Formation of Oxides of Nitrogen in Pulverized Coal Combustion

Nitrogen oxides are a potential atmospheric pollutant. Their formation and decomposition were studied in an experimental pulverized-coal-fired furnace. The concentration of nitrogen oxides (NO_x) was a maximum in the combustion zone and decreased as the combustion gas cooled. At a coal burning rate of 2 Ib/hr and 22% excess air, reduction of nitrogen oxides was obtained by selective secondary-air distribution. With 105% cf the stoichiometric air fed to the coal-combustion zone and 17% additional air fed just beyond the flame front, 62% reduction of NO_x occurred with good combustion efficiency. Lowering the quantity of excess air lowered the NO_x concentration, but at the expense of combustion efficiency. When 22% excess air was fed to the primary combustion zone, NO_x concentration in the effluent was 550 ppm and carbon in the fly ash 2.0%. With 5% excess air, the NO_x concentration fell to 210 ppm and carbon in the fly ash rose to 13.8%. With stoichiometric combustion the NO_x was 105 ppm a reduction of 81 %, and the carbon was 42.3%. Recirculation of combustion gas was not an effective means of lowering NO_x formation.     

Selective Reduction of Nitrogen Oxides In Combustion Flue Gases

The body of Information presented in this paper is directed to those Individuals concerned with the removal of NO_x in combustion flue gases. A catalytic process for the selective reduction of nitrogen oxides by ammonia has been investigated. Efforts were made toward the development of catalysts resistant to SO_x poisoning. Nitrogen oxides were reduced over various metal oxide catalysts in the presence or absence of SO_x(SO₂ and SO₃). Catalysts consisting of oxides of base metals (for example, Fe₂O₃) were easily poisoned by SO₃, forming sulfates of the base metals. A series of catalysts which are not susceptible to the SO_x poisoning has been developed. The catalysts possess a high activity and selectivity over a wide range of temperatures, 250—450°C. The catalysts were tested in a pilot plant which treated a flue gas containing 110-150 ppm NO_x, 660-750 ppm SO₂, and 40-90 ppm SO₃. The pilot plant was operated at 350°C and at a space velocity of 10,000 h^-1. The removal of nitrogen oxides was more than 90% for several months.

A mechanism of the NO-NH₃ reaction has also been investigated. It is found that NO reacts with NH₃ at a 1:1 mole ratio in the presence of oxygen and the reaction is completely inhibited by the absence of oxygen. The experimental data show that the NO-NH₃ reaction in the presence of oxygen is represented byNO + NH₃ + 1/4 O₂ = N₂ + 3/2 H₂O.     

Determination of Oxides of Nitrogen in Combustion Effluents with a Nitrate Ion Selective Electrode

The nitrate ion selective electrode was investigated as an alternative approach to the present colorimetric determination of nitrate resulting from oxidative absorption of nitrogen oxides from combustion effluents. The electrode offers advantages of speed and relatively simple experimental procedure. Replicate measurements of 10^?4–10^?2M nitric acid solutions using bracketing standards show that the electrode approach is capable of good precision (coefficient of variation = ±4%). Comparison of a method utilizing the nitrate electrode with the more laborious phenol disulfonic acid method for the measurement of nitrogen oxides in both oil and gas fired combustion effluents showed agreement within 4% of the mean even in the presence of high levels of SO₂. The correlation coefficient found for PDS vs nitrate electrode is 0.987.     

Studies on a New Method of Simultaneously Removing Sulfur Dioxide and Oxides of Nitrogen from Combustion Gases

Simultaneous reduction of SO₂ and NO by catalyzed reaction with carbon monoxide at space rates approaching 10⁴ vol/vol/hr has been shown. The reaction of sulfur dioxide with carbon monoxide results in the formation of carbon dioxide and elemental sulfur. Nitric oxide reacts with carbon monoxide to form carbon dioxide and molecular nitrogen. Metals supported on alumina appear to be the preferred catalysts. Among the effective metals are copper, silver, and palladium. A side reaction of carbon monoxide with elemental sulfur to form carbonyl sulfide requires that the initial amount of carbon monoxide be stoichio-metric for the amount of sulfur dioxide plus nitric oxide present. A furnace employing this method would have to be operated at low excess air, near stoichiometric fuel/air, or possibly slightly on the rich side.     

