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1.
This paper describes some technical and economic aspects of the nahcolite ore injection process for the simultaneous removal of fly ash and sulfur oxides from stack gases. The process is capable of removing greater than 99% of the particulate matter and greater than 70% of the sulfur oxides present in such gases. In the process, nahcolite ore, a naturally occurring material containing 70 to 90% sodium bicarbonate, is ground to 90% passing through —200 mesh screens. Approximately 20% of the ground ore is used to precoat the filter bags in a baghouse filter while the remainder of the material is fed into the flue gas Just ahead of the baghouse. The flue gas is drawn through the baghouse by induced draft fans and sent up the stack. Most of the SO 2 and practically all of the fly ash in the flue gas can be removed as the gas passes through the filter bags. The spent nahcolite ore and fly ash are collected and conveyed to waste disposal as landfill, or alternatively processed for insolubilization by coprecipitation prior to landfilling. The technical feasibility of the process has been demonstrated in both bench scale and pilot scale engineering studies. Economic analyses performed for the cases of plants located in the midwest and southwest indicate lower capital costs for the nahcolite injection process when compared to wet scrubbing. On an annual cost basis, the nahcolite ore Injection process is comparable in cost to wet scrubbing for the case of the southwestern power plant, and somewhat more expensive for the case of the midwestern plant. 相似文献
2.
EPA’s efforts to develop low cost, retrofitable flue gas cleaning technology include the development of highly reactive sorbents. Recent work addressing lime enhancement and testing at the bench-scale followed by evaluation of the more promising sorbents in a pilot plant are discussed here. The conversion of Ca(OH) 2 with SO 2 increased several-fold compared with Ca(OH) 2 alone when Ca(OH) 2 was slurrled with fly ash first and later exposed to SO 2 in a laboratory packed bed reactor. Ca(OH) 2 enhancement increased with the increased fly ash amount. Dlatomaceous earths were very effective reactivity promoters of lime-based sorbents. Differential scanning calorimetry of the promoted sorbents revealed the formation of a new phase (calcium silicate hydrates) after hydration, which may be the basis for the observed Improved SO 2 capture. Fly ash/lime and diatomaceous earth/lime sorbents were tested in a 100 m 3/h pilot facility incorporating a gas humidifier, a sorbent duct injection system, and a baghouse. The inlet SO 2 concentration range was 1000-2500 ppm. With once-through dry sorbent injection into the humidified flue gas [approach to saturation 10–20°C (18–36°F) in the baghouse], the total SO 2 removal ranged from 50 to 90 percent for a stoichiometric ratio of 1 to 2. Recycling the collected solids resulted in a total lime utilization exceeding 80–90 percent. Increased lime utilization was also investigated by the use of additives. 相似文献
3.
Abstract Emissions of sulfur trioxide (SO 3) are a key component of plume opacity and acid deposition. Consequently, these emissions need to be low enough to not cause opacity violations and acid deposition. Generally, a small fraction of sulfur (S) in coal is converted to SO 3 in coal-fired combustion devices such as electric utility boilers. The emissions of SO 3 from such a boiler depend on coal S content, combustion conditions, flue gas characteristics, and air pollution devices being used. It is well known that the catalyst used in the selective catalytic reduction (SCR) technology for nitrogen oxides control oxidizes a small fraction of sulfur dioxide in the flue gas to SO 3. The extent of this oxidation depends on the catalyst formulation and SCR operating conditions. Gas-phase SO 3 and sulfuric acid, on being quenched in plant equipment (e.g., air preheater and wet scrubber), result in fine acidic mist, which can cause increased plume opacity and undesirable emissions. Recently, such effects have been observed at plants firing high-S coal and equipped with SCR systems and wet scrubbers. This paper investigates the factors that affect acidic mist production in coal-fired electric utility boilers and discusses approaches for mitigating emission of this mist. 相似文献
4.
