METHOD FOR OPERATING A CLAUS BURNER

Abstract

In order to overcome the limitations and problems that earlier methods have experienced, a method for operating a burner used in the thermal step of a Claus process is disclosed. The burner has at least one combustion air port, at least one oxygen port, and at least one fuel port. The oxidant flow is made up of an oxygen flow of technical pure oxygen with an oxygen concentration of at least 90 vol. %, preferably at least 99 vol. %, and if necessary of a second gas flow, and it is determined whether the oxygen flow is below a pre-set minimum flow and if the oxygen flow is below a pre-set minimum flow the air flow is split into a main air flow and a side air flow and the oxygen flow is combined with the side air flow creating an oxygen-enriched side air flow which is fed to the oxygen port. A corresponding burner is also disclosed.

Claims

1. A method for operating a burner used in the thermal step of a Claus process, wherein the burner comprises at least one combustion air port, at least one oxygen port, and at least one fuel port, and wherein an air flow is fed to the combustion air port, an oxidant flow is fed to the oxygen port, and a hydrogen sulphide containing feed gas flow is fed to the fuel port, characterized in that the oxidant flow is made up of an oxygen flow of technical pure oxygen with an oxygen concentration of at least 90 vol. %, and if necessary of a second gas flow, and that it is determined whether the oxygen flow is below a pre-set minimum flow and if the oxygen flow is below a pre-set minimum flow the air flow is split into a main air flow and a side air flow and the oxygen flow is combined with the side air flow creating an oxygen-enriched side air flow which is fed to the oxygen port.

2. The method according to claim 1, characterized in that the oxygen concentration is at least 95 vol. %, and preferably at least 99 vol. %.

3. The method according to claim 1, characterized in that an oxygen supply line is provided between a source of technical pure oxygen and the oxygen port.

4. The method according to claim 3, characterized in that that the oxygen supply line comprises a flow control unit located upstream of the point where the oxygen flow is fed into the side flow.

5. The method according to claim 4, characterized in that the flow control unit comprises a low level enrichment control valve, and a mid level enrichment control valve.

6. The method according to claim 5, characterized in that the low level enrichment control valve and the mid level enrichment control valve are arranged in parallel.

7. The method according to claim 1, characterized in that the oxygen port is closer to the fuel port (2) than the combustion air port.

8. The method according to claim 1, characterized in that the air flow is controlled based on the acid gas flow and on the oxygen flow.

9. The method according to claim 1, characterized in that the air flow is controlled based on an analysis of the tail gas leaving the Claus process.

10. The method according to claim 1, characterized in that the feed gas flow is made up of a first gas stream comprising hydrogen sulphide but essentially no ammonia, and of a second gas stream comprising hydrogen sulphide and up to 50 percent by volume ammonia.

11. The method according to claim 10, characterized in that the second gas stream comprises the hydrogen sulphide and at least 30 percent by volume ammonia.

12. The method according to claim 1, characterized in that the oxygen port is designed as one or more oxygen lances.

13. The method according to claim 1, characterized in that low-level oxygen enrichment can be applied when design load has to be surpassed, and under and below design load conditions in order to increase the Claus furnace temperature.

14. The method according to claim 13, characterized in that the Claus furnace temperature is increased in order to maximize destruction of ammonia.

15. A burner comprising at least one combustion air port, at least one oxygen port, and at least one fuel port.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0043] For a more complete understanding of the present inventive embodiment disclosures and as already discussed above, there are several options to embody as well as to improve the teaching of the present invention in an advantageous manner. To this aim, reference may be made to the claims dependent on claim 1; further improvements, features and advantages of the present invention are explained below in more detail with reference to the following description of a preferred embodiment by way of non-limiting example and to the appended drawing FIGURE taken in conjunction with the description of the embodiment, of which:

[0044] FIG. 1 shows the flow schematics for carrying out the inventive method.

