Method for production of sulfur and sulfuric acid
10981788 · 2021-04-20
Assignee
Inventors
Cpc classification
C01B17/0404
CHEMISTRY; METALLURGY
International classification
Abstract
A process plant including a Claus reaction furnace, a means of Claus gas cooling, a Claus conversion section, a means for Claus tail gas oxidation and a sulfuric acid section, wherein a sulfuric acid outlet of the sulfuric acid section is in fluid communication with an inlet of said Claus reaction furnace, as well as a related process. The process has the associated benefit of such a process avoiding undesired production of sulfuric acid, as well as reducing the Claus process gas volume.
Claims
1. A process for production of sulfur from a feedstock gas comprising 30 vol % 100 to vol % H.sub.2S and a recycled stream of sulfuric acid, the process comprising: a. providing a Claus reaction furnace feed stream comprising said feedstock gas, an amount of recycled sulfuric acid, an amount of oxygen and optionally an amount of fuel, wherein the amount of oxygen is substoichiometric; b. directing said Claus reaction furnace feed stream to a Claus reaction furnace operating at elevated temperature, providing a Claus converter feed gas; c. cooling said Claus converter feed gas to provide a cooled Claus converter feed gas and optionally an amount of elemental sulfur; d. directing said cooled Claus converter feed gas to contact a material catalytically active in the Claus reaction; e. withdrawing a Claus tail gas and elementary sulfur, optionally by cooling the effluent from said material catalytically active in the Claus reaction; f. directing a stream comprising said Claus tail gas, oxygen and a fuel as a feedstock gas to a means for Claus tail gas oxidation operating at a temperature above 900° C. and/or a catalytic means for oxidation providing an SO.sub.2 converter feed gas; g. directing said SO.sub.2 converter feed gas to contact a material catalytically active in SO.sub.2 oxidation to SO.sub.3, providing an SO.sub.3 rich gas; and h. converting said SO.sub.3 rich gas to concentrated sulfuric acid and a SO.sub.3 depleted gas, either by absorption of SO.sub.3 in sulfuric acid or by hydration of SO.sub.3, cooling and condensation of sulfuric acid, wherein said recycled stream of sulfuric acid comprises an amount of said concentrated sulfuric acid and wherein the concentrated sulfuric acid contains from 90% w/w to 98.5% w/w H.sub.2SO.sub.4.
2. The process according to claim 1 wherein the Claus reaction furnace feed stream comprises less than 0.1 wt % non-elemental nitrogen.
3. The process according to claim 1 further wherein the Claus reaction furnace feed stream comprises less than 50 vol % N.sub.2.
4. The process according to claim 1 wherein the H.sub.2S:SO.sub.2 ratio of said Claus tail gas is below 2.
5. The process according to claim 1 wherein the H.sub.2S:SO.sub.2 ratio of said Claus tail gas is above 2.
6. The process according to claim 1 further comprising the step of directing an amount of a further feedstock gas to said means for Claus tail gas oxidation.
7. The process according to claim 6 wherein said further feedstock gas comprises more than 5 vol % non-elemental nitrogen.
8. The process according to claim 6 wherein the amount of sulfur in the further feedstock gas is at least 1 wt % of the total amount of elemental sulfur withdrawn from the process.
9. The process according to claim 1 wherein the material catalytically active in the Claus reaction comprises activated aluminum(III) or titanium(IV) oxide.
10. The process according to claim 1 wherein the amount of sulfur in the recycled stream of sulfuric acid is higher than 1 wt % and less than 25 wt % of the total amount of elemental sulfur withdrawn from the process.
11. The process according to claim 1 wherein the recycled stream of sulfuric acid is atomized in said Claus reaction furnace either using two fluid nozzles driven by compressed air, N.sub.2 or steam or using hydraulic nozzles and wherein the residence time in the Claus reaction furnace is from 1.5 second to 4 seconds.
