Pilot-scale Test Rig Research Articles

Numerical calculation of wall-to-bed heat transfer coefficients in Geldart B bubbling fluidized beds with immersed horizontal tubes

In dense solid-gas fluidized beds the knowledge of the wall-to-bed heat transfer is of great importance, since it often dominates reactor design and dimensioning. This heat transfer is strongly coupled to the hydrodynamic behavior of the bed material around the immersed objects. In this study the heat transfer coefficient at horizontal tubes in a Geldart B bubbling fluidized bed is determined experimentally and compared to the numerically predicted flow fields. The objective is to improve the understanding and quantify the coupling between hydrodynamics and heat transfer. The findings are applied to derive and verify a numerical-correlative approach for predicting the angle-dependent heat transfer coefficient. Experimental data are obtained from a pilot scale test-rig with different tubular heat transfer probes. Corundum is used as the solid bed material and air as the fluidization gas, entering the cylindrical geometry through a Tuyere nozzle type distributor. The angle-dependent heat transfer coefficient is measured at different superficial gas velocities and probe positions in the bed and compared to three dimensional numerical simulations. The applied CFD model of the fluidized bed treats both gas and powder as Eulerian phases. The size distribution and the shape of the particles is described by two granular phases with corresponding mean diameters and a sphericity factor. The Kinetic Theory of Granular Flow and a sphericity-adapted drag model are incorporated to consider the fluid-solid and solid-solid interactions. The hydrodynamics at the tube surface resulting from the numerical simulations (solid volume fraction, gas velocity and particle velocity fluctuation) are used for correlative calculations of the angle-dependent heat transfer coefficient between the bed material and the immersed tube. Results show that the CFD model is able to predict the magnitude and the tendency of the heat transfer around horizontal tubes correctly and therefore can be used as a valuable tool for designing heat exchanger structures in fluidized bed reactors.

Numerical Study of the Pyrolysis of Ellipsoidal Low-Rank Coal Briquettes

Low-rank coal (LRC) upgrading is essential to convert LRC to a more thermal-efficient and environmentally friendly fuel before utilization in coal-based industries. Briquetting and pyrolysis are the dominant route, where briquettes are usually in the shape of an ellipsoid through a two-roll briquetting process. In this work, an integrated numerical model is developed to predict the pyrolysis process of ellipsoidal LRC briquettes in a packed-bed pyrolyzer. A computational fluid dynamics (CFD) model is developed to describe the flow and thermochemical behaviors related to the pyrolysis of ellipsoidal LRC briquettes, including dewatering, pyrolysis, and other homo- and heterogeneous chemical reactions. A discrete element method (DEM) model is used to describe the packing density distribution of ellipsoidal briquettes. The model is validated against the measurements in a pilot-scale test rig in terms of the temperature history and gas species yields. Typical in-furnace phenomena are illustrated, including flo...

Hydrodynamics and heat transfer around a horizontal tube immersed in a Geldart b bubbling fluidized bed

In dense gas–solid fluidized beds the heat transfer to immersed objects is strongly coupled to the hydrodynamic behavior. The objective of this study is to experimentally and numerically assess the heat transfer coefficient around a horizontal tube in a Geldart B bubbling fluidized bed and derive a numerical-correlative approach for predicting the angular dependent heat transfer coefficient. The considered system consists of corundum as the solid bed material and air as the fluidization gas, entering the cylindrical geometry through a Tuyere nozzle distributor. Experimental data are obtained from a pilot scale test-rig with different tubular heat transfer probes and evaluated in a comprehensive uncertainty analysis. The resulting magnitude and angle dependent variations of the heat transfer coefficient at different superficial gas velocities are compared to three dimensional numerical simulations. The applied CFD model of the fluidized bed treats both gas and powder as Eulerian phases. The size distribution of the particles is described by two granular phases with corresponding mean diameters and a sphericity factor to account for their non-spherical shape. The fluid–solid interactions in this Multi Fluid Model are considered by incorporating the Kinetic Theory of Granular Flow and a sphericity-adapted drag model. The hydrodynamics at the tube surface, e.g. solid volume fraction, gas and particle velocities, are used for a novel numerical-correlative calculation of the angle dependent heat transfer coefficient between the bed material and the immersed tube. Special focus is set on depicting the particle contact time at the tube surface appropriately. The numerical results show the correct tendency of an increasing heat transfer coefficient with rising gas velocity and are partially in good agreement with the experimental observations.

