Question

A wet scrubber uses lime to remove HCl from a gas waste stream. The scrubber operation characteristics are as follows:

Scrubber efficiency                    90%

Minimum gas velocity              2.5 m/s

Gas flow rate                               18 m³/s

HCL Concentration                    120 ppmv

Calculate:

a) scrubber diameter

b )HCL removal rate, kg/day

c) Required stoichiometric CaO loading, kg/day (theoretical)

d) If the lime is only available in a 12% slurry concentration, what is the field application rate, kg/day

e) If the lime feed is feed at a factor of safety of 2.5:1, what is the lime feed rate, kg/day

Answer 1

a) Gas Velocity (V) = 2.5 m/s, Gas flow rate = 18 m³/s

Flow rate = Velocity (V) X Cross-sectional area (A)

Cross-sectional area (A) = Flow rate / Velocity (V) = 18 / 2.5 = 7.2 m²

A = πr²

7.2 = 3.14 X r²

r² = 7.2 / 3.14 = 2.29

r = 1.51 m

Scrubber diameter (d) = 2 X r = 2 X 1.51 = 3.02 m

b) Concentration of HCL = 120 ppmv or 120 g/m³

Theoretical HCL removal rate = Concentration of HCL X Gas flow rate = 120 g/m³ X 18 m³/s = 2160 g/s = (2160 X 24 X 60 X 60) / 1000 = 186624 kg/day

HCL removal rate with 90% scrubber efficiency = (186624 X 90) / 100 = 167962 kg/day