Antonio M. Pantaleo

Part Load Performance and Operating Strategies of a Natural Gas–Biomass Dual Fuelled Microturbine for CHP Generation

The focus of this paper is on the part load performance of a small scale (100 kWe) combined heat and power (CHP) plant fired by natural gas and solid biomass to serve a residential energy demand. The plant is based on a modified regenerative micro gas turbine (MGT), where compressed air exiting from recuperator is externally heated by the hot gases produced in a biomass furnace; then the air is conveyed to combustion chamber where a conventional internal combustion with natural gas takes place, reaching the maximum cycle temperature allowed by the turbine blades. The hot gas expands in the turbine and then feeds the recuperator, while the biomass combustion flue gases are used for pre-heating the combustion air that feeds the furnace. The part load efficiency is examined considering a single shaft layout of the gas turbine and variable speed regulation. In this layout, the turbine shaft is connected to a high speed electric generator and a frequency converter is used to adjust the frequency of the produced electric power. The results show that the variable rotational speed operation allows high the part load efficiency, mainly due to maximum cycle temperature that can be kept about constant.Different biomass/natural gas energy input ratios are also modelled, in order to assess the trade-offs between: (i) lower energy conversion efficiency and higher investment cost when increasing the biomass input rate; (ii) higher primary energy savings and revenues from feed-in tariff available for biomass electricity fed into the grid. The strategies of baseload (BL), heat driven (HD) and electricity driven (ED) plant operation are compared, for an aggregate of residential end-users in cold, average and mild climate conditions.Copyright

The Logistics of Bioenergy Routes for Heat and Power

This chapter aims to overview the logistics of bioenergy systems, focusing on the economic and sustainability implications of the different transport, processing and energy conversion systems for heat and power generation. The main research trends of biomass processing, de‐ coupling of treatment and energy conversion, integration into existing infrastructures and energy systems, and optimal location and sizing of bioenergy facilities are reviewed. For this purpose, a description of supply chains modelling and research trends, technical options and related cost figures for the various steps of the biomass supply chains are overviewed. Moreover, the opportunities to integrate bioenergy into existing energy systems are ex‐ plored, investigating the use of biofuels in combination with fossil fuels into existing plants and networks. Finally, the main research trends in the optimization of scale and location of the different steps of bioenergy routes are overviewed.

Externally Fired Micro Gas Turbine and ORC Bottoming Cycle: Optimal Biomass/Natural Gas CHP Configuration for Residential Energy Demand

Small scale Combined Heat and Power (CHP) plants present lower electric efficiency in comparison to large scale ones, and this is particularly true when biomass fuels are used. In most cases, the use of both heat and electricity to serve on site energy demand is a key issue to achieve acceptable global energy efficiency and investment profitability. However, the heat demand follows a typical daily and seasonal pattern and is influenced by climatic conditions, in particular in the case of residential and tertiary end users. During low heat demand periods, a lot of heat produced by the CHP plant is discharged. In order to increase the electric conversion efficiency of small scale micro turbine for heat and power cogeneration, a bottoming ORC system can be coupled to the cycle, however this option reduces the temperature and quantity of cogenerated heat available to the load. In this perspective, the paper presents the results of a thermo-economic analysis of small scale CHP plants composed by a micro gas turbine (MGT) and a bottoming Organic Rankine Cycle (ORC), serving a typical residential energy demand. For the topping cycle three different configurations are examined: 1) a simple recuperative micro gas turbine fuelled by natural gas (NG), 2) a dual fuel EFGT cycle, fuelled by biomass and natural gas (50% energy input) (DF) and 3) an externally fired gas turbine (EFGT) with direct combustion of biomass (B). The bottoming cycle is a simple saturated Rankine cycle with regeneration and no superheating. The ORC cycle and the fluid selection are optimized on the basis of the available exhaust gas temperature at the turbine exit. The research assesses the influence of the thermal energy demand typology (residential demand with cold, mild and hot climate conditions) and CHP plant operational strategies (baseload vs heat driven vs electricity driven operation mode) on the global energy efficiency and profitability of the following three configurations: A) MGT with cogeneration; B) MGT+ ORC without cogeneration; C) MGT+ORC with cogeneration. In all cases, a back-up boiler is assumed to match the heat demand of the load (fed by natural gas or biomass). The research explores the profitability of bottoming ORC in view of the following tradeoffs: (i) lower energy conversion efficiency and higher investment cost of high biomass input rate with respect to natural gas; (ii) higher efficiency but higher costs and reduced heat available for cogeneration in the bottoming ORC; (ii) higher primary energy savings and revenues from feed-in tariff available for biomass electricity fed into the grid.Copyright

Biomass Utilization in Dual Combustion Gas Turbines for Distributed Power Generation in Mediterranean Countries

In Mediterranean regions, such as Puglia in Italy, the supply chain constraints (i.e. local biomass availability, logistics of supply, storage and seasonality issues) limit the optimal size of a biomass fired power plant in a range of 5–15 MWe. In this scenario, innovative Dual Combustion Externally Fired Gas Turbine (DCGT) Power Plants cofired by natural gas and biomass are examined. For this purpose, biomass external firing is explored under two alternatives: direct combustion of solid biomass and atmospheric fixed bed biomass gasification with air. The proposed cycles are analyzed considering both the Net Overall Electric Efficiency and the Marginal Efficiency of biomass energy conversion, defined for the cofiring of biomass and natural gas. Since natural gas represents a quite expensive fossil fuel resource, a Marginal Efficiency higher than zero indicates the convenience to burn natural gas in this typology of power plant rather than in traditional Combined Cycle with higher efficiency. The energy analysis has been carried out by varying pressure ratio, turbine inlet temperature, heat exchanger efficiency and considering the further option of steam injection. The results of the thermodynamic assessment highlight that the gasification should be preferred to the direct combustion of biomass because of the higher marginal efficiency, although the net overall electric efficiencies of the two plants are almost the same (31%).Copyright

