Method and installation for vaporizing liquid CO2 and supplying gaseous CO2 to a user station

Abstract

A method for supplying gaseous CO2 to a user station (30) of this gaseous CO2 or a mixture of gases comprising gaseous CO2, station located on a producing site, according to which: A liquid CO2 reservoir (21) is available, connected to said user station of this gaseous CO2 or a mixture of gases comprising gaseous CO2, which reservoir contains, under a storage pressure greater than atmospheric pressure, CO2 in liquid phase at the bottom of the reservoir and in gaseous phase at the top of the reservoir; The user station is supplied with gas by drawing liquid CO2 from the lower part of the reservoir and by vaporizing this liquid CO2 on a line connecting the reservoir to the user station;where when the liquid level varies inside the tank, causing a pressure variation in the tank's gas head, this gas head is repressurized as necessary by drawing cryogenic liquid from the bottom of the tank, vaporizing this drawn liquid, and sending the gas thus produced into the storage gas head; characterized in that said vaporization of the liquid CO2 used to supply the user station with gas and said vaporization of the liquid CO2 drawn from the bottom of the tank to repressurize the tank's gas head are both carried out within the same single heat exchanger (23). Figure from the abstract: Fig. 2;

Description

Title of the invention: Method and installation for vaporizing CO 2 liquid and gaseous CO2 supply to a user station

[0001] The invention relates to so-called "bulk" storage of cryogenic liquids, for example liquid CO2, which requires equipment to maintain them under pressure.

[0002] Indeed, the withdrawal of liquid from storage typically results in a too rapid and / or significant drop in pressure in the reservoir (in the gaseous atmosphere above the liquid).

[0003] In general, repressurization is achieved by taking a little cryogenic liquid from the bottom of the tank, to vaporize it and return it to the storage area.

[0004] Conventionally, this repressurization system uses electricity to vaporize the cryogenic liquid, in the form of an electric heater / vaporizer.

[0005] Now, let us consider in the following the case of liquid CO2: the purpose of this liquid CO2 is in the vast majority of applications to be vaporized, to supply an end-user station, for example an application of CO2 in the food sector, for example an application of carbonation of drinks.

[0006] It is then known that different technical solutions are commonly used to achieve such vaporization of liquid CO2, and in particular solutions are known where this vaporization is achieved by means of an exchanger, powered by a heat or energy source, such as air, steam, hot water, electricity, it can therefore also be an electric heater / vaporizer like the one mentioned above to repressurize a tank. This (electric) can, in certain situations, be chosen in preference to an evaporator / exchanger using ambient air, which can be cold in winter (indeed, if the ambient temperature is too low, the temperature difference with the liquid CO2 (-25 to -30°C in general) is no longer large enough to allow evaporation of the liquid CO2 in equipment of reasonable size, it is then necessary to greatly increase the exchange surface of atmospheric evaporators of the finned tube type for example)..

[0007] This may therefore require, for the operation of such a bulk tank of liquid CO2, the implementation of a certain number of pieces of equipment, whether of the same type or of different types (therefore to repressurize the tank on the one hand and to vaporize the liquid towards the user station on the other hand), which in all cases implies a significant effort in terms of investment.

[0008] However, it can also be noted that the repressurization equipment and the main evaporator operate together, that is to say that the maximum heat requirement is concomitant: it is when the gaseous CO2 requirement is at its maximum at the end user station that the main evaporator consumes the maximum heat, and that then the pressure loss in the tank is the most rapid, and must be compensated by the maximum operation of the repressurization system.

[0009] One of the objectives of the present invention is then to propose a solution to the problem described above.

[0010] For this, as will be seen in more detail below, the present invention proposes to use a single piece of equipment to both repressurize the reservoir and to carry out the evaporation of a flow of liquid CO2 to supply gas to a final application, a user station for CO2 or a gas mixture comprising CO2.

[0011] One could of course consider using a single evaporator, and a small part of the evaporated flow could be returned to the storage sky in order to repressurize it.

[0012] We would then certainly have gains in terms of: • investment (a single piece of equipment). Of course, its cost does not only depend on its size but also on the number of accessory equipment (such as valves, safety devices, etc.) that are necessary for the proper functioning of the equipment. By using a single evaporator, we save a lot on investment since the number of equipment and the associated labor will be very limited, even if the equipment is larger. • simplification of utilities: a single electrical line to supply a single piece of equipment. • the reliability of the whole is increased by minimizing the number of pieces of equipment required.

