DE2430909A1 - Claus kiln waste gas purificn - with recycling of sulphuric acid from catalytic conversion - Google Patents

Abstract

In the purificn. of Claus kiln waste gases by oxind. of the S content and catalytic formation of H2SO4, the H2SO4 formed is recycled to the combustion chamber of the Claus kiln. The catalytic formation of H2SO4 pref. takes place on (unimpregnated) active C, with a BET surface area of over 1000 m2/g, a micropore vol. of 0.5-0.7 cm3/g, a macropore vol. of 0.45-0.60 m3/g and a hydrophobe quotient of 1.5-2.5, using gas with a relative humidity of 35-90%. The gas purificn. is simple, carried out very economically and gives no undesirable by-prods.

Description

Method for purifying Claus - O £ -en-Abse 'The invention relates a process for cleaning Claus furnace exhaust gases by oxidizing the sulfur contents to sulfur dioxide and catalytic formation of sulfuric acid.

In the oxidation of hydrogen sulfide to elemental sulfur In the Claus process, as is well known, an exhaust gas is produced which also contains hydrogen sulfide and sulfur dioxide and traces of other sulfur compounds, especially carbon oxysulfide A certain hydrogen sulfide and sulfur dioxide content of the exhaust gas can u. a. due to the position of the thermodynamic equilibrium must not be undershot.

For reasons of air pollution control and an improved yield Elemental sulfur is a large number of processes used to purify Claus furnace exhaust gases known. Some methods provide for the Claus furnace exhaust gas with a gaseous one Reducing agents, e.g. hydrogen or carbon monoxide, at elevated temperatures above conduct a catalyst so that all sulfur compounds become hydrogen sulfide be reduced. The hydrogen sulfide is washed out by suitable solvents and returned to the Claus process (GB-PS 1 332 337, DT-PS 22 14 959, Chemical Engng. from 13.13.71, page-71). The disadvantage of this method is that they are connected in series a catalytic process and a washing process associated with the need to having to use a suitable reducing agent.

Another method for cleaning Claus furnace exhaust gas is first of all a total oxidation of all sulfur compounds to Sclierefeldioxid and then carried out a sulfur dioxide wash. The sulfur dioxide that is driven off again is then converted into elemental sulfur with hydrogen sulfide in a catalytic reactor implemented. (Chem. Eng.

Progr August 1972, page 51/52). The complexity of the procedure results from the scheme shown in this publication.

Finally, Claus furnace exhaust gas can be oxidized to sulfur dioxide, which is then passed through a vanadium contact and converted into dilute sulfuric acid (cf. G.L. Farr, Oil and Gas Journ., October 19, 1970, pp. 72-75). The dilute sulfuric acid must be evaporated in its own concentrator.

Another process category is the dry process those on a catalyst made of activated carbon or aluminum oxide, the Claus furnace exhaust gas in the temperature range which is already more favorable in terms of equilibrium from 120 to -15O0C is converted to elemental sulfur. (DT-AS 1 544 084, 1 667 636, 1 943 297). Although these procedures are relatively easy to carry out, their inadequacy, however, is that even at the specified temperatures due to the naturally not exceedable equilibrium position, certain residual contents ~ are unavoidable in the exhaust gas.

The object of the invention is to provide a method that at high economic efficiency of the exhaust gas cleaning is easy to carry out and in addition, no undesired or per se unusable by-products can arise.

The object is achieved by the method of the aforementioned Kind is designed according to the invention such that the sulfuric acid formed into the combustion chamber of the Claus Furnace is returned.

The catalytic formation of sulfuric acid can take place at any suitable Contact, e.g. according to the principle of wet catalysis.

It is particularly useful to use activated carbon as a catalyst for the formation to use sulfuric acid. This can, for example, according to DT-AS 1 227 434 or DT-OS 17 67 224 done in which at temperatures below 100 ° C with an activated carbon is worked with metals such as Mn, Co, Au, Pt, Ir, Ti, Fe, Zn, Ni, Co, Cr, V, No, Sn and / or semimetals such as As, is impregnated. Iodine also increases activity Effect.

In order not to unnecessarily burden the Claus furnace with large amounts of water, the sprayed sulfuric acid should not be too dilute. You should at least 20% by weight, expediently more than 40% by weight, H2S04. Possibly. is a previous one Concentration is recommended.

A preferred embodiment of the method according to the invention, in the case of the catalytic conversion on activated carbon, this is one sufficient To achieve a high sulfuric acid concentration, the water vapor content in the sulfur dioxide-containing gas to an amount corresponding to a relative saturation from 35 to 90% and the gas through a continuously catalytically active to conduct non-impregnated activated carbon, which has a BET surface area of more than 1ooo m2 / g, a micropore volume of 0.5 to 0.7 cm3 / g, a macropore volume of 0.45 up to 0.60 cm3 / g and a hydrophobicity quotient of 1.5 to 2.5 b-es.

