TW200825020A - Process for the production of sulfuric acid - Google Patents

Abstract

Process of producing sulfuric acid from feed gases containing 0.1-30% SO2 comprising the steps of: (a) passing the feed gas to a first catalytic conversion step in which SO2 is oxidized to SO3over one or more catalyst beds, (b) cooling the SO3-containing gas from said first contacting step by passing said gas to an intermediate condensing stage withdrawing a gas containing unconverted SO2 and unabsorbed SO3 and withdrawing a product stream of concentrated sulfuric acid, (c) reheating said gas containing unconverted SO2and unabsorbed SO3, (d) passing the gas from step (c) to a second catalytic conversion step, in which unconverted SO2 is oxidized to SO3 over one or more catalyst beds, (e) cooling the gas from step (d) to a temperature of 0 to 100 DEG C above the acid dew point of said gas, (f) passing the gas from step (e) with a molar ratio of H2O to SO3 of at least 1.05 calculated under the assumption that SO3 is not hydrated to H2SO4, and acid dew point of below about 240 DEG C to a final wet condensing stage, in which the remaining sulfuric acid is condensed by cooling of said gas by indirect or direct heat exchange with a cooling medium, (g) providing in the gas, prior to conducting step (f), a content of 1010to 1013 solid particles per Nm3 per vol % SO3 calculated under the assumption that SO3 is not hydrated to H2SO4, (h) withdrawing from the final wet condensing stage of step (f) a stream of 70-98 wt% sulfuric acid.

Description

200825020 IX. Description of the invention: [Technical field to which the invention pertains] This is a method for preparing sulfuric acid from a sulfur dioxide feed gas. The invention relates in particular to a wet feed comprising a concentration from G1 vol% to 3% vol%, in particular from 6% to 30% by volume, and a molar ratio of H2 〇 to s〇2+s〇3 greater than one. A process for the preparation of sulfuric acid from a gas, such as a waste fuel from metallurgical operations and from a hydrogen-containing fuel such as from petrochemical alkylation, hydrogen sulfide, ammonium sulfate waste, and fossil fuels including heavy oil residues and petroleum coke. Exhaust gas. More particularly, the present invention relates to an improvement in acid management of a plant having a single wet condensation stage for the preparation of sulfuric acid after the s〇2 conversion stage, wherein the coolant in the condensation stage is a gaseous medium such as air. . [Prior Art] The preparation of a normal sulfuric acid system from an exhaust gas in a general industrial operation is carried out via a catalytic oxidation stage 'where S〇2 is converted into s〇3, followed by a hydration step of converting s〇3 into a sulfuric acid gas. Sulfuric acid is then condensed in the cooling step by indirect heat exchange with a cooling medium, typically air. U.S. Patent No. 5,198,206 discloses a process in which a gas containing S〇3 is subjected to a single wet coagulation stage with excess water to produce coagulated sulfuric acid. In this process, the sulfuric acid vapor condenses in a manner that substantially avoids the formation of fine acid mist droplets' thus facilitating acid mist filtration during contact of the gas with the high velocity filter. A small solid particle is supplied as a crystal nucleus on which sulfuric acid vapor is condensed before the start of coagulation to limit the amount of acid mist discharged. This patent further discloses the use of a synthetic feed gas in an experimental framework containing a glass tube for condensing sulfuric acid 7 200825020 where the synthesis gas has been modified to have an acid dew point of 1 8 5 〇c. The synthesis gas entering the single condensation stage corresponds to the gas normally obtained after the S02 conversion when the lean feed gas, i.e., a gas containing substantially less than 6% by volume, for example 0.1% by volume, of 802 is contained. However, in many practical situations, it is also necessary to treat a concentrated feed gas, i.e., a gas containing 6-3 0%, particularly 10-30% by volume of S02. In an apparatus having a single-chamber stagnation stage, such as in U.S. Patent No. 5,19,8,6, the need to substantially dilute the concentrated feed gas to the apparatus in air so that the acid dew point of the gas is in a single It is kept at about 26 前 before the wet condensation stage' because the higher the so2 and so3 content in the gas, the higher the acid dew point. In this manner, the acid mist emissions can be maintained at about 1 〇 2 〇 ppmv. The permeate air is diluted, for example, from a concentrated gas containing 14% by volume of S02 to a gas containing 5-6 vol% S 〇 2 to reduce its dew point to 260 ° C during the wet condensing stage. This method operates with a larger gas flow' thus requiring larger and more expensive equipment. This problem becomes more pronounced with the addition of S02 in the feed gas. Another disadvantage is that depending on the method conditions, there are still some acid mists that are condensed out. Although about 20 ppmv of acid mist emissions may be permissible now, it is expected that there will be more stringent environmental regulations in the near future, which will require even lower 5_10 ppmv emissions or even less than 5 ppmv. In particular, it comes from a volume of 6 vol% to 3 Torr. /. , especially the acid mist discharge of a single wet condensing device of 1 〇 vol% to 3 〇 vol% S〇2, which cannot be diluted to 26 by the air (the acid dew point is kept below 1 〇_2) 〇ppmv H2S04 〇200825020 It is therefore desirable to be able to supply an acid dew point below 26 〇t to the feed gas to the wet condensing stage without the need for substantial air dilution of the s〇2 containing feed gas At the same time, an acid mist discharge of about 20 ppmv is achieved according to the current acid mist emission requirement. It is also desirable to provide a method for preparing sulfuric acid from a feed gas containing s〇2 without the need for the feed gas. Substantial air dilution while achieving acid mist emissions of 5-10 ppmv or less. Another disadvantage of the method with a single wet condensation stage is the equilibrium limit of s〇2 conversion. Even with the most active commercial s〇 2 Oxidation catalyst, depending on the concentration of 〇2 in the gas, the maximum total s〇2 conversion rate is limited to 99·5·99·7%. For higher conversion rates, it is necessary to include the use of, for example, H202 or Expensive exhaust gas cleaning of NaOH. For example, air will contain 8_ The 9 vol% S 〇 2 feed gas is diluted into a gas containing 5-6 vol% of S02. In the catalytic converter upstream of the condensing stage, the equilibrium conversion rate of s 〇 2 to s 〇 3 at 380 ° C is only Increased from 99.5 to 99.7%, which does not meet the s〇2 conversion rate requirement of more than 99 7% today. It has been known for many years to increase S〇2 to s by introducing a second absorbent before the final conversion stage. Conversion rate of 3, but the final absorption stage has been normally carried out under dry conditions, wherein the molar ratio of S〇2 + S〇3 to water in the feed gas sent to the S02 converter is greater than i. For example, U.S. Patent No. 4,368,183 discloses a wet/dry process for the preparation of concentrated sulfuric acid using an intermediate absorption