DE2141944C3 - Process for the absorption of nitrous gases - Google Patents

Description

The invention relates to a method for economical Use of the nitrous content of exhaust gases, for example in the production of nitric acid by absorption of nitrogen oxides, during the digestion of rock phosphate with nitric acid or in pickling plants, in who work with nitric acid.

Numerous methods are already known for the absorption of residual nitrogen oxides in exhaust gases. You either work with alkaline absorbents, ι. B. with milk of lime or sodium hydroxide solution, or with reagents specific for nitrogen oxides, e.g. B. with sulfamic acids. In many cases an additional oxidation / iir support is the absorption of the nilrosen gases usually / wipe the Werligkeits / ustand Y ^ 2 and 4 are located and the / u nitric acid to be oxidized with nitrogen fünfweriigem by güfiihrl. Haiti is used for example O / on. Hydrogen peroxide, peracids or chlorine.

All of these procedures can be used here right iiinsltlnilftill, or you deliver products with only low marketability, / .. H, calcium nitrate. In Many cases are only dealt with in order to comply with the üMiwc'lihvgienischefi regulations.

We have therefore already passed over the nitrogen oxides by catalytic combustion and the like Destroy methods of division.

With the help of the invention it is possible to meet both the environmental hygiene requirements and to use the nitrogen oxides largely economically.

The inventive method for the absorption of NO / NOj from nitrous-containing exhaust gases consists in that fan either phosphate-containing. granular raw materials in the presence of water in the form of steam or spray mist or aqueous suspensions of feinslkörni like Phosphalgestem jls absorbent used. The resulting, parliellaiifgesclilosscnen absorption are compositions according to known SiCl usual Phosphataufschlußvei example moving zn fertilizers, \ iiitennilteln or phosphine acid aiiigeaibei let.

The invention evaluates the observation that rock phosphate and other PjOvenihailendci raw materials are capable of nitrogen oxides / n atisoiliiei'eii, if you have the The gases are so sensitive that they pass through fine-grained, pho.sphiilhallige layers caused by capillary condensation favors the absorption of nitrogen oxides

will. Mun also achieves good absorption nut yields, fine-grained ones that are soaked up in water Dry phosphate suspensions for absorption of Slick oxides used.

Calcium nitrate is formed during this absorption process and citric acid and mostly also water-soluble calcium phosphates. The resulting phosphates with Their water-soluble parts must be continuously or v. in batches from the Absorption space can be withdrawn and replaced with fresh material.

The phosphate-containing rock is thus to a certain extent pre-digested by treatment with nitrogen oxides. The absorption masses obtained can then be subjected to a further dilution process can be taken into account, whereby a saving in digestion acid can be taken into account.

In contrast to the previously common absorbents In the case of rock containing phosphate, the absorption mass is fully usable. In the developed Absorption devices is only a relatively low expenditure on equipment and a minor one Maintenance required so that the process can also be used in plants that are forced to use Nitrose treated absorption masses at phosphate digestion plants to sell is economical.

The method according to the invention has been successful Rohphosphalsorlen tested, of which only the initial analysis of two varieties in Table 1 the following are listed:

Tabel

component Morocco raiba- phosphate pliosphut Total P'O-, 34.5% 37.7 Neutral citrate soluble P> ()> <0.0I% 0.66 (F resenius - Neubauer) Ammonium citrate soluble Ρ2θι <0.01% 0.02 (after Petermann) Water soluble Ρ2ΟΊ <O, OI% 0.01 Total CaO 49.0% 52.6 Water soluble CaO <0.0?% 0.14 Alkali act Carbonates as% CO2 3.85% 1.3 pH value (5% solution) 5.8 4.8

In the same way, however, other phosphate-containing rocks, such as phosphorite, Thomas flour or superphosphate. use.

While one can use a relatively coarse-grained starting product for the Vim drive with I insat / of irockncm phosphate and moistened mtrosehalti like exhaust gas / wcikmaltgerweise a phosphate eiii / iiset / s, 111 the hoi listens I Gew ' Vn the particle is coarser than 1 mm. Samples with the particle size distributions given in Table 2 were used in the two types of process from the above-mentioned microphosphate. The fine-grained sample was obtained by appropriate preparation and screening of the coarser sample.

