EP3397912B1 - Method and heat exchanger for recovering cold during the re-gasification of cryogenic liquids - Google Patents

Description

field of use

The invention relates to the recovery of cold in the regasification of cryogenic liquids, in particular liquefied natural gas (LNG, Liquefied Natural Gas at -162 ° C and 1 bar atmospheric pressure), liquefied nitrogen (LN2) and liquefied oxygen (LO2). For this purpose, process characteristics are specified in connection with a heat exchanger for realizing the method. The heat exchanger is designed for, although in comparison to the fuel energy relatively small, yet valuable cooling capacity in the range below 100 kW and is characterized by simple design features and ease of use, which allow the refrigeration capacity reasonably low investment.

State of the art

Natural gas can be transferred under atmospheric pressure after cooling to -162 ° C and subsequent removal of the heat of condensation from the gaseous to the liquid phase. Thus, the reduction of the volume is connected to six hundredths of the value given at 1.013 bar and 15 ° C. Liquefied natural gas can thus be stored in an attractive manner and transported over long distances. The equally costly and value-adding process chain to be realized ranges from extraction and processing via liquefaction, storage, long-distance transport with tankers, re-storage in large tanks and repeated transport to the user until regasification. The end of this chain is very often a so-called satellite system, namely a double-walled, vacuum-insulated LNG storage without liquefaction. The satellite system has a regasification device, usually an atmospheric evaporator with vertical longitudinal tubes, at which liquefied natural gas, hereinafter referred to as LNG, is vaporized and overheated to ambient temperature, while the required heat from the ambient air is supplied by free convection.

The described prior art is extensive in the DE102011081673 "Process and plant for regasification of LNG" and set out in further publications, for example in the following documents: US6089022 "Regasification of liquefied natural gas (LNG) aboard a transport vessel", US 6367265 "Vaporizer for a low temperature liquid", US 6367429 "Intermediate fluid type vaporizer" and WO 2004031644 "Regasification system and method".

Unsatisfactory is that the existing energetic potential in the LNG in the form of cold in the regasification remains unused.

This results in the aim of the invention, namely the particularly simple utilization of the released in this process, albeit in comparison to the fuel energy relatively small, so valuable cold in the range below 100 kW and that on a demand for practical needs moderately low temperature level above -60 ° C, eg for low-temperature storage or cold storage with phase change material (PCM).

task

The inventive task is thus to be seen in the indication of technological and apparative features that make it possible to achieve the aforementioned objective.

Based on the procedure to be proposed, a heat exchanger for temperature levels above -60 ° C is to be developed, which controls the large temperature differences occurring in the regasification of the cryogenic liquids. Deep-frozen liquids in the context of the invention are specified in detail in the introduction.

Solution of the task

The solution of the problem is specified in the main claim 1. The respective subordinate claims contain expedient embodiments.

According to the invention, the following is suggested:

In terms of the process, the cold of the LNG is transferred to a liquid refrigerant, which is to be used down to the temperature level of about -60 ° C, without pumping phase change and thus remains safe. Advantageously usable, for example, Therminol D12, a synthetic liquid based on aliphatic hydrocarbons.

However, the energy transfer does not take place directly on the liquid refrigerant, but first on an intermediate medium (intermediate fluid) and from this then on the liquid refrigerant. The use of the intermediate medium serves to overcome the large difference in temperature between the low-temperature liquid to be regasified and the refrigerant without the refrigerant cooling too strongly, even to the point of solidification of the same. The temperature of the intermediate medium and thus the serial driving temperature differences according to the invention with the aid of the apparatus design of the heat transfer, in particular on the heat transfer surfaces, freely adjustable. Because of its favorable solidification line, the triple point data are -187.7 ° C and 0.0002 Pa, and because of the given by evaporation and condensation very good heat transfer properties propane is preferably used as the intermediate medium.

The heat transfer via this intermediate medium takes place at a selectable intermediate temperature by evaporation and condensation in natural circulation, ie without the use of a pump, in a heat exchanger according to the invention for cooling capacities below 100 kW.

This heat exchanger is expediently designed as a cylinder in vertical alignment and closed at the top and bottom by dished ends.

The container thus realized contains in the upper part at least one surface heat exchanger for evaporating the cryogenic liquid, for example LNG, and in the lower part at least one further surface heat exchanger for cooling the liquid refrigerant.

To realize the heat transport within the hermetically sealed container, this is filled with the intermediate medium, preferably propane, which is securely encapsulated. The propane is in the lower part to the level of a boiling liquid and in the upper region above the filling level condensing saturated steam.

Both surface heat exchangers are designed as tube helices.

Advantageously, these are arranged several times, with a numerical symmetry is not mandatory.

