(1) Calculate first the number of moles of nitrogen feed, and feed the same amount of steam to maintain the partial pressure of steam to meet the molar concentration 0.5 mol/mol for the case when no steam is consumed. But if steam is consumed by the reaction, additional steam shall be fed together. So far as the molar concentration is maintained at 3 bar, the partial steam pressure will be kept steadily under 6 atm of total absolute pressure.
Molar feed rate of N2 can be calculated from the ideal gas equation: n =(V*P)/(RT)
Where, V= 300 ml/min, P=absolute pressure of N2, R=ideal gas constant, T=absolute temperature; P and T is measured at the flow meter condition.
N2 feed rate, n mg-mole /min = (P atm)*(300 ml/min)/(R*T) ..........(1)
Ideal gas constant, R = (22.414 ml * 1 atm)/(1 mg-mole*273.15 K) = 0.082057 ml-atm/mg-mole/K
Then, water rate, w mg/min = (18.02 mg/mg-mole)*{(n mg-mole water/min) + (water consumption rate, m mg-mole/min)} ....(2)
(2) In case that the reaction system does not have any discharge of either liquid or gas phase, the first nitrogen fed to build up pressure will stay in the reactor. Then no additional nitrogen is required, feed steam only to make up for the consumption.
(3) At the beginning of the reactor start up, both nitrogen and total water to build up absolute pressure at 6 atm and 500℃ can be estimated as follows:
Reaction system volume: Vr [m3]
Initial pressure (purged by N2): Po = 1 [atm abs.]
Initial temperature of N2 in the reactor: 20℃, To =295.15 [K]
Initial number of moles of N2 in the reactor: No = (Vr*Po)/(R*To) .................(3)
Reactor temperature after feeding, heating up and pressurizing: Tr = 773.15 K
Final reactor pressure after feeding and heating up: Pr 6 atm abs.
Total number of moles of N2 and steam required in the reactor: Nt = Nn + Ns = (Vr*Pr)/(R*Tr).......(4)
Molar fraction of steam N2 in the reactor: Ns/Nt = 3 atm/ 6atm = 0.5;
- ditto - of N2: Nn/Nt = (Nt-Ns)/Nt =1- Ns/Nn =1-0.5 = 0.5
Nitrogen required for pressurizing = Nn - No = Nt/2 - No ....(5) <---initially charged N2 in the reactor to be deducted.
Steam required for pressurizing = Ns = Nt-Nn = Nt/2.............(6)
After heating up and pressurizing, the same amount of steam as N2 plus consuming steam additionally shall be fed to the reactor.
Stefano
Edited by sgkim, 13 October 2016 - 12:15 AM.