JP2008032311A - Ammonia absorption refrigerator and its corrosion inhibitor - Google Patents

Abstract

The present invention provides an ammonia absorption refrigerating machine and a corrosion inhibitor that are excellent in environmental protection and can sufficiently prevent corrosion of equipment in a refrigeration system even when the aqueous ammonia solution is in a flowing state or boiling state.
An ammonia absorption refrigerator includes a refrigeration system including an evaporator 1, an absorber 2, a generator 7, a rectifier 6, a condenser 8, and the like, and an aqueous ammonia solution filled in the refrigeration system. . The ammonia aqueous solution contains ammonium molybdate and zinc hydroxide.
[Selection] Figure 1

Description

  The present invention relates to an ammonia absorption refrigerator and its corrosion inhibitor.

  Conventionally, an ammonia absorption refrigerator includes a refrigeration system including an evaporator, an absorber, a heat exchanger, a generator, a rectifier, a condenser, and an expansion valve, and an aqueous ammonia solution filled in the refrigeration system. An aqueous ammonia solution containing ammonium molybdate instead of sodium dichromate has been proposed as a corrosion inhibitor (inhibitor) (Patent Document 1: Japanese Patent No. 2769657).

  This ammonium molybdate is superior in terms of environmental protection compared to sodium dichromate which is generally used as a corrosion inhibitor.

However, the proposed ammonia absorption refrigerator has not been put into practical use. This is because, unlike sodium dichromate, which is an oxidation-type inhibitor, ammonium molybdate, which is an adsorption-type inhibitor, is not sufficiently effective in preventing corrosion in a fluid state or a boiling state. However, ammonium molybdate has an advantage that the pitting corrosion and crevice corrosion of stainless steel that occurs in sodium dichromate does not occur, so that it is strongly desired to put it to practical use.
Japanese Patent No. 2769657

  Accordingly, an object of the present invention is to provide an ammonia absorption type refrigerator that is excellent in terms of environmental protection and that can sufficiently prevent corrosion of equipment in a refrigeration system even in a fluid state or a boiling state, and a corrosion inhibitor thereof. It is in.

In order to solve the above problems, the ammonia absorption refrigerator of the present invention is
A refrigeration system;
An aqueous ammonia solution filled in the refrigeration system;
With
The ammonia aqueous solution contains ammonium molybdate and zinc hydroxide.

  According to the above configuration, since ammonium molybdate is contained in the aqueous ammonia solution instead of dichromic acid, the environment is not impaired, and since zinc hydroxide is contained in the aqueous ammonia solution in addition to ammonium molybdate, Corrosion of the equipment of the refrigeration system can be sufficiently prevented even when the aqueous ammonia solution is in a flowing state or boiling state.

  In one embodiment, at least a portion of the refrigeration system is made of iron.

  The ammonium molybdate and zinc hydroxide in the ammonia aqueous solution can sufficiently exhibit an anticorrosive effect against iron such as carbon steel even in a fluid state or boiling state of the ammonia aqueous solution.

  In one embodiment, at least a part of the refrigeration system is made of stainless steel.

  The ammonium molybdate and zinc hydroxide in the ammonia aqueous solution can sufficiently exhibit the anticorrosion effect on the stainless steel even in the fluid state or boiling state of the ammonia aqueous solution. Moreover, since ammonium molybdate is used, the natural potential of stainless steel is far from the local corrosion potential of stainless steel compared to using sodium chromate, so crevice corrosion and pitting corrosion occur. Can be effectively prevented.

  In one embodiment, the concentration range of ammonium molybdate to the aqueous ammonia solution is 1000 ppm or more and 30000 ppm or less.

  According to the above embodiment, since the concentration range of ammonium molybdate in the aqueous ammonia solution is 1000 ppm to 30000 ppm or less, a sufficient anticorrosion coating is formed on the surface of the equipment of the refrigeration system, and sufficient corrosion resistance is obtained. It is done. In addition, when the concentration range of ammonium molybdate in the aqueous ammonia solution is less than 1000 ppm, the corrosion resistance rapidly decreases, and when the concentration range of ammonium molybdate in the aqueous ammonia solution exceeds 30000 ppm, the anticorrosion effect is saturated and improved. This is not preferable in terms of cost.