stage. The S〇2-containing gas system is catalytically converted to SO in a first contacting stage in a s〇2 converter. The gas containing s〇3 and the water vapor (in which the molar ratio of water to S〇3 is less than 1) is passed to an absorption stage containing 9 200825020 in Venturi, in which sulfuric acid is produced. The intermediate stage of the dry exit gas returns to the so, converter, so that the residual s〇2 is in the second contact stage Catalytically converted to s〇3, and finally passed to the terminal absorbent, wherein in the dry state, the final sulfuric acid preparation is carried out in a substantially SO2-free gas. Therefore, this method can treat S02+S03 to water. a feed gas having an ear ratio greater than about 1, whereby the gas system exiting the intermediate absorption tower is dried by sulfuric acid. For a feed gas having more molar water than S02+S03, from The gas coming out of the intermediate absorption stage contains water vapor, which condenses into an acid mist in the final absorption tower, which is difficult to remove in an economical manner. What is desired is that it can be treated to contain a molar compared to S〇2 + S〇3 Excessive spa gas feed gas and still capable of producing greater than 98% by weight of concentrated sulfuric acid, as this moist feed gas is common in industrial operations, such as from sulfur burners, metallurgical operations such as ore roasting, and from hydrogen-containing fuels such as Combustion of spent acid from alkylation of petrochemicals, hydrogen sulfide, ammonium sulfate waste, and fossil fuels including heavy oil residues and petroleum coke. It is especially desirable to treat these gases while properly handling the more stringent requirements for S〇2 conversion rates greater than 99.7% and acid mist emissions of 5_1〇 ppmv or less. SUMMARY OF THE INVENTION Therefore, the object of the present invention is to provide a feed gas from 〇% by volume to 〇3 vol% S 〇 2, particularly a concentrated feed gas containing 6 vol% to 30 vol% 8 〇 2 A process for preparing concentrated sulfuric acid which allows the gas entering the final wet-breaking stage to have an acid dew point below 260 ° C while achieving the now required acid mist discharge of about 20 PPmv without relying on the concentrated feed gas 200825020 Substantial air dilution. The object of the present invention is also to provide a method for preparing n酉夂 from a concentrated feed gas containing (M iL 30% by volume of S〇2: a feed gas, in particular, containing 6 to 3 vol% s〇2, It can achieve more stringent acid mist emission requirements, ie 5 - 1 〇 ppmv or less than 5 ppmv without relying on the substantial air dilution of the concentrated feed gas. Another goal of this is to provide a slave volume. %至Μ Volume X) S02 feed gas, in particular a concentrated feed gas containing 6 vol% to vol% s 〇 2 to prepare a solution of greater than 98% by weight of concentrated sulfuric acid, wherein the S02 conversion rate is greater than 99.5% or Even greater than 99.7% while avoiding substantial air dilution of the concentrated feed gas. These and other objects are achieved by the method of the present invention. According to the present invention, there is provided a process for the preparation of sulfuric acid from a feed gas comprising 〇1_3〇%s〇2, comprising the steps of: U) passing the feed gas to a first catalytic conversion step, wherein the s〇2 system Is oxidized to s〇3 on one or more catalyst beds; (b) cooling the gas by passing the s〇3 gas from the first contacting step to an intermediate condensation stage, extracting unconverted s〇2 And the unabsorbed gas of S〇3 and the concentrated concentrated sulfuric acid product stream; (C) reheating the gas containing unconverted S〇2 and unabsorbed s〇3; (d) from step (C) The gas passes to a second catalytic conversion step in which unconverted s〇2 is oxidized to s〇3 on one or more catalyst beds; (e) cooling the gas from step (d) to the gas The temperature above the acid dew point to 100 ° C; 11 200825020 (f) Let the gas from step (e) pass to the final wet condensation stage, the gas is calculated under the assumption that S〇3 does not synthesize H2S〇4 The molar ratio of h20 to so3 is at least 1.05 and the acid dew point is less than about 240 ° C. In this stage, residual sulfuric acid is used by the cooling medium. Indirect or direct heat exchange to cool the gas to condense; (g) Before the step (f), provide 8 3 3 〇 to 10 i 3 solid particles per standard cubic meter per volume of the standard. The content, which is calculated under the assumption that s〇3 does not synthesize H2S042; (h) Extract 70-98% by weight of sulfuric acid stream from the last wet condensation stage of step (f). We have found that the acid mist emission value from a concentrated gas plant (containing about 6% to 30% 'especially 1% by volume to 3% by volume of s〇2 gas) cannot always remain below 10-20 H2S04 of ppmv, because of the acid mist control window defined by the number of solid particles used to capture the crystal nucleus of HjO4 and added to the gas before the final condensation stage, it will narrow as the acid dew point of the gas increases And the acid dew point above 240 ° C will be particularly intensely narrowed. It has been recognized that the minimum acid mist emissions from the final condenser increase as the sulfuric acid dew point of the feed gas entering the final condenser increases, and if the dew point remains below 260 ° C, preferably below At 250 ° C, and more preferably below 240 ° C, acid mist emissions can be kept below 5_10 ppmv. More specifically, we have found that by condensing sulfuric acid in the second stage, the acid dew point of the feed gas to the final wet condenser can be kept low, normally below 240 ° C, for example 220 ° C, Therefore, it is possible to expand the acid mist control window in the final wet condensation 12 200825020, so that the acid mist control is easy and the emission can be kept below Η) ppmv' or even less than 5 ppmvi. The upper portion is added and used as a solid particle for capturing the crystal nucleus for sulfuric acid, and the window can be expanded up to about an order of magnitude. For example, in the absence of an intermediate absorber 'there is already in the gas of the most condensed condenser, the SO 2 gas is diluted with air to the equivalent of Xiao 26 (the rc dew point of 5_6 lake 2) can be finally The window of the coagulator upstream to hold the acid mist at a solid particle below 5 PPmv will be closed, ie the addition of this granule will not hinder the formation of acid mist greater than 5 ppmv. The gas in the condenser has been used to dilute the 纟s〇2 gas to about 25 generations of dew point', which is equivalent to the window of solid particles that can be added upstream of the last fisher condenser when it is about 3.5 vol. A single individual value of about 2·2 Χίο6 particles per standard cubic centimeter (under the assumption that s〇3 does not synthesize H2S〇4. Ten W) is turned on. When the gas entering the final wet condenser has an acid of about 2201 The dew point, equivalent to the S02-containing gas that is strongly diluted to about 0.8% by volume of S02, will increase the window of particle addition required to maintain acid mist emissions below 5 ppmv to a wide range. With the present invention, acid mist control By lowering the final condensation stage The acid dew point of the gas is promoted without substantial air dilution. The humid feed gas of H2〇 to S〇2+s〇3 with a molar ratio greater than i can be treated in the double condensation method, typically 99 9_99 99% S02 conversion rate, while maintaining acid mist emissions at 5-1 () ppmv or less than 5 ppmv. It is to be understood that the gas entering the final condensation stage has a molar ratio of H2 〇 to S03 of at least 1.05, preferably at least Wet gas of 1;1. According to the invention, the method can also be provided with a dry feed gas, that is, a gas having a molar ratio of less than 1 to 12 200825020 S〇2+S〇3 in order to enter the middle The gas in the condensation stage will have a molar ratio of HW to s〇2+s〇3 below 1, while

