C. David Cooper

Control of Nitrogen Oxide Emissions by Hydrogen Peroxide-Enhanced Gas-Phase Oxidation Of Nitric Oxide

Nitrogen oxides (NOX) and sulfur oxides (SOX) are criteria air pollutants, emitted in large quantities from fossil-fueled electric power plants. Emissions of SOX are currently being reduced significantly in many places by wet scrubbing of the exhaust or flue gases, but most of the NOX in the flue gases is NO, which is so insoluble that it is virtually impossible to scrub. Consequently, NOX control is mostly achieved by using combustion modifications to limit the formation of NOX, or by using chemical reduction techniques to reduce NOX to N2. Low NOX burners are relatively inexpensive but can only achieve about 50% reduction in NOX emissions; selective catalytic reduction (SCR) can achieve high reductions but is very expensive. The removal of NOX in wet scrubbers could be greatly enhanced by gas-phase oxidation of the NO to NO2, HNO2, and HNO3 (the acid gases are much more soluble in water than NO). This oxidation is accomplished by injecting liquid hydrogen peroxide into the flue gas; the H2O2 vaporizes and dissociates into hydroxyl radicals. The active OH radicals then oxidize the NO and NO2. This NOX control technique might prove economically feasible at power plants with existing SO2 scrubbers. The higher chemical costs for H2O2 would be balanced by the investment cost savings, compared with an alternative such as SCR. The oxidation of NOX by using hydrogen peroxide has been demonstrated in a laboratory quartz tube reactor. NO conversions of 97% and 75% were achieved at hydrogen peroxide/NO mole ratios of 2.6 and 1.6, respectively. The reactor conditions (500 °C, a pressure of one atmosphere, and 0.7 seconds residence time) are representative of flue gas conditions for a variety of combustion sources. The oxidized NOX species were removed by caustic water scrubbing.

Estimating the Lower Heating Values of Hazardous and Solid Wastes

A new equation is proposed to predict the lower heating value of hazardous and non-hazardous materials. The equation was developed by a statistical correlation of heating value and composition data for a variety of materials as reported in a number of sources. The model takes into account the carbon, hydrogen, oxygen, chlorine, and sulfur content of the material being combusted.

The Economic Feasibility of Using Hydrogen Peroxide for the Enhanced Oxidation and Removal of Nitrogen Oxides from Coal-Fired Power Plant Flue Gases

Research at the University of Central Florida has determined that the injection of hydrogen peroxide (H2O2) into a simulated flue gas stream effectively oxidizes NO to NO2, and NO2 to HNO2 and HNO3. These oxides of nitrogen are much more soluble in water than NO, and therefore may be more easily scrubbed from the flue gas in a typical wet scrubber. Oxidation and NOx removal efficiencies of greater than 90% were demonstrated in the laboratory. An economic comparison between the H2O2 injection-wet scrubbing method and the selective catalytic reduction (SCR) method of NOx removal was conducted for a design base case and a variety of alternative cases. This study illustrates the trade-off between capital and operating costs for the two alternatives. The single largest factor in determining whether the total cost of the H2O2 injection-wet scrubbing method compares favorably with the total cost of the SCR method is the H2O2:NOx molar ratio. At the H2O2:NOx molar ratio demonstrated in the laboratory (1.92:1.0), the H2O2 injection-wet scrubbing method of NOx removal was shown to be uneconomical. However, the molar ratio in a full-size coal-fired power plant could be lower than that found in the laboratory. Based on all the cost assumptions stated in this article, at a molar ratio of 1.37:1.0, the hydrogen peroxide injection method was calculated to be an economically feasible alternative to the SCR method for NOx control.

Using a traffic simulation model (VISSIM) with an emissions model (MOVES) to predict emissions from vehicles on a limited-access highway

