Torrefaction - Biomass Gasification, Pyrolysis and Torrefaction - page 144

Q loss

W g

W g ,T gi

W v W f ,T 0

Q gen

W' g ,T go

W vl

W t ,T o

FIGURE 4A.1 Control volume of torrefier.

Air required for burning oil with an excess air coefficient, α is

A
F W oil
From here, the fraction of gas recirculation, X, is calculated as:

W air 5 α

5 ½

W g 2 W oil :ðαð A = F Þ 1 1 Þ

X (A.4)

W 0 g

ENERGY BALANCE
Torrefier: Control Volume of Torrefaction Zone ( Figure 4.11 )
From the mass balance around the torrefier ( Figure 4A.1 ), we get:

Enthalpy in energy generated by mild exothermic process enthalpy out

1 5 1

energy loss through reactor latent heat carried away by the moisture content

1

Q gen 5 ð W vl C g Þ

W g C g T gi 1 W f C b T o 1 W g C g 1 W v C v 1 T g0 1 W t C d T t 1 Q loss 1 W v L

where L is latent heat of vaporization of moisture.
Assuming that heat losses and heat generated by mild exothermic reac-
tion are negligible, the above can be simplified as:

W g C g ð T gi T g0 Þ 1 W f C b T 0 ð W v C v 1 W vl C g Þ T g0 W t C d T t W v L 0

5

So, the mass flow of heating medium, W g ,is
W g 5 ð

W v C v 1 W vl C g Þ T g0 1 W t C d T t 2 W f C b T 0 1 W v L

C g ð T gi 2 T g0 Þ

or

A

W g 5 (A.5)

C g ð T g0 Þ T gi 2