A process and plant for operating a fired heater with fuel gas having been efficiently desulfurized prior to its use in the fired heater

Abstract

A process for operating a fired heater with fuel gas comprises the following steps: a) providing fuel gas containing at least one sulfur containing compound and having a temperature of at least 150°C, b) desulfurizing the fuel gas provided in step a) by contacting it with at least one catalyst and also with at least one adsorbent and / or with at least one catalyst being simultaneously an adsorbent so as to obtain a desulfurized fuel gas having a total content of sulfur and sulfur containing compounds of 8 ppmv or less, wherein the at least one catalyst and / or the at least one catalyst being simultaneously the adsorbent converts the at least one sulfur containing compound into hydrogen sulfide, and the at least one absorbent and / or the at least one catalyst being simultaneously the adsorbent adsorbs hydrogen sulfide and optionally non-converted residuals of the at least one sulfur containing compound from the fuel gas, c) feeding the desulfurized fuel gas obtained in step b) and feeding an oxygen containing combustion gas into the fired heater and combust the desulfurized fuel gas in the fired heater.

Description

[0001] A process and plant for operating a fired heater with fuel gas having been efficiently desulfurized prior to its use in the fired heater

[0002] The present invention relates to a process and to a plant for operating a fired heater with fuel gas having been efficiently desulfurized prior to its use in the fired heater.

[0003] Fired heaters, which are also designated as furnaces, are a primary source of thermal energy, wherein the thermal energy is generated by combustion of fuel gas with an oxygen containing combustion gas, such as air. Such fired heaters are applied in various technical fields, such as for process heating operations in chemical plants, petrochemical plants, refinery plants, mining plants and others. Usually, such fired heaters are the largest energy consumers in such plants and it is therefore of particular importance to increase their efficiency as much as possible. However, impurities included in the fuel gas limit the efficiency of such fired heaters so that they have a low efficiency of about 85 to 90%. More specifically, fuel gas contains sulfur compounds as impurities, such as in particular hydrogen sulfide, carbonyl sulfide and other sulfides, mercaptans etc., which are mainly converted during the combustion to sulfur dioxide and sulfur trioxide. In particular sulfur trioxide is, however, corrosive, if it condenses in the cooled flue gas from the fired heater. Accordingly, the fired heater has to be operated above the acid dew point of sulfur trioxide or, in other words, the fired heater has to be operated so that the flue (exhaust) gas has a temperature above the acid dew point of sulfur trioxide, in order to reduce the risk of acid corrosion of equipment processing flue gas from the fired heater, which will mandatorily occur if the flue gas temperature would be below the acid dew point of sulfur trioxide. Therefore, in order to avoid reaching the acid dew point, most fired heaters are operated so that the flue gas temperature is 150°C or higher and often even 220°C or higher. This leads to a maximal thermal efficiency of the process of 85% to 90%, since maintaining this comparable high flue gas temperature strongly limits the thermal efficiency of the fired heater. On account thereof, it is desired to control the process so that the flue gas temperature can be significantly reduced in order to thereby increase the thermal efficiency of the fired heater, which is, however, only possible, if the risk of acid dew point corrosion during the process can be eliminated.

[0004] Various methods are currently employed in order to address the issue of acid dew point corrosion caused by sulfur trioxide in cooled flue gas from fired heaters. One of these methods is based on condition monitoring, i.e. on the monitoring of the process temperature, of the corrosion, of the feed and of other process parameters. However, this method is difficult to maintain, does not fix the problem and still does not achieve a fired heater thermal efficiency of 95% or higher. Another known method is the use of corrosion inhibitors in order to prevent a surface corrosion at the point of condensation of flue gas in the fired heater, but this method does not neutralize the sulfuric acid. Also chemical treatments and additives may be employed, such as magnesium oxide reacting to magnesium sulfate, but such a method requires large effluent streams. It has been also contemplated to use polymeric construction and coating materials in order to prevent or limit downstream corrosion, but also this method does not eliminate the condensation of sulfuric acid. Moreover, sulfur oxides, such as sulfur dioxide and sulfur trioxide, may be reduced from the flue gas of fired heaters by subjecting the flue gas to a scrubber; however, also this does not eliminate sulfur oxides in the flue gas heat recovery system and related acid dew point corrosion in equipment upstream of the flue gas scrubbers.

[0005] In view thereof, the object underlying the present invention was to provide a process for operating a fired heater with fuel gas and a respective plant having an increased thermal efficiency and in particular a thermal efficiency of 95% or even higher.

[0006] In accordance with the present invention, this object is satisfied by providing a process for operating a fired heater with fuel gas, wherein the process comprises the following steps: a) providing fuel gas containing at least one sulfur containing compound and having a temperature of at least 150°C, b) desulfurizing the fuel gas provided in step a) by contacting it with at least one catalyst and also with at least one adsorbent and / or with at least one catalyst being simultaneously an adsorbent so as to obtain a desulfurized fuel gas having a total content of sulfur and sulfur containing compounds of 8 ppmv (11 .45 mg / Nm3) or less, wherein the at least one catalyst and / or the at least one catalyst being simultaneously the adsorbent at least partially converts the at least one sulfur containing compound into hydrogen sulfide, and the at least one absorbent and / or the at least one catalyst being simultaneously the adsorbent adsorbs hydrogen sulfide and optionally nonconverted residuals of the at least one sulfur containing compound from the fuel gas, c) feeding the desulfurized fuel gas obtained in step b) and feeding an oxygen containing combustion gas into the fired heater and combust the desulfurized fuel gas in the fired heater.

