Patent Application
20140246365
1. Field of the Invention
This invention relates to apparatus for purifying critical fluids in an adverse environment where improved performance in terms of pressure drop or flow is required or time of replacement is critical and/or exposure to the environment hazardous. More particularly, this invention relates to an underdrain strainer apparatus for removing dissolved and undissolved impurities from liquids such as water and the like, where such dissolved and undissolved impurities originate from liquid process filtration vessels or power generation facilities, and may even be radioactive, as generally occurs with respect to underdrain filtration systems employed in nuclear power plants.
2. Description of Related Art
Generally, the purpose of an underdrain system is to provide support for filtered drainage, including directing fluid through filter media, collecting treated fluid, and channeling it to a retaining reservoir. Then, typically as the filter media becomes dirty, the underdrain is used to evenly distribute backwash fluid used to flush out the solids, although not all systems are designed for efficient backwash.
One of the principal methods employed to remove undissolved solids from water, or other fluids, is to pass the fluid through a mechanical filter, such as a filter screen, filter cloth, filter leaf, or the like. With respect to the removal of dissolved impurities from water or other fluids, the use of ion exchange resins has become well known in the art. Such resins, which may be bead type or powdered type as is known in the art, when contacted by a fluid, exchange free ions between the fluid and the resin. Accordingly, when a fluid is passed through a bed or beds of these ion exchange resins, the ions of the dissolved impurities are captured by the ion exchange resin particles and replaced by more desirable or innocuous ions released by the ion exchange particles to the fluid. Therefore, the undesirable ions in the water are exchanged for desirable or innocuous ions given off by the resin particles. In this manner, a form of filtration and purification is achieved.
As will be recognized by those skilled in the arts, however, particular and unique problems are presented when the fluid contaminants are radioactive. The removal of dissolved and undissolved solids from fluids when such dissolved and undissolved solids are radioactive inevitably results in a build-up of radioactive material within the purification apparatus. Passage of undissolved solids through mechanical filter devices causes a build-up of the undissolved solids on the filter structure with a resultant concentration of radioactivity at the filter. Similarly, the removal of dissolved solids by passage through a demineralizer bed of ion exchange resins also results in a build-up of radioactive materials or activity within the demineralizer bed.
The inaccessibility of an underdrain when installed, and the major part it plays in total filter efficiency and operating cost, make the underdrain a very important part of a power generation facilities' or liquid process filtration vessel's fluid system. This criticality is heightened when the underdrain system entraps impurities, for example, radioactive impurities, or becomes radioactive by exposure to radioactive conditions, and users must access, remove, and substitute replaceable components. There remains a need in the prior art to develop a more efficient underdrain filtration system that lends itself to easy installation and removal, both from a standpoint of ease of maintenance, timeliness of repair and/or reduced exposure to working personnel.
Various underdrain systems have been developed for filter systems that filter water, wastewater, and other critical liquids. The underdrain systems are a key component of a filter system as they receive liquid and/or air throughout virtually all phases of filtering including washing phases and filtration phases. In washing phases, the underdrain typically directs liquid and/or air upwardly through the filter bed to remove impurities trapped in the filter bed during a filtration phase. The liquid and/or air must be uniformly distributed over the filter bed to ensure the filter bed is properly cleaned. In an up flow filter, the underdrain, during the filtration phase, directs influent upwardly through the filter bed so that impurities may be removed therefrom. In a downflow filter, the underdrain receives the effluent and conveys it to a suitable storage location for subsequent use. Because of the key nature of underdrain filters to the operation of the filter system, an underdrain failure often results in shutdown of the filter system for prolonged periods. Consequently, repair and replacement activities must be performed quickly, especially when dealing with radioactive impurities and exposure to radiation during maintenance.
Known in the art are wedge wire screens which are utilized in a broad range of industrial fields as a rugged screen which have little likelihood of clogging owing to their wires with a flat surface and a V-shaped continuous slit. In some instances, these wedge wire screens are recognized as filters which are generally deemed for particular applications to be superior to conventional filters made of mesh-wires and punched plates.
