JP2007175624A - Method for operating membrane filtration system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a method for operating a membrane filtration system capable of stabilizing the water quality of permeate when a water supply is started from a state of terminating the water supply to a water supply tank. <P>SOLUTION: This operation method comprises the closure of a water supply line 3 between a filtration membrane part 4 and a water supply tank 6, carrying out reflux operation for refluxing the permeate from the filtration membrane part 4 from the water supply line 3 on the upstream side of the closed place to the water supply line 3 on the upstream side of the filtration membrane part 4 for a predetermined time when the water supply is terminated to the water supply tank 6, then starting the water supply to the water supply tank 6, and carrying out water quality recovery operation reducing the discharge amount of water concentrate from the filtration membrane part 4 smaller than a predetermined amount for a predetermined time after the water supply is started. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of operating a membrane filtration system including a filtration membrane unit that removes impurities in feed water and a feed water tank that stores feed water to be supplied to equipment.

  As a water treatment system for water supplied to equipment, there is a membrane filtration system provided with a filtration membrane section for filtering impurities contained in the feed water, for example, dissolved salts, and a water supply tank for storing water to be supplied to the equipment. .

  For example, Patent Document 1 discloses an example using a nanofiltration membrane (NF membrane) as the filtration membrane of the filtration membrane portion. The nanofiltration membrane is a liquid separation membrane that can prevent permeation of particles or polymers (substances having a maximum molecular weight of about several hundreds) smaller than about 2 nm. In the membrane filtration system using the nanofiltration membrane, feed water flows from one side of the filtration membrane portion, and the nanofiltration membrane captures corrosion promoting components and alkali components and allows corrosion inhibiting components to permeate. It has become so. Here, for example, when the equipment is a once-through boiler, the corrosion promoting component is made of a non-passivated metal and acts on the inner surfaces of a plurality of heat transfer tubes and lower headers in contact with boiler water to promote the corrosion. It usually contains sulfate ions, chloride ions and other substances. In addition, the corrosion inhibiting component refers to a component that acts on the inner surface of each heat transfer tube and the lower header in contact with boiler water in the once-through boiler, and is usually silica (that is, Silicon dioxide). Examples of the alkali component include hydrogen carbonate and carbonate, and these alkali components generate hydroxide by thermal decomposition in each of the heat transfer tubes and the lower header. This hydroxide has the effect of increasing the pH of boiler water in each heat transfer tube and in the lower header, and suppressing corrosion of each heat transfer tube and the lower header.

From the other side of the filtration membrane part, permeated water containing a corrosion inhibiting component and concentrated water containing a corrosion promoting component and an alkali component are separated and flow out. Then, the permeated water is supplied to the device, a part of the concentrated water is drained, and the remaining part is returned to the upstream side of the filtration membrane part.
JP 2004-290829 A

  In the membrane filtration system, when water is supplied to the water supply tank, a predetermined water supply pressure is applied by a pump provided on the upstream side of the filtration membrane unit to supply water to the filtration membrane unit, and the nanofiltration membrane By using the reverse osmosis phenomenon, the feed water is filtered. However, in order to stop water supply to the water supply tank, when the pump is stopped and water supply to the filtration membrane unit is stopped, water supply pressure from the water supply side is not applied to the nanofiltration membrane. A permeation phenomenon occurs in the vicinity of the filtration membrane, and the impurity concentration on the permeate side increases and the impurity concentration on the water supply side decreases.

  In this manner, in the vicinity of the nanofiltration membrane, the permeate side impurity concentration is high and the feedwater supply side impurity concentration is low, so that water is supplied to the filtration membrane unit and supplied to the water supply tank. When the water supply is started, the impurity concentration of the permeated water once becomes higher than usual immediately after the start of water supply, and then gradually rises to a normal concentration after becoming lower than normal. The reason why the impurity concentration of permeated water increases immediately after the start of water supply is that the impurity concentration on the permeate side increases in the vicinity of the nanofiltration membrane. In addition, the permeated water impurity concentration decreases after the start of water supply because the impurity concentration on the water supply side is low in the vicinity of the nanofiltration membrane, so the concentrated water from the filtration membrane portion is removed from the filtration membrane portion. This is because the impurity concentration of the feed water supplied to the filtration membrane portion is lower than usual even when refluxed upstream. Further, the impurity concentration of the permeated water gradually increases and becomes a normal concentration because the concentration of water supplied to the filtration membrane portion gradually proceeds with time.

  As described above, when water supply is started from the state where water supply to the water supply tank has been stopped, permeated water having a higher impurity concentration than usual is stored in the water supply tank as water supply immediately after the start, and then impurities Permeated water having a lower concentration than usual is stored in the water tank as water supply. As a result, in the water supply tank, first, permeated water having a higher corrosion promoting component concentration than usual is stored, and then permeated water having a corrosion inhibiting component concentration and an alkali component concentration lower than usual is stored. . Here, when feed water having a high corrosion promoting component concentration or feed water having a low corrosion inhibitor component concentration is supplied to the once-through boiler, the heat transfer tubes and the lower header are likely to be corroded, and the alkali component concentration is reduced. When low feed water is supplied to the once-through boiler, the pH of the boiler water does not increase in an area where the alkali component concentration of the raw water is low, and corrosion of the heat transfer tubes and the lower header tends to occur. In particular, when the water supply to the water supply tank is frequently stopped or when the time during which the water supply is stopped becomes long, or when the capacity of the water supply tank is small, the corrosion promoting component in the water supply tank Since the concentration is high and the corrosion-inhibiting component concentration and the alkali component concentration are likely to be low, the problem of corrosion of the lower header and the heat transfer tubes becomes significant. Therefore, when water supply is started from the state where water supply to the water supply tank is stopped, the increase in the corrosion promoting component concentration is suppressed as much as possible, and the decrease in the corrosion suppressing component concentration and the alkali component concentration is suppressed as much as possible. It is desirable to stabilize the quality of the permeated water as much as possible.

