JPH01250698A - Method of evaporating liquefied natural gas - Google Patents

Abstract

PURPOSE: To reduce the cost of equipment by making a partial flow of heated natural gas branch into a first circuit and, after being set at work, expanded, congulated, boosted, remixing it with the liquefied natural gas. CONSTITUTION: Liquefied natural gas in a conduit 1 is heated in three heat exchangers E1, E2 and E3, and then its partial flow is made to branch into a conduit 2a. Subsequently it is expanded at work in an expansion turbine X1, and it is congulated in the heat exchanger E1 by way of a conduit 2b and, after being boosted by a pump P1, this heated partial flow is remixed with the liquefied natural gas in the conduit 1. With this constitution, since a fluid is expanded by only one process, the numbers of the expansion turbine and the pump become lessened, and thus a reduction in the cost of equipment is well promotable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention provides a method for discharging liquefied natural gas from the atmosphere by heat exchange with a fluid flowing through a separate circuit, where it is expanded with work, condensed, and reevaporated. The present invention relates to a method for the evaporation of liquefied natural gas combined with the harvesting of energy so that it is heated to a temperature.

[Prior art] The heat required to evaporate liquefied natural gas is generally generated from air,
It is intended to be supplied by a heat carrier such as sea water or river water. In this case, when the refrigeration of the liquefied natural gas is additionally utilized by an auxiliary circuit with an expansion turbine to generate electrical energy, the energy required to be obtained from the heat carrier water is reduced by the same amount. be done.

The amount of water required and the driving costs for supplying the water are therefore reduced. However, the more auxiliary circuits are constructed, the higher the installation cost of heat exchange equipment and machinery becomes. Therefore, the best economic situation is to use two (or three) auxiliary circuits. A method of operating with two fluids flowing through a circuit as heat exchange media is described in West German Publication No. 2633.
It is described in No. 713. In this publication, a liquefied natural gas stream is first heated in a number of heat exchange steps and then evaporated. A portion of the evaporated natural gas itself forms the first fluid circuit. A portion of the evaporated natural gas is branched from the natural gas stream, expanded with work, exchanged heat with the heated liquefied natural gas, condensed, and compressed to liquefied natural gas pressure to form the liquefied natural gas stream again. It is done so that it is mixed with

As fluid in the second circuit, ethane is used in this known method. In this case, the ethane stream that is evaporated by exchanging heat with river water, seawater, or air is expanded by performing work. The expanded ethane stream is split, and the first part performs further work, expands, and is subsequently condensed in countercurrent with natural gas, heated again, and combined with the second part of the ethane stream. and then evaporated again. A second portion of the ethane stream is condensed by heat exchange with heated natural gas and remixed with the first ethane stream.

Because of the double expansion of the heat exchange medium and to keep the expansion process performing the work in order, both ethane streams are compressed to a common pressure after being condensed by heat exchange with heated natural gas. be.

Although the energy gain of this method is good, this −
Good energy gains can only be obtained with a two-step ethane circuit.

OBJECT OF THE INVENTION It is therefore an object of the invention to design the method mentioned at the outset in such a way that the installation costs are low and/or a better energy harvest is ensured.

MEANS AND OPERATIONS FOR SOLVING THE PROBLEMS The above-mentioned objects, according to the present invention, provide that the fluid in the first circuit is natural gas, which is branched from the natural gas heated to atmospheric temperature and is heated while doing work. A fluid is expanded, condensed by heat exchange with the liquefied natural gas, and remixed with the liquefied natural gas, and a fluid is introduced into the second circuit so that the fluid is processed in a single step. It is solved by doing work and allowing it to expand.

In the method of the present invention, it is not necessary to perform work and expand the fluid in the second closed circuit in two steps to obtain a good energy gain. Because the fluid is expanded in one step, fewer expansion turbines and pumps are required, yet still provide good energy recovery as in prior art methods. In this way, C7-06-hydrocarbons, in particular C+/Cz-mixtures or c2/Cx-mixtures, are used as the fluid of the second circuit, with 02
The component is reduced to less than 90 mol%.

In a more detailed embodiment of the method according to the invention, propane is used as the fluid in the second circuit.

