EP4211072A1

EP4211072A1 - Improvement to claus unit and process

Info

Publication number: EP4211072A1
Application number: EP21778540.1A
Authority: EP
Inventors: Peter Frank CROSS
Original assignee: Rossati Stefano
Current assignee: Rossati Stefano
Priority date: 2020-09-14
Filing date: 2021-09-14
Publication date: 2023-07-19
Also published as: GB202014455D0; WO2022053837A1

Abstract

The invention relates to a process comprising (i) passing some or all feed gases through (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and two or more Claus catalytic reactors, and (b) a tail gas treating unit (TGTU) comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; (ii) collecting acid gas from the tail gas treatment unit (TGTU) and (iii) adding said acid gas from the tail gas treatment unit downstream of a first Claus catalytic reactor and upstream of a second Claus catalytic reactor in the Claus unit or sulphur recovery unit.

Description

IMPROVEMENT TO CLAUS UNIT AND PROCESS

Field of the Invention

The present invention is directed to a process and a system, in particular for destroying contaminants in feed gases passing through a Claus unit or sulphur recovery unit and/or for increasing the furnace temperature of a Claus unit or sulphur recovery unit.

Background to the Invention

Claus units are used to recover sulphur from acid gases (sulphur containing gases) formed during refinery or gas processing operations. The acid gases are mainly from one or both of amine units and sour water strippers. The acid gas from the sour water stripper (SWS) and often from amine units contains ammonia which must be destroyed if the Claus unit is to operate without blockages caused by ammonium salts. The tail gas from a Claus unit is treated in a tail gas treatment unit (TGTU) to reduce sulphurous emissions to atmosphere. The reduction and control of emissions is of prime importance as refineries must comply with environmental regulations.

A Claus unit in this context refers to the modified Claus process (German patent 666,572 (1936)) which comprises a thermal stage (at least a burner, furnace and waste heat boiler) followed by one or more catalytic stages (at least a catalytic reactor and condenser for recovery of sulphur). A TGTU in this context comprises at least the following steps: hydrogenation, water removal, amine washing for removal of H2S and regeneration of the rich amine. This follows the principles as taught by a combination of US patent 3,752,877 for the hydrogenation and water removal and US patent 4,085, 192 for the amine washing and amine regeneration.

A common process to destroy ammonia from the SWS acid gas is based on variations of US patent number 4,038,036 (Beavon) which uses a two section reaction furnace upstream of the waste heat boiler and Claus catalytic stages (two section furnace process). However, the two section furnace process does not effectively destroy contaminants such as ammonia contained in the amine acid gases fed to the second section of the furnace. Residual sulphur trioxide (SO3) and nitrogen oxides (NOx) from the combustion process in the first section of the furnace can lead to acid formation in the Claus unit. There is also potential for carbon formation as cold amine acid gas is added to the hot combustion products in the second section of the furnace. Fouling caused by ammonia salts or by carbon formed in the furnace reduces the Claus unit’s run time and can cause unscheduled shutdowns. In addition poor mixing is inherent in the two section furnace process and there are risks to operation caused by too much or too little acid gas fed to the second section of the furnace.

This two section furnace process is long established and mitigation measures such as choke rings, checker walls and special mixing devices in the furnace have been introduced to alleviate some of the operating issues. The acid gas recycled from the tail gas treatment unit (TGTU) is normally more dilute in hydrogen sulphide than the acid gas from the upstream amine unit. Introducing acid gas from the TGTU to the furnace or mixing it with the feed gas reduces the furnace outlet temperature and reduces the effectiveness of ammonia destruction. For this reason very selective proprietary amines for the tail gas treatment unit (TGTU) have been introduced to alleviate some of the operating issues.

Therefore there is a need for a process which allows contaminants to be removed from feed gases, such as amine acid gases and/or sour water stripper gases, and also avoids the complexity and cost of the two section furnace process and the selectivity requirements in the TGTU.

Summary of the Invention

The process of the present invention is for destroying contaminants contained in the feed gases.

The process of the present invention is for increasing the furnace temperature of the Claus unit or sulphur recovery unit.

In a first aspect, the invention provides a process comprising (i) passing some or all feed gases through (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and two or more Claus catalytic reactors, and (b) a tail gas treating unit (TGTU) comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; (ii) collecting acid gas from the TGTU and (iii) adding said acid gas from the TGTU downstream of a first Claus catalytic reactor and upstream of a second Claus catalytic reactor in the Claus unit or sulphur recovery unit.

In one embodiment, the temperature of the second Claus catalytic reactor is less than 240°C.

In one embodiment the acid gas from the tail gas treatment unit (TGTU) is added to between an outlet of the first Claus catalytic reactor and an inlet of the second Claus catalytic reactor.

In one embodiment the acid gas from the tail gas treatment unit is added to the gases exiting the first Claus catalytic reactor in the Claus unit or sulphur recovery unit upstream of the inlet of the second Claus catalytic reactor in the Claus unit or sulphur recovery unit.

In a second aspect, the invention provides a system, for example for destroying contaminants contained in feed gases and/or for increasing the furnace temperature of the Claus unit or sulphur recovery unit, comprising (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and two or more Claus catalytic reactors; and (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; and (c) means for connecting and recycling the acid gas from the tail gas treating unit to the Claus unit or sulphur recovery unit, downstream of a first Claus catalytic reactor and upstream of a second Claus catalytic reactor.

In a third aspect, the invention provides a process comprising (i) passing some or all feed gases through (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and a Claus catalytic reactor, and (b) a tail gas treating unit (TGTU) comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; (ii) collecting acid gas from the tail gas treatment unit and (iii) adding said acid gas from the tail gas treatment unit, downstream of the waste heat boiler and upstream of the catalytic reactor in the Claus unit or sulphur recovery unit.

In one embodiment the process further comprises purifying the acid gas from the tail gas treatment unit before adding said acid gas downstream of the waste heat boiler and upstream of the catalytic reactor in the Claus unit or sulphur recovery unit. In one embodiment the acid gas from the TGTU is purified using silica, alumina or activated carbon.

In one embodiment the acid gas from the tail gas treatment unit (TGTU) is added to between the waste heat boiler outlet and a first Claus catalytic reactor inlet.

In one embodiment the acid gas from the tail gas treatment unit is added to the gases exiting the waste heat boiler (e.g. to the process gas stream) upstream of the inlet of the first catalytic reactor in the Claus unit or sulphur recovery unit

In a fourth aspect, the invention provides a system, for example for destroying contaminants contained in feed gases and/or for increasing the furnace temperature of the Claus unit or sulphur recovery unit, the system comprising (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and a Claus catalytic reactor; (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; and (c) means for connecting and recycling the acid gas from the tail gas treating unit to the Claus unit or sulphur recovery unit, downstream of the waste heat boiler and upstream of the catalytic reactor.

Description of the Drawings

A number of embodiments of the invention will now be further described, by means of example only, with reference to the drawings, in which:

Figure 1 is a schematic process flow diagram of a known Claus unit followed by a tail gas treatment unit. The Claus unit uses a conventional two section furnace.

Figure 2 is a schematic process flow diagram of a known Claus unit followed by a tail gas treatment unit. The Claus unit uses a conventional single section furnace.

Figure 3 is a schematic of a process according to the invention.

Figure 4 is a schematic of a process according to the invention. Figure 5 is a schematic of the process according to the invention.

Figure 6 is a schematic of a process according to the invention.

Figure 7 is a schematic of a process according to the invention.

Figure 8 is a schematic of a process according to the invention.

Figure 9 is a schematic of a process according to the invention.

Figure 10 is a schematic of a process according to the invention

Figure 11 is a schematic of a process according to the invention

Figure 12 is a schematic of a process according to the invention

Figure 13 is a schematic of a process according to the invention

Figure 14 is a graph showing furnace temperature °C versus CO2 slip in the TGTU.

Detailed Description of the Invention

Known Claus and TGTU processes are represented in figures 1 and 2.

As explained above, in the context of the present invention a Claus unit (1), also known as a sulphur recovery unit (1), comprises a thermal stage (comprising at least a burner (6), a Claus or reaction furnace (7’, 7”) and a waste heat boiler (8)) and one or more catalytic stages (comprising at least a Claus catalytic reactor (9) and at least one condenser (10) for recovery of sulphur (12)). Typical Claus units or sulphur recovery units (1) may also comprise at least one reheater (11). The Claus or reaction furnace (7’, 7”) may be a two section furnace (7’) or a single section furnace (7”).

A Claus unit or sulphur recovery unit may include or be used with a tail gas treatment unit (TGTU) (2). In the context of the present invention a tail gas treating unit (2) comprises at least a hydrogenation reactor (13), water removal (14), a TGTU absorber (15) and a TGTU regenerator (16). Typically an incinerator (17) processes the effluent gas from the TGTU absorber (15) and discharges it to the atmosphere (18).

In the context of the present invention feed gases or Claus unit feed gases can include sour water stripper gases (3) and/or amine acid gases (5). The feed gases may include sour water stripper gases (3) and amine acid gases (5). The feed gases may, in some embodiments, not include sour water stripper gases (3). The feed gases may include amine acid gases (5). In addition, air or an oxygen containing gas (4) is introduced to the burner to achieve the required reaction stoichiometry. One or more of the feed gases, air or oxygen containing gases (4) could also be pre-heated if pre-heat is used.

