Sulphuric Acid

Topics: Sulfur, Sulfuric acid, Sulfur dioxide Pages: 7 (1528 words) Published: March 8, 2013
MATERIAL BALANCE GIVEN: TO DESIGN A 1000TPD CAPACITY H2SO4 ACID PLANT BASIS: 1 HOUR OF OPERATION. PURITY: PRODUCT WHICH IS TO BE MANUFACTURED IS ASSUMED TO HAVE STRENGTH OF 98% ACID. 1000TPD implies that we have Acid 1000 x 10 / 24 = 41666.67 Kg/Hr of 3

With 98% purity, the acid that is produced per hour = (98 x 41666.67) / 100 = 40833.34 Kg/Hr Kmoles of Sulfuric acid to be produced = 40833.34 / 98 = 416.667 Kmoles/Hr

It’s assumed that overall absorption of the acid is 100 % = 416.667 / 1.0 Then, SO3 required = 416.67 Kmoles/Hr Also its assumed that the overall conversion of SO2 to SO3 in the reactor is 99.8% Then SO2 required= 416.67 / 0.998 = 417.51Kmoles/Hr Assuming 100% combustion of Sulfur, Then S required = 417.5 Kmoles/Hr = 13360.3 Kgs

Amount of oxygen required to convert 1Kmole of S to SO3 = 1.5 Kmoles Then, amount of Oxygen required = 417.51 x 1.5 = 626.26 Kmoles

As cited in the literature that some amount of excess oxygen must be used,

Using 40% excess, O2 required = 626.26 x 1.4 = 876.76 Kmoles From this the total dry air that is coming in can be calculated as. Dry air in •

= (876.76 x 100)/ 21 = 4175 Kmoles/Hr

At 30 C, assuming 65% Relative Humidity, Humidity as calculated from the psychometric chart is, Humidity = 0.0165 Kg water/ Kg dry air Then, water entering with dry air = 4175 x 29 x 0.0165 = 1997.73 Kg/Hr = 110.980 Kmoles/Hr Total weight of entering air = 4175 x 29 + 110.980 x 18 = 123073 Kgs

DRYING TOWER: Q (121075 Kgs) (Dry Air)

R (193806 Kgs)

P (123073 Kgs)

S (195804 Kgs)

Making a Mass balance around the Drying Tower P+R=Q+S As water is being removed from the incoming air to make it dry, the 98% acid that is being recycled to the tower, decreases in concentration and let this concentration be assumed as 97%, then we can write,

0.02 x R + 1998 = S x 0.03 H2SO4 Balance will give, R x 0.98 = S x 0.97 Solving the above equations R = 193806 Kgs S = 195804 Kgs (2)

(1)

SULFUR BURNER: SULFUR (13360.3 Kgs)

DRY AIR SO2 (26720.6 Kgs) (121075Kgs) Kgs) N2 Kgs) The combustion reaction takes place inside the burner where Sulphur is oxidized to Sulphur Dioxide Moles of Sulfur coming in Moles of Oxygen coming in = 417.51 Kmoles = 876.76 Kmoles O2 (14696 (92352.4

As mentioned before we have assumed 100% combustion of sulphur, Sulfur Dioxide Formed = 417.51 Kmoles Oxygen leaving = 876.76 – 417.51 = 459.25 Kmoles Nitrogen leaving = (876.76 x 79)/ 21 = 3298.3 Kmoles

REACTOR: As cited in the reference by author NORMAN SHREVE et al Pg 337, the temperature and conversions in Each Stage of a Monsanto Converter is given as follows: LOCATION Gas entering first pass Gas leaving first pass Rise in temperature Gas entering second pass Gas leaving second pass Rise in temperature Gas entering third pass Gas leaving third pass Rise in temperature Gas entering fourth pass Gas leaving fourth pass Rise in temperature TOTAL RISE TEMPERATURE ( C) 410.0 601.8 191.8 438.0 485.3 47.30 432.0 444.0 12.00 427.0 430.3 3.300 254.4 1.30 98.0% 18.4 •

EQUIVALENT CONVERSION (%)

74.0

4.3

Note: As we see from the table that the overall conversion in the reactor is 98% but to validate our assumption that was made earlier, we assume that the conversion in the last stage of the reactor is 3.1% instead of 1.3% so that the assumption of 99.8% as overall conversion remains unaffected and thus temperature for the gas leaving the fourth pass is • then assumed to be 437 C. COMPONENT S I STAGE 74% CONVERSION II STAGE 18.4% CONVERSION III STAGE 4.3% CONVERSION

I/LET KMOLS

O/LET KMOLS

I/LET KMOLS

O/LET KMOLS

I/LET KMOLS

O/LET KMOLS

N2 SO2 SO3 O2 TOTAL Kmols

3298.3 417.51 0.0 459.26 4175.1

3298.3 108.55 308.95 304.7 4020.6

3298.3 108.55 308.95 304.7 4020.6

3298.3 31.73 385.77 266.36 3982.2

3298.3 31.73 385.77 266.36 3982.2

3298.3 13.77 403.73 257.39 3973.2

N2 = 3298.3 Kmoles SO2 = 417.51 Kmoles SO3 = 0.0 Kmoles I
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