DE102019001817A1 - Regasification of cryogenic fluids through supercritical expansion with increased recirculation for power generation - Google Patents

Abstract

The invention relates to a device (1) for generating electricity during regasification, comprising a tank (2), a first pump (4) connected to the tank (2) via a first line (3), one to the first pump (4) via a second line (5) connected second pump (6), a first heat exchanger (7) connected downstream of the second pump (6), a second heat exchanger (8) connected downstream of the first heat exchanger (7), and a first heat exchanger (8) connected downstream of the second heat exchanger (8) Turbine (9) with first generator (14), characterized in that a third line (10) branches off from the outlet of the first turbine (9) and opens into the first heat exchanger (7) and from this first heat exchanger (7) a fourth line (11) branches off and opens into the second line (5) between the first pump (4) and the second pump (6). The invention also relates to a method for generating electricity.

Description

The invention relates to a device for generating electricity during regasification of cryogenic fluids and a corresponding method for generating electricity.

The liquefaction of gases such as Natural gas, oxygen, nitrogen or air for transport or storage purposes is associated with high energy consumption.

Natural gas is liquefied for transport purposes, which requires a lot of energy. In LNG terminals, liquid natural gas (LNG) is pressurized, vaporized and fed into a pipeline. Due to the high cost and the low level of efficiency, the regasification of LNG is only used in exceptional cases to produce electricity. In many cases, part of the natural gas is even used to provide the heat required for evaporation.

Liquid air storage systems store energy in the form of liquid air in large tanks. In order to call up the energy when required, the liquid air is pressurized, evaporated and expanded in a turbine with the output of electrical power. In order to increase the overall efficiency of the storage unit, the cold potential of the liquid air can be used to cool down cold storage units during the withdrawal, which during the liquefaction operation are used to lower the condensing capacity when the tanks are filled with liquid air. This in turn is associated with a high outlay in terms of equipment and limits the flexibility of the plant operation.

In the German patent application, official file number 17203813.5 , describes an “improved method for generating electricity during the regasification of a fluid through supercritical expansion”. This method reduces the outlay on equipment by using the cold potential of the cryogenic fluid to increase the electrical power. If it is used for a liquid air store, there is therefore no need for a cold store, which lowers the liquefaction capacity while the tank is being filled.

The object of the invention is to provide a device and a method for the efficient regasification of cryogenic fluids, which recovers the energy used for the liquefaction as far as possible and is inexpensive, simple and reliable.

The invention achieves the object directed to a device by providing that in such a device for generating electricity during regasification, comprising a tank, a first pump connected to the tank via a first line, and a first pump connected to the first pump via a second line second pump, a first heat exchanger downstream of the second pump, a second heat exchanger downstream of the first heat exchanger, and a first turbine with a first generator downstream of the second heat exchanger, a third line branches off from the outlet of the first turbine and opens into the first heat exchanger, and from this A fourth line branches off from the first heat exchanger and opens into the second line between the first and second pumps.

It is useful if a fifth line branches off from the outlet of the first turbine and opens into a pipeline. Alternatively, and depending on the medium used, a gas turbine combustion chamber, a heat exchanger for preheating (recuperator) before entering a gas turbine combustion chamber or a blow-off into the atmosphere after further expansion in a second turbine is also conceivable.

It is also useful if a third heat exchanger is connected in the fifth line.

In an advantageous embodiment, a fourth heat exchanger is connected in the second line and in the third line upstream of the first heat exchanger. With the help of this fourth heat exchanger, partial flows can be branched off, the temperature of which lies between the outlet temperature of the second pump and the outlet temperature at the warm end of the fourth heat exchanger. In addition, this can reduce thermal stresses.

In an alternative advantageous embodiment, a sixth line branches off from the third line between the third and the first heat exchanger and opens into the second line upstream of the second heat exchanger. A compressor is connected into this sixth line, which sucks in a partial flow and compresses it to the pressure level upstream of the first turbine. The compression of the partial flow increases the achievable output of the first turbine and thus the achievable total electrical output of the device, but is not absolutely necessary, so that the sixth line and the compressor can also be omitted in order to save investment costs. If the sixth line and the compressor are omitted, the achievable total electrical output of the device drops by approx. 10%.