Water is added before the final coagulation stage, preferably after the second catalytic conversion step in which the unconverted s Q is oxidized to S〇3 on one or more catalyst beds, so that the gas entering the final condensation stage will Has a molar ratio of H2〇 to S〇3 greater than 1〇5, more preferably greater than 1·1. The acid strength of the product from the intermediate condensation stage increases as the temperature of the feed gas increases, but even at this point When the temperature in the feed gas of the stage is 4 〇〇〇c, the maximum acid strength does not exceed 98.4% by weight due to the water content of the feed gas. By the insufficient amount of water in the intermediate condensation stage ( HW has a molar ratio of s〇2+s〇3 less than 1) and excess water in the final condensation stage (H2〇 vs. 莫3 has a molar ratio greater than 1.05). A particularly high acid strength product stream of the intermediate condenser, ie greater than 99% by weight, while achieving an S〇2 conversion rate of 99·9 to 99.99% and maintaining acid mist emissions at or below 5 ppmv %You add water to the method of selecting the gas to provide a disaster in the gas. Water may also be passed to the first catalytic conversion step (wherein ς n is oxidized from a V.., u, A S 2 in one or more catalyst beds to so; after and in the middle Condensation of the priests / one, ° ° section of the enthalpy, for example, by immediately after the gas containing S 〇 3 into the intermediate condensation stage ^ ^ ^ ^ 仅 white only I 刖 water is added to the S03 containing gas. When this situation is inconsistent with the product flow of the special southern acid strength as defined above, it is desirable. The small amount of gas is needed in the gas behind the condenser. The way to achieve the most. For the waste from the metallurgical operation 14 200825020 gas 'this water content can be increased to the desired degree by increasing the / star in the upstream aqueous gas purification equipment. In this way, in the There will be no need for a separate watering system in the sulphuric acid plant. Water can also be injected into the hot process gas of the s〇2 converter by water mist (which will evaporate rapidly at high temperatures) or by steam (in Figure 2 below) Line 23). In this way, it will be available in the gas cooler (21〇 and 211 in Figure 2) The recovered part comes from the water a heat generated by s〇3. Or 'water can be added downstream of the converter (line 221 in Figure 2). This is advantageous because the gas flow will not be in the upstream equipment because of the pound Increased by the influx of water vapor. For the combustion method containing a source of sulfur (such as elemental sulfur, used alkylated acid or Hj), water can be added to the combustion of the two gases in this way, avoiding Add potential rot problems at the location. Water can also be added directly to the combustion chamber to ensure rapid evaporation. The particles in process step (g) can be added to the gas at any stage prior to entering the final wet condensing stage, for example, The gas added to the s〇2 converter is either before step (a) or added to the gas which is passed to the middle of step (b) to condense P white & Preferably, the particles are supplied to the gas &# generated from step (e) and added to the gas stream from the SO 2 converter prior to entering the final wet condensation stage. & enables particles to be properly mixed in the gas as it flows to the final condenser, and avoids last particle loss, as they can pass through a number of different devices upstream, such as heat exchangers, intermediate spins, mouthpieces, and so2 The converter catalyst occurs and the particles have been added at any other stage prior to entering the final wet condensation stage. More preferably, the particles are immediately added downstream of the s〇2 converter, thus increasing the mixing length and time of the particles in the gas stream prior to entering the final wet condensing stage. 15 200825020 Normally there is no limit to the chemical composition of solid particles or their size so that they can be used as nucleating cores. However, they should be as small as possible so as not to cause significant contamination of the prepared sulfuric acid. The particle size (diameter) is preferably less than 1 〇 micrometer, more preferably less than 1 micrometer, such as in the range of 0_001 to 10 micrometers, such as in the range of 〇 2 to 〇 1 micrometer. Based on the assumption that each particle forms an acid droplet, it can be easily calculated that, for example, 3·2χ1〇ι particles/standard cubic meters are required to condense i% H2S in the feed gas in the form of 6 micron sulfate droplets in the feed gas. 〇4, the droplets were separated in the filtration to a concentration of 75% by weight of sulfuric acid and a density of 6 g/cm 3 . At least the range of good confidence can be inferred that for the most ideal separation of sulfuric acid droplets, the feed gas per standard cubic meter should be added to the feed gas per volume %s 〇 3 present in ι〇1〇 1 to 13 particles (calculated under the assumption that S〇3 is not hydrolyzed) The method may further comprise cooling the gas from the step (^ to the acid dew point of the gas before performing step (b). Up to 1 〇〇t, preferably 3 (rc to 40t: temperature. This avoids the risk of condensing h2S〇4 before it is separated from the gas from step (4), for example after the first catalytic conversion step of the S02 converter This may cause damage to the mechanical components in any downstream equipment that may be in contact with the flow. According to the present invention, water is supplied in the process of treating the dry so2 feed gas to provide excess water in the cesium (10) 3 gas, It is advantageously carried out by adding water to the gas after cooling the gas from step (a) and before it enters the intermediate coagulation stage. The feed enthalpy of the 而 含 含2 is integrated into 6 volumes each. 