DE1195283B - Process for the production of ammonia from coke oven gases - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

COIc

German class: 12 k-1/12

Number: 1195 283

File number: U 9343IV a / 12 k

Filing date: October 25, 1962

Opening day: June 24, 1965

The subject of the invention is a process for the production of ammonia from coke oven gases, in particular according to patent 1153 733, in which the ammonia present in the coke oven gas is absorbed in a solution of ammonia and phosphoric acid and which according to the invention is characterized in that from the solution enriched with ammonia the Ammonia is stripped off at a pressure between 7 and 21 kg / cm ^2.

Processes for recovering ammonia from a gas stream, in which the ammonia is absorbed in a solution of ammonia, phosphoric acid and water and subsequently stripped off, are known. In these processes, the molar ratio of NH ₃ to H ₃ PO ₄ in the solution intended for absorption is below 1.5. After the ammonia is absorbed from the gas, this molar ratio is over 1.5.

Absorption and stripping are two separate process steps that can be carried out at different pressures. The absorption is usually carried out at the pressure present in the gas. The stripping is carried out at a slightly increased pressure between 7 and 21 kg / cm ² .

The known technical experience suggests that strong superatmospheric pressures should be avoided if the temperature of the cooling water present is not too high for the condensation of the product emerging from the top of the furnace, so that cooling would be necessary when normal pressure is used. In addition, the equilibrium conditions and the thermodynamics of the distillation and stripping processes usually become more unfavorable when the pressure and, accordingly, the temperature are increased. In addition, tests of corrosion resistance on ammonium phosphate solutions show that carbon steels are unsuitable for wiping devices, even when operating at atmospheric pressure. This is particularly true of lean solutions, which gradually become more acidic as the molar ratio of NH ₃ to H ₃ PO ₄ falls below 1.5. The stainless austenitic steels, e.g. B. AISI 304 and 316, showed a satisfactory corrosion resistance in lean solutions at their boiling point only at atmospheric and moderately elevated pressure. Their susceptibility to corrosion increases disproportionately at pressures of more than 6.3 kg / cm ² , so stripping at such pressures should therefore be uneconomical.

Process for the production of ammonia from
Coke oven gases

Addendum to the patent: 1153 733

Applicant:

United States Steel Corporation,

Pittsburgh, Pa. (V. St. A.)

Representative:

Dipl.-Ing. M. Licht, patent attorney,

Munich 2, Theresienstr. 33

Named as inventor:

Marvin Chester Fields, Monroeville, Pa .;

Robert Dare Rice, Pitcairn, Pa. (V. St. A.)

Claimed priority:

V. St. of America of October 31, 1961 (149 111)

Although these test results were known, it was unexpectedly found that above a critical pressure the susceptibility to corrosion is not excessively high. It has been found that when the process cycle of the invention is used to recover ammonia from coke oven gases, the susceptibility of these and other stainless steels to corrosion is unexpectedly moderate and acceptable ^{at absolute pressures in excess of 7 kg / cm 2.} It has also been found that at pressures greater than 7 kg / cm ² the stripping provides a more enriched and purer ammonia water and a lean, more acidic stripped absorbent solution with less steam or heat consumption. These effects allow further savings in equipment and processing during the absorption and stripping cycle and in the fractionation of the ammonia water to provide predominantly anhydrous ammonia.

A detailed knowledge of the invention should be obtained from the detailed description below

509 597ß39

the drawing are conveyed, which represents a preferred embodiment of the invention. The drawing represents the method according to the invention schematically.

To explain the drawing, it should be said that the coking plant exhaust gas is introduced through a line 10 into the lower end 11 of an absorbing device 12. The gases rise through the lower end 11 and the upper end 13 in countercurrent to the downwardly directed jets of the absorbent solution which are introduced through a conduit 14 into the upper end 13. The solution flows from there through a float 15 into the lower part 11. The absorbent solution is again fed by pumps 16, 17 to the spray devices 18, 19 in parts 11 and 13, respectively, so that a dense spray takes place in each of the areas. The absorbing solution consists of ammonia, phosphoric acid and water. The molar ratio of NH ₃ to H ₃ PO ₄ has the lowest value in the line 14, a slightly higher value in the upper part 13 and an even higher value in the lower part 11. According to the invention, the expression "lean solution" refers to the leanest solution in line 14 and the term "rich solution" is applied to the richest solution delivered by the successive absorption steps. In accordance with the present invention, a lean solution has a molar ratio less than about 1.5 and a rich solution has a molar ratio greater than 1.5. The molar ratio of NH ₃ to H ₃ PO ₄ in the solution, together with the temperature and the water concentration, determines the ammonia content of the solution and its ability to absorb further ammonia.

