Control of salt laden particulate emissions from hogged fuel boilers

This paper presents the results of an evaluation of excessive salt emissions from 16 hogged fuel boilers in Washington, Oregon, and Alaska. Logs transported or stored in sea water, absorb substantial amounts of salt which is noncombustible, and is emitted as a fine particulate when the hogged fuel is burned, contributing to opacity and particulate emissions. Control measures considered are fuel pretreatment, combustion modification, use of conventional particulate control devices (electrostatic precipitators, fabric filters, and wet scrubbers), and several novel particulate control devices.The best available control technology appears to be a mechanical collector-fabric filter combination; some electrostatic scrubber type devices have also shown excellent capability.     

Tubular electrostatic precipitators of two-stage design

Although the “two stage” electrostatic precipitator concept was first developed in 1910, until recently most of their use was confined to in-plant air cleaning. In the last decade, plate type designs have been modified to make them suitable for industrial applications involving organic emissions, most notably in asphalt saturating, plastic curing, food processing, printing, textile finishing, and heat treating industries. However, plate type designs are inadequate in applications where very high loading and/or high particulate content are involved.Tubular design with wider spacing and higher voltages incorporates the best features of both the single stage and two stage type precipitators. These units have been used in molybdenum roasting, zirconium calcining, ammonia scrubbing of oxides of sulfur, meat broiling, foundry exhaust, etc.The paper discusses design parameters, field test data, and operating data on these units. Comparisons with single-stage type precipitators are made wherever applicable. Advantages and disadvantages of two stage precipitators are also discussed.     

Electrode cleaning systems: Optimizing rapping energy and rapping control

Methods for improving electrostatic precipitator performance by increasing electrode excitation level during rapping, and by optimizing rapping control, are presented in this paper. Design modifications can reduce mechanical impedence to vibration transmission during rapping. These same modifications can eliminate areas of high stress concentration where fatigue failure often occurs. Rapping system control parameters are presented as they relate to variations in field collection and shedding rates. Anti-coincident rapping control for plate rappers minimizes peak opacity levels during rapping if sufficient “rest times” between raps can be maintained. When anti-coincidence must be sacrificed due to insufficient rest times on large installations, suggestions for anti-coincident rapping by section are presented. Methods for optimizing field rapping repeat rates using available opacity, ash pull, and precipitator power information are discussed.     

Predicting fly ash resistivity—an evaluation

Recently a technique for predicting fly ash resistivity from an as-received, ultimate coal analysis and the chemical composition of the coal ash produced by simple laboratory ignition was published. This paper evaluates this technique by comparing predicted resistivity data with laboratory measured values, in situ resistivity data, and precipitator performance information acquired from 12 field test programs. Considering the precision of measurement generally encountered in precipitator technology and the limited amount of certain laboratory data available, the results are encouraging and the evaluation is favorable.     

Design guidelines for an optimum scrubber system

The revised New Source Performance Standards (NSPS) for the utility industry mandates reduced particulate matter and sulfur dioxide emissions from new utility boilers. A wet scrubber system can be an advantage in controlling both of these emissions. Existing wet scrubber systems may meet the new standards with significant increase in power consumption. A careful design of the entire scrubber system, based on the experience gained at the existing installations, is necessary to ensure cost effectiveness. The experience with existing wet scrubber systems used on coal-fired utility boilers is reviewed and their performance is correlated with power consumptions. Based on a correlation of scrubber pressure drop against outlet concentration, conventional scrubber systems would be able to meet the revised NSPS for particulate matter with a theoretical scrubber pressure drop of 43±5 cm H₂O. Overall system pressure drop, however, could easily run as high as 76 cm H₂O. Novel scrubber systems such as the electrostatically augmented scrubber may provide the necessary collection performance at lower pressure drops. The performance of the various scrubber components such as mist eliminators and reheaters is reviewed. Operating problems are also discussed.     

Application of slipstreamed air pollution control devices on waste-as-fuel processes

The recovery of energy from the combustion of municipal solid wastes is becoming an attractive alternative as landfill space becomes scarce and the availability of fossil fuels decreases. Particulate emissions from “waste-as-fuel” processes, however, may differ significantly in chemical and physical properties from particulate emissions produced by firing only coal. Such differences can affect the design and operation of air pollution control equipment. Presented in this paper are the results of a 2-month test program at Ames, Iowa, with a mobile electrostatic precipitator (ESP) and a mobile scrubber supplied by the U.S. Environmental Protection Agency (EPA), Industrial Environmental Research Laboratory (IERL), Research Triangle Park. PEDCo Environmental, Inc., and Acurex Corporation jointly conducted the test program to examine the effect of burning refuse-derived fuel (RDF) on particulate and heavy metal control efficiencies. The mobile ESP was used only as a primary control device, whereas the mobile scrubber was tested both upstream and downstream of the existing full-scale ESP. This paper also presents a status report on a PEDCo test program with a pilot fabric filter at Ames.     