12. The process according to claim 1 wherein the molar ratio H.sub.2S:O.sub.2 of the combined streams directed to the Claus reaction furnace is greater than 2.5.
13. The process according to claim 1 wherein the molar ratio H.sub.2S:O.sub.2 of the combined streams directed to the Claus reaction furnace corrected for other oxygen consuming species in the feedstock and corrected for products of incomplete oxidation in the Claus tail gas is greater than 2.1.
14. The process according to claim 1 wherein an amount of gas in the process is optionally cooled and directed to an upstream position for controlling a process temperature.
15. The process according to claim 1 wherein one or more streams directed to said Claus reaction furnace are pre-heated by heat exchange with a hot process stream.
16. The process according to claim 1 wherein one or more streams directed to said means for Claus tail gas oxidation are pre-heated by heat exchange with a hot process stream.
17. The process according to claim 1 wherein said material catalytically active in SO.sub.2 oxidation to SO.sub.3 comprises vanadium.
18. The process according to claim 1 wherein condensation of sulfuric acid according to step (h) is carried out in a condenser where cooling medium and SO.sub.3 rich gas is separated by glass.
19. The process according to claim 1 wherein the amount of recycled sulfuric acid is selected such that the temperature in the Claus reaction furnace is from 800° C. to 1500° C., without addition of support fuel to the Claus reaction furnace.
20. The process according to claim 1, wherein, in (b), the Claus reaction furnace feed stream is directed to a Claus reaction furnace operating at a temperature above 900° C.
21. A process plant comprising a Claus reaction furnace, a means of Claus gas cooling, a Claus conversion section, a means for Claus tail gas oxidation and a sulfuric acid section, wherein the Claus reaction furnace has an inlet, an outlet, and one or more atomization nozzles configured for adding sulfuric acid to the Claus reaction furnace as droplets, the means of Claus gas cooling has a gas inlet, a gas outlet and an elemental sulfur outlet, the Claus conversion section has a gas inlet, a gas outlet and an elemental sulfur outlet, the means for Claus tail gas oxidation has a Claus tail gas inlet, a Claus tail gas oxidant inlet, an optional fuel inlet and optionally a further feedstock inlet and an outlet and the sulfuric acid section has a gas inlet, a gas outlet and a sulfuric acid outlet, and wherein the inlet of the Claus reaction furnace is configured for receiving a feedstock gas, sulfuric acid and a Claus reaction furnace oxidant, and the outlet of the Claus reaction furnace is configured for being in fluid communication with the inlet of the means of Claus gas cooling, wherein the outlet of the means of Claus gas cooling is configured for being in fluid communication with the inlet of the Claus conversion section and wherein the Claus tail gas inlet of the means for Claus tail gas oxidation is configured for being in fluid communication with the outlet of said Claus conversion section gas outlet, the process gas outlet of the means for Claus tail gas oxidation is configured for being in fluid communication with the inlet of the sulfuric acid section, and the sulfuric acid outlet of the sulfuric acid section being in fluid communication with the inlet of said Claus reaction furnace.
22. The process plant according to claim 21, wherein said sulfuric acid section comprises a sulfur dioxide oxidation reactor having an inlet and an outlet and a sulfuric acid condenser having a process side having a process gas inlet, a process gas outlet and a sulfuric acid outlet and a cooling medium side, having a cooling medium inlet and a cooling medium outlet, and wherein the sulfuric acid condenser is configured for at least one of the Claus reaction furnace oxidant and the Claus tail gas oxidant to be pre-heated by being directed to the inlet of the cooling medium side of the sulfuric acid condenser and being withdrawn from the outlet of the cooling medium side of the sulfuric acid condenser.
23. The process plant according to claim 21 further comprising at least one heat exchanger having a hot heat exchanger side and a cold heat exchanger side, configured for the cold heat exchanger side pre-heating one of said feedstock gas, sulfuric acid and oxidant prior to being directed to said Claus reaction furnace and for the hot heat exchanger side being configured for cooling a hot process stream.
