JP2012192321A - Energy-saving membrane filtration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an energy saving membrane filtration system that can make effective use of thermal energy of a discharged hot cleaning water.SOLUTION: The energy-saving membrane filtration system includes: a membrane modules 41, 42 having a filtration membrane for filtering raw water; a water heater 6 for supplying hot water to the inside of the membrane modules to clean the filtration membrane; a reverse cleaning lines L6, L61, L62 provided between the water heater and the membrane modules; a hot water discharge lines L7, L71, L72 through which used hot water discharged from the membrane modules after cleaning flows; a thermo-electric converter 7 provided to exchange heat with the discharged hot water flowing through the hot water discharge lines, and for converting the thermal energy of the discharged hot water into electric energy; and cleaning equipment 8 actuated with the electric energy obtained by the thermo-electric converter, and for cleaning the filtration membrane.

Description

  Embodiments of the present invention relate to an energy saving membrane filtration system that effectively uses energy in an operation cycle in which membrane filtration and washing are repeated.

  In the membrane filtration system, in order to reduce the cost required for chemical cleaning and membrane exchange, a temperature-responsive compound that causes expansion / contraction and reversible change of hydrophilicity / hydrophobicity at a predetermined temperature is added to the membrane surface, and the membrane surface is added. Or the deposit | attachment (fouling cause substance) in a membrane hole is removed by washing | cleaning with warm water.

  Such a hot water washing technique for a filtration membrane is described in Patent Document 1, for example. In the conventional hot water cleaning process, a large amount of hot water is consumed in order to keep the membrane module tube at a constant temperature from the start to the end of the heat retention and cleaning of the membrane module.

JP 2008-259945 A

  However, since the conventional membrane filtration system has a multiple structure in which bundles of membrane module tubes are stacked and filled in a container, the amount of hot water consumed is increased in proportion to the number of membrane module tubes. . Since the temperature of the hot waste water after being used for the cleaning treatment is as low as 50 ° C. or less, it is difficult to use heat similarly to the high temperature waste water discharged from the heating furnace system or the steam turbine system. Therefore, a large amount of hot water washing water heated by a heat pump is discharged out of the system together with the thermal energy held by the washing operation, and a large amount of heat energy is wasted.

  An object of the present invention is to provide an energy-saving membrane filtration system that can effectively use thermal energy held by warm water washing wastewater.

  An energy saving membrane filtration system according to the present invention includes a membrane module having a filtration membrane for filtering raw water, a water heater for supplying warm water into the membrane module to wash the filtration membrane, and from the water heater to the membrane module. A reverse cleaning line provided between, a warm drainage line through which the warm drainage discharged from the membrane module flows, and a warm drainage flowing through the warm drainage line so as to be able to exchange heat, and the warm drainage A thermoelectric converter having a thermoelectric conversion element for converting the thermal energy possessed by the electric energy, a cleaning device that is driven using the electric energy obtained by the thermoelectric converter, and that cleans the filtration membrane; It is characterized by having.

The block diagram which shows the energy saving membrane filtration system of this embodiment. The characteristic diagram which shows the change of the pressure loss in the repetition cycle of the process of a membrane filtration and a washing | cleaning.

  Hereinafter, various preferred embodiments for carrying out the present invention will be described.

  (1) An energy saving membrane filtration system according to an embodiment of the present invention includes a membrane module having a filtration membrane for filtering raw water, a water heater for supplying warm water into the membrane module to wash the filtration membrane, and the hot water Heat exchange is possible with the reverse cleaning line provided between the vessel and the membrane module, the warm drainage line through which the warm drainage discharged from the membrane module flows, and the warm drainage flowing through the thermal drainage line. A thermoelectric converter having a thermoelectric conversion element for converting the thermal energy held by the hot wastewater into electric energy, and driven by using the electric energy obtained by the thermoelectric converter, And a cleaning device for cleaning.

  According to this embodiment, the thermal energy of the hot water washing wastewater that has been discarded in the past is recovered by converting it into electric energy, and this collected energy is used as an energy source to drive the filtration membrane cleaning device, which is effective in system operation. Can be used.

