We evaluate a novel energy strategy, underground coal thermal treatment (UCTT); it involves slowly pyrolyzing coal in-situ, transforming it to a synthetic gas stream containing hydrogen and low molecular-weight hydrocarbons, liquid fuel and char. This evaluation assesses the life-cycle energy and greenhouse gas (GHG) impacts of UCTT for all process stages. It is based on experimental results at two scales, a simple heat-transfer model and literature results. The results show that UCTT can produce a high-quality liquid product and a gas mixture. UCTT's GHG emissions are in the range of those reported for in situ processing of oil shale. Net energy returns (NERs) of 0.48–4.7 are in the range reported oil sands (2.8) and oil shale (0.48–2.6). Product yield at low temperatures, heater temperature, the number of heaters and the moisture content of the coal are key factors in determining the feasibility of the UCTT process.

•GHG emissions from Utah oil shale are much greater than from conventional crudes.•A LCFS will present a challenge for crude oil from Utah's unconventional resources.•Oxyfiring could help crude oil sourced from unconventional fuels meet a LCFS.•The GHG emissions resulting from O2 production via air separation are significant.•Oxyfiring with CO2 capture reduces NER.

More stringent regulations for NOx control in pulverized coal combustors have made the scientific community focus on sources of emissions that were traditionally considered less relevant to the overall NOx production. The oxidation to NO of the nitrogen that is organically bound to the char is one of them. In this study, an experimental evaluation of the influence of the reduction of NO by char was carried out. The experiments with three different carbonaceous materials were conducted at temperatures close to that of pulverized combustion conditions (1700 K) in a laminar drop tube reactor and under inert and oxidizing atmospheres. The results obtained show that the process of NO reduction on the char plays an important role on the total amount of char-N converted to NOx . This NO destruction pathway becomes less important at low NO background concentration and doesn't seem to strongly dependant on the char nature. The predictions of a single particle model were compared to the experimental results. Although the model predicts a reduction on the conversion of char-N to NO that increases in propOliion to NO concentration, it overpredicts the general value. A higher value for the rate of NO destruction on char surface doesn't seem to explain this phenomena that seems to be more related to the availability of char surface for the destruction of NO.

It is essential to objectively evaluate the many CO2 mitigation strategies in order to prioritize investments of capital and research. Aqueous CO2 mineralization is one potential strategy to permanently sequester CO2, without the associated long-term monitoring and liability issues. Investigators are studying and optimizing aqueous CO2 mineralization for the production of inorganic carbonates and are scaling up some of these processes. This paper adopts a life-cycle approach toward the evaluation of energy requirements and discusses other potential barriers for three CO2 mineralization pathways: industrial caustics, naturally occurring minerals, and industrial wastes. This analysis is based on CO2 capture from a 1 GW coal-fired power plant using one of the three mineral mineralization pathways. The investigators utilize consistent system boundaries and process-modeling assumptions, standard engineering calculations to estimate energy requirements, and publicly available data for upstream energy requirements and for the production of products/co-products. The results suggest that some industrial wastes show promise for CO2 mineralization, but their availability is limited. The other pathways currently have large energy penalties and face other significant barriers, such as the production of large quantities of potentially hazardous waste and large-scale mining. (C) 2011 Elsevier Ltd. All rights reserved.

The fate of char-N (nitrogen removed from the coal matrix during char oxidation) has been widely studied at fluidized bed conditions. This work extends the study of char-N to pulverized coal conditions. Coal chars from five parent coals were prepared and burned in a laboratory-scale pulverized coal combustor in experiments designed to identify the parameters controlling the fate of char-N. The chars were burned with natural gas (to simulate volatiles combustion) in both air and in a nitrogen-free oxidant composed of Ar, CO2, and O2. In some experiments, the char flames were doped with various levels of NO or NH3 to simulate formation of NOx from volatile-N (nitrogen removed during coal devolatilization). The conversion of char-N to NOx in chars burned in the nitrogen-free oxidant was 50–60% for lignites and 40–50% for bituminous coals. In char flames doped with NOx, the apparent conversion of char-N to NOx (computed using the NOx measurements made before and after the addition of char to the system) decreased significantly as the level of NOx doping increased. With 900 ppm NOx present before the addition of char, apparent conversion of char-N to NOx was close to 0% for most chars. While there is no clear correlation between nitrogen content of the char and char-N to NOx conversion at any level of NOx in the flame, the degree of char burnout within a given family of chars does play a role. Increasing the concentration of O2 in the system in both air and nitrogen-free oxidant experiments increased the conversion of char-N to NOx. The effects of temperature on NOx emissions were different at low (0 ppm) and high (900 ppm) levels of NOx present in the flame before char addition.

