NL8401979A - PROCESS FOR THE EXTRACTION OF ORGANIC SUBSTANCES FROM GASES BY ADSORPTION AND THEN CONFIRMATION WITH COMBUSTION. - Google Patents

Description

NL 32169-Kp / Pf / ed - 1 - * * *

Process for the extraction of organic matter from gases by means of adsorption and subsequently rendering it harmless by combustion.

The invention relates to a process for the extraction of organic substances from gases by means of adsorption and subsequently rendering harmless by combustion.

In many industrial technologies, gas flows are formed / containing the vapors of organic substances. Such gas mixtures are used, for example, in the manufacture of compound fabrics, adhesive tapes, tapes, photo paper, synthetic fibers (acetate, viscose fibers), in the manufacture of cellophane, plastic foils, metal foils, in gravure and ironing processing in the manufacture of synthetic leather and impregnated textile goods, in lacquers in the furniture industry, in pharmaceutical factories, in the preparation of active substances and intermediates, in dry cleaning, in the degreasing of metals, leather and wool free.

The organic substances most frequently used in the listed and other manufacturing technologies are: alcohol. caves, ethers, esters, ketones, aliphatic and aromatic hydrocarbons, chlorine and sulfur-containing organic substances. These substances generally come into contact with the carrier gas flow (air).

The removal of said substances from the industrial waste gases (exhaust air) is desirable for economic and also ecological reasons, and in some cases necessary. These substances are valuable on the one hand, while most of them are toxic to the human and animal organism, which is why they must be prevented from entering the environment.

Condensation, physical and chemical absorption, adsorption as well as catalytic and thermal post-combustion can be used to reduce the emission of the organic substances. Recovery is possible with the first of the mentioned .. methods.

Due to the low concentration of the organic substances (from a few tenths of a gram up to 20 g / m 2), the condensation and the physical absorption are generally not applicable. The chemical absorption is only eligible in special cases, where the organic matter to be extracted reacts well with the absorbent and the process is reversible.

Adsorption is most commonly used for the removal of organic substances, for example solvent vapors, from gas streams, for example exhaust air, which are present in only a small concentration. The organic substances are bound to adsorbents with a large specific surface area, usually to activated carbon (Kohl-Riesenfeld:

Gas Purification, McGraw-Hill, New York-Toranto-London, 1960, page 415). Due to the adsorption, the organic substances accumulate strongly on the surface of the active carbon.

The adsorbed organics are generally desorbed from the active carbon with low pressure water vapor at 380-400 ° K. The vapors are condensed to give an organic phase (water-insoluble organic substance) and an aqueous phase (condensed water vapor and the organic substances dissolved in the water).

The organic phase, when it contains a number of organic substances, is split into its components by distillation. The organic substances are generally separated from the aqueous phases by distillation. This process is rather expensive because the content of the aqueous phase in the organics is generally low (10-20 wt.%) And the separation is hindered by the formation of azeotropic mixtures.

Catalytic and thermal post-combustion are also used for the destruction and calorific utilization of organic substances present in the air stream in low concentration. The thermal afterburning is carried out at 870-1270 ° K, and accordingly much auxiliary combustion material (in the form of auxiliary flames) is consumed, making the process expensive. However, with increasing concentration of the organic matter 35, the need for additional combustible material decreases rapidly and the efficiency of the process increases (Chimia 36;

No. 2.87 / 1982 /).

The catalytic afterburning is carried out at 570-770 ° C and thus the required heat is less than that of the thermal combustion. However, it is disadvantageous that the catalyst is often deactivated quickly in many cases.

For the extraction and calorific utilization of in. In the last few years, organic substances present in the air streams have been developed by combining the adsorption with the thermal post-combustion, the so-called adsorption oxidation process (AdSOX).

In this process, the organic substances are extracted from the air in an active carbon adsorber, then desorbed with hot (approx. 670 ° K) flue gas and the flue gas containing the organic substances is led to a thermal combustion device (Wasser, Luft u. Betrieb 25 (4) 38/1981 /).

