KR20120016568A - Natural gas liquefaction process and system using the same - Google Patents

Abstract

PURPOSE: A process for liquefying natural gas is provided to simplify process structure and to easily operate a liquefaction system. CONSTITUTION: A process for liquefying natural gas comprises: a step of precooling natural gas through thermal exchange with coolant in a first thermal exchange area(121); a step of liquefying the pre-cooled natural gas through thermal exchange; a step of separating coolant into a liquid phase coolant part and a vapor coolant part; a step of precooling the natural gas in the first thermal exchange area; a step of liquefying the natural gas; a step of pressing the coolant part which precools the natural gas; a step of pressing the coolant part which liquefies the natural gas; and a step of mixing the coolant parts.

Description

Natural gas liquefaction process and natural gas liquefaction system using the same {NATURAL GAS LIQUEFACTION PROCESS AND SYSTEM USING THE SAME}

The present invention relates to a natural gas liquefaction process and a natural gas liquefaction system, and more particularly, by using a single closed loop refrigeration cycle employing a mixed refrigerant, the structure of the liquefaction process is simple, the system can be compact and the operation of the liquefaction system The present invention relates to a natural gas liquefaction process that is easy and has excellent efficiency of the liquefaction process.

Thermodynamic processes for liquefying natural gas to produce liquefied natural gas (LNG) have been developed since the 1970s to meet a variety of challenges, including the need for higher efficiency and greater capacity. In order to increase the efficiency and capacity of the liquefaction process, various attempts have been made to liquefy natural gas using different refrigerants or different cycles. little.

One of the most popular liquefaction processes in operation is the 'Propane Pre-cooled Mixed Refrigerant Process' (or C3 / MR Process). The basic structure of the C3 / MR process is as shown in FIG. As shown in FIG. 15, the feed gas is pre-cooled to approximately 238 K by a multi-stage propane (C3) Joule-Thomson (JT) cycle. The precooled feed gas is liquefied and sub-cooled to 123 K through heat exchange with a mixed refrigerant (MR) in a heat exchanger. The C3 / MR process has a disadvantage in that the liquefaction process is complicated and the operation of the liquefaction system is difficult because a refrigeration cycle employing a single refrigerant and a refrigeration cycle employing a mixed refrigerant are used.

One of the other successful liquefaction processes in operation is by Conoco Phillips, which is based on the Cascade process. As conceptually illustrated in FIG. 16, the liquefaction process of 'Conoco Phillips' uses three Joules using methane (C1), ethylene (C2), and propane (C3), which are pure-component refrigerants. It consists of a Thompson cycle. Since the liquefaction process does not use a mixed refrigerant, there is an advantage that the operation of the liquefaction process is safe, simple and reliable. However, there is a disadvantage in that the size of the liquefaction system is inevitably increased because an individual compressor, heat exchanger, etc. are required for each of the three cycles.

Another liquefaction process in operation is the 'Single Mixed Refrigerant Process' (or SMR Process). The basic structure of the SMR process is as shown in FIG. As shown in Fig. 17, the feed gas is liquefied through heat exchange with the mixed refrigerant in the heat exchange zone. The SMR process uses one closed loop refrigeration cycle with mixed refrigerant. In this refrigeration cycle, the mixed refrigerant is compressed and precooled and then expanded after condensing the mixed refrigerant through heat exchange in the heat exchange zone. The expanded refrigerant flows back into the heat exchange zone to condense the precooled mixed refrigerant and liquefy the feed gas. This SMR process has the advantage that the system is compact due to its simple structure, but has the disadvantage that the efficiency of the liquefaction process is not good.

Therefore, the present invention has been made to solve the above problems, the problem of the present invention is to use a single closed loop refrigeration cycle employing a mixed refrigerant, the liquefaction process is simple, the system is compact and the operation of the liquefaction system is easy It is to provide a natural gas liquefaction process with excellent efficiency of the liquefaction process.

According to a preferred embodiment of the present invention for achieving the above object of the present invention, by using a single closed loop refrigeration cycle employing a mixed refrigerant to pre-cool natural gas through heat exchange with the refrigerant in the first heat exchange zone In the natural gas liquefaction process of liquefying natural gas precooled through the heat exchange with the refrigerant | coolant in a 2nd heat exchange area, the said closed-loop refrigeration cycle isolate | separates the partially condensed mixed refrigerant into the liquid refrigerant | coolant part and gaseous-phase refrigerant part. Separation step, pre-cooling step of pre-cooling the natural gas in the first heat exchange zone using the liquid refrigerant portion, liquefaction step of liquefying natural gas pre-cooled in the second heat exchange zone using the gaseous refrigerant section, pre-cooling step after the pre-cooling step The first compression step of compressing the refrigerant portion of the pre-cooled natural gas through the liquefaction step after the liquefaction step A second compression step of compressing a refrigerant part liquefied gas, and a mixing step of mixing respective refrigerant parts compressed through the first and second compression steps, wherein the liquid refrigerant part and the gaseous refrigerant part are separated from each other. After the separation through the step through the independent loop without mixing with each other characterized in that the mixing in the mixing step.

