BRPI1003929A2 - process and device for obtaining liquid nitrogen by low temperature air fractionation - Google Patents

Abstract

PROCESS AND DEVICE FOR OBTAINING NITROGEN LIQUID BY LOW TEMPERATURE AIR FRACTIONING. The present invention relates to a process and device for obtaining liquid nitrogen by low temperature air fractionation in a nitrogen-oxygen separation distillation column system which comprises a high pressure column (28). ), a low pressure column (30), and an upper high pressure column condenser (29) which is constructed as a condenser - evaporator and comprises a liquefaction compartment and an evaporation compartment. The supply air (1) is compressed to a first pressure within a main air compressor (3) and is subsequently purified (5). A choke flow (21) which is formed by a part of the purified supply air (6) is liquefied or pseudoliquefied in a main heat exchanger (19) at a second pressure which is higher than the first one. pressure. The liquefied or pseudo-liquefied choke flow (21) is expanded (33) and subsequently introduced into the expansion column system for nitrogen-oxygen separation. At least part (35) of the suspended gas (34) of the high pressure column (28) is introduced into the liquefaction compartment of the high pressure column upper condenser (29) and is at least partially liquefied therein. In the low pressure column (30) a nitrogen product (46) is generated and at least partly removed as a liquid product (51). At least part of the expanded choke flow is introduced as a refrigerant flow (33, 233, 270) into the evaporation compartment of the high pressure column upper condenser (29). The nitrogen - oxygen separation distillation column system further comprises an upper low pressure column condenser (31) which is constructed as a condenser - evaporator and comprises a liquefaction compartment and an evaporation compartment. At least part of the suspended nitrogen (46) from the low pressure column (30) is introduced into the liquefaction compartment of the upper low pressure column condenser (31) and is at least partially liquefied therein. An oxygen enriched liquid (80) from the lower region of the low pressure column (30) is introduced into the evaporation compartment of the upper low pressure column condenser (31) and is at least partially vaporized therein.

Description

Report of the Invention Patent for "PROCESS AND DEVICE FOR OBTAINING LOW TEMPERATURE AIR FRACTION NITROGEN".

The present invention relates to a process as per the preamble of claim 1.

The "first pressure" in which the supply air is purified is, for example, from 0.5 MPa to 1.2 MPa (5 to 12 bar), preferably 0.55 MPa to 0.7 MPa (5.5 at 7.0 bar). It is approximately the same as or just above the operating pressure of the high pressure column. The "second pressure" is significantly above the first

pressure. This is for example at least 5 MPa (50 bar), specifically 5 to 8 MPa (50 to 80 bar), preferably 5.5 to 7 MPa (55 to 70 bar).

The "main heat exchanger" may be formed from one or more parallel and / or series heat exchanger sections, for example one or more plate heat exchanger blocks.

The "nitrogen - oxygen separation distillation column system" comprises exactly two distillation columns, namely a high pressure column and a low pressure column (30). Additional distillation columns for nitrogen - oxygen separation do not exist in the system. Additional distillation columns for other separation tasks, for example to obtain a noble gas may in principle be provided. Preferably, however, the invention relates to methods and devices which, in addition to the high pressure column and the low pressure column, comprise no additional separation column. In addition, the "separation distillation column system"

Nitrogen - Oxygen System "also comprises a single upper high pressure column condenser for liquefying the suspended high pressure column gas, whose upper high pressure column condenser is constructed as a condenser - evaporator and comprises a compartment. liquefaction chamber and a single evaporation compartment.In the process and device, therefore, no additional condenser is used to liquefy the suspended gas from the high-pressure column. evaporation, that is to say, all parts of the evaporation compartment communicate with each other.The upper high pressure column condenser specifically is not operated using a plurality of cooling media of different compositions, but preferably only on with a single cooling medium.Usually, the upper column high condenser The pressure pressure also comprises only a single liquefying compartment within which at least part of the high-pressure column suspension gas is liquefied. The "choke flow" is cooled and liquefied by exchange of

indirect heat within the main heat exchanger or - at supercritical pressure, pseudoliquefied. Expansion of the choke flow prior to its introduction into the distillation column system for nitrogen - oxygen separation is usually performed on a regulating valve; alternatively, an expansion of work output can be performed on a liquid turbine. In expansion of the choke flow a two phase mixture is formed which consists predominantly of liquid.