[0007] By reducing the total content of sulfur and sulfur containing compounds in the fuel gas to 8 ppmv or less, before the so obtained desulfurized fuel gas is fed into the fired heater and is combusted therein by reacting it with combustion gas, such as air, the acid dew point temperature of the flue gas is drastically reduced. This, in turn, allows the process to operate with a significantly lower flue gas temperature, i.e. exhaust gas temperature, and still reliably avoids any acid dew point corrosion, which, in turn, saves fuel gas, reduces the total volume of emissions and increas- es the thermal efficiency of the fired heater by heat recovery to be maximized from fired heater flue gas. The present invention was possible since the inventors have found suitable catalysts and adsorbents, which are described further below, which allow to efficiently desulfurize fuel gas to a total content of sulfur and sulfur containing compounds of 8 ppmv or less. Ppmv means in this connection parts per million by volume.

[0008] In accordance with the present invention, a fuel gas containing at least one sulfur containing compound and having a temperature of at least 150°C is provided in step a). The present invention is not particularly limited concerning the content of sulfur and sulfur containing compounds in the fuel gas. Good results are obtained, when the fuel gas provided in step a) has a total content of sulfur and sulfur containing compounds of at least 10 ppmv (14.31 mg / Nm3), preferably of at least 15 ppmv (21 .46 mg / Nm3) and more preferably of at least 20 ppmv (28.61 mg / Nm3), such as of 10 to 1 ,000 ppmv (14.31 to 1430.71 mg / Nm3) and preferably 15 to 100 ppmv (21.46 to 143.07 mg / Nm3).

[0009] Also concerning the kind of sulfur containing compound contained in the fuel gas, the present invention is not particularly restricted. The method in accordance with the present invention is in particular suitable for fuel gas being provided in step a), which comprises as sulfur containing compound at least one compound being selected from the group consisting of hydrogen sulfide, carbonyl sulfide, sulfur dioxide, sulfur trioxide, carbon monosulfide, carbon disulfide, sulfides other than carbon monosulfide, disulfides other than carbon disulfide, mercaptans, thiophenes and arbitrary combinations thereof. For instance, the fuel gas provided in step a) comprises 0 to 50 ppmv of hydrogen sulfide, 0 to 10 ppmv of carbonyl sulfide, 0 to 20 ppmv of sulfur dioxide, 0 to 10 ppmv of carbon monosulfide, 0 to 10 ppmv of carbon disulfide, 0 to 50 ppmv of mercaptan(s) and 0 to 20 ppmv of thiophene^). The aforementioned mercaptan is preferably a light mercaptan, i.e. a mercaptan according to the formula RSH, wherein R is a C1 -5-alkl group. In a further development of the present invention, it is suggested that step a) comprises the heating of fuel gas in a preheater to a temperature of at least 150°C, preferably to a temperature of 200 to 400°C and more preferably to a temperature of 200 to 300°C. An additional fuel gas heater may be used in addition to the preheater, if the preheater should be not sufficient to heat the fuel gas to an aforementioned temperature.

[0010] If the fuel gas has already a temperature of at least 150°C, preferably to a temperature of 200 to 400°C and more preferably to a temperature of 200 to 300°C from an upstream application, the aforementioned preheater may be omitted.

[0011] In accordance with a further preferred embodiment of the present invention, step a) further comprises the reduction of the total amount of olefins, diolefins and acetylenes in the fuel gas to at most 5,000 ppmv and preferably to at most 1 ,000 ppmv. This reduction may be achieved by processing the fuel gas through a hydrogenation reactor system upstream of the fuel gas desulfurization reactor(s). This embodiment is preferred, because olefins, diolefins and acetylenes, especially diolefins and acetylenes, may oligomerize in the fuel gas can and cause damage to the catalysts or leads to a fouling of the upstream lines and equipment. Therefore, if these compounds are present in a significant amount of more than 1 % by volume in the fuel gas and are not removed prior to the desulfurization, it is preferred that the temperature of the fuel gas is controlled to be below 250°C in steps a) and b) of the process in accordance with the present invention.

[0012] While small amounts of water may be tolerated during the desulfurization of the fuel gas, high concentrations of water may cause issues for the catalysts and adsorbents used during the desulfurization of the fuel gas. In view thereof, it is preferred to reduce the water content in the fuel gas to at most 5,000 ppmv and preferably to at most 1 ,000 ppmv. The reduction of the water content of the fuel gas may be accomplished by a drying process. The drying process may include one or more of cooling of the fuel gas or other condensation means, of passing the fuel gas through a packed drying column, of subjecting the fuel gas to phase separation and of subjecting the fuel gas to absorption by liquid desiccants or adsorption by solid desiccants.

[0013] Fuel gas usually contains light hydrocarbons and in particular Ci-5-hydrocarbons. Ce-hydrocarbons and heavier hydrocarbons are undesirable as they do not bum as cleanly as Ci-5-hydrocarbons. Furthermore, Ce-hydrocarbons and heavier hydrocarbons may form coke during combustion. Therefore, it is preferred that the method in accordance with the present invention comprises in step a) a reduction of the content of Ce+-hydrocarbons in the fuel gas to at most 5,000 ppmv and preferably to at most 1 ,000 ppmv. The reduction of the content of Ce+-hydrocarbons in the fuel gas may be accomplished by condensation and separation of the condensed heavy hydrocarbons from the fuel gas or by adsorption to remove the heavier hydrocarbons from the fuel gas.

