Model calibration for pressure drop in a pulse-jet cleaned fabric filter

A model based on Darcy's law allows prediction of pressure drop in a pulse-jet cleaned fabric filter. The model considers the effects of filtration velocity, dust areal density added during one filtration cycle, and pulse pressure. Data used to calibrate the model were collected in experiments with three fabric surface treatments and three dusts conducted at three filtration velocities, for a total of 27 different experimental conditions. The fabric used was polyester felt with untreated, singed, or PTFE-laminated surface. The dusts used were granite, limestone and fly ash. Filtration velocities were 50,75 and 100 mm s⁻¹. Dust areal density added during one filtration cycle was constant, as was pulse pressure. Under these conditions, fabric surface treatment alone largely determined the values for two of the three constants in the model; the third constant depends on pressure drop characteristics of the venturi at the top of each filter bag.     

Pesticide decontamination from fabric by laundering and simulated weathering

This laboratory study investigated the effectiveness of selected detergents and the phenomenon of simulated environmental conditions (weathering) on the removal of a commercial-grade mixture of parathion and methyl parathion from a three-layer laminated fabric. The weathering treatment consisted of exposure and non-exposure to simulated environmental conditions of heat, light, and humidity. Contaminated fabric samples were laundered in one of three detergents containing an anionic, a nonionic, and a combined anionic and nonionic surfactant. The test fabric, a three-layer fabric containing an impermeable microporous film laminated between two layers of nylon, was pipette-contaminated with 400 microliters of field strength pesticide solution and allowed to dry. Half of the contaminated samples were weathered in an Atlas Fade-Ometer. All of the contaminated samples were subsequently laundered in a Launder-Ometer. Percent of pesticide residue was determined by gas chromatography. Weathering did significantly reduce both parathion and methyl parathion residues remaining in the test fabric. No statistically significant difference was found among the three detergents. High amounts of both parathion and methyl parathion remained in the test fabric after weathering and laundry treatments. Before the test fabric can be recommended for use in protective garments further research is needed to develop more effective decontamination procedures.     

Study of the effects of air pollution on textiles exposed to Cairo's ambient atmosphere

Cotton fabric (100% cotton) and synthetic fabric (65% polyester and 35% cotton) were exposed at five selected sites in urban and industrial districts in Cairo city for a period of 15 months. The changes in the physical properties of the exposed textiles were investigated. The results indicated that the tensile strength of all the exposed samples was decreased, for warp and weft directions by different ratios, at all sites as a function of time of exposure. The highest deterioration in tensile strength was 86.2%, detected for cotton samples exposed in the industrial area. The lowest percentage loss of tensile strength was 58%, detected in the purely residential area of low population density. The loss in tensile strength of synthetic textile samples ranged from 54 to 73%. The difference between the tensile strength for sheltered and unsheltered textile samples increased with increasing time of exposure, especially with increasing solar radiation intensity in the summer. The cotton fabric lost about 25% of its tensile strength, and the synthetic fabric lost about 19.5% of its tensile strength after 15 months exposure to direct solar radiation. The percentage loss of elongation (elasticity) for cotton and synthetic fabric ranged from 72% to 89% and from 67.2% to 88.2%, respectively. Several conclusions and recommendations are also given.     

Pesticide decontamination from fabric by laundering and simulated weathering1

Abstract

This laboratory study investigated the effectiveness of selected detergents and the phenomenon of simulated environmental conditions (weathering) on the removal of a commercial‐grade mixture of parathion and methyl parathion from a three‐layer laminated fabric. The weathering treatment consisted of exposure and non‐exposure to simulated environmental conditions of heat, light, and humidity. Contaminated fabric samples were laundered in one of three detergents containing an anionic, a nonionic, and a combined anionic and nonionic surfactant. The test fabric, a three‐layer fabric containing an impermeable microporous film laminated between two layers of nylon, was pipette‐contaminated with 400 microliters of field strength pesticide solution and allowed to dry. Half of the contaminated samples were weathered in an Atlas Fade‐Ometer. All of the contaminated samples were subsequently laundered in a Launder‐Ometer. Percent of pesticide residue was determined by gas chromatography. Weathering did significantly reduce both parathion and methyl parathion residues remaining in the test fabric. No statistically significant difference was found among the three detergents. High amounts of both parathion and methyl parathion remained in the test fabric after weathering and laundry treatments. Before the test fabric can be recommended for use in protective garments further research is needed to develop more effective decontamination procedures.     