A modified drop-tube reactor that allows particle distribution over the reactor cross-sectional area, and oxidation of chars produced in situ, was used to study the conversion efficiency of char nitrogen to nitric oxide (αNO). The results confirm previous findings by other investigators that αNO decreases as the weight of char burned increases. αNO for coal was the same as (at 4% O2) or lower than (at 20% O2) that for an equal mass of char during oxidation. Since coal will yield approximately half its mass as fixed carbon, these results suggest that the local stoichiometry surrounding the particle is responsible for the observed reduction in αNO as sample size increases. The analysis of the exhaust gases showed increases in HCN concentration and a decrease in CO2/CO ratio as sample size increased, suggesting that local stoichiometry influences αNO. Additional experiments showed that αNO decreased as the background NO concentration was increased, at rates that diminished as the oxygen concentration increased, independent of particle size. The steep reduction in NO production as the background NO concentration increased was explained by the destruction of NO in the gas phase.

Coal continues to be one of the principal energy sources for electric power generation in the United States. One of the biggest environmental challenges involved with coal utilization is the reduction of nitrogen oxides (NO{sub x}) formed during coal combustion. The most economical method of NO{sub x} abatement in coal combustion is through burner modification. Air-staging techniques have been widely used in the development of low-NO{sub x} pulverized coal burners, promoting the conversion of NO{sub x} to N{sub 2} by delaying the mixing in the fuel-rich zone near the burner inlet. Previous studies have looked at the mechanisms of NO{sub x} evolution at relatively low temperatures where primary pyrolysis is dominant, but data published for secondary pyrolysis in the pulverized coal furnace are scarce. In this project, the nitrogen evolution behavior during secondary coal pyrolysis will be explored. The end result will be a complete model of nitrogen evolution and NO{sub x} precursor formation due to primary and secondary pyrolysis.

This study presents an experimental evaluation of the rate of nitric oxide reduction on the char surface. It addresses the claim that the rate for the destruction of nitric oxide on the char surface has been underpredicted due to char deactivation in the process of char formation. Experiments conducted with chars produced in situ, char previously produced at pulverized combustion conditions, and char produced with an activated carbon showed the existence of three phenomena during the reduction of nitric oxide: (1) the homogeneous reaction of the volatiles that evolved after the injection of the solid into the reaction with nitric oxide; (2) the accumulation of nitrogen on the char surface, probably through the formation of C(N) complexes, and (3) the heterogeneous reaction of nitric oxide with char.The nitric oxide reaction with char was found to be dominant at pulverized combustion conditions (T > 1500 K) with a rate within I order of magnitude of that predicted by an expression recommended in previous studies. At fluidized-bed conditions (T < 1300 K), the second phenomenon may be important and traditional rate expressions may underpredict the nitric oxide conversion to N-2 when used at combustion conditions when the nitric oxide-char reactions begin immediately after char formation and before a pseudo-steady state is reached. For the solid used in this study, the increase in nitric oxide reduction due to formation of C(N) sites was a factor of 2-3.

