GB1569639A

GB1569639A - Process for the decomposition of ammonia vapours having a high content of hydrogen sulphide

Info

Publication number: GB1569639A
Application number: GB17086/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-04-24
Filing date: 1977-04-25
Publication date: 1980-06-18
Also published as: SE434221B; FR2348961A1; FR2348961B1; IT1075144B; ES457960A1; DE2618027C2; JPS5520131B2; BE853897A; JPS52130475A; DE2618027A1; SE7704614L

Description

(54) PROCESS FOR THE DECOMPOSITION OF AMMONIA VAPOURS HAVING A HIGH CONTENT OF HYDROGEN SULPHIDE (71) We, FIRMA CARL STILL, a German Company, of 435 Recklinghausen, Postfach 1480, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment:- The invention relates to a process for the decomposition of ammonia vapours having a high content of hydrogen sulphide. The invention is especially but not exclusively applicable to deacidifier vapours from the NH3-H2S circulatory scrubbing of crude coke-oven ; the decomposition of gasses.

Processes fr the decomposition of deacidifier vapours are known, in which the vapours are heated by combustion of a heating medium with which the vapours are mixed, and the hot mixture is conveyed through a decomposition zone which may be empty or filled with packing material unaffected by temperature changes or with a catalyst of any type. In one process, the hot gases leaving the decomposition zone are completely combusted in a second stage by renewed addition of air.

It is also known - to Thtroduce into a decomposition zone vapours that are obtained without previous deaciditication by distillation from the gas scrubbing waters and condensates.

It is furthermore known to eliminate completely the entire amount of free ammonia in deacidifier vapours by combustion of the vapours in their entirety in- only one stage, wherein the combustion heat of the ammonia is obtained in the form of highly superheated steam, the condensate is separated off and the sulphur dioxide contained in the combustion gases is worked up to form sulphuric acid. With suitably restricted supply of air, it is thereby possible to obtain sulphur also in place of sulphuric acid.

The known processes for the two-stage combustion of the NH3 have the advantage that only traces of oxides of nitrogen are formed during the combustion of the NH3.

However, it has been shown that the twostage processes (when carried out not only thermally but also catalytically) lead to problems when the ammonia vapours to be decomposed have a high content of H25 as well as the HCN from the crude coke-oven gases. In this case, the H25 reacts, in the first stage of the combustion, with atmospheric oxygen to form elementary sulphur.

This amorphous sulphur settles not only in the direct condenser, which is connected after the waste-heat boiler of the decomposition stage, but is also carried by the decomposition stage, but is also carried by the decomposition gases into the subsequent gas pipes and apparatus, and deposits there as a pasty mass and leads to blockages. A small amount of the H3S is also oxidised further to form SO2 which dissolves in the condensates and also in cooling waters used in the circulation. These waters then take on an acid disposition and cause corrosion of the apparatus.

The task on which the invention is therefore based is to propose a method for the process defined at the beginning, in which the formation of elementary sulphur and the partial further oxidation to SO2 does not take place and therefore blockages and corrosions no longer occur.

The present invention provides a process for the decomposition of ammonia vapours containing hydrogen sulphide, in which gaseous fuel is burned by itself and the combustion gases therefrom are then mixed with the ammonia vapours to heat the latter, the hot mixture being conveyed through a decomposition zone. Advantageously, the mixture takes on a temperature in the range of from 1,000 to 1,200 C before it enters the decomposition zone.

Preferably, the decomposition zone - is filled with a catalyst, for example a nickel catalyst, for the ammonia decomposition.

However, as in the known process, it may alternatively be empty or filled with packing material unaffected by temperature changes.

Metallic nickel deposited on bodies, for example rings or balls, of magnesite or aluminium oxide as supports, have proved especially successful as catalyst.

If air is used for the combustion of the gaseous fuel, then a high discharge speed for the air from the port of any burner has a particularly favourable- effect; Air speeds in the range of from 6 to 12 m per second, especially 8 m per second, are advantageous.

It has also proved to be advantageous to the mixing of the combustion gases with the ammonia vapours to arrange a burner for the gaseous fuel and an inlet for the ammonia vapours at the head of the decomposition zone or of a decomposition reactor.

The gas stream is then forced, against its upward thrust, from top to bottom of the decomposition zone, which makes for a particularly intensive, thorough mixing.

When carrying out a process according to the invention on deacidifier vapours (which, compared with, say, distiller vapours have a higher content of H2S) the tendency to form organic sulphur compounds increases, As is known, the H2S from the deacidifier vapours reacts with the CO and CO2, which comes from the decomposition of the hydrogen cyanide contained in the deacidifier vapours and is contained in the combustion gases, to form COS and CS2. Water vapour in the reaction mixture promotes the decomposition of these substances and it has been shown to be an advantage to add water vapour to the gaseous fuel or to the air used for combustion or to both. COS and CS2 can, as is known, be eliminated from gases only by complex processes.Apart from this, by the addition of water vapour the tendency for carbon black to form is reduced.

A process in accordance with the invention is illustrated by way of the following comparative example.