[0014] In accordance with the present invention, the fuel gas provided in step a) is desulfurized in step b) to a desulfurized fuel gas having a total content of sulfur and sulfur containing compounds of 8 ppmv or less. Preferably, the fuel gas provided in step a) is desulfurized in step b) to a desulfurized fuel gas having a total content of sulfur and sulfur containing compounds of 5 ppmv (7.15 mg / Nm3) or less.

[0015] In a further development of the present invention, it is proposed that the desulfurization step b) is performed in one or more desulfurization reactors, in which at least one catalyst and also at least one adsorbent and / or at least one catalyst being simultaneously the adsorbent is / are immobilized, wherein the fuel gas provided in step a) is flowed around and / or through the at least one catalyst and the optional at least one adsorbent. Good results are in particular obtained, when the fuel gas provided in step a) is contacted in step b) with at least one catalyst and / or at least one adsorbent and / or at least one catalyst being simultaneously the adsorbent, such as a solid bed comprising at least one catalyst and / or at least one adsorbent and / or at least one catalyst being simultaneously the adsorbent, being selected from the group consisting of: i) activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed alumina-magnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve used, which is used as such or which carries or which is mixed with one or more transition metal or the corresponding transition metal oxides and one or more alkaline metal oxides, wherein the one or more transition metal is preferably selected from the group consisting of nickel, zinc, copper, titanium, zirconium, manganese, molybdenum, chromium, cobalt, wolfram, cerium, tin, silver, palladium, platinum, iron and arbitrary combinations thereof, and wherein the one or more alkaline metal oxides are preferably selected from the group consisting of lithium oxide, sodium oxide, potassium oxide and arbitrary combinations thereof, ii) activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed alumina-magnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve used, which is used as such or which carries or which is mixed with a) molybdenum and cobalt and / or with b) molybdenum and nickel and / or c) nickel and tungsten, iii) activated alumina, silica alumina, silica zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve, which carries or which is mixed with one or more alkaline earth metal oxides and with one or more alkali metals, wherein the one or more alkaline earth metal oxides are preferably selected from the group consisting of magnesium oxide, calcium oxide, strontium oxide and arbitrary combinations thereof, iv) molecular sieves being selected from zeolite or zeotype (SAPO [si licoalu- minophosphates] / AIPO [aluminophosphates]) molecular sieves selected from the group consisting of MFI (Mobil-type five), such as ZSM-5 Zeolite Socony Mobil-5) or silicalite I, of FAU (faujasite), such as Y-zeolite, of BETA, of CHA (chabazite), of AEI (AIPO-18), of MOR (mordenite), of FER (ferrierite) types and of combinations thereof, v) a material comprising at least 0.1 % by weight of one or more transition metal oxides being preferably selected from the group consisting of nickel oxide, zinc oxide, copper oxide, manganese oxide, molybdenum oxide, chromium oxide, cobalt oxide, tungsten oxide, cerium oxide, tin oxide, silver oxide, palladium oxide, platinum oxide, iron oxide and arbitrary combinations thereof, and one or more alkaline metal oxides preferably selected from the group consisting of lithium oxide, sodium oxide, potassium oxide and arbitrary combinations thereof, and arbitrary combinations of one or more of i) to v).

[0016] While the function of the catalyst is to convert sulfur containing components, such as carbonyl sulfide or mercaptans, into hydrogen sulfide, the function of the optional adsorbent is to adsorb and to thereby remove from the fuel gas the hydrogen sulfide as well as non-converted sulfur containing compounds, such as in particular those being selected from the group consisting of carbonyl sulfide, sulfur dioxide, sulfur trioxide, carbon monosulfide and mercaptans. Some of the aforementioned materials function as catalyst as well as as adsorbent. In this case, the fuel gas may be contacted in step b) only with one material, i.e. catalyst being simultaneously an adsorbent. If the catalyst does not simultaneously function as adsorbent, in step b) a catalyst as well as an adsorbent are used. The aforementioned catalysts / adsorbents i) to iii) comprise activated alumina, which is manufactured by dehydroxylation of boehmite or of bayerite, which produces a highly porous substance having a specific surface typically in a range of 150 to 380 m2 / gram. The term “activated alumina” refers to the activation due to calcination. The activated alumina can be doped with different elements, such as preferably with magnesium, boron, fluorine, lanthanum and / or silicon.

[0017] In a preferred embodiment of the present invention, the catalyst and / or adsorbent is pretreated, before it is used in step b), more preferably in one of a flow of hydrogen so as to form metal phase from the oxide phase, in a flow a sulfidation agent (such as dimethyl disulfide and / or hydrogen sulfide) so as to form metal sulfides from metal oxides, in an inert gas or air so as to dry the solid or in a combination thereof. Good results are in particular obtained, when the pretreatment temperature in an inert gas, in air or in hydrogen is at least the same or higher than the operational temperature, preferably above 300°C and more preferable between 400 and 600°C. The pretreatment temperature for sulfidation is preferably between 150 and 300°C.

[0018] In a further preferred embodiment of the present invention, the catalyst and / or adsorbent is regenerated in-situ or ex-situ by stripping with hydrogen at a temperature above 300°C or by coke burning in oxygen-containing environment at temperature above 400°C.

