Integration and Interpretation 361 Fuel Focused Costs and Emissions

Figure 3.9 shows the range of fuel costs given in $ per gallon of gasoline equivalent (gge) for the thermochemical technologies and process configurations evaluated. The scale economics of CTL and the low cost of coal contribute to the relatively low liquid fuel cost for FT synthesis even thought the process requires a large capital investment. These cost estimates are internally consistent; but as a group, they depend on the capital and operating cost assumptions and the operating performance.

The breakeven crude oil price is about $56/bbl for CTL-FT-RC operated in the CO2 venting configuration. The fuel cost and breakeven crude oil price are about $1.60/gge and $65/bbl respectively, or about 10% higher, in the case of FT with

A

Fig. 3.9 Cost of liquid transportation fuels produced from coal (CTL), biomass (BTL), and coal plus biomass (CBTL) by Fischer-Tropsch (FT) and by methanol synthesis followed by methanol to gasoline (MTG) operated in the recycle mode with either venting the CO2 (V) or geologic storage of CO2 (CCS)

CCS than if the CO2 is vented. The resultant CO2eq avoided cost is $11 per tonne CO2eq. In the case of methanol synthesis followed by methanol to gasoline (MTG), the capital costs are lower because of higher product selectivity, reduced process complexity, and resultant reduced costs associated with the MTG technology, and the cost of the fuel produced is lower on an energy equivalent basis. The CO2eq avoided cost is also about $10/tonne. Sale of LPG rather than producing power from it, could further reduce the cost of gasoline produced.

Fuels produced from biomass only are significantly more costly because of the smaller plant size and higher biomass cost (Fig. 3.9). In this case, the breakeven crude oil price is about $125/bbl ($3.1/gge fuel) and $140/bbl ($3.3/gge fuel) for BTL with venting and with CCS respectively. The CO2eq avoided cost is about $20/ tonne CO2eq in this case, driven by the higher costs. When coal and biomass are combined in the same plant, the gains in economies of scale and in reduced feedstock cost driven by the addition of coal result in reduced liquid transportation fuel cost ($2.30/gge with CO2 venting and $2.50/gge with geologic storage) as shown in Fig. 3.9.

Figure 3.10 shows the full LC GHG emissions for transportation fuels produced by the process configurations discussed above for coal, biomass, and coal plus biomass. LC GHG emissions for petroleum-based gasoline and diesel are included for reference. The figure illustrates that CTL-RC without CCS (CTL-V, FT) produces almost twice the LC CHG emissions as petroleum-derived fuels; and that when CO2 is geologically stored (CCS), the LC GHG emissions are essentially equivalent to those from the same fuels produced from petroleum. LC GHG emissions from BTL (BTL-V, FT) can be negative without CCS due to unburned

Diesel Gasoline CBTL-CCS,FT | BTL-V,FT

CTL-MTG,CCS

CTL-V,MTG

Life Cycle Greenhouse Gas Emissions, kg CO2eq/gge

Fig. 3.10 Full life-cycle greenhouse gas emissions for transportation fuels produced from coal, biomass, and coal plus biomass using the indicated technologies, operated in the recycle mode, without and with CO2 storage carbon that is permanently sequestered with the char. With CCS, BTL (BTL-CCS, FT) has a large negative LC GHG emissions footprint (—16 kg CO2eq/gge) because CO2 is being permanently removed from the atmosphere through geologic storage.

None of these biomass situations involve the potential reductions offered by the storage of carbon in the soil via root mass, which require more controlled agricultural practices. Soil carbon loss can also occur in biomass production, making the LC GHG problem worse. However, this situation is hard to predict, monitor, and verify, and as such, has not been included here; although in the end, soil carbon storage may be important in enhancing CO2 reductions.

