Investigation of a Mercury Speciation Technique for Flue Gas Desulfurization Materials

Abstract

Most of the synthetic gypsum generated from wet flue gas desulfurization (FGD) scrubbers is currently being used for wallboard production. Because oxidized mercury is readily captured by the wet FGD scrubber, and coal-fired power plants equipped with wet scrubbers desire to benefit from the partial mercury control that these systems provide, some mercury is likely to be bound in with the FGD gypsum and wallboard. In this study, the feasibility of identifying mercury species in the FGD gypsum and wallboard samples was investigated using a large sample size thermal desorption method. Potential candidates of pure mercury standards including mercuric chloride (HgCl₂), mercurous chloride (Hg₂Cl₂), mercury oxide (HgO), mercury sulfide (HgS), and mercuric sulfate (HgSO₄) were analyzed to compare their results with those obtained from FGD gypsum and dry wallboard samples. Although any of the thermal evolutionary curves obtained from these pure mercury standards did not exactly match with those of the FGD gypsum and wallboard samples, it was identified that Hg₂Cl₂ and HgCl₂ could be candidates. An additional chlorine analysis from the gypsum and wallboard samples indicated that the chlorine concentrations were approximately 2 orders of magnitude higher than the mercury concentrations, suggesting possible chlorine association with mercury.     

Study of the use of coal fly ash as an additive to minimise fluoride leaching from FGD gypsum for its disposal

The use of coal fly ash as a fluoride retention additive has been studied as a way of treating flue gas desulphurisation (FGD) gypsum for its disposal in landfills. With this end leaching studies following the standard EN-12457-4 [Characterization of waste- Leaching-Compliance test for leaching of granular waste materials and sludges - Part 4: One stage batch test at a liquid to solid ratio of 10l/kg for materials with particle size below 10mm (without or with size reduction)] have been performed on FGD gypsum samples treated with different proportions of fly ash (0.1-100%). It was found that the fluoride leachable content in FGD gypsum was reduced in the range 1-55%, depending on the fly ash proportion added to FGD gypsum. High levels of fluoride leaching reduction (close to 40%) were achieved even at relatively low fly ash additions (5%). So, low fly ash incorporations assure the characterization of this by-product as a waste acceptable at landfills for non-hazardous wastes according to the Council Decision 2003/33/EC [Council Decision 2003/33/EC of 19 December 2002 establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC] on waste disposal. Furthermore, the effectiveness of the proposed FGD gypsum stabilization method was also studied in column leaching systems, proving its good performance in simulated conditions of disposal. In such conditions a fluoride leaching reduction value slightly higher than 25% was displayed for a fly ash added amount of 5%.     

Summary of the 1991 EPRI/EPA/DOE SO2 Control Symposium

The 1991 SO₂ Control Symposium was held December 3-6, 1991, in Washington, D.C. The symposium, jointly sponsored by the Electric Power Research Institute (EPRI), the U.S. Environmental Protection Agency (EPA), and the U.S. Department of Energy (DOE), focused attention on recent improvements in conventional sulfur dioxide (SO₂) control technologies, emerging processes, and strategies for complying with the Clean Air Act Amendments of 1990. Its purpose was to provide a forum for the exchange of technical and regulatory information on SO₂ control technology. Over 800 representatives of 20 countries from government, academia, flue gas desulfurization (FGD) process suppliers, equipment manufacturers, engineering firms, and utilities attended. In all, 50 U.S. utilities and 10 utilities in other countries were represented. In 11 technical sessions, a diverse group of speakers presented 111 technical papers on development, operation, and commercialization of wet and dry FGD, Clean Coal Technologies, and combined sulfur dioxide/nitrogen oxides (SO₂/NO_x processes.     

