JPS5913919B2 - Method for preventing the adhesion of silicic acid scale in geothermal hot water utilization systems - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing the adhesion of silicic acid schools in geothermal hot water utilization systems.

Generally, geothermal hot water contains harmful components such as arsenic, and there are few that can be used as is.

It is also possible to use heat after removing these harmful components, but this would require fairly sophisticated water treatment and would require a large amount of heat to be dissipated, making it practically impossible.

On the other hand, when attempting to effectively utilize the heat contained in geothermal hot water by exchanging heat with a heat medium such as fresh water or an organic liquid, the silicic acid contained in the geothermal hot water polymerizes and is not easily dissolved by monoacids. It becomes scale and adheres to heat transfer surfaces and pipe walls, reducing not only heat transfer efficiency but also clogging of pipes.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for preventing a decrease in heat transfer efficiency of a heat exchanger and closure of pipes due to formation and adhesion of hardly soluble silicic acid scale in a geothermal hot water utilization system. .

To achieve this objective, in one aspect of the present invention, prior to heat exchange, geothermal hot water is added to
Ca(OH)2 or CaO is added to prevent the silicic acid component contained in the geothermal hot water from becoming a polymer.
Provided is a method for preventing the adhesion of silicic acid scale in a geothermal hot water utilization system, which is characterized by adding a Ca2+ compound to the geothermal hot water after heat exchange to convert the silicic acid component into a calcium salt and separating and removing it. be done.

On the other hand, in order to achieve the same objective, in another aspect of the present invention, geothermal hot water is heated to pH 5 to
9 for 0.5 to 3 hours to polymerize and colloidize the silicic acid component contained in the geothermal hot water, and then add Ca (OH
) 2 or CaO is added to prevent further polymerization of the silicic acid component, and after heat exchange, the geothermal hot water is further added with a Ca2+-based compound to convert the silicic acid component into calciura salt and then separated and removed. A method for preventing the adhesion of silicic acid scale in a geothermal hot water utilization system is provided.

Through various experimental studies on geothermal hot water, we discovered the following about silicic acid contained in geothermal hot water.

In other words, there are two types of silicic acid in hot water: polymerized silicic acid and monomeric silicic acid. When ejected from a well, most of the silicic acid is monomeric silicic acid, but when the temperature drops, it becomes monomeric silicic acid. It was found that the solubility of monomeric silicic acid decreased, and supersaturated monomeric silicic acid polymerized to form a polymer.

Generally, the hot water that is effectively used by heat exchange is hot water in which monomeric silicic acid is supersaturated or in a mixed state of monomeric and polymeric silicic acid.If the temperature is further lowered by heat exchange, Supersaturated monomeric silicic acid polymerizes in such a way that it also crosslinks polymeric silicic acid, and it adheres to heat exchangers, etc., forming a strong scale.

Therefore, if the polymerization of this monomeric silicic acid is prevented, scale growth can be prevented.

Generally, when Ca2 compounds are added to this hot water, these silicic acids are converted to non-adhesive calcium salts.

On the other hand, if this calcium salt is separated and removed, harmful substances such as arsenic can also be adsorbed and removed in many cases, and a removal system in the form of calcium silicate using a Ca2 dry compound is considered to be effective.

However, even if a Ca2+ compound is added to geothermal hot water to convert silicic acid into a non-adhesive calcium salt, if this is done before heat exchange, it can be considered as a non-thermal calcium salt of silicic acid. Since it is expected that the heat transfer efficiency will decrease due to sedimentation within the heat exchanger, it is desirable to have as few suspended solids in the hot water as possible during one heat exchange.

One aspect of the present invention has been made with this in mind.

That is, in one aspect of the present invention, the pH of the geothermal hot water is adjusted to a range of 9 to 11 prior to heat exchange.

When the pH of the hot water is within this range, the silicic acid contained in the hot water becomes anions or anion-bearing particles, which prevent collisions with each other and prevent polymerization.

