Search

The present paper describes an experimental characterisation of a biomass powered micro-cogeneration system based on the coupling between a gasifier and an internal combustion engine. The ECO 20 unit is sized to deliver a maximum electrical and thermal power of 20 kWe and 40 kWth, respectively. In order to highlight possible inefficiencies along the biomass-to-energy conversion chain, the global energy balance of the system under real working conditions is derived. Ultimate and proximate analyses of the processed biomass are performed, accompanied by temperature and mass flow rate measurements and gas chromatograph characterization of collected samples of the produced syngas. The greatest inefficiency is found in the gasification section with a value of the cold gas efficiency in the range of 57–60%. The low quality of the syngas (lower heating value equal to 3731 kJ/Nm3) affects the engine combustion efficiency, hence its electrical efficiency that does not exceed 22.5%. The global electrical efficiency of the plant is equal to about 13.5%. As a further analysis, waste heat recovery is considered under different conditions by decreasing the temperature of the water flowing in the secondary circuit from 68.35 °C to 20.50 °C for the use of the provided thermal energy. This determines an increase of the thermal efficiency of the engine from 11.3% to 56.2%, while the global thermal efficiency increases from 6.46% to 33.72%. A feature of the ECO 20 system is the cooling of the syngas delivered to the engine by its same cooling water, for a considerable advantage on volumetric efficiency with respect to other analogous systems, also in the cases the thermal power is not utilised.

The valorization of residual biomass plays today a decisive role in the concept of &ldquo, circular economy&rdquo, according to which each waste material must be reused to its maximum extent. The collection and energy valorization at the local level of biomass from forest management practices and wildfire prevention cutting can be settled in protected areas to contribute to local decarbonization, by removing power generation from fossil fuels. Despite the evident advantages of bioenergy systems, several problems still hinder their diffusion, such as the need to assure their reliability by extending the operating range with materials of different origin. The Italian project &ldquo, INNOVARE&mdash, Innovative plants for distributed poly-generation by residual biomass&rdquo, funded by the Italian Ministry of Economic Development (MISE), has the main scope of improving micro-cogeneration technologies fueled by biomass. A micro-combined heat and power (mCHP) unit was chosen as a case study to discuss pros and cons of biomass-powered cogeneration within a national park, especially due to its flexibility of use. The availability of local biomasses (woodchips, olive milling residuals) was established by studying the agro-industrial production and by identifying forest areas to be properly managed through an approach using a satellite location system based on the microwave technology. A detailed synergic numerical and experimental characterization of the selected cogeneration system was performed in order to identify its main inefficiencies. Improvements of its operation were optimized by acting on the engine control strategy and by also adding a post-treatment system on the engine exhaust gas line. Overall, the electrical output was increased by up to 6% using the correct spark timing, and pollutant emissions were reduced well below the limits allowed by legislation by working with a lean mixture and by adopting an oxidizing catalyst. Finally, the global efficiency of the system increased from 45.8% to 63.2%. The right blending of different biomasses led to an important improvement of the reliability of the entire plant despite using an agrifood residual, such as olive pomace. It was demonstrated that the use of this biomass is feasible if its maximum mass percentage in a wood matrix mixture does not exceed 25%. The project was concluded with a real operation demonstration within a national park in Southern Italy by replacing a diesel genset with the analyzed and improved biomass-powered plant and by proving a decisive improvement of air quality in the real environment during exercise.

Syngas deriving from biomass gasification is receiving increased interest as an alternative fuel in spark ignition (SI) engines for power generation, despite problems related to the variability of its composition and the low energy density. Syngas release from gasifiers is indeed strongly affected by the quality of the feedstock and by the specific features and control strategy of the reactor. The paper considers the possibility to achieve, at the same time, high efficiency and low pollutant emissions of a syngas powered engine by acting on operating variables as the spark timing and the air-to-fuel ratio, with also the possible inclusion of exhaust gas recirculation (EGR). Model-based design and multi-objective optimization methods are applied as a feasible approach to address this issue, hence to improve the energetic and the environmental performances of power generation under a flexible fuel quality. A one-dimensional (1D) model of a naturally aspirated SI engine fuelled by syngas, properly developed and validated through a specific experimental campaign, is here presented to investigate the effect of the main controlling variables on power output and emissions. A proper design of experiment (DoE) space is considered. The 1D model is coupled with a genetic optimization algorithm for the search of the best compromise solution between maximum performance and minimum pollutants amount. The identified optimal solution allows a reduction up to the 50% for both nitrogen oxides and carbon monoxide emissions with a negligible worsening of the power output.