Laboratory and Field Evaluation of the Controlled Condensation System for S03 Measurements in Flue Gas Streams

The study reported by this paper involves the use of the Controlled Condensation System (Goksoyr/Ross Coil) for flue gas S0₃ measurements in both the laboratory and the field, under low and high mass loadings. The Controlled Condensation System cools the flue gas to below the dewpoint of H₂S0₄ but above the H₂0 dewpoint. The resulting aerosol is collected either on the coil walls or on the back-up glass frit. The laboratory recovery of the H₂S0₄ in streams of varying S0₂, H₂0, and H₂S0₄ content was found to be 95 ± 6%. A new quartz filter holder was designed to meet the filtration problems encountered in collecting S0₃ from particle laden flue gas streams. This quartz system, when heated to above 250°C, quantitatively passed the H₂S0₄ into the condensation coil. Later studies with this filter system preloaded with fly ash equivalent to a mass loading of 1.3 g/m³ yielded a 80-85% recovery of H₂S0₄. The laboratory system was simultaneously tested at a 150 megawatt, pulverized coal-fired power plant prior to and after a wet limestone FGD. The inlet grain loading to the FGD ranged from 0.06 g/m³ to 11.4 g/m³ with S0₂ concentrations as high as 4000 ppm. The average inlet H₂S0₄ value was 8.3 ppm and the outlet from the FGD was 3.1 ppm. The source fluctuation value was determined to be ±65%.     

Performance of an Innovative Two-Stage Process Converting Food Waste to Hydrogen and Methane

Abstract

This study was conducted to evaluate the performance of an innovative two-stage process, BIOCELL, that was developed to produce hydrogen (H₂) and methane (CH₄) from food waste on the basis of phase separation, reactor rotation mode, and sequential batch technique. The BIOCELL process consisted of four leaching-bed reactors for H₂ recovery and post-treatment and a UASB reactor for CH₄ recovery. The leaching-bed reactors were operated in a rotation mode with a 2-day interval between degradation stages. The sequential batch technique was useful to optimize environmental conditions during H₂ fermentation. The BIOCELL process demonstrated that, at the high volatile solids (VS) loading rate of 11.9 kg/m³-day, it could remove 72.5% of VS and convert VS_removed to H₂ (28.2%) and CH₄ (69.9%) on a chemical oxygen demand (COD) basis in 8 days. H₂ gas production rate was 3.63 m³/m³ ·day, while CH₄ gas production rate was 1.75 m³/m³ ·day. The yield values of H₂ and CH₄ were 0.31 and 0.21 m³/kg VS_added, respectively. Moreover, the output from the post-treatment could be used as a soil amendment. The BIOCELL process proved to be stable, reliable, and effective in resource recovery as well as waste stabilization.     

Stabilization of FGD gypsum for its disposal in landfills using amorphous aluminium oxide as a fluoride retention additive

The applicability of amorphous aluminium oxide as a fluoride retention additive to flue gas desulphurisation (FGD) gypsum was studied as a way of stabilizing this by-product for its disposal in landfills. Using a batch method the sorption behaviour of amorphous aluminium oxide was evaluated at the pH (about 6.5) and background electrolyte conditions (high chloride and sulphate concentrations) found in FGD gypsum leachates. It was found that fluoride sorption on amorphous aluminium oxide was a very fast process with equilibrium attained within the first half an hour of interaction. The sorption process was well described by the Langmuir model, offering a maximum fluoride sorption capacity of 61.7 mg g(-1). Fluoride sorption was unaffected by chloride co-existing ions, while slightly decreased (about 20%) by competing sulphate ions. The use of amorphous aluminium oxide in the stabilization of FGD gypsum proved to greatly decreased its fluoride leachable content (in the range 5-75% for amorphous aluminium oxide doses of 0.1-2%, as determined by the European standard EN 12457-4 [EN-12457-4 Characterization of waste-leaching-compliance test for leaching of granular waste materials and sludges-Part 4: one stage batch test at a liquid to solid ratio of 10 l/kg for materials with particle size below 10mm (without or with size reduction)]), assuring the characterization of this by-product as a waste acceptable at landfills of non-hazardous wastes according to the Council Decision 2003/33/EC [Council Decision 2003/33/EC of 19 December 2002. Establishing criteria and procedures for the acceptance of waste at landfills pursuant to Article 16 of and Annex II to Directive 1999/31/EC] on landfill of wastes. Furthermore, as derived from column leaching studies, the proposed stabilization system proved to be highly effective in simulated conditions of disposal, displaying a fluoride leaching reduction value about 81% for an amorphous aluminium oxide added amount of 2%.     