[0013] And yet nevertheless, this single exchanger configuration would still require spending electrical energy to operate it.

[0014] It is therefore proposed according to the present invention to optimize a solution with a single exchanger, by using an exchanger composing an assembly called in this technical field an “ecochiller”.

[0015] We will recall below what the person skilled in the art understands by the concept of ecochiller.

[0016] An “Ecochiller” is a complete solution implementing a heat exchanger which combines in the same equipment the vaporization of the cryogen, without the need for electrical energy, with the recovery of the cooling energy generated during vaporization.

[0017] This cooling energy is generally used in the water cooling system of the producer site using this gaseous CO2, which makes it possible to save electrical energy linked to the water cooling usually practiced on this site.

[0018] Indeed, usually for this type of industry, the gaseous CO2 supply is carried out according to the classic scheme, that is to say by connecting after the outlet of a liquid CO2 storage behind an atmospheric or electric heater. When using the gas and its vaporization, a lot of energy available in the form of frigories is then lost (not recovered) in the atmospheric exchanger with the ambient air.

[0019] However, moreover, on the same site using this gaseous CO2, it is very common for the manufacturer to also need to cool one of its other processes, one of its fluids and in particular water.

[0020] Thus, many industrial processes, using gases and heat, require in parallel and simultaneously a water cooling system which is very energy-intensive, in order to generate and satisfy the cold requirement of the process. Optimizing and rationalizing the environmental, economic, safety or regulatory impact of these processes is an essential challenge to be met.

[0021] The CO2 “Ecochiller” is an alternative heat exchanger solution that combines both the vaporization of the cryogen and the recovery of frigories generated during this vaporization. Vaporization is carried out without the use of electrical energy and the frigories obtained during the heat exchange are then used in the site’s industrial cooling unit, thus saving electrical energy again.

[0022] As an illustration of the above, a site which carbonates beverages wishes to cool its water before carbonation in order to improve the dissolution of CO2 in this water (Henry's law).

[0023] Still as an illustration, other industrialists need to cool the water in the treatment plants because below a certain temperature, the bacterial flora is no longer as effective, while others need to lower the temperature of their water to cool or maintain the plants at 4°C (for example the salad family) etc.... the applications, as we can see, are numerous.

[0024] This “Ecochiller” exchanger can use different heat sources to evaporate liquid CO2, such as water or steam for example.

[0025] Also, in addition to the advantages mentioned above, we can also mention: • Non-consumption of electrical energy, which remains the most expensive energy. Usable utilities are much cheaper on a site which generally already has the means of production. The operating cost is therefore optimized. • Simplification and therefore reduction of investment since here, only one utility is used. • Minimization of energy costs through the recovery of the cold contained in the liquid CO2 which will contribute to cooling the water utility.

[0026] [Fig.l] attached provides a partial schematic view of a conventional tank of cryogenic liquid such as liquid nitrogen or liquid CO2, equipped with usual means for re-pressurizing its gaseous atmosphere as liquid is drawn from the bottom of the tank to supply gas to a user station (station 2 in [Fig.l]).

[0027] The figure shows a nitrogen tank 1, containing liquid nitrogen at the bottom, also called the tank, and gaseous nitrogen under a pressure of approximately 2 bars at the top, also called the head. The liquid level inside the tank is indicated by the reference N.

[0028] The bottom of the tank 1 is connected to a consuming installation 2, for example a deep-freezing tunnel, via a connecting pipe 3 provided with a closing valve 4. The point of connection of the pipe 3 to the tank 1, which is noted P, is commonly called the draw-off point.

[0029] The tank 1 comprises means 5 for pressurizing the gas at the top of the tank. These means 5 here comprise a line 6 connecting the bottom of the tank to its top, and is provided, from upstream to downstream, with a device 7 for measuring the pressure of the liquid nitrogen, for example a pressure gauge, a closing valve 8 (preferably a solenoid valve) and a vaporizer 9.

