BACKGROUND OF THE INVENTION
[0002] The production of air products in the liquid or gaseous state by cryogenic
15 fractionation of air in air fractionation plants is known and described, for
example, in H.-W. Häring (editor), Industrial Gases Processing, Wiley-VCH,
2006, in particular Section 2.2.5, "Cryogenic Rectification."
[0003] Air fractionation plants of the classic type have column systems that can be
20 designed as two-column systems, in particular as double-column systems, but also as
triple-column or multi-column systems. In addition to rectification columns for
obtaining nitrogen and/or oxygen in the liquid and/or gaseous state, i.e., rectification
columns for nitrogen-oxygen separation, rectification columns for obtaining further
air components, in particular of noble gases, can be provided.
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[0004] The rectification columns of the mentioned column systems are operated at
different pressure levels. Known double-column systems have a so-called pressure
column (also referred to as a high-pressure column, medium-pressure column or
lower column) and a so-called low-pressure column (also referred to as an upper
30 column). The high-pressure column is typically operated at a pressure level of 4 to 7
bar, in particular about 5.6 bar; the low-pressure column on the other hand is
3
operated at a pressure of typically 1 to 2 bar, in particular about 1.4 bar. In certain
cases, even higher pressure levels may be used in either rectification column. The
pressures cited here and below are absolute pressures at the top of the respective
columns indicated.
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[0005] The object of the present invention is to improve methods for the lowtemperature fractionation of air and for the provision of air products - and, in
particular, to design them more efficiently.
10 DISCLOSURE OF THE INVENTION
[0006] This object is achieved by a method for obtaining one or more air
products, and by an air fractionation plant having the features of the independent
claims. Embodiments are respectively the subject matter of the dependent claims
15 and of the description below.
[0007] In the following, a few principles of the present invention are first
explained and terms used to describe the invention are defined.
20 [0008] Methods utilizing a main (air) compressor and a booster air compressor
(MAC/BAC), and also so-called high air pressure (HAP) methods, may be used
for air fractionation. The methods using a main air compressor and a booster air
compressor are the more conventional methods; high air pressure methods are
increasingly used as alternatives nowadays.
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[0009] Main air compressor/booster air compressor methods are characterized in
that only a portion of the total feed air quantity that is supplied to the column
system is compressed to a pressure level which is substantially – - i.e., at least 3,
4, 5, 6, 7, 8, 9, or 10 bar – above the pressure level of the pressure column, and is
30 thus the highest pressure level used in the column system. A further portion of the
feed air quantity is compressed only to the pressure level of the pressure column
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or to a pressure level which differs by no more than 1 to 2 bar therefrom, and is
fed into the pressure column at this lower pressure level without decompression.
An example of a main air compressor/booster air compressor method is disclosed
in Häring (see above) in Fig. 2.3A.
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[0010] In a high air pressure method, on the other hand, the entire feed air
quantity that is supplied in total to the column system is compressed to a pressure
level which is substantially, i.e., by 3, 4, 5, 6, 7, 8, 9, or 10 bar, above the pressure
level of the pressure column, and is therefore the highest pressure level used in the
10 column system. The pressure difference can be up to 14, 16, 18, or 20 bar, for
example. High air pressure methods have been described in detail, for example,
from EP 2 980 514 A1 and EP 2 963 367 A1.
[0011] Regarding the devices or apparatuses used in air separation units, reference is
15 made to specialist literature, such as Häring (see above), in particular section 2.2.5.6,
"Apparatus." Hereinafter, some aspects of corresponding devices are explained in
more detail for clarity and a clearer delimitation.
[0012] Multi-stage turbocompressors, which are referred to here as "main air
20 compressors," or "main compressors" for short, are used in air fractionation plants
to compress the total fractionated air. The mechanical construction of
turbocompressors is generally known to the person skilled in the art. In a
turbocompressor, the compression of the medium to be compressed takes place by
means of turbine blades and/or impellers which are arranged on a turbine wheel or
25 directly on a shaft. A turbocompressor forms a structural unit that, however, may
have a plurality of compressor stages in a multi-stage turbocompressor. A
compressor stage normally comprises a turbine wheel or a corresponding
arrangement of turbine blades. All of these compressor stages may be driven by a
common shaft. However, it may also be provided that the compressor stages are
30 driven in groups with different shafts, wherein the shafts may also be connected to
one another via gearing.
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[0013] The main air compressor is further characterized in that the entire quantity of
fractionated air which is supplied to the column system and used for the production of
air products, i.e., the entirety of air in the system, is compressed by said main air
5 compressor. Accordingly, a "booster air compressor" may also be provided in which,
however, only a portion of the air quantity compressed in the main air compressor is
brought to an even higher pressure. This may also be designed a turbocompressor. In
order to compress partial air quantities, further turbocompressors are typically
provided, also referred to as boosters, that only perform compression to a relatively
10 small extent in comparison to the main air compressor or the booster air compressor.
A booster air compressor may also be present in a high air pressure method, but this
compressor then compresses a sub-quantity of the air starting from a correspondingly
higher pressure level.
15 [0014] Air can also be decompressed at a plurality of locations in air separation
units, for which purpose decompression machines in the form of turboexpanders,
also referred to herein as "decompression turbines," may also be used, among
other things. Turboexpanders may also be coupled to and drive turbocompressors.
If one or more turbocompressors are driven without externally supplied energy,
20 i.e., only via one or more turboexpanders, the term "turbine booster" or "booster
turbine" is also used for such an arrangement. In a turbine booster, the
turboexpander (the decompression turbine) and the turbocompressor (the booster)
are mechanically coupled, wherein the coupling may take place at the same
rotational speed (for example via a common shaft) or at different rotational speeds
25 (for example via an interposed transmission).
[0015] In typical air separation units, corresponding decompression turbines are
present at different points for refrigeration and liquefaction of mass flows. These
are in particular what are known as Joule-Thomson turbines, Claude turbines, and
30 Lachmann turbines. In addition to the following explanations, reference is made
regarding the function and purpose of corresponding turbines to the technical
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literature, for example F.G. Kerry, Industrial Gas Handbook: Gas Separation and
Purification, CRC Press, 2006, in particular sections 2.4, "Contemporary
Liquefaction Cycles," 2.6, "Theoretical Analysis of the Claude Cycle," and 3.8.1.
"The Lachmann Principle."
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[0016] In the language as used herein, liquid fluids, gaseous fluids, or also fluids
present in a supercritical state may be rich or poor in one or more components,
wherein "rich" may refer to a content of at least 75%, 90%, 95%, 99%, 99.5%,
99.9%, or 99.99%, and "poor" may refer to a content of at most 25%, 10%, 5%, 1%,
10 0.1%, or 0.01% on a molar, weight, or volume basis. The term "predominantly" may
correspond to the definition of "rich" as was just given, but in particular denotes a
content of more than 90%. For example, if "nitrogen" is discussed here, this may refer
to a pure gas but also to a gas rich in nitrogen.
15 [0017] In the following, the terms "pressure level" and "temperature level" are
used to characterize pressures and temperatures, whereby it should be expressed
that pressures and temperatures do not need to be used in the form of exact
pressure or temperature values in order to realize an inventive concept.
However, such pressures and temperatures typically fall within certain ranges
20 that are, for example, ± 1%, 5%, or 10% around an average. Different pressure
levels and temperature levels may be in disjoint ranges or in ranges which
overlap one another. In particular, pressure levels, for example, include
unavoidable or expected pressure losses, for example due to cooling effects. The
same applies to temperature levels. The pressure levels indicated here in bar are
25 absolute pressures unless otherwise stated.