As explained above common processes used to destroy ammonia in acid gases from a sour water stripper (SWS) are based on variations of the two section furnace process described in US Patent Number 4,038,036. In this process, see figure 1, the Claus furnace (7’) is fed by gas from a SWS (SWS off gas or sometimes called SWS acid gas) (3), combustion air (4) and amine acid gas (AAG) (5). All of the ammonia containing SWS off gas (3) passes through the burner (6) and into the first section of the furnace which operates at a higher temperature than the second section with the aim being that it destroys ammonia and other contaminants introduced to the first section of the furnace. Part of the amine acid gas (5), which is rich in sulphur containing gases is bypassed to the second section of the two section furnace whilst the remainder is fed into the first section through the burner (6) with the SWS off gas (3) and combustion air (4). The aim of by-passing a portion of the AAG (5) to the second section of the furnace is to increase the temperature in the first section by reducing the amount of non-combusting gas in the first section. This means that a part of the AAG (5) does not pass through the burner (6) so any contaminants (such as ammonia) that it contains are not destroyed in the hot section of the furnace and carbon formation is a risk. Carbon can be formed from hydrocarbons contained in the bypassed portion of amine acid gas or by the Boudouard reaction as CO formed in the first section of the furnace is rapidly cooled by the bypassed acid gas. A tail gas treatment unit (TGTU) (2) is normally a mandatary part of modern sulphur recovery units. Known processes recycle the acid gas from the tail gas unit (2) to join the AAG (5) feeding the Claus furnace (7’). Therefore some of this recycled gas enters the burner (6) with the AAG (5) and some is bypassed to the second section of the furnace, however this reduces the combustion temperature in the reaction furnace (7’) because the acid gas from the TGTU (2) introduces more CO2 into the furnace (7’).

As in the two section furnace (7’) (figure 1), in known single section furnaces (7”) (figure 2) the acid gases from the tail gas treatment unit (2) joins the AAG (5) feeding the single section furnace (7”). However systems which direct all the acid gases (the recycled acid gas from the tail gas unit and the AAG (5)) to the burner (6) may not achieve sufficient furnace temperatures because the acid gas from the TGTU (2) introduces CO2 into the furnace (7”) which reduces the combustion temperature in the furnace. Specific furnace temperatures must be achieved in order to destroy hydrocarbons or to ensure flame stability, so typically a single furnace is used when the feed gases do not contain ammonia or other contaminants which require a high furnace temperature, so there may not be any SWS off gas present in the feed gases to existing single section furnace. These single section furnaces (7”) are often used in non-refinery situations. In addition, existing processes used to increase the temperature of a single section furnace (7”) are fuel gas support and operation with oxygen or oxygen enriched air. The process with oxygen increases the operating cost. Fuel gas support increases operating cost, the plant size and introduces unwanted side reactions into the process.

As explained above a common Claus unit or sulphur recovery unit, comprises one or more catalytic stages (comprising at least a Claus catalytic reactor). In certain cases the acid gas from the TGTU can contain impurities which would decompose at the temperatures in the first Claus catalytic reactor (~300°C) and so deactivate the Claus catalytic reactor over time. So bypassing or recycling the acid gas from the TGTU directly to Claus catalytic reactors is little used in refinery applications because of the risk of fouling and deactivation of the Claus catalytic reactor.

The present invention provides a process comprising (i) passing some or all feed gases through (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and two or more Claus catalytic reactors, and (b) a tail gas treating unit (TGTU) comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; (ii) collecting acid gas from the TGTU and (iii) adding said acid gas from the TGTU downstream of a first Claus catalytic reactor and upstream of a second catalytic reactor in the Claus unit or sulphur recovery unit. Thus the acid gas from a TGTU is collected and recycled by adding it downstream of a first Claus catalytic reactor and upstream of a second catalytic reactor, wherein the first Claus catalytic reactor is upstream of the second catalytic reactor in the Claus unit or sulphur recovery unit. In one embodiment the temperature of the second Claus catalytic reactor is less than 240°C. In one embodiment the temperature of the second Claus catalytic reactor is between 240°C and 190°C.

A process where the acid gas from the TGTU is added or recycled downstream of a first Claus catalytic reactor and upstream of a second Claus catalytic reactor is advantageous as the temperatures in second Claus catalytic reactors are lower and would not decompose the impurities in the acid gas.

As explained above, and as seen in figures 3 to 6, in the context of the present invention a Claus unit (1), also known as a sulphur recovery unit (1), may further comprise a thermal stage (comprising at least a burner (6), a Claus or reaction furnace (7’, 7”) and a waste heat boiler (8)) and optionally an additional condenser 10’ (e.g. a thermal condenser) and two or more catalytic stages (comprising at least a Claus catalytic reactor (9a, 9b) and at least a condenser (10a, 10b) for recovery of sulphur). The Claus or reaction furnace (7’, 7”) may be a two section furnace (7’) or a single section furnace (7”). The Claus unit (1) or sulphur recovery unit (1), may have a first catalytic stage comprising a first reheater (I la), a first Claus catalytic reactor (9a) and a first condenser (10a) and a second catalytic stage comprising a second reheater (11b), a second Claus catalytic reactor (9b) and a second condenser (10b). The second catalytic stage is downstream the first catalytic stage. This Claus unit or sulphur recovery unit (1) may include or be used with a tail gas treatment unit (TGTU) (2) as described above.

The present invention also provides a process comprising: (i) passing some or all feed gases through (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and a Claus catalytic reactor, and (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; (ii) collecting acid gas from the tail gas treatment unit and (iii) adding said acid gas from the tail gas treatment unit , downstream of the waste heat boiler and upstream of the Claus catalytic reactor in the Claus unit or sulphur recovery unit. Thus the acid gas from a tail gas treatment unit is collected and recycled by adding it downstream of the Claus unit waste heat boiler and upstream of the Claus catalytic reactor.

The impurities of the acid gas from the TGTU may be removed or minimised before said acid gas is added downstream of the waste heat boiler and upstream of the Claus catalytic reactor in the Claus unit or sulphur recovery unit. Thus the present invention provides a process where the acid gas from the TGTU is purified before being added to a first Claus catalytic reactor (e.g. downstream of the waste heat boiler and upstream of a first catalytic reactor in the Claus unit or sulphur recovery unit) therefore avoiding fouling and deactivation of the first Claus catalytic reactor. This reduces the risk of fouling and deactivation of the Claus catalytic reactor. In one embodiment the acid gas from the tail gas treatment unit is purified using silica, alumina or activated carbon before being added downstream of the waste heat boiler and upstream of the Claus catalytic reactor in the Claus unit or sulphur recovery unit. These agents may be used as a bed inside a vessel and are effective removing amines and hydrocarbons. Thus in one embodiment the acid gas from the tail gas treatment unit is collected and recycled by passing it through a purification vessel and adding the purified acid gas to downstream of the Claus unit waste heat boiler and upstream of the Claus catalytic reactor. In the present invention, the Claus unit or sulphur recovery unit may comprise a burner. The burner may have one or more gas inlets. The burner may have an inlet for each feed gas. The burner may have a single inlet for introduction of feed gases that have been mixed.

The burner may have an inlet for an oxygen containing gas.

The burner and reaction furnace may be joined or integrally formed. The burner may have an outlet that forms or joins to an inlet to the reaction furnace.

In the present invention, the Claus unit or sulphur recovery unit may comprise a first Claus catalytic reactor. The Claus unit may have a first Claus catalytic reactor and a second Claus catalytic reactor. The Claus unit may comprise two or more Claus catalytic reactors. The Claus unit may have a first Claus catalytic reactor, a second Claus catalytic reactor. The Claus unit may have a first Claus catalytic reactor and a second Claus catalytic reactor, wherein the first Claus catalytic reactor is upstream of the second Claus catalytic reactor. The Claus unit may have a first Claus catalytic reactor, a second Claus catalytic reactor and a third Claus catalytic reactor. In the present invention, the Claus unit or sulphur recovery unit may comprise one or more catalytic stages. The Claus unit or sulphur recovery unit may have a first catalytic stage and a second catalytic stage. The Claus unit or sulphur recovery unit may have a first catalytic stage and a second catalytic stage, wherein the first catalytic stage is upstream of the second catalytic stage. Each catalytic stage may comprise a Claus catalytic reactor, a condenser and a reheater.

In the present invention, the reaction furnace may contain one or more sections, for example one or two sections.

In the present invention some or all feed gases are added to or pass through the burner and/or reaction furnace (e.g. a two section Claus furnace and or a single section Claus furnace of the Claus unit or sulphur recovery unit). In the process of the present invention the feed gases do not include the acid gas from a tail gas treatment unit (TGTU). In one embodiment all the feed gases are added to or pass through the burner and/or reaction furnace of the Claus unit or sulphur recovery unit. In another embodiment the feed gases comprise SWS off gas and amine acid gas and all of the SWS off gas but only some of the amine acid gas is added to or passes through the burner and/or reaction furnace of the Claus unit or sulphur recovery unit. In yet another embodiment the feed gases comprise amine acid gas and only some of the amine acid gas is added to or passes through the burner and/or reaction furnace of the Claus unit or sulphur recovery unit.

In one embodiment the process may further comprise feeding all, or substantially all, of the feed gases into the furnace through a burner.

