DE19728153C2 - Process for liquefying a hydrocarbon-rich stream - Google Patents

Abstract

A hydrocarbon-enriched stream, especially natural gas, is liquefied by a new route. Heat is exchanged indirectly, with coolant(s) and coolant mixture(s) of coolant circuit(s). In novel aspects of the process, the feed (4) at 50-200 bar, preferably 90-100 bar, is pre-cooled (E2) to -20 to 20 deg C, preferably -10 to10 deg C, by the stream produced as follows. The pre-cooled stream (5) is expanded (T2) to 25-80 bar. It (6) is then re-heated to -20 to 20 deg C by the pre-cooled feed (4). The resulting stream (7) is then cooled and liquefied by indirect heat exchange (E3, E4, E5) with coolant(s) and/or coolant mixture(s) of the coolant(mixture) circuit.

Description

The invention relates to a method for liquefying a hydrocarbon rich electricity, in particular a natural gas stream, in which the reheated Hydrocarbon-rich electricity through indirect heat exchange in at least one Heat exchanger with one or more refrigerants and / or one or more Refrigerant mixtures of one or more refrigerant (mixture) circuits cooled and is liquefied.

Nowadays most of the Baseload LNG plants are called so-called dual flow Refrigeration processes designed. This is used to liquefy the coal Hydrogen-rich electricity or natural gas requires cooling energy by means of two separate refrigerant mixture circuits leading to a refrigerant mixture circuit cascade are provided. Such is a liquefaction process e.g. B. from GB 895 094 A.

Furthermore, liquefaction processes are known in which those for the liquefiers cooling energy required by means of a refrigerant circuit cascade, but not a mixed refrigerant cycle cascade is provided; see e.g. B. LINDE- Reports from technology and science, issue 75/1997, pages 3 to 8. The therein The refrigerant circuit cascade described consists of a propane or propylene, an ethane or ethylene and a methane refrigeration cycle. This refrigerant Circulation cascade can be viewed as energetically optimized, but it is comparatively complicated due to the 9 compressor stages.

DE 197 16 415 describes a process for liquefying a coal hydrogen-rich electricity through indirect heat exchange with the refrigerants a refrigerant mixture circuit cascade known. Here is the refrigerant mixed circuit cascade from at least three different refrigerants together refrigerant mixture circuits.

The borehole pressure of a natural gas / condensate reservoir is usually in one Range between 90 and 300 bar. Depending on the further procedure, the  the extracted natural gas is subjected to this pressure by means of a control valve reduced to a pressure level at which subsequent processing is possible.

The natural gas is extracted from a deposit located under the seabed and funded on land via a so-called multi-phase pipeline, there is a Pressure loss in the order of 30 to 100 bar, from which a corresponding Energy loss results.

In recent times, so-called production ships have been increasingly used on which the natural gas transported by means of flexible risers is immediately (further) processed or is liquefied. Here, the gas stream emerging from the borehole with a Pressure between 150 and 200 bar is fed directly to a high pressure separator. The natural gas is then brought up to a pressure level that is Removal and suitable for possible drying processes, relaxed. After that is, for the purpose of further processing, the dried, carbon dioxide-free Natural gas to a pressure level in the order of 130 to 190 bar, that is necessary for the transportation of natural gas. The one for recompression compressors used are usually directly with the or the expansion turbines coupled to the relaxation mentioned.

The object of the present invention is to provide a method for liquefying a Hydrocarbon-rich stream, especially a natural gas stream, to indicate that compared to the state of the art liquefaction process has a reduced specific energy consumption and the Realization of a smaller plant size and associated smaller Investment costs enabled.

This object is achieved in that the liquefied Hydrocarbon-rich electricity with a pressure of 50 to 200 bar in a first Heat exchanger with itself through indirect heat exchange to one temperature pre-cooled from 20 to -20 ° C, then to a pressure of 25 to 80 bar relaxed and in the heat exchanger for reheating to a temperature of -20 to 20 ° C is returned.

Here, the pressure of the hydrocarbon-rich stream to be liquefied is preferably 90 to 130 bar, during the pressure of the pre-cooled hydro substance-rich current is preferably 40 to 65 bar.  

According to an advantageous embodiment of the method according to the invention the temperature of the pre-cooled hydrocarbon-rich stream is 10 to -10 ° C and the temperature of the reheated hydrocarbon-rich stream is -10 to 10 ° C.

Further refinements of the method according to the invention for liquefying a hydrocarbon-rich stream are distinguished by the fact that the reheated hydrocarbon-rich stream is produced by indirect heat exchange

• - With a refrigerant circuit cascade consisting of at least two refrigerants circuits,
• - With a refrigerant mixture circuit cascade consisting of at least two Refrigerant mixture circuits,
• - With a cascade consisting of at least one refrigerant circuit and at least one refrigerant mixture circuit, or
• - with a mixed refrigerant circuit
  cooled and liquefied.