Determination of Nitrogen Oxides in Auto Exhaust

A new procedure for determining nitrogen oxides in automobile exhaust has been developed. The new procedure was included in a Bureau of Mines comparative study that aimed at evaluating various widely used methods for determining NO_x in auto exhaust. The methods included in the evaluation study follow: (1) Static oxidation in tank (ST method). The method involves oxidation of NO in residence with O₂ in a stainless steel tank. (2) Bureau of Mines method (BM method). The method involves application of the ST procedure in exhaust samples from which the hydrocarbons have been removed by combustion over catalyst. (3) Chevron Research method (CR method), as described in the literature. (4) Phenoldisulfonic acid method (PDS method), as described in the literature. The principal objective of this study was to generate experimental evidence which would lead to defining an optimum procedure for converting NO, present in exhaust gas, into NO₂; this conversion is desired so that the total of NO + NO₂ can be determined quantitatively in the form of NO₂. In pursuing this objective, the procedures prescribed by the foregoing methods were comparatively tested. The results indicated that all four methods are subject to error, the extent of which depends on the conditions employed. The BM method was superior from the standpoint of accuracy because it was less affected by interferences due to hydrocarbon-NO₂ reactions.     

测量试样中的氮氧化物含量不确定度评定

以实际监测数据为例，详细描述测量试样中的NOx含量不确定度评定方法，包括不确定度源的分析，A类标准不确定度评定、B类标准不确定度评定、合成标准不确定度和扩展不确定度等，对不确定度的分量作了详尽的分析和计算。     

Catalytic Reduction of Nitrogen Oxides in Automobile Exhaust

The catalytic reduction of oxides of nitrogen from leaded automobile exhaust has been demonstrated to be technically feasible. These studies made with copper-containing catalysts are based upon the reducing nature of exhaust caused by the carbon monoxide present. The reaction involves 2 CO + 2 NO → + N₂ + CO₂ + 178.5 Kcal.     

Considerations in Setting Standards for Oxides of Nitrogen

Since 1959 the California Department of Public Health has held responsibility for setting standards for ambient air quality and for motor vehicle emissions. The need for standards for oxides of nitrogen involves consideration both of direct effects and effects resulting from participation in photochemical smog reactions. This paper discusses the various effects of concern and describes the department’s program for establishing air quality standards which will become the basis for vehicle emission standards and serve as guides for control of other sources of oxides of nitrogen.     

A New Catalytic Reactor for Nitrogen Oxides Removal

The body of information presented in this paper is directed to those individuals concerned with the catalytic NO_x removal reactor for a dirty (containing dust) flue gas. In the case of treating a dirty flue gas, the concentration of dust is the most important factor. While the dirty gas passes through the catalytic reactor, dust particles deposit and plug up the catalyst causing the reactor pressure loss to rise. As a result, the NO_x reduction efficiency decreases more and more, and continuous operation becomes impossible. A new type of NO_x removal reactor for dirty flue gas, the intermittent moving bed reactor, has been developed. The following characteristics have been evaluated: (1) method of calculating reactor pressure loss caused by dust particles, (2) static pressure distribution across the catalyst bed in the reactor, (3) method of evaluating uniform movement of catalyst and (4) reentrainment pattern of dust by catalyst movement. After carrying out various successful pilot plant tests, the information needed for construction and operation of a commercial plant has been developed.     

