The interactions of coal with CO2 and its effects on coal structure

The interactions of coal with CO2 at pressures of up to 30 bar concerning mechanisms of diffusion, the strength of interactions, and the irreversibility of uptake for the permanent disposal of CO2 into coal fields have been studied. Differential scanning calorimetry was used to investigate coal/CO2 interactions for North Dakota, Wyodak, Illinois No. 6, and Pittsburgh No. 8 coals. It was found that the first interactions of CO2 with coals led to strongly bound carbon dioxide on coal. Energy values attributed to the irreversible storage capacity for CO2 on coals were determined. The lowest irreversible sorption energy was found for North Dakota coal (0.44 J/g), and the highest value was for the Illinois No. 6 coal (8.93 J/g). The effect of high-pressure CO2 on the macromolecular structure of coal was also studied by means of differential scanning calorimetry. It was found that the temperature of the second-order phase transition of Wyodak coal decreases with an increase in CO2 pressure significantly, indicating that high-pressure CO2 diffuses through the coal matrix, causes significant plasticization effects, and changes the macromolecular structure of the Wyodak coal. Desorption characteristics of CO2 from the Pittsburgh No. 8 coal were studied by temperature-programmed desorption mass spectrometry. It was found that CO2 desorption from the coal is an activated process and follows a first-order kinetic model. The activation energy for CO2 desorption from the Pittsburgh No. 8 coal increased with the preadsorbed CO2 pressure, indicating that CO2 binds more strongly and demands more energy to desorb from the Pittsburgh No. 8 coal at higher pressures.

Thermodynamical studies of irreversible sorption of CO2 by Wyodak coal

Differential scanning calorimetry (DSC), temperature programmed desorption mass spectrometry (TPD-MS) and small angle neutron scattering (SANS) were used to investigate CO2 uptake by the Wyodak coal. The adsorption of carbon dioxide on Wyodak coal was studied by DSC. The exotherms evident at low temperatures are associated with the uptake of CO2 suggesting that carbon dioxide interacts strongly with the coal surface. The reduction in the value of the exotherms between the first and second runs for the Wyodak coal suggests that some CO2 is irreversibly bound to the structure even after heating to 200 °C DSC results also showed that adsorption of CO2 on the coal surface is an activated process and presumably at the temperature of the exotherms there is enough thermal energy to overcome the activation energy for adsorption. The adsorption process is instantly pursued by much slower diffusion of the gas molecules into the coal matrix (absorption). Structural rearrangement in coal by CO2 is examined by change in the glass transition temperature of coal after CO2 uptake at different pressures. The amount of gas dissolved in the coal increases with increasing CO2 pressure. TPD-MS showed that CO2 desorption from the Wyodak coal follows a first order kinetic model. Increase in the activation energy for desorption with pre-adsorbed CO2 pressure suggests that higher pressures facilitate the transport of CO2 molecules through the barriers therefore the amount of CO2 uptake by the coal is greater at higher pressures and more attempts are required to desorb CO2 molecules sorbed at elevated pressures. These conclusions were further confirmed by examining the Wyodak coal structure in high pressure CO 2 by SANS.

Study of structural change in Wyodak coal in high pressure CO2 by small-angle neutron scattering

Small angle neutron scattering (SANS) has been applied to examine the effect of high pressure CO2 on the structure of Wyodak coal. Significant decrease in the scattering intensities upon exposure of the coal to high pressure CO2 showed that high pressure CO2 rapidly adsorbs on the coal and reaches to all pores in the structure. This is confirmed by strong and steep exothermic peaks observed on DSC scans during coal/ CO2 interactions. In situ small angle neutron scattering on coal at high pressure CO2 atmosphere showed an increase in scattering intensities with time suggesting that after adsorption, high pressure CO2 immediately begins to diffuse into the coal matrix, changes the macromolecular structure of the coal, swells the matrix and probably creates microporosity in coal structure by extraction of volatile components from coal. Significant decrease in the glass transition temperature of coal caused by high pressure CO2 also confirms that CO2 at elevated pressures dissolve in the coal matrix, results in significant plasticization and physical rearrangement of the coal’s macromolecular structure.

