Soon-Jai Khang

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.

Pyrolysis Behavior of Tire-Derived Fuels at Different Temperatures and Heating Rates

Abstract Pyrolytic product distribution rates and pyrolysis behavior of tire-derived fuels (TDF) were investigated using thermogravimetric analyzer (TGA) techniques. A TGA was designed and built to investigate the behavior and products of pyrolysis of typical TDF specimens. The fundamental knowledge of TGA analysis and principal fuel analysis are applied in this study. Thermogravimetry of the degradation temperature of the TDF confirms the overall decomposition rate of the volatile products during the depolymerization reaction. The principal fuel analysis (proximate and ultimate analysis) of the pyrolytic char products show the correlation of volatilization into the gas and liquid phases and the existence of fixed carbon and other compounds that remain as a solid char. The kinetic parameters were calculated using least square with minimizing sum of error square technique. The results show that the average kinetic parameters of TDF are the activation energy, E = 1322 ± 244 kJ/mol, a pre-exponential constant of A = 2.06 ± 3.47 × 1010 min−1, and a reaction order n = 1.62 ± 0.31. The model-predicted rate equations agree with the experimental data. The overall TDF weight conversion represents the carbon weight conversion in the sample.

A model for dry sodium bicarbonate duct injection flue gas desulfurization

A mathematical model is developed for simulation of dry sodium bicarbonate (NaHCO ) duct injection for the 3 removal of sulfur dioxide (SO ) in flue gases across a fabric filter (baghouse). The model employs parallel reaction 2 kinetics and assumes that the sodium bicarbonate injection process can be separated into two stages. The first stage is a transport duct section where NaHCO particles are injected into the sulfur dioxide laden gas stream. The second 3 stage is the fabric filter section where sodium sorbents are collected and behave as a variable depth fixed bed reactor. The process simulation for the efficiency of desulfurization in flue gas is performed and evaluated for a variety of operating conditions such as system temperature, particle size, residence time, normalized stoichiometric ratio, concentration of sulfur dioxide and decomposition time. It is found that the removal of SO within the duct section 2 is small and negligible for most practical conditions, with a contribution normally less than 5% of total SO removal. 2 The major removal of SO occurs across the filter cake, which accumulates the sorbent particles on the fabric filter. 2 These particles are periodically disposed as the filter is cleaned. The major factors for the process are temperature, particle size and SO gas concentration for all operating conditions. At low temperatures, the removal of SO 2 2 increases as temperature increases, but the removal decreases at higher temperatures due to the impact of the thermal decomposition reaction of NaHCO on SO removal. It was found that the temperature for the highest removal of 32 SO is within the range of 127-150 8C and the removal efficiency also depends on particle size. 2

A NEW SILICON-BASED MATERIAL FORMED BY PYROLYSIS OF SILICON RUBBER AND ITS PROPERTIES AS A MEMBRANE

A new, highly porous silicon-based membrane was developed by pyrolyzing a silicon-rubber material (polydimethyl siloxane)in two steps. The first step was performed under an inert-gas environment below 800°C. The second step was performed in air below 950°C to oxidize and cross-link Si-O chains. The resulting silicon-based material was highly porous and had a fine pore structure (maximum porosity of 50%, BET surface area of I40m2/g) suitable for hot industrial gas separation even in a highly oxidizing environment. Gas permeability studies were performed at several different temperatures using a material derived by the pyrolysis of commercial silicon-rubber tubes. The results indicated that the flow through the membrane could be adequately explained by the Knudsen diffusion mechanism. The average permeabilities were 10 to 50 times those of porous Vycor glass.

Kinetics of the sodium bicarbonate—sulfur dioxide reaction

Abstmct-A parallel reaction path model has been developed to explain the reaction between sodium bicarbonate (NaHCO,) particles and sulfur dioxide (SO,) gas. This reaction is atypical compared to other alkali and alkaline compounds with SOi in that the optimum reaction temperature occurs where thermal decomposition of the parent particles is pronounced. The model accounts for the concomitant thermal decomposition reaction which occurs at the temperatures where this reaction is industrially significant. The subsequent reaction between the product of the thermal decomposition, micro-grains of sodium carbonate (Na,CO,) and SO2 is considered in the reaction path by the use of a pore plugging model. The model has been applied to published kinetic data for the NaHCOs-SO2 reaction in order to obtain the reaction rate constants which are shielded from observation by the thermal decomposition reaction and the subsequent reaction between Na,CO, and SOz. An expression for the reaction rate constant for the reaction of NaHCO, with SO1 has been found and is of the form k, = 2.2625 x 106e-*3*5’2/RT. The model has been applied to conversion of the bicarbonate particles for up to 600s reaction time, with good agreement with the data. This model can be used to predict the reactivity of NaHCOI with SO1 in typical gas-solid reactors.

THE DISSOLUTION RATE OF Ca(OH)2 IN AQUEOUS SOLUTIONS

Abstract The dissolution rate of reagent grade Ca(OH)2 in aqueous solutions has been determined by means of a spinning disc method. The dissolution rate was found to be independent of disc velocity at a disc Reynolds Number above 9×l03. The dissolution rate is important for environmental applications such as flue gas desulfurization using Ca(OH)2 in wet scrubbers and spray dryer reactors, and for pH control. The lime discs were prepared under high pressure in a cylinder and determined to have similar thermogravimetric response to temperature as that of the parent lime powder. The discs were tested in a pH slat device where the dissolution rate was correlated to acid consumption required to maintain a preset value of pH. Limestone powder was used to verify the experimental system as the results could be compared with published data. Lime dissolution rate was measured as a function of disc velocity, ω (rpm), solution pH and temperature (K). The variation of dissolution rate with temperature was found to fo...