[0030] The tank 1 also comprises means 10 for venting the gas at the top of the tank. These means 10 comprise a line 11 for evacuation to the outside, provided from upstream to downstream with a pressure gauge 12, a closing valve 13 and possibly an air exhaust member not shown, commonly called a silencer.

[0031] A unit 15, ensuring the control of the means 5 for pressurizing the top, as well as the means 10 for venting the top, is connected, for example by electrical connections, on the one hand to the pressure measuring devices 7 and 12, and on the other hand to the valves 8 and 13. The control unit 15 is thus adapted, on the one hand, to know, continuously or at regular intervals, the pressure of liquid nitrogen at the bottom of the tank 1 and of gaseous nitrogen at the top of this tank and, on the other hand, to compare the value of the pressure at the bottom with a chosen predetermined value, modifiable by the user. The unit 15 is also capable of controlling the opening, total or partial, as well as the closing of the valves 8 and 13 so as to regulate the tank bottom and top pressures 1.

[0032] Nitrogen supply means 16 are also provided, so as to regularly, possibly continuously, supply liquid nitrogen to the tank 1. Conventionally, these means 16 comprise a supply pipe 17 through the bottom of the tank 1 allowing so-called “spring” filling, and possibly a supply pipe 18 through the top of the tank allowing so-called “rain” filling. The tank 1 also comprises an overflow member 19 known per se, intended to limit the height of the liquid inside the tank. In the single figure, the level of the liquid N is shown at its maximum.

[0033] [Fig.2] attached provides a partial schematic view of CO2 vaporization equipment according to the invention.

[0034] The following installation elements can be seen in [Fig.2]: - 21. Liquid CO2 storage - 22. Liquid CO2 - 23. The “Ecochiller” exchanger - 24. The site's water cooling system - 25. Gaseous CO2 directed to the user station 30 - 26. Flow of heat transfer fluid (water) between the cooling system 24 and the user station 30, which by heating up (and therefore recovering the heat generated by the station 30) will return to evacuate it into the cooling source 24. This flow is then cooled there and can return to cool the station 30. - 27. Cooled water in exchanger 23. - 28. Water from user station 30 and directed towards exchanger 23. - 29. Gas produced by the exchanger 23 used to repressurize the gaseous atmosphere of the tank 21 - 30. CO2 user station.

[0035] The invention then relates to a method for supplying gaseous CO2 to a station using this gaseous CO2 or a mixture of gases comprising gaseous CO2, a station located on a producer site, according to which: • A liquid CO2 tank is available, connected to said user station for this gaseous CO2 or a mixture of gases comprising gaseous CO2, which tank contains, under a storage pressure greater than atmospheric pressure, CO2 in the liquid phase at the bottom of the tank and in the gaseous phase at the top of the tank; • The user station is supplied with gas by drawing liquid CO2 from the lower part of the tank and vaporizing this liquid CO2 on a line connecting the tank to the user station; • When the liquid level varies inside the tank, causing a pressure variation in the gaseous headspace of the tank, this gaseous headspace is repressurized if necessary by taking cryogenic liquid from the bottom of the tank, vaporizing this taken liquid, and sending the gas thus produced into the gaseous headspace of the storage;

[0036] characterized in that: - Said vaporization of liquid CO2 allowing the user station to be supplied with gas; and - Said vaporization of liquid CO2 taken from the bottom of the tank to repressurize the gaseous atmosphere of the tank;

[0037] are both produced within the same single heat exchanger, preferably a plate exchanger, an exchanger capable of ensuring the evaporation of a flow of liquid CO2 from said reservoir, to produce a flow of gaseous CO2 which is conveyed according to the following two destinations:

[0038] • a first part of this gas flow is, where appropriate, returned to the gaseous headspace of said liquid CO2 reservoir in order to provide additional gas to this reservoir and thus contribute, where appropriate (if necessary), to repressurizing its gaseous headspace; • a second part of this gas flow is conveyed to said user station or to a mixing system capable of supplying the user station with the gas mixture containing gaseous CO2 that it requires.

[0039] It is understood that the single exchanger (23) which aims to evaporate the cryogenic liquid received (line 22) from the tank, must therefore be supplied with heat.