In addition, according to another preferred embodiment of the present invention, by using a closed loop refrigeration cycle employing a mixed refrigerant to pre-cool the natural gas through the heat exchange with the refrigerant in the first heat exchange zone and the refrigerant in the second heat exchange zone; In the natural gas liquefaction process of liquefying the natural gas pre-cooled through the heat exchange of the, the closed loop refrigeration cycle, the first condensation step, the first condensation step of partially condensing the mixed refrigerant through heat exchange in the first heat exchange region Separation step of separating the mixed refrigerant partially condensed through the liquid refrigerant portion and the gaseous refrigerant portion, the pre-cooling step of pre-cooling the natural gas in the first heat exchange region using the liquid refrigerant portion separated through the separation step, Liquefaction step of liquefying the pre-cooled natural gas in the second heat exchange zone by using the gaseous refrigerant portion separated through A first compression step of compressing the refrigerant part in which the natural gas is precooled through the precooling step after the system, a second compression step of compressing the refrigerant part in which the natural gas is liquefied through the liquefaction step, and first and second And mixing each refrigerant portion compressed through the compression step, wherein the liquid refrigerant portion and the gaseous refrigerant portion are separated through the separation step and then pass through separate loops without mixing with each other. Characterized in that they are mixed with each other.

And according to another preferred embodiment of the present invention, a natural gas liquefaction system for liquefying natural gas using one closed loop refrigeration cycle employing a mixed refrigerant, the partial refrigerant condensed mixed refrigerant and the first refrigerant portion Separation means for separating into two refrigerant portions, a first heat exchange region in which natural gas is precooled through heat exchange with the first refrigerant portion, and a second heat exchange region in which natural gas pre-cooled through heat exchange with the second refrigerant portion is liquefied. Heat exchange means comprising: first compression means for compressing a first refrigerant portion precooled with natural gas in a first heat exchange region, second compression means for compressing a second refrigerant portion liquefied with natural gas in a second heat exchange region, Mixing means for mixing the refrigerant portion compressed through the first and second compression means, a first conduit for guiding the first refrigerant from the separating means to the first compression means, and in FIG. And a second conduit to guide the second refrigerant from the separating means to the second compression means without mixing with the first refrigerant, wherein the first refrigerant portion has a higher boiling point than the second refrigerant portion. do.

Furthermore, according to another preferred embodiment of the present invention, one closed loop refrigeration cycle employing a mixed refrigerant is used to cool the natural gas primarily through heat exchange with the refrigerant in the first heat exchange zone, and In a natural gas liquefaction process of cooling a natural gas primarily cooled through heat exchange with a refrigerant, the closed loop refrigeration cycle is a separation step of separating a partially condensed mixed refrigerant into a liquid refrigerant portion and a gaseous refrigerant portion. ; First cooling the natural gas in the first heat exchange region using the liquid refrigerant portion, secondly cooling the natural gas primarily cooled in the second heat exchange region using the gaseous refrigerant portion, and first cooling A first compression step of compressing the refrigerant part that primarily cooled the natural gas through a first cooling step, and a second cooling step of the refrigerant part that secondly cooled the natural gas after a second cooling step. And a mixing step of mixing respective refrigerant parts compressed through the first and second compression steps, wherein the liquid refrigerant part and the gaseous refrigerant part are separated from each other after the separation step. Via separate loops without mixing of The agitating step cools the natural gas to a lower temperature than the primary cooling step.

The natural gas liquefaction process and the natural gas liquefaction system according to the present invention use a single refrigeration cycle employing a mixed refrigerant, so the structure of the liquefaction process is simple, the system is compact, and the operation of the system is easy, and the mixed refrigerant is After separating into two refrigerant parts, the steps of condensation (cooling), expansion, heat exchange and compression are carried out separately without mixing between the refrigerant parts. It can be applied, thereby improving the efficiency of the liquefaction process.

1 is a flowchart illustrating a natural gas liquefaction process according to Embodiment 1 of the present invention.
2 is a flow chart showing a first modification to the liquefaction process according to FIG.
3 is a flow chart showing a second modification to the liquefaction process according to FIG.
4 is a flow chart showing a third modification to the liquefaction process according to FIG.
5 is a flowchart illustrating a natural gas liquefaction process according to Embodiment 2 of the present invention.
6 is a flow chart showing a modification to the liquefaction process according to FIG.
7 is a flow chart showing a modification to the liquefaction process according to FIG.
8 is a flowchart showing a natural gas liquefaction process according to Embodiment 3 of the present invention.
9 is a flowchart showing a natural gas liquefaction process according to Embodiment 4 of the present invention.
10 is a flow chart showing a modification to the liquefaction process according to FIG.
11 and 12 are flowcharts illustrating basic concepts that can represent the above-described embodiments.
13 and 14 are flowcharts illustrating the case where the liquefaction process according to the above-described embodiments is used as part of the overall liquefaction process.
15 is a flowchart conceptually illustrating a conventional C3 / MR process.
16 is a flow chart conceptually illustrating a conventional cascade process.
17 is a flowchart conceptually illustrating a conventional SMR process.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited or limited by the embodiments. For reference, in the present description, the same numbers refer to substantially the same elements, and may be described by quoting contents described in other drawings under these rules. And it can be omitted that it is determined or repeated to those skilled in the art to which the present invention pertains.

Example 1

1 is a flowchart illustrating a natural gas liquefaction process according to Embodiment 1 of the present invention. The liquefaction process according to the present embodiment is a process for producing liquefied natural gas (LNG) by cooling natural gas to a liquefaction temperature by using a closed loop refrigeration cycle as shown in FIG. Can be applied. In particular, one closed loop refrigeration cycle employing mixed refrigerants or multi-component refrigerants is used to precool the natural gas through heat exchange with the refrigerant in the first heat exchange zone, and the refrigerant in the second heat exchange zone. It can be applied to the natural gas liquefaction process to liquefy the pre-cooled natural gas through heat exchange with. The liquefaction process according to the present embodiment may further include an auxiliary refrigeration cycle for cooling the mixed refrigerant or cooling the natural gas.

