NO811891L - PROCEDURE FOR THE MANUFACTURE OF SULFUR TRIOXYD. - Google Patents

Abstract

Process for the production of sulfur trioxide according to the catalyst process using a fluidized bed technique, in which SO -, - containing gases with a temperature of approx. 20-700 ° C and a content of up to 6 6.7% sulfur dioxide, is reacted in a one-stage vortex layer of catalyst material with oxygen-containing gases to over 90% to sulfur trioxide, the SO-j-containing reaction gases are fed to an intermediate absorption and the sulfur trioxide-liberated gases is further reacted in a 1- or 2-stage catalyst, the height of the 1-stage fluidized bed in the fluidized state being approx. 0.1-2 m, the average grain size of the catalyst mass between approx. 0.4-2 mm, the gas velocity in the empty reactor space approx. 0.1-0.6 msec., The gas velocity after the inflow bottom before contact with the catalyst grains is less / equal to 9 msec., And the catalyst mass is thermostatized over heat exchangers.

Description

The object of the invention is a method for the production of sulfur trioxide by the contact method using the fluidized bed technique, the catalyst mass being thermostatized over heat exchangers.

In the production of sulfur trioxide by catalysis

technical oxidation of sulfur dioxide, large-scale solid-storage catalysts are used. Thereby, in a known manner, the SO2-containing gases are brought into contact with the catalyst masses in the 2nd or 3rd stage, mainly using vanadium oxide catalysts. In order for the reaction to proceed at the required rate, the SC^-containing gases must be preheated to temperatures of over 400°C. Above all, with highly concentrated SC^-containing gases, large amounts of energy are released during the conversion in fractions of a second, which must be removed in a controllable manner to avoid overheating of the gases, as well as of the catalyst masses and the catalyst boiler. Temperatures that far exceed 600°C

is to be avoided, so that no damage occurs to the catalyst material. As the optimal calculable equilibrium temperature depending on S02~ and oxygen content of the gases is significantly lower than the above-mentioned temperature, one strives in the last catalyst stage to work at the lowest possible temperatures, i.e. at approx. 420 to 460°C, to achieve a high S02 gas conversion. For temperature regulation, the gases are usually cooled between the individual stages by means of heat exchange.

German patent 1.9 29,388 already mentions a method for producing sulfur trioxide according to the catalyst method using the fluidized bed technique,

where the cooling of the reaction space takes place by blowing in SO2-containing gases with a correspondingly low temperature.

In the method mentioned in USppatent 2,595,254, work is carried out at storage temperatures from 4 26 to 5 38°C.

According to this known method, sales are also achieved in

the usual range of the precatalysts, one is however forced to choose a grain size of the catalyst of 50>y. However, this requires either small outputs or a technically difficult to handle dust problem at high temperatures and corresponding gas velocities. Refrigeration is also suggested

the fluidized beds during the SC^-catalysis in built-in heat exchangers.

The object of the invention is a method for producing sulfur trioxide according to the catalyst method. with intermediate absorption using the fluidized bed technique, the method being characterized by SO2-containing gases with a temperature of approx. 20°C to approx. 700°C

and a content of up to 66.7% S02 is converted in a fluidized bed of catalyst material with oxygen-containing gases to over 90% to SO^/the SO^-containing reaction gases are supplied to an intermediate absorption and the SO^-free gases are converted in a one- or two- stage catalyst, the height of the fluidized bed being 0.1 to 1.5 m, the average grain size of the catalyst mass 0.4 to 2 mm, the gas velocity in the empty reactor space 0.1 to 0.6 m^/sec., the gas velocity after the inflow bottoms before contact with the grains of the catalyst mass is less than/equal to 9 mN/sec., and the catalyst mass is thermostatized over a heat exchanger located in the reaction space.

The method offers advantages in particular when using gases with a high sulfur dioxide content, as an approximately isothermal reaction course can be achieved by the thermostatization according to the method.

In the method according to the invention, the S02-containing gases are primarily reacted as best as possible, i.e. to approx.