Chemical and Biological Characterization of Products of Incomplete Combustion from the Simulated Field Burning of Agricultural Plastic

Chemical and biological analyses were performed to characterize products of Incomplete combustion emitted during the simulated open field burning of agricultural plastic. A small utility shed equipped with an air delivery system was used to simulate pile burning and forced-air-curtain incineration of a nonhalogenated agricultural plastic that reportedly consisted of polyethylene and carbon black. Emissions were analyzed for combustion gases; volatile, semi-volatile, and particulate organics; and toxic and mutagenlc properties. Emission samples, as well as samples of the used (possibly pesticide-contaminated) plastic, were analyzed for the presence of several pesticides to which the plastic may have been exposed. Although a variety of alkanes, alkenes, and aromatic and polycyclic aromatic hydrocarbon (PAH) compounds were identified in the volatile, seml-volatlle, and particulate fractions of these emissions, a substantial fraction of higher molecular weight organic material was not identified. No pesticides were Identified in either combustion emission samples or dlchloromethane washes of the used plastic. When mutagenlcity was evaluated by exposing Salmonella bacteria (Ames assay) to whole vapor and vapor/partlculate emissions, no toxic or mutagenlc effects were observed. However, organic extracts of the particulate samples were moderately mutagenlc. This mutagenlcity compares approximately to that measured from residential wood heating on a revertant per unit heat release basis. Compared to pile burning, forced air slightly decreased the time necessary to burn a charge of plastic. There was not a substantial difference, however, in the variety or concentrations of organic compounds Identified In samples from these two burn conditions. This study highlights the benefits of a combined chemical/biological approach to the characterization of complex, multi-component combustion emissions. These results may not reflect those of other types of plastic that may be used for agricultural purposes, especially those containing halogens.     

Cleaning of Stack Gases Containing High Concentrations of Nitrogen Oxides

Multistage gas absorption of 1–50% nitric oxide, nitrogen dioxide, and nitrogen tetraoxide from air with water or caustic solutions can produce colorless stack discharges. The rate at which NO is oxidized to No₂ in the gas phase and the solubility rate of No₂ in water or solution are highly concentration dependent so that reductions of stack gas concentrations of nitrogen oxides below approximately 200 ppm appear to be impractical. High efficiency absorption combined with elevated discharge of the cleaned, colorless gases is an acceptable method of air pollution control for many troublesome operations. Experiences in the fields of rocketry and nuclear energy are cited. Engineering modifications of metal pickling operations have been found especially helpful in producing effective control at an acceptable cost.     

Environmental Appraisal: And Oxides of Nitrogen Oxidants,Hydrocarbons

The relationships between criteria, standards, and control of air pollutants involve complex multidisciplinary interactions. Their over-all impact on the public health and welfare is directly related to the confidence level held by members of government, industry, and universities in the validity of the data upon which these criteria are based. The Environmental Appraisal section of the preliminary draft of the Air Quality Criteria Document “Photochemical Oxidant” prepared by the State of California, Department of Public Health, is reviewed. In general, it is a thoughtful and extensive effort to present the current status of information concerning the physical and chemical aspects of photochemical oxidant. Suggestions as to how it might be extended, revised, or updated are presented along with a brief discussion of two new research areas of possible interest, singlet molecular oxygen as a possible environmental oxidant, and the photochemistry of mixed lead halides in the atmosphere.     

Characterization of Products from Fluidized-Bed Combustion of Coal

ABSTRACT

The technology of fluidized-bed combustion (FBC) of coal generates byproducts that have a series of unique characteristics and potential uses in technological practice. In this study, the products of fluidized-bed combustion (FBC-P) of coal derived from Moravian heat stations, a.s. Zlin, Cinergy Global Resources, Czech Republic, were characterized. Particular attention was paid to determining the chemical composition of FBC-P, the content of polycyclic aromatic hydrocarbons (PAHs) and toxic metals in the water leachates of these FBC-P, the content of unburned carbon, the capability of FBC-P to solidify with water and form a solid matrix, and the method for discovering optimum mixing water content for FBC-P solidification. The results suggest that one of the qualitatively more important means of utilizing FBC-P could be their application during solidification/stabilization (S/S) of wastes, particularly wastewa-ter treatment sludges.     