[0019] Preferably, the desulfurization is performed in one or more desulfurization reactors, which comprise(s) at least one solid bed, which contains a catalyst and an adsorbent so that the catalyst coverts the at least one sulfur containing compound to hydrogen sulfide and / or sulfur dioxide, which is then easily captured by the adsorbent. In accordance with a particular preferred embodiment of the present invention, the desulfurization is performed in one or more desulfurization reactors, which comprise^) at least two solid beds, one of which containing a catalyst and one of which containing an adsorbent. This allows to operate both beds at different temperatures, which is preferred, since the catalyst bed usually requires higher temperatures, namely 150°C or higher, whereas the adsorption is more efficient at a lower temperature, preferably of 100°C or below. Both beds may contain the same material, if the material functions as catalyst as well as as adsorbent, or two different materials, one only functioning as catalyst and the other functioning as adsorbent. Both beds are then subjected to different temperatures, namely the catalyst bed to a temperature of at least 150°C and the adsorbent bed to a temperature of at most 100°C.

[0020] The aforementioned catalyst / adsorbent type i) comprises activated alumina, borated alumina, fluorated alumina, alumina doped with La, Mg, mixed aluminamagnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia, titania, or a combination of at least one of the aforementioned materials with molecular sieve used as such or carrying or being mixed with one or more transition metal or the corresponding transition metal oxides and one or more alkaline metal oxides, wherein the one or more transition metal is preferably selected from the group consisting of nickel, zinc, copper, titanium, zirconium, manganese, molybdenum, chromium, cobalt, wolfram, cerium, tin, silver, palladium, platinum, iron and arbitrary combinations thereof, and wherein the one or more alkaline metal oxides are preferably selected from the group consisting of lithium oxide, sodium oxide, potassium oxide and arbitrary combinations thereof. Good results are in particular obtained, when the catalyst / adsorbent comprises, based on 100% by weight of the catalyst / adsorbent, 1 to 99% by weight and preferably 5 to 80% by weight of activated alumina, borated alumina, fluorated alumina, alumina doped with La, Mg, mixed alumina-magnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia or titania, 0.1 to 5% by weight and preferably 0.5 to 2% by weight of tran- sition metal(s) or transition metal oxide(s) and 0.1 to 5% by weight and preferably 0.5 to 2% by weight of alkaline metal oxides. Most preferably, the cata- lyst / adsorbent comprises as transition metal oxide one or more of zinc oxide, iron oxide and copper oxide. In addition, it is preferred that the catalyst / adsorbent further comprises one or more secondary elements exhibiting promoter function, which are preferably selected from the group consisting of molybdenum, chromium, cobalt, cerium, nickel and combinations thereof, and / or with one or more secondary elements exhibiting stabilizer function, which are preferably selected from the group consisting of titanium, zirconium, aluminum, silicon and combinations thereof. If contained, the content of the secondary element(s) in the catalyst / adsorbent is 1 to 20% by weight and preferably 5 to 10% by weight.

[0021] In turn, the aforementioned catalyst / adsorbent type ii) comprises activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed alumina-magnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve used, which is used as such or which carries or which is mixed with a) molybdenum and cobalt (CoMo) and / or with b) molybdenum and nickel (NiMo) and / or with c) nickel and tungsten (NiW). Preferably, the catalyst / adsorbent comprises, based on 100% by weight of the catalyst / adsorbent, 20 to 99% by weight and preferably 80 to 95% by weight of activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed alumina-magnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia or titania, 0.1 to 15% by weight and preferably 1 to 12% by weight of molybdenum and 0.1 to 5% by weight and preferably 0.5 to 2% by weight alkaline of either cobalt or nickel or tungsten.

[0022] The aforementioned catalyst / adsorbent type iii) comprises activated alumina, silica alumina, silica zirconia, titania or a combination of at least one of the aforementioned materials with molecular sieve, which carries or which is mixed with one or more alkaline earth metal oxides and with one or more alkali metals, wherein the one or more alkaline earth metal oxides are preferably selected from the group consisting of magnesium oxide, calcium oxide, strontium oxide and arbitrary combinations thereof. Preferably, the one or more alkali metals are selected from the group consisting of lithium, sodium, potassium and arbitrary combinations thereof. Good results are in particular obtained, when the catalyst / adsorbent comprises, based on 100% by weight of the catalyst / adsorbent, 20 to 99% by weight and preferably 80 to 95% by weight of activated alumina, silica alumina, silica zirconia or titania, 0.1 to 15% by weight and preferably 1 to 12% by weight of alkaline earth metal oxide(s) and 0.1 to 5% by weight and preferably 0.5 to 2% by weight of alkali metal(s).

[0023] In turn, the aforementioned catalyst / adsorbent type v) comprises a material comprising at least 0.1 % of one or more transition metal oxides being preferably selected from the group consisting of nickel oxide, zinc oxide, copper oxide, manganese oxide, molybdenum oxide, chromium oxide, cobalt oxide, tungsten oxide, cerium oxide, tin oxide, silver oxide, palladium oxide, platinum oxide, iron oxide and arbitrary combinations thereof, and wherein the one or more alkaline metal oxides are preferably selected from the group consisting of lithium oxide, sodium oxide, potassium oxide and arbitrary combinations thereof. Preferably, the catalyst / adsorbent consists of the one or more transition metal oxides. In addition, it is preferred that the catalyst / adsorbent further comprises one or more secondary elements exhibiting promoter function, which are preferably selected from the group consisting of molybdenum, chromium, cobalt, cerium, nickel and combinations thereof, and / or one or more secondary elements exhibiting stabilizer function, which are preferably selected from the group consisting of titanium, zirconium, aluminum, silicon and combinations thereof. If contained, the content of the secondary element(s) exhibiting promoter function in the catalyst / adsorbent is 1 to 20% by weight and preferably 5 to 10% by weight and / or the content of the sec- ondary element(s) exhibiting stabilizer function is 0.1 to 2% by weight and preferably 0.5 to 2% by weight.

