Thermo-economic Assessment of Small Scale Biomass CHP: Steam Turbines vs ORC in Different Energy Demand Segments☆

AbstractThe energy performance and profitability of CHP plants, and the selection of the optimal conversion technology and size, are highly influenced by the typology of energy demand (load-duration curve, temperature of heat demand, heat and electricity load patterns). In the small scale range, where CHP can be particularly promising to match local heat and power demand, the technologies based on boilers coupled to steam turbines (ST) and bottoming Organic Rankine Cycle (ORC) can be operated in flexible mode to match the energy demand. This is particularly important when high temperature heat is required (i.e. industrial end users). In the case of solid biomass fired CHP, the boiler + ST/ORC option could be competitive with the alternatives of boiler + Stirling engine, externally fired GT or gasification + ICE. In this paper, a thermo-economic comparison of the following biomass-CHP configurations is proposed: (A) boiler + ST + bottoming ORC, (B) boiler + ST, (C) boiler + ORC and (D) configuration (A) with option to switch on or off the bottoming ORC on the basis of the heat demand available. The focus is on a 1 MWt biomass boiler, and the plants are operated to serve residential (r), tertiary (t) and industrial (i) heat and power demand. The thermodynamic cycles are modeled by Cycle-Tempo, while the energy demand is modeled through simplified indicators (temperature of heat demand, equivalent thermal demand hours). On the basis of the results of thermodynamic simulations, upfront and operational costs assessment, and Italian energy policy scenario (feed-in tariffs for biomass electricity), the global energy conversion efficiency and investment profitability is estimated, for each CHP configuration and energy demand segment. The results indicate the optimal CHP configuration for each end user and the key technical and economic factors in the Italian legislative framework

GT2006-90590 PERFORMANCE OF GAS TURBINE POWER PLANTS CONTROLLED BY MULTIAGENT SCHEME

ABSTRACT In latter years the idea of artificial intelligence has been focused around the concept of a rational agent. An agent is a (software or hardware) entity that can receive signals from the environment and act upon that environment through output signals. In general an agent always tries to carry out an appropriate task. Seldom agents are considered as stand-alone systems. Their main strength can be found in the interaction with other agents in several different ways in a multiagent system. In the present work, multiagent system approach will be used to manage the control process of a single-shaft heavy-duty gas turbine in Multi Input Multi Output mode. The results will show that the multiagent approach to the control problem effectively counteracts the load reduction (including the load rejection condition) with limited overshoot in the controlled variables (as other control algorithms do) while showing good level adaptivity readiness, precision, robustness and stability

Flame Describing Function analysis of spinning and standing modes in an annular combustor and comparison with experiments

This article reports a numerical analysis of combustion instabilities coupled by a spinning mode or a standing mode in an annular combustor. The method combines an iterative algorithm involving a Helmholtz solver with the Flame Describing Function (FDF) framework. This is applied to azimuthal acoustic coupling with combustion dynamics and is used to perform a weakly nonlinear stability analysis yielding the system response trajectory in the frequency-growth rate plane until a limit cycle condition is reached. Two scenarios for mode type selection are tentatively proposed. The first is based on an analysis of the frequency growth rate trajectories of the system for different initial solutions. The second consid- ers the stability of the solutions at limit cycle. It is concluded that a criterion combining the stability analysis at the limit cycle with the trajectory analysis might best define the mode type at the limit cy- cle. Simulations are compared with experiments carried out on the MICCA test facility equipped with 16 matrix burners. Each burner response is represented by means of a global FDF and it is considered that the spacing between burners is such that coupling with the mode takes place without mutual interac- tions between adjacent burning regions. Depending on the nature of the mode being considered, two hypotheses are made for the FDFs of the burners. When instabilities are coupled by a spinning mode, each burner features the same velocity fluctuation level implying that the complex FDF values are the same for all burners. In case of a standing mode, the sixteen burners feature different velocity fluctua- tion amplitudes depending on their relative position with respect to the pressure nodal line. Simulations retrieve the spinning or standing nature of the self-sustained mode that were identified in the exper- iments both in the plenum and in the combustion chamber. The frequency and amplitude of velocity fluctuations predicted at limit cycle are used to reconstruct time resolved pressure fluctuations in the plenum and chamber and heat release rate fluctuations at two locations. For the pressure fluctuations, the analysis provides a suitable estimate of the limit cycle oscillation and suitably retrieves experimental data recorded in the MICCA setup and in particular reflects the difference in amplitude levels observed in these two cavities. Differences in measured and predicted amplitudes appear for the heat release rate fluctuations. Their amplitude is found to be directly linked to the rapid change in the FDF gain as the velocity fluctuation level reaches large amplitudes corresponding to the limit cycle, underlying the need of FDF information at high modulation amplitudes

