JPH07313993A - Apparatus and method for treating boiler supply water - Google Patents

Abstract

PURPOSE:To reduce the carry-over of silica and to prevent the adhesion of scale to steam piping by softening raw water and polymerizing silica in softened water and adding a predetermined amt. of alkali to the treated softened water to prepare boiler supply water. CONSTITUTION:At first, raw water supplied from raw water piping 1 is introduced into a softening device 2 utilizing an ion exchange agent and a magnesium ion or a calcium ion is removed to soften raw water. Next, softened water is treated in a silica polymerizing device 3 and silica in the softened water is polymerized to be suspended and dispersed in water. Continuously, the treated softened water is supplied to a low pressure boiler 7 heretofore as supply water from a storage tank 4 by a pump 5 but, in this case, a chemical injection device 6 is used to add a predetermined amt. of alkali to the supply water. At this time, alkali is added so that the acid consumption amt. of boiler water becomes at least 1.7 times the content of silica. By this constitution, the carry-over of silica is reduced and the adhesion of scale is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for treating boiler makeup water, and is particularly suitable for treating raw water having a high silica content to obtain boiler makeup water.

[0002]

BACKGROUND ART In Japan, the hardness of raw water (industrial water, etc.) is generally low, so in many boilers, the raw water is treated with a water softening device filled with an ion exchange agent and used as makeup water. Was. Recently, as the temperature and pressure of boilers have increased, ion-exchanged water treated with a deionizer using both cation and anion exchange resin has come to be used as makeup water, but many boilers, especially low-pressure boilers. However, the above softened water is still used.

[0003]

By the way, natural water in Japan generally has a high silica concentration, and therefore the silica concentration in raw water is also high. Of these, suspended and colloidal silica is
It can be separated by coagulation-sedimentation and filtration, and hydrolyzes in alkaline boiler water at high temperature to change to ionic silica. Silica, which becomes ionic and dissolves in water, can be adsorbed on a strongly basic anion exchange resin and separated by using a pure water device, but cation exchange resin used in a water softening device, etc. Can't separate. Since silica has a relatively low solubility in water, if the silica concentration in the boiler make-up water is high, the silica concentration in the boiler water will also be high, and the scale will be easily attached to the boiler drum and the water pipe. Further, the carry-over of boiler water facilitates the attachment of hard scale to the steam pipe. For this reason, in a boiler that uses softened water, the generated scale reduces the thermal efficiency of the boiler, which is also a cause of a blockage accident.

Two methods are practically used to prevent the formation of silica scale in a boiler using softening water as makeup water. The first is to convert silica to a soluble compound to prevent precipitation, for example JIS B8223-1.
989, using the reaction shown in the following formula, so that alkali in the boiler water so that the silica in the boiler water becomes soluble sodium metasilicate, acid consumption of the boiler water (pH 8.3, The same applies hereinafter).

SiO ₂ + 2NaOH = Na ₂ SiO ₃ + H ₂ O The second is a method in which silica is polymerized so as not to be precipitated, suspended and dispersed, blown, and discharged. In order to float and disperse, for example, boiler research No. 251 (Boiler Association) and other methods using synthetic polymer electrolytes, and "Magnetic treatment of water" (Ve Krassen) and other high frequency magnetic fields (including electric fields, the same applies below) There is a method of treating makeup water inside. A method for polymerizing silica in a high-frequency magnetic field has been recently developed and its principle has not been fully clarified, but it is adopted in various places because it can prevent silica from scaling on the boiler drum and water pipe with a simple device. It has started to be done.

By the way, according to the first method, the acid consumption of boiler water required to keep silica in sodium metasilicate according to the above formula is at least 1.7 times (1 mg).
It is necessary to keep 1.33 mg of sodium hydroxide and about 1.7 mg of calcium carbonate based on the above silica. However, in order to prevent obstacles to acid consumption of boiler water, JIS
There is a drawback that it is difficult to add chemicals to maintain the acid consumption of boiler water to 1.7 times or more in makeup water having a high silica concentration. On the other hand, in the method using a high-frequency magnetic field that has been used instead of this, surprisingly, when the silica concentration in the boiler water is high, silica far exceeding the expectation is carried over to the steam side, and a scale is added to the steam pipe. It has been found that there is a problem of forming and blocking.

