Process for preparing ozone

(42) Date of commencement of the patent: 15. 8.1990 (45) Date of issue: 25. 2.1991 (73) Patentee:

VOEST-ALPINE INDUSTRIEANLAGENBAU SOCIETY MBH

A-4020 LINZ, UPPER AUSTRIA (AT).

(72) Inventor:

LEHNER FRANZ DIPL.ING.

PASCHING, UPPER AUSTRIA (AT).

WAWRINA RAINER

LEONDING, UPPER AUSTRIA (AT).

(54) PROCESS FOR THE PRODUCTION OF OXYGEN AND / OR OZONE

CQ (57) In a process for producing 0 ₂ and / or ozone for an oxygen and / or ozone consumer (2,4), from which residual oxygen is withdrawn and purified in a pressure swing adsorption plant (5) and at least partially the oxygen consumer (2) or with the interposition of an ozonizer (3) the ozone consumer (4) is recycled, beyond the traceable amount of oxygen addition amount for the needs of the consumer (2,4) one of the pressure swing adsorption plant (5) for purifying the recirculated oxygen separate source of oxygen ( 6,7).

Preferably, the amount of gas desorbed from the pressure swing adsorption system (5) during regeneration is at least partially fed into the gas flow withdrawn from the consumer (2,4) and recirculated via the pressure swing adsorption system (5).

AT 392 256

<img file="AT392256B_D0001.tif" />

INR 0079318

The invention relates to a process for the preparation of O.₂ and / or ozone for an oxygen and / or ozone consumer, is deducted from which residual oxygen and purified in a pressure swing adsorption and at least partially the oxygen consumer or with the interposition of an ozonizer the ozone consumer is recycled.

In connection with pulp bleaching, which come into consideration, for example, as an ozone consumer, it has already been proposed to purify the oxygen withdrawn from the pulp bleaching and again to pass it via an ozonizer, whereupon ozone can be supplied to the bleach. Such cycles of &lt;?,

Oxygen is particularly important when ozone from enriched oxygen, especially from more than 90% oxygen existing gases is produced because at elevated oxygen concentration, the ozone yield in the ozonizer is much cheaper than when using air. The recirculation allows 2 to substantially maintain the degree of enrichment of oxygen in the gaseous medium, although oxygen is consumed to a greater or lesser extent depending on the nature of the ozone consumer.

Especially when large amounts of organic substances are to be oxidized, but also in pulp bleaching, significant amounts of oxygen are consumed in the unit time and it has already been proposed for example in EP-Al 297 090, to carry out the cleaning in a pressure swing adsorption system for the removal of impurities from the oxygen stream and to enrich the possibly required additional amount with this pressure-swing adsorption unit for air used for the cleaning. However, such an arrangement requires a very large dimensioning of the pressure swing adsorption, since for example for the replacement of an amount of oxygen to the extent of 10% when using the same pressure swing adsorption plant as used for the purification of recirculated gas, one order powers higher Air quantity must be enforced by the pressure swing adsorption to replace the desired oxygen demand can. With the required additional air volume, which is to be cleaned in the pressure swing adsorption plant for the recovery of technical oxygen, It is not only the circumstance that must be taken into account, that oxygen in air is enriched much less than in technical oxygen, but also taking into account the circumstance that the efficiency of such a pressure swing adsorption plant reaches 50% in the best case, if air is used as feedstock, to gain technical oxygen. For the previously known methods in which the recirculated residual oxygen is purified in a pressure swing adsorption and on the same pressure swing adsorption the required amount of oxygen was supplemented from air, thus very large pressure swing adsorption were required, thereby at the same time taking into account the Desorb the withdrawn volume had grazed considerable losses of pure oxygen in purchasing.

The invention now aims to provide a method of the type mentioned, in which with the smallest possible plant size a higher degree of efficiency is enceicht, and the losses of already enriched oxygen can be kept as low as possible. To solve this problem, the procedure according to the invention essentially consists in that the excess amount exceeding the traceable oxygen quantity for the consumer's needs is taken from a source of oxygen separate from the pressure swing adsorption system for purifying the recirculated oxygen.

