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In Situ Coal Gasification:. An Emerging Technology. Kristin M. Brown, Hydrologist. B.S. Geology – West Virginia University M.S. Hydrology – Colorado School of Mines Office of Surface Mining 1999 Broadway Ste 3320 Denver, Colorado 80202 (303)293-5048. Introduction.
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In Situ Coal Gasification: An Emerging Technology
Kristin M. Brown, Hydrologist • B.S. Geology – West Virginia University • M.S. Hydrology – Colorado School of Mines • Office of Surface Mining 1999 Broadway Ste 3320 Denver, Colorado 80202 (303)293-5048
Introduction • In Situ Coal Gasification is the process of injecting an oxidant (air or steam) into a coal seam that reacts with the coal and water present underground to produce Synthesis gas (Syngas). • Syngas is can be used as fuel or feedstock for other chemical processes such as ammonia or liquid fuels. It can also be used for electricity production.
PH = rgz • PH = Hydrostatic Pressure • r = Fluid Density • g = Gravitational Acceleration • z = Height of the Liquid Column Assuming the fluid is incompressible and z is reasonably small compared to the Earth’s radius
Hydrostatic Pressure Courtesy of Susannah Strauss with www.UCG-GTL.com.
Chemical Reactions for UCG Processes • Volatiles Oxidation • Char Oxidation • Water Evaporation • Pyrolysis • Gasification • Boudouard Reaction • Water Gas Shift • Methanation • Hydrogenating Methanation • O2 + CO, H2, CH4, HCs = CO2 + H2O • C + O2 = CO2 • H2O(l) = H2O(g) • Coal + Heat = Char + Ash + HCs + CH4 + H2 + H2O + CO + CO2 • C + H2O = H2 + CO • C + CO2 = 2CO • CO + H2O = H2 + CO2 • CO + 3H2 = CH4 + H2O • C + 2H2 = CH4
Site Characterization • No high production aquifers within the expected vertical subsidence volume • Coal Seams > 30 feet thick are suitable • Coal seam depths 500 to 2,000 feet below ground surface are considered ideal • Immediate overburden unit should a thick vertical section of claystone or shale • Structural (faulting and Folding) considerations need to be made for UCG site selection.
Well Completion and Linking • Air Pressurization between two wells • Injecting into man built galleries in the coal seam (i.e. to utilize remaining coal after underground mining) • Directional drilling in the coal seam with controlled injection • Injection in simultaneous channels is known as the Controlled Injection Procedure (CRIP)
Environmental Effects • Surface Subsidence • Groundwater Contamination • Carbon Capture and Sequestration (CCS)
Surface Subsidence • Subsidence is the downward movement of subsurface material due to mining and the creation of an underground void that caves in. • surface disruptions, • excessive groundwater influx into the UCG reactor • mixing of separate water bearing units and • groundwater contamination • Subsidence can be and is controlled as it is in underground mining where surface movement is not desired. • UCG is analogous to conventional longwall mining with respect to subsidence
Surface Subsidence At Hoe Creek, Wyoming, the cavity experienced a massive chimney collapse that propagated approximately 40 meters to the surface several weeks after the well was shut-in (LLNL, 2011).
Groundwater Contamination • Groundwater contamination is considered the most serious potential environmental risk related to UCG. • Major groundwater pollutants include • Polynuclear and phenolic organic compounds • Ammonia • Sulfate and • Calcium
Groundwater Contamination • Primary source of inorganic pollutants is ash leachate • Primary source of organic contaminants and ammonia is condensed vapors • Adsorption of organics to clay and lignite is an effective removal mechanism of the contaminant from groundwater
Environmental Benefits • No Discharge of Tailings • Reduced Sulfur Emissions • Reduced discharge of Ash, Mercury and Tar • Carbon Capture and Sequestration
Carbon Capture and Sequestration • CCS is the process to remove and store “greenhouse gases” from process streams to reduce the buildup of these gases in the atmosphere. • Involves the process of extraction, • Seperation • Collection • Compression • Transporting and • Geologic Strorage • CCS can be synergistically applied to Enhanced Oil Recovery or Enhanced Coal Bed Methane Recovery
Conclusions • Groundwater plays an important role in UCG • Positive Hydraulic Gradient towards the gasification chamber is needed. • Establishing a hydraulic circulation system is important so the gasification chamber can be flushed and cleaned • Hydraulic control is the most important feature of UCG. • Controls the UCG process and prevents groundwater contamination. • Site Characterization and well completion are also of utmost importance for a successful UCG operation. • Coal resources not suitable for conventional mining are ideally suited for UCG • Environmental Benefits to UCG (i.e. Carbon Capture and Sequestration)