WO2007033838A1 - Air cryogenic separation method and device - Google Patents

Abstract

The invention relates to a method for the air cryogenic separation consisting in compressing an airflow (air quantity 2) in an air compressor, in cleaning at leas one part of the compressed air in a cleaning device, in cooling at least one part of the cleaned air, in introducing at least a part of the cooled air in the form of a used airflow (air quantity 1) into a distillation column system, in producing at least one product (GOX-product 2) is obtained in said distillation column system and in using at least one part thereof in the form of a first final product (GOX-product 1). The inventive cleaning device comprises at least two cyclically operating containers. A cycle consists of a loading phase, a thermal regeneration phase and a pressure build-up phase. During said pressure build-up phase, a part of the compressed air is directed to the container corresponding to the cleaning device. Prior to starting the pressure build-up phase, said used airflow is introduced into the capacity of the first used quantity in the distillation column system. During said pressure build-up phase, said used airflow is introduced into the capacity of the second used quantity which is less than the first used quantity in the distillation column system. A product flow is introduced into a buffer container and the final product flow is extracted therefrom. Prior to beginning the pressure build-up phase, the product flow is extracted from one part of a first quantity of product outside of the distillation column system and the final product is extracted from the buffer container in a first discharge quantity. During the pressure build-up phase, the product flow is extracted from the distillation column system in a quantity lesser than the first quantity and the second quantity of the final product is extracted from the buffer. The ratio between the second and first quantities is greater than the ratio between the second and second product quantities.

Description

 description

Method and apparatus for the cryogenic separation of air

The invention relates to a method for the cryogenic decomposition of air according to the preamble of patent claim 1, ie with thermally regenerated cleaning device (TSA - temperature swing adsorption).

Methods and devices for the cryogenic decomposition of air are known, for example, from Hausen / Linde, Tiefftemperaturtechnik, 2nd edition 1985, Chapter 4 (pages 281 to 337).

The distillation column system of the invention can be designed as a single-column system for nitrogen-oxygen separation, as a two-column system (for example as a classic Linde double column system), or as a three-column or multi-column system. It may have, in addition to the columns for nitrogen-oxygen separation, other devices for obtaining other air components, in particular noble gases, for example an argon recovery.

The monograph by Hausen and Linde (pages 307 to 309) also describes the cleaning of the feed air for such an air separation plant by means of a thermally regenerated molecular sieve in at least two containers. There impurities are removed from the air, which could hinder the cryogenic decomposition, especially water and carbon dioxide, possibly also other substances such as ethylene and nitrous oxide. While one of the two containers is being charged by air to be cleaned, the other can be regenerated by means of a Regeneriergasstroms heated to at least 100 ° C, preferably 150 to 200 ⁰ C. The regeneration gas used is normally a pressureless residual gas from the low-temperature decomposition, for example impure nitrogen from the low-pressure column of a two-column system. After completion of the regeneration phase, therefore, follows a pressure build-up phase, in which the pressure of the regenerated container is brought back to the outlet pressure of the air compressor. Only then can the feed air be switched to the regenerated container. During the pressure build-up phase, the throughput at the air compressor is usually increased in TSA processes and the additional amount of air as pressure build-up gas (switching air) is fed into the regenerated tank. Subsequently, the throughput at the air compressor is reduced back to normal. Thus, the amount of feed air introduced into the cryogenic decomposition can be kept constant. This section of the process does not "feel" anything about the build-up phase. This known method is shown in FIG. 1: FIG. 1, like all subsequent drawings, represents the time course of various amounts of current for a period of approximately 50 minutes. This period forms a section of a cycle, which in the examples lasts 100 to 300 minutes in total. The product stream is formed here by a gaseous oxygen stream ("GOX product"), which is taken directly from the distillation column system The curve "air quantity 2" represents the amount of air flow that is compressed in the air compressor (compression amount) The "application rate" is referred to as "air quantity 1." The "switching air quantity" forms the pressure buildup gas and is equal to the difference between the amount of compression and the amount used.

Alternatively, according to Figure 2, the compression amount can be kept constant. This has the advantage that the air compressor does not have to be dimensioned larger especially for the pressure build-up phase. However, the amount of use is reduced to the distillation column system according to the branched switching air quantity during the pressure build-up phase. Accordingly, the amount of product ("GOX product") and / or product purity decreases. Such a method is known from EP 947790 A1, where the aim is to avoid adverse effects on the separation process in the distillation column system.

The invention has for its object to further improve the economy of the method described above and the corresponding device.

This object is solved by the characterizing features of claim 1. The amount of feed air for the cryogenic separation is also lower here during the pressure build-up phase than during normal operation (before the start of the pressure build-up phase). After completion of the pressure build-up, the amount used is again increased accordingly. The corresponding difference between the amount of compression and the amount used is available as pressure build-up air (switching air) for air cleaning. The throughput at the air compressor must be correspondingly less or not increased. As a result, the air compressor needs to have correspondingly little overcapacity compared to the normal operation, the investment costs decrease accordingly. Is in electric drive of the air compressor maximum power consumption (power limit) specified or there are constraints in steam drive short-term increase in steam consumption, such boundary conditions can be optimally utilized in the inventive method, because during the pressure build-up phase little or no change in power consumption Air compressor are necessary.