Comparative Study on the Combustion Performance of Coals on a Pilot-Scale Test Rig Simulating Blast Furnace Pulverized Coal Injection and a Lab-Scale Drop-Tube Furnace

Direct evaluation of the combustibility of pulverized coals in ironmaking blast furnace pulverized coal injection (PCI) is difficult. A pilot-scale PCI rig may be used to test the combustion performance of a PCI coal. However, the replication of the conditions in the blowpipe–tuyere–raceway region is complicated and costly. Drop-tube furnaces (DTFs), which have been widely used in coal combustion research, are seen as an alternative to such combustion tests. This study therefore compares coal combustion performances in a DTF and a PCI rig, where the coal is burned at the as-ground size distribution to assess the suitability of a DTF to replace a PCI rig. In addition, this study tries to establish the methodology for ranking the PCI coal combustion performance through coal burnouts produced in the DTF. The measured burnouts from both the DTF and the pilot-scale PCI rig produced a linear relationship against the coal volatile matter (VM) content, although the trend of the DTF burnouts have a steeper slope. ...

Mass Transfer Characteristics of Gypsum-Fly Ash Slurry for Wet Flue Gas Desulfurization

In the limestone/gypsum wet flue gas desulfurization pilot-scale test rig, key parameters such as SO2 absorption rate, mass transfer were experimentally determined．The results show that desulphurizing capacity of gypsum and fly ash is relatively weaker, which is only equivalent to fresh limestone with a content of 0.27% and 1.5% respectively. pH-t curve of slurry with different levels of fly ash could be divided into a sharply increasing stage and a steadily increasing stage. The leaching content of Mn2+ is about 9 times of Fe3+ , Mn2+ can form intermediate complex with HSO3- in the solution, which can induce catalytic reaction and accelerate SO2 absorption. Fly ash in gypsum slurry can obviously promote desulfurization. The pH value of slurry is high at the initial reaction stage, and effect of fly ash on SO2 absorption rate is less than 1.5%. when the pH value is decreased to 5.0, The leaching content of Mn2+ will grow with the decrease of pH value, better catalytic efficiency can be gained, effect of fly ash on SO2 absorption rate can increase 6.0% at most. The reaction is controlled by liquid phase resistance; the ratio of gas phase resistance to overall resistance is less than 38%. Mn2+ concentration of slurry increases with pH value decreasing and fly ash concentration increasing, which has significant effect on catalyzed oxidation of SO32-.

Oxy-fuel circulating fluidized bed combustion in a small pilot-scale test rig

Coal combustion under the elevated partial pressure of oxygen in a circulating fluidized bed environment was investigated. The fuel used was bituminous coal. The concentration of oxygen in the air was increased to 35% per volume. Excess oxygen ranged from 1.1 to 1.3 and the temperature ranged from ca. 1073 K to 1273 K. A 0.1 MW th CFB combustor was adapted for oxy-combustion. The conversion ratios respectively studied were: carbon, sulfur and nitrogen to CO, SO 2 and NO X. An increase of nitrogen and sulfur conversion ratios and a strong decrease of incomplete combustion losses were found under the oxygen-enriched conditions. Moreover, a strong increase in temperature was noticed during oxy-combustion.

