FI57391C - FOERFARANDE FOER FRAMSTAELLNING AV SVAVELTRIOXID - Google Patents

Description

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Patent and Registry Office. Nlhttvlkalpwon and heard public date_

Patent and registration authorities Anattkan utligd och utl.ikrlfun publkarad 30. Ol. 80 (32) (33) (31) Requested in front of office — Begird prlorltet 10.06.69

Federal Republic of Germany Förbundsrepubliken Tyskland (DE) P 1929388.0 "(71) Bayer Aktiengesellschaft, Leverkusen, Federal Republic of Germany Förbundsreepubliken Tyskland (DE) (72) Harke Haeseler, Leverkusen, Ludwig Dorn, Möln, Cologne Leverkusen, Franz Rubs am, Leverkusen, Gerhard Heinze, Schildgen, Federal Republic of Germany Förbundsrepubliken Tyskland (DE) (7M Oy Kolster Ab (5M Process for the production of sulfur trioxide - Förfarande för framställning av svaveltrioxid (62) -Avdelad frän ansökan 1596/70 (utläggningsskrift 57088)

The invention relates to a process for the preparation of SO 2 by catalytic oxidation of SO 2 in fluidized bed and solid bed reactors, including the intermediate absorption of SO 2 formed.

In the large-scale technical production of sulfur trioxide for the catalytic production of sulfur trioxide, solid-layer contacts are used. The SO 2 -containing gases are then contacted with the catalyst masses in a known manner in two or three steps, in which case vanadium oxide contacts are mainly used. In order for the reaction to take place at a sufficient rate, the SC4-containing gases must be preheated to a temperature above 400 ° C. Especially in the case of very concentrated SC 2 -containing gases, large amounts of energy are released during fractions of a second, which must be able to be removed in a controlled manner in order to avoid overheating of the gases as well as the contact masses and the contact chamber. Temperatures well above 600 ° C must be avoided, 2 57391 to avoid damaging the contact material. Since, depending on the SC 2 and oxygen contents of the gases, the optimum equilibrium temperature is substantially lower than the above-mentioned temperature, an attempt has been made to keep the working temperature of the last contact stage as low as possible (420-460 ° C) in order to maximize the total SO 2 conversion. Especially in the first step, the degree of conversion must be small, because then the reaction rates occurring at high temperatures are more important.

To control the temperatures, the gases are cooled between different stages using heat exchange. In addition, methods are known in which the contact mass is also cooled. This can be done either by blowing cold gases into the contact chamber or also by fitting cooling systems to the contact boiler. In large production plants, the methods described above usually lead to a 98% conversion in the long run.

The yield can be increased by removing the sulfur sulfur oxide formed in between. Thus, in recent years, several sulfuric acid plants have been introduced in which the sulfur trioxide formed in the first stages is removed by sulfuric acid after about 90% pre-conversion by absorption, after which the remaining SC> 2-containing gas is reacted almost quantitatively in the final stage at relatively low temperatures. (DE Patent Publications 1,136,988 and 1,181,181). In large production plants such as those described above, the conversion is 99.6% and even higher in the long run. In the so-called double-contact plants, SC 1 -containing gases from a wide variety of sources can be treated, i.e. sulfur fuel gases, pyrite roasting gases as well as other smelting gases and gases cleaving from sulphate-containing waste products are recyclable.

Since the intermediate absorption requires additional energy compared to normal catalysis - the reaction gases of the first contact stage are cooled before the intermediate absorption and reheated to the start temperature of the last contact stage after removal of the sulfur trioxide formed in the intermediate stage. . In addition to the fact that highly concentrated gases have a beneficial effect on the thermal economy of the process in the form of higher enthalpy, the use of concentrated SO 2 -containing gases also makes the plant structures and operating modes more economical.

The above-mentioned calculations of the advantage of energy use are mainly valid only if the energy balance of the contact system as such is considered. If the energy generated in the production of SO2 is at least partially available for heating the cauldrons in the contact system, relatively dilute SO2-containing gases are also processable. However, it should be noted that as the gas volumes increase, so does the amount of heat exchanged.

It has been found that the so-called double-contact method can easily treat SO 2 -containing gases with a concentration of 8.5% and higher, especially if a contact material is used in the first step which is still active but not sensitive to temperature fluctuations. This applies to both sulfur flue gases and pyrite gases. However, when using very high concentrations of gases, such as are currently technically possible, temperatures in the first contact phase are present which limit the use of high concentrations of gases, although this in itself would be desirable due to the associated advantages - better volume time yields.

Integration of so-called cold gas control into sulfuric acid production technology, i. passing the dried air partially between the contactor furnaces, enables the construction of ever larger plants. Reactors with a capacity of more than 900 tonnes SC> 3 per day have already been built. Equipment of this size is a relatively compact device, so it has been necessary to incorporate Lei-layer technology into the production of sulfuric acid. A process is known in which a gas containing 12% SO 2 and only 13% oxygen is reacted 98% in a four-stage reactor. Heat is dissipated by cooling the layers with water or introducing cold gas. It has further been proposed that the fluidized bed be limited to a single-stage precontact with 70-90% conversion and that the gases are then allowed to react further in a multi-stage solid catalyst reactor after separation of the darkened dust.

