Sizing and Costing of Electrostatic Precipitators

This is the second of a two-part article that reviews electrostatic precipitation theory, presents size estimating methods, and gives costing procedures for a variety of electrostatic precipitator (ESP) types and sizes. Part I of the article, which appeared in the April 1988 issue of JAPCA, discussed theory and sizing; this part presents costing. Information is given for estimating total capital investment including separate costs for the bare ESP (five types) and auxiliaries. Factors are given for installation and for indirect costs. Direct and indirect annual costs are discussed. An example problem is given.     

Polyfunctional Plants for Industrial Waste Disposal—Part II: Economics and Model Evaluation

ABSTRACT

This is the second part of a two-part paper dealing with the preliminary design and costing of polyfunctional waste treatment plants. In this article, we present some criteria for estimating capital investment and annual operating costs of polyfunctional plants for industrial waste treatment. The process and equipment design methods presented in Part I of this article, together with the economic approach proposed here, allow for complete technical/economic analyses. The overall mathematical model appears to be a useful tool in economic feasibility studies. The accuracy of the developed computer mathematical model has been demonstrated, referring to actual cost data from the literature.     

Capital and Operating Costs of Selected Air Pollution Control Systems—V

Several methods are available for estimating the capital costs of systems and each has its own degree of accuracy. These methods range from presenting overall installed costs on a per unit basis, to detailed cost estimates based on preliminary designs, schematics, and contractor quotes. The least accurate method is the equating of overall capital costs to a basic operating parameter such as tons per hour or cfm since this method only produces accuracies in the "order of magnitude" category, at best. The detailed cost estimate, in turn, can produce accuracies of ±5 % depending on the amount of preliminary engineering involved. These estimates, however, take many months of engineering effort and require process and engineering flow sheets, material and energy balances, plot plans, and equipment arrangement drawings before a cost estimate can be developed. For first-cut estimating purposes, the technique described in this article for developing capital costs for a specific pollution control system is based on the factored method of establishing direct and indirect installations costs as a function of known equipment costs. The cost factors developed are based on both quoted and estimated installation costs of pollution control systems. The annual operating costs for these systems are based on unit costs for utilities and operating and maintenance labor together with fixed percentages of capital costs for the indirect costs.     

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 design and operation on performance.     

Effect of flow distributors on uniformity of velocity profile in a baghouse

In recent years, the utility industry has turned to baghouses as an alternative technology for particulate emission control from pulverized-coal-fired power plants. One of the more significant issues is to improve poor gas distribution that causes bag failures in baghouse operation. Bag failures during operation are almost impossible to prevent, but proper flow design can help in their prevention. This study investigated vertical velocity profiles below the bags in a baghouse (the hopper region) to determine whether flow could be improved with the installation of flow distributors in the hopper region. Three types of flow distributors were used to improve flow distribution and were compared with the original baghouse without flow distributors. Velocity profiles were measured by a hot-wire anemometer at an inlet velocity of 18 m/sec. Uniformity of flow distribution was calculated by the uniformity value U for the velocity profile of each flow distributor. Experimental results showed that the velocity profile of the empty configuration (without flow distributors) was poor because the uniformity value was 2.048. The uniformity values of type 1 (flow distributor with three vertical vanes), type 2 (flow distributor with one vertical and one inclined vane), and type 3 (flow distributor with two inclined vanes) configurations were reduced to 1.051, 0.617, and 0.526, respectively. These results indicate that the flow distributors designed in this study made significant improvements in the velocity profile of a baghouse, with the type 3 configuration having the best performance.     

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

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 variables that influence baghouse performance. A database was assembled including measured characteristics of coal and dustcake ash, and data describing operating parameters and performance of full-scale and pilotscale baghouses. Predictions of performance can be based on physical characteristics of the ash to be filtered (discussed in Part I of this article), as well as chemical characterizations of the ash, or empirical correlations with the alkali content of the source coal The effects of design and operational variables can be included in these predictions. Baghouse performance can be optimized by exercising proper operating practices and by selecting a filtering fabric and cleaning method matched to the cohesivity of the ash to be collected.     

Fabric Filter Technology for Utility Coal-Fired Power Plants

This is the sixth and last part in a series of papers discussing the experience of electric utilities in applying baghouse technology for the collection of particulate matter at coal-fired electric power generating plants. The series presents new data obtained in research sponsored by the Electric Power Research Institute (EPRI) on reverse-gas and shake/deflate cleaned baghouses, and specifically addresses a number of unresolved issues in the design and operation of these units. This paper discusses research, development and demonstration activities now underway or planned to further understand baghouse technology to ensure efficient, economic and reliable service in utility applications. In addition, it summarizes the major findings reported in Parts I through V.     

