JP2021109128A - Boiler water treatment method and device - Google Patents

Abstract

To provide boiler water treatment method and device capable of leaving an appropriate amount of monovalent cations such as Na during supply of boiler water.SOLUTION: In a boiler water treatment method in which raw water is treated by RO devices 1, 2 and permeable water is so made as to be boiler supply water, the RO device is operated so that a concentration of a monovalent cation in the boiler supply water falls within a prescribed range. In a boiler water treatment device which comprises RO devices 1, 2 for treating raw water and uses permeable water of the RO device as boiler supply water, at least one of a supply water amount, a permeable water amount, and a condensed water amount of the RO device 1 is controlled so that a concentration of monovalent cation in the boiler supply water falls within a prescribed range.SELECTED DRAWING: Figure 1

Description

The present invention relates to a water treatment method and an apparatus for producing water supplied to a boiler.

In a normal boiler system, a water treatment device removes hardness components, oxygen, etc. from raw water such as city water, groundwater, and industrial water to produce boiler water supply. After injecting a boiler treatment agent such as a boiler compound, it is supplied to the boiler.

As a water treatment device for removing a hardness component, a water softener equipped with a cation exchange resin and a desalting device equipped with a filtration membrane such as a nanofiltration membrane or a reverse osmosis membrane (RO membrane) are used. (Patent Document 1).

A water treatment device for a boiler using an RO membrane can remove not only hardness components but also dissolved organic substances, but Na (sodium) is excessively removed. In order to enhance the corrosion resistance of the boiler, it is preferable that an appropriate amount of Na is present in the boiler water.

Patent Document 2 states that when a reverse osmosis membrane of a water treatment apparatus for a boiler is used with an evaluation pressure of 0.3 to 1.5 MPa and a NaCl solution of 500 to 2000 mg / L, the removal rate of NaCl is 93% or more, 99. It is stated that less than 4% reverse osmosis membrane is used.

JP-A-2017-74550 Japanese Unexamined Patent Publication No. 2017-12991

An object of the present invention is to provide a water treatment method and apparatus for a boiler capable of leaving an appropriate amount of monovalent cations such as Na in the boiler water supply.

The boiler water treatment method of the present invention is a boiler water treatment method in which raw water is treated by an RO device and permeated water is used as boiler water supply, so that the monovalent cation concentration in the boiler feed water is within a predetermined range. It is characterized by controlling at least one of a water supply amount, a permeated water amount, and a concentrated water amount.

In one aspect of the present invention, the RO membrane of the RO apparatus is a loose RO membrane having a monovalent cation removal rate of less than 90%.

In one aspect of the present invention, the RO device is installed in two stages, and the amount of water supplied and the amount of permeated water of the RO device in the previous stage are adjusted so that the monovalent cation concentration of the permeated water of the RO device in the subsequent stage is within a predetermined range. And control at least one of the concentrated water amounts.

In one aspect of the invention, the predetermined range of the monovalent cation concentration is 0.1 to 5 mg / L.

In one aspect of the invention, the monovalent cation is Na.

The boiler water treatment device of the present invention is provided with an RO device for treating raw water, and in a boiler water treatment device in which the permeated water of the RO device is used as boiler water supply, the monovalent cation concentration of the boiler supply water is within a predetermined range. It is characterized in that the RO apparatus is provided with a control means for controlling at least one of a water supply amount, a permeated water amount, and a concentrated water amount.

In one aspect of the present invention, the RO device is installed in two stages, and the control device supplies water to the RO device in the previous stage so that the monovalent cation concentration of the permeated water of the RO device in the subsequent stage is within a predetermined range. Control at least one of the amount, the amount of permeated water, and the amount of concentrated water.

One aspect of the present invention includes a degassing device that degass at least one of water supply to the front-stage RO device, permeated water of the front-stage RO device, and permeated water of the rear-stage RO device.

According to the boiler water treatment method and apparatus of the present invention, an appropriate amount of monovalent cations such as Na can remain in the boiler feed water, and the anticorrosion effect of the boiler can be enhanced.

It is explanatory drawing of the water treatment method and apparatus for a boiler of this invention.

Examples of raw water to be treated by the present invention include city water, groundwater, and industrial water. It is preferable that the raw water is turbidized by an MF membrane or the like and then supplied to the RO apparatus. The concentration of a monovalent cation (Na in this embodiment) such as Na in the water supply to the RO apparatus (RO water supply) is preferably about 10 to 500 mg / L, particularly about 50 to 200 mg / L.

In the present invention, by controlling at least one of the amount of water supplied to the RO device, the amount of permeated water of the RO device, and the amount of concentrated water, the Na concentration is preferably 0.1 to 5 mg / L, particularly 0.5 to 2 mg / L, especially. Boiler water supply of 0.8 to 1 mg / L is used.

