KR20010067037A - Process and apparatus for the purification of air - Google Patents

Abstract

PURPOSE: Provided is an air cleaning system by heat regenerating adsorption method capable of surely removing with high removing efficiency not only carbon dioxide and/or moisture but also trace gas component such as nitrogen monoxide, ethylene and/or propane from the air to be cleaned and capable of appropriately operating even in energy consumption respect. CONSTITUTION: At an adsorption cycle, the air to be cleaned is passed in order through the first adsorption zone housing the first adsorbent and the second adsorption zone housing the second adsorbent at the first temperature. At a regeneration cycle, regeneration gas is introduced into the first adsorption zone at the second temperature higher than the first temperature. Steam and/or carbon dioxide are almost completely removed in the first adsorption zone. The second adsorption zone is provided with the adsorbent containing a metal ion capable of strongly bonding nitrogen.

Description

Air purification method and apparatus {PROCESS AND APPARATUS FOR THE PURIFICATION OF AIR}

The present invention relates to an air purification method for removing impurities such as water, carbon dioxide, nitrogen oxides, ethylene and / or propane by temperature swing adsoorption.

This process typically uses cold air separation for the purification of the feed air, and the atmosphere is compressed and fed to the purifier. The purified air is then cooled and at least some of it is fed to the rectification column.

In thermal regeneration, impurities fixed in the adsorption cycle by the adsorbent are desorbed again by passing the adsorbent regeneration gas at a temperature T ₂ above the temperature T ₁ in the adsorption cycle. The temperature difference T ₂ -T ₁ is at least 30 K, for example in the range of 30 to 250K, preferably 80 to 180K. The process is carried out in at least a pair of switch-operable containers which are loaded in sequence (adsorption cycle) and desorption (regeneration cycle) as described, for example, in DE 2064137A. Typical adsorption temperatures are 5 to 35 ° C, preferably 7 to 20 ° C.

The adsorber pair (molecular sieve station), optionally thermally regenerated at a temperature of 80 to 250 ° C. for prepurification of the air before the cooling part of the air separation by rectification, consists of a well-known technique (DE 2064137 A). . Mainly, water and CO ₂ are separated as in acetylene (C ₂ H ₂ ) and are quite dangerous in liquid oxygen (LOX). Prior to 1970, there was no molecular sieve available industrially as an adsorbent, but instead at ambient temperature (water at 190 K (CO ₂ removal) for removal of hydrocarbons from liquid oxygen (LOX adsorber) to obtain the same effect. Multiple silica gel adsorbers operating at different temperatures down 90 K) were used. However, over the last 30 years, due to the burning of fossil fuels worldwide, safety-related trace gases have accumulated in the air and must be effectively removed before or during low temperature separation. This gas consists of N _X O _y and in particular unsaturated N ₂ O (0.3 to 0.5 Vppm) and also contains saturated hydrocarbons such as ethylene and propane (0.02 to 0.1 Vppm). If the gases are not removed effectively, they can cause shifts and agglomeration in the condenser at LOX cycles, especially at points involving oxygen vaporization, and have significant risks.

Conventional temperature-circulating adsorption processes with activated alumina and / or molecular sieve (zeolite) 13x beds have been adapted for the removal of CO ₂ within operating hours for economic reasons and generally switch from 2 to 8 hours, preferably 5 hours. Take up time. In practice, the shorter the switch run time, the greater the loss of containers and pipelines, resulting in a significant lower cost amount that requires more regeneration gas (heat is transferred through the adsorber within a corresponding short time) and more renewable energy. Ingredients are required. For molecular sieve type 13X (NaX), the specific capacity of the molecular sieve station (ratio of loading to gas phase concentration) when N ₂ O and propane are 35%, respectively, and operation at 6 to 10 bar and 5 to 20 ° C. Under the conditions 60% ethylene (in each case compared to the specific amount of CO ₂ ) has the specific capacity of the molecular sieve station. As a result, under conventional operating conditions where the concentration of CO ₂ decreases to 1:10 ⁶ , 60 to 80% is retained for N ₂ O and C ₃ H ₈ and 70 to 90% is retained for C ₂ H ₄ do. More than 95% of the hold required for safe operation is achieved after half the operating time. However, operating costs of more than 30% are foreseeable, and not unusual, if a larger volume of regeneration gas stream is available in the process.