  The present invention has been made in view of the above circumstances, and the problem to be solved is to stabilize the quality of permeated water when water supply is started from a state where water supply to the water supply tank is stopped. It is to realize a method of operating a membrane filtration system capable of

  This invention was made in order to solve the said subject, and the invention of Claim 1 is connected with the water supply line to an apparatus, The filtration membrane part which removes the impurity in feed water, This filtration membrane part A water supply tank that is connected to the water supply line on the downstream side of the tank and stores water supplied to the device, and supplies water to the filtration membrane when the water supply to the water supply tank is filtered. While the permeated water from the filter membrane is stored in the water supply tank, a part of the concentrated water from the filtration membrane part is drained out of the system by a predetermined amount, and the remaining part is returned to the upstream side of the filtration membrane part. A method for operating a membrane filtration system, wherein the water supply line between the filtration membrane portion and the water supply tank is closed, and the permeated water from the filtration membrane portion is removed from the water supply line upstream of the closed portion. The water supply upstream of the filtration membrane section The recirculation operation for recirculating to the in is performed for a predetermined time when the water supply to the water supply tank is stopped, and then the water supply to the water supply tank is started. A water quality recovery operation is performed in which the amount of concentrated water discharged from the water is less than the predetermined amount.

  In the first aspect of the present invention, when the water supply to the water supply tank is stopped, the reflux operation is performed for a predetermined time until the water supply to the water supply tank is started. By recirculating the permeated water to the water supply line upstream of the filtration membrane part, the water pressure on the feed water supply side is higher than the permeate side in the filtration membrane part, so that the feed water flows from the feed water supply side to the permeate side, and vice versa. Due to the permeation phenomenon, impurities in the feed water are removed by the filtration membrane. In addition, the water supply to the filtration membrane unit is performed by performing the water quality recovery operation for a predetermined time after the start of water supply to the water supply tank to reduce the drainage amount of the concentrated water from the filtration membrane unit to be less than the predetermined amount. Concentration of the supplied water will proceed.

  According to a second aspect of the present invention, in the operation method of the membrane filtration system according to the first aspect, when water supply to the water supply tank is stopped, the water level in the water supply tank drops to a predetermined water level. The recirculation operation is started, and water supply to the water supply tank is started after a lapse of a predetermined time from the start of the recirculation operation.

  In the invention according to claim 2, when the water level in the water supply tank falls to a predetermined water level, the reflux operation is started and the permeated water from the filtration membrane portion is upstream of the filtration membrane portion. By recirculation to the water supply line, the water supply flows from the water supply side to the permeate side in the filtration membrane part, and impurities in the water supply are removed by the filtration membrane.

  The invention according to claim 3 is the operation method of the membrane filtration system according to claim 1 or 2, wherein water supply to the filtration membrane unit, permeated water from the filtration membrane unit, and concentrated water from the filtration membrane unit The length of the operation time of the reflux operation is set based on any one of the water quality.

  In the invention according to claim 3, the impurities in the water supply are sufficiently reduced based on the quality of any of the water supplied to the filtration membrane part, the permeated water from the filtration membrane part, and the concentrated water from the filtration membrane part. The length of the operation time of the reflux operation is set so as to reduce the deterioration of the quality of the permeated water.

  According to a fourth aspect of the present invention, in the operation method of the membrane filtration system according to the first or second aspect, the reflux operation is performed based on a length of time during which supply of water supply to the filtration membrane unit is stopped. The operation method of the membrane filtration system according to claim 1 or 2, wherein the length of the operation time is set.

  In invention of Claim 4, based on the length of time which the supply of the feed water to the said filtration membrane part was stopped, the impurity in feed water is fully removed and the water quality deterioration of permeated water is reduced. The length of the operation time of the reflux operation is set so that

  The invention according to claim 5 is the operation method of the membrane filtration system according to claim 1 or 2, wherein water supply to the filtration membrane unit, permeated water from the filtration membrane unit, and concentrated water from the filtration membrane unit The length of the operation time of the reflux operation is set based on any one of the above water quality and the length of time during which the supply of water supply to the filtration membrane unit has been stopped.

  In the invention according to claim 5, the water quality of any one of water supply to the filtration membrane part, permeated water from the filtration membrane part and concentrated water from the filtration membrane part, and supply of water supply to the filtration membrane part On the basis of the length of time during which the water is stopped, the length of the operation time of the reflux operation is set so that impurities in the feed water can be sufficiently removed to reduce the quality of the permeated water.

  A sixth aspect of the present invention is the operation method of the membrane filtration system according to the first, second, third, fourth or fifth aspect, wherein water is supplied to the filtration membrane unit, permeated water from the filtration membrane unit, and the filtration. Based on the temperature of any of the concentrated water from the membrane, the amount of concentrated water discharged and / or the length of the operation time in the water quality recovery operation is set.

  In the invention according to claim 6, the water is supplied to the filtration membrane unit based on the temperature of any one of water supplied to the filtration membrane unit, permeated water from the filtration membrane unit, and concentrated water from the filtration membrane unit. The amount of concentrated water discharged and / or the length of the operation time in the water quality recovery operation are set so that the feed water is concentrated in a range that does not excessively concentrate and the quality of the permeated water is restored to a predetermined quality.

  The invention according to claim 7 is the operation method of the membrane filtration system according to claim 1, 2, 3, 4 or 5, wherein water is supplied to the filtration membrane unit, permeated water from the filtration membrane unit and the filtration Based on the quality of any of the concentrated water from the membrane, the amount of concentrated water discharged and / or the length of the operation time in the water quality recovery operation is set.

  In the invention according to claim 7, the water is supplied to the filtration membrane unit based on the water quality of any one of water supplied to the filtration membrane unit, permeated water from the filtration membrane unit, and concentrated water from the filtration membrane unit. The amount of concentrated water discharged and / or the length of the operation time in the water quality recovery operation are set so that the feed water is concentrated in a range that does not excessively concentrate and the quality of the permeated water is restored to a predetermined quality.

  According to an eighth aspect of the present invention, in the operation method of the membrane filtration system according to the first, second, third, fourth, or fifth aspect, the length of time during which the supply of water supply to the filtration membrane section is stopped is stopped. Based on the above, the drainage amount of concentrated water and / or the length of operation time in the water quality recovery operation is set.

  In the invention according to claim 8, based on the length of time during which water supply to the filtration membrane unit has been stopped, the water supplied to the filtration membrane unit is concentrated within a range not excessively concentrated, and permeated. The amount of concentrated water discharged and / or the length of operation time in the water quality recovery operation are set so that the water quality is restored to a predetermined quality.