90% and more, in a fluid bed. The SO2-containing gases can have a content of up to 66.7 T^ sulfur dioxide. When processing the gases produced by burning sulfur with air, a sulfur dioxide content of from 10 to 13.5% by volume is preferably set, particularly preferably from 11.5 to 12.5% by volume. At a concentration above approx. 13.0 volume% sulfur dioxide, oxygen or oxygen-enriched air is added.' For the conversion achieved according to the invention, of more than 90%, the oxygen excess is selected above the stoichiometrically necessary amount

(for the reaction: sulfur dioxide plus oxygen = sulfur trioxide)

so that it amounts to approx. 1 to 10% by volume. The oxygen excess is preferably set the higher the higher the sulfur dioxide content of the gas to be processed, e.g. by

12 volume% SC>2 approx. 3 volume% oxygen excess, up to

62 volume% sulfur dioxide approx. 7-8 volume% oxygen excess over the stoichiometrically required quantity which is then set to 100.

In the case of sulfur dioxide-containing gases originating from sulfur combustion, a temperature is preferably set between approx. 170°C to 550°C. If these gases are supplied with additional oxygen or with oxygen-enriched air, these gases can also at temperatures between approx. 0°C to 170°C is fed into the catalysis reactor. The temperatures in the vortex layer are set between approx. 430 to 530°C, preferably 460 to 500°C. The gas velocity in the fluidized bed should be the single to double minimum fluidization velocity of the catalyst material. The gas velocity in the fluidized bed is, with reference to the empty reactor, at 20°C, at 0.1 to 0.6 m^/sec, preferably at 0.1 to 0.35 m^/sec. The height of the fluidized bed is set between 0.1 and 2 m, preferably between 0.6 and 1.3 m. For the inflow bottoms, a concentration is preferably chosen such that the gas velocity at the point where the gas touches the catalyst materials is not higher than 9 m/sec ., preferably not higher than 3-4 m/sec.

The catalyst material used must have an average grain size between approx. 0.4 to 2 mm, preferably 0.7 to 1.3 mm.

The production of wear-resistant catalyst supports for fluidized bed reactions, which are suitable for the SC^-catalysis, is discussed e.g. in DOS 1,767,754 resp. German patent 1,926,564.

Substantially improved catalysts are obtained according to a previously unpublished proposal when, when manufacturing on the basis of precipitated silicic acid, only so much clay minerals are added that the dry catalyst carrier contains a maximum of 4% Al2O3, preferably no more than 2% Al-^O^/ and the calcination takes place at temperatures of no more than 600°C, preferably at 200 to 500°C. This support material is then impregnated without previous acid treatment with a weak sulfuric acid solution of vanadyloxysulphate and then dried. In this drying process, temperatures of 150 to 250°C are sufficient. In each case, there should be no temperature treatments of the carrier, as also of the finished catalyst, which transfers the crystal lattice of the aluminum contained in the clay minerals in reaction form.

It is also possible to combine both temperature treatments in one step, so that the carrier material is only dried before the impregnation and the curing then takes place on the finished catalyst at temperatures below 60 0°C, preferably at temperatures of 200 to 500°C.

Catalyst masses are obtained which are distinguished both by their high wear resistance and by their consistently high activity during long-term use.

Production of the carrier mass can take place both according to the method according to German patent 1,926,564, and also according to other known granulation methods, such as e.g. on granulation plates. Precipitated silicic acid fillers are used with a specific surface according to BET of 40 to 80 m 2 /g, which preferably contain approx. 5 to 10% by weight calcium oxide. The amounts of filler are dimensioned so that in the carrier material referred to as anhydrous granules, there is approx. 20 to 60% by weight, preferably 35 to 50% by weight filler. This filler is premixed in an aqueous, stable silicic acid sol with a specific surface area of o 150 to 450 m 2 /g according to BET, gel formation taking place in a known manner with the addition of smaller amounts of highly active magnesium oxide. Preferably, hydrated magnesium oxide is added in amounts from approx. 0.1 to 3% by weight. When suspending the filler in silica sol or when granulating, clay minerals are added in amounts from approx. 10 to 15% by weight. As clay minerals, it is suitable e.g. kaolinite, montmorillonite, attapulgite, bentonite and/or kaolin.

The granules are dried and then hardened either at temperatures of no more than 600°C, preferably at 200 to 500°C or added after drying immediately for impregnation.

The impregnation takes place with a sulfuric acid solution of vanadyloxysulphate, which preferably does not contain more than 6% by weight, particularly preferably not more than 3% by weight, of free sulfuric acid. The impregnation solution contains vanadyloxysulfate, where vanadium is present in oxidation stage + IV in amounts from 5 to 30% by weight, preferably from 12 to 23% by weight and 15 to 40, preferably 20 to 30% by weight of potassium hydrogen sulfate, each time referred to the overall solution. These solutions can be greatly supersaturated, so that they can be applied both cold and hot to the carrier material.

