JP2000024444A - Method and apparatus for producing highly purified dry air - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for producing high-purity dry air which can supply high-purity dry air efficiently and stably. SOLUTION: The method includes a raw air compression step, a catalyst purification step for removing hydrogen and carbon monoxide, and an adsorption purification step for removing moisture and carbon dioxide.
000 h ^-1 or less, and the adsorption purification step is performed with a desiccant bed and a gas impurity remover bed, and the space velocity of the desiccant bed is 110
00h ^-1 or less, the space velocity of the gas impurity removing agent bed is 600
0h ^-1 or less. Further, in the adsorption purification step, the switching time is set to 4 to 12 hours, the regeneration temperature is set to 100 ° C. or more, and the regeneration gas ratio is set to 40% or less by using two adsorption cylinders used for switching. As a result, carbon monoxide, hydrogen, carbon dioxide, and moisture in the raw material air are removed to 10 ppb or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing high-purity dry air, and more particularly to a method for producing dry air used not only in water but also in a semiconductor manufacturing plant or a liquid crystal manufacturing plant. The present invention relates to a method and an apparatus for producing high-purity dry air that can be supplied with as little impurities as possible.

More specifically, it is also used as a gas for protecting a wafer at a place where it may come into contact with the outside air, for example, when storing and transporting a wafer (a thin substrate or a substrate) in a semiconductor manufacturing plant. METHOD AND APPARATUS FOR PRODUCING POSSIBLE HIGH CLEAN DRY AIR.

[0003]

2. Description of the Related Art Conventionally, dry air used in semiconductor manufacturing factories and liquid crystal manufacturing factories is mainly used for driving a machine, operating a valve, pumping a chemical solution, purging a pure water tank, and the like. there were. Therefore, the manufacturing apparatus and method are also very common, in which the air is sucked, the air is compressed to a predetermined pressure by an air compressor, and, depending on the situation, particles are removed using a filter, and then adsorption separation or separation is performed. General-purpose dry air is produced and supplied by removing water contained by membrane separation.

[0004] The specifications of dry air normally used include a pressure of 0.5 to 0.7 MPa, a dew point of -70 ° C, and a flow rate of 1500 to 1500.
3000 Nm ³ / h is general, and the user installs each of the above-described devices in the premises of the company's factory and performs self-management.

[0005] On the other hand, wafers and the like in the manufacturing process of semiconductor manufacturing factories and liquid crystal manufacturing factories are exposed to air if the protective measures are not sufficiently taken when moving or storing between machines. Due to the effects of moisture, oxygen, hydrocarbons, etc. in the air, impurities adhere to the surface, which causes various problems such as deterioration of characteristics and increase in the number of cleaning steps, and causes of cost increase. I have.

In order to prevent this, there is an example in which a simple box is manufactured and measures such as purging with nitrogen gas are performed.

[0007]

However, strict quality is required for manufacturing technology in future semiconductor manufacturing plants and liquid crystal manufacturing plants, and further economic and efficient production of products is required due to price competition. Have been.

In particular, protection measures for wafers and the like in a manufacturing process in a semiconductor manufacturing factory, a liquid crystal manufacturing factory, and the like are regarded as important items from the viewpoint of maintaining product characteristics and reducing costs.

For the above purpose, highly purified dry air is required as a protective atmosphere gas as a highly sophisticated need. At present, high-purity dry air, which is required as an atmospheric gas in semiconductor manufacturing factories and liquid crystal manufacturing factories, specifies that impurities contained in air, for example, impurities such as moisture, carbon monoxide, carbon dioxide, and hydrogen are each 10 ppb. It is a strict thing to supply in the following.

Therefore, in order to satisfy such specifications, the purification conditions in each step require strict values even in the purification method.

Accordingly, an object of the present invention is to provide a method and apparatus for producing high-purity dry air that can supply the high-purity dry air efficiently and stably.

[0012]

In order to achieve the above object, a method for producing highly purified dry air according to the present invention comprises a compression step of compressing raw air, and removing hydrogen and carbon monoxide in the raw air. This is a method for producing highly purified dry air by a catalyst refining step and an adsorption refining step for removing water and carbon dioxide. In the first configuration, the catalyst refining step is performed at a space velocity of 3000 h ^-1 or less, preferably 2,000 h. ~ 3000h
^-1 .

