DD142534A2 - PROCESS FOR ABSORPTION AND FINAL CLEANING OF DAMAGE & PROCESSING EXHAUST GASES - Google Patents

Description

Title of the invention

Process for the absorption and final cleaning of pollutant-containing exhaust gases

Applicability of the invention

The invention relates to a process for the absorption and final cleaning of pollutant-containing exhaust gases according to patent 117 428, in addition to easily absorbable gaseous pollutants and especially dusty

Contain fibrous impurities that tend to composting and solid approaches in Äbsorptionseinrichtungen. These include a large number of dust-laden exhaust gases that are produced in various industries with different pollutant compositions and quantities.

C characteristic of the known technical solutions

For the absorption and final cleaning of hydrogen fluoride and / or hydrogen chloride-containing exhaust gases, a process has been proposed in the main patent 117 428, in which water or dilute acid is fed as an absorbent in pure countercurrent without .Plussigkeitszwangsführung to pollutant-containing exhaust gases. The final purification of these waste gases takes place in absorption columns with several rain sieve trays which have free opening cross sections of 25 to 35 % and operate at high gas velocities. Even under very low liquid loads (up to δ, 2 l / nr of gas)

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conditions, stable bubble baths, which lead to an effective mass transfer. This method is very advantageous for such pollutant-containing exhaust gases, especially good soluble gaseous contaminants such. HCl or HF. But as soon as approaches tending pollutants such. B. coarse water-insoluble dust or silicon tetrafluoride (SiF ₂ ,) are contained in the exhaust gas, the method according to DD-PS 117 is no longer applicable, since the sieve bottom clog at the low fluid loads. Now DD-PS 67408 and DD-PS 88078 a method for the absorption of siliziumtetrafluoridhaltiger exhaust gases has been proposed that works with slot-bottom columns and very high liquid loads by means of liquid circulation. By the

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very high irrigation densities (30 to 60 nr / mh) and the special design of the slot bottom is achieved in addition to the absorption effect, a high washing and self-cleaning effect, so this method especially for the coarse cleaning SiF ₂ , -containing exhaust gases, as in the fertilizer industry in the digestion of crude phosphates, is well suited. However, this method has the great disadvantage of a relatively high pollutant breakdown after absorption due to the necessary circulation of the absorbent and the resulting backmixing.

For the absorption of SiF ₂ -containing exhaust gases, DD_PS 128 694 proposed a process in which hexafluorosilica concentrated in a slot-bottom column unit in the column bottom was used.

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Acid is pumped in the circulation and in the column top slotted bottom with water on the flow principle without circulation be sprinkled. However, this process according to DD-PS 128 694 has the disadvantage that a poor liquid distribution and mixing takes place on the floors and that in the lower part of the column unit a very high liquid circulation of 50 to 100 times the value of the sprinkling in the column top is required. Besides that is. this method is only suitable for the absorption of SiF _z , which is readily absorbable due to its very good water solubility and its low vapor pressure over aqueous HpSiFg solutions.

Object of the invention

The aim of the invention is to eliminate the aforementioned deficiency and to achieve maximum efficiency for the absorption and final purification of such pollutant-containing exhaust gases containing except readily absorbable gaseous pollutants and such impurities that can lead to incrustations and solid approaches in absorption equipment. The emission value of these pollutants should be less than 5 mg pollutant per nr of exhaust gas.

Explanation of the essence of the invention

The invention is based on the object, a process for the absorption and final cleaning pollutant

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containing Abgas.zu, with which the encrustation of the equipment used is avoided. According to the invention the object is achieved in that a final cleaning stage according to DD-PS 117 428, which works in pure countercurrent with very low fluid loads (0.05 to 0.2 1 / nr exhaust gas), upstream of a pre-cleaning stage with special Regensiebböden and in this stage This allows soluble and wettable pollutants of any kind to be continuously absorbed to a final level of less than 5 mg / m of exhaust gas.

Weiterbin was found that under these conditions in the Vorreinigungsstufe on special Großlochsiebböden stable bubble layers can form, which still have a good absorption effect even V / asch- and self-cleaning effect, if the gas velocity in the free cross section of the pre-cleaner depending on the Sieblochgröße between 2 and 3 m / s · It has been found that Regensiebböden excellent with large free opening cross-sections of 35 ~ to 45 % t, 40% of the total cross section and large Sieblochdurchmessern 10-20 mm at normal liquid loads for coarse or pre-cleaning Such pollutant-containing exhaust gases are prone to incrustations or solid approaches.

It has also been found that not only rain screen bottoms with circular screen holes but also a mesh of round bars with square openings with a free opening

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cross-section of 35- "to 45 $ of Gesaintquerschnittes also good for this purpose.

The advantages of the solution according to the invention over the prior art are that this solution makes it possible to produce highly dusty and solid incrustation-prone industrial emissions continuously up to high purities of less than 5 mg pollutant per nr. exhaust gas, which meet environmental requirements. to clean. The economic effort is minimized by this effective method, which works with very effective bubble layers, high gas velocities and low pressure drops.

embodiment

2000 nryh saturated with water vapor polluted exhaust gas v / earth sucked via the gas line 1 in the pre-cleaning stage 2. The exhaust gas contains 10 g / m ^ pollutant in the form of hydrogen chloride, hydrogen fluoride, silicon tetrafluoride and dust. By means of circulating pump δ 6 m-yh pollutant-containing liquid are continuously pumped through the acid line 7 and 9 in the circulation. By means of this circulating liquid, which runs countercurrently to the exhaust gas through the rain screen bottoms A and forms stable bubble layers over these trays, a pre-cleaning and washing effect is achieved whereby "13 kg / h of the pollutants contained in the exhaust gas are absorbed of 40 % of the total cross-section with a hole pitch of 1.5 ·

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The pre-cleaned exhaust gas is sucked through the fan 4 via the gas line 3 ^a us the pre-cleaning stage and printed via the gas line 5 in the Endreinigungsstufe. 200 "kg / h of water are introduced via the absorbent feed line 11 over the uppermost rain sieve bottom B. The water or the waste acid which is produced by the absorption is conducted in pure countercurrent without liquid circulation to the waste gas of 30 % of the total cross section, stable bubbling layers are formed, which cause final purification of the exhaust gas up to a permissible emission level of 5 mg pollutant per second exhaust gas entrained liquid droplets are retained in the droplet separator C. Via line D the purified exhaust gas is removed from the final purification stage 6 derived. * ..

In the bottom of the column of the final purification stage runs, continuously, the resulting from the Nachabsorption

1% dilute acid, through the overflow line 10 into the pre-purification stage 2. From the pre-purification stage

2 are continuously discharged via the drain line 12 22 kg / h of pollutant suspension containing 20 kg / h of pollutants according to the Abgaszusaminensetzung.

Claims (2)

-ϊ- 21 14 Claim for invention 1. A process for the absorption and final purification of pollutant-containing exhaust gases according to patent 117 428 in columns with Regensiebböden over which form stable bubbles layers, characterized in that the Endreinigungsstufe according to patent 117 428 at least one pre-purification is preceded by the back-mixing principle with liquid circulation at works a maximum 50-f.acher liquid load compared to the Endreinigungsstufe and whose Regensiebböden have a free opening cross-section of 35- 45%, preferably 40%, · 2. The method according to item 1, characterized in that the Regensiebböden from circular sieve holes are provided with or consist of a network of round bars with square openings, their ratio, pitch to between 1.4 and 1.6, preferably at 1.5 and the distance from hole center to hole center is at least 15 mm. , For this 1 page drawings