WO2019171632A1

WO2019171632A1 - Method for heating ultra-pure water

Info

Publication number: WO2019171632A1
Application number: PCT/JP2018/033812
Authority: WO
Inventors: 重希堀井
Original assignee: 栗田工業株式会社
Priority date: 2018-03-06
Filing date: 2018-09-12
Publication date: 2019-09-12
Also published as: TW201938965A; JP2019152411A; JP6948012B2

Abstract

Secondary pure water from a sub system 4 is heated by a heat exchanger 6, a heat exchanger 10, and a heat exchanger 12 and is sent to a use point. The heat source of the heat exchanger 6 is warm ultra-pure water returned from the use point. Medium water heated by a heater 40 is circulated in the heat exchanger 10. A pump 46 for circulating medium water is subjected to inverter control, and a bypass flow rate is controlled by a three-way valve 43, in accordance with the amount of ultra-pure water used at the use point.

Description

Ultrapure water heating method

The present invention relates to a method for heating ultrapure water, and more particularly, to a method for heating ultrapure water for heating ultrapure water from a secondary pure water production apparatus with a heat exchanger and supplying it to a use point as warm ultrapure water.

The ultrapure water used as the semiconductor cleaning water is, as shown in FIG. 2, a pretreatment system 50, a primary pure water production apparatus 60, and a secondary pure water production apparatus (often referred to as a subsystem) 70. It is manufactured by treating raw water (industrial water, city water, well water, etc.) with an ultrapure water manufacturing apparatus composed of (Patent Document 1). In FIG. 2, the role of each system is as follows.

In the pretreatment system 50 comprising agglomeration, pressurized flotation (precipitation), filtration (membrane filtration) apparatus, etc. (in this conventional example, agglomeration filtration apparatus), suspended substances and colloidal substances in raw water are removed. In this process, it is also possible to remove high molecular organic substances, hydrophobic organic substances, and the like.

Pre-treated water tank 61, heat exchanger 65, reverse osmosis membrane treatment device (RO device) 62, ion exchange device (mixed bed type or 4 bed 5 tower type etc.) 63, tank 63A, ion exchange device 63B, And in the primary pure water manufacturing apparatus 60 provided with the deaeration apparatus 64, the ion and organic component in raw | natural water are removed. Steam is supplied to the primary side of the heat exchanger 65 as a heat source fluid. The reverse osmosis membrane treatment device 62 removes salts and removes ionic and colloidal TOC. The

ion exchange devices

63 and 63B remove salts and inorganic carbon (IC) and remove TOC components adsorbed or ion exchanged by an ion exchange resin. In the deaerator 64, inorganic carbon (IC) and dissolved oxygen are removed.

The primary pure water produced by the primary pure water production apparatus 60 is sent to the secondary pure water production apparatus 70 via the pipe 69. The secondary pure water production apparatus 70 includes a sub-tank (sometimes referred to as a pure water tank) 71, a pump 72, a heat exchanger 73, a low-pressure ultraviolet oxidation apparatus (UV apparatus) 74, an ion exchange apparatus 75, and a limiter. An outer filtration membrane (UF membrane) separation device 76 is provided. The heat exchanger 73 is for temperature control of secondary pure water. In general, the supply temperature of secondary pure water (room temperature ultrapure water) is 23 to 25 ° C., and a heat exchanger 73 is a cooler for controlling the temperature range. Cold water is used as a cooling source for the cooler.

In the low-pressure ultraviolet oxidizer 74, the TOC is decomposed to an organic acid and further to CO ₂ by 185 nm ultraviolet rays emitted from a low-pressure ultraviolet lamp. Organic substances and CO ₂ produced by the decomposition are removed by the ion exchange device 75 in the subsequent stage. In the ultrafiltration membrane separation device 76, the fine particles are removed, and the outflow particles from the ion exchange resin are also removed.

The treated water of the ion exchanger 75 is heated by ultrapure water (room temperature ultrapure water) sent from the ultrafiltration membrane separator 76 to the use point 90 via the pipe 81 and

heat exchangers

85 and 86. And ultrapure water (warm ultrapure water) sent to the use point 90 via the ultrafiltration membrane separator 87 and the pipe 88.