The effect of slurry storage and anaerobic-digestion on survival of pathogenic bacteria

The decline in viable numbers of Salmonella typhimurium, Yersinia enterocolitica and Listeria monocytogenes in beef cattle slurry is temperature-dependent; they decline more rapidly at 17-degrees-C than at 4-degrees-C. Mesophilic anaerobic digestion caused an initial rapid decline in the viable numbers of Escherichia coli, Salm. typhimurium, Y. enterocolitica and L. monocytogenes. This was followed by a period in which the viable numbers were not reduced by 90%. The T90 values of E. coli, Salm. typhimurium and Y. enterocolitica ranged from 0.7 to 0.9 d during batch digestion and 1.1 to 2-5 d during semi-continuous digestion. Listeria monocytogenes had a significantly higher mean T90 value during semi-continuous digestion (35.7 d) than batch digestion (12.3 d). Anaerobic digestion had little effect in reducing the viable numbers of Campylobacter jejuni.

Detection of Mixing Dynamics During Pumping of a Flooded Coal Mine

In complex hydrogeological environments the effective management of groundwater quality problems by pump-and-treat operations can be most confidently achieved if the mixing dynamics induced within the aquifer by pumping are well understood. The utility of isotopic environmental tracers (C-, H-, O-, S-stable isotopic analyses and age indicators—14C, 3H) for this purpose is illustrated by the analysis of a pumping test in an abstraction borehole drilled into flooded, abandoned coal mineworkings at Deerplay (Lancashire, UK). Interpretation of the isotope data was undertaken conjunctively with that of major ion hydrochemistry, and interpreted in the context of the particular hydraulic setting of flooded mineworkings to identify the sources and mixing of water qualities in the groundwater system. Initial pumping showed breakdown of initial water quality stratification in the borehole, and gave evidence for distinctive isotopic signatures (d34S(SO4) ~= -1.6‰, d18O(SO4) ~= +15‰) associated with primary oxidation of pyrite in the zone of water table fluctuation—the first time this phenomenon has been successfully characterized by these isotopes in a flooded mine system. The overall aim of the test pumping—to replace an uncontrolled outflow from a mine entrance in an inconvenient location with a pumped discharge on a site where treatment could be provided—was swiftly achieved. Environmental tracing data illustrated the benefits of pumping as little as possible to attain this aim, as higher rates of pumping induced in-mixing of poorer quality waters from more distant old workings, and/or renewed pyrite oxidation in the shallow subsurface.

The Coal Jetty; Shadows

Two new original poems

Farmer perception of suitable conditions for slurry application compared with decision support system recommendations

The application of slurry nutrients to land can be associated with unintended losses to the environment depending on soil and weather conditions. Correct timing of slurry application, however, can increase plant nutrient uptake and reduce losses. A decision support system (DSS), which predicts optimum conditions for slurry spreading based on the Hybrid Soil Moisture Deficit (HSMD) model, was investigated for use as a policy tool. The DSS recommendations were compared to farmer perception of suitable conditions for slurry spreading for three soil drainage classes (well, moderate and poorly drained) to better understand on farm slurry management practices and to identify potential conflict with farmer opinion. Six farmers participated in a survey over two and a half years, during which they completed a daily diary, and their responses were compared to Soil Moisture Deficit (SMD) calculations and weather data recorded by on farm meteorological stations. The perception of land drainage quality differed between farmers and was related to their local knowledge and experience. It was found that the allocation of grass fields to HSMD drainage classes using a visual assessment method aligned farmer perception of drainage at the national scale. Farmer opinion corresponded to the theoretical understanding that slurry should not be applied when the soil is wetter than field capacity, i.e. when drainage can occur. While weather and soil conditions (especially trafficability) were the principal reasons given by farmers not to spread slurry, farm management practices (grazing and silage) and current Nitrates Directive policies (closed winter period for spreading) combined with limited storage capacities were obstacles to utilisation of slurry nutrients. Despite the slightly more restrictive advice of the DSS regarding the number of suitable spreading opportunities, the system has potential to address an information deficit that would help farmers to reduce nutrient losses and optimise plant nutrient uptake by improved slurry management. The DSS advice was in general agreement with the farmers and, therefore, they should not be resistant to adopting the tool for day to day management.