The heat transfer from the condensing propane to the regasifizierende, cryogenic liquid thus takes place via the upper tube coils. These protrude from above freely down into the container interior. Likewise, the lower coiled tubings project freely from below into the interior of the container.

As fasteners on the container, the pipe coils associated collecting pipes are useful, with other fastening solutions can be realized.

The heat transfer from the refrigerant to be cooled to the liquid intermediate medium can be done on the lower tube coils.

With the choice of the material stainless steel for tanks and coiled tubing a sufficient Tiefkaltzähigkeit and a high corrosion resistance are guaranteed.

The use of coiled tubing makes it possible to accommodate relatively large heat transfer surfaces in a confined space.

The heat transfer from the upper coiled tubing to the deep-frozen liquid to be evaporated is particularly effective because of the long flow path and the resulting on a circular path secondary flow in the interior of the coiled tubing. Here is the largest transport resistance, the reduction of which has a particularly positive effect on the entire heat transfer result. The use of a turbulator can further reduce this transport resistance.

As already mentioned, in the lower part of the cylindrical container, further tube spirals protruding freely from below into the inner space, but at least one coiled tubing, are located. Here, the brine gives off the heat required for the evaporation of the intermediate medium propane in the manner described above. Here, too, leads to a very good heat transfer, because here is cold carrier the largest transport resistance.

The cylindrical container is after its evacuation with the intermediate medium, preferably propane, taking into account temperature, density and mass sustainably filled so that the upper tube coils remain free at each subsequent operating state, while the lower tube coils of liquid intermediate medium in the boiling state are completely flooded.

This is according to the invention, the consideration of an appropriate distance between the upper and lower tube coils ahead.

This distance can be calculated with the help of the material values of the intermediate medium. It corresponds approximately to the diameter of the coiled tubing.

Characteristic properties of the intermediate medium propane are the following:
At 25 ° C, the pressure of the propane (saturated steam and liquid in the boiling state are in phase equilibrium.) About 9.6 bar. The density of the liquid is then about 492 kg / m ³ .

At -70 ° C, the phase equilibrium at about 0.27 bar a. The density of the liquid phase is then about 612 kg / m ³ .

With the help of the spaced arrangement of the coiled tubing in the container and with their dimensions, ie design of the heat transfer surfaces, which determines the temperature of the natural medium evaporating and condensing intermediate medium and an inherent security achieved such that with the shutdown of the heat exchanger by interrupting the brine and The thermal equilibrium associated with the LNG mass flow never leads to a solidification of the refrigerant.

embodiments

The following embodiments are related to the regasification of cryogenic liquefied natural gas LNG (Liquefied Natural Gas) stored in a satellite tank farm. At 1 bar LNG bearing pressure its temperature is approx. -162 ° C and at 5 bar LNG bearing pressure approx. -138 ° C.

In the embodiments, the inventive method for recovering cold from liquefied natural gas (LNG) in conjunction with heat exchangers for brine temperature levels above -60 ° C and for cooling capacities in the range below 100 kW, explained in more detail with reference to drawings. The heat exchangers used differ in their design.

An inventive heat exchanger is in FIG. 1 shown as a section along its vertical axis system.
It is a cylindrical container 1 in vertical orientation, which is closed with an upper and a lower dished bottom 2 and 3 and is completely covered with an insulation 5.
In the region of the upper dished bottom 2, a coiled tubing 6 and at the lower dished bottom 3, a coiled tubing 7 is arranged directly or indirectly in each case in freely projecting into the container interior. The attachment to the container 1 is realized only on one side. For the purpose of heat transport within the hermetically sealed container 1, this is filled with the intermediate medium 8, namely propane 8, which is thus securely encapsulated. The level 9 of the liquid intermediate medium 8 in the container 1 is adjusted so that the upper tube coil 6 is surrounded in each operating state of gaseous intermediate medium 8.1 and the lower tube coil 7 is flooded with liquid intermediate medium 8.2. For this purpose, an appropriate distance of approximately the diameter of the coiled tubing 6 or 7 is present between the two coiled tubing 6 and 7 and the corresponding mass of the intermediate medium 8 is filled into the container.

The container 1 and the tube coils 6 and 7 are advantageously made of stainless steel. This guarantees sufficient cryogenic toughness and high corrosion resistance.
The heat transfer from the condensing propane saturated steam 8.1 to the deep-frozen liquid LNG to be regasified is thus effected via the upper coiled tubing 6. As already mentioned, this protrudes freely from above into the interior of the container. This has the advantage that mechanical stresses due to the large temporal temperature changes occurring during operation are sufficiently avoided.
The heat transfer from the coolant to be cooled to the liquid, boiling propane 8.2 takes place at the lower coiled tubing. 7
Since the lower coiled tubing 7 is mechanically connected in the same way to the lower region of the container, the described advantages of this attachment result analogously to the upper coiled tubing 6.
As a refrigerant advantageously Therminol D12 is used.

