Preparation and Characterization of Porous Composite Filter Medium by Polytetrafluoroethylene Foam Coating
Abstract The high costs of ceramic and Teflon filter media for hot gas cleaning has limited their industrial applications. This paper presents a foam coating technology that can be used to produce an inexpensive and highly efficient filter for industrial applications. A new apparatus was designed and built that coats porous glass mats with liquid-phase polytetrafluoroethylene (PTFE). The machine generates bubbles, enables the formation of uniform micropores less than 45 μm in diameter, and produces a product with air permeability greater than 5.5 cm3/cm2/sec. The resulting filter was found to be thermally stable up to 270 °C without any visible distortion and was comparable in dust collection efficiency to other commercial filter media. In addition, its de-dusting efficiency was greater than 85%, which is similar to that of other test filter media.
Dust removal characteristics of fabrics used in pulse-jet filters
Abstract 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.
Adsorbed protein layers at fluid interfaces: interactions, structure and surface rheology
Abstract Properties of adsorbed layers of proteins at air–water and oil–water interfaces are reviewed. Emphasis is placed on recent developments in understanding the adsorption and surface rheology of individual globular proteins, especially the milk protein β-lactoglobulin, in the absence and presence of other proteins or small-molecule surfactants. Problems of modelling adsorbed layer structure and surface equation of state against a background of irreversibility and molecular complexity are addressed. Similarities and differences are described between impenetrable solid and mobile fluid surfaces, between air–water and oil–water interfaces, between shear and dilatational surface deformations, and between globular proteins and disordered proteins (caseins). A new simulation model is discussed in which the adsorbed globular protein monolayer is modelled mesoscopically as a flexible bonded network of spherical particles. The model can describe various characteristic properties of viscoelastic gel-like protein layers, including time-dependent changes in properties arising as a result of large-scale dilatational deformations. Competitive displacement of β-lactoglobulin from the air–water interface by non-ionic surfactant has been demonstrated directly by neutron reflectivity. While some good correlations have now been established between properties of mixed protein+surfactant layers and the stability of foam and emulsion systems, the detailed relationship between surface rheology and colloid stability is still poorly understood.