Page 168 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

Chapter | 4 Torrefaction 145

Recycled
flue gas X.W’ ,T go
g
W ,T’’ o
oil
Burner
W ,T gi
g
with
dilution
W ,T’ o air
air
FIGURE 4A.2 Control volume of burner with gas mixing chamber.

where,
A 5 ðW v C v 1 W vl C g ÞT g0 1 W t C d T t 2 W f C b T 0 1 W v L

Oil Burner: Control Volume of Oil Burner

We assume that X fraction of the flue gas leaving the torrefier is fed into the
burner along with fresh air W air . Since the recycled gas (XW ) contains
0
g
some unburnt volatiles (XW vl ), we assume this to supplement oil in the
burner. We assume fuel oil is preheated to temperature Tv 0 .
Q vl 5 heat energy released from the combustion of volatile gases
5 XW vl LHV vl η

where η is combustion efficiency.
From Figure 4A.2, we write the energy balance as:

0 0
W g C g T gi 5 XW C g T g0 1 XW vl LHV vl η 1 W air C a T 1 W oil LHVη 1 W oil C oil Tv 0
g 0
So, the mass fraction, X, of torrefier product gas recycled is
0
W g C g T gi αðA=FÞC a T 2 W oil LHVη 2 W oil C oil Tv 0
0
X 5 (A.6)
W C g T g0 1 W vl LHV vl η
0
g
Substituting values from Eqs. (A.4) and (A.6), we have
0
½W g 2W oil ðαðA=FÞ11ފ W g C g T gi 2W oil αðA=FÞC a :T 2W oil LHVη2 Woil C oil Tv 0
0
5
W 0 W C g T g0 1W vl LHV vl η
0
g g
Amount of oil consumed in the burner is calculated from here as:
1 W g C g T gi
W oil 5 3 0 2 1 (A.7)
K 2 P W g 0 C g T g0 1 VL LHV vl η
fr
where,

0
αðA=FÞC a :T 1 LHVη 1 C oil Tv 0 ðαA=F 1 1Þ 0 W vl
0
K5 ; P5 and VL 5
W C g T g0 1 W vl LHV vl η W 0 g fr W 0 g
0
g