Full-Scale Evaluation of Mercury Control with Sorbent Injection and COHPAC at Alabama Power E.C. Gaston

Abstract

The overall objective of this project was to determine the cost and impacts of Hg control using sorbent injection into a Compact Hybrid Particulate Collector (COHPAC) at Alabama Power’s Gaston Unit 3. This test is part of a program funded by the U.S. Department of Energy’s National Energy Technology Laboratory (NETL) to obtain the necessary information to assess the costs of controlling Hg from coal-fired utility plants that do not have scrubbers for SO₂ control. The economics will be developed based on various levels of Hg control.

Gaston Unit 3 was chosen for testing because COHPAC represents a cost-effective retrofit option for utilities with existing electrostatic precipitators (ESPs). COHPAC is an EPRI-patented concept that places a high air-to-cloth ratio baghouse downstream of an existing ESP to improve overall particulate collection efficiency. Activated carbons were injected upstream of COHPAC and downstream of the ESP to obtain performance and operational data.

Results were very encouraging, with up to 90% removal of Hg for short operating periods using powdered activated carbon (PAC). During the long-term tests, an average Hg removal efficiency of 78% was measured. The PAC injection rate for the long-term tests was chosen to maintain COHPAC cleaning frequency at less than 1.5 pulses/bag/hr.     

Modeling sorbent injection for mercury control in baghouse filters: II--pilot-scale studies and model evaluation

Activated carbon injection for Hg control in a 500-lb/hr pilot-scale coal-fired furnace equipped with a fabric filter for particulate control was evaluated at different operating conditions. The pilot-scale tests showed that Hg removal was improved at lower temperatures and higher C/Hg ratios. The two-stage mathematical model developed to describe Hg removal using powdered activated carbon injection upstream of a baghouse filter was used to obtain Langmuir isotherm parameters as a function of temperature by fitting the model to a subset of experimental data. The predictive capability of the model was then tested by comparing model calculations with additional experimental data from this system obtained using different operating temperatures and sorbent to Hg ratios. Model predictions were in good agreement with experimentally measured Hg removal efficiency. Based on the model predictions, Hg removal in the duct appears to be limited and higher C/Hg ratio, lower operating temperature, and longer cleaning cycle of the baghouse filter should be utilized to achieve higher Hg removal in this system.     

Assessment of PCDD/F and PBDD/F emissions from coal-fired power plants during injection of brominated activated carbon for mercury control

The effect of the injection of brominated powdered activated carbon (Br-PAC) on the emission of brominated and chlorinated dioxins and furans in coal combustion flue gas has been evaluated. The sampling campaigns were performed at two U.S. Department of Energy (DOE) demonstration sites where brominated PAC was being injected for control of mercury emissions. The results of the sampling campaigns showed that injection of the brominated PAC upstream of the electrostatic precipitator (ESP) did not increase the emissions of total and Toxic EQuivalent (TEQ) chlorinated and brominated dioxin compounds. Rather, the data suggested the sorbent may capture these compounds and reduce their concentration in the flue gas stream. This effect, when seen, was small, and independent of the type of plant emission controls, temperature at the point of injection, or fuel-chlorine content. The addition of the brominated PAC sorbent resulted in slight increases the total content of chlorinated dioxins and furan in the particulate matter (ash) collected in the ESP, but did not increase its overall toxicity.     