The Intergovernmental Panel on Climate Change (IPCC) estimates that baseline global GHG emissions may increase 25–90% from 2000 to 2030, with carbon dioxide (CO2) emissions growing 40–110% over the same period. On-road vehicles are a major source of CO2 emissions in all the developed countries, and in many of the developing countries in the world. Similarly, several criteria air pollutants are associated with transportation, for example, carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). Therefore, the need to accurately quantify transportation-related emissions from vehicles is essential. The new U.S. Environmental Protection Agency (EPA) mobile source emissions model, MOVES2010a (MOVES), can estimate vehicle emissions on a second-by-second basis, creating the opportunity to combine a microscopic traffic simulation model (such as VISSIM) with MOVES to obtain accurate results. This paper presents an examination of four different approaches to capture the environmental impacts of vehicular operations on a 10-mile stretch of Interstate 4 (I-4), an urban limited-access highway in Orlando, FL. First (at the most basic level), emissions were estimated for the entire 10-mile section “by hand” using one average traffic volume and average speed. Then three advanced levels of detail were studied using VISSIM/MOVES to analyze smaller links: average speeds and volumes (AVG), second-by-second link drive schedules (LDS), and second-by-second operating mode distributions (OPMODE). This paper analyzes how the various approaches affect predicted emissions of CO, NOx, PM2.5, PM10, and CO2. The results demonstrate that obtaining precise and comprehensive operating mode distributions on a second-by-second basis provides more accurate emission estimates. Specifically, emission rates are highly sensitive to stop-and-go traffic and the associated driving cycles of acceleration, deceleration, and idling. Using the AVG or LDS approach may overestimate or underestimate emissions, respectively, compared to an operating mode distribution approach. Implications: Transportation agencies and researchers in the past have estimated emissions using one average speed and volume on a long stretch of roadway. With MOVES, there is an opportunity for higher precision and accuracy. Integrating a microscopic traffic simulation model (such as VISSIM) with MOVES allows one to obtain precise and accurate emissions estimates. The proposed emission rate estimation process also can be extended to gridded emissions for ozone modeling, or to localized air quality dispersion modeling, where temporal and spatial resolution of emissions is essential to predict the concentration of pollutants near roadways.

A Robust Method for Estimating Landfill Methane Emissions

Abstract Because municipal solid waste (MSW) landfills emit significant amounts of methane, a potent greenhouse gas, there is considerable interest in quantifying surficial methane emissions from landfills. The authors present a method to estimate methane emissions, using ambient air volatile organic compound (VOC) measurements taken above the surface of the landfill. Using a hand-held monitor, hundreds of VOC concentrations can be taken easily in a day, and simple meteorological data can be recorded at the same time. The standard Gaussian dispersion equations are inverted and solved by matrix methods to determine the methane emission rates at hundreds of point locations throughout a MSW landfill. These point emission rates are then summed to give the total landfill emission rate. This method is tested on a central Florida MSW landfill using data from 3 different days, taken 6 and 12 months apart. A sensitivity study is conducted, and the emission estimates are most sensitive to the input meteorological parameters of wind speed and stability class. Because of the many measurements that are used, the results are robust. When the emission estimates were used as inputs into a dispersion model, a reasonable scatterplot fit of the individual concentration measurement data resulted.

Enhancement of organic vapor incineration using hydrogen peroxide

Abstract Incineration of dilute mixtures of volatile organic compounds (VOCs) in air was studied in an externally heated quartz tube reactor. Dilute solutions of hydrogen peroxide in water were injected into the flowing air stream at various molar ratios of H2O2 to VOCs. A number of trials were made to determine global destruction kinetics for two VOCs — heptane and isopropanol. Temperatures studied ranged from 637°C to 700°C and residence times varied from 0.26 to 0.94 seconds. It was shown that H2O2 definitely increased the rate of destruction of the primary organics. However, at the residence times and temperatures studied, both organic intermediates and CO persisted. A surprising experimental result was that position of the H2O2 injector relative to the reaction zone made a dramatic difference in the results.

Mobile Source Emission Inventories—Monthly or Annual Average Inputs to MOBILE6?

Abstract In many urban areas, on-road vehicles are the biggest contributing source category of volatile organic compounds (VOCs) and nitrogen oxides (NOx). Based on a recently completed emission inventory study for three counties in central Florida, the major source by far of anthropogenic VOCs and NOx was on-road mobile sources, even though other sources (such as construction equipment, lawn and garden equipment, and various point sources) were also significant. Although there is specific guidance for conducting an ozone-season inventory for mobile sources, there is a lack of detailed guidance as to how to employ the U.S. Environmental Protection Agencys (EPA) latest mobile source emission factor program, MOBILE6, for an annual inventory. Several of the MOBILE6 inputs that significantly influence emission factors (e.g., temperature) can vary widely throughout the year, and the annual average value may not be appropriate. Rather, it may be better to utilize monthly values of these parameters. This paper investigated the sensitivity of the annual emission inventory results to using annual or monthly values of temperature, Reid Vapor Pressure of gasoline, and humidity. The results show that, for a three-county area in central Florida representing metropolitan Orlando, the annual emission inventory based on the sum of individual monthly averages is not significantly different from that calculated using one set of annual average inputs to MOBILE6.

