FI57088B - FOERFARANDE FOER FRAMSTAELLNING AV SVAVELTRIOXID - Google Patents

Description

E35F1 M (11) MOON, LUTUS, EXTERNAL, SU 57088

WA lJ K} UTLÄGGNINGSSKRIFT

5¾¾¾ C (45) Patent ay'Jr, No. 10: 6 1030

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Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) P 1929388.0 (71) Bayer Aktiengesellschaft, Leverkusen, Federal Republic of Germany-Förbundsrepubliken Tyskland (DE) (72) Harke Haeseler, Leverkusen, Ludwig Dorn, Möln, Cologne, Wil

Leverkusen, Jurgen Wokulat, Leverkusen, Franz Rubsam, Leverkusen,

Gerhard Heinze, Schildgen, Federal Republic of Germany Förbundsrepubliken Tyskland (DE) (7U) Oy Kolster Ab (5U) Method for the production of sulfur trioxide - Förfarande för framställ-Ning av svaveltrioxid

The invention relates to a process for the preparation of SO 2 from 10-16% by volume of SO 2 by catalytic oxidation first in a fluidized bed reactor and then in several contact steps, the first of which is optionally a fluidized bed step, and by intermediate absorption after two steps of 75-90.

In the production of sulfur trioxide catalytically from SO 2, solid-state contacts are used in large-scale technical production. The SOg-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, SO 2 -containing gases must be preheated to a temperature above 100 ° C. Especially in the case of very concentrated S ° 2 -containing gases, the reaction takes place in fractions of a second in large amounts of energy, 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 to avoid damaging the contact material. Since, depending on the SO 2 and oxygen contents of the gases, the optimum equilibrium temperature is substantially lower than the above-mentioned temperature, the working temperature of the last contact stage has been kept as low as possible (U20-1 * 60 ° C) in order to maximize the total SO 2 reaction. Especially in the first step, the degree of reaction must be low, because then the reaction rates at high temperatures are more important.

To control the temperatures, the gases are cooled between different stages using heat exchange. In addition, methods are also 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 building cooling systems in the contact boiler. In large-scale plants, the methods described above usually cause 90% of the reaction to take place over a long period of time.

The yield can be increased by removing the sulfur trioxide formed in between. Thus, in recent years, several sulfuric acid plants have been put into operation, in which the sulfur trioxide formed in the first stages is removed by absorption into sulfuric acid after about 90% pre-reaction, after which the remaining SOg-containing gas is reacted almost quantitatively to SO0 in the last stage at relatively low temperatures (FI U0 1 * 55 and Uo 161) In large-scale production plants such as those described above, the response is 99.6% and even higher, even in long-term conditions, and so-called double-contact plants can process SO 2 -containing gases from a wide variety of sources, i.e. refined gases. flue - gases, pyrite roasting gases as well as other smelting gases and fissile gases from sulphate - containing waste products.

Since the intermediate absorption requires additional energy compared to the normal catalysis - the reaction gases of the first contact stage are cooled before the intermediate ab s orbing and reheated to the starting temperature of the last contact stage after removal of the sulfur trioxide formed in the intermediate stage. can be made particularly economical by using these gases. In addition to the fact that the 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 methods more economical.

The above-mentioned calculations of the cost-effectiveness 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 SO 2 is at least partially 3,57088 available for heating the gases in the contact system, relatively low concentrations of SO 2 -containing gases are also suitable for treatment. However, it must be taken into account 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 active without being sensitive to temperature fluctuations. This applies to both sulfur fuel gases and pyrite gases. However, when very high concentrations of gases, such as are currently technically possible, are used in the first contact stage, temperatures are present which limit the use of high concentrations of gases, although this in itself would be desirable due to the associated advantages - improved volume-time catches.

Integration of so-called cold gas control into sulfuric acid production technology, i. the passage of dried air partly between the furnaces of the contactor, makes it possible to build ever larger plants. Converters with a capacity of more than 900 tons of SO ^ per day have already been built. Equipment of this size is a relatively compact device, so work has had to be done to incorporate fluidized bed technology into the production of sulfuric acid. A method has been described in which a gas containing 12% SO 2 and only 13% oxygen has been reacted 98% in a four-layer converter. 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% reaction and then the gases be allowed to react further in a multi-stage solid catalyst converter after separation of the entrained dust.

