Sulfur Burning Furnace

Fig. 25.11. Sankey energy flow diagram for a 1000ton/day sulfur-burning double absorption sulfuric acid plant (feed gas 10% S02). A Blower B Sulphur furnace C Waste heat boiler D Catalyst bed 1 E Steam superheater F Catalyst bed 2 G Boiler H Catalyst bed 3 J Intermediate heat exchangers K Intermediate absorber L Converter bed 4 M Economizer N Final absorber O Air dryer P Acid coolers. (Courtsey Lurgi GmbH, Frankfurt, Germany.)...

Sulfur burning furnace Sulfide mineral smelters and roasters Spent acid decomposition furnace... 

Fig. 1.1. Schematic of sulfur burning sulfuric acid plant, courtesy Outokumpu OYJ www.outokumpu.com The main components are the catalytic S02 + A02 — S03 converter (tall, back), twin H2S04 making ( absorption ) towers (middle distance) and large molten sulfur storage tank (front). The combustion air filter and air dehydration ( drying ) tower are on the right. The sulfur burning furnace is hidden behind. Catalytic converters are typically 12 m diameter.

Fig. 3.0. View of spinning cup sulfur burner from inside sulfur burning furnace - burning capacity 870 tonnes of molten sulfur per day. The thermocouple at top and central blue sulfur-rich flame are notable. Photograph courtesy of Outokumpu OYJ. www.outokumpu.com...

Fig. 3.1. Sulfur burning flowsheet - molten sulfur to clean dry 700 K S02, 02, N2 gas. The furnace is supplied with excess air to provide the 02 needed for subsequent catalytic oxidation of S02, to SO3. Table 3.1 gives industrial sulfur burning data.

Fig. 3.3. Burner end of sulfur burning furnace. Atomized molten sulfur droplets are injected into the furnace through steam-cooled lances. Dry combustion air is blown in through the circular openings behind. The sulfur is oxidized to S02 by Reactions (3.1) and (3.2). Atomization is done by spiral or right angle flow just inside the burner tip.

Fig. 3.4. Entrance to fire tube boiler tubes after Fig. 3.3 s sulfur burning furnace. 1400 K gas ( 11 volume% S02, 10 volume% 02, 79 volume% N2) leaves the furnace and enters the boiler. It turns 90° in the boiler and flows into the tubes. The tubes are surrounded by water. Heat is transferred from the hot gas to the water - cooling the gas and making (useful) steam. The tubes are typically 0.05 m diameter. Table 3.1 gives industrial furnace data. Sulfur furnace boilers are discussed by Roensch (2005).

Air for sulfur burning is filtered through fabric and dried. It is then blown into the sulfur burning furnace. It is blown in behind the sulfur spray to maximize droplet-air contact. 

The dried air is blown into the sulfur burning furnace by the acid plant s main blower. 

The blower is a steam or electricity driven centrifugal blower (Jacoby, 2004). It blows air into the sulfur burning furnace - and the furnace s offgas through the remainder of the acid plant. 0.3 to 0.5 bar pressure is required. 

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. 

The composition and temperature of sulfur burning s product gas are controlled by adjusting the sulfur burning furnace s ... 

Sulfur burning furnace input mass air/input mass sulfur ratio... 

An alternative way to increase S02 concentration (and decrease furnace exit gas volume) is to feed less N2 to the sulfur burning furnace - by replacing some air with oxygen (Miller and Parekh, 2004). 

Decreasing sulfur burning s air/sulfur ratio raises product gas temperature, Fig. 3.6. If carried too far (i.e. to raise % S02-in-gas), this may damage the sulfur burning furnace or boiler. 

Sulfur burning s product gas composition and temperature are readily controlled by adjusting the sulfur furnace s input air/input sulfur ratio. Replacement of some of the input air with oxygen gives the process independent 02/S02, temperature and volume control. 

Heat for this reaction is mainly provided by burning molten sulfur and other fuels with preheated air (occasionally oxygen-enriched) and the 02 from Reaction (5.1). A small amount of heat is obtained from oxidizing the spent acid s hydrocarbons. Sulfur burning has the advantages that it increases S02 concentration in decomposition furnace offgas and H2S04 production rate. 

This problem is avoided by dehydrating (i) sulfur burning air and (ii) scrubbed metallurgical/spent acid furnace offgas by contacting these gases with strong sulfuric acid. Dehydration is represented by the reaction ... 

S02 oxidation requires 02. Sulfur burning furnace offgas already contains 02, Table 7.1. None needs to be added. Metallurgical and waste acid decomposition furnace offgases often contain little 02, so some must be added before catalytic S02 oxidation. It is added in air or ventilation gas before gas dehydration. 

Table 7.1. Compositions of furnace offgases and catalyst bed feed gases. Sulfur burning gases don t change. Metallurgical and waste acid decomposition furnace offgases lose S03 and H20(g). The SO3 is removed during water scrubbing. The H20(g) is removed during condensation and dehydration. ...

The major source of sulfur oxides in the atmosphere is the burning of sulfur-containing coal in power plants. As this type of coal burns in a furnace, sulfur dioxide gas, SO2, is produced. The SO2 escapes into the atmosphere, where it reacts with more oxygen to form sulfur trioxide, SO3. 

Gases produced contain about 6% SO2 but the composition is not constant. Hence, there is an additional sulfur burning furnace to maintain thennal stability in... 

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