AIR FRACTIONATION PLANT, OPERATING METHOD AND CONTROL FACILITY

Abstract

An air fractionation plant in which a cooling water circuit having a recooling apparatus is provided for cooling compressed air, where the recooling apparatus is configured for cooling cooling water using cooling air. The recooling apparatus is configured so as to cool the cooling water, at least at a wet bulb temperature of the cooling air of more than 289 K, to a temperature which is not more than 3 K above the wet bulb temperature. A corresponding operating method and a control facility are likewise provided.

Claims

1. An air fractionation plant in which a cooling water circuit having a recooling apparatus is provided for cooling compressed air, where the recooling apparatus is configured for cooling cooling water using cooling air, characterized in that the recooling apparatus is configured so as to cool the cooling water, at least at a wet bulb temperature of the cooling air of more than 289 K, to a temperature which is not more than 3 K above the wet bulb temperature.

2. The air fractionation plant according to claim 1, wherein the recooling apparatus is configured so as to cool the cooling water to a temperature which is at least 0.5 K above the wet bulb temperature.

3. The air fractionation plant according to claim 1, wherein the recooling apparatus comprises a cooling tower.

4. The air fractionation plant according to claim 3, wherein the recooling apparatus has forced ventilation.

5. The air fractionation plant according to claim 1, wherein the cooling water circuit comprises a heat exchanger which is arranged downstream of a compressor.

6. The air fractionation plant according to claim 1, wherein a cooling zone range of from 5 to 25 K is provided.

7. A method of operating an air fractionation plant in which a cooling water circuit having a recooling apparatus is provided for cooling compressed air, where the recooling apparatus is configured for cooling cooling water using cooling air, characterized in that the recooling apparatus is configured and operated so as to cool, at least at a wet bulb temperature of the cooling air of more than 289 K, the cooling water to a temperature which is not more than 3 K above the wet bulb temperature.

8. The method according to claim 7, wherein the specific surface area of the packing and/or the ratio of liquid to gas and/or the pressure drop in the recooling apparatus is selected and/or set in such a way that, at least at a wet bulb temperature of the cooling air of more than 289 K, the cooling water is cooled to the temperature which is not more than 3 K above the wet bulb temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention will be illustrated below with reference to the accompanying drawings which show preferred embodiments of the invention.

[0026] FIG. 1 shows an air fractionation plant according to an embodiment of the invention in the form of a schematic process flow diagram.

[0027] FIG. 2 depicts the cooling water temperatures and the corresponding wet bulb temperatures to illustrate an embodiment of the invention.

[0028] FIGS. 3A and 3B show the additional cooling of cooling water made possible according to the invention and the associated energy savings.

DETAILED DESCRIPTION OF THE INVENTION

[0029] In FIG. 1, an air fractionation plant according to a particularly preferred embodiment of the invention is shown in the form of a schematic process flow diagram and is designated overall by 100.

[0030] A feed air stream a is fed via a filter 101 into the air fractionation plant 100, is compressed by means of a main air compressor 102 and cooled in a direct contact cooler 103 which is supplied, inter alia, with a cooled water stream b from an evaporative cooler 104. The water stream b is introduced by means of a pump which is not separately indicated into the direct contact cooler 103. To provide the cooled water stream b, the evaporative cooler 104 is supplied with water of a stream c which can partly also be fed into the direct contact cooler 103 without prior cooling in the evaporative cooler 104. A water stream d is taken off from the direct contact cooler 103.

[0031] The water streams b, c and d shown and also the direct contact cooler 103 and the evaporative coolers 104 are integrated into a cooling water circuit denoted here by 10, which can also comprise any further water streams, pumps, direct and indirect heat exchangers, etc, which are not shown. For example, the main air compressor 102 can, as shown here in greatly simplified form, have at least two compressor stages 1 and 2 between which intermediate cooling by means of an intermediate cooler 3 occurs. Typical main air compressors 102 of air fractionation plants comprise from five to nine compressor stages and a corresponding number of intermediate coolers. Cooling water in the form of the stream s can be fed into the illustrated intermediate cooler 3 which is configured for indirect heat exchange. The stream s can, in particular, be a substream of the stream c, i.e. cooling water which likewise circulates in the cooling water circuit 10. An analogous situation applies to further (after-)coolers as explained below. Further water streams can be fed at any place into the cooling water circuit 10, for example in order to compensate for evaporation losses, as indicated here by the water stream e. Furthermore, cross-connections between water streams, regulating devices, measurement sensors and the like can be arranged at advantageous places in the cooling water circuit 10.

[0032] The central component of the cooling water circuit 10 is a recooling apparatus 11, which is shown here as a wet cooler and can be configured, for example, as a cooling tower having forced ventilation. However, as mentioned above, any other embodiments are also possible. The recooling apparatus 11 is configured for operation according an abovementioned embodiment of the invention. A stream f of atmospheric air having a wet bulb temperature prevailing at the location of the air fractionation plant 100 is fed to the recooling apparatus 11. The recooling apparatus 11 is, for example, configured for cooling water of a water stream g to be cooled, formed in the depicted example by the water streams d and e, to a temperature level which is not more than 3 K above the wet bulb temperature of the air stream f. This applies particularly when the wet bulb temperature of the air stream f is above 289 K.

