A Method for Predicting the Effective Volume Resistivity of a Sodium Depleted Fly Ash Layer

Research has been conducted to develop a technique for predicting the effective volume resistivity of a fly ash layer that has been exposed to circumstances leading to a hot-side precipitator problem known as sodium depletion. Eight fly ashes, representing a major portion of U.S. coals, were evaluated by subjecting 0.5 cm ash layers to a continuously applied voltage gradient of 4 kV/cm for periods of time up to 35 days at a temperature of 350°C (662°F). Resistivity was determined at 350°C before the test started and after the long period of applied voltage used to create the sodium depleted situation. In this condition, resistivity was also determined at 280°C (536°F) for an average electric field Intensity of 4 kV/cm and immediately prior to breakdown. This experimental method can be used with any ash sample to estimate resistivity In a sodium depleted condition. But in addition, a correlation resulting from these resistivity data has been developed. This correlation Is combined with an existing technique for predicting resistivity to produce a method for calculating the expected ash layer resistivity after sodium depletion has occurred.     

滤料负载粉尘层对气态汞脱除性能的实验研究

通过不同性能纤维滤料负载燃煤飞灰粉尘层,来模拟袋式除尘器滤袋表面粉尘附着层,进而研究袋滤器用不同性能纤维滤料和粉尘附着层对燃煤烟气中Hg0的联合脱除性能。在固定床实验系统上分别进行了不同纤维滤料和燃煤飞灰粉尘层,以及经实验优选得到的华博特滤料负载燃煤飞灰粉尘层脱除燃煤烟气中Hg0的实验研究。结果表明,燃煤飞灰粉尘层和华博特滤料对Hg0分别有一定的脱除作用,脱除效率可达35%和42.5%,它们对Hg0的脱除是物理吸附和化学吸附共同作用的结果;同时,华博特滤料负载燃煤飞灰粉尘层对Hg0的联合脱除效率受到吸附反应温度、入口汞浓度和烟气停留时间等因素的影响,最佳脱汞率可达64.4%;吸附反应温度越高,脱除效率越低;烟气停留时间越大,脱除效率越高;入口汞浓度的提高并不一定提高华博特滤料负载飞灰粉尘层的脱汞效果。     

The Effective Collection of Fly Ash At Pulverized Coal-Fired Plants

The relationship between sulfur in coal, boiler exit gas temperature, and the carbon portion of fly ash have a major effect on the electrical properties of fly ash. Whether effective collection of fly ash is obtained by the electrostatic precipitator installation alone or the precipitator—mechanical combination depends primarily on a knowledge of this relationship. Fly ash electrical properties can range from a highly "resistive" to a highly "conductive" state which can appreciably alter the precipitator collection performance. A correlation of coal sulfur and boiler exit flue gas temperature is given to indicate the probability of expecting an optimum voltage—current relationship with different combinations of these factors. Carbon affects the electrical conditioning of fly ash by providing parallel paths of current leakage through the deposited dust layer. Therefore, removal of the carbon particles in a mechanical collector placed before the precipitator can alter the precipitator electrical characteristics.     

The Trielectrode Electrostatic Precipitator for Collecting High Resistivity Dust

High resistivity dust is normally the major problem in electrostatic precipitation. Even though the corona current is only a fraction of a microampere per cm² the resulting RI drop exceeds the breakdown voltage gradient of the dust layer. This breakdown or sparking through the collected dust causes the familiar back corona and premature sparkover. The Trielectrode Electrostatic Precipitator (TEP) is an effort to make precipitator performance insensitive to dust resistivity. The TEP (U. S. Patent 3,915,672) is based on the concept that the layer of collected dust behaves like capacitance and resistance in parallel so that the corona can occur in short pulses and yet maintain a moderately constant current through the dust layer. In between corona pulses the precipitating field is supplied by a third set of electrodes. Initial bench scale tests using high resistivity particulate indicate that the concept is sound. Recent testing has extended the effective operating range of the TEP for particulate resistivities of 10¹⁰-10¹³ ohm-cm indicating that the TEP is essentially insensitive to particulate resistivity and can give a constant high collection efficiency regardless of the type of coal burned in a utility application.     