Effects of EGR,swirl augmentation techniques on combustion of biodiesel/ethanol and their blends in a diesel engine

The diminishing resources and continuously increasing cost of petroleum in association with their alarming pollution levels from diesel engines have caused an interest in finding alternative fuels to diesel which are renewable and sustainable. Emission control and engine efficiency are two most important parameters in current engine design. The impending introduction of emission standards such as Euro IV and Euro V is forcing the research towards developing new technologies for combating engine emissions. The classification of Euro IV and V norms is applicable to heavy-duty engines in Europe, where as Euro 5 is applicable to light-duty engines. This paper presents the effects of exhaust gas recirculation (EGR), swirl augmentation techniques and ethanol addition on the combustion of Honge oil methyl ester (HOME) and its blends with ethanol in a diesel engine. From the experimental work conducted, it is found that the combustion of HOME plus up to 15% ethanol blend in a diesel engine operated with optimised parameters of injection timing 23° Before Top Dead Centre and compression ratio 17.5 results in acceptable combustion emissions and improved brake thermal efficiency (BTE). The addition of ethanol increased BTE with reduced hydrocarbons (HCs), CO and smoke emissions. However, NO _x emissions increased dramatically. Use of appropriate EGR reduces NO _x to acceptable levels. The implementation of swirl augmentation techniques further resulted in increased BTE and considerable reduction in tail pipe emissions such as smoke, HCs, CO and NO _x . The effect of swirl by providing grooves on the piston was taken into consideration to find the overall biodiesel engine performance, which gives scope for further studies.     

Electrostatic enhancement of moving-bed granular filtration

The electrostatic granular filter developed by Combustion Power Company combines a moving-bed filter with an electrostatic grid for high-efficiency collection of particulate. The coulomb charge occurring naturally on particulate from combustion or other processes in which tribocharging occurs is sufficient such that imposition of an electric field substantially enhances mechanical collection in the packed filter. A mathematical model is presented which accounts for the major parameters affecting electrostatic performance. Experimental data developed in an industrial unit retrofitted with electrostatic equipment and a pilot-scale filter demonstrates dramatic improvement in opacity and outlet loading; the industrial unit achieved 99% collection efficiency with less that 4 Iwd (1kPa) pressure drop. Data from the pilot-scale filter has shown that collection of micron-size particulate is especially enhanced with the electric field and has confirmed the 99% overall collection capability demonstrated in the industrial unit. The design of a 420,000 acfm (1200 m³/min) system being installed at Weyerhaeuser Company's Longview, Washington plant is also discussed.     

Precipitator energization utilizing an energy conserving pulse generator

The performance of a conventional two-electrode type precipitator collecting high resistivity dust can be improved by pulse energization. Pulses of a suitable duration and repetition rate superimposed on the DC voltage permit higher peak-voltage without sparkover, improve particle charging and current distribution, and allow independent regulation of the precipitator voltage and current. A considerable quantity of energy, however, is required for each pulse to charge the precipitator to the pulse voltage level. For high pulse voltages only a minor part of this energy is necessary for the discharge current in the precipitator. For reasons of economy, the recovery of the energy stored in the precipitator capacitance during each pulse is therefore extremely important for pulse energization of large precipitators. An energy conserving pulse generator with pulse transformer, a pulse initiating switch element, and a feed-back diode for the energy recovery is described. The design and the instrumentation of a pilot precipitator specially developed for the comparison of different kinds of precipitator energization are outlined. The ability of the applied pulse energization system for controlling the corona discharge current independently of the precipitator voltage is demonstrated. Further, results from field tests showing the performance of the system under operating conditions are presented.     

Effects of compression ratio,swirl augmentation techniques and ethanol addition on the combustion of CNG–biodiesel in a dual-fuel engine

The diminishing resources and continuously increasing cost of petroleum in association with their alarming pollution levels from diesel engines has led to an interest in finding alternative fuels to diesel. Emission control and engine efficiency are two of the most important parameters in current engine design. The impending introduction of emission standards such as Euro IV and Euro V has forced research towards developing new technologies for combating engine emissions. This paper examines the effects of compression ratio, swirl augmentation techniques and ethanol addition on the combustion of compressed natural gas (CNG) blended with Honge oil methyl esters (HOME) in a dual fuel engine. The present results show that the combustion of HOME and 15% ethanol blend with CNG induction in a dual-fuel engine operated in optimized parameters at an injection timing of 27° Before Top Dead Centre and a compression ratio of 17.5 resulted in acceptable combustion emissions and improved brake thermal efficiencies. The implementation of swirl augmentation techniques increased brake thermal efficiencies (BTEs) and considerably reduced combustion emissions such as smoke, HC, CO and NO_x. The addition of ethanol also increased BTEs. However, at more than 15% of ethanol in HOME, NO_x emissions increased dramatically.     