In a further advantageous embodiment, a fifth heat exchanger is connected in the second line between the first and fourth heat exchangers. With the help of this fifth heat exchanger, thermal stresses in the first and fourth heat exchanger can be reduced if the fluid in the second heat exchanger is heated to a temperature well above the ambient temperature. In this case, the temperature of the fluid in the fifth heat exchanger is adjusted to the ambient temperature by releasing heat to the surroundings or absorbing heat from the surroundings. It is obvious that the fifth heat exchanger can also be switched into the third line between the fourth and first heat exchanger.

In a further advantageous embodiment, the first heat exchanger, fourth heat exchanger and the branch point of the sixth line from the third line are in one component, i.e. an integrated heat exchanger, integrated.

If the fifth line leads to a second turbine with a second generator for further expansion, it is expedient if a seventh line branches off from the outlet of this second turbine and opens into the integrated heat exchanger. As a result, the partial flow conducted via the sixth line can be increased and thus the achievable output of the first turbine and thus the achievable total electrical output of the device can be increased further.

In a preferred embodiment of the invention, the tank contains liquid air. But also liquid gas (LNG), liquid nitrogen, liquid oxygen or liquid argon are fluids in question.

The basic idea of the invention is that, for example, liquid air as the working medium is expanded to a supercritical pressure in the first turbine. As a result, a large partial flow can be returned, pumped under pressure and absorb heat from the environment and / or other processes before the expansion in the turbine. The electrical power can thus be increased with very little effort. The return of the partial flow to a pump that works with sufficiently low power consumption is only possible through supercritical relaxation, because the two material flows in the air-to-air heat exchanger show a similar temperature profile, small gradients are created and thus good heat transfer is achieved can. The pump inlet temperature is therefore sufficiently low and the pump output is correspondingly small. In contrast to the above-mentioned "improved process for generating electricity in the regasification of a fluid by supercritical expansion", which is called German patent application with the official file number 17203813.5 has been submitted, the changed arrangement of the second pump achieves a significantly lower pump inlet temperature and thus better efficiency. Instead of only pumping the partial flow returned from the first turbine via the first heat exchanger to pressure, in the present invention the second pump now pumps the recirculated partial flow plus the fluid flow withdrawn from the tank by means of the first pump. This new arrangement of the second pump also offers the advantage that the delivery head of the first pump is significantly lower than in the "improved method for generating electricity when regasifying a fluid through supercritical expansion".

The object directed to a method is therefore achieved by a method for power generation in which a fluid is brought to a first pressure and thus a first fluid flow with supercritical pressure is generated, this first fluid flow with a second fluid flow that is greater than the first fluid flow , is brought together, the resulting total fluid flow is brought to a second pressure and thus a high pressure flow is generated, which is led to a first heat exchanger, in which the high pressure flow is heated by the second fluid flow, the heated high pressure flow then in a second heat exchanger by entry is further heated by ambient heat and / or waste heat from other processes and the further heated high-pressure flow is expanded in a first turbine with the output of electrical power to a lower, but supercritical pressure, the total fluid flow emerging from the first turbine being in the second n fluid flow and divided into a smaller third fluid flow and the second fluid flow, after it has given its heat to the high pressure flow, is merged with the first fluid flow.

The fluid is expediently taken from a tank. The process ultimately relates to the regasification of liquid media that are stored in tanks.

It is advantageous if the recirculated fluid flow plus the fluid flow withdrawn from the tank is brought to a pressure of over 160 bara by means of a second pump.

It is advantageous if the further heating leads to the highest possible turbine inlet temperature. If only ambient heat is available, it is advantageous if the further heating comes as close as possible to the ambient temperature, but at least to 5 ° C takes place below ambient temperature. It is advantageous if the ambient heat is taken from air or sea water.

It is also advantageous if the lower, but supercritical pressure is above 50 bara. The advantages of supercritical relaxation have already been mentioned above.

A possible sensible use of the third fluid flow is its further expansion in a second turbine with a second generator with delivery of electrical power to increase the achievable total electrical power, for example if the fluid taken from the tank is liquid air.