OBJECTIVE

The unburned carbon in the fly ash produced by low-NOx pulverized coal combustion has been shown by electron microscopy to be a mixture of porous coal char particles and aggregates of submicron particles, which are thought to be soot. The carbon is bimodally distributed with large soot aggregates mixed with the char in the particles larger than 10μm and dispersed soot found with the submicron particles. A method for determining the mass of soot and char by liquid-suspension gravity separation was used with both laboratory-scale and power plant fly ash samples. For low-NOx, staged, pilot-scale combustion of bituminous coal the soot in the furnace exit ash was estimated to be 0.2–0.6% of the fuel carbon, which was about 35% of the total unburned carbon.

The contribution of nitrogen present in the char on the production of nitrogen oxides during char combustion was analyzed, A literature review summarizes the current understanding of the mechanisms that account for the formation of NO and N(2)O from the nitrogen present in char. The review focused on: (1) the functionalities in which nitrogen is present in the coal and how they evolve during coal devolatilization; (2) the mechanism of nitrogen release from the char to the homogeneous phase and its further oxidation to NO; and (3) the reduction of NO on the surface of the char. The critical analysis of these three issues allowed identification of uncertainties and well-founded conclusions observed in the literature for this system. The existing models for the production of nitrogen oxides from char-N were also reviewed. A critical analysis of the assumptions made in these models and how they affect the final predictions is presented, Finally, a simplified version of these models was used to perform a parametric analysis evaluating the impact of several parameters on the total conversion of char-N to NO. These parameters include: (1) the rate of NO reduction on the char surface; (2) the rate of carbon oxidation; and (3) early vs, late nitrogen release during the char oxidation process. The results underscore the importance of the reaction of NO reduction on the char surface to the final conversion of char-N to NO. (C) 2000 Elsevier Science Ltd, All rights reserved.

The Center for the Simulation of Accidental Fires and Explosions (C-SAFE) at the University of Utah is focused on providing state-of-the-art, science-based tools for the numerical simulation of accidental fires and explosions, especially within the context of handling and storage of highly flammable materials. The objective of the C-SAFE effort is to provide a scalable, high-performance system composed of a problem-solving environment in which fundamental chemistry and engineering physics are fully coupled with non-linear solvers, optimization, computational steering, visualization and experimental data verification. The availability of simulations using this system will help to better evaluate the risks and safety issues associated with fires and explosions. Our five-year product, termed Uintah 5.0, will be validated and documented for practical application to accidents involving both hydrocarbon and energetic materials.

Direct coal combustion needs to be a primary energy source for the electric utility industry and for heavy manufacturing during the next several decades because of the availability and economic advantage of coal relative to other fuels and because of the time required to produce major market penetration in the energy field. However, the major obstacle to coal utilization is a set of ever-tightening environmental regulations at both the federal and local level. It is, therefore, critical that fundamental research be conducted to support the development of low-emission, high-efficiency pulverized coal power systems. The objective of this program was to develop fundamental understanding regarding the impact of fuel and combustion changes on NOx formation, carbon burnout and air toxic emissions from pulverized coal (pc) combustion. During pc combustion, nitrogen in the coal can be oxidized to form nitrogen oxides (NO{sub x}). The 1990 Clean Air Act Amendments established much stricter NO{sub x} emissions limits for new and existing coal-fired plants, so there has been renewed interest in the processes by which NO{sub x} forms in pc flames. One of the least understood aspects of NO{sub x} formation from pc combustion is the process by which char-N (nitrogen remaining in the char after devolatilization) forms either NO{sub x} or N{sub 2}, and the development of a fundamental understanding of this process was a major focus of this research. The overall objective of this program was to improve the ability of combustion system designers and boiler manufacturers to build high efficiency, low emission pulverized coal systems by improving the design tools available to the industry. The specific program goals were to: Use laboratory experiments and modeling to develop fundamental understanding for a new submodel for char nitrogen oxidation (a critical piece usually neglected in most NOx models.); Use existing bench scale facilities to investigate alternative schemes to stabilize slowly mixed flames which have the potential of producing ultra-low NOx levels with high carbon burnout. Also characterize the air toxic emissions from these flames; and Develop new char nitrogen model for use with a comprehensive combustion model that can be applied to the design and analysis of new and existing boilers.