Impact of Free Calcium Oxide Content of Fly Ash on Dust and Sulfur Dioxide Emissions in a Lignite-Fired Power Plant

Abstract

Emitted pollutants from the Agios Dimitrios lignite-fired power plant in northern Greece show a very strong linear correlation with the free calcium oxide content of the lignite ash. Dust (fly ash) emissions are positively correlated to free calcium oxide content, whereas sulfur dioxide (SO₂) emissions are negatively correlated. As a result, at present, the Agios Dimitrios Power Plant operates very strictly within the legislative limits on atmospheric particulate emission. In the present study, the factors to be considered in assessing the impact of lignite combustion on the environment are presented and evaluated statistically. The ash appears to have a remarkable SO₂ natural dry scrubbing capability when the free calcium oxide content ranges between 4 and 7%. Precipitator operating problems attributable to high ash resistivity can be overcome by injecting sulfur trioxide to reduce the ash resistivity, with, of course, a probable increase in operating costs.     

Natural desulfurization in coal-fired units using Greek lignite

This paper analyzes the natural desulfurization process taking place in coal-fired units using Greek lignite. The dry scrubbing capability of Greek lignite appears to be extremely high under special conditions, which can make it possible for the units to operate within the legislative limits of sulfur dioxide (SO2) emissions. According to this study on several lignite-fired power stations in northern Greece, it was found that sulfur oxide emissions depend on coal rank, sulfur content, and calorific value. On the other hand, SO2 emission is inversely proportional to the parameter gammaCO2(max), which is equal to the maximum carbon dioxide (CO2) content by volume of dry flue gas under stoichiometric combustion. The desulfurization efficiency is positively correlated to the molar ratio of decomposed calcium carbonate to sulfur and negatively correlated to the free calcium oxide content of fly ash.     

From Air Repair to EM: A&WMA’s Publications through a Century of Change

Abstract

This paper analyzes the natural desulfurization process taking place in coal-fired units using Greek lignite. The dry scrubbing capability of Greek lignite appears to be extremely high under special conditions, which can make it possible for the units to operate within the legislative limits of sulfur dioxide (SO₂) emissions. According to this study on several lignite-fired power stations in northern Greece, it was found that sulfur oxide emissions depend on coal rank, sulfur content, and calorific value. On the other hand, SO₂ emission is inversely proportional to the parameter y _CO2max, which is equal to the maximum carbon dioxide (CO₂) content by vol ume of dry flue gas under stoichiometric combustion. The desulfurization efficiency is positively correlated to the molar ratio of decomposed calcium carbonate to sulfur and negatively correlated to the free calcium oxide content of fly ash.     

Joint US/USSR Test Program for Reducing Fly Ash Resistivity

An electrostatic precipitator preceded by a wet scrubber was tested at the Reftinskaya Power Station. The unit collects a high resistivity fly ash from the combustion of low sulfur Ekibastuz coal. The operating parameters of the precipitator were measured as well as the mass emissions and the in-situ electrical resistivity of the fly ash. Density, particle size distribution, electrical resistivity, and chemical composition were determined for collected samples of the fly ash. The fly ash was also characterized by x-ray diffraction and scanning electron microscopy. When a centrifugal wet wall scrubber was installed ahead of the electrostatic precipitator, the temperature of the flue gas entering the precipitator was decreased and the moisture content increased. The electrical resistivity of the fly ash was attenuated a decade, but not enough to overcome the adverse effects of back corona in the precipitator. Lowering the flue gas temperature to about 85°C by the addition of a venturi scrubber ahead of the centrifugal scrubber reduced the electrical resistivity of the fly ash another decade and allowed the operation of the precipitator without back corona.     