Hereinafter, a liquefaction process according to an embodiment of the present invention applied to a natural gas liquefaction process including one refrigeration cycle as described above will be described with reference to FIG. 1. The partially condensed mixed refrigerant flows into the separating means 110 and is separated into a first refrigerant portion and a second refrigerant portion having a lower boiling point than the first refrigerant portion according to the difference in boiling point. That is, the partially condensed mixed refrigerant may be divided into a first refrigerant portion separated into the liquid refrigerant portion because of the high boiling point through the separating means 110 and a second refrigerant portion separated into the gaseous refrigerant portion because of the low boiling point. have. Such separation means 110 may be a conventional vapor-liquid separator.

The separated first refrigerant part may undergo a series of cooling and expansion processes and then precool the natural gas in the first heat exchange area through heat exchange. As described above, the separated first refrigerant part is introduced into the first heat exchange region 121 through a conduit 161 connecting the separation means 110 and the first heat exchange region 121. And the first refrigerant portion is cooled through heat exchange in the first heat exchange region 121. Cooling of this refrigerant portion is accomplished through heat exchange with the refrigerant entering the first heat exchange region 121 through conduits 163 and 175. The cooled refrigerant portion enters and expands to expansion means 131 through conduit 162. At this time, the expansion means 131 may be a conventional expansion valve (expansion valve).

The expanded refrigerant portion enters the first heat exchange region 121 again through the conduit 163. The refrigerant portion introduced into the first heat exchange region 121 cools other refrigerants and precools natural gas through heat exchange in the first heat exchange region 121. The portion of the refrigerant having undergone heat exchange in the first heat exchange region 121 is introduced into the first compression means 141 through the conduit 164 and compressed. In this case, the first compression means 141 may be a conventional compressor, and the second compression means 142, which will be described later, may also be a conventional compressor. The first and second compression means may have a form in which a plurality of compressors and cooling means are connected in series. In this way, if the refrigerant portion is compressed in multiple stages, the required power of the compressor can be reduced.

The separated second refrigerant part is introduced into the first heat exchange area 121 through the conduit 171 and cooled. Cooling of this refrigerant portion is accomplished through heat exchange with the refrigerant entering the first heat exchange region 121 through conduits 163 and 175. The cooled refrigerant portion enters and condenses the second heat exchange region 122 through conduit 172. Condensation of this refrigerant portion takes place through heat exchange with the refrigerant entering the second heat exchange region 122 through the conduit 174. The condensed refrigerant portion enters and expands through expansion conduit 173 to expansion means 132. At this time, the expansion means 132 may be a conventional expansion valve (expansion valve). The expanded refrigerant portion flows back through the conduit 174 into the second heat exchange zone 122 to condense other refrigerants through the heat exchange and liquefy the precooled natural gas. For reference, the liquefied natural gas may be expanded by the expansion valve 136 and then introduced into the storage tank.

The two heat exchange regions 121 and 122 described above may be provided in one heat exchange means 120 as shown in FIG. 1, or may be provided in two heat exchange means, respectively. The heat exchange means may also be a conventional heat exchanger. For the convenience of illustration, the portion where the actual heat exchange is performed in the heat exchange region is shown in a form similar to a triangular wave as shown in FIG. 1, and the portion where the actual heat exchange is not performed in the heat exchange region is represented by a straight line. For example, the portion shown in a straight line in the heat exchange means 120 of FIG. 1 does not actually pass through the second heat exchange region 122, that is, does not perform heat exchange with other refrigerants, but is merely for convenience of illustration. It is shown as passing through the second heat exchange region 122.

The refrigerant portion having completed the heat exchange in the second heat exchange region 122 may be introduced into the first heat exchange region 121 through the conduit 175 to further cool other refrigerants or additionally pre-cool natural gas through heat exchange. Since the refrigerant portion in which the other refrigerant and the natural gas are cooled in the second heat exchange region 122 has a sufficiently low temperature even after the heat exchange, the refrigerant may be cooled even though the refrigerant flows into the first heat exchange region 121 as described above. . The refrigerant portion having completed this heat exchange is introduced into the second compression means 142 through the conduit 176 and compressed. In some cases, however, the refrigerant portion having completed the heat exchange in the second heat exchange region 122 may be introduced into the second compression means 142 without passing through the first heat exchange region 121.

The first refrigerant portion compressed through the first compression means 141 and the second refrigerant portion compressed through the second compression means 142 enter the cooling means 146, 147 through the conduits 165, 177, respectively. And the cooling, whereby each refrigerant portion may be partially condensed. Such cooling means 146, 147 may be conventional chillers. Each refrigerant portion is then mixed into one refrigerant portion via mixing means. Such mixing means may be a conventional mixer. Alternatively, such mixing means may refer to two conduits 166 and 178 connected between the conduits, ie interconnected to induce mixing of the first and second refrigerant portions, as shown in FIG. 1. The refrigerant portion thus mixed is introduced into separation means 110 through conduit 167 in a partially condensed state and repeats the aforementioned refrigeration cycle.