In the latter line, the ultrapure water from the secondary pure water production apparatus 70 is heated to about 65 to 75 ° C. by the front side heat exchanger 85 and the rear side heat exchanger 86 and supplied to the use point 90. The warm return water from this use point 90 is circulated through the pipe 91 to the heat source side of the pre-stage side heat exchanger 85. The return water that has passed through the heat source side of the pre-stage side heat exchanger 85 has been cooled to about 30 to 40 ° C. and is returned to the sub tank 71 via the pipe 92. The rear stage heat exchanger 86 uses steam as a heat source.

FIG. 3 is a system diagram showing an example of a conventional ultrapure water heating apparatus.

Primary pure water is introduced into the subsystem 4 via the pipe 1, the sub tank 2, and the pipe 3, and the temperature is adjusted by a heat exchanger at the rear stage of the sub tank to produce ultra pure water of about 25 ° C. The produced ultrapure water flows in the order of the pipe 5, the first heat exchanger 6, the pipe 9 and the second heat exchanger 10, and is heated to about 45 to 70 ° C. by the heat exchanger 6. It is heated to about 75 ° C., and is sent to the use point through the pipe 11 as warm ultrapure water. In the pipe 11, a UF membrane separation device 11A is installed immediately before the use point.

The return temperature ultrapure water (return water) of about 75 ° C. from the use point is introduced into the heat source fluid flow path of the heat exchanger 6 through the pipe 7. The return temperature ultrapure water is heat-exchanged with the ultrapure water from the subsystem 4 by the heat exchanger 6 and cooled to about 30 ° C., and then sent to the subtank 2 through the pipe 8.

The first medium water (water as the heat transfer medium) heated by the heat pump 20 and the steam heat exchanger 15 is circulated through the heat source fluid flow path of the heat exchanger 10. That is, the first medium water of about 65 ° C. flowing out from the heat exchanger 10 is heated to about 75 ° C. by the condenser 23 of the heat pump 20 in the first circulation flow path, and then heated to about 80 ° C. by the steam heat exchanger 15. Heat to flow into heat exchanger 10.

Steam (steam) from a boiler or the like is circulated in the heat source fluid flow path of the heat exchanger 15.

The heat pump 20 compresses the heat medium such as CFC substitute from the evaporator 21 by the pump 22 and introduces it into the condenser 23, and introduces the heat medium from the condenser 23 into the evaporator 21 through the expansion valve 24. It is configured.

The first medium water from the heat exchanger 10 is introduced into the condenser 23 of the first circulation channel (high temperature side channel) through the pipe 12, and the first medium water heated by the condenser 23 passes through the pipe 14. Then, the water is fed to the heat exchanger 15. A part of the first medium water from the heat exchanger 15 is returned to the pipe 12 via the bypass pipe 19. Thereby, the water temperature of the first medium water introduced into the condenser 23 becomes about 70 ° C. The bypass pipe 19 is provided with a flow rate adjustment valve (not shown).

The piping 12 is provided with a circulation pump (not shown).

In order to pass the second medium water (heat pump heat source water) through the heat source fluid flow path (low temperature side flow path) of the evaporator 21, a flow path including a pipe 25 and a pipe 27 is provided.

Heat pump heat source water at about 30 ° C. is introduced into the heat source fluid flow path of the evaporator 21, and heat exchange with the heat medium of the heat pump 20 is performed to lower the temperature to about 25 ° C., and then is sent to another process via the pipe 25. .

As an operation method of the heat pump 20, for example, the input power of the heat pump compressor is adjusted so that the outlet temperature of the first medium water becomes a constant temperature. A plurality of heat pumps may be used, and the number control may be performed according to the heat load.

In the ultrapure water heating apparatus of FIG. 3, the amount of the first medium water to be bypassed from the pipe 14 to the pipe 12 via the bypass pipe 19 is a three-way valve (not shown) provided at the branch from the pipe 14 to the bypass pipe 19. ). When the amount of bypass water is increased, the amount of heat given to the ultrapure water in the heat exchanger 10 is reduced, and when the amount of bypass water is reduced, the amount of heat applied in the heat exchanger 10 is increased. Therefore, when the temperature of the ultrapure water flowing into the heat exchanger 10 from the pipe 9 changes due to the change in the amount of return-pure ultrapure water from the pipe 7, the first medium water amount to be bypassed to the pipe 19 is controlled. Thus, the temperature of the warm ultrapure water fed from the pipe 11 to the use point is maintained constant (75 ° C. in the above case).