The present invention solves these problems, particularly the carryover problem of silica treated in a high frequency magnetic field, and provides a treatment apparatus and a treatment method for boiler make-up water, which enables stable boiler operation for a long period of time. It is something to do.

[0008]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention multimerizes a softening device for softening raw water and silica in the softened water treated by the softening device by using high frequency. Characterized in that it comprises a silica multimerizing device, and a chemical dosing device that makes a boiler makeup water by adding a predetermined amount of alkali to the softening water treated by the silica multimerizing device.
A treatment device for boiler makeup water is provided. Further, the raw water is softened using an ion exchange agent, the resulting softened water is passed through a high-frequency magnetic field to polymerize silica contained therein, and the softened water passed through the high-frequency magnetic field is added to the acid of the boiler water. Characterized in that an alkali is added so that the consumption is at least 1.7 times the silica content to obtain boiler make-up water.
A method for treating boiler makeup water is provided.

[0009]

Actions and Examples of Embodiments A boiler makeup water treatment apparatus and a treatment method of the present invention will be described with reference to the drawings by way of example embodiments. FIG. 1 is a flow sheet showing an embodiment of the present invention.

In the present invention, the raw water supplied from the raw water pipe 1 is first treated by the softening device 2 using an ion exchange agent.
And removes mainly magnesium ions and calcium ions to soften and water. In the present invention, it is general to use a softening device using an ordinary cation exchange resin,
It is also possible to use an inorganic exchange agent such as zeolite. When the raw water to be supplied contains solid components, it is removed in advance by using a coagulating sedimentation device or a filtration device.

Next, the softening water treated by the softening device 2 is
The treatment is performed by using the silica multimerization apparatus 3, and the silica contained therein is polymerized to be suspended / dispersed in water. Although the theoretical explanation has not been established, the silica multimerization device 3 treats water in the transmitter by a resonance high frequency that is supposed to be tuned to the natural vibration of silica. It is said that it is resonated with vibration and activated to become a polymer (polymer). This silica multimerizer 3
Is easily available in the city as a water treatment device. 4 is a storage tank.

Conventionally, the softening water treated by the silica multimerization apparatus 3 was replenished to the low-pressure boiler 7 from the storage tank 4 by the pump 5 as make-up water. A predetermined amount of alkali is added to water.
As the alkali to be added, an aqueous sodium hydroxide solution is preferably used in terms of economy, but the alkali is not limited to this, and an aqueous potassium hydroxide solution or the like may be used. The alkali is added so that the acid consumption of the boiler water is at least about 1.7 times the silica content. 1.7
If the amount is less than double, the amount of silica that is scaled up increases due to carryover and adhesion to steam pipes. The acid consumption of boiler water may be measured by the method described in JIS B8224-1993, and the alkali injection amount may be adjusted. The chemical injection device is not particularly limited as long as it can quantitatively supply the alkali into the makeup water. Reference numeral 8 is a steam separator, and 9 is a steam pipe.

[0013]

EXAMPLES Next, the boiler make-up water treatment apparatus and the treatment method of the present invention were applied to the boiler which was operated by using the make-up water treated by the conventional method. The results will be explained.

Evaporation rate 1000 kg / h, maximum pressure 1MP
a, a small once-through boiler with a normal pressure of 0.7 MPa (TW-1
Type 000: Takuma Co., Ltd., softening device (resin amount 54
Lithium: TS-54BF: manufactured by Takuma Co., Ltd.) and a commercially available silica multimerization apparatus using a high frequency magnetic field were used to treat the raw water and use it as make-up water for operation. Table 1 of driving situation
Shown in. As shown in Table 1, the silica concentration in the boiler water was high, and the operation had to be stopped after about 2500 hours to remove the silica scale adhering to the steam pipe.