According to Rumjantseva & et al., Chem., Ind., UdSSR, No. 6, 1966, pp. M8-U50, a fluidized bed reactor can be used for the complete oxidation of sulfur dioxide to sulfur trioxide or also as precontact. In a four-stage reactor, a conversion of 95-9% can be achieved using 11-16% SO 2 gas, which, however, can only be achieved by cooling between stages or by the stages themselves. Said publication also discloses a conventional four-stage solid-bed contact plant in front of which is connected a fluidized-bed reactor to which the gas is introduced at a temperature of 370-00 ° C; however, this can only be used at a conventional SOg concentration because the temperature of the fluidized bed reactor would otherwise rise too high.

U.S. Patent No. 2,190,190 relates to the conversion of SO 2 from sulfur-containing feedstocks to SO 2 using a fluidized bed in a first step, in which the catalyst is recycled to cool it, as well as a material that has not completely reacted.

The integration of fluidized bed technology achieves a number of advantages. Converter 57088 can be considered smaller. In the first step, 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 water vapor and dried gases are used, the iron compounds also have no effect on the activity of the catalyst. Following the development of abrasion-resistant catalysts following the development of new types of contact masses, the technology has attracted interest in economically viable sulfuric acid plants using circulating contacts.

A process has now been invented for producing SO 2 by a contact process using intermediate absorption, which method is characterized in that the inlet temperature of the SO 2 -containing gases to the first fluidized bed stage is about 300 ° C or less and that the gas in the second contact stage is blown at least 60 ° C. for cooling, in a manner known per se, a side stream of cold reaction gases.

The method is particularly advantageous when using gases with high SO 2 concentrations, because due to the efficient movement of the contact material in the fluidized bed, temperature differences are smoothed out and by adjusting conditions such as gas preheating, gas velocities, etc. the reaction is almost isothermal.

In the process according to the invention, the SC 2 -containing gases are first reacted in a fluidized bed. Catalyst particles with a diameter of 0.2 to k mm, mainly 0.1 to 2 mm, with high mechanical strength and especially low abrasion are used in the fluidized bed.

The preparation of abrasion-resistant catalyst supports for fluidized bed reactions is known, especially in the fields of petrochemistry. Particularly suitable pores, wear-resistant and bead-shaped catalyst supports can be prepared by suspending solids in an aqueous preservative silica sol having a specific surface area of 150-1 * 00 m / g as determined by BET, and gelling the resulting suspensions by mixing these with hydrated magnesium oxide. that MgO is 0.1 to 3% by weight based on the weight of the anhydrous granulate, and by disintegrating this gelling mixture into droplets in a water-immiscible liquid. The obtained granulate is then separated from the liquid and cured by thermal treatment at a temperature of 500-1000 ° C. Silica fillers with a specific surface area of 20-200 m / g, determined according to BET, 20-60% by weight and 5 ~ 30% by weight of kaolinite, montmorillonite and attapulgite clay minerals are added to the silicon sol as solids. For the preparation of sulfuric acid, the catalyst supports are then immersed in potassium or sodium vanadium solutions, then heated to about 500 ° C and finally sulphated in the usual manner at a temperature of 1 * 50 ° C in the presence of low SO 2 gases. The catalysts can then be used to oxidize SO 2 to SO 2. According to another proposal, better catalysts can be obtained by treating the catalyst supports with an acid solution to remove acid-soluble cations before impregnation with a vanadium / solution.

5 57088

The finished catalyst should contain about 5 ~ 6 weight percent V 2 O 2 based on the amount of annealed catalyst support. The amount of catalyst used depends on the desired amount of reaction and the SO 2 concentration of the feed gas. When the gases remain in the reaction space for 1.2 U seconds, the catalysts then require 3 0.5 ~ 1.0 kg / m SOg-containing gas with a concentration of 10-16 t.

The method according to the invention is further clarified in the following in connection with Figures 1-3:

Figure 1 shows arrangements for applying the method to the treatment of combustion gases, while Figure 2 shows similar arrangements for using sulfur combustion gases in the reaction. Figure 3 illustrates an improved normal equipment by means of a front-mounted fluidized bed converter. The figures in the figures have the following meanings: 1. Heat exchanger 2. Contact furnace, phase 1 (vortex contact) 3. Filter 1 *. Heat exchanger upstream of the intermediate absorber 5 · Intermediate absorber 6. Contact furnace, stage 2 7. Final absorber 8. Sulfur incinerator 9 * Steam boiler 10. Fixed mattress part of the first contact furnace 11. Cooling device between the layers of the contact furnace (stage 2) 12. Contact furnace with 1+ , of which 2 before the intermediate absorber and 2 after this.