Tests for outdoor window profiles: 90° mortise tenon corner joints strength assessment

Abstract The research focuses on the assessment of the performances of glued laminated wood corner joints for outdoor window profiles applications, proposing a methodology to appreciate the strength of 90° tenon mortise corner joints. The rationale relies on the potential damage (i.e. breaking of the frame) that can be caused by poor glueing processes and/or typology of adhesives. There is a number of standards for assessment of wood-adhesive bonds for outdoor windows; however, there is a lack of specific standards related to glueing assessment for outdoor wood frames, which can take into account all the factors influencing the glueing quality. The proposed methodology was tested on red oak window profiles. A commercially available polyvinyl acetate-based adhesive was used for corner joints. Bending strength of 90° tenon mortise corner joints was measured and compared with maximum admissible loads on the frame to limit its deformations within admissible ranges. The test results show that the 90° tenon mortise corner joints strength exceeds the admissible load to preserve the functionality of the frame. In order to appreciate the influence of conditioning processes on adhesion, shear strength tests of the flatwise glued joint samples (bond lines of lamellae) were carried out after different conditioning processes.

Hybrid solar-biomass combined Brayton/organic Rankine-cycle plants integrated with thermal storage: Techno-economic feasibility in selected Mediterranean areas

This paper presents the thermodynamic analysis and techno-economic assessment of a novel hybrid biomass-solar combined-cycle system configuration composed of an externally fired gas-turbine (EFGT) fuelled by biomass (wood chips) and a bottoming organic Rankine cycle (ORC) plant. The main novelty arises from the consideration of heat recovery from the exhaust gases of the EFGT via the use of thermal energy storage (TES), with the thermal energy store also receiving heat from a field of parabolic-trough collectors (PTCs) with molten salts used as a heat-transfer fluid (HTF), adopting the ENEA technology of the Archimede project. The presence of TES between the topping and bottoming cycles facilitates the flexible operation of the system, allows the system to compensate for solar energy input fluctuations, and increases capacity factor and dispatchability. A TES with two molten salt tanks (one cold at 200 °C and one hot at 370 °C) is chosen. The selected bottoming ORC is a superheated recuperative cycle suitable for heat conversion in the operating temperature range of the TES with good cycle efficiency. The whole system is modelled by means of a Python-based software code, and three locations in the Mediterranean area are used in order to perform energy-yield analyses: Marseille in France, Priolo Gargallo in Italy and Rabat in Morocco. In each case, the thermal store that minimizes the levelized cost of energy (LCE) is selected on the basis of the estimated solar radiation and CSP size. The results of the thermodynamic simulations, capital and operational costs assessments and subsidies (feed-in tariffs for biomass and solar electricity available in the Italian framework), allow estimates of the global energy conversion efficiency and investment profitability in the three locations. Sensitivity analyses on the biomass costs, size of PTCs, feed-in tariff and share of cogenerated heat delivered to the load are also performed. The results show that the high investment costs of CSP in the proposed size range and hybridization configuration allow investment profitability only in the presence of a dedicated subsidy framework such as the one available in the Italian energy market. In particular, the LCE of the proposed system is around 140 Eur/MWh (with the option to discharge the cogenerated heat) and the IRR is around 15%, based on the Italian electricity subsidy tariffs. The recovery of otherwise discharged heat to match thermal energy demand can significantly increase the investment profitability and compensate the high investment costs of the proposed technology.

Optimisation of Integrated Bioenergy and Concentrated Solar Power Supply Chains in South Africa

Abstract Climate change and energy security are complex challenges whose solutions depend on multi-faceted interactions between different actors and socio-economic contexts. Energy innovation through integration of renewable energies in existing systems offers a partial solution, with high potential identified for bioenergy and solar energy. In South Africa there is potential to further integrate renewable energies to meet local demands and conditions. Various concentrated solar power (CSP) projects are in place, but there is still land available to generate electricity from the sun. In combination with sustainable biomass resources these can offer synergetic benefits in improving the power generation’s flexibility. While thermodynamic and thermo-economic modelling for hybrid CSP-Biomass technology have been proposed, energy modelling in the realm of supply chains and demand/supply dynamics has not been studied sufficiently. We present a spatially and temporally Mixed Integer Linear Programming (MILP) model, to optimize the choice and location of technologies in terms of economic cost while being characterised by realistic supply/demand constraints as well as spatially-explicit environmental constraints. The model is driven by electricity demand, resource availability and technology costs as it aspires to emulate key energy and sustainability issues. A case study in the South African province of Gauteng was implemented over 2015-2050 to highlight the potential and challenges for hybrid CSP-Biomass and integrated systems assessment and the applicability of the modelling approach. From the range of hybrid CSP-Biomass technologies considered, based on detailed techno-economic characteristics from the literature, the Biomass only EFGT plant is identified as the cost optimal. When distributed generation (DG) technologies, small-scale Solar PV and Wind Turbines were introduced to the model as a competing alternative, they were demonstrated to be more economically optimal (€65 mil against €85 mil with CSP-Biomass Industrial scale), driven by technology learning cost reductions, evidencing the case for DG technologies to gain momentum. Together these scenarios highlight the possible carbon savings from integrating multiple renewable energy technologies.