24. The process plant according to claim 23 wherein the hot process stream is taken from the group consisting of the stream of the outlet from the means for means for Claus tail gas oxidation, the stream of the outlet from the Claus reaction furnace and the stream of the outlet from the sulfur dioxide oxidation reactor.
25. The process plant according to claim 21 wherein the Claus reaction furnace comprises two or more atomization nozzles, configured for adding sulfuric acid to the Claus reaction furnace as droplets.
26. The process plant according to claim 21 further comprising a means of SO.sub.3 reduction, having an inlet and an outlet configured for the inlet of the means of SO.sub.3 reduction being in fluid communication with the outlet of the Claus reaction furnace and for the outlet of the means of SO.sub.3 reduction being in fluid communication with the inlet of the Claus conversion section.
27. The process plant according to claim 21, wherein the one or more atomization nozzles is a fluid atomization nozzle(s), or a hydraulic atomization nozzle(s).
Description
FIGURES
(1)
(2)
(3)
(4) In
(5) In a variation of the process the conversion and condensation of sulfuric acid may be carried out in two stages, where remaining SO.sub.2 is oxidized, hydrated and condensed, with the associated benefit of providing increased sulfur removal.
(6) In a further variation the SO.sub.2 converter feed gas 38 may be dried, such that the SO.sub.3 rich gas 48 will contain little or no water. In that case the sulfuric acid condenser 50 may be replaced with an absorber, in which SO.sub.3 may be absorbed in sulfuric acid, to provide concentrated sulfuric acid, by a dry sulfuric acid process.
(7) In a further variation an amount of elemental sulfur may also be transferred to the combustor 32, which will have the effect of providing SO.sub.2 to the sulfuric acid process without introduction of water, which may be beneficial if it is desired to increase the SO.sub.3 concentration, which may be beneficial in a dry sulfuric acid process.
(8) In a further variation, an amount of the feedstock gas 2 rich in H.sub.2S may also be split in an amount directed for the reactor of the Claus process 8 and an amount directed to the combustor 32, for oxidation.
(9) In a further variation, an amount of fuel gas is directed to combustor 32 in order to be able to sustain a stable flame and a sufficiently high temperature for complete oxidation of reduced species, such as H.sub.2S, CO, H.sub.2, COS, present in the final Claus tail gas 26.
(10) In
(11) In order to maintain a stable flame and sufficient high temperature for complete oxidation of H.sub.2S, CO, CS.sub.2, COS and H.sub.2, fuel gas may be directed to the combustor 32. Oxygen is also supplied, typically via air, in order to supply oxygen for both the combustion reactions in combustor 32 but also the oxygen required for the oxidation of SO.sub.2 in the SO.sub.2 converter. To reduce fuel consumption, the oxygen for SO.sub.2 oxidation can be added between the combustor 32 outlet and the SO.sub.2 converter 40 inlet.
(12) In
(13) The SO.sub.2 converter feed gas is typically cooled in a waste heat boiler (not shown) to provide optimal temperature for the first catalyst layer 42 in the SO.sub.2 converter 40. The SO.sub.2 converter feed gas 34 is directed to an SO.sub.2 converter 40, containing one or more beds/layers of catalytically active material 42, 44, 46 optionally with interbed cooling, from which an SO.sub.3 rich gas 48 is withdrawn. As the SO.sub.3 rich gas contains water, the SO.sub.3 may hydrate to form H.sub.2SO.sub.4. H.sub.2SO.sub.4 is condensed as concentrated sulfuric acid 52 in a sulfuric acid condenser 50. If the amount of water is insufficient for full hydration of SO.sub.3, addition of steam in a position upstream the sulfuric acid condenser 50 may be preferred. From the sulfuric acid condenser 50 a substantially pure gas 62 may be withdrawn and directed to stack 64. Typically, all sulfuric acid 52 is recycled to the Claus reaction furnace 66, but optionally an amount of sulfuric acid may be withdrawn for other process purposes.