Joint US/USSR Test Program for Reducing Fly Ash Resistivity

An electrostatic precipitator preceded by a wet scrubber was tested at the Reftinskaya Power Station. The unit collects a high resistivity fly ash from the combustion of low sulfur Ekibastuz coal. The operating parameters of the precipitator were measured as well as the mass emissions and the in-situ electrical resistivity of the fly ash. Density, particle size distribution, electrical resistivity, and chemical composition were determined for collected samples of the fly ash. The fly ash was also characterized by x-ray diffraction and scanning electron microscopy. When a centrifugal wet wall scrubber was installed ahead of the electrostatic precipitator, the temperature of the flue gas entering the precipitator was decreased and the moisture content increased. The electrical resistivity of the fly ash was attenuated a decade, but not enough to overcome the adverse effects of back corona in the precipitator. Lowering the flue gas temperature to about 85°C by the addition of a venturi scrubber ahead of the centrifugal scrubber reduced the electrical resistivity of the fly ash another decade and allowed the operation of the precipitator without back corona.     

Effects of Sorbent Injection on Participate Properties: Part I. Low-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 ash and sorbent mixtures can cause electrical reentrainment in electrostatic precipitators. Deliquescent additives such as calcium chloride cause the water to be retained on the particle surface, thereby increasing cohesivity.

Sorbent injection has been reported to increase the particulate mass loading by a factor of 1.8 to 10, depending upon the reagent ratio and the coal sulfur content. Conventional and in-duct spray drying processes tend to shift the particle size distribution toward larger particles, while dry injection processes tend to shift the particle size distribution toward smaller particles.     

An Interpretation of the Deteriorative Performance of Hot-Side Precipitators

A severe problem has developed with respect to the efficiency of certain hot-side electrostatic precipitators. The problem is manifested by a time dependent degradation of performance in which back corona related to a condition of high ash resistivity is the influencing factor. Performance can be restored by thorough cleaning of the precipitator only to experience the degradation once again. This paper hypothesizes an explanation for these observations. Experiments with both high and low resistivity ashes using resistivity test cells and a laboratory corona discharge device have been run to prove the validity of the suggested explanation. Data substantiate the idea that in the precipitation process a thin layer of ash more or less permanently remains on the collection plates and that the sodium ions serving as charge carriers in the conduction process through the layer are depleted leaving a thin layer of ash having extremely high resistivity. This phenomenon is called electrode polarization, sodium depletion, or an ash layer space charge depending on one's scientific discipline. Suggestions of remedial steps which may be of benefit in counteracting this difficulty are given.     

Impact of free calcium oxide content of fly ash on dust and sulfur dioxide emissions in a lignite-fired power plant

Emitted pollutants from the Agios Dimitrios lignite-fired power plant in northern Greece show a very strong linear correlation with the free calcium oxide content of the lignite ash. Dust (fly ash) emissions are positively correlated to free calcium oxide content, whereas sulfur dioxide (SO2) emissions are negatively correlated. As a result, at present, the Agios Dimitrios Power Plant operates very strictly within the legislative limits on atmospheric particulate emission. In the present study, the factors to be considered in assessing the impact of lignite combustion on the environment are presented and evaluated statistically. The ash appears to have a remarkable SO2 natural dry scrubbing capability when the free calcium oxide content ranges between 4 and 7%. Precipitator operating problems attributable to high ash resistivity can be overcome by injecting sulfur trioxide to reduce the ash resistivity, with, of course, a probable increase in operating costs.     

Medium-Sulfur Coal and Fly Ash Resistivity

Electric generating plants burning medium-sulfur coal need a way to predict when ESP performance will be limited by high electrical resistivity of the collected fly ash. The main uncertainty in mathematical predictions of fly ash resistivity lies in the marginal effect of naturally occurring SO₃ vapor in the flue gas. This paper results from a project to expand the data base of SO₃/SO₂ concentrations and fly ash resistivities measured in utility fly ash precipitators. Complete data sets are presented from three plants in the Southern Company electric system. In situ resistivity data are compared with laboratory measurements and with two different mathematical predictions of resistivity based on coal and ash analyses. The revised version of the resistivity predictor gives results in good agreement with resistivity values measured both in situ and in the laboratory.     

泛比电阻电除尘器收尘性能实验研究

泛比电阻电除尘器是一种具有辅助电极和交错平板收尘电极的新型电除尘器.通过对其伏安特性及除尘效率的试验研究,并与传统线板式静电除尘器进行比较,结果表明辅助电极对电晕电流具有明显的抑制作用,在相同的外加电压下,泛比电阻电除尘器对高比电阻锅炉飞灰的收尘效率比普通的线板式电除尘器明显要高.     