Japanese Patent No. 6149993 Japanese Patent No. 6149992

In FIG. 3, when the amount of return-pure ultrapure water from the pipe 7 fluctuates greatly and the temperature of the ultrapure water flowing from the pipe 9 into the heat exchanger 10 fluctuates greatly, control of the first medium water amount to be bypassed to the pipe 19 is performed. However, the temperature of the ultrapure water that is sent to the use point may deviate from the target temperature.

That is, the amount of warm ultrapure water used at the point of use may fluctuate greatly every few seconds. When the amount of warm ultrapure water used at the use point varies, the flow rate of “warm ultrapure water return” in FIG. 3 varies. Thereby, the amount of heat recovery in the heat exchanger 6 varies, and the temperature of the ultrapure water flowing from the pipe 9 into the heat exchanger 10 also varies.

For example, in the case of the system shown in FIG. 3, if the amount of warm ultrapure water used is rapidly increased at the use point and the amount used is maintained, the temperature of ultrapure water at the inlet of the heat exchanger 10 is lowered. In this case, in order to maintain the ultrapure water outlet temperature of the heat exchanger 10, the amount of bypass water to the pipe 19 is decreased and the flow rate is increased. However, if the three-way valve is adjusted so that the amount of bypass water to the pipe 19 becomes zero, the amount of water to the heat exchanger 10 cannot be increased any more, and the temperature of the warm ultrapure water sent from the pipe 11 to the use point Cannot be maintained at the target temperature.

Since the temperature of the ultra-pure water at the use point must be controlled within a strict range of plus or minus 1 ° C, the fact that the control temperature of the ultra-pure water cannot be maintained may cause a major problem in the use of the ultra-pure water at the use point. There is.

Conventionally, in order to avoid the above problem, the first medium water amount (high-temperature circulating water amount) circulating through the pipe 14, the pipe 12, and the bypass pipe 19 has been set to a sufficient amount. In other words, considering the maximum value of warm ultrapure water usage estimated from past results, even if the warm ultrapure water usage rapidly increases to such maximum value, it becomes possible to control the temperature of the ultrapure water delivered to the use point As such, a sufficient amount of bypass circulation water was set.

According to such a method, the temperature of the ultrapure water supplied to the use point is maintained constant even if the use amount of the ultrapure water at the use point is remarkably increased. However, in a normal state (when the amount of warm ultrapure water used is near the average value), there is a problem that the amount of bypass water is large and the operation cost is high. That is, in the normal state, since the return temperature ultrapure water is large, the temperature of the ultrapure water flowing from the pipe 9 into the heat exchanger 10 does not decrease so much, and therefore the required amount of heating by the high-temperature circulating water (first medium water) is also low. Since it was not large, the operation was continued while the flow rate of the first medium water bypassed to the pipe 19 was large.

As described above, simply taking the measure of reducing the amount of high-temperature circulating water (first medium water) avoids the risk that the temperature of the ultra-pure water cannot be maintained when the use of the ultra-pure water is rapidly increased at the point of use. I couldn't.

The present invention solves such problems and avoids the risk that the temperature of ultra-pure water cannot be maintained due to a rapid increase in the amount of use of hot ultra-pure water at the point of use, while reducing the amount of hot circulating water and reducing the bypass flow rate. It aims at providing the heating method of a pure water.

The ultrapure water heating method of the present invention includes a first heat exchanger that heats ultrapure water from an ultrapure water production apparatus using return water from a use point as a heat source, and the first heat exchanger. A heating unit that further heats the heated ultrapure water and supplies the heated ultrapure water to a use point, wherein the heating unit is heated by the first heat exchanger; A second heat exchanger through which the ultrapure water is passed through the heated fluid passage, and a circulation passage for circulating and circulating the medium water as the heat transfer medium in the heat source fluid passage of the second heat exchanger The amount of ultrapure water used at the point of use in a method of heating ultrapure water by a heating device comprising a heater for heating the medium water flowing through the circulation channel and a pump provided in the circulation channel The pump is controlled accordingly.

