Hydromethanation of a carbonaceous feedstock
The present invention relates generally to processes for hydromethanating a carbonaceous feedstock in a hydromethanation reactor to a methane product stream and a char by-product, and more specifically to removal of the char by-product from the hydromethanation reactor.
1. A process for generating a methane-enriched raw product gas stream and a gas-stripped char stream from a non-gaseous carbonaceous material, the process comprising the steps of:
(a) preparing a carbonaceous feedstock from the non-gaseous carbonaceous material;
(b) introducing the carbonaceous feedstock and a hydromethanation catalyst into a hydromethanation reactor, wherein the hydromethanation reactor comprises a char-withdrawal standpipe having a withdrawal end extending into the hydromethanation reactor and a discharge end extending out of the hydromethanation reactor;
(c) reacting the carbonaceous feedstock in the hydromethanation reactor in the presence of carbon monoxide, hydrogen, steam and hydromethanation catalyst, and at an operating temperature of at least about 1000° F. (at least about 538° C.) and an operating pressure of at least about 250 psig (about 1825 kPa) to produce a methane-enriched raw product gas and a solid by-product char;
(d) withdrawing a stream of the methane-enriched raw product gas from the hydromethanation reactor as the methane-enriched raw product gas stream, wherein the methane-enriched raw product gas stream comprises methane, carbon monoxide, hydrogen, carbon dioxide, hydrogen sulfide, steam and heat energy;
(e) withdrawing a stream of the solid by-product char from the hydromethanation reactor via the withdrawal end of the char-withdrawal standpipe, wherein the stream of solid by-product char flows from the withdrawal end to the discharge end of the char-withdrawal standpipe, and wherein the withdrawn solid by-product char comprises an entrained gas;
(f) feeding a stripping gas into the char-withdrawal standpipe such that the stripping gas flows in a countercurrent direction to the flow of the stream of by-product char within the char-withdrawal standpipe to generate (1) a stripped gas stream enriched in the entrained gas and (2) a gas-stripped char stream depleted in the entrained gas;
(g) feeding the stripped gas stream into the hydromethanation reactor via the char-withdrawal standpipe;
(h) feeding the gas-stripped char stream to a screw discharge unit in communication with the discharge end of the char-withdrawal standpipe;
(i) discharging the gas-stripped char stream from the screw discharge unit at a superatmospheric pressure.
2. The process of claim 1 , wherein the screw discharge unit is a cooling screw discharge unit, and the gas-stripped char stream is cooled in the cooling screw discharge unit to generate a cooled char stream.
3. The process of claim 2 , wherein the cooling char stream is discharged from the cooled screw discharge unit at a temperature of about 700° F. (about 371° C.) or less.
4. The process of claim 2 , wherein the cooling screw discharge unit cools the gas-stripped char stream using water or steam as a heat exchange medium.
5. The process of claim 4 , wherein the cooling screw discharge unit comprises a hollow screw member and a housing surrounding the hollow screw member, wherein the heat exchange medium is circulated through the hollow screw member.
6. The process of claim 1 , wherein the stripping gas comprises steam, carbon dioxide or both.
7. The process of claim 6 , wherein the stripping gas additionally comprises oxygen.
8. The process of claim 1 , wherein the gas-stripped char stream is discharged from the screw discharge unit into a quench tank and contacted with a quench medium in the quench tank.
9. The process of claim 1 , wherein the gas-stripped char stream is discharged from the screw discharge unit at a superatmospheric pressure of at least of at least about 75% of the operating pressure of the hydromethanation reactor.
10. The process of claim 8 , wherein the gas-stripped char stream is discharged from the screw discharge unit at a superatmospheric pressure of at least about 75% of the operating pressure of the hydromethanation reactor.
11. The process of claim 2 , wherein the cooled char stream is discharged from the screw discharge unit into a quench tank and contacted with a quench medium in the quench tank.
12. The process of claim 2 , wherein the cooled char stream is discharged from the screw discharge unit at a superatmospheric pressure of at least about 75% of the operating pressure of the hydromethanation reactor.
13. The process of claim 11 , wherein the cooled char stream is discharged from the screw discharge unit at a superatmospheric pressure of at least about 75% of the operating pressure of the hydromethanation reactor.
14. The process of claim 1 , wherein in step (c) the carbonaceous feedstock is reacted in the hydromethanation reactor in the presence of carbon monoxide, hydrogen, steam, oxygen and hydromethanation catalyst.
15. The process of claim 1 , wherein in step (c) the operating temperature is to about 1500° F. (about 816° C.).
16. The process of claim 1 , wherein the operating pressure is to about 1000 psig (about 6996 kPa).