Pulse-jet Filter Research Articles

Long-term operation of pulse-jet filters for wood dust

Long-term operation of pulse-jet filters for wood dust. The study specifies the value of flow resistance and separation efficiency of filter material during long-term use in pulse-jet filters for wood dust. The experiments were carried out for one type of material working in two different filtration installations in one furniture factory. The bags were obtained from the installations after working for 67, 133 and 272 days, respectively. All tests were performed on the pilot-scale test stand under identical filtration conditions. Studies have shown that long-term filter material use increases airflow resistance and improves filtration efficiency. The range of these changes depends on the operating conditions of the pulse-jet filters. The obtained results made it possible to determine the properties of the long-term use of filter materials in various filtration conditions.

Comparative analysis of residual pressure drop behavior between electrostatically assisted flat based and pilot pulse jet filter unit using conductive filter media

Comparative analysis of residual pressure drop behavior between electrostatically assisted flat based and pilot pulse jet filter unit using conductive filter media

Movement of flexible filter media under pulse-jet filter cleaning conditions

Reverse pulse-jet cleaned bag filters are widely used for the removal of fine particles from gas streams. Based on the material properties of a single fiber, the entire filter medium is modeled which shows an elastic and apparent viscous property mainly due to the restoration of the weaving pattern. Thus, for the pulse-jet cleaning, the actual transient pressure difference can be linked directly to the deflection of the filter medium. The filter medium displacement is simulated for the filtration and cleaning measures by finite element method (FEM) for a clamped filter test sample and the large-scale bag filter situation, respectively. As expected a high curvature of the filter medium coincides with a high equivalent tensile stress which in turn is a pre-curser for the probability for cake breakage.

Principles of pulse-jet filters used in the woodworking industry

Principles of pulse-jet filters used in the woodworking industry. The pulse-jet filters used to separate wood dust and factors influencing their operation were described in this paper. The analysis of the possibility of the use of pulse-jet filters for wood dust separation presented in this work was based on two basic quantitative criteria. These are the separation efficiency and the pressure drop in the filtration process performed in a dust collector. The influence of wood dust type, filtration velocity and air relative humidity the separation efficiency and the pressure were described.

Pilot-scale study on the influence of wood dust type on pressure drop during filtration in a pulse-jet baghouse

Abstract Experimental filtration processes were carried out to investigate the air flow resistance during separation of three types of wood dusts in a pilot-scale pulse-jet filter. Three types of dust were compared: dust from sanding pine wood, dust from sanding beech wood and dust from working particl,eboard. These dusts are characterized by different particle-size distribution. The resistance coefficient K1 was determined for the filter fabric used in tests. Basing on the results of pressure drop across the filter measured during the experimental processes in condition of three levels of filtration velocity Vf (0.0405; 0.0484 and 0.0583 m s−1) the specific dust cake resistance coefficient K2 was calculated. It value depends on the dust type and filtration velocity used. The lowest K2 (20,085 s−1) has pine wood dust at filtration velocity 0.0484 m s−1. While the highest value (28,925 s−1) was calculated at Vf = 0.0583 m s−1 for dust from working of particleboards.

Gas turbine air filter elements under fog endurance tests

Pulse-jet filter systems for gas turbines installed in humid and foggy areas rarely achieve their promised life-time. Here, we look at test methods to evaluate fog endurance of filter elements under laboratory conditions.

Air flow resistance across nonwoven filter fabric covered with microfiber layer used in wood dust separation

Modern nonwoven filter fabrics covered with a microfiber layer make it possible to carry out surface filtration. A dust cake forms only on their upstream side and influences the air flow resistance across the filter. The mode of formation of the flow resistance caused by such a fabric during the separation of very fine wood dust particles was the subject of a comparative investigation using a homogeneous, standard nonwoven filtering fabric. The experiments carried out in a pilot-scale pulse-jet bag filter enabled a detailed description of the increase in pressure drop across the dust cake formed during filtering cycles repeated hundreds of times. Based of the results obtained the difference in this filtration parameter between polyester-based nonwoven filter fabrics with a standard and a layered structure with microfiber was also shown.

Pulse-jet filtration: An effective way to control industrial pollution Part II: Process characterization and evaluation of filter media

The fundamental concept of design and development of the pulse-jet filter have been discussed in Part I of this monograph series [Textile Progress, Vol. 41, No. 4]. For successful running of the industrial pulse-jet filter, fundamentals of the filtration process and operating principle should be well understood. In view of the above, the monograph is intended to develop in-depth understanding of the mechanism and factors governing the filtration process. Modeling and simulation aspect related to filtration process is also included, which is helpful to judge process performance for effective process monitoring, and also to set the process and design parameters at an optimum level. In view of selection and designing of new filter media, a comprehensive examination of various methods of testing and evaluation of filter media is incorporated.

