Method of liquefying a contaminated hydrocarbon-containing gas stream

Abstract

A method of liquefying a contaminated hydrocarbon-containing gas stream includes cooling the stream in a first heat exchanger and cooling the cooled stream in an expander to obtain a partially liquefied stream. The method further includes separating the partially liquefied stream in a separator to obtain a gaseous stream and a liquid stream. The liquid stream is expanded to obtain a multiphase stream containing at least a vapour phase, a liquid phase and a solid phase. The multiphase stream is separated in a separator to obtain a gaseous stream and a slurry stream. The slurry stream is separated in a solid/liquid separator to obtain a liquid hydrocarbon stream and a concentrated slurry stream. The gaseous stream is passed through the first heat exchanger to obtain a heated gaseous stream. The heated gaseous stream is compressed and combined with the contaminated hydrocarbon-containing gas stream.

Claims

1. A method of liquefying a contaminated hydrocarbon-containing gas stream, the method comprising at least the steps of: (a) providing a contaminated hydrocarbon-containing gas stream; (b) cooling the contaminated hydrocarbon-containing gas stream in a first heat exchanger thereby obtaining a cooled contaminated hydrocarbon-containing stream; (c) cooling the cooled contaminated hydrocarbon-containing stream in an expander thereby obtaining a partially liquefied stream; (d) separating the partially liquefied stream in a first separator thereby obtaining a first gaseous stream and a liquid stream; (e) expanding the liquid steam obtained in step (d) thereby obtaining a multiphase stream, the multiphase stream containing a vapour phase, a liquid phase and a solid phase; (f) separating the multiphase stream in a second separator thereby obtaining a second gaseous stream and a slurry stream; (g) separating the slurry stream in a solid/liquid separator thereby obtaining a liquid hydrocarbon stream and a concentrated slurry stream; (h) passing the first gaseous stream obtained in step (d) through the first heat exchanger thereby obtaining a heated gaseous stream; and (i) compressing the heated gaseous stream thereby obtaining a compressed gas stream; and (j) combining a first portion of the compressed gas stream obtained in step (i) with the contaminated hydrocarbon-containing gas stream provided in step (a); (k) cooling a second part of the compressed gas stream obtained in step (i) through a second heat exchanger thereby obtaining a cooled compressed gas stream; (l) expanding the cooled compressed gas stream thereby obtaining an expanded gas stream; and (m) combining the expanded gas stream with the first gaseous stream obtained in step (d).

2. The method according to claim 1, wherein the contaminated hydrocarbon-containing gas stream comprises at least 50 vol. % methane.

3. The method according to claim 1, wherein the cooled contaminated hydrocarbon-containing stream obtained in step (b) has a temperature of at most 40 C.

4. The method according to claim 1, wherein the multiphase stream obtained in step (e) has a temperature of at most 100 C.

5. The method according to claim 1, further comprising: passing the second gaseous stream obtained in step (f) through the second heat exchanger thereby obtaining a second heated gaseous stream; compressing the second heated gaseous stream thereby obtaining a second compressed gas stream; and combining the second compressed gas stream with the heated gaseous stream obtained in step (h).

6. The method according to claim 1, wherein the liquid hydrocarbon stream obtained in step (g) is stored in a storage tank, and wherein a boil-off gas stream from said storage tank is combined with the second gaseous stream obtained in step (f).

7. The method according to claim 5, wherein the liquid hydrocarbon stream obtained in step (g) is stored in a storage tank, and wherein a boil-off gas stream from said storage tank is combined with the second gaseous stream obtained in step (f).

Description

(1) Hereinafter the invention will be further illustrated by the following non-limiting drawing. Herein shows:

(2) FIG. 1 schematically a process scheme for performing the method according to the present invention.

(3) For the purpose of this description, same reference numbers refer to same or similar components.

(4) FIG. 1 schematically shows a process scheme for performing a method of liquefying a contaminated hydrocarbon-containing gas stream. The process scheme is generally referred to with reference number 1.