  Furthermore, the invention according to claim 9 is the operation method of the membrane filtration system according to claim 1, 2, 3, 4 or 5, wherein water supply to the filtration membrane unit, permeated water from the filtration membrane unit, and The water temperature of any of the concentrated water from the filtration membrane unit, the water quality of the water supplied to the filtration membrane unit, the permeated water from the filtration membrane unit, and the concentrated water from the filtration membrane unit, and the filtration membrane The amount of concentrated water drainage and / or the length of operation time in the water quality recovery operation is set based on any two or more of the lengths of time during which the supply of water to the section has been stopped And

  In the invention according to claim 9, water temperature to any one of the water supply to the filtration membrane part, the permeated water from the filtration membrane part and the concentrated water from the filtration membrane part, the water supply to the filtration membrane part, Either the quality of any of the permeated water from the filtration membrane part and the concentrated water from the filtration membrane part, and the length of time during which the supply of water supply to the filtration membrane part was stopped On the basis of the amount of drainage and / or operation of the concentrated water in the water quality recovery operation so that the feed water supplied to the filtration membrane unit is concentrated in a range not excessively concentrated and the quality of the permeated water is restored to a predetermined quality. The length of time is set.

  According to the first aspect of the present invention, when the water supply to the water supply tank is stopped, by performing the reflux operation for a predetermined time until the water supply to the water supply tank is started, the filtration membrane is obtained. Since the impurities in the water supply are removed in the section, the water quality deterioration of the permeated water when water supply to the water supply tank is started can be reduced. Further, by performing the water quality recovery operation for a predetermined time after the start of water supply to the water supply tank, the concentration of the water supplied to the filtration membrane portion proceeds, the impurity concentration increases, and the quality of the permeated water Can be recovered to a predetermined water quality in a short time. And by removing the impurities in the feed water in this way, the water quality deterioration of the permeated water can be reduced, and the impurity concentration of the feed water supplied to the filtration membrane part is increased, and the quality of the permeated water is reduced. Since the water quality can be recovered to a predetermined level in a short time, the quality of the permeated water can be stabilized. Therefore, even if the water supply to the water supply tank is frequently stopped or the time during which the water supply is stopped becomes long, or the capacity of the water supply tank is small, the water supplied to the device The predetermined water quality can be maintained.

  According to the second aspect of the present invention, when the water level in the water supply tank falls to a predetermined water level, impurities in the water supply are removed by starting the reflux operation, and thus impurities in the water supply Since the water supply to the water supply tank is started after the elapse of a predetermined time from the start of the reflux operation in which water is removed, deterioration of the quality of the permeated water when the water supply to the water supply tank is started can be reduced.

  According to invention of Claim 3, 4, the operation time of the said recirculation | reflux operation | movement can be set to the optimal thing so that the impurity in feed water can fully be removed.

  According to the invention described in claim 5, the length of operation time of the reflux operation is any one of water supply to the filtration membrane part, permeated water from the filtration membrane part and concentrated water from the filtration membrane part. Is set based on the quality of the water and the length of time during which supply of water to the filtration membrane unit has been stopped, so that the impurities in the water supply can be sufficiently removed. The length of time can be set to a more optimal one.

  According to the invention of claim 6, 7 or 8, the feed water supplied to the filtration membrane part is concentrated in a range not excessively concentrated, and the quality of permeate is recovered to a predetermined quality. The amount of concentrated water discharged in the water quality recovery operation and / or the length of operation time can be set to an optimum value.

  According to the ninth aspect of the present invention, the drainage amount of concentrated water and / or the length of the operation time in the water quality recovery operation is determined by the supply water to the filtration membrane unit, the permeated water from the filtration membrane unit, and the filtration membrane. The temperature of any of the concentrated water from the section, the water supply to the filtration membrane section, the quality of any of the permeated water from the filtration membrane section and the concentrated water from the filtration membrane section, and the filtration membrane section Since it is set based on any two or more of the length of time during which the supply of water supply has been stopped, the water supplied to the filtration membrane is concentrated in a range that does not excessively concentrate, The amount of concentrated water discharged and / or the length of the operation time in the water quality recovery operation can be set to be more optimal so that the water quality of the water is restored to a predetermined quality.

  Next, an embodiment of the present invention will be described. The operation method of the membrane filtration system according to the embodiment of the present invention includes a filtration membrane unit connected to a water supply line to equipment, a drainage line of concentrated water connected to the filtration membrane unit, the drainage line and the A circulating water line connecting the water supply line upstream of the filtration membrane part, an on-off valve provided in the water supply line downstream of the filtration membrane part, and a connection to the water supply line downstream of the on-off valve Implemented in a membrane filtration system comprising a water supply tank, a permeated water return line connecting the water supply line between the filtration membrane unit and the on-off valve and the water supply line upstream of the filtration membrane unit Is done.

  Examples of the equipment include thermal equipment such as a steam boiler, a hot water boiler, a cooling tower, and a water heater.

  The said filtration membrane part filters the impurity contained in feed water with a filtration membrane. Specifically, the filtration membrane is a nanofiltration membrane (NF membrane). This nanofiltration membrane is a liquid separation membrane that can block the passage of particles and polymers (substances having a maximum molecular weight of about several hundreds) smaller than about 2 nm, and in terms of filtration function, it is an ultrafiltration membrane (molecular weight). Separation of substances with a molecular weight of 1,000 to 300,000) and reverse osmosis membranes (liquid separation membranes with a molecular weight of several tens of substances) It is a membrane.

  Supply water flows into the filtration membrane part from one side, and impurities contained in the feed water are filtered by the nanofiltration membrane. Specifically, the nanofiltration membrane captures the corrosion promoting component and the alkali component and allows the corrosion inhibiting component to permeate.

  Here, the corrosion promoting components are those described in the background art section, and usually contain sulfate ions, chloride ions and other substances. Incidentally, both sulfate ions and chloride ions are important as corrosion promoting components. By the way, JIS B 8223: 1999 specifies various control items and recommended standards regarding the water quality of boiler water in these boilers from the viewpoint of suppressing the corrosion of special circulation boilers including once-through boilers. A reference value for the ion concentration is provided. On the other hand, although the sulfate ion concentration in boiler water is not mentioned, in the applicant of the present application, sulfate ions contained in boiler water act on each heat transfer tube and lower header of the once-through boiler as a corrosion promoting component. Make sure that

  Further, the corrosion inhibiting component is also described in the background art section. This corrosion inhibiting component usually includes silica (ie, silicon dioxide). By the way, silica contained in water supply is a component usually contained in tap water, industrial water, groundwater, etc. used as water supply, and is generally recognized as a scale generating component in each of the heat transfer tubes and the lower header. It is considered preferable to suppress the concentration as much as possible. However, the applicant of the present application has confirmed that silica contained in boiler water acts on each of the heat transfer tubes and the lower header as a corrosion inhibiting component.

