CLAUS UNIT TREATMENT OF SHUTDOWN TAIL GAS

Abstract

The process for configuring or reconfiguring a sulfur removal plant having a plurality of Claus units that is greater than the number of downstream tail gas treating units (TGTUs) is disclosed. The process allows for the regeneration of one of the Claus units without shutting down any of the downstream TGTUs or the other Claus units. Specifically, the regeneration tail gas can be diverted to the reaction furnace of an in-service Claus unit, thereby allowing excess oxygen to be used to regenerate the Claus unit more efficiently, and without exceeding environmental SO.sub.2 emission requirements.

Claims

1. A method for regenerating a Claus unit in a sulfur removal complex comprising a plurality of Claus units and a smaller number of tail gas treating units (TGTUs), the method comprising the steps of: (a) switching the feed to the regenerating Claus unit's reaction furnace to natural gas; (b) combusting the natural gas in the reaction furnace using an approximately stoichiometric amount of oxygen; (c) sending the tail gas from the regenerating Claus unit to an in-service TGTU; (d) once liquid sulfur is no longer produced from the regenerating Claus unit in step (b), sending the tail gas to an in-service Claus unit's reaction furnace; and (e) adding excess oxygen to the regenerating Claus unit's reaction furnace.

2. The method of claim 1, wherein the excess oxygen is increased incrementally up to about 10%.

3. The method of claim 1, further comprising: (f) once the tail gas from the regenerating Claus unit after step (e) contains an environmentally acceptable concentration of sulfur, sending the tail gas to an incinerator.

4. The method of claim 1, wherein the tail gas in step (d) is sent to the combustion air piping for the in-service Claus unit's reaction furnace.

5. The method of claim 1, wherein the tail gas in step (d) is sent to the air plenum for the in-service Claus unit's reaction furnace.

6. The method of claim 1, wherein the tail gas in step (d) is sent to a dedicated nozzle on the in-service Claus unit's reaction furnace.

7. A method for regenerating a single Claus unit in a sulfur removal complex comprising a plurality of Claus units and a smaller number of tail gas treating units (TGTUs), the method comprising the steps of: combusting natural gas in the regenerating Claus units' reaction furnace with excess oxygen; and sending the resulting tail gas to an in-service Claus unit's reaction furnace; wherein no other Claus unit or TGTU is shut down during the regeneration of the single Claus unit.

8. A system for removing sulfur from a refinery acid gas stream, comprising: a plurality of Claus units, wherein each Claus unit has a reaction furnace; at least one tail gas treating units (TGTUs), wherein the number of TGTUs is smaller than the number of Claus units; and means for connecting the tail gas from any of the plurality of Claus units to the reaction furnace of any of the plurality of Claus units.

9. The system of claim 8, wherein the tail gas from a regenerating Claus unit can be sent to the reaction furnace of an in-service Claus unit.

10. The system of claim 8, wherein the connecting means includes piping for connecting the tail gas from any of the plurality of Claus units to the combustion air piping for the reaction furnace

11. The system of claim 8, wherein the connecting means includes piping for connecting the tail gas from any of the plurality of Claus units to the air plenum for the reaction furnace of any of the plurality of Claus units.

12. The system of claim 8, wherein the connecting means includes piping for connecting the tail gas from any of the plurality of Claus units to a dedicated nozzle on the reaction furnace of any of the plurality of Claus units.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0011] FIG. 1 (PRIOR ART) is a simple flow diagram depicting a prior art sequence for shutting down one Claus unit while other parallel Claus units remain online processing refinery acid gas.

[0012] FIG. 2 is a simple flow diagram depicting a novel sequence for shutting down one Claus unit while other parallel Claus units remain online processing refinery acid gas, in accordance with the present invention.

[0013] FIG. 3 depicts illustrative configurations for a sulfur removal plant having two Claus units and a single TGTU, in accordance with the present invention.

DETAILED DESCRIPTION

[0014] The present invention relates to a process re-configuration of a sulfur removal plant having a plurality of Claus units that is greater than the number of downstream tail gas treating units (TGTUs). It is often desirable to shut down and regenerate one of the Claus units without shutdown of any of the downstream TGTUs or the other Claus units. The present invention solves this problem, and can be implemented as both a grassroots design for a new sulfur removal plant, or can be implemented as a relatively low cost retrofit of an existing plant.

[0015] Referring to FIG. 2, a simple flow diagram depicting a novel regenerating sequence for shutting down one Claus unit while other parallel Claus units remain online processing refinery acid gas, in accordance with the present invention, is provided. According to this sequence, the Claus unit that is being shut down is switched from refinery acid gas to natural gas firing at stoichiometric O.sub.2 concentrations (i.e., less than 0.5% excess O.sub.2). The tail gas from this unit is directed to the running TGTU until sulfur production stops, at which time the tail gas is then diverted to the feed of the other Claus unit's reaction furnace, which is still operating on refinery acid gas. At this time, excess O.sub.2 is added in increasing increments, up to about 10 mol % or greater, to the shutdown furnace to remove additional sulfur-containing species. When the shutdown tail gas is substantially free of sulfur-containing species, the tail gas can then be diverted to the incinerator for environmentally safe disposal.

