JPH05301002A - Evaporating concentrator - Google Patents

Abstract

PURPOSE:To take out noncondensable gas which is retained in an evaporation vessel (heating chamber) to improve heat transfer efficiency and simultaneously to restrain the lowering of partial pressure of stream to check the lowering of the temp. difference of heat transfer without incurring a loss in heat energy. CONSTITUTION:Degassing pipes 1a, 2a for taking out noncondensable gas generated from an evaporation process together with a part of evaporated steam are connected to evaporation vessels 1, 2. The inert gas and the entrained steam are taken out from the degassing pipes 1a, 2a to guide them to a preheater 8 and exchange heat with liquid to be concentrated to preheat the liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-vapor mechanical compression type evaporative concentrator, and more particularly to efficiently evaporating a liquid to be concentrated which produces a non-condensable gas such as ammonia gas or carbon dioxide gas together with water vapor in an evaporation process. The present invention relates to an evaporative concentrator for concentrating.

[0002]

2. Description of the Related Art As a conventional self-vapor mechanical compression type evaporative concentrator, for example, there is an evaporative concentrator as shown in FIG. This evaporative concentrator is a double-effect evaporative concentrator, and includes a first effect evaporative can 101 and a first effect evaporative can 10.
The first effect evaporation can 102 that utilizes the first effect evaporation steam and the evaporation effect steam of the second effect evaporation can 102 are compressed and heated to
A mechanical compressor 103 for circulation as a heating source of the effect evaporator 101 is provided. The second effect evaporator 10
2 is a vacuum line 1 for maintaining a predetermined degree of vacuum in the system.
08 is connected, and the vacuum line 108 is provided with a condenser 109.

In this conventional evaporative concentrator, the liquid to be concentrated (raw material liquid) supplied from the supply pipe 104 to the first effect evaporation can 101 first reaches a predetermined concentration in the first effect evaporation can 101. After being concentrated, it is introduced into the second effect evaporator 102 through the pipe 105, further concentrated to a predetermined concentration, and the concentrated liquid is extracted from the pipe 106 to the outside. On the other hand, the vaporized steam in the second effect evaporator 102 is
It is sent to the mechanical compressor 103 via 07, where it is compressed,
The temperature is raised and supplied again to the first effect evaporator 101 as a heating source.

As described above, the conventional self-vapor mechanical compression type evaporative concentration apparatus is economical by compressing and raising the temperature of the steam evaporated in the evaporator by the mechanical compressor and circulatingly using this as a heat source. Driving. Also, in the case of self-vapor mechanical compression type evaporative concentrator, when economic efficiency is pursued, the compression degree in the mechanical compressor is reduced to save energy consumption, and the compression degree is reduced to reduce the evaporation can (heating chamber It is often advantageous to compensate for the decrease in the temperature difference (heat transfer temperature difference) between the steam and the liquid to be heated (concentrated liquid) in (1) by increasing the heat transfer area of the evaporator (heating chamber). Therefore, usually, the degree of compression in the mechanical compressor is often designed to be low (that is, the heat transfer temperature difference in the heating chamber is small).

[0005]

However, in the above-described self-vapor mechanical compression type evaporative concentrator, a gas (hereinafter When non-condensable gas) is generated, the non-condensable gas stays and accumulates in the evaporator (heating chamber), which not only serves as heat transfer resistance, but also lowers the dew point due to the decrease in the partial pressure of water vapor. Temperature difference (heat transfer temperature difference) between (compressed heated steam) and heated liquid (concentrated liquid)
Is reduced. Therefore, there is a problem that the heat transfer area must be increased in order to secure the required heat transfer amount. In particular, when the degree of compression of the mechanical compressor is reduced and the heat transfer temperature difference is designed to be small, there is a problem that an increase in heat transfer resistance and a slight decrease in dew point lead to a large increase in heat transfer area.

On the other hand, in order to solve the above-mentioned problems, a method of preventing the noncondensable gas from staying by continuously withdrawing the noncondensable gas and the accompanying steam from the evaporator (heating chamber) (particularly not shown) However, this method has a problem that the amount of water vapor entrained in the non-condensable gas is large and the loss of thermal energy is large.

The present invention is intended to solve the above-mentioned problems. Even when non-condensable gas such as ammonia gas is generated from the liquid to be concentrated, the heat transfer area is greatly increased and the heat energy is greatly increased. To provide a self-vapor mechanical compression type evaporative concentrator capable of efficiently evaporating and concentrating by extracting the non-condensable gas accumulated and accumulated in the evaporating can (heating chamber) without causing any significant loss. With the goal.

