Liquid purification or separation – With repair or assembling means
Reexamination Certificate
2001-04-24
2004-05-04
Lithgow, Thomas M. (Department: 1724)
Liquid purification or separation
With repair or assembling means
C210S323200, C210S333010, C285S361000, C285S376000
Reexamination Certificate
active
06730218
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to filter cartridges for filter vessels in fluid purification systems, and more particularly to coupling devices that connect replaceable filter cartridges to outlet tubes in filter vessels for purification of radioactive or other hazardous fluids.
BACKGROUND OF THE INVENTION
Power plants and other facilities with fluid purification processes frequently have filter tanks or filter vessels to purify a variety of different liquids or gases, such as fluid fossil fuels, or radioactive steam or water at nuclear power plants. Known filter vessels have an inlet supplying a fluid to a main filtration chamber holding a number of tubular filters. Long tubes support and act as the core for the tubular filters. These long tubes extend from a tube sheet that separates the main chamber from a plenum for holding purified fluid. An outlet leads from the plenum to the exterior of the filter vessel.
In conventional practice, on the opposite end of the filters from the tube sheet, separate mount assemblies use compression to secure the filters to the tubes while sealing that end of the tube. Since the mount assemblies contain numerous parts, these parts frequently fall into the filter vessel while disassembling the mount assembly to replace the filters. Parts falling into the vessel must be removed to prevent damage to filter elements caused by motion of the loose parts during service flow, and in nuclear powered generating plants, Nuclear Regulatory Commission oversight mandates the retrieval of the loose parts. Regardless of the application, if loose parts cannot be located and removed with suitable “fishing” tools, filter elements must be removed to permit access to the vessel to retrieve the loose parts. U.S. Pat. No. 5,667,679 to Bozenmayer et al. attempts to solve this problem by providing a mount assembly that is removed quickly without losing parts. This design, however, is made of stainless steel parts that are difficult to dispose or recycle when radioactive.
Referring to
FIG. 1
, another conventional filter vessel
100
has an inlet
102
that delivers unpurified, typically pressurized, fluids to a main chamber
104
. The arrows F indicate direction of flow for the fluid during normal operations.
The fluid enters replaceable filter cartridges
106
, as known in the art, and through known tubular filters contained thereby that remove unwanted particulate or foreign matter. The purified fluid then flows downward through tubes or pipes
108
that open up into a plenum
110
. The plenum is separated from the main chamber
104
by a stainless steel false bottom or tube sheet
112
conventionally welded to the tubes
108
. The fluid then exits the filter vessel
100
through an outlet
114
. Conventional filter vessels
100
typically vary in diameter from six inches to seven feet (and three foot to eight foot heights) depending on the quantity and size of filter elements contained therein. Vessels are known to accommodate anywhere from two to over 1000 filter cartridges.
Some conventional filter cartridges
106
are held in place by a hold down plate
116
as known in the art. The filter cartridges
106
are single open-ended with a closed top and a protruding bolt, post, rod or other connector
118
to extend upward through a hole in the hold down plate
116
for lateral support and to maintain distances between adjacent filter cartridges. The hold down plates
116
are usually bolted to the perimeter of the vessel or secured to the bottom by long connecting rods (not shown). Either mechanism provides downward force to seal the cartridges
106
to the tube sheet
112
. Cartridges
106
that are held down by hold down plates
116
typically have a spigot that fits into holes in the tubesheet
112
, and is sealed with either a flat gasket or one or more O-rings (not shown).
Some filter cartridges
106
have threaded bottoms for securing the filter cartridge to the tubesheet
112
and affecting a liquid tight seal, which does not require a hold down plate. However, a steel threaded lower end (not shown) must be rotated numerous times by robot, hand, wrench, other special tool or automatic mechanism to thread each filter cartridge
106
onto one of the tubes
108
.
Since a filter cartridge
106
that is threaded requires numerous turns, a worker or mechanism must use a relatively long amount of time to unscrew an old filter cartridge from the end of the tube
108
and then screw a new filter cartridge
106
back onto the tube. When radioactive or hazardous materials are being purified, the longer it takes to replace a filter cartridge, the longer a person or tool is exposed to the dangerous environment. Thus, when special tools are used, frequent replacement is required which is expensive. Alternatively, when a worker is required to replace a filter cartridge by placing his gloved hand in the vessel to turn the filter cartridge, the filter replacement may take a long period of time relative to a safe maximum exposure time available to a single worker. Limited by the maximum safe time periods, changing a filter either requires a number of workers taking turns, which raises labor costs, or requires a single worker to take breaks to reduce the exposure levels obtained in a single period, which is time consuming. Otherwise, the worker may feel encouraged to complete filter replacements within an unsafe period of time.
As shown in
FIG. 2
, an improvement over the threaded filter cartridge is a guide rod and hook design used to mount a filter cartridge
200
onto a tube
202
welded to a tube sheet
204
such as an Aegis™ Fossil Assembly as is known in the art. The filter cartridge
200
has a guide rod
206
welded to a plate
208
with an end with a hook (as disclosed in U.S. Pat. No. 3,279,608 to Soriente et al.), or in the illustrated case, a rivet
210
, to latch on the end of the tube
202
. A coil spring
212
and nut
214
are used to seal the top of the filter
216
while compressing the filter cartridge
216
against the tube
202
and to hold it in place against an adapter
218
threaded permanently to the tube
202
.
The upper end of the guide rod
206
is used to attach to a positioning lattice (not shown) for lateral stabilization. This design, however, still requires the unthreading of the nut
214
to remove the filter cartridge
200
from the tube
202
, and the rivet hook is not considered of adequate strength for high pressure and highly corrosive nuclear power plant applications.
Referring to
FIG. 3
, in a similar manner as filter cartridge
200
, filter cartridge
300
has a guide rod
302
welded to a plate
304
. However, the plate
304
has a tubular connector pipe
306
with two opposing holes
308
(only one is shown) that receives a pin (not shown). The pin is permanently press-fit into connector pipe
306
before the filter cartridge
300
is placed on a tubesheet tube
312
within the vessel. Connector pipe
306
, with the pin attached, is inserted downward through slots in adapter
310
which is previously attached to the tubesheet tube
312
. The connector pipe is pressed downward against tension from a top spring, and is rotated 60 to 90 degrees in either direction to engage cam slots (not shown) on the inside of the adapter
310
. The pin is not removed separately, but remains with connector pipe
306
and guide rod
302
, and the entire assembly is removed by pressing downward against spring compression and rotating until the pin ends pass upward through the slots in adapter
310
.
The top post
314
and mount assembly
316
are also similar to corresponding structures in filter cartridge
200
. While this design (named an Aegis™ Nuclear Assembly ) provides two places of contact (two holes) on the tube
312
, the pin blocks the interior of the tube
314
reducing the flow cross-section within the tube
312
.
Some of the problems of the threaded and guide rod filter cartridges have been addressed by the Ecolock™ system by Graver Technologies. Referring to
FIG. 4
, the filter cartridge
400
has an adapter
402
th
Graver Technologies, Inc.
Lithgow Thomas M.
Piper Rudnick LLP
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