JPH03169302A - Operation of vacuum pump in degassing membrane separation apparatus - Google Patents

Abstract

PURPOSE:To efficiently perform liquid-gas separation even when a diaphragm type vacuum pump is used by parallelly providing two vacuum pumps and alternately performing operation for discharging the accumulated liquid generated by condensing the vapor of the liquid transmitted through a membrane and evaporated from the vacuum pumps and operation for performing the drawing of a vacuum on a vapor transmission side. CONSTITUTION:A valve V11 is opened and a valve V21 is closed and the evacuation of the transmitted gas chamber 14 of a membrane module is performed for a definite time by the suction and discharge operation of a vacuum pump P1. Subsequently, the valve V11 is closed and the valve 21 is opened to perform the evacuation of the transmitted gas chamber 14 by a vacuum pump P2. Even when the vacuum pump P2 is operated, the suction and discharge operation of the vacuum pump P1 is continued for a definite time as it is. Since a valve V12 is opened at this time, a large amount of air is sucked/discharged and the accumulated liquid in the vacuum pump P1 is discharged because of the violent stream of air. After discharge, the vacuum pump P1 is stopped. The discharge operation of the accumulated liquid and the evacuation of the transmitted gas chamber are alternately repeated by both pumps. Therefore, the transmitted gas chamber can be held to a continuous vacuum state.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Publication Field> The present invention relates to a method of operating a vacuum pump in degassing membrane separation of carp.

Conventional technology> When separating gas from a liquid containing dissolved gas,
The permeation side of the membrane module is depressurized by a vacuum pump, the liquid is passed through the raw liquid side of the module, and the pressure condition is maintained below the vapor pressure held by the dissolved gas by the depressurization,
The so-called method that vaporizes and separates the dissolved gas in the circulating liquid
The degassing membrane module method is well known. This degassing membrane module method requires a vacuum pump, and examples of this vacuum pump include water ring vacuum pumps, oil rotary vacuum pumps, and diaphragm vacuum pumps. A water ring vacuum pump has an impeller installed inside a cylinder that has an inlet and an outlet.Water is placed inside the cylinder, and as the impeller rotates, water is brought to the outer periphery by centrifugal force, and the air from the inlet is drawn into the air. The system traps the trapped air between cars, seals it with water, and discharges it at the exhaust port. An oil rotary vacuum pump has a rotor with spring-biased blades attached, the rotor is housed in a cylinder, and the entire cylinder is sealed to maintain airtightness. A diaphragm type vacuum pump is a Sakaki type vacuum pump in which a diaphragm is attached to a header having an inlet valve and a 171 outlet valve, and the volume of the diaphragm chamber is increased or decreased by operating a crank. However, the usable pressure range of water ring vacuum pumps is 760 to 100 MHg, and depending on the type of gas contained, efficient deaeration is a national problem. Oil rotary vacuum pumps do not have this disadvantage, but they are expensive and
It is not easy to maintain as it requires an oil seal. In addition, all of these vacuum pumps are large, disadvantageous in terms of installation space, and also expensive. Compared to these vacuum pumps, diaphragm vacuum pumps are smaller, cheaper, and have a usable range of 760=IO.
However, in the degassing membrane module method described above, the liquid also evaporates under reduced pressure, and this vapor is converted into water droplets within the diaphragm chamber, and the accumulation of these water droplets causes the chamber to The vacuum pump is filled with water, reducing vacuum efficiency and making it difficult to separate liquid and gas, which can guarantee a specified degree of decompression. An object of the present invention is to propose a method for operating a vacuum pump in a degassing membrane separation device that enables liquid-gas separation, and to reduce the cost of the vacuum pump. The method for operating a vacuum pump in a degassing membrane separation device is to connect the inlet of a vacuum pump, which has a variable volume chamber with an inlet valve and a discharge valve, to the permeate side of the membrane module, and to operate the vacuum pump under reduced pressure on the permeate side. In a degassing membrane separation device that permeates and separates gas in a gas-containing liquid, two of the above vacuum pumps are installed in parallel,
In each of these pumps, the liquid passes through the membrane under reduced pressure on the permeate side, evaporates, and condenses in the vacuum pump to discharge the accumulated liquid produced from the vacuum pump, and the vapor permeation side is evacuated. 3. A method of operating a vacuum pump in a degassing membrane separation device, which is characterized in that the following steps are performed alternately. Description of Embodiments 191> Hereinafter, embodiments of the present invention will be explained with reference to the drawings. Ru. In the figure, l is a membrane module, and a gas permeable membrane is used for the membrane, 11 is a low-liquid chamber, l2 is a raw liquid inlet,
13 indicates the raw solution outlet, 14 indicates the permeation gas chamber, P, , P, are two vacuum pumps installed in parallel, and the chamber whose volume is increased or decreased is provided with an intake valve and an exhaust valve. For example, a diaphragm type vacuum pump can be used. ■． , ■■ is each vacuum pump PI, P
This is an automatic valve installed between (1) and the permeation gas chamber (14) of module (1). Vlf%v0 is for each vacuum pump i', ,
p, and valve V. This is an automatic valve installed between ,■■. 4 is the vacuum needle. 5 is an automatic stop valve (cuts off the water when the equipment is stopped or there is an abnormality). 6 is a constant flow valve, 7
is a pressure gauge, and 8 is a flow meter. In the above, vacuum pump P. , P. The permeate gas chamber 1 of the membrane module 1 is depressurized by the alternating operation. A stock solution containing dissolved gas is passed through the stock solution chamber 11 of the module 1, and the gas is permeated through the membrane while the degree of vacuum is kept below the vapor pressure. It is evacuated by a running vacuum pump. In this case, there is also evaporation of the stock solution, and the vapor enters the vacuum pump chamber, cools and condenses on the chamber wall, forms droplets, and accumulates inside the chamber. However, according to the present invention, the pump can be operated smoothly despite such liquid accumulation. In the above, when the valve V++ (Vt+) is closed, the vano rev v1 (Vzw) is open, and the valve V++ (Vt+) is open.
z+) is open, the Vth valve (Vzz) is closed.
Assume that valve Vll is open, valve vII is closed, and the module permeate gas chamber 14 is evacuated by suction and discharge operations of pump 1). When this evacuation force is applied for a certain period of time, the valve V. is closed, valve V■
opens, pump P starts suction/discharge operation, and pump! >> The module permeate gas chamber is evacuated by z. Even if the pump P8 is activated, the pump P8 will remain active for a certain period of time.
The suction/exhaust operation of l continues. At this time, since the Vth valve is open, a large amount of air is taken in and discharged, and due to the strong air flow, the above-mentioned accumulated liquid in the pump P1 can be discharged. After this discharge, the pump P1 is stopped. This operation of draining the accumulated liquid and evacuation of the module permeate gas chamber is repeated alternately for both pumps. Therefore, the permeate gas chamber of the module can be maintained in a continuously reduced pressure state. Furthermore, when a stopped vacuum pump that has discharged accumulated liquid is operated next time, normal depressurization can be guaranteed because there is no accumulated liquid. The evacuation operation duration (stop time) of one pump is 0.9 when the standard vacuum is 11 g.
AmmHg, preferably within the time it reaches 1.1AmmHg. By evacuating both pumps alternately at such time intervals, J! i The degree of reduced pressure on the side of the overgas chamber can be maintained within ±10% of the standard value, and liquid-gas separation can be performed with a reasonable amount of permeation. In the above, the vacuum pump may be of a type in which a piston is attached to a cylinder having an intake valve and an exhaust valve, and the chamber volume is increased or decreased by reciprocating the piston. Moreover, any of a spiral membrane module, a hollow fiber membrane module, a tubular membrane module, a plate type membrane module, etc. can be used as the III module.