The coking plant exhaust gases pass through a separating device 20 and leave the absorption device through a line 21 which is predominantly free of ammonia. The solution enriched with ammonia is, overflows from the lower part 11 into a chamber 22 in which it is in contact with steam which has been distilled from an ammonia liquid in an ammonia bubble (not shown). The distillation of ammonia liquids produced in coking plants is known. The steam is sent through line 23, after being compressed if necessary, and into the chamber 22 initiated below the liquid level. Part of the vapor from the ammonia bubble condenses and is absorbed by the solution, making it more enriched with ammonia and up their boiling point is heated. The uncondensed part of the vapor escapes from the ammonia bubble out of the chamber and rises with the coke oven gases through the absorption device.

The "rich solution" leaves the chamber 22 through a line 24 and is fed to a pump 25, which ^{sends it through a line 26 at a pressure between 7 and 21 kg / cm 2} into a stripping column 27. The solution is first heated in a heat exchanger 29 by the product emerging from the top of the column 27 in the line 28 and then brought to its boiling point by a heat exchanger 30. In the column 27, the solution sinks in countercurrent to a vapor stream generated at the bottom, and is thereby stripped of the absorbed ammonia. The steam for stripping could be supplied by direct injection through a conduit 31 or by indirect heating in a cooker (not shown) or by a combination of these means.

The ammonia-water vapor mixture leaves the top of the stripping device through line 28. The mixture is partially condensed and cooled in heat exchanger 29 and fully condensed in heat exchanger 32. A pump 33 then pumps it through line 34 under pressure more than 10.5 kg / cm ² in a fractionation column 35 where it descends in countercurrent to a steam flow rising from the bottom and which is generated by steam supplied through line 36. A part of the fractionating column 35 escapes at the bottom through a line 37, which consists predominantly of water, while the part which leaves the top of the column through a line 38 consists predominantly of anhydrous ammonia. Neutral and basic oils, which come from the coking plant exhaust gases, easily collect in the middle section of the fractionation column. They can be drawn off as a vaporous secondary stream through a line 39, condensed in a heat exchanger 40 and decanted in a decanter 41. On the other hand, a liquid secondary stream can be drawn off and the oils can be decanted in the decanter 41. The oil layer is withdrawn through line 42 and the Amomniak water layer is returned through line 43 to the column. The anhydrous ammonia in line 38 is condensed in a heat exchanger 44, part is fed back through a line 45 of the column 35 as reflux, the remainder flows through an activated carbon absorber 46, in which all remaining oils are removed, and then through a line 47 in a storage container in which it is stored as ammonia for cooling purposes.

The warm, lean, regenerated solution flows from the bottom of stripping column 27 through line 48 into an evaporator 49, which operates under vacuum, so that the excess water through a pipe 50 is withdrawn as vapor, which contains only a negligible amount of ammonia. The water vapor is in a directly working cooling device 51 by water from a line 52 condensed and discharged through a barometric line 53. The vacuum is created by a steam jet pump 54 upheld. The cooled in the evaporator 49 for evaporation Solution can be in their water content through a line 58 with the help of a (not shown) regulator for the specific weight can be adjusted accordingly. Then the solution flows out of the evaporation column through a line 55 and a pump 56 into a storage container 57. The storage container 57 can contain any missing amount of phosphate ions in the form of phosphoric acid or an ammonium phosphate can be added. The lean solution is pumped through the pump 59 at a controlled rate Line 14 is pumped into absorbent 12 to repeat the cycle.

The absorption device, the stripping column and the fractionation column are expediently multistage Arrangements for gas-liquid contact processes, e.g. B. shielded, plated or sprayed intended pillars. The absorbing device is preferably a two- or three-stage Column, and the stripping and fractionating columns are columns with ten or more stages. The chamber

22, which is shown as a simple pot within the absorbent device 12, can be a separate one Be a vessel and can also be a plated, shielded column.