In one aspect of the present invention, a bypass flow path that bypasses the second heat exchanger is provided in the medium water circulation flow path, and depending on the amount of ultrapure water used at a use point, Control the bypass flow rate.

In one aspect of the present invention, a three-way valve for controlling the bypass flow rate is provided, and the opening degree of the three-way valve is controlled according to the amount of ultrapure water used at the use point.

In one aspect of the present invention, a three-way valve for controlling the bypass flow rate is provided, and a three-way valve opening after 1 to 5 minutes is predicted from an actual measured value of the operation data. The amount of hot circulating water is controlled so that it is almost constant.

In one aspect of the present invention, based on past operation data, a multiple regression model or an artificial intelligence model having a “predicted value of the three-way valve opening” as an objective variable is constructed, and the current operation data measured value is included in the model. Is input, the “predicted value of the three-way valve opening” is obtained.

In one aspect of the present invention, the explanatory variables of the multiple regression model or the artificial intelligence model include at least the “current value of the three-way valve opening” and the “ultra pure water outlet temperature of the first heat exchanger”.

According to the present invention, by reducing the amount of hot circulating water and reducing the bypass flow rate,
i) Reduce the power consumption of the circulating water pump;
ii) When there is a heat pump in the circulation process of the high-temperature circulating water, the heat pump inlet temperature decreases and the temperature difference between the high-temperature circulating water and the heat pump heat source water decreases, so the COP (coefficient of performance) of the heat pump is improved. be able to;
iii) When there are both heat pumps and steam heat exchangers in the circulation process of high-temperature circulating water, it is possible to reduce the amount of steam used in the steam heat exchanger and increase the heating rate by the heat pump with a low unit price per supply heat quantity. it can;
The effect is obtained.

It is a block diagram of the heating apparatus which concerns on embodiment of this invention. It is a block diagram of the heating apparatus of a prior art example. It is a block diagram of the heating apparatus of a prior art example.

Hereinafter, an embodiment will be described with reference to FIG. In addition, although the water temperature is illustrated in the following description, it is an example and does not limit this invention.

FIG. 1 is a system diagram showing an ultrapure water heating apparatus according to an embodiment.

Primary pure water is introduced into the subsystem 4 via the pipe 1, the sub tank 2, and the pipe 3, and the temperature is adjusted by a heat exchanger included in the subsystem to produce ultra pure water of about 25 ° C. The produced ultrapure water flows in the order of the pipe 5, the first heat exchanger 6, the pipe 9 and the second heat exchanger 10, and is heated to about 45 to 70 ° C. by the heat exchanger 6. It is heated to about 75 ° C., and is sent to the use point through the pipe 11 as warm ultrapure water. In the pipe 11, a UF membrane separation device (not shown) is installed immediately before the use point.

The medium water heated by the heater 40 such as a heat pump or a steam heat exchanger (water as a heat transfer medium) is circulated through the heat source fluid flow path of the heat exchanger 10. That is, about 50 to 70 ° C. medium water flowing out from the heat exchanger 10 is introduced into the heater 40 by the pipe 45, the pump 46 and the pipe 47 and heated to about 80 ° C., and then the pipe 42, the three-way valve 43 and the pipe are heated. It flows into the heat exchanger 10 through 44.

A part of the medium water from the heater 40 is returned from the three-way valve 43 to the pipe 45 via the bypass pipe 48.

The temperature sensor 50 is provided in the pipe 11, and the measured temperature is input to the control device 51, and the three-way valve 43 and the pump 46 are controlled by the control device 51. From the three-way valve 43, a signal indicating the current opening degree (an opening degree of flowing medium water from the pipe 42 to the pipe 44) is input to the control apparatus 51.

In this embodiment, the medium water circulating water amount is adjusted so that the opening degree of the three-way valve 43 (an opening degree for flowing the medium water from the pipe 42 to the pipe 44) becomes a constant value. If the opening degree of the three-way valve 43 is expressed by 0% to 100%, it is preferable to increase / decrease the motor rotation speed of the pump 46 and automatically adjust the medium water circulation water amount so that the opening degree becomes 75% to 80%, for example. . For example, an inverter attached to the pump adjusts the motor rotation speed by increasing or decreasing the voltage and frequency.