[0033] The further processing of the compressed and cooled feed air stream a, which is now designated by h, corresponds largely to that in conventional air fractionation plants, for example in an air fractionation plant as described in H. W. Hring (editor), Industrial Gases Processing, Wiley-VCH, 2006, in particular section 2.2.5, Cryogenic Rectification:

[0034] The compressed and cooled feed air stream h is fed to an adsorber set 105 which comprises alternately operated adsorber vessels and can be regenerated by means of a regeneration gas stream i. The regeneration gas stream i can be heated by means of an electrically operated and/or steam-operated regeneration gas heating device 106. To provide the regeneration gas stream i, it is possible to use a stream k, the provision of which will be described in more detail below.

[0035] A compressed air stream which has been dried in the adsorber set 50 is denoted by l. Depending on the configuration of the air fractionation plant 100, the compressed air stream l can be provided at a pressure which makes after-compression necessary or dispensable (the latter in the case of High Air Pressure processes). In the example shown, a substream m of the compressed air stream l is fed to an after-compressor 107. An after-cooler, which is not designated separately, of the after-compressor 107 can likewise be cooled using water from the cooling water circuit 10.

[0036] The substream m and a substream n which has not been after-compressed of the compressed air stream l are, according to the embodiment depicted, fed to a main heat exchanger 108 and taken off from this at different temperature levels. The stream m can be depressurized by means of a generator turbine 109 and, after being combined with the stream n, be fed into a high-pressure column 111 of a distillation column system 110. Further substreams of the compressed air stream l can be formed, cooled, after-compressed, depressurized and likewise fed into columns of the distillation column system 110 in an advantageous way, for example a known throttle stream which is not shown here.

[0037] The high-pressure column 111 together with a low-pressure column 112 forms a double column system of a known type. In the example shown, the distillation column system additionally comprises an argon enrichment column 113 and a pure argon column 114, but these do not have to be provided. Further distillation columns can be provided.

[0038] The operation of the distillation column system 110 is known and will therefore not be explained. In the example shown, the distillation column system 110 is supplied, inter alia, with a gaseous nitrogen stream o, impure nitrogen in the form of the stream p, from which the stream k and/or a stream q can be formed after heating in the main heat exchanger 108 and can be fed to the regeneration gas heater 106 or the evaporative cooler 104, and a liquid, oxygen-rich stream r can be taken off. Instead of the stream q, it is also possible to use, for example, a cold, nitrogen-enriched stream. Further streams will not be explained in detail. Any streams can be heated in the main heat exchanger 108, compressed or pressurized upstream or downstream of the main heat exchanger 108, combined with other streams and divided into substreams.

[0039] FIG. 2 shows the average cooling water temperatures of the months of a year and the corresponding wet bulb temperatures in order to illustrate an embodiment of the invention. The cooling water temperature is plotted in K on the ordinate versus the wet bulb temperature in K on the abscissa. In the graph, the wet bulb temperature is shown in the form of the data points 201, the cooling water temperature in a conventional design of a recooling apparatus configured as cooling tower is shown in the form of the data points 202 and the cooling water temperature in a design according to an embodiment of the invention is shown in the form of the data points 203.

[0040] The conventional design results in a cooling limit difference of 8 K of a wet bulb temperature of 289 K. According to the embodiment of the invention depicted, the cooling limit difference is reduced by five kelvin to 3 K. The use of a more efficient cooling tower and thus a lowering of the cooling limit temperature leads to two effects, namely firstly colder cooling water and secondly a smaller relative difference between the cooling water temperature and the wet bulb temperature. This means that the efficiency loss of the cooling towers is fundamentally lower in relatively cold months for a design having a relatively small cooling limit difference. The reason for the lower efficiency loss of a large cooling tower in the cold months is the water/air ratio which can be shifted in favour of air. The mass flow of water is the same for both cooling tower variants, and the critical factor is that a larger amount of air can flow through the cooling tower in the case of a large cooling tower for the same amount of cooling water, and this air takes up the evaporating water and at the same time allows great convective cooling. This effect makes a positive contribution especially at low air temperatures at which the air can take up little water.

[0041] FIGS. 3A and 3B show the additional cooling of cooling water (FIG. 3A) made possible according to the invention and the associated energy savings (FIG. 3B). In FIG. 3A, a temperature difference in K and in FIG. 3B an energy difference in kW is plotted on the ordinate versus the months January (J) to December (D) on the abscissa.

[0042] As can be seen from FIG. 3A, virtually 5 K cooler cooling water is obtained on average. The energy saving which can correspondingly be seen in FIG. 3B is from 270 to 450 kW per month and leads to an annual average saving of 340 kW. The decrease in the compressor power consumption by 340 kW corresponds to 1.5% of the total compressor power consumption.