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.
History of In Situ Coal Gasification (UCG)
Over 30 pilot tests were carried out in the
U.S.
1976-1990s
Linc Energy began a large scale pilot test in Australia called
Chinchilla
2000Currently, UCG projects are being carried out all
over the worldPresent
History of In Situ Coal Gasification Continued
• Sir William Siemens• Dmitri Mendeleyev
1976-1996
The first UCG patent was issued to A.G.
Betts1909 Stalin began the
Soviet UCG Program1928
HYDROSTATIC PRESSURE
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)
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?