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Abstract The research of renewable alternatives to decarbonize the transport sector and to reduce the consumption of fossil fuels pushes towards the development of more sustainable solutions for fuel production. Among the diesel substitutes, hydrotreated vegetable oil (HVO) is considered one of the most promising options, since it can be blended with fossil diesel without limitations. In this context, this paper assesses the technical and economic feasibility of producing HVO using waste vegetable oil (WVO) as feedstock, with the help of a simulation model that maximizes the integration of renewable energy sources. The process to synthesize HVO requires a large amount of hydrogen that, in this study, is supplied through an upstream high-temperature electrolysis process occurring in solid oxide electrolysis cells (SOECs), which are fed by low-carbon electricity. The use of waste oils as feedstock eliminates the competition with food crops (e.g. soybean or rapeseed) and promotes the recycling of substances that need to be disposed. The results of the study prove the technical feasibility of a plant with an annual capacity of 100 kt of HVO, having an energy efficiency of 80%. Also, the breakeven point of such investment would be reached before the fourth year of operation, considering a WVO price of 400 €/t, which is assumed as target price. However, the uncertainty on the market prices of WVO, HVO and electricity, as well as on other fixed and variable production costs, can significantly affect the projected results.

The reduction of the dioxin levels in the exhausts of today waste-to-energy plants relies on the control of the thermo-fluid-dynamic processes occurring within the combustion chamber, rather than on policies aimed at restricting the amount of chlorine in the waste material to be treated. This is a consequence of the fact that waste-to-energy plants currently receive the bulk of discarded PVC and other chlorine sources that are deliberately burned in order to increase the waste heating value. Indeed, severe law regulations are into force in many industrialised countries, posing constraints on the value of some relevant in-chamber thermo-fluid-dynamic variables, such as temperature and residence time of the gases resulting from the combustion process, whose accurate experimental monitoring is extremely expensive and difficult to achieve. The present work analyses the shortcomings of the methods generally employed in full scale plants for the verification of the temperature and residence time of gases produced during the combustion process, and presents the advantages of using a new procedure developed by authors, based on the numerical simulation of the waste combustion process to optimise monitoring of the quantities of interest. The verification of the developed model, which accounts for both the solid and the gaseous phases, and for the various modes of heat and mass transfer between these phases, is obtained through a comparison with the results of an experimental campaign carried out on a full scale plant in Italy. The temperature distribution in the combustion chamber is calculated considering various waste compositions, and both forced and mixed convection. In fact, it is also shown that neglecting buoyancy effects may lead to appreciable errors.

Abstract In recent years, the world has witnessed a rapid rise in waste production and energy demand, which has increased interests in waste to energy processes, particularly the co-pyrolysis of wood and plastic waste. Nonetheless, for plastic waste, most research studies narrowly focus on polyolefins because of their abundance in waste streams and their high oil yields from pyrolysis. In this paper, we study the co-pyrolysis of non-polyolefins – polystyrene (PS) and polyvinyl chloride (PVC) – and poplar wood (PW), in order to investigate the synergistic effect of PS and PVC content on product yield, gas specie yield and heating value. The experiments were performed using a fixed-bed reactor, heated to 750 ° C at a rate of 20 ° C/min under nitrogen atmosphere. Our results show that PVC has a large positive synergy on char yield with a maximum value of 8 wt% at 30 wt% PVC content, whereas PS only showed a slightly positive synergy (2.5 wt% maximum). Concerning oil and gas production, PS provides a small synergy. However, PVC showed a significant positive synergy on oil yield with a maximum value of 11 wt% at 50 wt% PVC content, which was linked to a strong negative synergy in gas production. Regarding gas specie yields, the addition of PS led to positive synergies in the formation of H2, CH4, CO and CO2, although insignificant interactions were observed for C x H y compounds. Furthermore, by comparing the distribution of chloride species in the products of co-pyrolysis with PVC, using experimental and theoretical methods, we discovered that the negative synergy in HCl yield observed was mainly due to the dissolution of HCl in the water fraction of the condensed oil phase, rather than the formation of chlorinated organic compounds, as suggested in previous literature works. Our study therefore consolidates the understanding of the synergistic interactions between wood, PS and PVC co-pyrolysis, under conditions that favour gas production.

Abstract In recent years coal-fired power plants have increased their role in the global energy scenario and in this framework environmental issues require a sustainable use of coal and great efforts for greenhouse gas reduction. With this aim, this paper reports on a comparative performance assessment of two power generation technologies: the Ultra Super Critical (USC) steam plant and the Integrated Gasification Combined Cycle (IGCC) plant. Performances were assessed referring to typical commercial size plants (400–500 MW) integrated with CO 2 capture systems. The study is based on simulation models specifically developed through Aspen-Plus® and Gate-Cycle® software platforms. The USC plant is integrated with a SNOX section that removes simultaneously nitrogen and sulfur oxides without producing process wastes and with lower power requirements compared to traditional FGD systems. The USC plant is also integrated with a low temperature CO 2 capture/compression section based on a MEA chemical absorption process. The IGCC plant is based on a Texaco entrained bed gasifier, fed by a coal–water slurry and high purity oxygen, integrated with a triple-pressure reheat combined cycle. The IGCC is integrated with a syngas cooling and treatment section composed of radiant and convective coolers, a water gas shift section and a low temperature CO 2 capture system based on a physical absorption process. The performance assessment of USC and IGCC power plants was carried out by varying the main operating parameters of both power sections and gas treatment sections. For both plants an in-depth analysis of performance penalties due to the CO 2 capture systems was carried out, evaluating the influence of CO 2 removal technology and efficiency.