The concentration of vanadium and potassium in the acidic solution is to be chosen so that in the dry catalyst there is a molar ratio between potassium and vanadium of 3 to 1: 2 to 1 and the vanadium content, calculated as vanadium pentoxide, is

4 to 9, preferably 4 to 6% by weight.

Vanadyl salts, preferably sulfates, are used as salts of tetravalent vanadium. For the preparation of the impregnation solution preferred according to the invention in a single step, the required amount of water is added, the amount of acid required for reduction and for the bisulphate preparation is added, then the calculated amount of vanadium pentoxide is suspended and the solution is then reduced with sulfur dioxide or sulfur dioxide-containing gas until all vanadium pentoxide is present dissolved as vanadyl sulfate (VOSO^). Then, at a temperature of at least 40°C, preferably from 60 to 90°C, potassium sulfate is introduced into the acidic solution.

After completion of bisulphate formation, there is only a small excess of sulfuric acid. This solution can be used immediately to impregnate the carrier material.

Preferably, the impregnation takes place in a fluidized bed. The material is fluidized at a sufficient fluidization rate and then sprayed with impregnation solution. After that, a finishing treatment with hot air (150 to 300°C) takes place until the material no longer emits moisture.

Especially when the carrier material before the impregnation process was hardened at temperatures up to 600°C, preferably at temperatures of around 400°C, it can be used immediately without reducing pretreatment in the fluidized bed catalyst for oxidation of SC>2 to SO^. It shows at the aqueous operating temperatures of approx. 380 to 500°C a significantly higher activity than other fluidized bed catalysts, and even after several years of operation still has a high wear resistance and an unchanged activity.

If the curing does not take place before the impregnation, can

it also takes place in connection with the impregnation.

With the new catalyst material, e.g. at an operating temperature in the fluidized bed of approx. 470°C and a gas containing 12% by volume of sulfur dioxide, in a single fluidized bed stage a conversion of over 93% from sulfur dioxide to sulfur trioxide was achieved.

The inflow bottoms for the fluidized bed must be constructed so that on the one hand a uniform gas distribution over the overall bottom is achieved, on the other hand, however, the least amount of energy loss occurs due to pressure loss at the bottom. It has been shown that in the case of a vortex layer below 6 m in diameter a pressure loss of 0.2 bar is sufficient, in the case of 8 m in diameter a pressure loss of 0.3 bar was necessary. The even distribution of the gas over a fluid bed bottom is achieved, e.g. by a plurality of nozzle bores in the vortex bed bottom.

The decisive advantage of using a fluidized bed catalyst lies in the fact that the catalytic reaction can take place at a defined, precisely chosen temperature and temperature inhomogeneities and overheating due to released heat of reaction can be avoided by corresponding heat exchanger buildings.

The catalyst mass is thermostated over a pipe register using water vapor and/or air or SC^- or SO-j-containing gases. If the amount of heat released during the reaction is greater than necessary to heat the incoming gases to the desired fluidized bed temperature, heat must be removed above the register in the fluidized bed. Hereby, it has proven advantageous to distribute the register tubes evenly in the layer and to remove heat via water vapor and/or air or S02-containing gases. Preferably, the gases flow through the register from below upwards, i.e. in a direction in direct current with the reaction gas so that, in particular, the upper part of the fluidized bed does not form temperature gradients between the register and the fluidized bed catalyst above 100°C, preferably not above 50°C. It is necessary to remove very large amounts of heat from the vortex layer, e.g. by the reaction of gases that are hotter than the fluidized bed's operating temperature. If working with pure oxygen or with oxygen-enriched air, according to the invention, an evaporator register is operated in the lower part of the layer in the vortex layer. That of the vortex layer, e.g. with the help of superheated air or preferably superheated water vapor, heat carried away can then be extracted at such a high temperature level that in a further heat exchanger, superheating heat can be extracted as useful heat. If the fluidized bed plant is operated with strongly fluctuating gas concentrations, as this e.g. is the case with voice systems, split systems and exhaust gas utilization systems, the fluidized bed must be thermostatized above the register. In this case, the flow-through individual tubes in the fluidized bed should not be too long so that the residence time of the hot gas in the tubes for the next cooling process, e.g. in an evaporator drum does not affect the temperature constants in the fluidized bed. If the heat of reaction released by gas mixtures with a low SO^ concentration and low entry temperature is not sufficient to maintain the desired fluidized bed temperature, the entering gas must be heated to the temperature of the fluidized bed. Such thermostatization is easily possible via the built-in pipe register.