〇/〇 to 30 vol / 〇S〇 2, more preferably 10 to 3 〇 volume 4 / 虱 。. At these S0 concentration 16 200825020 degrees, the substantial air dilution benefit of avoiding the feed gas containing s 〇 2 is most obvious. In the method of the invention, the steps ( The intermediate condensation stage of b) may be carried out in a packed sulfuric acid column comprising a concentration and condensation zone by passing a gas stream containing s〇3 with a liquid sulfuric acid having a strength of 70-98% by weight (which is countercurrent to the gas containing s〇3) The contact is carried out. Therefore, the cooling of the SR-containing gas stream is carried out by direct heat exchange with liquid sulfuric acid. This type of condenser provides a convenient way to prepare 98% by weight or more of sulfuric acid, and can also be derived from another part of the process. The individual sulfuric acid stream is incorporated into the upper portion of the sulfuric acid column (intermediate condenser) and the acid is recycled back to the line. Thus, the method of the present invention may further comprise resetting 7〇_98 of step (}1). The sulphuric acid stream, i.e., the acid stream from the final condensing stage, is returned to the intermediate stage (b). The acid stream is returned to the intermediate condensing stage as compared to other ways in which the sulphuric acid stream from the final condensing stage is not passed to the intermediate condensing stage. Preferably, the acid recycle loop is capable of producing a higher concentration (greater than about 98% by weight) sulfuric acid. In some instances, the returned stream may advantageously be an acid flow of about 85% by weight sulfuric acid, such as The condition of the final coagulation stage is carried out by passing the gas containing s〇3 in the same direction as the condensed sulfuric acid, as described below. In other examples, the returned stream may be an acid stream of approximately 98% by weight sulfuric acid, Such as in the case of performing the final condensation stage by passing the S?3 containing gas with the condensed sulfuric acid countercurrently, as also described below. The intermediate condensation stage of step (b) can also be carried out in a substantially vertical tube, The cooling of the SO3 gas stream is carried out by indirect heat exchange with a cooling medium, wherein the cooling medium is a countercurrent flowing air. In a particular embodiment, the SO3-containing gas stream is countercurrent to the condensed sulfuric acid. 17 200825020 Therefore, the sulfuric acid produced in this method travels downward when it condenses in the tube wall, while the gas containing S〇3 travels in the opposite direction. It is preferred that the air flow flows countercurrently outside the tube. In this mode of operation, the normal system obtains sulfuric acid having a strength in the range of 70 to 98% by weight at the bottom of the condenser, and if necessary, an acid strength of more than 98% by weight, for example, 9 8 · 5 % by weight, possibly _ got it. The intermediate condensation stage of step (b) can also be carried out in a substantially vertical tube wherein the cooling of the S〇3 gas stream is carried out by indirect heat exchange with the cooling medium, wherein the cooling medium is a countercurrent flowing air and wherein The gas containing $ 流动 flows in the same direction as the condensed sulfuric acid. This type of condenser is particularly advantageous because it is less expensive and easier to operate than conventional counterflow condensers such as those described above. The reduced genus allows the S含3-containing gas to flow down with the sulphuric acid formed in the tube, thus eliminating the risk of possible overflow problems, which may otherwise be countercurrent to the s〇3 gas and the formed sulphuric acid stream. Encountered in the cooling tube. The overflow is a condition in which sulfuric acid which is condensed by the upward movement of the SO3-containing gas is prevented from colliding, and it causes an undesired gas pressure drop to increase the flow of air upstream of the tube in a countercurrent flow. Since the strength of the sulfuric acid at the bottom of the condenser is usually relatively thin, i.e., in the range of 70-85% by weight, it is suitable to use this type of condenser as the intermediate condensation stage, for example, when the demand for acid strength is less important. If necessary, the acid strength of more than 98% by weight can be obtained by transferring the 4 lb L of the acid strength 70-85 wt% from the intermediate coagulation stage to the Ik after one step, which can be described in U.S. Patent No. 9, _ , 364. Thus, the concentration stage proceeds advantageously in a packed column wherein hot air is passed under the column section containing an acid resistant body ’ such as a ceramic Raschig ring or saddle. In 200825020, the air leaving the top of the fill soil mixes with the s 〇 gas entering the intermediate condensing stage, while the concentrated sulphuric acid leaves at the bottom and proceeds to a flow of desired acid strength (normally greater than 98% by weight). 70% In the middle of the crucible, the cooling of the gas in the final condensation stage is preferably carried out in a vertical tube on the babe by indirect heat exchange with the cooling medium, and the medium 4 cooling medium is air. Similar to the condition of the intermediate condensation stage, in a particular embodiment, the +S03 gas is countercurrent to the condensed sulfuric acid. Therefore, the sulfuric acid produced in this method travels downward as it skeins in the tube wall, while the SO3-containing gas travels upward in one or more vertical tubes. It is preferred that air flows countercurrently outside the tube. By coagulation in this form, sulfuric acid having a strength in the range of 70 to 98% by weight in the bottom of the condenser is normally obtained, and if necessary, an acid strength of more than 98% by weight, for example, 98,5% by weight, is also possible. In another embodiment, the S03-containing gas flows in the same direction as the condensed sulfuric acid. The formation of sulphuric acid according to this type of condenser is particularly advantageous' because it is less expensive and easier to handle than conventional counterflow condensers as described above. The condenser allows the S含s-containing gas to flow down with the sulfuric acid formed in the tube, thus eliminating the risk of possible flooding problems, which may otherwise flow countercurrent to the sulfuric acid stream formed by the S〇3 containing gas. Encountered in the cooled tube. It is preferred that air flows countercurrently outside the tube. Since the strength of the sulphuric acid at the bottom of the condenser is usually relatively thin, that is, in the range of 70-85 wt/◦, it is appropriate to use this type of condenser as the final condensation stage'. For example, when the acid strength requirement is less important, or It is expected that the desired acid strength can still be obtained by returning 70-85% by weight of the acid gas stream to the intermediate condensation stage. Thus, it will be appreciated that with the present invention, the final condensation stage can be carried out in a relatively inexpensive and normal and relatively easy-to-operate apparatus in which the confluent gas containing the S〇3 gas and the condensed sulfuric acid stream is countercurrent to flow in 19 200825020. The lower acid strength obtained in the final condensation stage is compensated by returning the acid stream to the intermediate condensation stage, preferably in a packed sulfuric acid column. If desired, an acid strength of greater than 98% by weight can be obtained by further passing sulfuric acid from the final coagulation stage and having an acid strength of 70-85% by weight to the subsequent concentration stage, as described in U.S. Patent No. 9,090,364. Thus, the concentration stage can advantageously