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.     

Particle size measurements of automotive diesel emissions

The automative diesel engine has long been acknowledged as being “dirtier” than the spark ignition engine and its particulate emissions may be carcinogenic. Possible solutions to the diesel emission problem are combustion modification or aftertreatment devices. Selection of candidate aftertreatment devices requires knowledge of the physical and chemical properties of the particles, including particle morphology, size distribution, mass concentration and emission rates in the exhaust gas stream. The study reported here represents the first of a series of experiments designed to characterize the exhaust emissions and test various aftertreatment devices. This paper deals only with the particulate characterization phase of the program. Results of size distribution, particle concentration and mass emission rate measurements for a 5.71 displacement Oldsmobile diesel engine are given for a variety of engine operating conditions.     

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.     

Pilot field study: Carbon monoxide exposure monitoring in the general population

A pilot field study was conducted with nine members of the general public to measure carbon monoxide exposure using personal monitors. The principal study objectives were to design and evaluate the research protocol and the instrumentation performance for application to the conduct of a large-scale personal monitoring program. Integrated carbon monoxide exposure was monitored and recorded according to type of activity such as “commuting” or “at work” for approximately 45 days by each subject. All subjects except one were able to handle both the equipment and data recording requirements with no significant problems. Actual data recording responsibilities consumed less than 10 min daily. The data consisted of 355 person-days each over 6-h duration, and weekdays only, from which 8-h average personal exposure levels could be computed. The 9 ppm (μL/L) ambient air quality standard was exceeded on 22 person-days. Elevated carbon monoxide concentrations during the commuting activity were frequently associated with the exceedences.     

Efficient ventilation in office rooms

Results from a two-box model for calculation of tracer gas concentrations in rooms are given and consequences of different definitions of “ventilation efficiency” are discussed. Results from three different series of experiments are presented. The first two series were dilution experiments; examples of the results are given and discussed. The third series of tests was performed with one person working at a desk in the test room. Above the person;s head, a tracer gas (N₂O) was injected into the convection plume, with as low momentum as possible. Starting with zero concentration, a test continued until steady-state conditions were established for the concentration levels in the different parts of the room. The tests included simulation of summer, autumn/spring, and winter daytime conditions. The results indicate a tendency towards lower tracer gas concentrations in the “breathing zone” when the supply air (typical flow rate equivalent to two air changes per hour) is brought into the room at a low level as compared to a high level close to the ceiling. The exhaust air terminal device in all tests was situated high in the “corridor” wall.     

Consultative mechanisms in Sweden's environment protection policy

The institutional and legislative framework of Swedish environmental protection is presented with special reference to the role of consultation in the policy process. The functions and duties of the National Environment Protection Board, the Franchise Board for Environment Protection, the Environment Advisory Board, and the Product Control Board are outlined. The main thrust of the 1969 Environment Protection Act, the 1972 Hazardous Products Control Act, and the environmental impact assessment requirements of the Planning and Building Legislation is presented. The character of consultation within this framework is also discussed, with reference to the role of public participation and of organized regulated interests. It is found that the main functions of consultation in policy-making are “feeding back on former policy,” “foreseeing future policies,” and “canvassing for consensus.” In the stage of policy clarification, consultation is found to be a means of “catering for compliance” and “creating coherence.” In policy implementation, consultation is an important means of gathering information from parties possibly affected by implementative decisions.     

Branching processes, Markov chains, and competing risks

This paper re-proves and generalizes results by Hardin and Sweet on the time to absorption in certain Markov chains by using a theorem on the time to extinction in multitype branching processes. Renaming “absorption” as “death” and “state immediately before absorption” as “cause of death” makes possible an interpretation in terms of competing risks. This is of very limited value, however, due to the rather severe mathematical restrictions on the Markov chains at hand.     

