JPS5949077B2 - Method for preventing scale adhesion in geothermal hot water - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for preventing scale from precipitating and adhering in a reinjection well when waste hot water is returned underground after being used for geothermal power generation, etc. It is.

Conventionally, geothermal hot water used in geothermal power generation and the like is generally returned underground as waste hot water through a reinjection well.

In this case, if the reinjection well is used for a long time, changes in the groundwater level and scale components such as silica, calcium, and salt, which are contained in large amounts in geothermal hot water, may precipitate and adhere to the reinjection well. The wastewater treatment capacity of the area was decreasing.

It is not allowed to pump out an amount of hot geothermal water that exceeds the wastewater treatment capacity of the reinjection well, so the amount of power generated by geothermal power generation may be affected by the wastewater treatment capacity of the reinjection well. When the wastewater treatment capacity of a plant declines, it is often necessary to drill additional reinjection wells at great expense.

For this reason, measures have been taken to prevent scale from adhering to reinjection wells.
A method is used in which waste hot water is allowed to stay in a retention tank for a certain period of time, active colloidal silica, which tends to adhere, grows into inert silica, the inert silica is removed, and then the water is returned to a reinjection well.

However, with this method, silica could not be removed sufficiently.

The present invention is characterized in that the waste hot water of geothermal hot water is cooled to precipitate and recover scale components, and the waste hot water from which the scale components have been recovered is heated again and returned to the reinjection well. The present invention provides a method for preventing scale buildup in reinjection wells more effectively than conventional methods.

In the present invention, as described above, after cooling the waste water of geothermal hot water to precipitate and recover scale components, it is heated again and returned to the reinjection well in the state of an unsaturated solution.
Even if the above-mentioned waste hot water comes into contact with the walls of the reinjection well and the temperature drops, the precipitation of scale components is extremely small, and therefore, it is possible to effectively prevent the deterioration of the waste hot water treatment capacity due to scale adhesion in the reinjection well. I can do it.

Hereinafter, the most preferred embodiment of the present invention will be described with reference to FIG. A pair of fixed pipe walls 5a, 5b, a plurality of 6 groups of cooling pipes whose both ends are fixed to the pipe walls 5a, 5b, and a plurality of heat exchange chambers 7a, 7b, 7C...・
Partition plates 8a, 8b, 8C...
In addition, the above-mentioned partition plates 8a, 8b
, 8C...... the above hot water tank 4 every other
Outflow ports 9a, 9b, .

The drainage chamber 10, which is composed of the pipe wall 5a and the side wall of the hot water tank 4, is connected to the reinjection well 12 by an outlet pipe 11, and the other end is connected to the upper edge of the other pipe wall 5b. One end of a cooling partition plate 14 extending into the retention tank 13 is fixed.

The cooling partition plate 14 forms a reciprocating path within the cooling-type retention tank 13, and the return path is connected to the pipe wall 5 on the side.
b and a side wall of the hot water tank 4.

In the heat exchange chambers 7a, 7b, 7C, etc., particles 16 such as sand, which tend to form the nucleus of precipitated scale, are added and suspended in the hot water 1, thereby forming a fluidized bed 17. ing.

The present embodiment is configured as described above, and the approximately 95° C. waste hot water 1 after being used in a geothermal power plant (not shown) is led to the first stage heat exchange chamber 7a through the inlet pipe 2. After that, it flows from the outlet 9a to the second stage heat exchange chamber 7b,
Furthermore, it passes over the upper edge of the second stage partition plate 8b and enters the third stage heat exchange chamber 7C.

The waste hot water 1 that has entered the third stage heat exchange chamber 7C flows through the outlet 9b to the fourth stage heat exchange chamber 7d.

Thereafter, the same action is repeated, and the waste hot water 1 is cooled to about 55° C. and discharged to the outward path of the cooling type retention tank 13 over the upper edge of the pipe wall 5b.

In this case, silica and the like adhering to the outer surface of the cooling pipe 6 are scraped off by contact with the floating particles 16.

To explain the precipitation of scale contained in the hot waste water 1 in the above process using the example of silica, in the solubility curve of silica shown in Figure 2, the hot water 1 at point A (in this case, the hot water The temperature of 1 is about 95℃, the concentration of silica is 5
00pp was measured.

) The saturated waste hot water 1 is cooled down to about 55° C. as shown at the point by passing through the heat exchanger 3 described above, and silica is precipitated from point to point.

The above precipitated silica etc. are continuously removed from the heat exchange chamber 7a,
They are carried by the suspended particles 16 thrown into the air-cooled retention tank 13, and are collected together with the suspended particles 16 by a collection device (not shown) provided at a suitable location on the outgoing path of the air-cooled retention tank 13.

Next, the waste hot water 1 from which the scale components have been recovered flows into the outgoing path of the air-cooled retention tank 13 in a saturated state as shown at point c in FIG. 2, and flows through the outgoing path while being cooled. It circulates around the tip of the partition plate 14 and flows in the return path until the temperature reaches about 45° C. and is led to the return chamber 15 of the hot water tank 4.

In this process, the waste hot water 1 is cooled from point C to point 2 in FIG. 2, and silica is deposited in the amount shown directly from point 2 to point 2.

In this case, some of the precipitated silica reacts with each other in the flow path, becomes inert particles, and flows into the return chamber 15 together with the waste hot water 1.

Furthermore, as shown by point E in FIG.
While flowing through the cooling pipe 6, it is heated by the waste hot water 1 flowing around the outer circumferential area of the cooling pipe 6 and is led to the drainage chamber 10 at a temperature of about 85°C.

In this process, when the waste hot water 1 is heated to the temperature of point C in Fig. 2, some solid particles of precipitated silica are completely redissolved in the waste hot water 1, and the waste hot water 1 becomes a saturated solution.After that, as it is heated from point C to point C, the unsaturated state of waste hot water 1 increases, and according to the measurement results, it becomes unsaturated at about 85°C and contains 250 pH of silica. It turned out to be a solution.

Since this unsaturated hot water 1 (indicated by dots 1 and 2 in FIG. 2) is returned to the reinjection well 12 through the outlet pipe 11,
Even if the hot water 1 is cooled by the outlet pipe 11 and the side wall of the reinjection well 12, the hot water that is returned to the reinjection well 12 via the drainage chamber 10 is heated as described above from the return chamber 15 to the drainage chamber 10. As shown by the middle point in Figure 2, it is heated again to about 8
Since the temperature is maintained at 5°C, there is sufficient temperature margin for scale precipitation, so the scale contained in the waste hot water 1 injected into the reinjection well 12 precipitates and flows into the reinjection well 12. There is almost no adhesion, and therefore, scale adhesion to reinjection wells can be prevented much more effectively than conventional methods.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, and FIG. 2 is a graph showing the temperature of waste hot water and the solubility of silica. 1... Exhaust hot water, 3... Fluidized bed heat exchange device, 11... Reduction well.

Claims (1)

[Claims] 1. A heat exchange section with a cooling pipe inside and a fluidized bed arranged outside the cooling pipe, a cooling section following this, and a flow path connected from the cooling section to the reinjection well via the cooling pipe, The hot geothermal hot water is passed through the fluidized bed section, the cooling section, and the cooling pipe to the reinjection well, and the waste hot water, which has been cooled in the fluidized bed section to precipitate and remove scale components, is passed through the cooling pipe. A method for preventing scale adhesion of geothermal hot water, which is characterized by heating it again and returning it to a reinjection well.