JP4387185B2 - Freeze-thaw system and freeze-thaw method - Google Patents

Description

  The present invention relates to a freeze-thaw system and a freeze-thaw method, and more specifically, a freeze-thaw tank, an ammonia absorption refrigerator that enables freezing and thawing of an object to be processed fed to the freeze-thaw tank, Freezing comprising a cooling tower that cools the ammonia absorption refrigerator, and a warm brine circuit that enables use of a cold heat source that is generated when the frozen workpiece is melted for cooling the absorber that constitutes the ammonia absorption refrigerator The present invention relates to a thawing system and a freeze-thaw method.

  In order to purify the wastewater, since solids such as sludge are mixed in the wastewater, it is necessary to separate the sludge from moisture, that is, solid-liquid separation. However, the properties of sludge vary depending on the state of raw water and the flocculant used, and its components are generally composed of aluminum hydroxide, clays, colloids, microorganisms and other organic and inorganic substances, and contain moisture. Many are gelatinous. Accordingly, the filterability is poor, and the water content of the separated sludge is high, so that there is a considerable burden on post-treatment such as transportation costs and landfill incineration. For this reason, a method that utilizes the aggregating action by chemical injection before post-processing is used. When inorganic flocculating agent lime and ferric chloride are used as injection chemicals, the filterability is improved, but there is a problem that the amount of sludge to be disposed is increased by the chemical injection.

  On the other hand, since organic polymer flocculants inevitably contain modified polymers, if they leak into the environment, they may act as environmental hormones that inhibit biological growth. Limited.

  Therefore, as a method for dewatering sludge, a non-chemical injection method is preferable, and filtered water can be returned to raw water and reused, so that water resources can be used effectively. Of these, the freeze-thaw method is particularly preferred because it has good filtration performance and does not significantly affect the environment. This freezing and thawing method can be applied to all sludges, resulting in low water content dehydrated sludge, no increase in the amount of sludge disposed of because no chemicals are used, and no problem in soil reduction. There are excellent features.

The principle of the freezing and thawing method is that the water contained in the sludge and the water adhering to the surface exist, and the water is grown as ice crystals by freezing. As a result, the fine particles are concentrated while being combined in a large block to improve filtration characteristics. Furthermore, when the whole is frozen, a strong compressive force is applied to the sludge due to the expansion force of ice formation, and the sludge tissue (such as protein or carbohydrate micelle structure or gel-like substance gel structure) is destroyed inside. The contained water flows out, and the dehydration effect becomes higher.
JP 2001-38400 A

  However, since the conventional freeze-thaw method uses an electric compression refrigerator as a refrigerator, there is a problem that the burden of power consumption is large and the economy is inferior.

  By the way, in recent years, among the ammonia refrigerators that use ammonia as a non-fluorocarbon refrigerant, the absorption refrigerator operates the refrigeration cycle by heat drive, and therefore, waste heat energy such as sludge incineration and cogeneration system (CGS) is used. It has been found that the power consumption of the absorption refrigerator is about 1/10 compared to the electric compression refrigerator, and that a remarkable power saving effect can be realized.

  The inventors can effectively cool the absorber that constitutes the ammonia absorption refrigerator by using a cold heat source that is generated when the frozen workpiece is melted to increase the thermal efficiency of the entire apparatus and realize power saving. (Patent Document 1).

  However, it is not necessary to use all of the cold heat source generated when the frozen workpiece is thawed for cooling the absorber, and a relatively low cold heat source of 5 ° C. or lower is not necessarily effective for cooling the absorber. In some cases, it was found that the use value of thermal energy becomes higher when used for other purposes.

  Therefore, in view of the above-mentioned problems of the prior art, the object of the present invention is to use a particularly low cooling source among the cooling sources generated at the time of thawing of the frozen object to be processed. An object of the present invention is to provide a freeze-thaw system and a freeze-thaw method that are excellent in performance.

The above object can be achieved by the invention described in the claims. That is, the freeze-thaw system according to the present invention is
A freezing and thawing tank, an ammonia absorption refrigerator that freezes and thaws an object fed to the freezing and thawing tank, a cooling tower that cools the ammonia absorption refrigerator, and the ammonia absorption refrigerator switch between absorber constituting a temperature brine circuit to the cold heat source available that occurs upon melting of the frozen the processing object, and a cold brine circuit for feeding cold brine, a temperature bran circuit and a cold brine circuit In a freeze-thaw system having a cold temperature switching valve ,
In the middle of the warm brine circuit, a heat exchanging means for taking out and using a part of a cold heat source generated when the object to be processed is melted is provided,
When the object to be processed frozen by the cold brine is dissolved, the cold brine circuit is closed by the cold temperature switching valve to open the warm brine circuit, and the temperature of the warm brine flowing through the warm brine circuit is lowered. Thus, a cold heat source is obtained, and the cold heat source is taken out by the heat exchange means .

