GB2383001A

GB2383001A - Filter with means for retarding cake formation

Info

Publication number: GB2383001A
Application number: GB0129700A
Authority: GB
Inventors: Shih-Chang Chang
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-12-12
Filing date: 2001-12-12
Publication date: 2003-06-18
Anticipated expiration: 2021-12-12
Also published as: GB2383001B; GB0129700D0

Abstract

A filter unit with inside-out flow though a cylindrical filter element 3 has a diffuser 41 inside the filter element to induce a cross-flow of raw fluid across the inside surface of the filter element to retard cake deposition, and so prolong operational time between cleaning sessions. The diffuser 41 is a body housing a flowpath with a reducing section 410, a throat section 411 and an expanding section 412. As fluid enters through inlet 61, low-pressure and high pressure areas are produced at the inlet 413 and outlet 414 respectively of the diffuser to create a cross-flow 5 in the gap D between the filter element 3 and the diffuser 41. This prevents particles settling on the inside of the filter element and allows filtrate to pass through the filter element to the outlet 62 for a longer time before clogging. The inlet 61 may have a nozzle (610, Fig 4) to increase flow velocity into the unit. In Fig 5, the cross-flow between the diffuser 110 and the filter element 13 follows a spiral path along fins 112. The diffuser may also carry brushes on the tips of the spiral fins 112 and be rotated by fluid flow to keep particles away from the filter surface.

Description

A FILTRATION DEVICE WITH CROSS-FLOW FUNCTION AND ITS FILTRATION METHOD The present invention is related to a filtration devices with cross-flow function and its filtration method, especially the filtration devices which uses cross-flow for preventing cake formation on filter media.

Particles being derived by technology improvements and environmental awareness, the quality of supply liquids and treatment of waste liquids for all applications have become more and more stringent. Filtration is one of the most important process in liquid treatments and plays a major role in achieving these requirements and regulations.

The prior filtration devices (shown as figure 1), which consists of a filter media 1 and a cylindrical case 2. The cylindrical case 2 is able to contain the filter media 1. There are an inlet 21 and an outlet 22 on cylindrical case 2; the fluid to be filtered comes from the inlet 21 and flow through the filter media 1, which remove and retain particles too large to pass trough the openings of the filter media, but allow the"carrier"fluid, the filtrate, to pass. The filtrate is then going out from outlet 22.

Obviously, the effective filtering area of prior filtration devices is larger than inlet area, thus the flow speed of passing through filter media is much slower than the flow speed in the inlet, and the flow through the filter media 1 is perpendicular to the surface of filter media 1. This situation makes impurities and particles easily forming cakes on filter media and then blocking the openings of the filter media, the effective filtration area is then decreased. When the effective area of filter media becomes smaller than inlet area, the differential pressure (AP) between inlet 21 and outlet 22 is promptly increased. For typical applications, there is a maximum pressure drop AP allowed for the filter device, and when AP reaches the maximum value, it is required to shut down the whole process to change or clean the filter media by removing the cake formed on the surfaces or to switch to another set of filter device for not interrupting normal operation.

Please refer to figure 2, which shows the relationship of operation time v. s. pressure drop across filtration devices. In the beginning of filtration operation, pressure drop is almost constant as long as the effective filtration area is larger than the cross-sectional area of the pipe. The effective filtration area will gradually be decreased due to the formation of cake on the filter surface, which blocks the openings of filter media. When the effective filtration area becomes smaller than the cross-section area of the inlet pipe, the pressure drop across the filter device will suddenly be increased and quickly exceed the maximum value of filter device, and certain action should be taken to maintain normal operation.

To avoid shortcoming of prior art, the inventor has studied and provided a logical method to improve prior art effectively.

The main object of the present invention is to offer a method to produce cross-flow for extending operation time of filtration devices and improving filtration efficiency.

The second object of the present invention is to offer a filtration devices with cross-flow function, which consists of a case, a filter media and a diffuser; wherein the filter media is set inside the case, and there are an inlet and an outlet on the case; the diffuser is inside the filter media along longitudinal direction for producing cross-flow, and that prevents impurities accumulating on the surface of filter media to form cake. The diffuser consists of a reducing section, a throat section and a expanding section; the fluid coming out from the inlet of the filter enters the reducing section of the diffuser and flows through the throat section, expanding section and then along the passage formed between the outer surface of the diffuser and the inner surface of the filter media, circulates back to the reducing section of the diffuser. Thus a cross-flow on the surface of filter media is formed.

