Filter barriers

Particulate removal requirements vary depending on the use of the product gas. For example, particulate levels must be reduced to below 50 mg/Nm3 for gas engines and below about 15 mg/Nm3 (>5 im) for turbines, and to perhaps 0.02 mg/Nm3 for synthesis gas systems. The primary types of systems include cyclonic filters, barrier filters, electrostatic filters, and wet scrubbers. 

Barrier filters include a range of porous materials that allow gases to penetrate but prevent the passage of particulates. These filters effectively remove small-diameter particulates in the range of 0.5 to 100 pm in diameter from gas streams. Barrier filters can be designed to remove almost any size of particulate, including those in the sub-micron range, but the pressure differential across the filter will increase as the pore size decreases. 

Barrier filters are cleaned by periodically passing pulsing clean gas through the filter in the reverse direction of normal gas flow. To reduce the overall particulate load, these filters are typically placed downstream from cyclone filters. Barrier filters are effective for removing dry particulates but are less suitable for wet or sticky contaminants such as tars. 

Tars have a tendency to cling to the filter surface and can undergo subsequent carbonization reactions that lead to fouling and plugging. Even in the absence of further decomposition, tars are difficult to remove from these materials. Examples of barrier filters suitable for biomass systems include rigid, porous-candle, or cross-flow filters constructed of metal or ceramic bag filters constructed of woven material, and packed-bed filters. 

Barrier filters have been tested and shown to have potential in gasification demonstration systems. Ceramic and metal candle-type filters were both tested at a commercial demonstration facility at Varnamo, Sweden, that is an integrated... 

Fluorescence microscope equipped with appropriate excitation filter, dichroic mirror, and barrier filter. For this example, an Olympus BHT compound microscope equipped with a BP490 excitation filter, BH-2DM500 dichroic mirror, and a LP515 barrier filter is used. 

Fig. 1. Comparisons of the wide-field, flying spot, pinhole detector, and pinhole confocal microscopes. Components include an excitation light source (V), an excitation filter (E), a dichromatic mirror (DM), an emission barrier filter (B), an objective lens (n), a detector (D), and a pinhole (P).

The flue gas passes through a number of small diameter high-efhciency cyclonic elements arranged in parallel and contained with the separator vessel. The UOP design uses an axial flow cyclone. After the catalyst particles are removed, the clean flue gas leaves the separator. A small stream of gas, called the underflow, exits the separator through the bottom of the TSS. In an environmental application, the underflow is diverted to a fourth stage separator (FSS) that is typically a barrier filter. The underflow rate is typically 2-5% of the total flue gas rate and is set by use of a critical flow nozzle. 

Another option to improve TSS performance is use of a sintered metal filter. This technology has typically been applied only as a fourth stage application on the TSS underflow. Pall has commercialized this barrier filter on the entire FCC flue gas on one commercial unit. 

A fabric baghouse is a common technology in the utility industry for removal of PM. These devices can achieve very high PM reductions since they are a barrier filter. However, the bags are prone to tear, do not react well to temperature excursions,... 

Yellow or orange filter (e.g, OG1 barrier filter from I.F.-microscope)... 

In UV fluorescence photography, the fluorescence of a substance excited by UV illumination is captured. The source of ultraviolet radiation filtered with an ultraviolet transmission filter, or excitation filter, is aimed at the subject in a completely darkened room. The subject reflects the ultraviolet light, but can also emit a visible fluorescence. The ultraviolet light is then prevented from reaching the film by a barrier filter that only allows visible light to be transmitted to the film. 

Examine as soon as possible with a fluorescence microscope (excitation filter No.l (BG12) and barrier filter No.47). 

The Ploemopak illuminator block (Fig. 1C and D, e,) for NAD(P)H excitation comprises 2 mm thick special UG11 filter prepared by Leitz (Fig. 1C and D, e2,e3) + BP 365 interference filter (Zeiss) with very low transmittance above 390 nm for excitation, (Fig. 1C and D, e4) and a TK 380 as the dichromatic beam splitter (Fig. 1C and D, el). The illuminator block for hydrocarbon (benzpyrene) fluorescence excitation comprises 2 nm UG 1 + BP 365 nm interference filter from Zeiss for excitation, a neutral beam splitter instead of the dichromatic beam splitter, and no barrier filter. 

For the estimation of Chi formation in hairy roots, the root cells were examined on a laser scanning confocal image system attached to a microscope. The filter package with a laser (excitation 568 nm) and a 590-610 nm band pass barrier filter for red fluorescence was employed. Digital image analysis was performed by a computer-aided image processing system with software. 

Fig. 5. Schematic drawing of the microsheath flow apparatus combined with two-photon excitation fluorescence microscopy. DM dichroic mirror BF barrier filter M mirror changing light path and L lens for bearing images.

Figure l6-3 Fluorescein photograph of conjunctival staining taken without barrier filter. (From Courtney RC, Lee JM. Predicting ocular intolerance of a contact lens solution by use of a filter system enhancing fluorescein staining detection. Int Contact Lens CUn 1982 9 302-310.)... 

Tear breakup time (TBUT) is used clinically as a diagnostic aid in dry eye syndromes and for testing the efficacy of therapeutic approaches. Assessment of TBUT, typically defined as the interval between the last complete blink and the development of the first randomly distributed dark spot in the tear film, is commonly used to estimate tear film stability. Fluorescein can be instilled into the eye with either a pipette or wetted fluorescein strip and observed with cobalt blue excitation and with or without a yellow barrier filter for observation. Unfortimately, there is still no global standard as to how TBUT should be determined and no consensus as to appropriate cut-off values. 

ICG s primary use is as a fluorescent dye for retinal and choroidal angiography. Its low fluorescence property initially limited its use in angiography smdies. Improvements in video technology, the introduction of appropriate excitation and barrier filters, and the development of the scanning laser ophthalmoscope with a modification to permit infrared recording ultimately allowed choroidal angiograms with high temporal and spatial resolution. 

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