WO2020089099A1 - Method for production of sulfur - Google Patents

Method for production of sulfur Download PDF

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Publication number
WO2020089099A1
WO2020089099A1 PCT/EP2019/079233 EP2019079233W WO2020089099A1 WO 2020089099 A1 WO2020089099 A1 WO 2020089099A1 EP 2019079233 W EP2019079233 W EP 2019079233W WO 2020089099 A1 WO2020089099 A1 WO 2020089099A1
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Prior art keywords
claus
gas
process according
reaction furnace
claus reaction
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PCT/EP2019/079233
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French (fr)
Inventor
Morten Thellefsen
Lars Piilmann BRORHOLT
Per Aggerholm SØRENSEN
Mads Lykke
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Topsoe AS
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Haldor Topsoe AS
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Priority to CN201980070586.XA priority Critical patent/CN112930320B/en
Priority to MYPI2021001773A priority patent/MY208535A/en
Publication of WO2020089099A1 publication Critical patent/WO2020089099A1/en
Anticipated expiration legal-status Critical
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/02—Preparation of sulfur; Purification
    • C01B17/04—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides
    • C01B17/0404—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by processes comprising a dry catalytic conversion of hydrogen sulfide-containing gases, e.g. the Claus process
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8603—Removing sulfur compounds
    • B01D53/8612—Hydrogen sulfide
    • B01D53/8615—Mixtures of hydrogen sulfide and sulfur oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/869—Multiple step processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8693—After-treatment of removed components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
    • B01J20/28042—Shaped bodies; Monolithic structures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3202—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the carrier, support or substrate used for impregnation or coating
    • B01J20/3204—Inorganic carriers, supports or substrates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/32—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating
    • B01J20/3231—Impregnating or coating ; Solid sorbent compositions obtained from processes involving impregnating or coating characterised by the coating or impregnating layer
    • B01J20/3234—Inorganic material layers
    • B01J20/3236—Inorganic material layers containing metal, other than zeolites, e.g. oxides, hydroxides, sulphides or salts
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B17/00—Sulfur; Compounds thereof
    • C01B17/02—Preparation of sulfur; Purification
    • C01B17/04—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides
    • C01B17/0404—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by processes comprising a dry catalytic conversion of hydrogen sulfide-containing gases, e.g. the Claus process
    • C01B17/0426—Preparation of sulfur; Purification from gaseous sulfur compounds including gaseous sulfides by processes comprising a dry catalytic conversion of hydrogen sulfide-containing gases, e.g. the Claus process characterised by the catalytic conversion
    • C01B17/0434—Catalyst compositions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/50—Inorganic acids
    • B01D2251/506—Sulfuric acid
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines

Definitions

  • the present invention is related to a process for conversion of I-I2S to elemental sulfur in a Claus process plant in which H2SO4 is added to the thermal stage of the Claus pro- cess plant.
  • H2S is a common side product in many processes, including hydrodesulfurization of re- finery streams, production of viscose and natural gas sweetening. It is desirable to con- vert H2S prior to emission to the atmosphere as H2S is highly toxic, odorous and an en- vironmental challenge.
  • Refinery processes besides producing the well-known high concentration H2S gas, may often also produce a so-called sour water stripper gas, which comprises H2S, H2O and NH 3 in around equal molar amounts.
  • the chosen process for H2S abatement has been the Claus pro- cess, which has been known and optimized for more the 8 decades.
  • the Claus pro- cess proceeds by sub-stoichiometric combustion of H2S producing SO2 in a Claus re- action furnace, providing a Claus converter feed gas.
  • the subsequent Claus process will convert the remaining H2S and the formed SO2 to form elemental sulfur, which may be condensed and withdrawn.
  • H2SO4 is a concentrated source of O2 and a temperature moderator. Both proper- ties are valuable for capacity boosting of the Claus process. It has also been identified that this addition of H2SO4 may damage the catalyst of the Claus process by sulfation and thus require an SO3 guard prior to the catalytic Claus process.
  • H2SO4 Condensation of H2SO4 It is recognized that the H2SO4 product is not always desirable and it is suggested to recycle the sulfuric acid to the upstream Claus reaction furnace or the H2S oxidation step as described above. However, the recycling of sulfuric acid is merely thought as an abatement of sulfuric acid, and the consequences of recycling the H2SO4 on the sul- furic acid or Claus process have not been evaluated, i.e. it is not recognized that H2SO4 recirculation requires a reduction in the amount of O2 directed to the Claus reaction fur- nace, nor are the beneficial effects on the Claus and sulfuric acid process realized.
  • the sulfuric acid does not have to be recycled from a downstream sulfuric acid plant acting as a Claus tail gas treatment plant, but can come from other sources.
  • the bene- fit of adding H2SO4 to the Claus process plant can justify purchase of H2SO4, as the H2SO4 both acts as an efficient O2 carrier and temperature moderator as described in patent application PCT/EP2017/080721.
  • the addition of H2SO4 can boost the capacity of the Claus process plant by up to 50% without affecting the process gas flow in the Claus process plant.
  • the present invention relates to a process for production of a sub- stantially SO 3 free Claus converter feed gas from a feedstock gas comprising 30 vol%, 40 vol% or 50% to 99 vol% or 100 vol% H2S and a stream of sulfuric acid involving the steps of a.
  • a Claus reaction furnace feed stream comprising said feedstock gas, an amount of sulfuric acid, an amount of molecular oxygen and optionally an amount of fuel, wherein the amount of molecular oxygen is substoichiometric
  • said SO 3 guard material being different from said material catalytically active in the Claus reaction, wherein said SO 3 guard material active in SO 3 removal en- sures a long operation of the catalyst active in the Claus reaction, if droplets of sulfuric acid are not fully evaporated and reduced in the gas phase, such that long operation of the Claus process plant can be maintained, even when said material catalytically active in the Claus reaction has no activity or only temporary activity in SO 3 conversion or ab- sorption.
  • the SO 3 guard is an SO 3 absorbent, in which the content of SO 3 is increased over time, such as alumina or titania, with the associated benefit of such an absorbent being inexpensive, and with the further benefit of alumina and tita- nia having a moderate catalytic effect, allowing for some conversion of absorbed SO 3 .
