Conventional Flue Gas Desulfurization Research Articles

Thermodynamic study of regenerative barium-based materials towards barium sulfide for catalytic sulfur dioxide reduction

Flue gas with high SO2 content presents a series of human health and environmental problems, which prompted Flue Gas Desulfurization (FGD) technologies widely utilised in industries. However, the conventional FGD using absorbents or adsorbents could generate secondary sulfur-containing pollutants. Thus, a regenerative FGD reaction system that eliminates secondary pollutants while recovering valuable S has been researched. Ba-based materials, viz. Ba(OH)2, BaCO3 and BaO as the precursors, are involved in a regenerative BaS/BaSO4 reaction system of this research. Current thermodynamic study via minimization of Gibbs free energy explored the feasibility of BaS production from these Ba-based materials and reviewed its potential in SO2 reduction to S. Formation of BaS from Ba-based materials was feasible but the yield depends strongly on the temperature and sulfidizing agent used. Compared to BaCO3-systems, Ba(OH)2- and BaO-systems showed better performance in BaS synthesis due to their high equilibrium conversion, even at temperatures< 773 K. Besides, H2S is a better sulfidizing agent for BaS synthesis due to higher BaS yield (maximum 99%). Synthesis routes of different Ba-systems were confirmed by their respective Keq profiles. The feasibility of BaS catalyst in SO2 reduction to S was proven by the excellent SO2 reducing activity and high S yield (100%) at 273 – 1173 K with S8 and S2 as major products. BaS regeneration via H2 was also validated by high BaS yield (100%) at 473 – 1273 K.

Performance of sulfite/FeIIIEDTA fuel cell: Power from waste in flue gas desulfurization process

In conventional flue gas desulfurization processes, a large amount of sulfite (SO32−) is produced as a byproduct through dissolution of SO2(g). Meanwhile, sulfite has a strong oxidizing power in an alkaline condition (E0= −0.93 V vs SHE), so we designed a fuel cell utilizing sulfite as a fuel and examined its performance. In the fuel cell, sulfite is oxidized at the anode into non-hazardous and stable sulfate. Simultaneously, FeIIIEDTA (ferric ethylenediaminetetraacetic acid) is reduced at the cathode, since the reduced form, FeIIEDTA, can be an effective nitric oxide absorbent in a flue gas NOx removal process. Cell performance was enhanced with pH of electrolyte and operating temperature adjustments. The highest power density was 7.51 mW cm−2 in strong alkaline anolyte and acidic catholyte conditions at 80 °C. This study shows that the chemical energy in waste originating from air pollutants could be a good electricity source.

Experimental study on zero liquid discharge (ZLD) of FGD wastewater from a coal-fired power plant by flue gas exhausted heat

Recent research determined that the conventional flue gas desulfurization (FGD) wastewater zero liquid discharge(ZLD)processes have many limitations, such as long process, high investment, high operating cost, and maintenance. In this experimental study, a FGD wastewater was evaporated using the exhausted heat from the flue gas in a 330 MW coal-fired power plant. The numerical simulation and engineering practice results were compared, and the key operating parameters were obtained, such as boiler load conditions, the ratio number of droplets captured by the flue wall to the total number of droplets, optimization of atomizing nozzle layout, the atomization droplet diameter, flue gas enthalpy value, accurate calculation on the change of flue gas, and fly ash characteristics after the injection of FGD wastewater. We found that under different boiler load conditions, the higher temperature and the faster the speed of the flue gas, the less time it takes for the complete evaporation of the wastewater droplets. Different amounts of FGD wastewater can be completely dried, the properties of fly ash do not change much, and no negative impacts were found on the downstream process. Moreover, it was found that when the optimum atomization cone angle of a single flue structure was 65°, the size of vortex inversely proportional related to the distance between sprayer and the wall of flue duct, that was conducive to the continuous diffusion of the local droplets in the nozzle region to other regions. This wastewater evaporation treatment method is a feasible technology for ZLD of FGD wastewater with characteristics of short process, lower investment, low operating cost, and less maintenance than conventional membrane method for wastewater reduction and evaporative crystallization system.