Indirect source impact analysis - carbon monoxide modeling

This paper reviews current methods and models used in estimating the impacts of indirect sources on CO air quality, an important process in rapidly growing areas. The paper gives an overview of the modeling process, reviews how to obtain fleet average emission factors, presents a commonly used set of worst-case meteorology, identifies dispersion models available for predicting local CO concentrations and tells how to predict an 8-hour average CO concentration given a 1-hour prediction. The paper also discusses background CO concentrations and some of the issues involved in choosing reasonable receptor locations. Several problems exist with indirect source impact analysis—in both the technical area and the policy area. Increased effort is needed to correct these problems, especially to quantify the probability of the worst-case meteorology and to define the locations of reasonable receptors.

Accounting for acceleration and deceleration emissions in intersection dispersion modeling using MOVES and CAL3QHC.

Near-road dispersion modeling with CAL3QHC has traditionally been accomplished by assuming vehicles are either idling in queue links or flowing freely in cruise links. With the introduction of the new mobile-source emissions model MOVES, second-by-second activity patterns can be used to produce emission factors (EFs) that vary by vehicular modal activity, that is, acceleration, deceleration, idle, and cruise. By using these EFs in unique modal links in CAL3QHC input files, the predicted concentration of pollutants near roadways can be modeled with greater precision in regard to real-world intersection vehicle behavior. It is noted that this work does not include any comparisons with real-world monitored data, and thus only the precision and not the accuracy of the proposed method is addressed. This work poses the question of how best to include modal links into near-road dispersion modeling. Specifically, it examines dividing acceleration and deceleration segments into multiple sublinks for greater resolution. It is shown that such an approach can produce much higher CO predictions at an intersection (up to 400% higher) compared with the current cruise-and-idle-links modeling approach. A method of dividing links by increments of speed change is suggested. The method relies upon obtaining EFs from standstill to various cruise speeds (or from cruise speed to stopped) and using those results to obtain position-specific acceleration (or deceleration) EFs needed for dispersion modeling inputs. Acceleration EFs (in g/mile) are an order of magnitude larger than cruise EFs; deceleration EFs are smaller than cruise EFs. The number of sublinks used to model one acceleration link makes a difference in the predicted concentrations. MOVES can produce erratic EFs when longer links are broken into smaller sublinks. Implications: MOVES now affords modelers the ability to account for the varying vehicle emissions that occur under various modal operations including acceleration, deceleration, idle, and cruise. These modal activities are dominant near large intersections, and can greatly affect the results of dispersion modeling to predict near-road concentrations of various pollutants. More accurate near-road dispersion modeling techniques are important to engineers and planners for determining which projects likely may cause exceedances of National Ambient Air Quality Standards (NAAQS). The method described herein is also applicable to the modeling of PM2.5 and NOx, which is likely to be of more interest than CO in the near future.

Kinetic modeling of the H2O2 enhanced incineration of heptane and chlorobenzene

The addition of hydrogen peroxide (H2O2) into a stream of heated air containing volatile organic compounds (VOCs), such as heptane and chlorobenzene, has been found to increase the destruction of those VOCs. Detailed kinetic models for the enhanced oxidation of heptane (44 chemical species, 144 reactions), and chlorobenzene (62 species, 212 reactions) were developed. The computer code CHEMKIN was used for the model simulations, and sensitivity analyses were performed using the code SENKIN. Additional thermodynamic data needed for the model were calculated using the group addition methods of Benson, and the computer code THERM. It was concluded that the H2O2 enhancement effect in the oxidation of heptane occurs by the thermal dissociation of the peroxide molecule, providing two OH radicals, followed by hydrogen abstraction of the heptane molecule by an OH radical. In the un-enhanced case the key reaction is the thermal dissociation of the heptane molecule into two radicals. For chlorobenzene the major VOC destruction pathway seems to be the attack of an HO2 radical to generate the phenoxy radical. The HO2 radicals are supplied by the peroxide indirectly, through OH radical attack on other H2O2 molecules, and by other downstream reactions. This is a plausible explanation for the experimental observation of the need for much higher concentrations of H2O2 with chlorobenzene than with heptane, and for the apparent delay in the destruction of chlorobenzene.