DE1022247B - Process for pumping the lower-boiling component, which originates from a fractionation of a mixture of low-boiling gases, in the liquid phase to a relatively high pressure - Google Patents

Description

Process for pumping the from fractionation of a mixture low-boiling gases originating low-boiling component in the liquid phase relatively high pressure when operating announcements to generate oxygen and nitrogen by liquefaction and fractionation of air, it is often desirable to ensure a supply of nitrogen under a pressure which is considerably higher than that with nitrogen as a separate product at some point in the fractionation is available. So far, such a supply has been achieved by making the definitive gaseous product re-compressed as it normally would from the nitrogen Warm air exchanger essentially at atmospheric temperature and pressure accrues.

Recompressing expanded gaseous products to high Pressure is a wasteful and undesirable process in several ways. It requires multi-stage compressors that lubricate the compressed gas with oil with coal: contaminate hydrogen, while with water lubrication normally the compressed gas is re-dried by an adsorbent such as silicon gel will. got to. Therefore the whole system is expensive and takes up a lot of valuable space and requires a relatively high expenditure of force.

It is known to use nitrogen in the condenser of an air separation plant to be taken to obtain smaller amounts of liquid nitrogen. It is further known that liquid nitrogen can be conveyed by a pump that is operated by a coolant, e.g. B. a nitrogen bath, or an apparatus surrounded in which the nitrogen is subcooled by a relatively cold stream such as oxygen will. Furthermore, liquid oxygen from a decomposition plant is no longer new relatively cold by heat exchange with a stream, e.g. B. by nitrogen subcooled liquid and then in the liquid state on a relatively compressing high pressure. So far, however, it has not been possible to create one to pump liquid nitrogen withdrawn from a separation plant into which, the liquid nitrogen to be pumped through a derived from the system Liquid is hypothermic.

It has now been found that you can get an essential and useful Proportion of the nitrogen content of the air that is fed to an air fractionation, in liquid form and can subcool to a temperature at which it can the pump can be pumped in liquid form without the risk of gas blockage, and: that such a supercooling .by using column products of nitrogen can be achieved by having appropriate pressure differentials between the cooling means and the liquid to be cooled.

If you pump highly volatile liquids to the higher pressure, for storage in pressure tanks or cylinders or for emptying in pipes needed, and when you have the highly volatile liquid under high pressure evaporated and heated in a heat exchanger by the incoming air, achieved you get significant advantages from the amount of cooling that results from the difference the heat content of compressed and expanded gas results. These benefits enclose. a great economy: the system and a saving in floor space, there a simple liquid pump of the normal plunger type instead of the high quality one Can use pressure equipment and also the complete avoidance of contamination achieved because such pumps do not require any liquid lubrication. In addition, will increases safety, since there is a reduction in size and temperature the pressure medium and the prevention of contamination by lubricants achieved will. Finally, one usually obtains desired reductions in power consumption, in the need for monitoring and in maintenance.

The invention can be either single-stage or a two-stage column can be used, as shown, for example, on the basis of the Drawings is explained.

Fig. 1 shows a scheme for a single column process in which the Nitrogen withdrawn as vapor from a partial fractionation, through the liquid Oxygen in the main column is liquefied and through the gaseous Product nitrogen from this column is supercooled; Fig '. 2 shows a similar one Process in which liquid nitrogen from the high pressure stage is a two-stage Column withdrawn and expanded by high pressure nitrogen from the high pressure stage chilled wind.

The essential elements of the system shown in Fig. 1 are: the main heat exchanger A, which can be of one of the usual designs, however must have four rounds; a nitrogen separator or pre-fractionator B, from can consist of a filled column or a column provided with bubble cap trays; a smooth tube or spiral tube condenser C with reflux to this fractionator; a one-step fractionation column e D, both designed as a filled column. but preferably with bubble caps can be equipped; a nitrogen condenser E surrounding the main column D. or is arranged in the lower part thereof; a nitrogen cooler F, which basically as a two-stream ousta.uscher, but often because of the better usability and adaptability is designed as a three-flow exchanger; and a pump G for highly volatile Liquids is suitable.

A course according to FIG. 1 proceeds as follows: Air under a desired, relatively high pressure of 35 to 175 atmospheres, which has essentially been freed of water vapor and carbonic acid, is at 10 in a coil 11 of the exchanger _-I introduced in which it exchanges heat in countercurrent with the nitrogen and oxygen product and with the pumped nitrogen stream. When leaving the heat exchanger through the line 12, the partially recooled air flow expands during its passage through the expansion valve 13 to a mean pressure which usually fluctuates between 6 and 20 atmospheres. This expansion liquefies part of the air, some of which enters separator B, as a mixture of liquid and saturated vapor.

The air enriched with oxygen, which is below in the liquid "swamp" 14 of the separator collects, goes through line 15 and expansion valve 16, which reduces its pressure to 1 atm, through a coil 17 in the condenser C. The jacket of this condenser is charged with nitrogen vapor through inlet 18, while the condensate runs back through 19 to the column. The one enriched with oxygen Air then flows through 20 and 21 and through the check valve 22 as at 23 in FIG medium height into column D.

