JP7520766B2 - Distillation Apparatus - Google Patents

Description

The present invention relates to a distillation apparatus using a heat pump, and more specifically, to a distillation apparatus used to distill a raw material liquid containing a lower proportion of low-boiling-point components than high-boiling-point components to separate the low-boiling-point components.

The need for energy conservation in distillation equipment has been increasing in recent years, and various proposals have been made.

One such energy-saving technology is a distillation apparatus that uses a heat pump to pump up the heat contained in the cooling water used to cool the overhead vapor in an overhead condenser, which cools the overhead vapor of the distillation tower, and uses this heat as a heat source for a reboiler that reheats the bottom liquid of the distillation tower, thereby achieving energy savings (see Patent Document 1).

Patent No. 6612936

However, in the case of the distillation apparatus of Patent Document 1, the heat pumped up by the heat pump is used to heat the bottom liquid of the distillation tower. Therefore, if the bottom liquid of the distillation tower contains substances that cause scale formation, such as calcium or silica, for example, there is a problem that scale will form on the heat transfer surface (surface in contact with the bottom liquid) of the reboiler (heater) used to reheat the bottom liquid of the distillation tower, reducing the heat transfer efficiency and impairing the energy saving effect. In other words, if scale forms on the heat transfer surface (surface in contact with the bottom liquid) of the heat exchanger (reboiler heater) and the heat transfer efficiency decreases, it will lead to a situation where the intended energy saving effect cannot be obtained, even though the heat pump is used to pump up and utilize the heat from the overhead condenser.

In addition, one known method for removing low-boiling components such as low-boiling solvents and ammonia contained in the effluent is to perform distillation by directly injecting steam generated in a boiler into the bottom of the distillation tower, condensing the top vapor of the distillation tower, which contains a high proportion of low-boiling components, in an overhead condenser, recovering part of the condensate as a distillate, and refluxing the remainder of the condensate to the top of the distillation tower. However, this method has the problem of high running costs because steam generated in the boiler is used for distillation.

The present invention aims to provide a distillation apparatus that can effectively utilize the heat contained in the cooling water used to cool the overhead vapor by pumping it up with a heat pump as a heat source for distillation operations, and that can suppress the formation of scale on the equipment even when the treated liquid contains substances that cause scale formation, without requiring a reboiler to reheat the bottom liquid of the distillation tower as in the distillation apparatus of Patent Document 1, and can perform stable, continuous operation with high energy efficiency.

In order to solve the above problems, the distillation apparatus of the present invention comprises:
a first distillation column for distilling a raw material liquid containing a low boiling point component and a high boiling point component;
a steam generator for heating pure water to generate steam to be blown into the bottom liquid of the first distillation column;
a first condenser for cooling a first overhead vapor taken out from a top of the first distillation column with circulating cooling water for a first condenser to separate the first overhead vapor into a first condensate and a first vapor containing a higher proportion of low boiling point components than the first condensate;
a heat pump configured to recover heat from the first condenser circulating cooling water, the temperature of which has been increased by being used to cool the first column overhead vapor in the first condenser, and to raise the temperature level of the recovered heat by using electric power to supply the recovered heat to the steam generator as high-temperature water;
a second distillation column for distilling the first vapor, which is the vapor after partial condensation in the first condenser, by gas-liquid contact with a second condensate described below;
a second condenser for cooling and condensing a second overhead vapor taken out from the top of the second distillation column with circulating cooling water for a second condenser, and recovering a second condensate mainly composed of a low boiling point component;
a first reflux line for refluxing the first condensate in the first condenser to the first distillation column as a reflux liquid for the first distillation column;
a second reflux line for refluxing a portion of the second condensate in the second condenser to the second distillation column as a reflux liquid for the second distillation column;
and a pressure control mechanism for controlling the pressure within the system so that the temperature of the bottom liquid of the first distillation column is maintained at a predetermined temperature.

In the present invention, the "pure water" that is heated to generate steam in the steam generator refers to water from which components that cause scale formation, such as calcium and silicon, have been removed in advance using, for example, a water softener that uses ion exchange resin (so-called soft water), or water from which components that cause scale formation, such as calcium and silicon, have been removed in advance by purifying the water using a reverse osmosis membrane filter (so-called RO water).

