JP2008188514A - Compressor for steam in reduced pressure type evaporator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the compression ratio of steam in an evaporator which compresses steam generated by boiling and evaporating under a reduced pressure condition by indirectly heating a volatile liquid such as water and uses the compressed steam as the heat source for indirectly heating the liquid. <P>SOLUTION: Compression of the steam is performed by compression with a front stage centrifugal compressor 12 and by compression with a back stage volume type compressor 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is, for example, an evaporative concentration apparatus that concentrates the liquid by boiling and evaporating the evaporative liquid such as water in a reduced pressure state or indirectly evaporating liquid such as seawater or wastewater by indirect heating. Evaporating liquid such as water is boiled under reduced pressure in a reduced pressure type evaporator such as an evaporation desalination unit that produces boiled water by condensing a part of its vapor under reduced pressure. The present invention relates to a device for compressing vapor generated by evaporation so as to be a heat source for boiling and evaporating the liquid.

  In general, in the various types of evaporators listed above, an evaporating liquid such as water is indirectly heated and then boiled and evaporated at a reduced pressure below atmospheric pressure, and the vapor generated by the boiling evaporation is compressed to indirectly inject the liquid. In the case of using a heat source for heating, the compression of steam generated by boiling evaporation in the reduced pressure state is performed by rotating the impeller at high speed as described in, for example, Patent Document 1 as a prior art. In addition, a so-called centrifugal compressor that uses a centrifugal force flowing in the radial direction between the blades is used.

  That is, the specific volume of the saturated steam generated by boiling evaporation at a reduced pressure lower than the atmospheric pressure increases rapidly as the degree of vacuum increases, so that the steam generated by boiling evaporation at the reduced pressure becomes A centrifugal compressor suitable for handling a large amount of gas is used for compressing the vapor because it must be sucked and compressed in a state of a large specific volume.

Further, Patent Document 2 as another prior art discloses that a steam having a large specific volume generated by boiling evaporation in a reduced pressure state is compressed by a centrifugal compressor in the previous stage and then a steam ejector disposed in the subsequent stage. It is proposed to compress at.
No. 2-339521 Japanese Patent Laid-Open No. 10-57702

  However, although the centrifugal compressor is suitable for compressing a large amount of gas, the compression by the centrifugal compressor can compress only about 5 ° C. at a temperature difference. , The compression ratio cannot be increased, and as a result, the temperature difference in the case of indirect heating so that the evaporating liquid is boiled and evaporated cannot be increased. In order to increase the processing capacity and to increase the processing capacity, it is necessary to increase the heat transfer area during the indirect heating, leading to an increase in the size of the entire apparatus, and an increase in the boiling point of the evaporating liquid. There is a problem that it cannot be applied to evaporation in high cases.

  On the other hand, when configured as in Patent Document 2, the compression ratio can be increased by the amount of use of the steam ejector in the subsequent stage, but this technique can be applied to drive the steam ejector. It is limited to places where high-pressure steam is present, and is not applicable to places where high-pressure steam is not present. In addition, the degree of increasing the compression ratio is low, and a large amount of high-pressure steam is required. Therefore, there is a problem that the thermal efficiency is low and the operation cost increases.

  As described above, a rotary compressor such as a well-known roots type or movable blade type (rotating body of a special shape provided in a casing is rotated at high speed for compressing steam by boiling evaporation in a reduced pressure state. It is also conceivable to use a positive displacement compressor represented by

  However, this positive displacement compressor compresses the gas by repeatedly reducing the volume, so that the compression ratio is the same as when the centrifugal compressor is used and when the centrifugal compressor is used. Although it can be much higher than when using a steam ejector (about 15 ° C difference in temperature), it is not suitable for compressing a large amount of gas. In order to secure the required processing capacity by applying to the vacuum evaporator of this type, there is a problem that a large capacity and high-priced compressor must be used as the positive displacement compressor. was there.

  This invention makes it a technical subject to apply the vapor compression apparatus which eliminated these problems.

In order to achieve this technical problem, claim 1 of the present invention provides:
“Vaporization configured to compress steam generated by indirect heating of evaporative liquid such as water and boiling and evaporating under reduced pressure, and to use the compressed steam as a heat source for indirectly heating the liquid. In the device,
The vapor was compressed by the former centrifugal compressor, followed by the latter positive displacement compressor. "
It is characterized by that.