  Further, examples of the alkali component include bicarbonate and carbonate.

  From the other side of the filtration membrane portion, permeated water containing a corrosion inhibiting component and concentrated water containing a corrosion promoting component and an alkali component flow out. The permeated water flows in the water supply line and is stored in the water supply tank as water to be supplied to the device. On the other hand, a part of the concentrated water is drained out of the system by a predetermined amount from the drainage line, and the remaining part is returned to the upstream side of the filtration membrane part through the circulating water line. .

  In the membrane filtration system, when water is supplied to the water supply tank, water is supplied to the filtration membrane unit, and corrosion promoting components and alkali components in the water supply are filtered by the nanofiltration membrane. Then, the permeated water containing the corrosion inhibiting component is stored in the water supply tank. Further, a part of the concentrated water containing the corrosion promoting component and the alkali component is drained from the drainage line in a predetermined amount, and the remaining part is passed through the circulating water line to the water supply line upstream of the filtration membrane part. Reflux.

  By supplying water to the water supply tank, when the water level in the water supply tank rises and reaches a predetermined water level at which water supply is stopped, the supply of water to the filtration membrane unit is stopped and the water supply tank is Stop water supply.

  And when water supply to the water supply tank is started, before the water supply starts, the on-off valve is closed to close the water supply line, and the permeated water from the filtration membrane part is passed through the permeated water return line. Then, the reflux operation for returning to the water supply line upstream of the filtration membrane portion is performed for a predetermined time until the water supply to the water supply tank is started. When this reflux operation is performed and the permeated water from the filtration membrane part is refluxed to the water supply line upstream of the filtration membrane part, the water pressure on the feed water supply side is higher than the permeate side in the filtration membrane part. The feed water flows from the feed water supply side to the permeate side, and corrosion promoting components in the feed water are removed by the nanofiltration membrane by the reverse osmosis phenomenon.

  The reflux operation is started, for example, when the water level of the water supply tank is lowered to a predetermined water level.

  In addition, the operation time of the reflux operation is set to a length that can sufficiently remove impurities in the feed water and reduce deterioration of the permeated water quality. Specifically, since the quality of the raw water (here, the impurity concentration) varies depending on the region and season, water supply to the filtration membrane unit, permeated water from the filtration membrane unit, and concentrated water from the filtration membrane unit Based on one of the water qualities, the length of the recirculation operation time is set so that impurities in the feed water can be sufficiently removed to reduce deterioration of the quality of the permeated water.

  Further, the longer the time during which the supply of water to the filtration membrane unit is stopped, the higher the permeation side impurity concentration in the vicinity of the filtration membrane. Therefore, since the concentration of impurities on the permeate side in the vicinity of the filtration membrane varies depending on the time during which the supply of water to the filtration membrane unit has been stopped, the length of operation time of the reflux operation is determined by the filtration membrane unit. Based on the length of time during which the supply of water to the water has been stopped, impurities in the water supply may be sufficiently removed to reduce deterioration of the quality of the permeated water.

  Furthermore, the length of operation time of the reflux operation is such that the water quality of any one of water supply to the filtration membrane part, permeated water from the filtration membrane part and concentrated water from the filtration membrane part, and to the filtration membrane part Based on the length of time during which the supply of the feed water is stopped, impurities in the feed water may be sufficiently removed to reduce deterioration of the quality of the permeated water.

  When the reflux operation is performed for a predetermined time, the on-off valve is opened, and water is supplied to the filtration membrane unit to start water supply to the water tank. When the water supply to the water supply tank is started, a water quality recovery operation is performed for a predetermined time from the start so that the drainage amount of the concentrated water from the filtration membrane portion is smaller than the predetermined amount at the normal time. That is, in the water quality recovery operation, the ratio of the permeated water amount to the sum of the permeated water amount and the drainage amount (hereinafter referred to as “recovery rate”) is set higher than usual. By performing the water quality recovery operation to increase the recovery rate in this way, the concentration of the feed water supplied to the filtration membrane portion proceeds and the impurity concentration increases. As a result, the concentration of the permeated water corrosion-inhibiting component is increased, and the amount of the alkaline component that permeates the nanofiltration membrane is increased to increase the concentration thereof. .

  The amount of concentrated water discharged and / or the length of operation time in the water quality recovery operation is such that the feed water supplied to the filtration membrane part is concentrated in a range not excessively concentrated, and the quality of the permeated water is recovered to a predetermined quality. Set the amount and length.

  Specifically, the solubility of silica, which is a corrosion inhibiting component, and the solubility of bicarbonate, carbonate, which is an alkaline component, vary depending on the water temperature, so water supplied to the filtration membrane portion, permeated water from the filtration membrane portion Based on the temperature of any of the concentrated water from the filtration membrane part, the feed water supplied to the filtration membrane part is concentrated in a range not excessively concentrated so that the quality of the permeated water is restored to a predetermined quality. In addition, the drainage amount of concentrated water and / or the length of the operation time in the water quality recovery operation are set.

  In addition, since the quality of the raw water (here, the impurity concentration) varies depending on the region and season, the quality of any of the water supplied to the filtration membrane, the permeated water from the filtration membrane, and the concentrated water from the filtration membrane Based on the amount of concentrated water discharged in the water quality recovery operation and / or so that the feed water supplied to the filtration membrane part is concentrated in a range that does not excessively concentrate and the quality of the permeated water is restored to a predetermined quality. The length of the operation time may be set.

  In addition, the longer the time during which the supply of feed water to the filtration membrane unit is stopped, the lower the impurity concentration on the feed water supply side in the vicinity of the nano filtration membrane. That is, since the concentration of impurities on the feed water supply side in the vicinity of the nanofiltration membrane varies depending on the time during which the feed water supply to the filtration membrane unit is stopped, the supply of feed water to the filtration membrane unit is stopped. Concentrated water in the water quality recovery operation so that the quality of the permeated water is recovered to a predetermined quality by concentrating the feed water supplied to the filtration membrane unit based on the length of time that is not excessively concentrated. The amount of drainage and / or the length of operation time may be set.