Such liquid processes in which cold is transferred in a heat exchanger to a high pressure air flow (the "foreign flow") are known from EP 316768 A2 (Figure 1), US 5660059 or DE 102004046344. All of these processes comprise a conventional two-column system in which the upper high pressure column condenser (main condenser) is cooled by the bottom liquid of the low pressure column.

A disadvantage of these known processes is the high preliminary liquefaction of air introduced into the distillation column system. This leads to decreased separation efficiency and thereby a relatively high system energy consumption. Therefore, the aim of the invention is to indicate a process of the type

mentioned at the beginning and a corresponding device which has a specifically low power consumption. Expenditure on the device must be kept within limits in this case.

This objective is achieved by the characteristics of the characterizing part of claim 1, that is to say by a process in which the classical double column is replaced by two columns which both have an upper condenser. The expanded choke flow is introduced at least in part into the upper high pressure column condenser and generates liquid nitrogen there which can be applied as a backflow to the high pressure column and / or the low pressure column and / or can be obtained directly as a pressurized liquid product. In this way the cold contained in the choke flow can be used specifically efficiently and a specifically low energy consumption results.

Although such column systems are known per se, for example from US 6499312, in these known processes the upper high pressure column condenser is not cooled with a foreign air flow but with the column bottom liquid. high pressure. In contrast, the invention has the advantage that a constant composition fraction (and thus a constant boiling temperature) is used on the evaporation side of the upper high pressure column condenser. Specifically, under a shifting load (underload / overload) this therefore provides specifically stable column operation. Even if under a load change the composition of the fractions within the columns changes, the upper temperature of the high pressure column remains constant and the operating pressures of the columns need not be adjusted. In addition, the choke flow liquid air (approximately 21 mole% oxygen content) boils at a lower temperature than the high pressure column background liquid (at least 32 mole%, usually 36 to 40 mole). % mol of oxygen content); therefore the operating pressure of the high pressure column can be kept relatively low in the invention and the process operates specifically favorably energetically. The expanded choke flow can be fed directly from

directly or indirectly to the evaporator compartment of the high-pressure column upper condenser. In the first case, the refrigerant flow is introduced directly into the evaporator compartment of the high pressure column upper condenser immediately downstream of the choke flow expansion. In this case the refrigerant flow may be formed by the entire choke flow or a part which is branched immediately after expansion.

Alternatively, or in addition, at least part of the expanded choke flow is subjected to phase separation and the refrigerant flow is formed by at least part of the liquid phase phase separation. Preferably, phase separation is performed at an intermediate point of the high pressure column. In this case, the choke flow (or part thereof) is introduced into the high pressure column at an intermediate point and the refrigerant flow is withdrawn again from a liquid collection equipment (eg a cup). provided for in this intermediate point. The intermediate point is, for example, immediately above the sixth to the twelfth, preferably from the eighth to the eleventh, theoretical bottom plate for a total length of, for example, 40 to 90, preferably 40 to 60, theoretical plates within the high pressure column (according to the desired product purity). Preferably, the cold required to produce liquefaction is generally

In a two-turbine air circuit as described in claim 4, the two expansion machines are generally formed by expansion turbines. These preferably have the same inlet pressure (at or above intermediate pressure level) and / or the same outlet pressure (at first pressure level).

It is convenient if the mechanical energy generated in the expansion machines is transferred by mechanical coupling to two serially connected recompressors in which part of the air is additionally compressed from intermediate pressure to high pressure as is the subject of claim 5. High pressure flow can then be used as the choke flow. Alternatively, or in addition, the two turbine flows are formed by the high pressure flow; In this case the generation of cold and thereby the production of liquid can be further increased without energy having to be supplied from outside.

In a preferred embodiment, all the cold used in the upper high pressure column condenser is made available by the refrigerant flow. The choke flow refrigerant flow is therefore the only supply flow to the evaporator compartment of the upper high pressure column condenser.

In addition, steam generated within the evaporator compartment of the high-pressure column upper condenser may be introduced into the low-pressure column, specifically at its bottom. It serves there as upward steam, preferably it forms all upward steam within the low pressure column.