According to an advantageous embodiment of the invention Process, the precooled and expanded hydrocarbon-rich stream against one or more refrigerants to be cooled and / or condensed and / or against one or more refrigerant quantities to be cooled and / or condensed mixed reheated.

The method according to the invention and further refinements of the same are explained in more detail with reference to the figure.

The method according to the invention for the liquefaction of a Hydrocarbon-rich stream, especially a natural gas stream, described, the pre-cooled natural gas stream after a relaxation and Separation of heavier components against a refrigerant mixture circuit cascade, consisting of three refrigerant mixture circuits liquefied and supercooled becomes.

The refrigerant mixture circuit cascade consists of a so-called pre-cooling circuit 20 , which serves for cooling and partial / complete condensation of the liquefaction and supercooling circuit, the pre-cooling of the natural gas to be liquefied and its own subcooling. The second refrigerant mixture circuit, the so-called liquefaction circuit 21 , serves the partial / complete condensation of the supercooling circuit, the condensation of the natural gas and its own subcooling. The third refrigerant mixture circuit 22 is a so-called subcooling circuit, which serves both the subcooling of the natural gas and its own subcooling.

It must be emphasized that the process of liquefaction according to the invention of a hydrocarbon-rich stream not only in combination with one as in The refrigerant mixture circuit cascade shown in the figure makes sense and advantages Has. Rather, the method according to the invention can be used with any one Refrigerant or refrigerant mixture circuit as well as combinations of refrigerant and use or combine mixed refrigerant circuits.

Since the natural gas to be liquefied is preferably at a pressure of 50 to 200 bar from 90 to 130 bar, this comparatively high pressure level can do so can be used to provide cold by expanding the natural gas. By the reheating of the natural gas cooled by the expansion becomes the Condensation of the refrigerant mixture of the pre-cooling circuit on a very allows low pressure level. This results, especially if that Method according to the invention with a refrigerant mixture circuit cascade connected, a highly efficient liquefaction process.

The method according to the invention is suitable, since only so-called standards components are used, also for this purpose, in existing systems to be realized. Because of the higher efficiency of the liquefaction process can either be built smaller or it can, at identical heat exchangers and machines, a higher condensing capacity be achieved.

Natural gas supplied via line 1 to an expansion turbine T1 is expanded in the expansion turbine T1 to a pressure level of approximately 40 to 100 bar in order to enable the separation of undesired components such as carbon dioxide, mercury, water, etc. The expanded natural gas is fed via line 2 to a separation unit R, which serves to remove the aforementioned components. The natural gas dried and pretreated in this way is fed via line 3 to a compressor V and compressed to a pressure level of 150 to 200 bar, preferably 90 to 130 bar. This compressor V is expediently driven by the expansion turbine T1 and, if appropriate, by the expansion turbine T2. The compressed natural gas is cooled in a cooler E1 to a temperature between 8 and 30 ° C., preferably against cooling water. The natural gas to be liquefied is then fed via line 4 to the heat exchanger E2 and pre-cooled in it to a temperature between -20 and 20 ° C., preferably -10 and 10 ° C.

The precooled natural gas is then fed via line 5 to an expansion turbine T2, in which it is expanded to a pressure level between 25 and 80 bar, preferably between 40 and 65 bar, and cooled to a temperature between -10 and -40 ° C. The expanded natural gas is now conducted via line 6 through the heat exchanger E2, in countercurrent to the natural gas flow to be pre-cooled in line 4 .

The expanded natural gas in the heat exchanger E2 serves both for its own pre-cooling as well as for cooling and condensing the refrigerant mixtures of the three refrigerant mixture circuits 20 , 21 and 22 . As a result, the refrigerant circuits are cooled down to a temperature level between -10 and 10 ° C and thus a complete condensation of the pre-cooling circuit at a very low pressure level of 8 to 20 bar.

The natural gas reheated to a temperature between -20 and 20 ° C., preferably between -10 and 10 ° C., is drawn off from the heat exchanger E2 via line 7 and fed to a separation column K. This separation column K is used to separate undesired heavy hydrocarbons which are withdrawn via line 8 from the bottom of the separation column K. The gas fraction withdrawn via line 9 at the top of the separation column K is partially condensed in the heat exchanger E3, which, as is also the case with the heat exchangers E4 and E5 to be described below, is preferably a plate or wound heat exchanger.

The two-phase flow withdrawn via line 10 from the heat exchanger E3 is fed to a separator A and separated there. The gas fraction from the separator A is fed to the heat exchanger E4 via line 14 , while the liquid fraction from the separator A is fed to a pump P via line 11 . By means of the pump P, the liquid fraction is pumped to a pressure level which enables the partial flow of the liquid fraction to be fed as a return line 12 to the separation column K. That part of the liquid fraction which does not serve as reflux for the separation column K is mixed via line 13 into the gas fraction drawn off at the top of the separator A in line 14 .

In principle, it is conceivable that the separation column K and the separator A can be dispensed with; however, this is only the case if the concentration of the heavy hydrocarbons in the hydrocarbon-rich liquefied Current is so low that there is no solid failure at low temperatures can.

