JPS60219388A - Prevention of calcium carbonate scale in geothermal power generation plant - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application and Purpose of the Invention The present invention is a method for preventing calcium carbonate scale in a geothermal power generation system. The purpose of this invention is to enable steady operation of geothermal power generation by safely and inexpensively preventing the adhesion of calcium carbonate scale within the geothermal water circulation system of hot water type geothermal power generation.

Conventional hydrothermal geothermal power generation employs a system in which geothermal water gushes out from within the earth's crust via a production well, separates the steam for power generation, and then returns to the earth's crust via a reinjection well.

It is also believed that some or most of the reduced geothermal water is reheated within the earth's crust and circulated to production wells.

In such a geothermal hot water circulation system, calcium carbonate scale can form anywhere in the system depending on the amount of chemical components in the geothermal water, especially the concentration of carbonate ions and calcium ions, and temperature and pressure conditions. There is sex.

Conventionally, it has been known to inject scale inhibitors into production wells as a method to prevent scale from forming within production wells and above-ground pipelines. There are methods such as burying a thin injection pipe between the production well's protection pipe and the earth's crust during drilling.

In addition to the above-mentioned conventional method requiring injection pipes for all production wells where scale is generated, in the former method, the injection pipes are exposed to flows at high temperatures with flow velocities of several tens of meters per second. Therefore, it is necessary to periodically inspect and replace the injection pipe, which is several hundred meters to several thousand meters long, and in the latter method, if the injection pipe is clogged or deteriorated, it is impossible to replace it.

In other words, equipment costs for either method.

Not only are maintenance costs high, but there are still technical problems.

Additionally, injecting antiscalants into production wells does not prevent calcium carbonate scale that has already formed within the Earth's crust.

As a result of research to improve the above-mentioned conventional drawbacks, the present inventors have developed the structure described in the claims,
We have successfully established a method that can easily and safely prevent calcium carbonate scale from accumulating in the geothermal water circulation system.

As a means to solve the problem, the present invention provides a geothermal power generation system in which the geothermal water that is returned from the geothermal water return well into the earth's crust has an average molecular weight of 1.50.
A method for preventing calcium carbonate scale in a geothermal power generation system, which is characterized by injecting sodium polyacrylate of 0 to 20,000 to prevent calcium carbonate precipitation in geothermal water circulating between the earth's crust and the geothermal power generation system. be.

Effect: When injecting a scale inhibitor into a reinjection well as in the present invention, the scale inhibitor is heated to a high temperature within the earth's crust.

Since it is exposed to high pressure for long periods of time, it is required to maintain thermal stability and scale prevention ability at high temperatures. Therefore,
In order to examine and verify these points, we conducted laboratory tests and field tests at a geothermal power plant as follows.

Test Example 1 A 10% aqueous solution of various calcium carbonate scale inhibitors (hereinafter simply referred to as scale inhibitors) was prepared.
This was placed in an autoclave with an internal volume of 500 m/400 m.
6. After heat treatment at 250℃ for 24 hours, it was cooled to room temperature in a sealed state, the decomposition gas was measured with a pressure gauge, and the state of decomposition of the scale inhibitor was investigated. The results are as shown in Table 1. It is.

Table 1 Test Example 2 Regarding the sodium polyacrylate in Test Example 1, the cracked gas pressure was measured in the same manner as in Test Example 1 for various types having different average molecular weights.

In addition, Ca++80p was prepared by dispersing CaCO3 powder in distilled water in advance and introducing CO2 gas without stirring.
100+nJ of a solution obtained by adding 20 ppm each of the sample before heat treatment and the sample after heat treatment to 2 pm Ca (HCO3) liquid was placed in a 300wt1 Erlenmeyer flask equipped with a reflux condenser, and the mixture was heated at 110% in an oil bath. After boiling at ℃ for 2 hours, the solution was filtered through N (L5C p paper) and the concentration of calcium ions in the solution was measured, and the results shown in Table 2 were obtained.