In a specific embodiment of the process according to the invention, neither the high pressure column nor the low pressure column comprises a referrer for generating the upward liquid vapor of the corresponding column.

In addition, it is convenient if, within the high-pressure column upper condenser evaporation compartment, only partial evaporation is performed and the remaining liquid fraction is introduced into the low-column upper condenser evaporation compartment. pressure. Of the latter, a small amount of purge may be removed in the liquid state.

At least part of the liquid obtained within the high pressure column upper condenser liquefaction compartment may be translated into the low pressure column and further separated therein.

A flow of gross liquid oxygen from the bottom of the high pressure column is preferably introduced into the low pressure column.

In addition to the choke flow, a fractional air flow which is formed by another part of the purified feed air is introduced in the gaseous state into the high pressure column, specifically at its bottom. The fractionation air flow may be formed by the two turbine flows downstream of the work output expansion. In a process according to the invention, preferably at least 50 mol%, specifically 50 to 60 mol%, of the total amount of feed air introduced into the nitrogen-oxygen separation distillation column system is introduced. in liquid form in the distillation column system for nitrogen - oxygen separation.

The invention furthermore relates to a device for obtaining liquid nitrogen by low temperature air fractionation according to claim 14.

The invention as well as further details of the invention will be described in more detail hereinafter with reference to exemplary embodiments shown schematically in the drawings. In the drawings:

Figure 1 shows a first exemplary embodiment of a process according to the invention,

Figure 2 shows a second exemplary embodiment in which only the distillation column system is shown,

Figure 3 shows the cooling system of the first exemplary embodiment in detail and

Figures 4 to 6 show additional variants of the cooling system. Figure 1 is subdivided by three dashed rectangles on the parts of the air pretreatment process, the cold system and the nitrogen-oxygen separation distillation system (from left to right).

The incoming air 1 is fed through a filter 2 to a main air compressor 3 and compressed there for a first pressure of 0.55 to 0.7 MPa (5.5 to 7.0 bar) and to a Pre-cooling 4 is cooled back to approximately room temperature, for example by indirect heat exchange in a heat exchanger or by direct heat exchange in a direct contact chiller.

The pre-cooled air is purified at first pressure in a purification equipment 5 which contains molecular sieve adsorber. Purified air 6 (AIR) is fed to the cold system which serves to cool the supply air and to generate the liquefaction cold. There, the purified feed air 6 is first at least partly mixed with a return air flow 7 to provide a loop flow 8. The loop flow 8 is further compressed to an intermediate pressure of 3 to 4 MPa. (30 to 40 bar) on a circuit compressor 9 that has an aftercooler 10.

All intermediate pressure air 11 is further compressed into two serially connected recompressors 12, 14 for a high pressure of at least 5 MPa (50 bar), specifically between 5 to 8 MPa (50 and 80 bar), preferably 5 0.5 to 0.7 MPa (55 to 7 bar). The recompressors 12, 14 are followed by aftercoolers 13, 15, respectively. High pressure air 16 is divided into two subflows 17, 18. The

The first subflow 17 comprises a choke flow and a first turbine flow which together enter the hot end of a main heat exchanger 19 and are cooled to a first intermediate temperature which is between room temperature and the point. of air dew. At this intermediate temperature, the first turbine flow 20 is branched from the first subflow. The remainder is further cooled to the cold end of the pseudolysed main heat exchanger and forms the choke flow 21 which comprises slightly more than half of the total air flow 1. The first turbine flow 20 is expanded producing work inside a first (cold) turbine 22 to approximately the first pressure and to a temperature which is a few degrees above the dew temperature. The first expanded turbine flow 23 is completely or substantially completely gaseous and forms a first part of a gaseous fractionation air flow 24. The remainder 25 is fed to the cold end of the main heat exchanger 19 and reheated to approximately the ambient temperature.

The second high pressure air subflow 16 forms a second turbine flow 18. This is expanded to produce work of approximately ambient temperature and high pressure in a second (hot) turbine 26, similarly to approximately the first pressure. . The second expanded turbine flow 27 enters, at a second intermediate temperature, the main heat exchanger 19 again and is combined there with part 25 of the first expanded subflow 23 to form the return flow 7 and again to be fed to the main heat exchanger. circuit compressor 9.