  In one embodiment, the concentration range of ammonium molybdate to the aqueous ammonia solution is 3000 ppm or more.

  According to the above embodiment, since the concentration range of ammonium molybdate in the aqueous ammonia solution is 3000 ppm or more, the anticorrosion coating is more sufficiently formed on the surface of the refrigeration system equipment, and more sufficient corrosion resistance is obtained. It is done.

  In one embodiment, the concentration range of zinc hydroxide with respect to the ammonia aqueous solution is 100 ppm or more and 5000 ppm or less.

  According to the above embodiment, since the concentration range of zinc hydroxide in the aqueous ammonia solution is 100 ppm to 5000 ppm, the anticorrosion coating is smoothly applied to the surface of the equipment of the refrigeration system even in the flow state or boiling state of the aqueous ammonia solution. It is sufficiently produced and more sufficient corrosion resistance is obtained. The effect of zinc hydroxide becomes significant when the concentration range of zinc hydroxide in the aqueous ammonia solution is 100 ppm or more. In addition, even if the concentration range of zinc hydroxide in the aqueous ammonia solution exceeds 5000 ppm, the anticorrosion effect is saturated, and conversely, zinc hydroxide that is not very soluble precipitates, causing problems such as clogging of the expansion valve. May occur.

  The corrosion inhibitor for an ammonia absorption refrigerator according to the present invention is characterized by containing ammonium molybdate and zinc hydroxide.

  Since the corrosion inhibitor for an ammonia absorption refrigerator having the above-described configuration contains ammonium molybdate and zinc hydroxide, corrosion of equipment in the refrigeration system can be sufficiently prevented even in a flowing state or a boiling state of an aqueous ammonia solution.

  In one embodiment, the weight ratio of the zinc hydroxide to ammonium molybdate ranges from 1/300 to 5.

  In the above embodiment, since the weight ratio of the zinc hydroxide to ammonium molybdate is in the range of 1/300 to 5, a more sufficient corrosion prevention effect can be obtained.

  In one embodiment, the weight ratio of the zinc hydroxide to ammonium molybdate ranges from 1/300 to 5/3.

  In the above embodiment, since the weight ratio of the zinc hydroxide to ammonium molybdate is in the range of 1/300 to 5/3, a further sufficient corrosion prevention effect can be obtained.

  The ammonia absorption refrigerator of the present invention contains ammonium molybdate and zinc hydroxide in the aqueous ammonia solution, so that it is excellent in terms of environmental protection, and even in a flowing state or boiling state of the aqueous ammonia solution, Equipment corrosion can be sufficiently prevented.

  Further, the corrosion inhibitor for an ammonia absorption refrigerator according to the present invention contains ammonium molybdate and zinc hydroxide, so that corrosion of the equipment of the refrigeration system can be achieved even in a flowing state or boiling state of an aqueous ammonia solution without damaging the environment. Can be sufficiently prevented.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  As shown in FIG. 1, this ammonia absorption refrigerator includes an evaporator 1, an absorber 2, a solution pump 3, a heat exchanger 5, a rectifier 6, a pressure reducing valve 11, a generator 7, a condenser 8, and an expansion. A refrigeration system in which the valve 9 and the reflux pump 12 are connected by piping and an aqueous ammonia solution filled in the refrigeration system are provided.

  The generator 7 is made of stainless steel (for example, SUS304, SUS316, etc.) because of high temperature, and the other evaporator 1, absorber 2, etc. are made of iron, for example, carbon steel.

