CA1093791A

CA1093791A - Method of stripping chemically combined ammonia from the aqueous condensates and waste waters of low and high temperature carbonization processes

Info

Publication number: CA1093791A
Application number: CA259,491A
Authority: CA
Inventors: Heinrich Weber; Hubert Schmitt; Georg Abendroth; Dieter Laufhutte
Original assignee: Carl Still GmbH and Co KG
Current assignee: Carl Still GmbH and Co KG
Priority date: 1975-08-23
Filing date: 1976-08-20
Publication date: 1981-01-20
Also published as: NL7607273A; JPS5647832B2; DE2537640B2; FR2322096A1; FR2322096B1; IT1076914B; GB1557478A; DE2537640A1; JPS5226503A

Abstract

259,491 (#13,255) METHOD OF STRIPPING CHEMICALLY COMBINED AMMONIA
FROM THE AQUEOUS CONDENSATES AND WASTE WATERS
OF LOW AND HIGH TEMPERATURE CARBONIZATION PROCESSES

ABSTRACT OF THE DISCLOSURE

A method of stripping the chemically combined ammonia in aqueous liquids of low- and high-temperature carbon-ization of bituminous and sub-bituminous coal, bituminous skale and peat, and from the waste waters of processing gases thereof comprises, mixing the aqueous liquids with alkaline solution or suspensions and heating the mixture to form water soluble pro-ducts.

Description

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BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION
.
; ~ This invention relates, in general, to a method of removing chemically combined~ammonia from aqueous liquids and, in particular, to a method for removîng this ammonia from con-derlsates and waste waters of various processes by mixing them with alkaline substances and heating the mixture.

DESCRIPTION OF THE PRIOR ART

A known treatment for the condensates of carbon-ization gases and waste wakers of gas scrubbing operations is ; described for example in "O. Grosskinski, Handbuch des Kokereiwese (Manual of the~ Goking Industry), Vol. II, DUsseldorf, on pages 94 et seq.. Calcium~hydroxide LCa(OH)2¦ alone is there indlcated as having a strong alkaline~reaction.

The use of calcium hydroxide in the form of lime mllk is particularly troublesome due to its low solubility in water. In addition, since carbonates are always present in the aqueous condensates which are treated together with the waste water from the scrubbing of carbonization gases, the formation of insoluble calcium carbonate cannot be avoided.
Although there is a problem of clogging in the pipes of the processing system due to this suspended material7 it is not economically feasible to use alkaline substances such as sodium hydroxide which form soluble carbonates.

Substances other ~han hydroxides have not been used in the past for liberating the chemically combined ammonia in these known processes.

SU~ Y OF THE INVRNTION

The present invention relates to a method similar to the one described above for removing the chemically combined ammonia from aqueous liquids using substances which form water soluble products. This simplifies the method and reduces the expense of equipment used.

In accordance with the invention, ammonia is removed from the aqueous liquids or condensates and waste waters of low or high-temperature carbonization processes, by using aqueous solu~ions. of carbonates and sulfides Qr their hydrogen compounds, and cyanides and polysulfides of the first group o~ elements in the periodic chart. Examples of such compounds are the simple and cheaply produced carbonates of sodium, and potassium and lithium waste liquors from various industrial processes. The use of waste liquors which are often worthless make the inventive method parti-; cularly economical. The alkali in these liquors is not necessarily combined with carbonic acid but may be combined with one of the above mentioned weak acids such as hydrogen sulfide or hydrogen cyanide.

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Also suitable are any alkali salts of weak acids which dissolve in water upon hydrolysis and fcrm hydroxyl ions.
Stoichiometric quantities of the alkali salt solutions have been found to produce sufficient alkalinity when they are hydrolyzed in the condensates and waste waters, ~o csmpletely liberate ammonia from combination wlth strong acids such as hydrochloric acid. The mixture is then heated to the boiling point to strip the free ammonia. The waste water from this process has an ammonia concentration of less than 0.1 g per liter and this waste water may be removed.