In an embodiment of the process of the invention all of the feed gases are fed into the reaction furnace through a burner. Therefore in this embodiment there are no contaminant containing gases fed into any part of the reaction furnace without having passed through a burner. This maximises contaminant destruction. Thus, for example, the process of the present invention can be used in a single section or a two section furnace process in which all of the feed gases are fed into the reaction furnace through a burner and wherein none of the acid gas from a tail gas treatment unit is added into the burner but instead is added downstream of a waste heat boiler and upstream of a Claus catalytic reactor, so the acid gas from the tail gas treatment unit does not join the feed gases, in particular the amine acid feed gas. The process of the present invention may also be used in a single section or a two section furnace process in which all of the feed gases are fed into the reaction furnace through a burner and wherein none of the acid gas from a tail gas treatment unit is added into the burner but instead is added downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor, so the acid gas from the tail gas treatment unit does not join the feed gases, in particular the amine acid feed gas.

In a further embodiment the process may comprise feeding a portion of the feed gases directly into the TGTU upstream of the TGTU absorber. In one embodiment, the portion of the feed gases fed directly into the TGTU upstream of the TGTU absorber is some of the amine acid gas. Thus the process of the present invention can also be used in a single section furnace process in which a portion of the feed gases is fed directly into the TGTU upstream of the TGTU absorber and wherein none of the acid gas from a tail gas treatment unit is added into the burner or the single section furnace but instead is added downstream of a waste heat boiler and upstream of a Claus catalytic reactor. In one embodiment the acid gas from a tail gas treatment unit is purified (e.g. by passing the acid gas from the TGTU through a purification vessel or using silica, alumina or activated carbon) and then added downstream of the waste heat boiler and upstream of the Claus catalytic reactor. The process of the present invention can also be used in a single section furnace process in which a portion of the feed gases is fed directly into the TGTU, upstream of the TGTU absorber, and wherein none of the acid gas from a tail gas treatment unit is added into the burner or the single section furnace but instead is added downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor. Therefore the acid gas from the tail gas treatment unit does not join the feed gases, in particular the amine acid feed gas. In one embodiment, a portion of the amine acid gas of the feed gases is bypassed to the TGTU upstream of the TGTU absorber whilst the remainder is fed into the single section furnace through the burner (for example with the SWS off gas, if present, and oxygen containing gas).

Thus, the process of the invention further comprises (i) passing the feed gases through the Claus unit or sulphur recovery unit comprising a single section furnace, by adding a portion of the feed gases to the single section furnace through a burner and the remaining portion of the feed gases is added directly into the TGTU upstream of the TGTU absorber, wherein the portion added directly into the TGTU upstream of the TGTU absorber comprises amine acid gas; (ii) collecting acid gas from the tail gas treatment unit and (iii) adding said acid gas from the tail gas treatment unit, downstream of the waste heat boiler and upstream of the catalytic reactor in the Claus unit or sulphur recovery unit. In one embodiment the process further comprises purifying the acid gas from the TGTU before is being added downstream of the waste heat boiler and upstream of the Claus catalytic reactor in the Claus unit or sulphur recovery unit. The Claus unit or sulphur recovery unit may also comprise two or more Claus catalytic reactors, so the purified gas is added downstream of the waste heat boiler and upstream of the first Claus catalytic reactor.

The process of the present invention may also comprise (i) passing the feed gases through the Claus unit or sulphur recovery unit comprising a single section furnace, by adding a portion of the feed gases to the single section furnace through a burner and the remaining portion of the feed gases is added directly into the TGTU upstream of the TGTU absorber, wherein the portion added directly into the TGTU upstream of the TGTU absorber comprises amine acid gas; (ii) collecting acid gas from the tail gas treatment unit and (iii) adding said acid gas from the tail gas treatment unit downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor in the Claus unit or sulphur recovery unit. In one embodiment the temperature of the second Claus catalytic reactor is less than 240°C (e.g. between 240 °C and 190 °C).

In a further embodiment the process of the present invention may comprise feeding a portion of the feed gases directly into the reaction furnace. In one embodiment, the furnace is a two section furnace and a portion of the feed gases is fed directly into the second section of the reaction furnace. The portion of the feed gases fed directly into a second section of a reaction furnace may be some of the amine acid gas. Thus the process of the present invention can also be used in a two section furnace process wherein a portion of the feed gases is fed directly into a second section of the two section furnace and wherein none of the acid gas from a tail gas treatment unit is added into the burner or the two section furnace but instead is added downstream of a waste heat boiler and upstream of a Claus catalytic reactor. The process of the present invention can also be used in a two section furnace process wherein a portion of the feed gases is fed directly into a second section of the two section furnace and wherein none of the acid gas from a tail gas treatment unit is added into the burner or the two section furnace but instead is added downstream of the first Claus catalytic reactor and upstream of the second catalytic reactor in the Claus unit or sulphur recovery unit. Therefore the acid gas from the tail gas treatment unit does not join the feed gases, in particular the amine acid feed gas. In one embodiment, a portion of the amine acid gas of the feed gases is bypassed to the second section of a two section furnace whilst the remainder feed gases is fed into the first section through the burner (with the SWS off gas and oxygen containing gas).

So for example, when the reaction furnace has two sections a portion of the feed gases may be fed directly into the reaction furnace, for example into a second section of the two section furnace but none of the acid gas from a tail gas treatment unit is added into the burner or the two section furnace but instead is added downstream of a waste heat boiler and upstream of a catalytic reactor.

When the reaction furnace has two sections a portion of the feed gases may be fed directly into the reaction furnace, for example into a second section of the two section furnace but none of the acid gas from a tail gas treatment unit is added into the burner or the two section furnace but instead may be added downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor in the Claus unit or sulphur recovery unit.

Thus, the process of the invention further comprises (i) passing the feed gases through the Claus unit or sulphur recovery unit comprising a two section furnace, by adding a portion of the feed gases to the first section of the two section furnace through a burner and the remaining portion of the feed gases is added to the second section of the two section furnace, wherein the portion added directly into the second section of the two section furnace comprises amine acid gas; (ii) collecting acid gas from the tail gas treatment unit and (iii) adding said acid gas from the tail gas treatment unit, downstream of the waste heat boiler and upstream of the catalytic reactor in the Claus unit or sulphur recovery unit.

The process of the invention also comprises (i) passing the feed gases through the Claus unit or sulphur recovery unit comprising a two section furnace, by adding a portion of the feed gases to the first section of the two section furnace through a burner and the remaining portion of the feed gases is added to the second section of the two section furnace, wherein the portion added directly into the second section of the two section furnace comprises amine acid gas; (ii) collecting acid gas from the tail gas treatment unit and (iii) adding said acid gas from the TGTU, downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor in the Claus unit or sulphur recovery unit.

The Claus unit or sulphur recovery unit may include or be used with one or more catalytic reactors. An outlet from the waste heat boiler may join to an inlet for the catalytic reactor. In the or each catalytic reactor the cooled gas from the waste heat boiler, or another catalytic reactor, is reheated, reacted under catalytic conditions to achieve a more complete conversion of the gases containing sulphur to elemental sulphur and condensed.

The Claus unit or sulphur recovery unit of the present invention may include two or more catalytic stages wherein each catalytic stage comprises a reheater, a Claus catalytic reactor and a condenser. The Claus unit or sulphur recovery unit of the present invention may include a first catalytic stage and a second catalytic stage, wherein the first catalytic stage is upstream of the second catalytic stage.

Thus a Claus unit or sulphur recovery unit may include first catalytic reactor. The Claus unit or sulphur recovery unit may also include a first catalytic reactor and a second catalytic reactor, wherein the first catalytic reactor is upstream of the second catalytic reactor. The Claus unit or sulphur recovery unit of the present invention may include a first catalytic stage comprising a first reheater, the first Claus catalytic reactor and a first condenser, and a second catalytic stage comprising a second reheater, the second Claus catalytic reactor and a second condenser. The first catalytic stage is upstream of the second catalytic stage.

In one embodiment the acid gas from a tail gas treatment unit is added downstream of the waste heat boiler and upstream of a first Claus catalytic reactor in the Claus unit or sulphur recovery unit.

In one embodiment the acid gas from a tail gas treatment unit is purified before being added downstream of the waste heat boiler and upstream of a first Claus catalytic reactor in the Claus unit or sulphur recovery unit. Thus the Claus unit or sulphur recovery unit of the present invention may comprise a reaction furnace (e.g. a single reaction furnace or a two section reaction furnace), a waste heat boiler and at least one Claus catalytic reactor (e.g. two or more Claus catalytic reactors), and (b) a tail gas treating unit (TGTU) comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; (ii) collecting acid gas from the TGTU, (iii) purifying said acid gas and (iv) adding the purified acid gas downstream of the waste heat boiler and upstream of a first Claus catalytic reactor. The Claus unit or sulphur recovery unit may include one or more catalytic stages. Thus the Claus unit or sulphur recovery unit may include a first catalytic stage comprising a first reheater, the first Claus catalytic reactor and a first condenser, and a second catalytic stage comprising a second reheater, the second Claus catalytic reactor and a second condenser, wherein the first catalytic stage is upstream of the second catalytic stage and the acid gas from the TGTU is purified before being added downstream of the waste heat boiler and upstream of the first Claus catalytic reactor. In one embodiment, the acid gas from the TGTU is purified using a silica, alumina or activated carbon to remove impurities before being added downstream of the waste heat boiler and upstream of the first Claus catalytic reactor in the Claus unit or sulphur recovery unit. In one embodiment the acid gas from the TGTU passes through a bed of silica, alumina or activated carbon inside a vessel and is then added downstream of the waste heat boiler and upstream of the first Claus catalytic reactor.