Gaseous fractionation air flow 24 (AIR) and choke flow 21 (JT-AIR) enter the nitrogen-oxygen separation distillation column system which comprises a high pressure column 28, an upper condenser high pressure column 29, a low pressure column 30 and an upper low pressure column condenser 31. The operating pressure of high pressure column 28 is between 0.55 and 0.7 MPa (5.5 and 7 .0 bar). The fractionating air flow 14 is fed immediately to the bottom of the high pressure column 28 in the gaseous state. choke flow 21 is expanded within a regulating valve 32 to a pressure below 0.4 MPa (4 bar) and is introduced completely as refrigerant flow 33 into the evaporator compartment of the upper column condenser. high pressure.

The suspended gas 34 of the high pressure column 28 consists of virtually pure nitrogen and is conducted as a first part 35 (in a molar amount which is slightly less than half the amount of air that enters 1). in the liquefaction compartment of the high pressure column upper condenser 29 and is completely liquefied. The liquid 36 generated within the high pressure column upper condenser is applied as a first part 37 as a return to the high pressure column 28. The remainder 38 after cooling in a subcooling countercurrent heat exchanger 39 is cooled and applied through a regulating valve 40 as a return to the low pressure column 30 which is operated at a pressure below 0.4 MPa (4 bar). The fluid flowing at the bottom of the high pressure column 28 is fed as a flow of raw liquid oxygen 41 through the subcooling countercurrent heat exchanger 39 and a regulating valve 42 into the evaporator compartment of the high pressure column. upper low pressure column condenser 31.

Refrigerant flow 33 is virtually completely vaporized within the upper high pressure column condenser, only a relatively small amount required to purge and control is withdrawn in the liquid state. The vapor 43 generated within the evaporator compartment of the upper high pressure column condenser 29 is introduced directly into the lower region of the low pressure column 30. The remaining liquid fraction 44 of the upper condenser evaporation compartment high pressure column 29 is passed through a regulating valve 45 into the evaporator compartment of the upper low pressure column condenser 31. The oxygen enriched liquid 80 which occurs at the bottom of the

low pressure column 30 is, after subcooling inside the subcooling countercurrent heat exchanger 39 and throttling, likewise introduced into the evaporation compartment of the upper low pressure column condenser 31. Suspended nitrogen 46 the low pressure column 30 is passed

into the liquefaction compartment of the upper low pressure column condenser 31 and essentially completely liquid therein. The liquid that occurs at the bottom of the high pressure column 28 is fed as a flow of raw liquid oxygen 41 through the subcooling countercurrent heat exchanger 39 and a regulating valve 42 into the upper column condenser evaporation compartment low pressure 31 which is at a pressure of 0.14 to 0.16 MPa (1.4 to 1.6 bar).

The cold gas from the upper low pressure column condenser 31 is first passed through the subcooling countercurrent heat exchanger 39, cooling the liquids. Subsequently, it flows through lines 56 and 57 to the main heat exchanger and cools the hot air flows there. Through line 62 the upper low pressure column condenser 31 is also purged by removing a small amount of liquid (purging). Remaining gas 57/58 (Waste Gas / Reg.) Is supplied hot to the environment (amb) either directly (60) or indirectly (61) after use as regeneration gas 59 in regeneration equipment 5. Liquid 47 from compartment The lower pressure column upper condenser liquefaction valve 31 is applied as a first part 48 as a return to the low pressure column 30. The remaining 49.51 is available at a pressure greater than 0.3 MPa (3 bar) as a liquid nitrogen product (LIN for storage) and stored in a liquid tank which is not shown. By throttling 53 of a small subquantity 52, liquid nitrogen 49, 51 can be subcooled in a nitrogen subcooler 50. The vaporized nitrogen 54 in the course of this is mixed with the remaining gas 56 of the upper column condenser. low pressure 31 (scrap).

A small amount of the suspended gas 35 of the high pressure column 28 may be obtained in the gaseous state as a pressurized nitrogen product 63, 64. This fraction (PGAN) of the high pressure column 28 is likewise conducted through the exchanger. 19 and contributes to the cooling of hot air flows.