In addition, the position of the above-mentioned cooling means is not limited to the position shown in FIG. That is, as shown in FIG. 1, two cooling means 146 and 147 may be provided separately after the first and second compression means 141 and 142 to cool each refrigerant portion, respectively. As shown, cooling means 148 may be provided to cool the mixed refrigerant portion after mixing the refrigerant portions. 2 is a flowchart illustrating a first modification of the liquefaction process according to FIG. 1. As shown in FIG. 3, additional recompression may be performed on the mixed refrigerant part after the refrigerant is mixed. 3 is a flowchart illustrating a second modification to the liquefaction process according to FIG. 1. That is, as shown in FIG. 3, the mixed refrigerant portion may be compressed once again through the recompression means 144, and the recompressed refrigerant portion may be cooled once again and partially condensed. For reference, in the embodiment according to FIG. 1, the refrigerant parts are partially condensed due to cooling by the coolers 146 and 147, and in the embodiment according to FIG. 2, the mixed refrigerant part is partially due to cooling by the cooler 148. 3, the mixed refrigerant portion is recompressed and recooled and then partially condensed in the embodiment according to FIG. 3.

Since the liquefaction process according to the present embodiment consists of only one refrigeration cycle as described above, the liquefaction process is basically simple, the system is compact, and the operation of the liquefaction system is easy. In addition, as described above, in the liquefaction process according to the present embodiment, after the partially condensed mixed refrigerant is separated into the first refrigerant portion and the second refrigerant portion by the separating means, the first refrigerant portion and the first refrigerant portion are not mixed between the refrigerant portions. The two refrigerant sections are each mixed via separate loops until they reach mixing means. That is, the first conduits 161 to 164 for guiding the first refrigerant from the separating means 110 to the first compression means 141, and the second refrigerant from the separating means 110 to the second compression means 142. There is no intersection between the guiding second conduits 171-176. Accordingly, in the liquefaction process according to the present embodiment, the first refrigerant and the second refrigerant undergo condensation (cooling), expansion, heat exchange, and compression, respectively, between the separating means and the compression means.

As described above, when each refrigerant part individually performs a refrigeration cycle, the efficiency of the liquefaction process may be improved. In detail, when the mixed refrigerant is separated into the first refrigerant portion and the second refrigerant portion by the separating means 110, each refrigerant portion may have a difference in composition. Accordingly, each refrigerant portion exhibits different thermodynamic characteristics according to its composition, and as a result, a difference occurs in a region in which each refrigerant portion can exert cooling heat effectively.

In order to provide optimum heat exchange conditions to each of the separated refrigerant parts by reflecting these characteristics, in the liquefaction process according to the present embodiment, after the mixed refrigerant is separated into the first refrigerant part and the second refrigerant part, each refrigerant The portions are subjected to condensation (cooling), expansion, heat exchange and compression without mixing with each other (ie without mixing between the first and second refrigerant portions). For example, by providing separate compression means for each refrigerant portion to give different and optimal pressure conditions to each refrigerant portion that has undergone heat exchange in the heat exchange zone, each refrigerant portion is treated with natural gas at optimum conditions. The liquefaction process can be designed to exchange heat, and as a result, the efficiency of the entire liquefaction process can be improved.

Meanwhile, an expander may be further provided between the aforementioned second heat exchange region 122 and the expansion valves 131 and 132 in order to further increase the efficiency of the liquefaction process. That is, as shown in FIG. 4, the first refrigerant portion may pass through the first heat exchange zone 121 and then enter the expander 191 through the conduit 1621 and may be primarily expanded, after which the conduit It is introduced into the expansion valve 131 through the 1622, it can be expanded second. Similarly, the second refrigerant portion also passes through the second heat exchange region 122, then enters the expander 192 through the conduit 1731 and is primarily expanded, and then through the conduit 1732 to the expansion valve 132. Inflow and secondary expansion.

Conventional expansion valves (JT valves) only serve to lower the temperature of the fluid through pressure drop. In contrast, the expander also causes work to go out with pressure drop, allowing more energy to flow out of the fluid, which can result in a lower temperature of the fluid. It is also possible to drive the compressor or the like through the work generated from the expander. As a result, the overall efficiency of the liquefaction process can be improved, and compared with the liquefaction process according to FIG. 1, the liquefaction process according to FIG. 4 was confirmed to have an efficiency improvement of approximately 1.7%.

In addition, the mixed refrigerant used in the liquefaction process according to the present embodiment includes methane (C1), ethane (C2), propane (C3), butane (C4), pentane (C5) and nitrogen (N2). It is preferable in terms of. Generally, the mixed refrigerant includes methane (C1), ethane (C2), propane (C3) and nitrogen (N2), but if it contains more butane (C4) and pentane (C5), the mixed refrigerant may cover it. Since the temperature range is wider, the efficiency of the liquefaction process using such a mixed refrigerant can be improved.

In detail, the boiling point at atmospheric pressure of each component is -198.8 占 폚, methane -161.5 占 폚, ethane -88.8 占 폚, propane -42.09 占 폚, butane -0.5 占 폚 and pentane 27.84 占 폚. Accordingly, in the case of the mixed refrigerant composed of methane (C1), ethane (C2), propane (C3) and nitrogen (N2) as described above, a temperature gradient from ultra low temperature to about -40 ° C is possible at atmospheric pressure. ), A mixed refrigerant consisting of ethane (C2), propane (C3), butane (C4), pentane (C5) and nitrogen (N2) is capable of temperature gradients from ultra low to about 30 ° C at atmospheric pressure. Considering that the refrigerant temperature at the rear end of the natural gas or the coolant introduced into the liquefaction system may be 35 to 40 ° C, the efficiency of the liquefaction process may be higher when there is a corresponding refrigerant portion.

