JP7265256B2 - circulation heating device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a circulation heater that heats a fluid while circulating it in a channel.

Evaporative concentration is a method for removing water from liquid foods such as vegetable and fruit juices and soups. For example, Patent Literature 1 describes a concentrating device for heating and concentrating milk. This concentrating device includes an outer wall that forms a sealed space and milk is introduced and placed in the outer wall. The milk in the reservoir is heated by heating the reservoir with a heater and supplying superheated steam, ie dry steam, to the sealed space. The milk is concentrated by discharging the steam generated by heating to the outside.

Patent Document 2 describes a vapor compression evaporator, which has an evaporator that evaporates a stock solution and a compressor that adiabatically compresses the generated vapor. is returned to the evaporator to serve as a heat source for heating the stock solution, and the heated steam is cooled to produce condensed water.

JP 2017-85956 A JP 2015-205240 A

Compared to the freeze concentration method, which freezes and removes moisture, the evaporation method, which concentrates the liquid by heating the liquid to evaporate the liquid components such as water contained in the liquid, uses relatively simple equipment. Liquids can be concentrated.

However, when a heater or steam is used as a heat source for heating the liquid, the liquid is heated by heat transfer from the heat source to the liquid, and it takes time to heat the liquid. In particular, in the case of a highly viscous liquid, heat transfer takes a long time, and heat treatment cannot be performed efficiently. Therefore, in the evaporation method in which the temperature of the heat source is transferred to the liquid to heat the liquid, it takes time to heat the liquid to the evaporation temperature, and the liquid cannot be efficiently heated.

An object of the present invention is to enable efficient heating of liquids.

The circulating heater of the present invention has a supply pipe connected to a stock solution storage tank that stores a stock solution, and is connected to the lower end of the supply pipe . and a raw solution outlet provided at a position lower than the liquid level of the raw solution at the upper end of the heating and evaporating pipe and the raw solution storage tank, and heated by the heating and evaporating pipe. a circulation pipe for returning the undiluted solution to the undiluted solution storage tank; a steam extraction pipe for discharging the vapor generated from the undiluted solution to the outside; and an electrode member for generating Joule heat by supplying a current from the power supply unit, wherein the power supply unit includes an output transformer having a plurality of power supply taps that output different output voltages, and a plurality of the power supply taps. A tap changer that outputs power to the electrode member by switching on any one of the above, and when the current flowing through the stock solution approaches the maximum current at the set maximum power of the power supply tap in the ON state, the current is increased. a controller for controlling the tap changer to switch to a power supply tap with a lower voltage, for discharging the vapor component generated from the stock solution by the Joule heat to the vapor extraction pipe .

The undiluted solution storage tank and the heating/evaporation pipe are connected by a circulation pipe to form a circulation path for returning the undiluted solution from the undiluted solution storage tank through the heating/evaporation pipe to the undiluted solution storage tank, and the electric current from the electrode member provided in the heating/evaporation pipe is generated. Feed stock solution. Thereby, the undiluted solution is heated by Joule heat, and the solvent of the undiluted solution can be evaporated. Any one of a plurality of feed taps of the output transformer is turned on by a tap changer to supply power to the electrode members. As the temperature of the stock solution increases and the concentration of the stock solution progresses, when the current through the stock solution approaches the maximum current at the set maximum power of the on-state feed tap, the output voltage is switched to a lower feed tap to increase the current. , the set maximum power of the power transformer can be effectively used to efficiently heat the undiluted solution.

It is the schematic which shows a circulation-type heater. FIG. 2 is a block diagram showing a power supply unit of the circulation heater shown in FIG. 1; FIG. 4 is a characteristic diagram showing the relationship between the voltage and current for outputting the set maximum power of the output transformer; (A) is a vertical cross-sectional view showing a modification of the heating evaporation tube, and (B) is a cross-sectional view taken along the line BB in (A).

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the circulating heater 10 includes a stock solution storage tank 11 that holds the stock solution to be heated, that is, the stock solution M, and a heating and evaporation pipe 12 that heats the stock solution M to generate steam, A heating channel 13 for conveying the undiluted solution M is formed in the heating evaporation pipe 12 . The concentrate M is supplied to the concentrate storage tank 11 through an injection pipe 14 . The undiluted solution to be supplied is mainly a liquid substance that is concentrated and commercialized, such as fluid liquid foods and drinks such as vegetable and fruit juices and soups. In addition, as described in Patent Document 2, the circulation heater 10 can also be applied to the case of concentrating a waste liquid as a stock solution. In addition, the circulating heater 10 can also be used for brewing natural products for the production of herbal medicines and herbal medicines.

