EP3397912A1 - Method and heat exchanger for recovering cold during the re-gasification of cryogenic liquids - Google Patents

Abstract

The invention relates to the recovery of cold during the re-gasification of cryogenic liquids, in particular, liquefied natural gas, liquefied nitrogen and liquefied oxygen. The cold is initially transferred from the cryogenic liquid to an intermediate medium and then from same to a liquid coolant, which remains without a phase change down to a temperature level of -60°C and can be safely pumped in this way. The heat transfer occurs by evaporating and condensing the intermediate medium without use of pumps in natural circulation. The temperature of the intermediate medium can be set in the range of -20°C to -100°C by defining the equipment or construction features of the heat exchanger. The heat exchanger is characterised by relatively simple construction features and easy operability, which enable a suitably low capital expenditure for the cooling capacity.

Description

 description

Title Procedure and heat exchanger for the recovery of cold in the

Regasification of cryogenic liquids

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 (L02). These are process characteristics in connection with a heat exchanger for

Realization of the method indicated. The heat exchanger is for, although relatively small in comparison to the fuel energy, so valuable

Cooling capacity in the range below 100 kW designed and characterized by simple design features and ease of use, which is one of the

Cooling capacity allow reasonable low investment costs.

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. This is the reduction of the volume on the

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 very often forms one

so-called satellite system, namely a double-walled,

Vacuum-insulated LNG storage without liquefaction facility. The satellite system has a regasification device,

usually an atmospheric evaporator with vertical longitudinal finned tubes, at which the liquefied natural gas, hereinafter referred to as LNG, is vaporized and overheated to ambient temperature, while the LNG

required heat from the ambient air is supplied by free convection.

 The described prior art is extensively described in DE10201 1081673 "Process and plant for the regasification of liquefied natural gas" and in further publications, for example in the following documents:

No. 6,667,265 "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 on one for practical use

demanded moderately low temperature above -60 ° C, e.g. for the

 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 develop, the

Regasification of cryogenic liquids occurring large

Controlled temperature differences. 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 proposed: 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

 Brine, 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 existing between the low-liquid liquid to be regasifizierenden and the refrigerant large

Temperature difference without the refrigerant cools too much, to the 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 very good given by evaporation and condensation

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 an inventive

Heat exchanger 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 at least one in the upper part

Surface heat exchanger for evaporating the cryogenic liquid, such as LNG, and at least one further in the lower part

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 are appropriate to the coiled tubing

associated headers available, 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 the evaporation of the

Intermediate propane required heat 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 propane (saturated steam and liquid in

Boiling state are in phase equilibrium.) Approximately 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 circulation evaporating and condensing intermediate medium and an inherent security achieved such that with the switching off of the heat exchanger by interrupting the

Brine and the LNG mass flow associated thermal

Equilibrium 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.

A heat exchanger according to the invention is shown in FIG. 1 as a section along its vertical system axis.

 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, between the two coiled tubing 6 and 7 a

appropriate distance of about the diameter of the coiled tubing 6 or 7 present and the corresponding mass of the intermediate medium 8 in the

Container filled. The container 1 and the tube coils 6 and 7 are advantageously made of stainless steel. Thus, a sufficient Tiefkaltzähigkeit and a high

Corrosion resistance guaranteed.

 The heat transfer from the condensing propane saturated steam 8.1 to the deep-frozen liquid LNG to be regasified thus takes place via the upper one

 Pipe helix 6. This protrudes, as already stated, from above freely down into the container interior. 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 heat exchanger according to the invention is also shown in FIG. 2 as a section along its vertical system axis.

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 proven to be advantageous to inflow 10 of the LNG

To make intermediate connection of a manifold 15 directly and to realize the outflow 1 1 of the regasified LNG via a manifold 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.

According to the method allow the described invention

Heat exchanger effective heat transfer from the refrigerant to be cooled to the boiling intermediate medium 8.2 in the lower

 Pipe helix or pipe helix 7 and of the condensing, gaseous intermediate medium 8.1 to be evaporated deep-frozen liquid in the region of the upper coiled tubing or coiled tubing 6. The natural circulation of the intermediate medium comes by the dripping of the condensate of the or the upper

Pipe helices 6 to conditions.

LIST OF REFERENCE NUMBERS

1 container,

 2 upper dished bottom,

 3 lower dished bottom,

 4 pressure transmitters,

 5 insulation,

 6 upper coiled tubing,

 7 lower coiled tubing,

 8 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 LNG to coiled tubing 6 and to the coiled tubing 6,

1 1 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 and aus

 Coiled tubing 7,

 14 device for emptying and filling with intermediate medium 8,

 for example with propane 8

 15 distributors,

16 manifold.