  The ammonia evaporated in the evaporator 1 is absorbed in the ammonia dilute aqueous solution by the absorber 2 to become a concentrated ammonia aqueous solution. This aqueous ammonia solution is sent to the rectifier 6 by the solution pump 3. From the rectifier 6, the aqueous ammonia solution is sent to the generator 7. This aqueous ammonia solution is heated by the generator 7 to separate the ammonia vapor. Since the separated ammonia vapor contains water vapor, it is returned to the rectifier 6 and rectified. The ammonia gas, which has been rectified and has a high purity, is liquefied by the condenser 8. The liquefied ammonia is sent to the evaporator 1 through the expansion valve 9 to cool the object to be cooled.

  On the other hand, the ammonia dilute aqueous solution from the generator 7 is cooled by the heat exchanger 5 and returned to the absorber 2 through the pressure reducing valve 11 to absorb ammonia.

The aqueous ammonia solution contains ammonium molybdate and zinc hydroxide (Zn (OH) ₂ ). This makes it possible to sufficiently prevent corrosion of equipment in the refrigeration system even when the aqueous ammonia solution is in a flowing state or boiling state.

  The mixture of ammonium molybdate and zinc hydroxide constitutes a corrosion inhibitor for ammonia absorption refrigerators. That is, this mixture of ammonium molybdate and zinc hydroxide can be produced as a corrosion inhibitor for an ammonia absorption refrigerator and can be transferred alone.

  The concentration range of ammonium molybdate in the aqueous ammonia solution (expressed by weight ratio, hereinafter the same) is set to 1000 ppm or more and 30000 ppm or less to form a strong molybdate coating with high corrosion resistance on the surface of carbon steel and stainless steel. Like to do. In addition, although the concentration range of the ammonium molybdate has the effect as described above, it is more preferably 3000 ppm or more.

  FIG. 2 is a graph showing the grounds for the above numerical limitation. In FIG. 2, the horizontal axis indicates the concentration (ppm) of ammonium molybdate in the aqueous ammonia solution, and the vertical axis indicates each concentration of ammonium molybdate relative to the corrosion amount (weight) of carbon steel when no ammonium molybdate is added. The amount of corrosion of the carbon steel when added at is expressed in%.

  As can be seen from FIG. 2, when the concentration of ammonium molybdate in the aqueous ammonia solution is less than 1000 ppm, the corrosion amount at that time is about 85% of the corrosion amount when no additive is added, and the surface of the carbon steel In addition, the anticorrosion coating having high corrosion resistance cannot be sufficiently formed, and the corrosion prevention effect is reduced. In contrast, when the concentration of ammonium molybdate in the aqueous ammonia solution is 1000 ppm or more, the amount of corrosion at that time is drastically reduced with respect to the amount of corrosion when no additive is added, and the corrosion prevention effect is increased. I understand that. On the other hand, even if the concentration of ammonium molybdate in the aqueous ammonia solution exceeds 30000 ppm, the corrosion prevention effect is already saturated and almost no improvement is observed. Therefore, the concentration of ammonium molybdate in the aqueous ammonia solution is preferably 30000 ppm or less so as not to increase the cost of the corrosion inhibitor.

  Therefore, in this embodiment, the concentration range of ammonium molybdate to the aqueous ammonia solution is set to 1000 ppm or more and 30000 ppm or less.

  Furthermore, when the concentration range of ammonium molybdate with respect to the aqueous ammonia solution is 3000 ppm or more, the amount of corrosion at that time is about 11% with respect to the amount of corrosion when no additive is added.

  The concentration range of zinc hydroxide in the aqueous ammonia solution is set to 100 ppm or more and 5000 ppm or less, and a highly corrosion-resistant coating film is smoothly formed on the surface of carbon steel and stainless steel even in the flow state or boiling state of the aqueous ammonia solution. I try to do it.

  FIG. 3 is a graph showing the basis for the above-described numerical limitation. In FIG. 3, the horizontal axis indicates each concentration (ppm) of zinc hydroxide in the aqueous ammonia solution with 5000 ppm of ammonium molybdate included in the aqueous ammonia solution, and the vertical axis indicates when no zinc hydroxide is added. The corrosion amount of carbon steel when zinc hydroxide is added at various concentrations with respect to the corrosion amount (weight) of carbon steel is expressed in%.