In the method according to the invention, the product stream is introduced into a buffer vessel and the end product is removed from the buffer vessel. The product can be buffered in gaseous form, for example in a gas pressure vessel; this can also be formed by the piping system with which the end product is distributed and / or transported. Alternatively or additionally, the buffer container may be a liquid storage vessel, for example a liquid tank. As a liquid buffer but also existing containers can be used with liquid level, for example, a separator, the bottom of one or more columns or the evaporation space of a condenser-evaporator.

With liquid buffering, the end product can be dispensed in liquid form. Alternatively or additionally, the end product can be removed from the buffer container in liquid form, brought to an elevated pressure in the liquid state, vaporized against a process stream of high pressure (or pseudo-vaporized at supercritical pressure) and finally delivered as a gaseous pressure product.

Also combinations between gas and liquid buffering are possible.

According to the invention, although a reduced amount of product is generated during the pressure build-up phase. However, this only leads to a short-term reduced liquid level or storage pressure in the buffer tank. The delivery amount of The final product either only partially accounts for the reduction or remains completely constant.

It is preferable that the second discharge amount is equal to or substantially equal to the first discharge amount.

By "substantially the same" is meant a deviation of less than 1%, preferably less than 0.5%, most preferably less than 0.2%. "Essentially the same" includes complete equality.

It is favorable if a first compression amount is compressed in the air compressor before the start of the pressure build-up phase, during the pressure build-up phase a second compression amount is compressed in the air compressor and the first compression amount and the second compression amount are substantially equal. In short, the flow rate at the air compressor is kept unchanged at the beginning of the pressurization phase. Preferably, the flow rate at the air compressor remains constantly constant, if the control of the pressure build-up air is not superimposed by an automatic load adjustment.

In a further embodiment of the method according to the invention, the distillation column system is controlled by an automatic load control. Even if the discharge amount of the final product is constant, an automatic load control (ALC) is used in the method according to the invention. However, this is not (or not only) for adjusting the output of the final product to a fluctuating need, but vice versa for maintaining the required product purity with reduced amount of feed air during the pressure build-up phase.

In particular, when the discharge amount is constant over a long period of time, it proves to be advantageous if, before the start of the pressure build-up phase, the product quantity is greater than the discharge amount. In normal operation between two pressure build-up phases, a little more product is then produced in the distillation column system than is delivered to the consumers, preferably just enough to compensate for the temporarily reduced production during the pressure build-up phase. Thus, the amount of product and the amount of delivery over time or over one or several cycles of the cleaning device the same. For this purpose, although the entire system must be oversized accordingly, but only by a factor in the per thousand range, for example, by 4% ₀ . This is to be compared with the method according to FIG. 1, which requires an over-dimensioned air compressor of about 5%. Thus 4.6% of the compressor capacity is saved in the invention. This means a significant saving in investment costs, especially for very large plants.

The invention also relates to a device for cryogenic separation of air according to claim 6.

The invention and further details of the invention are explained in more detail below with reference to exemplary embodiments, to which the figures 3 to 5 relate.

Hereby show:

FIG. 3 shows the time course of important mass flows in a first exemplary embodiment of the invention with gaseous oxygen as the product and end product stream,

FIG. 4 shows an enlarged representation of data from FIG. 2 and FIG. 5 shows curves to a second exemplary embodiment with internal compression of oxygen.

The first embodiment relates to a classic two-column process for cryogenic air separation in which the distillation column system has a high pressure column and a low pressure column which are thermally coupled. Atmospheric air is filtered, compressed in an air compressor and then fed to a cleaning device. At least a portion of the purified air stream is cooled in a main heat exchanger against backflow and introduced as a "feed air stream" into the distillation column system. Gaseous oxygen is withdrawn from the lower region of the low pressure column as a "product stream", cooled in the main heat exchanger in indirect heat exchange with the feed air stream, and fed to a piping system which is the "buffer vessel." From the pipeline system, oxygen is withdrawn at several points for one or more consumers. The sum of these currents forms the "end product stream". FIGS. 3 and 4 show the time profile of the quantities of the following streams of the first embodiment:

GOX product 1 = Product flow ("Product quantity") GOX product 2 = End product flow ("End product quantity") Air volume 1 = Feed air ("Use quantity")

Air volume 2 = Air volume through air compressor ("Compression quantity") Switching air = Air volume for pressure build-up of the cleaning device = Difference between air volume 2 and air volume 1

During the pressure build-up phase (between times 2 and 5), the amount of compression remains constant. During this period switching air is diverted. The amount used decreases accordingly.