Example 2

5 is a flowchart showing a natural gas liquefaction process according to Embodiment 2 of the present invention. As shown in Fig. 5, the liquefaction process according to the present embodiment basically has the same configuration as the liquefaction process according to the first embodiment described above. However, in the liquefaction process according to the present embodiment, the refrigerant part mixed through the mixing means is introduced into the separating means 112 through the conduit 1676 and further separated into the liquid refrigerant part and the gaseous refrigerant part according to the first embodiment. It is different from the liquefaction process. For reference, the same (or equivalent) reference numerals are given to the same (or equivalent) parts as the above-described configuration, and detailed description thereof will be omitted.

Referring to the liquefaction process according to the present embodiment centering on the above-described differences, first, the refrigerant portion mixed through the mixing means is introduced into the additional separation means 112 through the conduit 1676 to further add the liquid refrigerant portion and the gas phase refrigerant portion. Separated by. At this time, the additional separation means 112 may be a conventional gas-liquid separator. The liquid refrigerant portion separated through the additional separation means 112 can enter the expansion valve 133 through the conduit 181 and expand. For reference, unlike FIG. 5, the liquid refrigerant portion flowing through the conduit 181 may be introduced into the first heat exchange region 121, cooled, and then introduced into the expansion valve 133 to expand. That is, the liquid refrigerant portion may be introduced into the first heat exchange region and cooled between the additional separation means 112 and the expansion valve 133.

The expanded refrigerant portion enters the first heat exchange zone 121 through the conduit 182 to further precool the natural gas. The refrigerant portion additionally precooled with natural gas is then introduced into the third compression means 143 through the conduit 183 and compressed. As such, the refrigerant portion separately compressed through the first to third compression means 141, 142, and 143 may be mixed into one refrigerant portion through the above-described mixing means.

Alternatively, instead of compressing the liquid refrigerant portion separated through the additional separating means 112 through the separate compression means 143 as described above, the liquid refrigerant portion separated through the additional separating means 112 is mixed with other refrigerant portions. Can then be compressed. That is, as shown in FIG. 6, the liquid refrigerant portion separated through the additional separating means 112 is introduced into the first heat exchange region 121 through the conduits 181 and 182 to further precool the natural gas. After being separated through another refrigerant part, that is, through the separating means 110, the refrigerant may be introduced into the first heat exchange region 121 through the conduit 163 through various processes and mixed with the refrigerant part that precools the natural gas. The mixed refrigerant portion is introduced into the first compression means 141 through the conduit 1644 and compressed. The liquefaction process illustrated in FIG. 6 can reduce the number of compression means compared to the liquefaction process illustrated in FIG. 5, and thus, the structure of the entire liquefaction system can be simplified.

In addition to the liquefaction process illustrated in FIG. 5 or 6, the liquid refrigerant portion separated through the separating means 110 may be separated from the liquid refrigerant portion separated through the separating means 110, as shown in FIG. 7. After mixing, it can be used as one refrigerant stream. That is, as shown in FIG. 7, the liquid refrigerant portion separated through the additional separating means 112 through the conduit 1811, and the liquid refrigerant portion separated through the separating means 110 passes through the conduit 1616. And the mixed refrigerant portion is introduced into the first heat exchange region 121 through the conduit 1617 as one refrigerant flow.

On the other hand, the gas phase refrigerant portion separated through the additional separation means 112 is introduced into the separation means 110 through the recompression and recondensation process as in the embodiment shown in FIG. That is, as shown in FIGS. 5, 6, and 7, the gaseous refrigerant portion separated through the additional separation means 112 is further compressed through the additional compression means 144, and then the cooling means 149 is removed. Partially condensed through and enters the separation means 110.

Example 3

8 is a flowchart illustrating a natural gas liquefaction process according to Embodiment 3 of the present invention. As illustrated in FIG. 8, the liquefaction process according to the present embodiment differs from the above-described embodiment in that a distillation column is used as a separation means. Referring to the liquefaction process according to the present embodiment, the refrigerant portion mixed through the mixing means is introduced into the compression means 144 through the conduit 1701 and compressed. After being compressed in this way, the refrigerant portion is introduced into the distillation column 114 through the conduit 1802 and is precisely separated into the gaseous refrigerant portion and the liquid refrigerant portion with the required composition.

The portion of the liquid refrigerant separated through the distillation tower 114 is cooled through conventional cooling means and then introduced into the first heat exchange zone 121 through the conduit 1612 and cooled. The coolant portion thus cooled is expanded through the expansion valve 131 and flows back into the first heat exchange region 121. During this process, the refrigerant portion may precool the natural gas in the first heat exchange region 121. As a result, the liquid refrigerant part separated through the distillation column 114 plays the same role as the first refrigerant part of the first embodiment.

And the gaseous refrigerant portion separated through the distillation column is introduced into a conventional cooling means through conduit 1683 and partially condensed. The refrigerant portion condensed as described above is separated into the gaseous refrigerant portion and the liquid phase refrigerant portion through the conventional gas-liquid separator 116, and the separated gaseous refrigerant portion performs the same role as the second refrigerant portion of Embodiment 1 described above. do. And the separated liquid refrigerant portion is supplied back to the distillation column (114). In this way, when the low-temperature liquid refrigerant is supplied to the distillation column, the refrigerant portion may be separated into the liquid refrigerant portion and the gaseous refrigerant portion more precisely in the distillation column. In addition, if the refrigerant portion is precisely separated into two parts through a distillation column, the efficiency of the liquefaction process can be improved because the characteristics of each refrigerant part can be more accurately utilized.