A micro-structured 5kW complete fuel processor for iso-octane as hydrogen supply system for mobile auxiliary power unitsPart II—Development of water–gas shift and preferential oxidation catalysts reactors and assembly of the fuel processor

Abstract Microstructured reactors for water–gas shift and the preferential oxidation of carbon monoxide were developed for a fuel processing/fuel cell system running on iso-octane and designed for an electrical power output of 5 kWel. The target application was an automotive auxiliary power unit (APU). The work covered both catalyst and reactor development. A platinum/ceria catalyst was applied for water–gas shift, while platinum on zeolite/alumina carrier served as catalyst for preferential oxidation. These catalysts were introduced into the final full size prototype reactors, which were constructed from microstructured stainless steel foils. Testing in a pilot scale test rig revealed conversion close to the thermodynamic equilibrium for the water–gas shift reactors at a WHSV range of 17–41 Ndm3/(h gcat). The preferential oxidation, which was performed at higher WHSV in the range of 48–98 Ndm3/(h gcat) revealed up to 90% conversion in a first stage, while in the second stage reactor the carbon monoxide content of the reformate was decreased to less than 50 ppm. The reactors were then incorporated into a complete bread-board fuel processor of 5 kWel power equivalent, which comprised also of an autothermal reformer reactor. The fuel processor was operated at a steam to carbon ratio of 3.3 and an oxygen to carbon ratio of 0.67. Under these conditions, it converted the iso-octane feed completely to purified reformate with an overall efficiency of 74%.

A micro-structured 5kW complete fuel processor for iso-octane as hydrogen supply system for mobile auxiliary power unitsPart I. Development of autothermal reforming catalyst and reactor

A micro-structured autothermal reformer was developed for a fuel processing/fuel cell system running on iso-octane and designed for an electrical power output of 5 kWel. The target application was an automotive auxiliary power unit (APU). The work covered both catalyst and reactor development. In fixed bed screening, nickel and rhodium were identified as the best candidates for autothermal reforming of gasoline. Under higher feed flow rates applied in microchannel testing, a catalyst formulation containing 1 wt.% Rh on alumina prepared by the sol–gel synthesis route proved to be stable at least in the medium term. This catalyst was introduced into the final prototype reactor designed to supply a 5 kW fuel cell, which was based upon micro-structured stainless steel foils. The reactor was optimised for equipartition of flows by numerical simulation. Testing in a pilot scale test rig, which was limited to a specified power equivalent of 3.5 kWel, revealed more than 97% conversion of gasoline at 124 Ndm3/min total flow-rate of reformate, which corresponded to a WHSV of 316.5 Ndm3/(h gcat).

Intrusion within a Simulated Water Distribution System due to Hydraulic Transients. II: Volumetric Method and Comparison of Results

A pilot-scale test rig was used to simulate intrusion behavior associated with hydraulic transient initiated by rapid valve closure in a water distribution system. In Part I, the test rig apparatus and operating conditions were described and intrusion volumes were reported based on a chemical tracer and mass balance calculations. In this paper, the experimental study is extended to determine intrusion volumes by a volumetric method that used video recordings of water fluctuations in the observation column. The results obtained using the volumetric and chemical tracer methods were compared to theoretical calculations. Intrusion volumes associated with a 12.7-mm ~1/2-in.! diam orifice were evaluated in addition to 3.2 ~1/8-in.! and 6.4-mm ~1/4-in.! orifices. The impact of the external head on the intrusion volume was also assessed by comparing results using 0.91 ~ 3f t! versus 1.37 m ~4.5 ft! of external head. The average intrusion volumes obtained using the volumetric approach ranged from 47.3 to 550.2 mL. These volumes were 64 -298% greater than intrusion volumes determined by the chemical tracer method reported in Part I. However, the theoretical calculations indicate that the volumetric approach could underestimate intrusion volumes by as much as 50%.