The process of the present invention may alternatively comprise adding the acid gas from the TGTU downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor in the Claus unit or sulphur recovery unit. In one embodiment the temperature of the second Claus catalytic reactor is less than 240°C (e.g. between 240°C and 190 °C).

In one embodiment the Claus unit or sulphur recovery unit further comprises a first condenser between the first and second Claus catalytic reactors so the acid gas from the TGTU is added downstream said first condenser and upstream the second Claus catalytic reactor. In one embodiment the Claus unit or sulphur recovery unit further comprises a first reheater between the waste heat boiler and the first Claus catalytic reactor and a second reheater between the first condenser and the second Claus catalytic reactor so the acid gas from the TGTU is added downstream of said first condenser and upstream of the second reheater. The Claus unit or sulphur recovery unit may further comprise a second condenser downstream the second Claus catalytic reactor. The Claus or reaction furnace may be a two section furnace or a single section furnace as described above. In one embodiment the temperature of a second Claus catalytic reactor is less than 240°C (e.g. between 240°C and 190 °C).

In one embodiment the Claus unit or sulphur recovery unit further comprises a first condenser between the first and second Claus catalytic reactors so the acid gas from TGTU is added downstream of the first Claus catalytic reactor and upstream of the first condenser. In one embodiment the Claus unit or sulphur recovery unit further comprises a first reheater between the waste heat boiler and the first Claus catalytic reactor and second reheater between the first condenser and the second Claus catalytic reactor so the acid gas from the TGTU is added downstream of the first Claus catalytic reactor and upstream of the first condenser. The Claus unit or sulphur recovery unit may further comprise a second condenser downstream the second Claus catalytic reactor. The Claus or reaction furnace may be a two section furnace or a single section furnace as described above. In one embodiment the temperature of a second Claus catalytic reactor is less than 240°C (e.g. between 240°C and 190 °C).

The Claus unit or sulphur recovery unit may also comprise as additional condenser or thermal condenser between the waste heat boiler and the first reheater. The thermal condenser may be considered as an extension or continuation or a part of the waste heat boiler.

The Claus unit or sulphur recovery unit includes or is used with a tail gas treatment unit (TGTU). Gases from the catalytic reactor are sent to the TGTU.

In one embodiment the acid gas from the tail gas treatment unit (TGTU) is added between the waste heat boiler outlet and the first Claus catalytic reactor inlet. In one embodiment the acid gas from the TGTU is added to the gases exiting the waste heat boiler, namely to the process gas stream exiting the waste heat boiler. In one embodiment the acid gas from the TGTU is added to the process gas stream upstream of the first catalytic reactor in the Claus unit or sulphur recovery unit, for example upstream the inlet of the first catalytic reactor. In one embodiment the acid gas from the tail gas treatment unit (TGTU) is added between the waste heat boiler outlet and the first Claus catalytic reactor inlet. In one embodiment the acid gas from the TGTU is added to the gases exiting the waste heat boiler, namely to the process gas stream exiting the waste heat boiler. In one embodiment the acid gas from the TGTU is added to the process gas stream upstream of the first catalytic reactor in the Claus unit or sulphur recovery unit, for example upstream the inlet of the first catalytic reactor. In one embodiment the acid gas from the tail gas treatment unit (TGTU) is added to the inlet of the first Claus catalytic reactor. In one embodiment the acid gas from the tail gas treatment unit (TGTU) is added to the inlet of the first Claus catalytic reactor together with the process gas stream.

In one embodiment the acid gas from the tail gas treatment unit (TGTU) is added downstream of the first condenser of the first catalytic stage and upstream of the second reheater of the second catalytic stage, wherein the first catalytic stage is upstream of the second catalytic stage. In one embodiment the acid gas from the TGTU is added between an outlet of the first condenser of the first catalytic stage and an inlet of the second reheater of the second catalytic stage. In one embodiment the acid gas from the TGTU is added to the gases exiting the first condenser of the first catalytic stage. In one embodiment the acid gas from the TGTU is added to the process gas stream upstream of the second reheater in the second catalytic stage, for example upstream of the inlet of the second reheater. The Claus or reaction furnace may be a two section furnace or a single section furnace as described above. In one embodiment the temperature of a second Claus catalytic reactor downstream of the second reheater is less than 240°C (e.g. between 240°C and 190 °C).

An example of the process according to the invention used in a Claus unit with a single section furnace (7”) is shown in Figure 3 in which the acid gas from the TGTU is added downstream of the first condenser (10a) of the first catalytic stage and upstream of the second reheater (11b) of the second catalytic stage, wherein the first catalytic stage is upstream of the second catalytic stage. In one embodiment the temperature of a second Claus catalytic reactor (9b) downstream of the second reheater (11b) is less than 240°C (e.g. between 240°C and 190 °C). An example of the process according to the invention used in a Claus unit with a two section furnace (7’) is shown in Figure 4 in which the acid gas from the TGTU is added downstream of the first condenser (10a) of the first catalytic stage and upstream of the second reheater (11b) of the second catalytic stage, wherein the first catalytic stage is upstream of the second catalytic stage. In one embodiment the temperature of a second Claus catalytic reactor (9b) downstream of the second reheater (11b) is less than 240°C (e.g. between 240°C and 190 °C).

In one embodiment the acid gas from the tail gas treatment unit (TGTU) is added downstream of the first Claus catalytic reactor and upstream of the first condenser, wherein the first Claus catalytic reactor is upstream of the first condenser. In one embodiment the acid gas from the tail gas treatment unit (TGTU) is added between the outlet of the first Claus catalytic reactor of the first catalytic stage and the inlet of the first condenser of the first catalytic stage. In one embodiment the acid gas from the TGTU is added to the gases exiting the first Claus catalytic reactor of the first catalytic stage. In one embodiment the acid gas from the TGTU is added to the process gas stream upstream of the first condenser in the first catalytic stage, for example upstream of an inlet of the first condenser. The Claus or reaction furnace may be a two section furnace or a single section furnace as described above. In one embodiment the temperature of a second Claus catalytic reactor of a second catalytic stage is less than 240°C (e.g between 240°C and 190 °C), wherein the second catalytic stage is downstream of the first catalytic stage.

An example of the process according to the invention used in a Claus unit with a single section furnace (7”) is shown in Figure 5 in which the acid gas from the TGTU is added downstream of a first Claus catalytic reactor (9a) of a first catalytic stage and upstream of a first condenser (10a) of the first catalytic stage. In one embodiment the temperature of a second Claus catalytic reactor (9b) of the second catalytic stage is less than 240°C, wherein the second catalytic stage is downstream the first catalytic stage.

An example of the process according to the invention used in a Claus unit with a two section furnace (7’) is shown in Figure 6 in which the acid gas from the TGTU is added downstream of a first Claus catalytic reactor (9a) of a first catalytic stage and upstream of a first condenser (10a) of a first catalytic stage. In one embodiment the temperature of a second Claus catalytic reactor (9b) of the second catalytic stage is less than 240°C, wherein the second catalytic stage is downstream the first catalytic stage.

As set out above a tail gas treatment unit (TGTU) is normally a mandatary part of modern sulphur recovery units. Known processes recycle the acid gas from the tail gas treatment unit to join the amine acid gas feeding the Claus unit or sulphur recovery unit, however this reduces the combustion temperature in the furnace because the acid gas from the TGTU introduces more CO2 into the furnace. On the contrary, the present invention has found that by adding the acid gas from the TGTU to the catalytic stages instead of the furnace, the furnace temperature is increased. This is because the amount of carbon dioxide absorbed by the TGTU does not dilute the gases in the furnace. The furnace temperature is also increased because an increased proportion of H2S fed to the furnace is burnt in order to keep the correct ratio of H2S and SO2 concentration ratio in the gases leaving the Claus unit.

The process of the present invention is for increasing the furnace temperature of a Claus unit or sulphur recovery unit and so more effectively destroying contaminants contained in the feed gases.

With the process of the present invention the temperature in the furnace is surprisingly almost independent of the amount of carbon dioxide in the acid gas from the tail gas treatment unit. This is in sharp contrast with the existing process where the amount of recycled CO2 affects the furnace temperature and a solvent highly selective for H2S compared with CO2 is recommended for use in the TGTU (Ben Spooner, Farsin Derakhshan,- "Reduce CO2 in acid gas from amine-based TGTUs" Hydrocarbon Processing March 2012 Special Report Corrosion Control, gives 1230 °C as the temperature needed for ammonia destruction). Advantageously in the process of the present invention the TGTU does not need to use very selective solvents and allows for a wider choice of solvents which can be used in the TGTU.

Moreover with the process of the present invention the temperature rise across the catalytic reactor is increased because some of the reaction between H2S and SO2 from the furnace is transferred to the catalyst. The first catalytic reactor is normally operated to achieve a certain outlet temperature (for example 300 °C) to destroy carbon-sulphur compounds. For the process of invention this outlet temperature can be achieved at a reduced inlet temperature. The reduction in inlet temperature can be of great practical utility because the steam pressure needed to heat the incoming gases to the catalyst bed can be reduced.