Mercury mass balances: a case study of two North Dakota power plants

The Energy & Environmental Research Center (EERC) conducted a mercury-sampling program to provide data on the quantity and forms of Hg emitted and on the Hg removal efficiency of the existing air pollution control devices at two North Dakota power plants--Milton R. Young Station and Coal Creek Station. Minnkota Power Cooperative, Great River Energy, the North Dakota Industrial Commission, and EPRI funded the project. The primary objective was to obtain accurate measurements of Hg released from each plant, as verified by a material balance. A secondary objective was to evaluate the ability of a mercury continuous emission monitor (CEM) to measure total Hg at the stack. At both plants, speciated Hg measurements were made at the inlets and outlets of both the electrostatic precipitators (ESPs) and the flue gas desulfurization (FGD) systems. A Semtech Hg 2000 (Semtech Metallurgy AB) mercury CEM was used to measure the total Hg emissions at the stack in real time. Using these measurements and plant data, the measured Hg concentrations in the coal, FGD slurries, and ESP ash, a Hg mass flow rate was calculated at each sampling location. Excellent Hg mass balances were obtained (+/- 15%). It was also found that the Hg was mostly in the elemental phase (approximately 90%), and the small amount of oxidized Hg that was generated was removed by the FGD systems. Insignificant amounts of particulate-bound Hg were measured at both plants. However, 10-20% of the elemental Hg measured prior to the ESP was converted to oxidized Hg across the ESP. The data show that, at these facilities, almost all of the Hg generated is being emitted into the atmosphere as elemental Hg. Local or regional deposition of the Hg emitted from these plants is not a concern. However, the Hg does become part of the global Hg burden in the atmosphere. Also, the evidence appears to indicate that elemental Hg is more difficult to remove from flue gas than oxidized Hg is.     

Mercury Mass Balances: A Case Study of Two North Dakota Power Plants

ABSTRACT

The Energy & Environmental Research Center (EERC) conducted a mercury-sampling program to provide data on the quantity and forms of Hg emitted and on the Hg removal efficiency of the existing air pollution control devices at two North Dakota power plants—Milton R. Young Station and Coal Creek Station. Minnkota Power Cooperative, Great River Energy, the North Dakota Industrial Commission, and EPRI funded the project. The primary objective was to obtain accurate measurements of Hg released from each plant, as verified by a material balance. A secondary objective was to evaluate the ability of a mercury continuous emission monitor (CEM) to measure total Hg at the stack.

At both plants, speciated Hg measurements were made at the inlets and outlets of both the electrostatic precipi-tators (ESPs) and the flue gas desulfurization (FGD) systems. A Semtech Hg 2000 (Semtech Metallurgy AB) mercury CEM was used to measure the total Hg emissions at the stack in real time. Using these measurements and plant data, the measured Hg concentrations in the coal, FGD slurries, and ESP ash, a Hg mass flow rate was calculated at each sampling location. Excellent Hg mass balances were obtained (±15%). It was also found that the Hg was mostly in the elemental phase (~90%), and the small amount of oxidized Hg that was generated was removed by the FGD systems.

Insignificant amounts of particulate-bound Hg were measured at both plants. However, 10-20% of the elemental Hg measured prior to the ESP was converted to oxidized Hg across the ESP. The data show that, at these facilities, almost all of the Hg generated is being emitted into the atmosphere as elemental Hg. Local or regional deposition of the Hg emitted from these plants is not a concern. However, the Hg does become part of the global Hg burden in the atmosphere. Also, the evidence appears to indicate that elemental Hg is more difficult to remove from flue gas than oxidized Hg is.     

Mass transfer within electrostatic precipitators: trace gas adsorption by sorbent-covered plate electrodes

Varying degrees of mercury (Hg) capture have been reported within the electrostatic precipitators (ESPs) of coal-fired electric utility boilers. There has been some speculation that the adsorption takes place on the particulate-covered plate electrodes. This convective mass transfer analysis of laminar and turbulent channel flows provides the maximum potential for Hg adsorption by the plate electrodes within an ESP under those conditions. Mass transfer calculations, neglecting electrohydrodynamic (EHD) effects, reveal 65% removal of elemental Hg for a laminar flow within a 15-m-long channel of 0.2-m spacing and 42% removal for turbulent flow within a similar configuration. Both configurations represent specific collection areas (SCAs) that are significantly larger than conventional ESPs in use. Results reflecting more representative SCA values generally returned removal efficiencies of <20%. EHD effects, although potentially substantial at low Reynolds numbers, diminish rapidly with increasing Reynolds number and become negligible at typical ESP operating conditions. The present results indicate maximum Hg removal efficiencies for ESPs that are much less than those observed in practice for comparable ESP operating conditions. Considering Hg adsorption kinetics and finite sorbent capacity in addition to the present mass transfer analyses would yield even lower adsorption efficiencies than the present results. In a subsequent paper, the author addresses the mass transfer potential presented by the charged, suspended particulates during their collection within an ESP and the role they potentially play in Hg capture within ESPs.     