  According to this configuration, it is possible to reliably take out a cold heat source generated at the time of melting, for example, a cold heat source of about 5 ° C. or less, among the cold heat sources generated when the frozen workpiece is thawed, through the warm brine circuit, It can be effectively used for a cooling heat source of various air conditioners, an air supply cooling of a gas turbine, and a jacket cooling for an ozone generator of an advanced water treatment facility in a water purification plant.

  As a result, it was possible to provide a freeze-thaw system with higher energy efficiency and excellent economic efficiency by effectively using a particularly low-temperature heat source among the cold-heat sources generated when the frozen object to be melted.

In the warm brine circuit, the warm brine is passed to the freeze-thaw tank by bypassing the first line through which the warm brine flows to the freeze-thaw tank and the heat recovery unit of the cooling water system line of the absorber. A switching means for switching between the flowing second line is provided on the downstream side of the heat exchange means,
The switching means is configured to switch from the first line to the second line on the basis of the temperature of the warm brine or after a predetermined period has elapsed since the opening of the warm brine circuit .

  According to this configuration, the initial cold heat source at which the object to be processed has started to be melted can be taken out and used effectively, and when the temperature of the warm brine rises as the object to be processed melts, Can be used for the absorber, and the thawing of the freeze / thaw tank can be promoted, and the thawing time of the freeze / thaw tank can be shortened.

  It is preferable that a heat storage water tank is connected to the heat exchange means.

  According to this configuration, as long as the freeze-thaw tank is operated, it can be used all day and night, so that it can be easily used for facilities and apparatuses that require various cold heat sources.

In addition, the freeze-thaw method according to the present invention includes
The object to be processed is frozen by an ammonia absorption refrigerator and thawed, and an absorber constituting the ammonia absorption refrigerator and a cold heat source generated when the object to be processed frozen through a warm brine circuit is thawed are provided. In the freeze-thaw method to make available,
When the object to be processed frozen by the cold brine from the ammonia absorption refrigerator is dissolved, the cold brine circuit is closed by a cold temperature switching valve, the warm brine circuit is opened, and the warm brine circuit is passed through. to obtain a cold heat source by lowering the temperature of the brine, by the heat exchange means provided in the middle of the warm brine circuit, to make available removed part of said cold heat source generated during the melting of the workpiece Features.

  According to this configuration, it is possible to provide a freeze-thaw method that is more efficient in energy efficiency and more economical by effectively using a particularly low-temperature heat source among the cold-heat sources generated when the frozen workpiece is thawed. .

Based on the temperature of the warm brine or after a predetermined period of time has elapsed since the opening of the warm brine circuit, the switching brine provided downstream of the heat exchanging means in the warm brine circuit causes the warm brine to be frozen. It is the structure which switches from the line which flows into a melting tank to the line which bypasses the heat recovery device of the cooling water system | strain line of the said absorber, and flows into the said freeze-thaw tank .

  According to this configuration, it is possible to take out the initial cold heat source at which the object to be melted begins to be used effectively, and to promote the melting of the freezing / thawing tank, and to shorten the melting time of the freezing / thawing tank. Is good.

  It is preferable that a heat storage water tank is connected to the heat exchange means so that a cold heat source stored in the heat storage water tank can be used.

  According to this configuration, as long as the freeze-thaw tank is operated, it can be conveniently used day and night.

  Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic overall configuration of a freeze-thaw system according to the present embodiment.

  This freezing and thawing apparatus includes a cooling tower 1 as a cooling source, a freezing and thawing tank 2 for freezing or thawing sludge as an object to be processed, and an ammonia absorption refrigerator 3 (hereinafter sometimes simply referred to as “absorption refrigerator”). Consists of. The cooling tower 1 is provided for cooling the cooling water for cooling the refrigerant ammonia used in the absorption refrigerator 3, and is passed through the condenser 4 and the absorber 6. Although only one freeze-thaw tank 2 is shown in FIG. 1, usually a plurality of freeze-thaw tanks 2 are installed in parallel. Although not shown, the sludge extracted from the sludge settling basin is sent to the concentrating tank through the sludge pond and concentrated to about several percent, and then fed to the freezing and thawing tank 2. .

  The absorption refrigerator 3 includes a condenser 4 that liquefies ammonia as a refrigerant, an evaporator 5 that evaporates ammonia, an absorber 6 that absorbs ammonia vapor evaporated in the evaporator 5 in water as an absorbent, A generator pump 7 that heats the ammonia aqueous solution with a driving heat source and a solution pump (not shown) that supplies an aqueous ammonia solution sufficiently containing a refrigerant to the generator 7 by the absorber 6 and separates it into an ammonia vapor and an absorbent. And a rectifier 8 that increases the ammonia concentration and sends it to the condenser 4. Further, as a driving source for operating the absorption refrigerator 3, although not shown, exhaust heat energy such as incineration of sludge and cogeneration is supplied.