Characterized in that in addition to the used for the purification of the circulated, oxygen-enriched gas pressure swing adsorption a separate source of oxygen is provided, which the required additional amount of oxygen can be removed, the pressure swing adsorption system used for cleaning can be made much smaller , whereby desorbing or

Dissolve the contaminant smaller volumes of already enriched with oxygen gas are deducted. Preference is given to proceeding so that the excess of the traceable amount of oxygen addition amount is taken at smaller amounts of consumption from bottles or liquid tanks and in larger demand quantities but in a separate pressure swing adsorption for oxygen production from air generated wild and the recycled oxygen before Ozoneizeuger or oxygen consumers mixed becomes.

If the oxygen or Ozone consumers consumed only small amounts of oxygen, the additional amount can be easily removed from an oxygen cylinder or a liquid tank. In the case of a correspondingly higher additional oxygen demand, another separate pressure swing adsorption plant is used for the preparation of the additional oxygen amount, which can still be dimensioned much smaller than a pressure swing adsorption, with which simultaneously cleaning the recirculated gas and the production of the required Added amount of oxygen from air was made. The circulated amount of oxygen can optionally in the case of an ozone consumer below.

Intermediate circuit of an ozonizer can be recycled, wherein in the line to the ozonizer, the respective additional amount of oxygen can be fed. When using the recirculated oxygen amount for oxygen-consuming processes, the interposition of an ozonizer naturally »eliminated. For the use of recirculated oxygen in an ozonizer safety measures should be followed in the following, which will be discussed later. In the case of an oxygen consumer but can increase the economy by reducing the Desorptionsverluste be achieved that, as it corresponds to a preferred embodiment of the inventive method, the procedure is such that the from the pressure swing adsorption during regeneration

-2AT392 256B desorbed gas is at least partially fed into the withdrawn from the consumer gas stream and circulated through the pressure swing adsorption. This advantage arises regardless of the use of the thus purified gas for an oxygen-consuming process or subsequent ozone formation for the performance of an ozone-consuming process. The circulated amount of the gas stream is enriched in this case with impurities and can be discharged after reaching a predetermined proportion of the impurities in the gas stream subsequent to a desorption.

In the case of the use of recirculated gas through an ozone consumer, an ozonizer must naturally be used for the renewed production of ozone, preferably this is done, that the ozonizer fed, amount of oxygen withdrawn from the pressure swing adsorption plant is fed to the ozonizer via an oxidation stage for destroying lower hydrocarbons, wherein a portion of the ozone generated in the ozonizer is recycled to the oxidation state. In such an oxidation state in particular volatile, low hydrocarbons can safely to CO₂ and H₂O be oxidized. This process step is therefore of importance, since the process described above would take place if the oxidation state in the ozone generator itself were omitted. The resulting water would trigger a spark discharge instead of a deliberate silent electrical discharge in the ozone generator, whereby the efficiency would be significantly reduced. Of course, organic impurities and also the majority of lower hydrocarbons are already largely retained in the pressure swing adsorption plant. However, even under favorable conditions residual amounts of more than 10 ppm light hydrocarbons leave the pressure swing adsorption together with the purified gas and such small amounts of low hydrocarbons already lead to a sensitive impairment of the safe operation of the ozonizer. The organic compounds still to be destroyed in the subsequent oxidation state, especially methane, but can be reliably destroyed by feeding ozone into the clean gas stream following the pressure swing adsorption system in a short way, and in the destruction of such lower hydrocarbons with ozone, one of the reaction products is water, is done with advantage, so that withdrawn from the pressure swing adsorption, purified gas, especially after the oxidation stage is subjected to drying. In this way, disturbances of the ozonizer by steam are avoided with certainty.

However, a large part of organic contaminants can already be separated from the gas stream prior to the introduction of the gas withdrawn from the consumer, in order thus to increase the loading times and thus the cycle times of a small-scale pressure-swing adsorption plant. Advantageously, according to the invention hiebei proceeded so that the withdrawn from the consumer gas is supplied via a scrubber and optionally an acid separator of the pressure swing adsorption, whereby a majority of the withdrawn from the consumer organic contaminants, especially längeikettige impurities and organic acids, already can be removed before entering the pressure swing adsorption.

To ensure that no significant amounts of ozone are released into the atmosphere during the discharge of the enriched for enrichment of impurities in the desorption via the pressure swing adsorption in the gas stream, it is advantageously done so that the via the pressure change Adsoiptionsanlage in circulation guided, desorbed gas on reaching a predetermined concentration of impurities via an ozone filter such. B. a carbon filter is discharged. Ozone filters may be formed in a simple manner as a carbon filter, wherein at correspondingly high levels of organic substances in the withdrawn from an ozone consumer gas, then, if the withdrawn gas significant amounts of ozone are withdrawn, an ozone or an analog ozone filter immediately after the ozone consumer may be provided in order to avoid the risk of explosion in subsequent parts of the system or to eliminate a release to the environment.