  (2) In the membrane filtration system of the above (1), the cleaning device oscillates ultrasonic waves using the electrical energy obtained by the thermoelectric converter, and propagates the oscillated ultrasonic waves to the filtration membrane to remove the filtration membrane. An ultrasonic oscillator for ultrasonic cleaning is preferable.

  According to this embodiment, a large film cleaning effect can be obtained by using an ultrasonic oscillator that consumes relatively little power. Ultrasonic oscillators are small, high-performance products that are readily available at low prices, and consume less power than other cleaning equipment (eg, spray nozzles). Small energy recovered from low temperature hot waste water (50 ° C. or less, usually about 35-50 ° C.) such as washing can be used effectively. In particular, combining ultrasonic cleaning with warm water cleaning that does not use chemicals has the advantage of not burdening the environment. It should be noted that in ultrasonic cleaning, the vibrator is attached to the object so that the ultrasonic wave oscillated from the vibrator of the ultrasonic oscillator is efficiently propagated to the filtration membrane. Hot water is suitable as a transmission medium for propagation, and there is a great merit in combining hot water cleaning and ultrasonic cleaning in that respect.

  (3) In the membrane filtration system according to (1) or (2), a membrane module group formed by connecting a plurality of membrane modules in parallel, and a treated water tank for storing treated water filtered by the membrane module group A treated water supply line provided from the treated water tank to the water heater, an electric heater attached to the water heater and heating the treated water supplied from the treated water tank through the treated water supply line, It is preferable to further have.

  In a large-scale membrane filtration system with several tens to several hundreds of membrane modules installed, the amount of energy that can be recovered from the warm drainage of each membrane module is small, but it can be obtained from the membrane module group that is an assembly of them. Since the total amount of collected energy is considerably large as a total amount, there is a possibility that it can serve as an energy supply source for electrical equipment having a relatively large rated capacity. It is possible to apply at least another electric energy generation source such as a solar cell and the energy recovery system of the present embodiment to an actual machine. As described above, according to the present embodiment, the recovered electrical energy can be used for the electric heater of the hot water heater.

  Hereinafter, preferred embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, the energy saving membrane filtration system 1 of this embodiment includes a raw water tank 2, a pump P1, a strainer 3, a plurality of membrane modules 41 and 42 having filtration membranes, a treated water tank 5, a water heater 6, and a thermoelectric conversion. And a controller 7, an ultrasonic oscillator 8, a gas supply device 9, a controller (not shown), a sensor, a pump, and valves.

  The entire energy-saving membrane filtration system 1 is constantly monitored by a controller (not shown), is constantly operated according to the set process conditions, and does not greatly deviate from the set process conditions even when a large disturbance enters. The operation of each part is controlled to return from the unsteady state to the steady state, and the filtration membrane in the membrane module is washed with hot water periodically and / or as needed as shown in FIG. Yes.

  The raw water tank 2 is a storage tank for receiving and temporarily storing wastewater (raw water) containing a large amount of suspended solids (water-soluble organic matter) in sewage treatment, food wastewater treatment, chemical wastewater treatment, and the like. A flocculant addition hopper (not shown) is provided above the raw water tank 2, and the flocculant is added to the raw water in the raw water tank 2 from the flocculant addition hopper. A drain pipe (not shown) is attached to the bottom of the raw water tank 2 so that the aggregated / precipitated sediment is discharged from the raw water tank 2 periodically and / or as needed.

  The outlet of the raw water tank 2 is connected to the raw water supply line L1. The raw water supply line L1 is connected to the suction port of the pump P1. The discharge port of the pump P1 is connected to the inlet of the strainer 3. The outlet of the strainer 3 is connected to the pretreatment water supply line L2, and the pretreatment water supply line L2 is branched into two lines L21 and L22. The two branch lines L21 and L22 are connected to the first and second membrane modules 41 and 42, respectively.

  The strainer 3 is a pretreatment device for separating and removing solid contents (sand particles, metal particles, plastic pieces, etc.) contained in the raw water. In this embodiment, the strainer is used as the pretreatment device, but the pretreatment device is not limited to this, and a sand filter or the like may be used as another pretreatment device.