Microscopy and chemistry of particles collected on TEOM filters: Swansea,south Wales, 1998–1999

Tapered element oscillating microbalances (TEOMs) are used in the UK Automatic Monitoring Network for the continuous measurement of ambient airborne particles. Used TEOM filters from Swansea, Cardiff and Pembroke were examined under high-resolution field emission scanning electron microscopy (FESEM). Clusters of calcium sulphate crystals, gypsum (CaSO₄·2H₂O) and anhydrite (CaSO₄) were abundant on spring and summer filters, and not present on autumn and winter filters. From textural considerations, the sulphates must have crystallised on the filter surfaces, either by dissolution and recrystallisation of CaSO₄ collected as particles, or by direct precipitation from saline water collected on the filters; in much the same way as the formation of ‘desert roses’ by the evaporation of saline pore waters in desert sands. The proposed mechanism for the formation of these crystals has two important implications. Firstly, if the filters are episodically saturated with water, then on occasion the recorded masses will consist of both particles plus water, causing errors in the results of continuous monitoring; an important consideration for epidemiological studies based on TEOM data. Secondly, past toxicological experiments undertaken on TEOM-derived ‘PM10’ may have investigated material containing a significant component of in situ formed crystals, rather than the original PM10.     

Preparation of Calcium Silicate Absorbent from Iron Blast Furnace Slag

ABSTRACT

Calcium silicate hydrate (CSH) solids were prepared from hydrated lime and iron blast furnace slag in an aqueous agitated slurry at 92 °C. While it was hoped a minimal lime/slag ratio could be used to create near-amorphous CSH, the surface area of the product improved by increasing the lime/slag weight ratio to 2. The addition of gypsum to the lime/slag system dramatically improved the formation of surface area, creating solids with 139 m²/g after 30 hr of reaction when only a minimal amount of lime was present. The SO₂ reactivity of solids prepared with gypsum greatly exceeded that of hydrated lime, achieving greater than 70-80% conversion of the alkalinity after 1 hr of reaction with SO₂. The use of CaCl₂ as an additive to the lime/slag system, in lieu of gypsum, also produced high-surface-area solids, 115 m²/g after 21 hr of reaction. However, the SO₂ reactivity of these sorbents was relatively low given the high surface area. This emphasized that the correlation between surface area and SO₂ reactivity was highly dependent on the solid phase, which was subsequently dependent on slurry composition.     

Metolachlor and chlorothalonil dissipation in gypsum-amended soil

This work focused on the interactive effects of the fungicide chlorothalonil (2,3,4,6-tetrachloro-1,3-benzendicarbonitrile) and gypsum on the persistence of the soil-residual herbicide metolachlor (2-chloro-N-(6-ethyl-o-tolyl)-N-[(1RS)-2-methoxy-1-methylethyl]acetamide). Gypsum application was included due to its widespread use on peanut (Arachis hypogaea). Both agricultural grade gypsum and reagent CaSO₄-2H₂O were tested. A laboratory soil incubation was conducted to evaluate interactive effects. Results indicated 1.5X greater metolachlor half-life (DT₅₀) in soil amended with chlorothalonil (37 d) as compared to control soil (25 d). The two gypsum sources alone increased metolachlor DT₅₀ to about 32 d and with the combination of chlorothalonil and gypsum, DT50 was 50 d, 2-fold greater than the control. Chlorothalonil dissipation was rapid (DT₅₀ < 4d). A possible explanation for metolachlor dissipation kinetics is a build-up of the chlorothalonil intermediate (4-hydroxychlorothalonil) which limited soil microbial activity and depleted glutathione S-transferase (GST) from chlorothalonil detoxification. Further information related to gypsum impacts is needed. Results confirm previous reports of chlorothalonil impeding metolachlor dissipation and showed the gypsum application extended persistence even longer. Farming practices, such as reducing metolachlor application rates, may need to be adjusted for peanut cropping systems where chlorothalonil and gypsum are used.     