In Fig. 2, the throttling flow 21 is expanded within the regulating valve 232 first only to the operating pressure of the high pressure column 28 and passed to it at an intermediate point. Within the high pressure column a phase separation occurs. At least part of the liquid fraction of the expanded choke flow is then introduced as the refrigerant flow 270, 233 after a corresponding additional leakage 271 within the high pressure column upper condenser evaporation compartment. The gas fraction of the throttling flow 21 is hereby available as rising steam within the high pressure column 28.

In Figures 3 to 7 various circuits of the cold system are shown each of which may be combined with any of the distillation column systems described in Figures 1 and 2.

Fig. 3 merely shows a detail enlargement of Fig. 1. This variant has the advantage that the hot turbine 26 expands from a specifically high pressure (the high pressure at which the throttling flow 21 is also) and a temperature relatively high corresponding. Pre-cooling of the second turbine flow 18 in the main heat exchanger 19 is not required in this case. No lines are required from the main heat exchanger 19 to the hot turbine 26, and the heat exchanger can be produced simply and economically.

In Figure 4, as a variant, the second turbine flow 18 is

also pre-cooled on main heat exchanger 419.

In the exemplary embodiment of FIG. 5 the inlet pressure of the second (hot) turbine 26 is lower and is at the intermediate pressure level. For this purpose the second turbine flow 518 is already branched from the compressed circuit flow 11 to the intermediate pressure upstream of the two recompressors 12, 14, pre-cooled in the main heat exchanger 19 and finally fed to the turbine. 26

In figure 6 the main heat exchanger 19 is further cooled by a cold machine 666. Such a cold machine may also be supplemented in the variant of figure 4.

Claims (14)

