DE3128591A1 - "METHOD FOR OBTAINING AMMONIA FROM PROCESS FLOWS" - Google Patents

Description

TiEDTKE - BuHL.NO - KlNNE ....... Grupe - Pellmann: - ^: - ^: ■ ^: - - SrS

-Z> Dipl.-lng. R. Kinne

Dipl.-Ing. R group. Dipl.-Ing. B. Pellmann

^ Bavariaring 4, P.O. Box 202403

8000 Munich 2

Tel .: 089-539653

Telex: 5-24 845 tipat

cable: Germaniapatent Munich

17 July 1981 DE 1332 / case 1878

USS Engineers and Consultants, Inc.

Pittsburgh, USA

Process for the recovery of ammonia from process streams

The invention relates to a method for obtaining ammonia from ammonia and containing acid gases Process streams.

Ammonia was previously obtained from gas streams containing ammonia and acidic gases by converting the ammonia in a aqueous solution of ammonium phosphate, was absorbed. The solution absorbs a major part of the ammonia and a small part of the acid gases. Ammonia is stripped from the solution and the solution is circulated. That Ammonia and the water vapor leaving the ammonia wiper, are condensed and sent to a column for ammonia enrichment. Such procedures are in the U.S. Patents 2,797,148, 3,024,090, 3,186,795, 3,718,731 and 4,060,591; such procedures are for treatment from process streams such as coke oven gas and overhead vapors Ammonia stills used in the recovery of ammonia from wastewater are suitable. For treatment

VIII / rs

Deutsche Biink (Munich) KIo nt'1,1070 Drcsdnei Bank (Munich) KIo 3W044 Postscheck (Munich) KtO 670-43-804

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development of both process streams was proposed initially ,, ■ the ammonium phosphate solution j to be contacted and then bring the solution to the ammonia-rich ammonia vapors driven in contact with the coke oven gas flow. This procedure is described in US-PSS 3,024,090 A and 3,186,795. One of the tasks was to remove the acidic gases from the ammonium phosphate solution. However, in general, the acid gases were not removed from the absorbent solution. Therefore, in most technical systems, the. Ammonia distillation vapors simply combined with the coke oven gas stream before the absorption stage. The ammonia-rich ammonium phosphate solution is heated by means of a separate heating source to strip off the acidic gases.

The invention is a method for recovering ammonia from a gas stream and a Wastewater stream, both ammonia and acidic streams Gases contained by adding alkali to the sewage stream

™ is added to the thus treated stream of a distillation with steam, withdraws a hot ammonia-containing steam stream from the distillation stage, the gas stream through an aqueous absorption solution of ammonium phosphate conducts the hot ammonia-containing steam

■ "current through the absorption solution for stripping the directs acid gases from the absorbent solution and the absorbent solution to stripping ammonia from the Solution heated.

The invention is hereinafter referred to

explained to the accompanying drawing, which is a graphic representation of a system for carrying out the invention Procedure shows.

A gas stream containing ammonia and acidic gases,

for example coke oven gas, is passed through line 101 at the bottom. '< an absorber 102 introduced. The gases rise *,

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the absorber in countercurrent to the descending spray of the absorption solution within the absorber 102. The absorption solution is an aqueous solution of Ammonium phosphate.

The gases leave the absorber 102 through line 103, which are essentially free of ammonia. The ammonia-enriched solution overflows from the bottom of the absorber into a chamber 104 by the '0 Contact with a hot stream of steam containing ammonia he follows. Part of the ammonia-containing vapor stream condenses and is absorbed in the solution, the solution being further enriched in ammonia, and it up their boiling point is heated. The acid gases absorbed in the solution are driven off by this heating and applied by the uncondensed portion of the steam. To achieve boiling can If necessary, steam or another heating source can be used to remove the hot ammonia-containing

^u to supplement the heating source coming from the steam flow. The chamber 104 can be incorporated within the absorber 102 as shown, or it can be present as a separate container to which the rich solution from the bottom stage of the

Absorber 102 is pumped.
25th

From the chamber 104, the rich solution flows through line 105 to an ammonia stripper 106, in the solution to the steam, which is introduced for example at the bottom through line 108, in countercurrent

descends and thereby its absorbed ammonia is stripped off. Water vapor and ammonia leave the Head of scraper 106 through line 107.

The hot, regenerated lean solution flows from the bottom of the scraper 106 through line 109 to the Reuse in the absorber 102.

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The wastewater, which is a dilute solution of ammonia,

acid gases, bound ammonium salts and organic Materials, for example from a. Coking plant or contains another coal conversion plant, flows through line 110 into a still 111 in which the ammonia present in free form is driven off (hereinafter referred to as free distillation apparatus for short) and in an upward flowing stripping medium is enriched with more volatile components of the solution. The stripping medium can be a condensable gas or a non-condensable gas, for example steam, air, hydrogen, nitrogen or methane, or a combination of these gases. The stripping medium can be removed by evaporation the liquid or by bubbling a gas or vapor into the still or through a Combination of these can be generated. The 'stripping medium will generally be steam. The overhead steam that exiting free distiller 111 through line 112, a major portion of the stripping medium, e.g. Have steam and essentially all of the acidic gases and free ammonia from the wastewater. One Line 113 carries the overhead vapor to line 101. Bottom liquid from free distiller 111 flows through line 115 and is treated with alkali, for example lime or sodium hydroxide in a container 116 mixed. This alkali treated liquid is then passed through line 117 to a still 118, in which ammonia is driven off, which was previously in a bound or fixed form (hereinafter referred to as fixed Ammonia distiller). In this still the ammonia released by alkali is expelled from the liquid by vapor, which is caused by line 119 is injected and an overhead stream of ammonia vapor and water vapor is over the line 120 away. Bottom liquid is removed from fixed still 118 through line 126. The overhead vapor, which is essentially free of acidic

