Underground Coal Gasification for Power Generation: High Efficiency and CO2-Emissions

Abstract

Underground Coal Gasification (UCG) is a gasification process carried out in non-mined coal seams using injection and production wells drilled from the surface, enabling the coal to be converted into product gas. The UCG process practiced by Ergo Exergy is called Exergy UCG or εUCG. εUCG was applied in the Chinchilla UCG-IGCC Project in Australia. The IGCC project in Chinchilla, Australia has been under development since July 1999. The project involves construction of the underground gasifier and demonstration of UCG technology, and installation of the power island. Since December 1999 the plant has been making gas continuously, and its maximum capacity is 80,000 Nm3/h. Approximately 32,000 tonnes of coal have been gasified, and 100% availability of gas production has been demonstrated over 30 months of operation. The UCG operation in Chinchilla is the largest and the longest to date in the Western world. The εUCG facility at Chinchilla has used air injection, and produced a low BTU gas of about 5.0 MJ/m3 at a pressure of 10 barg (145 psig) and temperature of 300° C (570° F). It included 9 process wells that have been producing gas manufactured from a 10 m thick coal seam at the depth of about 140 m. The process displayed high efficiency and consistency in providing gas of stable quality and quantity. The results of operations in Chinchilla to date have demonstrated that εUCG can consistently provide gas of stable quantity and quality for IGCC power projects at very low cost enabling the UCG-IGCC plant to compete with coal-fired power stations. This has been done in full compliance with rigorous environmental regulations. A wide range of gas turbines can be used for UCG-IGCC applications. The turbines using UCG gas will demonstrate an increase in output by up to 25% compared to natural gas. The power block efficiency reaches 55%, while the overall efficiency of the UCG-IGCC process can reach 43%. A UCG-IGCC power plant will generate electricity at a much lower cost than existing or proposed fossil fuel power plants. CO2 emissions of the plant can be reduced to a level 55% less than those of a supercritical coal-fired plant and 25% less than the emissions of NG CC.

Fault Reactivation Can Generate Hydraulic Short Circuits in Underground Coal Gasification—New Insights from Regional-Scale Thermo-Mechanical 3D Modeling

“…Permeability, in consideration of the difference between hydrostatic and UCG reactor pressure, controls fluid in-and outflow into and out of the reactor, respectively [31,60]. Figure 4 illustrates that permeability changes resulting from isothermal and non-isothermal simulations exhibit significant deviations in the close UCG channel vicinity.…”

Early Ideas in Underground Coal Gasification and Their Evolution

“…UCG has numerous economic and environmental benefits [2]. Compared to conventional use of coal, UCG has the same advantages as above-ground gasification.…”

“…As result of this surge, knowledge of UCG is sought again and more than 30 trials are conducted or planned in Australia, China, India, South Africa, New Zealand, Canada and the USA. Many of these trials are carried out under technological auspices of Ergo-Exergy -the leading supplier of modern commercial UCG technology and the holder of proprietary rights for the process called εUCG [2].…”

“…UCG was used on a large scale in the former USSR and tested in many countries. Minimal disturbance to land, reduction of air pollution and even a 25% reduction in CO 2 production due to better energy utilization (as compared to conventional coal-fired power plants -see reference [2,4]) are combined in UCG with the prospect of obtaining inexpensive energy and fuels from domestic sources [2]. While being a solution for many environmental problems, UCG has an environmental concern of its own -the possibility of groundwater contamination.…”

Energy and exergy analysis of alternating injection of oxygen and steam in the low emission underground gasification of deep thin coal

“…Blinderman and Anderson [12] studied the data of the εUCG process applied to a 10 m thick coal layer at 140 m depth in Chinchilla, Australia. They showed that the overall efficiency of the electricity production from the UCG-IGCC (Integrated Gasification Combined Cycle) can reach 43%, which is comparable to a natural gas combined cycle (NGCC).…”