An underdrain filter constructed of wedge wire has an inherently lower flux rate or open area that decreases even further based on increased obstructions on the surface, plugging slots and reducing the flow passage area until total flow blockage is reached. An exploded view of a typical wedge wire assembly is depicted in
A wedge wire screen is the solid-liquid separation apparatus of choice for underdrain systems for nuclear power generation. The wedge wire filtering apparatus uses screens having slits of specified dimensions provided among wedge wires, by forming wedge wires of metal wire rods of a wedge shaped section in multiple rows in parallel. This filtering apparatus is widely used in various industrial fields, for the purpose of removing floating matter in wastewater treatment plants, including solid-liquid separation of crude liquid in the treatment process of various industrial waste water in paper pulp industry, food industry, textile industry, chemical industry, and others.
The wedge wire screen forms a filter having closely spaced wedge wire windings defining a permanent filter media by allowing liquid flow through the gaps, in which the outer face of the wedge wire strands are ground away to eliminate the radiused corners on each strand, which corners create a small convergent region intermediate adjacent strands of wedge wire tending to trap solids and clog the filter when particles sizes are present in a range tending to wedge in those regions.
The slit spacing width between wedge wires in a screen device using wedge wires is generally on the order of 0.5 mm (500 microns), but solid matter is likely to deposit and accumulate on the side surfaces of the wedge wires on the back side of the screen, causing clogging of slits, and in these instances, the solid-liquid separation performance may be lowered.
The steel wire making up the screens is relatively thin and is prone to erode. Furthermore, standard screens may collapse under excessive suction. Pressure drop monitoring and automatic control is vital to keep the system in operation. Typically, backwash and airburst mechanisms are initiated to unplug flow slots and let the fluid pass. In the event these mechanisms fail, the screens may collapse. The wedge wire may deform and break, thereby allowing resins to escape downstream and potentially into the reactor vessel. There is a need in the prior art to replace wedge wire underdrain filters with filters capable of performing at least as efficient filtering of solids, while providing for easy maintenance and replacement of filters.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an underdrain filter for a nuclear power generation facility, other power generation facilities, sugar refining manufacturing process facilities, facilities for ion exchange applications, and liquid process filtration vessels, to name a few, that is as efficient as the existing wedge wire filters.
It is another object of the present invention to provide an underdrain filter for a nuclear power generation facility, other power generation facilities, sugar refining manufacturing process facilities, facilities for ion exchange applications, liquid process filtration vessels, and the like, that can be easily replaced in a time efficient manner to reduce maintenance and outage time to reduce cost and exposure of radiation to maintenance personnel.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects, which will be apparent to those skilled in the art, are achieved in the present invention which is directed to an underdrain filter comprising a sintered, stainless steel mesh or wire-cloth filter media having a pore structure with pore size ranging approximately from one micron to two hundred microns, the filter media having a plurality of filter media layers including a perforated inner core bonded to at least one drainage wire mesh, a filtration wire mesh, and a protective wire mesh forming an outer diameter, the layers being diffusion bonded to form a single monolithic laminate.
The underdrain filter may include a quick-release end fitting to facilitate removal and replacement in a radiation environment, a confined space entry environment, or both. The quick-release end fittings may be constructed of rigid stainless steel end fitting couplings.
An adapter for leak proof mounting of the underdrain filter to existing underdrain piping may be employed.
A grooved portion may be formed in each end of the filter to form a mating connection with a removable end fitting.
In a second aspect, the present invention is directed to an underdrain filter system for an ion exchange filtration system comprising: a pipe array; sintered, stainless steel mesh or wire-cloth underdrain filter media for each pipe line or branch in the pipe array having a pore structure with pore size ranging approximately from one micron to two hundred microns, the filter media having a plurality of filter media layers including a perforated inner core bonded to at least one drainage wire mesh, a filtration wire mesh, and a protective wire mesh forming an outer diameter, the layers being diffusion bonded to form a single monolithic laminate; quick-release end fittings to facilitate removal and replacement of the underdrain filter media in an environment requiring a confined space entry; an adapter at each end of the filter for leak proof mounting the underdrain filter to existing underdrain piping; and a grooved portion at each end of the underdrain filter to form a mating connection with a removable end fitting.