The fate and behavior of mercury in coal-fired power plants

For the past 22 years in the Netherlands, the behavior of Hg in coal-fired power plants has been studied extensively. Coal from all over the world is fired in Dutch power stations. First, the Hg concentrations in these coals were measured. Second, the fate of the Hg during combustion was established by performing mass balance studies. On average, 43 +/- 30% of the Hg was present in the flue gases downstream of the electrostatic precipitator (ESP; dust collector). In individual cases, this figure can vary between 1 and 100%. Important parameters are the Cl content of the fuel and the flue gas temperature in the ESP. On average, 54 +/- 24% of the gaseous Hg was removed in the wet flue-gas desulfurization (FGD) systems, which are present at all Dutch coal-power stations. In individual cases, this removal can vary between 8% (outlier) and 72%. On average, the fate of Hg entering the power station in the coal was as follows: <1% in the bottom ash, 49% in the pulverized fuel ash (ash collected in the ESP), 16.6% in the FGD gypsum, 9% in the sludge of the wastewater treatment plant, 0.04% in the effluent of the wastewater treatment plant, 0.07% in fly dust (leaving the stack), and 25% as gaseous Hg in the flue gases and emitted into the air. The distribution of Hg over the streams leaving the FGD depends strongly on the installation. On average, 75% of the Hg was removed, and the final concentration of Hg in the emitted flue gases of the Dutch power stations was only -3 microg/m3(STP) at 6% O2. During co-combustion with biomass, the removal of Hg was similar to that during 100% coal firing. Speciation of Hg is a very important factor. An oxidized form (HgCl2) favors a high degree of removal. The conversion from Hg0 to HgCl2 is positively correlated with the Cl content of the fuel. A catalytic DENOX (SCR) favors the formation of oxidized Hg, and, in combination with a wet FGD, the total removal can be as high as 90%.     

A Model to Predict the System Performance of an Electrostatic Precipitator for Collecting Polydisperse Particles

Abstract

This paper presents a model for predicting the performance of an electrostatic precipitator (ESP) for collecting polydisperse particles. The particle charge was obtained by modifying Cochet’s charge equation; the particle size distribution was approximated by a lognormal function; and then the statistic method of moments was employed to obtain a set of the first three moment equations. The continuous evolution of the particle size distribution in an ESP is easily taken into account by the first three moment equations. The performance of this model was validated by comparing its predictions with the existing data available in the literature. Effects of the particle size distribution on the ESP performance were examined, and the results indicated that both overall mass and number efficiencies are lower for inlet particles with a larger mass median diameter and a higher geometric standard deviation. The methodology introduced may be applied to develop design criteria and determine optimal operating conditions of an ESP for improving the collection efficiency of the submicron particles.     

The Fate and Behavior of Mercury in Coal-Fired Power Plants

Abstract

For the past 22 years in the Netherlands, the behavior of Hg in coal-fired power plants has been studied extensively. Coal from all over the world is fired in Dutch power stations. First, the Hg concentrations in these coals were measured. Second, the fate of the Hg during combustion was established by performing mass balance studies. On average, 43 ± 30% of the Hg was present in the flue gases downstream of the electrostatic precipitator (ESP; dust collector). In individual cases, this figure can vary between 1 and 100%. Important parameters are the Cl content of the fuel and the flue gas temperature in the ESP. On average, 54 ± 24% of the gaseous Hg was removed in the wet flue-gas desulfurization (FGD) systems, which are present at all Dutch coal-power stations. In individual cases, this removal can vary between 8% (outlier) and 72%.