A method may be used in which a signal related to the current three-way valve opening is input to the control device 51, calculation processing is performed by the control device 51, the result is sent to an inverter attached to the pump 46, and the inverter adjusts the voltage and frequency of the motor. . Alternatively, a method may be used in which a relational expression between the opening degree of the three-way valve 43 and the inverter output value is derived in advance and the inverter output value is adjusted based on the relational expression.

When there is a large change in the amount of hot ultrapure water used at the use point 90, there is a time delay of several minutes before the effect affects the opening of the three-way valve 43. For this reason, it is more desirable to use a predicted value in the future instead of the current three-way valve 43 opening. Here, the future means one to five minutes after the present time.

For example, based on the operation data for the past several months, “the three-way valve opening after 2 minutes” is the objective variable, “the current three-way valve opening”, “ultra-pure water flowing from the pipe 9 to the heat exchanger 10” By constructing a multiple regression model with explanatory variables such as “temperature of” and inputting actual measured data of the current operation into the model, the temperature of the ultrapure water detected by the temperature sensor 50 after 2 minutes is maintained at 75 ° C. To predict the "three-way valve opening after 2 minutes". By adjusting the high-temperature circulating water amount (pump 46 discharge amount) based on the predicted value of “the three-way valve opening after 2 minutes”, it is possible to respond more rapidly to the sudden increase in the amount of hot ultrapure water used. For example, when the predicted value of the three-way valve opening after 2 minutes exceeds 80%, the motor speed of the pump 46 is increased so that the opening is within the range of 75 to 80%.

An artificial intelligence model or the like may be used instead of the multiple regression model.

In this way, while avoiding the risk that the temperature of the ultra-pure water cannot be maintained due to the rapid increase in the amount of use of the ultra-pure water at the point of use, the amount of bypass water can be reduced and the production cost of the ultra-pure water can be reduced.

When the amount of warm ultrapure water used at the use point increases, the temperature of ultrapure water flowing from the pipe 9 to the heat exchanger 10 decreases, and the opening of the three-way valve 43 starts to increase correspondingly. The circulating water amount of the medium water can be automatically increased, and the risk of deviating from the control target value of the warm ultrapure water temperature can be avoided.

Further, by predicting the opening of the three-way valve after several minutes from the actual measured values of the "warm ultrapure water return flow rate" and the "temperature of ultrapure water flowing into the heat exchanger 10 from the pipe 9" at the present time, The high-temperature circulating water volume can be adjusted even faster than adjusting the high-temperature circulating water volume only by the valve opening, and the risk of deviating from the control target value of the warm ultrapure water temperature can be avoided more reliably.

Next, more specific operation examples will be described.

As the heater 40, both a heat pump using refrigeration waste water as a heat source and a steam heat exchanger using steam as a heat source are used so that circulating water flows in the order of pump 47 → heat pump → steam heat exchanger. The input power of the heat pump is adjusted so that the heat pump outlet temperature is constant. Further, the amount of steam is supplied so that the outlet temperature in the steam heat exchanger (that is, the temperature of the medium water flowing in the pipe 42) is constant.

Note that (heat pump outlet temperature of the present invention) = (heat pump outlet temperature of the comparative example), (steam heat exchanger outlet temperature of the present invention) = (steam heat exchanger outlet temperature of the comparative example).

In this embodiment, the output value of the inverter attached to the pump 46 is adjusted so that the opening of the three-way valve 43 is normally 75 to 80% (that is, the bypass water amount is 20 to 25%). As a result, the average value of the medium water circulating water amount is reduced by about 40% compared to the conventional case. Accordingly, the power consumption of the circulating water pump is reduced, and the heating rate by the heat pump with a low unit price per heat quantity is increased. As a result, the overall operation cost can be reduced by about 15%.

That is, in FIG. 3, the amount of ultrapure water used at the point of use is remarkably increased, the amount of returned ultrapure water from the pipe 7 is remarkably reduced, and the temperature of the ultrapure water flowing into the heat exchanger 10 is considerably low ( For example, even when the temperature becomes 40 to 45 ° C. or lower), a sufficiently large amount of high-temperature medium water is allowed to flow through the heat exchanger 10 so that 75 ° C. hot ultrapure water can be sent from the pipe 11 to the use point 90. When the amount of medium water bypassed from the pipe 14 to the pipe 19 is increased in normal times and the amount of ultrapure water used at the use point 90 is significantly increased, it is necessary to secure the amount of medium water from the pipe 14 to the heat exchanger 10 was there. For this reason, even during normal times (a state in which the amount of ultrapure water used at the use point 90 is almost an average amount), the amount of hot water discharged from the heat pump 20 to the pipe 14 (medium water amount) is increased, and the amount of bypass medium water is increased. It was necessary to prepare for an increase in the amount of ultrapure water used at the point of use. And in order to bypass a large amount of medium water in this way, pump electric power cost etc. have increased.