Enzyme hydrolysis of polyester knitted fabric: A method to control the microfiber shedding from synthetic textile

Synthetic textile materials are noted as one of the major contributors to microfiber release from household laundry. The higher usage of synthetic textiles was noted as one of the major reasons for the leaching of microfibers into the aquatic system. Though few laundry aids are available to control the release of microfiber from laundry, no successful methods were developed to control it in the fabric itself. Hence, this research aimed to analyze the effectiveness of surface modification of polyester fabric using lipase enzyme and its impact on microfiber shedding. Taguchi’s L9 orthogonal array was adopted to optimize the enzyme treatment process parameters to reduce microfiber shedding. The results showed that enzyme concentration was the major influencing factor with a contribution of 35.56%, followed by treatment pH (35.247%), treatment time (17.46%), and treatment temperature (11.74%). The optimization with S/N ratio showed minimum microfiber shedding at an enzyme concentration of 0.5 gram per liter (gpl), treatment temperature of 55°C, 6.5 pH, and a treatment time of 45 minutes. Knitted polyester fabric treated with the optimized enzyme treatment condition showed a significant reduction (p<0.05) in microfiber shedding (count—79.11% and mass—85.68%). The surface changes and the interaction of the enzyme on the fabric were confirmed by hydrolytic activity and FTIR analysis. The optimized treatment on different knit structures and fabric with different grams per square meter (GSM) indicated the versatility of the treatment irrespective of fabric parameters. The repeated laundry process (20 washing cycles) showed that the enzyme-treated samples had a significant level (p<0.05) of reduction in shedding than the control sample. The difference in shedding after 20 washes supports the efficiency and longevity of the enzyme treatment process in reducing microfiber shedding.

     

The penetration of formulated guthion® spray through selected fabrics

Abstract

A technique for comparing pesticide penetration through fabric was devised. It involved passing fabric swatches through a controlled spray system and measuring the pesticide residue transferring on and through the tested fabric. Six variations in fabric were selected for testing: 100% cotton woven chambray,

Scotch‐guard^® treated chambray, Tyvek^® , Crowntex^® , and two variations of Gore Tex^®. Guthion^® (azinphos‐methyl) was chosen as the insecticide for controlled use in this experiment because of its widespread use and relatively high toxicity.

Gas Chromatographie analysis of the amount of Guthion^® transferred through the outer fabric was made by the use of analysis of variance (ANOVA) and Duncan's multiple range test. The ANOVA for experiment replication showed no significant difference among the replications of each fabric. The treatment ANOVA was highly significant at the 0.01 level.

Duncan's multiple range test further analyzed the differences in the treatment, and three groups were found to be significantly different from each other. The two types of Gore Tex^®, Tyvek^® and Crowntex^® comprised the group permitting the least penetration. Scotch‐guard^® treated chambray followed, and untreated chambray allowed the greatest penetration.     

Closing Comments

“Industrial fabric filtration, the sleeping giant, is stirring. It appears that we are about to experience a new period of innovation and development similar to the one that occurred during the 1950’s.” The above remarks by Professor First, as presented in the Symposium, unerscore the renewed interest in filtration as a means for controlling submicron particulate emissions. Bur-chard and others pointed out the significance of fine particulate emissions, especially with regard to health effects and visibility degradation, and Walsh discussed the data required to employ fabric filters appropriately for particulate emission control.     

Types of Fabric Filter Installations

The basis for evaluating fabric filters is examined. Properly applied and maintained fabric filters perform at highly satisfactory efficiency levels.     

Collection Efficiency as a Function of Particle Size,Shape and Density: Theory and Experience

The performance features of both industrial and experimental fabric filter systems with respect to the concentration and particle size properties of the collector effluents are examined. From a qualitative viewpoint the factors that should influence significantly the collection characteristics of a fabric filter are dust properties, fabric properties, operating parameters, filter cleaning method, and critical interdependencies. The quantitative prediction of performance and the establishment of design parameters are limited for a generalized approach but data have been reported that provide excellent support for limited applications.     

Size removal on polyester fabrics by plasma source ion implantation device

Plasma treatment was evaluated as an alternative clean desizing technology in this work. As indicated by weight loss, O2 plasma treatment efficiently removed sizing agents such as polyvintyl alcohol (PVA), polyacrylic acid esters and their mixture (MIX) on polyethylene terephthalate (PET) fabrics. SEM pictures of the plasma treated samples directly proved the disappearance of the sizing agents. XPS analysis showed apparent changes in chemical composition and functional groups of the PET surface after O2 plasma treatment. Carbon content decreased due to the removal of sizing agents while oxygen content increased. O2 plasma treatment also increased hydrophilic functional groups of sizing agents, which is confirmed by C1s and O1s deconvolution analyses. After O2 plasma treatment, the PET fabric was subjected to conventional desizing process at different temperatures. Except for the PET fabric sized with PVA, plasma-treated fabrics showed more efficient desizing results when compared with untreated fabrics. Furthermore, the desizing effluent from the treated fabric gave lower TOC, COD and BOD values.     