Natural gas-biomass dual fuelled microturbines: Comparison of operating strategies in the Italian residential sector

This paper compares different operating strategies for small scale (100 kWe) combined heat and power (CHP) plants fired by natural gas and solid biomass to serve a residential energy demand. The focus is on a dual fuel micro gas turbine (MGT) cycle. Various biomass/natural gas energy input ratios are 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. On the basis of the results from thermodynamic assessment and simulation at partial load operation, CAPEX and OPEX estimates, and Italian energy policy scenario (incentives available for biomass electricity, on-site and high efficiency CHP), the maximum global energy efficiency, primary energy savings and investment profitability is found, as a function of biomass/natural gas ratio, plant operating strategy and energy demand typology. The thermal and electric conversion efficiency ranged respectively between 46 and 38% and 30 and 19% for the natural gas and biomass fired case studies. The IRR of the investment was highly influenced by the load/CHP thermal power ratio and by the operation mode. The availability of high heat demand levels was also a key factor, to avoid wasted cogenerated heat and maximize CHP sales revenues. BL operation presented the highest profitability because of the higher revenues from electricity sales. Climate area was another important factor, mainly in case of low load/CHP ratios. Moreover, at low load/CHP power ratio and for the BL operation mode, the dual fuel option presented the highest profitability. This is due to the lower cost of biomass fuel in comparison to natural gas and the high subsidies available for biomass electricity by feed-in tariffs. The results show that dual fuel MT can be an interesting option to increase efficiencies, flexibility and plant reliability at low cost in comparison to only biomass systems, facilitating an integration of renewable and fossil fuel systems

Biomass integrated gas turbine and ORC combined cycle: Layout and performance analysis

Starting from a previously proposed Integrated Gasification Combined Cycle power plant with an externally fired gas turbine and a bottoming heat recovery steam generator, in this paper a new plant scheme is proposed. The main changes concern, on one hand, a plant layout simplification by removing a regenerative heat exchanger, on the other hand, the replacement of the Water Rankine Cycle with an Organic one. The thermodynamic model of the entire system has been developed by means of the Cycle-Tempo software. The gasification process has been supposed to occur at ambient pressure and air is used as gasifying agent. Moreover, considering the small size (below 1 MW) of this Combined Cycle power plant, the new configuration embodying an Organic Rankine Cycle appears to be more suited for the biomass conversion process even though shows a slightly lower conversion efficiency

Cycle configuration analysis and techno-economic sensitivity of biomass externally fired gas turbine with bottoming ORC

This paper focuses on the energy analysis of a combined cycle composed by a topping 1.3 MW Externally Fired Gas Turbine (EFGT) with direct combustion of biomass and a bottoming Organic Rankine Cycle (ORC). A non recuperative scheme is assumed for the EFGT in order to avoid the costs of the recuperator. This scheme presents lower conversion efficiency in comparison to a recuperative one, however the heat available for the bottoming cycle is at a higher temperature (about 400 °C). In the present work, evaporation pressure and superheating temperature of ORC cycle are ranged in order to examine different bottoming cycles, including supercritical ones. Different organic fluids are investigated, such as siloxanes and toluene, aiming to analyze how the fluid choice influences both the plant performance and important features for the ORC turbine design. On the basis of the results of the thermodynamic simulation, a thermo-economic assessment is proposed, to investigate the profitability of the bottoming ORC in comparison to only topping EFGT, and the most influencing techno-economic factors that influence the selection of the optimal cycle. In order to propose real case studies, the Italian bioenergy subsidy framework is assumed, and the sensitivity assessment includes the options of only electricity and CHP, at different biomass cost, thermal energy demand and heat selling price values

