APPARATUS AND METHOD FOR THE PRODUCTION OF DRY ICE

Abstract

Apparatus for the production of dry ice comprising: - feeding means (2) for supplying carbon dioxide in the liquid state; - means (20) for the transition of state of the carbon dioxide to the liquid state flowing along the feeding means (2); said transition of state means (20) causing the desired solidification of the carbon dioxide in order to produce dry ice and the undesirable formation of carbon dioxide in the gaseous state; - a system (3) for collecting and recovering the carbon dioxide in the gaseous state; said collection and recovery system (3) collecting the carbon dioxide in the gaseous state downstream of the transition of state means (20) and comprising: i) a compressor (4) for compressing the carbon dioxide collected by the collection system (3);ii) a heat exchanger (5) which thermally connects the carbon dioxide downstream of the compressor (4) and the carbon dioxide upstream of the compressor (4), iii) storage means (6) for storing the carbon dioxide from the compressor (4). Figure from the Abstract = [FIG.1];

Description

Title of the invention: APPARATUS AND METHOD FOR THE PRODUCTION OF DRY ICE

[0001] The present invention relates to an apparatus and method for the production of dry ice. There are known solutions that involve supplying liquid carbon dioxide to an expansion element. This causes expansion, leading to the production of dry ice. A disadvantage of this solution is related to the fact that during the production of dry ice, a considerable part of the carbon dioxide passes into the gaseous state, which, being volatile, is thus dispersed into the environment. The object of the present invention is to provide an apparatus and method for the production of dry ice which make it possible to optimize the available resources while minimizing the risk of the disadvantages described above. The stated technical task and specified objectives are substantially achieved by an apparatus and method comprising the following technical characteristics. In more detail, the invention relates to an apparatus for the production of dry ice comprising: - supply means for supplying carbon dioxide in liquid state; - means for transitioning the state of at least a portion of the carbon dioxide flowing along the supply means from the liquid state to the solid state, said state transition means causing the desired solidification of the carbon dioxide to produce dry ice and the undesirable formation of carbon dioxide in the gaseous state; - a system for collecting and recovering carbon dioxide in the gaseous state; said collection and recovery system collecting carbon dioxide in the gaseous state downstream of the state transition means and comprising: (i) a compressor for compressing the carbon dioxide collected downstream of the state transition means; (ii) storage means for storing carbon dioxide from the compressor. The device is characterized in that: - the compressor is a volumetric piston compressor capable of compressing the outgoing carbon dioxide to a pressure between 25 and 28 bar, - the collection and recovery system includes a heat exchanger which puts the carbon dioxide downstream of the compressor and the carbon dioxide upstream of the compressor into thermal communication, - storage means are means for storing liquid carbon dioxide under pressure between 18 and 20 bar. The apparatus of the invention also comprises at least one of the following features: - said exchanger is a plate exchanger, - the carbon dioxide collection and recovery system comprises a line for the flow of the carbon dioxide collected downstream of the means to the storage means, said flow line comprising: - a first section located upstream of the heat exchanger; - a second section which extends downstream of an intermediate outlet of the exchanger and upstream of an intermediate inlet into the exchanger; - a third section downstream of the interchange. - the carbon dioxide collection and recovery system further includes electric heaters located in the first section between the exchanger and the compressor, - the collection and recovery system includes a non-return valve interposed between the compressor and the storage means, - the collection and recovery system includes a homogenizer placed between the compressor and the storage means. The invention also relates to a method for producing dry ice comprising the following steps: - causing at least a portion of the carbon dioxide to solidify in the liquid state, thereby producing dry ice by state transition means; said state transition means causing the desired solidification of the carbon dioxide to produce dry ice and the undesirable formation of carbon dioxide in the gaseous state; - collect, downstream of the state transition means, carbon dioxide in the gaseous state; - compressing said carbon dioxide to a gaseous state by means of a compressor in the form of a volumetric piston compressor compressing the outgoing carbon dioxide to a pressure of between 25 and 28 bar, thereby transforming said gaseous carbon dioxide into liquid carbon dioxide; - store said liquid carbon dioxide in storage means under pressure between 18 and 20 bar, - carry out a heat exchange between the liquid carbon dioxide present downstream of the compressor having a temperature of 15 to 20°C and the gaseous carbon dioxide present upstream of the compressor having a temperature of -70 to -78.5°C. Additional features and advantages of the present invention will become more apparent from the brief, and therefore non-limiting, description of an apparatus and method for