[0008]

To achieve the above object, the evaporative concentration apparatus of the present invention is a self-vapor mechanical compression type evaporative concentration method for evaporating and concentrating a liquid to be concentrated which generates a non-condensable gas in an evaporating process. In the apparatus, an evaporation can connected to a degassing pipe for extracting the noncondensable gas generated in the evaporation process together with the vaporized water vapor accompanying it, a steam containing the noncondensable gas extracted from the degassing pipe, and a liquid to be concentrated. And a mechanical compressor that heats the liquid to be concentrated to preheat the liquid to be concentrated, and a mechanical compressor that compresses and raises the temperature of vaporized steam generated in the evaporator and circulates it as a heating source of the evaporator. Characterize.

[0009]

[Function] The non-condensable gas generated in the evaporation can, together with a considerable amount of evaporated steam, is larger than in the conventional evaporation can (heating chamber).
Because it is extracted from the evaporator, the amount of non-condensable gas that remains in the evaporator (heating chamber) decreases (that is, the partial pressure of water vapor increases).
However, the heat transfer resistance decreases and the heat transfer efficiency improves,
It is possible to suppress a decrease in dew point and a decrease in heat transfer temperature difference. In addition, steam containing non-condensable gas extracted from the evaporation pipe (heating chamber) is guided to the preheater and exchanges heat with the liquid to be concentrated to recover heat, thus preventing loss of thermal energy. It becomes possible to perform efficient driving. The steam extracted together with the non-condensable gas is heat-exchanged with the liquid to be concentrated at a low temperature in the preheater, so that the heat transfer temperature difference is large, and the dew point reduction width due to the inclusion of the non-condensable gas is Since the ratio to the heat transfer temperature difference is small, the increase in the heat transfer area in the preheater is larger than the increase in the heat transfer area in the evaporator (heating chamber) when the vapor containing the noncondensable gas is not sufficiently extracted. Ignoring becomes small, and the efficiency as a whole can be greatly improved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an evaporative concentration apparatus according to an embodiment of the present invention. The evaporative concentrator of this embodiment is a double-effect evaporative concentrator for concentrating a liquid (concentrated liquid) that generates ammonia gas in the evaporating process, and has a first effect evaporative can (thin film evaporative can). ) 1, a second effect evaporator (thin film evaporating can) 2 that uses evaporated water vapor from the first effect evaporator 1 and a second effect evaporator 2 that compresses and heats the evaporated water vapor in the second effect evaporator 2 A mechanical compressor 3 that circulates as a heat source of No. 1 is provided.

Degassing pipes 1a, 2a are provided above the first effect evaporator 1 and the second effect evaporator 2 to extract the non-condensable gas generated in the evaporation process together with part of the evaporated steam.
Are connected, and the degassing pipes 1a and 2a are connected to a preheater 8 for preheating the liquid to be concentrated. Preheater 8
Is a vacuum line 11 for maintaining a predetermined degree of vacuum in the system.
Are connected, and a condenser 12 is arranged in the vacuum line 11.

A case of evaporating and concentrating a liquid to be concentrated which produces a non-condensable gas (ammonia gas) by using the evaporative concentrator of this embodiment will be described below. First, the concentrated liquid (raw material liquid) sent to the preheater 8 via the pipe 4a and preheated to a predetermined temperature is supplied to the first effect evaporator 1 via the pipe 4b and the pipe (circulation line) 9 and circulated. It is circulated through the line 9 and concentrated by evaporation. Then, the liquid to be concentrated concentrated in the first effect evaporator 1 to a predetermined concentration is introduced into the second effect evaporator 2 through the pipe 5 and the pipe (circulation line) 10, and circulates through the circulation line 10. While being evaporated and concentrated to a predetermined concentration. Then, the concentrated liquid concentrated to a predetermined concentration in the second effect evaporation can 2 is extracted from the pipe 6, flashed in the flash can 14, and then recovered via the pipe 13. On the other hand, the vaporized water vapor of the second effect evaporator 2 is sent to the mechanical compressor 3 via the pipe 7, where it is compressed,
It is heated and supplied to the first effect evaporator 1 as a heating source through the pipe 15.

Further, the non-condensable gas generated in the evaporation process and staying in the first effect evaporator (heating chamber) 1 and the second effect evaporator (heating chamber) 2 is degassing pipe 1a at a predetermined ratio. 2a
Is extracted together with the vaporized steam that accompanies it. Then, the non-condensable gas and the entrained water vapor are guided to the preheater 8 and exchange heat with the liquid to be concentrated to recover the thermal energy.

