• Energy Research

This study looked at the potential synergy of co-pyrolysis of residual lignocellulosic biomass in the form of olive stone with low-density polyethylene in the absence/ presence of solid acid catalyst in a bench scale continuous bubbling fluidised bed reactor. Despite the catalyst lowering the pyrolytic oil yield, there was significant transition in the class of hydrocarbon derivatives formed with catalytic co-pyrolysis yielding much more deoxygenated hydrocarbons in contrast to the product class from the inert sand bed. .-alumina performed much better improving the H/C molar ratio of bio-oil by ~20% over the inert bed co-pyrolysis experiment, both the .-alumina and HZSM-5 catalyst significantly lowered the O/C molar ratio of bio oil recovered. The product stream from both catalysts was relatively high in polycyclic aromatic hydrocarbons (PAHs)due to the strong acid catalysed reactions which promotes strong aromatisation. Proceedings of the 29th European Biomass Conference and Exhibition, 26-29 April 2021, Online, pp. 817-823

Abstract In the last decades several looping processes for clean utilization of fossil resources have been proposed with the aim of providing transient/long-term solutions to the challenge of near-zero emission energy production. A selection of solids looping processes for both carbon oxidation/gasification and CO2 capture/utilization will be surveyed, with a specific focus on the contribution given by the research group active in Naples. A novel concept has been developed (CarboLoop) to accomplish capture-ready combustion/gasification of carbon through iterated oxidation/desorption cycles. The idea is that alternated oxygen chemisorption on carbon followed by thermal desorption of oxides as CO/CO2 provide a path with inherent oxygen separation and concentrated CO/CO2 streams. The path to exploitation of the CarboLoop is laid by elucidation of the thermochemistry of carbon oxidation throughout dynamic oxidizing/reducing cycles. Calcium Looping (CaL) provides a feasible path to accomplish carbon capture from CO2-bearing exhaust. Its efficiency is affected by sorbent thermal sintering and by particle attrition/fragmentation. There is still a lack of characterization of the concurrent effect of steam and SO2 in terms of sorbent availability and selective uptake of CO2. The performance of Ca-based sorbents has been scrutinized in the frame of ternary CO2-SO2-H2O environments. Methanation is an attractive path to CO2 utilization. Sorption-Enhanced Methanation (SEM) exploits the favourable effect on thermodynamics of continuous in-situ removal of steam generated by methanation by a sorbent. SEM is conveniently performed as a looping process, whose performance has been characterized by means of a novel test rig configuration based on two-interconnected fluidized beds.

Abstract The aim of this study is to investigate the effect of the concentration of sulphur dioxide and steam, in the flue gas subjected to CO2 capture by calcium looping, on the performance of two limestone-based sorbents. The experimental calcium looping tests were carried out in a purposely-designed Twin Bed lab-scale apparatus (consisting of two identical interconnected bubbling fluidised bed reactors), able to reproduce a realistic particle thermal/chemical/mechanical history. The two natural limestones (particle size range 0.4–0.6 mm) were selected in view of their remarkably “high” and “poor” reactivity to CO2, respectively. Calcium looping tests consisted of ten calcination/carbonation cycles (plus an eleventh calcination). Carbonation was carried out at 650 °C in an atmosphere containing 15% CO2 to simulate a typical combustion flue gas, while calcination was operated at 940 °C at 70% CO2 to simulate oxy-combustion conditions. Six different operating conditions for carbonation were tested to study the effect of SO2 and/or H2O, where steam (when present) was fed at 10%, and SO2 (when present) either at 75 ppm (a typical concentration in a pre-desulphurised combustion flue gas) or 1500 ppm (raw flue gas). The CO2 capture capacity was calculated for each carbonation stage, and the attrition rate was obtained by collection of elutriated fines from both reactors. At the end of the test, sorbent particles were further analysed for the determination of: degree of calcium sulphation, particle size distribution, porosimetric and microscopic properties. Relationships among sorbent type, operating conditions and experimental results are here discussed in detail, with the aim of originally outlining general trends arising from the comparison of the performance of the two limestones, which are characterised by very different reactivity.

