In Situ Coal Gasification: An Emerging Technology.

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?