  • the SO 3 guard material is a material catalytically ac- tive in reducing SO 3 by reaction with H 2 S, providing a substantially SO 3 free Claus con- verter feed gas, with the associated benefit of the lifetime of the SO 3 guard material not being limited by an absorption capability.
  • the SO 3 guard material is arranged downstream the Claus re- action furnace and upstream the Claus converter, with the associated benefit of the SO 3 guard material being remote and thus independent from the flame in the Claus re- action furnace.
  • the SO3 guard material is arranged as top layer on material catalytically active in the Claus reaction, with the associated benefit of avoiding the cost of a separate reactor for the SO 3 guard.
  • the support comprises diatomaceous earth and/or cordierite with the associated benefit of such materials being stable and having a high surface area.
  • the material active in the reduction of SO 3 is in shape of pellets or a monolith, with the associated benefit of pellets being cost effective to produce, whereas monoliths benefit from having a low pressure drop.
  • the Claus reaction furnace is operated at a temperature of be- tween 900°C and 1500°C with the associated benefit of this temperature range being appropriate for decomposition of H 2 SO 4 to H 2 O and SO 3 , for further decomposition of SO 3 to SO 2 , for partial oxidation of H 2 S and for decomposition of impurities.
  • the material catalytically active in reducing SO 3 is operated at a temperature of between 130°C and 1500°C with the associated benefit of the temper- ature being appropriately inside the interval of catalytic Claus reaction and non-catalytic Claus reaction furnace temperatures.
  • the material catalytically active in reducing SO 3 is operated at a temperature of between 250°C and 500°C, with the associated benefit of operating in a temperature range where conversion from SO 3 to SO 2 and/or sulfur is rapid without requiring high resistance materials.
  • the material catalytically active in reducing SO 3 is operated at a temperature of between 300°C and 400°C, with the associated benefit of operating in a temperature range where conversion from SO 3 to SO 2 or sulfur is rapid without re- quiring exotic materials.
  • the stream of sulfuric acid is produced in a wet type sulfuric acid plant treating the tail gas from the Claus plant with the associated benefit of such a process being thermally efficient and able to reduce emission of sulfurous compounds to a very high extent.
  • the liquid phase term sulfuric acid means a mixture of H2SO4 and H2O as H2SO4 is hy- groscopic and will absorb water from the gas phase.
  • any concentration of H2SO4 can be injected into the Claus reaction furnace, but high concentrations are de- sired as that will reduce the energy required for evaporation and minimize the dilution of Claus reaction furnace off gas with the associated water.
  • sulfuric acid with >90 %w/w H2SO4 is considered most relevant.
  • H2SO4 sulfuric acid
  • SO 3 sulfuric anhydride
  • SO3 sulfuric anhydride
  • SO3 + H2O ⁇ ® H2SO4 The gas phase terms H2SO4 (sulfuric acid) and SO 3 (sulfuric anhydride) are often just called“SO3” as the hydration reaction of SO3 (SO3 + H2O ⁇ ® H2SO4) is considered very fast and safely can be considered to be in chemical equilibrium.
  • the distribution be- tween SO 3 and H2SO4 depends on the temperature, pressure and H2O concentration in the gas, SO 3 is favored at high temperatures and low H2O concentrations and H2SO4 is favored at low temperatures and high H2O concentration. Above 400 °C, very little H2SO4 exist and below 200 °C, very little SO 3 exist and in the range 200-400 °C both molecules will be present in varying amounts (in case of a wet gas).
  • S represents elemental sulfur in any form from S 2 to Ss
  • Reactions (5) and (6) are the overall reactions for the Claus process in which the H2S in the feed gas is combusted with O2 deficiency to form a combustion gas with a H2S/SO2 ratio around 2, which is the optimal ratio for highest conversion into elemental S.
  • Reaction (1 ) describes the evaporation of the liquid sulfuric acid after injection into the reaction furnace.
  • the sulfuric acid stream is atomized into a“fog” consisting of small droplets, the droplet size distribution is determined by the method of atomiza- tion.
  • the droplets evaporate from the outer droplet surface and thus the initial droplet size is essential for the time required for complete evaporation.
  • the time for complete evaporation depends on the 3 rd power of the droplet diameter, i.e. a doubling of the droplet diameter increases the evaporation time by a factor of 8.
  • Process gas tempera- ture and gas/droplet mixing also have a significant impact on the evaporation time of the droplets.
  • an atomi- zation media which typically is compressed air, N2 or steam, is used to“cut” the liquid stream into fine droplets.
  • Reaction (2) is a very fast gas phase reaction and chemical equilibrium between SO 3 and H 2 SO 4 can be safely assumed.
  • Reaction (3) and (4) describes the overall reactions for destruction of the SO 3 into ei- ther SO 2 and O 2 , which can then react with H 2 S via reaction (5) and (6) or react directly with H 2 S to form SO 2 and S, where the SO 2 can react with H 2 S via reaction (6).
  • Reaction (3) is highly temperature dependent and only takes place at higher tempera- ture, i.e. > 800 °C, unless a catalyst is present.
  • Reaction (4) takes place at lower temperatures too, but the reaction rate at tempera- tures below 400 °C may be too low to be relevant for industrial applications.
  • reactions (2) to (6) are very fast and will typ- ically proceed to chemical equilibrium within less than 0.5 seconds.
  • the residence time in a reaction furnace is typically less than 1-2 seconds. According to chemical equilibrium calculations, neither H 2 SO 4 , SO 3 nor O 2 will be pre- sent in the process gas at Claus reaction furnace gas conditions.
  • the stoichiometric balance between H 2 S and O 2 in the absence of H 2 SO 4 is 2:1. How- ever, in the presence of H 2 SO 4 less O 2 is required.
  • a substoichiometric amount of mo- lecular oxygen is therefore defined as an molar amount being less than half of the mo- lar amount of H 2 S.
  • the Claus reaction furnace is preferably operated at a temperature between 900 and 1500°C.
  • reaction (1 ) will be the limiting step for the reactions to pro- ceed to equilibrium and the available 1-2 seconds of residence time can become too short for the completion of the reactions.
  • Such situations can arise if e.g. the nozzle for the sulfuric acid atomization has become worn and/or the flow or pressure of the atomi- zation media is out of the normal range.
  • H 2 SO 4 / SO 3 leaves the Claus reaction furnace not fully converted and enters the heat exchanger (waste heat boiler) that cools the Claus reaction furnace gas to around 300-400 °C.