The increase of capital investments and operation and maintenance (O&M) costs represents a current limitation to the diffusion of carbon capture systems for the clean combustion of fossil fuels. However, post-combustion systems, such as calcium looping (CaL), for CO2 capture from flue gas are the most attractive carbon capture systems since they can be installed at new plants and retrofitted into existing power plants. This work investigates the pros and cons of employing a calcium looping system for CO2 capture and also as a desulphurization unit. A preliminary techno-economic analysis was carried out comparing a base case consisting of a coal-based power plant of about 550MWe with a desulphurization unit (Case 1), the same plant but with a CaL system added for CO2 capture (Case 2), or the same plant but with a CaL system for simultaneous capture of CO2 and SO2 and the removal of the desulphurization unit (Case 3). Case 2 resulted in a 67% increase of capital investment with respect to the benchmark case, while the increase was lower (48%) in Case 3. In terms of O&M costs, the most important item was represented by the yearly maintenance cost of the desulphurization unit. In fact, in Case 3, a reduction of O&M costs of about 8% was observed with respect to Case 2.

Crude bio-oil obtained from fast pyrolysis of biomass and wastes is typically characterised by the presence of high levels of oxygenated compounds, which are mainly responsible for its unfavourable characteristics (e.g., low heating value, high acidity, and poor storage stability). In order to overcome this drawback and favourably produce drop-in fuels, the fast pyrolysis of olive stone (OS), has been studied by giving particular attention to the exploration of operating conditions (i.e. pyrolysis temperature) and strategies (i.e. catalytic pyrolysis and co-pyrolysis) suitable to promote efficient de-oxygenation of bio-oils and improve the quality of the product streams. Steady state fast pyrolysis tests were performed in a bench scale fluidized bed reactor (gas residence time ~1s). Pyrolysis tests were carried out at 500 °C and 600 °C by using either inert sand or ?-alumina catalyst as bed material. Outcomes from the non-catalytic and the catalytic co-pyrolysis of low-density polyethylene (LDPE) and OS (plastic-to-biomass ratio of 20/80) at two different temperatures (500 and 600 °C) are also presented. Preliminary findings highlight that the co-processing of LDPE and OS under non-catalytic conditions stands out for the formation of long-chain aliphatic hydrocarbons in the form of both liquid paraffins and wax deposits, which are well-known to be the primary products evolved from the pyrolysis of polyolefins. The addition of ?-alumina catalyst significantly affects both the distribution and the quality of the pyrolytic products (char, bio-oils, and gas). Under catalytic co-pyrolysis conditions, a marked reduction in the yield of bio-liquid is observed, compensated by a remarkable improvement in its quality, particularly in terms of the formation of light mono-aromatics and a marked decrease in the total amount of the oxygenated compounds. On the downside, however, a significant increase in the production of polycyclic aromatic hydrocarbons (PAHs) is detected. Remarkable benefits are also detected by increasing the co-pyrolysis temperature to 600 °C, particularly in terms of content of oxygenated compounds in the bio-oils, as well as in terms of PAHs and water formation, which decreased considerably. Altogether, preliminary findings of this study suggest that further research efforts are required in order to improve the process performance, for example by optimizing the operating conditions as well as the physicochemical properties of catalysts.

The success of a Chemical Looping Combustion (CLC) process for solid fossil fuel combustion is critically affected by the performance of the oxygen carrier and by proper design and operation of the fuel reactor.In this study, a novel configuration of the fuel reactor for chemical looping combustion with oxygen uncoupling of solid fossil fuels is proposed. The configuration is based on a two-stage reactor with the aim of overcoming the main drawbacks of the single-stage design: limited conversion, slip of unburnt volatiles, extensive elutriation of char fines. The two stages of the configuration operate in series and accomplish different tasks. The bottom bed is mainly devoted to conversion of the char, taking advantage of the full oxidative power of the oxygen carrier coming from the air reactor. The top reactor exploits the residual oxidative power of the oxygen carrier to oxidize volatile matter and gasification products as well as the unconverted char issuing from the bottom bed.A mathematical model has been developed with the aim of assessing the performances of the two-stage fuel reactor varying operating conditions in comparison with a benchmark case consisting of a single-stage fuel reactor. Two options were considered in the benchmark, depending on whether the single stage fuel reactor is or is not equipped with a carbon stripper at the exhaust. The operation of the fuel reactor has been simulated by considering chemical looping combustion of a bituminous coal with an oxygen carrier consisting of CuO supported on zirconia.

