Tim C. Keener

Potential Flue Gas Impurities in Carbon Dioxide Streams Separated from Coal-Fired Power Plants

Abstract For geological sequestration of carbon dioxide (CO2) separated from pulverized coal combustion flue gas, it is necessary to adequately evaluate the potential impacts of flue gas impurities on groundwater aquifers in the case of the CO2 leakage from its storage sites. This study estimated the flue gas impurities to be included in the CO2 stream separated from a CO2 control unit for a different combination of air pollution control devices and different flue gas compositions. Specifically, the levels of acid gases and mercury vapor were estimated for the monoethanolamine (MEA)-based absorption process on the basis of published performance parameters of existing systems. Among the flue gas constituents considered, sulfur dioxide (SO2) is known to have the most adverse impact on MEA absorption. When a flue gas contains 3000 parts per million by volume (ppmv) SO2 and a wet flue gas desulfurization system achieves its 95% removal, approximately 2400 parts per million by weight (ppmw) SO2 could be included in the separated CO2 stream. In addition, the estimated concentration level was reduced to as low as 135 ppmw for the SO2 of less than 10 ppmv in the flue gas entering the MEA unit. Furthermore, heat-stable salt formation could further reduce the SO2 concentration below 40 ppmw in the separated CO2 stream. In this study, it is realized that the formation rates of heat-stable salts in MEA solution are not readily available in the literature and are critical to estimating the levels and compositions of flue gas impurities in sequestered CO2 streams. In addition to SO2, mercury, and other impurities in separated CO2 streams could vary depending on pollutant removal at the power plants and impose potential impacts on groundwater. Such a variation and related process control in the upstream management of carbon separation have implications for groundwater protection at carbon sequestration sites and warrant necessary considerations in overall sequestration planning, engineering, and management.

The organic composition of diesel particulate matter, diesel fuel and engine oil of a non-road diesel generator.

Diesel-powered equipment is known to emit significant quantities of fine particulate matter to the atmosphere. Numerous organic compounds can be adsorbed onto the surfaces of these inhalable particles, among which polycyclic aromatic hydrocarbons (PAHs) are considered potential occupational carcinogens. Guidelines have been established by various agencies regarding diesel emissions and various control technologies are under development. The purpose of this study is to identify, quantify and compare the organic compounds in diesel particulate matter (DPM) with the diesel fuel and engine oil used in a non-road diesel generator. Approximately 90 organic compounds were quantified (with molecular weight ranging from 120 to 350), which include alkanes, PAHs, alkylated PAHs, alkylbenzenes and alkanoic acids. The low sulfur diesel fuel contains 61% alkanes and 7.1% of PAHs. The identifiable portion of the engine oil contains mainly the alkanoic and benzoic acids. The composition of DPM suggests that they may be originated from unburned diesel fuel, engine oil evaporation and combustion generated products. Compared with diesel fuel, DPM contains fewer fractions of alkanes and more PAH compounds, with the shift toward higher molecular weight ones. The enrichment of compounds with higher molecular weight in DPM may be combustion related (pyrogenic).

Attrition and changes in particle size distribution of lime sorbents in a circulating fluidized bed absorber

The attrition data of calcium oxide pellets in a circulating fluidized bed absorber (CFBA) are presented with a modified second-order attrition model incorporating an asymptotic minimum bed weight and an excess gas velocity from the minimum fluidization. Two sizes (903 and 1764 μm) of calcium oxide pellets are fluidized with several superficial gas velocities. The experimental attrition rate constants obtained from the attrition model are used to fit a modified Arrhenius equation, with a pseudo activation energy term proportional to the excess fluidizing energy. The model with the measured rate constants for single-particle size is used to predict the changes in size distribution in a bed with a mixture of various particle sizes. The present method may be applicable for batch and continuous operations of fluidized beds in which size reduction predominantly results from attrition and elutriation frequently seen in a fast fluidized bed and in a circulating fluidized bed.