Therefore, the solubility of silicic acid in hot water increases, so that supersaturated silicic acid also exists stably.

Therefore, by Ca(OH)2 or CaO, the pH
By adjusting the amount of silicic acid in hot water, it is possible to prevent silicic acid from polymerizing and polymerizing without creating new suspended matter that is not adhesive but can be deposited by making silicic acid an anion. be able to.

In this way, if heat exchange is performed while preventing polymerization of silicic acid, there will be no scale growth and heat exchange can be performed efficiently.

Thereafter, when a Ca2+-based compound is further added, silicic acid in the hot water can be precipitated and separated as a calcium salt together with Ca2+ ions of Ca(OH)2 or CaO used for pH adjustment.

The Ca2+-based compounds herein refer to calcium compounds such as Ca(OH)2, CaO, and Ca(42) that form Ca''f-on in water.

On the other hand, suspended solids contained in hot water slightly reduce heat transfer efficiency during heat exchange, but this is much less than the reduction in heat transfer efficiency caused by scale that forms on the heat transfer surface of the heat exchanger. small.

Therefore, as long as the amount of suspended solids contained in hot water is kept within an allowable range, the resulting decrease in heat transfer efficiency during heat exchange can be suppressed to a non-problematic level.

The other invention of the present invention was made in consideration of this ε, and although the amount of suspended solids in hot water during heat exchange increases somewhat, the amount of Ca-based compounds added after heat exchange increases. The aim is to improve economic efficiency by reducing the amount.

That is, prior to heat exchange, hot water with a pH in the range of 5 to 9 is
．． When allowed to stay for 5 to 3 hours, the supersaturated silicic acid polymerizes to some extent and becomes colloidal.

In this case, the structure of the retention tank makes it possible to prevent heat loss as much as possible.

Next, when Ca(OH)2 or CaO is added to the retained hot water to adjust the pH to a range of 9 to 11, colloidal silicic acid also becomes negatively charged and crosslinking polymerization is prevented, and some of the It becomes a suspended solid whose phase is calcium silicate.

After heat-exchanging this hot water, a Ca2+-based compound is added and silicic acid is removed.The amount of Ca2+-based compound added is correlated with the amount of monomeric silicic acid before heat exchange, so a retention tank is used. By polymerizing supersaturated silicic acid at the inlet temperature of the heat exchanger, the amount of Ca2+ compound added can be halved.

As is clear from the above description, in any aspect of the present invention, it is possible to completely prevent silicic acid scale from adhering to the heat transfer surfaces of heat exchangers and pipe walls in geothermal hot water utilization systems. According to one aspect, even a slight decrease in heat transfer efficiency due to suspended matter is completely prevented, and according to the other aspect, although there is a slight decrease in heat transfer efficiency due to suspended matter, the Ca2+ system used It is possible to reduce the amount of the compound and ensure economic efficiency to compensate for it.

Claims (1)

[Claims] 1. Prior to heat exchange, geothermal hot water has a pu of 9 to 11.
Add Ca(0'H)2 or CaO to prevent the polymerization of the silicic acid component contained in the geothermal hot water, and further add Ca2+ compounds to the geothermal hot water after heat exchange. A method for preventing the adhesion of silicic acid scale in a geothermal hot water utilization system, characterized by separating and removing silicic acid components by converting them into calcium salts. 2. Prior to heat exchange, geothermal hot water is subjected to R distillation at a pH of 5 to 9 for 0.5 to 3 hours to polymerize and colloidize the silicic acid component contained in the geothermal hot water. Adding Ca(OH)2 or CaO to water to adjust the pH to 9 to 11 to prevent further polymerization of the silicic acid component,
A method for preventing the adhesion of silicic acid scale in a geothermal hot water utilization system, which comprises further adding a Ca2+ type compound to the geothermal hot water after heat exchange to convert the silicic acid component into a calcium salt and then separating and removing the silicic acid component.