JPS6042163B2 - Dry ice manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing dry ice.

Conventionally, dry ice is produced by compressing and cooling carbon dioxide gas, ejecting liquefied carbon dioxide gas into a pressure molding machine under reduced pressure, solidifying it into fine particles, and then molding it under pressure. It was manufactured. To obtain dry ice using this conventional method, it is necessary to liquefy carbon dioxide gas, so carbon dioxide gas is heated to a triple point pressure of 5.28 at 91dab.
It is necessary to compress the carbon dioxide gas to a temperature of 50 to 70 s and to cool it to remove the heat of compression.
After compressing to daYf■, it is cooled. Therefore, the theoretical energy required for producing dry ice is about 200 Kcalk9 for compression energy and 380 Kcalk9 for cooling energy per dry ice product (according to the carbon dioxide Mollier diagram). However, low-temperature liquefied gases having a boiling point lower than the temperature at which dry ice sublimes at a pressure above normal pressure and below the triple point pressure, i.e., liquid nitrogen with a boiling point of -196°C under atmospheric pressure, liquid oxygen with a boiling point of -183°C, or If carbon dioxide gas is cooled with a mixture of these or liquefied natural gas at -161°C and converted from gas to solid without passing through liquefied carbon dioxide gas, the energy required to produce dry ice will be reduced.

In addition, the cold energy contained in low-temperature liquefied gas, which serves as a cooling source, is extremely valuable from the standpoint of efficient energy use and because it is extremely low-temperature energy.Furthermore, cold energy is imported in large quantities along with liquefied natural gas. However, its use is currently limited to some uses such as air separation and food freezing, and most of it is discarded after exchanging heat with seawater.The present invention therefore reduces the energy required for production. It is possible to utilize the cold energy of liquefied natural gas with a small and simple heat exchanger, or to effectively utilize the cold energy of liquid nitrogen, liquid oxygen, or a mixture thereof that is effectively produced using the cold energy of liquefied natural gas. The purpose of the present invention is to provide a method for producing dry ice.That is, in producing dry ice, carbon dioxide is mixed with liquid nitrogen, liquid oxygen, a mixture thereof, or liquefied natural gas at a pressure of normal pressure or higher and lower than the triple point pressure. The method is characterized by directly contacting the low-temperature liquefied gas and carbon dioxide gas by blowing into the low-temperature liquefied gas, cooling and solidifying the carbon dioxide gas, and then vaporizing and separating the low-temperature liquefied gas.
The invention is characterized in that in this separation, the low-temperature liquefied gas contained in the dry ice is vaporized by passing carbon dioxide gas through the dry ice containing the low-temperature liquefied gas, and the cold heat is used to further generate dry ice. shall be. According to the present invention, in the case of normal pressure, the theoretically necessary energy required for producing dry ice is only the energy for cooling, which is 160Kcal/Ik per dry ice product.
9, which can be significantly reduced compared to the conventional method. In addition, since the present invention blows carbon dioxide gas into low-temperature liquefied gas at a pressure lower than the triple point pressure, there is no need to compress carbon dioxide gas to high pressure, and the equipment does not become under high pressure, so the danger is low and a high-pressure compressor is not required. Since the entire device can be operated at low pressure, it can be made compact. Also, to bring carbon dioxide gas into contact with low-temperature liquefied gas, carbon dioxide gas is blown into the low-temperature liquefied gas. Therefore, it has advantages such as a faster heat exchange rate than when using a heat exchanger. Furthermore, the present invention makes it possible to utilize the cold energy of liquefied natural gas, or to effectively utilize the cold energy of liquid nitrogen and liquid oxygen, which are advantageously produced using the cold energy of liquefied natural gas! It is Noh. In this case, the carbon dioxide content in the gasified product of the low-temperature liquefied gas, i.e., nitrogen, oxygen, or a mixture thereof, or natural gas, which is produced by blowing carbon dioxide into the low-temperature liquefied gas, is Since it is insoluble in gas and does not produce substances other than dry ice, such as intermolecular compounds, the mixing ratio depends on the individual vapor pressure ratio of liquefied gas and dry ice. According to actual measurements, the amount is 6 ppm or less, which is close to the value calculated from the vapor pressure, and is a small amount, so these gasified products can be used for various purposes without any problems. The fine-grained dry ice obtained by the method of the present invention is equivalent to the fine-grained dry ice obtained by the conventional method, and can be press-molded.

Furthermore, by heating and melting the obtained dry ice under a pressure equal to or higher than the triple point pressure, it is possible to produce liquefied carbonic acid with less energy than in conventional methods. ) Furthermore, the method of the second invention has the following effects in addition to the above.