In this and the following description, those are identified by numbers Valves are of course open, unless otherwise stated.

That part of the nitrogen vapor that does not liquefy in condenser C. is, escapes through 24 to the nitrogen condenser E, where it is exchanged by heat with. the pure oxygen boiling in the "sump" 25 in the column: D is liquefied will. The liquid that forms flows through line 26 and shut-off valve 27 and the line 28 to the coil 29 through the exchanger F, in which it is in a "is cooled down as explained below. The cooled liquid flow runs through line 30 and valve 31 to the suction side of pump G. At this point he still has an essentially medium pressure. He will then go through the Liquid pump brought to a desired higher pressure. The power is on then through the line 32 to the coil 33 in the exchanger A, into the liquid evaporated and the steam is brought to atmospheric temperature. The gaseous one Current is eventually increased 'at 34 under one by the liquid pump Pressure on steel cylinders, storage tanks or pipelines that are not shown, submitted.

The gaseous nitrogen that is under low pressure and in the column D is separated, flows through the lines 45, 46 and the valve 47 to the jacket 48 surrounding the cold end of the pump G to absorb the heat, which either penetrates the pump through the insulation or through friction in it arises. From there it flows through line 49 into jacket 50 of the heat exchanger A, where it is brought to atmospheric temperature and through 51 out of circulation escapes.

The pure oxygen that is separated in the column flows through lines 52, 53 and 54 and through valve 55 into a coil 56, from which he is discharged at 57 under atmospheric temperature and pressure.

If the system according to FIG. 1 is used for the production of oxygen if compressed nitrogen is not desired, it runs in the condenser F_ Liquefied nitrogen flow through the nitrogen subcooler F, through the lines 30 and 42 and through valve 43 at the top into column D, for example at 44. There it serves as a useful reflux liquid.

As mentioned above, the stream of liquefied nitrogen is used when flowing through the coil 29 on its feg to the suction side of the pump cooled down in the exchanger F. This cooling down is done by a gaseous A stream of nitrogen reached, which for the purpose of heat exchange with the Rohrschlan @ ge 29 to the jacket of the exchanger F flows. To this end, part of the gaseous Nitrogen product escaping from column D. through line 45, the Valve 58 and the lines 59, 60 and 61 are passed into the jacket 62 of the exchanger F. After the heat exchange with the coil 29, the flow of nitrogen gas leaves the jacket 62 through the line 71, from where it is through the line 63 to the line 49 is performed. There he unites on his way to the exchanger _d with the Flow of gaseous nitrogen products from the jacket 48 of the pump. The valves 47 and 58 are at the required flow rate of the gaseous nitrogen products set by the diver F in order to achieve the desired cooling down.

The essential elements of the apparatus shown in FIG. 2 are as follows: the first heat exchanger H; an expansion machine I, which can be a calving machine or a turbo machine, a two-stage fractionating column T of any customary or special type; a two-way heat exchanger K for cooling down liquid nitrogen; a liquid pump L, which can be designed as a rotary piston pump, a centrifugal pump or, preferably, a simple plunger pump.

The course according to FIG. 2 proceeds as follows: Air, the first brought to a desired pressure of 17.5 to 70 atmospheres and cleaned if possible is inserted into the coil 101 of the first exchanger H at 100. there it is cooled down by heat exchange with cold column products. A Part of the air flow is sucked off in the middle of the pipe coil and goes through the line 102 and a regulating and shut-off valve 103 to the expansion machine 1. This reduces the pressure to that which prevails in the high pressure stage of the column, for example to 5 to 6 atü. The expansion machine's exhaust goes through the line 104 and the shut-off valve 105 in the lower part of the column J.

The rest of the air supplied: crosses the entire length of the snake 101 and is also through lines 106 and 107 and through the expansion valve 108 fed to the lower part of the column.

The amounts of air caused by the expansion. Machdne and, the expansion valve go, can be measured in their mutual relationship as desired, and it is possible without use by a suitable regulation of the initial air pressure the expansion machine get along.

The raw oxygen. which separates in the high pressure stage of the column, goes in the usual way through line 109, expansion valve 110 and the Line 112 in the low pressure side of the column. This will be under a lower one Maintained pressure of about 0.15 to 0.7 atmospheres.

The liquid nitrogen that is in the sump 113 in the upper end of the High pressure part collects, flows through lines 114 and 115, the expansion valve 116 and line 117 in the upper end of the low pressure part.

The low pressure gaseous nitrogen, which is in The upper part of the column separates, flows through lines 118 and 120 to the jacket 121 surrounding the cold end of the liquid pump L. From there goes it through line 122 to jacket 123 of the first heat exchanger and is from there at 124 released into the open.

Pure oxygen, which is secreted in the low-pressure stage, flows through lines 125, 126 and 128 to coil 129 of the first heat exchanger H and is released from there at 130.