Predicting Pressure Loss for Pulse Jet Filters

The analysis of pressure loss characteristics for pulse jet filters suggests that the relationship between dust adhesion to the fabric and the opposing force generated by pulse jet action plays a major role in dust removal. Hence, fabric cleanability is examined in terms of the adhesion-cohesion forces bonding the dust to the fabric vs. the intensity and frequency of the dust dislodgement forces produced by the high energy air pulses. The effect of jet size and location, jet air volume, and the intensity (pressure) and duration of the jet pulses is related to operating pressure loss.

The mechanics of energy transfer from the jet pulse to the dustladen fabric are explored in terms of jet pressure, solenoid valve action, the ratio of delivered pulse air volume to bag (tube) volume, and the elastic and flex properties of the felt bags. Effective and actual fabric dust holdings before and after cleaning are discussed with respect to steady-state dust deposition and removal rates, and operating pressure losses. Finally, predictive equations are proposed for estimating pressure loss over a broad range of design and operating parameters.     

Formation of organochlorine by-products in bleached laundry

Laundering fabrics with chlorine bleach plays a role in health and hygiene as well as aesthetics. However, laundry bleaching may create chlorinated by-products with potentially adverse human health effects. Studies have shown that toxic chlorinated gases are produced in the headspace of washing machines when hypochlorite-containing bleach is used. Laundry bleaching has also been implicated in contributing dissolved organochlorine to municipal wastewater. However, there have been no reports of organochlorines produced and retained in fabric as a result of laundry bleaching. We have used a chlorine-specific X-ray spectroscopic analysis to demonstrate the formation of organochlorine by-products in cotton fabrics laundered with chlorine bleach under typical household conditions. Organochlorine formation increases at higher wash temperature. At least two pools of organochlorine are produced in bleached fabric: a labile fraction that diminishes over several months of storage time as well as a more stable fraction that persists after more than 1 year. Our results also suggest that residual hypochlorite remains in fabric after laundering with bleach, presenting the possibility of direct and sustained dermal contact with reactive chlorine. This study provides a first step toward identifying a new risk factor for elevated organochlorine body burdens in humans.     

Performance of a Pulse-Jet Filter at High Filtration Velocity III. Penetration by Fault Processes

Performance data for fabric filters using either woven or felt bags can be better understood when fault processes such as pinhole bypass and seepage are considered. Penetration straight through the dust cake and fabric may not be important by comparison. Observed trends of increased penetration with increased filtration velocity, constant or slightly increased penetration with increasing particle diameter, and constant penetration with additional dust loading can be explained by fault processes. The pulse-jet experimental work described here, done over many filtration and cleaning cycles, shows that penetration increases substantially with increasing filtration velocity and that this increase is due entirely to seepage.     

A Fabric Denuder for Sampling Semi-Volatile Species

ABSTRACT

A new style of diffusion denuder has been evaluated specifically for sampling HNO₃. A coated fabric is used as the denuder substrate, which can be loaded directly into a standard filter holder. This approach allows direct denuder sampling with no additional capital costs over filter sampling and simplifies the coating and extraction process.

Potential denuder materials and coatings were evaluated in the laboratory to test the removal efficiency. NaCl coatings were used to assess more than 20 materials for HNO₃ collection efficiency. Particle retention, which would cause a denuder to have a positive bias for gas concentration measurements, was evaluated by ambient air sampling using particulate sulfate as the reference aerosol. Particle retention varied from 0 to 15%, depending on the denuder material tested. The best performing material showed an average particle retention of less than 3%.

Denuder efficiency of four fabric materials was tested under ambient conditions to determine removal efficiency. The fabric denuder method was compared with a long path-length Fourier transform infrared (FTIR) spectrometer, a tunable diode laser absorption spectrometer (TDLAS), and a denuder difference sampler to independently measure HNO₃. HNO₃ collection efficiency was typically 90% for the denuders, whether coated with NaCl or not. For 10-L/min sampling rates with the fabric denuder, the square of the correlation coefficient with the FTIR spectrometer was 0.73, compared to 0.24 with the TDLAS.     

