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 (303)

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.

History of In Situ Coal Gasification (UCG) Over 30 pilot tests were carried out in the U.S s Linc Energy began a large scale pilot test in Australia called Chinchilla 2000 Currently, UCG projects are being carried out all over the world Present

History of In Situ Coal Gasification Continued Sir William Siemens Dmitri Mendeleyev The first UCG patent was issued to A.G. Betts 1909 Stalin began the Soviet UCG Program 1928

HYDROSTATIC PRESSURE

P H =  gz  P H = Hydrostatic Pressure   = 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

Chemical Reactions for UCG Processes  Volatiles Oxidation  Char Oxidation  Water Evaporation  Pyrolysis  Gasification  Boudouard Reaction  Water Gas Shift  Methanation  Hydrogenating Methanation  O 2 + CO, H 2, CH 4, HCs = CO 2 + H 2 O  C + O 2 = CO 2  H 2 O (l) = H 2 O (g)  Coal + Heat = Char + Ash + HCs + CH 4 + H 2 + H 2 O + CO + CO 2  C + H 2 O = H 2 + CO  C + CO 2 = 2CO  CO + H 2 O = H 2 + CO 2  CO + 3H 2 = CH 4 + H 2 O  C + 2H 2 = CH 4

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)

Well Completion and Linking

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

Carbon Capture and Sequestration

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)

Questions?