Simultaneous removal of NOx,SO2, and Hg from flue gas in FGD absorber with oxidant injection (NaClO2)– full-scale investigation

ABSTRACT

This article presents the results of an industrial-scale study (on 400 MW_e lignite fired unit) of simultaneous NO_x, SO₂, and Hg^T removal in FGD absorber with oxidant injection (NaClO₂) into flue gas. It was confirmed that the injection of sodium chlorite upstream the FGD (Flue Gas Desulfurization) absorber oxidize NO to NO₂, Hg⁰ to Hg²⁺, and enhancing NO_x and Hg^T removal efficiency from exhaust gas in FGD absorber. Mercury removal efficiency grows with the rise of degree of oxidation NO to NO₂ and was limited by the phenomenon of re-emission. For NO_x removal the most critical parameters is slurry pH and temperature. There was no negative effect on sulfur dioxide removal efficiency caused by oxidant injection in tested FGD absorber. Based on the data provided, NO_x and Hg^T emissions can be reduced by adjusting the FGD absorber operating parameters combined with oxidant injection.     

Influence of dust composition on cloud droplet formation

Previous studies suggest that interactions between dust particles and clouds are significant; yet the conditions where dust particles can serve as cloud condensation nuclei (CCN) are uncertain. Since major dust components are insoluble, the CCN activity of dust strongly depends on the presence of minor components. However, many minor components measured in dust particles are overlooked in cloud modeling studies. Some of these compounds are believed to be products of heterogeneous reactions involving carbonates. In this study, we calculate Kohler curves (modified for slightly soluble substances) for dust particles containing small amounts of K⁺, Mg²⁺, or Ca²⁺ compounds to estimate the conditions where reacted and unreacted dust can activate. We also use an adiabatic parcel model to evaluate the influence of dust particles on cloud properties via water competition. Based on their bulk solubilities, K⁺ compounds, MgSO₄·7H₂O, Mg(NO₃)₂·6H₂O, and Ca(NO₃)₂·4H₂O are classified as highly soluble substances, which enable activation of fine dust. Slightly soluble gypsum and MgSO₃·6H₂O, which may form via heterogeneous reactions involving carbonates, enable activation of particles with diameters between about 0.6 and 2 μm under some conditions. Dust particles>2 μm often activate regardless of their composition. Only under very specialized conditions does the addition of a dust distribution into a rising parcel containing fine (NH₄)₂SO₄ particles significantly reduce the total number of activated particles via water competition. Effects of dust on cloud saturation and droplet number via water competition are generally smaller than those reported previously for sea salt. Large numbers of fine dust CCN can significantly enhance the number of activated particles under certain conditions. Improved representations of dust mineralogy and reactions in global aerosol models could improve predictions of the effects of aerosol on climate.     

IAPCS: A Computer Model that Evaluates Pollution Control Systems for Utility Boilers

The IAPCS model, developed by U.S. EPA’s Air and Energy Engineering Research Laboratory and made available to the public through the National Technical Information Service, can be used by utility companies, architectural and engineering companies, and regulatory agencies at all levels of government to evaluate commercially available technologies for control of SO₂, NO_x, and particulate matter emissions from coal-fired utility boilers with respect to performance and cost. The model is considered to be a useful tool to compare alternative control strategies to be used by utilities to comply with the requirements of the CAA, and to evaluate the sensitivity of control costs with respect to many of the significant variables affecting costs.

To illustrate the use of the model for site-specific studies, the authors used the model to estimate control costs for SO₂ and NO_x control at Detroit Edison’s Monroe plant and two hypothetical plants under consideration and at three plants operated by New York State Electric and Gas Corporation. The economic and technical assumptions used to drive the model were those proposed by the utilities if cited, and if not cited, the model default values were used. The economic format and methodologies for costs cited in the Electric Power Research Institute’s Technical Assessment Guide are used in the IAPCS model. Depending on the specific conditions and assumptions for the cases evaluated, SO₂ control costs ranged from $417 to $3,159 per ton of SO₂ removed, and NO_x control costs ranged from $461 to $3,537 per ton of NO_x removed or reduced.     