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Gases, flows through line 120 to chamber 104, in which he used to heat the bottom liquid from the absorber 102 is used for boiling as described above. If necessary, a portion of the overhead vapors flows from the free distiller 111 through line 114 for mixing with the overhead vapors from the fixed Still. Optionally, some of the overhead vapors from the fixed still can pass through the conduit 121 flow and the heat contained therein can be used by either the vapors directly can be added to the free distiller 111 or by passing them through a heat exchanger 122 will. In the event that the heat exchanger is used, the liquid flows from the bottom of the free distiller through line 123 through heat exchanger 122 and back to free distiller 111 through line 124. Any non-condensed vapors from the fixed still flow from heat exchanger 122 through line 125 for association with the vapors from the fixed still in the line 120 stream. It is essential that a major portion of the vapors flowing to chamber 104 be from the fixed The still comes that are not the free still 11 have happened so that the concentration of acid gases in the ammonia distillation fumes that come with the rich liquid in chamber 104 is sufficiently low that the acidic gases in the rich solution in chamber 104 from the solution

can be stripped off.
30th

The ammonia fumes from the fixed still have a noticeably higher ammonia concentration than the gas stream and a low content of acid gases, preferably below about 200 ppm. The ammonia content of

these fixed still ammonia vapors are typically about 10 to 40 percent by volume.

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• j in the context of the present invention means a

fixed ammonia distiller or ammonia expeller a still in which the feed stream is containing a strong and non-volatile alkali such as sodium hydroxide or calcium hydroxide is made alkaline so that the pH of the liquid is above about 9.5 anywhere is held in the still. Sufficient alkali (other than ammonia) is present in the feed so that the bottom stream preferably has a pH of 9.5-12.0 and preferably in the range of 10.0-11.0. Of the Fixed ammonia still can be the only still in such processes where the feed is made alkaline prior to distillation, or it can be the second still in those processes be where free ammonia is first distilled off with acidic gases and the bottoms streams from the free ammonia still made alkaline and redistilled in a second or fixed ammonia still will.

Using the invention, it is now possible to strip the acid gases from the ammonia-enriched aqueous ammonium phosphate solution from the absorber without the need for a special heat exchanger or vapors from the ammonia scraper. The fixed still operates under highly alkaline conditions which greatly counteract the volatility of the acidic gases, and therefore the vapors from the fixed still will have a low acidic gas content. Thus, within the scope of the invention, the vapors from the fixed still are vapors from any still receiving a highly alkaline feed _; regardless of whether the free still works wholly or partially _with a separate heating source or not.

Even if there is no free still, ¹ ^ d of the total supply containing free and fixed ammonia

electricity, for example with sodium hydroxide or lime alkaline is made, is

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the overhead vapor have little acidic gases and according to the invention be usable.

It is preferred that substantially all of the hot ammonia-containing vapor stream from the fixed Ammonia still comes from. Depending on the relative amounts of steam from the fixed Distillation apparatus. And those to be heated and of acidic Gases to be purified ammonia-rich phosphate solution, it may be necessary to use steam from the fixed still with steam from the free still or to be supplemented with steam. However, it is important that the concentration of acid gases in the Steam stream that with the rich ammonium phosphate solution contacted is kept sufficiently low to allow the acid gases to strip off from the solution can be done.

The absorbing solution in the absorber preferably has a temperature of about 35 to 60 ⁰ C and in particular about 45 to 60 ⁰ C. The temperature can go up jeüoch up to about 100 ⁰ C. «

The absorption and stripping steps can be carried out at different pressures. Generally the absorption is carried out at the available gas pressure. The stripping is preferably absolute at a pressure between about 7.03 to about 21.1 kg / cm ²

carried out.
30th

The aqueous ammonium phosphate solution generally has an ammonium phosphate concentration of about 10% to saturation. A concentration of about

25 to 40% is preferred.
35

Claims (3)

Claims 1. A method of recovering ammonia from a gas stream and a waste water stream, both streams being ammonia and contain acidic gases by adding alkali to the waste water stream, the so treated stream of a distillation Subjected with steam, a hot ammonia-containing steam stream is withdrawn from the distillation stage, the gas stream passes through an aqueous absorbent solution of ammonium phosphate and the absorbent solution to ammonia stripping heated by the solution, characterized in that the hot ammonia-containing vapor stream (120) is passed through the absorption solution (104) to strip the acidic gases from the absorption solution. 2. The method according to claim 1, characterized in that that the waste water stream (110) before the addition (116) of the alkali of a steam distillation (111) to remove the acidic Gases and free ammonia is subjected. 3. The method according to claim 1 or 2, characterized in that the hot ammonia-containing steam stream (120) has a higher ammonia content than the gas stream (101). 35 VIII / rs