In other words, dry ice obtained by blowing carbon dioxide gas into low-temperature liquefied gas is scattered as fine solid particles in the low-temperature liquefied gas, so dry ice is obtained by separating the low-temperature liquefied gas. However, ordinary solid-liquid separation methods such as filtration and centrifugation can be applied to separate the low-temperature liquefied gas and dry ice. The dry ice separated in this manner usually contains a large amount of low-temperature liquefied gas, and from the viewpoint of subsequent separation, it is best to vaporize the low-temperature liquefied gas. However, mere vaporization is not appropriate from the standpoint of energy conservation. Therefore, in the second invention,
By passing carbon dioxide gas through dry ice containing low-temperature liquefied gas separated by filtration, centrifugation, etc., the low-temperature liquefied gas can be vaporized and separated, and part or all of the carbon dioxide gas can be recovered as dry ice. Carbon dioxide gas for ventilation can be used as pre-cooling for blowing, making effective use of the cold energy of the low-temperature liquefied gas contained in the dry ice and the sensible heat up to the sublimation temperature of the dry ice, which has the same temperature as the low-temperature liquefied gas. made possible.

Furthermore, by passing carbon dioxide gas through dry ice containing low-temperature liquefied gas, the low-temperature liquefied gas can be separated more easily and in a shorter time than indirect heat exchange. Embodiments of the present invention will be described in detail below with reference to FIG.

The raw material carbon dioxide passes from the pipe 1 through the pre-cooling heat exchanger 2, contains about 3 to 6 ppm of carbon dioxide, and is sent from the dry ice production tank 3 to the delivery pipe 4, which is a low-temperature liquid natural gas, liquid nitrogen, or liquid oxygen. The liquefied gas is precooled by heat exchange with the gasified product. The pre-cooled carbon dioxide gas is sent to the separation chamber 5, and
exchanges heat with the low-temperature liquefied gas contained in the dry ice,
While the low-temperature liquefied gas is vaporized, a portion of the introduced carbon dioxide gas is cooled and becomes dry ice, and the remaining carbon dioxide gas is sent from the pipe 11 into the low-temperature liquefied gas in the dry ice production tank 3. On the other hand, low-temperature liquefied gas is sent from the pipe 11 to the dry ice manufacturing tank 3. The amount of hot liquefied gas is adjusted to be constant. The carbon dioxide gas introduced into the low-temperature liquefied gas is cooled and becomes powdered dry ice, and the low-temperature liquefied gas becomes cloudy. The low-temperature liquefied gas containing cloudy powdered dry ice is sent to the separation chamber 5 by opening the valve 6, and after being filtered and separated to some extent by the wire mesh conveyor 12, the raw material carbon dioxide is sent from the pipe 1 as described above. complete separation of low-temperature liquefied gas and dry ice. The low-temperature liquefied gas separated by filtration is collected in the low-temperature liquefied gas tank 7 and returned to the dry ice production tank 3 by the pump 8. On the other hand, the dry ice completely separated from the low-temperature liquefied gas in the separation chamber 5 is sent to the dry ice storage chamber 9, and the dry ice is sequentially taken out by the rotary valve 10. Next, a more specific example based on the above example will be shown.

Example 1 In a dry ice production tank 3, 600f of carbon dioxide gas was added to liquid nitrogen 10' under atmospheric pressure at a pressure of 50fImjn1 and a pressure of 0.2k9.
When the liquid nitrogen was fed for 1 day, the liquid nitrogen became cloudy due to fine particles of dry ice.

When this cloudy liquid nitrogen containing fine particles of dry ice was filtered through a 200-mesh wire mesh conveyor 12 and solid-liquid separation was performed by vaporizing the liquid nitrogen, the result was 950y.
(yield: 81%) of fine granular dry ice was obtained. When this fine-grained dry ice was pressure-molded, ice with a specific gravity of 1.5, which is the same as commercially available dry ice, was obtained. On the other hand, the amount of liquid nitrogen used at this time, that is, the amount of vaporized liquid nitrogen, was 4.7k9, and the amount of liquid nitrogen used per single dry ice position was 4.9k91k9 (dry ice), which was converted into energy 375Kca11kg (dry ice)
It was hot. Theoretical required energy 160Kca11k
134% more than 9 (dry ice), and the theoretical energy required for cooling using the conventional method is 380 Kc.
It was almost the same as a11k9 (dry ice), but
This seems to be due to heat loss due to insufficient cold storage. However, in addition to this energy, the conventional method uses
Gas compression energy of 200 Kca and 11 kg (dry ice) was required, which was reduced by this amount. Example 2 In a dry ice manufacturing tank 3, 600e of carbon dioxide gas was added to 10e of liquid nitrogen under atmospheric pressure at a pressure of 50'Iminl and 0.2kg.
When the liquid nitrogen was added at 1 d, the liquid nitrogen became cloudy due to fine particles of dry ice.

Carbon dioxide gas 600e was fed from below the wire mesh conveyor 12 at 50 eImin into the dry ice 1950y containing liquid nitrogen obtained by filtering this cloudy liquid nitrogen containing fine particles of dry ice through a 200 mesh wire mesh conveyor 12. . As a result, 1,000 y of liquid nitrogen contained in the dry ice is separated, and by heat exchange between liquid nitrogen and carbon dioxide, 20% of the cold heat for 1,000 y of liquid nitrogen is removed.
was recovered as dry ice. The drying time after filtration using the wire mesh conveyor 12 was 12 minutes. The low proportion of recovered cold energy is thought to be due to heat loss due to insufficient cold storage. In addition to the process shown in FIG. 1, it is also possible to make the dry ice production tank and the separation chamber for low-temperature liquefied gas and dry ice the same as shown in FIG. 2.

