THERMOCHEMICAL CONVERSION: DIRECT COMBUSTION - Biomass as a Sustainable Energy Source for the Future - page 295

KEY CONCEPTS

Thermal conversion
Shrinking sphere
Shrinking core
Shrinking density
Thiele modulus
Biot number
d 2 -law
Spalding number
Combustion systems
Emissions from complete and incomplete combustion
Primary and secondary emission reduction measures

SHORT-ANSWER QUESTIONS

9.1 What are the main modes of particle conversion?

9.2 What dimensionless numbers are indicative for these modes?

9.3 Which model applies in film behavior?

9.4 Give three examples of emissions from complete combustion.

9.5 Give three examples of emissions from incomplete combustion.

9.6 What is the main NO formation mechanism in biomass combustion applications?

9.7 Name three different particle control technologies.

PROBLEMS

9.1 Draw the temperature profile that is assumed in the derivation of the d 2 -law for
evaporation inside and outside of a droplet as a function of the radius.

9.2 Draw the droplet diameter and its square as a function of time at a certain ther-
mal load.

9.3 There are problems in a biomass power plant with the burnout time of the
particles. A too large amount of the biggest particles needs to be separated in
the exhaust system and fed into the reactor again. The distance of the reacting
volume to the exhaust system is 20 m, and the main flow-through velocity is
40 m s −1 . The size of the biggest particles is 1 mm. Calculate the critical rate

constant in m 2

s −1 that is needed to convert the largest particles assuming a
shrinking sphere model. What is the critical diameter of the biggest particle if
it is required that it burns out in half the distance to the exhaust?

9.4 In Example 9.1, evaporation of boiling octane is considered. If we take combus-
tion into account as well, we have to consider a laminar diffusive combustion