Another possible sensible use of the third fluid flow is to feed it into a pipeline for further use, for example if the fluid removed from the tank is liquefied natural gas. But other fluids can also be used in the inventive method, e.g. liquid nitrogen, liquid oxygen, or liquid argon.

Another possible sensible use of the third fluid flow is to feed it into a gas turbine combustion chamber when the fluid withdrawn from the tank is, for example, liquid air. In order to increase the efficiency, it makes sense to preheat the air in a heat exchanger before it enters the combustion chamber with the aid of hot exhaust gas from the gas turbine. In addition, if the combustion chamber pressure is sufficiently low, an expansion turbine for the hot air can be connected upstream before entering the combustion chamber.

To further improve the efficiency, it can be advantageous if the first turbine is relieved and temporarily heated in multiple stages.

It is also advantageous to branch off a partially cooled partial flow from the second fluid flow, to compress it and to merge it with the high pressure flow upstream of the second heat exchanger. As a result, the cold potential of the high-pressure flow, which has a higher specific heat capacity than the second fluid flow, is fully used in order to increase the fluid flow via the first turbine and thus the total electrical output.

• - Der Wirkungsgrad ist vergleichsweise hoch.
• - Es ist ein sehr einfaches Konzept. Mit wenig Aufwand können eine robuste Regelung und Automatisierung erstellt werden.
• - Durch die geringe Anzahl von Komponenten und Maschinen ist eine große betriebliche Flexibilität möglich. Schnelle Lastwechsel stellen ebenfalls kein großes Problem dar.
• - Außer dem Fluid selber ist kein weiteres Arbeitsmedium erforderlich..
• - Auf Grund der geringen Komplexität bietet das neue Verfahren eine geringe Fehleranfälligkeit und demzufolge eine hohe Verfügbarkeit, was für die Kundenakzeptanz sehr wichtig ist.
• - Es ist im Gegensatz zu anderen in der Literatur theoretisch behandelten Verfahren kein Aufwand für die Neuentwicklung von Komponenten erforderlich.
• - Durch die große übertragene Wärme zwischen den (beispielsweise) Luftströmen ist die Temperatur der Luft, welche noch durch Umgebungswärme angewärmt werden muss, schon recht hoch. Dadurch ergeben sich kostengünstigere Wärmeübertrager, da nun das Einfrieren von Meerwasser bzw. Ausfrieren von Luftfeuchtigkeit deutlich weniger Probleme bereitet.
• - Das neue Verfahren kann vorteilhaft mit anderen Prozessen wie z.B. Kälteauskopplung kombiniert werden.

The invention has the following advantages:

• - The efficiency is comparatively high.
• - It's a very simple concept. Robust control and automation can be created with little effort.
• - The small number of components and machines enables great operational flexibility. Rapid load changes are also not a major problem.
• - Apart from the fluid itself, no further working medium is required.
• - Due to the low complexity, the new method offers a low susceptibility to errors and consequently high availability, which is very important for customer acceptance.
• - In contrast to other processes treated theoretically in the literature, no expenditure is required for the new development of components.
• - Due to the large amount of heat transferred between the (for example) air streams, the temperature of the air, which still has to be warmed by ambient heat, is already quite high. This results in more cost-effective heat exchangers, since the freezing of sea water or freezing out of air humidity now causes significantly fewer problems.
• - The new process can be combined with other processes such as cold extraction.

The costs for energy storage systems that work with liquid air can be reduced significantly due to the elimination of the cold storage system. In addition, the complexity is reduced and the liquefaction cycle is decoupled from the withdrawal cycle, which increases operational flexibility. The integration of black start capability is possible with little effort with the help of a pressure vessel for liquid air.

Complete solutions for power generation during regasification can be offered as retrofitting for planned LNG terminals as well as for existing terminals. From the customer's point of view, there is the possibility of significantly reducing the operating costs with manageable investment costs, since the new solution can be used to generate internal requirements and excess electricity can be fed into the grid. In addition, well-paid control reserves such as Primary frequency support can be provided.

Compared to conventional regasification solutions, in which part of the natural gas is burned for evaporation, the profitability increases significantly, since the entire electricity can now be fed into the pipeline and electricity is also produced.

