Sulfur Dioxide Generation

Sulfur burning process

Eka Engineering sulfur
 

Sulfur dioxide is generated by several processes. Large amounts are generated by burning sulfur-containing oils and by the production of metals through the roasting and smelting processes. For economic reasons, this sulfur dioxide can be purified and liquefied or converted to sulfuric acid, however, today this is also done for environmental reasons. Often sulfur dioxide is needed as a feed chemical for other processes ( i.e. reducing agent). In these cases sulfur dioxide is most often produced from burning elemental sulfur.
Sulfur dioxide has many commercial and industrial uses such as; cooking liquor and SO2 water in the paper pulp industry, sulfuric acid production, ore and metal refining, solvent extraction of lubricating oils, disinfecting and fumigating, oxidizing agent, reducing agent, and antioxidant.

As early as 1960, the first Eka Engineering Spiral Flame Sulfur Burner, type SF, was sold to a Pulp Mill in Sweden. Since then more than 180 sulfur burning plants have been sold. The sulfur burner developed in 1960 required only 1/3 the volume of a conventional burner of that day. This was achieved by introducing high velocity combustion air tangentially to the combustion chamber, and thus giving the flame a spiral path. Because of the turbulence created by this feeding method, a very efficient mixing of the reacting gas components was achieved. An afterburning unit located downstream makes it possible to achieve up to 19% SO2 concentration without risk of sublimation. Many different size burners, ranging from 2 metric tons of sulfur per day (MTPD) up to 600, have been provided by Eka Engineering.

Twenty years later, the Eka Engineering Cyclone Flame Sulfur Burner, type CF, was developed to meet customer demand for an even smaller burner installation. A further optimization of the flame path resulted in a burner volume of only 1/4 the size of the larger SF burner. A stable gas concentration of 18% SO2 is achievable without risk of sublimation. The designed capacity range is from 0.5 - 8.0 MTPD of sulfur.

Chemistry
Burning sulfur in air causes two different reactions:
S + O2 → SO2 + heat  
SO2 + 1/2 O2 → SO3 + heat

The latter reaction is an undesirable secondary reaction, which must be suppressed in favor of the first. This can be accomplished by keeping the SO2 concentration and the combustion temperature high. The maximum theoretical SO2 content, when using air in the combustion process, is 21%. Operating close to this figure in other conventional burners is very difficult without risk of sublimation of sulfur.

When SO3 contacts water it will form sulfuric acid which can result in downstream corrosion problems and formation of acid mist, which is difficult to eliminate. Burning sulfur in Eka Engineering sulfur burners to an SO2 concentration of 18% gives an SO3 concentration as low as 0.1%. SO3 is readily formed at temperatures around 500-700oC. However, when achieving high SO2 concentrations, the normal combustion temperature in the furnace is 1000 - 1300oC and the formation of SO3 is suppressed.

Sulfur Handling
The sulfur is supplied either in liquid form or as a solid. Eka Engineering burner operations require liquid sulfur, therefore solid sulfur must be melted by heating on site. The sulfur is melted by indirect steam heating. The steam used is normally saturated, 450 kPa (g) steam, to bring the liquid sulfur to it's lowest viscosity at 150oC.

Purchased liquid sulfur from trucks or railcars, is unloaded by compressed air or by pumping, into a storage tank. The tank should be equipped with heating coils.

The Eka Engineering Spiral Flame Sulfur Burner
Type SF - The SF Burner consists of the following main parts:

  • Sulfur Gun Station

  • Combustion Chamber

  • After Burner Chamber.

Filtered, molten sulfur is introduced into the combustion chamber in atomized form, by using compressed air. The sulfur gun, as well as the nozzles for combustion air, is specifically located within the combustion chamber to maximize burning efficiency and minimize space.
To react any remaining free sulfur, final combustion takes place in the after burner chamber. This chamber consists of a bed of inert pebbles creating very high turbulence and an intimate mixing of the gases. Efficient oxidation of the remaining free sulfur is thus assured. This is the primary reason a concentration of 19% SO2 can be achieved without risk of sublimation.
The SF burners in the capacity range of 5-100 MTPD of sulfur are standardized. The largest burner built has a capacity of 600 MTPD and the smallest 2 MTPD.

The Eka Engineering Cyclone Flame Sulfur Burner
Type CF - The CF Burner consists of the following main parts: 

  • Sulfur Gun Station. 

  • Combustion Chamber.

The CF Burner is fed with liquid sulfur via a dosing pump.
Filtered, molten sulfur is introduced into the combustion chamber in atomized form, by using compressed air. The sulfur gun, as well as the nozzles for combustion air, is specifically located within the combustion chamber to maximize burning efficiency and minimize space.
The capacity is easily varied to suit subsequent processes. The CF burner may be operated manually, or automatically by flow ratio control of liquid sulfur and combustion air. Changing capacity takes only a few seconds and it could be done from the control room.
Two sizes of the CF burners are available. Practical operating capacity range is 0.5-4.0 and 1.0-8.0 MTPD of sulfur respectively.

A plant, based on the CF burner may be supplied as complete, skid mounted units to enable a simplified installation with a compact layout. One unit contains the sulfur melter, filters and sulfur pumps. Another unit contains the CF burner, the gas cooling tower, strainers, pump and cooler for the circulating water. The units have the size of a normal 20-foot container.

Pressurized Operation
The entire plant is gas tight. The burners as well as the other components in the plant may be operated under pressure. The pressure is created by the sulfur burner fan, blower or compressor for combustion air. This eliminates the need for SO2 fans or gas compressors, thus reducing costly maintenance and simplifies operation. The standard operating pressure is around 20 kPa (g), although burners have been installed for operations of over 100 kPa(g).

Heat Recovery Boiler
For larger sulfur burning capacities, it is often economical to recover the heat energy produced. This is done by passing the hot SO2 gas from the burner through a waste heat boiler, generating steam.

Gas Cooling
Hot SO2 gas of approximately 1000 -1100oC enters the cooling tower. The tower works without packing. The main cooling is done by quenching with sprayed water. Adiabatic cooling by evaporation of water, which saturates the SO2 gas, cools the gas to around 80oC. By addition of external cooling of the circulating water, the gas can be further cooled to 40-50oC, depending on the cooling water temperature.

Gas Absorption
The cooled SO2 gas is normally absorbed in water or chemically reacted with other reaction media. Eka Engineering supplies absorption systems for the following applications: 

  • SO2 water 
  • Sulfite (caustic soda, soda ash, ammonia, slaked lime, magnesium hydroxide).

Appropriate material selection and a long experience ensures reliable operation of the absorption systems.

Typical Technical Data  
 

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