An alternative to additional SO3 injection for fly ash conditioning

Small concentrations, approximately 2-10 parts per million (ppm), of injected sulfur trioxide (SO3) have improved particulate collection efficiencies of electrostatic precipitators burning lower-sulfur coal. However, the addition of extra SO3 not only incurs costs but also presents negative environmental effects. This work explored a method that could be applied to existing coal-fired power plants to convert the sulfur dioxide (SO2) already present in the flue gas to sufficient levels of SO3 for fly ash conditioning as an alternative to adding SO3 by burning elemental sulfur. During this research, a pre-mixed natural gas flame was used to promote the conversion of SO2 to SO3 in a drop-tube furnace with average non-flame, free stream gas temperatures of 450 and 1000 K. SO3 concentrations measured by wet chemistry and confirmed using elemental balances of other sulfur species measured by gas chromatography revealed that as much as 7% of SO2 was homogeneously transformed to SO3. The results also showed that at low temperatures, the rate at which SO3 is converted back to SO2 decreased, thus extending the time period during which SO3 concentrations would be sufficient for ash conditioning. An additional benefit of this technique is speculated to result from increased flue gas humidity.     

Emissions of sulfur trioxide from coal-fired power plants

Emissions of sulfur trioxide (SO3) 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 SO3 in coal-fired combustion devices such as electric utility boilers. The emissions of SO3 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 SO3. The extent of this oxidation depends on the catalyst formulation and SCR operating conditions. Gas-phase SO3 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.     

Product Gudie/1987

A computer program has been written to determine the cost of building and operating wet scrubbers on individual coal fired utilities in the states where emissions are likely to affect the acid rain problem in the eastern United States. The program differs from many other estimates since it calculates the cost for each of 831 individual sites. The capital costs for installing scrubbers on the top fifty sulfur oxide emitting plants will be about $20 billion. This will result in an increase in the cost of electricity on an average of 0.88 cents/kWh and a reduction of sulfur oxide emissions from 1980 of 7,100,000 tons per year. An additional reduction of at least 1,000,000 tons per year can be obtained by requiring all plants burning oil to burn low sulfur oil. These figures assume utilities will use least emissions dispatching and will use local coals containing at least 3.5 percent sulfur. The use of local coals should result in a further saving of at least 0.2 cents/kWh. This should make available a large supply of low sulfur coal which could reduce emissions of sulfur oxides by up to 1,000,000 tons per year. The SO₂ reductions will be continued for at least the next thirteen years and have a very significant effect through the year 2010.     

Emissions from carpet combustion in a pilot-scale rotary kiln: comparison with coal and particle-board combustion

The use of post-consumer carpet as a potential fuel substitute in cement kilns and other high-temperature processes is being considered to address the problem of huge volumes of carpet waste and the opportunity of waste-to-energy recovery. Carpet represents a high volume waste stream, provides high energy value, and contains other recoverable materials for the production of cement. This research studied the emission characteristics of burning 0.46-kg charges of chopped nylon carpet squares, pulverized coal, and particle-board pellets in a pilot-scale natural gas-fired rotary kiln. Carpet was tested with different amounts of water added. Emissions of oxygen, carbon dioxide, nitric oxide (NO), sulfur dioxide (SO2), carbon monoxide (CO), and total hydrocarbons and temperatures were continuously monitored. It was found that carpet burned faster and more completely than coal and particle board, with a rapid volatile release that resulted in large and variable transient emission peaks. NO emissions from carpet combustion ranged from 0.06 to 0.15 g/MJ and were inversely related to CO emissions. Carpet combustion yielded higher NO emissions than coal and particle-board combustion, consistent with its higher nitrogen content. SO2 emissions were highest for coal combustion, consistent with its higher sulfur content than carpet or particle board. Adding water to carpet slowed its burn time and reduced variability in the emission transients, reducing the CO peak but increasing NO emissions. Results of this study indicate that carpet waste can be used as an effective alternative fuel, with the caveats that it might be necessary to wet carpet or chop it finely to avoid excessive transient puff emissions due to its high volatility compared with other solid fuels, and that controlled mixing of combustion air might be used to control NO emissions from nylon carpet.     