A known solution to the trace problem is a short-term adsorber without a regeneration gas heater, which is regenerated only by pressure circulating adsorption (PSA) as described in EP 862938A and DE 3702190A. This process is characterized by a reduction in specific load by two factors for traces and five factors for CO ₂ that are less affected by temperature reduction than steel-bonded CO ₂ . Typical operating time is 2 to 25 minutes. Because the variable reductions in capacity for initial components such as CO ₂ , N ₂ O / C ₃ H ₈ , and C ₂ H ₄ remain approximately the same, a retention of 99% is achievable, respectively. However, due to the desorption of water at low temperatures, the process requires 2.5 times the amount of regeneration gas compared to the TSA variant, has a larger switch operating loss due to more frequent switch operations and a high compressor power of approximately 10%. in need. O ₂ plants that can provide excess nitrogen from known separations for regeneration due to the lack of use of the product are suitable. Another disadvantage of the PSA process is the reduction of the CO ₂ concentration compared to the TSA variant due to the residual load during cold regeneration. It is reduced from 1:10 ⁶ to a value of approximately 1:10 ³ , allowing only impurities in the range of 0.1 to 1 Vppm. This is, for example, in the case of a large air separator of 300,000 m ³ (STP) per day of air, the amount of CO ₂ transferred to the cooling section is 10 Kg. More frequent thawing is required to reduce circulation to the cold box in the main heat exchanger. TSA systems, on the other hand, use 0.01 Kg of CO ₂ per day and can be easily moved in the gas stream.

Another solution to the trace problem is to supplement an additional LOX adsorber with silica gel to filter N ₂ O from LOX. Disadvantages from complex designs due to large temperature changes during regeneration, in particular, lead to LOX losses and the loss of expensive useful material xenon in part to the regeneration gas. Moreover, the most suitable material for use with LOX and N ₂ O consists of a small amount of hydrocarbon.

Accordingly, it is an object of the present invention to remove safety-related trace gases, such as nitrogen oxides, ethylene and / or propane, which can be easily purified from CO ₂ and / or air and can be particularly preferably operated from an energy standpoint. It is to provide a temperature cycle adsorption process and a corresponding apparatus.

This object is achieved by the features of claim 1. Particularly preferred embodiments are described in claims 2 to 5. As used herein, the term "essentially complete removal" means a retention of at least 80%, preferably at least 90%, most preferably at least 95% or at least 99%.

1 shows a device of an embodiment according to the invention.

* Description of the symbols for the main parts of the drawings *

2: filter 3: main air compressor

10: main heat exchanger 13: heater

100: purification device 101-108: valve

110, 111: Container

In the present invention, the various separation operations are distributed over at least two adsorption zones each installed with specific adsorbents adapted for the separation operation, through which the air is continuously purified. The two regions can be perceived by two beds arranged one above the other. Optionally, the second region may be arranged in an independent container connected by a line to the container comprising the first adsorption region. In two variations, the second adsorption zone can be heat generated together with the first adsorption zone, and in the second case the regeneration of the two zones can be influenced independently of each other. For example, the second adsorption zone may have a different regeneration temperature and may use pressure cycling adsorption (PSA) instead of temperature cycling adsorption.

The first adsorption region contains, for example, a non-substituted zeolite such as 13X and / or a conventional adsorbent such as silica gel and activated alumina. It in turn has a two-layer structure, forming a three-layer structure as a whole. For example, the air to be purified first flows through a first partial region consisting of activated alumina or silica gel, predominantly removes water vapor, passes through a zeolite (e.g., CaX), in particular to a second adsorption region. Strongly adsorb carbon dioxide before passing through.

In the second adsorption zone, a strong nitrogen bound adsorbent is used. "Strongly nitrogen-binding" is the removal of atomic nitrogen in relatively large amounts by adsorption compared to gas streams, in particular conventional adsorbents which are commonly used for the purification of water and / or carbon dioxide from air. I understand. Thus, the addition of strong nitrogen, i.e. nitrogen formation, causes metal ions to increase in nitrogen loading by at least 1.5, preferably 2.5 factors in the adsorbent compared to the undoped material.

For example, the typical specific adsorption capacity for 0 ° C (1 (S.T.P.) / Kg bar) is

Activated Alumina / Silica Gel: 0.5 to 2

Activated Carbon: 9

NaX Zeolite Molecular Sieve 13X: 11

CaA Molecular Sieve 5A: 20 and

CaX Molecular Sieve: 28

In the present invention, the material having a value of at least approximately 18 l (S.T.P.) / Kg bar at 0 ° C is a strong nitrogen bond. Adsorption temperature is important as a reference dose for the comparison of materials as it affects the capacity. Such materials are known for nitrogen / oxygen separation, for example by adsorption.