Impurities and particles in the fluid are then evenly distributed in the liquid volume inside the filter media by the circulating cross-flow, which prevents the accumulation of impurities and particles on the surface of filter media and extends the effective operation time of the filtration devices.

The third object of the present invention is to offer a filtration devices with cross-flow function for drain further extending the effective filtration time, wherein, a drain outlet is installed on the filter housing for draining the

impurity-concentrated solution inside the filter media and with a valve on the drain outlet; a continuous or intermittent blow-down can be controlled automatically or manually.

For your esteemed review committee members to further understand and recognize the object, the characteristic and the function of the present invention, a detailed description with corresponding diagrams are presented as follow drawings, in which: Figure 1 is the sectional view of prior filtration devices.

Figure 2 is the relationship scheme of the filtration devices operation time and the differential pressure between inlet and outlet of the filter.

Figure 3 is the sectional view of the first embodiment of the invention.

Figure 4 is the sectional view of the second embodiment of the invention.

Figure 5 is the portion sectional view of the present invention.

The present invention is related to a filtration devices with cross-flow function and its filtration method, especially the filtration devices which uses cross-flow for preventing cake formation on filter media. The structure of the present invention is simple, and it has two advantages: the first is the increased effective operation time; the second is the continuously filtration operation without interruption.

According to Darcy's Law, which is

wherein, J is representing permeate flux; A is representing effective surface area of filter media; t is representing filtration time; Ap is representing the differential pressure across the cake and the filter media; 77 is representing the viscosity of the permeate; Rm is representing the resistance of the filter media; Rc is representing the resistance of cake. Thus, the equation above

shows the permeate flux is proportional to the reverse of the sum of the resistance of the filter media and the resistance of the cake. Another 1

equation is as following:

wherein, J is representing permeate flux; c is a coefficient; y is shear rate; a is solid particle size; \If is solid volume fraction in the suspension; L is the filter length; no is viscosity of the suspension; n, m, p, q and r are parameters.

Because n is positive, thus the permeate flux is proportional to the shear rate.

To conclude the above two equations, higher shear rate of the fluid on the filter surface gives higher permeate flux due to the retardation of cake formation.

Figure 3 is the sectional view of the first embodiment of the invention.

The filtration devices with cross-flow function consists of a filter media 3, a diffuser 41 and a case 6, wherein the case 6 is able to contain the filter media 3, and there are an inlet 61 and an outlet 62 set on top and one side of case 6. Liquid directly enters into diffuser 41 via inlet 61, and the permeate goes out from outlet 61. The diameter of diffuser 41 is smaller than filter media 3, and diffuser 41 is installed inside filter media 3 along longitudinal direction. Top of diffuser 41 is set plural supporters 43 for supporting diffuser 41, thus the outer surfaces of diffuser 41 and inner surfaces of filter media 3 form passages for liquid flowing through outlet 414 on bottom of diffuser 41 then to inlet 413 on top of diffuser 41. The circulating flow then creates cross-flow 5 on inner surface of filter media 3 and prevents cake formation on filter media 3. The diffuser 41 consists of a reducing section 410, a throat section 411 and an expanding section 412, wherein, the reducing section 410 is correspondingly designed for inlet 61 of case 6, therefore liquid can enter into reducing section 410 via inlet 61, then passing through throat section 411 to expanding section 412. The fluid flows through reducing section 410 and produces a local low-pressure section, thus the liquid outside diffuser 41 is entrained into diffuser 41 from inlet 413 and through the throat section 411. When liquid entering the expanding section 412, the kinetic energy of the liquid is transferred to pressure energy, and a local high-pressure section is then formed at the bottom of the expanding section 412. The local low-pressure and local high-pressure areas at the inlet and outlet of the diffuser produce cross-flow 5, which results in a much larger shear rate for effectively disturbing impurities and particles in the fluid, thus the impurities and particles are evenly distributed in the liquid

volume inside the filter media 3, and not forming cake on the surface of filter media 3. Thus the filter operation time can be extended due to the low-pressure drop can be sustained for a longer period of time for not forming cake on the filter surface (shown as figure lob).