be carried out in a packed column wherein hot air is passed under the column section containing the acid resistant body filler, such as a ceramic Raschig ring or saddle. At the end of the filling tower, the air system leaving the junction and the s〇3 gas entering the final condensation stage are combined. At the same time, the concentrated sulfuric acid leaves at the bottom and is further cooled to have the desired acid strength (normally greater than 98% by weight). flow. Cooling of the gas during the final condensation stage can also be carried out in a packed sulfuric acid column by direct heat exchange with recycled sulfuric acid. Accordingly, the present invention also includes a method in which the remaining 4 &C in a gas stream containing SO; and HjO4 vapor is condensed by cooling the gas in the final condensation stage by using circulating sulfuric acid in a sulfuric acid column. . Preferably, the sulfuric acid is passed through a concentration or absorption zone containing the filler body in a countercurrent flow to the gas stream containing the S03 and ΗΑ〇4 vapors, thereby absorbing H2s〇4 in the recycled sulfuric acid. For example, it is described in U.S. Patent No. 4,348,373. [Embodiment] Detailed Description of Preferred Embodiments We have found that the higher the acid dew point of the rolled body entering the condensed state, the narrower the acid mist control is from the mouth, and within this time, the addition of the six-day core can still make Acid mist row 20 200825020 put below 5 ppmv. This is illustrated by the figure i, which shows an example of a gas containing an excess of water relative to S〇3 in the final wet coagulation stage = % s 〇 3 vol% + 7) and wherein the temperature of the gas is Its acid dew point is above 35t:. A concentrated gas or any other concentrated gas from the chemical operation of spent acid, which can be air-diluted to about 8% by volume to 9% by volume of S〇2 in S〇2 conversion (equivalent to #8〇2 converter) 8-9 vol% of H2S〇4(g) in the gas in the coagulation stage, and having a dew point of about 27n: is outside the range of the acid mist control window. At this acid dew point, acid mist emissions from the final wet condenser can only be controlled by adding particles in a very narrow range of 3 〇 · 1 〇 6-3.2 · 1 〇 6 particles per standard cubic centimeter. 〇_9〇PPmv. This problem can be mitigated by vigorously diluting the gas in air to form a gas containing 5-6 vol% S〇2 (its dew point is about 26 〇t:), but the gas will still be outside the range of the acid mist control window. . At this acid dew point, the acid mist discharge from the final house reducer can only be controlled at 10 by adding particles in a wide range, normally 2.0 1 / 6 - 2.7 · 106 particles per standard cubic centimeter. -20 ppmv. Below the acid dew point of about 250 ° C, the acid mist control window will open. At this waypoint 'the window is still very narrow (only in the last wet condensation stage before the addition of particles in a very narrow range, the acid mist emissions can be maintained below 5 ppmv) and in the air A significant dilution of the so2 containing gas, as mentioned above, is not appropriate due to the need to operate a larger capacity device. By the present invention, there is provided a method wherein the moist gas entering the final coagulation stage has an acid dew point of less than about 240 ° C, allowing a window of solid particles to be added upstream of the final condenser to cause the acid mist to be less than 5 ppmv to be 21 200825020 Opening and selective expansion, for example, from air equivalent to entering the final wet condenser to air diluted to approximately 24 (each standard cubic centimeter of rc dew point 8·8 · 1〇6-1·8 · 106 Particles (to a wide range of standard cubic centimeters per square centimeter · 2 · 106-1 · 〇 · 1 〇 6 particles, wherein the acid dew point is 22 〇〇 c. The supply of particles used as a solidified nucleus can be used Means for carrying out, as disclosed in, for example, U.S. Patent No. 5,198,2,6, which is owned by the present invention, by the addition of a gas containing or containing more than two carbon atoms from an electric arc or fusion welding The smoke generated by the 5 o'clock oxygen oil is carried out. The gas entering the final wet condensation stage step is preferably heated from the inlet temperature τΑ1 to the outlet temperature Ta2, which satisfies the following conditions: TA2 > One (75 - 4 · S - 2 · W) · (1 +hi/hJ (1) where D8 and T! are expressed by t; \ is the temperature of the gas entering the final condensation stage; s is so3 vol%; and W is H2 〇 vol%, so3 in the gas Calculated under the assumption of hydration; hi is the heat transfer coefficient inside the pipe, expressed in watts per square meter / κ; and h° is the heat transfer coefficient outside the pipe, expressed in watts per square meter / Κ. 2 shows a flow chart of a double-condensation wet sulfuric acid process in which 18,000 standard cubic meters per hour of feed gas stream 21 containing feed gases of s〇2, 3% and 23% H2〇 is used. It is diluted by the preheated air indicated by the gas stream 22 by means of the 9620 standard: square & scale/small to provide oxygen with molar ratio /2/S〇2==i. The resulting pass to the reactor 24 (s The feed gas 23 of the 〇2 conversion 22 200825020 comprises 9.1% S 〇 2 which is converted to s 〇 3 on three adiabatic catalytic beds 25, 26, 27 with intermediate bed coolers 28 and 29. The SO3 gas is then cooled in heat exchangers 210 and 211 to a temperature of 3 m to produce a gas stream 212 which is sufficiently above its acid dew point (278 ° C). In the intermediate condensation column 2 13 ' The sulfuric acid component of the gas is condensed to a final product of 98.3% by weight in stream 2 14. The intermediate condenser 2 1 3 is provided at its bottom 2 15 with an adiabatic concentrated zone in which the acid system is from 96% by weight. Concentrated to greater than 98% by weight and provided with a cooled condensed zone at its upper portion 216 having an acid recycle 217. Preferably, the S?3-containing gas 2 12 from the first contacting stage is introduced into the intermediate condenser The concentrated area of 213 is 2 1 5 . This allows a relatively high temperature, normally about 300-320 ° C, to be maintained at the bottom of the intermediate condenser, i.e., in the concentrated zone, thereby producing a relatively high concentration, i.e., 98.3 〇 / 重量 by weight of sulfuric acid. The gas leaves the intermediate condenser 213 at a flow rate of 2 1 8 at 150 °C and contains 0.42% S02, 0.38% H2S04 vapor and possibly some sulfuric acid mist. The gas is reheated to 375t in heat exchanger 210: the acid mist is evaporated. The remaining S02 in the gas stream 2 19 is converted over the fourth catalyst bed 220. This results in a total SO: conversion rate of up to 99.95%. The outlet gas 221 is cooled in the boiler 222 from about 390 ° C to 260 ° C. It is carried by the gas stream 221 with about 0.1% by volume of S03, 0.7 volume. /〇H2S04, 8% H20 and residual sulfuric acid vapor at about 220 ° C acid dew point, condensed in a standard air-cooled wet sulfuric acid condenser 223, wherein the condenser has: an air-cooled vertical glass tube having a countercurrent passage containing S03 gas and condensed sulfuric acid; a coil for improving heat transfer; a tube