After the desorption of a pressure swing adsorption, in which the retained impurities are released in turn, the pressure swing Adsoiptionsanlage must again be brought to the suitable operating pressure for adsorption, which is advantageously done so that the pressure swing adsorption to recirculate the recirculation Gas after desorption with purified or additional oxygen is brought to operating pressure. An economical operation, however, can be achieved if the renewed pressure buildup with purified product gas of a cyclically settable with an adsorber in connection with another adsorber of the same pressure swing adsorption plant is put in connection. In the same sequence, the drying stages downstream of the oxidation stage are desorbed, wherein the regeneration of the drying stage is preferably carried out so that the drying stage are regenerated together with the Adsorptionsbehältem the pressure swing adsorption by evacuation and optionally rinsing at the end of the desorption by means of a common vacuum pump.

The specific energy input of ozone generators is the higher, the higher the ozone yield is selected. By the proposed method, which allows the recycling of unused oxygen with minimal oxygen losses, it makes economic sense to operate the ozone generator with high oxygen flow rate and relatively low conversion rate to ozone and therefore with the lowest possible total energy input. It is preferred that the ozone generator with high oxygen flow rate and

-3AT392 256B is significantly lower than the maximum conversion rate of oxygen to ozone.

As ozone consumers, for example, a water treatment, pulp bleaching, special waste processing and in particular a treatment of hazardous waste in the chemical industry come into consideration. Oxygen consumers are to be seen in particular in the field of oxygen biology, for example in the context of wastewater treatment facilities or similar facilities. In particular, for the production of ozone may, as mentioned above, only dry oxygen are used and low hydrocarbons must be largely separated quantitatively. In the case of use in pulp bleaching plants, an essential part of the organic decomposition products of humic acids is lignin cleavage, whereby such humic acids can be removed to a large extent in a scrubber. With such a scrubber, the temperature of the recirculated gas is simultaneously reduced, which has a beneficial effect on a subsequent pressure swing adsorption. The scrubber, a further acid separator can be followed, with such a scrubber is advantageously arranged in front of the downstream acid separator, since here also the temperature reduction achieved in the scrubber has an advantageous effect and already largely the acid moieties were washed out.

The invention will be explained in more detail with reference to embodiments schematically illustrated in the drawings. 1 shows a schematic representation of a device for carrying out the method according to the invention, and FIG. 2 shows a schematic representation of the pressure swing adsorption system for purifying the gas stream withdrawn from the oxygen or ozone consumer.

In Fig. 1 is (1) an oxygen fan, which provides high-purity oxygen either directly to an oxygen consumer (2) or via an ozonizer (3) an ozone consumer (4). The high-purity oxygen originates for the most part from a pressure swing adsorption plant (5), which from the consumers (2) or (4) withdrawn gas stream is supplied, as will be described in more detail below, and to a lesser extent to replace the consumed in the consumer oxygen from an additional source of oxygen, which in particular for small amounts added or Substitute amounts of oxygen from an oxygen cylinder (6) and for larger quantities, for example, from another pressure change Adsoiptionsanlage (7) for the decomposition of air can originate.

The from the consumers (2) or (4) via the line (8) withdrawn gas stream is for a first pre-cleaning or Cooling to improve the efficiency of the pressure swing adsorption plant (5) according to the intended use of the oxygen or Pre-treated ozone in the consumer, wherein, for example, for originating from a pulp bleach contaminated gas an acid separator (9) and downstream of a heat exchanger (10) may be provided. However, it is also possible to provide a scrubber (11) in front of the acid separator (9), which partly entails cleaning the gas stream and at the same time lowering the temperature, as a result of which a downstream acid separator (9) can be operated more economically.

From the pressure swing adsorption system (5) for cleaning the consumer (2) or (4) used oxygen-rich gas on the one hand highly pure oxygen via the line (12) the oxygen fan (1) and returned via a vacuum pump (13) desorbing from the pressure swing adsorption (5) especially the impurities with a residual oxygen content over the line (14) deducted. At the same time, the drying stage downstream of the oxidation stage is desorbed via line (29). In order to be able to recover a large part of the oxygen contained therein from the desorption stream withdrawn via line (14), d. H. In order to achieve a correspondingly high concentration of the impurities in the desorption stream, a large part of the withdrawn through the vacuum pump desorption via a line (15) via the line (8) from the consumer (2) or (4) withdrawn gas stream and in turn passes into the pressure swing Adsoiptionsanlage (5). By appropriate control of a valve (16) with sufficient accumulation of the impurities in the desorption an appropriate proportion via a filter (17) which is formed in an ozone consumer (4), for example, as a carbon filter for setting a safety regulations corresponding ozone concentration, via a line (18 ) deducted.

