Negative emissions technologies (NETs) feature in many climate models that comply with 2°C scenarios; and efforts to aim towards a 1.5°C target, as outlined in the Paris Agreement, have drawn further attention to the need for options that reduce the overall stock of emissions in the atmosphere. Negative emissions are also an important tool for offsetting residual emissions from the hard-to-abate sectors like aviation, cement and steel industry, as well as agriculture to achieve overall carbon-neutrality. A range of plausible NETs have been proposed, and some of them are currently more developed than others, in terms of both technological maturity and the amount of CO2 removal that could potentially be offered. As NETs are growing in prominence in energy planning, better understanding is needed of the many trade-offs that achieving negative emissions have on cost, emissions and the required resources.
The longer-term growth of transport biofuels in the IEA's 2DS relies on the widespread supply of novel advanced biofuels produced by processes that are generally not yet mature. Advanced biofuels are sustainable fuels produced from non-food crop feedstocks that are capable of delivering significant life-cycle GHG emissions savings without competing with food and feed crops for agricultural land use. Advanced biofuels can also be called "second generation" (2G) biofuels, to differentiate them from "first generation" (1G) crop-based biofuels.
The sustainable conversion of biomass feedstocks to biomass-derived fuels and chemicals are often referred to as "biorefining". In addition to biofuel, such "biorefineries" typically produce also by-products and CO2. The CO2 from biomass processing is normally vented to atmosphere, but if it were captured and securely sequestered in geological formations (BECCS), the produced biofuel could be characterised by net negative GHG emissions because of the storage of biogenic CO2.
The aim of this study is to provide a techno-economic assessment of biorefinery concepts with and without CCS as well as a comparative assessment of 1G and 2G biorefineries. The results of this study will be of interest to developers of biorefinery and CCS projects and policy makers.
- The cost of adding CCS on the high-concentration streams of biorefineries varies between 22 and 24 $/tCO2. If CCS is extended also to flue gas streams, the cost of CCS varies between 27 and 66 $/tCO2. The wider range of cost is explained by differences between biorefineries in the share of CO2 that needs to be captured from low-concentration streams.
- The lowest cost of CCS is achieved with gasification-based configurations using base case CCS design (22 $/tCO2) followed closely by ethanol plants with base case CCS design (24-25 $/tCO2).
- Several of the cost estimates are developed for first-of-a-kind (FOAK) commercial plants and contain a lot of uncertainty as they are derived from a small handful of demonstration projects. Cost reductions could be achieved over the coming decades through learning from these technologies at relevant scale.
- Biorefineries with CCS show potential for negative emissions. First generation corn ethanol plants with CCS can only produce carbon negative fuels if natural gas inputs are switched to a low-carbon energy source. For second generation biorefineries with CCS, based on woody biomass, emissions range between -59 gCO2eq/MJ and -164 gCO2eq/MJ. The deepest emissions reductions in comparison to the fossil reference are associated with second generation wheat straw plants with CCS, which can achieve -274 gCO2eq/MJ in the maximum capture configuration.
- Biorefineries with CCS seem very attractive, especially for decarbonising the hard-to-abate transport sector. On the other hand, the cost of biofuel is currently too high to compete with petroleum fuels and out of the examined configurations only two have currently been demonstrated at commercial scale.
Recommendations for further work include:
- Implementation of large-scale demonstration projects in order to reduce risk and increase investor confidence.
- More data should be made available from projects in order to refine the techno-economic assessment of biorefineries with CCS and reduce uncertainties.