JP7378129B2 - Separation device and method for low boiling point substances - Google Patents

Description

The present invention relates to a separation device and a separation method for separating low-boiling substances such as ammonia from a raw solution such as waste water containing the above-mentioned low-boiling substances .

For example, a steam stripping method is known as a method for separating and removing ammonia-containing wastewater. A general ammonia recovery device using this steam stripping method is equipped with a distillation column that performs steam stripping, and the ammonia-containing vapor discharged from the top of the distillation column is condensed in a condenser, and the condensed water is It is returned to the top of the distillation column as a reflux liquid, and the remaining concentrated ammonia-containing vapor is supplied to an absorption column where it is absorbed by water and taken out as recovered ammonia water.

By the way, the steam stripping method used in such ammonia recovery equipment is a method in which steam is directly blown into the bottom of the distillation column, and since a large amount of steam is used, running costs are high and there is a need to reduce processing costs. ing. On the other hand, with this method, almost the same amount of ammonia-containing steam is generated as the input steam, but in order to use this as reflux liquid and recovered ammonia liquid at the top of the distillation column, it is necessary to It must be cooled by a heat exchanger (condenser), and the energy is disposable.

In order to solve these problems, a method has been proposed in which the steam discharged from the top of the distillation column is compressed by a steam compressor, and the heat is recovered by a reboiler to reduce the amount of water vapor (see the following patent document). (see 1). In addition, make-up water is supplied to a condenser that condenses the ammonia-containing vapor discharged from the top of the distillation column, and the make-up water is evaporated by exchanging heat with the ammonia-containing vapor, and is led to a vapor compressor for compression and compression. A configuration has been proposed in which the temperature is raised and the water vapor is reused as water vapor (see Patent Document 2 below).

Japanese Patent Application Publication No. 2002-28637 Japanese Patent Application Publication No. 2004-114029

The conventional examples disclosed in Patent Documents 1 and 2 mentioned above effectively utilize the heat of ammonia-containing steam discharged from the top of the distillation column to save energy and reduce running costs.

However, in such a conventional structure including at least a distillation column, a heat exchanger (reboiler or condenser: these reboilers or condensers correspond to the evaporator of the present application), and a vapor compressor, for example, 20 wt% or more When attempting to recover highly concentrated ammonia, the following problems arise. In other words, if you try to increase the concentration to a high concentration using only a heat exchanger (equivalent to the evaporator in this application), the temperature difference between the inlet and outlet of the ammonia-containing vapor in the heat exchanger will increase, and the load on the vapor compressor will increase accordingly. becomes too large, which goes against the request to save energy by using a vapor compressor. Note that the above-mentioned problem is common to recovery apparatuses that contain not only ammonia but also a wide range of low-boiling substances. Therefore, there has been a demand for a low boiling point substance recovery device that can effectively save energy.

The present invention was devised in view of the above-mentioned problems, and its purpose is to provide a separation device and a separation method for low-boiling substances that effectively save energy.

In order to achieve the above object, the invention according to claim 1 brings a stock solution containing a low boiling point substance into contact with steam for heating, separates the low boiling point substance from the stock solution and gasifies it, and converts the low boiling point substance into vapor containing the low boiling point substance to the top of the column. A distillation column that stores treated water from which low-boiling substances have been removed from the raw solution at the bottom of the column, and steam containing low-boiling substances discharged from the top of the distillation column and water for heat exchange. By this, the vapor containing the low boiling point substance is partially condensed, the vapor containing the low boiling point substance is concentrated, and the water vapor is evaporated and the water vapor is discharged as water vapor. A device for separating low boiling point substances, comprising: a compression device for raising the temperature, compressing the heated steam, and guiding the heated steam to the distillation column to use it as heating steam used in the distillation column, wherein the evaporation section is , has a configuration in which at least two divided evaporators are connected in series along the flow direction of the vapor containing the low boiling point substance, the two divided evaporators are each provided with the compression device, and the two divided evaporators are each provided with the compression device; The compression device provided in the upstream divisional evaporation section in the flow direction of the vapor containing the low-boiling point substance compresses the water vapor more than the compression device installed in the downstream divisional evaporation section. It is characterized by a small temperature difference during compression heating .

According to the above configuration, the upstream compression device has a smaller temperature difference when compressing and heating water vapor than the downstream compression device, so the load on the upstream compression device is smaller. Energy saving of the device can be achieved. In addition, since the water vapor compressed and heated by the upstream compression device has a relatively high temperature, its specific volume becomes small, so the upstream compression device can be made smaller accordingly. .

The invention according to claim 2 is the low boiling point substance separation device according to claim 1, characterized in that the two divided evaporation sections are formed by partitioning one evaporator.
In the present invention, the terms "(divided) evaporator" and "evaporator" can also be paraphrased, for example, as "(divided) heat exchange section" and "heat exchanger."

Although it is possible to use two evaporators as the two divided evaporators, the above-mentioned configuration in which one evaporator is partitioned makes it possible to make the device more compact and reduce costs. can be achieved.

The invention according to claim 3 is the low boiling point substance separation device according to claim 1 or 2 , wherein the compression device provided in the upstream divided evaporation section is arranged in the downstream divided evaporation section. It is characterized in that it is smaller than the provided compression device .

According to the above configuration, it is possible to further save energy and make the device more compact .
Note that one compressor stage of two compressors is smaller than the other means that one compressor stage is smaller in power consumption and/or size than the other. Also, for example, by preparing three or more compression devices, dividing them into two groups, and configuring one group with fewer compression devices than the other group, it is possible to configure a compression device smaller than the other group. Can be done.