  Although not shown, the rectifier 8 has a vertical structure provided with a plurality of special perforated plate trays, and is divided into a lower recovery part and an upper concentration part. Then, the ammonia vapor supplied from the generator is sent to the recovery unit, the ammonia vapor rises from the recovery unit and is concentrated in the concentration unit, and the concentration of the ammonia water is reduced to the recovery unit below. It comes to descend.

  The high-pressure, high-concentration ammonia vapor is sent to the condenser 4 where it is heat-exchanged with the cooling water from the cooling tower 1 to be condensed and liquefied. In FIG. 1, reference numeral 14 is a cooling water circulation pump for sending cooling water.

  Further, a brine circuit is connected to the evaporator 5. The brine circuit includes a cold brine circuit B1 including a low temperature cold brine tank 9 and a cold brine circulation pump 10 for supplying cold brine, and a hot brine circulation pump 12 for supplying high temperature warm brine tank 11 and warm brine. And a pair of cold temperature switching valves 13 for switching between the warm brine circuit B2 and the cold brine circuit B1 are provided. The evaporator 5 is connected with a cold brine circuit B1, and the absorber 6 is connected with cooling water for heat exchange of the warm brine circuit B2.

  When the sludge fed to the freeze / thaw tank 2 is frozen, the cold brine cooled by the evaporator 5 of the absorption refrigerator 3 is directly sent to the freeze / thaw tank 2 to freeze the sludge. For example, about 90 minutes after the cold brine cooled to −30 ° C. in the evaporator 5 is sent, the sludge is completely frozen (about −15 ° C.) to separate the water contained in the sludge and to remove the solid matter. Aggregation occurs. The cold brine is heated somewhat (about −25 ° C.) and sent to the evaporator 5 via the cold brine tank 9. After the sludge is reformed, the cold brine circuit B1 is closed and the warm brine circuit B2 is opened by the cold / warm switching valve 13.

In the present embodiment, the heat exchange means connected to the heat storage water tank 16 in order to use a relatively low temperature heat source of 5 ° C. or less among the heat sources generated when the frozen workpiece is thawed. A heat exchanger 15 is provided in the middle of the warm brine circuit B2. That is, in order to melt the sludge frozen in the freeze / thaw tank 2 by the action of the cold brine circuit B1, when the cold brine switching valve 13 is switched to the warm brine side and the warm brine circuit B2 is activated, the warm brine circuit B2 flows. The temperature of the hot brine to be rapidly lowered, and the temperature of the heat storage water tank 16 connected to the heat exchanger 15 and subjected to heat exchange is lowered by the warm brine lowered to around 0 ° C. In this case, the temperature of the warm brine is monitored by the temperature indicator 18, and based on the result, the three-way switching valve 17 which is one kind of switching means is switched. When the warm brine rises to about 5 ° C., preferably about 3 ° C., the warm brine is passed to the heat recovery unit 20, and at the same time, the cold heat recovery water circulation pump P is stopped and passed to the freezing and thawing tank 2 ( from the B11 circuit). Switching to B12 circuit).

Since the temperature of the heat storage water tank 16 that exchanges heat with the heat exchanger 15 is also lowered by the warm brine that has been lowered to zero degrees or less from the beginning of melting, the cold water and ice in the heat storage water tank 16 can be used as a heat source for various air conditioners. It can be used for cooling the supply air of a gas turbine, and further for cooling the jacket of an ozone generator of an advanced water treatment facility at a water purification plant. The cold water in the heat storage water tank 16 can be used day and night as long as the freeze-thaw tank 2 is operated. In particular, it is very useful because it can be used when the peak of power consumption is high during the daytime in summer, such as when it is used for air supply cooling of a gas turbine. P is a cold heat recovery water circulation pump.

As the sludge melting in the freeze-thaw tank 2 progresses, the temperature of the warm brine also rises to 0 ° C. or higher, and heat is not exchanged by the heat exchanger 15, so that the water temperature in the heat storage water tank 16 does not become about 5 ° C. or lower. At that time, the three-way switching valve 17 is switched by the temperature indicator 18, that is , by switching from the B11 circuit to the B12 circuit and allowing the liquid to pass through the heat exchanger 20, the heated brine is used for cooling the absorber 6. (B11 switching from circuit to circuit B12).

Since the warm brine temperature after passing the warm brine through the heat recovery device 20 in the state of B12 is heated to about 30 ° C., the melting of the sludge in the freeze-thaw tank 2 is accelerated. Normally, this melting is completed in about 90 minutes, so that it does not become longer than when all of the warm brine is used for cooling the absorber 6 as in the prior art.

