Operating characteristics of a fabric filter on a peaking/cycling boiler without auxiliary preheat or reheat

A fabric filter has been on-line for one year on a coal-fired boiler that is primarily a peaking unit within the power schedule. For the first six months, Eastern Kentucky coal with 2.5% sulfur was the fuel source for 30% of the time, with low-sulfur Montana coal constituting the remaining fuel during the operation period. Bag life has been excellent with no bag failures reported to date, and the pressure drops have been low. There has never been an auxilliary heat source to preheat the fabric filter for start-up, nor to reheat the fabric filter when operating at reduced load with associated low back-end temperatures. Conclusions are that the filter cake formed does protect the bags from blinding at low load conditions, and a special acid-resistant finish applied to the glass fibers protects the bags when high-sulfur coal is burned at low temperatures. Overall, this installation provides an excellent data base for cycling service and high-sulfur coal usage with a fabric filter.     

Selection, preparation, and disposal of sodium compounds for dry SOx scrubbers

A program has been initiated to assess an SO₂ removal method wherein dry powdered sodium compounds are injected into the gas stream ahead of the baghouse filter. The compounds are collected on the surface of the filter bags for reaction with the gaseous SO₂. Initial program efforts include a survey of suitable and available sodium compounds, methods of preparing the compounds for injection, and an invistigation of environmentally acceptable methods of disposal.     

Pressure drop in electrostatic fabric filtration

Fabric filtration systems have been employed in industry for over a century with relatively few technological modifications. However, with the recent substantial increase in energy costs, conservation in energy consumption has become vitally important. As a result, the filtration systems of yesteryear may not be the best approach for future applications. Recently, an external electrical field was considered in fabric filtration of industrial dust with very promising initial results. An increase in the collection efficiency, particularly for fine particulates, and a decrease in the pressure drop was observed. In this paper the further results of an experimental program in the investigation of pressure drop in the electrostatic fabric filtration in industrial dust control are presented. The basic apparatus, a bench-scale electrostatic fabric filtration system, creates a representative dust cake under specific conditions of operating parameters and charge levels. The results clearly indicate that filter and dust cake resistance, or pressure drop, decreases substantially with the increased electrostatic field strength for all industrial dust samples tested, regardless of fabric type and other relevant parameters.     

Removal of nitrogen oxides with organic amines and metal complexes

Aqueous solutions containing organic amines and metal complexes were applied for the removal of nitrogen oxides. Organic amines were effective for the removal of the mixture composed of nitric oxide and nitrogen dioxide. In particular, methyl and ethyl amines removed these species with 1 : 1 ratio from the mixture at fairly rapid rates. Dinitrogen trioxide (N₂O₃) was suggested to be involved in the course of the removal.Metal complexes removed nitrogen dioxide efficiently. As has been previously reported for a number of inorganic or organic redox systems, it was concluded that the removal of nitrogen dioxide by metal complexes proceeded also by the redox mechanism.Iron (ii) chelate complexes were highly effective for the removal of nitric oxide and this was attributed to a reversible coordination to the complex.     

Efficiency of locally available filter media on fluoride and phosphate removal for household water treatment system

Since conventional water treatment is not affordable in developing countries,looking for locally available and alternative treatment options is mandatory.Removal of fluoride and phosphate can be achieved by designing appropriate filtration media from different materials such as sand,calcined clay,pumice,scoria and bone char.This study was designed to determine the removal efficiency of these locally available filter media with respect to detention time and pH.The filtration apparatuses(tank)were filled separately with stone,gravel with grain size 0.6-4.75 mm and 40 cm deep,sand(ES=0.15-0.35 mm and UC=1.5-3),calcined clay,pumice,scoria and bone char with grain size 0.25-0.5 inch.Water samples were prepared using glass bottles with fluoride concentrations of 6 and 8 mg/l and phosphate concentration of 4 mg/1.Laboratory analysis was carried out before and after filtration to determine the removal efficiency of each medium.It was found that the highest removal of fluoride was achieved by bone char(89.65%),followed by pumice(82.4%).However,bone char has rather increased the concentration of phosphate by 63.8%.Sand was the most efficient media to remove phosphate,managing to remove by 70%.Therefore,it is an attractive option to use these locally available,environmental friendly and appropriate technologies for efficient removal of both fluorine and phosphate at the household or community water treatment level.     