Eliminating Reheat from Existing FGD Systems

The Clean Air Act Amendments of the early 1970_s required coal burning utilities to reduce their emissions of sulfur dioxide. Lime or limestone based wet systems were employed for flue gas desulfurization (FGD). These systems reduced flue gas temperatures to below acid dew point conditions. Concerned about the prospect of ductwork exposed to a saturated, acid-rich environment, most utilities turned to stack gas reheat (SGR) to increase flue gas temperatures. By 1980, 82 percent of all FGD facilities employed SGR. Today there are about 130 FGD systems of which 101 employ some form of stack gas reheat.     

A Reexamination of the Ozone Limiting Approach to Estimating Short-Term NO2 Concentrations

The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, “green” gypsum wallboard, and “green” carpet) under three relative humidity (RH) conditions (20%, 50%, and 70% RH). The “green” materials contained recycled materials and were friendly to environment. A dynamic dual-chamber test method was used. Results showed that a higher relative humidity led to a larger effective diffusion coefficient for two kinds of wallboards and carpet. The carpet was also found to be very permeable resulting in an effective diffusion coefficient at the same order of magnitude with the formaldehyde diffusion coefficient in air. The partition coefficient (K _ma) of formaldehyde in conventional wallboard was 1.52 times larger at 50% RH than at 20% RH, whereas it decreased slightly from 50% to 70% RH, presumably due to the combined effects of water solubility of formaldehyde and micro-pore blocking by condensed moisture at the high RH level. The partition coefficient of formaldehyde increased slightly with the increase of relative humidity in “green” wallboard and “green” carpet. At the same relative humidity level, the “green” wallboard had larger partition coefficient and effective diffusion coefficient than the conventional wallboard, presumably due to the micro-pore structure differences between the two materials. The data generated could be used to assess the sorption effects of formaldehyde on building materials and to evaluate its impact on the formaldehyde concentration in buildings.

Implications: Based on the results of this study, the sink effects of these commonly used materials (conventional and “green” gypsum wallboards, “green” carpet) on indoor formaldehyde concentration could be estimated. The effects of relative humidity on the diffusion and partition coefficients of formaldehyde were found to differ for materials and for different humidity levels, indicating the need for further investigation of the mechanisms through which humidity effects take place.     

Kinetics and the mass transfer mechanism of hydrogen sulfide removal by biochar derived from rice hull

The biochar derived from rice hull was evaluated for its abilities to remove hydrogen sulfide (H₂S) from gas phase. The surface area and pH of the biochar were compared. The biochar derived from rice hull was evaluated for its abilities to remove hydrogen sulfide (H₂S) from gas phase. The surface area and pH of the biochar were compared. The different pyrolysis temperature has great influence on the adsorption of H₂S. At the different pyrolysis temperature, the H₂S removal efficiency of rice hull-derived biochar was different. The adsorption capacities of biochar were 2.09 mg·g^–1, 2.65 mg·g^–1, 16.30 mg·g^–1, 20.80 mg·g^–1, and 382.70 mg·g^–1, which their pyrolysis temperatures were 100 °C, 200 °C, 300 °C, 400 °C and 500 °C respectively. Based on the Yoon-Nelson model, it analyzed the mass transfer mechanism of hydrogen sulfide adsorption by biochar.

Implications: The paper focuses on the biochar derived from rice hull–removed hydrogen sulfide (H₂S) from gas phase. The surface area and pH of the biochar were compared. The different pyrolysis temperatures have great influence on the adsorption of H₂S. At the different pyrolysis temperatures, the H₂S removal efficiency of rice hull–derived biohar was different. The adsorption capacities of biochar were 2.09, 2.65, 16.30, 20.80, and 382.70 mg·g^?1, and their pyrolysis temperatures were 100, 200, 300, 400, and 500 °C, respectively. Based on the Yoon-Nelson model, the mass transfer mechanism of hydrogen sulfide adsorption by biochar was analyzed.     