9 pages, 6 figures, 6 tables.-- Available online Sep 29, 2007. The lime enhanced gasification (LEGS) process uses CaO as a CO2 carrier and consists of two coupled reactors: a gasifier in which CO2 absorption by CaO produces a hydrogen-rich product gas, and a regenerator in which the sorbent is calcined producing a high purity CO2 gas stream suitable for storage. The LEGS process operates at a pressure of 2.0 MPa and temperatures less than 800°C and therefore requires a reactive fuel such as brown coal. The brown coal ash and sulfur are purged from the regenerator together with CaO which is replaced by fresh limestone in order to maintain a steady-state CaO carbonation activity (a(ave)). Equilibrium calculations show the influence of process conditions and coal sulfur content on the gasifier carbon capture (>95% is possible). Material balance calculations of the core process show that the required solid purge of the sorbent cycle is mainly attributed to the necessary removal of ash and CaSO4 if the solid purge is used as a pre-calcined feedstock for cement production. The decay in the CaO capture capacity over many calcination–carbonation cycles demands a high sorbent circulation ratio but does not dictate the purge fraction. A thermodynamic analysis of a LEGS-based combined power and cement production process, where the LEGS purge is directly used in the cement industry, results in an electric efficiency of 42% using a state of the art combined cycle. The work presented here was performed within the framework of two projects funded by the European Commission RFCS and the FP6 programs, through Projects No. RFC-CR-03009 and SES6-CT03-502743. Peer reviewed

Abstract In order to evaluate the influence of pellet quality classes, as defined by the ISO 17225-2, particulate matter and gaseous pollutants were characterized for different class fueled pellets in the emissions of a stove at partial and nominal load. Total suspended particulate (TSP) was sampled with a dilution system, then characterized for total carbon (TC), inorganic carbon (IC), water soluble organic carbon (WSOC) polycyclic aromatic hydrocarbons (PAHs) and the main soluble ions. Gas monitoring shows that CO and NO emission factors are higher for lower quality pellet. Low quality pellet emission factors are also higher for TSP and soluble ions, thus the pollutants linked to pellet ash content. On the other hand, carbonaceous component emission factors are higher for higher quality pellet; nevertheless, at nominal load, lower quality pellet emits more toxic PAHs. The higher stove power restricts instead the emissions of incomplete combustion products: CO, TSP and carbonaceous components. Principal Component Analysis (PCA) allows to have a complete overview of the obtained results: the effect of operating phase on emission factors is less strong then pellet quality, even if the pollutants produced by low heat power are more hazardous than the ones connected with pellet quality. In conclusion, the study provides not only quantitative information on the influence of pellet quality classes on stove emissions, but also their chemical fingerprint. Moreover, it indicates that the amount of hazardous emissions is also linked to stove power.

Abstract The simultaneous ethanol production and removal during sequential cell recycle fed batch fermentation provides a complementary route to produce this biofuel from sugar mixtures, which may greatly improve yields and productivity from lignocellulosic hydrolysates. Spathaspora passalidarum is a wild-type strain able to naturally convert glucose, fructose, xylose and arabinose into ethanol. Therefore, the present work has focused on 2G bioethanol production by S. passalidarum aiming at the consumption of all sugars released after pre-treatment and enzymatic hydrolysis of sugarcane bagasse in a single fermentation step. The fermentation strategy with sequential cell recycle, fed-batch mode and ethanol removal in situ was performed on a hemicellulosic hydrolysate medium supplemented with molasses. This strategy gave improved fermentation performance and enabled the co-fermention of all sugars under microaerobic conditions. The maximum ethanol yield and productivity was 0.482 g.g−1 and 9.5 g·L-1·h−1, respectively, showing a process efficiency of 94.3%. The selective ethanol removal enables the operation of the bioreactor at low levels of ethanol (20–30 g·L-1), even with high sugar concentration inputs, accelerating the fermentation performance and avoiding inhibitory effects on yeast metabolism. Applying the cell recycle strategy, S. passalidarum was able to increase its robustness, as shown by a 10-fold increase in ethanol productivity, and it was also able to tolerate a high acetic acid concentration (4.5 g·L-1) during long-term fermentations. These results demonstrate that the bioprocess strategy has a strong potential to improve bioethanol production of rich mixed sugar from lignocellulosic hydrolysates in a single fermentation step.

Abstract Hydrothermal carbonization of the organic fraction of municipal solid waste (OFMSW) could mitigate landfill issues while providing a sustainable solid fuel source. This paper demonstrates the impact of processing conditions on the formation and composition of hydrochars and secondary char of OFMSW. Harsher conditions (higher temperatures, longer residence times) decrease generally the solid yield while increasing the higher heating value (HHV), fixed carbon, and elemental carbon. Energy yields upwards of 80% can be obtained at both intermediate and high temperatures (220 and 260–280 °C), but the thermal stability and reactivity of the intermediate hydrochars suggest the formation of a reactive secondary char that condenses on the surface of the primary hydrochar. This secondary char is extractable with organic solvents and is comprised predominantly of organic acids, furfurals and phenols, which peak at 220 and 240 °C and decrease at higher carbonization conditions. The HHVs of secondary char are significantly higher than those of primary char.