(5) The process scheme 1 comprises a compressor 2, a heat exchanger 3 (the first heat exchanger), an expander 4, a first separator 5, a JT-valve 6, a second separator 7, a pump 8, a third (solid/liquid0 separator 9, an LNG storage tank 11, a slurry heater 12, further compressors 13 and 14, a second heat exchanger 15, an expander 16 and a methanol separator 17. The process scheme may comprise further heat exchangers in addition to the first heat exchanger 3 and second heat exchanger 15. Preferably, the first heat exchanger 3 and second heat exchanger 15 are separate heat exchangers.

(6) During use of the process scheme 1 according to the present invention, a contaminated hydrocarbon-containing gas stream 20 is provided (which has previously been compressed as stream 10 in compressor 2). This contaminated hydrocarbon-containing gas stream 20 is typically a natural gas stream. The contaminated hydrocarbon-containing gas stream 20 is cooled (as stream 30) in the first heat exchanger 3 thereby obtaining a cooled contaminated hydrocarbon-containing gas stream 40. The first heat exchanger 3 is (like the second heat exchanger 15) an indirect heat exchanger; hence no direct contact between the streams takes place, but only heat exchanging contact.

(7) As shown in the embodiment of FIG. 1, the cooled contaminated hydrocarbon-containing stream 40 is passed to the methanol separator 17 to separate methanol (as stream 50) that has been previously injected (e.g. into stream 20) to prevent hydrate formation. After the methanol separator 17, the (methanol-depleted) cooled contaminated hydrocarbon-containing gas stream is further cooled as stream 60 in the expander 4 thereby obtaining a partially liquefied stream 70. This partially liquefied stream 70 is separated in separator 5 thereby obtaining a gaseous stream 80 and a liquid stream 90. The liquid steam 90 is expanded in JT-valve 6 thereby obtaining a multiphase stream 100. The multiphase stream 100 is separated in the separator 7 thereby obtaining a gaseous stream 110 and a slurry stream 120.

(8) The slurry stream 120 is separated in the solid/liquid separator 9 thereby obtaining a liquid hydrocarbon stream 170 and a concentrated slurry stream 140. The solid/liquid separator 9 is not particularly limited and can for example be selected from a cyclone, settler, filter or a combination thereof.

(9) The liquid hydrocarbon stream 170 is the product stream and is typically an LNG stream. The liquid stream 170 as obtained according to the present invention may have a composition that is different from known compositions, in terms of CO.sub.2 and C.sub.5+.

(10) The concentrated slurry stream 140 may be further processed if desired; typically, it is a CO.sub.2-rich stream. Preferably, the concentrated slurry stream 140 is heated in slurry heater 12 and separated into a liquid phase 160 and a gaseous phase 160; the gaseous phase 160 may be combined with a fuel gas stream.

(11) As shown in FIG. 1, the slurry stream 120 may be pumped to higher pressure before being separated (as stream 130) in the solid/liquid separator 9.

(12) The gaseous stream 80 is passed through the first heat exchanger 3 thereby obtaining a heated gaseous stream 270; if desired some inerts (such as N.sub.2) may be removed from the heated gaseous stream 270 as (minor) stream 280. As stream 80 is used to cool the stream 30, this is an auto-refrigeration step.

(13) The heated gaseous stream 270 is compressed in compressor 13 thereby obtaining a compressed gas stream 220. Part 230 of the compressed gas stream 220 is combined with the contaminated hydrocarbon-containing gas stream 20.

(14) As can be seen in the embodiment of FIG. 1, a part 240 of the compressed gas stream 220 is passed through the second heat exchanger 15 (and cooled therein) thereby obtaining a cooled compressed gas stream 250. The cooled compressed gas stream 250 is expanded in expander 16 thereby obtaining an expanded an expanded gas stream 260. Subsequently, the expanded gas stream 260 is combined with the gaseous stream 80 to form stream 265.