As explained above, the first Claus catalytic reactor (of a first catalytic stage) is normally operated to achieve a certain outlet temperature (for example 300 °C) to destroy carbon-sulphur compounds. This high temperature is sufficient to “crack” hydrocarbons and amine contained in the acid gas and form carbon on the catalytic reactor, and thus it might deactivate and short catalytic reactor life. With the process of the present invention the acid gas from the TGTU is added or recycled to between the first Claus catalytic reactor and the second Claus catalytic reactor, wherein the first Claus catalytic reactor is upstream of the second Claus catalytic reactor. Because the temperature in the second Claus catalytic reactor does not exceed 240 °C the “cracking” of contaminants (e.g. amine and hydrocarbons) on the catalytic reactors is minimised, prolonging the life of the Claus catalytic reactors. This also means that the operating pressure of the TGTU regenerator can be reduced compared with a system recycling acid gas to the Claus feed. The advantages of this reduction in the regenerator pressure and resultant reduction in temperature are the reduced thermal degradation of amine, better stripping of amine for a given heat input to the reboiler and opportunity to use lower pressure steam for heating the regenerator reboiler.

In an embodiment of the process of the invention all of the acid gas collected from the TGTU is added downstream of a waste heat boiler and upstream of a Claus catalytic reactor (e.g. to the inlet of the first Claus catalytic reactor or to the process gas stream exiting the waste heat boiler). In an embodiment of the process of the invention all of the acid gas collected from the TGTU is added downstream of the first Claus catalytic reactor of a first catalytic stage and upstream of the second Claus catalytic reactor of a second catalytic stage in the Claus unit or sulphur recovery unit. (e.g. to the inlet of the second reheater, or to the inlet of the first condenser, or to the process gas stream exiting the first condenser or to the process gas stream exiting the first Claus catalytic reactor). Therefore in this embodiment none of the acid gas collected from the TGTU is mixed with the AAG and none of the acid gas collected from the TGTU is added to the burner or reaction furnace. So the process of the present invention can also be used to improve the performance of existing two section furnace systems. Also in known processes, a low Claus sulphur recovery efficiency will also reduce the furnace temperature because the amount of CO2 co-absorbed with the H2S in the TGTU increases. However, for the process of the present invention low sulphur recovery efficiency increases the furnace temperature because an increased proportion of H2S fed to the furnace is burnt in order to keep the correct ratio of H2S and SO2 concentration ratio in the gases leaving the Claus unit.

Accordingly adding the acid gas from the TGTU to the catalytic stages instead of the furnace causes an increase of the furnace temperature and in the proportion of sulphur dioxide in the furnace gases. Both these factors reduce the amount of residual ammonia passing to the catalyst stages. The acid gas from the TGTU normally contains no components which can damage the catalyst if the Claus catalytic reactor is at low temperature (below 240 °C). The acid gas from the TGTU can contain traces of amine and hydrocarbons which can “crack” at higher temperatures typical of the first Claus catalytic reactor (approximately 300°C) and deactivate the catalyst. Thus as explained above by adding the acid gas from the TGTU downstream of the first Claus catalytic reactor and upstream of the second catalytic reactor (e.g. to the inlet of the second reheater, or to the inlet of the first condenser, or to the process gas stream exiting the first condenser or to the process gas stream exiting the first Claus catalytic reactor) the “cracking” of contaminants (e.g. amine and hydrocarbons) on the catalytic reactors is minimised, prolonging the life of the Claus catalytic reactors.

In one embodiment the process of the present invention further comprises adding acid gas from the tail gas treatment unit downstream of a waste heat boiler and upstream of a Claus catalytic reactor (e.g. between the waste heat boiler outlet and a first Claus catalytic reactor, for example between the waste heat boiler outlet and the inlet of the first Claus catalytic reactor or for example to the inlet of the first Claus catalytic reactor) in order to increase the furnace temperature in the Claus unit or sulphur recovery unit .

Increasing the Claus furnace temperature can improve operation of the Claus unit or sulphur recovery unit by destroying ammonia and other contaminants. In addition, the increase in temperature provided by the process of the present invention can facilitate flame stability in the Claus unit burner. The process of the invention also destroys contaminants contained in the feed gases passing through or being added to the Claus unit or sulphur recovery.

In one embodiment the process of the invention destroys ammonia and/or hydrocarbon contaminants contained in the feed gases (amine acid gas and SWS off gas).

In one embodiment the process of the invention destroys hydrocarbons contained in the feed gases. In one embodiment the process of the invention destroys ammonia in the feed gases.

In one embodiment the process of the invention destroys ammonia and hydrocarbon contaminants contained in the feed gases (amine acid gas and SWS off gas).

In one embodiment the process of the invention facilitates flame stability in a Claus unit burner.

The present invention achieves higher furnace temperatures for lower H2S concentrations than existing processes so it reduces or eliminates the pre-heat needed to achieve a specific furnace temperature.

As explained above feed gases can include amine acid gases. Said amine acid gases fed to a Claus unit or sulphur recovery unit can vary in H2S concentration and in the amount of impurities such as hydrocarbons. The amount of hydrocarbon, in particular, affects the furnace temperature.

In the process of the present invention, by adding the acid gas from a tail gas treatment unit downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor (e.g. to the inlet of the second reheater, or to the inlet of the first condenser, or to the process gas stream exiting the first condenser or to the process gas stream exiting the first Claus catalytic reactor), the temperature of the reaction furnace in the Claus unit or sulphur recovery unit is increased to at least 975 °C.

In the process of the present invention, by adding the acid gas from a tail gas treatment unit downstream of a waste heat boiler and upstream of a Claus catalytic reactor (e.g. by adding it to the inlet of a first catalytic reactor or between a waste heat boiler outlet and a first Claus catalytic reactor inlet or to the process gas stream exiting the waste heat boiler) the temperature of the reaction furnace in the Claus unit or sulphur recovery unit is increased to at least 975 °C.

This temperature provides suitable conditions to facilitate flame stability in the Claus unit burner.

The process of increasing the temperature to 975 °C in the furnace can be achieved for amine acid gases with a H2S concentration as low as 45%, so with a H2S concentration of 45% or more. Pre-heating may be required for lower H2S concentrations, for example, H2S concentrations as low as 34%, so with a H2S concentration of from 34% to less than 45 %, can be processed with a preheat of up to 240 °C to achieve a temperature of 975 °C in the furnace. With the process of increasing the temperature of the present invention, the desired furnace temperature of 975 °C can be achieved with H2S concentrations approximately 8% lower than with conventional processes.

In the process of the present invention, by adding the acid gas from a tail gas treatment unit downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor (e.g. to the inlet of the second reheater, or to the inlet of the first condenser, or to the process gas stream exiting the first condenser or to the process gas stream exiting the first Claus catalytic reactor), the temperature of the reaction furnace in the Claus unit or sulphur recovery unit is increased to at least 1050 °C.

In the process of the present invention, by adding the acid gas from a tail gas treatment unit downstream of a waste heat boiler and upstream of a Claus catalytic reactor (e.g. by adding it to the inlet of a first catalytic reactor or between a waste heat boiler outlet and a first Claus catalytic reactor inlet or to the process gas stream exiting the waste heat boiler) the temperature of the reaction furnace in the Claus unit or sulphur recovery unit is increased to at least 1050 °C.

This temperature provides suitable conditions to destroy hydrocarbon contaminants contained in the feed gases. The process of increasing the temperature to 1050 °C in the furnace can be achieved for amine acid gases with a H2S concentration of as low as 55%, so with a H2S concentration of 55% or more. Pre-heating may be required for lower H2 S concentrations, for example, H2S concentrations as low as 44%, so with a H2S concentration of from 44% to less than 55 %, can be processed with a preheat of up to 240 °C to achieve a temperature of 1050 °C in the furnace. With the process of increasing the temperature of the present invention, the desired furnace temperature of 1050 °C can be achieved with H2S concentrations approximately 9% lower or 8% lower than with conventional processes.

In the process of the present invention by adding the acid gas from a tail gas treatment unit downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor (e.g. to the inlet of the second reheater, or to the inlet of the first condenser, or to the process gas stream exiting the first condenser or to the process gas stream exiting the first Claus catalytic reactor) the temperature of the reaction furnace in a Claus unit or sulphur recovery unit is increased to at least 1250 °C.

In the process of the present invention by adding the acid gas from the tail gas treatment unit downstream of the waste heat boiler and upstream of the Claus catalytic reactor (e.g. by adding it to the inlet of a first catalytic reactor or between a waste heat boiler outlet and a first Claus catalytic reactor inlet or to the process gas stream exiting the waste heat boiler) the temperature of the reaction furnace in a Claus unit or sulphur recovery unit is increased to at least 1250 °C.

This temperature provides suitable conditions to destroy the ammonia contained in the feed gases.

The process of increasing the temperature to 1250 °C in the furnace can be achieved for refinery feed with SWS off gas and with an amine acid gas concentration of 79% or more. Pre-heating may be required for lower amine acid gas concentrations, for example, of 57% or more, for example from 57% to less than 79 %, or amine acid gas concentrations of 58% or more, for example from 58% to less than 79 %, can be processed with a preheat of up to 240 °C to achieve a temperature of 1250 °C in the furnace. With the process of increasing the temperature of the present invention, the desired furnace temperature of 1250 °C can be achieved with an amine acid gas concentration approximately 10% lower or 9% lower than with conventional processes.

The pre-heat systems referred to above would heat the Claus furnace feeds and combustion air using any convenient heating medium, such as steam. For specific cases different pre-heat temperatures may be appropriate.

Re-routing the TGTU acid gas to the catalytic stages downstream of the waste heat boiler instead of the furnace can improve the operation of existing two section furnace processes. The temperature of both sections of the furnace is increased. The acid gas bypassed to the second section of the furnace can be reduced while maintaining the needed temperature in the front section of the furnace. This has the benefit of reducing the amount of SO3 and NOx formed in the front section of the furnace and improving contaminant destruction in the second section of the furnace.

