Processes for gasification of a carbonaceous feedstock
First Claim
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1. A process for generating a plurality of gaseous products from a carbonaceous feedstock and recovering a methane product stream, the process comprising the steps of:
- (a) supplying a carbonaceous feedstock, an oxygen-rich gas stream, an alkali metal gasification catalyst, and steam to a catalytic gasifier;
(b) reacting the carbonaceous feedstock in the catalytic gasifier in the presence of steam, hydrogen, carbon monoxide, the oxygen-rich gas stream and the alkali metal gasification catalyst, and at a temperature of from about 450°
C. to about 800°
C. and pressure of from about 400 psig to about 1000 psig, to form a first gas stream comprising a plurality of gaseous products comprising methane, carbon dioxide, hydrogen, carbon monoxide and hydrogen sulfide, wherein the first gas stream comprises at least 50 mol % methane plus carbon dioxide based on the moles of methane, carbon dioxide, carbon monoxide and hydrogen in the first gas stream;
(c) optionally reacting at least a portion of the carbon monoxide and at least a portion of the hydrogen present in the first gas stream in a catalytic methanator in the presence of a sulfur-tolerant methanation catalyst to produce a methane-enriched first gas stream;
(d) removing a substantial portion of the carbon dioxide and a substantial portion of the hydrogen sulfide from the first gas stream (or the methane-enriched first gas stream if step (c) is present) to produce a second gas stream comprising a substantial portion of the methane from the first gas stream (or the methane-enriched first gas stream if step (c) is present);
(e) optionally, if the second gas stream comprises hydrogen and greater than about 100 ppm carbon monoxide, reacting the carbon monoxide and hydrogen present in the second gas stream in a catalytic methanator in the presence of a methanation catalyst to produce a methane-enriched second gas stream; and
(f) recovering the second gas stream (or the methane-enriched second gas stream if step (e) is present),wherein;
(i) at least one of step (c) and step (e) is present,(ii) the second gas stream (or the methane-enriched second gas stream if step (e) is present) is the methane product stream, or the second gas stream (or the methane-enriched second gas stream if step (e) is present) is purified to generate the methane product stream;
(iii) a solid char product is produced in step (b), which is periodically withdrawn from the catalytic gasifier; and
(iv) carbon monoxide in the first gas stream is subjected to a water-gas shift reaction in the presence of an aqueous medium to convert a portion of the carbon monoxide to carbon dioxide and to increase the fraction of hydrogen in the first gas stream.
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Abstract
The present invention relates to processes for preparing gaseous products, and in particular, methane via the catalytic gasification of carbonaceous feedstocks in the presence of steam and an oxygen-rich gas stream. The processes comprise using at least one catalytic methanator to convert carbon monoxide and hydrogen in the gaseous products to methane and do not recycle carbon monoxide or hydrogen to the catalytic gasifier.
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Citations
21 Claims
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1. A process for generating a plurality of gaseous products from a carbonaceous feedstock and recovering a methane product stream, the process comprising the steps of:
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(a) supplying a carbonaceous feedstock, an oxygen-rich gas stream, an alkali metal gasification catalyst, and steam to a catalytic gasifier; (b) reacting the carbonaceous feedstock in the catalytic gasifier in the presence of steam, hydrogen, carbon monoxide, the oxygen-rich gas stream and the alkali metal gasification catalyst, and at a temperature of from about 450°
C. to about 800°
C. and pressure of from about 400 psig to about 1000 psig, to form a first gas stream comprising a plurality of gaseous products comprising methane, carbon dioxide, hydrogen, carbon monoxide and hydrogen sulfide, wherein the first gas stream comprises at least 50 mol % methane plus carbon dioxide based on the moles of methane, carbon dioxide, carbon monoxide and hydrogen in the first gas stream;(c) optionally reacting at least a portion of the carbon monoxide and at least a portion of the hydrogen present in the first gas stream in a catalytic methanator in the presence of a sulfur-tolerant methanation catalyst to produce a methane-enriched first gas stream; (d) removing a substantial portion of the carbon dioxide and a substantial portion of the hydrogen sulfide from the first gas stream (or the methane-enriched first gas stream if step (c) is present) to produce a second gas stream comprising a substantial portion of the methane from the first gas stream (or the methane-enriched first gas stream if step (c) is present); (e) optionally, if the second gas stream comprises hydrogen and greater than about 100 ppm carbon monoxide, reacting the carbon monoxide and hydrogen present in the second gas stream in a catalytic methanator in the presence of a methanation catalyst to produce a methane-enriched second gas stream; and (f) recovering the second gas stream (or the methane-enriched second gas stream if step (e) is present), wherein; (i) at least one of step (c) and step (e) is present, (ii) the second gas stream (or the methane-enriched second gas stream if step (e) is present) is the methane product stream, or the second gas stream (or the methane-enriched second gas stream if step (e) is present) is purified to generate the methane product stream; (iii) a solid char product is produced in step (b), which is periodically withdrawn from the catalytic gasifier; and (iv) carbon monoxide in the first gas stream is subjected to a water-gas shift reaction in the presence of an aqueous medium to convert a portion of the carbon monoxide to carbon dioxide and to increase the fraction of hydrogen in the first gas stream. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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Specification