In the face of growing concerns about global warming, carbon intensity has become an important aspect in assessing liquid fuels production technologies.
In 2010 Enefit together with the help of Jacobs Consultancy performed a life-cycle carbon intensity study for the production of liquid fuels from oil shale in Estonia. The purpose of the study was to Establish, through LCA, the carbon intensity for diesel and gasoline derived from oil shale using the Enefit280 technology, subsequent oil upgrading and downstream refinery processing.
Life Cycle carbon intensity of shale oil derived liquid fuels in Estonia
The carbon intensity values calculated for oil shale derived gasoline and diesel include all processing and transport steps from "mine to wheel":
- Mining of shale rock
- Transport of shale rock to site by rail
- Upgrading (and associated facilities such as H2 production)
- Fuel cycle (emissions relating to any fuel/power supply)
- Transport of shale oil products to downstream refining
- Refinery processing
- Transport of refined diesel and gasoline to end user
- Product combustion
- Credits from power generation from excess fuel/steam
- Credits from ash sales for clinker substitution in cement production.
As well as considering the direct CO2 emissions produced within the Enefit280 process, it is important in any life cycle assessment (LCA) to consider the emissions associated with utility import, as well as the impact in terms of emissions of exported by-products. Despite significant internal demand for power, the Enefit280 process, as implemented in the Narva Oil Factory, has an overall surplus of power, and hence is a net power exporter. This power export will offset on-purpose power generation within the Estonian grid, thereby reducing CO2 externally. It is therefore reasonable to take into account the emissions credits from this offsetting of external power production.
It is planned to sell part of the ash from the Enefit280 factory as clinker substitute to the cement industry, creating CO2 savings that offset emissions from the Narva Oil factory. Clinker substitution by suitable ash is widely accepted in the cement industry worldwide as a means of reducing CO2 emissions from cement production. The Narva Power Plant is already selling ash for this purpose and Enefit has discussed likely additional future demand with existing and potential buyers. It is reasonable to take credit for CO2 emissions resulting from the use of clinker substitute material, as long as the sold ash is used to back out clinker production, and not replace another clinker substitute material from the cement market.
Carbon intensity of oil shale derived liquid fuels in Estonia is approximately 128 gCO2/MJ.