producing dry ice as illustrated in the accompanying figures, in which: - [Fig.l] shows a schematic view of an apparatus for the production of dry ice according to the present invention; - [Fig. 2] shows a system for collecting and recovering carbon dioxide in an apparatus for producing dry ice according to the present invention. In the attached figure, reference numeral 1 designates an apparatus for producing dry ice (or more generally carbon dioxide in the solid state). The apparatus 1 comprises supply means 2 for supplying carbon dioxide in the liquid state. These supply means 2 suitably comprise a reservoir 21. The supply means 2 comprise a transport line 22 for transporting the carbon dioxide in the liquid state which suitably extends from / downstream of the reservoir 21 (see [Fig.l]). Suitably, the carbon dioxide in the reservoir 21 is at a temperature below -18°C, practically between -20 and -25°C, and at a pressure above 7 bar, in particular between 18 and 20 bar. The apparatus 1 comprises means 20 for the transition of at least a portion of the carbon dioxide in the liquid state flowing along the supply means 2 (or more precisely along the transport line 22) from the liquid state to the solid state. The state transition means 20 cause the desired solidification of the carbon dioxide to produce dry ice and the undesirable formation of carbon dioxide in the gaseous state. The means 20 comprise / are expansion means. Typically, the means 20 comprise / are an expansion valve. The apparatus 1 conveniently comprises a collection tank 23 for collecting the dry ice. The apparatus 1 comprises a system 3 for collecting and recovering carbon dioxide in the gaseous state. The collection and recovery system 3 collects the carbon dioxide in the gaseous state downstream of the state transition means 20. Suitably, the collection and recovery system 3 collects the carbon dioxide in the gaseous state at the collection tank 23. Therefore, carbon dioxide which, for whatever reason, is not transformed into dry ice can be reused. The collection and recovery system 3 comprises a compressor 4 for compressing the carbon dioxide collected by the collection system 3. Preferably, the compressor 4 is a positive displacement compressor. Even more preferably, the compressor 4 is a piston compressor. Suitably, compressor 4 has a liquid separator on the inlet side. Suitably, compressor 4 has a particularly efficient two-stage oil separator on the outlet side. Preferably, the compressor 4 compresses the outgoing carbon dioxide to a pressure of between 25 and 28 bar. The collection and recovery system 3 comprises storage means 6 for storing the carbon dioxide from the compressor 4. The storage means 6 may comprise a pressure vessel, for example a pressurized cylinder. The storage means 6 are means for storing the liquid carbon dioxide under pressure, in particular between 17 and 25 bar, preferably between 17 and 22 bar, advantageously between 18 and 20 bar. Therefore, the carbon dioxide can be recovered (advantageously in liquid form) in order to be subsequently reused in the dry ice production system. The collection and recovery system 3 comprises a heat exchanger 5 which thermally connects the carbon dioxide downstream of the compressor 4 and the carbon dioxide upstream of the compressor 4. In particular, the heat exchanger 5 thermally connects the carbon dioxide immediately downstream of the compressor 4 and the carbon dioxide upstream of the compressor 4. Advantageously, the exchanger 5 is a plate exchanger, preferably a countercurrent plate exchanger. The thermal communication makes it possible to reduce the temperature of the gaseous carbon dioxide before it enters the compressor, from a temperature range of between -70 and -78.5°C, to a temperature of approximately -40 to -45°C in order to liquefy it in the volumetric piston compressor. The presence of said thermal communication optimizes the operation of the volumetric piston compressor and makes it possible to save energy. Suitably, the collection system 3 comprises a line 30 for the flow of the carbon dioxide collected downstream of the means 20 towards the storage means 6. This flow line 30 advantageously comprises: - a first section 31 located upstream of the heat exchanger 5; - a second section 32 which extends downstream of an intermediate outlet 320 of the exchanger 5 and upstream of an intermediate inlet 321 in the exchanger 5 (the compressor 4 is located along the second section 32); - a third section 33 downstream of interchange 5. Appropriately, - between exchanger 5 and compressor 4 (in the second section 32), the gaseous carbon dioxide is at a temperature between -45 and -40°C, - between compressor 4 and exchanger 5 (in the second section 32), the liquefied carbon dioxide is at a temperature between 15 and 20°C, - immediately downstream of the exchanger 5 (in the third section 33), the liquid carbon dioxide is at a temperature between -10 and -40°C, preferably between -25 and -30°C. The first, second and third sections 31, 32, 33 define the same pipeline. They are arranged one after the other in series. The carbon dioxide in the first section 31 is used to cool the carbon dioxide in the third section 33. In this description, the expressions "upstream of" and "downstream of" are to be understood with respect to the direction of flow of carbon dioxide. Upstream of the compressor 4, the system 3 may comprise a safety valve 41 (it is conveniently located upstream of the compressor 4 and downstream of at least part of the exchanger 5; it is suitably located in the second section 32). The safety valve 41 