(14) In a further embodiment the conversion and condensation of sulfuric acid may be made in two stages, where remaining SO.sub.2 from the first stage is further oxidized, hydrated and condensed, with the associated benefit of providing increased sulfur removal.
(15) In a further embodiment, additional SO.sub.2 conversion can be achieved by installed a tail gas cleaning plant downstream the sulfuric acid process. Numerous of these tail gas solutions exist, where alkaline scrubbers optionally combined with mist filters, are the most common type. Scrubbers using H.sub.2O.sub.2 or NH.sub.3 are preferred as the effluent from these scrubbers is H.sub.2SO.sub.4 and (NH.sub.4).sub.2SO.sub.4 respectively, both of which can be recycled to the Claus reaction furnace for thermal destruction, i.e. eliminating a waste stream.
(16) In a further embodiment the SO.sub.2 converter feed gas 34 may be dried, such that the SO.sub.3 rich gas 48 will contain little or no water. In that case the sulfuric acid condenser 50 may be replaced with an absorber, in which SO.sub.3 may be absorbed in sulfuric acid, to provide concentrated sulfuric acid, by a dry sulfuric acid process.
(17) In a further embodiment an amount of elemental sulfur may also be transferred to the combustor 32, which will have the effect of providing SO.sub.2 to the sulfuric acid process without introduction of water, which may be beneficial if it is desired to increase the SO.sub.3 concentration, which may be beneficial in a dry sulfuric acid process.
(18) In a further embodiment an amount of fuel gas 68 is directed to the means for Claus tail gas oxidation 32 to ensure sufficiently high temperature for complete oxidation of all reduced compounds in the Claus tail gas 20.
(19) In a further embodiment, an amount of the feedstock gas 2 rich in H.sub.2S may also be split in an amount directed for the combustor of the Claus process (i.e. the Claus reaction furnace) 66 and an amount directed to the means for Claus tail gas oxidation 32. This will reduce the need for fuel gas addition to the means for Claus tail gas oxidation 32.
(20) In a further embodiment, the entire amount of second feedstock containing NH.sub.3 and H.sub.2S 70 is directed to the means for Claus tail gas oxidation 32, eliminating the risk of NH.sub.3-salt formation in the sulfur condensation units (i.e. the Claus condensers) 16. In this embodiment a system for reduction of NO.sub.X 33, located between the means for Claus tail gas oxidation 32 outlet and the inlet of the SO.sub.2 converter 40 will be installed. Typically, a so-called SCR (Selective Catalytic Reaction) catalytic reactor will be used, requiring addition of NH.sub.3 for the SCR reaction to proceed. The NH.sub.3 addition can be from an external source or could be a small stream of the second feedstock containing NH.sub.3 and H.sub.2S 70, which is then bypassed the means for Claus tail gas oxidation.
(21) In a further embodiment a for catalytic reactor 35 for oxidation of remaining impurities such as hydrocarbons, CO, COS, CS.sub.2, S and H.sub.2S may be installed.
(22) In a further embodiment a part of the Claus tail gas 20 is bypassed the means for Claus tail gas oxidation 32 and combined with the hot off gas 34 from the means for Claus tail gas oxidation in a gas mixing point just downstream the means for Claus tail gas oxidation. This reduces the amount of fuel gas 68 needed for the means for Claus tail gas oxidation to maintain a sufficiently high temperature. The combined means for Claus tail gas oxidation off gas and bypassed Claus tail gas must have a mixed gas temperature in excess of 400° C. to ensure homogeneous (i.e. gas phase) oxidation of H.sub.2S. To ensure complete oxidation of “difficult” species such as COS and CO, an optional oxidation catalyst 35 can be installed between the gas mixing point and inlet to the SO.sub.2 converter 40. To ensure optimal control of the temperature to the oxidation catalyst, a waste heat boiler or any other heat exchanger can be installed between the gas mixing point and inlet to the oxidation catalyst. The oxidation catalyst typically comprises a noble metal such as Pt or Pd.
