Draw a labeled diagram showing raw sludge being fed to an anaerobic digester tha

Question

Draw a labeled diagram showing raw sludge being fed to an anaerobic digester that is producing three products: a gas, a liquid supernatant, and digested sludge. Also show the gas product going to a furnace along with a separated stream of air, and show combustion gases leaving the furnace. Given the following data, calculate the total molar flow rate of CO2 gas coming out of the furnace, in gmol/day

- 1000 kg/day of raw sludge is fed into the digester

- 40% by mass of the raw sludge is converted to digested sludge

- 58% by mass of the raw sludge is converted to supernatant

- 70% by volume of the digester gas product is CH4, the other 30% is CO2

- the density of the gas product at 1 atm pressure and 25 degrees C is 1 kg/m3

- enough air is used in the furnace to burn all of the methane to CO2 and H2O

Explanation / Answer

Answer

In a day, of 1000 kg, 2% is converted to gas or 20kg of gas, of which methane is 20*0.7 = 14 kg and CO2 is 6kg. (because density is 1 kg/m3, vol% and mass% are equal)

mole of methane = 14000/16 = 875 moles which produces, when combusted fully, 875 mole of CO2

total CO2 = 875 + (6000/44) = 1011.36 gmol

Flow rate of CO2 is 1011.36 gmol/day.

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