The invention according to claim 4 is the low boiling point substance separation device according to any one of claims 1 to 3, characterized in that the stock solution contains water and a low boiling point substance. do.
As the "low boiling point substance", for example, a substance having a boiling point lower than that of water can be used, and more specifically, alcohols such as ammonia and methanol, ketones such as acetone, esters such as methyl acetate, etc. can be used.
As "water", pure water, soft water, ion exchange water, etc. can be used .

The invention according to claim 5 is the low boiling point substance separation device according to any one of claims 1 to 4, characterized in that the compression device includes a heat pump and/or a steam ejector .
Examples of the "heat pump" include vapor compressors such as roots-type vapor compressors, turbo-type vapor compressors, screw-type vapor compressors, and vane-type vapor compressors.

In the invention as set forth in claim 6, steam containing a low boiling point substance is generated from a stock solution containing a low boiling point substance and introduced into the evaporation section, and the steam containing the low boiling point substance is heat exchanged with water. The steam containing the substance is condensed and concentrated, the water is evaporated and discharged as steam, and this steam is heated in a compression device and used as heating steam to generate the steam containing the low boiling point substance. A method for separating a low-boiling point substance, wherein the evaporation section has a structure in which at least two divided evaporation sections are connected in series along the flow direction of vapor containing the low-boiling point substance, and the two divided evaporation sections The compression device is provided in each of the two divisional evaporation sections, and the compression device is installed in the upstream divisional evaporation section in the flow direction of the vapor containing the low boiling point substance among the two divisional evaporation sections, and the compression device is installed in the downstream divisional evaporation section. The present invention is characterized in that the temperature difference when heating the water vapor is smaller than that of the compression device .

According to the above configuration, a method for separating low-boiling substances that effectively saves energy is constructed.

According to the present invention, it is possible to effectively save energy when separating low boiling point substances such as ammonia from a stock solution such as ammonia-containing wastewater.

FIG. 1 is an overall configuration diagram of an ammonia recovery device according to an embodiment. FIG. 2 is an enlarged view of the vicinity of the evaporator in the ammonia recovery device of FIG. 1. FIG. 2 is an enlarged view of the vicinity of the concentration column in the ammonia recovery device of FIG. 1. This is a vapor-liquid equilibrium diagram of a mixture of water and ammonia at atmospheric pressure, showing the ammonia concentration from 0 to 100%. This is a vapor-liquid equilibrium diagram of a mixture of water and ammonia at atmospheric pressure, showing ammonia concentrations ranging from 0 to 50%. An enlarged view of a modified example for comparison, in which the evaporation section is configured with a single evaporator. FIG. 7 is an enlarged view of a modification example in which a plurality of divided evaporation sections are formed by partitioning one evaporator. FIG. 8 is a plan view of the evaporator of FIG. 7; An enlarged view of a modified example using a steam ejector as a temperature raising means.

Hereinafter, the present invention will be described in detail based on embodiments. In the following embodiments, an ammonia recovery apparatus that uses ammonia-containing wastewater as a stock solution and separates and removes ammonia from the ammonia-containing wastewater to recover it will be described as an example of a low-boiling point substance separation apparatus. In addition to ammonia, the low boiling point substance can also be applied to alcohols such as methanol, ketones such as acetone, and esters such as methyl acetate.

(Embodiment) FIG. 1 is an overall configuration diagram of an ammonia recovery apparatus according to an embodiment. An ammonia recovery device (corresponding to the low boiling point substance separation device of the present invention) 1 includes a distillation column 2 into which heating steam is blown and performs steam stripping, and ammonia-containing steam and water discharged from the top of the distillation column 2. an evaporator 3 that exchanges heat and evaporates water; a compressor 18 that compresses and heats the water vapor discharged from the evaporator 3 and discharges it to the distillation column 2 as heating steam; and ammonia concentrated in the evaporator 3. A concentrating tower 5 that takes in the steam containing the ammonia, cools the steam, removes moisture, and increases the concentration of the ammonia-containing steam to a high concentration (for example, 20 wt% or more); The first absorption tower 6 generates recovered ammonia water with a predetermined concentration, and the second absorption tower 7 prevents uncondensed ammonia-containing vapor in the first absorption tower from being discharged to the outside. Here, to briefly explain the features of the ammonia recovery apparatus 1 according to the present embodiment, the evaporator 3 has two evaporators 3A and 3B as two divided evaporators along the flow direction of ammonia-containing vapor. These two evaporators 3A and 3B are respectively provided with vapor compressors 18A and 18B as heating means, and the ammonia-containing The vapor compressor 18A provided in the upstream evaporator 3A in the vapor flow direction has a smaller temperature difference when compressing and heating water vapor than the vapor compressor 18B provided in the downstream evaporator 3B. That's true.

Hereinafter, the specific configuration of the ammonia recovery apparatus 1 will be explained, including the above-mentioned characteristic configuration.
The distillation column 2 may have multiple stages, or may not be limited to this, and may also have non-multistages. That is, the distillation column 2 can be a tray column or a packed column. A stock solution (ammonia-containing wastewater) is supplied to the top of the distillation column 2 via a stock solution supply pipe L1. Note that the pH of the stock solution may be adjusted in advance.

Heating steam from the steam ejector 10 is supplied to the bottom of the distillation column 2 via a heating steam supply pipe L3. The bottom of the distillation column 2 is connected to the heat recovery tank 11 via a pipe L4, and the liquid stored at the bottom of the column (low concentration aqueous ammonia) is supplied to the heat recovery tank 11 via the pipe L4. It has become. The steam ejector 10 is a steam compression means that sucks and compresses steam, and the steam suction side 10a includes a steam supply pipe L5 through which steam supplied from a high-pressure steam source (not shown) such as a boiler flows, and a heat pipe. A steam reuse pipe L6 extending from the recovery tank 11 is connected. With such a configuration, the stored liquid in the heat recovery tank 11 is flash-evaporated, sucked and compressed by the steam ejector 10, mixed with steam from the steam supply pipe L5, and is supplied to the bottom of the distillation column 2 as heating steam. is blown into. In this way, the liquid stored in the heat recovery tank 11 flash-evaporates and is reused as part of the heating steam, thereby recovering heat.