allows the compressor 4 to be bypassed or carbon dioxide to be released. The safety valve 41 may be a motorized valve. Suitably, the carbon dioxide immediately upstream of the exchanger 5 (in the first section 31) is at about 1 bar and advantageously at a temperature below -76.8°C, for example at a temperature of -78.5°C, substantially between -70°C and -78.5°C. Suitably, the liquid carbon dioxide immediately downstream of the compressor 4 (in the second section 33) is at a pressure of between 25 and 28 bar, and at a temperature of between 15 and 20°C. Suitably, immediately upstream of the heat exchanger 5 (for example in the first section 31), the flow rate of carbon dioxide is between 300 and 500 m3 / h, preferably about 400 m3 / h. Advantageously, immediately upstream of the heat exchanger 5, the carbon dioxide flow rate is between 700 and 900 kg / h, preferably approximately 800 kg / h. Advantageously, the system 3 comprises a non-return valve 60 interposed between the compressor 4 and the storage means 6 (for example in the third section 33). This prevents / limits the return of carbon dioxide present in the storage means 6. A safety valve 61 may be present between the compressor 4 and the check valve 60 (for example in the third section 33). The safety valve 61 allows the valve 60 to be bypassed or carbon dioxide to be released. The safety valve 61 may be a motorized valve. In a particular solution, the system 3 could possibly comprise a homogenizer 7. Suitably, the homogenizer 7 is placed between the compressor 4 and the storage means 6 (typically in the third section 33). The homogenizer 7 allows, for example, to compress the carbon dioxide to a pressure also higher than 100 bar, suitably also between 200 and 250 bar. In this way, storage can take place in the means 6 at a higher pressure. Downstream of the homogenizer, the temperature is between -20 and -25 °C. Suitably, the system 3 may comprise one or more temperature sensors 81; for example, in the solution of [Fig. 2], one temperature sensor is present in the first section 31, two temperature sensors in the second section 32 (one upstream and one downstream of the compressor 4) and one temperature sensor in the third section 33. Suitably, the system 3 may include electric heaters (not shown in the figures) located in the first section 31 between the heat exchanger 5 and the compressor 4. If the temperature of the carbon dioxide gas is too low before it enters the compressor 4, the electric heaters adjust the temperature to a range of -40 to -45°C. Suitably, the system 3 may comprise one or more pressure sensors 82 (for example in the solution of [Fig.2], it is placed downstream of a part of the exchanger 5 and upstream of the compressor 4). The pressure measured by this specific sensor is approximately 5 bar. The subject matter of the present invention relates to a method for the production of dry ice. In particular, it is a method for the production of dry ice which provides for at least partial recovery of the carbon dioxide not transformed into dry ice. More generally, it can also be defined as corresponding to a plant for the treatment of carbon dioxide in the liquid state. Suitably, this method is implemented by an apparatus 1 for the production of dry ice having one or more of the characteristics described above. The method comprises the steps of causing carbon dioxide (in the liquid state) to solidify, thereby obtaining dry ice. This is typically achieved with state transition means 20 (typically expansion means). The state transition means 20 causes the desired solidification of carbon dioxide to produce dry ice and the undesirable formation of carbon dioxide in the gaseous state. So there is a transition of carbon dioxide from the liquid state to the solid state. This is achieved by expanding the carbon dioxide in expansion means. The method also comprises collecting, downstream of the state transition means 20, carbon dioxide in the gaseous state. The method also comprises a step of compressing said carbon dioxide into the gaseous state by means of a compressor 4, thus transforming it into carbon dioxide in the liquid state. The method comprises a step of storing said carbon dioxide in the liquid state in storage means 6. Conveniently, the method may comprise a step of exchanging heat between the carbon dioxide present downstream of the compressor 4 having substantially a temperature of 15 to 20°C and the carbon dioxide present upstream of the compressor 4 having substantially a temperature of -70 to -78.5°C. Suitably, this heat exchange takes place in a heat exchanger 5. The carbon dioxide present downstream of the compressor 4 and the carbon dioxide present upstream of the compressor 4 (which are in thermal communication via the heat exchanger 5) circulate along the same transport line. This makes it possible to cool the carbon dioxide present downstream of the compressor 4 with the carbon dioxide present upstream of the compressor 4. This arrangement in combination with a positive displacement piston pump makes it possible to save energy. The present invention has significant advantages. First, it allows for the recovery of volatile carbon dioxide in the production of dry ice. This reduces the consumption of raw materials and energy consumption. The invention thus developed is susceptible to numerous modifications and variations, all falling within the inventive concept which characterizes it. In addition, all details can be replaced by technically equivalent elements. All materials used, as well as dimensions, can in practice be any, according to requirements.