  • reaction (1 ) and (2) are still active, whereas reaction rates for (3) to (6) are too low to be of any practical significance.
  • the 300-400 °C Claus reaction furnace off gas is sent to a catalytic Claus reactor in which a catalyst active in reaction (6) is in- stalled.
  • This catalyst is well known in the industry and is most often used as pellets with the active material being T1O2 or AI2O3. Also well known is that this catalyst is sensitive to“sulfation”, i.e. the active sites of the catalyst become“poisoned” with sulfate and thus the catalyst loses catalytic activity with the consequence of less product being formed and increased emissions of H2S and SO2.
  • the sulfate can be formed by reac- tion between SO2 and O2, forming SO3 on the catalyst surface, or SO3 present in the process gas can directly attach to the catalyst surface.
  • the 300-400 °C Claus reaction furnace off gas is di- rected to a sulfur condenser, in which the process gas is cooled to 130-160 °C to con- dense the elemental sulfur and withdraw the product.
  • the process gas is then reheated and directed to a catalytic Claus reactor as described above. If there is SO3 present in the Claus reaction furnace off gas, there is a risk of condensing sulfuric acid in the ele- mental sulfur product, producing an off-spec product and there is an increased risk of corrosion of the sulfur handling equipment.
  • the off gas from the sulfur condenser will also contain a fraction of the SO 3 (as H 2 SO 4 ) present in the Claus reaction furnace off gas and this SO 3 will poison the downstream Claus catalyst.
  • the Claus reaction furnace off gas does not contain substantial amounts of SO 3 as it can have a detrimental effect on the down- stream catalyst, equipment and operation of the Claus process plant.
  • the catalyst is also able to suppress the reaction with SO 3 forming O 2 (reaction 3) as a O 2 slip is just as problematic as a SO 3 slip.
  • the catalyst is preferably to be installed be- tween the outlet of the waste heat boiler connected to the Claus reaction furnace and the inlet to equipment and/or catalysts that can be damaged by the presence of SO 3 .
  • This new catalyst can either be installed in a separate reactor as would be necessary in the Claus process layout in which the cooled Claus reaction furnace off gas is sent to a sulfur condenser before the catalytic Claus reactor or as a top layer in the existing Claus reactor which is possible in the layout where the process gas goes directly to the catalytic Claus reactor.
  • the catalyst is installed at the outlet of the Claus reaction fur- nace, taking advantage of the high temperature and high reaction rates.
  • the catalyst can be of any shape and size, considered optimal for the Claus process plant layout. If to be installed as a top layer in the Claus reactor, a pellet shaped cata- lyst would be most desirable as the Claus catalyst typically is pellet shaped.
  • AI2O3 and T1O2 alone are prone to sulfate poisoning, the compounds can be used for support for the compounds active in the conversion of SO3 into SO2 and S, which are harmless for the downstream Claus catalysts. It is further considered likely that AI 2 O 3 and T1O 2 may act as guards by ab- sorption of SO 3 by sulfation, and thus such materials without active metals may func- tion as guard, but require occasional replacement or re-activation.
  • the material catalytically active in reducing SO 3 (and H 2 SO 4 ) by reaction with H 2 S is operated at a temperature of between 130 and 1500°C, such as between 250 and 500°C or between 300 and 400°C.
  • Figure 1 shows a Claus reaction furnace with 1 st Claus reactor upstream 1 st sulfur con- denser
  • Figure 2 shows a Claus reaction furnace with 1 st sulfur condenser upstream 1 st Claus reactor
  • the feeds to the Claus reaction furnace are one or more acid gases comprising H2S (2), an optional fuel gas (4), an oxygen source (6) be- ing typically air with 21 vol% O2 or enriched air with 21-100 vol% O2 and a sulfuric acid stream (8).
  • the sulfuric acid stream can optionally be concentrated sulfuric acid pro- **d in a sulfuric acid plant installed as a tail gas treatment plant for the Claus pro- cess plant.
  • the sulfuric acid atomization method that produces the smallest droplets is a two-phase atomization in which an atomization media (10) is used to“cut” the sulfuric acid liquid into droplets.
  • the atomization media is most often pressurized air or steam, but other media are also possible, such as fuel gas, enriched air or process gas.
  • part of the H2S is oxidized to SO2 which then combines with H2S to form elemental sulfur.
  • Sulfuric acid is evaporated and reacts with H2S to from SO2 and elemental sulfur.
  • the temperature in the reaction furnace is typically above 900 °C and the average residence time is typically 1-2 seconds.
  • the off gas from the reaction chamber (14) is led through heat exchanger (16), where the pro- cess gas is cooled to 300-400 °C.
  • the heat exchanger is typically a waste heat boiler, producing high pressure steam. If elemental sulfur is condensed in the heat exchanger, it is drained via the liquid outlet (18).
  • the cooled Claus reaction furnace off gas (20) is then passed through one or more layer(s) of catalyst (22) in which any SO 3 in the Claus reaction furnace off gas is effi ciently converted to SO 2 and S by reaction with H 2 S, producing a substantial SO 3 free feed gas (24) to be directed to the Claus catalyst layer in the Claus reactor (26). It can be possible to combine (22) and (26) such that the SO3 destruction catalyst in (22) can be a top layer in the Claus reactor (26).
  • the Claus reactor (26) more elemental sulfur is formed by reaction between H2S and SO2 and the Claus reactor off gas (28) is passed to a first sulfur condenser (30) in which the process gas is cooled and a fraction of the elemental sulfur condensed and withdrawn as a liquid via outlet 32.
  • the off gas (34) is typically reheated and passed through one or more Claus reactor - sulfur condenser - reheater passes to ensure suf- ficiently high conversion of H2S into elemental sulfur.
  • the Claus reaction furnace (12) and waste heat boiler (16) are similar to the layout and operation as described for figure 1.
  • the difference in the layout is that the cooled Claus reaction furnace off gas (20) is passed directly to the first sulfur conden- ser (30) to condense and withdraw elemental sulfur product via line 32 before the con- denser off gas (34) is reheated and passed to 1 st Claus reactor.
  • the Claus reaction equilibrium is favored in the 1 st Claus reactor and thus a higher overall conversion out of 1 st Claus reactor can be achieved.
  • reaction chamber which consist of a 40 cm long 013 mm glass tube installed in a temperature controlled oven.