[0013] In the second configuration, the adsorption and purification step is performed by passing the raw material air in the flow direction through a desiccant bed and a gas impurity removing agent bed, and the space velocity of the desiccant bed is set to 11000 h. ^-1 or less, preferably 9000
And 11000H ^-1, the space velocity of the gaseous scavenger bed 6000h ^-1 or less, preferably 4000～6000H ^-1
It is characterized in that each is performed.

Further, in a third configuration, the adsorption / purification step is performed by using two adsorption cylinders that are switched, and the switching time is 4 to 12 hours, preferably 6 to 10 hours, and the regeneration temperature is 100 ° C. or higher. , Preferably at 120 ° C. or higher, and the regeneration gas ratio at 40% or lower, preferably 20% or lower.

In particular, the method for producing highly purified dry air of the present invention comprises a compression step of compressing raw air, a catalyst purification step of removing hydrogen and carbon monoxide in the raw air, and a step of removing water and carbon dioxide. The catalyst purification step is performed at a space velocity of 3000 h ^-1 or less, and the adsorption purification step is performed by passing the raw material air through a desiccant bed and a gas impurity removing agent bed in the flow direction. And the space velocity of the desiccant bed is set to 11000 h ^-1 or less, and the space velocity of the gas impurity removing agent bed is set to 6000 h ^-1 or less. The switching time is 4 to 12 hours, the regeneration temperature is 100 ° C. or more, and the regeneration gas ratio is 40% or less, so that the carbon monoxide, hydrogen, carbon dioxide, water It is characterized in that less 10ppb each.

In the method for producing highly purified dry air according to the present invention, the highly purified dry air which has undergone the above-mentioned adsorption purification step is collected as a product and a part thereof is supplied to an air liquefaction / separation apparatus. Collecting and purifying high-purity dry air after use in the used equipment, increasing the pressure, and mixing it into either the raw air before the catalyst purification step or the raw air before or after the adsorption purification step. I have.

Further, the present invention is characterized in that the used highly purified dry air or the exhaust gas of the air liquefaction / separation apparatus is used as a regeneration gas in the adsorption / purification step.

Further, the apparatus for producing highly purified dry air of the present invention comprises an air compressor for compressing raw air, a catalyst purifier for reacting hydrogen and carbon monoxide in the raw air with oxygen,
An apparatus for producing high-purity dry air comprising an adsorption purifier for removing impurities such as water and carbon dioxide contained therein,
The catalyst used in the catalyst purifier is Pd, Pt, Au,
A metal catalyst mainly composed of one or a combination of a plurality of metals such as Fe, Cr, Ni, Co, Mn, Cu, Sn and Zn, or an alloy composed of any combination of these metals. And the metal catalyst is filled in the catalyst purifier in an amount of 0.33 liter or more per unit air amount.

Further, the apparatus for producing high-purity dry air of the present invention comprises an air compressor for compressing raw air, a catalyst purifier for reacting hydrogen and carbon monoxide in the raw air with oxygen, and An apparatus for producing high-purity dry air, comprising: an adsorption purifier for removing impurities such as carbon, comprising: at least two cylinders used by the adsorption purifier for switching, wherein activated alumina and / or silica gel are sequentially supplied from the inlet. It has a desiccant bed filled with 0.09 liter or more per unit air amount (1 Nm ³ ) and a gas impurity removing agent bed filled with 0.17 liter or more of synthetic zeolite per unit air amount. And

Further, the synthetic zeolite is characterized in that it is a single or a combination of a plurality of Na-X-type zeolites, Ca-X-type zeolites, and Ca-A-type zeolites.