On the other hand, in the present invention, the amount of bypass medium water is kept small, for example, 20 to 25% in normal times, and when an increase in the amount of supply medium water to the heat exchanger 10 is predicted (that is, the degree of opening of the three-way valve 43). When a significant increase in water is predicted), the amount of tapping water from the heater 40 is increased. As a result, the amount of high-temperature medium water supplied from the heater 40 (the amount of tapping water) at normal times can be considerably reduced as compared with the conventional case.

The controller 51 controls the opening degree of the three-way valve 43 and the motor speed of the pump 46 so that the temperature of the ultrapure water going to the use point 90 via the pipe 11 is always maintained at a constant temperature (75 ° C. in this case). The amount of medium water (high-temperature circulating water amount) supplied to the heat exchanger 10 is controlled by the control. The three-way valve 43 and the bypass pipe 48 may be omitted as long as the warm ultrapure water can be maintained at a constant temperature only by controlling the amount of medium water to the heat exchanger 10 by controlling the pump 46. However, the supply medium water amount control to the heat exchanger 10 by the bypass water amount control by the three-way valve 43 is quick and easy, and can quickly cope with the load fluctuation of the heat exchanger 10. In the present embodiment, since the opening degree of the three-way valve 43 is increased to 75 to 80%, a significant load increase in the heat exchanger 10 cannot be dealt with by the three-way valve 43 alone. Therefore, as described above, the control of the pump 46 is also used.

The above embodiment is an example of the present invention, and the present invention may be other than illustrated.

Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2018-039836 filed on Mar. 6, 2018, which is incorporated by reference in its entirety.

2 Sub tank 4 Sub system 6 1st heat exchanger 10 2nd heat exchanger 43 Three-way valve 48 Bypass piping 50 Temperature sensor

Claims

A first heat exchanger for heating the ultrapure water from the ultrapure water production apparatus using the return water from the use point as a heat source;
A heating means for further heating the ultrapure water heated by the first heat exchanger, and supplying the heated ultrapure water to the use point,
The heating means includes
A second heat exchanger in which ultrapure water heated by the first heat exchanger is passed through the heated fluid channel;
A circulation flow path for circulating and circulating medium water as a heat transfer medium in the heat source fluid flow path of the second heat exchanger;
A heater for heating the medium water flowing through the circulation channel;
In a method of heating ultrapure water by a heating device provided with a pump provided in the circulation channel,
An ultrapure water heating method, characterized in that the pump is controlled according to the amount of ultrapure water used at a use point.
The medium water circulation channel is provided with a bypass channel that bypasses the second heat exchanger,
2. The ultrapure water heating method according to claim 1, wherein a bypass flow rate to the bypass flow path is controlled in accordance with a use amount of ultrapure water at a use point.
3. The ultrapure water heating according to claim 2, wherein a three-way valve for controlling the bypass flow rate is provided, and the opening degree of the three-way valve is controlled according to the amount of ultrapure water used at a use point. Method.
A three-way valve for controlling the bypass flow rate is provided, and the three-way valve opening after 1 to 5 minutes is predicted from the actual operation data measurement value so that the predicted opening value is substantially constant. 3. The ultrapure water heating method according to claim 2, wherein the amount of high-temperature circulating water is controlled.
Based on past operation data, a multiple regression model or artificial intelligence model with the `` predicted value of the three-way valve opening '' as an objective variable is constructed, and the actual operation data actual measurement value is input to the model, The ultrapure water heating method according to claim 4, wherein a “predicted value of the three-way valve opening” is obtained.
6. The ultrapure water heating method according to claim 5, wherein the explanatory variables of the multiple regression model or the artificial intelligence model include at least the “current value of the three-way valve opening” and the “ultrapure water side outlet temperature of the first heat exchanger”.