• 1 eine Grundschaltung zum Prozess für Stromerzeugung nach der Erfindung,
• 2 eine Schaltung zur Reduzierung der thermischen Spannungen in den Wärmeübertragern,
• 3 eine Schaltung zur Verbesserung des Wirkungsgrads,
• 4 eine Ausführung mit integriertem Wärmeübertrager und
• 5 eine Schaltung mit Entspannung eines Teilstroms auf atmosphärischen Druck.

The invention is explained in more detail by way of example with reference to the drawings. They show schematically and not to scale:

• 1 a basic circuit for the process for power generation according to the invention,
• 2 a circuit to reduce the thermal stresses in the heat exchangers,
• 3 a circuit to improve the efficiency,
• 4th a version with an integrated heat exchanger and
• 5 a circuit with expansion of a partial flow to atmospheric pressure.

The 1 shows schematically and by way of example the basic circuit for the device 1 for power generation with regasification according to the invention. The device 1 includes a tank 2 for a cryogenic fluid, preferably liquid air, but also liquid natural gas (LNG), liquid nitrogen, liquid oxygen or liquid argon are possible. A first pump 4th is via a first line 3 with the tank 2 connected. A second line 5 connects the first pump 4th with the second pump 6th , which is a first heat exchanger 7th and a second heat exchanger 8th downstream is a first turbine 9 with the first generator 14th is downstream. According to the invention branches from the first turbine 9 a third line 10 and flows into the first heat exchanger 7th , of which in turn a fourth line 11 branches off and into the second line 5 flows out. In the embodiment of 1 branches a fifth line 12 from the third line 10 from. The fifth line 12 can flow into a pipeline, for example. Also in the fifth line 12 a third heat exchanger 13 switched.

The circuit of the 2 is optimized to minimize thermal stresses. Here is a fourth heat exchanger 15th into the second line 5 and into the third line 10 upstream of the first heat exchanger 7th switched. As an example for the case that the inlet temperature into the first turbine is significantly above the ambient temperature, between the first heat exchanger 7th and the fourth heat exchanger 15th into the second line 5 a fifth heat exchanger 16 switched, via which heat can be given off to the environment or absorbed by the environment.

The embodiment of 3 serves to improve the efficiency. From the third line 10 branches between the fourth heat exchanger 15th and the first heat exchanger 7th a sixth line 17th from and opens upstream of the second heat exchanger 8th into the second line 5 . In this sixth line 17th is a compressor 18th switched. The compression of the partial flow causes the fluid mass flow to flow through the first turbine 9 further increased so that the achievable output of the first turbine 9 increased and the gradient at the warm end of the fourth heat exchanger 15th minimized.

4th finally shows a version with an integrated heat exchanger 19th , ie first heat exchanger 7th , fourth heat exchanger 15th and the junction of the sixth line 17th from the third line 10 are integrated in one component.

The circuit of the 5 is for the relaxation of the about the fifth line 12 branched off partial flow in a second turbine 20th with a second generator 22nd optimized for ambient pressure. From the exit of the second turbine 20th branches a seventh line 21st and flows into the integrated heat exchanger 19th at a point that corresponds to the temperature level at the outlet of the second turbine 20th corresponds. The one on the seventh line 21st guided low pressure flow is in the integrated heat exchanger 19th warmed up before it is blown into the atmosphere, for example. As a result, the cold potential of the low-pressure flow is used to reduce the flow via the sixth line 17th to be able to increase the branched, compressed partial flow and thus the achievable total electrical output.