The RO membrane used in the present invention is preferably a loose RO membrane having an evaluation pressure of 0.75 MPa and a NaCl removal rate of less than 90% at 25 ° C. when a 500 mg / L NaCl solution is used.

The NaCl removal rate is defined by the following formula.

Na removal rate (%) = (1-permeated water Na concentration) / (RO water supply Na concentration) x 100

In an RO membrane having a NaCl removal rate of 90% or more, the Na concentration in the permeated water may become excessively low. However, if the removal rate of NaCl in the RO membrane is less than 80%, the chloride ion concentration in the boiler feed water, which is the RO membrane treated water, becomes high, the concentration ratio cannot be increased, and corrosion occurs in the boiler can. Is likely to occur, so the NaCl removal rate is preferably 80% or more.

The removal rate of silica (SiO ₂ ) by this RO film is preferably 95% or more.

FIG. 1 is a flow chart showing an example of the present invention, in which raw water is pressurized by a pressure pump (not shown), supplied to the first RO apparatus 1, and membrane-separated into first permeated water and first concentrated water. NS. The first permeated water is supplied to the second RO device 2 and is membrane-separated into the second permeated water and the second concentrated water. The second permeated water is sent to the degassing device 3 and degassed to become boiler water supply. A part of the first concentrated water is discharged to the outside of the system, and the rest is returned to the raw water side. The entire amount of the second concentrated water is returned to the raw water side.

The degassing device 3 may be installed so as to supply water to the first RO device 1 or degas the permeated water of the first RO device 1. The degassing device may be installed at two or more of these locations. As the degassing device, in addition to the membrane degassing device, various devices such as a nitrogen purge type degassing device can be used.

In this embodiment, a Na sensor (not shown) is installed so as to detect the Na concentration in the permeated water of the second RO device 2. The Na concentration in the permeated water of the second RO device 2 is within a predetermined range, preferably 0.1 to 5 mg / L, particularly preferably 0.5 to 2 mg / L, and most preferably 0.8 to 1 mg / L. , Preferably, at least one of the water supply amount, the permeated water amount, and the concentrated water amount of the RO device 1 in the previous stage is controlled.

In order to control the amount of water supply, it is preferable to control the rotation speed of the pressurizing pump by inverter control or the like. In order to control the amount of permeated water and the amount of concentrated water, it is sufficient to control the flow rate adjusting valve provided in the permeated water take-out pipe and the concentrated water take-out pipe of each RO device. In addition, the amount of the first concentrated water discharged to the outside of the system is controlled.

In the present invention, the Na concentration of the boiler feed water may be a value directly measured by a Na ion sensor or the like, and other index values having a correlation with the Na concentration (for example, conductivity, resistivity, pH, etc.) It may be an estimated Na value obtained based on the silica concentration, etc.) or this index value.

Although the RO devices 1 and 2 have the Na removal rate as described above, it is preferable to use a RO film having a Na removal rate lower than that of the RO film of the second RO device as the RO film of the first RO device 1.

1,2 RO device 3 Degassing device

Claims (8)

In a boiler water treatment method in which raw water is treated by an RO device and permeated water is used as boiler water supply.
A water treatment method for a boiler, characterized in that at least one of a water supply amount, a permeated water amount, and a concentrated water amount of the RO apparatus is controlled so that the monovalent cation concentration in the boiler feed water is within a predetermined range. The method for treating water for a boiler according to claim 1, wherein the RO membrane of the RO apparatus is a loose RO membrane having a monovalent cation removal rate of less than 90%. The RO device is installed in two stages, and at least one of the amount of water supplied, the amount of permeated water, and the amount of concentrated water of the RO device in the previous stage so that the monovalent cation concentration of the permeated water of the RO device in the subsequent stage is within a predetermined range. The method for treating water for a boiler according to claim 1 or 2, wherein the method is controlled. The method for treating water for a boiler according to any one of claims 1 to 3, wherein the predetermined range of the monovalent cation concentration is 0.1 to 5 mg / L. The method for treating water for a boiler according to any one of claims 1 to 4, wherein the monovalent cation is Na. In a boiler water treatment device provided with an RO device for treating raw water and using the permeated water of the RO device as boiler water supply,
A boiler water treatment apparatus provided with a control means for controlling at least one of the water supply amount, the permeated water amount, and the concentrated water amount of the RO apparatus so that the monovalent cation concentration of the boiler feed water is within a predetermined range. .. The RO device is installed in two stages, and the control device has a water supply amount, a permeated water amount, and a concentration of the RO device in the previous stage so that the monovalent cation concentration of the permeated water of the RO device in the subsequent stage is within a predetermined range. The water treatment apparatus for a boiler according to claim 6, wherein at least one of the amounts of water is controlled. The water treatment device for a boiler according to claim 7, further comprising a degassing device for supplying water to the front-stage RO device, degassing at least one of the permeated water of the front-stage RO device and the permeated water of the rear-stage RO device.

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