A preferred embodiment of the method according to the invention, the required amounts is given below.

example

In one of the usual coking plants, which delivers 2830Nm ³ coke oven gas per minute with a content of 0.8 volume percent NH ₃ and 51.3 kg ammonia bubble vapor per minute with a content of 10 weight percent ammonia, 450 kg of a lean solution with a content of 41 Percentage by weight of ammonium phosphate salts per minute used to absorb the ammonia in the manner described above. The salts of the lean solution have a molar ratio of NH ₃ to H ₃ PO _{4 of} 1.25. The solution enters through line 14 below 60 ° C. The coke oven gases enter through line 10 below 45 ° C., at which temperature they are saturated with water; the pressure is slightly higher than atmospheric. The solution overflows from the lower part 11 into the chamber 22. The ammonia bubble vapor enters chamber 22 through line 23 below 99 ° C. The gas leaves the absorber through line 21 which contains 0.004 percent by volume NH ₃ , which corresponds to a recovery of 99.6% of the total ammonia in the coking plant exhaust gases and the ammonia bubble vapor. The rich solution exits chamber 22 through line 24 which contains 44% salts and has a molar ratio of 1.95. The rich solution is pumped through the pump 25 under a pressure of 14 kg / cm ^2, heated to 165 ° C. by the stream exiting the top of the column 27 in the heat exchanger 29 and to 180 ° C. by steam in the heat exchanger 30, before being heated in the twenty-stage stripping column 27 enters, which is operated at a pressure of 14 kg / cm ² and is fed through line 31 with 99 kg of steam per minute. The warm, lean solution leaves the bottom of the column below 198 ° C. through line 48, which contains 39 percent by weight of salts and has a molar ratio of 1.25. The solution is cooled to about 60 ° C. and concentrated to a content of 41 percent by weight of salts in the evaporator 49, which is operated under an absolute pressure of 180 mm of mercury and is fed with a stream of water through line 58, so that the specific gravity is kept under control. The net amount of water that is withdrawn is approximately 5.7 kg per minute. 450 kg of the cooled, lean solution are pumped into the storage container 57 per minute in order to be fed back to the absorbing device.

Steam leaves the top of the stripping column 27, namely 73.35 kg per minute under a pressure of 14 kg and 180 ° C., with a content of 29% ammonia and, moreover, with traces of organic and inorganic impurities. The steam is partially condensed in heat exchanger 29 and completely condensed in heat exchanger 32 and ^{pumped at 120 °} C. and 16.8 kg / cm ² into fractionation column 35, which is fed through line 36 at the bottom with about 32 kg of steam per minute. A small vaporous secondary stream, which is relatively highly enriched with oils that were taken up from the coking plant exhaust gases, flows from the fractionation column through line 39 into the cooling device 40 and the decanter 41 for separating the oils and recirculating the ammonia-water layer through the Line 43 into the column. The water exiting the bottom fractionation column through line 37 contains no more than about 0.3 weight percent ammonia. The water-

xo free ammonia of line 38 contains no more than about 0.01 weight percent water and is in the cooling device 44 condenses. Part of it is fed back into the fractionation column as reflux, and the remainder is reduced to less than 0.3% in an activated carbon absorber 46 de-oiled, so that there are about 21.15 kg per minute of ammonia, which is suitable for cooling purposes.

The above embodiment describes a preferred method. However, other conditions can also be selected within the scope of the invention. The molar ratio of NH ₃ to H ₃ PO ₄ in the lean solution can be varied between about 1.1 and 1.3 if ammonia is to be absorbed from coking plant exhaust gases under predominantly atmospheric pressure in a two-stage absorption device. It can be up to 1.4 or 1.5 if the gas is supplied at a higher pressure or a lower temperature or a lower moisture content, or if the existing operating conditions make a three- or four-stage absorber desirable. The rich solution can have a higher or lower molar ratio than 1.95, e.g. B. between about 1.5 and 2.2, which depends on the ammonia concentration in the gas, the temperature and pressure of the Absorbiervornchtung, the number of stages in this and the manner in which the ammonia bubble vapors are treated, which from originate from the distillation of the ammonia liquid and have been separated from the coking plant exhaust gases.

A high concentration of ammonia in the gas, the use of an absorbent with many Stages, the operation of the absorbing device under high pressure and low temperature and the separate Use of the ammonia bubble vapor to enrich the solution in chamber 22 Place of an admixture to the gases before entry into the absorption device favor the development a rich solution with a high molar ratio. The salt concentration of the solution should be below the saturation limit and are more than 10%. The saturation limit depends on the molar ratio and the temperature of the solution. A solution with a molar ratio of 1.95 and a lean one For example, solutions with a molar ratio of 1.25 are both at a temperature of 40 ° C have a saturation limit of about 45% for the salt concentration in the absorbent.

In a method using ammonium phosphate suspensions, the saturation limit of the suspension is higher than that of the Solution. In the embodiment described, a salt concentration of more than 45% but less than about 80% when using a suspension.