In FIG. 2, reference numerals 23 and 24 are dry ice production tanks. One dry ice production tank 23 is filled with low-temperature liquefied gas, and the other dry ice production tank 24 is filled with dry ice containing low-temperature liquefied gas, which will be used in the process described later. Suppose that it is contained in The carbon dioxide gas precooled by the heat exchanger 22 passes through the pipe 21 and is fed into dry ice containing low-temperature liquefied gas in the dry ice production tank 24. At this time, valves 27, 28, 3
4 is a open, valves 26, 29, 30, 31, 32, 3
3 and 35 are closed. The carbon dioxide gas sent to the dry ice production tank 24 undergoes a heat exchange with the low temperature liquefied gas contained in the dry ice, the low temperature liquefied gas is vaporized, a part of the carbon dioxide gas becomes dry ice, and the remaining 7 is precooled. It is sent into the low temperature liquefied gas in the dry ice production tank 23.

Here, the carbon dioxide becomes dry ice, and the dry ice in the low-temperature liquefied gas in the dry ice production tank 23 gradually increases, while the low-temperature liquefied gas in the dry ice in the dry ice production tank 24 gradually decreases, and eventually When only dry ice remains, open the valve 32 and take it out. Next, open the valve 30, feed the low temperature liquefied gas into the dry ice production tank 24, open the valves 26, 29, 35, and open the valves 27, 28,
30, 31, 32, 33, and 34, and reverse the flow of carbon dioxide gas. That is, the carbon dioxide gas is sent to the dry ice production tank 23, where it is separated from the dry ice and the low temperature liquefied gas contained in the dry ice, and then sent into the low temperature liquefied gas in the dry ice production tank 24. . As described above, dry ice production and separation are performed alternately in the dry ice production tanks 23 and 24. Moreover, by using the liquid nitrogen of this example that is advantageously produced by air separation using the cold energy of liquefied natural gas as shown in FIG. 3, further economical benefits are added.

In the air separation device j shown in FIG. 3 that utilizes the cold energy of liquefied natural gas, raw air 50 is compressed by an air compressor 41, precooled by an air heat exchanger 42, and sent to a high-pressure distillation column 43. In this step, nitrogen moves to the top of the column and oxygen moves to the bottom of the column, and liquid nitrogen 51 is taken out from the top of the column. On the other hand, the oxygen-rich liquid coming out from the bottom of the high pressure distillation column 43 is transferred to the low pressure distillation column 43.
liquid oxygen 52 is taken out from the bottom of the column. Nitrogen-rich gas 49 contained in the oxygen-rich liquid is discharged from the bottom of the low-pressure distillation column 44 and transferred to the air heat exchanger 4.
2 and used to pre-cool the raw air. On the other hand, the circulating nitrogen 48 used for cooling the high-pressure distillation column is supplied to the circulating nitrogen compressor 4.
6, liquefied natural gas 47 and LNG heat exchanger 45
It is liquefied by heat exchange and reaches the high pressure distillation column 43,
The gas is vaporized in the air heat exchanger 42 and reaches the circulating nitrogen compressor 46, while the heat exchanger 45 vaporizes the liquefied natural gas 47.
vaporizes and becomes natural gas.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus used in an embodiment of the present invention, FIG. 2 is a schematic diagram of another example of the apparatus, and FIG. 3 is a schematic diagram of an air separation apparatus that utilizes the cold energy of liquefied natural gas. 1...Pipe, 2...Precooling heat exchanger, 3
...Dry ice production tank, 4...Delivery pipe, 5...Separation chamber, 6...Valve, 7.
...Low temperature liquefied gas tank, 8...Pump, 9
...Dry ice storage chamber, 10...Rotary valve, 11...Pipe, 12...
・Wire mesh conveyor, 13, 21... pipe, 22...
...Heat exchanger, 23, 24...Dry ice production tank, 25...Pipe, 26, 27, 28, 29
,30,31,32,33934200'' valve.

Claims (1)

[Claims] 1. Low-temperature liquefied gas such as liquid nitrogen, liquid oxygen, a mixture thereof, or liquefied natural gas by blowing carbon dioxide gas at a pressure of normal pressure or higher and lower than the triple point pressure. A method for producing dry ice, which is characterized by directly contacting carbon dioxide with carbon dioxide, cooling and solidifying it, and then vaporizing and separating surplus low-temperature liquefied gas. 2. By blowing carbon dioxide gas into low-temperature liquefied gas such as liquid nitrogen, liquid oxygen, a mixture thereof, or liquefied natural gas at a pressure of normal pressure or higher and lower than the triple point pressure, these low-temperature liquefied gases and carbon dioxide gas are brought into direct contact. , to cool and solidify, and then to vaporize and separate the low-temperature liquefied gas from the dry ice, by aerating carbon dioxide gas through the dry ice containing the low-temperature liquefied gas, the low-temperature liquefied gas contained in the dry ice is vaporized, A method for producing dry ice, characterized by producing dry ice using cold heat possessed by low-temperature liquefied gas.