After being press-fitted, it was heated at 250°C for two months, and then cooled and extracted. The four kinds of heat-treated solutions were made into F),'Ca 80++ ppm solutions by the method of Test Example 2, and the calcium ion concentration in the F solution after boiling was measured. In addition, the calcium ion concentration in the F solution was also measured for the solution before heat treatment by the method of Test Example 2, and the third
The results are as shown in the table.

Table 3 According to Tables 1 to 3, among the six types of scale inhibitors tested, polyacrylic acid-based ones are resistant to heat. If it exceeds 20.000, the scale prevention ability is degraded. Moreover, even if it is heated for a long time in conditions similar to those in the earth's crust, its ability to prevent scaling remains unchanged.

Average molecular weight 1,500-20. Since O'OO's sodium polyacrylate maintains its ability to prevent scale even when heated at high temperatures for long periods of time, it can be confirmed that it is optimal as a scale inhibitor to be injected into hot water in the Earth's crust.

Additionally, as is clear from the above tests, it is possible to safely remove scale inhibitors by adding them to the geothermal water circulating between the earth's crust and the geothermal power generation system by injecting them into reinjection wells. It can also be used to prevent calcium carbonate from precipitating in the geothermal water that exists in the earth's crust, and eliminates the need to install injection pipes that are conventionally required to add scale inhibitors into geothermal steam production wells. Not only is there no need for periodic inspection or replacement of injection pipes, but the scale inhibitor is not exposed to the flow of high-temperature steam, and workability can be greatly improved.

However, instead of injecting the scale preventive agent into the reinjection well, the present invention involves drilling a separate chemical injection well for the scale preventive agent injection at a location in the earth's crust where the diffusion of geothermal water is greatest. It may also be added and diffused from a well into geothermal water within the earth's crust.

Furthermore, since the present invention involves adding a scale inhibitor to geothermal water within the earth's crust, the scale inhibitor is added at a higher concentration (approximately 10 to 1100 pp) compared to the case where the scale inhibitor is added into production wells. It is desirable to add about 1.000 to 10,000 ppm for a chemical injection valve.

As described above, the present invention adds an anti-scaling agent to the geothermal water circulating between the geothermal power generation system and the earth's crust through a reinjection well, so it is safe and there is no need for injection of an anti-scaling agent. Since there is no need for injection pipes to be installed, it can be installed at a low location, and the precipitation of calcium carbonate scale within the geothermal power generation system can be greatly reduced, thus making steady operation of geothermal power generation possible. It's effective.

Example: Existing reinjection well (pile diameter 85/8 inch, depth 1,500 m)
, reduction flow rate 300 m3/hour), average molecular weight 4.50
While continuously injecting geothermal water with 15 ppm of sodium polyacrylate added into the earth's crust, we continuously monitored changes in the amount of geothermal water ejected from production wells and the concentration of sodium polyacrylate in the ejected geothermal water. It was measured.

As a result, 0.5 to 3 ppm of polyacrylic acid was detected in the erupted geothermal water several days to several dozen hours after the injection began.

In addition, before injection of conventional scale inhibitors, calcium carbonate scale is generated for 1 to 2 months, and this builds up in the geothermal water piping system of the geothermal power generation system, causing the geothermal water injection from the geothermal production well to stop or erupt. On the other hand, in the case of the present invention, even five months after injection of the scale inhibitor, it was observed that the ejection had stopped and the rate of decrease in the ejection amount was small.

In addition, there was hardly any calcium carbonate scale adhesion within the geothermal water piping system of the geothermal power generation system, even after 5 months, and steady operation of the geothermal power generation was able to continue.

patent applicant Japan Heavy Chemical Industry Co., Ltd. Agent Rikichi Ichikawa

Claims (1)

[Claims] In a geothermal power generation system, geothermal water that is returned from a geothermal water return well into the earth's crust has an average molecular weight of 1.500 to 20,00.
1. A method for preventing calcium carbonate scale in a geothermal power generation system, which comprises injecting sodium polyacrylate of 0.0 to prevent calcium carbonate precipitation in geothermal water circulating between the earth's crust and the geothermal power generation system.