Experimental Study on the Solids Residence Time Distribution in Multiple Square-Based Spouted Beds

The present work aims at investigating the residence time distribution (RTD) of a multiple spouted bed reactor, which will be applied for the pyrolysis and gasification of residual biomass. The unit is composed of square-based spouted beds, placed in series and at descending heights, and communicating with each other through an opening in the lateral wall. The gas is fed evenly in parallel. The experimental analysis is based on tracer experiments in cold-flow units, assessing the influence of the number of units and the bed height. The tests proved the good mixing properties of the spouted beds, which create a stable fluidization regime and do not feature dead zones. Each spouted bed can generally be well assimilated to an ideal continuous stirred tank reactor (CSTR). The RTD of the device seems adequate for the application, and also seems to be well tuneable through the selection of the bed height and number of units. Given the good similarity with ideal reactor networks, these represent a valid tool to estimate the final behavior in terms of RTD.

Modelling the Effect of External Flue Gas Recirculation on NOx and CO Emissions in a Premixed Gas Turbine Combustor With Chemical Reactor Networks

The increasing amount of renewable energy and emission norms challenge gas turbine power plants to operate at part-load with high efficiency, while reducing NOx and CO emissions. A novel solution to this dilemma is external Flue Gas Recirculation (FGR), in which flue gases are recirculated to the gas turbine inlet, increasing compressor inlet temperature and enabling higher part load efficiencies. FGR also alters the oxidizer composition, potentially leading to reduced NOx levels. This paper presents a kinetic model using chemical reactor networks in a lean premixed combustor to study the impact of FGR on emissions. The flame zone is split in two perfectly stirred reactors modelling the flame front and the recirculation zone. The flame reactor is determined based on a chemical time scale approach, accounting for different reaction kinetics due to FGR oxidizers. The recirculation zone is determined through empirical correlations. It is followed by a plug flow reactor. This method requires less details of the flow field, has been validated with literature data and is generally applicable for modelling premixed flames. Results show that due to less O2 concentration, NOx formation is inhibited down to 10–40% and CO levels are escalated up to 50%, for identical flame temperatures. Increasing combustor pressure leads to a rise in NOx due to thermal effects beyond 1800 K, and a drop in CO levels, due to the reduced chemical dissociation of CO2. Wet FGR reduces NOx by 5–10% and increases CO by 10–20%.

A Semi-Empirical Model to Predict Aircraft Soot Emission in Rich Zone of RQL Combustor

The reduction of particulate matter emissions is becoming a requirement for aircraft turbine engine combustor design. This requirement leads to the need to estimate particulate emissions during the conceptual design phase. Current prediction methods are based on detailed numerical simulation techniques such as CFD, which are unsuitable for conceptual design due to high computational cost. This paper introduces a new approach employing a semi-empirical model for prediction of the soot emission indices of RQL combustors. The proposed approach dramatically improves computational efficiency by avoiding complex numerical calculations. The model is based on the response surface developed from experimental data for turbulent non-premixed flames. The data has been extracted from the literature, employing statistical methods such as machine learning techniques and polynomial regressions to apply the turbulent flame data to the actual operating conditions in the primary zone of aircraft engine combustors. The model is developed by first representing the combustor primary zone by chemical reactor networks constructed in CHEMKIN based on a statistical PDF approach to simulate the non-uniform distribution of time-evolving local mixture fraction with a beta distribution. The reactor networks are used to estimate the concentrations of soot precursor species in the rich zone. The empirical equations are then used with the predicted concentrations to predict the soot formation rate. Finally, these results are used along with the turbulent non-premixed flame data to develop the final model through a model calibration process.