EP0171298A1 - Process for desulfurizing a combustible gas containing sulfur - Google Patents

Abstract

The invention relates to a process for effecting a high desulphuration of a fuel gas containing sulphur issuing from the gasification of sulphurous fuels, wherein the gas is subjected to the action of vapors of manganese and/or zinc and/or oxides thereof (in the form of aerosols) while it is at a temperature ranging from 1 600 DEG C. to 350 DEG C.

Description

The present invention relates to a process for desulfurization of a combustible synthesis gas containing sulfur, such as in particular a combustible gas obtained by gasification of coals or petroleum residues.

The invention relates in particular to a combustible gas obtained by gasifying coal on a bath of ferrous metal maintained in the liquid state, the coal being injected in a sprayed form into the metal bath by an injection lance, simultaneously with gaseous oxygen and vapor.

The gas thus produced contains a residual content of sulfur compounds in particular in the form of H ₂ S and COS which is of the order of 100 to 600 ppmv in H ₂ S + COS. It may be noted that, with respect to the sulfur content of the gas initially produced, a first significant desulfurization by iron has already taken place to transform the sulfur compounds into iron sulfide, but this desulfurization is insufficient for certain uses of the gas.

The present invention aims to solve this problem of advanced desulfurization of a combustible gas resulting from the gasification of sulfurous fuels.

It therefore relates to a process for the desulfurization of a combustible gas containing sulfur resulting from the gasification of sulfurous fuels, characterized in that it is subjected to the action of manganese and / or zinc vapors and / or their oxides in the form of aerosols while it is at a temperature ranging from 1600 ° C to 350 ° C.

Manganese desulfurization is preferably carried out by bringing the combustible gas into contact with the vapors of Mn and / or its oxides in the form of aerosols while it is at a temperature ranging from 1600 ° C. to 600 ° C.

Desulfurization with zinc is preferably carried out by contacting the combustible gas. with vapors of zinc and / or its oxides in the form of aerosols while it is at a temperature ranging from 1000 ° C to 350 ° C.

In steel gasification, on a pure (unalloyed) iron bath, the vaporization of iron is rapid and the quantity of vaporized iron, condensing in the form of an aerosol of metallic iron particles and iron oxides, is very important. The considerable specific surface of iron and iron oxide, causes the desulfurization of the gas, provided that this one is sufficiently reducing (low content of C0 ₂ and H ₂ 0). The desulfurization reaction occurs from 1100 ° C and can continue up to approximately 400 ° C provided that the capture installations are suitably designed to give sufficiently long gas residence times, in particular in the range from 600 ° to 800 ° C. Under these conditions, whatever the initial sulfur content of the gas (mainly as H ₂ S and COS, S ₂ , etc.), the sulfur content of the gas cooled in the presence of iron aerosols and iron oxide, is reduced to values between 100 and 600 ppmv of sulfur, in the form of H 2S, of COS, etc. The sulfur is eliminated, by purification and advanced gas dedusting in the form of iron sulphides and oxysulphides.

This desulfurization by iron, inherent in the very process of gasification of coal on a cast iron bath maintained at a temperature above 1300 ° C., is however insufficient for certain applications, taking into account the residual sulfur content.

According to the invention, in order to obtain faster and more thorough desulfurization, manganese and / or zinc vapors or their oxides are introduced into the gas produced by gasification.

Manganese is very volatile. Its vapors react at high temperature, immediately, with the sulfur compounds contained in the gas, if the latter is sufficiently reducing (CO ₂ content <5%). At 1500 ° C, the sulfur content of gases is already reduced to 900 ppmv. During the cooling of the gas, in the presence of vapors (in the form of aerosols), manganese and manganese oxides, the desulfurization continues and, at 800 ° C. there remains only 50 ppmv of sulfur in the gas . In a suitably designed installation (sufficient volume and residence time), the reaction can continue at lower temperatures, given the large specific surface area of the aerosol produced.

If the reaction can continue up to 600 ° C and even 400 ° C, the residual sulfur content is extremely low: around a few ppmv.

Zinc is a desulfurizer even more effective than manganese at less than 950 ° C. It completes the action of the manganese vapors introduced into the gas. From 850 ° C, zinc sulfide is more stable than manganese sulfide and zinc vapors, in aerosols quickly fix the sulfur of the gas in the form of zinc sulfide and oxysulfides, so that at 800 ° C , the gas contains less than 10 ppmv sulfur. At 600 ° C, the residual sulfur content in the gas is less than a few ppmv.

The sulfur is removed from the gas, purified and dusted, in the form of fine sulphide dust and oxysulphides of zinc, manganese and iron.

Fig. 1 is a graph illustrating the separate action of the vapors of Fe, Mn and Zn on the desulphurization of a gas resulting from the siderurgical coal gasification in which the initial sulfur content is 4000 ppmv and the initial content of each of the metals (M) is 0.5 to 1 g / _{N m} 3.

To obtain an average desulphurization (industrial gas, the sulfur content of which must be lowered below 1000 ppmv), we see on examining the graph in FIG. 1, that desulfurization by iron vapors is sufficient insofar as an appropriate vaporization of iron vapors takes place from the bath maintained at a temperature ranging from 1300 ° C to 1600 ° C.

For fuels and in particular coals with normal sulfur content, it is possible to operate by maintaining the iron bath at temperatures preferably between 1450 ° C. and 1550 ° C.

For fuels with a very high sulfur content, it is preferable that the iron bath be maintained at a temperature between 1500 ° C and 1550 ° C.