Table 2 for the dry fine-grained Grain size distribution and the wet process > Shares Name of the sample 0.6% coarse-grained > 5 mm 0.5% 5 to 4 mm 0.1% 48.0% ¹ 4 to 3 mm 0.1% 51.4% 3 to 2 mm 1.4% 2 to 1 mm 2.8% 1 to 0.2 mm <0.2 mm 47.0% 48.1%

For the absorption devices are in the following for the dry process and for the wet process two embodiments each described. However, other corresponding facilities can be more expedient Use type as well.

Two of the devices used are shown in Fig. la, Ib and Ic and 2 shown.

The Fig. La shows in a schematic manner the Material flow in a form of the apparatus in which the

) ■, absorption of the moistened nitrogen oxide-containing waste se takes place on dry, coarse-grained phosphate. The phosphate granulate flows continuously from the bunker 1 between two sieve plates from Absland i / or. by two touching parallel rows of 1 filter candles

in (see Fig. Ic) with the diameters I) through. The phosphate purifications in this plane, or in the double-row roller arrangement, represent filters for the transverse flow of the nitrous-containing exhaust gas. The filter space 3 must therefore be used for the

See the entire cross-section of the exhaust gas routine Absorbent be filled.

The phosphate sluices 2 under the bunker 1 always remain fully open, as a result, so much always flows Phosphate according to, as in the I nileerungsslut / en 4 des

id I illerraumes is deducted

It could be established that the Ahsorplioiiscf Only insignificantly depends on the thickness of the .ibsorptionsf.i higen '' is dependent on phosphate. As it is expedient is. the pressure loss in the exhaust gas flow as low as

To keep π possible, one becomes the effective thickness of the Select the filter layer as small as possible. For example, in one Apparalurform. in which the The flow cross-section of the nitrous-containing exhaust gases has a diameter / 1 of 1000 mm and the total length /> des

-, n Filters 3 was 1550 mm, a filter diameter of (/ = 150 mm proven. For the double rows of candles, a core diameter is correspondingly required of 100 mm attached.

Fin (not shown) fan 16 pulls the

> i mtrosehi'lt'gen exhaust gases through the filter 3. Above one Steam injection 17 b / w. 13 are the nitroscn Exhaust gases through low-pressure steam 100% with water saturated. For the separation of liquid particles / wipe the steam injection 13 and the filter 3 cm

hi droplet separator 14 provided over the valve 18 drained wtrder. Can

If the Rohphosph.iidurihs.il/ has been dug down through the filter 3 / u , it happens. that the formed in the phosphathalligLMi rock

ι, -, Kalz.iumniifal the pofefi of the lilterplaileii clogged, so that then the pressure loss in the stream of nitrous gases increases. In such a case, the filter pl <it (s are cleaned. This can be achieved by using the

Valves 2, 12 and 15 closes and initially the entire Drain the rock phosphate by opening the valve 6 of the finllüflungssUitzens (from 100 to 0, for example) opens. Then the drain valve 4 is also closed and through the Prcßluflslutzcn 7 and Compressed air blown in behind the niter arrangement. Then the l'illcrraum 3 can again with fresh Absorbents are filled from the bunker 1.

Fig. Ib shows a section with a projection perpendicular through the image plane of Fig. La. and the B i I d Ic is the arrangement of i ^; iltcrkcr7.cn in double row in top view. On a corresponding representation of the fillet of the line at Liinsalz. of plate files was dispensed with.

With the correct adjustment of the phosphate flow rate through the chamber 3 with the exhaust gas flow rate of 12 after 15, the absorption mass can be continuously deducted through the drain valve 4. She will be on most appropriate eieni Äüfschiuüöchäiicr for production supplied by complex fertilizers or by phosphoric acid.