[0024] In accordance with a further preferred embodiment of the present invention, the total content of halogens, such as chlorine, bromine and fluorine, nitrogen containing compounds, such as ammonia, and oxygenated compounds is reduced in step b) to at most 8 ppmv and preferably to at most 1 ppmv. This is achieved by contacting the fuel gas with at least one of the aforementioned catalysts and optionally with at least one of the aforementioned adsorbents.

[0025] Furthermore, it is preferred that a preheated oxygen containing combustion gas is fed in step c) into the fired heater, namely an oxygen containing combustion gas which has been preheated in a preheater to a temperature of 100 to 500°C. Good results are in particular obtained, when the combustion gas is air, but it may be also any oxygen enriched air for instance having an oxygen content of 21 to 99% by volume or pure oxygen.

[0026] In a further development of the idea of the present invention, it is proposed that the heat of the flue gas being generated in the fired heater is at least partially recovered. This may be for example achieved by recovering heat from the flue gas, which is generated during the combustion in the fired heater, by heat exchange between the flue gas and the fuel gas having a temperature of at least 200°C, before the fuel gas is desulfurized in step b), and / or by heat exchange between the preferably pre-heated oxygen containing combustion gas, before it is fed in step c) into the fired heater. Good results are in particular achieved, when the aforementioned heat exchange is conducted so that the flue gas temperature is reduced thereby to 120°C or less, more preferably to 100°C or less and most preferably to 85°C or less. Alternatively, the heat exchange may be effected between the flue gas and boiler feed water or other process streams or by generating steam. A particular advantage of the process in accordance with the present invention is that it has on account of the reasons set out above a high thermal efficiency. Preferably, the thermal efficiency of the fired heater is 95% or more.

[0027] In accordance with a further preferred embodiment of the present invention, step c) is performed in a high efficiency low NOx-burner so that the content of NOx in the flue gas is adjusted to 50 ppmv or less and preferably to 20 ppmv or less. Low NOx-burners minimize the formation and release of nitrogen oxide emissions during the combustion process. More specifically, low NOx burners achieve emissions reductions through various design features and techniques, such as optimized burner geometry, advanced designs and controls to minimize flame temperatures and optimize oxygen content, staged combustion, flue gas recirculation and fuel staging.

[0028] In accordance with another aspect, the present invention relates to a plant in particular for performing the aforementioned process, wherein the plant comprises: a) a preheater comprising an inlet for fuel gas and an outlet for preheated fuel gas, b) a desulfurization reactor comprising an inlet being connected via a line with the outlet for preheated fuel gas of the preheater a) and an outlet for desulfurized fuel gas and c) a fired heater comprising an inlet for oxygen containing combustion gas, an inlet for desulfurized fuel gas being connected via a line with the outlet for preheated fuel gas of the preheater a) and an outlet for flue gas, wherein the desulfurization reactor b) contains at least one catalyst and at least one adsorbent, and / or at least one catalyst being simultaneously an adsorbent being selected from the group consisting of: i) activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed alumina-magnesia oxide, silica alumina, silica, magnesia, silica magne- sia, zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve used, which is used as such or which carries or which is mixed with one or more transition metal or the corresponding transition metal oxides and one or more alkaline metal oxides, wherein the one or more transition metal is preferably selected from the group consisting of nickel, zinc, copper, titanium, zirconium, manganese, molybdenum, chromium, cobalt, wolfram, cerium, tin, silver, palladium, platinum, iron and arbitrary combinations thereof, and wherein the one or more alkaline metal oxides preferably selected from the group consisting of lithium oxide, sodium oxide, potassium oxide and arbitrary combinations thereof, ii) activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed alumina-magnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve used, which is used as such or which carries or which is mixed with a) molybdenum and cobalt and / or with b) molybdenum and nickel and / or c) nickel and tungsten, iii) activated alumina, silica alumina, silica zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve, which carries or which is mixed with one or more alkaline earth metal oxides and with one or more alkali metals, wherein the one or more alkaline earth metal oxides are preferably selected from the group consisting of magnesium oxide, calcium oxide, strontium oxide and arbitrary combinations thereof, iv) molecular sieves being selected from zeolite or zeotype (SAPO [si licoalu- minophosphates] / AIPO [aluminophosphates]) molecular sieves selected from the group consisting of MFI (Mobil-type five), such as ZSM-5 Zeolite Socony Mobil-5) or silicalite I, of FAU (faujasite), such as Y-zeolite, of BETA, of CHA (chabazite), of AEI (AIPO-18), of MOR (mordenite), of FER (ferrierite) types and of combinations thereof, v) a material comprising at least 0.1 % by weight of one or more transition metal oxides being preferably selected from the group consisting of nickel oxide, zinc oxide, copper oxide, manganese oxide, molybdenum oxide, chromium oxide, cobalt oxide, tungsten oxide, cerium oxide, tin oxide, silver oxide, palladium oxide, platinum oxide, iron oxide and arbitrary combinations thereof, and one or more alkaline metal oxides preferably selected from the group consisting of lithium oxide, sodium oxide, potassium oxide and arbitrary combinations thereof, and arbitrary combinations of one or more of i) to v).

[0029] Preferably, the plant further comprises a preheater d) for the oxygen containing combustion gas comprising an inlet for oxygen containing combustion gas and an outlet for preheated oxygen containing combustion gas, wherein the outlet is connected via a line with the inlet for oxygen containing combustion gas of the fired heater.

