DE2546353C2 - Design of the method for removing sulfur oxides from gas mixtures - Google Patents

Description

The invention relates to an embodiment of the method for the removal of sulfur oxides from a gas mixture by passing over the gas mixture Temperatures from 20 ° to 120 ° C above activated carbon, the impregnated with oxides of cobalt and molybdenum or tungsten or of nickel and molybdenum or tungsten is, until the breakthrough of the sulfur oxides, and regeneration of the activated carbon with hydrogen or hydrogen-containing gas at temperatures of 200 ° to 450 ° C, with the sulfuric acid adsorbed on the activated carbon is converted to a gas mixture consisting of H2S and SO2, from which one can through the Claus reaction contains elemental sulfur as the end product, according to patent 24 19 103.

In the known method of DE-AS 19 42 519, an activated carbon is used to remove the sulfur oxides from exhaust gases used, which is impregnated with vanadium oxide, which accelerates the formation of sulfuric acid but does not have a hydrating effect.

DE-OS 21 59 845 describes a process in which the activated carbon with at least one metal oxide Impregnated by a spinel crystal structure to act as a catalyst to promote the oxidation of SO2 to SOj; the loaded coal is regenerated by washing with water. In DE-OS 15 94 673 it is proposed the activated carbon with metal catalysts, e.g. B. iron or manganese, to impregnate and through to regenerate thermal treatment. Only SO2 is obtained during regeneration. In the case of the DE-OS 17 67 224 is the activated carbon with precious metals

impregnated.

The object of the invention is to provide the method of the initially designed so that a high loading of the adsorbent is achieved and at the same time is worked inexpensively. This object is achieved in that such a gas mixture over the activated charcoal conducts the water vapor at least corresponding to a dew point of over 45 ° C and at most corresponding to a relative saturation of about 90 ° and its oxygen content for quantitative Oxidation of SO2 contained in the exhaust gas to SOj is sufficient until the activated carbon is 20 to 80% by weight Contains sulfuric acid, based on unloaded activated carbon.

is The water vapor content in the gas mixture to be treated ensures that the adsorbent loaded with sulfuric acid rather than SO2. The absorption capacity of the adsorbent is thereby increased quite considerably, at least by a factor of 10, compared to methods which the sulfur oxides in gaseous form, d. H. completely or temporarily dry, adsorb.

The desorption of the adsorbed sulfuric acid with a hydrogenation gas proceeds without loss of catalyst material, whereas thermal regeneration, for example, would result in carbon consumption. At the In contrast, the process according to the invention only consumes an equivalent proportion of the hydrogenation gas.

As a result of the desorption with a hydrogenation gas, which is part of the process according to the invention, H2SO4 and possibly still remaining SO2 partially hydrogenated to H2S. The oxides of cobalt, nickel, Molybdenum or tungsten, with which the adsorbent is impregnated, as the desired hydrogenation catalyzing substances. The Desorpticnsgas thus contains the sulfur compounds as a mixture of SO2 and H2S, which can easily be converted into elemental sulfur.

Activated charcoal or activated coke are particularly suitable as adsorbents. The adsorbent can impregnated up to 10% of its own weight with the metal oxides already mentioned as hydrogenation catalysts be. Mixtures of these catalysts can give a composition that matches the molar ratio CoO or NiO to MO2O3 or W2O3 of about 1: 1.5 is equivalent to.

Some hydrogen can act as a reducing gas for the desorption of the sulfur compounds.

Carbon monoxide or the cheaper natural gas are used or even gases that contain these components mostly included.

The desorption gas mixture formed during the regeneration of the adsorbent is expedient passed over a large-surface substance that catalyzes the Claus reaction and elemental sulfur deposited. The Claus implementation (2H2S + SO2 - <· A3S + 2H2O) can in a manner known per se be carried out on aluminum oxide catalysts or activated carbon. The elemenUirc formed in the process Sulfur is a very desirable end product of gas desulfurization. It is useful to do this through the Claus implementation hydrogenating gas for the desorption, at least predominantly freed from the sulfur compounds to reuse the adsorbent.

The desorption with the hydrogenating gas can be carried out in this way in a further embodiment of the invention be that already the desorption gas approximately

clic stoichiometric composition of 2 mol H2S and 1 mol SO2 of the Claus reaction

Both the adsorbent and the catalyst for the Claus reaction not only in a fixed bed, .but can also be used in moving or fluidized beds.

The following is a circuit example for the erfinclungsgemiißc Process explained with the help of the drawing.

A gas mixture containing SCh is introduced into line 1, which is approximately up to 90% saturated with water vapor. The water vapor content in the gas mixture should correspond to at least a dew point of over 45 ° C. In addition, there is still enough oxygen in the gas that the SO2 can be quantitatively converted into SO3. The gas mixture in line 1 is mixed with temperatures of 20 ° to 120 ° C, passed preferably 50 to 100 ⁰ C, through a reactor 2 containing the activated carbon with oxides of cobalt and molybdenum or tungsten or nickel and molybdenum or tungsten is impregnated. The SO2 withdrawn from the moist gas mixture is bound to this adsorbent as H2SO4. To improve the catalytic effect, the adsorbent can also contain substances known per se, such as metal oxides, which accelerate the H2SO4-BÜ-dung (cf. German patents 11 76 101, 11 76 621 and 17 67 224 and DE-AS 12 27 434 ). The purified gas leaves the reactor 2 through line 3.

