PPE/11/6 The principles for the blast furnace process were ...

PPE/11/6
The principles for the blast furnace process were described in PPE/10/2; iron bearing
materials (Fe 2 O 3 ,Fe 3 O 4 and inert components) and coke (mostly C) are charged into the
furnace. In the furnace coke burns with the combustion air (O 2 and N 2 ) and the gases
formed heat, reduce and melt the iron bearing materials. The molten materials flow into
the blast furnace hearth, where the more dense pig iron (Fe with 4.5 mass-% C) collects
on the bottom and slag (inert components) on top of it. Pig iron and slag are then tapped
from the furnace through tapholes. The flue gases (N 2 , CO 2 and CO) flow out from the top
of the furnace.
The molten materials are at 1500 ºC, combustion air is at 1100 ºC and the flue gases at
150 ºC. Heat losses from the furnace can be approximated as Q loss = 360 MJ/t pig iron .
a) Calculate the pig iron production when the following data is given
Composition of iron-bearing material
sinter
mass-% of Fe 2 O 3 47.18
mass-% of Fe 3 O 4 41.46
Mass ratio of iron-bearing material and coke 3.3
Inflow rate of combustion air
135000 m 3 n/h
Also check the molar relation CO/CO 2 in the flue gases (should be ≈ 1).
Does this blast furnace perform well according to this criterion?
b) Check the influence of heat losses on the process by increasing and decreasing
Q loss by 30 %.
c) If one of the cowpers (regenerative heat exchanger where the combustion air is
heated) is temporarily out of use, the temperature of the combustion air may fall to
900 ºC. How would this influence the process? If needed, adjust the mass ratio of
iron-bearing material and coke so that the relation CO/CO 2 =1 in the flue gases.
General assumptions:
Coke contains 90 weigth-% C and the rest is inert material. The oxygen enriched
combustion air contains 26 mol-% O 2 while the flue gase contains no oxygen.
The enthalpy of the pig iron can be approximated as the enthalpy of molten Fe and solid C
at 1500 ºC. The enthalpy of the slag can be estimated by
ϑslag
kJ
h slag
= ( 1600 + 1.838⋅
( −1300))
° C kg
if the inert components’ enthalpy is 0 when taken into the furnace.

H m,i -values
O2_in 1100 ºC 36.25*1000 kJ/kmol
N2_in 1100 ºC 34.52*1000 kJ/kmol
O2_in 900 ºC 29.21*1000 kJ/kmol
N2_in 900 ºC 27.86*1000 kJ/kmol
N2_ut 150 ºC 4.40*1000 kJ/kmol
Fe2O3_in 25 ºC 2.56*1000 kJ/kmol
Fe3O4_in 25 ºC 123.53*1000 kJ/kmol
CO2_ut 150 ºC 5.99*1000 kJ/kmol
CO_ut 150 ºC 287.19*1000 kJ/kmol
C_in 25 ºC 393.68*1000 kJ/kmol
C_ut 1500 ºC 423.45*1000 kJ/kmol
Fe_ut 1500 ºC 484.78*1000 kJ/kmol