An inorganic chemical sulfuric acid production by Lead chamber process with description and flow sheet:
Lead Chamber process is one of the sulphuric acid production methods which gives only about 50-60 Be grade acid. The main principle behind the process is that the moist SO2 (sulphur dioxide) in presence of nitrogenous oxides (active catalyst) is oxidized to sulphur trioxide with the oxygen present in the air. Sulphur trioxide is made to react with water to produce sulphuric acid. The reactions would be like below:
- 2SO2 + O2 → 2SO3
- SO3 + H2O → H2SO4
Description of Lead Chamber process:
Sulphur is burned with air to produce sulphur dioxide gas and due to excess air burning, oxygen and nitrogen are present along with the sulphur dioxide. By means of filters, solid particles are filtered leaving out the clean gas mixture. Now the gas mixture is passed from combustion chambers to Glower’s tower through nitre pots where NO2 and NO are mixed. Glower tower is the brick made chamber which are acid resistance, Burner gases that are SO2, O2, N2, NO2 and NO are at the temperature 450-650oC are passed to the bottom of Glower tower. In counter-current to these gases dilute sulphuric acid scrub down the Glower tower, the gases are cooled down to 70-80oC.
The acid scrub collected the bottom of Glower tower is passed to air cooler to bring the temperature from 130-150oC to 40oC which is to maintain the feed of the lead chambers. A parallel set of lead chambers are set up where the walls and roof of the chamber are fitted with lead sheets. Low-pressure steam and filtered water are introduced at top of the chamber through spray nozzles. The acid thus formed condenses on the wall and collected as chamber acid which is a dilute sulphuric acid. The reaction carried by the nitrogen oxides at nitre pots are
- 2ONOSO2OH + H2O → 2H2SO4 + NO + NO2
- SO2 + NO2 + H2O → H2SO4 + NO
The unabsorbed gases from the lead chamber are ready to enter into the Gay-Lussac’s tower where dilute concentration HNO3 used to react the upcoming gases of nitrosyl sulphuric acid. The reaction takes place in the tower would be
HNO3 + NO.HSO4 → 2NO2 + H2SO4
The oxides of nitrogen are absorbed by the glower acid forming nitrosyl sulphuric acid.
NO + NO2 + 2H2SO4 ↔ 2.NOHSO4 + H2O
The whole set up is explained by the following flowsheet of lead chamber process.
The concentration of sulphuric acid is tested from the outlet of the tower frequently to ensure the quality and it is conducted continuously by indirect measurement method called specific gravity. It is calculated as the ratio of sulphuric acid density and water density measured at the same temperature. Twaddell scale is one of the famous scale used in hydrometer to find specific gravity of acids which is related to the weight percentage. The formula for calculation of the degree of Twaddell of sulfuric acid using specific gravity is: 200(Sp.Gravity-1.0)