DE1960515B1 - Method and device for liquefying a gas - Google Patents

Description

The invention relates to a method for liquefying an under increased initial pressure of standing gas by heat exchange with an evaporating in the process lower-boiling liquefied auxiliary gas, which before the heat exchange to a higher Pressure is pumped, after its evaporation, relaxed to perform work and then is again brought into heat exchange with the gas.

A method of this type is known (German Auslegeschrift 1 435), with the methane to be liquefied to a supercritical pressure of about 70 ata is compressed, cooled and relaxed to 1 ata. The cooling takes place with the help of liquid nitrogen, which after going to a supercritical pressure of 90 ata has been promoted, in the heat exchange with the methane to ambient temperature warmed up, relaxed to atmospheric pressure while performing work and again in heat exchange with which methane is brought. With the relaxation gained during work Energy is operated by the liquid nitrogen pump. The nitrogen has after the work-performing relaxation a temperature that is higher than that of the liquid Nitrogen as it exits the pump. To liquefy 1 kg of methane is required one under the described conditions 1.5 kg of liquid nitrogen.

If this amount of nitrogen is to be undershot, an additional Cooling system are available. The energy required for this can only be used Partly covered by work-performing expansion of the nitrogen, d. H. the Procedure is dependent on an external energy source.

In addition, the gas to be liquefied when the nitrogen cold should be used economically, with about 70 ata must be available.

However, the final pressure of the pipelines is usually lower, e.g. B. at 40 ata. In these cases, the known method can only be carried out with advantage if if the methane can be compressed with the help of an external energy source.

Most of all, however, most of the cold has to come from heat exchange be transferred to the methane, this heat exchange mainly between Gas flows takes place that are under supercritical pressure. The heat exchangers therefore, because of the large amounts of heat to be transferred, they have to have correspondingly large surfaces and also be designed for high pressures.

The object of the invention is to overcome the disadvantages of the known To overcome the way of working and to create a process that reduces the need of liquid nitrogen not tied to the presence of an external source of energy and can be carried out in smaller and simpler heat exchangers.

This object is achieved according to the invention in that a first Part of the gas doing work is expanded to bearing pressure and then through heat exchange with the auxiliary gas flow, the weight of which is related to that of the first part of the gas such as about 2: 1, is cooled and liquefied and that the remaining second part of the gas with the consumption of at least part of the amount of the work performed Relaxation of the first part of the gas and the auxiliary gas recovered energy and cooled and liquefied by heat exchange with the expanded auxiliary gas and is then relaxed to bearing pressure.

This procedure offers the following advantages: By the work-performing Relaxation of the gas generates additional energy, which depends on whether a greater or lesser expenditure on equipment appears worthwhile, in more or more can be implemented to a lesser extent in further condensing capacity. this means first of all that the gas can be delivered under low pressure, so that too no additional compression is required if the final pipeline pressure is relatively low is. Above all, however, is the amount of liquid auxiliary gas that is used at a given Amount of liquid to be generated is required to run the process regardless of to perform an external energy source, less than in the known method. So that is enough for the work-performing expansion of the first part of the gas as well of the auxiliary gas from the energy obtained, with complete independence from a external energy source the rest, the amount of which is at least 0.55 times the first Partly amounts to liquefy.

Since the work-performing expansion of the first part of the gas at the same time its precooling causes the necessary for further cooling of this amount of gas Heat exchanger kept small because of the lower amount of heat to be dissipated will. For the same reason they also only need to be designed for low pressures to become. The method according to the invention thus has a structural reduction Costs for the heat exchanger result. Since furthermore the heat exchange at least always takes place on the gas side at sub-critical pressure, is formed condensate after falling below the dew temperature; thereby the heat transfer conditions are Well. In addition, the auxiliary gas is not at ambient temperature, but only at one Heated temperature below that after the work-performing expansion of the gas reached temperature. Therefore, the auxiliary gas can after its work-performing Relaxation can be used again to cover peak cold.

