Federal Energy Technology Center Research Articles

Computer simulations of gas–solid flow in spouted beds using kinetic–frictional stress model of granular flow

A gas–solid two-fluid flow model is presented. The kinetic–frictional constitutive model for dense assemblies of solids is incorporated in the simulations of spouted beds. This model treats the kinetic and frictional stresses of particles additively. The kinetic stress is modeled using the kinetic theory of granular flow, while the friction stress is from the combination of the normal frictional stress model proposed by Johnson et al. (J. Fluid Mech. 210 (1990) 501) and the modified frictional shear viscosity model proposed by Syamlal et al. (MFIX documentation. US Department of Energy, Federal Energy Technology Center, Morgantown, 1993). The body-fitted coordination is used to make the computational grids best fit the shape of conical contour of the base in the spouted beds. The effects of inclined angle of conical base on the distributions of particle velocities and concentrations in the spout, annulus and fountain zones were numerical studied. Calculated particle velocities and concentrations in spouted beds were in agreement with experimental data obtained by He et al. (Can. J. Chem. Eng. 72 (1994a) 229; (1994b) 561) and San Jose et al. (Chem. Eng. Sci. 53 (1998) 3561).

Biomass cofiring: the technology, the experience, the combustion consequences

Cofiring, the practice of supplementing a base fuel with a dissimilar fuel, is an extension of fuel blending practices common to the solid fuels community. Recently, there has been considerable emphasis on cofiring biomass opportunity fuels with coal in pulverized coal (PC) and cyclone boilers owned and operated by electricity generating utilities in order to address such issues as potential portfolio standards, voluntary actions to reduce fossil CO 2 emissions, customer service, and the generation of green power within the context of deregulation. Biomass fuels considered for cofiring include wood waste, short rotation woody crops, short rotation herbaceous crops (e.g., switchgrass), alfalfa stems, various types of manure, landfill gas and wastewater treatment gas. Of these, the solid biofuels such as sawdust, urban wood waste and switchgrass have received the most attention. The Electric Power Research Institute (EPRI), along with the Tennessee Valley Authority (TVA), GPU Genco, Northern Indiana Public Service Company (NIPSCO), Central and South West Utilities (C&SW), Southern Company, Madison Gas & Electric (MG&E), New York State Electric and Gas (NYSEG) and others developed a concerted effort to commercialize direct combustion cofiring of biomass with coal. The USDOE joined the program with a cooperative agreement between the Federal Energy Technology Center (FETC) — now the National Energy Technology Laboratory (NETL) and EPRI; this agreement was extensively supported by the energy efficiency and renewable energy (EERE) element of USDOE. European cofiring programs also have been extensive and include gasification-based cofiring in Lahti, Finland and straw cofiring in Denmark. Three general techniques comprise the cofiring technology family: blending the biomass and coal in the fuel handling system and feeding that blend to the boiler; preparing the biomass fuel separately from coal, and injecting it into the boiler without impacting the conventional coal delivery system; and gasifying the biomass with subsequent combustion of the producer gas in either a boiler or a combined cycle combustion turbine (CCCT) generating plant. Commercialization has proceeded on the direct combustion approaches to cofiring, beginning with engineering and economic studies, parametric testing and the construction of demonstration projects. The direct combustion cofiring techniques are now ready for commercial deployment. This paper reviews the key projects, and details some of the influences of cofiring on the combustion process.

An integrated fine coal preparation technology: the GranuFlow Process

In order to alleviate the problems of fine coal handling and processing and to enhance the utilization of fines by utilities, US Department of Energy's (DOE's) Federal Energy Technology Center (FETC) developed and patented the GranuFlow Process. This paper summarizes recent test results of the GranuFlow Process with pilot-scale and plant-scale centrifuges in commercial plants. The main benefits of the GranuFlow Process are that it can potentially reduce the amount of waste coal that is stored in refuse impoundments, reduce the moisture content of the final clean coal product, improve handling by converting wet sticky fines to a granular, free-flowing material, prevent frozen coal problems in rail cars, and reduce the dustiness and fugitive dust losses during transportation and handling. Since Orimulsion is a low cost bitumen emulsion, this technology provides the coal industry with a cost-effective technology for fine coal processing.