Further, a path for supplying high-purity dry air derived from the adsorption purifier as a product to a facility to be used, a path for recovering the high-purity dry air after use in the facility, and a path for recovering the high-purity dry air Means for increasing the pressure, and a path for mixing the recovered high-purity dry air into the raw material air in at least one place before or after the catalyst purifier, before or after the adsorption purifier, and provided in each of these paths. A heat exchanger for exchanging heat between the raw material air in the outlet path of the catalyst purifier and the highly purified dry air in a path branched from the outlet path of the adsorption purifier. It is characterized by that.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram showing one embodiment of the apparatus for producing highly purified dry air of the present invention. The apparatus for producing high-purity dry air includes an air compressor 1 for compressing raw air, a catalyst purifier 2 for reacting hydrogen and carbon monoxide in the raw air with oxygen, and an impurity such as carbon dioxide contained therein. The catalyst purifier 2 removes hydrogen and carbon monoxide from the raw material air compressed by the air compressor 1 by reacting with oxygen in the catalytic purifier 2. By removing water and carbon dioxide in the
10p each of carbon monoxide, hydrogen, carbon dioxide and water
The high-purity dry air removed to pb or less is produced and supplied to the use equipment 4 as the product high-clean dry air.

The air compressor 1 sucks the atmosphere and raises the pressure to a required pressure. Any type can be used according to the compression pressure and the flow rate. For example, when the required pressure is 0.75 MPa and the flow rate is 5000 Nm ³ / h, a turbo type can be used.

The catalyst purifier 2 has a cylinder filled with a metal-based catalyst.
Pd, Pt, Au, Fe, Cr, Ni, Co, Mn, C
Metals such as u, Sn, Zn and the like can be used as a main component by a single substance or a combination of a plurality of metals, or an alloy mainly composed of an alloy composed of any combination of these metals can be used.

When a noble metal-based catalyst, for example, a Pd-based catalyst is used, the Pd-based catalyst is filled in at least 0.33 liter per 1 Nm ^{3 of} air, and the space velocity is increased to 3000.
h ^-1 or less, preferably 2000 to 3000 h
By setting to ^-1 , hydrogen and carbon monoxide in the raw material air can be oxidized to water and carbon dioxide by catalytic reaction,
The contents of hydrogen and carbon monoxide can each be reduced to 10 ppb or less. At this time, if the space velocity is too high, the removal efficiency may decrease. If the space velocity is too low, the treatment amount decreases and the catalyst amount increases, resulting in uneconomic.

The above-mentioned catalytic reaction can be carried out at 150 ° C. to 190 ° C. in the case of removing hydrogen and carbon monoxide, and when the trace amount of methane, ethane, propane, etc. is also removed simultaneously, the temperature is raised to about 350 ° C. And do it.

In the present embodiment, as a means for raising the temperature of the raw material air to the above-mentioned catalytic reaction temperature, the catalyst purifier 2
Before and after, a heater 5 and a heat exchanger 6 are provided.

That is, when the catalyst reaction temperature is higher than the temperature due to the compression heat of the air compressor 1, the catalyst purifier 2
The heat of the hot air after the reaction is recovered by exchanging heat between the inlet air and the outlet air in the heat exchanger 6.
Further, the shortage is heated by the heater 5.
With such a configuration, the device can be operated with improved thermal efficiency.

On the other hand, a pre-cooling facility 7 is provided upstream of the adsorption purifier 3. This precooling equipment 7 is for cooling the inlet air of the adsorption purifier 3 to 5 to 10 ° C. The pre-cooling equipment 7 is formed by, for example, a water cooler and a drain separator (not shown). The pre-cooling equipment 7 cools the raw material air to condense the water and removes the water as a drain in advance, so that the adsorption purifier 3 is removed. The amount of water brought into the interior is reduced. Thereby, the operation efficiency of the adsorption purifier 3 can be improved.

At this time, the lower the cooling temperature of the raw material air, the higher the drain amount increases and the load on the adsorption purifier 3 can be reduced. However, the cooling temperature may be within the above temperature range, and the cooling method is not particularly limited. Not something.

The adsorption purifier 3 has a cylinder filled with an adsorbent for adsorbing and removing moisture and carbon dioxide. The adsorbent can be filled with a suitable adsorbent singly or in a mixture of plural kinds in the entire cylinder, but in order from the inlet of the raw material air, a water removing agent such as activated alumina or silica gel is filled. A desiccant bed for absorbing and removing moisture;
It is preferable to provide a gas impurity removing agent bed filled with a synthetic zeolite in which a single zeolite or a combination of a plurality of X-type zeolites, Ca-X-type zeolites and Ca-A-type zeolites are provided.

