JPH0747110B2 - Membrane treatment method - Google Patents

Description

The present invention relates to a method for membrane treatment of a stock solution as a gas-liquid mixed two-phase flow.

(Prior Art) The applicant of the present invention has previously disclosed, as a method for maintaining a high concentration of anaerobic bacterial cells for treating wastewater and sewage in a reactor and for separating and concentrating a solution in the food industry. No. 104609 proposes a method in which a stock solution is supplied as a two-phase flow of gas-liquid mixture into a membrane module and treated by a cross-flow filtration method.

(Problems to be Solved by the Invention) When the gas-liquid two-phase flow described above is used, the gel layer composed of fine particles and solute components adhering to the film surface is scraped off due to the turbulent flow promoting effect, so that permeation compared to liquid single-phase flow The flux should be high.

However, since the gas-liquid two-phase flow exhibits a complicated flow in which the distribution of the gas phase and the liquid phase is non-uniform, the gas-liquid two-phase flow always has a larger permeation flux than the liquid single-phase flow. As a result of experiments, it was found that the above is not the case. Especially, when the membrane module is composed of a large number of thin tubular membranes, the above tendency becomes stronger.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a gas amount that feeds a stock solution as a gas-liquid two-phase flow into a membrane module and naturally circulates the gas amount that gives a maximum circulation flow rate. 1 to 7
The range is doubled.

(Operation) When the permeation flux J is in the range of 0.7 to 2.0 [m ³ · m ^-2 · d ^-1 ], the gas-liquid two-phase flow consumes less power than the liquid single-phase flow,
In order to obtain the permeation flux in the above range, the supply gas amount may be 1 to 7 times the gas amount giving the maximum circulation flow rate.

(Example) Below, the Example of this invention is described based on an accompanying drawing.

FIG. 1 is an overall view of a membrane treatment apparatus for carrying out the method of the present invention. A stock solution tank 2 filled with a stock solution 1 is equipped with a stirrer 3 and a temperature control device 4, and a stock solution 1 in the stock solution tank 2 is pumped by a pump 5. The separator 7 is supplied through the supply pipe 6.

A downcomer pipe 8 is led out from the separator 7 and
An electromagnetic flow meter 9 is provided in the middle of the, and the lower end of the downcomer pipe 8 is curved in a U shape and connected to the upcomer pipe 10.
A gas-liquid mixer 11 equipped with a wire-cylinder scattering cylinder is provided in the middle of 10, and gas (air) is supplied from the blower 12 to this gas-liquid mixer 11, and the supply gas amount is the gas flow rate provided in the middle of the pipe. I try to measure with a meter.

A static mixer 13 is provided above the gas-liquid mixer 11, and five membrane modules 14 ... Are vertically connected above the static mixer 13. A tubular permeable membrane is arranged in each membrane module 14, the inner passage of the tubular permeable membrane is connected to the ascending pipe 10 and the return pipe 10a to the separator 7, and an outer flow passage of the tubular permeable membrane and a permeate extraction pipe. 15, and the tip of the take-out pipe 15 faces the backwash buffer 16,
Compressed air is supplied to the backwash buffer 16 by a compressor 17, and the permeated water in the buffer 16 is sent to the water collecting tank 19 or the switching decompression tank 20 placed on the electronic balance 18 by air pressure. There is.

An exhaust pump 21 for applying a transmembrane pressure difference is connected to the water collection tank 19 and the switching decompression tank 20, and the water level gauge is provided in the water collection tank 19.
22 are attached. Thus, the permeation flux can be obtained by measuring the weight increase rate of the water collection tank 19 with the electronic balance 18, and the fact that a predetermined amount of permeated water has accumulated in the water collection tank 19 is displayed on the liquid surface. If it is detected by the total 22, it will automatically switch to the collection in the switching depressurization tank 20, during which the depressurized state in the water collection tank 19 is released to atmospheric pressure, and the permeated water in the water collection tank 19 Is returned to the stock solution tank 2. Similarly, the permeated water in the switching decompression tank 20 is also returned to the stock solution tank 2, and the pre-circulation filtration method is adopted as the entire apparatus.

Furthermore, the U-shaped portion connecting the downcomer pipe 8 and the ascending pipe 10 is detachable, and when supplying the stock solution into the membrane module 14 as a liquid single-phase flow, the circulation pump 23 is connected to this part. ing.

In the above, the undiluted solution 1 supplied from the undiluted solution tank 2 into the separator 7 through the supply pipe 6 by driving the pump 5 descends through the downcomer pipe 8 and enters the upcomer pipe 10, and
In the gas-liquid mixer 11 of 10, the gas-liquid mixture becomes a two-phase flow (gas in the central part and liquid in the outer peripheral part) and flows into the tubular permeable membrane.

