and modeled turbulent viscosity. Lagrangian flow tracers were also used to quantify species concentrations along path lines emanating from the jet tips. Transient simulation data were compared to results from RANS simulations using the k-ω shear stress transport (SST) model and Reynolds Stress Model (RSM). Transient simulations showed spatial mixing patterns which were more consistent with experimental data and helped elucidate the process of particle formation observed in experiments.

Methane coupling in nanosecond pulsed plasmas: Correlation between temperature and pressure and effects on product selectivity

We present a zero-dimensional kinetic model to characterise specifically the gas-phase dynamics of methane conversion in a nanosecond pulsed discharge (NPD) plasma reactor. The model includes a systematic approach to capture the nanoscale power discharges and the rapid ensuing changes in electric field, gas and electron temperature, as well as species densities. The effects of gas temperature and reactor pressure on gas conversion and product selectivity are extensively investigated and validated against experimental work. We discuss the important reaction pathways and provide an analysis of the dynamics of the heating and cooling mechanisms. H radicals are found to be the most populous plasma species and they participate in hydrogenation and dehydrogenation reactions, which are the dominant recombination reactions leading to C2H4 and C2H2 as main products (depending on the pressure).

Bimetallic cobalt catalysts promoted by La2O3 for the production of high-calorie synthetic gas

A new catalytic route for the production of a high-calorie synthetic gas (40–60 MJ/Nm3), composed by C1-C4 hydrocarbons, has industrial interest for gas applications and locations with high heating requirements. In this work, a series of bimetallic Co-X (X = Ni, Pt and Fe) catalysts supported on La2O3 promoted Al2O3 micro-spheres were evaluated using both CO2 and CO carbon sources under mild temperature (T = 200–300 °C), moderate pressure (P = 10 bar·g) and relatively high gas hourly space velocity (40,000 N mL/gcat·h). Experimental results proved that the incorporation of nickel as a second metal is beneficial for high-calorie gas application. Besides, catalytic results showed that the utilization of CO as carbon source is beneficial in both conversion and C1-C4 hydrocarbon selectivities. Co-Ni presented the most interesting results, leading to a heating value of 57.9 MJ/Nm3 (40.01 % CH4 and 50.04 % C2-C4 hydrocarbon) at 250 °C through CO hydrogenation. The enhanced catalytic performance achieved over bimetallic Co-Ni was attributed to CoNi alloy catalytic activity, high reducibility (73.82 %), active metal content (9.65x10-4 mmol/g) and appropriate acid-basic sites for COx activation. In contrast, the conversion of CO2 to high-calorie gas was found to be more challenging and lower gas heating values were achieved (39.73 MJ/Nm3). In this case, an adapted reactor concept using a dual bimetallic catalyst and different reaction conditions is hereby proposed to shift selectivity towards the targeted products. This findings represent a step forwards in catalytic engineering for the development of high-calorie synthetic gas reactors.

Conceptual design of a process for hydrogen production from waste biomass and its storage in form of liquid ammonia

In this work we present the simulation of a plant for the exploitation of renewable hydrogen (e.g. from biomass gasification) with production of renewable ammonia as hydrogen vector and energy storage medium. The simulation and sizing of all unit operations were performed with Aspen Plus® as software. Vegetable waste biomass is used as raw material for hydrogen production, more specifically pine sawdust.The hydrogen production process is based on a gasification reactor operating at high temperature (700–800 °C), in the presence of a gasifying agent such as air or steam. At the outlet, a solid residue (ash) and a certain amount of gas, which mainly contains H2, CH4, CO and some impurities (e.g. sulphur or chlorine compounds) are obtained. Subsequently this gas stream is purified and treated in a series of reactors in order to maximize the hydrogen yield. In fact, after the removal of the sulphur compounds through an absorption column with MEA (to avoid poisoning of the catalytic processes), 3 reactors are arranged in series: Methane Steam Reforming (MSR), High temperature Water-Gas Shift (HT-WGS), Low temperature Water-Gas Shift (LT-WGS).In the first MSR reactor, methane reacts at 1000 °C in presence of steam and a nickel-based catalyst, in order to obtain mainly H2, CO and CO2. Subsequently two steps of WGS are present to convert most of the CO into H2 and CO2. Also these reactions are carried out in the presence of a catalyst and with an excess of water.All the oxygenated compounds must be carefully eliminated: the remaining traces of CO are methanated while CO2 is removed by a basic scrubbing with MEA (35 wt%) inside an absorption column. The Haber-Bosch synthesis of ammonia was carried out at 200 bar and in a temperature range between 300 and 400 °C, using two catalysts: Fe (wustite) and Ru/C.As overall balance, from an hourly flow rate of 1000 kg of dry biomass and 600 kg of nitrogen, 550 kg of NH3 at 98.8 wt% were obtained, demonstrating the proof of concept of this newly designed process for the production of hydrogen from renewable waste biomass and its transformation into a liquid hydrogen vector to be easily transported and stored.