[0030] In a further development of the idea of the present invention, it is suggested that the plant comprises an integrated heat recovery. Good results are for instance achieved, when the outlet for flue gas of the fired heater is connected via a line with an inlet and an outlet of the preheater a) for preheated fuel gas and is further connected via a line leading from the outlet of the preheater a) for preheated fuel gas with an inlet and an outlet of the preheater d) for the oxygen containing combustion gas.

[0031] Subsequently, the present invention is described by means of an illustrative, but not limiting figure, in which:

[0032] Fig. 1 is a schematic view of a plant for operating a fired heater with fuel gas in accordance with one embodiment of the present invention. Fig. 2 is a schematic view of a plant for operating a fired heater with fuel gas in accordance with another embodiment of the present invention.

[0033] The plant 10 shown in figure 1 comprises an inlet line 12 for fuel gas, a preheater 14 comprising an inlet for fuel gas and an outlet for preheated fuel gas, a desulfurization reactor 16 comprising an inlet being connected via a line 18 with the outlet for preheated fuel gas of the preheater 14 and an outlet for desulfurized fuel gas as well as a fired heater 20 comprising an inlet for desulfurized fuel gas being connected via a line 22 with the outlet for preheated fuel gas of the preheater 14, an inlet line 24 for oxygen containing combustion gas and an outlet 26 for flue gas. In turn, the inlet line 24 for oxygen containing combustion gas is connected with a preheater 28 for oxygen containing combustion gas, which further comprises a feed line 30 for oxygen containing combustion gas. The desulfurization reactor 16 comprises a bed of an aforementioned catalyst 32.

[0034] During the operation of the plant 10, fuel gas is fed into the preheater, in which the fuel gas is preheated to a temperature of for instance 220°C, before the preheated fuel gas flows through line 18 into the desulfurization reactor 16. In the desulfurization reactor 16, the fuel gas flows through the bed of catalyst 32 and is thereby desulfurized. More specifically, the sulfur containing compounds are converted by the catalyst to hydrogen sulfide, wherein the hydrogen sulfide and remaining traces of unconverted sulfur containing compounds are adsorbed on the surface of the catalyst. In other words, the catalyst acts as catalyst as well as as adsorbent. Thereby, the content of sulfur and sulfur containing compounds is reduced in the fuel gas to 8 ppmv or less. The desulfurized fuel gas then flows via line 22 into the fired heater 20, in which it reacts with air as oxygen containing gas, which is fed into the fired heater 20 via the inlet line 30, the preheater 28 and line 24. The reaction between fuel gas and air or the combustion of fuel gas with air, respectively, leads to the generation of flue gas, which leaves the fired heater 20 via the outlet 26. The plant 10 shown in figure 2 corresponds to that of figure 1 except that it further comprises an integrated heat recovery. More specifically, the outlet 26 of the fired heater 20 is connected with an outlet line 34, from which a heat recovery line 36 splits off. The heat recovery line 36 firstly leads to the preheater 14 for fuel gas and is connected with an inlet and an outlet of the preheater 14, from which the heat recovery line 36 then secondly leads to the preheater 28 for air, where it is connected with an inlet and an outlet of the preheater 28. The heat recovery line 36 then thirdly leads from the preheater 28 to the outlet line 34 of the fired heater 20. An induced draft fan 38 is provided in the portion of the heat recovery line 36 extending between the preheater 28 and the outlet line 34 of the fired heater 20.

[0035] During the operation of the plant 10, the portion of the flue gas, which is led through the heat recovery line 36, preheats in the preheater 14 the fuel gas to a temperature of 220°C and then preheats in the preheater 28 air to a temperature of also 220°C, before the thereby cooled flue gas is led back into the outlet line 34 of the fired heater 20. Since the flue gas does not contain any or, if at all, only minimal amounts of sulfur trioxide, because the fuel gas has been effectively desulfurized in the desulfurization reactor 16, before it has been led into the fired heater so that no sulfur oxides can be generated during the combustion, no sulfuric acid condensation may occur in the fired heater 20 or in the heat recovery line 36. On account of these reasons, the flue gas can be cooled in the process in accordance with the present invention to temperatures of as low as 85°C or even cooler, thereby maximizing the heat recovery and significantly increasing the thermal efficiency of the fired heater to more than 95%. Reference Numeral List

[0036] 10 Plant

[0037] 12 Inlet line for fuel gas

[0038] 14 Preheater for fuel gas

[0039] 16 Desulfurization reactor

[0040] 18 Fuel gas line to desulfurization reactor

[0041] 20 Fired heater

[0042] 22 Fuel gas line from reactor to fired heater

[0043] 24 Inlet line for oxygen containing combustion gas

[0044] 26 Outlet for flue gas

[0045] 28 Preheater for oxygen containing combustion gas (air).

[0046] 30 Feed line for oxygen containing combustion gas

[0047] 32 Bed of catalyst

[0048] 34 Outlet line of the fired heater

[0049] 36 Heat recovery line containing cooled flue gas

[0050] 38 Induced draft fan

Claims

Claims:1 . A process for operating a fired heater with fuel gas, wherein the process comprises the following steps: a) providing fuel gas containing at least one sulfur containing compound and having a temperature of at least 150°C, b) desulfurizing the fuel gas provided in step a) by contacting it with at least one catalyst and also with at least one adsorbent and / or with at least one catalyst being simultaneously an adsorbent so as to obtain a desulfurized fuel gas having a total content of sulfur and sulfur containing compounds of 8 ppmv or less, wherein the at least one catalyst and / or the at least one catalyst being simultaneously the adsorbent at least partially converts the at least one sulfur containing compound into hydrogen sulfide, and the at least one absorbent and / or the at least one catalyst being simultaneously the adsorbent adsorbs hydrogen sulfide and optionally non-converted residuals of the at least one sulfur containing compound from the fuel gas, c) feeding the desulfurized fuel gas obtained in step b) and feeding an oxygen containing combustion gas into the fired heater and combust the desulfurized fuel gas in the fired heater.

