silicon for the chemical and solar industry XIII

It must be noted that fast pyrolysis is different from the pyrolysis process applied in this

work and is used to maximize the yield and quality of the condensate. Hence, the

obtained pyrolysis oil in this work is expected to have somewhat lower quality than that

of the fast pyrolysis oils. This is also reflected on the heating value of 15.3 MJ/kg,

which is lower compared to about 17 MJ/kg reported for fast pyrolysis oils. However,

when calculated back on dry basis the heating values are on par with each other at

around 22.8 MJ/kg. The pH for the condensate is similar as for fast pyrolysis oil at 2.5

but the total acid number (TAN) is almost twice as high at 205 mg KOH/g. Hence, from

a combustion point of view, the condensate can be regarded as a "high" moisture

content pyrolysis oil. From an upgrading point of view (to chemicals or engine fuels),

larger challenges can be expected mainly due to the high TAN and high oxygen content.

In Table 2 the mass and chemical energy balance for the experiment is showed together

with the elemental balance. The overall mass yield have been normalized whilst the

others are showed as measured and calculated, hence they do not sum to unity and the

difference can be interpreted is a reflection of the experimental uncertainty. The largest

uncertainty here lays with the oxygen balance at +10.8%. Three different methods have

been used to determine the composition of the different fractions and there is also an

inherent uncertainty whilst weighing the different samples. However, current efforts

are focused towards reducing the experimental uncertainties.

Table 2.

The overall mass and chemical energy balance including the balance for the major

elements C, H and O. Notice that the amount of gas in the overall mass balance was calculated

by difference.

On mass basis; 25.7% of the dry biomass is converted into charcoal with the

composition showed in Table 1. However, close to 45% of the chemical energy is found

in the charcoal, around 55% is found in the condensate and the remaining 4.4% in the

gas. It should be emphasized that in a larger scale pyrolyser less condensate and more

gas is expected since the pyrolysis vapours can be given longer residence time.

Typically longer vapour residence time results in secondary reactions which again

results in a small increase in charcoal production but a significant increase in gas

production and a consequential decrease in condensate production. However, since the

condensate may have a larger outside-gate value then the inside-gate value of the gas

this needs to be taken into account when different full scale pyrolysis technologies are

considered. The carbon content of the biomass feedstock is more or less equally

distributed between the charcoal and the condensate with a remainder of 6.9 % found

in the gas. For hydrogen and oxygen the condensate dominates; claiming 85% and 90%

of the available atoms, respectively.

Charcoal Condensate Gas Sum

Yield

25.7

64.3 10.0 100

42.7

42.8 6.9 92.4

11.2

85.3 3.1 99.6

5.4

90.1 15.3 110.8

Yield

47.0

55.4 4.4 106.8

a) gas calculted by differnce

Mass balance

(

wt-%

)

ner

balance

(

)