(23) In a further embodiment the gas comprising oxygen 72 may be pure oxygen or atmospheric air enriched in oxygen, such that it comprises less than 50%, 20%, 10% or even 1% N.sub.2+Ar.
EXAMPLES 1-3
(24) Three examples have been investigated by process modelling of a typical Claus feed, which includes hydrocarbons, without immediate relevance to the present invention.
(25) The feedstock gas (2), is a rich H.sub.2S gas from a refinery and has the following composition:
(26) Feedstock gas flow: 1593 Nm.sup.3/h
(27) H.sub.2S concentration: 91.6 vol %
(28) H.sub.2O concentration: 3.7 vol %
(29) H.sub.2 concentration: 1.9 vol %
(30) CO.sub.2 concentration: 2.8 vol %
(31) Example 1 relates to a process as illustrated in
(32) Example 2 relates to a process as illustrated in
(33) Example 3 relates to a process according to the prior art as illustrated in
(34) It is clear from the above examples, that integration of the Claus process and the WSA® process, significant equipment cost savings are possible. The integration may avoid the requirement of a combustor, and in addition the number of Claus stages may also be reduced.
EXAMPLES 4-7
(35) Four further examples have been analyzed for the process shown in
(36) These examples are based on the following feedstock gases:
(37) Feed stock gas rich in H.sub.2S (stream 2 in
(38) Total gas flow: 8190 Nm.sup.3/h
(39) H.sub.2S concentration: 94 vol %
(40) H.sub.2O concentration: 6 vol %
(41) The rich H.sub.2S gas is typical for refineries, and will also contain varying amounts of light hydrocarbons.
(42) Feed stock gas rich in H.sub.2S and NH.sub.3 (stream 70 in
(43) Total gas flow: 3669 Nm.sup.3/h
(44) H.sub.2S concentration: 28 vol %
(45) NH.sub.3 concentration: 45 vol %
(46) H.sub.2O concentration: 27 vol %
(47) These streams comprising H.sub.2S and NH.sub.3 are typically waste gases from so-called sour water strippers and recognized as SWS-gases. They may also contain varying amounts of light hydrocarbons.
(48) The fuel gas is a light hydrocarbon mixture (primarily CH.sub.4), with a lower heating value of 12,200 kcal/Nm.sup.3.
(49) Feed streams, combustion air and Claus tail gas are preheated to the extent possible by utilizing heat evolved in the combined Claus+sulfuric acid processes.
(50) In these examples the Claus process operates with 94-95% recovery of sulfur from the feed, i.e. can be a well operated Claus plant with only 2 catalytic stages.
EXAMPLE 4: SEQUENTIAL CLAUS+SULFURIC ACID PROCESS ACCORDING TO PRIOR ART
(51) In example 4 all feed streams are treated in the Claus process, providing a stream of 11.7 t/h elemental sulfur and a Claus tail gas comprising ˜5% of the S in the feed gases. In the means for Claus tail gas oxidation, the sulfur species present in the Claus tail gas are oxidized and fuel gas is provided to maintain a combustor temperature of 1,000° C., such that all reduced species, such as CO, COS, H.sub.2, H.sub.2S, S.sub.X and CS.sub.2, are fully oxidized to CO.sub.2, H.sub.2O and SO.sub.2.
(52) The production of concentration sulfuric acid is 2.4 t/h, calculated as 100% w/w H.sub.2SO.sub.4.
(53) The total sulfur and sulfuric acid recovery is >99.9% of the S in the feed, in compliance with even strict environmental legislation.
EXAMPLE 5, RECYCLE OF H.SUB.2.SO.SUB.4 .TO CLAUS REACTION FURNACE
(54) In this example H.sub.2SO.sub.4 is not desired as a product and the entire acid production from the sulfuric acid process is recycled to the Claus reaction furnace. The amount of H.sub.2SO.sub.4 recycle corresponds to ˜6% of the total S in the feed streams.