In addition, a discharge pipe L7 for discharging treated water (for example, low concentration ammonia water of 30 ppm or less) is connected to the bottom of the heat recovery tank 11, and on this discharge pipe L7, a pump P1 for discharging treated water, and three heat exchangers H1, H2, H3 are provided. The heat exchanger H1 is a water heater that heats water by exchanging heat between water and treated water. Water heated by this heat exchanger H1 is supplied to the bottoms of the evaporators 3A and 3B via a water supply pipe L8. The heat exchanger H2 is a stock solution preheater that exchanges heat between the stock solution and the treated water to preheat the stock solution. The stock solution preheated by the heat exchanger H2 is supplied to the top of the distillation column 2 via the stock solution supply pipe L1. The heat exchanger H3 is a cooler that exchanges heat between cooling water and treated water to cool the treated water. The treated water cooled by the heat exchanger H3 is discharged to the outside of the system via the discharge pipe L7.
The heat exchangers H1, H2, and H3 are located downstream of the treated water discharge pump P1 on the discharge pipe L7, and are installed in the following order. That is, on the discharge pipe L7, the heat exchanger H1 is installed upstream of the heat exchanger H2. By installing in this order, the amount of heat given from the treated water to the water is maximized, so that energy saving can be achieved in the evaporation section 3 that heats the water. Moreover, since the reason for installing the heat exchanger H3 is to cool the treated water, the heat exchanger H3 is installed downstream from the heat exchangers H1 and H2.

The evaporation section 3 is configured by connecting two evaporators 3A and 3B in series in this order along the flow direction of the ammonia-containing vapor between the top of the distillation column 2 and the top of the concentration column 5. , these evaporators 3A and 3B are respectively constituted by horizontal tube type evaporators 12A and 12B, and are equipped with diffusers 13A and 13B and indirect heaters 14A and 14B. In addition, the evaporator is not limited to the horizontal tube type, and for example, a thin film falling (vertical tube) type evaporator may be used. Of the two evaporators 3A and 3B, in the flow direction of the top vapor (ammonia-containing vapor) discharged from the top of the distillation column 2 and supplied to the evaporation section 3 through the steam supply pipe L10 described below. In the evaporator (hereinafter also referred to as "upstream evaporator") 3A disposed on the upstream side, the indirect heater 14A includes a heat exchanger tube group 15A consisting of one or more horizontal heat exchanger tubes, as shown in FIG. and a pair of headers 16R and 16L on the upstream side and downstream side (right side and left side in the figure). Further, the bottom of the evaporator 12A is a storage section 17A that stores water supplied through the pipe L8. The stored liquid (water) in the storage section 17A is supplied by the circulation pump P2A via the pipe L9A to the sprayer 13A provided in the upper part of the evaporator 12A, and from the sprayer 13A to the outer surface of the heat transfer tube group 15A. After being sprayed toward the evaporator 12A, the evaporator 12A is configured to perform a circulation in which the evaporator 12A flows down to the lower storage section 17A.
On the other hand, of the two evaporators 3A and 3B, the indirect heater 14B and the storage in the evaporator 3B (hereinafter also referred to as "downstream evaporator") arranged on the downstream side in the flow direction of the tower top vapor The configurations of the section 17B, the circulation pump P2B, the pipe L9B, and the sparge device 13B are all the same as in the case of the upstream side evaporator 3A, so the description thereof will be omitted.

The upstream header 16R in the upstream evaporator 3A is connected to the top of the distillation column 2 via a steam supply pipe L10, and the top vapor (ammonia-containing vapor) discharged from the top of the distillation column 2 is , is guided to the upstream header 16R through the steam supply pipe L10, and further flows through the heat exchanger tube group 15A. Here, the pressure of the upstream evaporator 3A is lower than the pressure of the tower top steam, so the circulating liquid (water) sprayed by the sprayer 13A evaporates in a thin film on the surface of the heat transfer tube group 15A. , water vapor is generated. This water vapor is supplied to a vapor compressor (hereinafter also referred to as "upstream vapor compressor") 18A provided in the upstream evaporator 3A in the compression device 18. Here, to explain in more detail the principle of vaporizing water in the upstream evaporator 3A, in the upstream evaporator 3A, the heat exchanger tube in which the water is heated is heated from the tower top steam (inside the heat exchanger tube) which is the heating source. The water evaporates because the pressure outside is low. Note that the pressure difference is generated by the compression device 18 (specifically, the upstream vapor compressor 18A). This is because the pressure on the outside of the evaporator heat exchanger tube connected to the suction side of the compression device 18 is low, and the pressure in the distillation column 2 connected to the discharge side of the compression device 18 and the pressure at the top of the column is high. In addition, the pressure in the distillation column 2 also increases due to the steam supplied from the steam ejector 10, which becomes a factor in the evaporation of water in the upstream evaporator 3A.
Further, the condensed water (low concentration ammonia water) that flows through the heat transfer tube group 15A and condenses is stored in the downstream header 16L. The downstream header 16L is connected to the upstream header of the downstream evaporator 3B, and the condensed water (low concentration ammonia water) stored in the downstream header 16L of the upstream evaporator 3A is transferred to the pipe L19. By driving the condensed water pump P3, the condensed water is returned from the downstream header of the downstream evaporator 3B to the top of the distillation column 2 as a reflux liquid via the pipe L11. The remaining surplus vapor (concentrated ammonia-containing vapor) is discharged from the downstream header of the downstream evaporator 3B to the top of the concentrating column 5 via the pipe L12.