Technology Innovations and Experience Curves for Nitrogen Oxides Control Technologies

Abstract

This paper reviews the regulatory history for nitrogen oxides (NO_x) pollutant emissions from stationary sources, primarily in coal-fired power plants. Nitrogen dioxide (NO₂) is one of the six criteria pollutants regulated by the 1970 Clean Air Act where National Ambient Air Quality Standards were established to protect public health and welfare. We use patent data to show that in the cases of Japan, Germany, and the United States, innovations in NO_x control technologies did not occur until stringent government regulations were in place, thus “forcing” innovation. We also demonstrate that reductions in the capital and operation and maintenance (O&M) costs of new generations of high-efficiency NO_x control technologies, selective catalytic reduction (SCR), are consistently associated with the increasing adoption of the control technology: the so-called learning-by-doing phenomena. The results show that as cumulative world coal-fired SCR capacity doubles, capital costs decline to ~86% and O&M costs to 58% of their original values. The observed changes in SCR technology reflect the impact of technological advance as well as other factors, such as market competition and economies of scale.     

Nitrogen Oxides Emission Control Options for Coal-Fired Electric Utility Boilers

Abstract

Recent regulations have required reductions in emissions of nitrogen oxides (NO_x) from electric utility boilers. To comply with these regulatory requirements, it is increasingly important to implement state-of-the-art NO_x control technologies on coal-fired utility boilers. This paper reviews NO_x control options for these boilers. It discusses the established commercial primary and secondary control technologies and examines what is being done to use them more effectively. Furthermore, the paper discusses recent developments in NO_x controls. The popular primary control technologies in use in the United States are low-NO_x burners and overfire air. Data reflect that average NO_x reductions for specific primary controls have ranged from 35% to 63% from 1995 emissions levels. The secondary NO_x control technologies applied on U.S. coal-fired utility boilers include reburning, selective noncatalytic reduction (SNCR), and selective catalytic reduction (SCR). Thirty-six U.S. coal-fired utility boilers have installed SNCR, and reported NO_x reductions achieved at these applications ranged from 15% to 66%. Recently, SCR has been installed at >150 U.S. coal-fired utility boilers. Data on the performance of 20 SCR systems operating in the United States with low-NO_x emissions reflect that in 2003, these units achieved NO_x emission rates between 0.04 and 0.07 lb/10⁶ Btu.     

Global Emissions of Nitrogen and Sulfur Oxides from 1860 to 1980

Statistical models have been developed that relate the rate of emissions of a pollutant to the rate of fuel consumption. These relations may be used to estimate emissions in other regions, or at other times, if fuel consumption data are available. This approach has been used to estimate global emissions of nitrogen and sulfur oxides in fossil fuel combustion at ten year intervals from 1860 to 1980. Emissions from each of the populated continents, i.e., North America, South America, Asia, Europe, Africa and Oceania from 1930 to 1980 are also presented. When averaged globally over the 1860 to 1980 period, sulfur emissions increased at the rate of 2.9 percent per year and the nitrogen emissions at the rate of 3.4 percent per year. The ratio of global sulfur emissions to nitrogen emissions has declined steadily; it was nearly 5 in the 19th century and became 3 by 1980. After the second world war, the most rapid increases in emissions have been registered in Asia, South America, and Africa.     

Emissions of Trace Products of Incomplete Combustion from a Pilot-Scale Incinerator Secondary Combustion Chamber

Abstract

Experiments were performed on a 73 kW rotary kiln incinerator simulator equipped with a 73 kW secondary combustion chamber (SCC) to examine emissions of products of incomplete combustion (PICs) resulting from incineration of carbon tetrachloride (CC14) and dichloromethane (CH2C12). Species were measured using an on-line gas chromatograph (GC) system capable of measuring concentrations of eight species of volatile organic compounds (VOCs) in a near-realtime fashion. Samples were taken at several points within the SCC, to generate species profiles with respect to system residence time. For the experiments, the afterburner on the SCC was operated at conditions ranging from fuel-rich to fuellean, while the kiln was operated at a constant set of conditions. Results indicate that combustion of CH2C12 produces higher levels of measured PICs than combustion of CC14, particularly 1, 2 dichlorobenzene, and to a lesser extent, monochlorobenzene. Benzene emissions were predominantly affected by the afterburner air/fuel ratio regardless of whether or not a surrogate waste was being fed.