The process of the present invention can be used in a Claus unit or sulphur recovery unit as described herein above, wherein the Claus unit or sulphur recovery unit comprises a two section furnace Claus system. This would be especially useful in a revamp situation if the amine acid gas contained ammonia or if the second section of the furnace was not hot enough to destroy hydrocarbons in the acid gas or the first section of the furnace could not achieve the temperature needed to destroy ammonia.

The process of the present invention comprises adding said acid gas from the TGTU downstream of the waste heat boiler and upstream of a Claus catalytic reactor of a Claus unit or sulphur recovery unit with a two section reaction furnace.

A process of the present invention may comprise adding said acid gas from the TGTU downstream of a first Claus catalytic reactor and upstream of a second Claus catalytic reactor in the Claus unit or sulphur recovery unit with a two section reaction furnace. An example of a process according to the invention used in a Claus unit with a two section furnace (7’) is shown in Figures 4 and 6.

An example of a further process according to the invention used in a Claus unit with a two section furnace (7’) is shown in Figures 9 and 10 in which the acid gas from the TGTU is added downstream of the waste heat boiler and upstream of a Claus catalytic reactor. In one embodiment the process of the present invention may further comprise purifying the acid gas from the tail gas treatment unit before adding said acid gas downstream of the waste heat boiler and upstream of a Claus catalytic reactor of a Claus unit or sulphur recovery unit with a two section reaction furnace. An example of the process according to the invention used in a Claus unit with a two section furnace (7’) is shown in Figure 10 in which the acid gas from the TGTU is purified using a purification vessel (19) (e.g. silica, alumina or activated carbon in a vessel) and then added downstream of the waste heat boiler (8) and upstream of a Claus catalytic reactor. The Claus catalytic reactor of a Claus unit or sulphur recovery unit may have one or more Claus catalytic reactors, so the purified acid gas is added downstream of the waste heat boiler and upstream of a first Claus catalytic reactor which is upstream of a second and any further Claus catalytic reactors.

As explained above, the process of the present invention can also be used in a single section furnace (7”) system. So the process of the present invention may eliminate the need for a two section furnace for most refinery feeds, and provides the opportunity to convert the heat from low pressure (LP) steam into medium or high pressure steam generated in the waste heat boiler if pre-heat with LP steam is used.

Thus, in one embodiment the process of the present invention is used with a Claus unit or sulphur recovery unit as described herein above, wherein the Claus unit or sulphur recovery unit comprises a single section furnace. A single section furnace may be used with or without pre-heat in order to simplify controls and furnace construction.

The process of the present invention allows the use of a single section furnace and the full volume of the furnace can be used for contaminant destruction and the sulphur forming reactions. All the reactants (combustion air and acid gases) are well mixed in the burner and the poor mixing of part of the acid gas feed injected into the second section of the furnace is avoided.

A process of the present invention further comprises adding said acid gas collected from the TGTU downstream of a first Claus catalytic reactor and upstream of a subsequent second Claus catalytic reactor of a Claus unit or sulphur recovery unit with a single section reaction furnace. An example of the process according to the invention used in a Claus unit with a single section furnace (7”) is shown in Figures 3 and 5 as described herein above.

A further process of the present invention further comprises adding said acid gas collected from the TGTU downstream of the waste heat boiler and upstream of a Claus catalytic reactor of a Claus unit or sulphur recovery unit with a single section reaction furnace. An example of the process according to the invention used in a Claus unit with a single section furnace (7”) is shown in Figures 7 and 8 in which the acid gas from the TGTU is added downstream of the waste heat boiler and upstream of a Claus catalytic reactor. The process of the present invention may further comprise purifying the acid gas from the tail gas treatment unit before adding said acid gas downstream of the waste heat boiler and upstream of a Claus catalytic reactor of a Claus unit or sulphur recovery unit with a single section reaction furnace. An example of the process according to the invention used in a Claus unit with a single section furnace (7”) is shown in Figure 8 in which the acid gas from the TGTU is purified using a purification vessel (19) (e.g. silica, alumina or activated carbon in a vessel) and then added downstream of the waste heat boiler and upstream of a Claus catalytic reactor. The Claus catalytic reactor of a Claus unit or sulphur recovery unit may have one or more Claus catalytic reactors, so the purified acid gas is added downstream of the waste heat boiler and upstream of a first Claus catalytic reactor which is upstream of a second and any further Claus catalytic reactors.

For known systems with a single section furnace where ammonia is not present there is still a minimum furnace temperature needed. For contaminant destruction this temperature is typically 1050 °C and for flame stability this is 975 °C. The process of the present invention can also be applied to feeds with low concentrations of H2S to economically achieve the needed temperatures. Thus with the process of the present invention in acid gas feeds without ammonia but with low concentrations of H2S the temperature needed for contaminant destruction is more easily achieved and the operating range in terms of H2S concentration in the acid gas can be extended.

For amine acid gas feeds dilute in H2S where the needed furnace temperature cannot be reached the amine acid gas feed can be divided so that part of said acid gas is fed to the burner and part fed to any point in the tail gas treatment unit upstream of the TGTU absorber. The acid gas from the tail gas treatment unit may be added between the waste heat boiler, for example the waste heat boiler outlet, and the Claus catalytic reactor in the in the Claus unit or sulphur recovery unit. The acid gas from the tail gas treatment unit may be purified as described herein above before being added between the waste heat boiler, for example the waste heat boiler outlet, and the Claus catalytic reactor in the in the Claus unit or sulphur recovery unit. The acid gas from the tail gas treatment unit may be added between the first Claus catalytic reactor and the second Claus catalytic reactor in the in the Claus unit or sulphur recovery unit (e.g. to the inlet of the second reheater, or to the inlet of the first condenser, or to the process gas stream exiting the first condenser or to the process gas stream exiting the first Claus catalytic reactor).

In one embodiment of the present invention, the amine acid gas of the feed gases is divided and part is sent to a burner and/or reaction furnace of the Claus unit or sulphur recovery unit and part is added between the outlet of the last Claus catalytic converter to the inlet of the tail gas treatment unit absorber.

In one embodiment of the present invention, sufficient of the amine acid gasses contained in the feed gas are fed to the burner so that no free oxygen and some hydrogen sulphide is present in the reaction furnace outlet gases and the balance of the amine acid gas contained in the feed gases is fed to upstream of the TGTU absorber of the tail gas treatment unit.

For example with the acid gas divided so that 40% of the flow is fed to the TGTU upstream of the TGTU absorber a furnace temperature of 1050 °C is achieved for acid gases with H2S concentrations as low as 30% without pre-heat and as low as 23% with pre-heat to 240 °C.

A further example of the process according to the invention used in a Claus unit or sulphur recovery unit (1) with a single section furnace (7”) in which the feed gases are divided and part (e.g. part of the amine acid gas) is sent to a burner (6) and/or the single section furnace (7”) of the Claus unit or sulphur recovery unit (1) and part is added between the outlet of the last Claus catalytic stage or converter and the inlet of the tail gas treatment unit absorber (15) is shown in Figure 11, 12 and 13.

In a further example of the process according to the invention shown in Figure 12, the Claus unit or sulphur recovery unit (1) comprises a single section furnace (7”) in which the feed gases are divided and part (e.g. part of the amine acid gas) is sent to a burner (6) and/or the single section furnace (7”) of the Claus unit or sulphur recovery unit (1) and part is added between the outlet of the last Claus catalytic stage or converter and the inlet of the tail gas treatment unit absorber (15), and the acid gas from the TGTU is purified by passing it through a purification vessel (19) (e.g. using a bed of silica, alumina or activated carbon inside a vessel) and adding the purified acid gas to downstream the waste heat boiler and upstream of a Claus catalytic reactor (e.g. first Claus catalytic reactor).

In a further example of the process according to the invention shown in Figure 13, the Claus unit or sulphur recovery unit (1) comprises a single section furnace (7”) and two or more Claus catalytic reactors, the feed gases are divided and part (e.g. part of the amine acid gas) is sent to a burner (6) and/or the single section furnace (7”) of the Claus unit or sulphur recovery unit (1) and part is added between the outlet of the last Claus catalytic stage or converter and the inlet of the tail gas treatment unit absorber (15) and the acid gas from the TGTU is added downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor (e.g. to the inlet of the second reheater, or to the inlet of the first condenser, or to the process gas stream exiting the first condenser or to the process gas stream exiting the first Claus catalytic reactor).

The invention also provides a process for recycling acid gases from a tail gas treatment unit, the process comprising (i) passing some or all feed gases through (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and a Claus catalytic reactor, and (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; (ii) collecting acid gas from the tail gas treatment unit and (iii) adding said acid gas downstream of the waste heat boiler and upstream of the catalytic reactor in the Claus unit or sulphur recovery unit (e.g. between the waste heat boiler and a first catalytic reactor or to the inlet of a first Claus catalytic reactor or to the process gas stream exiting the waste heat boiler).

Recycling the acid gas from the TGTU to the catalytic stages instead of the furnace causes an increase of the furnace temperature and in the proportion of sulphur dioxide in the furnace gases. Both these factors reduce the amount of residual ammonia passing to the catalyst stages and improve the performance of existing furnace systems.