In the distillation apparatus of the present invention, it is preferable that the pressure control mechanism is equipped with a vacuum suction means that draws a vacuum through the second condenser so that a predetermined degree of vacuum is achieved within the system.

In addition, the distillation apparatus of the present invention is preferably configured so that the pressure in the system is controlled by the pressure control mechanism so that the temperature of the bottom liquid of the first distillation column is 88°C or less.

In addition, in the distillation apparatus of the present invention, it is preferable that the raw material liquid contains a smaller proportion of low boiling point components than high boiling point components.

In the distillation apparatus of the present invention, pure water (e.g., soft water or RO water) from which components that cause scale such as calcium and silica have been removed is supplied to the steam generator, and high-temperature water supplied from a heat pump is used as a heating source to evaporate the pure water. The generated steam is then directly injected into the bottom liquid of the first distillation tower. Therefore, even if the bottom liquid contains components that cause scale such as calcium and silica, there is no risk of scale formation on the heat transfer surface of the reboiler, which would otherwise result in a decrease in heat transfer efficiency, as occurs when a reboiler is used to heat the bottom liquid of the distillation tower.

As a result, it is possible to provide a distillation apparatus that can stably and continuously perform highly energy-efficient distillation operations without causing problems such as the formation of scale on heat transfer surfaces, by using a heat pump to pump up the heat contained in the cooling water used to cool the overhead vapor and effectively utilize the heat as a heat source for the distillation operations.

In addition, since the steam generator only comes into contact with pure water, the high-temperature fluid (working fluid) that carries the heat pumped by the heat pump, there is no risk of scaling or corrosion, and a sufficient heat transfer coefficient can be ensured, so there is a high degree of freedom in selecting the type and constituent materials of the steam generator, making it possible to reduce costs.

In the distillation apparatus of the present invention, the pressure control mechanism is equipped with a vacuum suction means that draws a vacuum through a second condenser so that the system is at a predetermined vacuum level. This makes it possible to control the temperature in the system to a level that allows efficient use of the heat recovered by the heat pump without the need for equipment with a complex structure, thereby making the present invention more effective.

Furthermore, when the pressure in the system is controlled by a pressure control mechanism so that the temperature of the bottom liquid of the first distillation column is 88°C or lower, the heat pump can be operated under conditions with a high COP, thereby achieving higher energy saving efficiency.
That is, the maximum temperature of the high-temperature side fluid (working fluid) (high-temperature water) obtained from a general-purpose heat pump is about 95° C., and if the return temperature of the working fluid (low-temperature side fluid) returning from the steam generator to the heat pump is 90° C., the temperature of the steam generated in the steam generator will be about 88° C. Therefore, by adjusting the operating pressure in the system including the inside of the distillation column so that the temperature of the bottom liquid of the first distillation column is 88° C. or less, the steam generated from the steam generator can be stably blown into the bottom liquid of the first distillation column, making it possible to perform an efficient and stable distillation operation.

In addition, in the distillation apparatus of the present invention, steam generated by the steam generator is blown into the bottom liquid of the first distillation column. Therefore, when the raw material liquid contains a smaller proportion of low boiling point components than high boiling point components, it is possible to perform efficient stripping and separate the low boiling point components, making the present invention more effective.

1 is a flow sheet showing the configuration of a distillation apparatus according to one embodiment of the present invention.

Below, we will present an embodiment of the present invention and explain the features of the present invention in more detail.

In this embodiment, a distillation apparatus is used as an example to distill a raw material liquid (liquid to be treated) that contains 1.0 wt% acetone, a low boiling point component, and the remainder (99.0 wt%) is water, a high boiling point component, to separate and recover acetone.

The distillation apparatus 100 in this embodiment is a distillation apparatus that uses a heat pump to improve energy conservation.

As shown in FIG. 1, the distillation apparatus 100 of this embodiment includes a first distillation column 1, a steam generator 1a, and a first condenser 11 that cools the overhead vapor (first overhead vapor) extracted from the top of the first distillation column 1.