(15) Furthermore, in the embodiment of FIG. 1, the gaseous stream 110 is passed as stream 190 through the second heat exchanger 15 thereby obtaining a second heated gaseous stream 200. The second heated gaseous stream 200 is compressed in compressor 14 thereby obtaining a second compressed gas stream 210; this second compressed gas stream 210 is combined with the heated gaseous stream 270 (to form stream 215).

(16) Also, it is preferred that the liquid hydrocarbon stream 170 is stored in storage tank 11, and that a boil-off gas stream 180 from said storage tank 11 is combined with the gaseous stream 110 to form stream 190.

(17) Table 1 below shows an actual non-limiting example, providing information on conditions and composition of the various streams, whilst using the scheme of FIG. 1 for processing a natural gas stream contaminated with CO.sub.2. The composition of LNG stream 90 is given in Table 2. Stream 120 comprised 84% of stream 110 (and stream 100 16%).

(18) TABLE-US-00001 TABLE 1 Composition and properties of various streams Amount Amount Amount Amount Pressure Temp. of CH.sub.4 of CO.sub.2 of C.sub.2+ of N.sub.2 Stream [bara] [ C.] State [mol %] [mol %] [mol %] [mol %] 10 45 30 Gas 82 2 14 2 20 95 30 Gas 82 2 14 2 30 95 30 Gas 80 1 5 14 40 95 74 Gas/liquid 80 1 5 14 50 95 74 Liquid n.d. n.d. n.d. n.d. 60 95 74 Gas 80 1 5 14 70 20 111 Gas/liquid 80 1 5 14 80 20 111 Gas 74 0.2 0.8 25 90 20 111 Liquid 84 1.4 9.6 5 100 2 152 Liquid/solid/ 84 1.4 9.6 5 gas 110 2 152 Gas 87 13 120 2 152 Liquid/solid 47 42 0.7 0.3 130 6 152 Liquid/solid 47 42 0.7 0.3 140 5 152 Liquid/solid 47 42 0.7 0.3 150 5 10 Gas 47 42 0.7 0.3 160 5 10 Liquid 1 3.5 95.5 170 2.5 148 Liquid 84 0.1 15.3 0.6 180 2.5 148 Gas 88 12 190 2 148 Gas 87 1 1 13 200 2 26 Gas 87 1 1 13 210 20 30 Gas 87 1 1 13 215 20 30 Gas 78 0.2 0.8 21 220 95 30 Gas 78 0.2 0.8 21 230 95 30 Gas 78 0.2 0.8 21 240 95 30 Gas 78 0.2 0.8 21 250 95 9 Gas 78 0.2 0.8 21 260 20 81 Gas 78 0.2 0.8 21 265 20 92 Gas 77 0.2 0.8 22 270 20 28 Gas 77 0.2 0.8 22 280 20 28 Gas 77 0.2 0.8 22

(19) TABLE-US-00002 TABLE 2 Composition of stream 170 Component [mol %] Nitrogen 0.56 CO.sub.2 0.08 Methane 83.85 Ethane 7.77 Propane 4.43 i-Butane 1.11 n-Butane 1.11 C.sub.5+ (sum of the below 4) 1.09 i-Pentane 0.43 n-Pentane 0.43 n-Hexane 0.22 Benzene 0.01

(20) As can be seen from Table 2, the composition of LNG stream 170 differs from a common LNG product (see e.g. Small-scale LNG facility development, B.C. Price, Hydrocarbon Processing, January 2003) in that it contains more CO.sub.2 (0.08 mol % vs. 0.0125 mol % in the above reference), and more benzene (0.01 mol % vs. 0.001 mol % in the above reference). Also, the composition of LNG stream 170 has an uncommonly high C.sub.5+ content (1.09 mol %, whilst it is typically lower).

(21) The person skilled in the art will readily understand that many modifications may be made without departing from the scope of the invention.