河流渗滤系统中苯系物污染去除机理实验模拟研究

河流渗滤是一种自然净化过程，污染河水通过该过程在河流沉积层中发生各种物理、化学和生物作用，使得污染物浓度降低，河水水质得到净化，从而达到增加地下水开采量的目的。通过静态吸附实验和淋滤实验模拟了苯系物（BTEX）在河流渗滤系统中的吸附行为和降解行为。两种环境行为中吸附作用对于BTEX的净化效果较为有限，当吸附达到饱和之后，并存在电子受体的情况下，BTEX能够发生厌氧微生物降解，降解作用能够更有效的去除BTEX污染物。其中去除效率最高的是间二甲苯，其次是乙苯、甲苯，去除率最差的是苯。微生物降解作用相对于BTEX浓度变化存在一个滞后期。BTEX各组分的土壤 水吸附分配系数Kd越大，总的降解效率也就越低。通过河流渗滤系统这一自然净化过程，可以有效地去除浓度较高的BTEX混合污染，在两种电子受体的情况下各组分平均去除效率都超过了60%，最高去除率均超过了80%。对于持续不断入渗的污染河水，当土壤吸附达到饱和、微生物活性受到抑制情况下，去除效率会大大降低，从而使BTEX穿透包气带进入含水层，对地下水产生危害     

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.     

Air filtration and radon daughter levels

The authors investigate the effect of filtration and aerosol loading of the air on the level of short-lived air-borne daughter products of radon. By the use of a combination of filtration and aerosol loading, it is possible to shift the partitioning of the radon daughters in the room between the states: airborne, plated-out on the walls, and trapped by filters; the airborne fraction will shift between being attached to aerosol particles and existing as molecular-sized clusters. When the air filtered the equilibrium factor decreases with increasing filtration rate. At high aerosol concentrations the decrease can be explained solely as an effect of the filter removing the daughter products from the air passing through it. As the aerosol production and concentration is lowered, the decrease in equilibrium factor becomes larger. This is caused by an increase in the unattached fraction of the airborne activity and hence in the wall-deposited fraction of the total activity. At a given radon concentration, the dose delivered to a certain portion of the respiratory tract depends not only upon the equilibrium factor but also upon the fraction of, especially, ₈₄²¹⁸Po in the unattached state. It is further demonstrated that, according to the dose model of Harley and Pasternak, the dose to the basal cells of the epithelium of the bronchii will in general decrease with increasing filtration rate and increase with decreasing aerosol concentration.     

Removal of hydrocarbons from Nile water

The need to remove hydrocarbons from water supply sources raises questions on the efficiency of the present water treatment processes in removing hydrocarbons. Therefore, the effectiveness of physicochemical processes involving chlorination, chemical coagulation and sand filtration were investigated. The effect of variable filtration media was also examined. In addition, the use of an activated carbon column was considered, and the effect of different retention times was evaluated. Results of this study showed that chemical coagulation using alum and Nalco removed only 32% of the total hydrocarbons and 80% of turbidity. Use of sand and a mixture of anthracite and sand filters showed additional removal of hydrocarbons and turbidity during the continuous filtration process. Increasing the anthracite depth relative to the total effective filtration depth increases the efficiency of the filter. Adsorption on granular activated carbon was shown to be an effective means for the removal of hydrocarbons. Results obtained indicated that the carbon adsorption capacity increases linearly as the retention time increases.     