  • the H2S was supplied from a gas cylinder and diluted with N2 before added to reaction chamber.
  • a 2 nd N2 stream was saturated with water to have H2O present in the process gas.
  • a 3 rd small N2 stream was passed through an oleum solution to saturate the stream with SO 3 .
  • Table 1A shows initial experiments at undefined residence times around 1 second, where these three streams were added and let to react at controlled temperatures in the 300-400 °C interval.
  • the results shown in Table 1A show that there is some gas phase reaction taking place between SO3 and H2S, but also that the reaction is relatively slow and not sufficiently fast to ensure complete SO3 destruction in an industrial Claus process plant.
  • Table 1 B shows additional experiments at controlled residence times, where these three streams were added and let to react at controlled temperatures at 350 °C with re- action chamber residence times of 0.4 second to 1 second.
  • Table 1 B also show some gas phase reaction taking place be- tween SO3 and H2S, but also that the gas phase reaction is relatively slow and not suf- ficiently fast to ensure complete SO3 destruction in an industrial Claus process plant. Contrary to this fast and near complete SO3 destruction is possible by application of a catalyst.
  • the chemical reactions taking place in the Claus reaction furnace are numerous and have been calculated using a very detailed kinetic model including more than 50 chem- ical species and more than 1000 chemical elementary reactions, each reaction de- scribed with a temperature dependent rate constant.
  • the model has been used to calculate both the kinetics of the Claus reaction furnace and the chemical equilibrium of the Claus reaction furnace mixture, i.e. the model was used to predict whether the sulfuric acid feed would react completely with the hhS in the reaction furnace.
  • the acid gas feed to the Claus reaction furnace consisted of 91.4 vol% hhS, 2.1 vol% CO 2 , 3.3 vol% H 2 O, 1.4 vol% CH 4 and 1.9 vol% H 2 , representing a concentrated acid gas from e.g. a refinery process.
  • the sulfuric acid was 93 %w/w H2SO4, representing a concentration of the sulfuric acid product from a wet type sulfuric acid plant installed as a tail gas treatment plant down- stream the Claus process plant.
  • the sulfuric acid flow accounted for 9.8 % of the total sulfur input to the Claus reaction furnace.
  • reaction temperature was 1050 °C and the pressure 1.65 bar absolute.
  • Figure 3 shows that the chemical reactions in the Claus reaction furnace are very fast and in less than 0.5 seconds chemical equilibrium is achieved, i.e. the composition of the process gas does not change.
  • the kinetic model only includes gas phase species and the time needed for the evaporation of sulfuric acid droplets have not been included. If the evaporation of the droplets is achieved in less than 0.5 seconds, the process gas from the Claus reac- tion furnace (with 1 second residence time) will be substantial SO3 free and the opera- tion of the Claus process plant will be unproblematic. However, if the evaporation of some of the droplets takes more than 1-2 seconds, the reaction furnace off gas cannot be considered SO3 free and unproblematic Claus process plant operation is not guar- anteed.

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Abstract

The present invention relates to process plant comprising a Claus reaction furnace, a Claus waste heat boiler, a SO3 destruction section and a Claus conversion section, wherein the Claus reaction furnace has an inlet and an outlet, the Claus waste heat boiler has a gas inlet, a gas outlet and optional an elemental sulfur outlet, the SO3 destruction section has a gas inlet and a gas outlet and the Claus conversion section has a gas inlet, a gas outlet and an elemental sulfur outlet, and wherein the inlet of the Claus reaction furnace is configured for receiving a feedstock gas, sulfuric acid, fuel, an oxidant and an optional sulfuric acid atomization media, and the outlet of the Claus reaction furnace is configured for being in fluid communication with the inlet of the Claus waste heat boiler, wherein the outlet of the Claus waste heat boiler is configured for being in fluid communication with the inlet of the SO3 destruction section, wherein the outlet of the SO3 destruction section is in fluid communication with the inlet of the Claus conversion section. The process has the associated benefit of such a process avoiding undesired poisoning (sulfation) of Claus catalyst and contamination of elemental sulfur product with sulfuric acid in the Claus conversion section.

Description

Title: Method for production of sulfur
The present invention is related to a process for conversion of I-I2S to elemental sulfur in a Claus process plant in which H2SO4 is added to the thermal stage of the Claus pro- cess plant.
H2S is a common side product in many processes, including hydrodesulfurization of re- finery streams, production of viscose and natural gas sweetening. It is desirable to con- vert H2S prior to emission to the atmosphere as H2S is highly toxic, odorous and an en- vironmental challenge.
Refinery processes, besides producing the well-known high concentration H2S gas, may often also produce a so-called sour water stripper gas, which comprises H2S, H2O and NH3 in around equal molar amounts.
Especially in refineries, the chosen process for H2S abatement has been the Claus pro- cess, which has been known and optimized for more the 8 decades. The Claus pro- cess proceeds by sub-stoichiometric combustion of H2S producing SO2 in a Claus re- action furnace, providing a Claus converter feed gas. The subsequent Claus process will convert the remaining H2S and the formed SO2 to form elemental sulfur, which may be condensed and withdrawn.
It has now been identified that addition of sulfuric acid to the Claus reaction furnace provides opportunities for optimization of the Claus process plant size and operational cost. H2SO4 is a concentrated source of O2 and a temperature moderator. Both proper- ties are valuable for capacity boosting of the Claus process. It has also been identified that this addition of H2SO4 may damage the catalyst of the Claus process by sulfation and thus require an SO3 guard prior to the catalytic Claus process.
In WO 2012/152919 A1 , a sulfuric acid process for treatment of Claus tail gas is pre- sented in which the conversion of H2S to H2SO4 in a Claus tail gas is described. The steps in the process are:
1. Sub-stoichiometric oxidation in Claus reaction furnace
2. Claus conversion
3. Oxidation of reduced sulfur species (H2S) in the Claus tail gas in oxygen rich at- mosphere at 400-700 °C
4. Catalytic oxidation of SO2 to SO3
5. Condensation of H2SO4 It is recognized that the H2SO4 product is not always desirable and it is suggested to recycle the sulfuric acid to the upstream Claus reaction furnace or the H2S oxidation step as described above. However, the recycling of sulfuric acid is merely thought as an abatement of sulfuric acid, and the consequences of recycling the H2SO4 on the sul- furic acid or Claus process have not been evaluated, i.e. it is not recognized that H2SO4 recirculation requires a reduction in the amount of O2 directed to the Claus reaction fur- nace, nor are the beneficial effects on the Claus and sulfuric acid process realized.