DETAILED DESCRIPTION OF THE DRAWINGS

Best Way of Embodying the Present Invention

[0045] Before explaining the present inventive embodiment in detail, it is to be understood that the embodiment is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawing, since the present invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

[0046] In the following description, terms such a horizontal, upright, vertical, above, below, beneath and the like, are used solely for the purpose of clarity illustrating the invention and should not be taken as words of limitation. The drawings are for the purpose of illustrating the invention and are not intended to be to scale.

[0047] FIG. 1 shows the flow schematics for carrying out the inventive method. A burner 1 comprises one or more fuel ports 2, one or more oxygen ports 3, and one or more combustion air ports 4. The burner 1 is used in the thermal step of a Claus plant for partial oxidation of H.sub.2S.

[0048] The oxygen port 3 is connected to a source 5 of technical pure oxygen via an oxygen supply line 6. The oxygen has a purity of at least 90 percent by volume, preferably of at least 95 percent by volume, and more preferably of at least 99 percent by volume.

[0049] The oxygen supply line 6 comprises a flow control unit 7 wherein the flow control unit 7 comprises two parallel flow paths 8 and 9 with a low-level enrichment control valve 10 in flow path 8 and with a mid-level enrichment control valve 11 in flow path 9.

[0050] Low-level enrichment control valve 10 and mid-level enrichment control valve 11 are control valves to control the flow of oxygen from the oxygen source 5. Low-level enrichment control valve 10 is designed for lower oxygen flows and higher precision whereas mid-level enrichment control valve 11 is designed for higher oxygen flows.

[0051] The combustion air port 4 is connected to an air source 12 via an air supply line 13. The air source 12 could be an air compressor for supplying air as an oxidant to the combustion process.

[0052] The oxygen supply line 6 and the air supply line 13 are connected via line 14 which is provided with a flow control valve 15 for controlling the side air flow from air supply line 13 to oxygen supply line 6. Via fuel supply line 17 the fuel port 2 is connected to a source 16 of acid gas, that is a feed gas containing hydrogen sulphide (H.sub.2S). Additional lines 18, 19 are connected to the fuel supply line 17 and may be used for supply of sour water stripper (SWS) gases 20 or another fuel gas 21 to the fuel port 2.

[0053] The burner could be controlled to allow several modes of operation by varying the gas streams to the different burner ports: [0054] start-up/hot stand-by mode; [0055] air operation mode; [0056] low-level oxygen enrichment operation mode; [0057] mid-level oxygen enrichment operation mode.

[0058] Start-Up and Hot Stand-by Mode:

[0059] For cold start the Claus unit is provided with fresh catalyst and there is no sulphur in the unit. For future restarts, the Claus unit already contains sulphur compounds and the burner 1 will be started by firing fuel gas (for example hydrocarbons) 21 and combustion air 12 in stoichiometric conditions.

[0060] In this mode, the combustion air flow 12 goes to both the oxygen ports 3 and the combustion air port 4. Flow control unit 7 in the oxygen supply line 6 is closed so that oxygen flow to the oxygen port 3 is disabled.

[0061] Fuel gas (hydrocarbons) 21 is introduced through the fuel port(s) 2 and the flame is ignited. Once the flame is stable, the total combustion air 12 (supplied via the oxygen port 3 and the combustion air port 4) and the fuel gas (hydrocarbons) flow 21 are set at a ratio slightly sub-stoichiometric.

[0062] A gradual temperature rise is controlled by increasing the fuel gas (hydrocarbons) 21 and the combustion air flow 12. Steam 22 can be added to the fuel gas 21 to prevent soot formation while firing at sub-stoichiometric firing conditions and to provide cooling at stoichiometric firing conditions.

[0063] Air Operation Mode;

[0064] Once the furnace is hot and the rest of the Claus unit is at operating temperature, acid gas (H.sub.2S feed) 16 may be introduced to the process. Acid gas flow 16 is fed to the fuel ports 2 via supply line 17. The acid gas 16 is a gas stream containing hydrogen sulphide. Acid gas flow 16 is increased in small steps and followed by a gradual reduction of the fuel gas (hydrocarbons) flow 21.

[0065] Combustion air 12 goes to both the oxygen ports 3 and the combustion air ports 4. The total air flow 12 is calculated and set to the correct amount of air required for both fuel gas 21 and acid gas 16.

