Paolo Laranci

CFD Simulation of Biomass Pyrolysis Syngas vs. Natural Gas in a Microturbine Annular Combustor

Biomass to energy conversion is particularly attractive on the microscale were internal combustion engines such as microturbines may be utilized coupled to an indirect gasification system. The authors have developed the IPRP technology based on rotary kiln pyrolisys and a pilot plant was built in Italy powered by an 80 kWEl microturbine fired by pyrolysis biomass syngas. This paper describes CFD numerical investigations carried out to study the combustion process occurring inside the annular rich-quick-lean combustion chamber of the given microturbine. A RANS analysis has been performed in order to simulate both natural gas and syngas combustion. A mechanisms based on two reduced and detailed chemical kinetic were taken into account and applied to carry out the CFD simulations. The numerical results obtained for NG are presented and compared with the experimental data on emission to validate the numerical assumptions. The combustion mechanism are used also in pyrolysis gas combustion case to investigate the operation of the microturbine fuelled with this biomass derived fuel.Copyright

CFD Simulation of a Microturbine Annular Combustion Chamber Fuelled With Methane and Biomass Pyrolysis Syngas: Preliminary Results

Micro gas turbines could be profitably used, for distributed energy production, also exploiting low calorific value biomass-derived fuels, obtained by means of integrated pyrolysis and/or gasification processes. These synthesis gases show significant differences with respect to natural gas (in terms of composition, low calorific value, hydrogen content, tar and particulate matter content) that may turn into ignition problems, combustion instabilities, difficulties in emission control and fouling. CFD simulation of the combustion chamber is a key instrument to identify main criticalities arising when using these gases, in order to modify existing geometries and to develop new generation combustion chambers for use with low calorific value gases. This paper describes the numerical activity carried out to analyze the combustion process occurring inside an existing microturbine annular combustor. A CFD study of the combustion process performed with different computational codes is introduced and some preliminary results are reported in the paper. A comparison of results obtained with the different codes is provided, for the reference case of methane combustion. A first evaluation of the pollutant emissions and a comparison with the available experimental data is also provided in the paper, showing in particular a good matching of experimental data on NOx emissions at different load conditions. Moreover, the carried out investigation concerns the case of operation with a syngas fuel derived from pyrolysis of biomass and finally the case of syngas and natural gas co-firing. This combustion condition is simulated with a simple reduced chemical kinetic scheme, in order to assess only the key issues rising with this fuel in comparison with the case of methane combustion. The analysis shows that in case of syngas operation the combustor internal temperature hot spots are reduced and the primary zone flame tends to stabilize closer to the injector, with possible implications on the emission release.Copyright

Numerical Analysis of a Microturbine Combustion Chamber Modified for Biomass Derived Syngas

A CFD analysis was carried out to study the performance of a modified combustion chamber of a micro gas turbine with the objective to change its fuelling from natural gas to biomass pyrolysis gas. The micro gas turbine is a component of a pilot IPRP (Integrated Regenerated Pyrolysis Plant), a distributed energy system, based on a rotary kiln reactor for the pyrolysis of biomass. This paper describes the combustion process occurring inside the combustion chamber of the micro gas turbine. In particular, a new, revised kinetic scheme was implemented in the RANS analysis to better reproduce CO oxidation and flue gases temperature, for both methane and pyrolysis gas combustion; further investigation was undertaken on NOx formation mechanisms, which are now modeled through a non-adiabatic PPDF approach, also taking into account the effects of turbulence interaction. CFD simulations for natural gas and pyrolysis gas combustion were performed for two different annular rich-quench-lean combustion chamber configurations, one with the original design for natural gas and one with a modified design optimized for syngas, in order to quantify the advantage of using a dedicated design. Furthermore, through the numerical analysis, the hot spots of the combustor have been identified and monitored the to study the possible effects of material corrosion due to high temperatures.Copyright

Thermal degradation of driftwood: Determination of the concentration of sodium, calcium, magnesium, chlorine and sulfur containing compounds

The annual production of driftwood in Italy has been estimated to be more than 60,000 tonnes. This wood can be used as an energy source. Particular attention should be paid to its content of alkali and alkaline earth metals, sulfur and chlorine. Few works are available in the literature on this topic. For this reason, the authors propose experimental tests of combustion, gasification and pyrolysis, to evaluate the fate of alkali and alkaline earth metals, sulfur and chlorine in the solid residues and compare the three thermal degradation technologies. The results show a release of alkaline earth metals of about 45% of the initial quantity for gasification and a release of 55% of the initial quantity for combustion (while pyrolysis at 600°C has a very low release). The release of sodium is about 65% for gasification and 80% for combustion. It can be seen that the release of sodium is higher than that of alkaline earth metals; this is due to the divalency of the last ones. Dealing with the release of major elements (chlorine, sulfur and AAEMs) the tests have shown that pyrolysis process is a low emitting technology.