Impact of engine lubricant properties on regulated gaseous emissions of 2000-2001 model-year gasoline vehicles

The impact of the sulfur (S) content in lubricating oil was evaluated for four ultra-low-emission vehicles and two super-ultra-low-emission vehicles, all with low mileage. The S content in the lube oils ranged from 0.01 to 0.76%, while the S content of the gasoline was fixed at 0.2 ppmw. Vehicles were configured with aged catalysts and tested over the Federal Test Procedure, at idle and at 50-mph cruise conditions. In all testing modes, variations in the S level of the lubricant did not significantly affect the regulated gas-phase tailpipe emissions. In addition to the regulated gas-phase emissions, a key element of the research was measuring the engine-out sulfur dioxide (SO2) in near-real-time. This research used a new methodology based on a differential optical absorption spectrometer (DOAS) to measure SO2 from the lubricants used in this study. With the DOAS, the contribution of SO2 emissions for the highest-S lubricant was found to range from less than 1 to 6 ppm on a gasoline S equivalent basis over the range of vehicles and test cycles used. The development and operation of the DOAS is discussed in this paper.     

Estimates of 1973–1982 Annual Sulfur Oxide Emissions from Electric Utilities

Estimates of 1973–1982 annual SO₂ emissions from electric utility plants are presented in this paper. Results are based on analyses of plant level data collected by the U.S. Department of Energy on consumption and quality of fuels burned. Emissions are estimated from known information about fuel consumption, sulfur content, ash content, and control equipment. Results show that electric utility emissions decreased 16% from 1973 to 1982 and that these reductions were due to the use of lower sulfur coals and to the operation of flue gas desulfurization equipment.     

The Relationship of Carbon Dioxide Emissions with Coal Rank and Sulfur Content

Carbon dioxide emissions, on an equivalent energy basis, were calculated for 504 North American coals to explore the effects of coal rank and sulfur content on CO₂ emissions. The data set included coals ranging in rank from lignite through low-volatile bituminous from 15 U.S. states and Alberta, Canada. Carbon dioxide emissions were calculated from the carbon content and gross calorific value of each coal. The lowest CO₂ emissions are calculated for the high-volatile bituminous coals (198 to 211 lbs CO₂/MMBtu) and the highest for lignites and subbituminous coals (209 to 224 lbs CO₂/MMBtu). The lower CO₂ emissions from the high-volatile bituminous coals result in part from their generally higher sulfur content. However, even at equivalent sulfur contents the high-volatile bituminous coals give lower CO₂ emissions than the lower-rank coals. On average, the lowerrank coals produce 5 percent more CO₂ upon combustion than the highvolatile bituminous coals, on the basis of gross calorific value. This difference increases to 9 percent on the basis of estimated net calorific value. The net calorific value is better indicator of power plant energy production than the gross calorific value. The difference in CO₂ emissions resulting from the use of high-volatile bituminous coals and lower-rank coals is of the same order of magnitude as reductions expected from near-term combustion efficiency improvements. These results are useful to those interested in current and future CO₂ emissions resulting from coal combustion.     

Relating summer ambient particulate sulfur, sulfur dioxide, and light scattering to gaseous tracer emissions from the MOHAVE Power Project

Project MOHAVE was initiated in 1992 to examine the role of emissions from the 1580 MW coal-fired MOHAVE Power Project (MPP) on haze at the Grand Canyon National Park (GCNP), located about 130 km north-north-east of the power plant. Statistical relationships were analyzed between summertime ambient concentrations of a gaseous perfluorocarbon tracer released from MPP and ambient SO2, particulate sulfur, and light scattering to evaluate whether MPP's emissions could be transported to the GCNP and then impact haze levels there. Spatial analyses indicated that particulate sulfur levels were strongly correlated across the monitoring network, regardless of whether the monitoring stations were upwind or downwind of MPP. This indicates that particulate sulfur levels in this region were influenced by distant regional emission sources. A significant particulate sulfur contribution from a point source such as MPP would result in a non-uniform pattern downwind. There was no suggestion of this in the data. Furthermore, correlations between the MPP tracer and ambient particulate sulfur and light scattering at locations in the park were virtually zero for averaging times ranging from 24 hr to 1 hr. Hour-by-hour MPP tracer levels and light scattering were individually examined, and still no positive correlations were detected. Finally, agreement between tracer and particulate sulfur did not improve as a function of meteorological regime, implying that, even during cloudy monsoon days when more rapid conversion of SO2 to particulate sulfur would be expected, there was no evidence for downwind particulate sulfur impacts. Despite the fact that MPP was a large source of SO2 and tracer, neither time series nor correlation analyses were able to detect any meaningful relationship between MPP's SO2 and tracer emission "signals" to particulate sulfur or light scattering.     