On average, the fate of Hg entering the power station in the coal was as follows: <1% in the bottom ash, 49% in the pulverized fuel ash (ash collected in the ESP), 16.6% in the FGD gypsum, 9% in the sludge of the wastewater treatment plant, 0.04% in the effluent of the wastewater treatment plant, 0.07% in fly dust (leaving the stack), and 25% as gaseous Hg in the flue gases and emitted into the air. The distribution of Hg over the streams leaving the FGD depends strongly on the installation. On average, 75% of the Hg was removed, and the final concentration of Hg in the emitted flue gases of the Dutch power stations was only ~3 μg/m_STP ³ at 6% O₂. During co-combustion with biomass, the removal of Hg was similar to that during 100% coal firing.

Speciation of Hg is a very important factor. An oxidized form (HgCl₂) favors a high degree of removal. The conversion from Hg⁰ to HgCl₂ is positively correlated with the Cl content of the fuel. A catalytic DENOX (SCR) favors the formation of oxidized Hg, and, in combination with a wet FGD, the total removal can be as high as 90%.     

Fine particle migration and collection in a wet electrostatic precipitator

Electrostatic precipitation is considered as an effective technology for fine particle removal. A lab-scale wet electrostatic precipitator (ESP) with wire-to-plate configuration was developed to study particle migration and collection. The performance of the wet ESP was evaluated in terms of the corona discharge characteristics, total removal efficiency and fractional removal efficiency. The corona discharge characteristics and particle removal abilities of the wet ESP were investigated and compared with dry ESP. Particle removal efficiency was influenced by discharge electrode type, SO₂ concentration, specific collection area (SCA) and particle/droplet interaction. Results showed that the particle removal efficiency of wet ESP was elevated to 97.86% from 93.75% of dry ESP. Three types of discharge electrodes were investigated. Higher particle removal efficiency and larger migration velocity could be obtained with fishbone electrode. Particle removal efficiency decreased by 2.87% when SO₂ concentration increased from 0 ppm to 43 ppm as a result of the suppression of corona discharge and particle charging. The removal efficiency increased with higher SCA, but it changed by only 0.71% with the SCA increasing from 25.0 m²/(m³/s) to 32.5 m²/(m³/s). Meanwhile, the increasing of particle and droplet concentration was favorable to the particle aggregation and improved particle removal efficiency.

Implications: This work tends to study the particle migration and collection under spraying condition. The performance of a wet electrostatic precipitator (ESP) is evaluated in terms of the corona discharge characteristics, total particle removal efficiency, and fractional particle removal efficiency. The effects of water droplets on particle removal, especially on removal of particles with different sizes, is investigated. The optimization work was done to determine appropriate water consumption, discharge electrode type, and specific collection area, which can provide a basis for wet ESP design and application.     

Powdered activated carbon coupled with enhanced coagulation for natural organic matter removal and disinfection by-product control: application in a Western Australian water treatment plant

The removal of organic precursors of disinfection by-products (DBPs), i.e. natural organic matter (NOM), prior to disinfection and distribution is considered as the most effective approach to minimise the formation of DBPs. This study investigated the impact of the addition of powdered activated carbon (PAC) to an enhanced coagulation treatment process at an existing water treatment plant on the efficiency of NOM removal, the disinfection behaviour of the treated water, and the water quality in the distribution system. This is the first comprehensive assessment of the efficacy of plant-scale application of PAC combined with enhanced coagulation on an Australian source water. As a result of the PAC addition, the removal of NOM improved by 70%, which led to a significant reduction (80-95%) in the formation of DBPs. The water quality in the distribution system also improved, indicated by lower concentrations of DBPs in the distribution system and better maintenance of disinfectant residual at the extremities of the distribution system. The efficacy of the PAC treatment for NOM removal was shown to be a function of the characteristics of the NOM and the quality of the source water, as well as the PAC dose. PAC treatment did not have the capacity to remove bromide ion, resulting in the formation of more brominated DBPs. Since brominated DBPs have been found to be more toxic than their chlorinated analogues, their preferential formation upon PAC addition must be considered, especially in source waters containing high concentrations of bromide.     

