Energy balance of Diesel Production plant in refinery. Calculation of make up hydrogen requirement in the reactor. Calculation of Steam requirement in fractionator for distillation.

1. Chapter 4: Energy Balance
The increasing cost of energy has caused the industries to examine means of reducing
energy consumption in processing. Energy balances are used in the examination of the
various stages of a process, over the whole process and even extending over the total
production system from the raw material to the finished product.
Enthalpy balance can be done as
Enthalpy In + Heat added = Enthalpy Out + Heat Removed
Enthalpy for any stream can be found out by
H = m*Cp* T
Where, H = Enthalpy change
m = Stream molar/mass flow rate (kmol/hr)
Cp = Heat capacity (J/ (kmol*K))
T = Tstream – Treference (K)
We cannot calculate enthalpy but instead calculate enthalpy change. Assuming reference
temperature as ambient temperature (Treference = 298.15 K). For any Stream,
H = m*Cp*(Tstream -298.15)
In the entire stream no pure component, so heat capacity of each stream can be found out
by knowing heat capacity of pure component
Cpavg = xi * Cpi
Where, Cpavg= heat capacity of stream
Cpi = Heat capacity of component i
Xi = mole fraction of component i in stream
Physical Properties:
Reference Temperature: 298.15

2. Stream Temperature (K) Flow rate
(Kg/hr.)
Specific Heat (KJ/Kg
K)
Q (KJ/hr.)
1 658.15 5000 3.2 65189195.9
2 658.15 644 14.57
3 686.15 16451.42 11.188 7141699
4 338.15 10807.4 14.406 6227656.1
6 573.15 7112.5 3.2 6259000
7 375.15 91.67 2.22 15670
8 375.15 241.67 1.67 31076
9 375.15 641.67 2.54 125497
10 463.15 166.67 2.37 65175.1
11 508.15 1989.17 2.35 981653.9
12 573.15 1981.67 2.52 1373295.2
13 616.15 2000 3.04 1933440
14 616.15 308 14.55 142508.5
15 644.15 5647.63 10.536 20517839.7
16 338.15 3339.63 14.56 1945000.5
Specific Heat calculation:
For Reactor 2
For VGO at T = 343O
C
API = 14.09

3. Specific Gravity = (141.5/ (131.5+API))
= (141.5 / (131.5+ 14.09))
= 0.971
Specific Heat Cp = (1.685+0.0034*T)/ Sqrt(S.G)
= (1.685+ .0034*343)/sqrt(0.971)
= 2.893 kJ/kg K
Make up Hydrogen Specific Heat = 14.55 kJ/kg K
Quench hydrogen specific Heat = 14.4 kJ/kg K
Average Specific Heat for reactor 2 inlet stream:
= (0.35*2.893) + (.05*14.55) + (0.59*14.4)
= 10.39 kJ/kg K
For Reactor 1:
Qin = M * Cp * T
= (16451.4)*(11)*(658.15 - 298.15)
= 65189195.9 KJ/hr.
Qout = M * Cp * T
= (16451.4) * (11.188) * (686.15-298.15)
= 71416990 KJ/hr.
Difference = Oout – Qin
= 71416990-65189195.9
= 6227794.8 kJ/hr.
Calculation of Hydrogen quench requirement:
Q = M * Cp * T
M = Q/Cp / T
= 6227794.8 / 14.6 / (338.15-298.15)
= 10807.4 kg/hr.

4. For Reactor 2:
Qin = M * Cp * T
= (5647.6)*(10.39)*(616.15 - 298.15)
= 18663709.5 KJ/hr.
Qout = M * Cp * T
= (5647.6) * (10.536) * (644.15-298.15)
= 20588178.3 KJ/hr.
Difference = Oout – Qin
= 205881783.8 – 186637095.5
= 1924468.8 kJ/hr.
Calculation of Hydrogen quench requirement:
Q = M * Cp * T
M = Q/Cp / T
= 1924468.8/ 14.6 / (338.15-298.15)
= 3339.6 kg/hr.