DE3137905A1 - METHOD FOR REMOVING AMMONIA AND HYDROGEN SULFUR FROM A VAPOR FLOW - Google Patents

Description

- β / ΐυιΐΜΛ - KiMMC ι ^ / 90-> patent attorneys and m

- DÜHLING - (VlNNß .- «..« -.,; Representative at the EPO ^

Grupe - ^D - * ■ * ■ ^{": ·:} * ''^{'-' '':} ° ^{Dipl" "lns 'H} - ^Tiedfke'

Dipl.-Chem. G. Bühling Dipl.-Ing. R. Kinne Dipl.-Ing. R Group Dipl.-Ing. B. Pellmann

Bavariaring 4, Postfach 202403 8000 Munich 2

Tel .: 089-539653

Telex: 5-24845 tipat

cable: Germaniapatent Munich

September 23, 1981

DE 1531

case 1893

USS ENGINEERS AND CONSULTANTS, INC., Pittsburgh, U.S.A.

Process for removing ammonia and hydrogen sulfide from a steam stream

The invention relates to a method for removing hydrogen sulfide and ammonia from a steam stream.

Methods for removing hydrogen sulfide are numerous and ammonia from steam streams, e.g. known from coke oven gas. Hydrogen sulfide is generally used removed from such steam streams by passing the steam stream through a hydrogen sulfide scrubber, which works with aqueous ammonia as a washing liquid. By maintaining a high concentration of ammonia in the scrubber or trickle tower, based on the hydrogen sulfide concentration in the steam stream, it is possible to have a high percentage, for example about Remove 98% hydrogen sulfide from the vapor stream.

VIII / 22

Deutsche Bank (Munich) KIo. 51/61070 Dresdner Bank (Munich) KIo. 3939 Β1Ί Poslacheck (Miinchfin) KIo 670-43-B04

^:: ~ ^: - :. 3Ί 37905

DE 1531

Furthermore, various procedures have become known in which ammonia is removed from the vapor stream and this ammonia is reused in a hydrogen sulfide scrubber. Some of these procedures are in the US Pat. No. 4,009,243 describes from which the distillation of wash water from the hydrogen sulfide scrubber for Generation of a steam stream with hydrogen sulfide and ammonia can be seen. This steam flow and also the one leaving the hydrogen sulfide scrubber Steam streams are then treated to separate the ammonia. This treatment is carried out by these steam streams are passed through one or more absorbers or absorption apparatus, such as those who use aqueous ammonia phosphate solutions. the

Ammonia vapors are then removed from the ammonia-enriched solution by distillation. These ammonia fumes are then recycled to the hydrogen sulfide scrubber.

The invention relates to a method for removing hydrogen sulfide and ammonia from one Steam stream and from a dilute aqueous solution containing free and bound ammonium salts and acid gases, in which the steam stream is washed in a hydrogen sulfide scrubber or trickle tower, in the steam stream with an aqueous ammonia washing solution for the removal of hydrogen sulfide and for

Generation of a 30th enriched with hydrogen sulfide

aqueous ammonia solution is brought into contact,

subjecting the dilute aqueous solution to a first multi-stage, continuous countercurrent distillation, by heating the solution with the help of a Abstreifgg steam is carried out, an overhead steam stream from the first distillation stage withdraws the acidic

DE 1531

Gases from the solution and the ammonia from the free ammonium salts contains, withdraws an aqueous bottom stream or bottom stream from the first distillation stage, which contains essentially all bound or fixed ammonium salts, alkali is added to the bottom stream withdrawn and then the withdrawn bottom stream of a second multistage, continuous countercurrent distillation subject to an aqueous sump stream and an overhead

Steam stream containing ammonia, released from the bonded-10

NEN ammonium salts ^ from the second distillation stage withdraws the overhead vapor stream from the second distillation stage through an indirect or indirect heat exchanger for partial condensation of the steam flow

conducts the liquid from the first distillation stage. 15th

through the indirect heat exchanger to generate a

Stripping steam passes and the ammonia in the overhead stream the second distillation stage passes from the indirect heat exchanger to a sulfur water scrubber, 2Q by at least partially the ammonia in the washing solution to be provided.

