Operating Conditions Gas Research Articles

Numerical simulation and verification of a gas-solid jet fluidized bed

From the Navier-Stokes equations and the Newtonian equations, which describe gas flow and the movement of a single particle respectively, a two-phase model describing gas-solid flow macroscopically in fluidized beds was derived by using volume averaging and the parameters of the model were determined. This general model can be reduced to several forms of simpler models reported in the literature. An improved interphase slip algorithm (IPSA) method based on finite volume approach was used in the solution of the model equations. The influences of the velocity of the central jet, height of the bed and superficial gas velocity in the bed on jet penetration height were obtained by numerical simulation. The computed flow patterns of the binary mixture were also obtained. The theoretical prediction was verified against the experiments made on a two-dimensional jet fluidized bed with both unitary and binary component materials. Under the operating conditions of an industrial ash-agglomerating coal gasifier, the arithmetical mean based upon particle number was introduced to calculate the mean diameter of the binary components. Thus the simulation of the binary components was simplified. All the computed jet penetration heights under various conditions were in good agreement with experimental and literature data.

Thermodynamic analysis of SOFC fuelled by biomass-derived gas

Abstract A thermodynamic evaluation of an integrated biomass catalytic gasifier-solid oxide fuel cell (SOFC) system has been made, as a preliminary approach to assess the technical feasibility of electrical energy production from a renewable source such as biomass. Equilibrium calculations have been made to predict conversion levels in a chemical reacting system including cellulose as a typical biomass feedstock and water vapor or CO 2 as the gasifying agent. The allowable electrical efficiencies of the cellulose product-gas-fuelled SOFC have been calculated for different gasifier operating conditions, namely H 2 O (CO 2 )/biomass ratio and gasifier operating temperature. For a gasifier temperature of 700°C, electrical efficiencies in the SOFC are 47% and 51% for steam (steam/biomass = 1.12) and CO 2 (CO 2 /biomass = 1.30), respectively.

Modelling of flow at Thulin underground coal gasification experiments

During the underground coal gasification experiments at Thulin, a series of tracer tests using 133xenon or helium as injected material were effected. These tests illustrated the hydrodynamics of the flow profile inside the underground reactor during the main operating periods: the series of reverse combustion tests and the gasification phase. The models developed to simulate the flow conditions are based on the material exchange between flowing fluid and the dead zone. The dead zone is represented either by a stagnant zone exchanging material with the flowing fluid in accordance with film theory or by a homogeneous porous zone exchanging material with the flowing fluid by pure molecular diffusion. With these models, excellent fits were obtained and physical significance of the parameters is possible in correlation with the gasifier operating conditions. The results show a little evolution of the flow conditions inside the underground reactor during the series of reverse combustion tests. On the other hand, during the gasification phase, the reactor volume calculated from the tracer results is proportional to the cumulative quantity of coal consumed.

CO2 gasification kinetics of two alberta coal chars

AbstractCO2 gasification kinetics of chars from two Alberta coals (Obed Mountain, high volatile bituminous and Highvale, subbituminous) have been studied using a thermogravimetric analyzer (TGA) and a fixed bed reactor. Charification and gasification reactions were performed sequentially in both the TGA instrument and in the fixed bed reactor to simulate real gasifier operating conditions. TGA and fixed bed data were processed numerically to evaluate the kinetic rate of CO2 gasification of the chars. Calculated gasification kinetics could be correlated using both the volume reaction and the grain models. Activation energies of the kinetic rate constants were near 200 kJ/mol for both Highvale and Obed Mountain coal chars using the TGA data. The activation energies calculated for the Obed Mountain coal char using the fixed bed reactor were about 250 kJ/mol. For all the cases studied the calculated activation energies were nearly the same for both the volume and grain reaction models.

Modeling and simulation of co-current moving bed gasification reactors — Part II. A detailed gasifier model

A detailed modeling program was developed for the simulation of co-current moving bed (down-draft) reactors fed carbonaceous materials. The model development consisted of formulating a non-isothermal particle model and applying the principles of thermodynamics, transport processes, hydrodynamics of solid and gas flows, and the mass and energy balances. The completed gasifier modeling program was used to simulate the reactor performance and to evolve the design criterion, specifically the dimension of the gasification zone. The gasifier model was validated using literature data. The dependence of reactor performance on operating variables (such as feedstock moisture contents, particle sizes, reactor insulation, input air temperatures and gasifier loads) has been studied with poplar wood chips as a feedstock. An increasing moisture content causes the feedstock conversion efficiency to decrease because of lower oxidation temperatures. Smaller particle size (not less than 0·5 cm), reactor insulation, and high input air temperature were all proven beneficial to gasifier operation. An increase of reactor load, causing a reduced residence time, resulted in declined efficiencies. However, the reactor can meet the demand variation by varying the air input rates. As for the design of the reactor dimension, a length of 100 cm below the primary air inlet is recommended for various gasifier operating and feedstock conditions.

Characterization of a Lignite Ash from the Metc Gasifier I. Mineralogy

AbstractUtilization or disposal of gasification ash requires detailed characterization of its chemistry and phase formation (mineralogy). A North Dakota lignite ash produced in the Morgantown Energy Technology Center (METC) gasifier has been studied in detail by x-ray diffraction and electron microprobe analysis. The ash was coarse (84% of grains larger than 1.0 mm) but a typical grain was composed of a dozen or more crystalline phases with dimensions on the micrometer scale as well as less abundant glass phases. Hard centimeter-size clinkers suggested partial melting followed by crystallization. Silicates (dicalcium silicates (C2S), merwinite, Ca-Na-silicate (CNS), quartz), aluminosilicates (melilite, nepheline, carnegieite), oxides (ferrite spinels, periclase, hematite), calcite and minor zeolites comprised the dominant mineralogy. Microprobe analyses were obtained for large numbers of grains of the C2S phases, CNS, merwinite, melilite, ferrite spinels and calcite. The remaining phases had crystal sizes too small for analysis. A model is proposed for the genesis of this ash based on the inorganic constituents of lignite and the gasifier operating conditions.