Thus, the present invention provides a fluid that does not require any external refrigeration for storage under pressure. Storage can therefore be carried out without problems, for example at ambient temperature and at a pressure of 20 bar, thereby eliminating the disadvantage of large energy-consuming cooling.

In more detailed configurations of the invention, ammonia can be used as the fluid in the second circuit. In this case as well, storage under pressure at atmospheric temperature becomes possible.

In a variant of the method according to the invention, a further third circuit driven by the expansion of one step is inserted between the first circuit and the second circuit.

In this configuration, it has proven advantageous to use ethane as the fluid in the third circuit. In this variant according to the invention, although the number of expansion turbines is the same as in the known method mentioned at the beginning, the energy gain is greater for the method according to the invention compared to the known method. be.

In a suitable configuration of the method according to the invention, the fluid in the first circuit is expanded by performing work in two steps. In this case, the natural gas heated in the first step is expanded and brought into thermal contact with seawater. This heated stream is split into two parts, where one part of the evaporated natural gas is drawn out, and the other part does further work, is expanded, and is condensed again by heat exchange with the heated natural gas. It is mixed with liquefied natural gas. The fluid in the second circuit is expanded with one additional step of work.

A suitable explanation corresponding to this configuration can be found in the example according to FIG.

In a variant of the method of the invention not shown, the heated natural gas stream is split into two. One partial stream of this constitutes the first fluid circuit, and the other partial stream is expanded to perform work once more before being withdrawn.

EXAMPLES The invention will be explained in more detail below by means of examples shown schematically in the drawings.

Now, FIG. 1 is a principle explanation of the method according to the invention.

The flow of liquefied natural gas in conduit 1 first passes through heat exchanger E.
It is heated by exchanging heat with the condensed natural gas in the conduit 2b. Within heat exchanger E2, conduits 3a and 3b
Further heating of the natural gas stream takes place by heat exchange with the heat exchange medium propane which is conducted in the circuit. The final heating of the natural gas stream takes place in countercurrent with the seawater, which is cooled in heat exchanger EaB. A portion of the gaseous natural gas in conduit 1 leaving heat exchanger E3B is drawn off via conduit 2a, expanded with work in an expansion turbine Xl, and heated in heat exchanger El through conduit 2b. The liquefied natural gas is condensed by heat exchange with the liquefied natural gas, and after being pressurized to the liquefied natural gas pressure by the pump P1, it is mixed with the liquefied natural gas in the conduit 1 again. The fluid of the second circuit, propane, receives energy for doing work and for heating the natural gas from the seawater supplied in conduit 4. After passing through heat exchanger E3A, the propane is completely evaporated in conduit 3a and expanded with work in expansion turbine X2. Via line 3b, this propane stream passes through a heat exchanger E2 in countercurrent with the propane stream in line 3a and the natural gas to be heated in line 1, in which case the propane is condensed and a liquefied propane stream is formed. is compressed by pump P2 and passed through conduit 3a to heat exchanger E2 where it is heated. In this way, the second fluid circuit is closed. The seawater drawn in for energy gain and evaporation of natural gas is conducted through conduit 4 and connected in parallel to a heat exchanger E3A (in thermal contact with the evaporating fluid of the second circuit). condition) and heat exchanger E3B
(in thermal contact with the natural gas stream to be heated) and discharged through conduit 5 after the heat has been extracted.

The method according to the invention, such as the example shown in FIG.
A comparison with No. 713 yielded almost the same good results. The gain calculations described above were performed using similar natural gas compositions and similar capacity machines. In both cases,
Calculated with the following boundary conditions. That is, the initial pressure of liquefied natural gas is 82.4 bar, the discharge pressure is 80 bar, the flow rate of natural gas is 130 t/h, and the inlet temperature of liquefied natural gas is 1.
It was on the 25th.

With the above assumptions, the gain of the known method is 3880 kW,
In the method according to the present invention, the power was 3720 kW. According to this, the method according to the invention is about 4% less capable than the known method, but finally, because of the lower mechanical outlay and the storage of the medium in the circuit, no external refrigeration is required. As a result, the above-mentioned work gain was obtained.