demister; and an acid mist controlled by previously adding a condensed crystal nucleus. The glass tube is provided with an acid mist filter for separating sulfuric acid droplets from the gas in 23 200825020. The filter is advantageously mounted adjacent to, at or above the top end of each of the glass tubes in a gas-tight connection thereto, whereby the droplets flow back down through the tubes. The acid mist filter in each tube is preferably a high speed filter having a gas velocity of 1 to 7 meters per second and comprising filaments or fibers having a diameter of from 5 mm to 5 mm. The fibers or filaments are present in an amount, thickness and morphology that ensures a pressure drop of from 2 mbar to 20 mbar through the filter. Acid control can be achieved by providing a control system in which the acid mist meter in the gas stream exiting the final fishing condensation stage is adapted to the process computer. A signal from the acid mist meter indicating an acid mist value of less than 1 〇 ppmv, preferably about 5 ppmv, is received by the process computer for adjustment as a reduced crystalline solid particle to, for example, from the last fish as described above The addition of a flue form of hydrocarbon combustion upstream of the condensation stage. Thus, the rate of addition of particles which act as a coagulated nucleus is controlled according to known principles by means of a control loop comprising a continuously operating acid mist meter located downstream of the final wet coagulator. With the present invention, the automatic control system for particle addition is greatly enhanced because the particles of the wider window (the number of particles) can be added to the gas stream prior to the final spinning stage without the risk of a sudden increase in the acid mist value. In order to safely maintain low acid mist emissions at any time, such as 5 ppmv or less. The concentrated sulfuric acid having a strength of 9 5 · 5 wt% leaves the last suspected state 2 2 3 ' with a flow of 2 2 4 at 2 2 0 and enters the recirculation system 2 1 7 of the intermediate condenser 2 13 . 2 5 C cold part air flow 2 2 5 is used as a cooling medium and leaves the final condenser at 2 〇 〇 c. The gas from the final condenser exits at about 100 ° C with an acid mist content of about 5 ppmv and is then directed to the smoke 24 200825020 (not shown). Table 1 summarizes the relevant flow composition of the method of Figure 2. The total s〇2 conversion rate obtainable in the s〇2 converter 24 can be determined by the concentration of S〇2+H2S04 from the intermediate condenser 213 and the inlet temperature to the fourth bed 220. If the gas is cooled to a lower temperature in the condensation zone 21 of the intermediate condenser 2 13 , the s〇 2 conversion rate may increase or the contact volume in the bed 220 may decrease. The acid mist emissions from the final condenser 223 are low, typically about 5 ppmv, and are easily controlled due to the low dew point of the feed gas 221 (which is about 220 °C). Small particles that act as nucleuses can be added to the gas as a fumes of smoke or solid particles before the gas flows into the final condenser, in an amount equivalent to 103% by volume per standard cubic meter of gas in the gas stream at the final condenser inlet. Up to 13 particles (calculated under the assumption that SO3 is not hydrolyzed to h2S04). Low acid mist emissions indicate a significant advantage over normal conditions, which contain 6-30 volumes of 〇/〇S02 'specially 10-30% by volume of S02 concentrated feed gas, which is in s〇2 conversion Thereafter, it is treated by a single coagulation stage, whereby the feed gas reaching the coagulation stage has been air-diluted to 5-6 vol% of S02, resulting in an acid dew point of 260 ° C and an acid mist discharge of more than 5 ppmv. 40 bar g of saturated vapor can be produced in steel furnaces 211 and 222. In order to control the temperature in the S〇2 converter, the intermediate bed coolers 28 and 29 are preferably steam superheaters. The dilution air 22 can be taken at about 200. (: the heat leaving the final condenser cooling air flow 225, but an additional load must be provided to heat the air to an inlet temperature of the S02 converter 24 of 410 ° C. If the hot cooling air 225 can be used as a combustion, for example Combustion air recirculation in the incineration step prior to the S〇2 converter in an apparatus for the burning of acid or h2S or sulphur 25 200825020 Only "recycling the heat transferred in the final condenser 223. Reheating the acid mist comprising waste air 218 from the intermediate condenser in heat exchanger 210 may require heating in a two-step, acid-resistant heat exchanger, adjacent to the intermediate condenser, mounted at For example, in the top end of the intermediate condenser 2 13 , which causes the gas temperature to be above the dew point; and a second heat exchanger: the temperature of the gas stream 219 is equal to 375 C before re-entering the so2 converter 24. The latter may include - Bypass, in order to control the temperature to 375 C or, the first heating step can be carried out by recycling the hot gas. Furthermore, a heat transfer salt can be used as an intermediate for future heat transfer to the special process for cooling. Material gas a vapor system in which the helium gas from the boiler is too small to be supplied to the intermediate bed cooler. The intermediate condenser 213 is preferably a sulfuric acid column containing a concentrated and condensed zone, wherein the liquid sulfuric acid contains s〇s and H2S〇 The vapour gas stream travels countercurrently through a concentration or absorption zone comprising a filler body, whereby H2S4 is absorbed in the recycled sulfuric acid, as described, for example, in U.S. Patent No. 4,3,48,373. The condenser 213 can also be constructed as a brick lining tower containing a ceramic pottery filler, such as a Torus saddle for an example of a 2 mm diameter vessel. Further, as described above, the intermediate condenser can be The same type of seat acid coagulator is subsequently eliminated, wherein the final coagulation is provided with an air-cooled glass tube. The exhaust stream 218 from the intermediate condenser 213 may contain some acid mist and is not present. The acid mist of up to 1〇〇〇ppmv is acceptable depending on the total S〇2 conversion rate required in the preparation (the conversion rate in the fourth bed 220 is determined by the concentration of s〇2+s〇3). The teaching of Patent No. 4,348,373, if satisfied The following 26 200825020 heart τ's work can be used to prepare sulfuric acid intermediate condensers in the exhaust gas without substantial acid mist: Τ > 140 + 6α + β + 0.2(H) (7) where Τ is the middle The temperature of the acid to be recycled by the condenser is pc]; α is the concentration of the feed gas 212 defined by SOJHJO4 [mol%], and β is the water concentration of the feed gas 212 [mole %]; The temperature of the feed gas 212 is pc]; and Td is the dew point temperature of the feed gas 212 [.〇]. According to the formula (2), excessive acid mist emission can be avoided because the temperature D is higher than that calculated from the formula The value is 2 1 8 °C. The need for high concentrations of acid in the alkylation plant in an oil refinery requires 98.5 to 99% by weight of the sulfuric acid product. The acid strength of the product increases as the temperature of the feed gas in the gas stream 212 increases, but even at 4 〇〇c>c, the maximum acid strength in the feed gas does not exceed the water content of the feed gas 212. 