Peabody Energy has entered into a memorandum of understanding with ArcLight Capital Partners to advance project development of a commercial-scale coal gasification project in Illinois that would transform coal into pipeline-quality synthetic natural gas.
The plant would be one of the largest coal-to-natural-gas plants in the United States and would be sited in Illinois. Peabody would develop a coal mine to fuel the plant using its Illinois Basin reserves, and ArcLight, through an affiliate, would contribute its Illinois-related coal-to-natural-gas development assets.
The project would require at least 3 million tons of coal per year to fuel two gasifier trains that could produce more than 35 billion cubic feet of synthetic natural gas.
The initial project would be designed with ConocoPhillips E-Gas Technology, featuring an oxygen-blown gasification system. ConocoPhillips and Fluor have begun preliminary engineering design work for the project.
ConocoPhillips and Fluor Corporation signed a partnership agreement in 2004 to facilitate the development, design and construction of new projects utilizing ConocoPhillips’ E-Gas Technology.
|The E-Gas Gasifier. Click to enlarge.|
The E-Gas process incorporates a unique, two-stage proprietary gasification system design which can be applied with gas turbine and steam power generation in an advanced Integrated Gasification Combined Cycle configuration to produce electric power, as well as co-producing synthesis gas, hydrogen and steam in highly flexible combinations. The syngas can be upgraded to pipeline quality natural gas, or used for refinery hydrogen, synthetic liquid fuels (Fischer-Tropsch) and chemicals production.
The E-Gas process is an oxygen-blown coal gasification technology featuring a slurry-fed, two-stage gasifier, a slagging first stage and an entrained flow second stage.
Wet crushers produce slurries with the raw feed coal. Dry coal slurry concentrations range from 50 to 70 wt%, depending on the inherent moisture and quality of the feed coal.
About 80% of the total slurry feed is fed to the first (or bottom) stage of the gasifier. All the oxygen is used to gasify this portion of the slurry. This stage is best described as a horizontal cylinder with two horizontally opposed burners. The highly exothermic gasification/oxidation reactions take place rapidly at temperatures of 2,400 to 2,600° F.
The coal ash is converted to molten slag, which flows down through a tap hole. The molten slag is quenched in water and removed in a novel continuous-pressure letdown/dewatering system. The slag may be used for various construction applications.
The hot raw gas from the first stage enters the second (top) stage, which is a vertical cylinder perpendicular to the first stage. The remaining 25% of the coal slurry is injected into the hot raw gas. The endothermic gasification/devolatilization reactions in this stage reduce the final gas temperature to about 1,900°F and add some hydrocarbons to the product gas.
Char is produced in the second stage. However, the yield of this char is relatively small because only about 25% of the coal is fed to the second stage. Char yield is dependent on the reactivity of the feed coal and decreases with increasing reactivity. The char is recycled to the hotter first stage, where it is readily gasified.
The gasifier is refractory-lined and not cooled. The hotter first stage section of the gasifier is lined with a special slag-resistant refractory. The 1,900° F hot gas leaving the gasifier is cooled in a fire-tube product gas cooler to 1,100° F, generating saturated steam which is sent to the steam turbine in a power-generating application.
The raw syngas exiting the syngas cooler is filtered to remove the unreacted entrained solids, which are recycled to the gasifier. The filtered “sour” gas consists mainly of Hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), water (H2O), and smaller quantities of Nitrogen (N2), methane (CH4), hydrogen sulfide (H2S), and carbonyl sulfide (COS).
The sour gas is cooled further to about 100° F. The cooling is accomplished within several heat exchangers. Water condenses from the gas as it is cooled, generating a condensate containing ammonia (NH3), some of the H2S and CO2, which is sent to water treatment.
The cooled sour gas enters an acid gas removal system (AGR) based on methyldiethanolamine solvent, which removes the H2S and a portion of the CO2 contained in the gas. Once cleaned of the H2S, the gas is ready for use as a fuel gas for the gas turbine in the power block. In addition, an acid gas stream is produced which is directed to a sulfur recovery unit.
In the water treatment system, dissolved gaseous contaminants are removed by steam stripping. The stripped gas is integrated into the gasification process while a major portion of the stripped water is recycled to the slurry preparation area and the remainder to the outfall.
E-Gas Technology is in use at the Wabash River Coal Gasification Power Plant in Indiana.
(A hat-tip to Rajeev Narayan!)