As part of an automatic load control, the operation of the distillation column system is adapted to the reduced amount used. Accordingly, the amount of product withdrawn from the distillation column system decreases. However, the end product quantity does not decrease, but the consumers are supplied with unchanged amounts of end product.

During the pressurization phase, the reservoir pressure in the pipeline drops slightly. However, between two stages of pressure build-up, it is increased back to its original value, because during this period the product quantity is slightly (0.4% in the example) above the final product quantity.

Of course, the stated time course can be superimposed by other load adjustments, which usually have a much larger period and depend, for example, on a varying demand for the end product.

The product stream is formed here by a gaseous oxygen stream ("GOX product 1") which is taken directly from the distillation column system The curve "air quantity 2" represents the amount of air flow that is compressed in the air compressor (compression amount The "amount used" is called "Air quantity 1". The "switching air quantity" forms the pressure buildup gas and is equal to the difference between the compression and the input quantity.

The second embodiment only differs from the first in that the "product stream" is formed by liquid oxygen from the low pressure column ("LOX product" in Figure 5) and a liquid tank is used as the "buffer tank". Liquid oxygen is taken from this liquid tank as a "final product stream", evaporated in the main heat exchanger and warmed and finally fed to the consumer or consumers ("GOX product" in FIG. 5).

Claims

claims

1. A process for the cryogenic decomposition of air, wherein

compressed air flow in an air compressor,

cleaned at least a part of the compressed air stream in a cleaning device,

cooled at least a portion of the purified air stream,

at least a part of the cooled air stream is introduced as feed air stream into a distillation column system,

at least one product stream is recovered in the distillation column system and at least partly discharged as end product stream,

the cleaning device has at least two containers which are operated cyclically,

a cycle has in each case a loading phase, a thermal regeneration phase and a pressure build-up phase, and

- During the pressure build-up phase, a portion of the compressed air flow is passed into the corresponding container of the cleaning device, wherein

- Before the start of the pressure build-up phase of the feed air stream in the amount of a first amount used in the distillation column system is initiated and

- During the pressure build-up phase of the feed air stream in the amount of a second application amount, which is less than the first amount used, is introduced into the distillation column system. characterized in that

- The product stream is introduced into a buffer tank and

- The end product stream is removed from the buffer tank, wherein

- Before the beginning of the pressure build-up phase, the product stream is removed from the buffer in the amount of a first product quantity from the distillation column system and the final product stream in a first discharge quantity, and

- During the pressure build-up phase, the product stream in the amount of a first product amount, which is smaller than the first product amount, from the distillation column system and the end product stream in a second discharge amount is removed from the buffer, and

the ratio between the second delivery quantity and the first delivery quantity is greater than the ratio between the second product quantity and the first product quantity.

2. The method according to claim 1, characterized in that the second discharge amount is equal to or substantially equal to the first discharge amount.

3. The method according to claim 1, characterized in that

- Before the start of the pressure build-up phase, a first compression amount is compressed in the air compressor,

- During the pressure build-up phase, a second compression amount is compressed in the air compressor and

- The first compression amount and the second compression amount are equal or substantially equal.

4. The method according to claim 1 or 2, characterized in that the distillation column system is controlled by an automatic load control.

5. The method according to any one of claims 1 to 4, characterized in that before the beginning of the pressure build-up phase, the product amount is greater than the discharge amount.

6. Apparatus for cryogenic separation of air with

an air compressor for compressing an air stream,

a cleaning device for cleaning at least a part of the compressed air stream which has at least two containers,

a main heat exchanger for cooling at least part of the purified air stream,

an input line for introducing at least part of the cooled air stream as feed air stream into a distillation column system,

Means for obtaining a product stream in the distillation column system,

Means for withdrawing at least a portion of the product stream as the final product stream and with

- Control means which cause a cyclical operation of the container of the cleaning device, wherein

a cycle has in each case a loading phase, a thermal regeneration phase and a pressure build-up phase, - During the pressure build-up phase, a part of the compressed air flow is passed into the corresponding container of the cleaning device, and

- The control means are designed so that

- Before the start of the pressure build-up phase of the feed air stream in the amount of a first amount used in the distillation column system is initiated and

- During the pressure build-up phase of the feed air stream in the amount of a second application amount, which is less than the first amount used, is introduced into the distillation column system. marked by

Means for introducing the product stream into a buffer tank and

- means for removing the end product stream from the buffer tank, wherein

- The control means are designed so that

- Before the beginning of the pressure build-up phase, the product stream is removed from the buffer in the amount of a first product quantity from the distillation column system and the final product stream in a first discharge quantity, and

- During the pressure build-up phase, the product stream in the amount of a first product amount, which is smaller than the first product amount, from the distillation column system and the end product stream in a second discharge amount is removed from the buffer, and

the ratio between the second delivery quantity and the first delivery quantity is greater than the ratio between the second product quantity and the first product quantity.