JPS5944118B2 - How to treat geothermal water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating geothermal hot water accompanying the extraction of steam for geothermal power generation.

In recent years, geothermal energy has attracted attention as an alternative energy to oil energy, and geothermal power generation is being developed in various places. However, when extracting geothermal steam by polling underground that has geothermal resources, Rather than spouting only steam, a large amount of hot water is often spewed out along with the steam.

In this case, geothermal fluid consisting of steam and hot water is separated into steam and hot water by a steam separator, and this steam is used to generate electricity.

On the other hand, the hot water separated by the above-mentioned steam-water separator has a huge amount of energy, but at present it is returned underground at a high temperature, and there is a strong need for its effective use. .

One of the major reasons for this is that geothermal water contains 1 to 10
Because the water contains arsenic at levels exceeding the environmental standard of 0.05 ppm, hot water cannot be discharged as is after the heat has been used effectively.

Several methods have been reported to date for removing arsenic from hot water, but among them, iron compounds and oxidizing agents such as hypochlorous acid are added, and then the pH is adjusted to form iron hydroxide. The most well-known and effective method is to co-precipitate iron hydroxide and arsenic, and it has been reported that this method can remove arsenic to below the environmental standard of 0.05 ppm. has been done.

However, as is well known, hot water contains a large amount of silica, and when performing arsenic removal treatment by co-precipitation with iron hydroxide, silica is also adsorbed and co-precipitated at the same time. The amount of sludge becomes large, making it difficult to dispose of this sludge.

In addition, since the iron added only for arsenic removal treatment is also consumed by silica, the effective ingredients decrease and the environmental standard is 0.05.
A large amount of iron compound was required to remove arsenic to below ppm.

It is important to reduce the amount of arsenic removal sludge as much as possible in terms of reducing the processing cost of the generated arsenic removal sludge.On the other hand, it is important to reduce the amount of chemicals such as iron compounds used for arsenic removal treatment. Needless to say, this is necessary from the viewpoint of reducing arsenic removal treatment costs.

As a result of various studies, the present inventors have determined that the geothermal fluid, in which steam and hot water are spouted in a two-phase flow, is separated into steam and hot water using a steam-water separator, and the pH of the hot water is adjusted to between 4 and 6. After adding acid to stabilize the monosilicic acid in the hot water, this hot water is further introduced into a flasher to separate it into steam and hot water again, and the above iron compound is added to this hot water. By carrying out arsenic removal treatment, we succeeded in reducing the amount of silica in the arsenic-free sludge, reducing the amount of arsenic-free sludge, and reducing the amount of iron compounds added.

It is generally known that silica dissolved in hot water becomes colloidal silica as the silica becomes supersaturated, exceeding its solubility at each temperature, as the temperature drops and the passage of time polymerizes.

The present inventors have discovered that when performing arsenic removal treatment using iron hydroxide, the more colloidal silica is present, the more adsorption and coprecipitation of silica by iron hydroxide occur, resulting in a larger amount of dearsenic sludge. .

At this time, it has been found that when the pH of the hot water is set to 6 or less, the speed at which silica colloids is formed is reduced, and substantial colloid formation is not observed within several hours.

However, if the pH is set to 4 or less, equipment such as pipes and valves for transporting hot water will be severely corroded, so it is not appropriate to set the pH to 4 or less.

The formation of colloidal silica can also be prevented by adjusting the pH of the hot water to 10 or higher, but since the pH will be adjusted to 2 to 3 in the subsequent arsenic removal process, the use of acid required for pH adjustment is It is not economical considering the quantity.

Therefore, to suppress the colloidalization of silica in hot water,
It is suitable to adjust the pH of the hot water to 4-6.

In the method of the present invention, in order to adjust the pH of the hot water to 4 to 6, the hot water in the hot water pipe between the steam separator in the first step and the flasher in the second step is used. The reason for this is as follows.

That is, the hot water before the steam separator is in the form of a gas-liquid two-phase flow, which is a mixture of steam and hot water, making it difficult to inject and mix acid. Bumping occurs and separates into steam and hot water at a lower temperature, but due to the fact that a large amount of silica turns into colloid at this time, the pH of the hot water must be adjusted to 4 to 6 before being introduced into the flasher. This is because no effect has been observed.