The gap between the outer rim of diffuser 41 and inner surface of filter media 3 is D. The present invention can adjust gap D for reducing cross-section area of liquid passages, and flow speed is increased to produce a cross-flow 5 of larger shear rate, the filtration efficiency is then further increased.

Although the devices in last paragraph prevents the formation of cake and highly promotes effective operation time of filtration devices, as operation time is increased, the concentration of impurities and particles are increased and eventually the filtration efficiency will be decreased, the present invention can further install a drain outlet 63 on case 6 corresponding to the position of inside filter media. One end of the drain outlet 63 is installed a drain valve 631, and the valve 631 can be a manual drain valve or an electromagnetic valve. Drain valve 631 could be manually or automatically controlled to drain liquids with high concentration of impurities and particles, thus the effective operation time (shown as figure 1 c) of filtration devices is further increased.

The control of the drain valve 631 can be calculated based on the concentrations and flow rates or by test runs on the actual fluid samples to be filtered.

Referring to figure 4, the flow rate of the cross-flow on the filter surfaces are increased by reducing the gap D; or by installing a nozzle 610 on the end of inlet 42 for increasing the speed of the entering flow into the reducing section 410 of diffuser 41, thus cross-flow effect is enhanced for better filtration efficiency.

Please refer to figure 5, wherein, the present invention is further designed a spiral diversion devices 7 for promoting cross-flow efficiency. The spiral diversion devices 7 is mainly designed a spiral fins 112 on the outer rim of diffuser 110. Via the spiral fins 112, the liquid flows out the bottom of diffuser 110 could flow up to the top inlet of diffuser 110 along

spiral fins 112, thus spiral cross-flow 12 is then produced. Due to the spiral 'i

cross-flow 12, particles in liquid can then be more effectively disturbed and prevented from firming cake.

Spiral diversion devices could be designed as an rotating devices.

Liquid flow moves and rotates the spiral diversion devices, and by installing hairbrush (not shown in figure) on the tips of the spiral fins 112, the spiral diversion devices could clean the inner surface of filtration devices constantly when spiral flange 112 rotating and keeping impurities and particles away from the filter surfaces.

As a conclusion of the above mention, the present invention is with the following merits:

I 1. The liquid diversion devices of the present invention is simple, inexpensive and easy for manufacturing, further the present invention is suitable for all applications of prior filtration devices.

2. The present invention effectively keeps impurities and particles from accumulation and the operation time of filtration devices is highly extended.

3. The present invention could adjust the gap between diffuser and inner surface of filter media to achieve the best performance of the system.

4. The present invention could further extend operation time by adding a drain outlet and drain valve to keep continuous filtration operation.

The above descriptions are the preferable embodiments of the present invention. The covered scopes of the present invention are not restricted on the embodiments shown in the present invention. All the changes according to the contents of the present invention, the generated functions and characteristics similar to those of the embodiments of the present invention and any ideas thought by the persons well-known such technologies are all within the scopes of the present invention.

Claims

1. A filtration devices with cross-flow function, comprising: a filtration media; a case, which has an inlet and an outlet; fluid directly flows into the case through the inlet and, after filtered by filtration media, flows out from the outlet; a diffuser, which is inside the filter media and is set along longitudinal direction, the diffuser has plural supports connected to the case and causes the cross-flow circulating inside the filter media for preventing cake formation on the surface of the filter media, thus extends the operation time of the filtration process.

2. The filtration devices with cross-flow function of claim 1, wherein the diffuser consists of a reducing section, a throat section and an expanding section.

3. The filtration devices with cross-flow function of claim 2, wherein the inlet includes a nozzle for accelerating flow velocity into the diffuser.

4. The filtration devices with cross-flow function of claim 1, wherein the diffuser is designed with a spiral diversion devices for producing spiral cross-flow and promoting cross-flow efficiency.

5. The filtration devices with cross-flow function of claim 4, wherein the spiral diversion devices is of spiral fins on the outer rim of diffuser.