For example, by filling alumina gel as a water removing agent near the bottom of the cylinder at the compressed air inlet and Na-X type synthetic zeolite at the outlet side, the water and carbon dioxide in the raw material air and the catalyst purification can be purified. The water and carbon dioxide generated by the reaction in the vessel 2 can be efficiently adsorbed and removed together. At this time, the filling ratio between the alumina gel and the synthetic zeolite is usually about 1: 2 in volume ratio.

Then, the space velocity of the desiccant bed is set to 110
00h ^-1 or less, preferably a 9000～11000H ^-1, the space velocity of the gaseous scavenger bed 6000h ^-1 or less, preferably by performing each as 4000～6000H ^-1, carbon dioxide, water, respectively 10pp
b or less. At this time, if the space velocity is too high, the removal efficiency may decrease. If the space velocity is too low, the treatment amount is reduced and the adsorbent amount is increased, which is not economical.

The adsorption purifier 3 is provided with two adsorption columns filled with the adsorbent, and a switching operation is performed such that when one adsorption column is in the adsorption step, the other adsorption column is in the regeneration step. The raw material air is continuously purified.

The regeneration process of the adsorption cylinder is performed by a heating regeneration stage and a cooling stage. The heating and regeneration gas used in the heating and regeneration stage and the cooling gas used in the cooling stage are basically based on a part of the purified gas (product high-purity dry air) that has completed the adsorption process. By using gas containing no or very little hydrogen, carbon monoxide, etc., for example, high-purity dry air used in the use equipment 4 or exhaust gas from the air liquefaction / separation unit, the product high-purity dry air can be regenerated. Since it is not used, the yield can be improved.

The regeneration temperature in the heating regeneration step varies depending on the heating regeneration time, the heating regeneration gas amount, and the like.
150 ° C. In the apparatus of the present embodiment, the heat exchanger 8 is used as a heating means for raising the temperature of the heated regeneration gas to this temperature.
And a heater 9 are provided. The heat exchanger 8 exchanges heat between the outlet air of the catalyst purifier 2 that has passed through the heat exchanger 6 and a gas used for the heating and regeneration gas, recovers the heat of the exit air, and raises the temperature of the heating and regeneration gas. When the temperature is not raised to a predetermined temperature by the heat exchange in the heat exchanger 8, the heater 9 is further heated to the predetermined temperature.

When the temperature can be raised to a predetermined temperature by the heat exchanger 8, the heater 9 is unnecessary, and the heater 9 can be formed so as to heat only the heater 9 without providing the heat exchanger 8.

On the other hand, the cooling gas in the cooling stage is supplied to the heat exchanger 8
It is sufficient to directly introduce the gas into the adsorption column without passing through the heater 9.

When the purification of the raw material air is performed by switching the two adsorption columns between the adsorption step and the regeneration step, the switching time between the two steps is 4 to 12 hours, preferably 6 to 10 hours.
By setting the time and the regeneration temperature to 100 ° C. or higher, preferably 120 ° C. or higher, and the regeneration gas ratio to 40% or lower, preferably 20% or lower, efficient operation can be performed.

When a gas from another process, such as a used high-purity dry air or an exhaust gas from an air liquefaction separator, is used for regeneration, the operation balance of the process is taken into consideration. The heat exchanger 5 and the heat exchanger 8
May be exchanged, and the outlet air of the catalyst purifier 2 may be introduced first into the heat exchanger 8 to raise the temperature of the heated regeneration gas.

The high-purity dry air purified by the adsorption purifier 3 is supplied through a path 10 to use equipment 4 such as a semiconductor manufacturing plant, a high-density recording medium manufacturing plant, or a liquid crystal manufacturing plant. Further, by providing the branch path 11 in the path 10, a part of the high-purity dry air can be supplied as a raw material of the air liquefaction / separation apparatus.

Further, in the present embodiment, the high-purity dry air used in the use facility 4 after use is recovered from the passage 12. The recovered high-purity dry air is used as a heating / regenerating gas via a path 13 and a valve 14 or is supplied through a path 15 and a valve 16 depending on the degree of contamination and the amount of recovery. Mix and circulate in clean dry air, or route 1
7. It can be mixed into the raw material air before the adsorption purifier 3 through the valve 18. Further, it can be mixed into the raw air before the catalyst purifier 2 via the path 19 and the valve 20.