  Furthermore, the temperature of any of the water supply to the filtration membrane part, the permeated water from the filtration membrane part and the concentrated water from the filtration membrane part, the water supply to the filtration membrane part, and the permeated water from the filtration membrane part And the filtration membrane unit based on any two or more of the quality of any of the concentrated water from the filtration membrane unit and the length of time during which the supply of water to the filtration membrane unit was stopped Set the amount of concentrated water discharged and / or the length of operation time in the water quality recovery operation so that the water supplied to the water is concentrated in a range that does not excessively concentrate and the quality of the permeated water recovers to a predetermined quality. Also good.

  According to the membrane filtration system of this embodiment, when the water supply to the water supply tank is stopped, the filtration operation is performed by performing the reflux operation for a predetermined time until the water supply to the water supply tank is started. Since the corrosion promoting component in the water supply is removed in the membrane portion, the deterioration of the quality of the permeated water when the water supply to the water supply tank is started can be reduced.

  In addition, by performing the water quality recovery operation in which the recovery rate is higher than usual for a predetermined time after starting the water supply to the water supply tank, the concentration of the water supplied to the filtration membrane section proceeds, and the permeated water Corrosion inhibiting component concentration and alkali component concentration are increased, and the water quality of the permeated water can be recovered to a predetermined water quality in a short time.

  Therefore, it is possible to suppress the increase in the corrosion promoting component concentration as much as possible and to suppress the decrease in the corrosion inhibiting component concentration and the alkali component concentration as much as possible, so that the quality of the permeated water can be stabilized. Accordingly, even if the water supply to the water supply tank is frequently stopped or the time during which the water supply is stopped increases or the capacity of the water supply tank is small, the water supplied to the device is supplied. The predetermined water quality can be maintained.

  Moreover, the length of the operation time of the reflux operation can be set to an optimum value so that impurities in the water supply can be sufficiently removed.

  Furthermore, the length of operation time of the reflux operation is set to any one of the water quality of the water supply to the filtration membrane unit, the permeated water from the filtration membrane unit and the concentrated water from the filtration membrane unit, and the filtration membrane unit. The length of the recirculation operation time is more optimal so that impurities in the water supply can be more sufficiently removed by setting based on the length of time during which the water supply of the water supply has been stopped. Can be set.

  Further, the amount of drainage and / or operation time of the concentrated water in the water quality recovery operation so that the feed water supplied to the filtration membrane section is concentrated in a range not excessively concentrated and the quality of the permeated water is restored to a predetermined quality. Can be set to an optimal length.

  Further, the amount of concentrated water discharged in the water quality recovery operation and / or the length of the operation time is set to any one of water supplied to the filtration membrane unit, permeated water from the filtration membrane unit, and concentrated water from the filtration membrane unit. Water temperature, the quality of any of the water supply to the filtration membrane part, the permeated water from the filtration membrane part and the concentrated water from the filtration membrane part, and the time during which the supply of water supply to the filtration membrane part was stopped If it is set based on any two or more of the lengths of the water, the feed water supplied to the filtration membrane part is concentrated in a range not excessively concentrated, and the quality of the permeated water is restored to a predetermined quality. In addition, the drainage amount of concentrated water and / or the length of operation time in the water quality recovery operation can be set to be more optimal.

  Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic explanatory view showing an example of the configuration of a membrane filtration system for carrying out the present invention, and FIG. 2 is an enlarged explanatory view of a water supply tank of the membrane filtration system shown in FIG.

  A membrane filtration system 1 shown in FIG. 1 supplies to a boiler 2 feed water obtained by treating raw water supplied from a water source such as tap water, industrial water, or groundwater. The membrane filtration system 1 includes a water supply line 3 to the boiler 2, and further includes a filtration membrane unit 4 and a deaeration membrane unit 5 connected to the water supply line 3 in this order from the upstream side. The membrane filtration system 1 is provided on the upstream side of the water supply tank 6 for storing water supply and the filtration membrane unit 4, and includes a pump 7 for supplying the water supply to the filtration membrane unit 4, and an upstream side of the pump 7. A valve 8 provided in the water supply line 3 and an on-off valve 9 provided in the water supply line 3 between the filtration membrane unit 4 and the deaeration membrane unit 5 are provided. Further, the membrane filtration system 1 has permeated water connecting the water supply line 3 between the filtration membrane unit 4 and the on-off valve 9 and the water supply line 3 between the pump 7 and the valve 8. A reflux line 10 is provided. The permeate recirculation line 10 is provided with a recirculation control valve 11.

  The membrane filtration system 1 includes temperature sensors 12, 12 ', 12 "and balloons B, B', B" connected to any one of the balloons A, A ', A ". It has water quality sensors 13, 13 ', 13 "connected to any position. These water quality sensors 13, 13 ′, and 13 ″ respectively obtain water quality information of water supplied to the filtration membrane unit 4, water quality information of permeated water from the filtration membrane unit 4 and concentrated water from the filtration membrane unit 4. For example, an electrical conductivity sensor that measures the electrical conductivity of water.

  The filtration membrane unit 4 includes a nanofiltration membrane (not shown). This nanofiltration membrane is a synthetic polymer membrane such as polyamide-based or polyether-based, and is a liquid separation membrane that can prevent permeation of particles and polymers (substances having a maximum molecular weight of several hundreds) smaller than 2 nm. It is. The nanofiltration membrane is usually configured as a filtration membrane module. Examples of the form of the filtration membrane module include a spiral module, a hollow fiber module, and a flat membrane module.

  Water supplied from the pump 7 flows into one side of the filtration membrane unit 4. The feed water that has flowed into the filtration membrane portion 4 captures the corrosion promoting component and the alkali component and allows the corrosion inhibiting component to permeate through the nanofiltration membrane.

  From the other side of the filtration membrane part 4, the permeated water containing the corrosion inhibiting component and the concentrated water containing the corrosion promoting component and the alkali component are separated and flow out. The permeated water flows through the water supply line 3 and is stored in the water supply tank 6. On the other hand, a part of the concentrated water is drained from the drain line 14 in a predetermined amount, and the remaining part flows through a circulating water line 15 that connects the drain line 14 and the water supply line 3 upstream of the pump 7. Thus, the refrigerant is returned to the upstream side of the pump 7.