Biomass gasification for the release of a syngas and its use in combined heat and power (CHP) generation systems are attracting realities in the European market, due to the perspective to provide energy to remote districts by using local renewable sources, as residuals of forest practices or agro-food industries. The syngas produced from biomass gasification is a feasible alternative to traditional fuels in internal combustion engines at the micro and small power scales, although the quality of the produced gas is poorer in terms of calorific value and laminar flame speed. Therefore, as a direct consequence, proper modifications and optimizations of engines are needed to enhance energy efficiency and reduce the environmental impact. In the present work, a numerical model for the simulation of a compression ignition engine fueled in the dual-fuel mode with syngas and biodiesel is presented. The aim is to highlight the main influences on the combustion process related to the use of syngas and the effects of different biomass moisture contents on power output and main pollutants emission. The used extended coherent flamelet model for turbulent combustion is preliminary validated on the basis of experimental data of engine pressure cycles collected under only biodiesel fueling.

A Combined Heat and Power (CHP) system fuelled with rice husk is analysed from the thermodynamic, exergetic and economic point of view. The system is based on a gasification process coupled with a rice drying system. The produced syngas is employed to power a Spark Ignition (SI) Internal Combustion Engine (ICE) working as an electric generator, while the jacket cooling water powers a bottoming Organic Rankine Cycle (ORC) to produce electricity for plant self-consumption. A parametric analysis is carried out to investigate thermodynamic performances by varying the gasifier Equivalent Ratio (ER): as the ER increases, the ICE produced power and combustion efficiency decrease, while the thermal efficiency increases. However, the system is always capable to produce power for self-consumption and the desiccant flow for drying. The characterization of the engine is then better assessed by means of a dedicated GT-Power engine model, optimized for syngas fuelling, revealing a power derating of the 30% with respect to the natural-gas feeding operation. Other main findings suggest that the global exergetic efficiency ranges between 10.6% and 8.5%, while the economic profitability, represented by the Simple Pay Back, Net Present Value and Profit Ratio, cannot be considered satisfactory due to the consistent investment cost.

Model-based optimization offers the appealing opportunity of interpolating performance of a physical system between settings and of inferring its behaviour from previously unobserved areas of the parameter space, up to the optimal one. Application of this technique to micro-Combined Heat and Power (m-CHP) generation based on biomass gasification allows better exploiting the potential of this renewable energy source (RES) and of the specific technology for thermo-chemical conversion. A numerical model of a real CHP plant of the micro-scale of power, the ECO20 manufactured by the Italian Company Costruzioni Motori Diesel S.p.A., is presented in this paper as coupled with an optimization algorithm for the search of the best performance in terms of electric power output. The considered m-CHP system, made of a gasifier, a syngas cleaning system and a spark ignition Internal Combustion Engine (ICE) working as a co-generator, is fueled by woodchip. The plant model is realized by schematizing the whole biomass-to-energy chain within the Thermoflex™ environment and, simultaneously, by improving the prediction of the ICE performance through a properly developed and validated one-dimensional (1D) model in GT-Suite®. Simulation of the combustion process is specifically customized for syngas use, namely to account for the extreme variability of this fuel that strongly depends upon the kind of processed biomass and the gasifier operating conditions. The system model is validated on the ground of experimental data collected on the real plant and is coupled with the modeFRONTIER™ software for the optimal choice of the main operating parameters. The final purpose of the work is the assessment of a framework for the energetic and environmental optimization of biomass-powered cogeneration systems suitable of being used under various conditions and for various purposes. The here reported case study consists of the optimization of the electric power output by the considered m-CHP unit as a function of the equivalence ratio at the gasifier and of the ICE spark advance. Starting from an electric output of 17 kW, measured during the experimental campaign, it is demonstrated that an improvement of 6% on the electric power can be reached by acting only on the system parameters settings, without changing the system components.