[0015]

[Table 1] Boiler water pH 10 to 10.3 Acid consumption (pH 4.8) 300 to 500 mg / l Acid consumption (pH 8.3) 280 to 470 mg / l Silica 200 to 300 mg / l Electrical conductivity 500 to 1000 μS / C
m Acid consumption (pH 8.3) / silica Approx. 1.5 No scale adhesion to water pipe No silica adhesion to steam pipe Approximately 2500 hours of operation blockage Therefore, an alkali injection device was installed and the acid consumption of boiler water was silica concentration. 48% by weight aqueous solution of sodium hydroxide was diluted with about 5 times the softening water, and the resulting solution was added to the makeup water at an average of 2 ml / min using a commercially available electromagnetic pump injection device. The acid consumption of boiler water is JIS B82.
Initially, the method described in 24 is used to measure every 7 days, the amount of alkali injection is confirmed, and thereafter, water quality analysis is performed every month. The measurement results are shown in Table 2. When the inside was inspected about 1000 hours after the start of operation, there was no sign of scale adhesion on the steam piping, and there was no scale adhesion on the water pipe of the boiler body or the upper and lower headers, and no progress of corrosion was observed. It should be noted that although the operation of the present invention is still being carried out and the effects of the present invention are still being confirmed, no sign of analogy to scale adhesion is observed and the good operation state is continued.

[0016]

[Table 2] Boiler water pH 11 to 11.5 Acid consumption (pH 4.8) 520 to 700 mg / l Acid consumption (pH 8.3) 400 to 600 mg / l Silica 200 to 300 mg / l Electrical conductivity 1100 to 1700 μS / C
m Acid consumption (pH 8.3) / silica About 2 No scale adhered to water pipe No silica adhered to steam pipe

[0017]

EFFECTS OF THE INVENTION By using the boiler makeup water treatment apparatus or treatment method of the present invention, even if raw water having a high silica concentration is treated as boiler makeup water, the alkali concentration of the boiler water is kept high and silica can be treated. Although it cannot be clearly explained theoretically at present at the time of solubilization, the carry-over of silica is reduced, and there is a remarkable effect of preventing scale adhesion on steam pipes and the like. Further, if a chemical such as a boiler agent or an oxygen scavenger is used for treating boiler water, it may be mixed in the steam, but in the present invention, normally, a degassing tower is installed or an oxygen scavenger is injected. No need. Since only alkali such as sodium hydroxide is used, the safety of steam is high. In addition, the effect on the drainage problem is small. Further, recently, there is an increasing number of cases in which the electric conductivity of boiler water is measured to control the concentration of boiler water. If the amount of insoluble silica is large, the electrical conductivity is unlikely to increase even though the silica is concentrated, but the addition of alkali enables stable concentration management. Therefore, there is an effect that the raw water having a high silica concentration can be used without anxiety. Can be processed economically with a simple device.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the present invention.

[Explanation of symbols]

1: Raw water supply pipe 2: Softening device 3: Silica multimerization device 4: Storage tank 5: Water supply pump 6: Alkali injection device 7: Boiler main body 8: Steam separator 9: Steam pipe

Claims (2)

[Claims] 1. A softening device for softening raw water, a silica multimerizing device for polymerizing silica in softened water treated by the softening device by using high frequency, and a silica multimerizing device for treating. A treatment device for boiler make-up water, comprising a chemical injection device for adding a predetermined amount of alkali to softened water to make boiler make-up water. 2. Raw water is softened using an ion exchange agent, and the obtained softened water is passed through a high frequency magnetic field to polymerize silica contained therein. The softened water passed through the high frequency magnetic field is then converted into a boiler. A method for treating boiler make-up water, which comprises adding an alkali so that the acid consumption amount (pH 8.3) of water is at least 1.7 times the silica content to obtain boiler make-up water.