PROCESSES: BASICS OF PROCESS DESIGN - Biomass as a Sustainable Energy Source for the Future - page 217

5. Nominal Liquid Fuel Production Rate
The mass-based production rate of the liquid fuel (C 4+ ), P 5 , C 4+ , mass , is chosen as
an input design parameter of this FT process. The relation between the mass
(kg s −1 ) and molar (kmol s −1 ) liquid fuel production rate is given by

F 5 , C 4+ , mass = φ 5 , C 4+ MW C 4+ ð Eq : 7 : 13 Þ

The mass fuel production rate F 5 , C 4+ , mass is a design input parameter.
6. Nominal Values for Design Parameters and Production Rate
Nominal values must be given as inputs to the model for the chain growth prob-
ability ( α ), the CO-to-CO 2 conversion factor ( β ), the single-pass CO conversion

in the FT reactor ( η ), the recycle fraction ( r ), the separation technology factor

( ), and the C 4+ production rate, F 5 , C 4+ (see Table 7.3).

The CO conversion per pass must be kept relatively low due to an opera-
tional limitation on the formation of water. Too high, a syngas conversion could
result in the production of excessive amounts of water, hampering the catalytic
conversion.

λ

7. Ecological Performance Indicators and Technological Constraints
In a real process plant, there is one or more ecological performance indicators
and often many technological constraints. Here, we will consider only one of
each. In this problem, the ecological performance is represented by the carbon
(atom) efficiency, indicating how much of the carbon intakes through the feeds
end up in the main product. The carbon efficiency ε C is defined as

ε C = carbon flowOUT
carbon flow IN

ε C φ 1 , CO + φ 1 , CO 2 + φ 1 , C 1 +2 φ 1 , C 2 +3 φ 1 , C 3

=0

φ 5 , C 2 +3 φ 5 , C 3 + n a φ 5 , C 4+ : :

− φ 5 , C 1 +2 ð Eq 7 14 Þ

The technological constraint is the molar fraction of water in the gas-phase
outlet stream of the FT conversion block (stream 3). For simplicity, a simple

TABLE 7.3 Nominal input values
Design parameter

Value

Chain growth probability, α (−) 0.90

Conversion of CO to CO 2 , β nom (−) 0.050

CO conversion per pass, η nom (−) 0.50

Syngas recycle fraction, r nom (−) 0.90

Separation technology factor, λ nom (−) 1.0

Production rate of liquid fuel (C 4+ lump):
F 5 , C 4+ (kgs −1 )

9.2

s −1 ) φ 5 , C 4+ (kmol 0.050