(55) The total elemental sulfur product flow is now equal to the S in the feed streams, corresponding to 107% of the base case as described in example 4.
(56) The temperature in the Claus reaction furnace decreases by −200° C. due to the evaporation and decomposition of the H.sub.2SO.sub.4, but the temperature is still well above the minimum for complete burnout of hydrocarbons and NH.sub.3. No fuel gas is needed in the Claus reaction furnace.
(57) As H.sub.2SO.sub.4 is an excellent O.sub.2 carrier, the combustion air requirements decrease and thus the process gas volume decreases as the flow of inert N.sub.2 decreases. Overall the process gas flow out of the Claus reaction furnace decreases to 94% of the base flow and the process gas flow out of the means for Claus tail gas oxidation decreases to 93% due to this reduction in N.sub.2 flow. As less process gas needs to be heated to 1,000° C. in the means for Claus tail gas oxidation, the fuel gas consumption is only 92% of the base case.
(58) The benefit of recycling H.sub.2SO.sub.4 has been found surprisingly high as not only has the sulfur forming capacity of the Claus plant increased by 7% but at the same time the process gas volume has been decreased by 6-7%. This corresponds to a Claus plant capacity increase of ˜15%, provided that the process gas flow is at 100% of the base case.
EXAMPLE 6, RECYCLE OF H.SUB.2.SO.SUB.4 .TO CLAUS REACTION FURNACE AND SWS GAS BYPASS TO MEANS FOR CLAUS TAIL GAS OXIDATION
(59) In this example, fuel gas consumption in the means for Claus tail gas oxidation has been minimized by bypassing a fraction of the SWS gas to the means for Claus tail gas oxidation. The SWS gas has a high heating value and can easily act as a fuel gas. The concentrated H.sub.2S feed gas could also have been used, but since the SWS gas can be problematic in the Claus process and is unproblematic in the WSA® process, the bypassing of SWS gas has greater benefits than bypassing the H.sub.2S gas. Process gas wise there will also be a reduction in gas volume as the NH.sub.3 in the SWS gas will increase the process gas volume in the Claus process due to the oxygen (air) requirements for combustion of NH.sub.3 to N.sub.2 and H.sub.2O.
(60) The amount of SWS gas recycled is adjusted such that 1,000° C. is achieved in the means for Claus tail gas oxidation, ensuring complete burnout of reduced species from the Claus tail gas, such as H.sub.2S, COS, CO, H.sub.2, S.sub.X and CS.sub.2.
(61) Since the fuel gas in the means for Claus tail gas oxidation now contains H.sub.2S, the H.sub.2SO.sub.4 production will increase, now accounting for ˜13% of the S in the feed streams. This large amount of sulfuric acid recycle result in a significant reduction in Claus reaction furnace temperature.
(62) With proper feed stream preheating it is still possible to achieve sufficiently high temperature in the Claus reaction furnace without needing support fuel.
(63) The effect on the size of the Claus process is substantial: the process gas volume is reduced to 65% of the base case, still with 107% elemental sulfur production. This process gas volume reduction can be either used for capacity boosting of an existing plant or significant cost reduction of a new plant.
(64) Also the sulfuric acid plant will become smaller as the process gas flow is only 90% of the base case flow. This is surprising as the H.sub.2SO.sub.4 production has been more than doubled compared to the base case, but it is mainly due to the large reduction in Claus tail gas flow.
(65) What is most remarkable is the reduction in fuel gas consumption that is now only 16% of the base case flow, contributing to a significantly lower operational cost of the integrated Claus+sulfuric acid process.