Adsorption of arsenic(V) onto fly ash: a speciation-based approach

Arsenic (As) poses a significant water quality problem and challenge for the environmental engineers and scientists in the world. The large volume of coal fly ash produced around the world is a potentially significant anthropogenic source of arsenic. Currently the leaching behavior of arsenic from fly ash is not well understood. Batch methods were used in this study to investigate arsenic leaching using a raw ash, and arsenic adsorption using a clean, washed ash. Experimental results indicated that pH had a significant effect on arsenic leaching or adsorption. Between pH 3 and 7, less arsenic was in the dissolved phase. When pH was less than 3 or greater than 7, increasing amounts of arsenic were leached or desorbed from fly ash. The leaching and adsorption behavior of arsenic was interpreted with the speciation of surface sites and arsenic. In a new approach, a speciation-based model was developed to quantify the arsenic adsorption as a function of pH and surface acidity parameters. This work is important in offering insight into the leaching mechanism of arsenic from coal fly ash, and providing a robust model based upon specific, measurable parameters to quantify arsenic adsorption by other solid media in addition to fly ash.     

Impact of Free Calcium Oxide Content of Fly Ash on Dust and Sulfur Dioxide Emissions in a Lignite-Fired Power Plant

Abstract

Emitted pollutants from the Agios Dimitrios lignite-fired power plant in northern Greece show a very strong linear correlation with the free calcium oxide content of the lignite ash. Dust (fly ash) emissions are positively correlated to free calcium oxide content, whereas sulfur dioxide (SO₂) emissions are negatively correlated. As a result, at present, the Agios Dimitrios Power Plant operates very strictly within the legislative limits on atmospheric particulate emission. In the present study, the factors to be considered in assessing the impact of lignite combustion on the environment are presented and evaluated statistically. The ash appears to have a remarkable SO₂ natural dry scrubbing capability when the free calcium oxide content ranges between 4 and 7%. Precipitator operating problems attributable to high ash resistivity can be overcome by injecting sulfur trioxide to reduce the ash resistivity, with, of course, a probable increase in operating costs.     

粉煤灰的改性及其在垃圾渗滤液深度处理中的应用研究

实验采用物理方法和化学方法对粉煤灰进行改性,并用改性粉煤灰深度处理垃圾渗滤液。通过扫描电镜和X-射线衍射对改性前后粉煤灰的表面结构和主要晶相组成进行分析,同时考察其在垃圾渗滤液深度处理中的吸附效果。结果表明,改性后粉煤灰的比表面积和孔隙度增大,吸附能力增强。通过比较,吸附能力最强的改性粉煤灰是将引发剂A与粉煤灰以质量比为1∶9的比例混合,在800℃下恒温焙烧2 h所制得的改性粉煤灰,该改性粉煤灰对垃圾渗滤液中COD和色度的去除率可达到67.3%和87.3%,相对于改性前去除率提高了96.0%和57.8%。     

Conditioning of Fly Ash with Ammonia

This paper presents the results of an investigation of the conditioning of fly ash with ammonia in electrostatic pre-cipitators of power plants operated by the Tennessee Valley Authority. It focuses attention primarily on the mechanisms of conditioning encountered under the particular circumstances available for study. No effect of ammonia on the electrical resistivity of fly ash was evident. Instead, the effect of ammonia appeared to be an enhancement pf the space-charge component of the electric field used for charging and precipitating particles of fly ash. In addition, a second effect appeared to be an increase in the cohesiveness of precipitated ash and a reduction in the quantity of ash reentrained during electrode rapping. Data demonstrating the value of ammonia conditioning for lowering the emission pf fly ash during three precipitator studies are presented. Reasons for the ineffectiveness of ammonia conditioning during a fourth precipitator study are discussed. In conclusion, comments are made about the effects to be expected from ammonia conditioning under circumr stances different from those investigated experimentally, particularly with ammonia as a conditioning agent for fly ash from low sulfur western coal.     

Source apportionment of PM10 in six cities of northern China

Ambient PM₁₀ was sampled in six northern China cities (Urumqi, Yinchuan, Taiyuan, Anyang, Tianjin and Jinan) from December 1999 to July 2002, and analyzed for 16 chemical elements, two water-soluble ions, total carbon, and organic carbon. In addition, chemical source profiles consisting of the same particulate components were obtained from a number of naturally occurring geological sources (soil dust from exposed lands) and sources of atmospheric particulates resulting from human activities (resuspended dust, cement, coal combustion fly ash, vehicle exhaust, and secondary particles). Ambient and source data were used in a chemical mass balance (CMB) receptor model to determine the major source of PM₁₀ in these six cities. Results of CMB modeling showed that the major source of ambient PM₁₀ in all the cities was resuspended dust. Significant contributions from coal fly ash were also found in all six cities.     

