Search

Integrating bioenergy and carbon capture and storage (BECCS) presents a great opportunity for power production with negative global CO2 emissions. This work explores a novel synergetic system that integrates membranes, partial biomass oxycombustion and the calcium looping (CaL) process. Polymeric membranes generate oxygen-enriched air (OEA) with an O2 concentration of 39%v/v, which is used for partial oxycombustion of biomass waste. The CO2-enriched flue gas evolves from the waste-to-energy plant to the CaL unit, where CO2 concentration is increased up to 90–95%v/v, ready for purification and sequestration. Compared to only oxycombustion systems, the proposed concept presents fewer technological challenges in retrofitting boilers to waste-to-energy plants. Moreover, this new approach is highly efficient as integrating membranes to produce OEA instead of cryogenic distillation systems significantly reduces energy consumption. A novel integration concept is modelled to evaluate the whole process efficiency and the effect of key parameters on the system performance, such as the temperature of the reactors, the membrane surface area, and the partial oxy-combustion degree. The results show that the so-called mOxy-CaL system has an energy consumption associated with CO2 capture below 4 MJ/kg CO2 (a 31% lower than that for a conventional CaL process), with a higher CO2 capture efficiency than oxycombustion and the CaL process separately. On the other hand, the economic analysis shows a higher CO2 capture cost for the novel configuration than for the typical CaL configuration due to the additional investment cost of the membrane system. Improvements in membrane performance by increasing its permeance and diminishing the required surface area would significantly reduce the economic cost of this novel integration. Using membranes with permeance over 400 GPU would boost the system's competitiveness.

This work analyzes the relevant influence of milling on the CO capture performance of CaO derived from natural limestone. Diverse types of milling mechanisms produce contrasting effects on the microstructure of the CaO formed after calcination of the milled limestone samples, which affects crucially the kinetics of carbonation at conditions for CO capture. The capture capacity of CaO derived from limestone samples milled using either shear or impact based mills is impaired compared to as-received limestone. After calcination of the milled samples, the resulting CaO porosity is increased while crystallinity is enhanced, which hinders carbonation. Conversely, if the material is simultaneously subjected to intense impact and shear stresses, CaO porosity is promoted whereas CaO cristanillity is reduced, which enhances carbonation in both the reaction and solid-state diffusion controlled regimes.

This paper proposes a novel CO capture technology from the integration of partial oxy-combustion and the Calcium-Looping capture process based on the multicycle carbonation/calcination of limestone derived CaO. The concentration of CO in the carbonator reactor is increased by means of partial oxy-combustion, which enhances the multicycle CaO conversion according to thermogravimetric analysis results carried out in our work, thus improving the CO capture efficiency. On the other hand, energy consumption for partial oxy-combustion is substantially reduced as compared to total oxy-combustion. All in all, process simulations indicate that the integration of both processes has potential advantages mainly regarding power plant flexibility whereas the overall energy penalty is not increased. Thus, the resulting energy consumption per kilogram of CO avoided is kept smaller than 4 MJ/kg CO, which remains below the typical values reported for total oxy-combustion and amine based CO capture systems whereas CO capture efficiency is enhanced in comparison with the Calcium-Looping process.

Deep penetration of renewable energies into the grid relies on the development of large-scale energy storage technologies using cheap, abundant, and nontoxic materials. Concentrated solar power (CSP) is particularly suitable to massively store thermal energy for dispatchable electricity generation. This is currently accomplished in a few demonstration plants by using molten salts albeit in a not competitive way yet. Process simulation studies indicate that thermochemical energy storage of CSP by means of the calcium looping (CaL) technology would reduce the cost of storage and increase the flexibility of energy supply provided that widely available and cheap CaO precursors with high and stable multicycle activity are used. In this work, we investigate the behavior of calcium rich steel slag at CaL conditions that would expectedly maximize the efficiency of CSP energy storage and power production. When treated with acetic acid, this nontoxic widely abundant waste yields a CaO rich solid with stable conversion near 0.8 over successive carbonation/calcination cycles at these CaL conditions.

One of the major drawbacks that hinder the industrial competitiveness of the calcium looping (CaL) process for CO capture is the high temperature (∼930-950 °C) needed in practice to attain full calcination of limestone in a high CO partial pressure environment for short residence times as required. In this work, the multicycle CO capture performance of dolomite and limestone is analysed under realistic CaL conditions and using a reduced calcination temperature of 900 °C, which would serve to mitigate the energy penalty caused by integration of the CaL process into fossil fuel fired power plants. The results show that the fundamental mechanism of dolomite decomposition under CO has a major influence on its superior performance compared to limestone. The inert MgO grains resulting from dolomite decomposition help preserve a nanocrystalline CaO structure wherein carbonation in the solid-state diffusion controlled phase is promoted. The major role played by the dolomite decomposition mechanism under CO is clearly demonstrated by the multicycle CaO conversion behaviour observed for samples decomposed at different preheating rates. Limestone decomposition at slow heating rates yields a highly crystalline and poorly reactive CaCO structure that requires long periods to fully decarbonate and shows a severely reduced capture capacity in subsequent cycles. On the other hand, the nascent CaCO produced after dolomite half-decomposition consists of nanosized crystals with a fast decarbonation kinetics regardless of the preheating rate, thus fully decomposing from the very first cycle at a reduced calcination temperature into a CaO skeleton with enhanced reactivity as compared to limestone derived CaO.

The aim of this work was to evaluate the effect of methyl salicylate (MeSA) treatments of sweet cherry trees on fruit quality properties at harvest time and during cold storage. Experiments were performed during two consecutive years by using two cultivars, ‘Sweet Heart’ and ‘Sweet Late’ in 2013, and three cultivars, ‘Sweet Heart’, ‘Sweet Late’ and ‘Lapins’ in 2014. In the 2013 experiments, three MeSA concentrations (0.5, 1 and 2 mM) were applied at three key points of on-tree fruit development and results showed that the 1 mM concentration was the most appropriate in terms of increasing fruit size and quality parameters (improved colour, firmness and total soluble solids) at the time of harvest. Sensory analysis revealed that appearance, firmness and sweetness scores were higher in 1 mM MeSA treated cherries than in the control ones. Thus, 1 mM concentration was chosen for the 2014 experiments, in which it was found that MeSA treatments did not affect total fruit yield. The fruits from both control and 1 mM MeSA treated trees was stored at 2 °C and a relative humidity (RH) of 85% for 28 days and results showed that preharvest MeSA treatments delayed the postharvest ripening process, manifested by a lower degree in colour changes, and less loss of acidity and firmness in treated fruits with respect to controls, leading to maintenance of fruit quality. Overall, preharvest treatments with 1 mM MeSA at three key dates of sweet cherry growth and ripening improved fruit quality attributes at the time of harvest and after postharvest storage, showing that MeSA could be a safe and environmentally friendly tool with potential practical application to improve sweet cherry fruit quality.