[0066] Low-Level Oxygen Enrichment Operation Mode:

[0067] Low-level oxygen enrichment can be used to increase furnace temperature for ammonia destruction and/or for incremental capacity increase. While at air operation mode, once a minimum of load is reached, oxygen can be introduced through the low-level enrichment control valve 10.

[0068] The combustion air 12 still goes to both the oxygen ports 3 and the combustion air port 4. The combustion air flow 12 is split in a main air flow which is passed to the combustion air port 4 and a side air flow which is passed to the oxygen ports 3. The split of the main air flow and the side air flow is based on a pre-set percentage.

[0069] With the increase in oxygen flow 5, the total combustion air flow 12 is reduced, and then split to the pre-set ratio before they go to the oxygen port 3 and the combustion air port 4. With oxygen enrichment, the acid gas by-pass 24 is disabled.

[0070] Once the oxygen flow 5 reaches the pre-set minimum flow for the oxygen port 3, any further increase in oxygen enrichment will require moving to the mid-level oxygen enrichment mode.

[0071] Mid-Level Oxygen Enrichment Operation Mode:

[0072] Once the oxygen flow is above the oxygen ports 3 pre-set minimum flow requirement, it can be switched to the mid-level enrichment mode if there is sufficient increase in throughput. The side air flow (of the combustion air 12) to the oxygen ports 3 is disabled in this mode. All the combustion air 12 will flow to the combustion air ports 4.

[0073] As the oxygen flow 5 still goes to the oxygen ports 3 and it is above the pre-set minimum flow setting, there is no nitrogen make-up flow required during the transition. The overall operation point and its flow rates to all the ports can be maintained during the transition.

[0074] In the mid-level oxygen enrichment mode, the overall oxygen enrichment level can be manually inputted. Feed forward control of the combustion air 12 is based on the acid gas flow 16, taking into consideration of oxygen enrichment, and feedback control of combustion air 12 is based on the tail gas analyser, as described above.

[0075] Shutdown:

[0076] One of the primary shut downs while in oxygen enrichment modes is high temperature. When the temperature exceeds a certain maximum temperature the oxygen flow 5 will be disabled. Nitrogen flow 23 will be automatically switched on to maintain a pre-set minimum flow to the oxygen ports 3 in order to provide cooling. If the temperature continues to rise the unit is shut down.

[0077] During the shutdown, the minimum flow to the three ports 2, 3, 4 remains enabled. The purge rates required to protect the burner 1 during shutdown are lower than the minimum flow requirement. The flows may be reduced to the specified purge rates for a continued shutdown.

[0078] When the furnace temperature drops below a certain temperature, the purge flow to the combustion air ports 4 and the fuel ports 2 can be switched off.

[0079] However, the purge flow to the oxygen ports 3 must be continued until completely shut down at a further reduced rate. This prevents back flow contamination of the oxygen equipment and lines.

[0080] It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result.

LIST OF REFERENCE SIGNS

[0081] 1 burner [0082] 2 fuel port [0083] 3 oxygen port, in particular at least one oxygen lance [0084] 4 combustion air port [0085] 5 source of oxygen, in particular of technical pure oxygen [0086] 6 oxygen supply line [0087] 7 flow control unit [0088] 8 first flow path, in particular with low-level enrichment control valve 10 [0089] 9 second flow path, in particular with mid-level enrichment control valve 11 [0090] 10 low-level enrichment control valve, in particular designed for lower oxygen flow [0091] 11 mid-level enrichment control valve, in particular designed for higher oxygen flow [0092] 12 air source, in particular air compressor, for example for supplying air as an oxidant to the combustion process [0093] 13 air supply line [0094] 14 line [0095] 15 flow control valve [0096] 16 source of acid gas, in particular of H.sub.2S [0097] 17 fuel supply line [0098] 18 first additional line [0099] 19 second additional line [0100] 20 sour water stripper (SWS) gas [0101] 21 fuel gas, in particular hydrocarbon [0102] 22 steam [0103] 23 nitrogen flow [0104] 24 acid gas by-pass