Mild catalytic steam gasification process

Abstract

The present invention provides an improved alkali metal catalyzed steam gasification process that utilizes a CO2 trap material and / or a mineral binder material within the gasifier. The process optimally achieves over 90% carbon conversion with over 80% yield of methane. The raw gas product can be used directly as fuel. The catalyst can be recovered from the solid purge and recycled to the gasifier and / or the CO2 trap can be regenerated and recycled to the gasifier.

Description

[0001] This application claims priority under 35 U.S.C. 119(e) to provisional application 60 / 695,994 which is hereby incorporated by reference.FIELD OF THE INVENTION [0002] The present invention relates to low temperature catalytic gasification of carbonaceous material. More particularly, the present invention relates to an improved process for gasifying carbonaceous material that achieves high carbon conversion to methane at mild temperatures. BACKGROUND—DESCRIPTION OF RELATED ART [0003] The world-wide availability of petroleum is predicted to peak and then decline rapidly. Rapid economic, technological and industrial growth of populous countries such as China and India serves to increase this demand, making the need for alternative sources of energy even more severe. To meet this growing demand it has been suggested to convert coal into more useful and transportable forms. One such technique is to gasify coal into combustible gases. A coal gasification process for producing pipeli...

AI Technical Summary

Benefits of technology

[0020] It has been found that using calcium salts to remove or “trap” carbon dioxide and other oxidizing agents from a catalytic coal gasification environment can shift the kinetics towards greater carbon conversion to methane, and can also drive the conversion of CO to CO2 such that the process can yield a dry raw gaseous product comprised mainly of H2 and CH4 and substantially free of carbon oxides. The overall coal / carbon conversion can be at least 50% but conversions greater than 95% are also obtainable. The process disclosed herein can directly produce a dry raw gaseous product comprised of about 40% methane or more, by volume, without the need for substantial recycling or feeding H2 and CO to the environment. Advantageously, the dry raw gaseous product can be used as a fuel without further enrichment, and can provide pipeline quality methane with little additional treatment.

[0021] Calcium salts and other compounds can react with CO2 and H2S and form solids which can be withdrawn in a solid purge, thereby eliminating or greatly reducing the need to treat the raw gaseous product for acid gas removal. According to the present invention, calcium salts can also bind with, and render inert or relatively inert, mineral constituents of the carbonaceous feed so the alkali metal salt catalysts can remain active longer. By preventing such minerals from reacting with and deactivating the alkali metal catalysts, greater catalyst recovery from the solid purge can be achieved and catalyst losses can be reduced. The process can allow for up to ˜90% catalyst recovery.

[0022] While the invention is not limited to any theory, it is believed that CO2 in the gasifier causes the catalyst to deactivate, so that by eliminating the CO2, high catalytic activity can be sustained and more complete conversion can be achieved. In addition, removal of CO2 from the gas phase can substantially alter the ratio of hydroxide to carbonate forms of the catalyst. Eliminating CO2 effectively increases the activity of the catalyst and enables a high rate of gasification to occur at mild operating temperatures. At mild temperatures, the kinetics favor greater direct conversion of coal (or other carbonaceous materials) to methane, and the coal, which can convert to less reactive char at conventional catalytic coal gasification temperatures, can remain more reactive. Mild temperature operation can also reduce catalyst losses and corrosion of system components caused by volatilization of the catalyst and hazardous trace elements in the carbonaceous feed.

[0023] The catalytic gasification processes of the present invention can also be simpler and less costly to build and operate than known prior processes, and can be less prone to overheating, corrosion, char build-up and other problems long associated with other gasification processes and systems. The estimated Btu in, versus Btu out, efficiency can be on the order of 80 to 85% overall.

Problems solved by technology

Rapid economic, technological and industrial growth of populous countries such as China and India serves to increase this demand, making the need for alternative sources of energy even more severe.

Commercial, non-catalyzed, coal gasification systems and designs face a number of economic and technical challenges.

These processes are expensive to operate since, in order to drive the endothermic non-catalytic gasification of carbonaceous materials, they utilize severe temperatures (2400 to 2600° F.) and can consume high levels of oxygen.

Slagging and corrosion also can present operating and maintenance issues which reduce economic viability and increase product cost.

There is also no suggestion that the presence of calcium can improve catalyst recovery.

However, catalysts have not heretofore been identified that can catalyze mild temperature gasification at acceptably high reaction rates.

Several metals (other than alkali metals) have been identified that can catalyze steam / coal gasification, but have not shown promise for mild temperature gasification.

For example, the article by Yasuo Ohtsuka and Kenji Asami, “Highly active catalysts from inexpensive raw materials for coal gasification”, Catalysis Today 39:111 (1997) reports that calcium salts, such as CaCO3 or Ca(OH)2, that have been “kneaded” with coal particles, can promote steam gasification of lignite at about 550° C., but are reportedly not effective with low-oxygen containing higher rank coals.

Though coal gasification catalysis has been extensively researched, it is still not completely understood.

The alkali metal catalysts can also become inactive or ineffective by volatilizing and / or binding with mineral constituents of coal.

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