98.4% by weight. As a result, it is difficult to achieve the preparation of > 98·5 wt% sulfuric acid. In the intermediate coagulation stage of the conventional wet/dry process, such as U.S. Patent No. 4,368,183, the water vapor pressure on fuming sulfuric acid, i.e., sulfuric acid containing dissolved s〇3, is very low, so it is easy to Remove ^ at this stage. However, when the gas contains an excess of water relative to sos, the s〇3 will react with water at a molar ratio of 1··1 to produce sulfuric acid. At equilibrium, the acid will absorb additional water, thus reducing its acid strength until the water vapor pressure exceeds the acid, as determined by the acid strength, and the temperature is the same as the water content in the gas. It has been found that in the double condensation method according to the present invention, if a temperature of 4 〇〇 55 (rc, preferably 5 〇〇 C) is introduced in the concentrated region at the bottom of the middle condensed star 27 200825020 tower 213, the normal air is replaced. The acid strength can be increased in the process gas of 300_320 ° C. The same feed gas conditions as in Figure 2 are shown in Figure 3. The S03 gas stream 312 from the S〇2 converter 34 is sent directly to the middle. / condensed state 3 1 3 of the condensation zone 3 丨 6 , and the acid product flows to the concentration zone 315 where it is concentrated to 98.6% by weight by contact with 500 Torr of hot air in a countercurrent manner. The air has been previously heated from 150-300 ° C in the heat exchanger 329 to 400-550 ° C, preferably 500 ° C. Thus, in a particular embodiment of the invention, the method further comprises allowing the temperature 400-55 0 °C hot air passes to the concentrated area of the intermediate condensation stage, and the s〇3 gas from the first catalytic conversion step is directly passed to the condensation zone of the intermediate condensation stage, whereby the concentrated sulfuric acid is used The hot air is manufactured in reverse contact. The summary of Table 2 is shown in the third Related Flow Composition of the Method. In another embodiment of the invention, the method further comprises dividing the intermediate condensation stage into at least one upper portion and a bottom concentration region to allow the S〇3 gas from the first catalytic conversion step Passing to the upper concentration zone of the intermediate condensation stage; and letting 400-55 (the hot air of rc pass to the bottom concentration zone, whereby concentrated sulfuric acid is produced by countercurrent contact with the hot air. Therefore, the intermediate condensation stage is Separated into at least two concentrated zones. In the first upper concentration zone, the acid from the condensation zone is concentrated from 95% by weight to 98 by contact with the S〇3 containing gas stream at a temperature of about 300 ° C to the intermediate condensation stage. 2% by weight; and in the second bottom concentration zone, wherein 450-550 ° C, preferably 50 (TC of hot air) is added, the acid is further concentrated to the desired value of 98.6% by weight. This makes for the last to 98 · 6 wt% 28 The concentration of 200825020 is only about half (standard cubic meters per hour) of the amount of hot air required in the method of Figure 3. This method is the same as The same feed gas conditions for Figure 2 or 3 are illustrated in Figure 4. The relevant flow composition is summarized in Table 3. The s〇3 gas stream 412 from the s〇2 converter 44 is sent directly to the first concentration zone 43 1. The acid product is then passed to a second concentration zone 43 where it is finally concentrated to 98.6% by weight by retro contacting with hot air at 400-550 ° C, preferably 500 ° C. The air has previously been in the heat exchanger Preheated from 150-300 ° C to 450-550 ° C, preferably 500 in 429. (: In a further embodiment of the invention, the method may further comprise from having been in the intermediate coagulation stage with sulfuric acid The exhaust stream of hot air in contact is diverted to the final condensation stage by combining the exhaust stream with the cooled S03-containing gas stream extracted from the second catalytic conversion step. Therefore, the exhaust gas from the hot air concentration zone of the intermediate condensation stage is sent to the final condensation stage. This can reduce the size of the intermediate condenser and reduce the size of one or more beds in the second contacting phase of the s〇2 converter. This illustration is illustrated in Figure 5, in which the exhaust stream 531 from the concentrated zone 532 of the intermediate condensation stage 513 is combined with the gas stream 521 from the second catalytic conversion step of the S02 converter 54 to enter the final condenser 523 with the gas stream 522. Table 4 summarizes the relevant flow compositions for this particular example of the process. The process of the present invention can also be used to upgrade a sulphuric acid plant that already includes a S02 converter and a single wet condensing stage. Then, an existing single wet condenser can be used as the final wet condenser, and the S02 converter can also be reused. In the update of existing equipment, the new intermediate condenser, the additional catalyst bed in the S02 converter and the heat recovery system were adapted to the equipment. In addition to the advantages of including low acid mist emission values, this update also has the possibility of making minor modifications in both existing and standby equipment to increase the capacity of the equipment. In the method of the present invention, the arrival of the equipment can be increased. The amount of dilute air is reduced by the same amount of gas in the (10) $ gas, so that the total flow through the device is maintained substantially constant before and after the update. EXAMPLES · Table 5 shows a comparative example of a method having an intermediate condensation stage and a final wet condensation stage according to the present invention and a method according to the prior art in which the towel s〇2 conversion step followed by the single-seat reduction stage. In the method according to the prior art comprising the (10)2 conversion stage and the single-fishing condensation stage, for the package supplied to the method, 14% by volume of the feed gas of the S〇2 is diluted with air to form an inlet at the final condensation stage. A gas dew point 26 (rc containing 5-6 vol% so2) is provided. According to the method of the present invention, corresponding to FIG. 2 and Table, compared to the prior art, no substantial air dilution is required, 1 simultaneously providing a higher S〇. 2 conversion rate and low acid mist emissions. 30 200825020