Mercury Measurement and Its Control: What We Know, Have Learned, and Need to Further Investigate

ABSTRACT The U.S. Department of Energy (DOE), through the Federal Energy Technology Center (FETC), manages the largest funded program in the country for developing (1) an understanding of mercury emissions, (2) measurement of these emissions, and (3) control technology (-ies) for these emissions for the U.S. coal-fired electric generating industry. DOE has initiated, or has collaborated with other government and industrial organizations in, these and other efforts relating to mercury and other hazardous air pollutants (HAPs), also known as air toxics. One of DOE's first reports on trace elements in coal was conducted from 1976 through 1978 by researchers at DOE's Pittsburgh Energy Technology Center (PETC, now FETC) and the Pittsburgh Mining Operations of the Department of the Interior's Bureau of Mines. The report was completed less than two years after DOE was formed, and 13 years before Title III of the 1990 Clean Air Act Amendments was enacted (Cavallaro et al., March 1978).

The use of coal liquefaction catalysts for coal/oil coprocessing and heavy oil upgrading

The catalytic hydrogenation of heavy oil and mixed coal-heavy oil (coprocessing) systems has been the focus of a recent study at the Federal Energy Technology Center (FETC). The intent of this effort was to extend the use of coal liquefaction technologies to heavy oil upgrading and coprocessing systems. Specifically, new dispersed molybdenum-based catalysts developed at FETC and a novel silica-doped hydrous titanium oxide (HTO : Si)-supported NiMo catalyst developed at Sandia National Laboratories (SNL) were tested in these systems. The results indicate the potential of coal liquefaction catalysts for use in coprocessing and heavy oil upgrading. High conversions of coal–oil mixtures were observed with dispersed catalyst loadings as low as 100 ppm Mo. Similar results were observed in heavy oil systems. Also, the novel NiMo/HTO : Si catalyst was at least as effective as commercially-available supported catalysts (e.g. Amocat 1C) for conversion of high boiling point material to distillable products and aromatics removal.

Analysis of operational filtration data Part II: Incomplete cleaning of candle filters

Abstract A model has been developed for hot-gas filtration by candle filters, which includes incomplete removal of the filter cakes by the cleaning backpulses of compressed air. Operational data from the filtration system of the Integrated Gasification and Cleanup Facility at the Federal Energy Technology Center were analyzed with the model and used to estimate the cake permeability, thickness of cake left on the filter after each backpulse, and total cake thickness vs. time. The statistical R 2 for the fit of the incomplete-cleaning model was 0.93, compared to the R 2 = 0.78 previously obtained for a fit of the ‘ideal filtration’ model to the same data set.

A sorbent regenerator simulation model in copper oxide flue gas cleanup processes

AbstractSorbent regeneration is an important step in copper oxide flue gas cleanup processes because poor regeneration performance could require higher sorbent circulation rate and inventory, resulting in increased process costs. This article describes a countercurrent moving‐bed regeneator model using natural gas as the reducing agent. The model incorporates several aspects important for predicting the regenerator performance, such as gas expansion effects, deviation from first‐order kinetics with respect to copper sulfate, and mass transfer limitations. The sorbent residence time predicted by this model is in good agreement with data obtained from the life‐cycle test system at the Federal Energy Technology Center. The tests conducted include effects of reactor temperature, the methane to copper sulfate feed ratio, and sorbent residence time, on sorbent regeneration. The regenerator modeling also details the impact of gas velocity on the reactor performance.

Particle Transport and Deposition in a Hot-Gas Cleanup Pilot Plant

ABSTRACT Development of hot-gas filtration systems for advanced clean coal technologies has attracted considerable attention in recent years. The Integrated Gasification and Cleanup Facility (IGCF), which is an experimental pilot plant for testing performance of ceramic candle filters for hot-gas cleaning, has been operational at the Federal Energy Technology Center (FETC) in Morgantown, West Virginia, for several years. The present work describes a computer simulation study of gas flow and particle transport and deposition in the IGCF filter vessel with four filters. The stress transport model of FLUENT™ code is used for evaluating the gas mean velocity and the root mean-square fluctuation velocity fields in the IGCF filter vessel. The instantaneous fluctuation velocity vector field is simulated by a filtered Gaussian white-noise model. Ensembles of particle trajectories are evaluated using the recently developed PARTICLE code. The model equations of the code include the effects of lift and Brownian moti...