Coal desulfurization by mild pyrolysis in a dual-auger coal feeder

Abstract A dual-screw coal feeder reactor was constructed and tested for desulfurization of coal. The reactor consists of two concentric screw tubes, the inner tube acting as a coal pyrolyzer and the outer tube acting as a desulfurizer with hot calcined lime (CaO) pellets or other renewable sorbent pellets. The experimental results showed that under mild pyrolysis conditions, the devolatilization and the desulfurization processes of Ohio #8 coal could be represented by a pseudo first-order reaction model. Up to 33.2% of the total sulfur, which includes almost all the organic sulfur, was removed at a temperature of 475°C and a residence time of 6 min using a coal particle size of 4–35 mesh. The activation energies for the devolatilization and the desulfurization processes were estimated to be 170,021 kJ/kg mol and 78,732 kJ/kg mol, respectively. The H2S concentration in the pyrolyzed gas was reduced from 4% to an undetectable level in the outer tube desulfurizer indicating a high sulfur removal efficiency of CaO pellets in the dual-screw feeder reactor.

The effect of coal volatility on mercury removal from bituminous coal during mild pyrolysis

Abstract Two high volatile and one low volatile bituminous coals (Lower Freeport #6A, Pittsburgh #8 and Lower Kittanning, respectively) used primarily for electricity production were tested to determine the percentage of mercury content removed during mild pyrolysis. Size-segregated samples of the well-characterized coals were tested in a tube furnace with a nitrogen blanket at different residence times for different processing temperatures through the range 275–600°C. The resulting char was analyzed for mercury and compared to the original parent coal concentration to determine the percentage of removal. Experiments have shown that as much as 80% of the original mercury is removed from these coals at these conditions. The percentage mercury removal was found to be a function of residence time and temperature. The high volatile bituminous coals show a near-constant mercury removal rate as the temperature increases until the temperature reaches a level where mercury removal is inhibited and the rate decreases with increasing temperature. For the low volatile coal, the rate of mercury does not show a change in mechanism as temperature increases and follows the Arrhenius form throughout the temperature range studied. The results were modeled as a homogeneous reaction with distinct maximum percent mercury available for conversion ( X max ) for a specified temperature. Data analysis indicates the following: at 500°C, mild pyrolysis of the Lower Kittanning low volatile sample resulted in 75% maximum mercury removal and the corresponding reaction rate coefficient is 1.56 min −1 ; mild pyrolysis of Lower Freeport #6A coal sample at 500°C resulted in 74% maximum mercury removal and the corresponding reaction rate coefficient is 0.42 min −1 ; the Pittsburgh #8 coal sample had a maximum mercury removal amount of 80% at a furnace temperature of 400°C and a reaction rate coefficient of 0.44 min −1 .

The Effect of Diesel Fuel Sulfur Content on Particulate Matter Emissions for a Nonroad Diesel Generator

Abstract The effect of sulfur content on diesel particulate matter (DPM) emissions was studied using a diesel generator (Generac Model SD080, rated at 80 kW) as the emission source to simulate nonroad diesel emissions. A load simulator was used to apply loads to the generator at 0, 25, 50, and 75 kW, respectively. Three diesel fuels containing 500, 2100, and 3700 ppm sulfur by weight were selected as generator fuels. The U.S. Environmental Protection Agency sampling Method 5 “Determination of Particulate Matter Emissions from Stationary Sources” together with Method 1A “Sample and Velocity Traverses for Stationary Sources with Small Stacks or Ducts” was adopted as a reference method for measurement of the exhaust gas flow rate and DPM mass concentration. The effects of various parameters on DPM concentration have been studied, such as fuel sulfur contents, engine loads, and fuel usage rates. The increase of average DPM concentrations from 3.9 mg/Nm3 (n cubic meter) at 0 kW to 36.8 mg/Nm3 at 75 kW is strongly correlated with the increase of applied loads and sulfur content in the diesel fuel, whereas the fuel consumption rates are only a function of applied loads. An empirical correlation for estimating DPM concentration is obtained when fuel sulfur content and engine loads are known for these types of generators: Y = Zm (αX + β), where Y is the DPM concentration, mg/m3, Z is the fuel sulfur content, ppmw (limited to 500-3700 ppmw), X is the applied load, kW, m is the constant, 0.407, α and β are the numerical coefficients, 0.0118 ± 0.0028 (95% confidence interval) and 0.4535 ± 0.1288 (95% confidence interval), respectively.

