On the potential for BECCS efficiency improvement through heat recovery from both post-combustion and oxy-combustion facilities

Abstract

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 CO2 capture 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 GJheat per tCO2 at 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.

Bio-energy with carbon capture and storage (BECCS): Opportunities for performance improvement

“…Heat recovered from the stripper overhead condenser and the CO 2 compressor intercoolers in the capture process were used to pre-heat the power plant steam cycle condensate and combustion air [74]. Alternatively, ue gas heat recovery can supply energy for solvent regeneration in the CO 2 capture process [80,81,82,83,84]. For this approach, the amount of heat that is recoverable from ue gas depends on: (i) the point along the pollution control pathway (e.g., exit of boiler, electrostatic precipitator, ue gas desulphurisation); and (ii) fuel type and quality [55].…”

Bio-Energy with CCS (BECCS) performance evaluation: Efficiency enhancement and emissions reduction

“…However, there is relatively little work on eciency improvement in biomass-red plants. In a 500 MW supercritical power station co-ring biomass and coal, the temperature of the exhaust gas leaving the boiler can reach 370°C [55]. Therefore, the additional recovery of relatively low-grade heat from the boiler system has the potential to improve the power generation eciency of a BECCS power plant, albeit at the cost of the additional capital associated with the heat recovery system.…”

“…Importantly, the moisture content of biomass can vary signicantly; as table A1 demonstrates it varies between 560 wt%. As moisture content increases, lower heating value (LHV) decreases due to reduced content of combustible matter per kilogram of biomass [56], which in turn decreases net eciency of the power plant [55]. However, increased moisture content in the fuel enhances heat transfer properties of the ue gas, thereby improving heat recovery [57].…”

“…Subsequently, the multi-phase ue gas mixture was cooled from the AFT to 370°C, representing an energy transfer to the power plant steam cycle. The analysis of SO X and NO X emissions were analysed at 370°C (ue gas temperature of the boiler exit predicted by IECM [55]). Note, however, the temperature of the ue gas at the boiler exit is a function of the AFT, which in turn, varies with dierent fuels and co-ring proportion.…”

Inefficient power generation as an optimal route to negative emissions via BECCS?

“…This implies a low efficiency at converting biomass into electricity, thus producing and capturing the maximum CO 2 per MWh (or per year) possible. Therefore, BECCS plants that are less efficient at converting biomass to electricity may be preferred from the perspective of removing the maximum amount of CO 2 from the atmosphere [25]. This leads to a seemingly paradoxical arrangement-an inefficient thermal power plant operating in baseload fashion in an energy system with substantial amounts of iRE 5 .…”