The use of biomass-derived fuels aimed at integrating and/or replacing conventional fossil fuels, has attracted increasing interest in the last decade following the pattern of the sustainable transport development in the context of the 'Initiative for Global Leadership in Bioenergy'. Among the multiplicity of processes adopted for biomass conversion, fast pyrolysis looks very promising, resulting in a liquid product (i.e., bio-oil) that represents a green alternative to crude oil for the production of liquid fuels, chemicals and intermediate materials within the bio-refinery context. Moreover, the conversion of biomass into bio-oil, fits well with the concept of the progressive transition from traditional 'short chain' biomass conversion methods, typically characterized by lower energy conversion yields, towards "long chain" transformation processes, based on intermediate bioenergy vectors, as reported in the IRENA (2016) and IEA (2016) bulletins on the implementation of advanced liquid biofuels. Pyrolysis oil is, in fact, an energy-dense intermediate that can be economically transported, thus offering an opportunity for connecting decentralized conversion processes with centralised upgrading treatments. In principle, the process is suitable for a broad range of feedstocks and may tolerate variations in feedstock composition, potentially taking advantage of lower-cost feedstocks. The heart of fast pyrolysis processes is the pyrolyzer; among the several technologies currently available, fluidized bed reactors stand out since they are able to ensure superior thermal and fluid dynamic performance. Strategies commonly adopted for optimizing the pyrolysis process include the use of catalysts and co-pyrolysis, which can be either catalytic or non-catalytic. The use of catalysts (mainly acidic zeolites and metal oxides), in particular, pushes the selectivity to specific products, ensures lower energy consumption and shorter reaction times, in addition to deoxygenation and reforming of the pyrolysis vapours coming from the parent feedstock. However, the downside of this approach is the reduction in the bio-oil yield caused by additional contribution of catalytic cracking. In this context, the present work reports on the preliminary results obtained, within the BIOFEEDSTOCK project, with the aim of comparing the performances, in terms of yield and quality of bio-oils, of the catalytic and the non-catalytic fast pyrolysis treatment of different biomass feedstocks in a fluidized bed reactor. In more details, the performed experimental campaign includes four main macro-activities, namely: i) characterization of the selected biomass feedstock by commonly used analysis techniques (i.e., proximate and ultimate; calorific value, ICP-MS analysis, etc.); ii) non-catalytic pyrolysis tests at 500 °C on the investigated feedstocks including high quality spruce wood (SW), wheat straw (WS) and olive stone (OS), which are characterized by different chemical-physical properties (water content, quantity of ash, etc.); iii) in situ catalytic pyrolysis tests on two of the investigated biomass feedstock; iv) preliminary study of the impact of the temperature on the performance of non-catalytic fast pyrolysis.

Power-to-methane represents an innovative approach to convert electrical into chemical energy. Such a technology could actually be successful only when the coupling of a cost-effective source of electrical energy and a pure CO2 stream is carried out. Under this perspective, this paper numerically investigates an inno-vative process layout that integrates a fluidized beds chemical looping system for the combustion of solid fuels and a renewable-based power-to-methane system. Process performances were evaluated by considering a coal and three sewage sludge, differing in water content, as fuels, CuO supported on zirconia as oxygen carrier, hydrogen production via water electrolysis, and Ni supported on alumina as methanation catalyst. Autothermal feasibility of the process was assessed by considering that part of the produced CH4 can eventually be burned to dry high-moisture-content fuels. Finally, by considering that only electric energy from renewable sources is used, the capability of the proposed process to be used as an energy storage system was evaluated.