Energy valorization of organic waste material is nowadays an assessed practice of circular economy. Combined heat and power (CHP) technologies based on biomass gasification represent viable substitutes to traditional energy conversion units based on combustion, whose need has recently experienced a huge growth, due to the increasing concerns about the release of greenhouse gases (GHGs) emissions and the related effects on climate changes. At present, only a few solutions have yet achieved a level of full development for commercialization. One of them is the system developed by CMD, the CMD ECO20, made of a gasifier, a syngas cleaning system and a spark ignition internal combustion engine working as a co-generator. In the present work, a numerical model is developed to study this system into detail and search for optimal controlling parameters. The simulation relies on a combined use of the Thermoflex™ environment and a proper one-dimensional (1D) model of the engine module built within GT-Suite®. An original contribution is given to the turbulent combustion model that accounts for the laminar flame speed of the specific syngas. The numerical model, that covers the entire biomass-to-energy conversion process, is validated under real operative conditions. The final purpose of the work is the optimization of input parameters, as the initial biomass moisture content, the equivalence ratio at the gasifier or the timing of spark advance, to maximize the system electrical energy output., Proceedings of the 26th European Biomass Conference and Exhibition, 14-17 May 2018, Copenhagen, Denmark, pp. 1547-1559

The present paper describes an experimental characterisation of a biomass powered micro-cogeneration system based on the coupling between a gasifier and an internal combustion engine. The ECO 20 unit is sized to deliver a maximum electrical and thermal power of 20 kWe and 40 kWth, respectively. In order to highlight possible inefficiencies along the biomass-to-energy conversion chain, the global energy balance of the system under real working conditions is derived. Ultimate and proximate analyses of the processed biomass are performed, accompanied by temperature and mass flow rate measurements and gas chromatograph characterization of collected samples of the produced syngas. The greatest inefficiency is found in the gasification section with a value of the cold gas efficiency in the range of 57-60%. The low quality of the syngas (lower heating value equal to 3731 kJ/Nm3) affects the engine combustion efficiency, hence its electrical efficiency that does not exceed 22.5%. The global electrical efficiency of the plant is equal to about 13.5%. As a further analysis, waste heat recovery is considered under different conditions by decreasing the temperature of the water flowing in the secondary circuit from 68.35 °C to 20.50 °C for the use of the provided thermal energy. This determines an increase of the thermal efficiency of the engine from 11.3% to 56.2%, while the global thermal efficiency increases from 6.46% to 33.72%. A feature of the ECO 20 system is the cooling of the syngas delivered to the engine by its same cooling water, for a considerable advantage on volumetric efficiency with respect to other analogous systems, also in the cases the thermal power is not utilised.

The paper presents the experimental validation of a one-dimensional (1D) model of biomass gasification in a downdraft gasifier. The model considers the main processes underlying the thermo-chemical transformation of the biomass into a syngas suitable of being used as a fuel in reciprocating internal combustion engines. The downdraft gasifier is discretized as a sequence of layers where drying, pyrolysis, combustion and gasification take place. The biomass is assumed as entering the system with its content of moisture, volatile matter, ash and fixed carbon. Nine species participate chemical reactions: O2, N2, H2O, CO2, H2, CO, CH4, H2S, TAR. The mass and energy conservation equations are written by considering the heat transfer between the solid particles, the gaseous phase and the reactor walls. The resulting system of differential-algebraic equations is numerically solved by splitting it into two sub-systems: one made of differential equations solved through algorithms suitable for the solution of stiff problems, one made of non-linear algebraic equations solved through the Newton-Raphson algorithm. The developed 1D model is a suitable tool to study the influence of process parameters as biomass size and composition, equivalence ratio, kind of gasification agent and gasifier geometry. A validation of the proposed model is presented with reference of a real gasifier, being a part of the CMD ECO20 biomass powered micro-cogeneration system under development by CMD. The system is analysed in its operation as connected to a reciprocating spark ignition engine and a generator. Woodchip is the treated biomass, whose composition is determined through proper proximate and ultimate analyses. Biomass composition is given as input to the 1D gasifier model. Obtained results in terms of gasification temperature and chemical species conversion along the gasifier axis are reported and compared with measurements effected through thermocouples in the reactor and with gas chromatograph analyses of syngas samples collected at the plan site.