When using the in Fig. 1 shown device for an oxygen consumer (2) can in general from the pressure swing adsorption (5) withdrawn and purified oxygen directly after appropriate replacement of the consumed quantities from the additional oxygen sources (6) or (7) in turn the oxygen consumer (2) supplied become. When used in an ozone-consuming plant dry and especially of low hydrocarbons, especially methane, purified oxygen must be supplied to the ozonizer (3) to ensure safe and economical operation of the ozonizer (3). Although the majority of impurities have been removed from the gas stream withdrawn from the consumer into the devices upstream of the pressure-swing adsorption plant (5) or the pressure-swing adsorption plant (5) itself, generally the values ​​for lower hydrocarbons, especially methane, which are removed in the purified gas stream from the pressure swing adsorption plant (5), exceed a value of 10 ppm, which is generally too high for safe and economical operation of the ozonizer (3). To further lower the content of low hydrocarbons, it is therefore intended to via a branch line (19) in the ozonizer (3) generated ozone fed to one of the pressure swing adsorption (5) downstream oxidation stage, generally by the addition of

-4AT392256B

Ozone at this point an immediate destruction of low hydrocarbons, especially of methane, is made. For subsequent drying of the treated in this way, from the DrackwechselSadisanlage (5) withdrawn clean gas, a drying stage (20) is provided, in which the resulting during the destruction of the low hydrocarbons, inter alia, water is removed from the oxygen stream. The procedure for removing low hydrocarbons from the purified product gas withdrawn from the pressure-swing adsorption system (5) is shown in FIG. 2 explained in more detail

By the use of a pressure swing adsorption system (5) only to clean the from the consumers (2) or (4) withdrawn, polluted gas, this pressure swing adsorption system can be formed with a small size and it can deliberately via the partial return of the desorbed stream enrichment of impurities in the line (18) withdrawn desorbed gas stream and thus a reduction of simultaneously discharged with it Oxygen flow can be achieved. Furthermore, such a pressure-swing adsorption plant (5) can be operated with a high efficiency in the range of over 80%, since the supplied gas originating from the consumers, despite the impurities contained therein, has a much higher oxygen content than air. It must therefore on the additional oxygen sources (6) or (7) only a small amount of oxygen is provided, wherein when using a further pressure swing adsorption system (7) to provide the additional amount of oxygen, this can also be made small, since they are only for the provision of the additional amount of oxygen and not for the entire, the oxygen consumer (2) or the ozonizer (3) and the Ozonveibraucher (4) provided high-purity amount of oxygen must be designed.

The in Fig. 2 illustrated pressure swing adsorption plant (5) is designed for cyclic operation and has three pressure swing adsorber (21), which each release purified product gas in the line (12). The Druckwechseladsorbem (21) is via the line (8) from the consumers (2) or (4) supplied gas via valves (22), wherein purified and a high percentage of oxygen-containing product gas via valves (23) from the Druckwechseladsorbem the dryers (20), which is a gel contained to eliminate the water. The system shown here is designed for an ozone-consuming process, in which after the individual pressure swing adsorber (21) a supply of ozone via valves (24) for the removal of low hydrocarbons, especially methane, is supplied. From the Druckwechseladsorbem gas is withdrawn via valves (25) for desorption of strongly enriched gas via the vacuum pump (13), wherein the operation of the three pressure swing adsorber is cyclic, so that in each case the same time an adsorber is loaded, from an adsorber impurities be desorbed and the third adsorber wiedemm by purified or additional oxygen is brought to operating pressure. In order to bring the adsorber in turn to operating pressure, the line (12) immediately upstream valves (26) are each closed and there is a supply of oxygen from the line (12) in the dryer (20) and the pressure swing adsorber (21) via valves (27) with open valve (23). In this phase, via the valves (27) also a purge with purified or supplemented oxygen. To clean the dryer (20) can be done via valves (28) in the conduit (29) evacuating the dryer by the vacuum pump (13).