A laboratory size spray dry scrubbing unit consisting of a spray dryer and a pulse Jet baghouse was used to study the effect of grinding recycle waste on SO 2 removal across the spray dryer and on sorbent utilization. The equipment treats simulated flue gas with a dry flow rate of 1.5 m 3 h ?1 (stp) and utilizes an ultrasonic nozzle for atomization. The apparatus was initially tested over a broad range of operating conditions; a close agreement in SO 2 removal was found with data from much larger units. The effect of grinding the FGD recycle material on the SO 2 removal across the spray dryer was found to be great. Grinding the recycle material can enhance the SO 2 removal efficiency to a level comparable to operation with a large excess of fresh lime. 相似文献
5.
ABSTRACT The visual impact of primary particles emitted from stacks is regulated according to stack opacity criteria. In-stack monitoring of the flue gas opacity allows plant operators to ensure that the plant meets U.S. Environmental Protection Agency opacity regulations. However, the emission of condensable gases such as SO 3 (that hydrolyzes to H 2SO 4), HCl, and NH 3, which may lead to particle formation after their release from the stack, makes the prediction of stack plume opacity more difficult. We present here a computer simulation model that calculates the opacity due to both primary particles emitted from the stack and secondary particles formed in the atmosphere after the release of condensable gases from the stack. A comprehensive treatment of the plume rise due to buoyancy and momentum is used to calculate the location at which the condensed water plume has evaporated (i.e., where opacity regulations apply). Conversion of H 2SO 4 to particulate sulfate occurs through nucleation and condensation on primary particles. A thermodynamic aerosol equilibrium model is used to calculate the amount of ammonium, chloride, and water present in the particulate phase with the condensed sulfate. The model calculates the stack plume opacity due to both primary and secondary particles. Examples of model simulations are presented for three scenarios that differ by the emission control equipment installed at the power plant: (1) electrostatic precipitators (ESP), (2) ESP and flue gas desulfurization, and (3) ESP and selective catalytic reduction. The calculated opacity is most sensitive to the primary particulate emissions. For the conditions considered here, SO 3 emissions showed only a small effect, except if one assumes that most H 2SO 4 condenses on primary particles. Condensation of NH 4Cl occurs only at high NH 3 emission rates (about 25 ppm stack concentration). 相似文献
6.
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. H 2O, 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 (NH 3) into the flue gas significantly decreases ash bleedthrough, so that with NH 3 injection "standard" bag materials may perform adequately. Currently, fullcompartment testing of four fabrics, with and without NH 3 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. 相似文献
7.
Sulphur compounds, including (NH 4) 2SO 4 and pyrite, were tested as suppressants in a hazardous waste incineration facility. The test results suggested that adding sulphur compounds only slightly reduced PCDD/F stack emissions; this restricted effect was attributed to the release of fly ash in large amounts during the sulphur adding experiments, i.e., it was due to a malfunctioning of the baghouse filter. Nevertheless, for the combined flow of flue gas + fly ash a reduction of more than 50% was achieved for the total PCDD/F concentrations and the total toxic concentrations, and an even higher inhibition capability was observed for PCDD. Also, a simulation of the thermodynamic equilibrium conditions by sulphur dioxide was conducted in the domain of experimental interest. Deactivation of catalysts, which promote PCDD/F formation, was found to be the dominant inhibition mechanism in low temperature PCDD/F formation. SO 2 could also inhibit the formation of molecular Cl 2 via the Deacon reaction, but that was not the main reason for inhibition. 相似文献
8.
Abstract In the In-Duct Injection Process, a lime slurry is sprayed into the flue gas between the air preheater and solids collection equipment, and about 30-60 percent removal of SO 2 is achieved. A simple model of this process has been developed based on heat and mass transfer theories, and this model was fitted to the data obtained at proof-of-concept test units. Data taken with separate injection of dry lime and water were also modeled, but the SO 2 removal was less than for slurry injection, probably because of incomplete capture of lime particles by the water droplets. 相似文献
9.