  The drainage line 14 is branched to a first drainage line 16, a second drainage line 17, and a third drainage line 18 on the downstream side of the connection location of the circulating water line 15. Each of these drain lines 16, 17, 18 is provided with a first drain valve 19, a second drain valve 20, and a third drain valve 21, respectively.

  Here, each of the drain valves 19, 20, 21 has a constant flow valve mechanism (not shown). This constant flow valve mechanism is set to a different flow rate value in each of the drain valves 19, 20, and 21. The amount of drainage from each of the drain valves 19, 20, 21 is set as follows, for example. That is, the drainage amount when only the first drain valve 19 is opened is set so that the recovery rate is 95%, and the drainage amount when only the second drain valve 20 is opened is recovered. The rate is set to 90%, and the amount of drainage when only the third drain valve 21 is opened is set so that the recovery rate is 80%. Here, in the following description, the amount of drainage is described as the ratio of the amount of drainage to the sum of the amount of permeate and the amount of drainage. For example, the drainage amount when only the first drain valve 19 is opened, that is, the drainage amount when the recovery rate is 95% is referred to as 5% drainage, and when only the second drain valve 20 is opened. The amount of drainage, that is, the amount of drainage when the recovery rate is 90% is called 10% drainage, and the amount of drainage when only the third drain valve 21 is opened, that is, the amount of drainage when the recovery rate is 80%, is drained by 20%. It is said.

  The amount of concentrated water discharged can be adjusted in stages by opening and closing the drain valves 19, 20, and 21, respectively. For example, by setting only the second drain valve 20 to the open state and closing the first drain valve 19 and the third drain valve 21, the drainage can be 10% (that is, the recovery rate is 90%). ). Further, for example, by setting the first drain valve 19 and the second drain valve 20 in an open state and only the third drain valve 21 in a closed state, 15% drainage can be achieved (that is, a recovery rate of 85). %). Therefore, the drainage amount of the concentrated water can be adjusted in steps of 5% from 5% drainage to 35% drainage by the combination of the drain valves 19, 20, 21. In other words, the recovery rate Can be adjusted in steps of 5% from 65% to 95%.

  Here, the circulating water line 15 may be provided with a flow rate control valve (not shown) for making the amount of concentrated water recirculated upstream of the pump 7 constant. In this case, even when the drainage amount of the concentrated water is adjusted, the flow rate control valve is adjusted so that the reflux amount of the concentrated water to the upstream side of the pump 7 becomes constant.

  The degassing membrane unit 5 includes a gas permeable membrane module (not shown) having a large number of gas permeable membranes, and a water-sealed type that vacuums the dissolved gas in the feed water, specifically, dissolved oxygen through the gas permeable membrane module. And a vacuum pump (not shown).

  The water supply that has passed through the degassing membrane unit 5 is stored in the water supply tank 6 and is supplied from the water supply tank 6 to the boiler 2. The water supply tank 6 is provided with a water level sensor 22.

Here, when the water level sensor 22 detects that the water level in the water supply tank 6 has reached the water level H (see FIG. 2, not shown in FIG. 1), the water supply to the water supply tank 6 is stopped. It has come to be. When the water level sensor 22 detects that the water level in the water supply tank 6 has reached the water level L ₀ (see FIG. 2, not shown in FIG. 1), the present invention relates to the present invention as will be described later. The reflux operation, which is the main part of the operation method, is started. Further, when the water level sensor 22 detects that the water level in the water supply tank 6 has reached the water level L (see FIG. 2, not shown in FIG. 1), water supply to the water supply tank 6 is started. It has become so.

  In this embodiment, the valve 8 is a pressure reducing valve, and the valve 8 adjusts the water pressure of the water supply line 3 in a portion where the permeate recirculation line 10 is connected to a predetermined pressure or less. .

  In this embodiment, the on-off valve 9 is an electromagnetic valve or a motor operated valve. The reflux control valve 11 is a relief valve. The relief valve is closed when the pump 7 is operated and the on-off valve 9 is opened to supply water to the water supply tank 6, and the pump 7 is operated and the on-off valve 9 is closed. When performing the reflux operation in the state, the valve opening pressure is set so as to be in the open state.

  Next, an operation method of the membrane filtration system 1 will be described. In the membrane filtration system 1, when water is supplied to the water supply tank 6, the pump 7 first supplies water to the filtration membrane unit 4, and the nanofiltration membrane removes corrosion promoting components and alkali components from the water supply. Filter by (not shown). At this time, the corrosion inhibiting component in the water supply permeates the nanofiltration membrane. Next, dissolved oxygen contained in the permeated water flowing out from the filtration membrane unit 4 is deaerated by the deaeration membrane unit 5, and this water is stored in the feed water tank 6 as feed water to be supplied to the boiler 2.

  On the other hand, concentrated water also flows out from the filtration membrane portion 4, and a portion of the concentrated water is drained from the drain line 14 by a predetermined amount, and the remaining portion of the pump 7 is passed through the circulating water line 15. Reflux to the upstream side.

By supplying water to the water supply tank 6, when the water level sensor 22 detects that the water level in the water supply tank 6 rises and reaches the water level H, the pump 7 is stopped and the filtration is performed. The supply of water supply to the membrane unit 4 is stopped, and the water supply to the water supply tank 6 is stopped. Then, when the water level sensor 22 detects that the water level in the water supply tank 6 has dropped to the water level L ₀ while the water supply to the water supply tank 6 is stopped, the reflux operation is started. .

  In the reflux operation, the on-off valve 9 and the drain valves 19, 20, and 21 are closed, and the permeate from the filtration membrane unit 4 is passed through the permeate reflux line 10 to the filtration membrane. This is an operation for refluxing to the upstream side of the section 4. In this embodiment, the on-off valve 9 is closed and the pump 7 is operated. As a result, the water pressure on the upstream side of the reflux control valve 11 becomes equal to or higher than a predetermined value, the reflux control valve 11 is opened, and the permeated water from the filtration membrane portion 4 flows through the permeate reflux line 10. To return to the water supply line 3 between the pump 7 and the valve 8.