The invention will now be explained in more detail with reference to the accompanying drawing, which is a flow diagram shows a preferred embodiment of the invention.

Referring to the drawing, a stream of steam flows, for example coke oven gas with a content of acidic

Gases and ammonia through line 201 into a hydrogen sulfide scrubber or hydrogen sulfide trickle tower

202, in which the steam stream with washing liquids and Vapor is brought into contact via the lines

203, 204, 205 and 206 are introduced. A watery one

ammonia solution enriched with hydrogen sulfide leaves the scrubber through line 217 and an ammonia

DE 1531

containing vapor stream flows through line 207 to an ammonia absorber 208, in which the ammonia-containing Steam stream in contact with a lean absorption solution, for example an aqueous ammonium phosphate solution

is brought. The stripped steam stream leaves the

Absorber 208 through line 210. An ammonia-rich absorber solution leaves absorber 208 through line 211 and flows to a second ammonia absorber 212. 10

An aqueous solution, for example a waste water from a coal plant, with a content of bound and free Ammonium salts and acid gases, flows through line 213 in a first, multi-stage, continuously operating Countercurrent Distillation Column 214. The overhead vapors with a content of acidic gases, ammonia and water vapor leave the first distillation column 214 through line 215. The vapors in line 215 flow

to a deacidification tank 216 together with the aqueous ammonia solution enriched by hydrogen sulfide from the line 217. Steam is introduced into the deacidification tank 216 via the line 218 _{to remove O} r ammonia and hydrogen sulfide by distillation, the. leave the container via line 219 to flow to the second ammonia absorber 212. The bottom liquid from the container 216 flows through the line 203 to the scrubber 202. A steam stream with it

a content of acidic gases leaves the second absorber 212 through the line 220 and an ammonia-enriched one The absorber solution leaves the second absorber 212 through the line 221. The ammonia can be removed from the through the

Line 221 discharged absorber solution by stripping 35

removed.

DE 1531

The pH in the first distillation column 214 is adjusted so that essentially all of the acidic gases and essentially all of the ammonia from the free ones

Ammonium salts are removed from the aqueous solution, 5

which is introduced into column 214 via line 213. An aqueous sump stream with a pH of less than 8 (preferably 5 to 6) and containing bound ammonium salts flows out of the column 214 through line 222. This sump stream is lime was added at point 223. Deposited solids can be removed at this point. The bottom stream, which now has a higher pH value, flows into a second, multi-stage, continuously operating one Countercurrent distillation column 224 to which steam is added through line 226. A stream of steam with essentially pure ammonia and steam leaves the column 224 via line 225. An aqueous Bottom stream with a pH of 9.5 to 12 leaves

the second column 224 through line 227 where the stream is directed to a biological treatment plant can be.

The steam flow in line 225 is indirect Heat exchanger 226a passed, in which a liquid passed through line 227 between the first Distillation column 214 and the heat exchanger 226a flows, is evaporated to be used as stripping steam for the

SQ to serve first distillation column. A partially condensed vapor stream from heat exchanger 226a flows through line 228 and may or may not be directed to hydrogen sulfide scrubber 202

can, as shown, in liquid and vapor streams 35

be separated in a cutting or separating device 229. An aqueous ammonia stream leaves the separation

DE 1531

direction 229 via line 230. At this point, the aqueous ammonia stream can pass through line 231 to the second distillation column 224

or can through line 232 to the sulphate water g

Cloth washer 202 are performed. The ammonia vapor stream from the separator 229 flows through the line 233, through which it can flow directly to the hydrogen sulfide scrubber. Alternatively, the ammonia vapor stream, as shown, are passed through a condenser 234 in which the steam is converted to a liquid stream and passed through line 204 to the scrubber 202.