The amount of acid used here is because part of the acid required to adjust the pH of the hot water to 2 to 3 in the subsequent arsenic removal step is added in advance in the previous step, so the overall amount of acid is consumption will not increase.

Table 1 shows the results of experiments to determine the relationship between the pH of hot water introduced into the flasher and the amounts of total silica, dissolved silica, and colloidal silica in the hot water after separation in the flasher.

As is clear from Table 1, it can be seen that when the pH of the hot water is lowered to 6 or less, the production of colloidal silica is extremely reduced.

That is, by injecting acid into hot water separated by a two-phase geothermal fluid steam-water separator to adjust the pH to 4 to 6,
By suppressing the production of colloidal silica, it is possible to reduce the amount of silica in the arsenic-removed sludge using a small amount of iron hydroxide, and to reduce the amount of arsenic-removed sludge.

It goes without saying that the gist of the present invention is to reduce the amount of sludge during arsenic removal treatment and to reduce the amount of chemicals used. The pH of the hot water separated into steam and hot water by the water separator is 4.
By adjusting the temperature to ~6, all of the silica scale that had conventionally adhered to piping, valves, etc. was not observed, and it was recognized that it was highly effective in preventing the adhesion of silica scale.

In addition, when using hot water with a pH of 4 to 6, almost no corrosion of piping, etc. was observed.

Examples of the present invention will be described below.

Example 1 5.5 kg/(11i
0.0 in hot water. 40ppm of IN sulfuric acid as H2SO4
After increasing the pressure, the pressure was flushed down to atmospheric pressure to obtain hot water at 95°C.

The pH at this time was 5.3. Fe2 in 1 ton of this hot water
Ferrous sulfate and sulfuric acid were added so that + was 40 ppm and pH was 2.8, and then sodium hypochlorite was added as an oxidizing agent so that available chlorine was 40 ppm, and the mixture was thoroughly stirred.

Thereafter, calcium carbonate was added until the pH of the hot water reached 38 to form a precipitate of ferric hydroxide.

The hot water composition after treatment at this time was as shown in Table 3.

Table 4 shows the amount of precipitate produced and the composition of the precipitate in comparison with the case where the arsenic removal treatment was performed in the same manner without adjusting the pH in advance.

Example 2 As in Example 1, 0.0% was added to 150°C hot water. 40 ppm of IN sulfuric acid as H2SO4 was added to adjust the pH of the hot water to 4.
1 ton of hot water adjusted to pH 8 contains 20 ppm of Fe2+ and pH
Ferrous sulfate and sulfuric acid were added so that the pH of the hot water was 2.8, then 40 ppm of sodium hypochlorite was added as available chlorine, and after thorough stirring, the hot water was heated until the pH of the hot water reached 3.8. Calcium carbonate was added to form a ferric hydroxide precipitate.

At this time, about 4 ppm of a polymer flocculant was added to accelerate the sedimentation of the precipitate.

Table 5 shows the composition of the hot water after this treatment.

Further, the amount of precipitate produced and the composition of the precipitate obtained at this time are shown in Table 6 in comparison with the case where the arsenic removal treatment was performed in the same manner without pH adjustment.

As described above, the geothermal fluid in which steam and hot water spout in a two-phase flow is separated into steam and hot water by a steam-water separator, and immediately after that, acid is injected into the hot water to adjust the pH to 4 to 6. By doing so, the amount of arsenic removal sludge can be reduced, and arsenic can be removed from hot water even if the amount of iron compounds added is reduced, reducing the amount of iron compounds required for arsenic removal treatment. things became possible.

Furthermore, it was found that this pH adjustment was effective in preventing silica scale, as no silica scale was observed.

Claims (1)

[Claims] 1. A first step in which a geothermal fluid consisting essentially of steam and hot water that is gushing out from a geothermal steam extraction well is introduced into a steam water separator and separated into steam and hot water; A second step in which the hot water is introduced into a flasher and separated into steam and hot water again, and the hot water separated in the second step is treated with an acid,
A method for treating geothermal hot water comprising a third step of adding an iron salt and an oxidizing agent to separate the arsenic contained in the hot water by coprecipitation with iron hydroxide, the method comprising: adding an iron salt and an oxidizing agent to the hot water in the third step; Adding a part of the acid to the hot water separated in the first step and introduced into the flasher in the second step to adjust the p)I of the hot water to 4 to 6. A method for treating hot geothermal water characterized by: