Controlling NOx Emissions From Steam Generators

The information presented is directed to those individuals concerned with reducing nitrogen oxides (NO _x ) emissions from gas, oil, or coal fired utility steam generators. First, this paper presents NO _x emission data obtained in the testing of tangentially fired utility boilers; second, it relates these data to the general body of information developed by other investigators in the areas of theoretical analysis and bench scale and full scale testing; and finally, it discusses current design practice in relation to NO _x emission control and the continuing R&D effort required to assure acceptable control technology.     

Identification and Control of NOx Emissions Using Neural Networks

ABSTRACT

We investigate the application of two classes of artificial neural networks for the identification and control of discrete-time nonlinear dynamical systems. A fully connected recurrent network is used for process identification, and a multilayer feedforward network is used for process control. The two neural networks are arranged in series for closed-loop control of oxides of nitrogen (NO_x) emissions of a simplified representation of a dynamical system. Plant data from one of Commonwealth Edison's coal-fired power plants are used for testing the approach, with initial results indicating that the method is feasible. However, further work is required to determine whether the method remains feasible as the number of state variables and control variables are increased.     

Impact of NOx Emissions Released from a Gas Turbine-Based Power Plant on the Ambient Air Quality

The number of gas turbine- (GT-) based power plants is rapidly increasing to meet the world’s power demands. Until a few years ago, fossil fuel, and specifically fuel oil, was considered the major energy source for gas turbine operation. Due to the high amount of pollution that fuel oil generates, natural gas has become a popular source of energy due to its lower emissions compared to fuel oil. As a result, many GTs have switched to natural gas as an alternative to fuel oil. However, pollutants expelled from GT-based power plants operating on natural gas impact surrounding air quality. The objective of this study was to examine the dispersion of nitrogen oxides (NO_x) emitted from a GT-based power plant located in the Sultanate of Oman. Supported by CALPUFF dispersion modeling software, six scenarios were investigated in this study. The first four scenarios considered a case where the GT-based power plant was operating on natural gas during winter and summer and for open and combined cycle modes. The remaining two scenarios considered, for both open and combined cycle modes, the case where the GT-based power plant was operating on fuel oil. Whether run by natural gas or fuel oil, CALPUFF simulation results for both seasons showed that NO_x concentrations were higher when GTs were used in the combined cycle mode. The concentrations were still lower than the allowable concentrations set by the United States Environmental Protection Agency (U.S. EPA) standards. In contrast, for the case where the power plant operated on fuel oil, the NO_x one-hour average simulated results exceeded the allowable limits only when the combined cycle mode was activated.     

Quantification of Hourly Variability in NOx Emissions for Baseload Coal-Fired Power Plants

Abstract

The objectives of this paper are to (1) quantify variability in hourly utility oxides of nitrogen (NO_x) emission factors, activity factors, and total emissions; (2) investigate the autocorrelation structure and evaluate cyclic effects at short and long scales of the time series of total hourly emissions; (3) compare emissions for the ozone (O₃) season versus the entire year to identify seasonal differences, if any; and (4) evaluate interannual variability. Continuous emissions monitoring data were analyzed for 1995 and 1998 for 32 units from nine baseload power plants in the Charlotte, NC, airshed. Unit emissions have a strong 24-hr cycle attributable primarily to the capacity factor. Typical ranges of the coefficient of variation for emissions at a given hour of the day were from 0.2 to 0.45. Little difference was found when comparing weekend emissions with the entire week or when comparing the O₃ season with the entire year. There were substantial differences in the mean and standard deviation of emissions when comparing 1995 and 1998 data, indicative of the effect of retrofits of control technology during the intervening time. The wide range of variability and its autocorrelation should be accounted for when developing probabilistic utility emission inventories for analysis of near-term future episodes.     

Electricity from Fossil Fuels without CO2 Emissions: Assessing the Costs of Carbon Dioxide Capture and Sequestration in U.S. Electricity Markets

ABSTRACT

The decoupling of fossil-fueled electricity production from atmospheric CO₂ emissions via CO₂ capture and sequestration (CCS) is increasingly regarded as an important means of mitigating climate change at a reasonable cost. Engineering analyses of CO₂ mitigation typically compare the cost of electricity for a base generation technology to that for a similar plant with CO₂ capture and then compute the carbon emissions mitigated per unit of cost. It can be hard to interpret mitigation cost estimates from this plant-level approach when a consistent base technology cannot be identified. In addition, neither engineering analyses nor general equilibrium models can capture the economics of plant dispatch. A realistic assessment of the costs of carbon sequestration as an emissions abatement strategy in the electric sector therefore requires a systems-level analysis. We discuss various frameworks for computing mitigation costs and introduce a simplified model of electric sector planning. Results from a “bottom-up” engineering-economic analysis for a representative U.S. North American Electric Reliability Council (NERC) region illustrate how the penetration of CCS technologies and the dispatch of generating units vary with the price of carbon emissions and thereby determine the relationship between mitigation cost and emissions reduction.     

秸秆发电的现状和展望

介绍了秸秆发电的重要意义以及在国内外的发展现状，分析了秸秆发电存在的问题，并提出相应的解决办法，最后展望了秸秆发电在国内的市场前景。     

NOx Removal with Combined Selective Catalytic Reduction and Selective Noncatalytic Reduction: Pilot-Scale Test Results

Pilot-scale tests were conducted to develop a combined nitrogen oxide (NO_x) reduction technology using both selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR). A commercially available vanadium- and titanium-based composite honeycomb catalyst and enhanced urea (NH₂CONH₂) were used with a natural-gas-fired furnace at a NO_x concentration of 110 ppm. Changes in SNCR chemical injection temperature and stoichiometry led to varying levels of post-furnace ammonia (NH₃), which acts as the reductant feed to the downstream SCR catalyst. The urea-based chemical could routinely achieve SNCR plus SCR total NO_x reductions of 85 percent with less than 3 ppm NH₃ slip at reductant/NO_x stoichiometries ranging from about 1.5 to 2.5 and SCR space velocities of 18,000 to 32,000 h^?1. This pilot-scale research has shown that SNCR and SCR can be integrated to achieve high NO_x removal. SNCR provides high temperature reduction of NO_x followed by further removal of NO_x and minimization of NH₃ slip by a significantly downsized (high-space velocity) SCR.     

NOx Reduction in a Gas Fired Utility Boiler by Combustion Modifications

Data on the effect of several combustion modifications on the formation of nitrogen oxides and on boiler efficiency were acquired and analyzed for a 110 MW gas fired utility boiler. The results from the study showed that decreasing the oxygen in the flue gas from 2.2% to 0.6% reduced the NO_x formation by 33% and also gave better boiler efficiencies. Flue gas recirculation through the bottom of the firebox was found to be ineffective. Staged combustion was found to reduce the NO_x emissions by as much as 55 % while decreasing the efficiency by about 5%. Adjustment of the burner air registers reduced the NO_x formation by about 20 ppm. The lowest NO_x emissions of 42 ppm (at about 3% O₂) in the stack was obtained for air only to one top burner and 0.5% oxygen in the flue gas.     

Removal of NOx from Flue Gas with Iron Filings Reduction Following Complex Absorption in Ferrous Chelates Aqueous Solutions

Abstract

A novel process for removal of nitrogen oxides (NO_x) from flue gases with iron filings reduction following complex absorption in iron-ethylenediaminetetraacetic acid aqueous solution is proposed. The reaction mechanism involved in the process is discussed briefly. The parameters influencing the process, including the concentration of ferrous chelates, initial pH, amount of iron filings, temperature, flow rate of the flue gas, and inlet nitric oxide concentration and oxygen content of the flue gas, are researched in detail. The optimal NO_x removal conditions are established. The regeneration and circular utilization of the absorption solution also is studied.     

Emission of NOx from urine-treated pasture

Emission of NO(x) from urine-treated pasture was determined using a system of enclosures coupled to a chemiluminescence NO(x) analyser. Rates of emission ranged from 0 to 190 microg NO(x) - Nm(-2)h(-1), with a mean of 43 microg N m(-2) h(-1). The lowest rates were associated with periods of heavy or persistent rain. On average, NO comprised 68% of the NO(x) produced. Emissions of NO(x) were apparently associated with the nitrification of ammonium N derived from hydrolysis of organic N constituents in the urine applied. Emissions from untreated pasture occurred at a mean rate of 1.7 microg NO(x) -N m(-2) h(-1). NO(x) comprised only a small proportion (<0.1%) of the emission of other nitrogenous gases (NH(3), N(2) and N(2)O) following application of urine. The mean rate of NO(x) emission suggested a total release to the atmosphere of 2.3 x 10(-8) g N year(-1) from urine returned to pasture in the UK. This loss is not significant in agronomic terms and is equivalent to only 0.04% of the estimated anthropogenic emissions for the UK.     

Reduction of Open Hearth Furnace Particulate Emissions via a Parametric Study

A linear relationship has been found between oxygen usage and particulate mass emission rate for a basic open hearth furnace. Particulate emissions were found to pass through a minimum at 50% hot metal addition to the furnace which also corresponded to minimum oxygen consumption. Number 2 dealer scrap and hot metal addition were found to have a secondary effect on the particulate emissions. Variation of number 2 dealer scrap from 0 to 15% of the charge and hot metal from 10 to 70% resulted in a maximum 44% increase in particulate emissions. Aerodynamic particle size distributions for all heats and within heats were relatively invariant with an average mass median diameter of 1.4µ     

A New Alternative Fuel for Reduction of Polycyclic Aromatic Hydrocarbon and Particulate Matter Emissions from Diesel Engines

Abstract

This study investigated the emissions of polycyclic aromatic hydrocarbons (PAHs), carcinogenic potential of PAH and particulate matter (PM), brake-specific fuel consumption (BSFC), and power from diesel engines under transient cycle testing of six test fuels: premium diesel fuel (PDF), B100 (100% palm biodiesel), B20 (20% palm biodiesel + 80% PDF), BP9505 (95% paraffinic fuel + 5% palm biodiesel), BP8020 (80% paraffinic fuel + 20% palm biodiesel), and BP100 (100% paraffinic fuel; Table 1). Experimental results indicated that B100, BP9505, BP8020, and BP100 were much safer when stored than PDF. However, we must use additives so that B100 and BP100 will not gel as quickly in a cold zone. Using B100, BP9505, and BP8020 instead of PDF reduced PM, THC, and CO emissions dramatically but increased CO₂ slightly because of more complete combustion. The CO₂-increased fraction of BP9505 was the lowest among test blends. Furthermore, using B100, B20, BP9505, and BP8020 as alternative fuels reduced total PAHs and total benzo[a]pyrene equivalent concentration (total BaP_eq) emissions significantly. BP9505 had the lowest decreased fractions of power and torque and increased fraction of BSFC. These experimental results implied that BP9505 is feasible for traveling diesel vehicles. Moreover, paraffinic fuel will likely be a new alternative fuel in the future. Using BP9505 instead of PDF decreased PM (22.8%), THC (13.4%), CO (25.3%), total PAHs (88.9%), and total BaP_eq (88.1%) emissions significantly.     

A Strategy for Reduction of Particulate Emissions in the Boston Area

Initial implementation plans provided for particulate reduction largely through the imposition of emission limitations on industrial processes, large steam generators, and solid waste disposal, requiring, in turn, application of control equipment for compliance. In many urban areas, this approach is not adequate to achieve the secondary air quality standards so that a more general strategy must be employed. Such strategy may include restrictions on fuel burning, combustion equipment, maintenance programs, utility steam distribution, etc. The potential abatement achievable through such strategies is described using Boston as a case study. Cost and technical factors associated with each strategy are discussed.     

Workshop on the Intercomparison of Methodologies for Soil NOx Emissions: Summary of Discussion and Research Recommendations

A workshop on the intercomparison of methodologies for soil NO_x emissions was held on March 14-15, 1994 at North Carolina State University (NCSU) in Raleigh, North Carolina, in preparation for a field experiment tentatively scheduled for May-June, 1995 involving measurement of rural site NO_x emissions. The workshop was sponsored jointly by the U.S. Environmental Protection Agency (EPA) and NCSU. Representatives from several agencies will participate in the experiment, including the EPA, NASA, NOAA, DOE, NCAR, Atmospheric Science from the University of Maryland, and Atmospheric Sciences and Soil Sciences from NCSU. Approximately 50 workshop attendees, which included national experts on all aspects of flux measurement technologies, met for a day and a half to discuss techniques for measuring soil NO_x (= NO + NO₂) emissions and to suggest how to best incorporate these techniques into a field experiment to compare NO_x measuring methodologies. The need for more knowledge in the area of soil NO_x emissions is related to the uncertainty of the relationship between rural NO_x emissions and the production of tropospheric ozone. In particular, the role of nitrogen-based fertilizers spread over rural agricultural areas in the production or emission of NO_x is not well documented. To determine the best way to document and model these relationships, a full experimental comparison of NO_x emission measurement techniques over a rural agricultural area is needed. Thus, it was recommended that a study of the intercomparison of methodologies for soil NO_x emissions (both intensive field experiments and analysis) should be undertaken. The primary goal of this study will be to relate chamber techniques to micrometeorological flux estimates of NO_x. The study should include (i) an intensive four-to-six-week experiment for the intercomparison of methodologies for soil NO_x emissions, (ii) and soil and air quality characterization of the experimental site.     

Treatment of Halogenated Organic Vent Streams for the Reduction of Air Emissions

Abstract

This work presents a three-stage treatment system to process halogenated organic vent streams for compliance with the Hazardous Organic NESHAP (HON) Rule. The three stages are incineration, energy recovery, and wet scrubbing. In particular, this work concentrates on the design of the scrubber, which the HON Rule states must remove at least 99% of any halogens or hydrogen halides generated during the combustion step. Computerized process simulation was found to be ineffective in designing a scrubber for this application, so laboratory data on the partial pressure of the hydrogen halide species over aqueous solutions was employed. The number of overall gas transfer units required for 99% removal was found to be slightly less than 5, and the overall gas transfer unit height was found to be approximately 0.5 m.     

The Kinetics of Formaldehyde Oxidation and Emissions Reduction in Methanol Fueled Vehicles

Oxidation of formaldehyde over supported platinum catalyst produced CO₂ as a major product and CO as a minor product under a wide range of Inlet concentrations and reaction temperatures. The temporal variation of CO yield proceeded through a maximum suggesting that it was produced as an intermediate in the pathway leading to CO₂. CO selectivity (S _co = y _co/x _HCHO) was maximized by operating at oxygen concentration below the stoichiometric point and at high reaction temperatures. A mechanism for formaldehyde oxidation is proposed which involves adsorption of formaldehyde followed by catalytic decomposition to CO and H₂ and oxidation of the surface species; the rate limiting step apparently shifts from the decomposition at high oxygen concentration to the oxidation of surface species at low concentration. The rate expression was obtained from the postulated mechanism and found to be consistent with the experimental results. The maximum for the yield of CO provided a second method by which to confirm the postulated rate expression.     

Plasma versus Thermal Effects in Flue Gas NOx Reduction Using Ammonia Radical Injection

Abstract

A plasma-assisted ammonia injection technique was previously demonstrated as having the potential to remove NO_x from combustion flue gases at SCR-comparable levels without the use of catalysts. However, these demonstrations did not prove the advantage of plasma assistance because they did not explicitly account for enhanced radical production by bulk thermal heating. An experiment using hot ammonia injection was performed to separate this thermal effect from the effect of radical production via interaction with a plasma. Under excess air conditions, results show that a thermal effect does provide improved NO_x reduction, but not to the level achieved with the use of a plasma source. However, heating the injection gases provides only a minor improvement in NO_x reduction at NH₃/NO_x ratios and temperatures typical of commercial cold SNCR applications. The plasma effect in ammonia radical injection was also found to be significant, accounting for an additional 15% to 35% of absolute NO_x reduction beyond any thermal benefit at typical excess air conditions. The ammonia radical injection technique continues to show promise as an effective NO_x reduction alternative.     