Also the effect on the chemistry in the Claus plant has not been considered. Finally, the document contains no consideration of incomplete conversion of H2SO4 to SO2 - there- fore absence of SO3 in the Claus process is a core assumption in this document, and no considerations are given to requirements for removal of SO3.
The sulfuric acid does not have to be recycled from a downstream sulfuric acid plant acting as a Claus tail gas treatment plant, but can come from other sources. The bene- fit of adding H2SO4 to the Claus process plant can justify purchase of H2SO4, as the H2SO4 both acts as an efficient O2 carrier and temperature moderator as described in patent application PCT/EP2017/080721. The addition of H2SO4 can boost the capacity of the Claus process plant by up to 50% without affecting the process gas flow in the Claus process plant.
In Danish patent application PA 2018 00057 different means of adding the liquid H2SO4 stream to the thermal stage of the Claus process plant, also known as the Claus reac- tion furnace, is described. It is important to ensure that the injection does not interfere significantly with the flame in the reaction furnace, while still being close to the hot flame for fast evaporation and subsequent mixing with the gas phase to carry out the desired Claus reaction.
The prior art relating to feeding H2SO4 to the thermal stage of the Claus process plant has assumed full evaporation of sulfuric acid and quantitative conversion to SO2. How- ever, the present disclosure is related to the realization that this conversion of H2SO4 to SO2 may not be complete.
In a broad aspect the present invention relates to a process for production of a sub- stantially SO3 free Claus converter feed gas from a feedstock gas comprising 30 vol%, 40 vol% or 50% to 99 vol% or 100 vol% H2S and a stream of sulfuric acid involving the steps of a. providing a Claus reaction furnace feed stream comprising said feedstock gas, an amount of sulfuric acid, an amount of molecular oxygen and optionally an amount of fuel, wherein the amount of molecular oxygen is substoichiometric,
b. directing said Claus reaction furnace feed stream to a Claus reaction furnace operating at elevated temperature, such as above 900°C, providing a Claus reaction furnace off gas
c. cooling said Claus reaction furnace off gas and optionally withdrawing ele- mental sulfur from the gas
d. directing said cooled Claus reaction furnace off gas to contact an SO3 guard material, absorbing and/or converting SO3, providing a substantially SO3 free Claus converter feed gas
e. directing said substantially SO3 free Claus converter feed gas to contact a ma- terial catalytically active in the Claus reaction
f. withdrawing elemental sulfur, optionally by cooling the effluent from said mate- rial catalytically active in the Claus reaction,
characterized in said SO3 guard material being different from said material catalytically active in the Claus reaction, wherein said SO3 guard material active in SO3 removal en- sures a long operation of the catalyst active in the Claus reaction, if droplets of sulfuric acid are not fully evaporated and reduced in the gas phase, such that long operation of the Claus process plant can be maintained, even when said material catalytically active in the Claus reaction has no activity or only temporary activity in SO3 conversion or ab- sorption.
In a further embodiment, the SO3 guard is an SO3 absorbent, in which the content of SO3 is increased over time, such as alumina or titania, with the associated benefit of such an absorbent being inexpensive, and with the further benefit of alumina and tita- nia having a moderate catalytic effect, allowing for some conversion of absorbed SO3.
In a further embodiment, wherein the SO3 guard material is a material catalytically ac- tive in reducing SO3 by reaction with H2S, providing a substantially SO3 free Claus con- verter feed gas, with the associated benefit of the lifetime of the SO3 guard material not being limited by an absorption capability. In a further embodiment the SO3 guard material is arranged downstream the Claus re- action furnace and upstream the Claus converter, with the associated benefit of the SO3 guard material being remote and thus independent from the flame in the Claus re- action furnace.
In a further embodiment the SO3 guard material is arranged as top layer on material catalytically active in the Claus reaction, with the associated benefit of avoiding the cost of a separate reactor for the SO3 guard.
In a further embodiment the material catalytically active in the reduction of SO3 corn- prises one or more elements taken from the group consisting of V, Mn, Fe, Co, Cu, Zn, Ni, Mo, W, Sb, Ti and Bi and a support comprising one or more elements taken from the group consisting of Al, Ti, Si, Zr and Mg, with the associated benefit of such materi- als being active in the conversion of SO3 to SO2 or sulfur.
In a further embodiment the support comprises diatomaceous earth and/or cordierite with the associated benefit of such materials being stable and having a high surface area.
In a further embodiment the material active in the reduction of SO3 is in shape of pellets or a monolith, with the associated benefit of pellets being cost effective to produce, whereas monoliths benefit from having a low pressure drop.
In a further embodiment the Claus reaction furnace is operated at a temperature of be- tween 900°C and 1500°C with the associated benefit of this temperature range being appropriate for decomposition of H2SO4 to H2O and SO3, for further decomposition of SO3 to SO2, for partial oxidation of H2S and for decomposition of impurities.
In a further embodiment the material catalytically active in reducing SO3 is operated at a temperature of between 130°C and 1500°C with the associated benefit of the temper- ature being appropriately inside the interval of catalytic Claus reaction and non-catalytic Claus reaction furnace temperatures.
In a further embodiment the material catalytically active in reducing SO3 is operated at a temperature of between 250°C and 500°C, with the associated benefit of operating in a temperature range where conversion from SO3 to SO2 and/or sulfur is rapid without requiring high resistance materials.
In a further embodiment the material catalytically active in reducing SO3 is operated at a temperature of between 300°C and 400°C, with the associated benefit of operating in a temperature range where conversion from SO3 to SO2 or sulfur is rapid without re- quiring exotic materials.
In a further embodiment the stream of sulfuric acid is produced in a wet type sulfuric acid plant treating the tail gas from the Claus plant with the associated benefit of such a process being thermally efficient and able to reduce emission of sulfurous compounds to a very high extent.