Pulse-jet filtration: An effective way to control industrial pollution Part I: Theory, selection and design of pulse-jet filter

Pulse-jet filtration is described as one of the most efficient technologies in controlling industrial pollution across the world. The monograph provides the fundamental concept of design and development of pulse-jet filters under varied siutations. For successful running of a filter unit, a comprehensive knowledge base as regards a selection of design and development of filter media is essential; thus, this is incorporated in the monograph. I also discuss technical and commerically attractive solutions for successful operation of industries integrated with pollution control equipment maintaining clean air requirements.

De-dusting Filter Bags Reduce Indian Petcoke Mill Emissions

BWF Envirotec has installed more than 400 filter bags in a pulse jet clean filter system at an Indian industrial mill producing petroleum coke, a fuel commonly used in rotary kilns for cement production. The pulse jet filter separates the fine grain ‘petcoke’ product from the exhaust gases escaping out of the mill. The installation by the German-based company has reduced the mill’s measured emissions over the last nine months to under 10 mg/Nm 3.

Pulse-jet driven injectors for fabric dust filters: (Part 1) The significance of jet-injector interaction

Application of steady-state jet mixing studies to simple venturis and injectors indicates that the form of the output pressure wavefront is sensitive to the geometry of the assembly; the wavefront will be modified further by the transient nature of the pulse-jet in dust filter applications. Using high-speed digital techniques, typical pressure wavefronts at selected points adjacent to the filter fabric have been recorded with accurate resolution of the initial attack of the pulse, and of peak and trough transient pressures. The pressure wavefront can be optimised by simple application of jet mixing principles. A comparison is made between commercial venturi and experimental injector combinations likely to have direct applications to pulse-jet filters.

The role of venturis in pulse-jet filters

The normal operation of a pulse-jet fabric filter involves two stages. First, the filter collects dust and the pressure drop increases according to the characteristics of the dust, the gas, and the way the filter is operated. Second, the filter is then cleaned; in the case of pulse-jets with a pulse of compressed air into the mouth of the bag. The point in the filtration cycle at which cleaning takes place is usually decided by the filter manufacturer, either at a set time, or at a given pressure drop. His choice is usually based on experience of the filter performance and the characteristics of the dust. The settings on the cleaning controls are usually adjustable and ‘fine tuning’ of the cleaning parameters is possible. The choice of optimum settings is not, however, straightforward. The designs of venturies in common use differ widely, ranging from straight tubes or no venturi at all, to complex smooth shapes designed for maximum performance. Little or no data are published on the performance of these venturis, and no published theory exists by which performance can be satisfactorily predicted. This paper highlights the problems involved in predicting the pressure drop of a pulse-jet filter, and goes on to present theories by which improved filter performance and stability may be achieved. Data are presented on the performance characteristics of six assorted venturi designs, and a detailed discussion on the selection procedure for venturis is included.

Fabric cleaning in pulse-jet filters

In pulse-jet filters, bag cleaning is accomplished by a compressed air pulse being injected into the clean side of a filter bag. This causes an abrupt increase in pressure within it, leading to a flow reversal as well as to acceleration of the filter cloth. Investigations with a 2.5 m long filter bag have shown that it is not the forces arising from the fabric acceleration, but those arising from the reverse air flow which play the major role in bag cleaning, and that the dust-cake release is related to the peak pressure built up inside the bag. In order to achieve complete dust dislodgement, a critical overpressure is necessary at every location along the length of a bag for a certain period of time. This overpressure depends on the dust-cake-fabric interaction. Experiments with flat-geometry fabric samples have shown that the critical overpressure can be found from a laboratory-scale experiment.

Changing patterns in dust filtration research

Early studies of dust filtration arose from the need to understand the action of fibrous filters challenged by smokes developed for chemical warfare. Concepts of depth filtration have subsequently been translated, via napped woven cloths into needlefelts used in pulse-jet filters. Modern surface-finished felts, used commercially, promote true dust cake formation although the distinction between depth filtration and cake filtration is not always recognised. The performance of practical dust filters cannot be predicted from such academic studies due to by-products of cake release mechanisms. Future areas for research will be found in the action of pulse-jets, efficiency of cake release and partial re-collection of the discharged dust cake. In this connection the penetration and percolation of needlefelt by a dust cloud becomes important and we must return to considering mechanisms of depth filtration. In conclusion some comments are made on the changing pattern of the climate for future academic researches.