The distillation apparatus 100 according to this embodiment also includes a heat pump HP that recovers heat from the circulating cooling water for the first condenser, a second distillation column 2 that distills the vapor (first vapor) after partial condensation in the first condenser 11, and a second condenser 22 that cools the top vapor (second top vapor) taken out from the top of the second distillation column 2.

In this embodiment, the first condenser 11 for cooling the first column top vapor and the second distillation column 2 for distilling the vapor (first vapor) after partial condensation in the first condenser 11 are integrally constructed. That is, the second distillation column 2 is disposed so as to be directly connected to the upper side of the first condenser 11, and the first vapor, which is the vapor after partial condensation in the first condenser 11, is directly supplied to the column bottom of the second distillation column 2.
However, as long as the first vapor, which is the vapor after partial condensation in the first condenser 11, is configured to be supplied to the bottom of the second distillation column 2, it is also possible to have a structure in which the first condenser 11 and the second distillation column 2 are separated.

The distillation apparatus 100 according to this embodiment is also equipped with a pressure control mechanism 40 that controls the pressure within the system so that the temperature of the bottom liquid of the first distillation column 1 is maintained at a predetermined temperature.

The pressure control mechanism 40 is configured to include a vacuum suction means 34 that performs vacuum suction via a second condenser so that the system is at a predetermined vacuum level. In this embodiment, a vacuum pump is used as the vacuum suction means 34.

In addition, in the distillation apparatus 100 according to this embodiment, as described below, the pressure in the system is controlled by the pressure control mechanism 40 so that the temperature of the bottom liquid in the first distillation column 1 is 88°C or lower.

Furthermore, the distillation apparatus 100 according to this embodiment is equipped with a first reflux line 31 for refluxing the condensate from the first condenser 11 to the first distillation column 1, and a second reflux line 32 for refluxing the condensate from the second condenser 22 to the second distillation column 2.
The following provides a detailed explanation.

The first distillation column 1 of the distillation apparatus 100 of the present invention is a distillation column that distills a raw material liquid that is an acetone aqueous solution (water 99.0 wt%) containing acetone at a ratio of 1.0 wt%.

In this embodiment, a packed tower is used as the first distillation tower 1. However, as the first distillation tower 1, it is possible to use towers of various configurations other than a packed tower, such as a plate tower.

The steam generator 1a heats the pure water to generate steam for directly heating the bottom liquid of the first distillation column 1. In this embodiment, an indirect heat exchanger that uses high-temperature water at 95°C from the heat pump HP (described below) as a heat source is used as the steam generator 1a.

Specifically, a falling film type heat exchanger made of stainless steel (SUS304) is used as the steam generator 1a.

In this embodiment, the pure water supplied to the steam generator 1a is RO water, which has been purified using a reverse osmosis membrane filter to remove components such as calcium and silicon that cause scale formation.

In addition, in this embodiment, the pure water supplied to the steam generator 1a is heated in the preheater 42 by heat exchange with the bottoms discharged from the bottom of the first distillation column 1, and energy is recovered.

In the first distillation column 1, acetone is distilled by gas-liquid contact between the steam generated in the steam generator 1a, the raw material liquid (feed liquid) that has been heated by passing through the preheater 41, and the reflux liquid that is the condensate condensed in the first condenser 11. The column bottom liquid (bottom liquid) from which acetone has been separated (removed) is discharged outside the system, while the column overhead vapor (first column overhead vapor), which contains a higher proportion of acetone than the raw material liquid, is supplied to the first condenser 11.

The first condenser 11 of the distillation apparatus 100 according to this embodiment cools the overhead vapor (first overhead vapor) taken out from the top of the first distillation column 1 with circulating cooling water for the first condenser, and separates it into a first condensate and a first vapor containing a higher proportion of acetone than the first condensate. This first condensate is then returned to the top of the first distillation column 1 as a reflux liquid.

That is, in the first condenser 11, mainly the high boiling point components (water) are condensed, and the condensate (aqueous acetone solution) containing 20 wt % acetone is returned to the top of the first distillation column 1 as a reflux liquid.

