Environmental Engineering Reference
In-Depth Information
So far, critical information as to which key parameter is the most sensitive to
mercury speciation and transformation among the flue gas species, was missing
from the literature. Maybe it is a good approach to obtain such information as above
with the aid of a thermochemical equilibrium calculation.
However, modeling the impact on mercury transformation by the gas species at
the inlet of the web scrubber predicted from a thermochemical equilibrium calcu-
lation is rarely observed in practice. If only to measure the formation of mercury, it
is vital to conduct the mercury absorption experiments in a pilot-scale web scrubber.
With the assistance of the thermochemical equilibrium calculation, a subtle reaction
between gas components and mercury compounds will be shown. The reaction
products of both will be represented as well.
4.4.1 Introduction
The equilibrium product amounts are positive, satisfy the mass balance constraints
with respect to the system components and correspond to the lowest possible Gibbs
energy for this particular selection of possible products.
The Equilib module is the Gibbs energy minimization workhorse of FactSage
and the most popular program. It calculates the concentrations of chemical species
when specified elements or compounds react, or partially react, to reach a state of
chemical equilibrium. Equilib
employs the Gibbs energy minimization algorithm
and thermochemical functions of ChemSage and offers great flexibility in the way
the calculations may be performed. For example, the following are permitted: a
choice of units (K, C, F, bar, atm, psi, J, cal, BTU, kW·h, mol, wt.%, ...); dormant
phases in equilibria; equilibria constrained with respect to T, P, V, H, S, G, U or A or
changes thereof; user-specified product activities (the reactant amounts are then
computed); user-specified compound and solution data; and much more. Phase
targeting and one-dimensional phase mappings with automatic search for phase
transitions are possible. For example, you can calculate all equilibrium (or
Scheil-Gulliver non-equilibrium) phase transitions as a multicomponent mixture is
cooled.
Chemical thermodynamics is the study of the interrelation of heat and work
with chemical reactions or with physical changes of state within the confines of the
laws of thermodynamics. The primary objective of chemical thermodynamics is the
establishment of a criterion for the determination of the feasibility or spontaneity of
a given transformation. In this manner, chemical thermodynamics is typically used
to predict the energy exchanges that occur in the reactions assumed to be at equi-
librium.
The chemical thermodynamics model, which is of homogeneous
zero-dimensional, only takes account of global parameters, i.e. pressure and tem-
perature, instead of those of gradient. In a boiler case, the equilirium will be met in
the high temperature zone where the reaction rate is fast enough, whilst the reac-
tions in the low temperature zone can barely reach equilibrium states even with long
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