Example 4

9 is a flowchart illustrating a natural gas liquefaction process according to Embodiment 4 of the present invention. As illustrated in FIG. 9, in the liquefaction process according to the present embodiment, the refrigerant part mixed through the mixing means passes through the first heat exchange region 221 and then is separated into a gaseous refrigerant part and a liquid refrigerant part. There is a difference from the embodiments. That is, as shown in FIG. 9, the refrigerant portion mixed through the mixing means flows into the first heat exchange region 221 through the conduit 261 and partially condenses through heat exchange in the first heat exchange region 221. do. The condensed refrigerant portion is introduced into the separating means 210 through the conduit 262 and is separated into the liquid refrigerant portion and the gaseous refrigerant portion according to the difference in boiling point.

The separated liquid refrigerant portion is introduced into the expansion valve 231 through the conduit 263 and expanded, and then flows back into the first heat exchange region 221 through the conduit 264 to cool other refrigerants and precool the natural gas. Let's do it. The refrigerant portion is then introduced into the first compression means 241 through the conduit 265 and compressed. The separated gaseous refrigerant portion is introduced into and condensed into the second heat exchange region 222 through the conduit 271. The condensed refrigerant portion thus enters and expands through conduit 272 through passage expansion valve 232. The coolant portion then flows back through the conduit 273 into the second heat exchange zone 222 to cool the other refrigerant and liquefy the natural gas. As such, the portion of the refrigerant having undergone heat exchange with natural gas may flow into the first heat exchange region 221 through the conduit 274 to further precool the natural gas and the other refrigerant. After completing all of these processes, the refrigerant portion is introduced into the second compression means 242 through the conduit 275 and compressed.

This liquefaction process can be modified as shown in FIG. In detail, the partially condensed mixed refrigerant is separated into the gaseous refrigerant portion and the liquid phase refrigerant portion through the separating means 210. The separated refrigerant parts thus precool and liquefy the natural gas as in the liquefaction process according to the first embodiment as shown in FIG. 10. Unlike the above-described embodiments, the modification according to FIG. 10 further includes a third heat exchange region 223. This third heat exchange zone 223 partially condenses the refrigerant portion mixed by the mixing means (see heat exchange zone between conduit 261 and conduit 262) and removes the natural gas prior to precooling in the first heat exchange zone 221. Precool. This cooling is achieved by the introduction of refrigerant portions that have precooled or liquefied natural gas into the third heat exchange zone 223 through conduits 2634 and 2716 (heat exchange zone between conduits 2634 and conduit 2635 and between conduits 2716 and 2717). Heat exchange zones). After this heat exchange, the respective refrigerant portions passing through the third heat exchange zone 223 enter the compression means 241, 242 through the conduits 2635, 2717, respectively.

There are common technical features among the liquefaction processes described through the above embodiments. That is, in the above-described embodiments, all of the partially condensed mixed refrigerant is separated into the first refrigerant portion and the second refrigerant portion through the separating means, and then the first refrigerant portion is not mixed between the first refrigerant portion and the second refrigerant portion. It is a technical feature that the and the second refrigerant portions are each intermixed only after reaching the mixing means via separate loops. In addition, the first refrigerant part and the second refrigerant part passing through the independent loop each serve to precool and liquefy natural gas. This common technical feature may be represented by a dotted box as shown in FIG. 11 or 12. That is, the configuration of pre-cooling and liquefying natural gas to each refrigerant portion by separating the mixed refrigerant can be variously modified. The above-described embodiments are specific examples in which the liquefaction efficiency is excellent among various modifications.

On the other hand, in the case of mixing the separated refrigerant portions, even if each is mixed again into one refrigerant portion under the same pressure and temperature conditions, the temperature of the mixed refrigerant may be higher than the temperature before mixing depending on the composition of the separated refrigerant portions or It may be low. Accordingly, the arrangement of the cooling means according to FIG. 11 is preferable when the mixture is mixed again and the temperature of the refrigerant is lower than before, and the arrangement of the cooling means according to FIG. 12 is preferable when the temperature is higher than before. That is, in the case of FIG. 11, the efficiency of the liquefaction process can be improved because the refrigerant portions are cooled by the cooling means, respectively, and then mixed so that the temperature of the refrigerant portions can be lowered as a result of the mixing. In the same case, since the coolant portion whose temperature is increased by mixing the coolant portions can be cooled below a predetermined temperature by only one cooling means, that is, the number of cooling means can be reduced.

For reference, the efficiency of the liquefaction process according to the above embodiments is compared with the existing SMR process (see FIG. 17) or C3 / MR process (see FIG. 15) as shown in the following table. Considering that the existing C3 / MR process (see FIG. 15) has very high efficiency as summarized in the table below, the liquefaction process according to the above embodiments is the same as the conventional SMR process (see FIG. 17). It can be seen that the efficiency is very good while using one closed loop refrigeration cycle. In the C3 / MR process, only nitrogen (N2), methane (C1), ethane (C2), and propane (C3) are generally used as the refrigerant. Therefore, nitrogen is also used as the refrigerant in the examples shown in the table below, and the C3 / MR and SMR processes. Performance comparisons were made using only (N2), methane (C1), ethane (C2) and propane (C3). For reference, the comparison result may have some differences depending on how to determine the components of the mixed refrigerant in each process or how to determine the performance of the compressor.