In addition to the upstream vapor compressor 18A, the compression device 18 also includes a vapor compressor (hereinafter also referred to as "downstream vapor compressor") 18B provided in the downstream evaporator 3B. The downstream vapor compressors 18A and 18B connect the bottom of the distillation column 2 to the upper portions of the upstream evaporator 3A and downstream evaporator 3B, respectively. That is, the inlet side of the upstream vapor compressor 18A is connected to the upper part of the evaporator 12A in the upstream evaporator 3A via a pipe L15, and the outlet side of the upstream vapor compressor 18A is connected to the distillation column 2 via a pipe L16. is connected to the bottom of the tower. The inlet side of the downstream vapor compressor 18B is connected to the upper part of the evaporator 12B in the downstream evaporator 3B via a pipe L17, and the outlet side of the downstream vapor compressor 18B is connected to the column of the distillation column 2 via a pipe L18. Connected to the bottom.

Here, roots-type vapor compressors with a large maximum differential pressure are used as the upstream and downstream vapor compressors 18A and 18B. However, in the present invention, the present invention is not limited to the Roots-type vapor compressor, and any of a turbo-type vapor compressor, a screw-type vapor compressor, a vane-type vapor compressor, or other vapor compressors may be used. Although the compression device 18 in this embodiment is composed of two vapor compressors 18A and 18B, one each on the upstream side and the downstream side, two or more vapor compressors 18A and 18B are provided on at least one of the upstream side and the downstream side, It may be configured with a total of three or more vapor compressors.

As shown in FIG. 1, the concentration tower 5 is composed of a spray type scrubber. The stored liquid (condensed liquid) stored at the bottom of the concentration tower 5 flows through a spray pipe (corresponding to the circulation line of the present invention) L20, is guided to the top of the tower, and is sprayed into the top of the tower. It has become. A circulation pump P4 and a heat exchanger H4 are provided in the middle of this spray pipe L20. The stored liquid flowing through the spray pipe L20 is cooled by exchanging heat with the cooling water in the heat exchanger H4. As shown in FIG. 3, a control valve V1 is provided in the pipe L21 through which the cooling water flows, and its opening degree is controlled by a temperature sensor T that detects the temperature of the stored liquid stored at the bottom of the concentrating tower 5. There is. That is, the opening degree of the control valve V1 is controlled according to the detection result of the temperature sensor T, and the flow rate of the cooling water passing through the heat exchanger H4 is adjusted. Thereby, by cooling the stored liquid (condensed liquid) to a predetermined temperature and spraying it, ammonia-containing vapor with a predetermined high concentration ( for example, 20 wt % or more) can be generated.

Further, the spray pipe L20 is branched in the middle, and this branched branch pipe L22 is connected to the top of the distillation column 2. A control valve V2 is provided in the middle of the branch pipe L22. Further, the concentration tower 5 is provided with a liquid level sensor S1 that detects the liquid level of the stored liquid. The liquid level sensor S1 includes a level switch S1a that detects an upper limit setting level and a level switch S1b that detects a lower limit setting level. This liquid level sensor S1 controls the opening degree of the control valve V2, so that the stored liquid is maintained at a predetermined liquid level, and the stored liquid that has overflowed the predetermined liquid level is refluxed to the top of the distillation column 2. It has become.

As shown in FIG. 1, the first absorption tower 6 is composed of a spray type scrubber similar to the concentration tower 5, and a circulation pump P5 is connected to the spray pipe L23 through which the liquid stored in the first absorption tower 6 is circulated. , and a heat exchanger H5. In the heat exchanger H5, the stored liquid flowing through the spray pipe L23 and the cooling water exchange heat, and the stored liquid is cooled. The cooled stored liquid is sprayed onto the highly concentrated (for example, 20 wt% or more) ammonia-containing steam taken in from the concentration tower 5 via the pipe L24, thereby condensing and recovering the ammonia-containing steam, and converting the recovered ammonia water into generate. The spray pipe L23 is branched in the middle, and the recovered ammonia water is discharged out of the system via this branch pipe L25.

The second absorption tower 7 is composed of a spray type scrubber similar to the first absorption tower 6, and water is supplied to the bottom of the second absorption tower 7 via a pipe L30 and stored at the bottom of the tower. Water is sprayed from the top of the tower through a spray pipe L31 by driving a circulation pump P6. Between the first absorption tower 6 and the second absorption tower 7, there is a pipe L32 that guides the uncondensed ammonia-containing vapor in the first absorption tower 6 to the top of the second absorption tower 7, and a pipe L32 inside the second absorption tower 7. A pipe L33 for returning the condensed water to the first absorption tower 6 is provided. Furthermore, an exhaust pipe L34 is provided at the top of the second absorption tower 7 to exhaust the steam from which ammonia has been removed.
In addition, in FIGS. 1 to 3, L40 is a cooling water supply pipe, L41 is a pipe branched from the cooling water supply pipe L40, L21 is a pipe branched from the cooling water supply pipe L40, and there is no pipe on the cooling water supply pipe L40. A heat exchanger H5 is provided, a heat exchanger H3 is provided on the tube L41, and a heat exchanger H4 is provided on the tube L21.

Next, the processing operation of the ammonia recovery apparatus 1 having the above configuration will be explained. The distillation column 2 is blown with heating steam to perform steam stripping. That is, in the distillation column 2, the stock solution is brought into contact with heating steam, ammonia is separated from the stock solution, gasified, and discharged from the top of the column as ammonia-containing vapor, and low-concentration ammonia water from which ammonia has been removed from the stock solution (e.g. 30 ppm or less) is stored at the bottom of the tower as treated water.