Figure 1 shows an embodiment of the process according to the invention for the preparation of 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 fixed bed converter 6. The SO 2 content of the roasting gases can be between 10 and 16% by volume. The roasting gas is reacted in a fluidized bed converter 8a 2 at a temperature of about U80-580 ° C, most preferably U90-530 ° C, to 65 ~ d5 ~% SO 2. When the reaction is about 75%, the gas leaving the first stage is fed to the fixed bed reactor 10 in order to obtain a total reaction of at least 6 S7088 of 75% before the intermediate absorption device. The reaction gases are then cooled in a heat exchanger 1 * and the previously formed SO 2 is removed from the gas in the absorption atom 5 by washing with sulfuric acid. The gas released from SO 2 is then reheated in a heat exchanger to a temperature of about U20 ° C and then passed through a solid bed contact 6. In the present case, the fixed layer contact 6 is constructed in two phases with its intercoolers 11. The gas leaving the fixed bed converter 6 is passed through a heat exchanger 1, where it is used for preheating the roasting gases, and is then removed from the SO 2 in a terminal absorber 7 *. While Figure 1 shows an arrangement for refining roasting gases, Figure 3 shows a corresponding arrangement for refining sulfur combustion gases.

Even existing plants can be greatly improved by connecting a fluidized bed contact to the front. Figure 3 shows an arrangement for the production of sulfuric acid during roasting of pyrite gases, using a four-stage contact device in which an intermediate absorption device is placed after the second contact stage. by placing a fluidized bed contact in front of the first stage, the overall reaction is 99.8%. Gases from sulfur combustion can also be used in a similar way. If, by connecting the fluidized bed contact, partially reacted gases are introduced into the first stage of the previously constructed fixed bed converter, the temperature of the gases leaving the first stage of the fixed bed converter can be considerably reduced, thus saving building material and also catalyst life.

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

Example 1

The apparatus according to Figure 1 is introduced at a temperature of 50 ° C

O

50,000 Nm / h roasting gas with 9 »1% SO 2 and about 9% 0This gas is heated in a heat exchanger to 1,300 ° C and then passed with hot air to a vortex device 2 preheated to over UU0 ° C with 33 to high friction granular vanadium catalyst is vortexed by a gas stream having a velocity of 0.15 m / s in a fluidized bed. The temperature of the catalyst bed is set at 520 ° C, and the introduced SO 2 reacts 8% to SO 4.

The gas leaving the vortex device 2 at about 520 ° C is cooled to about U60 ° C by blowing in 7300 Nm ^ / h of cold dry air and passing it to the fixed bed catalyst 10. Here the SOg part reacts 9% as Sodium, with an outlet temperature of about U80 C. Instead of the fixed mattress catalyst according to Figure 1, a second fluidized bed can also be used, through which the gas flows under normal conditions in the empty state at a speed of 7 57088 at 0.17 m / s. The amount of catalyst is 20 to. The gas passing through the second catalyst is passed as described above through the intermediate absorption system and the fixed bed catalyst, however, the SO 2 content of the gas leaving the intermediate absorber is only 0.55% · Upon entering the solid catalyst 6, the gas temperature is 410 ° C. The response across the entire hardware is over 99.8%. As described above, the gas is passed through a heat exchanger 1 to a terminal absorber 7, where the rest of the SO 4 is recovered as sulfuric acid.

Example 2 A gas cooled to 230 ° C in a steam boiler at a rate of 50,000 Nm 2 / h with 7% + SO 2 and 7% O 2 is introduced into the apparatus of Figure 2 and allowed to react as described above in a fluidized bed 2 at 75% temperature. is 5-4 ° C. The hot gas is then blown with 8,800 Nm'Vh of cold, s,,, ..... · i O · dried air and its temperature drops to about 470 ° C. It then passes through a fixed mattress converter 10, from where it exits at a temperature of 530 ° C and the reaction of SO 2 to about 92% SO 2. The gas is then cooled in a heat exchanger to 4-160-220 ° C and the SO 2 is removed in an intermediate absorber (or in an oil absorber followed by a sulfuric acid intermediate absorber) which is removed as the acid produced. In the intermediate absorber, the gas cooled to 60 ° C acts as a condenser in the heat exchanger U and then heats to 1 * 20 ° C.

The gas is passed through a second fixed mattress converter 6, which in this case is made single-stage. The gas reacts 96% in it and its outlet temperature rises to about 450 ° C. The overall response in the equipment is 99.7%. The response can be further improved by replacing the single-stage second contact device 6 with a two-mattress system with intercooling.