Efficiency of the activated carbon filtration in the natural organic matter removal

The removal and transformation of natural organic matter were monitored in the different stages of the drinking water treatment train. Several methods to measure the quantity and quality of organic matter were used. The full-scale treatment sequence consisted of coagulation, flocculation, clarification by flotation, disinfection with chlorine dioxide, activated carbon filtration and post-chlorination. High-performance size-exclusion chromatography separation was used to determine the changes in the humic substances content during the purification process; in addition, a UV absorbance at wavelength 254 nm and total organic carbon amount were measured. A special aim was to study the performance and the capacity of the activated carbon filtration in the natural organic matter removal. Four of the activated carbon filters were monitored over the period of 1 year. Depending on the regeneration of the activated carbon filters, filtration was effective to a degree but did not significantly remove the smallest molar mass organic matter fraction. Activated carbon filtration was most effective in the removal of intermediate molar mass compounds (range 1,000-4,000 g/mol). Regeneration of the carbon improved the removal capacity considerably, but efficiency was returned to a normal level after few months.     

A badge-type personal sampler for measurement of personal exposure to NO2 and NO in ambient air

A badge-type personal sampler was developed for measuring personal exposure to nitrogen dioxide (NO₂). An absorbent sheet containing triethanolamine (TEA) solution absorbed NO₂ which diffused through five layers of hydrophobic fiber filter. Wind effects on absorption rate were suppressed by these filter layers. NO₂ was measured by the sampler with a sensitivity of 124.8 μg h/m³ (66 ppb h) and an accuracy of within ± 20%. It could be used for measuring personal exposure to NO₂ without interfering with the wearer's daily activities. Nitric oxide (NO) could be measured after a small modification to the sampler provided oxidation ability to the layers of diffusion filter. Three layers of hydrophobic fiber filter were replaced by 12 layers of glass fiber filter containing chromium trioxide solution. NO was oxidized to NO₂ in the oxidation layers and absorbed by the absorbent sheet together with the coexisting NO₂. Sensitivity and accuracy of the sampler for NO were nearly equal to that for NO₂.     

Fabric filters versus electrostatic precipitators

Control of particulate emissions from pulverized coal fired steam generators is becoming a significant factor in the siting and public acceptability of large coal burning power plants. The particulate emission limit established by the EPA for new coal fired boilers is 0.03 lb/10⁶ Btu (13 ng/J) Possibly more restrictive than this is the state of New Mexico's particulate regulation which calls for no more than 0.05 lb/10⁶ Btu (22 ng/J) total, and no more than 0.02 lb/10⁶ Btu (9 ng/J) less than 2 microns in diameter. This paper will evaluate the effect of these stringent limitations on the technical feasibility and economics of dry particulate removal. Electrostatic precipitators have been the dominant particulate collection device in the electric utility industry for many years because of their low capital and operating cost. However, increasingly stringent emission standards have led to substantially higher costs for precipitators. These costs have increased sufficiently for fabric filtration to become a competitive alternative in achieving cost effective control. This paper will compare the economics and performance of fabric filtration with respect to conventional electrostatic precipitators. The paper will also address the preliminary evaluation procedures that should be followed in order to select the appropriate device for new or existing coal-fired boilers.     

Consumer attitudes on the use of plastic and cloth bags

This paper examines consumer attitudes and behavior on the use of plastic and cloth bags in Eski?ehir, Turkey. To this end, a structural equation model is proposed. Environmental consciousness regarding the use of plastic bags, social pressure, support for the banning of plastic bags, the intention to use cloth bags and behavior to reduce plastic bag use are employed as latent variables in the model. The intention to use cloth bags and the behavior to reduce the use of plastic bags are defined as endogenous latent variables in the structural model. In the conclusion of the study, it is identified that consumers who are environmentally conscious and feel under social pressure, tend to reduce the use of plastic bags and switch to using cloth bags.     

