P. Vann Bush

Laboratory analyses of corona discharges

Abstract An experimental research program was conducted to characterize corona generation from different electrode geometries in a range of conditions comparable to those found in electrostatic precipitators. A wire-parallel plate device and a wire-cylinder device were used to monitor the spatial distribution and temporal stability of corona discharges. Visual observations of corona phenomena were made with a sensitive video camera. Conditions that were varied in the experiments included temperature, corona electrode design, corona polarity, and method of energization. Measurements of the distributions of corona current and statistical analyses permit an assessment of the impact of corona electrode design on electrostatic precipitator performance. A description of the laboratory apparatus and a summary of experimental results is included.

Effects of Sorbent Injection on Particulate Properties: Part II. High-Temperature Sorbent Injection

Abstract This article is the first of a two-part series dealing with the effects of sorbent injection processes on particulate properties. Part I reviews the effects on particulate properties of low-temperature sorbent injection processes (those processes that treat flue gas at temperatures near 300 °F). Part II reviews the effects on particulate properties of high-temperature sorbent injection processes (those processes that involve sorbent injection into the combustion or economizer sections of a boiler). In this article, we review what is currently known about the effects of the low-temperature sorbent injection processes on electrical resistivity, particulate mass loading, particulate size distribution, particulate morphology and cohesivity. Mixtures of ash and sorbent produced by low-temperature sorbent injection processes are typically less cohesive than most types of fly ash. At temperatures within 30 °F of the water dew point, the combination of low cohesivity and low electrical resistivity of the...

Advanced CFD Post-Processing for Pulverized Fuel Flame Structure and Emissions

The simulation strategy described in this paper provides an alternative to conventional CFD post-processing to estimate exhaust NOX emissions. The method first analyzes a CFD furnace simulation to specify temperature histories and mixing rates. Then the bulk flow patterns are represented with an equivalent network of idealized reactor elements. Detailed reaction mechanisms are then applied over the reactor network, including the most fully validated reaction mechanisms for coal devolatilization and char oxidation and complete elementary reaction mechanisms for chemistry in the gas phase and in soot. The analysis predicted the NOX emissions from 1.7 MWt pilotscale flames of coal and coal/biomass blends within experimental uncertainty over a broad range of O2 concentrations, with and without staging. The predicted unburned carbon emissions were qualitatively correct, but char reactivity parameters would need to be specified in a one-point calibration for quantitative predictions. The analysis also characterized distinctive chemistry within the flame core, a mixing layer for secondary air entrainment, an overfire air zone, and a char burnout zone. The main practical benefit of the mechanistic complexity is that simulations based on detailed mechanisms require fewer parameter adjustments than CFD simulations whenever different fuels are considered.Copyright

Determination of Baghouse Performance from Coal and Ash Properties: Part I

Baghouse performance at utility coal-fired power plants is determined by baghouse design, operating procedures, and the characteristics of the ash that is collected as a dustcake on the fabric filter. The Electric Power Research Institute has conducted laboratory research to identify the fundamental properties of dustcake ash that influence baghouse performance. A database was assembled including measured characteristics of dustcake ash and data describing operating parameters and performance of full-scale and pilot-scale baghouses. Semi-empirical models were developed that describe the effects of particle morphology, particle size, ash cohesivity and ash chemistry on filtering pressure drop and particulate emissions. Cohesivity was identified as the primary ash characteristic affecting baghouse performance. Predictions of performance can be based on physical or chemical characterizations of the ash to be filtered. Part II of this article will discuss the effects of ash and coal chemistry, and baghouse de...

Laboratory analysis of back-corona discharge

Abstract An experimental research program was designed and performed to characterize back-corona generation and behaviour in a range of environments and geometries common to electrostatic precipitators (ESPs). A wire-parallel plate device was utilized to monitor the intensity and distribution of back-corona discharges. Back-corona was generated by subjecting a deposited layer of fly ash to corona current. Visual observations of back-corona emissions were made with a sensitive video camera. These observations provided new insight into the characteristics of back-corona phenomena. Conditions that were varied in the experiments included ash resistivity, corona electrode design, corona polarity, and ash-layer thickness and surface condition. The effect of pulsed energization on back-corona was also studied. Analyses of visual observations and measured distributions of corona- and back-corona current allowed an assessment of the effects of back-corona emissions on ESP-operating parameters.