The distillation apparatus 100 according to this embodiment further includes a heat pump HP, which is used to cool the first overhead vapor in the first condenser 11, recovers heat from the heated circulating cooling water for the first condenser (54.5°C in this embodiment), and is configured to raise the temperature level of the recovered heat using electricity so that it can be supplied to the steam generator 1a as high-temperature water (95°C in this embodiment).

That is, in the distillation apparatus 100 according to the present invention, the heat pump HP recovers heat, for example, from the circulating cooling water for the first condenser used in the first condenser 11, raises the temperature level using electricity, and supplies it to the steam generator 1a, thereby circulating and utilizing the thermal energy.

Specifically, the circulating cooling water for the first condenser 11 is used to cool the first tower overhead vapor, and the heated temperature of the circulating cooling water for the first condenser is 54.5°C, which is then heat-recovered in the heat pump HP, and the circulating cooling water for the first condenser, whose temperature has been reduced to 49.5°C, is circulated and supplied to the first condenser 11.

Meanwhile, in the heat pump HP, the high-temperature water side circulating water (high-temperature water) whose temperature level has been raised to 95°C by electricity is supplied to the steam generator 1a, and the high-temperature water side circulating water used in the steam generator 1a and whose temperature has been reduced to 90°C is returned to the heat pump HP, where it is raised to a temperature level of 95°C and then supplied again to the steam generator 1a.

The distillation apparatus 100 of this embodiment further includes a second distillation column 2 that distills the first vapor, which is the vapor after partial condensation in the first condenser 11, and a second condenser 22 that cools the top vapor (second top vapor) extracted from the top of the second distillation column 2.

The second distillation column 2 is a distillation column that distills the first vapor, which is the vapor after partial condensation in the first condenser 11, by bringing it into gas-liquid contact with the second condensate condensed in the second condenser 22, and extracts a top vapor (second top vapor) having a higher acetone concentration from the top of the column. In this embodiment, a packed column is used as the second distillation column 2. However, as the second distillation column 2, various configurations such as a plate column, other than a packed column, can be used.

In the second distillation column 2, the vapor after partial condensation of the first condenser 11, which has a high acetone concentration, is distilled, and acetone is selectively extracted into the second condenser 22.

This second condenser 22 cools the second overhead vapor, which is the top vapor of the second distillation column 2, using circulating cooling water for the second condenser, and serves the function of condensing the acetone and water contained in the second overhead vapor.

A portion of the condensate condensed in the second condenser 22 is recovered as a recovery solvent, and the remaining condensate is returned to the top of the second distillation column 2 as a reflux liquid.

The distillation apparatus 100 of this embodiment is equipped with a first reflux line 31 so that the condensate in the first condenser 11 can be refluxed to the first distillation column 1 as a reflux liquid for the first distillation column 1.

In addition, a second reflux line 32 is provided so that the condensate in the second condenser 22 can be refluxed to the second distillation column 2 as reflux liquid for the second distillation column 2.

To explain further, in the distillation apparatus 100 of this embodiment, the gas in the system is discharged through the second condenser by the vacuum suction means 34, so that the distillation apparatus 100 is operated at an operating pressure (e.g., 25 kPaA or more and atmospheric pressure or less) such that the temperature of the bottoms liquid (bottoms) discharged from the bottom of the first distillation column 1 is 88°C, and the temperature level is raised by the heat pump HP so that the temperature of the high-temperature water supplied to the steam generator 1a is 95°C.

This is because, if the maximum temperature of the high-temperature side fluid (working fluid) (high-temperature water) obtained from a general-purpose heat pump HP is about 95°C, and the return temperature of the working fluid (low-temperature side fluid) returning from the steam generator 1a to the heat pump HP is 90°C, the temperature of the steam generated in the steam generator 1a will be about 88°C. Therefore, by adjusting the pressure (operating pressure) inside the equipment such as the first distillation column 1 and the second distillation column 2 so that the temperature of the bottom liquid of the first distillation column 1 is 88°C or lower, the steam generated from the steam generator 1a can be stably blown into the bottom liquid of the first distillation column 1, enabling efficient and stable distillation operations to be performed.