  The membrane modules 41 and 42 contain a membrane module in which a number of hollow tubular filtration membranes are bundled. The first and second membrane modules 41 and 42 are controlled to perform rotation processing or simultaneous parallel processing. In the rotation operation, filtration and cleaning are alternately performed between the first and second membrane modules 41 and 42 as shown in FIG. In the simultaneous parallel operation, the first and second membrane modules 41 and 42 are simultaneously filtered, and the membrane is back-washed at the same time. Permeate water supply lines L31 and L32 and backwash lines L61 and L62 are connected to the membrane modules 41 and 42, respectively.

  The treated water tank 5 receives the permeated water that has passed through the filtration membrane from the first and second membrane modules 41 and 42 through the permeated water supply lines L31 and L32, temporarily stores them, and is used as a post-process facility (not shown). Permeated water is sent out via the line L4, and a part of the permeated water is sent to the hot water heater 6 via the line L5 and heated by the hot water heater 6 to be used as hot water washing water.

  The water heater 6 has an electric heater 61 that heats the permeated water sent from the treated water tank 5, and the heated hot water is pumped to the membrane modules 41 and 42 via backwash lines L 61 and L 62. Water is supplied by driving, and the filtration membrane is back-washed. The electric heater 61 is a resistance heating type electric heating device that heats the water in the treated water tank 5 to 60 ° C. or higher (preferably 60 to 70 ° C.). Backwash water discharge lines L71 and L72 are connected to the membrane modules 41 and 42, respectively, and the warm waste water after backwashing the filtration membrane is discharged to the thermoelectric converter 7.

  The thermoelectric converter 7 has a bismuth-tellurium-based thermoelectric conversion element and a charge / discharge circuit, and utilizes sensible heat held by hot drainage (50 ° C. or less) introduced from the backwash water discharge lines L71 and L72. It has a function of generating electric energy by thermoelectric conversion, charging the generated electricity in a charge / discharge circuit, and discharging it as needed.

  The ultrasonic oscillator 8 has an ultrasonic transducer attached so that ultrasonic waves are propagated to the filtration membranes in the membrane modules 41 and 42. The power circuit of the ultrasonic oscillator 8 is connected to the thermoelectric converter 7.

  The gas supply device 9 blows gas into the membrane modules 41 and 42 when the membrane is back cleaned.

  Next, various filter membranes that can be subjected to hot water cleaning will be described.

  In the warm water washing process, in order to enhance the washing effect, a temperature responsive compound that causes expansion / contraction or reversible change of hydrophilicity / hydrophobicity at a predetermined temperature is added to the surface of the filtration membrane, and the temperature responsive compound is brought into contact with warm water. By causing a reversible change, the pores of the membrane are expanded so that the fouling-causing substances attached in and around the pores are easily detached.

  As such a functional filtration membrane, a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), a reverse osmosis membrane (NF membrane or RO membrane) and the like are used. For example, PTFE type MF1, MF2 (product number) as the MF membrane, acetate cellulose type UF100 and UF30 (product number) as the UF membrane, and sulfonated polysulfone type NTR7410 (product number), NTR7430 (product) No.), NTR7450 (product number) and polyethylsulfone PES10 (product number) are used.

  Next, the filtration process will be described.

  The treated water from the previous stage of membrane treatment is supplied to the membrane filtration system as raw water. The raw water supplied from the membrane supply pump P1 flows through the supply line L2 via the strainer 3, and is supplied to the membrane modules 41 and 42. The treated water separated by the membrane modules 41 and 42 is sent to the treated water tank 5 through the permeated water line L3. The treated water stored in the treated water tank 5 is further sent to the treatment tank (not shown) of the next process through the treated water supply line L4. The process so far is the membrane filtration process during steady operation.

  Next, the cleaning process will be described.

  After a predetermined filtration time has elapsed, or when the membranes of the membrane modules 41 and 42 are clogged due to adhesion of solids or solutes, that is, when fouling has occurred, hot water cleaning is performed. In the warm water cleaning process, first, the treated water is heated by the heater 61, and the warm water is sent from the permeate side to the filtration membrane via the reverse cleaning water lines L61 and L62. Further, air is sent from the permeate side of the gas supply device 9 through the gas supply line L14 to perform hot water cleaning.