  Thus, when the permeate from the filtration membrane part 4 flows through the permeate reflux line 10 and returns to the upstream side of the filtration membrane part 4, the water pressure on the supply water supply side of the filtration membrane part 4 is higher than the permeation side. The feed water flows from the feed water supply side to the permeate side and the corrosion promoting components are removed by the nanofiltration membrane due to the reverse osmosis phenomenon, so that the quality of the permeate water deteriorates when the feed water to the feed water tank 6 is started. Can be reduced.

  Here, since the water pressure between the pump 7 and the valve 8 is always reduced to a constant water pressure by the valve 8, even if the supply water pressure of the raw water fluctuates, the water pressure from the permeate recirculation line 10 The reflux amount of the permeated water is always a constant flow rate.

  When the reflux operation is performed, the drain valves 19, 20, and 21 may be closed, or any of the drain valves 19, 20, and 21 may be opened. When the drain valves 19, 20, 21 are closed, water can be saved. On the other hand, when any one of the drain valves 19, 20, 21 is opened, the impurity concentration of the concentrated water from the filtration membrane portion 4 is lowered, and the quality of the permeated water is improved.

  If the water level in the water supply tank 6 becomes the water level L during the reflux operation, the on-off valve 9 is opened and water supply to the water supply tank 6 is started. At this time, the water pressure upstream of the recirculation control valve 11 becomes lower than the opening pressure of the recirculation control valve 11, the recirculation control valve 11 is closed, and the recirculation operation ends.

The length of the operation time of the reflux operation is set to a length that can sufficiently remove the corrosion promoting component in the feed water and reduce the deterioration of the quality of the permeated water. As can be secured such operating time, the water level L ₀ to start the return operation is set.

Specifically, the length of operation time of the reflux operation is such that each of the water quality sensors 13, 13 ′ can reduce the deterioration of permeated water quality by sufficiently removing the corrosion promoting components in the feed water. , 13 ″. That is, since the quality of the raw water (impurity concentration here) varies depending on the region, season, etc., the electric conductivity sensors which are the water quality sensors 13, 13 ′, 13 ″. the higher detection value of the water level L ₀ is longer higher by setting the operating time of the return driving, to sufficiently remove corrosion promoting component in water. On the other hand, each of the water sensor 13, 13 ', 13 detection value becomes lower for ", the because of the low impurity concentration on the permeate side of the nanofiltration membrane around the set lower the water level L ₀ accordingly Thus, the operation time of the reflux operation is shortened.

In addition, the length of operation time of the reflux operation is such that the supply of water to the filtration membrane unit 4 is performed so that the corrosion promoting components in the water supply can be sufficiently removed to reduce the quality of the permeated water. You may set based on the time which has stopped. That is, the longer the time during which the supply of water supply to the filtration membrane unit 4 is stopped, the higher the concentration of impurities on the permeate side near the nanofiltration membrane. Therefore, if the time during which the supply of the feed water to the filtration membrane unit 4 has been stopped is long, the water level L ₀ is set higher to increase the operation time of the reflux operation, and the corrosion promoting component in the feed water is sufficient. To remove. On the other hand, the Invite is short filtration membrane unit time that has been stopped the supply of water to 4, since the low impurity concentration on the permeate side of the nanofiltration membrane near, set lower the water level L ₀ accordingly Thus, the operation time of the reflux operation is shortened.

That is, the reflux predetermined time operation, the water level in said water supply tank 6 is set as the time from the water level L ₀ to reach the water level L.

  Further, the length of operation time of the reflux operation is such that each of the water quality sensors 13, 13 ′, 13 ″ can reduce the deterioration of the quality of the permeated water by sufficiently removing the corrosion promoting components in the feed water. May be set based on the detected value and the length of time during which the supply of water to the filtration membrane unit 4 has been stopped.

Here, the like the boiler 2 after starting the reflux operation is stopped, depending on the operating conditions of the boiler 2, the time from the water supply tank the water level L ₀ water level within 6 to reach the water level L is assumed The water level in the water supply tank 6 may not reach the water level L even after the predetermined time has elapsed after the start of the reflux operation. Therefore, even before the water level in the water supply tank 6 reaches the water level L, after a predetermined time has elapsed since the start of the reflux operation, the on-off valve 9 is opened to supply water to the water supply tank 6. And the reflux operation may be terminated.

  Now, when the reflux operation is finished and water supply to the water supply tank 6 is started, the drainage amount of the concentrated water from the filtration membrane part 4 is made smaller than the predetermined amount for a predetermined time from the start, and the recovery rate is increased. Perform water quality recovery operation to make it higher than normal. Thereby, concentration of the feed water supplied to the said filtration membrane part 4 advances, and impurity concentration becomes high. As a result, the concentration of the permeated water corrosion-inhibiting component is increased, the amount of the alkali component that permeates the nanofiltration membrane is increased, and the concentration is increased, so that the quality of the permeated water is restored.

  The amount of concentrated water discharged in the water quality recovery operation and the length of operation time are such that the feed water supplied to the filtration membrane unit 4 is concentrated within a range not excessively concentrated, and the quality of the permeated water is restored to a predetermined quality. Set to the amount and length that can be.

  Specifically, the drainage amount of the concentrated water and the length of the operation time in the water quality recovery operation are such that the feed water supplied to the filtration membrane unit 4 is concentrated in a range that does not excessively concentrate, and the quality of the permeated water is predetermined. In order to recover the water quality, the temperature is set based on the detection values of the temperature sensors 12, 12 ′, 12 ″. That is, the solubility of silica, which is a corrosion inhibiting component, increases as the water temperature increases. Therefore, if the detected value of each temperature sensor 12, 12 ', 12 "is high, the amount of decrease in the amount of concentrated water discharged in the water quality recovery operation is increased to increase the recovery rate. On the other hand, if the detected value of each temperature sensor 12, 12 ', 12 "is low, the reduction rate of the drainage amount of the concentrated water in the water quality recovery operation is reduced to lower the recovery rate than at high temperatures. If the detection values of the temperature sensors 12, 12 ', 12 "are high, the operation time of the water quality recovery operation is shortened, while if the detection values of the temperature sensors 12, 12', 12" are low, Increase the operation time of water quality recovery operation.

