## Lesson 9. Energy analysis of gasification

Mass and energy balance of gasifier system can be carried out when gasifying the selected feedstocks studies.

i. Mass balance

Mass balance study can be conducted for the gasification of biomaterials.  The various mass input and out put to be considered and the corresponding calculation procedure is given below.

Mass input

1. Feed rate, kg h-1                             :           Fr
2. Air flow, kg h-1                               :           Fa
3. Charcoal, kg                      :           Mc

Total mass input (MI)              =          Fr + Fa + Mc

Mass output

1. Product gas, kg h-1             :           Qt x Fr x ρG
2. Tar, kg h-1                                          :           Mt
3. Char/ dust, kg h-1                         :           Mch
4. Ash, kg                             :           MA
5.  Char coal, kg                    :           Mco

where

Qt        -           quantity of producer gas generated, Nm3 h-1

ρG        -           density of producer gas, kg Nm-3

Total mass output (MO)           =          Qt x Fr x ρG + Mt + Mch + MA + Mco

Mass balance is given as,

Total mass input (MI) - Total mass output (MO) = 0

Fr + Fa + Mc – (Qt x Fr x ρG + Mt + Mch + MA + Mco) = 0

From the mass difference worked between input and out put, accuracy of the method adopted for calculation can be determined by mass closure procedure.

ii. Energy balance

The procedure adopted for the calculation of energy balance for fluidized bed gasification of all biomaterials are given below.

Energy input

1. Feed, MJ h-1                                     :           Fr x CVF
2. Charcoal, kg                      :           Mc x CVC

where

CVF     -           calorific value of feed material, MJ kg-1

CVC     -           calorific value of char, MJ kg-1

3. Air (if preheated)                    :           ma cpa dta

where

ma        -           mass of air, kg

cpa       -           specific heat of air, MJ kg-1ºK-1

dta          -           temperature difference in air, ºK

Total energy input (EI)            =          (Fr x CVF) + (Mc x CVC)

Energy out put

1. Gas energy output, MJ h-1 (Eg)

=(Qt x Fr x ρG x CVG) + (Qt x Fr x ρG x cpG x ∆Tg)

where

ρG           -           density of producer gas, kg Nm-3

cpG       -           specific heat of producer gas, MJ kg-1

∆Tg      -           temperature difference of producer gas to atmosphere, ºC

2. Char energy out put MJ h-1 (Ec) =      (Mch x CVC) + (Mch x cpch x ∆Tc)

where

cpG       -           specific heat of char, MJ kg-1

∆Tc      -           temperature difference of char to atmosphere, ºC

3. Energy loss,  MJ h-1 (Ec)         =          U x Sre x hr x ∆Tr

where

U         -           overall heat loss coefficient

Sre        -           Surface area of the reactor, m2

hr         -           heat transfer coefficient, kCal m-2 ºC

∆Tr      -           temperature difference of reactor to atmosphere, ºC

Total energy out put (Eo)        :           Eg + EC + EL

Energy balance is given as,

Total energy input (EI) - Total energy output (MO) = 0

(Fr x CVF) + (Mc x CVC) – [(Qt x Fr x CVG) + (Qt x Fr x ρG x cpG x ∆Tg) + (Mch x CVC) + (Mch x cpch x ∆Tc) + EL] = 0

The difference in energy between input and out put of the study gives the accuracy of the method adopted for calculation of energy balance and the corresponding energy closure calculation.