From the liquid nitrogen collecting in the sump 113 can part as desired through the # 'enti.l 131 and line 132 to the inlet in the pump L can be directed. The current flows through a coil 133 in the cooler K, in which it is set to the desired lower temperature in the above Way is brought. The cooled down liquid passes through the pipe 134 approximately under the pressure prevailing in the high pressure part of the column to the suction side the pump and is brought to the desired higher pressure by this to finally delivered through line 135 into coil 136 of the first exchanger will. In this pipe coil, the liquid is evaporated and through heat exchange brought to about atmospheric temperature with incoming air. Then that will Gas through line 137 under the pressure generated by the pump into reservoir or transport vessels or in a pipeline, which are not shown.

Cooling down the flow of liquid nitrogen in the coil 133 of the cooler h can be brought about by exchanging heat with the Serpent 133 is an expanded stream of high pressure liquid Nitrogen leads. For this purpose, a stream of liquid nitrogen is emitted withdrawn from the sump 113 through line 115 and valve 154. The branched off Current is through line 155, expansion valve 156 and line 145, 140 passed to the jacket 141 of the cooler K. The branched off stream of liquid, stick material flows after heat exchange with the coil 133 from the jacket 141 through the line 142, which communicates with line 122, and joins on the way to the main diver H with the stream of gaseous nitrogen product flowing from the pump jacket 121 is coming.

Usually there are liquids that are in a gas fractionating Column are dismantled, with the overlying gases in pressure equalization. Pumps one such liquids out of the column causes the liquid friction in the supply line and the weight of the inlet valve from the associated one Pump a pressure drop between their point of introduction and the pump cylinder. This creates a vapor development that leads to a new equilibrium at lower Pressure leads. With these extremely volatile liquids already caused a very slight drop in pressure generates sufficient steam to produce a soft and make it difficult or impossible for the pump to operate continuously.

This difficulty is avoided by the operations described, by cooling the liquid on its way to the pump to such an extent that that the unavoidable pressure drop is no longer sufficient to reduce the liquid at Bring the temperature into a new equilibrium. A sufficient temperature reduction provided that this measure is an effective remedy against blistering, and it ensures uninterrupted pumping without incorrect strokes.

The extent to which the pump liquid must be cooled depends naturally from the pressure drop between the feed point and the pump cylinder in the respective arrangement, also on the amount of heat that the liquid strand is supplied by the insulating material surrounding it.

\ Normally, a temperature decrease that is sufficient for the Lowering the vapor pressure of the liquid by approximately one atmosphere. from However, this number becomes within fairly wide limits with different pressure drops and heat absorption through the supply line differ.

Since nitrogen in air is the main component with the lower evaporation temperature is and there usually no coolant finitely lower boiling point with the same Pressure is available, this must be relieved to a pressure that is below the supply pressure of the liquid nitrogen in the pump. The required Pressure difference can be created by artificial pressurization of the cooling coils flowing coolant or by evacuating the chamber into: the the coolant is introduced. According to the invention, however, it becomes simpler Way by pumping out the flow of nitrogen from that point in the fractionation process reached, at which it is still noticeably above atmospheric pressure, and further by Expanding the coolant to about atmospheric pressure; d. H. at the lowest Pressure at which it. through the passages at the required speed can flow to cover the cooling value still to be replaced.

Claims (3)

PATENT CLAIMS: 1. @T learn about the pumping of the lower-boiling component originating from a fractionation of a mixture of low-boiling gases in the liquid phase to a relatively high pressure for the purpose of obtaining a gaseous, lower-boiling component and a liquid, higher-boiling component, both of which are under relatively low pressure, especially for Pumping nitrogen in the liquid phase to a relatively high pressure during fractionation. of air in liquid oxygen and gaseous nitrogen under relatively low pressure, characterized in that the liquid (E in Fig. 1) intermediate product of the lower-boiling component (nitrogen), which is under its evaporation pressure and consists of a part (12 in Fig. 1) of the gas mixture (air) originates, or a part (132 in Fig. 2) of the liquid (113 in Fig. 2) intermediate product of the lower boiling component (nitrogen), which is under its evaporation pressure and consists of a part (104, 107 in Fig. 2) of the gas mixture (air) originates, by heat exchange (29 in Fig.1 or 133 in Fig. 2) with a cooler gas of the lower-boiling component (nitrogen) is subcooled at a pressure which is lower than that of the corresponding liquid intermediate, whereupon the supercooled liquid (nitrogen) is pumped to the relatively high pressure (G in Fig. 1 or L in Fig. 2). 2. The method according to claim 1, characterized in that the supercooling of the liquid intermediate product of the lower-boiling component through heat exchange with a part (58, 59, 62) of the product obtained in the main column (D) lower-boiling component (nitrogen) takes place (Fig. 1). 3. The method according to claim 1, characterized in that the subcooling of the removed part of the liquid Intermediate product of the lower-boiling component by heat exchange with a other part removed and relaxed to the lower final pressure (154,155,156,141) this intermediate takes place (Fig. 2). Considered publications: German Patent Nos. 495 795, 729 657, 873 251; U.S. Patent No. 2 480 094.