EXAMPLE 7, RECYCLE OF H.SUB.2.SO.SUB.4 .AND COMPLETE BYPASS OF SWS GAS TO MEANS FOR CLAUS TAIL GAS OXIDATION
(66) This example focus on the complete elimination of the SWS gas to the Claus plant, ensuring that ammonia salt formation in the sulfur condensers is impossible and thus decreases the risk of failure of the Claus plant.
(67) The process gas flow out of the Claus reaction furnace is 69% of the base case, but a little higher compared to example 6 where only a fraction of the SWS gas is bypassed. The increase in process gas flow is due to requirement of fuel gas addition to the Claus reaction furnace to maintain the high operating temperature.
(68) The H.sub.2SO.sub.4 production in the WSA® plant has now increased to 17% of the S in the feed gases, recycling of the entire production now quenches the Claus reaction furnace temperature to an extent where fuel gas is required. The process gas from the means for Claus tail gas oxidation has increased to 107% of the base case, due to the increased sulfur feed to the sulfuric acid plant.
(69) Even if fuel gas is needed in the Claus reaction furnace, the total flow of fuel gas is only 41% of the base case.
(70) From a plant size and operational cost point of view, this example seems less optimal than example 6, i.e. there is an optimum of H.sub.2SO.sub.4 recycle ratio which depends on the actual feed gas flows and compositions. Bypassing even more feed stock gas will result in an increased sulfuric acid production, which will quench the Claus reaction furnace even more which again will require more fuel gas and therefore the Claus tail gas flow will increase.
(71) For the feed gas compositions and flows described above, the optimum with regard to plant sizes and fuel consumption is with a H.sub.2SO.sub.4 recycle flow between 13% and 17% of the S feed in the feed streams.
(72) In general, the optimal feed stock gas bypass is close to the point where the Claus reaction furnace operates at the minimum allowable temperature, i.e. the feed stock can be bypassed to produce more sulfuric acid until the Claus reaction furnace temperature reaches the limit for thermal destruction of hydrocarbons and sulfuric acid. Increasing the feed stock bypass ratio will reduce the fuel gas need in the means for Claus tail gas oxidation, but will increase the fuel gas consumption in the Claus reaction furnace by a much larger ratio as the fuel gas in the Claus reaction furnace need to evaporate and decompose the sulfuric acid and heat up the process gas, whereas in the means for Claus tail gas oxidation only heating up of process gas is required.
(73) For a feed stock gas with e.g. 50 vol % H.sub.2S, the optimal H.sub.2SO.sub.4 recycle flow is ˜7% of the S feed in the feed stream. The acid gas bypass to the means for Claus tail gas oxidation is only 2% as the relatively low H.sub.2S concentration result in a low temperature in the Claus reaction furnace and thus the sulfuric acid will quickly reduce the temperature and require fuel gas addition in the Claus reaction furnace. Using O.sub.2 enriched air in the Claus reaction furnace will allow for a higher H.sub.2SO.sub.4 recycle flow.
EXAMPLE 8, RECYCLE OF H.SUB.2.SO.SUB.4., BYPASS OF SWS GAS TO MEANS FOR CLAUS TAIL GAS OXIDATION AND USE OF O.SUB.2 .ENRICHED AIR
(74) To boost Claus plant capacity, a well-known revamp option is to install special burners which can handle enriched air with >21 vol % O.sub.2, a common O.sub.2 quality is 93-99 vol % O.sub.2.
(75) In this example an enriched air with 80 vol % O.sub.2 is used as in the Claus process, whereas atmospheric air is used in the sulfuric acid process.
(76) The effect of the enriched air is a significantly reduced process gas flow out of the Claus reaction furnace, mainly due to the reduced amount of N.sub.2 associated with the O.sub.2 flow. Also the lower process gas flow enables operation of the Claus reaction furnace without fuel addition, as less inert gas has to be heated.
(77) Since the process gas flow out of the Claus reaction furnace is now reduced to only 38% of the base case, the Claus tail gas feed to the means for Claus tail gas oxidation is also significantly decreased. The process gas out of the means for Claus tail gas oxidation is only 56% of the base case, it is relatively higher than the Claus plant flow due to the large amount of SWS gas bypass to the WSA® plant.