Feasibility Study of New Limestone Flue Gas Desulfurization Process

AbstractA new method based on conventional limestone flue gas desulfurization (FGD) has been developed. The main difference compared to the conventional wet FGD is the utilization of granular limestone with acetic acid additives as the absorbent, which should save on the power required for pulverization of limestone and pumping the circulation slurry. This paper focuses on a feasibility study of the new limestone FGD process by comparing SO2 removal efficiency, SO2 absorption rate, limestone utilization and FGD system stability of the new FGD with those of the conventional FGD, in the same absorption equipment under the same experimental conditions. The results show that when the coarse limestone slurry (–80+100 mesh, US standard) is used directly as the absorbent, its utilization and SO2 removal efficiency, are very low at 44 and 60.7%, respectively. When the mixed slurry, which is composed of coarse limestone and 10–30 mmol/L acetic acid absorbs SO2, the degree of desulfurization is increased to 95% and the limestone utilization is enhanced to 93.5%. Finally, for the absorbent consisting of a fine limestone slurry (–300 mesh), the desulfurization efficiency and limestone utilization are 88 and 92.9%, respectively, under the same operating conditions. Therefore, the new desulfurization process is shown to be very feasible.

Advantage of Illinois Coal for FGD Removal of Mercury

An investigation was conducted to characterize and modify mercury speciation in Illinois coal combustion flue gas so that a mercury control strategy can be implemented in conventional flue gas desulfurization (FGD) units. Mercury is readily volatilized during coal combustion and leaves the high-temperature zone as gas-phase elemental mercury (Hg°). As the flue gas is cooled, a portion of the Hg° is converted, primarily to mercuric chloride (HgCl 2 ), in the presence of catalytically active surfaces. Unlike Hg 0 , HgCl 2 is highly soluble in water and has a high affinity for alkaline sorbents; it can, therefore, be easily removed in wet scrubbers and spray dryers (FGD units). This study specifically examined the effect of injection of Illinois coal combustion residues (ICCRs) on the conversion of Hg° to HgCl 2 in coal combustion flue gases. Tests were conducted in two tasks. Task I studied Hg° oxidation using a fixed-bed, bench-scale reactor in a simulated Illinois coal combustion environment. Various types of ICCRs were examined to determine active residues in the oxidation of Hg°. A scrubber sludge and two bottom ash samples were determined to be active Hg° catalysts. The most active ICCR (a bottom ash sample) was chosen for Task II. Task II was performed in two subtasks. In Subtask I, the active bottom ash sample was injected in a pilot-scale combustor while burning natural gas doped with appropriate amounts of Hg°, hydrogen chloride (HCl), nitrogen oxides (NO X ), and sulfur dioxide (SO 2 ). Injection of this bottom ash sample did not contribute to the background gas-phase oxidation of Hg°, indicating that in-flight oxidation of Hg° in the pilot-scale combustor may be mass transfer limited. In Subtask II, a representative Illinois coal was combusted in the pilot-scale combustor. As with most bituminous coals, the combustion flue gas of this coal was dominated by oxidized forms of mercury. Additional Hg° was doped into this flue gas, and significant oxidation of Hg° was observed. It was determined that the fly ash generated from combustion of this coal is very active in oxidation of Hg°. Additional pilot-scale tests were performed to investigate the activity of the Illinois coal fly ash. It was determined that packed-bed flow modes, such as those observed in baghouses, are required to catalytically oxidize Hg° using this Illinois coal fly ash.

Anion-Exchange Resin-Based Desulfurization and Dechlorination of Spent Sorbent Material

Emissions of acid gases such as SO{sub 2} and HCl/Cl{sub 2} from energy conversion or waste incineration facilities are unacceptable. Alkali metal sorbents can remove these acid gases more efficiently than the lime/limestone type sorbents used in the conventional flue gas desulfurization (FGD) systems. It is desirable that the spent sorbent materials obtained from such emissions control systems be converted to sulfur- and chlorine-free forms, so that they can be reused. The weak-base, anion-exchange resin-based desulfurization concept, developed and tested at the University of Tennessee Space Institute (UTSI), can also simultaneously remove sulfur- and chlorine-containing species from such spent sorbent materials. Under the U.5. Department of Energy`s (DOE) sponsorship, bench scale studies have been carried out to evaluate the feasibility of removing sulfur- and chlorine-containing species using this resin-based concept. Preliminary cost estimates for a regeneration scheme employing reactivated alkali metal-based spent sorbent material using the ion-exchange resin-based concept seem attractive and comparable to currently available options. 22 refs., 6 figs., 10 tabs.