The Bechtel Confined Zone dispersion Process for FGD Retrofit Situations Proof-of-Concept Tests

The Bechtel Confined Zone Dispersion (CZD) process for FGD retrofit situations was tested at two sites: one at a level of 5 MWe; the other at 70 MWe. The CZD process involves injecting a finely atomized slurry of hydrated lime into a straight run of duct between a boiler's air heater and its electrostatic precipitator (ESP). The effect of process variables on SO₂ removal and ESP performance was investigated for dolomitic/calcitic lime. Removals of SO₂ in excess of 50 percent were achieved for either lime type at the 5 MWe site. A very short duct length limited injection rate at the 70 MWe site, limiting sulfur removals to a maximum of 30 percent. SO₂ removal data for both sites were successfully correlated on a common basis. ESP performance was not fully acceptable during lime injection at both sites, but it is felt that optimization of ESP operations should eliminate this problem. Additional testing is recommended to further explore ESP performance and to optimize lime injection parameters. The results obtained to date continue to indicate that the CZD process is an attractive and economical candidate for FGD retrofit situations.     

Control of mercury emissions from a municipal solid waste incinerator in Japan

The control of Hg emissions from a municipal solid waste incinerator (MSWI) is very important, because more than 78% of municipal solid waste (MSW) is incinerated. The Hg content of coal used in utility boilers is relatively low in Japan. In this study, recent trends in the Hg content of MSW in Japan and activated carbon (AC) injection as a control technology of Hg emission from an MSWI are discussed. The effect of AC injection on Hg removal from flue gas in an MSWI was investigated by pilot-scale experiments using a bag filter (BF). The injection of AC increases the Hg reduction ratio by 20-30% compared with cases without AC injection. The Hg reduction ratio increases as the flue gas temperature decreases. The Hg reduction ratio is closely related to the inlet Hg concentration and was expressed with a Langmuir-type adsorption isotherm.     

Removal of pesticides from surface waters by combined physicochemical processes. Part I: Dodine

The simultaneous action of powdered activated carbon and several coagulant agents on the removal of the fungicide dodine from spiked distilled water, was studied. As coagulants, ferric chloride (FeCl₃) and basic polyaluminium chlorosulfate ([Al(OH)_xCl_y(SO₄)_z]_n) were examined, using polyacrylamide, in certain cases, as coagulant aid (polyelectrolyte). The efficiency of dodine removal was investigated with respect to the added amount of powdered activated carbon (PAC), the pH value, as well as the type and dose of coagulant and polyelectrolyte. The experiments were performed applying the standard jar-test procedure. The initial concentration of dodine was 250 μg/L. At this concentration and pH range 5–8 it was found that a dose of 100 mg/L PAC was necessary to achieve more than 98% removal of dodine, whereas lower removal (91–93%) was obtained applying half the dose of PAC under the same conditions. However, when 10–100 mg/L FeCl₃ were simultaneously added with PAC, the removal efficiency increased to >98%, even with the half PAC dose.     