However, to obtain a thorough desulfurization which is the aim of the invention, according to a first embodiment, manganese is added to the gasification zone while the gas is maintained at a temperature ranging from 1600 ° C. to 600 °. vs.

The Mn can be added in the form of an oxide such as, for example, a concentrate or a manganese ore, directly mixed with the pulverized coal injected by the lance.

14n can also be added to the bath in the form of ferro-manganese or spiegel or any other alloy containing Mn.

The Mn content of the bath is preferably maintained between 0.5 and 1.5% and for example around 0.8%.

The introduction of manganese, to ensure desulfurization, is particularly recommended in the case of the gasification of fuels with a high sulfur content, such as sulfurous coals, asphalts, petroleum coke. This could be hindered by an excessive sulfur content in the liquid metal bath. It is necessary, in fact, to maintain, if possible, the sulfur content of the bath at less than 2% to obtain a complete and efficient gasification of the injected carbon, without excess of vapor and oxygen in order to obtain a good quality gas of which the C0 ₂ content remains below 5%.

It is also under these conditions that an effective desulfurization is also obtained with the manganese aerosol.

As explained above, under these injection conditions, the manganese introduced is rapidly vapo risé and ensures a desulfurization of the bath at the same time as gas (which can not ensure only desulfurization with iron vapors which occurs only at lower temperature as indicated above).

According to a complementary embodiment of the invention, to obtain a gas with a very low sulfur content (<10 ppm), the action of desulphurization of manganese is completed by the addition of Zn vapors which react when the gas is at a temperature below 1000 ° C and up to 350 ° C.

This bringing the gas into contact with the Zn vapors can be carried out according to two variants.

• - soit en introduisant des déchets métalliques contenant du zinc dans le bain métallique. Ces déchets peuvent provenir de récupération de démolition d'automobiles par exemple (alliages Zn-Al-Mg et Zn-Cu à bas point de fusion, etc...).
• - soit sous forme de poussières contenant du zinc, qui seront additionnées au charbon pulvérisé, typiquement concentrés d'oxydes de zinc, sous diverses formes. On peut utiliser avantageusement des poussières de fours électriques qui constituent des résidus industriels dont la teneur en zinc peut atteindre 18 à 25 %.

According to a first variant, the vapors of Zn are created:

• - either by introducing metallic waste containing zinc into the metallic bath. This waste can come from the recovery of car demolition for example (Zn-Al-Mg and Zn-Cu alloys with low melting point, etc.).
• - Or in the form of dust containing zinc, which will be added to the pulverized coal, typically concentrated with zinc oxides, in various forms. It is advantageous to use dust from electric ovens which constitute industrial residues whose zinc content can reach 18 to 25%.

Zinc, introduced into a high temperature zone, is completely volatilized. However, its consumption is not negligible because it occurs, as explained above, at a temperature below about 950 ° C in competition with the manganese aerosol, while the sulfur content of the gas is still around from 20 to 40 ppmv of sulfur compounds.

According to a second variant making it possible to reduce the consumption of Zn, it is vaporized in a plasma torch which injects the vapor of Zn into the gas when the latter is at a temperature below 600 ° C., when the manganese has already reduced the sulfur content of the gas less than 10 ppmv.

Fig. 2 is a graph illustrating the simultaneous action of the vapors of Mn and Zn on the desulphurization of a gas resulting from the steel gasification of coal in which the initial sulfur content is 4000 ppmv (COS + H ₂ S + ... ), the Mn content being greater than 0.3 g / m ³ N and in particular from 0.5 to 1 g / m ³ N, the Zn content being greater than 0.01 g / m ³ N, in particular from 0.05 to 0.1 g / _m ³ _N.

The gas desulphurization products which are in the form of fine dusts of sulphides and oxysulphides of Fe, Mn and Zn are eliminated by a thorough purification by electrostatic filter after conditioning of the gas.

Claims (8)

1. A process for advanced desulphurization of a combustible gas containing sulfur resulting from the gasification of sulfurous fuel on a liquid iron bath, characterized in that it is subjected to the action of manganese and / or zinc vapors and / or their oxides (in the form of aerosols) while it is at a temperature ranging from 1600 ° C to 350 ° C. 2. Method according to claim 1, characterized in that the gas is subjected to the action of manganese vapors and / or its oxides in the form of aerosols, while it is at a temperature of 1600 ° C at 600 ° C. 3. Method according to claim 2, characterized in that the desulphurization is completed by bringing this gas into contact with zinc vapors and / or its oxides in the form of aerosols while it is at a temperature ranging from 1000 ° C to 350 ° C. 4. Method according to any one of the preceding claims, characterized in that the gas is a gas resulting from the gasification of coal and / or petroleum residues, on a cast iron bath maintained at a temperature of 1300 ° C to 1600 ° C, preferably 1450 to 1550 ° C, depending on the sulfur content of the gas. 5. Method according to any one of the preceding claims, characterized in that the manganese is added to the coal to be gasified in the form of fine ores of Mn. 6. Method according to any one of claims 1 to 4, characterized in that the manganese is added to the iron bath in the form of ferro-manganese or Mn alloy. 7. Method according to any one of the preceding claims, characterized in that the zinc is added to the iron bath in the form of waste or residues containing zinc, such as dust from electric ovens or waste Zn alloys. 8. Method according to any one of claims 1 to 6, characterized in that the zinc is brought into con tact of the gas previously desulphurized by iron and manganese vapors, downstream of the points of contact with iron and manganese, in the form of zinc vapors produced by a plasma torch, the gas being at a temperature below 600 ° vs.

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