An inflow port 15 is provided at the lower end of the heating evaporation pipe 12 , and a supply pipe 17 is connected between the inflow port 15 and a discharge port 16 provided at the lower end of the undiluted solution storage tank 11 . A pump 18 is provided in the supply pipe 17 , and the concentrate M discharged from the discharge port 16 of the concentrate storage tank 11 by the pump 18 is passed through the supply pipe 17 from the inlet 15 of the heating evaporation pipe 12 to the heating channel 13 . supplied.

A raw solution outlet 21 is provided at the upper end of the heating and evaporating pipe 12 , and a circulation pipe for returning the raw solution M to the raw solution storage tank 11 is provided between the circulation port 22 of the raw solution storage tank 11 and the raw solution outlet 21 . 23 are provided. Through this circulation pipe 23 , the concentrate M that has flowed to the upper end of the heating passage 13 of the heating evaporation tube 12 flows out from the concentrate outlet 21 and is returned to the concentrate storage tank 11 . In this manner, the concentrate storage tank 11, the heating evaporation pipe 12, the supply pipe 17, and the circulation pipe 23 allow the concentrate M to return from the concentrate storage tank 11 to the concentrate storage tank 11 via the heating flow path 13. It is formed.

The heating evaporation tube 12 shown in FIG. 1 has five ring-shaped electrode members 24 and a cylindrical member 25 arranged therebetween. The electrode member 24 is made of a conductor such as titanium or stainless steel, and the cylindrical member 25 is made of an insulating material such as resin. Two electrode members 24 adjacent to each other in the flow direction of the stock solution M in the heating channel 13 form a pair, and the heating evaporation tube 12 has four pairs of electrode members 24 . An inflow-side joint 26 is attached to the electrode member 24 at the lower end, and an outflow-side joint 27 is attached to the electrode member 24 at the upper end. The joint portion 26 is provided with the inlet 15 , and the joint portion 27 is provided with the concentrate outlet 21 .

A high-frequency current is supplied to each electrode member 24 from a power supply unit 28 so that the two electrode members 24 forming a pair have opposite polarities. The number of electrode members 24 constituting the heating evaporation tube 12 is not limited to five, and may be any number as long as it is plural. Moreover, the electrode member 24 is not limited to a ring shape, and may be a plate-shaped electrode member. Although the supply pipe 17 and the circulation pipe 23 are indicated by lines in FIG. In FIG. 1, the heating and evaporating tubes 12 are shown in a substantially vertical orientation, but the heating and evaporating tubes 12 may be arranged at an angle.

When the pump 18 is driven while the concentrate M is stored in the concentrate storage tank 11 , the concentrate M flows through the supply pipe 17 and into the heating channel 13 from the inlet 15 of the heating evaporation pipe 12 . The raw liquid M that has flowed into the heating channel 13 is held so that the liquid surface S is higher than the raw liquid outlet 21 , and flows into the circulation pipe 23 from the raw liquid outlet 21 . As a result, the concentrate M is returned to the concentrate storage tank 11 . In this manner, power is supplied from the power supply unit 28 to the electrode member 24 while the undiluted solution M is circulating in the heating channel 13, that is, under the circulation process. The power supply unit 28 has a low potential side common terminal COM connected to one of the two paired electrode members 24 and a high potential side output terminal Hi connected to the other. A high-frequency current is applied to the electrode member pair from. When an electric current flows through the stock solution M between the pair of electrode members 24, Joule heat is generated in the stock solution M, and a heating process is performed to heat the stock solution M by the Joule heat. When the concentrate M in the heating evaporation pipe 12 is heated, the concentrate M is returned to the concentrate storage tank 11 and circulated in the concentrate tank 11, so that the temperature of the concentrate M in the concentrate tank 11 is also raised. As a result, a vapor component of the solvent is generated from the circulating undiluted solution M.

A raw solution outlet 21 is provided at a position lower than the liquid surface S of the raw solution M in the heating and evaporating pipe 12 so that the vapor component generated in the heating and evaporating pipe 12 does not enter the circulation pipe 23 from the raw solution outlet 21. ing. Furthermore, the circulation pipe 23 is provided with a bent portion 29 whose upper portion is located at a position substantially equal to or higher than the liquid surface S, and the circulation pipe 23 is arranged so that the gas in the heating flow path 13 does not flow into the inside thereof. is in a water-sealed state.