Then, the stock solution that has entered the permeable membrane is separated into permeated water and concentrated solution, the permeated water is taken out through the take-out pipe 15, and the concentrated solution is taken through the return pipe 10a and the separator 7 through the stock solution tank 2
Returned inside.

Here, gas is present in the flow path of the rising portion (including the rising pipe and the membrane module), and the apparent specific gravity is lowered, and
The density difference (water head difference) with the stock solution inside becomes the driving force, and the stock solution circulates naturally.

FIG. 2 is a graph showing the relationship between the permeation flux and the power consumption of the blower when the liquid single-phase flow is changed to the gas-liquid mixed two-phase flow using the membrane processing apparatus having the above-described configuration.

The specific conditions for obtaining the results shown in FIG. 2 are as follows.

Undiluted solution: Suspension of dried baker's yeast dispersed in 0.9% saline. Baker's yeast concentration: 10Kg ・ m-3 Temperature: 25 ℃ Permeable membrane dimensions: outer diameter 5.2mm, inner diameter 3.8mm, length 500mm ceramic 200 membranes / module Membrane structure: Membrane with a pore size of 0.5 μm or asymmetric membrane with 0.2 μm Transmembrane pressure difference: 60 kpa From Fig. 2, the permeation flux J is 0.7 [m ³ · m ^-2 · d ^If it is less than ^-1 ], the power consumption will be smaller if it is a liquid single-phase flow, and if the permeation flux exceeds 2.0 [m ³ · m ^-2 · d ^-1 ], it will be a single-phase or two-phase flow. Nevertheless, it can be seen that the power consumption increases significantly.

Therefore, the permeation flux is 0.7 ~ when using gas-liquid two-phase flow.
It should be in the range of 2.0 [m ³ · m ^-2 · d ^-1 ].

By the way, in the present invention, the natural circulation as a gas-liquid two-phase flow as described above depends exclusively on the gas supplied from the gas-liquid mixer 11. Therefore, FIG. 3 (A) shows the relationship between the supply gas amount Qg and the permeation flux J.

From FIG. 3 (A), the permeation flux J of 0.7 to 2.0 [m ³ · m ^-2 · d ^-1 ] is that the supply gas amount Q is 0.06 to 0.42 [Nm ³ · min.
^-1 ]. However, supply gas amount
The relationship between Qg and the permeation flux J is not uniquely determined by the arrangement of the membrane modules 14 ... Or the pore size of the membrane.

However, the supply gas amount Qg and the circulation flow rate Ql have a certain relationship. This is shown in FIG. 3 (B). That is, as shown in FIG. 3 (B), the supply gas amount that gives the maximum circulation amount is 0.06 [Nm ³ · min ⁻¹ ], and the effective gas supply amount (0.06 to 0.42) is the maximum circulation amount. It is 1 to 7 when divided by the amount of supply gas (0.06) that gives, and thus, by setting the amount of supply gas Qg to be 1 to 7 times the amount of supply gas that gives the maximum circulation flow It is possible to use a two-phase flow of gas-liquid mixing, which is advantageous in terms of consumption capacity.

(Effects of the Invention) As described above, according to the present invention, the running cost of the membrane module is controlled by setting the supply gas amount within a predetermined range when the raw solution is sent to the membrane module as a gas-liquid two-phase flow for processing. Power consumption, which is said to occupy about half of the above, can be significantly reduced compared to the liquid single-phase flow.

[Brief description of drawings]

FIG. 1 is an overall view of a membrane treatment apparatus for carrying out the method of the present invention, FIG. 2 is a graph showing the relationship between permeation flux and power consumption, and FIG.
Figures (A) and (B) are graphs showing the relationship between the supply gas amount, the permeation flux and the circulating liquid flow rate, respectively. In the drawings, 1 is a stock solution, 2 is a stock solution tank 2, 7 is a separator, 8 is a downcomer, 10 is a riser, 11 is a gas-liquid mixer, and 14 is a membrane module.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Shigeru Yoshino 2-8-1 Motomura, Chigasaki-shi, Kanagawa Tochi Kikai Co., Ltd. Chigasaki Plant (56) Reference JP-A-63-104609 (JP, A) Actual Kaisho 62-130799 (JP, U)

Claims (1)

[Claims] 1. A membrane module having a permeable membrane is provided in an ascending pipe which constitutes a part of a circulation path, and gas is supplied to a stock solution in the ascending pipe at a position lower than the membrane module to mix gas and liquid. In a membrane treatment method in which the gas-liquid mixed two-phase flow is supplied to a membrane module and purified, concentrated or separated by a cross-flow filtration method, the stock solution is used as a gas-liquid mixed two-phase flow. The amount of gas supplied for the natural circulation is in the range of 1 to 7 times the amount of gas that gives the maximum circulation flow rate (the maximum amount of the amount of the undiluted solution supplied to the membrane module by the natural circulation). Membrane treatment method.