JPS5944117B2 - Treatment method for geothermal power generation heat wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing clogging of a reinjection well due to silica contained in the thermal wastewater when returning the thermal wastewater underground after underground hot water is used for power generation.

The underground hot water used for geothermal power generation has a temperature of 200°C or higher, and silica (Sin2) is dissolved in a saturated state.

As can be estimated from the second plotted saturated solubility curve 50, solid silica is precipitated due to temperature drop during the power generation process.

When silica precipitates, fine activated silica first appears, which then gradually becomes larger and becomes colloidal silica.

If solid silica is left in hot water and returned to the ground,
Due to clogging, reinjection wells become unusable in a short period of time.

This is said to be a phenomenon that occurs when colloidal silica becomes fine silica particles that adhere to the valve wall due to the activation of colloidal silica due to the temperature rise of the thermal waste water in the reinjection well.

As a countermeasure against this clogging, attempts have been made to create fine bubbles by introducing chemicals, and to trap silica particles in these bubbles and float them apart, but this is not always sufficient.Therefore, in the present invention, the following method has been adopted. The aim was to prevent clogging of the reinjection well.

That is, thermal wastewater containing silica used for geothermal power generation is cooled through a first direct contact heat exchanger, most of the silica is precipitated as fine particles, air is dissolved in this thermal wastewater under pressure, and then Fine silica particles are collected and separated on air bubbles by reducing the pressure, and the heated waste water is heated through a second direct contact heat exchanger to dissolve and reduce the remaining solid silica. The refrigerant is returned to the well, and the refrigerant is
heat exchanger.

This will be explained using the system diagram in FIG. 1 and the curves in FIGS. 2 and 3.

(a) The hot water leaving the power plant reaches the state 1 in Figure 1 by the hot water pump on the power plant side, and the silica in the hot water is in the state shown in ■ in Figure 2.

That is, solid silica corresponds to A'-A, and dissolved silica corresponds to point A.

This enters a direct contact heat exchanger (cooler) 2 and is cooled by contacting a cold medium 30.

At this time, in the exchanger 2, the hot water 1 constitutes a continuous phase and the medium 30 constitutes a dispersed phase.

A temperature diagram inside this heat exchanger is shown at the left end of FIG.

The temperature difference for heat exchange is expressed as the average of ■-0, ■-[phase].

(o) The cooled hot water 1a containing solid silica as much as A'-A in FIG. Direct contact dissolves air in an amount commensurate with temperature and pressure.

The undissolved air 41 is discharged to the atmosphere via the pressure regulator 5, and the low-temperature hot water 1b in which the air 40 has been dissolved is reduced in pressure to near atmospheric pressure by the pressure reducing valve 7, and flows into the separator 6.

The dissolved air becomes bubbles in an amount corresponding to the differential pressure,
It rises while clinging to fine silica.

By collecting the bubbles and silica that have risen, the solid silica in the hot water will be removed.

This separation operation does not necessarily require complete collection.

(/c) In the state of the pump 8, the hot water 1c having a silica solubility close to point B in FIG. It dissolves the solid silica present and forms a state [phase] that enters the reinjection well.

The state of 0 corresponds to the 0 point in FIG. 2, and there is less dissolved silica than the saturated solubility at the same temperature.

The temperature change inside the heater 9 is as shown at the right end of FIG.

(b) The temperature of the medium 30 is raised by the cooler 2, and then lowered by the heater 9. However, since the temperature drops only to the temperature of the central part 10 in FIG. ] to the 00 point.

This amount of heat is theoretically the same as the amount of heat based on the temperature difference between (1) and [phase], and the smaller the terminal temperature difference of the heat exchanger, the smaller the amount of heat to be cooled.

(e) After all, in FIG. 2, the system changes the inlet point A' to the outlet point C, and the silica corresponding to A'-C is separated from the silica outlet 12 in FIG.

(→Cooling loss during refrigerant circulation is compensated for by the cooler 11.

The method of the present invention as described above has the following advantages.

Since only physical phenomena are used, there is no need for chemicals, and as a direct contact heat exchanger is used, equipment costs are low, and it is also necessary to consider phenomena such as a decrease in efficiency of the heat exchanger due to silica adhesion to the heat transfer surface. There isn't.

Further, conventionally, the lower limit of the temperature at which hot water can be used has not been lowered and the heat utilization effect has been small, but by implementing the present invention, there is no need to consider clogging of reinjection wells, so hot water can be used at lower temperatures.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of the method for treating geothermal power generation heat wastewater of the present invention,
Figure 2 is the same operation diagram, Figure 3 is hot water cooling (medium heating),
It is a temperature diagram of the decomposition process (medium transfer, medium cooling) and hot water heating (medium cooling). 1... Heat wastewater containing silica, 2... First direct contact heat exchanger (cooler), 3, 8...
・Heat drainage pump, 4... Air dissolution tank, 5...
...Pressure regulator, 6...Separator, 7...
... pressure reducing valve, 9 ... second direct contact heat exchanger (heater), 10, 13 ... refrigerant pump,
11... Auxiliary refrigeration system, 12...
Solid silica outlet, 16... Treated thermal wastewater, ■,
■. [Phase]・・・・・・・・・・・・・・・ [Phase], 0...
...Temperature, 20...Cooling water, 30...
... Refrigerant, 40 ... Air, 50 ... Saturation solubility curve.

Claims (1)

[Claims] 1 The thermal wastewater containing silica used for geothermal power generation is cooled through the first direct contact heat exchanger, most of the silica is precipitated as fine particles, air is dissolved in this thermal wastewater by pressurization, and then the pressure is reduced. The fine silica particles are collected on the air bubbles and separated, and the heat waste water is transferred to a second
Treatment of geothermal power generation heat wastewater by raising the temperature through a direct contact heat exchanger, dissolving the remaining solid silica, and returning it to the reinjection well, and circulating the refrigerant between the first and second heat exchangers. Method.