Particulate Collection Technologies

Settling chambers, low-pressure-drop cyclones, and dynamic precipitators are among the most common and important devices applied in end-of-pipe control applications for dust and particulate matter. 

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The selection of the optimum type of particulate collection device (i.e., ESP or fabric filter oaghouse) is often not obvious without conducting a site-specific economic evaluation. This situation has been brought about by both the recent reductions in the allowable emissions levels and advancements with fabric filter and ESP technologies. Such technoeconomic evaluations can result in application and even site-specific differences in the final optimum choice (see Piecip New.sLetter, 220, June, 1994 and Fabric Filter Newsletter, 223, June, 1994). 

Baylis, A.P. Russell-Jones, A. Collecting electrode rapping designed for high efficiency electric utility boiler electrostatic precipitators. Proceedings of the Fourth EPA/EPRI Symposium on the Transfer and Utilization of Particulate Control Technology Houston, TX, U.S.A., October 1982 EPRI Palo Alto, CA. 

The cost of the cyclones required to meet the particulate collection requirements exceeds that of other technologies. 

Static sampling systems are defined as those that do not have an active air-moving component, such as the pump, to pull a sample to the collection medium. This type of sampling system has been used for over 100 years. Examples include the lead peroxide candle used to detect the presence of SO2 in the atmosphere and the dust-fall bucket and trays or slides coated with a viscous material used to detect particulate matter. This type of system suffers from inability to quantify the amount of pollutant present over a short period of time, i.e., less than 1 week. The potentially desirable characteristics of a static sampling system have led to further developments in this type of technology to provide quantitative information on pollutant concentrations over a fked period of time. Static sampling systems have been developed for use in the occupational environment and are also used to measure the exposure levels in the general community, e.g., radon gas in residences. 

Note that the presented particle collection efficiencies cannot be assumed to be for the best available technology and are shown for equipment existing in industry. Dimensioning of particle removal equipment makes it possible to achieve better removal efficiencies in most cases presented in Table 13.1. All particulate and gas-cleaning equipment must be separately designed to meet specified local conditions. 

Pollution control devices for particulates do not depend upon new technology whereas SO2 control does. Since the first decade of this century, as a result of Cottrell s original work (9j, the electrostatic precipitator had been used to collect fly ash particulates. These devices were used on many of the older coal burning plants which had converted to oil. On the reconversion to coal, they were put back in operation or else new ESP units were put in the place occupied by the older ones. The performance of these systems, when designed for a specific coal, was... 

As with any chemical facility, process economics and transportation costs are critical factors in determining whether gasification syngas and the recovery of byproducts will be profitable. Environmental factors such as the existence of proven technology for the recovery of SO,., particulates, and mercury has made gasification attractive. When coal is nsed as a feedstock at Eastman Chemical, for instance, over 90% of the mercury contained in the coal is rontinely collected. ... 

Particulate control is by means of either a wet scrubber or a wet electrostatic precipitator located after the condensing heat exchanger. The choice of particulate control equipment depends on the degree of control required. The particulate slurry collected by the scrubber or precipitator is circulated through a pug mill that de-waters and pelletizes the ash. The ash pellets are spread on the tree fields as a fertilizer. The ash content of the wood is less than 1% so that a maximum of 5 t/day are collected and pelletized. The particulate emission standard to be met for new wood fired power plants in the State of Wisconsin, for exan le, is based on best available control technology (BACT) and can be expected to be about 21 g/ 10 kj. 

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