PRODUCTION OF SULPHURIC ACID BY CONATACT PROCESS

Introduction of Oleum 

The Cyanamid oleum plant specially designed for the manufacturing of H2SO4 of 98.5% to 99.55% strength and H₂S₂O₇ which is 100% sulphuric acid containing 20% of dissolved SO3 which is equivalent to 105% concentration.

Raw material

The raw materials used are as under:

SULPHUR………………………………4 S/TONS per day

H2SO4……………………….10 M/TONS for initial start up

D-MIN water feed…………… 3000 g/day approx

Catalyst……………………….20 drums to fill convertor

Plant capacity

The plant was designed to produce 10 m/tons of 100% H₂SO₄ per 24 hours as 99% H₂SO₄.

Production procedure

The oleum plant consists of a store for sulfur with means of wighing and trolly support slufting from store to plant. A melting sulphur pit with fetter a pump to pressurize the molten sulphur and feed to the the atomizing burner a furnace for combustion. The air for combustion is supplied by a blower. It is dried to avoid the subsequent condensation of moisture in a scrubbing tower feed with 99% H2SO4. The blower blowing  the dry air through the drying tower. The sulpher is burnt with an exess of dried sulphur dioxide.

              The hot fumed gases are cooled in a W.H.B where some of heat of combustion and temperature at 450c is filtered through the graded crushed quartz. By mixing in additional dry air passed to the convertor. In this unit after filteration to remove impurities the convertor take place in three stages where a layer of vanadium penta-oxide catalytically converts the sulphur dioxide to the sulphur trioxide. The three such catalyst masses each followed by a cooler to remove the heat of reaction. The final cooler also bring the gases temp down to 50-30c.All these reactions are exothermic

SO₂ cooling:

Before the absorption the converted gases are cooled in the SO₃ cooler.

Absorption  for mixing 98.5% H₂so₄

The  gases from the SO3 cooler enter the bottom of the absorption tower just above the tower acid pump and pass up through the descending acid in which  they are absorbed. The spent gases mainly nitrogen and some unsaturated SO2+SO3 escape to atmosphere via the stack chimney at the top of the tower. A constant circulation of acid is maintained through the absorption tower and the air drying rings by means of a circulation pumps. Stronger acid from the absorption tower and relatively weaker acid from the drying towerare blent together in a manifold pipe which is converted to the suction of the circulating pump. The absorption of SO3  in 95% COV is an exothermic reaction . the warm acid from the tower is cooled to a temp of 25-35c before recirculation over the tower maintain production sufficient treated water to balance the SO3 input is feed to the tower this water should be free from chlorides.

Sulphur melting

Crushed sulphur is normally used and it is melted in brick lined pits fitted with steam heat coils.

Sulphur burning

Molten sulphur is burnt by spraying it into a furnace chamber under pressure for efficient burning of sulphur good atomization is necessary. This depends upon the low viscosity of the molten sulphur.

The pressure produced by the turbine pump. Care should be taken to supply the excess of air for combustion as otherwise sulphur may be sublimbed and will pass on to the later stages unburnt and causes of cheeking.

The exact temp of the furnace is related to the furnace. Safe conditions and their temp is 900C. Certain amount of air is allowed to by pass the furnace and reduces the gas strength to 6-8%.

Air Drying

It is necessary to dry the air used for combustion of sulphur to prevent damage to the catalyst from acid condensation.

Utilization of waste heat

Conversion of SO2 to SO3 is carried out above 440c so the burner gases have to be cooled to 500c. This heat is used for producing steam which is then utilized for melting sulphur, to drive the steam turbine and surplus steam is put into the factory.

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