ABSTRACT At conditions typical of a bag filter exposed to a coal-fired flue gas that has been adiabatically cooled with water, calcium hydroxide and calcium silicate solids were exposed to a dilute, humidified gas stream of nitrogen dioxide (NO 2) and sulfur dioxide (SO 2) in a packed-bed reactor. A prior study found that NO 2 reacted readily with surface water of alkaline and non-alkaline solids to produce nitrate, nitrite, and nitric oxide (NO). With SO 2 present in the gas stream, NO 2 also reacted with S(IV), a product of SO 2 removal, on the exterior of an alkaline solid. The oxidation of S(IV) to S(VI) by oxygen reduced the availability of S(IV) and lowered removal of NO 2. Subsequent acidification of the sorbent by the removal of NO 2 and SO 2 facilitated the production of NO. However, the conversion of nitrous acid to sulfur-nitrogen compounds reduced NO production and enhanced SO 2 removal. A reactor model based on empirical and semi-empirical rate expressions predicted rates of SO 2 removal, NO 2 removal, and NO production by calcium silicate solids. Rate expressions from the reactor model were inserted into a second program, which predicted the removal of SO 2 and NO x by a continuous process, such as the collection of alkaline solids in a baghouse. The continuous process model, depending upon inlet conditions, predicted 30-40% removal for NO and 50-90% removal for SO 2. These x 2 results are relevant to dry scrubbing technology for combined SO 2 and NO x removal that first oxidizes NO to NO 2 by the addition of methanol into the flue duct. 相似文献
10.
The removal of SO 2 with atomization of a slaked lime slurry and supplemental injection of gaseous NH 3 were tested in a conventional spray dryer/baghouse system for SO 2 concentrations of 2000 ppm and 3000 ppm and a 30° F approach to saturation. Results at 3000 ppm of SO 2 showed an average SO 2 removal efficiency of 90.3 percent at a combined stoichiometric ratio of 0.95-1.10 and an average overall sorbent utilization of 91.6 percent. The overall molal ratio of NH 3/SO 2 reaction was found to be 2:1 under the test conditions Particle size analyses, and EP toxicity tests were conducted on the products of the reactions. 相似文献
11.
An experimental investigation on sulfur dioxide removal in a pilot-scale spray dryer from the flue gas generated by combustion of low-sulfur (S) heavy oil is reported. A limewater slurry was sprayed through an ultrasonic two-fluid atomizer in the spray-dry chamber, and the spent sorbent was collected downstream in a pulse-jet baghouse together with fly ash. Flue gas was sampled at different points to measure the desulfurization efficiency after both the spray-dry chamber and the baghouse. Parametric tests were performed to study the effect of the following variables: gas inlet temperature, difference between gas outlet temperature and adiabatic saturation temperature, lime-to-S ratio, and average size of lime particles in the slurry. Results indicated that spray drying is an effective technology for the desulfurization of low-S fuel oil flue gas, provided operating conditions are chosen carefully. In particular, the lowest gas inlet and outlet temperatures compatible with baghouse operation should be selected, as should a sufficiently high lime-to-S ratio. The attainment of a small lime particle size in the slurry is critical for obtaining a high desulfurization efficiency. A previously presented spray-dry flue gas desulfurization model was used to simulate the pilot-scale desulfurization tests, to check the ability of the model to predict the S capture data and its usefulness as a design tool, minimizing the need for pilot-scale experimentation. Comparison between model and experimental results was fairly good for the whole range of calcium/S ratios considered. 相似文献
12.
A procedure was developed for the 24-h determination of SO 2 and CO 2 in effluent gas from fossil fuel combustion sources. Laboratory experiments were conducted to test absorption of SO 2 in hydrogen peroxide solution and absorption of CO 2 by sodium hydroxide on an inert substrate at expected ambient temperatures of 15 to 45°C. Isopropyl alcohol cannot be used to trap sulfuric acid and particulates because it permeates the sampling train and prevents complete absorption of CO 2. Elemental analysis of stack particulates revealed that at least 31 elements were present. Iron and other elements interfered with SO 2 analysis. These particulates were completely removed by a heated borosilicate glass filter. Both laboratory and field experiments showed that molecular sieves are a promising alternative for CO 2 absorption. Statistical evaluation of data collected at three units equipped with flue gas desulfurization scrubbers proved that the new procedure is accurate and precise. 相似文献
13.
