Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
1999-08-11
2001-08-28
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S321690, C210S321890, C210S332000, C210S500230, C210S650000
Reexamination Certificate
active
06280626
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a novel construction for a membrane assembly suitable for solid-liquid separation, especially solid-liquid separation techniques designed to obtain purified water.
2. Description of the Related Art
Sand filtration and gravity precipitation techniques are known for performing solid-liquid separation in water purification treatments, treatments of sewage and waste water, and treatments of industrial waste water. However, the solid-liquid separation of such to-be-treated water (also referred to herein as object water) based on these conventional techniques often produces treated water of insufficient quality. To raise the quality to an acceptable level, vast and complex sites are needed to carry out the solid-liquid separation with these conventional techniques.
In recent years, the use of membrane modules containing separating membranes, such as precision filtration membranes or ultra-filtration membranes, have been proposed as alternative methods for solid-liquid separation of object water. When object water is subjected to filtration treatment with separation membranes, high quality treated water can be obtained, thus overcoming the drawbacks of the conventional sand filtration and gravity precipitation techniques.
However, prolonged use of separating membranes for solid-liquid separation of object water can cause suspended solids to clog the membranes, thereby decreasing he filtration flow rate and/or increasing the differential pressure between membranes.
In order to restore a normal solid-liquid separation condition, the suspended solids are removed from the surfaces of the membranes by vibrating the separating membranes with diffusing air supplied from air diffusion pipes provided below the membrane modules. Vibration of the separating membranes only provides a temporary solution, however, since suspended solids tend to clog even diffusion-vibrated membranes, especially after long periods of use. Thus, it is necessary to conduct frequent maintenance work to maintain a normal filtration flow rate.
Japanese Patent Laid-Open No. 257378/1996 proposes a method in which a substantially parallel gas-liquid mixed flow is created in a membrane module unit by providing enclosure walls in direct contact with outermost membrane modules. However, although a parallel flow is created by this arrangement, the present inventors have found that this arrangement results in a low membrane scrubbing efficiency.
A system for moving air diffusion members has been proposed by Japanese Patent Laid-Open No. 24596/1996. In this system, movement of the diffusion members creates a turbulent flow of bubbles. This turbulent flow increases the efficiency of the system, but at the same time increases the power requirements for the system due to the need to move the diffusion members. Moreover, the movable members are prone to breakage, thereby increasing maintenance work frequency and cost.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to overcome the above-discussed drawbacks by providing a solid-liquid separating membrane assembly which operates in such a manner that the clogging of membrane surfaces with suspended matter is rarely encountered, even when filtration of the object liquid is carried out over a prolonged and continuous period of time.
In accordance with the principles of this invention, the above and other objects are attained by the provision of a liquid-solid separating membrane assembly for separating solids from water. The membrane separator assembly comprises at least one membrane module unit (or subassembly) comprising a plurality of membrane modules, a gas diffuser disposed below the membrane modules, and an enclosure subassembly comprising opposing enclosure wall structures. The gas diffuser is constructed and arranged to diffuse a gas therefrom and clean the surfaces of vertically oriented separating membranes of the membrane modules with a gas-liquid mixed flow generated by the diffused gas. The enclosure wall structures are constructed and arranged to guide the gas diffused by the gas diffuser to the surfaces of the separating membranes, yet permit the liquid to flow through the enclosure subassembly.
At least some of the membrane modules each respectively comprise at least two membrane fixing members and one or more of the vertically oriented separating membranes extending between the membrane fixing members. At least one of the membrane fixing members has a main passageway formed therethrough. The main passageway is in fluid communication with one or more membrane passageways. According to one embodiment, the membrane passageway is defined by opposing spaced separating membrane sheets. According to an alternative embodiment, the membrane comprises one or more yarn-like members comprising hollow fibers, such as polyolefin fibers, which each individually define a membrane passageway. The membrane passageways are characterized by being accessible to water via permeation through the separating membranes and being inaccessible to solids which are impermeable relative to the separating membranes.
At least two of the enclosure wall structures are arranged parallel to the membrane modules positioned therebetween and are respectively spaced by a clearance from separating membranes of outermost ones of the membrane modules.
Another object of this invention is to operate the above-discussed membrane separator assembly as a filtration system in such a manner that operation of the filtration system effectively maintains the membranes of the assembly substantially sludge free so that maintenance requirements are significantly reduced compared to conventional assemblies. In preferred embodiments of the invention, gas discharged from a gas diffuser of the assembly is discharged at a rate of from about to about 150 Nm
3
/m
2
per horizontal cross-sectional area of the membrane assembly, at average vertical and horizontal flow velocities of from 0.01 m/sec to 1.5 m/sec.
Another object of this invention is the provision of a detergent for a membrane assembly, especially the above-discussed liquid-solid separating membrane assembly of this invention. In a preferred embodiment, the detergent contains percarbonate, such as sodium percarbonate, and optionally a bivalent iron salt and one or more additives selected from the group consisting of an oxidizer other than hypochlorite and hydrogen peroxide, a surfactant, a chelating agent, and a pH regulator.
Other objects, aspects and advantages of the invention will be apparent to those skilled in the art upon reading the specification and appended claims which, when read in conjunction with the accompanying drawings, explain the principles of this invention.
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Honjyo Kenji
Inoue Noriko
Itakura Masanori
Kato Osami
Kinoshita Ikuo
Drodge Joseph W.
Fitch Even Tabin & Flannery
Mitsubishi Rayon Co. Ltd.
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