Theoretical methods for computing electrical conditions in wire-plate electrostatic precipitators

A new semi-empirical, approximate theory for predicting electrical conditions is described. In the approximate theory, analytical expressions are derived for calculating voltage-current characteristics and electric potential, electric field, and space charge density distributions. Comparisons of numerical and approximate solutions over a wide range of possible precipitator geometries and electrical operating points indicates that for practical purposes the approximate theory can be used in lieu of the more rigorous numerical theory. This saves large amounts of computer time and makes possible hand calculator usage. Recent in situ gaseous ion mobility data which are needed in the models are presented. For coal fired power plants, the reduced effective ion mobility in positive corona is found to be 1.6 times that for negative corona. Approaches for describing particulate space charge effects in the gas and electrical conditions in the collected particulate layer are briefly discussed.     

Ion current densities produced by energetic electrons in electrostatic precipitator geometries

A new laboratory test system for electron beam ionization in electrostatic precipitator geometries has been constructed to measure ion current density as a function of voltage difference for clean plate (no dust contamination) conditions. The new system incorporates improved electrodes which withstand an applied voltage of ± 55 kV, a factor of 5 increase over the previous test system. A 3 MeV Van de Graaff accelerator produced ionizing electron beams of 1.2 and 2 MeV energy with beam currents of 10.5 and 21 μA in place of corona wire ionization. Ion current densities of up to 130 mA/m² were measured before breakdown between the plates, and no ion current saturation was observed. A comparison of I-V curves and sparkover voltages for various beam energies, currents, and types of collimation is discussed and the need for measurements with good beam geometry is addressed.     

Experimental investigation of diesel engine using EGR and fuelled with Karanja oil methyl ester

Karanja oil methyl ester (KOME), a biodiesel prepared from Karanja oil, a potential source of non-edible oil in India and a prospective alternative to the diesel fuel, shows comparable performance and considerable reduction in emissions except NO_x. Exhaust gas recirculation (EGR) is a popular method of reducing the NO_x emission. The aim of this experimental work was to study the potential of the cooled EGR in a direct injection compression ignition engine operating with the KOME and its blend. The study was conducted with the different EGR rates. Performance and emission parameters were compared by using diesel, KOME and its blend employing EGR and with the same fuels without EGR. The study also differentiates the effect of EGR on KOME and its blend with the neat diesel. The effect of EGR was found to be slightly higher for KOME biodiesel and its blend than for neat diesel. Increased NO_x emission using KOME biodiesel was also found to be reduced by using EGR.     

Dynamic Changes,Regional Differences,and Influencing Factors of CO2 Emission Performance in China

Abstract

This paper proposes to use DEA models with undesirable outputs to construct the Malmquist index that can be use to investigate the dynamic changes of CO₂ emission performance. With the index, the authors have measured the CO₂ emission performance of 28 provinces and autonomous regions in China from 1996 to 2007; with the convergence theory and panel data regression model, the authors analyze the regional differences and the influencing factors. It is found that the performance of CO₂ emissions in China has been continuously improved mainly due to the technological progress, and the average improvement rate is 3.25%, with a cumulative improvement rate of 40.86%. In addition, the CO₂ emission performance varies across four regions. As a whole, the performance score of eastern China is the highest. The northeastern and central China has relatively lower performance scores, and the western China is relatively backward. The regional differences are decreasing, and the performance of CO₂ emissions is convergent. The influence of some factors on the performance of CO₂ emissions is significant, such as the level of economic development, the level of industrial structure, energy intensity, and ownership structure. The influence of some factors, such as opening-up to the outside world, on the performance of CO₂ emissions is not significant.     

The effects of corona electrode geometry on the operational characteristics of an ESP

Experiments were run in a pilot scale electrostatic precipitator (ESP) to determine the effects of corona wire-to-wire spacing on the operating conditions. Tests were run, using a reentrained low sulfur fly ash at both hot- and cold-side conditions. The effects of varying wire-to-wire spacing were determined. Results are given which show that varying wire spacing at cold-side conditions has little operational effect on the ESP while improved efficiency can be obtained at hot-side (low resistivity) conditions by reducing wire spacing. The increased efficiency results from a higher average operating voltage. The effects of back ionization are clearly demonstrated by a set of experiments in which dust was selectively removed from the wires or plate. These tests show that the lower operating voltage caused by back ionization is a combined effect of high resistivity dust on both the wires and plate.     