According to a preferred embodiment of the invention, the second Part of the gas with the work-performing expansion of the first part of the gas and the energy obtained from the auxiliary gas compressed to supercritical pressure, cooled, relaxed to subcritical, but increased pressure, cooled further and liquefied and then relaxed to warehouse pressure. With the help of work-performing relaxation of the first part of the gas it is possible in this way to produce a second part of this To liquefy gas, the amount of which is about 550/0 of the first part. It results depending on the efficiency of the machines used or less large excess of energy, which z. B. with the help of generators in electrical energy can be converted. This procedure eventually stands out also from the fact that to its implementation except for relatively light plant parts like low pressure heat exchangers and expansion turbines only one compressor for that Smaller part and a high pressure heat exchanger are necessary for their pre-cooling are. The system can therefore be easily installed on a ship.

Further refinements of the invention deal with the use of the above Procedure occurring excess of energy from the work-performing expansion of the first part of the gas and of the auxiliary gas. There is a method that is particularly well suited for this purpose in that the second part of the gas before its compression to the supercritical Pressure by an amount of the corresponding to the additional amount of energy to be used first part of the gas is increased and that this additional amount of gas subsequently is liquefied in a manner known per se. For a given total amount of gas So is the portion of the gas that relaxes work-performing and then through Heat exchange with the liquid auxiliary gas is to be liquefied, reduced. In order to however, the requirement also decreases with the condensing capacity remaining the same of liquid auxiliary gas.

The additional amount of gas is liquefied after the in the German Auslegeschrift 1 626325 described method. Then the additional, Amount of gas compressed to the supercritical pressure below or in the vicinity the critical temperature and then doing work in or in the liquid area relaxed, whereupon the liquefied part separated from the gaseous part and then, preferably after further cooling, in a throttle valve to bearing pressure is relaxed. The additional amount of gas is pre-cooled by means of work-performing Relaxation of part of this amount of gas and / or by heat exchange with the the individual relaxation processes remaining in gaseous form. The latter can if no other use is preferred, also with excess Energy from the work-performing expansion of the first part of the gas and the Auxiliary gas are compressed and fed back to the liquefaction.

Another measure that is also well suited is an excess to convert energy from work-related relaxation into liquefaction performance, is a further development of the inventive concept in this energy for compression to use the first part of the gas before its work-performing expansion. This can lower the enthalpy of the gas entering the turbine and the enthalpy gradient in the turbine can be increased, so that the enthalpy of the relaxed Gas becomes smaller. This also applies to the following low-pressure heat exchanger residual heat to be dissipated smaller.

Instead of using the second part of the gas directly with the work-performing Relaxation of the first part of the gas and the auxiliary gas to the energy obtained compress, this energy can also be fed to the compressor of a refrigerant circuit, z. B. a so-called "mixer refrigerant" cycle according to Kleemenko (Comptes-rendus du Congres du Froid de Copenhague 1959). With this variant of the The method according to the invention becomes the second part of the gas except through the heat exchange with the auxiliary gas, which is relaxed for work, with the help of a refrigerant circuit cooled and liquefied, its compressor with the work-performing relaxation the auxiliary gas and the first part of the gas recovered energy is operated.

An advantageous embodiment of the invention also consists in that the auxiliary gas relaxes work-performing in the wet steam area and the thereby formed Liquid to the pressure of the liquid auxiliary gas to be supplied to the heat exchange is promoted and united with this. This measure has a further mitigation the need for liquid auxiliary gas result.

The cold content of the work-relieved auxiliary gas can be Take advantage of this particularly well if this initially develops in a further development of the concept of the invention by heat exchange with the first part of the gas on one below that of the work-performing Relaxation of this first part reached temperature intermediate temperature warmed up and only then brought into heat exchange with the second part of the gas will. The intermediate temperature is a little below the boiling point of the gas Warehouse pressure.

Bearing pressure is to be understood as the pressure of the intermediate storage facility, in which the liquid obtained by the method according to the invention is collected. From here, the liquefied gas is transferred to the transport container, e.g. B. Ship tanks, pumped.