List of reference symbols

1

Device for generating electricity during regasification

2

tank

3

First line

4th

First pump

5

Second line

6th

Second pump

7th

First heat exchanger

8th

Second heat exchanger

9

First turbine

10

Third line

11

Fourth line

12

Fifth line

13

Third heat exchanger

14th

First generator

15th

Fourth heat exchanger

16

Fifth heat exchanger

17th

Sixth line

18th

compressor

19th

Integrated heat exchanger

20th

Second turbine

21st

Seventh line

22nd

Second generator

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 17203813 [0005, 0016]

Claims (20)

Device (1) for generating electricity during regasification comprising a tank (2), a first pump (4) connected to the tank (2) via a first line (3), and one to the first pump (4) via a second line (5 ) connected second pump (6), a first heat exchanger (7) connected downstream of the second pump (6), a second heat exchanger (8) connected downstream of the first heat exchanger (7), and a first turbine (9) connected downstream of the second heat exchanger (8) with a first generator (14), characterized in that a third line (10) branches off from the outlet of the first turbine (9) and opens into the first heat exchanger (7) and a fourth line (11) branches off from this first heat exchanger (7) and opens into the second line (5) between the first pump (4) and the second pump (6). Device (1) according to Claim 1 , whereby a fifth line (12) branches off from the first turbine (9). Device (1) according to Claim 1 and 2 , wherein a third heat exchanger (13) is connected in the fifth line (12). Device (1) according to one of the preceding claims, wherein a fourth heat exchanger (15) is connected in the second line (5) and in the third line (10) upstream of the first heat exchanger (7). Device (1) according to Claim 4 , whereby a sixth line (17) branches off from the third line (10) between the fourth (15) and the first heat exchanger (7) and opens into the second line (5) upstream of the second heat exchanger (8), the sixth Line (17) a compressor (18) is connected. Device (1) according to Claim 5 , the first heat exchanger (7), fourth heat exchanger (15) and the junction of the sixth line (17) from the third line (10) being arranged in an integrated heat exchanger (19). Device (1) according to Claim 6 , the fifth line (12) leading to a second turbine (20) with a second generator (22), a seventh line (21) branching off from the second turbine (20) and opening into the integrated heat exchanger (19). Method for power generation in which a fluid is brought to a first pressure and thus a first fluid flow is generated with supercritical pressure, this first fluid flow is combined with a second fluid flow that is greater than the first fluid flow, the resulting total fluid flow to a second pressure is brought and thus a high pressure flow is generated, which is led to a first heat exchanger (7), in which the high pressure flow is heated by the second fluid flow, the heated high pressure flow then in a second heat exchanger (8) by the introduction of ambient heat and / or Waste heat from other processes is further heated and the further heated high-pressure flow is expanded in a first turbine (9) with delivery of electrical power to a lower but supercritical pressure, the total fluid flow emerging from the first turbine (9) being converted into the second fluid flow and into a smaller third fluid stream m and the second fluid flow, after it has given its heat to the high pressure flow, is merged with the first fluid flow. Procedure according to Claim 8 , wherein the fluid is taken from a tank (2). Procedure according to Claim 9 , the fluid removed from the tank (2) being brought to a supercritical pressure of over 50 bara by means of a first pump (4). Procedure according to Claim 10 , wherein the total flow, which consists of the second fluid flow returned from the first turbine (9) and the first fluid flow exiting from the first pump (4), is brought to a pressure of over 160 bara by means of a second pump (6). Method according to one of the Claims 8 to 11 where the ambient heat is taken from air or sea water. Method according to one of the Claims 8 to 12 , further heating in the second heat exchanger (8) to at least 5 ° C below the ambient temperature. Method according to one of the Claims 8 to 13 , wherein the third fluid stream is fed into a pipeline. Method according to one of the Claims 8 to 13 , the third fluid stream being warmed in a heat exchanger by exhaust gas from a gas turbine and then being fed into a gas turbine combustion chamber. Method according to one of the Claims 8 to 13 , the third fluid flow being expanded and temporarily heated in a second turbine (20) in several stages. Method according to one of the Claims 8 to 16 , with the first turbine (9) being relaxed and intermediate heating in several stages. Method according to one of the Claims 8 to 17th , a partially cooled partial flow being branched off from the second fluid flow, compressed and merged with the high pressure flow upstream of the second heat exchanger (8). Procedure according to Claims 17 and 18th wherein the partially cooled partial flow branched off from the second fluid flow is compressed and merged downstream of the first stage of the first turbine (9) with the fluid flow partially expanded in the first turbine (9). Method according to one of the Claims 8 to 19th wherein the fluid withdrawn from the tank is liquid air, liquid natural gas, liquid nitrogen, liquid oxygen, or liquid argon.

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