The dilute aqueous solution introduced into the first distillation column 214 is typically CO2, H s and HCN as well as bound and free ammonium salts. Usually the gases make acidic and free and fixed ammonium salts up to about 0.6% by weight of the aqueous solution. If the solution is a sewage out Coking plants or coal conversion plants, other components such as tar, phenols, fluorides, Chlorides, sulfates, thiosulfates and thiocyanates may be included. Under these circumstances, the tar matter would

can be removed by decanting. The wastewater from coke ovens and other coal conversion plants is often used referred to as ammoniacal alkaline solutions. The main ones Free and bound salts in the alkalis are the following:

free salts. bound or fixed salts

Ammonium carbonate ammonium chloride ammonium bicarbonate ammonium thiocyanate Ammonium sulphide ammonium ferrocyanide ammonium cyanide ammonium thiosulphate

Ammonium sulfate

15th

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In addition to ammonia and ammonium salts, the wastewater can have low concentrations of suspended and dissolved
Contain tar compounds. The most important of these compounds are phenols or "tar acids", the concentration of which is usually in the range from about 0.3 to about 15 g / l of alkali. Pyridine bases, neutral oils and carboxylic acids are also present, but in much lower concentrations.

The following table illustrates the range of compositions in wastewater from a coking plant, which include aqueous solutions that are practical Implementation of the invention are particularly suitable.

Tabel

20th

30th

typical compositions, ppm

Z
component , compositional
area
ppm up to 10000 sewage
number 1 sewage
No. 2 sewage
No. 3 free ammonia 450 up to 4000 1900 770 1350 bound ammonia 700 up to 1000 1900 1190 2440 Cyanide 2 until 1300 210 35 65 sulfide 0 up to 4000 500 1 10 Carbonate 150 to "8500 2180 190 350 chloride 750 up to 3000 2300 1920 4460 Sulfate / sulfite 150 up to 600 310 325 415 Thiosulfate 90 up to 1000 440 115 300 Thriocyanafc 100 until 2000 700 150 310 Total sulfur 200 up to 150 1300 250 550 fluoride 30th up to 3600 60 40 75 Phenols 300 until 9.1 1500 400 725 pH 7th 9.0 7.5 7.6

35

- \ / - 40 DE 1531

The feed temperature at the inlet in line 213 can be

are in the range of about 15.6 to 129.5 ⁰ C; the temperatures of the overhead stream of line 215 can range from about 60 to 129.5 C; the temperatures of the

Bottom stream in line 222 can range from 71.1 to 135 ° C. The first distillation stage can take place at an absolute pressure in the range from about 0.3 to 3.0 be carried out in cash. During this first distillation, essentially all of the free ammonium salts, i.e. sulphide, carbonate and cyanide decomposed to ammonia and acidic gases which are removed by the stripping steam.

The lime added at point 223 reacts both

with the bound ammonium salts releasing ammonia as well as with any remaining acidic ones Gases.

1 ° of the second distillation stage can be the feed temperature in line 222 in the range of 68.4 to 132.2 ° C lie; the overhead vapors in line 225 can be a Have a temperature of about 60 to 143.3 ° C; the bottom stream in line 227 can have a temperature of about 71.1 to 146.1 ° C. The absolute pressure can be up to about 4 bar. The swamp flows out of the second Distillation stages have a low concentration of total ammonia and cyanides. The pH is in the range, from 9.5 to 12. The total ammonia can be as low as 25 ppm. All of the cyanides, including complexed cyanides and free cyanides as the equivalent of the HCN concentration, can be present in an amount as low as 2 ppm; The free

Cyanides (those cyanides that are attacked by chlorination 35

can even be less than 1 ppm in some cases. This sump stream can be cleaned and then used

-I ^ / J4. DE 1531

Removal of other organic materials, e.g. phenols.