(78) With this layout it is possible to operate without fuel gas in both Claus and sulfuric acid processes, even with this high recycle flow of H.sub.2SO.sub.4 from the sulfuric acid process.
EXAMPLE 9, EFFECT OF H.SUB.2.SO.SUB.4 .CONCENTRATION OF THE RECYCLED SULFURIC ACID ON CLAUS PLANT OPERATION
(79) In this example the effect of sulfuric acid concentration is demonstrated by comparing with a concentrated sulfuric acid comprising 45% H.sub.2SO.sub.4.
(80) The conditions in the example correspond to those of Example 6, i.e. a fraction of SWS gas is bypassed to the means for Claus tail gas oxidation to reduce fuel gas consumption. However, as the Claus plant receives a less concentrated sulfuric, more energy in the form of SWS gas, is required in the Claus combustor for evaporation of H.sub.2SO.sub.4 and H.sub.2O. The higher SWS gas flow results in higher combustion air flow and thus a higher process gas flow. In addition to that, the water in the sulfuric acid stream also significantly increases the process gas flow; the water accounts for ˜15% of the total process gas flow (in example 6, the water from the acid stream accounts for only ˜2% of the total process gas flow).
(81) The higher process gas flow from the Claus plant requires additional energy input in the means for Claus tail gas oxidation, and as the SWS gas flow is limited due to consumption in the Claus reaction furnace, a substantial fuel gas flow is required to maintain a high temperature.
(82) Comparing the data in Table 2, it is seen that the Claus and Claus tail gas synergy is significantly reduced in example 9, when comparing with the highly concentrated sulfuric acid recycling in example 6.
(83) The amount of energy addition required for the Claus reaction furnace receiving less concentrated sulfuric acid may be reduced if the amount of acid recirculated is reduced, but this would require increased Claus process efficiency, which could mean an additional Claus conversion stage.
(84) In conclusion, Examples 4-9 demonstrate that integration of the Claus process with the WSA® or another sulfuric acid process allows optimization of the related process costs. This may involve a reduced Claus process volume and a reduced amount of support fuel. Especially if the concentration of recycled sulfuric acid is above 60%, 80% or 90% the integrated process is highly efficient.
(85) TABLE-US-00001 TABLE 1 Process calculations for a Claus + WSA ® layout as shown in FIG. 1 Example 1 Example 2 Example 3 Sulfur production 70% 100% 70% H2SO4 production 30% 0% 30% H2SO4 recycle to combustor 0% 0% Process gas to Claus reactor 6,300 Nm.sup.3/h 4,400 Nm.sup.3/h 9,700 Nm.sup.3/h Claus tail gas 11,450 Nm.sup.3/h 6,800 Nm.sup.3/h 9,200 Nm.sup.3/h Process gas to SO2 converter 4,400 Nm.sup.3/h 3,000 Nm.sup.3/h 9,600 Nm.sup.3/h
(86) TABLE-US-00002 TABLE 2 Process calculations for a Claus + WSA ® layout as shown in FIG. 3 Example Example Example Example Example Example 4 5 6 7 8 9 Claus burner air O.sub.2 content 21% 21% 21% 21% 75% 21% Sulfur production 100% 107% 107% 107% 107% 107% H2SO4 production 6% No No No No No H2SO4 recycle 0% 6% 13% 17% 13% 9% H.sub.2SO.sub.4 concentration 93% 93% 93% 93% 93% 45% Acid gas feed to Claus 100% 100% 100% 100% 100% 100% SWS gas feed to Claus 100% 100% 33% 0% 19% 79% Process gas out Claus 100% 94% 65% 69% 38% 97% reaction furnace Process gas out means for 100% 93% 90% 107% 56% 97% Claus tail gas oxidation Fuel gas consumption 100% 92% 16% 41% 0% 79%