The purifying process according to the invention is preferably used upstream of the air separation plant to regenerate the air, in particular the main component of nitrogen, in particular at first glance purifying an adsorbent which can accurately and effectively adsorb one of the components required as the product. Can't detect in stage However, the loss of nitrogen lies in the range of 0.2-0.5% due to the long time for the strong nitrogen-bonded material, but this can be negligible compared to the loss of approximately 20% of regenerated gas.

In the present invention, it has further been found that strong nitrogen-bonded adsorbents effectively adsorb nitrogen oxides, ethylene, and propane. This relationship is not directly clear since the molecular properties of nitrogen compounds such as nitrogen oxides have extremely limited identity with those of atomic nitrogen, and since nitrogen atoms are not present in ethylene and propane. Possible interpretations of this have the common characteristics of chemical multiple bonds in molecules and the present invention is not limited to the above theory and substantially increases resistance to the center of the polar metal in the adsorbent.

In the present invention, the second adsorption zone is equipped with an adsorbent specifically tailored to the trace. CaX, Ca-exchange NaX materials are particularly suitable for this purpose. It has, for example, five times the specific adsorption capacity for N ₂ 0 compared to 13 ×, and twice the capacity for hydrocarbons.

However, these materials also have disadvantages. Thus, the adsorption capacity for CO ₂ is reduced to a value of approximately 80% compared to 13 ×. Because of this, the strength is weaker and the effective operating time is reduced to approximately 60% compared to 13X due to the very wide range of local adsorption fronts. When used in correspondence with 13X, the decrease in CO ₂ concentration drops to a value of approximately 1:10 ³ and reaches the same ratio as for the PSA modification. In addition, the exchanged materials are quite expensive, more complex to produce, and less stable to liquid water. Thus, it initially appears to be unsuitable as an adsorbent for the purification of the atmosphere upstream of the low temperature air separator.

According to the invention, a single element is distributed over the use of a plurality of materials having properties for the individual components. This may in each case be arranged in a layer in the adsorber in such a way that a more suitable material is present where the main concentration of the corresponding component is expected. For example, activated alumina can be provided at the air inlet to remove H ₂ O, C ₊₅ , SO _X , NO, NO ₂ , N ₂ O ₃ and nitrogen oxides and acidic components. Optionally, the celica gel or molecular sieve (13X) is suitable as a second layer to remove the main components of CO ₂ , C ₂ H ₂ , C ₃ H ₈ , C ₄₊ and C ₂ H ₄ and C ₃ H ₈ Do. These two layers form a two part region within the "first adsorption region". Finally, the "second adsorption zone" for removing residues of the third layer, N ₂ O and C ₂ H ₄ , C ₃ H ₈ is as follows. These materials are mainly Ca-exchanged Na zeolites such as CaA (5A) and / or CaX, but Li-, Ti-. It is also possible to use zeolites and / or gels with addition of boron. In addition to the multilayer structure, a material comprising two types of mixed crystals (composites) or a mixed bed comprising both materials can be used with a slight increase in efficiency in the region of the upper two molecular sieves.

In the present invention, N ₂ O, C ₂ H ₄ , and C ₃ H ₈ are withheld by adding a specific zeolite layer to the aforementioned traces without using an optimal 13X bed for CO ₂ removal for the overall non-specific material. It is additionally possible to augment conventional molecular sieve stations with TSA operation in order to include A or X materials or silicates containing pure or mixed dopants comprising Ca, Li, Ti and / or boron. do. For example, in the case of exchange doping with CaX and CaA, Li, Ti, and boron, the Ca-Na exchange degree of 20 to 100% Ca, preferably 70% is 50 to 100%, preferably 90%. Here, the Ca-exchanged zeolite and / or the doped silicate layer form a "second adsorption region" and the conventional molecular sieve station forms the "first adsorption region" in the present invention.

Inclusion of N ₂ O—, and hydrocarbon-active layers results in effective removal of the traces before the cooling portion of the air separator increases the safety of the entire plant by the determined TSA technique. Additional layer limitations for N ₂ O, C ₂ H ₄ , C ₃ H ₈ allow for materials that do not have high capacity of CO ₂ , such as in economical material 5A. Even when using expensive doped X zeolites, a high specific price is acceptable due to the fact that only a small bed fraction of the material is present. Furthermore, the retention of the 13X layer is suitable for CO ₂ guarantee or is reduced, or that only a small amount of decrease in the reduction of the CO ₂ concentration. The most distinctive advantage is that existing plants can be updated in a simple and economical way by providing an additional small amount of layers.