Effect of Flow Distributors on Uniformity of Velocity Profile in a Baghouse

Abstract

In recent years, the utility industry has turned to bag-houses as an alternative technology for particulate emission control from pulverized-coal–fired power plants. One of the more significant issues is to improve poor gas distribution that causes bag failures in baghouse operation. Bag failures during operation are almost impossible to prevent, but proper flow design can help in their prevention. This study investigated vertical velocity profiles below the bags in a baghouse (the hopper region) to determine whether flow could be improved with the installation of flow distributors in the hopper region. Three types of flow distributors were used to improve flow distribution and were compared with the original baghouse without flow distributors. Velocity profiles were measured by a hot-wire anemometer at an inlet velocity of 18 m/sec. Uniformity of flow distribution was calculated by the uniformity value U for the velocity profile of each flow distributor. Experimental results showed that the velocity profile of the empty configuration (without flow distributors) was poor because the uniformity value was 2.048. The uniformity values of type 1 (flow distributor with three vertical vanes), type 2 (flow distributor with one vertical and one inclined vane), and type 3 (flow distributor with two inclined vanes) configurations were reduced to 1.051, 0.617, and 0.526, respectively. These results indicate that the flow distributors designed in this study made significant improvements in the velocity profile of a baghouse, with the type 3 configuration having the best performance.     

The role of pressure drop and flow redistribution on modeling mercury control using sorbent injection in baghouse filters

A mathematical model based on simple cake filtration theory was coupled to a previously developed two-stage mathematical model for mercury (Hg) removal using powdered activated carbon injection upstream of a baghouse filter. Values of the average permeability of the filter cake and the filter resistance extracted from the model were 4.4 x 10(-13) m2 and 2.5 x 10(-4) m(-1), respectively. The flow is redistributed during partial cleaning of the filter, with flows higher across the newly cleaned filter section. The calculated average Hg removal efficiency from the baghouse is lower because of the high mass flux of Hg exiting the filter in the newly cleaned section. The model shows that calculated average Hg removal is affected by permeability, filter resistance, fraction of the baghouse cleaned, and cleaning interval.     

Electrostatic Stimulation of Fabric Filtration

The concept of electrostatic stimulation of fabric filtration (ESFF) has been investigated at pilot scale. The pilot unit consisted of a conventional baghouse in parallel with an ESFF baghouse, allowing direct comparison. All results reported in this paper are for pulse-cleaned bags in which the electric field was maintained parallel to the fabric surface. The performance of the ESFF baghouse has been superior to the parallel conventional baghouse by several measures. The ESFF baghouse demonstrated: (1) a reduced rate of pressure drop increase during a filtration cycle, (2) lower residual pressure drop, (3) stable operation at higher face velocities, and (4) improved particle removal efficiency. These benefits can be obtained with only minor modifications to conventional pulse-jet hardware and at low electrical power consumption. The indicated ability to operate at increased face velocities with only modest expenditure for electrical hardware leads to very favorable economic projections.     

Advanced Electrostatic Stimulation of Fabric Filtration

In advanced electrostatic stimulation of fabric filtration (AESFF), a high voltage electrode is placed coaxially inside a filter bag to establish an electric field between the electrode and the bag surface. The electric field alters the dust deposition pattern within the bag, yielding a much lower pressure drop than that found in a conventional bag. Pilot plant results show that AESFF bags can operate with a rate of pressure loss that is 70 percent below that for conventional bags. The presence of the electric field also affects the aging characteristics of the AESFF bags. On the average, the AESFF bags had residual drags that were 10 percent below those of conventional bags. The results show that AESFF baghouses can yield the same pressure drop performance as conventional baghouses while operating at much higher air-to-cloth ratios. An economic analysis evaluated the capital, operating, and maintenance costs for electric utility plants ranging from 200 to 1,000 MW. For AESFF baghouses the capital cost was found to be 25 to 48 percent below that of a conventional baghouse. A lifetime cost analysis predicts a net present value for an AESFF baghouse that is 10 to 30 percent below that of a conventional baghouse.     

Prediction of particulate loading in exhaust from fabric filter baghouses with one or more failed bags

Loss of filtration efficiency in a fabric filter baghouse is typically caused by bag failure, in one form or another. The degree of such failure can be as minor as a pinhole leak or as major as a fully involved baghouse fire. In some cases, local air pollution regulations or federal hazardous waste laws may require estimation of the total quantity of particulate matter released to the environment as a result of such failures. In this paper, a technique is presented for computing the dust loading in the baghouse exhaust when one or more bags have failed. The algorithm developed is shown to be an improvement over a previously published result, which requires empirical knowledge of the variation in baghouse pressure differential with bag failures. An example calculation is presented for a baghouse equipped with 200 bags. The prediction shows that a small percentage of failed bags can cause a relatively large proportion of the gas flow to bypass the active bags, which, in turn, leads to high outlet dust loading and low overall collection efficiency from the baghouse.     