The invention also provides, a system for increasing the furnace temperature of a Claus unit or sulphur recovery unit and/or destroying contaminants contained in Claus unit feed gases, comprising (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and two or more Claus catalytic reactors; (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; and (c) means for connecting and recycling the acid gas from the tail gas treating unit to the Claus unit or sulphur recovery unit, downstream of a first Claus catalytic reactor and upstream of a second Claus catalytic reactor. In one embodiment, the temperature of the second Claus catalytic reactor is less than 240°C (e.g. between 240°C and 190°C).

In one embodiment, the system may comprise means for connecting the first Claus catalytic reactor and the second Claus catalytic reactor, wherein the first Claus catalytic reactor is upstream the second Claus catalytic reactor. The system may further comprise means for collecting and adding the acid gas from the TGTU to the means connecting the first Claus catalytic reactor and the second Claus catalytic reactor. In one embodiment, the system further comprises means for connecting the waste heat boiler with a first reheater, means for connecting said first reheater with a first Claus catalytic reactor, means for connecting said first Claus catalytic reactor with a first condenser, means for connecting said first condenser with a second reheater, means for connecting said second reheater with a second Claus catalytic reactor, means for connecting said second Claus catalytic reactor with a second condenser. The system may further comprise means for collecting and adding the acid gas from the TGTU to the means connecting the first condenser and the second reheater or to the means connecting the first Claus catalytic reactor and the first condenser. The system may optionally comprise an additional condenser (e.g a thermal condenser) between the waste heat boiler and the first catalytic stage (e.g. between the waste heat boiler and the first reheater). In one embodiment, the temperature of the second Claus catalytic reactor is less than 240°C (e.g. between 240°C and 190°C. In one embodiment the system may comprise means for collecting and adding the acid gas from the TGTU to the means for collecting the gases exiting the first Claus catalytic reactor or exiting the first condenser, namely to the process gas stream exiting the first catalytic reactor or to the process gas stream exiting the first condenser.

In one embodiment the system may comprise a first catalytic reactor having an outlet. The system may further comprise means for connecting and adding the acid gas from the TGTU to the outlet of the first catalytic reactor.

In one embodiment the system may comprise a first condenser having an inlet and/or an outlet. The system may comprise means for connecting and adding the acid gas from the TGTU to the inlet and/or to the outlet of the first condenser.

In one embodiment the system may comprise a second reheater having an inlet. The system may further comprise means for connecting and adding the acid gas from the TGTU to the inlet of the second reheater.

The invention also provides a system for increasing the furnace temperature of a Claus unit or sulphur recovery unit and/or destroying contaminants contained in Claus unit feed gases, the system comprising (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and a Claus catalytic reactor; (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; and (c) means for collecting and adding the acid gas from the tail gas treating unit to the Claus unit or sulphur recovery unit downstream of the waste heat boiler and upstream of the catalytic reactor.

In one embodiment, the system further comprises means for connecting the waste heat boiler and the catalytic reactor. The system may further comprise means for collecting and adding the acid gas from the TGTU to the means connecting the waste heat boiler and the catalytic reactor.

In one embodiment the system further comprises means for collecting the gases exiting the waste heat boiler. The system may further comprise means for collecting and adding the acid gas from the TGTU to the means for collecting the gases exiting the waste heat boiler, namely to the process gas stream exiting the waste heat boiler. In one embodiment the system further comprises a catalytic reactor having an inlet. The system may further comprise means for connecting and adding the acid gas from the TGTU to the inlet of the catalytic reactor.

Examples

The examples are based on representative feed compositions. In practice higher or lower furnace temperatures will occur depending mainly on the relative feed flows, the compositions and the Claus unit efficiency.

Example 1: Equilibrium furnace temperature with changing CO2 slip in the TGTU

A standard refinery feed with amine acid gas (flow 100 kgmol/h) and sour water stripper (SWS) off gas (flow 50 kgmol/h) is used.

The amine acid gas contains 80% H2S, 13% CO2, 1% hydrocarbon (as ethane) and 6% H2O and is at 40°C. The SWS off gas (or SWS acid gas) contains 35% H2S, 35% NH3, 30% H₂O and is at 85 °C.

The CO2 slip in the TGTU ranges from 40% to 90% and the Claus efficiency is approximately 95%.

The results are shown in the chart of Figure 14.

Figure 14 clearly shows the advantages of the process of the present invention. The equilibrium furnace temperature is more than 1250 °C, which is a sufficient temperature needed to destroy ammonia (Ben Spooner, Farsin Derakhshan,- “Reduce CO2 in acid gas from amine-based TGTUs" Hydrocarbon Processing March 2012 Special Report Corrosion Control, gives 1230 °C as the temperature needed for ammonia destruction).

In no case does the process in which acid gas from the TGTU joins with the amine acid gas feed reach even 1230 °C. As can also be seen in Figure 14, the process of the present invention is not affected by changes in the amount of CO2 absorbed by the amine in the TGTU. Generic MDEA can be used for the TGTU and special solvents are not needed. Even DEA may be considered if more selective solvents are not available.

Example 2: Equilibrium furnace temperature with various H2S concentrations.

The feed flows and compositions from the example above are used except the amine acid gas, H2S and CO2 concentration are changed so that the H2S concentration ranges from 50% to 90%. The CO2 slip in the TGTU is a typical value of 80%. The Claus unit efficiency is approximately 95% based on the feed in the example above and changes slightly with the H2S concentration in the amine acid gas.

If the furnace temperature is below 1250 °C the combustion air and acid gases are preheated to achieve 1250 °C in the furnace (i.e. the feed and air temperatures are increased to reach 1250 °C in the furnace).

The following table summarises the results for refinery feed with a SWS acid gas stream: For refinery situations pre-heat up to 140 °C would use LP steam and preheat up to approximately 240 °C would use HP steam. Preheat temperatures higher than approximately 240 °C become progressively more difficult (and expensive) to implement.

For most refinery feeds the process of the present invention achieves the temperature needed for ammonia destruction and is insensitive to changes in the TGTU CO2 slip.

The temperature difference between the process of the present invention and conventional process increases as the Claus unit efficiency falls, so for dilute feeds the furnace temperature achieved by the process of the invention is progressively higher compared with the conventional process.

Dilute feeds as found in gas treating units do not contain ammonia but can contain hydrocarbons and mercaptans which need to be destroyed in the Claus reaction furnace.

The example below shows the results of the known process of adding the acid gas from the TGTU to the acid gas feed stream compared with the process of the present invention where the TGTU acid gas is added between the outlet of the first Claus catalytic reactor and the second Claus catalytic reactor (e.g. the inlet of the second catalytic reactor). Only amine acid gas is considered, with 6% H2O and 1% hydrocarbon as ethane. The CO2 slip in the TGTU is 80% as above.

The table includes examples with various H2S concentrations in the acid gas with and without pre-heat of the Claus unit feeds. The minimum H2S concentration need for hydrocarbon destruction (1050 °C) and flame stability (975 °C) can be estimated by interpolation from the table below.

From the table addition of the TGTU acid gas to between the first Claus Catalytic reactor and the second Claus catalytic reactor allows the H2S concentration in the acid gas feed to be reduced by approximately 10% compared with addition of the TGTU acid gas to join the acid gas feed.

Example 3: Equilibrium furnace temperature with various H2S concentrations.

The following table summarises the results for refinery feed with a SWS acid gas stream:

For refinery situations pre-heat to 140 °C would use LP steam and preheat to 223 °C or 235 °C would use HP steam. Preheat temperatures higher than approximately 240 °C become progressively more difficult (and expensive) to implement.

The example below shows the results of the known process of adding the acid gas from the TGTU to the acid gas feed stream compared with the process of the present invention where the TGTU acid gas is added between the waste heat boiler outlet and the first catalytic reactor (e.g. the first catalytic reactor inlet). Only amine acid gas is considered, with 6% H2O and 1% hydrocarbon as ethane. The CO2 slip in the TGTU is 80% as above. The table includes examples with various H2S concentrations in the acid gas with and without pre-heat of the Claus unit feeds. The minimum H2S concentration need for hydrocarbon destruction (1050 °C) and flame stability (975 °C) can be estimated by interpolation from the table below.

From the table addition of the TGTU acid gas to between the waste heat boiler and the first Claus catalyst reactor allows the H2S concentration in the acid gas feed to be reduced by approximately 10% compared with addition of the TGTU acid gas to join the acid gas feed.

Claims

38 Claims

1. A process comprising:

(i) passing some or all feed gases through (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and two or more Claus catalytic reactors, and (b) a tail gas treating unit (TGTU) comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator;

(ii) collecting acid gas from the tail gas treatment unit (TGTU) and

(iii) adding said acid gas from the tail gas treatment unit downstream of a first Claus catalytic reactor and upstream of a second Claus catalytic reactor in the Claus unit or sulphur recovery unit.

2. The process of claim 1, wherein the temperature of the second Claus catalytic reactor is 240°C or lower.

3. The process of claim 1 or claim 2, wherein the process is for destroying contaminants contained in the feed gases and, wherein optionally the contaminants destroyed are ammonia and/or hydrocarbon contaminants contained in the feed gases.

4. The process of claim any one of claims 1 to 3, wherein the process is for increasing the furnace temperature of a Claus unit or sulphur recovery unit.

5. The process of any one of claims 1 to 4, wherein the acid gas from the tail gas treatment unit is added between an outlet of the first Claus catalytic reactor and an inlet of the second Claus catalytic reactor.

