A techno-economic study of HTC processes coupled with power facilities and oxy-combustion systems

Abstract

In this work, the effects on industrial plant viability of using olive pruning (OP) and off-specification compost (OSC) as HTC feedstock have been studied on 1) only HTC facilities and 2) HTC coupled to a Rankine cycle (with combustor/oxy-combustor). After the experimental tests, the best blend composition for hydrochar production in higher heating value (HHV) terms was 75% OP + 25% OSC, and the hydrochar yield was identified as a critical variable to be optimized in future research. Technical simulations revealed the inconvenience of using OP instead of the mentioned OP–OSC blend because it could increase the cost of electricity (COE) by 35.2 €/MWeh (combustion) vs. 49.5 €/MWeh (oxy-combustion). Additionally, the use of hydrochar as fuel in combustors could increase the total capital investment (TCI) by 3.5, and the COE by 171.0 €/MWeh (combustion) vs. 227.9 €/MWeh (oxy-combustion). HTC plants coupled to Rankine cycles presented a worse viability than that of hydrochar production alone, and the fuel price was identified as the most sensitive variable in terms of net present value (NPV). Finally, the best plant in terms of viability and sustainability is hydrochar production with thermal integration with a Rankine cycle, albeit with the need for an extra grant of 52.2 €/MWeh based on the study assumptions.