The pressure of the intermediate storage and the transport container is usually at 1 ata, but it can also significantly exceed this value. The pressure on the the liquid auxiliary gas is pumped before the heat exchange, must so on this bearing pressure be matched that the cold content of the auxiliary gas to the work-performing the bearing pressure relaxed first part of the gas can be transmitted. For methane as gas, nitrogen as auxiliary gas and a storage pressure of 1 ata is the pressure on which the liquid nitrogen must be promoted before the heat exchange, at 14 ata. If the storage pressure is higher, the liquid auxiliary gas must also be adjusted accordingly increased pressure.

An apparatus for performing the method according to the invention is characterized in that a line for a first part of the gas to a turbine and a line for a second part of this gas to a compressor is led that the outlet of the turbine with the warm end of a gas under Bearing pressure designed cross section of a heat exchanger is connected, the cold end is connected to an interim storage facility for liquefied gas that a Another cross-section of this heat exchanger over the cold end to a pump for liquid auxiliary gas and via the warm end to the inlet side of a second Turbine is connected, the outlet side of which with the refrigerant cross-sections two further heat exchangers connected in series are connected, and that the compressor outlet via the second cross-sections of the heat exchanger as well via an expansion valve arranged between the latter and a downstream one Another expansion valve is connected to the interim storage facility.

The method according to the invention is primarily for liquefaction determined by natural gas or methane using nitrogen as an auxiliary gas. On the same Oxygen can also be liquefied. Do you want nitrogen with the help of this Liquefy process, the auxiliary gas is a lower boiling gas than this, z. B. hydrogen to choose. Finally, hydrocarbons such as ethylene, propane or butane can be liquefied with the lower-boiling methane as an auxiliary gas.

The method according to the invention will now be illustrated schematically with reference to five Illustrations explained, for example. According to FIG. 1 is through line 1 of CO2 and H2S freed and dried natural gas with a temperature of 30 ° C and a pressure of 40 ata. About two thirds of the incoming gas amount, per Nm³, i.e. 0.642 Nm³ or 0.460 kg, reach the turbine 3 via line 2, in which relaxes the natural gas to 1.1 ata and is thereby cooled to about 1510 K.

It enters the heat exchanger 4 at this temperature there cooled and liquefied and with a temperature of 111 ° K the intermediate storage 5 supplied. The cold required for this is supplied by liquid nitrogen, which is taken from a ship's tank with 1 ATA and 770 K.

To liquefy 0.642 Nm3 or 0.460 kg of natural gas, you need 0.8 Nm3 or 1.0. kg nitrogen. It is promoted by the pump 6 to 14 ata, one Pressure at which it can still be vaporized through heat exchange with the pressureless methane can.

Since the nitrogen is in the subcritical state here, that is Liquid evaporation is also present on the refrigerant side of the heat exchanger good heat transfer conditions given.

In the heat exchanger 4, the nitrogen is evaporated and to about 138 ° K warmed and then relaxed in the turbine 7 to 1.6 ata. The cools down Nitrogen to about 810 K. At this temperature it becomes the cold one again The end of the heat exchanger 4 supplied, there to about 108.0 K, a temperature so, the few degrees. is below the boiling point of methane at atmospheric pressure, warmed, withdrawn from the heat exchanger 4 at the level of this intermediate temperature and warmed to ambient temperature in the heat exchangers 8 and 9 in order to enter the Atmosphere to be dismissed.

About a third of the natural gas to be liquefied, per Nm³ of the incoming gas The amount of gas, i.e. 0.358 Nm³ or 0.256 kg, is supplied to compressor 11 via line 10 supplied and with the help of the work-performing expansion of the natural gas and the energy gained from nitrogen compressed to 200 ata. The high pressure natural gas is cooled in the heat exchanger 9 to about 164 ° K then in the valve 12 to one subcritical pressure of about 20 ata relaxed and in the heat exchanger 8 on the The boiling temperature of methane at atmospheric pressure, that is about 111 ° K, is felt and liquefied. The liquid natural gas leaving the heat exchanger 8. is in the Valve 13 relaxed to about 1 ata and fed to the intermediate store 5 with this pressure. From there it is together with the larger amount of natural gas liquefied in the heat exchanger 4 conveyed via a pump 14 into the tanker.

