Method for syngas clean-up of semi-volatile organic compounds

1. A method for removing solids and semi-volatile organic compounds (SVOC) from unconditioned syngas having steam contained therein, the unconditioned syngas having a first temperature above a SVOC condensation temperature, the method comprising:

(a) contacting the unconditioned syngas with a solvent and water to reduce the temperature of the syngas to below the SVOC condensation temperature to thereby form an intermediate SVOC-depleted syngas containing steam, and a first mixture comprising SVOC, solids, solvent and water;

(b) removing steam from the intermediate SVOC-depleted syngas containing steam to form: (i) a first depleted syngas stream which has a reduced amount of SVOC relative to the unconditioned gas stream, and (ii) a second mixture comprising SVOC, solids, solvent and water;

(c) separating the water within the second mixture based upon immiscibility so that the SVOC, solids and solvent collect together to form a third mixture above the water;

(d) separating the solids from the SVOC and solvent in a vessel having at least one liquid phase candle filter such that the solids agglomerate on a surface of the candle filter and form a filter cake having density greater than that of water within the vessel;

(e) backflushing the candle filter to loosen the filter cake so that the filter cake sinks into the water within the vessel; and

(f) removing the filter cake from a bottom of the vessel.

2. The method according to claim 1 , comprising using a Fischer-Tropsch liquid product as the solvent.

3. The method according to claim 2 , comprising using a mid-distillate or Medium Fraction Fischer-Tropsch Liquid (MFTL) as the solvent.

4. The method according to claim 1 , comprising:

removing the SVOC and solvent from the vessel through the candle filter; and

backflushing the candle filter using a recirculated portion of the removed SVOC and solvent.

5. The method according to claim 4 , comprising separating the SVOC from the solvent and recycling the solvent, after the SVOC and solvent have been removed from the vessel.

6. The method according to claim 4 , comprising separating the SVOC from the solvent using vacuum flashing, after the SVOC and solvent have been removed from the vessel.

7. The method according to claim 4 , comprising separating the SVOC from the solvent using membranes, after the SVOC and solvent have been removed from the vessel.

8. The method according to claim 1 wherein the unconditioned syngas comprises:

carbon monoxide from about 5 to 35 vol % dry,

hydrogen from about 20 to 60 vol % dry,

methane from about 1 to 15 vol % dry,

SVOC from about 10 to 1,000 ppmV dry, solids from about 0 to 1 wt %, and

VOC from about 500 to 10,000 ppmV dry.

9. The method according to claim 8 wherein the first depleted syngas stream has 80 to 99% less solids and has 95 to 99% less SVOC relative to the unconditioned gas stream.

10. The method according to claim 1 , comprising:

separating the water within the second mixture based upon immiscibility in a decanter;

transferring the third mixture from the decanter to the vessel having the candle filter therein.

11. The method according to claim 1 , wherein the solvent is a biodegradable solvent suitable for biodiesel residue.

12. The method according to claim 1 wherein the first depleted syngas stream has 80 to 99% less solids and has 95 to 99% less SVOC relative to the unconditioned gas stream.

13. A method for removing solids and semi-volatile organic compounds (SVOC) from unconditioned syngas having steam contained therein, the unconditioned syngas having a first temperature above a SVOC condensation temperature, the method comprising:

(a) contacting the unconditioned syngas with water to reduce the temperature of the syngas to below the SVOC condensation temperature to thereby form an intermediate SVOC-depleted syngas containing steam, and a first mixture comprising SVOC, solids and water;

(b) removing steam from the intermediate SVOC-depleted syngas containing steam to form: (i) a first depleted syngas stream which has a reduced amount of SVOC and solids relative to the unconditioned gas stream, and (ii) a second mixture comprising SVOC, solids and water;

(c) separating the water within the second mixture based upon immiscibility so that the SVOC and solids collect together to form a third mixture separate from the water;

(d) agglomerating the solids together to form a agglomerated cake having density greater than that of water; and

(e) applying mechanical pressure to the agglomerated cake to remove residual liquid therefrom to form a liquid depleted solids.

14. The method according to claim 13 wherein the unconditioned syngas comprises:

carbon monoxide from about 5 to 35 vol % dry,

hydrogen from about 20 to 60 vol % dry,

methane from about 1 to 15 vol % dry,

SVOC from about 10 to 1,000 ppmV dry, solids from about 0 to 1 wt %, and

VOC from about 500 to 10,000 ppmV dry.

15. The method according to claim 14 wherein the first depleted syngas stream has 80 to 99% less solids and has 95 to 99% less SVOC relative to the unconditioned gas stream.

16. The method according to claim 13 , wherein:

in step (a), the unconditioned syngas is contacted with water and a solvent; and

the solvent is a Fischer-Tropsch liquid product.

17. The method according to claim 16 , comprising using a mid-distillate or Medium Fraction Fischer-Tropsch Liquid (MFTL) as the solvent.

18. The method according to claim 13 wherein the first depleted syngas stream has 80 to 99% less solids and has 95 to 99% less SVOC relative to the unconditioned gas stream.

19. The method according to claim 13 , comprising:

separating the water within the second mixture based upon immiscibility in a decanter;

transferring the third mixture from the decanter to the vessel having the candle filter therein.

20. The method according to claim 13 , wherein:

in step (a), the unconditioned syngas is contacted with water and a solvent; and

the solvent is a biodegradable solvent suitable for biodiesel residue.