Claims

claims 1. A process and heat exchanger for recovering cold from the regasification of cryogenic liquids, namely liquefied natural gas (LNG), liquefied nitrogen (LN2) or liquefied oxygen (L02), characterized, that the cold of the cryogenic liquid in a heat exchanger, which is designed for cooling capacities in the range below 100 kW, initially to a Intermediate medium (8) and then from this to a liquid Brine is transferred, with the refrigerant down to a Temperature level of -60 ° C without phase change remains safe pumpable that the heat transfer also by evaporation and Condensation without pump use in natural circulation in the heat exchanger takes place, the temperature of the intermediate medium (8) in the range of -20 ° C to -100 ° C by the design of the heat transfer and the driving them Temperature differences is freely selectable, by means of the following Characteristic features of the heat exchanger:  A container (1) in vertical alignment with an upper and a lower dished bottom (2, 3), which is completely encased with an insulation (5), - Arrangement of at least one coiled tubing (6) in the region of the upper  Dished bottom (2) and at least one coiled tubing (7) in the region of the lower dished bottom (3) while maintaining a distance between the  Coiled tubing (6 and 7), - filling the hermetically sealed container (1) with the intermediate medium (8) thereby encapsulated for the purpose of transporting heat within the container (1) to a level (9) between the upper and lower tube coils (6 or 7), the lower ones Pipe helices (7) at each Operating state with liquid intermediate medium in the boiling state (8.2) are flooded, while the upper coiled tubing (6) of saturated steam (8.1) are surrounded, which condenses in operation at heat emission to the coiled tubing (6), and wherein the coiled tubing (6 and / or 7) are present in a single or multiple arrangement.  - Realization of the heat transfer from the condensing intermediate medium (8.1) to be regasifizierende deep cold liquid (LNG) by inlet (10) and outflow (1 1) of the same over the coiled tubing (6) or in a multiple arrangement on the coiled tubing (6) and the associated manifold (16),  Realization of the heat transfer from the refrigerant to be cooled to the liquid intermediate medium (8.2) through inflow (12) and outflow (13) of the  Refrigerant on the coiled tubing (7) or in multiple arrangement on the coiled tubing (7) and the associated manifold (16). 2. The method according to claim 1, characterized that a liquid refrigerant is used whose solidification temperature is lower than -60 ° C. 3. The method according to claim 1, characterized in that propane (8) is used as intermediate medium (8). 4. The method according to claim 1, characterized that the temperature of the natural circulation evaporating and condensing intermediate medium (8) substantially by the apparatus or constructive Design of heat transfer, i.e., the flows and the Heat transfer surfaces of the coiled tubing (6 and 7) is fixed so that with the switching off of the heat exchanger by interrupting the Brine and LNG mass flow associated thermal equilibrium never leads to a solidification of the refrigerant. 5. Heat exchanger for the recovery of cold in the regasification of cryogenic liquids, namely liquefied natural gas (LNG), liquefied  Nitrogen (LN2) or liquefied oxygen (L02), marked by, A container (1) in vertical alignment with an upper and a lower dished bottom (2, 3), which is completely encased with an insulation (5), - Arrangement of a coiled tubing (6) in the region of the upper dished bottom (2) and at least one coiled tubing (7) in the region of the lower dished bottom (3) while maintaining a distance between the coiled tubing (6 and 7),  - Filling the hermetically sealed container (1) with the intermediate medium (8) thereby encapsulated for the purpose of heat transport within the container (1) with a level (9) between the upper and lower tube coils (6 and 7), wherein the lower tube coils (7) at each  Operating state with liquid intermediate medium in the boiling state (8.2) are flooded, while the upper coiled tubing (6) of saturated steam (8.1) are condensed, which condenses during operation at heat emission to the tube coils (6), and wherein the coiled tubing (6 and / or 7 ) are present in single or multiple arrangement.  - Realization of the heat transfer from the condensing intermediate medium (8.1) to be regasifizierende deep cold liquid (LNG) by inlet (10) and outflow (1 1) of the same over the coiled tubing (6) or in a multiple arrangement on the coiled tubing (6) and the associated manifold (16),  Realization of the heat transfer from the refrigerant to be cooled to the liquid intermediate medium (8.2) through inflow (12) and outflow (13) of the  Refrigerant on the coiled tubing (7) or in multiple arrangement on the coiled tubing (7) and the associated manifold (16). 6. Heat exchanger according to claim 5, characterized in that between the coiled tubing (6 and 7) a calculable distance of at least the diameter of the coiled tubing (6 or 7) is realized, which ensures that the upper coiled tubing (6) surrounded by saturated steam (8.1) in each operating condition and the lower coiled tubing (7) of liquid Intermediate medium in the boiling state (8.2) are completely flooded. 7. Heat exchanger according to claim 5, characterized in that the coiled tubing (6 and 7) each protrude freely into the container interior in each case one-sided attachment to the container (1). 8. Heat exchanger according to claim 5, characterized in that the container (1) and the tube coils (6 and 7) are made of stainless steel. 9. Heat exchanger according to claim 5, characterized in that within the tube coils (6 and 7) each have a circular flow is realized. 10. Heat exchanger according to claim 5, characterized in that turbulators are used. 1 1. A heat exchanger according to claim 5, characterized in that in the arrangement of several coiled tubing (6) of the inflow (10) of the LNG with the interposition of a distributor (15) directly and the outflow (1 1) of the Regasified LNG via a manifold (16) in the upper part of the container (1) is realized. 12. A heat exchanger according to claim 5, characterized in that in arrangement of several coiled tubing (7) of the inflow (12) of the refrigerant with the interposition of a distributor (15) directly and the outflow (13) of the refrigerant via a manifold (16) in the lower part of the container (1) is realized. 13. Heat exchanger according to claim 5, characterized in that in the arrangement of a plurality of coiled tubing (6 or 7), the manifolds (16) both within and as an alternative outside of the container (1) can be arranged. 14. Heat exchanger according to claim 5, characterized in that the collecting pipes (16) for one-sided attachment of  Pipe helices (6 or 7) can be used. This is followed by two sheets of drawings (Figures 1 and 2)!