That amount of energy supplied by the turbines 3 and 7, which from Compressor 11 cannot be used up, is used to operate pumps 6 and 14 and the cooling water pumps of the non-calibrated compressor coolers. The procedure is independent of an external energy source and can still liquefy 0.022 kwb / Nm³ Release methane. Only 1.0 kg is required to liquefy 0.716 kg of natural gas Nitrogen required; that is a Weight ratio of 1: 1.4. The need for liquid So nitrogen is reduced by 6.7%. Because the amount of gas to be liquefied hourly when natural gas is transported by ship is extremely high, this means an essential one Improvement, In addition, the system required for this can be mounted on a ship is therefore not tied to a specific location.

In the method according to FIG. As mentioned, 1 remains an amount of energy of about 0.022 kwh per Nm3 of liquefied methane unused in the process.

This energy can be completely reduced with the aid of the method according to FIG exhaust: CQ2. H2S- and H2Q-free natural gas is supplied with a pressure of 40 ata and Ambient temperature is supplied to the compressor 11 via line 1. The first part of the Natural gas to be liquefied, 0.695 Nm3, based on 0.8 Nm3 or 1 kg of liquid Nitrogen, is compressed to about 81 ata, then via line 2a of the turbine 3 supplied and, as shown in FIG. 1 described, cooled and liquefied. The evaporation of liquid nitrogen is also done in the same way in FIG. q; the work-performing relaxation is carried out in the turbine 7 a so that 10% of the nitrogen is present as a liquid at the turbine outlet. This is in Separator 15 separated from the gaseous portion and via the pump 16 the the heat exchanger 4 is fed liquid nitrogen flowing in. Through this Measures can liquefy around 5.3% more methane with the same nitrogen requirement are than in the method according to FIG. 1.

The second part of the gas to be liquefied, 0.3.58 Nm³, is in the Compressor 11 compressed to 2.00 ata and then in connection with F i g. 1 described manner further treated.

From the ratio of the partial quantities of natural gas, 0.695 Nm3 to 0.358 Nm3z results in an increase in liquefied natural gas production to 1.053 Nm³ or 0.755 kg, based on 0.8 Nm³ or 1.0 liquid nitrogen used.

In Fig. 3 describes a method with the help of which those in the work-performing expansion of nitrogen and the first part of the Energy turned into natural gas. can also be fully exploited.

The amount of the first natural gas partial flow fed through line 2 to turbine 3 is again 0.642 Nm³, which is fed through line 10 to a liquefaction plant However, the second partial flow is 0.464 Nm³, based on 0.8 Nm³ of the liquid used Stiekstoffs, The. Cooling down. of the first partial flow through heat exchange with the Nitrogen takes place in the manner described in connection with FIG.

The second partial flow is via line 10 under pipeline pressure a Liquefaction plant 17 supplied and there with the help of a known. Refrigerant circuit liquefied, the compressor 18 operated with the aforementioned excess of energy will.

The cold of the nitrogen that is relaxed for work is also used in the liquefaction plant 17 exploited.

The method according to FIG. 3 thus offers over the procedure according to FIG. 1 has the advantage that with the same nitrogen requirement it is about 10.6% more liquid methane can be generated. This liquid yield is also greater than in the method according to FIG. 2. The method according to FIG. 3 required However an additional refrigeration circuit, for example with a hydrocarbon mixture as a cooling medium.

In Fig. 4 is the i-T diagram of the high pressure heat exchanger 9 and of the medium-pressure heat exchanger 8, in Fig. 5 the i-T diagram of the heat exchanger 4 according to the method of FIG. From this, the heat sales and the temperature differences between the methane to be cooled and the methane to be heated Read nitrogen. In Fig. 4, the jump point of the cooling curve marks for the methane at 1640 K the throttle expansion from 200 ata to 20 ata.