For the above operation control, automatic valve V I I % V
Time control that alternately opens and closes tI at regular intervals, or automatic valve Vll when the degree of pressure reduction reaches the lower limit.
, or the pressure control that switches the opening and closing of VZ+. Next, the test results of the operating method of the present invention will be explained in comparison with the conventional method. Flow rate of raw water with dissolved oxygen content of 8.1 ppm: 2.5 ton/
hr, IISfi module population pressure: 1.5kg/c
+a to flow into the membrane module to reduce the amount of dissolved oxygen to 0. 5p
This is a case where the raw water is treated to pm, and the permeate side is 4011.
It is necessary to keep it below 118g. Under such reduced pressure, oxygen passes through the membrane in a gaseous state, and 50 g of water vapor also passes through the membrane.
/ hr permeates through the membrane, and 45g/h of this water vapor
Although r can be dissipated into the atmosphere, 5 g/It r condenses and accumulates in the diaphragm chamber of the vacuum pump. However, in continuous operation of a single diaphragm vacuum pump, the degree of vacuum is 30 wHg at the initial operation, but after 2 hours, it becomes 4 (lmHg), and after 5 hours, it becomes 60 mHg, resulting in a significant deterioration in the performance of the degassing module. In contrast, based on the present invention, two vacuum pumps were used, and valves Vll and ■!1 were switched open and closed at one-hour intervals, and even after one valve was closed, the other pump did not operate. I
When the operation was continued for 0 minutes, the degree of vacuum could be maintained at 40 mHg or less during 8,000 hours of operation, and the oxygen degassing process could be performed as specified. <Effects of the Invention> As described above, according to the method of operating a vacuum pump in a degassing membrane separation device according to the present invention, the problem of condensation of water vapor permeating the permeation side can be eliminated despite using a diaphragm type vacuum pump. It is possible to maintain a predetermined degree of reduced pressure while reducing the pressure, and it is possible to degas a liquid containing dissolved gas without requiring the cost and equipment space required for a vacuum pump.

[Brief explanation of the drawing]

The drawing is a diagram illustrating a degassing membrane separation device that operates a vacuum pump according to the present invention. 1...Membrane module, l4...Permeation gas chamber, PI, p! ······Vacuum pump.

Claims (1)

[Claims] A degassing membrane separation device that connects the inlet of a vacuum pump with a suction valve and a discharge valve in a variable volume chamber to the permeation side of a membrane module, and permeates and separates gas in a gas-containing liquid under reduced pressure on the permeation side. In this method, two vacuum pumps are installed in parallel, and in each of these pumps, the liquid permeates through the membrane under reduced pressure on the permeate side, evaporates, and condenses in the vacuum pump to generate a accumulated liquid, which is discharged from the vacuum pump. 1. A method for operating a vacuum pump in a degassing membrane separation apparatus, comprising alternately performing the operation and the operation of vacuuming the permeate side.