Module 4 : Unit processes 2
  Lecture 37: Gassification material and heat balance
 
 



NCV of coal

= 81 %C + 341 [%H − %O/8] – 5.84 (9 %H + M)
= 81 × 79.1 + 341 [5 – 6.4/8] – 5.84 (9 × 5 + 1.7)
= 7566.32 Kcal

Enthalpy of water vapour in moist air

H2O (l) = H2O (g)

Heat absorbed = 584 Kcal/Kg H2O
                      = 584 × 1.7 /100   =   9.93 Kcal

Enthalpy of saturated steam:

Gauge pressure = 30.8 psi
Pressure 740 mm = 14.3 psi
Absolute pressure = 45.1 psi

Enthalpy of saturated steam at 45 psi referred to water at 0oC = 651 Kcal/Kg
Enthalpy difference between water at 25oC and water at 0oC = 24.94 Kcal/Kg
Enthalpy of steam referred to water at 25oC = 626 Kcal/Kg
Enthalpy of steam used = 626 × 0.266
                                    = 166 Kcal

Enthalpy of water vapour in hot gas at 900K

H2O (l) = H2O (g)                       ΔHo 298 = 10.5 Kcal/g mole H2O
H2O (g) , 298K = H2O (g) , 900K     ΔHo– 5.2 Kcal/g mole H2O
Enthalpy of water vapour referred to H2O (l) = 15.7 Kcal/g mole H2O
Enthalpy of water vapour in hot gas = 15.7 × 0.208 × 1000 × 2.5/100
                                                    = 81.64 Kcal


Sensible heat of dry producer gas at 900K

H900 – H298 | CO2 = 6708 Kcal/Kg mole
H900 – H298 | CO  = 4400 Kcal/Kg mole
H900– H298 | CH4 = 7522 Kcal/Kg mole
H900–H298 | H2  = 4224 Kcal/Kg mole
H900– H298 | N2 = 4358 Kcal/Kg mole


Heat Balance

Heat Input:

Input
Kcal
CV of coal
7566.32
Sensible heat in coal, air
0
Enthalpy of water vapour in air
9.93
Enthalpy of steam
166
Total
7742.25

 

Heat Output:

Output
Kcal
CV of dry PG
5640
Sensible heat of dry PG
932.8
Enthalpy of water vapour in hot gas
81.6
Heat losses
1087.85
Total
7742.25

 

Cold gas efficiency = 5640 ×100/7742.25
                               = 72.85%
Hot Gas efficiency = 6653.6 × 100/7742.25
                               = 85.9 %
Thermal efficiency = 5721.6 × 100/7742.25
                              = 73.9%

Source for thermodynamic values:

H.Alan Fine and G.H.Geiger: Handbook of material and energy balance calculations in metallurgical processes

A. Butts Metallurgical problems (for more problems)