The operating temperature and pressure in the absorption device are largely determined by the temperature

Claims (1)

7 8 temperature and pressure are determined under which the station must be added. The stripping Coke oven gases are present. The operating temperature may be as low as atmospheric pressure or otherwise between 30 and 60 ° C. The company requires pressure for economic reasons the coke oven gas is usually somewhat higher than that which one relies on for a less acidic solution. the atmospheric. The stripping column is grazed at 5, e.g. B. to a solution with a mole ratio an absolute pressure of at least 7 kg / cm ² and of 1.4. The desired extensive recovery operated not more than 21 kg / cm ² . The fractionation of ammonia from the coking plant exhaust gases is kolonne can hardly be operated at any pressure with such slightly acidic solutions sufficient to prevent condensation and requires an absorbent with many wanted ammonia product with the front anio stages, a larger volume for the circulation of the to allow cooling water. Usually solution and an increase in auxiliary equipment amounts this pressure in a fractionating column, the water- in addition to the need to absorb the acid Free ammonia supplies, between 10.5 and subtract gases. 21 kg / cm ² . Finally, the advantages described can make the The concentration of the salts in the absorbent 15 by stripping solutions under absolute pressure can be achieved by using a closed approximately 7 to 21 kg / cm ² , namely the genes digester in the stripping column and by obtaining a purer product at reduced Vaporize the water into the gas stream by increasing operating costs and lower capital expenditure, turning a warmer absorbent solution to quite unexpectedly at the recovery point of the evaporator being regulated. The before ammonia can be obtained from coking plant exhaust gases, however, cools the vacuum evaporator without the devices from rusting lean solution and at the same time removes excess steel, which is heavily corroded, as one would expect excess water. Thus, when dealing with lean solutions, the need for a lean solution cooler becomes gradually more acidic as the mole ratio and a closed cooker in the stripper falls below 1.5. Although you do not know which column falls. By transferring the heat, the corrosiveness of the solutions between the rich solution and the one above is inhibited, after the stream exiting the coking plant column 27, the heat exhaust gases acted, it has been found that their cores content of the lean solution, which leaves the stripping column for corrosion resistance in the case of austenitic stainless steels, for use in the evaporator. B. AISI 304 and 316, counter-stored by almost 90%. The scraped excess is condensed before the fraction - above expectations due to the earlier testing. fungen was decreased when one was under one The invention is characterized by some particular advantages of pressure from 14 kg / cm ² to a molar ratio of 1.25. Primarily, the stripping results in stripped. In the earlier tests, the volume of rich solutions at absolute pressures between about 7 and 21 kg / cm ^2, a much lower solution above 6.3 kg / cm ^{2, a} disproportionate steam or heat consumption. The required and became so great at an operating pressure of over steam amount for a lean solution at 7 kg / cm ² during stripping that an operation at a molar ratio of 1.25 by about 50% became impossible. Although the method according to the invention, if the pressure in stripping from 14 kg / cm ² to 40, the corrosion effects are lowered to ^{7 kg / cm 2 stainless.} However, it grows disproportionately - steels largely reduced, they grow with increasing steepness when the pressure during stripping increases to less pressure during stripping. So if the ger than 7 kg / cm ^{2 is} reduced until the pressure is increased to about 14 kg / cm ² , then also fifteen times the consumption at 14 kg / cm ² with corrosion and thus the disadvantages of atmospheric pressure achieved. 45 homely when using high pressure Second, the stripping results in a dung. The stripping column should Solute pressure of 7 to 21 kg / cm ^{2 is} a purer one, and for the reasons given, not with one ker concentrated ammonia water. The stripping pressure of more than 21 kg / cm ^{2 can be} operated. In at 14 kg / cm ² delivers 72.35 kg per minute of a steam- certain cases can have the advantages described fes with 29 percent by weight ammonia. The stripping 50 when stripping under a pressure of 7 to fening at 7 kg / cm ² delivers 126 kg per minute of steam 21 kg / cm ² the cost of a corrosion-resistant with an ammonia concentration of only 17 Ge system for the recovery of ammonia weight percent. In this case, too, the other than coking plants grow,
z & jgte steam and the dilution of ammonia disproportionate if the pressure at the ab- 55 patent claim: strip reduced to less than about 7 kg / cm ² Ammonia recovery process will. from coke oven gases, especially according to patent Third, the stripping at a pressure of 1153 733, at which the gas present in the coke oven ^{-14 kg / cm 2, is} economical for the production of ammonia present in a solution of poor solution with a molar ratio of 1.25. 60 monia and phosphoric acid is absorbed because such an acidic solution does not absorb acidic ones characterized by the fact that from the solution enriched with gases from the coke oven gases and the fractional ammonia-enriched solution enables the ammonia tioning of a purer product without being at a pressure between 7 and 21 kg / cm ^{2 from} alkalis in the fractionating column to neutralize. 1 sheet of drawings 509 597/339 6.65 © Bundesdruckerei Berlin