Deep Learning for Multigroup Cross-Section Representation in Two-Step Core Calculations

We investigate using deep learning, a type of machine-learning algorithm employing multiple layers of artificial neurons, for the mathematical representation of multigroup cross sections for use in the Griffin reactor multiphysics code for two-step deterministic neutronics calculations. A three-dimensional fuel element typical of a high-temperature gas reactor as well as a two-dimensional sodium-cooled fast reactor lattice are modeled using the Serpent Monte Carlo code, and multigroup macroscopic cross sections are generated for various state parameters to produce a training data set and a separate validation data set. A fully connected, feedforward neural network is trained using the open-source PyTorch machine-learning framework, and its accuracy is compared against the standard piecewise linear interpolation model. Additionally, we provide in this work a generic technique for propagating the cross-section model errors up to the keff using sensitivity coefficients with the first-order uncertainty propagation rule. Quantifying the eigenvalue error due to the cross-section regression errors is especially practical for appropriately selecting the mathematical representation of the cross sections. We demonstrate that the artificial neural network model produces lower errors and therefore enables better accuracy relative to the piecewise linear model when the cross sections exhibit nonlinear dependencies; especially when a coarse grid is employed, where the errors can be halved by the artificial neural network. However, for linearly dependent multigroup cross sections as found for the sodium-cooled fast reactor case, a simpler linear regression outperforms deeper networks.

Advancements and challenges in the fluidized bed gasification system: A comprehensive review

A gasifier employs partial ignition of biomass and conversion to gaseous fuels of high calorific value. Bubbling fluidized bed gasifier is a promising one amongst other gasification technologies like fixed bed, entrained flow etc. It has several noteworthy advantages like large- and small-scale applications, efficient heat and mass transfer rates due its fuel flexibility, low capital and operating costs, etc. However, low mixing rate of biomass feedstock and gasifying agent, high tar content in the product gas and low calorific value of producer gas are some of its limitations which need sincere attention to enhance its performance. The present study analyzes the effect of design variables of the proposed gasifier reactor for different feedstock along with the operating variables on the quality of producer gas. This review paper examines the present global status of biofuels, different types of gasification technologies, approaches adopted for the gasification, different parameters affecting gasification performance, enhancement of product gas conditioning, technical and cost-effective viability and the future prospects of gasification.

Techno-economic and environmental assessment of a novel polygeneration system based on integration of biomass air-steam gasification and solar parabolic trough collector

Renewable energy-based polygeneration energy systems, in addition to providing a variety of products, can effectively improve this planet's environmental conditions and reduce emissions. Therefore, in the present work, a novel polygeneration system has been proposed to produce power, heat, freshwater, and hydrogen-based on biomass and solar energy. In the present system, the Kalina cycle, Gas turbine cycle, double-pressure steam cycle, and organic Rankine cycle are used to produce power, Multi-effect desalination and reverse osmosis are used to produce freshwater, and the PEM electrolyzer is used to produce hydrogen. Also, the exhaust syngas from the gasification process has been used to supply steam to the gasifier reactor. Considering the determination of environmental laws and the need to transform Kish Island into a green island for residents and tourists, a proposed system has been defined for Kish Island in Iran. In the proposed system, the feasibility of three biomass fuels, Municipal Solid Waste (MSW), Mixed Paper Waste (MPW), and Date Palm Waste (DPW), was studied from a technical, economic, and environmental point of view. Air and steam agents have been used for the gasification of mentioned fuels. To evaluate the performance of the system in terms of thermodynamics, economics, and environment during the year, the analysis of the average monthly solar for the studied system has been used. MED has been analyzed using artificial intelligence techniques. Finally, a sensitivity analysis is performed for the main operational parameters. The results of the proposed system modeling show that MSW is the most economical fuel and the use of DPW has the least environmental impact on the system, but in terms of operating conditions, MPW with overall energy and exergy efficiency of 41.68% and 34.19% compared to other fuels perform better. The overall results of the 4E analysis for MSW fuel show that the overall energy and exergy efficiency of the polygeneration system is 39% and 32.01%, respectively. Power generation costs and environmental impacts for MSW biomass are 0.014 $/kWh and 0.002 Pts/kWh, respectively. The monthly analysis of the studied system for all three fuels shows that the net power generation decreases in the summer months. The results of the sensitivity analysis of the studied system show that the optimal design of gasification temperature, air compressor pressure ratio, condenser pressure, and the number of MED effects play a key role in the objective functions of the studied system.

CFD investigation of the complex multiphase flow of biomass gasification in industrial-scale dual fluidized bed reactor

In this work, the process of biomass steam-gasification via a dual fluidized bed with a thermal input of 8MWth is numerically modeled by applying the multiphase particle-in-cell method. This model is successfully validated with the experimental data. Based on the simulation, the results can be epitomized as: distinct fluidization regimes in gasifier and combustor reactors give rise to different flow pattern and dispersion coefficients of solid phase in both reactors. Large particle heat transfer coefficients mainly appear in the upper regions of both reactors due to violent reactions. In this industrial-scale apparatus, the time-averaged heat transfer coefficient of sand in the combustor is larger than that of gasifier sand for about 40 W/(m2·K). Relationships between key variables such as volume fraction, heat transfer coefficient, slip velocity, Reynolds number and temperature of solid phase are discussed. Particles with small volume fraction tend to possess large heat transfer coefficient and slip velocity. The results explored at the particle-level might be useful in the industrial operating regarding the biomass steam-gasification processes.