  In addition, the amount of concentrated water discharged in the water quality recovery operation and the length of the operation time are set so that the feed water supplied to the filtration membrane unit 4 is concentrated in a range not excessively concentrated, and the quality of the permeated water is recovered to a predetermined quality. The water quality may be set based on the detection values of the water quality sensors 13, 13 ′, 13 ″. That is, the water quality of the raw water varies depending on the region and season. If the detection value of the electrical conductivity sensor of 13 ′, 13 ″ is low, the reduction rate of the drainage amount of the concentrated water in the water quality recovery operation is increased to increase the recovery rate. On the other hand, if the detected value of each of the water quality sensors 13, 13 ', 13' 'is increased, the amount of decrease in the drainage amount of the concentrated water in the water quality recovery operation is reduced to lower the recovery rate than when the detected value is low. Further, if the detected value of each water quality sensor 13, 13 ', 13 "is increased, the operation time of the water quality recovery operation is shortened, while the detected value of each water quality sensor 13, 13', 13" is decreased. For example, the operation time of the water quality recovery operation is lengthened.

  In addition, the amount of concentrated water discharged in the water quality recovery operation and the length of the operation time are set so that the feed water supplied to the filtration membrane unit 4 is concentrated in a range not excessively concentrated, and the quality of the permeated water is recovered to a predetermined quality. It may be set based on the time during which the supply of water supply to the filtration membrane unit 4 has been stopped so that it can be performed. That is, the longer the time during which the supply of water to the filtration membrane unit 4 is stopped, the lower the impurity concentration on the water supply side near the nanofiltration membrane. Therefore, if the time during which the water supply to the filtration membrane unit 4 has been stopped is long, the reduction rate of the drainage amount of the concentrated water in the water quality recovery operation is increased to increase the recovery rate. On the other hand, if the time during which the water supply to the filtration membrane unit 4 has been stopped is short, the reduction rate of the drainage amount of the concentrated water in the water quality recovery operation is reduced to lower the recovery rate than when the stop time is long. Further, if the time during which the water supply to the filtration membrane unit 4 is stopped is long, the operation time of the water quality recovery operation is lengthened, while the time during which the water supply to the filtration membrane unit 4 is stopped is short. The operation time of the water quality recovery operation is shortened.

  Further, the amount of drainage of concentrated water and the length of operation time in the water quality recovery operation are such that the feed water supplied to the filtration membrane unit 4 is concentrated within a range not excessively concentrated, and the quality of the permeated water is recovered to a predetermined water quality. The detected values of the temperature sensors 12, 12 ', 12 ", the detected values of the water quality sensors 13, 13', 13", and the supply of water to the filtration membrane unit 4 can be performed. You may set based on any 2 or more among the time which has stopped.

  When the drainage amount of the concentrated water is set as described above, the drain valves 19, 20, and 21 are opened and closed so that the set drainage amount is obtained.

  As mentioned above, although this invention was demonstrated by the Example, this invention can be variously implemented in the range which does not change the meaning.

It is a schematic explanatory drawing which shows an example of a structure of the membrane filtration system for implementing this invention. It is expansion explanatory drawing of the water supply tank of the membrane filtration system shown in FIG.

Explanation of symbols

1 Membrane filtration system 2 Boiler (equipment)
3 Water supply line 4 Filtration membrane 6 Water supply tank

Claims (9)

A filtration membrane part that is connected to a water supply line to the device to remove impurities in the water supply, and a water supply tank that is connected to the water supply line on the downstream side of the filtration membrane part and stores the water supply to the device, At the time of water supply to the water supply tank, water is supplied to the filtration membrane unit and filtered, and the permeated water from the filtration membrane unit is stored in the water supply tank, while one of the concentrated water from the filtration membrane unit is stored. A membrane filtration system that drains the part out of the system in a predetermined amount and recirculates the remainder to the upstream side of the filtration membrane part,
The water supply line between the filtration membrane part and the water supply tank is closed, and the permeated water from the filtration membrane part is supplied to the water supply upstream of the filtration membrane part from the water supply line upstream of the closed part. The recirculation operation for returning to the line is performed for a predetermined time when the water supply to the water supply tank is stopped, and then the water supply to the water supply tank is started. A method for operating a membrane filtration system, comprising performing a water quality recovery operation in which the amount of concentrated water discharged from the water is less than the predetermined amount.   When water supply to the water supply tank is stopped, if the water level in the water supply tank falls to a predetermined water level, the reflux operation is started, and after a predetermined time has elapsed since the start of the reflux operation, 2. The method for operating a membrane filtration system according to claim 1, wherein water supply to the tank is started.   The length of the operation time of the reflux operation is set based on the quality of any one of water supplied to the filtration membrane unit, permeated water from the filtration membrane unit, and concentrated water from the filtration membrane unit. The operation method of the membrane filtration system according to claim 1 or 2.   The membrane filtration system according to claim 1 or 2, wherein a length of an operation time of the reflux operation is set based on a length of time during which the supply of water supply to the filtration membrane unit is stopped. Driving method.   The quality of any of the water supply to the filtration membrane part, the permeated water from the filtration membrane part and the concentrated water from the filtration membrane part, and the length of time that the supply of water supply to the filtration membrane part was stopped The operation method of the membrane filtration system according to claim 1 or 2, wherein the length of the operation time of the reflux operation is set based on the above.   Based on the temperature of any of the water supplied to the filtration membrane unit, the permeated water from the filtration membrane unit, and the concentrated water from the filtration membrane unit, the drainage amount and / or operation time of the concentrated water in the water quality recovery operation is set. The method of operating a membrane filtration system according to claim 1, 2, 3, 4 or 5.   Based on the quality of any of the water supplied to the filtration membrane unit, the permeated water from the filtration membrane unit, and the concentrated water from the filtration membrane unit, the drainage amount and / or operation time of the concentrated water in the water quality recovery operation is set. The method of operating a membrane filtration system according to claim 1, 2, 3, 4 or 5.   The drainage amount and / or operation time of the concentrated water in the water quality recovery operation is set based on the length of time during which the supply of water to the filtration membrane unit has been stopped. A method for operating the membrane filtration system according to 3, 4 or 5.   Water supply to the filtration membrane, water permeate from the filtration membrane and concentrated water from the filtration membrane, water supply to the filtration membrane, permeate from the filtration membrane and the water Concentration in the water quality recovery operation based on any two or more of the quality of any of the concentrated water from the filtration membrane and the length of time during which supply of water to the filtration membrane has been stopped 6. A method for operating a membrane filtration system according to claim 1, 2, 3, 4 or 5, wherein the amount of water discharged and / or the operation time is set.

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