According to another proposal that has not yet been published, the thermostatization can be carried out as follows: As a cooling medium, water vapor is taken from a direct-pressure heat reservoir, which is arranged separately from the reaction chamber, filled with boiling water, and is forced through several rows in the reaction chamber, superheated there and cooled each time thereafter in the heat store by indirect evaporative cooling, since in the heat store the water vapor is kept at the same pressure, since the number of superheating and recooling rows is chosen so that the ratio of the sum of the Enthalpie difference of the recooling stages to the Enthalpie difference between the saturated

in steam and supplied feed water amounts to at least 1.1.

The proposed system consists of superheating heating surfaces arranged in the reaction space or the product path and an indirectly charged direct pressure heat reservoir arranged outside the reaction space or the product path, as shown in fig. 3a.

i Here means:

The mode of operation is as follows:

Saturated steam is taken from the heat storage 4 via line 5, regulated by temperature sensor 6 and valve 7, and superheated in several rows each time in one of the at least 4, preferably 6-12, especially preferred 8-10, arranged superheating stages 8 in the fluidized bed 2, and is then cooled back in one of the cooling stages 9 arranged in the heat store 4.

Equilibrium between the heat extracted from the storage 4 in the form of steam for cooling the fluidized bed and the heat returned indirectly via the recooling stage 9 in the storage 4 is then present, when the sum of the Enthalpie difference of the steam cooled in the recooling stage 9 is equal to the Enthalpie difference between the feed water supplied via line 10 and the steam withdrawn via line 5.

According to the invention, this equilibrium is set independently of the given or selected steam conditions over the number of superheating and recooling rows.

Above the number of superheating and back-cooling rows, however, it is also possible to set arbitrarily other ratios greater than 1. With these precautions according to the invention, more steam is always produced in heat stores 4 than is withdrawn for cooling purposes.

The greater the ratio between the sum of the Enthalpie difference of the steam recooled in the recooling step and the Enthalpie difference between steam and feed water is chosen, the more elastic the system reacts to fluctuating amounts of heat that must be removed.

The excess steam not required for cooling is released via line 13, pressure-regulated through valve 12.

In order to get the useful steam released via line 20 to the desired degree of superheating, part of the amount of steam used to cool the fluidized bed after the last of the recooling stages 9 is temperature-regulated by means of valve 15 to the last of the superheating stages 8, so that after joining the lines 16 and 17 emerges mixer 18 and forwarding via line 19 through the combination of cooling steam with excess saturated steam the desired state.

The vapor states passing in the above-mentioned manner are shown in fig. 3b.

There means:

tw = feed water temperature

ts^= saturated vapor temperature

tu = superheat temperature

tk = temperature of the vortex layer

tD = temperature after the last superheating stage tA = temperature of released useful steam i = Enthalpy at the possible temperatures.

The diagram also clearly shows that by choice<u>. of the number of superheating and recooling rows, the temperature range of the steam used for cooling can be selected as desired.

In particular, with a smaller enthalpy difference in the steps, a corresponding increase in the number of steps is possible with a more extensive thermostatization of the reaction process.

The method according to the invention will be explained in more detail with the help of some examples.

Example 1 (cf. Fig. 1)

In the inflow chamber of a fluidized bed 1, 23,000 Nm 3 of sulfur combustion gas (gas produced by burning sulfur with air) flows with 12.3% by volume SC>2 with a temperature of 330°C. In a vortex layer of 6.4 m diameter, a standard velocity of 20 Nem/sec, referred to the void, was set. The vortex layer height in a calm state is 100 cm, in a fluidized state approx. 115 cm. The fluidized bed was thermostated to 475°C by means of horizontally built-in, evenly spaced tubes, through which steam flowed. The steam entered with approx. 200°C in several pipe coils from below and exited above with approx. 420°C. The superheating heat of the steam was given off in a steam drum by means of a hot steam cooler and with this it was extracted per hour approx. 3.2 tonnes of steam at 6 bar as useful heat. SC>2 was converted in the fluidized bed to 92%. The gas from the reactor was cooled as is known in cross-gas heat exchangers 2 and air preheater or feed water preheater 3 and supplied with intermediate absorption 4. After reheating in cross-gas heat exchanger 2, the remaining SC^ was converted by post-catalyst to a total conversion of over 99.6 to 99.8%. In one facility, per day produced 310 tonnes of 98% sulfuric acid.