Fig. 2 shows one of the possible ways of absorbing the NO / NOj content of "dry" nitro-switching exhaust gases shown on aqueous suspensions. That which comes out of a bunker, finely ground Phosphaigestcin is released through the! "Msehiil! Opening 31 introduced into the Vorinischer 32 and in this The vessel with the stirrer 33 is in proportion to the water flowing in via the filler neck 30 1: 2 mixed intimately. The phosphate-water suspension obtained is about you *. Drain valve 34 continuously fed into template 35. The Suspension kept in constant motion by a stirrer 36.

ί The phosphate suspension from the absorption vessel 35 is via the bottom outlet 37 with the aid of the pump 38 conveyed to the washing tower 51 with the riser 39. The suspension trickles over into the washing tower grids arranged in tiers gradually downwards,

while the stream of Nilrosenhalligcn gases flows towards it. She finally returns in over the inflow the absorption vessel 35 back in order to repipulate / ti will be. Hin part of the suspension is however constantly from the branch pipe 39 going out via the throttle 54 to the (not shown) Nachaufsehluß des Phosphate led. In a corresponding manner, Irish suspension is added to the storage vessel 32 via 34 after.

i? iC · iiiirinCnimigcM CjiiSC successful VOm dC! Tl Oi! their!*

2 (i Kntslclning 61 either under their own flow pressure or accelerated by a suitable fan via the inlrillsvcnlil 62 and the nozzle 63 in the absorption vessel 35. where they can be inflated onto the surface of the suspension. Afterward they flow through the oranges 52, which are arranged in a plurality of cages, to pass through the ventilation pipe 64 into the droplet separator 65 and the residual gas chimney 66 to escape. In the droplet separator 65 is Excess water vapor deposited and over

in 'the downpipe 67 returned to the absorption vessel.

Application examples

1. Use of an absorption apparatus as shown in Fig.1.

The essential data of the examples a to e carried out are recorded in Table 3.

Table 3

example
a

Feed area, m ²
Phosphor layer thickness. m
Amount of phosphate / filling, kg
Gas throughput, mVh
Gas velocity

on the filter, m / s
Residence time of the gas, see chap

1.0 0.15

240

360 0.1 0.1 1.5

Type of phosphate used Morocco rock phosphate, coarse Taibaphosplial, coarse

Nitrous content (NO / NO

calculated as g NO / Nm ³ )

in the salt gas, 8.2 6.2 5.6 3.5 1.3

g NO / Nm ³

in the residual gas, g NO / Nm ³ 1.2 1.2 1.0 0.7 0.23

Efficiency,% 853 80.7 823 80.1 82.3

Amount of absorbed 2.52 1.8 1.66 1.01 0385

Nitrous, kg NO / h

With the proviso that 1 mole of CaO 2MoI NO bind, in example la 4.6 kg of rock phosphate implemented.

To prevent the phosphate from cementing.

50 kg of rock phosphate were generally renewed per hour.

2. Experimental examples with an absorption preparation according to Fig.2.

21 4 7th 1 944 8th b 250 1.5 200 Table 4 Moroccan phosphate 0.5 IO example 4000 Aft of the phosphate a 7th 5.5 Washing tower _{height (rri} 5 1.5 1.4 1.1 Washing tower diameter, m 1.0 79 3.5 80 Internals 22nd I: 2 17.6 Art V 4 A grids Mesh size, mm 40 5 32 Distance from each other, hi number 10 Gas throughput, NmVh Gas velocity in the tower, m / s Dwell time, see relationship Rock phosphate: water Total amount of suspension in circulation, m ³ Pumped suspension mVh Removed or renewed Suspension, kg / h Nitrous content (NO / NO2 calculated as g NO / Nm *) in the feed gas, g NO / Nm ³ in the residual gas, g NO / Nm ³ Efficiency,% Amount of absorb. Nitrous, kg NO / h Amount of sales Rock phosphate (under the Prerequisite, kg / h that 1 mole CaO 2 moles NO tie)

The gas leading to the appanition apparatus should always be cooled to temperatures below 30T, because the temperature decreases with increasing temperatures The absorption yield - just like with the simple absorption of nitrogen oxides in water - falls sharply. Lower temperatures, on the other hand, favor absorption.

