Filter system

Abstract

The present invention is an improved filtration system, filtering method and unique chemical composition for capturing mercury and other pollutants in flue gases generated by process gas streams. The improved filtration system may take various forms depending on the type of filter system most desired for a particular application; however, the filter system includes at least a filter element or elements and an adsorbent component having a composition suitable for capturing mercury on the downstream side of the filter element.

Description

RELATED APPLICATIONS [0001] The present application is a division of copending U.S. patent application Ser. No. 10 / 272,487 filed Oct. 16, 2002.FIELD OF THE INVENTION [0002] The present invention is an improved filter system and components thereof for both collecting particulates and adsorbing chemical pollutants from process gas streams. More particularly, the filter system of the present invention is highly effective for removing pollutants such as gaseous and solid elemental mercury and its compounds, as well as other chemical pollutants, and for collecting particulates under a range of process gas stream conditions. BACKGROUND OF THE INVENTION [0003] The removal of particulates from a gas stream has long been a practice in a variety of industrial fields. Conventional means for filtering particulates and the like from gas streams include, but are not limited to, filter bags, filter tubes, filter cartridges and filter panels. These filter elements are typically oriented into a filt...

AI Technical Summary

Benefits of technology

[0018] The improved filtration system of the present invention, in a first embodiment, comprises a filtration system including one or more conventional or membrane filter elements (e.g., bags, cartridges, etc.) which incorporate a permanent or replaceable adsorbent insert on the downstream side of the filter element. Particulate filtration occurs on the upstream side of the filter element, and mercury removal occurs on the downstream of the filter element as the flue gas passes through the insert. The adsorbent insert comprises a suitable air-permeable high surface area support having thereon a mercury binder / promoter as described above. The adsorbent insert of the invention may be flexible or rigid. Examples of flexible inserts include woven or felted materials imbibed with activated carbon particles having the mercury binding agent / promoter thereon or even activated carbon fibers woven or felted into a flexible sheet having the mercury binding agent / promoter thereon. An example of a suitable rigid activated carbon insert material is a carbonized resin, such as that described in U.S. Pat. No. 5,834,114, to Economy et al. The insert may have any desired geometry such as a flat disk or panel, a sleeve or tube, a hub-and-spoke geometry, canister or the like, provided the insert fits into the filter element or is somehow attached to the downstream side of the filter element. The air permeability of an adsorbent insert having thereon a mercury binder / promoter should preferably have a Frazier number greater than 20, more preferably greater than 30 and most preferably greater than 40. In the filter system where the activated carbon insert component is installed inside a filter element, the air permeability of the combined layers should have a Frazier number greater than 1, preferably greater than 2. Depending on the desired pollutants to be adsorbed, multiple inserts, or inserts with multiple layers may be incorporated in the improved filter systems of the present invention. A particular benefit of such an insert construction is that the insert may be easily inserted into or attached to conventional or membrane filter elements to allow retrofitting of existing filtration systems.

[0021] Particular benefits of the present invention include providing a high efficiency of mercury removal during operation and collecting the particulate and fly ash by the filter element upstream of the mercury capture, thus reducing or eliminating contamination of the fly ash, which is a significant problem with carbon injection systems. Another benefit includes the ability to easily and cost-effectively retrofit existing filter systems for mercury control. A further benefit is the capability of a single filtration system to provide multi-pollutant control, including particulate, NOx, dioxins, furans, and mercury capture in a single system.

Problems solved by technology

[John H. Pavlish et. al., “Status Review of Mercury Control Options for Coal-Fired Power Plants”, Fuel Processing Technology, in press (2002), and references therein] Disadvantages of this approach include the need for large volumes of carbon to adsorb mercury to proposed regulatory levels due to the short contact time of the adsorbent carbon in contact with mercury vapor and the low capacity for mercury adsorption by PAC at temperatures above about 130° C. In addition, the requisite C / Hg injection ratios necessitate large volumes of injected carbon that can result in considerable contamination of the fly ash produced in coal-fired utility boilers.

Carbon contamination often reduces the commercial value of the ash as an additive for concrete.

Disadvantages associated with the use of such systems include expensive injection systems, limited collection efficiencies, particularly at high temperatures (i.e., above 130° C.

Initial testing with a Powder River Basin (PRB) ash determined that the presence of even trace amounts of activated carbon in the recovered ash rendered the material unacceptable for use in concrete (Bustard et al).

However, the adsorptive capacity reported in this work (52.5 micrograms Hg / gram activated carbon) is too low to allow this to be used as a bag filter or fixed bed in place of carbon injection.

Furthermore, a bag filter made from activated carbon fibers will trap fly ash particles within the depth of the fiber structure, causing a steep increase in pressure drop over time, and the cleanability of such bags is very limited.

However, none of these references discloses or suggests the removal of mercury from a flue gas stream or appropriate chemical composition for effective mercury removal.

Moreover, none of these references teaches the removal of particulate and mercury contaminants from a flue gas stream wherein the fly ash particulate is collected at a first location and the mercury is collected downstream of the particulate to minimize or prevent carbon contamination of the particulate fly ash.

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