Wet sulfuric acid process
The wet sulfuric acid process (WSA process) is one out of many gas desulfurization processes on the market today. Since its introduction in the 1980s, where it was patented by the Danish catalyst company Haldor Topsøe A/S, it has been recognised as an efficient process for recovering sulfur from various process gasses in the form of commercial quality sulfuric acid (H2SO4). The WSA process is applied in all industries where removal of sulfur is an issue.
Wet catalysis processes differ from other contact sulfuric acid processes in that the feed gas still contains moisture when it comes into contact with the catalyst. The sulfur trioxide formed by catalytic oxidation of the sulfur dioxide reacts instantly with the moisture to produce sulfuric acid in the vapour phase to an extent determined by the temperature. Liquid acid is subsequently formed by condensation of the sulfuric acid vapour and not by absorption of the sulfur trioxide in concentrated sulfuric acid, as is the case in contact processes based on dry gases.
The concentration of the product acid depends on the H2O/SO3 ratio in the catalytically converted gases and on the condensation temperature.[1] Cite error: The <ref> tag has too many names (see the help page).
The wet catalysis process is especially suitable for processing the wet gasses obtained by the combustion of hydrogen sulfide (H2S) containing off-gasses.[2] The combustion gasses are merely cooled to the converter inlet temperature of about 420-440 °C. To process these wet gasses in a conventional cold-gas contact process (DCDA) plant would necessitate cooling the gas to an economically unacceptable extent to remove the large excess of moisture. Therefore in many cases Wet catalysis processes is a more cost-efficient way of treating hydrogen sulfide containing off-gases.
Description of the wet sulfuric acid process (WSA)
In the first step, sulfur is burned to produce sulfur dioxide.
- S (s) + O2 (g) → SO2 (g)
or Hydrogen sulfide H2S gas is incinerated to SO2 gas.
- H2S + 3/2O2 → H2O + SO2 + 518KJ/mole
This is then oxidized to sulfur trioxide using oxygen in the presence of a vanadium (V) oxide catalyst.
- 2 SO2 + O2 → 2 SO3 + 99KJ/mole (in presence of V2O5)
The sulfur trioxide is hydrated into sulfuric acid H2SO4.
- SO3 + H2O → H2SO4 (g) + 101 KJ/mole
The last step is the condensation of the sulfuric acid to liquid 97-98% H2SO4
- H2SO4 (g) + 0.17H2O (g) → H2SO4(l) + 69 KJ/mole
Application
The technology is able to treat one or more sulfur containing streams such as:
- H2S gas from amine gas treating unit
- SWS gas
- Spent acid
- Claus process tail gas
- Heavy residue or petcoke-fired utility boiler off-gas
- FCC regenerator
- Boiler flue gas
About 80% to 85% of the world’s sulfur production is used to manufacture sulfuric acid. Half of the world’s sulfuric acid production is used in fertilizer production, mainly to convert phosphates to water-soluble forms, according to the Fertilizer Manual, published jointly by the United Nations Industrial Development Organization (UNIDO) and IFDC.
[3]
References
- ^ Sulphur recovery; (2007). The Process Principles in sulphur recovery by the WSA process.). Denmark: Jens Kristen Laursen, Haldor Topsøe A/S. Reprinted from Hydrocarbonengineering August 2007
- ^ Gary, J.H. and Handwerk, G.E. (1984). Petroleum Refining Technology and Economics (2nd Edition ed.). Marcel Dekker, Inc. ISBN 0824771508.
{{cite book}}:|edition=has extra text (help)CS1 maint: multiple names: authors list (link) - ^ [1]; (July 2008). IFDC FOCUS ON FERTILIZERS AND FOOD SECURITY,Issue 4; Global Shortage of Sulfuric Acid Contributes to Rising Fertilizer Costs