1,250 m2n per hour of deacidifier vapours having a NH2 content of 20% by volume, a H2S content of 12% by volume and a HCN content of 2% by volume were mixed in accordance with a known process, with 375 m3n of cokeoven gas (Hu=4,300 Kcal/m3n), and the mixture was combusted with 1,000 m3n of air (deficiency relative to the total sum of combustible portions), the gas mixture taking on a temperature of 1,100"C. The gas mixture was passed over a nickel catalyst (metallic nickel on balls of inagnesiter, and then cooled in a direct condenser.There was still 0.1 g of NH2 per m3n present in the decomposition gas. 85 mg of elementary sulphur per litre were detected in the circulation of cooling water of the direct condenser, and the pH-valué of the cooling water dropped to 6. In addition to this, the decomposition gas contained 6 g of organic sulphur compounds {COS, CS2) per man.

After a few months' of operation, the plant had to be taken out of operation as the loss in pressure in the plant had become too high. During cleaning of the plant, pasty deposits, which had caused the loss in pressure, were found in the gas pipe behind the direct condenser. In addition to this, extensive visible corrosion had occurred.

92% of the dry substance obtained from the deposits consisted of elementary sulphur.

After these experiences, the operation was modified as follows: a water vapour content of 50% by volume was established in the air for combustion; a speed of 8 m per second was established for the mixture of air and water vapour at the burner ports the heating medium was first of all burned by itself and the deacidifier vapours contailing the NH2, HCN and H2S were mixed only thereafter with the combustion gases having a Iow content of oxygen. The mixture afterwards had a temperature of 1,100"C.

Further treatment was carried out as described above. In this case also, the composition gas still contained 0.1 g of NH2 per m3n. In the cooling water circulation no elementary sulphur could be detected and the pH value of the cooling water did not drop below 7. The content of organic sulphur compounds in the decomposition gas was 2 mg per m3n.

For putting the process into operation, apparatus comprising a special burner placed on the NH2 decomposition reactor, has proved particularly successful.

The present invention accordingly also provides apparatus for use in a process according to the present invention the apparatus comprising a burner having a fuel chamber which is connected to receive the gaseous fuel and through which pass a plurality of air distributor pipes from an air chamber which is connected to receive air for combustion of the gaseous fuel; the gaseous fuel chamber having a floor through which the distributor pipes pass and in which are formed bores for the passage of gaseous fuel, from the fuel chamber, for combustion; the wall of the fuel chamber projecting beyond the floor and the distributor pipes having ports lying within that projecting wall portion whereby air issuing from the ports mixes with gaseous fuel issuing from the bores in the fuel chamber floor, for combustion of the gaseous fuel; the burner having a casing which, with the wail of the fuel chamber, forms an annular space connected to supply the ammonia vapours for mixing with gases from the combustion of the gaseous fuel; the burner being located on the decomposition zone to supply thereto the hot mixture of ammonia vapours and combustion gases.

A burner for use in a process in accord ance- with the present invention will be described, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates a longitudinal crosssection through the burner.

Figure 2 is a cross-section through Figure 1 at the height of the line Il-Il.

Figure 3 illustrates the inclination of the ports of the air distributor pipes.

Figure 4 indicates the direction of the inclinations of the air distributor pipes of.

Figure 3.

Air for combustion flows into the burner through a connecting pipe 1 into an air chamber 2 having a circular cross-section, and is distributed to air distributor pipes 3 which are arranged in concentric circles and are firmly and tightly set into the separating floor 2a of the air chamber 2. The air flows through the pipes 3, which extend through a fuel gas chamber 4, likewise of circular cross-section, as far as their inclined ports 8. The arrows 9 indicate the direction of inclination and show that, in the outer circle of pipes, the ports 8 are directed inwardly.

The air distributor pipes 3 arranged on the inner circles have ports with inclinations alternately in a clockwise and anti-clockwise direction.

Coke-oven gas is introduced through a connecting pipe 5 into the space of the fuel gas chamber 4 remaining between the air distributor pipes 3, and leaves through circular bores 10, which may also be specially equipped, in the floor 10a of the fuel gas chamber 4. The coke-oven gas mixes with the air issuing from the ports 8 and is combusted.

The casing 3a of the fuel gas chamber 4 projects beyond the floor 10a by about 0.2 m, and is partially surrounded by a casing 7b which carries a fastening flange ring 3b and which, together with the outer wall 3a of the combustion chamber 4, forms a space 7 between the casings. Deacidifier vapours are introduced into this space 7 through a connecting pipe 6 and they leave at port 7a and are then on the periphery of the flame of the coke-oven gas.

Before entering the decomposition reactor (not shown) which is connected subsequently, the coke oven gas which is already combusted and contains only a little 02, is now intensively mixed with the deacidifier vapours from port 7a and the mixture, takes on a temperature of 1,100"C. In this state, the mixed gases are passed over the nickel catalyst in the decomposition zone.

WHAT WE CLAIM IS: 1. A process for the decomposition of ammonia vapours containing hydrogen sul - - phide, in which gaseous fuel is burned by itself and the combustion gases therefrom are then mixed with the ammonia vapours to heat the latter, the hot mixture being conveyed through a decomposition zone.