Liquefaction Cycle kWh / kg LNG Existing SMR Standards Conventional C3 / MR Standard Conventional SMR Process (see Figure 17) 0.4760 100% 157% Conventional C3 / MR Process (see Figure 15) 0.3025 64% 100% Liquefaction process according to Figure 1 0.3103 65% 103% Liquefaction process according to FIG. 0.3022 63% 100% Liquefaction process according to Figure 6 0.3099 65% 102% Liquefaction process according to FIG. 0.3114 65% 103%

In addition, as described above, the liquefaction process according to the above-described embodiments may further include a refrigeration cycle for cooling the natural gas as shown in FIGS. 13 and 14. That is, as shown in FIG. 13, the natural gas is precooled through an additional refrigeration cycle, and then the liquefaction process according to the above-described embodiments (refer to FIG. 13 and FIG. Natural gas can be liquefied. As shown in FIG. 14, the natural gas may be cooled through the liquefaction process according to the above-described embodiments, and then the natural gas may be supercooled through an additional refrigeration cycle. As a result, the liquefaction process according to the above embodiments may be used as one independent liquefaction process for liquefying natural gas itself, but may be used together with other independent liquefaction processes to be used as part of the overall liquefaction process.

That is, the liquid refrigerant portion and the gaseous refrigerant portion separated through the separation step are routed through separate routes without mixing with each other. The natural gas may be primarily cooled in the first heat exchange zone, and the natural gas primarily cooled in the second heat exchange zone may be secondarily cooled using the gaseous refrigerant portion. The primary and secondary cooling as described above may perform various roles such as precooling and liquefaction, or liquefaction and subcooling depending on the configuration of the entire liquefaction process. The secondary cooling, however, cools the natural gas to a lower temperature than the primary cooling.

As described above, the present invention has been described with reference to preferred embodiments of the present invention, but a person of ordinary skill in the art does not depart from the spirit and scope of the present invention as set forth in the claims below. It will be understood that various modifications and variations can be made in the present invention. Therefore, the spirit of the present invention should be understood by the claims described below, and all equivalent or equivalent modifications thereof will belong to the scope of the present invention.

110: separation means 112: further separation means
114: distillation column 116: gas-liquid separator
120: heat exchange means 121: first heat exchange zone
122: second heat exchange zone
131, 132, 133, 136: expansion means
141, 142, 143, 144: compression means
146, 147, 148, 149: cooling means

Claims (20)