In order to discharge the vapor components generated from the circulating concentrate M to the outside, a vapor extraction pipe 31 is provided above the concentrate storage tank 11, and the vapor components generated in the concentrate storage tank 11 are discharged through the vapor extraction pipe. 31 to the outside. Furthermore, a steam outlet 32 of the heating and evaporating pipe 12 is connected to a steam extracting pipe 33 in order to discharge to the outside a vapor component separated from the raw liquid M in the heating and evaporating pipe 12. The extraction pipe 33 is connected to the steam extraction pipe 31 . By connecting a suction pump 34 to the steam extraction pipe 31, the pressure in the circulation flow path of the undiluted solution M can be set to be equal to or lower than the atmospheric pressure.

The circulation pipe 23 is provided with a sight glass 35 having transparency so that the undiluted solution M circulating therein can be visually observed from the outside. In order to extract a sample of the undiluted solution M flowing through the supply pipe 17, the supply pipe 17 is provided with a sample take-out valve 36. In order to extract a sample of the undiluted solution M flowing inside the circulation pipe 23, the circulation pipe 23 is provided with a sample take-out valve 37 . A three-way valve 38 is provided in the supply pipe 17 in order to discharge the residue in the stock solution storage tank 11 to the outside after the solvent of the stock solution M is evaporated and the concentration operation is completed. However, the residue may be discharged from the upper surface of the undiluted solution storage tank 11 .

The stock solution storage tank 11 is insulated by a heat insulating jacket 41. Hot water is supplied into the heat insulating jacket 41 from a hot water supply pipe 42 and discharged to the outside from a hot water discharge pipe 43. As a result, the hot water in the heat insulating jacket 41 is kept at a constant temperature.

In order to heat the concentrate M, the outside of the heating container is not heated, and the concentrate M is heated by Joule heat. It is possible to easily perform regular cleaning processing of the heating evaporation tube 12 .

The undiluted solution M circulates through the undiluted solution storage tank 11 and the heating/evaporating pipe 12. The steam generated in the undiluted solution storing tank 11 is discharged outside through the steam extraction pipe 31, and the steam generated in the heating/evaporation pipe 12 is discharged through the steam extraction pipe. 33 to the outside. By circulating the undiluted liquid M to evaporate the solvent component in this manner, the liquid is concentrated, so that the concentration efficiency can be enhanced. As shown in FIG. 1, when the pressure inside the heating channel 13 and the stock solution storage tank 11 is reduced to below atmospheric pressure by the suction pump 34, the solvent component can be vaporized more efficiently, and the concentration efficiency can be further increased. can.

FIG. 2 is a block diagram showing the power supply unit shown in FIG. The power supply unit 28 has an output transformer 51 with a primary side coil and a secondary side coil and a tap changer 52 . The secondary coil of the output transformer 51 has a low-potential feed tap V0 and a plurality of high-potential feed taps V1 to V4 having different output voltages. The tap changer 52 has a common terminal COM connected to the low potential side feed tap V0 of the output transformer 51 and a high potential side output terminal Hi connected to all the high potential side feed taps V1 to V4. have. When one of the two types of electrode members 24 forming a pair is connected to the common terminal COM on the low potential side and the other is connected to the output terminal Hi on the high potential side of the opposite polarity, the output transformer 51 outputs an electrode A current is applied to the stock solution M between the pairs. In order to supply a high-frequency current to the electrode pair, the alternating current of the commercial power supply is rectified to a direct current and then converted to a high frequency of, for example, 20 kHz by an inverter.

The tap changer 52 is provided with switches 53 to 56 such as relays on the output wiring connecting the power supply taps V1 to V4 to the output terminal Hi. Therefore, when one switch 53 is turned on and the other switches are turned off, the output terminal Hi is connected to the feed tap V4. The same applies to other feed taps. Each of the switches 53 to 56 is switch-controlled by a switching signal from the controller 60 .

The controller 60 receives a detection signal from a conductivity sensor 61 for detecting the conductivity of the stock solution M supplied to the heating evaporation tube 12 and a detection signal from a current sensor for detecting the current flowing through the electrode member 24. It is supposed to be sent. Furthermore, a detection signal from a temperature sensor 63 that detects the temperature of the stock solution M supplied to the heating evaporation tube 12 is sent to the controller 60 .