Evaluation of the George Neal electrostatic precipitator

The Electric Power Research Institute (EPRI) is currently supporting a major research program characterizing the performance of high efficiency electrostatic precipitators (ESP). One such effort evaluating the George Neal ESP of Iowa Public Service Company is described in this paper.Results show that under well tuned conditions the ESP overall collection efficiency was 99.7% at a specific collecting area of 745 ft²/kacfm (147 m²/m³/s) (520 MW) with associated mass concentrations of 0.025 lb/10⁶ Btu and stack opacity of 4.6%. The boiler outlet size distribution was found to be bimodal with submicron and large particle peaks at 0.2 and 5 microns diameter, respectively. Consequently, an apparent bimodal fractional efficiency curve results with efficiencies of 99.6%, 98%, and 90% measured for 20, 2 and 0.2 micron diameter particles, respectively. Rapping reentrainment losses were found to be insignificant except during episodes of high ash hopper levels resulting from a malfunctioning ash removal system, when large rapping puffs were observed. In addition, outlet emissions increased dramatically to 0.08 lb/10⁶ Btu (34 ng/J) during these periods, suggesting that an emission level more representative of daily operation lies somewhere between 0.025–0.08 lb/10⁶ Btu (10.8–34 ng/J).     

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.     

Toxicity assessment of wood preservatives

The article describes the influence of wood preservatives on water bioceonosis. The “battery” of toxicology tests was used to cover luminescent bacteria test, algae growth inhibition test, crustacean and fish lethal tests. The test samples used were pure wood preservative and water after the wood preservative leaching from wood sample. It was observed that the wood preservative is leaching from the wood sample in 10% within 1 month of exposition. Achieved results indicate the necessity of toxic assessment of wood preservative after wood element protection.     

Interactions between diesel emissions and gaseous copollutants in photochemical air pollution: Some health implications

A complete assessment of the health effects of diesel emissions must take into account the possible chemical transformations (and associated biological impacts) of particulate organic matter (POM) due to reactions with the many gaseous copollutants which have now been unambiguously demonstrated to be present in atmospheres burdened by photochemical air pollution. These copollutants include the “trace” species, nitric (HNO₃) and nitrous (HONO) acids, the nitrate radical (NO₃), formaldehyde (H₂CO) and formic acid (HCOOH), as well as the criteria pollutants, ozone (O₃) and nitrogen dioxide (NO₂). Techniques for establishing the atmospheric concentrations of the trace pollutants (and their spatial and temporal variations) are briefly described, and we present results of investigations into the reactions of polycyclic aromatic hydrocarbons (PAH) coated on filters and exposed to ambient concentrations of O₃ and NO₂. Environmental health implications of these results are discussed and include the potential for sampling “artifacts” and their possible effects on the correlation (or lack thereof) between ambient PAH levels and urban lung cancer rates, as well as the problems associated with understanding the appropriate POM “dose” to be employed in animal testing and assessments of impacts on human health.     

Air pollution control policy in the Federal Republic of Germany as a strategy for dealing with environmental risks

The paper describes criteria for the development of energy systems, with emphasis on “environmental compatibility.” It outlines the main objectives underlying political and regulatory action in the Federal Republic of Germany to ensure this compatibility through the management of environmental risks. The air pollution control policy in the Federal Republic of Germany is presented as a strategy for risk management, focusing on its philosophy and on the recent ordinances concerning air pollution control in large firing (combustion) installations.     

Olfactory and chemical characterization of indoor air. Towards a psychophysical model for air quality

The relationship between the odor strength of total air samples and the odor strengths of the constituents was investigated in three field experiments in an office building and a new preschool. The odor strength was scaled by magnitude estimation according to a master scale principle which results in comparable values for the total and the constituent odors. Between 60 and 120 chemical components were detected by GC/FID in the indoor air samples (N = 66). Most (81%) of the detected components in an air sample were odorous, even though most of them were of the low concentrations. By a method of pattern analysis, chemical as well as odor patterns of indoor air were found to be characteristics of different buildings. From the odor patterns (POG), the “odor print” of the outdoor air associated with the buildings was also recognized in the indoor air. Thus, the “odor print” of an air sample is different from its “chemical print”. A model was found that predicts the overall odor strength of an air sample from the number of FID-detected components most frequently reported to have a strong odor.     

Improving the efficiency of free-jet scrubbers

A free-jet scrubber is an innovative gas cleaner in which the primary liquid/gas contacting takes place in the turbulent mixing zone emanating from a jet nozzle. The first such devices, powered by supersonic steam or air ejectors, were exceptionally effective cleaners but were criticized as being high-energy users. A great reduction in the energy consumption of free-jet scrubbers has been accomplished in the last four years, a feat which may seem in contradiction to the “contacting power rule.” An explanation of what is happening in these devices must take into account the effectiveness with which energy and water are utilized. thereby leading one to a somewhat circular definition of “effective contacting power.” The theoretical implication of this analysis is primarily to remind us that there are many paths between two states and some are more energy efficient than others. The practical value is that such analysis generates information which aids in choosing between several design options, a direct benefit of the various free-jet configurations.     