Surprisingly, as Examples la to Ie show, the absorption yield falls as it falls Nitrösegehait of the exhaust gas used practically no away. It is therefore very possible to switch on several apparatuses one after the other and so / u extremely low ones Nitrous content in the residual gas.

It is also possible to use gaseous oxidizing agents, especially ozone to add to the gas stream. In the case of the pumping over of Rock phosphate suspensions through washing towers can be increased by the addition of hydrogen peroxide or by other oxidizing agents as well.

It is also useful to add suitable wetting agents to the suspensions, for example silicone oils, alkyl sulfonates to add.

Also by adding alkaline substances or those mentioned in the introduction (on page 1) Reagents to the suspensions can reduce the absorption can also be increased. Those caused by the absorption of the nitro-switching gases in the fine-grained Compounds obtained from phosphates are generally readily soluble. The main product is the gin soluble Ca (NOj)> 4 H2O. In addition, also form secondary and primary calcium phosphates. For example, in the test series la (see Table 3) the Values of the natural citrate soluble. ammonium citrate soluble and water-soluble P2O5 of less than 0.01% (see Table 1) to 3.30.3.08 and 2.56%.

It is also possible to carry out the two variants of the incinerii 'fluidized bed process; To this One can therefore use both dry and phosphorous Use rocks as well as those that have previously been moistened with water mixed with a wetting agent are. In the first case the whirling up must be accelerated by appropriately accelerated, previously by suitable means

bo measures moistened nitrogenous exhaust gas streams take place. In the second case, you can use the "dry" Nile rose-like exhaust gas flow after the appropriate Use acceleration.

For this purpose 3 sheets of drawings

Claims (11)

Patent claims: 1. Procedure for the absorption of NO / NO> from nitrous-containing exhaust gases by bringing them into contact with solid absorbents, thereby characterized in that one is used as an absorbent either granular raw materials containing phosphate in the presence of water in the form of steam or Spray mist or aqueous suspensions of fine-grained phosphate rock are used. 2. The method according to claim I, characterized in that the absorbent is dry begins and the nitrogen-containing exhaust gas stream either by water vapor injection or by a Trickle tower completely saturated with water vapor. 3. The method according to claim I and 2, characterized in that the granular phosphate rock poured continuously between filter surfaces while the nitrogen oxide-containing Gas flow qiier sent through for this purpose. 4. The method according to claim 1 and 2, characterized in that one finely powdered, phosphate-containing Rocks by a correspondingly accelerated, saturated with water vapor, containing nitrous Let the exhaust gas flow swirl in a continuously operating fluidized bed arrangement. 5. The method according to claim I _1, characterized in that phosphai-containing rocks are suspended in a very fine grinding in water and brought into intimate contact with your stickci'iidhaltigen gas stream. b. Method i.ach claim 1 and 5 thereby characterized that one "ine wi'Vige suspension of very finely ground phosphate rock by a washing tower with multi-layer hordes in the Circulation sends through and thereby in this tower in intimate contact with the nitrogenous Brings exhaust gas flow, which is first blown onto the surface of the suspension and then through absorption layers of its nitrous content and, through mist eliminators, of excess water content is practically liberated. 7. The method according to claim 1 and 5, characterized in that wetted with water, previously finely ground, phosphate-containing rocks in a continuously operating fluidized bed system whirled up by a dry, nitrous-containing exhaust gas. 8. The method according to claims 1 and ί and / or 6 and / or 7, characterized in that known to the water used to moisten the finely ground phosphate rock Adding wetting agent. 9. The method according to claims I and 5 and / or b and / uuer 7 and / or 8, thereby characterized in that known reagents which promote the absorption of nitrogen oxides are used Suspension adds. 10. The method according to claims 1 to 9, characterized in that the absorption of nitrogen oxides by the addition of oxidizing agents, like ozone, hydrogen peroxide or peracids. 11. Use »k'r according to claims I to K) After absorption of the nitrogen oxides, partially closed Absoiptinnsinseri / iir ΛιιΓ; ιγ drive in accordance with the usual phosphate classification to fertilizers, animal feed or phosphoric acid.