When the temperature of the undiluted liquid M rises, the electric conductivity increases and electricity flows easily. By circulating the concentrate M, the temperature of the concentrate M supplied from the inlet 15 to the heating channel 13 rises as the number of times of circulation increases with the passage of time. Therefore, when the heat evaporation treatment time elapses and the electric conductivity increases, the electric current easily flows through the undiluted solution M, and the electric current increases.

From the start of heating to the end of heating, when the undiluted liquid M is heated by always connecting one specific power supply tap to the electrode member, the current flowing from the power supply unit 28 to the electrode member 24 is the maximum power Wmax set for the output transformer 51. The current is set so that the maximum current is not exceeded. Therefore, when the current flowing through the concentrate M rises to the maximum current value due to the temperature rise of the concentrate M, the current value does not increase any further. Therefore, in the method of always connecting one specific power supply tap to the electrode member, the heating efficiency cannot be improved when Joule heating is performed by circulating the undiluted solution M.

Therefore, in the case of circulating the undiluted solution M, in order to perform heat treatment efficiently, when the electric conductivity of the undiluted solution increases and the current flowing through the undiluted solution M increases, the feed tap with a lower voltage is switched to the undiluted solution. Control the current through M to be high. By lowering the voltage and outputting the set maximum power Wmax of the output transformer 51, the current supplied to the concentrate can be increased. As a result, the temperature of the stock solution M can be raised quickly.

For example, the set maximum power Wmax of the output transformer 51 shown in FIG. is 1000V. In this case, when the 2500 V feed tap V4 is turned on, the maximum current flowing through the concentrate M is 28 A, and when the feed tap V3 is turned on, the maximum current through the concentrate M is 36.8 A. . Furthermore, when the feed tap V2 is turned on, the maximum current flowing through the stock solution M is 50A, and when the feed tap V1 is turned on, the maximum current flowing through the stock solution M is 70A.

In the case of this output transformer 51, when the switch 53 is turned on and the other switches are turned off, power is applied to the electrode member 24 from the feed tap V4 of the output transformer 51 so that the maximum current does not exceed 28 A. be done. When a voltage is applied from the power supply tap V4 from the start of heating of the stock solution M to the end of heating, the maximum current does not exceed 28 A, and even if the temperature of the stock solution M increases and the conductivity increases, , the maximum current of 28A is held. However, if this current continues to flow, it takes time to heat up to the target temperature. As described above, even if the electrical conductivity is increased, the stock solution M cannot be efficiently heated unless the current value is increased to 28 A or more.

Therefore, in the present invention, the output voltage of the output transformer 51 is automatically lowered when the maximum current of 28 A when the current value is 2500 V is approached or reached within a predetermined range. For example, the output voltage is lowered to 1900 V when the conductivity of the stock solution M becomes higher than that at the initial stage of heating. In the case of the output transformer 51 with the set maximum power of 70 kW, if the output voltage is 1900 V, the maximum current of 36.8 A can flow.

In this manner, when the power supply tap V4 is turned on and the maximum current of the power supply tap V4 is 28 A, when the current value approaches or reaches 28 A within a predetermined range, the power supply tap V4 is turned off and the power supply tap V3 is turned on. and set the voltage to 1900V. This allows the maximum current to be increased to 36.8A. Similarly, as the conductivity of the stock solution M rises due to the temperature rise, the feed tap V2 and the feed tap V1 are switched in sequence. As a result, the current value supplied to the concentrate M can be increased, so that the set maximum power can be supplied to the concentrate M from the output transformer 51, so that the concentrate can be rapidly heated in a short time and concentrated. Efficiency can be increased.

Depending on the type of the stock solution M, the stock solution M is heated and concentrated to the target temperature by switching from the power supply tap V3 to the power supply tap V2 without switching from the power supply tap V4 to the power supply tap V1.

FIG. 3 is a characteristic diagram showing changes in the output voltage and output current of the output transformer when the feed taps of the output transformer 51 shown in FIG. 2 are switched to the feed taps V4 to V1.

When the set maximum power Wmax is 70 kW, when the power supply tap V4 is turned on and the concentrate M is heated, the temperature of the concentrate M rises, the conductivity increases, and the current value reaches the upper limit of 2500 V. When the value of 28A is approached or reached, tap changer 52 turns off feed tap V4 and turns on feed tap V3. Thereby, the current value can be increased until the maximum current value approaches 36.8A. Similarly, when the temperature of the undiluted solution M further increases and the current approaches or reaches the upper limit of 36.8 A when the current value is 1900 V, the tap changer 52 turns off the feed tap V3 and turns on the feed tap V2. be. Thereby, the current value can be increased until the maximum current value approaches 50A. Further, when the current value approaches or reaches the upper limit value of 50 A when the current value is 1400 V, the feed tap V2 is turned off and the feed tap V1 is turned on. Thereby, the current value can be increased until the maximum current value approaches 70A.