OT configurations have a lower cost of liquid transportation fuels (Table 3.6) than their equivalent process using recycle and optimized for high liquid transportation fuels production (Table 3.5). OT configurations also produce large amounts of electricity to export to the grid (Table 3.6). Although there are many ways to allocate the CO2 emissions from the process plant, the approach used here was to calculate a greenhouse gas index (GHGI) which is the ratio of the total LC GHG emissions for the synthetic route to the total LC GHG emissions reduced by replacing the products produced by the current petroleum fuel/electricity route. Exported electricity was assumed to replace electricity with LC GHG emission equal to that generated by supercritical PC which vents CO2. For cost calculations, the exported electricity was valued at 6 0/kWe-h [18], which was the average generating cost of electricity in the U.S in 2007 [39].

Figure 3.11 [40] gives the GHGI for CTL and CBTL in several configurations and for CBTL with several biomass to coal feed ratios (energy %). Bars above 1.0

Fig. 3.11 GreenHouse gas index (GHGI) for several coal and coal plus biomass to liquid transportation fuels and electricity (Courtesy Williams and coworkers [20, 40])

result in increased LC GHG emissions vs. business as usual; bars below 1.0 result in reduced LC GHG emissions relative to business as usual. The figure indicates the important role that CBTL with CCS could play in decarbonizing the transportation sector and the electricity sector simultaneously. CBTL-RC-CCS and CBTL-OT-CCS with about 40% (energy basis) biomass in the feed produces essentially zero carbon transport fuels and carbon-free electricity. As indicated in the figure, different configurations provide different levels of LC GHG reduction allowing a country to balance addressing the issues of GHG emissions, energy supply, energy security, and crude oil replacement.

CTL-OT with CCS has a GHGI of 0.7 and thus produces only 70% of the LC GHG emissions of the products (transport fuels and electricity) produced conventionally. It produces lower carbon transportation fuels and partially decarbonized electricity. The extent attributable to each product depends on the allocation used. Furthermore, a high carbon price is not required to induce it, and the technology is effectively ready for commercial implementation today. This approach could address petroleum imports, energy security, and energy diversity while reducing CO2 emissions from the transportation sector. The lower carbon electricity is competitive with that from a PC or IGCC with venting, and it could be equivalent to IGCC with CCS if the liquid fuels were allocated the CO2eq of petroleum-derived fuels, making it a potential substitute for decarbonized baseload coal plants. A major challenge is the lack of interest shown by power companies in liquid fuels production and the resistance of the integrated oil companies in getting into the power business. This may change in the future.

As discussed in Chap. 2, supercritical CO2 has been used in enhance oil recovery for over 30 years, and there are three large-scale commercial applications of geologic CO2 storage that also have many years of successful experience. However, there is more work to do on CCS to answer questions and to gain public and political acceptance. The above analysis shows the importance of CCS in addressing our energy and CO2 challenges, and it assumes that the technology will be broadly available with careful siting.

For CBTL (with about 40% biomass on an energy basis) with CCS, both liquid transportation fuels and electricity are effectively decarbonized (Table 3.6, Fig. 3.11). CBTL combines the limited biomass resource with coal to produced decarbonized transportation fuels and decarbonized, base-load electricity at a reasonable cost and a low LC GHG emissions price. For biomass alone, the LC GHG emission rate is highly negative, but the cost of the produced fuel is higher. The CO2eq avoided cost for the OT mode is about twice as high as for the high liquid transportation fuels cases ($20/tonne CO2eq for coal once through vs. $11 per tonne CO2eq avoided for coal to liquids via recycle). The once-through cases have a lower cost of CO2eq avoided than the cost of CO2eq avoided for power generation. For IGCC, the CeO2eq avoided cost is ~$40/tonne CO2eq (IGCC-venting to IGCC-CCS). Once-through processes with coal, coal plus biomass, and biomass, which produce large fractions of both transportation fuels and electricity, appear to be an important approach for decarbonizing both electricity and liquid transportation fuels and in doing so at an acceptable cost.