Characterization of NO2 and SO2 Removals in a Spray Dryer/Baghouse System

Oxidation of NO to NO[sub 2] has been proposed as a method for enhancing NO[sub x] removals in conventional flue gas desulfurization (FGD) processes. This experimental investigation characterizes the removals of NO[sub 2] and SO[sub 2] in a 1.1 m[sup 3](standard)/min spray dryer/baghouse system. Flue gas was generated by burning a No. 2 fuel oil, which was subsequently spiked upstream of the spray dryer with NO[sub 2] or SO[sub 2] or both. Lime slurry was injected via a rotary atomizer into the spray dryer. Variables studied include the approach to the adiabatic saturation temperature, stoichiometric ratio, SO[sub 2] concentration, and NO[sub 2] concentration. Significant quantities of NO[sub 2] are scrubbed in this system, and over half of the total removal (at inlet NO[sub 2] > 400 ppm) occurs in the baghouse. Increasing NO[sub 2] concentrations enhance the amount of NO[sub x] removed in the system. Also, the presence of significant quantities of NO[sub 2] enhances the baghouse SO[sub 2] removal. Although up to 72% NO[sub 2] removals were obtained, concentrations of NO[sub 2] that exited the system were greater than 50 ppm for all conditions investigated.

Sorbent and ammonia injection at economizer temperatures upstream of a economizer temperatures upstream of a high—temperature baghouse

AbstractThe current technology of choice—world–wide—for post–combustion NOx control is selective catalytic reduction (SCR) with ammonia. The application of SCR to coal–fired units has proven to be somewhat more difficult than its application to natural gas and oil–fired units due to SO2 poisoning of the catalyst, catalytic oxidation of SO2 to SO3, and erosion and fouling of the catalyst by fly ash [1]. These problems could be potentially diminished if SO2 and particulate removal systems were placed upstream of the SCR reactor. However, this is not easily accomplished since SCR systems operate best in the temperature range of 600°F–800°F (315°C–425°C). Several SCR installations in Europe employ conventional flue gas desulfurization (FGD) and particulate control upstream of flue gas reheat and SCR. However, the flue gas reheat typically imposes a 1%–2% energy penalty [2]. Several recent technical developments now offer a technology whereby these limitations of SCR for coal applications can be alleviated.These technical developments are in the areas of high temperature filtration, improved SCR catalysts, and advances in sorbent injection. These advances have been incorporated into a patented process known as the SOxNOxRox Box™ (SNRB) process. Briefly, this process consists of a “hot” baghouse employing woven ceramic fabric bags, a zeolite SCR catalyst incorporated into the baghouse, and the injection of either calcium–or sodium–based sorbent upstream of the baghouse (see Figure 1).This paper deals with the status and development of the SNRB process, including some results from recently completed pilot–plant tests performed under a contract with the Ohio Coal Development Office (OCDO).

Assessment of Dry Sorbenf Emission Control Technologies Part II. Applications

The injection of dry alkaline compounds into the furnace or post-furnace regions of utility boilers to reduce SO2 is currently under development as a lower cost option to conventional flue gas desulfurization technology. Part I of this paper focused on the science and process development of the various dry sorbent technologies. Part II will address applications of these technologies, including SO2 removals in full-scale boilers, methodologies for designing sorbent injection systems, power plant impacts, process integration issues, and cost. Because the dry technologies use the furnace and/or ducts as the chemical contactor, potential impacts on power plant operation and reliability are as critical in assessing the commercial applicability of each technology as SO2 removal and sorbent utilization. Consequently, the technical and economic feasibility of the various dry processes is highly site specific.

Flue gas scrubbing process for sulfur dioxide and particulate emissions preceding CO2 absorption

AbstractThis article describes a 2‐stage scrubbing process which utilizes sodium hydroxide or sodium carbonate as the neutralizing chemical for sulfur dioxide and sulfur trioxide emissions to remove contaminants from gas streams preceding CO2 absorption processes.Amine absorption processes are adversely affected by sulfur dioxide in the gas stream, and it is desirable to reduce sulfur dioxide concentrations to less than 5 ppm (vol).Conventional flue gas desulfurization processes do not achieve outlet concentrations at this level. With appropriate controls on pH, ionic strength, and liquid recirculation rates, the sodium alkalies can achieve these outlet concentrations. When concentrations of sulfur dioxide absorbed become sufficiently large to make the economics of a simple throw‐away process uneconomical, the waste solutions can be regenerated in the double‐alkali process by reacting them externally from the scrubbing system with calcium compounds. This process is also described. Particular emphasis is placed on process design for reliability. Materials of construction, process controls, and process chemistry are discussed.