The following diagram shows the results of a series of tests in which coal water from which free ammonia had been removed but which contained chemically combined ammonia, was treated with aqueous solutions containing sodium carbonate and sodium hydrogen carbonate. After heating (distillation) and with a carbonate to hydrogen carbonate ratio by ~eight of 1:1, far less ~han O.l g per liter of ammonia remained combined in the solution.

Residual Quantity of NH3 as a Function of the Amount of NaOH which may Form by ~issociation and Hydrolysis Ratio:
Na2CO 3 : NaHCO
Curve 1 100 : O
' ~ 2 9S : S
~lo~ ~ 3 90 :10 ~60 .~ , ~;0 ~:) 8~ IQ~
THEOR Tl:AL % of N~OH

- 3a -~ t7~ ~

The waste liquors from the hydrogen sulfide scrubbers of carbonization gases which use sodium hydroxide or potassium hydroxide solutions have been found to be parti-cularly suitable for carrying out the inventive method. These compounds are converted to some carbonate, hydrogen carbonate, sulfide, hydrogen sul~ide and cyanide. The alkaline material is thus advantageousl~ used twice in ~e same plant; once to purify the ~ases and a second time to release the combined ammonia. The release of chemically combined ammonia insures that the waters which are returned to drainge ditches for removal are cleaner.

Experience wîth the method has shown that preliminary conventional purification of the oven-gases in an NH3-H2S circulation scrubbing process is particularly useful.
About 80% of the H2S in the crude oven-gases can be removed, leaving about 1.0 g per Nm of H S, without the requirement of additional substances such as gaseous ammonia. The residual H2S can be removed in an alkaline solution scrubbing process.
The simultaneous removal of acids and C02 in such a process results in the advantageous formation of an alkaline solution in just the quantities needed to release the combined ammonia in the ammoniated aqueous condensates and the scrubber waste water.
This fine purification of ~he oven-gases does not burden the waste waters with additional salts since, in an economically conducted operation, the waste liquors of the H2S scrubber does not contain free hydroxides but, as mentioned before, contains the converted products that are suitable for removln$ the combined ammonia.

Accord~n~y ? it is an object ~f the in~ent~ve method to provide an ammonia releasing process that prGduces ~30 few unsoluble products and advantageously and economicall~ uses the available materlals in a convent~ carbonization plantt ~ 3~

The various features of novelty which charac~erize the inventiGn are pointed out with particularity in ~e claims annexed to and forming a part of this disclosure. For a bPtter understanding of the invention, its operating advantages and specific objects attained by i~s uses, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The sole drawing is a flow chart representing a coke oven-gas and waste water processing method in accordance with the invention.

DF,SCRIPTION OF THE PREFERR~D EMBODIMENTS

Referring to the drawing, in particular, the invention embodied therein comprises a method of removing the chemically combined ammonia from:the was~e waters of a coking plant producing 100,000 Nm per hour of coke-oven gas having an H2S content of 8 g. per Nm3, which is to be removed also.
The crude coke-oven gas at a temperature of 25 to 30 Cis supplied through a Line l ~o ~he preliminary desulfurizer 2 of a desul~urizing device 2a. In preliminary desulfurizer 2, the gas is desulfurized to a concentration of 1.0 g per Nm3, inan NH3-H2S recirculation scrubbing process using 90 m per hour of a 2.5% aqueous solution of NH3. The water containing NH3 and enriched with H2S is pum~ed through line 3a ~o a deacidizer 4 where it is regenerated, i.e. the acid components H2S, CO and HCN and removed. In ~he desulfurizer 2a ~he pre-purified gas pas~ses from the preliminary desulfurizer 2 to a fine purifier 5 where it is mixed wi~h 12~5 m3 per hour of soda lya supplied through line 6. The amount o~ soda lye supplies 370 kg per hour of NaOH to 5. Finely purified ~oke-oven gas containing less than 0.1 g of H~S per Nm is discharge~ through a line 7.