Figure 3.12 shows the impact of LC GHG (CO2eq) price on the breakeven crude oil price of the liquids produced by the various feedstock and process combinations. At zero CO2eq price, CTL-OT-V produces the lowest product cost, and CTL-RC-V is next, both venting the CO2. However, the transportation fuel cost for CTL-OT-CCS is equivalent to the CTL-RC-V option at a zero CO2eq price and decreases with increasing CO2eq price; whereas the transportation fuel cost for CTL-RC-V increases with increasing CO2eq price.

The CBTL options in Fig. 3.12 involve a feed mix of about 60%/40% coal to biomass on an energy basis. CBTL2 is a case that provides liquid transportation fuels that have the same LC-GHG emissions as petroleum-derived liquid fuels and involves roughly 92%/8% coal to biomass on an energy basis. Technologies involving biomass also bring with them the opportunity to pick the option and to adjust the feedstock ratio to optimize cost as the price of CO2eq increases. The most expensive fuel-cost technology at zero CO2eq price, BTL-RC, becomes the cheapest when the price of CO2eq reaches $90/tonne (Fig. 3.12). The point at which lines cross in Fig. 3.12 indicate the LC GHG price at which economics would drive a shift from one technology to the other. The IEA projects a LC GHG emissions price of $90/ tonne of CO2eq by 2030 to realize 550 ppm stabilization [41].

It is also important to compare biomass-based hydrocarbon fuels produced by thermochemical routes, such as Fischer-Tropsch, with biomass-based fuels produced by biochemical routes, primarily cellulosic ethanol. With the accuracy that

GHG emissions price, $/tonne CO2eq

Fig. 3.12 Breakeven crude oil price for Fischer-Tropsch fuels produced by the various combinations of feedstock and process configurations as a function of GHG emissions price (Courtesy Williams and coworkers [18])

GHG emissions price, $/tonne CO2eq

Fig. 3.12 Breakeven crude oil price for Fischer-Tropsch fuels produced by the various combinations of feedstock and process configurations as a function of GHG emissions price (Courtesy Williams and coworkers [18])

the cost numbers are known from the data available, the cost of hydrocarbon fuels produced from biomass by gasification/FT synthesis and ethanol produced by biochemical conversion of cellulose are similar on an energy equivalent basis. Effective commercial demonstration programs of these two different biomass-based technologies would provide the cost, engineering and operating data that are required to move forward with appropriate technology commercialization.

Using available data (for example [17]), the cost of liquid transportation fuels on a gasoline energy equivalent basis is plotted in Fig. 3.13 as a function of LC GHG (CO2eq) price. For the biochemical route the cost range is from $3 to $4 per gge at zero CO2eq price. Starting at the mid-point ($3.55/gge) the cost is almost independent of the GHG emissions price. For BTL-RC-V the transportation fuel cost follows the biochemical-produced fuel cost but decreases slightly. The transportation fuel cost for thermochemical conversion of biomass and biomass plus coal to liquids with CCS decreases more rapidly as shown by BTL-RC-CCS and CBTL-OT-CCS. The cross-over point for gasoline produced from crude oil at $80/bbl is about $30/ tonne CO2eq price for CBTL-OT-CCS. Costs favor the thermochemical conversion options, particularly as the GHG emissions price increases because CCS stores more CO2 and more cheaply. The CBTL-OT-CCS option is the least costly and can provide zero-carbon liquid transportation fuel and decarbonized base-load electricity, each at a competitive cost. If this fuel production were coupled with future highly efficient hybrid electric vehicle (HEV) technology, it could provide a route toward significant reductions in GHG emissions from the light-duty vehicle fleet and in petroleum imports.

§■ 0 10 20 30 40 50 60 70 80 90 100 GHG Emissions Price, $ per tonne of CO2eq

§■ 0 10 20 30 40 50 60 70 80 90 100 GHG Emissions Price, $ per tonne of CO2eq

Fig. 3.13 Estimated cost of liquid transportation fuels produced from switchgrass by biochemical conversion and by thermochemical conversion routes as a function of GHG emissions price [14, 17] (Courtesy Williams [40])

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