In a third aspect, the present invention is directed to an underdrain filter system for a nuclear power generation facility comprising: a pipe array located in a demineralizing vessel of the nuclear power plant; sintered, stainless steel mesh or wire-cloth underdrain filter media for each pipe line or branch having a pore structure with pore size ranging approximately from one micron to two hundred microns, the filter media having a plurality of filter media layers including a perforated inner core bonded to at least one drainage wire mesh, a filtration wire mesh, and a protective wire mesh forming an outer diameter, the layers being diffusion bonded to form a single monolithic laminate; quick-release end fittings to facilitate removal and replacement of the underdrain filter media in a radiation environment; an adapter at each end of the filter for leak proof mounting the underdrain filter to existing underdrain piping; and a grooved portion at each end of the underdrain filter to form a mating connection with a removable end fitting.
The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which:
In describing the preferred embodiment of the present invention, reference will be made herein to
The present invention is employable as a new or replacement underdrain strainer for use with deep bed demineralizers as used in, but not limited to, nuclear power plants deep bed ion exchangers, other power generation facilities, sugar refining manufacturing process facilities, facilities for ion exchange applications, liquid process filtration vessels, and the like. The benefits of an underdrain filter of the present invention over the current prior art wedge wire filters include: 1) an increase in available filtration surface area; 2) ease of installation, which in the case of a nuclear power generating plan installation reduces radiation exposure due to the shorter installation time; 3) a lower operating differential pressure with higher flow rates; 4) instant alignment of the underdrain media to the system configuration; and 5) greater overall utilization and efficiency of the ion exchange resin.
In a preferred embodiment, a sintered stainless steel filter design replaces the current wedge wire filtration device. The sintered stainless steel filter is aligned with pore sizes on the order of about 100 microns, which greatly enhances filtration over the wedge wire design and provides a lower, more manageable pressure drop. Sintered screen technology may vary in construction. It is desirable to ensure that pore sizes on the order of 1-100 microns are achievable for optimum application in underdrain systems for nuclear power plants. One such sintered screen technology that may be employed in the construction of an underdrain filter is identified as Poroplate®, which is advanced by Purolator Facet, Inc., of Greensboro, North Carolina. Generally, in the Poroplate® construction, furnace sintering the metal at over 1100° C. in a controlled atmosphere causes the metal molecules to migrate across contact points of the various layers. In this manner, flocrystalization takes place to form a completely integrated structure.
An advantage of using a sintered stainless steel filter design over the current art in OEM underdrains is the ability to control filtration and provide a system that exhibits less back pressure. The design allows for the open area of the underdrain to include the full circumference of the underdrain design. Sintered stainless metal has more open area than OEM supplied wedge wire typically supplied in these vessels.
A sintered stainless steel mesh or wire-cloth filter allows for durable support for flow distribution and efficient, effective backwashing. This construction further lends itself to lower differential operating pressures and high collapse strength.
In contrast, vessel B was not retrofitted and remained unchanged. The flow of vessel B is always shown as the middle or center bar in the three-bar group delineation. The flow rate of vessel B was measured through the times to be about 400 gpm to 500 gpm lower than the retrofitted vessels.
The data indicates a throughput increase of approximately five percent (5%) when new underdrain filters are installed, with lower differential pressures realized (up to 5 psid savings in each retrofitted vessel).
The underdrain preferably includes a three-quarter inch diameter pipe welded vertically to the blind end. The underdrain filter of the present invention is preferably manufactured by a diffusion bonding process. High quality wire cloth layers are sheared and laid upon a custom perforated sheet of stainless steel, preferably, but not limited to, TINS S31603 stainless steel. The filtration layer is designed for 200 micron absolute filtration although other pore sizes may be desirable depending upon the specific application and the type of contaminants requiring filtration.
This composite is diffusion bonded at temperatures in excess of 2000° F. to form a single monolithic laminate. The wire mesh material is sheared to exacting widths to ensure uniform and consistent roundness after forming. The sheared wire mesh blank is formed into a tube using a two-stage cold forming process. An automated Jetline Gas Tungsten Arc Welder (GTAW) is used for seam welding with filler metal addition for its construction. The ferrules and end fittings are preferably attached utilizing the same type of welding method.
