Ozone concentrating process

Details Ozone concentrating process Ozone concentrating process

1996-10-04

1998-03-24

Spitzer, Robert

Gas separation: processes

Solid sorption

With plural indirect heat transfer steps on solid sorbent or...

95138, 95 11, 95 21, B01D 5304

Patent

active

057307830

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a process for concentrating ozone.


BACKGROUND ART

Ozone is generated by an ozonizer by means of high-voltage silent discharge employing air, an oxygen-rich gas or an oxygen gas as a feedstock gas. However, the concentration of ozone generated by high-voltage silent discharge is 15 wt % or less even when an oxygen gas is employed as the feedstock gas, and it is supplied to the spot where it is consumed usually at an ozone level of 6 to 7 wt % in view of efficiency, at most about 10 wt %. Ozone is usually generated by the ozonizer at a rate of about 1 kg/cm.sup.2 G. Accordingly, in the case where ozone having a pressure of about 4 to 6 kg/cm.sup.2 G is required, for example, for bleaching of pulp, the thus generated ozone-containing gas is compressed to a predetermined pressure by a compressor before it is supplied to the spot.
Meanwhile, on the spot where ozone is to be consumed, higher concentration ozone is desired so as to improve efficiency of ozone treatment. For example, since ozone has a property of being adsorbed on adsorbents such as silica gel at low temperatures, there is employed a method in which ozone is separated from oxygen by the thermal swing adsorption (hereinafter referred to as TSA) method utilizing such property to obtain ozone having a relatively high concentration.
Concentration of ozone according to the TSA method described above is generally performed employing a plurality of adsorption columns each packed with an adsorbent such as silica gel which preferentially adsorbs ozone. In this process, the plurality of adsorption columns are switched sequentially to an adsorption step where an ozone-containing gas supplied from an ozonizer is introduced to the adsorption column containing an adsorbent cooled to a low temperature, to adsorb ozone on the adsorbent; a desorption step where the adsorbent contained in the adsorption column having been subjected to the adsorption step is heated to desorb ozone therefrom, and a scavenger gas is introduced into the adsorption column from the opposite side with respect to the ozone-containing gas introducing side to discharge the desorbed ozone being carried on the scavenger gas; and a cooling step where the adsorbent in the adsorption column having been subjected to the desorption step is cooled again to the same level as in the adsorption step.
However, in the ozone concentration process according to the conventional TSA method, since the adsorption column in the desorption step is heated at a stretch like in the general TSA method, most of ozone is desorbed at the initial stage of the desorption step, and not only the ozone concentration of the gas discharged from the adsorption column in the desorption step but also flow rate of that gas fluctuate a lot, so that ozone cannot be supplied at a stable concentration unless some other means is taken. Accordingly, an extra equipment for stabilizing ozone concentration (ozone level stabilizer) must be disposed downstream the ozone concentrating apparatus.
As the ozone level stabilizer, for example, one described in Japanese Unexamined Patent Publication No. 128865/1975 has been employed. More specifically, a packed column packed with an adsorbent capable of adsorbing ozone, such as silica gel, is maintained at such a low temperature level that the adsorbent can adsorb ozone so as to maintain the concentration of ozone to be supplied substantially constant utilizing the correlation between the ozone concentration and the amount of adsorbed ozone.
However, in the case where the ozone concentration fluctuates a lot like in the conventional ozone concentration method, a packed column having a very large capacity must be employed, so that the amount of adsorbent to be charged therein, and also a large amount of refrigerant is required for maintaining the adsorbent at the low temperature.
Further, in order to compress a gas containing ozone having high oxidative power, a compressor of a special structure must be provided, and besides the temperature of th

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patent: 5507957 (1996-04-01), Garrett et al.
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