  As can be seen from FIG. 3, when the concentration of zinc hydroxide in the aqueous ammonia solution is less than 100 ppm, the corrosion amount at that time becomes 80% or more with respect to the corrosion amount when no zinc hydroxide is added, The anticorrosive effect of zinc hydroxide is small and insufficient for practical use. On the other hand, when the concentration of zinc hydroxide in the aqueous ammonia solution is 100 ppm or more, the corrosion amount at that time becomes about 30% of the corrosion amount when no zinc hydroxide is added, and it is drastically reduced. Thus, it can be seen that the corrosion prevention effect is increased. On the other hand, even when the concentration of zinc hydroxide in the aqueous ammonia solution exceeded 5000 ppm, the corrosion prevention effect was already saturated, and almost no improvement was observed in the corrosion prevention effect. Therefore, so as not to increase the cost of the corrosion inhibitor more than necessary, and to prevent zinc hydroxide having a low solubility from being deposited in the equipment (when zinc hydroxide is deposited, the expansion valve 9 and the pressure reducing valve). 11, equipment such as the solution pump 3 may be damaged.) The concentration of zinc hydroxide in the aqueous ammonia solution is preferably 5000 ppm or less. FIG. 3 shows a case where the concentration of ammonium molybdate is 5000 ppm, but when the concentration range of ammonium molybdate is 1000 ppm to 30000 ppm, the same tendency as in FIG. 3 was shown.

  Therefore, in this embodiment, the concentration range of zinc hydroxide with respect to the aqueous ammonia solution is set to 100 ppm or more and 5000 ppm or less.

  FIGS. 2 and 3 are data on carbon steel, but the same tendency as in FIGS. 2 and 3 was also obtained for stainless steel.

  When ammonium molybdate is used, the natural potential of stainless steel is far from the local corrosion potential of stainless steel compared to when sodium chromate is used. Can be prevented.

  FIG. 4 shows the test apparatus used to obtain the graphs of FIGS.

  In this test apparatus, a rotating shaft 33 having a shaft portion 33a and a flange portion 33b is disposed in a cylindrical pressure vessel 31 that contains an aqueous ammonia solution. Carbon steel disk-shaped corrosion test pieces 35, 35, 35, 35 are mounted on the shaft portion 33 a of the rotating shaft 33 at regular intervals. The disk-shaped corrosion test piece 35 has a shape as shown in FIGS. 5A and 5B, and is fitted with a hollow hole 35a in the shaft portion 33a of the rotating shaft 33, and is not shown. It is locked. A magnet 32 is disposed in the flange portion 33b, and a magnet 42 is opposed to the magnet 32. The magnet 42 is located outside the pressure vessel 31.

  On the other hand, the rotation drive device 40 is located outside the pressure vessel 31 and includes the magnet 42 and a motor 41 that rotates the magnet 42, and a rotation shaft is formed by magnetic coupling between the magnet 42 and the magnet 32. 33 can be rotated from the outside of the pressure vessel 31. In this way, the aqueous ammonia solution flows around the disk-shaped corrosion test piece 35 in the same manner as the aqueous ammonia solution flows on the surface of the actual refrigeration system equipment. In this way, it is possible to perform a test in a fluid state of an aqueous ammonia solution. Reference numeral 61 denotes the liquid level of the aqueous ammonia solution.

  In addition, an electric heater 51 is disposed outside the pressure vessel 31 so that the temperature of the aqueous ammonia solution in the pressure vessel 31 is controlled to, for example, 50 ° C. to 180 ° C., and the highest temperature in the refrigeration system. It can control to the same temperature as the generator 7 (refer FIG. 1) which is the most easily corroded. In this way, the test can be performed even in a fluid state and a boiling state of the aqueous ammonia solution.

