Hydrogen production and carbon dioxide recovery from KRW oxygen-blown gasification.

An oxygen-blown KRW integrated gasification combined-cycle plant producing hydrogen, electricity, and supercritical-CO{sub 2}, was studied in a full-energy cycle analysis extending from the cord mine to the final destination of the gaseous product streams. A location in the mid-western US was chosen 160-km from Old Ben No.26 mine which ships 3,866 tonnes/day of Illinois No.6 coal by diesel locomotive. Three parallel gasifier trains, each capable of providing 42% of the plant's 413.5 MW nominal capacity use a combined total of 3,488 tonnes/day of 1/4 inch prepared coal. The plant produces a net 52 MW of power and 3.71 x 10{sup 6} nm{sup 3}/day of 99.999% purity hydrogen which is sent 100 km by pipeline at 34 bars. The plant also produces 3.18 x 10{sup 6} nm{sup 3}3/day of supercritical CO{sub 2} at 143 bars, which is sequestered in enhanced oil recovery operations 500 km away. A CO{sub 2} emission rate of 1 kgCO{sub 2}/kWh was assumed for power purchases outside the fence of the IGCC plant.

Oxygen-blown gasification is used to convert Illinois #6 coal to synthesis gas Fig. 1]. After particulate removal, a shift reactor uses steam to convert the CO component of the gas to C02 and hydrogen (H2). NexL H2S is removed from the stream and processed to produce marketable sulfur. Carbon dioxide is then recovered in a glycol-based process and transported by pipeline for enhanced oil recovery. The gas stream after C02 recovery is processed using pressure-swing adsorption (PSA) to recover Hz at a purity suitable for fuel cells, although there is no restriction on the actual hydrogen end-use. The H2 stream is transported to end users via pipeline, while the residual gas from PSA-a combination of hydrogen, methane, and light hydrocarbons-is used to generate electricity by combustion turbine combined cycle. Part of the electricity generated supplies the internal needs of the plant, and the excess is sent to the grid.

MINJNG
The assumed power plant location is 100~(160 km) by diesel-rail transport from the Old Ben #26 underground mine in Sesser, Illinois. The plant receives 4,112 tons/day (155.4 metric tonnesh) of 2 x 4-in. cord, which is prepared to O x l/4in. with 3.5% weight loss. A summary of thk portion of the power cycle appears in Table 1.

INTEGRATED GASIFICATION COMBINED CYCLE CONVERSION
Previous process design studies to characterize integrated gasification combined-cycle (IGCC) power systems with C02capture technologies were modified using ASPEI@ modeling to evaluate a configuration producing both merchant hydrogen and electricity [1,2,3,4,5]. The power plant configuration employs three parallel gasifier trains, each capable of providing 42% of the plantfs 413.5 MW nominal capacity (for the base case with no COZrecovery.) After modification, the plant produces 131 MMsct7day (3.71 million standard cubic mlday) of 99.999% purity hydrogen at 287.7 Btu/scfi 119.9 KJ/g (LHV) which is sent 100 km by pipeline at 34 brws. At 100% efficiency, tlis could yield 460 MW of power. The plant also produces 112 MMsct7day (3.18 million standard cubic rnlday) of supercntical-C02 at 143 bars, which is sent 500-km for sequestering in enhanced oil recovery. PSA reject gas goes to a turbine cycle to produce 118 MW. After supplying 66 MW for internal power use this yields 52 MW Net power. The designed plant availability is 95%. This is largely reflected in higher projected maintenance costs.

Hz PIPELINE
A 100-km pipeline design was prepared and cost-swere estimated for a high purity hydrogen flow of 3.71 x 106 nm3/day through a 343 mm pipe at 30 bar. There appears to be no economic justification for going to higher pipeline pressures and an internal study of the costs for delivering energy as methane vs. energy as Hz showed a 13% advantage for methane at 500 psi rising to a 46% advantage at 800 psi. Economic assumptions were for an availabdity of 95% and capital recovery of 12% to jield transmission costs of 0.171 $/Mscfi 0.564 $/GJ. It is very important to observe that the high costs of a dedicated pipeline dictate the high availabilities. *Cunent address: Fuel Tech, 1001 Frontenac Rd., Naperville, IL 60563-1746 .

RBSULTS: FULL-ENERGY CYCLE BALANCES
The energy costs of delivering electricity100-km from the IGCC plant~e presented for threecasev the IGCCbase case with no C02 recovery (Table 2); the IGCC system with C02 recovery (Table 3); the IGCC system developed for this study with Hz production and COZrecovery (Table 4). For the B=e-case with no C@ recovery; delivered power was 396-MW full-cycle with emissions of 0.83 kgCOdlcWh. There is a derating with C@ recovery. Delivered power becomes 366-MW full-cycle at 0.20 kgC02/kWh. An additional derating takes place in the present case with both H2 production and C02 recovery where the hydrogen goes to 3-stage solid-oxide fuel cells. The delivered power now becomes 344-MW full-cycle at 0.22 kgCOdkWh. This is the combination of 52-MW busbar at the plant and 298-MW from fuel cells and a steam generator topping cycle.

APPLICATIONS
Carbon dioxide as a supercritical product (143 bar) can be recovered tiom coal gasification and power production.
Where there is an enhanced oil recovery marke~this actually is profitable. The need for high-pipeline utilization is critical. Hydrogen can be recovered at high purity (99.999%) for sale from coal gasification, however the need for high pipeline-utilization is critical. Pressures of 35 bm are optimal. Fuel-cell conversiomefficiencies need to approach 77% to match the base-case output, At presenq solid-oxide fuel cell efficiencies are 53-58%; while alkaline fuel cell efticiencios Me near 7070.   Recent consideration of fill-energy cycle analysis for power production (9) have emphasized the importance of greenhouse gases such as methane and N20 in addition to other than carbon dioxide. Modeling results suggest that a molecule of methane is equivalent to 56 molecules of C02 in its cliite-forcing impacg while each NzO molecule is equivalent to 280 molectdes of carbon dioxide (10). These "equivalent C02 impacts" were used as the basis for Fig. 2 which shows the equivalent C02 emissions to provide 396-MW of electricity 100-km from the IGCC system.