Improving Baghouse Performance at the Monticello Generating Station

At the Monticello station, operated by the Texas Utilities Generating Company, lignite coal obtained locally in Titus and Hopkins Counties fuels each of the three units. Units 1 and 2 are identical 575-MW Combustion Engineering (CE) boilers, each of which discharges its effluent to a 36- compartment shake/deflate cleaned baghouse paralleled with four electrostatic precipitators (ESP). Unit 3 is a larger boiler and is followed by an ESP and a scrubber. The Unit 1 and 2 baghouses were designed to clean 80 percent of the flue gas. Since startup, these baghouses have regularly experienced flange-to-flange pressure drops in excess of 10 in. H₂O, with large opacity spikes caused by ash bleeding through the bags after compartment cleanings. Because of higher-than-expected pressure drop, the baghouses receive only about 45-50 percent of the flue gas. Analysis has shown the Monticello lignite ash significantly differs from most other coal ashes. Testing has shown that the Monticello ash is not filtered effectively by many "standard" bag materials. However, this testing indicates that there are fabrics that show promise of eliminating the ash bleedthrough with little pressure drop penalty. Testing has also shown that injection of low concentrations (10-15 ppm) of ammonia (NH₃) into the flue gas significantly decreases ash bleedthrough, so that with NH₃ injection "standard" bag materials may perform adequately. Currently, fullcompartment testing of four fabrics, with and without NH₃ injection, is under way at the Unit 1 baghouse. The research conducted at the Monticello station is reviewed in this paper and the encouraging results from the full-compartment tests are presented.     

Fine particle removal performance of a two-stage wet electrostatic precipitator using a nonmetallic pre-charger

A novel two-stage wet electrostatic precipitator (ESP) has been developed using a carbon brush pre-charger and collection plates with a thin water film. The electrical and particle collection performance was evaluated for submicrometer particles smaller than 0.01- 0.5 micrometer in diameter by varying the voltages applied to the pre-charger and collection plates as well as the polarity of the voltage. The collection efficiency was compared with that calculated by the theoretical models. The long-term performances of the ESP with and without water films were also compared in tests using Japanese Industrial Standards dust. The experimental results show that the carbon brush pre-charger of the two-stage wet ESP had approximately 10% particle capture, while producing ozone concentrations of less than 30 ppb. The produced amounts of ozone are significantly lower than the current limits set by international agencies. The ESP also achieved a high collection rate performance, averaging 90% for ultrafine particles, as based on the particle number concentration at an average velocity of 1 m/sec corresponding to a residence time of 0.17 sec. Higher particle collection efficiency for the ESP can be achieved by increasing the voltages applied to the pre-charger and the collection plates. The decreased collection efficiency that occurred during dust loading without water films was completely avoided by forming a thin water film on the collection plates at a water flow rate of 6.5 L/min/m(2).     

Low-resistivity Related ESP Performance Problems in Dry Scrubbing Applications

This paper describes the evaluation of the performance of ESPs operating downstream of spray dryers in high- and medium-sulfur coal flue gas streams. Tests were conducted at the TV A10 MW Spray Dryer/ESP Pilot Plant and the EPRI High Sulfur Test Center. The results of the analysis of particle characteristics, spray dryer operating parameters, and ESP operating variables identify the occurrence of severe particle reentrainment due to the low resistivity (10⁸ ohm-cm and lower) of the sorbent/flyash mixtures at low approach-tosaturation temperatures. The reentrainment has a significant impact on the collection efficiency of ESPs which could represent a fundamental limitation on their ability to adequately perform in this environment. Although this program has been focused on spray dryer applications, because of the similarities of the gas and particle characteristics produced from spray drying and other dry scrubbing processes, the results also have implications to duct slurry injection, dry sorbent injection with humidification, and processes involving furnace sorbent injection with humidification.

The performance characteristics of the ESPs are presented under both baseline and spray dryer conditions. The results are analyzed and the Southern Research Institute ESP Computer Model was used to evaluate the data. Special techniques for measuring particle resistivity at these conditions are described. A theoretical examination of particle reentrainment was undertaken which indicated that at low-resistivity levels the electrostatic forces reverse and tend to pull the particles off the plates with a force proportional to the square of the electric field. This repulsion of particles from the plates at spray dryer conditions was confirmed by laboratory experiments. Chloride content of the coal was found to be an important parameter effecting the performance of the ESP. Implications of the results of this evaluation relative to ESP upgrades are presented.     