5 shows the cooling of the methane expanded in the turbine 3 and its liquefaction at 1120 K as well as the heating of the after the pump 6 with At a temperature of 770 K, the liquid nitrogen present cools to 1090 K, the evaporation at this temperature and the further heating to 1380 K. At a real natural gas, which contains nitrogen and heavier hydrocarbons, the cooling curve of methane becomes qualitative depending on the composition have the course indicated by dashed lines. Both Fig. 4 and Fig. 5 show that in the method according to the invention, the temperature differences that occur and so the energy losses can be kept small.

Claims: 1. Method for liquefying an under increased Initial pressure of standing gas through heat exchange with an evaporating one lower-boiling liquefied auxiliary gas, which before the heat exchange to a higher Pressure is pumped, after its evaporation, relaxed to perform work and then is again brought into heat exchange with the gas, characterized in that a first part of the gas is relieved of work at bearing pressure and then through Heat exchange with the auxiliary gas flow, the weight of which is different from that of the first part of the gas behaves like about 2: 1, is cooled and liquefied and that the remaining second part of the gas with consumption of at least a part of the work performed Relaxation of the first part of the gas and the auxiliary gas recovered energy and cooled and liquefied by heat exchange with the expanded auxiliary gas and is then relaxed to bearing pressure.

Claims (1)

2. The method according to claim 1, characterized in that the second Part of the gas with the work-performing expansion of the first part of the gas and the energy obtained from the auxiliary gas compressed to supercritical pressure, cooled, relaxed to subcritical, but increased pressure, cooled further and liquefied and then relieved of bearing pressure (Fig. 1). 3. The method according to claim 2, characterized in that the second Part of the gas before its compression to the supercritical pressure by one in addition amount of energy to be exploited corresponding amount of the first part of the gas increased will and that this additional Amount of gas below or near the critical temperature cooled down and then relaxed while doing work in or into the fluid area, whereupon the liquefied part is separated from the gaseous part and then, preferably after further cooling, relaxed in a throttle valve to bearing pressure will. 4. The method according to any one of claims 1 to 3, characterized in that that part of the work-performing expansion of the first part of the gas and the energy obtained from the auxiliary gas to compress this first part before it work-performing relaxation is exploited (Fig. 2). 5. The method according to claim 1, characterized in that the second Part of the gas except through the heat exchange with the work-performing relaxed Auxiliary gas is cooled and liquefied with the help of a refrigerant circuit, whose Compressor with the work-performing expansion of the auxiliary gas and the first Part of the gas recovered energy is operated (Fig. 3). 6. The method according to any one of claims 1 to 5, characterized in, that the auxiliary gas relaxes work-performing in the wet steam area and the thereby formed Liquid to the pressure of the liquid auxiliary gas to be supplied to the heat exchange is promoted and united with this. 7. The method according to any one of claims 1 to 5, characterized in, that the work-producing relaxed auxiliary gas flow initially through heat exchange with the first part of the gas on one of the under the pressure relaxation this first part reached temperature and only then with the second Part of the gas is brought into heat exchange. 8. The method according to claim 7, characterized in that the intermediate temperature is little below the boiling point of the gas at storage pressure. 9. Device for performing the method according to one of the claims 2 to 4, characterized in that a line (1) for a first part of the Gas to a turbine (3) and a line (10) for a second part of this gas is led to a compressor (11) that the outlet of the turbine with the warm End of a cross-section of a heat exchanger designed for gas under storage pressure (4) is connected, the cold end of which to an intermediate storage (5) for liquefied Gas is connected that another cross-section of this heat exchanger (4) via the cold end to a pump (6) for liquid auxiliary gas and via the warm one End is connected to the inlet side of a second turbine (7), the outlet side of which with the refrigerant cross-sections of two further heat exchangers connected in series (8; 9) is connected, and that the compressor outlet via the second cross-sections the heat exchanger (8; 9) and an expansion valve arranged between the latter (12) and a downstream expansion valve (13) with the intermediate bearing (5) is connected.