In this context it is particularly advantageous to use a dwell time adjust the gas in the activated carbon bed for more than 5 seconds and -the implementation if possible below 1200C, especially at a temperature of less than 90 ° C, to undertake. The temperature can be adjusted by the addition of air and, if necessary.

can be regulated by injecting water.

The activated carbon to be used in the preferred embodiment, usually has micropores with a radius in the range from 4 to 15 Å and macropores with a radius in the range of 104 to 5,104 Å. The one used to characterize the activated carbon The hydrophobicity quotient used is derived from the heat of wetting for water and benzene determined and by dividing the heat of wetting QB for benzene by the heat of wetting Received from QW for water, the set water vapor content determines on the one hand the concentration of the sulfuric acid running off and, on the other hand, the degree of purification achieved of the gas. If the water vapor content is at the upper limit, the acid concentration is in the lower part of the range from about 40 to 60 wt. Here is the sulfur dioxide removal practically 100% from the gas. When water vapor contents are at the lower limits Sulfuric acid concentration close to 60% by weight. Then the degree of purification lies dds gas at around 90 to 98%. Both in terms of the concentration of the obtained Sulfuric acid and the degree of purification of the gas are optimal conditions achieved when the water vapor content to an amount corresponding to a relative Saturation is set from 60 to 80%. This embodiment allows: Purification down to a residual sulfur dioxide content of less than 1 ppm when recovered a sulfuric acid with a concentration of about 45% by weight.

The relatively concentrated acid obtained in this way can be fed to the combustion chamber of the Claus furnace without any significant loading of the same weraen.

The sulfuric acid is already an oxidation product of sulfur is introduced into the Claus reaction is the usual addition of combustion air to reduce accordingly.

The necessary before the catalytic formation of sulfuric acid Oxidation of the sulfur compounds contained in the Claus furnace exhaust gas can be achieved by a Post-combustion take place. A particularly advantageous embodiment of the invention consists in the oxidation on a carbon-carbon catalyst at temperatures between 100 and 160 0C. An activated carbon that is particularly suitable for this is with Alkali silicate, preferably in amounts of 0.5 to 8% by weight (calculated as Si: O2) ' impregnated.

The advantage of using activated carbon for the oxidation of the sulfur contents in the Claus furnace Åbgas, is in particular that a heating of the gas to higher Temperature avoided and thereby the necessary energy can be saved.

As with the subsequent implementation of the Sulfur dioxide to sulfuric acid requires an excess of oxygen that is at least 1.5 times the stoichiometric amount.

Especially when the Claus furnace exhaust gases are still significant Have hydrogen sulfide and sulfur dioxide, can in an expedient development According to the invention, a post-purification prior to the oxidation of the sulfur contents to sulfur dioxide with activated carbon with the formation of elemental sulfur. This is an activated carbon with a BET surface area of 1200 to 1500 m² / g and an average Pore radius of 4 to 12 Å is particularly suitable. This coal will be sufficient after high inert gas load e.g. Nitrogen, conveniently at one temperature regenerated in the range from 300 to 550 ° C.

The invention is based on Figures 1 to 4, which schematically Illustrate the principle of the method, as well as using the exemplary embodiments, for example and explained in more detail.

In Figures 1 and 2, the Claus furnace system is denoted by.

It usually consists of a combustion chamber, a reaction chamber and a a sulfur condensation zone. Reaction and sulfur condensation zone can also exist several times.

The Claus plant 1 is via line 2 and hydrogen sulfide Line 3 supplied with air. Your exhaust gas passes through line 4 in a two-stage Reactor, on whose lower catalyst layer 5 a post-purification of the exhaust gases in Meaning the Claus reaction to elemental sulfur takes place. The sulfur formed in the process is withdrawn via line 6.

Air is added to the gas stream by means of line 8, so that on the catalyst 9, in which a conversion in the sense of the Claus reaction can sometimes take place, unreacted hydrogen sulfide is oxidized to sulfur dioxide that the reactor Gas leaving via line 10 is sent to reactor 13 to convert the sulfur dioxide fed to sulfuric acid.

Here, water is sprayed in via line 21, which has the task of to produce the desired degree of water vapor saturation and by evaporation a To effect cooling of the gas. In a preferred embodiment of the invention, at of the gas with a relative saturation of 35 - 90% through the uninterrupted catalytically active, non-impregnated activated carbon is fed, is an addition of water dispensable, and instead more air can be introduced via line 21.

At 15 the cleaned gas is discharged. Line 14 is the sulfuric acid formed is returned to the combustion chamber of the Claus furnace.

FIG. 2 shows a variant of the method according to FIG Reactor 13, in which sulfuric acid is produced, the gas and sulfuric acid flowing off are guided in countercurrent to one another. This can result in a higher concentration of sulfuric acid can be achieved.

