Furnaces elemental sulfur

Orga.nic Carbon. Organic materials interfere with plant operation because these compounds react with sulfuric acid under furnace conditions to form sulfur dioxide. There is a reducing atmosphere in the furnace which may reduce sulfur dioxide to elemental sulfur, which results in sulfur deposits in the gas handling system. 

Tlie H2S in equation 11 can, if desited, be converted into elemental sulfur in a Claus furnace. 

The carbonization by-products are usually refined, within the coke plant, into commodity chemicals such as elemental sulfur (qv), ammonium sulfate, benzene, toluene, xylene, and naphthalene (qv) (see also Ammonium compounds BTX processing). Subsequent processing of these chemicals produces a host of other chemicals and materials. The COG is a valuable heating fuel used mainly within steel (qv) plants for such purposes as firing blast furnace stoves, soaking furnaces for semifinished steel, annealing furnaces, and lime kilns as well as heating the coke ovens themselves. 

Sulfuric Acid. Essentially all sulfuric acid manufactured in this industry is produced by the contact process, in which SO2 and oxygen contact each other on the surface of a catalyst (vanadium pentaoxide) to form SO3 gas. Sulfur trioxide gas is added to water to form sulfuric acid. The sulfur dioxide used in the process is produced by burning elemental sulfur in a furnace. 

Elsewhere in this review we have commented on the problem of COS production as a result of high temperature reactions occurring in the front end furnace. Sulfur in this form is not subject to conversion to elemental sulfur in the catalytic redox Claus reaction and thus appears as COS in the tail gas where it is incinerated to SO2 thus adding to losses to the environment. The COS and any CS2 can be hydrolyzed to H2S which can then be converted by the redox Claus reaction. 

In a blast furnace, some of the CaSC>4 impurity in iron ore is reduced by carbon, yielding elemental sulfur and carbon monoxide. The sulfur is subsequently oxidized in the basic oxygen process, and the product reacts with CaO to give a molten slag. Write balanced equations for the reactions. 

The final step is desulfurization. A number of processes have been developed which are suitable for removing H2S from coke-oven gas. These include using solutions of potassium carbonate, monoethanolamine (MEA), or ammonia to absorb the H2S. If ammonia solution is used as the absorbent, desulfurization is frequently combined with the ammonia removal step. Recovered H2S can be converted to elemental sulfur or sulftiric acid. The product remaining after all the above steps is cleaned coke-oven gas, some of which is used to heat the coke ovens and produce more coke with the rest going to the boiler house and/or the blast furnace for direct injection. 

Worldwide, about 180 million tonnes of sulfuric acid are produced per year. 70% comes from burning elemental sulfur. The remainder comes from S02 in smelter, roaster and spent acid regeneration furnace offgases. 

Sulfur burning furnaces are 2 cm thick cylindrical steel shells lined internally with 30 to 40 cm of insulating refractory, Fig. 3.3. Air and atomized molten sulfur enter at one end. Hot S02, 02, N2 gas departs the other into a boiler and steam superheater (Fig. 3.4). Some furnaces are provided with internal baffles. The baffles create a tortuous path for the sulfur and air, promoting complete sulfur combustion. Complete sulfur combustion is essential to prevent elemental sulfur condensation in downstream equipment. 

Selectox Also called BSR/Selectox. A process for converting hydrogen sulfide in refinery gases to liquid elemental sulfur, without the need for a reaction furnace. The gases are passed over a fixed bed of a proprietary catalyst (Selectox 33) at 160 to 370°C. Claimed to be better than the Claus process in several respects. Often used in conjunction with the Beavon process. Developed by the Union Oil Company of California and the Ralph M. Parsons Company, and first operated in 1978. Twenty-one units had been installed by 2000. 

The conversion of hydrogen sulfide to elemental sulfur in the Claus process is limited by a combination of equilibrium and kinetic factors. Over the past decade, the pressures of air pollution control requirements have resulted in major improvements in the design and operation of Claus plants, with consequent increases in conversion and reduction of sulfur oxides emissions (74-79). Nevertheless, emissions still commonly exceed the permissible limits coming into force both in the United States and abroad. Sulfur dioxide reduction plants present similar problems. Apart from the initial furnace or reactor, they are essentially Claus plants. 

T he citrate process for the recovery of elemental sulfur from sulfur dioxide emissions in waste gas was conceived by Bureau of Mines investigators at the Salt Lake City Metallurgy Research Center in their initial laboratory research reported in 1970 (I). This work led to a scale-up of the process to a 400 cu ft/min (CFM) pilot unit which began treating reverberatory furnace gas at a copper smelter in Arizona in November 1970. While a series of mechanical difficulties allowed only... 

Electrolyte analysis showed a final composition of 20.4% sulfide and 79.6% carbonate. This compares with a theoretical composition of 18% sulfide and 82% carbonate. An overall sulfur balance showed 49.5% of the HjS removed either retained in the electrolyte as sulfide or oxidized to elemental sulfur and collected on the sweep tube wall. The remaining 50.5% is assumed to have been blown through the marginal seals on the sweep side of the cell and lost in the furnace, or converted back to at the anode since there was H2 difiusion through the membrane as evidenced by the transport of CO2 at cross-cell potentials above that required for reaction (10). 

Sulfates (e.g., iron sulfate) are decomposed in special furnaces with appropriate refractory finings. Operating temperatures often exceed 700 °C. Elemental sulfur coke, pyrites, fuel oil, etc., are also added to maintain the high temperature required for decomposition of sulfates. 

The Claus reaction continues in the catalytic step with activated aluminum(III) or titanium(IV) oxide, and serves to boost the sulfur yield. More hydrogen sulfide (H2S) reacts with the SO2 formed during combustion in the reaction furnace in the Claus reaction, and results in gaseous elemental sulfur. About one-third reacts via Eq. (34.11) and two-thirds via Eq. (34.12). Further process modification such as the COPE, Lurgi OxyClaus, BASF Catasulf, and Superclaus were described by Kohl and Nielsen [21]. 

A major source of sulfur is refinery and natural gas streams. This is done by the Claus process which was discovered more than 100 years ago and has been used by the natural gas and refinery industries for 50 years. In the Claus process, hydrogen sulfide from the gas stream is converted to elemental sulfur. Air is introduced into a furnace to oxidize about one-third of the hydrogen sulfide to sulfur dioxide. In the next stage, the reaction furnace, unconverted hydrogen sulfide reacts with the sulfur dioxide to form elemental sulfur. The Claus process generally produces an overall recovery of sulfur of 95-97%, but several modifications have been invented and sulfur recoveries of 99.9% are now achievable [6]. The chemistry is represented hy the following reactions the equilibrium to form elemental sulfur is favored at lower temperatures. 

L.S. Sun, Analyze on Ausmelt Furnace Elemental Sulfur of Flue Gas Excessive in Jin-Chang Smelter , China s Non-ferrous Metallurgy, (4)2007 30-33(in Chinese). 

The process was operated (with the exception of the conversion of elemental sulfur to hydrogen sulfide) in a pilot plant processing 400 cfin of reveibaatory furnace gas, located at the San Manuel, Arizona, smelter of Magma Copper Company. Opmnting data collected over a period of several months indicate sulfur dioxide removal efficimicies exceeding 90%. 

---