As a result, the utilization efficiency of the high-purity dry air can be increased, and the size and the operating cost of the high-purity dry air production apparatus can be reduced. In addition, when highly clean dry air is collected and reused, it may be compressed by the compressor 21 as needed.

[0044]

EXAMPLE With the apparatus configuration shown in the above embodiment, 4000N
A high-purity dry air producing apparatus for producing high-purity dry air of m ³ / h was manufactured. The operating conditions are shown below.

Air compressor Processing amount 5000 Nm ³ / h Outlet pressure 0.75 Mpa Catalyst purifier Operating temperature 150 ° C. Catalytic agent amount 2000 liter / unit treated air amount Space velocity 2500 h ⁻¹ Adsorption purifier Inlet temperature 10 ° C. Switching time 8 hours Regeneration temperature 120 ° C Alumina gel amount 500 liter / unit treated air amount Space velocity 10,000 h ^-1 Synthetic zeolite amount 1000 liter / unit treated air amount Space velocity 5000 h ^-1 Regenerated gas Product purified gas Regenerated gas amount 1000 Nm ³ / h Highly clean dry air Product amount 4000Nm ³ / h Pressure 0.7MPa

Under the above conditions, 4000 Nm ³ of highly purified dry air.
/ H was continuously measured for every 7000 minutes every 15 minutes when the / h was continuously manufactured. The average value is shown below.

Impurity concentration [ppb] Water content 2.6 Carbon dioxide 2.9 Carbon monoxide 5.1 Hydrogen 1.3

As described above, as a result of operating the manufacturing apparatus under the above operating conditions, all of the water, carbon dioxide, carbon monoxide, and hydrogen contained in the high-purity dry air as products were removed to 10 ppb or less. It was confirmed that the gas was purified so as to be sufficiently usable as a gas for protection.

[0049]

As described above, according to the present invention,
It stabilizes high-purity dry air required at semiconductor manufacturing factories and liquid crystal manufacturing factories, for example, high-purity dry air at the level of 10 ppb of impurities obtained by removing and purifying hydrogen, carbon monoxide, moisture, carbon dioxide, etc. to 10 ppb or less, respectively. And can be supplied economically.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of the apparatus for producing highly purified dry air of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Air compressor, 2 ... Catalyst refiner, 3 ... Adsorption refiner, 4
... Used equipment, 5 ... Heater, 6 ... Heat exchanger, 7 ... Pre-cooling equipment, 8 ... Heat exchanger, 9 ... Heater

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Yoshio Ishihara 1-16-7 Nishi-Shimbashi, Minato-ku, Tokyo F-term in Nippon Sanso Corporation 4D012 CA01 CA04 CA10 CB16 CD01 CE01 CE02 CE03 CF01 CF02 CF03 CF04 CF05 CG01 CG06 CH05 CK01 CK10 4D052 AA01 AA08 CE00 DA02 DA06 DB01 FA01 FA04 GA02 GA03 GA04 GB01 GB02 GB03 GB04 GB08 HA01 HA02 HA03

Claims (14)