Monitoring ambient air quality with carbon monoxide sensor-based wireless network

Introduction Carbon Monoxide (CO) is a poisonous air pollutant produced from the incomplete oxidation of carbon during the combustion process. It has a direct effect on the human body due to its affinity for blood hemoglobin, which inhibits the absorption of oxygen to the blood. The formation of carboxyhemoglobin complex can profoundly affect human health both on an acute and a chronic basis. CO can also be found inside any house at the level of 0.5-30 ppm [http://www.epa.gov/iaq/co.html] because it can be produced from the combustion of household utilities such as heater, stove, fireplace and automobile exhaust in the attached household garage. As CO is a colorless and an odorless gas, CO detectors need to be installed to monitor the CO concentration in a working environment. For an ambient environment, the most popular way of measuring CO uses the principles of nondispersive infrared absorption (NDIR). Other useful methods are Gas Chromatography with flame ionization detector (GC/FID) or Catalytic oxidation techniques. U.S. Environmental Protection Agency (USEPA) employs NDIR as a traditional reference method for CO monitoring regulation. This method is performed by an analyzer and required standard gas system, pump, monitoring station, air conditioner or heater, computing equipment with appropriate programming, and other related equipment. All the necessary equipment needs to be housed and operated inside a room, and protected from rain, dust, and sunlight. Such preventive issues make this method complicated, cumbersome, and expensive. Recent advances in wireless sensor networks (WSNs) make them an attractive solution for monitoring air quality. For instance, a wireless system designed to monitor indoor CO2 concentration is described in the literature. Lindsay Seders et al. deployed a sensor network to monitor water quality in St. Marys Lake on the University of Notre Dame campus. This wireless sensor network used nodes by Mica2 and MDA300 from Crossbow Inc. [http://www.epa.gov/iaq/co.html]. Cardell-Oliver et al. developed and evaluated a reactive sensor network for monitoring soil moisture, which can adaptively change the sampling rate based on rainfall events. The successful deployment of these systems demonstrates that WSNs can be useful for some environmental monitoring scenarios. Very little work has been done for CO monitoring with wireless sensor networks. Agrawal et al. have indicated that WSNs can provide continuous, real-time data of ambient air quality. The sensor systems, combined with the wireless communication network, give the benefit of convenience in deployment, and lower operation and maintenance cost when compared with NDIR technique. The sensor nodes can be powered by either batteries and/or solar energy sources. With the objective of monitoring the area around the University of Cincinnati (UC), 5 out of 15 planned CO sensors were placed on electric poles as shown in Figure 1. This was done to check the proof of the concept and the rest of sensors will be placed in the near future.

Effect of redox potential on leaching from stabilized/solidified waste materials

The effect of redox potential on leaching from solidified/ stabilized fly ash and flue gas desulfurization sludge wastes was studied. In all cases, metal leaching from both raw and fixed wastes was below regulatory limits as defined by the Toxicity Characteristic Leaching Procedure (TCLP) test, and the wastes can be considered nonhazardous. All raw waste leachate concentrations were significantly higher than drinking water limits, though. Research showed that redox potential has a significant effect on metals leaching. Chromium leaching increased significantly under highly oxidizing conditions (+250 to +500 mV); very little leached at an ORP of +50 mV or less. Arsenic, vanadium, lead and iron leaching rates all increased significantly under reducing conditions.

A Qualitative Analysis of the Effects of Water Vapor on Multi-Component Vapor-Phase Carbon Adsorption

The effects of water vapor on binary vapor adsorption of toluene and methylene chloride by activated carbon were investigated on a bench-scale experimental system. Three levels of relative humidity (15, 65 and 90 percent) in conjunction with different concentrations of individual adsorbates (from 400 to 1200 ppmv) were tested by tracing the breakthrough curves of each adsorbate eluted from a fixed-bed adsorber. The adsorption capacities of the activated carbon tested for each adsorbate under the various conditions were obtained from calculations based on area integration of the breakthrough curves. It was found that with increasing relative humidity, the shape of breakthrough curves was asymmetrically distorted and the width of the breakthrough curves was broadened for toluene and steepened for methylene chloride. The adsorption capacities for both toluene and methylene chloride were decreased with the increase of relative humidity. The magnitude of the effect of water vapor is greater at the lower toluen...

THERMAL DECOMPOSITION OF SODIUM BICARBONATE

The thermal decomposition of sodium bicarbonate, a candidate material for Hue gas desulfurization, has been investigated over the temperature range of 225-350°F (380-450K) and over the particle size range of 51 -140 μm. The shrinking core model, with chemical reaction as the rate controlling step, provides a good fit to the data in the temperature range investigated. However, caution should be exercised in extrapolating these results into the range of about 600°F (about 590K) where sintering of this material is reported to occur. The activation energy of the decomposition reaction is 20.5 kcal/mol (85.7 kj/mol)