Claims

Claims

1. An apparatus for producing dry ice comprising: - supply means (2) for supplying carbon dioxide in the liquid state; - means (20) for transitioning at least a portion of the carbon dioxide flowing along the supply means (2) from the liquid state to the solid state, said state transition means (20) causing the desired solidification of the carbon dioxide to produce dry ice and the undesirable formation of carbon dioxide in the gaseous state; - a system (3) for collecting and recovering the carbon dioxide in the gaseous state; said collection and recovery system (3) collecting the carbon dioxide in the gaseous state downstream of the state transition means (20) and comprising: i) a compressor (4) for compressing the carbon dioxide collected downstream of the state transition means (20);ii) storage means (6) for storing the carbon dioxide coming from the compressor (4). characterized in that: - the compressor (4) is a volumetric piston compressor capable of compressing the outgoing carbon dioxide to a pressure of between 25 and 28 bar, - the collection and recovery system (3) comprises a heat exchanger (5) which puts the carbon dioxide downstream of the compressor (4) and the carbon dioxide upstream of the compressor (4) into thermal communication, - the storage means (6) are means for storing the liquid carbon dioxide under pressure of between 18 and 20 bar.;

2. Apparatus according to claim 1, characterized in that said exchanger (5) is a plate exchanger.

3. Apparatus according to claim 1, characterized in that the system (3) for collecting and recovering carbon dioxide comprises a line (30) for the flow of the carbon dioxide collected downstream of the means (20) towards the storage means (6), said flow line (30) comprising: - a first section (31) located upstream of the heat exchanger (5); - a second section (32) which extends downstream of an intermediate outlet (320) of the exchanger (5) and upstream of an intermediate inlet (321) in the exchanger (5); - a third section (33) downstream of the exchanger (5).

4. Apparatus according to claim 3, characterized in that the system (3) for collecting and recovering carbon dioxide further comprises electric heaters located in the first section (31) between the exchanger (5) and the compressor (4).

5. Apparatus according to claim 1, characterized in that the collection and recovery system (3) comprises a non-return valve (60) interposed between the compressor (4) and the storage means (6).

6. Apparatus according to claim 1, characterized in that the collection and recovery system (3) comprises a homogenizer (7) placed between the compressor (4) and the storage means (6).

7. A method for producing dry ice comprising the following steps: - causing at least a portion of the carbon dioxide to solidify in the liquid state, thereby producing dry ice by state transition means (20); said state transition means (20) causing the desired solidification of the carbon dioxide to produce dry ice and the undesirable formation of carbon dioxide in the gaseous state; - collecting, downstream of the state transition means (20), the carbon dioxide in the gaseous state; - compressing said carbon dioxide in the gaseous state by means of a compressor (4) in the form of a volumetric piston compressor compressing the outgoing carbon dioxide to a pressure of between 25 and 28 bar, thereby transforming it into carbon dioxide in the liquid state;- storing said carbon dioxide in the liquid state in storage means (6) under pressure between 18 and 20 bar, - carrying out a heat exchange between the liquid carbon dioxide present downstream of the compressor (4) having a temperature of 15 to 20°C and the gaseous carbon dioxide present upstream of the compressor having a temperature of -70 to -78.5°C.;

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