When the undiluted solution M is heated by always connecting one specific power supply tap to the electrode member from the start of heating to the end of heating, the current value is maintained without exceeding the current value that becomes the set maximum power according to the applied voltage. . Therefore, it takes time to heat the stock solution M. On the other hand, if the voltage is reduced according to the conductivity so that the set maximum power Wmax is output, the current value is increased to match the reduced voltage, so the stock solution M is efficiently heated by Joule heat. can be heated to

As shown in FIG. 2, in the mode in which the tap changer 52 is switched and controlled based on the detection signal from the conductivity sensor 61, the voltage is switched according to the conductivity of the stock solution M. As shown in FIG. For example, when it is detected that the conductivity of the stock solution M has increased while the switch 53 is turned on at the beginning of heating, the switch 54 of the tap changer 52 is turned on by a signal from the controller 60, Other switches are set to off. In this manner, when the maximum power consisting of the voltage of the feed tap V4 and the output current corresponding to the voltage approaches the set maximum power of the output transformer 51, the tap changer 52 switches to the feed tap V3 with a lower voltage. . As the electrical conductivity increases, the tap changer 52 sequentially controls the on/off of the switches to decrease the voltage, so that the current value supplied to the stock solution M can be increased.

The controller 60 includes a microprocessor that calculates control signals for the tap changer 52 based on detection signals from the sensors, and a memory that stores control programs, map data, arithmetic expressions, and the like. In the mode in which the tap changer 52 is controlled based on the detection signal from the conductivity sensor 61, the controller 60 may be provided with map data or an arithmetic expression indicating the relationship between the range of the conductivity of the stock solution M and the voltage value corresponding to the conductivity. stored in On/off of the switch of the tap changer 52 is controlled based on the stored data and the arithmetic expression.

Since the current flowing through the electrode member 24 also changes when the conductivity of the stock solution M changes, it is also possible to control the tap changer 52 based on the detection signal from the current sensor 62 . In this case, as in the case where the tap changer 52 is controlled by the signal from the conductivity sensor 61 described above, the tap changer 52 is controlled as the current value rises, and the low-voltage feed tap is switched to the electrode member. connected to

As described above, the control form of the tap changer 52 includes a form of control based on the detection signal of the conductivity sensor 61 and a form of control based on the detection signal of the current sensor 62, either of which can be applied. is. However, the tap changer 52 is controlled based on the detection signals from both sensors, and the switches 53 to 56 are switched when the detection signals from both sensors approach the set maximum power of the output transformer 51. You can do it. Furthermore, the switches 53 to 56 may be switched when the detection signal from one of the sensors approaches the set maximum power of the output transformer 51 .

Since the conductivity changes depending on the temperature of the concentrate M, instead of directly detecting the conductivity, the temperature sensor 63 detects the temperature of the concentrate M, converts the temperature into conductivity, and switches the feed tap. Also good. Also in this case, the temperature sensor 63 may be used in combination with the conductivity sensor 61 and the current sensor 62, and the signals from the temperature sensor 63 alone may be used to control switching of the switches 53-56.

Next, a procedure for evaporating the solvent of the stock solution M and concentrating the stock solution using the above-described circulation type heater 10 will be described.

For example, in the case of concentrating fluid food such as juice or soup with the circulation heater 10 , the undiluted liquid M, which is the liquid to be concentrated, is supplied to the undiluted liquid storage tank 11 . The pump 18 is driven while a predetermined amount of the concentrate M is stored in the concentrate storage tank 11 . By driving the pump 18, the stock solution M is supplied from the lower end of the heating evaporation tube 12 to the heating channel 13 and flows upward inside. The concentrate M that has reached the concentrate outlet 21 in the heating channel 13 is guided by the circulation pipe 23 and returned to the concentrate storage tank 11 . In this way, the circulation process is executed, and the stock solution M in the stock solution storage tank 11 is circulated and supplied to the inside of the heating evaporation tube 12 .

Power is supplied from the power supply unit 28 to the electrode member 24 while the stock solution M is circulating. As a result, an electric current flows from the paired electrode members 24 to the undiluted solution M, and Joule heat is generated in the circulating flow. This exothermic step heats the stock solution M and evaporates the solvent of the stock solution. Since the circulating flow is evaporated, the stock solution in the stock solution storage tank 11 can be concentrated by the small heating evaporation pipe 12 without using a large heating pot.