The Use of Nahcolite Ore and Bag Filters For Sulfur Dioxide Emission Control

This paper describes some technical and economic aspects of the nahcolite ore injection process for the simultaneous removal of fly ash and sulfur oxides from stack gases. The process is capable of removing greater than 99% of the particulate matter and greater than 70% of the sulfur oxides present in such gases. In the process, nahcolite ore, a naturally occurring material containing 70 to 90% sodium bicarbonate, is ground to 90% passing through —200 mesh screens. Approximately 20% of the ground ore is used to precoat the filter bags in a baghouse filter while the remainder of the material is fed into the flue gas Just ahead of the baghouse. The flue gas is drawn through the baghouse by induced draft fans and sent up the stack. Most of the SO₂ and practically all of the fly ash in the flue gas can be removed as the gas passes through the filter bags. The spent nahcolite ore and fly ash are collected and conveyed to waste disposal as landfill, or alternatively processed for insolubilization by coprecipitation prior to landfilling. The technical feasibility of the process has been demonstrated in both bench scale and pilot scale engineering studies. Economic analyses performed for the cases of plants located in the midwest and southwest indicate lower capital costs for the nahcolite injection process when compared to wet scrubbing. On an annual cost basis, the nahcolite ore Injection process is comparable in cost to wet scrubbing for the case of the southwestern power plant, and somewhat more expensive for the case of the midwestern plant.     

Indirect Source Impact Analysis-Carbon Monoxide Modeling

This paper reviews current methods and models used in estimating the impacts of indirect sources on CO air quality, an important process in rapidly growing areas. The paper gives an overview of the modeling process, reviews how to obtain fleet average emission factors, presents a commonly used set of worst-case meteorology, identifies dispersion models available for predicting local CO concentrations and tells how to predict an 8-hour average CO concentration given a 1-hour prediction. The paper also discusses background CO concentrations and some of the issues involved in choosing reasonable receptor locations. Several problems exist with indirect source impact analysis—in both the technical area and the policy area. Increased effort is needed to correct these problems, especially to quantify the probability of the worst-case meteorology and to define the locations of reasonable receptors.     

A Probabilistic Production Costing Analysis of SO2 Emissions Reduction Strategies for Ohio: Emissions,Cost, and Employment Tradeoffs

A new approach for state- and utility-level analysis of the cost and regional economic impacts of strategies for reducing utility SO₂ emissions is summarized and applied to Ohio. The methodology is based upon probabilistic production costing and economic input-output analysis. It is an improvement over previous approaches because it: (1) accurately models random outages of generating units, “must-run” constraints on unit output, and the distribution of power demands; and (2) runs quickly on a microcomputer and yet considers the entire range of potential control strategies from a systems perspective. The input-output analysis considers not only the economic effects of utility fuel use and capital investment, but also those of increased electric rates. Two distinct strategies are found to be most attractive for Ohio. The first, more flexible one, consists of emissions dispatching (ED) alone to meet short run emissions reduction targets. A 75 percent reduction can then be achieved by the turn of the century by combining ED and fuel switching (FS) with flue gas desulfiirization, limestone Injection multistage burners, and physical coal cleaning at selected plants. The second is a scrubber-based strategy which includes ED. By the year 2000, energy conservation becomes a cost effective component of these strategies. In order to minimize compliance costs, acid rain legislation which facilitates emissions trading and places regional tonnage limits on emissions is desirable.     

Prediction of Particulate Loading in Exhaust from Fabric Filter Baghouses with One or More Failed Bags

Abstract

Loss of filtration efficiency in a fabric filter baghouse is typically caused by bag failure, in one form or another. The degree of such failure can be as minor as a pinhole leak or as major as a fully involved baghouse fire. In some cases, local air pollution regulations or federal hazardous waste laws may require estimation of the total quantity of particulate matter released to the environment as a result of such failures. In this paper, a technique is presented for computing the dust loading in the baghouse exhaust when one or more bags have failed. The algorithm developed is shown to be an improvement over a previously published result, which requires empirical knowledge of the variation in baghouse pressure differential with bag failures. An example calculation is presented for a bag-house equipped with 200 bags. The prediction shows that a small percentage of failed bags can cause a relatively large proportion of the gas flow to bypass the active bags, which, in turn, leads to high outlet dust loading and low overall collection efficiency from the baghouse.     

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 optimizing the cleaning system. Dustcake weight or drag are better indicators of performance than pressure drop and should be used to develop an optimum baghouse operating protocol.     

Dioxin contents in fly ash from large-scale MSW incinerators in Taiwan

In this study, fly ash samples were collected from three municipal waste incinerators (MWI) in Taiwan. These MWIs investigated are equipped with different air pollution control devices (APCDs). Preliminary results indicated that 2,3,7,8-PCDD/Fs homologue patterns of various types of fly ash were quite similar for all three MWIs. Concentrations of higher-chlorinated congeners of PCDDs and PCDFs were remarkably higher than those of lower-chlorinated congeners. In the case of MSW-A, the PCDD/PCDF ratios of ashes were found in the decreasing order for cyclone, boiler and baghouse. The PCDD/PCDF ratios in various types of fly ash of MWI-B was boiler-A < boiler-B < ESP < boiler-C. As for MSW-C, no obvious trend has been observed for PCDD/PCDF ratio. However, the ratio in boiler ash was higher than that in baghouse ash of MWI-A. The dioxin contents in fly ash would increase as the fly ash passed through APCD zones. In other words, the environmental conditions of APCD may actually cause the increase of the dioxin contents in fly ash. The trend for dioxin contents in fly ash collected from three MSW incinerators investigated was MSW-C < MSW-A < MSW-B.