In addition, in the distillation apparatus 100 according to this embodiment, the raw material liquid supplied to the first distillation column 1 is an aqueous acetone solution with an acetone concentration of 1.0 wt%, and the acetone concentration of the discharged liquid discharged from the bottom of the first distillation column 1 is set to 0.001 wt% or less (10 ppm or less).

In such a situation, by applying the distillation apparatus 100 of this embodiment, it is possible to perform efficient distillation to save energy while reliably separating and recovering acetone, a low-boiling point component, from the raw material liquid.

In addition, in the distillation apparatus 100 according to this embodiment, the power of the heat pump HP is added as heat to the steam generator 1a of the first distillation column 1, and since the amount of cooling heat in the first condenser 11 is insufficient for the amount of heat added by the steam generator 1a, it becomes possible to utilize the surplus heat in the second distillation column 2, and the heat load in the second distillation column 2 becomes smaller. As a result, it becomes possible to make the column diameter of the second distillation column 2 smaller than the column diameter of the first distillation column 1, and it is possible to reduce the equipment cost.

Next, we will explain an example of the operational results when distilling a raw material liquid (liquid to be treated) containing acetone and water using the distillation apparatus 100 according to this embodiment.

When distilling a raw material liquid using the distillation apparatus 100 according to the present embodiment, an aqueous acetone solution having a temperature of 20° C. and an acetone concentration of 1.0 wt % was supplied as the raw material liquid to the first distillation column 1 via the preheater 41 at a rate of 3000 kg/hr.
Here, the amount of acetone in the raw material liquid supplied to the first distillation column 1 is 30 kg per hour.

In addition, pure water was preheated in preheater 42 and then evaporated in steam generator 1a, and the generated steam was supplied by directly blowing it into the bottom liquid of first distillation column 1 at a rate of 158 kg/hr.

Meanwhile, water with a temperature of 25°C and an acetone concentration of 10 ppm or less (treated liquid from which most of the acetone had been separated) was discharged from the system as the bottom liquid from the first distillation column 1 at a rate of 3,127 kg/hr.

Here, the amount of acetone discharged from the system as the bottom liquid is approximately 0.03 kg/hr (3127 kg/hr x 0.001/100 = 0.03 kg/hr).

In addition, in the second distillation column 2, a vapor having a temperature of 43°C and an acetone concentration of 98.0 wt% is extracted from the top of the column as a top vapor (second top vapor) at a rate of 63.4 kg/hr.

Furthermore, in the second condenser 22, the overhead vapor of the second distillation column 2 (second overhead vapor) is cooled and condensed. This condensate has a temperature of 43°C, an acetone concentration of 98.0 wt%, and is produced at a rate of 63.4 kg/hr.

Of the 63.4 kg/hr of condensate, 33.0 kg/hr (acetone concentration: 98.0 wt%) is refluxed to the second distillation column 2, while 30.4 kg/hr of recovered solvent with an acetone concentration of 98.0 wt% is recovered as recovered solvent.

Here, the amount of acetone recovered as the recovered solvent is approximately 29.8 kg (30.4 kg/hr x 0.98 = approximately 29.8 kg).

When considering a conventional distillation apparatus that uses steam as a heat source, the amount of heat generated by the steam is 133.5 kW, so the primary energy is 133.5 kW. On the other hand, in the case of the distillation apparatus 100 that uses the heat pump HP in this embodiment, the power of the heat pump HP is 28.5 kW, and if the primary energy conversion coefficient is 2.57, the primary energy is 73.2 kW, which is the product of the power of the heat pump HP and the primary energy conversion coefficient.

Therefore, by using the distillation apparatus 100 according to this embodiment, the primary energy reduction rate is 45% compared to the conventional steam-type distillation apparatus described above, and it is clear that a significant energy saving effect can be obtained.

In the distillation apparatus 100 according to this embodiment, the steam generated by the steam generator 1a is blown into the bottom liquid of the first distillation column 1. Therefore, as described above, when the raw material liquid contains a smaller proportion of low boiling point components than high boiling point components (1.0 wt% acetone as a low boiling point component and 99.0 wt% water as a high boiling point component), efficient stripping can be performed to separate the low boiling point components.