  Compared to the case where all the heat of fusion is used to cool the absorber inlet cooling water temperature to about 20 ° C. as in the prior art, in this system, chilled water having a temperature of 5 to 12 ° C. that can be used for part of air conditioning, etc. As a result, the overall thermal efficiency of the system is made high.

The thawed sludge is further processed into a dehydrated cake by a dehydrating device such as a vacuum dehydrator (not shown), dried and processed. The dried sludge cake is incinerated by an incinerator or the like. The exhaust heat can be used as a drive source for the absorption refrigerator 3.
[Another embodiment]
(1) In the above embodiment, the method of switching the warm brine between the B11 circuit and the B12 circuit by switching the three-way switching valve 17 based on the result of the temperature indicator 18 is employed. After the predetermined time has elapsed, the three-way switching valve 17 may be switched. This can be employed when the freezing and thawing time in the freeze-thaw tank is known in advance, and can contribute to the reduction of the equipment cost.
(2) In the above embodiment, it has been shown that the warm brine tank 11 is provided in the middle of the warm brine circuit B2. However, when the cold heat source generated when the frozen workpiece is melted is used, the warm brine tank 11 is used. You may comprise so that it may not go through. This is preferable because the cold heat source generated when the frozen workpiece is thawed can be used more effectively without consuming the cooling of the warm brine tank 11.
(3) In the above embodiment, the cold heat source is taken out using the heat storage water tank, but cold heat may be obtained directly from the heat exchanger without using the heat storage water tank.
(4) As a to-be-processed object, the intermediate process thing etc. which are used for the food industry, the chemical industry etc. which need to freeze-thaw and dehydrate other than various sludges may be sufficient.

Schematic overall configuration diagram of the freeze-thaw system of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cooling tower 2 Freezing / thawing tank 3 Ammonia absorption refrigerator 6 Absorber 15 Heat exchange means 16 Thermal storage tank 17 Switching means 20 Heat recovery device B2 Hot brine circuit P Cold recovery water circulation pump

Claims (4)

A freezing and thawing tank, an ammonia absorption refrigerator that freezes and thaws an object fed to the freezing and thawing tank, a cooling tower that cools the ammonia absorption refrigerator, and the ammonia absorption refrigerator Switching between a configured absorber, a warm brine circuit that enables use of a cold heat source generated when the frozen workpiece is thawed, a cold brine circuit that supplies cold brine, and a warm bran circuit and a cold brine circuit In a freeze-thaw system having a cold temperature switching valve,
In the middle of the warm brine circuit, a heat exchanging means for taking out and using a part of a cold heat source generated when the object to be processed is melted is provided,
When the object to be processed frozen by the cold brine is dissolved, the cold brine circuit is closed by the cold temperature switching valve to open the warm brine circuit, and the temperature of the warm brine flowing through the warm brine circuit is lowered. to obtain a cold source Te, Ri configuration der which the cold source is retrieved by said heat exchange means,
In the warm brine circuit, the warm brine is passed to the freeze-thaw tank by bypassing the first line through which the warm brine flows to the freeze-thaw tank and the heat recovery unit of the cooling water system line of the absorber. A switching means for switching between the flowing second line is provided on the downstream side of the heat exchange means,
The freezing and thawing system characterized in that the switching means switches from the first line to the second line based on the temperature of the warm brine or after a predetermined period has elapsed since the opening of the warm brine circuit .   The freeze-thaw system according to claim 1, wherein a heat storage water tank is connected to the heat exchange means. The object to be processed is frozen by an ammonia absorption refrigerator and thawed, and an absorber constituting the ammonia absorption refrigerator and a cold heat source generated when the object to be processed frozen through a warm brine circuit is thawed are provided. In the freeze-thaw method to make available,
When the object to be processed frozen by the cold brine from the ammonia absorption refrigerator is dissolved, the cold brine circuit is closed by a cold temperature switching valve, the warm brine circuit is opened, and the warm brine circuit is passed through. Lowering the temperature of the brine to obtain a cold heat source, by means of heat exchange means provided in the middle of the warm brine circuit, a part of the cold heat source generated during melting of the object to be processed can be taken out and used.
Based on the temperature of the warm brine or after a predetermined period of time has elapsed since the opening of the warm brine circuit, the switching brine provided downstream of the heat exchanging means in the warm brine circuit causes the warm brine to be frozen. A freeze-thaw method characterized by switching from a line that flows to the melting tank to a line that bypasses the heat recovery unit of the cooling water system line of the absorber and flows to the freeze-thaw tank .   The freeze-thaw method according to claim 3, wherein a heat storage water tank is connected to the heat exchange means, and a cold heat source stored in the heat storage water tank is made available.

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