Claim 2 of the present invention includes:
“In the first aspect of the present invention, the steam compressed by the centrifugal compressor is brought into a saturated steam state or a saturated steam state between the preceding centrifugal compressor and the latter positive displacement compressor. It is equipped with a steam cooling means that cools it close to. "
It is characterized by that.

Claim 3 of the present invention provides:
“In the first or second aspect of the invention, the positive displacement compressor is a rotary compressor that rotates a rotating body in a casing.”
It is characterized by that.

  In the present invention, steam having a large specific volume generated by boiling evaporation under reduced pressure is first compressed by a centrifugal compressor in the previous stage to increase the pressure and reduce the specific volume. The one with a reduced volume is further compressed to a high pressure by a positive displacement compressor in the latter stage.

  As a result, the liquid can be compressed to increase the temperature difference during indirect heating so that the liquid is boiled and evaporated in a reduced pressure state, and a large amount of vapor generated by boiling evaporation in a state where the specific volume is large is compressed. Therefore, the processing capacity of various evaporators can be reduced only by a centrifugal compressor without increasing the heat transfer area of the indirect heating and, consequently, increasing the size of the evaporator. In addition to the improvement, it can be applied reliably even when the boiling point of the evaporable liquid is high.

  In addition, the positive displacement compressor can be reduced in capacity by reducing the specific volume by performing the compression by the centrifugal compressor in the previous stage, and thus the small and inexpensive positive displacement compressor. You can use the machine.

  By the way, since the vapor generated by boiling evaporation in the reduced pressure state of the liquid is almost saturated, it becomes a superheated vapor by compressing this vapor with the centrifugal compressor in the previous stage. In the latter-stage positive displacement compressor, scale adhesion occurs, and the superheated steam compressed by this latter-stage positive displacement compressor becomes higher superheated steam. When the liquid is indirectly heated, the heat transfer coefficient is reduced.

  Therefore, as described in claim 2, whether the steam compressed by the preceding centrifugal compressor is brought into a saturated steam state by the steam cooling means before being compressed by the latter positive displacement compressor, The cooling is performed so as to approach the state of saturated steam.

  As a result, the degree of superheat in the steam compressed by the preceding centrifugal compressor and the degree of superheat in the steam compressed by the latter positive displacement compressor can be reduced. In addition to being able to reliably reduce the occurrence, it is possible to reliably avoid a decrease in the heat transfer coefficient when the evaporative liquid is indirectly heated thereafter.

  As the steam cooling means, there are means for spraying water directly on the steam and means for cooling the steam by indirect heat exchange with water or air. Since the vapor volume increases due to the spraying of water, and the capacity of the positive displacement compressor in the subsequent stage is increased, it is preferable to use the former means by indirect cooling.

  In particular, by using a rotary type compressor such as a roots type, a movable blade type or a screw type as the positive displacement compressor in the latter stage, further miniaturization of the positive displacement compressor and improvement in thermal efficiency are achieved. There are advantages that can be made.

  An embodiment of the present invention will be described below with reference to the drawing of FIG.

  In FIG. 1, reference numeral 1 denotes an evaporator configured as a sealed type.

  In the middle stage in the evaporator 1, indirect heating means 2 formed by bundling a large number of heat transfer tubes 3 are provided so that the heat transfer tubes 3 are horizontally oriented. An inlet header 4 for one end of each heat transfer tube 3 and an outlet header 5 for the other end of each heat transfer tube 3 are provided.

  Further, the inside of the evaporator 1 is maintained at a reduced pressure lower than the atmospheric pressure by generating a vacuum from a vacuum pump 6 or the like connected to the outlet header 5.

  The evaporating liquid such as water or seawater accumulated at the bottom of the evaporator 1 is pumped out by the circulation pump 7, and the evaporating liquid such as water or seawater newly sent from the pipe 8 is added thereto. After supplying to the nozzle 9 provided in the upper part in the said evaporator 1 and spraying with respect to the outer surface of each heat exchanger tube 3 in the said indirect heating means 2 from this nozzle 9, it returns to the bottom part in the said evaporator 1 It is configured to circulate, and a part of the evaporating liquid accumulated at the bottom of the evaporator 1 is extracted from the pipe 10 as a concentrated liquid.

  Next, in FIG. 1, reference numeral 11 denotes a steam duct for guiding the steam in the evaporator 1 to the inlet header 4 in the indirect heating means 2.

  In the middle of the steam duct 11, a centrifugal compressor 12 and a roots compressor 13 are provided in series, and the steam generated in the evaporator 1 is first compressed by the centrifugal compressor 12 in the previous stage. Then, after further compression by a roots type compressor 13 in the subsequent stage, the heat is supplied to each heat transfer tube 3 through the inlet header 4 in the indirect heating means 2.