1. A process for obtaining liquid nitrogen by low temperature air fractionation in a nitrogen-oxygen separation distillation column system which comprises exactly two distillation columns, namely a high pressure column (28), a low pressure column (30), and also a single upper high pressure column condenser (29) for liquefying the suspended gas (34) of the high pressure column (28), whose upper high pressure column condenser is constructed as a condenser - evaporator and comprises a liquefaction compartment and a single evaporation compartment, wherein in the process the supply air (1) is compressed to a first pressure within a main air compressor (3) and is subsequently purified (5), a throttling flow (21) which is formed by a portion of the purified supply air (6) is liquefied or pseudoliquefied in a main heat exchanger. al (19) at a second pressure which is higher than the first pressure, - the liquefied or pseudoliquid throttling flow (21) is expanded (33) and subsequently introduced into the expansion column system for nitrogen separation - - at least part (35) of the high-pressure column (28) suspended gas (34) is introduced into the liquefaction compartment of the high-pressure column (29) upper condenser and is at least partially liquefied therein, and - in the low pressure column (30) a nitrogen product (46) is generated and at least partly removed as a liquid product (51) characterized in that - at least part of the expanded throttling flow is introduced. as a refrigerant stream (33, 233, 270) in the evaporator compartment of the upper high pressure column condenser (29), - the distillation column system for the separation of nitrogen - oxygen, in addition, comp is an upper low pressure column condenser (31) which is constructed as a condenser - evaporator and comprises a liquefaction compartment and an evaporation compartment - at least part of the suspended nitrogen (46) of the low pressure (30) is introduced into the liquefaction compartment of the low pressure upper column condenser (31) and is at least partially liquefied, and - an oxygen enriched liquid (80) from the lower region of the low pressure column (30) is introduced into the evaporation compartment of the upper low pressure column condenser (31) and is at least partially vaporized therein. Process according to Claim 1, characterized in that the refrigerant flow (33) is introduced directly into the evaporation chamber of the high-pressure column upper condenser (29) immediately downstream of the expansion (32). throttling flow (21). Process according to claim 1 or 2, characterized in that at least part of the expanded choke flow (232) is subject to phase separation and the refrigerant flow (233, (270) is formed by at least least part of the liquid phase of phase separation, wherein phase separation is performed specifically at an intermediate point of the high pressure column (28). Method according to any one of Claims 1 to 3, characterized in that - the purified supply air (6) is at least partly mixed with a return flow (7) to provide a circuit flow. (8), - the circuit flow (8) is compressed in a circuit compressor (9) to an intermediate pressure which is higher than the first pressure, - a first turbine flow (20) which is formed by a first part of the circuit flow (11) downstream of the circuit compressor (9) is expanded producing work on a first expansion machine (22), - a second turbine flow (18) which is formed by a second part of the circuit flow (11) downstream of the circuit compressor (9) is expanded producing work on a second expansion machine (26), and - at least part (25) of the first turbine flow (23) expanded producing work and / or at least part of the second expanded turbine flow (27) producing work is recirculated as the return flow (7) to the circuit flow (8). Process according to Claim 4, characterized in that - at least part of the compressed circuit flow (11) for intermediate pressure in two serially connected recompressors (12, 14) is compressed to a high pressure which is higher than the intermediate pressure and specifically approximately the same as the second pressure, wherein - the first expansion machine (22) is mechanically coupled to one (12) of the two recompressors, and - the second machine expansion (26) is mechanically copied to the other (14) of the two recompressors. Process according to any one of Claims 1 to 5, characterized in that all the cold used in the upper high-pressure column condenser (29) is made available by the refrigerant flow (33, 233, 270). Process according to any one of Claims 1 to 6, characterized in that the vapor (43) generated within the evaporation compartment of the upper high-pressure column condenser (29) is fed into the low-pressure column. (30), specifically in its background. Process according to any one of claims 1 to 7, characterized in that neither the high pressure column (28) nor the low pressure column (30) comprises a referrer for generating upward vapor of a column liquid. corresponding. Process according to any one of Claims 1 to 8, characterized in that a fraction (44) of liquid remaining in the upper-pressure column upper condenser evaporation compartment (29) is introduced into the condenser evaporation compartment. upper low pressure column (31). Process according to any one of claims 1 to 9, characterized in that at least part (38) of the liquid (36) obtained within the liquefaction compartment of the high pressure column upper condenser (29) is provided. ) is introduced into the low pressure column (30). Process according to any one of Claims 1 to 9, characterized in that a flow of crude liquid oxygen (41) from the bottom of the high pressure column (28) is introduced into the low pressure column (30). . Process according to any one of Claims 1 to 11, characterized in that the fractional air flow (24) which is formed by another part of the purified supply air (6) is introduced as the flow. gaseous throttling (21) in the high pressure column (28), specifically at its bottom, wherein the fractionation air flow (24) specifically comprises at least part of the first expanded turbine flow (23) producing and / or at least part of the second expanded turbine flow (27) producing work. Process according to any one of Claims 1 to 12, characterized in that at least 40 mole%, specifically at least 50 mole%, of the total amount of supply air (1) introduced into the control system. Nitrogen - oxygen separation distillation column is introduced in the liquid state into the Nitrogen - oxygen separation distillation column system (33,322). 14. A device for obtaining low temperature air fractionation liquid nitrogen which has - a nitrogen-oxygen separation distillation column system which comprises exactly two distillation columns, namely a high pressure column (28) , a low pressure column (30), and also a single upper high pressure column condenser (29) for liquefying the suspended gas (34) of the high pressure column (28), whose upper high pressure column condenser is constructed as a condenser - evaporator and comprises a liquefaction compartment and a single evaporation compartment, - a main air compressor (3) for compressing the supply air (1) to a first pressure, - a purification equipment for purifying (5) the compressed supply air for the first pressure, - a means for forming a choke flow (21) by a portion of the purified supply air (6), - a main heat exchanger (19) for pseudolyzing the choke flow at a second pressure which is higher than the first pressure, - a means for expanding (32) the choke flow (21); - a means for introducing the expanded choke flow into the nitrogen - oxygen separation distillation column system, - a means for introducing at least part (35) of the suspended gas (34) from the high column. pressure (28) in the high pressure column upper condenser liquefy housing (29) and which has - a means for removing as a liquid product (51) a nitrogen product (46) generated within the low pressure column (30), characterized by - a means for introducing at least part of the expanded slurry flow as a refrigerant flow (33, 233, 270) into the evaporation chamber of the high pressure column upper condenser (29) , - u A low pressure upper column condenser (31) which is constructed as a condenser - evaporator and comprises a liquefaction compartment and an evaporation compartment, - a means for introducing at least part of the suspended nitrogen (46) from the column. (30) into the low pressure column upper condenser liquefaction compartment (31) and by - a means for introducing an oxygen-enriched liquid (80) from the lower pressure column region (30) into the evaporation of the upper low pressure column condenser (31).