If the overhead vapor stream from the second distillation stage is passed through an indirect heat exchanger to generate stripping steam for the first distillation stage, instead of using the overhead vapor stream from the second distillation stage as stripping steam for the first distillation stage, the introduction of additional ammonia in the first distillation stage can be avoided and the pH in the first distillation stage can be kept low, preferably in the slightly acidic range, so that the removal of acidic gases in the first distillation stage is increased.
■ -

Since essentially all of the acidic gases and free ammonia are removed in the first distillation stage, can use the second distillation stage to optimally remove the ammonia from the alkaline solution bound ammonium salts are carried out. Furthermore, the solution with the bound ammonium salts has minimal Salt deposits that would arise in the presence of acidic gases.

A method for removing hydrogen sulfide and ammonia from a vapor stream and from a dilute one aqueous solution containing free and bound Ammonium salts and acid gases, is that

the steam stream is washed in a washer (202) by

the steam flow with an aqueous ammonia solution to Removal of hydrogen sulfide from the vapor stream is brought into contact with the dilute aqueous solution "P. a distillation process (214,224) for removal subject to free and bound ammonia, an over-

/ £. DE 1531

1 top vapor stream from the second distillation stage (224) through an indirect heat exchanger (226a) for heating the liquid in the first distillation stage (214) conducts and then the overhead steam flow to a

5 washers (202) for removing the hydrogen sulfide directs.

Claims (5)

Claims 1. A method for removing hydrogen sulfide and ammonia from a steam stream and from a dilute aqueous solution containing free and bound ammonium salts and acid gases, in which the steam stream is washed in a hydrogen sulfide scrubber by
the steam stream is brought into contact with an aqueous ammonia washing solution to remove hydrogen sulphide and to produce an aqueous ammonia solution enriched with hydrogen sulphide, the dilute aqueous solution is subjected to a first multi-stage, continuous countercurrent distillation, which takes place by heating the solution by means of a stripping steam, an overhead steam stream, which contains acid gases from the solution and ammonia from the free ammonium salts, withdraws from the first distillation stage, withdraws an aqueous bottoms stream from the first distillation stage, which essentially contains all bound ammonium salts, adds alkali to the withdrawn bottom stream and then the withdrawn bottom stream of a second subjected to multi-stage, continuous countercurrent distillation and an aqueous one from the second distillation stage VIII / 22 Deutsche Bank (Munich) Account 51/61070 Dresdner Bank (Munich) Account 3939 8 <! 4 Postal check (Munich) account 670-43-804 -3 ^ Λ / DE 1531 Bottom stream and an overhead vapor stream with a grade of ammonia is withdrawn from the bound ammonium salts, characterized in that the overhead vapor stream (225) from the second distillation stage (-224) through 5 directs an indirect or indirect heat exchanger (226a) for partial condensation of the steam flow, the liquid (227) from the first distillation stage (214) through the indirect heat exchanger (226) for production a stripping steam and the ammonia in the overhead stream of the second distillation stage (232, 233) from the indirect heat exchanger (226a) to the hydrogen sulfide scrubber (202) to at least partially to provide the ammonia in the washing solution. 2. The method according to claim 1, characterized in that the ammonia in the hydrogen sulfide scrubber (202) introduced as an aqueous ammonia stream (232, 204) will.
20th 3. The method according to claim 1, characterized in that the ammonia in the hydrogen sulfide scrubber (202) is introduced as a steam stream (233). 4. The method according to claim 1, characterized in that that the condensate (231) generated in the indirect heat exchanger (226a) to the second continuous distillation stage (224) and that the uncondensed part (233 or 204) of the steam flow into the hydrogen sulfide f washer (202) is introduced. 5. The method according to claim 1, characterized in that both the condensed (232) and the uncondensed (233 or 204) parts of the steam stream from the heat exchanger (226a) into the hydrogen sulfide scrubber (202).