Low greenhouse gas emission transport fuels: the impact of CO2 capture and storage on selected pathways

Publication Overview

In assessing the environmental impact of transport technology options, it is necessary to consider the impact of each of the stages of fuel extraction, refining, distribution and use in the vehicle. This needs to be done in a systematic way for the ‘novel’ systems considered, as well as for reference cases. The approach requires a form of life-cycle analysis which, in the transport, field has come to be known as Well-to-Wheels analysis (WTW). A subset of this analysis covers the production of the fuel up to the point where it is dispensed into the vehicle’s fuel tank – this is known as Well-to-Tank analysis; the second part of the chain is Tank-to-Wheels analysis (WTT and TTW respectively). In the main report the component WTT and TTW data are discussed in depth but in this overview the emphasis is on the overall WTW results. The study is set in the Netherlands; representative of a European location. The vehicle fleet for each type of fuel is assumed to be large enough that economies of scale can be expected in distribution and in vehicle costs. Some consideration is also given to how the results would be affected if set in a North American location.

Publication Summary

The main findings of this study have been presented separately for fuel supply to the retail outlet (Well to Tank  -WTT) and the full Well to Wheels  (WTW) pathway. The main conclusions related to fuel supply (WTT) are:

• WTT energy expenditure of all alternative fuel pathways are greater than gasoline, only CNG from remote natural gas is comparable. Values of energy expended are estimated to be in the range 0.25 – 2.0 MJ per MJ fuel supplied.  This compares with a figure of 0.14 MJ for gasoline.
• WTT energy expenditure of de-carbonisation routes (hydrogen and electricity) are at the top end of the range.
• CCS increases the energy expended in de-carbonisation routes for coal and biomass pathways by between 15 – 40%.
• Hydrogen production from natural gas is relatively efficient (ca 75% compared with ca 50 % for coal), and gas transmission and hydrogen compression losses are of similar magnitude to process losses. As a result, the impact of CCS is less apparent over the entire pathway.  The energy penalty of CCS for this pathway is only ca 8%.
• CNG and synthetic fuel pathways remove only a small percentage of input carbon and as a result, the energy penalty for CCS is marginal (1-8%).
• Greenhouse gas emissions without CO₂ capture mirror the trends for energy expenditure in all cases apart from biomass. As a result, use of CO₂ capture provides a significant net removal of CO₂ for biomass pathways. 
• CO₂ capture applied to non-biomass pathways reduces GHG emissions in most cases to levels within a range of 11 – 40 g CO2 eq./MJ fuel supplied. The one exception is coal to electricity (75 g CO₂/MJ electricity supplied), where the relatively high emissions from coal supply are amplified by the low efficiency of power generation.
• Emissions from CNG and synthetic fuels produced from remote gas are, with CCS, in the range 11 – 13 g CO2 eq./MJ fuel supplied, which are comparable with the gasoline pathway (12.8 g CO2 eq./MJ fuel supplied).
• The estimated costs of fuels produced from remote gas are comparable with gasoline on an energy basis. De-carbonised fuels produced from fossil fuels are 1.5 to 2.5 times more expensive than gasoline.  Fuels produced from biomass are the most expensive – 3-5 times that of gasoline.  Biomass has higher feedstock costs and does not benefit from economies of scale to the same extent as fossil fuels.
• Fuel supply costs are most sensitive to primary fuel costs and plant capex.
• CCS adds about a 15- 25% cost penalty to the cost of supplying de-carbonised fuels. The cost penalty is less (ca 2- 10%) for fuels from remote natural gas.
• The main conclusions related to the full fuel cycle (Well to Wheels) are:
• Electric vehicles with a reduced driving ranger (ca 350 km) are estimated to have a vehicle (Tank to Wheels) energy consumption of 46MJ/ 100km, approximately on quarter of the equivalent 2010 gasoline vehicle (190 MJ/100km)
• Electric vehicles and fuel cell vehicles powered by hydrogen from natural gas have the lowest overall WTW energy consumption ca. 130 – 170 MJ/100km, even with CCS. CCS adds a penalty of up to 25%.  WTW All of these pathways are less energy intensive than the gasoline reference pathway (218 MJ/100km travelled). 