The concentrations of fine particles and selected gas pollutants in the flue gas entering the stack were measured under several common operation modes in an operating coal power plant producing electricity. Particle size distributions in a diameter range from 10 nm to 20 μm were measured by a scanning mobility particle sizer (SMPS), and the flue gas temperature and concentrations of CO 2 and SO 2 were monitored by a continuous emission monitoring system (CEMS). During the test campaign, five plant operating modes were studied: soot blowing, bypass of flue-gas desulfurization (FGD), reheat burner operating at 0% (turned off), 27%, and 42% (normal condition) of its full capacity. For wet and dry aerosols, the measured mode sizes were both around 40 nm, but remarkable differences were observed in the number concentrations (#/cm 3, count per square centimeter). A prototype photoionizer enhanced electrostatic precipitator (ESP) showed improved removal efficiency of wet particles at voltages above +11.0 kV. Soot blowing and FGD bypass both increased the total particle number concentration in the flue gas. The temperature was slightly increased by the FGD bypass mode and varied significantly as the rating of reheat burner changed. The variations of CO 2 and SO 2 emissions showed correlations with the trend of total particle number concentration possibly due to the transitions between gas and particle phases. The results are useful in developing coal-fired power plant operation strategies to control fine particle emissions and developing amine-based CO 2 capture technologies without operating and environmental concerns associated with volatile amine emissions. Implications: The measurement of the fine particle size distributions in the exhaust gas under several common operating conditions of a coal-fired power plant revealed different response relations between aerosol number concentration and the operating condition. A photo-ionizer enhanced ESP was demonstrated to capture fine particles with higher efficiency compared to conventional ESPs, and the removal efficiency increased with the applied voltage. The characteristic information of aerosols and main gaseous pollutants in the exhaust gas is extremely important for developing and deploying CO2 scrubbers, whose amine emissions and operating effectiveness depends greatly on the upstream concentrations of fine particles, SO2, from the power plant. 相似文献
14.
The United Power Association’s dry FGD system at Stanton, North Dakota was the first utility-operated lime spray dryer to be put into service in the United States. At 60 MW in size, it utilizes a single spray dryer vessel with three rotary atomizers and a ten-compartment fabric filter. It is currently operating at better than expected efficiency and Is meeting state and federal air quality requirements. Start-up and operation have shown that certain areas of design and operating conditions are critical to reliable operation. Flue gas, slurry, and water distribution and mixing must be carefully controlled if reliable, long term operation is to be achieved. Likewise, water chemistry Is Important in the reagent preparation equipment. Start-up of the system was accomplished In a step-wise fashion to bring the baghouse on line first, followed by the spray dryer. The spray dryer was operated at gradually lower outlet temperatures until design conditions were met. Measures taken since start-up to ensure reliable operation, and operation over an eighteen month period are discussed. Both particulate and SO 2 emission performance are evaluated. 相似文献
15.
