Cleaningup Coal

Coal has the reputation of being dirty, largely based on criteria air emissions. Table 2.5 gives the commercially demonstrated and projected emissions performance of PC and IGCC technologies [14, 22]. Electrostatic precipitators (ESP) or bag houses are employed on all U.S. PC units, and particulate matter (PM) emissions are typically low. Improved ESP or wet ESP can reduce PM emissions further, but at a cost. Flue gas desulfurization (FGD) is applied on about one-third of U.S. PC capacity, and thus "typical (average) U.S." SOx emissions (Table 2.5) are quite high. "Best commercial" performance in Table 2.5 gives demonstrated, full commercial-scale levels of emissions reductions [14, 22, 23]. Additional reductions are possible. With CO2 capture, SOx emissions levels are expected to be even further reduced [24]. The best commercial emissions performance levels with IGCC is threefold to tenfold lower (Table 2.5). IGCC with CO2 capture should have even lower emissions. In addition, IGCC produces a dense, vitreous slag that ties up most of the toxic components in the coal mineral matter so that they are not easily leached [25],

Table 2.5 Commercially demonstrated and projected emissions performance with CO2 capture for PC and IGCC power generation [9, 10]

Technology Case

Particulates Lb/MM Btu

Lb/MM Btu

Lb/Mx M Btu

Mercury % removed

PC plant

IGCC plant

Typical

Best commercial Design w CO2 cap.

Best commercial Design w CO2 cap.

0.02

0.001 0.001

0.22

0.11

Table 2.6 Incremental cost of advanced PC generation emissions control vs. no emissions control [9]

Capital costa [$/kWe]

O&M [0/kWe-h]

COEb [0/kWe-h]

PM control

55

0.20

0.31

NO

40

0.15

0.23

SO2

200

0.30

0.71

Incremental cost vs. no control

295

0.65

1.25c

a Incremental capital costs are for a new-build plant b Incremental COE impact for Illinois #6 coal with 99.5% PM reduction, 99.4% SOx reduction, and >90% NOx reduction c When this is ¬°idded to the "no-control" COE for SC PC, the total COE is 5.80/kWe-h a Incremental capital costs are for a new-build plant b Incremental COE impact for Illinois #6 coal with 99.5% PM reduction, 99.4% SOx reduction, and >90% NOx reduction c When this is ¬°idded to the "no-control" COE for SC PC, the total COE is 5.80/kWe-h and IGCC uses about 30% less water than supercritical PC. Although this discussion does not address the whole life-cycle for coal's environmental footprint, coal-use in the electricity generation step can, in fact, be very much cleaner than it is today, and CO2 emissions can also be markedly reduced.

The estimated cost to achieve the emissions reductions used in the PC design basis, which is somewhat better than today's best demonstrated commercial performance vs. no emissions control is about 1.250/kWe-h (see Table 2.6) out of about 5.80/kWe-h total COE or about 20% [26-29]. CO2 capture and recovery will increase the COE more than this, about 40/kWe-h, based on today's PC technology. Cost reductions can be expected when this technology begins to be commercially practiced.

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