6. The filtration devices with cross-flow function of claim 1, wherein the case includes a drain outlet for adjusting impurities and particles concentrations of the fluid inside the filter.

7. The filtration devices with cross-flow function of claim 6, wherein at least one drain valve is set on the drain outlet.

8. The filtration devices with cross-flow function of claim 7, wherein the drain valve is an electromagnetic valve.

9. A filtration method with cross-flow function, which includes the following step:

(a) providing the filtration devices of claim 1, wherein, the diffuser consists of a reducing section, a throat section and an expanding section, and the position of the reducing section is corresponding to the inlet; (b) flowing fluid into the inlet, the reducing section of diffuser for producing a local low-pressure section, thus the fluid outside the diffuser is entrained into the reducing section; (c) fluid passes through the expanding section and the flow velocity is decreased gradually, thus converting kinetic energy into pressure energy to form a local high-pressure section at the exit of the diffuser; (d) fluid exiting from diffuser passes through a passage formed by outer surface of diffuser and inner surface of filter media, then entrained back again into the reducing section, therefore, forming the circulating cross-flow.

10. The filtration method with cross-flow function of claim 9, wherein the inlet is a nozzle for accelerating fluid flow velocity.

11. The filtration method with cross-flow function of claim 9, wherein the diffuser is a spiral diversion devices for producing spiral cross-flow to increase cross-flow efficiency.

12. A method as claimed in any one of claims 8 to 11, wherein the case includes a

drain outlet for adjusting the concentration of impurity and particle concentrations of tD the fluid inside the filter.

12. The filtration method with cross-flow function of claim 11, wherein the spiral diversion devices is of spiral fins on an outer rim of the diffuser.

13. The filtration method with cross-flow function of claim 9, wherein the case includes a drain outlet for adjusting the concentration of impurities and particles concentrations of the fluid inside the filter media.

14. The filtration devices substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.

Amendments to the claims have been filed as follows

1. A filtration device with cross-flow function, the device comprising a case, having an inlet and an outlet, whereby fluid directly flows into the case through the inlet and, after filtering by the filter, flows out from the outlet, and a diffuser positioned within the filter and set along a longitudinal direction, the diffuser having at least one support connected to the case adjacent to the inlet to cause cross-flow, which circulating inside the filter prevents cake formation on the surface of the filter, the diffuser having a tapered section, a throat section and a flared section.

2. A device as claimed in claim 1, wherein the inlet includes a nozzle for accelerating flow velocity into the diffuser.

3. A device as claimed in claim 1 or claim 2, wherein the diffuser is provided with a spiral diversion device for producing spiral cross-flow and promoting cross-flow efficiency.

4. A device as claimed in claim 3, wherein the spiral diversion device has spiral fins on an outer rim of the diffuser.

5. A device as claimed in any one of claims 1 to 4, wherein the case includes a drain outlet for adjusting impurity and particle concentrations of the fluid inside the filter.

6. A device as claimed in claim 5, wherein a drain valve is provided at the drain outlet.

7. A device as claimed in claim 6, wherein the drain valve is an electromagnetic valve.

8. A filtration method with cross-flow function, the method comprising : c

a) providing a filtration device having a case, a filter and a diffuser, the case having an inlet and an outlet, and the diffuser having a tapered section, a throat ZD-a tapered section, a throat section and a flared section; b) flowing fluid into the inlet, and through the tapered section of the diffuser for producing a local low-pressure whereby fluid outside the diffuser is entrained into the tapered section, and then through the throat section; c) flowing fluid continuously through the flared section gradually to decrease flow velocity and thus convert kinetic energy into pressure energy to form local high-pressure region at an exit of the diffuser; and d) passing the Fluid exiting from the diffuser through a passage formed by an outer surface of the diffuser and an inner surface of the filter, whereby the fluid is entrained back into the tapered section, to form the circulating cross-flow.

9. A method as claimed in claim 8, wherein the inlet is a nozzle for accelerating fluid flow velocity.

10. A method as claimed in claim 8 or claim 9, wherein the diffuser is a spiral

diversion device for producing a spiral cross-flow to increase cross-flow efficiency.

I 11. A method as claimed in claim 10, wherein the spiral diversion device has spiral fins on an outer rim of the diffuser.