[0040] Several heat sources can be considered, more or less adapted to the chosen exchange technology: - plate exchanger with electricity as heat source; - tank containing a liquid (often water), itself heated by electrical resistors (the volume of water serving as a heat reserve or so-called capacity, “steam pool”); - tank using the same principle but replacing the liquid with a metal.

[0041] It should also be noted that most often, the user site will have several utility networks to manage the heat exchanges (heating and cooling) within its application. The cooling utility network is generally composed of a loop containing a heat transfer liquid (water, glycolated water, etc.), lines 26, 27 and 28 in the Figure. This loop brings into contact one or more heat sources (to be cooled, such as equipment 30, for example) and one or more cold sources (cooling system 24). The application is maintained in tem temperature or cooled thanks to the continuous flow of heat transfer fluid (line 26) which, as it heats up (and therefore recovers the heat generated by the application 30), will evacuate it into the cooling source (device 24). This flow is then cooled and can return to cool the application(s) on the site.

[0042] In this context, it is proposed according to the present invention to use this heat transfer fluid loop as a heat source to evaporate the cryogenic liquid. The heat source required for the exchanger 23 therefore consists of a heated flow from the loop (line 28 in [Fig.2] - output from the application / use (equipment 30) which produces heat since it needs to be cooled (frigories) or to be maintained at temperature). This cooled flow (line 28 then 27) can then return to the utility loop.

[0043] Such an arrangement has several advantages: • the cooling source is unique, which represents a great simplification of utilities. • the evaporation of the cryogenic liquid makes it possible to recover cold (the opposite of heat, in other words to remove heat from the utility's heat transfer fluid loop). This is therefore a way of relieving the utility's cold source, hence a gain in size. • the tank repressurization supply line is then very simple: for example, a non-return valve, regulating valve or pressure reducer to manage the pressure downstream, therefore in the top of tank 21.

[0044] We therefore have in summary the fact that we organize within a single exchanger, without intervention of electrical energy, the recovery of the frigories generated during the vaporization of the liquid CO2, during a thermal exchange between this liquid CO2 and a utility fluid, for example water, used by the production site to cool one of its operations, thus using all or part of these frigories to cool this fluid.

Claims

Claims

1. Method for supplying gaseous CO2 to a user station (30) of this gaseous CO2 or of a mixture of gases comprising gaseous CO2, station located on a producer site, according to which: • A liquid CO2 tank (21) is available, connected to said user station for this gaseous CO2 or a mixture of gases comprising gaseous CO2, which tank contains, under a storage pressure greater than atmospheric pressure, CO2 in the liquid phase at the bottom of the tank and in the gaseous phase at the top of the tank; • The user station is supplied with gas by drawing liquid CO2 from the lower part of the tank and vaporizing this liquid CO2 on a line connecting the tank to the user station; • When the liquid level varies inside the tank, causing a pressure variation in the gaseous headspace of the tank, this gaseous headspace is repressurized if necessary by taking cryogenic liquid from the bottom of the tank, vaporizing this taken liquid, and sending the gas thus produced into the gaseous headspace of the storage; characterized in that: - Said vaporization of liquid CO2 allowing the user station to be supplied with gas; and - Said vaporization of liquid CO2 taken from the bottom of the tank to repressurize the gaseous atmosphere of the tank; are both produced within the same single heat exchanger (23), preferably a plate exchanger, an exchanger capable of ensuring the evaporation of a flow of liquid CO2 (22) from said reservoir, to produce a flow of gaseous CO2 which is conveyed according to the following two destinations: a first part of this gas flow is, where appropriate, returned (29) into the gaseous sky of said CO2 reservoir liquid in order to provide additional gas to this tank and thus contribute where appropriate to repressurizing its gaseous sky; • a second part of this gas flow is conveyed (25) to said user station or to a mixing system capable of supplying the user station with the gas mixture comprising gaseous CO2 that it requires; and in that said single exchanger (23) is supplied with heat in the following manner: - the production site is equipped with a cooling utility network(s), enabling it to cool one or more of its operations, a network comprising a loop containing a heat transfer liquid such as water or glycolated water; - the heat source required for the exchanger (23) is obtained by organizing within the exchanger (23) a heat exchange between the liquid CO2 and a flow of heated utility fluid from the loop, requiring cooling, to then return once cooled by exchange with the liquid CO2 in the loop of the cooling utility network.

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