The ammonia-containing vapor discharged from the top of the distillation column 2 is guided to the upstream header 16R of the upstream evaporator 3A through the vapor supply pipe L10, and further flows through the heat exchanger tube group 15A, thereby The circulating fluid (water) sprayed by the sprayer 13A evaporates into a thin film on the surface of the heat transfer tube group 15A, generating water vapor. This water vapor is supplied to the upstream vapor compressor 18A. On the other hand, the condensed water (low concentration ammonia water) flowing through the heat exchanger tube group 15A and condensed is stored in the downstream header 16L, and is stored in the tube L19, the upstream header in the downstream evaporator 3B, the heat exchanger tube group and the downstream. After passing through the side header, it is returned to the top of the distillation column 2 as a reflux liquid via the pipe L11, and the remaining surplus vapor (concentrated ammonia-containing vapor) is fed to the concentrating column 5 via the pipe L12.

In the compression device 18 (vapor compressors 18A and 18B), the supplied water vapor is compressed and heated, and is input into the bottom of the distillation column 2 as heating water vapor. Thereby, the heating steam supplied from the heating steam supply pipe L3 can be reduced, and energy saving can be achieved.

In addition, in the ammonia recovery apparatus 1 according to the present embodiment, as described above, the evaporator 3 uses two evaporators as two divided evaporators, that is, the upstream evaporator 3A and the downstream evaporator 3B, to produce ammonia-containing steam. The upstream evaporator 3A and the downstream evaporator 3B are respectively provided with an upstream vapor compressor 18A and a downstream vapor compressor 18B, which are temperature increasing means. , of the two evaporators 3A and 3B, the vapor compressor 18A provided in the upstream evaporator 3A in the flow direction of ammonia-containing vapor is the vapor compressor 18B provided in the downstream evaporator 3B. It is characterized by a smaller temperature difference when compressing and heating water vapor. Hereinafter, a detailed supplementary explanation will be given regarding this characteristic configuration.

As shown in FIG. 2, top vapor (ammonia-containing vapor) is supplied from the top of the distillation column 2 to the evaporation section 3, and the ammonia concentration in this top vapor is 4.94 wt%. The temperature until it is introduced into the evaporator 3, that is, the inlet temperature T5 in the upstream evaporator 3A is 98.6°C. In the evaporation section 3, the above-mentioned tower top vapor exchanges heat with water outside the tube supplied via pipe L8, and a part of the tower top vapor condenses to become liquid, so that the temperature of the tower top vapor increases. will decrease.

Here, FIGS. 4 and 5 show vapor-liquid equilibrium diagrams of a mixture of water and ammonia at atmospheric pressure (760 mmHg). FIG. 4 is a graph showing the ammonia concentration range from 0 to 100%, and FIG. 5 is a graph showing only the ammonia concentration range from 0 to 50%. This graph also represents the boiling point (x1) and dew point (y1) of a mixture of water and ammonia at atmospheric pressure, and the dew point is the same as the saturated steam temperature.

As shown in Figure 5, for example, when the temperature of the above mixture is 87.6°C at atmospheric pressure (760 mmHg), this mixture is in an equilibrium state, so the temperature is 87.6°C on both the gas side (y1) and the liquid side (x1). It is the same. At this time, the ammonia concentration on the gas side (y1) is 37.93 wt%, while the ammonia concentration on the liquid side (x1) is 3.79 wt%. Then, for example, if the top vapor drops from 98.6°C to 87.6°C, the ammonia concentration will rise from 4.94wt% to 37.93wt%, while the ammonia concentration of the condensed liquid will be 3. It becomes 79 wt%. That is, while the ammonia concentration on the gas side (y1) of the mixture of water and ammonia becomes high, the ammonia concentration on the liquid side (x1) becomes low. Therefore, as mentioned above, the ammonia concentration of the above-mentioned tower top vapor was 4.94 wt% at the entrance of the evaporation section, but when heat exchanged with the water outside the tube in the evaporation section, the top vapor at the exit of the evaporation section The ammonia concentration increases from 4.94 wt%, and the ammonia concentration of the condensed liquid becomes lower than 4.94 wt%, and the ammonia is returned to the distillation column as a reflux liquid, and the ammonia is recovered again.

At this time, in the ammonia recovery apparatus 1 according to the present embodiment, since the evaporation section 3 is divided into the upstream evaporator 3A and the downstream evaporator 3B, as described above, the top of the distillation column 2 The supplied top steam is first used as heating steam for the upstream evaporator 3A. The steam temperature at this time is 98.6°C as described above. In the upstream evaporator 3A, a part of the tower top vapor is condensed, so that the ammonia concentration of the tower top vapor increases. For example, if the ammonia concentration increases from 4.94 wt% to 20%, the graph shows that the saturated steam temperature (y1) with an ammonia concentration of 20 wt% is about 93°C, so the ammonia-containing steam becomes 93°C. Since this ammonia-containing steam of 93° C. becomes the heated steam of the downstream evaporator 3B, the evaporation temperature of water is lower than that of the upstream evaporator 3A (heated steam of 98.6° C.).

As described above, the ammonia concentration of the tower top vapor increases after heat exchange in the evaporation section, and as the ammonia concentration increases, the temperature of the tower top vapor decreases.

Based on the above principle, as a modification example for comparison with the ammonia recovery apparatus 1, for example, as shown in FIG. An example is a configuration in which the evaporator 3C is configured with only a single evaporator 3C, and two vapor compressors 18C and 18D are connected in parallel to the evaporator 3C as temperature raising means. In this modified example, the inlet temperature T1 of the tower top vapor (ammonia-containing vapor) in the evaporator 3C is 98.6° C. as described above, but in the evaporator 3C, the inlet temperature T1 is 98.6° C. In the overhead vapor after heat exchange with outside water, the ammonia content increases to 36.38 wt% and the outlet temperature T2 decreases to 88.3°C. Therefore, the temperature T3 of the water vapor supplied from the upper part of the evaporator 3C to the vapor compressors 18C and 18D has to be lowered to 85.6°C. Therefore, in this modified example, this water vapor is At step 18D, the temperature is compressed and heated to T4=100° C., and it is charged into the bottom of the distillation column 2 to be reused as steam for heating. That is, in this case, the compression temperatures (T4-T3) in the two vapor compressors 18C and 18D are 100-85.6=14.4°C.