[Claims] 1. A compression step of compressing raw air, a catalyst purification step of removing hydrogen and carbon monoxide in the raw air,
An adsorption purification step for removing water and carbon dioxide, wherein the catalyst purification step is performed at a space velocity of 3000 h ^-1 or less. 2. A compression step of compressing raw air, a catalyst refining step of removing hydrogen and carbon monoxide in the raw air,
An adsorption purification step for removing water and carbon dioxide, wherein the adsorption purification step is carried out by passing the raw material air through a desiccant bed and a gas impurity removal agent bed in the flow direction thereof,
A method for producing high-purity dry air, wherein the space velocity of the desiccant bed is set to 11000 h ^-1 or less, and the space velocity of the gas impurity removing agent bed is set to 6000 h ^-1 or less. 3. The method according to claim 2, wherein the adsorption purification step is switched and used.
3. The production of high-purity dry air according to claim 1, wherein the switching is performed by four adsorption cylinders, the switching time is 4 to 12 hours, the regeneration temperature is 100 ° C. or more, and the regeneration gas ratio is 40% or less. Method. 4. A compression step of compressing raw air, a catalyst purification step of removing hydrogen and carbon monoxide in the raw air,
An adsorption purification step for removing water and carbon dioxide, wherein the catalyst purification step is performed at a space velocity of 3000 h ^-1 or less, and the adsorption purification step is performed by feeding raw material air in the flow direction with a drying agent bed and a gas impurity removal agent bed. And the space velocity of the desiccant bed is 11,000 h ^-1 or less,
The space velocity of the gaseous impurity removing agent bed is set to 6000 h ^-1 or less, respectively, and furthermore, the switching time is 4 to 12 hours, and the regeneration temperature is 100 ° C. A method for producing high-purity dry air, wherein the content of carbon monoxide, hydrogen, carbon dioxide, and water contained in the raw material air is reduced to 10 ppb or less by performing the regeneration gas ratio at 40% or less. 5. The high-purity dry air that has passed through the adsorption purification step is collected as a product, and a part of the air is supplied to an air liquefaction / separation apparatus.
The method for producing highly purified dry air as described above. 6. The high-purity dry air that has passed through the adsorption purification step is supplied as a product to a use facility, and the high-purity dry air that has been used in the use facility is recovered and pressurized, and the pressure is increased before the catalyst purification step. The method for producing highly purified dry air according to claim 1, 2 or 4, wherein the method is mixed with raw air. 7. The high-purity dry air that has passed through the adsorption / purification step is supplied as a product to a use facility, and the high-purity dry air after use in the use facility is recovered and pressurized, before or before the adsorption / purification step. 5. The method for producing high-purity dry air according to claim 1, 2, or 4, wherein the air is mixed into the raw material air. 8. The method for producing highly purified dry air according to claim 1, wherein the highly purified dry air after use is used as a regeneration gas in the adsorption purification step. 9. As a regeneration gas in the adsorption purification step,
The method for producing high-purity dry air according to claim 5, wherein the exhaust gas of the air liquefaction / separation apparatus is used. 10. An air compressor for compressing raw air, a catalytic purifier for reacting hydrogen and carbon monoxide in the raw air with oxygen, and an adsorption purifier for removing impurities such as carbon dioxide contained therein. In the apparatus for producing high-purity dry air provided with the catalyst, the catalyst used in the catalyst purifier is Pd, Pt, A
u, Fe, Cr, Ni, Co, Mn, Cu, Sn, Zn
Or a combination of a plurality of such metals or a metal-based catalyst containing an alloy of any combination of these metals as a main component, and the metal-based catalyst is contained in the catalyst purifier. An apparatus for producing high-purity dry air, which is filled with 0.33 liter or more per unit air volume. 11. An air compressor for compressing raw air, a catalytic purifier for reacting hydrogen and carbon monoxide in the raw air with oxygen, and an adsorption purifier for removing impurities such as water and carbon dioxide contained therein. And at least two cylinders used by the adsorption purifier for switching, and from the inlet thereof, activated alumina and / or silica gel are charged in an amount of 0.09 liter or more per unit air volume. An apparatus for producing high-purity dry air, comprising: a dried desiccant bed; and a gas impurity remover bed filled with synthetic zeolite in an amount of 0.17 liter or more per unit air volume. 12. The highly purified zeolite according to claim 11, wherein said synthetic zeolite is a single or a combination of Na-X type zeolite, Ca-X type zeolite and Ca-A type zeolite. Dry air production equipment. 13. A path for supplying highly purified dry air derived from said adsorption purifier as a product to a facility for use, a path for collecting highly purified dry air after use in said facility for use, and a path for recovered high clean dry air. Means for increasing the pressure, and a path for mixing the recovered high-purity dry air into the raw material air in at least one place before or after the catalyst purifier, before or after the adsorption purifier, and provided in each of these paths. An apparatus for producing highly purified dry air according to claim 10 or 11, further comprising a valve provided. 14. A heat exchanger for exchanging heat between raw air in an outlet path of the catalyst purifier and highly purified dry air in a path branched from the outlet path of the adsorption purifier. Item 12. An apparatus for producing highly purified dry air according to item 10 or 11.