Note that the various quantities of the raw material liquid, bottom liquid, first and second condensate liquids, first and second vapors, etc., as well as the values of temperature, acetone concentration, energy consumption (kW), pressure, etc., described in the above embodiment or shown in FIG. 1 are merely examples, and the present invention does not exclude cases where these values are different from those in the above embodiment.

In the above embodiment, the case where acetone is recovered by distilling a raw material liquid in which the low boiling point component is acetone and the high boiling point component is water has been described as an example, but in the present invention, the type of low boiling point component is not limited to the above embodiment, and the low boiling point component may be ammonia, methanol, ethanol, propanol, butanol, isopropyl alcohol, ethyl acetate, methyl acetate, ethyl formate, methyl propionate, ethyl propionate, methyl ethyl ketone, acetaldehyde, acetonitrile, allyl alcohol, chloroform, cyclohexane, carbon tetrachloride, dichloroethane, dichloromethane, carbon disulfide, diethyl ether, tetrahydrofuran, trichloroethylene, benzene, heptane, hexane, etc.

The present invention is not limited to the above-described embodiments in any other respects, and applications and modifications are possible within the scope of the invention.

For example, in a distillation apparatus operated under conditions in which the top vapor of the distillation tower is heated, heat can be recovered from the cooling water of the condenser used to cool the top vapor of the distillation tower and used as a heating source. In this case, the cooling water of the condenser can be pure water, which is evaporated by heat exchange with the top vapor of the distillation tower in the condenser, the generated steam can be compressed in a steam compressor, and the resulting pressurized steam can be blown into the distillation tower.

Reference Signs List 1 First distillation column 2 Second distillation column 1a Steam generator 11 First condenser 22 Second condenser 31 First reflux line for refluxing the condensate of the first condenser to the first distillation column 32 Second reflux line for refluxing the condensate of the second condenser to the second distillation column 34 Vacuum suction means (vacuum pump)
40 Pressure control mechanism 41 Feed liquid preheater 42 Pure water preheater 51 Pure water circulation pump 52 Bottoms pump 100 Distillation apparatus HP Heat pump

Claims (4)

a first distillation column for distilling a raw material liquid containing a low boiling point component and a high boiling point component;
a steam generator for heating pure water to generate steam to be blown into the bottom liquid of the first distillation column;
a first condenser for cooling a first overhead vapor taken out from a top of the first distillation column with circulating cooling water for a first condenser to separate the first overhead vapor into a first condensate and a first vapor containing a higher proportion of low boiling point components than the first condensate;
a heat pump configured to recover heat from the first condenser circulating cooling water, the temperature of which has been increased by being used to cool the first column overhead vapor in the first condenser, and to raise the temperature level of the recovered heat by using electric power to supply the recovered heat to the steam generator as high-temperature water;
a second distillation column for distilling the first vapor, which is the vapor after partial condensation in the first condenser, by gas-liquid contact with a second condensate described below;
a second condenser for cooling and condensing a second overhead vapor taken out from the top of the second distillation column with circulating cooling water for a second condenser, and recovering a second condensate mainly composed of a low boiling point component;
a first reflux line for refluxing the first condensate in the first condenser to the first distillation column as a reflux liquid for the first distillation column;
a second reflux line for refluxing a portion of the second condensate in the second condenser to the second distillation column as a reflux liquid for the second distillation column;
and a pressure control mechanism for controlling the pressure within the system so that the temperature of the bottom liquid of the first distillation column is maintained at a predetermined temperature. The distillation apparatus according to claim 1, characterized in that the pressure control mechanism is equipped with a vacuum suction means that performs vacuum suction through the second condenser so that a predetermined degree of vacuum is achieved within the system. The distillation apparatus according to claim 1 or 2, characterized in that the pressure in the system is controlled by the pressure control mechanism so that the temperature of the bottom liquid of the first distillation column is 88°C or less. A distillation apparatus according to any one of claims 1 to 3, characterized in that the raw material liquid contains a lower proportion of low-boiling point components than high-boiling point components.

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