It 57391

The integration of fluidized bed technology achieves a number of advantages. The reactors may be smaller. In the first stage, concentrated gases can be treated, so that the dissipation of the heat of reaction does not present any difficulties. The typical toxicity of the contact material by arsenic trioxide is less. Furthermore, when steam and dried gases are used, the activity of the catalyst is not affected by the iron compounds either. Following the development of abrasion-resistant catalysts following the development of new types of contact masses, there has been interest in economically viable sulfuric acid plants using in-motion contacts.

A process has now been invented for the preparation of SO 2 by catalytic oxidation of gases containing 5 to 16 volumes of SO 4 in a fluidized bed reactor up to a reaction of 65 to 85%, by intermediate absorption and further oxidation of SO 4 free gases in one or two contact steps in a fixed bed reactor, that the feed gas is introduced into the fluidized bed reactor at a maximum temperature of 300 ° C.

The method is particularly advantageous when using gases with SO 2 concentrations of C.

are large because, due to the efficient movement of the contact material in the fluidized bed, the temperature differences are smoothed out, and by adjusting conditions such as gas preheating, gas velocities, etc., the course of the reaction is made almost isothermal.

A technically produced gas with an SO 2 content of 20% was reacted 80% by the process of the invention in a single-stage fluidized bed contact, whereby the temperature of the fluidized bed was measured to be about 520 ° C. Compared to solid-layer waste contact methods, significant energy savings are achieved or additional energy is gained. When using roasting gases in cleaning operations. o. o must be cooled to 50 C, heating to 100-300 C is unfortunately necessary, while sulfur combustion gases can be cooled to the above temperature limits. Thanks to the good heat exchange of the moving catalyst bed, the degree of conversion is made very high in a single contact step.

In the process according to the invention, the SO 2 -containing gases are first reacted in a fluidized bed. The fluidized bed uses 5,539,391 catalyst particles with a diameter of 0.2-4 mm, preferably 0.4-2 mm, and high mechanical strength and in particular low abrasion.

The preparation of abrasion-resistant catalyst supports for fluidized bed reactions is known in particular in the field of petrochemistry. Particularly suitable porous, wear-resistant and bead-shaped catalyst supports can be prepared by suspending solids in an aqueous stable silica sol having a specific surface area of 150 m / g, and gelling suspensions by mixing these with an aqueous slurry of hydrated magnesium oxide such that MgO is 0.1 to 3% by weight based on the weight of the anhydrous granulate, and disintegrating this gelling mixture into droplets in a water-immiscible liquid. The granulate obtained is then separated from the liquid and cured by thermal treatment at a temperature of 500 to 1000 [deg.] C. Silicic acid fillers having a specific surface area of 2 to 200 m / g, determined according to BET, are added to the silicon sol. 60% by weight and 5-30% by weight of kaol clay minerals of the i-rivet, montmorillonite, and attapulgite groups. For the preparation of sulfuric acid, the catalyst supports are then immersed in potassium or sodium vanadate solutions, then heated to about 500 ° C and finally sulphated in the usual manner at 450 ° C in the presence of low-SO 2 gases.

The catalysts can then be used to oxidize the SO 2 to the soils. According to another proposal, better catalysts can be obtained by treating the catalyst supports before impregnation with a vanadate solution with an acid to remove acid-soluble cations.

The finished catalysts must contain about 5 to 6% by weight of V2O, based on the amount of annealed catalyst support. The amount of catalyst used depends on the desired conversion and the SO ~ content of the feed gas. With the gases remaining in the reaction space for 1.2- ^ 3 4 seconds, the catalysts require 0.5-1.0 kg / m 2 SO 2 -containing gas with a concentration of 10-16%.

The method according to the invention is explained in more detail below with the aid of Figures 1 and 2:

Fig. 1 shows devices for applying the method in the treatment of kite-roasting gases, and 57391 6 Fig. 2 shows similar devices when using sulfur combustion gases in the reaction.

The figures in the figures have the following meanings: 1. Heat exchanger 2. Contact furnace, stage 1 (vortex contact) 3. Filter h. Heat exchanger upstream of the intermediate absorber 5. Intermediate absorber 6. Contact furnace, stage 2 7- End absorber 8. Sulfur incinerator 9 · Steam boiler

Figure 1 shows an embodiment of the process according to the invention for producing SO 2 or sulfuric acid using pyrite roasting gas. This method can be applied in the same way when using smelting or splitting gases (spaltgasen). The cold purified roasting gas is first heated to the required temperature in the heat exchanger 1. The heat exchanger is heated by the gases leaving the solid bed reactor 6. The SO 2 content of the roasting gases can be 5-20% by volume. In the fluidized bed converter 2, the roasting gas reacts to 65-85% SO 2, most preferably at a temperature of about +80-58 ° C! + 90-530 ° C. The gases are then passed through a filter 3 in order to separate the generated dust formed as a result of the abrasion of the catalyst. The reaction gases are then cooled in a heat exchanger U and the previously formed SO 4 is removed from the gas in the absorption tower 5 by washing with sulfuric acid. The gas released from SO 2 is then reheated in a heat exchanger U to a temperature of about 420 ° C and then passed through a single-stage or multi-stage solid bed contact 6. The gas leaving the solid bed reactor 6 is passed through a heat exchanger 1, where it is used to preheat the roasting gases, and then removed from the SO 2 in a terminal absorber 7 · Even when the solid bed contactor is made with only one stage, the conversion rpnil.te 93 -prosenttiseksi.

