Steam generating slurry gasifier for the catalytic gasification of a carbonaceous feedstock

This application claims priority under 35 U.S.C. §119 from U.S. Provisional Application Ser. No. 61/017,321 (filed Dec. 28, 2007), the disclosure of which is incorporated by reference herein for all purposes as if fully set forth.

The present invention relates to a steam generating slurry gasifier which produces steam and synthesis gas from an aqueous carbonaceous feed slurry. Further, the invention relates to processes for preparation gaseous products, and in particular, methane via the catalytic gasification of carbonaceous feedstocks in the presence of steam and synthesis gas generated by the slurry gasifier.

In view of numerous factors such as higher energy prices and environmental concerns, the production of value-added gaseous products from lower-fuel-value carbonaceous feedstocks, such as petroleum coke and coal, is receiving renewed attention. The catalytic gasification of such materials to produce methane and other value-added gases is disclosed, for example, in U.S. Pat. No. 3,828,474, U.S. Pat. No. 3,998,607, U.S. Pat. No. 4,057,512, U.S. Pat. No. 4,092,125, U.S. Pat. No. 4,094,650, U.S. Pat. No. 4,204,843, U.S. Pat. No. 4,468,231, U.S. Pat. No. 4,500,323, U.S. Pat. No. 4,541,841, U.S. Pat. No. 4,551,155, U.S. Pat. No. 4,558,027, U.S. Pat. No. 4,606,105, U.S. Pat. No. 4,617,027, U.S. Pat. No. 4,609,456, U.S. Pat. No. 5,0172,82, U.S. Pat. No. 5,055,181, U.S. Pat. No. 6,187,465, U.S. Pat. No. 6,790,430, U.S. Pat. No. 6,894,183, U.S. Pat. No. 6,955,695, US2003/0167961A1, US2006/0265953A1, US2007/000177A1, US2007/083072A1, US2007/0277437A1 and GB1599932.

The process for the catalytic gasification of a carbonaceous material to synthetic natural gas requires the presence of steam to react with carbon either in the gas phase or on the surface of the carbonaceous material to generate methane and carbon dioxide. It has generally been contemplated to utilize coal-fired boilers to generate the required steam. Such methods have the disadvantages of requiring an additional fuel source for the boiler, while producing an exhaust comprising additional acid gases (e.g, carbon dioxide, sulfur dioxide, nitrous oxides), which must be treated and exhausted to the atmosphere or otherwise sequestered. As such, there exists a need in the art to develop apparatuses and processes for the catalytic gasification of carbonaceous materials to synthetic natural gas which more efficiently utilize fuels sources while decreasing the carbon footprint of the overall process.

In a first aspect, a gasifier apparatus is provided for producing a first plurality of gases comprising methane and one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia and other higher hydrocarbons from a catalyzed carbonaceous feedstock, the gasifier apparatus comprising: a fluidized bed gasifier configured to receive the catalyzed carbonaceous feedstock and a second plurality of gases comprising steam, hydrogen and carbon monoxide, and to exhaust the first plurality of gases; and a slurry gasifier configured to supply to the fluidized bed gasifier the second plurality of gases, the slurry gasifier comprising, a gasifier chamber; a slurry conduit for supplying an aqueous carbonaceous slurry as a reactant to the gasifier chamber; an optional syngas conduit in communication with a syngas source and the gasifier chamber for optionally supplying a syngas to the gasifier chamber; an oxygen gas conduit for supplying enriched oxygen gas as a reactant to the fluidized bed gasifier chamber; and a heated gas conduit in communication with the fluidized bed gasifier for supplying the second plurality of gases from the slurry gasifier to the fluidized bed gasifier.

In a second aspect, a slurry gasifier is provided for generating a plurality of gases comprising steam, hydrogen and carbon monoxide from an aqueous carbonaceous slurry, the slurry gasifier comprising, a gasifier chamber; an optional syngas conduit in communication with a syngas source and the gasifier chamber for optionally supplying a syngas to the gasifier chamber; an oxygen gas conduit for supplying enriched oxygen gas as a reactant to the gasifier chamber; a slurry conduit for supplying an aqueous carbonaceous slurry as a reactant to the gasifier chamber; and a heated gas conduit for exhausting the plurality of gases.

In a third aspect, a process is provided for generating a plurality of gases comprising steam, hydrogen and carbon monoxide, from an aqueous carbonaceous slurry, the process comprising the steps of: (a) providing a slurry gasifier; (b) supplying the slurry gasifier with an aqueous carbonaceous slurry, an enriched oxygen gas, and optionally a syngas, the slurry comprising carbonaceous matter and water in a weight ratio of from about 5:95 to about 60:40; and (c) reacting the aqueous carbonaceous slurry in the slurry gasifier in the presence of oxygen and under suitable temperature and pressure so as to generate the plurality of gases.

In a fourth aspect, a process is provided for converting a carbonaceous material into a first plurality of gases comprising methane and one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia and other higher hydrocarbons, the process comprising the steps of: providing a gasifier apparatus having a fluidized bed gasifier and a slurry gasifier according to the first aspect; supplying a particulate composition comprising a carbonaceous material and a gasification catalyst to the fluidized bed gasifier, wherein the gasification catalyst, in the presence of steam and under suitable temperature and pressure, exhibits gasification activity whereby the first plurality of gases is formed; supplying an aqueous carbonaceous slurry, enriched oxygen gas and optionally a syngas to the slurry gasifier; reacting the aqueous carbonaceous slurry in the slurry gasifier in the presence of oxygen and under suitable temperature and pressure so as to generate a second plurality of gases comprising steam, hydrogen and carbon monoxide; introducing the second plurality of gases into the fluidized bed gasifier; reacting the particulate composition in the fluidized bed gasifier in the presence of the second plurality of gases, and under suitable temperature and pressure, to form the first plurality of gases; and at least partially separating the first plurality of gases to produce a stream comprising a predominant amount of one of the gases in the first plurality of gases, wherein the gasification catalyst comprises a source of at least one alkali metal and is present in an amount sufficient to provide, in the particulate composition, a ratio of alkali metal atoms to carbon atoms ranging from about 0.01 to about 0.08; and the aqueous carbonaceous slurry comprises a mixture of carbonaceous material and water at a weight ratio ranging from about 5:95 to about 60:40.