2. The process in accordance with claim 1 , wherein the fuel gas provided in step a) has a total content of sulfur and sulfur containing compounds of at least 10 ppmv, preferably of at least 15 ppmv and more preferably of at least 20 ppmv.

3. The process in accordance with claim 1 or 2, wherein the fuel gas provided in step a) comprises as sulfur containing compound at least one compound being selected from the group consisting of hydrogen sulfide, carbonyl sul-fide, sulfur dioxide, sulfur trioxide, carbon monosulfide, carbon disulfide, sulfides other than carbon monosulfide, disulfides other than carbon disulfide, mercaptans, thiophenes and arbitrary combinations thereof, wherein the fuel gas provided in step a) preferably comprises 0 to 50 ppmv of hydrogen sulfide, 0 to 10 ppmv of carbonyl sulfide, 0 to 20 ppmv of sulfur dioxide, 0 to 10 ppmv of carbon monosulfide, 0 to 10 ppmv of carbon disulfide, 0 to 50 ppmv of mercaptan(s) and 0 to 20 ppmv of thiophene(s).

4. The process in accordance with any of the preceding claims, wherein step a) comprises the heating of fuel gas in a preheater to a temperature of at least 150°C, preferably to a temperature of 200 to 400°C and more preferably to a temperature of 200 to 300°C.

5. The process in accordance with any of the preceding claims, wherein step a) further comprises one or more of the following: reducing the total amount of olefins, diolefins and acetylenes in the fuel gas to at most 5,000 ppmv and preferably to at most 1 ,000 ppmv, wherein the reducing step preferably comprises processing the fuel gas through a hydrogenation reactor system upstream of the fuel gas desulfurization reactor(s), reducing the water content in the fuel gas to at most 5,000 ppmv and preferably to at most 1 ,000 ppmv, wherein the reducing step preferably comprises a drying process, and reducing the content of Ce+-hydrocarbons in the fuel gas to at most 5,000 ppmv and preferably to at most 1 ,000 ppmv, wherein the reducing step preferably comprises condensation and separation of the condensed heavy hydrocarbons from the fuel gas or by adsorption to remove the heavier hydrocarbons from the fuel gas.

6. The process in accordance with any of the preceding claims, wherein in step b) a desulfurized fuel gas having a total content of sulfur and sulfur containing compounds of 5 ppmv or less.

7. The process in accordance with any of the preceding claims, wherein the desulfurization step b) is performed in one or more desulfurization reactors), in which at least one catalyst and also at least one adsorbent and / or at least one catalyst being simultaneously the adsorbent is / are immobilized, wherein the fuel gas provided in step a) is flowed around and / or through the at least one catalyst and adsorbent.

8. The process in accordance with any of the preceding claims, wherein the fuel gas provided in step a) is contacted in step b) with at least one catalyst and / or at least one adsorbent and / or at least one catalyst being simultaneously the adsorbent being selected from the group consisting of: i) activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed aluminamagnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve used, which is used as such or which carries or which is mixed with one or more transition metal or the corresponding transition metal oxides and one or more alkaline metal oxides, wherein the one or more transition metal is preferably selected from the group consisting of nickel, zinc, copper, titanium, zirconium, manganese, molybdenum, chromium, cobalt, wolfram, cerium, tin, silver, palladium, platinum, iron and arbitrary combinations thereof, and wherein the one or more alkaline metal oxides are preferably selected from the group consisting of lithium oxide, sodium oxide, potassium oxide and arbitrary combinations thereof,ii) activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed aluminamagnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve used, which is used as such or which carries or which is mixed with a) molybdenum and cobalt and / or with b) molybdenum and nickel and / or c) nickel and tungsten, iii) activated alumina, silica alumina, silica zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve, which carries or which is mixed with one or more alkaline earth metal oxides and with one or more alkali metals, wherein the one or more alkaline earth metal oxides are preferably selected from the group consisting of magnesium oxide, calcium oxide, strontium oxide and arbitrary combinations thereof, iv) molecular sieves being selected from zeolite or zeotype (SAPO [sili- coaluminophosphates] / AIPO [aluminophosphates]) molecular sieves selected from the group consisting of MFI (Mobil-type five), such as ZSM-5 Zeolite Socony Mobil-5) or silicalite I, of FAU (faujasite), such as Y-zeolite, of BETA, of CHA (chabazite), of AEI (AIPO-18), of MOR (mordenite), of FER (ferrierite) types and of combinations thereof, v) a material comprising at least 0.1 % by weight of one or more transition metal oxides being preferably selected from the group consisting of nickel oxide, zinc oxide, copper oxide, manganese oxide, molybdenum oxide, chromium oxide, cobalt oxide, tungsten oxide, cerium oxide, tin oxide, silver oxide, palladium oxide, platinum oxide, iron oxide and arbitrary combinations thereof, and one or more alkaline metal oxides preferably selected from the group consisting of lithium oxide, sodium oxide, potassium oxide and arbitrary combinations thereof, and arbitrary combinations of one or more of i) to v).