Performance of a High Velocity Pulse Jet Filter in a Wool Carbonizing Process

Experiments on a high velocity pulse jet filter used to control emissions from a wool carbonizing process have shown that it is necessary to use filter cloths with a surface skin to prevent premature blinding of the fabric. The skin partially prevents dust and wool fiber from penetrating into the depth of the fabric and, subsequently, the dust is more easily dislodged during cleaning. Although both Goretex® and a calendered needlefelt have given satisfactory performance at a filtration velocity of 65 mm/s, there is a gradual increase in the resistance to airflow through the fabrics with time. This is due to the accumulation of dust on the fabric, which is not removed by the normal cleaning pulse. After eight months service, 56% of the resistance of the Goretex cloth was due to dust that was not dislodged from the fabric during cleaning, 38% to dust which was dislodged during cleaning but immediately redeposited on the bag, and 6% to dust added during the filtration cycle and cleaned from the fabric by the cleaning pulse. The efficiency of the cleaning process can be improved by cleaning the filter off-line rather than the more normal on-line cleaning. Under these conditions the dust that is usually redeposited on the bag is allowed to reach the hopper.

Dust removal characteristics of fabrics used in pulse-jet filters

Dust removal characteristics of three fabrics used in pulse-jet filters were investigated. All fabrics were polyester felt but had different surface characteristics; fabrics with an untreated surface, a singed surface, and a surface with a microporous PTFE laminate were used. Three dusts (fly ash, limestone, and granite dust) were tested on each fabric at each of three filtration velocities (50, 75 and 100 mm/s), so that a total of 27 different operating conditions were examined. Both fabric cleaning efficiency, defined as the fraction of deposited dust that is removed from the fabric by cleaning, and system cleaning efficiency, defined as the fraction of deposited dust that reaches the hopper during a cleaning cycle, were measured for each operating condition. Resultant data fell into three groups. Group 1, consisting of the PTFE-laminated fabric collecting all dusts, had the highest fabric and system cleaning efficiencies. Group 2, consisting of limestone and granite dust deposited on untreated and singed fabrics, had the poorest fabric cleaning efficiency but a system cleaning efficiency intermediate between the other groups. Group 3, consisting of fly ash deposited on untreated and singed fabrics, had fairly high fabric cleaning efficiency but the lowest system cleaning efficiency; much of the fly ash removed from these fabrics probably redeposited on the fabrics instead of falling to the hopper. Fabric cleaning efficiency was independent of the filtration velocities tested here and dependent on the dust deposit areal density.

Dust Emission Characteristics of Pulse-Jet-Cleaned Fabric Filters

Essentially all dust penetration through a pulse-jet filter occurred by seepage of collected dust through the filter fabric rather than by a failure to collect the dust in the first place. The flux of dust through the fabric increased with time as the dust deposit on the fabric increased; this behavior is consistent with seepage theory. The flux of dust through pulse-jet cleaned bags was measured for dusts with three size distributions (granite dust, limestone dust, and fly ash), using polyester felt fabrics with three surface treatments (untreated surface, singed surface, and surface with microporous ptfe laminate), at three superficial filtration velocities (50, 75, and 100 mm/sec). Dust type and fabric type affected the amount of dust carried by the bag at steady state; the amount of dust carried determined the flux of dust through the fabric. Measurements of flux through the bags for all 27 tests correlated well with a single parameter, which was derived assuming seepage accounts for all penetrating dust.

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.

The effect of dust retention on pressure drop in a high velocity pulse-jet fabric filter

Pulse-jet fabric filters exhibit abnormally high pressure drops when operated at higher than normal superficial filtration velocities. The causes of high pressure drop are investigated for a pilot scale pulse-jet filter collecting fly ash at 50, 75, 100, 125 and 150 mm/s filtration velocities. The measured equilibrium pressure drops ranged from 0.35 kPa (1.4 in. H 2O) at low velocity to 10.2 kPa (40.8 in. H 2O) at high velocity. Retention of a large mass of dust on the fabric was found to have a significant effect on equilibrium pressure drop at all the tested filtration velocities. The dust deposit's distribution, total mass, and specific resistance ( K 2) all remained essentially constant at lower filtration velocities, but changed dramatically at the highest test velocity. At the 150 mm/s velocity the total dust mass doubled, the dust distribution equalized over the surface of each bag, and K 2 increased by a factor of 4.7.

Modeling Concepts for Pulse Jet Filtration

A new model is proposed for predicting system pressure loss for large, pulse jet filters. Key data inputs were derived from experiments involving single and three-bag systems filtering coal fly ash and talc with Dacron and wool felts. Pulse jet cleaning parameters, face velocity, and inlet concentration were the principal operating variables. Several techniques used in modeling reverse flow and mechanically shaken systems, such as the classical drag versus fabric loading relationships and dust dislodgement phenomena, have been applied successfully to pulse jet filtration. However, several new concepts are introduced to facilitate the physical description of the combined filtration and pulse jet cleaning processes. Highlighting the model design is the fact that steady state fabric dust loadings depend mainly on the adhesive force binding the dust layer to the fabric and the intensity of the cleaning pulse and not upon face velocity and inlet concentration. Additionally, the fabric dust loading is composed of two parts, a highly porous, “redeposited” phase and a freshly deposited layer whose K2 value is higher and readily predicted by filtration theory. The outgrowth of this study is a rational and relatively simple mathematical model whose output agrees well with test data from two independent sources.