Integrated steam gasification and entrained flow gasification systems and methods for low rank fuels

1. A gasification system for supplying syngas in an integrated gasification combined-cycle (IGCC) power plant that uses steam from a heat recovery steam generator (HRSG) heated via exhaust from a gas turbine engine, said system comprising:

a first gasifier for receiving a feed of low rank fuel and gasifying the low rank fuel to produce hydrocarbons and fixed carbon;

a second gasifier for producing a syngas stream using fixed carbon received from said first gasifier;

a cooler for receiving the svngas stream from said second gasifier and cooling the received syngas stream;

a first conduit selectively coupled between said cooler and said first gasifier for recycling at least a portion of the received syngas stream to said first gasifier to facilitate heating low rank fuel within said first gasifier such that the recycled syngas mixes with the hydrocarbons in said first gasifier to produce a hydrocarbon-rich syngas stream; and

a second conduit selectively coupled between the HRSG and said first gasifier for channeling steam from the HRSG to said first gasifier to facilitate heating the low rank fuel in said first gasifier.

2. The system of claim 1 , further comprising a drying unit coupled in flow communication with said first gasifier for drying the low rank fuel before said first gasifier receives the low rank fuel.

3. The system of claim 1 , wherein said cooler is at least one of a quench and a radiant syngas cooler.

4. The system of claim 1 , further comprising a bypass conduit selectively coupled to said first conduit for channeling at least a portion of the recycled syngas around said first gasifier.

5. The system of claim 1 , further comprising a slurry preparation unit selectively coupled in flow communication between said first gasifier and said second gasifier for receiving the fixed carbon and producing a slurry feed for said second gasifier.

6. The system of claim 1 , further comprising a methanation unit selectively coupled to said first gasifier for receiving the hydrocarbon-rich syngas stream from said first gasifier to facilitate producing a synthetic natural gas stream therefrom.

7. An integrated gasification combined-cycle (IGCC) power plant comprising:

at least one gas turbine engine that produces exhaust;

a heat recovery steam generator (HRSG) coupled in flow communication with said at least one gas turbine engine to receive exhaust from said at least one gas turbine engine for heating said HRSG to produce steam;

a steam turbine coupled in flow communication with said HRSG for receiving steam from said HRSG; and

at least one gasification system for supplying syngas to said at least one gas turbine engine, said at least one gasification system comprising:

a first gasifier for receiving a low rank fuel and gasifying the low rank fuel to produce hydrocarbons and fixed carbon;

a second gasifier for producing a syngas stream using fixed carbon received from said first gasifier;

a cooler for receiving the syngas stream from said second gasifier and cooling the received syngas stream;

a first conduit coupled between said cooler and said first gasifier for recycling at least a portion of the received syngas stream to said first gasifier to facilitate heating low rank fuel within said first gasifier such that the recycled syngas mixes with the hydrocarbons in said first gasifier to produce a hydrocarbon-rich syngas stream; and

a second conduit coupled between said HRSG and said first gasifier for channeling steam from said HRSG to said first gasifier to facilitate heating the low rank fuel in said first gasifier.

8. The plant of claim 7 , further comprising a drying unit coupled in flow communication with said first gasifier for drying the low rank fuel before said first gasifier receives the low rank fuel.

9. The plant of claim 7 , wherein said cooler is at least one of a quench and a radiant syngas cooler.

10. The plant of claim 7 , further comprising a bypass conduit coupled to said first conduit for channeling at least a portion of the recycled syngas around said first gasifier.

11. The plant of claim 7 , further comprising a slurry preparation unit coupled in flow communication between said first gasifier and said second gasifier for receiving the fixed carbon and producing a slurry feed for said second gasifier.

12. The plant of claim 7 , further comprising a methanation unit coupled to said first gasifier for receiving the hydrocarbon-rich syngas stream from said first gasifier to facilitate producing a synthetic natural gas stream therefrom.

13. A method of assembling an integrated gasification combined-cycle (IGCC) power plant, said method comprising:

coupling a heat recovery steam generator (HRSG) in flow communication with at least one gas turbine engine to receive exhaust from the at least one gas turbine engine for heating the HRSG to produce steam;

coupling a steam turbine in flow communication with the HRSG for receiving steam from the HRSG;

providing a first gasifier for receiving a low rank fuel and gasifying the low rank fuel to produce hydrocarbons and fixed carbon;

coupling a second gasifier in flow communication with the first gasifier for producing a syngas stream using fixed carbon received from the first gasifier;

coupling a cooler in flow communication with the second gasifier for receiving the syngas stream from the second gasifier and cooling the received syngas stream;

coupling the cooler in flow communication with the first gasifier via a first conduit for recycling at least a portion of the received syngas stream to the first gasifier to facilitate heating low rank fuel within the first gasifier such that the recycled syngas mixes with the hydrocarbons in the first gasifier to produce a hydrocarbon-rich syngas stream; and

coupling the HRSG in flow communication with the first gasifier via a second conduit for channeling steam from the HRSG to the first gasifier to facilitate heating the low rank fuel in the first gasifier.

14. The method of claim 13 , further comprising coupling a drying unit in flow communication with the first gasifier for drying the low rank fuel before the first gasifier receives the low rank fuel.

15. The method of claim 13 , further comprising providing the cooler as at least one of a quench and a radiant syngas cooler.

16. The method of claim 13 , further comprising coupling a bypass conduit to the first conduit for channeling at least a portion of the recycled syngas around the first gasifier.

17. The method of claim 13 , further comprising coupling a slurry preparation unit in flow communication between the first gasifier and the second gasifier for receiving the fixed carbon and producing a slurry feed for the second gasifier.

18. The method of claim 13 , further comprising coupling a methanation unit to the first gasifier for receiving the hydrocarbon-rich syngas stream from the first gasifier to facilitate producing a synthetic natural gas stream therefrom.