Environmental Engineering Reference
In-Depth Information
Transformation After Coal Combustion
residence time.
Due to the complex operational conditions in a coal-fired power plant, the re-
action system may not be well at perfect equilibrium. The causes could be, for
example, the catalysis effects of fly ash components on the mercury reactions, or the
mercury adsorption on the particles, unimaginative enough for a lower reaction rate
in the lower temperature zone. Nevertheless, the chemical thermodynamics analysis
will give reasonable and valuable results of the mercury speciation distribution in
the boiler and the sulfur removal unit, and the products from the mercury reactions.
So far, the chemical thermodynamics analysis is a good approach for calcula-
tion. The equilibrium will be reached at minimized Gibbs free energy. Gibbs energy
(also referred to as
G
) is the chemical potential that is minimized when a system
reaches equilibrium at constant pressure and temperature, that is (
G
)
T
,
P
0, so the
problem of solving the chemical equilibrium comes to be calculated for certain
agents composition
n
i
at minimized Gibbs free energy.
FactSage, one of the largest fully integrated database computing systems in
chemical thermodynamics in the world, was introduced in 2001 and is the fusion of
the FACT-Win/F*A*C*T and ChemSage/SOLGASMIX thermochemical pack-
ages. FactSage is the result of over 20 years of collaborative efforts between
Thermfact/CRCT (Montreal, Canada; www.crct.polymtl.ca) and GTT-Techno-
logies (Aachen, Germany; www.gtt-technologies.de).
FactSage 5.2 (Facility for the analysis of Chemical Thermodynamics) package
was developed both by GTT lnc. Germany and CRCT lnc. Canada.
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. In this work, this Equilib module is employed to simulate the chemical
reactions.
4.4.2 Comparison Between Calculation and Experimental Results
Based on the Gibbs energy minimization, the Equilib module of FACTsage5.2
software package provides a multi-element, multi-phase thermodynamic equilib-
rium model, mercury compounds in gas phase, liquid phase or solid phase which
react or partially react also taking everything into account. Chemical thermody-
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