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The resulting solution, containing unimportant quantities of NaOH and enriched with H2S, CO2 and HCN, accumulates at the bottom of fine purifier 5 and is drawn off through line 8 and supplied to the lower portion of an ammonia stripper 9. 45 m per hour of coal water, i.e. the aqueous condensates o~ the coke-oven gas, is supplied to stripper 9 through line 10. About 13 t of heating steam is also supplied to stripper 9 through , line 11. Waste water containîng only traces of ammonia is drained from the sump of stripper 9 through line 12. This waste water contains quantities of salts corresponding to the amounts of chemically combined ammonia now su~stantially removed. The volatile components of the coal water pass with water vapor through line 13 and 14 into the deacidizer 4. The steam supplied through line 11 to the stripper 9 is of an amount sufficient to also strip the acid components of the ammonia water which has been supplied to the deacidizer 4 from ~he desulfurizer 2a through line 3a. The regener~ed ammonia water then passes from deacidizer 4 to preliminary desulfurizer 2 through line 3 and closes the circulation of ammonia water. Water lost in the process is compensated by a water line 3b on line 3.

All ~he volatile and volatilized compounds leave deacidizer 4 through a line15 a~ the top of the column in the form of watery vapors. Thi.s includes the initially free ammonia, the initially combined ammonia, H2S, carbon dioxide and HCN.
These vapors may then be further processed in known ways to remove ammonia and hydrogen sulfide. The ammonia may also be burned or decomposed in other known processes.

S~oichiometrically, the 370 kg. per hour of NaOH
su?plied to the fine purifier 5 through line 6 corresponds to the chemically combined an~lonia in the 45 m3 of coal water supplied to the stripper through line 10.

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If~ with other conditlorls remaining constan~, 300 kg per hour of vaporous ammonia are supplied from stripper g to desulfurizer 2, for example through a connec~ing line leading ~rom line 13 i.nto desulfurizer ~ at a location above the connection of line 3, a H2S content in the gas of 0.5 g~l2$ per Nm3 is obtained in desulfurizer 2 and 0~02 g of H2S per N~3 of gas are obtained in desulfurizing device 2a and, thereby, -in the gas which is discharged from the.plant through line 7.
The invention is thus a process for purifying crude c~e oven gas of H25 and for strlpping chemically combined ammonia ro~ the aqueous condensates and waste waters of the cok-ing plant, using an aqueous solution of alkaline hydroxide comprising- ,' (a) introducing crude gas from the coke oven plant into a preliminary desulfurizing zone (2) of a des.ulfurizing unit (2a~ having the preliminary desulfurizing zone (2) for coarse scrubbing of H2S from the gas 7 and a final puriflcation zone (5) for fine scrubbing of H2S from the gas, (b~ contactîng the crude gas with a regenerated aqueous solution of ammonia in the preliminary desulfurizatlon zone (2~ of.said.desulurization unit (2a), and removing at least 8U weight percent of H2S from the crude coke oven gas, (c) subsequen~ly withdrawing once used aqueous solution o ammonia.from the preliminary desulfurizing zone of the desulfurization unit and passing the once used aqueous ammonia solution to a deacidifier unit (4), (d3 passing partially purified crude coke oven gas from the preliminary desulfurization zone (2) of the desuLfur~
izatîon unit to the final,fine scrubbing zone (5) of the ,~
~ ,~
. -7-. . .

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desulfurization uni~ C2a~, and mixing said partially purified gas with a quantity of an aqueous a~kaline hydroxide solution, whereby a finely purified coke oven gas is obtained havlng less than about 0.1 gm H2S per Nm3~
Ce) withdrawing and recovering the ~inely purified coke oYen gas from the desulfurizing unit, ~ ) withdrawing once used alkaline hydroxide solution enriched with H2S from the fine scrubbing zone (5) of the desulfuri ation unit (2a) and introducing the once used H2S ~riched alkaline hydroxide solution into an amrnonia stripper u~i~ (9) .
(g) contacting the H2S enriched alkalinP hydroxide solution in the amrnonia stripper unit ~9) with aqueous con-densates and waste water from the coke oven pla~t including chemically com~ined ammonia ~nd with steam, which are charged to the armnonia stripper unit (9), ~ h) removing waste water ~rom the ammonia stripper unit (9), whereby said waste water contains only traces of ammonia and salts therein;
(i.) removing ga~eous vapors containing ammonia fsom the a~monia stripper unit (9) and passing said vapors to the deacidiier unit ~4)~
~ ;) mixing the once used aqueous ammonia solution from the pre~.iminary zone (23 of the desulfurization unit (2a) in the dPacidiier unit (4~ with said gaseous vapors from the ammonia stripper~unit (9~, : (k~ separating and removing the volatile produc~s NH3, ~2S- HCN and C02 from the deacidifier unit (4) and recovering said w latile products; and :: ' .