The liquid phase term sulfuric acid means a mixture of H2SO4 and H2O as H2SO4 is hy- groscopic and will absorb water from the gas phase. In principle any concentration of H2SO4 can be injected into the Claus reaction furnace, but high concentrations are de- sired as that will reduce the energy required for evaporation and minimize the dilution of Claus reaction furnace off gas with the associated water. For practical purposes, only sulfuric acid with >90 %w/w H2SO4 is considered most relevant.
The gas phase terms H2SO4 (sulfuric acid) and SO3 (sulfuric anhydride) are often just called“SO3” as the hydration reaction of SO3 (SO3 + H2O <® H2SO4) is considered very fast and safely can be considered to be in chemical equilibrium. The distribution be- tween SO3 and H2SO4 depends on the temperature, pressure and H2O concentration in the gas, SO3 is favored at high temperatures and low H2O concentrations and H2SO4 is favored at low temperatures and high H2O concentration. Above 400 °C, very little H2SO4 exist and below 200 °C, very little SO3 exist and in the range 200-400 °C both molecules will be present in varying amounts (in case of a wet gas).
The following H2SO4 related chemical reactions will take place in the reaction furnace:
H2SO4 (liquid) H2S04 (gas) (1 )
H2SO4 (gas) < SO3 (gas) + H2O (gas) (2)
SO3 (gas) SO2 (gas) + 0.5 O2 (3)
SO3 (gas) + H2S (gas) SO2 (gas) + S (gas) + H2O (gas) (4)
H2S(gas) + 1.5 O2 SO2 (gas) + H2O (gas) (5)
SO2 (gas) + 2 H2S (gas) 3 S (gas) + 2 H2O (gas) (6)
“S” represents elemental sulfur in any form from S2 to Ss
Reactions (5) and (6) are the overall reactions for the Claus process in which the H2S in the feed gas is combusted with O2 deficiency to form a combustion gas with a H2S/SO2 ratio around 2, which is the optimal ratio for highest conversion into elemental S.
As H2SO4 is introduced it is seen from reaction (2) + (3) that the sulfuric acid is decom- posed to SO2 and O2, ultimately reducing the O2 requirement by 2 moles for each mole H2SO4 added. With air as the O2 source, the 2 moles of O2 are associated with 8 moles of N2 and thus the addition of H2SO4 significantly reduces the amount of inert gas in the process gas.
Reaction (1 ) describes the evaporation of the liquid sulfuric acid after injection into the reaction furnace. Typically, the sulfuric acid stream is atomized into a“fog” consisting of small droplets, the droplet size distribution is determined by the method of atomiza- tion. The droplets evaporate from the outer droplet surface and thus the initial droplet size is essential for the time required for complete evaporation. The time for complete evaporation depends on the 3rd power of the droplet diameter, i.e. a doubling of the droplet diameter increases the evaporation time by a factor of 8. Process gas tempera- ture and gas/droplet mixing also have a significant impact on the evaporation time of the droplets.
To achieve the smallest droplets, two phase atomization is required in which an atomi- zation media, which typically is compressed air, N2 or steam, is used to“cut” the liquid stream into fine droplets.
Reaction (2) is a very fast gas phase reaction and chemical equilibrium between SO3 and H2SO4 can be safely assumed.
Reaction (3) and (4) describes the overall reactions for destruction of the SO3 into ei- ther SO2 and O2, which can then react with H2S via reaction (5) and (6) or react directly with H2S to form SO2 and S, where the SO2 can react with H2S via reaction (6).
Reaction (3) is highly temperature dependent and only takes place at higher tempera- ture, i.e. > 800 °C, unless a catalyst is present.
Reaction (4) takes place at lower temperatures too, but the reaction rate at tempera- tures below 400 °C may be too low to be relevant for industrial applications.
At the Claus reaction furnace temperature, reactions (2) to (6) are very fast and will typ- ically proceed to chemical equilibrium within less than 0.5 seconds. The residence time in a reaction furnace is typically less than 1-2 seconds. According to chemical equilibrium calculations, neither H2SO4, SO3 nor O2 will be pre- sent in the process gas at Claus reaction furnace gas conditions.
The stoichiometric balance between H2S and O2 in the absence of H2SO4 is 2:1. How- ever, in the presence of H2SO4 less O2 is required. A substoichiometric amount of mo- lecular oxygen is therefore defined as an molar amount being less than half of the mo- lar amount of H2S.
The Claus reaction furnace is preferably operated at a temperature between 900 and 1500°C.
For relatively large droplets, reaction (1 ) will be the limiting step for the reactions to pro- ceed to equilibrium and the available 1-2 seconds of residence time can become too short for the completion of the reactions. Such situations can arise if e.g. the nozzle for the sulfuric acid atomization has become worn and/or the flow or pressure of the atomi- zation media is out of the normal range. The consequence of this is that H2SO4 / SO3 leaves the Claus reaction furnace not fully converted and enters the heat exchanger (waste heat boiler) that cools the Claus reaction furnace gas to around 300-400 °C. At this temperature reaction (1 ) and (2) are still active, whereas reaction rates for (3) to (6) are too low to be of any practical significance.
In a commonly used Claus process layout, the 300-400 °C Claus reaction furnace off gas is sent to a catalytic Claus reactor in which a catalyst active in reaction (6) is in- stalled. This catalyst is well known in the industry and is most often used as pellets with the active material being T1O2 or AI2O3. Also well known is that this catalyst is sensitive to“sulfation”, i.e. the active sites of the catalyst become“poisoned” with sulfate and thus the catalyst loses catalytic activity with the consequence of less product being formed and increased emissions of H2S and SO2. The sulfate can be formed by reac- tion between SO2 and O2, forming SO3 on the catalyst surface, or SO3 present in the process gas can directly attach to the catalyst surface.
In another Claus process layout, the 300-400 °C Claus reaction furnace off gas is di- rected to a sulfur condenser, in which the process gas is cooled to 130-160 °C to con- dense the elemental sulfur and withdraw the product. The process gas is then reheated and directed to a catalytic Claus reactor as described above. If there is SO3 present in the Claus reaction furnace off gas, there is a risk of condensing sulfuric acid in the ele- mental sulfur product, producing an off-spec product and there is an increased risk of corrosion of the sulfur handling equipment. The off gas from the sulfur condenser will also contain a fraction of the SO3 (as H2SO4) present in the Claus reaction furnace off gas and this SO3 will poison the downstream Claus catalyst.