FIG. 2 shows a configuration of the method according to the invention of FIG. 1, in which natural gas heated to ambient temperature is expanded to perform work in two steps. The heated natural gas is first subjected to work and expanded in the expansion turbine X3, and flows through the heat exchanger E3C so as to be heated again by the seawater in the conduit 4, after which a portion is further transferred to the heat exchanger X1 ( The remaining portion of the natural gas is withdrawn via conduit 7 while the remaining part of the natural gas is withdrawn via conduit 2a for further expansion (similar to that of FIG. 1).

The work gain obtained with this configuration example is 5600kHz.
reached. In this case the natural gas discharge pressure was estimated to be 45.2 bar, and the remaining boundary conditions were consistent with those in the comparison case described above.

FIG. 3 shows a variation of the method of FIG. A third fluid circuit is superimposed on the second fluid circuit. As the fluid, for example, propane can be used in the second circuit and ethane can be used in the circuit of the text box 3. An additional heat exchanger E4 is required to transfer the condensation energy of the ethane circuit. The temperature level of this heat exchanger is the temperature level of the natural gas condensing heat exchanger E1 and the propane condensing heat exchanger E2.
temperature level is in between. A further heat exchanger E3D is provided for the transfer of the heat of vaporization of the compressed ethane stream in the conduit 2a to the water.

The expansion step shown in FIGS. 2 and 3, i.e. heated natural gas -X3- and two stream segmented streams -X2-, occurs before a portion of the evaporated natural gas is expanded in X3. It can be modified to be branched to the first fluid circuit. The remaining part is discharged only after it has done work, expanded and branched.

[Effects of the Invention] Since the present invention is constructed as described above, unlike the prior art, the fluid in the second closed circuit is expanded by doing work in two steps in order to obtain a good energy gain. Because the fluid is expanded in one step, there is no need to
The number of expansion turbines and pumps is reduced and the equipment costs are lower to ensure a good energy recovery as in the prior art, or a similar equipment guarantees an even better energy gain than in the prior art. Excellent effects can be obtained by configuring the system to

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram illustrating a method according to the invention having an expansion step for performing one step of work for each of the fluids of the first and second circuits; FIG. 2 is a schematic diagram of a method according to the invention with a two-step expansion of the fluid in the first circuit and one step expansion of the fluid in the second circuit. FIG. 3 is a circuit diagram of a method according to the invention similar to that shown in FIG. 2 expanded to include a third fluid circuit; 1...Liquid natural gas flow conduit E1...Heat exchanger E2...Heat exchanger E3A...Heat exchanger E3B...Heat exchanger E3C... ... Heat exchanger E3D ... Heat exchanger Pi ... Pump P2 ... Pump Xl ... Expansion turbine X2 ... Expansion turbine X3 ... Expansion Turbine Patent Applicant Linda Akchengesellschaft Snig
,2

Claims (1)

[Claims] 1. Liquefied natural gas is heated to atmospheric temperature by heat exchange with a fluid flowing through a separate circuit, where it is expanded doing work, condensed and re-evaporated. In a method of evaporating liquefied natural gas combined with energy harvesting, the fluid in the first circuit is natural gas, which is branched from natural gas heated to ambient temperature and expanded to do work. , is condensed by heat exchange with the liquefied natural gas and remixed with the liquefied natural gas, and a fluid is introduced into the second circuit, which fluid performs work in a single step. An evaporation method characterized in that: 2. Process according to claim 1, characterized in that a mixture of C_1-C_6-hydrocarbons is used as the fluid of the second circuit, the C_2 component being less than 90 mol %. 3. Method according to claim 2, characterized in that a C_1/C_2 mixture or a C_2/C_3 mixture is used as the fluid of the second circuit. 4. The method of claim 1, wherein propane is used as the fluid in the second circuit. 5. A method according to claim 1, characterized in that ammonia is used as the fluid in the second circuit. 6. According to any one of claims 1 to 5, a third circuit driven in a single step is further added between the first circuit and the second circuit. the method of. 7. A method according to claim 6, characterized in that ethane is used as the fluid in the third circuit. 8. A method according to any one of claims 1 to 7, characterized in that the fluid in the first circuit is expanded by performing work in two steps.