Once fabricated, each lateral is bubble-point tested and ultrasonically cleaned in a halide-free solution.
This image shows a cross section of the sintered stainless steel filter media. Fine mesh captures contaminants on the upstream surface. Downstream support layers provide open flow channels for low differential pressure, high flow rates and long filtration cycles. Advantageously, this media backflushes well, yielding like-new filter elements after each clean cycle.
As noted, quick replacement and installation is important to reduce environmental exposure which could include radiation exposure of maintenance personnel. In a preferred embodiment, the ease of installation is facilitated by combining a quick connect end fitting with the sintered stainless steel wire mesh filter underdrain. One such end fitting used in industry is a Victaulic® end fitting. These preferred end fittings are cast of stainless steel or durable ductile iron to precise tolerances. Generally, the fittings or couplings are supplied with grooves to permit fast installation without field preparation. A preferred grooved fitting design permits flexibility for easy alignment. The coupling may be rigid or flexible. Rigid couplings include a pad which constricts the housing keys into a groove around the full circumference to create a rigid joint. These rigid couplings provide a rigid joint allowing no expansion, contraction, or linear movement. Standard flexible grooved-type couplings allow controlled angular, linear, and rotational movement at each joint to accommodate expansion, contraction, settling, vibration, noise, and other piping system movement.
End fittings, such as Victaulic® end fittings, allow for faster installation and help facilitate installation and removal under DOE protocol. The admonition to keep exposures As Low As is Reasonably Achievable (ALARA) has been the traditional position of the radiological protection community for several decades. ALARA is a nuclear power plant policy that is associated with a system of dose limitations consisting of three parts, including: (1) justification (no practice causing exposures of persons to radiation shall be adopted unless its introduction produces a positive net benefit, insomuch as practices should not cause more harm than they do good); (2) optimization (all exposures shall be kept as low as is reasonably achievable, economic and social factors being taken into account); and (3) dose limits (the dose equivalent to individuals shall not exceed the limits recommended for the appropriate circumstances). It is understood that the ALARA process is most effective when it is applied in the design of new facilities that have potential for exposing workers and members of the general public. Consequently, the present invention's introduction of a more efficient underdrain filtering system that reduces exposure time for installation, repair, and removal is in concert with the ALARA standards promulgated by the nuclear power industry.
Change out of typical NPT pipe threads takes considerably time. The present invention allows for the quick installation of the new underdrain strainers, which may be expeditiously clamped to the outlet piping, thus lending to an ALARA approved design. However, the invention is not limited to nuclear power plant underdrain configurations as the claims of faster installation combined with more open area are also needed in non-nuclear applications.
It is envisioned that the present invention would be employed for all problematic wedge wire ion exchange or other media type underdrains in nuclear power, fossil power, sugar refining, and all other underdrain installations.
The underdrain laterals include stainless steel threaded adapters that are typically installable in the 2½″, 3″ and 4″ NPT diameter pipe fittings located in the bottom of the nuclear power generator vessel. A threaded adapter will end in a rigid end fitting, preferably a stainless steel end fitting coupling, such as the Rigid Victaulic® or the like. A certified EPDM gasket is provided to seal the connection to the underdrain that is free of sulfates, chlorides, or sodium. If the design is employed for drinking water usage, the underdrain filter may be NSF 61 certified.
The present invention is directed towards replacing existing wire wedge filtration devices currently being used in power generating plants, sugar refining plants, and ion exchange facilities, to name a few, with a sintered stainless steel multilayer filter mesh. This substitution will yield lower initial pressure drop; longer on-stream life; reduced labor required to change out filters; fewer elements required for new installations; reduced operator exposure to hazardous chemicals; and reduced disposal of hazardous materials. It is especially useful in facilities having confined space entries since it expedites the removal and replacement of existing, spent filters.
While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.
| Number | Date | Country | |
|---|---|---|---|
| 61771479 | Mar 2013 | US |