2. A process according to claim 1, in which the ammonia vapours containing hydrogen sulphide are deacidifier vapours from the NH3-H2S circulatory. scrubbing of crude coke-oven gas.

3. A process according to claim 1 or claim 2 in which the mixture enters the decomposition zone with a temperature in.

the range of from 1,000 to 1,200"C.

4. A process according to any one of claims 1 to 3, in which the decomposiXtion zone is filled with a catalyst for the ammonia decomposition.

5. A process according to claim 4, in which the catalyst is a nickel catalyst.

6. A process according to claim 4 or claim 5, in which metallic nickel deposited on bodies of magnesite or aluminium oxide is used as catalyst.

7. A process according to any one of claims 1 to 6, in which an air current flowing out of a burner port at a speed in the range of from 6 to 12 m per second is used for the combustion of the gaseous fuel.

8. A process according to claim 7, in which the current of air leaves the burner port at a speed of 8 m per second.

9. A process according to any one of claims 1 to 8, in which the combustion gases and the ammonia vapours are passed from top to bottom through the decomposition zone.

10. A process according to any one of claims 1 to 9, in which water vapour is added to the gaseous fuel or to air used for combustion of the gaseous fuel or to both.

11. Apparatus for use in a process according to any one of claims 1 to 10, comprising a burner having a fuel chamber which is connected to receive the gaseous fuel and through which pass a plurality of air distributor pipes from an air chamber which is connected to receive air for combustion of the gaseous fuel; the gaseous fuel chamber having a floor through which the distributor pipes pass and in which are formed bores for the passage of gaseous fuel, from the fuel chamber, for combustion; the wall of the fuel chamber projecting beyond the floor, and the distributor pipes having ports lying within that projecting wall portion whereby air issuing from the ports mixes with gaseous fuel issuing from the bores in the fuel chamber floor, for oom- bastion of the gaseous fuel; the burner having a casing which, with the wall of the fuel chamber, forms an annular space connected to supply the ammonia vapours for mixing with gases from the combustion of the gaseous fuel; the burner being located

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the hot mixture of ammonia vapours and combustion gases. A burner for use in a process in accord ance- with the present invention will be described, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates a longitudinal crosssection through the burner. Figure 2 is a cross-section through Figure 1 at the height of the line Il-Il. Figure 3 illustrates the inclination of the ports of the air distributor pipes. Figure 4 indicates the direction of the inclinations of the air distributor pipes of. Figure 3. Air for combustion flows into the burner through a connecting pipe 1 into an air chamber 2 having a circular cross-section, and is distributed to air distributor pipes 3 which are arranged in concentric circles and are firmly and tightly set into the separating floor 2a of the air chamber 2. The air flows through the pipes 3, which extend through a fuel gas chamber 4, likewise of circular cross-section, as far as their inclined ports 8. The arrows 9 indicate the direction of inclination and show that, in the outer circle of pipes, the ports 8 are directed inwardly. The air distributor pipes 3 arranged on the inner circles have ports with inclinations alternately in a clockwise and anti-clockwise direction. Coke-oven gas is introduced through a connecting pipe 5 into the space of the fuel gas chamber 4 remaining between the air distributor pipes 3, and leaves through circular bores 10, which may also be specially equipped, in the floor 10a of the fuel gas chamber 4. The coke-oven gas mixes with the air issuing from the ports 8 and is combusted. The casing 3a of the fuel gas chamber 4 projects beyond the floor 10a by about 0.2 m, and is partially surrounded by a casing 7b which carries a fastening flange ring 3b and which, together with the outer wall 3a of the combustion chamber 4, forms a space 7 between the casings. Deacidifier vapours are introduced into this space 7 through a connecting pipe 6 and they leave at port 7a and are then on the periphery of the flame of the coke-oven gas. Before entering the decomposition reactor (not shown) which is connected subsequently, the coke oven gas which is already combusted and contains only a little 02, is now intensively mixed with the deacidifier vapours from port 7a and the mixture, takes on a temperature of 1,100"C. In this state, the mixed gases are passed over the nickel catalyst in the decomposition zone. WHAT WE CLAIM IS:

1. A process for the decomposition of ammonia vapours containing hydrogen sul - - phide, in which gaseous fuel is burned by itself and the combustion gases therefrom are then mixed with the ammonia vapours to heat the latter, the hot mixture being conveyed through a decomposition zone.

the range of from 1,000 to 1,200"C.

5. A process according to claim 4, in which the catalyst is a nickel catalyst.

on the decomposition zone to supply thereto the hot mixture of ammonia vapours and combustion gases.

12. Apparatus according to claim 11, in which the air chamber and the fuel chamber both having a circular cross-section and the air distributor pipes are arranged on concentric cirles, wherein the ports of the air distributor pipes arranged on the outer circle are inclined inwardly and those of the pipes arranged on the inner circles are inclined alternately in a clockwise direction and an anticlockwise direction.

13. A process according to any one of claims 1 to 10, substantially as herein described,

14. Apparatus for use in the decomposition of ammonia vapours, substantially as described herein with reference to, and as shown in, the accompanying drawings.