Another inventive heat exchanger is in FIG. 2 also shown as a section along its vertical axis system.
It differs from the above-described heat exchanger in that both the coiled tubing 6 and the coiled tubing 7 are present in multiple arrangement in the container 1 in otherwise analogous construction. In the example chosen, seven tube coils 6 and 7 are arranged in each case. All other features are taken apart from structural adjustments. It has proved to be advantageous to design the inflow 10 of the LNG directly with the interposition of a distributor 15 and to realize the outflow 11 of the regasified LNG via a collecting pipe 16 in the upper part of the container 1. The inflow 12 of the refrigerant to the coiled tubing 7 is also carried out with the interposition of a manifold 15 directly, while the drain 13 is realized via a further manifold 16 in the lower part of the container 1. The two manifolds 16 may alternatively be arranged outside the container 1. It is recommended to use the headers 16 for each one-sided attachment of the coiled tubing 6 and 7 on the container 1. Depending on the conditions of use, the upper and / or lower tube coils 6 and 7 can be connected individually or in bundles.

In accordance with the process, the described heat exchangers according to the invention enable effective heat transfer from the cooling medium to be cooled to the boiling intermediate medium 8.2 in the area of the lower coiled tubing or tube spirals 7 and from the condensing, gaseous intermediate medium 8.1 to the cryogenic liquid to be evaporated in the area of the upper coiled tubing or coiled tubing 6. The natural circulation of the intermediate medium comes through the dripping of the condensate from the or the upper coiled tubing 6 to conditions.

LIST OF REFERENCE NUMBERS

1

Container,

2

upper dished bottom,

3

lower dished bottom,

4

Pressure transmitter,

5

Insulation,

6

upper coiled tubing,

7

lower coiled tubing,

8th

Intermediate medium, for example propane,

8.1

Intermediate medium, for example propane, gaseous, condensing; Propane saturated steam,

8.2

Intermediate medium, for example propane, liquid or boiling,

9

Level of the liquid intermediate medium; Propane 8 in the boiling state,

10

Inflow of the LNG to the coiled tubing 6 or to the coiled tubing 6,

11

Outflow of the regasified LNG from the coiled tubing 6 or from the coiled tubing 6,

12

Inflow of the refrigerant to the coiled tubing 7 and to the coiled tubing 7,

13

Outflow of the refrigerant from the coiled tubing 7 or from the coiled tubing 7,

14

Device for emptying and filling with intermediate medium 8, for example with propane 8

15

distribution,

16

Manifold.

Claims (14)