  A steam cooling means 14 for steam compressed by the centrifugal compressor 12 is provided in a portion of the steam duct 11 between the centrifugal compressor 12 and the roots compressor 13.

  The steam cooling means 14 cools the steam compressed by the centrifugal compressor 12 from a superheated steam state to a saturated steam state or close to a saturated steam state. The cooling is performed by spraying water directly on the steam, or the steam is configured by indirect heat exchange with atmospheric air or cooling water. .

  In this configuration, the evaporative liquid accumulated at the bottom of the evaporator 1 is pumped out by the circulation pump 7 and then from the nozzle 9 in the upper part of the evaporator 1 to each heat transfer tube 3 in the indirect heating means 2. By being sprayed on the outer side surface, it is heated indirectly by the steam supplied to the inside of each heat transfer tube 3 and boiled and evaporated.

  The steam generated by the boiling evaporation is first compressed by the centrifugal compressor 12 in the previous stage through the steam duct 11.

  The steam compressed in the centrifugal compressor 12 reaches the steam cooling means 14 where the steam is cooled from the heated steam state to the saturated steam state or close to the saturated steam state, and then the subsequent stage. After further compression in the roots type compressor 13, it is supplied to the inside of each heat transfer tube 3 in the indirect heating means 2 and used for indirect heating of the evaporative liquid on the outer surface of each heat transfer tube 3.

  The condensed water condensed inside each heat transfer tube 3 in the indirect heating means 2 is collected in the outlet header 5 and taken out from the outlet header 5 through the pipe line 15 as distilled water or fresh water.

  With the above-described configuration, in the former centrifugal compressor 12, for example, the steam can be compressed so as to increase to about 5 ° C. due to the temperature difference, and in the root-type compressor 13, for example, the steam can be compressed according to the temperature difference. By being able to compress so as to increase to about 15 ° C., the temperature difference of indirect heating in the indirect heating means 2 can be increased to about 20 ° C. as a whole, so that the temperature difference during this indirect heating is increased. Therefore, the heat transfer area in the indirect heating means 2 is reduced as much as possible, so that the apparatus can be reduced in size and can be applied even when the boiling point of the evaporable liquid is high.

  Further, when the steam cooling means 14 is of a type in which water is sprayed directly on the steam, a part of the condensed water taken out from the outlet header 5 is used as the water sprayed directly on the steam. be able to.

  In the above-described embodiment, the indirect heating means 2 is built in the evaporator 1. However, the present invention is not limited to this, and the indirect heating means is disposed outside the evaporator. The present invention is also applicable to the case where the liquid heated indirectly by the indirect heating means is introduced into the evaporator and evaporated to the boil.

  In the above-described embodiment, the root-type compressor belonging to the category of the rotary compressor is used as the positive displacement compressor for the subsequent compression. However, the present invention is not limited to this, and the positive displacement compressor is used. As a compressor, a movable blade type compressor or screw type compressor, which also belongs to the category of a rotary compressor, can be used, and it is needless to say that a reciprocating compressor can be used. By using a rotary compressor including a movable blade compressor or a screw compressor, it is possible to further reduce the size and improve the thermal efficiency compared to the case where a reciprocating compressor is used. it can.

It is a figure which shows embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Evaporator 2 Indirect heating means 3 Heat exchanger tube 4 Inlet header 5 Outlet header 6 Vacuum pump 7 Circulation pump 9 Nozzle 11 Steam duct 12 Centrifugal compressor 13 Roots type compressor 14 Steam cooling means

Claims (3)

An evaporator configured to compress steam generated by indirect heating of an evaporating liquid such as water and boiling and evaporating under reduced pressure, and to use the compressed steam as a heat source for indirectly heating the liquid In
A vapor compression apparatus in a decompression type evaporation apparatus, wherein the vapor compression is performed by compression by a centrifugal compressor at a preceding stage and subsequent compression by a positive displacement compressor at a subsequent stage.   In the description of claim 1, the steam compressed by the centrifugal compressor is brought into a saturated steam state or a saturated steam state between the preceding centrifugal compressor and the latter positive displacement compressor. A vapor compression device in a vacuum evaporator, comprising vapor cooling means for cooling so as to approach.   3. The vapor compression apparatus according to claim 1, wherein the positive displacement compressor is a rotary compressor that rotates a rotating body in a casing.

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