Aerosol laser ablation mass spectrometry of suspended powders from PM sources and its implications to receptor modeling

Primary sources of particulate matter (PM) were analyzed by suspending powdered samples into an aerosol laser ablation mass spectrometer (LAMS). PM sources studied included vehicle exhaust particulates, dust from a non-ferrous smelter, cement powder, incinerator fly ash, two coal fly ash samples, and two soils. Marker peaks signified certain PM source sectors: construction particles could be distinguished by abundant Ca and Ca compounds, fuel combustion was marked by elemental carbon clusters, and nonferrous industrial particles showed inorganic As, Cu, Pb, Zn, and SOx. In addition to the distinction between particles from these different source sectors, mass spectral results also showed that for a single source, different particle types existed, and among different sources within a sector, similar spectra were present. The aerosol LAMS results show the difficulty in differentiating among separate fly ash sources as well as among different soil samples. A particle class balance receptor model that measures the amount of specific particle types rather than the amount of a chemical component is suggested as a means of source apportionment when particle spectra with overlapping source possibilities occur. The assumptions and limitations of receptor modeling aerosol LAMS data are also described. In particular, methods need to be developed to account for the contribution of secondary sources.     

Effect of fly ash characteristics on the removal of Cu(II) from aqueous solution

Fly ash is a particulate substance containing metal oxides, carbon and other microelements. In this study, fly ashes with different quantities of carbon and minerals prepared by a thermal process in the laboratory were used as adsorbents to investigate the contribution of precipitation and adsorption to the removal of aqueous Cu(II). Experimental results showed that the specific surface area of fly ash increased linearly with the quantity of carbon. The specific surface areas of the carbon and mineral fraction were 60 m2/g and 0.68 m2/g, respectively. The specific adsorption capacities of carbon ranged from 2.2 to 2.8 mg Cu/g carbon, while those for mineral were only about 0.63 to approximately 0.81 mg Cu/g mineral. Consequently, the carbon fraction in fly ash was important in the removal of Cu(II) at pH 5. However, Cu(II) removal owing to precipitation increases with a decreasing carbon fraction and the contribution of copper precipitation was estimated to be approximately 23% to approximately 82% of total removal, depending on the carbon fraction of fly ash.     

Balance Corrections for Buoyancy

This paper describes a versatile experimental facility for evaluating the collection of high resistivity fly ash by advanced electrostatic precipitator designs at near full scale. The unit will operate on a slipstream of up to 424 m³/min (15,000 acfm) from a boiler firing pulverized low sulfur Western coal with an ash resistivity of 10¹³ ohm-cm at 149°C (300°F). The test unit is designed so that if can be configured as either a single-stage or a two-stage unit and allows for easy installation of different charger and collector components for evaluation. A dampered heat exchanger provides control over the gas temperature from 93°C (200°F) to 370°C (700°F) so that tests can be run at either hot-side or cold-side conditions. Support equipment includes a gas circulating fan, venturi meter for measurement and control of the flow, an instrumentation trailer housing a computerized system for data collection and control of the ESP, and a gas analysis trailer and particulate sampling station for a comprehensive evaluation of the system.     

Effect of thermal processing on the characteristics of incineration fly ash

This work investigated the possibilities of immobilizing incineration fly ash by applying different processing methods. Direct sintering of fly ash at 1050 degrees C produced material with increased resistance to leaching; however, the high content of halides prevented the achievement of appropriate strength. Fly ash melting and casting into metallic moulds resulted in the formation of glass with good chemical resistivity and mechanical properties, which were further improved by devitrification, and the formation of glass-ceramics. The most successful combination of strength and resistance to leaching was obtained by a process consisting of fly ash melting, by pouring the melt into water, then grinding, and sintering without additives at 850-950 degrees C. In this way, a material was produced that cannot only be landfilled as a stabilised and non-reactive waste in landfills for non-hazardous wastes, but can also be utilized as a valuable material for manufacturing useful products. This article provided valuable results for policy-makers in Slovenia, about the handling fly ash from incineration plants. Implications: Fly ash from an incineration plant was thermally treated using several processing routes. Ash-melting, by pouring the melt into water and sintering, produced glass-ceramics having an optimal combination of strength and resistance to leaching that can find applications as useful products. These results provide important data for policy makers in Slovenia regarding the building of incineration plants, and handling the solid-waste products, especially fly ash.     

火力发电厂粉煤灰干燥特性研究

介绍了利用实验台对粉煤灰的干燥特性进行试验研究的情况 ,给出了粉煤灰的干燥曲线、干燥速率曲线和粉煤灰平衡湿含量计算式 ,分析了在干燥过程中粉煤灰的阻力特性 ,为粉煤灰干燥装置的工业化设计提供了理论依据