Hydrodynamics of Bubbling Fluidized Beds for Biomass Gasification: Influence of Particle-drag within an Eulerian Granular Model

Particles’ mixing and segregation have a strong influence on the performance of fluidized bed reactors for gasification and pyrolysis. The interaction forces between phases are crucial for modeling mixing and segregation. The nature of particle characteristics such as shape are also very important to consider for accurate modeling. In this work, the hydrodynamic study of binary mixture of biomass and sand is conducted in a 2-D fluidized bed using Computational Fluid Dynamics (CFD) based on the concept of Euler–Euler two-fluid combined with Kinetic Theory of Granular Flow (KTGF). Modified drag models of Gidaspow and Syamlal–O'Brien are used to determine the drag force between the two phases and the results are compared with the experimental data in literature. The default Gidaspow and Syamlal–O'Brien drag models failed to predict the experimental fluidization behavior. In comparison, the modified models show very good agreement with experiments in terms of pressure drop estimation and particle distribution in the bed. Syamlal–O'Brien model predicted the pressure drop very well, but failed to capture accurate mixing and segregation phenomenon. The Gidaspow model was found to provide better agreement with the experimental results of time-averaged biomass mass fraction along the bed height

CFD analysis of the combustion in the BERL burner fueled with a hydrogen-natural gas mixture

The regulatory restrictions, currently acting, impose a significant reduction of the Greenhouse Gas (GHG) emissions. After the coal-to-gas transition of the last decades, the fossil fuel-to-renewables switching is the current perspective. However, the variability of energy production related to Renewable Energy Sources requires the fundamental contribution of thermal power plants in order to guaranty the grid stability. Moving toward a low-carbon society, the industry is looking at a reduction of high carbon content fuels, pointing to Natural Gas (NG) and more recently to hydrogen-NG mixtures. In this scenario, a preliminary study of the BERL swirled stabilized burner is carried out in order to understand the impact of blending natural gas with hydrogen on the flame morphology and CO emissions. Preliminary 3D CFD simulations have been run with the purpose to assess the best combination of combustion model (Non Premixed and Partially Premixed Falmelets), turbulence model (Realizable k ɛ and the Reynolds Stress equation model) and chemical kinetic mechanism (GriMech3.0, GriMech 1.2 and Frassoldati). The numerical results of the BERL burner fueled with natural gas have been compared with experimental data in terms of flow patterns, radial temperature profiles, O2, CO and CO2 concentrations. Finally, a 30% hydrogen in natural gas mixture has been considered, keeping fixed the thermal power output of the burner and the global equivalence ratio

Slip Factor Correction in 1-D Performance Prediction Model for PaTs

In recent years, pumps operated as turbines (PaTs) have been gaining the interest of industry and academia. For instance, PaTs can be effectively used in micro hydropower plants (MHP) and water distribution systems (WDS). Therefore, further efforts are necessary to investigate their fluid dynamic behavior. Compared to conventional turbines, a lower number of blades is employed in PaTs, lowering their capability to correctly guide the flow, hence reducing the Euler’s work; thus, the slip phenomenon cannot be neglected at the outlet section of the runner. In the first part of the paper, the slip phenomenon is numerically investigated on a simplified geometry, evidencing the dependency of the lack in guiding the flow on the number of blades. Then, a commercial double suction centrifugal pump, characterized by the same specific speed, is considered, evaluating the dependency of the slip on the flow rate. In the last part, a slip factor correlation is introduced based on those CFD simulations. It is shown how the inclusion of this parameter in a 1-D performance prediction model allows us to reduce the performance prediction errors with respect to experiments on a pump with a similar specific speed by 5.5% at design point, compared to no slip model, and by 8% at part-loads, rather than using Busemann and Stodola formulas