Gas separation – Two or more separators
Reexamination Certificate
2000-01-07
2001-11-06
Simmons, David A. (Department: 1724)
Gas separation
Two or more separators
C055S508000, C055S518000, C055S523000, C055S525000
Reexamination Certificate
active
06312490
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates generally to hot-gas cleanup systems for feed gas to turbines; and more particularly, to a filter assembly for such systems that includes an all metal fail-safe/regenerator device, containing high aspect ratio interlocked, intertangled fibers. Use of such fibers provides effective particle capture and eliminates the need for heat transfer surfaces, such as Raschig rings, and coarse/fine mesh screen fail-safe elements. The nested fiber bed is extremely resistant to degradation due to thermal shock and so particularly effective in its regenerator function.
Background Information
Modern industrial methods have resulted in a need for an apparatus that is capable of efficiently filtering high temperature combustion or gasification gases containing particulate material. In combustion turbine applications, for example, a combustion turbine uses energy generated from hot pressurized combustion gases produced by burning natural or propane gas, petroleum distillates or low ash fuel oil. When coal and other solid fuels are burned, particulates carried over from the combustion of such solid fuels can cause turbine blade erosion and fouling. An efficient system for filtering of such hot combustion gases would permit the use of such solid fuels. As another example, in conventional boiler operations, the boilers undergo routine shutdown for cleaning the fireside surfaces and for inspection. An efficient hot gas filtering system would greatly extend the life and operational time for a boiler to operate between inspections. Fouling of the fireside surface due to ash deposition and corrosion would be eliminated or minimized.
Also, as a key component in advanced coal- or biomass-based power applications, hot gas filtration systems protect the downstream heat exchanger and gas turbine components from particle fouling and erosion, cleaning the process gas to meet emission requirements. When installed in either pressurized fluidized-bed combustion (PFBC) plants, pressurized circulating fluidized-bed combustion (PCFBC) plants, or integrated gasification combined cycle (IGCC) plants, lower downstream component costs are projected, in addition to improved energy efficiency, lower maintenance, and elimination of additional expensive fuel or flue gas treatment systems. A critical component for the hot gas filter system is an effective fail-safe/regenerator device. This device shuts down individual filter element operation in the event of the failure of the element, gasket leaks or other events that would allow particulate matter to escape to the downstream components.
U.S. Patent Specification Nos. 5,185,019; 5,433,771 and 5,876,471 (Haldipur et al.; Bachovchin et al. and Lippert et al., respectively), teach improved gasket assemblies that can be employed with conventional or thin-walled ceramic candle filters. All three show separate holders/chambers for fail-safe regenerator units. Bachovchin et al. teach a combination of one top coarse mesh metal screen and five bottom coarse/fine mesh metal screens, in combination with a bed of particles, such as stainless steel Raschig rings, as shown in their FIG.
6
. Fine screens trap particulate matter within the unit and prevent the collected particulate matter from being liberated during reverse cleaning pulsation. The Raschig rings form a thermal regenerator which heats pulses of cold gas during reverse flow cleaning, and the top coarse screen absorbs thermal shock during reverse pulse cleaning. In many instances, a fine mesh metal screen will also be used at the top the regenerator unit, supported by the coarse screen and the Raschig rings.
Lippert et al. in their
FIG. 4
show another such fail-safe/regenerator device which is permanently mounted within a filter housing having associated gaskets, in contact with a ceramic candle filter. The fail-safe/regenerator device similarly prevents particulate matter from traveling into the clean gas area of the pressure vessel if a ceramic filter element fails. Additionally, U.S. Ser. No. 09/263,436, filed on Mar. 4, 1999, now U.S. Pat. No. 6,123,746, provided an improved rolled/layered gasket, with an optional fail-safe/regenerator, and described possible use of metallic filter elements having the same connection and configuration as standard ceramic candle filters, and U.S. Ser. No. 09/393,561, filed on Sep. 10, 1999 pending teaches an all metal filter configuration with reduced use of gaskets, and an integral filter fail-safe/regenerator device similar to Bachovchin et al.
While these inventions provide advances in the art, enhanced particulate capture capabilities beyond screens and Raschig rings are needed, as well as the ability of any new assembly to be retrofit into existing filter systems, and, even more efficient heat transfer is needed during filter cleaning operations. Also, it has been found that Raschig rings and the like do not automatically plug and prevent flow in the event of a failed filter as quickly and completely as desired. The ability of these devices to trap very fine particulates has been a particular problem. Also, a major limitation of the current fail-safe regenerator design, as shown in Bachovchin et al., is the longevity of the fine mesh screens. High temperature oxidation, corrosion, embrittlement and thermal shock are probably responsible for the deterioration of the fine mesh screens in a relatively short period of service (that is, about 1650 hours). Furthermore, flexing of the fine screens against the relatively coarse mesh support screen material may lead to tearing of the fine screens. The screens have been observed to develop 0.32 cm (⅛ inch) wide holes and, in some cases, to ultimately disintegrate (and probably flow downstream).
In U.S. patent application Ser. No. 4,976,934 (Maringer et al.), a non-static bed of continuously flowing fibers with aspect ratios between about 50 and 170, engaged in a nested relationship, is utilized to filter liquids and gases containing undesirable particulates. There, it was found that a fixed bed of metal or refractory nested fibers provided a filter effective initial zone where most particulates were captured with the rest of the bed being essentially wasted volume. The bed of the invention is moved downward, denested, cleaned of contaminating particulates, recycled to the top of the bed and renested. This continuous movement would seem to allow breakage of a substantial amount of the needle-line particles, reducing the overall aspect ratio requiring substantial replacement after several cycles. Maringer et al. suggest a high void volume, about 90% (minimum) to 96% porous (voids), 4% to 10% fibers, within the nested bed to increase dendritic capture of particles and reduce pressure drop. One example of use was catalytic cracking of high-boiling hydrocarbons to gasoline fractions at 500° C.
There is still a need to develop higher reliability filter configurations for use in advanced coalfired operation applications. There is also a need for improved thermal shock protection from incoming cold gas flowing into the filter elements during back pressure cleaning of the filter elements. Finally, it would be desirable that any improved filter assembly be able to substitute into existing systems in the field.
SUMMARY OF THE INVENTION
Therefore, it is a main object of this invention to provide an improved fail-safe/regenerator device having improved particle capture capability, which is resistant to sulfur, alkali, chlorides, steam and other contaminants found in coal gas streams, and which will quickly and thoroughly plug in a fail-safe situation. It is another object of this invention to provide an improved fail-safe/regenerator device which, when integrated in a high temperature filter system, provides improved reliability.
It is a further object to improve thermal shock resistance of the fail-safe/regenerator during cleaning operations and provide a design that can easily substitute into existing units.
These and other objects are accomplished by providing a filter a
Alvin Mary Anne
Bruck Gerald J.
Lippert Thomas E.
Hopkins Robert A.
Siemens Westinghouse Power Corporation
Simmons David A.
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