As described, it is of great importance that the Claus reaction furnace off gas does not contain substantial amounts of SO3 as it can have a detrimental effect on the down- stream catalyst, equipment and operation of the Claus process plant.
To ensure a safe and long operation of the Claus process plant, a new catalyst, active in the reaction of SO3 with H2S to form a mixture of SO2 and S, has been developed. The catalyst is also able to suppress the reaction with SO3 forming O2 (reaction 3) as a O2 slip is just as problematic as a SO3 slip. The catalyst is preferably to be installed be- tween the outlet of the waste heat boiler connected to the Claus reaction furnace and the inlet to equipment and/or catalysts that can be damaged by the presence of SO3. This new catalyst can either be installed in a separate reactor as would be necessary in the Claus process layout in which the cooled Claus reaction furnace off gas is sent to a sulfur condenser before the catalytic Claus reactor or as a top layer in the existing Claus reactor which is possible in the layout where the process gas goes directly to the catalytic Claus reactor.
In another embodiment, the catalyst is installed at the outlet of the Claus reaction fur- nace, taking advantage of the high temperature and high reaction rates.
The catalyst can be of any shape and size, considered optimal for the Claus process plant layout. If to be installed as a top layer in the Claus reactor, a pellet shaped cata- lyst would be most desirable as the Claus catalyst typically is pellet shaped.
In case the material catalytically active in reducing SO3 (and H2SO4) by reaction with H2S is to be installed in a separate vessel, either pellet shape catalyst or monolithic cat- alyst can be installed, depending on the available pressure drop on the process gas side, space limitations for the reactor and which solution is the most cost efficient.
The material catalytically active in reducing SO3 (and H2SO4) by reaction with H2S corn- prises one or more compounds of V, Mn, Fe, Co, Cu, Zn, Ni, Mo, W, Sb, Ti and Bi sup- ported on one or more compounds of Al, Ti, Si, Zr, Mg, and cordierite, often with the support comprising diatomaceous earth. Although AI2O3 and T1O2 alone are prone to sulfate poisoning, the compounds can be used for support for the compounds active in the conversion of SO3 into SO2 and S, which are harmless for the downstream Claus catalysts. It is further considered likely that AI2O3 and T1O2 may act as guards by ab- sorption of SO3 by sulfation, and thus such materials without active metals may func- tion as guard, but require occasional replacement or re-activation.
The material catalytically active in reducing SO3 (and H2SO4) by reaction with H2S is operated at a temperature of between 130 and 1500°C, such as between 250 and 500°C or between 300 and 400°C.
Figures:
Figure 1 shows a Claus reaction furnace with 1st Claus reactor upstream 1st sulfur con- denser
Figure 2 shows a Claus reaction furnace with 1st sulfur condenser upstream 1st Claus reactor
In Figure 1 , the feeds to the Claus reaction furnace (Claus thermal stage) are one or more acid gases comprising H2S (2), an optional fuel gas (4), an oxygen source (6) be- ing typically air with 21 vol% O2 or enriched air with 21-100 vol% O2 and a sulfuric acid stream (8). The sulfuric acid stream can optionally be concentrated sulfuric acid pro- duced in a sulfuric acid plant installed as a tail gas treatment plant for the Claus pro- cess plant. The sulfuric acid atomization method that produces the smallest droplets is a two-phase atomization in which an atomization media (10) is used to“cut” the sulfuric acid liquid into droplets. The atomization media is most often pressurized air or steam, but other media are also possible, such as fuel gas, enriched air or process gas.
In the Claus reaction furnace chamber (12) part of the H2S is oxidized to SO2 which then combines with H2S to form elemental sulfur. Sulfuric acid is evaporated and reacts with H2S to from SO2 and elemental sulfur. The temperature in the reaction furnace is typically above 900 °C and the average residence time is typically 1-2 seconds. The off gas from the reaction chamber (14) is led through heat exchanger (16), where the pro- cess gas is cooled to 300-400 °C. The heat exchanger is typically a waste heat boiler, producing high pressure steam. If elemental sulfur is condensed in the heat exchanger, it is drained via the liquid outlet (18).
The cooled Claus reaction furnace off gas (20) is then passed through one or more layer(s) of catalyst (22) in which any SO3 in the Claus reaction furnace off gas is effi ciently converted to SO2 and S by reaction with H2S, producing a substantial SO3 free feed gas (24) to be directed to the Claus catalyst layer in the Claus reactor (26). It can be possible to combine (22) and (26) such that the SO3 destruction catalyst in (22) can be a top layer in the Claus reactor (26).
In the Claus reactor (26) more elemental sulfur is formed by reaction between H2S and SO2 and the Claus reactor off gas (28) is passed to a first sulfur condenser (30) in which the process gas is cooled and a fraction of the elemental sulfur condensed and withdrawn as a liquid via outlet 32. The off gas (34) is typically reheated and passed through one or more Claus reactor - sulfur condenser - reheater passes to ensure suf- ficiently high conversion of H2S into elemental sulfur.
In Figure 2 the Claus reaction furnace (12) and waste heat boiler (16) are similar to the layout and operation as described for figure 1. The difference in the layout is that the cooled Claus reaction furnace off gas (20) is passed directly to the first sulfur conden- ser (30) to condense and withdraw elemental sulfur product via line 32 before the con- denser off gas (34) is reheated and passed to 1st Claus reactor. In this layout, due to withdrawal of product, the Claus reaction equilibrium is favored in the 1st Claus reactor and thus a higher overall conversion out of 1st Claus reactor can be achieved. For such a layout it is necessary to install the material catalytically active in reducing SO3 (and H2SO4) by reaction with H2S in a separate vessel (22), such that a substantially SO3 free process gas (24) enters the first sulfur condenser (30), thereby avoiding possible contamination of sulfur product with sulfuric acid and avoiding passing uncaptured sul- furic acid to the downstream first Claus reactor.
Example 1 :
In a laboratory scale setup, the non-catalytic reaction between H2S and SO3 has been investigated in a reaction chamber, which consist of a 40 cm long 013 mm glass tube installed in a temperature controlled oven.
The H2S was supplied from a gas cylinder and diluted with N2 before added to reaction chamber. A 2nd N2 stream was saturated with water to have H2O present in the process gas. A 3rd small N2 stream was passed through an oleum solution to saturate the stream with SO3.