On the other hand, referring again to FIG. 2 showing the main parts of the ammonia recovery apparatus 1 according to the present embodiment, the ammonia content in the tower top vapor is 4.94 wt%, the inlet temperature T5 in the evaporation section 3 is 98.6°C, and the evaporation The outlet temperature T6 after being discharged from the section 3 is 88.3°C (ammonia content 36.38 wt%), and the temperature T7 of the steam supplied from the upper part of the downstream evaporator 3B to the downstream vapor compressor 18B is 85. 6°C is the same as in the above modification example, but the outlet temperature T8 of the ammonia-containing vapor in the upstream evaporator 3A is approximately 97.2°C (ammonia content approximately 10 wt%), and The temperature T9 of the water vapor supplied from the upper part of the upstream evaporator 3A to the upstream vapor compressor 18A can be kept at about 95° C. . As a result, the compression temperature (T10-T7) in the downstream vapor compressor 18B is 100-85.6 = 14.4°C, which is the same as in the above modification example, but the compression temperature in the upstream vapor compressor 18A is (T10-T9) is 100-95.0=5.0°C, which means that the compression is smaller than in the case of the above modification. That is, the load on the upstream vapor compressor 18A is reduced.

Therefore, according to the ammonia recovery apparatus 1 according to the present embodiment, (I) firstly, the compression temperature in the upstream vapor compressor 18A is only 5° C., and the power consumption is reduced; The advantage is that costs can be reduced.

The amount of reduction in running costs varies depending on the scale of the device, but is calculated as follows, for example. In other words, the total amount of steam (per two vapor compressors) that is compressed and heated by the temperature raising means from the evaporation section and input into the bottom of the distillation column 2 is 4,000 kg/hr (=96 tons/day). Then, in the case of the above modification, the power consumption per vapor compressor 18C and 18D is 2,000 kg/hr x 65 kWh/ton = 130 kW, and for two vapor compressors it is 130 kW x 2 = 260 kW. Therefore, the electricity cost is 260kW x 15 yen/kWh x 24 = 93,600 yen/day x 300 = 28,080,000 yen/year.

On the other hand, in the case of the ammonia recovery apparatus 1 according to the present embodiment, the power consumption of the upstream vapor compressor 18A is 2,000 kg/hr x 30 kWh/ton = 60 kW, and the power consumption of the downstream vapor compressor 18B is 2,000 kg/hr x 30 kWh/ton = 60 kW. ,000kg/hr×65kWh/ton=130kW, and with two units, 60kW+130kW=190kW. Therefore, the electricity cost will be 190kW x 15 yen/kWh x 24 = 68,400 yen/day x 300 = 20,520,000 yen/year, which is approximately 7.5 million yen/year compared to the above modification example. This results in cost reduction.

(II) Secondly, the temperature T9 of the water vapor supplied from the upper part of the upstream evaporator 3A to the upstream vapor compressor 18A can be kept at a high temperature of about 95°C without lowering too much. The specific volume of the upstream vapor compressor 18A is reduced, which provides the advantage that the upstream vapor compressor 18A can be made smaller accordingly.

In this case, in addition to making only the upstream vapor compressor 18A small, it is also possible, for example, to make both the upstream vapor compressor 18A and the downstream vapor compressor 18B small on average. It is. More specifically, for example, if the sizes of the two vapor compressors 18C and 18D according to the above modification example are the same and the ratio is 5:5, the ammonia recovery apparatus 1 according to the present embodiment, In addition to setting the size of the upstream vapor compressor 18A and the downstream vapor compressor 18B to 3:5, it is also possible to set the size to 4:4, for example.

Furthermore, if the top vapor generated from the distillation column does not contain ammonia, the temperature of the top vapor will be 100°C. During heat exchange in the evaporator, water is heated by the latent heat generated when the top vapor changes from gas to liquid, and as a result of this heat exchange, a portion of the top vapor condenses, but the top vapor In the case of no ammonia, the temperature of the overhead vapor remains at 100° C. even after heat exchange. Therefore, in this case, regardless of the number of evaporators, the temperature of the water vapor generated from any evaporator will be the same, and the effects of the present invention will not be obtained. (However, in actual equipment, the temperature will drop somewhat due to other factors.)

Furthermore, in the ammonia recovery apparatus 1 according to the present embodiment, even if the heated steam temperatures in the upstream evaporator 3A and the downstream evaporator 3B are, for example, 98.6° C. and 93° C. below 100° C., As mentioned above, since the outside of the heat transfer tube of the evaporator 3 is at low pressure (below atmospheric pressure) by the compression device 18, water can be evaporated even with heated steam of 100° C. or less.

Next, returning to the explanation of the processing operation of the ammonia recovery apparatus 1 according to the present embodiment, as shown in FIG. temperature is controlled and the flow rate of cooling water passing through heat exchanger H4 is adjusted. As a result, the stored liquid (condensate) cooled to a predetermined temperature is sprayed from the top of the concentrating tower 5, and the ammonia-containing vapor is partially condensed, resulting in a predetermined high concentration (for example, 20 wt% or more) ammonia-containing vapor. generated. Note that the entire amount of the condensed liquid is returned to the top of the distillation column 2 as a reflux liquid. In this way, the concentrating tower 5 takes in the ammonia-containing vapor after partial condensation in the evaporator 3, removes moisture, and further condenses the ammonia-containing vapor, so that a predetermined high concentration ( For example, the load on the compression device 18 can be further reduced compared to a configuration in which the content is concentrated to 20 wt% or more. As a result, it is possible to save energy and to generate ammonia-containing steam with a high concentration (for example, 20 wt% or more).