The AdSox process has the advantage over thermal post-combustion, "that due to the strong enrichment achieved by the adsorption and the desorption carried out at higher temperature, only a substantially smaller amount of gas has to be heated to 870-1270 ° K. Compared to the usual adsorption, however, it is a drawback that hot (approx. 670 ° K) flue gas is used for desorption, which also contains oxygen in a small amount. Due to the high temperature and the presence of oxygen, a portion of the of the organic compounds on the surface of the active carbon decompose, oxidize, and non-volatile, high molecular compounds are also formed, which cause a rapid deactivation of the active carbon. To compensate this, the active carbon must often reactivated (for example after every fifth cycle), which is carried out with high temperature flue gas (1020 ° K). Because of the high temperature, the adso rction devices are specially constructed devices of high quality materials, which increases costs.

In order to combat the disadvantages of the AdSox process and while taking advantage of the highly enriching effect of the adsorption, a new adsorption oxidation process has been developed according to the invention, with which organic substances present in air and other industrial gas streams are extracted in a low concentration. and can be rendered harmless by using their calorific value.

The main steps of the method are shown in Figure 1 40 of the accompanying drawing.

8 4 o 19 7 9 - *, - 4 -

The process according to the invention is characterized in that the organic substances present as impurities in air or other industrial gases are bound in an adsorber filled with active carbon and / or another adsorbent with a large surface area and after saturation of the adsorber with water vapor of the surface of the adsorbent, the organic substances contained in the mixture obtained in the desorbation are wholly or partly burned in incinerators and thereby rendered harmless and the amount of heat formed thereby to prepare the desorption required water vapor and / or is used for other purposes.

The organics in a small (from a few ten-15ths of a gram to about 20 g / m) concentration containing air and / or other industrial gas are blown at a uniform rate through a blower 3 through the adsorber 1 pressed from activated carbon. The organics are bound to the activated carbon and the purified gas exits from the free air adsorber. After the adsorber is saturated (loaded), the air contaminated with organics is diverted into another freshly regenerated adsorber and the loaded adsorber is regenerated.

The regeneration is carried out with pressurized and / or water vapor heated to the desired temperature using a burner 2 connected to the adsorption apparatus, utilizing the radiant heat of the combustion space and the heat content of the hot flue gas, of which 30 the flow direction in the adsorber is opposite to the flow direction of the air. The feed water required for the preparation of the vapor is pushed into the burner by a pump 5. The pressure and temperature of the vapor used for regeneration and the quantity of vapor guided to be charged in the adsorber are selected such that the desorption of the organic substances proceeds within 10-80 min, preferably 20-60 min.

After cessation of the vapor supply, the bed of active carbon is placed in the adsorber, which has a temperature of 370-470 ° C and at this temperature with water vapor 8401979-5.

is saturated, dried and cooled by introducing heated air if desired. The air required for drying and cooling is blown through a blower 4 at a uniform speed into the adsorber and exits, mixed with the purified gas of the adsorber currently in the operating position. During drying and cooling, the velocity of the air is 0.1-0.3 times the flow velocity used during saturation (in the working position). The time for drying and cooling is 10-50 min, preferably 25-35 min.

In order to be able to carry out the gas purification continuously, at least two adsorbers are required, one of which is just adsorbed (saturated, in the working position), while the other is just regenerated. It is important that the duration of the regeneration must be shorter than that of the saturation or at most the same value. In order to ensure uniform operation of the combustion device, it is expedient to connect four or more adsorbers to a single combustion device. In this case, at least one adsorber is always ready for supplying vapor, that is to say the vapor loaded with organic substances flows continuously to the combustion device.

The method according to the invention has the following advantages in comparison with the known AdSox process; The desorption of the organic substances of the adsorbent is carried out with water vapor with a temperature of at most 520 ° K, preferably 390-450 ° K. In the AdSox process, flue gas with a temperature of approx. 670 ° K is used for desorption. Compared to the flue gas, water vapor has the great advantage of not containing any polluting combustion products (soot, tar, sulfur compounds, etc.) and no oxygen. Therefore, the water vapor does not harm the activated carbon and does not react with the adsorbed organic substances. At the temperature of the regeneration, the water vapor itself is also adsorbed to a small extent on the active carbon, thereby exerting a displacing effect on the organic substances adsorbed there, which leads to a faster and more complete desorption.