Analysis of Operational Filtration Data Part III: Re-entrainment and Incomplete Cleaning of Dust Cake

ABSTRACT Operational data for the hot-gas filtration system of the Integrated Gasification and Cleanup Facility (IGCF) at the Federal Energy Technology Center are carefully analyzed. A model that includes re-entrainment of filter-cake fragments following cleaning of the candle filters, as well as incomplete removal of cake from the filters by the cleaning backpulses of compressed air, is developed and used to interpret the data. The parameters of the model are evaluated with a least-square error fit procedure. It is shown that inclusion of the re-entrainment model significantly improves the fit to the data during the short interval (∼50 s after each backpulse) during which re-entrainment is predicted to occur by particle-transport modeling. The re-entrainment/incomplete-cleaning model is used to evaluate the buildup of filter-cake thickness and the filter-cake permeability. Both effects were significant for the data analyzed.

Formation and Measurement of the Porosities, Tensile Strengths, and Deformation Coefficients of Gasification Filter Cakes at Operating Temperatures and Pressures

ABSTRACT Various physical properties of filter cakes formed and studied at operating temperatures and pressures and under appropriate gas compositions and flow rates are important for the development of hot-gas filtration for integrated gasification combined cycle (IGGC) use of coal. Elutriated particles from a gasification pilot plant at the Federal Energy Technology Center of the U.S. DOE were used in a laboratory-scale apparatus to prepare filter cakes at various gas-flow velocities and over a range of temperatures (25–515 °C) and pressures (100–300 kPa) characteristic of the pilot plant. This laboratory apparatus also was used to measure the porosities, tensile strengths, and deformation coefficients of the cakes at these same temperatures and pressures. Various properties of the filter cakes have been correlated. It is believed that the novel experimental methods and interpretational model employed allow accurate laboratory measurement of these filter-cake properties for the operating conditions of large-scale plants, for use in engineering models of operating data and in theoretical models of filter-cakes and filter-cleaning.

Analysis of operational filtration data part I. Ideal candle filter behavior

Operating data for the hot-gas filtration system of the Integrated Gasification and Cleanup Facility (IGCF) at the Federal Energy Technology Center are carefully analyzed. A model for candle filters is developed and used to describe the ideal filtration process. The parameters of the model are evaluated with a least-square error fit procedure. It is shown that the model predicts the time variation of the pressure drop with reasonable accuracy. The model is used to evaluate the buildup of filter-cake thickness and the filter-cake permeability.

THE USE OF COAL COMBUSTION RESIDUES TO CONTROL ACID MINE DRAINAGE

The Federal Energy Technology Center of the U.S. Department of Energy is monitoring changes in water quality at three inactive mining sites where a coal combustion residue (fly ash) was injected into the spoil to control the production of acid mine drainage. Since most combustion residues are alkaline, their addition to the subsurface environment raises the pH, limiting the propagation of pyrite oxidizing bacteria and reducing the rate of acid generation. Grouts of fly ash, lime and cement, when injected underground, decrease permeability and porosity diverting water away from the pyritic material. Both mechanisms, alkaline addition and water diversion, are expected to reduce the amount of acid produced. Changes in water quality parameters (pH, acidity, anions and cations) in water samples from wells and seeps are monitored to assess the effect of CCR injection. The concentration of heavy metals in the water flowing through the sites, before and after CCR injection, is also determined. The use of underground mine sites for disposal of coal combustion residues provides a stable, low maintenance alternative to landfills, benefitting the missing and electric power industries.

96/04446 Predicting the effects of changes in thermal envelope characteristics on energy comsumption: Application and verification of a simple model for Australlan and Canadian climates

In order to alleviate the problems of fine coal handling and processing and to enhance the utilization of fines by utilities, US Department of Energy's (DOE's) Federal Energy Technology Center (FETC) developed and patented the GranuFlow Process. This paper summarizes recent test results of the GranuFlow Process with pilot-scale and plant-scale centrifuges in commercial plants. The main benefits of the GranuFlow Process are that it can potentially reduce the amount of waste coal that is stored in refuse impoundments, reduce the moisture content of the final clean coal product, improve handling by converting wet sticky fines to a granular, free-flowing material, prevent frozen coal problems in rail cars, and reduce the dustiness and fugitive dust losses during transportation and handling. Since Orimulsion is a low cost bitumen emulsion, this technology provides the coal industry with a cost-effective technology for fine coal processing.