Worldwide escalating energy consumption of recent years, due to the earth population growth and the spreading of industrialization, has resulted in an increased concern about the environmental impact of energy conversion systems. Heavy exploitation and extensive use of fossil fuels have indeed also led to envisage their foreseeable depletion, thus opening the way to the use of alternative fuels as biomass. Among thermo-chemical treatments of biomass, gasification is particularly attractive for its release of syngas (or producer gas), suitable of being used in various combustion systems, including internal combustion engines. In principle, biomass contaminants and heavy hydrocarbons can be removed during syngas cleaning, before the actual combustion process, thus leading to an overall cleaner conversion process. At present, demonstrating operational feasibility and effectiveness of gasification technologies and proving long term sustainability, also through the enhancement of fuel flexibility, are recognized as key elements for the development and market diffusion of biomass energy systems. In fact, although gasification has been known for a long time, its control has long requested serious efforts by researchers and manufacturers. Nowadays, new perspectives are imaginable thanks to the use of simulation tools that may reveal particularly useful to improve gasification efficiency and increase the quality of the producer gas. In recent years, several numerical models have been indeed proposed to characterise and predict such a complex process, where drying, pyrolysis, gasification and combustion take place simultaneously. This article presents a general overview of gasification models available, with emphasis on those based on the stoichiometric method. Although this last may seem too restrictive under some circumstances, equilibrium models are useful to predict the maximum yield attainable by a reagent system, since they reproduce an ideal gasification performance. Due to their simplicity and the reduced computational time, these models are suitable of being employed in a first stage of an analysis or within optimization procedures, where the influence of a number of parameters has to be investigated or a choice of the optimal biomass to be treated for a certain scope is to be made.

The effects of splitting the injection event in a GDI (gasoline direct injection) engine operating with a HOS (homogeneous stratified) lean charge are analysed through experimental and numerical techniques. Injection is assumed as divided in two parts, each delivering the same gasoline amount, the first occurring during intake, the second during compression. The work is initially focused on the experimental characterization of the engine under study for the collection of data concerning the in-chamber combustion development. Beside measurements of in–cylinder pressure, UV chemiluminescence is applied to follow the OH radicals formation from spark ignition up to the late combustion phase, thanks to the optical accessibility to the combustion chamber. The collected data serve to the validation of a properly formulated three-dimensional (3D) CFDs model for the simulation of the whole engine working cycle. The definition of the control strategy leading to the greatest combustion efficiency and lowest pollutants emission is made in two steps through numerical optimization: the 3D CFD model is first run to build a low number of samples to be used within a Gaussian RSM (response surface method) to reconstruct, in the DOE (design of experiments) space, the integral of the in–cylinder pressure over volume in the closed valve period; in the second step, the coupling between the 3D engine model and the Simplex algorithm is performed in a restricted DOE subdomain defined according to the first step analysis. The assessed methodology highlights the synchronization of both spark ignition and split injection leading to the highest power output and the lowest pollutants release. The experimental verification of the numerical findings is finally carried out.

Present work applies both advanced experimental and numerical techniques to study the effects of splitting the injection event in a gasoline direct injection (GDI) engine operating with a homogeneous stratified (HOS) lean charge. Injection is assumed as divided in two parts, each delivering the same gasoline amount, the first occurring during intake, the second during compression. The work is initially focused on the experimental characterization of the engine under study for the collection of data concerning the in-chamber combustion development. Beside measurements of in-cylinder pressure, UV chemiluminescence is applied to follow the OH radicals formation from spark ignition up to the late combustion phase, thanks to the optical accessibility to the combustion chamber. The collected data serve to the validation of a properly formulated three-dimensional (3D) computational fluid dynamic (CFD) model for the simulation of the whole engine working cycle. The definition of the control strategy leading to the greatest combustion efficiency and lowest pollutants emission is made in two steps through numerical optimization: the 3D CFD model is first run to build a low number of samples to be used within a Gaussian response surface method (RSM) to reconstruct, in the DOE (design of experiments) space, the integral of in-cylinder pressure over volume in the closed valve period; in the second step, the coupling between the 3D engine model and the Simplex algorithm is performed in a restricted DOE subdomain defined according to the first step analysis. The assessed methodology highlights the spark ignition and split injection synchronization leading to the highest power output and the lowest pollutants emission. The experimental verification of the numerical findings is finally carried out.