In June 2019, the UK government declared a climate emergency and announced a target of net zero greenhouse gas (GHG) emissions compared to the 1990 emission levels by the year 2050. However, in order to effectively minimise and control the rise in global temperature to below 2 °C, negative emission technologies such as biomass energy with carbon capture and storage (BECCS), are recognised to be vital to meet the Paris Agreement climate targets, as stated in the 2018 Intergovernmental Panel on Climate Change (IPCC) report.
Despite promises for mitigating large volumes of CO2 and despite governmental incentives and regulatory drivers, the high cost of CCS (primarily from capture and compression, accounting for 75% of the total cost of CCS) has largely impacted its large-scale deployment.
Therefore, alternative economically-feasible processes with minimum environmental footprints must be developed, urgently. Adsorption for CCS is an attractive second generation technology for a number of reasons; importantly, it can be retrofitted to any power plant should the adsorption column be optimised to ensure acceptable footprint and cost.
Biomass combustion is accompanied by the generation of a large quantity of solid waste residue: bottom ash (BA) and fly ash (FA). A significant portion of this residue is currently being directly landfilled with no further useful application. With an anticipated increase in biomass combustion in the UK (e.g. Drax power plant, UK, has just converted 4 out of its 6 boilers to biomass), the co-generation of this solid residue will present an additional challenge for waste management, creating a great opportunity for exploring potential re-use of this increasingly available solid waste in the future.
Owing to the unique alkaline nature of biomass combustion ash (BCA) and its chemical properties, BCA could find niche applications in CO2 capture. Compared to coal fly ash, the elevated alkaline contents in biomass ash can make this type of ash more efficient in CO2 capture compared to coal ash. Therefore, investigations into the potential utilisation of BCA is not only environmentally beneficial but also of high economic and social significance, especially in the context of the UK economy with an ever-increasing interest in biomass combustion. High performance modified BCA could be a great competitor with the conventional and novel adsorbents such as activated carbons, zeolites and metal organic frameworks (MOFs) due to their low-cost, abundance and the possibility of in-situ applications at biomass combustion facilities.
In this research work, we are investigating the performance of raw and modified BCA as adsorbents in post-combustion CO2 capture. The industrially-generated biomass combustion ash will be chemically modified and characterised using a range of standard techniques. The equilibrium and kinetics of the adsorption process will then be studied using thermogravimetric methods. The effects of the operational parameters such as inlet gas flow rate, CO2 partial pressure and inlet gas temperature on breakthrough curves, pressure drop and mass transfer rates, will be studied on a lab-scale fixed-bed reactor.
This study has been supported by the UK Carbon Capture and Storage Research Centre (UKCCSRC) flexible funding research grant. The UKCCSRC is supported by the EPSRC as part of the UKRI Energy Programme.