SYNERGIES OF A NATURAL GAS LIQUEFACTION PROCESS IN A SYNTHESIS GAS PRODUCTION PROCESS

Abstract

A natural gas liquefaction process combined with a synthesis gas production process. At least one part of the heat source required in the synthesis gas production process is provided by at least a portion of the regeneration stream utilized to pretreat the natural gas to be liquefied.

Claims

1.-12. (canceled)

13. A process for the liquefaction of natural gas in combination with a process for the production of synthesis gas, the liquefaction process comprising: a) pretreating a feed natural gas by means of a pretreatment system using a regeneration stream, to remove impurities that will freeze during the liquefaction process, thereby producing a pretreated stream; b) extracting a stream enriched in hydrocarbons having more than two carbon atoms and of a stream depleted in hydrocarbons having more than two carbon atoms from the pretreated stream, thereby producing a hydrocarbon enriched stream; c) liquefying of the hydrocarbon enriched stream; the process for the production of synthesis gas comprising: a′) desulfurizing a natural gas feed stream at a temperature of greater than 350° C., thereby producing a desulfurized stream; b′) prereforming the hydrocarbon chains containing at least two carbon atoms in the desulfurized stream into methane at a temperature of greater than 500° C., thereby producing a prereformed stream; c′) reforming the desulfurized stream or the prereformed stream with steam at a temperature of greater than 800° C. in order to produce hydrogen, carbon dioxide and carbon monoxide; wherein at least a portion of the heat source required for the synthesis gas production process is produced by at least a portion of the regeneration stream.

14. The process as claimed in claim 13, wherein the pretreating is performed by an adsorption separation system.

15. The process as claimed in claim 13, wherein the pretreating is performed by an amine scrubbing system followed downstream by a drying unit, the drying unit comprising the regeneration stream.

16. The process as claimed in claim 14, wherein step a) consists of pretreating by adsorption by means of an adsorption system comprising between two and five containers of at least one layer of adsorbent and at least one device for heating and/or cooling an adsorption and/or regeneration stream circulating in the adsorption system and wherein the steam resulting from the process for the production of synthesis gas is employed to reheat the regeneration stream.

17. The process as claimed in claim 13, wherein, during step a′), all sulfur-comprising derivatives present in the feed gas are converted into H.sub.2S product by catalysis in a reactor.

18. The process as claimed in claim 17, wherein the product H.sub.2S is extracted by catalysis.

19. The process as claimed in claim 13, wherein the impurities that will freeze during the liquefaction process which are removed during step a) comprise water, carbon dioxide and sulfur-comprising derivatives present in the feed natural gas.

20. The process as claimed in claim 13, wherein during step c), the hydrocarbon enriched stream is liquefied at a temperature of less than −140° C. by means of a unit for the liquefaction of natural gas comprising at least one main heat exchanger and a system for producing frigories.

21. The process as claimed in claim 13, wherein the natural gas feed stream employed in step a) and the natural gas feed stream employed in step a′) originate from the same natural gas feed stream.

22. The process as claimed in claim 13, wherein the unit for the production of synthesis gas is a unit for the production of hydrogen by steam reforming has a hydrogen production capacity of at least 20 000 Nm.sup.3/h.

23. The process as claimed in claim 13, wherein the heat energy of the regeneration stream used during step a) represents from 5% to 35 of the amount of fuel required for the synthesis gas production process.

24. The process as claimed in claim 13, wherein the regeneration stream used during step a) produces an excess of the fuel balance of the synthesis gas production unit and is sent back to the feed stream of the synthesis gas production unit.

Description

[0066] An exemplary embodiment is illustrated by the following example.

[0067] The production of hydrogen by catalytic reforming requires a continuous supply of heat provided by a fuel gas network.

[0068] A steam reforming unit with a nominal hydrogen production capacity of approximately 130 000 Nm.sup.3/h is employed.

[0069] The heat requirements needed for the hydrogen production unit are mainly provided (about 75%) by the residual gas resulting from the last stage of purification of hydrogen in the hydrogen production unit (purification via molecular sieves (Pressure Swing Adsorption/PSA)). The makeup (about 25%) is provided by a source external to the hydrogen production unit (for example originating from the feed stream of the unit or from an external fuel system).

[0070] By placing a small natural gas production unit with a capacity of 40 000 tonnes of liquefied natural gas produced per year close to the hydrogen production unit, it is possible to return certain flows to the fuel network of the hydrogen production unit. The makeup provided by an external source will be reduced accordingly. [0071] In the case where the pretreatment of the natural gas is provided by an adsorption process, the regeneration gas returned to the fuel network would represent about 15% of the fuel balance. [0072] The heavy hydrocarbons extracted from the natural gas liquefier and the natural gas vapors generated in the storage of liquefied natural gas and/or in the loading bay will be less significant in the fuel balance (less than 1%).

[0073] The external heat source makeup is thus reduced from 25% to 10% approximately.

[0074] This integration makes it possible to drastically reduce the number of pieces of equipment dedicated to secondary streams of the natural gas liquefaction unit: [0075] heavy hydrocarbons: the integration makes it possible, for example, to avoid having an incinerator and/or a system for extracting heavy hydrocarbons which is expensive for small-sized units. [0076] natural gas vapors generated in the storage of liquefied natural gas and/or in the loading bay: the integration makes it possible for example to avoid having a compressor to recycle these vapors into the natural gas liquefaction stream. This compressor may be expensive in small-sized liquefiers.

[0077] If the capacity of the liquefied natural gas production unit unbalances the fuel balance, it is possible to return all or part of these streams to the synthesis gas stream that feeds the hydrogen production unit (at the cost of a compressor).

[0078] It is then possible for the units for the production of synthesis gas and for the liquefaction of natural gas to have in common all of the conveniences of the site, in particular: [0079] The connection to the natural gas network; [0080] The metering and optionally pressure reduction/compression station; [0081] A hot flare and optionally cold liquid network; [0082] All of the utilities of the site (electricity, cooling circuit, instrumentation air, nitrogen, and the like); [0083] The feed network.

[0084] Furthermore, in the case where the unit for the production of synthesis gas produces hydrogen, it is sometimes required to liquefy all or part of the hydrogen in order to facilitate the transportation or storage thereof, for example.

[0085] In this case, it is possible to “precool” the hydrogen produced in the natural gas liquefier down to a temperature of −160° C., for example, and then to finish liquefying it in a dedicated unit.

[0086] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.