1. Method for recovering cold during the re-gasification of cryogenic liquids, namely of liquefied natural gas (LNG), liquefied nitrogen (LN2), or liquefied oxygen (LO2), characterized
   in that the cold of the cryogenic liquid, in a heat exchanger, which is designed for refrigerating capacities in the region of less than 100 kW, is initially transferred to an intermediate medium (8), and subsequently from the latter to a liquid coolant medium, while the coolant medium remains without phase change down to a temperature level of -60°C, and thus is safely pumpable, and in that the heat transfer, furthermore, takes place by evaporation and condensation without using any pump during natural circulation in the heat exchanger, while the temperature of the intermediate medium (8), due to the design of heat transfer and of the temperature differences driving heat transfer, is freely selectable in a range of between -20 °C and -100°C, namely by the fact
   that the heat exchanger is an hermetically sealed vessel (1) integrally jacketed with an insulation (5), and having an upper and a lower torospherical head (2; 3) in vertical alignment,
   that a coiled tube (6) is located in the in the area of the upper torospherical head (2) and at least one coiled tube (7) is arranged in the area of the lower torospherical head (3) while observing a distance between the coiled tubes (6 and 7),
   that the hermetically sealed vessel (1) is filled with an intermediate medium (8) thus encapsulated, with a fill level (9) between the upper and the lower coiled tubes (6 and 7) for implementing the heat transport inside the vessel (1), while the lower coiled tubes (7) are flooded with liquid intermediate medium in the boiling state (8.2) in every operating state, while the upper coiled tubes (6) are surrounded with saturated steam (8.1) which condensates at the coiled tubes (6) when releasing heat during operation,
   that the coiled tubes (6 and/or 7) are installed in a single arrangement or in multiple arrangements,
   that the inflow (10) and the outflow (11) of the cryogenic liquid (LNG) via the coiled tube (6), or, in multiple arrangements, via the coiled tubes (6) and the corresponding header tube (16), allow a heat transport from the condensing intermediate medium (8.1) to the cryogenic liquid (LNG) to be re-gasified,
   and that the heat transport from the coolant medium to be cooled to the liquid intermediate medium (8.2) is implemented using the inflow (12) and the outflow (13) of the coolant medium via the coiled tube (7), or, in multiple arrangements, via the coiled tubes (7) and the corresponding header tube (16).
2. A method as claimed in claim 1, characterized in that a liquid cooling medium is used which has a solidification temperature lower than -60°C.
3. A method as claimed in claim 1, characterized in that propane (8) is used as intermediate medium (8).
4. A method as claimed in claim 1, characterized in that the temperature of the intermediate medium (8) evaporating and condensing during natural circulation is essentially definable by the instrumental design or constructional design of heat transfer, i.e., of the flows and heat transfer surfaces of the coiled tubes (6 and 7) so as to make certain that the thermal equilibrium accompanying the cut-off of the heat exchanger by interrupting the coolant medium and LNG mass flows never leads to the solidification of the cooling medium.
5. Heat exchanger for recovering cold during the re-gasification of cryogenic liquids, namely of liquefied natural gas (LNG), liquefied nitrogen (LN2) or liquefied oxygen (LO2), characterized
   in that the heat exchanger is an hermetically sealed vessel (1) integrally jacketed with an insulation (5), and having an upper and a lower torospherical head (2; 3) in vertical alignment,
   in that a coiled tube (6) is located in the area of the upper torospherical head (2) and at least one coiled tube (7) is arranged in the area of the lower torospherical head (3) while observing a distance between the coiled tubes (6 and 7),
   in that the hermetically sealed vessel (1) is filled with an intermediate medium (8) thus encapsulated, with a fill level (9) between the upper and the lower coiled tubes (6 and 7) for implementing the heat transport inside the vessel (1), while the lower coiled tubes (7) are flooded with liquid intermediate medium in the boiling state (8.2) in every operating state, while the upper coiled tubes (6) are surrounded with saturated steam (8.1) which condensates at the coiled tubes (6) when releasing heat during operation, and while the coiled tubes (6 and/or 7) are present in a single arrangement or in multiple arrangements,
   in that the inflow (10) and the outflow (11) of the cryogenic liquid (LNG) via the coiled tube (6), or, in multiple arrangements, via the coiled tubes (6) and the corresponding header tube (16) allow a heat transport from the condensing intermediate medium (8.1) to the cryogenic liquid (LNG) to be re-gasified,
   and in that the heat transport from the coolant medium to be cooled to the liquid intermediate medium (8.2) is implemented using the inflow (12) and the outflow (13) of the coolant medium via the coiled tube (7), or, in multiple arrangements, via the coiled tubes (7) and the corresponding header tube (16).
6. Heat exchanger as claimed in claim 5, characterized in that, between the coiled tubes (6 and 7), a computable distance of at least the diameter of the coiled tubes (6 or, respectively, 7) is implemented, which makes certain that, in every operating state, the upper coiled tubes (6) are surrounded with saturated steam (8.1) and the lower coiled tubes (7) are completely flooded with liquid intermediate medium in the boiling state (8.2).
7. Heat exchanger as claimed in claim 5, characterized in that the coiled tubes (6 and 7) each project freely into the vessel interior with each being fasted on one side to the vessel (1).
8. Heat exchanger as claimed in claim 5, characterized in that the vessel (1) and the coiled tubes (6 and 7) are made of stainless steel.
9. Heat exchanger as claimed in claim 5, characterized in that, inside the coiled tubes (6 and 7), a circular flow is implemented each.
10. Heat exchanger as claimed in claim 5, characterized in that turbulators are used.
11. Heat exchanger as claimed in claim 5, characterized in that, in arrangements with several coiled tubes (6), the inflow (10) of the LNG is implemented directly with the interposition of a manifold (15), and the outflow (11) of the re-gasified LNG via a header tube (16) in the upper part of the vessel (1).
12. Heat exchanger as claimed in claim 5, characterized in that, in arrangements with several coiled tubes (7), the inflow (12) of the coolant medium is implemented directly with the interposition of a manifold (15), and the outflow (13) of the coolant medium via a header tube (16) in the lower part of the vessel (1).
13. Heat exchanger as claimed in claim 5, characterized in that, in arrangements with several coiled tubes (6 or, respectively 7), the header tubes (16) can be arranged both inside and, as an alternative, also outside the vessel (1).
14. Heat exchanger as claimed in claim 5, characterized in that the header tubes (16) are usable for the one-sided fastening of the coiled tubes (6 or, respectively 7).

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