Dust Deposit Profiles in a High Velocity Pulse-Jet Fabric Filter

Dust deposit profiles in a pilot-scale pulse-jet fabric filter were measured using a beta gauge. Fly ash was collected on polyester needled felt bags, and the dust profiles were measured after the test system was operated to equilibrium at superficial filtration velocities of 50, 75,100,125, and 150 mm/s. The profiles measured show that a large mass of dust is retained on the fabric of a pulse-jet filter when operated at high filtration velocities. This dust mass retention can be caused by two mechanisms: the failure to remove dust from the fabric during a cleaning pulse, and the redeposition of suspended dust onto the fabric after a cleaning pulse. The dust deposit measured at the highest test velocity was found to be much different from the deposits measured at all other velocities. The deposit found at 150 mm/s had almost twice the average areal density and was more evenly distributed than the deposits found at lower velocities.     

Electric Utility Applications Of Fabric Filters

Encouraged by the successes attained with fly ash control by fabric filters in Pennsylvania Power & Light and Colorado Ute, other utilities are installing, planning, and/or considering baghouses as a practical and economical means for controlling emissions from the burning of low sulfur coals. Where deposits of alkaline reagents (i.e. nahcolite) are available, some power plants are also considering a process for dry scrubbing SO₂ from the flue gas. By introducing such reagents with the emission ahead of the fabric collector, both partlculates and SO₂ are removed.     

Trace metal distribution and control in the pilot-scale bubbling fluidized bed combustor equipped with the pulse-jet fabric filter,limestone injection,and the humidification reactor

This work focused on trace metal behavior and removal in a fabric filter or in a humidification reactor during the cofiring of sawdust and refuse-derived fuels (RDFs) in a pilot-scale bubbling fluidized bed (BFB) boiler. Trace metal emissions measurements before and after the fabric filter revealed that removal efficiency in the fabric filter was in the range of 80-100%, and that the European Union (EU) Directive on Incineration of Waste restrictions for trace metal emissions are easily achieved even if addition of RDFs substantially increases the concentration of trace metals in fuel blends. Limestone injection enhanced the removal of As and Se but had no noticeable effect on the removal of other trace metals. Extensive formation of HgCl2 and condensation on fly ash particles during sawdust plus 40% RDF cofiring resulted in a 92% Hg removal efficiency in the fabric filter. Limestone injection had no effect on the Hg removal in the fabric filter but decreased the Hg removal in a humidification reactor from 40 to 28%. Results of the bed material and fly ash analysis suggested capture of Cu, Pb, Mn, Ni, and Zn in the bed material but also suggested that these metals may be released from the bed if the fuel characteristics or process conditions are changed.     

Mobile Fabric Filter System: Design and Preliminary Results

In order to study the effects of fabric filter parameters when filtering an actual industrial effluent stream, it is necessary to vary these parameters in the field. A mobile fabric filter system has been designed, fabricated and operated to provide this information. The design characteristics and some preliminary field data collected with this system are summarized.     

Operation and Maintenance of Fabric Filters

Operation and maintenance and performing correct system monitoring of fabric filters is discussed. The anticipation of future problems at the time of start-up and the necessity of maintaining correct records on the system to assist in later troubleshooting is stressed. When all is going well, the fabric filter requires little but routine maintenance on moving parts, which is usually well identified in the service manuals. Problems usually appear as excessive emissions, high pressure drop, or inadequate bag life. In order to find the cause of these problems, one must have maintained sufficient Information on the system to identify what changed and when. With this information, there are logical paths to follow to the proper solutions.     

Filtration Properties of Fly Ash from Fluidized Bed Combustion

Some of the features of the fluidized-bed combustion (FBC) process have a direct bearing on the particulate properties that most strongly influence filtering pressure drop. A laboratory program was conducted to experimentally determine the relative pressure drop characteristics of ashes from the TVA-EPRI 20-MW bubbling bed, atmospheric pressure FBC (AFBC) pilot plant and six pulverized-coal combustion (PC) units. The combined influences of measured particle and dust cake properties on filtering pressure drop were estimated with existing filtration theories. These theories predict a higher pressure drop for a dust cake produced with the AFBC ash than for one consisting of any of the PC ashes. Laboratory measurements were made of the flow resistance of idealized, simulated dust cakes to confirm these predictions. Field operating data from the fabric filters collecting some of the tested ashes were available to validate the laboratory results. The laboratory and field data show relatively good agreement. The AFBC ash must be treated as a special case for fabric filters, and careful selection of cleaning method and fabric must be made to minimize the inherently high pressure drop characteristics of this ash.