A passive sampling device for determining formaldehyde in indoor air

A passive sampling device based on the principle of diffusion has been developed for the determination of formaldehyde in ambient air. The sampler consists of a capped glass tube (with approximate dimensions of 2.4 × 9 cm) containing a glass-fiber filter treated with NaHSO₃. In the field, the device collects a sample by being uncapped for a specified sampling time. After being recapped and returned to the laboratory, the filter is analyzed by the chromotropic acid (CTA) method. Laboratory validation studies were conducted by exposing the sampling devices for 1 week to dry formaldehyde gas generated by passing trioxane vapor over an acid catalyst bed. In these tests, formaldehyde concentrations ranged from 0.05 to 0.80 mL/m³. Reproducibility was excellent, with relative standard deviations averaging 5.4% for five constant concentrations. The lower detection limit was determined to be 3.6 mL/m³ h. In an occupational environment an 8-h sample would be sufficient to detect compliance with the OSHA permissible exposure limit of 3 mL/m³; in a residential environment a 1-week sample would allow detection of 0.025 mL/m³ for indoor air quality audits.     

Estimation of septic tank setback distances based on transport of E. coli and F-RNA phages

Setback distances between septic tank systems and the shorelines of Lake Okareka, New Zealand were determined from model simulations for a worst-case scenario, using the highest hydraulic conductivity and gradient measured in the field, removal rates of the microbial indicators (Escherichia coli and F-RNA phages) determined from a column experiment, and maximum values of the design criteria for the disposal system, and assuming an absence of an unsaturated zone, a continuous discharge of the raw effluent from a failed or non-complying treatment system (both indicators at concentrations of 1x10(7) counts/100 ml) into the groundwater and no sorption of pathogens in the aquifer. Modelling results suggest that the minimal setback distances were 16 m to satisfy the New Zealand Recreational Water Quality Guidelines for E. coli <126 per 100 ml (Ministry for the Environment, 1999) and 48 m to meet the Drinking-Water Standards for New Zealand 2000 for enteric virus <1 per 100 l (Ministry of Health, 2000). These distances may be applicable for other lakeshores in pumice sand aquifers with groundwater velocities <7 m/day. Findings of laboratory column and batch experiments provided an insight into the microbial attenuation and transport processes in pumice sand aquifers. Bacterial removal was predominately through filtration (87-88%) and partially by die-off (12-13%), while viral removal was by both die-off (45%) and filtration (55%). In addition, microbial die-off in groundwater without aquifer material (i.e., free microbes) was much lower than die-off in groundwater with aquifer material (i.e., sorbed microbes) and contributed only 2-6% to the total removal. This implies that the setback distances estimated from die-off rates for the free microbes, determined in the laboratory without considering aquifer media and other removal processes, which are often reported in the literature, could be larger than necessary.     

Dynamics of leaf litter and soil respiration in a complex multistrata agroforestry system,Pernambuco, Brazil

High litter inputs in agroforestry systems contribute to soil microbial activity, soil fertility and productivity. Considering that the cycling of organic matter is essential to the maintenance of physical–chemical and microbiological properties of the soil, the aims of this work were to estimate the production, accumulation and decomposition of litter, and assess soil microbial respiration in a complex multistrata agroforestry system located in the north-east of Brazil. This agroforestry system has three strata formed by forest and fruit trees and species of multiple uses. During 3 years (2011–2013), leaf litter was sampled monthly to account for litterfall and quarterly to account for litter accumulation. The rates of litter decomposition were estimated using the ratio produced-to-accumulated litter, and the correlation between litter fall and rainfall was calculated. Precipitation data were provided by the water and climate agency of Pernambuco (APAC). Soil samples (0–15 cm) were also taken quarterly, simultaneously with the litter accumulation samples, and soil microbial respiration was assessed using the capture, by a KOH solution, of the evolved CO₂. The annual production of leaf litter was stable in the 3 years of study in this agroforestry system, and the monthly input of litter to the soil was influenced by rainfall, being higher in the dry seasons. The accumulated litter on the ground was constant, as was microbial activity (respiration) through time. The estimated litter decomposition rates were 1.49 (first year), 1.33 (second year) and 1.42 (third year), being considered rapid rates of decomposition. This guarantees (to the farmer) that this system is capable of maintaining soil fertility and eliminates the need for chemical fertilizers.     

