Feasibility of CSP integration with coal and biomass co-fired power plant - prospects in different operation environments

Increased CO2 prices, renewable energy incentives and requirements for specific CO2 emissions (e.g. as gCO2/kWh produced electricity, a.k.a CO2 emission standards) applied in some regions and by different organisations have increased the feasibility of different renewable energy options, including concentrated solar power (CSP). The key challenges of CSP are intermittent production and high investment cost. One solution for the challenge of intermittency is to integrate CSP with conventional power plant with a water-steam cycle. This also decreases investment costs in comparison to separate new plants due to common equipment, auxiliaries and operators. The cost benefit may be even emphasized in the case of potential CSP retrofits on existing coal fired plants. In terms of CO2 emissions, important benefit of circulating fluidised bed (CFB) combustion technology is the inherent possibility for co-firing of biomass with high shares. However, integration with CSP field may be favourable in regions, where limited amount of sustainable biomass is available with reasonable costs. In this paper techno-economic case studies of two fictional CFB-CSP hybrid power plants are presented. The aim of the study was to develop a model to present situations where CFB-CSP could be economically feasible. The case studies include different mixtures of coal and biomass co-fired in a CFB boiler integrated with CSP plants. The first considered hybrid plant is based on dynamic modelling work which has been executed earlier at VTT and another based on significant scale-up of modelled data. In the first dimensioning, the steam produced in CSP field (100 MWpeak @ 75 bar) is used for preheating of CFB boiler's feedwater. This enables possibility to even steam properties before turbine section. The second one includes higher uncertainty as it includes several assumptions required for up-scaling. However, this case indicates the scale of the largest possible CSP plant for integration without a need for heat storage. For the both CSP scales, the irradiation model from Morocco region was used. The properties of modelled CFB boiler are based on existing about 400 MWe plant resulting very large solar field in the second case. The considered fuel mixes include the required biomass shares to reach levels of CO2 emission standards in the both dimensioning cases and with different operation schemes of the plants. In terms of annual average CO2 emissions of the plant, utilisation rates during nights, cloudy days and winters are very important. However, it seems that without an energy storage it is challenging to reach emission standards by utilising only coal and solar in the hybrid plant. The feasibility of different cases are compared with reference case (conventional CFB boiler with coal) and analysed in different market conditions.