Computation of phase and chemical equilibria in flue‐gas/water systems

Luckas, Michael; Lucas, Klaus; Roth, H.

doi:10.1002/aic.690401112

Cited by 16 publications

(12 citation statements)

References 18 publications

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“…The slurry or aqueous phase consists of dissolved species, cations, and anions representing the major intermediate compounds in FGD chemistry. Nonunity activity coefficients for the aqueous species were reported by Luckas et al 7 based on Pitzer/Debye/Huckel calculations for very similar operating conditions. The shifts for the different compositions imposed in our calculations are expected to be minor compared with the deviations from unity in the reference values.…”

Section: Thermochemical Equilibrium Analysismentioning

confidence: 68%

The Impact of Wet Flue Gas Desulfurization Scrubbing on Mercury Emissions from Coal-Fired Power Stations

Niksa¹,

Fujiwara

2005

Journal of the Air & Waste Management Association

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This article introduces a predictive capability for Hg retention in any Ca-based wet flue gas desulfurization (FGD) scrubber, given mercury (Hg) speciation at the FGD inlet, the flue gas composition, and the sulphur dioxide (SO2) capture efficiency. A preliminary statistical analysis of data from 17 full-scale wet FGDs connects flue gas compositions, the extents of Hg oxidation at FGD inlets, and Hg retention efficiencies. These connections clearly signal that solution chemistry within the FGD determines Hg retention. A more thorough analysis based on thermochemical equilibrium yields highly accurate predictions for total Hg retention with no parameter adjustments. For the most reliable data, the predictions were within measurement uncertainties for both limestone and Mg/lime systems operating in both forced and natural oxidation mode. With the U.S. Environmental Protection Agency's (EPA) Information Collection Request (ICR) database, the quantitative performance was almost as good for the most modern FGDs, which probably conform to the very high SO2 absorption efficiencies assumed in the calculations. The large discrepancies for older FGDs are tentatively attributed to the unspecified SO2 capture efficiencies and operating temperatures and to the possible elimination of HCl in prescrubbers. The equilibrium calculations suggest that Hg retention is most sensitive to inlet HCl and O2 levels and the FGD temperature; weakly dependent on SO2 capture efficiency; and insensitive to HgCl2, NO, CA:S ratio, slurry dilution level in limestone FGDs, and MgSO3 levels in Mg/lime systems. Consequently, systems with prescrubbers to eliminate HCl probably retain less Hg than fully integrated FGDs. The analysis also predicts re-emission of Hg(O) but only for inlet O2 levels that are much lower than those in full-scale FGDs.

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Section: Thermochemical Equilibrium Analysismentioning

confidence: 68%

The Impact of Wet Flue Gas Desulfurization Scrubbing on Mercury Emissions from Coal-Fired Power Stations

Niksa¹,

Fujiwara

2005

Journal of the Air & Waste Management Association

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“…In the literature there are two methods for equilibria calculation. The first and best makes use of a minimization of the Gibbs free energy of the system [12]. However, for its application the chemical potentials of every species appearing in the system must be known.…”

Section: Introductionmentioning

confidence: 99%

“…However, for its application the chemical potentials of every species appearing in the system must be known. In the case of pure substances, these data are widely accessible in the literature but the information concerning ions and ion pairs is rather poor and fragmented [12]. The second method is based on the simultaneous solution of equations describing the equilibrium constants of every species present in the system, and mass and charge balances [3,5].…”

Section: Introductionmentioning

confidence: 99%

Equilibria in a Limestone Based FGD Process: A Pure System and with Chloride Addition

Michalski¹

2001

Chem. Eng. Technol.

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“…As an example, a widely used flue gas treating modeling package involves a set of 36 chemical reactions in which 26 nonionic species participate. Additional ionic species are produced from these aqueous phase ionic reactions so that the system actually contains 22 additional components (80).…”

Section: Nonisothermal Scrubbers With Chemicalmentioning

confidence: 99%

Absorption

Laso

Stockar

2003

Kirk-Othmer Encyclopedia of Chemical Technology

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Absorption, or gas absorption, is a unit operation used in the chemical industry to separate gases by washing or scrubbing a gas mixture with a suitable liquid. One or more of the constituents of the gas mixture dissolves or is absorbed in the liquid and can thus be removed from the mixture. In some systems, this gaseous constituent forms a physical solution with the liquid or the solvent, and in other cases, it reacts with the liquid chemically. The purpose of such scrubbing operations may be gas purification, eg, removal of air pollutants from exhaust gases; product recovery; or production of solutions of gases for various purposes. Gas absorption is usually carried out in vertical countercurrent columns. The solvent is fed in at the top of the absorber, the gas mixture from the bottom. The absorbed substance is washed out by the solvent, which is often recovered in a subsequent stripping or desorption operation. The absorber may be a packed column, plate tower, or simple spray column, or a bubble column. The fundamental physical principles underlying the process of gas absorption are the solubility of the absorbed gas and the rate of mass transfer. Information on both must be available when sizing equipment for a given application. In standard packed absorption columns, a gas mixture travels up through a gas absorption tower and the solute is transferred to the liquid phase and thus gradually removed from the gas. The liquid accumulates solute on its way down through the column. Multicomponent mass‐transfer effects, nonisothermal gas absorption, and axial dispersion effects result in considerable departures from ideal flow assumptions. Neglect of axial dispersion results in an overestimation of the driving forces and may lead to an unsafe design. Bubble tray absorption columns may be designed graphically based on a so‐called McCabe‐Thiele diagram. The required number of actual plates, however, is larger than the number of theoretical plates. The computation of nonisothermal gas absorption processes is difficult because of all the interactions involved. A computer is normally required to establish the correct concentration and temperature profiles through the tower.

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Computation of phase and chemical equilibria in flue‐gas/water systems

Cited by 16 publications

References 18 publications

The Impact of Wet Flue Gas Desulfurization Scrubbing on Mercury Emissions from Coal-Fired Power Stations

The Impact of Wet Flue Gas Desulfurization Scrubbing on Mercury Emissions from Coal-Fired Power Stations

Equilibria in a Limestone Based FGD Process: A Pure System and with Chloride Addition

Absorption

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