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§CN 009 ο·ε<Ν orn 00801 0 inch one inch 0 inch s odOI 00081 03⁄4 d—rosffil 200825020 Table 5 Gas flow (phase prior art. Single condensation stage 1 Γοό 明57 so2 conversion rate (%) 99.5-99.72 99 95 Acid mist emissions 10-20 ppmv __J^£_ppmv supplied to the process containing 14% by volume of 8〇2 of feed gas. This gas has been air-diluted to a 5-6% SR before entering the S〇2 converter, corresponding to Enter 5-6% H2S〇4(g) in the gas in the single condensation stage so that the acid dew point is 260 ° C. 2 There is no exhaust gas washing. [Simplified illustration] The present invention is based on the accompanying drawings. To clarify, Figure 1 shows the acid mist control window (calculated under the assumption that SO3 does not synthesize ΗΘΟ4), where less than 5 ppmv of emissions from the final seat condensation stage can enter the acid dew point of the shouting phase The function is obtained. Fig. 2 is a flow chart according to a specific embodiment of the method, wherein the intermediate condensation stage is carried out in the filling sulfur, and the final condensation stage is carried out in a vertical tube containing s〇3 gas and coagulated Gas cooling in which sulfuric acid flows countercurrently This is carried out in a condenser. Figure 3 is a flow chart of a further embodiment of the invention for increasing the strength of the sulfuric acid in the intermediate condensation stage. Figure 4 is a flow chart showing another embodiment of the invention in which the intermediate condensation stage is provided. There are two acid concentration zones. Figure 5 shows a flow chart of another specific example in which the exhaust gas from the 1 hot air condenser is sent to the final wet condensation stage. [Main component symbol description] 21 Feed gas flow 22 dilution Air 33 200825020 23 24 25 26 27 28 29 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 Feed gas reactor (so2 converter) Adiabatic catalytic bed adiabatic catalytic bed adiabatic catalytic bed intermediate bed cooler Intermediate bed cooler heat exchanger heat exchanger with so3 gas intermediate condensation tower flow bottom concentration zone upper condensation zone acid recycle system waste gas flow gas flow fourth fuel bed outlet gas boiler final condenser flow cooling air flow gas stream 34 200825020 31 33 34 312 313 314 315 316 318 321 324 326 329 41 43 44 412 414 418 421 424 426 429 430 Feed Air stream feed gas S02 converter so3 gas stream intermediate condenser flow concentration zone condensation zone exhaust gas outlet outlet gas stream gas flow heat exchanger feed gas stream feed gas so2 converter so3 gas stream exhaust gas stream outlet gas stream gas flow heat exchanger Two concentration zone 35 200825020 431 51 53 54 512 513 514 518 521 522 523 524 526 531 532 First concentration zone feed gas feed gas so2 converter so3 gas flow intermediate condensation stage flow waste gas flow gas flow last condenser flow gas exhaust Flow concentration area 36

Claims (1)

200825020 X. Patent application: 1. A method for preparing sulfuric acid from a feed gas containing 0.1-30% S02, which comprises the following steps: (a) passing the feed gas to a first catalytic conversion step, wherein so2 Oxidizing into so3 on one or more catalyst beds; (b) cooling the gas by passing the gas containing s〇3 from the first contacting step to an intermediate condensation stage, extracting unconverted S02 and not Absorbing the gas of SO3 and extracting the concentrated sulfuric acid product stream; (0 reheating the gas containing unconverted s〇2 and unabsorbed 8〇3; (sentence gas from step (c) to second catalysis a conversion step in which unconverted s〇2 is oxidized to s〇3 on one or more catalyst beds; (e) cooling the gas from step (d) to above 100 °c above the acid dew point of the gas (0) Let the step (e) have a molar ratio of H2〇 to s〇3 of at least 1〇5 (calculated under the assumption that S〇3 does not synthesize H2S〇4) and the acid dew point is less than about 24 The gas of 〇c is passed to the final wet condensation stage, wherein the cooling is performed by indirect or direct heat replacement with the cooling medium. And condense the remaining sulfuric acid; (g) before the step (f), the content of each unit of the volume of S〇3 l〇w to 10!3 solid particles per standard cubic meter is provided in the gas. S〇3 Calculated on the assumption that H2S04 is not hydrolyzed; (h) Extracting 7〇_98% by weight of the sulfuric acid stream in the final wet condensation stage of step (1). 2. The method of claim i, wherein in the step The feed gas comprising s 〇 2 in (a) is comprised of 6% by volume to 30 vol% s of concentrated gas 37 200825020. 3. The method of claim i or 2, further comprising prior to performing step (8) Cooling the gas from step (4) to a temperature above the acid dew point of the gas 〇 ° C to 100. (: The temperature of the method of claim 1 or 2, further comprising the step (g) The particles are supplied to the gas produced in step (e). 5. The method of claim i or 2, wherein the intermediate condensation stage of step (8) is in a packed sulfuric acid column comprising a concentration and condensation zone, by Containing s〇3 gas flow and intensity 70_98% by weight and containing s〇3 The body is subjected to a countercurrent flow of liquid sulfuric acid. 6. The method of claim 142, further comprising returning the 70-98 wt% sulfuric acid stream of step (h) to the intermediate coagulation stage (8). The method of claim 5, wherein the intermediate condensation stage of the step (b) is carried out in a substantially vertical tube, wherein the cooling of the s〇-containing gas stream is performed by indirect heat exchange with the cooling medium. 3 The cooling medium is a countercurrent flowing air. 〃 8_ The method of claim 3, wherein in the ten vertical officials, the gas is finally exchanged by indirect heat exchange with a cooling medium. The cooling in the condensation stage, the air flowing in the mass flow. ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Direct heat exchange is carried out. The method of claim 5, further comprising the method of allowing 38 200825020 400-550 ° C hot air to pass to the concentrated zone of the intermediate condensation stage, and allowing the S03 gas from the first catalytic conversion step Directly passing to the concentrated zone of the intermediate condensation stage, whereby concentrated sulfuric acid is produced by contacting the hot air countercurrently. 11. The method of claim 5, further comprising dividing the intermediate condensation stage into at least one upper portion and a bottom concentration region, wherein the S03-containing gas from the first catalytic conversion step is passed to the upper portion of the intermediate condensation stage The concentrated area is passed, and hot air of 400-550 ° C is passed to the bottom concentrated zone, whereby concentrated sulfuric acid is prepared by contacting the hot air countercurrently. 12. The method of claim 1, further comprising: converting the exhaust stream from hot air that has been contacted with sulfuric acid in the intermediate condensation stage by converting the exhaust stream to a second catalyst from the S02 conversion stage The step of extracting the cooled SO3-containing gas stream combines and redirects it to the final condensation stage. 13. The method of claim 11, further comprising: passing the exhaust gas from the hot air that has been in contact with the sulfuric acid in the intermediate condensation stage, by the second catalytic conversion step of the exhaust gas stream with the conversion phase from S02 The extracted cooled SO3-containing gas stream is combined and redirected to the final condensation stage.十一,圈式·· 如次页 39