9. The process in accordance with claim 8, wherein the fuel gas provided in step a) is contacted in step b) with at least one catalyst and / or at least one adsorbent and / or at least one catalyst being simultaneously the adsorbent, which is: i) activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed aluminamagnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve used, which is used as such or which carries or which is mixed with one or more transition metal or transition metal oxides and one or more alkaline metal oxides and further with one or more secondary elements exhibiting promoter function, which are preferably selected from the group consisting of molybdenum, chromium, cobalt, cerium, nickel and combinations thereof, and / or with one or more secondary elements exhibiting stabilizer function, which are preferably selected from the group consisting of titanium, zirconium, aluminum, silicon and combinations thereof, and / or v) a material comprising at least 0.1 % of one or more transition metal oxides and further one or more secondary elements exhibiting promoter function, which are preferably selected from the group consisting of molybdenum, chromium, cobalt, cerium, nickel and combinations thereof, and / or one or more secondary elements exhibiting stabilizer function, which are preferably selected from the group consisting of titanium, zirconium, aluminum, silicon and combinations thereof.

10. The process in accordance with any of the preceding claims, wherein an oxygen containing combustion gas having been preheated in a preheater to a temperature of 100 to 500°C is fed in step c) into the fired heater, wherein the oxygen containing combustion gas is preferably air, oxygen enriched air having an oxygen content of 21 to 99% by volume or pure oxygen.11 . The process in accordance with any of the preceding claims, wherein heat from the flue gas being generated during the combustion in the fired heater is recovered by heat exchange between the flue gas and the fuel gas having a temperature of at least 200°C, before the fuel gas is desulfurized in step b), and / or by heat exchange between the preferably pre-heated oxygen containing combustion gas, before it is fed in step c) into the fired heater, thereby preferably reducing the flue gas temperature to 120°C or less, more preferably to 100°C or less and most preferably to 85°C or less.

12. The process in accordance with claim 11 , wherein the thermal efficiency of the fired heater is 95% or more.

13. A plant in particular for performing a process in accordance with any of the preceding claims, which comprises: a) a preheater comprising an inlet for fuel gas and an outlet for preheated fuel gas, b) a desulfurization reactor comprising an inlet being connected via a line with the outlet for preheated fuel gas of the preheater a) and an outlet for desulfurized fuel gas and c) a fired heater comprising an inlet for oxygen containing combustion gas, an inlet for desulfurized fuel gas being connected via a line with the outlet for preheated fuel gas of the preheater a) and an outlet for flue gas, wherein the desulfurization reactor b) contains at least one catalyst and at least one adsorbent, and / or at least one catalyst being simultaneously an adsorbent being selected from the group consisting of: i) activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed aluminamagnesia oxide, silica alumina, silica, magnesia, silica magnesia, zir-conia, titania or a combination of at least one of the aforementioned materials with a molecular sieve used, which is used as such or which carries or which is mixed with one or more transition metal or the corresponding transition metal oxides and one or more alkaline metal oxides, wherein the one or more transition metal is preferably selected from the group consisting of nickel, zinc, copper, titanium, zirconium, manganese, molybdenum, chromium, cobalt, wolfram, cerium, tin, silver, palladium, platinum, iron and arbitrary combinations thereof, and wherein the one or more alkaline metal oxides are preferably selected from the group consisting of lithium oxide, sodium oxide, potassium oxide and arbitrary combinations thereof, ii) activated alumina, borated alumina, fluorated alumina, alumina doped with lanthanum, alumina doped with magnesium, mixed aluminamagnesia oxide, silica alumina, silica, magnesia, silica magnesia, zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve used, which is used as such or which carries or which is mixed with a) molybdenum and cobalt and / or with b) molybdenum and nickel and / or c) nickel and tungsten, iii) activated alumina, silica alumina, silica zirconia, titania or a combination of at least one of the aforementioned materials with a molecular sieve, which carries or which is mixed with one or more alkaline earth metal oxides and with one or more alkali metals, wherein the one or more alkaline earth metal oxides are preferably selected from the group consisting of magnesium oxide, calcium oxide, strontium oxide and arbitrary combinations thereof, iv) molecular sieves being selected from zeolite or zeotype (SAPO [sili- coaluminophosphates] / AIPO [aluminophosphates]) molecular sieves selected from the group consisting of MFI (Mobil-type five), such as ZSM-5 Zeolite Socony Mobil-5) or silicalite I, of FAU (faujasite), suchas Y-zeolite, of BETA, of CHA (chabazite), of AEI (AIPO-18), of MOR (mordenite), of FER (ferrierite) types and of combinations thereof, v) a material comprising at least 0.1 % by weight of one or more transition metal oxides being preferably selected from the group consisting of nickel oxide, zinc oxide, copper oxide, manganese oxide, molybdenum oxide, chromium oxide, cobalt oxide, tungsten oxide, cerium oxide, tin oxide, silver oxide, palladium oxide, platinum oxide, iron oxide and arbitrary combinations thereof, and one or more alkaline metal oxides preferably selected from the group consisting of lithium oxide, sodium oxide, potassium oxide and arbitrary combinations thereof, and arbitrary combinations of one or more of i) to v).

14. The plant in accordance with claim 13, wherein the plant further comprises a preheater d) for the oxygen containing combustion gas comprising an inlet for oxygen containing combustion gas and an outlet for preheated oxygen containing combustion gas, wherein the outlet is connected via a line with the inlet for oxygen containing combustion gas of the fired heater.

15. The plant in accordance with claim 13 or 14, wherein the outlet for flue gas of the fired heater is connected via a line with an inlet and an outlet of the preheater a) for preheated fuel gas and is further connected via a line leading from the outlet of the preheater a) for preheated fuel gas with an inlet and an outlet of the preheater d) for the oxygen containing combustion gas.

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