Control strategies for particulate emissions from vehicular diesel exhaust

The advantages and disadvantages of several possible control strategies for particulate emissions from vehicular diesel exhaust are discussed. The evaluation of the potential usefulness of the various control strategies is based on available data concerning the mass loading and particle size distribution and on anticipated control standards. Several studies have been made on devices for removing particulate emissions from vehicular diesel exhaust. These studies, which include the techniques of filtration, wet scrubbers, and electrostatic precipitation, are summarized. A comparison of the various control devices is made based on such factors as size, efficiency, and maintenance requirements.     

Identifying key issues in environmental wetland research using scaling and uncertainty analysis

Quantification of the response of wetlands to environmental change and of climate change to wetland processes, is a pressing, but complex, issue. Findings of widely diverse investigations have to be generalised to identify the key issues and the gaps in knowledge. Two tools for generalisation, scaling and uncertainty analysis, were applied here to two case studies and act as stepping stones for analysis of key issues. The first case study is on methane emissions from wetland rice fields and the second is on the restoration of wet dune slacks. The type of problems encountered depends on the scale at which a process is studied. At the biogeochemical processes scale, knowledge on some key parameters, but especially on interactions between key parameters is limiting. At the vegetation scale, feedbacks between processes become especially important, whereas at even larger scales increasingly stringent approximations of interactions have to be made. Accumulating uncertainties at the landscape scale need careful evaluation. Apart from uncertainties in the approximations and their interactions, those introduced by spatial and temporal variability as well as by different data sources highly influence the accuracy of response estimates, while these last sources of uncertainty are neglected in many studies. Only by explicitly accounting for scaling effects and their resulting uncertainties, the interactions between wetlands and environment can be understood.     

Performance and emission characteristic studies on CRDI diesel engine fuelled with plastic pyrolysis oil blended with ethanol and diesel

ABSTRACT

This paper mainly focuses on the utilisation of plastic pyrolysis oil (PPO) and its’ blends with diesel and ethanol in different proportions in a modified diesel engine fitted with common rail direct injection (CRDI) facility. PPO was subsequently blended with diesel and ethanol and characterisation has been done. Experiments were conducted to investigate the impact of injection timing (IT) and injection pressure (IP) on the performance of modified CRDI engine fuelled with PPO and its blends with diesel and ethanol. From the experimental investigations, IT of 10°bTDC and IP of 900 bar were found as best operating parameters to obtain maximum brake thermal efficiency (BTE) with lowered emissions for the fuel combinations utilised in the investigations. PPO as substitute to diesel fuel could be viable if its major concern is to finding permanent resources.     

Size dependent cytotoxicity of fly ash particles

Fly ash samples were collected from the electrostatic precipitator of a coal-fired power plant in Hong Kong. The particles of the respirable range (smaller than 10 μm) were divided into 4 groups according to their particle size (mass median aerodynamic diameters). The surface morphology and the metal contents (Fe, Mn, Al and Zn) of fly ash particles were examined by a scanning electron microscope and an inductively coupled plasma spectrophotometer, respectively. The particles were very heterogenous in size and shape as well as the concentration of metals. The cytotoxicity of these four groups of fly ash particles was evaluated using an in vitro rat alveolar macrophages culture assay. The viability of alveolar macrophages was lower when incubated with smaller size particles. This relationship was also reflected by the damage of the surface morphology of the cells and the release of cytoplasmic (lactate dehydrogenase) and lysosomal (acid phosphatase and β-glucuronidase) marker enzymes into the culture media.     

Arsenic emissions and control gold roasting operations

Since arsenic is a significant compound of ores processed in the nonferrous metals industry, it is of interest to characterize and evaluate control strategies which have demonstrated the potential for lowering the emission rates of arsenic and other hazardous effluents from smelter operations. The Campbell Red Lake Mines Gold Smelter at Balmerton, Ontario, Canada, has developed and implemented a successful control strategy for arsenic emissions from a nonferrous smelting operation. The control system was designed and installed by Hatch Associates, Toronto, Canada. The Red Lake smelter uses cyclones and a hot electrostatic precipitator to recover metal values from roaster dusts with subsequent air quenching to condense (or desublime) arsenic trioxide which is recovered in a low-temperature baghouse. This paper is a review of a test program conducted at Red Lake designed to characterize the control systems and to evaluate the potential for transferring the technology to smelting operations in the United States.