  Using this test apparatus, the weight of the disk-shaped corrosion test piece 35 was measured before and after the test for various ammonium molybdate concentrations and zinc hydroxide concentrations, and the decrease in weight was taken as the amount of corrosion. The results shown in FIGS. 2 and 3 were obtained.

  On the other hand, even when a mixture of ammonium molybdate and zinc hydroxide was prepared as a corrosion inhibitor for an ammonia absorption refrigerator, and this corrosion inhibitor was added to an aqueous ammonia solution, a corrosion prevention effect was obtained.

  As described above, the concentration range of ammonium molybdate in the aqueous ammonia solution is preferably 1000 ppm to 30000 ppm, more preferably 3000 ppm or more, and the concentration range of zinc hydroxide in the aqueous ammonia solution is Since 100 ppm to 5000 ppm is preferable, the weight ratio of zinc hydroxide to ammonium molybdate in the corrosion inhibitor is preferably (1/300) to 5, and (1/300) to (5/3). More preferably.

  The refrigeration system used in the present invention is not limited to the refrigeration system shown in FIG. 1. For example, any refrigeration system that can be used in an ammonia absorption refrigerator such as a cascade-connected refrigeration system or a two-temperature simultaneous extraction refrigeration system can be used. It may be.

  In addition, the refrigeration system used in the present invention may be made of all equipment made of carbon steel, or made of all equipment made of stainless steel, or made of a plurality of different metal materials. Alternatively, a metal material and a non-metal material such as resin or ceramics may be combined.

1 is a block diagram of an embodiment of an ammonia absorption refrigerator according to the present invention. It is a figure which shows the relationship between the density | concentration of ammonium molybdate, and the corrosion amount of carbon steel. It is a figure which shows the relationship between the density | concentration of zinc hydroxide, and the corrosion amount of carbon steel. It is sectional drawing of a test apparatus. FIG. 5A is a plan view of a disk-shaped corrosion test piece, and FIG. 5B is a front view of the disk-shaped corrosion test piece.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Evaporator 2 Absorber 3 Solution pump 5 Heat exchanger 6 Rectifier 7 Generator 8 Condenser 9 Expansion valve

Claims (9)

A refrigeration system;
An aqueous ammonia solution filled in the refrigeration system;
With
An ammonia absorption refrigerator comprising the ammonium aqueous solution containing ammonium molybdate and zinc hydroxide. In the ammonia absorption refrigerating machine according to claim 1,
An ammonia absorption refrigerator, wherein at least a part of the refrigeration system is made of iron. The ammonia absorption refrigerator according to claim 1 or 2,
An ammonia absorption refrigerator, wherein at least a part of the refrigeration system is made of stainless steel. In the ammonia absorption refrigerating machine according to any one of claims 1 to 3,
The ammonia absorption refrigerating machine, wherein the concentration range of ammonium molybdate to the aqueous ammonia solution is 1000 ppm or more and 30000 ppm or less. In the ammonia absorption refrigerator according to claim 4,
The ammonia absorption refrigerating machine, wherein the concentration range of ammonium molybdate to the aqueous ammonia solution is 3000 ppm or more. In the ammonia absorption refrigerating machine according to any one of claims 1 to 6,
A concentration range of zinc hydroxide with respect to the ammonia aqueous solution is 100 ppm or more and 5000 ppm or less.   A corrosion inhibitor for an ammonia absorption refrigerator, comprising ammonium molybdate and zinc hydroxide. In the corrosion inhibitor for an ammonia absorption refrigerator according to claim 7,
A corrosion inhibitor for an ammonia absorption refrigerating machine, wherein the weight ratio of zinc hydroxide to ammonium molybdate is in the range of 1/300 to 5. In the corrosion inhibitor for an ammonia absorption refrigerator according to claim 8,
A corrosion inhibitor for an ammonia absorption refrigerating machine, wherein the weight ratio of zinc hydroxide to ammonium molybdate is in the range of 1/300 to 5/3.

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