Reaction behavior of SO2 in the sintering process with flue gas recirculation

The primary goal of this paper is to reveal the reaction behavior of SO₂ in the sinter zone, combustion zone, drying–preheating zone, and over-wet zone during flue gas recirculation (FGR) technique. The results showed that SO₂ retention in the sinter zone was associated with free-CaO in the form of CaSO₃/CaSO₄, and the SO₂ adsorption reached a maximum under 900ºC. SO₂ in the flue gas came almost from the combustion zone. One reaction behavior was the oxidation of sulfur in the sintering mix when the temperature was between 800 and 1000ºC; the other behavior was the decomposition of sulfite/sulfate when the temperature was over 1000ºC. However, the SO₂ adsorption in the sintering bed mainly occurred in the drying–preheating zone, adsorbed by CaCO₃, Ca(OH)₂, and CaO. When the SO₂ adsorption reaction in the drying–preheating zone reached equilibrium, the excess SO₂ gas continued to migrate to the over-wet zone and was then absorbed by Ca(OH)₂ and H₂O. The emission rising point of SO₂ moved forward in combustion zone, and the concentration of SO₂ emissions significantly increased in the case of flue gas recirculation (FGR) technique.

Implications: Aiming for the reuse of the sensible heat and a reduction in exhaust gas emission, the FGR technique is proposed in the iron ore sintering process. When using the FGR technique, SO₂ emission in exhaust gas gets changed. In practice, the application of the FGR technique in a sinter plant should be cooperative with the flue gas desulfurization (FGD) technique. Thus, it is necessary to study the influence of the FGR technique on SO₂ emissions because it will directly influence the demand and design of the FGD system.     

Environmental Irradiation Test Facility

Results from a detailed analysis of sulfur dioxide (SO₂) reductions achievable through “deep” physical coal cleaning (PCC) at 20 coal-fired power plants in the Ohio-Indiana-Illinois region are presented here. These plants all have capacities larger than 500 MWe, are currently without any flue gas desulfurization (FGD) systems, and burn coal of greater than l%sulfur content (in 1980). Their aggregate emissions of 2.4 million tons of SO₂ per year represents 55% of the SO₂ inventory for these states. The principal coal supplies for each power plant were identified and characterized as to coal seam and county of origin, so that published coal-washability data could be matched to each supplier. The SO₂ reductions that would result from deep cleaning each coal (Level 4) were calculated using an Argonne computer model that assumes a weight recovery of 80%. Percentage reductions in sulfur content ranged from zero to 52%, with a mean value of 29%, and costs ranged from a low of $364/ton SO₂ removed to over $2000/ton SO₂ removed. Because coal suppliers to these power plants employ some voluntary coal cleaning, the anticipated emissions reduction from current levels should be near 20%. Costs then were estimated for FGD systems designed to remove the same amount of SO₂ as was achieved by PCC through the use of partial scrubbing with bypass of the remaining flue gas. On this basis, PCC was more cost-effective than FGD for about 50% of the plants studied and had comparable costs for another 25% of the plants. Possible governmental actions to either encourage or mandate coal cleaning were identified and evaluated     

Impaction and Particle Bounce at High Stokes Numbers

The information in this paper is directed to those concerned with controlling SO₂ emissions from power plants, and particularly with retrofitting controls onto existing plants. The paper describes an FGD system based on the dolomitic lime process and the scrubber design that have proved successful at the Colstrip plant in eastern Montana. A single scrubber vessel sized to treat all the gas from a 350-MWe coal-fired unit combines the functions of prequenching, absorption, washing, mist elimination, and recycle storage. Downflow Injection of gas along the vessel centerline and regulation of gas flow by the wash tray make the gas velocity uniform and permit scaling up to this large size. A high concentration of dissolved alkalinity in the scrubbing slurry provides rapid absorption and permits low L/G—40 gal/1000 acf—when coal with 2.5% sulfur is burned. Complete oxidation of sulfite makes gypsum of wallboard quality and the process can discharge clarified liquor low in COD if necessary to control chlorides. Since only the single scrubber vessel and the recycle pumps must be located close to the back end of the boiler, the system is particularly well suited for retrofit applications.     

多层生物滤塔净化硫化氢废气研究

以木屑为填料,采用多层生物滤塔净化H2S气体,研究其适宜的工艺条件及生物降解宏观动力学.结果表明,填料分层可提高H2S去除率,当进气容积负荷＜153.2 g H2S/(m3·d)时,H2S的去除率保持在90%以上;进气浓度低于70 mg/m3,下层200mm填料对H2S总去除率的贡献在50%以上;填料含水率为50%～6...