THERMOCHEMICAL CONVERSION: AN INTRODUCTION TO FAST PYROLYSIS - Biomass as a Sustainable Energy Source for the Future - page 384

PROBLEMS
11.1 For the case where pyrolysis is not hindered by transfer limitations based on the
scheme in Figure 11.5, derive:
a. The equation for the mass loss (m = biomass + char) of a biomass particle as
a function of time for a given temperature
b. The equations for the product yields as a function of temperature
11.2 a. Derive an expression that relates the loss of vapors due the homogeneous
vapor cracking reaction in the hot zone above a fluidized bed as a function
of temperature and vapor residence time.
b. Consider a fluidized bed pyrolysis reactor that contains ideally mixed bio-
mass particles that are producing vapors. In the fluidized bed reactor, also,
vapor cracking proceeds, which can be described by a first-order reaction in
vapors. Derive an expression to calculate the fraction of the vapors that is
cracked relative to the amount produced in the pyrolysis reactions as a func-
tion of temperature and residence time. You may assume that the gas/vapors
show plug flow behavior.
11.3 Estimate the pyrolysis time for cylindrical biomass particles of aspect ratio
L/D > 3 as a function of the diameter at a reactor temperature of 500 C. Use
the estimation method discussed earlier.
11.4 Consider a process inwhichwet biomass is the feed. This biomass has to be dried
to 10 wt%moisture before being fed to the reactor. Estimate themaximum intake
moisture content that can be handled if the process is overall autothermal (no
external energy input) and the required energy for drying and reaction is gener-
ated by combustion of produced char and gas. Use the figures from Table 11.5.
11.5 For the case where sand is circulated between a hot utility and the pyrolysis
reactor, derive an equation that gives the required sand flow (in kg) per kg
biomass fed as a function of the temperature differences between the
pyrolysis reactor and the hot utility and the energy requirement of the reactor.
11.6 Calculate the amount (kg) of H 2 needed per kg product for complete deoxygen-
ation of pyrolysis oil and discuss the economics of the process based on this
number.
PROJECTS
P11.1 Perform TGA of woody biomass at a certain heating rate and derive the para-
meters of the first-order rate equation describing the weight loss. Examine
whether these parameters can predict the measured weight loss at a consid-
erably lower or higher heating rate. Discuss the results.