Las dos últimas reformas adoptadas en el caso español

The previous chapters compared the use of natural gas and coal for a specific use (electricity generation or liquid fuel production). Such comparisons can help us understand which of these two fuels is better suited for each use. It does not tell us, however, which is a better use of the fuel. In other words, the comparisons presented do not tell us if it is better to use coal for electricity or coal for the production of

transportation fuels. Such a comparison is not easy. Although in both cases coal is used for energy production, a Btu of electricity is used very differently than a Btu of gasoline. In this chapter, a comparison of coal/NG uses is presented. Here I concentrate on

comparing GHG emissions produced in each use. These emissions have been normalized to the energy content of the fuel used; so they are presented in terms of pounds of CO2

equivalents per million Btu of fuel used. Other parameters that could be included in a comparison of end use are: What is the resource depletion potential of each use? Are there viable alternative fuels that can meet the energy demands of the sector?

5.1

Comparing Coal for Electricity Generation and for the Production of

Transportation Fuels

Figure 31 shows the life cycle GHG emissions of coal used for the production of diesel, gasoline and electricity. It can be seen that if CCS were not available, using coal for any of these purposes would basically generate the same life cycle GHG emissions. This is because a Btu of coal will always have the same carbon content, regardless of the use. The same is not true in the case where CCS is available. When using coal for electricity, CCS performed at the plant can capture roughly 90% of the carbon in the coal. When producing transportation fuels, however, even if 90% CCS is available at the FT-plant, most of the carbon in the coal is transferred to the liquid fuels, which are then combusted

(without CCS) in regular vehicles. Thus, the effective CCS rate when producing liquid fuels is approximately 50%

Figure 31: Life Cycle GHG Emissions of Coal Consumption. The error bars presented in this figure represent the uncertainty/variability

associated with the upstream GHG emissions of coal.

5.2

Comparing Natural Gas for Electricity Generation and the

Production of Transportation Fuels

Similarly to the comparison of coal for electricity generation and coal for the production of transportation fuels, Figure 32, shows the comparison of uses of domestic natural gas. In this graph the use of Qatari or Malaysian natural gas for the production of liquid fuels that are then imported to the U.S. are also included. CNG is included for completeness. Because in the CNG life cycle there is no opportunity for CCS, no bar is shown for a CCS scenario. Notice than CNG has slightly higher life cycle GHG emissions than FT- liquids and than electricity. Even though the carbon content of natural gas is constant regardless of how it is used, the use of electricity in the CNG life cycle adds some carbon

to the life cycle of this natural gas. If CCS is available, it is better to use the natural gas to produce electricity.

Figure 32: Life Cycle GHG Emissions of "Domestic" Natural Gas Consumption. The error bars presented in this figure represent the uncertainty/variability associated with the upstream GHG emissions natural gas. NA-NG: North American

Natural Gas. GTL: Gas-to-Liquids. CNG: Compressed Natural Gas

Figure 33 shows the comparison of consumption of imported natural gas. In this figure, imported GTL fuels are also included. Notice that if no CCS is available, it is better to produce liquid fuels than to produce electricity when using LNG. This was also observed, to a smaller extent, in the comparisons of domestic natural gas consumption (Figure 32). The slight advantage of GTL fuels over electricity is because GTL plants without CCS also generate electricity, and the emissions shown below only represent the emissions allocated to the production of the diesel and the gasoline. If CCS is available, however, it is better to use these imported resources to produce electricity, where the capture rate is 90% (compared to the effective CCS rate of GTL fuels of approximately 25%).

The most significant result from the graph is that when no CCS is available, importing refined GTL fuels has the lower life cycle GHG emissions of all the consumption

alternatives. This is significant because Qatar has significant stranded natural gas resources. Thus, the better way (in terms of GHG emissions) for Qatar to export these resources to the U.S. market in the next 20 years (a period during which CCS will probably not be available) is to produce GTL fuels rather than shipping LNG. This decision however, must be weighted against the potential to be locked in a path that does not give the best life cycle GHG emissions once CCS becomes available.

Figure 33: Life Cycle GHG Emissions of Imported Natural Gas Consumption. The error bars presented in this figure represent the uncertainty/variability associated with the upstream GHG emissions natural gas. LNG: Liquefied Natural

6 CONTRIBUTION, GENERAL CONCLUSIONS AND