In the evaporative concentration apparatus constructed as described above, the non-condensable gas generated in the evaporating can is withdrawn from the degassing pipe together with a part of the evaporating water vapor, so that the evaporative can is introduced into the evaporating can (heating chamber). Increase in heat transfer resistance due to retention of non-condensable gas is suppressed, heat transfer efficiency is improved, and decrease in steam partial pressure is suppressed to suppress decrease in heat transfer temperature difference, preventing a large increase in heat transfer area. can do. Moreover, since the steam extracted together with the non-condensable gas is guided to the preheater to recover the heat, there is no loss of heat energy and the evaporative concentrator as a whole can operate efficiently. Since the steam extracted together with the non-condensable gas is heat-exchanged with the liquid to be concentrated at a low temperature in the preheater, the heat transfer temperature difference is large, and the dew point decreases due to the inclusion of the non-condensable gas. Since the ratio to the heat transfer temperature difference is small, the increase in the heat transfer area in the preheater is larger than the increase in the heat transfer area in the evaporator (heating chamber) when the vapor containing the non-condensable gas is not sufficiently extracted. It is small enough to be ignored and can be improved in thermal efficiency and cost can be reduced.

In the above embodiment, the degassing pipe 1a is provided above the first effect evaporator 1 and the second effect evaporator 2 in consideration of the fact that the specific gravity of the noncondensable ammonia gas is smaller than that of the water vapor. Although 2b is connected, it is desirable that the degassing pipe is installed at an appropriate position depending on the specific gravity of the non-condensable gas. That is, when the specific gravity of the non-condensable gas is smaller than that of the water vapor, the specific gravity of the non-condensable gas is larger than that of the water vapor in the upper part of the evaporator (heating chamber) (for example, when the non-condensable gas is carbon dioxide gas). In the case of (1) or the like), it is desirable to dispose it under the evaporation can (heating chamber). In addition, when a plurality of types of non-condensable gases having different specific gravities are generated, it may be necessary to connect degassing pipes to a plurality of locations such as an upper portion, a lower portion, and an intermediate portion.

Further, although the double effect type evaporative concentrator has been described in the above embodiment, the present invention is not limited to the double effect type evaporative concentrator, but may be a single effect type or a triple effect type. It is also possible to apply to a multi-effect evaporative concentrator of the above formula.

[0017]

As described above, the evaporative concentration apparatus of the present invention is connected with a degassing pipe for extracting the non-condensable gas generated in the evaporation process together with a part of the vaporized steam, and the non-condensable gas and the accompanying steam. Is extracted from the degassing pipe and introduced to the preheater to exchange heat with the liquid to be concentrated, so that the liquid to be concentrated is preheated. Therefore, the noncondensable gas accumulates in the evaporator (heating chamber) and It is possible to prevent the heat resistance from increasing and improve the heat transfer efficiency, and to suppress the decrease of the partial pressure of water vapor to suppress the decrease of the heat transfer temperature difference of the evaporator (heating chamber).

Further, the water vapor extracted together with the non-condensable gas is guided to the preheater and exchanges heat with the liquid to be concentrated to recover heat, so that loss of heat energy is prevented and efficiency is improved. It becomes possible to drive well.

That is, according to the evaporative concentration apparatus of the present invention, the non-condensable gas staying in the evaporator (heating chamber) is extracted to improve the heat transfer efficiency without causing the loss of thermal energy, and the partial pressure of water vapor is increased. It is possible to suppress the decrease of the heat transfer temperature difference and to efficiently evaporate and concentrate.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an evaporative concentration apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional evaporative concentration apparatus.

[Explanation of symbols]

 1 1st effect evaporation can 1a 1st effect evaporation can degassing pipe 2 2nd effect evaporation can 2a 2nd effect evaporation can degassing pipe 3 Mechanical compressor 8 Preheater 14 Flash can

Claims (1)

[Claims] 1. A self-vapor mechanical compression type evaporative concentrator for evaporating and concentrating a liquid to be concentrated which generates a non-condensable gas in the evaporating step, and withdraws the non-condensable gas generated in the evaporating step together with evaporative steam accompanying it. In the evaporator, an evaporator connected to a degassing pipe, a preheater for preheating the liquid to be concentrated by exchanging steam containing the non-condensable gas extracted from the degassing pipe with the liquid to be concentrated, and the evaporator. An evaporative concentrator, comprising: a mechanical compressor that compresses and raises the temperature of the generated evaporative steam and circulates the evaporative steam as a heat source for the evaporating can.