The natural gas flow supplied to the heat exchanger E4 is condensed in the heat exchanger E4 at a temperature between -100 and -70 ° C. Then the condensed natural gas stream is fed via line 15 to a last heat exchanger E5 and supercooled in it at a temperature between -160 and -150 ° C. The supercooled natural gas stream is withdrawn from the heat exchanger E5 via line 16 and expanded in a Joule-Thompson valve or a liquid expansion turbine - not shown in the figure - to essentially atmospheric pressure if this should be necessary for the purpose of removing nitrogen or e.g. B. fed directly to a liquefied natural gas storage container.

The pre-cooling circuit 20 has a refrigerant mixture composition consisting essentially of 0 to 65 mol% of ethylene or ethane and 30 to 60 mol of propane. The pre-cooling circuit is used to cool the hydrocarbon-rich stream to be liquefied, as well as the liquefaction and supercooling circuit, down to a temperature level of approx. -50 ° C. The compressed refrigerant mixture of the pre-cooling circuit 20 is cooled in the heat exchanger E2 against the reheated hydrocarbon-rich stream in the line 6 , then subcooled in the heat exchanger E3 against itself, in the expansion valve a or in a relaxation turbine, not shown in the figure, and after the subsequent recirculation fed back to compression by the heat exchanger E3.

The refrigerant mixture of the liquefaction circuit 21 consists essentially of 5 to 15 mol% methane, 70 to 90 mol% ethane or ethylene and 5 to 20 mol% propane. This mixture of refrigerants is applied to the E2 heat exchanger at a pressure of 10 to 30 bar. After cooling in the heat exchangers E2 and E3, the refrigerant mixture of the liquefaction circuit 21 is supercooled against itself in the heat exchanger E4, expanded in the expansion valve b or in an expansion turbine, not shown in the figure, and then, after recirculation by the heat exchanger E4, the compression again fed.

The refrigerant mixture of the supercooling circuit 22 consists essentially of a mixture of 5 to 15 mol% nitrogen, 40 to 70 mol% methane and 30 to 60 mol% ethane or ethylene. The pressure at the E2 heat exchanger is between 25 and 70 bar. The cooling of the refrigerant mixture of the supercooling circuit 22 takes place in the heat exchanger E2, E3 and E4. In the heat exchanger E5, the refrigerant mixture is subcooled against itself, expanded in valve c or in an expansion turbine, not shown in the figure, and then, after recirculation through the heat exchanger E5, fed back to the compression.

Claims (7)

1.Method for liquefying a hydrocarbon-rich stream, in particular a natural gas stream, in which the reheated hydrocarbon-rich stream by indirect heat exchange in at least one heat exchanger with one or more refrigerants and / or one or more refrigerant mixtures of one or more refrigerants (mixture ) circuits are cooled and liquefied, characterized in that the hydrocarbon-rich stream ( 4 ) to be liquefied at a pressure of 50 to 200 bar in a first heat exchanger (E2) with itself by indirect heat exchange to a temperature of 20 to -20 ° C pre-cooled ( 5 ), then relaxed to a pressure of 25 to 80 bar (T2) and returned to the heat exchanger (E2) for reheating to a temperature of -20 to 20 ° C ( 6 ). 2. A method for liquefying a hydrocarbon-rich stream according to claim 1, characterized in that the pressure of the hydrocarbon-rich ( 4 ) stream to be liquefied is 90 to 130 bar. 3. A process for liquefying a hydrocarbon-rich stream according to claim 1 or 2, characterized in that the pressure of the pre-cooled hydrocarbon-rich stream ( 6 ) is 40 to 65 bar. 4. A process for liquefying a hydrocarbon-rich stream according to one of the preceding claims, characterized in that the temperature of the pre-cooled hydrocarbon-rich stream ( 4 ) is 10 to -10 ° C. 5. A process for liquefying a hydrocarbon-rich stream according to one of the preceding claims, characterized in that the temperature of the reheated hydrocarbon-rich stream ( 7 ) is -10 to 10 ° C. 6. A process for liquefying a hydrocarbon-rich stream according to one of the preceding claims, characterized in that the reheated hydrocarbon-rich stream ( 7 ) by indirect heat exchange (E3, E4, E5)

• 1. with a refrigerant circuit cascade consisting of at least two refrigerant circuits, or
• 2. with a refrigerant mixture circuit cascade, consisting of at least two refrigerant mixture circuits, or
• 3. with a cascade consisting of at least one refrigerant circuit and at least one refrigerant mixture circuit, or
• 4. with a refrigerant mixture circuit

cooled and liquefied 7. A process for liquefying a hydrocarbon-rich stream according to one of the preceding claims, characterized in that the pre-cooled and expanded hydrocarbon-rich stream ( 6 ) against one or more refrigerants to be cooled and / or condensed and / or against one or more to be cooled and / or refrigerant mixtures to be condensed is reheated.