Trace metal distribution and control in the pilot-scale bubbling fluidized bed combustor equipped with the pulse-jet fabric filter,limestone injection,and the humidification reactor

This work focused on trace metal behavior and removal in a fabric filter or in a humidification reactor during the cofiring of sawdust and refuse-derived fuels (RDFs) in a pilot-scale bubbling fluidized bed (BFB) boiler. Trace metal emissions measurements before and after the fabric filter revealed that removal efficiency in the fabric filter was in the range of 80-100%, and that the European Union (EU) Directive on Incineration of Waste restrictions for trace metal emissions are easily achieved even if addition of RDFs substantially increases the concentration of trace metals in fuel blends. Limestone injection enhanced the removal of As and Se but had no noticeable effect on the removal of other trace metals. Extensive formation of HgCl2 and condensation on fly ash particles during sawdust plus 40% RDF cofiring resulted in a 92% Hg removal efficiency in the fabric filter. Limestone injection had no effect on the Hg removal in the fabric filter but decreased the Hg removal in a humidification reactor from 40 to 28%. Results of the bed material and fly ash analysis suggested capture of Cu, Pb, Mn, Ni, and Zn in the bed material but also suggested that these metals may be released from the bed if the fuel characteristics or process conditions are changed.     

The adsorptive capacity of vapor-phase mercury chloride onto powdered activated carbon derived from waste tires

Injection of powdered activated carbon (PAC) upstream of particulate removal devices (such as electrostatic precipitator and baghouses) has been used effectively to remove hazardous air pollutants, particularly mercury-containing pollutants, emitted from combustors and incinerators. Compared with commercial PACs (CPACs), an alternative PAC derived from waste tires (WPAC) was prepared for this study. The equilibrium adsorptive capacity of mercury chloride (HgCl2) vapor onto the WPAC was further evaluated with a self-designed bench-scale adsorption column system. The adsorption temperatures investigated in the adsorption column were controlled at 25 and 150 degrees C. The superficial velocity and residence time of the flow were 0.01 m/sec and 4 sec, respectively. The adsorption column tests were run under nitrogen gas flow. Experimental results showed that WPAC with higher Brunauer-Emmett-Teller (BET) surface area could adsorb more HgCl2 at room temperature. The equilibrium adsorptive capacity of HgCl2 for WPAC measured in this study was 1.49 x 10(-1) mg HgCl2/g PAC at 25 degrees C with an initial HgCI2 concentration of 25 microg/m3. With the increase of adsorption temperature < or = 150 degrees C, the equilibrium adsorptive capacity of HgCl2 for WPAC was decreased to 1.34 x 10(-1) mg HgCl2/g PAC. Furthermore, WPAC with higher sulfur contents could adsorb even more HgCl2 because of the reactions between sulfur and Hg2+ at 150 degrees C. It was demonstrated that the mechanisms for adsorbing HgCl2 onto WPAC were physical adsorption and chemisorption at 25 and 150 degrees C, respectively. Experimental results also indicated that the apparent overall driving force model appeared to have the good correlation with correlation coefficients (r) > 0.998 for HgCl2 adsorption at 25 and 150 degrees C. Moreover, the equilibrium adsorptive capacity of HgCl2 for virgin WPAC was similar to that for CPAC at 25 degrees C, whereas it was slightly higher for sulfurized WPAC than for CPAC at 150 degrees C.     

Control of Mercury Emissions from a Municipal Solid Waste Incinerator in Japan

Abstract

The control of Hg emissions from a municipal solid waste incinerator (MSWI) is very important, because more than 78% of municipal solid waste (MSW) is incinerated. The Hg content of coal used in utility boilers is relatively low in Japan. In this study, recent trends in the Hg content of MSW in Japan and activated carbon (AC) injection as a control technology of Hg emission from an MSWI are discussed. The effect of AC injection on Hg removal from flue gas in an MSWI was investigated by pilot-scale experiments using a bag filter (BF). The injection of AC increases the Hg reduction ratio by 20–30% compared with cases without AC injection. The Hg reduction ratio increases as the flue gas temperature decreases. The Hg reduction ratio is closely related to the inlet Hg concentration and was expressed with a Langmuir-type adsorption isotherm.