The Smogless Automobile

Demands for high performance and reliability of electrostatic precipitators for collection of fly ash from low sulfur fuels has led to rapid escalation of sizes and uncertainties in sizings of cold-side precipitators. This has led to utilization of the so-called “hot-side” precipitator. The underlying concept of hot-side precipitation is the avoidance of the necessity to operate the precipitator under high resistivity conditions. Data on in-situ measurements of resistivity of low sulfur fuel ash, as well as performance parameters of a number of operating installations, will be reviewed. These data will demonstrate the reduced sensitivity of hot-side precipitator sizing to fuel conditions. Other advantages of hot-side precipitators will be discussed.

Operating experience with hot-side precipitators has focused on structural problems which are peculiar to the larger, higher temperature installations. The nature and solution of these problems will be discussed. General comparative economics of hot-side and cold-side precipitators as they relate to fuel properties will be reviewed.     

The relationship between atmospheric pollutant emissions and fuel qualities of inland vessels in Jiangsu Province,China

Air pollution caused by ship exhaust emission is receiving more and more attention. The physical and chemical properties of fuels, such as sulfur content and PAHs content, potentially had a significant influence on air pollutant emissions from inland vessels. In order to investigate the effects of fuel qualities on atmospheric pollutant emissions systematically, a series of experiments was conducted based on the method of actual ship testing. As a result, SO2, PM and NOx emission rates all increased with the increase of main engine rotating speed under cruise mode, while PM and NOx emission factors were inversely proportional to the main engine rotating speed. Moreover, SO2 emission factor changed little with the increase of the main engine rotating speed. In summary, the fuel-dependent specific emission of SO2 was a direct reflection of the sulfur content in fuel. The PM emission increased with the increase of sulfur content and PAHs content in fuel. However, fuel qualities impacted little on NOx emissions from inland vessels because of NOx formation mechanisms and conditions.

Implications: Ship activity is considered to be the third largest source of air pollution in China. In particular, air pollutants emitted from ships in river ports and waterways have a direct impact on regional air quality and pose threat on the health of local residents owing to high pollutants concentration and poor air diffusion. The study on the relationship between air pollutant emissions and fuel quality of inland vessels can provide foundational data for local authority to formulate reasonable and appropriate policies for reducing atmospheric pollution due to inland vessels.     

粉煤灰烧制陶粒过程中二氧化硫的释放规律与形成机理

研究了粉煤灰烧制陶粒过程中烟气二氧化硫的释放规律,同时对烧结前后粉煤灰与陶粒中不同形态硫含量和硫平衡进行了分析,探讨了烟气中二氧化硫的来源和转化机理.结果表明,烟气中约55％的二氧化硫来源于硫酸盐的还原,其余主要来自有机硫燃烧和亚硫酸盐的分解.烧制每千克陶粒所产生的二氧化硫量约为7.8g.高温烧结过程中粉煤灰球内形成的还原性气氛导致了粉煤灰中硫酸盐向二氧化硫的还原转化.     

燃煤锅炉烟气达标排放下的地面浓度分析

对照国家环保总局最近发布的ＧＷＰＢ３－１９９９《锅炉大气污染物排放标准》,对几种日常最常用的中、小型燃煤锅炉进行了达标排放条件下的地面最大落地浓度预测。结果表明,在烟气达标排放和常规气象春造成的地面ＳＯ２最大落地浓度在国家环境空气质量标准（二级）的２８％以下,远小于规定浓度限值,烟尘的地面影响浓度更可忽略。因此在一般环境影响评价中,只要锅炉烟气做到达标排放,则可不作该两因子的地面浓度预测,由此可大     

The effects of simultaneous large acidic and alkaline airborne pollutants on forest soil