As described above, in the circulation heater 10, the raw liquid M is heated by Joule heat, so that the raw liquid M can be adjusted to the boiling point temperature of the solvent contained in the raw liquid, and the liquid can be efficiently concentrated. can do.

As the output transformer 51, not only an output of 70 kW but also an output of about 25 kW to 150 kW can be used. An output of about 80% of the available maximum output may be set as the set maximum power Wmax. Furthermore, the voltage may be lowered when the maximum current of the set maximum power is reached, or the voltage may be lowered when the maximum current is approached within a predetermined value range.

FIG. 4A is a vertical cross-sectional view showing a modification of the heating evaporation tube 12, and FIG. 4B is a cross-sectional view taken along the line BB in FIG. 4A.

The heating and evaporating tube 12 has a tubular member 45 made of an insulating material and having a rectangular cross section. The tubular member 45 is formed by abutting two tubular member pieces 45a and 45b having a U-shaped cross section. . A pair of plate-shaped electrode members 24 are attached to the inner surface of the pipe member 45 so as to face each other. One electrode member 24 is connected to a common terminal COM of the power supply unit 28, The member 24 is connected to the high potential side output terminal Hi of the power supply unit 28 .

A joint portion 26 having an inflow port 15 is integrally provided at one end of the pipe member 45, and a joint portion 27 having an undiluted solution outlet 21 is integrally provided at the other end. Thus, the heating evaporation tube 12 provided with the pair of electrode members 24 may be a ring-shaped electrode member 24 as shown in FIG. 1, or a plate-shaped electrode member 24 as shown in FIG. Also good.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, the circulation heater 10 is used to concentrate fluid foods such as juices and soups, but the circulation heater 10 can also be used to concentrate waste liquids and to decoction crude drugs and herbal medicines. Furthermore, the circulation type heater 10 can be used to produce distilled liquor in which the vaporized components are condensed.

10 Circulation heater 11 Stock solution storage tank 12 Heating evaporation pipe 13 Heating channel 14 Injection pipe 17 Supply pipe 21 Stock solution outlet 22 Circulation port 23 Circulation pipe 24 Electrode member 28 Power supply units 31, 33 Steam extraction pipe 34 Suction pump 51 Output Transformer 52 Tap changer 53-56 Switch 60 Controller

Claims (5)

a heating and evaporating pipe having a lower end connected to a supply pipe connected to a stock solution storage tank that stores the stock solution and generating an evaporating component from the stock solution while conveying the stock solution supplied from the stock solution storage tank to a heating channel;
It is connected between the undiluted solution storage tank and the undiluted solution outlet provided at the upper end of the heating evaporation pipe at a position lower than the liquid level of the undiluted solution, and the undiluted solution heated by the heating evaporation pipe is supplied to the undiluted solution storage tank. a return circulation pipe;
a steam extraction pipe for discharging the steam generated from the undiluted solution to the outside;
an electrode member that is provided in a pair with the heating and evaporating tube and supplies current from a power supply unit to the stock solution flowing through the heating channel to generate Joule heat;
The power supply unit
an output transformer having a plurality of feed taps for outputting different output voltages;
a tap changer for switching on any one of the plurality of feed taps to output power to the electrode member;
a controller for controlling the tap changer to switch to a lower output voltage or feed tap to increase current when the current through the stock solution approaches the maximum current at the set maximum power of the ON feed tap;
A circulating heater that discharges a steam component generated from the undiluted liquid by the Joule heat to the steam extraction pipe . In the circulation heater according to claim 1,
A circulating heater comprising a conductivity sensor for detecting the conductivity of the concentrate, calculating the current flowing through the concentrate based on the conductivity of the concentrate, and controlling the tap changer . In the circulation heater according to claim 1,
A circulating heater having a temperature sensor for detecting the temperature of the concentrate, calculating a current flowing through the concentrate based on the temperature of the concentrate, and controlling the tap changer. In the circulation heater according to claim 1,
A circulation type heater in which the circulation pipe is provided with a bent portion that is positioned at the same level as or higher than the liquid level of the raw solution at the upper end of the heating evaporation pipe. In the circulation heater according to claim 1,
A circulating heater, wherein a suction pump is connected to the steam extraction pipe, and the pressure in the heating channel is set below atmospheric pressure.

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