Therefore, desorption also takes place quickly at lower temperatures (below 8401979 - b - * * * and 470 ° K), and no decomposition and polymerization reactions of the organic substances occur.

- In the AdSox process, a special device for the preparation of inert gas (inert gas generator) is required for the regeneration of the adsorber, for the production of oxygen-poor flue gas, which increases the investment costs.

- The adsorber and accessories used for the AdSox process must be constructed of materials stable to a temperature of 1020 ° K, while the adsorber unit must be provided with air cooling, which requires the next blower. Heat-resistant gas blowers and expensive heat exchangers are necessary for the recirculation of the hot flue gas.

15 - The method according to the invention does not require any special materials for the devices, the gas blowers and the feed water pump operate at ambient temperature. In the burner, the amount of heat generated can be used easily and with good efficiency for the production of vapor. The system formed by adsorbers and a combustion device by means of a combination is easily controllable and can be easily automated.

The process is also suitable for partial recovery of organic substances if the gas to be purified also contains water-insoluble organic substances. This variant of the method is shown in figure 2 of the drawing.

This embodiment of the process according to the invention is characterized in that the organic substances bound in the adsorber 30 1 in the manner already described with vapor, which was prepared in the burner 7 directly connecting to the adsorber or in a boiler independent therefrom. the active carbon will be desorbed. The water vapor is condensed together with the vapors of the organic matter in a condenser 2, cooled in the cooler 3 to ambient temperature and the resulting mixture is then separated into organic phase and aqueous phase in a separator 4. The water-insoluble organic matter consisting of the organic phase is collected in the vessel 5, the water-soluble organic matter-containing aqueous phase in the vessel 6, 8401979 • · - 7 -. The components of the organic phase can be separated from each other by distillation and recycled into the technological process.

The aqueous phase is introduced into the burner or boiler by means of a pump 105, the organic compounds contained therein are rendered harmless by combustion and the heat generated is used to prepare the water vapor required for regeneration or for other purposes. .

On the one hand, this process variant has the advantage that part of the organic substances are recovered in quality suitable for reuse. On the other hand, it is advantageous that the organic substance in the condensed-state aqueous phase is present in a relatively high concentration, which means low volume, simplification of storage and transport. In this embodiment, the combustion device serving for combustion of the aqueous phase need not be directly connected to the adsorber, but the aqueous phase can also be burned in an already present boiler.

Further details and advantages of the method according to the invention are elucidated on the basis of three embodiments. The first two examples show those variants of the process, in which the mixture of vapor and organic substances emerging from the adsorber during the desorption is led directly to the incinerator without previous condensation.

The third example concerns the partial recovery of the organic substances.

Example I

In an apparatus with two adsorbers, both containing 1000 kg of active carbon, air was introduced at room temperature at a rate of 5000 m / h, which contained 6.12 g / m organic impurities, of which 58% were water-insoluble and 42% was well soluble in water. The saturation cycle (adsorption cycle) lasts for 2.65 h. During this time, 81 kg of organic matter was bound by the active carbon. Subsequently, the organics were desorbed with vapor at a temperature of 390 ° K and a pressure of 2 bar. The vapor supply lasted 50 minutes and required 324 kg of vapor.

8401979 - a -

The vapor mixture exiting from the adsorber had a temperature of 375 ° K and a combustion value of 1740 kcal / kg and was burned in the combustion device directly bonded to the device with the aid of an auxiliary flame. At a flue gas outlet temperature set at 523 ° K and 10% wall losses, 1412 kcal of useful heat was recovered per kg of vapor mixture burned.

With this amount of heat, 2.19 kg of saturated vapor at a temperature of 390 ° K could be prepared. Of these, 0.8 kg / kg mixture was consumed to desorb the organics. After this amount has been deducted, 1.39 kg of vapor / kg of mixture, which can still be used for other purposes, remains. In addition, the amount of vapor generated by the heat of the auxiliary flame.

15

Example II

In the manner described in Example I, 81 kg of organic matter was bound in the adsorber and subsequently desorbed with water vapor at a pressure of 1.2 bar and a temperature of 450 ° K. For this purpose, 243 kg of water vapor was used within a period of 40 min.