The effects of air pollutants on soil were studied in Scots pine (Pinus sylvestris L.) forests near the boundary of Russia and Estonia. The study area is characterized by large amounts of acidic and basic pollutants, mainly sulphur dioxide (SO(2)) and calcium (Ca). Several variables were measured in different horizons of the podzolic soil polluted by emissions from local sources in areas of several thousands of square kilometers. Alkalinization dominates the processes in the soil, since sulphur is absorbed only in small quantities and Ca is much better absorbed. Ca content in humus horizon may rise even to 100 000 mg kg(-1) and the pH of originally very acidic soil may rise to 8.3. Total aluminum (Al) content was high in the heavily polluted plots, since emissions contain much Al. On the other hand, the exchangeable Al was very low in these alkaline sites. A larger quantity of exchangeable Al occurred farther from the pollutant sources, even though total Al in these plots was low. These plots had acidic soils in which Al is in exchangeable form. Due to the neutralizing effect of acidic and basic pollutants, forest damage in the study area was not as serious as might be supposed. Complicated pollutant situations must be taken into consideration when pollution-caused environmental protection measures are planned. It is not reasonable to reduce only SO(2) emissions, but necessary to lower the basic emissions at the same time.     

Effects of Sorbent Injection on Participate Properties: Part I. Low-Temperature Sorbent Injection

Abstract

This article is the first of a two-part series dealing with the effects of sorbent injection processes on particulate properties. Part I reviews the effects on particulate properties of low-temperature sorbent injection processes (those processes that treat flue gas at temperatures near 300 °F). Part II reviews the effects on particulate properties of high-temperature sorbent injection processes (those processes that involve sorbent injection into the combustion or economizer sections of a boiler). In this article, we review what is currently known about the effects of the low-temperature sorbent injection processes on electrical resistivity, particulate mass loading, particulate size distribution, particulate morphology and cohesivity.

Mixtures of ash and sorbent produced by low-temperature sorbent injection processes are typically less cohesive than most types of fly ash. At temperatures within 30 °F of the water dew point, the combination of low cohesivity and low electrical resistivity of the ash and sorbent mixtures can cause electrical reentrainment in electrostatic precipitators. Deliquescent additives such as calcium chloride cause the water to be retained on the particle surface, thereby increasing cohesivity.

Sorbent injection has been reported to increase the particulate mass loading by a factor of 1.8 to 10, depending upon the reagent ratio and the coal sulfur content. Conventional and in-duct spray drying processes tend to shift the particle size distribution toward larger particles, while dry injection processes tend to shift the particle size distribution toward smaller particles.     

Sulfur dioxide and nitrogen oxides emissions from U.S. pulp and paper mills, 1980-2005

Comprehensive surveys conducted at 5-yr intervals were used to estimate sulfur dioxide (SO,) and nitrogen oxides (NO.) emissions from U.S. pulp and paper mills for 1980, 1985, 1990, 1995, 2000, and 2005. Over the 25-yr period, paper production increased by 50%, whereas total SO, emissions declined by 60% to 340,000 short tons (t) and total NO, emissions decreased approximately 15% to 230,000 t. The downward emission trends resulted from a combination of factors, including reductions in oil and coal use, steadily declining fuel sulfur content, lower pulp and paper production in recent years, increased use of flue gas desulfurization systems on boilers, growing use of combustion modifications and add-on control systems to reduce boiler and gas turbine NO, emissions, and improvements in kraft recovery furnace operations.     

Modelling the spatial distribution of SO2 and NOx emissions in Ireland

The spatial distributions of sulphur dioxide (SO2) and nitrogen oxides (NOx) emissions are essential inputs to models of atmospheric transport and deposition. Information of this type is required for international negotiations on emission reduction through the critical load approach. High-resolution emission maps for the Republic of Ireland have been created using emission totals and a geographical information system, supported by surrogate statistics and landcover information. Data have been subsequently allocated to the EMEP 50 x 50-km grid, used in long-range transport models for the investigation of transboundary air pollution. Approximately two-thirds of SO2 emissions in Ireland emanate from two grid-squares. Over 50% of total SO2 emissions originate from one grid-square in the west of Ireland, where the largest point sources of SO2 are located. Approximately 15% of the total SO2 emissions originate from the grid-square containing Dublin. SO2 emission densities for the remaining areas are very low, < 1 t km-2 year-1 for most grid-squares. NOx emissions show a very similar distribution pattern. However, NOx emissions are more evenly spread over the country, as about 40% of total NOx emissions originate from road transport.