Fate and effect of 2,4-dichlorophenol on biological treatment processes

The fate and effect of continuous feeding of increasing doses of 2,4-dichlorophenol (DCP) were investigated. At the beginning of each run, a drop in the efficiency of the system was recorded, after which a steady state was obtained. Continuous feeding of DCP up to a concentration of 50 mg L^?1 reduced BOD₅ and COD removal rates by 27% and 29%, respectively. Application of shock doses of DCP showed that adaptation increases the capacity of biological systems for removing toxic chemicals.     

Objectives and status of fabric filter performance study

In October 1977, Southwestern Public Service Company executed a contract with the U.S. Environmental Protection Agency that called for a study to assess the performance of a fabric filter system installed on a large utility boiler that utilizes low sulfur Western coal. The project is now into its second year and the objectives of this paper are to describe the scope and intent of the study, as well as to report progress to date. In addition, some of the difficulties that we have encountered are discussed. Although some of these problems have resulted in procedural changes, the intent of the study has not been altered. This paper describes work being done in specific areas with which both the EPA and Southwestern are connected. These include fabric assessment, data collection, selection and installation of instrumentation, and overall fabric filter system performance. Results of the first performance test are also reviewed and the installation of a pilot baghouse is discussed.     

Inhibition of microbial activity of activated sludge by ammonia in leachate

Leachate samples were collected from the West New Territory Landfill (WENT), Hong Kong, and characterized in the laboratory. The analytical results confirmed that it has a typical nature of aged leachate with a low BOD₅/COD ratio of 0.22 and a high strength of ammonia-nitrogen around 5 g/L. A lab-scale study was conducted to investigate the inhibition of microbial activity of the activated sludge. In the first test, glucose-based synthetic wastewater was used in two parallel reactors. The experimental results demonstrated that COD removal declined from 95.1 to 79.1% and the dehydrogenase activity of the sludge decreased from 11.04 to 4.22 μg TF/mg mixed liquor suspended solids (MLSS), when the ammonia-nitrogen concentration increased from 50 mg/L to 800 mg/L progressively. The remaining NH₃⁺-N residue in the treated wastewater increased from 0.58 mg/L to 649 mg/L extensively. In the second test, mixed wastewater samples containing glucose and raw leachate were fed into six parallel biological reactors and operated on batch mode. The experimental results showed COD removal decreased from 97.7 to 78.1% and the dehydrogenase activity decreased from 9.29 to 4.93 μg triphenyl formazon (TF)/mg MLSS, respectively, when the ammonia-nitrogen concentration increased within the same range. Microbial inhibition could also be substantiated by a decrease of specific oxygen uptake rate (SOUR) from 68 to 45 mg O₂/g MLSS. These results suggested leachate containing high-strength ammonia-nitrogen should be pretreated to an acceptable NH₄⁺-N level before it is fed into biological reactors.     

Solar-driven technology for freshwater production from atmospheric air by using the composite desiccant material “CaCl<Subscript>2</Subscript>/floral foam”

In this communication, experiments have been performed to check the capability of the newly formed composite desiccant material (CaCl₂/floral) for the extraction of freshwater from atmospheric air. Three numbers of solar glass desiccant box type system (SGDBS) with a captured area of 0.36 m² each, have been used. The design parameters for the water production are height of glass from desiccant bed at 0.22 m, inclination in angle as 30°, the effective thickness of glass as 3 mm and number of glazing as single. The maximum yield by the new composite desiccant material is 0.35 ml/cm³/day. The efficiency of the system SGDBS with 37 % concentration of CaCl₂ is 76.44 %.