• Energy Research

BECCS performance can be measured by a wide range of technical and sustainability indicators, which can be negatively correlated. An exclusive focus on BECCS technical performance – CO2 removal and electricity production, can result in negative consequences for the broader environment.

Measures to mitigate the emissions of carbon dioxide (CO2) can vary substantially in terms of the energy required. Some proposed CO2 mitigation options involve energy-intensive processes that compromise their viability as routes to mitigation, especially if deployed at a global scale. Here we provide an assessment of different mitigation options in terms of their energy usage. We assess the relative effectiveness of several CO2 mitigation routes by calculating the energy cost of carbon abatement (kilowatt-hour spent per kilogram CO2-equivalent, or kWh kgCO2e–1) mitigated. We consider energy efficiency measures, decarbonizing electricity, heat, chemicals and fuels, and also capturing CO2 from air. Among the routes considered, switching to renewable energy technologies (0.05–0.53 kWh kgCO2e–1 mitigated) offer more energy-effective mitigation than carbon embedding or carbon removal approaches, which are more energy intensive (0.99–10.03 kWh kgCO2e–1 and 0.78–2.93 kWh kgCO2e–1 mitigated, respectively), whereas energy efficiency measures, such as improving building lighting, can offer the most energy-effective mitigation. Carbon emission reduction measures have widely differing energy consumptions that have not been systematically compared. Babacan et al. estimate comparable energy use per unit emission reduction of various emission reduction measures, from efficiency improvements to renewable electricity generation to carbon removal.

Negative emissions technologies (NETs) in general and bioenergy with CO2 capture and storage (BECCS) in particular are commonly regarded as vital yet controversial to meeting our climate goals. In this contribution we show how the sustainability and carbon efficiency, or otherwise, of BECCS depends entirely on the choices made throughout the BECCS supply chain.

Energy intensive supply chains and low power generation efficiency could challenge the ubiquitous assumption that BECCS is a net provider of electricity. Deploying a net negative energy technology at the EJ scale could represent a threat to energy security.

In this study we evaluate the feasibility of the recovery of waste heat from the power plant boiler system of a pulverised fuel power plant with amine-based CO2 capture. This recovered heat can, as a function of fuel type and solvent selection, provide up to 100% of the heat required for solvent regeneration, thus obviating the need for withdrawing steam from the power plant steam cycle and significantly reducing the efficiency penalty imposed upon the power plant by the CO2 capture process. In studying the thermochemistry of the combustion process, it was observed that co-firing with low moisture biomass achieved higher adiabatic flame temperatures (AFT) than coal alone. The formation and emission of SOX reduced as biomass co-firing proportion increased, whereas NOX emissions were observed to be a function of AFT. The power generation efficiency of a 500MW 50% co-firing BECCS system increased from 31%HHV with a conventional MEA solvent, to 34%HHV with a high performance capture solvent. The heat recovery approach described in this paper enabled a further efficiency increase up to 38%HHV with the high performant solvent. Such a system was found to remove 0.83 MtCO2 from the atmosphere per year at 90% capacity factor.

In order to mitigate climate change to no more than 2 °C, it is well understood that it will be necessary to directly remove significant quantities of CO2, with bioenergy CCS (BECCS) regarded as a promising technology. However, BECCS will likely be more costly and less efficient at power generation than conventional CCS. Thus, approaches to improve BECCS performance and reduce costs are of importance to facilitate the deployment of this key technology. In this study, the impact of biomass co-firing rate and biomass moisture content on BECCS efficiency with both post- and oxy-combustion CO2capture technologies was evaluated. It was found that post-combustion capture BECCS (PCC-BECCS) facilities will be appreciably less efficient than oxy-combustion capture BECCS (OCC-BECCS) facilities. Consequently, PCC-BECCS have the potential to be more carbon negative than OCC-BECCS per unit electricity generated. It was further observed that the biomass moisture content plays an important role in determining the BECCS facilities’ efficiency. This will in turn affect the enthalpic content of the BECCS plant exhaust and implies that exhaust gas heat recovery may be an attractive option at higher rates of co-firing. It was found that there is the potential for the recovery of approximately 2.5 GJheatper tCO2at a temperature of 100 °C from both PCC-BECCS and OCC-BECCS. On- and off-site applications for this recovered heat are discussed, considering boiler feedwater pre-heating, solvent regeneration and district heating cases.

Abstract Bio-energy with carbon capture and storage (BECCS) is an important greenhouse gas removal (GGR) technology with the potential to provide significant reductions in atmospheric CO 2 concentration. The power generation efficiency of BECCS can be improved by using heat recovered from flue gas to supply energy requirements of the solvent regeneration process. This paper assesses the influence of solvent selection and biomass co-firing proportion on recoverable heat, energy efficiency and carbon intensity of a 500 MW pulverized fuel BECCS system. The effects of (i) coal type (high and medium sulphur content), (ii) biomass type (wheat straw and clean wood chips, (iii) variable moisture content, and (iv) biomass co-firing % on AFT and emissions of SO X and NO X was evaluated. Compared to firing of coal alone, co-firing low moisture biomass generated higher adiabatic flame temperature. As biomass co-firing proportion increased, SO X emissions decreased, whereas NO X emissions increased with greater AFT. Factors that enhanced BECCS efficiency included the use of high performance solvents and higher heat recovery (higher AFT and flue gas flow rate). These results lead to the development of a performance matrix which summarizes the effect of key process parameters.