A study of effects of ambient urban air pollution using personal samplers; a preliminary report

Air pollution has been associated with an increased incidence of respiratory disease. However, significant differences may exist between air pollution levels measured at conventional fixed monitoring stations and actual levels inhaled by a subject. Furthermore, studies of effects of air pollution might best be done using asthmatics as study subjects, since they have irritable airways. This is a preliminary report of a study using a control and asthmatic group in which effects of air pollution are assessed by sympton and medication diaries and simple pulmonary function tests. Air pollution exposure is measured using a small portable sampler for particulates, SO₂ and NO₂; these samplers are carried by the subject (“personal”) and are situated inside and outside the home. Levels obtained are compared to data obtained from the same type of sampler located at a fixed monitoring station. Preliminary analysis of the data shows that the levels of pollutants are low and there are significant differences between the four air pollution measurements, with weak correlations among the various measurements. In this preliminary report, change in pulmonary function during the day correlates only with personal NO₂ measurements. This suggests the need for estimating air pollution exposure using “personal” samplers, when investigating health effects.     

Precipitator upgrading and fuel control program for particulate compliance at Pennsylvania power and light company

Two cold side electrostatic precipitators handling low sulfur eastern bituminous coal flyash were upgraded from 94% to 99.4% efficiency in order to meet a particulate compliance limit of 0.1 lb/MMBtu (43 ng/J).The comprehensive upgrading was the result of a 2 year research and testing program during which various aspects of flue gas conditioning, electrical energization, rapping, coal quality control, and gas distribution were independently tested on three similar precipitators. The ensuing upgrading program included the installation of hardware for maximum performance and reliability as well as flue gas conditioning and a fuel ash control program.A cost and reliability analysis of the upgrading program as compared with the installation of an additional series precipitator is included.     

Towards a coherent conceptual framework for emergency preparedness/response and rehabilitation – the application of the new ICRP recommendations given in ICRP 103

In the past, most emphasis in planning for and response to an emergency situation has been placed on selected protective measures in the early phase of an emergency to keep the doses received below levels where severe deterministic health effects can be excluded and/or where the risk of stochastic effects in the population is considered “acceptable”. Less emphasis has been placed on the development of comprehensive protection strategies which include considerations of the consequences of all exposure pathways and all phases, e.g. long-term rehabilitation. In its new publication 103, ICRP proposed a coherent conceptual framework for protection in all types of exposure situations including “emergency exposure situations” and “existing exposure situations”. In the context of developing protection strategies for these exposure situations, the Commission recommends that national authorities set reference levels between, typically, 20 mSv and 100 mSv annual effective dose (emergency exposure situation) and 1 mSv and 20 mSv (existing exposure situation). In order to optimise protection strategies, it is necessary to identify the dominant exposure pathways, the timescales over which the dose will be received, and the effectiveness of available protection options. The characteristics of the development and implementation of such protection strategies is described.     

Noise susceptibility: A comparison of two naval aviator populations

The identification of characteristics of noise-susceptible (S) or noise-resistant (R) individuals is necessary for the development of noise-susceptibility risk profiles. Fifty-six naval aviators, categorized as having either incurred a hearing loss, i.e., hearing threshold levels (HTLs) > 40 dB at 4–8 kHz or retained normal hearing, i.e., HTLs ≤ 25 dB at 125 Hz-8 kHz, after thousands of flight hours were compared along several auditory and non-auditory dimensions. A number of variables occurred differentially in the two groups: Minimal Auditory Intensity Differential (MAID) scores at 2 kHz (p < 0.01) and 4 kHz (p < 0.001); iris pigmentation (blue eyes were over-represented in the S group; p < 0.05); systolic blood pressure (sitting; S group was higher; p < 0.05); calcium, albumin, and LDH levels (higher in the R group; p < 0.05); and present tobacco usage (more S aviators were currently smokers; p < 0.05). The S population also tended (p < 0.10) to exhibit elevated cholesterol and triglyceride levels as well as higher contralateral acoustic reflexes, and to have fewer individuals who had never smoked. Although no classic profile of the S or R individual definitely emerged, results suggested that at least one measurement device (MAID test) may serve as an “early warning” of imminent noise-induced damage. Further research, however, is required to test this possibility.