Next, as shown in FIG. 1, in the first absorption tower 6, the stored liquid at the bottom of the tower is sprayed from the top of the tower through a spray pipe L23, so that the liquid is introduced from the concentration tower 5 through a pipe L24. The ammonia-containing vapor is condensed to produce recovered ammonia water (recovered ammonia water) containing a high concentration of ammonia. In the second absorption tower 7, a slight amount of uncondensed ammonia gas remaining in the first absorption tower 6 is guided through a pipe L32, and water supplied from outside the system passes through a spray pipe L31 and is sprayed from the top of the tower. With this configuration, uncondensed ammonia gas is absorbed. The water that has absorbed ammonia is returned to the condensate of the first absorption tower 6. As a result, uncondensed ammonia gas is prevented from being discharged to the outside. Note that the gas from which ammonia has been removed is exhausted from the exhaust pipe L34.

(Other matters) (1) In the above embodiment, "water" is supplied to the evaporation section 3 and the second absorption tower 7, but this "water" specifically includes pure water, pure water, Soft water, ion exchange water, etc. can be applied.

(2) Also, for reference, in the case of a configuration in which the vapor of the distillation column is directly compressed and used as a heat source for the distillation column (for example, Patent Document 1, etc.), by directly compressing the vapor of the distillation column, There is a concern about corrosion due to the contained substances, and there is a possibility of corrosion or leakage at the sealing part. On the other hand, in the case of a configuration in which water is evaporated by an evaporator and used directly in the distillation column as in the above embodiment, the steam (steam) directly used in the distillation column does not contain any contained substances. , corrosion and leakage caused by contained substances can be prevented.

(3) In the above embodiment, the evaporator 3 has a configuration in which two evaporators, the upstream evaporator 3A and the downstream evaporator 3B, are used, that is, two evaporators are used as two divided evaporators. However, the two divided evaporation sections may be formed by partitioning one evaporator, as shown in FIGS. 7 and 8, for example.

In the example shown in FIGS. 7 and 8, an evaporator 20 having a generally horizontally elongated cylindrical outer shape is partitioned into two in the horizontal direction by a partition plate 21 extending vertically in the axial direction at the center. As a result, the evaporator 20 is formed with an upstream evaporator section 20A and a downstream evaporator section 20B. A first header 22 having a generally rectangular parallelepiped shape is provided on one end surface of the evaporator 20, and a second header 23 having a generally rectangular parallelepiped shape is provided on the other end surface of the evaporator 20.

The upstream evaporator 20A is provided with a heat transfer tube group 24A consisting of one or more horizontal heat transfer tubes, and the bottom of the upstream evaporator 20A serves as a reservoir for storing water supplied from outside the system. The liquid (water) stored in the storage section is supplied by a circulation pump P25A via a pipe L26A to a sprayer 27A provided at the upper part of the upstream evaporation section 20A, and from this sprayer 27A to the outside of the heat transfer tube group 24A. After being sprayed toward the surface, it is configured to perform a circulation in which it flows down to a storage section in the lower part of the upstream evaporation section 20A.

The downstream evaporator 20B is configured to be generally symmetrical to the upstream evaporator 20A, and therefore detailed description thereof will be omitted. The first header 22 is connected to the top of a distillation column (not shown) via a steam supply pipe L28, and the top steam (ammonia-containing steam) discharged from the top of the distillation column is transferred to the top of the distillation column (not shown) through the steam supply pipe L28. is guided to the first header 22, flows through the heat exchanger tube group 24A of the upstream evaporator 20A, turns back inside the second header 23, and flows through the heat exchanger tube group 24B of the downstream evaporator 20B. Then, it is discharged from the first header 22 and supplied to a concentration tower or an absorption tower (not shown) via a pipe L29. An upstream vapor compressor 30A is connected to the upper part of the upstream evaporator 20A, and a downstream vapor compressor 30B is connected to the upper part of the downstream evaporator 20B.

With the above configuration, the upstream evaporator 20A and the downstream evaporator 20B can function in the same manner as the upstream evaporator 3A and the downstream evaporator 3B according to the embodiment. In this way, since the two evaporators 20A and 20B are formed by partitioning the evaporator can 20, which is one evaporator, the device can be made more compact and the cost can be reduced compared to a configuration using two evaporators. It is possible to reduce the

(4) In the above embodiment, the same Roots-type vapor compressor is used as the upstream and downstream vapor compressors 18A and 18B, but for example, the temperature increasing The means may be smaller than the temperature raising means provided in the downstream divided evaporation section. According to this configuration, it is possible to further save energy and make the device more compact. For example, as mentioned above, in the present invention, the temperature raising means (upstream vapor compressor 18A) provided in the upstream divisional evaporator requires only a small amount of compression. Examples include changing to a new machine. Also, for example, by preparing three or more temperature raising means and dividing them into two groups, and configuring one group with fewer temperature raising means than the other group, a temperature raising means smaller than the other group can be constructed. You may also do so. For example, one vapor compressor may be used as the upstream temperature increasing means, and two vapor compressors may be connected in series as the downstream temperature increasing means. It is also possible to reduce the initial cost by using the same relatively inexpensive vapor compressor as the three vapor compressors.

In addition, as a temperature increasing means, in addition to vapor compressors (heat pumps) such as roots-type vapor compressors, turbo-type vapor compressors, screw-type vapor compressors, and vane-type vapor compressors, for example, as shown in FIG. A steam ejector or the like may also be used. In the example shown in FIG. 9, in the ammonia recovery apparatus 1 according to the embodiment described above, a steam ejector 31 is provided as an upstream temperature raising means in place of the upstream vapor compressor 18A. The steam ejector 31 is similar to the steam ejector 10 provided as a means for supplying heating steam to the bottom of the distillation column 2 via the heating steam supply pipe L3 in the ammonia recovery apparatus 1 according to the above embodiment. A steam supply pipe L32 through which steam supplied from a high-pressure steam source (not shown) such as a boiler flows is connected to the steam suction side 31a, and this steam is passed to the upstream evaporator 3A. The steam is mixed with water vapor supplied from the pipe L15 through the pipe L15, and is blown into the bottom of the distillation column 2 through the pipe L16 as heating steam.