Emissions from an automobile fire

The emissions from automobile fires have been investigated. The main gas phase components were analysed in small-scale tests with representative material from an automobile. A more detailed investigation of full-scale simulated automobile fires was also conducted, including the characterisation of gas phase components, particulates and run-off water from extinguishing activities. Three separate full scale fire tests have been characterised: a fire ignited and developed in the engine compartment; a fire ignited inside the coupé, that was extinguished in the early stages; and a similar fire ignited inside the coupé that was allowed to spread until the entire vehicle was involved in the fire. The quantitative analysis of the smoke gases from the full-scale fires showed that emissions with a potentially negative impact on the environment, or chronic toxic effect on humans, were produced in significant quantities. These emissions included HCl, SO2, VOCs (e.g. benzene), PAHs, and PCDDs/PCDFs. Analysis of run-off water indicated that it was severely contaminated, containing elevated levels of both organic compounds and metals. Comparison with data from other vehicle fires found in the literature shows that contamination by lead, copper, zinc, and antimony appears to be significant in water run-off from these types of fires.     

Reducing Emissions from Refuse Disposal

Estimates indicate that approximately 2.6% of the total atmospheric pollution in this country may originate as a result of refuse disposal. Although this may appear to be a comparatively low figure, it is important to note that refuse disposal is a universal problem: wherever we go, be the area urban, or rural, waste must be disposed of and in most cases the methods of disposal produce air pollution. Tabulated data indicates that the per capita rate of production has been increasing annually. In the city of Hartford, the quantity of refuse that is being burned in the municipal incinerator has been increasing at a rate of 5%/year. A comparison of the air pollutants emitted from open burning at a refuse disposal area, backyard burning and incineration of refuse in a municipal multiple chamber incinerator indicates that the quantity of pollutants emitted from the latter source is much less than those emitted from the other sources. The effect of having legislation with, enforcement authority and a program for regular inspections, has resulted in marked improvements of refuse disposal operations in Connecticut since June, 1966. Most of the burning still being done at refuse disposal areas is limited to only brush and demolition material. A multi-purpose incinerator is presently under construction in the city of Stamford, Conn. It is planned to demonstrate that not only bulky wastes and auto bodies, but also liquid wastes can be burned in the same unit without creating any adverse effect on the environment. This incinerator will be provided with an electrostatic precipitator for removing particulate emissions.

New methods of refuse disposal which are being tried are briefly described in this paper. All these methods tend to reduce or eliminate air pollution along with eliminating the health hazards normally related with open face dump type of operations.

The continual technological progress and improvements in methods of manufacture, packaging, and marketing of consumer products along with the economic, population, and industrial growth of the nation has resulted in an ever-mounting increase and change in the characteristics of the mass of material being discarded by the purchaser. In May 1967, a Three-State Conference on Air Resource Management was held at the City College of the City University of New York. This conference consisted of a number of panels or committees which discussed specialized areas of the problem of air pollution and its control. A portion of the introductory remarks from the panel report of the Solid Waste Committee1 is as follows:     

Atmospheric Emissions from Oxidation Ponds

The electrodes in industrial precipitators collect many tons of dust daily, and the efficient transfer of this dust burden to the hoppers is a challenging problem in mechanical engineering. Many varieties of devices have been tried; hammers, vibrators, scrapers, water flushing, gas blasting, etc. Impact devices for this purpose are usually called “rappers.” Laboratory experiments described in this paper show that normal (perpendicular) rapping is more effective than shear rapping; that thick dust layers are more easily removed by rapping than thin ones; that rapping becomes easier with increasing temperature, within limits; and that the electrostatic forces acting upon the precipitated dust layer play an important role. Quantitative data are shown graphically. The relation of these results to previous studies by other investigators is discussed.