ABSTRACT U.S. Environmental Protection Agency (EPA) Method 26A is the recommended procedure for capturing and speci-ating halogen (X 2) and hydrogen halide (HX) stack emissions from combustion sources. Previous evaluation studies of Method 26A have focused primarily on hydrogen chloride (HCl) speciation. Capture efficiency, bias, and the potential interference of Cl 2 at high levels (>20 ppm [u,g/m 3]) and NH 4Cl in the flue gas stream have been investigated. It has been suggested that precise Cl 2 measurement and accuracy in quantifying HX or X 2 using Method 26A are difficult to achieve at Cl 2 concentrations <5 ppm; however, no performance data exist to support this. Coal contains low levels of Cl, in the range of 5-2000 ppmw, which results in the presence of HCl and Cl 2 in the products of combustion. HCl is the predominant Cl compound formed in the high-temperature combustion process, and it persists in the gas as the products of combustion cool. Concentrations of Cl 2 in coal combustion flue gas at stack temperatures typically do not exceed 5 ppm. For this research, bench-scale experiments using simulated combustion flue gas were designed to validate the ability of Method 26A to speci-ate low levels of Cl 2 accurately. This paper presents the results of the bench-scale tests. The effect of various flue gas components is discussed. The results indicate that SO 2 is the only component in coal combustion flue gas that has an appreciable effect on Cl 2 distribution in Method 26A impingers, and that Method 26A cannot accurately speciate HCl and Cl 2 in coal combustion flue gas without modification. 相似文献
16.
Abstract Loss of filtration efficiency in a fabric filter baghouse is typically caused by bag failure, in one form or another. The degree of such failure can be as minor as a pinhole leak or as major as a fully involved baghouse fire. In some cases, local air pollution regulations or federal hazardous waste laws may require estimation of the total quantity of particulate matter released to the environment as a result of such failures. In this paper, a technique is presented for computing the dust loading in the baghouse exhaust when one or more bags have failed. The algorithm developed is shown to be an improvement over a previously published result, which requires empirical knowledge of the variation in baghouse pressure differential with bag failures. An example calculation is presented for a bag-house equipped with 200 bags. The prediction shows that a small percentage of failed bags can cause a relatively large proportion of the gas flow to bypass the active bags, which, in turn, leads to high outlet dust loading and low overall collection efficiency from the baghouse. 相似文献
17.
通过氯化和胺化两步反应合成了乙二胺基棉纤维(AEAC),并用于模拟烟气中SO 2的吸附研究。试验比较研究了不同种类的氯代试剂、胺化反应稀释剂和溶胀试剂对乙二胺基棉纤维制备和脱硫性能的影响。结果表明:乙二胺基棉纤维能有效吸附烟气中SO 2,饱和吸附容量可达120 mg/g干纤维;以N,N-二甲基甲酰胺(DMF)作为溶胀试剂,三氯氧磷(POCl 3)作为氯代试剂,并以正丁醇为胺化反应稀释剂可以大大改善乙二胺基棉纤维脱硫吸附剂的合成效果;样品含氮量和饱和硫容之间存在很好的正相关关系。 相似文献
18.
Simplified algorithms are presented for estimating the cost of controlling sulfur dioxide (SO 2) emissions from existing coal-fired power plants on a state-by-state basis. Results are obtained using the detailed Utility Control Strategy Model (UCSM) to calculate the Impacts of emission reductions ranging from approximately 30 percent to 90 percent of projected 1995 emissions for 18 different scenarios and 36 states. Scenarios include the use of two dry SO 2 removal technologies (lime spray dryers and LIMB) as potential options for power plant retrofit, in addition to currently available emission control options including coal switching, coal cleaning and wet flue gas desulfurization (FGD). Technical assumptions relating to FGD system performance and the upgrading of existing cold-side electrostatic precipitators (ESP) for reduced sulfur levels are also analyzed, along with the effects of interest rates, coal prices, coal choice restrictions, plant lifetime, and plant operating levels. Results are summarized in the form of a 3-term polynomial equation for each state, giving total annualized SO 2 control cost as a function of the total SO 2 emissions reduction for each scenario. Excellent statistical fits to UCSM results are obtained for these generalized equations. 相似文献
19.
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 m 2/g after 30 hr of reaction when only a minimal amount of lime was present. The SO 2 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 SO 2. The use of CaCl 2 as an additive to the lime/slag system, in lieu of gypsum, also produced high-surface-area solids, 115 m 2/g after 21 hr of reaction. However, the SO 2 reactivity of these sorbents was relatively low given the high surface area. This emphasized that the correlation between surface area and SO 2 reactivity was highly dependent on the solid phase, which was subsequently dependent on slurry composition. 相似文献
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