Intrusion within a Simulated Water Distribution System due to Hydraulic Transients. I: Description of Test Rig and Chemical Tracer Method

A pilot-scale test rig was designed and constructed to simulate intrusion behavior associated with hydraulic transients initiated by sudden events such as rapid valve closure or uncontrolled change in on/off pump status (“pump trip”) in a water distribution system. After establishing steady state flow conditions, intrusion volumes were determined for 3.2 (1/8-in.) and 6.4 mm (1/4-in.) diam orifices overlaid with a column of water that provided 91 mm (3 ft) of external head. Average intrusion volumes associated with hydraulic transient events were determined by mass balance calculations using cesium as the tracer chemical. Average intrusion volumes were 11.4 and 71.2 mL for the two diameters, respectively. Given similar conditions in a water distribution system (i.e., an available pathway and favorable pressures), pathogens in the soil and water surrounding a water main potentially can intrude into the pipe during short-term pressure transient events.

The Role of the Filter Cake in Hot Gas Cleaning with Ceramic Filters

Experiments were carried out in a pilot-scale test rig at temperatures of 600−770 °C to investigate the potential of filter cakes formed in hot gas filtration to remove sulfur dioxide, nitric oxide, and alkalis. The results demonstrate that a filter cake of fly ash particles is capable of contributing to SO2 capture, particularly with injection of a fresh sorbent. A filter cake of mixed limestone and alumina particles formed at 600 °C showed a higher resistance to flow than one formed at 700 °C. The efficiency of SO2 removal increased with the temperature over the range investigated. Both the cake and filter absorbed alkalis by chemical reaction, showing that the filter cake will help to protect the gas turbine, as well as the filter itself, against alkali attack. NOx emissions were not affected by the presence of the filter in an oxidizing atmosphere, while a considerable reduction of NO was obtained in the presence of CO.

Influence of coal quality on combustion performance

Three coals have been fired in a tangentially and an opposed fired full scale power plant (about 400 MW e) and in a pilot scale test rig (160 kW t) in order to investigate the influence of coal quality on nitrogen oxide (NO) formation and unburned carbon in relation to furnace design. In-flame and furnace gas temperatures have been measured, and substantial differences in temperature between the coals were observed in the full scale furnaces. Identical trends in NO emission as a function of coal type were obtained for the three furnaces. The emissions correlated well with the high temperature volatile yield obtained from heated wire mesh analysis. Under air staging conditions the pilot scale test rig was able to reproduce quantitatively the amount of NO from the tangentially fired plant, which operates with over fire air. This is probably due to the relatively small influence of the near burner mixing pattern on NO formation under these conditions. Emissions from the opposed fire plant with all combustion air introduced through the burners could only be qualitatively reproduced by the pilot furnace. Under single stage conditions the test rig provided higher NO levels. Carbon in ash levels did not show any correlation between the coals and the furnaces. An engineering, mathematical model has been developed describing radiation heat transfer and coal combustion in full scale furnaces. The model has been validated against measured temperatures and the amount of carbon in fly ash. The model was well able to predict average temperature and carbon in ash levels, but failed to predict the influence of coal quality on both temperature and carbon in ash. This may be due to a lack of knowledge on char reactivity and deactivation as a function of temperature and coal type. A brief parametric study has been performed on important model parameters.

Nitrogenous emissions from the delft pressurized fluidized bed combustor

Experimental and theoretical work on Pressurized Fluidized Bed Combustion (PFBC) of coal are main topics at the Laboratory for Thermal Power Engineering of the Delft University of Technology, The Netherlands. A sub pilot scale test rig is used operating at pressures up to 10 bar and a maximal thermal capacity of 1.6 MW. At present, emphasis is laid on chemical reactions within the combustor which play a role in the formation and destruction of CO, CO 2, NO, N 2O, NO 2 and SO 2. In the freeboard, downstream of the first cyclone and in the stack of the PFBC test rig gas concentrations have been measured using specially developed systems for flue gas sampling. Gas analysis has been performed using conventional gas analysis instruments and a Fourier Transform InfraRed (FT-IR) spectrometer. The effect of ammonia injection in the exhaust of the combustor (SNCR) and staged combustion on the emissions was determined.