As soon as the adsorbent in the reactor 2 sulfuric acid has absorbed an amount of at least 20% by weight of the unloaded adsorbent, the reactor is switched to regeneration. During this time, a second reactor, not shown, can take over the adsorption. For regeneration, a hydrogenating gas such. B. a water-free gas or methane, passed into the reactor 2 and through the adsorbent to desorb the sulfuric acid and at the same time convert it into a mixture of S (h and H ₂ S. Desorbed at temperatures in the range from 200 'to 450 ⁰ C.

The Dcsorptionsgas leaves the reactor 2 through the line 5, is cooled in the heat exchanger 6 and in the reactor 7 passed. In the reactor 7, the z. B. contains activated carbon or aluminum oxide is at temperatures about in the range of 120 to 140 ° C formed by the Claus reaction sulfur deposited. The residual gas, which consists predominantly of hydrogenation gas, is through the line 8, the Gehläse 9 and the heater 10 to the reactor 2 returned. Fresh hydrogenation gas to replace the amount used is fed in through line 11. As soon as the regeneration of the Adorptionsmit-IcIs in reactor 2 has ended, this can be used again SO2 removal can be put into operation.

The reactor 7 deposited sulfur is according to one or more regeneration cycles with inert gas, / .. as nitrogen, discharged, coming from the line 12 and having passed through a gas heater 13 isl. The sulfur in the reactor 7 is melted out by the heated inert gas; the sulfur-containing inert gas is fed in line 14 to the sulfur condenser 15. The inert gas, which has largely been freed of sulfur again, is returned for reuse through line 16, blower 17 and line 18; fresh inert gas comes from line 19 as required.

example

In a procedure according to the drawing, flue gas is treated with 0.2 _{% by volume SO 3} , 11% by _{volume CO 2} , 3% by volume O ₂ and 33% by volume water vapor. The water vapor content corresponds to a relative saturation of 70%.

The flue gas is at a temperature of 80'C with a residence time of 5 seconds through a fixed bed passed from granular activated carbon in reactor 2 The activated carbon is impregnated with cobalt-molybdenum oxide: the The amount of impregnation, expressed as CO and Mo metal, is 2.9% by weight of the activated carbon. Co and Mo lie in the stoichiometric ratio of the compound Co2 (MoO4). Be on this adsorbent 98% of the SO2 converted to H2SO4 and bound in this form.

After a running time of 35 hours, the adsorbent is loaded with 30% by weight of _{H2SO4 and the SO 2} rate has fallen below 98%. The H ₂ SO4 loading corresponds to an SO ₂ absorption of 196 g / kg adsorbent. Then, the reactor 2 is switched to regeneration, and passed technically pure hydrogen at a temperature of 37o C ^0. The Adorptionsmittel is heated to temperatures of 120 to 140 ⁰ C. In reactor 2, the desorption of SO2 and then the formation of H ₂ S begin. Both gases partially react with the formation of sulfur. However, most of the sulfur is formed in the reactor 7 on an aluminum oxide catalyst arranged in the fixed bed at a temperature of 120 to 140 ^° C. This sulfur is removed from the reactor 7 again after 3 regeneration cycles with nitrogen at a temperature of 300 ^{° C.} removed

In a desorption in the reactor 2 was only at the beginning of the regeneration low CO ₂ - are proven quantities desorption gas, but obviously came from the flue gas and were also adsorbed. When the adsorbent was further heated by the hot hydrogen, no new formation of CO _{2 was} observed. No consumption of activated carbon due to the reaction of the carbon with the sulfuric acid could be determined.

1 sheet of drawings

Claims (3)

Patent claims: 1 embodiment of the method for removing sulfur oxides from a gas mixture by passing the gas mixture at temperatures of 20 ° to 120 ⁰ C over activated carbon which is impregnated with oxides of cobalt and molybdenum or tungsten or nickel and molybdenum or tungsten, to breakthrough the sulfur oxides, and regeneration of the activated carbon with hydrogen or hydrogen-containing gas at temperatures of 200 ° to 450 ° C, whereby the sulfuric acid adsorbed on the activated carbon is converted into a gas mixture consisting of H2S and SO2, from which the Claus reaction becomes the end product Elemental sulfur is obtained according to Patent 24 19 103, characterized in that such a gas mixture is passed over the activated carbon, which contains water vapor at least corresponding to a dew point of over 45 ° C and at most corresponding to a relative saturation of about 90% and its oxygen content for quantitative oxidation from SO2 contained in the exhaust gas to SO3 sufficient t, until the activated carbon contains 20 to 80% by weight of sulfuric acid, based on uncharged activated carbon. 2. The method according to claim 1, characterized in that that the exhaust gas containing sulfur oxides, water vapor and oxygen at temperatures of 50'- to 100 ° C is passed over the activated carbon. 3. The method according to claim 1 and 2, characterized in that the activated carbon at temperatures between 200 ° and 400 ° C is regenerated.