The vapor mixture exiting from the adsorber had a temperature of 435 ° K and a combustion value of 2175 kcal / kg and was burned in the burner by means of an auxiliary flame. When an output flue gas temperature was set at 523 ° K and 10% wall loss, 1847 kcal of useful heat was obtained from 1 kg of mixture.

With this amount of heat, 2.78 kg of water vapor with a temperature of 450 ° K could be prepared. After deduction of the specific vapor requirement required for regeneration - 0.75 kg / kg - 2.03 kg of vapor / kg of mixture remains usable for other purposes. In addition, the amount of vapor generated by the heat of the auxiliary flame.

Examples I and II show that with the process according to the invention by combustion of the organic substances separated from the air, not only the amount of vapor required for regeneration, but two to three times this amount can be be prepared. It is furthermore visible that with the increase of the regeneration temperature 40 the amount of vapor to be extracted from the system grows absolutely and relatively.

The method according to the invention solves a problem of environmental protection, because the method removes the harmful substances from the air and other industrial gases and also guarantees - in the form of water vapor - the calorific utilization of the otherwise unused ·· on-going organic matter.

Example III

In the manner described in Example I and in the same device, 78.7 kg of organic matter was bound in the adsorber. 60% of the bound organic matter was readily water-soluble and 40% was water-insoluble. The organics were desorbed with 338 kg / vapor at a temperature of 390 ° K within one hour. Condensation of the vapor mixture yielded 31.5 kg of organic phase containing 0.1% by weight of water and 350 kg of aqueous phase with a content of 12.3% by weight of organic compounds. The organic substance forming the organic phase could be returned to the technological cycle after a treatment (drying).

The aqueous phase, which had a calorific value of 900 kcal / kg, was incinerated in an incinerator using 22.2 m / h methane as an additional combustion material. This produced 207 kg of water vapor per hour, which did not form about 60% of the amount of vapor required for regeneration.

With this method variant, organic matter separated from the air can thus be recovered in quality suitable for new use. The soluble organic substances are rendered harmless by combustion, while at the same time a significant part of the vapor required for regeneration is recovered.

8401 979 35

Claims (5)

1. A process for the extraction of organic substances from air and other industrial gas mixtures and subsequently rendering them harmless under the calorific utilization of their calorific value, which method is carried out in an adsorber connected to a combustion plant, characterized in that the organic substances present in the air or other industrial gas mixtures as impurities are bound in an adsorber filled with active carbon and / or other adsorbent with a large surface area and after saturation of the adsorber by means of pressurized saturated vapor or by means of superheated water vapor is desorbed, the vapor mixture formed from desiccants from organic substances and water is condensed if desired, the organic components which can be separated from the condensate are removed and the remaining part is burned with the aid of auxiliary energy and thereby harmless is made and the amount of heat generated is utilized. 2. A method according to claim 2, characterized in that at least two, optionally three or four adsorbers are used to ensure continuous operation. 3. Process according to claim 1 or 2, characterized in that the regeneration of the adsorbers with pressurized or superheated water vapor is carried out at 370-520 ° K, preferably 390-450 ° K. ^ 4ν. Process according to any one of claims 1 to 3, characterized in that water vapor is prepared by combustion of the organic compounds present in the vapors desorbed by water vapor and that it is partly recycled as desorbent to the adsorbers and partly is withdrawn from the system for other purposes. 5. A method according to any one of claims 1 to 3, characterized in that by combustion of a part of the vapor mixture desorbed from the adsorbers in a combustion device adjoining the adsorbers, the desorption of the organic compounds from the adsorbers required water vapor is prepared and the remaining part is burned in another incinerator, thereby rendered harmless and the amount of heat generated is utilized. 6. Process according to any one of claims 1-3, characterized in that the vapor mixture, which is formed during the vapor supply to the adsorbers, is condensed, cooled and split into an organic phase and an aqueous phase also containing organic substances, the organic phase is reused after a treatment and the organic substance-containing aqueous phase is burned using auxiliary energy in incinerators, thereby rendered harmless and the amount of heat generated is used to prepare the water vapor required for the vapor supply and / whether it is extracted from the system and used elsewhere. §401979