Experimental and CFD Evaluation of the Part Load Performance of a Micro Gas Turbine Fuelled With CH4-N2 Mixtures

There is a strong interest in numerical and experimental research on syngas combustion in GTs however experimental studies require syngas generation which is costly and also provides a variable and dirty fuel gas. To investigate the combustion behaviour and GT performance when fuelled with low LHV syngas, nitrogen diluted natural gas can be considered.To this aim the micro gas turbine (mGT) available at the IPRP (Integrated Pyrolysis Regenerated Plant) pilot facility of the University of Perugia, modified to use biomass pyrolysis gas, was fuelled with a CH4−N2 mixtures at different part load conditions obtained from pipeline (CH4) and cylinders (N2). The aim of the work is to analyze the functioning condition of the mGT which is monitored by a dedicated data acquisition system. Performances are evaluated and discussed showing that nitrogen dilution does not affect significantly efficiency and NOx production while CO emission increase slightly when increasing nitrogen content and this is more evident when decreasing the load.A CFD model of the combustion chamber, which was developed and tuned in previous works by the authors, was also run to reproduce experimental data showing a good agreement and also suggesting flame detachment in the mixing tube when nitrogen is present.© 2012 ASME

Numerical analysis of biomass-derived gaseous fuels fired in a RQL micro gas turbine combustion chamber - Preliminary results.

The economically sustainable availability of biomass residuals and the growing need to reduce carbon dioxide emissions from power generation facilities has driven the development of a series of processes that lead to the production of a variety of biomass-derived fuels gaseous fuels, such as syngas, pyrolysis gas, landfill gas and digester gas. These technologies can find an ideal coupling when used for fuelling micro gas turbines, especially for distributed power generation applications, in a range between 50 and 500 kWE . This paper features a report on numerical activity carried out at the University of Perugia on a 80 kWE micro gas turbine annular combustion chamber, featuring RQL technology, that has been numerically modeled in order to verify combustion requirements, principally in terms of air/fuel ratio and lower heating value, simulating mixtures with varying chemical composition. The use of CFD turbulence and combustion modeling, via both Eddy Break-up and non-adiabatic PPDF methods, allows us to evaluate flame temperatures and stability, NOx and unburnt hydrocarbons emissions, under various load conditions, for the different fuel mixtures taken into account.Copyright

Numerical Analysis of the Use of Vegetable Oil-Tars Mixtures From Syngas Scrubbing in a Microturbine Combustor

TARs are a mixture of heavy and light hydrocarbons produced from pyrolysis and gasification of biomass and waste, as condensable volatiles in the syngas. Given their relatively low dew point, they are usually removed from syngas to avoid condensation and fouling of engines and equipment. Vegetable oil scrubbing compared to water scrubbing yields oil tar mixtures which is a renewable fuel and may be useful successfully to power a gas turbine. The feasibility of burning TAR, blended vegetable oil, in a combustor of a turbine is investigated. Computational simulations with a CFD software were performed to analyze evaporation and combustion processes of vegetable oil-tars mixture compared with pure vegetable oil and diesel, in terms of residence time, temperature distributions, inlet turbine conditions.The results show difficulties in evaporation of both vegetable oil and vegetable oil-tar mixture compared to diesel, with consequences in the combustion in terms of temperature distributions and higher NOx emissions. Preheating of vegetable oil and vegetable oil-tar mixture improves their evaporation approaching the results to those of the diesel case.Copyright

Improving lifetime and manufacturability of an RQL combustor for microturbines: design and numerical validation

A new annular RQL combustion chamber of an 80 kWel Elliott TA80R micro gas turbine was designed and built with a modified geometry to overcome known failures at low running hours (around 2500 hrs) caused by overheating. Design considered simplified manufacturability and flow optimization to reduce emission while maintaining similar temperatures and efficiencies. A preliminary geometry was analyzed and also built to verify manufacturability and economics. It was easily built with overall brute costs around 3000 €. It has also run continuously for over 27.000 hrs.An optimized geometry, however, guaranteed similar TIT with respect to the original geometry with a considerable reduction in CO and NOx emissions.Given the installation of the mGT at the IRP (Integrated Pyrolysis Regenerated Plant) the modified geometry was tested through CFD analysis on syngas from biomass thermochemical processes. The results show that further modifications of the liner are required for optimal operation and to reach adequate values for Turbine Inlet Temperature.© 2015 ASME

CFD Analysis of an Annular Micro Gas Turbine Combustion Chamber Fuelled With Liquid Biofuels: Preliminary Results With Bioethanol

Liquid biofuels, such as bioethanol, biodiesel and vegetal oils, can effectively be used in internal combustion engines blended with liquid fuels of fossil origin or in their substitution, allowing a reduction of CO2 and pollutant emissions in the atmosphere. This work is supported by a CFD analysis to study the feasibility of using these fuels derived from biomass in a 80 kWel micro gas turbine, originally designed for operation with natural gas. In this paper preliminary results about the behavior of bioethanol in the MGT combustion chamber are presented. The complete investigation however includes biodiesel and also glycerin, a byproduct of biodiesel production. To carry out the computational simulations, combustion models included in a commercial software and oxidation mechanism of ethanol taken from the literature were used. The geometry of the NG injector was modified to optimize the liquid inlet into the combustor. Simulation results in terms of temperatures, pressures, and emissions were compared with data available for natural gas combustion in the original combustion chamber.Copyright