  In order to bring the membrane module tube to a predetermined temperature, it is heated using warm water. The hot water overflowing from the membrane module pipe is drained from the drain pipe, and the remaining heat energy is recovered from the drainage by the heat exchanger 11 during this period and converted into electric energy. Thereafter, ultrasonic waves are oscillated from the ultrasonic generator 8 using the generated electrical energy, and the filtration membrane is subjected to ultrasonic cleaning in parallel with the hot water cleaning.

  The synergistic action of hot water cleaning / ultrasonic cleaning increases the cleaning efficiency of the membrane module tube and shortens the hot water cleaning time. As a result, shortening of energy consumption time and reduction of the amount of hot water used are realized, and a desired energy saving effect is obtained.

  The effect of this embodiment will be described.

  It is possible to recover the thermal energy left in the wastewater and convert it into electrical energy. There is an advantage that ultrasonic cleaning can be performed together with hot water cleaning by driving the ultrasonic oscillator using the collected electrical energy.

  In this embodiment, first, thermal energy is recovered from a large amount of hot water discharged after cleaning, and the recovered thermal energy is converted into electrical energy. Ultrasonic waves are generated using the electrical energy thus recovered. By irradiating the generated ultrasonic wave to the filtration membrane in the membrane module, the cleaning efficiency is greatly improved as compared with hot water cleaning alone. Thus, the heat energy related to heating and the amount of hot water used for cleaning can be reduced, and energy saving can be achieved.

  According to this embodiment, a large film cleaning effect can be obtained by using an ultrasonic oscillator that consumes relatively little power. Ultrasonic oscillators are small, high-performance products that are readily available at low prices, and consume less power than other cleaning equipment (eg, spray nozzles). Small energy recovered from low temperature hot waste water (50 ° C. or less, usually about 35-50 ° C.) such as washing can be used effectively. In particular, combining ultrasonic cleaning with warm water cleaning that does not use chemicals has the advantage of not burdening the environment. It should be noted that in ultrasonic cleaning, the vibrator is attached to the object so that the ultrasonic wave oscillated from the vibrator of the ultrasonic oscillator is efficiently propagated to the filtration membrane. Hot water is suitable as a transmission medium for propagation, and there is a great merit in combining hot water cleaning and ultrasonic cleaning in that respect.

  According to the present invention, heat energy is recovered from waste water that has been heated in the hot water cleaning process, and the recovered heat energy is converted into electric energy, thereby supplying the ultrasonic generator with the obtained electric energy, Washing efficiency can be increased by performing membrane cleaning together with warm water.

1 ... membrane filtration system, 2 ... raw water tank, 3 ... strainer,
41, 42 ... Membrane module,
5 ... treated water tank, 6 ... water heater, 61 ... electric heater,
7 ... Thermoelectric converter, 8 ... Ultrasonic oscillator (cleaning device), 9 ... Gas supply device,
P1 ... pump,
L5 ... treated water supply line,
L6, L61, L62 ... Backwash line,
L7, L71, L72 ... Warm drainage line.

Claims (3)

A membrane module having a filtration membrane for filtering raw water;
A water heater for supplying warm water into the membrane module to wash the filtration membrane;
A backwash line provided between the water heater and the membrane module;
A warm drainage line through which the washed warm drainage discharged from the membrane module flows;
A thermoelectric converter having a thermoelectric conversion element that is provided so as to be capable of exchanging heat with the warm drainage flowing in the warm drainage line, and that converts the thermal energy held by the warm drainage into electrical energy;
A cleaning device that is driven using the electrical energy obtained by the thermoelectric converter and cleans the filtration membrane;
An energy saving membrane filtration system characterized by comprising:   The cleaning device is an ultrasonic oscillator that oscillates an ultrasonic wave using electrical energy obtained by the thermoelectric converter, and propagates the oscillated ultrasonic wave to the filtration membrane to ultrasonically clean the filtration membrane. The energy saving membrane filtration system according to claim 1. A group of membrane modules formed by connecting a plurality of the membrane modules in parallel;
A treated water tank for storing treated water filtered by the membrane module group;
A treated water supply line provided from the treated water tank to the water heater;
An electric heater attached to the water heater for heating the treated water supplied from the treated water tank through the treated water supply line;
The energy-saving membrane filtration system according to claim 1, further comprising:

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