The variants of the invention shown in FIGS. 3 and 4 Process dispense with a post-cleaning of the Claus furnace exhaust gases. They become: immediately via line 4 into the oxidation zone 9 for converting the sulfur contents into sulfur dioxide initiated, which in this case together with the catalyst layer 13 in one Reactor is housed. By installing an intermediate floor and an additional Pipeline, the one shown in FIG. 4 can also be used in this manner Countercurrent flow of gas: and sulfuric acid in the catalyst layer.

Example 1 (with reference to Figure 1) One of several catalysis and sulfur abs 3 The Claus plant is supplied with 2,396 Nm of gas via the line with a composition of 20.2% by volume of CO2 and 79.8% by volume. % H2S and via line 3 750 Nm3 Air supplied. The Claus plant leaves a gas in quantities of 1000 Nm with the Composition 1.6 vol.% H2S, 0.8 vol.% SO2, 8.0 vol.% CO2, 30.4 vol.% H20 and 59.2 Vol.% N2. It gets into the catalyst layer 5, which consists of an activated carbon with a Surface area from 1200 to 1500 m / g and a most common pore radius from 4 to 12 Å - with 4% by weight alkali silicate (calculated as SiO2) + -.

From the catalyst layer 5 for post-purification of the exhaust gas About 21 kg of elemental sulfur are withdrawn via line 6. The escaping gas arrives with the addition of air introduced via line 8 in amounts of 11.5 Nm³ into the Catalyst layer 9 containing the same activated carbon as the catalyst layer 5. The gas, which has the composition 0.2 vol.% SO2, 8 vol.% CO2, Has 32.6 vol.% H2O and 60.2 vol.% N2 and makes up an amount of 1000 Nm³, finally fed to the reactor 13. It contains an activated carbon with a BET surface of 1400 m² / g, a micro-3 3 pore volume of 0.6 cm / g, a macropore volume of 0.55 cm3 / g and a hydrophobicity quotient of 1.9. With the addition of 15 Nm3 LSt via line 21 are then 20 kg of sulfuric acid with a concentration of 45 wt. % formed, which is returned via line 14 to the combustion chamber of the Claus plant will. The exhaust gas discharged via line 15 contains less than 1 ppm H2S and less than 1 ppm SO2.

Example 2 (with reference to FIG. 3) Claus plant 1, catalyst bed 9 and the catalyst present in reactor 13 are identical to those of the example 1.

impregnated The Claus plant 1 will be on line 2,396 Nm3 exhaust gas with a composition of 20.2% by volume CO2 and 79.8% by volume H2S as well as over Line 3 700 Nm³ of air supplied. An exhaust gas exits via line 4, which is 0.6% by volume Contains H2S, 0.3 vol.% SO2, 8 vol.% CO2, 36 vol.% H2O and 54.4 vol.% N2. It gets with air fed in via line 8 in 3 quantities of 94 Nm into the catalytic converter 9. The 1110 Nm exhaust gas emerging from this layer with approx. 0.9 vol.% SO2 occur in the catalyst layer 13, in which with the addition of 80 kg of water, the over Line 21 is entered, 90 kg of sulfuric acid with a concentration of 45 wt. % are formed. This sulfuric acid is via line 14 in the combustion chamber of the Claus plant 1 returned.

The exhaust gas is discharged via line 15. It contains less than 1 ppm H2S and less than 200 ppm S02.

- patent claims -

Claims (5)

Claims method for cleaning Claus furnace exhaust gases by Oxidation of the sulfur contents to sulfur dioxide and the catalytic formation of sulfuric acid , d u r c h e k e n n n z e i c h n e t that the sulfuric acid formed is in the combustion chamber of the Claus furnace is returned. 2. The method according to claim 1, d a dur c h g e k e n n z e i c h -n e t that the catalytic formation of sulfuric acid is carried out on activated carbon. 3. The method according to claim 2, d a du r c h g e k e n n z e i c h -n e t that the water vapor content of the catalytic formation of sulfuric acid Sulfur dioxidelialtigen gas to an amount corresponding to a relative saturation set from 35 - 90% and the gas through an uninterrupted catalytically acting, not impregnated activated carbon is passed, which has a BET surface area 2 3 of more than 1000 m / g, a micropore volume of 0.5-0.7 cm / g 3 a macropore volume of 0.45-0.60 cm / g and a hydrophobicity quotient of 1.5-2.5. 4. The method according to one or more of claims 1 to 3, d a it is noted that the oxidation of the sulfur contents is increasing Sulfur dioxide is made on an activated carbon that is mixed with alkali silicate in quantities from 0.5 to 8% by weight (calculated as SiO2) is impregnated. 5. The method according to one or more of claims 1 to 4, d a d It is not stated that the Claus furnace exhaust gases are before their afterburning be subjected to cleaning on an activated carbon which has a BET surface area from 1200 to 2 1500 m / -g and an average pore radius of 4 to 12 Q owns.