In the upstream temperature raising means, the required compression temperature is small, so even if the steam ejector is used as described above, the suction ratio (efficiency) can be made good. Using a steam ejector increases running costs compared to using a vapor compressor (heat pump) such as a roots-type vapor compressor, turbo-type vapor compressor, screw-type vapor compressor, or vane-type vapor compressor. , the initial cost can be reduced. Depending on the throughput of the device, the unit price of electricity, industrial water, etc., it may be more advantageous to use a steam ejector.

( 5 ) In the above embodiment, the evaporator 3 has a configuration using two evaporators, an upstream evaporator 3A and a downstream evaporator 3B, that is, a configuration in which two split evaporators are provided. However, three or more divided evaporation sections may be provided. Even if there are three or more divided evaporation sections, the more upstream the divided evaporation sections are, the smaller the temperature difference in temperature increase by the temperature raising means becomes, thereby making it possible to save energy.

Furthermore, when two divided evaporation sections are formed by partitioning one evaporator, the number of divisions may be further increased to form three or more divided evaporation sections.

( 6 ) In the above embodiment, the concentration column 5 is provided after the evaporation section 3, and the ammonia-containing vapor discharged from the distillation column 2 is concentrated to a predetermined concentration by the evaporation section 3 and the concentration column 5 in two stages. Although the structure was configured to be able to recover aqueous ammonia at a concentration (for example, 20 wt% or more), the concentration column 5 may be omitted in the present invention.

Further, in the above embodiment, the first absorption tower 6 absorbs water into the ammonia-containing vapor from the concentrating tower 5 to produce recovered ammonia water with a predetermined concentration, and the uncondensed ammonia-containing vapor in the first absorption tower However, for example, instead of the first absorption tower 6 and the second absorption tower 7, a catalytic decomposition device is provided to decompose ammonia with a catalyst. It may also be configured to remove it by disassembling it.

In other words, in the low boiling point substance separation device according to the present invention, low boiling point substances such as ammonia separated from the stock solution through processing operations from supplying the stock solution from outside the system to heat exchange in the evaporation section are For example, it may be collected as in the above embodiment, or it may be decomposed and removed.

INDUSTRIAL APPLICATION This invention can be applied to the separation apparatus and separation method which separate the said low boiling point substance, for example from the raw|stock solution , such as waste water containing low boiling point substances , such as ammonia.

1: Ammonia recovery device (separation device for low boiling point substances) 3: Evaporation section 3A: Upstream evaporator (divided evaporation section) 3B: Downstream evaporator (divided evaporation section) 18: Compression device (temperature raising means) 18A: Upstream vapor compressor (temperature raising means) 18B: Downstream vapor compressor (temperature raising means)

Claims (6)

A process in which a stock solution containing a low-boiling point substance is brought into contact with steam for heating, the low-boiling point substance is separated from the stock solution, gasified, and discharged from the top of the tower as a vapor containing the low-boiling point substance, and the low-boiling point substance is removed from the stock solution. a distillation column that stores water at the bottom of the column;
By heat-exchanging the steam containing low-boiling substances discharged from the top of the distillation column with water, the vapor containing low-boiling substances is partially condensed and the vapor containing low-boiling substances is condensed, and , an evaporation section that evaporates the water and discharges it as water vapor;
a compression device that compresses and raises the temperature of water vapor discharged from the evaporation section, guides the compressed and heated water vapor to the distillation column, and uses it as heating steam used in the distillation column;
A low boiling point substance separation device comprising:
The evaporator has a configuration in which at least two divided evaporators are connected in series along the flow direction of vapor containing the low boiling point substance, and each of the two divided evaporators is provided with the compression device,
Of the two divided evaporation sections, the compression device provided in the upstream divided evaporation section in the flow direction of the vapor containing the low boiling point substance is better than the compression device provided in the downstream divided evaporation section. Also, a low boiling point substance separation device characterized in that the temperature difference when compressing and heating the water vapor is small. 2. The low boiling point substance separation apparatus according to claim 1, wherein the two divided evaporation sections are formed by partitioning one evaporator. 3. The low boiling point substance separation apparatus according to claim 1, wherein the compression device provided in the upstream divided evaporation section is smaller than the compression device provided in the downstream divided evaporation section. 4. The low boiling point substance separation apparatus according to claim 1 , wherein the stock solution contains water and a low boiling point substance . The apparatus for separating low-boiling substances according to any one of claims 1 to 4 , wherein the compression apparatus includes a heat pump and/or a steam ejector . The vapor containing the low boiling point substance is generated from the stock solution containing the low boiling point substance and introduced into the evaporation section, and the vapor containing the low boiling point substance is subjected to heat exchange with water, whereby the vapor containing the low boiling point substance is partially condensed. A method for separating low-boiling substances, in which the water is evaporated and discharged as steam, and this steam is heated in a compression device and used as heating steam to generate steam containing the low-boiling substances. There it is,
The evaporator has a configuration in which at least two divided evaporators are connected in series along the flow direction of the vapor containing the low boiling point substance, and each of the two divided evaporators is provided with the compression device,
Of the two divided evaporation sections, the compression device provided in the upstream division evaporation section in the flow direction of the vapor containing the low-boiling point substance is greater than the compression device provided in the downstream division evaporation section, A method for separating low boiling point substances, characterized in that the temperature difference when heating the water vapor is reduced.

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