Various adsorbents can be recognized as beds arranged on top of other (horizontal adsorbers) as concentric annular beds whose flow is radial (radial adsorbers). Suitable arrangements for use in the present invention are described in "Design of Adsorption Dryers in Air Separation Plants" by "LINDE reports from Industry and Science" on pages 71/1994, 8-12, and DE 3243656A, EP 402783B1, DE19600549A and DE 19735389C1. Is disclosed. The “second adsorption zone” for N ₂ O, C ₂ H ₄ , and C ₃ H ₈ can be regenerated without a heater if the adsorption zone is embedded in a separate container.

The invention also relates to a device according to claims 6 and 8 and is used in accordance with claims 7.

The invention and more details of the invention will be explained in more detail with reference to two embodiments.

Three process embodiments, which are variants of the bed, are described.

(1) A molecular sieve station comprising a cylindrical layered bed in which the flow is axial and one arranged on top of the other includes the prior art activated alumina and NaX zeolite (molecular sieve 13X).

(2) The upper bed area of the molecular sieve station, 13X, according to (1) is replaced with CaA zeolite (molecular sieve 5A) as the first embodiment of the present invention.

(3) The molecular bed station of 13X, another molecular sieve station according to (1), is replaced by CaX (86% calcium exchange molecular sieve 13X) zeolite as a second embodiment of the present invention.

The following applies in common to all variants.

Air inlet air volume: 21,500 m ³ (STP) / h

Pressure: 6.0 bar (a), temperature (T ₁ ): 12.5 ° C

Switch operation time of molecular sieve station: 7.0 h

Regenerative gas gas volume: 4400 m ³ (STP) / h

Heating temperature (T ₂ ): 185 ° C, cooling temperature: 17 ° C

Pressure: 1 bar (a), heating / cooling time: 2.2.h / 4.2h

Pressure cycle time: 0.6h

Trace concentration H ₂ O 2450 Vppm

CO ₂ 370 Vppm

N ₂ O 0.35 Vppm

C ₃ H ₈ 0.08 Vppm

SO _X 0.07 Vppm

NO _X 0.05 Vppm

C ₂ H ₄ 0.04 Vppm

C ₂ H ₂ 0.02 Vppm

C ₃ H ₈ 0.02 Vppm

C ₄₊ 0.02 Vppm

Inseparable Ne 18 Vppm

Trace CH ₄ 2 Vppm

H ₂ 0.5 Vppm

0.3 Vppm CO

Kr 0.3 Vppm

C ₂ H ₆ 0.1 Vppm

Xe 0.08 Vppm

(The above components are kept in amounts of up to 10% in all variants. However, this does not pose a safety hazard. In the case of rare gases, this is undesirable.)

Bed (Modification 1-3)

(1) 2000 kg (= 200 mm) activated alumina

7000 kg (= 900 mm) molecular sieve 13x

(2) 2000 kg (= 200 mm) activated alumina

5300 kg (= 680 mm) molecular sieve 13x

1900 kg (= 220 mm) molecular sieve 5A

(3) 2000 kg (= 200 mm) activated alumina

5200 kg (= 680 mm) molecular sieve 13x

1800 kg (= 220 mm) Molecular Sieve CaX

Container diameter (all variants): 4000 mm

Degree of Hold by Individual Variation (1-3)

(1) H ₂ O> 99.99999%

CO ₂ 99.9997%

C ₂ H ₂ , C ₃ H ₆ , C ₄₊ , NO _X (excluding N ₂ O) and SO _x 99.9%

N ₂ O 70%

C ₃ H ₈ 73%

C ₂ H ₄ 82%

(2) H ₂ O> 99.99999%

CO ₂ 99.995%

C ₂ H ₂ , C ₃ H ₆ , C ₄₊ , NO _X (excluding N ₂ O) and SO _x 99.9%

N ₂ O 92%

C ₃ H ₈ 88%

C ₂ H ₄ 93%

(3) H ₂ O> 99.99999%

CO ₂ 99.999%

C ₂ H ₂ , C ₃ H ₆ , C ₄₊ , NO _X (excluding N ₂ O) and SO _x 99.9%

N ₂ O 98%

C ₃ H ₈ 94%

C ₂ H ₄ 97%

Gradually from modifications (1) to (3) to (3), the average content of critical components in the exhaust air is as follows.