[0016] The benefits of this novel regenerating sequence are numerous. Excess air/O.sub.2 is necessary to fully remove sulfur species from the Claus reactor, however excess O.sub.2 in the shutdown tail gas can never be introduced to an operating TGTU without passivating and then permanently damaging the TGTU catalyst. Furthermore, as described with the prior art shutdown sequence of FIG. 1, shutdown tail gas cannot be sent directly to an incinerator either because of environmental exceedance of SO.sub.2 concentration limits. The present invention, as depicted in FIG. 2, provides a more efficient and timely Claus unit shutdown without damaging the operating TGTU and with no impact on sulfur plant incinerator SO.sub.2 emissions. Diverting shutdown tail gas to the operating Claus unit processing refinery acid gas provides little to no impact on that unit's operation, as the tail gas excess O.sub.2 contributes to the O.sub.2 demand for the in-service Claus unit.

[0017] As such, the primary benefit is the ability to shut down one Claus unit without shutting down downstream TGTUs or other parallel Claus units, which minimizes the impact of the Claus unit shutdown on overall refinery operations. Although the present invention is primarily directed to sulfur removal complexes having a number of Claus units that is greater than the number of downstream TGTUs, one of ordinary skill in the art will appreciate that the present invention provides benefit to a Claus unit that is dedicated to a single downstream TGTU. In this instance, diverting the shutdown tail gas will result in caustic savings as the TGTU quench tower does not have to be utilized as an SO.sub.2 scrubber.

[0018] One of ordinary skill in the art will appreciate that the present disclosure embodies numerous alternative configurations for accomplishing the regeneration sequence of FIG. 2. FIG. 3, for example, illustrates several configurations for a sulfur removal plant having two Claus units and one TGTU, in accordance with the teachings of the present invention. Natural gas is first combusted in the reaction furnace 10 of the Claus train being shut down to strip sulfur from the Claus section 12. Tail gas stream 14, consisting of natural gas combustion products (CO.sub.2, H.sub.2O, N.sub.2) and residual sulfur species (S, H.sub.2S, SO.sub.2, SO.sub.3, COS, CS.sub.2), is then blocked away from TGTU 16, and is diverted through jumpover piping 18 to the reaction furnace 20 of the in-service Claus train processing refinery acid gas. As shown in FIG. 3, tail gas stream 14 can be introduced to reaction furnace 20 at several points, including, but not limited to, combustion air piping 22, burner air plenum 24, or a reaction furnace dedicated nozzle 26. Jumpover piping 18 and associated valving is constructed such that either train's tail gas during shutdown can flow to the other reaction furnace. A person having ordinary skill in the art will appreciate that certain straightforward design aspects are important for jumpover piping 18, including, without limitation, heat conservation (such as steam jacketing), no low points, and a nitrogen purge for when it is not being used.

[0019] It is envisioned that the teachings of the present invention can be incorporated into the retrofit or debottleneck of an existing sulfur removal complex using well-known engineering and safety standards. The teachings of the present invention can also be utilized in the initial design of a grassroots sulfur removal complex, including the additional capital benefit of requiring fewer, shared TGTU units for the required Claus units.

ADDITIONAL EMBODIMENTS

[0020] According to certain teachings of the present invention, a method for regenerating a Claus unit in a sulfur removal complex comprising a plurality of Claus units and a smaller number of tail gas treating units (TGTUs) is provided. The method comprises the steps of: (a) switching the feed to the regenerating Claus unit's reaction furnace to natural gas, (b) combusting the natural gas in the reaction furnace using an approximately stoichiometric amount of oxygen, (c) sending the tail gas from the regenerating Claus unit to an in-service TGTU, (d) once liquid sulfur is no longer produced from the regenerating Claus unit in step (b), sending the tail gas to an in-service Claus unit's reaction furnace; and (e) adding excess oxygen to the regenerating Claus unit's reaction furnace. The tail gas in step (d) can be sent, without limitation, to the combustion air piping for the in-service Claus unit's reaction furnace, the air plenum for the in-service Claus unit's reaction furnace, or to a dedicated nozzle on the in-service Claus unit's reaction furnace. Once the tail gas from the regenerating Claus unit after step (e) contains an environmentally acceptable concentration of sulfur, sending the tail gas to an incinerator.

[0021] Another embodiment of the present invention is a method for regenerating a single Claus unit in a sulfur removal complex comprising a plurality of Claus units and a smaller number of tail gas treating units (TGTUs), the method comprising the steps of combusting natural gas in the regenerating Claus units' reaction furnace with excess oxygen; and sending the resulting tail gas to an in-service Claus unit's reaction furnace. No other Claus unit or TGTU is shut down during the regeneration of the single Claus unit in this embodiment.

[0022] Yet another embodiment of the present invention is a system for removing sulfur from a refinery acid gas stream, comprising a plurality of Claus units, wherein each Claus unit has a reaction furnace; at least one tail gas treating units (TGTUs), wherein the number of TGTUs is smaller than the number of Claus units; and means for connecting the tail gas from any of the plurality of Claus units to the reaction furnace of any of the plurality of Claus units. The connecting means includes piping for connecting the tail gas from any of the plurality of Claus units to either the combustion air piping, the air plenum, or a dedicated nozzle for any of the plurality of Claus units. In this manner, the system can be used to send the tail gas from a regenerating Claus unit to the reaction furnace of an in-service Claus unit.

[0023] Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings therein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Unless otherwise indicated, all numbers expressing quantities of ingredients, properties, reaction conditions, and so forth, used in the specification and claims are to be understood as approximations based on the desired properties sought to be obtained by the present invention, and the error of measurement, etc., and should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Whenever a numerical range with a lower limit and an upper limit is disclosed, a number falling within the range is specifically disclosed. Moreover, the indefinite articles “a” or “an”, as used in the claims, are defined herein to mean one or more than one of the element that it introduces.