6. The process of any one of claims 1 to 5, wherein the Claus unit or sulphur recovery unit further comprises a first condenser between the first and second Claus catalytic reactors and the acid gas from a tail gas treatment unit is added downstream said first condenser and upstream the second catalytic reactor.

7. The process of claims 6, wherein the Claus unit or sulphur recovery unit further comprises a first reheater between the waste heat boiler and the first Claus catalytic reactor and second reheater between the first condenser and the second Claus catalytic reactor and the acid gas from a tail gas treatment unit is added downstream said first condenser and upstream the second reheater. 39

8. The process of any one of claims 1 to 5, wherein the Claus unit or sulphur recovery unit further comprises a first condenser between the first and second Claus catalytic reactors and the acid gas from a tail gas treatment unit is added downstream the first Claus catalytic reactor and upstream the first condenser.

9. The process of claims 8, wherein the Claus unit or sulphur recovery unit further comprises a first reheater between the waste heat boiler and the first Claus catalytic reactor and second reheater between the first condenser and the second Claus catalytic reactor and the acid gas from a tail gas treatment unit is added downstream the first Claus catalytic reactor and upstream the first condenser.

10. The process of any one of claims 1 to 9, wherein by adding the acid gas from the tail gas treatment unit downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor, the temperature in the reaction furnace in the Claus unit or sulphur recovery unit is increased.

11. The process of any of claims 1 to 10, wherein by adding the acid gas from a tail gas treatment unit downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor the temperature in the reaction furnace in the Claus unit or sulphur recovery unit is increased to at least 975 °C.

12. The process of any of claims 1 to 11, wherein by adding the acid gas from the tail gas treatment unit downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor the temperature in the reaction furnace in the Claus unit or sulphur recovery unit is increased to at least 1050 °C.

13. The process of any of claims 1 to 12 wherein by adding the acid gas from a tail gas treatment unit downstream of the first Claus catalytic reactor and upstream of the second Claus catalytic reactor, the temperature in the reaction furnace in the Claus unit or sulphur recovery unit is increased to at least 1250 °C.

14. The process of any one of claims 1 to 13 wherein all the feed gases are fed into the reaction furnace through a burner.

15. The process of claim 14 wherein the feed gases fed into the reaction furnace through the burner comprises amine acid gas. 40

16. The process of any one of claims 1 to 13 wherein a portion of the feed gases are fed directly into a second section of a reaction furnace and the remaining feed gases are fed into a first section of a reaction furnace through a burner and the furnace is a two section reaction furnace.

17. The process of claim 16, wherein the portion of the feed gases fed directly into a second section of a reaction furnace comprises amine acid gas.

18. The process of any one of claims 1 to 13 wherein a portion of the feed gases are fed directly into the TGTU upstream of the TGTU absorber and the remaining feed gases are fed into the reaction furnace through a burner and the furnace is a single section reaction furnace.

19. The process of claim 18, wherein the portion of the feed gases fed directly into the TGTU comprises an amine acid gas.

20. The process of any one of claims 1 to 19 wherein none of the acid gas from a tail gas treatment unit is recycled into the burner or furnace.

21. A system for carrying out a process according to claims 1-20.

22. A system for destroying contaminants contained in feed gases, the system comprising (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and two or more Claus catalytic reactors; (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; and (c) means for connecting and recycling the acid gas from the tail gas treating unit to the Claus unit or sulphur recovery unit, downstream of a first Claus catalytic reactor and upstream of a second Claus catalytic reactor in the Claus unit or sulphur recovery unit.

23. A system for increasing the furnace temperature of a Claus unit or sulphur recovery unit, the system comprising (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and two or more Claus catalytic reactors; (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; and (c) means for connecting and recycling the acid gas from the tail gas treating unit to the Claus unit or sulphur recovery unit downstream of a first Claus catalytic reactor and upstream of a second Claus catalytic reactor in the Claus unit or sulphur recovery unit.

24. The system of claim 22 or claim 23 further comprising means for connecting the first Claus catalytic reactor and the second Claus catalytic reactor and means for collecting and adding the acid gas from the TGTU to the means connecting the first Claus catalytic reactor and the second Claus catalytic reactor.

25. The system of claim 24 further comprising means for connecting the waste heat boiler with a first reheater, means for connecting said first reheater with the first Claus catalytic reactor, means for connecting said first Claus catalytic reactor with a first condenser, means for connecting said first condenser with a second reheater, means for connecting said second reheater with the second Claus catalytic reactor, and means for connecting said second Claus catalytic reactor with a subsequent second condenser,

26. The system of claim 25 further comprising means for collecting and adding the acid gas from the TGTU to the means connecting the first condenser and the second reheater.

27. The system of claim 25 further comprising means for collecting and adding the acid gas from the TGTU to the means connecting the first Claus catalytic reactor and the first condenser.

28. A process comprising:

(i) passing some or all feed gases through (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and a Claus catalytic reactor, and (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator;

(ii) collecting acid gas from the tail gas treatment unit; and

(iii) adding said acid gas from the tail gas treatment unit downstream of the waste heat boiler and upstream of the catalytic reactor in the Claus unit or sulphur recovery unit.

29. The process of claim 28, further comprising purifying the acid gas from the tail gas treatment unit before adding said acid gas downstream of the waste heat boiler and upstream of the catalytic reactor in the Claus unit or sulphur recovery unit.

30. The process of claim 28 or claim 29, wherein the acid gas from the TGTU is purified using silica, alumina or activated carbon.

31. The process of claim any one of claims 28 to 30, wherein the process is for destroying contaminants contained in the feed gases and, wherein optionally the contaminants destroyed are ammonia and/or hydrocarbon contaminants contained in the feed gases.

32. The process of any one of claims 28 to 31, wherein the process is for increasing the furnace temperature of a Claus unit or sulphur recovery unit.

33. The process of any one of claims 28 to 32, wherein the acid gas from the tail gas treatment unit is added downstream of the waste heat boiler and upstream of a first catalytic reactor in the Claus unit or sulphur recovery unit.

34. The process of any one of claims 28 to 33, wherein the acid gas from a tail gas treatment unit is added between the waste heat boiler outlet and a first catalytic reactor inlet.

35. The process of any one of claims 28 to 34, wherein the acid gas from a tail gas treatment unit is added to the inlet of a first catalytic reactor.

36. The process of any one of claims 28 to 35, wherein by adding the acid gas from the tail gas treatment unit downstream of the waste heat boiler and upstream of the catalytic reactor the temperature in the reaction furnace in the Claus unit or sulphur recovery unit is increased.

37. The process of any of claims 28 to 36, wherein by adding the acid gas from a tail gas treatment unit downstream of the waste heat boiler and upstream of the catalytic reactor the temperature in the reaction furnace in the Claus unit or sulphur recovery unit is increased to at least 975 °C.

38. The process of any of claims 28 to 36 wherein by adding the acid gas from the tail gas treatment unit downstream of the waste heat boiler and upstream of the catalytic reactor the temperature in the reaction furnace in the Claus unit or sulphur recovery unit is increased to at least 1050 °C. 43

39. The process of any of claims 28 to 36 wherein by adding the acid gas from a tail gas treatment unit downstream of the waste heat boiler and upstream of the catalytic reactor the temperature in the reaction furnace in the Claus unit or sulphur recovery unit is increased to at least 1250 °C.

40. The process of any one of claims 28 to 39 wherein all the feed gases are fed into the reaction furnace through a burner.

41. The process of claim 40 wherein the feed gases fed into the reaction furnace through the burner comprises amine acid gas.

42. The process of any one of claims 28 to 39 wherein a portion of the feed gases are fed directly into a second section of a reaction furnace and the remaining feed gases are fed into a first section of a reaction furnace through a burner and the furnace is a two section reaction furnace.

43. The process of claim 42, wherein the portion of the feed gases fed directly into a second section of a reaction furnace comprises amine acid gas.

44. The process of any one of claims 28 to 39 wherein a portion of the feed gases are fed directly into the TGTU upstream of the TGTU absorber and the remaining feed gases are fed into the reaction furnace through a burner and the furnace is a single section reaction furnace.

45. The process of claim 44, wherein the portion of the feed gases fed directly into the TGTU comprises an amine acid gas.

46. The process of any one of claims 28 to 45 wherein none of the acid gas from a tail gas treatment unit is recycled into the burner or furnace.

47. A system for carrying out a process according to claims 28-46.

48. A system for destroying contaminants contained in feed gases, the system comprising (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and a Claus catalytic reactor; (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; and (c) means for connecting and recycling the acid gas from the tail gas treating unit to the Claus unit or sulphur recovery unit, downstream of the waste heat boiler and upstream of the catalytic reactor. 44

49. A system for increasing the furnace temperature of a Claus unit or sulphur recovery unit, the system comprising (a) a Claus unit or sulphur recovery unit comprising a reaction furnace, a waste heat boiler and a Claus catalytic reactor; (b) a tail gas treating unit comprising a hydrogenation reactor, water removal, TGTU absorber and TGTU regenerator; and (c) means for connecting and recycling the acid gas from the tail gas treating unit to the Claus unit or sulphur recovery unit downstream of the waste heat boiler and upstream of the catalytic reactor.

50. The system of claim 48 or claim 49 further comprising means for connecting the waste heat boiler and the catalytic reactor.

51. The system of claim 50 further comprising means for collecting and adding the acid gas from the tail gas treating unit to the means connecting the waste heat boiler and the catalytic reactor.