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~ 1) withdrawing from said deacidifier unit (4) the xegenerated aqueous solution of ammonia for recirculation in the preliminary zone (2) of the desulfurizing unit (2a);
(m) the quantity of the aqueous alkaline hydroxide solution corresponding stoichiometrically with the chemically com~ined ammonia in the aqueo~s condensates and waste water ~rom the coke ~ven pl~nt supplied to the ammonia stripper unit (~9~

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for purifying crude coke oven gas of H2S and for stripping chemically combined ammonia from the aqueous condensates and waste waters of a coking plant, using an aqueous solution of alkaline hydroxide comprising:
introducing crude gas from the coke oven plant into a preliminary desulfurizing zone of a desulfurizing unit having the preliminary desulfurizing zone for coarse scrubbing of H2S from the gas, and a final purification zone for fine scrubbing of H2S from the gas;
contacting the crude gas with a regenerated aqueous solution of ammonia in said preliminary desulfurization zone of said desukfurization unit, and removing at least 80 weight percent of H2S from the crude coke oven gas;
subsequently withdrawing once used aqueous solution of ammonia from said preliminary desulfurizing zone of said desulfurization unit and passing the once used aqueous ammonia solution to a deacidifier unit;
passing partially purified crude coke oven gas from said preliminary desulfurization zone of said desulfurization unit to said final purification zone of said desulfurization unit, and mixing said partially purified gas with a quantity of an aqueous hydroxide solution, whereby a finely purified coke oven gas is obtained;
withdrawing and recovering the finely purified coke oven gas from said desulfurizing unit;
withdrawing once used alkaline hydroxide solution enriched with H2S from said fine purification zone of said desulfurization unit and introducing the once used H2S enriched alkaline hydroxide solution into an ammonia stripper unit;
contacting the H2S enriched alkaline hydroxide solution in said ammonia stripper unit with aqueous condensates and waste water from the coke oven plant including chemically combined ammonia and with s steam, which are charged to said ammonia stripper unit;
removing waste water from said-ammonia stripper unit, whereby said waste water contains only traces of ammonia and salts therein;
removing gaseous vapors containing ammonia from said ammonia stripper unit and passing said vapors to said deacidifier unit;
mixing the once used aqueous ammonia solution from said preliminary zone of said desulfurization unit in said deacidifier unit with said gaseous vapors from said ammonia stripper unit;
separating and removing volatile products of NH3, N2S, HCN and CO2 from said deacidifier unit and recovering said volatile products; and withdrawing from said deacidifier unit the regenerated aqueous solution of ammonia for recirculation in said preliminary zone of said desulfurizing unit;
the quantity of the aqueous alkaline hydroxide solution corresponding stoichiometrically with the chemically combined ammonia in the aqueous condensates and waste water from the coke oven plant supplied to the ammonia stripper unit.

2. Process according to claim 1, wherein ammonia vapors are withdrawn from said ammonia stripper and passed to said desulfurizing unit at a point above the point where regenerated aqueous ammonia from said deacidifier unit is introduced to said desulfurizing unit.

3. Process according to claim 2, wherein about 300 kg per hour of ammonia vapors from said ammonia stripper unit are introduced into said desulfurizing unit.

4. Process according to claim 1, wherein about 370 kg per hour of NaOH are supplied to said final purifica-tion zone, whereby said NaOH corresponds stoichiometrically with the chemically combined ammonia in the aqueous condensates and waste water supplied to said ammonia stripper unit.
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