DEVELOPMENT OF A VALIDATED MODEL FOR USE IN MINIMIZING NOx EMISSIONS AND MAXIMIZING CARBON UTILIZATION WHEN CO-FIRING BIOMASS WITH COAL

This is the eighth Quarterly Technical Report for DOE Cooperative Agreement No. DE-FC26-00NT40895. A statement of the project objectives is included in the Introduction of this report. The final biomass co-firing test burn was conducted during this quarter. In this test (Test 14), up to 20% by weight dry switchgrass was comilled with Jim Walters No.7 mine coal and injected through the single-register burner. Jim Walters No.7 coal is a low-volatility, low-sulfur ({approx}0.7% S) Eastern bituminous coal. The results of this test are presented in this quarterly report. Progress has continued to be made in implementing a modeling approach to combine reaction times and temperature distributions from computational fluid dynamic models of the pilot-scale combustion furnace with char burnout and chemical reaction kinetics to predict NO{sub x} emissions and unburned carbon levels in the furnace exhaust. The REI Configurable Fireside Simulator (CFS) is now in regular use. Presently, the CFS is being used to generate CFD calculations for completed tests with Powder River Basin coal and low-volatility (Jim Walters No.7 Mine) coal. Niksa Energy Associates will use the results of these CFD simulations to complete their validation of the NOx/LOI predictive model. Work has started on the project final report.

Status and Future of Baghouses in the Utility Industry

Abstract The cumulative years of service of baghouses in the electric utility industry have doubled since the last industrywide review of their operating performance. We have gathered information from all 102 operating baghouses to develop an updated record of how this technology continues to serve the electric utility industry. In general, baghouse performance has met or exceeded the expectations for controlling emissions. There are, however, wide ranges of pressure drop and bag life performance. Most operators report a long-term trend of increasing pressure drop. The life expectancy of filter bags averages 7.5 years, with more than 20% of the population achieving more than 10 years of bag life. Factors such as coal and ash properties certainly affect baghouse operation, but another reason for variations in bag life is the lack of an optimized protocol for controlling the long-term buildup of residual dustcake. We conclude that many baghouses could operate with lower pressure drop and longer bag life by ...

Filtration Properties of Fly Ash from Fluidized Bed Combustion

Some of the features of the fluidized-bed combustion (FBC) process have a direct bearing on the particulate properties that most strongly influence filtering pressure drop. A laboratory program was conducted to experimentally determine the relative pressure drop characteristics of ashes from the TVA-EPRI 20-MW bubbling bed, atmospheric pressure FBC (AFBC) pilot plant and six pulverized-coal combustion (PC) units. The combined influences of measured particle and dust cake properties on filtering pressure drop were estimated with existing filtration theories. These theories predict a higher pressure drop for a dust cake produced with the AFBC ash than for one consisting of any of the PC ashes. Laboratory measurements were made of the flow resistance of idealized, simulated dust cakes to confirm these predictions. Field operating data from the fabric filters collecting some of the tested ashes were available to validate the laboratory results. The laboratory and field data show relatively good agreement. The...

Performance of Large-Diameter Wires as Discharge Electrodes in Electrostatic Precipitators

Conventional practice in the design of corona discharge electrodes for electrostatic precipitators tends toward those having a relatively low corona Inception voltage. But the theory indicates that maximal electric field strength is beneficial to both charging and collection of particles. Only those particles smaller than about 0.2 μm diameter are more readily charged by increasing the ion current density instead of the electric field strength. Tests carried out on high-resistivity fly ash In a large pilot system (30,000 acfm) comparing performance of 3/8-in. diameter wires with more nearly conventional 1/8-in. wires resulted in substantially superior performance for the larger electrodes

An electrostatic precipitator backup filter for sampling systems

Abstract An alternative technique for filtering the aerosol effluent from particle sampling systems has been developed. A two-stage electrostatic precipitation system was designed to collect with high efficiency the paniculate material in a gas stream. The principal advantage of an electrostatic precipitator over conventional glass fiber backup filters is the ability to sample for long times without encountering filter pluggage or an excessive pressure differential across the system. Tests of a prototype electrostatic precipitator backup indicate collection efficiency for submicrometer diameter particles of 97 to greater than 99%.