Example 2 (cf. Fig. 2)

In an air fluidization plant 8, pure oxygen was produced which was used in the furnace?9 for burning sulphur. After several additions of sulfur 10, 3000 Nm 3 of gas containing approx. 60 vol.% SC>2 and approx. 39 vol% 0^- After it had been cooled with ECO 11, this gas was reduced to approx. 200°C fed into the inflow chambers of the fluidized bed 12. In the fluidized bed with a diameter of 2.5 m, three heat exchange registers were arranged one above the other, in the bottom 13 water was evaporated at 32 bar, in the middle 14 and top register 15 heat removed ver superheating of steam. The vortex layer had a height of approx. 150 cm. In the upper third, a temperature of 450°C was set, in the area of the two lower registers, work was done at temperatures from 480 to 550°C. After cooling the gas after a conversion of 90 to 97% of S02, 60-65% oleum 18 was first produced in a superheater 16 and an ECO 17 in a 3-stage absorption, then 20- 35% oleum 19 and finally 98% sulfuric acid 20. The largest part of the gas that left the intermediate absorption was mixed again via a pressure-increasing fan 21 directly to the charge of the S incinerator, a smaller partial flow 22 was fed into the air liquefaction plant 8.

The plant produced approx. 150-160 tattoos S03. More energy was extracted than was necessary for the connected air liquefaction plant.

Claims (7)

1. Method for the production of sulfur trioxide according to the catalyst method using the vortex layer technique, characterized in that SG^ -containing gases with a temperature of approx. 20°C to 700°C and a content of up to 66.7% sulfur dioxide, is converted in a single-stage fluidized bed of catalyst material with oxygen-containing gases to over 90% to sulfur trioxide, the SO^ -containing reaction gases are supplied to an intermediate absorption and the gases freed from sulfur trioxide is further reacted in a 1- or 2-stage catalyst, the height of the 1-stage fluidized bed in the fluidized state being approx. 0.1 to 2 m, the average grain size of the catalyst mass between approx. 0.4 to 2 mm, the gas velocity in the empty reactor space between approx. 0.1 to 0.6 mn/sec., the gas velocity after the inflow bottom before contact with the catalyst grain less than/equal to 9 ir^/sec. and the catalyst mass is thermostated over heat exchangers. 2. Method according to claim 1, characterized in that the height of the fluidized bed lies between approx. 0.6 to approx. 1.3 m. 3. Method according to claim 1 or 2, characterized in that the average grain size of the catalyst mass used is between approx. 0.7 and approx. 1.3 mm. 4. Method according to one or more of claims 1-3, characterized in that the gas velocity in the empty reactor space is between approx. 0.5 to approx. 0.35 m^/sec. 5. Method according to one or more of claims 1-4, characterized in that the gas velocity after the inflow bottom before contact with the catalyst grain is less than/equal to 311^/sec. 6. Method according to one of the claims 1-5, characterized in that the cooling medium included in the thermostatization is water vapor from a device separated from the reaction space and arranged with equal pressure heat storage tanks filled with boiling water in forced circulation in several rows in the reaction space, superheated there and cooled back each time then in the heat store by indirect evaporative cooling, with water vapor being kept at the same pressure in the heat store, with the number of superheating and re-cooling rows being chosen such that the ratio between the sum of the Enthalpie difference and the re-cooling step and the Enthalpie difference between saturated steam and supplied feed water is at least 1.1. 7. Method according to one or more of claims 1-5, characterized in that a fluidized bed catalyst is used on the basis of silicic acid fillers, which on the basis of dry carrier material does not contain more than 4% A"*"2°3' fortri-nnsv;i-s not more than 2% A^O^, and impregnated with a weak sulfuric acid solution of vanadyloxysulphate, in which vanadium is present in oxidation stage IV and potassium hydrogen sulphate, the impregnation of the carrier material resp. the finished catalyst takes place at temperatures not exceeding 600°C, preferably at 200 to 500°C.