(1) (2) (3)

CO ₂ 0.001 0.019 0.004 Vppm

N ₂ O0.105 0.028 0.007 Vppm

C ₃ H ₈ 0.022 0.010 0.005 Vppm

C ₂ H ₄ 0.007 0.003 0.001 Vppm

The figure schematically shows the apparatus of embodiment (3).

Atmosphere is drawn into the main air compressor 3 via the filter 2 along the line 1. After recooling 4, the compressed air 5 flows to the water separator 6, from which the liquid water 7 is removed. Air 8 supplied from the liquid component is supplied to a purification apparatus 100 having two containers 110, 111. By means of valves 101-108, the purifier is operated so that in each case air 8 is supplied (adsorption cycle) to one of the containers 110, 111, while the other container 110, 111 is regenerated (regeneration cycle). do.

The purified air 9 is fed to the main heat exchanger 10 and cooled to the purge temperature for the return flow and finally at least partially supplied to the rectification column of the low temperature separation via line 11.

The residual gas 12 from the low temperature separation is heated to approximately ambient temperature in the main heat exchanger 10 and more heated in the heater 13 to the heating temperature T ₂ of the regeneration cycle. The hot regeneration gas then flows via line 14 to containers 110 and 111 placed in a heated state (hot flush) of the regeneration cycle. Downstream of the purification apparatus 100, residual gas is discharged to the atmosphere via line 15.

At a certain time, for example, container 110 is placed in an adsorption cycle. That is, valves 101 and 105 are open while valves 102 and 106 are closed.

The container 111 is placed in a regeneration cycle. Various phases: pressure reduction (only valve 104 is open), high temperature flushing (valve 108 is additionally open and heater 13 is active), cooling flushing (heater shut down), pressure composition (valve 103 ), Only open), etc. are generated continuously.

Then, the containers 110 and 111 are operated so that the containers 111 are placed in the adsorption cycle and the containers 110 are switched in such a manner that they are in the regeneration cycle.

Letters a, b, and c represent three beds in two containers.

a: activated alumina

b: molecular sieve 13x

c: molecular sieve CaX

In an embodiment, layers (a, b) form a first adsorption zone and side (c) forms a second adsorption zone. Optionally, the first adsorption region a + b may have a monolayer structure and may consist, for example, of activated alumina or molecular sieve 13x.

Impurities such as water, carbon dioxide, nitrogen oxides, ethylene, and propane can be removed by the temperature cycling adsorption according to the present invention.

Claims (8)

A method for purifying air to remove impurities such as water, carbon dioxide, nitrogen oxides, ethylene, and / or propane by temperature cycling adsorption, The air to be purified in the adsorption cycle is continuously passed at the first temperature T ₁ through the first adsorption zone containing the first adsorbent and the second adsorption zone containing the second adsorbent, At 2 temperatures T ₂ , regeneration gas is introduced into the first adsorption zone, In the first adsorption zone, water vapor and / or carbon dioxide is completely removed from the air, And the second adsorption zone comprises an adsorbent containing strong nitrogen-bonded metal ions. The method of claim 1 wherein said adsorbent in said second adsorption zone comprises calcium, lithium, titanium, and / or boron ions as strong nitrogen bonding metal ions. The method of claim 1 or 2, wherein the adsorbent in the second adsorption zone comprises zeolite and / or silicate as carrier material. 4. The method of any one of claims 1 to 3, wherein in the first adsorption zone, the air to be purified is successively passed into two zones: a first zone and a second zone containing different adsorbents. Wherein the first zone comprises activated alumina and / or silica gel and the second zone comprises a zeolite material. 5. The method of claim 1, wherein the second adsorption zone comprises mixed crystals and / or mixtures with a carrier material and a non-substituted zeolite doped with strong nitrogen bonded metal ions. 6. An apparatus for purifying air to remove impurities such as water, carbon dioxide, nitrogen oxides, ethylene and / or propane by means of temperature cycling adsorption, A first adsorption zone with a first adsorbent that predominantly binds water vapor and / or carbon dioxide, A second adsorption zone with a second adsorbent containing strong nitrogen-bonded metal ions, and And heating means connected by the regeneration gas line to the first adsorption zone and / or the second adsorption zone. As a method according to any one of claims 1 to 5 and the use of the device according to claim 6 in a process for low temperature separation of air, The purified air from the second adsorption zone is at least partially cooled and is supplied to the rectification column as feed air. A device for low temperature separation of air, At least one rectification column, and A supply air line leading to said rectifying column via a heat exchanger from a second adsorption zone of the device according to claim 6.