• Hydrogen fuelled ICEs, where the hydrogen is derived from coal and biomass have the highest WTW energy consumption ca. 400 – 550 MJ/100km travelled, although virtually all of the energy consumption in the biomass pathway is renewable.
• WTT energy consumption for CNG and synthetic fuels from remote natural gas are a greater than the gasoline reference pathway apart from the case of CNG fuelled hybrid vehicles. Of these particular pathways, FT diesel is the most energy intensive (312 – 379 MJ/100km travelled) because of the relatively low efficiency of the fuel manufacturing process.  Improvements in process energy efficiency and selectivity to diesel could reduce WTW energy consumption to a level comparable with the other remote gas pathways.
• For all pathways, vehicle energy efficiency is the key determinant of the WTW energy consumption. Vehicle energy efficiency determines the energy ranking of each pathway, and differences in vehicle technology exceed the penalties from CCS. 
• WTW GHG emissions follow the trends noted for energy expenditure, although biomass as a renewable energy supply has by definition the lowest net GHG emissions.
• Electric vehicles and fuel cell vehicles fuelled by hydrogen from natural gas generally have up to 25% lower WTW GHG emissions than the gasoline reference pathway, even without CCS.
• FT diesel without CCS has between 2 – 24% higher WTW GHG emissions than the gasoline reference depending on the vehicle type. This finding is a direct result of the JEC conclusion that gasoline vehicle energy efficiency will approach that of diesel engines for 2010 technology.
• With CCS, all decarbonisation routes (electricity and hydrogen) show significant emission reductions over the gasoline reference case. Fossil fuel based routes provide for reductions of between 60 –80% of GHG emissions over the reference case.  Biomass routes benefit from a net removal of CO₂, but as noted previously these figures should be treated with caution, since an increase in vehicle energy efficiency reduces the net removal of CO₂. 
• For CNG and DME from remote natural gas, CCS provides an additional 5-10 % GHG reduction, making the 30–40% benefit over the reference case. FT diesel with CCS shows a small benefit (5 – 22%) over the reference case.  Since the FT produces fuel with a relatively high carbon content and because the 2010 fuel efficiency benefit of diesel vehicles is eroded relative to the gasoline reference, CCS can only have a limited impact on GHG emissions relative to gasoline.
• CO₂ avoidance costs are an order of magnitude greater than those expected for the cost of traded CO₂ in the immediate future, or costs estimated for avoiding CO₂ emissions in fuels manufacturing. The reason for this is that running costs are dominated by vehicle investment costs at typical levels of utilisation (16,000 km/year).  At higher levels of vehicle utilisation (>40,000km/yer) fuel costs become a more significant factor.
• Avoidance costs are lowest for hydrogen ICE vehicles, where the hydrogen is derived from biomass with or without CCS, and for CNG vehicles. Avoidance costs tend to increase with increasing powertrain complexity.  In nearly all cases, the most cost-effective pathways employ carbon CCS combined with more ‘conventional’ powertrains. 
• Although, from the previous point, biomass (woody biomass only) has the lowest avoidance cost the conclusion should be set in the additional context that:
  • Woody biomass resources are limited and only likely to make a marginal contribution to hydrogen supply;
  • in the case of CCS, a lower efficiency increases the net quantity of CO2 stored ,  and has a beneficial impact on avoidance costs;
  • conversion technology is only at the demonstration stage and is yet to fulfil the high performance expectations.
• Hydrogen from natural gas provides the lowest avoidance cost for significant quantities of CO₂
• Based on avoidance costs, CNG appears to be the most cost-effective way of reducing GHG emissions from remote natural gas. FT diesel is the least cost-effective because of the limited impact of this pathway on GHG emissions relative to the gasoline reference, and because of the relatively high cost of diesel vehicles.
• Transposing the findings of this study to the US market suggest that, with the lower efficiency of US vehicles and US refineries, CCS applied to alternative fuel pathways may provide a lower cost of avoiding CO₂ than that estimated for Northern Europe.