Figure 2 shows an embodiment of the method according to the invention for treating sulfur combustion gases: Sulfur is burned in a sulfur burner 8. The combustion gases are cooled in a device 9 to recover steam. 4 through. The reheated gases then enter the solid bed contact 6 and from there they are led via the heat exchanger 1 to the terminal absorber 7. The air required for combustion is preheated in the heat exchanger 1. Also when using sulfur combustion gases, the solid bed reactor 6 can be built in one or more stages.

The method according to the invention is described in more detail with the following examples:

Example 1

At 50 ° C, 50,000 Nm 3 / h of roasting gas with 9.1% SO 2 and about 9% O 2 is introduced into the apparatus according to Figure 1. This gas is heated in a heat exchanger to 1,300 ° C and then led to hot air above 440 ° C. to a preheated fluidized bed apparatus 2, in which a 33 t high-friction granular vanadium catalyst is vortexed by a gas stream having a velocity in the fluidized bed of 0.15 m / s. The temperature of the catalyst bed reaches 520 ° C and the introduced SO 2 reacts 84% to SO 2. The gas then passes through a dust filter and is cooled in a heat exchanger 4 to about 160-220 ° C. In the intermediate absorption device 5, SO 2 is removed from the gas and recovered as sulfuric acid. The gas then still contains 1.75% SO 2 and about 5.2% C> 2 and has a temperature of 60 ° C. It acts as a cooler for the gas entering the intermediate absorber in the heat exchanger 5 and itself heats up to about 420 ° C. It is then passed through a solid bed contact 6, where it heats up to about 470 ° C and its SO 2 portion reacts 94% to Sod. The conversion on the entire device is 99%. The gas leaving the contact layer 6 acts as a heating substance in the heat exchanger 1 and cools there to 160-220 ° C. The rest of the SO 3 is degassed in the terminal absorber 7 and recovered as sulfuric acid.

β 57391

Example 2

A gas with an SC 2 content of 12.3% and an oxygen content of 8.2% is passed through the fluidized contact device 2 of the apparatus according to Fig. 1 at an inlet temperature of 287 ° C, a contact bed temperature of 525 ° C and a gas flow rate inside the fluidized device of 0.3 m / a, calculated in free space and under normal conditions. By the time the gas left the fluidized bed, 63.7% of the SC 2 had reacted to SO 2. Further treatment of the gas is carried out according to Example 1. The amount of catalyst 2 under the conditions of this example is 20.5 kg / to SO 3 per day.

In the apparatus according to Figure 2, gas produced by burning sulfur can be further processed in a similar manner.

Example 3

A gas with 5.0% SO2 and an excess of oxygen is introduced into the fluidized bed 2 of the apparatus according to Figure 1. The inlet temperature to the fluidized bed is 302 ° C and the contact layer temperature is 531 ° C. As the gas leaves the Lei apparatus, 85.3% of the introduced SC 3 has reacted to SO 3. The gas velocity in the fluidized bed is 0.16 m / s, calculated in free space and under normal conditions, the amount of catalyst in the fluidized bed is 130 kg / to SO 2 / day. The further processing of the gas takes place in a known manner.

In the apparatus according to Figure 2, a gas produced by burning sulfur can be treated in the same way.

Example 4

A gas with a SO 2 content of 16.2% is introduced into the apparatus according to Figure 1. The inlet temperature to the fluidizing device 2 is 210 ° C, and the temperature of the contact layer is 546 ° C. The conversion achieved is 68%. The gas velocity in the fluidized bed is 0.15 m / s, the amount of fluidized bed catalyst is 31 kg / to SO 2 per day. The further treatment of the process corresponds to the treatment described in Example 1.

The method according to Figure 2 can be used in the same way for the treatment of gases obtained by burning sulfur.

Claims (2)

57391 9 A process for the preparation of SO 2 by catalytic oxidation of gases containing 5 to 16 volumes of SO 2 in a fluidized bed reactor up to a reaction of 65-85%, by intermediate absorption and further oxidation of SO 2 free gases in one or two contact stages in a fixed bed reactor, characterized in that the feed gas introduced into the fluidised bed reactor up to o ..... At a temperature of 300 ° C. A method according to claim 1, characterized in that the solid bed contact treatment after intermediate absorption is performed in two steps and that the gases are cooled between the two steps.