One closed loop refrigeration cycle employing a mixed refrigerant precools natural gas through heat exchange with the refrigerant in the first heat exchange zone and precools through heat exchange with the refrigerant in the second heat exchange zone. In the natural gas liquefaction process for liquefying the natural gas,
The closed loop refrigeration cycle,
A separation step of separating the partially condensed mixed refrigerant into a liquid refrigerant portion and a gaseous refrigerant portion;
A precooling step of precooling the natural gas in the first heat exchange region using the liquid refrigerant portion;
Liquefying the natural gas pre-cooled in the second heat exchange zone by using the gaseous refrigerant portion;
A first compression step of compressing, after the pre-cooling step, a refrigerant part of the pre-cooled natural gas through the pre-cooling step;
A second compression step of compressing a refrigerant portion in which the natural gas is liquefied through the liquefaction step after the liquefaction step; And
A mixing step of mixing respective refrigerant portions compressed through the first and second compression steps,
And the liquid phase refrigerant portion and the gaseous refrigerant portion are separated through the separation step and then pass through separate loops without mixing with each other. The method according to claim 1,
The precooling step includes the steps of: cooling the liquid refrigerant portion separated through the separating step through heat exchange in the first heat exchange region, expanding the cooled refrigerant portion, and expanding the expanded refrigerant portion and the natural gas. And quenching the natural gas by exchanging heat in a first heat exchange region. The method according to claim 2,
The expanding comprises primarily expanding the condensed refrigerant portion through an expander and secondly expanding the primarily expanded refrigerant portion through an expansion valve. Natural gas liquefaction process. The method according to claim 1,
The liquefaction step includes the steps of: cooling the gaseous refrigerant portion separated through the separation step through heat exchange in the first heat exchange region, condensing the cooled refrigerant portion through heat exchange in the second heat exchange region, condensation Expanding said refrigerant portion and heat-exchanging said expanded refrigerant portion and said natural gas in said second heat exchange zone to cool said natural gas. The method of claim 4,
Further pre-cooling the natural gas in the first heat exchange region by using the refrigerant portion which has completed heat exchange with the natural gas in the second heat exchange region through cooling the natural gas, wherein the second gas is further cooled. The compressing step is a natural gas liquefaction process, characterized in that for compressing the refrigerant portion after the heat exchange with the natural gas in the first heat exchange region through the additional pre-cooling of the natural gas. The method of claim 4,
The expanding comprises primarily expanding the condensed refrigerant portion through an expander and secondly expanding the primarily expanded refrigerant portion through an expansion valve. Natural gas liquefaction process. The method according to claim 1,
A first cooling step of lowering a refrigerant temperature by cooling the refrigerant part compressed through the first compression step, and a second cooling step of lowering a refrigerant temperature by cooling the refrigerant part compressed through the second compression step; And the mixing step mixes each refrigerant part cooled through the first and second cooling steps. The method according to claim 7,
Re-compressing the mixed refrigerant portion through the mixing step, and the natural gas liquefaction process further comprising the step of cooling and partially condensing the recompressed refrigerant portion. The method according to claim 1,
The natural gas liquefaction process further comprises a condensation step of partially condensing by cooling the refrigerant portion mixed through the mixing step. The method according to claim 1,
The separating step is a natural gas liquefaction process, characterized in that for separating the partially condensed mixed refrigerant into a liquid refrigerant portion and a gaseous refrigerant portion through a distillation column. The method according to claim 10,
Cooling and partially condensing the separated gaseous refrigerant portion through the separating step; re-separating step of separating the partially condensed refrigerant portion into a liquid refrigerant portion and a gaseous refrigerant portion again through the condensing, and the re-separation And supplying the liquid refrigerant portion separated through the step to the distillation tower, wherein the liquefaction step includes liquefying the pre-cooled natural gas using the gas phase refrigerant portion separated through the re-separation step. Gas liquefaction process. The method according to claim 10,
A recompression step of recompressing the mixed refrigerant portion through the mixing step, and a cooling step of cooling the liquid refrigerant portion separated through the separation step, wherein the separation step is recompressed through the recompression step Natural gas liquefaction process, characterized in that the separated refrigerant portion is separated into a liquid refrigerant portion and a gaseous refrigerant portion. The method according to claim 1,
Introducing a refrigerant portion of the natural gas precooled through the precooling step into a third heat exchange region, introducing a refrigerant portion of the liquefied natural gas into the third heat exchange region through the liquefaction step, and the mixing And partially condensing the mixed refrigerant portion through heat exchange in the third heat exchange zone, wherein the natural gas is preliminarily subjected to heat exchange in the third heat exchange zone prior to the precooling step. And two refrigerant portions pre-cooled and introduced into the third heat exchange zone to complete the heat exchange, are respectively compressed through the first and second compression stages. The method according to claim 1,
The mixed refrigerant is methane (C1), ethane (C2), propane (C3), butane (C4), pentane (C5) and nitrogen (N2) characterized in that the natural gas liquefaction process with refrigerant separation. In a natural gas liquefaction system in which a natural gas is liquefied using a closed loop refrigeration cycle employing a mixed refrigerant,
Separating means for separating the partially condensed mixed refrigerant into a first refrigerant portion and a second refrigerant portion;
Heat exchange means having a first heat exchange region in which the natural gas is precooled through heat exchange with the first refrigerant portion, and a second heat exchange region in which the natural gas precooled through heat exchange with the second refrigerant portion is liquefied;
First compression means for compressing a first refrigerant portion in which the natural gas is precooled in the first heat exchange region;
Second compression means for compressing a second refrigerant portion in which the natural gas is liquefied in the second heat exchange region;
Mixing means for mixing the refrigerant portion compressed through the first and second compression means;
A first conduit for guiding said first refrigerant from said separating means to said first compression means; And
A second conduit independent of said first conduit and guiding said second refrigerant from said separating means to said second compression means without mixing with said first refrigerant,
And the first refrigerant portion has a higher boiling point than the second refrigerant portion. The method according to claim 15,
The first conduit includes the separation means and the first heat exchange region, expansion means for expanding the first heat exchange region and the first refrigerant, the expansion means and the first heat exchange region, and the first heat exchange. Natural gas liquefaction system, characterized in that for sequentially connecting the region and the first compression means. The method according to claim 15,
The second conduit includes the separation means and the first heat exchange region, the first heat exchange region and the second heat exchange region, expansion means for expanding the second heat exchange region and the second refrigerant, and the expansion means. And the second heat exchange region, and the second heat exchange region and the second compression means are sequentially connected. 18. The method of claim 17,
The second conduit further comprises the second heat exchange zone and the second compression means such that the second refrigerant portion having completed heat exchange with the natural gas in the second heat exchange zone further precools the natural gas in the first heat exchange zone. And between said second heat exchange region and said first heat exchange region and said first heat exchange region and said second compression means in sequence. The method according to claim 15,
First compression means for cooling the refrigerant portion compressed through the first compression means, second cooling means for cooling the refrigerant portion compressed through the second compression means, and recompressing the refrigerant portion mixed through the mixing means And a condensing means for cooling and partially condensing the recompressed refrigerant portion, wherein the mixing means mixes each refrigerant portion cooled by the first and second cooling means. Natural gas liquefaction system. One closed loop refrigeration cycle employing a mixed refrigerant allows the natural gas to be cooled first through heat exchange with the refrigerant in the first heat exchange zone and heat exchange with the refrigerant in the second heat exchange zone. In the natural gas liquefaction process of secondarily cooling natural gas cooled through
The closed loop refrigeration cycle,
A separation step of separating the partially condensed mixed refrigerant into a liquid refrigerant portion and a gaseous refrigerant portion;
Primarily cooling the natural gas in the first heat exchange region using the liquid refrigerant portion;
Secondarily cooling the natural gas cooled in the second heat exchange region by using the gaseous refrigerant portion;
A first compression step of compressing, after the primary cooling step, the refrigerant portion that primarily cools the natural gas through the primary cooling step;
A second compression step of compressing, after the second cooling step, the refrigerant part which secondarily cooled the natural gas through the second cooling step; And
A mixing step of mixing respective refrigerant portions compressed through the first and second compression steps,
The liquid phase refrigerant portion and the gaseous phase refrigerant portion are separated through the separation step and then pass through separate loops without mixing with each other. The liquid phase mixture is mixed with each other in the mixing step, and the secondary cooling step is performed more than the primary cooling step. Natural gas liquefaction process, characterized by cooling the natural gas to a lower temperature.

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