Table 1A shows initial experiments at undefined residence times around 1 second, where these three streams were added and let to react at controlled temperatures in the 300-400 °C interval. The outlet from the reaction chamber was analyzed for content of elemental sulfur, sul- furic acid (=SC>3 reacted with H2O in the gas) and SO2. The results shown in Table 1A show that there is some gas phase reaction taking place between SO3 and H2S, but also that the reaction is relatively slow and not sufficiently fast to ensure complete SO3 destruction in an industrial Claus process plant.
Table 1A:
Figure imgf000013_0001
Table 1 B shows additional experiments at controlled residence times, where these three streams were added and let to react at controlled temperatures at 350 °C with re- action chamber residence times of 0.4 second to 1 second.
The results shown in Table 1 B also show some gas phase reaction taking place be- tween SO3 and H2S, but also that the gas phase reaction is relatively slow and not suf- ficiently fast to ensure complete SO3 destruction in an industrial Claus process plant. Contrary to this fast and near complete SO3 destruction is possible by application of a catalyst.
Inspection of the materials have indicated that the SO3 removal over alumina may be due to sulfation of the alumina, rather than a catalytic conversion. Such a sulfation may however still be of commercial relevance, if an amount of alumina is used as guard ma- terial, since the subsequent Claus catalyst is protected from deactivation by SO3. Table 1 B:
Figure imgf000014_0001
Example 2
The chemical reactions taking place in the Claus reaction furnace are numerous and have been calculated using a very detailed kinetic model including more than 50 chem- ical species and more than 1000 chemical elementary reactions, each reaction de- scribed with a temperature dependent rate constant.
The model has been used to calculate both the kinetics of the Claus reaction furnace and the chemical equilibrium of the Claus reaction furnace mixture, i.e. the model was used to predict whether the sulfuric acid feed would react completely with the hhS in the reaction furnace.
The acid gas feed to the Claus reaction furnace consisted of 91.4 vol% hhS, 2.1 vol% CO2, 3.3 vol% H2O, 1.4 vol% CH4 and 1.9 vol% H2, representing a concentrated acid gas from e.g. a refinery process.
The sulfuric acid was 93 %w/w H2SO4, representing a concentration of the sulfuric acid product from a wet type sulfuric acid plant installed as a tail gas treatment plant down- stream the Claus process plant. The sulfuric acid flow accounted for 9.8 % of the total sulfur input to the Claus reaction furnace.
The reaction temperature was 1050 °C and the pressure 1.65 bar absolute. Figure 3 shows that the chemical reactions in the Claus reaction furnace are very fast and in less than 0.5 seconds chemical equilibrium is achieved, i.e. the composition of the process gas does not change.
However, the kinetic model only includes gas phase species and the time needed for the evaporation of sulfuric acid droplets have not been included. If the evaporation of the droplets is achieved in less than 0.5 seconds, the process gas from the Claus reac- tion furnace (with 1 second residence time) will be substantial SO3 free and the opera- tion of the Claus process plant will be unproblematic. However, if the evaporation of some of the droplets takes more than 1-2 seconds, the reaction furnace off gas cannot be considered SO3 free and unproblematic Claus process plant operation is not guar- anteed.
In such a situation, the newly developed material catalytically active in reducing SO3 (and H2SO4) by reaction with H2S is necessary for long operation of the Claus process plant.

Claims

Claims
1. A process for production of sulfur from a feedstock gas comprising from 30 vol%, from 40 vol% or from 50% to 99 vol% or to 100 vol% H2S and a stream of sulfuric acid involving the steps of
a. providing a Claus reaction furnace feed stream comprising said feedstock gas, an amount of sulfuric acid, an amount of molecular oxygen and op- tionally an amount of fuel, wherein the amount of molecular oxygen is substoichiometric,
b. directing said Claus reaction furnace feed stream to a Claus reaction fur- nace, providing a Claus reaction furnace off gas,
c. cooling said Claus reaction furnace off gas to provide a cooled Claus re- action furnace off gas and optionally withdrawing elemental sulfur from the gas
d. directing said cooled Claus reaction furnace off gas to contact an SO3 guard material, absorbing and/or converting SO3, providing a substantially SO3 free Claus converter feed gas
e. directing said SCh free Claus converter feed gas to contact a material cat- alytically active in the Claus reaction,
f. withdrawing elemental sulfur, optionally by cooling the effluent from said material catalytically active in the Claus reaction,
characterized in said SO3 guard material being different from said material catalytically active in the Claus reaction.
2. A process according to claim 1 , wherein the SO3 guard is an SO3 absorbent, in which the content of SO3 is increased over time, such as alumina or titania.
3. A process according to claim 1 , wherein the SO3 guard material is a material catalytically active in reducing SO3 by reaction with H2S, providing a substan- tially SO3 free Claus converter feed gas.
4. A process according to claim 1 , 2 or 3, wherein the SO3 guard material is ar- ranged downstream the Claus reaction furnace and upstream the Claus con- verter.
5. A process according to claim 1 , 2, or 3, wherein the SO3 guard material is ar- ranged as top layer on material catalytically active in the Claus reaction.
6. A process according to any one of claims 3, 4 or 5, wherein the material cata- lytically active in the reduction of SO3 comprises one or more elements taken from the group consisting of V, Mn, Fe, Co, Cu, Zn, Ni, Mo, W, Sb, Ti and Bi and a support comprising one or more elements taken from the group con- sisting of Al, Ti, Si, Zr, and Mg.
7. A process according to claim 6, wherein the support comprises diatomaceous earth and/or cordierite.
8. A process according to any one of claims 1 to 5, wherein the material active in the reduction of SO3 is in shape of pellets or a monolith.
9. A process according to any one of claims 1 to 6, wherein the Claus reaction furnace is operated at a temperature of between 900 and 1500°C.
10. A process according to any one of claims 1 to7, wherein the material catalyti- cally active in reducing SO3 is operated at a temperature of between 130 and 1500°C.
1 1. A process according to any one of claims 1 to 8, wherein the material catalyti- cally active in reducing SO3 is operated at a temperature of between 250 and
500°C.
12. A process according to any one of claims 1 to 9, wherein the material catalyti- cally active in reducing SO3 is operated at a temperature of between 300 and 400°C.
13. A process according to any one of claims 1 to 10, wherein the stream of sul- furic acid is produced in a wet type sulfuric acid plant treating the tail gas from the Claus plant.
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