Modeling of Contaminant Transport in Underground Coal Gasification

Abstract

In order to study and discuss the impact of contaminants produced from underground coal gasification on groundwater, a coupled seepage-thermodynamics-transport model for underground gasification was developed on the basis of mass and energy conservation and pollutant-transport mechanisms, the mathematical model was solved by the upstream weighted multisell balance method, and the model was calibrated and verified against the experimental site data. The experiment showed that because of the effects of temperature on the surrounding rock of the gasification panel the measured pore-water-pressure was higher than the simulated one; except for in the high temperature zone where the simulation errors of temperature, pore water pressure, and contaminant concentration were relatively high, the simulation values of the overall gasification panel were well fitted with the measured values. As the gasification experiment progressed, the influence range of temperature field expanded, the gradient of groundwater pressure decreased, and the migration velocity of pollutant increased. Eleven months and twenty months after the test, the differences between maximum and minimum water pressure were 2.4 and 1.8 MPa, respectively, and the migration velocities of contaminants were 0.24-0.38 m/d and 0.27-0.46 m/d, respectively. It was concluded that the numerical simulation of the transport process for pollutants from underground coal gasification was valid.

Underground coal gasification – A numerical approach to study the formation of syngas and its reactive transport in the surrounding strata

“…The UCG has been performed in over 75 trials throughout the world, and despite most of the UCG trials not experiencing significant environmental issues, potential pollution is the biggest public and regulatory concern [17]. Several researchers who focused on the generation and transport of contaminants via experimental and numerical analyses [18][19][20][21][22][23][24][25] have suggested that operating the UCG process above the hydrostatic pressure can pose an environmental concern due to the chemical reactions in the groundwater environment depending on mineral composition, temperature, concentration of syngas components and the chemical composition of groundwater. However, modelling of contaminant transport and reactions received less attention as it is a complex process with multiple aspects involving heat, mass, stress-strain and physico-chemical reactions [18,26].…”

Comparison of the Contaminants in the Wastewater Produced in the Ex Situ Underground Ortho- and Meta-Lignite Gasification

“…These effluents, if not treated appropriately, can pose a serious environmental risk to surface waters. Experimental simulations and field studies on the formation and migration of contaminants around the UCG test sites identified a broad range of hazardous species (Kapusta and Stańczyk 2011;Edgar et al 1981;Walters and Niemczyk 1984;DeGraeve et al 1980;Shackley et al 2006;Stuermer et al 1982;Yang 2009;Smoliński et al 2013). The major organic groundwater pollutants are typically phenolic compounds.…”

Chemical and toxicological evaluation of underground coal gasification (UCG) effluents. The coal rank effect

“…The major organic groundwater pollutants typical of UCG are phenols, benzene and its derivatives (BTEX), polycyclic aromatic compounds (PAHs) and certain heterocyclic compounds containing nitrogen, sulphur and oxygen heteroatoms. The inorganic matrix includes ionic compounds, such as ammonia, cyanides, sulphates, chlorides and wide range of metal and metalloid elements (Stuermer et al, 1982;Edgar et al, 1981;DeGraeve et al, 1980;Yang, 2009;Kapusta and Stańczyk, 2011;Liu et al, 2006aLiu et al, , 2006b.…”